<?xml version="1.0" encoding="utf-8"?>
<posts>
  <row Id="1" PostTypeId="1" CreationDate="2013-10-22T19:27:22.770" Score="13" ViewCount="3311" Body="&lt;p&gt;With all the advances in the field of electronics, microcontrollers, etc., is it a good option today to build my own amateur radio transceiver (or transmitter/receiver)? &lt;strong&gt;Why might one choose to build over buying, or the other way around? How should one weigh the time invested in building versus money spent buying?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some experience building ham radios, but that was several years ago and using almost only analog circuits. It was very hard to tune it. I know that you can't buy the fun and knowledge gained from building your own, but the question is more about the time/price balance of building one or buying one.&lt;/p&gt;&#xA;" OwnerUserId="6" LastEditorUserId="29" LastEditDate="2013-10-30T08:21:25.373" LastActivityDate="2013-10-30T08:21:25.373" Title="Is it a good idea to build your own radio transceiver today?" Tags="&lt;diy&gt;&lt;transceiver&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="2" ClosedDate="2013-10-23T17:55:15.790" ContentLicense="CC BY-SA 3.0" />
  <row Id="2" PostTypeId="1" AcceptedAnswerId="199" CreationDate="2013-10-22T19:29:19.063" Score="10" ViewCount="6275" Body="&lt;p&gt;I need to get Hawaii for Worked All States, and live on the East Coast (Virginia). Furthermore, I have a poor antenna, and thus only the prime times of the day seem to really be opened for me. What time of day/band is the best to make the QSO?&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-10-22T19:51:01.373" LastActivityDate="2021-02-25T15:10:46.653" Title="What is the best time of day/Band to make a contact with Hawaii from the East Coast?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="8" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3" PostTypeId="2" ParentId="1" CreationDate="2013-10-22T19:30:57.407" Score="16" Body="&lt;p&gt;If you are interested in the electronics and technical aspects of transmission and reception, then yes, now is a fine time to get involved in building your own radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are more interested in pursuing communicating with other users, though, your time and effort would be better spent using a good rig.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now is also a great time to get into Software Defined Radio (SDR) which puts much of the radio receiver into software, enabling one to quickly adapt and change their radio for specific uses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, some amateurs want the features of high-end stations without spending thousands of dollars.  A sufficiently motivated amateur radio enthusiast can, over time, build a very capable transceiver that rivals some of the professional stations for a fraction of the cost.  However, they are simply spending time rather than money - it's not a quick or easy path, but can be very rewarding.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-10-24T14:54:17.813" LastActivityDate="2013-10-24T14:54:17.813" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="4" PostTypeId="1" AcceptedAnswerId="3694" CreationDate="2013-10-22T19:31:35.777" Score="13" ViewCount="628" Body="&lt;p&gt;I'm wanting to view the CQ Zones in Google Earth, and I understand that a KML file will allow me to do so. Is there a place where I can get a KML file that shows all of the CQ Zones?&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-10-28T12:34:09.843" LastActivityDate="2015-03-12T12:02:09.213" Title="Is there a KML or similar file that shows all of the CQ Zones?" Tags="&lt;location&gt;&lt;cq-zones&gt;&lt;map&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5" PostTypeId="1" AcceptedAnswerId="251" CreationDate="2013-10-22T19:32:17.787" Score="9" ViewCount="832" Body="&lt;p&gt;What and how would I go about obtaining a licence for HAM radio in Australia?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do the licencing regulations vary significantly from state to state?&lt;/p&gt;&#xA;" OwnerDisplayName="user17" LastEditorDisplayName="user17" LastEditDate="2013-10-22T19:42:56.793" LastActivityDate="2019-08-25T06:36:57.430" Title="What is the procedure to obtain an amateur radio licence in Australia?" Tags="&lt;license&gt;&lt;australia&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6" PostTypeId="1" AcceptedAnswerId="11" CreationDate="2013-10-22T19:34:42.997" Score="13" ViewCount="5557" Body="&lt;p&gt;How can I properly use my ham radio license to operate an IEEE 802.11 WiFi access point within the US amateur radio service, rather than the US &quot;part 15&quot; regulations for unlicensed transmissions?&lt;/p&gt;&#xA;" OwnerUserId="11" LastEditorUserId="76" LastEditDate="2015-02-10T16:44:52.817" LastActivityDate="2015-02-10T16:44:52.817" Title="How to operate IEEE 802.11 WiFi AP within the amateur radio service?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;wifi&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7" PostTypeId="2" ParentId="2" CreationDate="2013-10-22T19:37:42.307" Score="1" Body="&lt;p&gt;I can only add the perspective as to when I had a phone contact with KH6LC on 11/17/12 @ 22:24.  I made the contact with 12W on 10m, I believe it was during ARRL November Sweepstakes contest.  That's likely a really good bet, a lot of stations get on the air around that time.  I'm hoping to snag AK as it's one of the remaining few that I need for my WAS.&lt;/p&gt;&#xA;" OwnerUserId="26" LastEditorUserId="7" LastEditDate="2013-10-22T19:42:09.590" LastActivityDate="2013-10-22T19:42:09.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8" PostTypeId="1" CreationDate="2013-10-22T19:41:56.480" Score="8" ViewCount="3190" Body="&lt;p&gt;I recently started playing with the digital modes, but have been frustrated with the difficulty in finding where certain modes are commonly used. Is there a digital mode band plan for the HF bands, to the level of which modes are commonly used on what frequencies?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in the United States.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="76" LastEditDate="2013-10-23T00:08:31.853" LastActivityDate="2013-10-23T00:08:31.853" Title="HF Digital Mode Band Plan for the USA" Tags="&lt;united-states&gt;&lt;hf&gt;&lt;band-plan&gt;&lt;digital-modes&gt;&lt;modes&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9" PostTypeId="2" ParentId="2" CreationDate="2013-10-22T19:42:04.460" Score="0" Body="&lt;p&gt;Depends on the band. You will have better success on 80m or top-band after dark. 20 will get you good DX all through the day, and 40, depending on conditions is good to ~1000km&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't mention where in the US you are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The current solar conditions indicate that 10m should get good results right now too.&lt;/p&gt;&#xA;" OwnerUserId="27" LastActivityDate="2013-10-22T19:42:04.460" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10" PostTypeId="1" CreationDate="2013-10-22T19:43:46.443" Score="10" ViewCount="504" Body="&lt;p&gt;Lets say that I get my amateur radio license in country A and then some time later I move to country B. Will I need to get a new license on country B or does the license obtained in country A works just fine?&lt;/p&gt;&#xA;" OwnerUserId="6" LastEditorUserId="13" LastEditDate="2013-10-22T19:50:32.577" LastActivityDate="2013-10-22T20:02:46.813" Title="Does an amateur radio licence work worldwide?" Tags="&lt;license&gt;&lt;international-operating&gt;" AnswerCount="5" CommentCount="3" ClosedDate="2013-10-23T13:22:42.393" ContentLicense="CC BY-SA 3.0" />
  <row Id="11" PostTypeId="2" ParentId="6" CreationDate="2013-10-22T19:44:43.933" Score="11" Body="&lt;p&gt;IANAL, but based on my limited knowledge of US amateur radio regulations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Disable all encryption, as encrypted communications are not allowed within the amateur radio service. Yes, WEP counts as encryption, too. So does HTTPS, SSH or SMTP with STARTTLS. One of the few things you can allow is plain-text HTTP.&lt;/li&gt;&#xA;&lt;li&gt;Set the network SSID to your call sign. This should be enough to identify the transmissions.&lt;/li&gt;&#xA;&lt;li&gt;Force select a channel which is within the boundaries of the amateur radio band.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This &lt;em&gt;should&lt;/em&gt; put you within the limits of the amateur radio service and allow you to operate the access point under the regulations relevant to amateur radio.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-10-22T19:44:43.933" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="12" PostTypeId="2" ParentId="6" CreationDate="2013-10-22T19:47:28.640" Score="0" Body="&lt;p&gt;What you could do, and I don't believe this would violate Part 15, would be to use packet (AX.25) to link two 802.11 AP's together.  You'd suffer a reduction in speed, most likely - I don't know what the maximum TX speed on packet is, but I doubt it's anything close to WiFi speeds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also High-Speed Multimedia Radio, but I'm not familiar enough with such to comment. &lt;a href=&quot;http://en.wikipedia.org/wiki/High-speed_multimedia_radio&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/High-speed_multimedia_radio&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="41" LastActivityDate="2013-10-22T19:47:28.640" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="13" PostTypeId="1" AcceptedAnswerId="110" CreationDate="2013-10-22T19:48:00.967" Score="14" ViewCount="6844" Body="&lt;p&gt;I have never understood how a balun or a unun works and under which situation I need to use either of them in an antenna feed line. &lt;/p&gt;&#xA;" OwnerUserId="36" LastEditorUserId="1246" LastEditDate="2015-02-11T19:01:29.943" LastActivityDate="2019-07-26T14:37:24.273" Title="What is the purpose of a balun and a unun in a feed line?" Tags="&lt;antenna-construction&gt;&lt;feed-line&gt;&lt;balun&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="14" PostTypeId="1" AcceptedAnswerId="28" CreationDate="2013-10-22T19:48:54.563" Score="8" ViewCount="1101" Body="&lt;p&gt;They seem to be broadbanded, small, and ground-independent relative to other cheap wire antennas, so what's the catch?&lt;/p&gt;&#xA;" OwnerUserId="43" LastEditorUserId="76" LastEditDate="2015-12-15T21:59:31.880" LastActivityDate="2015-12-15T21:59:31.880" Title="What are some drawbacks to delta loop antennas?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="15" PostTypeId="2" ParentId="2" CreationDate="2013-10-22T19:48:57.800" Score="9" Body="&lt;p&gt;In general, my experience is that band conditions are best for long-distance communication at sunrise and sunset. You generally want the sunset to be somewhere in between you and the person you are talking to, so probably something like 9 PM EST.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beyond that, things like solar weather can make a big difference. I tend to use &lt;a href=&quot;http://www.g4ilo.com/voaprop.html&quot;&gt;VOAProp&lt;/a&gt; for predicting when and on what band I can best make a contact. The ARRL also &lt;a href=&quot;http://www.arrl.org/propagation&quot;&gt;publishes propagation charts&lt;/a&gt; that show the best time of day. Their &lt;a href=&quot;http://www.arrl.org/files/file/Propagation%20Charts/11east129.pdf&quot;&gt;November 2013 chart&lt;/a&gt; shows that the best time is between 1600 and 0000 UTC, which is noon to 8 PM. Finally, &lt;a href=&quot;http://www.voacap.com/prediction.html&quot;&gt;voacap.com&lt;/a&gt; has an interactive web tool that can give you propagation predictions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, remember that power and spectral power density make a big difference as well. 1500W on CW will propagate much farther than 10W on SSB. During good propagation conditions, however, 10W may be all that you need.&lt;/p&gt;&#xA;" OwnerUserId="39" LastActivityDate="2013-10-22T19:48:57.800" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="16" PostTypeId="1" AcceptedAnswerId="25" CreationDate="2013-10-22T19:48:58.103" Score="14" ViewCount="1612" Body="&lt;p&gt;Given a middling-power rig (up to 100 W) requiring a 50 Ω antenna, a few options for the coaxial cable with a 50 Ω impedance are&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;RG-174&lt;/li&gt;&#xA;&lt;li&gt;RG-58A/U&lt;/li&gt;&#xA;&lt;li&gt;RG-8&lt;/li&gt;&#xA;&lt;li&gt;RG-213&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Apart from cost, what factors are relevant in deciding which coaxial cable to use?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2015-02-10T16:43:23.443" LastActivityDate="2015-02-10T16:43:23.443" Title="What should I consider when choosing a coaxial cable?" Tags="&lt;feed-line&gt;&lt;coaxial-cable&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="17" PostTypeId="2" ParentId="10" CreationDate="2013-10-22T19:49:46.973" Score="16" Body="&lt;p&gt;It very much depends on the two countries. In general, there are two large international groups with which operating within the same group is fairly easy. However, even for these two, if you move to another country you should get a license for that country. The two groups are (From &lt;a href=&quot;http://www.arrl.org/international-operating&quot;&gt;ARRL&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/cept&quot;&gt;CEPT&lt;/a&gt;- Primarily European countries&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/iarp&quot;&gt;IARU&lt;/a&gt;- Primarily the Americas.&lt;/li&gt;&#xA;&lt;li&gt;Many countries have direct reciprocal laws, check the laws for your country, or the new country.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Typically, a person making these calls will add in the country code where they are, followed by a / and their call. For instance, XE3/K5ENS is one from my log that did this, he was operating from Mexico region 3, with his US call sign of K5ENS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check with the rules of your country, or your Amateur Radio Union (ARRL for US, others have different groups) for more assistance. Bottom line is, get a license if you plan to stay there for a while, otherwise just use the temporary call.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="29" LastEditDate="2013-10-22T20:02:46.813" LastActivityDate="2013-10-22T20:02:46.813" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="18" PostTypeId="2" ParentId="10" CreationDate="2013-10-22T19:50:02.947" Score="2" Body="&lt;p&gt;No. Amateur Radio license works only in the country where it is granted. However, certain countries have reciprocation agreements under which licensed operators from one country may operate in another country as long as they follow the regulations laid down in that country.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While operating in a foreign country, the operator must identify him/erself as such with a suffix &lt;a href=&quot;http://www.arrl.org/reciprocal-permit&quot; rel=&quot;nofollow&quot;&gt;see this&lt;/a&gt;. KE5ABC in India shall be KE5ABC/VU2&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, this privilege may be revoked at any time by the host country - like times of war.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some countries require a registration (some paperwork) before starting operations. So you cannot just walk across the border ans start transmission.&lt;/p&gt;&#xA;" OwnerUserId="49" LastEditorUserId="49" LastEditDate="2013-10-22T19:55:39.713" LastActivityDate="2013-10-22T19:55:39.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="19" PostTypeId="2" ParentId="10" CreationDate="2013-10-22T19:51:11.030" Score="2" Body="&lt;p&gt;A CEPT license is valid in all CEPT signatory countries, and many such countries will take it as proof of having passed the relevant examinations and issue a local corresponding license on request.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The CEPT license is meant for when you visit another country, however, so in and of itself probably won't be as good as a local license. A local license will come with its own local call sign and be issued by the relevant local authority.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-10-22T19:51:11.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="20" PostTypeId="2" ParentId="10" CreationDate="2013-10-22T19:52:13.870" Score="3" Body="&lt;p&gt;Unfortunately, the best answer I can give you is &quot;it depends&quot;. Whether you can use a license issued in one country in another country depends on whether those countries have signed a treaty allowing such use. The ARRL has some information, mainly useful to US amateurs, on &lt;a href=&quot;http://www.arrl.org/reciprocal-permit&quot; rel=&quot;nofollow&quot;&gt;their site&lt;/a&gt;. If you'd like help Googling for specific country pairs, you can use the terms &quot;reciprocal license&quot; or &quot;reciprocal privileges&quot;.&lt;/p&gt;&#xA;" OwnerUserId="39" LastActivityDate="2013-10-22T19:52:13.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="21" PostTypeId="2" ParentId="10" CreationDate="2013-10-22T19:54:11.227" Score="0" Body="&lt;p&gt;You can visit and most likely be able to use your license, but to actually move, you'd need to reapply.&lt;/p&gt;&#xA;" OwnerUserId="20" LastActivityDate="2013-10-22T19:54:11.227" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="22" PostTypeId="1" AcceptedAnswerId="2106" CreationDate="2013-10-22T19:55:58.133" Score="15" ViewCount="3460" Body="&lt;p&gt;Are there any federal laws or FCC guidelines that allow ham radio operators to install antennas?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in an apartment building in a large city that bans outdoor antennas.  I recall reading that the FCC protected the installation of satellite dishes and what not for consumer television usage.  Are there similar protections for amateur radio?&lt;/p&gt;&#xA;" OwnerUserId="51" LastEditorUserId="19" LastEditDate="2013-10-22T20:00:43.087" LastActivityDate="2014-09-04T10:24:03.860" Title="Are there federal laws (US) protecting antenna installation?" Tags="&lt;antenna&gt;&lt;legal&gt;&lt;united-states&gt;" AnswerCount="4" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="23" PostTypeId="1" AcceptedAnswerId="31" CreationDate="2013-10-22T19:57:28.037" Score="27" ViewCount="31248" Body="&lt;p&gt;I'm a very casual/beginner level ham and as such have mostly avoided committing too much in the way of financial resources - I have a UV-5R for a personal radio, anything else I do I've used others' radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't mind the 5R's interface; I'm familiar enough with it now that it doesn't really bother me. That said, it'd be nice to give it a little boost without spending a bunch of money and/or buying a new radio. I typically operate at home, so mobility isn't required (though being able to pack it up to have along when traveling wouldn't hurt, either).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What kinds of low-cost options are there that could help improve its range (and/or SNR)?&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="8832" LastEditDate="2017-05-05T17:07:42.920" LastActivityDate="2019-04-08T19:56:04.797" Title="What's a cost-effective way to boost the range of my cheap 2m/70cm handheld?" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;ht&gt;&lt;uv-5r&gt;" AnswerCount="11" CommentCount="6" FavoriteCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="24" PostTypeId="2" ParentId="16" CreationDate="2013-10-22T20:00:30.853" Score="2" Body="&lt;p&gt;In addition to characteristic impedance (such as 50 ohms) and cost, which you've already considered, the two main factors for coax feed line types are line loss at a particular frequency, and velocity factor. The line loss varies depending on operating frequency, so it depends on your application. For line loss, the main factors are what frequency bands you're going to use over the feedline, and how long the distance is between the transmitter and the antenna. For VHF and above, line loss is a much bigger consideration. Velocity factor comes into play if you are going to create matching stubs or if you are working with non-resonant antennas like the G5RV and need to avoid certain lengths. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other factors include how flexible the line is (braided vs. solid wire), how much motion it will endure (rotors, portable operations), how waterproof it is (permanent or underground installation), how hard it is to work with (LMR-100 is notoriously hard to attach connectors to), etc.&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-10-22T20:00:30.853" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="25" PostTypeId="2" ParentId="16" CreationDate="2013-10-22T20:01:34.637" Score="7" Body="&lt;p&gt;The most important thing about the cable is how much loss are you willing to accept in the feed line. Figure out how much cable you will need, and then determine what the loss on said cable will be. As I mentioned on &lt;a href=&quot;http://www.kd7uiy.com/2013/03/the-quest-for-cable.html&quot;&gt;my website&lt;/a&gt;, here's a few good rules of thumb:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Keep the power loss to no more than 3 db in the cable. &lt;/li&gt;&#xA;&lt;li&gt;If you can, use the same impedance as your antenna/transmitter, but always keep the impedance to within a factor of 1.5 of your antenna/transmitter. But really, match them, it's not worth the hassle of mis-matched cable.&lt;/li&gt;&#xA;&lt;li&gt;If you can, use only a single strand of cable. Also, use the right connectors for both ends.&lt;/li&gt;&#xA;&lt;li&gt;Buy for the largest frequency that you think you will be using.&lt;/li&gt;&#xA;&lt;li&gt;Get a cable that is slightly larger than you need, but not excessively larger.&lt;/li&gt;&#xA;&lt;li&gt;The velocity factor only matters if you are trying to build a phase changing antenna.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Longer cable equals more loss. Higher frequency is also more loss. Here's a few websites that talk about what the loss is per length and frequency of each cable:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.pcs-electronics.com/guide_coax.php?osCsid=600b648260d42af6d62fe29eb5c9053d&quot;&gt;http://www.pcs-electronics.com/guide_coax.php?osCsid=600b648260d42af6d62fe29eb5c9053d&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hamuniverse.com/coaxdata.html&quot;&gt;http://www.hamuniverse.com/coaxdata.html&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.thewireman.com/coaxdatacurrent2.pdf&quot;&gt;http://www.thewireman.com/coaxdatacurrent2.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-22T20:01:34.637" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="26" PostTypeId="2" ParentId="14" CreationDate="2013-10-22T20:02:17.490" Score="3" Body="&lt;p&gt;Delta loops are popular on the low bands (7MHz and below) because they are much easier to set up mechanically than a quad, but they have a smaller internal area than a quad for the same frequency which slightly reduces their gain in comparison.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They have a higher effective mean height when the triangle is pointing &quot;downwards&quot;, but this requires two points of support and is thus less common.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are strongly dependant on their height above the ground, and work best at the same height as a dipole - half a wavelength above the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore the catch is that they are difficult to erect at a height which optimises their performance.&lt;/p&gt;&#xA;" OwnerUserId="58" LastActivityDate="2013-10-22T20:02:17.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="27" PostTypeId="2" ParentId="16" CreationDate="2013-10-22T20:02:23.243" Score="3" Body="&lt;p&gt;Your question is missing an important item; the frequency at which you're operating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I work a lot of VHF+ contests, and all four of the varieties of coax you mention pose far too much loss of signal to be viable for those frequencies.  I use LMR-400 Ultraflex for 6 meter, and 3/8&quot; Andrews Heliax hardline for 2 meter, 222, and 440 bands.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w4rp.com/ref/coax.html&quot; rel=&quot;nofollow&quot;&gt;http://www.w4rp.com/ref/coax.html&lt;/a&gt; is a great resource for tracking how much loss coax presents at various frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another point you don't mention is where you're intending to use the coax. Tower applications require different coax considerations than a mobile installation, and SOTA requirements are different still.  &lt;/p&gt;&#xA;" OwnerUserId="52" LastActivityDate="2013-10-22T20:02:23.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="28" PostTypeId="2" ParentId="14" CreationDate="2013-10-22T20:02:41.283" Score="2" Body="&lt;p&gt;Delta loops:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Perform poorly for multi-band use, so you need a separate antenna for each band you plan on using.  &lt;/li&gt;&#xA;&lt;li&gt;Require significant height for their benefits to surpass the typical dipole.  &lt;/li&gt;&#xA;&lt;li&gt;Due to the shape and height the supporting structure of the delta loop is more complicated than other antenna types.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These can be a small price to pay for the benefits offered by the Delta loop, but they can present significant hurdles for casual amateur radio operators.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-22T20:02:41.283" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="29" PostTypeId="2" ParentId="16" CreationDate="2013-10-22T20:02:42.003" Score="1" Body="&lt;p&gt;Although you could get into a length debate about all the different properties and what is best, most people boil down to the one big decision: &quot;what is the loss per foot or meter of this cable&quot;.  To check out various cables, you should use a &lt;a href=&quot;http://www.qsl.net/co8tw/Coax_Calculator.htm&quot; rel=&quot;nofollow&quot;&gt;Loss Calculator&lt;/a&gt; (there are many if you search the net).  These will let you put in the length of line, the type of line, etc and you can see the results for what you'll lose, power-wise, by sending a signal over it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another big component, is what does it have to go through?  Yeah, RG-8 is awesome but you're probably not going to run it throughout your car.  It's not flexible enough and would require some whopping big holes.  (ok, most people would suffer the holes, but the flexibility of using it would be a problem).  That's the reason that many antenna mounts come with something closer to RG-58 or worse.  The cable is much easier to run in small spaces.  It's a short distance, at least!&lt;/p&gt;&#xA;" OwnerUserId="661" LastActivityDate="2013-10-22T20:02:42.003" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="30" PostTypeId="2" ParentId="23" CreationDate="2013-10-22T20:05:01.473" Score="2" Body="&lt;p&gt;Take a look at getting a 5/8 wave telescoping antenna, and make a &quot;rat tail&quot; from a ring terminal and 18-19&quot; of wire to be the other end of the dipole.  &lt;/p&gt;&#xA;" OwnerUserId="52" LastActivityDate="2013-10-22T20:05:01.473" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="31" PostTypeId="2" ParentId="23" CreationDate="2013-10-22T20:05:45.347" Score="14" Body="&lt;p&gt;A homemade &quot;rat-tail&quot; ground plane costs 35 cents each to make. A crimp on eyelet to fit your antenna's connector, a string of speaker wire about 19-20 inches long and a little heat shrink tubing to dress it up and done. Soldering the the wire to the connector instead of crimping it will be a better option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Go here for some details about the &quot;Rat-Tail&quot; ground plane: &lt;a href=&quot;http://www.hamuniverse.com/htantennamod.html&quot;&gt;http://www.hamuniverse.com/htantennamod.html&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="36" LastActivityDate="2013-10-22T20:05:45.347" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="32" PostTypeId="1" CreationDate="2013-10-22T20:07:48.607" Score="31" ViewCount="4021" Body="&lt;p&gt;I've been having a hard time getting my Morse Code copying speed above 7-10 words per minute.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any techniques I can use to improve my skill?&lt;/p&gt;&#xA;" OwnerUserId="19" LastEditorUserId="414" LastEditDate="2014-01-07T21:34:40.573" LastActivityDate="2019-04-19T14:32:46.517" Title="Are there well-known methods that can help improve my CW copying speed?" Tags="&lt;cw&gt;" AnswerCount="11" CommentCount="1" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="33" PostTypeId="2" ParentId="22" CreationDate="2013-10-22T20:08:57.540" Score="11" Body="&lt;p&gt;&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.1.157.8&quot;&gt;FCC 97.15(b)&lt;/a&gt; provides a limited amount of protection for Amateur Radio Operators who desire to erect antenna structures in the pursuit of their radio activity:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Except as otherwise provided herein, a station antenna structure may be erected at heights and dimensions sufficient to accommodate amateur service communications. (State and local regulation of a station antenna structure must not preclude amateur service communications. Rather, it must reasonably accommodate such communications and must constitute the minimum practicable regulation to accomplish the state or local authority's legitimate purpose. See PRB–1, 101 FCC 2d 952 (1985) for details.) &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Local and state laws and regulations governing antenna structures may apply to amateur radio antennas as well, however they have to show a legitimate purpose for the rule that specifically precludes amateur radio antenna use.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-22T20:08:57.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="34" PostTypeId="1" AcceptedAnswerId="2189" CreationDate="2013-10-22T20:10:43.110" Score="13" ViewCount="8571" Body="&lt;p&gt;I've seen many installations, particularly at field day and also in second-floor installations, where RF grounding is ignored entirely. What are the drawbacks to this and when is it absolutely essential to have RF grounding?&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2014-09-28T19:58:42.850" Title="When is RF grounding necessary, and when is it not?" Tags="&lt;grounding&gt;&lt;installation&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="35" PostTypeId="5" CreationDate="2013-10-22T20:12:20.747" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-22T20:12:20.747" LastActivityDate="2013-10-22T20:12:20.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="36" PostTypeId="4" CreationDate="2013-10-22T20:12:20.747" Score="0" Body="Continuous Wave (CW), or Morse code over audible tones. Use this tag for any question relating to Morse code." OwnerUserId="13" LastEditorUserId="29" LastEditDate="2013-11-15T10:08:48.613" LastActivityDate="2013-11-15T10:08:48.613" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="37" PostTypeId="5" CreationDate="2013-10-22T20:13:48.177" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-22T20:13:48.177" LastActivityDate="2013-10-22T20:13:48.177" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="38" PostTypeId="4" CreationDate="2013-10-22T20:13:48.177" Score="0" Body="Very High Frequency is the frequency range 30-300 MHz." OwnerUserId="13" LastEditorUserId="29" LastEditDate="2013-11-15T10:05:28.740" LastActivityDate="2013-11-15T10:05:28.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="39" PostTypeId="5" CreationDate="2013-10-22T20:14:40.507" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-22T20:14:40.507" LastActivityDate="2013-10-22T20:14:40.507" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="40" PostTypeId="4" CreationDate="2013-10-22T20:14:40.507" Score="0" Body="Ultra High Frequency is the frequency range 300-3000 MHz." OwnerUserId="13" LastEditorUserId="29" LastEditDate="2013-11-15T10:05:44.990" LastActivityDate="2013-11-15T10:05:44.990" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="41" PostTypeId="5" CreationDate="2013-10-22T20:15:16.290" Score="0" Body="&lt;p&gt;Radio frequencies are commonly divided into ranges by frequency.  Here are some of the ranges:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Medium Frequency (MF), 300 kHz - 3 MHz&lt;/li&gt;&#xA;&lt;li&gt;High Frequency (HF), 3 - 30 MHz&lt;/li&gt;&#xA;&lt;li&gt;Very High Frequency (VHF), 30 - 300 MHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;HF frequencies have been used since the very earliest days of radio, and the HF bands remain very popular in amateur radio.  HF radio signals often bounce off the ionosphere, allowing communication far beyond line-of-sight ranges; ham radio contacts between continents are common.&lt;/p&gt;&#xA;&lt;p&gt;More information about HF is available at &lt;a href=&quot;https://en.wikipedia.org/wiki/High_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="322" LastEditorUserId="4665" LastEditDate="2020-12-17T16:25:01.137" LastActivityDate="2020-12-17T16:25:01.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="42" PostTypeId="4" CreationDate="2013-10-22T20:15:16.290" Score="0" Body="The frequency range 3-30 MHz.  HF radio waves often propagate by bouncing off the ionosphere, allowing communication between continents. This tag may also be used for questions about the 160 meter band (1.8 MHz), which while not HF is often referred to as such due to its similar propagation." OwnerUserId="13" LastEditorUserId="4665" LastEditDate="2020-12-17T16:25:01.137" LastActivityDate="2020-12-17T16:25:01.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="43" PostTypeId="2" ParentId="32" CreationDate="2013-10-22T20:16:55.017" Score="11" Body="&lt;p&gt;Just listen and copy.  Tune into areas of the band populated by higher level licensees and just start copying.  Don't dwell on the letters you miss, just skip them, leave a blank and focus on the next one.  Eventually you'll start picking up the words or phrases instead of just the letters.&lt;/p&gt;&#xA;" OwnerUserId="47" LastActivityDate="2013-10-22T20:16:55.017" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="44" PostTypeId="2" ParentId="32" CreationDate="2013-10-22T20:17:31.370" Score="28" Body="&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Morse_code#Learning_methods&quot;&gt;The Koch method&lt;/a&gt; is supposed to be very good at building fast Morse code receiving skills.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The basic idea is that you &lt;em&gt;start out&lt;/em&gt; by setting up to receive code sent at your desired target speed, usually a rate of 20 wpm or more, possibly staggered to a slightly lower speed; I've seen 20 wpm staggered to 15 wpm being relatively common, although for a pure Koch approach you should be copying at the full target speed. The big thing is that the character set you work with is &lt;em&gt;only two characters&lt;/em&gt;. If you miss one character in the stream, simply let it go; I found this to be the hardest part myself! Once you are able to copy this with good accuracy, with the usual target being around 90% correct copy, you add another character and work your way back up. Rinse and repeat until you have mastered the entire Morse code alphabet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way this works is by not allowing you to think; you have to learn to associate the &lt;em&gt;sound&lt;/em&gt; of each character &lt;em&gt;at high speed&lt;/em&gt; with the respective character &lt;em&gt;from the beginning&lt;/em&gt;. It also works by way of positive reinforcement: the simple realization that yes, you &lt;em&gt;can&lt;/em&gt; copy Morse code at 15-20 wpm or more, &lt;em&gt;because you just did it&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Peter Hicks N5KD has &lt;a href=&quot;http://www.n5kd.org/radio/morse/&quot;&gt;a pretty thorough page on Morse code&lt;/a&gt;, which includes mention of the Koch method, and &lt;a href=&quot;http://www.g4fon.net/&quot;&gt;Ray Goff G4FON&lt;/a&gt; has written a piece of software to do it on Windows (there are others, too).&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-25T18:01:08.157" LastActivityDate="2013-10-25T18:01:08.157" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="45" PostTypeId="1" AcceptedAnswerId="101" CreationDate="2013-10-22T20:19:20.520" Score="9" ViewCount="235" Body="&lt;p&gt;The UK has 3 licensing levels, foundation, intermediate and advanced. Aside from the allowed power output going up each time (10W, 100W, 400W) are there any other privileges one would gain?&lt;/p&gt;&#xA;" OwnerUserId="65" LastActivityDate="2015-06-14T19:18:32.893" Title="What privileges do I gain with each addition step of the license (in the UK?)" Tags="&lt;license&gt;&lt;united-kingdom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="46" PostTypeId="2" ParentId="32" CreationDate="2013-10-22T20:19:46.723" Score="9" Body="&lt;p&gt;There are numerous resources on the web for learning and practicing Morse code, with most of them agreeing on some basic principles. One is to learn the code by sound, not by charts of dashes and dots or mnemonics. Another is to learn the characters themselves at a high rate of speed, even if they are separated by large spaces (Farnsworth method) or reduced to a smaller number of symbols (Koch method) at first. Another important principle is to listen to code a little faster than you already know even if you miss a few characters, and to gradually increase your speed. &lt;a href=&quot;http://lcwo.net&quot; rel=&quot;noreferrer&quot;&gt;Learn CW Online&lt;/a&gt; is a great site for practicing these techniques.&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-10-22T20:19:46.723" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="47" PostTypeId="5" CreationDate="2013-10-22T20:19:54.290" Score="0" Body="&lt;p&gt;Coaxial cables have two conductors separated by an insulator. The outer conductor, or the shield, wraps completely around the insulated inner conductor. A coaxial cable is typically utilized to connect a device to an antenna, or to another device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Questions should relate specifically to the properties of coaxial cables in general or a specific type of coaxial cable. Questions about connectors, including soldering or crimping, or about adapters are also on topic. Finally, questions can be about the use of coaxial cable to create baluns or other matching &quot;circuits&quot;.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-23T17:32:14.137" LastActivityDate="2013-10-23T17:32:14.137" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="48" PostTypeId="4" CreationDate="2013-10-22T20:19:54.290" Score="0" Body="Questions about coaxial cables, including different types of cable, connectors, adapters, and other topics." OwnerUserId="5" LastEditorUserId="87" LastEditDate="2013-10-23T20:56:22.283" LastActivityDate="2013-10-23T20:56:22.283" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="49" PostTypeId="1" AcceptedAnswerId="220" CreationDate="2013-10-22T20:20:41.290" Score="6" ViewCount="260" Body="&lt;p&gt;With a full amateur license in the UK, up to 400W can be used - however, there are cases that might call for higher power, such as bouncing signals off the moon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any way I can obtain permission to use a higher power, even if this is temporarily and within a specific area? Or is it completely forbidden?&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="76" LastEditDate="2013-10-22T22:17:27.987" LastActivityDate="2013-10-23T12:11:56.133" Title="Using more than 400W in the UK" Tags="&lt;united-kingdom&gt;&lt;license&gt;&lt;rf-power&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="50" PostTypeId="2" ParentId="6" CreationDate="2013-10-22T20:21:45.303" Score="4" Body="&lt;p&gt;All the info you could ever want is being provided on this website..&lt;a href=&quot;http://hsmm-mesh.org/&quot; rel=&quot;nofollow&quot;&gt;http://hsmm-mesh.org/&lt;/a&gt;   They are using WRT54G routers for ham band wifi usage. There is a great community for support and lots of documentation..Type &quot;ham mesh net&quot; into your favorite search engine and you will find many answers.&lt;/p&gt;&#xA;" OwnerUserId="69" LastActivityDate="2013-10-22T20:21:45.303" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="51" PostTypeId="1" AcceptedAnswerId="1538" CreationDate="2013-10-22T20:22:09.903" Score="20" ViewCount="9549" Body="&lt;p&gt;A lot of aerials (almost by design) would be rather good attractors of lightning. What steps do I need to take in the field to keep my gear safe against a lightning strike?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm presuming the obvious already here (such as not operating in a storm), but are there any additional steps I should take?&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="29" LastEditDate="2013-12-08T13:00:00.577" LastActivityDate="2020-04-07T23:53:51.210" Title="How can I protect equipment against a lightning strike?" Tags="&lt;safety&gt;&lt;weather&gt;&lt;equipment-protection&gt;&lt;lightning&gt;" AnswerCount="5" CommentCount="4" FavoriteCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="52" PostTypeId="2" ParentId="8" CreationDate="2013-10-22T20:22:15.343" Score="4" Body="&lt;p&gt;There are a number of sites attempting to document HF digital band plans.  You'll have to poke around a bit, though, since people are experimenting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An internet search for &quot;HF digital band plan&quot; will provide new links as the following links go stale or change URL:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/band-plan&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.bandplans.com/?band=All&quot; rel=&quot;nofollow&quot;&gt;http://www.bandplans.com/?band=All&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://sharon.esrac.ele.tue.nl/dxpress/downloads/bandplannew.pdf&quot; rel=&quot;nofollow&quot;&gt;http://sharon.esrac.ele.tue.nl/dxpress/downloads/bandplannew.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9" LastEditorUserId="54" LastEditDate="2013-10-22T20:55:05.220" LastActivityDate="2013-10-22T20:55:05.220" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="53" PostTypeId="5" CreationDate="2013-10-22T20:22:24.917" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-22T20:22:24.917" LastActivityDate="2013-10-22T20:22:24.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="54" PostTypeId="4" CreationDate="2013-10-22T20:22:24.917" Score="0" Body="A hand-held electronic device; typically a transceiver for mobile operation. It may also be referenced as a walkie-talkie." OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-10-23T10:48:01.773" LastActivityDate="2013-10-23T10:48:01.773" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="55" PostTypeId="1" AcceptedAnswerId="76" CreationDate="2013-10-22T20:23:27.223" Score="19" ViewCount="8119" Body="&lt;p&gt;I've heard that when an antenna is set up, it needs to be tuned to reduce reflective power back into the radio. Is this always necessary, and if so how would I go about tuning it?&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="76" LastEditDate="2017-04-27T18:17:29.470" LastActivityDate="2017-04-27T18:17:29.470" Title="Why do I need to tune an antenna?" Tags="&lt;antenna&gt;&lt;impedance&gt;&lt;antenna-tuner&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="6" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="57" PostTypeId="2" ParentId="23" CreationDate="2013-10-22T20:26:24.297" Score="6" Body="&lt;p&gt;If you don't need mobility, purchase an inexpensive directional 4 element Yagi antenna for 2m and operate it in vertical polarization, that is with the prongs of the yagi pointing up and down.  You can sometimes find these small Yagi antennas used for ~$20-30.  But note this will only help you for 2m, and should not be used on 70cm.  For 70cm you can get a 70cm antenna, or perhaps find an antenna designed for both bands.  This will add cost, however.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One warning about external antennas:  convert from big coax down to smaller coax and a BNC or SMA plug near the HT instead of using the big coax with an adapter; a PL259 to BNC/SMA adapter may tear the bnc/sma plug from the wiring or circuit board of an HT.  &lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2013-10-22T20:26:24.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="58" PostTypeId="2" ParentId="23" CreationDate="2013-10-22T20:28:24.087" Score="1" Body="&lt;p&gt;Along with a higher gain antenna, I use an old Radio Shack HTX 20 amp. Found for around $50 on your favorite online auction or ham based classifieds. Gives 30 watts out for 5 in and only draws 6 amps. I use one with my Baofeng uv5ra and have no problem with it pluged into my acc plug in the dash..reaches repeaters with ease which I could not get before.&lt;/p&gt;&#xA;" OwnerUserId="69" LastEditorUserId="164" LastEditDate="2013-11-06T21:20:16.697" LastActivityDate="2013-11-06T21:20:16.697" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="59" PostTypeId="1" AcceptedAnswerId="106" CreationDate="2013-10-22T20:29:20.920" Score="49" ViewCount="5492" Body="&lt;p&gt;If I'm in the wilderness with ham equipment but no phone signal, how would I report an emergency? Is there a particular frequency I would use, a particular protocol or suchlike?&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="76" LastEditDate="2013-10-31T01:36:38.427" LastActivityDate="2019-06-27T15:09:03.787" Title="How do I report an emergency using ham radio?" Tags="&lt;united-kingdom&gt;&lt;emergency&gt;&lt;frequency&gt;&lt;procedure&gt;" AnswerCount="5" CommentCount="2" FavoriteCount="12" ContentLicense="CC BY-SA 3.0" />
  <row Id="60" PostTypeId="2" ParentId="2" CreationDate="2013-10-22T20:31:07.127" Score="2" Body="&lt;p&gt;By my read of &lt;a href=&quot;http://spacew.com/www/realtime.php&quot; rel=&quot;nofollow&quot;&gt;http://spacew.com/www/realtime.php&lt;/a&gt; it seems as if 10m could be open right now from Virginia.  (Virginia, which is a big state, as compared to Rhode Island or Washington DC (not technically a state, but a tiny pin-point on the map))  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your great circle distance from Washington National Airport to Honolulu International Airport is almost 7800km.  (calculated here: &lt;a href=&quot;http://www.gcmap.com/mapui?P=DCA-HNL&quot; rel=&quot;nofollow&quot;&gt;http://www.gcmap.com/mapui?P=DCA-HNL&lt;/a&gt;) As the Space Weather page explains, the MUF prediction is for a 3000km path (multiply MUF by 1.1 for a 4000km path), which means you'll have to look for the midway points and hope that your signal bounces an extra time.  Looking at the two midway points, I see that the MUF is just about 33MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More information here, too: &lt;a href=&quot;http://dx.qsl.net/propagation/propagation.html&quot; rel=&quot;nofollow&quot;&gt;http://dx.qsl.net/propagation/propagation.html&lt;/a&gt;  Also, here: &lt;a href=&quot;http://www.hamqsl.com/solar.html&quot; rel=&quot;nofollow&quot;&gt;http://www.hamqsl.com/solar.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a quick peek at what may very well be possible, you could look at the propagation predictor on the home page of &lt;a href=&quot;http://qrz.com&quot; rel=&quot;nofollow&quot;&gt;http://qrz.com&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do remember that this is all &quot;prediction&quot; - this is an experimental service so you must experiment!  In ham radio, there are no substitutes for &lt;strong&gt;listening&lt;/strong&gt; or &lt;strong&gt;transmitting&lt;/strong&gt; (on an open frequency!).    Often, you may find that you think a given band is dead, but once you call CQ a few times, someone else you haven't heard yet will pop on and tell you that he's in the middle of a conversation with someone else you can't hear.  If you're lucky, the station within earshot will have a conversation or at least a contact with you once he's done with the other fellow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many other factors affect your ability to make that contact: Are your antennas radiating in the correct direction? Is anyone listening? Are you scanning the bands to see which stations you can hear and where they're from? Are you calling CQ? If no-one is listening, you won't make a contact. If your antennas aren't right, you won't make a contact. If the conditions aren't right, you won't make a contact. If you don't call any stations, you won't make a contact. &lt;/p&gt;&#xA;" OwnerUserId="38" LastActivityDate="2013-10-22T20:31:07.127" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="61" PostTypeId="1" AcceptedAnswerId="92" CreationDate="2013-10-22T20:31:34.177" Score="4" ViewCount="79" Body="&lt;p&gt;Some factors, such as the antenna type and power output can be easily adjusted by an operator to manipulate the range of a radio signal. However, others (such as the weather) are out of operator control. What such factors can affect the range of a radio transmission, and how?&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="92" LastEditDate="2013-10-23T23:50:18.567" LastActivityDate="2013-10-23T23:50:18.567" Title="What factors (out of operator control) can affect the range?" Tags="&lt;weather&gt;&lt;space-weather&gt;&lt;range&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="62" PostTypeId="1" AcceptedAnswerId="99" CreationDate="2013-10-22T20:33:05.467" Score="4" ViewCount="108" Body="&lt;p&gt;A recent phenomena in amateur radio has been the influx of inexpensive handheld 2m/70cm radios from companies such as Baofeng. These claim to have the primary features like power output and frequency coverage that many other brands with a fraction of the price. For example I can purchase a Baofeng radio for $36.00, but the same style radio from Yaesu costs at least four times more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What am I getting for the increased cost of the name brand?&lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2013-10-22T21:31:27.237" Title="How do I evaluate the features and performance of radios?" Tags="&lt;ht&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="63" PostTypeId="1" AcceptedAnswerId="73" CreationDate="2013-10-22T20:33:43.090" Score="13" ViewCount="7180" Body="&lt;p&gt;My wife woke up several nights by a metallic &quot;thunk&quot;.  It happened to be while I was talking on 10 meters and turned out to be the ground fault circuit interrupter (GFCI) on her hair dryer cord.  Apart from the obvious answer of leaving it unplugged, I'm looking for a solution to preventing this because I'm concerned there are other effects of which I'm not aware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the time, I had not completed the grounding of my newly set up shack.  I've since established an earth ground using a backup water well point pipe in my basement (it's electrically isolated from the pump by a PVC connect pipe and is hardly used so I'm not worried about regular interference from that).  Unfortunately, the 12v supply for the HF radio doesn't seem to have a ground stud on it so I can't ground that apart from the regular mains cord ground.  The antenna mast is grounded to a typical 8ft ground rod using a 6AWG wire.  But despite my efforts at proper grounding, the problem still occurs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the GFCI tripping due to improper grounding or possibly due to RFI (which additional or better grounding wouldn't necessarily fix)?  And how could this tripping be prevented?  I'm concerned that whatever is causing this could be affecting other more sensitive (and expensive) devices in the house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Note that this is an older house - 1960s - and doesn't have any GFCI breakers or outlets where I'd expect there to be any such as the outside, garage or kitchen.  So I can't report on similar behavior in other GFCIs.)&lt;/p&gt;&#xA;" OwnerUserId="47" LastEditorUserId="8832" LastEditDate="2017-08-29T15:02:22.550" LastActivityDate="2017-08-29T15:02:22.550" Title="How do I prevent radio signals from tripping a GFCI?" Tags="&lt;rfi&gt;&lt;grounding&gt;&lt;gfci&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="64" PostTypeId="2" ParentId="55" CreationDate="2013-10-22T20:34:06.657" Score="2" Body="&lt;p&gt;Every location in which you install an antenna will be slightly different. For example there will be different characteristics of the soil, different nearby structures and plants, different heights above ground, different numbers of radials installed, and so on. Each of these factors affects the performance of the antenna, so final adjustments must be made at the site of installation. For the very best performance it is necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best tool for this is an antenna analyzer, but you can get by with the SWR meter on a transmitter. The important part of this process is to have the antenna in its final operating location when tuning, which might involve raising and lowering it multiple times.&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-10-22T20:34:06.657" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="65" PostTypeId="1" AcceptedAnswerId="75" CreationDate="2013-10-22T20:34:59.740" Score="10" ViewCount="418" Body="&lt;p&gt;The phonetic alphabet is often used on amateur radio to spell out names and callsigns more clearly, especially when the clarity may be poorer. However, there are cases where I simply forget certain parts of this - in this case, is it ok just to use any old word in its place, or would this just lead to confusion?&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="13" LastEditDate="2013-10-22T20:47:50.777" LastActivityDate="2013-10-22T21:52:49.373" Title="Is use of the phonetic alphabet mandatory?" Tags="&lt;phone&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="66" PostTypeId="2" ParentId="51" CreationDate="2013-10-22T20:35:11.280" Score="5" Body="&lt;p&gt;Many companies make lightning surge protectors.  the install in the coax to your radio and divert the strike to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;strong&gt;NOTE:&lt;/em&gt;&lt;/strong&gt; THERE IS NO SURE WAY TO PROTECT YOUR RADIO EXCEPT DISCONNECTING IT FROM POWER AND THE ANTENNA. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Search for polyphaser, they are well respected,  MFJ also makes some lower cost options..&lt;/p&gt;&#xA;" OwnerUserId="69" LastEditorUserId="63" LastEditDate="2013-10-22T20:56:57.040" LastActivityDate="2013-10-22T20:56:57.040" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="67" PostTypeId="2" ParentId="51" CreationDate="2013-10-22T20:36:43.083" Score="3" Body="&lt;p&gt;A &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-97h&quot; rel=&quot;nofollow&quot;&gt;discharge tube&lt;/a&gt; would serve to protect your rig from a close strike. Apart from that, make sure you have a decent ground for your shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, it's probably not a good idea to operate in heavy weather. Unless absolutely necessary to continue operation, I'd go QRT, and disconnect the coax from the rig.&lt;/p&gt;&#xA;" OwnerUserId="5" LastActivityDate="2013-10-22T20:36:43.083" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="68" PostTypeId="2" ParentId="8" CreationDate="2013-10-22T20:36:50.107" Score="3" Body="&lt;p&gt;As pointed out by @Michael Kjörling, the answer is different for different regions of the world. The DARC (German HAM Radio Club) published a rather good &lt;a href=&quot;http://www.darc.de/referate/hf/digitale-betriebsarten/vorzugsfrequenzen/&quot; rel=&quot;nofollow&quot;&gt;overview over the &lt;em&gt;preference frequencies&lt;/em&gt; for different digimodes on the HF bands&lt;/a&gt; valid for the &lt;strong&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/International_Amateur_Radio_Union#IARU_Region_1&quot; rel=&quot;nofollow&quot;&gt;IARU Region 1&lt;/a&gt;&lt;/strong&gt; (Africa, Europe, Middle East, northern Asia):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;CW&lt;/strong&gt;: 1'810-1'838, 3'500-3'580, 7'000-7'040, 10'100-10'140, 14'000-14'070, 18'068-18'095, 21'000-21'070, 24'890-24'915 &amp;amp; 28'000-28'070 kHz&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;PSK31&lt;/strong&gt;: 1'838, 3'580, 7'040&lt;sup&gt;#&lt;/sup&gt;, 10'140, 14'070, 18'100, 21'080, 24'920 &amp;amp; 28'120 kHz; 1 KHz bandwidth (e.g. 10'140-10'141 kHz) for QRP, +2 kHz (e.g. &gt;10'142 kHz) for PSK63 &amp;amp; PSK125&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;MFSK16&lt;/strong&gt;: 1'838-1'842, 3'583-3'600, 7'043-7'050, 10'143-10'150, 14'080-14'099, 18'103-18'109, 21'080-21'120, 24'923-24'929 &amp;amp; 28'080-28'150 kHz&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Olivia&lt;/strong&gt;&lt;sup&gt;+&lt;/sup&gt;: 1'843, 3'583, 7'043, 10'143, 14'073, 18'103, 21'073, 24'923 &amp;amp; 28'123 kHz (bandwidth &amp;lt; 500 Hz); 14'107.5 kHz (Olivia 32/1000)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;WSPR&lt;/strong&gt;: 1'836.6, 3'592.6, 5'287.2, 7'038.6, 10'138.7, 14'095.6, 18'104.6, 21'094.6, 24'924.6 &amp;amp; 28'124.6 kHz&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Hell&lt;/strong&gt;&lt;sup&gt;+&lt;/sup&gt;: 3'584, 7'044, 10'144&lt;sup&gt;§&lt;/sup&gt;, 14'074, 18'104, 21'074, 24'924 &amp;amp; 28'074 kHz&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Fax&lt;/strong&gt;: 3'735 &amp;amp; 7'165, 14'230, 18'110, 21'340, 24'930 &amp;amp; 28'680 kHz (partially also used by SSTV)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;SSTV&lt;/strong&gt;: 3'735, 7'165, 14'230, 21'340 &amp;amp; 28'680 kHz (also used by FAX)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Digital-SSTV&lt;/strong&gt;: 3'733, 7'173, 14'233, 18'1625 &amp;amp; 21'340 kHz&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;FreeDV&lt;/strong&gt;: 7'190 &amp;amp; 14'236 kHz&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;#&lt;/sup&gt; It's recommended to use frequencies above 7040 kHz (40m band goes up to 7200 KHz) for digimodes, as 7000-7040 kHz is reserved for CW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;+&lt;/sup&gt; center frequency&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;§&lt;/sup&gt; Used by the Aurora-Bake DK0WCY, too.&lt;/p&gt;&#xA;" OwnerUserId="54" LastActivityDate="2013-10-22T20:36:50.107" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="69" PostTypeId="1" AcceptedAnswerId="211" CreationDate="2013-10-22T20:39:39.443" Score="7" ViewCount="5078" Body="&lt;p&gt;Presumably setting up a 1m high antenna in a back garden isn't going to be an issue, but setting up an 80m high antenna would likely cause complaints! How high an antenna can I legally construct in the UK without going through the route of applying for planning permission (or other related red tape obstacles?)&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="63" LastEditDate="2013-10-22T20:55:43.597" LastActivityDate="2013-10-23T07:55:36.273" Title="How big can an antenna be before I need planning permission in the UK?" Tags="&lt;antenna&gt;&lt;united-kingdom&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="70" PostTypeId="2" ParentId="59" CreationDate="2013-10-22T20:40:25.193" Score="-3" Body="&lt;p&gt;Check out this website or search for &quot;ham radio wilderness protocol&quot;: &lt;a href=&quot;https://web.archive.org/web/20140108013353/http://k4jwm.com/wilderness-protocol.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ham Wilderness Protocol&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are certain frequencies that should be used but there is no guarantee. &lt;/p&gt;&#xA;" OwnerUserId="69" LastEditorUserId="4361" LastEditDate="2019-06-27T15:09:03.787" LastActivityDate="2019-06-27T15:09:03.787" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="71" PostTypeId="2" ParentId="55" CreationDate="2013-10-22T20:42:20.573" Score="5" Body="&lt;p&gt;Your transmitter has something called an &quot;output impedance&quot; and expects to be loaded with this impedance.  The standard is 50 ohms.  You don't need to look up the output impedance, it was standardized and anything made in the last 50 years will expect 50 ohms. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 50 ohms the tranmitter expects is measured at RF frequencies.  Many antennas look like short circuits (a loop) or open circuits (two independent wires, like a dipole) at DC, but change at radio frequencies.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern transceivers often include an SWR meter.  SWR, or standing wave ratio, should be 1 when there is no reflection.  Many transceivers will tolerate an SWR of up to 2.0, but the closer this number is to 1.0, the better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also buy an antenna analyzer as a stand alone instrument to measure impedance and SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dipole antenna (two wires, each 1/4 wavelength, travelling opposite directions) is between 50-70 ohms for its center frequency and can often be used as-is.  But you should still check it with an SWR meter or the SWR meter in your radio.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas that do not present 50 ohms require a circuit to transform the antenna impedance, whatever it is, to the 50 ohms expected by the transmitter output. This circuit can sometimes be made by adding funny shaped parts onto the antenna -- not just any funny shaped parts, though -- this is a matter for serious engineering.  Other times the transformation is solved by a box called an &quot;antenna tuner&quot;, which remains permanently in place.  You can find both manual old-timey antenna tuners and automated tuners for HF.  For VHF and up, the antenna usually has an adjustable component like a slider.  &lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2013-10-22T20:42:20.573" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="72" PostTypeId="1" AcceptedAnswerId="90" CreationDate="2013-10-22T20:43:36.913" Score="25" ViewCount="3785" Body="&lt;p&gt;Am I allowed to send encrypted traffic via any medium or any frequency, or is this completely barred (and thus everything has to be open with no exceptions?)&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="19" LastEditDate="2013-10-23T17:32:27.950" LastActivityDate="2017-08-17T20:28:33.940" Title="Encrypted traffic and amateur radio" Tags="&lt;united-kingdom&gt;&lt;legal&gt;&lt;encryption&gt;" AnswerCount="7" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="73" PostTypeId="2" ParentId="63" CreationDate="2013-10-22T20:44:04.683" Score="10" Body="&lt;p&gt;Some older GFCI circuits were known to be susceptible to stray RF. The &lt;a href=&quot;http://www.arrl.org/gfci-and-afci-devices&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL recommends&lt;/a&gt; replacing these older breakers with new ones that they have listed at the link I provided.&lt;/p&gt;&#xA;" OwnerUserId="43" LastEditorUserId="43" LastEditDate="2016-11-23T21:43:03.717" LastActivityDate="2016-11-23T21:43:03.717" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="74" PostTypeId="2" ParentId="65" CreationDate="2013-10-22T20:44:34.977" Score="6" Body="&lt;p&gt;It's not uncommon to use other words in place of the standard &lt;a href=&quot;http://en.wikipedia.org/wiki/NATO_phonetic_alphabet&quot; rel=&quot;nofollow&quot;&gt;NATO Phonetic Alphabet&lt;/a&gt;. For example, my callsign is K7FOS, and I typically say Kilo Seven Foxtrot Ocean Sugar after saying the NATO style because it can often be easier to interpret &quot;Sugar&quot; over &quot;Sierra&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use whatever works in order to get your message over the air effectively.&lt;/p&gt;&#xA;" OwnerUserId="80" LastEditorUserId="80" LastEditDate="2013-10-22T20:52:51.197" LastActivityDate="2013-10-22T20:52:51.197" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="75" PostTypeId="2" ParentId="65" CreationDate="2013-10-22T20:46:19.730" Score="12" Body="&lt;p&gt;Part 97, section 119 covers this.  &quot;Use of a phonetic alphabet as an aid for correct station identification is encouraged&quot;.  Most everyone has settled on the NATO phonetic alphabet, even though its elements have varying numbers of syllables (one to three!) and aren't comprised exclusively of trochees &lt;a href=&quot;http://xkcd.com/856/&quot;&gt;http://xkcd.com/856/&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To put this another way, if you make it difficult for another station to understand you, they're not likely to want to speak to you.&lt;/p&gt;&#xA;" OwnerUserId="38" LastActivityDate="2013-10-22T20:46:19.730" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="76" PostTypeId="2" ParentId="55" CreationDate="2013-10-22T20:46:44.520" Score="13" Body="&lt;p&gt;There are two different parts to antenna tuning: &lt;strong&gt;transmission line impedance matching&lt;/strong&gt; and &lt;strong&gt;resonance&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is at &lt;em&gt;resonance&lt;/em&gt; when it presents a purely resistive load to the transmitter. That is, the reactive component of the load is 0: there exists no inductance or capacitance in the load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, &lt;em&gt;resonance says nothing about the value of the resistive component of the load&lt;/em&gt;. Usually, you also want to reduce the impedance mismatch, because an impedance mismatch causes power to be reflected at the point of the mismatch. Most amateur radio equipment is built to expect a resistive load of 50 ohm impedance, which is the characteristic impedance of most coaxial cables used in radio applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An &lt;em&gt;antenna tuner&lt;/em&gt; or ATU doesn't actually tune the antenna; it provides a matching network. On one side the transmitter sees a nice, orderly, purely resistive 50 ohms. On the other side is an unwieldy antenna, the impedance of which at the given frequency can be anything from purely resistive at 50 ohms to some odd-ball combination of weird resistance and either inductance or capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is done by introducing either capacitance or inductance into the feedline, to cancel out the corresponding part of the load impedance. For a fixed antenna installation on a single frequency, you can even determine appropriate component values and use fixed-value components to make up such a matching network, but that lends itself poorly to the applications in which one wants to move frequencies, antennas and so on. &lt;em&gt;As a matter of fact, that is the approach taken by many electrically short antennas&lt;/em&gt; and it comes at the cost of reduced antenna bandwidth (because the fixed matching network can only compensate, with an acceptable SWR, within a limited range of frequencies).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;The SWR&lt;/em&gt; or Standing Wave Ratio is related to the (mis)match in impedance. This means that your perfectly resonant antenna which happens to present a nice, clean, purely resistive 150 ohms (pulling a number out of thin air here) at the feedpoint and at a given frequency will give you a 3:1 SWR against 50 ohm coax, &lt;em&gt;despite being at resonance.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, even with an ATU, it's important to remember that the reflected power must go somewhere, and in this case, at least some of it is being dissipated as heat rather than radiated as RF. While you aren't likely to do much harm with some reflected power from an over-the-counter 100W transceiver, this can be a serious consideration if you are running a high-powered transmitter and/or a large amplifier.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-02T19:46:33.783" LastActivityDate="2013-12-02T19:46:33.783" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="77" PostTypeId="1" AcceptedAnswerId="93" CreationDate="2013-10-22T20:47:17.867" Score="5" ViewCount="152" Body="&lt;p&gt;How would I go about setting up my own repeater in the UK? For instance, what license category would I need, what equipment would should be looking to purchase, and do I have to register it anywhere?&lt;/p&gt;&#xA;" OwnerUserId="65" LastActivityDate="2013-10-22T21:14:06.350" Title="How would I go about setting up my own repeater in the UK?" Tags="&lt;united-kingdom&gt;&lt;repeater&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="78" PostTypeId="5" CreationDate="2013-10-22T20:49:31.173" Score="0" Body="&lt;p&gt;This tag is for any questions about analog voice modes, including what bands are allocated for phone use, what modes qualify as phone, how the different modulation schemes compare, and how to make a QSO on a phone mode.&lt;/p&gt;&#xA;" OwnerUserId="322" LastEditorUserId="322" LastEditDate="2013-11-07T14:39:13.557" LastActivityDate="2013-11-07T14:39:13.557" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="79" PostTypeId="4" CreationDate="2013-10-22T20:49:31.173" Score="0" Body="Questions about the phone modes, most commonly SSB on HF and FM on VHF/UHF, but also including DSB-SC, PM, or AM." OwnerUserId="63" LastEditorUserId="322" LastEditDate="2013-11-07T14:40:12.547" LastActivityDate="2013-11-07T14:40:12.547" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="80" PostTypeId="1" CreationDate="2013-10-22T20:49:33.333" Score="5" ViewCount="189" Body="&lt;p&gt;A quick follow-up to &lt;a href=&quot;https://ham.stackexchange.com/questions/16/what-should-i-consider-when-choosing-a-coaxial-cable&quot;&gt;What should I consider when choosing a coaxial cable?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most commercial rigs come with a PL259/SO239 connector for use with something like the RG8/RG11. In the event the diameter of the cable used is significantly smaller; say RG58/RG59, it may be possible to marry the cable to the connector directly. I've even seen it done, but ...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The alternative, of course, is to use an adapter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When should I use an adapter to marry an outsized/narrow coax to a connector? &lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-05-04T15:07:57.623" Title="When should an adapter be used to marry a coax to a connector?" Tags="&lt;feed-line&gt;&lt;connectors&gt;&lt;coaxial-cable&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="81" PostTypeId="5" CreationDate="2013-10-22T20:51:29.323" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-22T20:51:29.323" LastActivityDate="2013-10-22T20:51:29.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="82" PostTypeId="4" CreationDate="2013-10-22T20:51:29.323" Score="0" Body="Use this tag for questions regarding RFI (Radio Frequency Interference)." OwnerUserId="63" LastEditorUserId="4665" LastEditDate="2020-12-17T16:29:37.483" LastActivityDate="2020-12-17T16:29:37.483" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="83" PostTypeId="2" ParentId="72" CreationDate="2013-10-22T20:51:31.987" Score="11" Body="&lt;p&gt;If you are in the USA, check &lt;code&gt;§ 97.113 Prohibited transmissions&lt;/code&gt; of the FCC rules.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(4) Music using a phone emission except as specifically provided&#xA;  elsewhere in this section; communications intended to facilitate a&#xA;  criminal act; &lt;strong&gt;messages encoded for the purpose of obscuring their&#xA;  meaning, except as otherwise provided herein&lt;/strong&gt;; obscene or indecent&#xA;  words or language; or false or deceptive messages, signals or&#xA;  identification.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As it stands now, encryption is prohibited regardless of your frequency.&lt;/p&gt;&#xA;" OwnerUserId="80" LastActivityDate="2013-10-22T20:51:31.987" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="84" PostTypeId="2" ParentId="80" CreationDate="2013-10-22T20:55:32.630" Score="3" Body="&lt;p&gt;Always use a connector intended for the size of coax you are using. Every adapter has a certain insertion loss - a cost, in decibels, of &quot;inserting&quot; it into the line. It's best to use the correct connectors directly on the coax whenever possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are PL-259 connectors available for RG-58. I don't want to endorse any particular vendor, so try your friendly local ham dealer or &lt;a href=&quot;https://www.google.com/search?q=PL259%20RG58&amp;amp;oq=PL259%20RG58&amp;amp;aqs=chrome..69i57j0l5.4408j0j8&amp;amp;sourceid=chrome&amp;amp;espv=210&amp;amp;es_sm=122&amp;amp;ie=UTF-8&quot; rel=&quot;nofollow&quot;&gt;Google&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T20:55:32.630" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="85" PostTypeId="2" ParentId="72" CreationDate="2013-10-22T20:56:03.683" Score="0" Body="&lt;p&gt;In India, the &lt;a href=&quot;http://www.qsl.net/vu2msy/asocrules.htm&quot; rel=&quot;nofollow&quot;&gt;Indian Wireless Telegraph Act (Amateur Service)&lt;/a&gt; rules mandate the operator transmit in plain language. Unfortunately I'm unable to locate a copy on the WPC web-site; hence a link to a copy by a fellow ham OM vu2mue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Defining the conduct of an Amateur Station in Annexure I - Section II.1.b &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(b) Transmissions shall be made in plain language and limited to messages of a technical nature relating to tests and to remarks of personal character (excluding business affairs or transactions) in which the licensee, or the person with whom he is in communication, are directly concerned and for which, by reason of their unimportance, recourse to the public telecommunication service is not justified. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-10-23T15:39:43.307" LastActivityDate="2013-10-23T15:39:43.307" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="86" PostTypeId="2" ParentId="72" CreationDate="2013-10-22T20:56:24.093" Score="6" Body="&lt;p&gt;It is prohibited in the US, with one exception. One is allowed to encrypt commands to an amateur satellite (Send from the ground to the satellite). Aside from that, encryption is prohibited.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-02-14T17:49:35.427" LastActivityDate="2014-02-14T17:49:35.427" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="87" PostTypeId="2" ParentId="80" CreationDate="2013-10-22T20:57:31.917" Score="3" Body="&lt;p&gt;Ideally you should use a connect on the cable that matches the radio connector.  But obviously, if you are going from say RG8 with a PL259 to an HT with a BNC/TNC/SNA, you are going to have a hard time finding a connector that fits that cable so you'll have to use an adapter.  But remember that adapters introduce loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are going from a small cable to a larger connector, like a PL259 on RG58, there are inserts to resize the outside shield collar to a small diameter to accommodate the cable.&lt;/p&gt;&#xA;" OwnerUserId="47" LastActivityDate="2013-10-22T20:57:31.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="88" PostTypeId="2" ParentId="65" CreationDate="2013-10-22T21:03:33.833" Score="0" Body="&lt;p&gt;Under difficult conditions, I have often found it effective to alternate between phonetics when giving my callsign, e.g.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alpha Alpha Six Yankee Quebec followed by America America Six Yokohama Queen&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes the QRM or QRN obscures some syllables more than others...&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-22T21:03:33.833" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="89" PostTypeId="2" ParentId="62" CreationDate="2013-10-22T21:03:51.487" Score="1" Body="&lt;p&gt;You generally get polish and and reliability from name brands that you may not get from the cheap knock off radios. That said, you really can't beat the price - it's worth it to get one and try it - just keep in mind it might be a little quirky.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;eHam is a good place to read reviews: &lt;a href=&quot;http://www.eham.net/reviews/&quot; rel=&quot;nofollow&quot;&gt;http://www.eham.net/reviews/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="81" LastActivityDate="2013-10-22T21:03:51.487" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="90" PostTypeId="2" ParentId="72" CreationDate="2013-10-22T21:08:34.040" Score="15" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;11(2) The Licensee shall only address Messages to other Amateurs or to the stations of those Amateurs and shall not encrypt these Messages for the purpose of rendering the Message unintelligible to other radio spectrum users.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://services.ofcom.org.uk/amateur-terms.pdf&quot;&gt;the terms and conditions spelt out by OFCOM (pdf)&lt;/a&gt;, the UK communications regulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, in &lt;a href=&quot;http://www.ofcom.org.uk/static/archive/ra/publication/ra_info/br68r11/br68.htm&quot;&gt;the license guidelines&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;1(4) The Licensee shall address Messages only to other licensed amateurs or the stations of licensed amateurs and shall send only:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) Messages relating to technical investigations or remarks of a personal character; or&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) Signals &lt;strong&gt;(not enciphered)&lt;/strong&gt; which form part of, or relate to, the transmission of Messages.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="22" LastActivityDate="2013-10-22T21:08:34.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="91" PostTypeId="2" ParentId="34" CreationDate="2013-10-22T21:08:34.850" Score="4" Body="&lt;p&gt;Two drawbacks to ignoring your grounding:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;You will have a poor(er) signal.&lt;/li&gt;&#xA;&lt;li&gt;&lt;em&gt;&lt;strong&gt;You&lt;/em&gt;&lt;/strong&gt; could become the ground and experience an RF burn first-hand.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;That said, VHF antennas are often not grounded - handhelds and VHF radios in cars, for example.  &lt;/p&gt;&#xA;" OwnerUserId="38" LastActivityDate="2013-10-22T21:08:34.850" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="92" PostTypeId="2" ParentId="61" CreationDate="2013-10-22T21:10:19.897" Score="3" Body="&lt;p&gt;On HF, &quot;range&quot; is a function of propagation, which is affected by the signal's frequency, the solar flux, geogmagnetic conditions (&quot;space weather&quot;), the state of the ionosphere along the path the signal traverses, the number of &quot;hops&quot; required between reflective ionospheric layers and the earth, and whether the earth reflections are over land or saltwater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Propagation prediction programs create models of the ionosphere and a signal's path through it to predict overall attenuation, which forecasts the fraction of the original signal's power that will be received at a particular destination.&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-22T21:10:19.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="93" PostTypeId="2" ParentId="77" CreationDate="2013-10-22T21:14:06.350" Score="5" Body="&lt;p&gt;Repeaters take time and money to set up and maintain. Many repeaters are operated by a club or a group - you may want to consider pooling resources with other local hams.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unlike in the US, UK amateur repeaters are &lt;a href=&quot;http://www.ofcom.org.uk/static/archive/ra/topics/amateur/document/guide.htm&quot; rel=&quot;noreferrer&quot;&gt;individually licensed&lt;/a&gt;. You must get approval from Ofcom, including a Notice of Variation. This is because your base license does not allow repeater operation, the Notice of Variation modifies the terms of your license. There are both technical and regulatory requirements, including yearly notifications to Ofcom that the repeater is still running.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before you do so, you'll need to find a frequency that isn't already used in your area. The frequency coordination is done through &lt;a href=&quot;https://www.rsgblicensing.org.uk/etccsecureforms/e1-secure.php&quot; rel=&quot;noreferrer&quot;&gt;ETCC&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Working with someone in your area directly is the best way to start this process. Don't try to dive in to all the forms until you've been able to work out your plan - including a site and the actual hardware - especially if this is your first repeater project.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T21:14:06.350" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="94" PostTypeId="1" CreationDate="2013-10-22T21:15:01.150" Score="8" ViewCount="121" Body="&lt;p&gt;A number of government agencies around the world provide ionospheric predictions, such as vertical foF2 or oblique path useable frequency range advice. Examples include &lt;a href=&quot;http://www.ips.gov.au&quot; rel=&quot;nofollow&quot;&gt;IPS&lt;/a&gt;, &lt;a href=&quot;http://www.swpc.noaa.gov/storm/index.html&quot; rel=&quot;nofollow&quot;&gt;SWPC&lt;/a&gt; and &lt;a href=&quot;http://www.iono.noa.gr/DIAS/&quot; rel=&quot;nofollow&quot;&gt;DIAS&lt;/a&gt;. Typically, the major customers of these agencies are in aviation and maritime (for HF comms) and defence (for comms and radar).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are these kinds of services used by amateur radio operators? If so, how useful are they (compared with having to operate without any such advice?).&lt;/p&gt;&#xA;" OwnerUserId="92" LastEditorUserId="92" LastEditDate="2013-10-23T21:24:48.093" LastActivityDate="2013-10-23T21:24:48.093" Title="Are ionospheric predictions useful in practice for ham radio operators?" Tags="&lt;propagation&gt;&lt;ionosphere&gt;&lt;space-weather&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="95" PostTypeId="1" AcceptedAnswerId="436" CreationDate="2013-10-22T21:15:06.167" Score="18" ViewCount="3944" Body="&lt;p&gt;Specifically, I understand that OCF dipoles change the SWR, but does it do this via reactance or resistance, or both?&lt;/p&gt;&#xA;" OwnerUserId="43" LastEditorUserId="76" LastEditDate="2015-12-15T20:41:43.630" LastActivityDate="2017-05-24T13:33:11.053" Title="How does moving a feedpoint off-center in a dipole affect the resonant frequency and resistive load?" Tags="&lt;antenna&gt;&lt;impedance&gt;&lt;dipole&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="96" PostTypeId="2" ParentId="65" CreationDate="2013-10-22T21:20:50.813" Score="5" Body="&lt;p&gt;The TL;DR; answer is No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The slightly longer answer is still No! - and listening to any pile-up will show it is not the case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, QRN, QRM and QSB are often referred to as &quot;Q R Nancy, Q R Mexico and Q S Baltimore respectively (not November, Mike and Sierra)...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The point of any &quot;code&quot; is to make sure the recipient understands the transmission... and the advantage of the NATO Standard Phonetic Alphabet is that most (if not all) operators (should) know the letters, which is especially important when dealing with non-English native-speakers.&lt;/p&gt;&#xA;" OwnerUserId="93" LastActivityDate="2013-10-22T21:20:50.813" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="97" PostTypeId="2" ParentId="51" CreationDate="2013-10-22T21:23:33.000" Score="6" Body="&lt;p&gt;QST magazine printed a comprehensive three part article in 2002 addressing lighting: &lt;em&gt;Lightning Protection for the Amateur Radio Station&lt;/em&gt;. They are &lt;a href=&quot;http://www.arrl.org/lightning-protection&quot; rel=&quot;nofollow noreferrer&quot;&gt;republished by the ARRL&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/0206056.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;QST June 2002, pp. 56-59&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/0207048.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;QST July 2002, pp. 48-52&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/0208053.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;QST August 2002, pp. 53-55&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The &lt;em&gt;surest&lt;/em&gt; way to protect your radio gear is to disconnect it from power, from the antenna, from your computer and even from ground. And even that is no guarantee -- a while back I had an &lt;strong&gt;enormous&lt;/strong&gt; bolt of lightning strike my backyard.  I had three transceivers; one rig was still connected to my computer and both the computer and rig were smoldering.  The other two rigs were also fried despite being disconnected from power and antenna.  My presumption is that the electromagnetic field from the lightning was powerful enough to destroy components in the rigs. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a hassle, but disconnect your rigs from power, antenna and computer.&lt;/p&gt;&#xA;" OwnerUserId="83" LastEditorUserId="9621" LastEditDate="2019-04-10T16:36:24.210" LastActivityDate="2019-04-10T16:36:24.210" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="98" PostTypeId="2" ParentId="94" CreationDate="2013-10-22T21:25:41.187" Score="2" Body="&lt;p&gt;As a (fairly) regular member of the &lt;a href=&quot;http://www.worked-all-britain.co.uk&quot; rel=&quot;nofollow&quot;&gt;Worked All Britain&lt;/a&gt; net on 40m, the foF2 (I use the &lt;a href=&quot;http://www.wdc.rl.ac.uk/cgi-bin/digisondes/latest_view2gif.pl?Station=chilton&quot; rel=&quot;nofollow&quot;&gt;Chiltern Ionogram&lt;/a&gt;) critical frequency is one that I watch carefully, as it gives a pretty reasonable indication as to whether inter-G contact (for the WAB squares) is possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that Chiltern can be temperamental, I do not rely on it, but it is certainly worth consulting before embarking on any mobile activity.&lt;/p&gt;&#xA;" OwnerUserId="93" LastActivityDate="2013-10-22T21:25:41.187" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="99" PostTypeId="2" ParentId="62" CreationDate="2013-10-22T21:31:27.237" Score="1" Body="&lt;p&gt;You're getting a better warranty and the ability to send it for repair if you have issues. You get a better manual, a programming and operation experience that has been improved based on the feedback of the ham community over every model of radio they've produced. The programming software is often better for established brands (although there's third party software for the Wouxun portables that isn't half bad). You probably get a better front end, meaning better sensitivity especially in RF noisy areas, as well as cleaner filters, meaning cleaner transmit and receive signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've used a Wouxun and a Yaesu side by side. I'm always afraid I'll break the Yaesu because it costs that much more. They're both pretty sturdy. The Wouxun menu is limited (six character display vs Yaesu's full LCD screen), the Yaesu has more features including wide band receive and 220MHz coverage. The Yaesu is much more comfortable to field program once you get the hang of it, whereas the Wouxun can't even have its scan list programmed in the field.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T21:31:27.237" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="100" PostTypeId="1" AcceptedAnswerId="105" CreationDate="2013-10-22T21:33:35.030" Score="2" ViewCount="1116" Body="&lt;p&gt;I'm living at the 6th's and top floor of an apartment building. I have a balcony with a metal balustrade. Above the balcony there is a metal roof rail. I need an antenna which won't be noticed by the house owner or which can be put away easily while not being used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One thought I had was talking to my neighbor, who has a balcony roughly 6m away, whether I could throw a cable over. If this is done close to the wall it might be hardly noticeable from the ground. The issue I see is that both ends will end close to the metal balustrades and be close to the house wall which I fear will be causing trouble with emitting and receiving radio waves in good quality.&lt;/p&gt;&#xA;" OwnerUserId="85" LastEditorUserId="87" LastEditDate="2013-10-26T16:44:01.123" LastActivityDate="2013-10-26T16:44:01.123" Title="What antenna to use for medium frequencies in an apartment building?" Tags="&lt;antenna&gt;&lt;hf&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="101" PostTypeId="2" ParentId="45" CreationDate="2013-10-22T21:38:44.020" Score="4" Body="&lt;p&gt;OK, I'm a mere Foundation Licence holder, but other than the increased power, no extra privileges open up at Intermediate Level - it is only with the Advanced/Full Licence that the extras arrive&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mostly these around Notice of Variations to hold &lt;a href=&quot;http://rsgb.org/main/operating/licensing-novs-visitors/special-event-stations/&quot; rel=&quot;nofollow&quot;&gt;Special Event calls&lt;/a&gt; and/or operate Club callsigns and/or to &lt;a href=&quot;http://rsgb.org/main/operating/licensing-novs-visitors/other-nov/&quot; rel=&quot;nofollow&quot;&gt;set up and run a repeater&lt;/a&gt; - and to operate on some extra bands (eg LF and 5MHz)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Foundation and Intermediate licensees cannot operate Special Event or Club Calls except under supervision, and cannot operate on LF or 5MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other bonus for Advanced Licencees (not available to Foundation of Intermediates) is to operate as Maritime Mobile (at sea) or overseas (&lt;a href=&quot;http://rsgb.org/main/operating/licensing-novs-visitors/operating-abroad/&quot; rel=&quot;nofollow&quot;&gt;under CEPT reciprocal terms&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;--&#xA;Edit: At the time of writing the first sentence was correct... but within seven months of that post, I'd progressed through the Intermediate to the Full Licence... but the answer still holds!&lt;/p&gt;&#xA;" OwnerUserId="93" LastEditorUserId="93" LastEditDate="2015-06-14T19:18:32.893" LastActivityDate="2015-06-14T19:18:32.893" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="102" PostTypeId="2" ParentId="59" CreationDate="2013-10-22T21:48:33.200" Score="7" Body="&lt;p&gt;If this is something you are interested in on an ongoing basis as a volunteer, then you should look into joining RACES and/or ARES in the US, and RAYNET in the UK:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Radio_Amateur_Civil_Emergency_Service&quot; rel=&quot;noreferrer&quot;&gt;http://en.wikipedia.org/wiki/Radio_Amateur_Civil_Emergency_Service&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Amateur_Radio_Emergency_Service&quot; rel=&quot;noreferrer&quot;&gt;http://en.wikipedia.org/wiki/Amateur_Radio_Emergency_Service&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Radio_Amateurs_Emergency_Network&quot; rel=&quot;noreferrer&quot;&gt;http://en.wikipedia.org/wiki/Radio_Amateurs_Emergency_Network&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.raynet-uk.net/&quot; rel=&quot;noreferrer&quot;&gt;http://www.raynet-uk.net/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, during major emergencies and disasters, one or both of these organizations may be the only hams allowed to operate, and it will be a very organized effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Outside of that, here are the US regulations for licensed hams:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;§ 97.403 Safety of life and protection of property.&#xA;No provision of these rules prevents the use by an amateur station of any&#xA;means of radio communication at its disposal to provide essential communication&#xA;needs in connection with the immediate safety of human life and immediate&#xA;protection of property when normal communication systems are&#xA;not available.&#xA;§ 97.405 Station in distress.&#xA;(a) No provision of these rules prevents the use by an amateur station in&#xA;distress of any means at its disposal to attract attention, make known its condition&#xA;and location, and obtain assistance.&#xA;(b) No provision of these rules prevents the use by a station, in the exceptional&#xA;circumstances described in paragraph (a) of this section, of any&#xA;means of radio communications at its disposal to assist a station in distress.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This basically says that under those circumstances in the US, you can operate in any band, in any mode, in an effort to communicate the distress, including the ones you are not licensed for.&lt;/p&gt;&#xA;" OwnerUserId="96" LastEditorUserId="285" LastEditDate="2013-11-04T17:31:00.337" LastActivityDate="2013-11-04T17:31:00.337" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="103" PostTypeId="2" ParentId="2" CreationDate="2013-10-22T21:51:38.450" Score="2" Body="&lt;p&gt;Start with the ARRL propagation forecasts. These are updated every month and there is a specific forecast for the path from the East coast to Hawaii.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/propagation&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/propagation&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a customized prediction, use the online VOACAP propagation predictor here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.voacap.com/&quot; rel=&quot;nofollow&quot;&gt;http://www.voacap.com/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, you may want to check in with the 3905 Century Club nets. Those are on several bands at several times per day, and are dedicated to WAS and similar awards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.3905ccn.com/newsite/index.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.3905ccn.com/newsite/index.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-10-22T21:51:38.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="105" PostTypeId="2" ParentId="100" CreationDate="2013-10-22T22:06:10.790" Score="4" Body="&lt;p&gt;So it sounds like you want to do everything. There's nothing wrong with that, but there's no single answer of one antenna that can do everything. You are going to hit a certain wall at either 40 or 80 meters where there's just nothing you can do with the space you have, but here are some solutions for frequencies above those. Google (try &quot;compromise antenna HF&quot;, &quot;apartment antenna ham&quot;, and the terms below for more) will find thousands of pages of people in the same position as you are!&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Lower HF bands (20m, 30m, 40m, 80m) - you're not likely to be able to get a dipole at these lengths to fit anywhere. You can try a loaded dipole to get it shorter but your best bet is likely to be either a random wire antenna or a magnetic loop antenna. There are ways to do either of those completely homebrew or completely commercial, and you'll be able to get a few different bands either way.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Higher HF bands (6m, 10m, 12m, 15m, 17m) - in addition to the solutions above, you may be able to get away with a dipole or random wire outside at these lengths. All you need is two points, a half wavelength apart. At 10 meters, that's pretty easy to do - a five meter antenna with the feed point in the center. Again, can be done with parts from the hardware store or you can buy a fully built and tested dipole, off-center fed dipole, or G5RV antenna.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;VHF/UHF (144MHz, 222MHz, 430MHz) - this one is easy. The antennas are tiny, you can easily mount one on a mag-mount base and stick it on your balcony. It won't be ideal because you won't have the same ground plane that a metal roof would get you, but it will be good enough. The J-pole is another common antenna at these frequencies. It's important to note that if you use a normal quarter wave dipole, you'll need to use it vertically, to match the vertical polarization of most handheld radios.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Microwave (GHz range) - this band is the experimenter's dream. You don't need a big antenna, but you do need specialized components and there isn't as much activity up here. Certainly something to consider, but you probably want to get something set up on one of the lower bands first.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T22:06:10.790" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="106" PostTypeId="2" ParentId="59" CreationDate="2013-10-22T22:16:55.827" Score="35" Body="&lt;p&gt;On voice, use &quot;Mayday Mayday Mayday&quot; at the beginning and end of the transmission. This is only for life-threatening emergencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Mayday_(distress_signal)&quot; rel=&quot;noreferrer&quot;&gt;http://en.wikipedia.org/wiki/Mayday_(distress_signal)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For other emergency situations, like reporting a wildfire that does not directly threaten you, use &quot;Break Emergency&quot; at the beginning of the call. This is a good guide to making emergency calls:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.dummies.com/how-to/content/operating-your-ham-radio-in-an-emergency.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.dummies.com/how-to/content/operating-your-ham-radio-in-an-emergency.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The IARU has established global emergency frequencies. They call these &quot;Emergency Centre of Activity Frequencies&quot;.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;15m  21.360 MHz&#xA;17m  18.160 MHz &#xA;20m  14.300 MHz&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;In the US, 14.300 MHz has an organized group of monitors (&lt;a href=&quot;http://14300.net/&quot; rel=&quot;noreferrer&quot;&gt;http://14300.net/&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A full list of regional and country-specific emergency frequencies is here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.iaru-r1.org/index.php?option=com_content&amp;amp;view=article&amp;amp;id=891&amp;amp;Itemid=246&quot; rel=&quot;noreferrer&quot;&gt;http://www.iaru-r1.org/index.php?option=com_content&amp;amp;view=article&amp;amp;id=891&amp;amp;Itemid=246&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Wilderness Protocol for VHF/UHF (&lt;a href=&quot;http://k4jwm.com/wilderness-protocol.htm&quot; rel=&quot;noreferrer&quot;&gt;http://k4jwm.com/wilderness-protocol.htm&lt;/a&gt;) is useful if you have line of sight communication. That might not be the case in mountainous terrain. The Wilderness Protocol was started in the US, so I have no idea how often it is used outside the US.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, amateur radio requires practice for effective emergency use. In a group, you need at least two practiced operators, because one of them might be injured. In most situations, a satellite phone is a better and more reliable choice for backcountry emergency communication. I go into more detail on that in this blog post:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://observer.wunderwood.org/2011/10/12/emergency-communication-in-the-wilderness/&quot; rel=&quot;noreferrer&quot;&gt;https://observer.wunderwood.org/2011/10/12/emergency-communication-in-the-wilderness/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One good way to get practice with back country operating is to participate in Summits on the Air (SOTA). The common SOTA frequencies might also be a good choice for secondary emergency frequencies, because the SOTA &quot;chasers&quot; often monitor those.&lt;/p&gt;&#xA;" OwnerUserId="10" LastEditorUserId="10" LastEditDate="2017-06-20T14:54:01.177" LastActivityDate="2017-06-20T14:54:01.177" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="107" PostTypeId="5" CreationDate="2013-10-22T22:26:55.753" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-22T22:26:55.753" LastActivityDate="2013-10-22T22:26:55.753" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="108" PostTypeId="4" CreationDate="2013-10-22T22:26:55.753" Score="0" Body="Handheld Transceiver, or Handie-Talkie. A hand-held radio that looks like a large walkie-talkie, capable of transmitting and receiving amateur radio bands. Often can receive other bands as well." OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-10-24T19:05:30.550" LastActivityDate="2013-10-24T19:05:30.550" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="109" PostTypeId="1" CreationDate="2013-10-22T22:33:59.823" Score="5" ViewCount="101" Body="&lt;p&gt;I want to get involved in emergency preparedness. What organizations, if any, are there in the United States that support disaster recovery and emergency management?&lt;/p&gt;&#xA;" OwnerUserId="19" LastEditorUserId="29" LastEditDate="2013-11-22T08:36:14.893" LastActivityDate="2013-11-22T08:36:14.893" Title="What organizations in the USA can I join to participate in emergency preparedness?" Tags="&lt;united-states&gt;&lt;emergency&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="110" PostTypeId="2" ParentId="13" CreationDate="2013-10-22T22:40:03.083" Score="10" Body="&lt;p&gt;A balun matches a balanced load to an unbalanced line, but it can also do other useful things. A current balun can present a high impedance to common-mode signals, which will help reject noise. Common mode signals are the same on both conductors, so are not &quot;balanced&quot; or differential.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An unun is an impedance transformer, usually &lt;code&gt;4:1&lt;/code&gt; or &lt;code&gt;9:1&lt;/code&gt;, which matches an unbalanced antenna to a feedline. A &lt;code&gt;9:1&lt;/code&gt; transformer is often used for an end-fed half wave antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This document by Jim Brown (K9YC) is long, but tremendously helpful in understanding baluns, chokes, and reducing RF noise:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing&quot;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10" LastEditorUserId="13000" LastEditDate="2019-07-26T14:37:24.273" LastActivityDate="2019-07-26T14:37:24.273" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="111" PostTypeId="1" AcceptedAnswerId="498" CreationDate="2013-10-22T22:42:21.263" Score="15" ViewCount="5477" Body="&lt;p&gt;What are the relative advantages and disadvantages of using 50 Ohm coaxial cable as opposed to 450 Ohm or 600 Ohm ladder or window line?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="87" LastEditDate="2013-10-30T13:23:33.223" LastActivityDate="2013-11-02T10:01:42.543" Title="50 Ohm coaxial cable vs 450 Ohm or 600 Ohm ladder or window line?" Tags="&lt;feed-line&gt;&lt;coaxial-cable&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="115" PostTypeId="1" CreationDate="2013-10-22T22:47:21.903" Score="2" ViewCount="97" Body="&lt;p&gt;Just for additional information, I live in the United States.&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="8832" LastEditDate="2017-08-31T03:39:20.957" LastActivityDate="2017-09-04T02:55:07.287" Title="What kind of additional privileges or access do I get with each successive US license?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="116" PostTypeId="1" CreationDate="2013-10-22T22:48:25.963" Score="10" ViewCount="278" Body="&lt;p&gt;What does this term mean? I'm not good with radio terms at all, but I was especially curious about this one...&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="87" LastEditDate="2013-11-11T03:02:12.463" LastActivityDate="2013-11-11T03:02:12.463" Title="What is Jamboree on the Air (JOTA)?" Tags="&lt;jargon&gt;&lt;jota&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="117" PostTypeId="1" CreationDate="2013-10-22T22:49:26.223" Score="16" ViewCount="3780" Body="&lt;p&gt;Can a licensed ham use or modify CB equipment to work the 10 Meter Amateur bands? If so, are there any advantages/disadvantages to this?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="873" LastEditDate="2015-06-23T03:47:53.533" LastActivityDate="2019-06-02T22:04:56.197" Title="Can a licensed ham use or modify CB equipment to work the 10 Meter Amateur bands?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;citizens-band&gt;" AnswerCount="5" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="118" PostTypeId="2" ParentId="109" CreationDate="2013-10-22T22:50:20.033" Score="7" Body="&lt;p&gt;The level to which amateur radio operators participate in emergency management varies between municipalities. &lt;a href=&quot;http://www.arrl.org/ares&quot;&gt;ARES&lt;/a&gt; is the most well known organization, it is managed by emergency managers in each ARRL section. To join, submit the &lt;a href=&quot;http://www.arrl.org/files/file/Public%20Service/fsd98.pdf&quot;&gt;application form&lt;/a&gt; to your &lt;a href=&quot;http://www.arrl.org/sections&quot;&gt;section emergency manager&lt;/a&gt;. You need not be an ARRL member to join.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.usraces.org/&quot;&gt;RACES&lt;/a&gt; is managed by state and local government - it's separate to but associated with ARES. Basically, ARES operates at most incidents and events. RACES assumes control when an emergency is declared, but it should be the same group of volunteers in both cases. The best explanation I've seen of the differences is on &lt;a href=&quot;http://www.arrl.org/chapter-4-ares-and-races&quot;&gt;the ARRL site&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you can also be useful as an amateur radio operator without being part of one of those organizations. Local volunteer fire and ambulance services, CERT teams, and even offices of emergency management need communications, and being able to work on their frequencies as well as on the ham bands can make you a valuable asset.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T22:50:20.033" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="119" PostTypeId="1" CreationDate="2013-10-22T22:50:38.337" Score="11" ViewCount="4381" Body="&lt;p&gt;Can my license from the United States be used to operate while I'm in the United Kingdom?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="106" LastEditDate="2013-10-22T23:11:19.903" LastActivityDate="2017-06-04T20:33:14.223" Title="Can I operate in the United Kingdom with a US license?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;international-operating&gt;&lt;united-kingdom&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="121" PostTypeId="1" CreationDate="2013-10-22T22:53:07.117" Score="5" ViewCount="1306" Body="&lt;p&gt;What kind of battery has the most capacity for the weight? I want to take my transceiver backpacking, so I care about weight.&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="22" LastEditDate="2013-10-23T21:25:05.920" LastActivityDate="2020-01-11T20:13:51.683" Title="Battery capacity vs. weight for portable transceivers" Tags="&lt;transceiver&gt;&lt;battery&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="123" PostTypeId="1" CreationDate="2013-10-22T22:55:22.727" Score="2" ViewCount="2576" Body="&lt;p&gt;What contest logging software exists for the GNU/Linux operating system?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="13" LastEditDate="2013-10-23T16:33:45.727" LastActivityDate="2013-11-02T18:53:03.277" Title="GNU/Linux contest logging software?" Tags="&lt;software&gt;&lt;linux&gt;&lt;contest&gt;&lt;logging&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ClosedDate="2013-11-05T19:01:30.643" ContentLicense="CC BY-SA 3.0" />
  <row Id="124" PostTypeId="2" ParentId="115" CreationDate="2013-10-22T22:55:40.963" Score="4" Body="&lt;h2&gt;Frequencies&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;The most significant difference between the license levels is that of band access. You can find a list of the various band allocations, with notes on what levels are allowed access, here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/frequency-allocations&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/frequency-allocations&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also a handy chart of the allocations available here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/graphical-frequency-allocations&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/graphical-frequency-allocations&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Power&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Some of the lower license classes also specify a lower maximum power level for certain bands (e.g. Novices are limited to 25W in the 1.25m band).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that higher levels of license are still subject to the overall maximum limit - ham radio in the US is limited to 1.5 kW PEP (peak envelope power).&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Type of operation&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Some of the lower license classes limit the operator to a certain type of operation such as CW (morse code) on certain bands.&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-10-22T23:02:30.273" LastActivityDate="2013-10-22T23:02:30.273" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="125" PostTypeId="1" CreationDate="2013-10-22T22:56:26.343" Score="4" ViewCount="7664" Body="&lt;p&gt;How and why do sunspots affect propagation in HF bands?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="92" LastEditDate="2013-10-23T21:25:27.827" LastActivityDate="2017-11-06T01:53:47.867" Title="How and why sunspots affect propagation in HF bands?" Tags="&lt;propagation&gt;&lt;sunspots&gt;&lt;space-weather&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="126" PostTypeId="1" CreationDate="2013-10-22T22:59:23.700" Score="8" ViewCount="1251" Body="&lt;p&gt;What are some of the advantages and disadvantages of using a vertical antenna on high frequency? Are there any better antenna types that I should use?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="87" LastEditDate="2013-11-06T20:41:17.737" LastActivityDate="2020-06-27T13:17:33.150" Title="Vertical antenna on HF?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;vertical-antenna&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="128" PostTypeId="2" ParentId="117" CreationDate="2013-10-22T23:00:49.443" Score="16" Body="&lt;p&gt;You can, but you probably don't want to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CB radios are limited to a set of 40 channels, most don't have frequency control. That somewhat limits the utility in the ham band where we have a very wide swath of frequency we can use. A converted CB radio would, at best, have control over only a narrow portion of the 10 meter band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are also limited in power. While external amplifiers for CB are available, they are illegal, and would not work well on the ham band anyway. If you wanted to operate at higher powers than those allowed by CB, you would need a ham amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most are also limited to AM operation. Most ham operations on 10 meters are SSB. You would not be able to join in most conversations, and most users would think your transmissions were either garbled or interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simply put, for the technical expertise, time, and parts required, the value just isn't worth it, when you can get a multi-band HF radio on eBay for a few hundred bucks.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T23:00:49.443" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="131" PostTypeId="1" CreationDate="2013-10-22T23:03:32.790" Score="3" ViewCount="8476" Body="&lt;p&gt;What are some antenna designs that balance manageable size/shape with effectiveness for use in an apartment?&lt;/p&gt;&#xA;" OwnerUserId="106" LastActivityDate="2013-10-23T06:37:33.680" Title="Antennas I can effectively use in an apartment?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ClosedDate="2013-10-30T08:29:40.600" ContentLicense="CC BY-SA 3.0" />
  <row Id="132" PostTypeId="1" CreationDate="2013-10-22T23:04:43.650" Score="7" ViewCount="1832" Body="&lt;p&gt;Is there a limit to the power a 50 ohm BNC connector can handle?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="76" LastEditDate="2013-10-23T10:43:30.657" LastActivityDate="2018-06-18T16:15:45.850" Title="Power limit of 50 ohm BNC connector?" Tags="&lt;rf-power&gt;&lt;connectors&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="133" PostTypeId="1" AcceptedAnswerId="227" CreationDate="2013-10-22T23:05:53.363" Score="2" ViewCount="883" Body="&lt;p&gt;What do I need to consider when choosing metal for an antenna? How do I determine what thickness to use?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="8832" LastEditDate="2017-09-21T21:06:39.107" LastActivityDate="2017-09-26T18:29:09.477" Title="Metal for antenna construction?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;bandwidth&gt;" AnswerCount="5" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="134" PostTypeId="2" ParentId="6" CreationDate="2013-10-22T23:06:59.353" Score="3" Body="&lt;p&gt;In 2006 the ARRL dropped its support for changing the rules to allow digital encryption. The rationale for their decision is that it was already legal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Their reasoning comes for the following FCC rule:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Part 97 : Sec. 97.105 Control operator duties&#xA;(a) The control operator must ensure the immediate proper operation of the station, regardless of the type of control.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL interprets this rule to mean that encryption to ensure the integrity and control of one's operations is legal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.qsl.net/kb9mwr/projects/wireless/Data%20Encryption%20is%20Legal.pdf&quot; rel=&quot;nofollow&quot;&gt;This document&lt;/a&gt; explains the entire rationale.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the United States no Control Operator has ever faced any disciplinary action for encrypting their WIFI transmissions as long as the encryption mode (but not the key) is public.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The article has lots of cautions, for example: Every control operator is still responsible for periodically transmitting their call-sign. It recommends you use your wifi-SSID for that purpose.&lt;/p&gt;&#xA;" OwnerUserId="19" LastEditorUserId="19" LastEditDate="2013-10-22T23:16:11.067" LastActivityDate="2013-10-22T23:16:11.067" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="135" PostTypeId="1" AcceptedAnswerId="162" CreationDate="2013-10-22T23:07:22.997" Score="63" ViewCount="8004" Body="&lt;p&gt;Why do people still use Morse code?&lt;/p&gt;&#xA;&lt;p&gt;What are its advantages over newer &lt;em&gt;voice&lt;/em&gt; or &lt;em&gt;data&lt;/em&gt; communication modes?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="366" LastEditDate="2021-01-19T18:03:49.857" LastActivityDate="2021-01-20T13:08:58.617" Title="Why is Morse code still in use?" Tags="&lt;modes&gt;&lt;cw&gt;" AnswerCount="18" CommentCount="0" FavoriteCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="136" PostTypeId="2" ParentId="119" CreationDate="2013-10-22T23:08:03.287" Score="10" Body="&lt;p&gt;Yes, with some extra paperwork. &lt;a href=&quot;http://www.arrl.org/international-operating&quot;&gt;ARRL has most of the rules for international operating&lt;/a&gt;. In the case of a US operator in the UK, you'd be operating under &lt;a href=&quot;http://www.arrl.org/cept&quot;&gt;CEPT&lt;/a&gt;. You'd need to be an Extra - General licenses are recognized in some countries, but not in the UK. You'd also need proof of license and US citizenship, and a copy of the &lt;a href=&quot;http://www.arrl.org/files/file/cept-ral.pdf&quot;&gt;FCC official notice&lt;/a&gt;. Of course, you'd be subject to local &lt;a href=&quot;http://www.arrl.org/amateur-frequencies-outside-the-us&quot;&gt;frequency range limits&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T23:08:03.287" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="137" PostTypeId="1" CreationDate="2013-10-22T23:08:28.407" Score="5" ViewCount="4751" Body="&lt;p&gt;What frequencies can I not use if I live north of line A in the USA?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="19" LastEditDate="2013-10-24T14:20:59.790" LastActivityDate="2017-01-30T21:01:54.740" Title="What frequencies am I not allowed to use north of line A in the USA?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;frequency&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="139" PostTypeId="1" CreationDate="2013-10-22T23:11:24.340" Score="5" ViewCount="132" Body="&lt;p&gt;What kinds of abilities does a Home Owners' Association (HOA) in the United States have to limit the use of antennas placed on a roof to an owner of a home in the area?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="13" LastEditDate="2013-10-23T17:32:24.933" LastActivityDate="2016-08-29T17:13:15.423" Title="Abilities to limit antenna use?" Tags="&lt;antenna&gt;&lt;united-states&gt;&lt;legal&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="140" PostTypeId="1" CreationDate="2013-10-22T23:12:26.390" Score="15" ViewCount="53268" Body="&lt;p&gt;What properties should I look for in a good wire for building a wire antenna? Could anyone recommend something specific for me?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="76" LastEditDate="2015-12-15T21:52:50.933" LastActivityDate="2021-04-20T20:29:24.847" Title="Good wire for wire antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="5" CommentCount="2" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="141" PostTypeId="1" CreationDate="2013-10-22T23:13:37.037" Score="5" ViewCount="396" Body="&lt;p&gt;How do I determine antenna spacing so that I don't end up overdriving the front end of a receiver when transmitting?&lt;/p&gt;&#xA;" OwnerUserId="106" LastActivityDate="2013-10-28T18:50:45.227" Title="How do I determine antenna spacing?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="142" PostTypeId="1" CreationDate="2013-10-22T23:15:05.120" Score="5" ViewCount="2957" Body="&lt;p&gt;What are the pros/cons of the PL259/SO239 connector (M type), and why is it used preferentially on civilian rigs vs military?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="76" LastEditDate="2013-10-23T10:48:07.023" LastActivityDate="2016-01-26T21:51:46.000" Title="Pros/cons of the PL259/SO239 connector (M type)?" Tags="&lt;pl259-so239-connector&gt;&lt;connectors&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="143" PostTypeId="2" ParentId="132" CreationDate="2013-10-22T23:15:35.797" Score="4" Body="&lt;p&gt;Note that the following may not apply to adapters, which may have lower power limits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?topic=24183.5;wap2&quot; rel=&quot;nofollow noreferrer&quot;&gt;This thread on eham&lt;/a&gt; contains a few suggestions. The third poster states that the design rating is 7 amps on the center pin, or 5 amps accounting for skin effect at different frequencies. This corresponds to 1250 watts for a 50 ohm feedline with a matched load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a 500 volt maximum rating, but this is not the best basis. This is based on the dielectric (insulator) effect between the pin and shell, not on the maximum power dissipation. The 1250 watt figure is based on the amount of heat that will be generated if 5 amps is run through the connector. Heat generation is the relevant effect when we're talking about maximum power, because that's what's going to melt the coax and light your shack on fire.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="9493" LastEditDate="2018-06-18T16:15:45.850" LastActivityDate="2018-06-18T16:15:45.850" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="144" PostTypeId="1" CreationDate="2013-10-22T23:16:30.360" Score="0" ViewCount="102" Body="&lt;p&gt;Could I use wood to build 6m quad? If not, what material(s) would be better/more useful?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="76" LastEditDate="2014-09-24T21:48:37.847" LastActivityDate="2014-09-24T21:48:37.847" Title="Can wood be used to build 6m quad?" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2013-10-23T17:52:30.660" ContentLicense="CC BY-SA 3.0" />
  <row Id="146" PostTypeId="1" AcceptedAnswerId="494" CreationDate="2013-10-22T23:18:56.293" Score="17" ViewCount="32067" Body="&lt;p&gt;If I only have the budget for one HF antenna, should I chose a vertical or a horizontal antenna?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="250" LastEditDate="2013-11-01T11:11:34.870" LastActivityDate="2017-08-15T01:29:38.213" Title="Should I chose a vertical or a horizontal HF antenna?" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;&lt;hf&gt;&lt;polarization&gt;" AnswerCount="8" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="147" PostTypeId="2" ParentId="135" CreationDate="2013-10-22T23:19:36.057" Score="24" Body="&lt;p&gt;One of the reasons it's still in use is because of its inherent simplicity - no real signal processing is needed. Thus, CW transmitters and receivers are very simple and thus inexpensive.&lt;/p&gt;&#xA;" OwnerUserId="110" LastActivityDate="2013-10-22T23:19:36.057" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="152" PostTypeId="1" AcceptedAnswerId="160" CreationDate="2013-10-22T23:25:45.230" Score="5" ViewCount="239" Body="&lt;p&gt;I bought a radio that can receive 4 ham bands, but only transmit on 2. Can I modify my radio to transmit on these frequencies legally?&lt;/p&gt;&#xA;" OwnerUserId="106" LastActivityDate="2013-10-22T23:35:12.070" Title="Can I modify my radio to transmit on frequencies that I can currently only listen to?" Tags="&lt;legal&gt;&lt;frequency&gt;&lt;modification&gt;&lt;transmission&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ClosedDate="2013-12-05T08:35:39.477" ContentLicense="CC BY-SA 3.0" />
  <row Id="153" PostTypeId="2" ParentId="137" CreationDate="2013-10-22T23:27:03.603" Score="4" Body="&lt;p&gt;According to Part 97.303(m)(1):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;No amateur station shall transmit from north of Line A in the 420–430 MHz segment.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Source: &lt;a href=&quot;http://www.arrl.org/files/file/Regulatory/Part%2097%20-%2004-28-2011.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/files/file/Regulatory/Part%2097%20-%2004-28-2011.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="111" LastActivityDate="2013-10-22T23:27:03.603" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="154" PostTypeId="2" ParentId="135" CreationDate="2013-10-22T23:27:49.257" Score="38" Body="&lt;p&gt;The advantage? &lt;strong&gt;Efficiency!&lt;/strong&gt; You get to put all of that power of your rig into a very small bandwidth, whereas voice modes need to spread the power out much more (for example, SSB uses roughly 2.8kHz of bandwidth).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quote from: &lt;a href=&quot;http://home.windstream.net/johnshan/cw_ss.html&quot;&gt;http://home.windstream.net/johnshan/cw_ss.html&lt;/a&gt; :&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Going a little bit further, assuming a SSB signal takes up 2000 Hz.,&#xA;  and comparing a 100 watt 25 WPM CW signal with a 100 watt SSB signal,&#xA;  we have the following. The average power density for CW is 100W / 100&#xA;  Hz. or 1 w/Hz. For SSB it's 100W / 2000 Hz. or .05 w/Hz. Follow&#xA;  closely now, it gets interesting although a little more technical. We&#xA;  could say that the gain in using CW over SSB is Gain(db) =&#xA;  10*log(1/.05) which is about 13db. &lt;strong&gt;That means that a 5 watt CW signal&#xA;  packs an equivalent punch to a SSB signal at 100 watts.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="80" LastActivityDate="2013-10-22T23:27:49.257" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="156" PostTypeId="1" CreationDate="2013-10-22T23:29:55.370" Score="9" ViewCount="518" Body="&lt;p&gt;Is a Technician license enough to assist in times of disaster/emergency or do I need General or higher?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="22" LastEditDate="2013-10-23T10:40:35.160" LastActivityDate="2017-07-27T15:14:17.787" Title="Is a Technician license enough to assist in times of emergency?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;emergency&gt;" AnswerCount="5" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="157" PostTypeId="2" ParentId="146" CreationDate="2013-10-22T23:32:15.973" Score="7" Body="&lt;p&gt;&lt;a href=&quot;http://forums.qrz.com/archive/index.php/t-190181.html&quot;&gt;It doesn't really matter&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're asking about a topic called polarization, which is really important in VHF and UHF. It's the reason why rotating your HT can improve or harm your reception, and it's also the reason why some 3D glasses and sunglasses work. But because of the way HF propagation works, it doesn't really matter. Any ionospheric propagation gets the polarization randomized anyway. Very short range (ground wave) HF works best with a vertical antenna, but it's very rare that you care more about short-range than long-range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In terms of limited space and cost, it's probably easier to set up a horizontal antenna (or an inverted V like a G5RV or OCF) than a vertical simply because it's easier to string a wire through some trees than it is to secure a flagpole or tower against gravity and wind loads.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T23:32:15.973" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="158" PostTypeId="1" CreationDate="2013-10-22T23:32:17.350" Score="-1" ViewCount="1422" Body="&lt;p&gt;What is the basic format for a QSO? How should I answer to &quot;CQ&quot;, how do I know when it is my turn to answer, when should I give the report, etc.?&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="76" LastEditDate="2014-09-24T21:48:06.827" LastActivityDate="2014-09-24T21:48:06.827" Title="Basic QSO format?" Tags="&lt;procedure&gt;" AnswerCount="2" CommentCount="3" ClosedDate="2013-10-23T04:25:00.470" ContentLicense="CC BY-SA 3.0" />
  <row Id="160" PostTypeId="2" ParentId="152" CreationDate="2013-10-22T23:35:12.070" Score="8" Body="&lt;p&gt;Assuming that you're operating in the jurisdiction of the FCC, there should be no legal issue with you modifying your radio and using it to transmit on those two bands providing the following:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Your modifications comply with good engineering practice, and&lt;/li&gt;&#xA;&lt;li&gt;You do not exceed the privileges (power or frequency) of your license&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Unlike other radio services in the US, hams get to build, repair, and modify their equipment.  Be safe, be careful, and have fun!&lt;/p&gt;&#xA;" OwnerUserId="111" LastActivityDate="2013-10-22T23:35:12.070" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="161" PostTypeId="2" ParentId="156" CreationDate="2013-10-22T23:35:22.487" Score="9" Body="&lt;p&gt;Most &lt;strong&gt;local&lt;/strong&gt; emergency communications use VHF and UHF repeaters. If we're talking about coordinating CERT or public safety, search and rescue, that sort of thing, then yes, a technician is enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, regional and larger emergency communications (like the hurricane net which covers a large area, or the national traffic system which passes traffic from all over the world) operates on HF, and will require at least a General class license.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T23:35:22.487" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="162" PostTypeId="2" ParentId="135" CreationDate="2013-10-22T23:37:42.707" Score="78" Body="&lt;ul&gt;&#xA;&lt;li&gt;because there are a large number of operators who had to learn it to get their licence&lt;/li&gt;&#xA;&lt;li&gt;because there is a large (but slowly diminishing) number of operators who learned it while serving in the armed forces&lt;/li&gt;&#xA;&lt;li&gt;because the transmitters and receivers can be &lt;a href=&quot;http://www.qrpme.com/?p=RM%20][&quot; rel=&quot;noreferrer&quot; title=&quot;Rockmite ][&quot;&gt;extremely simple&lt;/a&gt; and &lt;a href=&quot;http://www.qrpme.com/?p=product&amp;amp;id=EZB&quot; rel=&quot;noreferrer&quot; title=&quot;QRPme Two Tinned Tunas&quot;&gt;inexpensive&lt;/a&gt;, not needing much more than a key and headphones along with the rig, antenna and battery to send and receive&lt;/li&gt;&#xA;&lt;li&gt;because (in theory) it has a very tiny bandwidth, allowing small QRP transmitters to send a very effective signal. This also allows a large number of contesters to cram into a few kilohertz of bandwidth, each (with suitable filtering) able to be picked out individually&lt;/li&gt;&#xA;&lt;li&gt;because it's a point of pride for some operators that they know this thing that the young 'uns don't.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;CW can be sent exceptionally well by computer (with software like &lt;a href=&quot;http://www.w1hkj.com/Fldigi.html&quot; rel=&quot;noreferrer&quot; title=&quot;fldigi&quot;&gt;fldigi&lt;/a&gt;) or by any number of USB/serial keyers (such as the &lt;a href=&quot;http://hamcrafters.com/&quot; rel=&quot;noreferrer&quot; title=&quot;WinKeyer&quot;&gt;WinKeyer&lt;/a&gt; or &lt;a href=&quot;http://blog.radioartisan.com/arduino-cw-keyer/&quot; rel=&quot;noreferrer&quot; title=&quot;K3NG&quot;&gt;K3NG&lt;/a&gt; Arduino keyer). It can be copied reasonably well in software (fldigi again, or &lt;a href=&quot;http://www.dxatlas.com/cwskimmer/&quot; rel=&quot;noreferrer&quot; title=&quot;CW Skimmer&quot;&gt;CW Skimmer&lt;/a&gt;). The &lt;a href=&quot;http://www.reversebeacon.net/&quot; rel=&quot;noreferrer&quot; title=&quot;Reverse Beacon Network&quot;&gt;Reverse Beacon Network&lt;/a&gt; relies on multiple stations worldwide running CW Skimmer to report on propagation, and will show you where your CQ has been copied.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It can be thought of as a digital mode, but one that can be copied by ear with sufficient training. It's typically a little slower that PSK-31 or RTTY, and CW only supports a very limited single-case character set. Although it is no longer used commercially or by the military, it's likely to stick around in ham radio for a long time.&lt;/p&gt;&#xA;" OwnerUserId="90" LastEditorUserId="90" LastEditDate="2019-07-05T03:03:15.467" LastActivityDate="2019-07-05T03:03:15.467" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="164" PostTypeId="2" ParentId="146" CreationDate="2013-10-22T23:47:04.917" Score="1" Body="&lt;p&gt;It matters only for local RF interference purposes. Once the signal hits the ionosphere, the polarization is randomized, thus it really doesn't make a difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Polarization of RF Interference tends to be vertically polarized, but that's such a small effect that it really probably doesn't matter which way you do the antenna.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-22T23:47:04.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="165" PostTypeId="2" ParentId="139" CreationDate="2013-10-22T23:48:30.987" Score="8" Body="&lt;p&gt;The only power that an HOA holds is that which is specified in the contract signed by the homeowner. This may limit towers or visible antennas. Hams have found quite a few ways around this:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;It is possible to run a large dipole inside your roof rather than outside, supporting it from the main roof beam. You could use an off-center fed or loaded dipole to get multi-band coverage.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It is possible to run a horizontal antenna concealed under the eaves of your house&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It is possible to use a new or existing vertical metal object such as a flagpole as an antenna&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It is possible to conceal many types of antenna in a tree or yard&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It is possible and even ideal to conceal radial wires (used to improve the ground plane) underground&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some hams have had success challenging these HOA rules in court on the grounds that they interfere with emergency communications&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-22T23:48:30.987" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="166" PostTypeId="1" CreationDate="2013-10-22T23:54:58.153" Score="2" ViewCount="472" Body="&lt;p&gt;If I get involved in digital communications do I need to buy a soundcard?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, why, what does it do?&lt;/p&gt;&#xA;" OwnerUserId="19" LastActivityDate="2013-10-23T04:45:12.037" Title="What's the purpose of a soundcard in digital communication?" Tags="&lt;digital-modes&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="167" PostTypeId="5" CreationDate="2013-10-23T00:14:21.557" Score="0" Body="&lt;p&gt;The APRS system consists of the following components:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Trackers&lt;/strong&gt;, small microcontroller-based devices which, when connected to a GPS receiver and a transmitter, transmit their location regularly over radio. Some trackers feature integrated GPS and radio modules. Trackers are available as kits, ready-made, and they're also relatively easy to build from parts.&lt;/li&gt;&#xA;&lt;li&gt;Radio &lt;strong&gt;transceivers&lt;/strong&gt; implementing the APRS protocol, such as Kenwood and Yaesu commercial offerings, which can act as trackers and normal voice radios at the same time, and implement text messaging and other APRS features&lt;/li&gt;&#xA;&lt;li&gt;APRS &lt;strong&gt;applications&lt;/strong&gt; for computers and mobile devices, typically having a tactical real-time map view of APRS stations&lt;/li&gt;&#xA;&lt;li&gt;APRS &lt;strong&gt;web database sites&lt;/strong&gt;, which provide real-time map views and historical APRS data lookup functions&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;APRS-IS&lt;/strong&gt;, the APRS Internet System is a network of servers connecting radio-based APRS networks together over the Internet&lt;/li&gt;&#xA;&lt;li&gt;The &lt;strong&gt;protocol&lt;/strong&gt; itself, defining how the pieces of the system communicate&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Questions concerning the APRS system or any of its components should have the &lt;strong&gt;aprs&lt;/strong&gt; tag.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-25T13:58:33.227" LastActivityDate="2013-10-25T13:58:33.227" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="168" PostTypeId="4" CreationDate="2013-10-23T00:14:21.557" Score="0" Body="Automatic Packet Reporting System is a digital protocol used to transmit GPS position reports, telemetry, weather reports and text messages between APRS compatible devices and software." OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-25T13:58:30.507" LastActivityDate="2013-10-25T13:58:30.507" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="169" PostTypeId="2" ParentId="166" CreationDate="2013-10-23T00:17:02.183" Score="7" Body="&lt;p&gt;Most radios are analog, or use analog audio in and out, and the sound card is used to interface between a computer and these radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The computer running suitable software uses the sound card to implement a digital communications mode such as PSK31, RTTY, or AX25 Packet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most computers come with a sound card, which will be good enough to get you started. However, many prefer to use a second card (or a USB-attached external card and interface such as the Tigertronics Signalink) so that they can have both speakers/headphones and their radio attached at the same time. It also helps you to not transmit your computer's startup sound effect accidentally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many people also choose to place an audio isolation transformer to isolate the computer from the radio, so that RF or DC power won't accidentally burn the computer or radio. At this point you should also isolate any possible PTT keying line (serial port?) using an opto-isolator, unless you're using voice-activated keying (VOX) to automatically turn the transmitter on when there's audio coming out from the computer.&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2013-10-23T04:24:34.387" LastActivityDate="2013-10-23T04:24:34.387" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="170" PostTypeId="2" ParentId="144" CreationDate="2013-10-23T00:25:45.813" Score="2" Body="&lt;p&gt;Bamboo worked fine for me for a 6m full wave loop at 100 watts for mountaintop use in VHF contests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bamboo is just sticks in a plus shape and the loop antenna shape will be diamond shaped through holes.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a single loop, at the bottom of the diamond you need a matching transformer and balun.  A quarter wave of rg6 or other 75 ohm coax rolled into an air wound coil will work but won't yield a perfect match.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a multi loop quad, the impedance will be determined by loop spacing and sizes and can be engineered closer to 50 ohms.&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2013-10-23T00:31:47.310" LastActivityDate="2013-10-23T00:31:47.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="172" PostTypeId="1" AcceptedAnswerId="174" CreationDate="2013-10-23T00:40:33.250" Score="5" ViewCount="514" Body="&lt;p&gt;I'm quite interested in 802.11 over amateur radio frequencies; however, all I have done at this point is reading (I don't have a ham license yet).  The &lt;a href=&quot;https://ham.stackexchange.com/questions/72/encrypted-traffic-and-amateur-radio/112&quot;&gt;conventional wisdom (espoused in this ham.SE answer) is that you cannot encrypt radio communications at all&lt;/a&gt;.  This limitation seems to fly in the face of normal countermeasures used to secure data transfers through the internet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So encryption is off the table; however, that still leaves issues such as authentication and data integrity.  I have read that &lt;a href=&quot;https://en.wikipedia.org/wiki/CRAM-MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRAM-MD5&lt;/a&gt; hashes are sometimes used as part of data services implemented over 802.11 ham radio, because &lt;a href=&quot;https://en.wikipedia.org/wiki/CRAM-MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRAM-MD5&lt;/a&gt; hashes are allowed under the FCC rules.  The contents of messages signed with &lt;a href=&quot;https://en.wikipedia.org/wiki/CRAM-MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRAM-MD5&lt;/a&gt; are always visible; yet, the authorship of the message can be verified (because &lt;a href=&quot;https://en.wikipedia.org/wiki/CRAM-MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRAM-MD5&lt;/a&gt; works in the same way that PGP does).  As best I can tell, using &lt;a href=&quot;https://en.wikipedia.org/wiki/CRAM-MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRAM-MD5&lt;/a&gt; leaves you vulnerable because:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It does not perform mutual authentication (i.e. the client can't verify the server's identity)&lt;/li&gt;&#xA;&lt;li&gt;It's possible to run off-line dictionary attacks against captured hashes (although the underlying &lt;a href=&quot;https://en.wikipedia.org/wiki/HMAC-MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;HMAC-MD5&lt;/a&gt; hash doesn't have the same vulnerabilities as &lt;a href=&quot;https://en.wikipedia.org/wiki/MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;MD5&lt;/a&gt;).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The bigger concern to me is a man in the middle attack, since &lt;a href=&quot;https://en.wikipedia.org/wiki/CRAM-MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRAM-MD5&lt;/a&gt; offers no mutual authentication between client and server.  This kind of vulnerability is also the kind of dynamic that makes &lt;a href=&quot;http://blog.depthsecurity.com/2010/11/when-8021xpeapeap-ttls-is-worse-than-no.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;PEAP worse than no 802.11 authentication&lt;/a&gt; (since PEAP doesn't enforce mutual authentication between the wifi client and RADIUS server, like EAP-TLS does).  It has been shown that weak PEAP clients freely offer their password hashes to a wifi AP masquerading the same SSID as the real AP.  My concern with 802.11 over ham frequencies is determining that I'm giving my password / data to the right endpoint on the other side (and not an attacker).&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Questions&lt;/h2&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is there another authentication scheme besides &lt;a href=&quot;https://en.wikipedia.org/wiki/CRAM-MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRAM-MD5&lt;/a&gt;, that is both legal in the US and performs mutual authentication?&lt;/li&gt;&#xA;&lt;li&gt;If I wanted to implement an authenticated HTTP service over ham radio, is there another authentication scheme that I should consider besides &lt;a href=&quot;https://en.wikipedia.org/wiki/CRAM-MD5&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRAM-MD5&lt;/a&gt;?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="112" LastEditorUserId="8832" LastEditDate="2017-08-18T07:26:38.847" LastActivityDate="2017-08-18T07:26:38.847" Title="Secure communication over Amateur-band HSMM / 802.11 in the United States" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;security&gt;&lt;hsmm&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="173" PostTypeId="1" CreationDate="2013-10-23T00:49:59.233" Score="9" ViewCount="1462" Body="&lt;p&gt;I am looking for an Windows-based &lt;a href=&quot;http://en.wikipedia.org/wiki/Automatic_Identification_System&quot;&gt;AIS&lt;/a&gt; Decoder for RTL Dongles. Currently, there is a solution available using &lt;a href=&quot;http://gnuradio.org/&quot;&gt;GNU Radio&lt;/a&gt; and &lt;a href=&quot;http://sdrsharp.com/&quot;&gt;SDR#&lt;/a&gt; but it is complicated to set up and keep running.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Automatic_dependent_surveillance-broadcast&quot;&gt;ADSB&lt;/a&gt; has a dedicated solution called RTL1090 that connects directly to the &lt;a href=&quot;http://rtlsdr.org/&quot;&gt;RTL-Sdr&lt;/a&gt; stick and decodes the &lt;a href=&quot;http://en.wikipedia.org/wiki/Automatic_dependent_surveillance-broadcast&quot;&gt;ADSB&lt;/a&gt; messages in one application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone know of a project like this for &lt;a href=&quot;http://en.wikipedia.org/wiki/Automatic_Identification_System&quot;&gt;AIS&lt;/a&gt; Ship Tracking?&lt;/p&gt;&#xA;" OwnerUserId="116" LastEditorUserId="4076" LastEditDate="2020-04-26T13:36:54.653" LastActivityDate="2020-04-26T13:36:54.653" Title="AIS and RTL-SDR Dongles" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;gnuradio&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="174" PostTypeId="2" ParentId="172" CreationDate="2013-10-23T00:50:17.157" Score="7" Body="&lt;p&gt;I'd say your best bet is to avoid handing over your hashed password entirely. Instead, use a &lt;a href=&quot;http://en.wikipedia.org/wiki/Zero-knowledge_proof&quot; rel=&quot;nofollow noreferrer&quot;&gt;zero-knowledge authentication&lt;/a&gt; scheme; see &lt;a href=&quot;https://security.stackexchange.com/questions/4991/zero-knowledge-proof-and-its-protocol/9185/&quot;&gt;this security.SE question for more details&lt;/a&gt;. Zero Knowledge Authentication will make it so that it doesn't matter who you &quot;give&quot; your response to - even if a malicious server requests authentication (or intercepts other authentication), it doesn't actually learn anything about your password.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you incorporate the response to the zero-knowledge auth as part of the public-key signed request, you should be able to formulate a system that both (a) is signed by the client, and (b) does not reveal information to 3rd parties that would allow them to forge future requests, since the zero-knowledge challenge response would form a nonce.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as verifying the server goes, a public key signature should suffice.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;(Previous response, before OP clarified...)&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IANAL, but...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a difference between &lt;em&gt;encryption&lt;/em&gt; and &lt;em&gt;authentication&lt;/em&gt;. The former requires no one to be able to tell what data is being passed; the latter requires no one to be able to produce something that is accepted as legitimate without some (non-public) knowledge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, public-key based signatures allow for authentication of a message's sender without obscuring the contents of the message.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As long as you're okay with the content of your requests being &lt;em&gt;visible&lt;/em&gt; but not &lt;em&gt;forgeable&lt;/em&gt;, you could probably use such a public key system without running afoul of the FCC regs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If, on the other hand, you don't want anyone to be able to see what's in your requests and responses, you're out of luck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, IANAL.&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="-1" LastEditDate="2017-03-17T10:46:11.143" LastActivityDate="2013-10-24T15:49:21.570" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="175" PostTypeId="1" AcceptedAnswerId="179" CreationDate="2013-10-23T01:00:07.913" Score="3" ViewCount="1372" Body="&lt;p&gt;I have a Yaesu FT-60, and it can transmit on 2m, 70cm, and receive 1.25m and 33cm bands. I would really like to find a way to get it to transmit on 1.25 and 33cm. Is there a way to make this happen?&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-23T01:27:10.907" Title="Is there a way to modify my Yaesu FT-60 to transmit on all 4 ham bands it can receive?" Tags="&lt;ht&gt;&lt;modification&gt;&lt;yaesu&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="176" PostTypeId="2" ParentId="121" CreationDate="2013-10-23T01:01:27.973" Score="4" Body="&lt;p&gt;Lithium, NiMH, then Lead acid.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lithium batteries are expensive and potentially hazardous.  Among these, Lithium Iron Phosphate, or LiFePO4, is supposedly less dangerous, but still needs a charge/discharge controller.  You can find replacements for 12v batteries on eBay using LiFEPO4 and capable of high currents  of transmitting but those are still several hundred dollars.  If you can settle for around 10 amp hours you can get a lifepo4 cell pack and a controller and charger custom made for around $150-$200.  The charger I received charges the pack in about an hour and this is a huge plus and avoids the problem of having time but not being ready to go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can string 10 NiMH 10ah D cells in series to make a 12-14v pack.  I use an ordinary pvc water pipe as the shell, but a sheriffs deputy once told me it looks kinda like a pipe bomb....  This will cost over $100 and still takes a while to charge.  One advantage is that cells can be charged or replaced individually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lead acid  is comparably cheap, but heavy to lug around.  But use agm deep cycle batteries for this, not vehicle starting batteries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See also the beach portable discussion on &lt;a href=&quot;http://www.qrz.com/db/KI6CQ&quot; rel=&quot;nofollow&quot;&gt;my QRZ web page for KI6CQ&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2013-10-23T03:29:07.367" LastActivityDate="2013-10-23T03:29:07.367" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="177" PostTypeId="2" ParentId="142" CreationDate="2013-10-23T01:13:58.417" Score="8" Body="&lt;p&gt;UHF connectors are cheap and easy to install. In all other respects, they are inferior to more modern designs like BNC or N connectors. The major uses of UHF connectors are amateur and CB equipment in the US.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BNC and N connectors are constant impedance and weatherproof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The BNC connector handles as much power as a UHF connector (500V peak) and is easier to connect and disconnect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.amphenolrf.com/products/bnc.asp&quot;&gt;http://www.amphenolrf.com/products/bnc.asp&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The N connector handles more power (1500V peak).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.amphenolrf.com/products/typen.asp&quot;&gt;http://www.amphenolrf.com/products/typen.asp&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UHF connector specs:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.amphenolrf.com/products/uhf.asp&quot;&gt;http://www.amphenolrf.com/products/uhf.asp&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a good overview of the RF characteristics of average-quality UHF connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.qsl.net/vk3jeg/pl259tst.html&quot;&gt;http://www.qsl.net/vk3jeg/pl259tst.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the time, UHF connectors will not cause any problems. If you have lots of connections, low-quality connectors, or are operating above 300 MHz, you should probably consider a more modern connector.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-10-23T01:13:58.417" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="178" PostTypeId="2" ParentId="158" CreationDate="2013-10-23T01:20:44.587" Score="12" Body="&lt;p&gt;Although this question has votes to close, it's an important one. Anxiety about how to respond in QSO stops a lot of people with licences from becoming regular operators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are really only three places where QSO format is fixed:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;strong&gt;Contests&lt;/strong&gt; — you want to be as short and precise as possible. ZS1AN has a good example of the &lt;a href=&quot;http://www.qsl.net/zs1an/contesting_faq.html#example-qso&quot;&gt;very terse exchange&lt;/a&gt; that typically occurs in a &lt;a href=&quot;http://www.cqww.com/&quot;&gt;busy CW contest&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Nets&lt;/strong&gt; — these are run by the net controller, and you have to wait your turn to respond in the right way. Every net is different in the way traffic is handled; listen lots before chiming in.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Digital Modes&lt;/strong&gt; — because these are sent from computer, there is a tendency for QSOs to be scripted by macros. This can be rather tedious, but does make it quite easy to infer what the other party is trying to say if there is QSB or QRM. Here's a &lt;a href=&quot;http://www.randomizethis.co.uk/the-average-psk31-contact/&quot;&gt;typical scripted QSO&lt;/a&gt;. Some modes, particularly JT65a, have fixed QSO formats down to the number of characters.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;With voice QSOs, it's much less regulated. It's polite to give a report as early as convenient, or when the other party requests one. Just remember to identify as often as local laws require, and be clear when you're finished with the QSO. If you're on a calling frequency, the right thing to do is to move off it onto an agreed frequency as quickly as is practical.&lt;/p&gt;&#xA;" OwnerUserId="90" LastActivityDate="2013-10-23T01:20:44.587" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="179" PostTypeId="2" ParentId="175" CreationDate="2013-10-23T01:27:10.907" Score="2" Body="&lt;p&gt;No. You likely would need to build two new transmit stages and rewrite the firmware. Each transmit stage uses a precise final oscillator and mixer which is specific to the frequency band as well as a filter to suppress harmonics, use of the hardware for 70cm at a 33cm frequency would result in most of your transmit signal being filtered out - if it was even possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are quad-band transmitters - yaesu makes a few - I am not aware of any with 33cm coverage, however. This would likely be a simple mod in a desk unit, but any modification of this sort of a handheld or even mobile radio is extremely difficult due to the fact that so many functions are concealed inside multi-purpose chips, many signals are inaccessible due to multi-layer PCBs and components without exposed leads, and there is simply no room inside the case for any add-on boards that we could manufacture.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-23T01:27:10.907" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="180" PostTypeId="2" ParentId="116" CreationDate="2013-10-23T01:31:22.703" Score="13" Body="&lt;p&gt;The Jamboree-on-the-Air, or JOTA, is an annual Scouting event that uses amateur radio to link Scouts around the world. Held on the third full weekend of October each year since 1958, this worldwide jamboree requires no travel, other than to a nearby radio amateur’s ham shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Over 500,000 Scouts participate in JOTA, making it the largest single Scouting event and the largest amateur radio event.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Information from the World Organization of the Scouting Movement (WOSM) on JOTA:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.scout.org/jota-joti-about&quot;&gt;http://www.scout.org/jota-joti-about&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Information from the Boy Scouts of America (BSA) about JOTA:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.scouting.org/JOTA.aspx&quot;&gt;http://www.scouting.org/JOTA.aspx&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The BSA has a comprehensive list of the frequencies used for JOTA:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.scouting.org/jota/operators_guides.aspx&quot;&gt;http://www.scouting.org/jota/operators_guides.aspx&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-10-23T01:31:22.703" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="181" PostTypeId="2" ParentId="140" CreationDate="2013-10-23T01:36:23.997" Score="11" Body="&lt;p&gt;Because of the skin effect, which causes most of the electric current to be concentrated around the outer surface of the wire at high frequencies, larger gauge wire is needed for RF than for an equivalent DC current. As a general rule of thumb, 16 gauge is sufficient up to 100 watts, but 12 would be ideal. Any system exceeding 100 watts really needs to have the actual current and skin effect calculated, and that is dependent on frequency and also somewhat on antenna type. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since most antennas are used outdoors, you must use outdoor-rated wire. You can use uninsulated wire, but it is much better to use insulated wire for safety purposes if there is any chance that someone could come in contact with the wire while you are transmitting. If you are using insulated wire, make sure the insulation code (which is printed along the wire) has a &quot;W&quot; in it - it stands for water-resistant. Some examples are XHH &lt;strong&gt;W&lt;/strong&gt;, SOO &lt;strong&gt;W&lt;/strong&gt;, or TH &lt;strong&gt;W&lt;/strong&gt; N.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stranded copper or copper clad aluminum are the most common - copper clad aluminum is somewhat stronger and has the more conductive copper on the outside, where the current is concentrated. Stranded wire is ideal for flexibility and ease of soldering and crimping.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-23T01:36:23.997" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="182" PostTypeId="2" ParentId="133" CreationDate="2013-10-23T01:38:56.960" Score="2" Body="&lt;p&gt;Yes, but unless you get really carried away it doesn't matter. The amount of metal being used, whether it be a bar, pipe, or sheet, is enough to make any concerns about resistive losses meaningless.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-23T01:38:56.960" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="183" PostTypeId="1" AcceptedAnswerId="184" CreationDate="2013-10-23T01:49:32.390" Score="13" ViewCount="25341" Body="&lt;p&gt;An answer on &lt;a href=&quot;https://ham.stackexchange.com/questions/158/basic-qso-format&quot;&gt;Basic QSO format?&lt;/a&gt; mentions things like &quot;QRM&quot; and &quot;QSB&quot;. What do those terms mean?&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2019-12-24T15:17:05.297" Title="What do &quot;QRM&quot; and &quot;QSB&quot; refer to?" Tags="&lt;q-codes&gt;&lt;jargon&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="184" PostTypeId="2" ParentId="183" CreationDate="2013-10-23T01:49:32.390" Score="17" Body="&lt;p&gt;&quot;QRM&quot; is one of many &lt;a href=&quot;http://en.wikipedia.org/wiki/Q_code&quot;&gt;Q-codes&lt;/a&gt; used as abbreviations in radio communication. &quot;QRM&quot; in particular refers to human-generated interference (as opposed to &quot;QRN&quot; which is used to refer to atmospheric noise). &quot;QSB&quot; refers to fading (variation in signal strength over time).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The codes originated from the desire to keep CW (morse code) transmissions as brief as possible due to the format's inherent bandwidth limits, but have stuck around and now often show up as abbreviations in regular conversation as well.&lt;/p&gt;&#xA;" OwnerUserId="22" LastActivityDate="2013-10-23T01:49:32.390" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="185" PostTypeId="2" ParentId="158" CreationDate="2013-10-23T01:52:00.003" Score="5" Body="&lt;p&gt;The IARU has adopted a document titled &quot;Ethics and Operating Procedures for the Radio Amateur&quot;. This is an excellent guide to the basics of on-air behavior and the fine points of polite DX'ing. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can go to this page to find versions in more than 25 languages and those adopted by the amateur radio organizations of various countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ham-operating-ethics.org/versions.html&quot;&gt;http://www.ham-operating-ethics.org/versions.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every radio amateur should read this document and review it every few years.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-10-23T01:52:00.003" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="186" PostTypeId="1" AcceptedAnswerId="511" CreationDate="2013-10-23T02:42:06.400" Score="4" ViewCount="96" Body="&lt;p&gt;I have been trying to understand the finer points of HSMM, and I ran across &lt;a href=&quot;http://hsmm.wikispaces.com/hsmm&quot; rel=&quot;nofollow&quot;&gt;this statement about antenna feed points&lt;/a&gt; (emphasis mine):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;802.11 signals produce very broadband signals, typically 20-22 MHz. There is evidence to date that indicates the use of a same polarized antenna with one type of feed point at one end of the link and the use of a same polarized antenna with a different type of feed point at the other end of the link, &lt;em&gt;may introduce a problem with HS digital signals&lt;/em&gt;. A common example of this potential mixed-antenna issue would be if one HSMM radio station uses a horizontally polarized linear Yagi, while the other HSMM radio station at the opposite end of the link uses a horizontally polarized loop Yagi.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Can someone cite references that detail the specific evidence for these kind of problems?&lt;/li&gt;&#xA;&lt;li&gt;If it's known, what are the technical reasons that HSMM transmissions through a horizontally polarized linear Yagi would introduce HSMM signal problems when they are received by a horizontally polarized loop Yagi?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="112" LastActivityDate="2013-11-01T14:30:47.087" Title="HSMM problems introduced by mismatched antenna feed points" Tags="&lt;hsmm&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="187" PostTypeId="2" ParentId="166" CreationDate="2013-10-23T02:43:28.250" Score="-1" Body="&lt;p&gt;No, most computers have one already.  Look for 3.5mm TRS sockets on the computer that you would normally use for audio; speakers, earphones, microphone, or line connectors.&lt;/p&gt;&#xA;" OwnerUserId="123" LastActivityDate="2013-10-23T02:43:28.250" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="188" PostTypeId="2" ParentId="156" CreationDate="2013-10-23T02:49:12.720" Score="-1" Body="&lt;p&gt;In a personal emergency you do not need a license to use a radio transceiver.  It would help though, since it gives you knowledge and experience.&lt;/p&gt;&#xA;" OwnerUserId="123" LastActivityDate="2013-10-23T02:49:12.720" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="189" PostTypeId="2" ParentId="173" CreationDate="2013-10-23T03:23:08.017" Score="8" Body="&lt;p&gt;You could check out &lt;a href=&quot;http://www.coaa.co.uk/shipplotter.htm&quot;&gt;ShipPlotter&lt;/a&gt; which appears to be a windows-based AIS receiver.  It mentions in the webpage that it accepts audio through your sound card.  In the case of RTL-SDR, you'll want to use something like &quot;Virtual Audio Cable&quot; or &quot;&lt;a href=&quot;http://vb-audio.pagesperso-orange.fr/Cable/&quot;&gt;VB-Audio Cable&lt;/a&gt;&quot; to route the audio from sdrsharp to ShipPlotter.&lt;/p&gt;&#xA;" OwnerUserId="127" LastActivityDate="2013-10-23T03:23:08.017" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="190" PostTypeId="1" AcceptedAnswerId="205" CreationDate="2013-10-23T03:26:08.020" Score="8" ViewCount="182" Body="&lt;p&gt;I am a US ham with an Extra Class ticket. If I were to go Poland (or possibly some other part of Europe) on vacation and bring some radios, what legal stuff do I need to know about? I know that my Extra Class license converts into a CEPT license under the reciprocal operating treaty, but what does that mean for me with regard to frequencies, power levels, and things like that? Do I have to register somehow before operating? The information on the Internet seems a bit sparse.&lt;/p&gt;&#xA;" OwnerUserId="125" LastEditorUserId="13" LastEditDate="2013-10-23T16:33:55.150" LastActivityDate="2013-10-23T23:50:22.380" Title="What regulatory issues/differences should I be aware of as a US ham vacationing in Europe (Poland)?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;international-operating&gt;&lt;europe&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="191" PostTypeId="2" ParentId="125" CreationDate="2013-10-23T03:36:20.963" Score="4" Body="&lt;p&gt;The sunspots do not cause changes in propagation, but increase and decrease with other solar phenomena.  Another way to say this is that sunspots are correlated with solar activity.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The amount of solar activity seems to vary on an 11 year cycle.  Charged particles from the sun streaming by Earth affect the ability of the ionosphere to refract radio signals back to Earth. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will see sometimes see hams use the word reflection to describe what happens at the ionosphere where signals below the MUF, or Maximum Usable Frequency, return to Earth.  This is a simplification.  The ionopshere is not a mirror, where there is a sudden pronounced change of materials,  but rather varies in density bending the signal.  This bending is called refraction.  For more on this, including illustrations, see this page on &lt;a href=&quot;http://www.tpub.com/neets/book10/40e.htm&quot; rel=&quot;nofollow&quot;&gt;Refraction in the ionosphere&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF propagation occurs by way of the ionosphere.  The signal from the transmitting antenna travels up to the ionosphere, is bent (or refracted) back to Earth and is then audible hundreds or thousands of miles away.  The ionosphere consists of several layers, and the distance traveled by the radio signal in one hop depends on the height of the layer of the ionosphere that is involved. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Roughly, the effect of increased solar activity is to increase the usability of the bands from 14-28 Mhz, and sometimes 50 Mhz.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, solar &quot;storms&quot; can cause other effects, such as seeing aurora at lower latitudes, causing the ionosphere to absorb rather than refract signals (making bands unusable), or cause unusual phenomena such as 50 Mhz or even 144Mhz to be temporarily useful for long distance communications.  &lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2013-10-23T17:04:22.430" LastActivityDate="2013-10-23T17:04:22.430" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="192" PostTypeId="2" ParentId="125" CreationDate="2013-10-23T03:55:50.110" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;These spots are cool areas (relatively speaking) on the surface of&#xA;  the sun. The temperature is around only 3000C against a sizzling 6000C&#xA;  for the rest of the surface. It is much hotter under the surface&#xA;  reaching temperatures in excess of a million degrees Celsius.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;These sunspots are areas where there is intense magnetic activity. The&#xA;  fields in these areas are enormous and as a result the surface of the&#xA;  sun is disrupted. In these areas the surface cools dramatically&#xA;  causing a darker region to be perceived.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Around the sunspot there is an area called a plage. This is slightly&#xA;  brighter than the surrounding area and it is a large radiator of&#xA;  cosmic rays, ultra-violet light and X-rays. In fact it results in the&#xA;  overall level of radiation coming from the sun to increase. In turn&#xA;  this increased radiation level from around the sunspots causes the&#xA;  ionosphere to become ionised to a greater extent. This means that&#xA;  higher frequencies can be reflected from the ionosphere.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;— &lt;a href=&quot;http://www.radio-electronics.com/info/propagation/ionospheric/sunspots-cycle-activity.php&quot; rel=&quot;nofollow&quot;&gt;http://www.radio-electronics.com/info/propagation/ionospheric/sunspots-cycle-activity.php&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="88" LastEditorUserId="76" LastEditDate="2013-10-23T10:47:53.320" LastActivityDate="2013-10-23T10:47:53.320" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="193" PostTypeId="2" ParentId="111" CreationDate="2013-10-23T04:07:25.367" Score="4" Body="&lt;p&gt;The primary advantages of coax with respect to ladder line are&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;most transceivers are equipped with coax connectors, whereas using ladder line requires a balun or balanced tuner&lt;/li&gt;&#xA;&lt;li&gt;coax is not affected by nearby metal objects, unlike ladder line&lt;/li&gt;&#xA;&lt;li&gt;the impedance of coax doesn't change when it rains or snows, unlike ladder line&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The primary advantages of ladder line with respect to coax are&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;lower loss at frequencies of 28 MHz and up&lt;/li&gt;&#xA;&lt;li&gt;easier to make connections&lt;/li&gt;&#xA;&lt;li&gt;can drive a balanced antenna (e.g. a dipole) without a balun&lt;/li&gt;&#xA;&lt;li&gt;lower weight&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="88" LastEditorUserId="88" LastEditDate="2013-10-24T05:14:26.797" LastActivityDate="2013-10-24T05:14:26.797" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="195" PostTypeId="2" ParentId="126" CreationDate="2013-10-23T04:23:42.417" Score="13" Body="&lt;p&gt;The primary advantages of vertical antennas are that they are omnidirectional, and with an appropriate ground plane (radials) yield a low radiation angle; this reduces the number of &quot;hops&quot; that HF signals must make to reach their destination. Ignoring the ground plane, which might be radial wires or metallic screening buried just under the surface, vertical antennas don't take up much space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The primary disadvantages of vertical antennas are that they are vertically polarized, which makes them more sensitive to man-made noise when used for reception as compared to horizontally-polarized antennas like a dipole, and that they require a good ground plane to be effective when transmitting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Vertical antennas for the lower bands require a significant mechanical support; for 80m, for example, a quarter-wavelength vertical antenna would be 66' tall. Verticals can be made shorter with top-loading or various tuning schemes, but at the cost of lowered efficiency -- meaning less of the transmitted signal is effectively radiated.&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-23T04:23:42.417" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="196" PostTypeId="2" ParentId="166" CreationDate="2013-10-23T04:45:12.037" Score="0" Body="&lt;p&gt;Some recent transceivers (IC-7100, IC-7200, IC-7410, IC-7600, IC-9100, TS-590, TS-990) include a &quot;virtual soundcard&quot;, meaning that a simple USB connection between computer and transceiver creates a device that appears to the operating system as a soundcard that digital mode applications can use in the standard way. The USB connection also handles RX-TX switching via CAT commands. &lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-23T04:45:12.037" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="197" PostTypeId="1" AcceptedAnswerId="654" CreationDate="2013-10-23T04:51:08.007" Score="10" ViewCount="602" Body="&lt;p&gt;I found &lt;a href=&quot;http://www.miklor.com/COM/pdf/AntennaTestingW9MDB.pdf&quot; rel=&quot;noreferrer&quot;&gt;some data on antennas that had been tested for a specific radio&lt;/a&gt;. I'm trying to decipher what this data means and how one would go about gathering it. Are there any good resource for learning how to read and understand this data?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically, please explain the following metrics:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;dBS9&lt;/li&gt;&#xA;&lt;li&gt;The relationship between dBm (the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW)) and antenna length.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For instance, in the following chart, which group of antennas operates optimally: the one in the blue freehand circle, those in the red freehand circle, or neither?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/6tfh9.png&quot; alt=&quot;Antenna Length vs. dBm @ 145MHz&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What common methods/software exist for obtaining this kind of data?&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="128" LastEditDate="2013-10-23T15:48:01.553" LastActivityDate="2016-04-27T12:33:53.363" Title="How to Evaluate Antenna Data" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="198" PostTypeId="2" ParentId="135" CreationDate="2013-10-23T04:51:32.333" Score="8" Body="&lt;p&gt;In noisy conditions, CW is the most effective mode for &quot;real time&quot; communications. This is the primary reason that CW remains popular with DXers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some digital modes can succeed under even worse conditions, but they do so by employing redundancy, which makes for very slow QSOs.&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-23T04:51:32.333" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="199" PostTypeId="2" ParentId="2" CreationDate="2013-10-23T05:11:16.863" Score="3" Body="&lt;p&gt;Here's a propagation prediction made using PropView with the VOACAP engine; the thicker the line the higher the probability of an opening:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NQBJ3.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see, your best bet on the higher bands is 10m between 18Z and 23Z, followed by 12m around 18Z, and from 22-24Z. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On 40m and below, both ends of the path between you and HI must be in twilight or darkness, which as the screenshot shows means 4Z to 12Z. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Signal paths that parallel the solar terminator can be enhanced by &quot;greyline propagation&quot;, but your QTH is too close to Hawaii for that.&lt;/p&gt;&#xA;" OwnerUserId="88" LastEditorUserId="218" LastEditDate="2015-02-11T20:59:35.117" LastActivityDate="2015-02-11T20:59:35.117" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="201" PostTypeId="2" ParentId="131" CreationDate="2013-10-23T05:49:03.763" Score="1" Body="&lt;p&gt;For higher frequencies like 2m, two pieces of wire soldered to a BNC connector and hung by your window make a great dipole!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are also various &quot;apartment window flagpole&quot; antennas that can do the job. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For DX, you run into a problem with grounding... there's no way to make a counterpoise or ground radials big enough. Fortunately, neither dipoles nor magnetic loops need a counterpoise or ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;G4FON's 20/30/40m band magnetic loop for travelers looks nice:&#xA;&lt;a href=&quot;http://www.g4fon.net/MagLoop.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.g4fon.net/MagLoop.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that's too complicated, Scott Harden's DIY Stealth Apartment Antenna may also be something worth trying... it's essentially a 20/40m dipole folded to fit an apartment:&#xA;&lt;a href=&quot;http://www.swharden.com/blog/2010-02-07-simple-diy-stealth-apartment-antenna-for-20m-and-40m/&quot; rel=&quot;nofollow&quot;&gt;http://www.swharden.com/blog/2010-02-07-simple-diy-stealth-apartment-antenna-for-20m-and-40m/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="130" LastActivityDate="2013-10-23T05:49:03.763" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="203" PostTypeId="2" ParentId="131" CreationDate="2013-10-23T06:37:33.680" Score="3" Body="&lt;p&gt;The answer depends highly on what you wish to accomplish. What sort of frequencies, how high power, distance you're going after, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;VHF/UHF (145 MHz and up)&lt;/strong&gt; antennas are small - if your window points to the right direction, and you live on the 6th floor, a small yagi in front of it can be good for serious DX when the propagation is right. You can also hang a &lt;strong&gt;dipole&lt;/strong&gt; in front of the window, which will be good for local contacts and working the repeaters. &lt;strong&gt;Copper tape&lt;/strong&gt; isn't expensive, you can use it to tape a dipole or &lt;strong&gt;J pole&lt;/strong&gt; directly on the window surface, and solder a coaxial on the feed point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF antennas will never work very well inside, but even a bad antenna is always better than no antenna at all. High power is out of the question - some of the power will end up on the building's power and phone/network cables, and easily cause RF interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Magnetic loops are an interesting option for HF work&lt;/strong&gt; - they are relatively narrow-band and tunable, and have other properties which make them more immune against electrical noise from household appliances, relays, and electronics. They are relatively small and can be placed in front of a window or wall. They need to be constructed out of thick metal tube or thick hardline coaxial cable, which makes them a bit heavy, but they still don't take more space than a heavy hula hoop. To run more than a few watts you'll need a high-voltage tunable capacitor, but QRP is fun to work too. With WSPR and similar digital modes for weak signals you can quite easily get proper DX contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dipoles work too, but  they'll pick up more static / electrical noise than loops. They're also pretty long for lower frequencies.&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-10-23T06:37:33.680" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="204" PostTypeId="1" CreationDate="2013-10-23T06:53:39.293" Score="2" ViewCount="114" Body="&lt;p&gt;I'm thinking about putting up a 80m dipole in the back yard, the only place I have to put this (can't do inverted V since I don't have a high enough location) is close to a overhead telephone wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would putting up an antenna close to another wire of about the same length cause excessive interference on the telephone wire?&lt;/p&gt;&#xA;" OwnerUserId="135" LastEditorUserId="8832" LastEditDate="2017-10-08T01:06:21.590" LastActivityDate="2017-10-08T01:06:21.590" Title="Interference generated by antenna placement?" Tags="&lt;antenna&gt;&lt;rfi&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="205" PostTypeId="2" ParentId="190" CreationDate="2013-10-23T06:55:46.073" Score="4" Body="&lt;p&gt;There are a few important things you will need to remember, which are mainly outlined &lt;a href=&quot;http://www.arrl.org/cept&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;http://www.arrl.org/cept-information&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe you must follow the power limits and band plans as outlined by the Polish government while operating there. Information will be hidden somewhere in &lt;a href=&quot;http://www.pzk.org.pl/news.php&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;. Good luck with that. I believe your best bet would be to email some people on those pages and hope for the best.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You won't need to register with anyone in Poland when you arrive, but you will need to be carrying the documentation described in the first two links above.&lt;/p&gt;&#xA;" OwnerUserId="134" LastEditorUserId="22" LastEditDate="2013-10-23T23:50:22.380" LastActivityDate="2013-10-23T23:50:22.380" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="206" PostTypeId="2" ParentId="204" CreationDate="2013-10-23T07:11:00.087" Score="2" Body="&lt;p&gt;If you'd only use the antenna for receiving, there wouldn't be any problems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're going to transmit with higher power (more than some tens of watts), it is quite possible that the RF energy will cause interference on equipment on either end of the phone line. That'll depend much on the distance between the antenna and the phone line, and the quality of the equipment at both ends of the phone line. Even small power might cause problems if you're unlucky.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If, for example, you have an ADSL modem at the end of the telephone line, and it trips over due to the RF, it'll be possible to reduce the interference by installing a filter or choke on the line next to the modem. However, if you manage to cause interference to the telephone company's or ISP's equipment at the other end, they might not be pleased at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If all of the equipment on the telephone line is old and analog, they should be more immune to RF interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should help a bit if it would be possible to install the antenna perpendicular to the phone line.&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-10-23T07:11:00.087" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="207" PostTypeId="2" ParentId="135" CreationDate="2013-10-23T07:27:22.647" Score="7" Body="&lt;p&gt;In the UK, the terms of the licence start with:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;1(1) The Licensee shall ensure that the Radio Equipment is only used:&#xA;  (a) for the purpose of self-training in radio communications, including conducting technical investigations; and&#xA;  (b) as a leisure activity and not for commercial purposes of any kind.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;CW/morse lends itself to the self-training aspect due to the simplicity of the equipment required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, in the &lt;a href=&quot;http://www.sota.org.uk&quot; rel=&quot;noreferrer&quot;&gt;Summits on the Air&lt;/a&gt; program, there is an ongoing PP3 challenge - which making the most QSOs using one &lt;a href=&quot;https://en.wikipedia.org/wiki/Nine-volt_battery&quot; rel=&quot;noreferrer&quot;&gt;PP3 type 9V battery&lt;/a&gt;.  This is only possible by operating on very low power, and using CW.  OK, this is only for fun, but that is what most of us are in amateur radio for, are we not?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, I haven't mastered CW (yet?) but I am quite impressed to watch/listen to operators working the key...&lt;/p&gt;&#xA;" OwnerUserId="93" LastActivityDate="2013-10-23T07:27:22.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="208" PostTypeId="1" CreationDate="2013-10-23T07:29:50.927" Score="7" ViewCount="1799" Body="&lt;p&gt;We'd like to install an antenna for 80m at our club/contest station. Our club, OH2K, is housed at a school, and we can't fill the roof with a radial mesh. The roof is not metallic itself, either. We already have a horizontal dipole, but would like to have something with a lower radiation angle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We do have a 20-meter tower on the roof of the school building, but there are no guy wires attached to the top of the mast, so it's a bit hard to support a full-height 20-meter-long quarter-wave vertical. However, something in the 10-15 meter length range is easy to hang. A very short vertical would be too narrowband for contests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We operate multi-multi, with 1 KW linear amplifiers, and stub + bandpass filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What practical 80m vertical antenna designs should we look at?&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="76" LastEditDate="2013-10-24T09:09:46.107" LastActivityDate="2013-11-02T19:59:04.167" Title="Practical 80m vertical wire antennas without radials?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;vertical-antenna&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="209" PostTypeId="2" ParentId="156" CreationDate="2013-10-23T07:39:48.503" Score="7" Body="&lt;p&gt;Dan's answer about which frequencies tend to be used for emergency communication is good, but I'd like to add another aspect you seem to be overlooking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Don't dismiss the possibility of such communications being done &lt;em&gt;outside of the amateur bands&lt;/em&gt;.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the US (which appears to be the focus of this question because of its reference to Technician and General class licenses), there is &lt;a href=&quot;https://en.wikipedia.org/wiki/Military_Auxiliary_Radio_System&quot;&gt;MARS (the Military Auxiliary Radio System)&lt;/a&gt;, licensing for which is legally completely separate from amateur radio and hence for which there exists a different set of requirements. Operating on HF MARS frequencies would not be influenced by whether or not the operator holds a HF-allowed amateur radio license, or indeed any amateur radio license at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other countries have similar systems in place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, in Sweden, to the extent that volunteers participate in such communications most communication is done on frequencies allocated for civilian defense or military defense purposes generally through the Voluntary Radio Organization (&lt;a href=&quot;http://fro.se/&quot;&gt;FRO&lt;/a&gt;) (not to be confused with the Swedish National Defence Radio Establishment, &lt;a href=&quot;http://www.fra.se/&quot;&gt;FRA&lt;/a&gt;). I think it's safe to say that many countries that do it that way lean toward allocating such frequencies near the amateur radio bands to (at least as an unspoken goal) ease interoperability with off-the-shelf amateur radio equipment, but there is certainly no requirement that it is done that way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;That said, one should &lt;em&gt;never dismiss the value of the practice one can gain on the amateur radio bands&lt;/em&gt;.&lt;/strong&gt; Particularly on HF, amateur radio communications is often fraught with issues: you're working with relatively low power, possibly less-than-ideal antennas, sometimes lots of stations transmitting within your receiver standard passband, potentially high noise levels, fading, perhaps running off battery power, and so on and so forth. &lt;strong&gt;Learning to consistently pick a single station's signal out of all that when times are easy is &lt;em&gt;invaluable&lt;/em&gt; practice for being able to assist when the conditions are worse&lt;/strong&gt; such as during a loss of normal communication links and mains power, forcing reliance on a noisy HF link for regional communications and quite possibly battery power which limits the available output power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That signal processor between your ears needs a long training period and constant tuning to be able to pick out signals most effectively.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-23T08:30:42.483" LastActivityDate="2013-10-23T08:30:42.483" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="210" PostTypeId="2" ParentId="119" CreationDate="2013-10-23T07:41:08.310" Score="2" Body="&lt;p&gt;The UK is a signatory of European Conference of Postal and Telecommunications Administrations (CEPT) Recommendations T/R 61-01 or T/R 61-02.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, the Radio Society of Great Britain's page &lt;a href=&quot;http://rsgb.org/main/operating/licensing-novs-visitors/operating-for-visitors/&quot; rel=&quot;nofollow&quot;&gt;Operating for Visitors&lt;/a&gt; is &lt;em&gt;Under Constuction&lt;/em&gt; which is not very helpful :(&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there is some useful information of the &lt;a href=&quot;http://licensing.ofcom.org.uk/radiocommunication-licences/amateur-radio/faq/759498&quot; rel=&quot;nofollow&quot;&gt;OFCOM (the regulatory body) website&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simply put, you can operate here for three months using your own licence, or longer with a reciprocal licence.&lt;/p&gt;&#xA;" OwnerUserId="93" LastActivityDate="2013-10-23T07:41:08.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="211" PostTypeId="2" ParentId="69" CreationDate="2013-10-23T07:55:36.273" Score="1" Body="&lt;p&gt;The &lt;a href=&quot;http://www.planningportal.gov.uk/permission/commonprojects/antenna/&quot; rel=&quot;nofollow&quot;&gt;&quot;official&quot; Government Guidance&lt;/a&gt; is pretty clear (for once):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Unless your house (or the building in which you live) is in a&#xA;  designated area, you do not need to apply for planning permission to&#xA;  install an antenna on your property, as long as:&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;there will be no more than two antennas on the property overall. (These may be on the front or back of the building, on the roof, attached to the chimney, or in the garden);&lt;/li&gt;&#xA;  &lt;li&gt;if you are installing a single antenna, it is not more than 100 centimetres in any linear dimension (not including any projecting feed element, reinforcing rim, mounting and brackets);&lt;/li&gt;&#xA;  &lt;li&gt;if you are installing two antennas, one is not more than 100 centimetres in any linear dimension, and the other is not more than 60 centimetres in any linear dimension (not including any projecting feed element, reinforcing rim, mounting and brackets);&lt;/li&gt;&#xA;  &lt;li&gt;the cubic capacity of each individual antenna is not more than 35 litres;&lt;/li&gt;&#xA;  &lt;li&gt;an antenna fitted onto a chimney stack is not more than 60 centimetres in any linear dimension;&lt;/li&gt;&#xA;  &lt;li&gt;and an antenna mounted on the roof only sticks out above the roof when there is a chimney-stack. In this case, the antenna should not stick out more than 60 centimetres above the highest part of the roof, or above the highest part of the chimney stack, whichever is lower.&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Note that &lt;em&gt;linear dimension&lt;/em&gt; is defined as including &quot;only the antenna itself and not any attachment needed to fix it to the wall or roof, or connect it up to your equipment&quot; - so any pole is irrelevant, just the antenna on top.  A tower will be a different matter though!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately 100cm is not really much use for amateur radio (certainly not HF)...&lt;/p&gt;&#xA;" OwnerUserId="93" LastActivityDate="2013-10-23T07:55:36.273" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="212" PostTypeId="2" ParentId="72" CreationDate="2013-10-23T08:07:04.670" Score="4" Body="&lt;p&gt;Encryption on amateur radio is prohibited in most countries. There are some exceptions, in some countries, and for some specific use cases. You'll need to consult your local rules.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Some countries&lt;/strong&gt; (Australia being an example) allow encryption in &lt;strong&gt;emergency communications&lt;/strong&gt; and relevant training activities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some countries (US, for example) allow encryption for transmitting &lt;strong&gt;control commands to satellites&lt;/strong&gt;, so that unauthorized stations can be prevented from causing harm to the satellite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some protocols used in digital networking (IPSEC, SSL/TLS) allow you to disable traffic encryption (using a &quot;none&quot; cipher), but still use cryptographic algorithms such as HMAC to do &lt;strong&gt;strong authentication&lt;/strong&gt; and tampering prevention. Doing that does not conceal the contents of the traffic, so it's allowed, and sufficient for many use cases such as remote commands to satellites, or other restricted-access services.&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-10-23T08:07:04.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="213" PostTypeId="1" AcceptedAnswerId="236" CreationDate="2013-10-23T08:16:07.580" Score="13" ViewCount="3031" Body="&lt;p&gt;There are a number of repeaters in my area, each belonging to a particular amateur radio club. These guys are all friendly and willing to chat but I was wondering if it was bad form to make use of a repeater belonging to a club you aren't part of without first getting permission?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The repeaters in my area are all listed on the websites for each club but no operating conditions are mentioned. I'll ask but was thinking there might be a general rule.&lt;/p&gt;&#xA;" OwnerUserId="135" LastEditorUserId="8573" LastEditDate="2018-12-03T07:38:57.570" LastActivityDate="2018-12-03T07:38:57.570" Title="OK to use any repeater?" Tags="&lt;repeater&gt;&lt;procedure&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="214" PostTypeId="2" ParentId="213" CreationDate="2013-10-23T08:22:28.197" Score="10" Body="&lt;p&gt;The practices vary greatly between areas and countries. In many countries &quot;closed repeaters&quot; don't exist, or are forbidden. In some countries private repeater systems are common, but public ones still exist. Those private repeaters are still likely to happily accept visitors (travellers, for example).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's probably best to ask the guys on the repeater - they should be happy to tell you what's the local practice. Many repeaters have web sites too, which provide usage instructions and other policies. If it's not described as a closed or private repeater, it's safe to assume that it is open and free for all. If you become a regular visitor on the repeater, it's a good idea to join the club to share the operating costs.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-23T15:09:34.310" LastActivityDate="2013-10-23T15:09:34.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="215" PostTypeId="2" ParentId="59" CreationDate="2013-10-23T08:29:42.120" Score="24" Body="&lt;p&gt;Assuming that you have an amateur radio license makes this easier, but it's quite possible that the UK legal language includes provisions that may be applicable and allow transmission without a license. It depends on the specifics of the emergency in question. I would strongly recommend familiarizing yourself with the relevant definitions in the legal code of your country; it's perfectly possible that an emergency situation allows you to transmit on frequencies you otherwise wouldn't be allowed to, &lt;em&gt;even if the emergency situation does not revolve around you directly&lt;/em&gt; (for example, you tune your transceiver across the bands without a license and come across an emergency transmission by someone else).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If possible, find a frequency that is actually in use and where you can hear both stations; it makes it much more likely that someone will hear your call. Call &lt;strong&gt;mayday mayday mayday&lt;/strong&gt; (life-threatening emergency) or &lt;strong&gt;break break emergency&lt;/strong&gt; (non-life-threatening emergency) as soon as is practical (on a handover if you can afford to wait that amount of time), and unless the situation is extremely dire &lt;em&gt;wait a few moments for acknowledgement&lt;/em&gt;. Hopefully one of the stations will respond with something like &lt;em&gt;Jim, break for emergency, go ahead emergency&lt;/em&gt;. As the remote operator making such a go-ahead request, you want to be &lt;em&gt;extremely concise, clear, and unambigiously tell the breaking station to go ahead with its transmission and all others to cease transmission&lt;/em&gt;. Ideally, at this point the remote station operators will have grabbed a blank piece of paper and a writing utensil of some kind, &lt;em&gt;and be prepared to take notes&lt;/em&gt;. &lt;em&gt;For the receiving stations to be taking notes is absolutely essential; as a receiver you will not remember the details!&lt;/em&gt; Also, &lt;em&gt;all&lt;/em&gt; stations able to receive an emergency report should copy it down; if the station making the emergency report goes off the air for whatever reason, the chances are much better that even in the case of heavy interference a complete report can be pieced together by the remaining stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, I would suggest reporting things in logical order. &lt;em&gt;Stay calm.&lt;/em&gt; Consider what information is needed to offer assistance. For a wilderness emergency, I'd state:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The kind of emergency (broken leg, vehicle collision, wildfire, ...).&lt;/li&gt;&#xA;&lt;li&gt;The position, in some unambigious manner (for example &quot;Grothwick national park distance 30 miles east of Tadwick, distance 12 miles direction north from trail head on the length 72 miles trail&quot;). Spell out numbers (&quot;seven two&quot;, possibly even &quot;seven two point zero&quot; rather than &quot;seventytwo&quot;). GPS coordinates if available will greatly help, but if it's an actual emergency, I wouldn't wait for the GPS receiver to get a fix; you can always complement later.&lt;/li&gt;&#xA;&lt;li&gt;The assistance required (&quot;need transportation to nearest hospital&quot;, &quot;need fire prevention services&quot;, ...)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;After that, &lt;strong&gt;STOP.&lt;/strong&gt; Say &quot;any receiving station, confirm complete reception of emergency report&quot; or something equally unambigious. Hopefully someone will acknowledge, or at least ask for a repeat of some missed piece of information. &lt;em&gt;Note that there may be stations listening without transmission capability&lt;/em&gt; so a lack of response does not &lt;em&gt;necessarily&lt;/em&gt; mean that nobody heard you. The ability for a remote station to acknowledge is why I suggest finding a frequency that is actually in use and breaking into the communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With any luck, a remote station will respond with something like &quot;confirming complete reception of emergency report, stand by&quot;. &lt;em&gt;This is the kind of answer you want.&lt;/em&gt; It means they have received everything &lt;em&gt;and is contacting the proper emergency services&lt;/em&gt; through some alternate channel, whether that is radio relay, telephone, or some other means. Respond with a short &quot;emergency, standing by&quot; to acknowledge. Issue repeat &quot;emergency, standing by&quot; every 20-30 seconds or so to make it less likely that anybody thinks the frequency is free for use. Hopefully, a minute or two after the initial acknowledgement, the acknowledging station will get back to report that emergency services have been notified about the emergency. &lt;em&gt;At this point, they may relay questions, instructions or otherwise from the emergency services dispatch center. Answer those to the best of your ability, as clearly as you can, just as if you had been calling them yourself.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;You may notice an overall theme in all this: &lt;em&gt;clarity&lt;/em&gt;, and the &lt;em&gt;repeat transmission of &quot;emergency&quot;&lt;/em&gt;.&lt;/strong&gt; Both those serve to help everyone involved. A panicked report does not help anybody, as well as that a random radio amateur is less likely to be trained to deal with someone panic-struck than an emergency services dispatch operator. Repeatedly transmitting &quot;emergency&quot; informs others that the traffic should have extremely high priority. Clarity, &lt;em&gt;including avoiding the use of jargon&lt;/em&gt;, helps non-amateurs copy and possibly relay the message to the emergency authorities. All this helps ensure as speedy a response as possible. &lt;strong&gt;The exact wordings are much less important than doing your best to remain calm and to provide the pertient information as soon as possible.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a real emergency situation, I wouldn't worry too much about identification. Do it early if you have the time, but if not, it's better to wait until all essentials have been taken care of. And certainly don't bother with signal strength reports etc. unless the signal quality is exceptionally poor to the point of being outright hard to copy accurately. This is an &lt;em&gt;emergency report&lt;/em&gt;, not a rag-chewing amateur radio contact!&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-10-23T08:29:42.120" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="216" PostTypeId="2" ParentId="213" CreationDate="2013-10-23T09:44:43.590" Score="6" Body="&lt;p&gt;In my experience since 1992 with some traveling in MD, VA, PA, DE, WVA, NC, FL, CA, &amp;amp; OK I have yet to find a repeater group that has not been friendly to a newbie or visitor. I do usually have the ARRL repeater book with me and am careful to stay off of the few closed repeaters listed.&lt;/p&gt;&#xA;" OwnerUserId="142" LastActivityDate="2013-10-23T09:44:43.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="217" PostTypeId="5" CreationDate="2013-10-23T11:23:20.067" Score="0" Body="&lt;p&gt;This tag should be used on questions relating to the annual Scout and Guide Jamboree-on-the-Air (JOTA)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;JOTA (and its sister event &lt;a href=&quot;/questions/tagged/joti&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged 'joti'&quot; rel=&quot;tag&quot;&gt;joti&lt;/a&gt;) is an annual event during which Scouts and Guides all over the world speak to each other by means of amateur radio contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;http://www.scout.org/jota&quot; rel=&quot;nofollow&quot;&gt;http://www.scout.org/jota&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2013 saw the 56th year of JOTA and the 17th year of JOTI&lt;/p&gt;&#xA;" OwnerUserId="93" LastEditorUserId="93" LastEditDate="2013-10-23T16:33:33.540" LastActivityDate="2013-10-23T16:33:33.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="218" PostTypeId="4" CreationDate="2013-10-23T11:23:20.067" Score="0" Body="Jamboree-on-the-Air (JOTA) is an annual event during which Scouts and Guides all over the world speak to each other by means of amateur radio contacts." OwnerUserId="93" LastEditorUserId="93" LastEditDate="2013-10-23T16:33:21.553" LastActivityDate="2013-10-23T16:33:21.553" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="219" PostTypeId="2" ParentId="123" CreationDate="2013-10-23T11:55:13.907" Score="4" Body="&lt;p&gt;I've used &lt;a href=&quot;http://www.cqrlog.com/&quot; rel=&quot;nofollow&quot;&gt;CQRLOG&lt;/a&gt; which is built on MySQL but otherwise has many of the same features as other loggers and is fully customizable. If that's too much and you're looking for a simpler solution, &lt;a href=&quot;http://xlog.nongnu.org/&quot; rel=&quot;nofollow&quot;&gt;Xlog&lt;/a&gt; is a barebones logger that can still interchange data with some of the Linux PSK and other digital mode software. Both support all the popular export formats, including adif and Cabrillo. The &lt;a href=&quot;https://wiki.archlinux.org/index.php/Amateur_Radio#Logging&quot; rel=&quot;nofollow&quot;&gt;Arch Linux Wiki&lt;/a&gt; has links to another 8 programs that might help, including &lt;a href=&quot;http://fkurz.net/ham/yfktest.html&quot; rel=&quot;nofollow&quot;&gt;YFKtest&lt;/a&gt; or &lt;a href=&quot;http://home.iae.nl/users/reinc/TLF-0.2.html&quot; rel=&quot;nofollow&quot;&gt;TLF&lt;/a&gt; if you're looking for a barebones console logger or &lt;a href=&quot;http://www.fdlog.info/&quot; rel=&quot;nofollow&quot;&gt;FDLog&lt;/a&gt; with field-day-specific features and networking.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-23T11:55:13.907" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="220" PostTypeId="2" ParentId="49" CreationDate="2013-10-23T12:11:56.133" Score="6" Body="&lt;p&gt;This is not commonplace. Most operators in the UK get along fine with the 400W limit. Given the path losses inherent in Earth-Moon-Earth - hundreds of decibels - the antenna is a much more important factor than is the power. You need every extra bit of push you can get, but if you're not making it at 400W, 1500W isn't likely to be much better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that doubling the power equates to only half an S-unit at the receiver. Even going from 400W to 1600W would only give you an extra 6dB gain - and wouldn't help you receive other people's signals at all. Invest in a better antenna rather than a better amplifier, you'll see much better reception in both directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The process you'd have to use is an application for a Notice of Variation. These are issued by Ofcom, and there is an opportunity to apply for one for &lt;a href=&quot;http://licensing.ofcom.org.uk/binaries/spectrum/amateur-radio/apply-for-a-licence/ofw306.pdf&quot;&gt;Special Research&lt;/a&gt; - but you will not get it granted solely for the purposes of higher power for EME. This is the process used for example by the hams that are experimenting with lower frequency communications, like 500kHz and 2200m, before they are officially authorized to all operators.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-23T12:11:56.133" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="221" PostTypeId="1" AcceptedAnswerId="224" CreationDate="2013-10-23T12:24:04.597" Score="25" ViewCount="17894" Body="&lt;p&gt;I see that many contests, awards, and other items, use Grid Squares as a means to identify where one is. How can one figure out what one's grid square is, given lat/long?&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="29" LastEditDate="2016-07-27T16:55:46.833" LastActivityDate="2018-04-01T04:18:40.973" Title="How can one convert from Lat/Long to Grid Square?" Tags="&lt;location&gt;&lt;maidenhead-locator&gt;" AnswerCount="13" CommentCount="2" FavoriteCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="223" PostTypeId="2" ParentId="221" CreationDate="2013-10-23T12:32:42.230" Score="2" Body="&lt;p&gt;You can start by using a &lt;a href=&quot;http://www.google.com/imgres?imgurl=http://www.colorado.edu/geography/gcraft/notes/coordsys/gif/maiden1.gif&amp;amp;imgrefurl=http://www.colorado.edu/geography/gcraft/notes/coordsys/coordsys.html&amp;amp;h=350&amp;amp;w=501&amp;amp;sz=15&amp;amp;tbnid=WdToIvIyw0WBgM%3a&amp;amp;tbnh=90&amp;amp;tbnw=129&amp;amp;zoom=1&amp;amp;usg=__l8g9hPbA3w5CPgSlA_qXfDZ5SkU=&amp;amp;docid=rVvhcvYJVxzsPM&amp;amp;sa=X&amp;amp;ei=_8BnUp6KD8W_kQfc3IG4BA&amp;amp;ved=0CGkQ9QEwBw&quot; rel=&quot;nofollow&quot;&gt;map&lt;/a&gt;, but that gets out of hand once you get beyond the second set of digits. There are calculators online, like &lt;a href=&quot;http://www.qrz.com/gridfinder&quot; rel=&quot;nofollow&quot;&gt;this one from QRZ&lt;/a&gt; or &lt;a href=&quot;http://www.levinecentral.com/ham/grid_square.php&quot; rel=&quot;nofollow&quot;&gt;this map-based locator&lt;/a&gt;. It's possible to calculate it by hand as well - the &lt;a href=&quot;http://en.wikipedia.org/wiki/Maidenhead_Locator_System#Description_of_the_system&quot; rel=&quot;nofollow&quot;&gt;Wikipedia article&lt;/a&gt; has a good description on how they work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, the first two characters build a grid, just like on any map. The first character is longitude, the second is latitude, and the first pair is letters A-R, meaning the world is broken up into 18 slices. Since there are 360 degrees of longitude and 180 of latitude, that means that each grid square is about 18 degrees wide by 9 degrees tall. It starts at 180 degrees west and 90 degrees south, so if I'm in the sixth grid east of 180 degrees W (meaning my longitude is between 72 West and 90 W), my first character is F. Then, the second pair of digits divides that up into 10 equal slices, and so on.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-23T12:45:07.980" LastActivityDate="2013-10-23T12:45:07.980" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="224" PostTypeId="2" ParentId="221" CreationDate="2013-10-23T12:42:50.543" Score="25" Body="&lt;p&gt;First of all, if you don't want to do any math, then check out a grid square map, such as &lt;a href=&quot;http://f6fvy.free.fr/qthLocator/fullScreen.php&quot;&gt;this one&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is an excellent process at &lt;a href=&quot;http://www.newsvhf.com/my-grid.html&quot;&gt;this page&lt;/a&gt;, and additional resources from &lt;a href=&quot;http://www.arrl.org/grid-squares&quot;&gt;ARRL&lt;/a&gt;. Essentially, Grid Squares contain 3 pairs, the first and last letters, and the middle numbers. Longitude is always the first, followed by latitude, for each pair. For simplicity, let's assume that West and South are negative lat/long, as is a common convention. For example purposes, I'm going to use 32.123 W, 14.321 N. The key thing is to do the following.:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Longitude&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Add 180 to the longitude, and take the integer value /20, and add one. Then figure out which letter of the alphabet that corresponds to, usually written in upper case. The example will be 147.877/20=7. Adding one will give the 8th letter of the alphabet, or H. Note 7.877 is remaining.&lt;/li&gt;&#xA;&lt;li&gt;Take the remainder of what is left, and divide by 2, rounding down. This is the number, no conversion required. The example will give a value of 3. Note 1.877 is remaining.&lt;/li&gt;&#xA;&lt;li&gt;Take the remainder that is left, and multiply by 12, and add one. Round down to the nearest integer.. This is the letter of the alphabet, usually written in lower case. The example gives a value of 22+1=23. This will be the letter w.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Latitude&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Add 90 to the longitude, and take the integer value /10, and add one. Then figure out which letter of the alphabet that corresponds to, usually written in upper case. The example will be 104.321/10=10. Adding one will give the 11th letter of the alphabet, or K. Note 4.321 is remaining.&lt;/li&gt;&#xA;&lt;li&gt;Take the remainder of what is left, and round down. This is the number, no conversion required. The example will give a value of 4. Note 0.321 is remaining.&lt;/li&gt;&#xA;&lt;li&gt;Take the remainder that is left, and multiply by 24, and add one. Round down to the nearest integer.. This is the letter of the alphabet, usually written in lower case. The example gives a value of 7+1=8. This will be the letter h.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Putting them together by pairs, and alternating first longitude then latitude, gives the grid square for 32.123 W, 14.321 N to be HK34wh.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="-1" LastEditDate="2015-07-31T22:56:00.070" LastActivityDate="2015-07-31T22:56:00.070" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="225" PostTypeId="1" AcceptedAnswerId="291" CreationDate="2013-10-23T12:55:13.370" Score="3" ViewCount="332" Body="&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2013/2013%20Rules.pdf&quot; rel=&quot;nofollow&quot;&gt;ARRL Field Day Rules&lt;/a&gt; allow a GOTA station to be operated by &quot;a generally inactive licensee. &quot; There are members of my club which started to become active again after a long term of inactivity a few months before Field Day. Are they allowed to use the GOTA station, citing general inactivity?&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="76" LastEditDate="2014-06-11T19:09:51.393" LastActivityDate="2014-06-11T19:09:51.393" Title="How is a &quot;Generally Inactive&quot; ham determined for Field Day GOTA?" Tags="&lt;contest&gt;&lt;arrl&gt;&lt;field-day&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="227" PostTypeId="2" ParentId="133" CreationDate="2013-10-23T13:42:52.877" Score="3" Body="&lt;p&gt;My non-technical over-simplified answer; &lt;strong&gt;yes, the type of metal used for an antenna will present different characteristics&lt;/strong&gt;. The most obvious is the conductivity. Greater conductivity will yield higher radiation patterns, however, the size and dimension of the conductor also affects its performance. Cost, weight, and ease of manipulation of the material is often MORE of an issue than a slight percentage of increased performance due to the metal type. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aluminum for example, is a prime choice for beams as it is easy to cut and bend, provides great conductivity, and is lightweight. A copper beam would provide greater conductivity, but as a soft metal it would bend out of shape easily and become unusable. Likewise, a dipole is usually copper wire as its flexibility provides better ease of mounting and wind resistance, and low cost for a long wavelength antenna.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2013-10-23T13:42:52.877" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="228" PostTypeId="5" CreationDate="2013-10-23T13:47:38.430" Score="0" Body="&lt;p&gt;This tag should be used for any questions about US-specific regulations, including questions about operating privileges, secondary users, regulatory rules about interference caused by or to amateur operators. It can also be used for questions about clubs or other organizations using ham radio in the USA or for questions about nets that specifically target the USA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This tag should not be used simply because the person asking the question is in the USA, it should only be used if the answers need to be specifically directed towards US rules or practice.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-23T16:35:05.687" LastActivityDate="2013-10-23T16:35:05.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="229" PostTypeId="4" CreationDate="2013-10-23T13:47:38.430" Score="0" Body="Questions specific to rules, regulations, and practices in the United States of America." OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-10-24T09:10:32.953" LastActivityDate="2013-10-24T09:10:32.953" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="230" PostTypeId="5" CreationDate="2013-10-23T13:49:00.013" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-23T13:49:00.013" LastActivityDate="2013-10-23T13:49:00.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="231" PostTypeId="4" CreationDate="2013-10-23T13:49:00.013" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-23T13:49:00.013" LastActivityDate="2013-10-23T13:49:00.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="232" PostTypeId="5" CreationDate="2013-10-23T13:52:06.800" Score="0" Body="&lt;p&gt;This tag is appropriate for any question relating to an antenna. It should only be used if the question is about antennas, general questions about using or setting up a radio do not belong here, nor do general questions about reception or interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use this tag any time you're asking about a specific antenna, including practical questions (how to build it) and theoretical questions (how it works). This tag is also appropriate for mounting or setting up antennas, testing antennas for SWR or with an antenna analyzer, selecting materials to use for an antenna, or questions about commercial antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider also using a more specific tag, such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;/questions/tagged/antenna-theory&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;antenna-theory&amp;#39;&quot; rel=&quot;tag&quot;&gt;antenna-theory&lt;/a&gt; — for designing antennas&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;/questions/tagged/antenna-construction&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;antenna-construction&amp;#39;&quot; rel=&quot;tag&quot;&gt;antenna-construction&lt;/a&gt; — for building antennas&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;/questions/tagged/wire-antenna&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;wire-antenna&amp;#39;&quot; rel=&quot;tag&quot;&gt;wire-antenna&lt;/a&gt;, &lt;a href=&quot;/questions/tagged/dipole&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;dipole&amp;#39;&quot; rel=&quot;tag&quot;&gt;dipole&lt;/a&gt;, &lt;a href=&quot;/questions/tagged/loop-antenna&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;loop-antenna&amp;#39;&quot; rel=&quot;tag&quot;&gt;loop-antenna&lt;/a&gt;, &lt;a href=&quot;/questions/tagged/vertical-antenna&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;vertical-antenna&amp;#39;&quot; rel=&quot;tag&quot;&gt;vertical-antenna&lt;/a&gt; — for specific types of antennas&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Related subjects:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;/questions/tagged/feed-line&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;feed-line&amp;#39;&quot; rel=&quot;tag&quot;&gt;feed-line&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;/questions/tagged/balun&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;balun&amp;#39;&quot; rel=&quot;tag&quot;&gt;balun&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;/questions/tagged/antenna-tuner&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;antenna-tuner&amp;#39;&quot; rel=&quot;tag&quot;&gt;antenna-tuner&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="87" LastEditorUserId="76" LastEditDate="2015-12-15T20:43:58.590" LastActivityDate="2015-12-15T20:43:58.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="233" PostTypeId="4" CreationDate="2013-10-23T13:52:06.800" Score="0" Body="Questions about the design, selection, building, testing, mounting, or properties of antennas. See also specific tags: [antenna-theory], [antenna-construction], [dipole], etc." OwnerUserId="87" LastEditorUserId="76" LastEditDate="2015-12-15T20:38:16.243" LastActivityDate="2015-12-15T20:38:16.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="234" PostTypeId="2" ParentId="190" CreationDate="2013-10-23T13:56:23.180" Score="1" Body="&lt;p&gt;First of all Poland is a CEPT country, as is the US, so you can follow CEPT rules. CEPT rules require the following, per &lt;a href=&quot;http://www.arrl.org/cept&quot; rel=&quot;nofollow&quot;&gt;ARRL&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Bring their original US license&lt;/li&gt;&#xA;&lt;li&gt;Bring proof of US citizenship (generally in the form of a Passport)&lt;/li&gt;&#xA;&lt;li&gt;Bring a copy of the FCC's Public Notice (this notice contains its information in three languages, English, French and German) which details what US Amateurs need to consider, and bring with them, when traveling to a CEPT country.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;If you are Advanced/Extra, you will have full privileges. If you are General, you will be more restricted. If you have technician/novice, then you will not be able to operate. However, as they mention on &lt;a href=&quot;http://international.pzk.org.pl/index.html&quot; rel=&quot;nofollow&quot;&gt;this website&lt;/a&gt;, you can apply for one:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What if you have no valid CEPT license?  Foreign Radio Amateurs&#xA;  without a CEPT license or a CEPT Novice license can apply for a guest&#xA;  license with the Polish telecommunications authority, which is Office&#xA;  of Electronic Communications (UKE) in Warszawa. The license will be&#xA;  issued for 3 months at the expense of  82,00 PLN (approx. 21 €).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The proper way to identify yourself will be to add a SP/ to the beginning of your call sign. Mine would be SP/KD7UIY, for instance. You cannot operate outside of your US privileges, nor the country in which you are operating. Poland is a ITU Region 1, you can see what that signifies from &lt;a href=&quot;http://www.arrl.org/amateur-frequencies-outside-the-us&quot; rel=&quot;nofollow&quot;&gt;ARRL&lt;/a&gt;. The primary difference is in the 80/40m range. Lastly, make sure you don't go over the power restrictions. I'm not sure what the max power is, but I'm fairly confident it is at least 400W.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-23T13:56:23.180" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="235" PostTypeId="2" ParentId="146" CreationDate="2013-10-23T14:01:03.850" Score="1" Body="&lt;p&gt;Very good answers posted about polarization. I must point out an important caveat about polarization - while not so important for distant skip contacts ... it IS a vital consideration for LOCAL contacts. Cost and convenience is a prime factor for the popularity of rooftop vertical HF antennae. If your local friends are using verticals - you need to also be on a vertical (polarization) otherwise they may not hear you clearly or at all. As noted in another answer, vertical does draw more interference in a typical cityscape, but it varies depending on your location and proximity to interference sources.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If local contacts are important, and if other locals are using verticals, then you should consider a vertical. If DX is more important, then other horizontal options present themselves (which may even work well for local contacts).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A different factor to consider is the construction of the particular vertical you intend to use. Some are simply a 50 ohm &quot;dummy load&quot; with a wavelength/fraction wire sticking out it. Some have grounding radials. Some have coils. Just classifying it a vertical antenna is not entirely accurate.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2013-10-23T14:01:03.850" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="236" PostTypeId="2" ParentId="213" CreationDate="2013-10-23T15:34:42.453" Score="15" Body="&lt;p&gt;&lt;strong&gt;Do you have to get permission?&lt;/strong&gt; No. Few have issues with guests on a repeater (think of travelers passing through, for instance). In the U.S. they can legally prevent someone from using their repeater (&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=55730c6a1b98dd8340e658099cba6f1b&amp;amp;node=47:5.0.1.1.6.3.157.3&amp;amp;rgn=div8&quot; rel=&quot;noreferrer&quot;&gt;see ECFR Title 47, §97.205(e)&lt;/a&gt;), but this is not the case in many other countries (repeaters are generally open for all to use).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Should I frequently use a repeater that I don't financially support?&lt;/strong&gt; This is an ethical question, so subjectivity abounds. However, it should be kept in mind that repeaters aren't free nor cheap to set up and maintain. Consider paying membership dues or making a donation to the club(s) that maintain a repeater that you use frequently. This will help offset the operating costs and you'll gain some new friends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What operating conditions should I follow?&lt;/strong&gt; There is of course general repeater etiquette (listen first, wait for the courtesy tone, don't kerchunk, use plain language, don't call CQ, etc.), but some clubs may have specific etiquette or pet peeves that you will only find out about in their newsletter (or by attending their meetings). It is generally a good idea to remain somewhat connected to the club that is the control operator of the repeater &lt;em&gt;if you use it frequently&lt;/em&gt;. You may also be able to help the other repeater users by learning about a local jammer or other problem as well.&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="128" LastEditDate="2013-10-30T18:50:16.897" LastActivityDate="2013-10-30T18:50:16.897" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="237" PostTypeId="2" ParentId="72" CreationDate="2013-10-23T16:18:43.490" Score="2" Body="&lt;p&gt;Don N2IRZ wrote &lt;a href=&quot;http://hsmm-mesh.org/images/stories/DataEncryptionIsLegal.pdf&quot; rel=&quot;nofollow&quot;&gt;an article&lt;/a&gt; in CQ Magazine's August 2006 edition which made the case that data encryption is legal when it is used for the purpose of preventing unauthorized access. The context he's referring to is when using modified commercial WiFi routers which have channels that overlap with the amateur band (e.g. HSMM-Mesh/Broadband-Hamnet) and preventing part 15 users from joining part 97 mesh networks through the use of encrypted passwords such as WPA/WEP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure if his logic has held up in light of the recent &lt;a href=&quot;http://www.fcc.gov/document/order-dismissing-rolph-amateur-encryption-rulemaking-petition&quot; rel=&quot;nofollow&quot;&gt;FCC dismissal&lt;/a&gt; of a rulemaking petition to provide an exception for encryption for during disaster/public service operations, but it is an interesting read. &lt;/p&gt;&#xA;" OwnerUserId="156" LastActivityDate="2013-10-23T16:18:43.490" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="238" PostTypeId="2" ParentId="133" CreationDate="2013-10-23T16:22:51.713" Score="0" Body="&lt;p&gt;Apart from things already mentioned, I would also like to bring in the &lt;a href=&quot;https://en.wikipedia.org/wiki/Q_factor&quot; rel=&quot;nofollow&quot;&gt;Q-Factor&lt;/a&gt;. Although it is a figure of merit for Oscillators, it has some relevance to antennae as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you had a purely inductive antenna, it would radiate at a given frequency and very narrow bandwidth. &lt;a href=&quot;http://www.astrosurf.com/luxorion/qsl-antennas-basics.htm&quot; rel=&quot;nofollow&quot;&gt;This page&lt;/a&gt; explain the Q-Factors of antennae quite well.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Q = (2 * pi * f * L) / R&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So your antenna material better have some resistance.&lt;/p&gt;&#xA;" OwnerUserId="49" LastActivityDate="2013-10-23T16:22:51.713" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="239" PostTypeId="1" AcceptedAnswerId="240" CreationDate="2013-10-23T16:35:43.963" Score="9" ViewCount="197" Body="&lt;p&gt;Just what the title states.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here, in India, in the context of public service we hear of RACES (Radio Amateur Civil Emergency Service). I recently learnt about something called ARES in a similar context applicable to CONUS. Yet RACES, as far as I'm aware, was relevant to the US too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is ARES different from RACES? &lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="13" LastEditDate="2013-10-23T17:05:22.983" LastActivityDate="2013-10-23T17:29:01.220" Title="How is ARES different from RACES?" Tags="&lt;emergency&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="240" PostTypeId="2" ParentId="239" CreationDate="2013-10-23T16:39:36.230" Score="7" Body="&lt;p&gt;The ARRL actually has an FAQ that discusses this topic explicitly:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/ares-races-faq&quot;&gt;http://www.arrl.org/ares-races-faq&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;ARES is activated before, during and after an emergency. Generally, ARES handles all emergency messages, including those between government emergency management officials. RACES, on the other hand, almost never starts before an emergency and is active only during the emergency and during the immediate aftermath if government emergency management offices need communications support. RACES is normally shut down shortly after the emergency has cleared.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The FAQ continues into more detail, but the general gist is that RACES is specifically for coordinating actual civil services, whereas ARES is a more general communications network for overall messaging around emergencies.&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-10-23T17:05:10.243" LastActivityDate="2013-10-23T17:05:10.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="241" PostTypeId="1" CreationDate="2013-10-23T16:47:42.573" Score="4" ViewCount="402" Body="&lt;p&gt;The &lt;a href=&quot;http://aprs.org&quot; rel=&quot;nofollow&quot;&gt;APRS.org&lt;/a&gt; web site provides some good information but is not very well organized and does not appear to be actively maintained. What are some good resources for beginners seeking the following:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Minimum equipment needed to receive packets&lt;/li&gt;&#xA;&lt;li&gt;Minimum equipment needed to transmit packets&lt;/li&gt;&#xA;&lt;li&gt;Best practices for test transmissions&lt;/li&gt;&#xA;&lt;li&gt;Overall etiquette so as not to annoy the community&lt;/li&gt;&#xA;&lt;li&gt;Modern (still active in 2013) community resources for discussing the APRS system&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;As a newly-minted tech, I thank you for your insight.&lt;/p&gt;&#xA;" OwnerDisplayName="user157" LastActivityDate="2013-10-23T16:47:42.573" Title="Getting Started with APRS" Tags="&lt;aprs&gt;" AnswerCount="0" CommentCount="2" FavoriteCount="2" ClosedDate="2013-10-23T22:40:04.737" ContentLicense="CC BY-SA 3.0" />
  <row Id="242" PostTypeId="5" CreationDate="2013-10-23T17:02:09.103" Score="0" Body="&lt;p&gt;This tag is for questions about the use of amateur radio in support of public safety or disaster relief in a declared emergency, including any equipment, protocols, or techniques that are specifically applicable to emergency communications. This tag is not for general questions about the National Traffic System or nets in general, or about equipment that &lt;em&gt;could&lt;/em&gt; be used for emergency communications, unless the question is specifically &lt;em&gt;about&lt;/em&gt; that equipment's use in an emergency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also on topic is the use of amateur radio for personal safety to report an emergency, such as wilderness or maritime use. General questions about radios suitable for marine installation or HF radios for portable use are not applicable, only the use of those radios to report an emergency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Questions about rules and regulations or about organizations that amateur radio operators work with in a time of emergency are also welcome. &lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-23T17:32:35.967" LastActivityDate="2013-10-23T17:32:35.967" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="243" PostTypeId="4" CreationDate="2013-10-23T17:02:09.103" Score="0" Body="Questions about amateur radio emergency communication, either in support of emergency services or for use to report an emergency." OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-23T20:57:02.477" LastActivityDate="2013-10-23T20:57:02.477" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="244" PostTypeId="2" ParentId="221" CreationDate="2013-10-23T17:04:56.660" Score="7" Body="&lt;p&gt;If you'd like to do it yourself, you can use this Python program I wrote.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;# -*- coding: utf-8 -*-&#xA;&#xA;import sys&#xA;&#xA;# Convert latitude and longitude to Maidenhead grid locators.&#xA;#&#xA;# Arguments are in signed decimal latitude and longitude. For example,&#xA;# the location of my QTH Palo Alto, CA is: 37.429167, -122.138056 or&#xA;# in degrees, minutes, and seconds: 37° 24' 49&quot; N 122° 6' 26&quot; W&#xA;&#xA;upper = 'ABCDEFGHIJKLMNOPQRSTUVWX'&#xA;lower = 'abcdefghijklmnopqrstuvwx'&#xA;&#xA;def to_grid(dec_lat, dec_lon):&#xA;    if not (-180&amp;lt;=dec_lon&amp;lt;180):&#xA;        sys.stderr.write('longitude must be -180&amp;lt;=lon&amp;lt;180, given %f\n'%dec_lon)&#xA;        sys.exit(32)&#xA;    if not (-90&amp;lt;=dec_lat&amp;lt;90):&#xA;        sys.stderr.write('latitude must be -90&amp;lt;=lat&amp;lt;90, given %f\n'%dec_lat)&#xA;        sys.exit(33) # can't handle north pole, sorry, [A-R]&#xA;&#xA;    adj_lat = dec_lat + 90.0&#xA;    adj_lon = dec_lon + 180.0&#xA;&#xA;    grid_lat_sq = upper[int(adj_lat/10)];&#xA;    grid_lon_sq = upper[int(adj_lon/20)];&#xA;&#xA;    grid_lat_field = str(int(adj_lat%10))&#xA;    grid_lon_field = str(int((adj_lon/2)%10))&#xA;&#xA;    adj_lat_remainder = (adj_lat - int(adj_lat)) * 60&#xA;    adj_lon_remainder = ((adj_lon) - int(adj_lon/2)*2) * 60&#xA;&#xA;    grid_lat_subsq = lower[int(adj_lat_remainder/2.5)]&#xA;    grid_lon_subsq = lower[int(adj_lon_remainder/5)]&#xA;&#xA;    return grid_lon_sq + grid_lat_sq + grid_lon_field + grid_lat_field + grid_lon_subsq + grid_lat_subsq&#xA;&#xA;def usage():&#xA;    print 'This script takes two arguments, decimal latitude and longitude.'&#xA;    print 'Example for Newington, Connecticut (W1AW):'&#xA;    print 'python maidenhead.py 41.714775 -72.727260'&#xA;    print 'returns: FN31pr'&#xA;&#xA;def test():&#xA;    # First four test examples are from &quot;Conversion Between Geodetic and Grid Locator Systems&quot;,&#xA;    # by Edmund T. Tyson N5JTY QST January 1989&#xA;    test_data = (&#xA;        ('Munich', (48.14666,11.60833), 'JN58td'),&#xA;        ('Montevideo', (-34.91,-56.21166), 'GF15vc'),&#xA;        ('Washington, DC', (38.92,-77.065), 'FM18lw'),&#xA;        ('Wellington', (-41.28333,174.745), 'RE78ir'),&#xA;        ('Newington, CT (W1AW)', (41.714775,-72.727260), 'FN31pr'),&#xA;        ('Palo Alto (K6WRU)', (37.413708,-122.1073236), 'CM87wj'),&#xA;    )&#xA;    print 'Running self test\n'&#xA;    passed = True&#xA;    for name,latlon,grid in test_data:&#xA;        print 'Testing %s at %f %f:'%(name,latlon[0],latlon[1])&#xA;        test_grid = to_grid(latlon[0], latlon[1])&#xA;        if test_grid != grid:&#xA;            print 'Failed '+test_grid+' should be '+grid&#xA;            passed = False&#xA;        else:&#xA;            print 'Passed '+test_grid&#xA;    print ''&#xA;    if passed: print 'Passed!'&#xA;    else: print 'Failed!'&#xA;&#xA;def main(argv=None):&#xA;    if argv is None: argv = sys.argv&#xA;    if len(argv) != 3:&#xA;        usage()&#xA;        print ''&#xA;        test()&#xA;    else:&#xA;        print to_grid(float(argv[1]),float(argv[2]))&#xA;&#xA;main()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-10-23T17:04:56.660" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="245" PostTypeId="5" CreationDate="2013-10-23T17:06:22.490" Score="0" Body="&lt;p&gt;This tag is for RF (primarily coaxial) connectors. Questions that would be on topic include questions about what connectors may be appropriate at a certain frequency for a certain power or in certain environments (outdoor, direct burial). Questions can also be about crimping or soldering these connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Questions about non-RF connectors are most appropriate in the relevant tag for their purpose. For example, audio connectors in the audio tag, radio programming connectors in the programming tag.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-23T17:32:08.837" LastActivityDate="2013-10-23T17:32:08.837" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="246" PostTypeId="4" CreationDate="2013-10-23T17:06:22.490" Score="0" Body="Questions about RF connectors, including the properties of specific types and how to use them." OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-23T20:56:56.757" LastActivityDate="2013-10-23T20:56:56.757" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="247" PostTypeId="5" CreationDate="2013-10-23T17:11:04.883" Score="0" Body="&lt;p&gt;Questions on topic in this tag include anything to do with the use of any type of RF feed line, coaxial or otherwise. The selection of cables and connectors; how to route, solder, and splice cables; the use of cables in outdoor and other environments; the use of leaky coaxial cable as an incidental radiator; or the building of a balun or antenna using feed line are all on topic in this tag.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-23T20:55:29.530" LastActivityDate="2013-10-23T20:55:29.530" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="248" PostTypeId="4" CreationDate="2013-10-23T17:11:04.883" Score="0" Body="Questions about RF feed lines. Also tag with coaxial-cable if the feed line in question is a coaxial cable; also tag with connectors if the question is about connectors for an RF feed line." OwnerUserId="87" LastEditorUserId="76" LastEditDate="2013-11-12T01:49:46.120" LastActivityDate="2013-11-12T01:49:46.120" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="249" PostTypeId="2" ParentId="239" CreationDate="2013-10-23T17:13:45.327" Score="3" Body="&lt;p&gt;In addition to what @Amber said, in the US RACES is only activated by order of the President of the United States. When that happens, all other amateur services (including ARES) are shut down. So many ARES organizations encourage their members to also join RACES, so that they can just change hats and continue to operate when RACES is activated.&lt;/p&gt;&#xA;" OwnerUserId="105" LastEditorUserId="105" LastEditDate="2013-10-23T17:29:01.220" LastActivityDate="2013-10-23T17:29:01.220" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="250" PostTypeId="2" ParentId="125" CreationDate="2013-10-23T17:55:01.747" Score="1" Body="&lt;p&gt;Sun spots affect radio propagation by affecting the layer of the atmosphere called the ionosphere. The ionosphere contains electrified layers of ions. The layers are formed by the sun bombarding them with ultraviolet light. The intensity of the sun's bombardment of these layers with ultraviolet radiation varies depending on the hour of the day, the season of the year, and year to year resulting in great variations in the amount  of energy in these layers. Enter sunspots, they also add to ionization. Why do they add to ionization? The same reason as above - because they create ultraviolet radiation, a considerable amount of it. The more sun spots there are the greater the level of ultraviolet radiation emitted by the sun. Greater levels of ultraviolet radiation means more ultraviolet energy pumped into the ionosphere. Higher levels of ionization in the electrified layers encircling the earth increases its ability to bend HF radio waves and return them to the earth at great distances from their source. That's why when the sun surface is covered with a great number of sun spots that communications has a positive effect on propagation in HF bands.&lt;/p&gt;&#xA;" OwnerUserId="83" LastEditorUserId="83" LastEditDate="2013-10-23T18:36:05.637" LastActivityDate="2013-10-23T18:36:05.637" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="251" PostTypeId="2" ParentId="5" CreationDate="2013-10-23T18:07:35.337" Score="6" Body="&lt;p&gt;From the &lt;a href=&quot;http://www.wia.org.au/&quot;&gt;Wireless Institute of Australia&lt;/a&gt;, to get one of the 3 license classes, you have to take an assessment. The assessment covers various amateur radio related topics, each level increasing the difficulty and depth of knowledge required to operate. They are set at the country level, thus there is no difference between states. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To figure out where to take the test, take a look at the &lt;a href=&quot;http://www.wia.org.au/licenses/advanced/assessors/&quot;&gt;WIA's list of assessors&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-23T18:07:35.337" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="252" PostTypeId="5" CreationDate="2013-10-23T18:42:20.313" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-23T18:42:20.313" LastActivityDate="2013-10-23T18:42:20.313" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="253" PostTypeId="4" CreationDate="2013-10-23T18:42:20.313" Score="0" Body="Questions related to the licensing of amateur radio operators and stations. Please also tag your question with the relevant location." OwnerUserId="22" LastEditorUserId="4665" LastEditDate="2020-12-17T16:29:02.333" LastActivityDate="2020-12-17T16:29:02.333" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="254" PostTypeId="2" ParentId="197" CreationDate="2013-10-23T18:54:28.317" Score="1" Body="&lt;p&gt;For the first question:  DBS9 refers to the strength of a received signal. S Units are generally considered to be fairly arbitrary, but the IARU Region 1 recommends a S9 reading be -93 dBm in VHF frequencies higher than 144MHz, which is equivalent to 50 microvolts at 50 Ohms. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia has a pretty good article here: &lt;a href=&quot;http://en.wikipedia.org/wiki/S_meter&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/S_meter&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="52" LastActivityDate="2013-10-23T18:54:28.317" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="255" PostTypeId="2" ParentId="208" CreationDate="2013-10-23T18:54:49.460" Score="4" Body="&lt;p&gt;An angled full-wave delta loop can be hung from the tower at the height you are talking about and is very broadbanded (and can be fed from a corner so that it is vertically polarized. An advantage is that this also makes a very good receive antenna. See for example the October 1984 QST for an article on the subject.&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-10-23T18:54:49.460" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="256" PostTypeId="1" CreationDate="2013-10-23T18:55:55.283" Score="9" ViewCount="6828" Body="&lt;p&gt;I understand that certain antenna designs (particularly phased arrays) require feeding each radiating element with a certain number of degrees of phase separation in order to achieve a desired radiation pattern or beamwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found this &lt;a href=&quot;http://files.bluecrow.net/Amateur%20Radio/Antennas/2m-phased-array-ant.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;2-meter phased array&lt;/a&gt; [pdf] article which goes fairly in-depth into the design and theory but glances over the exact details involved in computing the coax lengths for the phasing harness:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Xh3Z3.png&quot; alt=&quot;phasing harness diagram from article&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna design in the article proposes using a T-connector with a 22&quot; length of coax going to one antenna and a 16&quot; length of coax going to the other antenna to (supposedly) achieve 135-degrees of phase separation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is... is there a general method or formula for computing these phasing line lengths? (Are the values shown in the article even correct?)&lt;/p&gt;&#xA;" OwnerUserId="8" LastEditorUserId="76" LastEditDate="2015-12-15T22:12:36.840" LastActivityDate="2020-10-31T03:39:34.953" Title="Phasing harness for antenna array" Tags="&lt;antenna&gt;&lt;feed-line&gt;&lt;phased-array&gt;&lt;antenna-system&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="257" PostTypeId="1" CreationDate="2013-10-23T19:00:13.340" Score="10" ViewCount="257" Body="&lt;p&gt;I know what things to note when selecting an analog amateur radio, but SDR devices have completely different specs, e.g. sample rate and resolution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What do I need to know about the device to make sure it is suitable for working Amateur Radio communications?&lt;/p&gt;&#xA;" OwnerUserId="101" LastEditorUserId="22" LastEditDate="2013-10-23T23:50:12.317" LastActivityDate="2013-10-24T13:47:15.840" Title="Which qualities/features does an SDR radio device need to be usable for Amateur Radio?" Tags="&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="258" PostTypeId="1" CreationDate="2013-10-23T19:46:13.640" Score="1" ViewCount="59" Body="&lt;p&gt;Yes, Amateur radio is a hobby. The general impression however is that it is a geeky/nerdy/kooky (I forget which carries a negative connotation!) hobby; either the ham sits at a transceiver, or is doing something with an oscilloscope, soldering iron, some meters &amp;amp; books at the other table. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only &lt;em&gt;fun&lt;/em&gt; activity that comes to mind which makes the hobby relatively visible is a fox-hunt. But ... I'm still a beginner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are some &lt;em&gt;fun&lt;/em&gt; activities that help increase the visibility of the hobby?&lt;/p&gt;&#xA;" OwnerUserId="5" LastActivityDate="2013-10-23T20:47:17.667" Title="What are some fun activities hams participate in?" Tags="&lt;fox-hunt&gt;" AnswerCount="2" CommentCount="3" ClosedDate="2013-10-23T20:50:45.003" ContentLicense="CC BY-SA 3.0" />
  <row Id="259" PostTypeId="1" AcceptedAnswerId="260" CreationDate="2013-10-23T20:01:01.013" Score="6" ViewCount="4635" Body="&lt;p&gt;I am very much out of practice with amateur radio (like many others), so to some, this question may seem obvious.  I don't have any specialised amateur radio equipment, but I do have a Sanyo AM/FM broadcast receiver (240V, 50 Hz, model no. MCD XP630).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is it possible, with minor modification if necessary, to listen to amateur radio enthusiasts using this AM/FM radio?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user17" LastEditorUserId="13" LastEditDate="2013-10-23T20:08:42.317" LastActivityDate="2017-02-16T10:08:14.040" Title="Can I listen to hams on a standard AM/FM broadcast receiver?" Tags="&lt;diy&gt;&lt;modification&gt;&lt;receiver&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="260" PostTypeId="2" ParentId="259" CreationDate="2013-10-23T20:07:56.170" Score="5" Body="&lt;p&gt;Using &lt;a href=&quot;http://www.getprice.com.au/Sanyo-MCDXP630-Portable-CD-Player.htm#more-details&quot; rel=&quot;nofollow&quot;&gt;this site&lt;/a&gt;, I determined the operating range is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;FM: 87.5 - 108 MHz, AM: 526.5 - 1606.5 KHz&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The closest ham bands are 144-148 MHz, 1800-2000 kHz. Thus, it cannot receive ham bands without modification. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With modification, essentially you need to open the radio and re-tune it's frequency calibration. There is &lt;a href=&quot;http://www.instructables.com/id/Transistor-Radio-Hack/&quot; rel=&quot;nofollow&quot;&gt;a website&lt;/a&gt; that documents how to do this. It is important that you have a non-digital radio for this to work correctly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, all of this assumes that you are trying to listen to AM or FM signals. You probably could get away with this if you can adjust the FM signal appropriately, although the typical FM broadcast signal is wider band than an FM Amateur Radio signal, but AM signals are rarely used on the HF bands, it's far more common to use SSB, which a typical AM radio cannot receive, without significant modification.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-10-24T10:04:25.303" LastActivityDate="2013-10-24T10:04:25.303" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="261" PostTypeId="1" AcceptedAnswerId="280" CreationDate="2013-10-23T20:11:49.927" Score="11" ViewCount="1486" Body="&lt;p&gt;I've been looking around for a spot that has the official definition of what the various ITU Zones are, but can't find one. What is the official definition? I'm hoping for more than just a map, unless said map is VERY detailed and can be downloaded as a KML or similar map. Something like the &lt;a href=&quot;http://www.cq-amateur-radio.com/cq_awards/cq_waz_awards/cq_waz_list.html&quot; rel=&quot;noreferrer&quot;&gt;CQ Zone definition&lt;/a&gt; would be adequate.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-10-23T20:24:18.957" LastActivityDate="2019-01-01T00:26:55.477" Title="Where can I find the official definition of ITU Zones?" Tags="&lt;location&gt;&lt;itu-zones&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="262" PostTypeId="2" ParentId="258" CreationDate="2013-10-23T20:12:48.370" Score="1" Body="&lt;p&gt;For me, the ability to interact in real time with a person on the other side of the planet and get to know them a bit has been &lt;strong&gt;lots&lt;/strong&gt; of fun.&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-23T20:12:48.370" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="263" PostTypeId="1" AcceptedAnswerId="268" CreationDate="2013-10-23T20:17:19.857" Score="2" ViewCount="123" Body="&lt;p&gt;There is a common DVB-T receiver chip capable of producing raw IQ samples, which makes it a good device for Amateur Radio SDR experimentation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The chips is used in some DVB-T USB dongles sold around 2012-2013. What is the model of that chip and which DVB-T dongles are known to use it?&lt;/p&gt;&#xA;" OwnerUserId="101" LastActivityDate="2013-10-23T20:45:45.660" Title="Model of a specific DVB-T tuner chip (circa 2013) that can be used to collect raw IQ samples" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="264" PostTypeId="2" ParentId="257" CreationDate="2013-10-23T20:19:08.587" Score="3" Body="&lt;p&gt;SDR's typically use a sound card or sound card hardware to convert from quadrature at audio frequency to digital samples. This is due to the availability and low cost of audio-frequency components for computer soundcards. The remaining hardware is usually a direct-conversion receiver. Then the digital sample signal is operated on by DSP hardware, often the CPU of a general-purpose computer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Analog to digital conversion of audio-frequency signals works by sampling the amplitude at a particular moment in time, over and over, and converting the amplitude to a binary number. This number is stored in a certain number of bits, such as 8 bits (values -128 to 127) or 16 bit (values -32768 to 32767). The highest frequency which can be received by a particular soundcard is determined by how frequently the amplitude is sampled. So, a 24 kHz sound card can only represent a frequency up to 12 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the dynamic range of the audio frequencies involved in amateur radio (voice mostly, or narrow bands of frequencies for digital modes) is small, the sample size (resolution) is is not particularly important. 16 bits is more than enough and 8 bits may even work. What is important is how fast the samples are taken, because this determines how much of the received signal can be converted to audio or digital signal. Even though frequencies above about 22khz are outside the range of human hearing, if they are digitized, they can be digitally converted to audible signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this way, an SDR can process a wide swath of bandwidth, and the end user can select which small window of that bandwidth (say 2.5 khz) to listen to at a time. Thus, a 192 kHz sound card can convert 96 kHz either side of the received frequency to digital signals, which can be represented by a waterfall, and the user can select which portion of that digitized signal to convert into audio (or other modes).&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-10-23T20:19:08.587" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="265" PostTypeId="2" ParentId="261" CreationDate="2013-10-23T20:30:03.720" Score="3" Body="&lt;p&gt;I found this reference table on the ITU site:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.itu.int/ITU-R/terrestrial/broadcast/hf/refdata/reftables/ciraf.txt&quot; rel=&quot;nofollow&quot;&gt;http://www.itu.int/ITU-R/terrestrial/broadcast/hf/refdata/reftables/ciraf.txt&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That appears to lay out lat/long coordinates for the points outlining the zones. It's linked to from this page titled &quot;Reference Data&quot;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.itu.int/ITU-R/terrestrial/broadcast/hf/refdata/index.html&quot; rel=&quot;nofollow&quot;&gt;http://www.itu.int/ITU-R/terrestrial/broadcast/hf/refdata/index.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-10-23T21:57:44.943" LastActivityDate="2013-10-23T21:57:44.943" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="267" PostTypeId="1" AcceptedAnswerId="275" CreationDate="2013-10-23T20:40:22.523" Score="6" ViewCount="8731" Body="&lt;p&gt;I know that the front-to-back ratio is 18dB in the below antenna radiation pattern diagram, but I don't know how to read the diagram to obtain this result. How does one read and understand such diagrams?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/8rbqI.png&quot; alt=&quot;Antenna Radiation Pattern Diagram&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="87" LastEditDate="2013-11-11T03:06:24.700" LastActivityDate="2013-11-11T03:06:24.700" Title="How to find the front-to-back ratio given an antenna radiation pattern diagram?" Tags="&lt;antenna&gt;&lt;math&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="268" PostTypeId="2" ParentId="263" CreationDate="2013-10-23T20:45:45.660" Score="5" Body="&lt;p&gt;You're likely referring to the Realtek RTL2832U&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dongle compatibility chart for this chip can be found here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.reddit.com/r/RTLSDR/wiki/compatibility&quot;&gt;http://www.reddit.com/r/RTLSDR/wiki/compatibility&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-23T20:45:45.660" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="269" PostTypeId="2" ParentId="258" CreationDate="2013-10-23T20:47:17.667" Score="1" Body="&lt;p&gt;I take part in four main activities as an activator:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Worked All Britain&lt;/li&gt;&#xA;&lt;li&gt;World Wide Flora &amp;amp; Fauna&lt;/li&gt;&#xA;&lt;li&gt;Castles and Stately Homes on the Air (affiliated to the World Castles Award)&lt;/li&gt;&#xA;&lt;li&gt;Summits on the Air (although this one has become rarer)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For all three activities, I've ended up in parts of the UK that I would probably not have visited, and seen places I wouldn't otherwise have done.  And once I get my Advanced Licence, this will extend to other countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've met some very nice people, and been offered cups of coffee in homes across the country.  I have a list of overseas visits to make.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only real downer is that I have failed (so far) to persuade my partner to get her licence... but my eldest daughter is very interested, so maybe I'll have an activation partner soon enough :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I appreciate that many operators cannot get out and about, and are shack-bound - but for those who can, I commend portable and mobile activity... it brings a very different dimension to the hobby.&lt;/p&gt;&#xA;" OwnerUserId="93" LastActivityDate="2013-10-23T20:47:17.667" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="270" PostTypeId="2" ParentId="256" CreationDate="2013-10-23T21:05:02.147" Score="4" Body="&lt;p&gt;There is, but it depends on the characteristics of the cable and the frequency of interest.  There are online calculators that can do the work for you.  For instance the two lengths of your cable have the following attenuation (almost none for RG-58) and phase delay.  The phase delay is noticeably different, but as I haven't evaluated the antenna design I don't know if it's correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The calculator: &lt;a href=&quot;http://www.mogami.com/e/cad/coax-freq.html&quot; rel=&quot;nofollow&quot;&gt;http://www.mogami.com/e/cad/coax-freq.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Phase delay and attenuation for the 16&quot; section:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.mogami.com/cgi-bin/uncgi.cgi/cad/coax-freq.cgi?Opt1=Linear&amp;amp;Opt2=yes&amp;amp;Start=144&amp;amp;Stop=148&amp;amp;Len=.4064&amp;amp;Rs=0&amp;amp;Cs=0&amp;amp;Rr=0&amp;amp;Cr=0&amp;amp;Name=RG-58%2FU&quot; rel=&quot;nofollow&quot;&gt;http://www.mogami.com/cgi-bin/uncgi.cgi/cad/coax-freq.cgi?Opt1=Linear&amp;amp;Opt2=yes&amp;amp;Start=144&amp;amp;Stop=148&amp;amp;Len=.4064&amp;amp;Rs=0&amp;amp;Cs=0&amp;amp;Rr=0&amp;amp;Cr=0&amp;amp;Name=RG-58%2FU&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Phase delay and attenuation for the 22&quot; section:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.mogami.com/cgi-bin/uncgi.cgi/cad/coax-freq.cgi?Opt1=Linear&amp;amp;Opt2=yes&amp;amp;Start=144&amp;amp;Stop=148&amp;amp;Len=.5588&amp;amp;Rs=0&amp;amp;Cs=0&amp;amp;Rr=0&amp;amp;Cr=0&amp;amp;Name=RG-58%2FU&quot; rel=&quot;nofollow&quot;&gt;http://www.mogami.com/cgi-bin/uncgi.cgi/cad/coax-freq.cgi?Opt1=Linear&amp;amp;Opt2=yes&amp;amp;Start=144&amp;amp;Stop=148&amp;amp;Len=.5588&amp;amp;Rs=0&amp;amp;Cs=0&amp;amp;Rr=0&amp;amp;Cr=0&amp;amp;Name=RG-58%2FU&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a reasonably comprehensive document that covers the calculations necessary for this here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://ve2azx.net/technical/CoaxialCableDelay.pdf&quot; rel=&quot;nofollow&quot;&gt;http://ve2azx.net/technical/CoaxialCableDelay.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This should give you more exact numbers if you need a particular solution.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-23T21:05:02.147" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="271" PostTypeId="5" CreationDate="2013-10-23T21:29:55.587" Score="0" Body="&lt;p&gt;Space weather is a catch all phrase describing short and long time scale variations in solar activity. This included changes in the ionising EUV flux emitted primarily from sun spots that is the primary driver of the strength of the ionosphere. Geomagnetic storms, X-ray flares, coronal hole high speed solar wind streams are other examples of short time scale events that can impact radio communications.&lt;/p&gt;&#xA;" OwnerUserId="92" LastEditorUserId="92" LastEditDate="2013-10-23T23:50:30.100" LastActivityDate="2013-10-23T23:50:30.100" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="272" PostTypeId="4" CreationDate="2013-10-23T21:29:55.587" Score="0" Body="Questions relating to variability in the Sun-Earth system and the impacts on radio communications." OwnerUserId="92" LastEditorUserId="92" LastEditDate="2013-10-23T23:50:27.270" LastActivityDate="2013-10-23T23:50:27.270" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="273" PostTypeId="1" AcceptedAnswerId="274" CreationDate="2013-10-23T21:30:18.853" Score="16" ViewCount="1132" Body="&lt;p&gt;Why is the solar-flux index measured at 10.7 cm? What makes that such a special frequency?&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="92" LastEditDate="2013-10-23T21:37:36.040" LastActivityDate="2020-02-17T09:13:17.307" Title="Why is the solar-flux index measured at 10.7 cm?" Tags="&lt;sunspots&gt;&lt;space-weather&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="274" PostTypeId="2" ParentId="273" CreationDate="2013-10-23T21:36:19.800" Score="10" Body="&lt;p&gt;So as it turns out, the reason behind this is fairly simple: the first receiver that was used to take recordings which wound up being linked with solar flux operated at 2800MHz (and thus a 10.7cm wavelength). In order to allow historical comparison of readings, that wavelength has been preserved ever since.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's &lt;a href=&quot;https://www.spaceweather.gc.ca/solarflux/sx-2-en.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;an article with the full origin story&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="873" LastEditDate="2020-02-17T09:13:17.307" LastActivityDate="2020-02-17T09:13:17.307" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="275" PostTypeId="2" ParentId="267" CreationDate="2013-10-23T21:44:18.350" Score="9" Body="&lt;p&gt;The diagram is a &lt;a href=&quot;http://en.wikipedia.org/wiki/Polar_coordinate_system&quot; rel=&quot;nofollow&quot;&gt;polar plot&lt;/a&gt; where 0 degrees (the 0 on the right-hand edge) corresponds to the front of the antenna and 180 degrees corresponds to the back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Within the diagram, a &lt;a href=&quot;http://en.wikipedia.org/wiki/Logarithmic_scale&quot; rel=&quot;nofollow&quot;&gt;logarithmic scale&lt;/a&gt; is utilized to represent radiation strength. This is in addition to the fact that the &lt;a href=&quot;http://en.wikipedia.org/wiki/Decibel&quot; rel=&quot;nofollow&quot;&gt;Decibel&lt;/a&gt; is a logarithmic unit. (The diagram really should explicitly list its units, but for the application of antenna radition, the unit is typically dB.) You can tell that a logarithmic scale is in use by observing that the distance between the $-6$ and $-12$ lines is the same as that between the $-12$ and $-24$ lines, so it's obviously not a linear scaling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the front-back ratio, we look at the values indicated on the plot for 0 and 180 degrees. In this particular instance, the value at 0 degrees is $0$, and the value at 180 degrees is approximately $-18$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since logarithmic scales transform division into subtraction, we calculate the ratio front to back by subtracting the logarithmic back value from that of the front.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since $0 - (-18) = 18$, the answer is 18dB.&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-10-28T18:29:10.807" LastActivityDate="2013-10-28T18:29:10.807" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="276" PostTypeId="2" ParentId="273" CreationDate="2013-10-23T21:46:38.910" Score="6" Body="&lt;p&gt;The component of the solar flux that actually impacts the ionospheric strength is the Extreme Ultra Violet (EUV) part of the spectrum. This is what causes the ionosation that produces the ionosphere. However, because the EUV is being absorbed by the upper atmosphere, it (fortunately!) doesn't make it to ground (at least the flux is much much lower at ground level). This means ground based receivers can't get a good handle on the actual solar EUV flux. In modern times we have access to satellites that measure the EUV flux outside the atmosphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Historically, there are two main proxy measurements of the EUV flux. The oldest is sunspots. Since the EUV is emitted from sunspot regions, the more sunspots the higher the EUV flux and hence the stronger the ionosphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 10.7cm radio flux was serendipitously found to also correlate with the sunspot number in the years after WWII. The physics behind this is complex, and not fully understood. Empirically though, there is a non-linear relationship between sunspot number and 10.7cm flux that has held for several decades. The 10.7cm flux is a simpler measure than subjectively counting sunspots and can be performed during cloudy weather. Interestingly, during the last 5-10 years, the relationship between sunspot number and 10.7cm solar flux has been changing, most probably due to an overall weakening of the solar coronal magnetic field as the Sun moves into a quieter phase after the space age 'grand maximum' that has been experienced over the last 50 years or so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Going forward, direct EUV measurements from satellites are becoming a more predominant method of measuring solar flux as relevant to the ionosphere although 10.7cm radio noise will still remain an important ground based back-up for many years.  &lt;/p&gt;&#xA;" OwnerUserId="92" LastActivityDate="2013-10-23T21:46:38.910" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="277" PostTypeId="1" CreationDate="2013-10-23T22:01:23.633" Score="2" ViewCount="75" Body="&lt;p&gt;What are some real-world problems that a Smith chart can help me solve? Ultimately I'd like to gain a more intuitive understanding of the space the chart represents, but it seems to me that actual, repeated use -- or reviewing concrete, detailed examples -- are the best way to get there.&lt;/p&gt;&#xA;" OwnerUserId="71" LastActivityDate="2013-10-23T22:01:23.633" Title="When and how do I use a Smith chart?" Tags="&lt;feed-line&gt;&lt;impedance&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2013-10-24T07:14:37.617" ContentLicense="CC BY-SA 3.0" />
  <row Id="278" PostTypeId="1" AcceptedAnswerId="281" CreationDate="2013-10-23T22:31:51.190" Score="3" ViewCount="5402" Body="&lt;p&gt;How do I calculate the peak-to-peak voltage of a sine wave given RMS voltage?&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="13" LastEditDate="2013-10-23T23:36:25.973" LastActivityDate="2013-10-29T23:18:26.350" Title="How to calculate the peak-to-peak voltage of a sine wave given RMS voltage" Tags="&lt;rf-power&gt;&lt;math&gt;&lt;voltage&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="279" PostTypeId="2" ParentId="259" CreationDate="2013-10-23T22:35:15.353" Score="1" Body="&lt;p&gt;No. Even if you modified it to tune amateur radio frequencies, it won't receive the modulation schemes used. Broadcast FM is wideband FM, which is not legal for amateurs on most frequencies. AM is legal for amateurs, but only rarely used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shortwave receivers that support SSB reception usually work for monitoring shortwave (HF) amateur radio transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are inexpensive shortwave SSB receivers. As of early 2017, the Tecsun PL-310ET is $42 on Amazon. Check reviews for the current models.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B0104J57GS&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amazon.com/dp/B0104J57GS&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10" LastEditorUserId="10" LastEditDate="2017-02-13T15:43:59.687" LastActivityDate="2017-02-13T15:43:59.687" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="280" PostTypeId="2" ParentId="261" CreationDate="2013-10-23T23:33:09.927" Score="6" Body="&lt;p&gt;Per &lt;a href=&quot;http://www.itu.hamatlas.eu/Strefy_strony/Introduction.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this document&lt;/a&gt;: Larry E. Price W4RA, the IARU president in 2002, requesting the definitive ITU zone definitions - wrote:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;You have to keep in mind that the ITU has one administrative purpose for having zones that has nothing at all to do&#xA;  with amateur radio.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;However, various amateur radio organizations decided to have both awards and operating events on the air based on the idea of&#xA;  zones.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;But, since this is not why the zones exist as far as ITU is concerned, the sponsors of these amateur events are free to&#xA;  interpret the zone boundaries any way they wish. So, there might not&#xA;  be a single &quot;official amateur radio zone list.&quot;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;For the US &amp;amp; Canada, the interpretation by ARRL is found in The ARRL Operating Manual, desk top reference, page 12 which&#xA;  defines the boundaries between US States and Canadian provinces.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;If you have more questions about any particular contest or award, they should be directed to the sponsor.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So the US official ITU zones are defined by ARRL. Amber has a list of some specified points that define certain zones, plus a rough map. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most official worldwide map is this one, although it is not necessarily the source for data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/0zINd.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.itu.hamatlas.eu/ITU%20Rules_en.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;HamAtlas&lt;/a&gt; has done a very good job of taking the ITU map, and other &quot;Official&quot; definitions, and creating a usable set. This is probably the best definition that exists.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-10-24T12:07:05.650" LastActivityDate="2013-10-24T12:07:05.650" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="281" PostTypeId="2" ParentId="278" CreationDate="2013-10-23T23:49:37.700" Score="7" Body="&lt;h3&gt;The short answer:&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\frac{V_{p-p}}{V_{rms}} = 2\sqrt{2}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;The long answer, or how to derive the above:&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;As noted on the Wikipedia page for &lt;a href=&quot;http://en.wikipedia.org/wiki/Root_mean_square&quot; rel=&quot;nofollow&quot;&gt;root mean square&lt;/a&gt;, the RMS of a sine wave is equal to its amplitude divided by the square root of two. (You can also derive this by doing the integral over a sine wave yourself.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;V_{rms} = \frac{a}{\sqrt{2}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The peak-to-peak voltage is twice the amplitude of the wave, since it's measuring from the tip of a peak to the tip of a trough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;V_{p-p} = 2a&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can rearrange these two equations:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;V_{rms} \cdot \sqrt{2} = a&#xA;\end{equation}&#xA;\begin{equation}&#xA;V_{p-p} = 2 \cdot (V_{rms} \cdot \sqrt{2})&#xA;\end{equation}&#xA;\begin{equation}&#xA;V_{p-p} = V_{rms} \cdot 2\sqrt{2}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, we multiply the RMS voltage by twice the square root of two - a factor of about 2.828 or so:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;2\sqrt{2} = 2.8284271247....&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, the process also works in reverse - if you can measure the peak-to-peak voltage, dividing that by the same factor will give you the RMS voltage assuming a perfect sine wave.&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="76" LastEditDate="2013-10-28T20:30:40.760" LastActivityDate="2013-10-28T20:30:40.760" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="282" PostTypeId="2" ParentId="137" CreationDate="2013-10-24T01:24:31.907" Score="11" Body="&lt;h2&gt;Line A&lt;/h2&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w5yi.org/page.php?id=202&quot; rel=&quot;noreferrer&quot;&gt;Part 97.303&lt;/a&gt; section &lt;code&gt;m&lt;/code&gt; states:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(1) No amateur station shall transmit from north of Line A in the 420–430 MHz segment. See §97.3(a) for the definition of Line A.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The definition of Line A in part 97.3(a) is:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(29) Line A. Begins at Aberdeen, WA, running by great circle arc to the intersection of 48 deg. N, 120 deg. W, thence along parallel 48 deg. N, to the intersection of 95 deg. W, thence by great circle arc through the southernmost point of Duluth, MN, thence by great circle arc to 45 deg. N, 85 deg. W, thence southward along meridian 85 deg. W, to its intersection with parallel 41 deg. N, thence along parallel 41 deg. N, to its intersection with meridian 82 deg. W, thence by great circle arc through the southernmost point of Bangor, ME, thence by great circle arc through the southernmost point of Searsport, ME, at which point it terminates.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This is a little hard to visualize so the FCC created this map(flash required):&lt;br /&gt;&#xA;&lt;a href=&quot;https://www.fcc.gov/reports-research/maps/frequency-coordination-canada/&quot; rel=&quot;noreferrer&quot;&gt;https://www.fcc.gov/reports-research/maps/frequency-coordination-canada/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Lines A and C refer to the geographic lines in the Lower 48 and Alaska which delimit with the national boarder area impacted by the Frequency Coordination. The Canadian sides of those areas are indicated by Lines B and D, B is opposite A, and D is opposite C.&lt;/p&gt;&#xA;&lt;p&gt;You can also check if you live north of line A on the FCC's &lt;a href=&quot;http://wireless.fcc.gov/uls/index.htm?job=line_a_c&quot; rel=&quot;noreferrer&quot;&gt;line A &amp;amp; C check&lt;/a&gt; page.&lt;/p&gt;&#xA;&lt;h2&gt;Other&lt;/h2&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w5yi.org/page.php?id=202&quot; rel=&quot;noreferrer&quot;&gt;Part 97.303&lt;/a&gt; section &lt;code&gt;n&lt;/code&gt; states:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(n) In the 33 cm band:&lt;/p&gt;&#xA;&lt;p&gt;...&lt;/p&gt;&#xA;&lt;p&gt;(2) No amateur station shall transmit from those portions of Texas and New Mexico that are bounded by latitudes 31°41' and 34°30' North and longitudes 104°11' and 107°30' West; or from outside of the United States and its Region 2 insular areas.&lt;/p&gt;&#xA;&lt;p&gt;(3) No amateur station shall transmit from those portions of Colorado and Wyoming that are bounded by latitudes 39° and 42° North and longitudes 103° and 108° West in the following segments: 902.4–902.6 MHz, 904.3–904.7 MHz, 925.3–925.7 MHz, and 927.3–927.7 MHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Which is roughly equivalent to these areas:&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/7zSk0.png&quot; alt=&quot;Map highlighting South-Central New Mexico and part of Texas&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/HQYaD.jpg&quot; alt=&quot;Map highlighting North-Central Colorado and South-Eastern Wyoming&quot; /&gt;&lt;/p&gt;&#xA;" OwnerUserId="63" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-01-30T21:01:54.740" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="283" PostTypeId="1" AcceptedAnswerId="292" CreationDate="2013-10-24T01:47:54.533" Score="12" ViewCount="25867" Body="&lt;p&gt;I have seen the following formulas for calculating half and quarter wavelength antennas:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formula for $\frac{1}{2}$-wavelength antenna (in free space):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\mathrm{Length~(feet)} = \frac{492}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Or is it...&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\mathrm{Length~(feet)} = \frac{468}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Formula for $\frac{1}{4}$-wavelength antenna (in free space):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\mathrm{Length~(feet)} = \frac{246}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Or is it...&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\mathrm{Length~(feet)} = \frac{234}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or is it none of the above? I believe the US FCC Technician class exam requires the use of 468/f. Are any of these equations helpful in calculating antenna length in reality, or is this only in theory for the exam?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What additional factors should be taken into account, if any? What would be a better equation if none of the above?&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="76" LastEditDate="2015-12-15T22:06:27.077" LastActivityDate="2019-09-04T00:56:24.357" Title="Calculating Antenna Length on the FCC Exam vs. in Reality" Tags="&lt;antenna&gt;&lt;united-states&gt;&lt;antenna-theory&gt;&lt;math&gt;&lt;physics&gt;" AnswerCount="6" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="284" PostTypeId="5" CreationDate="2013-10-24T01:53:41.940" Score="0" Body="&lt;p&gt;Radio in the UK is regulated by &lt;a href=&quot;https://www.ofcom.org.uk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ofcom&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://rsgb.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio Society of Great Britain (RSGB)&lt;/a&gt; is an amateur radio organization that provides training, books, events, etc.&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="76" LastEditDate="2017-10-04T18:53:41.383" LastActivityDate="2017-10-04T18:53:41.383" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="285" PostTypeId="4" CreationDate="2013-10-24T01:53:41.940" Score="0" Body="Questions specific to rules, regulations, and practices in the United Kingdom." OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-10-24T09:10:42.893" LastActivityDate="2013-10-24T09:10:42.893" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="286" PostTypeId="5" CreationDate="2013-10-24T01:54:34.383" Score="0" Body="&lt;p&gt;Amateur radio is a highly legislated hobby, and not all of those regulations are always crystal-clear. This tag should be used for questions that are related to the legalities of amateur radio, whether for your home country, other countries or internationally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Make sure to indicate within the question the location to which you want any answers to apply (using an appropriate location tag, or in the body of the question if a tag is not available). Questions about legal matters that do not specify a relevant locale are likely to be closed as not answerable without that information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur Radio Stack Exchange is not a forum for legal counsel. &lt;strong&gt;If in doubt, always seek professional legal advice.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="-1" LastEditorUserId="76" LastEditDate="2018-11-08T14:02:50.007" LastActivityDate="2018-11-08T14:02:50.007" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="287" PostTypeId="4" CreationDate="2013-10-24T01:54:34.383" Score="0" Body="Questions regarding laws or other legal regulations pertaining directly to amateur radio. Also tag your question with the relevant location. If in doubt, always seek professional legal advice." OwnerUserId="22" LastEditorUserId="76" LastEditDate="2018-11-08T14:02:50.007" LastActivityDate="2018-11-08T14:02:50.007" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="288" PostTypeId="5" CreationDate="2013-10-24T01:56:03.593" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-24T01:56:03.593" LastActivityDate="2013-10-24T01:56:03.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="289" PostTypeId="4" CreationDate="2013-10-24T01:56:03.593" Score="0" Body="Radio devices that use digital signal processing in place of analog electronic components to manipulate RF signals." OwnerUserId="22" LastEditorUserId="76" LastEditDate="2014-03-24T12:28:08.847" LastActivityDate="2014-03-24T12:28:08.847" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="290" PostTypeId="2" ParentId="283" CreationDate="2013-10-24T01:57:58.610" Score="5" Body="&lt;p&gt;For someone who knows how to convert between inches, feet, and meters, it's really quite simple. You only really need to know one formula to do it all, and that formula is $300=f\times wavelength$. If you find the wavelength for the given frequency, then just find the type of antenna (quarter-wave), take the appropriate fraction of the wavelength, and convert said quantity to the appropriate units. For example, the wavelength for a 146 MHz signal is 2.05 m, multiply by 39 and you have 80 inches. If you want a quarter wave whip, then your antenna is 20 inches long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to where this applies after the test, it does apply, but there is one huge catch. The antenna needs to have the provided wavelengths electrically, not physically. What does that mean? Basically, there's a quantity known as &lt;a href=&quot;http://en.wikipedia.org/wiki/Velocity_factor&quot; rel=&quot;nofollow&quot;&gt;Velocity Factor&lt;/a&gt; which takes into account how fast the waves move in the metal. However, most metals have a permittivity of about 1, making the electric distance equal to the physical distance. Some non-metal antenna materials could be different, however, so be warned. Also, cable is different, etc. Essentially, if the velocity factor of an antenna is 2, then an antenna could be made with half of the length and still be resonant. However, as the velocity factor for most metals is 1, and there are other reasons to use metal as antenna building material, this isn't usually a significant factor. It does make a small difference in certain types of phased antennas, however.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to your specific question, the half-wave formula is $(3.28/2)(300/f)$, or $492/f$, and the quarter wave is similarly $(3.28/4)(300/f)$ or $246/f$. This applies if the velocity factor is 1, which only holds true if the antenna is far away from conductive surfaces, including the ground. The distance required is at least 1 wavelength away typically.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="128" LastEditDate="2013-10-28T19:26:19.613" LastActivityDate="2013-10-28T19:26:19.613" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="291" PostTypeId="2" ParentId="225" CreationDate="2013-10-24T02:50:00.480" Score="5" Body="&lt;p&gt;For the 2013 Field Day rules, this is answered in the FAQ in the &lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2013/2013-FD-Packet-V3.pdf&quot; rel=&quot;nofollow&quot;&gt;information packet&lt;/a&gt;. Emphasis is in the original document.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Q. What is considered a generally inactive licensee? &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A. The GOTA station is not for everyone. The generally inactive licensee provisions pertain to someone who holds an amateur that &#xA;  has been inactive for a significant period of time. The intent and the spirit of this station is to provide an opportunity for persons to &#xA;  gain on-the-air experience and progress to operating the regular club stations in the future. The intent is not to develop a group of &#xA;  “permanent GOTA Field Day operators”. This is also not a station that a club “ringer” operates in order to rack up points. &lt;strong&gt;&lt;em&gt;The list &#xA;  of operators of this station must be submitted with the Field Day entry.&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;In order to claim the GOTA bonus, the club/group must provide a list of operators and the number of QSOs each operator makes at &#xA;  the GOTA station. &lt;strong&gt;&lt;em&gt;Clubs should use their best judgment in determining the operators of the GOTA station.&lt;/em&gt;&lt;/strong&gt; &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="10" LastEditorUserId="10" LastEditDate="2013-10-29T21:33:52.890" LastActivityDate="2013-10-29T21:33:52.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="292" PostTypeId="2" ParentId="283" CreationDate="2013-10-24T03:48:58.303" Score="18" Body="&lt;p&gt;The $492/f$ formula is for an ideal antenna in free space, the $468/f$ is an estimate for real antennas at a reasonable height over ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The $492/f$ formula is a conversion from metric units to English units for the fundamental frequency and wavelength ($\lambda$) formula. $c = 3\times 10^8_{m/s}$ (the velocity of light) and $f =$ frequency -- &lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda = \frac{c}{f}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This gives the length of a full wavelength in meters. This formula is correct if the conductor is infinitely thin and other objects are infinitely far away from the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The length of a real, installed antenna is affected by the diameter of the conductor (not a big effect for wire antennas) and the height above ground (a big effect). Capacitance to ground electrically shortens the antenna, so less wire is needed for resonance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$468/f$ is a good estimate for wire antennas at HF less than a wavelength above ground. This is an empirical formula, so there is no mathematical derivation. The $468/f$ formula was first published in the 1929 &lt;em&gt;ARRL Handbook&lt;/em&gt;. It is probably based on experience with 40m and 80m antennas at heights of 1/4 to 1/8 wavelength above ground, since those were common antennas at the time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A November 2009 &lt;em&gt;QST&lt;/em&gt; article by Ward Silver, N0AX, measured a 20m dipole at heights from 1/8 to 2 wavelengths and found the length varied from $466/f$ to $481/f$ depending on height. He recommends starting with a wire length of $490/f$ and expecting to shorten the antenna to resonance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most wire antennas need length adjustment for resonance after installation, because of the capacitance to nearby structures or trees, or local ground conductivity. It is much easier to shorten an antenna than to lengthen it, so it is a good idea to cut the antenna wire a little long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more on this publication history of this formula, see &lt;a href=&quot;http://www.eham.net/articles/23802&quot;&gt;this article by N0AX&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more information about wire antennas, I would start with Chapter 21 of the &lt;em&gt;ARRL Handbook&lt;/em&gt;. For details, read the &lt;em&gt;ARRL Antenna Book&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="10" LastEditorUserId="10" LastEditDate="2013-10-31T03:44:51.217" LastActivityDate="2013-10-31T03:44:51.217" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="293" PostTypeId="2" ParentId="2" CreationDate="2013-10-24T05:21:40.050" Score="-1" Body="&lt;p&gt;Over the last 24 hours, 5 Hawaiian stations were spotted by stations on the US East Coast:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;KH6OO on 30m at 0515Z&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NH6I on 10m from 2135Z to 2142Z&lt;/p&gt;&#xA;&#xA;&lt;p&gt;KH6QR on 10m from 2134 to 2250 Z&lt;/p&gt;&#xA;&#xA;&lt;p&gt;KH6L on 10m at 2225Z&lt;/p&gt;&#xA;&#xA;&lt;p&gt;KH6SAT on 12m at 2309Z&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-24T05:21:40.050" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="294" PostTypeId="1" AcceptedAnswerId="311" CreationDate="2013-10-24T05:52:42.157" Score="3" ViewCount="192" Body="&lt;p&gt;A dedicated/custom power-supply for an HF rig may, on occasion, be unavailable.&#xA;The internet lists any number of articles on the subject of modifying a computer power-supply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;E.g.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply&quot; rel=&quot;nofollow&quot;&gt;http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe/&quot; rel=&quot;nofollow&quot;&gt;http://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Apparently using a computer SMPS to power a transceiver bleeds hum into the signal. Is there any truth to this? Does using a computer SMPS to supply a transceiver bleed hum into the signal?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-10-24T06:13:12.930" LastActivityDate="2013-10-24T14:38:55.653" Title="Does using a computer SMPS to supply a transceiver bleed hum into the signal?" Tags="&lt;power-supply&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="295" PostTypeId="5" CreationDate="2013-10-24T06:16:08.567" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-24T06:16:08.567" LastActivityDate="2013-10-24T06:16:08.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="296" PostTypeId="4" CreationDate="2013-10-24T06:16:08.567" Score="0" Body="Questions regarding devices for supplying power to electronics." OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-10-24T09:09:27.293" LastActivityDate="2013-10-24T09:09:27.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="297" PostTypeId="1" CreationDate="2013-10-24T07:15:43.623" Score="4" ViewCount="380" Body="&lt;p&gt;In my vehicle, I have a Byonics TinyTrac4 paired with an AvMap G6. I also have a Kenwood TM-D710 that I'm currently using for voice. I live in a region of the US where both 2m APRS and 70cm High Speed APRS are in common use, and am interested in using BOTH radios, one on each band, to feed the G6.  I MIGHT be able to get away with an off-the-shelf NMEA0183 multiplexer, assuming they don't drop sentences they don't recognize, and they are a bit out of my budget. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, I would like to use a Raspberry Pi, paired with some good NMEA multiplexing software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, I do a lot of off-roading, and I like the idea of being able to digipeat across the bands as well, ensuring that 1) I'm heard in an emergency, regardless of what they are running, and 2) everyone else can see each other as well.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is where things get a bit fuzzy:&lt;br&gt;&#xA;To implement this functionality, I need to act as a digipeater, and I THINK that in turn requires the TNCs to be in KISS mode.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fine, I can put the TNC in kiss mode, use APRSDigi (Or something similar) to run as a digipeater... But how to generate an NMEA Kenwood Sentence stream from there?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I understand my problem correctly, I am looking for an APRS digipeater that generates an NMEA output... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or I'm looking for an AX.25 to NMEA converter of some kind.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or... Maybe I'm missing an obviously easy solution... &lt;/p&gt;&#xA;" OwnerUserId="126" LastActivityDate="2016-06-17T02:02:23.963" Title="AX.25 to Kenwood $PKWDWPL sentence" Tags="&lt;digital-modes&gt;&lt;aprs&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="298" PostTypeId="1" AcceptedAnswerId="328" CreationDate="2013-10-24T12:13:36.577" Score="11" ViewCount="771" Body="&lt;p&gt;FCC 97.113 &lt;em&gt;Prohibited transmissions&lt;/em&gt; reads:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(e) No station shall retransmit programs or signals emanating from any type of radio station other&#xA;  than an amateur station, except propagation and weather forecast&#xA;  information intended for use by the general public and originated from&#xA;  United States Government stations, and communications, including&#xA;  incidental music, originating on United States Government frequencies&#xA;  between a manned spacecraft and its associated Earth stations. Prior&#xA;  approval for manned spacecraft communications retransmissions must be&#xA;  obtained from the National Aeronautics and Space Administration. Such&#xA;  retransmissions must be for the exclusive use of amateur radio&#xA;  operators. Propagation, weather forecasts, and manned spacecraft&#xA;  communications retransmissions may not be conducted on a regular&#xA;  basis, but only occasionally, as an incident of normal amateur radio&#xA;  communications.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It is also a test question on the Technician license, that the only time that music can be transmitted using an amateur radio license is incidental music transmitted as a part of an authorized rebroadcast of a manned spacecraft and an Earth Station on a US Government frequency, when NASA has given permission for such. I have a few questions about this:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Why does this exception even exist?&lt;/li&gt;&#xA;&lt;li&gt;Has this been used for significant events, such as the Apollo Moon Landing? Or ever, to anyone's knowledge?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-10-24T12:21:12.040" LastActivityDate="2013-10-24T20:42:30.923" Title="Why is an exemption for music given to NASA broadcasts of manned space flight missions?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;music&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="299" PostTypeId="1" AcceptedAnswerId="324" CreationDate="2013-10-24T13:27:53.007" Score="10" ViewCount="1060" Body="&lt;p&gt;A friend who recently received his call is planning to setup an inverted-vee for 40/20m bands. Our take is the signal will take the path of least impedance into the correct length antenna wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something like the image attached; it depicts two wires running right next to each other. The tab in the middle of the wire marks the end of the 20M, the other tab marks the end of the 40M length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/uCiiu.jpg&quot; alt=&quot;Inverted-Vee for 40/20&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Can the antenna wires for both bands be fed at a common point by the coax?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2015-12-15T22:03:20.083" LastActivityDate="2015-12-15T22:03:20.083" Title="Can I have multiple inverted-vee antenna fed by a single coax?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;inverted-vee&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="300" PostTypeId="1" AcceptedAnswerId="320" CreationDate="2013-10-24T13:32:24.440" Score="6" ViewCount="9664" Body="&lt;p&gt;I want to install a 30W mobile UHF radio in my car. I already have an antenna and mounting bracket - but how do I get power to this radio? It has an SAE bullet connector on the back - do I just need a cigarette lighter adapter, or do I have to wire it in somewhere else? Do I need a fuse?&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2021-01-26T02:11:41.917" Title="How do I power my radio in a vehicle mobile install?" Tags="&lt;rf-power&gt;&lt;mobile&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="301" PostTypeId="1" AcceptedAnswerId="305" CreationDate="2013-10-24T13:32:44.260" Score="9" ViewCount="1905" Body="&lt;p&gt;I'm a very absentminded ham. I have a radio mounted in my car, wired directly to the vehicle battery. Fuses and high-gauge wire and all that good stuff. But, if I accidentally leave it on, my battery will be dead by the next morning! I don't know anything about ignition sense wires or anything like that. What's an easy way to prevent draining down my battery?&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-26T11:20:49.343" Title="How can I prevent my mobile radio from draining my vehicle's battery?" Tags="&lt;rf-power&gt;&lt;battery&gt;&lt;mobile&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="302" PostTypeId="1" AcceptedAnswerId="306" CreationDate="2013-10-24T13:34:10.653" Score="14" ViewCount="8504" Body="&lt;p&gt;Amateur radio operators are always referred to as Hams, it's basically the most common term for the hobby, at least around here. Where does the term come from? I heard that it's an acronym for something, is that true?&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2019-05-24T17:21:48.580" Title="What does Ham mean?" Tags="&lt;jargon&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="303" PostTypeId="1" AcceptedAnswerId="314" CreationDate="2013-10-24T13:47:03.073" Score="11" ViewCount="1364" Body="&lt;p&gt;I saw &lt;a href=&quot;https://ham.stackexchange.com/questions/72/encrypted-traffic-and-amateur-radio&quot;&gt;this question&lt;/a&gt; stating that it is illegal to encrypt traffic, at least in the US and UK. I also heard that there was recently an attempt to get the FCC to loosen this restriction, but a lot of hams argued against it. Why do Amateur Radio organizations in the United States oppose the relaxation of encryption prohibitions?&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-11-06T04:22:22.537" Title="Why do Amateur Radio organizations in the United States oppose the relaxation of encryption prohibitions?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;encryption&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="304" PostTypeId="2" ParentId="257" CreationDate="2013-10-24T13:47:15.840" Score="6" Body="&lt;p&gt;What you are really looking for in a SDR depends on your needs. Here are some factors to consider:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;ADC/DAC resolution: this is measured in bits. It pretty much represents how finely the analogue to digital converter or digital to analogue converter can represent changes in the waveform. Usually higher is better (12-16 bits), but you can get away with lower with some DSP techniques.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sampling rate: this is usually measured in MSPS (mega samples per second) or KSPS (kilo samples per second). It is a measurement of how much data the SDR can convert from analogue to digital or digital every second. Again,higher is usually better,as it will be more versatile,and versatility is one of the most important aspects of a SDR (in my opinion).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning range: this is usually reported as a range of frequencies. Pretty much self explanatory,it is how much of the of spectrum the SDR can tune to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Duplex: this is usually reported as one of the following: half-duplex, full-duplex, and 2x2. A half duplex SDR can only either transmit or receive at the same time. A full duplex SDR on the other hand, can do both at the same time,transmitting and receiving. A 2x2 (or higher) SDR will be able to transmit on two different frequencies AND receive on two different frequencies at the same time. A 3x3 can do it on three,and so on. There is no &quot;best&quot; option here per say, but it really depends on your needs. If you don't need to transmit and recieve at the same time, a half duplex is enough. However,if you do need to transmit and receive at the same time,such as a GSM base station, or something similar, you are going to need a full-duplex SDR. It really depends on your needs and your budget. A 2x2 is very versatile, but may be over budget and overkill in some situations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Link type: usually reported as a name. The link type varies from SDR to SDR. The most common right now is Ethernet and USB. The advantage of Ethernet is that you can place the SDR in a farther away location, away from any emi generated by your computer. You are unable to do that with USB, as the spec does not allow you to stretch it for a long distance. However, I find USB easier to work with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Price: usually reported as a multiple of a unit of currency. The price shouldn't be the main deciding factor when choosing a SDR. You should look at your current needs first, while also considering any future needs. Then, you should consider price. It is much better to spend a little more right now on a beefier SDR than to have to buy a new one down the road because it doesn't have the specs you need for a particular project.&lt;/p&gt;&#xA;" OwnerUserId="170" LastActivityDate="2013-10-24T13:47:15.840" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="305" PostTypeId="2" ParentId="301" CreationDate="2013-10-24T14:09:54.807" Score="6" Body="&lt;p&gt;If you search for &quot;&lt;a href=&quot;https://www.google.com/search?q=automatic%20power%20off%20car%20ham&quot;&gt;automatic power off car ham&lt;/a&gt;&quot; you'll find a number of solutions which don't require additional wiring.  When the engine is running the voltage supply is higher than when the engine is off, so these work by sensing when the voltage is high enough, and turning the radio on.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-24T14:09:54.807" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="306" PostTypeId="2" ParentId="302" CreationDate="2013-10-24T14:15:15.257" Score="18" Body="&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Etymology_of_ham_radio#Home_Amateur_Mechanic_magazine&quot;&gt;Etymology of Ham Radio&lt;/a&gt; Wikipedia article states that the term was originally used in a derogatory way by professional radiotelegraph operators about amateurs similar to the way an incompetent actor would be called a ham. The term was embraced by amateur radio operators and turned into a term to describe themselves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found some other interesting explanations which the Wikipedia article calls false etymologies:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Home Amateur Mechanic magazine as a popular magazine about amateur radio, but there is no evidence that the magazine ever existed.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Hertz-Armstrong-Marconi as the last names of several radio pioneers, but this is again debunked as Armstrong was unknown at the time the term first appeared.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Hammarlund was a company that made amateur radio equipment and their products became such a part of the early pioneering days of amateur radio that they were referred to as &quot;ham products&quot; and people who used them were &quot;ham operators&quot;. In reality, the company was a minor and mostly unknown company at the time the term came into use.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;These came from &lt;a href=&quot;http://www.qsl.net/n7jy/ham_name.html&quot;&gt;an article&lt;/a&gt; by n7jy:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Ham was originally a derogatory term short for &quot;ham fisted&quot; meaning the operator couldn't send CW very well. The term &quot;lid&quot; is more common today, I think.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Three members of the Harvard Radio Club (Alber S. Hyman, Bob Almy and Poogie Murray) called their station by their names (HYMAN-ALMY-MURRAY), but it was too long to send with CW so they eventually shortened it to HAM. When the Wireless Regulation bill, which impose regulations on amateur stations such as call signs, frequency allocations, and licensing fees, it was Hyman that testified in front of the committee considering the bill and their little HAM station became the symbol for all amateur stations at the time. (Another source: &lt;a href=&quot;http://www.rfcafe.com/references/electrical/origin-of-ham.htm&quot;&gt;Origin of the Name &quot;HAM&quot; for Amateur Radio Operators&lt;/a&gt;)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A newspaper article written in 1949 about a gathering of radio operators looking to form a club refers to them as hams with the explanation that they were so called because of &quot;the English attempt to pronounce the word amateur&quot;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="156" LastEditorUserId="229" LastEditDate="2013-10-30T00:58:22.090" LastActivityDate="2013-10-30T00:58:22.090" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="307" PostTypeId="2" ParentId="302" CreationDate="2013-10-24T14:15:17.753" Score="9" Body="&lt;p&gt;Originally, the term &quot;ham&quot; was used to describe an operator with poor skills. However, it gained usage pretty early on not only in a neutral but even positive way. The usage of the term seems to have solidified in the second half of the 1910s, as a neutral-to-positive word to describe an amateur (as in unpaid) operator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia lists several false etymologies, including &lt;a href=&quot;https://en.wikipedia.org/wiki/Etymology_of_ham_radio#Hertz-Armstrong-Marconi&quot;&gt;Hertz-Armstrong-Marconi&lt;/a&gt;, &lt;a href=&quot;https://en.wikipedia.org/wiki/Etymology_of_ham_radio#.22A_little_station_called_HAM.22&quot;&gt;&quot;A little station called HAM&quot;&lt;/a&gt; and &lt;a href=&quot;https://en.wikipedia.org/wiki/Etymology_of_ham_radio#Hammarlund_legend&quot;&gt;Hammarlund legend&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quoting from the Wikipedia article on &lt;a href=&quot;https://en.wikipedia.org/wiki/Etymology_of_ham_radio&quot;&gt;Etymology of ham radio&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The term &quot;ham operator&quot; was commonly applied by 19th century landline telegraphers to an operator with poor skills.[2][3][4] (&quot;Ham&quot; was also in more general use as a slang word meaning &quot;incompetent&quot;, as in the phrases &quot;ham handed&quot; and &quot;ham actor&quot;.)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;as well as&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;But only a few months [after December 1916], in an indication of the changing use of the term among amateurs, a QST writer uses it in a clearly complimentary manner, saying that a particular 16 year old amateur operator &quot;...is the equal of a ham gaining five years of experience by hard luck.&quot;[7]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Today, the term &quot;ham&quot; is used in many English-speaking countries and even some non-English speaking countries to refer to amateur radio licensees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The relevant Wikipedia sources are given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[2] Brady, Jasper Ewing (1899). &lt;a href=&quot;https://play.google.com/store/books/details?id=6BgZAAAAYAAJ&amp;amp;hl=en&quot;&gt;Tales of the telegraph&lt;/a&gt;. Doubleday &amp;amp; McClure Co. Retrieved February 1, 2013.&lt;br&gt;&#xA;[3] &lt;a href=&quot;http://www.arrl.org/ham-radio-history&quot;&gt;ARRL: Ham Radio History&lt;/a&gt; (undated retrieval)&lt;br&gt;&#xA;[4] &lt;a href=&quot;http://earlyradiohistory.us/1902slng.htm&quot;&gt;Early Radio History&lt;/a&gt; (undated retrieval)&lt;br&gt;&#xA;[7] &quot;Who's Who in Amateur Wireless&quot;, QST, March 1917, p30.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-10-24T14:15:17.753" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="308" PostTypeId="2" ParentId="300" CreationDate="2013-10-24T14:20:56.120" Score="2" Body="&lt;p&gt;A 30W UHF radio should consume less than 10A, which is the limit of most cigarette lighter outlets.  You can try it out, and if it blows the fuse, replace the fuse and choose a different option for powering it.  Since the outlet is fused, you don't need to add an additional fuse inline with the radio power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beyond that, I suggest you check your user manual and the manufacturer's suggestions for installation.  It'll vary based on the vehicle and whether you want it to work with the engine off or not.  You may be able to find an automotive radio/alarm installer that could perform the install for you as well, if not talk to your mechanic.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-24T14:20:56.120" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="309" PostTypeId="1" CreationDate="2013-10-24T14:24:37.593" Score="1" ViewCount="210" Body="&lt;p&gt;I'm new to radio and would like to know what amateur radio bands are. I'm also wondering about the range of these bands/how many there are.&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="76" LastEditDate="2014-10-23T17:56:09.547" LastActivityDate="2014-10-23T17:56:09.547" Title="What are amateur radio bands?" Tags="&lt;jargon&gt;&lt;range&gt;" AnswerCount="2" CommentCount="0" ClosedDate="2013-10-24T16:50:57.413" ContentLicense="CC BY-SA 3.0" />
  <row Id="310" PostTypeId="2" ParentId="309" CreationDate="2013-10-24T14:24:37.593" Score="3" Body="&lt;p&gt;Take out an old AM radio and look at the dial. You'll see frequencies marked from 535 to 1605 kilohertz. This is one radio &quot;band.&quot; There are many bands of radio spectrum, allocated for amateur, government, military and commercial radio uses. If you could hear the many different bands, you would find aircraft, ship, fire and police communication. You would also hear &quot;shortwave&quot; stations, which are worldwide commercial and government broadcast stations from the U.S. and abroad. Amateur radio operators (&quot;hams&quot;) are allocated 26 bands (groups of frequencies) spaced from 1.8 Megahertz, just above the broadcast radio frequencies, to 275 Gigahertz. Depending on which band is in use, we can talk across town, around the world or out to satellites in space. Hams can even bounce signals off the moon! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a picture from &lt;a href=&quot;http://www.arrl.org/graphical-frequency-allocations&quot; rel=&quot;nofollow noreferrer&quot;&gt;AARL&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/iC2ce.jpg&quot; alt=&quot;United States Amateur Radio Bands&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="106" LastEditorUserId="106" LastEditDate="2013-10-24T14:47:45.420" LastActivityDate="2013-10-24T14:47:45.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="311" PostTypeId="2" ParentId="294" CreationDate="2013-10-24T14:38:55.653" Score="2" Body="&lt;p&gt;The power supply usually recommended is an ATX computer power supply, which has minimum &lt;a href=&quot;https://www.google.com/search?q=atx%20specifications%20ripple%20regulation&quot; rel=&quot;nofollow&quot;&gt;specifications for ripple and regulation&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The minimum standard indicates that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The 12V supply must be within +/- 5% (11.40V to 12.60V)&lt;/li&gt;&#xA;&lt;li&gt;The ripple in the 10Hz to 20MHz band must be less than 120mV&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This is fine for computing requirements, but terrible for radio and analog use. Note that the specification doesn't care about ripple above 20MHz, and at that point you've only got the basic bare minimum protections the FCC requires Part B computing equipment to follow.  This can account for a significant amount of noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While you can use a PC power supply as a radio supply, the supply may not provide clean enough power to satisfy your personal signal requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note, however, that this will vary from supply to supply, and from radio to radio.  Radios with very good power supply noise rejection (such as mobile radios designed for vehicle power supplies) may be able to provide good signals with a poor power supply.  Similarly you may find that a particular PC power supply is very clean with low ripple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the noise inherent with switching power supplies, though, many hams insist on transformer style power supplies with linear regulation and would balk at any switch mode power supply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are concerned about signal quality, choose good power supplies, or quantify the noise your supply generates with a spectrum analyzer. You may also be able to add additional filtering on the output of the power supply to mitigate those issues, but that usually costs more than the savings you had from starting with a cheap PC power supply in the first place.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-24T14:38:55.653" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="313" PostTypeId="2" ParentId="309" CreationDate="2013-10-24T14:45:25.550" Score="3" Body="&lt;p&gt;&quot;Bands&quot; refer to frequency ranges, commonly allocated internationally for a particular purpose. Such purposes can be amateur radio, maritime mobile, broadcasting, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Within frequency bands, frequency allocation can either be basically free-for-all, as is the case in amateur radio (though by convention some frequencies are used for particular purposes), or on a channel basis (fixed allocation of frequencies with specific bandwidth allowances for a particular user and/or a particular purpose).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The exact frequency allocations vary from one country to another, but in general they are tied to which ITU region you are in. The world is split into &lt;a href=&quot;https://en.wikipedia.org/wiki/International_Telecommunication_Union_region&quot; rel=&quot;nofollow&quot;&gt;three ITU regions called regions 1, 2 and 3&lt;/a&gt;. For example, North America has one overall set of bands, whereas Europe has a mostly overlapping but somewhat different set of allocations. (The differences tend to get more pronounced the higher in frequency you get, due to the lesser need for international coordination.) Radio amateurs are allowed to use frequency spectrum basically across the entire RF range, with the lowest frequency band currently allocated internationally for amateur use without a special license being the 136 kHz band, also known by its wavelength as &lt;a href=&quot;https://en.wikipedia.org/wiki/2200-meter_band&quot; rel=&quot;nofollow&quot;&gt;the 2200 meter band&lt;/a&gt;, spanning the frequency range 135.7 - 137.8 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not possible to state a global number of available amateur bands, because some bands are only allocated in certain countries or regions (for example, the North American 220 MHz band is as a rule not available in Europe, and the UK 70 MHz band is generally not available in other parts of Europe) and others are sliced into several allocations (as an example of the latter, as I recall until fairly recently in Sweden the 160 meters band was split in two, 1810 - 1850 kHz and 1930 - 2000 kHz). However, there are &lt;em&gt;approximately&lt;/em&gt; two dozen frequency bands allocated on a primary or secondary basis to amateur radio. Each of these has characteristics different from the others, and many times a certain band may allow for a certain communication while others do not. (For example, night time 7 MHz and night time 24 MHz are quite different in terms of radio propagation.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Very broadly speaking,&lt;/em&gt; not considering such artificial enhancements as repeaters, satellites, Internet links and so on, there are two peaks in attainable communications range. At very low frequencies, antennas are small and close to the ground in terms of wave lengths, which influence range in a negative way. Around medium HF range has both the advantage of being able to communicate by ionospheric reflection as well as antennas being (relatively) manageable in terms of physical size. By the time you move into the upper HF range and up the ionosphere doesn't help you a lot anymore and thus the attainable range drops. By the time you get reasonably well into the VHF range and above, even fairly-high-gain antennas become physically small enough to be practical, so while you are generally limited to line-of-sight communications, attainable range rises again. Then by the time you start hitting microwave frequencies (roughly, upper UHF and up), &lt;em&gt;distances&lt;/em&gt; in terms of wavelength become a limiting factor, which means that the attainable range drops again.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-24T20:15:37.917" LastActivityDate="2013-10-24T20:15:37.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="314" PostTypeId="2" ParentId="303" CreationDate="2013-10-24T14:51:44.053" Score="13" Body="&lt;p&gt;The issue came up recently when one amateur radio user &lt;a href=&quot;http://www.arrl.org/news/rules-change-sought-to-permit-encryption-of-sensitive-emergency-communications&quot;&gt;petitioned the FCC to permit encrypted communications for emergency operations&lt;/a&gt; with the primary goal of complying with HIPAA health privacy laws.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.arrl.org/news/arrl-urges-denial-of-petition-to-permit-encryption-of-some-emergency-communications&quot;&gt;ARRL urged the denial of this petition&lt;/a&gt;, and the &lt;a href=&quot;http://www.arrl.org/news/fcc-dismisses-encryption-petition&quot;&gt;FCC subsequently denied the petition&lt;/a&gt;.  The major points of the ARRL's arguments were:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;it is ARRL’s considered view there is no factual or legal basis for the assumption that encryption of transmissions…is necessary in order to continue and enhance the utility of Amateur Radio emergency and disaster relief communications&lt;/li&gt;&#xA;&lt;li&gt;The ARRL also turned away Rolph’s assertion that the current prohibition in §97.113 “has impacted the relationship of Amateur Radio volunteers and served agencies and significantly limited the effectiveness of amateurs in supporting emergency communications.” The League said it’s unaware of any evidence that served agencies have been reluctant to utilize Amateur Radio as part of their emergency or disaster relief communications plans because of the encryption restrictions in Part 97.&lt;/li&gt;&#xA;&lt;li&gt;The League characterized as “erroneous” and “unfounded” Rolph’s assumption that encryption of certain information may be required under the provisions of HIPAA — the Health Insurance Portability and Accountability Act. &lt;/li&gt;&#xA;&lt;li&gt;Radio amateurs, the ARRL countered, are not “covered entities” under HIPAA, which applies only to health care providers, health plans and health care clearinghouses. &lt;/li&gt;&#xA;&lt;li&gt;there is no expectation of privacy in Amateur Radio communications.&lt;/li&gt;&#xA;&lt;li&gt;There is no evidence that emergency communications has been hampered by this issue, nor that care agencies subject to HIPAA have been reluctant or unwilling to utilize Amateur Radio services in emergency communication and disaster planning&lt;/li&gt;&#xA;&lt;li&gt;Adding the duty to encrypt certain transmissions to emergency communications workers would increase their workload.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;They did suggest that this need not be a permanent ruling, &quot;However, the ARRL said that should it become necessary in the future for radio amateurs to protect the privacy of individuals whose medical data may be transmitted by Amateur Radio during or after an emergency or disaster, “the Commission may be asked to revisit this matter.”&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-24T14:51:44.053" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="315" PostTypeId="1" AcceptedAnswerId="319" CreationDate="2013-10-24T15:01:47.473" Score="12" ViewCount="4821" Body="&lt;p&gt;I'm considering adding simple APRS transmitters to my vehicles.  I'd rather just put one in and forget about it, but I understand there are areas of the US where a stronger transmitter would be required to successfully send an APRS update packet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there coverage maps, similar to cell phone maps, which will help me understand where APRS should work and where it might not?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How powerful an APRS transmitter do I need to get approximately 75% coverage in the US?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-24T15:33:50.433" Title="How do I discover APRS coverage?" Tags="&lt;rf-power&gt;&lt;digital-modes&gt;&lt;aprs&gt;&lt;packet&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="316" PostTypeId="1" AcceptedAnswerId="321" CreationDate="2013-10-24T15:04:22.443" Score="8" ViewCount="789" Body="&lt;p&gt;My HT has 5 W of power, a sensitivity of about 0.2 µV, and I would like to talk to the SO-50 with it. How much gain do I need in my antenna to make this work?&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="29" LastEditDate="2013-11-07T20:12:29.300" LastActivityDate="2015-01-12T01:46:18.847" Title="What gain do I need to talk to SO-50 with my HT?" Tags="&lt;antenna&gt;&lt;ht&gt;&lt;satellites&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="317" PostTypeId="5" CreationDate="2013-10-24T15:23:27.343" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-24T15:23:27.343" LastActivityDate="2013-10-24T15:23:27.343" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="318" PostTypeId="4" CreationDate="2013-10-24T15:23:27.343" Score="0" Body="Transmission of digital signals over Amateur Radio, including modes like PSK-31, RTTY, JT-65, JT-9, etc." OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-10-24T19:05:21.580" LastActivityDate="2013-10-24T19:05:21.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="319" PostTypeId="2" ParentId="315" CreationDate="2013-10-24T15:33:50.433" Score="9" Body="&lt;p&gt;Coverage maps are a thing that is notoriously difficult to do right. There are some very complex programs (Radio Mobile is the one I know the most about) which can generate coverage maps if you're prepared to wade through the technical details and the quirks of the software. Unfortunately it's not as easy as drawing a circle of a certain size around each digipeater. Furthermore, power isn't the only factor - 5W vs 30W isn't going to make any difference at all compared to the night-and-day difference between an NMO-mounted mobile antenna vs an HT laying across your passenger seat. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use the &lt;a href=&quot;http://aprs.fi/heard/#!mt=roadmap&amp;amp;z=7&amp;amp;call=&amp;amp;others=1&amp;amp;timerange=86400&amp;amp;tail=0&quot;&gt;aprs.fi maps&lt;/a&gt; (warning: uses a google map overlay, it can be slow on some computers) to see all APRS activity. There's a button along the top right allowing you to filter out everything except APRS stations or digipeaters. You'll see that there are areas of very dense coverage - I'm looking right now at Baltimore, Philadelphia, up the NJ turnpike to NYC, and along the coast - but then there are wide areas that are empty, either because there are no digipeaters, or simply no one has sent a packet from there in the past 24 hours. An HT connected to a real mobile antenna, properly mounted on your vehicle, is equal to or better than 90% of the users you're seeing on that page, so if you use that setup you will get coverage anywhere that you see other users getting coverage on that page, with the possible exception of the outskirts of less heavily populated areas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could do better by using a 50W mobile, but even that is only a 10dB improvement and will only extend the coverage areas by a few more tens of miles, it will not magically give you coverage in the &quot;dead spots&quot; on that map. You also often do not want to run maximum power on something digital like APRS anyway unless it's a radio specifically intended for it - running &quot;at the limit&quot; can make your transmitted signal more dependent on the whims and quirks of the final amplifier, which can introduce nonlinearities which actually make your signal harder to decode. Plus, if you're signal is so powerful that digipeaters can hear you but you can't hear them, you risk stepping on signals that you can't hear, meaning that not only will you not get repeated, whoever you stepped on won't get repeated either.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-24T15:33:50.433" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="320" PostTypeId="2" ParentId="300" CreationDate="2013-10-24T15:48:41.153" Score="6" Body="&lt;p&gt;While many transceivers and scanners can be powered by a cigarette lighter adapter, you typically want to run at most one transceiver in this way, and should make absolutely certain that you know where that lighter is getting powered from. Most car fuseboxes are relatively easy to access, and most owners manuals will tell you what fuse is associated with each cigarette lighter - if the fuse is anything less than 10 Amps, do not use it. Absolutely do not change the fuse to something higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some possible concerns include the fact that your radio will likely start drawing it's full current only occasionally, but suddenly. Intermittent current draws like that are less likely to pop fuses than constant draws, even if the current is greater than the fuse's rating. On the other hand, you may experience voltage drops when you key up due to the resistance in the wire between your radio and battery. In the worst case, your cigarette lighter may be wired for &quot;chassis ground return&quot;, where that 10 amp current is not being returned through a copper ground wire, but through the car's steel chassis. This is OK for stuff like an AM/FM radio or the cabin lighting, but that same resistance equates to a higher voltage drop with your 10 amp radio, which can distort your output signal or even cause devices to sense an &quot;undervolt&quot; condition and shut down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And as an added bonus, guess what else is connected to your vehicle chassis? Yep, that's right, your antenna ground! So now you may have three different actual grounds all connected together, but at different voltages because of the resistance in the chassis: Your power supply ground at the radio, your RF ground at the antenna, and the actual negative post of the battery. This situation can mess with the bias of your final RF amplifier causing signal distortion or overheating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way, and the ways the pros do it, is to run a separate pair of wires from the battery to the radio. These wires must be rated for the maximum current draw of the radio (and then some, since every ham initially plans to install one radio and then winds up with 5) and both positive and negative leads must be fused at the battery. If they aren't, and come into contact with anything, you may short your car battery causing a fire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's another bonus of connecting directly to the battery - some cars shut off the cigarette lighter when the car is off, but if you connect straight to the battery, you have control over how the power is controlled. There are low voltage disconnects intended for this purpose which will detect when the car is turned off and shut off the radio a fixed amount of time later, but which can be overriden to allow you to operate the radio without turning on the car if needed.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-24T15:48:41.153" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="321" PostTypeId="2" ParentId="316" CreationDate="2013-10-24T17:55:23.713" Score="11" Body="&lt;p&gt;The specifications from AMSAT for the &lt;a href=&quot;http://www.amsat.org/amsat-new/satellites/sat_summary/so50.php&quot;&gt;SO-50&lt;/a&gt; are:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The repeater consists of a miniature VHF receiver with sensitivity of&#xA;  -124dBm, having an IF bandwidth of 15 KHz. The receive antenna is a 1/4 wave vertical mounted in the top corner of the spacecraft. The&#xA;  receive audio is filtered and conditioned then gated in the control&#xA;  electronics prior to feeding it to the 250mW UHF transmitter. The&#xA;  downlink antenna is a 1/4 wave mounted in the bottom corner of the&#xA;  spacecraft and canted at 45 degrees inward.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, what does all of that mean? First of all, the 5W signal you send has to make it to the spacecraft and be received. Let's just assume a uniform gain from the spacecraft to start with. Let's also start with a uniform gain from the HT. The satellite footprint is about 3000 miles, so let's just say the maximum distance to the satellite is 2500 km, accounting for height and the radial distance. It should be close enough to get an idea. That means the one way path loss is about 128 dB. That means your signal would need to be at least 100W to be received, given no gain, as can be calculated by $$10\times{}\frac{10^{128-124}}{1000}$$ Bottom line, you need a gain of at least 12dB to make the satellite, and a bit more margin would be helpful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as the receiving, that's where things are a bit trickier. The power can be found by $\frac{V^{2}}{R}$, and also converting the $V$ from peak to RMS. $R$ is usually 50 ohms. When you take all of that in to account, the specified minimum detection for the signal is $$-124 \log_{10}\left(\frac{\left(\frac{0.2\mathrm{e}-6}{\sqrt{2}}\right)^2}{50} \times 1000\right) \times 10$$ (Basically, find power $\frac{V^2}{R}$, convert to mW, and convert to dBm). The satellite signal is only 250mW, and you're looking at the same path loss of the signal. The gain required is $10 \times \log_{10}\left(\frac{10^{128-124} \times 10}{250 \mathrm{mW}}\right)$, or about 26 dB. This is quite difficult to achieve, and usually requires a pre-amp to be effective, or a really good antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bottom line- Tx is 12dB, Rx is 26 dB, at max distance, and less for an overhead pass. &lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="29" LastEditDate="2013-10-29T08:45:30.750" LastActivityDate="2013-10-29T08:45:30.750" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="322" PostTypeId="2" ParentId="141" CreationDate="2013-10-24T18:15:02.587" Score="5" Body="&lt;p&gt;If the antennas are at least one wavelength apart, you could use the &lt;a href=&quot;http://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow&quot;&gt;Friis transmission equation&lt;/a&gt;. This would allow you to determine, based on the power of the transmitter and the antenna gains, the power at the receive antenna. Subtract out any loss due to cables or duplexers. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you need to check two parameters of the reciever: the sensitivity and the specificity (may also be called adjacent channel selectivity). The sensitivity will be given in microvolts and is the weakest signal the reciever can understand. The specificity will be given in decibels and is the maximum ratio between a strong nearby signal and the desired signal that will allow the radio's filters to filter out the nearby signal on a different channel. Convert the receiver power from watts to volts using $$ V=\sqrt{P\times{}R} $$ and $R=50\Omega{}$. This is the voltage at the receiver caused by your nearby transmitter. Finally calculate the ratio between the two voltages - the one you just calculated and the sensitivity. Use the equation $$ 10 \times \log{\frac{V_1}{V_2}} $$ to calculate the ratio in decibels. If this ratio is less than the specificity (ideally by a good margin of error), then you're good. If the ratio is greater than the specificity, or they're within about 10dB from each other, then you may not be able to receive signals over the noise from the other nearby transmitter.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="29" LastEditDate="2013-10-28T18:50:45.227" LastActivityDate="2013-10-28T18:50:45.227" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="323" PostTypeId="2" ParentId="301" CreationDate="2013-10-24T18:35:29.273" Score="5" Body="&lt;p&gt;Some radios, such as the Yaesu FT-857D, have a feature in the menu that allows you to set the unit to automatically power off after a user-chosen period of time. Search the documentation of your radio for such an option.&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-10-24T18:35:29.273" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="324" PostTypeId="2" ParentId="299" CreationDate="2013-10-24T18:45:56.063" Score="8" Body="&lt;p&gt;Yes, this works fine. It is often called a &quot;fan dipole&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are separate resonant dipoles for each band, all fed from a common point. The wires should be separated by a foot or more. If you have enough tie points at the ends, you can run them in slightly different directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resonant dipole will have a low impedance, around 50 Ohms. The non-resonant one will have a higher impedance and will not accept much signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antennas will interact with each other, so you may need to tune them to length iteratively. Most people start by adjusting the length of the longer antenna first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 40m antenna will also be close to resonance on 15m, so you can probably use it on that band with an antenna tuner.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-10-24T18:45:56.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="325" PostTypeId="1" AcceptedAnswerId="326" CreationDate="2013-10-24T18:58:55.920" Score="10" ViewCount="351" Body="&lt;p&gt;I understand that in order to make the maths simpler, frequency ($f$) is expressed in megahertz (MHz) and the velocity of propagation in free space ($c$) for frequencies above 30 MHz is expressed as and rounded to 300 megameters/second (Mm/s). The actual speed of light is 299,792,458 meters/second, so expressing and rounding this to 300 Mm makes sense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm confused why it is rounded to 286 Mm when $f &amp;lt; 30\ \mathrm{MHz}$. Please explain. An excellent answer will show the maths.&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="76" LastEditDate="2013-10-29T18:32:40.443" LastActivityDate="2013-10-29T18:32:56.007" Title="Why is the speed of light rounded to 286 Mm in calculations involving frequencies below 30MHz?" Tags="&lt;math&gt;&lt;physics&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="326" PostTypeId="2" ParentId="325" CreationDate="2013-10-24T20:13:18.970" Score="8" Body="&lt;p&gt;Electrical wave propagation in wire is about 95% to 97% the speed of light.  Since wavelength is most commonly used for building antennas, which involve conducting the wave from air into the wire and vice versa, the calculation is adjusted assuming the slower propagation in an unshielded conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this 3% to 5% discrepancy is small enough at frequencies above 30 MHz that it is usually ignored for simplicity, and 300 is used instead. For frequencies below 30 MHz it becomes more significant and the adjusted value, &lt;em&gt;approximately&lt;/em&gt; 95% of 300 Mm, is used instead - about 286 Mm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda_{\mathrm{m}} = \frac{(300\ \mathrm{Mm})(0.95\overline{3})}{f_{\mathrm{MHz}}} = \frac{286\ \mathrm{Mm}}{f_{\mathrm{MHz}}}&#xA;\end{equation}&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2013-10-29T18:32:56.007" LastActivityDate="2013-10-29T18:32:56.007" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="327" PostTypeId="2" ParentId="301" CreationDate="2013-10-24T20:32:01.733" Score="3" Body="&lt;p&gt;Research automotive relays; They are essentially electronic switches that turn on when a current is present. In my vehicle, I have a large gauge wire and fuse running from the battery to high power pin on a relay under my seat; A small gauge wire runs from the back side of the cigerette lighter (which is only powered when the car is on) to the relay coil feed (trigger) pin, and another large gauge wire running to a fuse box that all my radio equipment connects to. It effectively creates the ignition sense you seek, and you will learn about the science as you go along! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have cited this resource in the past; It's thorough, and it applies well to this task: &lt;a href=&quot;http://www.mp3car.com/the-faq-emporium/117895-faq-relays-how-they-work-and-how-to-wire-it-up.html&quot; rel=&quot;nofollow&quot;&gt;http://www.mp3car.com/the-faq-emporium/117895-faq-relays-how-they-work-and-how-to-wire-it-up.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="126" LastActivityDate="2013-10-24T20:32:01.733" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="328" PostTypeId="2" ParentId="298" CreationDate="2013-10-24T20:39:20.373" Score="12" Body="&lt;p&gt;Prior to the internet getting a continuous stream of audio from a manned space mission was difficult, even when the mission was overhead, but, of course, due to orbital mechanics it often isn't overhead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur Radio enthusiasts would request and often gain permission to retransmit audio of space flights, and with some coordination and planning you could listen to space transmissions without having particularly expensive radio equipment - a few users would do the heavy lifting, and broadcast it as it passed overhead for them, and you'd simply tune into their retransmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, licensed amateur radio users aren't permitted to use their station for general broadcasting, and specifically restricted from playing music over the air.  These two rules prevented space mission broadcasts (which occasionally did feature music), and so a special rule was provided that, with permission, users could retransmit such transmissions for other enthusiasts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not commonly used now because NASA itself provides continuous broadcast access to most of their missions live via the internet, but in the heyday of the Apollo and similar space race programs Amateur Radio was often the only way to tap into these transmissions which were rarely broadcast via more general methods such as radio and television for exceptional events.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, it would be surprising to me if they gave specific permission now unless good reason was provided as to why the internet streams couldn't be used. Keep in mind that this rule is an exception.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-24T20:39:20.373" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="329" PostTypeId="2" ParentId="298" CreationDate="2013-10-24T20:42:30.923" Score="1" Body="&lt;p&gt;Several reasons exist, maybe some i don't even know. But some i have heard include:&#xA;NASA uses amateur radio as back up and emergency communications, and uses music to wake up the astronauts each day, as a sort of alarm clock; This naturally needs to be protected, as hams may be listening, recording and/or retransmitting these transmissions for various reasons. &#xA;NASA also broadcasts a lot of space flight video footage on NASA TV, and Amateur TV is authorized to use NASA TV for filler between transmissions, while the station is in automatic control; Allowing the retransmission of in-flight music protects this use. &lt;/p&gt;&#xA;" OwnerUserId="126" LastActivityDate="2013-10-24T20:42:30.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="330" PostTypeId="2" ParentId="283" CreationDate="2013-10-24T20:51:32.263" Score="4" Body="&lt;p&gt;&lt;strong&gt;Legend&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$c$ = velocity of propogation = speed of light (299,792,458 meters/second)&lt;/li&gt;&#xA;&lt;li&gt;$f$ = frequency&lt;/li&gt;&#xA;&lt;li&gt;$\lambda $ = wavelength&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Formulas&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The basic formula for calculating wavelength is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda = \frac{c}{f}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To make the math simpler, frequency ($f$) is expressed in megahertz (MHz) and the velocity of propogation in free space ($c$) for frequencies above 30 MHz is expressed as and rounded to 300 megameters (Mm). This will return a wavelength ($\lambda$) in meters. So for 1 wavelength &lt;em&gt;above&lt;/em&gt; 30 MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda_{m} = \frac{300}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, when $f &amp;lt; 30_{MHz}$, the velocity of propogation ($c$) is expressed as and rounded to 286 Mm because &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;[e]lectrical wave propagation in wire is about 95% to 97% the speed&#xA;  of light. Since wavelength is most commonly used for building antennas&#xA;  which involve conducting the wave from air into the wire and vice&#xA;  versa, the calculation is adjusted assuming the slower propagation in&#xA;  an unshielded conductor.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&quot;However, this 3% to 5% discrepancy is small enough at frequencies&#xA;  above 30 MHz that it is usually ignored for simplicity, and 300 Mm is&#xA;  used instead&quot; (&lt;a href=&quot;https://ham.stackexchange.com/questions/325/why-is-the-speed-of-light-rounded-to-286-mm-in-calculations-involving-frequencie#326&quot;&gt;Adam Davis, KD8OAS&lt;/a&gt;).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;When $f &amp;lt; 30_{MHz}$ the discrepancy becomes more significant and the adjusted value, approximately 95% of 300 Mm, is used instead, which is approximately 286Mm (which would actually be $0.95\overline{3}$). This results in the following formula for 1 wavelength &lt;em&gt;below&lt;/em&gt; 30 MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda_{m} = \frac{286}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To convert this into feet, multiply $c$ by 3.28084, which results in the following formula for receiving an answer in feet when $f &amp;gt; 30_{MHz}$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda_{ft} = \frac{(3.28084)300}{f_{MHz}} = \frac{984.252}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is rounded down to $984/f$ for the sake of simplicity. However, recall that when  $f &amp;lt; 30_{MHz}$, the velocity of propogation ($c$) is expressed as and rounded to 286 Mm. Applying this formula results in the following for converting this into feet &lt;em&gt;below&lt;/em&gt; 30 MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda_{ft} = \frac{(3.28084)286}{f_{MHz}} = \frac{938.32024}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is also rounded down to $938/f$ for the sake of simplicity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Calculating for half and quarter waves is just a manner of of dividing $c/2$ or $c/4$, respectively. So we end up with the following calculation for calculating the length of half wave antennas in feet when $f &amp;gt; 30_{MHz}$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda_{ft} = \frac{(3.28084)(300/2)}{f_{MHz}} = \frac{492.126}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When calculating the length of half wave antennas in feet where $f &amp;lt; 30_{MHz}$, we have the following formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda_{ft} = \frac{(3.28084)(286/2)}{f_{MHz}} = \frac{469.16012}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But this is generally expressed as $468/f$, not as 469. Why is this? First of all, remember that the velocity factor is &lt;em&gt;approximately&lt;/em&gt; 95-97% of the speed of light, so adjusting this value results in slightly different results. Also, whether we use the adjusted value of $c$ when $f &amp;lt; 30_{MHz}$ (286 Mm) or apply the velocity factor directly to $c$ will slightly alter our result. So for instance, the following calculation will get us closer to $468/f$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\lambda_{ft} = \frac{(3.28084)((300/2)(0.95))}{f_{MHz}} = \frac{467.5197}{f_{MHz}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would round up easily to $468/f$ when $f &amp;lt; 30_{MHz}$, and it is slightly more accurate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This shows why there are different equations and when each should be used.&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-10-28T18:56:14.780" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="331" PostTypeId="2" ParentId="22" CreationDate="2013-10-24T21:22:11.760" Score="6" Body="&lt;p&gt;In addition to 97.15, the FCC further published PRB-1 (&lt;a href=&quot;http://www.arrl.org/prb-1&quot; rel=&quot;noreferrer&quot;&gt;http://www.arrl.org/prb-1&lt;/a&gt;) to claify the restrictions of local jurisdictions to deny permits; Several hams have been successful in getting denied building permits reversed based on this in court; Other hams have been successful in using this to prove no permit was required in the first place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That being said, this restricts local and state governments, decidedly NOT HOAs. &lt;/p&gt;&#xA;" OwnerUserId="126" LastActivityDate="2013-10-24T21:22:11.760" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="332" PostTypeId="1" CreationDate="2013-10-24T21:29:00.270" Score="24" ViewCount="5890" Body="&lt;p&gt;I'd like to be able to show people what a QSO sounds like without having my transceiver available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way I can listen to amateurs talking in real-time (or using Morse code) on the HF bands using my internet connection and the speakers on my computer?&lt;/p&gt;&#xA;" OwnerUserId="19" LastEditorUserId="13" LastEditDate="2013-10-24T22:39:00.773" LastActivityDate="2014-12-09T16:04:52.227" Title="Is there a way to listen to live HF communications using the internet?" Tags="&lt;hf&gt;&lt;receiver&gt;&lt;internet&gt;" AnswerCount="1" CommentCount="6" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="333" PostTypeId="2" ParentId="173" CreationDate="2013-10-24T21:34:09.830" Score="4" Body="&lt;p&gt;Check out &lt;a href=&quot;http://groups.yahoo.com/neo/groups/aismon/info&quot; rel=&quot;nofollow&quot;&gt;AISMon&lt;/a&gt;; I've never used it, but it looks like it fits the bill. Here's a thorough tutorial: &lt;a href=&quot;http://www.rtl-sdr.com/rtl-sdr-tutorial-cheap-ais-ship-tracking/&quot; rel=&quot;nofollow&quot;&gt;http://www.rtl-sdr.com/rtl-sdr-tutorial-cheap-ais-ship-tracking/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="126" LastEditorUserId="76" LastEditDate="2013-10-25T10:05:16.167" LastActivityDate="2013-10-25T10:05:16.167" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="334" PostTypeId="2" ParentId="332" CreationDate="2013-10-24T21:49:31.190" Score="19" Body="&lt;p&gt;My two favorite locations for listening online are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://websdr.org/&quot;&gt;http://websdr.org/&lt;/a&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;WebSDR was first conceived as a means to make the 25 m radio telescope at Dwingeloo available to many radio amateurs for EME reception. In order to test a preliminary version of the software without using the 25m dish, a shortwave WebSDR was set up on Christmas Eve 2007 at the radio club of the University of Twente. After further development, its existence was publicly announced in April 2008. Interest for the project has been large since then, and many amateurs worldwide have expressed an interest in setting up their own WebSDR server. In November 2008, a beta testing phase has started with a few selected stations. By now, the software is made available to anyone serious about setting up a server; contact the author, PA3FWM, for information. A WebSDR server consists of a PC running Linux and the WebSDR server software, a fast internet connection (about a hundred kbit/s uplink bandwidth per listener), and some radio hardware to feed antenna signals into the PC. This radio hardware is typically a quadrature mixer connected to the PC's soundcard, like the popular SoftRock kits. &lt;a href=&quot;http://websdr.ewi.utwente.nl:8901/&quot;&gt;There is also an experimental version of this site hosted in the Netherlands that uses HTML5 rather than Java.&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://sdrspace.com/&quot;&gt;http://sdrspace.com/&lt;/a&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;SDRSpace is a place for folks using SDR-RADIO software to share their radio on the web. SDR-RADIO.com is a Windows console for Software Defined Radio (SDR) receivers and transceivers. Designed for the commercial, government, amateur radio and short-wave listener communities, the software provides a powerful interface for all SDR users.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="128" LastEditorUserId="128" LastEditDate="2013-10-24T22:00:33.137" LastActivityDate="2013-10-24T22:00:33.137" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="335" PostTypeId="2" ParentId="297" CreationDate="2013-10-24T21:51:58.387" Score="3" Body="&lt;p&gt;You're right, to make a properly working digipeater, you'll need to put both of the radios/TNCs in KISS mode, and use aprsdigi (or, my favourite, aprx), as a digipeater. But I don't think they can output both KISS and NMEA at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For NMEA, you'll then need some other software to receive APRS packets, decode them and output NMEA. That's not very difficult to do, but I don't think such application exists right now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd use the Linux AX.25 kernel tools to interface the KISS TNCs, so that you could run existing digipeater software, unmodified, just to do the digipeating, and at the same time run another program which also listens to traffic on the same TNCs and does the NMEA encoding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To implement the conversion program I'd personally just take the Ham::APRS::FAP perl parser (same APRS packet parser as used by aprs.fi), which can decode raw KISS / AX.25 frames, attach it to the raw packet socket to receive packets, and then write the new code necessary to generate NMEA.&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-10-24T21:51:58.387" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="337" PostTypeId="1" AcceptedAnswerId="343" CreationDate="2013-10-25T05:17:48.550" Score="14" ViewCount="616" Body="&lt;p&gt;Generally when I hear two conflicting signals they do not mix together, but rather one dominates then the other. This phenomenon can be observed on FM broadcast station when driving out of range from one station into the range of another. During the 'in between phase' they generally do not mix but rather one dominates and they flip flop being the dominant signal. Why is this?&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="87" LastEditDate="2013-11-11T03:02:43.840" LastActivityDate="2013-11-11T03:02:43.840" Title="Why do concurrent FM signals not mix together?" Tags="&lt;propagation&gt;&lt;physics&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="339" PostTypeId="2" ParentId="337" CreationDate="2013-10-25T06:27:42.727" Score="2" Body="&lt;p&gt;That's a property of FM demodulation known as the Capture Effect: when multiple signals are present, only the strongest is demodulated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This does not occur with AM or SSB demodulation, where multiple signals can be simultaneously demodulated.&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-25T06:27:42.727" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="340" PostTypeId="1" CreationDate="2013-10-25T12:43:21.097" Score="13" ViewCount="1551" Body="&lt;p&gt;As far as I know, all radio amateurs are assigned privileges on &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Power Output&lt;/li&gt;&#xA;&lt;li&gt;Mode of operation&lt;/li&gt;&#xA;&lt;li&gt;Operating bands&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;as a function of the class of licence they hold. These privileges differ from one jurisdiction to another.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When may a licencee operate &lt;strong&gt;beyond the privileges of their licence class yet within the privileges of a higher class of licence in that jurisdiction&lt;/strong&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;Is&lt;/em&gt;&lt;/strong&gt; there any such scenario?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="22" LastEditDate="2013-10-26T02:42:58.387" LastActivityDate="2013-10-30T04:55:06.253" Title="When may a ham operate beyond the privileges of their licence class?" Tags="&lt;license&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="342" PostTypeId="2" ParentId="340" CreationDate="2013-10-25T14:01:18.510" Score="14" Body="&lt;p&gt;In the US, any person may operate under the direct supervision of an operator of a higher class. This is how the GOTA (get-on-the-air) stations work at field day, but it's applicable at any time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In most cases when operating in foreign countries under e.g. CEPT you do not gain any additional bands, but in some cases you may gain some additional operating ability because either the country authorizes specific extra bands through something other than CEPT or because their band does not exactly overlap with ours.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any licensee (any service) may use any means necessary if normal channels are down if necessary for the protection of life or property against imminent danger. This is not quite what you asked because it does not grant them the privileges of a higher license class, rather &quot;any means necessary&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Recent graduates from one license class to another receive temporary operating privileges, signing CALLSIGN/AG or CALLSIGN/AE for new general or extra privileges as needed, until their upgrade is officially noted on the FCC ULS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many countries allow case-by-case exceptions for experimental purposes, such as permission to operate on an additional band for people experimenting with LF and MF communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some countries allow operators to use a repeater controlled by a higher-class licensee to access extra bands, for example if a general class licensee has a repeater input on 2 meters or 440 and output on 10 meters, a technician using that repeater may have his signal repeated into a band that he could not transmit on directly.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-25T14:01:18.510" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="343" PostTypeId="2" ParentId="337" CreationDate="2013-10-25T14:07:02.610" Score="9" Body="&lt;p&gt;I understand why you think it should mix - that's what happens with SSB, for example. The difference with FM is that in FM, at any instant, each station's signal is only at one frequency. If you slowed the signals down and watched through a spectrum analyzer, you could watch the two signals, and you'd see two peaks at constant amplitude, moving independently. The frequency (of the carrier) is modulated based on the audio signal amplitude, so that peak will move within the channel, but it's always one peak. Your receiver latches on to the stronger peak, and that's what it decodes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, in single sideband, you wouldn't ever see a single peak no matter how much you slowed the signal down. In single sideband, the amplitude of the carrier is being modulated - it isn't that the peak is moving, the peak is actually being mixed with (multiplied by) the audio amplitude, so all the peaks from the audio signal would appear on your spectrum analyzer. In this case, there's no distinction between audio components coming from one source vs another - you could separate the signals if you wanted to using directional antennas, but with a single receiver all you're going to see is the two signals superimposed.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-25T14:07:02.610" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="344" PostTypeId="2" ParentId="340" CreationDate="2013-10-25T17:41:37.913" Score="6" Body="&lt;p&gt;Generally speaking, and of course with the caveat that this may vary from country to country, &lt;strong&gt;a person may operate a radio station they normally are not licensed for, when doing so under the supervision of a properly licensed individual.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Examples may include, but not be limited to, for example:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Jamboree On The Air (JOTA), which has brought many a scout into the fold of radio amateurs by allowing them to try it out&lt;/li&gt;&#xA;&lt;li&gt;Publicity events arranged by amateur radio clubs, including special events stations&lt;/li&gt;&#xA;&lt;li&gt;Amateur radio classes introducing attendees to operating under actual conditions that cannot easily be simulated&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I myself first got on the air even before I had my own license permitting VHF and up only through a local club, where under supervision I could operate the club station on HF. And I dare say I did fairly well doing it, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also the implicit assumption in the question that amateurs are limited in the transmission modes they are allowed to use. &lt;em&gt;This is not always the case.&lt;/em&gt; For example, since before I got my license, Swedish amateurs regardless of license class have not been limited in terms of operating mode, as long as the transmissions meet the other criteria such as instantenous transmitted frequency, power output, spectral purity, non-interference, and so on. Particularly, band plans are not legally enforced. (You're likely to upset a lot of people if you start transmitting narrow-band FM on the digital modes center frequency 14070 kHz, but as long as you don't cause interference for other users -- which in such a case seems pretty likely that you would -- you are perfectly within your rights &lt;em&gt;legally&lt;/em&gt; to do so as a Swedish amateur.) &lt;em&gt;This may be particularly pronounced in countries where the only difference in requirements between various license classes has been or is the level of Morse code proficiency required.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-10-25T17:41:37.913" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="345" PostTypeId="1" AcceptedAnswerId="346" CreationDate="2013-10-25T18:50:52.633" Score="37" ViewCount="59168" Body="&lt;p&gt;Looking at amateur radio forums and email threads, oftentimes amateur radio operators will use &quot;73&quot; or &quot;73s&quot; where one might otherwise expect to find &quot;Sincerely&quot; or &quot;Regards&quot;. Why?&lt;/p&gt;&#xA;" OwnerUserId="22" LastActivityDate="2017-05-16T23:24:58.757" Title="Why do hams often conclude messages with &quot;73&quot;?" Tags="&lt;jargon&gt;" AnswerCount="6" CommentCount="0" FavoriteCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="346" PostTypeId="2" ParentId="345" CreationDate="2013-10-25T18:50:52.633" Score="40" Body="&lt;p&gt;The usage of &quot;73&quot; for such a purpose comes from the &lt;a href=&quot;http://www.signalharbor.com/73.html&quot;&gt;Phillips Code&lt;/a&gt;, originally devised in the era of telegraphs to speed up transmission of common messages by mapping them to numbers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;73&quot; mapped to &quot;best regards&quot; or &quot;my compliments&quot; and was intended as a general &lt;a href=&quot;http://en.wikipedia.org/wiki/Valediction&quot;&gt;valediction&lt;/a&gt; for transmitted messages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is still used for that purpose today in morse code transmissions and often makes its way into everyday correspondence among hams as a form of jargon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also &quot;88&quot; (which maps to &quot;love and kisses&quot;) that sometimes takes the place of &quot;73&quot; for communications between affectionate parties.&lt;/p&gt;&#xA;" OwnerUserId="22" LastActivityDate="2013-10-25T18:50:52.633" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="347" PostTypeId="5" CreationDate="2013-10-25T19:14:36.233" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-25T19:14:36.233" LastActivityDate="2013-10-25T19:14:36.233" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="348" PostTypeId="4" CreationDate="2013-10-25T19:14:36.233" Score="0" Body="Questions about acronyms, words, phrases, or other terminology specific to amateur radio." OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-10-27T21:05:25.260" LastActivityDate="2013-10-27T21:05:25.260" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="349" PostTypeId="1" CreationDate="2013-10-25T20:51:12.310" Score="3" ViewCount="145" Body="&lt;p&gt;All I've ever used is CW, and a some SSB; even then always replying; haven't seen much difference there in the manner of the QSO. But there are other modes which I have not used, and some that are superseded/not available in VU land.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apart from the obvious differences in equipment &amp;amp; perception, what differences in protocol are applicable to a QSO over A3F (double sideband full carrier amplitude modulation with video) as compared to J3E (single sideband telephony with suppressed carrier)?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2013-10-30T19:33:54.617" LastActivityDate="2013-10-30T19:33:54.617" Title="What are the differences in a QSO over A3F as compared to J3E?" Tags="&lt;modes&gt;&lt;procedure&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="350" PostTypeId="5" CreationDate="2013-10-25T20:53:50.150" Score="0" Body="&lt;p&gt;This tag covers all amateur radio communications with man-made Earth-orbiting objects, including communication over dedicated amateur radio satellites (AMSATs) and with astronauts aboard a space station such as the International Space Station (ISS).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It does not cover reflecting signals off passive, natural objects such as Earth-Moon-Earth communications (EME) or meteor scatter.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-27T21:05:35.527" LastActivityDate="2013-10-27T21:05:35.527" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="351" PostTypeId="4" CreationDate="2013-10-25T20:53:50.150" Score="0" Body="Amateur radio satellites refer to any artificial object in Earth orbit that are useful for amateur radio purposes." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-27T21:05:47.560" LastActivityDate="2013-10-27T21:05:47.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="352" PostTypeId="1" AcceptedAnswerId="353" CreationDate="2013-10-25T21:43:24.660" Score="27" ViewCount="4070" Body="&lt;p&gt;Like the question title says, what is a radio link budget? For what is it useful, and how do I make one?&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2018-11-17T12:54:33.917" LastActivityDate="2018-11-17T12:54:33.917" Title="What is a link budget, and how do I make one?" Tags="&lt;jargon&gt;&lt;range&gt;&lt;path-loss&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="12" ContentLicense="CC BY-SA 3.0" />
  <row Id="353" PostTypeId="2" ParentId="352" CreationDate="2013-10-25T21:43:24.660" Score="34" Body="&lt;p&gt;A link budget is a summary of a communications link that tries to take into account all factors which have an impact on the received signal strength. It is often used to determine the minimum amount of output power required at the transmitter for a given signal strength at the receiver, and takes into consideration power output, antenna gains, propagation losses, acceptable signal fading, and other factors (for example, for long cable runs, cable attenuation may be a factor, and at microwave frequencies, losses due to absorption in atmospheric gases become a significant factor for Earth-bound links).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few elementary values are required to make up a link budget. For unobstructed line of sight communications, which is the primary propagation mode on VHF and up, propagation losses can be estimated using the formula&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$L_{p} = -22 - 20\log{\frac{r}{λ}}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where &lt;em&gt;r&lt;/em&gt; is the distance covered and &lt;em&gt;λ&lt;/em&gt; is the wavelength of the operating frequency. When the two use the same units (for example, meters), &lt;em&gt;Lp&lt;/em&gt; comes out in dB and expresses the propagation attenuation (loss) between two isotropic antennas. For example, the propagation loss for a distance of 100 meters at 450 MHz is approximately 65.5 dB. Note that the determining factor is actually the distance in terms of wavelengths between the two antennas, so the loss goes up by 6 dB for every doubling of either the physical distance or the frequency (halving of the wavelength).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No antenna is perfectly isotropic, and the common dipole has a gain of approximately 2.15 dBi (dB over isotropic) broadside to the antenna. Directional antennas generally have their gain specified as either dBi or dBd (dB over dipole, which is dBi - 2.15 dB, so 3 dBd = 5.15 dBi).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To ease calculations, convert the power output of the transmitter to dBm. Using dB throughout turns many a multiplication and division into addition and subtraction, greatly simplifying calculations. For example, a 100 W transmitter puts out +50 dBm, and a 5 W transmitter puts out +37 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;To make the link budget, at a minimum add the transmitter output power, transmitter antenna gain in the desired direction, propagation loss and receiver antenna gain in the desired direction.&lt;/strong&gt; By making the calculations in dB relative to some known reference (generally dBm or dBW) this comes down to addition and subtraction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;As a very simple example,&lt;/strong&gt; for a 100 W transmitter with dipoles at both ends broadside to each other (+2.15 dBi × 2), over an unobstructed 20 km path using a frequency of 150 MHz (2.00 meters wavelength), we get:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;  +50    dBm   power output&#xA; +  2.15 dBi   transmitter antenna gain&#xA; -102    dB    propagation loss, 20 km at 150 MHz&#xA; +  2.15 dBi   receiver antenna gain&#xA; ===========&#xA;  -47.7  dBm   signal strength at receiver&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;If the minimum usable signal at the receiver for the modulation and bandwidth in use, taking into account natural and receiver noise, is -90 dBm, this gives us a margin of about 42 dB, which is huge. This of course means that in theory, we can reduce our output power by a corresponding amount, maintaining communications with only +8 dBm output, as seen below:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;   +8    dBm   power output&#xA; +  2.15 dBi   transmitter antenna gain&#xA; -102    dB    propagation loss, 20 km at 150 MHz&#xA; +  2.15 dBi   receiver antenna gain&#xA; ===========&#xA;  -89.7  dBm   signal strength at receiver&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Admittedly, the above link budget gives us for all intents and purposes no margin: to maintain communications over this path using this equipment and mode of transmission, everything must work out absolutely perfectly. To have a 10 dB margin for issues such as fading, we'd need to use +18 dBm (slightly less than 100 mW = +20 dBm) power output, which is trivially achievable with practically &lt;em&gt;any&lt;/em&gt; handheld radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A link budget for a HF link, or an obstructed VHF link, is much more complex because the propagation losses are harder to calculate than for a pure line-of-sight link, but the general principle remains exactly the same. A complete link budget for a line-of-sight link will at least include the following factors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;＋ Transmitter output power&lt;/li&gt;&#xA;&lt;li&gt;－ Attenuation in the transmitter's antenna cabling, including any impedance matching network&lt;/li&gt;&#xA;&lt;li&gt;＋ Transmitter antenna gain in the direction of the receiver&lt;/li&gt;&#xA;&lt;li&gt;－ Propagation loss in free space&lt;/li&gt;&#xA;&lt;li&gt;－ Attenuation due to absorption in atmospheric gases&lt;/li&gt;&#xA;&lt;li&gt;－ Margin for attenuation due to rain&lt;/li&gt;&#xA;&lt;li&gt;－ Margin for attenuation in tree foilage&lt;/li&gt;&#xA;&lt;li&gt;－ Margin for attenuation due to reflection against walls etc.&lt;/li&gt;&#xA;&lt;li&gt;－ Margin for signal fading&lt;/li&gt;&#xA;&lt;li&gt;＋ Receiver antenna gain in the direction of the transmitter&lt;/li&gt;&#xA;&lt;li&gt;－ Attenuation in the receiver's antenna cabling, including any impedance matching network&lt;/li&gt;&#xA;&lt;li&gt;＝ Signal strength at the receiver input terminals, to be compared with the minimum necessary signal strength&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It is important to note that several of these factors (propagation loss, atmospheric absorption, foilage losses, and so on) are heavily dependent on the operating frequency. This means that a link budget for one frequency is unlikely to be applicable at another frequency, even if nothing else changes.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-28T18:44:23.650" LastActivityDate="2013-10-28T18:44:23.650" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="354" PostTypeId="2" ParentId="32" CreationDate="2013-10-25T22:36:38.487" Score="9" Body="&lt;p&gt;So, my personal theory is that &quot;Koch was a good start&quot;.  But in the modern days of computers, why haven't we improved much since that period of time.  Huge advancements in education have also occurred since the time the Koch method was created.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I decided to test my theory that with computer assisted learning we could improve our speed by having the computer actually help us.  Koch is overwhelming, at first, and goes &lt;em&gt;too&lt;/em&gt; fast.  Why can't a computer specifically decide when to send us something based on how long we've taken in the past?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I wrote some software to train you using just these methods.  And others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find my software (free) at &lt;a href=&quot;http://www.hamtools.org/cutecw/&quot;&gt;the CuteCW&lt;/a&gt; home page.&lt;/p&gt;&#xA;" OwnerUserId="661" LastActivityDate="2013-10-25T22:36:38.487" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="355" PostTypeId="1" CreationDate="2013-10-26T00:46:14.620" Score="15" ViewCount="2208" Body="&lt;p&gt;When I listen to SSB, it has the very familiar tunnel-voice sound. What properties make it sound like this? With a Carrier and an extra sideband as AM, I don't hear the tunnel-effect at all. Is there special equipment to get rid of the effect?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="22" LastEditDate="2013-10-26T02:40:39.660" LastActivityDate="2017-05-03T17:06:59.340" Title="Why does SSB have the hollow voice sound?" Tags="&lt;ssb&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="356" PostTypeId="1" AcceptedAnswerId="367" CreationDate="2013-10-26T00:55:56.853" Score="18" ViewCount="3438" Body="&lt;p&gt;Sometimes when I access IRLP nodes, they have a very short melody telling you that you are connected; or when my local repeater's net begins, it does the famous doorbell 8-note sequence. What is the fine line of prohibited and allowed with respect to music?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it that overtone usage, like a Sine-wave 6 tone melody, is allowed, but if a piano is used, it would be prohibited?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or is it the length, like a 2-second little access melody, is allowed, but it can't go on forever?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or is it what we define as common music, like a 3 minute song, would be prohibited, but random sequences of sine waves for a few seconds would be allowed? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;DTMF in a sense could be avant-garde music from John Cage or Karlheinz Stockhausen, who loved the sounds on his shortwave radio and incorporated all of the unique sounds he heard in his music.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what breaks the barrier for the FCC rules on music or other non-voice audio transmissions?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="873" LastEditDate="2014-09-20T17:57:55.117" LastActivityDate="2021-02-17T02:00:47.193" Title="What defines music, per amateur radio regulations?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;&lt;music&gt;" AnswerCount="6" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="357" PostTypeId="1" AcceptedAnswerId="358" CreationDate="2013-10-26T01:01:21.520" Score="9" ViewCount="2401" Body="&lt;p&gt;Let's say I get my little 2 meter FM handheld out and make a little sine-wave generator with which I pulse a morse code and if I connect it to headphones a speaker, I hear the dits and dahs of a nice sine wave tone. Now let's say I connect this to the microphone port on my transceiver with the VOX setting turned to detect when I am entering the morse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this allowed, or is it illegal because of the wasted bandwidth when I could just use carrier? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My country is the USA.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8832" LastEditDate="2018-05-30T18:24:32.187" LastActivityDate="2018-05-30T18:24:32.187" Title="Is Morse code allowed on FM in the USA" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;cw&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="358" PostTypeId="2" ParentId="357" CreationDate="2013-10-26T01:09:49.513" Score="17" Body="&lt;p&gt;Completely legal. In fact, it's common practice to identify repeaters (both in the amateur service and in public safety/commercial) with exactly this method.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, you likely won't make many QSOs with it. There aren't many people who would be prepared to immediately respond if they started hearing FM morse on 146.52 (the typical hailing frequency for simplex operators on the 2m band), compared to people down in the CW section of the band.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="259" LastEditDate="2013-10-31T18:07:54.597" LastActivityDate="2013-10-31T18:07:54.597" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="359" PostTypeId="1" CreationDate="2013-10-26T03:23:20.573" Score="-1" ViewCount="155" Body="&lt;p&gt;I could be wrong on this one, but I understand that in some countries, radio frequencies are regulated, with licences being require to OPERATE on the the networks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As mentioned most channels are regulated (since commercial operators usually use them as well), so what sort of licences are given out ? and who are the bodies who usually issue these licences ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;for e.g- are licences limited to a specific range of channels any restrictions ?   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;edit: i'll make this clearer ... &amp;amp; AM/FM frequencies was wrong. my bad.&lt;/p&gt;&#xA;" OwnerUserId="187" LastEditorUserId="87" LastEditDate="2013-10-28T14:48:04.937" LastActivityDate="2013-10-28T14:48:04.937" Title="Are some frequencies regulated ? if not which ones are free to use?" Tags="&lt;license&gt;&lt;frequency&gt;" AnswerCount="3" CommentCount="4" ClosedDate="2013-10-26T16:54:27.930" ContentLicense="CC BY-SA 3.0" />
  <row Id="360" PostTypeId="1" AcceptedAnswerId="362" CreationDate="2013-10-26T03:49:22.077" Score="5" ViewCount="110" Body="&lt;p&gt;I recentley moved to Fairbanks AK, and was wondering if Alaska constituted being north of line A. Being that geographically, Alaska is north of line A, but in real world applications, Fairbanks is nowhere near Canada.&lt;/p&gt;&#xA;" OwnerUserId="11" LastEditorUserId="29" LastEditDate="2013-10-26T16:01:26.167" LastActivityDate="2013-10-30T04:16:29.953" Title="Is Alaska considered to be located north of line A?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="361" PostTypeId="2" ParentId="359" CreationDate="2013-10-26T04:19:13.577" Score="3" Body="&lt;p&gt;In most countries, all or almost all frequencies are by license. Some licenses are by class, e.g. FRS radios in the US are permitted automatically (by class) to almost anyone in the US (excluding agents of a foreign country), but it's still technically a license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every very low power radios, like the mini-FM transmitters that plug into smart phones and media players for those vehicles lacking Bluetooth or an Aux plug for audio input, are technically covered under Part 15, although one could argue there's no license like FRS has.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the need for more radio bandwidth from the carriers, I don't foresee any frequencies being made available in an unlicensed fashion. There's too much demand from companies capable of buying them. That's part of the reason why Amateur Radio exists - to allow experimentation and advancement of radio without requiring an upfront investment by each ham to compete with the cell carriers and public safety organizations of the world.&lt;/p&gt;&#xA;" OwnerUserId="55" LastActivityDate="2013-10-26T04:19:13.577" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="362" PostTypeId="2" ParentId="360" CreationDate="2013-10-26T04:25:24.367" Score="5" Body="&lt;p&gt;Reading &lt;a href=&quot;http://www.gpo.gov/fdsys/pkg/CFR-2012-title47-vol5/xml/CFR-2012-title47-vol5-sec90-7.xml&quot;&gt;http://www.gpo.gov/fdsys/pkg/CFR-2012-title47-vol5/xml/CFR-2012-title47-vol5-sec90-7.xml&lt;/a&gt;, I cannot find that any part of Alaska is &quot;north of line A&quot;, but some of it may be &quot;east of line C&quot;. Line A doesn't start until Aberdeen, Washington, so to be north of that line you would have to be in the northern Continential US or in Canada. Alaska is not geographically north of that line. This is why there's a Line C - to cover the Canadian/US border shared with Alaska.&lt;/p&gt;&#xA;" OwnerUserId="55" LastActivityDate="2013-10-26T04:25:24.367" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="363" PostTypeId="2" ParentId="301" CreationDate="2013-10-26T04:30:57.983" Score="2" Body="&lt;p&gt;Double-check to see if your radio can auto-turn off after a period of non-use - mine does and it's quite handy. Failing that, a product like &lt;a href=&quot;http://www.westmountainradio.com/product_info.php?products_id=apo3_pp&quot; rel=&quot;nofollow&quot;&gt;http://www.westmountainradio.com/product_info.php?products_id=apo3_pp&lt;/a&gt; can work quite well to do something similar based on the voltage from your alternator/battery &quot;detecting&quot; if your engine is running or not.&lt;/p&gt;&#xA;" OwnerUserId="55" LastActivityDate="2013-10-26T04:30:57.983" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="364" PostTypeId="2" ParentId="359" CreationDate="2013-10-26T06:11:11.473" Score="1" Body="&lt;p&gt;Most transmitting equipment requires a licence to use. There are a small number of band-segments that allow licence free operation, such as the 2.4 GHz and 5.8 GHz bands used for WiFi (etc).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming your question is specifically about Ham Radio allocations, then you need a licence to operate.  Within the terms of your licence, this gives you permission to transmit on those band segments allocated to amateur radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: there are regional variations, and these are detailed in the respective Band Plan (eg &lt;a href=&quot;http://rsgb.org/main/operating/band-plans/uk-band-plan/&quot; rel=&quot;nofollow&quot;&gt;here for the UK / IARU Region 1&lt;/a&gt;)&lt;/p&gt;&#xA;" OwnerUserId="93" LastEditorUserId="29" LastEditDate="2013-10-26T15:05:47.193" LastActivityDate="2013-10-26T15:05:47.193" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="365" PostTypeId="2" ParentId="359" CreationDate="2013-10-26T11:15:24.343" Score="0" Body="&lt;p&gt;When you say &quot;radio (AM or FM) frequencies&quot;, it makes me think you are talking about broadcast radio used by consumers.  Interpreting the question in that light alone; some countries do give an implied license to broadcast on these frequencies at a sufficiently low power to ensure there is little interference.&lt;/p&gt;&#xA;" OwnerUserId="123" LastActivityDate="2013-10-26T11:15:24.343" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="366" PostTypeId="2" ParentId="301" CreationDate="2013-10-26T11:20:49.343" Score="1" Body="&lt;p&gt;You might increase the capacity of the battery by replacing it with a higher rating, or add a second battery.  This will allow you more time before it is drained.  It also increases the time you can use the radio in an emergency where you are unable to run the engine.&lt;/p&gt;&#xA;" OwnerUserId="123" LastActivityDate="2013-10-26T11:20:49.343" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="367" PostTypeId="2" ParentId="356" CreationDate="2013-10-26T12:03:40.623" Score="10" Body="&lt;p&gt;&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.1.157.1&quot;&gt;FCC 97.113&lt;/a&gt; states that the following is prohibited:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(4) Music using a phone emission except as specifically provided&#xA;  elsewhere in this section; communications intended to facilitate a&#xA;  criminal act; messages encoded for the purpose of obscuring their&#xA;  meaning, except as otherwise provided herein; obscene or indecent&#xA;  words or language; or false or deceptive messages, signals or&#xA;  identification.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Looking around, the best I could find is that this rule is intended to prevent general purpose broadcasting, specifically with the purpose to entertain. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From this website, there is an interesting &lt;a href=&quot;http://nonbovine-ruminations.blogspot.com/2010/01/more-things-you-can-do-on-amateur-radio.html&quot;&gt;quote on music&lt;/a&gt;. I wouldn't take this as law, but it is worth considering:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Similarly, the transmission of music is also prohibited (with one&#xA;  exception: music incidental to an authorized retransmission of&#xA;  communications from the Space Shuttle is permitted).  However, there&#xA;  is reportedly a ruling that one ham singing &quot;Happy Birthday&quot; on the&#xA;  air to another ham does not count as the &quot;transmission of music&quot;,&#xA;  presumably because most hams seem to be unable to sing.  Again, this&#xA;  is a non-compete regulation; if you want to transmit music the FCC&#xA;  wants you to use the broadcast service or a low power service to&#xA;  accomplish your purpose, not amateur radio.  If your interest in radio&#xA;  is to be an on-air DJ, again, amateur radio might not be for you, and&#xA;  you should consider looking elsewhere.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Bottom line, if something that is purely incidental to the conversation, or if you are transmitting it digitally, you can actually have a bit of music and not get your hand slapped by the FCC. Thus, the doorbell seems fine, and most likely the types of &quot;Windows Sounds&quot; that sometimes come up, but personally, I wouldn't risk it. If you are trying to broadcast then you are almost certainly in violation of the law.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-26T12:03:40.623" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="368" PostTypeId="1" CreationDate="2013-10-26T12:40:22.217" Score="1" ViewCount="1666" Body="&lt;p&gt;Just what the title states. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio is international in nature covered by ITU/Radiocomm. Whether to allow  ham radio operators is, however, a matter of state policy. Here, in VU land, regulations mandate &lt;strong&gt;an amateur station may communicate only with licenced amateurs&lt;/strong&gt;. To the best of my knowledge such mandate is part-and-parcel of amateur service regulation in all nations where the service is allowed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this context, it seems proper to know &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What nations do not grant an Amateur Radio licence? &lt;/li&gt;&#xA;&lt;li&gt;What nations ceased to issue an Amateur Radio licence as a matter of policy?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I.e. What prefix/es should send me scrambling to get on the horn with the Monitor? (+:&lt;/p&gt;&#xA;" OwnerUserId="5" LastActivityDate="2013-12-24T20:06:37.440" Title="What nations do not grant an amateur radio licence?" Tags="&lt;license&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="1" ClosedDate="2013-10-27T15:46:43.237" ContentLicense="CC BY-SA 3.0" />
  <row Id="369" PostTypeId="1" AcceptedAnswerId="370" CreationDate="2013-10-26T15:43:18.283" Score="11" ViewCount="5262" Body="&lt;p&gt;I've seen these weird three-letter modulation codes like J3E, A3F, A1A, F3E and so on. Someone even wrote 2K40J3E or 12K5F3E. What do these codes stand for?&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-26T15:55:20.977" LastActivityDate="2013-10-26T15:55:20.977" Title="What do the three-letter modulation codes (emission designators) stand for?" Tags="&lt;jargon&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="370" PostTypeId="2" ParentId="369" CreationDate="2013-10-26T15:43:18.283" Score="15" Body="&lt;p&gt;The emission type specifier is made up of several fields, which are defined as follows.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First comes an (optional) specifier of the necessary radio bandwidth. This is four characters, mixed letters and numbers, with one of &lt;code&gt;H&lt;/code&gt; (Hz), &lt;code&gt;K&lt;/code&gt; (kHz), &lt;code&gt;M&lt;/code&gt; (MHz) or &lt;code&gt;G&lt;/code&gt; (GHz) where the decimal point would be. For example, &lt;code&gt;400H&lt;/code&gt; specifies a bandwidth of 400 Hz, &lt;code&gt;2K40&lt;/code&gt; specifies 2.40 kHz, &lt;code&gt;25K0&lt;/code&gt; specifies 25.0 kHz and &lt;code&gt;6M00&lt;/code&gt; specifies 6.00 MHz. This is the bandwidth used by the signal on the air, not the modulation bandwidth. For example, narrow-band FM modulated with a 3 kHz signal would be &lt;code&gt;12K5&lt;/code&gt; because it needs 12.5 kHz of bandwidth on the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is followed by three characters which specify, in turn, the modulation type, the nature of the modulating signal, and the type of information carried.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Modulation type&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;code&gt;A&lt;/code&gt; = amplitude modulation, two sidebands, full carrier&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;B&lt;/code&gt; = amplitude modulation, independent sidebands&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;C&lt;/code&gt; = amplitude modulation, vestigial sideband&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;D&lt;/code&gt; = amplitude and angle modulation of carrier&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;F&lt;/code&gt; = angle-modulated, straight frequency modulation&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;G&lt;/code&gt; = angle-modulated, phase modulation&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;H&lt;/code&gt; = amplitude modulation, single sideband, full carrier&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;J&lt;/code&gt; = amplitude modulation, single sideband, suppressed carrier&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;K&lt;/code&gt; = pulse, amplitude modulation&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;L&lt;/code&gt; = pulse, width modulation&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;M&lt;/code&gt; = pulse, with phase or position modulation&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;N&lt;/code&gt; = No modulation at all&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;P&lt;/code&gt; = pulse, no modulation&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;Q&lt;/code&gt; = pulse, with carrier angle-modulated during pulse&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;R&lt;/code&gt; = amplitude modulation, single sideband, reduced or controlled carrier&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;W&lt;/code&gt; = pulse, two or more modulation modes used&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;X&lt;/code&gt; = all other cases&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Nature of the modulating signal&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;code&gt;0&lt;/code&gt; = No modulating signal&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;1&lt;/code&gt; = Digital modulating signal, on/off or quantified with no further modulation&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;2&lt;/code&gt; = Digital modulating signal with modulation&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;3&lt;/code&gt; = A single analog channel&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;7&lt;/code&gt; = Two or more digital channels&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;8&lt;/code&gt; = Two or more analog channels&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;9&lt;/code&gt; = Composite modulating signal, one or more analog channels plus one or more digital channels&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;X&lt;/code&gt; = all other cases&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Type of information carried by the modulating signal&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;code&gt;A&lt;/code&gt; = aural telegraphy, for people (generally Morse code)&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;B&lt;/code&gt; = telegraphy for machine copying (generally RTTY or high-speed Morse code)&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;C&lt;/code&gt; = analog fax&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;D&lt;/code&gt; = data, telemetry, telecommand&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;E&lt;/code&gt; = telephony, voice or sound&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;F&lt;/code&gt; = video or television&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;N&lt;/code&gt; = no information carried&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;W&lt;/code&gt; = a combination of the above&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;X&lt;/code&gt; = all other cases&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This can be followed by two more characters giving details, which normally are not used for amateur radio purposes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Examples&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;J3E&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;amplitude modulation, single sideband, suppressed carrier&lt;/li&gt;&#xA;&lt;li&gt;a single analog channel&lt;/li&gt;&#xA;&lt;li&gt;telephony, voice or sound&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Also known as single-sideband transmissions or SSB,&lt;/em&gt; generally in amateur applications with voice modulation. 2K40J3E is J3E with a 2.40 kHz radio signal bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;A3F&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;amplitude modulation, two sidebands, full carrier&lt;/li&gt;&#xA;&lt;li&gt;a single analog channel&lt;/li&gt;&#xA;&lt;li&gt;video or television&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;A1A&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;amplitude modulation, two sidebands, full carrier&lt;/li&gt;&#xA;&lt;li&gt;digital modulating signal, on/off or quantified with no further modulation&lt;/li&gt;&#xA;&lt;li&gt;aural telegraphy, for people&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Also known as Morse code&lt;/em&gt; and informally CW. Actual CW (pure carrier) is N0N.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;F3E&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;angle-modulated, straight frequency modulation&lt;/li&gt;&#xA;&lt;li&gt;a single analog channel&lt;/li&gt;&#xA;&lt;li&gt;telephony, voice or sound&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Also known as frequency modulation or FM,&lt;/em&gt; generally in amateur applications with voice modulation. 12K5F3E is F3E with a 12.5 kHz radio signal bandwidth.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-26T15:54:22.913" LastActivityDate="2013-10-26T15:54:22.913" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="371" PostTypeId="5" CreationDate="2013-10-26T16:41:45.737" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-26T16:41:45.737" LastActivityDate="2013-10-26T16:41:45.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="372" PostTypeId="4" CreationDate="2013-10-26T16:41:45.737" Score="0" Body="Questions about power ratings and restrictions, including maximum power by law or for certain components, or about calculating power in certain situations." OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-27T21:05:07.683" LastActivityDate="2013-10-27T21:05:07.683" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="373" PostTypeId="1" AcceptedAnswerId="374" CreationDate="2013-10-26T17:07:49.147" Score="6" ViewCount="213" Body="&lt;p&gt;Working the bands it's quite possible to work in mixed-mode, albeit I doubt whether it is ever done. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Call this a thought experiment: Station A operates &lt;a href=&quot;http://en.wikipedia.org/wiki/Continuous_wave&quot; rel=&quot;nofollow&quot;&gt;CW&lt;/a&gt;, Station B operates &lt;a href=&quot;http://en.wikipedia.org/wiki/Single-sideband_modulation&quot; rel=&quot;nofollow&quot;&gt;SSB&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find myself wondering &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What is the &lt;strong&gt;&lt;em&gt;legal&lt;/em&gt;&lt;/strong&gt; status of such a QSO? &#xA;&lt;ul&gt;&#xA;&lt;li&gt;How would it be entered in the log?&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Is this situation covered by a regulation?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2013-10-30T19:33:47.180" LastActivityDate="2013-10-30T19:33:47.180" Title="Does mixed-mode operation qualify as a QSO?" Tags="&lt;legal&gt;&lt;modes&gt;&lt;logging&gt;&lt;procedure&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ClosedDate="2013-12-05T08:34:27.410" ContentLicense="CC BY-SA 3.0" />
  <row Id="374" PostTypeId="2" ParentId="373" CreationDate="2013-10-26T18:08:05.267" Score="12" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Does mixed-mode operation qualify as a QSO?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'd say &lt;em&gt;absolutely, yes.&lt;/em&gt; You're making contact with another amateur radio station on a frequency allocated to amateur radio; in my book, that qualifies as an amateur radio contact or QSO.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the legal status of such a cross-mode QSO?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Assuming that &lt;em&gt;your&lt;/em&gt; license allows you to transmit on the frequency and mode that &lt;em&gt;you&lt;/em&gt; are transmitting on, I see no reason why there would be any legal problems with such a QSO. The law can only apply to what you transmit, not to what you receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It &lt;em&gt;might&lt;/em&gt; be possible that in some jurisdictions there are restrictions imposed on what kind of receivers individuals may possess, but even so, I think we have to assume that your possession of the receiver is legal; if it is not, then that's a completely separate problem.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How would it be entered in the log?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I would enter the details of my transmission, with a suitable comment in the comments field for the received signal. For example, station A would write mode CW, comment &quot;received SSB&quot; or something like that; station B would write mode SSB, comment &quot;received CW&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One large part of the rationale for this is that if anyone ever complains about your station operating (for example, due to interference), what will matter is &lt;em&gt;your&lt;/em&gt; transmissions, not what you received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, certain jurisdictions may have specific requirements. If that is the case in your situation, you should refer to your local regulations for guidance on what exactly to write into the station log. That said, I would expect any such regulations to be centered around the own station's activities.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is this situation covered by a regulation?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I doubt it is, although you'd have to consult your locale-specific regulations to be certain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It &lt;em&gt;may&lt;/em&gt; complicate things slightly if you want to use that contact to apply for a mode-specific award, but that's about the only complication I can think of. If you want to claim such a QSO for credit toward a mode-specific award, you'd have to contact the issuer of that award and ask how exactly they will count it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And of course, the QSL card cannot say for example &lt;em&gt;mode 2xCW&lt;/em&gt; or &lt;em&gt;mode two-way CW&lt;/em&gt; because that would be inaccurate. For a cross-mode contact, I'd probably make it explicit which mode was used by which station, for example by writing &lt;em&gt;mode CW(CL1SGN), SSB(CL2SGN)&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-26T18:42:11.297" LastActivityDate="2013-10-26T18:42:11.297" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="376" PostTypeId="2" ParentId="368" CreationDate="2013-10-26T19:25:34.157" Score="3" Body="&lt;p&gt;There are numerous regions of the world where there are not well-established governments (some where various competing regimes continually overturn one another or a region is in a state of civil war). It would be futile to attempt to list these as they change so often. However, among established nation-states, the following &lt;strong&gt;do not grant amateur radio licenses&lt;/strong&gt;:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Yemen*&lt;/li&gt;&#xA;&lt;li&gt;North Korea&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There are also many countries that make it very difficult for people to obtain licenses (whether through bureaucracy or high costs), but currently these are the only two who do not grant them to citizens at all. Another example of note is the Vatican City. Amateur radio in the State of the Vatican City is club-station activity, with no individual station licenses granted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;* According to &lt;a href=&quot;https://en.wikipedia.org/wiki/Amateur_radio#Licensing_requirements&quot; rel=&quot;nofollow&quot;&gt;Wikipedia&lt;/a&gt;, but &lt;a href=&quot;http://www.arrl.org/select-countries-u-z&quot; rel=&quot;nofollow&quot;&gt;the ARRL has no information on file either way&lt;/a&gt;.&lt;/sub&gt;&lt;/p&gt;&#xA;" OwnerUserId="128" LastActivityDate="2013-10-26T19:25:34.157" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="377" PostTypeId="1" AcceptedAnswerId="379" CreationDate="2013-10-26T22:34:58.583" Score="6" ViewCount="313" Body="&lt;p&gt;I want to build a simple 40 meter CW transmitter and Receiver pair. What should I do to get started into home-brew HF RF devices?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2013-10-27T04:04:20.467" Title="How can I get started with a Home Brew QRP?" Tags="&lt;transceiver&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="378" PostTypeId="2" ParentId="368" CreationDate="2013-10-27T02:02:00.840" Score="2" Body="&lt;p&gt;A little dated but the IARU 2001 &lt;a href=&quot;http://www.iaru.org/uploads/1/3/0/7/13073366/calendar_2001.pdf&quot; rel=&quot;nofollow&quot;&gt;Status Summary of Amateur Stations&lt;/a&gt; listed the following nations as &quot;Information being sought&quot;. I assume these nations in particular either &lt;strong&gt;do not, &lt;em&gt;OR&lt;/em&gt; cannot&lt;/strong&gt; grant an amateur radio operator's licence&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDITED to reflect updated information available on the web vide. comment chain:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Burundi (?)&lt;/li&gt;&#xA;&lt;li&gt;&lt;strike&gt;Eritrea&lt;/strike&gt;&lt;/li&gt;&#xA;&lt;li&gt;Niger (?)&lt;/li&gt;&#xA;&lt;li&gt;&lt;strike&gt;Somalia&lt;/strike&gt;&lt;/li&gt;&#xA;&lt;li&gt;Yemen&lt;/li&gt;&#xA;&lt;li&gt;&lt;strike&gt;Afghanistan&lt;/strike&gt; Forgot about another OM there&lt;/li&gt;&#xA;&lt;li&gt;&lt;strike&gt;Cambodia&lt;/strike&gt; Forgot about XU1SS&lt;/li&gt;&#xA;&lt;li&gt;DPR Korea&lt;/li&gt;&#xA;&lt;li&gt;Myanmar (?)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Of this list, at the time of compilation, some nations were in a state of vigorous socio-political flux (as Dan pointed out in his answer). In the event an updated compilation is available, please feel free to edit this answer.&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="507" LastEditDate="2013-12-24T20:06:37.440" LastActivityDate="2013-12-24T20:06:37.440" CommentCount="4" CommunityOwnedDate="2013-10-27T02:02:00.840" ContentLicense="CC BY-SA 3.0" />
  <row Id="379" PostTypeId="2" ParentId="377" CreationDate="2013-10-27T04:04:20.467" Score="4" Body="&lt;p&gt;I built a &lt;a href=&quot;http://qrpkits.com/bitx20a.html&quot; rel=&quot;nofollow&quot;&gt;BitX 20a&lt;/a&gt;, which was fairly complex, but a really neat kit. If your soldering skills are ok, and you can wind small wire through tiny donut shaped cores, you will have a lot of fun. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://qrpkits.com/smk2.html&quot; rel=&quot;nofollow&quot;&gt;The SMK-2 40m kit&lt;/a&gt; might meet your needs (40 meter CW), but it's surface mount. Don't be afraid of that, with a good magnifying glass, and some inexpensive chinese made soldering tools and some solder paste, it's easy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also built a &lt;a href=&quot;http://jaunty-electronics.com/blog/2012/08/sudden-storm-hf-receiver-in-a-tuna-can/&quot; rel=&quot;nofollow&quot;&gt;Sudden Storm&lt;/a&gt; from &lt;a href=&quot;http://qrpkits.com/&quot; rel=&quot;nofollow&quot;&gt;KF5OBS&lt;/a&gt;. They have several simpler, small kits that might be a good fit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've found kits a great way to learn. I learned a lot trying to get my BitX to work, I found a few errors I made, but I learned a lot about the theory in the process. Don't be afraid to learn as you go!&lt;/p&gt;&#xA;" OwnerUserId="121" LastActivityDate="2013-10-27T04:04:20.467" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="380" PostTypeId="2" ParentId="355" CreationDate="2013-10-27T06:55:34.957" Score="0" Body="&lt;p&gt;Most transceivers limit the bandwidth of an SSB signal to 3000 Hz, whereas AM signals can be much wider and thus sound more natural. &lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2013-10-27T06:55:34.957" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="381" PostTypeId="1" CreationDate="2013-10-27T14:25:28.247" Score="2" ViewCount="149" Body="&lt;p&gt;I have 2 antennas which are quite close to each other. I would like to have at least a rough idea of the decoupling between those 2 antennas. I do not own a network analyzer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was thinking of using a transmitter set to a known power on the first antenna and a wattmeter terminated with a dummy load on the other antenna. Might this work ?&lt;/p&gt;&#xA;" OwnerUserId="195" LastEditorUserId="9" LastEditDate="2013-11-08T14:55:34.660" LastActivityDate="2013-11-08T14:55:34.660" Title="What simple method will measure decoupling betwen two antennas?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="382" PostTypeId="1" AcceptedAnswerId="385" CreationDate="2013-10-27T15:01:33.217" Score="24" ViewCount="12798" Body="&lt;p&gt;If an antenna analyzer shows 1:1, does that mean it's an ideal receiver as well? And what about the converse, will a well performing receive antenna show a 1:1 SWR? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've wondered this for a while, sometimes I want a wide band antenna just for listening, and I am not clear about this relationship.&lt;/p&gt;&#xA;" OwnerUserId="121" LastEditorUserId="76" LastEditDate="2015-12-15T20:35:02.623" LastActivityDate="2018-07-14T13:27:07.230" Title="What is the relationship between SWR and receive performance?" Tags="&lt;antenna&gt;&lt;impedance&gt;&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="383" PostTypeId="1" AcceptedAnswerId="400" CreationDate="2013-10-27T15:07:28.427" Score="6" ViewCount="1225" Body="&lt;p&gt;With the adjustments on a transmitter such as a Yaesu FT-101E, is there any purpose for an antenna tuner, or can you accomplish the same thing by adjusting the loading and other controls?&lt;/p&gt;&#xA;" OwnerUserId="121" LastEditorUserId="29" LastEditDate="2013-10-27T16:53:23.307" LastActivityDate="2019-03-27T16:15:52.900" Title="Does a tube based HF transmitter need an antenna tuner?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;antenna-tuner&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="384" PostTypeId="2" ParentId="383" CreationDate="2013-10-27T17:10:28.503" Score="0" Body="&lt;p&gt;I don't believe an antenna tuner is needed if the power levels are 100 W or less. Doesn't your manual tell you how to attach to an antenna and how to insure that power is going to the antenna? I remember tuning the power out to a light bulb and then attaching the antenna. Anyone else remember that?&lt;/p&gt;&#xA;" OwnerUserId="142" LastActivityDate="2013-10-27T17:10:28.503" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="385" PostTypeId="2" ParentId="382" CreationDate="2013-10-27T17:13:59.770" Score="19" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If an antenna analyzer shows 1:1, does that mean it's an ideal receiver as well?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;No.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming we're talking about a characteristic impedance of 50 ohms, a 50 ohm resistor (otherwise known as a dummy load) will show a SWR of 1:1, although it will almost certainly perform very poorly as either a receive or transmit antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The low SWR simply tells you that there are no impedance mismatches along the path from the transmitter (antenna analyzer in the case of your question) to the antenna feedpoint, at the current operating frequency.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And what about the converse, will a well performing receive antenna show a 1:1 SWR?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Yes and no.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Yes,&lt;/em&gt; a SWR of 1:1 means that &lt;a href=&quot;https://ham.stackexchange.com/q/55/29&quot;&gt;you aren't losing signal to impedance mismatch reflections&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;No,&lt;/em&gt; another issue is how efficient the antenna is at picking up the (desired) signal, preferably (especially in the case of directional antennas) while rejecting undesired signals as well. An antenna that is 5% of a full half-length dipole isn't going to pick up as much RF as the full-length dipole, let alone a full-sized directional antenna pointed in the proper direction, simply due to the much smaller physical (antenna aperture) size.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Generally speaking,&lt;/strong&gt; if an antenna analyzer or (other) transmitter shows that the antenna output presents a SWR of 1:1, then &lt;em&gt;what you have&lt;/em&gt; is probably about as good as it gets. &lt;em&gt;That does not necessarily mean that what you have is a good antenna setup&lt;/em&gt; as exemplified by the extreme example of a dummy load.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-10-28T09:15:16.453" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="386" PostTypeId="2" ParentId="382" CreationDate="2013-10-27T17:18:41.627" Score="3" Body="&lt;p&gt;&quot;If an antenna analyzer shows 1:1, does that mean it's an ideal receiver as well?&quot; - It means for this antenna for the frequency you've tested on the antenna is as good as it gets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;And what about the converse, will a well performing receive antenna show a 1:1 SWR?&quot; - Perhaps not. I have a loop antenna tacked to the ceiling in a bedroom. It is fed with 300 Ohm twin-lead and works very well for all the HF frequencies. I would NOT use it to transmit with a tuner. I have no idea what the SWR is, that is ONLY important to a transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most receivers can handle all sorts of mismatch it's the transmitter than needs the &quot;protection&quot; in order to push out full power. However, that said I will also say that one can work well enough with a tuner and receiver and tune for the most noise. Pick an unused frequency and use the tuner to increase the noise level. One you've maxed it out you'll have better reception for frequencies close to this one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope that helps.&lt;/p&gt;&#xA;" OwnerUserId="142" LastActivityDate="2013-10-27T17:18:41.627" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="387" PostTypeId="5" CreationDate="2013-10-27T17:18:47.063" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-27T17:18:47.063" LastActivityDate="2013-10-27T17:18:47.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="388" PostTypeId="4" CreationDate="2013-10-27T17:18:47.063" Score="0" Body="Standing wave ratio, a measure of efficiency for transmission of signals through cables." OwnerUserId="-1" LastEditorUserId="22" LastEditDate="2013-11-11T05:00:12.413" LastActivityDate="2013-11-11T05:00:12.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="389" PostTypeId="2" ParentId="381" CreationDate="2013-10-27T17:26:16.573" Score="1" Body="&lt;p&gt;Yes. But, how much decoupling do you need? In other words it all depends on how you're using the two antennas. If one is for your transmitter and the other for a receiver then you definitely do not want the receiver and transmitter on the same frequency when you transmit until you know if it is safe. Most receivers have limits as to signal levels that can be tolerated. You have to find that information and then a way to measure the signal level generated at the input to the receiver when your transmitter is transmitting and the power level you intend to use. Receiver signal levels are usually measured in microvolts, uV. Some maximum level is usually given, exceed it at the risk of destroying the receiver.&lt;/p&gt;&#xA;" OwnerUserId="142" LastActivityDate="2013-10-27T17:26:16.573" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="390" PostTypeId="1" AcceptedAnswerId="459" CreationDate="2013-10-28T04:04:22.067" Score="8" ViewCount="1320" Body="&lt;p&gt;I don't understand how you would go about giving an RF ground to your antenna. Would it not become an additional radial and affect the signal? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the proper way to ground your station's antenna?&lt;/p&gt;&#xA;" OwnerUserId="11" LastEditorUserId="8832" LastEditDate="2017-11-12T04:18:19.820" LastActivityDate="2019-02-16T15:46:55.520" Title="What is the proper way to ground your station's antenna?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;rfi&gt;&lt;grounding&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="391" PostTypeId="2" ParentId="382" CreationDate="2013-10-28T05:25:12.050" Score="2" Body="&lt;p&gt;SWR aka Standing Wave Ratio is &lt;strong&gt;calculated for the reflection&lt;/strong&gt; due to an impedance mismatch along the transmission-line. This is &lt;strong&gt;more relevant to Tx&lt;/strong&gt; because of the power levels involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ergo, SWR calculation will only be applicable to a receiver insofar as a 1:1 (or as close as may be achieved!) indicates the signal incident on the antenna is not reflected back from the receiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resonant frequency/band of the antenna is the ease with which that antenna will intercept signals for that frequency/band from the air. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best scenario is when the SWR is 1:1, and the receiver is tuned to the resonant frequency of the antenna itself.&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-11-08T05:09:31.207" LastActivityDate="2013-11-08T05:09:31.207" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="392" PostTypeId="2" ParentId="355" CreationDate="2013-10-28T08:12:21.480" Score="19" Body="&lt;p&gt;&lt;strong&gt;NO CARRIER,&lt;/strong&gt; said the modem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SSB has no carrier, and the transmitter does not transmit anything when the operator is not speaking. There is no way to transmit the presence of &lt;em&gt;silence&lt;/em&gt; to the receiver. Instead, you'll hear atmospheric noise, local and remote electrical noise (arcing in relays, remote thunderstorms and all that), RF hash from computers and other electronics. All of that will mix with the transmitted voice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Receiver off frequency&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With SSB it's really hard to tune the receiver to exactly the same frequency as the transmitter. If the receiver and transmitter are on slightly different frequencies, the received voice will be tuned equally high or low. A very little difference will make the voice sound slightly strange, although communication is still easy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Vocal sounds have natural harmonics, too. A vowel having a 400 Hz fundamental frequency will come out of your mouth with harmonics at precisely 800 and 1200 Hz (to &lt;em&gt;slightly&lt;/em&gt; simplify the example). If an USB receiver is just 20 Hz low, the received tone set will be 420, 820 and 1220, which are no  longer harmonically related (420*2 = 840, 420*3 = 1260). That can make a very small frequency difference sound strange.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Audio bandwidth&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SSB receivers &lt;strong&gt;and&lt;/strong&gt; transmitters generally have a more limited bandwidth. With modern DSP-filtered receivers you can easily tune the receiver's bandpass filter to be very wide, but that won't have any effect if the transmitter still uses a 2700 Hz filter. When testing, remember to adjust the transmitter too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Multipath effects&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Multiple SSB signals mix together nicely at the receiver, allowing you to hear the natural echo and reverb effects of multipath propagation. This effect can be heard on AM, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes they're less pronounced, creating just slightly spacious sound. If the receiver and transmitter are close to each other, the signal's &quot;&lt;em&gt;ground wave&lt;/em&gt;&quot; can be heard directly, but its reflection from some upper layer of the atmosphere can be heard too. With a longer distance between stations, the same signal could be reflected at multiple points of the atmosphere at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes, with good propagation, the signal can travel the &lt;em&gt;short path&lt;/em&gt; (shortest line around the planet), and &lt;em&gt;long path&lt;/em&gt; (around the world in the &quot;wrong&quot; direction), and the signal which has travelled the long path will be clearly delayed. &lt;em&gt;Polar echo&lt;/em&gt; is another variation on this subject.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-30T08:09:19.147" LastActivityDate="2013-10-30T08:09:19.147" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="393" PostTypeId="2" ParentId="349" CreationDate="2013-10-28T08:42:27.140" Score="3" Body="&lt;p&gt;With SSTV you'd typically do the same thing as with SSB/CW: You'll seek an unused frequency, and transmit your CQ call image, and then listen for a response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With SSTV you normally use an SSB transceiver and you'll be able to listen to the audible representation of the image transmission, or any other communications on that frequency using any other mode. You shouldn't transmit SSTV images on top of someone's voice QSO, either. Most SSTV software packages have a frequency scope or a waterfall display to aid tuning, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When doing ATV on UHF (regular analog or digital TV, not SSTV) you'll typically use specially allocated ATV frequencies, and possibly repeaters, which should not have any voice traffic on them. The presence of traffic should be obvious from the presence of audio (instead of FM &quot;no carrier&quot; noise) and video (instead of &quot;snow&quot;).&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-10-28T08:42:27.140" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="394" PostTypeId="1" AcceptedAnswerId="398" CreationDate="2013-10-28T09:22:28.550" Score="3" ViewCount="547" Body="&lt;p&gt;With vacuum-tube-based transmitters, you'd need to tune the output finals to achieve maximum power output, and this was commonly done into some sort of dummy load (either a purpose-made dummy load or something simple like a light bulb) while aiming for maximum power output on or near the desired operating frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, solid state equipment doesn't need the finals tuned to the operating frequency. On the other hand, they are much more sensitive to antenna impedance mismatches.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Seeing that antenna impedance mismatches are not caught or solved by first tuning into a dummy load, &lt;strong&gt;in what situations is a dummy load useful with a purely solid-state transmitter&lt;/strong&gt; (where any external amplifier is considered part of the transmitter)?&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-28T09:28:01.307" LastActivityDate="2013-10-28T12:01:42.417" Title="With solid-state equipment, when would one use a dummy load?" Tags="&lt;dummy-load&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="395" PostTypeId="1" AcceptedAnswerId="396" CreationDate="2013-10-28T10:58:10.990" Score="5" ViewCount="191" Body="&lt;p&gt;The suggested APRS digipeater path is &lt;code&gt;WIDE1-1,WIDE2-1&lt;/code&gt; for the most use cases. According to the specs, this ensures two retransmissions by fill-in / regular digipeaters around the sender, without the digipeaters adding their own callsign to the path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;code&gt;TRACEn-N&lt;/code&gt; path, as opposed to that, is intended to let digipeaters insert their callsign when forwarding. However, despite the use of &lt;code&gt;WIDEn-N&lt;/code&gt;, I see one or multiple digipeaters in the path of most packets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Are there still valid use cases for &lt;code&gt;TRACEn-N&lt;/code&gt;? Will a &lt;code&gt;TRACEn-N&lt;/code&gt; packet have the same coverage as a &lt;code&gt;WIDEn-N&lt;/code&gt; one?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="89" LastActivityDate="2013-10-28T11:52:56.107" Title="APRS: WIDEn-N vs. TRACEn-N" Tags="&lt;digital-modes&gt;&lt;aprs&gt;&lt;packet&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="396" PostTypeId="2" ParentId="395" CreationDate="2013-10-28T11:52:56.107" Score="5" Body="&lt;p&gt;Actually, current specifications &lt;a href=&quot;http://aprs.org/fix14439.html&quot; rel=&quot;noreferrer&quot;&gt;encourage or require digipeaters to add their callsigns to the WIDEn-N path&lt;/a&gt;, since including callsigns greatly helps in finding and fixing all sorts of network issues (look for &quot;traceable&quot; in the page). &lt;code&gt;WIDE1-1&lt;/code&gt; is often replaced by the callsign of a dumb digipeater, &lt;code&gt;WIDE2-1&lt;/code&gt; is usually prepended by the callsign of a digipeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;code&gt;TRACEn-N&lt;/code&gt; is often useful for diagnostics.&lt;/strong&gt; Many areas still have obsolete digipeaters in use, which don't add their own callsigns to the &lt;code&gt;WIDEn-N&lt;/code&gt; path, and those digipeaters often do add their callsign to &lt;code&gt;TRACEn-N&lt;/code&gt; paths. So someone might want to sometimes temporarily use &lt;code&gt;TRACEn-N&lt;/code&gt; to see which digipeaters are retransmitting your packets. If all digipeaters in your area have already been upgraded to make &lt;code&gt;WIDEn-N&lt;/code&gt; traceable, it should not make much difference at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unless there is a digipeater which completely ignores &lt;code&gt;TRACEn-N&lt;/code&gt; packets in your area (would be surprising), it should get the &lt;strong&gt;same coverage&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Prepending a few digipeater callsigns in the packet path does not have a significant practical effect on transmission time/size, since each callsign-SSID pair is only 7 bytes long (56 bits - 6 bytes for callsign, plus one byte for SSID as an integer), which at 1200 bits/s takes 46.7 ms to send. Kenwood TH-D72 has a default &lt;strong&gt;txdelay&lt;/strong&gt; setting of 300 milliseconds, which at 1200 bits per second already attributes to 360 bits of &quot;waste&quot; in the beginning of each transmission. Other radios and trackers have similar and sometimes longer default settings for txdelay - even up to 500 ms. And then there's the actual packet contents, which often are very long with uncompressed coordinates and verbose comment texts.&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-10-28T11:52:56.107" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="397" PostTypeId="1" AcceptedAnswerId="399" CreationDate="2013-10-28T11:55:50.073" Score="7" ViewCount="2501" Body="&lt;p&gt;There are already questions about the definition of &lt;a href=&quot;https://ham.stackexchange.com/questions/4/is-there-a-kml-or-similar-file-that-shows-all-of-the-cq-zones&quot;&gt;CQ zones&lt;/a&gt; and &lt;a href=&quot;https://ham.stackexchange.com/questions/261/where-can-i-find-the-official-definition-of-itu-zones&quot;&gt;ITU zones&lt;/a&gt;, but there is no information about what these zones are used for (and Google brings up various maps but no explanation).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Is this something a non-US novice-class amateur needs to know about?)&lt;/p&gt;&#xA;" OwnerUserId="89" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-10-28T12:32:54.603" Title="What are CQ/ITU zones used for?" Tags="&lt;cq-zones&gt;&lt;location&gt;&lt;itu-zones&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="398" PostTypeId="2" ParentId="394" CreationDate="2013-10-28T12:01:42.417" Score="6" Body="&lt;p&gt;Any time you don't want to transmit RF. For example, if you have an oscilloscope and spectrum analyzer and would like to test the output of your transmitter (e.g. to make sure it's on frequency, that the waveform is OK and not getting cut off, that you don't have any spurious signals being transmitted) you might want to transmit into a dummy load rather than an antenna to prevent interfering with another transmittion and taking up bandwidth that you don't really need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It can also be helpful to test your transmitter's power output in the absence of any SWR mismatch or reflected signal.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-28T12:01:42.417" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="399" PostTypeId="2" ParentId="397" CreationDate="2013-10-28T12:05:50.263" Score="4" Body="&lt;p&gt;Many contests use them as a convenient measure of how many different &quot;regions&quot; you've managed to contact. Since using countries as a contest multiplier isn't necessarily very accurate (within a certain radius, US can only easily reach Canada or Mexico or ocean, within the same radius, a station in central Europe could easily have their first 20 contacts come from 20 different countries) these equal-sized regions allow for a somewhat more equitable contest scoring system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They also go into awards - there is a Worked All Zones award for the ITU zones, so while getting DXCC (century club - contacts with 100 different countries) may be much easier from Germany than it is from Kansas, both stations will have similar difficulty getting the Worked All Zones award, because the zones are more uniform worldwide than countries are.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="29" LastEditDate="2013-10-28T12:11:00.640" LastActivityDate="2013-10-28T12:11:00.640" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="400" PostTypeId="2" ParentId="383" CreationDate="2013-10-28T12:27:10.487" Score="5" Body="&lt;p&gt;The original &lt;a href=&quot;http://foxtango.org/ft101/graphics/Transmitter%20Tune%20UP.JPG&quot; rel=&quot;nofollow&quot;&gt;Yaesu FT-101 tuning instructions&lt;/a&gt; state the following:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;em&gt;Do not use antennas which are untuned or exhibit an SWR of more than 2:1&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;An external antenna tuner can usually work with a much broader mismatch range. If you have a &quot;random wire&quot; or otherwise untuned antenna, a tuner is clearly required. A slight mismatch (2:1 or less) can be handled by the tube amplifier's controls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same advice will apply to other tube finals.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-30T05:37:39.857" LastActivityDate="2013-10-30T05:37:39.857" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="401" PostTypeId="2" ParentId="397" CreationDate="2013-10-28T12:32:54.603" Score="3" Body="&lt;p&gt;Both are a means of identifying where you are in the world. CQ Zones is managed by CQ Magazine, and the ITU Zones are managed by the ITU. You can see more information about how they are defined in the two questions you linked. Some contests use them as an identifier of where you are, the most notable being the ITU number used in the IARU competition in July, and the CQ Zones are used by various competitions, usually those sponsored by CQ Magazine. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both of these are an entry in to LOTW, which is where I became familiar with them. Most logging programs will ask for your CQ/ITU zone number. I'm sure there's other places they crop up as well.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-28T12:32:54.603" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="402" PostTypeId="1" AcceptedAnswerId="403" CreationDate="2013-10-28T14:18:17.027" Score="3" ViewCount="481" Body="&lt;p&gt;What is a good explanation of the different &quot;ground&quot; types that hams deal with? Specifically:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;grounding an antenna mast/tower (outside, lightning prevention)&lt;/li&gt;&#xA;&lt;li&gt;grounding transceiver/equipment (inside shack, RF leakage prevention)&lt;/li&gt;&#xA;&lt;li&gt;antenna ground plane (on/under antenna)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="152" LastActivityDate="2013-12-26T23:33:05.923" Title="Understanding &quot;ground&quot; in ham radio" Tags="&lt;grounding&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="403" PostTypeId="2" ParentId="402" CreationDate="2013-10-28T14:18:17.027" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;grounding an antenna mast/tower (outside, lightning prevention)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A tower or mast must be grounded to &quot;earth&quot;, usually through an 8' conductive (copper) rod driven into the ground as close to the antenna setup as humanly possible. Should the worst happen and lightning strike on or about the mast/tower, you offer the electricity a shorter path to &quot;earth&quot; and reduce the possibility of it entering the shack through your feed line.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;grounding transceiver/equipment (inside shack, RF leakage prevention)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Radio equipment may leak RF or high currents. Grounding the case (usually with a ground screw conveniently provided thereupon) will reduce the risk of operator injury and equipment damage.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;antenna ground plane (on/under antenna)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The antenna system requires a &quot;ground plane&quot; for the radio wave to form. With dipoles, one half of the antenna is your ground. In verticals, something below must provide ground to complete the RF wave. This is usually achieved with radials, either attached to the base of the vertical, or buried below a ground mounted antenna. The presence of a metal mast/tower (which is lightning grounded) may contribute/interfere with the ground plane but it is not considered the antenna ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While all three of these &quot;ground systems&quot; may end up connected directly or indirectly to &quot;earth&quot; (grounding rod, water pipe, etc) — they are actually all different.&lt;/p&gt;&#xA;" OwnerUserId="152" LastEditorUserId="507" LastEditDate="2013-12-24T20:18:29.387" LastActivityDate="2013-12-24T20:18:29.387" CommentCount="1" CommunityOwnedDate="2013-10-28T14:18:17.027" ContentLicense="CC BY-SA 3.0" />
  <row Id="404" PostTypeId="2" ParentId="402" CreationDate="2013-10-28T14:44:52.030" Score="2" Body="&lt;p&gt;There are two traditional meanings of an electrical &quot;ground&quot;. In DC systems, we often refer to the return conductor (the negative lead) as &quot;ground&quot;. You won't encounter that meaning very often in amateur radio, but when dealing with vehicles you need to ensure that you have a good &quot;ground&quot; connection from the battery to the negative lead at the radio, not for RF or safety reasons, but to prevent any voltage loss along the power supply. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The more well known use of a ground is a safety ground in an AC system. The purpose here is to have a conductor that has no voltage and ideally no current on it which is connected to the chassis of a device. That way, if there is a fault which puts a voltage on the chassis, it will trip a fuse or breaker, preventing injury to the user.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other advantage of a conductive chassis is RF shielding. In this case we don't actually rely on the fact that the chassis is grounded, as long as it encloses all the circuitry with a minimum size of holes (for connectors or buttons), it will significantly dampen any RF going in or out. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, when we're talking about antennas, the ground acts in a completely different manner, &quot;reflecting&quot; signals and enabling certain modes of propagation. Vertical antennas can often be modeled as if there is a &quot;&lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow&quot;&gt;mirror image&lt;/a&gt;&quot; underground, creating a dipole antenna with certain ideal characteristics. If the ground is missing or not ideal (such as a metal vehicle or roof instead of a true ground) then the properties of that antenna will be less than the perfect dipole model. Once again, the ground is acting as the &quot;return&quot; - current flows one way in the antenna and opposite through the ground, keeping the currents equal at every instant. Sometimes, especially in the case of HF verticals, we will &quot;help&quot; the ground by using radials - wires just slightly underground, cut to be a quarter wavelength on the desired frequency. This is all about making the actual ground more like the ideal model.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="218" LastEditDate="2013-12-26T23:33:05.923" LastActivityDate="2013-12-26T23:33:05.923" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="405" PostTypeId="2" ParentId="340" CreationDate="2013-10-28T15:19:45.647" Score="3" Body="&lt;p&gt;In the United States, &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.5.157.1&quot; rel=&quot;nofollow&quot;&gt;FCC Part 97 Subpart E&lt;/a&gt; provides for essentially unlimited operations in the case of emergency communications. For example, amateurs may transmit on commercial or government channels if they are experiencing an emergency:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;No provision of these rules prevents the use by an amateur station in&#xA;  distress of any means at its disposal to attract attention, make known&#xA;  its condition and location, and obtain assistance.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If &quot;normal communication systems are not available&quot;, this expands to essentially any radio transmission that concerns immediate safety of human life and property:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;No provision of these rules prevents the use by an amateur station of&#xA;  any means of radiocommunication at its disposal to provide essential&#xA;  communication needs in connection with the immediate safety of human&#xA;  life and immediate protection of property when normal communication&#xA;  systems are not available.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you read further on in that subpart, there are a variety of other situations where amateurs are also able to use additional operating privileges, though in more limited ways (e.g. the Alaska-Private Fixed Service, or the Radio Amateur Civil Emergency Service).&lt;/p&gt;&#xA;" OwnerUserId="39" LastActivityDate="2013-10-28T15:19:45.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="406" PostTypeId="1" AcceptedAnswerId="407" CreationDate="2013-10-28T16:04:55.950" Score="5" ViewCount="1304" Body="&lt;p&gt;I have a 5W HT that only kicks out about 1W by the time it hits my antenna (which I understand is the norm). How do I go about calculating power loss in various equipment?&lt;/p&gt;&#xA;" OwnerUserId="128" LastActivityDate="2013-10-28T18:39:08.763" Title="How to calculate power loss between radio and antenna" Tags="&lt;antenna&gt;&lt;rf-power&gt;&lt;math&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="407" PostTypeId="2" ParentId="406" CreationDate="2013-10-28T17:08:26.357" Score="4" Body="&lt;p&gt;There are a few possibilities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First of all, in larger assemblies (mostly important in repeater design) each component will have a parameter called insertion loss. This is the loss, in dB, through that componenet - the loss caused by inserting that component in your feed line. Filters have insertion loss, as do duplexers, and even inline wattmeters and adapters, although the last two should be pretty low. Typically this is about 0.5 dB for each filter or other component, at least in the installations I've seen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then you need to add in loss due to feedline. Different types of feed line have different losses at different frequencies. For example, to get the loss you've described (5W to 1W), and assuming a UHF HT in the 440MHz band, and 50 feet of RG-58 coax (a common small diameter coax) equates to about 5.6dB. This is a parameter that you would look up in a table or a graph from the manufacturer of the coax you're using. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also have some loss at the antenna itself. Especially &quot;rubber ducky&quot; antennas, which are electrically shorter than a true quarter wave antenna and compensated with loading coils, will have a certain amount of loss, also computed in dB. This basically accounts for the reactive and resistive losses in the antenna, decreasing the actual emitted power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, to calculate your actual radiated power, you can simply add up all these values. Every 3dB equates to cutting your signal in half, and 10dB equates to one tenth of your original power getting out. You would compute the actual power by multiplying your transmitter's power by $10^{(-\mathrm{loss~}(\mathrm{in~dB})/10)}$&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="22" LastEditDate="2013-10-28T18:39:08.763" LastActivityDate="2013-10-28T18:39:08.763" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="408" PostTypeId="1" CreationDate="2013-10-28T18:45:45.707" Score="6" ViewCount="814" Body="&lt;p&gt;The fan in the Kenwood D710 mobile radio is turning on on every transmission, including the periodic APRS beacons. This happens even when there is no actual need for spinning it, and is very annoying in a quiet shack (as opposed to under the car seat).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to disable the fan or make it temperature dependent? Alternatively a mod / description for how to replace it with a quieter one, suitable for a not-so-savvy operator?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;I am aware that any modification would void the device warranty.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="89" LastEditorUserId="13" LastEditDate="2013-10-28T20:57:19.370" LastActivityDate="2013-10-30T00:31:48.083" Title="Kenwood D710: loud fan noise when used in the shack" Tags="&lt;modification&gt;&lt;mobile&gt;&lt;kenwood&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="409" PostTypeId="1" CreationDate="2013-10-28T21:54:19.113" Score="8" ViewCount="10507" Body="&lt;p&gt;I have a Baofeng UV-82 dual-band (2m/70cm) HT with an SMA male connector for the stock &quot;rubber-ducky&quot; antenna. I would like to use it in my vehicle. I would like a high-quality magnetic mount dual-band antenna for the roof of my vehicle (so that I can easily move it between two vehicles). I intend to use the &lt;a href=&quot;http://www.hamradio.com/detail.cfm?pid=H0-011738&quot; rel=&quot;noreferrer&quot;&gt;Wouxoun WXUHF adapter&lt;/a&gt; with the &lt;a href=&quot;http://www.hamradio.com/detail.cfm?pid=H0-009826&quot; rel=&quot;noreferrer&quot;&gt;Tram BR-354 magnetic mount&lt;/a&gt; to connect to the antenna. I am specifically considering the following model and any comparable (or better) models:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hamradio.com/detail.cfm?pid=H0-001570&quot; rel=&quot;noreferrer&quot;&gt;Comet-NCG SBB-5&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;A comparable Diamond-brand antenna (recommendations welcome)&lt;/li&gt;&#xA;&lt;li&gt;Any other comparable/better antenna that would work well&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Will this model perform optimally for my circumstances and equipment? Are there any pitfalls I should be aware of? Are there any better/comparable brands/models I should also look at? Are the adapter and magnetic mount I chose good for this or do you have other recommendations?&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="128" LastEditDate="2013-10-29T21:19:31.950" LastActivityDate="2013-10-29T22:21:44.350" Title="How to improve VHF/UHF Baofeng UV-82 HT reception in vehicle" Tags="&lt;antenna&gt;&lt;ht&gt;&lt;mobile&gt;&lt;vhf&gt;&lt;uhf&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="410" PostTypeId="2" ParentId="409" CreationDate="2013-10-29T00:05:23.330" Score="5" Body="&lt;p&gt;Any reputable mag mount antenna will be a huge gain compared to the rubber ducky. I routinely can hit mid-level repeaters from about 15 miles away with my mag mount setup and 5W. If I'm extremely careful, I can hit the same repeaters from 5 miles away with the rubber ducky antenna, in order to pull that off, I have to hold the HT perfectly straight. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One thing to keep in mind is get a short cable. Measure what your needs are, and maybe get a few more feet, not more. Also, it's usually best to get a small adapter cable, such as &lt;a href=&quot;https://www.amazon.com/dp/B007PPHUO2/ref=as_li_ss_til?tag=httpwwwpearso-20&amp;amp;camp=0&amp;amp;creative=0&amp;amp;linkCode=as4&amp;amp;creativeASIN=B007PPHUO2&amp;amp;adid=1Y8BRWY7PMJYDBF646CX&amp;amp;&quot; rel=&quot;noreferrer&quot;&gt;this one&lt;/a&gt;. And good luck!&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-29T00:05:23.330" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="411" PostTypeId="2" ParentId="409" CreationDate="2013-10-29T05:05:44.720" Score="3" Body="&lt;p&gt;A &lt;a href=&quot;http://www.gigaparts.com/Product-Lines/Magnet-Mounts/MFJ-332S.html&quot; rel=&quot;nofollow&quot;&gt;magnetic mount antenna&lt;/a&gt;, or a permanent antenna mount (like a roof rack or trunk lip mount) will definitely help you out.  The point is to get the antenna out of the car!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a pinch, consider &lt;a href=&quot;http://www.gigaparts.com/Product-Lines/Window-License-Plate/MFJ-310S.html&quot; rel=&quot;nofollow&quot;&gt;this window-clip mount&lt;/a&gt; that you attach your hand-held antenna directly to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Actually, just putting it near the windshield will help at least a little bit.]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I am in no way shape or form recommending gigaparts or MFJ as better than other options; they're both excellent but so are most of their alternatives.  They were just who I linked to at the moment)&lt;/p&gt;&#xA;" OwnerUserId="661" LastEditorUserId="89" LastEditDate="2013-10-29T11:29:14.943" LastActivityDate="2013-10-29T11:29:14.943" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="412" PostTypeId="1" AcceptedAnswerId="420" CreationDate="2013-10-29T05:52:52.053" Score="13" ViewCount="1127" Body="&lt;p&gt;There's a blank carrier on a 433 MHz FM voice frequency here. How should we go on about finding the transmitter's location? Practical procedure? Could be somewhere downtown.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="13" LastEditDate="2013-10-29T13:06:15.547" LastActivityDate="2014-04-03T17:19:12.697" Title="Direction finding: How to find a stuck FM transmitter on 70cm?" Tags="&lt;uhf&gt;&lt;fox-hunt&gt;&lt;direction-finding&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="413" PostTypeId="1" AcceptedAnswerId="1039" CreationDate="2013-10-29T06:07:42.547" Score="1" ViewCount="1262" Body="&lt;p&gt;I have a Kenwood TS-590S with a VGS-1 voice guide/storage module, which I use in multi/multi contesting operations for voice keying (calling CQ). There's one drawback - it seems to only transmit recorded voice if:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I press PTT while the voice keyer is playing audio. I need to press PTT through the whole transmission: PTT down, press the voice keyer CH1 playback button, wait for it to speak out, release PTT. Not very practical for automated CQ (the keyer does have automatic retransmission every N seconds).&lt;/li&gt;&#xA;&lt;li&gt;VOX is enabled. We have some audio QRM in the contest operation room (small room, 4 stations), and my VOX sometimes activates when a fellow operator catches a &quot;rare one&quot; on another band and starts yelling in excitement, so I'd like to disable VOX.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Is there a way to set it up to drive PTT for the duration of the playback?&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="76" LastEditDate="2016-10-29T18:35:45.267" LastActivityDate="2016-10-29T18:35:45.267" Title="Kenwood TS-590S VGS-1: Voice keyer does not transmit unless VOX is enabled" Tags="&lt;kenwood&gt;&lt;equipment-operation&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="414" PostTypeId="1" AcceptedAnswerId="424" CreationDate="2013-10-29T06:21:25.707" Score="6" ViewCount="626" Body="&lt;p&gt;The FM broadcast radio, factory installed in my car and usually tuned to 88.6 MHz, gets some interference from the 5W APRS transmitter on 144.800 MHz. It sounds like if the sensitivity of the broadcast FM receiver would go down a bit temporarily: more static FM noise is heard during the APRS &quot;brraaap&quot;. The effect is more pronounced when I'm far away from my favourite station's transmitter and the signal is already weak. When I'm in town, it's barely noticeable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The APRS transmitter has a properly mounted antenna (hole-through-roof, 1/4 wave vertical). The broadcast radio of the Volvo V70 does not have visible external antennas - there's one painted on the left trunk window, and apparently a second one embedded within the back right light assembly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What can I do to fix this?&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="6496" LastEditDate="2016-04-20T17:58:37.097" LastActivityDate="2016-04-20T17:58:37.097" Title="FM radio in car gets interference from APRS beacon" Tags="&lt;mobile&gt;&lt;vhf&gt;&lt;rfi&gt;&lt;beacon&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="415" PostTypeId="5" CreationDate="2013-10-29T06:34:15.990" Score="0" Body="&lt;p&gt;Kenwood manufactures amateur radio equipment:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;TS series HF radios (TS-440, TS-590, TS-990...)&lt;/li&gt;&#xA;&lt;li&gt;TH series hand-held radios (TH-D7, TH-D72...)&lt;/li&gt;&#xA;&lt;li&gt;TM series mobile radios (TM-D700, TM-D710...)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Questions concerning Kenwood rigs should have the kenwood tag.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-29T14:20:08.797" LastActivityDate="2013-10-29T14:20:08.797" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="416" PostTypeId="4" CreationDate="2013-10-29T06:34:15.990" Score="0" Body="Kenwood is a manufacturer of amateur radio equipment." OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-29T14:20:18.563" LastActivityDate="2013-10-29T14:20:18.563" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="417" PostTypeId="5" CreationDate="2013-10-29T06:35:49.513" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-10-29T06:35:49.513" LastActivityDate="2013-10-29T06:35:49.513" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="418" PostTypeId="4" CreationDate="2013-10-29T06:35:49.513" Score="0" Body="Mobile operations (car, motorcycle, boat or other vehicle)" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-29T14:20:29.907" LastActivityDate="2013-10-29T14:20:29.907" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="419" PostTypeId="2" ParentId="121" CreationDate="2013-10-29T07:25:20.250" Score="3" Body="&lt;p&gt;Lithium batteries, either Lithium-Ion (LiIon) or Lithium-Polymer (LiPo) batteries currently have the most capacity for the weight. LiPo batteries are very popular in radio controlled cars and RC aircraft - their power-weight ratio is practical for flying things, and they can give out enough current for brushless DC motors, so they should be good for backpacking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The downside is that they can explode if improperly charged or physically damaged, and when they do, they can easily start a fire. RC folks sometimes charge LiPo batteries out in a balcony, and/or in some sort of container which will let out the blast but contain the fire. A purpose-built LiPo charger which charges each cell individually is a must - they're available in RC stores.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Seach for &lt;a href=&quot;http://www.youtube.com/watch?v=EseOhC8n7ro&quot; rel=&quot;nofollow&quot;&gt;&quot;lipo explosion&quot; on Youtube&lt;/a&gt; for videos. You don't want that happening in your backpack or ham shack, there's a lot of fire involved.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-29T10:11:52.053" LastActivityDate="2013-10-29T10:11:52.053" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="420" PostTypeId="2" ParentId="412" CreationDate="2013-10-29T13:06:05.297" Score="12" Body="&lt;p&gt;The best way is to get a high gain antenna, and figure out what direction it's coming from. Do this from 2-3 points. Take a map, and draw lines from each of the point of origins from the direction you heard the signal the strongest. That should give you at least an idea of where the signal is coming from.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have a rough idea, the next step is to go to said area, and repeat the process. You should be able to get a better idea of where the signal is coming from. Eventually, you're going to be unable to pick up the transmitter, as you will get high signal anywhere you point your antenna. The next step would require an attenuator, or even just using a rubber duck antenna and using your body as a shield. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;FYI, this is essentially the same thing as a fox hunt, except for a less cooperative subject, and you don't have to find the transmitter exactly.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-29T13:06:05.297" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="421" PostTypeId="1" CreationDate="2013-10-29T14:34:50.050" Score="11" ViewCount="367" Body="&lt;p&gt;If we could get a few HF stations on Mars, what would the propagation look like? Thought shamelessly copied from &lt;a href=&quot;http://hamgear.wordpress.com/2013/05/01/propagation-on-mars/#comment-3372&quot; rel=&quot;noreferrer&quot;&gt;this blog&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="76" LastEditDate="2019-06-30T02:47:22.587" LastActivityDate="2019-07-07T14:44:21.373" Title="What would propagation look like on Mars?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="422" PostTypeId="2" ParentId="409" CreationDate="2013-10-29T14:43:48.827" Score="2" Body="&lt;p&gt;I currently use an MFJ mag mount, but as previously suggested, any antenna that goes on the outside of the car is better than one on the inside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're not shy about putting holes in your car, an antenna physically attached to the car may provide an improved RF ground plane for a little more gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using an SMA adapter cable for your radio rather than an SMA adapter will reduce the strain on the HT connector and keep it from breaking &lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2013-10-29T14:43:48.827" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="423" PostTypeId="2" ParentId="421" CreationDate="2013-10-29T16:52:34.153" Score="8" Body="&lt;p&gt;According to &lt;a href=&quot;http://descanso.jpl.nasa.gov/Propagation/mars/MarsPub_sec2.pdf&quot; rel=&quot;noreferrer&quot;&gt;NASA TP 2000 209756&lt;/a&gt;, particularly section 2.5, it shouldn't be &lt;em&gt;too&lt;/em&gt; different from similar propagation on Earth &lt;em&gt;during daytime,&lt;/em&gt; except we'd need significantly lower frequencies than we are used to for similar results. According to that report,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Martian dayside ionosphere at solar maximum has a peak density similar to that of the Earth nightside ionosphere at solar minimum. (...) Even though the Martian ionospheric peak density and TEC [total vertical electron content] are lower than in the Earth’s ionosphere, we can still use them for ionospheric communication.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;According to table 2-2, &lt;em&gt;Usable Critical Frequency and Hop Distance for Various Launch Angles&lt;/em&gt;, and assuming I'm reading the data correctly, around 4 MHz would be about the upper bound for near-range communications (NVIS to almost-NVIS), and by the time you get a take-off angle of 60° this climbs to a whopping 8 MHz and a single hop distance of 400-450 km. (The table says 433 km.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to penetrate the ionosphere, section 2.6 &lt;em&gt;Summary and Recommendations&lt;/em&gt; says to use a frequency above 450 MHz. Nighttime communications beyond those offered by line of sight are tricky:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;[T]he nightside ionosphere has some limitations for global communication because of its low usable frequency and very unstable conditions.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The report specifies a critical frequency of 0.6 MHz during solar minimum night time. That isn't impossible to work with (it was at one time considered &quot;high frequency&quot;) but it takes a lot more than a &quot;rubber duck&quot; antenna on a handheld radio to produce useful results and bandwidth is highly limited, so nighttime ionospheric communications on Mars would be extremely limited at best. (You'd probably buffer up data for transmission after sunrise and focus your efforts on a higher frequency, near the boundary between what we consider MF and HF around 2-4 MHz in order to achieve reasonable antenna sizes as well as reliable communications even during solar minima.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can manage a take-off angle in the 75° range, the maximum usable frequency climbs to a whopping 15.5 MHz, says table 2-2. At those frequencies, it should be possible to pack quite a bit of data into a transmission.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-10-29T17:06:44.753" LastActivityDate="2013-10-29T17:06:44.753" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="424" PostTypeId="2" ParentId="414" CreationDate="2013-10-29T19:32:50.153" Score="4" Body="&lt;p&gt;There are a few ways the noise could be transmitted to the car radio, and the way to fix it will depend on how it's getting in there.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Antenna&lt;/li&gt;&#xA;&lt;li&gt;Power or ground&lt;/li&gt;&#xA;&lt;li&gt;Other EMI&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;If the transmission is swamping your radio's receiver, then it's not blocking the higher frequencies strongly enough. It might be worth looking at the output of the transmitter to see if it's broadcasting noise on other bands within the radio's region, and to take another transmitter that's not connected to the vehicle's power or ground and keying it up nearby.  If it disturbs the radio, then it's likely that the radio may need to be replaced.  Other options would be a different antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the transmission is coming through the power or ground, you might be able to add additional filtering and regulation at the radio.  This can be tested by attaching a dummy load to the transmitter while it's transmitting.  If the noise is present, it's likely EMI or power conduction.  Again, keying a separate radio outside the vehicle may narrow it down. Alternately, connect the APRS transmitter to a battery power supply and disconnect it from the car's power supply. It'll still be grounded to the car,  but it should narrow things down a little more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EMI is a tougher one without a spectrum analyzer.  If the transmitter and radio are far apart, though, and each have their own metal case, it shouldn't be the cause.  I'd look for antenna and power problems first.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-29T19:32:50.153" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="425" PostTypeId="1" CreationDate="2013-10-29T20:48:47.103" Score="11" ViewCount="2598" Body="&lt;p&gt;Mineral content in the ground varies from one place to another. I've visited places where the ground &amp;amp; waters were an orange-red shade from the high iron content; not good for trees either. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?ehamsid=s968k63iro1e50olsmkn1m3uh0&amp;amp;topic=83865.msg605608#msg605608&quot; rel=&quot;nofollow noreferrer&quot;&gt;This post&lt;/a&gt; on eHam.net, seems to indicate there may be propagation issues with high iron-ore content in the soil/environs&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The iron content of the under lying iron deposits were not conducive for good communications. Many dead spots.  The local iron deposits are on the high ground. I experienced  hf and vhf deficiencies. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The same was echoed &lt;a href=&quot;http://www.tompkins-co.org/pubinfo/pscs/geographic.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;elsewhere&lt;/a&gt; (pdf) about RF propagation in the Adirondack Upland, and also in the context of WWII Market Garden, and the WWII Philippines campaigns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, say in the future I want to operate from a location where the ground is rich in iron ore. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Does iron ore in the ground affect my signal?&lt;/li&gt;&#xA;&lt;li&gt;Assuming a fixed location, what can I do to mitigate the effect?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2019-04-13T20:30:41.413" LastActivityDate="2019-12-16T23:57:48.173" Title="Does iron ore in the ground affect my signal?" Tags="&lt;propagation&gt;&lt;earth&gt;" AnswerCount="6" CommentCount="4" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="426" PostTypeId="2" ParentId="425" CreationDate="2013-10-29T21:12:46.867" Score="12" Body="&lt;p&gt;If anything, living in an area with high metal deposits near to the ground will improve your conditions by improving the conductivity of your ground. That said, unless it's very near to the surface and high concentration, I doubt you'd notice any difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that when we model the ground as an ideal ground plane, anything underground has no impact on the signal at all - it is shielded. Of course our real ground isn't perfect, but metal deposits can only improve that, if they have any effect at all.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-29T21:12:46.867" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="427" PostTypeId="2" ParentId="337" CreationDate="2013-10-29T22:03:36.230" Score="9" Body="&lt;p&gt;This is called the &quot;FM capture effect&quot; and is mostly a characteristic of the demodulator design. Demodulators with a strong capture effect detect the zero crossings of the signal. The zero crossings are only slightly affected by mixing two signals until they are nearly equal amplitude. The steepness of the waveform at zero crossing means that the stronger signal dominates. It takes a larger interfering signal to change the slope enough that the zero crossing moves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM demodulators usually include an amplitude limiter to increase this effect. Unless the noise happens near the zero crossing in the signal, it is ignored. Effectively, the limiter increases the steepness of the zero crossing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When two FM signals of a similar strength mix, we get the distinctive &quot;doubling&quot; sound heard on repeaters. This distorted signal is caused by the non-linear mixing from the limiter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In an AM envelope detector, the detector is very sensitive to the mixed signals. Also, the signals are linearly combined, so our ears can often distinguish the two signals.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-10-29T22:03:36.230" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="428" PostTypeId="1" AcceptedAnswerId="429" CreationDate="2013-10-29T22:05:59.090" Score="12" ViewCount="1382" Body="&lt;p&gt;Recently, I have begun experimenting with JT-65A, mostly on 20 meters. I usually run about 5 watts with that mode, since I know that JT-65 is a weak-signal mode. Is that still too much power? What is generally considered excessive power on JT-65?&lt;/p&gt;&#xA;" OwnerUserId="125" LastEditorUserId="29" LastEditDate="2014-04-30T21:37:45.440" LastActivityDate="2017-06-25T20:12:38.523" Title="What is generally considered &quot;too much&quot; power for JT-65 on HF?" Tags="&lt;hf&gt;&lt;digital-modes&gt;&lt;jt65&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="429" PostTypeId="2" ParentId="428" CreationDate="2013-10-29T22:14:58.883" Score="7" Body="&lt;p&gt;5 watts is probably what most JT-65 purists will tell you to use, but in practice, I tend to aim for 20 watts. That gives you a good 6dB boost (every doubling of power is equal to +3dB) which is actually meaningful in JT-65. Any more than that, and you'll start finding certain problems. Note that the same is true for the WSPR family of protocols.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, that since everyone else is using less power than you are, you'll have many cases of people hearing you, but you can't hear them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That in turn means that you run the risk of interfering with a conversation that you can't even see, especially if you're running 100W and they're each at 5 or 20.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, many transceivers will cause distortions in the JT-65 waveform when run at above a quarter to a half of their maximum power. Transceivers are meant to work with analog data, not the sharp frequency transitions of the digital signal. Overdriving them can cause clipping, which will cause you to actually waste power and may even make your transmission unreadable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to answer the question, the standard maximum is either 20 or 30 watts - and there's really no point in exceeding that. Many people win awards on the mode at 5 watts! Most transceivers will distort your waveform above a certain limit, and there's no point in risking it for another 2 or 3 dB.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-29T22:14:58.883" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="430" PostTypeId="2" ParentId="409" CreationDate="2013-10-29T22:21:44.350" Score="1" Body="&lt;p&gt;Mag mounts really aren't all they're cracked up to be. You'll see some improvement just because the antenna is outside of the car, but a through-roof mount gives you a good ground connection and no risk of tossing your antenna into another car while on the highway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know the common argument. Yeah, you need to drill a hole, but that's in many ways less damaging than using a mag mount which can scrape your paint every time it moves. At least it's easy to plug the hole if you ever need to sell the car.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-29T22:21:44.350" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="431" PostTypeId="2" ParentId="278" CreationDate="2013-10-29T22:34:27.987" Score="0" Body="&lt;p&gt;In a pure sine wave $V_{RMS} \times 1.414$ will give you peak. $V_{Peak} \times .707$ will give you RMS.&lt;/p&gt;&#xA;" OwnerUserId="221" LastEditorUserId="87" LastEditDate="2013-10-29T23:18:26.350" LastActivityDate="2013-10-29T23:18:26.350" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="432" PostTypeId="2" ParentId="345" CreationDate="2013-10-29T22:43:42.390" Score="17" Body="&lt;p&gt;73 is, as Amber said, Phillips code for best regards or my compliments.  I just wanted to add that it's redundant to say 73s, which amounts to Best Regardses or My Complimentses.  This puts one in mind of Smeagol, talking to Hobbitses.&lt;/p&gt;&#xA;" OwnerUserId="68" LastActivityDate="2013-10-29T22:43:42.390" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="433" PostTypeId="2" ParentId="256" CreationDate="2013-10-29T22:54:50.887" Score="1" Body="&lt;p&gt;The easiest and most forgiving phase system for 2 element arrays is the &lt;a href=&quot;http://home.earthlink.net/~w6rmk/antenna/phased/christman.htm&quot; rel=&quot;nofollow&quot;&gt;Christman method&lt;/a&gt;.&#xA;Based on 1/4wl spacing, the phase lines are cut to 84 degrees and the lag line is cut to 71 degrees. &#xA;This system will work from 160 to 2 meters. And easy to make reversible.&lt;/p&gt;&#xA;" OwnerUserId="223" LastEditorUserId="218" LastEditDate="2013-12-15T21:45:32.783" LastActivityDate="2013-12-15T21:45:32.783" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="435" PostTypeId="1" CreationDate="2013-10-29T23:43:24.777" Score="6" ViewCount="253" Body="&lt;p&gt;I am planning to get a Yaesu FT2900R 2 meter rig for my 2001 Honda Accord.  With my 5w FT60, I wasn't able to reach repeaters that were any more than 10 miles distant (I live among mountains.)  How far can I reasonably expect to get with 75 watts and a mag mount antenna?  &lt;/p&gt;&#xA;" OwnerUserId="228" LastActivityDate="2013-10-29T23:51:52.123" Title="75 watts and a mag mount antenna" Tags="&lt;antenna&gt;&lt;mobile&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="436" PostTypeId="2" ParentId="95" CreationDate="2013-10-29T23:44:06.703" Score="13" Body="&lt;p&gt;I'm going to assume we are discussing &lt;em&gt;ideal&lt;/em&gt;, &lt;em&gt;resonant&lt;/em&gt; dipoles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider what's happening inside the dipole. Say you are transmitting a carrier. Say at one point in this carrier's cycle, the voltage is shoving all the charge carriers to the left.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What makes the dipole &lt;em&gt;resonant&lt;/em&gt; is this: those charge carriers get pushed down the wire. As the approach the end, they get compressed because they have nowhere to go. This over-abundance of charge carriers means a high voltage at the end of the wire. They can't shoot out the end of the wire, so that wave of force bounces back. In a center-fed half-wavelength dipole, the wave reaches the feedpoint after having bounced off the end at precisely when the transmitter has changed phase 180 degrees, and is now trying to push the charge carriers in the other direction. Thus, the natural bouncing back and forth action in the antenna is in phase with the transmitter, helping it to move more current, with less voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This explains two things on the FCC test:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The voltage distribution in a half-wave dipole is highest at the ends and lowest in the middle.&lt;/li&gt;&#xA;&lt;li&gt;The current distribution is highest in the middle and lowest at the ends.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;We know that our center-fed half-wavelength dipole has a feedpoint impedance of 75Ω. That means at the feedpoint, for every ampere, there are 75 volts (think of Ohm's law). This is true both of RMS measurements, and any instantaneous measurement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This last bit, that the instantaneous current or voltage at any time also have a ratio of 75V to 1A (that is, 75Ω), is just another way of saying that the feedpoint impedance is purely resistive. Our ideal dipole doesn't actually have any resistance: this resistance is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Radiation_resistance&quot; rel=&quot;nofollow noreferrer&quot;&gt;radiation resistance&lt;/a&gt; of the antenna. The antenna creates the illusion of a pure resistance from a tuned system of reactive components which, &lt;em&gt;at resonance&lt;/em&gt;, cancel each other to leave only a resistive impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;But what if the feedpoint isn't in the center?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This actually doesn't change the resonant frequency: it just changes the impedance, which remains resistive. Consider what happens if we move the feedpoint just a little closer to one end: we also get farther from the other end. We know that in the center of a half-wave dipole, current is at a maximum. This makes sense, because after the charge carriers pass the center, they are now closer to the other end, building up voltage there, which serves to slow them down. So, if we aren't in the center, we get less help with current, but we get more help with voltage. That is, impedance goes up. We can couple energy just as efficiently into this antenna, provided we can match its impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The common choice of the center of a half-wave dipole is usually selected because it's close enough to 50Ω coax that losses are acceptable without any additional matching. Wikipedia gives &lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna#Half-wave_dipole&quot; rel=&quot;nofollow noreferrer&quot;&gt;the math to calculate the impedance at an arbitrary point&lt;/a&gt; for a half-wave dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ R_r = \frac{75\ \Omega}{\sin^2(2 x \pi / \lambda)} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$x$ is the distance from the end of the dipole, and&lt;/li&gt;&#xA;&lt;li&gt;$\lambda$ is the wavelength (twice the length of the dipole).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For example, say we have a dipole for $\lambda = 100\:\mathrm m$. Fed at the center, $x = 25$ because this half-wave dipole is 50m long, so the middle is half of that, 25m from the end:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ R_r&#xA;= \frac{75\ \Omega}{\sin^2(2 \cdot 25 \cdot \pi / 100)}&#xA;= 75\:\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fed 1/3rd of the way from the end, $x=50/3=16.67$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ R_r&#xA;= \frac{75\ \Omega}{\sin^2(2 \cdot 16.67 \cdot \pi / 100)}&#xA;= 100\:\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further reading:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.radio-electronics.com/info/antennas/dipole/feed-impedance.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dipole antenna feed impedance, radio-electronics.com&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.amateurradio.com/200-ohm-feed-point-off-centre-fed-dipole/&quot; rel=&quot;nofollow noreferrer&quot;&gt;200 Ohm Feed Point Off-centre Fed Dipole, amateurradio.com&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-05-24T13:33:11.053" LastActivityDate="2017-05-24T13:33:11.053" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="437" PostTypeId="2" ParentId="435" CreationDate="2013-10-29T23:48:50.350" Score="4" Body="&lt;p&gt;Determining radio range is very difficult if not impossible to do.  There are loads of factors that will contribute to it and it's not something that can be easily quantified or predicted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have mountains in the way blocking signals, no amount of power will help.  That said, if the mountains, cliffs or ledges are arranged such that you might actually get some reflection, more power could help by increasing the amount of reflected signal that makes it to a repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Certainly, if you are going from an HT with a rubber duck antenna, going to an external and larger antenna is the most effective step.  Adding power can't hurt though either.&lt;/p&gt;&#xA;" OwnerUserId="47" LastActivityDate="2013-10-29T23:48:50.350" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="438" PostTypeId="2" ParentId="435" CreationDate="2013-10-29T23:51:52.123" Score="6" Body="&lt;p&gt;It's hard to make guesses about this sort of thing because there are too many different factors. The mag mount antenna certainly is better than your FT60 antenna, and the 75 watts is certainly better than the 5 watts - but how much is subject to a number of factors. To get a good guess you can use that doubling the range requires four times the power (which is equivalent to a 6dB gain), and accounting for your increase in power (15 times power = about 4x range) and the better antenna (depends on the antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are quite a few other factors involved. For example, the 75 watt radio probably also has a better receiver than the HT, and may be able to discern weaker signals - on the other hand, while the increased power may get your signal out much further, it has no effect at all on you being able to receive signals. The only factor that improves both TX and RX is your antenna gain.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-29T23:51:52.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="439" PostTypeId="2" ParentId="413" CreationDate="2013-10-30T00:17:39.857" Score="1" Body="&lt;p&gt;To be clear, there are two methods to transmit the recorded message.  One is to key the transceiver, then push the playback button.  The other is to turn on VOX and press the playback button.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple method would be to place a button in line with the microphone, and turn on VOX.  This would effectively disable the VOX from the contest room noise, and allow you to merely press the appropriate memory key to transmit the recorded message. If you set up the button to be activated by the PTT lever, then the microphone will still operate normally when you press the PTT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would all be built into the microphone, and you could either have two different microphones (one for normal VOX usage, and one as described above that delegates the VOX to the recordings) or you could install another switch that enables or disables the microphone disconnect button, so a single microphone can perform as normal, or, when desired, as above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other modifications might involve modifications to the radio itself, but it seems that a simple microphone mod like this would be easier and safer.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-30T00:17:39.857" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="440" PostTypeId="2" ParentId="408" CreationDate="2013-10-30T00:31:48.083" Score="1" Body="&lt;p&gt;As long as the fan is a 12V fan you can use one of a number of solutions computer building enthusiasts use to control their case fans.  One which might work for you is the following device:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.frozencpu.com/products/5301/tmp-33/NoiseMagic_ThemoControl_NMT-2_Solder_Version.html?tl=g47c17&quot; rel=&quot;nofollow&quot;&gt;http://www.frozencpu.com/products/5301/tmp-33/NoiseMagic_ThemoControl_NMT-2_Solder_Version.html?tl=g47c17&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This takes a 12V input, controls a 12V fan, and can be attached with the temperature sensor on the outflow of the case - whether near the fan or not.  If connected to your transceiver it will be off and on as normal, but unless the temperature goes high it will reduce the fan speed.  This means that it should be quiet except when the transmitter actually gets hot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are interested in electronics, you can build one from a project like this &lt;a href=&quot;http://alan-parekh.com/projects/pwm-fan-controller/&quot; rel=&quot;nofollow&quot;&gt;PWM fan controller&lt;/a&gt; which is also temperature controlled. This project is more general, and can control fans that run at higher and lower voltages as well with the appropriate transistor (Q1). That site sells the parts required, and it isn't a particularly difficult build.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can provide the dimensions of the fan and other parameters (voltage, current, model number) then there may be other suggestions that would work.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-30T00:31:48.083" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="441" PostTypeId="1" AcceptedAnswerId="510" CreationDate="2013-10-30T01:44:03.327" Score="0" ViewCount="1418" Body="&lt;p&gt;After clearing channels (menu option #28) to free them up for use, I have found that they become completely unusable for future frequencies. Switching back from VFO to channel mode and trying to go to those channels merely skips them and goes to the next one available. Clearing them and attempting to set them to a frequency just makes the channels unusable. Am I not supposed to 'clear' the channels first or is this a bug that others are experiencing?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had been following &lt;a href=&quot;http://www.miklor.com/COM/UV_ProgMem.php&quot; rel=&quot;nofollow&quot;&gt;these instructions&lt;/a&gt; to 'clear' the channels, but it seems to have the effect of deleting the channels.&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="128" LastEditDate="2013-10-30T03:12:06.897" LastActivityDate="2013-11-01T14:14:03.450" Title="Baofeng UV-82 Dual-Band (2m/70cm) HT Channel Clear Error" Tags="&lt;ht&gt;&lt;baofeng&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="442" PostTypeId="2" ParentId="428" CreationDate="2013-10-30T03:01:21.023" Score="5" Body="&lt;p&gt;As you stated, JT-65 is a &lt;em&gt;weak signal&lt;/em&gt; mode.  This should not be confused with a &lt;em&gt;low power&lt;/em&gt; mode.  Depending on your antenna and location, the amount of power you need to conduct a successful contact may vary, just as in any other mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good guideline would be to start at the lowest power setting you can, and if you're not able to work the stations you want (and can hear!), gradually increase power.  If possible, use some of the online spotting networks (&lt;a href=&quot;http://jt65.w6cqz.org/freceptions.html&quot; rel=&quot;noreferrer&quot; title=&quot;W6CQZ JT65 RB Network&quot;&gt;jt65.w6cqz.org&lt;/a&gt; or &lt;a href=&quot;http://hamspots.net&quot; rel=&quot;noreferrer&quot; title=&quot;HamSpots.net by VK3AMA&quot;&gt;hamspots.net&lt;/a&gt;) to see what signal reports you are getting.  If you are being received anywhere between -10 dB and -20 dB, you've nailed it!  If you are consistently getting numbers between -10 dB and 0 dB, you can reduce power.  If you aren't being heard or you get numbers below -20 dB, try increasing power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've worked stations using milliwatts who were booming in for me, and I've worked at least one station who claimed to be running 1 kilowatt.  The kilowatt guy got a -10 dB report from me, so I guess he wasn't using too much power!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck and 73!&lt;/p&gt;&#xA;" OwnerUserId="236" LastActivityDate="2013-10-30T03:01:21.023" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="443" PostTypeId="1" AcceptedAnswerId="450" CreationDate="2013-10-30T03:18:28.563" Score="9" ViewCount="2391" Body="&lt;p&gt;Some people believe that mag mount magnets lose their effectiveness over time, eventually causing a dangerous situation as the antenna could rip loose from the vehicle and become a projectile or distraction at an unfortunate time -- e.g. on a highway due to air forces or perhaps at a stoplight under heavy braking.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mitigating these concerns are the fact that the antenna is still attached by coax and that I personally have never seen it mentioned in the news nor have I heard of any traffic laws prohibiting mag mount antennas on a vehicle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Still, with safety in mind, I use the screw in trunk lip mounts.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I keep telling my friends to stay away from the mag mounts or are these supposed dangers merely paranoia and urban legend?&lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2018-04-10T01:40:19.837" Title="Has a vehicle magnetic antenna mount ever caused a road accident?" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;safety&gt;" AnswerCount="4" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="444" PostTypeId="2" ParentId="357" CreationDate="2013-10-30T03:43:46.943" Score="10" Body="&lt;p&gt;tl;dr: It's legal on any VHF or above frequency where phone modes are permitted. It is not allowed on HF or below, nor where phone modes are not allowed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you have described is called &quot;Modulated Continuous Wave&quot; (MCW), as defined in the US amateur radio rules under 47 CFR §97.3(c)(4), and would have the emission designator F2A.  (The usual CW used on HF has emission designator A1A.) In areas regulated by the FCC, it is &lt;em&gt;not&lt;/em&gt; legal on frequencies below 50.1 MHz, between 144.0 and 144.1 MHz, or between 219 and 220 MHz.  It is legal on any other amateur frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MCW is commonly used for automated identification of FM voice repeaters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is worth noting that some software capable of transmitting the many HF digital modes via an SSB transceiver can also generate CW in the same fashion.  When transmitted this way through an SSB transceiver, it is technically emission designator J2A, which is still within the definition of proper CW.  In areas regulated by the FCC, proper CW is legal on any frequency allocated to the amateur service (subject to certain limitations on the 60m band).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sources:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;47 CFR §97.3(c)(1), 47 CFR §97.3(c)(4), 47 CFR §97.3(c)(5), and 47 CFR §97.305(c)&lt;/li&gt;&#xA;&lt;li&gt;Wikipedia: &lt;a href=&quot;http://en.wikipedia.org/wiki/Modulated_continuous_wave&quot;&gt;Modulated Continuous Wave&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Wikipedia: &lt;a href=&quot;http://en.wikipedia.org/wiki/Types_of_radio_emissions&quot;&gt;Types of Radio Emissions&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="236" LastActivityDate="2013-10-30T03:43:46.943" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="445" PostTypeId="2" ParentId="441" CreationDate="2013-10-30T04:09:19.737" Score="0" Body="&lt;p&gt;You don't have to be &quot;on&quot; a channel to set it - hence why clearing a channel removes your ability to &quot;go&quot; to it. When you are setting a channel, you'll input the number of the channel you want to set via the numeric pad, and it will be saved to whatever channel you enter, after which you'll be able to &quot;go&quot; to that channel.&lt;/p&gt;&#xA;" OwnerUserId="22" LastActivityDate="2013-10-30T04:09:19.737" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="446" PostTypeId="2" ParentId="360" CreationDate="2013-10-30T04:16:29.953" Score="0" Body="&lt;p&gt;tl;dr: Line A is not relevant to Alaska.  Line C, however, is, but it is does not affect the Amateur Radio Service.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The surest way to get a clear answer about Lines A and C is likely to use the &lt;a href=&quot;http://wtbwww05.fcc.gov/cgi-bin/scripts/lineac.pl&quot; rel=&quot;nofollow&quot; title=&quot;FCC Line A &amp;amp; C Check&quot;&gt;FCC Line A &amp;amp; C Check utility&lt;/a&gt; to find out based on your latitude and longitude which side you're on. You can also consult the &lt;a href=&quot;http://transition.fcc.gov/oet/info/maps/canline/canline.html&quot; rel=&quot;nofollow&quot; title=&quot;FCC Lines A &amp;amp; C Map&quot;&gt;Line A &amp;amp; C map&lt;/a&gt; to get a quick sense of where the lines run.  If you are in Alaska east of 143 degrees West longitude, you should perform the more detailed check.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, Line C is not mentioned anywhere in the FCC Amateur Radio Rules (47 CFR §97).  It appears to apply predominantly to the General Mobile Radio Service (GMRS) and the Private Land Mobile Radio Services (PLMR).&lt;/p&gt;&#xA;" OwnerUserId="236" LastActivityDate="2013-10-30T04:16:29.953" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="447" PostTypeId="2" ParentId="340" CreationDate="2013-10-30T04:55:06.253" Score="2" Body="&lt;p&gt;&lt;em&gt;This answer applies to the USA and any other areas where the FCC has jurisdiction.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most precise answer to this question is &lt;strong&gt;never&lt;/strong&gt;.  There are a few cases mentioned in other answers, but they lack the fundamental distinction that a properly licensed operator, operating within the privileges of his license, is the &lt;strong&gt;control operator&lt;/strong&gt;.  A person other than the control operator may be supervised by the control operator in operating the equipment, but it is always the control operator who is in charge, and it is the control operator's privileges that may be used.  The control operator is fully responsible for all activities of the station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In cases where a person other than the control operator is at the mic (or on the key, or typing a data message), you must observe the restrictions on &lt;strong&gt;Third Party Messages&lt;/strong&gt;.  Specifically, you may not send a message for someone (to include letting them speak the message themselves) to any country except those &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=about_2&amp;amp;id=amateur#Third%20Party%20Communications&quot; rel=&quot;nofollow&quot; title=&quot;FCC Rules: Third Party Communications&quot;&gt;listed by the FCC&lt;/a&gt; as having the appropriate Third Party arrangements in place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a licensed ham operating at a club or other special event station where someone with a higher license class is acting as control operator, if ham with a lower license is operating outside their own privileges based on the privileges of the control operator, their status is &lt;em&gt;exactly the same&lt;/em&gt; as someone with no license operating under the control operator's supervision.  The control operator must always be responsible, and the Third Party Communication rules still apply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(There is also an exception in case of emergency, but a great many parts within the Code of Federal Regulations -- including 47 CFR 97, the part regulating amateur radio -- have an emergency provision that jettisons most or all of the rules in case of a &lt;em&gt;bona fide&lt;/em&gt; emergency.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Source:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;47 CFR §97.115&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="236" LastActivityDate="2013-10-30T04:55:06.253" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="448" PostTypeId="2" ParentId="213" CreationDate="2013-10-30T05:35:11.730" Score="6" Body="&lt;p&gt;The vast majority of repeaters you are likely to encounter are &lt;strong&gt;open repeaters&lt;/strong&gt; that allow anyone to use them.  Some of the features may be restricted, such as autopatch (connections to a telephone line), but chatting on the repeater is usually open.  If you use a particular repeater frequently, you may want to consider joining an associated club, but you shouldn't see it as an obligation.  In many areas, the repeater operator will be happy just to have the repeater used!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are &lt;strong&gt;closed repeaters&lt;/strong&gt; that are restricted to those authorized by the control operator.  Operation of a closed repeater is &lt;em&gt;perfectly legal&lt;/em&gt; in the USA according to 47 CFR §97.205(e), which states &quot;Limiting the use of a repeater to only certain user stations is permissible.&quot;  (IMO, this is contrary to the spirit of Amateur Radio, but it is specifically authorized by FCC.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually, closed repeaters are noted as such in the various online and printed repeater directories. Most likely, you will not be able to use a closed repeater accidentally because they tend to use CTCSS or other access tones that are only given to authorized users.  If you do find yourself accidentally using a closed repeater, you will likely be told as much in fairly short order.&lt;/p&gt;&#xA;" OwnerUserId="236" LastActivityDate="2013-10-30T05:35:11.730" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="449" PostTypeId="1" CreationDate="2013-10-30T06:34:28.537" Score="0" ViewCount="336" Body="&lt;p&gt;There is a chinese transceiver the X1M, look at x1m.wikia.com and on google. That is basically an SDR but no one has worked to build open firmware for it yet. i think we have a great chance to build something awesome from a cheap and solid chinese clone. &lt;/p&gt;&#xA;" OwnerUserId="242" LastActivityDate="2013-10-30T12:29:15.723" Title="Can we build an open source firmware for the X1M qrp transceiver" Tags="&lt;hf&gt;" AnswerCount="2" CommentCount="1" ClosedDate="2013-10-30T21:02:40.683" ContentLicense="CC BY-SA 3.0" />
  <row Id="450" PostTypeId="2" ParentId="443" CreationDate="2013-10-30T10:13:55.880" Score="8" Body="&lt;p&gt;&lt;strong&gt;Magnet mounts can come off, and they do fall occasionally.&lt;/strong&gt; I can't quote any statistics, but it has happened to me twice in the past - tall HF antenna combined with too small magnet mount and high speed. Luckily the cable held the thing on the roof. Short VHF/UHF sticks (think 1/4 wave for 2 meters) would never fall with the same mount - the wind load is just so much smaller. For my irregular HF use, I've switched to a larger magnet mount and thinner vertical, and the constantly used VHF/UHF sticks are drilled-through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are also stories of shattered glass (antenna comes off and hits your own back window) and scratches on roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna fell down and stopped in the middle of a highway, it would be dangerous to a motorcycle, but less of a hazard to a car. It might break a tire, which in turn could lead into a more serious accident. A thick HF antenna could puncture a car somehow. Large magnet mounts are heavy, and one &lt;em&gt;could&lt;/em&gt; bounce higher into air and penetrate a wind shield. In an accident it would probably get loose and fly away, but it would have the same velocity as the much heavier car, and the damage caused by the car would probably be dominant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you loose one of these on a road, do go back and pick it up immediately. If you loose one on a highway, in many places it's both dangerous and illegal to stop and go pick it up yourself, so you might have to call the police for assistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia has some information on how &lt;a href=&quot;http://en.wikipedia.org/wiki/Magnet#Demagnetizing_ferromagnets&quot; rel=&quot;nofollow&quot;&gt;magnets can be demagnetized&lt;/a&gt;. &lt;em&gt;Permanent magnets are made from &quot;hard&quot; ferromagnetic material&lt;/em&gt; which are &lt;em&gt;very hard to demagnetize&lt;/em&gt;. Magnets on the roof are unlikely to get hot enough to degauss (140 °C / 280 °F for neodymium, 300 °C / 570 °F for ferrite and SmCo), and they're not subject to strong external magnetic fields, either. &lt;em&gt;Hammering or jarring&lt;/em&gt; - some vibration is going to be present, and after a very long time that might have some effect, but that's just my guess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically a mag mount will be decommissioned quick enough that demagnetizing should not be a concern. Water tends to get into the connectors and cables, and the cables break from stress under doors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Magnet mounts are very popular.&lt;/strong&gt; I don't remember any documented serious accidents with them. If accidents would happen, there would be articles on the amateur magazines, blog posts, and pictures on the Internet. &lt;strong&gt;I would claim they're pretty safe, if the relation between antenna size, mag mount strength and vehicle velocity are in a good balance&lt;/strong&gt;.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-30T15:09:22.657" LastActivityDate="2013-10-30T15:09:22.657" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="452" PostTypeId="2" ParentId="449" CreationDate="2013-10-30T11:16:14.713" Score="2" Body="&lt;p&gt;Can we? Maybe.&#xA;Will we? Unlikely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a number of things that need to happen to pull it off. First, we have to figure out just how thoroughly they might have locked it down to prevent just that. While it seems unlikely that they went to great lengths, you never know. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible that the infrastructure to reprogram it on the fly isn't totally functional, which would make it difficult for the average ham to make use of the new firmware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another issue on this front is available hardware. If the internal hardware is fundamentally handicapped, and reports regarding CW performance and signal quality suggests it might be, then even new firmware may not be able to fix the real problems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A bigger impediment may be the community that builds up around it, or more precisely, the lack of it. A good development effort usually requires a core group of capable programmers, and the community support to make it worth their time and test the firmware. Given the somewhat concerning reports of poor signal quality and lackluster hardware, it may be hard to drum up that kind of community support.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the first shot across the bow though. More radios like it will come. It's an inevitable economic result of the inflated equipment prices you see on the market.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2013-10-30T11:16:14.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="454" PostTypeId="2" ParentId="449" CreationDate="2013-10-30T12:29:15.723" Score="0" Body="&lt;p&gt;We can, but it's not likely to happen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It wold take a considerable effort from capable developers to write it. First of all it will be needed to get access to one of those equipments, than a lot of other stuff had to be done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Honestly I dont think it will be done soon, since there are allready plenty of alternative firmwares for other radios.&lt;/p&gt;&#xA;" OwnerUserId="249" LastActivityDate="2013-10-30T12:29:15.723" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="455" PostTypeId="2" ParentId="390" CreationDate="2013-10-30T12:36:56.570" Score="1" Body="&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/K2Fz5.gif&quot; alt=&quot;Diagram for ground&quot;&gt;&#xA;If you are looking for the safety ground, as lighting protection, it's mostly done by inserting a copper rod in the ground, and when you are not using the sation, the anthena should be connected to that rod, so if a lighting hits it, there is no significant damage.&lt;/p&gt;&#xA;" OwnerUserId="249" LastActivityDate="2013-10-30T12:36:56.570" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="456" PostTypeId="5" CreationDate="2013-10-30T13:29:22.033" Score="0" Body="&lt;p&gt;Coaxial cables have two conductors separated by an insulator. The outer conductor, or the shield, wraps completely around the insulated inner conductor. A coaxial cable is typically utilized to connect a device to an antenna, or to another device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Questions should relate specifically to the properties of coaxial cables in general or a specific type of coaxial cable. Questions about connectors, including soldering or crimping, or about adapters are also on topic. Finally, questions can be about the use of coaxial cable to create baluns or other matching &quot;circuits&quot;.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-30T16:30:41.917" LastActivityDate="2013-10-30T16:30:41.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="457" PostTypeId="4" CreationDate="2013-10-30T13:29:22.033" Score="0" Body="Questions about coaxial cables, including different types of cable, connectors, adapters, and other topics." OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-30T16:30:38.950" LastActivityDate="2013-10-30T16:30:38.950" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="458" PostTypeId="1" CreationDate="2013-10-30T13:57:47.433" Score="8" ViewCount="1890" Body="&lt;p&gt;I want to put up a small tower and beam on my roof, but I don’t want the aluminum to “stick out” and want it to be unnoticeable as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would think black anodizing would be the best solution but it is very costly.&#xA;I have access to powder coating and fully understand that you can’t coat the traps entirely and you would have to mask where aluminum parts would come in contact with each other. Same with any kind of wet paint/coating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However I am worried that coating the antenna would affect performance or the factory would have coated it in the first place.&lt;/p&gt;&#xA;" OwnerUserId="151" LastEditorUserId="76" LastEditDate="2015-12-15T22:08:26.317" LastActivityDate="2015-12-15T22:08:26.317" Title="Will anodizing or powder coating or wetcoating (painting) antenna elements affect performance?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="459" PostTypeId="2" ParentId="390" CreationDate="2013-10-30T14:14:14.357" Score="5" Body="&lt;p&gt;To answer your first question, yes, it will affect the signal, but it's a good thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you do to (RF) ground your antenna(s) depends on what type of antenna you are using.  For instance, dipoles do not require a ground.  Typical vertical antennas do require a graound though some types such as the GAP Challenger use 3 wires insulated from ground (in this application they are referred to as a &lt;em&gt;counterpoise&lt;/em&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a typical vertical antenna installation, your radiator is λ/4 tall (electrically at least, it might be physically shorter through the use of coils or whatever).  This is referred to as a monopole and is half of a good antenna.  You make the ground be the other half of the antenna but creating a ground plane with radials.  This creates a virtual image antenna that completes the overall antenna effect.  These radials are usually buried just below the surface or stapled down to the ground and grass is allowed to grow through them to hold them down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's your RF ground.  In addition, it's usually desirable to have an electrical ground for lightning and static electricity protection.  This is achieved by making a lower impedence path to ground than you feedline presents.  Usually one or more 8' copper-clad rods are pounded into the ground at the base of the antenna and bound to it.  The area of effect of this is &lt;em&gt;below&lt;/em&gt; the ground plane and doesn't detract from the signal.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-10-30T14:14:14.357" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="460" PostTypeId="2" ParentId="458" CreationDate="2013-10-30T14:20:12.883" Score="5" Body="&lt;p&gt;Unless the coating contains metal, no it won't affect the performance.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you've surmised, you are going to have to take steps to ensure good metal to metal contacts between sections and anywhere electrical continuity is desired. Either through masking before hand or steel wool/etc afterwards.  You can paint traps, no problem.  You could paint coils, though I wouldn't unless you've tuned the antenna and don't see having to mess with it again.  Otherwise, you'll have to clean off a new place.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-10-30T14:20:12.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="461" PostTypeId="2" ParentId="443" CreationDate="2013-10-30T14:48:25.127" Score="1" Body="&lt;p&gt;They can absolutely come off. &lt;a href=&quot;http://www.stormtrack.org/forum/archive/index.php/t-3664.html&quot; rel=&quot;nofollow&quot;&gt;Here is a forum thread with numerous posters reporting antennas falling off from the wind of passing a semi&lt;/a&gt; - it's a storm chaser forum, but the storms weren't even mentioned as a factor in many of these incidents. &lt;a href=&quot;http://forums.qrz.com/archive/index.php/t-317750.html?s=0c36a0fc114359a3b93feb746b581c26&quot; rel=&quot;nofollow&quot;&gt;Here, several QRZ posters advise that mag mounts may fall off&lt;/a&gt;, and &lt;a href=&quot;https://groups.google.com/d/msg/rec.radio.amateur.antenna/gyD8ynPdtfM/LuEp9ZqsbRUJ&quot; rel=&quot;nofollow&quot;&gt;this poster reassures us that having the right size magnet is key: his has only fallen of &quot;a couple times&quot;&lt;/a&gt;!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not a function of not having a big enough magnet, it's the fact that even the best mag mount on the market will be the &quot;weakest link&quot; in your vehicle, and the first thing to give in to wind. Even when it's not falling off, it can move around and scuff your paint, especially if you move it between vehicles on a regular basis. In many ways, an NMO mount is less damaging to a vehicle than a magnet mount - the damage is confined to a very small area compared to a 3-5&quot; diameter magnet, the hole can be somewhat easily patched or even more easily plugged, and there's no damage to the surrounding paint.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-30T14:48:25.127" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="462" PostTypeId="2" ParentId="458" CreationDate="2013-10-30T15:06:05.630" Score="2" Body="&lt;p&gt;It almost definitely won't - but there are effects that could be some coatings that would cause problems. It isn't just metal content, there's also the possibility that some coatings could absorb RF at certain frequencies. There are many amateurs who have tried this sort of thing and tested it, so the best bet would be to search for the specific product you intend to use to see if anyone has posted results online. If not, test the antenna before and after to see if the resonant frequency or gain has changed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://forums.radioreference.com/amateur-radio-antennas/273332-plasti-dipping-antenna.html#post2030576&quot; rel=&quot;nofollow&quot;&gt;When using powder coating, make sure that whoever is doing it knows that the antenna may flex, otherwise the coating could become damaged too easily.&lt;/a&gt; Anodizing the antenna would prevent this problem, but may be more likely to alter the electrical properties - especially due to the &quot;skin effect&quot; causing more current to flow in and near the anodized layer than in the center of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other tricks include heat shrink tubing, which will form to the antenna. Some types will become stiff once activated, but will still allow enough &quot;flex&quot;, others will retain their flexibility. All are non-conductive, so no worries about skin effect or shielding, they should have little effect on the antenna's electrical properties.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-30T15:06:05.630" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="463" PostTypeId="2" ParentId="428" CreationDate="2013-10-30T15:45:17.303" Score="0" Body="&lt;p&gt;If you go with the US FCC license rule of 'minimum transmitter power necessary to carry out desired communication' then that should be a good rule of thumb. If you're making contacts with JT65 using using 5 watts then maybe that's 'just right'.&lt;/p&gt;&#xA;" OwnerUserId="252" LastActivityDate="2013-10-30T15:45:17.303" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="464" PostTypeId="1" AcceptedAnswerId="465" CreationDate="2013-10-30T15:52:35.820" Score="9" ViewCount="15927" Body="&lt;p&gt;Are there any 2m and/or 440cm FM mobile radios that have audio inputs for supporting digital modes, like PSK31 or SSTV?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a Rigblaster that I use with my HF radio so I could get a mike cable and connect it directly to the mike input in the same way, but is there any VHF/UHF radio available that has better options for connectivity for working digital modes on VHF/UHF?&lt;/p&gt;&#xA;" OwnerUserId="252" LastEditorUserId="29" LastEditDate="2013-10-31T08:42:22.390" LastActivityDate="2021-05-27T04:32:50.000" Title="2m or 70cm FM mobile radio for digital mode operation" Tags="&lt;digital-modes&gt;&lt;vhf&gt;&lt;uhf&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="465" PostTypeId="2" ParentId="464" CreationDate="2013-10-30T16:13:04.327" Score="11" Body="&lt;p&gt;&lt;strong&gt;Most modern VHF/UHF FM mobile rigs designed for Amateur Radio use have a &quot;data&quot; connector on the back.&lt;/strong&gt; Currently manufactured dual-band examples include Yaesu FT-7900, Kenwood TM-V71, Icom IC-208H - they all have the same 6-pin mini-DIN &quot;data&quot; connector using the same main pinout.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 6-pin data connector is originally designed for attaching packet radio TNCs and other data equipment, and usually has at least the following pins:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Ground&lt;/li&gt;&#xA;&lt;li&gt;TX audio in (transmitted audio)&lt;/li&gt;&#xA;&lt;li&gt;PTT (ground to transmit)&lt;/li&gt;&#xA;&lt;li&gt;RX audio out, &quot;1200 bit/s&quot; &quot;normal audio&quot;&lt;/li&gt;&#xA;&lt;li&gt;RX audio out, &quot;9600 bit/s&quot; discriminator output&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I quoted the bit rates, since the radio documentation often cites these standard packet radio speeds, although in reality it's just audio, and the radio doesn't really care about any bit rates as such. The &quot;9600&quot; pin audio output is taken before audio filter/amplifier stages of the radio, and has a flatter audio frequency response that is good for high speed data such as 9600 bit/s packet or AIS reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Technically, you can run SSTV or PSK31 over FM, and that &quot;data&quot; connector will suit that purpose perfectly.&lt;/strong&gt; But it's not overly popular in most areas, so you might have to talk some friends to play with it. Most of SSTV and PSK31 activity is on HF SSB, although VHF/UHF digital chat as such should be a lot of fun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PSK31 over FM in particular is quite strange and unusual, since PSK31 is designed to be a very narrow-bandwidth (31.25 Hz) mode for SSB transceivers, and transmitting it over FM (some 20 KHz) would be a waste of perfectly good radio spectrum and transmitter power. It works, but it's not efficient. Then again, it might be fun, and &lt;strong&gt;if&lt;/strong&gt; you live in an area where most of 70cm is almost completely quiet and inactive (like I do), a little inefficiency on an irregular basis is not going to do harm, if you're having fun. A lot of amateur FM voice communications don't have a lot of useful information content, either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SSTV isn't so narrow (about 3 kHz), and there have been more or less official FM channel allocations for it. Some US web sites cite VHF/UHF SSTV AFSK FM calling frequencies. IARU Region 1 (Europe) SSTV(FM/AFSK) frequency for 70 cm is currently 433.400.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also often use the &quot;data&quot; connector of my FT-7800 for recording received voice communications on a computer. Works fine.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-30T17:19:51.687" LastActivityDate="2013-10-30T17:19:51.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="466" PostTypeId="2" ParentId="464" CreationDate="2013-10-30T16:19:04.823" Score="8" Body="&lt;p&gt;Sure, most radios have the ability to patch in audio. If it isn't through the front microphone connector, it's through an accessory connector, which is available on every commercial radio I'm aware of - although perhaps only on a few amateur mobiles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But why would you want to? &lt;strong&gt;SSTV and PSK31 cannot be reasonably transmitted over FM.&lt;/strong&gt; FM transmits a carrier at a single frequency that is modulated. That is not the same as the SSB that is used in HF transceivers for digital mode operation - it's a &lt;strong&gt;completely different kind of modulation&lt;/strong&gt;. In SSB, the bandwidth actually occupied by the output signal is equal to the bandwith occupied by the input signal - so if your input audio shifts by 31.25Hz, your output RF shifts by 31.25Hz. In FM, &lt;strong&gt;every&lt;/strong&gt; input signal uses up the &lt;strong&gt;entire&lt;/strong&gt; channel width. You couldn't use something like fldigi to receive multiple PSK31 signals in the same FM channel at once, because your FM receiver is &lt;strong&gt;physically incapable&lt;/strong&gt; of receiving and demodulating more than one signal at a time. You would effectively be taking up an entire FM channel but only using &lt;strong&gt;less than one percent&lt;/strong&gt; of it. SSTV operates in a similar way. The properties of FM do not allow for use of digital modes in the same way as SSB does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to use digital in VHF/UHF, you need either an SSB transceiver (might be available for 2 meters?) or a digital radio (using D-STAR, TRBO, or something else) or an SDR (a software defined radio may allow the necessary types of operation).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a few modes that sacrifice radio efficiency in exchange for simplicity, such as APRS, however APRS has much shorter transmit durations than PSK31 allowing for the frequency to be shared (I've seen operators with an active PSK31 signal for over a minute, imagine the APRS pileup if every station in range was forced to wait that long for an open carrier). The root of the difference is that PSK31 - very small bandwidth but very slow - was designed for Frequency Division Multiple Access (&lt;strong&gt;FDMA&lt;/strong&gt;), while APRS was designed for Time Division Multiple Access (&lt;strong&gt;TDMA&lt;/strong&gt;) all on the same frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you'll excuse a few signal processing terms, SSB as a modulation scheme is a &lt;strong&gt;linear function&lt;/strong&gt; - that means that adding two audio signals together and passing it through SSB results in the same thing as if the audio signals had been encoded individually - whereas FM is not. This interesting property of SSB is what makes it possible to receive more than one signal at once. Linear modulation schemes like SSB preserve FDMA as well as TDMA, however nonlinear modulation schemes like FM preserve only TDMA, and not FDMA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;References:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://jaunty-electronics.com/blog/2012/11/why-psk31-over-fm-is-nonsense/&quot; rel=&quot;noreferrer&quot;&gt;Why PSK31 over FM is nonsense&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://forums.qrz.com/archive/index.php/t-163758.html&quot; rel=&quot;noreferrer&quot;&gt;&quot;FM only...is NOT a popular PSK mode&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://webcache.googleusercontent.com/search?q=cache%3aF1fuZMQBKKIJ%3awww.eham.net/ehamforum/smf/index.php%3Ftopic%3D13984.0+&amp;amp;cd=2&amp;amp;hl=en&amp;amp;ct=clnk&amp;amp;gl=us&quot; rel=&quot;noreferrer&quot;&gt;&quot;PSK31 would [lose] most of its benefits if run thru an FM system. Certainly it would no longer be narrow band. PSK31 via a 2M SSB system would be a good weak signal mode.&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://webcache.googleusercontent.com/search?q=cache%3aYsjTS4NJRQwJ%3awww.eham.net/ehamforum/smf/index.php%3Ftopic%3D26178.0+&amp;amp;cd=3&amp;amp;hl=en&amp;amp;ct=clnk&amp;amp;gl=us&quot; rel=&quot;noreferrer&quot;&gt;&quot;Using PSK31 over FM results in [losing] most of the benefits of PSK31. You are still transmitting a wide FM signal and the threshold needed by the FM receiver still requires the same signal level as voice FM.&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://comments.gmane.org/gmane.recreation.radio.hardware.kenwood.th-f6a/6016&quot; rel=&quot;noreferrer&quot;&gt;&quot;on FM? It would defeat the purpose of PSK31.&quot;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-30T17:26:38.323" LastActivityDate="2013-10-30T17:26:38.323" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="467" PostTypeId="1" CreationDate="2013-10-30T17:07:42.657" Score="8" ViewCount="285" Body="&lt;p&gt;To use auto patch, IRLP or other special repeaters, you need the club code from the local club I am part of, which is a DTMF code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I was thinking, DTMF can't be very hard to decode, and if someone (like an unlicensed guy with a receiver) records the repeater while someone uses the tones, and uses computer software to decode the tones, they could easily get the code and share it to anyone. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do repeaters just hope that doesn't happen? &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2013-10-31T18:27:16.747" Title="How do club codes stay secret?" Tags="&lt;repeater&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="468" PostTypeId="2" ParentId="467" CreationDate="2013-10-30T17:35:42.453" Score="5" Body="&lt;p&gt;They stay secret because it takes a certain amount of effort and time to decode them - at the very least you need to record the tones and then feed them into a computer program. That means you need to record the entire repeater audio until you catch someone using the autopatch. Of course, you're right - once you have it recorded, it's trivial to decode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would imagine the reason this doesn't happen all the time is that there's no reason why an amateur radio operator should be trying to access a system he isn't allowed to. The repeater's core community would quickly recognize an unauthorized operator. The repeater owner is allowed to deny access to an individual - if he's caught abusing the repeater features, he can be advised he isn't welcome there, and if he returns, &lt;a href=&quot;https://ham.stackexchange.com/a/236/87&quot;&gt;he may be warned and fined by the FCC&lt;/a&gt;. It could easily become an escalating issue the club changing the code and the attacker learning the new ones, but any persistent abuse like that would warrant a quick response from the FCC, which is really easy if the user is a licenced amateur and transmitting his call sign. If he isn't identifying himself, &lt;a href=&quot;https://ham.stackexchange.com/a/420/87&quot;&gt;clubs regularly use &quot;fox hunting&quot; to locate the source of a radio transmission&lt;/a&gt;, and any jamming would be persistent enough to allow an individual or small group to find the source's location pretty easily.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-10-30T17:35:42.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="469" PostTypeId="1" AcceptedAnswerId="470" CreationDate="2013-10-30T17:49:58.120" Score="5" ViewCount="759" Body="&lt;p&gt;I was wondering, does the impedance of a transmission line have any effect on the power it dissipates? I'm familiar with the fact that an impedance equal to the load will provide maximum power transfer (and dissipate just as much power as the load) but guess that's of no bearing when talking about transmission lines? If a line is rated as 50 Ohm, does it have any impact on power dissipation?&lt;/p&gt;&#xA;" OwnerUserId="135" LastEditorUserId="87" LastEditDate="2013-10-30T18:22:51.577" LastActivityDate="2013-11-07T15:21:12.607" Title="Power dissipation in transmission lines?" Tags="&lt;rf-power&gt;&lt;feed-line&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="470" PostTypeId="2" ParentId="469" CreationDate="2013-10-30T18:27:05.543" Score="4" Body="&lt;p&gt;No. The cause of power loss in a feed line is not due to the characteristic impedance, it actually varies among transmission lines of the same impedance. Otherwise all 50 ohm coax would be the same - but there are many different types and qualities of cable. The actual loss is measured not in ohms but in decibels per foot, and varies with both the type of cable and the frequency in use (with higher frequencies having greater loss, due to skin effect). If you need to get the loss of a particular cable, or compare two cables, you should get a chart or table from the manufacturer. &lt;a href=&quot;http://www.w4rp.com/ref/coax.html&quot; rel=&quot;nofollow&quot;&gt;This table&lt;/a&gt; lists some common types of coax at a variety of frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 50 ohm value being described is not the impedance of a circuit element, which is a word for the complex form of resistance. It has a 50 ohm characteristic impedance. It's still the ratio of the voltage to the current, but in this case of a wave travelling down the core and back along the shield. It's a property of how the line behaves in response to a wave travelling through it, and it's important because if it doesn't match at any given connection, since current coming in must equal current coming out and that means the two sides would have different voltages, part of the wave is reflected to allow everything to even out. However even though it's measured in ohms, it is not related to resistive loss.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-10-30T19:20:41.957" LastActivityDate="2013-10-30T19:20:41.957" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="471" PostTypeId="1" AcceptedAnswerId="472" CreationDate="2013-10-30T19:02:02.510" Score="8" ViewCount="2287" Body="&lt;p&gt;As I recall, it used to be in the U.S. that the ability to read and send Morse code over CW was a requirement for an amateur license (and was tested, I believe).  Is that still true in the U.S.?  If not when was it dropped?  Around the world, is Morse a requirement for amateur licensing?&lt;/p&gt;&#xA;" OwnerUserId="258" LastEditorUserId="13" LastEditDate="2013-10-30T19:10:28.793" LastActivityDate="2014-02-04T02:26:51.317" Title="Is Morse code a requirement for ham licensing?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;cw&gt;" AnswerCount="5" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="472" PostTypeId="2" ParentId="471" CreationDate="2013-10-30T19:07:25.030" Score="12" Body="&lt;p&gt;It is not required any more for any US license, as of 2008. It has not been required for the technician license since 1991. It is still required in some areas, and some international amateur radio licenses, in particular the IARP license, which may be used by US amateurs to operate outside of the US in IARP countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bottom line is, however, that fewer and fewer countries are requiring it, ever since the 2003 ruling from the ITU that no longer required knowledge of CW for operating on HF. &lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-10-30T19:07:25.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="473" PostTypeId="2" ParentId="443" CreationDate="2013-10-30T21:05:14.857" Score="1" Body="&lt;p&gt;Check with the antenna manufacturer.  They frequently have mounting recommendations.  For example, the following is straight from Diamond Antenna's website.  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Use of magnet mounts is not recommended with tall antennas, i.e SG7900A, SG7900ANMO, CR627B, CR627BNMO &amp;amp; HV7A, NR22L, NR7900A.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Source as of 30 October 2013: &lt;a href=&quot;http://www.diamondantenna.net/Product_Catalog/techno.html&quot; rel=&quot;nofollow&quot;&gt;http://www.diamondantenna.net/Product_Catalog/techno.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="261" LastActivityDate="2013-10-30T21:05:14.857" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="474" PostTypeId="1" AcceptedAnswerId="479" CreationDate="2013-10-30T23:40:11.053" Score="5" ViewCount="367" Body="&lt;p&gt;In packet radio, &lt;a href=&quot;http://en.wikipedia.org/wiki/AX.25&quot; rel=&quot;nofollow&quot;&gt;AX.25&lt;/a&gt; is a fairly common layer-2 protocol. Many TNCs implement AX.25 in firmware, so the operator interfaces to the TNC with a serial port, using the TNC's firmware from a shell-like interface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many TNCs also allow a &quot;raw mode&quot; where data packets are sent directly over the serial port for the host computer to manage. &lt;a href=&quot;http://en.wikipedia.org/wiki/KISS_%28TNC%29&quot; rel=&quot;nofollow&quot;&gt;KISS&lt;/a&gt; is a common protocol for this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;XKISS is &quot;extended KISS&quot; and it has about 3 very simple improvements over KISS. Kantronics TNC documentation indicates that it was conceived by John Wiseman, G8BPQ. Kantronics TNCs provide an XKISS mode, in addition to a standard KISS mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;TAPR has some detailed documents for &lt;a href=&quot;ftp://ftp.tapr.org/general/ax25.doc&quot; rel=&quot;nofollow&quot;&gt;AX.25&lt;/a&gt; and &lt;a href=&quot;ftp://ftp.tapr.org/general/kiss.txt&quot; rel=&quot;nofollow&quot;&gt;KISS&lt;/a&gt; on their &lt;a href=&quot;ftp://ftp.tapr.org/general/&quot; rel=&quot;nofollow&quot;&gt;FTP site&lt;/a&gt;. Where is some documentation to describe XKISS in detail?&lt;/p&gt;&#xA;" OwnerUserId="227" LastEditorUserId="129" LastEditDate="2013-10-31T13:47:51.273" LastActivityDate="2013-10-31T13:47:51.273" Title="Where is the Multi-Drop XKISS / BPQKISS spec?" Tags="&lt;packet&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="475" PostTypeId="1" AcceptedAnswerId="476" CreationDate="2013-10-31T00:26:00.943" Score="8" ViewCount="4207" Body="&lt;p&gt;I am using the Aether logging software and it has two fields I do not understand: TX Exchange and RX Exchange. I know TX and RX refer to transmit and receive, but I'm not sure what to populate in these fields. There is already a frequency field so I don't know what goes in these and could not find an answer via a Google search.&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="4665" LastEditDate="2021-05-17T22:02:25.413" LastActivityDate="2021-05-17T22:02:25.413" Title="What does TX/RX Exchange refer to?" Tags="&lt;software&gt;&lt;jargon&gt;&lt;contest&gt;&lt;logging&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="476" PostTypeId="2" ParentId="475" CreationDate="2013-10-31T00:40:19.023" Score="10" Body="&lt;p&gt;It's intended for contest logging. Most contests require that you &quot;exchange&quot; some information. Sometimes it's as simple as an RST signal report and you'd just enter whatever signal report you gave an received, other contests require a serial number (you send &quot;1&quot; to your first contact and increment that by one each time, so that each contact gets a unique number) or a state, grid square, ARRL section, and in the case of field day, operator class (which is a code describing how many transceivers your &quot;team&quot; is using, and whether it's a club or just you, and whether you're in the field, in a vehicle, at home, or in an EOC). The contest scorers will expect your TX exchange to match your contact's RX exchange, and in some cases your score depends on what other stations send you (for example in contests where you get a bonus for each unique state).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're not using the logger for a contest, you would leave those fields blank.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-31T00:40:19.023" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="477" PostTypeId="1" AcceptedAnswerId="493" CreationDate="2013-10-31T01:11:38.880" Score="9" ViewCount="161" Body="&lt;p&gt;I'm interested in modeling the radiation pattern of wire antennas for hf before I invest the resources necessary to erect the antenna. I'm familiar with tools such as 4nec2, but from what I can tell the ground is modeled as being flat. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, at my house, the terrain is sloped at roughly 25 degrees. My intuition says that this will affect the radiation angles of radiation. How can I model antennas to include local terrain?  Would a useful representation be rotating the antenna 25 degrees to account for the terrain? Does it really matter? &lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="8717" LastEditDate="2019-11-05T19:34:44.730" LastActivityDate="2019-11-05T19:34:44.730" Title="Antenna modeling on non-uniform terrain" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;hf&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="478" PostTypeId="2" ParentId="467" CreationDate="2013-10-31T01:12:33.737" Score="2" Body="&lt;p&gt;It's a bit of security through obscurity, but some repeaters won't transmit DTMF tones they receive. In those cases, unless you are monitoring the input frequency, you won't have anything to decode.&lt;/p&gt;&#xA;" OwnerUserId="146" LastActivityDate="2013-10-31T01:12:33.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="479" PostTypeId="2" ParentId="474" CreationDate="2013-10-31T06:10:06.313" Score="2" Body="&lt;p&gt;&lt;strong&gt;Karl Medcalf, WK5M&lt;/strong&gt;, of &lt;strong&gt;Kantronics&lt;/strong&gt;, has published a paper titled &lt;strong&gt;Multi-Drop KISS operation&lt;/strong&gt; for &lt;strong&gt;ARRL CNC v10&lt;/strong&gt; conference (San Jose, California, 1991). That document was distributed as a PostScript file, at some point a copy was in the source code of the Linux ax25-tools, in the &lt;em&gt;doc&lt;/em&gt; directory. It seemed a bit hard to find an URL for the file now, so I ran it through ps2pdf and placed a copy on my server:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://he.fi/pub/oh7lzb/bpq/multi-kiss.pdf&quot; rel=&quot;nofollow&quot;&gt;http://he.fi/pub/oh7lzb/bpq/multi-kiss.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I checked the old G8BPQ DOS software installers, which include the BPQKISS firmware, hoping to find an original spec. KISSROMS.DOC says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The protocol used for this multidropped option was changed from&#xA;  version 3.59a onwards to be compatible with similar software produced&#xA;  by KANTRONICS for their range of TNCs. The new version is called&#xA;  BPQKISS, and replaces the old JKISSP.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I would expect Karl's document to document XKISS as implemented by Kantronics.&#xA;&lt;a href=&quot;http://groups.yahoo.com/neo/groups/BPQ32/conversations/topics/3505&quot; rel=&quot;nofollow&quot;&gt;This recent post (2010)&lt;/a&gt; by &lt;strong&gt;John Wiseman, G8BPQ&lt;/strong&gt; seems to say so:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Kantronics XKISS uses the same enhancements as my BPQKISS.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The Linux kernel AX.25 implementation (mkiss module) is apparently based on that document, so that's one place to look into if you wish to see actual source code.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-10-31T06:34:23.357" LastActivityDate="2013-10-31T06:34:23.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="480" PostTypeId="2" ParentId="471" CreationDate="2013-10-31T07:17:52.013" Score="5" Body="&lt;p&gt;In Australia, the requirement for Morse was dropped when the new licence structure of three classes (Foundation, Standard and Advanced) was adopted. This happened in October 2005.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since that date there has been no requirement for any Australian amateur to demonstrate proficiency in Morse for any class of licence.&lt;/p&gt;&#xA;" OwnerUserId="265" LastActivityDate="2013-10-31T07:17:52.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="481" PostTypeId="2" ParentId="345" CreationDate="2013-10-31T09:02:18.060" Score="4" Body="&lt;p&gt;Most of these things come from morse code. They were used because they have a distinctive and musical signature, listen to the rhythm of '73' some time. Rhythm was (and should still be) the mark of a good operator. Alas, some non military operators in the early days were not, that is where 'ham' came from: because the operators sounded 'ham-fisted'. When I was a young boy my navy father taught me an exercise for learning rhythm it is:&#xA;best bent wire / g&#xA;Try it out some time on your morse key, you will be surprised how it improves your musicality. &lt;/p&gt;&#xA;" OwnerUserId="267" LastEditorUserId="267" LastEditDate="2013-10-31T09:07:19.330" LastActivityDate="2013-10-31T09:07:19.330" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="482" PostTypeId="2" ParentId="123" CreationDate="2013-10-31T13:25:28.867" Score="2" Body="&lt;p&gt;A simple way to get a Linux logger is to use a windows logger under WINE Windows Program Loader, or something similar. I've done it before and it works fine, however it can cause problems on a slow computer.&lt;/p&gt;&#xA;" OwnerUserId="243" LastActivityDate="2013-10-31T13:25:28.867" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="483" PostTypeId="2" ParentId="458" CreationDate="2013-10-31T15:36:54.910" Score="0" Body="&lt;p&gt;Yes.  &lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?topic=13243.0;wap2&quot; rel=&quot;nofollow&quot;&gt;Any coating will change the velocity factor of the conductor&lt;/a&gt;.  However, this change is minimal, and isn't generally worth considering.  The difference will be tuned out when you do your antenna tuning.  You might want to try to account for it for beam antennas at higher frequencies to get the best performance, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The amount of insulation you're suggesting, however, isn't enough to appreciably affect the velocity factor. Choose whichever option meets your other requirements, and once coated re-tune the antenna.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-10-31T15:36:54.910" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="484" PostTypeId="1" AcceptedAnswerId="487" CreationDate="2013-10-31T17:06:58.150" Score="9" ViewCount="3206" Body="&lt;p&gt;This applies to mobile and fixed installations. What are ground losses, and how can they be minimized? It seems to involve proximity to the ground, but what is the mechanism that causes loss? Does antenna installation height influence ground loss in any way?&lt;/p&gt;&#xA;" OwnerUserId="43" LastEditorUserId="76" LastEditDate="2014-05-28T17:09:58.927" LastActivityDate="2014-05-28T17:09:58.927" Title="What causes ground losses in a HF antenna system?" Tags="&lt;grounding&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="485" PostTypeId="2" ParentId="484" CreationDate="2013-10-31T17:44:13.210" Score="7" Body="&lt;p&gt;While ground effects are common concerns in almost every antenna and radio system, they are particularly important in the case of a monopole antenna. Monopole antennas, including quarter wave verticals along with many other electrically short verticals, are different from dipoles because the currents going into the elements do not balance. While a dipole has equal but opposite currents at all times, a monopole can't. One half of the signal goes into the antenna, and the other half has to come back through the shield of the coax, which is connected to ground. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When we're talking about antenna modeling, we describe the ground plane as an image plane - everything above it is mirrored below it. So in theory, the monopole should act as though there was another monopole directly below it, being fed 180 degrees out of phase. We do see the correct amount of current returning through the ground path for this model to work - we do have equal but opposite currents - but while your antenna is low-resistance wire and most of that current is being radiated, the ground typically has somewhat higher resistance. It's impossible to set a value here, because it is dependent on soil type, weather, how deep the water table is, and other factors, but it is greater than that of your antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because of this resistance in the ground, some of the power coming from your radio will be lost to normal resistive heating. Since, at a constant power and given $P=VI=I^2R$ the increased resistance in the ground results in decreased current into the ground (at constant power). Since the antenna and ground currents must be equal but opposite, that also decreases the current flowing into your antenna and therefore your actual radiated power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also can't just stick a multimeter into the ground to find this resistance - it's the resistance from your antenna feed point to the point where the coax shield is grounded, but it is frequency dependent because there is a capacitive component as well. An antenna analyzer can be used to detect the total resistance (including radiation resistance of the antenna) and this can be compared to a model with an ideal ground (perhaps obtained from EZNEC or another modelling program) to get the &quot;extra&quot; real-world losses, including ground loss. This also explains why height factors in: Your antenna system is effectively a series resistance (from ground loss and other factors), capacitance (between antenna and ground and other effects), and inductance (from loading coils and other effects). If the antenna is mounted further from ground, the capacitance decreases, and so the ground loss becomes a greater part of this total reactance, which is why it is better to have your antenna near to a ground and to have a ground that is as low resistance as possible. An extra way to help this is to install radials - wires underground at about a quarter wavelength which would act as a lower-resistance path for the return current to take. &lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-10-31T17:44:13.210" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="486" PostTypeId="2" ParentId="467" CreationDate="2013-10-31T18:27:16.747" Score="1" Body="&lt;p&gt;Basically, it's trivial to decode these tones with modern software, but there's no reason to.  First of all the &lt;em&gt;output&lt;/em&gt; of the repeater is in the clear.  You only need the code to transmit.  So you can listen all you want.  If you are not in the club (and these tend to be small insular clubs), who would you talk to? The regulars would instantly know you aren't an authorized user which they can deal with a number of ways.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-10-31T18:27:16.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="487" PostTypeId="2" ParentId="484" CreationDate="2013-10-31T19:49:37.130" Score="7" Body="&lt;p&gt;To add to what Dan is saying, for (horizontal) &lt;em&gt;dipole&lt;/em&gt; antennas, ground height is important because although a dipole doesn't require ground to work, ground is still a (lossy) conductive plane, and you still get an &lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;noreferrer&quot;&gt;image&lt;/a&gt;. That is, it appears that there's another dipole, fed in anti-phase, underground. Even if nothing in your transmitter or antenna is connected to the ground, your antenna will be capacitively coupled to the ground. There is no avoiding it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the dipole is close to the ground, then the currents in the ground can be quite strong, incurring significant resistive losses along the way. You could put radials (or any conductive mesh, really) in the ground to mitigate this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But also: this image makes your dipole a kind of &lt;a href=&quot;http://en.wikipedia.org/wiki/Phased_array&quot; rel=&quot;noreferrer&quot;&gt;phased array&lt;/a&gt;. Depending on the spacing of the antenna and it's image, this might make a phased array that helpfully directs most of the RF energy at the horizon (low takeoff angle, desirable for HF DX exploiting &lt;a href=&quot;http://en.wikipedia.org/wiki/Skywave&quot; rel=&quot;noreferrer&quot;&gt;skywave&lt;/a&gt; propagation), or unhelpfully straight up (useless, unless you are trying to exploit &lt;a href=&quot;http://en.wikipedia.org/wiki/Near_Vertical_Incidence_Skywave&quot; rel=&quot;noreferrer&quot;&gt;NVIS&lt;/a&gt; propagation on communicate with something in space).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.vias.org/radioanteng/radio_antenna_engineering_03_06_02.html&quot; rel=&quot;noreferrer&quot;&gt;&lt;em&gt;Radio Antenna Engineering&lt;/em&gt; has a more detailed explanation&lt;/a&gt;, and this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/LJuCI.png&quot; alt=&quot;radiation patterns for dipoles over ideal ground planes&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One interesting thing to note about this image: you can't get maximum gain in &lt;em&gt;any&lt;/em&gt; direction until the dipole is $0.25\lambda$ high. Remember, the image is twice this distance away, and anti-phase. Below this height, in any direction you will get at least partial phase-cancellation. At $h=0.25\lambda$, you have two antennas, in anti-phase, $0.5\lambda$ apart, which makes the &lt;em&gt;add&lt;/em&gt; instead of &lt;em&gt;cancel&lt;/em&gt;, but only if you are directly over the antenna, which isn't useful for skywave propagation. Thus, the general recommendation to get a dipole something like $0.5\lambda$ high, which sends &lt;em&gt;most&lt;/em&gt; of the energy at a reasonably low take-off angle, making the best of the transmit power available.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-10-31T22:27:53.943" LastActivityDate="2013-10-31T22:27:53.943" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="490" PostTypeId="1" AcceptedAnswerId="15619" CreationDate="2013-10-31T21:12:03.477" Score="7" ViewCount="6614" Body="&lt;p&gt;Some digital voice protocols are time slotted (TDMA), i.e. the transmitter of a station is not on all the time, and multiple stations may transmit digital voice on the same frequency at the same time by transmitting small digital bursts, one by one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, DMR (MotoTRBO), which is already somewhat popular in amateur radio circles, has a duty cycle of slightly less than 50%, and two voice transmissions can be retransmitted by the same repeater at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it be possible to make a digital &quot;simplex&quot; voice repeater which would listen on one time slot and immediately repeat the received voice frame on the next time slot, on the same frequency? Do such repeaters exist for some protocol?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It'd work fine with a single antenna, and wouldn't require duplex filters. Much easier to set up than traditional voice repeaters.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-11-01T04:45:51.577" LastActivityDate="2019-11-06T22:00:32.873" Title="VHF/UHF digital single-frequency repeater without duplexers?" Tags="&lt;repeater&gt;&lt;digital-voice&gt;&lt;tdma&gt;" AnswerCount="8" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="491" PostTypeId="2" ParentId="140" CreationDate="2013-10-31T21:20:13.933" Score="5" Body="&lt;p&gt;Be sure that the wire that you use is acceptable legally as well as physically.  In any place were the National Electric Code (NEC), that is used in much of the United States, is enforced as law the minimum size of wire that can be used for an amateur radio transmitting antenna is number fourteen American Wire Gauge (14AWG).  For people in other parts of the world that is equivalent to 1.63mm diameter or 2.08 square mm.  If you use a smaller gauge in such an area subject to that code than any harm that might result from the antenna failing and falling into contact with people or things is entirely on you.  For the sake of those who may be able to make direct use of the information the applicable section of the NEC is &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;ARTICLE 810 Radio and Television Equipment&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;III. Amateur Transmitting and Receiving Stations — Antenna Systems&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;810.52 Size of Antenna.&lt;br&gt;&#xA;  Antenna conductors for transmitting and receiving stations shall be of a size not less than given in Table 810.52.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The table requires 14 gauge for lengths up to 150 feet with larger gauges for longer lengths dependent on the type of wire used.  The important thing to know is that fourteen gauge is the smallest size of wire permitted for a amateur radio antenna and that there are no exceptions to permit a smaller gauge for any reason in areas were the NEC is enforced as law.  &lt;/p&gt;&#xA;" OwnerUserId="277" LastEditorUserId="76" LastEditDate="2019-11-10T19:18:43.680" LastActivityDate="2019-11-10T19:18:43.680" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="492" PostTypeId="2" ParentId="123" CreationDate="2013-10-31T22:37:50.310" Score="0" Body="&lt;p&gt;&lt;a href=&quot;http://writelog.com/&quot; rel=&quot;nofollow&quot;&gt;Writelog&lt;/a&gt;, &lt;a href=&quot;http://n1mm.hamdocs.com&quot; rel=&quot;nofollow&quot;&gt;N1MM&lt;/a&gt; and &lt;a href=&quot;http://hamsoft.ca/pages/mmtty.php&quot; rel=&quot;nofollow&quot;&gt;MMTTY&lt;/a&gt; all run under &lt;a href=&quot;http://www.codeweavers.com/products/crossover-linux/&quot; rel=&quot;nofollow&quot;&gt;Codeweavers CrossOver&lt;/a&gt;, the commercial version of Wine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apart from being much easier and convenient to use than Wine, my success rate with CrossOver is also a bit higher. Furthermore, I have no problem opening my wallet for this decently priced software in support of this company. (Disclosure: No conflict of interests.)&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2013-11-02T18:53:03.277" LastActivityDate="2013-11-02T18:53:03.277" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="493" PostTypeId="2" ParentId="477" CreationDate="2013-10-31T23:05:35.397" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Would a useful representation be rotating the antenna 25 degrees to account for the terrain?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'd think so, as long as you also then rotate all the results 25 degrees in the opposite direction. I can't think of anything that actually wouldn't rotate with the ground (gravity, geomagnetic field, ...) that would have any significant effects.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does it really matter?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No doubt the 25 degree slant will significantly affect many antenna designs. Not only will you have a hard time transmitting through a mountain, but the &lt;a href=&quot;https://ham.stackexchange.com/a/487/218&quot;&gt;ground will form an image antenna&lt;/a&gt; as if it were a mirror, creating a phased array. Turning the mirror 25 degrees will make a big difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, probably there's nothing you can do about it. Maybe you will feel better not knowing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides, there are plenty of other things that can make a big difference. Modeling results can be very wrong if they don't include everything near the antenna: the tower, the feedline, your gutters, trees, etc. Ground conductivity can change with weather. Then, the ionosphere swirls around and messes the whole thing up. So, from a practical standpoint, modeling can only solve some of the problems involved with making a good antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My personal approach would not bother with modeling. I have a &lt;a href=&quot;http://www.dxengineering.com/parts/hsr-4btv&quot; rel=&quot;nofollow noreferrer&quot;&gt;trapped vertical&lt;/a&gt; that wasn't too expensive and covers enough bands that one of them is always open. If you have the space, a couple of parallel-fed simple dipoles would probably work as well for less cost. I put in plenty of radials to keep the ground losses low, and tuned it carefully. The idea is to focus on radiating, and not where I'm radiating. I wouldn't win any DX contests, but I have no difficulty making an international contact any day.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-11-07T01:08:18.767" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="494" PostTypeId="2" ParentId="146" CreationDate="2013-10-31T23:48:42.640" Score="8" Body="&lt;h2&gt;Summary&lt;/h2&gt;&#xA;&lt;p&gt;If you can have only one antenna and can chose between a vertical HF antenna or &lt;em&gt;a relatively high&lt;/em&gt; horizontal HF antenna, &lt;strong&gt;go for the horizontal antenna.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;h2&gt;Modelling results&lt;/h2&gt;&#xA;&lt;p&gt;In January 2008, L. B. Cebik, W4RNL (SK) published what was going to be the last entry of his seminal &lt;em&gt;10-10 News&lt;/em&gt; series. It turned out to be an interesting gain comparison of &lt;a href=&quot;http://w4rnl.net46.net/ant58.html&quot; rel=&quot;noreferrer&quot;&gt;single element 28.4MHz antennas modelled over various ground types&lt;/a&gt; of which a summary is presented here (Table 1). His findings seem to fit well with what John Devoldere, ON4UN modelled and &lt;a href=&quot;https://www.arrl.org/shop/ON4UN-s-Low-Band-DXing&quot; rel=&quot;noreferrer&quot;&gt;published for equivalent antennas on the lower HF bands&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/TWeLF.png&quot; alt=&quot;Gain &amp;amp; elevation angle of single element 28.4MHz antennas over various ground types&quot; /&gt;&lt;/p&gt;&#xA;&lt;h2&gt;Horizontal HF antennas: near-by ground gain&lt;/h2&gt;&#xA;&lt;p&gt;At a height of about λ/2, the nearby ground reflection of a horizontal HF antenna will start to be constructive at interesting take-off angles for long- distance ionospheric contacts. This will provide a net &lt;em&gt;gain&lt;/em&gt; over the antenna in free-space.&lt;/p&gt;&#xA;&lt;h2&gt;Vertical HF antennas: near-by ground loss&lt;/h2&gt;&#xA;&lt;p&gt;This is not the case with vertical HF antennas. Nearby ground only contributes loss. This even more so when the ground forms part of the return path of the radiating structure. Even when far-away ground reflections may cause the &lt;em&gt;directivity&lt;/em&gt; of a vertical HF antenna at low take-off angles to be much higher than that of a horizontal HF antenna, its net &lt;em&gt;gain&lt;/em&gt; will still be lower at those angles. &lt;strong&gt;This makes the horizontal HF antenna a clear winner&lt;/strong&gt;, at least for what transmission is concerned. Note that gain and directivity are not synonyms; &lt;em&gt;gain takes into account losses, directivity does not.&lt;/em&gt;&lt;/p&gt;&#xA;&lt;h2&gt;Vertical HF antennas still remain useful&lt;/h2&gt;&#xA;&lt;p&gt;Vertical HF antennas do have their merit though. At the lower end of the HF spectrum, the λ/2 height requirement for horizontal antennas can become cumbersome (even though a horizontal phased array may weaken this requirement by allowing somewhat lower heights). A vertical HF antenna can get away with a height of only λ/4. Furthermore, the directivity of a vertical HF antenna can be effectively employed at the reception end to cancel out high-angle interference by near-by stations. This is why some stations use receive-only phased-arrays of verticals on the low bands.&lt;/p&gt;&#xA;&lt;h2&gt;Polarisation at HF&lt;/h2&gt;&#xA;&lt;p&gt;Polarisation is not really an issue at HF (apart from lightning and man-made noise considerations). This is so because the ionosphere is mainly an anisotropic medium, i.e. it messes up polarisation.&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-05-21T19:44:12.893" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="495" PostTypeId="1" CreationDate="2013-11-01T01:42:18.370" Score="23" ViewCount="4296" Body="&lt;p&gt;Dipoles have the 2 wires going to each leg of the antenna completing the circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Big AM towers use the second wire as a ground plane&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But how to handheld rigs transmit and recieve with just one wire sticking in the air?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2015-12-15T23:58:05.367" LastActivityDate="2020-03-16T11:23:11.620" Title="How do Handheld antennas work without ground?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;ht&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="496" PostTypeId="1" AcceptedAnswerId="499" CreationDate="2013-11-01T01:51:18.783" Score="8" ViewCount="810" Body="&lt;p&gt;I have a 5 watt 2 meter handheld transceiver and want to build a helmet with an antenna, microphone (with VOX enabled) and earpiece for the radio. For the antenna part, I just want to do something simple like a wire at the right length. I'm 15 and saving for so much other stuff (like a signal generator, bench power supply etc.) and can't really afford an SWR meter. &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2017-04-28T18:06:46.313" LastActivityDate="2017-04-28T18:06:46.313" Title="Do I need a SWR meter for a basic 2 meter antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;ht&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="497" PostTypeId="2" ParentId="495" CreationDate="2013-11-01T01:59:13.687" Score="17" Body="&lt;p&gt;Your body acts as the ground when using a handheld radio. By holding the radio, you are capacitively coupled to the radio and make the other leg of the antenna. This is one of the reasons to hold the radio in your hand away from your body while using it, rather than using it while attached to a belt clip. (The other reasons pertain to RF safety.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you aren't a very good ground system, so you can improve the efficiency of a handheld's antenna by attaching a counterpoise to the radio to be a better ground. There is a product called a &quot;rat tail&quot; designed for this purpose, but you can easily homebrew your own by attaching any handy piece of wire about a quarter wavelength long to the radio's case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As noted in a comment: &lt;a href=&quot;http://www.hamuniverse.com/htantennamod.html&quot;&gt;further details about adding your own ground/counterpoise&lt;/a&gt; to an HT.&lt;/p&gt;&#xA;" OwnerUserId="236" LastEditorUserId="236" LastEditDate="2013-11-01T06:32:07.253" LastActivityDate="2013-11-01T06:32:07.253" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="498" PostTypeId="2" ParentId="111" CreationDate="2013-11-01T02:03:18.813" Score="3" Body="&lt;h2&gt;Cheaper &amp;amp; less loss&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;The main advantage of two-wire transmission lines over coaxial cable is, apart from reduced cost, also much lower loss. This is because the dielectric in two-wire lines is predominantly air. Plastic dielectrics provide more loss.&#xA;In that respect, open-wire line has the least loss of all two-wire transmission lines, window-line a bit more and twin-lead ribbon line even more so.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Loss measurements&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;A classic paper by Wes Stewart, N7WS reports on &lt;a href=&quot;http://www.k6mhe.com/n7ws/LadderLineUpdate.PDF&quot; rel=&quot;nofollow&quot;&gt;loss measurements of 450Ω &quot;Wireman&quot; window-line&lt;/a&gt;. An impedance-matched, 100ft length of medium-grade type 552 window-line showed 0.24dB loss at 20MHz under dry conditions. In contrast, the &lt;em&gt;ARRL Antenna Book&lt;/em&gt; reports for an impedance-matched 100ft length of RG-213 coaxial cable at the same frequency a loss of slightly more than 1.0dB.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Additional mismatch loss&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Please, notice twice the use of the word &quot;impedance-matched&quot; in the previous paragraph. This is because a mismatched line will suffer additional power loss. The maximum voltage and current amplitudes on a mismatched line are proportional to the square root of the standing-wave ratio $(\sqrt{SWR})$. This increase in effective current raises the ohmic losses $(I^{2}R)$ accordingly, whereas the increase in effective voltage increases the losses in the dielectric $(\frac{E^{2}}{R})$.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Typical use case&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;From a practical point of view, suppose you happen to have a severely mismatched antenna and you chose to perform the impedance matching not at the antenna but in the shack. In such a case, it is in your interest to use a two-wire line of sufficient voltage and current rating over a coaxial cable. Not only will the loss and cost be much lower than with coax, also a voltage breakdown of the dielectric will be less likely to occur.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For insanely high power levels (broadcast), four- and five-wire lines may offer a solution.&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2013-11-02T10:01:42.543" LastActivityDate="2013-11-02T10:01:42.543" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="499" PostTypeId="2" ParentId="496" CreationDate="2013-11-01T02:03:21.640" Score="10" Body="&lt;p&gt;At power levels that low, you probably don't need an SWR meter permanently installed. You will find it useful to have an SWR meter or antenna analyzer available when building the antenna, though, to ensure it is properly operating on your chosen frequencies. Perhaps you can borrow one from a friend, mentor, or local radio club to use while building your kit?&lt;/p&gt;&#xA;" OwnerUserId="236" LastActivityDate="2013-11-01T02:03:21.640" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="500" PostTypeId="2" ParentId="490" CreationDate="2013-11-01T02:11:10.873" Score="0" Body="&lt;p&gt;There are store-and-repeat repeaters available for simplex, FM analog voice use. Such a repeater listens to the entire sent message, then repeats the entire message on the same frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another repeater-like option that works without a duplexer is a cross-band repeater. Unlike a typical FM repeater which has input and output on the same band, a cross-band repeater typically has one transceiver on a VHF frequency and one transceiver on a UHF frequency. Whatever it hears on one band, it repeats on the other, often (depending on configuration) in both directions.&lt;/p&gt;&#xA;" OwnerUserId="236" LastActivityDate="2013-11-01T02:11:10.873" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="501" PostTypeId="1" AcceptedAnswerId="502" CreationDate="2013-11-01T05:51:39.117" Score="9" ViewCount="3306" Body="&lt;p&gt;Just looking around at various rigs online for a fiend. Lots of them look really attractive TS-480, K2, K3, FT-450D, FT-950, IC-78, FT-897 to name just a few...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These rigs are mostly HF, albeit some are also VHF/UHF capable. Yet the antenna connector used is usually either PL259, or SO239. Both mentioned connectors are known UHF.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What is the rationale behind having a UHF connector attached to an (essentially) HF rig? &lt;/li&gt;&#xA;&lt;li&gt;Is it merely a matter of cost/convenience as listed in &lt;a href=&quot;https://ham.stackexchange.com/questions/142/pros-cons-of-the-pl259-so239-connector-m-type&quot;&gt;Pros/cons of the PL259/SO239 connector (M type)?&lt;/a&gt;?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-12-29T17:19:28.937" Title="Why do so many HF transceivers use a UHF connector?" Tags="&lt;transceiver&gt;&lt;connectors&gt;&lt;pl259-so239-connector&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="502" PostTypeId="2" ParentId="501" CreationDate="2013-11-01T06:57:29.310" Score="17" Body="&lt;p&gt;The &lt;a href=&quot;http://en.wikipedia.org/wiki/UHF_connector&quot; rel=&quot;noreferrer&quot;&gt;&quot;UHF&quot; PL259/SO239 connector&lt;/a&gt;, which was originally designed at World War II times as a &lt;em&gt;shielded banana plug&lt;/em&gt; is actually &lt;strong&gt;not a very good connector to be used on UHF frequencies&lt;/strong&gt;, due to its non-continuous impedance and other properties. The common name is a bit misleading, since it's old - at the time of the design, UHF referred to frequencies above 30 MHz, and by today's standards UHF is 300 MHz to 3 GHz. &lt;a href=&quot;http://www.qsl.net/vk3jeg/pl259tst.html&quot; rel=&quot;noreferrer&quot;&gt;This measurement&lt;/a&gt; shows 0.2 db insertion loss at 144 MHz and 1 db insertion loss at 432 MHz, and with low-quality connectors (or higher frequency such as 2.4 GHz) it would be worse. The connector works fine on the frequencies it was designed for: HF and VHF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most modern HF rigs come with these connectors mostly because it has become an industry standard for amateur HF transceivers, and it works. It might not be the best connector on the face of the earth, but everyone already has them on their rigs, cables, amplifiers, tuners and antenna switches. When someone produces an HF rig with some other connector, most users will have to use adapters or build adapter cables. &lt;strong&gt;Cost, convenience, standard solution.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-11-05T20:12:24.553" LastActivityDate="2013-11-05T20:12:24.553" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="503" PostTypeId="5" CreationDate="2013-11-01T08:42:52.463" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-01T08:42:52.463" LastActivityDate="2013-11-01T08:42:52.463" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="504" PostTypeId="4" CreationDate="2013-11-01T08:42:52.463" Score="0" Body="Time Division Multiple Access refers to the ability of multiple users to transmit on the same frequency, by using specific time &quot;slots&quot; and normally higher-speed burst transmissions compared to a single-user channel." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-01T14:23:26.010" LastActivityDate="2013-11-01T14:23:26.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="505" PostTypeId="1" CreationDate="2013-11-01T13:17:36.553" Score="2" ViewCount="399" Body="&lt;p&gt;I have the K1JEK Cobra UltraLite and it works exceptionally well. However that was when I had a larger yard. Moved to a house with a smaller lot and now can't use the JEK Cobra (max span between trees is 80 ft, antenna is about 108 ft). I thew up a temporary 40M dipole but it's turning out to be more of a cloud warmer than performer. Could I cut the Cobra UltraLite down to 75 feet or would I have issues with resonance? Besides a vertical, what other options do I have for 75, 40, and 20 meters which have good DX performance?&lt;/p&gt;&#xA;" OwnerUserId="283" LastActivityDate="2013-11-02T03:04:15.090" Title="Horizontal dipole for a 80 foot span?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="506" PostTypeId="2" ParentId="146" CreationDate="2013-11-01T13:27:44.120" Score="1" Body="&lt;p&gt;If I could have only one antenaa, any antenna, it be a 150' Big Bertha with stacked tribanders :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before a good answer can be made, we need some more information:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) What bands are you interested in working? 2) Can you get a horizontal antenna at least λ/4 high and preferably λ/2 high? 3) Do you have an antenna tuner?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were flat broke and had high trees, I would make a fan dipole with one leg on 80m/75m, one leg 40m (gives you 15m for free as it's the 3rd harmonic) and one leg 10m. Depending on the situation, you could probably pull 20m out of either 40m leg or 10m with a close enough match to not need a tuner.  Having one would tighten the match, but probably wouldn't make a noticable difference.  Not counting the optional tuner, you would be hard pressed to spend $50 on this solution.  You'd have resonant antennas on the primary bands and could work the world no problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If soldering 6 wires is a problem, and you had a tuner, a G5RV or clone would be an option.  It's an all band solution, but is a compromise on all bands and a tuner is required for a good match.  You can work a lot of countries with one, but it will set you back $75-$100 plus a tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I had no trees, or low trees or no good way to hang a dipole, I would go with a multiband vertical like the GAP Challenger DX.  It uses stub matching and gives a no tuner between than 1.5:1 on all the HF bands plus 6m and 2m.  It's a bit of a compromise on 80m and is worthless on 160m though.  It uses 3 couterpoise wires instead of a large radial field and you can work the work 40m and up no problem (I have one).  But it costs $350.  There are cheaper ones, but they are more and more of a compromise especially the ones that use coils to make up for their physical size.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have both a vertical and dipoles and I find the noise difference to be negligible, but that's certainly something that is going to vary by location.  In a city or dense suburban area, RF trash from the neighbor's plasma TV might rule out a vertical (as a previous poster noted, most man-made RFI is vertically polarized).&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-01T15:03:53.047" LastActivityDate="2013-11-01T15:03:53.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="507" PostTypeId="2" ParentId="505" CreationDate="2013-11-01T13:36:31.603" Score="3" Body="&lt;p&gt;According to the website, they are 41', 73' and 140' long.  Assuming you have the 140' model, do you have more than 2 trees such that you create a hoizontal V?  A shallow angle V isn't going to affect the pattern noticably.  You could also go with an inverted V especially if you can get the center high enough.  Or turn it into the 73' model and accept the loss of 160m (probably).&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-01T13:36:31.603" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="508" PostTypeId="1" CreationDate="2013-11-01T13:49:29.573" Score="1" ViewCount="1636" Body="&lt;p&gt;I google search &quot;&lt;a href=&quot;http://www.google.com/search?q=echolink%20nodes%20in%20germany&amp;amp;oq=echolink%20nodes%20in%20germany&amp;amp;aqs=chrome.0.69i59j0l2.4140j0j1&amp;amp;sourceid=chrome&amp;amp;ie=UTF-8&quot; rel=&quot;nofollow&quot;&gt;Echolink Nodes in Germany&lt;/a&gt;&quot; and no results show of nodes which are in Germany. I search repeater book, but it seems like it only has North American nodes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a good source where I can find all of the Nodes in a specific country?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use echomac which doesn't have the option to choose a country&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2013-11-01T14:03:23.223" LastActivityDate="2013-11-01T14:03:23.223" Title="Where to find a list of echolink nodes in a specific country" Tags="&lt;echolink&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="509" PostTypeId="2" ParentId="508" CreationDate="2013-11-01T14:00:22.100" Score="2" Body="&lt;p&gt;If you download and install the Echolink software, under Stations you can simply choose Locations/Europe/Germany and it will list all currently active nodes.&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-11-01T14:00:22.100" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="510" PostTypeId="2" ParentId="441" CreationDate="2013-11-01T14:14:03.450" Score="3" Body="&lt;p&gt;While I can't duplicate the issue, I have seen periodic eccentric behavior with the Baofeng HT memory locations. The solution was to use a PC and program the radio with the free &lt;a href=&quot;http://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow&quot;&gt;CHIRP software&lt;/a&gt;. Programming cable required.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2013-11-01T14:14:03.450" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="511" PostTypeId="2" ParentId="186" CreationDate="2013-11-01T14:30:47.087" Score="1" Body="&lt;p&gt;At a guess, the problem is probably a timing issue with the way the antennas receive signals.  At the speed you are using here, 2.4GHz or 5GHz, small things matter. Early tests with repurposed Part 15 hardware had problems initiating a link at 34 miles as the firmware designed for WiFi house networks (&amp;lt;100') had already given up waiting and was retrying before the ACK came back (IEEE 802.11 Experiments in Virginia’s Shenandoah Valley, QST July 2005).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;John Champa, KBOCL (SK), did a lot of writing popularizing HSMM in CQ VHF magazine.  The heyday of this seems to have been 2003-2008.  While otherwise hard to get, scans of some of his articles are to be found at &lt;a href=&quot;http://hsmm.wikispaces.com&quot; rel=&quot;nofollow&quot;&gt;http://hsmm.wikispaces.com&lt;/a&gt;.  In his Spring 2004 article called &quot;The Frontllnee: HSMM Part 2 - Developments in Amateur Radio&quot;, he mentions:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Mixed Antenna Design Problem: This is the possibility of a unique&#xA;  situation when using HSMM radio with certain antennas which requires&#xA;  more amateur radio study. It is often thought that as long as both&#xA;  antennas at the ends of an HSMM radio link are of broad-bandwidth&#xA;  design (the HSMM signal is 22 MHz wide) and of the same polarization&#xA;  (usually horizontal) then this is acceptable and all is okay. While&#xA;  this may be true for other wide signals, such as analog ATV VSB&#xA;  (vestigial sideband) signals or analog ATV-FM signals, it may not be&#xA;  true with even more broad-bandwidth high-speed digital signals. Some&#xA;  evidence seems to indicate that, for example, the use of a&#xA;  horizontally polarized dish antenna with a dipole feedpoint at one end&#xA;  ofthe link and the use of a horizontally polarized long loop Yagi at&#xA;  the other end (again both broad-bandwidth antennas and both&#xA;  horizontally polarized) may nonetheless introduce a problem (higher&#xA;  BER, or bit error rate) because of symbol errors caused by the manner&#xA;  in which each antenna manipulates the radio-signal wave front. Again,&#xA;  further radio amateur experimentation with HSMM radio signals is&#xA;  warranted to determine the impact of using mixed antenna types on the&#xA;  radio link .&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, he gives no specific references to his source on that an almost all the links mention in the acknowledge section are out of date.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-01T14:30:47.087" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="512" PostTypeId="2" ParentId="471" CreationDate="2013-11-01T16:16:09.233" Score="1" Body="&lt;p&gt;Here in VU land i.e. India following the &lt;a href=&quot;http://www.wpc.dot.gov.in/DocFiles/amateur_new_guidelines.pdf&quot; rel=&quot;nofollow&quot;&gt;2005/2009 notifications from WPC&lt;/a&gt; (Wireless Planning &amp;amp; Coordination Wing), CW is not required for the Indian equivalent of the combined US novice/tech called 'restricted'. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A nominal 8WPM CW &lt;em&gt;is&lt;/em&gt; however required for the Indian equivalent of US extra/general.&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-11-01T19:06:03.330" LastActivityDate="2013-11-01T19:06:03.330" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="513" PostTypeId="2" ParentId="23" CreationDate="2013-11-01T21:53:08.367" Score="0" Body="&lt;p&gt;I have the Baoefeng UV-5r+ (UV-5r with extra Rx capability) I've been able to get much better reception with a 14&quot; SMA Female DIAMOND antenna. (I wish I had a quantifiable measurement here other than 'better')&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've also been gifted a &lt;em&gt;backpackers&lt;/em&gt; j-pole antenna by a friend. (&lt;a href=&quot;http://www.ebay.com/itm/Dual-Band-VHF-UHF-HAM-MURS-GMRS-Commericial-Portable-Emergency-Antenna/111194576827?_trksid=p2047675.m1985&amp;amp;_trkparms=aid=444000&amp;amp;algo=SOI.CURRENT&amp;amp;ao=1&amp;amp;asc=13&amp;amp;meid=2403135518147337848&amp;amp;pid=100012&amp;amp;prg=1014&amp;amp;rk=1&amp;amp;rkt=3&amp;amp;sd=121158488980&amp;amp;#ht_862wt_1151&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;) This I can roll up about the same size as a small book. It gives me an amazing range, and cost him 24 bucks. That same friend bought the same version for a permanent mount (&lt;a href=&quot;http://www.ebay.com/itm/Dual-Band-VHF-UHF-Ham-Commercial-MURS-and-GMRS-versions-Base-Station-Antenna-/121158488980&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;), put it in his attic, and he is VERY satisfied and is able to conduct nets with his UV-5r. You'll need to adapt SMA Female -&gt; SMA Male -&gt; SO-239(?). I can hang it in my room or outside to run with the big boys. (and with only 75 bucks of equipment!) I believe the antenna can take up to 75 watts, so its a great piece of transition equipment as you get more into it.&lt;/p&gt;&#xA;" OwnerUserId="286" LastActivityDate="2013-11-01T21:53:08.367" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="514" PostTypeId="1" AcceptedAnswerId="547" CreationDate="2013-11-01T22:18:57.743" Score="3" ViewCount="1642" Body="&lt;p&gt;I broke out my 2AT after a number of years.  The nicads in it are dead.  What kind of replacement inserts should I be looking for?  Nicads are so 1980s.  What is the current 'best' technology?&lt;/p&gt;&#xA;" OwnerUserId="287" LastEditorUserId="63" LastEditDate="2013-11-06T11:09:21.093" LastActivityDate="2017-08-19T06:57:47.553" Title="What is the best battery type for replacing old NiCds in a Icom 2AT?" Tags="&lt;ht&gt;&lt;battery&gt;" AnswerCount="3" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="515" PostTypeId="2" ParentId="23" CreationDate="2013-11-02T00:48:30.423" Score="2" Body="&lt;p&gt;For home use, I'd recommend a dual-band J-Pole or Ground Plane antenna.  There are many instructions on the web for building your own.  Or you could go the commercial route as well.  I personally own the dual band J-Pole antenna from Arrow Antennas and it works incredibly well.&#xA;&lt;a href=&quot;http://www.arrowantennas.com/osj/j-pole.html&quot; rel=&quot;nofollow&quot;&gt;http://www.arrowantennas.com/osj/j-pole.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the home brewed stuff, start here then do a quick search on the web:&#xA;&lt;a href=&quot;http://www.hamuniverse.com/jpole.html&quot; rel=&quot;nofollow&quot;&gt;http://www.hamuniverse.com/jpole.html&lt;/a&gt;&#xA;I'd give you some more links.  But this website is limiting me to two links until my reputation improves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As other people have mentioned, your best bang for the buck is in an antenna.  Good luck!&lt;/p&gt;&#xA;" OwnerUserId="261" LastActivityDate="2013-11-02T00:48:30.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="516" PostTypeId="1" AcceptedAnswerId="620" CreationDate="2013-11-02T01:23:06.353" Score="17" ViewCount="3266" Body="&lt;p&gt;I see on the allocation chart all modes and frequencies are allowed above 275 gigahertz. Has anybody experimented with this? Are there interesting things you can do on these extremely high frequencies?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bandwidth must be amazing here; maybe someone could make something like wifi but faster!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is it even possible to make the electronic circuits operate at these frequencies?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2013-11-10T19:20:25.047" LastActivityDate="2017-05-17T05:31:47.653" Title="Ham radio above 275 GHz" Tags="&lt;ehf&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="517" PostTypeId="5" CreationDate="2013-11-02T01:24:38.753" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-02T01:24:38.753" LastActivityDate="2013-11-02T01:24:38.753" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="518" PostTypeId="4" CreationDate="2013-11-02T01:24:38.753" Score="0" Body="Extremely High Frequency, or signals between 30-300 Giga-Hertz.&#xD;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2013-11-04T17:31:13.557" LastActivityDate="2013-11-04T17:31:13.557" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="519" PostTypeId="2" ParentId="505" CreationDate="2013-11-02T02:49:46.340" Score="1" Body="&lt;p&gt;Build a set of square full wave loops, one for each band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note this antenna, while taking up similar vertical space to a 1/4-3/8 wave vertical takes much less side to side than a dipole (1/4-3/8 wave vs 1/2 wave), and is &lt;strong&gt;horizontally polarized&lt;/strong&gt; when fed from the bottom.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want DX, the loop should be in the vertical plane and oriented so that the perpendicular from the plane of the loop points towards two spots (front and back) that are desirable to contact.    &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gain has a price and edge on will suffer, a bit more than edge on with a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a 80m square loop it is obviously 20m on a side, or about 66 feet.  The hard part will be getting the top leg 66 feet above the bottom leg.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you make it diamond shaped instead of square the top will be higher:  20m * sqrt(2), which is 20m*1.414 = 28m  = 92 feet from top apex to bottom and also side apex to side apex.   This violates your side to side size limit of 80 feet.  So if you want an 80m loop you have room for the square variety if you can figure out how to suspend a wire up high.  If you have two trees that are at least 70 feet high and 66 feet apart, it may be worth considering.  There are a number of devices that can get wires to height, and as I'll show below a perfect square shape is not required.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, 20m and higher frequency versions are proportionally smaller and easily done on the lot you describe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is useful to have an antenna analyzer to use the exact length of wire that will resonate at the frequency of interest.  However, the resistance component of impedance at resonance is not 50 ohms, so you'll need a balun transformer (try 2:1 or 3:1) or a homemade air wound balun coiled up from an electrical 1/4 wavelength of 75 or 92 ohm coax.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't need to get the shape perfectly square, as shown in this picture of a 15m beach loop below I made from 12 gauge solid wire, a jackite kite pole, and a bamboo cross arm.  A coil of white 75 ohm coax acting as the transformer/balun can be seen a little below the bottom apex of the loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Qj5EK.jpg&quot; alt=&quot;Full wave loop for 15m beach portable use&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2013-11-02T03:04:15.090" LastActivityDate="2013-11-02T03:04:15.090" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="520" PostTypeId="1" CreationDate="2013-11-02T11:49:47.850" Score="4" ViewCount="1819" Body="&lt;p&gt;I've been trying to install cuSDR64 on Ubuntu so as to have a 4-receiver 4-display SDR setup. I found the Windows repository on svn &lt;a href=&quot;http://svn.tapr.org/repos_sdr_hpsdr/trunk/DL3HVH/cuSDR64/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. But, it gives an error (&lt;a href=&quot;https://ham.stackexchange.com/questions/521/installing-cusdr64-on-windows-7-64-bit&quot;&gt;check this question&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cuSDR home page does mention that it can be built on Linux as well, but when I tried to find the source code, I found nothing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I install/build cuSDR64 on Ubuntu 13.04?&lt;/p&gt;&#xA;" OwnerUserId="288" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-11-03T09:38:15.860" Title="Installing cuSDR on Ubuntu 13.04" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;linux&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="522" PostTypeId="1" AcceptedAnswerId="535" CreationDate="2013-11-02T18:02:25.343" Score="10" ViewCount="4713" Body="&lt;p&gt;For the 20m - 10m and 6m bands, will having my dipoles below the tops of trees (I live in redwood forests) drastically affect the RF power out or radiation patterns of my dipoles if I can still get them at least 1/4 wavelength above the ground?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or will the greenery absorb and/or distort the radiation patterns?&lt;/p&gt;&#xA;" OwnerUserId="134" LastEditorUserId="76" LastEditDate="2015-12-15T22:19:08.517" LastActivityDate="2015-12-15T22:19:08.517" Title="How much RF energy do trees and branches absorb?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;dipole&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="523" PostTypeId="1" AcceptedAnswerId="691" CreationDate="2013-11-02T19:22:08.623" Score="6" ViewCount="827" Body="&lt;p&gt;My 22-years old Fluke 79 died on me today...&#xA;Luckily, it was a quiet dead, but nonetheless it left me a bit emotional...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I am in urgent need of a replacement digital multimeter. This made me wonder whether there would be a model around that is more interesting to own for a radio amateur? Perhaps one with an RF-probe included? Or should I just go with a run-of-the-mill model?&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="76" LastEditDate="2014-12-02T00:21:05.650" LastActivityDate="2014-12-02T00:21:05.650" Title="Is there a digital multimeter that is more interesting for a ham than a run-of-the-mill model?" Tags="&lt;voltage&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="2" ClosedDate="2014-12-01T23:58:17.717" ContentLicense="CC BY-SA 3.0" />
  <row Id="524" PostTypeId="2" ParentId="208" CreationDate="2013-11-02T19:59:04.167" Score="0" Body="&lt;p&gt;In your situation, I would shunt feed the 20m tower on the roof and drop one 20m wire from the roof if the building is tall enough. If the building is lower than that, you can end the wire in a T-shape, and/or load it or, alternatively, complete the return path by installing two or more elevated radials.&#xA;Loading will lower the bandwidth of the antenna significantly, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shunt-feeding offers the advantage that you can earth your roof tower for proper lightning protection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you feed with coaxial cable, do not forget to also install a sheath current choke.&lt;/p&gt;&#xA;" OwnerUserId="250" LastActivityDate="2013-11-02T19:59:04.167" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="525" PostTypeId="1" CreationDate="2013-11-02T20:14:08.000" Score="3" ViewCount="348" Body="&lt;p&gt;I am going to build a new home and I would like to use energy-saving fluorescent tube lamps in some rooms. Manufacturers are currently pushing electronic ballasts a lot in favour of switchstart series ballasts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have no experience with electronic ballasts. Should I be wary of them? Do these electronic ballasts cause more LF, MF or HF interference?&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="22" LastEditDate="2014-12-01T23:57:08.870" LastActivityDate="2014-12-06T21:04:02.173" Title="Do electronic ballasts for fluorescent tube lamps cause HF interference?" Tags="&lt;hf&gt;&lt;rfi&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="526" PostTypeId="1" CreationDate="2013-11-02T23:19:53.393" Score="9" ViewCount="21910" Body="&lt;p&gt;I have an old satellite dish just lying around and was wondering how to hook it up to my baofeng uv-5r plus.&lt;/p&gt;&#xA;" OwnerUserId="292" LastEditorUserId="70" LastEditDate="2013-11-04T17:31:07.510" LastActivityDate="2019-06-25T02:19:33.930" Title="How would I modify a satellite dish to transmit and/or receive to a Baofeng UV-5r plus? ( A handheld transceiver) If it's possible" Tags="&lt;ht&gt;&lt;antenna-construction&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="527" PostTypeId="1" AcceptedAnswerId="528" CreationDate="2013-11-03T03:40:29.957" Score="6" ViewCount="1843" Body="&lt;p&gt;The Yaesu FT-7900R has a single data port (mini DIN 6-pin) for 1200 and 9600 bps TNCs. Page 10 of &lt;a href=&quot;http://yaesu.com/downloadFile.cfm?FileID=5129&amp;amp;FileCatID=150&amp;amp;FileName=FT-7900R_OM_ENG_EH016M110.pdf&amp;amp;FileContentType=application/pdf&quot; rel=&quot;noreferrer&quot;&gt;the manual&lt;/a&gt; states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In accordance with industry standards, the signal levels, impedances, and bandwidths are significantly different on 9600 bps as opposed to 1200 bps. If your TNC does not provide multiple lines to accommodate such optimization, you may still be able to utilize your TNC, if it is designed for multiple-radio use, by connecting the TNC “Radio 1” port to the 1200 bps lines on the FT-7900R, and the “Radio 2” port to the 9600 bps lines.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Is it possible to follow these directions with a KPC-9612+?&lt;/p&gt;&#xA;" OwnerUserId="227" LastActivityDate="2016-03-25T19:30:38.527" Title="Can a Yaesu FT-7900R be physically connected to both KPC-9612+ ports?" Tags="&lt;packet&gt;&lt;yaesu&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="528" PostTypeId="2" ParentId="527" CreationDate="2013-11-03T06:27:43.333" Score="2" Body="&lt;p&gt;&lt;strong&gt;RX audio:&lt;/strong&gt; The FT-7900R has separate audio outputs for RX audio on the DIN connector for 1200 and 9600, so those can be simply wired to the two separate KPC-9612+ ports.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;PTT:&lt;/strong&gt; The PTT line has a little voltage provided by the radio, and the TNC's PTT pin grounds that pin to transmit. You can directly wire both TNC port PTTs to the radio, and it'll transmit when either of the TNC ports ground the pin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;TX audio:&lt;/strong&gt; The correct method would be to provide some mixing circuit to mix the audio signal outputs of the TNC. Some audio level loss is OK, since you can compensate by adjusting the output level of the TNC up, so a passive circuit is good. The most important thing is that the mixing may not affect the frequency response, since it's quite important for good 9600 bit/s operation. Simply wiring both the 9600 and 1200 bit/s audio outputs of the TNC together might work, or it might not, depending on the type of the outputs on the TNC. A simple resistor mixer might work better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's probably obvious, but you'll have to make sure the two TNC ports don't transmit at the same time - the transmit audio, mixed 1200/9600 data, would not make any sense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a community wiki, so if someone has better details on the TX audio connection, please edit it in.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-11-03T16:57:55.037" LastActivityDate="2013-11-03T16:57:55.037" CommentCount="1" CommunityOwnedDate="2013-11-03T06:27:43.333" ContentLicense="CC BY-SA 3.0" />
  <row Id="529" PostTypeId="2" ParentId="522" CreationDate="2013-11-03T09:22:10.107" Score="3" Body="&lt;p&gt;The greenery will always distort, but you're right, the distortion will be less as you increase the height of the dipoles above the greenery.  You get some reflection.  You get some polarisation effects as well, which may or may not be important depending on the transmission mode and the path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Get thee to a library and put in a request for&#xA;Radio Science, Volume 17, Issue 5, pages 1027–1036, September-October 1982, which contains a paper:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Brown, G. S., and W. J. Curry (1982), A theory and model for wave propagation through foliage, Radio Sci., 17(5), 1027–1036, doi:10.1029/RS017i005p01027.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or measure the RF power many wavelengths away, at various antenna heights.&lt;/p&gt;&#xA;" OwnerUserId="123" LastActivityDate="2013-11-03T09:22:10.107" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="530" PostTypeId="2" ParentId="520" CreationDate="2013-11-03T09:38:15.860" Score="1" Body="&lt;p&gt;I'm a software builder and packager.  While I don't have any use for cuSDR at the moment, I looked at the svn repository and home page, and did some googling:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;there was no Linux installation documentation that I could find.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;there was no common build scripting in the repository.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;there were no Linux packages prepared.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;there does seem to be discussions about cuSDR on the &lt;a href=&quot;http://lists.openhpsdr.org/listinfo.cgi/hpsdr-openhpsdr.org&quot; rel=&quot;nofollow&quot; title=&quot;hpsdr mailing list&quot;&gt;mailing list&lt;/a&gt;, and that would seem to be a good place to ask for help from people who may have done it.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;there is also a &lt;a href=&quot;http://groups.yahoo.com/neo/groups/apache-labs/conversations/topics/503&quot; rel=&quot;nofollow&quot; title=&quot;packaging discussion&quot;&gt;brief packaging discussion&lt;/a&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Good luck, you'll need it.  ;-)&lt;/p&gt;&#xA;" OwnerUserId="123" LastActivityDate="2013-11-03T09:38:15.860" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="531" PostTypeId="2" ParentId="525" CreationDate="2013-11-03T14:11:37.487" Score="2" Body="&lt;p&gt;To the question in your title - do they cause interference - the answer is absolutely yes. However, it's hard to answer which causes &lt;em&gt;more&lt;/em&gt; simply because there is a lot of variation between manufacturers and models. QST (the US ARRL magazine) recently ran an article on this topic - the conclusion was that the number one factor in RF interference, regardless of band, was whether the unit was labeled for residential use or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our FCC places stricter limits on residential ballasts than on commercial for RFI. I cannot find any specific regulatory information for the EU, but I suspect that you'll also be able to find residential units, as many of the big-name brands sell the same product worldwide and get it fully approved to every country's requirements.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-11-03T14:11:37.487" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="532" PostTypeId="1" AcceptedAnswerId="534" CreationDate="2013-11-04T01:21:37.827" Score="4" ViewCount="978" Body="&lt;p&gt;In searching for suitable materials for a wire antenna, I found a few mentions of using string trimmer line to hold up each end of the antenna. This would be a nice option as it is readily available locally.  For a long-term installation, I've seen the use of UV-resistant Dacron rope.  How does string trimmer line compare in terms of strength and UV resistance? Is string trimmer line an acceptable option for short or long-term antenna installation?&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="76" LastEditDate="2013-11-04T09:38:54.003" LastActivityDate="2015-10-06T22:04:29.580" Title="Is string trimmer line suitable for supporting antennas?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;antenna-construction&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="533" PostTypeId="2" ParentId="526" CreationDate="2013-11-04T07:20:42.747" Score="13" Body="&lt;p&gt;Maybe....  A big project and probably not practical starting out. Would make  a conversation piece or odd recycling project.  How are you going to point it? Smaller antennas may work just as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A modern &quot;Dish TV&quot; or &quot;DIREC TV&quot; (R) that is about a foot across is practically useless for amateur radio transmitting and receiving.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a stock picture (Wikimedia) of an old 1980s style home satellite tv dish, about 8 to 15 feet across.  That's what you want to play with, if you have the time, energy, and patience.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/BT5nv.jpg&quot; alt=&quot;popular 1980s satellite receiving dish:  source WikiMedia&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These were popular in the early 1980s to receive pay TV channels like HBO direct from the satellite, unencrypted, without paying.  Once these channels were encrypted and consumers were asked to pay, the huge dishes started disappearing from homes and into the landfills.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the Baofeng uv-5r is a 144 Mhz / 440 Mhz handheld radio with 5W output.  This kind of handheld radio is suitable for use with local repeaters.  With more gain you can get into repeaters a little further away. You &lt;strong&gt;might&lt;/strong&gt; be able to hear the SO-50 satellite with a gain antenna, but this depends on the noise figure of the Baofeng and I'm a bit skeptical.  A Yaesu VX-8R can sometimes do it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you don't necessarily need a 10 foot dish for this.  You might hear the satellite with something handheld, like this &lt;a href=&quot;http://www.arrowantennas.com/arrowii/146-437.html&quot; rel=&quot;noreferrer&quot;&gt;portable yagi made by Arrow Antennas from aluminum arrow shafts&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more practical choice for adding range is a 2m/440 vertical or a 2m/440 yagi.  To hook these to your radio you would need an adapter cable to go from the PL259 or N connector on the coax from the external antenna down to the radio connector.  Don't use a straight through adapter as torque from the large coax and connector can tear the SMA antenna jack from the PC board inside the Baofeng.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So back to the topic of dishes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some examples of dish recycling by Hams:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://hackaday.com/2012/05/21/fta-dish-used-to-receive-l-band-amateur-radio/&quot; rel=&quot;noreferrer&quot;&gt;Converted to 1296 Mhz antenna, looks like a small helix is feeding it&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.youtube.com/watch?v=GECJx_wHpoc&quot; rel=&quot;noreferrer&quot;&gt;VE2AZ converted a TVRO dish to 1296 Mhz for Moonbounce&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So let me tell you why the dish is not such a great choice for 144 Mhz or 440 Mhz, but how you might be able to turn it into something interesting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dish is a good choice for high gain at microwave frequencies (several Ghz = several 1000 Mhz, wave length is a few inches or centimeters).  It is worth noting that Internet Wifi is around 2400 Mhz and there is an overlapping ham radio band.... so an old large TV dish might make a great wifi antenna. It works by focusing the signal onto a feed point.  At these frequencies the radio waves act more like light and the curved dish surface reflects a chunk of the radio waves the diameter of the dish from the target to arrive in phase and combine at the much smaller feed point suspended above the dish.  The principal is the same in a reflector telescope, with the dish and the bottom mirror the reflectors.  These work in part because the dish/reflector surface is large compared to the wavelength of the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But at VHF frequencies a wavelength of the radio signal is 2m or around 6 feet. A dish is little more effective than a simple single element reflector in a yagi or quad.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At UHF frequencies the dish still has some gain.  But not a lot. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many of these dishes were steel, so you could find a magnet mount 2m/440 antenna (like for an automobile), attach it to the dish and call yourself &quot;done&quot;.  I can't imagine a good reason for doing this.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A large dish could also be used on 440 Mhz either by modifying the feed or turning it into a helix antenna.  It might be usable on 144 Mhz by turning it into a helix antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modifying the feed is described in some of the old ARRL Antenna Handbook articles.  I seem to recall one suggested feed for a dish is a dipole or set of crossed dipoles.  The dipole or dipoles run parallel to the dish surface at some height above on the feedpoint axis.  If you want to try to use it for 440 Mhz you would make a 1/2 wave dipole wire antenna and attach it to the center support above the dish, near the old feedpoint.  It might be best to remove the old feedpoint and arm entirely and replace it with something non conductive that can allow moving the dipole up and down.  You would need to adjust the height of the feed above the dish for best signal strength before determining where to make a permanent attachment. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You would also need to check the SWR if you want to use it for transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A bit more challenging is to create a 2m helix based on the satellite dish, with the dish as the rear reflector.  This involves supporting a helix of wire above the dish, and admittedly it is a project.  Each loop of the helix is about a wavelength worth of wire and the travel is a little less than a 1/4 wavelength per round trip around the helix.  See &lt;a href=&quot;http://www.antenna-theory.com/antennas/travelling/helix.php&quot; rel=&quot;noreferrer&quot;&gt;Helical Antenna Theory&lt;/a&gt; or &lt;a href=&quot;http://en.wikipedia.org/wiki/Helical_antenna&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia Helical Antenna&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've made a &lt;a href=&quot;http://qrz.com/db/KI6CQ&quot; rel=&quot;noreferrer&quot;&gt;70cm helix antenna suitable for receiving low earth orbit ham radio satellites from bamboo and a Wal Mart Pizza Pan as the reflector&lt;/a&gt;.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/oKZHm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transmitting to the satellite is done on 2m with a more traditional antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But with a large dish, and a way to point it, it becomes possible to make a 2m helix antenna, or perhaps make a dual band helix by making the spirals concentric.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;While a conversation piece, helix antennas do not have more gain than yagis or quads that you can build or buy in the ham radio marketplace.&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2013-11-04T08:10:09.950" LastActivityDate="2013-11-04T08:10:09.950" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="534" PostTypeId="2" ParentId="532" CreationDate="2013-11-04T14:24:18.727" Score="6" Body="&lt;p&gt;String trimmer line is engineered for high tensile strength, resisting breakage, but it isn't meant for 1) long term outdoor exposure and 2) long, stable lengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Number 2 means it will stretch over time.  Not a lot, but at the lengths needed to support antennas will needed to be tightened repeatedly over the first day or two, whenever the temperature warms up, and monthly in general.  Number 1 means that the plastic will break down over time due mostly to UV exposure, but also because it is hydrophilic (absorbs water) and will be damaged by cold weather, and normal mechanical stress.  It should easily last a year, though, for moderate loads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It isn't rated for tensile strength in long lengths, so you'd have to do some experimentation to find a safe tension and load range, but for most HAM antennas it should be more than enough.  Don't try to use it as a guy wire for a mast, though.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-11-04T14:24:18.727" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="535" PostTypeId="2" ParentId="522" CreationDate="2013-11-04T14:41:27.303" Score="7" Body="&lt;p&gt;Trees do absorb some RF energy. So do buildings, hills, and other structures. There are very few cases where higher isn't better for antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I'd guess that most amateur radio dipoles are below the treetops. Will some energy be lost? Yes. Will the antenna still work? Absolutely. Without the specifics of yours trees, and your antenna, we can't say exactly what effect trees will have, but it's a fair guess that the absorption by trees will be somewhere between negligible to significant but probably not drastic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part of the reason trees aren't a huge problem is that at HF, they are electrically small. That is, their size is smaller, relative to the wavelength of interest. Longer wavelengths pass through things more easily, such as the thumping bass through those annoying cars.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, get your antenna as high as you can, but if you don't have a tower sticking above the redwoods, don't worry. Your antenna will still work.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-11-04T14:41:27.303" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="536" PostTypeId="2" ParentId="523" CreationDate="2013-11-04T15:54:51.430" Score="2" Body="&lt;p&gt;I believe the Fluke 79 did not have inductance/capacitance measurement built in. This is an affordable feature on modern multimeters which is quite useful for the ham. For example, it can be used to measure inductance on self-wound toroids which are used in kit-built radios and for repairs when OEM parts are not available. Likewise, capacitors are often unlabelled or poorly labelled these days, so it can help with that too.&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-11-04T15:54:51.430" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="537" PostTypeId="1" AcceptedAnswerId="545" CreationDate="2013-11-04T16:01:35.277" Score="9" ViewCount="894" Body="&lt;p&gt;I'm new to directional beam antennas, and saw that K9W Wake Island DXpedition was working 10 meters &quot;long-path&quot; at 1230z, or 6:30a.m. in Texas. This was late enough for the sun to be coming up, but is it even possible to make the &quot;long path&quot; connection that far around? I would have thought Wake Island was totally in the dark at that time. More generally, what is an ideal situation for long path, and is it simply a matter of pointing 180 degrees away from the listed direction on QRZ.com?&lt;/p&gt;&#xA;" OwnerUserId="43" LastEditorUserId="76" LastEditDate="2015-12-15T22:00:27.170" LastActivityDate="2015-12-15T22:00:27.170" Title="What is the correct procedure to beam long-path?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;long-path&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="538" PostTypeId="1" CreationDate="2013-11-04T23:02:11.077" Score="39" ViewCount="39459" Body="&lt;p&gt;I am preparing to construct a resonant, center-fed, horizontal dipole. I have seen people use baluns at the feedpoint of the antenna, and some people swear by them, but I have never gotten a satisfactory answer on &lt;em&gt;why&lt;/em&gt; you would use/need a balun. All the resonant dipole antennas I have made previously seemed to function just fine when used with 50 Ω coax and no balun. This consisted of connecting one leg of the dipole to the center conductor, and the other leg to the coax shield. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do know that the normal impedance of a center-fed dipole at resonance is about 75 Ω, so I can see that there would be an impedance matching benefit of a balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What benefits (and/or drawbacks) does a balun provide in a resonant dipole antenna?&lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2018-09-15T12:28:44.970" Title="Using a balun with a resonant dipole" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;balun&gt;" AnswerCount="7" CommentCount="1" FavoriteCount="17" ContentLicense="CC BY-SA 3.0" />
  <row Id="539" PostTypeId="2" ParentId="23" CreationDate="2013-11-05T12:18:37.037" Score="0" Body="&lt;p&gt;I was told that my signal would picket fence while I was in the car albeit I was only a couple miles from the repeater purchased this antenna for my yaesu vertex ft60r and the improvement was immediately noticable&#xA;&lt;a href=&quot;http://www.eham.net/reviews/detail/7741&quot; rel=&quot;nofollow&quot;&gt;http://www.eham.net/reviews/detail/7741&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="298" LastEditorUserId="87" LastEditDate="2013-11-05T15:56:57.723" LastActivityDate="2013-11-05T15:56:57.723" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="540" PostTypeId="1" AcceptedAnswerId="542" CreationDate="2013-11-05T12:50:48.280" Score="9" ViewCount="102" Body="&lt;p&gt;It's a fact of life that &lt;a href=&quot;http://en.wikipedia.org/wiki/Variable_capacitor#Mechanically_controlled&quot; rel=&quot;noreferrer&quot;&gt;air-gang capacitors&lt;/a&gt;, are increasingly more difficult to come by - having been superseded by the far more compact &lt;a href=&quot;http://en.wikipedia.org/wiki/Varicap&quot; rel=&quot;noreferrer&quot;&gt;varactor&lt;/a&gt; diodes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My part of the world components such as the venerable &lt;a href=&quot;http://pdf.datasheetcatalog.com/datasheet/philips/BB212.pdf&quot; rel=&quot;noreferrer&quot;&gt;BB212&lt;/a&gt;, MPN3700, MV1662 are almost unheard of at the local stores; anyway I'm only getting started at attempting home-brew. Real VCO stuff will &lt;em&gt;hopefully&lt;/em&gt; happen sometime in the future. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basic theory tells me applying multiple capacitors in parallel adds up the effective capacitance a circuit will see. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would I see the same behavior if several make-shift varicaps (say, 1N4007) were connected in parallel? i.e. does capacitance add up using varicaps in a tank that it does for any other capacitor?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="87" LastEditDate="2013-11-07T12:32:36.713" LastActivityDate="2013-11-07T12:32:36.713" Title="Can two diodes be parallelled in RB to get double the capacitance?" Tags="&lt;diy&gt;&lt;varicap&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="541" PostTypeId="2" ParentId="538" CreationDate="2013-11-05T13:46:54.463" Score="0" Body="&lt;p&gt;A so-called &quot;current balun&quot; consists of a bunch of ferrite cores with the coaxial feed line running through their centers. This greatly reduces RF current flow on the outside of the shield, which, in turn, reduces RF losses. It doesn't affect the impedance mismatch, but that's minor.&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2013-11-05T13:46:54.463" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="542" PostTypeId="2" ParentId="540" CreationDate="2013-11-05T14:16:14.100" Score="5" Body="&lt;p&gt;The short answer is yes, they do add in parallel.  But remember, the Cmin is doubled as well as the Cmax, so the tuning ratio hasn't changed.  Depending on what you are using them for, this may or may not matter. Of course you can offset this with an inductor.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-05T14:16:14.100" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="543" PostTypeId="2" ParentId="538" CreationDate="2013-11-05T14:17:14.687" Score="38" Body="&lt;p&gt;Well, the canonical answer is that the balun converts the dipole (BAlanced) to coax (UNbalanced). But what does that &lt;em&gt;mean&lt;/em&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For transmission lines (twin-lead or coax) to not radiate, each conductor must carry equal and opposite currents. It's these equal and opposite currents canceling each other that results in zero net field away from the transmission line. If the currents are not equal and opposite, then they don't cancel, and the difference results in an external electromagnetic field, and your transmission line radiates like an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is generally undesirable. When transmitting, it can mean high RF in the shack, messing with speakers, digital electronics, etc. If attached to a directional antenna, it causes problems transmitting and receiving because the actual radiation pattern is a combination of the intended antenna, and the unintentional antenna formed by the feedline, which probably isn't directional at all. If you've modeled your antenna, the model assumes a feedline that does not radiate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;OK fine, you need equal and opposite currents in coax to make it not radiate. If you attach it to a dipole, you should get that. It looks pretty symmetrical, right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well yes, the dipole is symmetrical, but the coax isn't. Usually, the shield is attached to ground somewhere. Even if it isn't, the geometry of the shield and the center conductor are not identical, so the shield will have a different impedance with respect to the dipole than the center conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regardless of the coax, the dipole may not be really symmetrical anyway. Consider not just the antenna, but everything in its near field. Is it perfectly level to the ground? Is one end closer to a metal gutter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The result of all these asymmetries is that each side of the dipole presents different impedances to the feedpoint. Ideally, the antenna would accept all the power sent to it by the transmitter. The equal and opposite currents put into the coax by the transmitter each go down opposite legs of the dipole where the EM energy is radiated away. But when the dipole is not balanced, the currents accepted by each leg of the dipole can't be equal. But, all the current must go somewhere, so the difference in current between the dipole legs is reflected back down the coax, back at the transmitter. (Note, this is distinct from reflection from impedance mismatches that causes high SWR.) However, this current doesn't have an equal and opposite current on the center conductor, so it radiates off the coax, like an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you operate a dipole fed with coax without a balun, this is happening to you, though you may not notice. The coax shield radiates just fine, and if your signal still finds its way to the other station and you don't give yourself RF burns, then there's no problem. A good RF ground at the feedline's entrance to the shack can reduce the RF re-entry. Even without any special attention to grounding, at 100W, the RF in the shack probably won't do more than make some speakers buzz, which might be considered &quot;normal&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By adding a balun, you are avoiding this issue. By isolating the feedline, you won't get RF in the shack, and your dipole will behave like a dipole described in textbooks. Your antenna tuning and performance won't be altered by other objects near the coax, because the coax won't be part of the antenna. If your dipole is in a good location for an antenna and your coax isn't, then you will have overall a better antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-12-23T17:59:58.413" LastActivityDate="2016-12-23T17:59:58.413" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="544" PostTypeId="2" ParentId="538" CreationDate="2013-11-05T14:49:48.893" Score="0" Body="&lt;p&gt;Phil did a good job of explaining what is going with the currents at work.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to the why you need to care, weel, as you note in the question, the feedpoint impedence is 75Ω and you are feeding it with 50Ω coax.  If the currents are not perfectly balanced, some of that RF is going to see that feedline as a lower impedence path and use it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will it still work? Yep, no problem.  Feed line radiation will affect the pattern of the antenna, but let's be honest here, a dipole not directional anyway, so you almost certainly won't notice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RF coming back may or may not matter. It depends on the power level you are using and the frequency. If you are running QRP on 80m, no issue.  If you are cranking 1500w, at almost any frequency, now you have a problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution is to add impedence to the outside of the coax sufficent to convince the RF to stay in the antenna.  How impedence depends on who you ask?  I have seen references state as little as 500Ω to be sufficent (ARRL Handbook), others say 1000Ω (W1HIS) and have read a long and compelling paper that states that the goal should be 5000Ω (K9YC).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the impedence presented by ferrite cores varys with frequency (and temperature). the two main variables in selecting ferrite are form factor and &quot;mix&quot; (what they are made of). You need to select ones targeted to your operating range (typically mix 43 or 31) and large enough to handle the power without heating up too much.  All ferrite has a magic temperature once crossed, the impedence drops to nothing but the resistence goes UP resulting in a thermal runnaway that melts your coax.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-05T14:49:48.893" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="545" PostTypeId="2" ParentId="537" CreationDate="2013-11-05T15:06:14.890" Score="4" Body="&lt;p&gt;You are correct, the long path azimuth is simply 180 from the bearing listed in QRZ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether it's going to work depends on a number of varibles: your power, your antenna, their antenna, the band, atmospheric conditions, the time of day, the terrain on the path and probably a few others I have forgotten.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doing 10m, a &quot;daytime&quot; band long path to the east at local dawn might work given favorable propigation conditions.  And the fact that when 10m is open, it can be really open.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have never made a long path QSO personally (well, on purpose anyway), but those folks that do work that way seem to be working &quot;diagonally&quot; if you will.  For instance, the long path to Europe from Australia is mostly over ocean (salt water being good for this).  And don't forget the great circle route is the true route you are looking at here, not the obvious &quot;straight line&quot; paths you see on flat maps.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-05T15:06:14.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="546" PostTypeId="2" ParentId="538" CreationDate="2013-11-05T15:40:38.957" Score="9" Body="&lt;p&gt;Another answer mentions the paper by K9YC, Jim Brown. This is the best reference on baluns in amateur radio. See: &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot;&gt;http://audiosystemsgroup.com/RFI-Ham.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Chapter 6 is about baluns and antennas. He says, &quot;The primary function of most baluns, at least in our ham stations, is to minimize the interaction of our antennas with the transmission lines that connect them to our radios.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The interactions we are minimizing are two, &quot;RF in the shack&quot; and common-mode noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Real antennas are unbalanced by their surroundings: trees, buildings, ground conductivity, and so on. This causes unequal impedances presented to the two terminals of the transmission line and problems with RF going other places. Any imbalance turns into a common-mode voltage on both conductors of the transmission line. This can radiate and cause problems with transmitted RF in your radios and in other electronic devices in your home and your neighbors'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common-mode signals can also be received. Nearly all nearby noise sources will be picked up equally by the two elements (and the transmission line) and show up at the radio summed with the desired signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A current balun (the only kind you want) will present a high impedance to common-mode signals and a low impedance to differential signals. If the two are 5000Ω and 50Ω, that is a 100X attenuation of the common-mode signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a dipole at about 30', strung between two trees and over our house. The house has a steel beam just off-center under the dipole. This is obviously unbalanced, even though the elements (separate for 40m and 20m) are equal length. Adding a balun dropped the received noise by about 6dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Drawbacks of a balun? Cost and attenuation. My balun (from Balun Designs) cost $55, a significant addition to the cost of a wire antenna. A well-designed toroidal balun will have an insertion loss of 0.1db (see &lt;a href=&quot;http://www.balundesigns.com/servlet/the-58/QRP-1-cln-1-baluns-balun/Detail&quot;&gt;http://www.balundesigns.com/servlet/the-58/QRP-1-cln-1-baluns-balun/Detail&lt;/a&gt;). A balun made from coiled coax may have significant attenuation due to the amount of coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I strongly recommend reading chapter 6 of K9YC's paper.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-11-05T15:40:38.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="547" PostTypeId="2" ParentId="514" CreationDate="2013-11-05T19:13:16.830" Score="4" Body="&lt;p&gt;Nickle Cadmium (NiCd) batteries are still quite popular for a variety of uses, however Nickle Metal Hydride (NiMH) and Lithium-Ion (Li-Ion) batteries have, for the most part, replaced NiCds.&lt;/p&gt;&#xA;&lt;p&gt;Lithium Ion batteries are generally considered the better of the two, but each have their pros/cons.&lt;/p&gt;&#xA;&lt;h2&gt;Lithium-Ion&lt;/h2&gt;&#xA;&lt;h3&gt;Pros:&lt;/h3&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Li-ion batteries have over twice the energy density of NiCds and about 30% more energy density than NiMHs.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Considerably less self discharge than both NiMH and NiCd.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;More recharge cycles which means longer battery life (as a whole).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Little to no &lt;a href=&quot;http://en.wikipedia.org/wiki/Memory_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;memory effect&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Cold resistant.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Lighter than both NiCd and NiMH.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h3&gt;Cons:&lt;/h3&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Expensive. Lithium Ion batteries are more expensive than both NiCd and NiMH.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h2&gt;NiMH&lt;/h2&gt;&#xA;&lt;h3&gt;Pros:&lt;/h3&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Cheaper than Li-ion&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;About 40% higher energy density than NiCd.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Less toxic than NiCd.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;More common (at least, for HTs).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h3&gt;Cons:&lt;/h3&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;More self discharge than both NiCd and Li-ion, means battery should be plugged in as much as possible when not is use.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Experiences memory effect.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Cold susceptible.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Here are some interesting charts I found. Please note that this data is for camera batteries, although still applicable.&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/5UBUp.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/wuSQl.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/XHutq.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/hHDVI.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;(Primary) Sources:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;http://www.ehow.com/info_12127670_rechargeable-nimh-batteries-vs-rechargeable-lithiumion-batteries.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;eHow&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;http://batterydata.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;BatteryData&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Personal experience.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="63" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2013-11-06T02:22:58.327" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="548" PostTypeId="1" CreationDate="2013-11-05T20:06:08.283" Score="9" ViewCount="1912" Body="&lt;p&gt;When operating analog voice, we give a qualitative (or possibly just arbitrary) signal report, 'scoring' the signal either out of a maximum 'five by five', or a maximum '599'. How do you report the quality of the received signal when using digital modes? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When working a digital QSO, what are some different quantitative ways to report received signal quality or strength, and does the specific digital mode have any bearing on what type of report is given?&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2020-06-20T03:33:20.000" Title="Digital-mode signal reports" Tags="&lt;digital-modes&gt;&lt;snr&gt;&lt;rssi&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="549" PostTypeId="2" ParentId="23" CreationDate="2013-11-05T20:28:50.443" Score="0" Body="&lt;p&gt;You &lt;em&gt;could&lt;/em&gt; add an external amplifier, but the most popular I could find reviews &lt;a href=&quot;http://www.eham.net/reviews/products/35&quot; rel=&quot;nofollow&quot;&gt;http://www.eham.net/reviews/products/35&lt;/a&gt; for, the Mirage BD-35 &lt;a href=&quot;http://www.eham.net/reviews/detail/3281&quot; rel=&quot;nofollow&quot;&gt;http://www.eham.net/reviews/detail/3281&lt;/a&gt; seems to have significant QC and support issues.   Really, having a J-pole for omnidirectional operation stuck on a bamboo or PVC pipe pole, and/or a vertical yagi aimed at your repeater of choice, is the realistic way to boost reception and transmission.&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-11-05T20:28:50.443" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="550" PostTypeId="2" ParentId="548" CreationDate="2013-11-05T21:55:16.897" Score="6" Body="&lt;p&gt;On digital modes (particularly PSK31)  RSQ (Readability, Strength, and Quality) is usually used for signal reports, instead of RST (Readability, Strength, CW Tone).  There is some interesting &lt;a href=&quot;https://web.archive.org/web/20161105152348/http://psb-info.net/History.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;history&lt;/a&gt; and &lt;a href=&quot;https://web.archive.org/web/20131125210454/http://psb-info.net/RSQ-discussion.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;background&lt;/a&gt; information on the RSQ system available at &lt;a href=&quot;https://web.archive.org/web/20161009145610/http://psb-info.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;psb-info.net&lt;/a&gt; a site dedicated to the RSQ signal report.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&lt;strong&gt;R = RSQ Readability (Percent characters correctly received):&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;R 1 – 0% Undecipherable&lt;/li&gt;&#xA;&lt;li&gt;R 2 – 20% Occasional words distinguishable&lt;/li&gt;&#xA;&lt;li&gt;R 3 – 40% Considerable difficulty, many missed characters&lt;/li&gt;&#xA;&lt;li&gt;R 4 – 80% Practically no difficulty, occasional missed characters&lt;/li&gt;&#xA;&lt;li&gt;R 5 – 95%+ Perfectly readable&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;S = RSQ Strength (Signal over Noise rather than S-Meter):&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;S 1 – Barely perceptible trace&lt;/li&gt;&#xA;&lt;li&gt;S 3 – Weak trace&lt;/li&gt;&#xA;&lt;li&gt;S 5 – Moderate trace&lt;/li&gt;&#xA;&lt;li&gt;S 7 – Strong trace&lt;/li&gt;&#xA;&lt;li&gt;S 9 – Very Strong trace&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;Q = RSQ Quality:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Q 1 – Splatter over much of the spectrum&lt;/li&gt;&#xA;&lt;li&gt;Q 3 – Multiple visible pairs&lt;/li&gt;&#xA;&lt;li&gt;Q 5 – One easily visible pair&lt;/li&gt;&#xA;&lt;li&gt;Q 7 – One barely visible pair&lt;/li&gt;&#xA;&lt;li&gt;Q 9 – Clean signal – no visible unwanted sidebar pairs&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Here is a minified table version I found:&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/EuQHK.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;Another way signal reports are exchanged on the digital modes is by giving the Intermodulation Distortion (or IMD).&lt;/p&gt;&#xA;&lt;p&gt;A quote &lt;a href=&quot;https://web.archive.org/web/20161105154141/http://psb-info.net/IMD-Measurement.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;from the RSQ website about what IMD is&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Inter-Modulation Distortion (IMD) is a report often exchanged during a PSK QSO as a figure of merit for the received signal. It is widely&#xA;assumed that a very good IMD report for an idling signal is around&#xA;-30db, a poor report around -20db with the worst possible at -10db.&lt;/p&gt;&#xA;&lt;p&gt;Howard (Skip) Teller KH6TY who developed the first panoramic PSK31&#xA;transceiver and Digipan software advises that great care must be taken&#xA;when attempting to measure IMD at the receiving station. The following&#xA;advice was received from KH6TY:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&amp;quot;...IMD is the measurement of the first pair of unwanted sidebands to&#xA;the desired ones, and if the signal to noise ratio is not around 26&#xA;db, you will start to measure the noise instead of the unwanted&#xA;sidebands, which will be under the noise threshold. Also, if there is&#xA;any distortion in the receiver, you create a false IMD reading.&#xA;Whenever I measure a station's IMD, I have to be sure the S/N is good,&#xA;and then I reduce the RF gain of my transceiver until the IMD stops&#xA;falling and starts rising. At this point, I believe I have almost&#xA;eliminated IMD caused by the receiver distorting the signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="63" LastEditorUserId="7798" LastEditDate="2020-06-20T03:33:20.000" LastActivityDate="2020-06-20T03:33:20.000" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="551" PostTypeId="2" ParentId="303" CreationDate="2013-11-06T04:22:22.537" Score="11" Body="&lt;p&gt;So as another take on it, you can engage in the thought experiment of &quot;what happens if encryption is legal&quot;. Let's say you're a taxi operator and you want to dispatch via radio. Well usually you'd need a commercial license to do this, since amateur radio is strictly non-commercial. But if you can encrypt your traffic, who's to say it's commercial or not? You'd save a few bucks in the process, but that's not the point of the service.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC doesn't have the resources to keep an eye on the amateur service. They rely mostly on self-policing, and it works fine. But that would be impossible if the traffic was encrypted - you wouldn't be able to tell the taxi service from two buddies talking about the game.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, ham radio is &quot;supposed&quot; to be public, experimental, academic, etc. Anybody can homebrew a rig or antenna and send more-or-less any signal they want subject to the rules - but anybody else can hook their rig up to their computer and decode it, or maybe even send it themselves. Everybody has the chance to learn from everyone else, and encryption would take that away.&lt;/p&gt;&#xA;" OwnerUserId="303" LastActivityDate="2013-11-06T04:22:22.537" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="552" PostTypeId="1" CreationDate="2013-11-06T04:45:13.797" Score="7" ViewCount="1498" Body="&lt;p&gt;Note that this question isn't about battery capacity, at least not per se. I have a 100 Watt mobile transceiver. At 12 V and assuming 50% efficiency, that means it draws a little under 20 Amps at full power. It's currently being powered by a pair of 15Ah SLA batteries in parallel. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not concerned about battery life - I know I won't get much which is why there's a solar system keeping the batteries topped off while I'm in the field. But even with high gauge wire, when I key down the transmitter, I get a voltage drop at the battery terminals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I need a bigger battery? How can I determine what size battery I need for a certain load? Amps, Amp-Hours, and Cold Cranking Amps - which is the important factor here?&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2014-08-26T15:18:21.563" Title="Battery sizing for power draw" Tags="&lt;mobile&gt;&lt;battery&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="553" PostTypeId="2" ParentId="552" CreationDate="2013-11-06T08:23:46.930" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;But even with high gauge wire, when I key down the transmitter, I get a &#xA;  voltage drop at the battery terminals. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Some voltage drop on load is normal. Every power source will show some voltage drop when being put under load.&lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="306" LastEditDate="2014-08-26T11:18:38.033" LastActivityDate="2014-08-26T11:18:38.033" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="554" PostTypeId="2" ParentId="501" CreationDate="2013-11-06T10:14:16.287" Score="0" Body="&lt;p&gt;Yaesu FT-857 and FT-897 actually have separated HF from UHF/VHF. SO239 is used for HF but N connector is used for VHF/UHF.&lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="103" LastEditDate="2013-11-06T18:55:08.533" LastActivityDate="2013-11-06T18:55:08.533" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="555" PostTypeId="2" ParentId="538" CreationDate="2013-11-06T13:53:57.483" Score="16" Body="&lt;p&gt;A dipole is a particular machine for creating EM fields. The idea is to set up a voltage between the two halves of the dipole in such a way that an EM field is created and efficiently radiated away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, &lt;a href=&quot;http://en.wikipedia.org/wiki/Voltage&quot; rel=&quot;noreferrer&quot;&gt;voltage&lt;/a&gt; is a difference between two things. When we consider just an dipole, with no feedline or anything else around it, it's very simple to see that the dipole is symmetrical. The currents in one leg create voltages against the other leg, because there's nothing else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we feed the dipole with &lt;a href=&quot;http://en.wikipedia.org/wiki/Twin-lead&quot; rel=&quot;noreferrer&quot;&gt;twin-lead&lt;/a&gt;, it's still easy to see how the dipole can be symmetrical. Each leg is now working against the feedline, but since both leads of the feedline are very close to each other, they are affected equally by whatever the antenna is doing, and there is no net effect. Of course, everything else (the Earth, trees, gutters, towers, etc) around the antenna would also need to be symmetrical, and this is unrealistic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we feed the dipole with &lt;a href=&quot;http://en.wikipedia.org/wiki/Coaxial_cable&quot; rel=&quot;noreferrer&quot;&gt;coax&lt;/a&gt;, the situation is very different. The shield intercepts any EM fields, effectively hiding the center conductor from any external fields. You don't have a symmetrical arrangement anymore: one leg of the dipole is connected to the shield, so really, it's an L shape. In fact, the shield is just as much part of the antenna as the dipole it's intended to feed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Nh6Co.jpg&quot; alt=&quot;physical model of coax-fed dipole&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;from an excellent article at &lt;a href=&quot;http://www.antenna-theory.com/definitions/balun.php&quot; rel=&quot;noreferrer&quot;&gt;antenna-theory.com&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now consider what happens to the currents traveling down the coax. The signal from the transmitter consists of $I_A$ and an equal and opposite $I_B$. $I_A$ must flow down one leg of the dipole, because it has nowhere else to go. However, at the feedpoint, $I_B$ has two options: it can flow down the attached leg of the dipole, or it can reflect back down the coax shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, $I_B$ will split, with some of it ($I_C$) returning on the coax, and the difference ($I_B-I_C$) going down the dipole, as intended. The degree of the split will be determined by the relative impedances of these two options.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This isn't often a problem, because the coax shield makes just as fine of an antenna as the dipole. It distorts the radiation pattern horribly, but since a dipole wasn't a directional antenna to begin, it hardly matters. It could mean that you get a lot of RF in the shack, but if you are transmitting with 100W this is unlikely to cause any serious problems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are however, some more subtle problems: if you are transmitting RF in the shack, you are also receiving RF from the shack (&lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_%28electromagnetism%29&quot; rel=&quot;noreferrer&quot;&gt;reciprocity&lt;/a&gt;). You might be able to get your antenna far away from the powerlines, switching power supplies, computers, and other noise sources in the shack, but if your feedline is actually part of the antenna, then you are receiving all this noise anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By employing a balun, you are somehow forcing the currents on each leg of the dipole to be equal, so that no current returns on the coax, so that the coax does not radiate and act as part of the antenna. There are many designs, but one of the most common and effective is a simple &lt;a href=&quot;http://en.wikipedia.org/wiki/Choke_%28electronics%29#Common-mode_choke&quot; rel=&quot;noreferrer&quot;&gt;common mode choke&lt;/a&gt;, also known as a 1:1 current balun. This clever device has the effect of inserting a large impedance between the feedpoint and the outside of the shield ($I_B$ and $I_C$ in image above), making it relatively more appealing for the current to go down the dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/sQq1P.png&quot; alt=&quot;dipole without balun&quot;&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/hwdsb.png&quot; alt=&quot;dipole with balun&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;from &lt;a href=&quot;http://en.wikipedia.org/wiki/Dipole_antenna#Feeding_a_Dipole_with_Baluns&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the mismatch of 50Ω coax to a 75Ω antenna isn't relevant to any of this. If your feedline and antenna are mismatched, you will get some power reflections, but those reflections would be &lt;em&gt;inside&lt;/em&gt; the feedline, and not cause the feedline to become part of the antenna. There are balun designs that also perform impedance transformation, but this is not the function denoted by &lt;em&gt;balun&lt;/em&gt;. On a practical note, 75Ω is a good enough match to 50Ω, and typical feedline losses at HF low enough, that in my opinion most attempts at impedance matching in this situation are unnecessary, and likely waste more energy through inefficiencies than they gain in obtaining a better match.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-12-30T12:07:43.817" LastActivityDate="2013-12-30T12:07:43.817" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="556" PostTypeId="2" ParentId="552" CreationDate="2013-11-06T14:10:54.020" Score="2" Body="&lt;p&gt;Most manufacturers publish their power requirements.  20A sounds like a reasonable estimate.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The more important part of voltage drop is what's due to your wiring.  Small gauge and long runs can cause persistent voltage drops.  Using heavier gauge wiring like you are, will solve most of that problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As was said,  temporary voltage drops at the reading on the battery are to be expected.  A voltmeter is a very small load that is calibrated to show you the voltage in the system.  Adding a significant load (20A draw) on a parallel circuit will result in a measured voltage drop.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You seem to understand your capacity limitations.  With a 20A load and 30Ah battery bank, assuming a duty cycle of 10%, you should expect 4.5-5h.  Lower duty cycle, longer life.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For better battery calculations, also read about peukerts constant, understand the way batteries are rated (at a rate that drains the battery over a specific amount of time) and experiment with your batteries to figure out their approximate peukerts constant (as most manufacturers don't publish that data).&lt;/p&gt;&#xA;" OwnerUserId="308" LastActivityDate="2013-11-06T14:10:54.020" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="557" PostTypeId="2" ParentId="552" CreationDate="2013-11-06T16:11:07.720" Score="6" Body="&lt;p&gt;Batteries can be approximated as an ideal voltage source in series with a resistor. So it's perfectly normal for a battery's terminal voltage to drop when the current it is delivering increases. To determine whether that's actually a problem, you only need to consider two things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is the new voltage too low to power your transceiver?&lt;/li&gt;&#xA;&lt;li&gt;Are you exceeding the current rating of the battery?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Most battery spec sheets will list the maximum current draw from the battery. For a 15 Ah lead acid battery, that's going to be at least 10 A, so you should be fine with two in parallel. Yuasa, a lead acid battery manufacturer, has &lt;a href=&quot;http://www.battery-usa.com/Catalog/NPAppManual%28Rev0500%29.pdf&quot;&gt;an application manual&lt;/a&gt; that shows discharge curves for different currents (page 7). They only list discharge curves up to 3C (meaning, discharging the battery in 1/3 of an hour, or at 45 A per battery in your case), so that's probably what they feel comfortable with for their batteries. You should check your own battery's specifications to confirm.&lt;/p&gt;&#xA;" OwnerUserId="39" LastActivityDate="2013-11-06T16:11:07.720" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="558" PostTypeId="1" CreationDate="2013-11-06T16:18:29.480" Score="14" ViewCount="1980" Body="&lt;p&gt;In studying for the exam, one question came up about RF Exposure. &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;G0A&#xA;07&#xA;What effect does transmitter duty cycle have when evaluating RF exposure?&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;My understanding of Radio is that it is non ionizing electromagnetic radiation. How can RF be damaging? &lt;/p&gt;&#xA;" OwnerUserId="309" LastEditorUserId="87" LastEditDate="2013-11-27T15:31:52.223" LastActivityDate="2013-11-27T15:31:52.223" Title="How can RF exposure hurt you?" Tags="&lt;safety&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="559" PostTypeId="1" CreationDate="2013-11-06T16:28:22.573" Score="6" ViewCount="8017" Body="&lt;p&gt;How can I construct a practical loop antenna for 2m band to use in a fox hunt? Is it even possible to construct a hand-held antenna for the 2m and 70 cm bands? I tried to calculate the dimensions using a few online tools and formula, and the dimensions seemed impractical to hold and walk around.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can this antenna be miniaturized in any way? I have a Yamaha receiver that can receive AM band  (few thousand kHz) and it is really small - less than 15cm across.&lt;/p&gt;&#xA;" OwnerUserId="49" LastEditorUserId="76" LastEditDate="2014-04-05T22:45:36.243" LastActivityDate="2014-04-05T22:45:36.243" Title="How can I construct a practical loop antenna for 2m band?" Tags="&lt;antenna&gt;&lt;fox-hunt&gt;&lt;direction-finding&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="560" PostTypeId="5" CreationDate="2013-11-06T16:35:44.843" Score="0" Body="&lt;p&gt;While summing two signals for amplitude modulation, two image signals are formed. To keep the bandwidth requirements low, one side band is discarded and only side band is transmitted. The side band above the carrier frequency is called the Upper Side Band and the frequency lower than the carrier is called the Lower Side Band. To conserve transmitter power, often the carrier is discarded as well.&lt;/p&gt;&#xA;" OwnerUserId="49" LastEditorUserId="29" LastEditDate="2014-11-14T12:27:05.407" LastActivityDate="2014-11-14T12:27:05.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="561" PostTypeId="4" CreationDate="2013-11-06T16:35:44.843" Score="0" Body="Single Side Band - Amplitude Modulated signals transmitted using only one side band, often with suppressed carrier." OwnerUserId="49" LastEditorUserId="29" LastEditDate="2014-11-14T12:27:05.407" LastActivityDate="2014-11-14T12:27:05.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="562" PostTypeId="5" CreationDate="2013-11-06T16:45:06.543" Score="0" Body="&lt;p&gt;Repeaters are usually used to boost the range of transmitters. For example, the range of a 5W hand held can be greatly increased. Repeaters designed for duplex operations have different transmit and receive frequency. The repeaters also have to be keyed on by sending certain tone frequency - or a sequence of tones.&lt;/p&gt;&#xA;" OwnerUserId="49" LastEditorUserId="49" LastEditDate="2013-11-06T18:55:00.360" LastActivityDate="2013-11-06T18:55:00.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="563" PostTypeId="4" CreationDate="2013-11-06T16:45:06.543" Score="0" Body="A device that receives a signal and re transmits it either in the same band or by re-modulating it in a different band." OwnerUserId="49" LastEditorUserId="49" LastEditDate="2013-11-06T18:55:25.737" LastActivityDate="2013-11-06T18:55:25.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="564" PostTypeId="2" ParentId="558" CreationDate="2013-11-06T16:57:07.707" Score="4" Body="&lt;p&gt;Heating; it can burn you the same way a microwave cooks food, or UV from the sun gives you sun burn. The wikipedia article about radiation burns generally covers RF a bit: &lt;a href=&quot;http://en.wikipedia.org/wiki/Radiation_burn&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Radiation_burn&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="35" LastActivityDate="2013-11-06T16:57:07.707" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="565" PostTypeId="2" ParentId="558" CreationDate="2013-11-06T16:58:10.837" Score="1" Body="&lt;p&gt;The best, and most extreme, example to answer your question would be a microwave oven.  You're applying RF radiation to your food and it gets heated as a result.  Tissue damage can occur when your body isn't able to dissipate the heat generated by absorbing the RF radiation quickly enough.&lt;/p&gt;&#xA;" OwnerUserId="254" LastActivityDate="2013-11-06T16:58:10.837" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="566" PostTypeId="2" ParentId="558" CreationDate="2013-11-06T16:58:50.597" Score="12" Body="&lt;p&gt;The direct effects of RF on people are:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Tissue Heating&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Electric_shock&quot; rel=&quot;nofollow&quot;&gt;Electric shock&lt;/a&gt; (shocks and burns) and &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrocution&quot; rel=&quot;nofollow&quot;&gt;electrocution&lt;/a&gt; (death)&lt;/li&gt;&#xA;&lt;li&gt;Interference with implanted medical devices&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The General test question quoted is about evaluating the exposure for the purposes of tissue heating.  I assume everyone &quot;gets&quot; not grabbing a wire you are pumping 1500W into.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tissue heating is a problem because unlike being in a hot place, where the heat is outside the body, the heating is internal.  The only mechanism for the body to deal with this is blood flood, so areas with little flow (for instance, the eyes) are particularly vulnerable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To give you an idea of how you absorb the RF, consider this: the human body, standing and somewhat grounded, is a 1/4 wave vertical antenna, resonant at 4x your height.  But is somewhat lossy and high impedance compared to a metal antenna.  Of course, that high impedance is the problem, the RF is &quot;lost&quot; as heat, in you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Safety experts consider the most the human body can tolerate is 4W/kg of heating.  To put this in perspective, you generate about 1W/kg sleeping, 2-3W/kg in heavy exercise.  Exceed this and you body has trouble dumping the extra heat and the core temperate begins to rise.  Cell death begins to occur at 107 deg F (that's why 105 def F is a tripwire in fevers).  Natually you can tolerate some of this.  Depending on for how long and what's getting heated.  I don't recommend some organs like the brain, liver, kidneys, things you occasionally need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A somewhat wordy reference can be found here: &lt;a href=&quot;http://hps.org/hpspublications/articles/rfradiation.html&quot; rel=&quot;nofollow&quot;&gt;http://hps.org/hpspublications/articles/rfradiation.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="250" LastEditDate="2013-11-12T17:11:10.563" LastActivityDate="2013-11-12T17:11:10.563" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="567" PostTypeId="2" ParentId="559" CreationDate="2013-11-06T17:11:28.723" Score="1" Body="&lt;p&gt;If a simple magnetic loop antenna is what you want, you should have a look at&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.m0ukd.com/Magnetic_Loop/&quot; rel=&quot;nofollow&quot;&gt;http://www.m0ukd.com/Magnetic_Loop/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The loop he constructed is about 10cm in diameter (which is approx. 4 inches) which is not that much to carry around.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For 70cm you might want to go for a small Yagi design since it provides you with some additional gain. For a 4-Element yagi the boom would be about 35cm (&amp;lt;14inch) long. A good design will give you around 7.5 dBd gain and a F/B ratio of around 13dB.&#xA;For more information about that please visit&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.qsl.net/dk7zb/70cm/70cm-kurz.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.qsl.net/dk7zb/70cm/70cm-kurz.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With regard to the shortwave antenna you mentioned: These are normally wound around a ferrite core in order to increase the inductivity while keeping the antenna itself very small. Please note that most of these cores will not be suited for use in the UHF/VHF bands.&lt;/p&gt;&#xA;" OwnerUserId="310" LastActivityDate="2013-11-06T17:11:28.723" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="568" PostTypeId="2" ParentId="559" CreationDate="2013-11-06T18:50:15.090" Score="4" Body="&lt;p&gt;Here is my dumbed-down experience. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are looking at T-hunts.  I have always made sniffer loops about 1/10th or less then actual wavelength. Many times we would add a trimmer-cap across the antenna feed point but most the time would not. Even before I was a serious ham I did this quite successfully on the CB band for &quot;Skunk Hunts&quot; where we would all put a few bucks in the winner's pot.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I did find is the &quot;null&quot; on the gain was much more precise then the strong side. I would use the back mounted vertical on my vehicle and do a &quot;doughnut&quot; in a vacant parking lot to take a heading.  I would either mentally (if I knew the area well) or on paper (pre-internet) maps from the front of pone books, draw a line for the heading.  Then I would move to the side a couple blocks and quickly do it again, sometimes a few times.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once I could triangulate the approximate area I s could move in and with an antenna switch I could switch between my back mounted vertical and the small loop maybe 9 or 10 inches in diameter mounted on a 2 or 3 foot wooden stick or &quot;wand&quot;.  The 'Null' (which IIRC was the feed point forward) was sharp as a tack and working with the RF-Gain on the receive radio I could confidently move in for the kill even when the transmitter was &quot;hidden&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now AM broadcast?  That will be a different monster.  The middle of the band will be 300 meters wavelength and a tenth would still be nearly 10 feet in diameter.  Not something you will be able to easily mount on a piece of PVC pipe and hang out the sun-roof of your car!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could do as others have suggested and look and the true magnetic loops and maybe &quot;Multi-turn-Mag-loops&quot;. Also most cheap AM receivers with loop sticks are also VERY directional.  Sometimes it can be tricky picking which is &quot;front&quot; and &quot;back&quot; but they are directional.  There are also various after market &quot;ferrite coil&quot; antennas for the AM band usually marketed to improve reception but I am sure you could use it to 'DF' AM broadcast band transmitters as well.  You might ask some real old-timers but I think I heard the idea for C.Crane ferrite coil may have come from coils used in WW2 by the military aircraft to home in on a target city.  That may be ham radio urban-myth but I have heard similar claims since I first became a ham in the mid 80s.  &lt;/p&gt;&#xA;" OwnerUserId="312" LastActivityDate="2013-11-06T18:50:15.090" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="569" PostTypeId="2" ParentId="23" CreationDate="2013-11-06T19:00:15.063" Score="13" Body="&lt;p&gt;There have been a number of good answers already, though I think there are a few additional points worth sharing.  Answers would also be more relevant if we knew what situation(s) you were coming up short range wise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For portable use (out in the field):&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The stock Baofeng rubber duck antenna has been shown to be a poor performer.  All of the stock rubber duck antennas tend to be a compromise and not perform very well, but the stock, stiff, short baofeng antenna seems to perform worse than others.&lt;/li&gt;&#xA;&lt;li&gt;An antenna that is physically close to the right wave length (1/4 wave, 1/2 wave, or 5/8th wave) on the frequency you want to operate on will perform better (have less signal loss) than a shorter antenna.  While it's inconvenient to carry around, a 14-15 inch &quot;gain&quot; antenna can help in many cases where a 4-8 inch stock duck can't be heard.&lt;/li&gt;&#xA;&lt;li&gt;The standard rubber duck antennas are 1/4 wave, which are half of a 1/2 wave dipole, oriented vertically. Your body is making up the other half, the ground plane. The rat tail suggestions are good ones, which are providing a better ground plane to complete the other half of the antenna.&lt;/li&gt;&#xA;&lt;li&gt;Get the radio off your belt!  If you are using the headset with the radio attached to your belt, your body is absorbing much of the signal.  Bring the radio up to your mouth when transmitting.&lt;/li&gt;&#xA;&lt;li&gt;Make sure your battery is fully charged.  Your radio is only putting out the rated power when it is getting the design voltage.  The lower the voltage from your battery, the less your power output (in watts) will be.  Several graphs of power vs. battery voltage have been published for the Baofeng and the similar Wouxun online and in the Yahoo groups.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;For use in a car:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Get your antenna OUTSIDE of the car.  The body of the car will absorb much of the signal.  A magnetic mount antenna can be a good non-permanent solution.  Make sure you've got enough metal in the roof and that the antenna is as close to the center of the roof as you can.&lt;/li&gt;&#xA;&lt;li&gt;Power the radio from the car to ensure you are getting the full output power your radio is capable of.  Use a 12 volt battery eliminator. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;For use indoors:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Get your antenna outside, especially if you are using 2 meters.  The shorter 70cm waves have a much easier time getting through window openings than the longer 2 meter waves.  There are many simple choices that don't involve trying to put a large antenna on a roof.  A magnetic mount antenna for a car placed on a window air conditioner works well.&lt;/li&gt;&#xA;&lt;li&gt;Use 70 cm where possible instead of 2 meters if it's appropriate for your area.&lt;/li&gt;&#xA;&lt;li&gt;Use a power supply to make sure you a getting full output power.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;General:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Height and Line of Sight are your friend.  &lt;/li&gt;&#xA;&lt;li&gt;2 meters and 70 cm perform differently and have different advantages depending upon the surrounding terrain.  It's good to know which one to use.  70cm is better in urban areas.  2 meters will give you longer distance propagation in open areas.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Important General Tip:  &lt;strong&gt;The pin inside the SMA antenna connector will eventually break!&lt;/strong&gt; The connector is rated by design for approximately 500 connection cycles.  If you use one antenna and rarely disconnect it you'll be fine.  If you change antennas frequently, consider using a low profile BNC adapter where the base sits on top of the radio and isn't completely dependent on the SMA jack for all of its mechanical strength.&lt;/p&gt;&#xA;" OwnerUserId="311" LastActivityDate="2013-11-06T19:00:15.063" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="570" PostTypeId="2" ParentId="4" CreationDate="2013-11-06T19:18:39.713" Score="0" Body="&lt;p&gt;&lt;a href=&quot;http://www.hamatlas.eu/Gg/KML_en.htm&quot; rel=&quot;nofollow&quot;&gt;This&lt;/a&gt; may be helpful.  Specifically the link titled &quot;Map of QTH Locators for whole World&quot;.  I was able to successfully determine my grid square using it and it covers the globe.&lt;/p&gt;&#xA;" OwnerUserId="254" LastActivityDate="2013-11-06T19:18:39.713" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="571" PostTypeId="2" ParentId="552" CreationDate="2013-11-06T19:35:42.193" Score="5" Body="&lt;h3&gt;Voltage drop is caused by internal resistance&lt;/h3&gt;&#xA;&lt;p&gt;Using batteries you will always experience a voltage drop when drawing significant currents, due to the internal resistance of the battery.  This can be thought of as a resistor that is always in series with the battery, and consumes energy depending on the current drawn from the battery.&lt;/p&gt;&#xA;&lt;p&gt;It’s the main reason batteries appear to have lower capacity for high current draws, and higher capacity for low current draws. It also accounts for battery heating, and is one of the ways a battery may damage itself.&lt;/p&gt;&#xA;&lt;h2&gt;Internal resistance depends on the battery&lt;/h2&gt;&#xA;&lt;p&gt;Most general-purpose SLA batteries should have 100 mΩ (0.1 ohms) or less of internal resistance when new.  A battery that has a higher internal resistance may be damaged, and will not be as useful as a battery with low internal resistance. It may also be designed that way for high capacity, low current draw applications.  You should be able to find the intended internal resistance from the manufacturer’s data sheet.  If your cells have a very different internal resistance they may be damaged.&lt;/p&gt;&#xA;&lt;p&gt;As batteries go, though, 100 mΩ is a lot of internal resistance.  At a 20 A current draw you will see up to a 2 V drop. You’ve already done well to put the two batteries in parallel: each will see 1/2 the current, leaving you with a more reasonable 1 V drop when you transmit.&lt;/p&gt;&#xA;&lt;h2&gt;How to measure internal resistance&lt;/h2&gt;&#xA;&lt;p&gt;You can measure the internal resistance of your batteries by watching the voltage drop at a 1 A load and a 10 A load.  The internal resistance will be the same on both loads.  So take the two currents and the two voltage drops, and solve for the one resistance common to both. If your SLAs have resistances above 100 mΩ, you may want to put them into a lower demand job and replace them with newer batteries for your radio use.&lt;/p&gt;&#xA;&lt;h2&gt;How to obtain lower internal resistance&lt;/h2&gt;&#xA;&lt;p&gt;Putting cells in parallel, as you’ve done, is one method that reduces the overall internal resistance of the pack.  You could go further and use four 7.5 AH batteries to get even lower internal resistance, for instance.&lt;/p&gt;&#xA;&lt;p&gt;You can purchase better SLA batteries with lower internal resistance, but there are generally a host of tradeoffs you make depending on the capacity, lifetime, power density, and other factors that should be weighing into your decision.  If this is for a specific use, consider asking a new question with your desired use case and we may be able to recommend a few specific battery types and sizes that should better meet your needs.&lt;/p&gt;&#xA;&lt;p&gt;Generally speaking you might want to focus on SLA batteries meant for high rate discharge applications, such as UPS batteries.  These typically have an internal resistance at or below 10 mΩ, which would give you a 0.2 V drop for a single cell driving your 20 A load.  Note that even with such batteries, you still have a voltage drop; what you need to determine is how much voltage drop is acceptable, and then choose the batteries that meet that requirement and any other requirements you may have.&lt;/p&gt;&#xA;&lt;p&gt;You might also want to look into super-capacitors if your transmissions are generally short.  By using batteries and super-capacitors in parallel you can reduce the instantaneous current draw on the batteries during short transmissions.  This will have the additional benefit of reducing the effect of the internal resistance, giving you more capacity from the battery, and may extend the life of your batteries somewhat.&lt;/p&gt;&#xA;&lt;p&gt;If voltage drop is unacceptable, you may want to look into voltage regulators that will take the battery power and provide a stable voltage regardless of the load.  For radio use this is generally overkill — most radios work well with even a 2-3 V drop, and significant energy is lost in the conversion, so it’s only recommended for special applications.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-08-26T15:18:21.563" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="572" PostTypeId="5" CreationDate="2013-11-06T20:26:46.410" Score="0" Body="&lt;p&gt;This tag is for questions which relate to gauging the strength of a received signal or comparing the strengths of received signals. &lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-11-07T14:39:40.077" LastActivityDate="2013-11-07T14:39:40.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="573" PostTypeId="4" CreationDate="2013-11-06T20:26:46.410" Score="0" Body="Received Signal Strength Indicators, also known as the &quot;bars&quot; that display your signal reception. Questions about how they work and how to use them belong here!" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-11-07T14:39:55.107" LastActivityDate="2013-11-07T14:39:55.107" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="574" PostTypeId="1" AcceptedAnswerId="582" CreationDate="2013-11-06T20:27:59.023" Score="16" ViewCount="26270" Body="&lt;p&gt;I pursued Amateur Radio primarily for local emergency communications and as part of my electronics education.  My only radio right now is an inexpensive 2m/70cm HT which is good for local weather spotting and emergency operations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm interested in talking to other Amateur Radio users around the US, but I'm trying to keep my costs down.  I know that many amateurs can make contacts worldwide on various bands at very low power levels, but many of them require specific conditions.  I'd like to be able to talk with others around the US regardless of the conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What bands and modes best suit these requirements, in order of importance:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;USA Amateur Radio bands&lt;/li&gt;&#xA;&lt;li&gt;Voice contacts&lt;/li&gt;&#xA;&lt;li&gt;Long distance (3,000 miles, 4,800km, or more)&lt;/li&gt;&#xA;&lt;li&gt;Unconditional access (don't want to worry about time of day, minor weather effects, etc)&lt;/li&gt;&#xA;&lt;li&gt;Low cost of setup (including antenna cost)&lt;/li&gt;&#xA;&lt;li&gt;Low power usage&lt;/li&gt;&#xA;&lt;li&gt;Small footprint (doesn't require acres of antennas)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The first four are critical.  If there is no band or mode at any cost that fits these needs, then the question cannot be answered.  If multiple solutions exist for the first four, then narrow them down or rank them according to each of the next three requirements.  For instance a lower cost with a bigger antenna footprint would be preferable to a solution that cost more but had a smaller antenna footprint.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2014-10-23T17:55:33.243" LastActivityDate="2014-10-23T17:55:33.243" Title="What bands and modes will give me voice at 3,000 miles?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;phone&gt;&lt;range&gt;" AnswerCount="4" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="575" PostTypeId="5" CreationDate="2013-11-06T20:35:13.617" Score="0" Body="&lt;p&gt;This tag is for any question about detecting the Signal to Noise Ratio of a given signal, improving the SNR of a transmitter or amplifier, lowering your receiver's noise floor, or anything else to do with extracting a signal from noise.&lt;/p&gt;&#xA;" OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-11-07T14:40:00.310" LastActivityDate="2013-11-07T14:40:00.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="576" PostTypeId="4" CreationDate="2013-11-06T20:35:13.617" Score="0" Body="Signal to Noise Ratio - any questions about improving or detecting an SNR or lowering your noise floor." OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-11-07T14:40:33.080" LastActivityDate="2013-11-07T14:40:33.080" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="577" PostTypeId="5" CreationDate="2013-11-06T20:38:49.223" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-06T20:38:49.223" LastActivityDate="2013-11-06T20:38:49.223" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="578" PostTypeId="4" CreationDate="2013-11-06T20:38:49.223" Score="0" Body="Varicaps are electronic components with a variable capacitance. They are a type of diode that, when operated under reverse bias, vary the width of their depletion zone and therefore their capacitance." OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-11-07T14:39:32.293" LastActivityDate="2013-11-07T14:39:32.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="579" PostTypeId="5" CreationDate="2013-11-06T20:46:22.357" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-06T20:46:22.357" LastActivityDate="2013-11-06T20:46:22.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="580" PostTypeId="4" CreationDate="2013-11-06T20:46:22.357" Score="0" Body="Anything to do with long path propagation - intentionally pointing a signal directly away from the intended recipient, such that it will go around the Earth before reaching them." OwnerUserId="87" LastEditorUserId="87" LastEditDate="2013-11-07T14:39:07.260" LastActivityDate="2013-11-07T14:39:07.260" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="581" PostTypeId="2" ParentId="574" CreationDate="2013-11-06T20:53:07.213" Score="6" Body="&lt;p&gt;Based on the parameters given I would say 20M is the best band to aim for.  There's usually a lot of activity, it tends to give reliable propagation, your antenna can be relatively small and there's a little bit of everything happening on it (CW, voice, digital and SSTV).  From south-central Canada I've worked as far south as Cuba and as far east as Germany on a horizontal dipole hanging about 3 meters (10 feet) off the ground and most of North America with a sloper hanging off a tree at the edge of a field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For straight distance it's hard to beat digital or CW though, so it may be worth learning Morse Code or finding some software to encode/decode it for you on the fly.&lt;/p&gt;&#xA;" OwnerUserId="254" LastActivityDate="2013-11-06T20:53:07.213" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="582" PostTypeId="2" ParentId="574" CreationDate="2013-11-06T21:19:13.590" Score="18" Body="&lt;p&gt;You are going to have a very difficult time achieving the first 4 with any band on a low budget. But in general, I'll say a few words to get you started.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;You probably want to be able to use digital modes. Your best bet to get consistently across the country will be via digital modes, as they can add something like 20-30 dB effectively to your signal. Olivia in particular might be a good choice. This is achieved because digital modes are more sensitive, able to read signals below the noise floor.&lt;/li&gt;&#xA;&lt;li&gt;If you want to be able to reach your &quot;neighborhood&quot; consistently, and occasionally around the world, then your best bet is probably 40 m. In fact, 40m is a highly recommended band to start out on. It works very reliably up to about 700 miles during the day, a bit further at night, and if you get it high enough, can work really well at night. Plus it's less crowded and generally more friendly than 20m.&lt;/li&gt;&#xA;&lt;li&gt;20m is the best band overall to work around the world, but you often will have difficulties with things that are closer. &lt;/li&gt;&#xA;&lt;li&gt;If you really want voice to anywhere in the world, you'll want a huge yagi antenna on a large tower, transmitting at the full legal power in a quiet RF area. Other than that, you will have some compromise.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;My set up is a G5RV in my attic, which I can talk routinely to Europe on 20m, most of the East part of North America on 40m, and occasionally further on 10 and 15m. I live in Virginia (FM19), to give you an idea.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-02-21T21:48:17.040" LastActivityDate="2014-02-21T21:48:17.040" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="583" PostTypeId="2" ParentId="532" CreationDate="2013-11-06T21:23:43.063" Score="-1" Body="&lt;p&gt;String trimmer line is not UV stable, it will likely break down within a year in sunlight - sooner depending on your climate. Therefore, no, it's not suitable.&lt;/p&gt;&#xA;" OwnerUserId="314" LastEditorUserId="21" LastEditDate="2013-11-06T23:09:52.777" LastActivityDate="2013-11-06T23:09:52.777" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="584" PostTypeId="1" CreationDate="2013-11-06T21:50:53.977" Score="4" ViewCount="99" Body="&lt;p&gt;I have been tasked with teaching a one hour class to adults who lead Boy Scout troops about &quot;Radios in Scouting&quot;. What should I teach them?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Possible subjects include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Teaching the &lt;a href=&quot;http://www.scouting.org/scoutsource/boyscouts/advancementandawards/meritbadges/mb-rado.aspx&quot; rel=&quot;nofollow&quot;&gt;Radio Merit&#xA;Badge&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Operating a &lt;a href=&quot;http://www.scouting.org/JOTA&quot; rel=&quot;nofollow&quot;&gt;Jamboree on the Air&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;Use of radios on campouts/trips or to run events&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Any other ideas or refinements?&lt;/p&gt;&#xA;" OwnerUserId="316" LastEditorUserId="87" LastEditDate="2013-11-07T12:31:49.680" LastActivityDate="2013-11-12T19:41:51.793" Title="What should be in a one hour class about Radios in Boy Scouts" Tags="&lt;united-states&gt;&lt;education&gt;" AnswerCount="3" CommentCount="6" ClosedDate="2013-11-07T21:29:01.253" ContentLicense="CC BY-SA 3.0" />
  <row Id="585" PostTypeId="2" ParentId="538" CreationDate="2013-11-07T01:42:26.010" Score="0" Body="&lt;p&gt;All great answers, Most rfi is caused by severely mismatched antennas subjected to high power. I agree that a 1 to 1 balun will help in certain dipole installations close to ground or when coax feedline is configured in a non symetrical layout when departing the antenna. A 1 to 1 balun does not affect the matching, 75 to 50 ohms or whatever, not what it is designed for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do not use a balun on any of my various wire beams and would seriously consider the center weight added by a balun and the cost vs most non problems on simple dipoles at 1/4wl and higher will show that the addition of a current balun is not needed.&lt;/p&gt;&#xA;" OwnerUserId="223" LastEditorUserId="218" LastEditDate="2013-11-08T15:26:43.313" LastActivityDate="2013-11-08T15:26:43.313" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="587" PostTypeId="2" ParentId="559" CreationDate="2013-11-07T03:42:16.127" Score="3" Body="&lt;p&gt;There are two kinds of &quot;loop antennas&quot;. There are resonant loops, which are loops where the length of the loop is long enough to be resonant. These can be considered &lt;a href=&quot;http://www.antenna-theory.com/antennas/foldeddipole.php&quot; rel=&quot;nofollow&quot;&gt;folded dipoles&lt;/a&gt;, which have been folded into a loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A quite distinct antenna is the &lt;a href=&quot;http://www.antenna-theory.com/antennas/smallLoop.php&quot; rel=&quot;nofollow&quot;&gt;small loop&lt;/a&gt;. These antennas have a perimeter that is electrically small, meaning less than one-tenth of the wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The two are quite different. The small loop has nulls in two directions perpendicular to the plane of the loop. The resonant loop has nulls in two directions on the plane of the loop. The small loop has a highly inductive impedance. The resonant loop has a purely resistive impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyhow, small loops are frequently used for direction finding at HF because they are small and easy to construct. They are quite inefficient antennas, but it's easy to make low-noise amplifiers at HF which can make up for the low efficiency and poor impedance match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;em&gt;electrically&lt;/em&gt; small loop can be made &lt;em&gt;physically&lt;/em&gt; smaller in three ways:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Make more turns of wire. A small loop with two turns encircling area $A$ is equivalent to a larger loop with one turn encircling area $2A$.&lt;/li&gt;&#xA;&lt;li&gt;Increase the permittivity of the space encircled by the loop. For example, by winding the loop around a ferrite material.&lt;/li&gt;&#xA;&lt;li&gt;Just make it smaller. Decreasing the area encircled by the loop reduces the antenna's efficiency and sensitivity, but provided the signal is still above the noise floor, this isn't a problem. The small loop wasn't very efficient or sensitive to begin, anyway.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;An example of an antenna that does both of these things, and most likely the type of antenna employed by your AM receiver, is a &lt;a href=&quot;http://radio-timetraveller.blogspot.com/2011/01/unassuming-antenna-ferrite-loopstick.html&quot; rel=&quot;nofollow&quot;&gt;loopstick antenna&lt;/a&gt;. These consist of very many turns around a high-permittivity ferrite rod. In doing so, they make the antenna appear electrically much bigger than it is physically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I doubt you will meet success with either of these techniques at 2m. Adding more turns increases the DC resistance, and thus loss of an already not very sensitive antenna. Low noise amplifiers to overcome this are easy at low frequencies, but not at 2m. Also, ferrite materials are lossier with increasing frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, you may not need to employ such techniques. An electrically small antenna at 2m is only $2\mathrm{m}/10 = 20\mathrm{cm}$ &lt;em&gt;or less&lt;/em&gt;. It's already pretty small.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-11-07T03:42:16.127" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="588" PostTypeId="1" CreationDate="2013-11-07T07:46:36.630" Score="9" ViewCount="2627" Body="&lt;p&gt;A follow-up to &lt;a href=&quot;https://ham.stackexchange.com/questions/140/good-wire-for-wire-antenna&quot;&gt;Good wire for wire antenna?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm QRT at present - thanks to fooling around with just a couple of diodes and PVC capacitors instead of a well-regulated supply. The antenna I used earlier was a mono-bander inverted-vee for 20M. I may be able to get a 40M inverted-vee, possibly even a 40M dipole on the premises but the lower bands are out of the question ... which is where I'd like to try out sometime.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm toying with the idea of an &lt;strong&gt;end-fed catenary&lt;/strong&gt; held aloft. Perhaps a weather balloon, or two may provide the necessary lift capacity. A relative rigid wire such as the SWG16/14/12 might puncture the balloon though, and prove a difficult lift to boot. The rig I used (on loan from an elmer) is capable of 20W. On the 160 though I'd like to try no more than 5W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;To the best of my knowledge there is no restriction on gauge hereabouts (VU), as there &lt;strong&gt;may be&lt;/strong&gt; in other parts of the world.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the &lt;strong&gt;constraints&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;QRP&lt;/li&gt;&#xA;&lt;li&gt;Antenna wire flexibility&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Assuming&lt;/strong&gt; the antenna may be reasonably matched &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What guage wire can I use without the wire itself giving up the ghost on Tx? &lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-12-15T23:56:49.493" Title="What is the largest gauge (thinnest diametre) wire I may use as an antenna?" Tags="&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="589" PostTypeId="2" ParentId="588" CreationDate="2013-11-07T13:29:30.837" Score="7" Body="&lt;p&gt;You can make the wire as thin as you want. There are two non-obvious things to point out:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly, as you make it thinner, resistive losses go up. You could make a worst-case calculation of the resistive losses by assuming the current is at a maximum everywhere in the antenna. If you put 20W into a 50Ω antenna, the current will be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;I^2 R &amp;amp;= P \\&#xA;I^2 (50\Omega) &amp;amp;= 20\text{W} \\&#xA;I^2 &amp;amp;= \frac{20\text{W}}{50\Omega} \\&#xA;  I &amp;amp;= \sqrt{\frac{20\text{W}}{50\Omega}} \\&#xA;  I &amp;amp;\approx 632\text{mA}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That should give you some idea of the kind of conductor you need. Of course, this is the current only at the point where the impedance is 50Ω; if we are talking about a center-fed dipole, the impedance approaches infinity at the ends, and consequently the voltage approaches infinity, and the current approaches zero. Consequently, your resistive losses will be lower than what this suggests, but it's a simple calculation that will give you a rough idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another way to approach it: the &lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_efficiency&quot;&gt;antenna efficiency&lt;/a&gt;, if we assume there are no losses but resistive losses can be defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{efficiency} = \frac{R_\text{radiation}}{R_\text{radiation}+R_\text{conductor}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the resistance you add with your thin wire isn't significant compared to the radiation resistance, then you aren't significantly impacting the antenna's efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other concern is this: some materials (namely iron) exhibit &lt;a href=&quot;http://en.wikipedia.org/wiki/Magnetic_hysteresis&quot;&gt;magnetic hysteresis&lt;/a&gt;, which represents another significant loss at RF. This rules out most steel cables, though you may find a stainless steel cable that works. Finding data on the magnetic properties of a cable at the hardware store will be difficult, however, so it might be simplest to avoid all steel.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="29" LastEditDate="2013-11-07T13:44:43.397" LastActivityDate="2013-11-07T13:44:43.397" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="590" PostTypeId="5" CreationDate="2013-11-07T14:08:41.803" Score="0" Body="&lt;p&gt;&lt;strong&gt;RF propagation&lt;/strong&gt; is the behavior of radio waves when they are transmitted. As a form of electromagnetic radiation radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization and scattering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RF propagation is affected by the daily changes of water vapor in the troposphere, ionization in the upper atmosphere due to the Sun, the frequency of the emission, the path over ground of the transmission.  If the path is over-the-horizon path aided by refraction in the ionosphere, it will be influenced by factors that include sporadic-E, spread-F, solar flares, geomagnetic storms, ionospheric layer tilts, and solar proton events.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;strong&gt;Propagation Modes&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Surface modes (groundwave)&lt;/strong&gt;&#xA;&amp;mdash; LF (between 30 and 3,000 kHz) have the property of following the curvature of the earth via groundwave propagation. In this mode the radio wave propagates by interacting with the semi-conductive surface of the earth. The wave &quot;clings&quot; to the surface and thus follows the curvature of the earth. Vertical polarization is used to alleviate short circuiting the electric field through the conductivity of the ground. Since the ground is not a perfect electrical conductor, ground waves are attenuated rapidly as they follow the earth’s surface. Attenuation is proportional to the frequency making this mode mainly useful for LF and VLF frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Direct modes (line-of-sight)&lt;/strong&gt;&#xA;&amp;mdash; Line-of-sight is the direct propagation of radio waves between antennas that are visible to each other. This is probably the most common of the radio propagation modes at VHF and higher frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Ionospheric modes (skywave)&lt;/strong&gt;&#xA;&amp;mdash; Skywave propagation, also referred to as skip, is any of the modes that rely on refraction of radio waves in the ionosphere, which is made up of ionized layers in the upper atmosphere. F2-layer is the most important ionospheric layer for long-distance, multiple-hop HF propagation, though F1, E, and D-layers can also play significant roles. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The D-layer, when present during sunlight periods, causes significant amount of signal loss, as does the E-layer whose maximum usable frequency can rise to 4 MHz and above and thus block higher frequency signals from reaching the F2-layer. The layers, or more appropriately &quot;regions&quot;, are directly affected by the sun on a daily cycle, a seasonal cycle and the 11-year sunspot cycle and determine the utility of these modes. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Meteor scattering&lt;/li&gt;&#xA;&lt;li&gt;Auroral backscatter&lt;/li&gt;&#xA;&lt;li&gt;Sporadic-E propagation&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Tropospheric modes&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Tropospheric scattering&lt;/li&gt;&#xA;&lt;li&gt;Tropospheric ducting&lt;/li&gt;&#xA;&lt;li&gt;Tropospheric delay&lt;/li&gt;&#xA;&lt;li&gt;Rain scattering&lt;/li&gt;&#xA;&lt;li&gt;Lightning scattering&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Other effects&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Diffraction&lt;/li&gt;&#xA;&lt;li&gt;Absorption&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-04T19:22:18.920" LastActivityDate="2013-12-04T19:22:18.920" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="591" PostTypeId="4" CreationDate="2013-11-07T14:08:41.803" Score="0" Body="Questions about RF propagation including measurements, beacons, modes (ionospheric, tropospheric, ground wave), etc." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-07T14:40:29.983" LastActivityDate="2013-11-07T14:40:29.983" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="592" PostTypeId="5" CreationDate="2013-11-07T14:12:16.633" Score="0" Body="&lt;p&gt;Questions related directly to the mode of communication (SSB, CW, digital, etc).&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-07T14:39:49.373" LastActivityDate="2013-11-07T14:39:49.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="593" PostTypeId="4" CreationDate="2013-11-07T14:12:16.633" Score="0" Body="Questions related directly to the mode of communication (SSB, CW, digital, etc)." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-07T14:39:52.090" LastActivityDate="2013-11-07T14:39:52.090" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="594" PostTypeId="5" CreationDate="2013-11-07T14:19:04.090" Score="0" Body="&lt;p&gt;Some example questions in this tag include resistance/impedance calculations, filter transfer functions, calculating signal levels at different parts of a circuit, or anything else that may have to do with math or equations.&lt;/p&gt;&#xA;" OwnerUserId="322" LastEditorUserId="322" LastEditDate="2013-11-07T14:40:23.483" LastActivityDate="2013-11-07T14:40:23.483" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="595" PostTypeId="4" CreationDate="2013-11-07T14:19:04.090" Score="0" Body="Questions which may involve math, including calculations about signal levels, the math theory of certain modulations or modes, or anything else." OwnerUserId="322" LastEditorUserId="322" LastEditDate="2013-11-07T14:40:27.127" LastActivityDate="2013-11-07T14:40:27.127" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="596" PostTypeId="5" CreationDate="2013-11-07T14:20:45.620" Score="0" Body="&lt;p&gt;Anything to do with wire antennas, including how to build one, how different wire antennas perform, how to tune them or when to use a balun, and what types of wire work best in certain antennas.&lt;/p&gt;&#xA;" OwnerUserId="322" LastEditorUserId="322" LastEditDate="2013-11-07T14:39:45.903" LastActivityDate="2013-11-07T14:39:45.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="597" PostTypeId="4" CreationDate="2013-11-07T14:20:45.620" Score="0" Body="Anything to do with wire antennas, including how to build one, how different wire antennas perform, how to tune them or when to use a balun, and what types of wire work best in certain antennas." OwnerUserId="322" LastEditorUserId="322" LastEditDate="2013-11-07T14:39:18.620" LastActivityDate="2013-11-07T14:39:18.620" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="598" PostTypeId="2" ParentId="584" CreationDate="2013-11-07T14:56:12.500" Score="0" Body="&lt;p&gt;General Ohm's law theory, amplification, modulation and de-modulation, types of frequency control, AM/FM, the basic phoenetic alphabet and radio etiquette.&lt;/p&gt;&#xA;" OwnerUserId="323" LastActivityDate="2013-11-07T14:56:12.500" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="599" PostTypeId="2" ParentId="558" CreationDate="2013-11-07T15:05:39.457" Score="3" Body="&lt;p&gt;There is a government doctrine on this very subject entitled OET-65.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You must remember that RF exposure is cumulative and does the most damage over a long period of time. The symptoms of over-exposure to RF are stomach pains, scratchy/sandy feeling eyes, the internal feeling of overheating (possibly followed by stroke).&#xA;The most effective ways of avoiding the effects of RF exposure are limiting your exposure times, RF reflective clothing and wearing an exposure badge.&lt;/p&gt;&#xA;" OwnerUserId="323" LastActivityDate="2013-11-07T15:05:39.457" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="600" PostTypeId="2" ParentId="469" CreationDate="2013-11-07T15:21:12.607" Score="1" Body="&lt;p&gt;I think you've got to figure in the dielectric material as well as the length, tuning and antenna types of the TX line. For example, waveguide will be much more efficient than 1/2&quot; foam-filled. Phased tuned array structures will always have considerably lower SWR (and therefore better TX characteristics than a standard whip or yagi antenna.&lt;/p&gt;&#xA;" OwnerUserId="323" LastActivityDate="2013-11-07T15:21:12.607" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="601" PostTypeId="1" AcceptedAnswerId="604" CreationDate="2013-11-07T16:06:34.777" Score="11" ViewCount="3931" Body="&lt;p&gt;What can be done to reduce RF in the shack (riding back along the coax) when using a vertical 10M antenna (without radials due to space constraints)? The antenna is an IMax-2000 at 32' elevation (20' over roof) with a 125' coax LMR-400, SWR is under 1.5 across 10M band. No balun, no tuner. Cable length is required to reach the shack room (basement). Max power 100 W with interference level increasing with greater power output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is causing interference with capacitive touch lamps (on, off on transmit); as well as causing speakers around the house (even when turned off) to broadcast the operator's voice (a ghoulish combination with the flickering lights).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The height of the mast was adjusted from 1' to its present 32' over ground level, with no change to SWR or interference as described above. The mast was tried with and without grounding (to an 8' ground rod at its base), no effect to SWR or interference level.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2020-05-23T10:19:59.240" Title="How to reduce RF in the shack when using vertical HF antenna (no radials)" Tags="&lt;hf&gt;&lt;vertical-antenna&gt;&lt;rfi&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="602" PostTypeId="2" ParentId="584" CreationDate="2013-11-07T16:23:26.113" Score="0" Body="&lt;p&gt;A one-hour class has almost enough time to explain a radio, station accessory or antenna that you bring in for a demonstration.  I might suggest to bring in a FUNcube Dongle Pro + from &lt;a href=&quot;http://funcubedongle.com&quot; rel=&quot;nofollow&quot;&gt;http://funcubedongle.com&lt;/a&gt; with your laptop and free SDR software and a short length of thin wire to serve as a &quot;wet noodle&quot; antenna.  Or bring in anything else from your ham shack or mobile station.  Or walk them through the ARRL Web site and all the golden nuggets under there.  Have fun!!&lt;/p&gt;&#xA;" OwnerUserId="324" LastEditorUserId="218" LastEditDate="2013-11-07T17:29:05.753" LastActivityDate="2013-11-07T17:29:05.753" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="603" PostTypeId="2" ParentId="584" CreationDate="2013-11-07T16:33:20.460" Score="0" Body="&lt;p&gt;If a demo to &quot;tease&quot; them is not appropriate for this audience then show them the list of requirements for the merit badge and make comments, line by line, what it takes to complete each item in high-level terms.  Bring with you a syllabus of the ARRL Technician Class FCC license class and go over the content in general terms.  You will fill an hour easily!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, have fun.  Let your passion on the subject shine!&lt;/p&gt;&#xA;" OwnerUserId="324" LastEditorUserId="76" LastEditDate="2013-11-12T19:41:51.793" LastActivityDate="2013-11-12T19:41:51.793" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="604" PostTypeId="2" ParentId="601" CreationDate="2013-11-07T16:42:25.753" Score="14" Body="&lt;p&gt;You may be surprised to hear this, but the antenna you describe isn't &lt;em&gt;actually&lt;/em&gt; a vertical, but a dipole. One half of the dipole is the IMax-2000, and the other half is your feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can not simply not have radials and still have an antenna. An antenna works by making EM fields between two things. A dipole has two halves. A vertical works because the ground plane under it creates an &lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot;&gt;image antenna&lt;/a&gt; under it, making it appear as a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get the RF currents off of the feedline, you have to give it some other place to go. You could:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;install a dipole&lt;/li&gt;&#xA;&lt;li&gt;install elevated radials&lt;/li&gt;&#xA;&lt;li&gt;mount the vertical on the ground&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You can also put a high impedance on the feedline to make that path less desirable to RF currents. An easy and effective way to do this is to slip ferrite beads over the coax. However, if you don't first provide a more desirable place for them to go, then you are just putting ferrite beads on your antenna, which will reduce the RF in the shack, and also everywhere else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would also point out that a SWR of 1.5:1 does not in itself indicate that the antenna is working well. SWR only indicates that that the antenna is decently matched to the feedline, and thus accepting (and not reflecting) power: it doesn't indicate that the power accepted is actually being radiated as intended. One way to make an antenna get a good match across a wide band is to make it very lossy. As an extreme example, I have a dummy load that has a 1:1 SWR from DC up to beyond the capability of my test equipment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-11-07T16:47:52.207" LastActivityDate="2013-11-07T16:47:52.207" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="605" PostTypeId="2" ParentId="532" CreationDate="2013-11-07T16:48:02.453" Score="1" Body="&lt;p&gt;I never use any single strand or monofilament line.  The weed whacker string is an example of the latter.  Evaluate strings, chords and narrow gauge ropes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Go to a hardware store (e.g., Lowe's, Home Depot), go to the rope and string section and read the notes on the different packages that provide info on load strength, shock strength, moisture performance, UV performance, cold weather performance and other characteristics.&lt;/p&gt;&#xA;" OwnerUserId="324" LastEditorUserId="76" LastEditDate="2013-11-12T19:41:38.020" LastActivityDate="2013-11-12T19:41:38.020" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="606" PostTypeId="1" AcceptedAnswerId="608" CreationDate="2013-11-07T17:27:42.133" Score="29" ViewCount="33963" Body="&lt;p&gt;Recently, the power was out in my neighborhood for an extended period of time. I fired up my HF rig using battery power and was amazed at the lack of noise across the HF bands. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the power grid came back online, the noise returned. The difference was drastic. S2 vs. S9 drastic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that said, is there a good way to reduce RFI/noise at the antenna? Specifically a dipole antenna? Is there a better way to solve this problem?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The houses are packed so close together in my neighborhood, the likelihood of eliminating the noise at the source(s) is nil. For reference, the type of &quot;noise&quot; I'm hearing is more of a white noise rather than a noise pattern coming from an interfering appliance. (Though, I do hear RFI with a pattern to it from time to time on certain bands as well.)&lt;/p&gt;&#xA;" OwnerUserId="100" LastEditorUserId="250" LastEditDate="2013-11-12T04:02:08.560" LastActivityDate="2021-02-20T03:30:53.253" Title="Can I reduce RFI/noise at the antenna?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;rfi&gt;&lt;snr&gt;" AnswerCount="6" CommentCount="0" FavoriteCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="607" PostTypeId="1" AcceptedAnswerId="609" CreationDate="2013-11-07T17:39:40.107" Score="18" ViewCount="4966" Body="&lt;p&gt;I'm looking at data converter chips for a homebrew SDR design, and I see that I can choose not just the sampling frequency, but also the bits per sample.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously the sampling frequency has to be several times the target frequency, but what effect does the bits per sample have on the signals I can receive and transmit?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will I be ok with cheaper 8 bit ADC and DAC devices, or will I need to look at 10, 12, or 16 bit converters to experiment with SDR?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My primary concern is for HF usage with 200Msps converters and above, with sampling at the antenna, essentially, rather that downconverting, or mixing prior to the sampler.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2013-11-07T23:59:57.817" LastActivityDate="2018-07-25T14:11:00.270" Title="SDR sampling bandwidth - do the bits per sample matter?" Tags="&lt;software-defined-radio&gt;&lt;diy&gt;&lt;theory&gt;&lt;electronics&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="608" PostTypeId="2" ParentId="606" CreationDate="2013-11-07T18:17:08.897" Score="17" Body="&lt;p&gt;First, I'd be sure it's actually the antenna picking up the noise, and not something else. &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;If you don't have a balun on that dipole&lt;/a&gt;, probably your feedline is picking up all the noise in your house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any other wires attached to your receiver can also make good noise antennas, especially the power cord, which is attached to your home's wiring, and coupled to all the noisy stuff running on it. Get some ferrite beads designed for EMI control, and start snapping them on any wire attached to the receiver. Keep snapping them on until you stop getting improvement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have cooperative neighbors, do the same to their noisy electronics. Ferrite beads work for keeping EMI out of your receiver, and also for preventing it from leaving the source in the first place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once that's done, the next thing is to get the antenna as far away from other noise sources as possible. Powerlines, neighbors, etc. Put it on the tallest tower allowed in your neighborhood. In urban areas, your options are limited, but do what you can.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rest is just trying to null the noise based on its direction, or it's polarization, or something else. Every antenna has a particular polarization and radiation pattern. You don't know the same of your noise sources, but just by playing with the orientation of the antenna you might by chance find an arrangement that works well. Try not to be parallel to power lines, etc. A directional antenna helps, but is probably impracticably large at HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this point, you are running out of options. Some of the noise is in the &lt;a href=&quot;http://en.wikipedia.org/wiki/Near_and_far_field&quot; rel=&quot;nofollow noreferrer&quot;&gt;far field&lt;/a&gt; of the antenna, and there just isn't much you can do about this besides move.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other noise is in the near field, which at HF, can be quite big. In this region your antenna isn't acting as an antenna, but rather one winding of a transformer, or one plate of a capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is one additional game you can play here that might help. Remember that &lt;a href=&quot;http://en.wikipedia.org/wiki/Electromagnetic_radiation&quot; rel=&quot;nofollow noreferrer&quot;&gt;electromagnetic radiation&lt;/a&gt; is made of two fields: an electric field and a magnetic field. In the far field, these two are inseparably linked, related by the &lt;a href=&quot;http://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance of free space&lt;/a&gt;. However, in the near field, you can have a strong electric field and a weak magnetic field (capacitors), or vice-versa (transformers).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can build different antennas which, at some distance in the near-field, have a different sensitivity to one type of field or the other. &lt;a href=&quot;http://www.w8ji.com/magnetic_receiving_loops.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI has a good article on small loop antennas&lt;/a&gt;, and describes this in some detail. In particular, there's this great graph:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/7vVbu.gif&quot; alt=&quot;dipole and loop impedance vs. distance&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A high impedance means the antenna is more sensitive to electric rather than magnetic fields. So, you can see that if your noise source is very close (less than 10 meters for this antenna) and is largely E-field noise, you'd want a loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, keep in mind:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the impedance of all antennas are &lt;em&gt;identical&lt;/em&gt; and equal to &lt;a href=&quot;http://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;nofollow noreferrer&quot;&gt;the impedance of free space (377Ω)&lt;/a&gt; in the far-field. This only makes a difference for noise sources in the near-field, which couple to your receiver by mutual inductance or capacitance, &lt;em&gt;not&lt;/em&gt; EM radiation.&lt;/li&gt;&#xA;&lt;li&gt;the impedance changes up and down in the near-field with distance, and if a particular antenna seems to have less noise, it's due to chance and your particular noise source's characteristics, not some magical  &quot;noise immunity&quot; intrinsic to some antenna design.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;That said, most people already have dipoles, so if they find them noisy, sometimes they have luck switching to a loop, which provides a complementary near-field impedance, and just might be better in a particular environment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="1362" LastEditDate="2017-09-09T00:39:02.413" LastActivityDate="2017-09-09T00:39:02.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="609" PostTypeId="2" ParentId="607" CreationDate="2013-11-07T18:35:18.750" Score="18" Body="&lt;p&gt;The bits per sample will affect the &lt;a href=&quot;http://en.wikipedia.org/wiki/Dynamic_range&quot; rel=&quot;nofollow noreferrer&quot;&gt;dynamic range&lt;/a&gt; of your receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a lot of math that I'm sure you can find, but here's the intuitive explanation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A digital signal can represent only discrete quantities, where an analog signal can represent infinitely many quantities between any two discrete quantities the digital signal might represent. The difference between the actual analog signal, and the represented digital signal, is an error, and is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Quantization_%28signal_processing%29#Quantization_noise_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;quantization noise&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have more bits, the error, and the noise is less. Of course, if there are larger sources of noise (the preamplifier, ambient RF noise, etc) then the additional noise introduced by quantization doesn't matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, it makes sense on as SDR to adjust the preamplifier's gain so that the noise floor is just above the quantization noise. Otherwise, you are wasting a lot of bits just carrying noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This maximizes the bits available for actual signal, which is good, because it also maximizes dynamic range, or how much power can be received by the receiver before it clips (the digital signal can represent a signal only so big). This is of particular concern for SDRs because of their wide receive bandwidth: you may not be listening to that guy with the S9+ signal, but your receiver is. If that signal is strong enough to hit the limits of your ADC, then you get clipping, which will introduce harmonics all over the band, making you unhappy. You could turn down the receiver's gain, but then the very weak DX station that is just above the RF noise floor will be below the quantization noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resolution (number of bits) for the DAC is not really as critical, since you don't need a lot of dynamic range to transmit. You will still have quantization noise, but since the digital signal can trivially be scaled to use the full range of the DAC, the noise is usually negligible. An approximate model is the noise floor will be 6 dB below the signal for each DAC bit. For an 8 bit DAC this gives a noise floor of -48 dBc, sufficient for many applications. Further improvements can be made by &lt;a href=&quot;https://en.wikipedia.org/wiki/Noise_shaping&quot; rel=&quot;nofollow noreferrer&quot;&gt;noise shaping&lt;/a&gt; combined with analog filtering of the output. Or simply upgrading the precision of the DAC may be the most economical solution: DACs are cheaper than ADCs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, 8 bits is more than sufficient for experimentation, but this is definitely a &quot;more is better&quot; situation. It all depends on the performance you require, and also your ability to build the rest of the receiver to utilize the full capabilities of the ADC.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;As mentioned by others in comments and answers, it is also possible to reduce the quantization noise by oversampling the signal of interest, then decimating the resulting data. For example, say we are interested in signals up to 30 MHz, so we require a 60 MHz ADC. If we use a 240 MHz ADC, but the analog input has no frequencies above 30 MHz, then we have four times more samples than required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could simply keep only 1 in 4 samples, but if we first use a digital low-pass filter we can actually remove some of the quantization noise. This is because the quantization noise will be distributed through the spectrum: from 0 to 120 MHz, the maximum at our 240 MHz sample rate. Low-pass filtering then removes the noise between 30 MHz (our upper range of interest) and 240 MHz, so we've effectively removed some of the noise by averaging it out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The math works out so that for every 4x in excess samples, it effectively adds another bit to the resolution, or increases dynamic range by 3dB. For example, an 8-bit, 240 MHz ADC is equivalent to a 9-bit, 30 MHz ADC.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-07-25T14:11:00.270" LastActivityDate="2018-07-25T14:11:00.270" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="610" PostTypeId="1" AcceptedAnswerId="611" CreationDate="2013-11-07T21:55:22.047" Score="7" ViewCount="596" Body="&lt;p&gt;It's been more than a year since I passed my Technician and General exams and obtained my license. If I were now to go for my Extra class license, would it simply be a matter of taking and passing the Extra exam, or would I need to pass the previous exams again? Under what circumstances is it necessary to &quot;start from the beginning&quot; in terms of testing?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am in particular interested in the rules for the United States, but a broader treatment would certainly be more generally useful.&lt;/p&gt;&#xA;" OwnerUserId="276" LastActivityDate="2013-11-11T02:49:43.993" Title="License upgrade - retake required?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="611" PostTypeId="2" ParentId="610" CreationDate="2013-11-07T22:10:09.990" Score="5" Body="&lt;p&gt;If you can bring proof of having passed Element 3 (the General class exam), such as your paper license or a Successful Completion of Examination (CSCE) you will only have to take Element 4 (the Extra class exam).&lt;/p&gt;&#xA;" OwnerUserId="63" LastEditorUserId="63" LastEditDate="2013-11-07T22:19:06.643" LastActivityDate="2013-11-07T22:19:06.643" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="612" PostTypeId="1" CreationDate="2013-11-08T01:00:53.793" Score="8" ViewCount="323" Body="&lt;p&gt;The &lt;a href=&quot;http://transition.fcc.gov/oet/spectrum/table/fcctable.pdf&quot; rel=&quot;noreferrer&quot;&gt;FCC table of frequency allocations&lt;/a&gt; clearly states on page 27 that the Amateur allocation for 70cm is 420-450MHz, but I've seen a lot of transceivers that limit transmit to 430-450MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is this?&lt;/p&gt;&#xA;" OwnerUserId="227" LastEditorUserId="227" LastEditDate="2013-11-08T05:25:19.730" LastActivityDate="2013-11-09T16:06:13.060" Title="Why do USA transceivers limit transmit to 430-450MHz?" Tags="&lt;united-states&gt;&lt;band-plan&gt;&lt;70cm-band&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="613" PostTypeId="2" ParentId="612" CreationDate="2013-11-08T01:00:53.793" Score="8" Body="&lt;p&gt;It is probably due to the fact that Canada does not include 420-430MHz in their 70cm band plan. The &lt;a href=&quot;http://en.wikipedia.org/wiki/70-centimeter_band#Band_allocation&quot; rel=&quot;nofollow&quot;&gt;United States agrees not to allow their amateurs to interfere&lt;/a&gt;, by restricting 420-430MHz &lt;a href=&quot;http://transition.fcc.gov/oet/info/maps/canline/canline.html&quot; rel=&quot;nofollow&quot;&gt;north of Line A and east of Line C&lt;/a&gt;.  (See also FCC Title 47 Part 97.303.m which I can't find a good way to link to.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the manufacturer decides to restrict 420-430MHz, then the transceiver can be sold in both the US and Canada, and US customers are unlikely to mistakenly infringe.&lt;/p&gt;&#xA;" OwnerUserId="227" LastEditorUserId="227" LastEditDate="2013-11-09T16:06:13.060" LastActivityDate="2013-11-09T16:06:13.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="615" PostTypeId="1" AcceptedAnswerId="619" CreationDate="2013-11-08T05:39:31.677" Score="14" ViewCount="16400" Body="&lt;p&gt;Just what the title says.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An &lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_tuner&quot; rel=&quot;noreferrer&quot;&gt;Antenna Tuner&lt;/a&gt;, henceforth AT, is almost a &lt;a href=&quot;http://en.wikipedia.org/wiki/De_facto&quot; rel=&quot;noreferrer&quot;&gt;de facto&lt;/a&gt; piece of equipment in a shack; working the bands without one is tantamount to leaping off the diving board into a swimming pool with tarantula nests in it ... or worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason for the AT is primarily to match the antenna to the transmitter for the &lt;a href=&quot;http://en.wikipedia.org/wiki/Standing_wave_ratio&quot; rel=&quot;noreferrer&quot;&gt;Standing Wave Ratio&lt;/a&gt;. The greater the SWR, the more the risk to the transmitter. But before one uses an AT, one either designs the antenna (balanced/unbalanced, array-type, length, impedance ... and constructs it), or purchases the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Keeping it simple&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Say, A simple mono-band centre-fed dipole is constructed after calculating the length for that band&lt;/li&gt;&#xA;&lt;li&gt;Say further, neither an AT nor an SWR meter is available &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Given the above assumptions, what I would like to know&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How can I transmit without an antenna tuner? &lt;/li&gt;&#xA;&lt;li&gt;Are there any rule-of-thumb tests/calculations I may do to determine whether an antenna is a decent fit for a given band?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;As a corollary&lt;/em&gt; &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What if the antenna is &lt;strong&gt;not&lt;/strong&gt; a simple centre-fed mono-band antenna? &lt;/li&gt;&#xA;&lt;li&gt;How did they tune antennas back when the hobby was still new? I guess &lt;a href=&quot;https://ham.stackexchange.com/questions/383/does-a-tube-based-hf-transmitter-need-an-antenna-tuner&quot;&gt;Does a tube based HF transmitter need an antenna tuner?&lt;/a&gt; may be relevant to this part of the question&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2018-08-14T23:19:49.370" Title="How can I safely transmit without an antenna tuner or SWR meter?" Tags="&lt;antenna&gt;&lt;impedance&gt;&lt;antenna-tuner&gt;" AnswerCount="12" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="616" PostTypeId="5" CreationDate="2013-11-08T05:46:41.170" Score="0" Body="&lt;p&gt;Amateur radio is possessed of a long, and chequered history. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Technology&lt;/li&gt;&#xA;&lt;li&gt;Spectrum usage&lt;/li&gt;&#xA;&lt;li&gt;Modes&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;(to name just a few) have evolved over the decades. There may, upon occasion, be questions of a historic nature - technical, and otherwise; for them, this tag.&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-11-08T15:26:56.267" LastActivityDate="2013-11-08T15:26:56.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="617" PostTypeId="4" CreationDate="2013-11-08T05:46:41.170" Score="0" Body="Questions pertinent to historic developments in the Amateur Radio arena" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-11-08T15:26:59.517" LastActivityDate="2013-11-08T15:26:59.517" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="618" PostTypeId="2" ParentId="615" CreationDate="2013-11-08T14:02:33.063" Score="3" Body="&lt;p&gt;The key piece of information required to know if an Antenna Tuner is required is the SWR. If the SWR is higher than 1.5, you probably need an antenna tuner. If not, they it's not really a requirement. The SWR changes based on frequency, so you need to keep that in mind as well. SWR can be measured by various meters, just keep your eyes opened for one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Okay, so what can cause the SWR to change? A lot of things really. The antenna needs to be at least a wavelength off of the ground to have optimal performance. It should be far away from metal objects. It might even change based off of local topology, and mineral content. These considerations are especially true for HF, which is why HF often has an antenna tuner. However, for VHF/UHF, the use of a tuner is rare, I certainly don't use one.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-11-08T14:02:33.063" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="619" PostTypeId="2" ParentId="615" CreationDate="2013-11-08T14:02:52.017" Score="6" Body="&lt;p&gt;The SWR meter helps you match the impedance of the radio to the antenna.  If the impedance is mismatched, you lose power.  If the impedance mismatch is large, you risk damaging your radio, particularly on the lower frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tube based transmitters and amplifiers have more leeway for mismatch than semiconductor based amplifiers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lower power transmitters also have more leeway for mismatch before damage occurs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;em&gt;ideal is to borrow an SWR meter and tune your antenna for the intended frequency, or send the antenna to someone who can do that for you.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If you don't have any of these tools and can't get help from others easily, you can get as close to the right frequency by building the antenna according to the design, then start transmitting on low power and make contacts.  Find someone willing to work with you, and ask for signal quality reports. Then make a small adjustment to the antenna and ask for another report.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a long process, but they will receive more signal the better your radio is matched to your antenna, so it's an easy check.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do this at low power though, so you reduce the risk of damaging your transmitter.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="5" LastEditDate="2013-11-10T22:06:02.030" LastActivityDate="2013-11-10T22:06:02.030" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="620" PostTypeId="2" ParentId="516" CreationDate="2013-11-08T14:27:30.783" Score="8" Body="&lt;p&gt;Occasionally you'll find &lt;a href=&quot;https://www.google.com/search?q=ehf%20transmitter&quot; rel=&quot;nofollow&quot;&gt;researchers and amateur radio enthusiasts who have created transmitters and receivers that operate in the EHF band&lt;/a&gt;.  This band goes from 30GHz to 300GHz, and covers the frequencies you are interested in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At these frequencies, conventional electronics and oscillators aren't very useful, and typically oscillators are built by using resonant cavities.  This is akin to a pipe organ, but at radio frequencies.  One example is the magnetron in the typical microwave oven - while it operates at a much lower frequency, it uses the same principle.  At higher frequencies you might use a &lt;a href=&quot;http://en.wikipedia.org/wiki/Klystron&quot; rel=&quot;nofollow&quot;&gt;Klystron&lt;/a&gt;, which is a special tube that contains the parts needed to create an EHF oscillator while controlling the amplitude, frequency and phase.  The Klystron may be used as the antenna itself as well, directing what you might consider a microwave beam of radio energy, or the energy might be coupled into suitable coaxial cables as in a typical radio setup.  The Klystron and Magnetron technically operate on different principles, but they are both examples of ways to generate EHF waves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the next band up, running from 300GHz to 3,000GHz, referred to as terahertz, is the same band that newer airport scanners run at, imaging human bodies below their clothing.  Many frequencies in EHF and THF bands will not travel very far through many materials, and so aren't very useful for general radio use.  But there are specialized uses where these frequencies are used, such as airport security scanners and particle accelerators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are looking for faster wifi, keep in mind that we haven't fully exploited the spectrum we're already using.  MIMO is being used to double and triple throughput, for instance.  Channel bonding and wider channels are being used it increase throughput.  Going another 10 GHz higher isn't going to buy us much with our current technology, but will further limit transmission range and penetration.  &lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="29" LastEditDate="2013-11-10T17:35:04.197" LastActivityDate="2013-11-10T17:35:04.197" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="621" PostTypeId="2" ParentId="490" CreationDate="2013-11-08T14:49:53.460" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Would it be possible to make a digital &quot;simplex&quot; voice repeater which would listen on one time slot and immediately repeat the received voice frame on the next time slot, on the same frequency? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, the protocol could be used this way.  It wouldn't be simple to setup without the radios specifically supporting such a mode of operation, though.  You could use two radios for the repeater - each set the the opposing timeslot, feeding into each other, with VOX enabled, but it would be, at best, a hack and probably wouldn't be very robust without additional control equipment.  It would eliminate the need for resonant filters, though.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Do such repeaters exist for some protocol?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I understand that some Hytera radios support this mode.  Mototrbo radios support TDMA operation, but when in TDMA mode you select a single time slot for both transmitting and receiving.  The repeater would have to be set up to to always receive on one time slot and transmit on the other, and the users would have to set their radio to receive on the correct timeslot, except when they want to transmit.  At that point they'd have to manually switch the radio to the other timeslot, then when done immediately switch it back to the timeslot the repeater transmits on.  This is not automated in the Mototrbo radios, so they couldn't easily be used for this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it is possible, and it may be interesting to do, merely from the viewpoint of eating up only one 12.5kHz channel and removing the need for expensive, large filters.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-11-13T12:43:57.463" LastActivityDate="2013-11-13T12:43:57.463" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="622" PostTypeId="2" ParentId="381" CreationDate="2013-11-08T14:52:02.347" Score="1" Body="&lt;p&gt;That will give you a rough idea of the coupling, but note that the dummy load would have an SWR of 1:1, while the antenna to the radio might not.  Your coupling will depend on the impedance matching between the radio as well as the antenna, so you can only get so far with an SWR meter and a dummy load.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-11-08T14:52:02.347" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="623" PostTypeId="1" AcceptedAnswerId="625" CreationDate="2013-11-08T15:29:41.727" Score="17" ViewCount="117877" Body="&lt;p&gt;I have a few walkie talkies at home and sometimes I connect my UV-5R to them to talk to them and act as another walkie talkie. At one time, I built a little simplex repeater out of it. Should I not be doing this? I don't think the other walkie talkie users care about me doing this, just knowing the FCC, they might freak out or something crazy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used the 462.562 frequency.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="13" LastEditDate="2013-11-08T19:00:51.227" LastActivityDate="2015-03-26T19:03:48.597" Title="Using my Baofeng UV-5R to talk to walkie talkies" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;ht&gt;&lt;frs&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="624" PostTypeId="2" ParentId="606" CreationDate="2013-11-08T15:51:43.350" Score="2" Body="&lt;p&gt;Another approach would be nulling one signal (say: your neighbor's plasma TV) to allow other signals to come over. Devices known as &quot;noise cancellers&quot; or &quot;phasers&quot; do exactly this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try searching videos demonstrating MFJ-1026, Quantum Phaser and Timwave ANC-4 to have an idea how they work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They have some constraints: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;a) they can only null one signal at a time. You will either null the Plasma TV or the cell-phone charger jamming;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;b) they have narrow bandwidth, you will have to re-tune every time you move 10-20KHz away;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;c) they require a 'sense' antenna that capture the interfering signal. In practical terms, you would need to have a second antenna outside.&lt;/p&gt;&#xA;" OwnerUserId="234" LastActivityDate="2013-11-08T15:51:43.350" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="625" PostTypeId="2" ParentId="623" CreationDate="2013-11-08T16:05:06.770" Score="18" Body="&lt;p&gt;The GMRS and FRS bands are governed by the FCC and have &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=e593ed9f147a6ee87a8803d05b9667c9&amp;amp;tpl=/ecfrbrowse/Title47/47cfr95_main_02.tpl&quot; rel=&quot;noreferrer&quot;&gt;specific requirements&lt;/a&gt; not just for use and power output, but for equipment that is allowed.  One of the requirements is that radios used for GMRS service be &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=e593ed9f147a6ee87a8803d05b9667c9&amp;amp;tpl=/ecfrbrowse/Title47/47cfr95_main_02.tpl&quot; rel=&quot;noreferrer&quot;&gt;part 95&lt;/a&gt; certified and FCC certified for GMRS use:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§95.129   Station equipment.&lt;/p&gt;&#xA;&lt;p&gt;Every station in a GMRS system must use transmitters the FCC has certificated for use in the GMRS. Write to any FCC Field Office to find out if a particular transmitter has been certificated for the GMRS. All station equipment in a GMRS system must comply with the technical rules in part 95.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The FRS rules are just as strict:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§95.194   (FRS Rule 4) FRS units.&lt;/p&gt;&#xA;&lt;p&gt;(a) You may only use an FCC certified FRS unit. (You can identify an FCC certified FRS unit by the label placed on it by the manufacturer.)&lt;/p&gt;&#xA;&lt;p&gt;(b) You must not make, or have made, any internal modification to an FRS unit. Any internal modification cancels the FCC certification and voids your authority to operate the unit in the FRS.&lt;/p&gt;&#xA;&lt;p&gt;(c) You may not attach any antenna, power amplifier, or other apparatus to an FRS unit that has not been FCC certified as part of that FRS unit. There are no exceptions to this rule and attaching any such apparatus to a FRS unit cancels the FCC certification and voids everyone's authority to operate the unit in the FRS.&lt;/p&gt;&#xA;&lt;p&gt;(d) FRS units are prohibited from transmitting data in store-and-forward packet operation mode.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The FCC does not have a process to self-certify radios, so you can't declare the radio certified.  If you have an Amateur Radio license you'll find that the FRS and GMRS frequencies aren't available under that license.&lt;/p&gt;&#xA;&lt;p&gt;So according to FCC rules, your use of the UV-5R is not acceptable on that frequency.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2013-11-08T16:05:06.770" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="626" PostTypeId="2" ParentId="615" CreationDate="2013-11-08T16:59:35.933" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How can I transmit without an antenna tuner?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Simple. You use an antenna that's already tuned. There are &lt;em&gt;plenty&lt;/em&gt; of radios that operate without any tuner. For example, basically every VHF radio. One reason for this is that most VHF antennas are purchased rather than manufactured by the amateur, and the antenna manufacturer has already tested and tuned the antenna design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also relevant to mention that an antenna tuner doesn't actually make the antenna tuned. With a perfectly matched antenna (SWR 1:1), all the power sent down the feedline by the transmitter will be accepted by the antenna and radiated away. When the antenna isn't perfectly matched, some of the power is accepted by the antenna, and some is reflected back at the transmitter. When it reaches the transmitter, the transmitter's RF amplifier sees an impedance other than the 50 ohms for which it designed, which can mean currents or voltages high enough to cause damage. Some radios sense this condition and reduce output power to prevent damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By inserting a tuner between the transmitter and the feedline, the power reflected back from the feedpoint is then reflected again back at the antenna. The transmitter now sees no reflected power: it sees a well-matched load. However, the power is &lt;em&gt;still&lt;/em&gt; being reflected back-and-forth between the feedpoint and the tuner, encountering &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;losses in the feedline&lt;/a&gt; each time. So, the tuner doesn't make the antenna work any better: it just takes some load off your transmitter.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-03-17T13:14:42.650" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="627" PostTypeId="2" ParentId="623" CreationDate="2013-11-08T17:18:30.563" Score="0" Body="&lt;p&gt;I recommend using the MURS frequencies. These are license free. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Multi-Use_Radio_Service&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Multi-Use_Radio_Service&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="329" LastActivityDate="2013-11-08T17:18:30.563" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="628" PostTypeId="5" CreationDate="2013-11-08T19:01:13.993" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-08T19:01:13.993" LastActivityDate="2013-11-08T19:01:13.993" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="629" PostTypeId="4" CreationDate="2013-11-08T19:01:13.993" Score="0" Body="Family Radio Service, most common &quot;Walkie Talkies&quot;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-11-10T15:10:02.073" LastActivityDate="2013-11-10T15:10:02.073" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="630" PostTypeId="2" ParentId="615" CreationDate="2013-11-09T04:51:33.440" Score="3" Body="&lt;p&gt;&lt;strong&gt;Reduce Power&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the bad effects of SWR is heating of the power amplifier inside the radio. This heating occurs because of reflected power.  The higher the SWR, the less power is transmitted out the antenna and more of the power is reflected back to the radio to become heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can reduce reflected power by reducing output power.  For instance, operate a 100W radio into an unknown antenna with the power set to only 5W.  &lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2013-11-09T04:51:33.440" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="632" PostTypeId="2" ParentId="316" CreationDate="2013-11-09T18:16:28.633" Score="2" Body="&lt;p&gt;I've personally worked SO-50 with a 5W HT using an Arrow antenna (&lt;a href=&quot;http://www.arrowantennas.com/arrowii/146-437.html&quot; rel=&quot;nofollow&quot;&gt;http://www.arrowantennas.com/arrowii/146-437.html&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't actually know what the gain would be with that antenna, but with 5W and an antenna like that, you can work SO-50!&lt;/p&gt;&#xA;" OwnerUserId="57" LastActivityDate="2013-11-09T18:16:28.633" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="633" PostTypeId="1" CreationDate="2013-11-10T03:17:14.730" Score="7" ViewCount="130" Body="&lt;p&gt;Does there exist a &lt;em&gt;de facto&lt;/em&gt; standard data (file) format, or even several common formats, for representing information about radio stations, channels, and/or bands? I am writing software which would like to be able to make use of such data sets where they exist.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To clarify the sort of data sets I care about, the minimum information such a file would need to contain is a list of frequencies; useful associated information would be name or callsign, mode/protocol, and geographic coordinates. An example of a data set I would like to be able to obtain and process would be a list of amateur radio repeaters for a given location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My research so far has found data sets provided in the following forms:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Not-completely-regular HTML tables on web pages (e.g. &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;noreferrer&quot;&gt;ARRL Band Plan&lt;/a&gt;)&lt;/li&gt;&#xA;&lt;li&gt;Columnar text files of no standard layout&lt;/li&gt;&#xA;&lt;li&gt;CSV files used by &lt;a href=&quot;http://chirp.danplanet.com/&quot; rel=&quot;noreferrer&quot;&gt;CHIRP&lt;/a&gt;, a tool for configuring radios&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This last has been somewhat useful, in that it is &lt;a href=&quot;http://chirp.danplanet.com/projects/chirp/wiki/MemoryEditorColumns&quot; rel=&quot;noreferrer&quot;&gt;relatively well-defined&lt;/a&gt; and the first two can often be semi-automatically converted into CSV files, but I would like to know if there is something common that I simply haven't learned the right terminology to find or recognize.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2013-11-10T03:24:20.343" LastActivityDate="2013-11-13T12:37:59.050" Title="Is there a standard data format for station/channel/band information?" Tags="&lt;software&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="634" PostTypeId="2" ParentId="607" CreationDate="2013-11-10T15:59:15.313" Score="4" Body="&lt;p&gt;The number of bits in the converter will set the maximum dynamic range of the resulting data stream. This is approximately $\textrm{SNR} = 6\,\textrm{dB} \times \textrm{Bits} + 4.8\,\textrm{dB}$ (for a full scale input sine wave). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, as with everything in life, this is only the beginning of the story. The data sheets for the converters will typically list the SNR achievable with the chip when used in the most efficient manner. For fast, larger bit sized converters, this is almost always less than the $\textrm{SNR}$ shown above, so bit size becomes much less critical than the rated $\textrm{SNR}$ at the operating point you expect. In addition, since you appear to be leaning towards the faster wide-band ADCs, I will assume you are interested in block processing of entire bands. In this situation the $\textrm{SFDR}$, or spurious free dynamic range, is important since large signals may end up covering up small signals on other bands or other regions of the band. This is often less than the $\textrm{SNR}$ spec and may be your limiting factor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the heart of your question was “How do I choose the bit size of my converter?” Well, the simplest answer is that you must match it to the dynamic range of your RF front end output, meaning to make sure your $P_{1\,\textrm{dB}}$ or saturation point is near the top of your ADC's range and the noise floor is less than $\textrm{SNR}$ below that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far I have only spoken of ADC's. For the DAC's you do not have to worry much about the quantization noise since you will be following your DAC output with a filter. For the DAC the number of bits will set your dynamic range, of course; however, you do not have the near signal-far signal dynamic range problem so the bits are much less important. The $\textrm{SFDR}$ is still very important since you do not want to send spurs out or have to manage them.&lt;/p&gt;&#xA;" OwnerUserId="331" LastEditorUserId="76" LastEditDate="2013-11-10T19:20:29.047" LastActivityDate="2013-11-10T19:20:29.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="635" PostTypeId="1" CreationDate="2013-11-10T16:13:00.423" Score="17" ViewCount="346" Body="&lt;p&gt;In movies that depict amateur radio in emergencies, the hams' worldwide communication network invariably is able to pass messages between individuals. As an amateur that has been primarily interested in the technical sides of the hobby I am not at all familiar with how messages might be passed long distances through nets. I would like to pose the following two hypothetical questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;If the power grid and cell phones were down while I was a hundreds of miles from home with no direct communication path, what would be the best way to get a message to my family if my home and I both had access to a battery powered radio and small easily stored antennas?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In the preceding situation, what could I do at home to facilitate that kind of message traffic for others?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;For purposes of the question it should be assumed that when far from home no knowledge of the remote Amateur community and frequencies is know prior to the disaster. Knowing this for the home location seems reasonable. It is also assumed that direct communication is not possible.&lt;/p&gt;&#xA;" OwnerUserId="331" LastEditorUserId="8832" LastEditDate="2018-04-27T22:26:38.373" LastActivityDate="2018-04-27T22:26:38.373" Title="How do emergency nets work?" Tags="&lt;procedure&gt;&lt;emergency&gt;&lt;net&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="636" PostTypeId="1" CreationDate="2013-11-10T16:23:20.563" Score="3" ViewCount="1172" Body="&lt;p&gt;I have read the description of the &lt;a href=&quot;http://k4jwm.com/wilderness-protocol.htm&quot; rel=&quot;nofollow&quot;&gt;Wilderness Protocol&lt;/a&gt;. I have attempted to use it (only after the 4 min emergency window) on multiple occasions at multiple wilderness locations and never received a response. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this the best way to call for help in the wilderness when out of cell phone coverage? &#xA;What can I do to improve my chances of this working if I were to need help?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The givens are that I can only carry an HT, but I would be willing to use a web page to determine a procedure ahead of time.&lt;/p&gt;&#xA;" OwnerUserId="331" LastActivityDate="2013-11-10T20:22:47.317" Title="Is the Wilderness Protocol dead?" Tags="&lt;emergency&gt;&lt;procedure&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2013-11-11T08:25:36.080" ContentLicense="CC BY-SA 3.0" />
  <row Id="637" PostTypeId="2" ParentId="635" CreationDate="2013-11-10T17:31:03.460" Score="12" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If the power grid and cell phones when down while I was a few hundred miles from home what would be the best way to get a message to my family if my home and I both had access to a radio and small antennas?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm going to make a few assumptions, here. You may want to consider them restrictions on when this answer is valid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, I'm going to assume that &quot;having access to radios&quot; means that you have a means to power them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, I'll take a shot at &quot;a few hundred miles&quot; being 200 miles, or 300 km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Third, I'll assume that the small antenna, while perhaps not optimal, &lt;a href=&quot;https://ham.stackexchange.com/a/76/29&quot;&gt;presents a good match to the transmitter&lt;/a&gt; at the height and operating frequency in use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fourth, I'll assume you have access to HF, both in terms of license restrictions as well as in terms of equipment. A few hundred km on VHF is not trivial; while certainly doable, it pretty much requires a fixed installation because of the limitations of line-of-sight propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If those assumptions hold,&lt;/strong&gt; then establishing communications even in a grid-down scenario is fairly easy. You'd probably be using a low HF band, depending on conditions most likely either 3.5 MHz (during the night) or 7 MHz (daylight), with the antenna near the ground. This results in what is called &lt;a href=&quot;https://en.wikipedia.org/wiki/Near_Vertical_Incidence_Skywave&quot; rel=&quot;nofollow noreferrer&quot;&gt;NVIS or Near-Vertical Incidence Skywave&lt;/a&gt;, in which the signal take-off angle is close to vertical. To achieve NVIS, the antenna should be &lt;a href=&quot;https://en.wikipedia.org/wiki/Near_Vertical_Incidence_Skywave#Antennas&quot; rel=&quot;nofollow noreferrer&quot;&gt;no higher than a quarter of a wavelength above ground&lt;/a&gt;, which incidentally is what you'll usually end up with when setting up a temporary antenna to operate on the lower bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From there, those at your home would simply need to know where and when to monitor for your calls. The amateur term for this is a &quot;sked&quot; or scheduled contact. This can be as simple as &quot;keep the radio turned on and tuned to 3755 kHz at all times&quot; or something more elaborate like &quot;listen for me at 7115 kHz at fifteen minutes past the hour 11, 12, 13 and 14 local time, and at 3845 kHz at fifteen minutes before the hour 20, 21 and 22 local time&quot;. The latter example gives you a total of seven opportunities per day to establish communications, four during mid-day and three in the evening.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To make it easier for those at home, you might want to pre-program any applicable frequencies in your transceiver's memory, or write them down clearly, as well as write down the &lt;a href=&quot;https://ham.stackexchange.com/q/55/29&quot;&gt;tuner settings&lt;/a&gt; for each frequency and a quick guide to operating the radio itself. While not strictly a requirement, it does make operating much easier; if something bad has happened, such as the power grid and cell phone network being down, anyone operating the equipment will likely be under stress; do what you can to make it easier on them.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In the preceding situation what could I do at home to facilitate that kind of message traffic for others?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Join a traffic-passing net, or even just regularly participate in informal &quot;net-like&quot; on-the-air gatherings and make others aware that they exist. Depending on your location this will take different shapes, but your local amateur radio club will likely be able to provide locale-specific guidance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that, as the question indicates, traffic-handling nets are point-to-point (as radio communications) but &lt;em&gt;not necessarily endpoint-to-endpoint&lt;/em&gt;. The idea is to get traffic &lt;em&gt;closer to its intended destination&lt;/em&gt;, not necessarily to get it to its destination immediately. It may be possible to get the traffic to its intended destination with a single &quot;hop&quot;, but more likely is that it will require a few hops between the original sender and the intended recipient. (In the simplest of cases, neither the sender nor the recipient has access to amateur radio, but the traffic is passed over amateur radio without relays, in which case you have three hops: sender to operator, operator to operator, and operator to recipient.)&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-11-22T08:30:14.080" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="638" PostTypeId="5" CreationDate="2013-11-10T20:22:20.107" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-10T20:22:20.107" LastActivityDate="2013-11-10T20:22:20.107" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="639" PostTypeId="4" CreationDate="2013-11-10T20:22:20.107" Score="0" Body="Questions dealing with handmade (Do It Yourself) radios and radio accessories." OwnerUserId="-1" LastEditorUserId="22" LastEditDate="2013-11-11T04:14:29.660" LastActivityDate="2013-11-11T04:14:29.660" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="640" PostTypeId="2" ParentId="636" CreationDate="2013-11-10T20:22:47.317" Score="3" Body="&lt;p&gt;Probably because the Wilderness Protocol is not widely known and requires someone listening. While this might happen near some popular National Parks, in general you'd be better off checking the frequencies of the local repeaters in that area before heading off into the woods.  There are several large, multi-state linked repeater networks that are actively monitored.  Of course, their coverage may or may not work for you depending on terrain. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want fail resistant emergency help anywhere, buy a &lt;a href=&quot;http://www.findmespot.com/en/&quot; rel=&quot;nofollow&quot;&gt;SPOT GPS Messenger&lt;/a&gt;.  A unit costs about US$120&lt;/p&gt;&#xA;&#xA;&lt;p&gt;with a year of service is around US$100.  These use GPS to fix your location and sends a message with your location to a service using commercial satellites.  For obvious reasons, the coverage area is most of the planet.  If your into the wild for more than a couple days, add a solar panel and you'd be set.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to stick purely to ham radio, learn CW.  A small QRP rig would run on a 9V battery for many hours. That, plus enough wire for a 40m end fed would still weight less than your typical HT.  And cost far less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have more weight budget, carry an FT-817.  With the W4RT battery, I get 4-6 hours of operating time on SSB.  And besides, you actually intent to operate while your out in the woods and have some fun.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-10T20:22:47.317" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="641" PostTypeId="1" CreationDate="2013-11-10T20:56:21.093" Score="6" ViewCount="4451" Body="&lt;p&gt;The only remote control units I have used before was those little cheap 27Mhz puny range cheap units. I would like to build some sort of RC unit, which has a range up to 1km line of sight. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a general license. How can I get started with remote control using Amateur frequencies, and what bands allocate remote control?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2013-11-10T22:04:40.557" LastActivityDate="2015-12-15T16:31:27.110" Title="How to build a remote control unit that works on amateur radio frequencies?" Tags="&lt;diy&gt;&lt;remote-control&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="642" PostTypeId="2" ParentId="610" CreationDate="2013-11-10T22:22:58.600" Score="3" Body="&lt;p&gt;You will not need to test for anything you have been licensed for again -- as long as your license is not expired or still in the grace period. At the previous exam, you were issued a white slip of paper called a CSCE (Certificate of Successful Completion of Exam). CSCEs are good for one year. To apply the credit of either your license or an unexpired CSCE, you will need to bring the original document and a copy. The examiners will review the original, and submit the copy with your application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;http://www.arrl.org/what-to-bring-to-an-exam-session&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/what-to-bring-to-an-exam-session&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck with your Amateur Extra exam.&lt;/p&gt;&#xA;" OwnerUserId="332" LastEditorUserId="87" LastEditDate="2013-11-11T02:49:43.993" LastActivityDate="2013-11-11T02:49:43.993" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="643" PostTypeId="1" CreationDate="2013-11-11T00:51:46.903" Score="6" ViewCount="126" Body="&lt;p&gt;Let's say I have a very small device, like an RC airplane, which transmits information as well as receiving commands for control. The body is made out of non-conductive foam, therefore not much ground is available. How can quality transmissions be achieved with very little ground available?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2015-12-15T22:08:06.867" LastActivityDate="2015-12-15T22:08:06.867" Title="How to ground with little surface area?" Tags="&lt;antenna&gt;&lt;grounding&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="644" PostTypeId="1" CreationDate="2013-11-11T00:56:13.357" Score="13" ViewCount="2900" Body="&lt;p&gt;A problem with handheld devices is poor grounding. I read from &lt;a href=&quot;https://ham.stackexchange.com/questions/390/how-do-you-rf-ground-an-antenna&quot;&gt;someone else's question&lt;/a&gt; that dipoles don't need a ground. Why don't they make little handhelds with two antennas instead of one, or a little T antenna, which has extendable arms?&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;   _ _  Little dipole arms, which can extend out, and collapse for portability&#xA;    |&#xA;   HT&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="174" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-07-10T21:11:36.297" Title="Handheld Dipoles" Tags="&lt;antenna&gt;&lt;grounding&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="645" PostTypeId="2" ParentId="623" CreationDate="2013-11-11T01:00:15.607" Score="1" Body="&lt;p&gt;You cannot use it to communicate with any standard walkie talkies, whether they use CB, FRS, GMRS, or MURS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Everything has been addressed except the MURS &amp;amp; CB ones(well, one did but they got it wrong, no offense.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a pretty good website if you want a detailed explanation of why you can't use MURS &lt;a href=&quot;https://sites.google.com/site/mursradio2/mursradiocertificationforpart95&quot; rel=&quot;nofollow&quot;&gt;https://sites.google.com/site/mursradio2/mursradiocertificationforpart95&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To sum it up, it has to be MURS Part 95 certified or be grandfathered in, of which the Baofeng is neither.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course CB uses way different frequencies but I'll tell why it isn't legal, in case it helps someone. It has to be certified and it has to be able to operate on ONLY the CB channels. &lt;/p&gt;&#xA;" OwnerUserId="333" LastActivityDate="2013-11-11T01:00:15.607" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="646" PostTypeId="2" ParentId="643" CreationDate="2013-11-11T01:24:19.993" Score="7" Body="&lt;p&gt;&quot;Ground&quot; is not the same thing as &quot;Earth&quot;. It may be confusing because the surface of the Earth is sometimes called &quot;the ground&quot;, but still this is an entirely different thing than electrical &quot;ground&quot;. It is often convenient to define ground to be Earth, but that's no requirement. In a battery powered system far away from Earth, &quot;ground&quot; is likely the negative terminal of the battery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may be confused because &lt;a href=&quot;http://en.wikipedia.org/wiki/Monopole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;monopole antennas&lt;/a&gt; require a good &quot;ground&quot; to function. To amateurs the most familiar monopole antenna is the common vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the &quot;ground&quot; need not be Earth. It can simply be some elevated conductive wires or tubes:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/cbVpf.jpg&quot; alt=&quot;vertical with elevated radials&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here, the three sloping tubes are the &quot;ground&quot;. Drooping them results in a better match to 50Ω coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are of course many antenna designs besides monopole antennas. Here are just a few, none of which require any special ground to operate:&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Dipole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;dipole&lt;/a&gt;&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/TzfMc.png&quot; alt=&quot;dipole&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Horn_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;horn&lt;/a&gt;&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/zdNVD.jpg&quot; alt=&quot;horn&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-11-11T01:24:19.993" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="647" PostTypeId="2" ParentId="644" CreationDate="2013-11-11T02:48:00.487" Score="1" Body="&lt;p&gt;I believe it would be more appropriate to say that the problem with handhelds is a lack of adequate ground plane, which (to me anyway) is not the same as saying they are poorly grounded.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All antennas need a ground. With a dipole, the ground is one half of the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You certainly could make a dipole for an HT. For 2m, you'd be carrying around an antenna that's about 1m long though, which might be a little unwieldy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.hamuniverse.com/dipivcal.html&quot; rel=&quot;nofollow&quot;&gt;http://www.hamuniverse.com/dipivcal.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="73" LastEditorUserId="63" LastEditDate="2013-11-11T04:41:18.140" LastActivityDate="2013-11-11T04:41:18.140" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="648" PostTypeId="2" ParentId="117" CreationDate="2013-11-11T03:12:02.453" Score="13" Body="&lt;p&gt;To extend on the legal part of the answer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hams can use any radio to transmit, as long as they are in the right frequency band, are transmitting using allowed power, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Non-licensed&lt;/em&gt; radio services on the other hand are subject to a host of restrictions, generally including fixed antennas, small power limits, radio-by-radio certification, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To put this another way, the FCC trusts you to keep your equipment legal with ham radio; for no-license services the FCC trusts the equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use whatever you want as long as it legal. No white lists or certification. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That being said, it would probably be a pain. &lt;/p&gt;&#xA;" OwnerUserId="333" LastEditorUserId="76" LastEditDate="2015-08-03T17:55:19.533" LastActivityDate="2015-08-03T17:55:19.533" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="649" PostTypeId="5" CreationDate="2013-11-11T09:07:43.207" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-11T09:07:43.207" LastActivityDate="2013-11-11T09:07:43.207" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="650" PostTypeId="4" CreationDate="2013-11-11T09:07:43.207" Score="0" Body="Citizens Band or CB radio is in the United States an unlicensed radio service operating on 27 MHz." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-11T09:07:43.207" LastActivityDate="2013-11-11T09:07:43.207" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="651" PostTypeId="1" AcceptedAnswerId="652" CreationDate="2013-11-11T10:40:54.703" Score="2" ViewCount="1424" Body="&lt;p&gt;I am an owner of a Yaesu VX-6R. This radio works great on amateur bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a glider pilot I often need to hear the frequency of the local airport. I would like to find out whether this radio is suitable for listening on the airband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many times, especially when the antenna is not vertical to the ground, the frequency I am listening on is jammed (the squelch breaks — lasting for 1-2 seconds each time) and I hear something that sounds like humming from local FM radio stations. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was wondering if the antenna (30 cm long rubber duck) has something to do with this.&#xA;It is important to note that my other radio, a Yaesu VX-3, doesn't seem to have the same problem while listening on the same frequency.&lt;/p&gt;&#xA;" OwnerUserId="133" LastEditorUserId="76" LastEditDate="2013-11-11T20:35:55.690" LastActivityDate="2016-03-27T06:22:44.687" Title="Airband Jammed on Yaesu VX-6R" Tags="&lt;antenna&gt;&lt;yaesu&gt;&lt;airband&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="652" PostTypeId="2" ParentId="651" CreationDate="2013-11-11T16:55:28.357" Score="1" Body="&lt;p&gt;The cheapest and surest way to test for this is to swap antennas, as both use an SMA connector for the stock rubber duck.  Experience with a VX-5R found a similar problem with a cold solder joint on the jack, not the antenna, that was sensitive to orientation, but you can rule out the antenna by sw&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-11-11T16:55:28.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="653" PostTypeId="2" ParentId="641" CreationDate="2013-11-11T19:52:16.753" Score="1" Body="&lt;p&gt;This might be better as a comment than an answer (Mods feels free...) but...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given your callsign is from the USA, your terms are different from mine in the UK, but please check the terms of your licence... I could be wrong but I suggest that what you are proposing using ham bands for is outside the privileges contained therein.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, &lt;em&gt;remote control&lt;/em&gt; implies operating on a fixed frequency - therefore if used on ham bands, you are at risk of causing interference (QRM) of other users.&lt;/p&gt;&#xA;" OwnerUserId="93" LastActivityDate="2013-11-11T19:52:16.753" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="654" PostTypeId="2" ParentId="197" CreationDate="2013-11-11T20:25:31.370" Score="3" Body="&lt;p&gt;Without a lot of information on the person's testing methodology, I'll assume that dBS9/dBm refer to the signal strength received by the radio the antenna being tested is attached to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several different ways to interpret what's in the graph.&#xA;You could ask &quot;For a given antenna length, which antenna performs best&quot; (look at the cluster around 15 inches for example), in which case it would be the one that gives the highest dBS9/dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also look at the graph as one of those cost/performance type graphs. If you define your criteria as &quot;short antenna and high dBS9/dBm&quot;, then the best antennas would be towards the upper left portion of the graph while the worst ones would be in the lower right portion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Operating optimally&quot; requires you to define what &quot;optimally&quot; means, and this is going to be different for different circumstances. Do you want the highest dBm? Shortest antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For just received signal strength, the ones you circled in red are great performers. Do you want to be carrying around a 35-45&quot; antenna with you though?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Conversely, the one circled in blue is a great antenna if you want something short, but receive performance kind of sucks.&lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2013-11-11T20:25:31.370" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="655" PostTypeId="2" ParentId="644" CreationDate="2013-11-11T20:31:58.373" Score="2" Body="&lt;p&gt;There is one major reason why what you are suggesting isn't done, and it isn't the size of a two-part dipole versus a single (possibly shortened) quarter-wave utilizing the radio and operator as a ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Polarization.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of what you'd do with a handheld transceiver on VHF/UHF is probably FM, and with that combination, it's almost all vertically polarized. The setup you are suggesting, unless it's being held at an awkward angle (and putting huge stress on the antenna connector) would be horizontally polarized, which means you instantly lose about 20 dB to the cross-polarization on both transmit and receive. You'd also suffer from the dipole's radiation pattern: a little over 2 dBi broadside to the antenna, meaning that if you turn 90° you will suddenly lose a fair amount of signal strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, of course a vertically polarized dipole is perfectly doable; I would hazard a guess that it's a fairly common setup for a repeater antenna. However, there is one additional problem in that case: you need to get the antenna some distance away from the feedline, to avoid coupling leading to RFI and all kinds of strange resonance effects. You'd want to get the antenna at least half a wavelength from the feedline, and one wavelength if possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means you have to have something (likely attached to the transceiver) which can support the weight of not only the antenna, but also a supporting structure to hold it at about a meter or farther out horizontally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is going to place a lot of stress on whatever supporting structure is being used, which in turn means it needs to be built to allow for that stress. That makes it relatively bulky, or in other words heavy. And you really don't want it falling off the radio; imagine the stress that would place on the antenna connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Of course, you could make an antenna that comes with a simple ground plane.&lt;/strong&gt; Quite a few people do that, especially when using a handheld transceiver in a semi-fixed setup with an external microphone; they attach a wire to something they can insert in the shield part of the antenna connector, and then mount the antenna &quot;on top of&quot; that. That provides a ground plane, while maintaining the vertical polarization and thus avoiding the cross-polarization issue.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-11-11T20:31:58.373" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="656" PostTypeId="5" CreationDate="2013-11-11T20:40:46.387" Score="0" Body="&lt;h1&gt;What is Packet?&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;While the term can apply to a specific digital mode, it is often used a general label for digital data modes in ham radio.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Packet&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;The term &quot;packet&quot; refers to &quot;packet switching&quot;, the basic structure of the network protocol used to transfer information.  This is the same basic protocol that runs the Internet.  In fact, the common packet protocol is AX.25 a derivation of the Internet's X.25 protocol.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As one of the first &quot;modern&quot; digital modes, packet radio transmits data in groups or &quot;packets&quot; of 10s or 100s of bytes. This allows improved throughput and error control.  Transmission speeds typically range from 300 bps on the HF bands to 1200 and 9600 bps on VHF or UHF.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Other Digital Modes&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;PSK31&lt;/strong&gt; is probably the most popular keyboard to keyboard digital mode in use today. PSK31 is normally generated and decoded using PC soundcards with one of many available software packages.  PSK31 occupies very small bandwidths (approximately 100 Hz) and offers effective communication at low power. PSK31 uses Phase Shift Keying for data encoding&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;RTTY&lt;/strong&gt; (radio teletype) is the original keyboard to keyboard mode, based on the 5-bit Baudot code and it began with mechanical teletypes.  It is still a popular communications mode, but now uses PC soundcards for coding and decoding, using 170 Hz frequency shift keying at a 45.45 baud rate -- 60 words per minute.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;For More Information&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;There are many many others.  See: &lt;a href=&quot;http://www.hamuniverse.com/hfdigitalmodessoftware.html&quot; rel=&quot;nofollow&quot;&gt;HF Digital Modes&lt;/a&gt; on Ham Universe for a tabular list of the more popular software packages and the modes they support with links.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-14T14:59:04.430" LastActivityDate="2013-11-14T14:59:04.430" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="657" PostTypeId="4" CreationDate="2013-11-11T20:40:46.387" Score="0" Body="Questions related to sending digital data over amateur radio including hardware, protocols, and related software." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-14T14:59:16.187" LastActivityDate="2013-11-14T14:59:16.187" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="658" PostTypeId="5" CreationDate="2013-11-11T20:42:45.647" Score="0" Body="&lt;p&gt;Questions about Linux in the context of amateur radio. Specifically ham-related software (logging, radio control, etc.) and distributions that are particularly useful to hams. For questions not directly relating to amateur radio, consider asking on the &lt;a href=&quot;http://unix.stackexchange.com/&quot;&gt;Unix &amp;amp; Linux&lt;/a&gt; Stack Exchange instead.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="29" LastEditDate="2013-11-11T20:47:21.773" LastActivityDate="2013-11-11T20:47:21.773" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="659" PostTypeId="4" CreationDate="2013-11-11T20:42:45.647" Score="0" Body="Questions about linux in the context of amateur radio. Specifically ham-related software (logging, rig-control, etc.) and distributions that are particularly useful to hams." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-11T20:51:39.607" LastActivityDate="2013-11-11T20:51:39.607" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="660" PostTypeId="5" CreationDate="2013-11-11T20:44:33.297" Score="0" Body="&lt;p&gt;Questions about amateur radio &amp;quot;fox hunting&amp;quot; (organized direction-finding events), including rules and necessary equipment.  Also see the related &amp;quot;rdf&amp;quot; tag.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="4665" LastEditDate="2020-11-04T18:08:14.100" LastActivityDate="2020-11-04T18:08:14.100" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="661" PostTypeId="4" CreationDate="2013-11-11T20:44:33.297" Score="0" Body="Questions about fox hunting - using radio direction finding to locate a hidden transmitter -  including the rules and necessary equipment." OwnerUserId="164" LastEditorUserId="87" LastEditDate="2013-11-11T20:51:23.403" LastActivityDate="2013-11-11T20:51:23.403" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="662" PostTypeId="5" CreationDate="2013-11-11T20:46:00.523" Score="0" Body="&lt;p&gt;Use this tag for questions related to vertical antennas, the construction, characteristics and performance.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-11T20:51:29.107" LastActivityDate="2013-11-11T20:51:29.107" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="663" PostTypeId="4" CreationDate="2013-11-11T20:46:00.523" Score="0" Body="Use this tag for questions related to vertical antennas, the construction, characteristics and performance." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-11T20:49:21.983" LastActivityDate="2013-11-11T20:49:21.983" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="664" PostTypeId="5" CreationDate="2013-11-11T20:51:06.350" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-11T20:51:06.350" LastActivityDate="2013-11-11T20:51:06.350" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="665" PostTypeId="4" CreationDate="2013-11-11T20:51:06.350" Score="0" Body="Use this tag for questions about specific radio procedures and practices.  These are &quot;How do I...?&quot; questions, not about equipment or other issues." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-11T20:51:25.073" LastActivityDate="2013-11-11T20:51:25.073" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="666" PostTypeId="5" CreationDate="2013-11-11T20:53:06.860" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-11T20:53:06.860" LastActivityDate="2013-11-11T20:53:06.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="667" PostTypeId="4" CreationDate="2013-11-11T20:53:06.860" Score="0" Body="Use this tag for questions relating to RF and DC grounding in radio equipment.  Specifically suggested methods, practices, equipment and regulations regarding grounding." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-11T20:54:26.337" LastActivityDate="2013-11-11T20:54:26.337" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="668" PostTypeId="5" CreationDate="2013-11-11T20:55:46.140" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-11T20:55:46.140" LastActivityDate="2013-11-11T20:55:46.140" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="669" PostTypeId="4" CreationDate="2013-11-11T20:55:46.140" Score="0" Body="Questions regarding the modification of existing radio equipment to add features or improve performace" OwnerUserId="164" LastEditorUserId="87" LastEditDate="2013-11-11T21:16:49.923" LastActivityDate="2013-11-11T21:16:49.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="670" PostTypeId="2" ParentId="641" CreationDate="2013-11-11T21:12:45.757" Score="2" Body="&lt;p&gt;A remote control is just a radio transmitter (maybe even a receiver if you expect to get data back from whatever you're controlling). To get started, you'll need to learn how to build a transmitter/transceiver that operates at the appropriate frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's probably the easy part. schematics for VHF/UHF transmitters shouldn't be too hard to find.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The harder part would probably be adding the controls and making them tell the transmitter to send the appropriate modulated signals out, which would require some kind of microcontroller to read the status of the controls, and then appropriately key the transmitter in response. That's probably your next step.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then you'll need a receiver on the device you're controlling. Receivers are generally fairly easy objects to build, but now you've got to make it control things on your device in response to the signals it receives. More microcontroller stuff.&lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2013-11-11T21:12:45.757" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="671" PostTypeId="5" CreationDate="2013-11-11T21:18:19.167" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-11T21:18:19.167" LastActivityDate="2013-11-11T21:18:19.167" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="672" PostTypeId="4" CreationDate="2013-11-11T21:18:19.167" Score="0" Body="Questions related to logging procedures, software and logging sites." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-11T21:20:27.517" LastActivityDate="2013-11-11T21:20:27.517" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="673" PostTypeId="2" ParentId="601" CreationDate="2013-11-11T21:21:18.207" Score="3" Body="&lt;p&gt;(a partial self-answer)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bad grounding on the mast was part of the problem. After reconnecting the ground wire to ensure a clean contact on both mast end and ground rod - the blinking lights stopped. The RF return was almost eliminated (slight deflection on FS meter against coax but I think that is to be expected).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Per Phil Frost's answer, I believe the shack ground was providing a better RF ground since the mast was improperly grounded, causing the RF to ride back indoors. Once connections were sandpapered and tightened to the outside grounding rod, it took the shorter route to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Update after getting my General and attempting to go beyond the 10m band with this vertical antenna. Testing SWR on 12m (SWR 1:2) and 17m (SWR 1:3) both resulted in the same common current RF problem - and the lights getting turned on and off. Will update again after I try using an antenna tuner.&lt;/p&gt;&#xA;" OwnerUserId="152" LastEditorUserId="152" LastEditDate="2013-11-18T15:19:41.627" LastActivityDate="2013-11-18T15:19:41.627" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="674" PostTypeId="5" CreationDate="2013-11-11T22:21:13.653" Score="0" Body="" OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-11-11T22:21:13.653" LastActivityDate="2013-11-11T22:21:13.653" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="675" PostTypeId="4" CreationDate="2013-11-11T22:21:13.653" Score="0" Body="The portion of the VHF spectrum allocated to use in civilian aviation." OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-11-11T22:21:13.653" LastActivityDate="2013-11-11T22:21:13.653" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="676" PostTypeId="5" CreationDate="2013-11-11T22:22:16.423" Score="0" Body="" OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-11-11T22:22:16.423" LastActivityDate="2013-11-11T22:22:16.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="677" PostTypeId="4" CreationDate="2013-11-11T22:22:16.423" Score="0" Body="A manufacturer of radio equipment, including ham radios and accessories." OwnerUserId="22" LastEditorUserId="22" LastEditDate="2013-11-11T22:22:16.423" LastActivityDate="2013-11-11T22:22:16.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="678" PostTypeId="1" CreationDate="2013-11-12T00:07:28.590" Score="5" ViewCount="1251" Body="&lt;p&gt;I know antennas can have 1/4 wavelength, 1/8th etc. but if you are operating from UHF bands, can the antenna be lets say twice as long?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2017-02-13T23:49:50.457" Title="Can antennas have reverse harmonics" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="679" PostTypeId="2" ParentId="678" CreationDate="2013-11-12T01:48:43.303" Score="7" Body="&lt;p&gt;The answer is yes (sort of), but it isn't because of &quot;reverse harmonics&quot;. That doesn't actually mean anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quarter-wave antennas work for the same reasons as dipoles do - due to the physics of the situation, the feed point impedance works out to be just right - about 50 ohms - and most of the power is radiated instead of reflected. Other lengths may require matching or may not work at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, 5/8 wave is common for vehicle antennas because you get slightly better gain at a slightly different angle. But any 5/8 wave antenna will have a little &quot;bulge&quot; at the bottom that contains a coil (or some other type of matching circuit) which adjusts the feed point impedance to that magic 50 ohms to prevent the signal from being reflected right back into the radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is what we measure with SWR, by the way - if the impedances all match out, the standing wave ratio will be 1:1. If there's an impedance mismatch, the SWR will vary and you lose power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While the exact &quot;good&quot; and &quot;bad&quot; points will vary due to other conditions, typically, any radiator that is close to an odd number of quarter wavelengths will be good, and close to an even number will be bad. Anything in between may not be good, but can probably be impedance matched (like 5/8ths), whereas anything too close to 1/2 or a multiple of 1/2 will have a feedpoint impedance that is so extreme that it cannot be practically matched.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In HF, we have this sort of question come up in relation to long wire (or random-wire) antennas. Here, we choose an antenna that is an odd multiple of a quarter wavelength on many different bands to get a simple multi-band setup - one good length is around 85 feet, which is close enough to tune on most of the HF bands. In UHF we probably only care about one band at a time, but the idea is the same. A plain 1/2, full, or double wavelength vertical won't tune up very well (unless it's secretly a dipole), but 3/4, 5/4, and so on will, and 5/8, 7/8, and so on can be tuned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So how do we choose? Well we usually just use a quarter wave, it's smaller and cheaper and never a bad choice. Other antennas come into play when we need either a different radiation pattern or some such. For example, yes a 5/8 wave has &quot;better&quot; gain, but it also has a higher radiation angle, which may or may not work out depending on what you're trying to do. To determine this sort of thing, we use computer modeling programs like EZNEC to calculate an antenna's radiation pattern and can then use other software like Radio Mobile to generate coverage maps based on that pattern.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-11-12T01:48:43.303" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="680" PostTypeId="1" CreationDate="2013-11-12T04:03:56.887" Score="8" ViewCount="254" Body="&lt;p&gt;I've been experimenting with some 2.4ghz based mesh networks similar to &lt;a href=&quot;http://hsmm-mesh.org/&quot;&gt;http://hsmm-mesh.org/&lt;/a&gt;. I'd like to have something on the bench where I could simulate roving between nodes, and create hidden nodes and varying signal strengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a better solution than a network of coax cables with splitters and attenuators (variable and fixed)? Any pitfalls in this approach (I'm turning the power way down and using a lot of attenuation)? Any suggestions on how to build a setup like this without breaking the bank (the attenuators and splitters get expensive!)?&lt;/p&gt;&#xA;" OwnerUserId="121" LastActivityDate="2013-11-12T12:24:59.460" Title="What is a good way to bench test a mesh network?" Tags="&lt;mesh-network&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="681" PostTypeId="2" ParentId="678" CreationDate="2013-11-12T04:30:59.140" Score="7" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;can the antenna be lets say twice as long?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. 1/2 wave dipoles are the common choice, because it's the minimum length for a resonant dipole without using tricks like a loading coil or capacitive hat to make the antenna appear longer electrically than it is physically. Verticals are 1/4 wave for the same reason, but the &lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;image antenna&lt;/a&gt; formed by the reflection of the vertical through the ground makes it appear as a 1/2 wave dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a 1/2 wave dipole, a standing wave forms on the wire, with voltage and current distributed like so:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/1WMa2.gif&quot; alt=&quot;1/2 wave dipole standing wave&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you increase that to 3/2 wave, you still get a standing wave, like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/s6Mph.gif&quot; alt=&quot;3/2 wave dipole standing wave&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These images from an &lt;a href=&quot;http://www.radio-electronics.com/info/antennas/dipole/feed-impedance.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;article on radio-electronics.com&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice that the feedpoint is still at a node where voltage is at 0, and current is at a maximum. This works for any odd harmonic, 1/2, 3/2, 5/2, ...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Off-center fed dipoles exploit this: by getting the feedpoint at just the right spot, the feedpoint can end up on a similar impedance point on the antenna for a number of bands, even when those bands aren't odd harmonics of each other. For example, 40 meters (7 MHz) and 20 meters (14 MHz).&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-02-13T23:49:50.457" LastActivityDate="2017-02-13T23:49:50.457" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="682" PostTypeId="2" ParentId="641" CreationDate="2013-11-12T04:36:01.560" Score="1" Body="&lt;p&gt;I would strongly consider a &lt;a href=&quot;http://en.wikipedia.org/wiki/ZigBee&quot; rel=&quot;nofollow&quot;&gt;Zigbee&lt;/a&gt; or 802.11 based approach. Both have cheap hardware available, are relatively easy to integrate with electronics (via a microcontroller such as an &lt;a href=&quot;http://en.wikipedia.org/wiki/Arduino&quot; rel=&quot;nofollow&quot;&gt;arduino&lt;/a&gt;), and operate on frequencies which you have extra privileges with your ham license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on what you are wanting to control, it would be fairly easy to control via software on a PC or tablet, you could even connect a game controller. If you want something that doesn't require a PC on the transmitter side, there are a lot of options to connect a USB joystick directly to a Arduino type micro controller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would favor a digital approach like I described above, but I'm a software guy. If you wanted something more old-school and analog, you could implement a protocol like the RC transmitters use. Essentially you send digital pulses of varying lengths, and the length of each pulse determines the value of the control. More info on that can be found online, for instance this site: &lt;a href=&quot;http://rcarduino.blogspot.com/2012/11/how-to-read-rc-receiver-ppm-stream.html&quot; rel=&quot;nofollow&quot;&gt;http://rcarduino.blogspot.com/2012/11/how-to-read-rc-receiver-ppm-stream.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="121" LastActivityDate="2013-11-12T04:36:01.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="683" PostTypeId="1" AcceptedAnswerId="685" CreationDate="2013-11-12T06:00:17.383" Score="9" ViewCount="262" Body="&lt;p&gt;I am the president of a small school club. We plan an participating in the ARRL SSB Sweepstakes this weekend, which is our (new) club's first real multi-op contest effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do multioperator/club contest stations with only one transceiver usually operate? Is it common practice to have one person handling the radio while having another logs? I was thinking of setting up some parts of the contest up like that.&lt;/p&gt;&#xA;" OwnerUserId="125" LastActivityDate="2015-03-18T12:59:33.403" Title="How are multiple-operator contest stations with one radio usually operated?" Tags="&lt;hf&gt;&lt;contest&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="684" PostTypeId="2" ParentId="574" CreationDate="2013-11-12T06:19:00.573" Score="3" Body="&lt;p&gt;For long range voice contacts that work all the time, day or night, you need a satellite phone. Especially if you are considering emergency use, that is your best bet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to do the same thing on amateur bands, you need high power, high gain antennas for several bands, and several years of intensive practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could set up an Elecraft K-line station (500 Watts), plus a tower and a beam for maybe $10K. That is about the cheapest setup that satisfies your top four requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are OK with digital contacts instead of voice, things could be a lot cheaper. It is common to talk cross-country with 10 Watts and simple antennas on digital modes.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-11-12T06:19:00.573" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="685" PostTypeId="2" ParentId="683" CreationDate="2013-11-12T06:44:51.057" Score="6" Body="&lt;p&gt;My advice won't necessarily be good for a competitive score, but here is what I've found from running a school Club station during Sweepstakes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The main thing is to have fun! Don't take it too seriously if it's your (or anyone that's operating) first time contesting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For running multi op, it really depends on how many people you have and their experience level and time availability. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have people who are completely new, then it usually helps to have two pairs of ears listening with one person operating while the other logs the contacts. Two people at the radio means that there is a double check on the exchange, and that it's easy to swap positions for a break. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That being said, it isn't that hard to log and operate at the same time. I prefer working alone, and use the multi op to avoid spending a whole day in the station. &lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2013-11-12T06:44:51.057" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="686" PostTypeId="2" ParentId="680" CreationDate="2013-11-12T12:17:55.787" Score="8" Body="&lt;p&gt;You can simulate. The idea is to model your RF channel(s) numerically by adding things like &lt;a href=&quot;http://en.wikipedia.org/wiki/Additive_white_Gaussian_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;AWGN&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/Multipath_interference&quot; rel=&quot;nofollow noreferrer&quot;&gt;multipath&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/Clock_skew&quot; rel=&quot;nofollow noreferrer&quot;&gt;clock skew&lt;/a&gt;, and so on. And, you want a way to model a lot of these channels, and twiddle the parameters and see how the system responds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many software libraries out there that will make this easier. I'd suggest &lt;a href=&quot;http://gnuradio.org/redmine/projects/gnuradio/wiki&quot; rel=&quot;nofollow noreferrer&quot;&gt;GNU Radio&lt;/a&gt;. It has blocks that can be chained together to model an RF channel, and blocks to implement most basic digital modulation schemes. It has a graphical interface where you can connect them together, which is good for experimentation, and it also has bindings to several programming languages so you can automate the creation of a complex network of channels and implement your own blocks. It also has blocks to interface to real hardware, like the &lt;a href=&quot;http://ettus.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;USRP&lt;/a&gt;, or an audio card that can in turn interface to inexpensive SDR platforms like &lt;a href=&quot;http://wb5rvz.com/sdr/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Softrock&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/HLjfJ.png&quot; alt=&quot;GNU Radio screenshot&quot;&gt;&#xA;&lt;em&gt;&lt;a href=&quot;http://pwnhome.wordpress.com/tag/gnuradio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;image source&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you also want to simulate the OS running the hardware on your nodes, you'll need a somewhat more powerful computer, and a way to programatically create virtual machines. Again, many options, but for an easy start, I'd look at &lt;a href=&quot;http://www.vagrantup.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Vagrant&lt;/a&gt;. With this, you could conceivably create a handful of virtual nodes, each running virtual RF interfaces implemented by GNU Radio.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-11-12T12:24:59.460" LastActivityDate="2013-11-12T12:24:59.460" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="687" PostTypeId="2" ParentId="641" CreationDate="2013-11-12T14:11:31.010" Score="1" Body="&lt;p&gt;I recommend you don't reinvent the wheel.  There are two amateur radio bands in the US the FCC sets aside for line-of-sight remote control for planes and surface craft (boats, cars, etc).  The RC community has determined standard frequencies and uses the same modulation and protocols as on other license free bands, so as long as you follow their guidelines you can get equipment off-the-shelf that allows you to use your general license to access RC frequencies that are uncluttered by other unlicensed users.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RC frequencies are located at 27MHz, 50MHz, 72MHz, and 75MHz.  License free users can only use frequencies in the 27MHz and 72MHz bands. The RC community has already created a channel list for all the available frequencies:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://rcsource.hobbypeople.net/faqs/freqlist.htm&quot; rel=&quot;nofollow&quot;&gt;http://rcsource.hobbypeople.net/faqs/freqlist.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find transmitters and receivers that work across that range from RC retailers, though it's unlikely that local stores will stock Amateur Radio band RC equipment.  They can be special ordered, or found from online retailers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can often find suppliers by searching for keywords such as &quot;RC&quot;, &quot;50MHz&quot;, &quot;75MHz&quot;, &quot;transmitter&quot;, and &quot;receiver&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have a working system at your desired frequency, then you might want to improve on it.  Starting with a good system makes the next step easier, rather than starting from scratch.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-11-12T14:11:31.010" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="688" PostTypeId="2" ParentId="633" CreationDate="2013-11-12T15:02:22.567" Score="2" Body="&lt;p&gt;No such universal standard exists currently. &lt;a href=&quot;http://www.repeaterbook.com/&quot; rel=&quot;nofollow&quot;&gt;RepeaterBook&lt;/a&gt;, &lt;a href=&quot;http://www.radioreference.com/apps/subscription/&quot; rel=&quot;nofollow&quot;&gt;Radioreference&lt;/a&gt;, and &lt;a href=&quot;http://www.rfinder.net/&quot; rel=&quot;nofollow&quot;&gt;RFinder&lt;/a&gt; have differing format they use for transmitters and repeaters which you may find nominally useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC maintains databases of &lt;a href=&quot;http://www.fcc.gov/encyclopedia/tv-query-broadcast-station-search&quot; rel=&quot;nofollow&quot;&gt;TV&lt;/a&gt;, &lt;a href=&quot;http://www.fcc.gov/encyclopedia/fm-query-broadcast-station-search&quot; rel=&quot;nofollow&quot;&gt;Radio&lt;/a&gt;, and other licensed transmitters and their locations in the US.  You may find their format interesting, though I doubt you'd want to adopt it for your purposes. I expect other countries have similar databases for their radio licensees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Several manufacturers have developed different formats for their radios, though they are probably more limited than what you want as they are meant to be programmed into the radio, but they usually include at minimum location, frequency information, and station ID.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CHIRP accepts a number of formats, and converts between many of them.  I'd suggest working with the CHIRP team to develop a standard that could be used as default.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-11-13T12:37:59.050" LastActivityDate="2013-11-13T12:37:59.050" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="689" PostTypeId="1" CreationDate="2013-11-12T16:01:56.687" Score="9" ViewCount="1928" Body="&lt;p&gt;I have an old transceiver. I have a problem where ocassionally the received signal will drop out when switching from transmit to receive. I've narrowed it down to the transmit/receive relay. When bench-testing the relay, it &quot;clicks&quot; over to receive, but shows a very high resistance. The contacts aren't visibly corroded or damaged. I have heard that the contacts may have to be cleaned - what's the best way to do this? Are there any cleaners that should be avoided?&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-11-12T20:45:10.657" Title="Cleaning relay contacts?" Tags="&lt;maintenance&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="690" PostTypeId="1" CreationDate="2013-11-12T16:17:07.503" Score="12" ViewCount="1114" Body="&lt;p&gt;Consider a small town's emergency operations center. While there are amateur radio operators involved, they primarily work for government or public safety, and there is no active ARES participation. The EOC is reasonably well-equipped, with redundant power, (questionable) redundant internet, phone lines, and drop-box public safety radios for coordination or dispatch. Assuming that the EOC cannot guarantee a dedicated amateur operator, but can have an operator working dispatch take on some additional responsibility, what is the highest-impact amateur service to monitor? How should it be operated? (Monitor a specific frequency or set up a scan list? Periodically announce that they are listening?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some ideas - monitoring a local repeater has a poor signal to noise ratio, APRS has relatively few users due to the need for specialized equipment, and HF would be somewhat less useful due to the small coverage area. Or am I selling one of these short?&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2019-08-12T14:13:27.000" Title="Amateur radio in an EOC?" Tags="&lt;emergency&gt;&lt;procedure&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="691" PostTypeId="2" ParentId="523" CreationDate="2013-11-12T16:20:30.303" Score="4" Body="&lt;p&gt;Living down-under and apparently also off-the-wall, hyper-enthusiast David L. Jones made following excellent digital multimeter (DMM) reviews:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.eevblog.com/2010/06/04/eevblog-91-50-multimeter-shootout/&quot; rel=&quot;nofollow&quot;&gt;EEVblog #91 – \$50 Multimeter Shootout&lt;/a&gt;: Extech EX330, Amprobe AM220, Elenco, Vichy VC99 &amp;amp; GS Pro-50,&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.eevblog.com/2010/07/11/eevblog-99-100-multimeter-shootout-extech-amprobe-bk-precision-ideal-uei-uni-t-part-1of2/&quot; rel=&quot;nofollow&quot;&gt;EEVblog #99 – \$100 Multimeter Shootout&lt;/a&gt;: Extech, Amprobe, BK Precision, Ideal, UEi &amp;amp; Uni-T.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;David actually opens up all multimeters for a thorough and very revealing inspection. His very surprising findings made me conclude that you really get what you pay for. So it might be more advantageous to open the wallet a little bit wider whilst ignoring the special gimmicks... For example; the VC97 measures up to 30MHz, but its construction is not so great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the end of the day, I was able to repair my Fluke 79 which, by the way, does measure capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.robotroom.com/Multimeter-Reviews-2.html&quot; rel=&quot;nofollow&quot;&gt;Another review by robot-room&lt;/a&gt; also deals with the RSR MS8268 digital multimeter which, unfortunately, was not included in the reviews mentioned above.&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2013-11-12T21:31:40.700" LastActivityDate="2013-11-12T21:31:40.700" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="692" PostTypeId="2" ParentId="689" CreationDate="2013-11-12T16:36:07.320" Score="5" Body="&lt;p&gt;Cleaning relay contacts is usually done mechanically. Use fine grade garnet paper (&lt;strong&gt;not&lt;/strong&gt; generic sandpaper -- it can leave conductive dust behind), fold a strip in half and put it between the relay contacts, push the contacts together, and pull the paper out. Repeat until done.&lt;/p&gt;&#xA;" OwnerUserId="105" LastEditorUserId="105" LastEditDate="2013-11-12T20:45:10.657" LastActivityDate="2013-11-12T20:45:10.657" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="693" PostTypeId="1" CreationDate="2013-11-12T17:13:33.607" Score="9" ViewCount="354" Body="&lt;p&gt;At ~34ppt the Southern Ocean is significantly less saline than other major water bodies (Arctic Ocean excluded). The Southern Continent also shares proximity to the &lt;a href=&quot;http://en.wikipedia.org/wiki/South_Atlantic_Anomaly&quot;&gt;South Atlantic Anomaly&lt;/a&gt; -  where the Earth's inner Van Allen radiation belt comes closest to the Earth's surface. The Antartica itself is also (apparently) lots of ice, &#xA;ice, and more ice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the temporary home to several scientific expeditions - these usually include one, or more, ham radio stations - one wonders about the HF band propagation in Antarctica.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does the South Atlantic Anomaly affect propagation in the HF bands?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="29" LastEditDate="2013-11-14T08:31:30.660" LastActivityDate="2013-11-14T08:31:30.660" Title="How does the South Atlantic Anomaly affect propagation in the HF bands?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="694" PostTypeId="2" ParentId="588" CreationDate="2013-11-12T17:22:55.700" Score="5" Body="&lt;p&gt;The &quot;rule of thumb&quot; for keeping the skin effect at bay is to use conductors that have a diameter greater the twice 3-5 skin depths. Twice the depth because if you can envision the wire having RF current develop a tapered current density from the surface inwards to the center, you go half way in and half way out, 2x. So for 1-skin depth in copper of 1.37 mils at 3.5 MHz, 3-5 skin depths is 4-6.8 mils. Doubling 6.8 (to be conservative) you get 14 mils diameter. That diameter is 27AWG wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For 7 MHz, the skin depth is 0.97 mils. 3-5 skin depths is 2.9-4.9 mils, and doubled, that is 10 mils, giving 30AWG wire.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-11-12T17:22:55.700" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="695" PostTypeId="1" CreationDate="2013-11-12T17:32:01.030" Score="2" ViewCount="144" Body="&lt;p&gt;Just what the title states.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The extreme temperatures could kill any power-supply such as an SLA&lt;/li&gt;&#xA;&lt;li&gt;A dipole antenna may collect ice and break&lt;/li&gt;&#xA;&lt;li&gt;Vostok Station holds the record for -89C; whereas a typical RG213 is rated for -40C to +75C&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Given such conditions, and issues&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How would one plan precautions to setup an amateur radio station on Antarctica? &lt;/li&gt;&#xA;&lt;li&gt;Do amateur radio stations on Antarctica go QRU in winter there?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5" LastEditorUserId="87" LastEditDate="2013-11-12T18:50:56.470" LastActivityDate="2013-11-12T18:50:56.470" Title="How would one plan to setup an amateur radio station on Antarctica?" Tags="&lt;procedure&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="696" PostTypeId="2" ParentId="690" CreationDate="2013-11-12T17:43:44.403" Score="3" Body="&lt;p&gt;I've been thinking about this off and on since touring my local county's EOC (a very worthwhile trip).  Probably monitoring a 2m frequency (that's not a repeater) has the best chance of providing value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I have come up with, assuming the EOC could have a licensed amateur available at least some of the time is to have them come on the area repeaters a few times a day and announce that the EOC is monitoring 146.52 (or pick a locally clear frequency) for emergency traffic and to report it there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You aren't trying to reach people having an emergency necessarily, but to create the general knowledge in the local community that the EOC is monitoring a frequency.  Then, if anyone comes along with a problem, they've either heard the announcements or someone on the repeater has and can direct them to the appropriate frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the EOC's area of responsibility includes some wilderness area, they could also scan the &quot;Wilderness Protocol&quot; frequencies on the specified times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This solution is the cheapest I could come up with since it only requires one staff member with at least a Tech license (in the US) and common 2m rig with a decent external antenna.  If the EOC were to get more $$ or operators, they could consider something more ambitious using more bands or whatever is appropriate in their area.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-12T17:43:44.403" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="697" PostTypeId="1" AcceptedAnswerId="938" CreationDate="2013-11-12T17:46:12.377" Score="6" ViewCount="1046" Body="&lt;p&gt;I recently built an antenna for my attic inspired by &lt;a href=&quot;http://degood.org/coaxtrap/&quot; rel=&quot;nofollow&quot;&gt;http://degood.org/coaxtrap/&lt;/a&gt;. I found making the coax traps very time consuming and frustrating to tune. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I got to thinking about 3D printers, and I've been wondering if there is a better option (at the very least using a 3D printed form instead of PVC pipe.) With modern construction capabilities like CNC mills and 3D printers, not to mention inexpensive high quality circuit board production available, are there any better choices these days?&lt;/p&gt;&#xA;" OwnerUserId="121" LastEditorUserId="76" LastEditDate="2015-12-15T22:25:53.537" LastActivityDate="2015-12-15T22:25:53.537" Title="Are there easier ways to make traps than coax and plastic pipe?" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="698" PostTypeId="2" ParentId="695" CreationDate="2013-11-12T18:24:40.840" Score="4" Body="&lt;p&gt;Most people leave Antarctica in the winter.  According to &lt;a href=&quot;http://www.worldpopulationstatistics.com/antarctica-population-2013/&quot; rel=&quot;nofollow&quot; title=&quot;worldpopulationstatistics.com/&quot;&gt;worldpopulationstatistics.com&lt;/a&gt;, the summer population of approximately 5000 drops to 1000 in the winter.  In the interior the winter minimum temperature does drop into the -80C to -90C &lt;em&gt;outside&lt;/em&gt;. In the coastal areas (where almost all the bases are located), the summer temperatures hit highs in the 5C to 15C range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given all that, I think it's safe to say that the station would be indoors at one of the established bases.  Even in the interior in the winter, most of the equipment would not be exposed to temperatures outside their specs.  That leaves only the antenna and feedline problems.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For feedline, Andrews or Heliax hardline is good for operations down to between -55C and -70C depending on the size/brand and can be idle at even lower temperatures.  The research stations probably use something like this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The good news for antennas is that Antarctica is mostly a desert with the average precipitation in the 4&quot;-8&quot; range.  So, icing up might not be much of a problem.  But is does get pretty windy.  Most of Antarctic is at 3000-5000m altitude and the cold dense air runs &quot;downhill&quot; at the coast, especially in the presence of an approaching low preasure system, causing &lt;a href=&quot;http://en.wikipedia.org/wiki/Katabatic_wind&quot; rel=&quot;nofollow&quot;&gt;katabatic winds&lt;/a&gt; of as much as 220 km/hr.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, depending on how long you want those dipoles to last, you could consider copper coated steel cables strung between a couple towers or posts.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a Yahoo! Group for  &lt;a href=&quot;http://groups.yahoo.com/neo/groups/AntarcticHamRadio/conversations/topics&quot; rel=&quot;nofollow&quot;&gt;Antarctic Hams&lt;/a&gt; which is open, poking around there might answer some additional questions.  Since we are coming into the Southern Hemisphere summer, activity there is starting to pick up.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-12T18:24:40.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="699" PostTypeId="2" ParentId="693" CreationDate="2013-11-12T18:52:01.753" Score="3" Body="&lt;p&gt;To answer the question posed in the final paragraph, it looks like the South Atlantic Anomaly doesn't affect HF propagation much if at all.  The &lt;a href=&quot;http://spacew.com/www/realtime.php&quot; rel=&quot;nofollow&quot;&gt;Near-Real-Time MUF Map&lt;/a&gt; seems to show MUF contours consistent with the time of day (and the southern hemisphere late spring) with nothing specific to the SAA area. I also found the following statement:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;At last, recall that the F2 region is also the home of the South Atlantic Anomaly (SAA), the lower limit of Van Allen belts that goes down to 200 km of altitude between South America and South Atlantic ocean. Constituted of fast electrons and heavy protons released by the solar wind trapped by the geomagnetic field, during quiet days, the SAA doesn't affect radio propagation in this region of the world. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;http://www.astrosurf.com/luxorion/qsl-propa2.htm&quot; rel=&quot;nofollow&quot;&gt;The radio propagation&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-12T18:52:01.753" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="700" PostTypeId="2" ParentId="693" CreationDate="2013-11-12T19:32:10.057" Score="2" Body="&lt;p&gt;Good question!  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;May I stir it up a bit?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SAA is a bit of concern to LEO satellites -- including the ISS -- because the bottom of a &quot;radiation bubble&quot; dips down into that area, thus its name.  It is a region or volume where the frequency of Single Event Effects on Integrated Circuits is slightly higher than other points at that altitude.  Or, conversely, matches the frequency of upsets that you would expect at a slightly higher altitude.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;bubble&quot; bottom and overall volume (roughly donut shaped) I speak of are part of the lower Van Allen radiation belt and of course is related to the ionosphere that influences our terrestrial radio wave propagation.  But, my best guess is that on a global scale, the bubble bottom has negligible effect if any at all on signals NOT passing through that particular volume, and likely little affect on signals through that volume.  I've made contact with McMurdo station several times but not enough to notice any SAA effects that I know of.  I am interested in such  observations by others.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My contribution to this discussion is limited to helping describe how the SAA volume is only a small part of a much larger volume(s) surrounding our planet.  FWIW, I work with electronics that pass through the SAA on a regular basis, and have also done simulations and testing on ICs w.r.t. SEE/SEU bit flips, latch up and related phenomena.  And I still enjoy HF ops to boot.&lt;/p&gt;&#xA;" OwnerUserId="324" LastEditorUserId="63" LastEditDate="2013-11-14T01:51:12.197" LastActivityDate="2013-11-14T01:51:12.197" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="701" PostTypeId="2" ParentId="689" CreationDate="2013-11-12T20:21:17.873" Score="4" Body="&lt;p&gt;To follow up on my comment to Pete's answer, the contacts probably have some oxidation (tarnish) on them, depending on the metal involved.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you don't want to do is gouge up the contact surface with something that's too abrasive.  You just want to clean the surface and restore conductivity. Rag based bond paper works well (a crisp US dollar bill, for instance).  Insert the paper, gently hold the contacts together and swipe out the paper.  Should only take a few swipes.  If the contacts are plated over a base metal, any cleaning process will have a limited number of uses as the plating in these cases is very thin.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-12T20:21:17.873" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="702" PostTypeId="1" CreationDate="2013-11-12T20:50:49.200" Score="8" ViewCount="369" Body="&lt;p&gt;A number of geostationary satellites are quite large and/or appear in clusters.&#xA;Moreover, many of them have large reflectors pointing to Earth (e.g. satellite TV sats).&#xA;Finally, these satellites are located at roughly $\frac{1}{10}$ the distance Earth-Moon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This made me wonder: Have hams ever used (clusters of) geostationary satellites as &lt;a href=&quot;http://en.wikipedia.org/wiki/Project_Echo&quot;&gt;passive microwave reflectors?&lt;/a&gt; What equipment would be necessary?&lt;/p&gt;&#xA;" OwnerUserId="250" LastActivityDate="2014-01-27T19:55:19.553" Title="Have hams ever used (clusters of) geostationary satellites as passive microwave reflectors?" Tags="&lt;satellites&gt;&lt;microwave&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="703" PostTypeId="2" ParentId="702" CreationDate="2013-11-12T22:34:20.530" Score="9" Body="&lt;p&gt;I'm going to make an educated guess and say &lt;em&gt;no&lt;/em&gt;. Here's my reasoning:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider the difficulty in just communicating with a satellite. See &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;What is a link budget, and how do I make one?&lt;/a&gt; or &lt;a href=&quot;https://ham.stackexchange.com/q/316/218&quot;&gt;What gain do I need to talk to SO-50 with my HT?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Geostationary orbit is much farther away than SO-50 and thus requires more gain, or more power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if we are using this as a passive reflector, reasonable assumptions are that:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;even with a pretty high gain antenna, most of our transmitted energy will miss the satellite.&lt;/li&gt;&#xA;&lt;li&gt;most of the reflected energy won't be reflected back at the intended receiver back on Earth.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;We can estimate both of these effects. Let's say we are transmitting with an isotropic antenna. (We wouldn't actually, but we can then work backwards to figure out how much gain we would need actually). Say we transmit with 1W. Any sphere centered on that transmitter will have 1W of power in it. By the time that sphere reaches the satellite at geostationary orbit, the sphere will be 35,786km in radius, and its area will be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A = 4 \pi (35786km)^2 \approx 1.6 \cdot 10^{16} m^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, our power density at geostationary orbit is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{1W}{1.6 \cdot 10^{16} m^2} = \frac{6.3 \cdot 10^{-17}W}{m^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How much of this might be intercepted? Let's say we have something really big, like &lt;a href=&quot;http://en.wikipedia.org/wiki/Envisat&quot; rel=&quot;nofollow noreferrer&quot;&gt;Envisat&lt;/a&gt;. It's largest face is 26m by 10m, for an area of $260m^2$. Let's say everyone is launching huge satellites into geostationary orbit for us to use as reflectors, and we can hit 100 of them. We then have an area of $26000m^2$ to intercept our transmission. Given our power density at that distance, the power intercepted is then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \require{cancel} \frac{6.3 \cdot 10^{-17}W}{\cancel{m^2}} \cdot 26000\cancel{m^2}&#xA;\approx 1.6 \cdot 10^{-12}W $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Compared to the 1W we were transmitting with, our loss is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 10 \cdot \log_{10} \frac{1.6 \cdot 10^{-12}W}{1W} \approx -118dB $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can make up for some of this with antenna gain. You can increase transmitter power. But then, you have to have enough power left to communicate from the satellite reflectors back to Earth, which is a similar problem to talking to an ordinary communication satellite. Only, you must do it without the benefit of antenna gain on the satellite, since they are just pieces of trash unlikely to be pointed in the right direction. Plus, they probably aren't very efficient reflectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say you transmit with 1000W and have a 40dBi antenna. The reflected signal is like a transmitter with an isotropic antenna in geostationary orbit with a power of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 1000W \cdot 10^{(-118dB + 40dB)/10} = 0.015mW $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you think you could hit a satellite without any antenna gain and 0.015mW? I'm thinking no.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This might seem an odd conclusion, when &lt;a href=&quot;http://en.wikipedia.org/wiki/EME_%28communications%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;moon bounce&lt;/a&gt; and &lt;a href=&quot;http://en.wikipedia.org/wiki/Meteor_burst_communications&quot; rel=&quot;nofollow noreferrer&quot;&gt;meteor scatter&lt;/a&gt; work. However, the problem is that satellites in geostationary orbit have such a &lt;em&gt;tiny&lt;/em&gt; &lt;a href=&quot;http://en.wikipedia.org/wiki/Angular_diameter&quot; rel=&quot;nofollow noreferrer&quot;&gt;angular diameter&lt;/a&gt; compared to the moon or the ionization left by meteors. There simply isn't enough area up there to intercept RF energy, so most of it goes uselessly into space.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-11-12T22:42:37.090" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="704" PostTypeId="2" ParentId="702" CreationDate="2013-11-12T23:59:17.650" Score="4" Body="&lt;p&gt;There was a conversation that I saw once about what it would take to bounce a signal off of the ISS, which is much closer and larger than GEO satellites. &lt;a href=&quot;http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html#.UoK90uIudFs&quot; rel=&quot;nofollow noreferrer&quot;&gt;The area&lt;/a&gt; is approximately $400\,\mathrm{m}^2$, but varies significantly depending on the orientation of the arrays. That figure should be good enough for now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's assume a distance of between 400 and 3000 km, similar to the SO-50 &lt;a href=&quot;https://ham.stackexchange.com/q/316/13&quot;&gt;link budget&lt;/a&gt;. Assuming an isotropic antenna, 1 W, and perfect reflection, the power reflected will be between&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\frac{4\cdot10^5}{5\cdot10^{6\cdot2}} = -77\,\mathrm{dBm}$ and&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\frac{4\cdot10^5}{5\cdot10^{7\cdot2}} = -93\,\mathrm{dBm}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The loss will follow a similar $r^2$, and thus be anywhere from an additional &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$10\cdot\log_{10}(\frac{1}{5\cdot10^6})=-133\,\mathrm{dB}$ to&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$10\cdot\log_{10}(\frac{1}{6\cdot10^7})=-149\,\mathrm{dB}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bottom line, the path loss is very high, on a very fast moving target. Add it together, best case that's a 200 dB loss, worst case that's 242 dB loss. And that assumes perfect reflection and orientation! A &lt;a href=&quot;http://www.g1ogy.com/www.n1bug.net/prop/eme.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;typical EME&lt;/a&gt; is around 220 dB loss, with a stationary target and world wide communication possible, I'd just stick with that.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-01-27T19:55:19.553" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="705" PostTypeId="1" AcceptedAnswerId="706" CreationDate="2013-11-13T00:38:50.577" Score="10" ViewCount="97" Body="&lt;p&gt;For years, I have been using &lt;a href=&quot;http://www.sk3bg.se/contest/index.htm&quot;&gt;SM3CER Contest Service&lt;/a&gt; for HF contests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is always good to have a backup, so I am looking for more or better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What do &lt;em&gt;you&lt;/em&gt; recommend?&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="22" LastEditDate="2014-12-01T23:58:32.650" LastActivityDate="2014-12-01T23:58:32.650" Title="Where on the web can I find a calendar of upcoming contests?" Tags="&lt;contest&gt;&lt;internet&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="706" PostTypeId="2" ParentId="705" CreationDate="2013-11-13T01:04:10.443" Score="8" Body="&lt;p&gt;I use the &lt;a href=&quot;http://www.hornucopia.com/contestcal/index.html&quot;&gt;WA7BNM Contest Calendar&lt;/a&gt;, usually the 8 Day version is enough for me, I can't plan much farther in advance. This one is nice with links to the rules and such so I check it regularly.  There is also the &lt;a href=&quot;http://www.arrl.org/contest-calendar&quot;&gt;ARRL Contest Calendar&lt;/a&gt;, it usually only has the ARRL sponsored contests though.  And there is always the handy &lt;a href=&quot;http://www.3830scores.com/index.php&quot;&gt;3830 Scores&lt;/a&gt; site for the post contest chest-beating :). But the quickest way to get a sense of how you did.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-13T01:04:10.443" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="707" PostTypeId="1" AcceptedAnswerId="714" CreationDate="2013-11-13T11:16:46.353" Score="7" ViewCount="903" Body="&lt;p&gt;The amateur satellite community used to have a small fleet of &lt;strong&gt;pacsat&lt;/strong&gt; satellites (AO-16 and friends), which were capable of &lt;strong&gt;store-and-forward&lt;/strong&gt; message passing: you could upload messages to the LEO satellite on one side of the world, and download the message once the satellite has travelled to the other side. 1200 bit/s BPSK on 2m/70cm. At the time, as a kid, I didn't have the budget to set up a ground station for them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are any amateur satellites with digital store-and-forward capability in usable status these days? It might be fun to try them out.&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2021-05-11T23:10:19.700" Title="Store-and-forward capable satellites in operation?" Tags="&lt;digital-modes&gt;&lt;satellites&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="708" PostTypeId="1" AcceptedAnswerId="709" CreationDate="2013-11-13T11:22:52.540" Score="5" ViewCount="394" Body="&lt;p&gt;Probably all amateurs recognize QSB as the &lt;a href=&quot;http://en.wikipedia.org/wiki/Q_code&quot;&gt;q-code&lt;/a&gt; to represent 'fading'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recently encountered the terms &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Shallow QSB&lt;/li&gt;&#xA;&lt;li&gt;Deep QSB&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A quick google search failed to yield fruit; What do the above terms mean?&lt;/p&gt;&#xA;" OwnerUserId="5" LastActivityDate="2013-11-13T11:34:23.157" Title="What is a shallow/deep QSB?" Tags="&lt;jargon&gt;&lt;q-codes&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="709" PostTypeId="2" ParentId="708" CreationDate="2013-11-13T11:34:23.157" Score="7" Body="&lt;p&gt;Deepness of QSB refers to the magnitude of fading. A very deep fade-out can make the received signal so weak that it becomes unreadable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A shallow fade-out would be one where the signal level drops only slightly, not affecting readability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio propagation conditions often change quite quickly over time. For example, QSB might start in the middle of a longer QSO, being quite shallow in the beginning. It'd be noticeable on the signal meter. On FM you'd hear a little noise on top of the carrier from time to time, on SSB the audible volume of the received signal would go down temporarily. If conditions would continue to go worse, the QSB could soon become too deep for successful communications - you would start to miss words, then whole sentences.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;shallow: of little depth&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-11-13T11:34:23.157" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="710" PostTypeId="5" CreationDate="2013-11-13T11:59:42.533" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-13T11:59:42.533" LastActivityDate="2013-11-13T11:59:42.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="711" PostTypeId="4" CreationDate="2013-11-13T11:59:42.533" Score="0" Body="Questions related to operating on frequencies above 902MHz." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-13T12:34:11.083" LastActivityDate="2013-11-13T12:34:11.083" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="712" PostTypeId="2" ParentId="690" CreationDate="2013-11-13T14:29:04.783" Score="3" Body="&lt;p&gt;If a local repeater is operated by a cooperative trustee, having a net control station who would agree to place the repeater into a controlled net status in case of emergency could be useful. In my community the National Weather Service monitors one of our local repeaters during extreme weather events, and one of the skilled net control station will place the repeater into emergency mode during such events.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the specialized hardware needed for APRS operation isn't as formidable an obstacle as it might have been a few years ago.&lt;/p&gt;&#xA;" OwnerUserId="351" LastActivityDate="2013-11-13T14:29:04.783" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="713" PostTypeId="2" ParentId="690" CreationDate="2013-11-13T15:31:22.730" Score="5" Body="&lt;p&gt;The two most important parts of any emergency are logistics and communication. There are two primary means of communication which are important.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The EOC should have access to a variety of communication systems, including police, fire, phone, internet, and amateur bands, with the ability to clearly communicate with the entire city easily, and the key outlying communities.&lt;/li&gt;&#xA;&lt;li&gt;I don't know anything about police/fire, except that I'm assuming if you ask around the police/fire departments you can find some sort of a suitable rig to assist with communications.&lt;/li&gt;&#xA;&lt;li&gt;Amateur bands are useful for reporting local events to the EOC's attention with a lack of communication. Many of these will come via mobile or even HT, the ideal EOC should be able to receive an HT signal and understand it sent anywhere within it's domain of operations. If it is not possible to do via simplex, then it should be coordinated with local repeaters, many of which are willing to take on such responsibilities.&lt;/li&gt;&#xA;&lt;li&gt;Some ability needs to be available to communicate with the next level up in emergency handling. This could be a county seat, or the state capital, or another designated area. This could be done via a dedicated yagi connection for 2m if fairly close, or even better done over HF bands. At the very least, a 40/80m capable wire antenna should be placed on the roof of the EOC, with the cable running down to the center. This will allow amateurs to bring their own rig to supplement the EOC.&lt;/li&gt;&#xA;&lt;li&gt;If you are running an EOC on a remote island, you probably want a tri-bander yagi antenna (10, 15, 20m yagi), 2-3 elements, which would do wonders for your communication. You'd have to be pretty remote, ie, more than 500 km, for this to be the ideal solution.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I suspect that purchasing and installing a 2m/440 J-pole antenna, HF 40/80m antenna, lightning protection, and the supporting cables will only run \$200 or less, if purchased wisely. A 2m/440 rig could be purchased for another \$200, battery for \$100, and you have a capable setup that should manage in most emergencies, if supplemented by an experienced ham. It would be good to have hams practice using such equipment on a regular basis, maybe once or twice a year.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2013-11-13T18:10:00.533" LastActivityDate="2013-11-13T18:10:00.533" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="714" PostTypeId="2" ParentId="707" CreationDate="2013-11-13T16:25:25.880" Score="3" Body="&lt;p&gt;Some otherwise operational amateur radio satellites have store and forward, however none of them appear to have store and forward enabled or working at this time:&lt;/p&gt;&#xA;&lt;h2&gt;AO-7&lt;/h2&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://ww2.amsat.org/?page_id=1031&quot; rel=&quot;nofollow noreferrer&quot;&gt;AO-7&lt;/a&gt;, launched in 1974, included a store and forward message unit, Codestore, cablae of storing and repeatedly retransmitting 18-word Morse code messages loaded by ground stations.  It's the same design as was flown on &lt;a href=&quot;http://en.wikipedia.org/wiki/AMSAT-OSCAR_6&quot; rel=&quot;nofollow noreferrer&quot;&gt;OSCAR 6&lt;/a&gt;.  The unit is not currently in use, and it's unclear if it's still operational, though many other parts of AO-7 are still functioning.&lt;/p&gt;&#xA;&lt;h2&gt;FO-29 (JAS-2)&lt;/h2&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://ww2.amsat.org/?page_id=1024&quot; rel=&quot;nofollow noreferrer&quot;&gt;FO-29&lt;/a&gt;, launched in 1996, included a digital BBS that is not longer operational.&lt;/p&gt;&#xA;&lt;p&gt;You can find &lt;a href=&quot;http://en.wikipedia.org/wiki/OSCAR&quot; rel=&quot;nofollow noreferrer&quot;&gt;a list of operating Amateur Radio satellites&lt;/a&gt; on Wikipedia, and searching their names will bring up sites that show their capability.  There is also a list of Amateur Radio satellites, including cubesats, and on the &lt;a href=&quot;http://www.dk3wn.info/satellites.shtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;SatBlog&lt;/a&gt; which may prove useful.&lt;/p&gt;&#xA;&lt;p&gt;Also note that another &lt;a href=&quot;http://ww2.amsat.org/?p=1864&quot; rel=&quot;nofollow noreferrer&quot;&gt;launch of many cubesats&lt;/a&gt; is occurring at the end of November, 2013, and some of these satellites may have store and forward.  Keep in mind that cubesats are very often short-lived without altitude or attitude control, so you will want to focus on the OSCAR satellites that are still operational.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2013-11-18T20:00:38.133" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="715" PostTypeId="1" AcceptedAnswerId="970" CreationDate="2013-11-13T20:57:07.530" Score="4" ViewCount="834" Body="&lt;p&gt;I am investigating using a Tiny Trak 4 with my portable HF radio to self-spot on &lt;a href=&quot;https://en.wikipedia.org/wiki/Summits_on_the_Air&quot; rel=&quot;nofollow&quot;&gt;SOTA&lt;/a&gt; activations via &lt;a href=&quot;https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System&quot; rel=&quot;nofollow&quot;&gt;APRS&lt;/a&gt; on 30m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I usually self-spot via a text message. When I don't have any cell coverage, I can sometimes spot using APRS on 2m. I am looking for a solution for relatively remote areas where I don't have any cell coverage and don't have any 2m digipeater coverage. If I can get APRS messages out on 30m that would do the job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can find references on the Internet to using APRS on 30m, but I don't find any information on where or how many 30m IGates there are or what the coverage is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I generate or where can I find a list of APRS igates on 30m?&lt;/p&gt;&#xA;" OwnerUserId="355" LastEditorUserId="87" LastEditDate="2013-11-22T21:00:54.937" LastActivityDate="2019-04-19T03:20:10.737" Title="How can I generate a list of APRS IGates on 30m?" Tags="&lt;hf&gt;&lt;digital-modes&gt;&lt;aprs&gt;&lt;packet&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="716" PostTypeId="5" CreationDate="2013-11-14T03:22:56.617" Score="0" Body="&lt;p&gt;An antenna tuner, also known as a &lt;em&gt;transmatch&lt;/em&gt; or &lt;em&gt;antenna tuning unit (ATU)&lt;/em&gt; is a device connected between a radio and its antenna to improve power transfer between them by matching the impedance of the radio to that of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transmitters transfer maximum power when they are presented with a fully resistive load of a specified value (typically of 50 ohms).  Antennas are resonant only at particular frequencies. Operating into an antenna at other frequencies is possible, but at a reduced efficiency.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna tuner contains a matching network of capacitors and inductors designed to cancel out the reactance that occurs when operating an antenna at non-resonant frequencies leaving just the resistive load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, an ATU allows the use of one antenna on a broader range of frequencies. An antenna and transmatch are not as efficient as a resonant antenna due to feedline losses and losses in the ATU itself. Note that an ATU does not change the resonant frequency of the antenna, merely changes the impedance.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="87" LastEditDate="2013-11-14T03:23:34.567" LastActivityDate="2013-11-14T03:23:34.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="717" PostTypeId="4" CreationDate="2013-11-14T03:22:56.617" Score="0" Body="Questions relating to the setup and use of antenna tuners, the virtues and shortcomings of various types of tuners, etc." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-14T03:23:39.503" LastActivityDate="2013-11-14T03:23:39.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="718" PostTypeId="1" AcceptedAnswerId="726" CreationDate="2013-11-14T14:25:54.363" Score="17" ViewCount="2572" Body="&lt;p&gt;Some antenna tuners claim to match any “random wire” to any HF frequency. Can one really use a random wire as a practical antenna system?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From everything I have heard, the resonance of the antenna (length, material) is what defines its performance on a given frequency. Is this only a minimalist emergency use concept, a fraction of a watt being better than no antenna at all?&lt;/p&gt;&#xA;" OwnerUserId="152" LastEditorUserId="76" LastEditDate="2015-12-15T20:42:33.330" LastActivityDate="2018-08-13T01:51:59.993" Title="What is a &quot;random wire antenna&quot;?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;wire-antenna&gt;&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="719" PostTypeId="2" ParentId="718" CreationDate="2013-11-14T14:37:17.753" Score="4" Body="&lt;p&gt;It is amazing what can be used for antennas. On a lark, I tried what I read in a club newsletter once and connected a tuner to my downspout. I was able to work south americans on 10 meters!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A random wire is just that -  a random length of wire, possibly thrown over a tree limb or whatever gets it as high as possible fed with a tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're right - it won't be resonant, and the tuner is just 'making the radio think' the antenna is resonant, but it could be very effective!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best part is experimenting - try it out!&lt;/p&gt;&#xA;" OwnerUserId="359" LastActivityDate="2013-11-14T14:37:17.753" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="720" PostTypeId="5" CreationDate="2013-11-14T14:42:50.730" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-14T14:42:50.730" LastActivityDate="2013-11-14T14:42:50.730" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="721" PostTypeId="4" CreationDate="2013-11-14T14:42:50.730" Score="0" Body="Questions about safely installing and operating ham radio equipment in homes or vehicles." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-14T14:59:12.403" LastActivityDate="2013-11-14T14:59:12.403" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="722" PostTypeId="5" CreationDate="2013-11-14T15:40:14.817" Score="0" Body="&lt;h1&gt;Location&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Location is one of those important pieces of information that is commonly exchanged between radio amateurs during a QSO.  However, there are many systems in place to describe your (or your contact's) location depending on the situation.  This article attempts to be a primer on the most common ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Lat/Lon&lt;/strong&gt;&amp;mdash;The old standby, the earth is divided into 360° (+- 180°) starting at the Royal Observatory in Greenich England as the Prime Meridian (or 0°).  West from here the Longitude is positive, East from here, negative.  for the North/South dimension, the Earth is divided into 180° (+-90°) starting at the equator.  North of the equator, the value is positive, south of the equator, it's negative.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both values can be further divided into minutes, seconds and fractions of seconds for higher resolution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;GPS Coordinates&lt;/strong&gt;&amp;mdash; Uses a high resolution model of the Earth and precise time measurements to give highly accurate Latitude/Longitude figures as will as altitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;ARRL Section&lt;/strong&gt;&amp;mdash;The ARRL has divided the US and Canada (I imagine in cooperation with RAC) into sections along state/province lines.  Populous states/provinces are split into more sections as needed.  There are (currently) 86 sections. You can find a nice map &#xA;&lt;a href=&quot;http://www.mapability.com/ei8ic/maps/sections.php&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;CQ Zones&lt;/strong&gt;&amp;mdash;CQ Amateur Radio  Magazine has divided the Earth into 40 zones for the purposes of their contests.  You can find a complete description of them &lt;a href=&quot;http://www.cq-amateur-radio.com/cq_awards/cq_waz_awards/cq_waz_list.html&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;ITU Zones&lt;/strong&gt;&amp;mdash;The ITU (International Telecommunication Union) is the United Nations specialized agency for information and communication technologies.  They have divided the Earth broadly into 3 Regions and further divided down to 90 Zones.  You can find good maps &lt;a href=&quot;http://www.itu.hamatlas.eu/menu.htm&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Grid Square&lt;/strong&gt;&amp;mdash;(&lt;em&gt;Maidenhead Locator System&lt;/em&gt;) was conceived as a simple way to describe your general location anywhere on the Earth in a way that's suitable for easy communication over the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Maidenhead Locator System (named after the town near London where it was conceived by a meeting of European VHF managers in 1980), a grid square measures 1° latitude by 2° longitude and measures approximately 70 × 100 miles in the continental US. A grid square is indicated by two letters (the field) and two numbers (the square), as in FN31, the grid square within which W1AW, ARRL's Maxim Memorial Station, resides.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Occasionally you will need to use a subsquare for more precise location. Each subsquare is designated by the addition of two letters after the grid square, as FN44ig. These more precise locators are used as part of the exchange in the 10-GHz contest. They measure 2.5 minutes latitude by 5 minutes longitude, roughly corresponding to 3 × 4 miles in the continental US.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A nice article in the January 1989 QST describes the system and conversion between lat/lon and grid squares: &lt;a href=&quot;http://www.arrl.org/files/file/protected/Group/Members/Technology/tis/info/pdf/18929.pdf&quot; rel=&quot;nofollow&quot;&gt;Conversion Between Geodetic and Grid Locator Systems&lt;/a&gt;. This website: &lt;a href=&quot;http://www.levinecentral.com/ham/grid_square.php&quot; rel=&quot;nofollow&quot;&gt;Grid Square Locator Map&lt;/a&gt; will determine your grid square location based on either your address or call sign or is you give it a grid square (either 4 digit or 6 digit), it will show you on a map the area that square encompasses.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-14T16:52:41.160" LastActivityDate="2013-11-14T16:52:41.160" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="723" PostTypeId="4" CreationDate="2013-11-14T15:40:14.817" Score="0" Body="Questions relating to determining your location or the location of a QSO based on one of the various systems of measurement (lat/lon, GPS coordinates, ARRL section, CQ Zones, ITU Zones, Maidenhead Grid, etc)." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-14T16:52:47.190" LastActivityDate="2013-11-14T16:52:47.190" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="724" PostTypeId="1" AcceptedAnswerId="732" CreationDate="2013-11-14T16:11:11.423" Score="10" ViewCount="2884" Body="&lt;p&gt;I just bought a cheap 1/4-wavelength, 2m. mag-mount antenna. The package says it can handle 50 watts. I can think of three things that could limit the capacity:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;$I^2R$ losses in the connection to the feedpoint and in the antenna wire itself: increases with increasing current, produces gradual breakdown of materials;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;dielectric heating at the feedpoint: increases with increasing voltage and frequency, produces gradual breakdown of materials;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;dielectric breakdown at the feedpoint, happens suddenly when voltage is too large, produces immediate failure.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Are these right? Are there others?&lt;/p&gt;&#xA;" OwnerUserId="105" LastEditorUserId="13" LastEditDate="2013-11-14T16:51:18.370" LastActivityDate="2013-11-15T14:45:18.597" Title="What determines power handling capacity of an antenna?" Tags="&lt;antenna&gt;&lt;rf-power&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="725" PostTypeId="2" ParentId="724" CreationDate="2013-11-14T16:59:49.917" Score="5" Body="&lt;p&gt;Cheap mag mounts, like many physically short antennas, have a coil in them to make up the correct electrical length.  I am sure it's made with the finest materials available.  But it's probably not.  Even if it was, inexpensive means smaller gauge wire, cheaper connectors, etc.  And so driving it at higher than it's rated capacity is going cause it to heat up and the dielectric is going to breakdown and melt until you get a short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And of course, all the heat is power that isn't leaving the antenna, so your efficiency is poor too.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-14T16:59:49.917" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="726" PostTypeId="2" ParentId="718" CreationDate="2013-11-14T17:28:08.100" Score="10" Body="&lt;p&gt;Yes, a random wire can be a practical antenna. Anything conductive can be loaded up.  Somethings work better than others.  But if you want to play around, there's no reason the antenna has to be an &quot;antenna&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are, of course, some drawbacks:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You must have a tuner. &lt;/li&gt;&#xA;&lt;li&gt;You might not get a match on every band you'd like to work.&lt;/li&gt;&#xA;&lt;li&gt;For efficiency, you need a counterpoise, an insulated wire that attaches to the ground of your tuner. Ideally, this is 1/4 wave long at the lowest band you'll operate on.  Note that this is not a radial, so it doesn't have to be straight.&lt;/li&gt;&#xA;&lt;li&gt;The &quot;antenna&quot; starts at the back of your tuner (i.e., in the shack), so power levels must be low unless you like living in an RF fields and collecting RF burns.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-14T17:28:08.100" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="727" PostTypeId="5" CreationDate="2013-11-14T17:30:38.143" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-14T17:30:38.143" LastActivityDate="2013-11-14T17:30:38.143" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="728" PostTypeId="4" CreationDate="2013-11-14T17:30:38.143" Score="0" Body="Use this tag for questions about which frequencies to use or not use in certain locations/situations." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-14T17:35:56.923" LastActivityDate="2013-11-14T17:35:56.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="729" PostTypeId="5" CreationDate="2013-11-14T17:32:26.527" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-14T17:32:26.527" LastActivityDate="2013-11-14T17:32:26.527" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="730" PostTypeId="4" CreationDate="2013-11-14T17:32:26.527" Score="0" Body="Use this tag for general questions relating to transceivers." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-14T17:35:54.297" LastActivityDate="2013-11-14T17:35:54.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="731" PostTypeId="2" ParentId="140" CreationDate="2013-11-14T19:29:52.683" Score="8" Body="&lt;p&gt;Here is an answer for the European hams among us.&#xA;&lt;a href=&quot;http://hamwaves.com/wire/en/index.html&quot; rel=&quot;noreferrer&quot;&gt;Printable copies&lt;/a&gt; are available from my web site.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Wire myths&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;There happens to be a lot of fuss out there about antenna wire. Most amateur radio shops sell &quot;special&quot; antenna wire at unreasonably high price, whilst most of the claims made about these wires are untrue. The situation reminds me a bit of the many loudspeaker cable myths. However, for those living in Europe, a less expensive and even better alternative exists.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;What I use&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;&#xA;For all my wire antenna projects I always use extremely flexible and comparatively cheap black-coloured 4mm²-sized &lt;strong&gt;tinned HO7 V-K 4 wire.&lt;/strong&gt; As a comparison, 4mm² corresponds to about &lt;a href=&quot;http://en.wikipedia.org/wiki/Awg&quot; rel=&quot;noreferrer&quot;&gt;AWG&lt;/a&gt; 11. &quot;HO7 V-K 4&quot; is the European harmonisation code for this wire. Rather unfortunately, this harmonisation code did not foresee a means of specifying the property of being &quot;tinned&quot;. So, &lt;strong&gt;make sure to specify &quot;tinned&quot; when ordering this wire!&lt;/strong&gt; In Belgium, the country of its original manufacturer, tinned HO7 V-K 4 is more commonly known as &lt;em&gt;&quot;VOBst 4 carré.&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Tinned HO7 V-K &lt;em&gt;x&lt;/em&gt; specs&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Tinned HO7 V-K 4&lt;/strong&gt; is a 4mm² wire made out of 51 tinned-copper braided strands and insulated with a 0.8mm thick layer of soft PVC. Tinned HO7 V-K wire is also available in other cross-sections, the last figure in the wire code indicating the conductor area in mm². Below spec links list all available wire sizes. However, at least for permanent installations, I would stick to the 4mm² size. Keep in mind that at radio frequencies the skin effect greatly reduces the current carrying capacity of any wire. Additional benefits of this wire gauge are its greater breaking strength and a slightly broader VSWR bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://hamwaves.com/wire/doc/ho7_v-k.pdf&quot; rel=&quot;noreferrer&quot;&gt;HO7 V-K spec sheet&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://hamwaves.com/wire/doc/vobst.pdf&quot; rel=&quot;noreferrer&quot;&gt;VOBst spec sheet&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The tinned-copper braided strands are what make the wire so &lt;em&gt;extremely flexible.&lt;/em&gt; The tin around each of the copper strands makes soldering the wire a breeze and, moreover, prevents the copper from oxidizing, especially in salty coastal environments. After all, VOBst wire is designed for use in bathrooms and on board of ships. Nevertheless, I always make sure to cap the wire ends with a dot of solder and clear glue to prevent moisture from entering through capillary action. It is better to be safe than sorry!&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Modelling PVC insulation&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;The 0.8mm thick black-coloured soft polyvinyl chloride (soft-PVC) insulating sheet is perfectly UV-resistant; it will withstand exposure to sun rays. For those who would like to model wire antennas with NEC, the only data I have found for the relative permittivity $ε_r$ of soft PVC is the wide range of 4.0 to 8.0$^1$. The &lt;a href=&quot;http://hamwaves.com/wire/doc/4nec2.rtf&quot; rel=&quot;noreferrer&quot;&gt;4nec2 internal manual&lt;/a&gt; mentions a range of 4.0 to 5.0 for soft-PVC without quoting any reference. The actual value for a particular sample will depend on the amount of softener used in it; more softener will result in a higher permittivity. However, &lt;em&gt;a value of $ε_r=5$ would be a plausible estimate for most PVC-insulated wires.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of NEC-2-based antenna modelling programs (e.g. &lt;a href=&quot;http://www.qsl.net/4nec2/&quot; rel=&quot;noreferrer&quot;&gt;4nec2&lt;/a&gt; and &lt;a href=&quot;http://www.eznec.com/&quot; rel=&quot;noreferrer&quot;&gt;EZNEC&lt;/a&gt;) will model insulated wires. Please, refer to their respective user manuals for more information. L. B. Cebik, W4RNL (SK), also wrote about &lt;a href=&quot;http://www.antennex.com/w4rnl/col0105/amod83.html&quot; rel=&quot;noreferrer&quot;&gt;modelling insulated wires with NEC-2&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Leave some sag!&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;I have been operating my antennas for many years now without any issues despite some severe weather, salt and strain exposure. Of course, be sure to leave some sag when hanging up wire antennas. Check out Owen Duffy's, VK1OD, &lt;a href=&quot;http://vk1od.net/calc/awcc/awcc.htm&quot; rel=&quot;noreferrer&quot;&gt;antenna wire catenary calculator&lt;/a&gt; to know how much sag would be required for your particular application.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Electrical supply store&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;I am not selling this wire! If you are living in Europe, the good news is this wire can be ordered from your local electrical supply store. It is normally deliverable without much delay. To give you an indication of its price; in November 2006, I bought from a wholesaler 100m VOBst 4mm² for €66.33 (incl. VAT) and 100m of the lighter 2.5mm² VOBst for €40.35 (incl. VAT).&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;References&lt;/h1&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The American Radio Relay League, Inc. The ARRL handbook for radio amateurs. In: 69 ed.; 1992:p.35–34.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2013-11-18T01:13:56.503" LastActivityDate="2013-11-18T01:13:56.503" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="732" PostTypeId="2" ParentId="724" CreationDate="2013-11-14T21:53:12.737" Score="6" Body="&lt;p&gt;I think you pretty much summarized limiting factors in the general case. I'd add that there can be dielectric losses or breakdown at the ends, as well as the feedpoint. Common antenna designs (quarter-wave verticals, center-fed half-wave dipoles) are fed at a low-impedance node, and the ends are high-impedance nodes, so I'd expect dielectric breakdown (arcing) to be more likely at the ends than the feedpoint. At high power levels, the antenna ends can reach voltages high enough to cause arcing to nearby conductors (towers, trees, gutters) or &lt;a href=&quot;http://en.wikipedia.org/wiki/Corona_discharge&quot; rel=&quot;nofollow&quot;&gt;corona discharge&lt;/a&gt;. Unlikely at your 50W example, however.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd also consider RF exposure. Consider that this is is a VHF antenna, and that exposure limits are lower with increasing frequency. Also consider that this antenna isn't installed in a fixed location, no one is going to test the RF exposure levels, and there's nothing preventing anyone from getting close to the antenna. In fact, given that most people will stick them to cars, it's not only possible, but &lt;em&gt;likely&lt;/em&gt; that someone will be close. So, the manufacturer may specify a power limit due to regulatory or liability concerns.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-11-15T14:45:18.597" LastActivityDate="2013-11-15T14:45:18.597" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="733" PostTypeId="1" AcceptedAnswerId="734" CreationDate="2013-11-14T22:08:40.170" Score="6" ViewCount="312" Body="&lt;p&gt;I live in a small valley, surrounded on three sides by 200-300 foot ridges. I'm trying to figure out where to place an antenna mast to receive 1280&amp;nbsp;MHz video from a long range aerial vehicle (20-30 mile radius).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this frequency, how important will line-of-sight transmission be in this situation? Will it be worth it to haul a 50-foot mast to the top of one of the ridges, and set it up there? (requires a solar panel / battery, and possibly a wireless relay to my shack). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My current plan is a mast at my station; in the middle of the valley, which would get above the surrounding trees, but not above the ridges. Does it matter that aforementioned valley is populated with pine trees, which, as I understand it, will wreak havoc on the signal? What about a 433&amp;nbsp;MHz transmission from the valley floor to the aerial vehicle?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S.: Please presume that there isn't any &lt;a href=&quot;https://en.wikipedia.org/wiki/Homeowner_association&quot; rel=&quot;nofollow&quot;&gt;HOA&lt;/a&gt; / building code in the area; this is a problem of physics, not legality. &lt;/p&gt;&#xA;" OwnerUserId="361" LastEditorUserId="76" LastEditDate="2015-12-15T21:55:43.657" LastActivityDate="2015-12-15T21:55:43.657" Title="1280 MHz propagation out of a mountain valley" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;uhf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="734" PostTypeId="2" ParentId="733" CreationDate="2013-11-14T22:43:32.597" Score="8" Body="&lt;p&gt;For the most part, propagation for VHF/UHF (1280 MHz is UHF) is line-of-sight because it doesn't tend to get the benefit of ionospheric reflection like HF does. This will also apply to your mentioned 433 MHz transmission, which is in the UHF range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While there are occasionally atmospheric events that result in indirect UHF/VHF propagation (e.g. tropospheric ducting), they are not nearly as consistent as HF's ability to DX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd almost certainly get much better reception (both ways) with an antenna located on the ridge where it can get a direct sight line to the aircraft.&lt;/p&gt;&#xA;" OwnerUserId="22" LastEditorUserId="87" LastEditDate="2013-11-15T19:46:47.287" LastActivityDate="2013-11-15T19:46:47.287" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="735" PostTypeId="5" CreationDate="2013-11-15T13:42:49.397" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-15T13:42:49.397" LastActivityDate="2013-11-15T13:42:49.397" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="736" PostTypeId="4" CreationDate="2013-11-15T13:42:49.397" Score="0" Body="Questions related to how the ITU divided the Earth up into 90 zones and how to determine where you and/or your contact it located. " OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-15T13:58:11.360" LastActivityDate="2013-11-15T13:58:11.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="737" PostTypeId="5" CreationDate="2013-11-15T14:25:53.253" Score="0" Body="&lt;h2&gt;Basic Dipole Theory&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;The dipole is one of the simplest and most widely used types of antenna.  A dipole is a very basic antenna structure consisting of two straight, symmetrical, collinear wires. The driving current from the transmitter is applied between the two halves of the antenna where each side of the feedline is connected to one of the two wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can we explain the fact that you can drive current into a dipole when the ends are open circuited? The simplest way is to consider the parasitic capacitance between the two arms of the antenna as the return current path. At high frequency this capacitance will represent a low impedance. Current through this uncontrolled parasitic capacitance represents radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, a dipole antenna requires two parts in order to radiate and the amount of radiation will be proportional to the dipole current. Note also that, a dipole does&#xA;not require a “ground” to work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dipoles are &lt;em&gt;resonant&lt;/em&gt; antennas, meaning that the elements serve as resonators, with standing waves of radio current flowing back and forth between their ends. The length of the dipole elements is determined by the wavelength of the radio waves used. The most common form is the half-wave dipole, in which each of the two elements is approximately λ/4 long, so the whole antenna is λ/2 long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without diverting into serious math, the length of a λ/2 dipole in meters = 143/f(MHz).  In practice, the actual length will be somewhat shorter due to ohmic losses in the wire itself and the connection to the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A common practice is to construct the dipole using the above formula, hang it temporarily and measure the resonant frequency.  Then determine the difference between the resonant frequency and the desired frequency, calculate the difference and trim half that amount off both ends.  The result should be resonant at the desired frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The maximum theoretical gain of a λ/2-dipole is 2.15 dBi. In practice, it's going to be somewhat less due to ohmic losses in the wire itself and the connection to the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally, a λ/2 dipole should be fed with a balanced line matching the theoretical 73Ω impedance of the antenna.  In practice, that's unlikely.  Good results can be obtained by directly feeding the antenna using 50Ω coax.  This will give a 1.5:1.  It's common to place a choke or current balun at the feedpoint to transform the unbalanced coax feed into a balanced line feed suitable for feeding a dipole antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This won't change the 1.5:1 impedance match, but it will be more efficient and reduce the chance that your feedline becomes part of the radiator.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="8713" LastEditDate="2018-09-07T13:03:21.650" LastActivityDate="2018-09-07T13:03:21.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="738" PostTypeId="4" CreationDate="2013-11-15T14:25:53.253" Score="0" Body="Use this tag for questions relating to dipole antennas." OwnerUserId="164" LastEditorUserId="29" LastEditDate="2013-11-15T14:50:44.720" LastActivityDate="2013-11-15T14:50:44.720" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="739" PostTypeId="1" AcceptedAnswerId="740" CreationDate="2013-11-15T17:04:40.567" Score="2" ViewCount="607" Body="&lt;p&gt;In my (new) setup, I will have a solid-state HF radio driving an antenna through an antenna tuner. Both my radio and the antenna tuner have internal SWR meters, of the type that requires you to adjust the SWR meter reading based on your output power. My previous experience has been with meters that directly read SWR (either electrically or through cross needles).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand how to use these meters to make SWR measurements, but my concern is with the internal protection circuits of the radio. If the SWR is too high, the radio will automatically reduce the output power to protect the radio. When you're tuning an antenna tuner, the SWR may cause the radio to enter or leave this protection region, resulting in an inaccurate measurement of SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do you approach using an antenna tuner with this type of SWR meter?&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="76" LastEditDate="2014-05-23T18:34:08.583" LastActivityDate="2014-05-23T18:34:08.583" Title="Tuning an antenna with a SWR meter that relies on output power" Tags="&lt;impedance&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="740" PostTypeId="2" ParentId="739" CreationDate="2013-11-15T17:50:29.310" Score="5" Body="&lt;p&gt;Most radios with SWR protection don't detect SWR, they just detect reflected power.  It's a much simpler (read that as cheaper) circuit to implement and it's what really matters anyway.  The manufacturer will have established a threshold for reflected power, based on the MOSFET's tolerance.  If the circuit sees more than this it will either clamp it at the threshold level, cut in some sort of limiter or cut out completely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I would set the power low (say, 5-10W for a 100W rig) and tune there.  Then go to full power.  Since SWR is a ratio, you'll have accurate readings without frying your radio.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-15T17:50:29.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="741" PostTypeId="1" CreationDate="2013-11-17T02:20:34.743" Score="6" ViewCount="229" Body="&lt;p&gt;I have a UHF/VHF transceiver capable of transmitting on UHF and receiving on VHF or vice versa on channel mode. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I finally got a directional Yagi antenna so reception/transmission shouldn't be a problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in Colorado, USA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which frequencies should I use to listen to it, and eventually transmit?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What other frequencies should I program in for the doppler shift? (I will be switching between channels)&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2013-11-17T12:56:43.003" Title="How to talk to the ISS" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="742" PostTypeId="1" CreationDate="2013-11-17T02:30:12.853" Score="2" ViewCount="93" Body="&lt;p&gt;I understand the reason repeaters can't operate simplex transmitting and receiving at the same time is because they will pick up their own signal. Lets say two people are on different sides of a mountain and 2 Uni-Directional antennas were pointed two different directions, one for each side of the mountain. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would this enable SIMPLEX same-time repeating or would it be impossible to filter out the signal from the other antenna?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2013-11-17T03:54:41.840" Title="Uni-Directional Simplex repeater?" Tags="&lt;simplex&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="743" PostTypeId="2" ParentId="742" CreationDate="2013-11-17T03:54:41.840" Score="3" Body="&lt;p&gt;&quot;Uni-directional&quot; antennas are usually not truly &quot;uni&quot;-directional - that is, they don't only radiate signal in a single direction. Instead, they radiate much more &lt;em&gt;strongly&lt;/em&gt; in their frontal direction, with a weaker degree of radiation in other directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, if you have two uni-directional antennas near each other but pointed in different directions, you're still going to get signal between them due to their relative proximity. You could try to diminish the signal still further (e.g. by placing other things that would block the signal between the two antennas to further attenuate strength), or you could try spacing the antennas further apart (perhaps via feed lines) to put the mountain itself between them, but just having two separate antennas would not be enough.&lt;/p&gt;&#xA;" OwnerUserId="22" LastActivityDate="2013-11-17T03:54:41.840" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="745" PostTypeId="2" ParentId="741" CreationDate="2013-11-17T12:56:43.003" Score="6" Body="&lt;p&gt;According to &lt;a href=&quot;http://www.issfanclub.com/frequencies&quot;&gt;the ISS Fan Club's Frequencies page&lt;/a&gt;, for FM voice transmissions the downlink (your listening) frequency is 145.800 MHz and the uplink (your transmission) frequency is 144.490 MHz, when covering ITU regions 2 and 3, including North America.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In ITU region 1 the corresponding frequencies are downlink 145.800 MHz and uplink 145.200 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are other frequencies listed as well, but these would appear to be the ones that you would be most likely to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the ISS is in a low orbit, Doppler shift will be relatively significant. Software designed to calculate such things will likely be useful, but for a starting point you may want to consider the table included in the Yaesu FT-897D manual, page 68, for the frequencies involved in operating over the UO-14 satellite, which itself listens on two meters and retransmits on 70 cm:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{array}{ c r r l }&#xA;\text{Channel #} &amp;amp; \text{Receive Frequency} &amp;amp; \text{Transmit Frequency} &amp;amp; \text{Notes} \\&#xA;1 &amp;amp; 435.080\text{ MHz} &amp;amp; 145.9700\text{ MHz} &amp;amp; \text{Acquisition of signal (beginning of pass)} \\&#xA;2 &amp;amp; 435.075\text{ MHz} &amp;amp; 145.9725\text{ MHz} &amp;amp; \\&#xA;3 &amp;amp; 435.070\text{ MHz} &amp;amp; 145.9750\text{ MHz} &amp;amp; \text{Mid pass} \\&#xA;4 &amp;amp; 435.065\text{ MHz} &amp;amp; 145.9775\text{ MHz} &amp;amp; \\&#xA;5 &amp;amp; 435.060\text{ MHz} &amp;amp; 145.9800\text{ MHz} &amp;amp; \text{Loss of signal (end of pass)}&#xA;\end{array} $$&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-11-17T12:56:43.003" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="746" PostTypeId="1" AcceptedAnswerId="773" CreationDate="2013-11-17T14:06:59.230" Score="6" ViewCount="10442" Body="&lt;p&gt;I'm planning on setting up a low-HF antenna for near to mid-range contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my particular case, &lt;em&gt;ideally&lt;/em&gt; I would like to be able to cover a radius of approximately 1000-1200 km with good reliability, operating on 3.5 MHz and possibly supplanted by 7 MHz. (Using a combination of the two bands to achieve full coverage is perfectly acceptable.) At a minimum, I want to be able to cover something like a 600-700 km radius. I'm at approximately 58°N, locator JO68; this of course means that I need to take into consideration large seasonal variations in ionosphere illumination.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, such coverage seems to me to be a nearly ideal fit for NVIS.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Given an antenna height above ground and operating frequency, how do I determine an approximate resultant coverage radius in the case of NVIS?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Or alternatively, given an operating frequency and desired coverage radius, how do I determine how high above ground the antenna needs to be?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm preferably looking for a (mathematical) answer that does not involve using antenna modeling software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For simplicity's sake, let's just assume a straight half-wave dipole at an even height above perfect ground.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-17T14:19:09.863" LastActivityDate="2013-11-19T19:44:27.307" Title="How to determine antenna height for given HF frequency and coverage radius?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;propagation&gt;&lt;range&gt;&lt;nvis&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="747" PostTypeId="5" CreationDate="2013-11-17T14:10:00.243" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-17T14:10:00.243" LastActivityDate="2013-11-17T14:10:00.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="748" PostTypeId="4" CreationDate="2013-11-17T14:10:00.243" Score="0" Body="Near Vertical Incidence Skywave refers to (normally HF) signals being radiated nearly vertically from the antenna, then reflected in the ionosphere resulting in an almost circular transmission coverage pattern. It is achieved by placing the antenna at low height and is commonly used for near-range communications on the lower HF bands, particularly 3.5 MHz." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-17T14:10:00.243" LastActivityDate="2013-11-17T14:10:00.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="749" PostTypeId="1" CreationDate="2013-11-17T19:54:21.823" Score="9" ViewCount="9010" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;When I was in high school, we had 8 hams at once. (Probably rare)  4&#xA;  of us built little 10 meter walkie-talkies and had great fun using&#xA;  them on Field Day, hiking or around town.  It was especially fun&#xA;  because this was pre-cellphone and ordinary non-ham folks could not&#xA;  buy any kind of walkie-talkie.  We were hi-tech and really cool.  Now&#xA;  the average kid has unused Radio shack talkies in his dresser and&#xA;  couldn't care less about them.&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That is from the author of Crystal Sets to Sideband. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I'm in the generation of the &quot;radio shack unused walkie talkies&quot; and I want to build myself a 10 meter walkie talkie. I have fairly descent soldering skills and I have been building electronics for about 5 years (I probably started when I was 10)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I build a 10 meter handheld, and what parts do I need. I would like getting transistors, inductors, etc and building the whole thing with discrete components (no IC's)&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2016-01-18T17:44:13.550" Title="Home-brew 10 meter walkie talkies?" Tags="&lt;diy&gt;" AnswerCount="5" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="750" PostTypeId="2" ParentId="749" CreationDate="2013-11-18T15:43:21.677" Score="8" Body="&lt;p&gt;I am not sure if you are asking about converting a CB walkie-talkie to 10m or building one from scratch so I will address both, not feeling like working at the moment:&lt;/p&gt;&#xA;&lt;h2&gt;Converting a CB walkie-talkie&lt;/h2&gt;&#xA;&lt;p&gt;What it will take to Convert a CB walkie-talkie is going to depend on how it's contructed, of course.  It can be as simple as replacing one or more crystals. A cheap one will have one offset crystal to move the channels up into the CB range.  Fancier ones might have several crystals. Basically you want to move it &amp;quot;up&amp;quot; 2MHz to get you into about 29MHz. You'll be stuck with the channel concept on the frequencies of the crystals, of course, but that can be OK.&lt;/p&gt;&#xA;&lt;p&gt;A newer CB will probably have some sort of DDS which would make it much much harder to convert.&lt;/p&gt;&#xA;&lt;p&gt;As a note, CB radios are (usually) AM, and while this is fine on 10m, that's something to remember.  Newer ones support SSB as well, but might be much more difficult to mod.&lt;/p&gt;&#xA;&lt;p&gt;If you want to get crazy you can figure out how to supress the carrier and do DSB or supress both the carrier and the lower sideband.  Even more adventurous would be to disconnect the AM modulator, add an FM detector chip (I know you want discrete, but this is just blue sky stuff) and modulating the VCO, then you'd be doing FM.  Although these days most repeaters have a PL, which makes this mod a lot less useful.&lt;/p&gt;&#xA;&lt;h2&gt;Homebrew 10m walkie-talkie&lt;/h2&gt;&#xA;&lt;p&gt;Poking around on the net, there are a bunch of QRP 10m transceivers that could be built into a walkie-talkie form factor.  This one looks pretty doable:&#xA;&lt;img src=&quot;https://i.stack.imgur.com/M9i36.gif&quot; alt=&quot;10m SSB Transceiver&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;The only IC is a small op-amp for the audio out.  Looking the schematic over, it's setup for 220V AC power (the author is Australian, but he's probably OK despite that :) ).  Since you are going to want to run on battery, you can axe that whole section and wire the DC source right in.&lt;/p&gt;&#xA;&lt;p&gt;Another option is a 14MHz SSB transceiver.  This &lt;a href=&quot;http://www.qsl.net/yo5ofh/projects/14mhz_ssb_trx/14mssb10w.htm&quot; rel=&quot;noreferrer&quot;&gt;page&lt;/a&gt; details an all discrete component version that will run on battery power.  You can either roll with it on 20m or convert it up to 10m.&lt;/p&gt;&#xA;&lt;p&gt;Happy Soldering.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2013-11-18T15:43:21.677" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="751" PostTypeId="1" AcceptedAnswerId="752" CreationDate="2013-11-18T19:13:20.347" Score="8" ViewCount="542" Body="&lt;p&gt;I frequently hear talk about SSNs in Amateur Radio, and somehow if the number is high, that's a good thing. I just don't really understand what they are, and what they mean, and I'd like to better understand them. What is the big deal about SSNs, what does it mean when they are high and low, etc?&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="29" LastEditDate="2013-11-18T20:13:34.927" LastActivityDate="2013-11-18T21:27:54.443" Title="How do sunspot numbers (SSN) affect radio operations?" Tags="&lt;propagation&gt;&lt;sunspots&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="752" PostTypeId="2" ParentId="751" CreationDate="2013-11-18T19:43:41.403" Score="3" Body="&lt;p&gt;It refers to &lt;strong&gt;'smoothed' sunspot number&lt;/strong&gt;, and is needed by many software utilities to calculate optimal propagation. This refers to the current number of dark spots on the sun associated with high magnetic activity. When the number is high, the whole HF range up to 30 MHz can be used usually around the clock and F2 propagation up to 50 MHz is observed frequently depending upon daily solar flux 10.7cm radiation values. During solar minima, or minimum sunspot counts down to zero, propagation of frequencies above 15 MHz is generally unavailable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, high levels of sunspot activity lead to better signal propagation on HF bands, although they also increase the levels of solar noise and ionospheric disturbances (caused by impact of the increased level of solar radiation on the ionosphere).&lt;/p&gt;&#xA;" OwnerUserId="128" LastActivityDate="2013-11-18T19:43:41.403" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="753" PostTypeId="2" ParentId="751" CreationDate="2013-11-18T21:27:54.443" Score="3" Body="&lt;p&gt;Sunspots correlate with a higher solar wind, which when it hits the ionosphere, makes the F layer more reflective to HF frequencies. So, hams can bounce signals more effectively when the SSN is high and reach further with their signals.&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-11-18T21:27:54.443" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="754" PostTypeId="1" AcceptedAnswerId="757" CreationDate="2013-11-18T21:55:24.863" Score="18" ViewCount="25671" Body="&lt;p&gt;I've been thinking for some time about magnet mount mobile antennas and wondering how they establish their ground plane.  Consider that many mag mount antennas have some kind of protective coating on the magnet.  Consider also that most cars have a coat of paint between the mag mount and the sheet metal.  Both of these should result in some level of electrical isolation between the antenna feed shield and the sheet metal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess what I'm simply not clear on is how a mag mount antenna's ground plane is connected electrically.  Or is this accomplished through inductance?&lt;/p&gt;&#xA;" OwnerUserId="47" LastEditorUserId="76" LastEditDate="2015-12-15T21:50:24.600" LastActivityDate="2020-04-14T12:34:53.513" Title="How does a mag mount antenna achieve a ground plane?" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;theory&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="756" PostTypeId="1" CreationDate="2013-11-19T02:32:25.940" Score="12" ViewCount="3417" Body="&lt;p&gt;I recently built this circuit, and could hear a nice full quieting signal on my short-wave radio with a 7.2 megahertz crystal for the 40 meter band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the simplest way I could Amplitude Modulate this signal with a microphone or computer output port so my Short wave radio could hear this signal and I could potentially make some HAM contacts?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And yes, I know AM is very rarely used, but I want to start out with this because of the complexity of sideband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/AMgGu.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="87" LastEditDate="2013-11-20T02:39:00.890" LastActivityDate="2021-04-17T13:13:03.283" Title="How can I add amplitude modulation to this transmitter?" Tags="&lt;diy&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="757" PostTypeId="2" ParentId="754" CreationDate="2013-11-19T02:52:41.423" Score="23" Body="&lt;p&gt;There's &lt;em&gt;always&lt;/em&gt; a ground.  Whether it's what you intend it to be or not is another issue...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A mag-mount antenna is grounded through capacitive coupling between that magnet and the metal it's stuck to.  At VHF/UHF frequencies, this effect is adequate for good results which explains the popularity of these mounts.  Some folks advocate adding a wire instead of relying on the coupling effect, but in most cases, this has little or no effect.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At HF frequencies, it's a different story.  The capacitive effect is not enough and thorough grounding of the vehicle is usually indicated.  There are several good guides out on the internet, I suggest starting with K0BG's excellent &lt;a href=&quot;http://www.k0bg.com/&quot;&gt;site&lt;/a&gt; on the ins and outs of mobile amateur radio oeprating.   &lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-19T02:52:41.423" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="758" PostTypeId="2" ParentId="756" CreationDate="2013-11-19T03:19:47.423" Score="7" Body="&lt;p&gt;Take heart, there are some diehard AM operators out there on various bands. I am not one of them, but I have seen messages about skeds and frequencies for them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not really sure how you can AM that circuit specifically.  I suppose you could substitute the mic input from the usual circuit with that oscillator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A typical, simple, AM transmitter consists of a MIC pre-amp feeding into an oscillator of some kind and thence into a tuned tank circuit for matching out to the antenna. You also probably want some sort of bandpass filter in there to minimize splatter. This can be accomplished with just a pair of 2N2222A and a handful of other components.  An example circuit is:&#xA;&lt;img src=&quot;https://i.stack.imgur.com/O9jBN.png&quot; alt=&quot;IC AM Transmitter&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and a nice project description can be found &lt;a href=&quot;http://www.zen22142.zen.co.uk/Circuits/rf/amtx.htm&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want something a little more advanced, you could use an op amp like the venerable 741 or the NE5532 as your audio pre-amp.  Then, instead of driving the 2N2222, you could use the 74HC4060 oscillator and divider to generate a carrier at the appropriate frequency depending on your crystal's frequency.  From there you'll still need a good filter to remove the remaining DC component, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The circuit for doing this is:&#xA;&lt;img src=&quot;https://i.stack.imgur.com/Mj9Zi.gif&quot; alt=&quot;enter image description here&quot;&gt;&#xA;Looks pretty cool, actually, I am tempted to warm up the soldering iron myself.  The complete project description can be found &lt;a href=&quot;http://www.giangrandi.ch/electronics/am-mod/am-mod.shtml&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt; including a complete bill of goods and how to tune and test it.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-19T03:19:47.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="759" PostTypeId="1" AcceptedAnswerId="760" CreationDate="2013-11-19T05:45:31.110" Score="11" ViewCount="4897" Body="&lt;p&gt;I have a technician class license, and my license expires in March 2014.  How do I renew my license?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I received a notification in the mail from W5YI-VEC informing me that I could renew my license through them.  They included a form that I can fill out and mail to them, along with a $7.00 fee.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to renew directly with the FCC?  What are the advantages and disadvantages to renewing with a service like W5YI-VEC?&lt;/p&gt;&#xA;" OwnerUserId="208" LastEditorUserId="208" LastEditDate="2013-12-06T15:29:24.910" LastActivityDate="2017-05-08T03:26:24.257" Title="How do I renew my FCC amateur license?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="760" PostTypeId="2" ParentId="759" CreationDate="2013-11-19T06:33:18.287" Score="10" Body="&lt;p&gt;The ARRL renewals page (&lt;a href=&quot;http://www.arrl.org/renewals&quot;&gt;http://www.arrl.org/renewals&lt;/a&gt;) says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Amateur applications can be filed manually using paper forms or&#xA;  electronically over the Internet. Amateurs may electronically renew&#xA;  their FCC-issued licenses &quot;on line&quot; via the FCC web using FCC ULS .&#xA;  FCC permits on-line renewals at 90 days or less before a license will&#xA;  expire, and when the license has expired but is still within the&#xA;  two-year grace period for renewal. Licenses that have been expired for&#xA;  more than two years are not eligible for renewal or reinstatement. If&#xA;  you have a Vanity License renewal, remember to have your credit card&#xA;  accessible to pay the FCC Regulatory Fee.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Amateurs may also renew their licenses within 90 days before the&#xA;  license expiration date, or within the two-year license grace period&#xA;  after expiration, by using FCC Form 605 by mail to: FCC, 1270&#xA;  Fairfield Rd, Gettysburg PA 17325-7245. Vanity Renewals will also need&#xA;  to submit FCC Payment Form 159 and the required FCC Regulatory Fee,&#xA;  along with the FCC Form 605. After completing both forms, you can mail&#xA;  your FCC Form 605, FCC Form 159 and your payment to: FCC, Wireless&#xA;  Bureau Applications, PO Box 358130, Pittsburgh, PA 15251-5130.&#xA;  Licenses that have been expired for more than two years are not&#xA;  eligible for renewal or reinstatement.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;For a complete list of FCC filing instructions and filing fees go to&#xA;  the ARRL page Instructions for License Renewals or Changes.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Basically you can either use ULS online at &lt;a href=&quot;http://wireless.fcc.gov/uls/index.htm?job=home&quot;&gt;http://wireless.fcc.gov/uls/index.htm?job=home&lt;/a&gt;&#xA;Or download form 605 (&lt;a href=&quot;http://www.fcc.gov/forms#605&quot;&gt;http://www.fcc.gov/forms#605&lt;/a&gt;) and file manually. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I can tell, the W5YI site just makes it easier to fill out the forms, and they file it for you.  I can not determine any specific advantage to using their site.  The only disadvantage I can discern is the additional fee for their service.&lt;/p&gt;&#xA;" OwnerUserId="308" LastActivityDate="2013-11-19T06:33:18.287" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="761" PostTypeId="1" AcceptedAnswerId="782" CreationDate="2013-11-19T11:43:22.990" Score="6" ViewCount="128" Body="&lt;p&gt;Are there any mobile phone models there that contain 2 way radio functionality? &lt;/p&gt;&#xA;" OwnerUserId="389" LastEditorUserId="164" LastEditDate="2013-11-20T01:47:32.203" LastActivityDate="2013-11-20T03:51:25.030" Title="Mobile phone models that contain 2 way radio functionality" Tags="&lt;ht&gt;&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="762" PostTypeId="2" ParentId="761" CreationDate="2013-11-19T11:59:12.133" Score="5" Body="&lt;p&gt;The smarmy answer is of course, that cell phones &lt;em&gt;are&lt;/em&gt; two way radios on either the 800Mhz band (Sprint &amp;amp; US Cellular) or the 1900MHz band (all the others).  Not what you meant, I know.  The old Nextel phones with their &quot;push-to-talk&quot; feature were two-way radios using the old 50 MHz taxi-dispatcher band.  Later versions of this technology used 900MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found a couple of references to cell phones that incorporate what looks like FRS service in the 446 MHz band with a claimed range of 5km (&lt;a href=&quot;http://www.alibaba.com/product-gs/693379680/Cell_Phone_Two_Way_Radio.html&quot;&gt;http://www.alibaba.com/product-gs/693379680/Cell_Phone_Two_Way_Radio.html&lt;/a&gt; is an example).&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-19T11:59:12.133" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="763" PostTypeId="1" AcceptedAnswerId="778" CreationDate="2013-11-19T15:16:12.647" Score="10" ViewCount="424" Body="&lt;p&gt;Does the modulation scheme, whether OOK, SSB, AM, FM, a digital mode, etc, affect the propagation of a signal?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2018-04-11T16:13:05.333" Title="Does modulation affect propagation?" Tags="&lt;propagation&gt;&lt;transmission&gt;&lt;modes&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="764" PostTypeId="2" ParentId="756" CreationDate="2013-11-19T15:27:06.913" Score="10" Body="&lt;p&gt;The first AM transmitters were made by hacking the power supplies of CW transmitters. Replace the 9V battery with a variable voltage source and you have yourself an AM transmitter. Not an especially great one, but if simple is your primary concern, it can't get much simpler.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many ways you might do that, but if &quot;simple&quot; means &quot;low parts count&quot;, then the simplest way is to put the secondary of an audio transformer in series with the 9V supply that's already there. The audio then adds or subtracts from the 9V, and bam, you are modulating the envelope.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html&quot; rel=&quot;noreferrer&quot;&gt;sci-toys.com has a detailed article&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/brMSL.gif&quot; alt=&quot;AM transmitter schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The oscillator you've already built. All you need to add is the transformer and the plug.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-11-19T15:27:06.913" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="765" PostTypeId="1" AcceptedAnswerId="800" CreationDate="2013-11-19T17:42:59.690" Score="7" ViewCount="181" Body="&lt;p&gt;How do different sized coaxial cables, such as RG-58 and RG-8, compare in terms of electrical properties such as loss? Do different cable types have different losses at different frequencies?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From test pool question: T9B10&lt;/p&gt;&#xA;" OwnerUserId="185" LastEditorUserId="185" LastEditDate="2013-11-20T18:07:51.330" LastActivityDate="2013-11-20T18:47:41.527" Title="What are the electrical differences between smaller and larger coaxial cables?" Tags="&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="766" PostTypeId="1" AcceptedAnswerId="776" CreationDate="2013-11-19T17:51:07.607" Score="5" ViewCount="417" Body="&lt;p&gt;Why is coaxial cable the most common feedline in use? What are the advantages/ disadvantages of coax compared to other feedline types?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From test pool question: T9B03&lt;/p&gt;&#xA;" OwnerUserId="185" LastActivityDate="2013-11-19T20:16:57.553" Title="Why is coax the most common feedline?" Tags="&lt;feed-line&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="767" PostTypeId="1" AcceptedAnswerId="771" CreationDate="2013-11-19T17:57:21.263" Score="3" ViewCount="533" Body="&lt;p&gt;I've heard that &quot;rubber duck&quot; antennas shouldn't be used inside an automobile. What is the reason for this, and are there any other types of antennas that shouldn't be used inside a vehicle?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From test pool question: T9A07&lt;/p&gt;&#xA;" OwnerUserId="185" LastActivityDate="2013-11-19T19:24:01.927" Title="Are there any antennas I shouldn't use in my car?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="768" PostTypeId="1" AcceptedAnswerId="786" CreationDate="2013-11-19T18:07:04.993" Score="6" ViewCount="1009" Body="&lt;p&gt;Why do signals from satellites experience &quot;spin fading&quot; as the satellite rotates? What are the effects that spin fading has on a radio signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From test question: T8B09&lt;/p&gt;&#xA;" OwnerUserId="185" LastEditorUserId="185" LastEditDate="2013-11-19T19:43:15.127" LastActivityDate="2013-11-20T11:26:00.993" Title="What is spin fading in satellite signals?" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="769" PostTypeId="1" AcceptedAnswerId="780" CreationDate="2013-11-19T18:16:04.537" Score="5" ViewCount="4334" Body="&lt;p&gt;Many types of solder are available today, such as acid-core, silver, rosin-core and aluminum solder. What kind should I use for building antennas and radio equipment? Why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From test question: T7D08&lt;/p&gt;&#xA;" OwnerUserId="185" LastActivityDate="2019-03-02T16:20:49.760" Title="What type of solder is best suited for radio and electronic use?" Tags="&lt;antenna&gt;&lt;feed-line&gt;&lt;diy&gt;&lt;wire-antenna&gt;&lt;antenna-construction&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="770" PostTypeId="1" AcceptedAnswerId="785" CreationDate="2013-11-19T18:47:43.560" Score="4" ViewCount="158" Body="&lt;p&gt;What can happen if I don't properly ground my equipment?&lt;/p&gt;&#xA;" OwnerUserId="185" LastActivityDate="2013-11-20T11:10:46.850" Title="What are the consequences of poor station grounding?" Tags="&lt;grounding&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="771" PostTypeId="2" ParentId="767" CreationDate="2013-11-19T19:24:01.927" Score="5" Body="&lt;p&gt;There's nothing particularly wrong with them. Cars, being mostly made of metal, do a pretty good job of shielding any RF signals, which is why you probably get worse reception when your HT is in your car. It doesn't help that rubber duck antennas aren't that good to start with - they are &quot;electrically short&quot;, meaning that they are shorter than a true quarter wavelength, and they are monopoles, meaning that there is no &quot;counterpoise&quot; or &quot;ground return&quot; like in a dipole antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rubber duck antennas just perform worse than an ideal antenna, especially in a car. But that said, that hasn't stopped me from using my Wouxun with a rubber duck from inside my car, or a Motorola HT from inside an ambulance without any problems. Nothing terribly bad will happen, it's just not as good as using a real mobile radio with a real mobile antenna mounted to the roof of your car.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-11-19T19:24:01.927" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="772" PostTypeId="2" ParentId="763" CreationDate="2013-11-19T19:32:00.003" Score="4" Body="&lt;p&gt;Usually, the answer is no. While modulation may affect the acceptable Signal to Noise ratio, allowing a given signal to be received from further away or in worse conditions than a different modulation, that happens at the receiver, the propagation is the same. The only factors of a radio wave that affect propagation, once it's in the air, are the field strength, frequency, and polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only slight wrinkle in this that I can think of has to do with multipath distortion. Multipath distortion happens when signals are reflected by multiple surfaces and take more than one path from transmitter to receiever, of different lengths. Radio waves move at about $3*10^8 m/s$, so if one path is $35cm$ longer than another, and the radio wave is at $440MHz$ (with a $70cm$ wavelength), then they will arrive and cancel out perfectly. The modulation can affect this somewhat - but not by very much - simply because a CW signal has a much tighter bandwidth and is affected much more uniformly by multipath distortion than a very wide band (or even frequency-hopping) signal would.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-11-19T19:32:00.003" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="773" PostTypeId="2" ParentId="746" CreationDate="2013-11-19T19:44:27.307" Score="5" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Near_Vertical_Incidence_Skywave&quot; rel=&quot;noreferrer&quot;&gt;Near Vertical Incidence Skywave (NVIS)&lt;/a&gt; is already pretty well defined in both radius and antenna height by definition.  The antenna achieves best performance no more than 1/4 wavelength above the ground, and typically reaches receivers 50km-650km (30-400 miles) away.  It isn't going to help you out much with receivers 1000-2000km away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately there isn't a single, simple, good calculation for antenna height vs transmission distance, which is why so many antenna modeling packages exist.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll get line of sight at close distances, which uses one equation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can get groundwave propagation distances further out with another equation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Skywave and NVIS propagation distances will get you even further which each have their own calculations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna modeling package takes into account all these various radiation modes, and can account for many other factors to bring you to a reasonable decision.  You might not want to use one, but they were actually created to make this problem simpler to solve.  Doing it by hand is more difficult, but can be rewarding if you want to learn more about propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest answer is that the &quot;ideal&quot; height for an antenna at these frequencies is 1/2 wavelength - but even there &quot;ideal&quot; depends on whether you want optimum ground reflection.  If you can't get your 3.5MHz antenna 140 feet in the air, though, then &quot;as high as you can&quot; is the ideal height.  Technically this is actually shifted up a little bit - &lt;a href=&quot;http://www.voacap.com/antennas/squeezing-decibels-out-of-dipole/&quot; rel=&quot;noreferrer&quot;&gt;the ideal height is 0.6 wavelengths above the ground, and every additional half wavelength thereafter&lt;/a&gt; (1.1wl, 1.6wl, etc).&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-11-19T19:44:27.307" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="774" PostTypeId="1" AcceptedAnswerId="783" CreationDate="2013-11-19T19:58:51.767" Score="10" ViewCount="480" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/MIMO&quot;&gt;MIMO, Multiple Input, Multiple Output&lt;/a&gt;, is used widely in commercial data transmission.  802.11n and LTE devices use it to increase throughput, link reliability, and channel usage without increasing transmission power or using more bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While there are many examples of Amateur Radio enthusiasts building and used phased arrays, I haven't found any examples of MIMO use in the Amateur Radio community.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there good reasons MIMO isn't used in Amateur Radio?&#xA;Are there examples of Amateur Radio enthusiasts building and experimenting with MIMO systems?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems that the increasing adoption of &lt;a href=&quot;http://en.wikipedia.org/wiki/Software-defined_radio&quot;&gt;SDR&lt;/a&gt; and the continued interest in &lt;a href=&quot;http://en.wikipedia.org/wiki/QRP_operation&quot;&gt;QRP&lt;/a&gt; would lead some down this path, but I haven't found any information about it in the Amateur community.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-11-19T20:04:00.133" LastActivityDate="2017-06-14T09:06:45.700" Title="Using MIMO in Amateur Radio?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;mimo&gt;&lt;phased-array&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="775" PostTypeId="1" AcceptedAnswerId="777" CreationDate="2013-11-19T20:13:35.887" Score="9" ViewCount="133" Body="&lt;p&gt;Is it possible to transmit a signal around the world and receive it?  Has anyone done it, and how?  If not, how could this be accomplished? Assuming a complete path around the world, what kind of time delay should one expect on their transmission?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-11-19T20:32:08.537" Title="Around the world propagation?" Tags="&lt;propagation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="776" PostTypeId="2" ParentId="766" CreationDate="2013-11-19T20:16:57.553" Score="4" Body="&lt;p&gt;At most amateur radio frequencies, there are really only two feedline types that are readily available and effective:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Twin-lead&quot; rel=&quot;nofollow noreferrer&quot;&gt;twin-lead&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Coaxial_cable&quot; rel=&quot;nofollow noreferrer&quot;&gt;coaxial&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The goal of the feedline is to move electromagnetic energy from one end to the other without much loss. This means not absorbing it, and not radiating it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not absorbing EM energy is pretty easy. Use good conductors, like copper, and low-loss dielectrics, like PTFE or air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not radiating is harder. EM energy consists of electric and magnetic fields that &lt;em&gt;want&lt;/em&gt; to radiate. You have to somehow have fields in the cable (because this is the energy you want to move) but not everywhere else. So you somehow have to make opposing fields that cancel each other everywhere outside your feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Twin-lead does this in a pretty simple way: because each of the conductors carry equal and opposing currents (&lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;or it should, if the station is operating properly&lt;/a&gt;), they make equal and opposing fields. If you are far away from the cable, then the two conductors are close enough together that they mostly cancel each other out. There is no field far away from the cable, i.e., it doesn't radiate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is also the problem with twin-lead. If there is a significant difference between the distances to the two conductors, then you aren't far enough away for the fields to have canceled. If you are a conductive material, your charges will be pushed around by these fields, and you will alter the electrical properties of the cable, and your own electrical properties will be altered. If you are, for example, another feedline, your signal will be coupled with the signal in the other feedline. Further, the &lt;a href=&quot;http://en.wikipedia.org/wiki/Characteristic_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;characteristic impedance&lt;/a&gt; of each feedline will likely be altered, making it harder to match to the transmitter, resulting in a poor SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consequently, when installing twin-lead, one must mount the feedline in such a way that it doesn't come close (relative to the spacing of the conductors) to anything conductive. Usually this means running it up the tower and into the shack with stand-offs:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/SaxOa.gif&quot; alt=&quot;twin-lead standoff&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;(from &lt;a href=&quot;http://www.starkelectronic.com/cmig7.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Stark Electronic&lt;/a&gt;)&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, this can be a real pain. How do you get it through the wall? What if there are two antennas on the tower? What if you have a rotator? What if it snows?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coax solves this problem. The shield acts as a &lt;a href=&quot;http://en.wikipedia.org/wiki/Faraday_cage&quot; rel=&quot;nofollow noreferrer&quot;&gt;Faraday cage&lt;/a&gt;, entirely containing the electric field between the shield and the center conductor. Thus, coax can be installed directly on a tower, bundled with other coax feedlines, or buried without significantly altering its properties. The disadvantage is a higher cost, as the coax geometry is more difficult to manufacture, and requires more copper.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-11-19T20:16:57.553" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="777" PostTypeId="2" ParentId="775" CreationDate="2013-11-19T20:32:08.537" Score="6" Body="&lt;p&gt;It's possible on HF (and below), and people have done it. It takes some combination of:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;high power transmitter&lt;/li&gt;&#xA;&lt;li&gt;sensitive receive antenna&lt;/li&gt;&#xA;&lt;li&gt;directional antenna(s)&lt;/li&gt;&#xA;&lt;li&gt;quiet RF location&lt;/li&gt;&#xA;&lt;li&gt;lucky propagation conditions&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In this case, the path is (roughly) any great circle around earth, so the distance is the Earth's circumference. The signal moves at the speed of light, so we can &lt;a href=&quot;http://www.wolframalpha.com/input/?i=circumference%20of%20the%20earth%20at%20the%20speed%20of%20light&quot; rel=&quot;nofollow noreferrer&quot;&gt;ask Wolfram Alpha for &quot;circumference of the Earth at the speed of light&quot;&lt;/a&gt; and get&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{24901.47\text{mi}}{c} \approx 134 \text{ milliseconds} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course there are less spectacular ways to communicate around the world:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/707/218&quot;&gt;store-and-forward amateur satellites&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;linked VHF / UHF repeaters (example: &lt;a href=&quot;http://www.echolink.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EchoLink&lt;/a&gt;)&lt;/li&gt;&#xA;&lt;li&gt;traffic nets&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-11-19T20:32:08.537" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="778" PostTypeId="2" ParentId="763" CreationDate="2013-11-19T22:58:08.093" Score="8" Body="&lt;p&gt;It depends on what you mean by &lt;em&gt;propagation&lt;/em&gt;. If you mean, &lt;em&gt;does the modulation scheme affect the physical means by which EM energy gets from point A to point B?&lt;/em&gt;, then the answer is &lt;em&gt;no&lt;/em&gt;. Mostly, EM propagation is &lt;a href=&quot;http://en.wikipedia.org/wiki/Linear_system&quot; rel=&quot;nofollow noreferrer&quot;&gt;linear&lt;/a&gt;, so the differences in modulation have little effect on how the wave propagate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you expand &lt;em&gt;propagation&lt;/em&gt; to include the intelligibility of the signal at the other end, modulation can make a very big difference. Though propagation can practically be considered linear, it is not &lt;a href=&quot;http://en.wikipedia.org/wiki/Time-invariant_system&quot; rel=&quot;nofollow noreferrer&quot;&gt;time-invariant&lt;/a&gt;. On VHF and UHF it's common for the transmitter or receiver to be moving. At HF, the ionosphere constantly changes, significantly altering propagation. Across all the amateur frequencies, there are properties about the radio channel that vary with time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Different modulation schemes may be more or less robust against the disruptions encountered in practical RF channels. For example, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency-division_multiplexing&quot; rel=&quot;nofollow noreferrer&quot;&gt;frequency division multiplexing&lt;/a&gt; used in &lt;a href=&quot;https://freedv.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV&lt;/a&gt; provides good robustness against &lt;a href=&quot;http://en.wikipedia.org/wiki/Comb_filter&quot; rel=&quot;nofollow noreferrer&quot;&gt;comb filtering&lt;/a&gt; caused by &lt;a href=&quot;http://en.wikipedia.org/wiki/Multipath_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;multipath propagation&lt;/a&gt;. It also provides &lt;a href=&quot;http://en.wikipedia.org/wiki/Forward_error_correction&quot; rel=&quot;nofollow noreferrer&quot;&gt;forward error correction&lt;/a&gt; for additional robustness. This is why FreeDV can transmit a 1275 bit/s voice codec with better reliability and less bandwidth than 300 baud &lt;a href=&quot;http://en.wikipedia.org/wiki/Frequency-shift_keying&quot; rel=&quot;nofollow noreferrer&quot;&gt;FSK&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The differences among analog modulation schemes are less complex, but they still exist. CW works well for communication under adverse conditions because all of the transmitter power is focused in a very narrow carrier. On the other hand, AM spreads this same transmitter power over a wider bandwidth, and in that same bandwidth there is more noise the transmitter must overcome. Thus the principal advantage of SSB: it eliminates power wasted in the carrier and the 2nd sideband which carry no information. Furthermore, the &lt;a href=&quot;http://en.wikipedia.org/wiki/Wetware_%28brain%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;wetware&lt;/a&gt; that decodes the baseband signal in analog modulation schemes is much better at detecting the pure tone of CW vs. the complex sound of a human voice in AM or SSB.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-04-11T12:21:02.443" LastActivityDate="2018-04-11T12:21:02.443" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="779" PostTypeId="2" ParentId="5" CreationDate="2013-11-19T23:59:18.040" Score="2" Body="&lt;p&gt;I've just sat my Foundation License on Sunday. It really depends what license you want to go for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have no knowledge of radio (and to a lesser degree, electronics), you may want to start with the Foundation license.  It's the easiest one to get.  To get it, buy a copy of the Foundation License Manual and study it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.wia.org.au/licenses/foundation/foundationmanual/&quot; rel=&quot;nofollow&quot;&gt;https://www.wia.org.au/licenses/foundation/foundationmanual/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then when you reckon you know it all, sit a few of the practice theory exams:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.wia.org.au/licenses/foundation/trialexam/&quot; rel=&quot;nofollow&quot;&gt;http://www.wia.org.au/licenses/foundation/trialexam/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may even be worth while to go to a local radio club to see if they can show you the practical side of things (how to set up a radio and configure it for transmitting etc).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you feel confident enough, book in with one of the assessors that PearsonArtPhoto listed above.  It'll be a two day course most likely.  The first day and half is pretty much covering everything in the Manual.  Then they'll sit you down, do the practical side of the test, then do the theory (25 question multiple choice, only need 70% to pass).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Congrats, you've got your Foundation license!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to sit for your Standard or Advanced license, you will need to know a lot more about radios (and electronics as well, since you are allowed to build and modify equipment on a Standard or Advanced license).  The two ways of doing it are&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1 - Book in with a local club who are teaching these courses (not every radio club have people available to teach these two license grades).  These courses normally go for 1 day a week for 6 months before they reckon you are good enough to sit the test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2 - Go to &lt;a href=&quot;http://www.res.net.au/&quot; rel=&quot;nofollow&quot;&gt;Ron Bertrands radio school website&lt;/a&gt;. Order the Standard or Advanced license kit, do all the paper work, sit the trial exams and then book in for the exams.  This option can be done at your own pace.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only problem with going straight for your Standard or Advanced license is you will still need to sit the practical part of the exam.  Still may be a good idea to have a talk with a local radio club to see if you can sit down with a tutor (if they have one available) to show you the proper way of doing things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you sit the Foundation license exam and practical first, you will never have to do the practical again afterwards even if you upgrade to the Standard or Advanced license in the future.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a friend of mine who designs circuit boards for a living.  He's going straight for his Advanced license but still came down to my radio club to get a hands on for the practical side of things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Out of curiosity, which state are you in? I'm in NSW, so I can give you further details if you require it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT - Forgot to add, the licenses don't vary from state to state.  It is an Australian wide certification.  If you move states permanently, you will have to change callsigns as they are dependant on state (VK2 callsigns are NSW, VK1 is ACT, VK0 is Antartica!) &lt;/p&gt;&#xA;" OwnerUserId="404" LastEditorUserId="6675" LastEditDate="2016-06-03T12:54:19.733" LastActivityDate="2016-06-03T12:54:19.733" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="780" PostTypeId="2" ParentId="769" CreationDate="2013-11-20T00:47:45.997" Score="5" Body="&lt;p&gt;First of all, acid-core solder is never used for electronics any more, that just isn't what it's for. I think it's still used for plumbing or other soldering where there aren't sensitive components involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, aluminum solder isn't a thing. The best I can find is that there's some solder specifically for soldering aluminum to other stuff, but you shouldn't use that for electronics soldering either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By silver solder, I can only assume you mean lead-free solder, which also contains silver. That's fine, as is standard lead-tin solder. Rosin-core solder can be either tin-lead or lead-free, it just has a core of flux which helps to remove the oxidization on the surface of components for better soldering.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-11-20T00:47:45.997" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="782" PostTypeId="2" ParentId="761" CreationDate="2013-11-20T03:51:25.030" Score="4" Body="&lt;p&gt;&lt;a href=&quot;http://www.engadget.com/2013/01/15/runbo-x5-x3-x1/&quot; rel=&quot;nofollow&quot;&gt;Yes indeed!&lt;/a&gt; Legally, you can only use these if you're a part 90 operator, or a ham, just like the Baofeng/Wouxun/Chinese radios, and the cellular side works as an unlocked phone. &lt;/p&gt;&#xA;" OwnerUserId="392" LastActivityDate="2013-11-20T03:51:25.030" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="783" PostTypeId="2" ParentId="774" CreationDate="2013-11-20T04:25:32.523" Score="7" Body="&lt;p&gt;There are a few radios that support diversity reception, but only to minimize effects of propagation rotation and multipath, not to increase data rates. This isn't true MIMO. It's more like SISO where the input is whichever one of two antennas has the strongest signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which brings up another point - data. There really isn't that much data being used on ham radio at the moment. D-STAR is around, then Yaesu came out with a digital radio, and a lot of work is being done on things like Codec2 and FreeDV, but in general, it's not all that prolific. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, MIMO in ham radio will still be reserved to things like HSMM and HamWan that actually have very large bandwidths. With that, the equipment is off-the-shelf. Some of it has MIMO capability, like 802.11N routers modified for use on amateur frequencies - just like you mentioned in your post. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be cool to have MIMO on lower bitrate and digital voice, but I don't think the gains would be that great.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do undergrad research in statistical channel precoding using SDR MIMO transceivers on amateur bands, and man, is it cool...but people don't have $40,000 to spend on a MIMO IQ vector generator/demodulator. I have yet to see a QRP MIMO homebrew rig, but that would be great! &lt;/p&gt;&#xA;" OwnerUserId="392" LastActivityDate="2013-11-20T04:25:32.523" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="784" PostTypeId="1" CreationDate="2013-11-20T09:05:47.453" Score="8" ViewCount="399" Body="&lt;p&gt;I noticed this after updating fldigi to decode a Voice of America Radiogram. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only thing I could find in the &lt;a href=&quot;http://www.w1hkj.com/downloads/fldigi/fldigi_changes.txt&quot;&gt;fldigi changelog&lt;/a&gt; was this: &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;MFSK HF Long Modes&#xA; * Added MFSK64L and MFSL128L new modes&#xA; * 6.25 Second interleaver for very-robust HF reception&#xA; * Assigned new RSIDs&#xA; * Mode MFSK-64L : 1026&#xA; * Mode MFSK-128L : 1029&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Is the 6.25s interleaver all that has changed? What does this mean explicitly? &lt;/p&gt;&#xA;" OwnerUserId="392" LastEditorUserId="9450" LastEditDate="2019-07-04T15:39:27.643" LastActivityDate="2019-07-04T15:39:27.643" Title="What is the difference between MFSK64 and MFSK64L?" Tags="&lt;digital-modes&gt;&lt;fldigi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="785" PostTypeId="2" ParentId="770" CreationDate="2013-11-20T11:10:46.850" Score="3" Body="&lt;p&gt;There are several &quot;ground&quot; issues for a station. Lightning ground from your antenna(e), and antenna ground plane are two on the outdoors. I assume your question is about the grounding within the shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Safety - a power ground will protect the operator from electrical (high voltage) malfunctions. Simply put, a ground to the &quot;third pin&quot; on the outlet or a convenient cold water pipe could save one from a nasty electrical shock if something malfunctions catastrophically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RFI - this one is a little more complex. Depending on your feedline, antenna and outside grounding; you may get RF riding back into the shack. A good RF ground can prevent many of the RF interference and RF burns issues within the shack. What makes a good RF ground? You could ask ten operators and get a different answer from each. Some believe the electrical ground will suffice. Some believe a separate ground to an outside grounding rod is necessary. Yet others believe multiple ground paths are required. And there are some that do NOT use any ground as they believe it simply provides RF and lightning a path through the shack. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regardless of the myriad of opinions, a &quot;ground&quot; of any kind within the shack is always a good safety measure to protect against power supply failures or other high voltage accidents, at the very least.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2013-11-20T11:10:46.850" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="786" PostTypeId="2" ParentId="768" CreationDate="2013-11-20T11:26:00.993" Score="7" Body="&lt;p&gt;Take the simplest case of a VHF dipole receiving antenna on board a spin stabilized satellite.  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;-----------O-------------   Here is the satellite now.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;\&#xA; \ &#xA;  \&#xA;   \&#xA;    \&#xA;     O                       and here is is a bit later&#xA;      \&#xA;       \&#xA;        \&#xA;         \&#xA;          \&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;As the satellite spins, the dipole rotates, and the resulting polarization of the dipole also rotates.  For instance it may go from horizontal polarization to vertical and back again.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you transmit to the satellite with a horizontal or vertical polarized yagi, your transmit yagi will sometimes have the same polarization as the receive at the satellite and sometimes it will not.  When the polarizations are different there can be cross polarization loss of up to 20-30db.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the phenomena behind spin fading. It can be corrected by using circular polarization at the transmitting or receiving location or both.  The loss of a linear polarization antenna from/to a circular one is about a constant 3db over the case where both of the antennas are circular polarized, and because it is constant it is not affected by spin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a couple of loose polarized sunglass lenses, you can place them against each other and rotate one of them while keeping the other stationary, you will see a similar effect with the variable attenuation of light travelling through the pair of lenses.&lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2013-11-20T11:26:00.993" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="787" PostTypeId="1" AcceptedAnswerId="792" CreationDate="2013-11-20T12:01:18.843" Score="10" ViewCount="1720" Body="&lt;p&gt;Can anyone give me some insight into the different &lt;a href=&quot;http://www.buddipole.com/&quot;&gt;Buddipole&lt;/a&gt; models available? They look pretty similar to me except for the sizes. What would make you choose one over the other?&lt;/p&gt;&#xA;" OwnerUserId="135" LastEditorUserId="218" LastEditDate="2013-11-20T14:59:08.073" LastActivityDate="2013-11-20T16:33:21.007" Title="Buddipole model comparison" Tags="&lt;antenna&gt;&lt;mobile&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="788" PostTypeId="2" ParentId="787" CreationDate="2013-11-20T13:15:33.507" Score="3" Body="&lt;p&gt;All of the buddipoles appear to be electrically the same antenna. The mini takes the two longest parts and puts a joint in the middle, so instead of having two 22&quot; parts, you have four 11&quot; parts, so it's a little more portable. The deluxe is the same antenna, it just comes with some more options - a tripod, one of two heights of mast, and some spare parts. The regular buddipole doesn't come with any of that, you'd need to mount it yourself or buy the other parts separately - but all their buddipole kits have the same antenna characteristics.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-11-20T13:15:33.507" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="789" PostTypeId="1" CreationDate="2013-11-20T15:16:10.897" Score="7" ViewCount="99" Body="&lt;p&gt;XLR microphone cables, for example, make use of the dual channels out of phase to cancel noise by injecting the inverted and non-inverted signal into one end of the cable. Then any noise injected along the way will presumably be equal, and re-inverting the signal at the other end negates the noise. Since the AM sidebands are opposite, does a similar principle come into play?&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-11-20T22:32:21.920" Title="Does AM demodulation make use of the redundant information in both sidebands to eliminate noise?" Tags="&lt;modes&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="790" PostTypeId="2" ParentId="784" CreationDate="2013-11-20T15:25:20.690" Score="5" Body="&lt;p&gt;Yes, that's all that's changed. MFSK uses &lt;a href=&quot;http://en.wikipedia.org/wiki/Forward_error_correction&quot; rel=&quot;noreferrer&quot;&gt;forward error correction&lt;/a&gt;, a technique of adding redundant information to the transmitted data so that if some of it is lost, it can be reconstructed from the redundant data. Because errors tend to happen in bursts (static crashes, fast fading, etc), it's common for FEC schemes to also use &lt;a href=&quot;http://en.wikipedia.org/wiki/Forward_error_correction&quot; rel=&quot;noreferrer&quot;&gt;interleaving&lt;/a&gt;, which takes the bits to be transmitted and spreads them out over time. This way, if a burst of noise causes a string of bits to be mangled, after de-interleaving they won't be consecutive bits, thus the FEC will have a better chance of correcting the error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On HF, long interleaving can be especially useful. The ever-changing ionosphere can make phase cancellations that come and go with a period of seconds. If the interleaving is done over long periods (in this instance, 6.25s), then this doesn't matter so much. To the decoder, it looks not as if the signal is fading and recovering, but just that the bit error rate is increased uniformly everywhere. As long as the FEC encodes enough redundancy, the message is still successfully decoded. The cost is increased latency: the transmission can't possibly be complete until 6.25s after the entire message is available. Rather annoying for conversations. Contrast with &lt;a href=&quot;http://aintel.bi.ehu.es/psk31.html&quot; rel=&quot;noreferrer&quot;&gt;PSK31&lt;/a&gt;, which has no FEC, and no interleaving, so each character is transmitted as soon as it is typed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to dive into the &lt;em&gt;really specific&lt;/em&gt; details, &lt;a href=&quot;http://www.arrl.org/mfsk-spec&quot; rel=&quot;noreferrer&quot;&gt;ARRL specifies the interleaving for MFSK&lt;/a&gt; as &quot;self-synchronizing, based on 10 concatenated 4 × 4 bit &lt;a href=&quot;http://www.qsl.net/zl1bpu/MFSK/Interleaver.htm&quot; rel=&quot;noreferrer&quot;&gt;IZ8BLY diagonal interleavers&lt;/a&gt;.&quot; You can also consult the &lt;a href=&quot;http://www.w1hkj.com/downloads/fldigi/fldigi-3.21.77.tar.gz&quot; rel=&quot;noreferrer&quot;&gt;Fldigi source code&lt;/a&gt;, or &lt;a href=&quot;http://git.berlios.de/cgi-bin/gitweb.cgi?p=fldigi;a=commitdiff;h=45fc67910e3d90264e29a898ef2e1ca9ffdfb371&quot; rel=&quot;noreferrer&quot;&gt;browse the particular commit responsible on Berlios&lt;/a&gt;. Comparing two modes in &lt;a href=&quot;http://git.berlios.de/cgi-bin/gitweb.cgi?p=fldigi;a=blob;f=src/mfsk/mfsk.cxx;h=e3a1f77adc30fdfff4fd3307078b09c9eada78ff;hb=45fc67910e3d90264e29a898ef2e1ca9ffdfb371#l206&quot; rel=&quot;noreferrer&quot;&gt;mfsk.cxx&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;case MODE_MFSK64:&#xA;        samplerate = 8000;&#xA;        symlen =  128;&#xA;        symbits =    4;&#xA;        depth = 10;&#xA;        basetone = 16;&#xA;        numtones = 16;&#xA;        preamble = 180;&#xA;        cap |= CAP_IMG;&#xA;        break;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;[...]&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;case MODE_MFSK64L:&#xA;        samplerate = 8000;&#xA;        symlen =  128;&#xA;        symbits =    4;&#xA;        depth = 400;&#xA;        preamble = 2500;&#xA;        basetone = 16;&#xA;        numtones = 16;&#xA;        break;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;we can see the two differ in just a few parameters.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-11-20T15:38:27.410" LastActivityDate="2013-11-20T15:38:27.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="791" PostTypeId="2" ParentId="789" CreationDate="2013-11-20T15:47:46.300" Score="4" Body="&lt;p&gt;No, not really. By essentially transmitting the same information twice (two sidebands), you'd think there would be more information there about the signal. But, the transmitter's power is divided between these two sidebands, so each has less transmitter power behind it. Also, in this additional bandwidth, there is more noise. Since the &lt;a href=&quot;http://en.wikipedia.org/wiki/Noise_spectral_density&quot; rel=&quot;nofollow&quot;&gt;noise spectral density&lt;/a&gt; is roughly the same everywhere, more receive bandwidth necessarily means more noise received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, not a small part of the power transmitted in AM is in the carrier, which has no information about the signal at all in it. This is a poor use of available transmitter power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are the reasons behind the development of &lt;a href=&quot;http://en.wikipedia.org/wiki/Single-sideband_modulation&quot; rel=&quot;nofollow&quot;&gt;SSB&lt;/a&gt;. SSB beats AM in almost every respect. It requires less spectrum for the same information, and makes better use of transmitter power. Because more of the transmitter's power can go into useful signal, this increases the signal to noise ratio. The disadvantage is in the more complex electronics required of the receiver and transmitter. The lack of a carrier also makes tuning more difficult: if the receiver and transmitter are not tuned to the same frequency, the sound of the received voice is shifted up or down in pitch, making a weird, inhuman sound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Interestingly, although more difficult to implement electronically, SSB is simpler conceptually. USB is simply all the frequency components of your voice, shifted up to the desired frequency. LSB is the same thing, with the whole thing flipped left-for-right, if you were to view it on a spectrograph. To &quot;demodulate&quot; it, just shift them back down. Though this is difficult to realize with discrete electronics, it's actually trivial in an SDR.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-11-20T22:32:21.920" LastActivityDate="2013-11-20T22:32:21.920" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="792" PostTypeId="2" ParentId="787" CreationDate="2013-11-20T16:33:21.007" Score="6" Body="&lt;p&gt;I own some of Buddipole products.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Buddipole is really a system rather than a product per say.  It's based around being able to create an effective antenna that is both portable and has flexibility for configuration.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The real heart of the system is the VersaTee and the fact that all the parts for all the products use the same size threaded connector.  All the pieces are made light for portability and the sizes are such that you can construct a variety of &lt;em&gt;effective&lt;/em&gt; antennas based on your situation.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a more typical product, you have, say, a portable 10m dipole, period.  With any of the three main Buddipole packages, you have the parts to make a number of types of antennas: vertical, dipole, even a yagi (with a few extra parts) on any of the ham bands (except 160m).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So really before answering the question of which one to buy, you have to identify how you are going to use it and what bands you plan to work.  I really encourage you to download and read the free book &lt;a href=&quot;http://lib.store.yahoo.net/lib/buddipole/buddipoleinthefield2.pdf&quot;&gt;Buddipole in the Field&lt;/a&gt; by NE1RD.  It's great.  This guy took the Buddipole system through about every conceivable configuration and measured the results.  Each section ends with a &quot;cookbook&quot; show the best recipe for each band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For my needs, I wanted to operate portable (SOTA) on 10m, 15m &amp;amp; 20m.  So, using the information in the book, I bought the 8' mast, the VersaTee, the Coax and the radial connectors.  I didn't need the coils or the tripod, so I saved a ton of money versus the deluxe package.  For the radiator, I used the MFJ 17' telescoping whip, which is full sized for 20m (and of course on 10, 12 and 15 by retracting some of it).  I used the radial connectors to connect 4 elevated radials to the sides of the VersaTee, two off each side.  These are supported at the ends by 2' fiberglass rods (former 4' driveway markers, $1.99@).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Packed up for the trip, the whip sides into the hollow center of the mast and the 4 2' rods are strapped to that making a nice compact bundle.  Everything else is just wire and rope and 3 stakes all of which fits in a large ZipLock bag.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it work?  When I set everything up for 20m in my backyard, I got through to a station  from Venezuala on the second call QRP from suburban Maryland and got a 59 even after telling him my setup.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-20T16:33:21.007" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="794" PostTypeId="5" CreationDate="2013-11-20T18:17:43.317" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-20T18:17:43.317" LastActivityDate="2013-11-20T18:17:43.317" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="795" PostTypeId="4" CreationDate="2013-11-20T18:17:43.317" Score="0" Body="American Radio Relay League (ARRL), the largest association of amateur radio enthusiasts in the USA" OwnerUserId="185" LastEditorUserId="185" LastEditDate="2013-11-20T18:36:32.727" LastActivityDate="2013-11-20T18:36:32.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="796" PostTypeId="5" CreationDate="2013-11-20T18:19:15.510" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-20T18:19:15.510" LastActivityDate="2013-11-20T18:19:15.510" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="797" PostTypeId="4" CreationDate="2013-11-20T18:19:15.510" Score="0" Body="Materials and methods for building antennas, and design of supporting (non-conductive) structures. For design of antennas themselves, use [antenna-theory] instead." OwnerUserId="185" LastEditorUserId="76" LastEditDate="2015-12-16T00:09:25.897" LastActivityDate="2015-12-16T00:09:25.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="798" PostTypeId="1" AcceptedAnswerId="811" CreationDate="2013-11-20T18:28:41.903" Score="13" ViewCount="648" Body="&lt;p&gt;Emergency operations are typically reliant on voice traffic today. Are digital data modes used at all in emergency operations, and why/ why not? Couldn't data modes be used to pass information more efficiently than voice?&lt;/p&gt;&#xA;" OwnerUserId="185" LastEditorUserId="76" LastEditDate="2013-11-20T21:27:28.110" LastActivityDate="2016-12-24T21:25:23.910" Title="What is the role of digital data modes in emergency communications?" Tags="&lt;digital-modes&gt;&lt;emergency&gt;&lt;modes&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="800" PostTypeId="2" ParentId="765" CreationDate="2013-11-20T18:47:41.527" Score="2" Body="&lt;p&gt;There are three basic electrical characteristics: characteristic impedance, loss per unit distance, and velocity factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most amateur radio rigs and antennas expect to see a characteristic impedance of 50 ohms. There is coaxial cable with difference impedances, such as 75 ohms. Attempting to use a 75 ohm coaxial cable with a rig expecting to see 50 ohms of impedance will result in a portion of your transmitted signal being reflected back into the radio (or amplifier). This raises your SWR and will either cause your radio to decrease (fold back) its power (if it's a newer rig), or can cause your final amplifier to heat up faster than it should and can burn it out. (Don't get confused - characteristic impedance is measured in ohms, but it isn't measured with a multimeter. This has nothing to do with resistive power loss, it has to do with the ratio between voltage and current of a wave on that cable.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Loss per unit distance is the big one. Generally speaking, the larger the cable, the lower the loss - but it also depends on frequency. Higher frequencies typically result in higher loss. This is usually given in decibles per hundred feet, and a value of $3dB/100ft$ means that if you use 100 ft of that coax at that frequency, you'll lose half of your power. If you need to get the loss of a particular cable, or compare two cables, you should get a chart or table from the manufacturer. &lt;a href=&quot;http://www.w4rp.com/ref/coax.html&quot; rel=&quot;nofollow&quot;&gt;This table&lt;/a&gt; lists some common types of coax at a variety of frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Velocity factor isn't something you'll need often. It tells you how fast a wave will propagate along that cable - which you can use if you want to build a phased array, for example. This is where you have two (or more) antennas spaced a certain distance apart, and also delay the signal going to some of the antennas so that they constructively interfere with each other in the direction of the array. It allows you to create a much tighter beam, at the cost of needing more space and supplies.&lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-11-20T18:47:41.527" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="801" PostTypeId="1" AcceptedAnswerId="807" CreationDate="2013-11-20T18:52:00.223" Score="7" ViewCount="354" Body="&lt;p&gt;Does APRS have a limited capacity in terms of beacons? What happens when an APRS frequency experiences a large number of packets?&lt;/p&gt;&#xA;" OwnerUserId="185" LastActivityDate="2013-11-22T20:51:34.377" Title="Is it possible to overload APRS?" Tags="&lt;aprs&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="802" PostTypeId="2" ParentId="789" CreationDate="2013-11-20T18:58:26.203" Score="1" Body="&lt;p&gt;No, they don't.  The key is that while the sidebands are opposites, they are symetrical about the carrier frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The popularity of DSB-AM (broadcast AM) has to do with the capabilities of the receiver.  The simple, early mass-market receivers needed the carrier in order to reproduce undistorted audio on recieve.  More sophisticated receivers can generate the carrier locally and feed that into the mixer.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-20T18:58:26.203" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="803" PostTypeId="5" CreationDate="2013-11-20T19:18:08.220" Score="0" Body="&lt;p&gt;Use this tag when you are asking specifically about the FCC itself in a way which is not covered by either &lt;a href=&quot;/questions/tagged/license&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;license&amp;#39;&quot; rel=&quot;tag&quot;&gt;license&lt;/a&gt; or &lt;a href=&quot;/questions/tagged/legal&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;legal&amp;#39;&quot; rel=&quot;tag&quot;&gt;legal&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If your question is about what amateur radio operators in the United States are allowed to do, use &lt;a href=&quot;/questions/tagged/legal&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;legal&amp;#39;&quot; rel=&quot;tag&quot;&gt;legal&lt;/a&gt; and &lt;a href=&quot;/questions/tagged/united-states&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;united-states&amp;#39;&quot; rel=&quot;tag&quot;&gt;united-states&lt;/a&gt; instead.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If your question is about obtaining and holding an amateur radio license in the United States, use &lt;a href=&quot;/questions/tagged/license&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;license&amp;#39;&quot; rel=&quot;tag&quot;&gt;license&lt;/a&gt; and &lt;a href=&quot;/questions/tagged/united-states&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;united-states&amp;#39;&quot; rel=&quot;tag&quot;&gt;united-states&lt;/a&gt; instead.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="-1" LastEditorUserId="76" LastEditDate="2017-04-16T15:04:20.813" LastActivityDate="2017-04-16T15:04:20.813" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="804" PostTypeId="4" CreationDate="2013-11-20T19:18:08.220" Score="0" Body="Questions about the practices of the Federal Communications Commission (FCC), a US government agency that regulates communications, including amateur radio. For questions not about the FCC per se, use [united-states] and either [license] or [legal] as appropriate, instead." OwnerUserId="185" LastEditorUserId="76" LastEditDate="2017-04-16T15:04:20.813" LastActivityDate="2017-04-16T15:04:20.813" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="805" PostTypeId="5" CreationDate="2013-11-20T19:36:27.737" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-20T19:36:27.737" LastActivityDate="2013-11-20T19:36:27.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="806" PostTypeId="4" CreationDate="2013-11-20T19:36:27.737" Score="0" Body="High-speed multimedia radio (HSMM) includes wireless data networks over amateur radio frequencies using commercially available hardware, such as 802.11 access points" OwnerUserId="185" LastEditorUserId="185" LastEditDate="2013-11-20T19:59:32.227" LastActivityDate="2013-11-20T19:59:32.227" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="807" PostTypeId="2" ParentId="801" CreationDate="2013-11-20T19:50:14.590" Score="5" Body="&lt;p&gt;When two packets are transmitted simultaneously on the APRS frequency in a local area, it is unlikely that either will be understood.  As the packet density in an area increases, the chances that two packets will be transmitted simultaneously increases.  This issue is compounded by the presence of &lt;a href=&quot;http://wiki.argentdata.com/index.php?title=APRS_digipeaters&amp;amp;redirect=no&quot; rel=&quot;noreferrer&quot; title=&quot;description of APRS digipeaters&quot;&gt;digipeaters&lt;/a&gt; which can unintentionally flood an area with packets from a small number of sources.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question then isn't a matter of the number of beacons, but the frequency of packets in a local area.  Given a local area of 2 people where each send a 1 second packet once in a 10 minute interval, there's a 1/600 chance you will overlap with the other station.  Once you get 100 stations together, without getting too much into probability, you can expect to get an APRS packet out a little over once an hour.  &lt;/p&gt;&#xA;" OwnerUserId="394" LastActivityDate="2013-11-20T19:50:14.590" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="808" PostTypeId="1" AcceptedAnswerId="810" CreationDate="2013-11-20T19:54:14.620" Score="6" ViewCount="486" Body="&lt;p&gt;Amateur television has long used the NTSC (analog) television standards to transmit video and audio. Several years ago, the digital broadcast television transition made higher-quality television signals possible. Can amateurs acquire and use digital television (ATSC or DVB) transmission equipment?&lt;/p&gt;&#xA;" OwnerUserId="185" LastEditorUserId="8832" LastEditDate="2018-03-08T01:01:59.340" LastActivityDate="2018-03-08T01:01:59.340" Title="Is it possible for an amateur to transmit ATSC?" Tags="&lt;digital-modes&gt;&lt;modes&gt;&lt;atv&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="809" PostTypeId="1" AcceptedAnswerId="813" CreationDate="2013-11-20T20:40:43.060" Score="13" ViewCount="2052" Body="&lt;p&gt;What is preventing a software-defined radio from transmitting the D-Star protocol?&lt;/p&gt;&#xA;" OwnerUserId="178" LastEditorUserId="76" LastEditDate="2014-09-25T23:09:57.490" LastActivityDate="2015-03-08T21:26:22.503" Title="Is is possible to operate D-Star from a software-defined radio?" Tags="&lt;modes&gt;&lt;software-defined-radio&gt;&lt;digital-voice&gt;&lt;d-star&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="810" PostTypeId="2" ParentId="808" CreationDate="2013-11-20T21:06:06.590" Score="7" Body="&lt;p&gt;FCC Regulations, Title 97.307(f)(8) says yes, you can transmit with ATSC modulation in the US, BUT you can't use frequencies which match US ATSC channels. You would need to find a receiver (maybe PC controlled?) flexible enough to  listen to amateur frequencies.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to DVB-T or DVD-S, well, they'll work with about 2MHz of bandwidth instead of the 6MHz slice required for ATSC. Again, a flexible receiver is called for.&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-11-20T21:06:06.590" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="811" PostTypeId="2" ParentId="798" CreationDate="2013-11-20T21:10:51.633" Score="6" Body="&lt;p&gt;In the US, disaster declarations need to be approved and that declaration with approval must be transmitted to a state EOC before state aid can be approved. Therefore, early in the game, packet has become popular to get that declaration to the state capital.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although HIPPA does not apply to amateur radio (as operators are not healthcare providers), there's still a great desire not to reveal names and other details of aid recipients. Packet and other modes provide 'security through obscurity' and are more popular in sending long lists of data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some places need to survey vulnerable infrastructure, and a ham with digital camera capability can deliver pictures back to where the Internet works so engineers can look at, say, a dam face, or a bridge support. Just had an exercise last month where hams on mountain bikes were asked to offroad and do that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://static.danplanet.com/preserve/KK7DS_QST_D-RATS.pdf&quot; rel=&quot;nofollow&quot;&gt;http://static.danplanet.com/preserve/KK7DS_QST_D-RATS.pdf&lt;/a&gt; explains how D-STAR was used in 2007 to improve comms in severe flooding in Western Oregon, about 30 klicks from where I sit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are more examples, but those are the three big ones which come to mind based on my experience with ARES and ARC in disaster.&lt;/p&gt;&#xA;" OwnerUserId="285" LastEditorUserId="285" LastEditDate="2015-08-04T02:55:09.560" LastActivityDate="2015-08-04T02:55:09.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="812" PostTypeId="2" ParentId="809" CreationDate="2013-11-20T21:20:34.413" Score="2" Body="&lt;p&gt;The propretary AMBE codec prevents you from using D-Star for voice. Without that codec, you can't talk over D-STAR. However, you can use the DV Dongle &lt;a href=&quot;http://www.dvdongle.com/DV_Dongle/Home.html&quot; rel=&quot;nofollow&quot;&gt;http://www.dvdongle.com/DV_Dongle/Home.html&lt;/a&gt; to talk with D-Star users over the Internet. &lt;/p&gt;&#xA;" OwnerUserId="285" LastEditorUserId="285" LastEditDate="2013-11-21T00:09:09.970" LastActivityDate="2013-11-21T00:09:09.970" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="813" PostTypeId="2" ParentId="809" CreationDate="2013-11-20T21:30:08.407" Score="16" Body="&lt;p&gt;Nothing is preventing an SDR from transmitting the D-STAR protocol, other than the need to implement it as such. It is open, and currently I know that &lt;a href=&quot;http://www.rtl-sdr.com/rtl-sdr-radio-scanner-tutorial-decoding-digital-voice-p25-with-dsd/&quot;&gt;Digital Signal Decoder (DSD)&lt;/a&gt; can actually decode some data and textual frames. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What prohibits transmission of D-STAR Digital &lt;strong&gt;Voice&lt;/strong&gt; is the codec used to encode the voice - it's &lt;a href=&quot;http://en.wikipedia.org/wiki/Advanced_Multi-Band_Excitation&quot;&gt;AMBE2000&lt;/a&gt;, which is patented and proprietary. A license for one of these is in the ballpark of $100,000, allowing only large businesses to use it. Icom, having already developed P25 hardware using the AMBE codec, is the only one to do so thus far, aside from the DVDongle (though I don't know how they can afford to use it). The reason why AMBE was chosen was because it was the only low-bitrate RF speech codec available at the time.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, if &lt;a href=&quot;http://en.wikipedia.org/wiki/Codec2&quot;&gt;codec2&lt;/a&gt; can be implemented over D-STAR (or its own protocol, like FreeDV), it would be completely open. This is certainly a future development. &lt;/p&gt;&#xA;" OwnerUserId="392" LastActivityDate="2013-11-20T21:30:08.407" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="814" PostTypeId="1" AcceptedAnswerId="832" CreationDate="2013-11-20T21:37:38.950" Score="10" ViewCount="725" Body="&lt;p&gt;Software Defined Radio is opening up many new possibilities for amateur digital modes. One family of technologies that interests me is cellular. 2G GSM voice/sms and 2.5G GPRS data has been proven to work with &lt;a href=&quot;http://openbts.org/&quot;&gt;OpenBTS&lt;/a&gt; on a &lt;a href=&quot;http://www.ettus.com/&quot;&gt;USRP SDR&lt;/a&gt; using licensed cellular bands. Can this technology be used by amateurs? Could an amateur cellular network be deployed sometime in the future?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: I know that there are many small practical considerations to doing this. Cellular technologies are heavily patented, but patents on many older GSM technologies have recently expired. Also, some deployment tweaks will be needed to adhere to amateur regulations, such as disabling encryption. Answers should focus on the fundamentals of amateurs using cellular technologies via sdr and not these small hangups. &lt;/p&gt;&#xA;" OwnerUserId="185" LastEditorUserId="185" LastEditDate="2013-11-20T22:04:44.277" LastActivityDate="2013-11-22T20:42:24.950" Title="Can an amateur use cellular technologies with SDR?" Tags="&lt;digital-modes&gt;&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="815" PostTypeId="5" CreationDate="2013-11-20T21:43:30.843" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-20T21:43:30.843" LastActivityDate="2013-11-20T21:43:30.843" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="816" PostTypeId="4" CreationDate="2013-11-20T21:43:30.843" Score="0" Body="Discussion related to the rtl-sdr project, which enables certain television dongles and other hardware to be used as a cheap SDR receiver" OwnerUserId="185" LastEditorUserId="29" LastEditDate="2014-01-03T21:27:33.250" LastActivityDate="2014-01-03T21:27:33.250" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="817" PostTypeId="5" CreationDate="2013-11-20T21:47:28.640" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-20T21:47:28.640" LastActivityDate="2013-11-20T21:47:28.640" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="818" PostTypeId="4" CreationDate="2013-11-20T21:47:28.640" Score="0" Body="Matters related to amateur radio operation beyond the jurisdiction of a ham's licensing entity." OwnerUserId="185" LastEditorUserId="22" LastEditDate="2013-11-20T22:22:48.987" LastActivityDate="2013-11-20T22:22:48.987" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="819" PostTypeId="2" ParentId="809" CreationDate="2013-11-20T22:17:13.047" Score="6" Body="&lt;p&gt;Nothing. In fact, the &lt;a href=&quot;http://nwdigitalradio.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;UDR56k&lt;/a&gt; is an SDR and transmits D-STAR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want D-STAR digital voice, you do need to &lt;a href=&quot;http://nwdigitalradio.com/products&quot; rel=&quot;nofollow noreferrer&quot;&gt;purchase an add-on card&lt;/a&gt; which contains an &lt;a href=&quot;http://www.dvsinc.com/products/a2000.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;ASIC from DVSI&lt;/a&gt; implementing the propritary &lt;a href=&quot;http://en.wikipedia.org/wiki/Multi-Band_Excitation&quot; rel=&quot;nofollow noreferrer&quot;&gt;AMBE codec&lt;/a&gt;, or pay a substantial (but undisclosed publicly) licensing fee. One can safely assume that any licensing agreement would forbid any free proliferation of the implementation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.dvdongle.com/DV_Dongle/Technical_Info.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;DVDongle&lt;/a&gt; contains the same ASIC, visible here as the large IC on the right, with &quot;AMBE-2000&quot; printed on it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/TQimo.jpg&quot; alt=&quot;DVDongle internals&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The middle IC is at Atmel microcontroller, and the IC on the left looks like an FTDI USB interface. There's not much else to it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-12-30T13:23:35.257" LastActivityDate="2014-12-30T13:23:35.257" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="820" PostTypeId="2" ParentId="109" CreationDate="2013-11-21T00:23:46.590" Score="1" Body="&lt;p&gt;In the United States, major NGOs maintain amateur radio capability; specifically, the American Red Cross &lt;a href=&quot;http://www.redcross.org/find-your-local-chapter&quot; rel=&quot;nofollow&quot;&gt;http://www.redcross.org/find-your-local-chapter&lt;/a&gt; plus the Salvation Army with its North American SATRN network &lt;a href=&quot;http://www.satern.org&quot; rel=&quot;nofollow&quot;&gt;http://www.satern.org&lt;/a&gt; . &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also military affiliated organizations. MARS &lt;a href=&quot;http://www.netcom.army.mil/mars&quot; rel=&quot;nofollow&quot;&gt;http://www.netcom.army.mil/mars&lt;/a&gt; &lt;a href=&quot;http://www.afmars.org/mars1.shtml&quot; rel=&quot;nofollow&quot;&gt;http://www.afmars.org/mars1.shtml&lt;/a&gt; &lt;a href=&quot;http://www.navymars.org/national/mission.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.navymars.org/national/mission.htm&lt;/a&gt; , the Civil Air Patrol &lt;a href=&quot;http://www.gocivilairpatrol.com/&quot; rel=&quot;nofollow&quot;&gt;http://www.gocivilairpatrol.com/&lt;/a&gt; and the USCG Auxiliary &lt;a href=&quot;http://cgaux.org/about.php&quot; rel=&quot;nofollow&quot;&gt;http://cgaux.org/about.php&lt;/a&gt; all need communicators. &lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-11-21T00:23:46.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="821" PostTypeId="2" ParentId="774" CreationDate="2013-11-21T00:27:23.933" Score="1" Body="&lt;p&gt;Broadband Hamnet &lt;a href=&quot;http://hsmm-mesh.org/&quot; rel=&quot;nofollow&quot;&gt;http://hsmm-mesh.org/&lt;/a&gt; right now is focused on 802.11G devices, but it could grow to encompass MIMO in the future.&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-11-21T00:27:23.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="822" PostTypeId="1" AcceptedAnswerId="825" CreationDate="2013-11-21T03:17:37.947" Score="22" ViewCount="514" Body="&lt;p&gt;I'm considering getting a U.S. amateur radio operator license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to &lt;em&gt;study to pass a license test&lt;/em&gt;, there are many resources to learn the answers to the entirety of the question pool: online practice exams and study aids, “ham cram” courses, etc. I came across one document (not quickly finding the link again) which basically takes the entire question pool and rephrases each question into a paragraph which briefly describes the broader topic and gives the question and answer as an example of that topic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I've looked through the question pool, and it seems obvious to me that the questions are not comprehensive; just like any test one might find in school, they are intended to &lt;em&gt;sample&lt;/em&gt; your grasp of a larger body of knowledge. So, where's a copy of the syllabus for “U.S. Amateur Radio 101”?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What topics &lt;em&gt;should&lt;/em&gt; the holder of a Technician, General, or Extra license have knowledge of?&lt;/strong&gt; What would be the content of the question pool if test-takers had infinite patience, and could be tested on every fact rather than a sampling?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, addressing my actual plans: &lt;strong&gt;what topics should I ensure are contained in my study materials,&lt;/strong&gt; given that&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I remember best when I have theory rather than only disconnected facts,&lt;/li&gt;&#xA;&lt;li&gt;and I've looked at what the question pool is testing and it seems worthwhile to me to also know the material that obviously could be in the pool, but happens not to be,&lt;/li&gt;&#xA;&lt;li&gt;but I also fully expect to learn just-in-time as I start projects, so material which is neither on the test nor “you need to know not to do this” is a lower priority.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If I just wanted to pass the test, then judging by some online practice tests, I could get all the way to Extra on my electrical knowledge, common sense, and a bit of luck, but that's not what I want to do!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;(I could ask “What book/resource is appropriate for this learning style?” but &lt;a href=&quot;http://blog.stackoverflow.com/2010/11/qa-is-hard-lets-go-shopping/&quot;&gt;that would be shopping&lt;/a&gt;. If you have such a suggestion, you could turn that into a description of what it covers and how that is relevant.)&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2013-11-21T04:35:54.010" LastActivityDate="2019-11-20T20:48:47.040" Title="What is the body of knowledge the U.S. written exams test?" Tags="&lt;united-states&gt;&lt;fcc&gt;&lt;education&gt;&lt;license&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="823" PostTypeId="2" ParentId="749" CreationDate="2013-11-21T03:24:19.753" Score="5" Body="&lt;p&gt;The &lt;em&gt;only&lt;/em&gt; HT kit I've ever seen in my searches was the &quot;TJ2B MK2 5 Band SSB Handheld Transceiver&quot; from &lt;a href=&quot;http://youkits.com/&quot; rel=&quot;noreferrer&quot;&gt;Youkits&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;From Youkits themselves:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;TX/RX: &lt;em&gt;5-21MHz&lt;/em&gt;, covering  60m, 40m, 20m,17m and 15m band (No TX on 30m)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it won't work on the 10m band, but it will work on 5 other bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;However&lt;/em&gt; &lt;a href=&quot;http://www.eham.net/reviews/detail/11189#120189&quot; rel=&quot;noreferrer&quot;&gt;WB8YQJ's eHam&lt;/a&gt; review says this:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The new TJ2B &quot;Kit B&quot; seemed ideal, offering &lt;em&gt;14Mhz to 30Mhz&lt;/em&gt; SSB +(CW Receive) in a handheld case and $269 plus ship.&#xA;&lt;img src=&quot;https://i.stack.imgur.com/WvqOP.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="237" LastActivityDate="2013-11-21T03:24:19.753" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="824" PostTypeId="2" ParentId="822" CreationDate="2013-11-21T13:15:37.923" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I just wanted to pass the test, then judging by some online practice tests, I could get all the way to Extra on my electrical knowledge, common sense, and a bit of luck, but that's not what I want to do!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's how I did it. Many of the questions are about electrical engineering, having to do with antennas, feedlines, Ohm's and Joule's laws, Smith charts, and so on. The higher-class tests have more of this. If you are well-versed in RF engineering, can do basic arithmetic, and read a polar graph, you are set in this department.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are also questions about regulations. If you really want to study the body of knowledge itself and not the question pool, then go read the &lt;a href=&quot;http://www.arrl.org/part-97-amateur-radio&quot; rel=&quot;nofollow&quot;&gt;FCC's part 97&lt;/a&gt;. But really, most of this falls under common sense (don't declare an emergency because you can't find your keys) and the rest is rote memorization (the 20 meter band starts at 14 MHz). Reading the rules directly is dry, painful reading, and it all boils down to &quot;operate within the allocated frequencies, and don't be a jerk&quot; anyway.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-11-21T13:15:37.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="825" PostTypeId="2" ParentId="822" CreationDate="2013-11-21T14:30:20.300" Score="15" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I just wanted to pass the test, then judging by some online practice tests, I could get all the way to Extra on my electrical knowledge, common sense, and a bit of luck, but that's not what I want to do!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I think that they body of knowledge they are testing may once have been fairly focused, but it has become a bit muddled by attempts to include new technologies without completely losing touch with the roots of the hobby.  At least that is my perspective as someone who took the Tech exam, then the General 4 weeks later and the Extra 4 weeks after that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple summary is this:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The rules (FCC Part 97)&lt;/li&gt;&#xA;&lt;li&gt;Operating practices, including customs not required by FCC rules&lt;/li&gt;&#xA;&lt;li&gt;Amateur radio &quot;technology&quot;: operating modes, types of antennas, etc.&lt;/li&gt;&#xA;&lt;li&gt;Enough physics to understand propagation and basic electronics&lt;/li&gt;&#xA;&lt;li&gt;Basic electronics sufficient to understand, build and maintain basic radio equipment&lt;/li&gt;&#xA;&lt;li&gt;Safety practices (physical, electical and RF)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For someone who's technically oriented, the new material is really just the first 3 items.  Like you I wanted to be sure I understood the material so I could fully participate.  As you have already guessed, it's completely impractical to comprehensively test anyone.  Again, as a new ham myself, some glaring omissions in the testing is actual operating practices: how to get onto a repeater and what the protocol is for participating, similar for HF nets, contest rules and practices, what the heck are all these knobs for on this radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think in other countries they include a practical portion on the test and these things have to be known in advance.  I didn't have an Elmer (teacher/mentor), I just got the books and did the tests and didn't get a radio until I was a General, so all this had to be learned on the fly and took a while.  If you have access to a live ham, this part will go a lot more smoothly for you.  I am still learning what some of these knobs do 6 months later...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As @Phil Frost related, it's pretty easy to just pass the test if that's your goal.  The US tests are 4 distractor multiple choice tests with 74% for mastery.  So you need only 28 out of 35 for the Technician and General tests and 37 out of 50 on the Extra class test. The tests are constructed such that each section of the material is represented by at least one question.   &lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-02-19T15:41:02.143" LastActivityDate="2014-02-19T15:41:02.143" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="826" PostTypeId="1" AcceptedAnswerId="828" CreationDate="2013-11-21T19:31:34.357" Score="6" ViewCount="2853" Body="&lt;p&gt;I seem to have forgotten some things I learned years ago for my amateur radio exams.  If I am building a 2 band shortened dipole and want a trap between 80 and 160 do I make the trap resonant on 80 or 160 or elsewhere?  I guess I may be mistakenly viewing the trap as a gate that allows certain frequencies and not others.  Is this correct thinking (albeit simplified)?  Can anyone tell me what I should be shooting for here or help me understand the function of traps in a shortened dipole and how I would go about making a trap for a 80/160 dipole?  Full length 80 is fine, with a short 160, would be best.&lt;/p&gt;&#xA;" OwnerUserId="68" LastEditorUserId="1246" LastEditDate="2015-02-01T19:47:19.853" LastActivityDate="2015-02-01T19:47:19.853" Title="80/160m Shortened Dipole Trap Questions" Tags="&lt;dipole&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="827" PostTypeId="2" ParentId="814" CreationDate="2013-11-21T19:45:42.267" Score="2" Body="&lt;p&gt;Honestly, the key technology to making this work has been around for quite a while, and that is the phone patch. Essentially, you can get on a repeater and dial a person from said repeater. The area of operations is fairly limited for such, but it has been done. And an SDR might help with this process, but it isn't required. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as digital, the key thing to remember is that Amateur bands prohibit encryption. Most of the useful things that one does over a cellular network require encryption of some form. Thus, it isn't likely to be of huge use. But yes, in principal it could be done.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-11-21T19:45:42.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="828" PostTypeId="2" ParentId="826" CreationDate="2013-11-21T19:48:10.937" Score="2" Body="&lt;p&gt;Traps are L-C cicuits that become high impedance at their resonant frequency.  It's common to make traps by winding lengths of coax around circular forms like PVC pipe of various diameters.  The center conductor of one end is soldered to the shield of the other end, and the remaining center conductor and shield connections are connected to the antenna elements. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The series-connected inner conductor and shield of the coiled coaxial-cable act like a bifilar or parallel-turns winding, forming the trap inductor, while the same inner conductor and shield, separated by the coaxial-cable dielectric, serve as the trap capacitor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resultant parallel-resonant LC circuit exhibits a high impedance at the resonant frequency of the trap and effectively disconnects everything after the trap from the antenna. Any inner traps (which are operating below their resonant frequency) function as loading coils and shorten the overall physical length of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case you'll want at least 3 traps.  One will be resonant at the lower end of the 80m band.  This will disconnect the 160m portion of the antenna when you are transmitting on 80m.  You'll want one between there and the feedpoint with a resonant frequency &lt;em&gt;above&lt;/em&gt; the highest frequency you'll use on this antenna.  This one is really a loading coil to make up for the physcilally short antenna length.  The other will be between the 80m trap and the end of the entenna.  This one should be resonant &lt;em&gt;below&lt;/em&gt; the 160m band and will serve as a loading coil on 160m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A couple of notes are in order:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Coaxial-cable traps have a relatively high Q, which results in a relatively sharp frequency resonance.&lt;/li&gt;&#xA;&lt;li&gt;Which means traps need to be &lt;em&gt;tuned&lt;/em&gt; for their resonant frequency, you can't use a cookbook approach here, if they are not right on, you've just made a dummy load.  To tune the traps, you'll need a dip meter or a sufficiently featured antenna analyzer&lt;/li&gt;&#xA;&lt;li&gt;Top band (160m) is a harsh mistress.  It rewards the dilligent worshiper who builds full size antennas and punishes all others.  You might consider a folded dipole if you have room for a full sized 80m dipole.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;A Further Edit:&lt;/strong&gt;&#xA;A folded dipole is a dipole antenna with the ends folded back around and connected to each other, forming a loop as shown below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/qNMNb.jpg&quot; alt=&quot;enter image description here&quot;&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The folded dipole antenna is resonant and radiates well at odd integer multiples of a half-wavelength (0.5λ, 1.5λ, etc.), when the antenna is fed in the center like a regular dipole. It can be made resonant at even multiples of a half-wavelength ( 1.0λ, 2.0λ, etc.) by offsetting the feed of the folded dipole (closer to the top or bottom edge of the folded dipole in the picture).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you could make an off-center fed folding 80m dipole that will also be resonant on 160m.  The feed point impedance will be higher than for a typical dipole, but that's usually not a problem.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-21T20:12:30.380" LastActivityDate="2013-11-21T20:12:30.380" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="829" PostTypeId="2" ParentId="826" CreationDate="2013-11-21T23:11:31.190" Score="2" Body="&lt;p&gt;There are many kinds of traps, but the most common kind is a parallel &lt;a href=&quot;http://en.wikipedia.org/wiki/LC_circuit&quot; rel=&quot;nofollow noreferrer&quot;&gt;LC circuit&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/lTFEW.jpg&quot; alt=&quot;enter image description here&quot;&gt;&#xA;&lt;br&gt;&lt;em&gt;Source: &lt;a href=&quot;http://www.w8ji.com/traps.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;article from w8ji.com&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At resonance, this circuit presents a high impedance. At all other frequencies, it presents a low impedance. So, an 80/160m trapped dipole will be an 80m dipole, with traps at the end of that, with additional wire to resonate it at 160m. To 80m, the traps look like high impedances, effectively disconnecting the extra wire for 160m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The traps themselves will shorten the amount of wire necessary to achieve resonance at 160m, similarly to a &lt;a href=&quot;http://en.wikipedia.org/wiki/Loading_coil&quot; rel=&quot;nofollow noreferrer&quot;&gt;loading coil&lt;/a&gt;. However, they don't shorten the 80m section of the antenna. If you barely have enough room for an 80m dipole as it is, you need some additional shortening action.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Easiest is probably to bend the antenna to make it fit. You can stick a 90 degree bend in the antenna and it will still work. The tuning will be somewhat changed, but not radically. You could also add additional loading coils or hats, though these are somewhat harder to construct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option, if an 80m dipole is already very close to your maximum size, is to put up a simple 80m dipole, forget the traps, and instead have a tuning network near the feedpoint that you switch in (or isolate with filters) for 160m operation. The advantage to a trapped antenna is the additional length on the longer bands maintains higher efficiency there, but if your 160m sections are extremely shortened then you aren't gaining any efficiency, but you are making the antenna difficult to construct and tune. If you put loading coils in the 80m sections then you shorten the whole antenna, but compromise performance on 80m when you don't need to. If you have a low-loss feedline, you can even do this with a tuner in the shack, especially considering how low feedline losses can be at 160m.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-11-22T02:33:04.260" LastActivityDate="2013-11-22T02:33:04.260" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="830" PostTypeId="1" CreationDate="2013-11-22T12:38:10.260" Score="18" ViewCount="14269" Body="&lt;p&gt;This is something I've read in passing, but never encountered an explanation of why. For example, &lt;a href=&quot;http://en.wikipedia.org/wiki/Dipole_antenna#Folded_dipole&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia says&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Another common place one can see dipoles is as antennas for the FM band; these are folded dipoles. The tips of the antenna are folded back until they almost meet at the feedpoint, such that the antenna comprises one entire wavelength. This arrangement has a greater bandwidth than a standard half-wave dipole.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Wikipedia isn't the only one with this notion: see comments to &lt;a href=&quot;https://ham.stackexchange.com/a/828/218&quot;&gt;this answer&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;it was my understanding that a folded dipole is still full length, just doubled over to increase bandwidth. Am I incorrect?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.antenna-theory.com/antennas/foldeddipole.php&quot; rel=&quot;noreferrer&quot;&gt;antenna-theory.com&lt;/a&gt;, which I'd consider at least three times more reliable than Wikipedia, doesn't say anything about bandwidth, but does say this:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Because the characteristic impedance of twin-lead transmission lines are roughly 300 Ohms, the folded dipole is often used when connecting to this type of line, for optimal power transfer. Hence, the half-wavelength folded dipole antenna is often used when larger antenna impedances (&gt;100 Ohms) are needed.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I could then see how, if you had to use 300Ω transmission line, you might get better bandwidth with a folded dipole as you wouldn't need a matching network, which might limit bandwidth or incur additional loss, but that's a long guess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, really why do folded dipoles have greater bandwidth? Or is that just an unsubstantiated rumor?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2020-06-01T00:33:28.603" Title="Why do folded dipoles have greater bandwidth than ordinary resonant dipoles?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;bandwidth&gt;&lt;folded-dipole&gt;&lt;antenna-theory&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="831" PostTypeId="2" ParentId="830" CreationDate="2013-11-22T13:55:25.233" Score="6" Body="&lt;p&gt;A little capacitive reactance is what gives you the greater bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a regular ½λ dipole, the current that flows along the conductors are in phase.  When we add the second conductor in a folded dipole, what we are really doing is extending the dipole. As a result the current in the new section flows in the same direction as those in the original dipole. The currents along both the half-waves are therefore in phase and the antenna will radiate with the same characteristics as a regular simple ½λ dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps an illustration will help (ARRL Extra Class License Manual):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/p5b8q.png&quot; alt=&quot;Folded Dipole Current Flow&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, this is AC current.  At points B and C (the ends of a simple dipole) it drops to zero.  Since a folded dipole is like extending a dipole by a 1/4λ at each end, we will observe the current reversing at B &amp;amp; C as we start a new cycle.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the current is now evenly divided into the two sections, the impedance must increase according to Ohm’s Law (W = I^2R) by a factor of 4.  This makes the folded dipoles an attractive option to hams that like to use twin lead or ladder line for feed lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another way to look at the situation is that the impedance of the dipole appears in parallel with the impedance of the folded sections.  At a frequency away from resonance, the reactance of the dipole is of the opposite form from that of the folded section and as a result there is some reactance cancellation at the feed point of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in essence you get some “free” matching right at the feedpoint of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-02T23:57:26.233" LastActivityDate="2013-12-02T23:57:26.233" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="832" PostTypeId="2" ParentId="814" CreationDate="2013-11-22T20:42:24.950" Score="7" Body="&lt;p&gt;Yes it can be done, and there are some huge advantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Better use of bandwidth&lt;/li&gt;&#xA;&lt;li&gt;Existing chipsets/support/implementation&lt;/li&gt;&#xA;&lt;li&gt;Low power&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In fact there's little reason why one couldn't essentially replace DSTAR and competing systems with a standard based on GSM and GPRS technologies.  Even for those parts that are patented, the patents running out means we'd be using technology that's advanced well beyond DSTAR and similar systems, and it's completely open.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would take a few individuals building up an example design and example infrastructure for it to be picked up widely.  But once that happened you could build a cellular network over Amatuer Radio frequencies, and you could expand functionality to support specific Amateur Radio needs such as public safety and emergency communications.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-11-22T20:42:24.950" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="833" PostTypeId="2" ParentId="801" CreationDate="2013-11-22T20:51:34.377" Score="3" Body="&lt;p&gt;In areas with a lot of APRS traffic, when you as a receiver are seeing a lot of collisions, one way to reduce the problem is to reduce your receiver sensitivity.  You make your area of reception smaller, and thus see fewer beacons.  As the spectrum grows crowded and people do this the problem will manage itself to some degree.  Of course you reduce your area, but as long as you and others intelligently repeat the messages (via radio or internet) then everything will still get through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the future I expect some to start using sector antennas, and possibly MIMO technologies to resolve the issue.  It's not trivial to separate simultaneous transmissions, but it is possible.  You can start experimenting with SDR, multiple antennas, and not only separate different simultaneous transmissions, but also provide some amount of positioning information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the moment most don't view it as a big problem.  Transmissions are often rather redundant and repeated frequently enough with enough random jitter that even blind beacons will get their message out more often than not, and if you wait you'll eventually get the information you're looking for.  Certainly it would be good for those in congested areas to use more advanced beacons that pay attention to traffic and avoid stepping on other transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're trying to collect every 10 minute temperature reading from a remote station, though, and the station doesn't provide history or redundancy, then APRS is not the right solution.  It's really a &quot;best effort&quot; but not guaranteed service, and should be treated as such.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-11-22T20:51:34.377" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="834" PostTypeId="1" CreationDate="2013-11-22T20:58:50.327" Score="2" ViewCount="1583" Body="&lt;p&gt;I'm looking for as simple as possible homebrew 20M SSB receiver design.  I just want to start listening, but at the same time learn some radio fundamentals.  So rather than buying a shortwave receiver I'd like to build one, but that also handles SSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something online and free would be ideal, but if there are particularly good designs in an older issue of a magazine, for instance, please point them out.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="29" LastEditDate="2013-11-23T09:26:48.110" LastActivityDate="2013-11-23T12:36:33.003" Title="Homebrew 20M SSB receiver design?" Tags="&lt;diy&gt;&lt;receiver&gt;&lt;ssb&gt;&lt;20m-band&gt;" AnswerCount="1" CommentCount="4" ClosedDate="2013-11-23T20:11:35.293" ContentLicense="CC BY-SA 3.0" />
  <row Id="835" PostTypeId="1" AcceptedAnswerId="847" CreationDate="2013-11-22T21:10:11.993" Score="17" ViewCount="1532" Body="&lt;p&gt;Looking to build a cheap (not even inexpensive, just dirt cheap) APRS beacon transmitter.  Right now you can get a dual band handheld transceiver with rechargeable battery, antenna, etc for under $31 [USD], for instance.  I can't find a cheaper transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the downsides to using a Baofeng, Wouxun, or similar cheap HT for APRS?&#xA;Are there ways to mitigate the problems, if any, of these units? &lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9844" LastEditDate="2018-05-17T00:36:45.183" LastActivityDate="2018-05-17T00:36:45.183" Title="Is there a disadvantage to using a cheap HT for APRS?" Tags="&lt;digital-modes&gt;&lt;ht&gt;&lt;aprs&gt;&lt;beacon&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="836" PostTypeId="2" ParentId="834" CreationDate="2013-11-23T00:52:22.333" Score="1" Body="&lt;p&gt;It's quite difficult to get simpler than an SDR design such as the &lt;a href=&quot;http://www.wb5rvz.com/sdr/New_SR_Lite/v6.2%20SoftRock%20Lite%20%20schematic%2030m_20m_15m.pdf&quot; rel=&quot;nofollow&quot;&gt;Softrock Lite 20m&lt;/a&gt;. It's little more than a quadrature mixer based on standard 74 series logic and an analog switch, an op-amp, a crystal oscillator, and a really simple input filter. The kit, including the PCB and all the components (but not a case) can be had for $30.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, it achieves this simplicity by putting all the complicated parts in the computer, to which it attaches. However, this has some distinct advantages, like extreme flexibility, and if learning is your objective, SDR provides a great platform to experiment with modulation techniques. You get enough of the radio fundamentals in hardware with the kit, you can work out the higher-level concepts in software, then come back and implement an SSB receiver in hardware later, if you want. Performance can be &lt;em&gt;really great&lt;/em&gt; because it's easy to build good filters in software. And, you can watch a big slice of the band all at once, which is really cool. And it's cheap, and easy to build.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-11-23T12:36:33.003" LastActivityDate="2013-11-23T12:36:33.003" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="837" PostTypeId="5" CreationDate="2013-11-23T09:28:45.933" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-23T09:28:45.933" LastActivityDate="2013-11-23T09:28:45.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="838" PostTypeId="4" CreationDate="2013-11-23T09:28:45.933" Score="0" Body="Use this tag for questions relating specifically to the amateur radio HF allocation of 14 000 to 14 350 kHz." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-23T09:28:45.933" LastActivityDate="2013-11-23T09:28:45.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="839" PostTypeId="5" CreationDate="2013-11-23T09:30:32.677" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-23T09:30:32.677" LastActivityDate="2013-11-23T09:30:32.677" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="840" PostTypeId="4" CreationDate="2013-11-23T09:30:32.677" Score="0" Body="Use this tag for questions relating specifically to the amateur radio HF allocation of 14 000 to 14 350 kHz." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-11-23T09:30:32.677" LastActivityDate="2013-11-23T09:30:32.677" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="841" PostTypeId="5" CreationDate="2013-11-24T05:43:46.443" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-24T05:43:46.443" LastActivityDate="2013-11-24T05:43:46.443" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="842" PostTypeId="4" CreationDate="2013-11-24T05:43:46.443" Score="0" Body="Multiple-input and multiple-output, or MIMO, is the use of multiple antennas at both the transmitter and receiver to improve communication performance" OwnerUserId="185" LastEditorUserId="185" LastEditDate="2013-11-24T18:39:36.840" LastActivityDate="2013-11-24T18:39:36.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="843" PostTypeId="5" CreationDate="2013-11-24T05:47:00.610" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-24T05:47:00.610" LastActivityDate="2013-11-24T05:47:00.610" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="844" PostTypeId="4" CreationDate="2013-11-24T05:47:00.610" Score="0" Body="Questions related to determining and improving the transmission distance of radio communications" OwnerUserId="185" LastEditorUserId="185" LastEditDate="2013-11-24T18:39:45.573" LastActivityDate="2013-11-24T18:39:45.573" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="845" PostTypeId="5" CreationDate="2013-11-24T05:52:24.020" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-11-24T05:52:24.020" LastActivityDate="2013-11-24T05:52:24.020" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="846" PostTypeId="4" CreationDate="2013-11-24T05:52:24.020" Score="0" Body="Designing and using radio systems that involve battery power sources" OwnerUserId="185" LastEditorUserId="185" LastEditDate="2013-11-24T18:40:01.340" LastActivityDate="2013-11-24T18:40:01.340" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="847" PostTypeId="2" ParentId="835" CreationDate="2013-11-24T18:43:05.793" Score="7" Body="&lt;p&gt;Most of the common disadvantages for Baofengs et al have to do with usability (e.g. poor user interface, odd squelch performance). The actual reception and transmission power is just fine. The majority of the disadvantages are negated when working with APRS, since it's the APRS modem interacting with the radio rather than a human being.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The main thing you'd probably still want to be aware of is the antennas; most of the cheap HTs come with poor-performing rubber duck antennas. Replacing the antenna is probably a good thing to plan for if you go with one of them, to help get a more reasonable signal strength.&lt;/p&gt;&#xA;" OwnerUserId="22" LastActivityDate="2013-11-24T18:43:05.793" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="848" PostTypeId="1" AcceptedAnswerId="865" CreationDate="2013-11-24T21:52:20.923" Score="4" ViewCount="205" Body="&lt;p&gt;I'm currently picking up signal from a beacon using RTL-SDR and decoding the Morse code on a computer using gMFSK program. &#xA;The beacon is sending message which decodes as &quot;T DE YU1VHF LOC KN04OO&quot;.&lt;br&gt;&#xA;I still haven't started learning how to decode the Morse code by &quot;hand&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I understand, DE is from &quot;this is&quot;, YU1VHF is the beacon's callsign and LOC KN04OO looks like Maidenhead system location. The only part which I don't get at the moment is &quot;T&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ideas what that would be?&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="29" LastEditDate="2013-11-25T08:32:11.150" LastActivityDate="2013-11-26T21:20:18.097" Title="What would letter T mean in this radio beacon message?" Tags="&lt;procedure&gt;&lt;cw&gt;&lt;beacon&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="849" PostTypeId="1" AcceptedAnswerId="851" CreationDate="2013-11-25T02:53:50.253" Score="13" ViewCount="3758" Body="&lt;p&gt;I've had people tell me, anecdotally, that a vertical is noisier than a dipole. Is this true, and if so, why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it is true:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this additional noise, such that SNR is degraded, or is the vertical just more sensitive overall, making noise and signals equally louder?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the noise particular to vertical monopoles? How would a vertical dipole be affected?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-08-22T00:12:50.217" Title="Is a vertical noisier than a dipole, and if so, why?" Tags="&lt;antenna&gt;&lt;snr&gt;&lt;noise&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="850" PostTypeId="1" AcceptedAnswerId="852" CreationDate="2013-11-25T10:05:44.240" Score="12" ViewCount="5965" Body="&lt;p&gt;There seem to be almost as many choices for the intermediate frequency (IF) as there are superheterodyne receivers and transceivers out there. The ones I have come across are 455 kHz, 452 kHz, 1.6 MHz and 6 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be the rationale for choosing a particular IF for a superhet?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="29" LastEditDate="2013-11-25T10:52:04.963" LastActivityDate="2013-11-25T14:59:39.460" Title="How is the IF for a superhet selected?" Tags="&lt;superheterodyne&gt;&lt;equipment-design&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="851" PostTypeId="2" ParentId="849" CreationDate="2013-11-25T13:20:32.833" Score="6" Body="&lt;p&gt;I have read this too.  I don't have personal data to back this up, but the reasoning I have read stated that local RFI (like household appliances) tended to be vertically polarized and hence more able to induce noise onto a vertical antenna than a horizontal one.  I'll edit the answer when I find the references.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meanwhile there are a few really excellent papers on the use of ferrite to eliminate noise from all facets of your shack, I highly recommend them:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf&quot; rel=&quot;nofollow&quot;&gt;Common Modes Chokes (W1HIS)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ifwtech.co.uk/g3sek/in-prac/inpr1005_ext_v2.pdf&quot; rel=&quot;nofollow&quot;&gt;Cost Effective Ferrite Chokes and Baluns (GM3SEK)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt;&#xA;After some perusal of the literature, including the ARRL Antenna Handbook, I see nothing scientific to back up the anecdote.  Which reminds me of a quote, from whom I forget: &quot;the plural of anecdote is not data&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, I found 2 addition items of interest:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;vertical antennas are omni-directional and therefore can pick all the noise there is to hear.&lt;/li&gt;&#xA;&lt;li&gt;A reference that stated that RF noise had random angles of polarization (something that sounds more credible to me) and that RFI noise below VHF travels mostly by ground wave and interaction with the earth attenuates the horizontal component leaving only the vertical component.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I don't know if item 2 is any less of an anecdote than the question at hand, but that's what I have found so far.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-25T14:31:58.330" LastActivityDate="2013-11-25T14:31:58.330" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="852" PostTypeId="2" ParentId="850" CreationDate="2013-11-25T14:59:39.460" Score="11" Body="&lt;p&gt;The short answer is that these are &quot;standard&quot; frequencies set aside for IF use and are reasonable free from interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The longer answer follows if you are interested in the why.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The choice of an IF frequency is one of those design tradeoffs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The lower the IF frequency used, the easier it is to achieve a narrow bandwidth to obtain good selectivity in the receiver and the greater the IF stage gain. On the other hand, the higher the IF, the further removed the image frequency is from the signal frequency and hence the better the image rejection. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One problem of the problems of a superheterodyne receiver, is its ability to pick up a second or image frequency that is twice the intermediate frequency away from the signal frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if we have a signal frequency of 1 MHz which is mixed with an IF of 455kHz. A second or image signal, with a frequency equal to 1 MHz plus (2 x 455) kHz or 1.910 MHz, can also mix with the 1.455 MHz to produce the 455 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The choice of IF is also affected by the selectivity of the RF end of the receiver. If the receiver has a number of RF stages, it is better able to reject an image signal close to the signal frequency and hence a lower IF channel can be tolerated.  This is why modern rigs have 2 or even 3 IF stages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The chosen IF frequency should be free from radio interference. Standard intermediate frequencies have been established and these are kept dear of signal channel allocation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you have noted, 455KHz is a common IF.  This is because broadcasters settled on this as a standard frequency during the broadcast AM days.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a design point of view 455KHz it leads to poor image response when used above 10 MHz. One commonly used IF for shortwave receivers is 1.600 MHz and this gives a much improved image response for the HF spectrum.  Ham band SSB HF transceivers have commonly used 9 MHz as a receiver intermediate frequency &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This frequency is a little high for ordinary tuned circuits to achieve the narrow bandwidth needed in speech communication, however, when used with ceramic crystal filter networks it leads to good results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some recent amateur transceivers use intermediate frequencies slightly below 9 MHz. A frequency of 8.830 MHz can be found in various Kenwood transceivers and a frequency of 8.987.5 MHz in some Yaesu transceivers. This change could possibly be to avoid the second harmonic of the IF falling too near the edge of the 17m WARC band. &lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-25T14:59:39.460" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="853" PostTypeId="1" AcceptedAnswerId="867" CreationDate="2013-11-25T21:49:33.890" Score="8" ViewCount="243" Body="&lt;p&gt;I'm considering hosting a foxhunt for a local youth group (scouts, in this case), and one of the questions asked was whether those searching for the hidden transmitter need have a license of any sort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will they need licenses if they are handling amateur radios, but only intending to receive transmissions?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If they don't need a license, are there precautions or steps I should take to ensure compliance with laws and regulations during the hunt?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This will occur in the US, north of Line A, if that affects the answer.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-11-26T00:29:54.540" LastActivityDate="2013-11-27T15:25:43.623" Title="Is any licensing require to receive in the amateur radio bands?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fox-hunt&gt;&lt;outreach&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="854" PostTypeId="1" AcceptedAnswerId="869" CreationDate="2013-11-25T21:57:05.387" Score="8" ViewCount="383" Body="&lt;p&gt;I'm currently looking to do a foxhunt for a youth group, and need to keep it inexpensive and easy enough that it won't be impossible for those new to foxhunting and ham radio, but difficult enough that it will still be rewarding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm a relatively new ham, so don't have any of the required equipment.  What is an inexpensive way to have a fox and two hunting setups?  Can I buy three cheap HTs, fabricate two antennas, and use a ham operator for the fox to avoid the need for additional electronics automation? Is there a cheaper or better set of equipment?  Note that the HTs would be under $100 [USD] total for 3 cheap dual band 4W units.  Any reason this wouldn't work, or would be frustrating for the hunters?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-11-27T17:30:43.327" Title="Simple cheap foxhunting?" Tags="&lt;antenna&gt;&lt;fox-hunt&gt;&lt;outreach&gt;&lt;equipment&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="855" PostTypeId="1" AcceptedAnswerId="868" CreationDate="2013-11-25T22:02:41.690" Score="7" ViewCount="437" Body="&lt;p&gt;I'm thinking about an inexpensive way to create a foxhunt kit for youth groups, and am wondering if the cheap dual band HTs could be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it occurs to me that FM doesn't provide any good audio queues for signal strength, and the SWR meters on these units are typically useless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can such FM radios be used for foxhunting, and how?  If there's a better and cheaper method, please consider addressing it in my related question &lt;a href=&quot;https://ham.stackexchange.com/questions/854/simple-cheap-foxhunting&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-11-27T17:33:13.030" Title="Is FM appropriate for foxhunting?" Tags="&lt;ht&gt;&lt;modes&gt;&lt;fox-hunt&gt;&lt;direction-finding&gt;&lt;fm&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="856" PostTypeId="1" AcceptedAnswerId="872" CreationDate="2013-11-25T22:09:29.560" Score="10" ViewCount="273" Body="&lt;p&gt;I've heard that you might not need a special directional antenna to participate in a foxhunt, that some people are able to use their body to help determine the direction of a signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does this work?  More specifically, what is the process to do this, and why does it work?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this only work on specific frequencies, or can this be used for 2M and 70cM dual band HTs with stock antennas? Is it tricky and requires practice, or could someone new to ham radio be taught it and effectively using it in a handful of minutes?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-09-17T18:47:50.157" Title="What is body blocking, and does it work with a stock HT on a foxhunt?" Tags="&lt;antenna&gt;&lt;ht&gt;&lt;fox-hunt&gt;&lt;direction-finding&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="857" PostTypeId="1" AcceptedAnswerId="862" CreationDate="2013-11-25T22:15:37.897" Score="7" ViewCount="608" Body="&lt;p&gt;I'm looking at designs for low cost DIY yagi antennas for a fox hunt, and pondering coat hanger wire and PVC piping.  I'd like them to be built by the youth who will be doing the fox hunt, but that requires some safety considerations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I plan to bend the tips of the coathanger wire back on themselves to avoid safety issues with the sharp ends, will I cut them to length prior to the bend, or should they be at length after the bend? The bend will be about a plier's width of material, so maybe 5-8 mm, turned back 180 degrees, or nearly so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have equipment to test for antenna matching, so I can't experiment on this, however these will be used for hunting, not transmitting, so I don't expect it's going to be critical.  I'd like to get close, though.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-11-26T13:39:30.657" Title="Is bending the tips of the antenna wires going to affect the effective length?" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;fox-hunt&gt;&lt;direction-finding&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="858" PostTypeId="1" CreationDate="2013-11-25T23:29:26.883" Score="6" ViewCount="1682" Body="&lt;p&gt;SO-239, PL-259, UHF, NMO, SMA male/female, reverse SMA, oh my! Some of these may even refer to the same thing with different names. Can someone list the most common connector types and show a picture of each? Also, please explain common acronyms or slang terms used for various connectors. I could not find a comprehensive list online that included all of this in one place - this will be a helpful reference for new hams.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please RF connectors only for this question.&lt;/p&gt;&#xA;" OwnerUserId="128" LastEditorUserId="128" LastEditDate="2013-11-26T03:11:38.577" LastActivityDate="2013-11-26T03:11:38.577" Title="What are the most common RF connectors encountered in amateur radio?" Tags="&lt;connectors&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="2" ClosedDate="2013-11-26T08:26:49.220" ContentLicense="CC BY-SA 3.0" />
  <row Id="859" PostTypeId="2" ParentId="858" CreationDate="2013-11-26T00:44:35.567" Score="6" Body="&lt;p&gt;Connector use varies based on frequency band and also based slightly on power. The most common that I see, I have bolded, and while they are sorted by band, a VHF/UHF connector can be used on HF - it may not be common, but it's OK. On the other hand, an HF connector will be unacceptable at VHF/UHF, and only GHz/microwave connectors will be acceptable at those frequencies.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;HF connectors&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;UHF connector&lt;/strong&gt; - no, that isn't in the wrong category. Also known as &lt;strong&gt;PL-259&lt;/strong&gt; (male) or &lt;strong&gt;SO-239&lt;/strong&gt; (female). When this connector was first developed, the nomenclature of HF, VHF, and UHF was different than it is now. This connector is commonly found on HF equipment, and is relatively large.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Bare wire/twin lead&lt;/strong&gt; - certain antennas and feedline, like twin lead (also known as window cable) or random wire or loop antennas on HF use bare wire connections. These may not be insulated, so don't touch unless you're damn sure that the transmitter is off and disconnected.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;VHF and UHF connectors&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;SMA&lt;/strong&gt; and varieties. This is near universal for portable radios, and common on mobiles, at VHF and UHF. The standard configuration has a male with a center pin and threads on the inside, and a female with threads on the outside. The reverse configuration (sometimes known as &lt;strong&gt;RP-SMA&lt;/strong&gt;) has a male with a center pin but threads on the outside. There is also a similar connector used only for HTs where there is no center pin - the threads are the same size as an SMA connector, but the antenna side is just solid metal. Since HT antennas are monopoles anyway, there isn't any downside to using this - but be careful: if you use one of the traditional &lt;a href=&quot;http://www.universal-radio.com/catalog/hamantht/2714.html&quot; rel=&quot;noreferrer&quot;&gt;rat tail&lt;/a&gt; or tiger tails on this antenna, it will not work properly and will be carrying full antenna current.&lt;/li&gt;&#xA;&lt;li&gt;BNC connectors - this is a quick-mate connector. It takes less than a half turn to mate/unmate the connector, which is great for anything that's being replaced often. If I had an HT that I used both as a portable and in my vehicle on a mobile antenna, I'd use the BNC connector because repeated mate/unmate cycles can damage the connectors on both sides, both the crimp and the solder to the circuit board - especially if you overtighten your connectors, which is surprisingly common.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;Microwave connectors&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Type N&lt;/strong&gt; connectors - while certified often up to 18GHz, these are often also used for UHF. I've seen them more on commercial gear than ham gear, but hams do use them also. This connector has an extra &amp;quot;circle&amp;quot; of metal shielding the center pin on each end. It's larger than even PL-259 - about 0.8&amp;quot; in diameter. You see a lot of these on RF test equipment.&lt;/li&gt;&#xA;&lt;li&gt;TNC connectors - a threaded version of BNC. It's about the same side, but is rated up to about 11GHz (BNC is only rated to 4GHz). Not common, but you might see it. There is also a reverse version (like for SMA).&lt;/li&gt;&#xA;&lt;li&gt;Type C connectors are another variation on BNC, which are weatherproof and rated up to 11GHz, but are quick-mate.&lt;/li&gt;&#xA;&lt;li&gt;Mini-UHF - more confusion abounds here! This connection can be rated well over 20GHz, unlike the UHF connector above that it seems to be based off of. It may appear similar to or slightly larger than a (standard polarity) SMA connector. Whereas SMA uses 1/4&amp;quot; threads,&#xA;Mini-UHF uses 3/8&amp;quot;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="87" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2013-11-26T00:44:35.567" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="861" PostTypeId="1" AcceptedAnswerId="887" CreationDate="2013-11-26T04:07:31.150" Score="9" ViewCount="6197" Body="&lt;p&gt;I've seen people refer to &lt;a href=&quot;https://ham.stackexchange.com/a/859/9&quot;&gt;avoiding touching&lt;/a&gt; an antenna or bare transmission line that might be transmitting.  What voltage potentials and currents are commonly found on typical ham radio antennas?  Do both the voltage and current increase with increased transmitter power, or mainly one more than the other?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the general safety measures one should take concerning antennas, specifically from the power going into the antenna purposefully? Antenna safety around powerlines and other power sources is a different question.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-11-29T01:52:01.420" Title="What is the electrical shock risk of an antenna?" Tags="&lt;antenna&gt;&lt;safety&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="862" PostTypeId="2" ParentId="857" CreationDate="2013-11-26T13:39:30.657" Score="3" Body="&lt;p&gt;I would bend the tips back, twisting the free end around the standing end so you make a loop with good electrical contact between them. Measure from the base to the end of the loop for the purposes of calculating the length. The loop is almost entirely cosmetic and won't affect the electrical length of the antenna much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to make the loop bigger, you would have a capacitive hat, which would electrically lengthen the antenna. However, if you keep it small, and you fold it back and short the end back to the antenna, the capacitance added at the end will be negligible.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-11-26T13:39:30.657" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="863" PostTypeId="2" ParentId="861" CreationDate="2013-11-26T14:56:55.500" Score="3" Body="&lt;p&gt;Touching a &quot;live&quot; (transmitting) antenna could impart a serious RF burn if the power level was high enough. This is different from the classic &quot;electric shock&quot; obtained by putting a finger into a live wall socket. Radio frequencies heat tissue (non-ionizing radiation), proximity and contact with high RF fields will cause a RF burn.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a risk of electrocution if the antenna is in contact with an overhead power line, although a well placed antenna should NOT be near any such hazards.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2013-11-26T14:56:55.500" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="864" PostTypeId="2" ParentId="861" CreationDate="2013-11-26T19:46:44.750" Score="3" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Radiation_burn&quot; rel=&quot;nofollow&quot;&gt;RF burns&lt;/a&gt; aside (these often occur without physical contact), the voltage on the antenna can reach very high levels. There is a good discussion of this at &lt;a href=&quot;http://forums.qrz.com/showthread.php?243998-Voltage-at-antenna&quot; rel=&quot;nofollow&quot;&gt;http://forums.qrz.com/showthread.php?243998-Voltage-at-antenna&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Paraphrasing the linked discussion, Ohm's law applies, so if you're dumping 50W into a 35 ohm load:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$P = I^2R$, so $I = \sqrt{\frac{50}{35}} = 1.195$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$V = IR = 1.195 \cdot 35 = 41.83 V_{RMS} \cdot \sqrt{2} = 59.16 V_{PEAK}$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Toward the tip of the antenna, the impedence changes, so the voltage can be orders of magnitude higher (and the current lower).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Yes, I know V should be E, but old habits are hard to break. I also know that I'm using the RMS for a sine wave, but it's a reasonable approximation.)&lt;/p&gt;&#xA;" OwnerUserId="276" LastEditorUserId="276" LastEditDate="2013-11-26T19:55:47.050" LastActivityDate="2013-11-26T19:55:47.050" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="865" PostTypeId="2" ParentId="848" CreationDate="2013-11-26T21:20:18.097" Score="2" Body="&lt;p&gt;As mentioned in my comment, it appears that the software I'm using, gMFSK, is decoding the long tone as a letter &quot;T&quot;, because there is a short pause between the tone beacon transmits and the message itself. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2013-11-26T21:20:18.097" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="866" PostTypeId="2" ParentId="853" CreationDate="2013-11-27T07:11:50.817" Score="4" Body="&lt;p&gt;In general, reception of radio signals does not require a license. (Even if a government wanted to try, it'd be nearly impossible to regulate - after all, there's inherently no emission from a reception-only station, so there's no way to tell it's even happening.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A license is only required for a &lt;em&gt;transmitting&lt;/em&gt; operator. The HTs you're using for the hunt are probably transmission-capable, but if there's a way to prevent them from easily being keyed on (e.g. if you can preset a frequency, set a reasonable squelch, and then turn on the keypad lock) that would probably help to prevent accidental transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wanted to be on the safe side, and had the human resources available, you could also have a licensed ham accompanying each group, in which case they could act as the control operator for the radio (and thus satisfy licensing requirements, as long as they're also willing to hold responsibility for any transmissions).&lt;/p&gt;&#xA;" OwnerUserId="22" LastActivityDate="2013-11-27T07:11:50.817" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="867" PostTypeId="2" ParentId="853" CreationDate="2013-11-27T15:25:43.623" Score="5" Body="&lt;p&gt;As discussed, yes it's perfectly legal to receive anything.  It's the transmitting that is regulated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One easy solution is to not use a transceiver at all.  Since the transmitter half of the device is your problem.  So take the transmitter out of the transceiver and you end up with just a receiver.  So what can you use as a receiver?  The simplest thing to use would be a scanner!  There are many many hand held scanners that can receive things in the HAM bands and if you used one, then you don't need to worry about giving it to someone that isn't allowed to transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also &quot;build your own&quot; and the good news is that building receivers is a lot less complicated and expensive than building a transmitter, and there are lots of project instructions online or even available for purchase with parts that would let you build your own for fairly cheap.  The trick is building one for the transmission mode you want to use during the game.  For something like FM, for example, there should be some generally available FM receiver parts or ICs that you could use.&lt;/p&gt;&#xA;" OwnerUserId="661" LastActivityDate="2013-11-27T15:25:43.623" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="868" PostTypeId="2" ParentId="855" CreationDate="2013-11-27T17:26:34.523" Score="2" Body="&lt;p&gt;Yes they can.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are right that the cheap HTs don't have much of a useful meter (I own a couple). Two easy solutions are 1) body fade and 2) directional antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Body Fade&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hold your HT close to your chest and turn around slowly, looking for the direction where your body blocks the most signal (the signal null).  Now you know that the signal is coming from behind you.  turn around, walk that way, rinse and repeat.  The signal should get stronger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the null you are creating is rather shallow.  At VHF/UHF frequencies, it can be filled in by signal reflections off of nearby objects.  So try to avoid large buildings, chain-link fences, metal signs, etc.  If you are not getting a good null, move to a clearer location and try again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the signal is so strong that you can't find the null, tune 5 or 10 KHz off frequency to put the signal into the skirts of the receiver's IF passband.  If your hand-held is dual-band (144/440 MHz) and you are hunting on two meters, try tuning to the much weaker third harmonic of the signal in the 70 cm band while performing the &quot;body shield.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Disconnecting the HT's &quot;rubber duck&quot; antenna will knock down the signal even more.  Hearing the signal with antenna off is usually a &quot;You are here!&quot; indicator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Directional Antennas&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fox hunting on 2m means there are a variety of simple directional antennas you could build that are also quite inexpensive.  A 3 element yagi is a good choice as a small loop.  there are several examples of yagis made from steel measuring tape, making them quite durable and easy to pack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See the site &lt;a href=&quot;http://www.homingin.com/&quot; rel=&quot;nofollow&quot;&gt;http://www.homingin.com/&lt;/a&gt; for lots of good information.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-11-27T17:33:13.030" LastActivityDate="2013-11-27T17:33:13.030" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="869" PostTypeId="2" ParentId="854" CreationDate="2013-11-27T17:30:43.327" Score="2" Body="&lt;p&gt;This should work fine.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These cheap Chinese HTs don't have many bells and whistles, but they are decent radios especially with non-stock antennas.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For beginners I would start with some real simple scenarios and fairly open terrain.  You don't want a ton of multi-pathing scatter to confuse the new hunters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See my answer to your other questions for some methods.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See the site &lt;a href=&quot;http://www.homingin.com/&quot; rel=&quot;nofollow&quot;&gt;http://www.homingin.com/&lt;/a&gt; for lots of good information.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-27T17:30:43.327" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="870" PostTypeId="1" AcceptedAnswerId="871" CreationDate="2013-11-27T18:33:05.310" Score="1" ViewCount="248" Body="&lt;p&gt;And what will I need to mount it in my wall?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ppJzV.jpg&quot; alt=&quot;Antenna Base&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/hJtQ5.jpg&quot; alt=&quot;Cable&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/fHScy.jpg&quot; alt=&quot;Connector&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to mount it similar to the below images in my wall. Will I need any additional adapters/converters?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JJEYn.jpg&quot; alt=&quot;Wall Jacks&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;So to put all my questions in one place:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What is this RF connector(s)?&lt;/li&gt;&#xA;&lt;li&gt;What additional hardware/adapters will I need to mount it in my wall like in the picture (connector types in the image are irrelevant, it's just an example of how I want to mount the jacks in the wall)?&lt;/li&gt;&#xA;&lt;li&gt;What helpful advice can you give (how big of a whole to drill in a wall faceplate, advice on selecting adapters or other needed hardware, comments on condition of equipment shown in images, etc.)?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="128" LastEditorUserId="22" LastEditDate="2013-11-27T18:59:19.257" LastActivityDate="2013-12-02T19:22:11.857" Title="What is this RF connector?" Tags="&lt;connectors&gt;&lt;installation&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="871" PostTypeId="2" ParentId="870" CreationDate="2013-11-27T22:27:35.910" Score="5" Body="&lt;p&gt;For Question 1: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;As others have said, this does look like a PL-259/SO-239, commonly&#xA;called a UHF Connector.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Question 2:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You can get wall mount adapters for these connections too, I'm not&#xA;sure I can post links here, but search for &quot;SO-239 wall plate&quot;. In&#xA;the event you can't find this specific one, you could potentially use&#xA;others, like the one in your photo on the right which looks to be a&#xA;BNC connector. You can get UHF to BNC adapters fairly readily at most&#xA;electronics stores.&lt;/li&gt;&#xA;&lt;li&gt;As &lt;a href=&quot;https://ham.stackexchange.com/users/218/phil-frost&quot;&gt;Phil Frost&lt;/a&gt; pointed out, check the rating on ALL connectors that you use, meet the requirements for the power you are going to run.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Question 3:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The wall plate you end up purchasing, should come with instructions&#xA;for mounting, this will let you know how big a hole to cut.&#xA;&lt;strong&gt;&lt;em&gt;Definitely do not cut holes in your wall until you have selected the wall plate you want to place&lt;/em&gt;&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;Make sure you sketch out your implementation, as this will let you&#xA;build a list of required components.&lt;/li&gt;&#xA;&lt;li&gt;Make sure however you bring this cable in from the outside, it is&#xA;very well weather proofed, cutting holes in exterior walls is easy,&#xA;but you need to be careful you aren't destroying any moisture membranes&#xA;or anything else in the process.&lt;/li&gt;&#xA;&lt;li&gt;Be VERY careful when you make the hole to bring this into the house&#xA;that you aren't drilling near any pipes or electrical wires, you can&#xA;buy tools (or borrow as they can be expensive) to detect wires and&#xA;pipes in walls before you start drilling.&lt;/li&gt;&#xA;&lt;li&gt;I'm not sure how tall your antenna there is, but the usual safety&#xA;precautions around harnesses for climbing and staying WELL clear of&#xA;any overhead power lines apply. &lt;/li&gt;&#xA;&lt;li&gt;You don't mention what your living    situation is, but you should&#xA;also check if you are allowed to erect    an antenna like this, as&#xA;often there are restrictions.&lt;/li&gt;&#xA;&lt;li&gt;As &lt;a href=&quot;https://ham.stackexchange.com/users/105/pete-nu9w&quot;&gt;Pete NU9W&lt;/a&gt; pointed out - One additional point about the&#xA;entrance from the outside: when it leaves the wall on the outside the&#xA;cable should initially go down, even if its destination is up. That&#xA;forms a drip loop, which makes it harder for water to follow the&#xA;cable into the wall.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="172" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-02T19:22:11.857" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="872" PostTypeId="2" ParentId="856" CreationDate="2013-11-27T22:36:59.480" Score="4" Body="&lt;p&gt;Essentially this involves using your body as a barrier to fade the signals. Holding the HT close to you, and rotating until you get the weakest signal, then the source of that signal will be on the other side of you. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In an &lt;a href=&quot;https://ham.stackexchange.com/a/868/1568&quot;&gt;answer to a different question&lt;/a&gt;, WPrecht - AB3RY quoted the following &lt;a href=&quot;http://www.homingin.com/equipment.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Handie-Talkie Tricks&lt;/a&gt; tip from Joe Moell, KØOV's Homing In website: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;When the signal is so strong that you can't find the null, tune 5 or 10 KHz off frequency to put the signal into the skirts of the receiver's IF passband. If your hand-held is dual-band (144/440 MHz) and you are hunting on two meters, try tuning to the much weaker third harmonic of the signal in the 70 cm band while performing the &quot;body shield.&quot;&#xA;  Disconnecting the HT's &quot;rubber duck&quot; antenna will knock down the signal even more. Hearing the signal with antenna off is usually a &quot;You are here!&quot; indicator.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="172" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-09-17T18:47:50.157" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="873" PostTypeId="1" AcceptedAnswerId="918" CreationDate="2013-11-27T23:49:08.873" Score="7" ViewCount="225" Body="&lt;p&gt;Moving from Australia to the US, is there a way to transfer my license in any way, or do I need to sit the exams in full? I'm wondering if there is any concept of &quot;credit&quot; towards licensing, so I wouldn't need to sit all three exams (assuming I was going for Extra). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: Moving permanently. &lt;/p&gt;&#xA;" OwnerUserId="172" LastEditorUserId="172" LastEditDate="2013-12-02T19:16:17.703" LastActivityDate="2013-12-02T23:22:26.483" Title="Moving from Australia to the US, Amateur radio license transfer?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;australia&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="874" PostTypeId="1" CreationDate="2013-11-27T23:50:51.210" Score="6" ViewCount="5378" Body="&lt;p&gt;Way back when, if my recollection is correct, the requirement for using ham radio was to have a license and the required skill was some level of Morse code proficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have heard that Morse code is no longer required — if that's true, does a person still need a license to operate ham radio equipment?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm in Canada.&lt;/p&gt;&#xA;" OwnerUserId="399" LastEditorUserId="76" LastEditDate="2013-11-27T23:57:09.273" LastActivityDate="2018-04-23T05:17:59.603" Title="Does a person still need a ham radio license?" Tags="&lt;license&gt;&lt;canada&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="875" PostTypeId="2" ParentId="874" CreationDate="2013-11-28T00:00:33.317" Score="6" Body="&lt;p&gt;Referencing this page which outlines the licensing requirements &lt;a href=&quot;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01862.html&quot;&gt;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01862.html&lt;/a&gt; you do need to obtain a license to transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, it's good that you mention you are from Canada, as it seems Canada still requires Morse code as part of the licensing scheme to operate in certain scenarios. If you only obtain the &quot;Basic&quot; license, with no honors or Morse proficiency for example, you are very limited in where you can transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a table that outlines what you can and can't do, based on your Canadian license level.&#xA;&lt;a href=&quot;https://www.rac.ca/en/rac/services/bandplans/allband.php&quot;&gt;https://www.rac.ca/en/rac/services/bandplans/allband.php&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="172" LastActivityDate="2013-11-28T00:00:33.317" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="876" PostTypeId="1" AcceptedAnswerId="878" CreationDate="2013-11-28T00:18:56.080" Score="20" ViewCount="4123" Body="&lt;p&gt;If during normal operation, I receive a mayday or pan-pan call, how should I handle this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I required to provide help in this situation, and what can I do to make sure I give all the assistance needed, what information should I try and get?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If someone else is working with the station on the distress call, should I join in and help?&lt;/p&gt;&#xA;" OwnerUserId="172" LastActivityDate="2013-12-03T20:48:34.890" Title="If I hear a distress call, what is the correct procedure for helping the person?" Tags="&lt;procedure&gt;&lt;emergency&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="877" PostTypeId="1" AcceptedAnswerId="881" CreationDate="2013-11-28T12:25:24.617" Score="2" ViewCount="3397" Body="&lt;p&gt;I'm planning on putting up a G5RV. From the ladder line I connect 5m coax to the shack; would it be worth doing a common mode current choke at both the antenna feedpoint and the coax feedpoint? (I read somewhere that it's recommended at the coax.)&lt;/p&gt;&#xA;" OwnerUserId="135" LastEditorUserId="76" LastEditDate="2013-11-28T15:11:15.730" LastActivityDate="2013-11-30T12:58:12.583" Title="Choke at antenna and feedpoint?" Tags="&lt;antenna&gt;&lt;feed-line&gt;&lt;coaxial-cable&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="878" PostTypeId="2" ParentId="876" CreationDate="2013-11-28T15:55:30.123" Score="20" Body="&lt;p&gt;First, if you hear a distress call: &lt;strong&gt;STOP!&lt;/strong&gt; &lt;em&gt;Immediately&lt;/em&gt; end any transmission in progress. Do not touch any antenna or radio controls except as needed to turn off split operation etc. Lock the VFO to avoid inadvertantly bumping the frequency setting. Particularly, &lt;em&gt;do not reorient the antenna&lt;/em&gt; in an attempt to get a better signal. Focus on copying what you can and avoiding any activities that may cause interference. This is something you can actually practice: how long does it take you to reset RIT, turn off split, lock the VFO and getting ready to actually &lt;em&gt;write things down&lt;/em&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, I view it as a multiple steps process.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Copy&lt;/strong&gt; the message. &lt;em&gt;You will not remember the details.&lt;/em&gt; Write down everything, &lt;em&gt;clearly marking anything you are not absolutely certain about.&lt;/em&gt; This is a major reason why I feel one should &lt;em&gt;always&lt;/em&gt; have writing utensils within easy reach from one's operating location; the odds that you'd receive a distress call are small, but if you do, any old pencil and back of a log book page will help tremendously.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Wait&lt;/strong&gt; to see if a station better equipped to handle the distress call responds. Maybe there's someone closer, or with necessary knowledge (for example, there's the possibility that a doctor hears a distress call that is about a medical emergency).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If nobody answers within a few seconds (and you are sure that nobody does and you aren't simply out of range of the other station), &lt;strong&gt;briefly identify yourself&lt;/strong&gt; and then stop transmitting again. This might be something as simple as &quot;amateur radio station VK2VXK received distress call - distressed station please confirm, over over&quot;. Your transmission lets anyone within range of you but out of range of the distressed station know that the frequency is in use for emergency traffic (a definite signal to cease transmissions), and if you get a confirmation from the remote station you have established two-way communications. I'd use the remote station's call sign if they gave one, but don't worry if they didn't. In many jurisdictions, emergency communications is allowed on any frequency unlicensed if needed to solicit help. &lt;em&gt;In many jurisdictions this also means that you can respond to a distress call even if you are normally not authorized to transmit on the frequency in question, if doing so is necessary to provide emergency assistance.&lt;/em&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;As soon as you have &quot;claimed&quot; the distress signal by receiving confirmation from the remote station, tell the remote station to stand by and &lt;strong&gt;pick up the phone and call emergency services.&lt;/strong&gt; Immediately inform them that you have received a distress call over radio (so that they do not rely on locating your phone line to determine the location of the emergency), and &lt;em&gt;accurately&lt;/em&gt; relay &lt;em&gt;all&lt;/em&gt; information in the distress call. Particularly important are &lt;em&gt;the type of emergency, how many people are involved, and the distressed party's location.&lt;/em&gt; Be prepared to relay questions and answers between the emergency operator and the distressed station. &lt;em&gt;Stay calm&lt;/em&gt; (easier said than done, but very important). &lt;strong&gt;Maintain communications with both parties&lt;/strong&gt; until you receive confirmation that emergency services have arrived. If you hear anyone transmitting on the frequency, immediately calmly inform them that the frequency is in use for emergency distress traffic.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If someone else has already established communications with the distressed station, then &lt;em&gt;do not interfere.&lt;/em&gt; Also, &lt;em&gt;do not play radio cop.&lt;/em&gt; If some other station starts transmitting on the frequency, let either of those already communicating deal with it. Instead, simply copy all details you can, stay on the frequency and do your best to &lt;em&gt;be prepared to jump in if either of the stations ask for assistance which you are able to provide or the station that is in communication with the distressed station clearly goes off the air, but not under any other circumstances.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I doubt you would be legally required to provide assistance to a distressed station, but if it was me, I would sleep considerably better at night knowing I did whatever I could to help, even if it was something as simple as ceding a frequency to a station in distress. &lt;strong&gt;Actual emergency or distress communications always has precedence over all other communications.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-03T20:48:34.890" LastActivityDate="2013-12-03T20:48:34.890" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="879" PostTypeId="2" ParentId="877" CreationDate="2013-11-28T17:14:57.360" Score="2" Body="&lt;p&gt;A canonical answer is difficult, a lot depends on the antenna location and it's environment.  There is a ton of information on common mode chokes and baluns in the answer @Phil Frost linked above.  Some of these references suggest at the feed point is all you need, other say both the feed point and the shack entry point, still others say all of the above, plus points along the coax to break up potential 1/4 wave lengths that could pick up RF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Five meters is pretty short run.  If it were me, I would put one at the feed point and see what I got.  If you have more ferrite laying around, add one at the shack end and measure the effects.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-11-28T17:14:57.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="881" PostTypeId="2" ParentId="877" CreationDate="2013-11-28T21:05:27.253" Score="4" Body="&lt;h2&gt;Avoid common-mode sheath currents&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Common-mode sheath currents on the coaxial feed line should be avoided because:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;At the antenna feed point or the transition point of balanced line to coax, common-mode currents interfere with your radiation pattern.&lt;/li&gt;&#xA;&lt;li&gt;In the shack, common-mode sheath currents will interfere with your  electronic equipment (RFI).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h2&gt;Origin of the common mode&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Most often, the common mode on the coaxial feeding cable is a continuation of the standing wave that exists over the length of most antennas. (Aperiodic resistive antennas and leaky-wave antennas are notable exceptions.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This standing wave, in turn, results from the abrupt change in conductivity $\sigma$ and/or permitivity $\epsilon_{r}$ that is encountered at the antenna ends. This is called &lt;em&gt;the boundary condition&lt;/em&gt; in technical literature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being a standing wave implies that, for any given frequency, the common mode will show current minima every halve wavelength, starting from the antenna ends. Without a current balun and/or a sheath current choke, these current minima will repeat further down the coaxial feed line.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Optimal placement of a sheath current choke&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;A sheath current choke typically inserts only about 500Ω impedance in series with the sheath of the coaxial cable. This means that sheath current chokes are ineffective at places along the feed line where the common mode wave has a current minimum, because the common mode impedance there will be high (typically about 2kΩ). &lt;strong&gt;Sheath current chokes are most effective at common-mode current maxima.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Practical considerations&lt;/h2&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;By all means, use a decently made, properly rated (frequency and power) &lt;strong&gt;current balun&lt;/strong&gt; at your antenna feed point. This will be a first, &lt;strong&gt;broadband&lt;/strong&gt; defence against common-mode sheath currents.&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Current baluns tend to be less effective at lower frequencies because they produce their common-mode series impedance from inductance. Therefore, common-mode sheath current rejection may not be sufficient at the lower frequency bands. A &lt;strong&gt;sheath current choke&lt;/strong&gt; may be placed &lt;strong&gt;at current maxima&lt;/strong&gt; of the lowest frequency band, i.e.:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;At $\frac{\lambda}{4}$ distance measured from the antenna ends, where $\lambda$ is the wavelength of the lowest frequency band, and/or&lt;/li&gt;&#xA;&lt;li&gt;At odd multiples of this length, i.e. $\frac{3\lambda}{4}$, $\frac{5\lambda}{4}$, ...&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This will normally also handle the common-mode wave rejection for the second lowest frequency band if this is a harmonic of the lowest. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Sheath current chokes close to the antenna feed point will help to preserve the radiation pattern of the antenna. Sheath current chokes closer to shack may help more against RFI.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you can, connect the coax sheath to earth at both ends and place the coaxial cable on or below ground.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2013-11-29T12:45:24.343" LastActivityDate="2013-11-29T12:45:24.343" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="882" PostTypeId="1" CreationDate="2013-11-28T21:16:52.077" Score="3" ViewCount="1173" Body="&lt;p&gt;I would like to compile a list of HF transceivers that feature an Ethernet port (RJ45) for remote internet operation.&#xA;It would also be interesting to add the supported operating system(s) for remote operation in this list (Microsoft Windows, Mac OSX, GNU/Linux, Android, ...).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finding this information on the net via a search engine is difficult because the word &quot;transceiver&quot; is abundantly used in the context of Ethernet chip design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, only few HF transceivers currently feature an Ethernet port. Compiling a list here in the form of &lt;strong&gt;one answer per model&lt;/strong&gt; would help as a future buying guide for the hams with an interest in remote operation.&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2013-11-28T21:23:37.377" LastActivityDate="2013-11-28T21:31:46.917" Title="Which HF transceivers feature a built-in Ethernet port for remote operation?" Tags="&lt;hf&gt;&lt;transceiver&gt;&lt;internet&gt;&lt;remote-control&gt;" AnswerCount="2" CommentCount="3" ClosedDate="2013-11-28T21:30:36.390" ContentLicense="CC BY-SA 3.0" />
  <row Id="883" PostTypeId="2" ParentId="882" CreationDate="2013-11-28T21:23:10.890" Score="1" Body="&lt;p&gt;Ten-Tec &lt;a href=&quot;http://www.tentec.com/omni-vii-hf-6m-transceiver/&quot; rel=&quot;nofollow&quot;&gt;Omni VII HF+6m Transceiver&lt;/a&gt; supports MS Windows. The remote GUI program can be downloaded &lt;a href=&quot;http://www.rfsquared.com/&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;. I do not know about Mac OSX or GNU/Linux.&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2013-11-28T21:31:46.917" LastActivityDate="2013-11-28T21:31:46.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="884" PostTypeId="2" ParentId="882" CreationDate="2013-11-28T21:27:00.690" Score="1" Body="&lt;p&gt;The not yet commercialised FlexRadio &lt;a href=&quot;http://www.flexradio.com/FLEX-6000_v2.pdf&quot; rel=&quot;nofollow&quot;&gt;FLEX-6000 series&lt;/a&gt; is said to be going to offer OS-independent remote operation.&lt;/p&gt;&#xA;" OwnerUserId="250" LastActivityDate="2013-11-28T21:27:00.690" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="885" PostTypeId="2" ParentId="830" CreationDate="2013-11-29T00:05:28.527" Score="8" Body="&lt;h1&gt;Loaded &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt;-factor&lt;/h1&gt;&#xA;&lt;p&gt;Like any resonant circuit, the bandwidth of an antenna is determined by its loaded quality factor, defined by &lt;span class=&quot;math-container&quot;&gt;$Q_{\ell}\overset{.}{=}\frac{X}{R}$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;The lower the loaded &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt;-factor, the broader the antenna's bandwidth will be:&lt;/strong&gt; &lt;span class=&quot;math-container&quot;&gt;$BW_{-3dB}=\frac{f_{res}}{Q_{\ell}}$&lt;/span&gt;, with &lt;span class=&quot;math-container&quot;&gt;$f_{res}$&lt;/span&gt; the resonant frequency.&lt;/p&gt;&#xA;&lt;h1&gt;Analysis of the loaded &lt;span class=&quot;math-container&quot;&gt;$Q_{\ell}$&lt;/span&gt; of a folded dipole in free space&lt;/h1&gt;&#xA;&lt;h3&gt;Resistance &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; (identical to that of an ordinary dipole)&lt;/h3&gt;&#xA;&lt;p&gt;In above formula for &lt;span class=&quot;math-container&quot;&gt;$Q_{\ell}$&lt;/span&gt;, the resistance &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; in the loaded resonant circuit will be half the radiation resistance &lt;span class=&quot;math-container&quot;&gt;$R_{rad}$&lt;/span&gt; when the antenna is perfectly matched. Hence, &lt;span class=&quot;math-container&quot;&gt;$R=\frac{R_{rad}}{2}$&lt;/span&gt;. Note that this value is not any different from that of an ordinary dipole, even though the input impedance &lt;span class=&quot;math-container&quot;&gt;$R_{in}$&lt;/span&gt; of a folded dipole is four times that of an ordinary dipole. The higher input resistance &lt;span class=&quot;math-container&quot;&gt;$R_{in}$&lt;/span&gt; is merely due to the impedance transforming property of closely spaced parallel wires. In conclusion, &lt;strong&gt;&lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; provides no explanation for the higher bandwidth.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;h3&gt;Reactance &lt;span class=&quot;math-container&quot;&gt;$X$&lt;/span&gt; (lower than that of an ordinary dipole)&lt;/h3&gt;&#xA;&lt;p&gt;Now, let us evaluate reactance &lt;span class=&quot;math-container&quot;&gt;$X$&lt;/span&gt; in above formula for &lt;span class=&quot;math-container&quot;&gt;$Q_{\ell}$&lt;/span&gt;. For a dipole in free space, &lt;span class=&quot;math-container&quot;&gt;$X$&lt;/span&gt; is determined by the self-reactance of the antenna conductor. This will be a combination of self-inductance of the element conductor and self-capacitance between the two element halves.&lt;/p&gt;&#xA;&lt;p&gt;Moreover, the closely spaced parallel conductors of a folded dipole &lt;strong&gt;should really be seen as one very thick conductor.&lt;/strong&gt; Hence, &lt;strong&gt;its self-inductance will be lower and its self-capacitance higher&lt;/strong&gt; than that of an ordinary dipole. Both effects result in a &lt;strong&gt;lower reactance &lt;span class=&quot;math-container&quot;&gt;$X$&lt;/span&gt;, hence lowering the loaded &lt;span class=&quot;math-container&quot;&gt;$Q_{\ell}$&lt;/span&gt; and broadening the bandwidth of the folded dipole.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-07-28T13:58:55.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="886" PostTypeId="2" ParentId="849" CreationDate="2013-11-29T00:46:31.687" Score="1" Body="&lt;p&gt;Vertical antennas are noisier on HF and below for three main reasons:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;At HF and below, vertical antennas have &lt;strong&gt;more ohmic losses&lt;/strong&gt; than horizontal antennas (mainly ground losses). Any ohmic resistance produces white, thermal &lt;a href=&quot;http://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;Johnson–Nyquist noise&lt;/a&gt; (QRN) which power is proportional to the square root of the resistance &lt;span class=&quot;math-container&quot;&gt;$\sqrt{R}$&lt;/span&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Vertical antennas are &lt;strong&gt;often not DC-grounded to earth.&lt;/strong&gt; This may allow for static electricity to build up under the influence of wind and precipitation. Eventually, a high static voltage will arc over and cause noise at that moment.&lt;span class=&quot;math-container&quot;&gt;$^{[1]}$&lt;/span&gt; This may happen at a relatively high frequency. Furthermore, arcing is a non-linear event, causing strong higher frequency harmonics.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Lightning&lt;/strong&gt; discharges in thunderstorms are mainly vertically polarised. The emissions of lightning peak at around 5 kHz and drop off as a function of &lt;span class=&quot;math-container&quot;&gt;$\frac{1}{f}$&lt;/span&gt;.&lt;span class=&quot;math-container&quot;&gt;$^{[2]}$&lt;/span&gt; Again, a lightning discharge is a non-linear event, causing strong harmonics. At 500 kHz, the signal of all kinds of lightning (earth-cloud, cloud-cloud,...) is still strong. Hence, most lightning detectors listen on 500 kHz because antennas are easier to build than on 5 kHz.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I see little valid argument in that human-made noise (QRM) were predominantly vertically polarised. Wiring in buildings is both vertical and horizontal.&lt;/p&gt;&#xA;&lt;p&gt;However, overhead power lines are horizontal and do have a vertical electrical field component to earth. Low-voltage overhead power lines are also more prevalent in the US than in Europe, where mainly underground cabling is used for low-voltage domestic power. In absence of any good study data, I would call the debate still open on this point.&lt;/p&gt;&#xA;&lt;h2&gt;References&lt;/h2&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.repeater-builder.com/antenna/static.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.repeater-builder.com/antenna/static.html&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Le Vine D. M., &amp;quot;Review of Measurements of the RF Spectrum of Radiation from Lightning,” &lt;em&gt;Meteorology and Atmospheric Physics&lt;/em&gt;, Vol. 37, No. 3, 1987&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2020-08-22T00:12:50.217" LastActivityDate="2020-08-22T00:12:50.217" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="887" PostTypeId="2" ParentId="861" CreationDate="2013-11-29T01:16:27.193" Score="2" Body="&lt;p&gt;Most antennas have a standing wave along there length and are therefore  effective impedance transformers. The feed impedance of a dipole might be of the order of 73Ω, at its ends, the impedance will be at least 2kΩ, if not higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Solving for voltage at the antenna ends, we will have:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$P=\frac{V^2}{R}\Rightarrow V_{rms}=\sqrt{P\cdot R}$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Peak voltage is indeed $\sqrt{2}\cdot V_{rms}$, but the voltages at the ends of a dipole antenna are balanced with respect to ground so: $V_{peak}=\frac{\sqrt{2}}{2}V_{rms}$, only half that value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming a transmitter power of 1kW: $V_{peak}=\frac{\sqrt{2}}{2}\sqrt{P\cdot R}=\sqrt{\frac{P\cdot R}{2}}=\sqrt{\frac{10^3 \cdot \not 2 \cdot 10^3}{\not 2}}=10^\frac{6}{2}=10^3=1kV$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna is loaded with a coil, the impedance will be transformed up to an even higher value. This is how a Tesla coil works. The resulting corona effect might be quite dramatic as shown in the picture below (1kW on 80m in short W4JRW dual-band dipole @ HB9DWU).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/nWUoI.jpg&quot; alt=&quot;1kW on 80m&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2013-11-29T01:52:01.420" LastActivityDate="2013-11-29T01:52:01.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="889" PostTypeId="1" AcceptedAnswerId="890" CreationDate="2013-11-29T04:42:38.237" Score="9" ViewCount="11855" Body="&lt;p&gt;High-end transceivers apparently come equipped with a water-fall display - something to do with improved spectrum visibility. This is supposed to lead to potentially higher QSO count and rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is a waterfall display? &lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="87" LastEditDate="2013-11-30T02:39:57.257" LastActivityDate="2013-11-30T02:39:57.257" Title="What is a waterfall display?" Tags="&lt;transceiver&gt;&lt;equipment&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="890" PostTypeId="2" ParentId="889" CreationDate="2013-11-29T08:50:09.730" Score="14" Body="&lt;p&gt;A waterfall display is a graphical representation of the signals across a frequency range, generally color-coded to indicate signal amplitude or strength, displayed over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Vg8jw.jpg&quot; alt=&quot;Sample waterfall display&quot;&gt;&lt;br&gt;&#xA;image source: &lt;a href=&quot;http://www.arrl.org/news/10-tips-for-the-psk31-digital-mode&quot;&gt;ARRL&lt;/a&gt; and K2NCC&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pictured in the image above is a number of signal traces. Since the above was taken across a frequency range where PSK31 is used, the signals are very narrow (only a few tens of Hz wide each), but it could easily cover a much larger frequency range &quot;zoomed out&quot; and still look basically the same. Here, black and dark blue is basically background noise, and bright white represents a very strong signal. We can also see that the station around 2450 Hz into the receiver passband appears to have insufficient sideband suppression (notice the additional, weaker signals centered on the main signal frequency).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having an overview of all signals across a portion of the spectrum allows you to quickly and easily determine whether there are any strong signals, which usually indicates stations that would be easy for you to make contact with. Not having to scan across the band to locate any station that might happen to be transmitting at the exact moment you pass over its frequency but rather being able to locate stations transmitting while you are working another station, means that you can immediately jump to the frequency when you are done with the previous station.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-11-29T08:50:09.730" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="891" PostTypeId="1" CreationDate="2013-11-29T16:37:09.810" Score="10" ViewCount="331" Body="&lt;p&gt;Situations that call for emergency operating usually have some hams working in field conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Relying on the mains grid could be problematic. A lead-acid battery would probably be heavy to lug around should the operator need to relocate in a hurry. The same could be argued for a generator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Under emergency conditions, what kind(s) of source(s) of power would be available and useful to an amateur radio operator?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2016-04-22T18:48:20.100" LastActivityDate="2020-04-13T17:19:48.740" Title="What sources of power are useful in emergency situations?" Tags="&lt;emergency&gt;&lt;power-supply&gt;&lt;dc-power&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="892" PostTypeId="2" ParentId="891" CreationDate="2013-11-29T20:35:08.203" Score="4" Body="&lt;p&gt;The most convenient power source would in fact be the lead-acid battery. However, not carried by hand, but in a vehicle. This provides an easy source of recharging power (just start the car), mobility to quickly relocate (driving), and the lead acid battery does have enough amperage to power most field radios (100 W+). As a lighter alternative, a Lithium battery pack may be a QRP solution, but the weight would be almost comparable to a lead acid for greater power levels. As a heavier alternative, a portable (gasoline) generator along with sufficient fuel may be plausible if many hands are available to carry equipment.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2013-11-29T20:35:08.203" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="893" PostTypeId="2" ParentId="891" CreationDate="2013-11-30T01:11:28.390" Score="1" Body="&lt;p&gt;There are two primary situations where emergency power is frequently needed:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Some sort of a field. In these situations, one tends to have a HT. Some HTs have AA batteries. These are the preferred source. Many times in such situations, one is working directly with first responders, whose equipment almost entirely uses batteries.&lt;/li&gt;&#xA;&lt;li&gt;Deployment at some facility. These tend to be fixed stations somewhere, where a power source is needed, along with the means to charge such a power source via AC power.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Ideally, one should be prepared for both situations.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-11-30T01:11:28.390" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="894" PostTypeId="1" CreationDate="2013-11-30T02:57:37.307" Score="3" ViewCount="159" Body="&lt;p&gt;I've heard the Houston AMSAT Net sends slow scan television pictures as part of its regular proceeding.  Is this unique to them or are there other examples out there?&lt;/p&gt;&#xA;" OwnerUserId="406" LastEditorUserId="29" LastEditDate="2013-12-02T08:47:38.563" LastActivityDate="2013-12-02T22:40:23.130" Title="Conducting a slow scan television net via an FM repeater" Tags="&lt;procedure&gt;&lt;repeater&gt;&lt;net&gt;&lt;sstv&gt;" AnswerCount="1" CommentCount="0" ClosedDate="2013-12-05T08:43:15.717" ContentLicense="CC BY-SA 3.0" />
  <row Id="895" PostTypeId="2" ParentId="877" CreationDate="2013-11-30T12:58:12.583" Score="0" Body="&lt;p&gt;A G5RV uses the ladder-line portion of its feed to help match the impedance of the antenna. I'm skeptical about putting a choke at the connection between the ladder-line and the antenna (which is what the question refers to as the &quot;antenna feed-point&quot;). But try it, after you've used the antenna without it and have a sense of how well it operates. If it's not as good after adding the choke, remove it.&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2013-11-30T12:58:12.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="896" PostTypeId="1" CreationDate="2013-11-30T19:35:44.363" Score="6" ViewCount="2570" Body="&lt;p&gt;I am looking for a reference list of the default repeater offsets by frequency and country on the 70cm band, to supply it into a radio control software. Most radios come with a list built-in, but the respective data is hard to collect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is an &lt;a href=&quot;http://cs.yrex.com/ke3fl/htm/RepeaterOffsets.htm&quot; rel=&quot;noreferrer&quot;&gt;US repeater offset list&lt;/a&gt;, that lists +-5MHz for the 440MHz range, but I know from Germany at least that +-7.6MHz are used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that a repeater operator may divert from the defaults, but most are following them and it is sane to provide them as the default radio configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What repeater shifts are used by default on 70cm in different countries?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Update:&lt;/strong&gt; Please provide the start frequency, end frequency and according shift where possible.&lt;/p&gt;&#xA;" OwnerUserId="89" LastEditorUserId="89" LastEditDate="2013-12-02T16:10:00.663" LastActivityDate="2013-12-02T16:10:00.663" Title="What are the default repeater offsets on 70cm in different countries?" Tags="&lt;repeater&gt;&lt;frequency&gt;" AnswerCount="2" CommentCount="5" ClosedDate="2013-12-03T05:45:35.490" ContentLicense="CC BY-SA 3.0" />
  <row Id="897" PostTypeId="2" ParentId="896" CreationDate="2013-11-30T21:38:37.713" Score="2" Body="&lt;p&gt;In Argentina and the USA, the offset for 70cm repeaters is +- 5.0 MHz.&lt;/p&gt;&#xA;" OwnerUserId="146" LastActivityDate="2013-11-30T21:38:37.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="898" PostTypeId="2" ParentId="896" CreationDate="2013-12-01T10:53:03.693" Score="2" Body="&lt;p&gt;In Slovenia (S5) the offset for 70cm repeaters is -7.6 MHz.&lt;/p&gt;&#xA;" OwnerUserId="103" LastActivityDate="2013-12-01T10:53:03.693" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="899" PostTypeId="1" AcceptedAnswerId="2423" CreationDate="2013-12-01T12:59:00.313" Score="14" ViewCount="6180" Body="&lt;p&gt;A small shielded loop is an antenna with a loop of wire, smaller than 1/10th of a wavelength in diameter, also surrounded by a shield. Often, they are constructed from coax. There is a gap in the shield somewhere. Feedpoint arrangements differ among implementations. Here's an example from the 1988 ARRL handbook:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/T61Wz.jpg&quot; alt=&quot;shielded loop&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are more examples, these actually designed as &lt;a href=&quot;http://www.compliance-club.com/archive/old_archive/030718.htm&quot; rel=&quot;noreferrer&quot;&gt;magnetic field probes for compliance testing&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/0S8oO.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such antennas are said to be quieter than ordinary small loops, and thus ideal for receiving, and popular for HF direction finding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, why? Why does the addition of a shield actually do, and why is it desirable?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2015-12-15T21:51:01.687" LastActivityDate="2015-12-15T21:51:01.687" Title="What does the addition of a shield to a small loop accomplish?" Tags="&lt;antenna&gt;&lt;equipment-design&gt;&lt;antenna-theory&gt;&lt;small-loop&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="900" PostTypeId="5" CreationDate="2013-12-02T08:51:48.240" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-02T08:51:48.240" LastActivityDate="2013-12-02T08:51:48.240" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="901" PostTypeId="4" CreationDate="2013-12-02T08:51:48.240" Score="0" Body="Use this tag for questions relating to Slow-Scan Television (SSTV) operations." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-02T08:51:48.240" LastActivityDate="2013-12-02T08:51:48.240" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="902" PostTypeId="5" CreationDate="2013-12-02T11:48:22.187" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-02T11:48:22.187" LastActivityDate="2013-12-02T11:48:22.187" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="903" PostTypeId="4" CreationDate="2013-12-02T11:48:22.187" Score="0" Body="a loop antenna having an electrically small circumference, often less than 1/10th wavelength." OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-12-02T13:29:28.760" LastActivityDate="2013-12-02T13:29:28.760" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="904" PostTypeId="1" CreationDate="2013-12-02T17:18:26.563" Score="3" ViewCount="125" Body="&lt;p&gt;Just what the title reads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An amateur may operate outside his own shack from another operator's station, or from a club-station etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a matter of protocol, the guest operator is expected to identify the host-station at-least at the beginning, and end of the QSO. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur Service regulations in &lt;strong&gt;VU-land&lt;/strong&gt; mandate the active participants in a QSO maintain their own log. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it necessary that the host-station log the QSO of a guest operator? &#xA;What about else-where on Earth?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-12-03T04:48:50.487" LastActivityDate="2013-12-03T05:47:29.967" Title="Is a guest-operator QSO recorded in the host-station log too?" Tags="&lt;legal&gt;&lt;logging&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="905" PostTypeId="2" ParentId="382" CreationDate="2013-12-02T19:29:55.803" Score="13" Body="&lt;p&gt;Simplified answer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;There is no relationship between SWR and receive performance.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is one condition for this simplification to be true: the received RF noise floor must be above your receiver's noise floor. Beyond this, anything you might do to increase the output from the antenna does nothing to increase the &lt;a href=&quot;http://en.wikipedia.org/wiki/Signal-to-noise_ratio&quot; rel=&quot;nofollow noreferrer&quot;&gt;signal to noise ratio&lt;/a&gt;, which is a better measure of receive performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SWR is a measure of the impedance mismatch between your antenna and transceiver. Whether transmitting or receiving, a higher SWR correlates with a less efficient coupling of energy between the transceiver and antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This inefficiency is problematic when transmitting because it can make a lot of heat, and it limits one's ability to overcome noise at the intended receiver. We could compensate with an amplifier, but high-power amplifiers are expensive, and big, and hot, etc. However when receiving, losses are easy to overcome. The heat generated is insignificant, and at the extremely low power levels involved in receiving, amplifiers are not large or expensive or difficult to design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember also that losses attenuate the signal, &lt;em&gt;and also the noise equally&lt;/em&gt;. Improving the SWR will increase the power received, but this is signal and noise, and thus does nothing to make the signal more intelligible, unless both are attenuated so much that most of the noise is no longer coming from the antenna, but instead from the electronics of the receiver. At HF, low-noise amplifiers are easy to design, and the ambient &lt;a href=&quot;https://ham.stackexchange.com/a/9833/218&quot;&gt;RF noise floor is relatively high&lt;/a&gt;, so antenna efficiency (including SWR-related losses) is not usually the limiting factor in receive performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a wide-band antenna for receiving, then you may do well with a non-resonant antenna. Such an antenna will be very inefficient, but this easily compensated with a low-noise amplifier. Because it is not operated at resonant frequencies, bandwidth is hardly a concern. A &lt;a href=&quot;http://en.wikipedia.org/wiki/Loop_antenna#Small_loops&quot; rel=&quot;nofollow noreferrer&quot;&gt;small loop&lt;/a&gt; or its electrical dual, the &lt;a href=&quot;http://en.wikipedia.org/wiki/Dipole_antenna#Elementary_doublet&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hertzian dipole&lt;/a&gt; could work. Or, consider a &lt;a href=&quot;http://en.wikipedia.org/wiki/Beverage_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Beverage antenna&lt;/a&gt; if you want directionality, which &lt;em&gt;does&lt;/em&gt; increase signal-to-noise ratio, provided it's pointing in the right direction.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-07-14T13:27:07.230" LastActivityDate="2018-07-14T13:27:07.230" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="906" PostTypeId="5" CreationDate="2013-12-02T19:45:43.327" Score="0" Body="&lt;p&gt;Being involved in Amateur Radio is a constant learning experience in itself. Part of the joy most operators receive is imparting knowledge onto others. The Education Tag and it's synonyms, should be used when the asker needs information on learning about a particular topic. More specifically, how and or where to learn about a given topic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This Tag should be used for questions relating to learning about Amateur Radio. While every question is technically about learning, this is not the purpose of the Tag. For example, If a user wants to know about a training resource for a given exam, this would be a good Tag to use. Another example may be that a user is interested in learning Morse-Code, and want's to know about good resources for learning this.&lt;/p&gt;&#xA;" OwnerUserId="172" LastEditorUserId="172" LastEditDate="2013-12-02T20:56:23.180" LastActivityDate="2013-12-02T20:56:23.180" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="907" PostTypeId="4" CreationDate="2013-12-02T19:45:43.327" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-02T19:45:43.327" LastActivityDate="2013-12-02T19:45:43.327" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="908" PostTypeId="2" ParentId="904" CreationDate="2013-12-02T20:06:47.973" Score="4" Body="&lt;p&gt;The question doesn't specify that the guest operator is a licensed amateur in the jursdiction in question and/or covered by a reciprocal operating agreement, otherwise we open up the 3rd party comminication bag of snakes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Speaking only for the US rules:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no &lt;em&gt;requirement&lt;/em&gt; that a guest operator logs be kept.  However, according to FCC §97.103(b): &quot;The FCC will presume that the station licensee is also the control operator, unless documentation to the contrary is in the station records.&quot; So, you don't have to log individual contacts, but it might well be a &lt;em&gt;very good idea&lt;/em&gt; to keep at least a record of who operated your station, with time and date and probably the frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reference: FCC Part 97: &lt;a href=&quot;http://www.gpo.gov/fdsys/pkg/CFR-2000-title47-vol5/pdf/CFR-2000-title47-vol5-part97.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.gpo.gov/fdsys/pkg/CFR-2000-title47-vol5/pdf/CFR-2000-title47-vol5-part97.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&#xA;The Canadian rules look quite similar (shocking, I know).  The relevant rules are located in their Radiocommunications Regulations: &lt;a href=&quot;http://laws-lois.justice.gc.ca/eng/regulations/SOR-96-484/page-11.html#h-44&quot; rel=&quot;nofollow&quot;&gt;http://laws-lois.justice.gc.ca/eng/regulations/SOR-96-484/page-11.html#h-44&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-02T20:18:23.720" LastActivityDate="2013-12-02T20:18:23.720" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="909" PostTypeId="1" AcceptedAnswerId="933" CreationDate="2013-12-02T20:08:07.070" Score="7" ViewCount="403" Body="&lt;p&gt;I live in the centre of a seaside town in the UK. Because of lack of space I have a random wire antenna in the loft of a small house, and pick up a lot of noise on the top band Sunday morning CW ragchew. I am about twenty hilly miles from most of my friends and the noise overwhelms many of their signals. I have a Maplin &quot;Super Scan Mk2&quot; all band vertical antenna with a built in amplifier chip, which I have never used. I would like to try mounting the Maplin antenna on a pole a few feet above the roof to see if I can cut down the noise on reception. Normally I run 25 Watts on transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My rig is an Elecraft K2 with KPA100, which has a separate dedicated receive antenna socket, so no RF will be transmitted directly into the Maplin antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, my question is: is the RF from my own transmission into the loft antenna likely to damage the nearby Maplin antenna internal amplifier chip during my tests?&lt;/p&gt;&#xA;" OwnerUserId="297" LastEditorUserId="76" LastEditDate="2015-12-15T22:04:34.017" LastActivityDate="2015-12-15T22:04:34.017" Title="Is it safe to mount an active scanning antenna close to an hf antenna?" Tags="&lt;antenna&gt;&lt;equipment-protection&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="910" PostTypeId="2" ParentId="904" CreationDate="2013-12-02T20:22:38.093" Score="3" Body="&lt;p&gt;&lt;strong&gt;In Sweden,&lt;/strong&gt; there is no requirement that &lt;em&gt;any&lt;/em&gt; logs be kept; keeping a station log is purely voluntary, and I know that many don't, particularly for mobile or repeater QSOs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only really relevant example I can think of is when I was an operator at the &lt;a href=&quot;http://web.comhem.se/sk0tm/&quot; rel=&quot;nofollow&quot;&gt;SK0TM&lt;/a&gt; station at the technical museum in Stockholm; the log book did not indicate the control operator, but other records did. SK0TM being the &lt;a href=&quot;http://www.ssa.se/&quot; rel=&quot;nofollow&quot;&gt;Swedish Amateur Radio Association's&lt;/a&gt; promotion station it was probably a bit more formal than most club stations; to be allowed as a control operator, you not only needed a license of your own but also to sign a legal agreement, receive training in the museum's policies as well as specific station instructions, prove by showing your operator badge (matched against the list of planned control operator by day) to the cashier that you were authorized to take care for the day of the key to the station room, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've operated club stations where I recall no formal records being kept as to who was the control operator at the time, though I do think most keep a thorough log. Even for club stations though, a station log is voluntary.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-12-02T20:22:38.093" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="911" PostTypeId="2" ParentId="904" CreationDate="2013-12-02T20:39:15.430" Score="2" Body="&lt;p&gt;Here in Serbia, logs of a station must be kept for two years.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a club radio station, each operator must sign the log for every use of the station; however the case of a guest using the station doesn't seem to be explicitly defined. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ratel.org.rs/editor_files/File/Regulativa/Pravilnici/Pravilnik%20o%20radioamaterima,%20korigovan.pdf&quot; rel=&quot;nofollow&quot;&gt;The relevant document&lt;/a&gt; says the following (translated by me):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;III.3. Log of an amateur radio station&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;Article 39&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The data relating to amateur radio communications of any amateur radio&#xA;  station shall be entered in the logbook of the amateur radio station.  &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The log of an amateur radio station shall be kept in a manner that&#xA;  provides a permanent record of written or electronic form.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Mandatory data to be entered in the logbook of amateur radio stations&#xA;  are:&lt;/p&gt;&#xA;  &#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;the day, month and year of actual amateur radio communication;&lt;/li&gt;&#xA;  &lt;li&gt;start time of amateur radio communication, and in&#xA;  case of longer transmissions, the start and end of the transmission;&lt;/li&gt;&#xA;  &lt;li&gt;The call sign which identified emission correspondent amateur station;&lt;/li&gt;&#xA;  &lt;li&gt;the name of the used amateur frequency band;&lt;/li&gt;&#xA;  &lt;li&gt;the type of emission;&lt;/li&gt;&#xA;  &lt;li&gt;the signature of the radio amateur (for club stations).  &lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;  &#xA;  &lt;p&gt;Day and month are entered as a group of four Arabic numbers.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The time is expressed as Coordinated Universal Time (UTC), and is&#xA;  always entered as groups of four Arabic numerals marking the hours and&#xA;  minutes (00 00).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;In addition to the information specified in&#xA;  paragraph 3 of this article, the information about signal quality and&#xA;  reception quality, the location of the amateur radio station whose&#xA;  transmission is received, the name of the operator of the&#xA;  correspondent station, the type and intensity of disturbance, etc. can&#xA;  be logged.  &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The log of an amateur radio station shall be kept for at least two years&#xA;  from the date of last entry.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="77" LastEditorUserId="76" LastEditDate="2013-12-03T05:47:29.967" LastActivityDate="2013-12-03T05:47:29.967" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="912" PostTypeId="5" CreationDate="2013-12-02T20:39:20.410" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-02T20:39:20.410" LastActivityDate="2013-12-02T20:39:20.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="913" PostTypeId="4" CreationDate="2013-12-02T20:39:20.410" Score="0" Body="Use this tag for questions relating to protection of equipment from undesired external inputs such as overvoltages, RF coupling, and other potentially damaging inputs." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-02T20:39:20.410" LastActivityDate="2013-12-02T20:39:20.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="914" PostTypeId="5" CreationDate="2013-12-02T20:41:17.047" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-02T20:41:17.047" LastActivityDate="2013-12-02T20:41:17.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="915" PostTypeId="4" CreationDate="2013-12-02T20:41:17.047" Score="0" Body="Use this tag for questions about physical installations, including physical mounting of equipment and equipment interconnections." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-02T20:41:17.047" LastActivityDate="2013-12-02T20:41:17.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="916" PostTypeId="2" ParentId="873" CreationDate="2013-12-02T21:48:00.900" Score="2" Body="&lt;p&gt;There isn't a way of transferring the credit towards a permanent license. Luckily, the US exams consist of a large degree of practical knowledge. Bottom line is, you should be close to getting the same level of license from your knowledge base. I've periodically taken the tests, and I score higher ever time than I did when I was studying originally, because I have learned through working with Amateur Radio the knowledge included in the test.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-12-02T21:48:00.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="917" PostTypeId="2" ParentId="894" CreationDate="2013-12-02T22:40:23.130" Score="1" Body="&lt;p&gt;Appleton WI &lt;a href=&quot;http://www.apleinc.com/WB9KMW/SSTV_2M.html&quot; rel=&quot;nofollow&quot;&gt;http://www.apleinc.com/WB9KMW/SSTV_2M.html&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Columbus OH &lt;a href=&quot;http://www.qsl.net/n/n8tut//sstv/&quot; rel=&quot;nofollow&quot;&gt;http://www.qsl.net/n/n8tut//sstv/&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Kokomo IN &lt;a href=&quot;http://www.youtube.com/watch?v=UGVMJu_1MpI&quot; rel=&quot;nofollow&quot;&gt;http://www.youtube.com/watch?v=UGVMJu_1MpI&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sacramento CA &lt;a href=&quot;http://www.n6na.org/nets/sstv-net&quot; rel=&quot;nofollow&quot;&gt;http://www.n6na.org/nets/sstv-net&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, a 2005 list, some of which are sure to be active still &lt;a href=&quot;http://www.hffax.de/html/net.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.hffax.de/html/net.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-12-02T22:40:23.130" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="918" PostTypeId="2" ParentId="873" CreationDate="2013-12-02T23:22:26.483" Score="2" Body="&lt;p&gt;There is no reciprocity agreement between Australia and the USA, and the US Federal Communications Commission rules for amateur radio licensing and operations also do not provide for any way to get a license except by taking the test(s).&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-12-02T23:22:26.483" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="919" PostTypeId="1" CreationDate="2013-12-03T00:10:46.313" Score="13" ViewCount="4604" Body="&lt;p&gt;A folded dipole is like an ordinary dipole, but with the ends extended and folded back, until they meet. Although it looks like a loop, I'm told it behaves similarly to a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/p5b8q.png&quot; alt=&quot;folded dipole&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does this thing work? If I could see the voltages and currents in the antenna, what would they look like? Why are the currents and voltages like that?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2015-12-15T21:59:50.307" LastActivityDate="2020-05-13T09:47:45.213" Title="How does a folded dipole work?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;folded-dipole&gt;" AnswerCount="5" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="920" PostTypeId="2" ParentId="899" CreationDate="2013-12-03T01:28:32.623" Score="2" Body="&lt;p&gt;The short answer is that the shield becomes the actual antenna.  It's addition makes it easier to construct a balanced loop which has deep nulls broadside to the loop.  These nulls would obviously be helpful in fox hunting / direction finding.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The long answer follows:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First of all the picture included from the 1988 ARRL Handbook has been shown to be a flawed design.  Current balance is critical to the performance of the antenna and that one has the shield gap next to the feed point.  So any current flowing on the outside of the feedline flows into one side of the loop where it is coupled to the inner conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best location for the gap is opposite the feed point as shown here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/n8uSH.png&quot; alt=&quot;Balanced Shielded Loop Antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna works when EM fields excite on the shield's surface. Skin effect isolates the outer shield wall from the inner shield wall.  Across the gap, the current on the outside of the shield produces a voltage, and that voltage in turn excites a current flow on the inner wall of the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The current flowing on the inner wall of the shield creates a current in the inner conductor through induction field coupling, and that current (and voltage) is coupled to the receiver feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; to clarify the use of the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At HF frequencies loops are subject to what is know as the &lt;em&gt;antenna effect&lt;/em&gt; because their size is a only a fraction of a wavelength, and they can pick up interference from a signal that is derived from the electric, rather than the magnetic, field. This distorts the loop's directional pattern, making shallow side nulls, if any.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To reduce the antenna effect, the loop can be shielded as discussed here and shown in the illustration I linked above.  This electrostatic shield balances the loop by making sure that all parts of it will have the same capacitance to ground. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The shield also protects the loop from the &lt;strong&gt;induction field&lt;/strong&gt; created by wires and other metal objects in the antenna's &lt;em&gt;near field&lt;/em&gt; (up to λ∕2π away). These items can take energy from a passing wave and produce magnetic fields that can induce spurious voltages in the loop. This energy is reactive (not radiated) and a product of the transformer effect; it fades rapidly with distance (inverse cube-power law).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is in contrast to the &lt;strong&gt;radiation field&lt;/strong&gt;, which is the part we are interested in, made up of electrical and magnetic fields at right angles to each other and originating in the antenna's far field (&gt; 2λ).  The power of this field always varies according to the inverse-square law.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The shield over the loop antenna will not appreciably decrease the amount of magnetic flux that passes through (and links with) the loop when a wave goes by as long as it is not complete (i.e., shorted to itself).  A gap must be left or the shield would form a shorted turn and it would reduce the magnetic field linking to the loop so that no signal could be received by the center conductor.  Using the gap, alternating currents can be induced in the metal shield, and voltages will be induced in the internal wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also use the antenna effect to intentionally detune the loop with second small antenna (usually a vertical).  This creates a pattern where there is only one null.  This would be in the plane of the loop, off one of the ends, rather than the sides.  This is also useful for direction finding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;ARRL Extra Class License Manual (2008)&lt;/li&gt;&#xA;&lt;li&gt;Radio-Electronics Magazine (June 1983)&lt;/li&gt;&#xA;&lt;li&gt;Wikipedia - &lt;a href=&quot;http://en.wikipedia.org/wiki/Near_and_far_field&quot; rel=&quot;nofollow noreferrer&quot;&gt;Near and Far field&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Wikipedia - &lt;a href=&quot;http://en.wikipedia.org/wiki/Electromagnetic_radiation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Electromagnetic Radiation&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;OSHA Field Memo - &lt;a href=&quot;https://www.osha.gov/SLTC/radiofrequencyradiation/electromagnetic_fieldmemo/electromagnetic.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Electromagnetic Radiation&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-04T16:28:43.527" LastActivityDate="2013-12-04T16:28:43.527" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="921" PostTypeId="5" CreationDate="2013-12-03T01:30:28.057" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-03T01:30:28.057" LastActivityDate="2013-12-03T01:30:28.057" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="922" PostTypeId="4" CreationDate="2013-12-03T01:30:28.057" Score="0" Body="Questions about the rules, processes and procedures in amateur radio contesting." OwnerUserId="164" LastEditorUserId="22" LastEditDate="2013-12-03T05:47:04.543" LastActivityDate="2013-12-03T05:47:04.543" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="923" PostTypeId="5" CreationDate="2013-12-03T01:47:55.970" Score="0" Body="&lt;p&gt;The original Q codes were created, circa 1909, by the British government to facilitate communication between maritime radio operators speaking different languages and were soon adopted internationally. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As their use grew, some structure was imposed as follows:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;QAA to QNZ - Assigned by the International Civil Aviation Organization (ICAO).&#xA;QOA to QQZ - For the Maritime Services.&#xA;QRA to QUZ - Assigned by the International Telecommunications Union (ITU).&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;These Q codes were originally used in Morse code (CW) transmissions to shorten lengthy phrases and were followed by a Morse code question mark (‏·‏·‏—‏‏—‏·‏·‏) if the phrase was a question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, Q codes are commonly used in voice communications as shorthand nouns, verbs, and adjectives making up phrases. For example, an amateur radio operator will complain about QRM (man-made interference), or tell another operator that there is &quot;QSB on the signal&quot; (fading); &quot;to QSY&quot; is to change your operating frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An extensive list of Q codes can be found here: &lt;a href=&quot;http://en.wikipedia.org/wiki/Q-codes#Q_codes_applicable_for_use_in_amateur_radio&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Q-codes#Q_codes_applicable_for_use_in_amateur_radio&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-03T05:47:13.077" LastActivityDate="2013-12-03T05:47:13.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="924" PostTypeId="4" CreationDate="2013-12-03T01:47:55.970" Score="0" Body="Questions about the meaning and customary use of Q-codes." OwnerUserId="164" LastEditorUserId="22" LastEditDate="2013-12-03T05:47:20.560" LastActivityDate="2013-12-03T05:47:20.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="925" PostTypeId="5" CreationDate="2013-12-03T01:52:48.480" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-03T01:52:48.480" LastActivityDate="2013-12-03T01:52:48.480" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="926" PostTypeId="4" CreationDate="2013-12-03T01:52:48.480" Score="0" Body="Questions about sunspots, how they are measured, what those measurements mean and how they affect amateur radio activity." OwnerUserId="164" LastEditorUserId="22" LastEditDate="2013-12-03T05:46:55.057" LastActivityDate="2013-12-03T05:46:55.057" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="927" PostTypeId="5" CreationDate="2013-12-03T01:53:43.407" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-03T01:53:43.407" LastActivityDate="2013-12-03T01:53:43.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="928" PostTypeId="4" CreationDate="2013-12-03T01:53:43.407" Score="0" Body="Questions related to fox hunting (chasing in some areas) and radio direction finding." OwnerUserId="164" LastEditorUserId="22" LastEditDate="2013-12-03T05:46:38.290" LastActivityDate="2013-12-03T05:46:38.290" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="929" PostTypeId="5" CreationDate="2013-12-03T01:55:16.930" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-03T01:55:16.930" LastActivityDate="2013-12-03T01:55:16.930" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="930" PostTypeId="4" CreationDate="2013-12-03T01:55:16.930" Score="0" Body="This tag is for questions of radio theory and/or the underlying physics." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-03T05:46:23.900" LastActivityDate="2013-12-03T05:46:23.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="931" PostTypeId="5" CreationDate="2013-12-03T01:58:13.380" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-03T01:58:13.380" LastActivityDate="2013-12-03T01:58:13.380" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="932" PostTypeId="4" CreationDate="2013-12-03T01:58:13.380" Score="0" Body="Use this tag for questions relating to the ever popular &quot;UHF&quot; connector (SO-239 is the &quot;female&quot; type mounted on a chassis; PL-259 is the &quot;male&quot; connector usually found on the ends of coax). " OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-03T05:46:15.853" LastActivityDate="2013-12-03T05:46:15.853" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="933" PostTypeId="2" ParentId="909" CreationDate="2013-12-03T05:54:12.183" Score="3" Body="&lt;p&gt;Generally speaking you should not place an active antenna near a transmitting antenna unless you know the active antenna can handle the power. Some can, but most, particularly generic wideband scanner antennas, aren't intended to be used near transmitting antennas and the input stage may be easily damaged with a powerful transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically discussing the antenna you mention, reports online indicate that this active antenna &lt;em&gt;is&lt;/em&gt; sensitive to nearby transmitters:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Unfortunately the Maplin Superscan Mk II is no longer available, or&#xA;  at least it wasn't when I bought one of their last two in the country&#xA;  a few years ago.  I'm now on my third  (having blown the first two by&#xA;  transmitting too much power too close to them) and am treating it very&#xA;  carefully.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(&lt;a href=&quot;https://groups.google.com/forum/#!topic/alt.radio.scanner.uk/hgCpmekkzz4&quot; rel=&quot;nofollow&quot;&gt;source&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other accounts suggest it's otherwise a very good wide spectrum active scanner antenna.  Were I in your shoes I'd look for other ways to resolve the noise problems and save the active antenna for more appropriate and safe uses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have details on the type of communications you're trying to receive, and the type of noise you're experiencing, ask another question and we may be able to help you solve your issue without putting your Super Scan Mk2 in harm's way.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-03T06:00:22.490" LastActivityDate="2013-12-03T06:00:22.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="934" PostTypeId="2" ParentId="876" CreationDate="2013-12-03T08:59:34.863" Score="5" Body="&lt;p&gt;As an addendum to the answer provided by Michael, there's also the point of what information to obtain from the distressed party. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If they're a &quot;professional&quot; or have otherwise had some sort of relevant training, they'll probably rattle off a whole checklist of bits for you to record and relay. Listen carefully, write fast, and &lt;em&gt;read back&lt;/em&gt; to confirm all of their data points once they've finished talking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If instead they're just someone with a radio, then you'll probably have to ask questions to direct their attention to the important details. Ideally you'll want to get the specific questions to ask from the emergency services you call. But depending on the circumstances, maintaining a three-way conversation may not be possible. So here are some important details you'll want to gather in pretty much every instance. Much of this is taken from aviation emergency handling, but applies in the general case as well:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;What is the nature of the emergency&lt;/strong&gt; - Plane crash? Hiking accident? Lost? Typically you won't have to ask, this is almost certainly going to be the first thing they tell you.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Who are you&lt;/strong&gt; - Again, another obvious one, but getting an identity can help focus rescue efforts.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Where are you&lt;/strong&gt; - You may have to ask for further clarification as they may assume you already know more than you do. Which state? Nearest city? Closest road? Landmarks? &quot;What do you see?&quot; If a search party is going to have to be sent, then the more detail you can get the better.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;How many people are there&lt;/strong&gt; - this is the &quot;number of souls on board&quot; question from maritime and aviation emergency handling. Most people won't even think to offer this detail, but it's one that every emergency responder will want to know. A head-count is invaluable, but if you can get it, a list of names is even better.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;What are your intentions&lt;/strong&gt; - Though most emergency advice boils to &quot;stay where you are&quot;, you probably won't be in a position to make recommendations.  But you can get an idea of what they are thinking. Find out their plan, their backup plan, and what they intend to do if &lt;em&gt;that&lt;/em&gt; doesn't work out. While the individual may say &quot;I intend to stay right here,&quot; it can be helpful to ask, &quot;if you &lt;em&gt;do&lt;/em&gt; leave, which direction do you think you'll you go?&quot; Lots of rescue effort is spent on guessing people's backup plan.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;What do you need&lt;/strong&gt; - While you're not in a position to offer aid, it is helpful to get a list of their needs, so that rescuers can prepare accordingly. (&quot;Alice has a broken leg and Tommie needs insulin&quot;)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;You'll need to use your judgement to determine what to ask, or indeed whether you should ask &lt;em&gt;any questions at all&lt;/em&gt;. As a rule, keep your communication clear but &lt;em&gt;very&lt;/em&gt; brief. It's not uncommon for someone to have only a few moments to get a transmission out while being otherwise busy managing their emergency.&lt;/p&gt;&#xA;" OwnerUserId="408" LastActivityDate="2013-12-03T08:59:34.863" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="936" PostTypeId="1" AcceptedAnswerId="937" CreationDate="2013-12-03T19:21:01.850" Score="8" ViewCount="5132" Body="&lt;p&gt;I have a piece of 75 ohm coaxial cable of unknown type (outer diameter is around 7 mm) which has developed a breakage in the center conductor (which is stranded). This cable is an adapter cable which connects my RG-6 type coaxial cable to my RTL-SDR card. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as I understand, the best way to solve the issue would be to simply replace the cable with another cable of higher quality. Unfortunately, this solution is not applicable to me, since the ends of the cable are attached to connectors of types which I can't easily obtain. The card end uses MCX connector and the RG-6 end uses a type of Belling-Lee connector suited for work with thin coaxial cables. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second idea that came to me and which I used with success with some other coaxial cables is to cut out the middle, damaged, section and leave short pieces of cable near the connectors I can't replace. After that, connect easily obtainable connectors to the healthy ends of the cable and mate the new connectors or use another coaxial cable in the middle. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;SMA and RP-SMA connectors come to my mind here, but the problem is that they are 50 ohm connectors in general. I also don't have the tools to install them and this one-off repair doesn't justify obtaining such tools. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another idea that I like the least but am currently most likely going to go with would be to directly connect the two healthy ends of the cable. Solder together the inner conductors, cover the joint with heatshink tube, then carefully solder together outer braided conductors and cover them in heatshrink tube as well. Problem here is that I don't like the reliability of the resulting work. A variation of this theme would be to solder the healthy ends of the existing cable to a new piece of a different, but similar, coaxial cable. The effect of this is that I'd have more room to work with. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally the worst solution I see right now would be to replace the connector on the card which uses the damaged coaxial cable with an SMA connector. The problem with this is that SMA connectors are in general 50 ohm connectors and this is a 75 ohm system. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is basically how do I repair this cable? Which of the options I could work with is the least bad and are there any better ideas I didn't think of?&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2013-12-03T20:58:03.477" LastActivityDate="2019-06-14T10:26:05.033" Title="How do I extend broken coaxial cable?" Tags="&lt;diy&gt;&lt;connectors&gt;&lt;coaxial-cable&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="937" PostTypeId="2" ParentId="936" CreationDate="2013-12-03T20:32:06.703" Score="4" Body="&lt;p&gt;A complete replacement will be the most reliable solution.  Barring that, replacement of one end if the resulting size is acceptable.  I would rate a manual repair dead last.  Soldered joints are rigid and even if the repair holds, it will place stress on adjacent sections of coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These connectors and in fact, complete cables with MCX on one end and a Belling-Lee connector on the other are available, inexpensively, on eBay.  One UK shop lists them all: &lt;a href=&quot;http://stores.ebay.com/RFShopUK&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://stores.ebay.com/RFShopUK&lt;/a&gt;.  They cost from about 2.00USD for the ends to about 10.00USD for the whole cable.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="9621" LastEditDate="2019-06-13T10:33:29.687" LastActivityDate="2019-06-13T10:33:29.687" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="938" PostTypeId="2" ParentId="697" CreationDate="2013-12-03T20:40:12.560" Score="1" Body="&lt;p&gt;&lt;a href=&quot;http://w6nbc.com/&quot; rel=&quot;nofollow&quot;&gt;W6NBC&lt;/a&gt; had an article published in QST in February 2011. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://w6nbc.com/articles/2011-02QSTtraps.pdf&quot; rel=&quot;nofollow&quot;&gt;Here's a link to it&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He details creating traps without forms, and they certainly look easier (once you got the technique down anyway) to build.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He summarizes four key points that make them advantageous:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Easier to make with a whole number of turns&lt;/li&gt;&#xA;&lt;li&gt;Lighter in weight&lt;/li&gt;&#xA;&lt;li&gt;Lower in Cost&lt;/li&gt;&#xA;&lt;li&gt;Simpler fabrication&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="172" LastActivityDate="2013-12-03T20:40:12.560" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="939" PostTypeId="1" AcceptedAnswerId="940" CreationDate="2013-12-04T00:13:07.407" Score="6" ViewCount="1360" Body="&lt;p&gt;I'm building my own dummy load, consisting of resistors submerged in liquid paraffin (or something similar, not 100% decided). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had some questions around heat dissipation and how I can calculate and avoid the thing over-heating. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is there a particular fluid that is better than other in both&#xA;performance and cost?  &lt;/li&gt;&#xA;&lt;li&gt;What sort of volume of fluid should I use assuming I would be using up to 100W, such that it won't start heating up quickly? Is there even a way to accurately calculate this?&lt;/li&gt;&#xA;&lt;li&gt;Are there any non-obvious safety concerns I need to think about when constructing and using this? I don't want to miss anything simple but obscure.&lt;/li&gt;&#xA;&lt;li&gt;In a sealed system like this, is there any risk of explosion due to pressure from the liquid heating?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="172" LastActivityDate="2013-12-04T17:58:32.933" Title="Dummy load construction and heat dissipation" Tags="&lt;diy&gt;&lt;equipment-design&gt;&lt;dummy-load&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="940" PostTypeId="2" ParentId="939" CreationDate="2013-12-04T03:27:08.050" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there a particular fluid that is better than other in both performance and cost?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://what-if.xkcd.com/71/&quot; rel=&quot;nofollow&quot;&gt;Water is hard to beat in both respects&lt;/a&gt;. The trouble is it has this tendency to become a conductor as it dissolves salts, so it must be insulated, or somehow kept very pure. Sometimes the trouble of this is too much, so some sort of oil is easier.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What sort of volume of fluid should I use assuming I would be using up to 100W, such that it won't start heating up quickly? Is there even a way to accurately calculate this?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Heat_capacity&quot; rel=&quot;nofollow&quot;&gt;Heat capacity&lt;/a&gt; is perhaps the relevant physical property here. &lt;a href=&quot;http://www.wolframalpha.com/input/?i=specific+heat+capacity+water&quot; rel=&quot;nofollow&quot;&gt;The specific heat capacity of liquid water&lt;/a&gt; is about $4.8J/(gK)$, and since 1mL of water weighs about 1g, we can also say the volumetric heat capacity of liquid water is about $4.8J/(mLK)$. We know that $W=1J/s$, and from these two things, given a power, and some volume of water, we can calculate at what rate the temperature will rise, if the temperature is uniform throughout, and no heat energy is being lost elsewhere. Let's use 100W and 1L as an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \require{cancel}&#xA;\frac{100\cancel{J}}{s}&#xA;\cdot \frac{\cancel{mL}K}{4.8\cancel{J}}&#xA;\cdot \frac{1}{1000\cancel{mL}}&#xA;= 0.21\frac{K}{s}\\&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since we are talking about a rate of change, you might as well consider $K=^\circ C$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, this involves two assumptions we know to not be true, the first being that the temperature of the water (or whatever coolant) is uniform everywhere. If the coolant is actively stirred, then it might be close enough to true. Otherwise, you are dependent on conductive currents and conduction to distribute the heat energy throughout the coolant, some parts are hotter and some are cooler, but the average temperature increases at this rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But this is somewhat moot, given the second assumption: that no heat energy is otherwise being lost. Probably you won't wrap the dummy load in blankets then operate it until it overheats, but rather construct it with a surface designed to radiate heat into the ambient environment well enough that it can be operated indefinitely without overheating. The job of the coolant is really just to provide a good thermal coupling between the heat sink and the heat sources, and to average out any transient thermal loads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The relevant physical property for the heatsink is absolute &lt;a href=&quot;http://en.wikipedia.org/wiki/Thermal_resistance&quot; rel=&quot;nofollow&quot;&gt;thermal resistance&lt;/a&gt;. This quantity has units $K/W$ and tells you, for a given constant power, what the temperature increase above ambient will be. It will be specified by the manufacturer's datasheet. You also need to add to this the thermal resistance of everything between the heat sources and the heat sink. Unfortunately calculating the absolute thermal resistance of your tank of coolant is hard, because it has a complex geometry, and the things likely to be used in the tank (water, oil) are actually not especially good thermal conductors: they move the heat around mostly by convection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the general approach is this: figure out, for your design power and allowable temperature rise, how big the heatsink would need to be assuming the best case, then make it bigger to account for other factors. &lt;a href=&quot;http://www.urbandictionary.com/define.php?term=TLAR&quot; rel=&quot;nofollow&quot;&gt;TLAR&lt;/a&gt; is probably the most economical method, and if you need something more precise, then pump a known power into a prototype, and if it gets too hot, make it bigger.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Are there any non-obvious safety concerns I need to think about when constructing and using this? I don't want to miss anything simple but obscure.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Besides the obvious ones of having a potentially large quantity of possibly flammable, probably very hot fluid, potentially heated beyond its boiling point, connected to an electrical energy source that might be capable of generating sparks or heating (especially under fault conditions) materials above said fluid's flash point? No, I can't really think of any. I don't think it's the non-obvious safety concerns that are going to kill you.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In a sealed system like this, is there any risk of explosion due to pressure from the liquid heating?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Very yes, see last question. I wouldn't seal it if I could help it, and if I did, I'd be sure it wasn't sealed very well, so an overpressure fault would just dribble rather than explode. Also couldn't hurt to make sure the pressure release mechanism indeed &lt;em&gt;dribbles&lt;/em&gt; and not &lt;em&gt;shoots a hot jet of oil&lt;/em&gt;. &lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-12-04T03:27:08.050" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="941" PostTypeId="1" AcceptedAnswerId="942" CreationDate="2013-12-04T15:36:26.150" Score="4" ViewCount="560" Body="&lt;p&gt;Sometimes on my Chinese uhf/vhf amateur transceiver, which goes all the way to 520 megahertz, i listen to GMRS/FRS/MURS frequencies. I always hear little kids messing around in the neighborhood on GMRS. Does the FCC really care about this? And what are they going to do about kids buying a Walmart radio and not having a license. &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2013-12-05T08:42:22.290" LastActivityDate="2013-12-05T08:42:22.290" Title="Do people really do GMRS liscenses" Tags="&lt;legal&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2013-12-05T08:42:33.667" ContentLicense="CC BY-SA 3.0" />
  <row Id="942" PostTypeId="2" ParentId="941" CreationDate="2013-12-04T16:50:11.017" Score="7" Body="&lt;p&gt;No license is required for FRS frequencies, and the power restriction is one-half (0.5) watt. As GMRS shares some of these frequencies, &quot;licensed&quot; GMRS users can use up to 5 watts on these. Obviously there is no way to differentiate between these users or power levels just by listening in. The higher GMRS-only frequencies are enforceable, but unless there is blatant jamming or deliberate interference it is unlikely the FCC would even bother with it.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2013-12-04T16:50:11.017" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="943" PostTypeId="2" ParentId="939" CreationDate="2013-12-04T17:21:34.730" Score="1" Body="&lt;p&gt;100W isn't very much power, compared to the load fluid dummy loads were meant to handle. 1kW dummy loads might use a 100W rated tubular resister inside the fluid.  You could, in fact, use a &lt;a href=&quot;http://www.digikey.com/product-detail/en/CHF8838CNF500L/CHF8838CNF500L-ND/3786086&quot; rel=&quot;nofollow&quot;&gt;100W 50Ω resister&lt;/a&gt; in air with a heatsink and skip the fluid altogether. You may want to enclose it in a Faraday cage of some sort (another reason loads were often made in paint cans) such as a mesh screen so you still have good airflow through the resister.  The kicker here is that you need a non-inductive resistor, and most tubular 100W resisters are coils.  Still, you can get thick film 100W resisters and use a regular cheap heatsink, or a chunk of random metal you probably already have lying around to get the same load rating. Use it as a hotplate to warm your beverage this winter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is little reason to go to the trouble of calculating the fluid needed for a 100W intermittent load.  If you still want to use a fluid dummy load, then just use a liter or more, watch the temperature if you need to transmit for more than a minute at a time, and move on with your testing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that most fluid dummy loads are only designed for intermittent use. They do not actually move the heat into the air at the same rate they receive it, they simply absorb it.  They are meant for short periods of testing, with the transmitter running, at most, 1 minute out of every ten minutes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They will overheat and explode if used beyond their design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the information you really need to provide is your duty cycle, and how long a testing period would you be using it for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're going to run 10-20 hundred watt tests, each lasting a minute or less with a break between each test of 10 minutes or more, then nearly any simple liter fluid dummy load will be able to handle the 10 to 20 watt hours of total energy you'll be putting into them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you need to do continuous testing, and need to dissipate 100W for hours at a time, then you'll have to look at a different solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, as mentioned above, 100W simply isn't that much.  Getting a 100W non-inductive power resistor, attaching it to a heatsink that can dissipate 100W continuously isn't going to be very expensive.  Then you can test as much as you like and never worry about your duty cycle, or the dummy load temperature and risk.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you want to test kW level transmitters at a low duty cycle, you can't beat the price of a fluid filled DIY dummy load.  For any other situation (lower power, or continuous use) fluid filled dummy loads aren't as attractive as other solutions.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-04T17:58:32.933" LastActivityDate="2013-12-04T17:58:32.933" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="944" PostTypeId="1" AcceptedAnswerId="945" CreationDate="2013-12-04T19:26:58.717" Score="6" ViewCount="293" Body="&lt;p&gt;Looking at HF antennas I've noticed that occasionally I'll see power ratings similar to &quot;200W (SSB)&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why would the modulation matter for an antenna's power output rating, and in the absence of other information how does one properly derate such an antenna for other modes?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-04T21:24:03.423" Title="Why do some antennas list modulation type alongside power rating?" Tags="&lt;antenna&gt;&lt;modes&gt;&lt;rf-power&gt;&lt;transmission&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="945" PostTypeId="2" ParentId="944" CreationDate="2013-12-04T19:55:32.220" Score="7" Body="&lt;p&gt;&lt;strong&gt;It's about transmission duty cycles.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, FM has a very high duty cycle during transmission: the transmitter's output power is constantly at 100% regardless of the amount of modulation. AM varies between 50% (carrier only) and 100% (full modulation). SSB varies with modulation between 0% and 100%. CW is like FM, 100% power output during transmission, but the actual periods of transmission are shorter for an overall much lower duty cycle than FM. PSK31 is somewhere in between FM and CW, with a high transmit power and moderate length transmissions. And so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What the manufacturer is telling you is mostly &lt;strong&gt;how much sustained power the antenna can tolerate.&lt;/strong&gt; This is a matter more of heat buildup than e.g. the risk of arcing across components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What this means is of course also that without a specified duty cycle, the &quot;SSB&quot; figure is largely meaningless. If you have weak modulation, you can run the transmitter at a much higher power output setting than the 200W indicated because you really aren't pushing very much power to the antenna. Conversely, if you have a very strong modulation, it's possible that the antenna can't take the power even though you have tuned the transmitter to a lower power output, because the &lt;em&gt;actual&lt;/em&gt; power being fed to the antenna is higher than the manufacturer intended.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you know what duty cycle (in percent) the manufacturer's specifications assumes, then you can work backwards to a safe continuous power. For example, if the maximum is 200W at 60% duty cycle, then the maximum safe continuous power is in the neighborhood of 60% * 200W = 120W. If the antenna is sold for amateur radio use we should also assume that the transmitter is not active 100% of the time, giving the antenna time to cool off. For a &lt;em&gt;truly continuous transmission&lt;/em&gt;, you'd probably want to reduce the number to about one tenth, to simulate a 10% transmit 90% receive cycle. &lt;em&gt;Once you know the safe continuous power, you can easily work your way backwards to any transmission mode.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The other side of the coin&lt;/strong&gt; is the maximum instantaneous power that the antenna can handle. This is easier, since we can fairly safely assume that the manufacturer wouldn't say 200 W &lt;em&gt;anything&lt;/em&gt; unless the antenna is capable of handling an instantaneous 200 W of RF. This is where issues such as arcing across coil windings, power handling capability at the feedpoint, etc., come in.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-04T21:24:03.423" LastActivityDate="2013-12-04T21:24:03.423" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="946" PostTypeId="1" CreationDate="2013-12-04T20:39:16.710" Score="11" ViewCount="270" Body="&lt;p&gt;Most satellites I've found transmit on VHF and receive on UHF or vice versa. Why is this? I would think there's enough space on a single band.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-02-04T14:54:31.887" LastActivityDate="2015-01-05T11:15:23.890" Title="Why do satellites receive and transmit on different bands?" Tags="&lt;uhf&gt;&lt;satellites&gt;&lt;vhf&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="947" PostTypeId="1" CreationDate="2013-12-04T20:42:52.997" Score="7" ViewCount="150" Body="&lt;p&gt;Lets say I want to do a bit of experimenting with some high bandwidth uses for transmitting data, high quality voice, etc. Which Amateur band will give me the maximum bandwidth, and what is the maximum width?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="22" LastEditDate="2013-12-04T22:04:35.020" LastActivityDate="2013-12-05T18:28:14.230" Title="Which band will I be authorized the most bandwidth?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;bandwidth&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="948" PostTypeId="1" CreationDate="2013-12-04T20:45:30.943" Score="3" ViewCount="291" Body="&lt;p&gt;Lets say 2 people can receive on 2 repeaters equally, but one hits a repeater transmitting better and the other person hits the other repeater better. Am I allowed to transmit on one repeater, and receive on another and my buddy does opposite?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2017-01-07T20:13:48.043" Title="Am I allowed to transmit on one repeater and receive on another?" Tags="&lt;repeater&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="949" PostTypeId="1" CreationDate="2013-12-04T20:48:06.327" Score="6" ViewCount="764" Body="&lt;p&gt;Lets say I want to call out CQ on 145.340, 145.940, and 146.140 at the same time, am I allowed to call simultaneously on all three then monitor all three for replies?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="9" LastEditDate="2013-12-04T21:12:38.293" LastActivityDate="2017-09-12T19:25:31.067" Title="Can I transmit on 2 frequencies simultaneously?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;procedure&gt;&lt;band-plan&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="950" PostTypeId="2" ParentId="948" CreationDate="2013-12-04T20:50:03.623" Score="4" Body="&lt;p&gt;As long as you are both operating according to your license there is no technical or legal reason why you couldn't, but more on this at the end.  At minimum it may be very confusing to other users of the repeaters and repeaters are individually owned and operated - you should make sure your specific use of the repeaters in this manner is acceptable to the individuals or clubs that operate them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as whether your license permits it, in the US the rule is &lt;em&gt;&quot;Each station licensee and each control operator must cooperate in selecting transmitting channels and in making the most effective use of the amateur service frequencies. (FCC Part 97.101(b))&quot;&lt;/em&gt; and this is generally the same around the world.  The spectrum granted for your use is a shared medium, and using more than what is necessary for a communication may be breaking the spirit of this rule.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that when you're tying up a single repeater, you're actually using two channels.  Your friend is tying up two channels as well.  So effectively your conversation is eating up four channels, during which time no one else can use them.  Using two repeaters to hold a single conversation is very excessive, and should only be done when necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using two repeaters for rag chewing is likely to annoy other operators in the area also interested in using the repeaters.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-04T21:09:12.547" LastActivityDate="2013-12-04T21:09:12.547" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="951" PostTypeId="2" ParentId="949" CreationDate="2013-12-04T21:24:42.653" Score="7" Body="&lt;p&gt;A relevant rule your license requires is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Each station licensee and each control operator must cooperate in selecting transmitting channels and in making the most effective use of the amateur service frequencies. (FCC Part 97.101(b))&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;While spamming multiple channels with the same transmission will save &lt;em&gt;you&lt;/em&gt; time, it clearly isn't the most effective use of the bandwidth you're sharing with others.  Further you can only respond to one at a time, so if you receive contacts on two of those channels, you'll essentially be ignoring a response to your question while you handle the other one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not good use of the bandwidth, it could be considered selfish and annoying to other operators, and may be in violation of your license.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-04T21:24:42.653" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="952" PostTypeId="2" ParentId="946" CreationDate="2013-12-04T21:26:40.903" Score="13" Body="&lt;p&gt;They don't always do that, but the reason for it is simply separating the transmitted RF from the received RF. A ground-based repeater uses a fairly large &lt;a href=&quot;http://www.wadsworthsales.com/siteimages/COMPD%20W.jpg&quot;&gt;duplexer&lt;/a&gt; to make sure that its transmissions don't feed back into its receiver; with a satellite, size and weight are at a premium, and having two widely separated frequencies requires much less hardware than two closely-spaced frequencies with a duplexer.&lt;/p&gt;&#xA;" OwnerUserId="105" LastEditorUserId="105" LastEditDate="2013-12-04T22:37:13.560" LastActivityDate="2013-12-04T22:37:13.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="953" PostTypeId="1" AcceptedAnswerId="958" CreationDate="2013-12-04T21:30:13.940" Score="8" ViewCount="1050" Body="&lt;p&gt;There are SWR/power meters with two separate gauges, and others that have them mounted so the gauge needles cross over each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aside from looking cool, does the cross-over point of the two meters provide specific or useful information?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2017-04-26T17:16:00.223" LastActivityDate="2017-04-26T17:16:00.223" Title="What is the point of a SWR/power meter where the needles cross over each other?" Tags="&lt;impedance&gt;&lt;rf-power&gt;&lt;equipment&gt;&lt;measurement&gt;&lt;swr-meter&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="954" PostTypeId="1" AcceptedAnswerId="956" CreationDate="2013-12-04T21:36:33.277" Score="11" ViewCount="1174" Body="&lt;p&gt;An SSB signal is an AM signal with the carrier and other sideband filtered out, if I understand correctly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, when specifying an SSB frequency do you specify the carrier frequency, then state which sideband, or do you specify the frequency the sideband is &lt;em&gt;actually&lt;/em&gt; centered on?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="87" LastEditDate="2013-12-05T15:58:03.990" LastActivityDate="2017-08-21T08:04:10.123" Title="What does a SSB frequency actually indicate?" Tags="&lt;modes&gt;&lt;frequency&gt;&lt;theory&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="955" PostTypeId="1" AcceptedAnswerId="966" CreationDate="2013-12-04T21:48:06.417" Score="19" ViewCount="721" Body="&lt;p&gt;The modern cellphone can carry on a full duplex conversation for a time period measured in hours on a battery half the size of my handheld transceiver.  My transceiver can barely receive for that length of time on its pack, nevermind transmit, and that's if I have a huge antenna much more unwieldy than the antennas included in modern phones..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One issue is that the cellphone in urban areas only needs to transmit a few miles, and the receiver can be significant more energy expensive to pick out weak signals.  In terms of our hobby, Repeaters are equivalent - allowing a smaller, more energy efficient handheld appear to be a big transmitter nearby - but the handheld is still an energy hog, and still limited to a small area around the repeater. Besides, the average cellular phone will still work for hours of talk time even when the nearest cell site is 10 miles away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that the technology exists, what is it that's preventing our amateur radios from achieving such good energy efficiency while still reaching a dozen miles for voice communications? &lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-05T20:22:20.613" Title="What makes cellphone transmissions so energy cheap?" Tags="&lt;rf-power&gt;&lt;efficiency&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="956" PostTypeId="2" ParentId="954" CreationDate="2013-12-04T21:49:06.913" Score="11" Body="&lt;p&gt;Normally in amateur radio when specifying a frequency you specify the nominal carrier frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For SSB and other suppressed-carrier transmission modes, you specify the frequency to which the BFO needs to be tuned to re-insert the suppressed carrier. For this to work, you also need to specify which sideband you are transmitting on; lower, upper, or both. (Remember it's possible to have suppressed carrier double sideband, with identical or separate modulation of the sidebands.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if you specified the center frequency rather than the suppressed-carrier frequency, you'd still need to specify which sideband you are modulating. If you get the sideband wrong, the audio will sound very strange because the demodulation will be inversed compared to the modulating signal. You can try this out for yourself by e.g. using USB to scan across the 7 MHz amateur radio band, where by convention the lower sideband is used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For CW and other carrier-only transmission modes, it means that you specify the actual center frequency of your transmission. (It's a center frequency because the on/off keying causes sidebands to appear around the center frequency.) The receiver's actual BFO frequency is offset from this value by some amount, normally 400-700 Hz, to generate an audible tone at a reasonable frequency. Most modern transceivers allow you to configure the BFO offset for CW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above, combined with the fact that SSB often uses a 300-2700 Hz modulation passband, means that on SSB you normally aren't actually transmitting on the indicated frequency, only near it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that other services may do things differently, and that channel-based amateur radio allocations may actually specify the center frequency rather than the BFO frequency. This is done e.g. for &lt;a href=&quot;https://www.fcc.gov/document/amateur-radio-service-5-mhz&quot;&gt;the 5 MHz amateur radio channels in the US&lt;/a&gt;, which are legally specified as center frequencies with a maximum total transmission bandwidth.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-04T21:54:09.847" LastActivityDate="2013-12-04T21:54:09.847" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="957" PostTypeId="2" ParentId="953" CreationDate="2013-12-04T22:27:35.003" Score="6" Body="&lt;p&gt;A properly calibrated cross-needle power meter such as e.g. the &lt;a href=&quot;http://www.mfjenterprises.com/pictures/MFJ-842.jpg&quot;&gt;MFJ-842&lt;/a&gt; actually tells you something more than just the forward and reflected power, which as you point out can just as easily be indicated by two separate instruments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The intersection of the needles gives you a pretty good indication of the actual standing wave ratio or SWR&lt;/strong&gt; because the SWR is directly related to the relationship between the forward and reflected power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, there's more utility to this than simply &quot;saving space&quot; or &quot;looking cool&quot;. Of course, you could have a &lt;em&gt;third&lt;/em&gt; meter showing the resultant SWR based on forward and reflected power indicated on two separate instruments, but why bother when you can put all the information into one and at the same time reduce the risk of measurement inconsistencies?&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-12-04T22:27:35.003" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="958" PostTypeId="2" ParentId="953" CreationDate="2013-12-04T22:29:20.480" Score="10" Body="&lt;p&gt;A cross-meter is capable of showing you three measurements simultaneously:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Output Power&lt;/li&gt;&#xA;&lt;li&gt;Reflected Power&lt;/li&gt;&#xA;&lt;li&gt;SWR&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://en.wikipedia.org/wiki/File:MFJ_tuner.jpg&quot; rel=&quot;noreferrer&quot;&gt;this image by Axel Schwenke on Wikipedia&lt;/a&gt;, you can see that the needle on the left indicates forward power, and the needle on the right indicates reflected power. The observed intersection of the two needles can be used to indicate the SWR of the system. The lines in the middle of the meter indicate what the SWR is for a given forward and reflected power reading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/rYvl4.png&quot; alt=&quot;cross-meter&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="29" LastEditDate="2013-12-04T22:31:57.277" LastActivityDate="2013-12-04T22:31:57.277" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="959" PostTypeId="2" ParentId="947" CreationDate="2013-12-04T23:02:40.347" Score="0" Body="&lt;p&gt;If you intend to follow the &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow&quot;&gt;national band plan&lt;/a&gt;, your best options lie within the 3300MHz to 3500MHz band, specifically at 3360.000 to 3400.000 and 3460.000 to 3500.000 you are allowed up to 22MHz bandwidth transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your next options occur in the 33cm and 70cm bands:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;420.000MHz - 426.000MHz - ...and experimental&#xA;909.000MHz - 915.000MHz - Analog and Digital broadband multimedia&#xA;915.000MHz - 921.000MHz - Analog and Digital broadband multimedia&#xA;921.000MHz - 927.000MHz - Analog and Digital broadband multimedia&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Check into the bandplan further, and look for local and regional bandplans to make sure you aren't stomping on anyone else's signal.  Otherwise keep in mind that one of the primary missions of Amateur Radio is to experiment and advance the art of radio communication.  It is likely that you can use more bandwidth in some areas outside the bandplan if you coordinate with others, and the bandplan can be changed if your use provides new opportunities to everyone.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-04T23:02:40.347" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="960" PostTypeId="2" ParentId="955" CreationDate="2013-12-05T00:08:01.397" Score="5" Body="&lt;p&gt;There are far more cell phone towers than repeaters. Imagine if you lived only 2 miles from a repeater. You'd probably hit it with only 1W all the time, and have no problems getting a full quieting signal. Cell phone towers are commonly even closer than that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as receive only, you should be able to receive for a long time on a simple battery. Perhaps there's some amplification of weak signals going on, but I'm not sure. Think of a portable FM radio, the batteries in that should last for quite a while, especially if using headphones and low volume, which is probably comparable to a cell phone near someone's ear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, cell phones have a protocol designed specifically to use low power, ie, digital modes. There is a strong signal sent to get their attention, then they automatically drop in power to the lowest transmission power required to make the connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bottom line is, for Amateurs to have similar service levels, there would have to be some sort of a centralization, which would complicate the system. It could be attempted, and I think has been, for SHF signals, but overall, Amateur Radio is decentralized. However, some gains could definitely be made by moving to digital modes, and some sort of feedback to the device on the signal quality so the power transmission could be appropriately managed.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-12-05T00:08:01.397" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="961" PostTypeId="1" AcceptedAnswerId="974" CreationDate="2013-12-05T00:30:46.057" Score="5" ViewCount="835" Body="&lt;p&gt;It's wintertime, which drives the concept of emergency preparedness here above the 45th Parallel. Am emergency-capable QRP rig is an excellent item to stuff into one's Go Bag or vacation gear, always but especially now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's an essential minimum for a QRP HF rig suited for rural (no-repeater)?&lt;/p&gt;&#xA;" OwnerUserId="285" LastEditorUserId="285" LastEditDate="2013-12-06T17:35:11.273" LastActivityDate="2013-12-06T17:35:11.273" Title="What makes a good emergency-capable QRP rig for travel?" Tags="&lt;emergency&gt;&lt;transceiver&gt;&lt;equipment&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="962" PostTypeId="1" CreationDate="2013-12-05T00:45:49.290" Score="5" ViewCount="216" Body="&lt;p&gt;Note!!!!: I am not looking for help with how make a map using Google Maps API (that part is done). I need help with finding data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am building a shortwave radio/HF listening log book online, and it uses Google Maps for the plotting of receiving and transmitting stations when logs are made. I wanted to add a layer for real-time critical frequencies to the map, like the one provided by the Australian Space Weather Agency &lt;a href=&quot;http://www.ips.gov.au/HF_Systems/6/5&quot; rel=&quot;noreferrer&quot;&gt;http://www.ips.gov.au/HF_Systems/6/5&lt;/a&gt; (which is an image file). Is there data anywhere that provides plot points for this map?&lt;/p&gt;&#xA;" OwnerUserId="412" LastEditorUserId="412" LastEditDate="2014-01-09T18:44:49.957" LastActivityDate="2014-01-09T18:44:49.957" Title="How to obtain raw data for Global Real Time foF2 Map" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;map&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="963" PostTypeId="2" ParentId="955" CreationDate="2013-12-05T13:15:06.127" Score="8" Body="&lt;p&gt;You are making an unfair comparison. HTs and amateur repeaters use the same technology now as they did forever ago. If you want to compare HT performance with cell phones, compare it with one of these:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/W4EQY.jpg&quot; alt=&quot;brick phone&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In that light, I think HTs fare favorably. Modern HTs have grown more modern batteries (NiCd -&gt; Ni-MH -&gt; Li-ion), but the RF bits have seen about as much technological advancement as the brick phone above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern cell phones have a whole ton of technological development that HTs haven't. For example, beam forming, digital modulation (&lt;a href=&quot;http://en.wikipedia.org/wiki/4G&quot; rel=&quot;nofollow noreferrer&quot;&gt;many generations of it!&lt;/a&gt;), sophisticated DSP, and dynamic transmit power. All of these things serve to make better use of transmit energy. Economies of scale dictate that cell phones have received orders of magnitude more engineering time than HTs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for why amateurs haven't adopted these technologies, I guess laziness. There is no economical incentive for amateurs to do all this stuff. The profitability of a repeater isn't tied to the number of the number of customers it can service. Development of HTs is limited by compatibility with repeaters and other HTs. There's no service contract that expires in two years, which, if renewed, subsidizes the purchase of a new transceiver. And, the FCC isn't likely to regulate more strictly how amateurs are allowed to use their spectrum, as they do with cell carriers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only time you might get some development is when some HT manufacturer thinks they might be able to sell some repeaters (Icom, D-STAR). Occasionally there are innovations among a small subset of hams that are more technologically inclined (codec2), but I'd wager it will be a long, long time before support for such things becomes ubiquitous, simply because most people are content with what they have, and there's little economical incentive for change.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-12-05T20:22:20.613" LastActivityDate="2013-12-05T20:22:20.613" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="964" PostTypeId="2" ParentId="954" CreationDate="2013-12-05T13:32:37.653" Score="5" Body="&lt;p&gt;SSB is, as you say, half of AM, without a carrier. That's the way to think about it if you are implementing it with traditional analog electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, here's a simpler way to think about it: SSB is the baseband signal shifted up into RF. Human hearing works from about 20Hz to 20,000Hz. Human voice needs only up to about 4000Hz. So, take your voice from 20Hz to 4000Hz, and shift that up to 14,000,020Hz to 14,004,000Hz, and you have SSB. (Although you are in the CW band, I won't tell anyone.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically, this is USB. LSB is the same, except all the frequencies are backwards: higher frequency in baseband is lower frequency in RF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dial frequency in either SSB mode is the one that corresponds to 0Hz in baseband. So, for USB, the dial frequency is the lowest frequency in the transmission passband, and for LSB it's the highest frequency. Typically the passband is 4kHz wide to accommodate human voice with reasonable fidelity.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="29" LastEditDate="2017-08-21T08:04:10.123" LastActivityDate="2017-08-21T08:04:10.123" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="965" PostTypeId="1" CreationDate="2013-12-05T17:06:10.653" Score="2" ViewCount="112" Body="&lt;p&gt;When using &lt;a href=&quot;http://freedv.org/tiki-index.php&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;FreeDV&quot;&gt;FreeDV&lt;/a&gt; or other digital voice modes, what's the preferred signal report? The software has a single &lt;a href=&quot;http://freedv.org/tiki-index.php?page=Microsoft+Windows+Quick+Start+Guide#Other_Features:&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;SNR&quot;&gt;SNR&lt;/a&gt; number, but that fluctuates quickly. Since it's a digital mode, you either get the transmission, or you don't, so the &lt;a href=&quot;https://web.archive.org/web/20161009145610/http://psb-info.net/&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;RSQ&quot;&gt;RSQ&lt;/a&gt; system doesn't seem ideal.&lt;/p&gt;&#xA;" OwnerUserId="90" LastEditorUserId="7798" LastEditDate="2020-06-20T16:39:12.643" LastActivityDate="2020-06-20T16:39:12.643" Title="Preferred signal report format for Digital Voice?" Tags="&lt;hf&gt;&lt;snr&gt;&lt;digital-voice&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="966" PostTypeId="2" ParentId="955" CreationDate="2013-12-05T17:55:04.913" Score="12" Body="&lt;p&gt;Remember that carriers are selling bandwidth, that’s it.  Actually, they are overselling it, exactly like cable modems (but that's another story).  If everyone in the coverage area of a cell tower tried to make a call at once, most of them would be unhappy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The carriers paid a boat load of money for their chunk of spectrum and their overriding goal is to maximize their use of their chunk. Since there is (in theory) competition, there is a focus on quality of service since all the plans seem strangely similar in price. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Towers are expensive, but as the others have mentioned, phones only have to transmit a few km at most to hit a tower and often less than 1 km in urban areas.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cell phones use a heavily optimized spread spectrum digital mode that is focused on short haul weak signal work.  Towers have a limit of 100W (omnidirectional) or 500W directional, however, in practice towers typically transmit in the range of 25-60 watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In most countries cell phones are limited to 2W PEP, however most modern cell phones have a peak power of about 300mW and are typically transmitting in the 100mW range.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to limit interference with adjacent sites, cell towers actively manage the transmit power both in the tower and on phones throughout a call, even between words.  In this case, what’s good for the carrier is good for the consumer since their drive to minimize power use means the phone’s battery lasts that much longer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;strong&gt;Contrast this with HTs&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;First batteries&lt;/strong&gt; – Economy of scale has let cell phone manufacturers use custom LiPo batteries for years where these are only now becoming standard on HTs.  Lots of the HTs out there have NiMH or even NiCd batteries still; a lower energy density.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Power&lt;/strong&gt; – If a cell phone were to transmit 5W PEP FM, it would run dead just as fast as an HT with the same size battery. The energy efficiency is in the mode used and the fact that the required range is very low.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Role&lt;/strong&gt; – Cell phones are designed to work only where people typically go: on the roads, shopping areas, cities and the infrastructure is sited to handle that.  However, people that use HT’s typically spend a good part of their time in places people don’t go as much: parks, woods, mountains.  So you’d need more range even if you were using the same mode. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Phil mentioned, we’ll see advanced features in add on modes first like D-STAR (Icom) and C4FM FDMA (Yaesu).  Of course, these guys are looking to sell radios, to there’s no incentive (yet) to agree on a protocol.  Initially this will just allow add on services.  It would take something major before people start replacing repeaters with ones that actively manage power.  Heck, it’s all some clubs can do to keep a basic 2m repeater up 24/7/365 on volunteer labor.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-05T17:55:04.913" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="967" PostTypeId="2" ParentId="965" CreationDate="2013-12-05T18:04:03.907" Score="2" Body="&lt;p&gt;There is no standard preferred signal report for digital voice.  At the moment it's best to provide the number, and then explain where you got that number from and perhaps provide additional information as needed so the recipient can understand the meaning of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As digital voice codecs advance and as users seek to evaluate them a few key characteristics will stand out as being measurable, and perhaps someone will combine those into a single report and report style.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As it's fairly early on for the codec mentioned, and others, I expect that we'll have to simply report what we hear and see using plain english and work on making a standard.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-05T18:04:03.907" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="968" PostTypeId="2" ParentId="947" CreationDate="2013-12-05T18:19:54.110" Score="4" Body="&lt;p&gt;Without a doubt, the 300GHz band. All frequencies above 300GHz are authorized for amateur use. There is no bigger band, amateur or otherwise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's all the &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow&quot;&gt;national band plan&lt;/a&gt; has to say about it:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All modes and licensees (except Novices) are authorized Amateur Bands above 10.5 GHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Also, it has the &lt;em&gt;coolest&lt;/em&gt; band designation: &lt;a href=&quot;http://en.wikipedia.org/wiki/Tremendously_high_frequency&quot; rel=&quot;nofollow&quot;&gt;Tremendously high frequency&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While there may be &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.4.159.3&quot; rel=&quot;nofollow&quot;&gt;some restrictions&lt;/a&gt; on what you can do here, they are woefully outdated and &lt;a href=&quot;http://www.arrl.org/news/arrl-files-symbol-rate-petition-with-fcc&quot; rel=&quot;nofollow&quot;&gt;likely to be revised&lt;/a&gt;. Given that you stick to &quot;good amateur practice&quot; (essentially, play nice), I really doubt you will be arrested. The 300GHz+ band is &lt;em&gt;all about&lt;/em&gt; experimenting with weird stuff, so it would almost be bad practice (and thus illegal) to &lt;em&gt;not&lt;/em&gt; try some extremely high-bandwdith experiment there.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-12-05T18:28:14.230" LastActivityDate="2013-12-05T18:28:14.230" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="969" PostTypeId="2" ParentId="962" CreationDate="2013-12-05T18:27:10.450" Score="4" Body="&lt;p&gt;The map projection used in the mentioned webpage is a cylindrical map projection, with the degrees latitude and longitude marked off on the left and bottom edges.  Each 10 degrees latitude is about 24 pixels, and each degree longitude is about 27 pixels. It shouldn't be too hard to take each pixel and convert it to a latitude and longitude from this data.  Then you'd use the google API to change the latitude and longitude back to the google's projection, which is a variant of the mercator projection.  The projections are different, so you can't simply overlay this image on a google map and expect it to match.  You'll have to collect the data points in terms of lat/lon pairs, then place them on the google projection using google's tools.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's reasonably obvious that they are extrapolating this map from limited data, though - the curves and contours suggest that there are only a handful of data points which they then process to generate the map. They themselves suggest this is the case in the text on that page explaining where they get the data from. It appears they don't release their aggregated data in any other form than the map, though.  You have two options - contact them and see if they will publish the hourly data in a way you can easily gather it, or go to the sites they list as their sources of data and collect the data yourself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neither option is particularly easy, but one or the other should work.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-05T18:27:10.450" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="970" PostTypeId="2" ParentId="715" CreationDate="2013-12-05T20:59:55.853" Score="3" Body="&lt;p&gt;The APRS system and protocol itself doesn't track iGate type or frequency.  There is a list of active iGates, but there is no frequency information for them, or for the packets they receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further no one appears to maintain a database of such stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However those that have used it indicate that the coverage is good enough that you really don't need to worry about coverage.  Depending on the propagation you will almost always make it to an iGate regardless of your position on any of the continents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it should be easy to generate such a list yourself over time.  Start broadcasting APRS packets on HF and watch APRS-IS feeds for your packets.  You should be able to determine what iGate passed them to the internet, and you can then find out the location of that iGate from its own APRS packets.  This will have to be done slowly over time as propagation changes, and to avoid preventing others from using the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that in order to make packets as small as possible, repeating stations strip some information from the packet as they repeat it.  This information would tell you what station(s) your packet has already gone through - in other words, your generated list of iGates will only show those iGates that actually placed your packet on the internet, not any inbetween that have repeated it.  Further, some HF igates may not be directly connected to the internet, thus you might find a packet gets received on HF, repeated on 2M, then received by a 2M iGate connected to the internet.  You'd see the last repeater in the packet on the internet, however since 2M is generally short-haul, it's likely that even if some packets are repeated via radios before hitting the internet you'll still get a good idea of the position of the actual HF receiver, since you're most likely interested in general regional positions of HF APRS gateways and repeaters.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-05T20:59:55.853" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="971" PostTypeId="1" AcceptedAnswerId="972" CreationDate="2013-12-05T21:25:39.593" Score="17" ViewCount="2138" Body="&lt;p&gt;Repeaters apparently often use large, expensive cavity filters to connect the receiver and transmitter to the same antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why aren't typical electrical circuits, such as inductors and capacitors used instead?  Wouldn't they be cheaper and smaller?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2018-09-01T05:15:31.720" Title="Why do repeaters use cavity filters?" Tags="&lt;repeater&gt;&lt;filter&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="972" PostTypeId="2" ParentId="971" CreationDate="2013-12-05T22:10:50.497" Score="19" Body="&lt;p&gt;A cavity filter is inductors and capacitors. Something like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/3waMG.jpg&quot; alt=&quot;enter image description here&quot;&gt;&#xA;(from &lt;a href=&quot;http://www.amateur-radio-wiki.net/index.php?title=What_is_a_cavity_filter%3F&quot; rel=&quot;noreferrer&quot;&gt;amateur-radio-wiki.net&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several reasons these are not constructed from more common discrete inductors and capacitors. Firstly, these filters must handle a bit of power. Not that you can't get high-power discrete capacitors and inductors, but they aren't cheap, or small.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But perhaps more importantly, the cavity filter is a notch filter. Since we want to pass some frequencies while deeply attenuating some other frequencies that are not very far apart, we need a deep, narrow, steep notch. The notchiness comes from the resonance of the capacitors and inductors, and with ideal components, at resonance, the stopband attenuation is infinite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sadly, we can't have ideal components. Any real inductor or capacitor will have some resistance and other non-ideal behaviors (self-resonance, etc) which serve to dampen the resonance of the filter. As this resonance is dampened, you get less of a notch, and more of a shallow trough. Too much damping and now the notch isn't deep or steep enough to accomplish the objective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Q_factor#Electrical_systems&quot; rel=&quot;noreferrer&quot;&gt;Q factor&lt;/a&gt; is one way to quantify the damping in an RLC circuit such as this. The cavity filter is a way of constructing an RLC circuit with a very low R, and thus, very high Q.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good cavity filter will also account for other practical considerations. Its tuning must be stable over temperature changes. It shouldn't leak a lot of RF, since it's probably collocated with other RF equipment. It should be able to handle high power without damage. It should be durable, since it's probably at a difficult to access location. It should come from the factory tested, and perhaps already tuned to the desired frequency. All these things add to the cost.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-12-06T03:49:53.333" LastActivityDate="2013-12-06T03:49:53.333" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="973" PostTypeId="1" AcceptedAnswerId="975" CreationDate="2013-12-06T00:09:39.617" Score="5" ViewCount="3970" Body="&lt;p&gt;Are there any special instructions for accessing a P25 repeater? What makes it different from a CTCSS/PL-tone-encoded repeater? What special features does a radio need to access it?&lt;/p&gt;&#xA;" OwnerUserId="128" LastActivityDate="2019-01-29T05:58:00.053" Title="How to access a P25 repeater?" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="974" PostTypeId="2" ParentId="961" CreationDate="2013-12-06T14:53:52.947" Score="5" Body="&lt;p&gt;This is a huge area and personal preference is going to drive the choices to a great degree.  For a good answer some parameters need to be defined:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;strong&gt;Are you only going to operate the rig if you are in trouble?&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This defines the size/cost/weight of your choice.  If you are going to also operate “normally”, the rig can take up more of your space/weight budget.  If you intend to only operate in emergencies, then something small and light is probably best.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;strong&gt;What mode will you be using?&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CW, SSB, or both?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;strong&gt;Define travel.  Are you going to be on foot, horseback, dog sled, snowmobile or other motorized transport?&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously this makes a huge impact in the weight and size categories.  Anything other than on foot realistically opens you up to just about any portable transceiver.  On foot, then something small with small (light) batteries is appropriate.  But the size there depends on how far you are going and if you will operate at other times than an emergency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;strong&gt;Who would you be trying to reach: other preppers, State Troopers, Alaska National Guard SAR, USCG, Mom and Dad? How far away are these people and what are the conditions (propagation-wise, in general) you will face where you are going?&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would define the capabilities needed in your rig. Your cute ¼W 40m CW only Tuna Tin II won’t do you much good for contacting the State Troopers, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don’t have a “go bag”, I live on the coastal plain between Baltimore and DC and there’s no hope to escape the region for a sudden event.  And if it’s not sudden, I have time to pack and being an organized individual, I could probably still get out of the house faster than many with prepared plans.  If I did live away from large cities with only 1 or 2 roads out of the area, my bag would look like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1)  My Android Smart phone with spare batteries. This has the usual assortment of apps loaded including a repeater listing app that only requires your GPS fix, not a connection to the network, to function.  Gives you bearing and range all repeaters in 25/50 miles depending on the setting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2)  SPOT Personal Tracker -- 99USD MSRP.  This is a GPS / Satellite unit that you can use to check in as OK or to summon help.  Uses commercial satellites to route “911” calls to the nearest SAR outfit to your location.  They make larger units that also function as regular GPS devices. I wouldn’t hike outside of cell coverage without this or something similar, emergency conditions or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3)  Cheap Chinese 2m/440MHz HT.  I have a couple.  These are small, light and so cheap and useful, even if you have a nice HT, having a few of these around is handy and at $35 each they are some of the cheapest ham gear you could own.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4)  Small folding Yagi for 2m and/or 440MHz.  These weigh almost nothing when made from an old tape measure and take up no room.  With one of these, the Chinese HT and the repeater book off the phone, the chances of hitting a repeater just went up dramatically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After that it would depend on answers to the above questions.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;For me&lt;/em&gt; the answer is my FT-817.  It’s hard to beat the DC to daylight coverage including the 5MHz Alaska Emergency Frequency.  For casual use or emergency only use, the internal batteries are all you need.  I have the W4RT NiMH pack in mine and it lasts me for hours.  If I want more time, I have a pair of NiMH packs from RC planes that I have set up with power poles.  Together the 3 packs last me 15-20 hours.  It has an internal keyer, so add a set of travel paddles, a 20m dipole and a VHF/UHF dummy load, I mean rubber duckie and I am set.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can use the dipole on 40m and 10m with acceptable SWR in a pinch.  If we are talking non-foot travel, then adding a tuner would be good.  Perhaps other antennas, my BuddiPole/MFJ vertical has given me contacts out to a couple thousand km at 5W.  the whole thing packs up to about 70cm long and 1-2kg.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;YMMV, but here's a start.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-06T14:53:52.947" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="975" PostTypeId="2" ParentId="973" CreationDate="2013-12-06T15:20:25.000" Score="4" Body="&lt;p&gt;P25 is a suite of standards for digital radio communications.  P25 is intended to facilitate interoperability between different public safety agencies during emergencies and/or joint operations.  Note that this is a North American standard (and a few other places), Europe has a similar but imcompatible standard called TETRA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A radio needs to be specially designed for P25 use.  The public safety agencies use reallocated TV frequencies in the 700MHz range. Most of the usual suspects make HTs for P25 and a couple make dual band radios for amateur use. Due to the audio quality and extra features, some amateur clubs are setting up P25 repeaters usually on the 70cm band, but some on the 2m band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P25 repeaters use whats called a NAC (Network Access Code) in place of the PL tone/CTCSS access common to amateur repeaters.  This a 12-bit prefix that is attached to every packet (including the digitized voice packets).  12 bits means 4096 possible access codes, quite a lot more room than the previous analog methods.  There are a few special codes, a default and an &quot;open&quot; code that will pass all traffic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To program a radio, you need to use a computer, it's too complex to allow keypad programming.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The commerical / public safety versions also support encryption using DES, triple-DES, and AES though it's not consider all that secure do to implementation flaws.  However, it's good enough to meet privacy concerns for first responders.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-06T15:20:25.000" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="976" PostTypeId="5" CreationDate="2013-12-06T19:23:42.513" Score="0" Body="&lt;p&gt;Questions that surround the items and objects used to take part in Amateur Radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;While most if not all questions could be related to equipment in some way, this Tag is specifically for questions about the equipment itself. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if I was to ask &quot;How does JT65 work?&quot;, while this would involve equipment, it would not be appropriate to Tag this question with the Equipment Tag. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the question was, &quot;How can I interface with my Yaesu FT-817 for JT65?&quot; this would relate to that equipment, and the Tag would be appropriate.&lt;/p&gt;&#xA;" OwnerUserId="172" LastEditorUserId="172" LastEditDate="2013-12-08T02:27:59.860" LastActivityDate="2013-12-08T02:27:59.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="977" PostTypeId="4" CreationDate="2013-12-06T19:23:42.513" Score="0" Body="Questions relating to equipment for Amateur Radio operation." OwnerUserId="172" LastEditorUserId="172" LastEditDate="2013-12-08T02:27:29.437" LastActivityDate="2013-12-08T02:27:29.437" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="978" PostTypeId="5" CreationDate="2013-12-06T19:25:15.037" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-06T19:25:15.037" LastActivityDate="2013-12-06T19:25:15.037" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="979" PostTypeId="4" CreationDate="2013-12-06T19:25:15.037" Score="0" Body="Programs and applications that are used to assist with Amateur Radio operations." OwnerUserId="172" LastEditorUserId="172" LastEditDate="2013-12-08T02:27:46.267" LastActivityDate="2013-12-08T02:27:46.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="980" PostTypeId="5" CreationDate="2013-12-06T19:26:30.060" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-06T19:26:30.060" LastActivityDate="2013-12-06T19:26:30.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="981" PostTypeId="4" CreationDate="2013-12-06T19:26:30.060" Score="0" Body="Questions specific to rules, regulations, and practices in Australia." OwnerUserId="172" LastEditorUserId="172" LastEditDate="2013-12-08T02:27:37.733" LastActivityDate="2013-12-08T02:27:37.733" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="982" PostTypeId="5" CreationDate="2013-12-06T19:27:35.973" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2013-12-06T19:27:35.973" LastActivityDate="2013-12-06T19:27:35.973" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="983" PostTypeId="4" CreationDate="2013-12-06T19:27:35.973" Score="0" Body="Questions specific to rules, regulations, and practices in Canada." OwnerUserId="172" LastEditorUserId="172" LastEditDate="2013-12-08T02:27:52.720" LastActivityDate="2013-12-08T02:27:52.720" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="984" PostTypeId="1" AcceptedAnswerId="1026" CreationDate="2013-12-07T06:02:37.427" Score="6" ViewCount="2785" Body="&lt;p&gt;I have an antenna that's well above the treeline, and I've heard I can add some small amount of protection by placing two bolt heads a short distance from each other, one connected to the antenna, the other connected to the ground rod.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What distance should I have the bolt heads apart to induce spark over on lightning strikes, but not interfere with my normal transmissions?  I won't be using more than 100W in the HF bands with this antenna.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="1362" LastEditDate="2019-01-11T21:40:05.497" LastActivityDate="2019-01-11T21:40:05.497" Title="DIY lightning arrestor - gap size?" Tags="&lt;antenna&gt;&lt;grounding&gt;&lt;safety&gt;&lt;lightning&gt;&lt;equipment-protection&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="985" PostTypeId="1" AcceptedAnswerId="991" CreationDate="2013-12-07T06:11:56.857" Score="8" ViewCount="363" Body="&lt;p&gt;I'm thinking about phased antenna arrays, and am wondering if it's possible to have three fixed position antennas, and vary the length of their individual feedlines to the common point through mechanical means.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to describe what I'm thinking is making a section of coax out of two telescoping sets of tubes, one outside shielding, and one inside conducting. I'd probably shoot for something other than telescoping antennas, and I'd be using a cheap DC drill with either woven thread or an acme screw to move the inner parts relative to the outer parts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can leave one antenna connected to the common point via fixed length coax, and then connect the other two with these variable length coax devices in the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like it's overly complicated, and that someone probably has come up with something better for switching a phased antenna array to point in any direction.  Surely someone has already built one (or perhaps it exists commercially and I just haven't seen it yet) or people have considered it, but other solutions are better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are other options I should consider?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-08T19:51:59.637" Title="Variable phase antenna" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="986" PostTypeId="1" AcceptedAnswerId="988" CreationDate="2013-12-07T18:24:54.457" Score="16" ViewCount="6858" Body="&lt;p&gt;It seems like 220MHz is the bastard step-child of the amateur world. Every HT is either 2m or 2m/70cm.  Some companies offer tri-banders, but they almost always add 6m (?!), not 220MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only way to get this band easily is the Chinese radios. I have a BAOFENG UV-5RC which is 2m/220MHz, and I have seen for sale single band 220 MHz mobile unit from TYT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In an otherwise competitive market, it seems odd to me that none of the major makers have 220 in their lineup.  Why?&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="29" LastEditDate="2013-12-08T12:37:09.910" LastActivityDate="2015-12-12T20:05:37.137" Title="What's wrong with 220MHz?" Tags="&lt;ht&gt;&lt;mobile&gt;&lt;vhf&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="987" PostTypeId="1" AcceptedAnswerId="995" CreationDate="2013-12-08T08:33:12.587" Score="3" ViewCount="1204" Body="&lt;p&gt;After reading &lt;a href=&quot;https://ham.stackexchange.com/questions/949/can-i-transmit-on-2-frequencies-simultaneously&quot;&gt;this question&lt;/a&gt;, I was wondering: is frequency hopping considered ``the most effective use'' of the frequency as stated in the FCC regulation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, is there any restrictions on how the hopping should be performed?&lt;/p&gt;&#xA;" OwnerUserId="165" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-09T16:06:07.063" Title="Legitimacy and Practice of Frequency Hopping in Ham Radio in United States" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="988" PostTypeId="2" ParentId="986" CreationDate="2013-12-08T12:36:19.767" Score="15" Body="&lt;p&gt;While for an authoritative answer to this I believe you'd have to ask the manufacturers directly (unless we happen to have someone here on the site who works for one of them), there is a pretty big &lt;em&gt;plausible&lt;/em&gt; reason why so few multiband radios include 220 MHz capability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The band is allocated to amateur radio mostly in the United States and Canada.&lt;/strong&gt; (Source: &lt;a href=&quot;https://en.wikipedia.org/wiki/1.25-meter_band#Countries_with_known_allocations&quot;&gt;Wikipedia&lt;/a&gt;.) Outside of ITU Region 2, the &lt;em&gt;only&lt;/em&gt; country listed as having an allocation there is Somalia. On the other hand, with minor differences in frequency ranges for which it is trivial to implement restrictions in software only, two meters and 70 cm are both allocated to amateur radio practically worldwide.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since 220 MHz also is not harmonically related to the band pair two meters and 70 cm, adding it to an existing design would probably require a fairly significant outlay in new electronics, filters etc. You would, at the very least, need to fix up the receiver so it performs well on the band, add the ability to tune the VFO to the band (assuming you don't already have a wide coverage VFO) and add a proper band pass filter to filter the transmitted signal. Other steps might be needed as well depending on the particular transceiver design. There is also the related problem that a 2m/70cm antenna is not resonant at 1.25 meters, which increases the risk of damage due to mistakenly transmitting into an unmatched load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would seem that manufacturers don't consider the demand for 220 MHz capability to outweigh the cost of such design changes for a relatively limited market. The conclusion we can draw from this line of reasoning is that the reason why none of the major manufacturers include a multiband HT with 220 MHz capability in their lineup is precisely &lt;em&gt;because&lt;/em&gt; it is a competitive market.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-12-08T12:36:19.767" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="989" PostTypeId="1" CreationDate="2013-12-08T13:33:33.617" Score="6" ViewCount="6409" Body="&lt;p&gt;So I'm still QRT; apart from a brown-out on the rig, the support on the inverted-vee toppled over in high winds. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks to the topple-over I discovered the conductors (SWG 16 bare copper) had started to turn greenish-black; a sure sign of oxidation. This &lt;em&gt;may&lt;/em&gt; be because I was QRT for a while before the mast came down. It could probably happen of it's own accord eventually even if the station were on the band with any regularity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My antenna was an inverted-vee with exposed conductors. It may possibly happen on other wire antennas (sp. antennae??) as well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which brings me to my questions&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Does oxidation of the antenna elements have any impact on the signal quality of the station?&lt;/li&gt;&#xA;&lt;li&gt;Is there a simple mechanism to avoid/mitigate such oxidation on the antenna elements?&#xA;&lt;ul&gt;&#xA;&lt;li&gt;E.g. Use a laminated conductor instead of bare&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Is any &lt;em&gt;regular&lt;/em&gt; maintenance activity necessary on an antenna?&#xA;&lt;ul&gt;&#xA;&lt;li&gt;E.g. In &lt;strong&gt;my&lt;/strong&gt; case, how much should the conductors be allowed to darken before replacing/abrading/scoring the conductors?&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2015-12-15T22:06:52.527" LastActivityDate="2015-12-15T22:06:52.527" Title="Does oxidation of the antenna elements have any impact on the signal quality of the station?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;maintenance&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="990" PostTypeId="2" ParentId="989" CreationDate="2013-12-08T19:20:39.777" Score="2" Body="&lt;p&gt;I don't know if a little oxidation affects the radiation of the elements.  I guess it could, but I suspect, not enough to matter in the big picture.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an 80m inverted-vee that I soldered up out of spare parts and it's exposed, but hasn't been in the air all that long.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there is still good, solid electrical contact on the connectors, then it's probably fine.  If you wanted to be sure though, clean them off and then coat them with spray paint or lacquer.  As long as it's non-metallic paint, it will be fine and keep the connectors from oxidizing. Seems like cheap insurance since the antenna is down already.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-08T19:20:39.777" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="991" PostTypeId="2" ParentId="985" CreationDate="2013-12-08T19:51:59.637" Score="3" Body="&lt;p&gt;I don't know about mechanically steerable arrays, but there are several hams locally here that swear by a four-square electronically steerable arrays.  The setup is typically done for 40m and is an array of four 1/4λ verticals arranged in a square 1/4λ apart. You run one feedline to a remote switch located in the center of the square and 4 identical length feedlines go from there to the individual antennas. You orient the square so the sides point in the directions you want to favor.  A controller goes in the shack to steer the array.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One company here in the US that makes an excellent controller is DXEngineering.  The controller runs about 200USD, one plus the remote switch is about 600USD.  The manual is available online so you can read up on it and see if it's something you're interested in.  I don't have a stake in them, but I have personally found their customer service and shipping speed to be excellent.  If I had the room at this QTH I would definitely put up one of these.  Alas, it will have to wait a few years...&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-08T19:51:59.637" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="993" PostTypeId="1" CreationDate="2013-12-09T10:27:08.530" Score="3" ViewCount="187" Body="&lt;p&gt;By FCC law. How many kHz away for a QSO are you allowed to start another QSO?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe that 3 kHz is the FCC rule.  Another Ham says that it's two.&lt;/p&gt;&#xA;" OwnerUserId="244" LastEditorUserId="29" LastEditDate="2013-12-09T13:22:39.810" LastActivityDate="2017-10-11T05:07:29.520" Title="How close in frequency to another transmission can I legally transmit?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="994" PostTypeId="2" ParentId="993" CreationDate="2013-12-09T11:56:54.760" Score="6" Body="&lt;p&gt;The truth is, there is no such regulation, except for this one, from &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.4.159.2&quot; rel=&quot;noreferrer&quot;&gt;Part 97&lt;/a&gt;. Bottom line is, the law is to not cause harmful interference. Good practice is to be at least 2 kHz to prevent bleed through, although 3 kHz is better. SSB emissions take 2.8 kHz. Of course, if you are using a digital mode, you can be quite a bit closer, and cause no interference at all.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;§97.311   SS emission types.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) SS emission transmissions by an amateur station are authorized&#xA;  only for communications between points within areas where the amateur&#xA;  service is regulated by the FCC and between an area where the amateur&#xA;  service is regulated by the FCC and an amateur station in another&#xA;  country that permits such communications. SS emission transmissions&#xA;  must not be used for the purpose of obscuring the meaning of any&#xA;  communication.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) A station transmitting SS emissions must not cause harmful&#xA;  interference to stations employing other authorized emissions, and&#xA;  must accept all interference caused by stations employing other&#xA;  authorized emissions.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(c) When deemed necessary by a District Director to assure compliance&#xA;  with this part, a station licensee must:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(1) Cease SS emission transmissions;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(2) Restrict SS emission transmissions to the extent instructed; and&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(3) Maintain a record, convertible to the original information (voice,&#xA;  text, image, etc.) of all spread spectrum communications transmitted.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-12-09T11:56:54.760" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="995" PostTypeId="2" ParentId="987" CreationDate="2013-12-09T16:06:07.063" Score="1" Body="&lt;p&gt;To answer your second question first:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC doesn't regulate the use of frequency hopping within the amateur radio spectrum.  The band plan has suggested modes of operation, which don't include mention of frequency hopping, within the amateur radio spectrum, but also include many &quot;experimental&quot; allocations where you could engage in any form of frequency hopping you might want to attempt.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as whether frequency hopping is considered the most effective use of a given chunk of bandwidth, the answer is no.  No one officially states or implies that frequency hopping is a particularly effective or most effective use of a frequency.  Depending on what form of frequency hopping you use, you may be able to more effectively or efficiently use a frequency than with some other modes, but not always.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note, however, that the wording is very subjective, &quot;most effective use of the amateur service frequencies&quot; doesn't restrict users from consuming a 25kHz FM channel with slow morse code, even though one couldn't easily prove that this is the most effective use of that frequency.  It may be that they should be using a different mode, but it's possible that they're running an experiment that is most effectively carried out in this manner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a wide range of what might be considered most effective, and as long as people aren't regularly abusing the spectrum we're given, there's little need to try to force &quot;one true way&quot; on the community, and add artificial restrictions to stop theoretical problems.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-09T16:06:07.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="996" PostTypeId="1" AcceptedAnswerId="1011" CreationDate="2013-12-09T16:12:17.510" Score="8" ViewCount="140" Body="&lt;p&gt;I'm considering tinkering with a new mode.  Of course I'll stick to experimental channels and low power for now, but as people notice my transmissions they won't immediately understand what is being transmitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I disseminate information that shows others how to receive and read my transmissions so as to avoid the appearance of encrypted or secret transmissions?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I have to disseminate that information before I start my testing, or can I do the testing, finalize the design, then publish?  What I'm worried about here is that as the mode evolves and changes, keeping already published information up to date is time consuming, and I'd rather publish a little overview, do the work until it's complete, then publish the final details.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-10T13:59:47.283" LastActivityDate="2015-11-13T12:41:29.747" Title="How do I notify and publish information on experimental modes?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;modes&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="997" PostTypeId="2" ParentId="989" CreationDate="2013-12-09T16:29:43.377" Score="2" Body="&lt;p&gt;Similar to &lt;a href=&quot;https://ham.stackexchange.com/questions/458/will-anodizing-or-powder-coating-or-wetcoating-painting-antenna-elements-affec&quot;&gt;anodizing and powder coating antenna elements&lt;/a&gt;, oxidation will affect the velocity factor of the antenna element, which in turn will affect the tuning of the antenna.  The change will be very slight, though for the typically very long antennas in the HF band it might be noticeable and measurable.  But that also means it's correctable.  You can use an antenna tuner to mitigate the effects, but you'll probably want to retune your antenna yearly.  Even with the oxidation, the antenna is perfectly fine as long as it's treated like any other bare antenna, and is well insulated from nearby conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The green is typical copper oxidation, the black may indicate &lt;a href=&quot;http://en.wikipedia.org/wiki/Copper%28II%29_oxide&quot; rel=&quot;nofollow noreferrer&quot;&gt;Copper(II) oxide&lt;/a&gt;, which typically requires higher temperatures to form, so it might be something else.  It can be a skin irritant, though, so wear gloves when handling it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As mentioned in WPrecht's answer, the oxidation will get in the way of transferring power to the antenna at any point where you want conductors to contact.  Make sure they are clean, consider using a good anti-oxidation conductive joint compound, and sealing the joint to make it airtight so you don't have to perform maintenance frequently.  You'll want to check it yearly as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wouldn't recommend spending much time replacing the wire with something different. The few problems of oxidation aren't significant enough to warrant replacement, or the effort removing the oxidation and coating it.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-11T21:20:15.083" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="998" PostTypeId="2" ParentId="986" CreationDate="2013-12-09T16:42:41.833" Score="13" Body="&lt;p&gt;220MHz has a &lt;a href=&quot;http://en.wikipedia.org/wiki/1.25-meter_band&quot;&gt;long and storied history&lt;/a&gt; which leads to the lack of available equipment, and thus low adoption rates in the Amateur Radio community.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The short version is that two things contributed to its lack of usage:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Few commercial bands are near enough that existing equipment can be simply modified to serve this band.  There are numerous commercial bands near 2M and 70CM, thus many, many commercial products can be modified, or simply used without modification, to serve those bands.  However there are few products ready-made that can easily be modified to run in the 220MHz amateur radio allocation, and it's been this way for decades.  &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The band has been, at various times, allocated and reallocated, divided, and placed on secondary use for some portions over the last several decades.  Some are hesitant to invest in a band with such a variable history, which suggests that it may not be available in the long term.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;We do have a handful of products now, and enterprising amateurs are setting up repeaters and encouraging use so that, unlike in the 90's, a commercial service can't easily show that it's not well used by the amateur community.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But due to its history, and the lack of nearby commercial bands and equipment, it simply isn't as popular as 2M and 70CM.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-09T16:42:41.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="999" PostTypeId="1" AcceptedAnswerId="1012" CreationDate="2013-12-09T17:19:46.070" Score="5" ViewCount="118" Body="&lt;p&gt;I've seen suggestions that it's better to practice a month prior to a contest, rather than at any other time prior to the contest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is special about a that time frame that it would be suggested so often?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="172" LastEditDate="2013-12-10T13:02:15.603" LastActivityDate="2013-12-10T14:26:14.060" Title="Why should I practice one month before a contest, rather than the week before?" Tags="&lt;contest&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1000" PostTypeId="1" AcceptedAnswerId="1002" CreationDate="2013-12-09T17:26:46.567" Score="11" ViewCount="197" Body="&lt;p&gt;I got into Amateur Radio for emergency preparation and to allow me to expand my electronics hobby.  My needs are being met, but I'm wondering if I'm missing out on increasing my skills by avoiding contesting which, in and of itself, doesn't particularly interest me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What will I learn in contesting that isn't as easily or quickly mastered if I don't participate in contesting?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In what other ways would contesting benefit me?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-15T21:50:01.587" Title="What skills will I learn from contesting?" Tags="&lt;contest&gt;&lt;education&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1001" PostTypeId="1" AcceptedAnswerId="1005" CreationDate="2013-12-09T17:31:44.960" Score="9" ViewCount="785" Body="&lt;p&gt;I got into Amateur Radio for emergency preparation and to allow me to expand my electronics hobby. Initially I didn't find much value in contesting or making contacts, but apparently there are some &lt;a href=&quot;https://ham.stackexchange.com/questions/1000/what-skills-will-i-learn-from-contesting&quot;&gt;valuable skills one can gain from contesting&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I spent some time listening to voice contacts, and the process appears to be fairly consistent, but I'm worried I might do something wrong, so before I jump in, what is the process of making a contact?  Is there a simple flowchart one might follow if exceptions happen during this process?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-10T08:21:12.703" Title="What is the process of making a voice contact?" Tags="&lt;procedure&gt;&lt;contest&gt;&lt;phone&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1002" PostTypeId="2" ParentId="1000" CreationDate="2013-12-09T17:53:18.953" Score="12" Body="&lt;p&gt;There are quite a few key things that can be learned by doing a contest. Here's a few key skills.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Learn to copy messages exactly.&lt;/li&gt;&#xA;&lt;li&gt;Improved recognition of faint signals.&lt;/li&gt;&#xA;&lt;li&gt;Ability to communicate in adverse situations. If a contest isn't an adverse situation, I don't know what is!&lt;/li&gt;&#xA;&lt;li&gt;Contesting often promotes mobile or portable communication, which is often useful in emergencies.&lt;/li&gt;&#xA;&lt;li&gt;One can learn a lot about propagation. For instance, I learned during the Sweepstakes Contest that if I wanted to make a contact with Alaska, I needed to do it in the afternoon hours.&lt;/li&gt;&#xA;&lt;li&gt;Learning one's equipment. The importance of fully knowing one's equipment cannot be overstated!&lt;/li&gt;&#xA;&lt;li&gt;Endurance. Quite frankly, talking on the radio can be quite difficult to do for long periods of time. I've been able to increase the amount of time that I can spend behind the radio from about an hour initially to 5-6 hours via contesting, which improves my skills.&lt;/li&gt;&#xA;&lt;li&gt;Improved recognition of weak signals. I learned how to get a signal out of the noise via contests.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;There are a bunch of other benefits as well, such as team building, getting to know your neighbors, getting WAS and DX done, etc. But those don't fully fit into the emergency preparedness category.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-12-09T17:53:18.953" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1003" PostTypeId="1" CreationDate="2013-12-09T18:32:02.770" Score="5" ViewCount="240" Body="&lt;p&gt;Lets say I use a computer to change my voices pitch, or use computer generated voices to hit a repeater. Is this allowed, or does it have to be my natural voice coming in on phone transmissions? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am in the United States of America.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="9" LastEditDate="2013-12-11T04:21:29.737" LastActivityDate="2013-12-11T11:57:58.527" Title="Is hiding your voice on phone legal?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;phone&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1005" PostTypeId="2" ParentId="1001" CreationDate="2013-12-09T20:03:34.397" Score="11" Body="&lt;p&gt;First off, amateur radio isn't very strict. With few exceptions, nobody is going to be very upset if you miss out on something during a casual contact. If you mess up too badly, you'll be asked to provide the missing piece of information, be it a signal report, location, repeat your call sign because it couldn't be copied, or whatever the issue may be. So don't be too worried about trying and failing. I've had people copy my call sign wrong on occasion too and it isn't a big deal; just grounds for a repeat of it, is about all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;For a non-contest (&quot;rag-chewing&quot;) contact, it's largely free-form.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first step is to announce your presence, or find someone looking to make contact themselves. On HF the standard way to do this is to call CQ (&quot;seek you&quot;); on repeaters practice varies, but it shouldn't be too bad calling CQ there either. You can also tail-end someone else's QSO, calling them up as they finish their contact. Don't make too long a CQ; you want to attract attention, not bore people to death before giving them a chance to respond. Even on HF SSB, a three-by-two CQ (three CQ followed by your call sign twice), possibly repeated twice, is usually plenty enough. If it doesn't attract attention you can always try again, or recognize that the frequency may be in use by a station you cannot hear. Or that simply nobody wants to talk to you, though that's quite rare. A CQ might be &quot;CQ, CQ, CQ, KD8OAS Kilo Delta Eight Oscar Alpha Sierra. CQ, CQ, CQ, KD8OAS Kilo Delta Eight Oscar Alpha Sierra, calling CQ and by&quot;. Here, &quot;calling CQ and by&quot; is a fairly common shorthand for &quot;calling CQ and standing by for a call&quot;. Don't rush things; someone hearing you may need to tune their antenna before they can answer, for example. Give it at least a minute or two before giving up on the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something that does irk me is when people get the order of the call signs wrong. It's &quot;&lt;strong&gt;to&lt;/strong&gt; &lt;em&gt;from&lt;/em&gt; &lt;strong&gt;from&lt;/strong&gt;&quot;, not the other way around. So if you were to call CL1SGN on amateur radio, it'd be &quot;CL1SGN from KD8OAS&quot;, &lt;em&gt;not&lt;/em&gt; &quot;KD8OAS to CL1SGN&quot;. Some people will actually go so far as to ignore a call if the call signs are given in the wrong order; and with a garbled transmission, you risk mistaking one station for the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming the remote station answers your call, unless they know you from before it will usually be a pretty brief transmission just to tell you they heard you and are willing to make a contact. Technically, at this point you have established contact. At that point, you'll usually give the call sign pair again, followed by your first name and location (to whatever precision is called for). Many also give a basic equipment report stating transceiver model and antenna type and (for non-repeater contacts) mention the amount of power they are putting out. If you are able to judge it at this point, also give a RST (signal) report, then hand over to the other station with something like &quot;CL1SGN from KD8OAS, go ahead&quot;, at which point the other station will generally respond with the same information. By the time they are finished, you should definitely be able to give an appropriate signal report. &lt;em&gt;Beyond that, the QSO may take off in almost any direction.&lt;/em&gt; Just keep in mind the legal limits on what can be discussed over amateur radio, as well as topics that are best not discussed (politics being one of them).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the time you feel happy with the contact, just courteously conclude it. This doesn't need to be very fancy at all. &quot;Well Jim, it's been nice talking to you. I'll be sending a QSL card via the bureau if that's fine with you. I'm OK in the call book or via the bureau. Have a good evening and maybe we'll talk again some other time. Seven-three and back to you.&quot; There are two ways of sending QSL cards, &quot;via bureau&quot; (through the amateur radio association in your country) or &quot;direct&quot; (mailing it directly to the other station). If you want a QSL card &quot;direct&quot;, be sure to say so as well as state whether (it better be!) your address is correct in the amateur radio call book. Also, don't &lt;em&gt;expect&lt;/em&gt; unsolicited QSLs for contest contacts, and don't give such extraneous details during a contest contact; just send a QSL yourself and write &quot;PSE QSL&quot; (&quot;please QSL&quot;) on it. The remote station will likely tell you either that they don't accept QSLs via the bureau or that they are OK in the call book as well. Either way, note it in your log if you want to send a QSL card later.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this point, it's pretty much up to what you want to do next. &lt;em&gt;As a general rule,&lt;/em&gt; it is commonly said that the station that called CQ &quot;owns&quot; the frequency (because they were &quot;there&quot; first), and it's courteous to either disown the frequency (&quot;you can have the frequency, Jim&quot;) and/or state that you are going off the air (&quot;KD8OAS going QR-tango&quot;, for QRT meaning you are closing down your station). Remember to finish with stating both call signs involved, so that anyone listening in will know who made contact with whom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once that's all over, write down the conclusion time for the contact in your log book, grab a blank QSL card from the pile, fill it out, put a stamp on it and place it in your &quot;out&quot; pile. Then, go reward yourself with a cup of hot cocoa or whatever strikes your fancy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The contents of a contest contact will depend very much on the specific contest,&lt;/strong&gt; but is generally pared down to the absolute minimum: call sign, signal report (normally a simple &quot;five nine&quot; even if the signal really isn't, to save time) and whatever the contest exchange happens to be; a locator, serial number, or something else. &lt;em&gt;The basic form&lt;/em&gt; is the same, only sped up about 10× or so. During a contest, if you are holding a frequency you might not even give your own call sign more often than every half dozen contacts or so. Of course, if you are scanning across the band and working whatever stations you can find, you'll need to give your call sign each time as nobody on the particular frequency will have any idea who you are otherwise. A contest CQ is also much shorter, sometimes shortened as much as to just your own call sign once followed by the word &quot;contest&quot;.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-10T08:21:12.703" LastActivityDate="2013-12-10T08:21:12.703" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1006" PostTypeId="1" AcceptedAnswerId="1833" CreationDate="2013-12-09T21:00:40.753" Score="6" ViewCount="710" Body="&lt;p&gt;I'm toying with a simple 1200 baud packet radio I built.  I'm attempting for it to be compatible with APRS, which uses the Bell 202 signaling, 1200Hz for mark and 2200Hz for space, which I assume map to 0 and 1 respectively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However it's not communicating with the commercial TNC I'm using or testing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried mapping 1 to space and 0 to mark as well, but that doesn't work either.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-05-27T10:47:39.673" Title="1200 baud packet radio can't communicate" Tags="&lt;diy&gt;&lt;modes&gt;&lt;packet&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1007" PostTypeId="1" AcceptedAnswerId="9251" CreationDate="2013-12-09T21:34:50.120" Score="3" ViewCount="209" Body="&lt;p&gt;I have a General class license.  If I'm working with an Extra class license holder, what do we have to do to allow me to work bands outside General, but inside Extra?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2013-12-09T21:44:37.423" LastActivityDate="2017-09-28T00:57:37.207" Title="How can I use all bands when I'm a guest on an Extra's station?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1008" PostTypeId="2" ParentId="1006" CreationDate="2013-12-09T22:32:02.077" Score="5" Body="&lt;p&gt;While 1200 baud packet radio uses AFSK with 1200 and 2200 tones, they don't correspond with digital 1's and 0's directly.  It employs NRZI encoding as well as bit stuffing. Non-return to zero inverted (NRZI) means that a 0 is encoded as a change in tone, and a 1 is encoded as no change in tone. This depends on having an accurate clock on both ends.  But even with a decent clock, a long string of unbroken 1's will end up providing no changes in tone, and after awhile the clocks will drift apart, and the receiver may think it's on the 50th 1 in a row, while the transmitter is on the 49th 1 in a row, because the tone is never changing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For that reason if there are five 1's in a row, a 0 is inserted at the end of the fifth 1.  This forces a tone change, so that the receiver can match its clock with the sender at least every 5 time periods based on the tone change.  The receiver, upon seeing a tone change after 5 time periods of no tone change, discards the tone change (the digital 0), realigns the clock, and continues to decode the bitstream.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is one time you might see 6 1's in a row, but that is a special flag on the AX.25 protocol, so it's not technically part of the 1200 baud system.  It's common in packet radio, though, so it should be kept in mind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found this, and more, at &quot;&lt;a href=&quot;http://n1vg.net/packet/&quot; rel=&quot;noreferrer&quot;&gt;1200 Baud Packet Radio Details&lt;/a&gt;&quot; by N1VG.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-09T22:32:02.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1009" PostTypeId="2" ParentId="1007" CreationDate="2013-12-10T00:36:07.040" Score="0" Body="&lt;p&gt;Technically to use an extra band, you have to use an extra call sign. So let's say your call sign was K1aaa, and your friends K2AA. You would have to identify by &quot;K1AAA/K2AA&quot;, or something like that. Or just have your friend ID every 10 minutes.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-12-10T00:36:07.040" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1010" PostTypeId="2" ParentId="1007" CreationDate="2013-12-10T13:31:51.113" Score="2" Body="&lt;p&gt;Relative to &lt;a href=&quot;https://ham.stackexchange.com/a/1009/5&quot;&gt;the above answer&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quite often during &quot;FIELD DAY&quot; operation an Extra Class operator will &quot;loan&quot; his call to a club or group in order to let them operate on all available frequencies, no matter what class of license the individual operator holds. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally speaking, a &quot;CLUB&quot; will elect an extra class operator as &quot;trustee&quot; for such activities.&lt;/p&gt;&#xA;" OwnerUserId="438" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-10T19:41:01.047" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1011" PostTypeId="2" ParentId="996" CreationDate="2013-12-10T13:42:59.547" Score="7" Body="&lt;p&gt;Back, before the Internet, the documents were published in magazines, conference papers and such – well after the protocols were designed and initial tests were done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some cases CWID (transmitting callsign using CW every now and then) has been used to make sure the transmissions are well identified even if the actual data is a bit hard to decode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nowadays, I think, people usually just experiment quite freely and publish when they have something ready.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're really worried, you can always do testing transmissions with a dummy load, keeping the radiated power so low that it cannot be considered a licensed transmission at all. After all, you can generally transmit on any frequency, any power, as long as you don't radiate that energy. If you're tinkering with a new mode, it might actually be easiest to do it using a &lt;strong&gt;simulated predictably noisy multipath software environment&lt;/strong&gt; without initially involving real radios at all!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Publication method ideas:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Set up a blog or wiki site&lt;/strong&gt;, let people know roughly which frequencies you're using, your callsign, and some general information about the mode.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Open Source&lt;/strong&gt; is the hip thing to do nowadays. Consider pushing your development code on Github or some other similar code repository - that's what I do myself. Your current code serves as pretty definite documentation as it is. As an added bonus you get an off-site backup of your code, and it might even attract other developers to help out.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-12-10T13:42:59.547" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1012" PostTypeId="2" ParentId="999" CreationDate="2013-12-10T14:17:43.963" Score="3" Body="&lt;p&gt;Sunspots significantly alter propagation characteristics, and &lt;a href=&quot;http://en.wikipedia.org/wiki/Solar_rotation&quot; rel=&quot;nofollow&quot;&gt;the sun revolves at a 26 to 38 day rate&lt;/a&gt;.  Since it's gaseous, it revolves differentially - faster at the equator and more slowly at the poles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While individual sunspots can last from days to weeks, sunspot activity on a position on the sun changes slowly over time.  While you can practice at any time prior to the contest the sunspot activity will be most similar about 28 days prior to the contest, and thus propagation conditions will be most similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;28 days works well because &lt;a href=&quot;http://www.suntrek.org/solar-surface-below/sunspots/where-sunspots-appear.shtml&quot; rel=&quot;nofollow&quot;&gt;sunspots most frequently appear just north and south of the equator&lt;/a&gt;, in the bands with the most turbulence, and it fits pretty well with the 7 day week we humans tend to follow.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-10T14:26:14.060" LastActivityDate="2013-12-10T14:26:14.060" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1013" PostTypeId="1" CreationDate="2013-12-10T17:40:13.343" Score="5" ViewCount="538" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Phase-shift_keying&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia indicates&lt;/a&gt; that in the digital domain ASK, FSK, and PSK are common.  It seems that only AM and FM are used for analog forms of communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why don't we use Phase Modulation techniques, and stick mostly to variants of AM and FM?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2018-08-20T16:25:30.943" Title="Is there such a thing as a phase modulation voice signal?" Tags="&lt;modes&gt;&lt;encoding&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1014" PostTypeId="1" CreationDate="2013-12-10T17:44:41.047" Score="3" ViewCount="247" Body="&lt;p&gt;Are there any existing codecs or modes, or are hams experimenting with modes that provide better than telephone/radio quality sound?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like there's a lot of opportunity here to stick to narrow band modulation schemes but at the same time provide better voice quality than what's currently experienced using cheap FM transceivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are the newer digital modes Icom and others coming out with better than telephone/radio quality?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-05-06T07:29:00.080" Title="HD quality voice?" Tags="&lt;modes&gt;&lt;digital-voice&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1015" PostTypeId="1" AcceptedAnswerId="1017" CreationDate="2013-12-10T18:16:28.030" Score="4" ViewCount="2650" Body="&lt;p&gt;I've seen a variety of radio block diagrams, and some have two mixers inline with the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the signal is already in a frequency range suitable to work with, what does the second conversion/mixer offer that the single-mixer design does not?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2013-12-10T19:40:44.653" LastActivityDate="2013-12-12T11:40:00.030" Title="What advantages does dual-conversion have over single-conversion superheterodyne?" Tags="&lt;receiver&gt;&lt;equipment-design&gt;&lt;superheterodyne&gt;&lt;mixer&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1016" PostTypeId="1" AcceptedAnswerId="1020" CreationDate="2013-12-10T18:32:02.637" Score="12" ViewCount="733" Body="&lt;p&gt;It is common wisdom that transmissions of any sort (perhaps unidentified, encrypted, in the FM broadcast band, etc.) are permitted if they are sufficiently low power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Where are the FCC regulations which permit this&lt;/strong&gt;, or &lt;strong&gt;where can I find a well-accepted interpretation of said rules?&lt;/strong&gt; People say they are in Part 15, but I read (well, skimmed) Part 15 and found mainly rules about offering equipment for commercial sale. I am specifically interested in permission for DIY or experimental transmitters and transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am also interested in how these rules compare to those applying to devices transmitting in the “ISM” bands; is the latter equal or lesser in restriction?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I am aware that while this question may be &lt;em&gt;amateur radio&lt;/em&gt;, it is not about &lt;em&gt;the Amateur Radio Service&lt;/em&gt;; I am asking it here in the hopes that it is a topic of sufficient interest to the community and that the relevant expertise is present.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="172" LastEditDate="2013-12-12T02:25:11.437" LastActivityDate="2013-12-12T02:25:11.437" Title="What are the (US) rules about unlicensed low-power transmissions?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;rf-power&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1017" PostTypeId="2" ParentId="1015" CreationDate="2013-12-10T19:04:56.793" Score="4" Body="&lt;p&gt;The reason that this is done is the difficulty of obtaining sufficient adjacent channel &lt;a href=&quot;http://en.wikipedia.org/wiki/Selectivity_%28electronic%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;selectivity&lt;/a&gt; in the front-end tuning while still achieving high levels of &lt;a href=&quot;http://www.radio-electronics.com/info/rf-technology-design/receiver-selectivity/image-rejection-response.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;image rejection&lt;/a&gt; across a range of frequencies as wide as the HF bands.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first intermediate frequency is higher, often in the range of 10MHz.  This is used for adequate image rejection, while the lower second intermediate frequency, usually the common 455KHz, provides high selectivity and gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;High-end HF transceivers have usually &lt;strong&gt;3 IF stages&lt;/strong&gt;, for even higher selectivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also review this &lt;a href=&quot;https://ham.stackexchange.com/questions/850/how-is-the-if-for-a-superhet-selected&quot;&gt;question&lt;/a&gt; and it's answers for more insight into IF selection.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-12T11:40:00.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1018" PostTypeId="2" ParentId="1013" CreationDate="2013-12-10T19:34:02.283" Score="3" Body="&lt;p&gt;PM is actually quite similar to FM in terms of modulation effects. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With phase modulation, the change of the phase angle is proportional to the message that is to be modulated onto the signal. With frequency modulation, on the other hand, the instantaneous change in frequency is proportional to the message that is to be modulated onto the signal.  So with a little work, an FM modulator can be used to generate phase modulated signals and visa-verse. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, that little extra work is more circuit complexity, so to base a transceiver on it requires more circuits and more cost.  Plus, there is the potential for ambiguity on decoding between signals at +180deg and -180deg.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-10T19:34:02.283" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1019" PostTypeId="1" AcceptedAnswerId="1021" CreationDate="2013-12-10T19:54:47.567" Score="10" ViewCount="812" Body="&lt;p&gt;I have a magnetic loop antenna that takes a long time to tune and of course, while tuning it, I need to be transmitting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the best procedure for tuning on air? I understand I need to check the frequency and identify myself before transmitting, but what if I'm nowhere near resonant when I do this? I'll just be getting louder and louder as I reach resonance, and probably no one heard me calling that I was performing a test initially. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I guess my first question is, what's the procedure from start to finish for tuning on the air? Keeping in mind, I can't quickly tune with my radio; due to the magloop, tuning is very specific and the SWR is too far out for my radio to automatically fix this. It's a very long process to tune it properly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, is it acceptable to simply put out a carrier signal while tuning? This is definitely more accurate and quick than tuning against a phone transmission, but is it allowed?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm located in California in the United States in case this is a locale specific answer.&lt;/p&gt;&#xA;" OwnerUserId="172" LastEditorUserId="76" LastEditDate="2013-12-10T20:46:04.407" LastActivityDate="2017-06-14T13:02:26.953" Title="What is the best practice when tuning an antenna on air?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;procedure&gt;&lt;antenna-tuner&gt;&lt;transmission&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1020" PostTypeId="2" ParentId="1016" CreationDate="2013-12-10T20:52:00.697" Score="5" Body="&lt;h2&gt;Overview&lt;/h2&gt;&#xA;&lt;p&gt;Title 47 Part 15 defines regulations which cover any device that&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Radiates RF, whether intentionally, unintentionally, or incidentally&lt;/li&gt;&#xA;&lt;li&gt;Doesn't require an &lt;em&gt;individual&lt;/em&gt; license for operation&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;While a device might not require an individual license to be operated, it may still require FCC testing.  This applies most strongly to devices made to be sold to others, which is why you see a lot of commercial references.  Just because you are not commercializing your device, though, doesn't make you immune to the regulations affecting commercial devices.  In fact the only difference between home built devices and commercial devices in this section is that home built devices are not subject to testing, verification, and declaration of conformity.  They are otherwise subject to all the same rules.&lt;/p&gt;&#xA;&lt;h2&gt;Regulation summary for home built, non-commercial, intentionally radiating devices&lt;/h2&gt;&#xA;&lt;p&gt;Here is a list of some (out of many) of the regulations you will have to follow whether your device is commercial or not.  Your device must:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;not cause harmful interference, and must accept any interference caused by other devices that follow the regulations they are subject to. (15.5.b)&lt;/li&gt;&#xA;&lt;li&gt;be disabled upon notice from the FCC that the device is causing harmful interference. (15.5.c)&lt;/li&gt;&#xA;&lt;li&gt;be designed and constructed in accordance with good engineering design and manufacturing practice. (15.15.a)&lt;/li&gt;&#xA;&lt;li&gt;be designed so that any user-operable controls do not allow the device to operate outside the limits of these regulations (15.15.b)&lt;/li&gt;&#xA;&lt;li&gt;be labeled correctly (15.19)&lt;/li&gt;&#xA;&lt;li&gt;be built for personal use, not marketed, not constructed from a kit, and built in quantities of five or less (15.23.a, 15.201b)&lt;/li&gt;&#xA;&lt;li&gt;not transmit more than spurious RF inside restricted bands detailed in 15.205.&lt;/li&gt;&#xA;&lt;li&gt;not conduct emissions onto the AC line, if connected to the AC line, greater than the limits specified in 15.207.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;h2&gt;General RF field limits&lt;/h2&gt;&#xA;&lt;p&gt;For intentional radiators devices must not emit a field strength stronger than specified for the frequency ranges measured at the distance specified:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;   MHz            Field Strength (microvolts per meter)   Measurement distance(meters)&#xA;0.009 -   0.490     2400/F(kHz)                           300&#xA;0.490 -   1.705   24,000/F(kHz)                            30&#xA;1.705 -  30             30                                 30&#xA; 30   -  88            100                                  3&#xA; 88   - 216            150                                  3&#xA;216   - 960            200                                  3&#xA;960   -  ∞             500                                  3&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;Unless otherwise specified under Additional Provisions and elsewhere(15.211-15.2xx) any intentional radiator following all other regulations is not restricted to any specific mode, modulation, or transmission scheme. (15.215.a)&lt;/p&gt;&#xA;&lt;p&gt;Note that most of these bands have additional provisions&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2013-12-10T21:08:08.027" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1021" PostTypeId="2" ParentId="1019" CreationDate="2013-12-10T20:58:12.970" Score="7" Body="&lt;p&gt;I am pretty sure this isn't covered explicitly in Part 97 and probably falls under the &quot;don't cause intentional interference&quot; clause.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The practice I was taught is this:  &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Tune off the pileup you found several KHz to a 'clear' spot&lt;/li&gt;&#xA;&lt;li&gt;reduce power to the either the lowest the rig will go or the least that will facilitate the tuning process&lt;/li&gt;&#xA;&lt;li&gt;Switch to CW mode&lt;/li&gt;&#xA;&lt;li&gt;key the transmitter (hold down the PTT) and tune away&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;When you are done:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Unkey the transmitter&lt;/li&gt;&#xA;&lt;li&gt;Send your callsign to identify your transmission&lt;/li&gt;&#xA;&lt;li&gt;Go back to SSB mode&lt;/li&gt;&#xA;&lt;li&gt;Go back to full power (I forget to do this more often than I would like to admit)&lt;/li&gt;&#xA;&lt;li&gt;Tune back to where you were&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="164" LastEditorUserId="1362" LastEditDate="2016-12-19T15:47:09.450" LastActivityDate="2016-12-19T15:47:09.450" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1022" PostTypeId="2" ParentId="1014" CreationDate="2013-12-10T22:22:13.887" Score="1" Body="&lt;p&gt;Because of the US Federal mandate to make efficient use of spectrum, the digital modes (including, but not limited to, &lt;a href=&quot;https://en.wikipedia.org/wiki/Multi-Band_Excitation&quot; rel=&quot;nofollow&quot;&gt;AMBE/D-Link Voice&lt;/a&gt;, &lt;a href=&quot;http://wiki.radioreference.com/index.php/Project_25&quot; rel=&quot;nofollow&quot;&gt;APCO-25&lt;/a&gt;, Codec2 and &lt;a href=&quot;http://freedv.org/tiki-index.php%20%20FreeDV&quot; rel=&quot;nofollow&quot;&gt;FreeDV&lt;/a&gt; ) are mostly moving in the other direction, towards equivalent intelligibility within less spectrum. &lt;/p&gt;&#xA;" OwnerUserId="285" LastEditorUserId="285" LastEditDate="2013-12-10T23:30:18.103" LastActivityDate="2013-12-10T23:30:18.103" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1023" PostTypeId="1" AcceptedAnswerId="1027" CreationDate="2013-12-10T22:30:22.017" Score="6" ViewCount="134" Body="&lt;p&gt;The ARRL hosts many contests throughout the year, and maintains a leaderboard of sorts to encourage competition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to rank on any of the leaderboards without knowing or using morse code?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-10T23:49:42.570" Title="Is CW necessary to be competitive in most ARRL contests?" Tags="&lt;united-states&gt;&lt;modes&gt;&lt;contest&gt;&lt;cw&gt;&lt;arrl&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1024" PostTypeId="1" AcceptedAnswerId="1053" CreationDate="2013-12-10T22:46:12.857" Score="4" ViewCount="239" Body="&lt;p&gt;There appears to be &lt;a href=&quot;https://ham.stackexchange.com/questions/935/near-constant-hf-communication&quot;&gt;some&lt;/a&gt; significant &lt;a href=&quot;https://ham.stackexchange.com/questions/574/what-bands-and-modes-will-give-me-voice-at-3-000-miles&quot;&gt;interest&lt;/a&gt; in establishing a fool-proof&lt;sup&gt;*&lt;/sup&gt; HF communications method for location to location communication regardless of current propagation conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that there's a &lt;a href=&quot;http://www.ncdxf.org/beacon/intro.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;beacon network&lt;/a&gt; which provides good information about how signals are traveling in various bands, it seems like it should be possible to create a transceiver that listens for the beacons, then chooses a suitable band for communication to a user-specified location.  If the receiver has a similar radio, it too would see similar conditions, and assuming it was set up knowing the location of the first transceiver it could probably choose the same band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With some additional pre-setup (agreed on specific frequencies inside each band) and a few attempts at communicating, it seems like one could design such a radio that would essentially automate the process an operator would go through, trying to contact a specific station, and have good chances of making it on one of the available HF frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this possible, or are there problems that would prevent such an approach working?  Assuming proper identification is used, and probably using digital modes to do the searching are there legal problems to having the radio perform a quick automated search, or does the operator have to have more direct control over the transmissions?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Essentially what I'd like is an automated station that, given a few minutes, can often find a path to a distant receiver to provide the desired long-distance, always available communications without advanced training and significant effort each contact would normally require.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*&lt;sub&gt;Of course there is no guarantee that any band will be open, but if there's an opening an automated system to find it would be the bee's knees.&lt;/sub&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-15T18:13:42.350" Title="How would one automate HF communications to a specific location?" Tags="&lt;united-states&gt;&lt;hf&gt;&lt;emergency&gt;&lt;phone&gt;&lt;automation&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1025" PostTypeId="1" AcceptedAnswerId="1031" CreationDate="2013-12-10T22:52:24.790" Score="10" ViewCount="531" Body="&lt;p&gt;I know repeaters don't have to have a control operator at the radio in order to transmit given certain conditions are met.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any restrictions to setting up automated stations which transmit upon receiving specific transmissions from their operators or other operators, but do not act as repeaters?  I know beacons are a special case in that they transmit on a schedule.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What restrictions apply to unattended, automated stations?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://ham.stackexchange.com/questions/1024/how-would-one-automate-hf-communications-to-a-specific-location&quot;&gt;specific problem I'm trying to solve&lt;/a&gt; involves automating a connection between two distant radios.  The originating radio needs to make several transmissions in sequence due to a user instructing it to, without giving it specific frequencies, sequences, and data to transmit (ie, the radio decides what to transmit).  The receiving radio, however, may not have a control operator nearby. It still has to listen, and if it gets a &quot;call&quot; from the originating radio it needs to respond, even if there's no control operator nearby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Under what rules would this type of automation be acceptable?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-06-14T22:32:58.300" Title="Aside from repeaters, what station types allow automated transmissions?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;automation&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1026" PostTypeId="2" ParentId="984" CreationDate="2013-12-10T23:05:24.280" Score="3" Body="&lt;p&gt;One enthusiast &lt;a href=&quot;http://webpages.charter.net/aj8mh-radio/notebookind1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;reports&lt;/a&gt;, &quot;&lt;em&gt;.029&quot; spacing for a KW station, and .045&quot; spacing for 2.5 KWs&lt;/em&gt;&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that a lightning arrestor doesn't stop an electrical discharge event, it merely shunts most of the energy to ground.  There's still a lot of damaging current that ends up in the wire which will damage attached equipment.  See &lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt; for a better overview of all aspects of lightning protection.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2013-12-10T23:05:24.280" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1027" PostTypeId="2" ParentId="1023" CreationDate="2013-12-10T23:05:59.943" Score="3" Body="&lt;p&gt;ARRL Hosts a list of their annual contests &lt;a href=&quot;http://www.arrl.org/contest-calendar&quot; rel=&quot;nofollow&quot;&gt;here.&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see from the list, there are a lot of CW based contents, but also Phone and RTTY.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd imagine that you wouldn't rank at all in an RTTY contest using CW, so it is possible to participate and rank without CW knowledge in at least some of the contests.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also available &lt;a href=&quot;http://www.arrl.org/contest-results-articles&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt; is a list of contest results sorted by year, you can view the results for Phone and other contests.&lt;/p&gt;&#xA;" OwnerUserId="172" LastActivityDate="2013-12-10T23:05:59.943" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1028" PostTypeId="2" ParentId="135" CreationDate="2013-12-10T23:08:17.243" Score="22" Body="&lt;p&gt;One of the biggest advantages of CW is that users worldwide can contact each other without knowing English, or any specific language.  Conversation is limited to the common Q codes, but these provide significant flexibility and ability to communicate making Morse Code a common language of sorts.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-10T23:08:17.243" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1029" PostTypeId="2" ParentId="1023" CreationDate="2013-12-10T23:49:42.570" Score="5" Body="&lt;p&gt;Most of the ARRL contests have separate events for phone and CW, November Sweepstakes, for example.  Some contests have both modes, like Field Day; all the state QSO parties usually support all modes and bands. Non-ARRL contests run the full gamut of rules.  The guys at the top of the heap are serious operators; they have their equipment and workflow finely tuned to maximize their score.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That doesn't mean you need a superstation, but if you don't you need to focus on the area you can excel at where the big guns don't qualify or participate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you can place on the leaderboards with just phone, but you can place on the CW leaderboards without knowing CW either.  As you know, contest exchanges are highly scripted.  So scripted you can use &lt;em&gt;fldigi&lt;/em&gt; or some similar program to decode CW and send macros in CW (with the appropriate interface to your rig link a SignaLink).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Really, to search and pounce CW, you should be able to recognize you call as a backup to the decoder, but it's not necessary.  Then, you only need two macros: 1) your call, 2) the exchange, for CQ WW: &quot;5NN 5&quot; (being in zone 5).  That's it. Notice you never send the running station's call sign, you can do this all on macros.  Now, strictly speaking, that's a weak excuse for a contact, but that's pretty much true of all contests anyways.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-10T23:49:42.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1030" PostTypeId="2" ParentId="1003" CreationDate="2013-12-11T11:57:58.527" Score="4" Body="&lt;p&gt;Nowhere in FCC Part 97 does it specify you have to use &lt;em&gt;your&lt;/em&gt; natural voice.  And, as many commenters have noted, there are lots of places where you don't.  I will add to that list:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I am the control operator for an unlicensed (or lower class) user &lt;/li&gt;&#xA;&lt;li&gt;Anyone other than the trustee operating a club station.&lt;/li&gt;&#xA;&lt;li&gt;Using my XYL's voice to record CQ macros for contesting ;)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The key is that the control operator is identified in accordance with FCC rules and since that licensee's identity is clearly known from the ULS database, there's no attempt to really hide from anyone who cares enough to look you up.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-11T11:57:58.527" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1031" PostTypeId="2" ParentId="1025" CreationDate="2013-12-11T12:02:31.017" Score="3" Body="&lt;p&gt;Digital signals are allowed, so long as they follow this &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.3.159.11&quot; rel=&quot;nofollow&quot;&gt;FCC regulation&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;§97.221   Automatically controlled digital station.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) This rule section does not apply to an auxiliary station, a beacon&#xA;  station, a repeater station, an earth station, a space station, or a&#xA;  space telecommand station.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) A station may be automatically controlled while transmitting a&#xA;  RTTY or data emission on the 6 m or shorter wavelength bands, and on&#xA;  the 28.120-28.189 MHz, 24.925-24.930 MHz, 21.090-21.100 MHz,&#xA;  18.105-18.110 MHz, 14.0950-14.0995 MHz, 14.1005-14.112 MHz, 10.140-10.150 MHz, 7.100-7.105 MHz, or 3.585-3.600 MHz segments.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(c) Except for channels specified in §97.303(h), a station may be&#xA;  automatically controlled while transmitting a RTTY or data emission on&#xA;  any other frequency authorized for such emission types provided that:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(1) The station is responding to interrogation by a station under&#xA;  local or remote control; and&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(2) No transmission from the automatically controlled station occupies&#xA;  a bandwidth of more than 500 Hz.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;[60 FR 26001, May 16, 1995, as amended at 72 FR 3082, Jan. 24, 2007;&#xA;  77 FR 5412, Feb. 3, 2012]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In any case, if there's a human on one end, I would think it would be considered remote control, and thus eligible for those rules. But just in case, I would stick to these regulations.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-12-11T12:02:31.017" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1032" PostTypeId="1" AcceptedAnswerId="1033" CreationDate="2013-12-11T13:46:30.773" Score="8" ViewCount="3311" Body="&lt;p&gt;I'm close to my EE. BSc finale and I'm looking to play around a little bit with the stuff I've learned. To be honest, I'm a little bit upset that after 4 years of learning communications theory, I'm not able to choose the hardware I need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My idea is to build a half-duplex walkie-talkie with the following reqs:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Low voltage operation. Till 5V.&lt;/li&gt;&#xA;&lt;li&gt;Range about 1.5 km LOS.&lt;/li&gt;&#xA;&lt;li&gt;ISM frequency use. (I prefer 433 MHZ UHF bands.)&lt;/li&gt;&#xA;&lt;li&gt;Single chip that doesn't require extra elements such as crystal or filters.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The idea is to install 2 walkie-talkies, one on each house. House are about 900m range. One has a direct window outside while the other is an interior office.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The application is for voice only. Considering the FM advantages I'll prefer it, but if there is a big difference of value then AM could be an option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The chip I'm looking for must be the smallest that can be.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen many chips (such as the following links) but I'm not sure that their digital buffers support voice applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.hoperf.com/rf_fsk/fsk/21.htm&quot; rel=&quot;noreferrer&quot;&gt;http://www.hoperf.com/rf_fsk/fsk/21.htm&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://www.melexis.com/Wireless-Multi-Market--Sensing/RFIC-Transceivers-27-to-950MHz/TH7122-121.aspx&quot; rel=&quot;noreferrer&quot;&gt;http://www.melexis.com/Wireless-Multi-Market--Sensing/RFIC-Transceivers-27-to-950MHz/TH7122-121.aspx&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="444" LastEditorUserId="76" LastEditDate="2013-12-11T21:03:16.680" LastActivityDate="2014-02-14T01:09:36.620" Title="RF Transceiver for walkie talkie use" Tags="&lt;diy&gt;&lt;uhf&gt;&lt;equipment-design&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1033" PostTypeId="2" ParentId="1032" CreationDate="2013-12-11T14:52:31.830" Score="3" Body="&lt;p&gt;The chip you've linked is capable of analog FM transmission and reception, from 2.5kHz to 80kHz bandwidth.  In the frequency range you're looking at it has a frequency resolution of 12.5kHz. It's very low power, with the right antenna it should reach your target LOS.  Check out Figure 4.2 in the &lt;a href=&quot;http://www.melexis.com/Assets/TH7122-and-TH71221-Cookbook-3961.aspx&quot; rel=&quot;nofollow&quot;&gt;TH7122 and TH71221 Cookbook&lt;/a&gt; for an example showing how to use the chip as an analog FM transmitter, and figure 6.7 for an example of how to use it as an FM receiver.  By combining the two circuits with the typical application circuit you can build a single-chip analog FM transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that your requirement, &quot;Single chip that doesn't require extra elements as crystal or filters&quot; is going to be hard to meet with any radio design.  There are several inductors and capacitors used as filters outside most &quot;single chip&quot; transceivers.  If you want any frequency stability you're going to need a crystal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.nxp.com/documents/leaflet/75015689.pdf&quot; rel=&quot;nofollow&quot;&gt;Philips SA58646&lt;/a&gt; is also a good choice, but again you're going to have to deal with a few inductors, capacitors, and a crystal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that with such low power devices your antennas are going to have to be very, very good, and probably very large.  If you don't want to spend a lot of time and effort on antennas, or need small antennas, then you'll have to trade off some additional effort adding an RF amplifier to these devices and consuming more power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are you sure you don't simply want an &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B007F7MZ04&quot; rel=&quot;nofollow&quot;&gt;off-the-shelf transceiver&lt;/a&gt;?  If you're trying to avoid filters and crystals while building your own transceiver, it seems you might need a higher level solution than a DIY circuit.  The radio linked is a cheap HT for the UHF band, runs on 3.7V, and has a 3W output.  It's under $20, and if you remove the battery, casing, controls, connectors, then the one or two PCBs that are left are very small.  It does appear to have a low power TX setting, so you should be able to set it to 1W output rather than the full output power if you have power consumption concerns beyond requiring low voltage. You may even consider modifying the radio to remove the PA and use the very low output prior to the PA, saving significantly more power.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-11T15:19:05.430" LastActivityDate="2013-12-11T15:19:05.430" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1034" PostTypeId="1" AcceptedAnswerId="1035" CreationDate="2013-12-11T15:53:53.503" Score="10" ViewCount="2058" Body="&lt;p&gt;My neighbor has indicated that they can hear noise from their computer amplified speakers when I'm transmitting.  We've done a few tests and it does appear that it's my transmitter that's causing the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've performed some testing and determined that I'm well within my operating limits.  The transmissions are clean, within power limits, etc.  There is nothing I can do on my end to resolve the problem, other than cease transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My neighbor is unwilling to replace his speakers with a more noise resistant set, though he may be willing to allow minor modifications if it doesn't otherwise affect performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What should I try that should help remove, or at least reduce, the noise on the speakers?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2017-07-09T17:33:22.440" LastActivityDate="2020-03-25T03:08:56.970" Title="My neighbor is complaining about my transmissions, what can I do?" Tags="&lt;rfi&gt;&lt;procedure&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1035" PostTypeId="2" ParentId="1034" CreationDate="2013-12-11T16:13:21.443" Score="9" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Title_47_CFR_Part_15&quot;&gt;Wikipedia&lt;/a&gt; writes to say &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;By the regulation, the FCC DoC certification mark is mandatory for devices classified under part 15 (IT equipment like computers, switched-mode power supplies, monitors etc., television receivers, cable system devices, low-power transmitters, un-licensed personal communication devices) and part 18 (industrial, scientific, and medical (ISM) devices that emit RF radiation) of the FCC regulations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The subject is covered in some depth on &lt;a href=&quot;http://www.hamuniverse.com/rfi.html&quot;&gt;hamuniverse.com&lt;/a&gt; which writes to say (free-form edit applied by me)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Rectification and overload are both &lt;strong&gt;problems with the design of the affected equipment&lt;/strong&gt;, and after decades of investigation, the FCC knows this. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In your case, the issue &amp;amp; onus lies upon the manufacturer of the equipment &lt;strong&gt;experiencing interference&lt;/strong&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having made that clear to the neighbour, you might try introducing a low-pass filter (also mentioned in the article on hamuniverse referenced above)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another alternative (+: dump a load of ferrite beads over their speaker cables. More detailed reading is listed at &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot;&gt;this site&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-12-11T16:45:59.810" LastActivityDate="2013-12-11T16:45:59.810" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1036" PostTypeId="2" ParentId="1024" CreationDate="2013-12-11T19:17:12.790" Score="3" Body="&lt;p&gt;Your automated system would require a PC of some kind to evaluate the beacon reception so SDR, especially cognitive radio, looks like the way to go. I'd suggest getting familiar with &lt;a href=&quot;http://gnuradio.org/redmine/projects/gnuradio/wiki&quot; rel=&quot;nofollow&quot;&gt;GNU Radio&lt;/a&gt; and &lt;a href=&quot;http://www.kali.org/news/kali-linux-software-defined-radio-support/&quot; rel=&quot;nofollow&quot;&gt;Kali Linux&lt;/a&gt; as well as &lt;a href=&quot;http://sdrnuke.wces.net/&quot; rel=&quot;nofollow&quot;&gt;SDR-Radio&lt;/a&gt; and &lt;a href=&quot;http://wb5rvz.com/sdr/&quot; rel=&quot;nofollow&quot;&gt;SoftRock&lt;/a&gt; to work out the band-and-frequency selection process, using the aforementioned beacons as a starting point.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have a strong beacon signal, then evaluate it to see if it's good enough for phone and in a phone-permitted band; perhaps even consider digital modes as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, start looking for testing partners in multiple locales.&lt;/p&gt;&#xA;" OwnerUserId="285" LastEditorUserId="285" LastEditDate="2013-12-11T19:41:23.280" LastActivityDate="2013-12-11T19:41:23.280" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1037" PostTypeId="1" CreationDate="2013-12-11T19:39:09.360" Score="11" ViewCount="317" Body="&lt;p&gt;Listening to various operators at different times, I've sometimes noticed, especially during contests, that some operators are easier to understand than others, and it doesn't all seem to be due to their speech patterns. The audio doesn't sound &lt;em&gt;good&lt;/em&gt; but it's easy to &lt;em&gt;understand&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At other times I've listened to two operators ragchew for longer periods of time, and while the audio is understandable, it is easier to listen to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems to me that operators have a lot of control over how they sound over the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What makes these two sounds so different?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I adjust my transmitter to make these two sounds - one focused on intelligibility, and one focused on good/comfortable listening?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="8717" LastEditDate="2017-12-25T21:53:25.657" LastActivityDate="2017-12-26T00:18:08.857" Title="How do I increase my phone intelligibility?" Tags="&lt;contest&gt;&lt;ssb&gt;&lt;transmission&gt;&lt;phone&gt;&lt;audio&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1038" PostTypeId="1" AcceptedAnswerId="1068" CreationDate="2013-12-11T19:48:18.333" Score="9" ViewCount="3557" Body="&lt;p&gt;For some reason I've long believed that given I and Q, one corresponds to amplitude, and one to phase, so I thought that I could hold one steady and create AM, or hold the other steady and create FM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now that I'm delving more into it, though, it appears I'm completely wrong.  Or not.  I'm not really sure, and the articles I'm reading aren't helping the situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can AM and FM be demodulated from quadrature signals relatively easily?  I feel that if I understand this, I might be able to wrap my head around it.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-11-18T09:22:18.833" Title="What are the I and Q in quadrature sampling?" Tags="&lt;direct-conversion&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1039" PostTypeId="2" ParentId="413" CreationDate="2013-12-11T20:14:06.547" Score="5" Body="&lt;p&gt;Hannu OH1HAQ emailed me the true correct two-step answer:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;strong&gt;Set VOX GAIN to 0&lt;/strong&gt;: long press on VOX button, rotate MULTI knob to set the level to 0, long press on VOX button.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Enable VOX&lt;/strong&gt;.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;With VOX GAIN set to 0, noise picked up by the microphone will not key the transmitter. However, replaying from the voice keyer memory will still key the transmitter if VOX is enabled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case the VOX enable/disable state is analogous to the VOX setting in CW mode - with VOX disabled you'll only get the sidetone (voice playback to speaker), no transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tested, this works. I don't think the manual really spells it out.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-12-11T20:25:46.823" LastActivityDate="2013-12-11T20:25:46.823" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1040" PostTypeId="2" ParentId="1038" CreationDate="2013-12-11T20:20:26.813" Score="4" Body="&lt;p&gt;Quadrature samples are essentially &lt;em&gt;complex numbers&lt;/em&gt;. Complex numbers can be represented as two real numbers in two equivalent ways:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Cartesian form: real (here called I or &lt;em&gt;in-phase&lt;/em&gt;) and imaginary (here called Q or &lt;em&gt;quadrature&lt;/em&gt;).&lt;/li&gt;&#xA;&lt;li&gt;Polar form: magnitude (or absolute value) and phase (or angle, or argument).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;When you have I and Q signals or samples, those are in Cartesian form. However, when you want to &lt;em&gt;demodulate&lt;/em&gt;, or even describe mathematically, a complex signal, the magnitude/phase form is more relevant; this is because &lt;strong&gt;the received phase is arbitrary&lt;/strong&gt; (unless the transmitter and receiver have perfectly synchronized clocks and mixers and the path length never changes), which means that the signal has an arbitrary phase shift and therefore has no specific relationship with your I and Q &quot;axes&quot;.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;To help understand this, visualize an &lt;em&gt;unmodulated&lt;/em&gt; complex (analytic) signal as a helix in 3D space: the axes are I, Q, and time. Unlike a real-valued signal, &lt;strong&gt;there are no zero crossings&lt;/strong&gt;; the sample values follow a circle about the origin over time, and never meet it except when the amplitude is 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, if the signal is &lt;em&gt;baseband&lt;/em&gt; (after a receiver's mixer or before a transmitter's), then the rotation rate is 0 by definition: your samples have a constant value, except for the effects of the modulation. And this is the condition under which modulation and demodulation are typically done!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;You ask for analog demodulation examples:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Demodulating AM from complex samples consists of taking the &lt;em&gt;magnitude&lt;/em&gt; of the samples (and then subtracting the carrier amplitude from that, or equivalently using a high-pass filter), because that is exactly the amplitude of the original signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Demodulating FM from complex samples consists of taking the &lt;em&gt;difference&lt;/em&gt; between the &lt;em&gt;phase&lt;/em&gt; of successive samples, because that difference is the instantaneous frequency; if the signal is at baseband, then the instantaneous frequency is exactly the modulating signal!&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2013-12-11T20:20:26.813" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1041" PostTypeId="2" ParentId="1037" CreationDate="2013-12-11T20:32:37.193" Score="1" Body="&lt;p&gt;I've found that precise enunciation works better for the former, whereas controlled modulation (consistent volume and slurring over twixt-word gaps) works better for the latter. Neither is is a function of the transmitter.&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-12-11T20:32:37.193" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1042" PostTypeId="1" CreationDate="2013-12-11T21:09:12.100" Score="8" ViewCount="507" Body="&lt;p&gt;I've seen a few &lt;a href=&quot;http://w5vwp.com/sdr.shtml&quot; rel=&quot;nofollow&quot;&gt;references&lt;/a&gt; to full duplex SDR radios, and I'm wondering how can one transmit and receive at the same time without overwhelming the receiver, and without heavy filtering such as the cavity filters used in repeaters.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2014-12-20T00:25:25.020" LastActivityDate="2016-04-22T09:35:44.357" Title="How is full duplex implemented without swamping the receive circuitry?" Tags="&lt;software-defined-radio&gt;&lt;transceiver&gt;" AnswerCount="2" CommentCount="13" ContentLicense="CC BY-SA 3.0" />
  <row Id="1043" PostTypeId="2" ParentId="1037" CreationDate="2013-12-11T22:13:38.237" Score="11" Body="&lt;p&gt;Microphone technique has a good bit to do with clarity.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Talk &lt;em&gt;across&lt;/em&gt; the mic, not directly into it, unless it is a noise canceling type designed to be used that way.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Speak no more than 2&quot; away from the mic, even if it is a desk mic or a boom mounted type; many people make the mistake of thinking that just because they have a desk or boom mounted mic that they can sit back at arm's length (or more) and just turn up the gain on the transmitter. (No one wants to hear a lot of background noise unless necessary.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Speak clearly and consistently (take a lesson from the professional radio announcers [not necessarily the DJs]); keep an even and level tone.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If your transmitter or transceiver has an &quot;ALC&quot; function as part of its metering system, &lt;em&gt;watch&lt;/em&gt; that function while you are transmitting; keep your voice peaks within the ALC range on the meter, especially if using a compressor (about half scale or less is plenty).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some of the newer rigs have equalizers built in; get with a friend who &lt;em&gt;knows&lt;/em&gt; your natural voice to listen to you while you make adjustments to get the best sound.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="438" LastEditorUserId="76" LastEditDate="2013-12-12T08:10:15.150" LastActivityDate="2013-12-12T08:10:15.150" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1044" PostTypeId="1" CreationDate="2013-12-11T22:23:59.093" Score="4" ViewCount="428" Body="&lt;p&gt;I've observed a signal I'm unfamiliar with, and am wondering what it might be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/3wiDr.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The period of time it lasted is 5 seconds, and it occurs irregularly.  You might be able to see it too via &lt;a href=&quot;http://hackgreensdr.org:8901/&quot; rel=&quot;nofollow noreferrer&quot;&gt;WebSDR&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How would I discover what type of signal this is, generally, and does anyone know off the top of their head what it is?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2014-08-08T04:10:55.403" LastActivityDate="2014-08-08T04:10:55.403" Title="What is this short, wide band signal?" Tags="&lt;modes&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1045" PostTypeId="2" ParentId="1044" CreationDate="2013-12-12T00:03:58.490" Score="2" Body="&lt;p&gt;One possibility is Digital Radio Mondale (DRM), but given that it's only five seconds long each time - exactly - I'm not sure.  It does consume the same 10kHz bandwidth, and has some pattern similarities. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's one resource for visual signal identification: &lt;a href=&quot;http://www.rtl-sdr.com/signal-identification-guide/&quot; rel=&quot;nofollow&quot;&gt;http://www.rtl-sdr.com/signal-identification-guide/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Digital modes are given a pretty thorough treatment with included waterfall signatures here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://hfradio.org.uk/html/digital_modes.html&quot; rel=&quot;nofollow&quot;&gt;http://hfradio.org.uk/html/digital_modes.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-18T17:52:21.410" LastActivityDate="2013-12-18T17:52:21.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1046" PostTypeId="1" CreationDate="2013-12-12T00:18:43.480" Score="7" ViewCount="533" Body="&lt;p&gt;I plan to use a SoftRock Ensemble RX II to receive HF transmissions.  I'd like to be able to use it wherever I am when I have a few minutes, though, so I'm wondering what software exists that would allow me to control the receiver over the internet?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen websdr and it appears to support some of the functions of this receiver, but it also appears to publish itself to the websdr website, allowing others to control the station as well. The worst part is that it doesn't allow full control of the receiver, it appears you have to select the band and center frequency at the computer, and cannot operate those parameters remotely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While I'd prefer windows, if Linux applications are available that do this I'd be willing to set up a PC just for that purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also not necessary but desired is that it would work with iOS devices, either via HTML5 and javascript, or with a specific app.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-12T02:20:22.210" Title="What SDR software is available that provides internet control?" Tags="&lt;software-defined-radio&gt;&lt;software&gt;&lt;remote-control&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1047" PostTypeId="2" ParentId="1037" CreationDate="2013-12-12T00:56:46.757" Score="5" Body="&lt;p&gt;Eric Scace, K3NA wrote a two part article for the NCJ a few years back on all the adjustments you can make to your audio chain to improve it's quality.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;While the article focuses on audio quality for contesting, I think most of the points are relevant &quot;regular&quot; phone contacts.  He has 6 main areas that he addresses:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Operator training &amp;mdash; Things like posture, speaking volume, how to speak into a microphone, etc.&lt;/li&gt;&#xA;&lt;li&gt;Controls affecting the recording of audio signals &amp;mdash; focuses on making your contesting macros sound as much like your normal phone as possible to make copying your messages smooth and easy.&lt;/li&gt;&#xA;&lt;li&gt;Controls affecting the playback of message to the radio’s audio input jack &amp;mdash; more on the above&lt;/li&gt;&#xA;&lt;li&gt;Controls used for live speech routed through the soundcard.&lt;/li&gt;&#xA;&lt;li&gt;Transmitter mic and speech processor level, and any other internal audio bandwidth, threshold, or equalizer settings.&lt;/li&gt;&#xA;&lt;li&gt;Transmitter power output &amp;mdash; making sure you don't ruin your hard work by using too much power and distorting the signal.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There's a full copy on his web site: &lt;a href=&quot;http://www.k3na.org/articles/Transmit%20audio%20adjustment.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.k3na.org/articles/Transmit%20audio%20adjustment.pdf&lt;/a&gt;.  Definitely a useful read.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-12T13:51:12.317" LastActivityDate="2013-12-12T13:51:12.317" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1048" PostTypeId="2" ParentId="1046" CreationDate="2013-12-12T01:14:41.403" Score="2" Body="&lt;p&gt;OK: Windows host for SoftRock Ensemble RX II, remote control of digital modes - why not an COTS (Cheap Off the Shelf) solution, such as &lt;a href=&quot;http://www.tightvnc.com/download.php&quot; rel=&quot;nofollow&quot;&gt;TightVNC&lt;/a&gt; or other VNC solutions? Since you are talking about station control, not voice, the lack of voice is not an issue, is it? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's GPL open source (free as in beer), even cross-platform, and supports Android and anything else which runs Java, which would really give you spur-of-the-moment access. You can even get a &lt;a href=&quot;http://sourceforge.net/projects/vnc-reflector/&quot; rel=&quot;nofollow&quot;&gt;Reflector app&lt;/a&gt; to allow multiple viewers if you wished.&lt;/p&gt;&#xA;" OwnerUserId="285" LastEditorUserId="285" LastEditDate="2013-12-12T01:49:12.357" LastActivityDate="2013-12-12T01:49:12.357" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1049" PostTypeId="2" ParentId="1016" CreationDate="2013-12-12T01:47:27.490" Score="4" Body="&lt;p&gt;Page 15 of the &lt;a href=&quot;http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf&quot; rel=&quot;nofollow&quot;&gt;FCC's OET63&lt;/a&gt; specifies maximum emission of 100 µV/m measured three meters away, for consistent transmission in the US FM broadcast band, and 250 µV/m if you can keep the bandwidth down to 200KHz or less. That would permit &lt;a href=&quot;http://codec2.org/&quot; rel=&quot;nofollow&quot;&gt;Codec2&lt;/a&gt;, &lt;a href=&quot;http://freedv.org/tiki-index.php&quot; rel=&quot;nofollow&quot;&gt;FreeDV&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/Olivia_MFSK&quot; rel=&quot;nofollow&quot;&gt;Olivia&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/PSK63&quot; rel=&quot;nofollow&quot;&gt;PSK63&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/PACTOR&quot; rel=&quot;nofollow&quot;&gt;Pactor-I&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/RTTY&quot; rel=&quot;nofollow&quot;&gt;RTTY&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/Q15X25&quot; rel=&quot;nofollow&quot;&gt;Q15X25&lt;/a&gt; and many other digital modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, when you're talking about ISM, there are &lt;a href=&quot;http://en.wikipedia.org/wiki/ISM_band#ISM_bands&quot; rel=&quot;nofollow&quot;&gt;multiple bands available in the US&lt;/a&gt; and that link shows the frequencies and permitted bandwidth, which you can match up with the FCC table in the first line about for power limits.  If, forex, you're talking about the 902-928 MHz band, you have &lt;strong&gt;26 MHz&lt;/strong&gt; to play with and up to &lt;strong&gt;1W&lt;/strong&gt; output power for spread-spectrum use, so the answer is a qualified YES, depending on &lt;em&gt;which&lt;/em&gt; ISM band band you want to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the &lt;a href=&quot;http://www.hobbybroadcaster.net/&quot; rel=&quot;nofollow&quot;&gt;Hobby Broadcaster website&lt;/a&gt; may be a useful resource for you as well.&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-12-12T01:47:27.490" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1050" PostTypeId="2" ParentId="1046" CreationDate="2013-12-12T02:20:22.210" Score="1" Body="&lt;p&gt;&lt;strong&gt;If you're feeling technically adventurous,&lt;/strong&gt; then I have written something that might fit your needs. I wouldn't consider suggesting this if it weren't that as far as I know web-controllable SDR software is a very small field (there is only WebSDR, my thing, and another early-stages program I've forgotten the name of).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My &lt;strong&gt;&lt;a href=&quot;https://github.com/kpreid/shinysdr&quot; rel=&quot;nofollow&quot;&gt;ShinySDR&lt;/a&gt;&lt;/strong&gt; is a SDR application based on GNU Radio with a web-based UI. I regularly use it remotely myself. It already supports “sound-card” input, so the only thing you would need to do is write a plugin (in Python) to send the USB control commands to your device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll refrain from reiterating &lt;a href=&quot;https://github.com/kpreid/shinysdr#whats-shiny-about-it&quot; rel=&quot;nofollow&quot;&gt;the feature list&lt;/a&gt; here. There are several caveats worth noting for your scenario:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;There are a number of things the software should do, but doesn't, and some of them manifest as nonfunctional controls in the UI. I'm working on fixing them, but in my spare time.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The web UI only reliably works in Google Chrome, because I have not been making any effort to avoid features that are not yet implemented by other browsers (draft standards, &lt;em&gt;not&lt;/em&gt; implementation-specific).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It is currently receive-only (so is your hardware, but others might want to note this).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;No one with experience with “real” radios has been involved in the design of the UI or the feature set, so there may be important things missing, or just misguided.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The required network bandwidth has not yet been fully optimized.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;(I'd love to just go ahead and add support for your device and provide a complete solution, but since I don't have the hardware to test with that's unlikely to happen. Also, another path to support which would benefit more users would be to contribute the functionality to &lt;a href=&quot;http://sdr.osmocom.org/trac/wiki/GrOsmoSDR&quot; rel=&quot;nofollow&quot;&gt;gr-osmosdr&lt;/a&gt;, a multi-device plugin for GNU Radio.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2013-12-12T02:20:22.210" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1051" PostTypeId="1" AcceptedAnswerId="1067" CreationDate="2013-12-12T15:51:52.270" Score="2" ViewCount="255" Body="&lt;p&gt;I have an aluminum sided house, and when I'm using my HT I typically need to be near a window for it to work well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would I gain much if I put an antenna on the roof, an antenna in the middle of my house, and connect the two using coaxial cable?  I assume it wouldn't be better than sitting myself with my HT on the roof, but will it be much better than the HT would be alone in the middle of the house?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd use antennas with matching impedance, but would probably use a very nice omni on the roof, and a smaller omnidirectional in the house. Does the type and length of coax matter very much, or can I use one I'd typically use for an antenna connected to the HT?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What else can I do to make this setup succeed?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-12T21:45:57.920" LastActivityDate="2014-04-27T18:08:43.187" Title="Can I use two antennas and coax to couple RF into my aluminum sided house?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1052" PostTypeId="1" AcceptedAnswerId="1055" CreationDate="2013-12-12T16:21:53.743" Score="12" ViewCount="1146" Body="&lt;p&gt;Can I perform any transmission regardless of my license as long as I'm inside an RF sealed enclosure, such that no RF will be detectable from my transmissions off my property?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I imagine the answer is yes, but I'd like to be sure I understand.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="7804" LastEditDate="2019-10-03T12:47:58.660" LastActivityDate="2019-10-03T12:47:58.660" Title="Can I transmit anything inside a Faraday cage?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;faraday-cage&gt;" AnswerCount="7" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="1053" PostTypeId="2" ParentId="1024" CreationDate="2013-12-12T16:24:11.177" Score="4" Body="&lt;p&gt;You might already know about this, but the &lt;a href=&quot;http://en.wikipedia.org/wiki/Automatic_link_establishment&quot; rel=&quot;nofollow&quot;&gt;Automatic Link Establishment (ALE)&lt;/a&gt; system has similar goals and might be what you're looking for. &lt;/p&gt;&#xA;" OwnerUserId="57" LastEditorUserId="76" LastEditDate="2013-12-15T18:13:42.350" LastActivityDate="2013-12-15T18:13:42.350" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1054" PostTypeId="2" ParentId="1052" CreationDate="2013-12-12T17:41:58.320" Score="7" Body="&lt;p&gt;This is pretty much the same as transmitting into a dummy load (or using the stock rubber duck antennas :) ).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think a canonical answer is possible; Part 97 is silent on the issue.  But, if no one can hear you, you can't be interfering with anyone or &quot;using&quot; the spectrum, so I would say sure.  Depending on what you are planning on doing (and on which bands), you might want to make some RF checks at the edge of your property to be sure you aren't leaking RF.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-12T17:41:58.320" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1055" PostTypeId="2" ParentId="1052" CreationDate="2013-12-12T18:16:54.977" Score="7" Body="&lt;p&gt;I don't have an answer actually clearly applicable to this situation, but a couple of related scenarios come to mind:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Every shielded digital electronic device is radiating &quot;inside a RF sealed enclosure&quot;. Your scenario is different in that it's not a discrete device with built-in shielding.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=e08a2d71f72da516ce050e6c7df6c939&amp;amp;node=47:1.0.1.1.16.3.236.8&amp;amp;rgn=div8&quot; rel=&quot;noreferrer&quot;&gt;Part 15 §15.211&lt;/a&gt; permits &lt;em&gt;tunnel radio systems&lt;/em&gt; to “operate on any frequency” provided that the emissions meet usual limits as measured at the tunnel mouth. However, this specifically applies to “a tunnel, mine or other structure that provides attenuation to the radiated signal due to the presence of naturally surrounding earth and/or water”, and not artificial shielding.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These are two cases where analogous things are occurring; neither one applies specifically here but they're both precedents which match the common sense “if no one else can receive it, it's OK”. This does &lt;strong&gt;not&lt;/strong&gt; mean that it's actually legal.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2013-12-12T19:01:53.957" LastActivityDate="2013-12-12T19:01:53.957" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1056" PostTypeId="2" ParentId="1042" CreationDate="2013-12-12T18:55:50.857" Score="3" Body="&lt;p&gt;One method to achieve this is to invert, attenuate, and delay the transmitted signal and feed it back into the receiver.  This will cancel out most of the power of the transmission, so the input end of the receiver isn't swamped by the RF from the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://sing.stanford.edu/fullduplex/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://sing.stanford.edu/fullduplex/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JEisr.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This will have to be actively managed, but the report suggests that it works for ultrawide bandwidth signals.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-12T18:55:50.857" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1057" PostTypeId="1" AcceptedAnswerId="1069" CreationDate="2013-12-12T20:29:49.640" Score="4" ViewCount="1146" Body="&lt;p&gt;I will be assembling a Softrock Ensemble II HF receiver, and I know I'm going to want it on air as soon as I build it, so I'm challenging myself to build an antenna for it first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The plan is to do a simple balanced line inverted V dipole, such as the &lt;a href=&quot;http://www.qsl.net/wb1gfh/antenna.html&quot; rel=&quot;nofollow&quot;&gt;$4 special&lt;/a&gt;, but my receiver has a BNC antenna connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://fivedash.com/resource/RXEnsembleIISchematic.pdf&quot; rel=&quot;nofollow&quot;&gt;receiver schematic&lt;/a&gt; shows the antenna going into an ungrounded BNC connector, then connecting to a transformer which I'll be winding myself from the instructions. However I want to be able to connect all sorts of antennas so I don't want to alter the receiver just for this antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming the BNC isn't grounded, can I just attach a BNC to the 300Ω twinlead and that to the receiver, or should I attempt to do some amount of impedance matching between the twinlead and the receiver?  I'm not transmitting, so it won't destroy anything to try, but I'd like to have decent reception.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-12T21:22:17.780" LastActivityDate="2017-10-09T17:59:53.643" Title="What impedance matching do I need between my 300Ω feedline and Softrock receiver?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;diy&gt;&lt;feed-line&gt;&lt;impedance&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1058" PostTypeId="1" AcceptedAnswerId="1066" CreationDate="2013-12-12T20:43:32.350" Score="9" ViewCount="33060" Body="&lt;p&gt;So the &lt;a href=&quot;https://ham.stackexchange.com/questions/1057/what-impedance-matching-do-i-need-between-my-feedline-and-receiver&quot;&gt;antenna I'm thinking about doing&lt;/a&gt; might be&lt;sup&gt;*&lt;/sup&gt; way too large for my property.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there another simple, cheap, DIY antenna I could try on my receiver?  I know I'm going to want to hook it up and have a listen before the last solder joint has cooled.  Ideally it would cover 160 m to 10 m reasonably well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most complicated antenna I've built was a Gray Hoverman for UHF reception.  It would be nice if it weren't much more complex, but if it's inexpensive and good enough I'm willing to do a bit of work for an antenna I'll use a long time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not interested in aiming right now, so an omnidirectional antenna would be best.  I do have a 25' attic I can use if needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*&lt;sub&gt;Is almost certainly...&lt;/sub&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2020-05-11T17:18:02.790" Title="Is there a simple, DIY, antenna suitable for HF receive only?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;diy&gt;" AnswerCount="6" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1059" PostTypeId="1" AcceptedAnswerId="1063" CreationDate="2013-12-12T20:49:04.307" Score="3" ViewCount="65" Body="&lt;p&gt;Where can I go to find propagation forecasts?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How useful are propagation forecasts over time?  For instance, I've been told by meteorologists that weather forecasts three days out generally considered at best 50% accurate. How far out do propagation forecasts go, and how accurate are they at their limits?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-13T00:04:01.407" Title="What are some reliable sources of propagation forecasts?" Tags="&lt;propagation&gt;&lt;contest&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1062" PostTypeId="2" ParentId="1058" CreationDate="2013-12-12T23:20:24.343" Score="2" Body="&lt;p&gt;Not real thrilled about the attic; if you can go outdoors, I'd recommend a random length horizontal loop, as described at &lt;a href=&quot;http://www.k4qky.com/the-station/the-antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.k4qky.com/the-station/the-antenna&lt;/a&gt; and &lt;a href=&quot;http://www.smeter.net/antennas/large-transmitting-loop.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.smeter.net/antennas/large-transmitting-loop.php&lt;/a&gt; for its design simplicity.&lt;/p&gt;&#xA;" OwnerUserId="285" LastEditorUserId="9588" LastEditDate="2017-05-02T14:24:17.840" LastActivityDate="2017-05-02T14:24:17.840" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1063" PostTypeId="2" ParentId="1059" CreationDate="2013-12-13T00:04:01.407" Score="1" Body="&lt;p&gt;The interesting thing about weather is that you can see it coming. That's only partly true with space weather/solar activity.  In fact, for some events, we wouldn't have &lt;em&gt;any&lt;/em&gt; warning at all as in the case of a high energy burst aimed right at us.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the solar weather predictions are models based on trend fitting a bunch of solar parameters like solar flux, sunspots, magnetic field strength, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NOAA has a &lt;a href=&quot;http://www.swpc.noaa.gov/index.html&quot; rel=&quot;nofollow&quot;&gt;Space Weather Prediction Center&lt;/a&gt; site that includes &lt;a href=&quot;http://www.swpc.noaa.gov/ftpdir/latest/45DF.txt&quot; rel=&quot;nofollow&quot;&gt;45 day prediction&lt;/a&gt; of the &lt;a href=&quot;http://en.wikipedia.org/wiki/Solar_cycle#Solar_radio_flux&quot; rel=&quot;nofollow&quot;&gt;solar flux index&lt;/a&gt;, generally considered a useful indicator of propagation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, NOAA and other national level organizations around the world aren't necessarily focused on HF propagation particularly as there are many other concerns relating to solar weather.  The amateur community has stepped up to fill this gap, as you might expect.  One &#xA;good one can be found &lt;a href=&quot;http://prop.hfradio.org/&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.  This one includes a lot of information and educational resources that will help you make sense of the numbers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are also a number of PC based programs that will take the numbers and crunch you a forecast for specific bands/times/etc.  There is a review of many of them here &lt;a href=&quot;http://www.astrosurf.com/luxorion/qsl-review-propagation-software.htm&quot; rel=&quot;nofollow&quot;&gt;Review of HF propagation analysis &amp;amp; prediction programs&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something more immediately useful is: &lt;a href=&quot;http://spacew.com/www/realtime.php&quot; rel=&quot;nofollow&quot;&gt;Near-Real-Time MUF Map&lt;/a&gt;. Which tells you the current estimated MUF.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-13T00:04:01.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1064" PostTypeId="2" ParentId="1058" CreationDate="2013-12-13T00:23:37.737" Score="5" Body="&lt;p&gt;There is nothing simpler than a random length wire.  It doesn't have to be strung up or even straight, though, obviously, those would improve it's performance.  Of course the ironic thing about a random length wire antenna is that the most effective lengths aren't actually random.  They work best when the antenna is at least a quarter wavelength at the lowest operating frequency, 65' for 80m, for instance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To maximize the effectiveness, and have something useful down the line, you could build a small tuner. An L-network random wire tuner is probably the simplest matching network in existence, designs about on the net.  Like this one: &lt;a href=&quot;http://www.ehow.com/how_6543405_build-antenna-tuner-ham-radio.html&quot; rel=&quot;noreferrer&quot;&gt;How to Build a Cheap Antenna Tuner&lt;/a&gt; or this one: &lt;a href=&quot;http://www.qrp.pops.net/swl1.asp&quot; rel=&quot;noreferrer&quot;&gt;SWL Receiving Antenna Experiments&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-13T00:23:37.737" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1065" PostTypeId="2" ParentId="1051" CreationDate="2013-12-13T17:54:24.030" Score="1" Body="&lt;p&gt;Assuming the HT is VHF/UHF, yes, the type of coax is starting to matter. For example RG-8X, a common HF grade coax, loses about 8dB/100'(33m) at 70cm. You are going to want something like LMR-400 (2.5dB/100' (33m)) and keep the run as short as practical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After all, if you are losing 3dB (or more) in the coax and connectors (remember there is insertion loss for each connector), then you are at half power already.  So, given the usual HT, that's down to 2.5W.  Still plenty of juice to hit a local repeater, but you are using up the margin you might need to hit repeaters farther away or other folks on simplex.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I have done is set a mag-mount with a spare 2m 5/8&amp;lambda; whip outside the window on a steel post and run the coax in through the window and use a connector to go from SO-239 to SMA-Female, I think.  The coax was only 25', I think the total loss was less than 2dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You wouldn't have the freedom to wander around the house, but that wasn't one of my requirements because if I left the shack, all you'd hear would be the children screaming or something.  After all, there is a reason shacks have doors :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for the coupling of the two antennas, I imagine it might work, but I think your loses would be so high as to not be practical if you need to get out with any power.  Hard to saw canonically without more information and even then, it would probably come down to experimentation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reference for coax loses: &lt;a href=&quot;http://www.therfc.com/attenrat.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.therfc.com/attenrat.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-13T17:54:24.030" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1066" PostTypeId="2" ParentId="1058" CreationDate="2013-12-13T20:42:42.957" Score="18" Body="&lt;p&gt;Receive antennas are the &lt;em&gt;easiest thing ever&lt;/em&gt;. You just need two things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;something that conducts electricity&lt;/li&gt;&#xA;&lt;li&gt;another thing that conducts electricity&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Attach one to the center contact on a BNC connector. Connect another to the shield. Boom, done. If you can't find two things, then one can be the Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, you can use two ends of one thing that encircles something that permits magnetic fields (like, air).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Until you are approaching a significant fraction of a wavelength (like, 1/4 wavelength), then making either thing bigger will get you more signal. However, once you have enough signal that you are well above your receiver's noise floor, more signal won't make you receive any better: it will just give you louder noise. I'd say, however much space you have, make it that big.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't worry about tuning, or impedance matching. This also will increase the fraction of the energy received by your antenna coupled to the receiver, but again, once you have enough to overcome the receiver's noise, more is of absolutely no help. See &lt;a href=&quot;https://ham.stackexchange.com/q/382/218&quot;&gt;What is the relationship between SWR and receive performance?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't worry about polarization. At HF most of your signals will arrive via the ionosphere which is constantly swirling and changing the polarization of received signals. Whatever polarization you pick, it will be the wrong one in 30 seconds, so don't worry about it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you really &lt;em&gt;must&lt;/em&gt; worry about something, worry about getting your antenna away from noise sources. Your house, being full of all varieties of noisy digital electronics, is very noisy. If you can get an antenna away from these things, that's good. You must also take care to avoid making the feedline part of the antenna. See &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt; Although that question asks about resonant dipoles, the answers apply to &lt;em&gt;any&lt;/em&gt; type of antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-13T20:42:42.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1067" PostTypeId="2" ParentId="1051" CreationDate="2013-12-13T21:11:12.473" Score="2" Body="&lt;p&gt;You could do that, but it wouldn't be terribly effective. The reason is simple: most of the power transmitted by your HT isn't directed at whatever antenna you set up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could probably do better by cutting the right sized slot in your siding. By forcing the RF currents in the siding to go around the slot, you set up an electric field which radiates as well as a dipole. This is called a &lt;a href=&quot;http://www.antenna-theory.com/antennas/aperture/slot.php&quot; rel=&quot;nofollow&quot;&gt;slot antenna&lt;/a&gt;. Still though, losses will be very high, and probably not worth the effort.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-12-13T21:11:12.473" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1068" PostTypeId="2" ParentId="1038" CreationDate="2013-12-13T21:35:05.390" Score="8" Body="&lt;p&gt;Your understanding is almost correct. I/Q data represents phase and amplitude, but in &lt;a href=&quot;http://en.wikipedia.org/wiki/Cartesian_coordinate_system&quot; rel=&quot;noreferrer&quot;&gt;Cartesian coordinates&lt;/a&gt;. &lt;a href=&quot;http://en.wikipedia.org/wiki/Polar_coordinate_system#Converting_between_polar_and_Cartesian_coordinates&quot; rel=&quot;noreferrer&quot;&gt;Conversion between the two&lt;/a&gt; is elementary trigonometry:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ r = \sqrt{I^2+Q^2} \\&#xA;\theta = \text{atan2}(Q, I) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To demodulate AM, you just need $r$, and to demodulate FM, you just need $\theta$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually, an I/Q pair is represented as a &lt;a href=&quot;http://en.wikipedia.org/wiki/Complex_number&quot; rel=&quot;noreferrer&quot;&gt;complex number&lt;/a&gt;, with $I$ being the real part, and $Q$ being the imaginary part. This makes possible some interesting mathematical manipulations like multiplying a signal by a &lt;a href=&quot;http://en.wikipedia.org/wiki/Euler%27s_formula&quot; rel=&quot;noreferrer&quot;&gt;complex exponential&lt;/a&gt; to make a mixer. However, unlike a usual (&quot;non-complex&quot;) &lt;a href=&quot;http://en.wikipedia.org/wiki/Frequency_mixer&quot; rel=&quot;noreferrer&quot;&gt;mixer&lt;/a&gt;, this mixer does not make &lt;em&gt;two&lt;/em&gt; new signals (sum and difference), but rather &lt;em&gt;just one&lt;/em&gt;. This ability to shift a spectrum of frequencies without creating an additional sideband (which must then be filtered out, typically) is a big win in DSP.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-12-25T14:31:24.693" LastActivityDate="2013-12-25T14:31:24.693" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1069" PostTypeId="2" ParentId="1057" CreationDate="2013-12-14T19:22:30.460" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Assuming the BNC isn't grounded, can I just attach a BNC to the 300Ω twinlead and that to the receiver&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. Impedance matching will mean less losses between the antenna and your receiver, but the receiver's objective isn't energy harvesting. As long as the antenna is sensitive enough and the receiver's gain high enough that the predominant source of noise is RF noise, and not the receiver's internal noise, improving antenna efficiency will do nothing to help you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In particular on the softrock kit, receiver gain is fixed. If you notice no difference between a dummy load and your antenna on a quiet frequency, try increasing the gain. Increase it just until the RF noise floor is just a bit above the receiver's and your sound card's noise floor: this will give you the highest dynamic range.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-12-14T19:22:30.460" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1071" PostTypeId="2" ParentId="1000" CreationDate="2013-12-15T19:02:59.410" Score="1" Body="&lt;p&gt;In the ARRL 10m contest that's going on this weekend, I learned a lot about my new radio.  (point number 6 above)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I got myself a radio with some nice DSP options with features to reduce interference and make signals more copyable.  I took yesterday and today to learn these features through activities such as enhancing a weak signal out of the noise level so I can copy it, blocking nearby signals (sideband from a signal on 28303 made copying a signal on 28305 &quot;interesting&quot; so I used a combination of features to make it go away, and basically ensuring that there were no features on my rig I didn't understand at least basically how to use them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've had no practice with split operation on my rig yet, but that'll come during another big international contesting week.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if you don't participate in the contest (I never do) making contacts is encouraged.  If you choose not to make contacts, listening and making your rig do what you want with the received signal.&lt;/p&gt;&#xA;" OwnerUserId="308" LastActivityDate="2013-12-15T19:02:59.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1072" PostTypeId="2" ParentId="1000" CreationDate="2013-12-15T21:50:01.587" Score="2" Body="&lt;p&gt;@PearsonArtPhoto has a good list started.  I've been getting into contesting lately and I would elaborate on No. 7 to say that for good scores, you need to plan your operating time carefully and then have your butt in the chair the whole time you plan to operate.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some contests run for, say 48 hours, but you can only operate 36 hours, or something like that, it varies.   This is where planning comes in:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How much operating time can I get away with and stay married?  (YMMV)&lt;/li&gt;&#xA;&lt;li&gt;How do I break up my operating time to maximize my score, take advantages of openings, etc.&lt;/li&gt;&#xA;&lt;li&gt;Given those answers, arrange sleep and food so when I am at the radio, I am fresh and not distracted.&lt;/li&gt;&#xA;&lt;li&gt;If you don't talk for a living, consider your voice.  I don't and I didn't and I went hoarse my first few contests.  My wife came up with a nice tea that stretches my voice, but I decided a voice keyer was needed to extend my time.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Continuing on that list:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;You learn the limitations of your equipment.  With experience you can tell which pileups you can just skip and how loud (S meter wise) a signal has to be for you to have a good chance of getting him to come back to you.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you do any running, you will learn to pull call signs out of a pileup and that helps with copying information in adverse conditions.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Also expanding on both the previous answers, you will learn your radio better.  I always end up pushing a button I don't mean to in the heat of battle and then have to diagnose things on the fly.  And to tease out those weak signals without (in my case) any fancy DSP, you learn some more of those knobs to eliminate adjacent signals as much as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lot s of folks hate contesting and say those QSOs with their ritual &quot;59&quot; RSTs don't count for much.  In some ways I agree, but it's just a different facet of the hobby.  Instead of a quality contact, it's about quantity and, as we've tried to show here, uses some different skills or the same skills in different ways.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-15T21:50:01.587" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1073" PostTypeId="1" AcceptedAnswerId="1074" CreationDate="2013-12-16T09:31:43.567" Score="20" ViewCount="548" Body="&lt;p&gt;Like it says in the title. When you design a QSL card (intended for use for both local VHF-and-up contacts as well as international HF contacts), what information needs to be present, and what information might be considered &quot;nice to have&quot; but not strictly needed?&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2013-12-16T14:02:28.270" Title="What information should be on a QSL card?" Tags="&lt;qsl-card&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1074" PostTypeId="2" ParentId="1073" CreationDate="2013-12-16T11:43:13.737" Score="17" Body="&lt;p&gt;QSL cards vary greatly in design and is one of those areas of creativity.  Some hams end up with fancy double sided full color cards, spending a lot of $$.  But they could be simple as well; just text with the pertinent information on it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Need to have info:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Your call sign (on both sides)&lt;/li&gt;&#xA;&lt;li&gt;Your mailing address (so you can receive a reciprocal card)&lt;/li&gt;&#xA;&lt;li&gt;Details of the contact:&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Call sign of the remote station (thanks Michael)&lt;/li&gt;&#xA;&lt;li&gt;band or frequency of contact&lt;/li&gt;&#xA;&lt;li&gt;mode of contact (SSB/FM/CW/etc)&lt;/li&gt;&#xA;&lt;li&gt;date of contact (in UTC)&lt;/li&gt;&#xA;&lt;li&gt;time of contact (in UTC)&lt;/li&gt;&#xA;&lt;li&gt;signal report&lt;/li&gt;&#xA;&lt;li&gt;whether or not you want a reciprocal card&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Nice to have info:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Your &lt;a href=&quot;http://en.wikipedia.org/wiki/Maidenhead_Locator_System&quot;&gt;Maidenhead Grid Square&lt;/a&gt; location&lt;/li&gt;&#xA;&lt;li&gt;Your county (in the US)&lt;/li&gt;&#xA;&lt;li&gt;Your Lat / Long&lt;/li&gt;&#xA;&lt;li&gt;A cool picture of your area to make them wish they lived in the same paradise you do :)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-16T14:02:28.270" LastActivityDate="2013-12-16T14:02:28.270" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1075" PostTypeId="1" CreationDate="2013-12-16T16:58:35.473" Score="10" ViewCount="337" Body="&lt;p&gt;I know that in many contests, sitting on a frequency and calling CQ is a very effective strategy to rack up points. However, during very popular contests it can be very difficult to find an open frequency. How can I find a frequency that I can use to call CQ during a busy contest?&lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2013-12-17T13:02:24.220" Title="How do I find a frequency to call CQ on during a contest?" Tags="&lt;hf&gt;&lt;contest&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1076" PostTypeId="1" CreationDate="2013-12-16T17:08:58.923" Score="8" ViewCount="173" Body="&lt;p&gt;Suppose I am operating a busy HF contest, and I have found an open frequency to call CQ. I make a number of contacts, and then suddenly another station starts to call CQ right on top of me. The other station is either matching my frequency or within about 1.5 kHz, so filtering  is not a practical option. His signal strength is greater than most of the stations that are trying to contact me, so any time he transmits, I lose any exchange details. There isn't really any room for me to adjust my frequency (it's a busy contest). How should I manage this situation?&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="29" LastEditDate="2013-12-16T19:53:49.930" LastActivityDate="2013-12-16T19:53:49.930" Title="How do I maintain my frequency during a contest?" Tags="&lt;hf&gt;&lt;procedure&gt;&lt;contest&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1077" PostTypeId="2" ParentId="1076" CreationDate="2013-12-16T17:30:31.707" Score="9" Body="&lt;p&gt;The first thing to realize is that you can't make anyone move. So you can contact him and tell him (politely) the frequency was in use and he's interfering with you.  At that point he may apologize and QSY.  Yes, that does work, I have seen it happen. Or he'll tell you to pound sand or just plain ignore you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that happens, there is really nothing to be done but to try and find a new run frequency.  If it's real busy, then spend an hour on S&amp;amp;P and try to pick up some multipliers while keeping an eye out for a new run spot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last thing you should do is waste time on it.  A good score is all about rate.  IF you are struggling and he won't move, move or go S&amp;amp;P for a while.  Or depending on the rules and schedule, take a break now.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-16T17:30:31.707" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1078" PostTypeId="2" ParentId="1075" CreationDate="2013-12-16T17:36:30.307" Score="8" Body="&lt;p&gt;One strategy is to camp a frequency starting before the contest.  No, those QSOs don't count for the contest, but it lets you get into the rhythm of things and shake down any issues with your setup before the clock starts running.  Lots of contesters do this and you might pick up some DX while running like that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In multi-band contests, one strategy is to move down a little early, i.e., ahead of the pack, and stake out a spot.  You give up a little in moving while the higher band is still productive, but you could get a choice spot for the next band and that should more than make up for it. &lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-16T17:36:30.307" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1079" PostTypeId="1" CreationDate="2013-12-16T18:28:25.457" Score="5" ViewCount="692" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/X_band#Amateur_radio&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia&lt;/a&gt; writes to say&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Radio Regulations of the International Telecommunication Union allow amateur radio operations in the frequency range 10.000 to 10.500 GHz, and amateur satellite operations are allowed in the range 10.450 to 10.500 GHz. This is known as the 3-centimeter band by amateurs and the X-band by AMSAT.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Is the 3-cm band serviced by any commercial main-stream ham radio transceiver?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="29" LastEditDate="2013-12-18T08:27:15.020" LastActivityDate="2013-12-18T08:27:15.020" Title="Is the 3-cm band serviced by any commercial main-stream ham radio transceiver?" Tags="&lt;transceiver&gt;&lt;shf&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1080" PostTypeId="2" ParentId="1079" CreationDate="2013-12-16T18:48:34.327" Score="4" Body="&lt;p&gt;At least in Finland you are allowed to use the entire band from 10.0 GHz to 10.5 GHz with &quot;secondary rights&quot;. Maximum TX powers are 30 W (basic class) and 150 W. The 3 cm band is also available at least in the USA: &lt;a href=&quot;http://www.arrl.org/frequency-allocations&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/frequency-allocations&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="194" LastActivityDate="2013-12-16T18:48:34.327" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1081" PostTypeId="5" CreationDate="2013-12-16T19:59:11.900" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-16T19:59:11.900" LastActivityDate="2013-12-16T19:59:11.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1082" PostTypeId="4" CreationDate="2013-12-16T19:59:11.900" Score="0" Body="Super High Frequency is the frequency range 3-30 GHz." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2013-12-16T19:59:11.900" LastActivityDate="2013-12-16T19:59:11.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1083" PostTypeId="1" CreationDate="2013-12-16T20:34:21.197" Score="6" ViewCount="124" Body="&lt;p&gt;Suppose I hear a station during a contest that is an eligible contact, but not necessarily a multiplier (worth points, but only a nominal amount of points). This station is relatively faint, (maybe 2-3 S-units above the noise floor) but intelligible. How can I tell if the station is going to be a quick, easy contact or a slow, painful, drawn-out exchange that will hurt my score? When do I cut my time losses and move on to the next station?&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="70" LastEditDate="2013-12-17T01:07:39.053" LastActivityDate="2013-12-17T01:50:46.293" Title="During a radio contest, how do I determine if a station is &quot;too faint&quot; to be worth trying to contact?" Tags="&lt;hf&gt;&lt;contest&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1084" PostTypeId="2" ParentId="1083" CreationDate="2013-12-16T20:45:49.293" Score="6" Body="&lt;p&gt;Trial and error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A lot depends on your equipment, antenna, definition of worthwhile.  Also, the band and propagation conditions.  The cool thing about HF is that while he might be faint to you, how he hears you could be completely different.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For me personally, they typically need to be 3 S units up for a smooth exchange, but other folks have had other answers.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-16T20:45:49.293" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1085" PostTypeId="1" AcceptedAnswerId="1087" CreationDate="2013-12-16T23:53:02.353" Score="5" ViewCount="2503" Body="&lt;p&gt;I keep increasing my frequencies and want to get up the spectrum more and more. My current project is pointing a powerful focused LED from a peak and I will try to pick it up with a telescope and some sort of photo detector to receive the AM light. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I keep wondering about even higher frequencies. I am assuming Ultra violet should not be too much more difficult than Light unless the air absorbs that band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, going higher, could x-rays be used to communicate, maybe just CW or is it not possible at all and x-rays will not propagate. &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-09-24T21:47:40.110" LastActivityDate="2014-11-23T09:29:18.097" Title="Can X-rays be used for communication?" Tags="&lt;optical&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1086" PostTypeId="2" ParentId="1083" CreationDate="2013-12-17T01:50:46.293" Score="2" Body="&lt;p&gt;In telephony, speech quality is reduced to a number, such as a &lt;a href=&quot;http://en.wikipedia.org/wiki/PESQ&quot; rel=&quot;nofollow&quot;&gt;PESQ&lt;/a&gt; score.  Which is not to say that radio amateurs should start using formal methods from telephony, but to highlight that the need to put a number on the quality of reception exists, and there are ways to do it. Once you have a number obtained in some consistent way, then you can easy set a limit, like &quot;anything less than 1.0 is effectively out of coverage&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any kind of formal method would require the station to transmit some known standard sample of voice. You have to control the input and measure the output. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't control what is transmitted, then it's purely subjective.&lt;/p&gt;&#xA;" OwnerUserId="468" LastActivityDate="2013-12-17T01:50:46.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1087" PostTypeId="2" ParentId="1085" CreationDate="2013-12-17T05:13:23.657" Score="11" Body="&lt;p&gt;If you can control its emissions, and detect it, then you can use it for communications. X-rays are no exception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However there are many reasons they are not widely used, including expensive and limited optics, short distance line of sight outside a vacuum, and not as safe as many other forms of communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Still X-rays have some uses and there are &lt;a href=&quot;http://gsfctechnology.gsfc.nasa.gov/TechSheets/XRAY_Goddard_Final.pdf&quot;&gt;X-ray communication systems&lt;/a&gt; in development. They can be used over vast distances in space with relatively low power, can communicate with spacecraft during re-entry when traditional communications are disrupted due to electron activity in the heat of re-entry, and can penetrate some types of RF shielding, which has some interesting use cases.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-17T05:13:23.657" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1088" PostTypeId="2" ParentId="1075" CreationDate="2013-12-17T13:02:24.220" Score="3" Body="&lt;p&gt;You can also use anything with a waterfall display to help you find open space. If you're set up for digital mode operation, you can run fldigi even for CW contests, use that to find the best &quot;gap&quot;, and tune to it without actually using fldigi to transmit. &lt;/p&gt;&#xA;" OwnerUserId="87" LastActivityDate="2013-12-17T13:02:24.220" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1089" PostTypeId="1" AcceptedAnswerId="1090" CreationDate="2013-12-17T16:27:13.253" Score="4" ViewCount="223" Body="&lt;p&gt;I am relatively new to contesting, and I have heard of a category called SO2R (Single Operator, Two Radios).  Are they really talking about 2 radios, or just 2 VFOs in one radio?  Running one radio seems to be a full time job, especially with the logging involved.  How is the second radio used?  What are the advantages over a single radio?&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="76" LastEditDate="2013-12-17T19:07:12.177" LastActivityDate="2013-12-18T01:06:54.417" Title="How is a second radio managed when operating SO2R (Single Operator Two Radios)?" Tags="&lt;procedure&gt;&lt;contest&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1090" PostTypeId="2" ParentId="1089" CreationDate="2013-12-17T17:46:51.627" Score="4" Body="&lt;p&gt;Generally SO2R means one person (&quot;Single Operator&quot;) with two separate transceivers attached to two separate antennas (&quot;Two Radios&quot;). The operator doesn't actively transmit and receive on both at the same time, as you say it's a full time job with just one radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second radio (that is, which ever radio is not currently being transmitted on), is typically used to listen on a different band while they are transmitting with the first radio. The only real advantage of this in a contest sense is to score more points. The more people you can hear calling the more you can respond to, and more contacts equals more points.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, assuming you aren't actively transmitting, you will be receiving on two separate bands, which increases your chances of hearing someone calling. &lt;/p&gt;&#xA;" OwnerUserId="172" LastActivityDate="2013-12-17T17:46:51.627" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1091" PostTypeId="1" AcceptedAnswerId="1092" CreationDate="2013-12-17T18:17:59.847" Score="6" ViewCount="256" Body="&lt;p&gt;Is there a material suitable for use as RF shielding that would allow at least 50% light transmission in the visible range? Thinking about a sensitive light receiver.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-17T18:53:06.733" Title="Optically clear RF shielding?" Tags="&lt;receiver&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1092" PostTypeId="2" ParentId="1091" CreationDate="2013-12-17T18:38:16.173" Score="5" Body="&lt;p&gt;Yes, this is actually a pretty common product in these security conscious days: RF shielded glass or add-on plastic sheeting.  Many firms market this for the construction of office buildings where you want to reduce EM emissions to prevent eavesdropping.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Picking one of these at random, Holland Shielding Systems BV markets a glass that transmits 84% of the light and attenuates RF between 24 dB and 98 dB depending on frequency. I imagine this is a spendy product, but the company website I looked at offered free samples; considering your project, that might be enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another company, &lt;a href=&quot;http://www.lessemf.com/plastic.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;LessEMF&lt;/a&gt;, sells a variety of plastics that shield RF and can be added to existing windows.  This firm lists prices that seem to start around 29 USD per linear foot with the following characteristics:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/MeZ1U.gif&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="76" LastEditDate="2013-12-17T18:53:06.733" LastActivityDate="2013-12-17T18:53:06.733" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1093" PostTypeId="2" ParentId="1079" CreationDate="2013-12-17T21:21:31.997" Score="5" Body="&lt;p&gt;None of the major amateur radio manufacturers make a rig for the 3cm band (or most of the microwave bands for that matter).  The common practice is for hams to buy or build a &lt;a href=&quot;http://en.wikipedia.org/wiki/Transverter&quot; rel=&quot;noreferrer&quot;&gt;transverter&lt;/a&gt; which downconverts the received signal from 10GHz to (often) 146MHz and upconverts the transmitted signal from 146MHz to 10GHz.  In essence, 146MHz becomes an Intermediate Frequency for the microwave band radio.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transverter can be a simple frequency conversion affair or a more complex arrange with pre-amps, amplifies and filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For an example of such a device, look at Kuhne Ectronics's &lt;a href=&quot;http://www.kuhne-electronic.de/en/products/transverter/kit-10-ghz-10g2.html&quot; rel=&quot;noreferrer&quot;&gt;KIT 10 GHz 10G2&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-17T21:21:31.997" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1094" PostTypeId="5" CreationDate="2013-12-17T21:31:24.957" Score="0" Body="&lt;p&gt;A radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form, usually in the form of sounds, images or data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The technology of detecting RF energy has progressed since it was first demonstrated at the end of the 19th Century.  Moving from early crystal detectors through vacuum tubes (thermistors) to solid state transistors.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-20T22:24:40.330" LastActivityDate="2013-12-20T22:24:40.330" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1095" PostTypeId="4" CreationDate="2013-12-17T21:31:24.957" Score="0" Body="Use this tag for questions about the theory and structure of receivers." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-20T22:00:04.320" LastActivityDate="2013-12-20T22:00:04.320" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1096" PostTypeId="1" CreationDate="2013-12-18T00:07:34.670" Score="1" ViewCount="79" Body="&lt;p&gt;I want to communicate 2.7 miles from a peak on a mountain. I will be using a very bright LED and some type of photo-element (photo multiplier tube, avalanche photo diode etc.) to receive the amplitude modulated signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One problem I have is: what optics will I use to receive the signal to &quot;zoom in&quot; to the light? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.youtube.com/watch?v=PvAF0nlyhpQ&quot; rel=&quot;nofollow&quot;&gt;I would like to build a system like this YouTube video.&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in short... Where can I get the optics which the people there ↑↑↑ used. I do not want to buy a telescope because of the expense and then my project won't be considered D.I.Y.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will be starting out at the night time, and probably not doing any day experiments for a while.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Im sorry if this question is considered off topic, I thought it should fit this site at least because it has to do with communications, and optical is above 275Ghz which is on the chart.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-09-24T21:46:41.640" LastActivityDate="2014-09-24T21:46:41.640" Title="Optics for open-air visible spectrum communications" Tags="&lt;optical&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1097" PostTypeId="2" ParentId="1096" CreationDate="2013-12-18T00:31:15.320" Score="3" Body="&lt;p&gt;What you will want to do is not just concentrate on the receiver, but also the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the receiver you will want a lens to focus the signal from the transmitter down to as tight a point as possible. 2.7 miles means your light will be near enough parallel once it hits the lens*. If you have a 5cm (for example) distance between the LED and the lens, you want a lens with a focal length of 5cm.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Now, in order to improve your efficiency, and signal strength, build the same setup at the transmitter. Use the same lens at the same distance from the LED, and the output will be a stronger beam; as much of the light that would have escaped out to the sides will be focused into that parallel beam.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Your best bet for getting lenses? There are lens stores online that cater to astronomers, photographers etc. The ones in that video look like &lt;a href=&quot;http://en.wikipedia.org/wiki/Fresnel_lens&quot; rel=&quot;nofollow&quot;&gt;Fresnel&lt;/a&gt; lenses, which are certainly cheaper than traditional optical lenses.&lt;/p&gt;&#xA;" OwnerUserId="50" LastEditorUserId="164" LastEditDate="2013-12-18T14:11:31.197" LastActivityDate="2013-12-18T14:11:31.197" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1098" PostTypeId="2" ParentId="1089" CreationDate="2013-12-18T01:06:54.417" Score="2" Body="&lt;p&gt;I believe you can also call CQ on one radio while search and pouncing on the other. I imagine this takes some level of skill to use effectively.&lt;/p&gt;&#xA;" OwnerUserId="43" LastActivityDate="2013-12-18T01:06:54.417" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1099" PostTypeId="1" CreationDate="2013-12-18T03:11:12.423" Score="7" ViewCount="1867" Body="&lt;p&gt;I keep reading and hearing the 70cm band (420-450 MHz depending on local regulation) referred to as the 432 MHz band, particularly by older hams. Why?&lt;/p&gt;&#xA;" OwnerUserId="227" LastEditorUserId="76" LastEditDate="2013-12-18T08:43:37.170" LastActivityDate="2015-07-02T23:55:13.730" Title="Why is the 70cm band commonly referred to as the 432MHz band?" Tags="&lt;uhf&gt;&lt;70cm-band&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1100" PostTypeId="2" ParentId="1099" CreationDate="2013-12-18T11:19:24.467" Score="1" Body="&lt;p&gt;I assume it's because the national calling frequency is 432.10, and a lot of the signals of interest in the &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow&quot;&gt;ARRL band plan&lt;/a&gt; are around 432. Repeater work is usually higher of course, but there is still plenty of interest around 432.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2013-12-18T11:19:24.467" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1101" PostTypeId="1" CreationDate="2013-12-18T14:17:51.930" Score="2" ViewCount="641" Body="&lt;p&gt;A fellow ham recently acquired a &lt;a href=&quot;http://www.kenwood.com/i/products/info/amateur/ts_480/&quot; rel=&quot;nofollow&quot;&gt;TS-480SAT&lt;/a&gt;. His working condition is complemented by an inverted-vee for the 20m band around 10m above ground; solid 59+ reports. Trying to tune the same antenna on other bands using the in-built tuner fails outright.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm curious; what range of mismatch can the internal tuner on the 480SAT accommodate?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2013-12-18T16:47:26.230" LastActivityDate="2013-12-18T16:47:26.230" Title="What range of mismatch can the internal tuner on the TS-480SAT accommodate?" Tags="&lt;antenna-tuner&gt;&lt;kenwood&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1102" PostTypeId="2" ParentId="1101" CreationDate="2013-12-18T15:59:09.880" Score="1" Body="&lt;p&gt;Oddly, the range is not mentioned in the manual.  Discussion about the feature on the web seems to agree that it's limited to a 3:1 match.  That's sounds right as that is a pretty common figure for internal tuners from other manufacturers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can borrow him an SWR meter to test the unit, he could verify that figure empirically pretty easily.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-18T15:59:09.880" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1103" PostTypeId="1" AcceptedAnswerId="1109" CreationDate="2013-12-18T17:28:48.140" Score="6" ViewCount="137" Body="&lt;p&gt;It seems that using a CW skimmer with an SDR one could fully automate a contest station, and even handle multiple contacts simultaneously in the case of pile-ups.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has this been done or discussed before?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What rules are common that would prevent this type of operation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What checking is done or can contests perform to find people using such methods?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-18T20:13:31.413" Title="What prevents automation in contests?" Tags="&lt;contest&gt;&lt;automation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1104" PostTypeId="1" AcceptedAnswerId="1108" CreationDate="2013-12-18T17:34:51.040" Score="9" ViewCount="1040" Body="&lt;p&gt;I've heard some DX indicate &quot;CQ up 5&quot; for instance, indicating that they are listening on a different frequency than they are transmitting on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the reasons one might want to do that?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-19T13:40:00.517" Title="Why do some DX listen on a different frequency than they transmit on?" Tags="&lt;contest&gt;&lt;frequency&gt;&lt;dx&gt;&lt;split-frequency&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1105" PostTypeId="1" AcceptedAnswerId="1111" CreationDate="2013-12-18T17:57:35.573" Score="5" ViewCount="1998" Body="&lt;p&gt;The FCC disallows amateur spread spectrum communications below 220MHz.  At the moment the relatively new digital mode, ROS, is considered, by some, to be spread spectrum.  So this mode is getting little to no use in the US.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It doesn't seem much different than other tone digital modes though, and never claims a bandwidth larger than phone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the definition of &quot;spread spectrum&quot; according to the FCC?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In what ways could ROS be considered spread spectrum?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What about ROS suggests that it's not spread spectrum?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only page on ROS I've been able to find, &lt;a href=&quot;http://rosmodem.wordpress.com/&quot; rel=&quot;noreferrer&quot;&gt;http://rosmodem.wordpress.com/&lt;/a&gt; , doesn't seem to have an in-depth explanation of what the mode is and does.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2013-12-18T22:35:08.380" LastActivityDate="2015-01-05T19:50:37.397" Title="What about the digital mode ROS causes some to consider it spread spectrum?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;modes&gt;&lt;digital-modes&gt;" AnswerCount="5" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1106" PostTypeId="1" AcceptedAnswerId="1107" CreationDate="2013-12-18T18:14:49.343" Score="3" ViewCount="729" Body="&lt;p&gt;I am thinking of a large (circumference $\approx \lambda$) loop antenna at low (HF) frequencies. At higher frequencies the loops are used as quad antennas that have relatively high gain towards the axis of the loop. However, at HF band these are often positioned horizontally above the ground. One would think that the ground would act as a reflector and the power would be directed upwards which is obviously undesired. Are the reasons purely mechanical or is there some other reason to use horizontal loops instead of vertical ones?&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="172" LastEditDate="2013-12-18T19:09:28.080" LastActivityDate="2013-12-18T19:09:28.080" Title="Why are loop antennas placed horizontally in HF" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;magnetic-loop&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1107" PostTypeId="2" ParentId="1106" CreationDate="2013-12-18T18:32:44.260" Score="4" Body="&lt;p&gt;I suspect they are built horizontally simply because they are easier to construct and support, especially at HF sizes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to constantly changing ionospheric conditions, the received phase of HF signals is random, so that's not a reason to prefer any particular polarization. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, the ground does affect radiation patterns, but it's not so simple as &quot;reflecting&quot; RF energy straight up. Were this the case, dipoles also wouldn't work. What the ground actually does is create an &lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;image antenna&lt;/a&gt; as if a second antenna appeared reflected through the ground, fed in opposite phase. This can result in peak radiation in &lt;a href=&quot;https://ham.stackexchange.com/a/487/218&quot;&gt;many patterns&lt;/a&gt;, depending on antenna height.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also some folk-wisdom that &lt;a href=&quot;https://ham.stackexchange.com/questions/849/is-a-vertical-noisier-than-a-dipole-and-if-so-why&quot;&gt;horizontally-polarized antennas are quieter&lt;/a&gt;. I think the magnitude of this effect is much less than the belief in it, but even if the technical foundations are weak, it is a reason for human behavior anyway.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-18T18:32:44.260" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1108" PostTypeId="2" ParentId="1104" CreationDate="2013-12-18T19:26:10.540" Score="10" Body="&lt;p&gt;This is called operating &quot;split&quot; and it takes a certain amount of skill to work a DX operator working split and even more to operate split.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason this is done is to help manage the pileup. If too many stations are calling and the pileup becomes unmanageable it takes longer and longer to complete an exchange.  This is less fun for everyone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By working split, the DX operator keeps his transmit frequency clear so that the callers will hear him well making the exchange go more smoothly.  He also has the opportunity to spread out the calling stations on several frequencies near his transmit frequency.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance he starts out simplex, then gets spotted and the rush begins.  So he calls &quot;Up 5&quot; meaning call him on this frequency + 5KHz.  After a while he might announce &quot;Up 10&quot; and realistically at this point callers are spread from +3KHz to +12KHz or so in their eagerness to get through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The DX station will go through the calling stations in some order (usually).  Perhaps starting at the top of the window and calling a station every 1KHz or every other KHz, or some other system.  The key to navigating these waters is to LISTEN for a while and figure out how it's being managed before jumping in.  This will greatly improve you odds of getting this guy in your log.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The convention seems to be to work split &quot;up&quot; on the USB bands and &quot;down&quot; on the LSB bands.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-18T19:26:10.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1109" PostTypeId="2" ParentId="1103" CreationDate="2013-12-18T19:52:23.330" Score="5" Body="&lt;p&gt;Nothing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And this is a point of some controversy.  In contests that allow electronic aids (like spotting networks and skimmers), the users are generally in a separate category.  In some cases you go from Single Operator to Single Operator Unlimited, in other cases: Multi-Op Single transmitter. Other contests prohibit aids of any kind, including skimmers.  Most state QSO parties prohibit aids under the philosophy that while they are contests, they are for &quot;fun&quot; and folks shouldn't take them seriously enough to go to the effort of electronic aids.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of the folks that do log checking swear they can detect the use of skimmers based on the logs but decline to explain how. Being a software developer, I can imagine how it could be done.  Whether it is or not, I don't know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Needless to say there are folks that claim that all these aids ruin the tradition and spirit of contests.  To others, this is just the natural evolution of technology.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-18T20:13:31.413" LastActivityDate="2013-12-18T20:13:31.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1110" PostTypeId="1" AcceptedAnswerId="1112" CreationDate="2013-12-19T00:16:49.347" Score="1" ViewCount="88" Body="&lt;p&gt;Most designs appear to filter most of the harmonics out of the oscillator before modulation, then apply additional filtering as needed for the specific modulation they are using after modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it be reasonable to modulate with the square wave, and do all the filtering after modulation?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-19T05:29:15.133" Title="Can I filter after modulation when using a square wave oscillator?" Tags="&lt;modes&gt;&lt;filter&gt;&lt;oscillator&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2014-01-10T22:51:22.203" ContentLicense="CC BY-SA 3.0" />
  <row Id="1111" PostTypeId="2" ParentId="1105" CreationDate="2013-12-19T01:51:34.067" Score="5" Body="&lt;p&gt;Some consider ROS Modem Spread Spectrum because of statements on the author's website call it: Frequency Hopping Spread Spectrum. It's worth noting that the author is European and in Europe, spread spectrum is allow on the HF bands. Undoubtedly, part of this is marketing.  Describing a new mode as Spread Spectrum gives it a more techy feel and spread spectrum is something that came out of the military, further increasing the cool factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC's definition of Spread Spectrum:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Spread spectrum techniques are emissions that use bandwidth-expansion modulation &gt;techniques to intentionally spread the information transmitted over a wide bandwidth. At any frequency in the frequency segment or bandwidth the SS emission occupies, either the spectral power density of the transmitted signal is reduced to a comparatively low level or the duration of the transmitted signal is very brief.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Source: &lt;em&gt;WT Docket No. 10-62&lt;/em&gt; &lt;strong&gt;RM-11325&lt;/strong&gt; &lt;em&gt;REPORT AND ORDER&lt;/em&gt;&lt;br&gt;&#xA;Adopted: February 22, 2011 Released: March 4, 2011&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC's ruling on the matter simply reaffirms what SS is and where it's allowed.  They didn't rule that ROS &lt;em&gt;is&lt;/em&gt; SS or not.  This probably has more to do with conflicting information and lack of clear guidance.  The author calls it SS, but examining the actual protocol reveals that it's not.  It's not very popular in the US (largely due to this conflict) and so the FCC didn't have the number of opinions it usually gets when considering a ruling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To lump the remaining two questions together:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not spread spectrum; it doesn’t hop the VFO frequency. It is simply FSKs according to a programmable algorithm, and it meets the infamous 1kHz shift 300 baud rule (FCC §97.307(f)3):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Only a RTTY or data emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must not exceed 300 bauds, or for frequency-shift keying, the frequency shift between mark and space must not exceed 1 kHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Digging into it further, ROS uses multiple tones over either a 2kHz or 500Hz bandwidth, (the frequencies for each mode/bandwidth are hard coded in the software). According to the rather thin documentation, ROS has three main speeds, 16 baud, 8 baud and 4 baud. There are some special modes, such as 7bd/100Hz for 136 and 502kHz (and 80m for some reason), plus an ‘EME’ mode for use on 2m and some other bands, for weak signal work as it has, in theory at least, the capability to decode signals that have a Signal to Noise Ratio (SNR) of -35dB, which is even lower than WSPR.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="218" LastEditDate="2015-01-05T19:48:30.660" LastActivityDate="2015-01-05T19:48:30.660" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1112" PostTypeId="2" ParentId="1110" CreationDate="2013-12-19T05:29:15.133" Score="4" Body="&lt;p&gt;Filtering square wave aims to produce as pure as possible sine wave as the local oscillator frequency. If you would feed all the harmonics to the non-linear modulator, the output would contain all the strange sum frequencies that can be very close to the wanted signal. For example in SSB transmitter the unwanted sideband could mix with a harmonic of the local oscillator to the same frequency as the wanted sideband and the base frequency.&lt;/p&gt;&#xA;" OwnerUserId="194" LastActivityDate="2013-12-19T05:29:15.133" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1113" PostTypeId="2" ParentId="1104" CreationDate="2013-12-19T13:40:00.517" Score="4" Body="&lt;p&gt;Another advantage of the &quot;split&quot; comes from the US Extra test material.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The DX station can call CQ on a frequency that may be out-of-band for broadcast for a lower license class (say General/Technician) OR for other countries which may have a slightly different band limit (but who can still listen to the CQ call frequency). And the CQ station can listen on the lower or higher split frequency which the responding station is licensed to transmit on. This allows use of additional frequencies in a crowded DX environment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, DX station calls CQ on 14.220 MHz and listens &quot;up 10&quot; which is at 14.230 MHz. In the US, the General Class license is authorized only above 14.225 MHz - this would allow the General Class (and higher) responders to transmit on a valid frequency while listening on what otherwise only a higher US class would be able to transmit on.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2013-12-19T13:40:00.517" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1114" PostTypeId="1" AcceptedAnswerId="1118" CreationDate="2013-12-19T17:44:04.737" Score="2" ViewCount="88" Body="&lt;p&gt;In the HF bands loop antennas are common, which, if I understand correctly, emit most of their radio energy into the magnetic field, whereas most dipoles emit largely into the electric field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To take advantage of propagation effects, would one prefer electric field emissions over magnetic field emissions?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-19T18:37:10.277" Title="Does propagation affect magnetic and electric fields equally?" Tags="&lt;propagation&gt;&lt;dipole&gt;&lt;loop-antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1115" PostTypeId="1" AcceptedAnswerId="1116" CreationDate="2013-12-19T18:00:44.193" Score="1" ViewCount="144" Body="&lt;p&gt;I'm evaluating a helix antenna, and wanted to try out a reverse circular polarization than it's designed for.  I do know that it's balanced and has no other components that would preclude polarity reversal, so as long as I take care for grounding issues around the connector I won't damage the receiver or antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I correct in thinking that simply reversing the connection to the receiver will also reverse the circular polarization of the antenna?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-19T18:21:03.187" Title="Will swapping receiver polarity on a spiral antenna change right hand to left hand polarization?" Tags="&lt;antenna&gt;&lt;polarization&gt;&lt;circular-polarization&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1116" PostTypeId="2" ParentId="1115" CreationDate="2013-12-19T18:20:02.260" Score="3" Body="&lt;p&gt;What do you mean by reversing connection? If you just swap the ground and center wire of the feeding coaxial you create 180 phase shift, not change the polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The polarization of a helix antenna is determined by the rotation direction of the helix (right handed helix radiates right handed circular polarization). If you want to change the helix designed for RHCP to radiate LHCP, you must re-wire the entire helix. &lt;a href=&quot;http://en.wikipedia.org/wiki/Helical_antenna&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Helical_antenna&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="194" LastActivityDate="2013-12-19T18:20:02.260" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1117" PostTypeId="2" ParentId="1115" CreationDate="2013-12-19T18:21:03.187" Score="3" Body="&lt;p&gt;No. Reversing the conductors of the feed line produces a 180° phase shift (which is generally completely irrelevant) and has no effect on polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One way you could reverse the polarization without modifying the antenna would be to reflect the signal once.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2013-12-19T18:21:03.187" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1118" PostTypeId="2" ParentId="1114" CreationDate="2013-12-19T18:32:56.163" Score="3" Body="&lt;p&gt;&lt;em&gt;[This is not my best area of knowledge, but I figured I'd give answering a try; please correct me if this is wrong.]&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Electric and magnetic fields are only usefully distinguished from each other in steady-state (DC or static charge) or “near field” (distances comparable to the wavelength) conditions. Propagating radio waves are both electric fields and magnetic fields, equally and inseparably.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At a distance, the only things the design of your antenna can affect are &lt;strong&gt;gain&lt;/strong&gt; and &lt;strong&gt;polarization&lt;/strong&gt;. (And polarization matters only if the type of propagation you're hoping to use does not randomize polarization.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2013-12-19T18:32:56.163" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1119" PostTypeId="2" ParentId="1114" CreationDate="2013-12-19T18:37:10.277" Score="3" Body="&lt;p&gt;In a traveling plane wave the ratio of the electric ($\vec{E}$) and magnetic field ($\vec{H}$) is always the wave impedance of the medium (377 $\Omega$ for air or vacuum). Further, the fields are always perpendicular to each other and to the direction of the wave ($\vec{k}$) This is a very fundamental property of electromagnetic radiation. The wave you transmit propagates always the same way without knowing what kind of an antenna you used to transmit it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the notion that loops are more &quot;magnetic&quot; and the dipoles &quot;electric&quot; is totally correct: in the near field, or close to the antenna as name suggests, a part of the power you feed to your antenna is stored in the electric and magnetic fields. In loop antenna the magnetic fields dominate and with dipoles the electric fields. In other words, close to the loop antenna $\frac{E}{H} &amp;lt; 377 \Omega$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Near_and_far_field&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Near_and_far_field&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="194" LastActivityDate="2013-12-19T18:37:10.277" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1120" PostTypeId="1" CreationDate="2013-12-19T19:14:41.953" Score="6" ViewCount="291" Body="&lt;p&gt;When I was growing up, I lived about three blocks from a Heathkit, and envied every device on the shelves. Now that I'm older, am teaching myself electronics and have a background in film and television broadcasting, I think I'm coming down with the ham radio sickness. :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I know precious little about where to even start understanding what's available and learning the correct search terminology that'll help Google give me relevant results for DIY kits and what I need to get started.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are some good sites that help newbies understand the basics of the different types of amateur radios that're out there, understanding the right questions to ask of vendors, and hooking up with other local operators for networking and support?&lt;/p&gt;&#xA;" OwnerUserId="482" LastEditorUserId="8717" LastEditDate="2020-10-26T20:13:21.963" LastActivityDate="2020-10-26T20:13:21.963" Title="What does a first-time operator need to know when looking for a DIY kit?" Tags="&lt;diy&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1122" PostTypeId="1" AcceptedAnswerId="1123" CreationDate="2013-12-20T02:13:37.903" Score="3" ViewCount="1175" Body="&lt;p&gt;Just a simple question and the answer is probably no, but am I allowed to transmit a picture using SSTV on an FM 2 meter or 70 centimeter repeater?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am in the United States.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2013-12-20T15:52:50.100" LastActivityDate="2017-05-26T19:25:05.947" Title="SSTV on repeaters?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;repeater&gt;&lt;sstv&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1123" PostTypeId="2" ParentId="1122" CreationDate="2013-12-20T02:15:44.503" Score="4" Body="&lt;p&gt;Depends on the band plan and the repeaters operator. You wouldn't be violating any FCC rules, though, but if you're outside the US the answer may be different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To expand on this, you are allowed to transmit any permitted mode on any permitted frequency your license is good for.  That frequency and mode happening to correspond to an open repeater another station operates does not preclude you from making your transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, as a licensee, you've agreed to cooperate with other operators to make the most efficient use of the spectrum provided.  This means that unless you have good reason to, or have coordinated with others, you generally follow the band plans in effect in your region.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally the band plans keep voice repeater and SSTV operations in separate frequencies.  However the band plan is a way to coordinate effort, and not a rigid standard.  As shown in &lt;a href=&quot;https://ham.stackexchange.com/questions/894/conducting-a-slow-scan-television-net-via-an-fm-repeater&quot;&gt;this question&lt;/a&gt;, there are may groups that regularly use repeaters to send SSTV signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the repeater is regularly used by other operators for voice, or is in service to a community for emergency operations, weather spotting, or other frequent uses, you'd probably be better off not tying it up with SSTV images. It'll be really annoying to those that keep their HT on all the time to hear the SSTV coming through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's a quiet repeater and happens to be in an SSTV portion of the band plan, I wouldn't even bother asking, just go ahead and send and see what the response, if any, is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's outside the SSTV band plan, but appears to be an underutilized repeater, it's your call.  Asking might result in people saying 'no' without good reason, but doing it without getting explicit permission may irritate some. It may also intrigue others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, being honest with yourself, consider the question, &quot;Who is likely to be listening to this repeater with an SSTV receiver?&quot;  If you're communicating specifically with someone who is set up to receive your images, direct communications isn't reasonable, and the repeater appears to be open and available for community use, I'd say go for it.  If you're just sending random images to no one in particular, though, or merely experimenting with the mode, you probably don't need to use the repeater to accomplish your goals.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-20T16:09:42.010" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1124" PostTypeId="1" AcceptedAnswerId="1130" CreationDate="2013-12-20T07:40:08.223" Score="17" ViewCount="9058" Body="&lt;p&gt;Most HF rigs have a &lt;strong&gt;noise blanker&lt;/strong&gt; (NB) feature. It does reduce some types of noise (car ignition noise and such). How does it really work?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've read it has negative side-effects with strong signals, which is why it is not enabled all the time.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="8832" LastEditDate="2017-09-16T01:04:40.317" LastActivityDate="2018-05-15T23:15:38.130" Title="What does a noise blanker really do, and what are the side effects?" Tags="&lt;hf&gt;&lt;noise-blanker&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1125" PostTypeId="1" AcceptedAnswerId="1128" CreationDate="2013-12-20T08:17:19.163" Score="4" ViewCount="69" Body="&lt;p&gt;In most big contests, the total score is calculated by multiplying the number of QSO points by the amount of worked DXCC entities (&quot;countries&quot;), or prefixes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be a good strategy to divide effort between keeping our QSO rate up and collecting multipliers?&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-12-20T12:25:20.373" Title="How much should we invest time in collecting multipliers in the big contests?" Tags="&lt;contest&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1128" PostTypeId="2" ParentId="1125" CreationDate="2013-12-20T12:25:20.373" Score="1" Body="&lt;p&gt;The advice given to me was to go for rate and the multipliers will take care of themselves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if your goal is to spend a fair amount of time running, there sill be times when you get bumped off your run frequency or you are looking for a run frequency or you are warming up or winding down and can spend some time doing search and pounce.  During these time you can still go for rate but how long you wait in pileups might be guided by whether it's a new multiplier or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Exactly how much time to spend on these is operator dependent, but you can game it pretty easily with a spreadsheet.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Take your rate running, say 100 QSOs / hour&lt;/li&gt;&#xA;&lt;li&gt;Take your rate cherry picking S&amp;amp;P, say 35 QSOs / hour&lt;/li&gt;&#xA;&lt;li&gt;Take your rate banging rare multiplier DX, say 12 / hour&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And graph that in a spreadsheet based on your current totals.  It changes over time, at the beginning, multipliers don't mean much, you give up 8 QSOs per S&amp;amp;P multiplier and it doesn't move the score much.  Later on, when you have 1300 QSOs, that multiplier is worth a rare DX costs 8 (rounding down) QSOs&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, using the rates above, say you have 1300 QSOs and 80 multipliers.  Your score is 104000.  If you go for one more multiplier, you are at 1301 * 81 = 105381, versus continuing to run, 1308 * 80 = 104670 a difference of 741 points.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, as time goes on, new multipliers are harder and harder to get so that rate goes down. This is where graphs are handy you can plot this all out with your rates as you go and that will tell you when to switch.  You can also add rate goals to your spreadsheet and things that will help you notice when a band is becoming unproductive and it may be time to switch bands or take a break.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-20T12:25:20.373" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1130" PostTypeId="2" ParentId="1124" CreationDate="2013-12-20T16:09:15.647" Score="15" Body="&lt;p&gt;Some types of noise are very short bursts of energy. Car ignition noise is one example. Power-line noise caused by switching triacs in light dimmers is another. For example, see the top image here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/kdCJH.jpg&quot; alt=&quot;pulse noise on a scope&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(&lt;a href=&quot;http://www.ka7oei.com/syn_blank.html&quot; rel=&quot;noreferrer&quot;&gt;source: &lt;em&gt;A Line-Synchronous Noise Blanker&lt;/em&gt; by KA7OEI&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This image also illustrates the effect of band-pass filtering on these pulses. The middle image shows the effect of filtering the pulses through a SSB filter, and the bottom image through a narrower CW filter. Though the filters remove the higher harmonics of the pulses, they do this at the expense of introducing ringing and &quot;smearing&quot; the pulse over a longer time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why noise blankers are desirable for this kind of noise: if you can chop out the noise in the time domain, just for those very brief pulses, without introducing the ringing that a bandpass filter would introduce. A noise blanker detects when these noise pulses occur, and then attenuates the receiver for the duration of the pulse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The downside is that this has the potential to introduce more noise and distortion than it removes. Attenuating the signal for these brief periods is equivalent to multiplying the signal by a square wave which is usually 1 but is 0 for the brief periods where the attenuation is happening.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can be viewed as a kind of amplitude modulation or mixing, and what you get at the output are frequency components that are the sum and the difference of the frequency components of the original signal, and the square wave from the noise blanker. The square wave, being very rich in harmonics, creates frequency components over a wide band. An analogous and more familiar phenomenon happens in CW: if the carrier is switched on or off too quickly we get &quot;key clicks&quot; or &quot;splatter&quot;. In a noise blanker we aren't switching on and off a carrier, but rather whatever signal we might be receiving, but the mechanism by which noise is introduced is the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, practical noise blankers filter the square wave, such as by limiting the slew rate of the attenuation or such. This reduces the harmonic content of that square wave, thus reducing the distortion introduced by the blanker. There's a trade-off to be made here: more filtering of the blanking square wave means it can't cut out the pulses with the same precision because it can't respond as quickly, so the trick is to adjust the response to remove as much as the pulse as possible, as little of everything else as possible, while introducing a minimum of distortion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The main problem with strong signals is that it makes it more difficult to find the noise pulses. Recall from the image that if the signal is filtered, the pulses get smeared and the noise blanker becomes ineffective. Thus, the noise blanker is most effective where receive bandwidth is greatest: right at the antenna, and not behind any receive filters. However, if there are strong signals present anywhere, even not necessarily at the tuned frequency, then these signals contain peaks which can look, to the noise blanker, like noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Different kinds of noise blankers have different ways of deciding what peaks are &quot;noise&quot; and what are not, and may be more or less susceptible to being confused in a particular situation. There are many kinds of noise, and many kinds of band conditions, so there is no one noise blanker design that works in all situations. Thus, one will always want the ability to enable or disable the noise blanker.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-12-20T16:09:15.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1131" PostTypeId="1" AcceptedAnswerId="1158" CreationDate="2013-12-20T16:15:42.457" Score="2" ViewCount="187" Body="&lt;p&gt;SSTV permits transmission of single images, or if one desires image sequences at a very low framerate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there specific Amateur Modes that are meant for real time (motion pictures) video transmission, or do amateurs simply use NTSC, PAL, or digital modes to transmit video?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2018-03-08T02:03:39.530" LastActivityDate="2018-03-08T02:03:39.530" Title="What modes are used for transmitting motion pictures video?" Tags="&lt;modes&gt;&lt;sstv&gt;&lt;atv&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1132" PostTypeId="1" AcceptedAnswerId="1133" CreationDate="2013-12-20T16:28:21.113" Score="19" ViewCount="2319" Body="&lt;p&gt;There's nothing worse to getting home, turning on the radio, and being unable to find a clear frequency that isn't full of a bunch of meaningless QSOs where somehow everyone is 599 and no one has anything to say. Are there any designated &quot;contest-free zones&quot;, or other ways I might be able to enjoy amateur radio &lt;em&gt;without&lt;/em&gt; contests?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-05-23T04:14:42.880" Title="I hate contests. How can I avoid them?" Tags="&lt;contest&gt;&lt;band-plan&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1133" PostTypeId="2" ParentId="1132" CreationDate="2013-12-20T17:03:24.890" Score="19" Body="&lt;p&gt;Most countries follow the band plans that disallow contesting on WARC frequencies, which include three narrow slices of shortwave frequencies at 30M, 17M, and 12M. If you stick to these frequencies you will rarely, if ever, be bothered by contests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a small slice of spectrum though, so you might simply consider doing what some amateurs do and simply note the days the contests are operating, and plan activities other than amateur radio on those days. Given that most contests are short duration, occur mostly on weekends, and don't occur more than a few times a year, it's not unreasonable to simply avoid affected bands on affected days.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-20T17:03:24.890" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1134" PostTypeId="1" AcceptedAnswerId="1144" CreationDate="2013-12-20T17:26:14.760" Score="9" ViewCount="222" Body="&lt;p&gt;At the moment I only have an HF receiver (or I will when I build it, hopefully soon).  Are there any contests I can participate in, or ways for me to participate in a contest without borrowing a transmitter or working with an amateur who has one?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2016-04-10T16:21:17.847" Title="Are there ways for people with receivers to participate in contests?" Tags="&lt;contest&gt;&lt;receiver&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1135" PostTypeId="1" AcceptedAnswerId="1136" CreationDate="2013-12-20T17:52:38.750" Score="8" ViewCount="125" Body="&lt;p&gt;What is the logic behind the names of different RG cables? The Wikipedia's &lt;a href=&quot;http://en.wikipedia.org/wiki/Coaxial_cable#Standards&quot;&gt;Coaxial cable&lt;/a&gt; page has a list of different coaxial cable standards but I cannot find the internal logic of the naming. I would assume that coding pretty much anything would be easier if you give meaning to the number, such as outer diameter or insulator material. Now the numbers seem totally random.&lt;/p&gt;&#xA;" OwnerUserId="194" LastActivityDate="2013-12-20T18:19:55.390" Title="What is the logic behind RG cable codes" Tags="&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1136" PostTypeId="2" ParentId="1135" CreationDate="2013-12-20T18:19:55.390" Score="10" Body="&lt;p&gt;&quot;RG&quot; stems from old, obsolete military specifications, standing for &quot;radio guide&quot;, and the number is actually arbitrary.  Part of the reason they are obsolete is that they weren't specific enough - RG-6 can reasonably be assumed to have an 18 gauge solid center conductor, but beyond that the dielectric, velocity factor, or completeness of the shielding conductor aren't always specified.  Some amount of standardization exists, as shown in the wikipedia article, with additional characters after the &quot;RG-6&quot; type code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whenever you see generalizations like &quot;RG-6 has better performance than RG-59 for application X&quot; you must ask for manufacturer and part number for the two cables, because the performance advantage might not exist with two other &quot;RG-6&quot; and &quot;RG-59&quot; cables.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While we don't necessarily need to shy away from using the generic name, be sure to specify important cable parameters whenever they matter if you are ordering or sharing project information. Otherwise you may end up with a cable that doesn't meet your needs, or someone attempting to replicate your project or solve your problem will be unsuccessful at duplicating your setup.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-20T18:19:55.390" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1137" PostTypeId="1" AcceptedAnswerId="1138" CreationDate="2013-12-20T18:28:41.410" Score="5" ViewCount="290" Body="&lt;p&gt;The background, I got a US Tech+ license back in the 1990's when I was in middle school. At the time I did it for the novelty of getting licensed in something and not a bit to imitate my brother. Since I wasn't using the license at the time I let it lapse in the 2000's. Now I am thinking of relicensing to either Tech or General. The question though is could I petition the FCC to let me have my old call sign or would I have to just get a new one? I checked out the FCC website and couldn't find any relevant information in the publications or FAQs.  &lt;/p&gt;&#xA;" OwnerUserId="486" LastActivityDate="2013-12-20T18:41:07.443" Title="Relicensing after a decade, can I reacquire my old call sign?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1138" PostTypeId="2" ParentId="1137" CreationDate="2013-12-20T18:41:07.443" Score="8" Body="&lt;p&gt;Once you are re-licensed and obtain a new automatically generated call sign, you may request your old call sign as a &quot;vanity call sign&quot;. If it isn't presently assigned to anyone else, you'll be given it.  You'll have to pay the fees for the vanity call sign, though, there's no other way for you to re-license under the old call sign after the two year waiting period.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2013-12-20T18:41:07.443" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1139" PostTypeId="1" AcceptedAnswerId="1141" CreationDate="2013-12-20T19:14:12.160" Score="9" ViewCount="4532" Body="&lt;p&gt;I know that in the High Frequency regions of the ham bands, the antennas have to be sub-wavelength because most people just can't put up a 160 meter full-size antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say we're in the 23 centimeter or an even higher band. Can the antenna lengths there be, let's say, twice, four times, etc., as large?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2015-12-15T22:06:11.780" LastActivityDate="2016-02-02T16:20:17.827" Title="Is a multiple-wavelengths antenna possible in UHF and up?" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1140" PostTypeId="2" ParentId="1139" CreationDate="2013-12-20T20:20:13.147" Score="1" Body="&lt;p&gt;Yes, you could create, instead of a 1/2 wave dipole, a full wave dipole. They get very directional after you pass full-wave in length as shown in graphs at &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow&quot;&gt;http://www.antenna-theory.com/antennas/dipole.php&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, most folks instead use a collinear dipole array of multiple dipoles stacked, or side-by-side, or both, for gain.&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2013-12-20T20:20:13.147" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1141" PostTypeId="2" ParentId="1139" CreationDate="2013-12-21T12:26:01.167" Score="3" Body="&lt;p&gt;People can, and do, put up full size 160m antennas. Usually &quot;full size&quot; means a 1/2 wavelength dipole, or a 1/4 wave vertical. The vertical works because the 1/4 element is &quot;mirrored&quot; by the ground plane, creating an image antenna, which makes it very much like a 1/2 wave dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1/2 wavelength seems like a magic number because it is the minimum length required to attain resonance. Antennas can be made smaller and resonated by introducing additional, non-radiating reactive components like inductors or capacitors. However, shortening the antenna in this way makes the antenna less efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Making the antenna &lt;em&gt;longer&lt;/em&gt; than 1/2 wavelength isn't frequently done because in most cases there isn't much point to it. As the antenna first becomes longer than 1/2 wavelength, it stops being resonant. If made longer to 1.5 wavelengths, it becomes resonant again. However, it isn't any more efficient than a 1/2 wavelength antenna. In fact, it's likely &lt;em&gt;less&lt;/em&gt; efficient, because the current must now travel over more antenna, which has more resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What making the antenna longer does do is alter the radiation pattern. For example, compare a 1/2 wave dipole (in free space):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/rN8Y0.jpg&quot; alt=&quot;1/2 wave dipole radiation pattern&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;to a 1.5 wave dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/C9wzr.jpg&quot; alt=&quot;1.5 wave dipole radiation pattern&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are from &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna-theory.com&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this really useful? Usually no. One possible exception might be for verticals, where making the antenna longer (to a point, usually 5/8 wavelength) lowers the takeoff angle a bit.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-01-31T08:35:57.827" LastActivityDate="2016-01-31T08:35:57.827" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="1142" PostTypeId="1" AcceptedAnswerId="1143" CreationDate="2013-12-21T13:21:57.033" Score="22" ViewCount="14278" Body="&lt;p&gt;An ordinary 1/4 wavelength vertical is smaller and resonant without any loading coil or matching network. What's the advantage to a 5/8 wavelength vertical? Why 5/8 in particular, and not something longer or shorter?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-11T14:02:32.720" Title="What makes a 5/8 wavelength vertical desirable?" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1143" PostTypeId="2" ParentId="1142" CreationDate="2013-12-21T15:26:44.127" Score="24" Body="&lt;p&gt;Indeed, why?  A 5/8λ isn't resonant where a 1/4λ or 1/2λ would be.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is the radiation pattern.  The pattern for a 1/4λ monopole is essentially a doughnut, tasty and a pretty good pattern especially for a VHF antenna. Extending the antenna changes the current distribution.  This flattens out the pattern removing power from the useless (for VHF purposes) vertical dimension and giving more horizontal gain and at a lower angle.  See the following illustration from the late great L. Cebik:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/oJZ2v.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on the source, they will quote anywhere from 1.2dB to 3.5dB gain over the 1/2λ design.  There has also been some discussion that in some areas (urban and mountainous terrain) the lower angle of radiation is a detriment and a standard 1/4λ or 1/2λ antenna is to be favored.  I don't know. I guess they are pretty cheap, if this is a concern you can buy one mount and two and antenna, compare them for a bit and return the loser.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, why 5/8λ?  Why not long longer? After all more gain is better right?  Well, inspecting the figure above you will notice the appearance of high angle lobes.  As you lengthen the antenna past 5/8λ these lobes become more pronounced and break up the pattern in undesirable ways. Making it shorter maintains a good pattern, but the gain is less.  So, 5/8λ is about optimal for this style of antenna.  &lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-21T15:26:44.127" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1144" PostTypeId="2" ParentId="1134" CreationDate="2013-12-21T17:48:04.427" Score="3" Body="&lt;p&gt;Summits on the Air (SOTA) is not a contest, but an ongoing activity with awards. You can participate as an activator (transmitting from summits), a chaser (working those on summits), or an SWL (listening to contacts and logging them). All the chaser awards are available to SWLs (shortwave listeners).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More info is here: &lt;a href=&quot;http://www.sota.org.uk/Awards&quot; rel=&quot;nofollow&quot;&gt;http://www.sota.org.uk/Awards&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other activities also have SWL awards. There appears to be one for IOTA (Islands on the Air).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This site is dedicated to &quot;shortwave amateur radio listening&quot; and has a news about awards and a registry: &lt;a href=&quot;http://swarl.org/&quot; rel=&quot;nofollow&quot;&gt;http://swarl.org/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2013-12-21T17:48:04.427" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1145" PostTypeId="1" CreationDate="2013-12-21T19:00:16.433" Score="9" ViewCount="1589" Body="&lt;p&gt;I just coined the term &quot;field antenna&quot;. It is by analogy to the &lt;a href=&quot;http://en.wikipedia.org/wiki/Light-field_camera&quot; rel=&quot;noreferrer&quot;&gt;lightfield camera&lt;/a&gt; or the &lt;a href=&quot;http://en.wikipedia.org/wiki/Soundfield_microphone&quot; rel=&quot;noreferrer&quot;&gt;soundfield microphone&lt;/a&gt;. Essentially, it is an antenna that captures not only the strength of an RF field, but also the &lt;em&gt;direction&lt;/em&gt; of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, these antennas already exist in forms, such as &lt;a href=&quot;http://en.wikipedia.org/wiki/Phased_array&quot; rel=&quot;noreferrer&quot;&gt;phased arrays&lt;/a&gt; used for radar, or four-square antennas popular on the lower bands. However, I have a somewhat different use case in mind: I want it to work at HF, for receive only, and I don't want to implement the phasing with a fixed network (or maybe a few switched networks) as in the four-square antenna. Instead, I want to perform the phasing in software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One possible application: listening to radio in stereo, with the sound heard corresponding to the direction from which the signal was received, a &quot;&lt;a href=&quot;http://en.wikipedia.org/wiki/Wetware_%28brain%29&quot; rel=&quot;noreferrer&quot;&gt;wetware&lt;/a&gt; rotator&quot; of sorts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the usual way to doing this processing is to decompose the signal into circular harmonics. These are like &lt;a href=&quot;http://en.wikipedia.org/wiki/Spherical_harmonics&quot; rel=&quot;noreferrer&quot;&gt;spherical harmonics&lt;/a&gt;, but in two dimensions (circles) instead of 3 (spheres). For the sake of simplicity I'm stopping at the first harmonic (first-order), so I will have, perhaps after some processing, three signals:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;an omnidirectional signal (0-th order)&lt;/li&gt;&#xA;&lt;li&gt;a figure-of-eight pattern aimed East-West&lt;/li&gt;&#xA;&lt;li&gt;a similar figure-of-eight, but aimed North-South&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Described mathematically, I'm looking for the responses in azimuth defined by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{1}{\sqrt{2\pi}},&#xA;\frac{\cos \theta}{\sqrt{\pi}},&#xA;\frac{\sin \theta}{\sqrt{\pi}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or described graphically:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/BNlej.png&quot; alt=&quot;1st order circular harmonics polar plot&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now here's the question: how might one realize such an antenna? Remember the antennas need not actually have these responses: they might have other responses from which these responses can be calculated.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2013-12-22T12:51:35.647" LastActivityDate="2013-12-22T14:52:49.640" Title="How might one realize a first order, two dimensional RF field antenna for HF?" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;&lt;phased-array&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1146" PostTypeId="2" ParentId="1145" CreationDate="2013-12-21T20:20:42.483" Score="5" Body="&lt;p&gt;OK, this is an interesting one.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At first blush you could achieve this with two tuned magnetic loops at right angles to each other (visualize an egg-beater) and a 1/2 wave vertical for the omnidirectional part.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, someone has thought of this crossed loop arrangement before, in 1907 Bellini and Tosi invented the Bellini-Tosi Goniometer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NFybI.jpg&quot; alt=&quot;Bellini-Tosi Goniometer&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A coil is rotated inside an electrical field fed from the N-S and E-W antenna signal components such finding the angle of maximum signal. The antenna can be either be a circular array of 1/4 wave verticals or a Crossed-Loop Antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/PIO7O.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Systems based on this principal were the basis of the first radio navigation systems for aircraft until replaced by radar following WWII.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back to the original question though, I think the loops would have to be tuned fairly precisely and high-Q loops are rather narrow in bandwidth so you'll have to pick your operating frequencies with care.  But I don't see any obvious reason why it couldn't be done. &lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-21T20:20:42.483" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1147" PostTypeId="2" ParentId="1145" CreationDate="2013-12-22T14:52:49.640" Score="1" Body="&lt;p&gt;Three verticals (or three vertical dipoles) arranged in a triangle, spaced less than $\frac{1}{2}\lambda$ apart should do it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any pair of these antennas could be considered as an &lt;a href=&quot;http://en.wikipedia.org/wiki/Adcock_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Adcock antenna&lt;/a&gt;. Each has the desired figure-of-eight response, and with the three antennas, we have three of these, each aimed sixty degrees apart. Unlike a traditional Adcock antenna, we won't be combining the antennas electronically, but rather connecting each element to an SDR (each phase-synchronized) and the combining is done in software. This allows each antenna to be arbitrarily combined with any others, in perhaps multiple ways simultaneously.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could describe the azimuthal responses of each of the three possible pairs as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;f_1(\theta) &amp;amp;= \cos \theta \\&#xA;f_2(\theta) &amp;amp;= \cos (\theta + \frac{\pi}{3}) \\&#xA;f_2(\theta) &amp;amp;= \cos (\theta + \frac{2 \pi}{3}) \\&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These can be combined in some ratio to arrive at the desired patterns from the question. We can see that the ratios will be multiples of $\frac{\pi}{2}$ because:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \int_0^{2\pi} f_2(\theta) \cos (\theta)\,d\theta = \frac{\pi}{2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So we can then reconstruct the first-order circular harmonics as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;h_{1a}(\theta)&#xA;  &amp;amp;= f_1(\theta)&#xA;  &amp;amp;+\frac{\pi}{2}f_2(\theta)&#xA;  &amp;amp;-\frac{\pi}{2}f_3(\theta) \\&#xA;h_{1b}(\theta)&#xA;  &amp;amp;=&#xA;  &amp;amp;-\frac{\pi}{2}f_2(\theta)&#xA;  &amp;amp;-\frac{\pi}{2}f_3(\theta)&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A graph might help:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/DPyma.png&quot; alt=&quot;polar plot of functions&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This shows the response of the three possible pairings. $f_1$ is red, $f_2$ is yellow, and $f_3$ is green. $h_{1a}$ is cyan, and $h_{1b}$ is blue. Only the positive lobes are shown to make the polarity of the signals easier to see.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 0th order response, the omnidirectional one, is easy: it's simply the average of the three antennas. This is equivalent to a vertical antenna in the middle of the triangle array. This serves to sense the phase of the signal so we can know if it is in the positive or negative lobe of the 1st harmonics. Without it, there would be a 180 degree direction ambiguity in any measurements.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-12-22T14:52:49.640" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1149" PostTypeId="1" AcceptedAnswerId="1151" CreationDate="2013-12-22T17:32:10.057" Score="5" ViewCount="292" Body="&lt;p&gt;I am in 12th std, the reason why I am mentioning this is that we are given a PROJECT to do in Physics subject. And then one day I searched the internet and found this amazing thing called 'Crystal Radio'. And when I showed it to my group(since it is a group project), their faces were like WTF??? Because the crystal radio works only on the energy of radio waves and no external power source!!! And my friends then started to ask me that how can this be possible... Then we went to our Physics teacher and he said that he made a crystal radio when he was in 11th and it didn't worked for him since the energy produced by the receiver is very small... I didn't knew what to answer to my friends then... So my short and simple question is that &quot;Does the Crystal Radio really works??&quot; And if yes then can you please provide the link to where can I find the working mechanism of a crystal radio... Thank You!!&lt;/p&gt;&#xA;" OwnerUserId="492" LastActivityDate="2013-12-22T21:34:36.147" Title="Does the Crystal Radio really work?" Tags="&lt;rf-power&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1151" PostTypeId="2" ParentId="1149" CreationDate="2013-12-22T20:50:47.633" Score="10" Body="&lt;p&gt;&lt;strong&gt;Yes, crystal radios convert radio signals to audio without any additional power.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it is true that there is not much energy in a radio signal at any significant distance from the station, so a few tricks are involved to produce audio from that weak signal without any additional electricity:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The earphones are special models that are high impedance and require very little current to operate.  Modern earbuds like you use with a mp3 player or cellphone have a low impedance and will not work.&lt;/li&gt;&#xA;&lt;li&gt;These earphones are connected as the load to a high Q resonant circuit, which collects and concentrates energy at the desired radio frequency.&lt;/li&gt;&#xA;&lt;li&gt;AM radio in particular can be decoded to audio with a diode or crystal.  Other more modern modulation types (FM, Digital Audio) can not be decoded in this way.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Getting a crystal radio to work depends upon having some strong local stations, a good antenna AND ground, and not having a good ground will keep it from working.  If you have copper plumbing, attaching to the cold water service can be a good ground if the water service arrives from the ground without any plastic PVC pipes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some links which may give you a fuller understanding:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Crystal_radio&quot;&gt;http://en.wikipedia.org/wiki/Crystal_radio&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://scitoys.com/scitoys/scitoys/radio/radio.html#crystal&quot;&gt;http://scitoys.com/scitoys/scitoys/radio/radio.html#crystal&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.crystalradio.us/&quot;&gt;http://www.crystalradio.us/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2013-12-22T21:34:36.147" LastActivityDate="2013-12-22T21:34:36.147" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1152" PostTypeId="1" AcceptedAnswerId="1153" CreationDate="2013-12-23T00:34:18.757" Score="5" ViewCount="654" Body="&lt;p&gt;Do vacuum variable capacitors have higher Q than air variable capacitors?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are not commonly seen in tuners or crystal sets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But they are mentioned as superior to air variables for resonating magnetic loop antennas opposite the feed point -- because of the plate voltages involved in bringing a magnetic loop antenna to resonance.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do vacuum variable have any Q advantage in lower voltage applications?&lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2013-12-23T01:36:24.440" Title="Do vacuum variable capacitors have higher Q than air variable capacitors?" Tags="&lt;antenna-tuner&gt;&lt;electronics&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1153" PostTypeId="2" ParentId="1152" CreationDate="2013-12-23T01:36:24.440" Score="5" Body="&lt;p&gt;Q isn't related to the voltage. A simple definition of Q could be the ratio of the total energy in a system to the energy lost per cycle.  So the biggest factor in Q is the loss in the dielectric. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, vacuum variable capacitors (VVC) have a higher Q than air variable capacitors (AVC) but there is some overlap.  A common range for VVCs is a Q of 5000 to 10000, for AVC, a Q of 5000 is near the top end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Vacuum would qualify as a better dielectric than air, but another reason to prefer VVC would be stability and endurance.  The VVCs are sealed in a glass or ceramic vessel and therefore less sensitive to temperature changes and immune to other environmental changes such as humidity, dust, insects, children, dog fur, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When considering the Q of a tuned circuit, Q = frequency / bandwidth where the frequency is the resonant frequency of the tank and the bandwidth is the frequency difference between the 3 dB points. As shown (&lt;a href=&quot;http://en.wikipedia.org/wiki/Q_factor&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/7e7m9.png&quot; alt=&quot;Curve of a tuned circuit&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to why VVC are not commonly seen in crystal radios, it could be because crystal radios are generally inexpensive radios.  Vacuum variables are considerably more expensive than the usual air variables.  Although there are some highly sought after air variables that could set you back &gt;100USD used due to some of their features and the fact they haven't been produced in some time.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-23T01:36:24.440" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1155" PostTypeId="1" CreationDate="2013-12-23T07:24:20.170" Score="1" ViewCount="75" Body="&lt;p&gt;I have a usb stick that communicates with a medical device.  I am attempting to decode the communication. I have figured out the basic radio parameters (916.5MHz, ook, bit rate, preamble, sync words), but there is still some radio related parameter I haven't figured out yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can give the USB stick different destination device ids, and can see segments of the short (~12bytes) packet change. In fact, for each character of the 6-digit device id, I see 6 bits change in the packet, with a consistent mapping as follows:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&quot;010101&quot; =&amp;gt; &quot;0&quot;,&#xA;&quot;110001&quot; =&amp;gt; &quot;1&quot;,&#xA;&quot;110010&quot; =&amp;gt; &quot;2&quot;,&#xA;&quot;100011&quot; =&amp;gt; &quot;3&quot;,&#xA;&quot;110100&quot; =&amp;gt; &quot;4&quot;,&#xA;&quot;100101&quot; =&amp;gt; &quot;5&quot;,&#xA;&quot;100110&quot; =&amp;gt; &quot;6&quot;,&#xA;&quot;010110&quot; =&amp;gt; &quot;7&quot;,&#xA;&quot;011010&quot; =&amp;gt; &quot;8&quot;,&#xA;&quot;011001&quot; =&amp;gt; &quot;9&quot;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;So device id 123456 is encoded as &quot;110001110010100011110100100101100110&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are some other 6-bit sequences I see in the data as well, like:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;001011 =&amp;gt; ?&#xA;001101 =&amp;gt; ?&#xA;101010 =&amp;gt; ?&#xA;101100 =&amp;gt; ?&#xA;011100 =&amp;gt; ? &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The second bit in each code to be a parity bit for the remaining 5 bits. The first bit seems special in some way as well, but I haven't figured it out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ideas?&lt;/p&gt;&#xA;" OwnerUserId="496" LastActivityDate="2013-12-23T07:24:20.170" Title="Data encoding puzzle" Tags="&lt;uhf&gt;&lt;encoding&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2013-12-23T11:57:55.063" ContentLicense="CC BY-SA 3.0" />
  <row Id="1156" PostTypeId="1" AcceptedAnswerId="1157" CreationDate="2013-12-23T20:14:55.333" Score="8" ViewCount="3704" Body="&lt;p&gt;A loopstick antenna, if you don't know, is a coil of many turns around a high permeability core. They are frequently encountered in AM receivers and look like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/1b0KM.jpg&quot; alt=&quot;loopstick antenna photo&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This particular example is actually two antennas on one core.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What type of material is an appropriate core for these antennas? What material parameters are relevant in the selection of an appropriate core, and how do they affect antenna performance?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2015-12-15T22:16:50.250" LastActivityDate="2015-12-15T22:16:50.250" Title="What's an appropriate core material for a loopstick antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;ferrite&gt;&lt;magnetic-loop&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1157" PostTypeId="2" ParentId="1156" CreationDate="2013-12-25T01:31:06.673" Score="3" Body="&lt;p&gt;As it's name implies, a loopstick antenna is a magnetic loop antenna and is one of the best choices for an electrically short antenna; necessary because broadcast AM wavelengths are hundreds of meters long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rather than a regular loop, a loopstick utilizes a large amount of (usually &lt;a href=&quot;http://en.wikipedia.org/wiki/Litz_wire&quot; rel=&quot;nofollow noreferrer&quot;&gt;Litz&lt;/a&gt;) wire wrapped around a ferrite rod.  This forms an inductor which is tuned to resonance by a variable capacitor as the radio is tuned to a frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The material for the core of these antennas is ferrite -- a powdered iron based magnetic material with a variety of other metals added. The exact composition of the ferrite material (called it's &quot;mix&quot;) governs it's characteristics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The goal of the ferrite is to produce a very high Q inductor with a high electrical resistance.  The efficiency of the inductor is governed by the permeability of the ferrite core and the core's permeability changes with frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is because the ferrite itself absorbs power. This arises from the energy required to change the magnetic alignment of the magnetic domains inside the granular structure of the ferrite. The higher the frequency, the greater the number of changes and hence the higher the loss, generally dropping off sharply.  See the following chart (lifted from the Fair-Rite catalog) for example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/95A4l.gif&quot; alt=&quot;Fair-Rite Mix 61 Perm&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the chart, μ' is the permeability of the ferrite and μ&quot; is the ferrite induced losses. While the permeability continues to rise until about 11 MHz, the loses begin to rise dramatically starting at about 4.5MHz.  This is why &lt;a href=&quot;http://www.fair-rite.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fair-Rite Corp&lt;/a&gt; only recommends this mix through about 5MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a chart of their &quot;mix 61&quot;, which uses Nickel and Zinc in the iron to achieve it's characteristics and is recommended as the proper one for AM broadcast frequency antenna material.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For HF frequencies, they recommend &quot;mix 73&quot;, a combination of Nickel and Manganese which performs well up to about 50MHz as shown here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NNLdk.png&quot; alt=&quot;Fair-Rite Mix 73&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's worth noting in this chart that the losses are much higher than the MF band material, but so is the permeability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is probably a good time to underline an important characteristic of ferrite: while it concentrates the magnetic fields, it has a very high electrical resistance.  This isn't very important for receiving.  But the use of ferrite in a transmitting antenna, or as is more common among hams, as a transformer in &lt;a href=&quot;http://en.wikipedia.org/wiki/Balun&quot; rel=&quot;nofollow noreferrer&quot;&gt;baluns&lt;/a&gt; or ununs, it can be important.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ferrite's resistance is inversely related to it's permeability.  The less permeable ferrite becomes, the more resistant it becomes.  Ferrite's permeability is also affected by temperature.  As the ferrite warms up, it's permeability increases until it reaches what's called it's &lt;a href=&quot;http://en.wikipedia.org/wiki/Curie_temperature&quot; rel=&quot;nofollow noreferrer&quot;&gt;Curie temperature&lt;/a&gt;, for this mix, about 160° C.  At that point ferrite rapidly loses it's permeability as shown in this graph:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/zQ0YK.png&quot; alt=&quot;Mix 73 curie temp graph&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And this is how &lt;a href=&quot;http://en.wikipedia.org/wiki/Balun&quot; rel=&quot;nofollow noreferrer&quot;&gt;baluns&lt;/a&gt; and ununs fail.  Power through the transformer warms the material due to the ferrite related loses.  All is OK until the curie temperature it reached and then the permeability falls off a cliff and the resistance &lt;strong&gt;increases&lt;/strong&gt; causing more heating in a runaway thermal loop until your coax melts and shorts the inner conductor to the shield.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2013-12-25T17:51:41.880" LastActivityDate="2013-12-25T17:51:41.880" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1158" PostTypeId="2" ParentId="1131" CreationDate="2013-12-26T11:26:58.593" Score="1" Body="&lt;p&gt;With Amateur televison (ATV) one can transmit 800x600 pixels with 25 images (&quot;frames&quot;) per second and thus have nicely moving pictures (for reference, NSTC is 29.97 frames per second). This requires a bandwidth of 6 MHz and can be done at frequencies starting at 430 MHz in different amateur bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;People also make use of NTSC and PAL modes. &lt;a href=&quot;http://en.wikipedia.org/wiki/Amateur_television&quot; rel=&quot;nofollow&quot;&gt;Wikipedia has a few frequencies&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Longer waves with lower frequencies don't offer enough bandwidth for &quot;nice&quot; video.&lt;/p&gt;&#xA;" OwnerUserId="85" LastEditorUserId="5046" LastEditDate="2015-07-31T23:19:34.577" LastActivityDate="2015-07-31T23:19:34.577" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1159" PostTypeId="1" CreationDate="2013-12-26T14:27:15.457" Score="15" ViewCount="3734" Body="&lt;p&gt;Datasheets for ferrite materials are usually filled with incomprehensible graphs with greek letters. For example, &lt;a href=&quot;http://www.fair-rite.com/newfair/materials73.htm&quot; rel=&quot;noreferrer&quot;&gt;Fair-Rite's 73 material&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/GQRMu.gif&quot; alt=&quot;Fair-Rite 73 material datasheet&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's a $\mu'_s$ and a $\mu''_s$? What do these numbers represent, and how can I use them in amateur radio? Do they allow me to predict inductance or losses of inductors made on cores of this material? What is the relevant math? Why are these parameters dependent on frequency, and what are the relevant consequences for amateur radio?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-10-04T16:52:44.400" Title="How does one read a ferrite datasheet?" Tags="&lt;diy&gt;&lt;ferrite&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1160" PostTypeId="2" ParentId="1159" CreationDate="2013-12-27T01:42:42.367" Score="2" Body="&lt;p&gt;&lt;strong&gt;Permeability&lt;/strong&gt; is the measure of the ability of a material to support the formation of a magnetic field within itself or more simply, the inductance per unit length. Magnetic permeability is typically represented by the Greek letter μ (mu) and is measured in &lt;a href=&quot;http://en.wikipedia.org/wiki/Henry_%28unit%29&quot; rel=&quot;nofollow&quot;&gt;henries&lt;/a&gt; per meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's helpful to remember that inductance here is a complex number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the context of these ferrite material data sheets, $\mu'_s$ represents the ‘effective’ relative magnetic permeability (the real part of the permeability). This depends upon the choice of material and the size and shape of the rod or core. This permeability also varies with the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why does this vary with frequency? Because ferromagnetic material becomes more and more magnetized as the current increases.  Initially, the magnetic domains within the ferrite are randomly oriented and the ferrite exhibits no particular magnetic properties.  As the magnetic flux increases, more and more of these magnetic domains become aligned with the magnetic field.  At a certain point the material becomes &lt;a href=&quot;http://en.wikipedia.org/wiki/Saturation_%28magnetic%29&quot; rel=&quot;nofollow&quot;&gt;saturated&lt;/a&gt; and all the domains aligned, no further increase in permeability can occur. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is this useful in radio?  For an antenna constructed around a ferrite rod, like the AM broadcast antennas discussed previously, the radiation resistance of the antenna is raised by a factor of μ&lt;sup&gt;2&lt;/sup&gt; by winding the antenna around a ferrite rod.  This is extremely useful as the radiation resistance of such an electrically short antenna is on the order of tenths of ohms, not very efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, &quot;there's ain't no such thing as a free lunch&quot;.  Ferrite needs to absorb some of the signal power to work it's magic (flipping the magnetic alignment of the magnetic domains inside the ferrite structure) so here $\mu''_s$ represents that loss and it increases with frequency as shown in the chart on the upper left above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's worth pointing out that ferromagnetic material behaves non-linearly once it's driven into saturation and this can lead to things like the generation of harmonics and intermodulation distortion so it's useful to design the circuit to prevent the core from going into saturation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sorry Phil, the relevant maths are right at the edge of my range. It's possible to predict the inductive losses as a series resistance in the circuit, but I would just use an ohmmeter once I built a prototype ;)&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-27T01:42:42.367" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1161" PostTypeId="2" ParentId="835" CreationDate="2013-12-28T11:21:37.173" Score="4" Body="&lt;p&gt;Some of the cheap HTs, which were designed for voice, key up the transmitter quite slowly, and the transmitter also stays on for quite a while after the PTT is released. At least my older Puxings behave this way - they require a long txdelay in the tracker (delay from PTT down to the start of data transmission), and there's also a long &quot;tail&quot; after the data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It might have to do with power saving methods, which can be disabled in radios which were designed for data (like the ham rigs with built-in APRS).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can compare transmitter key-up/key-down timings by attaching another receiver to a computer, opening the squelch completely, and recording the APRS transmissions using a wave editor such as &lt;a href=&quot;http://audacity.sourceforge.net/&quot; rel=&quot;nofollow&quot;&gt;Audacity&lt;/a&gt; (free). Zoom in to the start of the transmission - it'll be quite easy to see where the txdelay flags end and actual data starts. If your tracker has a txdelay setting of 20 (200 ms - they're traditionally set in 10s of milliseconds), and you're seeing 50 ms of flags before data, the transmitter takes 150 ms to transmit. If you're seeing 150 ms of flags before data, the transmitter only takes 50 ms to wake up. On some of these SDR-based HTs the delay varies a lot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Zoom in to the end of the transmission and see how long the transmitter transmits after the end of data, too. Some stay on longer, wasting more bandwidth than others for the same amount of transmitted data.&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2013-12-28T11:21:37.173" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1162" PostTypeId="1" AcceptedAnswerId="1165" CreationDate="2013-12-28T19:30:15.377" Score="5" ViewCount="384" Body="&lt;p&gt;I obtained my Canadian Basic with Honours certificate in the late 90's and haven't done much with it since. Was looking to get back into the hobby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has my certificate expired? Do I need to take the test again?&lt;/p&gt;&#xA;" OwnerUserId="499" LastEditorUserId="29" LastEditDate="2013-12-30T12:59:43.023" LastActivityDate="2013-12-30T16:19:01.187" Title="Does a Canadian amateur radio operator’s certificate expire?" Tags="&lt;legal&gt;&lt;license&gt;&lt;canada&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1163" PostTypeId="2" ParentId="1162" CreationDate="2013-12-28T21:58:01.903" Score="0" Body="&lt;p&gt;In the U.S. it expires after ten years if you don't renew it. Don't know about Canada. [note to potential down voters: at the time I wrote this answer neither the title nor the question explicitly mentioned Canada]&lt;/p&gt;&#xA;" OwnerUserId="105" LastEditorUserId="105" LastEditDate="2013-12-30T16:19:01.187" LastActivityDate="2013-12-30T16:19:01.187" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1164" PostTypeId="2" ParentId="1162" CreationDate="2013-12-29T14:35:58.707" Score="3" Body="&lt;p&gt;As a friend has just gone through exactly this, I can confirm that yes, your certificate and callsign are still valid. As wkm noted above, the RAC states that “&lt;a href=&quot;https://www.rac.ca/en/amateur-radio/regulatory/certification/&quot; rel=&quot;nofollow&quot; title=&quot;The Amateur Radio Certificates are valid for your lifetime&quot;&gt;The Amateur Radio Certificates are valid for your lifetime&lt;/a&gt;”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wile this is great for returning operators, it does mean that the Canadian &lt;a href=&quot;http://apc-cap.ic.gc.ca/pls/apc_anon/query_amat_cs%24.startup&quot; rel=&quot;nofollow&quot; title=&quot;Amateur Radio Operator Certificates&quot;&gt;Amateur Radio Operator Certificates&lt;/a&gt; database contains many SKs and inactive hams. &lt;/p&gt;&#xA;" OwnerUserId="90" LastActivityDate="2013-12-29T14:35:58.707" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1165" PostTypeId="2" ParentId="1162" CreationDate="2013-12-29T16:23:43.340" Score="2" Body="&lt;p&gt;According to &lt;a href=&quot;https://www.rac.ca/en/amateur-radio/regulatory/certification/&quot; rel=&quot;nofollow&quot;&gt;RAC&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;The Amateur Radio Certificates are valid for your lifetime.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="499" LastActivityDate="2013-12-29T16:23:43.340" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1166" PostTypeId="2" ParentId="1159" CreationDate="2013-12-29T20:31:42.917" Score="5" Body="&lt;p&gt;For the purposes of amateur radio, ferrite materials are usually useful for making inductors where an air-core coil could not feasibly achieve the necessary inductance. Three relevant questions which the datasheet can answer for us are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;what &lt;a href=&quot;http://en.wikipedia.org/wiki/Inductance&quot; rel=&quot;nofollow&quot;&gt;inductance&lt;/a&gt; will a coil on this core have?&lt;/li&gt;&#xA;&lt;li&gt;what losses will this core material introduce?&lt;/li&gt;&#xA;&lt;li&gt;at what current will this inductor &lt;a href=&quot;http://en.wikipedia.org/wiki/Saturation_%28magnetic%29&quot; rel=&quot;nofollow&quot;&gt;saturate&lt;/a&gt;?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;To know what inductance our coil will have, we need to know the permeability of the core material. The complete equations to calculate inductance are complex and depend on the geometry (E-I, toroid, wire gauge, turn spacing, number of turns, ...) of the inductor, but it all cases, higher permeability means more inductance per turn of wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first, and simplest measure of permeability is in the table, under &lt;em&gt;initial permeability&lt;/em&gt;. This table doesn't specify units, but it could be &lt;a href=&quot;http://en.wikipedia.org/wiki/Gauss_%28unit%29&quot; rel=&quot;nofollow&quot;&gt;gauss&lt;/a&gt;/&lt;a href=&quot;http://en.wikipedia.org/wiki/Oersted&quot; rel=&quot;nofollow&quot;&gt;oersted&lt;/a&gt; or G/Oe, which are &lt;a href=&quot;http://en.wikipedia.org/wiki/Centimetre_gram_second_system_of_units&quot; rel=&quot;nofollow&quot;&gt;CGS&lt;/a&gt; units. The nice thing about G/Oe is that the permeability of air or vacuum (conventional symbol: $\mu_0$) is 1G/Oe, so permeability in G/Oe is also &lt;a href=&quot;http://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29#Relative_permeability_and_magnetic_susceptibility&quot; rel=&quot;nofollow&quot;&gt;relative permeability&lt;/a&gt;, which is usually what inductance calculators expect. This is not true when using &lt;a href=&quot;http://en.wikipedia.org/wiki/International_System_of_Units&quot; rel=&quot;nofollow&quot;&gt;SI units&lt;/a&gt;, where $\mu_0 = 4\pi\cdot10^{−7}\:\mathrm{H/m}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the permeability of ferrite is not linear. Due to its physical properties, the permeability effectively drops with frequency. The picture is further complicated at high frequencies because it takes some time for the core to magnetize, so at high frequencies, the magnetic flux density (B) might lag significantly behind the magnetizing field (H). From the perspective of the electrical circuit, this looks like higher losses in the form of a series resistance, and reduced inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can break this &quot;lag&quot; into in-phase and out-of-phase components, and it becomes a complex number. The first graph, &lt;em&gt;Complex Permeability&lt;/em&gt; shows this. , $\mu'_s$ is the in-phase part of permeability, the part that makes inductance. $\mu''_s$ is the out-of-phase part of permeability, the part that makes losses. This is very similar to how we might represent impedance, with one part being reactance (capacitance or inductance) and the other part being resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ratio $\mu''/\mu'$ is also the ratio of energy lost vs. energy stored in the inductor. This quantity is called the loss tangent, and is also written as $\tan \delta$. It is also the reciprocal of the &lt;a href=&quot;http://en.wikipedia.org/wiki/Quality_factor&quot; rel=&quot;nofollow&quot;&gt;quality factor&lt;/a&gt; $Q$. If you've calculated or measured the inductance $L$, you can also calculate the &lt;a href=&quot;http://en.wikipedia.org/wiki/Equivalent_series_resistance&quot; rel=&quot;nofollow&quot;&gt;equivalent series resistance&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \tan \delta&#xA;= \frac{\mu''}{\mu'}&#xA;= \frac{1}{Q}&#xA;= \frac{R_\text{ESR}}{2\pi f L} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A related parameter, &lt;em&gt;loss factor&lt;/em&gt;, is expressed in the table. This is simply the loss tangent, divided by the initial permeability. It is done this way because including an &lt;a href=&quot;http://info.ee.surrey.ac.uk/Workshop/advice/coils/gap/&quot; rel=&quot;nofollow&quot;&gt;air gap&lt;/a&gt; in the core reduces the loss tangent at the expense of decreasing the permeability. Note that the loss factor in the table is specified for a low frequency; at high frequencies $\tan \delta$ increases significantly and you will have to calculate the loss factor for yourself from the graph.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last concern we have is core saturation. This one is pretty easy if we can assume all the magnetic flux is inside the ferrite. For inductors wound on closed shapes like toroids or E-I cores, this is reasonable. There's an entry in the table: &lt;em&gt;Flux Density @ Field Strength&lt;/em&gt;. This is where this material saturates. It can also be determined graphically from the &lt;em&gt;Hysteresis Loop&lt;/em&gt;: the point where the two black lines meet at the upper-right is saturation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All we have to do is translate between current in the coil around the core and field strength. This is pretty easy if we convert oerstead to the equivalent SI unit: ampere/meter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 1 \mathrm{Oe}&#xA;= {1000 \:\mathrm A \over 4 \pi \:\mathrm m}&#xA;\approx 79.58 \: \mathrm A / \mathrm m $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here, &lt;em&gt;ampere&lt;/em&gt; might more intuitively be called an &lt;a href=&quot;http://en.wikipedia.org/wiki/Ampere-turn&quot; rel=&quot;nofollow&quot;&gt;ampere-turn&lt;/a&gt;. They are the same thing dimensionally. The &quot;per meter&quot; part refers to the nominal length of the magnetic circuit: for example, the circumference of a toroidal core. So for example, say we have a toroidal core with a circumference of 4cm, with 10 turns on it, with 500mA. The field strength is then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;\frac{10 \cdot 0.5 \:\mathrm A}{0.04 \:\mathrm m} &amp;amp;= 125\:A/\mathrm m \\&#xA;125\: \mathrm A/ \mathrm m \cdot \frac{4 \pi}{1000} &amp;amp;\approx 1.57\: \mathrm{Oe}&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is less than the 5 Oe in the datasheet, so the core is not saturated.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-10-04T16:52:44.400" LastActivityDate="2016-10-04T16:52:44.400" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1167" PostTypeId="1" CreationDate="2013-12-30T04:27:36.950" Score="2" ViewCount="700" Body="&lt;p&gt;I would like to use some software packages, such as rtl_433, that are written with the RTL-SDR library with a FUNcube Dongle instead.&#xA;Is there a wrapper that would allow the FUNcube Dongle to be used with RTL-SDR?&lt;/p&gt;&#xA;" OwnerUserId="520" LastEditorUserId="76" LastEditDate="2013-12-30T13:00:52.090" LastActivityDate="2014-01-25T18:16:48.167" Title="Is there a rtl-sdr wrapper for the funcube dongle?" Tags="&lt;software-defined-radio&gt;&lt;software&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1168" PostTypeId="1" CreationDate="2013-12-30T04:31:39.443" Score="2" ViewCount="595" Body="&lt;p&gt;So I was reading some fiction about where the character bought a television and&#xA;&quot;and the fanciest pair of rabbit ears available. The rabbit ears even had a large tuner knob built in to it that I'm sure didn't do a damn thing for reception but man did it ever make it look hi-tech.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;OK now this is obviously a receive only setup with the old ntsc television standard, and I remember owning a set top antenna with a knob or two I know the first one was 300 ohm (I took that one apart), latter ones may have been 75 ohm. but I never understood what the knob was supposed to do or how it worked. the one I took apart had (if my fuzzy memory is right, this was at least 15 years ago) a hybrid mutli-throw switch where both poles were on opposite sides of the sweep arm and a bunch of induction coils. I don't remember seeing any capacitors, but I have slept since then.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what is this supposed to do and how does it work?&lt;/p&gt;&#xA;" OwnerUserId="385" LastActivityDate="2013-12-30T04:31:39.443" Title="The knob on rabbit ears" Tags="&lt;antenna&gt;&lt;receiver&gt;" AnswerCount="0" CommentCount="1" ClosedDate="2013-12-30T12:57:58.577" ContentLicense="CC BY-SA 3.0" />
  <row Id="1169" PostTypeId="1" AcceptedAnswerId="1176" CreationDate="2013-12-30T13:46:02.383" Score="5" ViewCount="81" Body="&lt;p&gt;I used to use the &lt;a href=&quot;http://www.amsat.org/amsat-new/satellites/status.php&quot; rel=&quot;noreferrer&quot;&gt;Amsat&lt;/a&gt; website for finding out the status of Sats and other info, like operating frequency etc. It was proving useful, and I like the pass predictor also. Seems nowadays though there's error messages with the database, I get:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;em&gt;*&lt;/em&gt; Database Error - sql - InitDB line 14&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;on a lot of pages, particularly with the status page of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any good sites out there? I'm stuck for a current list of functional sats that I should track and their associated operating frequency detail, modes, beacons etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cheers, 73&lt;/p&gt;&#xA;" OwnerDisplayName="user521" LastActivityDate="2013-12-31T04:40:51.687" Title="Website for Sat details" Tags="&lt;satellites&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1170" PostTypeId="2" ParentId="1120" CreationDate="2013-12-30T16:51:28.223" Score="2" Body="&lt;p&gt;The first place I'd start is joining a local ham radio club. Depending on where you are, just simply google and see what comes up. Or try looking on the &lt;a href=&quot;http://www.arrl.org/clubs&quot; rel=&quot;nofollow&quot;&gt;ARRL&lt;/a&gt; site and see if there's one nearby. Being involved with other hams will really whet your appetite for all sorts of sides to the hobby. As per the previous comments, the question is broad, but so is the hobby. Some people like to operate TV in the GHz bands, others like me, prefer low power CW at HF, some like optical communication and others like satellite communication or moon bounce, data modes, ssb, the list goes on. There really is something for everyone, but finding what interests you is the name of the game.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for starting out in the homebrew side of things, a good website I regularly use is &lt;a href=&quot;http://homepage.tinet.ie/~ei9gq/&quot; rel=&quot;nofollow&quot;&gt;Eamon Skeltons&lt;/a&gt; homebrew page. He writes in the RSGB Radcom magazine here in the UK and his projects are so simple, well thought through, documented and things to really get your teeth into.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, keep us posted on what you're up to, always great to hear of people getting involved.&lt;/p&gt;&#xA;" OwnerDisplayName="user521" LastEditorUserId="218" LastEditDate="2013-12-30T18:23:33.583" LastActivityDate="2013-12-30T18:23:33.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1171" PostTypeId="2" ParentId="1169" CreationDate="2013-12-30T18:22:58.420" Score="2" Body="&lt;p&gt;AMSAT's &lt;a href=&quot;http://www.amsat.org/amsat-new/satellites/status.php&quot; rel=&quot;nofollow&quot;&gt;website&lt;/a&gt; appears broken.  I wonder if they even know?  I don't what functionality it had, but N2YO's site &lt;a href=&quot;http://www.n2yo.com/satellites/?c=18&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt; has all the satellites listed and tracking information and is the one I use. &lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-30T18:22:58.420" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1172" PostTypeId="1" AcceptedAnswerId="6559" CreationDate="2013-12-30T18:27:48.383" Score="5" ViewCount="1996" Body="&lt;p&gt;I'd like to build a &lt;strong&gt;simple AM receiver for 25 and/or 28 MHz&lt;/strong&gt; to receive DCF77-formatted time code. It doesn't have to be extremely sensitive or selective - the local clock oscillator will keep time while it cannot receive the time code during my rare HF transmitting activities. Frequency stability should be relatively good (crystal controlled). Could anyone suggest a basic schematic or kit for the purpose?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a local 25.000 MHz reference transmitter which has good local coverage, and I'd like to receive that. In addition I'd like to build a version for 28 MHz to receive a local amateur beacon and my own testing transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please not that this is not the DCF77 station (77.5 kHz) in Germany, this is a local reference transmitter on &lt;strong&gt;25 MHz&lt;/strong&gt; which just happens to use the same time code format.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd prefer a traditional standalone receiver (one that doesn't require a computer for SDR), since I'd like to decode the time code in a low-power Atmel microcontroller.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2013-12-31T12:57:01.633" LastActivityDate="2016-08-31T08:48:49.823" Title="Simple DIY AM receiver for 25/28 MHz" Tags="&lt;hf&gt;&lt;diy&gt;&lt;receiver&gt;&lt;am&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1173" PostTypeId="2" ParentId="1172" CreationDate="2013-12-30T19:53:32.377" Score="2" Body="&lt;p&gt;&lt;a href=&quot;http://www.qrp.pops.net/wwv_receiver.asp&quot; rel=&quot;nofollow&quot;&gt;10 MHz WWV Receiver Experiments&lt;/a&gt; has a basic schematic for you as well as some good detail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, &lt;a href=&quot;https://en.wikipedia.org/wiki/WWV_(radio_station)&quot; rel=&quot;nofollow&quot;&gt;as per Wikipedia&lt;/a&gt;, the 25 MHz broadcasts were discontinued in 1977. I also confirmed at &lt;a href=&quot;http://www.nist.gov/pml/div688/grp40/wwv.cfm&quot; rel=&quot;nofollow&quot;&gt;the WWV website&lt;/a&gt; that 25 MHz is no longer used.&lt;/p&gt;&#xA;" OwnerUserId="285" LastEditorUserId="76" LastEditDate="2013-12-31T01:21:19.947" LastActivityDate="2013-12-31T01:21:19.947" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1174" PostTypeId="1" AcceptedAnswerId="1175" CreationDate="2013-12-30T20:38:00.017" Score="8" ViewCount="13434" Body="&lt;p&gt;I've recently received an RTL-SDR dongle, and I'm picking up a lot of noise that is probably coming from my PC, especially a lot of &quot;spikes&quot; on the 2M band. I've already started using a USB extension cable instead of plugging the dongle into the PC. What else can I do to reduce the noise floor and get rid of the RFI on 2 meters?&lt;/p&gt;&#xA;" OwnerUserId="125" LastEditorUserId="76" LastEditDate="2017-07-09T17:33:34.547" LastActivityDate="2018-05-02T01:52:39.190" Title="How can I reduce the noise coming in from an RTL-SDR dongle?" Tags="&lt;rfi&gt;&lt;rtl-sdr&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1175" PostTypeId="2" ParentId="1174" CreationDate="2013-12-30T21:00:04.030" Score="7" Body="&lt;p&gt;Here is an assortment of common ideas and recommendations for RTL-SDR devices:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Mount the device directly on your antenna, or otherwise minimize the amount of feed line used.&lt;/strong&gt; (This does not directly remove noise but rather increases signal, but that's just as good if not better. It may also remove noise by moving the device further from your computer equipment.) Of course, if your antenna is outdoors you will need a weatherproof enclosure, and you must make sure the USB line meets USB specs despite its increased length (such as by using an &lt;em&gt;active extension cable&lt;/em&gt; designed for the purpose).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Make sure you have the &lt;strong&gt;RF gain set correctly&lt;/strong&gt;!&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Too little gain will bury real signals in the noise floor; turn it up until you see the noise floor rising a bit so that &lt;a href=&quot;https://ham.stackexchange.com/a/905/76&quot;&gt;you're seeing the noise from the antenna&lt;/a&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Too much gain will overload and produce duplicated signals across the spectrum; turn it down until those extra spikes go away.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I have found that the built-in AGC may err in the direction of too much gain.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Build a &lt;strong&gt;shielded enclosure around the device&lt;/strong&gt;; they come in plastic cases with no RF shielding at all.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Add &lt;a href=&quot;http://en.wikipedia.org/wiki/Ferrite_bead&quot; rel=&quot;nofollow noreferrer&quot;&gt;snap-on ferrite beads&lt;/a&gt;&lt;/strong&gt; near the ends of cables, if they didn't come with built-in ferrites.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;An RTL-SDR-specific suggestion I have frequently heard is to modify a USB extension cable by removing the shield at the female-A end. (One could also modify the device's male-A plug but that might interfere with the mechanical connection.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The argument given is that the ground and shield are tied together on the PCB, and by disconnecting the USB cable shield from the ground you prevent noise carried on the outside of the shield from entering the RF section's ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have not yet tried this modification myself, and a few comments here suggest it is not worthwhile.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2013-12-31T15:11:12.950" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1176" PostTypeId="2" ParentId="1169" CreationDate="2013-12-30T21:37:55.877" Score="3" Body="&lt;p&gt;I reported the problem with Amsat.org and received a reply indicating the site is under re-construction but usable in part.  More than a year ago they were hacked and had to move to a new platform.  The old SQL database is not operational and so old links and some of the pages linked to from up-to-date pages may get the &quot;sql - InitDB line 14&quot; error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Old links are likely to have problems, but if you start at &lt;a href=&quot;http://www.amsat.org&quot; rel=&quot;nofollow&quot;&gt;www.amsat.org&lt;/a&gt; some of the functionality is available.  The pass prediction page linked from there actually looks like it mostly works despite showing the database error at the bottom.  Their &quot;Current Status&quot; submenu links off to another site, &lt;a href=&quot;http://oscar.dcarr.org&quot; rel=&quot;nofollow&quot;&gt;oscar.dcarr.org&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="258" LastEditorUserId="76" LastEditDate="2013-12-31T04:40:51.687" LastActivityDate="2013-12-31T04:40:51.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1177" PostTypeId="2" ParentId="1172" CreationDate="2013-12-31T12:20:27.370" Score="2" Body="&lt;p&gt;The &lt;a href=&quot;http://softrocksdr.wikispaces.com/Current+Soft+Rock+Kits&quot; rel=&quot;nofollow&quot;&gt;SoftRock SDR kits&lt;/a&gt; could qualify as &quot;simple&quot;, if you mean simple electronics. Some of them cost as little as $10 USD. They have fixed-frequency crystal oscillators, and you could probably swap the crystal for a nearby frequency in any of the kits as desired. The slightly more expensive and higher part count kits have a LO variable from DC to VHF and are usually limited by the input filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, the simplicity of the electronics is balanced by the complexity of the computer necessary to demodulate the received signal, and you'd have to become familiar with SDR operation, but maybe you don't mind.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2013-12-31T12:20:27.370" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1178" PostTypeId="1" AcceptedAnswerId="1186" CreationDate="2013-12-31T20:17:17.473" Score="6" ViewCount="1225" Body="&lt;p&gt;I've been studying the U.S. license examination question pools. For the most part, it is reasonably obvious what the questions and answers mean even when I am not yet able to come up with the answers on my own. However, the correct answer to this question in the Extra class pool is confusing me:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;E4E04 (D)&lt;br&gt;&#xA;  How can conducted and radiated noise caused by an automobile alternator be suppressed?  &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A. By installing filter capacitors in series with the DC power lead and by installing a blocking capacitor in the field lead&lt;br&gt;&#xA;  B. By installing a noise suppression resistor and a blocking capacitor in both leads&lt;br&gt;&#xA;  C. By installing a high-pass filter in series with the radio's power lead and a low-pass filter in parallel with the field lead&lt;br&gt;&#xA;  &lt;strong&gt;D. By connecting the radio's power leads directly to the battery and by installing coaxial capacitors in line with the alternator leads&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What is the purpose of specifying “coaxial” capacitors? Why does it say “in line”, which in the absence of further information I would interpret as “in series”? I would think that low-pass rather than high-pass filtering would be desirable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this just a sloppily phrased answer, or is there something subtle here?&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-01-02T03:40:46.247" Title="&quot;Coaxial capacitors in line” in E4E04?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;rfi&gt;&lt;filter&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1179" PostTypeId="2" ParentId="1174" CreationDate="2013-12-31T20:18:47.430" Score="3" Body="&lt;p&gt;I've just mounted mine in an eddy stone box. I put a BNC on the end and swapped the USB plug for a socket and made a hole in the box to fit the cable from a USB extension. Works a treat, rugged, mobile and no noise. 73&lt;/p&gt;&#xA;" OwnerDisplayName="user521" LastActivityDate="2013-12-31T20:18:47.430" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1180" PostTypeId="2" ParentId="1178" CreationDate="2013-12-31T20:25:06.827" Score="3" Body="&lt;p&gt;While writing the question I found a picture that clarifies the “in line” part on this web page I found in a search, &lt;a href=&quot;http://www.dieselduck.ca/machine/03%20electricity/radio_interference.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio Frequency Interference: A small vessel guide&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;To cure alternator noise, which is pulses radiate from the output lead, it is necessary to filter the output lead as close as possible to the alternator. The most effective filter is a 0.5 microfarad coaxial capacitor. A coaxial capacitor is one which passes current through its center with the capacitor completely surrounding the current carrying lead. As the alternator current flows through the capacitor, it should be rated to handle the alternator’s maximum output current. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;...&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/FcPxk.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, a coaxial capacitor in this context is in fact a three-terminal device of a sort, and this explains why it could be described as being “in line” with the alternator leads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This doesn't explain why a coaxial capacitor is specifically good for this application, though.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2013-12-31T20:34:48.767" LastActivityDate="2013-12-31T20:34:48.767" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1181" PostTypeId="2" ParentId="1178" CreationDate="2013-12-31T23:05:32.530" Score="2" Body="&lt;p&gt;Coaxial (also known as cylindrical) capacitors are usually electrolytic type capacitors and are sometimes know as feed-through capacitors when used in automotive applications like is illustrated in the exam question. Feed-through capacitors are designed to withstand very high currents as you'd see across an alternator.  The third lead is also to ground reducing the effective series inductance to nearly zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to the structure of the component, I imagine placing the leads on opposite sides of the capacitor simplifies construction and reduces the chance of the leads arcing over considering even a modest alternator these days produces 90+ amps. &lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2013-12-31T23:05:32.530" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1182" PostTypeId="2" ParentId="1120" CreationDate="2014-01-01T03:04:54.270" Score="0" Body="&lt;p&gt;I see two questions. The title asks about kits. A really useful option is one of those solderless breadboards. You just plug in ICs or discreet components, and the interconnects allow frapid prototyping. Here is one: &lt;a href=&quot;http://www.digikey.com/product-detail/en/922306/922306-ND/180285&quot; rel=&quot;nofollow&quot;&gt;http://www.digikey.com/product-detail/en/922306/922306-ND/180285&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Join the ARRL! Gotta do that. You get QST. Read a few back issues at the library and you will come up to speed quickly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bump 1 on joining a local ham club.&lt;/p&gt;&#xA;" OwnerUserId="528" LastActivityDate="2014-01-01T03:04:54.270" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1183" PostTypeId="1" CreationDate="2014-01-01T03:14:19.873" Score="3" ViewCount="5249" Body="&lt;p&gt;I'm planning on using 2 receivers that operate on the same frequency. So there's no confusion I'm talking about WiFi signals (but I'm trying to do some cool amateur radio stuff with it!) so the frequency is 2.4GHz. One of the main things I'm working on is building a nice big antenna (high gain) to be able to have a usable signal over more than 10s of meters. Now ideally, since these two receivers will have the same frequency, I could place both receivers at the focal point of the antenna and have the one dish with 2 receivers - but I'm worried that there will be a loss of signal since the antennas are blocking each other to some extent. Is this the case? I'm looking for an experienced person to give me there best guess really!&lt;/p&gt;&#xA;" OwnerUserId="529" LastEditorUserId="218" LastEditDate="2014-01-01T14:03:49.943" LastActivityDate="2014-04-02T16:49:11.800" Title="What effect will placing two receiving antennas next to one another be on the received signals" Tags="&lt;receiver&gt;&lt;wifi&gt;" AnswerCount="3" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="1185" PostTypeId="1" CreationDate="2014-01-01T12:24:51.413" Score="4" ViewCount="190" Body="&lt;p&gt;I understand high speed CW is used with meteor scatter, because the path only exists for a few seconds after the meteor passes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was wondering if automated high speed CW has an effective &quot;speed limit&quot;. I suppose bandwidth regulation would impose a theoretical limit for a noiseless channel and while that is relevant, I am looking for a more practical answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the record for the highest CW wpm rate that has been successfully achieved in amateur communications?&lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2014-01-29T17:29:06.150" Title="What is the record for highest successful (automated) CW transmission rate?" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1186" PostTypeId="2" ParentId="1178" CreationDate="2014-01-01T13:49:53.650" Score="4" Body="&lt;p&gt;What they mean by &quot;coaxial capacitor&quot; might be described by more people as a &lt;a href=&quot;https://www.google.com/search?q=feed-through%20capacitor&amp;amp;safe=off&quot; rel=&quot;nofollow noreferrer&quot;&gt;feed-through capacitor&lt;/a&gt;. For an example, see &lt;a href=&quot;http://www.mouser.com/ProductDetail/Tusonix/4300-002LF/?qs=MAKYsf4oimlBe9I7PrmywA==&amp;amp;gclid=CMPOhayK3bsCFYlAMgod9BUAPQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;Tusonix 4300-002LF at Mouser&lt;/a&gt;. The &lt;a href=&quot;http://tusonix.com/data/search/4300-001.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;datasheet&lt;/a&gt; contains these images, which are pretty informative:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/9TOuY.png&quot; alt=&quot;drawing of capacitor&quot;&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/LgNTH.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, the two leads are effectively a wire, ideally having zero impedance between them. However, this conductor also has some capacitance to the case, which is usually connected to ground. This particular part is designed to be dropped in a hole the size of the case, then soldered in place. Another design has a tab on the case for screw mounting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantage of this arrangement is that it's possible to use as a filter on some wire with high $\mathrm{d}v/\mathrm{d}t$ without creating a stub which could also act as an EMI radiator. It's also possible to preserve the continuity of a shield or enclosure, and get a really good connection to it. With an ordinary capacitor, the ground connection would go through a lead, which would have more inductance and resistance, reducing the filter effectiveness.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a similar looking, but different thing: &lt;em&gt;axial&lt;/em&gt;-leaded capacitors. These are frequently electrolytic. Example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NV3dZ.jpg&quot; alt=&quot;axial-leaded capacitor&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's nothing special about this capacitor. Sometimes this arrangement of leads just fits better.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-01-02T03:40:46.247" LastActivityDate="2014-01-02T03:40:46.247" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1188" PostTypeId="1" AcceptedAnswerId="1189" CreationDate="2014-01-02T19:42:46.557" Score="6" ViewCount="187" Body="&lt;p&gt;In &lt;a href=&quot;https://ham.stackexchange.com/a/1068/9&quot;&gt;https://ham.stackexchange.com/a/1068/9&lt;/a&gt; it's shown that one can use&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ r = \sqrt{I^2+Q^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;to decode AM signals from a direct conversion receiver.  It appears that, in this particular case, I and Q are interchangeable, thus the SDR doesn't care which is which.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this true, and for straight AM they can be switched without issue?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there other modes, such as SSB and CW, where switching I and Q wouldn't matter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I'm operating an SDR, what clues can I look for that would indicate a swapped I and Q?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2019-03-21T20:55:39.117" Title="What happens when I and Q are switched?" Tags="&lt;software-defined-radio&gt;&lt;direct-conversion&gt;&lt;am&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1189" PostTypeId="2" ParentId="1188" CreationDate="2014-01-02T20:09:22.693" Score="6" Body="&lt;p&gt;Swapping I and Q reverses all the frequencies. For example, a signal 5 kHz above the mixer's LO will appear at -5 kHz, instead of 5kHz. CW and AM are symmetrical in the frequency domain, so it doesn't matter for the purposes of demodulation, though your software is likely to display the wrong frequency. SSB is not: reversing I and Q will make USB look like LSB, and LSB look like USB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a waterfall with lower frequencies on the left, then tuning to a higher frequency should shift everything to the left. If it goes to the right instead, you know I and Q are reversed.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-01-02T20:09:22.693" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1190" PostTypeId="1" AcceptedAnswerId="1253" CreationDate="2014-01-02T21:41:35.660" Score="4" ViewCount="429" Body="&lt;p&gt;I'm thinking about dropping a bluetooth module into my Softrock receiver so I can use it with my computers and portable devices wirelessly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The receiver runs from 1.8MHz to 30MHz, and the bluetooth transceiver operates in the 2.4GHz band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will I need to add shielding or take any special measures to prevent the bluetooth device from causing noise problems with the receiver?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-01-15T17:18:09.410" Title="How to avoid Bluetooth intereference?" Tags="&lt;hf&gt;&lt;rfi&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1192" PostTypeId="2" ParentId="1183" CreationDate="2014-01-03T20:05:55.787" Score="0" Body="&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Main factor for transmission distance is so-called effective heights of antennas on both sides. Basically it is about how high antennas are located - the higher is the better.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Another important factor is lack of obstacles in line of sight - hills, trees, buildings, etc.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Length/size of antenna elements is important only to extent you keep original antenna design. No special need to make it bigger.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;At some height of antenna you will need protection from wind (well-engineered mechanical mount) and lightings (grounding within electric code rules) - both are safety protections and law-regulated across most of world.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If your antennas are directed, it is important you orient them on each other along direct visibility.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Your idea about two receivers is waste of time/effort/money - you can do even hundreds of meters without it, on basic equipment, if you keep rules above done. Area of radiocommunications (antennas, receivers, transmitters, etc) is well-studied during XX century due to high impact on military operations - it is unlikely that coolness of your idea makes something new.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can rather spend some time experimenting in making your own antenna from Pringle chips can, so called &lt;a href=&quot;https://en.wikipedia.org/wiki/Cantenna&quot; rel=&quot;nofollow&quot;&gt;Cantenna&lt;/a&gt; - it will be cheaper and have more impact. Reading books on topic in local library will give you even more boost.&lt;/p&gt;&#xA;" OwnerUserId="540" LastActivityDate="2014-01-03T20:05:55.787" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1193" PostTypeId="1" CreationDate="2014-01-04T22:04:45.170" Score="3" ViewCount="200" Body="&lt;p&gt;I willing to try really hard on working with Very Low Frequency waves to get a signal through the earth a few Km. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I go about putting a signal at the frequency (probably near 10 kilohertz) into the ground?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been searching for schematics everywhere, but just nothing shows up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know it is possible, I have seen some amateur radio really low frequency contacts through the earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know it is slow-speed CW, but that is still worth the joy of experimenting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I use ground rods instead of a HUGE antenna?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="285" LastEditDate="2014-01-08T13:55:22.903" LastActivityDate="2014-01-08T17:31:36.183" Title="How can I communicate with VLF ground waves" Tags="&lt;vlf&gt;" AnswerCount="1" CommentCount="3" ClosedDate="2014-01-22T15:29:49.257" ContentLicense="CC BY-SA 3.0" />
  <row Id="1194" PostTypeId="1" CreationDate="2014-01-04T22:13:13.307" Score="5" ViewCount="172" Body="&lt;p&gt;Someone told me that 10 meters was the biggest band because you can fit the most channels in it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;He said that in higher frequencies like 2 meter etc, you have to separate the signals more apart for them to work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this true? Can HF frequencies have more signals clustered together, or is he just getting confused because FM takes up more bandwidth?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8573" LastEditDate="2019-05-29T22:46:13.663" LastActivityDate="2019-05-29T22:46:13.663" Title="Do signals have to be more separated on higher frequencies?" Tags="&lt;bandwidth&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="1196" PostTypeId="1" AcceptedAnswerId="1204" CreationDate="2014-01-05T06:48:06.320" Score="19" ViewCount="8317" Body="&lt;p&gt;I see that many SDRs use a quadrature demodulator and sample I and Q signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But is it possible to downconvert the RF signal instead, sample it with only one ADC, and get the same capabilities of digital postprocessing?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if we want to observe 100-150 MHz bandwidth: we pass it through a 100-150 MHz bandpass filter, downconvert it to DC-50 MHz, and sample it with a 100 MHz ADC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will it work? And if it will - why is IQ so widely used?&lt;/p&gt;&#xA;" OwnerUserId="546" LastEditorUserId="76" LastEditDate="2014-01-05T17:50:39.533" LastActivityDate="2019-07-31T18:44:43.657" Title="SDR: Quadrature demodulation vs direct RF sampling" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;direct-conversion&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1199" PostTypeId="2" ParentId="1194" CreationDate="2014-01-05T17:11:44.923" Score="1" Body="&lt;p&gt;First of all, I'm going to assume you aren't including microwaves into things. Some of them can hold a truly enormous amount of data, something on the order of thousands of channels. For instance, the highest band is 241-250 GHz, which could hold about 10,000 FM radio quality (200 kHz) stations at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Comparing 2m to 10m, let's look at the band plans, and see what we can gleam. I'm getting this from &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow&quot;&gt;ARRL&lt;/a&gt;. One big thing to note is that 10M has some FM signals, but is primarily SSB, while 2m has some SSB, but is primarily FM:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;10 Meters (28-29.7 MHz)&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;28.000-28.070   CW&#xA;28.070-28.150   RTTY&#xA;28.150-28.190   CW&#xA;28.200-28.300   Beacons&#xA;28.300-29.300   Phone&#xA;28.680  SSTV&#xA;29.000-29.200   AM&#xA;29.300-29.510   Satellite Downlinks&#xA;29.520-29.590   Repeater Inputs&#xA;29.600  FM Simplex&#xA;29.610-29.700   Repeater Outputs&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;2 Meters (144-148 MHz)&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;144.00-144.05   EME (CW)&#xA;144.05-144.10   General CW and weak signals&#xA;144.10-144.20   EME and weak-signal SSB&#xA;144.200     National calling frequency&#xA;144.200-144.275     General SSB operation&#xA;144.275-144.300     Propagation beacons&#xA;144.30-144.50   New OSCAR subband&#xA;144.50-144.60   Linear translator inputs&#xA;144.60-144.90   FM repeater inputs&#xA;144.90-145.10   Weak signal and FM simplex (145.01,03,05,07,09 are widely used for packet)&#xA;145.10-145.20   Linear translator outputs&#xA;145.20-145.50   FM repeater outputs&#xA;145.50-145.80   Miscellaneous and experimental modes&#xA;145.80-146.00   OSCAR subband&#xA;146.01-146.37   Repeater inputs&#xA;146.40-146.58   Simplex&#xA;146.52  National Simplex Calling Frequency&#xA;146.61-146.97   Repeater outputs&#xA;147.00-147.39   Repeater outputs&#xA;147.42-147.57   Simplex&#xA;147.60-147.99   Repeater inputs&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Okay, for simplicity I'm going to just block these into total SSB and FM signals, and ignore anything else.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;10m- Total of 180 kHz FM, 1 MHz SSB.&lt;/li&gt;&#xA;&lt;li&gt;2 100 kHz SSB, 3.5 MHz FM (Or so)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And the channel bandwidths are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;SSB- 3 Hz (2.8 technically, but...)&lt;/li&gt;&#xA;&lt;li&gt;FM- 15 kHz.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Note that SSB takes up a lot less space than FM. Given that, here's the number of channels per band:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;10m- 334 SSB, 12 FM&lt;/li&gt;&#xA;&lt;li&gt;2m- 33 SSB, 200 FM&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Bottom line is, due to the efficiency of SSB over FM, more channels can be used on 2m than 10m at the same time.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-01-05T17:11:44.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1200" PostTypeId="2" ParentId="1194" CreationDate="2014-01-05T17:26:36.490" Score="2" Body="&lt;p&gt;In principle? No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, on the wider bands, &lt;em&gt;wider transmission modes&lt;/em&gt; are often used as well. 28 MHz, for example, is the only HF band that has allocations in the band plan for FM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Early on, a common trick for going higher in frequency was to employ a frequency multiplier. That works well with FM, but of course also widens the signal. So if you had 25 kHz FM on 144 MHz and frequency-multiplied it by three, you'd end up at 432 MHz but also with a 75 kHz bandwidth. The naïve approach doesn't work nearly as well with amplitude-modulated modes such as AM or SSB though because you'd change the actual modulation as well, so whoever was listening would have to have a receiver built to the same standard that you are using in transmission. (For example, a first intermediate frequency at 144 MHz, obtained by frequency division from the received frequency.) I can't cite sources, but I expect the relative ease of doing frequency multiplication is a major reason why many amateur bands are on harmonically related frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider the SSB portion of 2 meters during an active contest; there's more room to spread out and there are fewer stations within range of any one given station than on HF, but you can easily find stations as cramped together as on HF if it's an active contest, and it's no more or less difficult to work any particular one than under similar conditions on HF.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2014-01-05T17:26:36.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1201" PostTypeId="5" CreationDate="2014-01-05T17:29:48.597" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-05T17:29:48.597" LastActivityDate="2014-01-05T17:29:48.597" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1202" PostTypeId="4" CreationDate="2014-01-05T17:29:48.597" Score="0" Body="Very Low Frequency is the frequency range 3-30 kHz." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-05T17:29:48.597" LastActivityDate="2014-01-05T17:29:48.597" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1203" PostTypeId="2" ParentId="1120" CreationDate="2014-01-05T23:11:13.580" Score="1" Body="&lt;p&gt;I found that finding schematics of respected kits and knocking circuits together was a really good way to get started - I built a clone of a Ramsey 80m QRP receiver as my first &quot;hammy&quot; project and it was great fun.  Ramsey make a whole load of kits, most of which are reasonably simple and they're a good way to get in to low(ish) cost, low(ish) part count circuits.  Try &lt;a href=&quot;http://www.ramseyelectronics.com/b/6290131011&quot; rel=&quot;nofollow&quot;&gt;http://www.ramseyelectronics.com/b/6290131011&lt;/a&gt; for a selection of ham related kits.  Schematics and board layouts can be found if you want to go your own way rather than buy the kits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A page I find myself looking at repeatedly is &lt;a href=&quot;http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Homebrew_RF_Circuit_Design_Ideas.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Homebrew_RF_Circuit_Design_Ideas.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Breadboards are OK, but I personally prefer working on perforated copperless board, then drawing up prototype circuits in Eagle and etching the boards myself.  I'm just a RXer at the moment, I want to get to grips with as much theory as I can before getting a license. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to Google around, try &quot;QRP&quot; as a search term, along with &quot;homebrew&quot;.  You'll soon see terms which pop up again and again (HF, QRP, nicknames of the various bands, radio circuit types like TRF, reflex, superhet and so on).  Whatever route you take, have a great time - I've learned more about electonics from a year of hacking about than I did in the previous 30-odd years!&lt;/p&gt;&#xA;" OwnerUserId="551" LastActivityDate="2014-01-05T23:11:13.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1204" PostTypeId="2" ParentId="1196" CreationDate="2014-01-06T13:56:19.160" Score="13" Body="&lt;p&gt;Sure, it would work. In fact, if you've ever used something implementing some digital mode that interfaces with an SSB tranciever, this is exactly what is happening. Many TNCs and most PSK-31 software is an example of this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason I/Q is more frequently used is that it's simpler. If you want an SDR with 50 MHz bandwidth, you can do that with a single 100 MHz ADC as you describe, or two 50 MHz ADCs and I/Q sampling. Either way, it's 100 million samples per second, so the ADC complexity is essentially the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference is in the mixing. An ordinary mixer works by multiplying two signals. This creates two sidebands, the sum and the difference of the frequency components of the two mixer inputs. One of these sidebands must then be filtered out. Good filters are hard to realize, digital or analog.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you have the signal in I/Q form, the signal can be multiplied by a &lt;a href=&quot;http://en.wikipedia.org/wiki/Euler%27s_formula&quot;&gt;complex exponential&lt;/a&gt;. This doesn't create sidebands: it directly shifts all the frequencies up or down by some frequency. This is more directly what we usually want to accomplish with a mixer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are additional benefits: the &lt;a href=&quot;http://en.wikipedia.org/wiki/Discrete_Fourier_transform&quot;&gt;discrete Fourier transform&lt;/a&gt; (DFT), used in a great many DSP techniques, works on complex numbers. When we don't have I/Q data to provide it, then we must arbitrarily set Q to something (usually 0). As a result, half the result of the DFT (all the negative frequencies) are just a mirror of the positive frequencies, so they are discarded. This is computationally inefficient.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-01-06T13:56:19.160" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1205" PostTypeId="2" ParentId="1194" CreationDate="2014-01-06T14:09:31.747" Score="7" Body="&lt;p&gt;Someone was wrong. The 300 GHz band is the biggest, because it has no upper bound. You can fit an unlimited number of channels in it. See &lt;a href=&quot;https://ham.stackexchange.com/questions/947/which-band-will-i-be-authorized-the-most-bandwidth&quot;&gt;Which band will I be authorized the most bandwidth?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no theoretical requirement that signals be more &quot;spread out&quot; at higher frequencies. However, as VHF and up tend to be larger bands, the band plans tend to include wider modulations. FM is much wider (25 kHz) than SSB (4 kHz). Consequently, if the band is primarily FM (such as 2 meters), then signals must be spread further apart to avoid interfering with each other. Nothing to do with the frequency: just the modulation in use.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-01-06T14:09:31.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1206" PostTypeId="2" ParentId="1194" CreationDate="2014-01-06T14:34:20.387" Score="0" Body="&lt;p&gt;Consider you have 10 channels, each of BW=10kHz.&#xA;Now, if you are allocated 2-3MHz band (i.e., a bandwidth of 1Mhz) then you can have 100 (1MHz/10kHz) channels.&#xA;But, if you are allocated 200-300MHz band (i.e., a bandwidth of 100MHz) then you can have 10000 (100MHz/10kHz) channels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So obviously, the higher your frequency you have, the more channels you can fit in.&lt;/p&gt;&#xA;" OwnerUserId="552" LastEditorUserId="552" LastEditDate="2014-01-07T06:15:11.970" LastActivityDate="2014-01-07T06:15:11.970" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1208" PostTypeId="1" CreationDate="2014-01-06T15:12:42.287" Score="2" ViewCount="1634" Body="&lt;p&gt;Lets say I want to make a VLF loop antenna for a Sub AM radio band. I don't want a full wavelength because that would be a humongous antenna. Would I wind more turns of wire to decrease the frequency it can operate on, or is there any other way without a phisically enormous loop? &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2014-01-06T20:57:12.443" LastActivityDate="2014-01-06T23:02:28.957" Title="Does increasing the number of turns on a loop antenna decrease frequency operation?" Tags="&lt;antenna&gt;&lt;loop-antenna&gt;&lt;vlf&gt;&lt;short-antenna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1209" PostTypeId="2" ParentId="1208" CreationDate="2014-01-06T15:49:52.933" Score="6" Body="&lt;p&gt;There are plenty of ways to make antennas smaller. Unfortunately, all of these things also make the antenna less efficient. Economics provides a compelling proof: if efficient, small, low-frequency antennas could be realized, why do AM broadcast stations erect huge, expensive towers to support their enormous antennas?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/guxSR.jpg&quot; alt=&quot;AM broadcast antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna inefficiency isn't necessarily a problem for receiving, as long as the received power is enough to overcome your receiver's noise floor. See &lt;a href=&quot;https://ham.stackexchange.com/a/905/218&quot;&gt;What is the relationship between SWR and receive performance?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For transmitting, an inefficient antenna can still work, but it's much more difficult to come up extra transmitter power, and find a way to handle all that heat. A longer wire is usually cheaper than a 10kW amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To your specific case: the type of antenna you are describing is a &lt;em&gt;small&lt;/em&gt; loop antenna. These antennas are not resonant, by definition. When resonant operation is desired, a capacitor is added at the feedpoint to create an LC resonant circuit which greatly increases sensitivity at the resonant frequency, and greatly decreases bandwidth. Since the small loop is an inductor, adding more turns increases the inductance, and thus lowers the resonant frequency if the capacitor is not changed. Increasing the &lt;a href=&quot;http://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;permeability&lt;/a&gt; of the material inside the loop also increases the inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you think a lot of turns around some high permeability core is a good idea, you have conceived a &lt;a href=&quot;http://en.wikipedia.org/wiki/Loop_antenna#Small_loop_receiving_antennas&quot; rel=&quot;nofollow noreferrer&quot;&gt;loopstick antenna&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/wRcHw.jpg&quot; alt=&quot;loopstick antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, such an antenna will not work well for transmitting. The ferrite will saturate at very low transmit powers, and the ohmic losses of the many turns of wire at any reasonable transmit power will make it a better heater than an antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-01-06T15:49:52.933" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1210" PostTypeId="5" CreationDate="2014-01-06T20:58:24.480" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-06T20:58:24.480" LastActivityDate="2014-01-06T20:58:24.480" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1211" PostTypeId="4" CreationDate="2014-01-06T20:58:24.480" Score="0" Body="Use this tag for questions relating to the design, manufacture, theory and use of electrically short antennas. Electrically short antennas are commonly those that have a physical radiating element dimension of 1/10 of a wavelength or less." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-06T20:58:24.480" LastActivityDate="2014-01-06T20:58:24.480" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1212" PostTypeId="2" ParentId="1208" CreationDate="2014-01-06T23:02:28.957" Score="1" Body="&lt;p&gt;If you're going to be using this antenna strictly for reception, then increasing the windings is fine, but as the previous answer stated you're on increasing inductance, and when you increase inductance, you are by nature adding more radiation resistance. So, for transmitting that is not ideal at the wavelengths of VLF. These are small loops and can only radiate a small amount of the power from the transmitter. So increasing the windings will get you properly tuned for reception (i.e. the small magnetic loop in AM radios), but not very effective for transmitting.&lt;/p&gt;&#xA;" OwnerUserId="412" LastActivityDate="2014-01-06T23:02:28.957" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1213" PostTypeId="2" ParentId="135" CreationDate="2014-01-07T09:35:49.293" Score="9" Body="&lt;p&gt;Morse code requires an extremely small bandwidth (and is usable in a channel that has a relatively low S/N) for a mode that requires no digital processing hardware or computer/digital logic chips (instead requiring just the skill of a couple of human brains) to communicate.  Some people value accomplishing things using personally learned skills rather than software and DSPs/CPUs designed by others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A legal Morse code transmitter is about as simple as possible as that which can be constructed from basic analog components, although a CW receiver might require more parts than for AM (not sure about a pure regenerative receiver design).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Morse code is also a useful cross-over skill that could potentially be very useful to have in certain survival or medical situations, such as signaling by mirror when lost in the woods, eye blinking when partially paralyzed (or captured behind enemy lines), using one-button or blow/puff controllers by the severely disabled, etc.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-05-28T12:45:15.617" LastActivityDate="2019-05-28T12:45:15.617" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="1214" PostTypeId="2" ParentId="32" CreationDate="2014-01-07T09:48:04.513" Score="4" Body="&lt;p&gt;There are several PC and iOS/iPhone (etc.) apps that will play Morse code at controllable speeds (letters, random groups, common words, whole QSOs, etc.).  One can sometimes just keep increasing the speed at which these apps generate Morse Code as ones proficiency adapts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For apps that support Farnsworth timing, you can first increase the dot speed by a few WPM, and then later increase the word speed by smaller WPM increments.  Some apps allow one to use a custom limited character set, so you can start at a higher WPM with just a few letters, and the gradually add new characters as your accuracy catches up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes, just increasing a minimal number of things (maybe learning just a couple letters at a time at a new faster WPM, or just a couple whole words, or just trying a higher dot speed at a much slower character WPM) can help one get past a WPM hurdle, better than trying to copy everything faster all at once.  These things are easy to modify with many of the Morse code software applications.  Don't just try one same method (even if it has a name: Koch, Farnsworth).  Try varying different things in what you change and practice.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-09-16T19:54:26.233" LastActivityDate="2018-09-16T19:54:26.233" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="1215" PostTypeId="1" CreationDate="2014-01-07T10:03:42.573" Score="4" ViewCount="1899" Body="&lt;p&gt;What sidetone frequency range (or VFO/BFO receiver offset) will allow one to copy CW when trying to learn to copy QRQ? (high-speed Morse code, 40 WPM and higher)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like there will be very few audio waveform cycles in short QRQ dots when using a very low tone frequency at a very high WPM, so why might some CW operators say they prefer that?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-12-15T00:41:34.497" LastActivityDate="2019-03-09T15:06:08.727" Title="How low a sidetone frequency will allow QRQ CW to be copied?" Tags="&lt;cw&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="1216" PostTypeId="1" AcceptedAnswerId="1220" CreationDate="2014-01-07T10:10:56.883" Score="8" ViewCount="4150" Body="&lt;p&gt;Back when Morse code  proficiency was required for certain radio licenses, what audio frequency was used by the exam tapes, equipment or examiner that generated the Morse code audio?  Was there a legal or recommended testing standard for this audio tone frequency?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-01-07T22:25:06.890" Title="Audio frequency used for Morse code in licensing exams?" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1217" PostTypeId="2" ParentId="135" CreationDate="2014-01-07T15:22:39.327" Score="9" Body="&lt;p&gt;I am a new ham, and I decided to learn it, and use it, strictly for the purpose of efficiency. CW operation is low bandwidth, and therefore requires very little power to get a signal out over long distances. You will not get the same results from voice transmissions or other larger bandwidth data modes (although JT-65A and PSK31 are relatively efficient data modes). It's very gratifying to work around the world with ease in CW mode, whereas doing so in voice is doable, but a lot more difficult. The best advantage I can think of over other data modes is that you don't need to depend on a computer or external device to create Morse code messages. It's a human rendered data mode.&lt;/p&gt;&#xA;" OwnerUserId="412" LastActivityDate="2014-01-07T15:22:39.327" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1218" PostTypeId="2" ParentId="1132" CreationDate="2014-01-07T16:05:10.373" Score="2" Body="&lt;p&gt;One of my approaches to avoiding contests is operating on the opposite end of the band. During a big contest weekend it can be tough to avoid, when calling CQ, and someone comes back with ID and contest requirement, so the best thing to do is find the extremities of the band. Usually it's the upper end of the band, like for instance on 20 meters, I'll just call CQ in the 14.330 MHz to 14.350 MHz area. It's generally quiet there, and I have found that most call backs are other hams looking to rag chew. Like an earlier answer pointed out, just avoid the traffic by going around it.&lt;/p&gt;&#xA;" OwnerUserId="412" LastEditorUserId="412" LastEditDate="2014-01-08T20:18:42.780" LastActivityDate="2014-01-08T20:18:42.780" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1219" PostTypeId="2" ParentId="1193" CreationDate="2014-01-07T17:22:35.997" Score="3" Body="&lt;p&gt;The point of a huge antenna is efficiency. Ground rods alone will result in a very small signal being received, and high transmitter mismatch. VLF antennas are massive and require both very large grounding radials as well as antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Very_low_frequency#External_links&quot; rel=&quot;nofollow&quot;&gt;links from the VLF page at Wikipedia&lt;/a&gt;, especially the &lt;a href=&quot;http://www.lwca.org&quot; rel=&quot;nofollow&quot;&gt;Long Wave Radio Club of America&lt;/a&gt; and &lt;a href=&quot;http://www.virhistory.com/navy/xmtr-vlf.htm&quot; rel=&quot;nofollow&quot;&gt;K4NYW's page on vintage Navy radio gear&lt;/a&gt; has some schematics. If you can find a schematic for an &lt;a href=&quot;http://www.armyproperty.com/product/80058/AN-FRT-96/&quot; rel=&quot;nofollow&quot;&gt;AN/FRT-96&lt;/a&gt; which was &lt;a href=&quot;https://www.usajobs.gov/GetJob/PrintPreview/323811000&quot; rel=&quot;nofollow&quot;&gt;still in use by the USN as of two years ago&lt;/a&gt;, you'll be in business. Perhaps a search on LinkedIn for &lt;a href=&quot;https://duckduckgo.com/?q=site%3alinkedin.com%20AN/FRT-96&amp;amp;t=lm&quot; rel=&quot;nofollow&quot;&gt;folks who list that in their skill set&lt;/a&gt; might help.&lt;/p&gt;&#xA;" OwnerUserId="285" LastEditorUserId="285" LastEditDate="2014-01-08T17:31:36.183" LastActivityDate="2014-01-08T17:31:36.183" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1220" PostTypeId="2" ParentId="1216" CreationDate="2014-01-07T22:25:06.890" Score="3" Body="&lt;p&gt;Since you are in California, let's use FCC examinations. &lt;a href=&quot;http://www.qsl.net/wj5o/mcode.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.qsl.net/wj5o/mcode.htm&lt;/a&gt; said 600-800Hz and &lt;a href=&quot;http://en.wikipedia.org/wiki/Morse_code#Link_budget_issues&quot; rel=&quot;nofollow&quot;&gt;Wikipedia agreed&lt;/a&gt;. Also, a review of the FCC's &lt;a href=&quot;http://wireless.fcc.gov/commoperators/index.htm?job=examinations&quot; rel=&quot;nofollow&quot;&gt;First Class RT Licensing&lt;/a&gt; requirements did not state anything about pitch. &lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2014-01-07T22:25:06.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1221" PostTypeId="1" CreationDate="2014-01-08T16:16:41.460" Score="4" ViewCount="200" Body="&lt;p&gt;I'm trying to understand how radio works, and the concepts of AM/FM modulation are relatively clear to me. My next hurdle, however, is the following: How does differentiating between signals with different frequencies work? I can't picture the different channels/frequency bands in the time domain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How should I look at this?&lt;/p&gt;&#xA;" OwnerUserId="562" LastActivityDate="2014-01-08T19:16:14.173" Title="What does channel spacing look like in the time domain?" Tags="&lt;bandwidth&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1222" PostTypeId="2" ParentId="1215" CreationDate="2014-01-08T16:55:37.547" Score="2" Body="&lt;p&gt;For folks who may be unaware, &lt;a href=&quot;http://en.wikipedia.org/wiki/Sidetone#Radiotelegraphy&quot; rel=&quot;nofollow&quot;&gt;sidetone&lt;/a&gt; is generated locally and except in the case of modulated CW, it has no effect on the on-the-air-signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This question is hard to answer definitively, in fact, it's impossible.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The research I did had answers all over the map from 400 Hz to 800 Hz with waveforms from sawtooth (short rise/fall times) to a more sinusoidal form depending on the taste and/or experience of the operator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two basic camps, one that doesn't change the ~700-800 Hz frequency, ever.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other camp changes frequency for a variety of reasons. Commonly these operators lower the pitch for weak signal work or Top Band work claiming it's easier to pull out a signal at lower pitches.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other folks doing conversational QRQ change the tone, say 50Hz or so, from time to time just to keep fresh while copying.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-01-08T16:55:37.547" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1223" PostTypeId="2" ParentId="1221" CreationDate="2014-01-08T17:38:34.050" Score="2" Body="&lt;p&gt;Just picture (or graph) the sum of 2 sinewaves of very different frequencies.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In &quot;real-life&quot; RF, the bandwidth including modulation is so small, in relation to the carrier frequency, that a single modulated signal would look just like a plain sinewave when graphed.  If the bandwidth of different channels don't overlap in the frequency domain, then, given enough time (or length of captured signal), a filter (analog or digital) can unmix several channels much more closely spaced in frequency (than in your graph) within a summed signal, even if your eye can't on a graph of a shorter segment.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-01-08T17:38:34.050" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1224" PostTypeId="2" ParentId="1221" CreationDate="2014-01-08T19:16:14.173" Score="5" Body="&lt;p&gt;Easy enough to &lt;a href=&quot;http://www.wolframalpha.com/input/?i=graph%20sin%20t,%20sin%20%2815t%29,%20sin%20t%20%2b%20sin%20%2815t%29%20from%200%20to%2010&quot; rel=&quot;nofollow noreferrer&quot;&gt;graph at wolframalpha.com&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/MEUx5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This shows two signals: one at some frequency (blue), and another at 15 times that frequency (magenta). The brown line is the two added together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you took this brown signal and put it through a low-pass filter, you could recover the blue signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you put it through a high-pass filter, you could recover the magenta signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, if you had many signals in here, separated by less than a factor of 15, it would be quite difficult to separate them by looking at the time domain signal. But this is why we don't think of this problem in the time domain: it's hard. Separating the signals in the frequency domain is easy.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-01-08T19:16:14.173" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1225" PostTypeId="1" AcceptedAnswerId="1226" CreationDate="2014-01-08T20:26:43.210" Score="9" ViewCount="950" Body="&lt;p&gt;Per &lt;a href=&quot;http://www.swpc.noaa.gov/&quot;&gt;NOAA/NWS Space Weather Prediction Center&lt;/a&gt;, &quot;SWPC Forecasters are anticipating G3 (Strong) Geomagnetic Storm conditions to occur January 9 and 10.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does that mean, very generally, for amateur radio communications?  Does it depend on the type of geomagnetic storm and how it hits us exactly, or are there general effects we can predict?  Does it increase or decrease propagation in all or some bands?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-01-09T12:54:41.897" Title="What are the general effects of a geomagnetic storm on propagation?" Tags="&lt;propagation&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1226" PostTypeId="2" ParentId="1225" CreationDate="2014-01-09T01:10:13.800" Score="5" Body="&lt;p&gt;Geomagnetic storms are the result of solar events that subsequently impact earth's ionosphere.  They are graded from G1 (the mildest) to G5 (most severe) and the grade can be derived from the &lt;a href=&quot;http://en.wikipedia.org/wiki/K-index&quot; rel=&quot;nofollow&quot;&gt;K-index&lt;/a&gt; (one of the many solar related values published &lt;a href=&quot;http://www.swpc.noaa.gov/index.html&quot; rel=&quot;nofollow&quot;&gt;NOAA&lt;/a&gt;).  A Kp index value of 5 equates to a G1 and a value of 9 equates to a G5.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The predicted G3 storm for tomorrow is classified as a &lt;em&gt;Strong&lt;/em&gt; storm by NOAA's standards and is the result of a  Coronal Mass Ejection (CME).  CMEs are large clouds of plasma (ionized gases) that have been ejected from the surface of the sun. They are directional, and occur with some regularity, but are only a problem if the mass of particles heads our way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When they do head our way and impact the ionosphere, they cause a number of changes.  Due to increased ionization of the lower levels of the ionosphere, signals between 2MHz and 30MHz will experienced increased absorption; if the storm is bad enough, that's 100% absorption.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Areas in the auroral zones are hardest it.  During these storms they can experience rapid&#xA;and deep signal fading due to the ionospheric irregularities that scatter the radio signal to the point that communication is impossible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On frequencies above 30MHz, unexpected reflections of the radio waves by the ionosphere may cause radio interference. Ionospheric irregularities may produce fluctuating signals (a phenomenon known as &lt;a href=&quot;http://en.wikipedia.org/wiki/Interplanetary_scintillation&quot; rel=&quot;nofollow&quot;&gt;scintillation&lt;/a&gt;) and may distort the paths of radio waves. If strong enough, this can adversely impact phase-sensitive systems on frequencies above 1 GHz (e.g., the Global Positioning System; talk about potential mayhem). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other effects include Auroral absorption, multipathing, and non-great-circle propagation.  One possible happy effect (for those living in the mid and upper latitudes) is that the auroral zone moves equatorward giving folks who are not normally able to experience the aurora a chance to see them.  And since propagation will be garbage, you may as well go outside and look.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other effects that could be important: some minor impact on the power grid by inducing some voltage fluctuations. Spacecraft may observe some surface charging on satellite components, drag may increase on low-Earth-orbit satellites, and corrections may be needed for orientation problems.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="29" LastEditDate="2014-01-09T12:54:41.897" LastActivityDate="2014-01-09T12:54:41.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1227" PostTypeId="1" CreationDate="2014-01-09T16:22:43.003" Score="9" ViewCount="1063" Body="&lt;p&gt;If I want to minimize &quot;RF in the shack&quot; and lightning hazard, what some good ways to ground a transmitter and indoor antenna in a top floor room or attic with no exterior access?  (say a multi-story wood-framed building with large non-opening glass windows)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2015-12-15T23:57:01.380" LastActivityDate="2018-12-20T22:10:31.763" Title="What are some ways to ground a transmitter+antenna in an enclosed attic?" Tags="&lt;grounding&gt;&lt;antenna-system&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1228" PostTypeId="1" AcceptedAnswerId="1236" CreationDate="2014-01-09T16:28:19.137" Score="3" ViewCount="1316" Body="&lt;p&gt;Asking this for a web challenged friend:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He lives in an HOA restricted townhouse, so no external antennas.  He only does VHF FM, so it's not a big deal.  To participate in the local nets he uses his Kenwood TM-V71A in his car to crossband repeat from a HT in his house.  All works as it should if the HT is set to low power (1W).  If he runs it at 5W, the audio out of the Kenwood is clear, but low.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;He thinks this is the HT's doing, but I am not so sure. Could this be the Kenwood clamping the signal somehow?  He's inside a house, true, but it's a crappy plastic house :) and he's no more than 50' away from the car/radio at any given time.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-01-09T16:33:58.203" LastActivityDate="2015-07-02T14:51:47.423" Title="Low Audio out from Kenwood TM-V71A on cross band repeat" Tags="&lt;ht&gt;&lt;kenwood&gt;&lt;crossband-repeat&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1229" PostTypeId="5" CreationDate="2014-01-09T17:06:54.597" Score="0" Body="&lt;p&gt;The typical crossband repeater (CBR) scenario involves a dual-band mobile rig capable of being configured as a simplex cross-band repeater and one or more HTs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CBR can be a useful tool during emergency activation or public service events where net operations are being conducted on a 2 meter simplex frequency. The CBR effectively translates back and forth between a 2m simplex channel and a 70cm simplex channel. Thus, a low-power 70cm HT can work through a mobile CBR station to communicate with a 2m simplex net, taking full advantage of the mobile rig's hi-power capabilities. Any dual-band or dedicated 70cm HT can be used to operate through a CBR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some other situations where CBR operation may be useful:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;A net operator needs to be on foot away from the mobile rig. With the&#xA;mobile rig configured as a CBR, the operator can communicate with the&#xA;2m simplex net using a low-power 70cm HT.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A parked mobile station configured as a CBR and located on high&#xA;ground can be used to provide a 70cm simplex link into low-lying&#xA;areas with poor simplex coverage.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Using a low-power 70cm HT, an operator located deep within a building&#xA;can operate through a mobile CBR in the parking lot to communicate&#xA;with the 2m simplex net.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-01-10T18:56:40.367" LastActivityDate="2014-01-10T18:56:40.367" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1230" PostTypeId="4" CreationDate="2014-01-09T17:06:54.597" Score="0" Body="Crossband repeating is a relatively inexpensive means for extending the range of handheld radios. " OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-01-10T18:56:44.790" LastActivityDate="2014-01-10T18:56:44.790" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1231" PostTypeId="2" ParentId="1227" CreationDate="2014-01-09T17:09:39.810" Score="7" Body="&lt;p&gt;Your solution to &quot;RF in the shack&quot; should be proper antenna design first, and grounding second. See &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt; (or any other antenna, really). If you take care to address common-mode currents, you won't need a ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding lightning protection, you might just forget about it. If lightning has struck your indoor antenna, it's already struck your house. You have bigger problems. You can try to provide a path for that energy to ground, but keep in mind: it's a lot of energy, so you need a big conductor. You don't have exterior access, so that means going through the floor. If you don't mind a couple pieces of 6&quot; copper strap running straight through the living room you might accomplish something worthwhile. Otherwise, I'd suggest insurance.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-01-09T17:09:39.810" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1232" PostTypeId="1" AcceptedAnswerId="1233" CreationDate="2014-01-10T19:50:28.503" Score="5" ViewCount="3318" Body="&lt;p&gt;Having built my first HF receiver, I'd like to know if I'll need to search around for transmissions that happen to be occurring, or if there are reasonably strong signals I can count on being present regardless of the time or day? I just want a simple test that will tell me it's working or not without having to set up a sked with someone else, or having a transmitter handy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My receiver is capable of receiving from 1.8MHz to 30MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hopefully there are several signals of interest in this range that are common in the US.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2015-03-20T16:27:26.067" Title="Are there any good, consistently receivable signals in the US for HF receiver testing?" Tags="&lt;united-states&gt;&lt;receiver&gt;&lt;testing&gt;&lt;calibration&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1233" PostTypeId="2" ParentId="1232" CreationDate="2014-01-10T19:56:29.087" Score="7" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/WWV_(radio_station)&quot;&gt;WWV&lt;/a&gt; and &lt;a href=&quot;http://en.wikipedia.org/wiki/WWVH&quot;&gt;WWVH&lt;/a&gt; broadcast time and frequency reference information continuously, using AM on 2.5, 5, 10, 15 and 20 MHz, so you should be able to pick up all of them using your receiver, given an adequate antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At my location (San Francisco Bay Area) with lousy equipment, these signals are only slightly stronger than shortwave broadcast stations, but more reliably present.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-01-10T19:56:29.087" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1234" PostTypeId="1" AcceptedAnswerId="1239" CreationDate="2014-01-10T20:01:35.577" Score="8" ViewCount="449" Body="&lt;p&gt;What are my requirements as a licensed Amateur Radio operator in the US to keep to a single frequency?  How much drift can I have during transmission and still be within my license? Does it depend on the mode or band?  Note that I'm not asking about the band plan, simply the FCC rules.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm asking in relation to making transmitters.  I'm sure a crystal (20ppm) is more than sufficient, but should I decide to make a simpler oscillator, how much error is permissable?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to add how much error is preferable for a given activity (DX, contests, rag chewing, etc) then that's fine, but please note that I'm primarily interested in what my license permits, rather than what other operators might prefer (at this time, anyway).&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-01-11T19:09:15.767" Title="What is the permissible frequency error for US amateur radio transmissions?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;frequency&gt;&lt;transmission&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1235" PostTypeId="1" AcceptedAnswerId="1240" CreationDate="2014-01-10T20:08:44.323" Score="2" ViewCount="1793" Body="&lt;p&gt;I'd like to perform some simple receiver testing and calibration (mostly for frequency variance, not signal strength) and &lt;a href=&quot;https://ham.stackexchange.com/questions/1232&quot;&gt;have been told WWV/WWVH transmissions can be found throughout most of the US&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be a good, cheap, small antenna for receiving one or more of these transmissions at 2.5MHz, 5MHz, 10MHz, 15MHz, and 20MHz? I note that it's common for &quot;atomic&quot; clocks to have such an antenna internal, and if I find one lying about I'll use it, but I don't keep such clocks, nevermind random ferrite rods, lying about.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-01-10T23:26:32.430" Title="Simplest, smallest antenna for tuning WWV, WWVH?" Tags="&lt;receiver&gt;&lt;testing&gt;&lt;calibration&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1236" PostTypeId="2" ParentId="1228" CreationDate="2014-01-10T20:22:18.627" Score="1" Body="&lt;p&gt;The transmitted audio on the TM-V71A appears to come out of the box setup for particularly sensitive microphones.  It can be adjusted, but only using programming software, it's not available via front panel menus:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;From the open prgoram&lt;/p&gt;&#xA;&lt;p&gt;EDIT....Menu.....Select Transmit/Receive&lt;/p&gt;&#xA;&lt;p&gt;In the &lt;em&gt;Transmit/Receive&lt;/em&gt; dialogue box, change the microphone sensitivity to the desired setting. (High/Medium/Low).&lt;/p&gt;&#xA;&lt;p&gt;CLOSE the dialogue box and WRITE back to the Xcvr.&lt;/p&gt;&#xA;&lt;p&gt;My radio arrived with the setting at the medium level. Some stations said that my audio levels were &amp;quot;clean but low&amp;quot;. I hung the rig across a scope and the deviation read +3.8khz and -4.0khz (in the Medium senstivity setting and extreme close talking of the mic). Once the setting was changed to high, the deviation swing was in excess of 4khz both ways and &amp;quot;louder&amp;quot;. Since then the reports have been normal. &amp;quot;Sounds fine&amp;quot;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;(&lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?topic=54765.0;wap2&quot; rel=&quot;nofollow noreferrer&quot;&gt;source&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;While this is primarily intended to deal with microphone sensitivity differences, during crossband repeat the audio is fully demodulated, then passed through the same amplifiers prior to modulation as the microphone audio goes through.&lt;/p&gt;&#xA;&lt;p&gt;This should resolve your low audio issues, but if it doesn't you'll probably have to look at the FM deviation to find out whether it's the HT, the mobile, or an issue with the crossband repeat function.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-01-10T20:22:18.627" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1237" PostTypeId="2" ParentId="1235" CreationDate="2014-01-10T21:10:40.333" Score="1" Body="&lt;p&gt;An end-fed &lt;a href=&quot;http://www.aa5tb.com/efha.html&quot; rel=&quot;nofollow&quot;&gt;http://www.aa5tb.com/efha.html&lt;/a&gt; tuned for 2.5MHz will also serve well at the higher frequencies you seek.&lt;/p&gt;&#xA;" OwnerUserId="285" LastActivityDate="2014-01-10T21:10:40.333" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1238" PostTypeId="2" ParentId="1234" CreationDate="2014-01-10T21:29:04.323" Score="9" Body="&lt;p&gt;Part 97 doesn't have anything to say about frequency error or drift in particular. The question pool, however, does:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;http://ncvec.org/downloads/2014-2018%20Tech%20Pool.txt&quot; rel=&quot;noreferrer&quot;&gt;T1B09 (D) [97.101(a), 97.301(a-e)]&lt;/a&gt;&lt;br&gt;&#xA;  Why should you not set your transmit frequency to be exactly at the edge of an amateur band or sub-band?&lt;br&gt;&#xA;  A. To allow for calibration error in the transmitter frequency display&lt;br&gt;&#xA;  B. So that modulation sidebands do not extend beyond the band edge&lt;br&gt;&#xA;  C. To allow for transmitter frequency drift&lt;br&gt;&#xA;  &lt;strong&gt;D. All of these choices are correct&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Of the sections of Part 97 cited, &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.4.159.1&quot; rel=&quot;noreferrer&quot;&gt;§97.301(a-e)&lt;/a&gt; merely defines the permitted bands, but &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.2.159.1&quot; rel=&quot;noreferrer&quot;&gt;§97.101(a)&lt;/a&gt; is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In all respects not specifically covered by FCC Rules each amateur station must be operated in accordance with good engineering and good amateur practice.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Thus it would seem that in the opinion of the authors of the question pool, “good amateur practice” includes taking precautions to avoid inadvertently transmitting out of band. Having a well-calibrated and low-drift transmitter would merely be another such precaution.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-01-11T19:09:15.767" LastActivityDate="2014-01-11T19:09:15.767" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1239" PostTypeId="2" ParentId="1234" CreationDate="2014-01-10T21:39:01.363" Score="9" Body="&lt;p&gt;Your frequency error is the difference between where your transmitter indicates you are transmitting, and where you actually are transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC does not regulate where you think you are transmitting. They only regulate where you are &lt;em&gt;actually transmitting&lt;/em&gt;. Consequently, your frequency error can be whatever you want, as long as you keep it in the bands permitted by your license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are concerned about drift during a transmission, I wouldn't. Anything you build today is almost certainly more stable than tube equipment that was built decades ago. Your problem with drift will be that the other station can't follow you before it is violation of any regulation.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-01-10T21:39:01.363" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1240" PostTypeId="2" ParentId="1235" CreationDate="2014-01-10T23:26:32.430" Score="3" Body="&lt;p&gt;Depends on your receiver sensitivity and antenna location. I've seen some many-decades-old portable shortwave radios pick up at least one WWV frequency using their simple built-in half-meter to meter long metal whip antenna.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-01-10T23:26:32.430" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1241" PostTypeId="2" ParentId="1234" CreationDate="2014-01-11T18:48:49.820" Score="2" Body="&lt;p&gt;To add to Phil's answer the only time inaccuracies in frequency are of concern to the FCC are when you're at the edge of the band.  As Kevin's answer alludes to, as long as you aren't transmitting out of band, the only person who is concerned about what frequency you're transmitting on is you, and possibly someone you planned to meet on the air.&lt;/p&gt;&#xA;" OwnerUserId="308" LastActivityDate="2014-01-11T18:48:49.820" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1242" PostTypeId="1" AcceptedAnswerId="1244" CreationDate="2014-01-11T21:15:45.467" Score="2" ViewCount="239" Body="&lt;p&gt;What are the current privileges below 30 MHz for holders in the United States of a Technician class license?&lt;/p&gt;&#xA;" OwnerUserId="406" LastEditorUserId="29" LastEditDate="2014-01-14T12:38:33.993" LastActivityDate="2015-10-07T16:31:06.060" Title="Technician Class HF Privileges in the USA" Tags="&lt;united-states&gt;&lt;hf&gt;&lt;legal&gt;&lt;license&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1243" PostTypeId="1" AcceptedAnswerId="1246" CreationDate="2014-01-11T22:21:34.787" Score="9" ViewCount="770" Body="&lt;p&gt;If there are two antennas of 50 Ω and 377 Ω (same as the intrinsic impedance of air) impedance with 0 $\Omega$ ohmic resistance, and they are exactly matched with their transmission line, then which antenna is more effective in terms of radiating R.F. power into space? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is, if both antennas have VSWR = 1:1, then which one is more efficient? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: that the term 'efficiency' in above, does not mean the definition of antenna-efficiency. I know that antenna-efficiency is 100%, since there are ZERO ohmic loss and $\infty$ return-loss. So, from &quot;efficient&quot;, I mean the effectiveness of the antenna in radiating energy in space.&lt;/p&gt;&#xA;" OwnerUserId="574" LastEditorUserId="76" LastEditDate="2015-12-15T22:17:58.890" LastActivityDate="2015-12-15T22:17:58.890" Title="If two antennas of 50 Ω and 377 Ω have VSWR=1:1, then which one is more efficient?" Tags="&lt;antenna&gt;&lt;impedance&gt;&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1244" PostTypeId="2" ParentId="1242" CreationDate="2014-01-11T22:51:09.643" Score="3" Body="&lt;p&gt;There's some CW on 80, 40, and 15 meters, and some RTTY and SSB on 10. Limited to 200W in all cases. Here's a &lt;a href=&quot;http://www.arrl.org/files/file/Regulatory/Band%20Chart/Hambands_color.pdf&quot; rel=&quot;nofollow&quot;&gt;chart&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2014-01-11T22:51:09.643" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1245" PostTypeId="2" ParentId="1243" CreationDate="2014-01-12T13:59:00.723" Score="5" Body="&lt;p&gt;The antenna efficiency refers the ratio of radiated power and the power fed to the antenna. The rest of the fed power is transformed to heat by the losses in the antenna. Thus, the antenna efficiency is not directly linked to the radiation resistance alone, but also to the (resistive or dielectric) losses in the antenna. Higher radiation resistance does not necessarily mean higher efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can improve the radiation efficiency of your antenna by choosing more conductive materials (copper or copper coated steel over aluminum) and thicker wires (thick wire has more &quot;surface area&quot; decreasing the loss resistance). These changes improve your antenna efficiency while having only minor effect on the antenna impedance, as seen by your radio. However, the increasing resistance does not seem to reduce the performance of typical HAM antennas too dramatically: &lt;a href=&quot;http://personal.ee.surrey.ac.uk/Personal/D.Jefferies/antennexarticles/newantennexarticles/efficiency.pdf&quot; rel=&quot;noreferrer&quot;&gt;http://personal.ee.surrey.ac.uk/Personal/D.Jefferies/antennexarticles/newantennexarticles/efficiency.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can the behavior of an antenna with circuit model. The simplest circuit model for a resonant dipole would be a series RLC circuit. The circuit model transforms all impedances as they are seen in the feedpoint of the antenna. With the circuit model of the figure, the radiation efficiency becomes: $\eta = \frac{R_{rad}}{R_{rad}+R_{loss}}$, where $R_{rad}$ is the radiation resistance (power radiated to the far field) and $R_{loss}$ is loss resistance (power transformed to heat). $C$ and $L$ represent the reactive fields near the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/12hh0.png&quot; alt=&quot;Circuit model of $\lambda/2$ dipole near resonance.&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="194" LastEditDate="2014-01-12T18:40:01.753" LastActivityDate="2014-01-12T18:40:01.753" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1246" PostTypeId="2" ParentId="1243" CreationDate="2014-01-12T15:10:46.167" Score="14" Body="&lt;p&gt;With the information you've provided, there is no way to tell. Feedpoint impedance and VSWR have no relationship to antenna efficiency. See &lt;a href=&quot;https://ham.stackexchange.com/a/905/218&quot;&gt;What is the relationship between SWR and receive performance?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feedpoint impedance also has no relationship to antenna efficiency. A &quot;50Ω antenna&quot; means the impedance &lt;em&gt;at the feedpoint&lt;/em&gt; is 50Ω. The impedance at other points is probably something very different. In a dipole, for example, the impedance is about 72Ω at the feedpoint, and very much higher at the ends. This is why current is at a maximum at the feedpoint (low impedance), and at a minimum at the ends (high impedance).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Is there an advantage to an antenna with a feedpoint impedance equal to the impedance of free space?&lt;/em&gt; No. An antenna of any design transforms between the impedance of free space to its feedpoint impedance. An antenna can be designed to work at any feedpoint impedance. The losses come from things like resistance in the antenna wire and coils, and dielectric losses in tuning capacitors. To the extent that you don't have these things, an antenna can be efficient. A dipole, vertical, loop, or any other kind of antenna constructed from ideal materials is already 100% efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can easily be seen by considering the law of conservation of energy. If your antenna isn't getting hot, yet you are putting 100W of power into it, only two things can happen to that energy. It can be be:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;stored in reactance of the antenna&lt;/li&gt;&#xA;&lt;li&gt;radiated away&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;If the antenna has a purely resistive impedance, then there is no reactance to be storing energy, so it must be radiating away. The feedpoint impedance is irrelevant.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-01-14T21:06:52.510" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1247" PostTypeId="2" ParentId="1232" CreationDate="2014-01-13T18:27:31.657" Score="2" Body="&lt;p&gt;Another great way to listen for signals, especially stronger ones, other than WWV and WWVH, is to find some active AM broadcast stations within the 1.8 to 30MHz range. Head over to this site &lt;a href=&quot;http://www.short-wave.info/&quot; rel=&quot;nofollow&quot;&gt;http://www.short-wave.info/&lt;/a&gt;, and use the top most form, selecting any station, and preferred language, make sure NOW is checked, and hit GO! YOu can pretty much tune around to the listed frequencies, primarily those listed in red.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Canada has a time signal station as well that is fairly strong (as I can pick it up from California) &lt;a href=&quot;http://en.wikipedia.org/wiki/CHU_(radio_station)&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/CHU_(radio_station)&lt;/a&gt;, and pretty much is Canada's version of WWV and WWVH. It's frequencies are 3.330 MHz, 7.850 MHz, and 14.670 MHz&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're outside of North America check this page out for other time stations around the world &lt;a href=&quot;http://www.dxinfocentre.com/time.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.dxinfocentre.com/time.htm&lt;/a&gt;. It would also be cool to check these frequencies out too, just for fun, to see if you can hear around the world.&lt;/p&gt;&#xA;" OwnerUserId="412" LastActivityDate="2014-01-13T18:27:31.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1248" PostTypeId="2" ParentId="1242" CreationDate="2014-01-13T18:30:07.400" Score="0" Body="&lt;p&gt;I refer you to the ARRL's bands PDF. &lt;a href=&quot;http://www.arrl.org/files/file/Regulatory/Band%20Chart/Hambands_color.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/files/file/Regulatory/Band%20Chart/Hambands_color.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anything marked with a 'T' is Technician.&lt;/p&gt;&#xA;" OwnerUserId="412" LastEditorUserId="412" LastEditDate="2014-01-14T20:54:21.147" LastActivityDate="2014-01-14T20:54:21.147" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1249" PostTypeId="1" AcceptedAnswerId="1252" CreationDate="2014-01-15T05:05:12.080" Score="11" ViewCount="955" Body="&lt;p&gt;I want to use my Android mobile phone to send and receive over Echolink, like if I was using an amateur radio station. How can I do that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm a SWL and only plan to listen until I get my license, and my brother does have a valid amateur radio license.&lt;/p&gt;&#xA;" OwnerUserId="576" LastEditorUserId="29" LastEditDate="2014-01-15T09:30:43.837" LastActivityDate="2014-01-15T13:13:31.533" Title="How can I participate on Echolink with my Android phone?" Tags="&lt;echolink&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="1250" PostTypeId="2" ParentId="135" CreationDate="2014-01-15T12:11:41.127" Score="5" Body="&lt;p&gt;Morse code is a raw and ancient way to deliver a signal to its destination. Even in case of non-digitised communication, Morse code is a way to express signal. The science of this is known to all telecommunication personnel, and thus is still used in many cases. It is also easier to create than a digital code.&lt;/p&gt;&#xA;" OwnerUserId="589" LastEditorUserId="29" LastEditDate="2014-01-15T12:29:46.883" LastActivityDate="2014-01-15T12:29:46.883" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1251" PostTypeId="2" ParentId="135" CreationDate="2014-01-15T12:50:49.507" Score="9" Body="&lt;p&gt;I got my technician license in 1992 to play with packet and TCP/IP on VHF/UHF. I got bitten by the HF bug listening to the CW subbands. I decided to learn CW on my laptop on business trips. I struggled to pass 5 WPM for my Tech-plus but I did and I got on 80m CW. A few months later I had WAS and It wasn't long after that I passed 20 WPM for my Extra.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why do I operate CW? It is a blast!&lt;/p&gt;&#xA;" OwnerUserId="359" LastEditorUserId="218" LastEditDate="2014-01-16T15:01:13.820" LastActivityDate="2014-01-16T15:01:13.820" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1252" PostTypeId="2" ParentId="1249" CreationDate="2014-01-15T13:13:31.533" Score="10" Body="&lt;p&gt;There is at least one app on the Google app store which will connect to echolink, which can be found here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://play.google.com/store/apps/details?id=org.echolink.android&quot;&gt;https://play.google.com/store/apps/details?id=org.echolink.android&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are other apps that may also connect to Echolink, or are otherwise useful for Echolink users:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://play.google.com/store/search?q=echolink&amp;amp;c=apps&quot;&gt;https://play.google.com/store/search?q=echolink&amp;amp;c=apps&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-01-15T13:13:31.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1253" PostTypeId="2" ParentId="1190" CreationDate="2014-01-15T17:18:09.410" Score="1" Body="&lt;p&gt;I don't think you need to worry too much about the bluetooth causing direct electromagnetic interference to a receiver operating in the HF bands. There are probably a lot more things to be concerned with, like harmonic interference from the bluetooth device, or electronic adapters, consumer products, and such, but I have never heard or experienced either (&lt;a href=&quot;http://www.popularmechanics.com/technology/how-to/tips/how-to-fight-rf-interference-with-your-gadgets&quot; rel=&quot;nofollow&quot;&gt;http://www.popularmechanics.com/technology/how-to/tips/how-to-fight-rf-interference-with-your-gadgets&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have the technical chops, this guy (&lt;a href=&quot;http://kd0ar.blogspot.com/2010/04/cell-phone-interference-on-softrock.html&quot; rel=&quot;nofollow&quot;&gt;http://kd0ar.blogspot.com/2010/04/cell-phone-interference-on-softrock.html&lt;/a&gt;), uses a softrock and was receiving interference from his cellphone. If you manage to do what he did, maybe you could get the same results. RF chokes really do work. They're everywhere in my house, and have signigicantly reduced household and common device RFI.&lt;/p&gt;&#xA;" OwnerUserId="412" LastActivityDate="2014-01-15T17:18:09.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1254" PostTypeId="1" AcceptedAnswerId="1255" CreationDate="2014-01-16T18:06:43.540" Score="6" ViewCount="1330" Body="&lt;p&gt;Assuming:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Radio frame&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Subdivided in 15 slots&lt;/li&gt;&#xA;&lt;li&gt;Number of chips: 38.400&lt;/li&gt;&#xA;&lt;li&gt;Duration: 10 ms; each slots = 666.6 μs and has 2.560 chips&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Example of channels&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;DPDCH (Dedicated Physical Data Channel) (UL)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Spreading factor varies between 4 and 256&lt;/li&gt;&#xA;&lt;li&gt;Data rates 960, 480, 240, 120, 60, 30 and 15 kbit/s&lt;/li&gt;&#xA;&lt;li&gt;Spreading factor 4, 640 bits/slot, 15 slots/frame, 100 frames/s -&gt; 960 kbit/s&lt;/li&gt;&#xA;&lt;li&gt;Spreading factor 256, 640 bits/slot, 15 slots/frame, 100 frames/s -&gt;15 kbit/s&lt;/li&gt;&#xA;&lt;li&gt;A connection can have at most 6 DPDCH -&gt; 5, 74 Mbit/s&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Question&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't really understand how the bitrate for DPDCH is determined like &quot;960kbit/s&quot; for example. Which formula is used to derive these values?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a picture of the frame structure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/THRqk.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="593" LastEditorUserId="29" LastEditDate="2014-01-17T15:10:08.790" LastActivityDate="2014-01-17T15:10:08.790" Title="How to calculate UMTS bitrates?" Tags="&lt;digital-modes&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1255" PostTypeId="2" ParentId="1254" CreationDate="2014-01-16T18:37:41.323" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Spreading factor 4, 640 bits/slot, 15 slots/frame, 100 frames/s = 960 kbit/s&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I don't really understand how the bandwidth for DPDCH is determined like &quot;960kbit/s&quot; for example.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There's no equation. It's just another way of stating the information that's already there. By &lt;a href=&quot;http://en.wikipedia.org/wiki/Dimensional_analysis&quot; rel=&quot;nofollow&quot;&gt;dimensional analysis&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \require{cancel}&#xA;\frac{640\, \text{b}}{\cancel{\text{slot}}}&#xA;\frac{15 \cancel{\text{ slot}}}{\cancel{\text{frame}}}&#xA;\frac{100 \cancel{\text{frame}}}{s}&#xA;\frac{1\,\text{k}}{1000}&#xA;= \frac{960\,\text{kb}}{\text{s}}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also would not call &quot;960 kbit/s&quot; a &lt;em&gt;bandwidth&lt;/em&gt;. That may be acceptable in the context of say, a PCI bus, but in the context of a radio protocol, &lt;em&gt;bandwidth&lt;/em&gt; also means the width of the signal in the frequency domain. I'd call it a &lt;em&gt;bitrate&lt;/em&gt; to avoid that confusion.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2014-01-16T21:57:18.400" LastActivityDate="2014-01-16T21:57:18.400" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1256" PostTypeId="1" AcceptedAnswerId="7368" CreationDate="2014-01-17T16:49:25.873" Score="19" ViewCount="27554" Body="&lt;p&gt;Are there standard ways to connect a hand key (straight or paddle) to a contemporary computing device (PC laptop with no parallel port, Mac, Android, iOS device, etc.) for developing or improving ones Morse code sending skills?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, can one use this setup to do hand-key QSOs, either using a remote transmitter if appropriately licensed, or directly over the internet?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-11-26T15:42:39.940" Title="Using a Morse code key with a computer?" Tags="&lt;cw&gt;&lt;remote-control&gt;" AnswerCount="6" CommentCount="2" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1257" PostTypeId="2" ParentId="1256" CreationDate="2014-01-18T16:28:24.887" Score="2" Body="&lt;p&gt;Well, I can't answer as to “standard” as I'm just learning myself, but I can think of a couple of ways to do this without getting into completely custom interface hardware and drivers, or needing an interface with directly readable signal lines like a serial port or parallel port which is less common these days:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Connect the key to a &lt;em&gt;code practice oscillator&lt;/em&gt; that has a line-level audio output, then connect the audio to your computer's line-in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I can't find a good existing explanation to link here! A code practice oscillator is just a device with key input, audio output (usually with a built-in speaker), and an internal oscillator so that it can produce an audio tone that is switched on and off by the key input. I don't know how commonly available a line output is.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would allow you to practice using “decode Morse from audio” apps, which I understand are available on smartphone platforms, for example. It could be used to transmit using a remotely controlled transmitter; if in SSB mode (and the CPO's output is a good sine wave, which is worth checking), the result is equivalent to CW (though probably less clean), but in FM or AM modes it is &lt;a href=&quot;https://en.wikipedia.org/wiki/Modulated_continuous_wave&quot; rel=&quot;nofollow&quot;&gt;modulated continuous wave&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For practice rather than transmission purposes, it would be adequate to use a CPO without line output, and a regular microphone attached to your computer that picks the sound up.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Turn the key into a keyboard keyswitch. This could be done by connecting it to the appropriate points on the switch matrix of a regular keyboard; you might also be able to find a specific-purpose device (or plans for one) for connecting arbitrary switches as keyboards, for the arcade-cabinet or assistive-device (for disabilities) markets, but I haven't looked hard myself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This requires software which will interpret a keyboard key as a Morse key. I don't know anything about the existence of such; I just mention this option because from a computer-peripheral-interfacing perspective it's the most fitting.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-01-27T03:34:11.680" LastActivityDate="2014-01-27T03:34:11.680" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1258" PostTypeId="2" ParentId="1256" CreationDate="2014-01-20T04:08:51.240" Score="6" Body="&lt;p&gt;How you do this will be dictated by the software you select. However, most software I have seen uses some of the control lines on an RS-232 serial port. Calling it a &quot;standard&quot; might be a stretch, but there seems to be a convention:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/PHoXo.jpg&quot; alt=&quot;CW key connection&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More at the source, &lt;a href=&quot;http://www.f8eho.net/content/interfaces&quot; rel=&quot;noreferrer&quot;&gt;F8EHO.net&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible to use some of the other control lines to drive an opto-isolator or relay which in turn connects to the key jack on your radio. Thus, your computer looks, to the transmitter, as an external keyer. Again, no real &lt;em&gt;standards&lt;/em&gt;, besides those imposed by the software you select.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No doubt, it is possible to send Morse code over the internet. Any application that can send audio over the internet could do it, for example, Skype. You'd simply need to set the input of your audio-over-internet application to be the output of your morse-code-keyer application, instead of a microphone. Of course, there is no &lt;em&gt;standard&lt;/em&gt; way to do this either, just as there is no standard communication program, or standard keying software, or standard operating system.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-01-21T18:29:57.910" LastActivityDate="2014-01-21T18:29:57.910" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1259" PostTypeId="1" AcceptedAnswerId="1260" CreationDate="2014-01-20T04:32:02.197" Score="6" ViewCount="4578" Body="&lt;p&gt;I am interested in getting into ham radio however one of my concerns is could a ham radio affect current wireless communications in my house. I am particularly concerned when it comes to WiFi signals. Where I would likely put a radio, I currently have my computer which connects via WiFi to my router. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am concerned that if I set up a radio with an antenna on the roof above me, I could create interference for my already spotty WiFi signal. Is this a potential risk? &lt;/p&gt;&#xA;" OwnerUserId="611" LastActivityDate="2018-08-08T22:15:01.790" Title="How would operating a ham radio affect other wireless devices in my house?" Tags="&lt;rfi&gt;&lt;internet&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1260" PostTypeId="2" ParentId="1259" CreationDate="2014-01-20T07:02:54.267" Score="8" Body="&lt;p&gt;Well, mostly &lt;strong&gt;no&lt;/strong&gt; but &lt;strong&gt;yes&lt;/strong&gt; it is possible for the antenna to have an effect.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;No&lt;/strong&gt;.  I get more interference from wifi than interference to wifi.&lt;/p&gt;&#xA;&lt;p&gt;In the computer adjacent to my ham station, I have had lockups but the network does not drop.  It is not wifi related.  I assume the lockups are from RF entering on a supposedly shielded cable like a USB mouse or keyboard cable.  It happens rarely now that RF-blocking clip on toroids are on the shields of these cables.&lt;/p&gt;&#xA;&lt;p&gt;Interference from a D-Link to the HF radio receiver was only partially reduced by wrapping the D-Link in Alumnium foil (except for the antenna, of course) and adding toroids to the ethernet and power lines.  Routers can be noisy and some comparison shopping or additional internet questions may be in order.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Yes&lt;/strong&gt; Any large metal object around your house, an antenna, a refrigerator, a metal table, your car in the garage, metal such as steel studs in the walls or floors ... will reflect the microwaves from your wifi.  The level of wifi signal at a particular spot is affected by these reflections. This doesn't have anything to do with talking on the ham radio, we are just talking about microwave reflections off of passive metal objects.&lt;/p&gt;&#xA;&lt;p&gt;As far as talking on the ham radio goes, the frequency for Wifi is 2.4Ghz or 5Ghz, which is quite different from the frequencies for most ham radio 1.8 - 432 Mhz.  So they don't typically interfere.  Also, interference temporarily slows down Wifi, it doesn't typically stop wifi unless somehow the router stops operating. The transmission protocol of Wifi immediately resends information that was missed due to any reason (weak signal, interference from neighbors' wifi, etc) without action by the user.&lt;/p&gt;&#xA;&lt;p&gt;If you have ancient 1980s era 49 Mhz cordless phones or 49 Mhz baby monitors, get rid of those.   Some amplified speakers -- like computer speakers -- may receive you when you talk.  This does not indicate any fault, and is normal.  It is the speakers that are the problem.&lt;/p&gt;&#xA;&lt;p&gt;If you share your living situation with apartment neighbors or a home with a family or significant other, perception can be more important than fact. Perhaps strengthen the wifi first, and then worry about ham radio.&lt;/p&gt;&#xA;&lt;p&gt;That being said, a variety of wifi routers and wifi antennas can be had for around 100 US dollars, and often less, that, by trial and error, might improve your existing signal levels.  The typical $30 wifi router does not have a very powerful transmitter and you might pay attention to the output power (usually in milliwatts) if you upgrade it.&lt;/p&gt;&#xA;&lt;p&gt;Some people build focused wifi antennas out of &lt;a href=&quot;http://www.turnpoint.net/wireless/has.html#what&quot; rel=&quot;noreferrer&quot;&gt;various food cans&lt;/a&gt; or &lt;a href=&quot;http://www.mikestechblog.com/joomla/networking-section/wifi-wireless-category/58-extend-wireless-wifi-network-building-24-ghz-cantenna.html&quot; rel=&quot;noreferrer&quot;&gt;flashlights&lt;/a&gt; to obtain a gain in signal.  The construction of these wifi antennas is more of a do-it-yourself hobby among wifi hobbyists than necessitated by anything about ham radio.&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-01-20T07:37:25.857" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1261" PostTypeId="2" ParentId="1259" CreationDate="2014-01-20T16:11:20.437" Score="1" Body="&lt;p&gt;On which bands are you going to operate? I regularly operate on HF bands (160-10 meters) and never have any interference with the WiFi signal. Except if you operate on microwaves (e.g., 13 cm band, which overlaps with the frequency range used by 802.11b/g/n), I would not expect any interference on the WiFi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there is something else to care about: ADSL/VDSL modems use frequencies in the HF range to modulate the internet data on a analog telephone line (which uses unshielded cables). If your output power is high enough, and the telephone line picks up enough signal, transmitting might prevent your Internet connection from working. My ADSL modem (actually I tried 3 different models... all of them had some issue) almost instantly loses connectivity if I operate on 3.5 MHz with more than 10-15 W of output power — but the telephone line has a very long cable inside the apartment, which might pick up a lot of RFI. I know other ham radio operators who don't have any problems with ADSL and have far more output power than me... so this depends a lot on your local setup. And if you're going to operate in VHF/UHF, I wouldn't expect any interference on ADSL. Cable modems (as they use shielded cables for transmission) will probably be less prone to interference with HF, but I don't have any direct experience with that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Update&lt;/strong&gt;: I've switched from ADSL to VDSL (to increase Internet bandwidth, fiber was unfortunately not possible), and moved the modem to the living room, around 10 meters farther from the transmitter than before. The telephone line now goes straight to the modem, and the line branch passing near the transmitter has been disconnected. As a result, even operating with the linear amplifier (~500 W output) on 3.5 MHz (or on any other RF band) does not affect the Internet connection in a significant way any more. I didn't look at the line quality parameters to see if there's any effect, but the connection stays up and the throughput doesn't seem to really change during transmission. I occasionally had disconnections while tuning the linear amplifier, but it only happens once in a while.&lt;/p&gt;&#xA;" OwnerUserId="614" LastEditorUserId="614" LastEditDate="2018-08-08T22:15:01.790" LastActivityDate="2018-08-08T22:15:01.790" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="1262" PostTypeId="2" ParentId="1183" CreationDate="2014-01-21T17:07:52.383" Score="1" Body="&lt;p&gt;As your comment mentions, since you're &lt;em&gt;transmitting&lt;/em&gt; also, you will have issues.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Placing two antennas within ~1/2 wavelength of each other will cause them to inductively couple - effectively connecting themselves to each other. This results in detuning both antennas, as well as the high power Tx RF getting routed back down the other antenna, possibly damaging the receiver. I did this once with 2m mobile rigs - I had my HT connected to a magmount placed too close to the antenna for my 50w mobile, resulting in a fried protection diode in the HT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As others have asked, what is your goal in having two receivers? If you're trying to run two different networks, why not just overlay a virtual SSID on the same AP?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 de KD8EVL&lt;/p&gt;&#xA;" OwnerUserId="619" LastActivityDate="2014-01-21T17:07:52.383" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1264" PostTypeId="1" AcceptedAnswerId="1265" CreationDate="2014-01-21T19:54:40.540" Score="5" ViewCount="1592" Body="&lt;p&gt;What HF bands, times of day and/or conditions might be best for attempting to make non-local contacts using QRP transmitter power (around 1 Watt) and a small indoor folded or loop antenna?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-01-23T08:59:51.293" Title="Best QRP HF band for small antenna?" Tags="&lt;propagation&gt;&lt;band-plan&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1265" PostTypeId="2" ParentId="1264" CreationDate="2014-01-21T21:19:33.067" Score="4" Body="&lt;p&gt;The lower the frequency, the larger the antenna that is required to be resonant, so if you're aiming for something small then 10m might be best.  That band is usually best during the day, and during the summer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to go with a slightly longer antenna, 15m is also good, either day or night.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for the antenna being indoors, that could work, but usually (especially with QRP), you'll find that you get the best results with HF with the antenna outside.&lt;/p&gt;&#xA;" OwnerUserId="568" LastEditorUserId="29" LastEditDate="2014-01-23T08:59:51.293" LastActivityDate="2014-01-23T08:59:51.293" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1266" PostTypeId="2" ParentId="63" CreationDate="2014-01-22T10:44:13.597" Score="1" Body="&lt;p&gt;I had this happen in an apartment building.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The GFCI in the master bath would trip when a VHF quad was pointed towards it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same breaker would trip when a VHF HT was used next to the breaker box.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During renovation, I managed to get the electrical contractor for the building to insert a RFI supression snap-on ferrite about 1&quot; long onto one of the wires at the breaker box for the bathroom circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem went away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this permitted under the Electrical Code or are there good places or bad places to insert RFI suppression ?  I have no idea. That might become rather important if there were a fire or other misfortune.  That is why I make an effort to follow local and national codes by letting a professional take charge of this sort of thing instead of doing it myself.&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2014-01-22T10:52:47.113" LastActivityDate="2014-01-22T10:52:47.113" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1267" PostTypeId="2" ParentId="63" CreationDate="2014-01-22T16:07:01.693" Score="7" Body="&lt;p&gt;It's true, some GFCIs are just abnormally fussy, and you can attenuate RF on a conductor with ferrites.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, &lt;em&gt;a lot&lt;/em&gt; of amateur setups have improperly designed or installed antennas. Common-mode RF currents in the antenna feed system will travel right down the feedline, to your transmitter, down its power cord, and into every other device in your house which is connected by the mains wiring, including all your GFCI outlets. Your house, and all the wiring in it, is essentially an oddly shaped radial, and RF currents will use it, if you don't do something to stop them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A GFCI is effectively a common-mode current detector. When an electrical device isn't electrocuting someone, the current on the hot conductor is exactly balanced by current on the neutral conductor. That is, there is no common-mode current. When you are holding a cold water pipe with one hand, and a faulty hair dryer with another, now some of that current can return to ground through the water pipe. Now the currents on the hot and neutral conductors aren't balanced: there is a common-mode current. The GFCI concludes someone is being electrocuted, and opens the circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, a GFCI can't tell if the common-mode currents are due to you being electrocuted, or exist because your antenna finds your house's wiring as a favorable RF return. It pops either way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, before you go off replacing your GFCIs, or getting crazy with ferrite beads behind the walls in all the rooms, I suggest you look at your antenna feed. See &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt;. The problem is equally applicable to verticals also: if your antenna isn't on an ideal, infinite ground plane, you might need a balun anyway. Same goes for loops, or any other kind of antenna. Eliminate (to the extent possible) the common-mode currents at the source (your antenna) first.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-01-22T16:07:01.693" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1268" PostTypeId="1" AcceptedAnswerId="1276" CreationDate="2014-01-22T20:11:25.680" Score="4" ViewCount="424" Body="&lt;p&gt;There seem to be updates to the ARRL handbook every year, but I don't know if the updates are significant or not. Is the yearly update minor, and buying a new one every 10 years would be enough to avoid missing something important, or is the year-to-year content so different that I should consider buying each year's volume?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-01-22T22:28:39.430" Title="The ARRL handbook updates yearly. Is it useful to buy it every year?" Tags="&lt;arrl&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1270" PostTypeId="1" AcceptedAnswerId="1341" CreationDate="2014-01-22T20:36:12.177" Score="8" ViewCount="1868" Body="&lt;p&gt;I've been contacted by others who want to verify a DX with me, but I was not operating at that time!  It appears that someone made several contacts using my callsign for a short window of time one day.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been keeping my ears open, but haven't seen it myself, and the only information those who contacted me have are the dates, times, and frequencies of the contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What should I do once I find my call being used by someone else? Is there any reporting I should perform to the FCC?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there anything else I can do besides listening to catch them? If I do hear them, is there a method I can use to at least narrow down their location?  &lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2015-05-01T18:36:05.270" LastActivityDate="2015-05-11T00:29:37.110" Title="What should I do if my call is being used by someone else?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;station-identification&gt;&lt;callsign&gt;" AnswerCount="5" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1271" PostTypeId="1" CreationDate="2014-01-22T20:36:59.570" Score="20" ViewCount="10002" Body="&lt;p&gt;Let's say we already know that if &lt;a href=&quot;https://ham.stackexchange.com/questions/601/how-to-reduce-rf-in-the-shack-when-using-vertical-hf-antenna-no-radials/604#604&quot;&gt;your antenna is not suitably constructed or connected&lt;/a&gt; then you can get &lt;a href=&quot;https://ham.stackexchange.com/questions/63/how-do-i-prevent-radio-signals-from-popping-a-gfci-plug/1267#1267&quot;&gt;current on the shield of your coaxial feed line&lt;/a&gt; which will flow through the shielding/grounding of your equipment, becoming “RF in the shack”, and that this should be avoided for safety, transmit efficiency, and to avoid interfering with electronic equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I am not merely connecting together prebuilt equipment, but perhaps constructing an antenna/ground/balun system, &lt;strong&gt;how can I measure this phenomenon, so as to determine whether it has been eliminated&lt;/strong&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/601/how-to-reduce-rf-in-the-shack-when-using-vertical-hf-antenna-no-radials/673#673&quot;&gt;One of the previous questions&lt;/a&gt; mentioned a “FS meter” (I assume field strength meter), but I have not heard of this being a typical part of a ham's test equipment. Can a regular receiver be used? Even if this gives uncalibrated readings, can a reliable “null” (i.e. detection of the lack of current) be obtained?&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2021-05-23T20:35:09.290" Title="How to detect common-mode currents or “RF in the shack”?" Tags="&lt;rfi&gt;&lt;grounding&gt;&lt;antenna-construction&gt;&lt;equipment-design&gt;&lt;testing&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1272" PostTypeId="2" ParentId="1271" CreationDate="2014-01-22T21:25:32.913" Score="12" Body="&lt;p&gt;One way to tell is by its effects. Do you hear a garbled version of yourself in nearby speakers when you transmit SSB? Do GFCI outlets pop even though no one is being electrocuted? Does handling the transmission line give you RF burns when transmitting, or change what you hear when receiving? If you had these problems and now you don't, you must have been successful in reducing common-mode currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a more objective measurement, it's easy to make some test equipment with things you probably already have.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;snap-on ferrite detector&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;You can &lt;a href=&quot;https://electronics.stackexchange.com/q/78530/17608&quot;&gt;make a detector with a diode&lt;/a&gt;, and a current transformer from a snap-on ferrite, such as those used to snap onto cables for EMI suppression. This will work for HF, but at higher frequencies the loss in the ferrite will become significant. Higher frequency ferrites are available, but not usually as snap-on beads.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/2TdLI.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f2TdLI.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The component values are not at all critical. I've used a Schottky diode, but an ordinary 1N4148 will also work with reduced sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've made R2 small to maximize the current through the meter. If you are measuring larger currents, or have a very sensitive meter, increase R2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just use my digital multimeter, and left the components hanging off the ferrite. It's ugly, but effective. Keep the lead lengths short. The long meter leads are fine because the RF has been rectified to DC by that point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZarAq.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZarAq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This device can be roughly calibrated by measuring the current through a known load. I put two half-watt, 100 ohm resistors in parallel, soldered them onto a connector, and plugged them into my transmitter as a 50 ohm dummy load. I set the transmitter power to minimum, clamped the ferrite around the resistors, and keyed up briefly. 5 watts into 50 ohms should give about 316 milliamps, and I read about 3 milliamps on the meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The non-linear diode will make the relationship between actual and measured current not linear, but that's good enough for a gross calibration.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;other ideas&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;All kinds of devices can be used as detectors and probes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An oscilloscope can work: try simply laying the probe next to the wire being measured, or making a &lt;a href=&quot;http://emcesd.com/tt2004/tt070104.htm&quot; rel=&quot;noreferrer&quot;&gt;loop probe&lt;/a&gt;. Put more turns in the loop for more sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/I9O0x.jpg&quot; alt=&quot;magnetic field probe orientation&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 2nd radio works also, without an antenna, or with a dummy load to reduce sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;making the measurements&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Set up your probe. Transmit, and watch your detector. The strength of the signal it detects is proportional to the strength of the common-mode current. For long wires, take measurements at a few places: there may be standing waves with high impedance (low current) and low impedance (high current) nodes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Considering &lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_%28electromagnetism%29&quot; rel=&quot;noreferrer&quot;&gt;reciprocity&lt;/a&gt;, if you can measure common-mode currents in a thing when you transmit, then that thing is also helping you to receive. Either isolate these things from the antenna, or make sure they are noise-free. Insufficiently isolated feedlines, and digital electronics injecting noise into home wiring are the biggest offenders.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2017-01-29T16:29:27.737" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1273" PostTypeId="1" AcceptedAnswerId="1277" CreationDate="2014-01-22T22:06:48.527" Score="12" ViewCount="3427" Body="&lt;p&gt;I always believed that DX meant out of one’s own country, and in the continental US that can be pretty far. However, tooling around on the bands I’ll often hear people calling DX inside the US receive responses from others also inside the US. Sometimes the caller will respond, and sometimes not.  &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;What is the definition of DX?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is it impolite to answer a CQ DX inside your own country?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What should you do if you're calling CQ DX and someone responds to you who you don’t believe is DX?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2014-01-22T22:17:24.523" LastActivityDate="2018-03-02T17:17:16.580" Title="What is the definition of DX?" Tags="&lt;procedure&gt;&lt;dx&gt;&lt;etiquette&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1274" PostTypeId="2" ParentId="1264" CreationDate="2014-01-22T22:10:23.930" Score="0" Body="&lt;p&gt;There is no particular band more suited to QRP operation than another. A weak signal is still weak, whatever the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's easier to build efficient antennas on higher frequencies, since the wavelength is smaller, and antenna designs scale with wavelength. While it's always possible to electrically lengthen an antenna with loading coils, capacitive hats, etc, this makes the antenna less efficient, making poorer use of your already limited transmitter power. So, you likely want to stick to frequencies high enough where you have room for the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being indoors is never good: it means you can't get the antenna far away from noise sources and you can't get it very high. That's always bad regardless of frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Non-local contacts are possible on any of the HF bands. Which one is &lt;em&gt;best&lt;/em&gt; depends on &lt;em&gt;many&lt;/em&gt; factors, a large one being luck. HF propagation is significantly affected by solar activity, which follows some pattern regarding an 11 year sunspot cycle, and the obvious day/night changes, but also is &lt;em&gt;highly&lt;/em&gt; variable based on just chance. Higher frequency bands like 10m are mostly good during the day. Lower frequency bands like 40m and down are mostly good during the night. The bands between, 30m, 20m, 15m, are somewhere between. Exceptions to these &quot;rules&quot; are common, based on random solar weather. It also depends on where you are trying to communicate: each frequency refracts in the atmosphere at a different angle, so a particular frequency might happen to not work because the signal skips over the intended target. The sun is moving, and so is the ionosphere, so a frequency that's good now might not be good in 5 minutes. That's just luck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given all this, it should be pretty clear: we can't predict what the &lt;em&gt;best&lt;/em&gt; band will be. You can't get outdoors, you don't have space for a good antenna, and you have limited transmit power. On balance you have a poor station, and there's no way around it. Your size limitations restrict you to the higher frequencies, but on those for which you have enough room, the best band will be determined by luck.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-01-22T22:10:23.930" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1275" PostTypeId="1" AcceptedAnswerId="1278" CreationDate="2014-01-22T22:14:16.010" Score="1" ViewCount="191" Body="&lt;p&gt;Whether you refer to them as go-boxes, go-kits, or rapid deployment kits, powering a transportable ham shack is of utmost importance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While both battery chemistry types have much to recommend them in other uses, the go-box imposes certain requirements and operating conditions that many consider unique.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some still insist that Sealed Lead Acid is better for a generic go-box than any lithium chemistry, but I haven't found much reason to back that up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What about the go-box requirements or operating environment might suggest that SLA might be a better choice than a lithium chemistry battery?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-06-29T15:07:52.653" Title="What advantages does SLA have over a Lithium chemistry battery for a Go Box?" Tags="&lt;emergency&gt;&lt;battery&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1276" PostTypeId="2" ParentId="1268" CreationDate="2014-01-22T22:20:13.373" Score="3" Body="&lt;p&gt;I don't think there is a right answer here, but I will share mine and the one I suggest to new hams.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL Handbook is an awesome reference, especially for the price.  You simply get a ton of information from basic electronics on through all the major areas of amateur radio.  With the numbering system they use, there isn't even a good way to determine the number of pages in any given edition.  I think it's safe to say that it's current page count is north of 1200 pages and has grown steadily over the years.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact it was the Handbook that was one of the big draws of amateur radio when I was first introduced to it as a teenager.  It was simply the best collection of cool electronic information I had ever seen in one place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's too large a product for it to change substantively from year to year; the ARRL just doesn't have the staff for that.  But I think it's aim, as a handbook/reference is more like an encyclopedia than a be-all reference.  And the basics don't change that much from year to year.  What does change are the projects that accompany the articles.  These tend to be reprints from QST or other ARRL publications, but none-the-less serve to make concrete examples of the theory presented there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Technology changes and ham radio follows along (or leads!), so I think one every 5 years is probably fine.  I have the last 15 years on my shelf, except for the last two years.  That's because I don't buy them new.  As much as I like them, $50 a pop is just too big a chunk of my radio budget this year.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, I probably only spent around US\$100 on the 13 volumes I have by buying them used on eBay and at hamfests.  For instance, the last copy of the 2010 Handbook that sold on eBay went for US\$5.00 and the one that's up right now is at US\$0.99 with no bidders.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shop wisely and enjoy one of the best references out there.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-01-22T22:28:39.430" LastActivityDate="2014-01-22T22:28:39.430" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1277" PostTypeId="2" ParentId="1273" CreationDate="2014-01-22T22:35:18.863" Score="13" Body="&lt;p&gt;As &lt;a href=&quot;http://en.wikipedia.org/wiki/DXing&quot;&gt;Wikipedia puts it&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The name of the hobby comes from DX, telegraphic shorthand for &quot;distance&quot; or &quot;distant&quot;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There is no objective definition. If it's far enough that it might be a difficult contact, then it can be DX. Of course this all varies based on conditions, equipment, and perception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes, callers will specify just what kind of DX they are seeking. &quot;CQ DX Europe.&quot; &quot;CQ DX California&quot;. Etc. Frequently, they are seeking a specific contact to qualify for some award, like &lt;a href=&quot;http://www.arrl.org/was&quot;&gt;worked all states&lt;/a&gt;, and they may specify this in the call.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you hear &quot;CQ DX Europe&quot;, and you &lt;em&gt;aren't&lt;/em&gt; in Europe, then probably you shouldn't return the call. If the call didn't specify exactly what flavor of DX, then use your judgement. Working Maine to California can be DX, especially with a QRP station. If you think the contact might be challenging or rare due to distance and conditions, then it's fair game.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also consider what other stations might be trying to return the call. If you hear someone in the same country trying to work someone across the world, then you are not &quot;DX&quot; to the guy in the same country. It would probably be nice if you stayed quiet so he can complete the more difficult contact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During contests, keep in mind what the contest is about. People may explicitly mention the contest in their calls. Reply if you think your contact might be relevant to the contest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you receive a response to a DX call but you don't think it is good enough, reply anyway. Maybe the other guy has a question. Maybe he wants to tell you that your transmission is poorly modulated. Maybe &lt;em&gt;he&lt;/em&gt; thought &lt;em&gt;you&lt;/em&gt; were a challenging contact. Maybe he's transmitting with 1mW, and then you will think it was a good contact too, but you won't know this until you talk. The standard rules of social interaction still apply: be polite. If someone is calling you, they want to talk to you.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-01-22T22:35:18.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1278" PostTypeId="2" ParentId="1275" CreationDate="2014-01-23T00:23:15.883" Score="4" Body="&lt;p&gt;If near freezing or colder conditions is one of your possible operating environments, then SLA cells can still be (re)charged at slightly lower temperatures than lithium chemistry cells.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-01-23T00:23:15.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1279" PostTypeId="1" AcceptedAnswerId="1287" CreationDate="2014-01-23T00:57:16.577" Score="5" ViewCount="236" Body="&lt;p&gt;I've been doing a bit of work on optical open-air transmission, and have been thinking, any hays that varies the intensity of the light or whatever else would affect the amplitude. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it be possible to send and receive a frequency modulated light transmission? And if so how hard would it be?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-09-24T21:45:03.223" LastActivityDate="2017-08-21T07:50:39.837" Title="Frequency Modulated Light" Tags="&lt;modes&gt;&lt;optical&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1280" PostTypeId="1" AcceptedAnswerId="1416" CreationDate="2014-01-23T01:18:51.910" Score="2" ViewCount="197" Body="&lt;p&gt;There is a loop antenna that was thrown around an attic interior several decades ago, of long forgotten dimensions.  I found the feed line.  Is there a way to measure what (U.S. amateur) bands on which it might radiate most efficiently (if at all) without physical access?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Possible resources:  A vintage Philmore FS-45 field strength meter.  An old Versa Tuner with an SWR meter.  Two portable SW radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;ADDED: Is there a way to test or measure the characteristics of this antenna without keying a transmitter?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-02-08T20:08:16.887" LastActivityDate="2014-02-11T15:30:18.263" Title="Measuring antenna characteristics without physical access?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;loop-antenna&gt;&lt;measurement&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1281" PostTypeId="1" AcceptedAnswerId="1303" CreationDate="2014-01-23T02:58:04.260" Score="5" ViewCount="4296" Body="&lt;p&gt;Related to this &lt;a href=&quot;https://ham.stackexchange.com/questions/1185/what-is-the-record-for-highest-successful-automated-cw-transmission-rate&quot;&gt;question&lt;/a&gt;, but using humans, and in an actual QSO, not lab conditions:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a record for QSO QRQ speed?  And, if so, what is the record for the highest non-automated over-the-air CW/Morse Code WPM rate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, if so, are there separate speed records for keyer, vs. bug vs. straight key?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2019-07-28T08:24:47.317" Title="What is the record for the highest non-automated over-the-air CW WPM speed?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1282" PostTypeId="1" CreationDate="2014-01-23T03:07:19.077" Score="7" ViewCount="1113" Body="&lt;p&gt;Given that it is no longer a license requirement, are there any current statistics available on what percentage of licensed amateur radio operators still learn Morse Code to some degree of proficiency? (e.g. without needing to use a computer decoder)  U.S. or Worldwide?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-01-23T15:49:36.050" LastActivityDate="2019-07-07T19:29:08.240" Title="How many new amateur operators can currently use CW?" Tags="&lt;cw&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1283" PostTypeId="1" CreationDate="2014-01-23T03:26:22.353" Score="8" ViewCount="62" Body="&lt;p&gt;Some multi-story buildings in my region require earthquake isolation on some of the piping.  Thus my question.  Is there a way to determine whether a nearby metal water pipe is actually Earth grounded, versus floating?  Does this make a difference in terms of finding a suitable ground for a non-ground-floor HF radio and antenna?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-01-23T15:03:51.223" Title="Testing a possible grounding point?" Tags="&lt;grounding&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1285" PostTypeId="2" ParentId="1280" CreationDate="2014-01-23T14:57:13.073" Score="4" Body="&lt;p&gt;One way would be to connect a HF transceiver to the SWR meter, and that meter to the antenna. Assuming proper licensing to broadcast on bands - tune to the middle of each amateur band and check the SWR while transmitting a tone (or whilst whistling). The lower SWR reading would indicate closest resonance to that band. Checking at various points around that band could narrow the resonant frequency. Caveat (1) be licensed for the band/frequency you're going to test; (2) LISTEN on frequency before tuning and disrupting another QSO; (3) keep your test short and be sure to identify your call sign and the test as per regulations in your locale.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2014-01-23T14:57:13.073" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1286" PostTypeId="2" ParentId="1283" CreationDate="2014-01-23T15:03:51.223" Score="4" Body="&lt;p&gt;&quot;Electric&quot; ground and &quot;RF&quot; ground are different creatures. Water pipes may make a good RF ground if one is close to the point where the pipe goes underground. A floor above and it will not be (as) effective. Dropping a grounding strap/braid out of a convenient window to reach a real grounding rod is recommended. That being said, connect the ground and try it - sometimes you have to work with what is available or possible. If it improves performance, use it - or run without a ground if it works (sounds like an indoor or balcony antenna, so lightning hits are not a concern).&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2014-01-23T15:03:51.223" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1287" PostTypeId="2" ParentId="1279" CreationDate="2014-01-23T16:53:59.070" Score="4" Body="&lt;p&gt;Technically speaking, frequency modulation of light would involve shifting the color since, if you look at the EM spectrum, you basically see a rainbow in the visible part of it from red (lowest frequency) to violet (highest frequency).  If you wanted to, you could take the original signal, run it through an analog-to-digital converter, and do the calculations to modulate the different parts of an RGB LED.  The receiving side of that wouldn't be trivial, though, but it could be done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most light modulation that I've seen has instead been amplitude modulation.  The details for the circuit would depend on what you're using for a light source, but it's basically a matter of making the light bright or dim based on the input signal.  The receiving side for this could be a simple phototransistor circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One possibility that would combine both would work better for digital signals, and that would be to approach it like the way that RTTY works for radio waves.  Use two colors of light, the more distinguishable the better, one for your &quot;high&quot; and one for your &quot;low&quot; frequency.  You then shift between the two to transmit, and use 2 phototransistor circuits behind 2 color filters matching what you're sending to receive.  You would probably need to use amplitude modulation as well, if only to filter out stray light, just like IR remote controls do.&lt;/p&gt;&#xA;" OwnerUserId="568" LastEditorUserId="568" LastEditDate="2014-01-23T17:00:47.253" LastActivityDate="2014-01-23T17:00:47.253" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1288" PostTypeId="1" AcceptedAnswerId="1302" CreationDate="2014-01-23T18:07:29.167" Score="7" ViewCount="862" Body="&lt;p&gt;My two-storey house is wood with alumninum siding.  I had wanted to install an inverted-vee antenna with its midpoint hanging from the eave, and endpoints near the ground, but this would place the wire of the antenna about a foot from the siding.  The wall of the house at that point is perpendicular to a line in the direction of Japan.  I live in Washington state.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, how much is the siding going to affect the performance of the antenna?  Would the siding act as a kind of reflector, so I could hear Japanese stations better than New York City stations?  Or would it adversely affect all signals?&lt;/p&gt;&#xA;" OwnerUserId="414" LastActivityDate="2018-07-29T21:19:12.827" Title="How does aluminum siding on a house affect an inverted-vee antenna next to it?" Tags="&lt;antenna-construction&gt;&lt;inverted-vee&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1289" PostTypeId="1" CreationDate="2014-01-23T18:20:27.040" Score="1" ViewCount="232" Body="&lt;p&gt;I bought a 10m radio on eBay back in 2007 during the solar minimum when 10m propagation was nothing to write home about.  I verified that the radio worked at that time, though it didn't seem to work very well.  And I wasn't sure if it was the radio's fault or the band's.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was thinking of breaking the radio back out to see what is going on, but was wondering what the more experienced 10m band users are experiencing at this time.  How is propagtion on the 10m at this time as we are supposedly approaching the peak of this solar cycle?  I do note that this solar cycle (&lt;a href=&quot;https://en.wikipedia.org/wiki/Solar_cycle_24&quot; rel=&quot;nofollow&quot;&gt;the 24th&lt;/a&gt;) is much less active than the previous one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm kind of interested to hear from 10m enthusiasts about how well (or not) they are doing on the band, compared, say, with earlier years when the sun was quiet.&lt;/p&gt;&#xA;" OwnerUserId="414" LastEditorUserId="414" LastEditDate="2014-01-23T22:41:55.233" LastActivityDate="2014-01-23T22:41:55.233" Title="How is the 10 m band performing now in January 2014?" Tags="&lt;propagation&gt;" AnswerCount="2" CommentCount="2" ClosedDate="2014-02-03T20:05:12.200" ContentLicense="CC BY-SA 3.0" />
  <row Id="1290" PostTypeId="2" ParentId="1289" CreationDate="2014-01-23T18:32:47.997" Score="1" Body="&lt;p&gt;One way to see how the band is performing right now is to use the &lt;a href=&quot;http://www.dxmaps.com/spots/map.php?Lan=E&amp;amp;Frec=28&amp;amp;ML=M&amp;amp;Map=NA&amp;amp;DXC=N&amp;amp;HF=S&amp;amp;GL=N&quot; rel=&quot;nofollow&quot;&gt;DX Maps&lt;/a&gt; web site.&lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2014-01-23T18:32:47.997" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1291" PostTypeId="1" CreationDate="2014-01-23T18:58:51.280" Score="17" ViewCount="6721" Body="&lt;p&gt;I keep doing research, and trying to grasp it, but when it comes to RF impedances, and coax, I still have trouble trying to grasp it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So first, I think you have to have a 50 ohm coax for a 50 ohm transmitter to keep the impedances matched. I think I also need a tuner to make the antenna look like a 50 ohm resistor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After trying really hard to understand, I still don't know what &quot;50 ohm coax&quot; means; I know it's not 50 DC ohms in any way, but when RF is added, I just get totally confused.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, people are always like &quot;OMG DON'T USE 75 OHM&quot;, but then they use 300 ohm ladder line!?! I understand that they use a tuner to match the 300 ohm, but why wouldn't a tuner work for 75 ohm?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there's connectors. Why would a little piece of metal screw have that much effect on the antenna, and how can a connector have an ohm rating at all?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-01-24T01:19:12.773" LastActivityDate="2018-06-24T21:48:44.870" Title="Understanding coax impedance" Tags="&lt;feed-line&gt;&lt;coaxial-cable&gt;&lt;impedance&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1292" PostTypeId="2" ParentId="1289" CreationDate="2014-01-23T20:18:29.787" Score="0" Body="&lt;p&gt;One way to test propagation at your location is to use WWV and WWVH.  While they don't have frequencies up in the 10m range, you can get a good idea of propagation on 2.5, 5, 10, 15 and 20Mhz from CO and from Hawaii.&lt;/p&gt;&#xA;" OwnerUserId="308" LastActivityDate="2014-01-23T20:18:29.787" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1293" PostTypeId="1" AcceptedAnswerId="1298" CreationDate="2014-01-23T20:48:45.497" Score="9" ViewCount="370" Body="&lt;p&gt;In the U.S., regulations permit CW operations throughout the amateur bands.  That makes the phone section of a band look tempting when the CW/digital part of the band is busy with a contest.  I wonder if my friends and I can reasonably have our scheduled QSO in the phone part of the band when the CW/digital part is busy.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it acceptable to conduct a CW QSO in the phone part of a band?&lt;/li&gt;&#xA;&lt;li&gt;If so, what are good operating practices to avoid interfering with SSB operators?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="628" LastEditorUserId="76" LastEditDate="2014-01-23T21:42:01.643" LastActivityDate="2014-01-24T00:36:48.050" Title="CW on phone band" Tags="&lt;united-states&gt;&lt;procedure&gt;&lt;cw&gt;&lt;phone&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1294" PostTypeId="2" ParentId="1291" CreationDate="2014-01-23T21:17:03.700" Score="3" Body="&lt;p&gt;Transmission line theory is complicated by many factors.  Here's one simplified explanation that might help you understand a little better what you're asking about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you send a wave down a line, it doesn't appear instantly on the other end, the electrons push each other, and in a measurable, finite amount of time the wave is present on the other end of the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The line has a capacitance and an inductance, though, so when you start sending the wave the cable's capacitance and inductance absorb and release that energy as the wave travels down the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since all lines feature capacitance and inductance, then we have to treat them as part of the overall circuit.  If we ignore them then we may lose some of our wave, or it may be altered in some undesirable way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could quantify the capacitance and inductance seperately, and then call each cable according to those parameters, but we've come up with a simplification called impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you send a fast wave down the line and measure the voltage and current, then apply ohms law, regardless of what's connected at the other end of the line, during the fast transition you will see 50 ohms of load on the line for the wave.  This is the line's natural capacitance and inductance reacting to the AC wave you sent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If nothing is attached to the other end, or the other end is shorted out, the wave will be reflected back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you attach a 50 ohm resistor on the other end, then the waveform will be completely consumed by the resistor.  This is because the cable's capacitance and inductance only consumed enough current at the transmitter's voltage and waveform type to provide the wave at that same current at the output.  Since you put it in at a certain voltage, and it consumed enough current for a 50 ohm load, then the voltage, and more importantly waveform shape, are preserved at the output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you put too small a resistor, then it'll eat the current too quickly - faster than the waveform is actually traveling on the inductor/capacitor chain that the line is made of, and this will distort the waveform and voltage, and will reflect some of the waveform back.  You'll have lost energy, not everything you sent on the line will have been consumed at the other end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you put to large a resistor, then it won't eat the current fast enough, and again the voltage and waveform will be altered, and again some of it will be reflected back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This leads to two problems - energy loss, and changed waveform. So if your transmitter is designed for a 50 ohm impedance, you use a 50 ohm cable, and a 50 ohm antenna, then the majority of your transmitter's energy will go into the antenna, and will be radiated into the air, with the waveform shape the transmitter intended.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you instead replace your 50 ohm cable with a 75 ohm cable, the cable will consume less current than expected, which alters the way the waveform travels down the line, and when it's received by the 50 ohm antenna, not all of that energy will be properly coupled into the antenna.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-01-23T21:17:03.700" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1295" PostTypeId="2" ParentId="1291" CreationDate="2014-01-23T21:39:50.920" Score="7" Body="&lt;p&gt;It looks like you're looking for an intuitive, practical understanding rather than precise definitions, so I'll see what I can do with that, with my own recent learning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason you care about impedance matching is that &lt;em&gt;impedance mismatches cause the signal to be partially reflected&lt;/em&gt; — some of the energy is going the opposite direction than you want it to go. For transmission, this results in excessive voltage at the transmitter output, which can damage solid-state transmitters; in any case, even if the reflected component is reflected back again (standing waves), you have additional loss and effective multipath propagation (some of the signal took longer to exit the system through the antenna or receiver).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The characteristic impedance of a transmission line depends on the space between the conductors — its shape, and what it is filled with (the dielectric). A connector needs to be (electrically) &lt;em&gt;shaped like&lt;/em&gt; a simple continuation of the lines it joins, otherwise it's mismatched just like a piece of transmission line of a different characteristic impedance. This is also why you should avoid sharply bending coaxial cable — it distorts the cable and causes a change in impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why ohms? Lots of ways to describe this, but a good enough one is this: in the simplest case, an impedance is like a resistance, and resistances are measured in ohms. A resistor — a dummy load — is a simple load which has a constant impedance at all frequencies. Two facts:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If you connect a resistor of a certain impedance (resistance) to the end of a transmission line with the matched characteristic impedance, then there will be no mismatch and no reflections, and it will be measured as 50 ohms no matter the frequency. This is &lt;em&gt;termination&lt;/em&gt; of a transmission line.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you had — theoretically speaking — an infinitely long transmission line, and you connected a DC ohmmeter to it, the ohmmeter &lt;em&gt;would&lt;/em&gt; read the line's characteristic impedance. You can see this as being sort of like the reason we want to match impedances: so that the signal goes into the line without having to consider what is on the other end. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(If you have a transmission line with mismatches — say, an open circuit at the other end, or damage in the middle — then you can use the reflections to measure exactly how long the section before the reflection is. A &lt;em&gt;time-domain reflectometer&lt;/em&gt; is an instrument for doing this. There's a nifty video about how you can see this effect with a signal generator and an oscilloscope that I haven't found again.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;That's &lt;em&gt;why&lt;/em&gt;; everything else is &lt;em&gt;how&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;There's nothing wrong with using 75 ohm coax in particular. It's just that it is conventional for amateur radio equipment to be designed with 50 ohms characteristic impedance, so if you substitute 75 ohm coax without doing anything else you will have mismatches.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The reason for using 300 ohm balanced line is that it is a good match for certain types of antennas, and has lower loss than a typical coaxial line (because the EM field passes through more empty air than solid dielectric materials). This allows you to avoid placing a matching device at the antenna itself; instead, you must do so at the transmitter (assuming the transmitter has a 50 ohm output).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;When a load has a different impedance from a connected transmission line, the input end of the transmission line will appear to have a different impedance than its characteristic impedance. Furthermore, antennas have frequency-dependent impedance. Together, these are one of the main reasons why antenna tuners are used, as opposed to simply designing the entire system around fixed impedances: to increase the band over which an antenna can be used without excessive mismatch at the transmitter. However, even with a tuner, this results in &lt;em&gt;standing waves&lt;/em&gt; on the transmission line, which increase loss in the line.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Specifically designed changes in impedance can be used to produce specific effects, including impedance matching and baluns. However, such devices only work in a narrow band because they have to be a specific length relative to the wavelength of the signal. Conversely, if you want wideband performance you avoid mismatches so that the characteristics of the system don't change with frequency.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The main things I have &lt;em&gt;not&lt;/em&gt; mentioned here are is how impedance corresponds to a ratio of current and voltage (in accordance with Ohm's Law), and the concept of &lt;em&gt;reactance&lt;/em&gt; (or complex impedance). These matter for understanding the behavior of systems with mismatches; equal or matched impedance is a simple case which results in behavior which is independent of frequency and length of the line.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-06-24T21:48:44.870" LastActivityDate="2018-06-24T21:48:44.870" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="1296" PostTypeId="1" AcceptedAnswerId="1297" CreationDate="2014-01-23T22:01:42.817" Score="6" ViewCount="4097" Body="&lt;p&gt;Would like to have a 50W mobile in my SUV, but I'm not allowed to have a big whip on the outside.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What 2m/70cm dual band antennas are available that don't say, &quot;Ham Radio Operator&quot;? &lt;/li&gt;&#xA;&lt;li&gt;Are there three band antennas that replace the radio antenna?&lt;/li&gt;&#xA;&lt;li&gt;I'd probably be allowed a short, small antenna like the fin satellite antennas popular with the satellite radio crowd, are there any dual band antennas in a similar form factor?&lt;/li&gt;&#xA;&lt;li&gt;Are there good places inside the vehicle to hide an antenna?  I've heard some people are able to place them inside the plastic bumper, but given the rest of the car is metal I'm not aware of any other discreet locations.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9" LastActivityDate="2021-02-01T22:50:10.403" Title="What are some good options for covert dual band vehicle antennas?" Tags="&lt;antenna&gt;&lt;mobile&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1297" PostTypeId="2" ParentId="1296" CreationDate="2014-01-24T00:14:50.787" Score="4" Body="&lt;p&gt;Depending on how your terrestrial radio antenna is mounted, it may be possible to remove it and mount a small dual band antenna there and likely no one would notice. I tried that on my truck, but that area where the antenna mounts is on the plastic frame in front of the windshield, not down on the fender.  There was no way to really get in there and swap the bases out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also removed my terrestrial radio antenna anyway (just unscrewed the element) as I have satellite radio and that was unnecessary.  If you have that situation, there is always the option of drilling and installing a mount there on the fender.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other than that, all your other (effective) antenna options are going to be somewhat less discreet. For an SUV, a jam mount or lip mount on the rear door/hatch would work, a 1/4 &amp;lambda; antenna is only going to be about 20&quot; long for 2m.  Even shorter for 70cm. Black mount and black antenna and it should blend in well.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A useful dual or tri-band antenna is going to be 30&quot;+.  At that point it's going to be hard to call it anything other than what it is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on who you are hiding this from, another option is mounting on the roof rack, if you have one. There are these motorized mounts designed for people that park in garages that lay the antenna down for parking.  You could mount that and only raise the antenna when you are on the road and operating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are no good areas inside the vehicle, the body makes a moderately effective Faraday cage and the losses are brutal.  I can't imagine anything hidden in a plastic bumper being very effective since VHF is pretty much line of sight and the mass of the vehicle is always going to block out 1/2 the sky.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A final option is a small mag mount or a window mount that you put up only when operating and take off and toss in the back when you aren't operating.  Nothing permanent or too obvious.  Again, this all depends on whom you are hiding from.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-01-24T00:14:50.787" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1298" PostTypeId="2" ParentId="1293" CreationDate="2014-01-24T00:36:48.050" Score="8" Body="&lt;p&gt;Since we are talking about the United States, the &quot;phone&quot; portions of each band are actually described as phone, CW &amp;amp; image. So it's not only legal, but it's perfectly acceptable to operate CW in that portion of the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Contest rules generally confine contesters to the CW-only portion of the band making the rest of the band a viable option during CW or Digital only contests. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for good operating practices, they are the same as always: find a clear spot, listen, ask if the frequency is in use, listen, commence operation. Some bands, notably 40m and 80m have some long standing scheduled nets, you'll want to avoid those, otherwise you should be OK. CW takes so little bandwidth, it's pretty easy to slide past a CW QSO if you are looking for room to operate SSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Probably you will want to avoid contest style operation though to avoid causing any misunderstandings. A normal rag-chew style QSO will likely not bother anyone.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-01-24T00:36:48.050" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1299" PostTypeId="2" ParentId="1282" CreationDate="2014-01-24T00:44:31.870" Score="3" Body="&lt;p&gt;I don't think there is a way to answer this question definitively.  In my area (central Maryland, USA), there are three separate clubs that hold monthly exam sessions within an hour of my home. I used two of them to progress through my exams.  My club (one of the 3) gave approximately 200 exams last year.  I don't know a single new ham that learned CW before they took their exams.  Several, myself included, started learning CW afterwards.  How many are active? I can't really tell.  I would say not many, perhaps 5%?  Purely anecdotal information though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will say that the &quot;cred&quot; or attitude towards CW is improving now that it's not required.  The no code hams feel like it's a cool niche now, not something foisted upon them. &lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-01-24T00:44:31.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1300" PostTypeId="2" ParentId="1291" CreationDate="2014-01-24T04:14:06.210" Score="3" Body="&lt;p&gt;Here's the problem: information can only travel at the speed of light. So, say you have a resistor, connected to your ohmmeter by a pair of very long wires. When you connect the ohmmeter to the wires, it applies some voltage, but how much current flows? When this voltage is first connected, it sets off a wave in the electric field, but that wave hasn't yet reached the resistor. The resistor doesn't &quot;know&quot; there's an ohmmeter, and the ohmmeter doesn't yet &quot;know&quot; there's a resistor. So how much current flows in the instant the ohmmeter is connected?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;em&gt;characteristic impedance&lt;/em&gt; of a transmission line answers this question. If a transmission line has a 50Ω characteristic impedance, it means that for every 50V you apply, you get 1A. An ohm is a volt per amp ($R=E/I$ and $\Omega=V/A$), remember.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Eventually the wave set up when the ohmmeter was connected to the wires reaches the resistor at the end. If the resistor has the same impedance as the transmission line, then the current that flowed into the line initially works against the resistor to make the same voltage that the ohmmeter applied. Now voltage is the same throughout the circuit, and everything is in equilibrium. That was easy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the resistor at the end has a different impedance than the transmission line, then the current will work against it to create a &lt;em&gt;different&lt;/em&gt; voltage than the ohmmeter initially applied. The ohmmeter at this point is displaying the impedance of the transmission line, not the resistor at the end. Since the voltage at the resistor end is now different than everywhere else in the line, another wave is set in motion, propagating back to the ohmmeter. If the ohmmeter is maintaining a constant voltage, then when this reflected wave arrives, the current at the ohmmeter will have to change (and consequently, the measured resistance on the display changes) to keep the voltage at its end constant. Thus, another wave is sent towards the resistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These reflections go back and forth, each time getting closer to the equilibrium solution of dictated by the resistor on the end. You don't usually notice it because it happens at the speed of light. Try playing with a &lt;a href=&quot;http://helloworld922.blogspot.com/2013/04/online-transmission-line-simulation.html&quot; rel=&quot;nofollow&quot;&gt;transmission line simulator&lt;/a&gt; to see what happens on a more observable timescale.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It doesn't matter if the thing at the end of the example above is a resistor, or another transmission line, antenna, or a connector. Each of these things, in fact &lt;em&gt;anything&lt;/em&gt; that can have an electric field, has a characteristic impedance, and if this impedance doesn't match that of the transmission line, a wave is reflected back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, there's nothing wrong with 75Ω coax, as long as everything else is 75Ω, or you have added matching devices where there are impedance changes. This is exactly what is done when 300Ω ladder-line is used. The advice against using 75Ω coax is simply because cable TV is usually a 75Ω system, so people have a lot of it around and might ignorantly think it looks the same, so it should work the same as 50Ω coax.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-01-24T16:51:06.577" LastActivityDate="2014-01-24T16:51:06.577" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1301" PostTypeId="1" AcceptedAnswerId="1305" CreationDate="2014-01-24T13:09:06.947" Score="6" ViewCount="696" Body="&lt;p&gt;I use a cheap DVBT dongle that I control via RTL-SDR. Right now a very basic setup. The general consensus seems to be that a long usb cable should be used (to keep noise from the computer away from the dongle) and the antenna directly plugged into the dongle (without cable, or a short one, is this because ogf grounding?).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is only a simply telescoping piece of metal. Using an amplifying antenna that I got my hands on, the reception was better, with the simple antenna I practically only pick up noise. Now I want to have a better reception without spending much money - what should I look for? I want to be able to listen to radio standard radio stations, but also to to use it as a scanner, so I'll probably be looking for a broadband antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dongle was built for TV, do TV and RF antennas have the same connections?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit to add&lt;/strong&gt;&lt;br&gt;&#xA;I have a dongle with a PAL-connector, not an F connector (from comparing with pictures)&lt;/p&gt;&#xA;" OwnerUserId="631" LastEditorUserId="631" LastEditDate="2014-01-24T20:29:16.587" LastActivityDate="2014-01-24T20:41:21.463" Title="What should I look for in an antenna for a DVBT Dongle used for SDR?" Tags="&lt;antenna&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1302" PostTypeId="2" ParentId="1288" CreationDate="2014-01-24T14:13:35.517" Score="2" Body="&lt;p&gt;It's very difficult to predict. If your siding were an infinite, perfectly conducting plane, then the results would be the same as if you had another inverted V, positioned as if mirrored through the plane of the siding, but fed in antiphase. This is called an &lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;image antenna&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What this does depends on the distance between your antenna and the siding. It's not unlike the problem of a &lt;a href=&quot;https://ham.stackexchange.com/a/487/218&quot;&gt;dipole over ground&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the rub: your siding isn't infinite, and it isn't perfectly conductive. The geometry is going to significantly change the result. You might get some result by putting the measurements precisely into a modeling system like EZNEC, but short of that it's hard to say.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An inverted V isn't a very directional antenna to begin, so it's not too productive worrying about how it's going to affect the pattern. It will probably significantly affect the &lt;em&gt;tuning&lt;/em&gt; of your antenna. And, this siding is going to have some significant RF currents in it. If it's lossy, because it's not conductive, it's also going to degrade the efficiency of your antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, if this is the only good place you have to put an antenna, it will work. I doubt the losses will be too huge, if you can get it to tune. That's probably the hard part. Will it tune? Again, really hard to say. Wire antennas are cheap. The easiest thing to do is try it and see.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-01-24T14:13:35.517" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1303" PostTypeId="2" ParentId="1281" CreationDate="2014-01-24T17:08:31.843" Score="4" Body="&lt;p&gt;According to &lt;a href=&quot;http://books.google.com/books?id=pzkZPIXm89UC&amp;amp;lpg=PA168&amp;amp;ots=U11ipZKuY5&amp;amp;dq=guinness%20book%20of%20world%20records%20morse%20code&amp;amp;pg=PA168#v=onepage&amp;amp;q=guinness%20book%20of%20world%20records%20morse%20code&amp;amp;f=false&quot; rel=&quot;nofollow&quot;&gt;this book (1993)&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Ted R. McElroy received just over 75 WPM in 1939&lt;/li&gt;&#xA;&lt;li&gt;Harry A. Turner sent 35 WPM using a hand key in 1942 (using Continental code, believed to be equivalent to about 50 WPM in American Morse)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.guinnessworldrecords.com/world-records/1/fastest-speed-for-a-morse-code-transmission&quot; rel=&quot;nofollow&quot;&gt;Guinness&lt;/a&gt; seems to think that further improvements have been made:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Guinness World Records' record for the Fastest speed for a morse code transmission was set by Andrei Bindasov (Belarus), who successfully transmitted 216 Morse code marks of mixed text in one minute. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;However, the Guinness site &lt;a href=&quot;http://www.guinnessworldrecords.com/records-4000/fastest-morse-code-sent-and-received/&quot; rel=&quot;nofollow&quot;&gt;also lists&lt;/a&gt; a completely different set of individuals for &quot;morse code sent and received&quot;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Les Edwards using morse code sent the prescribed 160 character message to Ray Carter. Ray received the message by a morse code receiver and then typed it onto a piece of paper using an old fashioned typewriter in 1 minute and 8 seconds on the set of Guinness World Records at Seven Network Studios, Sydney, New South Wales, Australia, on 27 August 2005.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="22" LastEditorUserId="22" LastEditDate="2014-01-24T17:13:49.273" LastActivityDate="2014-01-24T17:13:49.273" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1304" PostTypeId="1" AcceptedAnswerId="1309" CreationDate="2014-01-24T18:17:51.863" Score="10" ViewCount="1595" Body="&lt;p&gt;Certain Hex Beam antennas use a coaxial center support post to send the RF to each antenna section, which is superior, in terms of maintenance, to a post with screw terminals connected by short lengths of coax used in previous designs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to use off the shelf stainless steel tubes and rods to accomplish this, but I have access to enough machining equipment that I can adjust some parts to give me better dimensions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically, if I'm aiming for a 1.5&quot; square outer stainless steel tube, what dimension should the inner stainless steel conductor be to attain 50Ω impedance, assuming air as the insulator between the two? The tube has a 0.065&quot; thick wall, so the inner dimensions are 1.37&quot; x 1.37&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, what are the equations I need to design such transmission lines with different dimensions, conducting materials, and impedance in the future?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="70" LastEditDate="2014-01-26T00:24:45.167" LastActivityDate="2014-01-26T13:49:22.607" Title="How do I design a round or square coaxial transmission line to have a specific impedance?" Tags="&lt;diy&gt;&lt;coaxial-cable&gt;&lt;impedance&gt;&lt;transmission-line&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1305" PostTypeId="2" ParentId="1301" CreationDate="2014-01-24T18:53:44.223" Score="1" Body="&lt;p&gt;There are a number of broadband receiving antennas marketed specifically as &lt;a href=&quot;https://www.google.com/search?q=scanner%20antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;scanner antennas&lt;/a&gt;.  Without more information on what attributes you specifically need, though, I can't recommend any specific antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without a picture of the connector, it will be hard to tell you what kind of adaptor to get, but it's unlikely to be a BNC connector, which is the most common type for these types of antennas.  Consider posting a new question with an image of the connector and adapter recommendations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a number of PAL to BNC connectors available from many online sources:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/SB1Qx.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2014-01-24T20:41:21.463" LastActivityDate="2014-01-24T20:41:21.463" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1308" PostTypeId="2" ParentId="1167" CreationDate="2014-01-25T18:16:48.167" Score="2" Body="&lt;p&gt;The librtlsdr is for RTL2832U based DVB-T dongles.  The Funcube Dongle has no RTL2832U chip. However, the overarching OSMOSDR project includes support for the Funcube Dongles (Pro and Pro+) and other SDR equipment. See &lt;a href=&quot;http://sdr.osmocom.org/trac/wiki/GrOsmoSDR&quot; rel=&quot;nofollow&quot;&gt;http://sdr.osmocom.org/trac/wiki/GrOsmoSDR&lt;/a&gt; for more information.&lt;/p&gt;&#xA;" OwnerUserId="636" LastActivityDate="2014-01-25T18:16:48.167" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1309" PostTypeId="2" ParentId="1304" CreationDate="2014-01-25T22:10:16.053" Score="8" Body="&lt;h3&gt;Executive Summary&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Assuming:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;air dielectric (insulator)&lt;/li&gt;&#xA;&lt;li&gt;50Ω &lt;a href=&quot;http://en.wikipedia.org/wiki/Characteristic_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;characteristic impedance&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Then for round coax, make the inside diameter of the outside conductor 2.302 times larger than the diameter of the inside conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the shield is square, and the inner conductor is still round, make the inside length of one side of the shield 2.134 times larger than the diameter of the inside conductor.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Explanation, for Round Coax&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;A coaxial &lt;a href=&quot;http://en.wikipedia.org/wiki/Transmission_line&quot; rel=&quot;nofollow noreferrer&quot;&gt;transmission line&lt;/a&gt; has some &lt;a href=&quot;http://en.wikipedia.org/wiki/Inductance&quot; rel=&quot;nofollow noreferrer&quot;&gt;inductance&lt;/a&gt; per unit length $L$, and some &lt;a href=&quot;http://en.wikipedia.org/wiki/Capacitance&quot; rel=&quot;nofollow noreferrer&quot;&gt;capacitance&lt;/a&gt; per unit length $C$. The conductors also have some (very low) resistance $R$, and the dielectric has some (very low) &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrical_resistance_and_conductance&quot; rel=&quot;nofollow noreferrer&quot;&gt;conductance&lt;/a&gt; $G$. Though it's important to note that &lt;a href=&quot;https://electronics.stackexchange.com/a/75384/17608&quot;&gt;these properties are distributed throughout the entire length of the transmission line&lt;/a&gt;, lumping them all together we can model a transmission line as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Z11yg.png&quot; alt=&quot;transmission line schematic model&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The characteristic impedance is then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_0=\sqrt{\frac{R+j\omega L}{G+j\omega C}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$R$ is the resistance per unit length, considering the two conductors to be in series,&lt;/li&gt;&#xA;&lt;li&gt;$L$ is the inductance per unit length,&lt;/li&gt;&#xA;&lt;li&gt;$G$ is the conductance of the dielectric per unit length,&lt;/li&gt;&#xA;&lt;li&gt;$C$ is the capacitance per unit length,&lt;/li&gt;&#xA;&lt;li&gt;$j$ is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Imaginary_unit&quot; rel=&quot;nofollow noreferrer&quot;&gt;imaginary unit&lt;/a&gt;, and&lt;/li&gt;&#xA;&lt;li&gt;$\omega$ is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Angular_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;angular frequency&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If we assume a good conductor and dielectric, then $R$ and $G$ are negligible&lt;sup&gt;1&lt;/sup&gt;. The equation then simplifies to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_0 \approx \sqrt{\frac{L}{C}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For &lt;em&gt;round&lt;/em&gt; coaxial transmission lines, we can calculate $C$ and $L$ as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ C = {2 \pi \epsilon_0 \epsilon_r \over \ln(D/d)} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ L = {\mu_0 \mu_r \over 2 \pi} \ln(D/d) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$d$ is the diameter of the inner conductor,&lt;/li&gt;&#xA;&lt;li&gt;$D$ is the inside diameter of the outer conductor,&lt;/li&gt;&#xA;&lt;li&gt;$\epsilon_0$ is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Vacuum_permittivity&quot; rel=&quot;nofollow noreferrer&quot;&gt;permittivity of free space&lt;/a&gt;, approximately $8.854 \cdot 10^{−12} F \cdot m^{-1}$&lt;/li&gt;&#xA;&lt;li&gt;$\mu_0$ is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Vacuum_permeability&quot; rel=&quot;nofollow noreferrer&quot;&gt;permeability of free space&lt;/a&gt;, approximately $1.256 \cdot 10^{-6} H \cdot m^{-1}$&lt;/li&gt;&#xA;&lt;li&gt;$\epsilon_r$ is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Relative_permittivity&quot; rel=&quot;nofollow noreferrer&quot;&gt;relative permittivity&lt;/a&gt; of the dielectric, and&lt;/li&gt;&#xA;&lt;li&gt;$\mu_r$ is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29#Relative_permeability_and_magnetic_susceptibility&quot; rel=&quot;nofollow noreferrer&quot;&gt;relative permeability&lt;/a&gt; of the dielectric.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Putting these together and simplifying we get:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align} Z_0 &#xA;&amp;amp;\approx \sqrt{\frac&#xA;  {{\mu_0 \mu_r \over 2 \pi} \ln(D/d)}&#xA;  {{2 \pi \epsilon_0 \epsilon_r \over \ln(D/d)}}&#xA;} \\&#xA;&amp;amp;\approx \sqrt{\frac&#xA;  {\mu_0 \mu_r \ln(D/d)^2}&#xA;  {(2 \pi)^2 \epsilon_0 \epsilon_r}&#xA;} \\&#xA;&amp;amp;\approx \sqrt{\frac&#xA;  {\mu_r}&#xA;  {\epsilon_r}&#xA;} \sqrt{\frac&#xA;  {\mu_0}&#xA;  {(2 \pi)^2 \epsilon_0}&#xA;} \ln(D/d) \\&#xA;&amp;amp;\approx \sqrt{\frac&#xA;  {\mu_r}&#xA;  {\epsilon_r}&#xA;} 59.96 \ln(D/d) \\&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For an air dielectric, $\epsilon_r$ and $\mu_r$ are so close to 1 than you can further simplify:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_0 \approx 59.96 \ln(D/d) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also see that only the &lt;em&gt;ratio&lt;/em&gt; of the diameters of the conductors are relevant, so it doesn't matter what units of length are used, as long as they are the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can solve for $D/d$, and set $Z_0 = 50 \Omega$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;56.40 \ln(D/d) &amp;amp;\approx Z_0 \\&#xA;\ln(D/d) &amp;amp;\approx \frac{Z_0}{59.96} \\&#xA;D/d &amp;amp;\approx e^{Z_0/59.96} \\&#xA;D/d &amp;amp;\approx e^{50/59.96} \\&#xA;D/d &amp;amp;\approx 2.302&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Explanation, for Square Shield with a Round Center Conductor&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;This is a rather less common situation. Kevin Schmidt, W9CF has a &lt;a href=&quot;http://fermi.la.asu.edu/w9cf/articles/square/square.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;full explanation&lt;/a&gt;. The equations are rather more complex, owing to the more complex geometry of the conductors, and are most easily solved by computer. However, a good approximation for impedances around 50Ω, with an air dielectric, is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_0 \approx 59.96 \ln(1.079 D/d) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or solved for $D/d$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ D/d \approx {e^{Z_0/59.96} \over 1.079} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$d$ is the diameter of the inner conductor, and&lt;/li&gt;&#xA;&lt;li&gt;$D$ is the inside length of one side of the shield.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: this is a valid assumption for all HF frequencies, and VHF with low-loss dielectrics. At higher frequencies, &lt;a href=&quot;http://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin effect&lt;/a&gt; and &lt;a href=&quot;http://en.wikipedia.org/wiki/Dielectric_loss&quot; rel=&quot;nofollow noreferrer&quot;&gt;dielectric loss&lt;/a&gt; make $R$ and $G$ more significant, but it's likely this will manifest as an impracticably lossy line before the impedance is significantly affected.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2014-01-26T13:49:22.607" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1310" PostTypeId="1" AcceptedAnswerId="1316" CreationDate="2014-01-26T15:13:14.547" Score="6" ViewCount="252" Body="&lt;p&gt;I have heard about radio &quot;contests&quot; but I haven't seen a real explanation of what they are and what they entail. What do I need to know about contests before getting a technician license for the first time? Is there any particular etiquette regarding them I should know?&lt;/p&gt;&#xA;" OwnerUserId="611" LastEditorUserId="76" LastEditDate="2014-01-26T22:45:22.173" LastActivityDate="2019-08-12T14:22:25.590" Title="What are contests? What do I need to know about them being new to ham radio?" Tags="&lt;contest&gt;&lt;procedure&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1312" PostTypeId="2" ParentId="1256" CreationDate="2014-01-27T02:15:08.810" Score="1" Body="&lt;p&gt;Many CW keyers (such as the &lt;a href=&quot;http://hamcrafters.com/&quot; rel=&quot;nofollow&quot; title=&quot;WinKeyer&quot;&gt;WinKeyer&lt;/a&gt;) will convert what you key back to text. I used &lt;a href=&quot;http://www.w1hkj.com/flwkey-help/index.html&quot; rel=&quot;nofollow&quot; title=&quot;flwkey&quot;&gt;flwkey&lt;/a&gt; to see what I was (attempting) to send as code practice.&lt;/p&gt;&#xA;" OwnerUserId="90" LastActivityDate="2014-01-27T02:15:08.810" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1313" PostTypeId="1" AcceptedAnswerId="1318" CreationDate="2014-01-27T10:10:32.303" Score="5" ViewCount="22986" Body="&lt;p&gt;I tried to use both:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.dxsoft.com/en/products/cwget/&quot; rel=&quot;nofollow&quot;&gt;Cwget&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hotamateurprograms.com/downloads.htm&quot; rel=&quot;nofollow&quot;&gt;CW decoder&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;But neither one worked. Can you recommend a tool or an alternative approach to decode a Morse message saved as an Mp3 file?&lt;/p&gt;&#xA;" OwnerUserId="641" LastEditorUserId="5222" LastEditDate="2015-08-28T20:18:55.703" LastActivityDate="2015-08-29T00:01:04.300" Title="How to convert a Morse Code Message/QSO from Mp3 file into text?" Tags="&lt;cw&gt;" AnswerCount="6" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1314" PostTypeId="1" CreationDate="2014-01-27T13:47:16.667" Score="2" ViewCount="983" Body="&lt;p&gt;Ok , so I know very very little about amateur radio, I've hear in some websdr frequencies morse code transmissions and I've got quite curious, what are they? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Who sends moresecode transmissions nowadays , are radio amateurs or the military?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I knew morse code could I understand it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I meant like 1820 at &lt;a href=&quot;http://hackgreensdr.org:8901/&quot; rel=&quot;nofollow&quot;&gt;http://hackgreensdr.org:8901/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="642" LastEditorUserId="642" LastEditDate="2014-01-29T21:34:25.167" LastActivityDate="2014-01-29T21:34:25.167" Title="What is morse code used for in amateur radio?" Tags="&lt;cw&gt;" AnswerCount="3" CommentCount="7" ClosedDate="2014-01-29T18:07:34.827" ContentLicense="CC BY-SA 3.0" />
  <row Id="1315" PostTypeId="2" ParentId="1314" CreationDate="2014-01-27T14:19:48.100" Score="3" Body="&lt;p&gt;The US military no longer uses Morse Code.  Amateur radio operators still use if for a variety of reasons many of which were explored in this &lt;a href=&quot;https://ham.stackexchange.com/questions/135/why-is-morse-code-still-in-use&quot;&gt;question&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Morse code isn't difficult to learn, but like anything, takes some practice. There are also software programs that can work with you SDR that will decode Morse (to varying degrees of success depending on signal quality and the quality of the sent Morse code). &lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-01-27T14:19:48.100" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1316" PostTypeId="2" ParentId="1310" CreationDate="2014-01-27T14:53:30.750" Score="2" Body="&lt;p&gt;There are all kinds of contests. Operators attempt to get the most contacts, the best contacts, or some combination. The scoring metrics are set by the contest organizer, who is usually some amateur radio club or organization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There isn't a lot you need to know about them to get your license. When there's a contest, bands in which that contest applies can be very busy with a lot of people. You should be prepared to either &lt;a href=&quot;https://ham.stackexchange.com/q/1132/218&quot;&gt;avoid this activity&lt;/a&gt;, or participate in it. If you don't participate in the contest you can still make contacts with people who are, but be aware that contest operators won't be interested in chatting (they are going for quantity, not conversation). They will want to exchange a minimum of information which is set by the contest rules to make the contact valid. Rules vary, but usually exchanged are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;call sign&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Maidenhead_Locator_System&quot; rel=&quot;nofollow noreferrer&quot;&gt;Maidenhead locator&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;signal report (which is always 599 to make things easier)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Contest rules usually require this information to be reported somehow for verification by the contest organizer. Again, methods vary from contest to contest, but some form of electronic submission is common. There are plenty of contest logging programs available to help with the task. Some contests require that both parties of the contest submitted matching log entries for a valid contact to make submitting false contacts harder.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-01-27T14:53:30.750" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1317" PostTypeId="2" ParentId="471" CreationDate="2014-01-27T16:31:03.467" Score="1" Body="&lt;p&gt;In Canada, CW Morse code skills  is not required, but you may elect to seek a CW exam, which confers the same honors now as the &quot;With Honors Basic&quot; qualification, to grant the same priveleges as you would obtain if you simply passed the Honors qualification with 80% or more.  Practically speaking there is almost zero reason to try to pass the CW exam in Canada, since it's easy to get over 80% on the Basic certificate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio operator certificates and their rules are overseen by Industry Canada, formerly DOC (department of Communications). Rules and priveleges and CW requirements are discussed &lt;a href=&quot;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01862.html&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Their site is hard to navigate but the gist of their current rules is that a Basic certificate has no mandatory CW requirements, but passing a CW (Morse code) test formerly conferred additional privileges. As of 2005, Basic certificates confer all the privileges, IF you pass with 80% or more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sources: IC, and this book: Canadian Amateur Radio Basic Qualification Study Guide, 8th edition, Coax Publications Inc. (&lt;a href=&quot;http://www.coaxpublications.ca/&quot; rel=&quot;nofollow&quot;&gt;http://www.coaxpublications.ca/&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Update:&lt;/em&gt; Formerly I had said you needed it for Advanced qualifications. You do not.&lt;/p&gt;&#xA;" OwnerUserId="643" LastEditorUserId="643" LastEditDate="2014-02-04T02:26:51.317" LastActivityDate="2014-02-04T02:26:51.317" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1318" PostTypeId="2" ParentId="1313" CreationDate="2014-01-27T16:58:27.527" Score="3" Body="&lt;p&gt;I'm not aware of a tool which will take an MP3 file as an input for CW decoding.  You should be able to set up either of the software you tried to use a line in, and connect your computer speaker to the line in jack, then play the mp3 using another program while running either of the above decoders.  There are ways to loop the sound through in software, but running a simple cable is easy to do and explain, so try that first.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-01-27T16:58:27.527" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1319" PostTypeId="1" AcceptedAnswerId="1321" CreationDate="2014-01-27T21:44:21.887" Score="14" ViewCount="2013" Body="&lt;p&gt;Most of the RF amplifiers advertised, and most of the questions about amplifiers, are &quot;linear&quot; amplifiers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is a linear amplifier, and what other common amplifier type(s) exist that requires people to say &quot;linear&quot; every time they talk about RF amplifiers?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-12-03T23:41:32.970" Title="What is a linear RF amplifier?" Tags="&lt;amplifier&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1320" PostTypeId="2" ParentId="1313" CreationDate="2014-01-27T21:47:05.037" Score="3" Body="&lt;p&gt;If you have an Apple Mac personal computer running a recent version of OS X, you can play the mp3 files using iTunes, or even the Safari web browser, out any built-in or external speaker, and run the HotPaw Morse Decoder app, &lt;a href=&quot;https://itunes.apple.com/us/app/morsedecoder/id313071325?mt=8&quot; rel=&quot;nofollow&quot;&gt;available as a commercial product&lt;/a&gt;  from the Mac App Store.  If the volume is turned up enough, the background noise and recorded QRM are low enough, and the Morse Code is stable and well formed enough, the Morse Decoder app should be able to decode it into text.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Disclaimer: The Mac Morse Decoder app is a commercial product that I developed.  An iOS version is also available. I used the above method, with mp3 recordings of actual over-the-air CW QSOs, to do regression testing and QA of the app.  Hopefully that allows this answer to be suitably on-topic.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="5222" LastEditDate="2015-08-28T20:16:28.720" LastActivityDate="2015-08-28T20:16:28.720" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1321" PostTypeId="2" ParentId="1319" CreationDate="2014-01-27T23:51:54.390" Score="14" Body="&lt;p&gt;Google defines &quot;linear&quot; as &quot;arranged in or extending along a straight or nearly straight line.&quot; Wikipedia tells me that &quot;&lt;a href=&quot;http://en.wikipedia.org/wiki/Linearity&quot; rel=&quot;nofollow noreferrer&quot;&gt;linearity&lt;/a&gt; refers to a function or relationship which can be graphically represented as a straight line&quot;. Such systems can be described by an equation of the form $y=mx+b$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of RF amplifiers, the relationship is the input voltage vs. the output voltage. The output is identical to the input, only &quot;louder&quot;. Mathematically, $V_{out} = A \cdot V_{in} + 0$, where $A$ is the voltage gain of the amplifier.&lt;sup&gt;1&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Linearity is a generally desirable property but it comes at the cost of reduced efficiency. At any instant, the amplifier's output is probably something somewhere between its power supply rails, and consequently, the output transistors will have some voltage $E$ across them and some current $I$ through them. The rate of electrical energy consumption is the product of these two: $P=IE$. That consumed energy can't vanish: it's converted into heat. This requires big heatsinks, and it drains your batteries faster or runs up your electric bill.&lt;sup&gt;2&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a solution to the heat problem: we amplify the input signal so much that the output is always greater than the supply rails. Now we are effectively connecting the load directly to one supply rail or the other. Now the output transistors either have 0V across it,&lt;sup&gt;3&lt;/sup&gt; or are passing no current. Thus, the power ($P=IE$) in the transistors is low because always either current or voltage is nearly 0. The energy is going to the antenna, not to heating the transistors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is now that the output is horribly distorted. If the input was a nice clean sine wave, the output will be a square wave, full of odd harmonics. We can remove&lt;sup&gt;4&lt;/sup&gt; the harmonics with a filter, and because the filter is made of reactive components like inductors and capacitors which alternately store and release electrical energy, rather than converting it to heat, they don't get so hot, and the amplifier is more efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This mostly solves the distortion problem, but something is lost: the amplitude of the input signal. Fortunately, the frequency is preserved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now we know when non-linear amplifiers are acceptable: when the amplitude of the signal is insignificant, such as FM, or frequency modulated digital modulations like &lt;a href=&quot;http://en.wikipedia.org/wiki/Frequency-shift_keying&quot; rel=&quot;nofollow noreferrer&quot;&gt;FSK&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/Phase-shift_keying#SOQPSK&quot; rel=&quot;nofollow noreferrer&quot;&gt;some PSK flavors&lt;/a&gt;, or &lt;a href=&quot;http://en.wikipedia.org/wiki/Minimum-shift_keying&quot; rel=&quot;nofollow noreferrer&quot;&gt;GMSK&lt;/a&gt;. Modes where amplitude is significant like AM, SSB, or digital modulations like &lt;a href=&quot;http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;QAM&lt;/a&gt; require a linear amplifier.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: RF amps tend not be to be marketed by their voltage gain, but by their maximum power output. Assuming a 50 ohm load, power is related to voltage by $P=E^2/50\Omega$. Take the output power and the input power, calculate the associated voltages, and the ratio of the two is the voltage gain of the amp.&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;2: To dive more deeply into the reasons linear electronic circuits make waste heat, check out &lt;a href=&quot;https://electronics.stackexchange.com/q/18478/17608&quot;&gt;My linear voltage regulator is overheating very fast&lt;/a&gt; on electronics.SE. Though that's about voltage regulators, the problem is common to a broad class of linear electronic circuits. You can also read about &lt;a href=&quot;http://en.wikipedia.org/wiki/Amplifier#Power_amplifier_classes&quot; rel=&quot;nofollow noreferrer&quot;&gt;power amplifier classes&lt;/a&gt;. Class AB is a common linear RF amplifier design. Class C is common for non-linear amps.&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;3: Real transistors will always have some small voltage across them, even when fully on, which means they will get a little warm. This is far better than the a lot warm they get in a linear amplifier, however.&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;4: really, just attenuate. Significantly and sufficiently. All amplifiers output harmonic distortion of some degree, and regulatory agencies regulate the maximum allowable harmonic distortion.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2014-07-11T14:10:24.843" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1322" PostTypeId="1" AcceptedAnswerId="1324" CreationDate="2014-01-28T10:42:34.590" Score="1" ViewCount="1126" Body="&lt;p&gt;I have been bugged with the idea of building a radio in a suitcase, but I have not many clues about where to start. My idea is to make a portable FM station so podcasts can be broadcasted in a small area and later uploaded to the Internet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The functions the &quot;case&quot; should accomplish are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Power the entire unit&lt;/li&gt;&#xA;&lt;li&gt;Take analog MIC/Line signals in a mixer&lt;/li&gt;&#xA;&lt;li&gt;(some long term magic here, such as digital processing)&lt;/li&gt;&#xA;&lt;li&gt;Modulate the analog signal for FM broadcasting&lt;/li&gt;&#xA;&lt;li&gt;Broadcast the signal trough a small antenna&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;My sub-questions here are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How much could it cost?&#xA;How great can I expect a &quot;small antenna&quot; to reach?&#xA;How much power do I need in relation to the whole equipment?&#xA;Which parts would I need?&lt;/p&gt;&#xA;" OwnerUserId="648" LastActivityDate="2015-02-06T02:10:32.347" Title="How do I build an portable FM transmitter?" Tags="&lt;fm&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1323" PostTypeId="2" ParentId="1313" CreationDate="2014-01-28T13:52:46.300" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Can you recommend a tool or &lt;strong&gt;an alternative approach&lt;/strong&gt; to decode a Morse message saved as an Mp3 file?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The old fashioned alternative approach is always available, using your ears.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantage of having a recorded (MP3) CW QSO is that you can pause, rewind, listen again. Print a chart of Morse code, listen, transcribe. You may even learn Morse in the process, and be able to listen to &quot;live&quot; CW.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2014-01-28T13:52:46.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1324" PostTypeId="2" ParentId="1322" CreationDate="2014-01-28T14:45:46.783" Score="1" Body="&lt;p&gt;If the output power is low and you know programming, then you can make such a device for under $30 in parts, if we don't count the suitcase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I made a device which is nearly the same as you need using a &lt;a href=&quot;http://www.ti.com/tool/ek-tm4c123gxl&quot; rel=&quot;nofollow&quot;&gt;TI Tiva C launchpad&lt;/a&gt; for 13 USD and a &lt;a href=&quot;https://dx.com/p/ad9850-dds-signal-generator-module-150060&quot; rel=&quot;nofollow&quot;&gt;AD9850 board&lt;/a&gt; for 10 USD. There are numerous similar boards on eBay and related sites, so you could get one for even less, if you shop around. You can replace the Launchpad for a similar board, such as for example &lt;a href=&quot;http://www.st.com/st-web-ui/active/en/catalog/tools/PF250863&quot; rel=&quot;nofollow&quot;&gt;STM32VLDISCOVERY&lt;/a&gt; or something like that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, the Launchpad has an analog to digital converter that I use to sample the audio. In my particular case, the ADC's internal reference is set to 3 V, so I used a 3.0 V voltage reference and a resistor divider plus a capacitor to move my audio input so that it's DC value is 1.5 V. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the launchpad, I have a loop that samples the ADC, waits for the sampling to complete and then based on the amplitude of the signal calculates the deviation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ADC has 12 bits of resolution, so we can expect values from 0 to 4095. Using a simple proportion, you can scale that to the range of -deviation to +deviation for your band. What I did next was to add the deviation to a fixed frequency which represents input when the ADC provides zero. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next step is to output the data to the AD9850 and set correct output frequency. A problem here appears if you want to use frequencies above around 40 MHz, due to the limitations of the chip. There is a way to work around that, by using harmonics of the output and a bandpass filter to just let the frequency range you want out. The procedure is explained in Analog Devices application note &lt;a href=&quot;http://www.analog.com/static/imported-files/application_notes/AN-543.pdf&quot; rel=&quot;nofollow&quot;&gt;AN-543: High Quality, All-Digital RF Frequency Modulation Generation with the ADSP-2181 and the AD9850 DDS&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using this procedure, I was able to output high-quality mono audio signal to an FM radio with very little effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The main advantage of this approach, compared to using an analog transmitter is that on the hardware side, except for the output filter, you don't really care about the frequency band you're using (as long as AD9850 can produce required frequency) and you don't care about the deviation, since you can set it in software. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for the power supply, m solution requires +5 V and uses less than 100 mA and is normally powered from a USB port.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the antenna, very little is needed. For example, just plugging the AD9850 module I got into a bread-board was enough to cover big part of my room. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the end, be sure to monitor the output of your radio transmitter to be sure that it only outputs in the band in which you have a license to operate! Additional filtering will probably be required for that. &lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2014-01-28T15:10:04.873" LastActivityDate="2014-01-28T15:10:04.873" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1325" PostTypeId="1" AcceptedAnswerId="1330" CreationDate="2014-01-28T17:04:39.997" Score="1" ViewCount="1500" Body="&lt;p&gt;I understand (and correct me if I'm wrong) that transmission power follows Ohm's law ($I = \frac{V}{R}$), that is that if I have a 50 Ω antenna that I know is transmitting at 1 W, then the current is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;V = IR\\&#xA;P = VI \\&#xA;P = (IR)R = I^2R\\&#xA;\frac{P}{R} = I^2\\&#xA;I = \sqrt{\frac{P}{R}}=\sqrt{\frac{1}{50}}=0.141\\&#xA;I = 0.141\,\mathrm{A}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then the voltage is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;V=IR=0.141\,\mathrm{A} \cdot 50\,\Omega=7.07\,\mathrm{A}\\&#xA;V=7.07\,\mathrm{A}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is that voltage RMS, peak to peak, or something else?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's RMS, then peak to peak voltage is: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;V_{\text{PEAK}}=V_{\text{RMS}}\cdot\sqrt{2}=&#xA;7.07\cdot\sqrt{2}=7.07\cdot1.414=10\\&#xA;V_{\text{PEAK}}=10\,\mathrm{V}\\&#xA;V_{PP} = V_{PEAK}\cdot2=10\cdot2=20\,\mathrm{V}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Am I correct in saying that I need a 20V peak to peak sinewave signal to generate 1W RF output on the 50Ω antenna?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is the maximum current I need to design for in my final amplifier 141 mA, or do I need to use $V_{\text{PP}}$ to calculate the maximum current? ($I=\frac{V}{R}=\frac{20\,\mathrm{V}}{50\,\Omega}=0.400\,\mathrm{A}$)&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2014-01-28T19:26:56.087" LastActivityDate="2014-01-28T19:26:56.087" Title="Is transmission wattage calculated using RMS?" Tags="&lt;rf-power&gt;&lt;math&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1326" PostTypeId="2" ParentId="1313" CreationDate="2014-01-28T17:06:42.397" Score="1" Body="&lt;p&gt;If you are using Windows you could probably use the commercial &lt;a href=&quot;http://www.dxatlas.com/CwSkimmer/&quot; rel=&quot;nofollow&quot; title=&quot;CW Skimmer&quot;&gt;CW Skimmer&lt;/a&gt; software in combination with a so called 'virtual audio cable'. A free (as in beer) virtual audio cable driver is &lt;a href=&quot;http://vb-audio.pagesperso-orange.fr/Cable/index.htm&quot; rel=&quot;nofollow&quot; title=&quot;VB-Cable&quot;&gt;VB-Cable&lt;/a&gt;. This installs as a virtual audio card in your system, which should make it possible to redirect the output of your MP3 player to CW Skimmer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, as suggested above, you could also use a physical cable to loop the signal from the output of your soundcard back into the computer. There are two drawbacks with this method though:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;You will probably need a second soundcard.&lt;/li&gt;&#xA;&lt;li&gt;The signal to noise ratio (SNR) will worsen slightly, since the analog connection outside of your computer will add noise. The D/A and A/D converters on the sound cards will add noise too.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Item number 2 above will not likely be a problem, unless you are listening to very weak morse signals. A shielded loop cable (made as short as possible) can be beneficial, but the noise from the A/D and D/A converters can only be remedied by use of a better (and likely more expensive) soundcard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What SNR you need is ultimately determined by the decoder in CW Skimmer and the 'quality' and signalling speed of the received morse code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately I don't know of any open source software to solve your needs.&lt;/p&gt;&#xA;" OwnerUserId="651" LastEditorUserId="651" LastEditDate="2014-01-30T23:31:58.050" LastActivityDate="2014-01-30T23:31:58.050" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1327" PostTypeId="1" AcceptedAnswerId="1331" CreationDate="2014-01-28T17:10:45.847" Score="3" ViewCount="1250" Body="&lt;p&gt;I don't have much experience with amateur satellites and I went to the AMSAT website to track a few passes. Two of the terms are &quot;Maximum Elevation&quot; and &quot;Max El Azimuth&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I go to look up the terms, and I find this link &lt;a href=&quot;http://forums.qrz.com/showthread.php?139260-Satellite-Tracking-Terms&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://forums.qrz.com/showthread.php?139260-Satellite-Tracking-Terms&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For Max El Azimuth, they say &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Max El Azimuth - this is the maximum height the satellite should reach on this pass, as viewed from your location - a height of 90 degrees would be straight overhead. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I see values higher than 90 on the AMSAT pass tracker online and am confused. And the Maximum elevation says values less than 90 degrees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just to be sure, what exactly is the difference between Maximum Elevation and Maximum El Azimuth?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8573" LastEditDate="2019-12-10T17:07:01.697" LastActivityDate="2019-12-10T17:07:01.697" Title="Max El vs Max El Azimuth" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="1328" PostTypeId="1" CreationDate="2014-01-28T17:48:21.260" Score="1" ViewCount="89" Body="&lt;p&gt;I'm new to satellites and I am trying to find all the information for everything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where can I find a list of all the operational FM amateur satellites with the down-link and up-link frequencies?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, where can I find the list of the ones that are only Beacon Downlink, and other like SSB?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8573" LastEditDate="2019-12-10T17:07:22.867" LastActivityDate="2019-12-10T17:07:22.867" Title="Where to find FM satellite information" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="1329" PostTypeId="2" ParentId="1328" CreationDate="2014-01-28T18:19:46.293" Score="1" Body="&lt;p&gt;Most of the satellites featuring Amateur Radio transmissions and access are listed at &lt;a href=&quot;http://amsat.org&quot; rel=&quot;nofollow&quot;&gt;amsat.org&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also find &lt;a href=&quot;http://en.wikipedia.org/wiki/OSCAR&quot; rel=&quot;nofollow&quot;&gt;a list of operating Amateur Radio satellites&lt;/a&gt; on Wikipedia, and searching their names will bring up sites that show their capability.  There is also a list of Amateur Radio satellites, including cubesats, and on the &lt;a href=&quot;http://www.dk3wn.info/satellites.shtml&quot; rel=&quot;nofollow&quot;&gt;SatBlog&lt;/a&gt; which may prove useful. These two sites are useful primarily because Amsat has occasional database issues.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-01-28T18:19:46.293" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1330" PostTypeId="2" ParentId="1325" CreationDate="2014-01-28T18:58:48.233" Score="2" Body="&lt;p&gt;The AC voltage and current you get from P=IE or Ohm's law in AC circuits are &lt;a href=&quot;http://en.wikipedia.org/wiki/Root_mean_square&quot; rel=&quot;nofollow noreferrer&quot;&gt;RMS&lt;/a&gt; values. I'll explain why.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a constant voltage into a resistor, the power is $P=E^2/R$. That is, power is proportional to the &lt;em&gt;square&lt;/em&gt; of voltage. The same is true for a constant current through a resistor: $P=I^2R$. Either of these equations can be derived by by substituting some arrangement of Ohm's law into $P=IE$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now say you have AC into a resistor. If you want to calculate the power, you can measure the voltage and current at each instant, multiply them together to get power, then average all these instants together to get the mean power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What if you measure just the voltage? Assuming a resistive load, you can still calculate power from voltage measured at some instant by $P=E^2/R$. However, if you simply take the &lt;a href=&quot;http://en.wikipedia.org/wiki/Arithmetic_mean&quot; rel=&quot;nofollow noreferrer&quot;&gt;arithmetic mean&lt;/a&gt; of the voltages at each instant, then try to calculate power with that average, you miss an important fact: doubling the voltage &lt;em&gt;quadruples&lt;/em&gt; the power. RMS is simply a way of averaging voltage that doesn't miss that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can make a simplified example. Let's just consider three instants at which we measured voltage and current into a 50 ohm load:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;voltage  current  power&#xA;1V       0.02A    0.02W&#xA;2V       0.04A    0.08W&#xA;3V       0.06A    0.18W&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;At each of these instants, $P=IE$ and $E/I = 50 \Omega$. Let's calculate some different kinds of averages:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;P_{mean} &amp;amp;= \frac{0.02 + 0.08 + 0.18}{3} &amp;amp;\approx 0.0933\mathrm{W} \\&#xA;V_{mean} &amp;amp;= \frac{1+2+3}{3} &amp;amp;= 2\mathrm{V} \\&#xA;V_{RMS} &amp;amp;= \sqrt{\frac{1^2 + 2^2 + 3^2}{3}} &amp;amp;\approx 2.16\mathrm{V} \\&#xA;I_{mean} &amp;amp;= \frac{0.02 + 0.04 + 0.06}{3} &amp;amp;= 0.04\mathrm{A} \\&#xA;I_{RMS} &amp;amp;= \sqrt{\frac{0.02^2 + 0.04^2 + 0.06^2}{3}} &amp;amp;\approx 0.0432\mathrm{A} \\&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now then, for which of these does $P=IE$ hold?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;V_{mean} I_{mean} &amp;amp;= 2\mathrm{V} \cdot 0.04\mathrm{A} &amp;amp;= 0.08\mathrm{W} &amp;amp;\text{   wrong!} \\&#xA;V_{RMS} I_{RMS} &amp;amp;= 2.16\mathrm{V} \cdot 0.0432\mathrm{A} &amp;amp;= 0.0933\mathrm{W} &amp;amp;\text{   correct!}&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are right that if you want to know the peak current your amplifier will need to supply, you need to convert this RMS value to something else. However, you got it backwards: $V_p = \sqrt{2} V_{RMS}$. So for the example above, your amplifier would be required to supply $\sqrt{2} \cdot 2.16\mathrm{V} = 3.05\mathrm{V}$ peak. Being AC, it would have to supply up to +3.05V and also down to -3.05V. Thus, the &lt;em&gt;peak to peak&lt;/em&gt; amplitude is 6.10V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Same math applies to current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that this math of converting between peak and RMS values with $\sqrt{2}$ only applies to &lt;em&gt;sine waves&lt;/em&gt;, which our example wasn't, so there was some wrongness there. However in radio, our transmissions are close enough to sine waves that assuming they are is usually a good enough approximation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note also that being able to RMS averages in equations like $P=IE$ or $P=I^2R$ only works for &lt;em&gt;resistive&lt;/em&gt; loads. It works for &lt;em&gt;reactive&lt;/em&gt; loads if what you care about is &lt;a href=&quot;http://en.wikipedia.org/wiki/AC_power#Real.2C_reactive.2C_and_apparent_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;apparent power and not real power&lt;/a&gt;, and it &lt;a href=&quot;https://electronics.stackexchange.com/a/97904/17608&quot;&gt;doesn't work at all for &lt;em&gt;non-linear&lt;/em&gt; loads&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2014-01-28T19:26:24.433" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1331" PostTypeId="2" ParentId="1327" CreationDate="2014-01-28T19:22:17.587" Score="2" Body="&lt;p&gt;That forum is bogus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Date&lt;/strong&gt; - Pretty obvious. The day the pass happens.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;AOS&lt;/strong&gt; - Acquisition of signal. This is the time of day at which the satellite first rises above the horizon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Duration&lt;/strong&gt; - This is simply the time between AOS and LOS, ie, for how long the satellite is visible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;AOS Azimuth&lt;/strong&gt; - The direction at which the satellite first becomes visible, in degrees to the right of North. 0 or 360 is North, 90 is East, 180 is South, and 270 is West.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Maximum Elevation&lt;/strong&gt; - How high the satellite will appear to go in the sky, in degrees above horizon. 0 is the horizon. 90 is directly overhead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Max El Azimuth&lt;/strong&gt; - &quot;Maximum Elevation Azimuth&quot;. This is the direction at which maximum elevation occurs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;LOS Azimuth&lt;/strong&gt; - The direction at which the satellite ceases to be visible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;LOS&lt;/strong&gt; - Loss of signal. The time of day at which the satellite goes below the horizon and the pass ends.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-01-29T14:57:12.120" LastActivityDate="2014-01-29T14:57:12.120" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1332" PostTypeId="1" AcceptedAnswerId="1333" CreationDate="2014-01-28T20:49:47.533" Score="4" ViewCount="644" Body="&lt;p&gt;Currently my 2m antenna is about 3m above the ground inside, my HF antenna is connected to 30m (2db loss) coax and is about 12m up. Since the loss for 2m is a lot more when traveling down such a long piece of coax will moving my 2m antenna to the same mast as the HF antenna be worth the gain in height?&lt;/p&gt;&#xA;" OwnerUserId="135" LastActivityDate="2014-01-30T00:57:14.737" Title="Height and feedline loss tradeoff for VHF" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;&lt;vhf&gt;&lt;transmission-line&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1333" PostTypeId="2" ParentId="1332" CreationDate="2014-01-28T21:33:27.957" Score="3" Body="&lt;p&gt;I'm not a feed line guru, but I'm not sure your question as its worded now has an academicly &quot;correct&quot; answer anyway as it's a matter of owner preference and local conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should clarify what you want from your VHF setup. If you can already effectively work all your local repeaters and are not concerned with simplex coverage, then maybe it won't be worth relocating your VHF antenna for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are concerned about simplex coverage for emergency use when repeaters could be down, then the height improvement may be worth any potential feed line loss to you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your living conditions or significant other require you to move the antenna for space/placement reasons, the top of the tower may be nice and out of the way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will need to weigh these benefits and costs against your desired performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course if you are running inexpensive feed line with your VHF antenna &lt;em&gt;indoors&lt;/em&gt;, moving it outside with good quality feed line may not cost you anything more than you are already losing with the antenna indoors! So its just a matter of cash and time to mount it right.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT After comments:&lt;/strong&gt; Taking into account your clarification in the comments above, I would say getting the antenna outdoors and replacing the &quot;car kit&quot; feed line with quality low loss feed line will likely give you an all around better setup. &lt;a href=&quot;http://www.arrl.org/feed-lines&quot; rel=&quot;nofollow&quot;&gt;ARRL seems to recommend Belden 9913 or LMR-400&lt;/a&gt;. &quot;For base stations in particular, always buy the lowest-loss coax you can afford.&quot; - from that same ARRL page.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen more than a few people put a VHF vertical above the apex of a dipole on a tower. But hopefully someone more knowledgeable than I can advise on a recommended minimum separation distance. If you can keep the vertical a few feet above the dipole that will help reduce any interaction between them. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whatever separation distance you can achieve, I'd be pretty confident your setup will improve getting your antenna outside with better feedline.&lt;/p&gt;&#xA;" OwnerUserId="608" LastEditorUserId="608" LastEditDate="2014-01-28T21:51:18.870" LastActivityDate="2014-01-28T21:51:18.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1334" PostTypeId="2" ParentId="1332" CreationDate="2014-01-28T22:00:35.423" Score="2" Body="&lt;p&gt;Usually, higher is better, assuming you are using coax that isn't exceptionally lossy. At VHF, this will be something other than the cheapest coax you can buy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, that's the most accurate answer you can get here, because the benefit of additional height depends on a lot of things about your environment that we don't know. Are there buildings in the way? Trees? What are ground conditions like around your location? What's the height of the other antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best height will be the one where coax loss + path loss are at a minimum. Calculating  the coax loss is easy: read the datasheet. Calculating path loss not feasible, but you can measure it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Put your antenna on a piece of coax long enough to reach to your highest height considered. Mount the antenna down low. Go far away. Make a test transmission. Measure the received signal strength. Now move the antenna up higher and repeat. Now you know what you stand to gain by putting the antenna higher. Compare that to what you will lose, calculated from the coax specifications, and you will know if higher is better.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-01-28T22:00:35.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1335" PostTypeId="2" ParentId="1314" CreationDate="2014-01-28T22:29:41.707" Score="2" Body="&lt;p&gt;Amateur radio operators still use Morse Code, as do a few other government services, such as aviation beacons, etc.  These Morse Code signals are usually just encoded text (roughly related to other text encoding schemes such as ACSII or Braille).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Morse code allows an extremely simple on-off transmission scheme (about as simple a modulation as can be done).  Letters and numbers can be encoded into sequences of long and short on-off signals, each character having a specific pattern in time.  Originally it was thought that these time sequences would have to be graphically charted out and read, or translated by some sort of machine.  But it turned out that after hearing it for awhile (and learning the distinctive sound of each letter) telegraph and radio operators could understand (and type out for telegrams, etc.) the Morse Code encoded messages just by listening to the relay ticks or the radio sidetones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, yes, if you learn what all the letters sound like (fast enough, which takes a bit of practice), you might be able to understand the message just by listening.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-01-28T22:29:41.707" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1336" PostTypeId="1" AcceptedAnswerId="1337" CreationDate="2014-01-29T00:31:12.807" Score="21" ViewCount="4524" Body="&lt;p&gt;As a relatively new ham operator, I understand that it is customary to use lower-sideband below 10 MHz and upper-side band above 10Mhz when operating single-sideband HF. I'm curious how we got to such a standard instead of just picking one or the other for all bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To further complicate it for new hams, it seems that RTTY operators use lower-sideband everywhere and PSK operators use upper-sideband everywhere. (&lt;a href=&quot;http://www.brats-qth.org/training/advanced/operate5.htm&quot; rel=&quot;noreferrer&quot;&gt;Reference&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any technical reason not to use upper-sideband everywhere? Or is this purely tradition to be passed on for the sake of tradition? Does anyone know some verifiable history for how this de-facto standard came to be?&lt;/p&gt;&#xA;" OwnerUserId="608" LastEditorUserId="4076" LastEditDate="2019-01-13T12:12:27.297" LastActivityDate="2019-01-13T12:12:27.297" Title="Why do we use LSB below 10 MHz and USB above 10 MHz when operating SSB HF?" Tags="&lt;hf&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="1337" PostTypeId="2" ParentId="1336" CreationDate="2014-01-29T02:35:42.063" Score="18" Body="&lt;p&gt;Amateur Radio operators use this rule of thumb for historical technical reasons. &lt;a href=&quot;http://forums.qrz.com/archive/index.php/t-312177.html&quot;&gt;SM0AOM on the QRZ forums writes&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The changing of ISB sideband positions at 10 MHz actually has an engineering background.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;In the earliest ISB exciters, it was found appropriate to change the final mixer scheme from subtraction to&#xA;  addition mixing at around 10 MHz due to spurious suppression concerns.&#xA;  This sometimes caused interoperability problems in international point-to-point ISB circuits.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;To overcome this, a practice was formalized in 1959 by the ITU/CCIR as the Recommendation 249, which prescribed&#xA;  that the ISB sideband positions could either automatically or manually be interchanged when the output frequency went through&#xA;  10 MHz. An often quoted reference where ISB exciter design considerations are handled with German thoroughness is&#xA;  W Kleische: &quot;Fernbedienbarer Steuervorsatz für Kurzwellen-Nachrichtensender&quot; in &quot;Telefunken-Zeitung&quot; December 1962.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Later advances in exciter design made this Recommendation obsolete, and later generations of exciters only had this facility as an option, and current production ISB equipment lacks it entirely.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9" LastEditorUserId="218" LastEditDate="2014-01-29T03:57:10.407" LastActivityDate="2014-01-29T03:57:10.407" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1338" PostTypeId="2" ParentId="1314" CreationDate="2014-01-29T02:43:41.987" Score="2" Body="&lt;p&gt;QRP (low power) is a challenging area of amateur radio that uses morse code -- mainly because every bit of signal strength matters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CW makes very efficient use of the available power, compared to some other modes.&lt;/p&gt;&#xA;" OwnerUserId="134" LastActivityDate="2014-01-29T02:43:41.987" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1340" PostTypeId="2" ParentId="1332" CreationDate="2014-01-29T17:12:16.177" Score="2" Body="&lt;p&gt;Some possible solutions would be:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Get better feedline, like &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B0013REMTE&quot; rel=&quot;nofollow&quot;&gt;LMR400&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Get an &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B0002NRKM6&quot; rel=&quot;nofollow&quot;&gt;LNA&lt;/a&gt;, this is a special amplifier that sits between your antenna and feedline and is powered by a supply at the other end of the feedline.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;http://www.kuhne-electronic.de/en/products/transverter.html&quot; rel=&quot;nofollow&quot;&gt;Transverter&lt;/a&gt;. A transverter will take for instance a 10m signal and convert it to 6m and vice-versa. You see these a lot in the GHz spectrum, as installing waveguide or LMR1200 is not practical.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="659" LastEditorUserId="218" LastEditDate="2014-01-30T00:57:14.737" LastActivityDate="2014-01-30T00:57:14.737" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1341" PostTypeId="2" ParentId="1270" CreationDate="2014-01-29T17:19:40.637" Score="4" Body="&lt;p&gt;If it continues to happen I would report it to the FCC via the FCC's website here.&#xA;&lt;a href=&quot;http://www.fcc.gov/complaints&quot; rel=&quot;nofollow&quot;&gt;http://www.fcc.gov/complaints&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="659" LastActivityDate="2014-01-29T17:19:40.637" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1342" PostTypeId="2" ParentId="1185" CreationDate="2014-01-29T17:29:06.150" Score="1" Body="&lt;p&gt;For 2013 looks like EU7KQ Nikolai Gelyasevich with a score of 297&lt;/p&gt;&#xA;&#xA;&lt;p&gt;source &lt;a href=&quot;http://www.hst2013.eu/TX.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.hst2013.eu/TX.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="659" LastActivityDate="2014-01-29T17:29:06.150" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1343" PostTypeId="2" ParentId="919" CreationDate="2014-01-29T17:41:58.843" Score="5" Body="&lt;p&gt;As explained by &lt;a href=&quot;http://www.antenna-theory.com/antennas/foldeddipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna-theory.com&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/s8QS4.jpg&quot; alt=&quot;Figure 1&quot;&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Typically, the width d of the folded dipole antenna is much smaller than the length L.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Because the folded dipole forms a closed loop, one might expect the input impedance to depend on the input impedance of a short-circuited transmission line of length L. However, you can imagine the folded dipole antenna as two parallel short-circuited transmission lines of length L/2 (separated at the midpoint by the feed in Figure 1). It turns out the impedance of the folded dipole antenna will be a function of the impedance of a transmission line of length L/2.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Also, because the folded dipole is &quot;folded&quot; back on itself, the currents can reinforce each other instead of cancelling each other out, so the input impedance will also depend on the impedance of a dipole antenna of length L.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Letting Zd represent the impedance of a dipole antenna of length L and Zt represent the impedance of a transmission line impedance of length L/2, which is given by:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/jFJ5e.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The input impedance ZA of the folded dipole is given by:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Yd1i9.jpg&quot; alt=&quot;enter image description here&quot;&gt; Folded Dipole Impedance&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The folded dipole antenna is resonant and radiates well at odd integer multiples of a half-wavelength (0.5 wavelength, 1.5 wavelength ...), when the antenna is fed in the center as shown in Figure 1. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The folded dipole antenna can be made resonant at even multiples of a half-wavelength ( 1.0 wavelength, 2.0 wavelength...) by offsetting the feed of the folded dipole in Figure 1 (closer to the top or bottom edge of the folded dipole).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="659" LastEditorUserId="218" LastEditDate="2014-12-16T16:05:16.470" LastActivityDate="2014-12-16T16:05:16.470" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1344" PostTypeId="1" CreationDate="2014-01-29T18:01:11.317" Score="4" ViewCount="371" Body="&lt;p&gt;I am looking for a repository (SVN ect) of modern Amateur transceiver schematics.&#xA;Most of the designs you can find with a simple Google search either use tubes, or now obsolete and hard to find components.&lt;/p&gt;&#xA;" OwnerUserId="659" LastActivityDate="2014-02-14T00:48:57.530" Title="Is there a repository of modern Amateur Radio transceiver schematics?" Tags="&lt;transceiver&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ClosedDate="2014-02-22T12:22:15.787" ContentLicense="CC BY-SA 3.0" />
  <row Id="1345" PostTypeId="1" AcceptedAnswerId="1347" CreationDate="2014-01-29T18:17:03.347" Score="2" ViewCount="396" Body="&lt;p&gt;I live 7.8 kilometers birds eye view from my friends house. We are in Denver, so there may be a bit of terrain but should be relatively flat. There are a few trees, and houses and maybe a few buildings between us. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the best practical antenna system to simplex on the 2 meter from my house to his? Would something like a Yagi be good?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it even possible to get a signal through a few houses and trees? Currently, I use an ht with rubber duck to hit repeaters on the mountains west, but I wanted to see if we could get simplex. My friend has a 50w 2m rig and I'm probably getting one of those soon also&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2014-01-30T12:11:13.557" LastActivityDate="2014-01-30T12:11:13.557" Title="Practical antenna for 2m line-of-sight over 7 km" Tags="&lt;simplex&gt;&lt;2m-band&gt;&lt;line-of-sight&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2014-02-27T04:36:03.160" ContentLicense="CC BY-SA 3.0" />
  <row Id="1346" PostTypeId="1" AcceptedAnswerId="1349" CreationDate="2014-01-29T18:20:00.123" Score="4" ViewCount="131" Body="&lt;p&gt;So I've heard every once and a while you have to update your satellite tracking software because of the fact that the satellites are falling towards Earth. Why can't the program automatically calculate every factor in so it doesn't have to update it?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="218" LastEditDate="2014-01-30T00:47:15.070" LastActivityDate="2014-01-30T10:57:12.367" Title="Why do satellite tracking programs have to be updated?" Tags="&lt;satellites&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1347" PostTypeId="2" ParentId="1345" CreationDate="2014-01-29T19:03:38.817" Score="3" Body="&lt;p&gt;You should have no problems doing 7 km with a (presumably 5W) HT even with the rubber duck antenna, outside.  If you wanted to talk from inside, you will probably want an exterior antenna, but almost any common 2m antennas will do the job.  A simple J pole is popular, you could even use a mobile antenna sited out a window.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-01-29T19:03:38.817" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1349" PostTypeId="2" ParentId="1346" CreationDate="2014-01-30T00:29:24.357" Score="4" Body="&lt;p&gt;You must update the orbital elements that your satellite tracking software uses to predict the location of satellites in order to get continued accuracy in the predictions.  Sometimes the orbital elements are not known exactly for a new or relatively unimportant satellite.  More importantly, the orbital elements can and will change over time.  Low earth orbit satellites will slow down due to friction from the remnants of atmosphere at their altitude.  All satellites will have their orbits affected by the gravitational influence of other bodies.  Although the principal gravitational effects will be from the Earth, Moon and Sun, other objects will also influence the orbit.&lt;/p&gt;&#xA;" OwnerUserId="355" LastActivityDate="2014-01-30T00:29:24.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1351" PostTypeId="2" ParentId="1346" CreationDate="2014-01-30T06:27:08.043" Score="2" Body="&lt;p&gt;Some of the factors, such as friction against the upper atmosphere, can have the same sort of predictive problems as with lower weather prediction (non-linear dynamical &quot;chaos&quot;, or sensitivity to initial conditions that is well beneath measurement error).  A satellite in orbit is also part of an N-body system, which does not have a clean closed form trajectory solution.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-01-30T06:27:08.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1352" PostTypeId="1" AcceptedAnswerId="1360" CreationDate="2014-01-30T10:49:33.230" Score="12" ViewCount="2924" Body="&lt;p&gt;Many different countries have different callsign formats. The US call signs typically fit into a very well defined category, but there are exceptions even there. I'm looking for a way to tell if a call sign is a real call sign, that works with international call signs. I'm looking for the full call sign, including after a '/'. I don't care if the call sign is actually assigned to a user, just if it is possible to assign the call to a user. I'm looking for rules as to what would be considered valid. A very general sense is okay too. I don't care if I filter something that could be a call sign, but isn't actually assigned, like &lt;code&gt;1S&lt;/code&gt; prefix calls, but I do want to make sure I get special edge cases, like &lt;code&gt;W100AW&lt;/code&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I can tell, the format that is valid appears to include a prefix, which can include up to 1 number and always includes 1 or 2 letters, followed by a number identifier, followed by 1-3 letters. An additional part of the call sign can be included before or after the call that can include a lot of things, including a &lt;code&gt;/AE&lt;/code&gt;,&lt;code&gt;/AG&lt;/code&gt;,&lt;code&gt;/KH6&lt;/code&gt; (Or other prefix), and possibly other things as well, which I'm not really certain of. I'm looking for something like this, but preferably more detailed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, I'm trying to tell if a callsign is likely to be real, so I can check to see if I have an invalid call sign in my logging program. &lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-01-30T13:56:35.943" LastActivityDate="2020-05-15T20:01:45.480" Title="How can I tell if a call sign is valid?" Tags="&lt;callsign&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1353" PostTypeId="2" ParentId="1346" CreationDate="2014-01-30T10:57:12.367" Score="5" Body="&lt;p&gt;There are at least 4 significant things that make satellites difficult to exactly determine:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The position and velocity of a satellite is only known at any one time with a finite precision. Without a perfect knowledge of where the satellite is and how fast it's moving, it's impossible to know where it will be in the future.&lt;/li&gt;&#xA;&lt;li&gt;The atmosphere is quite uncertain, sometimes it will drag more, other times drag less. The amount depends on the amount of solar activity. Also, the drag depends on the orientation of the spacecraft, so an anomaly in the spacecraft pointing can cause problems in determining where it is.&lt;/li&gt;&#xA;&lt;li&gt;There are complex gravitational factors that can influence where the spacecraft is. These are very difficult to program in.&lt;/li&gt;&#xA;&lt;li&gt;Thrusting, either in the form of an active propulsion from the spacecraft, or being hit by space debris or other objects, can cause problems.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Bottom line, it's just a hard problem to figure out, and it's much easier to get periodic updates to the satellite positions. But if you can't get them for a while, you should be fine for a period of time, several weeks at least. If you can't get them in that period of time, then your best bet is to try listening for the W1AW broadcasts, which give out the amateur satellite element sets.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-01-30T10:57:12.367" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1354" PostTypeId="5" CreationDate="2014-01-30T12:12:01.360" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-30T12:12:01.360" LastActivityDate="2014-01-30T12:12:01.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1355" PostTypeId="4" CreationDate="2014-01-30T12:12:01.360" Score="0" Body="Use this tag for questions relating specifically to the amateur radio VHF allocation around 144 MHz." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-30T12:12:01.360" LastActivityDate="2014-01-30T12:12:01.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1356" PostTypeId="5" CreationDate="2014-01-30T12:18:41.013" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-30T12:18:41.013" LastActivityDate="2014-01-30T12:18:41.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1357" PostTypeId="4" CreationDate="2014-01-30T12:18:41.013" Score="0" Body="Simplex refers to the transmission and reception on the same frequency, or using a single carrier (such as a cable). Also consider the line-of-sight tag." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-30T12:18:41.013" LastActivityDate="2014-01-30T12:18:41.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1358" PostTypeId="5" CreationDate="2014-01-30T12:20:16.897" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-30T12:20:16.897" LastActivityDate="2014-01-30T12:20:16.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1359" PostTypeId="4" CreationDate="2014-01-30T12:20:16.897" Score="0" Body="Use this tag for questions specifically about line of sight communications, as opposed to communications using active or passive reflectors (repeaters, meteor scatter, ionospheric propagation, etc.). Line of sight is the normal propagation mode on VHF and up, where on HF ionospheric propagation is normally used." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-01-30T12:20:16.897" LastActivityDate="2014-01-30T12:20:16.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1360" PostTypeId="2" ParentId="1352" CreationDate="2014-01-30T17:29:08.237" Score="12" Body="&lt;p&gt;Callsigns, per ITU regulations, consist of a prefix and a suffix.  The prefix must be obtained from this table:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.itu.int/online/mms/glad/cga_callsign.sh?lng=E&quot;&gt;Table of International Call Sign Series (Appendix 42 to the RR)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And is assigned on a per-country basis.  The suffix is then determined by that country's internal radio regulations, and there is no standard that will make this easy for you.  You'll need to research each country's regulation and standard and include hundreds of different rules if you need to determine validity to that degree.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you can eliminate a lot of bad callsigns simply by verifying that the prefix is valid, using the above list.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The general guidelines on the formation of a whole callsign, including what the suffix may contain, are fairly well explained in this wikipedia article:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/ITU_prefix_-_amateur_and_experimental_stations&quot;&gt;ITU prefix (amateur stations)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are rare exceptions, but generally you start with the country prefix, add a numeral, then add a suffix of between 1 and 4 alphanumeric characters. The last character has to be a letter, not a number, but otherwise there's no regulation internationally.  &lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2014-01-30T17:40:58.917" LastActivityDate="2014-01-30T17:40:58.917" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1362" PostTypeId="2" ParentId="1352" CreationDate="2014-01-30T22:37:50.330" Score="2" Body="&lt;p&gt;Starting with Adam's answer, I did a bit of research into the matter. Using a list of &lt;a href=&quot;http://wd5eae.org/HB9BZA_LoTWUsersList.html&quot; rel=&quot;nofollow&quot;&gt;LOTW call signs&lt;/a&gt;, I tried the following regular expression &lt;code&gt;\d?[a-zA-Z]{1,2}\d{1,4}[a-zA-Z]{1,4}&lt;/code&gt;, which simply says a number can optionally start, followed by 1 or 2 letters, followed by 1-4 numbers, and 1-4 letters. I'm filtering out any extra parts (Stuff before and after a &lt;code&gt;/&lt;/code&gt;. Given this, I still failed on the following call signs:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;4D71/N0NM&#xA;4X130RISHON&#xA;9N38&#xA;AX3GAMES&#xA;BV100&#xA;DA2MORSE&#xA;DB50FIRAC&#xA;DL50FRANCE&#xA;FBC5AGB&#xA;FBC5CWU&#xA;FBC5LMJ&#xA;FBC5NOD&#xA;FBC5YJ&#xA;FBC6HQP&#xA;GB50RSARS&#xA;HA80MRASZ&#xA;HB9STEVE&#xA;HG5FIRAC&#xA;HG80MRASZ&#xA;II050SCOUT&#xA;IP1METEO&#xA;J42004A&#xA;J42004Q&#xA;LM1814&#xA;LM2T70Y&#xA;LM9L40Y&#xA;LM9L40Y/P&#xA;OEM2BZL&#xA;OEM3SGU&#xA;OEM3SGU/3&#xA;OEM6CLD&#xA;OEM8CIQ&#xA;OM2011GOOOLY&#xA;ON1000NOTGER&#xA;ON70REDSTAR&#xA;PA09SHAPE&#xA;PA65VERON&#xA;PA90CORUS&#xA;PG50RNARS&#xA;PG540BUFFALO&#xA;S55CERKNO&#xA;TM380&#xA;TX9&#xA;TYA11&#xA;U5ARTEK/A&#xA;V6T1&#xA;VI2AJ2010&#xA;VI2FG30&#xA;VI4WIP50&#xA;VU3DJQF1&#xA;VX31763&#xA;WD4&#xA;XUF2B&#xA;YI9B4E&#xA;YO1000LEANY&#xA;ZL4RUGBY&#xA;ZS9MADIBA&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;So I guess there isn't a standard definition, but you should be able to recognize most of them with a similar pattern, and just be aware that there are others out there as well.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-01-30T23:19:55.633" LastActivityDate="2014-01-30T23:19:55.633" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1363" PostTypeId="1" AcceptedAnswerId="1364" CreationDate="2014-01-31T16:05:15.037" Score="10" ViewCount="2693" Body="&lt;p&gt;I understand what a mixer does, and when I see it in a block diagram it's obvious what purpose it serves and how it fits in the overall design of the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, when I look at the schematics and see how it's created, I don't understand how it works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the purposes of this question, I'm referring to only a switching mixer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/YfBrV.gif&quot; alt=&quot;Schematic representation of a switching mixer.  RF is brought to a switch which can choose the RF directly, or the RF inverted (180 degrees out of phase), where the LO controls the switch.&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does switching between the RF and the inverted RF at the LO frequency accomplish $RF \cdot LO$?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2014-01-31T23:35:58.500" LastActivityDate="2014-01-31T23:35:58.500" Title="How does a switching mixer multiply the two signals?" Tags="&lt;theory&gt;&lt;electronics&gt;&lt;mixer&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1364" PostTypeId="2" ParentId="1363" CreationDate="2014-01-31T17:09:36.860" Score="8" Body="&lt;p&gt;Switching to the inverted signal is equivalent to multiplying by -1. While in an ideal mixer, the RF input can be multiplied by a sinusoidal LO, the switching mixer multiplies by a square LO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It still works as any mixer would. That is, for each frequency component in the first input $f_1$, and each frequency component in the second input $f_2$, it produces at the output frequency components $f_1 + f_2$ and $f_1 - f_2$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, because the LO input must be a square wave (if it's not, the gain of the switching mixer's LO input will make it so), the frequency components of that input are the LO frequency, &lt;a href=&quot;http://en.wikipedia.org/wiki/Square_wave#Examining_the_square_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;plus all its odd harmonics&lt;/a&gt;. These must be removed with filtering somewhere up or down the line to avoid undesired mixing products. The advantage is that frequently it's easier to make a good switching mixer with a good filter than it is to make an ideal mixer that produces exactly $RF\cdot LO$ for arbitrary inputs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a related question on Electrical Engineering.SE: &lt;a href=&quot;https://electronics.stackexchange.com/q/97322/17608&quot;&gt;Can I input a square wave LO into a mixer?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2014-01-31T18:26:17.187" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1365" PostTypeId="1" AcceptedAnswerId="1366" CreationDate="2014-01-31T18:55:48.940" Score="8" ViewCount="782" Body="&lt;p&gt;I'm currently an ARRL member, and a volunteer examiner under the ARRL/VEC.  I find myself needing to cut back on expenses this year and may end up dropping the ARRL membership.  If I do so, am I still a valid examiner under the ARRL/VEC?  If so, will I also be able to renew with ARRL/VEC when my renewal date comes up?&lt;/p&gt;&#xA;" OwnerUserId="102" LastActivityDate="2014-01-31T19:06:50.447" Title="Would I still be a valid volunteer examiner?" Tags="&lt;license&gt;&lt;arrl&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1366" PostTypeId="2" ParentId="1365" CreationDate="2014-01-31T19:06:50.447" Score="6" Body="&lt;p&gt;According to the current &lt;a href=&quot;http://www.arrl.org/files/file/VEs/VE%20Manual%20Web%20FINAL%202013.pdf&quot; rel=&quot;noreferrer&quot;&gt;Volunteer Examiner manual from ARRL&lt;/a&gt;, you can meet the requirements without becoming an ARRL member, and your VE status is only affected by your license status:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;As a Volunteer Examiner (VE), you are the gatekeeper to the integrity of the Volunteer Examiner Program. To that end, you must have certain qualifications and be accredited by a Volunteer Examiner Coordinator.&lt;/p&gt;&#xA;&lt;p&gt;To qualify to be a Volunteer Examiner, you must:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;be 18 years of age or older; and&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;never have had your amateur station or operator licenses suspended or revoked; and&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;hold a valid General, Advanced or Extra Class license.[97.509]&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;If you meet these criteria, the ARRL/VEC would like to hear from you. To be accredited by the ARRL/VEC, you must complete a training program. Examiners may be accredited by more than one VEC. VEs are not required to work with only one VE Team or VEC and are not restricted to any particular area. A VEC does not have to accept the services of a VE if it&#xA;does not want to.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Further, even if there were such a requirement to become one, it doesn't expire on any other basis except that of your FCC license:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Once accredited as an examiner in the ARRL/VEC’s program, your accreditation credentials will be good until your FCC license expires. Your accreditation is valid at any ARRL/VEC coordinated session.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I expect that as it is a voluntary position through the FCC granted by an act of congress, they can't make membership in their organization a requirement to be accredited by them.  &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=licensing_5&amp;amp;id=amateur&quot; rel=&quot;noreferrer&quot;&gt;You can be accredited by another VEC&lt;/a&gt;, though, if the ARRL terms don't meet your needs.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-01-31T19:06:50.447" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1367" PostTypeId="1" CreationDate="2014-01-31T20:46:05.440" Score="13" ViewCount="1011" Body="&lt;p&gt;Going through a number of schematics for today's receivers (Elecraft KX3, for example) I note that most use LC circuits for filtering.  The &lt;a href=&quot;http://en.wikipedia.org/wiki/Crystal_filter&quot;&gt;wikipedia article for Crystal Filters&lt;/a&gt; suggests, however, that crystal filters are used in high quality receivers:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A crystal filter is very often found in the intermediate frequency (IF) stages of high-quality radio receivers. Cheaper sets may use ceramic filters ... or tuned LC circuits.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What are the disadvantages of crystal filters that make LC filters more popular for amateur radio transceivers?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="29" LastEditDate="2014-02-14T14:32:48.293" LastActivityDate="2019-07-31T18:44:54.223" Title="Why do today's transceivers use LC filters rather than crystal filters?" Tags="&lt;equipment-design&gt;&lt;filter&gt;" AnswerCount="4" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1368" PostTypeId="1" AcceptedAnswerId="1370" CreationDate="2014-01-31T20:59:42.913" Score="5" ViewCount="1191" Body="&lt;p&gt;I'd like to be able to provide my kids with the opportunity to build something a little better than a passive crystal set, but still very, very simple in terms of individual electronic parts count.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems to me that a CW receiver should be the easiest type to build, if I'm incorrect and an AM is easier, or just as easy, let me know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What is the lowest parts count receiver one can build that covers some portion of the HF spectrum likely to have CW signals in it?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd prefer low cost parts, but low parts count is still the most important requirement.  Ideally it could be breadboarded, but point to point wiring is fine. It doesn't have to be great audio quality, or even very selective and immune to noise.  It just needs to be able to pick up enough of a signal that a careful listener will notice the CW in the static.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is there a receiver design that needs 20 parts or less? 10 parts? Fewer?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2015-12-02T07:08:58.293" Title="Low parts count CW HF receiver?" Tags="&lt;diy&gt;&lt;receiver&gt;&lt;education&gt;&lt;outreach&gt;" AnswerCount="2" CommentCount="12" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1369" PostTypeId="2" ParentId="471" CreationDate="2014-02-01T17:12:51.670" Score="3" Body="&lt;p&gt;Apart from Licensing, CW is required for using some specific frequencies.  For a U.S. list of such frequencies see this ARRL page: &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/band-plan&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="669" LastEditorUserId="63" LastEditDate="2014-02-01T21:41:02.397" LastActivityDate="2014-02-01T21:41:02.397" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1370" PostTypeId="2" ParentId="1368" CreationDate="2014-02-01T18:14:26.140" Score="3" Body="&lt;p&gt;For CW, a simple regenerative receiver will produce an audio sidetone.  Such radios were actually usable and used by radio hobbyists to receive HF CW.  So I would search for a design of a 2 transistor regenerative receiver (2nd transistor used to isolate or drive some headphones) in vintage hobby electronic magazines and kits dating from the earliest decade of the availability of transistors to hobbyists.  Probably somewhere between 10 and 20 parts, depending on how you count them.  You might have to wind your own inductor coil(s).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-02-01T19:03:52.973" LastActivityDate="2014-02-01T19:03:52.973" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1371" PostTypeId="1" CreationDate="2014-02-03T02:30:13.593" Score="5" ViewCount="314" Body="&lt;p&gt;So, I know people in the space station need a HAM radio license for operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How Far exactly from earth do you have to be to transmit any RF wave you want without a license?  &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="13" LastEditDate="2014-02-03T16:22:07.427" LastActivityDate="2014-02-05T00:49:39.880" Title="How far from earth do FCC regulations apply?" Tags="&lt;legal&gt;&lt;satellites&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1372" PostTypeId="1" AcceptedAnswerId="1378" CreationDate="2014-02-03T02:31:40.167" Score="2" ViewCount="234" Body="&lt;p&gt;I am a 15 year old ham, and just got my Extra class. I was really bummed when I figured out I needed to be 18 to be a Volunteer Examiner administer. Why do they make that rule?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="218" LastEditDate="2014-02-03T23:56:53.300" LastActivityDate="2014-04-30T05:04:06.557" Title="Why do you have to be 18 to be a Volunteer Examiner in the US?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;volunteer-examiners&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1373" PostTypeId="1" CreationDate="2014-02-03T02:49:09.783" Score="1" ViewCount="2839" Body="&lt;p&gt;Here is what I have&lt;/p&gt;&#xA;&#xA;&lt;p&gt;• A Baofeng Uv-82 transceiver&lt;/p&gt;&#xA;&#xA;&lt;p&gt;• A 1/2 inch 10 foot PVC pipe&lt;/p&gt;&#xA;&#xA;&lt;p&gt;• 3 1/4 inch x 36 inch Aluminum rods&lt;/p&gt;&#xA;&#xA;&lt;p&gt;• 2 1/4 inch x 48 inch Steel rods (I know they'll rust, it's just temporary to get it to work, I'll get aluminum later)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have any coaxial cable (don't know the best type to get) and don't know how to match the impedance of the cable to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what is everything else I need, and instructions on how to get this built and working. I'm sorry if I'm asking for too much, and I don't want to ask for you to &quot;design&quot; an antenna for me, I just want a bit of help. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/6J6g0.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorDisplayName="user4168" LastEditDate="2019-01-23T00:56:48.723" LastActivityDate="2019-01-23T00:56:48.723" Title="Homebrew 2 meter Yagi construction" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="1374" PostTypeId="2" ParentId="1371" CreationDate="2014-02-03T11:31:05.540" Score="6" Body="&lt;p&gt;Strictly speaking, there are &lt;a href=&quot;http://classwww.gsfc.nasa.gov/gsams/greet_spectrumAllocationSummary.htm#Deep&quot; rel=&quot;nofollow&quot;&gt;3 categories of allocations&lt;/a&gt; for space missions, depending on what you are doing. And the laws never go away, although the enforcement might go away after a distance. The 3 categories are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Near Earth Communication- I can't find a specific definition, but this appears to be anything closer than the moon, or that orbits the moon. This does include Geostationary satellites.&lt;/li&gt;&#xA;&lt;li&gt;Deep Space Communication- For two way communication in deep space.&lt;/li&gt;&#xA;&lt;li&gt;Sensors in deep space- These frequencies can be used for sensors in deep space, but should not be used for communication with Earth.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Bottom line is, only the ability to enforce law allows one to get away from the international law concerning spectrum allocation. If you plan on communicating with Earth, either one or two way, you are subject to the laws of the location where you are talking with, which follows ITU law. There are looser restrictions if you never plan on communicating with Earth, however, and these probably won't be enforced. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the United States, the FCC requires the following &lt;a href=&quot;http://www.hallikainen.com/FccRules/2014/25/113/index.php&quot; rel=&quot;nofollow&quot;&gt;(25.113 g)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(g) Except as set forth in paragraph (h) of this section, a launch &#xA;  authorization and station license (i.e., operating authority) must be &#xA;  applied for and granted before a space station may be launched and&lt;br&gt;&#xA;  operated in orbit. Request for launch authorization may be included in&#xA;  an application for space station license.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-02-05T00:49:39.880" LastActivityDate="2014-02-05T00:49:39.880" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1375" PostTypeId="1" AcceptedAnswerId="1386" CreationDate="2014-02-03T15:21:09.377" Score="6" ViewCount="7104" Body="&lt;p&gt;How does a noise bridge work?  And how can a noise bridge be useful in building, testing, and/or tuning an antenna?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2016-03-22T07:36:36.637" Title="Noise bridge use in antenna construction?" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1376" PostTypeId="1" AcceptedAnswerId="1382" CreationDate="2014-02-03T15:26:40.993" Score="4" ViewCount="338" Body="&lt;p&gt;What regulations apply to radio operations in International waters?  How far offshore does one need to be?  Does the answer change between registered commercial vessels and home-made rafts or canoes?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-02-03T19:11:31.297" Title="What radio regulations apply in International waters?" Tags="&lt;legal&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1377" PostTypeId="2" ParentId="1373" CreationDate="2014-02-03T17:06:17.373" Score="1" Body="&lt;p&gt;You will find one decent design that will use the pieces you have in the article &quot;&lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/9304054.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;7 dB for 7 bucks&lt;/a&gt;&quot;, by Nathan Loucks, WB0CMT, which has a basic construction as follows:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/IpH2V.png&quot; alt=&quot;Three element Yagi. 37-39&amp;quot; dipole near center, 40&amp;quot; reflector 16 inches from dipole, 35&amp;quot; director 20&amp;quot; from dipole.&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The article recommends that if your radio is further than 15 feet you'll want a good low loss cable such as RG-213.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While you have the parts for a larger Yagi, you indicate you want to use it for satellite communication, which will require it to be handheld as you track the satellite.  This is a great starter antenna that can be handheld without being too unwieldy, and while it has modest gain it should be enough for you to accomplish both your goals with very little work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the driven element is adjustable - you'll need to adjust that for the lowest SWR in order to accomplish your impedance matching.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-03T17:06:17.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1378" PostTypeId="2" ParentId="1372" CreationDate="2014-02-03T17:22:49.907" Score="6" Body="&lt;p&gt;Congress sets the rules the FCC has to follow, and the rule in particular requiring an age limit is &lt;a href=&quot;http://www.gpo.gov/fdsys/pkg/CFR-2010-title47-vol5/pdf/CFR-2010-title47-vol5-part97-subpartF.pdf&quot;&gt;Title 47, Volume 5, Part 97, Subpart F&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;§ 97.509 Administering VE requirements.&lt;br&gt;&#xA;  ...&lt;br&gt;&#xA;  (b) Each administering VE must:&lt;br&gt;&#xA;  ...&lt;br&gt;&#xA;  (2) Be at least 18 years of age;  &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It would take an act of Congress to change this rule. I haven't discovered the reason for this rule, but if you look through the amendments to Part 97 over time you may be able to discover which congress made the change, and reading the congressional record may indicate why.  &lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2014-02-03T17:33:45.857" LastActivityDate="2014-02-03T17:33:45.857" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1379" PostTypeId="1" CreationDate="2014-02-03T17:51:34.427" Score="8" ViewCount="7163" Body="&lt;p&gt;Does the official International Morse code include alphabetic characters other than the 26 letters of the English alphabet?  If so, what are the most common other alphabets or characters that one might find used on HF CW bands?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do Greek and Cyrillic alphabets map to CW (Morse?) code?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-02-03T18:43:45.987" LastActivityDate="2015-11-19T05:19:32.573" Title="International characters in Morse Code?" Tags="&lt;cw&gt;" AnswerCount="6" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1380" PostTypeId="2" ParentId="1379" CreationDate="2014-02-03T18:38:06.560" Score="2" Body="&lt;p&gt;There are a few, as can be seen from &lt;a href=&quot;http://www.kd7uiy.com/2013/08/complete-morse-code-set.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;my blog&lt;/a&gt;. Note the list includes the entire alphabet I could find, including a few alphabetic characters. I haven't personally heard any of them on the air, but I haven't learned CW enough to really be able to say anything on the matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/hUoH8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-02-03T18:38:06.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1381" PostTypeId="2" ParentId="1379" CreationDate="2014-02-03T19:10:07.870" Score="9" Body="&lt;p&gt;There are. &lt;a href=&quot;http://en.wikipedia.org/wiki/Morse_code#Non-English_extensions&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia has a list&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Lswwc.png&quot; alt=&quot;non-English Morse code characters&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A little searching will turn up more. They don't always agree, since they are conventional extensions, not standards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usage is sporadic at best. Many languages have mechanisms to cram their orthography into 7-bit &lt;a href=&quot;http://en.wikipedia.org/wiki/ASCII&quot; rel=&quot;nofollow noreferrer&quot;&gt;ASCII&lt;/a&gt;, driven by the need for their language to work on computers.&lt;sup&gt;1&lt;/sup&gt; For example &lt;a href=&quot;https://german.stackexchange.com/questions/4992/conversion-table-for-diacritics-e-g-u-ue&quot;&gt;in German&lt;/a&gt;, &quot;ß&quot; can be written as &quot;ss&quot;, and &quot;ö&quot; as &quot;oe&quot;. These systems work for Morse code as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some languages, simply removing diacritics doesn't introduce much ambiguity, so some people will simply omit them from transmitted Morse code. This isn't too surprising, considering the already high degree of abbreviation used even by English speakers, where a transmission might not even include words:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;RRR FB QSO OM 73 DE AC8NJ I&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Morse code is, by definition, an encoding of the basic Latin alphabet, so languages that use something else (Chinese, Greek, Hebrew, Russian, to name a few) can not be represented in Morse code propper. This hasn't prevented those languages from developing similar dot-and-dash telegraph codes, and &lt;a href=&quot;http://en.wikipedia.org/wiki/Other_alphabets_in_Morse_code&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia has a list&lt;/a&gt;. They do tend to use similar codes where possible. For example, Greek &lt;a href=&quot;http://en.wikipedia.org/wiki/Alpha&quot; rel=&quot;nofollow noreferrer&quot;&gt;alpha&lt;/a&gt; shares the same code as &quot;A&quot;, as the two share some relatively recent history. Where letters are more distantly related (for example Hebrew), the mappings tend to shoot for similar sound. Where the orthographic systems have basically nothing in common (Chinese), no intuitive mapping is possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: multi-language support in computers is a relatively recent development, and still quite a few systems can't manage to get it right.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:42:15.607" LastActivityDate="2014-02-03T19:10:07.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1382" PostTypeId="2" ParentId="1376" CreationDate="2014-02-03T19:11:31.297" Score="3" Body="&lt;p&gt;For registered commercial vessels, you have to have permission from the country of the ship's registry AND permission from the operator of the ship AND permission from the captain. &lt;a href=&quot;http://www.arrl.org/maritime-mobile-operation-in-international-waters&quot; rel=&quot;nofollow&quot;&gt;Source&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For being in your own home-made craft, I imagine you just need your license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that everything changes when you're in territorial waters, and I'm not sure how you know (I'd guess maritime charts would indicate where they are).&lt;/p&gt;&#xA;" OwnerUserId="678" LastActivityDate="2014-02-03T19:11:31.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1383" PostTypeId="1" AcceptedAnswerId="1384" CreationDate="2014-02-03T19:29:56.383" Score="5" ViewCount="7116" Body="&lt;p&gt;I have a unused hula-hoop in my garage, and I ran some stranded speaker wire around it once, and attached one side of the wire to the coax shielding, and the other to the coax core wire. Is this the correct way to construct a loop antenna for receiving HF (500kHz to 30MHz) range frequencies?&lt;/p&gt;&#xA;" OwnerUserId="412" LastEditorUserId="29" LastEditDate="2014-02-04T14:56:14.080" LastActivityDate="2014-02-04T14:56:14.080" Title="How to construct a loop antenna for receiving HF?" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;loop-antenna&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1384" PostTypeId="2" ParentId="1383" CreationDate="2014-02-03T19:50:11.283" Score="3" Body="&lt;p&gt;That will work a little, but you might want to consider adding a variable capacitor to get more performance out of it by making the antenna resonant at the frequency you are interested in receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately add a high impedance amplifier at the antenna, such as in this &lt;a href=&quot;http://www.techlib.com/electronics/antennas.html&quot; rel=&quot;nofollow&quot;&gt;DIY hula hoop antenna&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that this will only by good for reception, though. A hula hoop of 4 feet in diameter is going to have a resonant frequency nearest the 10 meter band with a single loop of wire, and this will have a greater impact on transmission than reception.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-03T19:50:11.283" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1385" PostTypeId="2" ParentId="1383" CreationDate="2014-02-03T21:46:27.960" Score="8" Body="&lt;p&gt;Just about &lt;em&gt;anything&lt;/em&gt; connected to your feedline makes an antenna. A lot of the concerns in transmitting antennas (low SWR, high efficiency, etc) are of diminished importance for receiving antennas, so it's surprisingly easy to make a perfectly good receive antenna with very little design effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't necessarily need the antenna to be resonant or &quot;tuned&quot;. This will significantly increase the &lt;em&gt;sensitivity&lt;/em&gt; of the antenna at the resonant frequency, but may not increase its &lt;em&gt;performance&lt;/em&gt;, which for a receiver, probably means having a high signal-to-noise ratio (SNR). This is because tuning the loop will make it more sensitive to both signals and atmospheric noise. The only circumstance under which this will increase the SNR is if the antenna isn't already sensitive enough to overcome the internal noise of your receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, if you desire operation from 500kHz to 30MHz, you might want you antenna to be &lt;em&gt;not&lt;/em&gt; resonant. A small loop resonated with a capacitor has a very high &lt;a href=&quot;http://en.wikipedia.org/wiki/Q_factor&quot; rel=&quot;nofollow noreferrer&quot;&gt;Q factor&lt;/a&gt;. The consequence of this for your antenna is very small bandwidth. It so small that inexpensive AM receivers (the consumer kind) use just the antenna bandwidth to select a station. If you resonate the antenna with a capacitor, you should expect only a few kilohertz of bandwidth without adjusting the tuning capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether you use a tuning capacitor or not, the impedance of this loop isn't going to be anywhere near 50Ω. The resulting high SWR means higher losses in the antenna and feedline, however as with the lowered sensitivity of a non-resonant antenna, this isn't a problem as long as the antenna is &lt;em&gt;sensitive enough&lt;/em&gt;. See &lt;a href=&quot;https://ham.stackexchange.com/q/382/218&quot;&gt;What is the relationship between SWR and receive performance?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may additionally find that this design might not do a good job of isolating common-mode currents, and consequently the &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;feedline works as part of the antenna&lt;/a&gt;. This isn't a problem in itself, except when you consider that you want to move the antenna away from your house, where there is less noise, but you can't do that if the feedline is the antenna. Whether or not this is a problem for you depends on where the noise is that you are trying to avoid, and how the surroundings of your antenna tend to unbalance it. You can always &lt;a href=&quot;https://ham.stackexchange.com/questions/1271/how-to-detect-common-mode-currents-or-rf-in-the-shack&quot;&gt;test for common-mode currents&lt;/a&gt; if you suspect this is an issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, is this the &quot;correct&quot; way to make a loop antenna? As should be clear from the above, only you can tell. You will have to do some testing and gather some data to determine if the antenna is working well enough for you, and if so, congratulations, it's correct enough. If not, a more complex design might be necessary.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-03T21:46:27.960" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1386" PostTypeId="2" ParentId="1375" CreationDate="2014-02-04T03:23:05.857" Score="7" Body="&lt;p&gt;A Noise Bridge is a very useful piece of test kit, often described as a &quot;poor man's antenna analyzer&quot;.  It's capable of measuring the exact impedance of an antenna, both the resistive and reactive components, something that normally requires a pricey bit of lab equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unlike an SWR meter, the noise bridge, requires little or no transmitted power applied to the antenna. The SWR meter works by measuring the reflected wave from the antenna back to the transmitter when a transmission is made. But a noise bridge measures the impedance directly allowing an accurate antenna tuning to occur without transmitting, so there is no risk of transmitter damage or QRM on the bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, how does it work?  The bridge has four legs, one is a reference impedance (usually a calibrated variable resistor and a calibrated variable capacitor in series) and the other leg is the unknown impedance to be measured (say, an antenna).  A white noise generator injects noise into the circuit that can be monitored by an HF receiver.  Then, the circuit is tuned until a null is detected in the receiver, the impedances are now matched and the circuit is in balance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/DTFue.png&quot; alt=&quot;Noise Bridge Block Diagram&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A schematic look at the bridge:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/QXf1P.png&quot; alt=&quot;Noise Bridge Schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pretty nifty, but there are some other things you can do with them:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Trap dipoles:&lt;/strong&gt; The noise bridge will give a null on each band that the trap dipole resonates. Start with the highest frequency band and measure impedance and reactance as for a normal dipole. Adjust your antenna center section to resonance then repeat on the next lower band and so on. This method can be used on both horizontal and vertical trap antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Beam antenna:&lt;/strong&gt; Connect the noise bridge to the driven element. Tune your receiver to the operating frequency and read the impedance and reactance. Adjust the element length to bring to resonance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Testing Baluns:&lt;/strong&gt; You can't test a Balun or Unun with a VM because they usually have some or all of their legs tied off at DC, so it will read a dead short.  Instead, connect your noise bridge to the coax input of the balun. If its a 1:1 balun place a 50 ohm resistor across the output connectors. Now turn on the noise bridge and adjust for a noise null. You should see an impedance of close to 50 ohms and reactance of almost 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Tuning the Antenna Tuner:&lt;/strong&gt; You can set your antenna tuner without using your transmitter.  Connect the noise bridge to the transmitter side of the tuner and set the noise bridge controls for X=0 and R=50 and then adjust the tuner for null.  Don't leave the noise bridge in place, you'll probably smoke it if you transmit into it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are other less common, more technical uses such as determining the inductance of unknown ferrite material, pruning feedlines, etc.  Google is your friend here, it's a great piece of test gear to have around and very cheap to build if you don't want to drop $20 or so on a used Palomar R-X or old HeathKit 1422A.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Palomar R-X Noise Bridge Manual&lt;/li&gt;&#xA;&lt;li&gt;JADNDEK Noise Bridge Manual&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-02-04T16:03:58.297" LastActivityDate="2014-02-04T16:03:58.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1387" PostTypeId="2" ParentId="1371" CreationDate="2014-02-05T00:30:08.877" Score="2" Body="&lt;p&gt;I believe there is a limit to the elevation for which any nation can claim control over and such enforce its laws. A bit of searching led me to find that the exact elevation is not really agreed upon between nations but is &lt;em&gt;between 30 km (19 mi) - 160 km (99 mi)&lt;/em&gt; above sea level.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;There is no international agreement on the vertical extent of&#xA;  sovereign airspace (the boundary between outer space—which is not&#xA;  subject to national jurisdiction—and national airspace), with&#xA;  suggestions ranging from about 30 km (19 mi) (the extent of the&#xA;  highest aircraft and balloons) to about 160 km (99 mi) (the lowest&#xA;  extent of short-term stable orbits). The Fédération Aéronautique&#xA;  Internationale has established the Kármán line, at an altitude of 100&#xA;  km (62 mi), as the boundary between the Earth's atmosphere and the&#xA;  outer space, while the United States considers anyone who has flown&#xA;  above 50 miles (80 km) to be an astronaut; indeed descending space&#xA;  shuttles have flown closer than 80 km (50 mi) over other nations, such&#xA;  as Canada, without requesting permission first.&lt;a href=&quot;http://en.wikipedia.org/wiki/Airspace&quot; rel=&quot;nofollow&quot;&gt;1&lt;/a&gt; Nonetheless both&#xA;  the Kármán line and the U.S. definition are merely working benchmarks,&#xA;  without any real legal authority over matters of national sovereignty.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Taken from the &lt;a href=&quot;http://en.wikipedia.org/wiki/Airspace&quot; rel=&quot;nofollow&quot;&gt;Wikipedia Entry for Airspace&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think after a certain point respect for other's nations operating in space would be required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However it is worth noting that the consensus is that you would be subject to airspace over the US for any altitude at which aircraft or balloons can fly. So pretty much any regular amateur activity you can think of (weather balloons or telemetry) will be subject to the laws of the airspace for the country in which you are operating. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have the funds to personally launch satellites or space probes and really wanted to transmit out of band or intentionally interfere with some other equipment, I'm sure there is not much that can be done outside of friendly negotiation (or &lt;em&gt;perhaps&lt;/em&gt; you might find your personal space probe mysteriously destroyed without explanation).&lt;/p&gt;&#xA;" OwnerUserId="608" LastActivityDate="2014-02-05T00:30:08.877" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1388" PostTypeId="1" CreationDate="2014-02-05T19:13:55.457" Score="35" ViewCount="50207" Body="&lt;p&gt;Other than rust, corrosion, and other reactions with air that would make the use of a metal unfavorable, how do different metals affect the performance?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's give Yagi an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say I use 4 different metals for the directors&#xA;, reflector, and driven element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One antenna made out of copper, one made out of aluminum, and one made out of a higher resistance conductor, let's say graphite (I know it would snap, I'm just talking theoretical), and iron &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other then the metal variations, the antennas  are identical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, do different metals with different conductivity and permiability affect the performance of an antenna including gain, efficiency, impedance, elevation, or any other characteristic other then mechanical strength, and chemical reliability in open air. &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="3010" LastEditDate="2018-06-25T13:55:30.097" LastActivityDate="2019-11-19T11:14:28.273" Title="Effect of different metals for antenna elements" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;physics&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="1389" PostTypeId="2" ParentId="1388" CreationDate="2014-02-05T20:35:01.337" Score="4" Body="&lt;p&gt;There are two aspect you'll need to take into account.  The first can be more easily dismissed as insignificant, and that is the velocity factor of the metal.  For common conducting metals the difference between two metals is very small and is generally swamped by other things that affect velocity factor, such as insulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second, and more important aspect is the resistance of the metal.  The higher the resistance, the greater the losses to heat.  Stainless steel isn't a great conductor, and a simple 50W continuous transmission will heat it too hot to touch without much trouble - a lot of that power is going into heating the metal, and not transmitting the signal. Copper and aluminum are good conductors, but if you could use silver you'd have an even more efficient antenna - it could operate at higher power with thinner wire than the other conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beyond that, there's little electrically to take into account in choosing a metal for an antenna design - just mechanical, environmental, connection, and cost factors which often weigh more heavily in the decision than the above factors.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2014-02-06T14:10:57.347" LastActivityDate="2014-02-06T14:10:57.347" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1390" PostTypeId="2" ParentId="1388" CreationDate="2014-02-06T16:33:31.967" Score="42" Body="&lt;p&gt;Considering just electrical properties, the most significant parameter for your selection of antenna conductor is resistance. You want to keep the resistance to a minimum, because when current flows through a resistance, the electrical power is converted to heat, according to &lt;a href=&quot;http://en.wikipedia.org/wiki/Joule%27s_first_law&quot; rel=&quot;noreferrer&quot;&gt;Joule heating&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ P = I^2 R $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any energy you use to make heat is energy you aren't using to make electromagnetic waves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So first, you should consider the &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity&quot; rel=&quot;noreferrer&quot;&gt;resistivity&lt;/a&gt; (&lt;span class=&quot;math-container&quot;&gt;$\rho$&lt;/span&gt;) of various metals. A lower resistivity means you will need less of a metal to reduce the resistance to an acceptable target. Here's a selection, ordered from lowest to highest resistivity in nano-ohm-meters (nΩm), of some metals you might consider using in an antenna:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Silver: 15.9&lt;/li&gt;&#xA;&lt;li&gt;Copper: 16.8&lt;/li&gt;&#xA;&lt;li&gt;Gold: 24.4&lt;/li&gt;&#xA;&lt;li&gt;Aluminium: 26.2&lt;/li&gt;&#xA;&lt;li&gt;Zinc: 59.0&lt;/li&gt;&#xA;&lt;li&gt;Nickel: 69.9&lt;/li&gt;&#xA;&lt;li&gt;Iron: 100&lt;/li&gt;&#xA;&lt;li&gt;Tin: 109&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm not going to list stainless steel because there are so many kinds, but generally stainless steels are not great conductors, being over 100 on this scale.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A high &lt;em&gt;resistivity&lt;/em&gt; isn't bad in itself, because you can compensate by making the conductor thicker, and end up with the same &lt;em&gt;resistance&lt;/em&gt;. Thus, you might think copper is the best choice (ruling out silver due to high cost), but when you start making mechanical and cost considerations, you may find aluminium is better. This is because for a sample of copper and another of aluminium of equal resistance, the aluminium sample will be bigger, but stiffer, lighter, and cheaper. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's another effect to consider here: with increasing frequency, currents like to flow on the surfaces of conductors. This is called the &lt;a href=&quot;http://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;noreferrer&quot;&gt;skin effect&lt;/a&gt;. The current flowing only on the skin of a conductor effectively reduces the cross-sectional area, and thus the conductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since most of the RF current is only on the surface, it often makes sense to build antennas from tubing for antennas requiring rigid elements (a 440 MHz Yagi), or copper-clad steel for wire antennas requiring tensile strength (a 40 meter dipole). This saves weight and cost for a negligible increase in loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Magnetic_permeability&quot; rel=&quot;noreferrer&quot;&gt;Magnetic permeability&lt;/a&gt; is a factor in skin depth. With increasing permeability, the skin depth decreases, increasing loss. Of the metals listed above, only iron and nickel have significantly higher permeability. Iron by a factor of about 5000, and nickel by 100 to 600. You could compensate for the reduced skin depth by increasing the surface area of the conductor, but when you consider cost and mechanics, it usually makes more sense to simply avoid iron and nickel and alloys containing them.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2019-02-21T19:25:32.237" LastActivityDate="2019-02-21T19:25:32.237" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="1391" PostTypeId="1" CreationDate="2014-02-06T22:00:39.380" Score="6" ViewCount="4835" Body="&lt;p&gt;There are some &lt;a href=&quot;http://thewireman.com/antennap.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;people selling steel wire plated with copper&lt;/a&gt; for making wire antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps the most well-known brand of this product, Copperweld, makes at least two kinds of copper-clad wire, copper-clad steel (CCS), and copper-clad aluminum (CCA). On Copperweld's &lt;a href=&quot;http://fushicopperweld.com/en/applications/other.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;applications page&lt;/a&gt;, they write:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;CCA is a natural for antennas in a variety of applications such as large ground-based arrays or even ham radios or mobile phones. CCA is applicable to most localized RF transmitters and is being used near radio towers to shield other structures from creating interference.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(note: CCA, the A for &lt;em&gt;aluminum&lt;/em&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia on &lt;a href=&quot;http://en.wikipedia.org/wiki/Copper-clad_aluminium_wire&quot; rel=&quot;nofollow noreferrer&quot;&gt;copper-clad aluminum&lt;/a&gt; lists applications:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The primary applications of this conductor revolve around weight reduction requirements. These applications include high-quality coils, such as the voice coils in headphones, portable loudspeakers or mobile coils; high frequency coaxial applications; such as RF antennas; CATV distribution cables; and power cables.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The article on &lt;a href=&quot;http://en.wikipedia.org/wiki/Copper-clad_steel&quot; rel=&quot;nofollow noreferrer&quot;&gt;copper-clad steel&lt;/a&gt; lists nothing about RF applications:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Grounding, union of ground rods to metallic structures, meshes, substations, power installations and lightning arrestors.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To be fair, most of the amateur radio sites I've seen selling anything similar call it simply &quot;copper-clad wire&quot;, and don't specify if the core is steel, aluminum, or gold.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems to be understood that &lt;a href=&quot;https://ham.stackexchange.com/questions/1388/effect-of-different-metals-for-antenna-elements&quot;&gt;steel is not a good antenna wire&lt;/a&gt;. So, is copper-clad steel a good antenna wire, or no? Why?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-07-10T16:07:52.613" Title="Is copper-clad steel a good material for wire antennas?" Tags="&lt;wire-antenna&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1393" PostTypeId="2" ParentId="1391" CreationDate="2014-02-07T01:32:15.443" Score="5" Body="&lt;p&gt;Depending on the RF frequency and wire diameter, skin effect may dominate the effective resistance at that frequency.  If so, since copper has a lower resistance, any resistive losses of a copper skin might be lower.  Silver &lt;s&gt;or gold&lt;/s&gt; plating would be even better, but a little too expensive except in exotic applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, pure copper also has a lower tensile strength that steel, so would be more likely to fail under load (wind, etc.) without a stronger core.  Copper is usually more expensive than steel as well.  Steel is cheaper and stronger.  And AL is lighter, if weight is an important issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If corrosion or oxidation is likely to affect reliability, than gold plating might increase contact reliability, or wire lifetime in unusual chemical environments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, a blend may be the best trade-off, depending on all the constraints and requirements.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2016-07-10T16:07:52.613" LastActivityDate="2016-07-10T16:07:52.613" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1394" PostTypeId="1" AcceptedAnswerId="1398" CreationDate="2014-02-07T01:46:42.700" Score="5" ViewCount="13191" Body="&lt;p&gt;Gold is really expensive. Why then would anyone bother to plate connectors with it? Does it have some unique electrical characteristics that make it useful?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-12T23:35:14.297" Title="Why are some electrical contacts gold plated?" Tags="&lt;connectors&gt;" AnswerCount="8" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1395" PostTypeId="1" CreationDate="2014-02-07T05:46:44.787" Score="-3" ViewCount="174" Body="&lt;p&gt;What's the simplest way to make a radio station from my  home? I just want to bump this city with some slick tunes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What do I need to buy and about how much am I to spend?&lt;/p&gt;&#xA;" OwnerUserId="690" LastEditorUserId="76" LastEditDate="2014-10-23T17:55:11.577" LastActivityDate="2014-10-23T17:55:11.577" Title="How do I radio?" Tags="&lt;transmitter&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2014-02-07T12:14:45.283" ContentLicense="CC BY-SA 3.0" />
  <row Id="1396" PostTypeId="2" ParentId="1394" CreationDate="2014-02-07T05:49:38.490" Score="2" Body="&lt;p&gt;Surface conductivity that changes less over time after exposure to an oxidative environment (normal  room air).  Some oxides are insulators, the opposite of what most connectors are usually meant to do when used.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-02-07T05:49:38.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1397" PostTypeId="2" ParentId="1395" CreationDate="2014-02-07T07:12:04.033" Score="4" Body="&lt;p&gt;Transmitting on the FM broadcast band with any kind of power is illegal pretty much everywhere. Getting your ham license gives you some other bands to play with but music is only allowed on certain bands for very brief periods, ie, read &quot;no pirate stations allowed&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That being said, &lt;a href=&quot;https://dx.com/p/cze-15a-2w-15w-stereo-fm-audio-transmitter-w-antenna-for-car-silver-278498&quot; rel=&quot;noreferrer&quot;&gt;here's a 15W FM transmitter&lt;/a&gt; that will cover one bloody large area with the right antenna, using it will however have you tracked pretty soon and facing a really big fine. Do with this what you will but they really do fine people for this.&lt;/p&gt;&#xA;" OwnerUserId="135" LastActivityDate="2014-02-07T07:12:04.033" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1398" PostTypeId="2" ParentId="1394" CreationDate="2014-02-07T11:31:29.210" Score="8" Body="&lt;p&gt;Gold has several really unique properties that allow for it's frequent use:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Gold is the least likely metal to oxidize. From &lt;a href=&quot;http://hilaroad.com/camp/projects/lemon/electric_potential.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this table&lt;/a&gt;, it can be shown that Gold's electro-potential value is -1.1, meaning it should not oxidize at all, even in water. &lt;a href=&quot;http://en.wikipedia.org/wiki/Gold_plating#Electronics&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt; states this is the primary reason that some electrical contacts are gold plated.&lt;/li&gt;&#xA;&lt;li&gt;It is an extremely &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Resistivity_of_various_materials&quot; rel=&quot;nofollow noreferrer&quot;&gt;conductive material&lt;/a&gt;, one of the best known.&lt;/li&gt;&#xA;&lt;li&gt;Gold is very malleable, it is very easy to get a thin sheet of it.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Bottom line, it might be a bit overkill, but there are some advantages to gold plated materials.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="-1" LastEditDate="2018-01-12T04:34:03.977" LastActivityDate="2018-01-12T04:34:03.977" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1399" PostTypeId="1" AcceptedAnswerId="1404" CreationDate="2014-02-07T12:45:02.133" Score="5" ViewCount="5257" Body="&lt;p&gt;Silver is pretty expensive. &lt;a href=&quot;https://ham.stackexchange.com/q/1394/218&quot;&gt;Unlike gold&lt;/a&gt;, it will tarnish in air. Why then would anyone bother to plate connectors with it? Does it have some unique electrical characteristics that make it useful?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2020-08-16T14:59:35.630" Title="Why are some electrical connectors silver plated?" Tags="&lt;connectors&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1400" PostTypeId="1" AcceptedAnswerId="1401" CreationDate="2014-02-07T17:30:34.990" Score="3" ViewCount="161" Body="&lt;p&gt;It may happen that, at the start of a scheduled CW rag chew, the frequency is in use, but only one side can hear that it is in use.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A cannot hear the existing QSO.&lt;/li&gt;&#xA;&lt;li&gt;B &lt;em&gt;can&lt;/em&gt; hear the existing QSO.&lt;/li&gt;&#xA;&lt;li&gt;A begins by sending &quot;QRL?&quot; (&quot;is this frequency in use?&quot;)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;What should B do now?  If B responds to A's query with &quot;QRL&quot; (&quot;this frequency is in use&quot;), there is a danger of the stations in the existing QSO thinking that this is directed to &lt;em&gt;them&lt;/em&gt;, and having them cease or change frequencies as a result.  That doesn't seem right; they were there first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can B let A know that the frequency is in use while causing the least disruption to the existing QSO?&lt;/p&gt;&#xA;" OwnerUserId="628" LastActivityDate="2014-02-07T19:07:26.167" Title="How to tell other party of scheduled QSO that frequency is in use?" Tags="&lt;procedure&gt;&lt;cw&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1401" PostTypeId="2" ParentId="1400" CreationDate="2014-02-07T19:07:26.167" Score="2" Body="&lt;p&gt;Good practice would dictate that an ongoing QSO will yield the frequency to a scheduled QSO. The reason is simple: if you are already communicating with your other party, it's easy for you to move to another frequency. For the people with the sched, not so, because they haven't yet established communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do hear &quot;QRL?&quot;, you can respond with simply &quot;Y&quot;. This isn't likely to be misinterpreted, and it's quicker than responding with &quot;QRL&quot; too, which is good, since for as long as you are transmitting, you are interfering with the ongoing QSO, which is bad.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-07T19:07:26.167" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1402" PostTypeId="2" ParentId="1399" CreationDate="2014-02-07T20:11:32.987" Score="2" Body="&lt;p&gt;It's a whole lot easier to solder silver plated connectors (specifically I am talking about PL-259s and the like) than the white metal used on the cheaper connectors.  Some folks have great soldering setups and a lot of experience soldering.  The rest of us are better off spending a little more to make assembling coax a lot easier and more reliable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Electrically, of course, silver is an excellent conductor of both heat and electricity.  But it is soft and as @Phil noted, tarnishes. According to one study I read, as long as the tarnish layer is particularly thick, the conduction surface still performs well.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Silver tarnishes in the presence of water if a polar salt or sulfur is available.  Staying with the coax theme, protecting the connection from water intrusion (something you would want to do anyway) will probably mitigate the danger of tarnish reducing the current flow before something else happens to the cable (tree branches, squirrels, UV, etc.). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reference:&#xA;&lt;a href=&quot;http://www.te.com/documentation/whitepapers/pdf/Ag_use_connectors_503-1016.pdf&quot; rel=&quot;nofollow&quot;&gt;Overview of the Use of Silver in Connections&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-02-07T20:11:32.987" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1403" PostTypeId="2" ParentId="1394" CreationDate="2014-02-08T14:02:22.440" Score="5" Body="&lt;p&gt;Gold makes good contacts because it is very nonreactive, and thus won't corrode or tarnish over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Copper is a &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrical_conductivity#Resistivity_of_various_materials&quot; rel=&quot;noreferrer&quot;&gt;better conductor&lt;/a&gt; than gold, but copper will form a layer of oxide or other tarnish through normal exposure to the elements that will eventually increase the &lt;a href=&quot;http://en.wikipedia.org/wiki/Contact_resistance&quot; rel=&quot;noreferrer&quot;&gt;contact resistance&lt;/a&gt; of two mating copper contacts, rendering the connection faulty. See for example, architectural copper roofs:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Copper-Roof_Palace&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ucbGj.png&quot; alt=&quot;copper roof on Warsaw palace&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where this corrosion isn't desired in architectural applications, a protective coating is applied. This isn't feasible in electronic applications since such coatings are generally non-conductive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gold does not corrode. Check out this shiny roof:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Wat_Traimit&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KgFBB.jpg&quot; alt=&quot;gilded roof on Wat Traimit&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although gold is expensive, its physical properties also make it easy to deposit a very thin layer. The plating can be extremely thin while still being effective. Consequently, gold plated contacts aren't as expensive as one might think. Normally the determining concern in the thickness of the plating is wear resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In applications where extremely low cost is more important than maintaining a good connection over time, tin plating is frequently used. Tin is not as good as gold in the corrosion resistance department, but it is better than copper, and cheaper than gold.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-08T14:02:22.440" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1404" PostTypeId="2" ParentId="1399" CreationDate="2014-02-08T14:22:23.523" Score="6" Body="&lt;p&gt;Silver has the &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Resistivity_of_various_materials&quot; rel=&quot;noreferrer&quot;&gt;highest conductivity&lt;/a&gt; of ordinary metals. It's also soft, which means the mating connectors squish together making a larger contact area, and thus lower &lt;a href=&quot;http://en.wikipedia.org/wiki/Contact_resistance&quot; rel=&quot;noreferrer&quot;&gt;contact resistance&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Low, consistent contact resistance is important in RF connectors, because any significant change in contact resistance will change the impedance of the connector, resulting in increased SWR and attendant losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Silver is also easy to solder, which makes soldered connections to silver plated connectors likewise reliable and superbly conductive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Silver plating is not without disadvantages. Its softness also makes it not terribly durable. It's also prone to tarnish. However, in the RF connector applications where it is typically encountered, connectors are mated and unmated infrequently, and protected from water intrusion through an over-wrap of appropriate tape or such.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-08T14:22:23.523" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1405" PostTypeId="1" CreationDate="2014-02-08T19:52:16.213" Score="6" ViewCount="2445" Body="&lt;p&gt;There are some trees around with branchy tops that seem wider than half of 10M, maybe even half of 20M, and above the nearby rooftops.  Can a wire dipole or a vertical be mounted inside a tree?  If so, what kind of problems might such an antenna present?  And, even if functional, would there be any benefit to putting an antenna inside a tree, versus a ground mounted antenna below the rooftops and treetops.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="8717" LastEditDate="2021-05-18T18:06:00.570" LastActivityDate="2021-05-18T18:06:00.570" Title="Can an HF antenna be put inside a tree?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;hf&gt;&lt;wire-antenna&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1406" PostTypeId="2" ParentId="1405" CreationDate="2014-02-09T00:03:43.753" Score="2" Body="&lt;p&gt;Yes, you can mount an HF antenna in the tree tops.  I'd wager there are many many wire antennas strung through the trees around the world, two in my backyard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I imagine there is some effect, probably a greater one when there are leaves on the tress then now.  But, I have had plenty of stateside and DX contacts with this arrange, so it does work fine.  Now, I am sure it will work somewhat better in free space, but I don't have a choice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally speaking higher is better for antennas. In the trees there is less tree to go through to get to the sky than beneath them, so I am pretty sure there is little advantage to mounting a dipole beneath the canopy of the trees.  Although I have seen reference to mounting dipoles low to the ground in ECOMM situations where NVIS is desired.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Verticals will depend on the type and what they use for the image antenna.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-02-09T00:03:43.753" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1407" PostTypeId="1" AcceptedAnswerId="1408" CreationDate="2014-02-09T20:45:54.223" Score="9" ViewCount="347" Body="&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/FYsbR.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why do many SDR control apps have two frequency settings, even when the app is designed or set up only for listening to or decoding one signal?  Should the two SDR frequency controls be set differently or the same?  If different, how much for which modulation schemes (CW, USB, LSB, AM, etc.), in which direction, and why?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2015-07-01T20:30:12.577" LastActivityDate="2015-07-02T19:00:57.737" Title="Why do SDR control apps have two frequency settings?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1408" PostTypeId="2" ParentId="1407" CreationDate="2014-02-09T22:02:04.480" Score="10" Body="&lt;p&gt;One controls the hardware, and the other controls the software.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The &lt;em&gt;hardware&lt;/em&gt; selects some section of the entire RF spectrum (by a local oscillator and mixer), and down-converts it into a frequency an analog-to-digital converter can handle, filters it (to discard out-of-band signals), samples it, and delivers that data to the computer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This data determines what you can &lt;em&gt;see&lt;/em&gt; in the so-called “waterfall” or “panadapter” displays. It also sets the limit for the widest-bandwidth signal you can possibly demodulate.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Then the &lt;em&gt;software&lt;/em&gt; does a similar process in order to select a &lt;em&gt;single signal&lt;/em&gt; to demodulate; it shifts it to baseband (a “0 Hz” signal which only varies according to the modulation), applies a low-pass filter, and demodulates appropriately.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Both stages have their own controllable local oscillator, and those two controls are what you are seeing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some reasons for there to be these two separate stages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Analog hardware is imperfect; there are various sorts of garbage you can get in the digital signal (DC offset, IQ imbalance, insufficiently filtered out-of-band signals). You can change the hardware center frequency to shift the garbage &lt;em&gt;away&lt;/em&gt; from the signal of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if there is a DC offset (RTL-SDRs with E4000 tuners do) then you have garbage at the center frequency, so you would set it to be slightly different from the signal of interest so that the following digital filter removes that part. &lt;strong&gt;This is one of the main reasons to specifically set the two frequencies differently,&lt;/strong&gt; if your receiver has this problem. It doesn't matter which direction you offset, as long as the offset is enough that the bandwidth of the desired signal doesn't overlap the unwanted signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, filtering is imperfect and the way this shows up in the signal from the hardware is that signals which are &lt;em&gt;out&lt;/em&gt; of the tuned band, but strong, will be seen to “wrap around” and appear at an in-band frequency modulo the hardware bandwidth (sample rate). This is a reason to receive &lt;em&gt;close&lt;/em&gt; to the center; the hardware filtering is at its best at that point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I highly recommend playing with changing the (hardware) center frequency slowly and watching and listening to how the displayed signals change or don't. You will learn what to do.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you are interested in monitoring a whole band rather than a single station (e.g. a single amateur HF band) then keeping the hardware settings fixed leaves your waterfall display undisturbed to watch activity over the whole band while you are free to select which stations you are currently demodulating (listening to).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Digital filters can be optimized for the particular mode in use, and, if you don't care about power consumption, be extremely sharp (good at selecting exactly what is wanted) compared to analog filters. They can also be adjusted in bandwidth or shape to trade off filtering out nearby unwanted signals vs. better intelligibility in the absence of nearby signals. (Note that this is a reason for the two-stage architecture, but it isn't directly a reason to have independent tuning controls as you've asked.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-02-09T22:12:09.513" LastActivityDate="2014-02-09T22:12:09.513" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1409" PostTypeId="2" ParentId="1405" CreationDate="2014-02-10T09:54:22.987" Score="1" Body="&lt;p&gt;There are bits of anecdotal evidence on the internet that the end of a dipole can set fire to a tree. This is because the voltage at the end of the antenna is very high (compared to the feed-point voltage). Aggravating conditions include using a linear amplifier (increasing the voltage) and/or operating in rainy conditions (compromising the insulation). &lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2014-02-10T09:54:22.987" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1410" PostTypeId="1" CreationDate="2014-02-10T16:31:28.830" Score="17" ViewCount="11180" Body="&lt;p&gt;What is the peak voltage present at the very end tips of half-wave dipole antenna in free space, and how might this peak voltage relate to transmitter type, transmitter power, RF frequency vs. antenna half-wave frequency mismatch, feed line, SWR, wire diameter, and etc.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2015-12-15T23:58:52.397" LastActivityDate="2020-11-04T12:20:40.437" Title="What is the peak voltage at the tips of a dipole antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wire-antenna&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1411" PostTypeId="2" ParentId="1391" CreationDate="2014-02-10T17:05:49.933" Score="2" Body="&lt;p&gt;Copper clad steel is a good antenna wire.  It's not the best for every application, but it's good for most applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantages it has are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Doesn't stretch as much as copper and other good conductors (which changes the resonant frequency)&lt;/li&gt;&#xA;&lt;li&gt;Stronger than other wires, so when you don't need a large gauge for electrical reasons, you can save on weight and size and still have sufficient strength for self support&lt;/li&gt;&#xA;&lt;li&gt;Less expensive than copper wire of a similar gauge, strength, and electrical capacity at RF frequencies&lt;/li&gt;&#xA;&lt;li&gt;More conductive than steel&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It does have a few disadvantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;More expensive than steel wire of a similar gauge and strength&lt;/li&gt;&#xA;&lt;li&gt;Have to correctly seal the ends to avoid oxidation of the center steel conductor&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that at frequencies between 3.5MHz and 30MHz the conductor's skin depth, the depth at which 63% of the electrical current flows, is between 35uM and 12uM for copper wire.  The link you gave has 30% or more copper, which provides a total copper skin depth much greater than 35uM, so the majority of the current will be carried in the copper cladding at the frequencies we are interested in for HF and higher frequency antennas.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-10T17:05:49.933" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="1412" PostTypeId="1" CreationDate="2014-02-10T18:23:12.600" Score="11" ViewCount="9054" Body="&lt;p&gt;What is the RF bandwidth of a typical CW signal?  How is the signal bandwidth affected by WPM and/or transmitter rise-time?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the narrowest bandwidth that can still be copied by a human?  Or what is the narrowest receiver audio filter that operators find useful for Morse Code?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-05-29T22:19:22.187" Title="Bandwidth of a CW signal?" Tags="&lt;cw&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1413" PostTypeId="2" ParentId="1412" CreationDate="2014-02-10T19:23:17.650" Score="11" Body="&lt;p&gt;In the simplest form, CW consists of a pure sine wave multiplied with a square wave that's either 0 or 1, corresponding to the keying of the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As with a mixer, or amplitude modulation, multiplying two signals generates frequency components that are the sum and difference of each frequency component of the multiplicands. In our simple form above, where the switching waveform is a square, the bandwidth can be very large, because a square wave consists of an infinite series of odd harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Real transmitters filter this square wave to some extent, and perfect square waves can't exist in practice anyway. The slower the transition from &quot;on&quot; to &quot;off&quot; is made, the less bandwidth is required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you send faster, then there are more transmissions per second. Since each transition requires a certain amount of energy away from the carrier frequency, faster speed means more sideband power, that is, more bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because every transmitter is different, it's difficult to say what the bandwidth is, exactly. We'd have to define more precisely what we mean by &quot;bandwidth&quot; anyhow. Because CW consists of brief periods of high bandwidth (the transitions) mixed with relatively long periods of zero bandwidth (everything but the transitions), the measured bandwidth depends greatly on how it's measured, anyhow. Are we looking at the average spectral density function over the entire transmission, or just some brief period around an on-off transition?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CW receive filters with a passband around 500 Hz are typical. It's certainly possible to make them narrower, but remember, it takes more bandwidth to make a sharp transition from &quot;on&quot; to &quot;off&quot;. It doesn't matter if that bandwidth was never transmitted, or it was transmitted but we removed it with a filter. If the receive filter is too narrow, you won't hear a &quot;dit dit&quot; with clear starts and stops to the tone, you will hear a smeared &quot;waahwaah&quot;. If we think about this problem in the time domain, it's called &lt;a href=&quot;http://en.wikipedia.org/wiki/Ringing_%28signal%29&quot;&gt;ringing&lt;/a&gt;, if we think about the filter as a resonant system, we say it has a high &lt;a href=&quot;http://en.wikipedia.org/wiki/Q_factor&quot;&gt;Q factor&lt;/a&gt;. This is actually a case of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Uncertainty_principle#Harmonic_analysis&quot;&gt;uncertainty principle&lt;/a&gt;: the more sharply we localize a thing in frequency, the less sharply we can localize it in time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the type, width, and nature of filters for CW is a matter of preference and circumstance. Between each pair of human ears is a wetware filter which is already very good at selecting tones by frequency, without help. Moreover, &lt;a href=&quot;http://physicsworld.com/cws/article/news/2013/jan/31/human-hearing-is-highly-nonlinear&quot;&gt;wetware filters can include context that simple linear filters can not&lt;/a&gt;: CW has a particular rhythm, QSOs follow a particular format, etc. However, a wetware filter can't remove a nearby strong signal causing &lt;a href=&quot;http://en.wikipedia.org/wiki/Desensitization_%28telecommunications%29&quot;&gt;desensitization&lt;/a&gt;. &lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-10T19:23:17.650" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1414" PostTypeId="2" ParentId="1410" CreationDate="2014-02-10T21:42:55.453" Score="7" Body="&lt;p&gt;It's really hard to say, because it depends on so many things. Analyzing the antenna in free space simplifies some things, but we'd still have to consider the exact geometry of the antenna (How thick are the wires? Are they bent at all?) and the material from which they are made (any resistance will decrease the Q factor of the antenna, reducing the peak voltage).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you look to &lt;a href=&quot;http://www.aa5tb.com/efha.html&quot;&gt;analysis of end-fed dipoles&lt;/a&gt;, you can find that it's been determined empirically and by modeling that the impedance at the end of a real half-wave dipole is somewhere between 1800 to 5000 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Knowing this, we can calculate what the voltage is for a given power into the antenna. If we are putting 100W into the antenna, and we figure the impedance at the ends is 4000 ohms, then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA; P &amp;amp;= V^2/R \\&#xA;100\mathrm W &amp;amp;= V^2 / 4000\Omega \\&#xA;\sqrt{100\mathrm W \cdot 4000 \Omega} &amp;amp;= V \\&#xA;V &amp;amp;\approx 632 \mathrm V&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an &lt;a href=&quot;http://en.wikipedia.org/wiki/Root_mean_square&quot;&gt;RMS&lt;/a&gt; value. Knowing that our transmission is approximately sinusoidal, then the peak voltage is something like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 632 \cdot \sqrt{2} = \pm 894 \mathrm V $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the above equations, we can see that power is proportional to the square of voltage:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P \propto V^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the power delivered to the antenna. Transmitter type and the match to the antenna (SWR) are relevant only to the extent that they change the power delivered to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is all assuming that the antenna is operated at resonance. As the frequency moves away from resonance, the peak voltage decreases. The reason why is simple: this high voltage is attainable because each cycle reinforces the previous. If you take a limiting case where the antenna is operated at DC, the voltage at the ends is equal to the voltage at the feedpoint, because there is no resonance to reinforce the voltage at the ends.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-10T21:42:55.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1415" PostTypeId="1" CreationDate="2014-02-10T22:18:59.730" Score="10" ViewCount="8216" Body="&lt;p&gt;Assuming proper licensing for the frequency, what is the proper operating procedure to test whether an HT works and is within range of a (documented as open, 2M or 440) club repeater?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should one wait till someone comes on the repeater, and ask them for a signal report?  Or try to test against the repeater solo?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2014-02-10T23:08:05.983" LastActivityDate="2018-08-28T19:00:13.303" Title="Operating proceedures: testing an HT against a repeater?" Tags="&lt;procedure&gt;&lt;repeater&gt;&lt;testing&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1416" PostTypeId="2" ParentId="1280" CreationDate="2014-02-11T11:33:54.650" Score="1" Body="&lt;p&gt;Since you apparently have access to the feed line, borrow an antenna analyzer and sweep the bands to find the resonant points and make note of them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of us &quot;OF's&quot; still know how to use a &quot;Grid Dip Meter&quot; or &quot;GDO&quot; to loosely couple to the feed line and &quot;DIP&quot; the antenna to find it's resonant point(s).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But overall your best and easiest way would be with the &quot;antenna analyzer&quot; such as the MFJ-259 B or MFJ-269.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check with your local club or other Hams in the area: chances are someone has one they will loan out and or help you make the test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One other thought, since the antenna and feed line have been &quot;in place&quot; for a number of years.&#xA;You might want to replace the feed line with something newer like coax.&#xA;If you do test the antenna and find it useful, I would suggest a 1:1 balun at least at the feed point (depending on the frequencies involved and terminal impedance a 4:1 balun might be in order to give your transmitter a better &quot;match&quot;).&lt;/p&gt;&#xA;" OwnerUserId="438" LastEditorUserId="218" LastEditDate="2014-02-11T15:30:18.263" LastActivityDate="2014-02-11T15:30:18.263" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1417" PostTypeId="2" ParentId="1415" CreationDate="2014-02-11T11:58:52.250" Score="12" Body="&lt;p&gt;I'm still a beginner in this area, so take this answer with a gran of salt.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've had a chance to see a ham test repeaters few days ago, so I'll describe what he did:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First and the most obvious, make sure that the transmit and receive frequencies are correctly set on the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Go to frequency of interest and listen for a while. If there is a conversation going on, wait until there's a natural gap in the conversation and then announce your presence. A simple:&quot;This is &lt;code&gt;CALLSIGN&lt;/code&gt; testing link with &lt;code&gt;repeater name&lt;/code&gt;. Can anyone give me a signal report?&quot; seems to do the trick. If the crowd at the repeater shows interest, share some more information about your rig with them. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it looks like there are no users at the repeater, use the same procedure as if there are other users. You don't know if someone may be just listening to the repeater. If that's the case, you may receive a response even if it looks like the repeater is deserted. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there really aren't any other users at the repeater, then your experiments probably won't bother anyone. Repeaters, here in Serbia at least, keep transmitting for a few seconds after you finish transmitting. If you have an S meter, you can see if your transmission triggered the repeater. If you really want to have a signal report, you'll probably need another radio. If you're lucky, there could be a WebSDR station within the range of the repeater. Otherwise, you'd probably need another receiver. One thing you could try, depending on the friendliness of local hams, is to ask someone on some other frequency to listen to the repeater and give you a report. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2014-02-11T11:58:52.250" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1418" PostTypeId="2" ParentId="1415" CreationDate="2014-02-11T12:24:12.830" Score="2" Body="&lt;p&gt;Both of your procedures are workable, but be sure to &quot;IDENTIFY&quot; with your call sign when testing or talking to someone (see part 97).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A couple of thing's to keep in mind.&#xA;1. Just because you can hear the repeater doe's not mean that it can hear you, an HT's antenna is not an ideal antenna for transmitting (some are not much more than an &quot;AIR COOLED DUMMY LOAD&quot;).&#xA;2. Due to the nature of HT's (being portable) you may have to change position (location) in order to get a good signal to the repeater (see #1).&#xA;3. If you have not done so already, get with a friend or even listen to yourself on a scanner or other receiver and LISTEN to yourself transmitting in order to find out how close you need to talk to the ht's mic. (most HT's do not have a great deal of mic. gain, (they are designed this way to hold down background noise).&#xA;4. Talk &quot;ACROSS&quot; the mic. or the face of the radio, this reduces the &quot;PLOSIVE&quot; or &quot;PUFF&quot; of your breath with each word (this is a good practice to use with hand held mic.'s and even desk mic.'s unless they are designed for close talking (noise canceling Mic.'s) ).&lt;/p&gt;&#xA;" OwnerUserId="438" LastActivityDate="2014-02-11T12:24:12.830" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1419" PostTypeId="2" ParentId="989" CreationDate="2014-02-11T16:02:16.283" Score="3" Body="&lt;p&gt;If the oxidation is superficial, that is it hasn't penetrated to a significant depth, it will not affect the antenna. Most metal oxides are good insulators. The antenna is already surrounded by a good insulator: air. Adding a thin layer of another insulator (metal oxides) doesn't change the electrical picture in any significant way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should look for corrosion on any connectors or mechanical contacts. The corrosion might work its way into a connection, and since the corrosion is not a good conductor, the contact resistance will be increased.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas can be made to be nearly maintenance-free if you design the connections to avoid corrosion. Protect any connectors from the elements with &lt;a href=&quot;http://en.wikipedia.org/wiki/Self-amalgamating_tape&quot; rel=&quot;nofollow&quot;&gt;self-amalgamating tape&lt;/a&gt;, or pot them in epoxy, or somehow avoid environmental exposure. Welded connections are great, where they are practical. Be mindful of &lt;a href=&quot;http://en.wikipedia.org/wiki/Galvanic_corrosion&quot; rel=&quot;nofollow&quot;&gt;galvanic corrosion&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-11T16:02:16.283" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1420" PostTypeId="1" AcceptedAnswerId="1550" CreationDate="2014-02-11T16:16:11.720" Score="1" ViewCount="2032" Body="&lt;p&gt;I would appreciate it if someone could help me in designing a patch bowtie antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to know the frequency and the bandwidth in terms of the length, angle and the length and width of the gap. See the following image:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/TH8Z5.png&quot; alt=&quot;Bow Tie Antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems easy but I could not find anything useful on the internet or books. &lt;/p&gt;&#xA;" OwnerUserId="709" LastEditorUserId="164" LastEditDate="2014-02-11T18:08:24.497" LastActivityDate="2014-03-05T21:35:07.957" Title="Patch Bowtie Antenna Design" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1421" PostTypeId="1" CreationDate="2014-02-12T01:39:26.960" Score="2" ViewCount="413" Body="&lt;p&gt;I am trying to make a list of all ISS downlink/uplink frequencies including ham bands and non-ham bands for a net I just started up, the Amateur Satellite net. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where can I find all of this? I can only find snippets of stuff everywhere, and I feel like i'm missing some frequencies.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2014-02-12T15:57:13.767" LastActivityDate="2014-02-14T21:35:55.937" Title="Where to find All Space Station Frequencies?" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1422" PostTypeId="2" ParentId="1410" CreationDate="2014-02-12T03:48:25.423" Score="12" Body="&lt;p&gt;I'm going to approach this a little differently starting from roughly the same place.  Here I am going to use a resonant $\lambda$/2 20m dipole driven by 100 W as the model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's compute the &lt;em&gt;current&lt;/em&gt; at the feed point of a dipole at resonance, this is found with the input power (100 watts) and the feed point impedance; which for our dipole is assumed to be the theoretical 73 $\Omega$ :&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ I&#xA;= \left(\frac{W}{R}\right)^{\frac{1}{2}}&#xA;= \left(\frac{100 \mathrm W}{73 \Omega}\right)^{\frac{1}{2}}&#xA;= 1.17 \: \text{amps (RMS)} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore the driving voltage can be calulated with Ohm's Law: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ V_\text{feed} = I \cdot R = 1.17 \mathrm A_\text{RMS} \cdot  73 \Omega = 85.44 \:\mathrm V_\text{RMS} $$ (unmodulated signal)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The voltage at the end of the dipole would require us to calculate the Q and solve the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ V_\text{end} = \frac{Q\:V_\text{feed}}{2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trying to minimize the hand-waving, we can use some approximations from transmission line theory to give us the Q. (See Edmund Laport's &lt;a href=&quot;http://www.vias.org/radioanteng/&quot; rel=&quot;noreferrer&quot;&gt;Radio Antenna Engineering&lt;/a&gt; for a complete (and math heavy) explanation) To do this we need the characteristic impedance of the dipole (considered as a transmission line).  That is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_{0} = 276 \cdot \log_{10}\frac{l}{p} = 972.31 \Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $l$ is the total length of the dipole and $p$ is the radius of the conductor (all in the same units).  I am going to ignore calculating the exact length here, we know it's approximately 5% shorter than the real wavelength to make up for velocity factor and end effects.  This next bit leans on transmission line theory and can turn into a bag of snakes, if you want to know more about where these equations come from, check the reference quoted above. $Q$ here is the ratio of the voltage of the direct wave and the reflected wave:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Q = \frac{1+m}{1-m} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and $m$ is calculated from the feed point impedance $R$ and the characteristic impedance $Z_0$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ m = \frac{Z_0-R}{Z_0+R} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I calculate $\ Z_0 $, I am going to assume our dipole is made with 3mm wire. Now to crank through the numbers:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ m = \frac{972\Omega-73\Omega}{972\Omega+73\Omega} = .86 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Q = \frac{1+.86}{1-.86} = 13.29 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now we can solve for $ V_\text{end} $:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ V_\text{end} = \frac{(13.29 \cdot 85.44 \mathrm V)}{2} = 568 \:\mathrm V_\text{RMS} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, this is the RMS voltage we should convert to peak voltage:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 568 \:\mathrm V_\text{RMS} \cdot \sqrt{2} = \pm 804 \:\mathrm V_\text{peak} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is all for 100W, if we instead plug 1500W into the above math, we come up with&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 4397 \:\mathrm V_\text{RMS} \:\text{or} \: \pm 6200 \:\mathrm V_\text{peak} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's a pretty hefty jolt. So getting back to the OP's other questions, the input power has a substantial effect on the voltage.  The rest of the factors are all the same as for maximizing antenna efficiency (resonance, conductor size, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; Most of the above equations come from the section on &lt;a href=&quot;http://www.vias.org/radioanteng/radio_antenna_engineering_03_06_03.html&quot; rel=&quot;noreferrer&quot;&gt;Circuital Design&lt;/a&gt; in the reference listed above.  The book is more math heavy than typical amateur radio references, but not as bad as some of the more modern engineering texts.  It's slow going, but a worthwhile read.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-02-12T15:45:47.680" LastActivityDate="2014-02-12T15:45:47.680" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1423" PostTypeId="1" CreationDate="2014-02-12T15:49:07.003" Score="6" ViewCount="3009" Body="&lt;p&gt;What are &quot;key clicks&quot;?  How much does the rise time or bandwidth of a CW signal need to be limited to prevent other QSOs on adjacent frequencies from being annoyed by &quot;key clicks&quot;?  Is there a legal limit regarding this (in the U.S.)?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do (non-DSP) HF transmitters typically limit the bandwidth or rise/fall time of the keying on and off of a Morse Code dit or dah?  (Is there a particular circuit one should look for in the schematic of a simple CW transmitter?)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-02-12T20:54:22.060" Title="Preventing CW key clicks" Tags="&lt;cw&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1425" PostTypeId="1" AcceptedAnswerId="1552" CreationDate="2014-02-12T17:57:52.690" Score="2" ViewCount="1022" Body="&lt;p&gt;I just got a used Kenwood tm241a.&#xA;It was working fine on my friends antenna until I took it home and hooked it up to a used Larsen nla-mm antenna I bought at a ham-fest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seemed to work fine on that antenna for a bit until I was hearing a weird hum out of the speaker on the higher edge of the 2 meter band on 50 watts. My Baofeng handheld picked up all of this spurious emissions on any frequency I tuned to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I then decided to test it one more time with a friend on a repeater, and it transmitted this weird one-tone beep when I keyed up the microphone, and didn't stop when I unkeyed it, the transmitting stopped only when I unplugged the microphone, rebooted the radio, and plugged the mic back in. The beep pitch changed by pressing different buttons on the mic, but wasn't the familiar two-tone DTMF, and was a one-tone beeping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this radio fried, or is there a way to fix it? Does the DTMF mic possibly have a problem, or is it most likely an internal radio issue? The day I finally got a nice 50 watt radio for my net control, and the courage classic bike race, It burned out. I cant see a nice kenwood die, and as a cheapo high school student, cant afford a new radio :(&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2014-02-14T14:42:25.130" LastActivityDate="2014-03-03T01:53:18.333" Title="Kenwood TM241A making weird transmissions" Tags="&lt;kenwood&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="1426" PostTypeId="1" CreationDate="2014-02-12T18:00:25.577" Score="1" ViewCount="157" Body="&lt;p&gt;What is the easiest way to match a 50 ohm coax with a 75 ohm antenna? I have a Yagi-Udi built with a 2 meter dipole, a reflector, and 3 directors. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-02-12T19:22:12.773" Title="Easiest Matching Technique" Tags="&lt;yagi&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1427" PostTypeId="2" ParentId="1423" CreationDate="2014-02-12T18:10:23.820" Score="5" Body="&lt;p&gt;&lt;a href=&quot;http://www.w8ji.com/what_causes_clicks.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI has a great writeup on this topic&lt;/a&gt;. I'll summarize the key points.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Key clicks are generally undesired &quot;clicks&quot; or &quot;thumps&quot; generated by a CW transmitter as the key is put down or let up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They can be caused several things. The most obvious is that a fast transition from carrier on to carrier off requires a wide bandwidth. You can think of this by considering that CW is a special case of AM with 100% modulation, where the baseband signal is a square wave. This square wave, theoretically unlimited in frequency, when multiplied with the carrier, will generate infinite sidebands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Less obvious reasons arise from practical issues in transceiver construction. For example, a transceiver typically uses the same VCO for receive and transmit. When operating QSK and &lt;a href=&quot;https://ham.stackexchange.com/q/1104/218&quot;&gt;split&lt;/a&gt;, the VCO must change frequency with each change of the key. If the VCO does not settle fast enough, you get key clicks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modulating the carrier will always require some sideband power, so key clicks can't entirely be eliminated, but only reduced to an acceptable level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W8JI's article says &quot;The ARRL recommends a 5 mS [sic] rise and 5 mS fall time for CW, based on data in &lt;a href=&quot;http://www.law.cornell.edu/cfr/text/47/2.202&quot; rel=&quot;nofollow noreferrer&quot;&gt;section 2.202 of FCC rules&lt;/a&gt; and &lt;a href=&quot;http://en.wikipedia.org/wiki/Comit%C3%A9_consultatif_international_pour_la_radio&quot; rel=&quot;nofollow noreferrer&quot;&gt;CCIR&lt;/a&gt; Radio regulations.&quot; I don't care to dig into the original sources, but it sounds reasonable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this is just a simple guideline. Just specifying the rise and fall times doesn't say much about the shape of the rise and the fall, which can have as much effect in the frequency domain as the rise and fall times. Remembering again that CW is a special case of AM, we'd want the rise and fall to be a sinusoidal envelope, since this limits the bandwidth maximally. Anything that's not sinusoidal will contain harmonics, which is exactly what we don't want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, how can this be implemented? You can filter the envelope (the on-off signal coming from the key), or you can filter the output. Filtering the envelope can be viewed as &lt;a href=&quot;http://en.wikipedia.org/wiki/Pulse_shaping&quot; rel=&quot;nofollow noreferrer&quot;&gt;pulse shaping&lt;/a&gt;, a common technique among digital modulations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest approach would be to put a simple &lt;a href=&quot;http://en.wikipedia.org/wiki/RC_circuit&quot; rel=&quot;nofollow noreferrer&quot;&gt;RC filter&lt;/a&gt; on the envelope, which is a little better than nothing. However, with a single-pole filter, you can get at best a 3dB/octave reduction in the harmonics of the envelope. Remember, we want ideally a sinusoidal envelope. A single-pole filter gets us closer, but not all that much, because although the harmonics from the rectangular envelope are attenuated, such a simple filter can't attenuate them very much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can make a better filter with more poles, giving us a steeper frequency roll-off, better attenuation of the harmonics, and thus a better approximation of our sinusoidal envelope, but this comes with increased cost. However, all radios come with what should be a pretty good filter: the receive filter. As it turns out, most radios send the transmitted signal through the same filter as is used for receive, since this is the most practical approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W8JI elaborates in his article that many transmitters use the SSB filter for this purpose, which is great, except that it's a lot wider than it needs to be. SSB filters are around 3 kHz wide, while just around 200 Hz would give us the ARRL recommended rise and fall times of 5 ms. He argues (and I tend to agree) that radios should be transmitting through their CW filter, instead of the SSB filter.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-12T20:54:22.060" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1428" PostTypeId="2" ParentId="1415" CreationDate="2014-02-12T18:18:40.897" Score="3" Body="&lt;p&gt;Either of those choices are good, as long as you identify your transmission. Many repeaters transmit a courtesy tone after repeating their input in order to signal end of transmission. For those repeaters, you can TX your call sign and then listen for the courtesy tone on the repeater output. This will let you know if you're hitting the repeater, but not much else.&lt;/p&gt;&#xA;" OwnerUserId="207" LastEditorUserId="207" LastEditDate="2014-02-12T18:55:28.343" LastActivityDate="2014-02-12T18:55:28.343" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1429" PostTypeId="2" ParentId="1426" CreationDate="2014-02-12T19:22:12.773" Score="3" Body="&lt;p&gt;The easiest way is to simply connect them without any matching.  You'll suffer an additional SWR of 1.5:1 due to the mismatch, but that's well within most transmitter's capability without damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second easiest is to simply employ a tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neither method will give you the best output power, but they are certainly among the easiest methods of matching.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-12T19:22:12.773" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1430" PostTypeId="1" CreationDate="2014-02-12T20:12:02.673" Score="4" ViewCount="3621" Body="&lt;p&gt;There seem to be reports of people trying to see how far an HF DX contact can be made using the tiniest transmit power (mW or even sub-mW QRP).  But many of these contacts seem to be accomplished using fairly full-sized antenna installations (beams, towers, etc.)&lt;/p&gt;&#xA;&lt;p&gt;What's the equivalent of QRP DX for minimum antenna size rather than transmit power?  Assuming a typical, rather than QRP, transmit power, say 100W, what's the smallest antenna over which a HF DX, say at least 1000 miles distant, contact can realistically be made?  Do mobile operators manage to do HF DX with relatively short car roof or bumper mounted whip antennas?  Or with something even more portable?  Has anyones &amp;quot;dummy load&amp;quot; been clearly heard at a DX distance?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-02-17T20:27:27.633" LastActivityDate="2021-02-17T20:27:27.633" Title="Smallest HF antenna for DX?" Tags="&lt;antenna&gt;" AnswerCount="6" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="1431" PostTypeId="2" ParentId="1423" CreationDate="2014-02-12T20:13:12.163" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What are &quot;key clicks&quot;? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Morse code can be considered a square wave, and CW is then that square wave added to the carrier frequency.  The sharp edges at the start and stop of the carrier include a lot of frequencies that aren't necessary to send good code.  These frequencies interfere with adjacent spectrum, well outside the 80-200Hz needed for CW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since they are short in duration, they can sound like clicking to those listening on adjacent frequencies.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How much does the rise time or bandwidth of a CW signal need to be limited to prevent other QSOs on adjacent frequencies from being annoyed by &quot;key clicks&quot;? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;One can filter their bandwidth to 80-200Hz going out of their keyer, the same way one would filter CW reception to 500Hz. Some use pulse shaping techniques to attain a specific rise time, others use simple RC circuits to define the shape of the waveform before the carrier is applied.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, &quot;rise time&quot; is not a great way to put metrics on it.  It's one way to stay inside the desired bandwidth, but since good practices and legal regulations are centered around bandwidth considerations, one should verify their rig maintains the smallest bandwidth required for the communications desired.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there a legal limit regarding this (in the U.S.)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The only legal limit is the requirement to use only as much bandwidth as the specific communication requires.  For CW, this varies based largely on the sending speed.  20wpm Morse can be limited to 80Hz bandwidth.  Faster sending requires more bandwidth for good signal quality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is unlikely that you'll get in trouble for using more bandwidth than needed, but your fellow operators will appreciate your efforts.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How do (non-DSP) HF transmitters typically limit the bandwidth or rise/fall time of the keying on and off of a Morse Code dit or dah? (Is there a particular circuit one should look for in the schematic of a simple CW transmitter?)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A simple CW sender with some passive filtering will probably have a simple resistor in series with the key signal and a capacitor to ground after the resistor.  It has some drawbacks, but a simple circuit like this can provide basic key click filtering. There are some example circuits &lt;a href=&quot;http://www.sm5bsz.com/txmod/rt0282eng.htm&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-12T20:13:12.163" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1432" PostTypeId="2" ParentId="1430" CreationDate="2014-02-12T20:53:50.483" Score="4" Body="&lt;p&gt;In the August 2010 QST article, &quot;Who Are You Calling a Dummy?&quot;, Page 46, Steve Ford says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And speaking of veteran hams, these same old timers will also be quick to remind you that dummy loads &lt;em&gt;do&lt;/em&gt; radiate.  It's all a matter of degree, after all.  If you are pumping 500W into a dummy load, chances are at least some of the RF energy will escape.  Amateur Radio lore is replete with tales of contacts made with dummy loads - and even &lt;em&gt;between&lt;/em&gt; dummy loads!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As such, your question might be answerable by asking you how small a dummy load you can get, and how good the receiver is at the other end of the DX, and when you can find the best propagation conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem with asking for &quot;the smallest&quot; is that if anyone gives you an actual dimension for the supposed smallest HF antenna, you will have to ask them to prove a negative - that you can't DX on anything smaller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can't prove that, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the moment there's little interest in the community in building a &quot;small antenna&quot; equivalent to QRP.  Part of the problem is that antenna size depends directly on frequency, and gets larger the lower frequency you go.  It would be difficult to come up with a size that applies to all bands as an upper limit to count as a &quot;small antenna&quot; Perhaps one could come up with a table, or simple calculation.  Further, does weight factor into it?  How do you count environmental aspects - does using a small antenna on a large metal roof where the radio is grounded still count, even though the roof makes a better ground plane than someone able to complete the contact on the ground?  With QRP, there's only one measurement, it's valid across all bands, and performs a useful function in encouraging people to make better use of the spectrum and invent new techniques to run lower power.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-12T20:53:50.483" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1433" PostTypeId="2" ParentId="1430" CreationDate="2014-02-12T21:33:04.237" Score="3" Body="&lt;p&gt;Just as there is no &lt;em&gt;lowest&lt;/em&gt; power for QRP, there is no &lt;em&gt;smallest&lt;/em&gt; antenna. As antennas get smaller, they tend to approach, but &lt;em&gt;never reach&lt;/em&gt; 0% &lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_efficiency&quot; rel=&quot;nofollow noreferrer&quot;&gt;radiation efficiency&lt;/a&gt;. If a smaller antenna has say, 50% radiation efficiency, you can compensate by doubling the transmitter power. To anyone receiving your signal from some distance, there will be no observable difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can't double the transmitter power, then you can use a modulation technique that doubles the energy per unit of information. For example, you could switch from AM to SSB, or you could halve the bitrate for a digital modulation. If you can't do that, there's something else you can do. See &lt;a href=&quot;https://ham.stackexchange.com/q/1438/218&quot;&gt;How can I know over what distance or at what speed I can communicate?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-13T18:41:45.327" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1434" PostTypeId="1" AcceptedAnswerId="1436" CreationDate="2014-02-13T01:30:22.920" Score="2" ViewCount="883" Body="&lt;p&gt;What are the repercussions of using 2 transmitters on same frequency? Tx are ~50 feet apart and the freq is 447.800 mhz. &lt;/p&gt;&#xA;" OwnerUserId="714" LastActivityDate="2014-02-13T13:04:57.890" Title="Two transmitters on same frequency" Tags="&lt;frequency&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1435" PostTypeId="2" ParentId="1367" CreationDate="2014-02-13T02:54:38.420" Score="1" Body="&lt;p&gt;In the KX3, the filters are operating at audio frequencies, not IF (as there is no IF in a direct conversion design).&lt;/p&gt;&#xA;" OwnerUserId="35" LastActivityDate="2014-02-13T02:54:38.420" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1436" PostTypeId="2" ParentId="1434" CreationDate="2014-02-13T13:04:57.890" Score="3" Body="&lt;p&gt;In the simplest case, the result will be useless. It's like having two people with identical voices shout at your simultaneously, except that radio receivers are even worse than human brains at separating signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to have multiple transmitters operating simultaneously, you need to multiplex them somehow. There are &lt;a href=&quot;http://en.wikipedia.org/wiki/Channel_access_methods&quot; rel=&quot;nofollow&quot;&gt;many ways to do that&lt;/a&gt;. The simplest way is usually to put them on separate frequencies. This is precisely why companies that make money on wireless communications &lt;a href=&quot;http://news.cnet.com/8301-1035_3-57616673-94/t-mobile-buys-verizon-wireless-spectrum-in-%243.3-billion-deal/&quot; rel=&quot;nofollow&quot;&gt;exchange a lot of money for the right to use a frequency&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-13T13:04:57.890" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1437" PostTypeId="1" AcceptedAnswerId="1444" CreationDate="2014-02-13T17:05:52.100" Score="36" ViewCount="37808" Body="&lt;p&gt;On the 2 meter and 70 centimeter &lt;a href=&quot;http://www.arrl.org/band-plan&quot;&gt;band plans&lt;/a&gt; published by the ARRL, what is the difference in intended use between the calling frequencies (144.200, 432.10 MHz) and the &lt;em&gt;simplex&lt;/em&gt; calling frequencies (146.52, 446.00 MHz)?&lt;/p&gt;&#xA;" OwnerUserId="207" LastEditorUserId="873" LastEditDate="2015-05-10T16:09:59.967" LastActivityDate="2018-10-19T02:27:42.310" Title="What's the difference between national calling frequency and national simplex calling frequency in the 2m and 70cm band plans published by ARRL?" Tags="&lt;united-states&gt;&lt;band-plan&gt;&lt;2m-band&gt;&lt;70cm-band&gt;&lt;arrl&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1438" PostTypeId="1" AcceptedAnswerId="1442" CreationDate="2014-02-13T17:07:22.323" Score="3" ViewCount="418" Body="&lt;p&gt;Given some description of some parameters like:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;transmitter power&lt;/li&gt;&#xA;&lt;li&gt;frequency&lt;/li&gt;&#xA;&lt;li&gt;antenna&lt;/li&gt;&#xA;&lt;li&gt;location&lt;/li&gt;&#xA;&lt;li&gt;time of day&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;how can I know over what distance communication is possible? Can I know the limits to these things, like:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/1235/218&quot;&gt;Simplest, smallest antenna for tuning WWV, WWVH?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/574/218&quot;&gt;What bands and modes will give me voice at 3,000 miles?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/1264/218&quot;&gt;Best QRP HF band for small antenna?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/1430/218&quot;&gt;Smallest HF antenna for DX?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-13T19:13:40.777" Title="How can I know over what distance or at what speed I can communicate?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;modes&gt;" AnswerCount="2" CommentCount="9" FavoriteCount="1" ClosedDate="2014-02-14T14:14:01.267" ContentLicense="CC BY-SA 3.0" />
  <row Id="1439" PostTypeId="2" ParentId="1438" CreationDate="2014-02-13T17:07:22.323" Score="0" Body="&lt;p&gt;You can not know these things except by probabilities. Radio propagation is a &lt;a href=&quot;http://en.wikipedia.org/wiki/Stochastic_process&quot; rel=&quot;nofollow noreferrer&quot;&gt;stochastic process&lt;/a&gt;, the result of many random variables. There are many things that can be done to improve one's chances of success, or worsen them, but always when we are talking about whether something is possible or not, what is the smallest/best/simplest/cheapest piece of equipment, and so on, we are specifying only a small part of the system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider the &lt;em&gt;entire&lt;/em&gt; system involved in communicating between point A and point B, and some of the variables involved at each step.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, we must capture the information to be sent as a baseband signal. Is this a human voice? How intelligible is this voice? Are you repeating everything five times, or just once? Is a good microphone used?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The information must be modulated. Does the modulation limit the fidelity of the baseband signal? How robust in the modulation? Does it employ &lt;a href=&quot;http://en.wikipedia.org/wiki/Forward_error_correction&quot; rel=&quot;nofollow noreferrer&quot;&gt;forward error correction&lt;/a&gt; or other redundancy? Does it distort the baseband signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal must be amplified. What's the transmitter power?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All this must pass through the transmitter's electronics. Are they of good quality? Are they introducing any distortion?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This must pass through a feedline, to an antenna. What are the feedline losses? How efficient is the antenna? Is the antenna directional? Is it pointed in the best direction?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal must then propagate to the receiver. What are current propagation conditions? Are there any &lt;a href=&quot;https://ham.stackexchange.com/questions/1225/what-are-the-general-effects-of-a-geomagnetic-storm-on-propagation&quot;&gt;geomagnetic storms&lt;/a&gt;? Even ordinary lightning creates noise. For HF propagation, ionospheric conditions &lt;a href=&quot;https://ham.stackexchange.com/questions/1059/what-are-some-reliable-sources-of-propagation-forecasts&quot;&gt;are somewhat predictable&lt;/a&gt;, but still highly variable, just like the weather. Line-of-sight propagation is more predictable, but still, is there anything in the propagation path that can absorb/refract/disperse/distort the signal? Dense smog? Cars? Pedestrians? Buildings? Power lines? &lt;a href=&quot;http://avherald.com/h?article=445873f3&quot; rel=&quot;nofollow noreferrer&quot;&gt;Airplanes&lt;/a&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal must be received. Again, what's the receiving antenna and feedline? Of what quality is the receiver? Does it have good filters?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal must be demodulated. What's the noise floor at the receiver? Is there a nearby strong station &lt;a href=&quot;http://en.wikipedia.org/wiki/Desensitization_%28telecommunications%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;desensitizing&lt;/a&gt; the receiver? What &lt;a href=&quot;http://en.wikipedia.org/wiki/Diversity_scheme&quot; rel=&quot;nofollow noreferrer&quot;&gt;diversity schemes&lt;/a&gt; can the receiver employ? What's the operator's skill? What's the modulation's robustness to noise?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are just &lt;em&gt;a few&lt;/em&gt; of the factors that determine the possibility of communicating between A and B. At every step of the way, there are opportunities to improve our chances, or make them worse. To improve your chances of successful communication, you might:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;wait for exceptionally good propagation conditions&lt;/li&gt;&#xA;&lt;li&gt;increase transmitter power&lt;/li&gt;&#xA;&lt;li&gt;increase antenna gain (on either end)&lt;/li&gt;&#xA;&lt;li&gt;use a more robust modulation, like &lt;a href=&quot;http://www.physics.princeton.edu/pulsar/K1JT/wspr.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSPR&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;repeat the transmission multiple times, increasing redundancy&lt;/li&gt;&#xA;&lt;li&gt;put antennas on a high tower where there are fewer obstructions&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The list goes on, and technological advancement is always creating new possibilities. Thus, if we should ask &quot;what's the smallest antenna&quot; or &quot;what's the lowest power&quot; or any similar &quot;what's the worst X could be&quot; type question, the answer is nearly always that there is no limit, because there are always things that can be done to compensate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-13T17:07:22.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1440" PostTypeId="1" CreationDate="2014-02-13T17:59:16.760" Score="11" ViewCount="6616" Body="&lt;p&gt;Reading through an &lt;a href=&quot;http://ww1.microchip.com/downloads/en/DeviceDoc/70005083B.pdf&quot;&gt;RF power amplifier datasheet&lt;/a&gt;, I found the sheet only referenced dBm output power, rather than watts.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What is dBm?&lt;/li&gt;&#xA;&lt;li&gt;How do I convert it to watts?&lt;/li&gt;&#xA;&lt;li&gt;Why, or when, would you use dBm to specify power output rather than watts?&lt;/li&gt;&#xA;&lt;li&gt;Are there specific problems or equations that are easier to deal with in dBm vs watts?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9" LastActivityDate="2021-04-28T11:38:44.067" Title="What is dBm and why is it used rather than watts?" Tags="&lt;rf-power&gt;&lt;jargon&gt;&lt;equipment-design&gt;&lt;amplifier&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1441" PostTypeId="2" ParentId="1440" CreationDate="2014-02-13T18:17:47.890" Score="13" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What is dBm?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;dBm stands for &lt;em&gt;decibels&lt;/em&gt; relative to &lt;em&gt;one milliwatt&lt;/em&gt;. &lt;a href=&quot;http://en.wikipedia.org/wiki/Decibel&quot;&gt;Decibels&lt;/a&gt; represent multiplicative factors, or ratios; by establishing a specific reference level they can instead be used as absolute values: 0 dBm is 1 milliwatt, 3 dBm is approximately 2 milliwatts, etc.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How do I convert it to watts?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Convert the decibel value to a scale factor and multiply by one milliwatt. That is,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$x_{\mathrm{mW}} = 10^{x_{\mathrm{dBm}}/10} \cdot 1 \,\mathrm{mW}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$x_{\mathrm{W}} = 10^{x_{\mathrm{dBm}}/10} \cdot 0.001 \,\mathrm{W}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, the datasheet you link mentions a value of&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$17 \,\mathrm{dBm} = 10^{17/10} \,\mathrm{mW} \approx 50.1 \,\mathrm{mW}$$&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why, or when, would you use dBm to specify power output rather than watts?&#xA;  Are there specific problems or equations that are easier to deal with in dBm vs watts?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Gain and loss in all stages of an RF system (feed line, filters, amplifiers) &lt;strong&gt;is multiplicative&lt;/strong&gt; (if it were not, that would be nonlinearity), and therefore is typically written in dB so that the total gain or loss may be computed by adding, rather than multiplying, all the individual values together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you add a value in dB to a value in dBm, the result is in dBm. (Adding two dBm values is not usually meaningful since it would correspond to power squared.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-02-13T20:02:33.203" LastActivityDate="2014-02-13T20:02:33.203" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1442" PostTypeId="2" ParentId="1438" CreationDate="2014-02-13T18:21:05.250" Score="2" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem&quot; rel=&quot;nofollow&quot;&gt;Shannon's law&lt;/a&gt; on information communication provides statistical upper limits on data rate given a &lt;a href=&quot;http://en.wikipedia.org/wiki/Signal-to-noise_ratio&quot; rel=&quot;nofollow&quot;&gt;signal to noise ratio&lt;/a&gt;: &lt;em&gt;S/N&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There may be nice physics models on the power coupled between a pair of dipoles in free space, to get a best case on signal power received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, the transmission channel is usually not in outer space, but contains a huge number of absorptive and reflective bodies (perhaps including the &lt;a href=&quot;http://en.wikipedia.org/wiki/Ionosphere#Radio_communication&quot; rel=&quot;nofollow&quot;&gt;upper atmosphere&lt;/a&gt;), often in unknown or nearly randomly changing configurations, ruining any nice clean closed form equation for the the received &lt;em&gt;S&lt;/em&gt; in &lt;em&gt;S/N&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also unfortunately, the &lt;a href=&quot;http://en.wikipedia.org/wiki/Noise_floor&quot; rel=&quot;nofollow&quot;&gt;noise floor&lt;/a&gt; (the &lt;em&gt;N&lt;/em&gt; in &lt;em&gt;S/N&lt;/em&gt;) is almost always quite indeterminate in the real world, and has to be found by experimentation.  Background noise, interfering signals, receiver front-end noise, and etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can test yourself, or perhaps make a reasonable guess at what might be possible based on prior published results.  Assuming conditions are fairly similar and don't change much.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-02-13T19:13:40.777" LastActivityDate="2014-02-13T19:13:40.777" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1443" PostTypeId="2" ParentId="1421" CreationDate="2014-02-13T18:26:35.640" Score="1" Body="&lt;p&gt;Here is a list which I've used a few times from the ISS Fan CLub:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.issfanclub.com/frequencies&quot; rel=&quot;nofollow&quot;&gt;http://www.issfanclub.com/frequencies&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This one is has some frequencies from the ISS and associated craft:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.zarya.info/Frequencies/FrequenciesISS.php&quot; rel=&quot;nofollow&quot;&gt;http://www.zarya.info/Frequencies/FrequenciesISS.php&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the right hand side of this page, it gives the callsigns which &lt;em&gt;could&lt;/em&gt; be used:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://spaceflight.nasa.gov/station/reference/radio/&quot; rel=&quot;nofollow&quot;&gt;http://spaceflight.nasa.gov/station/reference/radio/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would recommend ISStracker for the location, although N2yo and heavens above are also useful for satellite tracking, especially for other types.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; I just came across this a second ago:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;a href=&quot;http://www.monitoringtimes.com/html/Monitoring%20NASA%20and%20Space%20Communications.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.monitoringtimes.com/html/Monitoring%20NASA%20and%20Space%20Communications.pdf&lt;/a&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It might be a bit out of date (2006) but it might be useful to you. I would also recommend a scanning directory, as they often list stuff like this!&lt;/p&gt;&#xA;" OwnerUserId="718" LastEditorUserId="718" LastEditDate="2014-02-14T21:35:55.937" LastActivityDate="2014-02-14T21:35:55.937" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1444" PostTypeId="2" ParentId="1437" CreationDate="2014-02-13T18:38:27.103" Score="28" Body="&lt;p&gt;The simplex calling frequencies (146.520/446.000 Mhz) are intended for &lt;strong&gt;FM&lt;/strong&gt; simplex communication, while the other pair (144.200/432.100) are for &lt;strong&gt;SSB&lt;/strong&gt;. In general use, the term &quot;simplex&quot; implies FM modulation since FM is commonly used in both simplex and duplex operation. SSB, CW, and other modes are generally used for longer distance, simplex-only communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This answer is based on the &lt;a href=&quot;https://plus.google.com/107308013584304553755/posts/Z1Br7v6Geyi&quot;&gt;discussion&lt;/a&gt; I generated from posting this question on &lt;a href=&quot;https://plus.google.com/communities/101567225799677082176&quot;&gt;the Amateur Radio G+ community&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="207" LastEditorUserId="207" LastEditDate="2014-02-17T16:27:18.247" LastActivityDate="2014-02-17T16:27:18.247" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1445" PostTypeId="2" ParentId="1430" CreationDate="2014-02-13T18:59:40.370" Score="-1" Body="&lt;p&gt;You could maybe try a random wire antenna that's made to lie flat or be suspended from your house to a pole at the end of your garden. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a table of the best calculated lengths for such:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.hamuniverse.com/randomwireantennalengths.html&quot; rel=&quot;nofollow&quot;&gt;http://www.hamuniverse.com/randomwireantennalengths.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm sure there might be some designs floating around that give you specifications for how you might make it smaller, but it's worth a try at the least!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know a HAM that does what I mentioned above, and manages to get the US and Romania on 10W, easy, but barely make it down the road, lol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good Luck!&lt;/p&gt;&#xA;" OwnerUserId="718" LastActivityDate="2014-02-13T18:59:40.370" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1446" PostTypeId="1" CreationDate="2014-02-13T19:12:19.137" Score="5" ViewCount="132" Body="&lt;p&gt;It used to be that if you wanted to power up an old tube radio, you'd use a variac and gradually bring up the line voltage to avoid damage to the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this needed or suggested for transformer powered semiconductor radios that have been sitting around unused for decades?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I expect the answer will be no for radios with switching power supplies, but there are a lot of radios with transformer based power supplies, and some even lacking basic regulation.  Will it make a difference in preserving such radios?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-13T19:31:01.680" Title="Is a gradual power-up recommended for non tube based radios?" Tags="&lt;repair&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1447" PostTypeId="2" ParentId="1446" CreationDate="2014-02-13T19:31:01.680" Score="4" Body="&lt;p&gt;So far as I'm aware, the reason for using a variac isn't that there are tubes, but that the radio is old and unused for a long time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is that &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrolytic_capacitor&quot; rel=&quot;nofollow&quot;&gt;electrolytic capacitors&lt;/a&gt; rely on a dielectric (insulation between the plates) that is maintained by an electrochemical reaction between the plates. This reaction requires a voltage across the plates to occur. If the radio is unused for a long time, the dielectric degrades, having no voltage to maintain it. With the weakened dielectric, the capacitor is unable to withstand as much voltage without failure. Bringing the voltage up slowly with a variac, or with a current-limited supply gently &lt;a href=&quot;http://www.qsl.net/g3oou/reform.html&quot; rel=&quot;nofollow&quot;&gt;reforms the capacitors&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is somewhat compounded by two factors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;old tube equipment was manufactured when electrolytic capacitors were a newer technology, lacking the reliability of modern electrolytic capacitors&lt;/li&gt;&#xA;&lt;li&gt;tube equipment tends to operate at a higher voltage than modern transistor equipment&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Because of these factors, and that any transistor radio won't be so old, this reforming procedure isn't so much of a concern for transistor radios. That's not to say it has no value, especially for very early transistor radios, but the utility is rather reduced, I'd say.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, in the specific case of switching power supplies you mention, bringing the voltage up slowly with a variac is futile. To a first approximation, a switching supply draws a constant power from the input, so if you provide it a lower input voltage, it will just draw more current from the input in order to produce the designed output voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you &lt;em&gt;can&lt;/em&gt; do in the general case is at least limit the damage that will occur if a capacitor, or anything else, is busted in a radio of unknown workingness. A current-limited supply is always a good idea. If you don't have a proper current-limited bench supply, at least assure a properly sized fuse is in place. It's possible a component may burn out, but at least you won't set the radio on fire.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-13T19:31:01.680" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1448" PostTypeId="2" ParentId="1132" CreationDate="2014-02-13T19:43:36.930" Score="0" Body="&lt;p&gt;Apart from the WARC bands you could possibly try CB radio. I know in the US is usually has a negative stigma attached to it, but alot of my local HAM's are similar to you, as in they hate contests, so they go on CB channel 38 when they can't get through on the other HF bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;10m doesn't get used very much here, and even if it does, we get horrible QRM, so 11m (CB) is the last resort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you want to be a 'reckless' ham, you could always transmit voice over the CW and data frequencies. People might hate you for it, but It's not illegal, at least not here (UK).&lt;/p&gt;&#xA;" OwnerUserId="718" LastEditorUserId="718" LastEditDate="2014-02-13T19:56:04.050" LastActivityDate="2014-02-13T19:56:04.050" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1449" PostTypeId="1" CreationDate="2014-02-13T19:50:42.387" Score="9" ViewCount="167" Body="&lt;p&gt;Some use contesting for personal accomplishment, some out of pure enjoyment, others to gather awards, and some to hone their ability to work their craft.  For instance, &lt;a href=&quot;https://ham.stackexchange.com/questions/1000/what-skills-will-i-learn-from-contesting&quot;&gt;you may learn or improve your skills merely by contesting&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm wondering if beyond personal enjoyment, contests perform a useful function for the Amateur Radio hobby as a whole?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-03-05T14:14:06.037" Title="How does contesting benefit Amateur Radio and its community?" Tags="&lt;contest&gt;" AnswerCount="3" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="1450" PostTypeId="2" ParentId="1440" CreationDate="2014-02-13T19:54:15.780" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Are there specific problems or equations that are easier to deal with in dBm vs watts?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Decibel units, dBm being an example of such, provide a more intuitive measure of some property that responds logarithmically, like power frequently does. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider, if you are transmitting now with 1W, and you add 1W more, you have &lt;em&gt;doubled&lt;/em&gt; your transmit power. That's a &lt;em&gt;big&lt;/em&gt; difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are transmitting with 100W, and you add 1W more, your transmit power is 101W. This is only 1% more power: hardly a relevant change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Decibels account for this. From 1W to 2W is a +3dB change. From 100W to 101W is a +0.043dB change. If you were to increase +3dB from 100W, the result would be 200W, which is the same degree of improvement as 1W to 2W is.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-13T19:54:15.780" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1451" PostTypeId="1" AcceptedAnswerId="1452" CreationDate="2014-02-13T20:49:29.293" Score="8" ViewCount="1147" Body="&lt;p&gt;The advice I have seen on lightning safety is that if you don't have high-quality lightning protection (and associated grounding) installed on your feed line, it is advisable to, during a storm and preferably whenever you are not using your station, is to disconnect the antenna feed line from your equipment and &lt;strong&gt;“throw it out the window”&lt;/strong&gt;, to separate it from the interior of the house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems like a perfectly reasonable idea to me, except for the fact that “out the window” is likely to be wet, especially under the circumstances. &lt;strong&gt;How can I protect the free end of the coaxial cable (a PL-259 connector in this case) from water and other environmental damage?&lt;/strong&gt; Permanent connections can be wrapped with amalgamating tape, but this is temporary and recurring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible I could arrange to hang the cable right under the eaves of the roof so as to avoid actual rain, but it would still be exposed to damp, windblown crud, bugs, and so on. I do have a rubber dust-cap the cable came with but it doesn't fully enclose the connector — would that be sufficient, assuming there isn't actually rain running down the cable?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or alternatively, what &lt;strong&gt;other approaches&lt;/strong&gt; should I consider for the safety of myself and my equipment, besides the above two? Note I am in a rented space and all of my current equipment is specifically installed “temporarily”. (Taking down the antenna itself is quite easy and I would probably do it in the event of a predicted storm, but even then the feed line is still a conductor outside of the building, and partly on the roof.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-12-15T23:53:59.373" LastActivityDate="2015-12-15T23:53:59.373" Title="How to keep a disconnected coaxial connector weatherproof?" Tags="&lt;coaxial-cable&gt;&lt;weather&gt;&lt;safety&gt;&lt;equipment-protection&gt;&lt;lightning&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1452" PostTypeId="2" ParentId="1451" CreationDate="2014-02-13T21:27:33.380" Score="5" Body="&lt;p&gt;I'd recommend one of two solutions:&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;1. Don't throw it out the window.&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Most lightning damage comes not from direct strikes but nearby strikes, which can still induce large-ish voltages on the feedline: not enough to make lightning, but enough to damage things. A couple feet of air between the feedline and the tranciever will protect against this. If you do get a direct strike, you will probably have a lot of problems, feedline out the window, or not. Sure, you are taking an additional risk, but it's a small one, and maybe acceptable. Unless you have a very large tower, it's probably nearly as likely that lighting will strike your home's wiring, so unless you are unplugging that also, the additional risk of feedline-not-out-the-window is negligible.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;2. Don't throw it out the window, but ground it really well, inside.&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;If you can arrange for a good Earth ground, and put a connector on it, you can detach your feedline and connect it to this ground. This is as good as throwing it out the window, without the difficulties of protecting the feedline's end from the elements. It still wouldn't hurt to have this grounding point be physically away from your valuable equipment, where possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that in this case, it's important that the ground you use for the feedline when it's disconnected is used &lt;em&gt;only&lt;/em&gt; for that purpose. It exists to reduces the chances that current from a strike traveling on the feedline will arc into your house wiring, ductwork, pipes, or desk.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to say, connect a radio chassis to this ground, you have now created a real problem, even if you disconnect the feedline, because you &lt;em&gt;haven't actually disconnected it&lt;/em&gt;. Should lightning strike the power lines, or even strike somewhere close to your house, there could be hundreds or maybe thousands of volts difference between the utility ground at the electric distribution panel, and the extra one you added for the feedline. Your radio is sitting between these two points, a lot of current will flow through it, and you might be sad. Lightning current from a strike on the antenna will likewise go through your radio, to the electric distribution panel. Bad.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-02-27T01:58:48.163" LastActivityDate="2014-02-27T01:58:48.163" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1453" PostTypeId="1" AcceptedAnswerId="1455" CreationDate="2014-02-13T21:31:38.433" Score="7" ViewCount="2314" Body="&lt;p&gt;So I'm developing my own SDR software from scratch (I like to &quot;own&quot; the code).  The channel between the RF-to-USB hardware and the software is 192kHz sample-rate IQ audio samples.  The degrees of freedom seem to include at least 4 frequencies and a switch.  The 4 frequencies are: RF filter frequency, external tuner reference oscillator frequency, software complex multiplication oscillator frequency, software bandpass filter center-frequency (also filter bandwidth).  Then select from I, Q, I+Q, I-Q, or abs(I,Q) for audio output.  Then resample as necessary to match the audio output API.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So assume I set the 1st frequency (front-end RF filter) to the HF band of interest, the 2nd HF reference oscillator to the middle of some CW HF band.  Now say I find a QSO 12.500 kHz up from the HF reference oscillator, and I'd like the resulting Morse Code audio side tone frequency to be 750 Hz.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where do I set my software oscillator frequency for the complex multiplication and what do I want my software bandpass filter center frequency to be to hear Morse Code with the desired side tone?  (Do I have 2 choices?  If so, how to choose?)  Which final IQ mux output do I select to feed the audio speaker?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2014-02-17T19:17:54.503" LastActivityDate="2014-07-12T00:37:22.713" Title="Configuring an SDR for CW?" Tags="&lt;cw&gt;&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1454" PostTypeId="2" ParentId="1451" CreationDate="2014-02-13T21:42:22.353" Score="3" Body="&lt;p&gt;There's no easy way to weatherproof it, but only you can know how bad the weather is likely to get, and balance the effort and cost of providing protection against the actual needed protection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do want to throw it outside and protect it, though, one method that works fairly well is to take a piece of capped PVC mounted so the cap is up, forming a tube with the open end down.  Mount it to the side of the house within reach of the window or access point, with a little dowel or notched section of the PVC extending from the bottom an inch or two. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you need to put it away, shove the cable end up into the PVC, then secure it on the dowel with a clip (clothespin, binder clip, etc), or rubber bands, velcro tie, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Taking it out is simply reversing the process.  Leave the clip/velcro/etc in place so you aren't scrounging for one when you need to deal with it next time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This isn't meant to be weather proof, only to provide temporary short term protection for brief storage periods.  If you want to store your cable end outdoors for more than a day or two, humidity, bugs, and other issues will arise that this solution isn't meant to solve.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-13T21:42:22.353" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1455" PostTypeId="2" ParentId="1453" CreationDate="2014-02-13T21:51:49.363" Score="7" Body="&lt;p&gt;Implementing a CW receiver in an SDR is pretty much like implementing a SSB receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will tune the RF bits to some band of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, you will multiply the I/Q signal so that the CW signal you want to receive is at 750 Hz, if that's your desired pitch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, you must filter. There are two reasons. The obvious reason: you don't want to hear everything in the band. But also, the I/Q data contains both positive and negative frequencies. Frequency 0 corresponds to the LO frequency (plus the shift you introduced in the multiplication step above). Negative frequencies are below that, positive frequencies above. We need to, at some point, get rid of these negative frequencies, because they correspond to the LSB sidebands which we don't want or need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After you've filtered, all the negative frequencies will be attenuated by the filter's stopband. Now we can take I, just Q, or I+Q, or I-Q (the only difference between each is the phase), and what you will hear is all the positive frequencies, plus all the negative frequencies. However, since we filtered the negative frequencies away, we in effect hear just the positive frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only difference between this and a USB receiver is the filter width. If you want to make it a LSB receiver, all you need to do is move the filter passband into the negative frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For an example, see this &lt;a href=&quot;http://www.oz9aec.net/index.php/grc-examples#ssbrx&quot; rel=&quot;nofollow noreferrer&quot;&gt;example in GNU Radio Companion by OZ9AEC&lt;/a&gt;. GNU Radio Companion can be a good source for examples because it's programmed by graphical flowcharts. Here's one from that article:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/wbTu6.png&quot; alt=&quot;SSB receiver in GRC&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are some &lt;em&gt;FFT Sinks&lt;/em&gt; which are graphical UI elements just to visualize the data at that point. &lt;em&gt;USRP Source&lt;/em&gt; configures his particular hardware. The &lt;em&gt;Frequency Xlating FIR filter&lt;/em&gt; performs the multiplication step, while additionally resampling the data (the USRP has a very high sample rate). Then there's a band pass filter, and he's added some automatic gain. &lt;em&gt;Rational Resampler&lt;/em&gt; resamples the data again to get it down to an audio sample rate. &lt;em&gt;Complex to Real&lt;/em&gt; discards &lt;em&gt;Q&lt;/em&gt; and gives you just &lt;em&gt;I&lt;/em&gt;. The multiplier at the end is a volume control, then it goes to the speakers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also if you look closely, the cutoff frequencies for the band pass filter are negative. As configured, this is an LSB receiver. Make those positive, and narrow, and you have a CW receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="1197" LastEditDate="2014-07-12T00:37:22.713" LastActivityDate="2014-07-12T00:37:22.713" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1456" PostTypeId="2" ParentId="1344" CreationDate="2014-02-14T00:48:57.530" Score="0" Body="&lt;p&gt;I did a few searches and I came across this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.cqham.ru/sch_eng.html&quot; rel=&quot;nofollow&quot;&gt;http://www.cqham.ru/sch_eng.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not a comprehensive listing, but I does cover a number of known modern brands and radios, such as those made by Icom, Alinco, Albrecht, Kenwood and Yaesu, for both HAM &amp;amp; CB radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you require a schematic for a specific radio, I would recommend trying out a term such as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;yaesu &quot;ft-60&quot; schematics&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Replacing the brand and model shown with your own.&lt;/p&gt;&#xA;" OwnerUserId="718" LastActivityDate="2014-02-14T00:48:57.530" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1457" PostTypeId="2" ParentId="1032" CreationDate="2014-02-14T01:09:36.620" Score="0" Body="&lt;p&gt;There is a large amount of low powered hardware that can be shipped in from Europe on the 433MHz band, as there is an EU wide treaty which allows for Low Powered Devices (LPD) to operate on 69 channels between 433.075 MHz to 434.775 MHz with a licence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apart from the the required of low power, there is little restrictions on what can be used, so you can get LPD433 devices for model control, analogue voice, digital voice and key less entry systems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are in the US, there should be little issues, but in the UK, channels 1 to 14 are UK Amateur repeater outputs and channels 62 to 69 are UK Amateur repeater inputs. Although HAM's are secondary users anyway as the Ministry of Defence has it as Primary. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;remember reading that the UK government campaigned against it as the background QRM was so bad in this band, something which apparently wasn't a issue in the test of Europe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a result, low powered walkie talkies are available, although ones of 446MHz are more common, which allows for up 500mW. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;10mW is the EU restriction of power regarding LPD433, however this may not be a massive problem if you are building it yourself from scratch. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good Luck!&lt;/p&gt;&#xA;" OwnerUserId="718" LastActivityDate="2014-02-14T01:09:36.620" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1458" PostTypeId="2" ParentId="1440" CreationDate="2014-02-14T01:12:27.200" Score="-3" Body="&lt;p&gt;dBm is an incomplete term&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also need the missing parameter which the datasheet writers assume you know: the impedance. For audio / telegraphy this is 600 ohms but for RF this is usually 50 ohms.&lt;/p&gt;&#xA;" OwnerUserId="720" LastActivityDate="2014-02-14T01:12:27.200" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1459" PostTypeId="1" AcceptedAnswerId="1460" CreationDate="2014-02-14T12:06:08.530" Score="10" ViewCount="267" Body="&lt;p&gt;When a US Amateur operates in Canada, IT and Canadian regs permit some lattitude on their identification. I have read that some will prefix a &quot;VE3&quot; plus their own home callsign (Ontario, meaning I am in Ontario right now, but my real callsign is the following US one) on their callsign, some will simply indicate that that they are mobile in some way, and some may continue to use their regular callsign without indicating that they are mobile?  What is actually most commonly done, and what expectations (if any) does the amateur radio community usually expect from mobile operators operating mobile in a friendly foreign nation, particularly Americans operating in Canada?&lt;/p&gt;&#xA;" OwnerUserId="643" LastEditorUserId="76" LastEditDate="2015-05-01T18:35:50.610" LastActivityDate="2017-03-06T18:51:42.713" Title="What is the most common amateur identification practice for mobile US amateurs operating in Canada?" Tags="&lt;united-states&gt;&lt;mobile&gt;&lt;canada&gt;&lt;station-identification&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1460" PostTypeId="2" ParentId="1459" CreationDate="2014-02-14T17:52:01.310" Score="6" Body="&lt;p&gt;According to &lt;a href=&quot;http://www.arrl.org/international-operating&quot;&gt;ARRL&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Identification for US amateurs is the US call separated by a stroke and the appropriate Canadian prefix identifier (e.g. N1KB/VE3)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In every case I can think of, one is required to identify the location from which they are transmitting, if it is not in their call sign, or at least a different country. And usually they want more than just the country, they also want to know the location of the country (VE3 in this case). So any amateur should be following this practice, period.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-02-14T17:52:01.310" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1461" PostTypeId="1" AcceptedAnswerId="1462" CreationDate="2014-02-16T02:55:39.003" Score="3" ViewCount="982" Body="&lt;p&gt;The Yaesu FT-897D has a so-called “Programmable Memory Scan (PMS)” feature, which allows limiting scanning to a user-defined band by creating special paired memory entries which set the upper and lower frequency bounds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've used it successfully on the first programmed band (M-P1L to M-P1U), but I can't figure out how to select a different programmed band to scan. I've tried selecting M-P1L before entering PMS mode and it just goes to PMS-1 instead of PMS-2, and none of the controls &lt;em&gt;in&lt;/em&gt; PMS mode change bands that I've noticed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.yaesu.co.uk/files/FT-897D%20Operating%20Manual.pdf&quot; rel=&quot;nofollow&quot;&gt;The manual&lt;/a&gt; on page 50 discusses how to enable PMS but not how to change bands. Searching for advice on the web only turned up &lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?topic=82545.0&quot; rel=&quot;nofollow&quot;&gt;this rather annoyed person's workaround&lt;/a&gt; of SKIPping the memories other than the one to use, which can't possibly be how it's supposed to work.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-02-16T03:06:29.183" Title="How do I select a programmed memory scan on the Yaesu FT-897D?" Tags="&lt;transceiver&gt;&lt;yaesu&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1462" PostTypeId="2" ParentId="1461" CreationDate="2014-02-16T02:55:39.003" Score="1" Body="&lt;p&gt;The PMS pairs interact with tuning similarly to the built-in band limits. Use the usual tuning controls (MEM/VFO CH or DIAL) to go past an end — higher than M-PxU or lower than M-PxL — and the transceiver will switch to the next or previous PMS pair.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as I've found, this is the &lt;em&gt;only&lt;/em&gt; way to change between PMS pairs. Pressing the BAND buttons will &lt;em&gt;not&lt;/em&gt; do so, and will merely disable PMS and change bands normally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you leave and re-enter PMS mode the last used PMS pair will be remembered, but the VFO will be reset to the M-PxL frequency.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-02-16T03:06:29.183" LastActivityDate="2014-02-16T03:06:29.183" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1463" PostTypeId="1" AcceptedAnswerId="1466" CreationDate="2014-02-16T17:22:04.957" Score="8" ViewCount="17608" Body="&lt;p&gt;What's the approximate range achievable by a 2.4 GHz signal of 1 watt in semi-urban areas?  I can see 2 km from our rooftop. Will a 2.4 GHz signal go that far, i.e. if I send WiFi signals from our rooftop is it possible to catch them on my phone 2 km away?&lt;/p&gt;&#xA;" OwnerUserId="731" LastEditorUserId="76" LastEditDate="2014-02-17T00:20:19.383" LastActivityDate="2016-12-26T09:40:13.130" Title="How far can a 2.4 GHz, 1 watt signal go in a rural area?" Tags="&lt;propagation&gt;&lt;wifi&gt;&lt;line-of-sight&gt;" AnswerCount="5" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1464" PostTypeId="2" ParentId="1463" CreationDate="2014-02-16T18:37:27.860" Score="2" Body="&lt;p&gt;It's unlikely that the transceiver at the fixed location will hear the relatively tiny signal from your phone 2km away well enough to establish a link.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need to have more power on both sides to make it work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even then, you might need specialized, large antennas or dishes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course if there are no restrictions then you should be able to establish such a link with huge dishes on either end at a fraction of that power.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-16T18:37:27.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1465" PostTypeId="1" CreationDate="2014-02-16T21:07:20.120" Score="10" ViewCount="823" Body="&lt;p&gt;On the back of my Yaesu FT-897, next to each of the antenna connectors, there are lightning-bolt-ish symbols. What do these mean, and is there something I ought to be doing because of that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have not found any description of a meaning for these symbols. My best guess so far is that they are warnings of possible high voltage (while transmitting), but they are not enclosed in a triangle as in the standard high-voltage warning symbol. I thought they might be archaic symbols for antennas, but there is an antenna symbol placed between the two connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/spZgT.jpg&quot; alt=&quot;There is a lightning bolt with arrowhead placed to the left of the left antenna connector, and one placed to the right of the right connector. They each point towards the center of the connector, as opposed to straight down.&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T18:24:31.727" LastActivityDate="2016-10-29T18:24:31.727" Title="What does a lightning bolt symbol next to an antenna connector mean?" Tags="&lt;transceiver&gt;&lt;jargon&gt;&lt;antenna-system&gt;&lt;yaesu&gt;&lt;equipment&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1466" PostTypeId="2" ParentId="1463" CreationDate="2014-02-16T21:32:48.793" Score="10" Body="&lt;p&gt;This is a strange sort of question, as in reality the signal will go infinitely far (effectively) however you are really asking at what distance might a receiver be able to pick up the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In testing a 2.4GHz signal with a 100mW omni antenna, the furthest distance I could receive a signal with less than 5% retries (802.11b kit) was 2 miles with a 100mW 3dB receiver. I could manage over 5 miles with a directional 10dB antenna, but had some trouble aiming it accurately.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your phone is going to have challenges at that range, but if you have a specific location, you could use a directional antenna on your rooftop aimed at that location. Even a basic Huber Suhner running at 1W could make that work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(disclaimer - I used to test 2.4GHz radio kit from Symbol, Telxon, Motorola and Cisco. I can't post the data tables, but more than happy to give indications of what might work)&lt;/p&gt;&#xA;" OwnerUserId="50" LastActivityDate="2014-02-16T21:32:48.793" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1467" PostTypeId="1" AcceptedAnswerId="1472" CreationDate="2014-02-16T22:25:47.890" Score="11" ViewCount="5413" Body="&lt;p&gt;My radio-club recently got a Yaesu FT-225RD transceiver and I'm trying to digest its manual (available for download &lt;a href=&quot;http://www.radiomanual.info/schemi/FT225RD_user.pdf&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;). This is the first ham radio that I'm learning how to use, so I could be missing something obvious.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the front panel there's a knob marked CLARIFIER and the manual has following description for it:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The clarifier control allows a means of offsetting the transceive or&#xA;  receive frequency by ±4 kHz from the frequency established by the main&#xA;  VFO dial.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I do understand that radio's frequency will drift with time and that not everyone's rig will be spot on channel and that in such cases minor adjustments may be needed to improve reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I don't understand is when would use of clarifier be preferable to use of the main frequency dial. From what I can see, the main dial offers pretty good resolution for frequency adjustment and clarifier isn't a fancy name for a fine-tune knob I've seen on on radio receivers for commercial FM band from the same time period. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPDATE: One thing that I didn't find relevant to the question at first is that in addition to the clarifier knob, there is a clarifier switch as well which is used to set clarifier to one of 3 settings: transceive, receive and off. This would imply (at least in my opinion) that in transceive setting, the clarifier would affect frequencies of both transmission and reception.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2014-02-17T12:54:21.723" LastActivityDate="2019-04-26T15:04:57.423" Title="How is &quot;clarifier&quot; control helpful?" Tags="&lt;yaesu&gt;&lt;equipment-operation&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1468" PostTypeId="2" ParentId="1465" CreationDate="2014-02-17T01:47:16.580" Score="2" Body="&lt;p&gt;The manual for this unit doesn't seem to explain or call out these symbols.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When talking about these jacks the manual warns about the following:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;don't leave them connected to antennas during lightning storms&lt;/li&gt;&#xA;&lt;li&gt;do not place antennas near power lines, or in a way that might allow them to contact power lines &lt;/li&gt;&#xA;&lt;li&gt;be aware of RF exposure&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-17T01:47:16.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1469" PostTypeId="1" AcceptedAnswerId="1479" CreationDate="2014-02-17T01:57:55.287" Score="20" ViewCount="94958" Body="&lt;p&gt;I am happy with my BaoFeng UV-5R Pro but the local UHV VHF repeater and simplex reception is terrible, even for contacts less than 50 kilometers. I assume that it's because the rubber-ducky antenna on it is terrible. What can I replace it with that is readily available commercially, costs less than $100 US, will give me a better handheld reception experience, and still maintain excellent portability (for my case, let's say that means less than 2.5 pounds antenna weight, less than 3 feet tall)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know much about dBi gain, but I have seen antennas claiming to be &quot;144Mhz 2.15dBi 430Mhz 3.0dBi&quot;, I'm still learning so I don't know how to interpret that information.&lt;/p&gt;&#xA;" OwnerUserId="643" LastEditorUserId="643" LastEditDate="2014-02-17T12:20:41.170" LastActivityDate="2019-01-11T12:09:56.817" Title="What antenna on a BaoFeng UV-5R Pro will give me better reception?" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;vhf&gt;&lt;baofeng&gt;" AnswerCount="10" CommentCount="4" FavoriteCount="6" ClosedDate="2019-01-11T17:03:31.210" ContentLicense="CC BY-SA 3.0" />
  <row Id="1470" PostTypeId="2" ParentId="1469" CreationDate="2014-02-17T02:25:57.727" Score="1" Body="&lt;p&gt;The Quansheng TG-UV2 antenna had about 1-1.5 dB gain on VHF with no difference on UHF under controlled conditions. Of course use maximum output and keep the antenna vertical. SUrecom and Nagoya antenna were marginal and with mixed results none were better than &amp;lt; 1.0db gain.&lt;/p&gt;&#xA;" OwnerUserId="733" LastActivityDate="2014-02-17T02:25:57.727" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1471" PostTypeId="2" ParentId="1467" CreationDate="2014-02-17T03:22:16.380" Score="2" Body="&lt;p&gt;For a single contact, as you say, it's pointless. When you're talking as part of a group and one or two members are slightly off frequency it lets you temporarily tune your receiver for their signals without leaving the main frequency that everyone else is on. When it's on it &quot;clarifies&quot; their signal; when it's off you hear the rest of the group clearly.&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2014-02-17T03:22:16.380" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1472" PostTypeId="2" ParentId="1467" CreationDate="2014-02-17T12:36:28.557" Score="8" Body="&lt;p&gt;I think &quot;RIT&quot;, for &quot;receiver incremental tuning&quot;, is a better name for that knob because it more directly explains what it does: it tunes the receiver, without tuning the transmitter. The result is that you receive and transmit on different frequencies. It is similar to &lt;a href=&quot;https://ham.stackexchange.com/q/1104/218&quot;&gt;operating split&lt;/a&gt;, with less frequency separation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is most useful when you've already started a contact, but now you want to change your tuning. If you re-tune by adjusting the main VFO, you also move your transmitter. Now the other guy will have to re-tune to you, then you re-tune to him, and so on, until you have walked out of the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning could be off for any number of reasons. There are some people who aren't very good at accurately tuning SSB, or perhaps they just don't mind the &lt;a href=&quot;https://ham.stackexchange.com/q/355/218&quot;&gt;weird way it makes voices sound&lt;/a&gt;, or they have old equipment without a stable VFO. Listen to any SSB net for an example. I suspect this is the origin of the term &quot;clarifier&quot;. In CW operation, not everyone tunes accurately to their sidetone frequency. Especially in CW operation, you might want to tune your receiver to get the signal into a narrow filter passband, or to get some noise in the stopband.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-17T12:36:28.557" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1473" PostTypeId="2" ParentId="1469" CreationDate="2014-02-17T12:46:44.037" Score="5" Body="&lt;p&gt;The antenna included with the BaoFeng is notably bad, even for a rubber duck. To answer your question of what would be better: &lt;em&gt;anything&lt;/em&gt; would be better. You'd have to switch to a dummy load to do worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whatever antenna you do select, it need not be anything specific to your radio. Any antenna suitable for whatever bands you wish to operate will be fine. The only gotcha with BaoFeng radios is they have a male SMA connector on the radio where every other radio made has a female connector. They are popular enough now you can find antennas with this connector, or you can find adapters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quality aside, rubber duck antennas trade size for efficiency. It generally true that the smaller an antenna is made, the less efficient it is. A full-size whip will be a quarter wavelength, so approximately half a meter long for the 2 meter band. There are designs with degrees of shortening anywhere between that and a rubber duck, so get the longest one that isn't &quot;too big&quot; for your preferences to maximize efficiency.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-02-17T16:26:20.490" LastActivityDate="2014-02-17T16:26:20.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1474" PostTypeId="2" ParentId="1469" CreationDate="2014-02-17T13:02:41.693" Score="2" Body="&lt;p&gt;Most HT antennas can be purchased for far less than \$100. You can buy a 1/2 wave VHF Nagoya antenna from most online sources for approximately \$10. Better brands will cost a little more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dBi value is the forward gain of the antenna when compared to a theoretical isotropic antenna (hence the &lt;em&gt;i&lt;/em&gt; in dBi) that radiates all its power evenly in all directions. To be of any use in your case, you'd also need to know the dBi gain of the rubber duck antenna, but, as was stated in another answer, rubber duck antennas have traded off performance for size so any whip antenna is almost guaranteed to perform better.&lt;/p&gt;&#xA;" OwnerUserId="207" LastEditorUserId="207" LastEditDate="2014-02-17T13:54:07.273" LastActivityDate="2014-02-17T13:54:07.273" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1475" PostTypeId="1" CreationDate="2014-02-17T13:25:33.687" Score="1" ViewCount="596" Body="&lt;p&gt;I'm trying to assemble a VHF/UHF FM base-station at home. Assuming I have the following pieces of equipment:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;VHF/UHF FM transceiver&lt;/li&gt;&#xA;&lt;li&gt;power supply - 30 amps, no meters&lt;/li&gt;&#xA;&lt;li&gt;antenna that's resonant on 2m and 70cm and a way to mount it&lt;/li&gt;&#xA;&lt;li&gt;proper grounding&lt;/li&gt;&#xA;&lt;li&gt;cabling to link them all together&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;What other gear and equipment, besides the list above, would most hams consider essential or at least highly recommend having at hand? The intended use of the station is local repeater and simplex operation for casual contacts, net participation, and possibly emergency operations (RACES/ARES).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To further clarify what I'm trying to ask, would any of the following be considered essential or at least really really useful to have under the above scenario with the previously mentioned equipment?&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;dummy load&lt;/li&gt;&#xA;&lt;li&gt;ammeter/multimeter (assuming the power supply doesn't display amperage)&lt;/li&gt;&#xA;&lt;li&gt;in-line antenna tuner&lt;/li&gt;&#xA;&lt;li&gt;informational resources (maps, log books, etc)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="207" LastEditorUserId="207" LastEditDate="2014-02-17T14:30:43.507" LastActivityDate="2014-02-17T20:32:50.410" Title="What is the essential gear to have in a VHF/UHF FM base station?" Tags="&lt;equipment&gt;&lt;70cm-band&gt;&lt;2m-band&gt;&lt;fm&gt;" AnswerCount="2" CommentCount="9" ClosedDate="2014-02-24T14:10:38.400" ContentLicense="CC BY-SA 3.0" />
  <row Id="1476" PostTypeId="2" ParentId="1475" CreationDate="2014-02-17T14:35:51.077" Score="3" Body="&lt;p&gt;Based on my somewhat short experience as a ham, these are some of the things I find very useful in my shack or would like to have:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;a comfy chair&lt;/li&gt;&#xA;&lt;li&gt;paper/writing instruments and/or computer for logging purposes&lt;/li&gt;&#xA;&lt;li&gt;a hook or clippy thing to hang your microphone from (if you're not using a desk or boom mic)&lt;/li&gt;&#xA;&lt;li&gt;shelves. you can never have enough shelves in the shack.&lt;/li&gt;&#xA;&lt;li&gt;a 24-h clock set for UTC time.&lt;/li&gt;&#xA;&lt;li&gt;Maps of the ITU and CQ zones&lt;/li&gt;&#xA;&lt;li&gt;ARRL band plan chart&lt;/li&gt;&#xA;&lt;li&gt;external speakers for your radio&lt;/li&gt;&#xA;&lt;li&gt;SWR/power meter&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;given that your antenna is resonant at 2m/70cm, an antenna tuner wouldn't be necessary unless you decide to start experimenting with other antennas.&#xA;Dummy load would be useful if you need to test your radio for some purpose.&lt;/p&gt;&#xA;" OwnerUserId="73" LastEditorUserId="73" LastEditDate="2014-02-17T20:32:50.410" LastActivityDate="2014-02-17T20:32:50.410" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1477" PostTypeId="2" ParentId="1475" CreationDate="2014-02-17T14:39:36.043" Score="2" Body="&lt;p&gt;Trouble shooting equipment such as an antenna analyzer and VOM, replacement parts (PL-259's, etc), a soldering iron.  Provisions for expansion as needed (another operator at your station during a disaster, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your initial list is a great start but it assumes nothing is going to go wrong.&lt;/p&gt;&#xA;" OwnerUserId="736" LastActivityDate="2014-02-17T14:39:36.043" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1478" PostTypeId="2" ParentId="1437" CreationDate="2014-02-17T15:55:40.667" Score="7" Body="&lt;p&gt;144.200/432.100 are intended for &lt;code&gt;SSB&lt;/code&gt; Modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;146.520/446.000 are intended for &lt;code&gt;FM&lt;/code&gt; Modulation.&lt;/p&gt;&#xA;" OwnerUserId="737" LastEditorUserId="737" LastEditDate="2015-05-07T15:40:12.250" LastActivityDate="2015-05-07T15:40:12.250" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1479" PostTypeId="2" ParentId="1469" CreationDate="2014-02-17T16:19:51.780" Score="19" Body="&lt;p&gt;Every time I purchase a cheap HT such as the Baofeng you mention I also spend another $10 or so on an antenna, as the stock antenna is noticeably worse than even an inexpensive antenna like the &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00BY3XN7E&quot;&gt;Nagoya NA-771&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are still better antennas than this, but there are always tradeoffs.  The stock antenna is one third to half the length of the NA-771, which is useful in certain situations.  There are vastly better, but more expensive, antennas that mount on and off the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you need will depend largely on what you're going to use the radio for.  Given that you've chosen an inexpensive, low power (even for handheld) radio, though, I suspect you're really looking to improve things as much as possible while still retaining the portability and use as a handheld, without a lot of cost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the above antenna is my current recommendation in this situation.  &lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-17T16:19:51.780" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1480" PostTypeId="1" CreationDate="2014-02-17T19:27:37.553" Score="4" ViewCount="260" Body="&lt;p&gt;Are there any frequencies (HF, 2m and 440) that are more suitable than others (assuming all are within those licensed to the operator) for testing new radios and/or antennas?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume that one should always listen before attempting to transmit a test signal, but any &quot;deafness&quot; in a new antenna and/or transceiver setup may not pick up a weak QRP or a distant QSO in progress.  So one assumption is that frequencies listed on some band charts as appropriate for QRP or DX (as well for as emergency communications) should be avoided for testing.  Which documents, band charts or operating procedure manuals (etc.) might list this info?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2014-02-18T18:05:02.580" LastActivityDate="2018-05-10T17:32:32.727" Title="Which frequencies in a band should I use for antenna and radio testing?" Tags="&lt;procedure&gt;&lt;band-plan&gt;&lt;testing&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1481" PostTypeId="1" CreationDate="2014-02-17T19:32:55.393" Score="1" ViewCount="130" Body="&lt;p&gt;Should one always identify ones station (say via CW keying) when building/testing an HF oscillator and/or anything that could amplify that oscillator, when powering the circuit on a breadboard and into a dummy load?  Or is there a lower power limit (U.S. FCC regulation and/or worldwide best practice) before this is required?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the answer different on any other non-HF bands?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I am specifically not assuming that dummy loads radiate zero power, since that can be (and likely is) false.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-02-17T20:34:15.217" LastActivityDate="2014-02-18T15:59:32.547" Title="ID station when testing an oscillator or transmitter into a dummy load?" Tags="&lt;procedure&gt;&lt;testing&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1483" PostTypeId="2" ParentId="1481" CreationDate="2014-02-18T01:57:22.233" Score="1" Body="&lt;p&gt;It is up to you, as a licensed amateur radio operator to determine what your emissions actually are, and to ID as appropriate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether your dummy load is radiating enough to count depends on too many variables to give you a nice, easy answer. If in doubt, ID anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Understand your emissions, understand your license, and operate accordingly.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-18T01:57:22.233" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1484" PostTypeId="1" AcceptedAnswerId="1489" CreationDate="2014-02-18T04:42:03.877" Score="2" ViewCount="266" Body="&lt;p&gt;I was wondering if anybody knew the maximum input wattage of the MFJ-1717PL Antenna. I was going to use this with the Yaesu FT-1900R mobile radio mounted in a Pelican case.&lt;/p&gt;&#xA;" OwnerUserId="536" LastEditorUserId="218" LastEditDate="2014-02-18T12:48:17.213" LastActivityDate="2014-02-18T17:17:40.453" Title="Maximum Input Wattage of MFJ-1717PL Antenna" Tags="&lt;antenna&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1485" PostTypeId="2" ParentId="1481" CreationDate="2014-02-18T13:05:54.553" Score="4" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Title_47_CFR_Part_15&quot; rel=&quot;nofollow noreferrer&quot;&gt;Part 15&lt;/a&gt; sets limits on unlicensed RF emissions. The limits vary by frequency, the type of device, the nature of the emissions, and so on. It's a pretty huge document and you need a lawyer and an &lt;a href=&quot;http://en.wikipedia.org/wiki/Electromagnetic_compatibility&quot; rel=&quot;nofollow noreferrer&quot;&gt;EMC engineer&lt;/a&gt; to approach it. However, you can get the &lt;em&gt;intent&lt;/em&gt; of it from this blurb that is &lt;a href=&quot;https://apps.fcc.gov/oetcf/kdb/forms/FTSSearchResultPage.cfm?id=27980&amp;amp;switch=P&quot; rel=&quot;nofollow noreferrer&quot;&gt;printed on just about every piece of consumer electronics&lt;/a&gt; sold in the US:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;This device complies with part 15 of the FCC rules. Operation is subject to the following two conditions: (1) this device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It never hurts to ID. However, if you are testing an oscillator that isn't even connected to an antenna or an amplifier, or if you are using a dummy load and modest power (less than 10 watts, say), your &lt;a href=&quot;http://en.wikipedia.org/wiki/Effective_radiated_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;effective radiated power&lt;/a&gt; is going to be less than a microwatt.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are in doubt, listen with another receiver. Can you hear your device under test above your switching power supplies, the power lines, touchlamps, and ambient atmospheric noise? If not, then it's unlikely you are &quot;causing harmful interference&quot;. If you don't have a second receiver, it's not terribly difficult to &lt;a href=&quot;https://electronics.stackexchange.com/questions/78530/how-can-i-tell-if-an-rf-transmitter-is-transmitting/78533#78533&quot;&gt;construct a field strength meter&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This doesn't &lt;em&gt;per se&lt;/em&gt; mean that you are complying with part 15 (that could require filing with the FCC, passing a compliance test, ...) but at some point, a little common sense is sufficient. You aren't mass producing a device that will be used by millions of people for years and years. You are performing a temporary test as a licensed amateur radio operator. Take reasonable steps to avoid causing interference and you will be fine.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2014-02-18T15:59:32.547" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1486" PostTypeId="1" AcceptedAnswerId="1487" CreationDate="2014-02-18T14:15:49.873" Score="4" ViewCount="388" Body="&lt;p&gt;I have two radios. Sensitivity is -84&amp;nbsp;dBm and transmitting EIRP is +30&amp;nbsp;dBm. How much distance should I expect?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want it to be somewhere near about 2-3&amp;nbsp;km. Is it possible? &lt;/p&gt;&#xA;" OwnerUserId="731" LastEditorUserId="129" LastEditDate="2014-07-28T20:42:52.840" LastActivityDate="2014-07-29T04:40:06.260" Title="What is the average fade margin required for proper operation at 2.4 GHz?" Tags="&lt;antenna&gt;&lt;amplifier&gt;&lt;wifi&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1487" PostTypeId="2" ParentId="1486" CreationDate="2014-02-18T16:36:58.673" Score="3" Body="&lt;p&gt;Your question can be answered by the &lt;a href=&quot;http://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow&quot;&gt;Friis transmission equation&lt;/a&gt;. One way to write it is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_r=P_t+20\log _{10}\left({\frac {\lambda }{4\pi R}}\right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$P_r$ is the received power (in dBm)&lt;/li&gt;&#xA;&lt;li&gt;$P_t$ is the transmitted power&lt;/li&gt;&#xA;&lt;li&gt;$\lambda$ is the wavelength&lt;/li&gt;&#xA;&lt;li&gt;$R$ is the distance between the antennas, in the same units as wavelength&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Wavelength at 2.4GHz is about 0.125m. With your numbers of 30dBm, and a maximum distance of 3km, the equation becomes:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;P_r&amp;amp;=30 \:\mathrm {dBm}+20\log _{10}\left({\frac {0.125\:\mathrm m}{4\pi \cdot 3000 \:\mathrm m}}\right) \\&#xA;&amp;amp;= 30 \:\mathrm{dBm}-109.6 \:\mathrm{dBm} \\&#xA;&amp;amp;= -79.59 \:\mathrm{dBm}&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is about 4dB above your specified minimum of -84dBm, so it's theoretically possible, but only barely. The Friis equation calculates received power for ideal propagation in free space between isotropic antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your receive antenna probably has some gain which gives you some additional margin. A resonant dipole has theoretically a 1.76 dBi gain, which adds to the number calculated above. Of course if you have a more directional antenna you get even better improvements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you also aren't propagating through free space. You can approach this with a very good path: antennas on towers, clear line of sight, and so on. You must also consider the &lt;a href=&quot;http://en.wikipedia.org/wiki/Fresnel_zone&quot; rel=&quot;nofollow&quot;&gt;Frensel zone&lt;/a&gt; around the path also. If all of these conditions are very good, your losses compared to free space will be small or negligible. If not, you will need additional antenna gain or transmit power to make your link work.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-18T16:36:58.673" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1488" PostTypeId="1" CreationDate="2014-02-18T16:54:00.117" Score="10" ViewCount="1125" Body="&lt;p&gt;I an studying for my technician class examination, and I came across this question:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What may result when correspondence from the FCC is returned as undeliverable because the grantee failed to provide the correct mailing address?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A. Fine or imprisonment&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;B. Revocation of the station license or suspension of the operator license&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;C. Require the licensee to be re-examined&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;D. A reduction of one rank in operator class&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The answer is B.  I wanted to research more about the distinction, but my Google powers were falling me.  I am using an &lt;a href=&quot;https://ankiweb.net/shared/info/3329283188&quot;&gt;Anki flashcard deck&lt;/a&gt; to study and this question was tagged with &quot;T1C07 (B) [97.23]&quot;, but I don't know what that means.&lt;/p&gt;&#xA;&#xA;Another Exam Question&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the normal term for an FCC-issued primary station/operator license grant?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A. Five years&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;B. Life&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;C. Ten years&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;D. Twenty years&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;T1C08 (C) [97.25]&lt;/p&gt;&#xA;" OwnerUserId="742" LastEditorUserId="207" LastEditDate="2014-02-18T19:11:19.827" LastActivityDate="2018-05-04T22:09:35.470" Title="What is the difference between FCC station and operator licenses?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;&lt;volunteer-examiners&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1489" PostTypeId="2" ParentId="1484" CreationDate="2014-02-18T17:17:40.453" Score="3" Body="&lt;p&gt;The antenna is specifically marketed for mobile and base station use, so I expect it to readily handle 20-50W without issue.  However, the manufacturer doesn't publish power specifications, and after looking at a few dozen reviews, sellers, and forums it appears that many have asked for this information and it has never been provided.  The reviews are generally good, but again no mention of power - however no mention of overheated antennas or damaged transceivers either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's an inexpensive enough antenna that if you're willing to experiment, then it's probably worth trying out at 20W for five minutes of solid transmission, then turn the transmitter off and check the antenna temperature along its length, particularly at any locations with components or connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it isn't warm, try it at 55W and check the temperature.  If it's not warming up appreciably, you might be safe at those transmitter levels.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If, however, you don't want to experiment or need more assurance that it won't fail spectacularly later, you should look for an antenna with a guaranteed manufacturer rated power handling capability.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-18T17:17:40.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1490" PostTypeId="2" ParentId="1488" CreationDate="2014-02-18T18:12:46.270" Score="5" Body="&lt;p&gt;&lt;strong&gt;Answer the first part of your question:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Based on &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=licensing_1&amp;amp;id=amateur&quot; rel=&quot;nofollow noreferrer&quot;&gt;the FCC description of club stations&lt;/a&gt;, I think the VE exam answer is referring to a club station license. The description of the club station license from the above source:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;A club station license allows members of an amateur radio club to have a station operating under a club call sign. The license is granted only to the trustee of the club. It conveys no operating privileges.&lt;/p&gt;&#xA;&lt;p&gt;To be granted a club station license, a club must have:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;A name&lt;/li&gt;&#xA;&lt;li&gt;A document of organization&lt;/li&gt;&#xA;&lt;li&gt;Management&lt;/li&gt;&#xA;&lt;li&gt;A primary purpose devoted to amateur service activities consistent with the FCC Rules&lt;/li&gt;&#xA;&lt;li&gt;At least four persons&lt;/li&gt;&#xA;&lt;li&gt;A license trustee designated by an officer of the club&lt;/li&gt;&#xA;&lt;li&gt;Trustee must hold an amateur service operator license grant. (&lt;a href=&quot;http://wireless.fcc.gov/rules.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;See Section 97.5(b)(2) of the FCC Rules&lt;/a&gt;)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;To answer the second part of your question:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;The numbers in brackets, 97.23 and 97.25, are the FCC part 97 sections that are relevant to the exam question.&lt;/p&gt;&#xA;&lt;p&gt;T1C07 and T1C08 are ID codes for the questions, which are published by the &lt;a href=&quot;http://www.ncvec.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;National Conference of Volunteer Exam Coordinators (NCVEC)&lt;/a&gt;. These questions are from the technician question pool (T), section 1C, and are questions 07 and 08 in that section.&lt;/p&gt;&#xA;" OwnerUserId="207" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-02-18T22:32:45.383" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1491" PostTypeId="1" AcceptedAnswerId="1493" CreationDate="2014-02-18T19:53:23.470" Score="10" ViewCount="1369" Body="&lt;p&gt;What rule allows Amateur Operators to establish and operate remote, automated stations like APRS weather stations or beacons?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there different rules specifically for beacons, or do they all fall under the same rules?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-18T20:43:29.893" Title="What Part 97 rule allows unattended, automated transmissions, such as APRS weather stations and beacons?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;aprs&gt;&lt;remote-control&gt;&lt;automation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1492" PostTypeId="1" AcceptedAnswerId="1641" CreationDate="2014-02-18T20:31:40.980" Score="8" ViewCount="164" Body="&lt;p&gt;I want to be able to sign my own LOTW entries, without using the provided library (My application is pure Java). Is there a document that explains in enough detail how to do this, assuming of course that I'm provided with a certificate (.tq8 I believe)?&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-02-19T21:49:28.337" LastActivityDate="2014-05-08T23:30:36.543" Title="Does LOTW have an interface document?" Tags="&lt;logging&gt;&lt;lotw&gt;&lt;software-development&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1493" PostTypeId="2" ParentId="1491" CreationDate="2014-02-18T20:43:29.893" Score="8" Body="&lt;p&gt;There's a few parts:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;§97.109 Station control.&lt;/strong&gt; (d) When a station is being automatically controlled, the control operator need not be at the control point. Only stations specifically designated elsewhere in this part may be automatically controlled. Automatic control must cease upon notification by a District Director that the station is transmitting improperly or causing harmful interference to other stations. Automatic control must not be resumed without prior approval of the District Director.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;§97.113 Prohibited transmissions.&lt;/strong&gt; (d) No amateur station, except an auxiliary, repeater, or space station, may automatically retransmit the radio signals of other amateur station.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;§97.213 Telecommand of an amateur station.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;An amateur station on or within 50 km of the Earth's surface may be&#xA;under telecommand where:&lt;/p&gt;&#xA;&lt;p&gt;(a) There is a radio or wireline control link between the control&#xA;point and the station sufficient for the control operator to perform&#xA;his/her duties. If radio, the control link must use an auxiliary&#xA;station. A control link using a fiber optic cable or another&#xA;telecommunication service is considered wireline.&lt;/p&gt;&#xA;&lt;p&gt;(b) Provisions are incorporated to limit transmission by the station&#xA;to a period of no more than 3 minutes in the event of malfunction in&#xA;the control link.&lt;/p&gt;&#xA;&lt;p&gt;(c) The station is protected against making, willfully or negligently,&#xA;unauthorized transmissions.&lt;/p&gt;&#xA;&lt;p&gt;(d) A photocopy of the station license and a label with the name,&#xA;address, and telephone number of the station licensee and at least one&#xA;designated control operator is posted in a conspicuous place at the&#xA;station location.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Beacons have their own rules, which are too numerous to just copy/paste. The section is entitled &lt;strong&gt;§97.203 Beacon station.&lt;/strong&gt;, and can be found at &lt;a href=&quot;http://www.arrl.org/part-97-text&quot; rel=&quot;noreferrer&quot;&gt;ARRL&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-02-18T20:43:29.893" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1494" PostTypeId="2" ParentId="1492" CreationDate="2014-02-18T20:52:52.393" Score="1" Body="&lt;p&gt;The &lt;a href=&quot;http://www.arrl.org/files/file/LoTW_Developer/DeveloperIntro.pdf&quot; rel=&quot;nofollow&quot;&gt;developer introduction&lt;/a&gt; has an overview and links to further resources. If you can link against a C++ library, you can use &lt;a href=&quot;http://sourceforge.net/projects/trustedqsl/&quot; rel=&quot;nofollow&quot;&gt;TrustedQSL&lt;/a&gt; to deal with the signing portion, or read the code to understand the process and create a Java version of it.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-18T20:52:52.393" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1495" PostTypeId="5" CreationDate="2014-02-19T14:37:03.747" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-02-19T14:37:03.747" LastActivityDate="2014-02-19T14:37:03.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1496" PostTypeId="4" CreationDate="2014-02-19T14:37:03.747" Score="0" Body="Use this tag for questions relating to the ARRL's Logbook Of The World project." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-02-19T14:37:03.747" LastActivityDate="2014-02-19T14:37:03.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1497" PostTypeId="1" AcceptedAnswerId="1498" CreationDate="2014-02-19T15:53:46.910" Score="6" ViewCount="597" Body="&lt;p&gt;What are the lowest EIRP and antenna gain requirements that make possible use of troposcatter at the distances of 100 to 150 kilometers assuming conventional WiFi (6 Mbit/s data rate with OFDM/BPSK modulation)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While this is unlikely to work in practice (for legal reasons, among others) I'm curious if such links can be established.&lt;/p&gt;&#xA;" OwnerUserId="565" LastEditorUserId="565" LastEditDate="2014-02-19T16:00:07.613" LastActivityDate="2014-02-19T18:06:51.557" Title="Can tropospheric scatter effect be used by 802.11 links?" Tags="&lt;propagation&gt;&lt;wifi&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1498" PostTypeId="2" ParentId="1497" CreationDate="2014-02-19T18:06:51.557" Score="5" Body="&lt;p&gt;I don't see why not. Of course, it's subject to the biggest problem with troposcatter: extremely high loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's work out an example to see how bad this is. Let's say we want a link at a distance of 150km. Borrowing numbers from &lt;a href=&quot;https://ham.stackexchange.com/q/1486/218&quot;&gt;this question&lt;/a&gt;, let's further assume that we need -84dBm at the receiver to make the link work. And just for now, let's assume we have an ideal, free-space path between the stations. We can apply the &lt;a href=&quot;http://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Friis transmission equation&lt;/a&gt; to determine the EIRP necessary to make this work:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;P_r&amp;amp;=P_t+20\log_{10}\left(\frac{\lambda}{4\pi R}\right) \\&#xA;-84\:\mathrm{dBm}&amp;amp;=P_t+20\log_{10}\left(\frac{0.125\:\mathrm m}{4\pi \cdot 150000\:\mathrm m}\right) \\&#xA;-84\:\mathrm{dBm}&amp;amp;=P_t - 143.6\:\mathrm{dBm} \\&#xA;59.6\:\mathrm{dBm}&amp;amp;=P_t \\&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, our free-space path losses are -143.6dBm, and we'd need an EIRP of about 60dBm to make it work, assuming an isotropic receiving antenna. If we can have a 40dBi antenna at each end, then we'd need a -20dBm transmitter. Easy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Only trouble is that paths of this length aren't even remotely like free space. There's probably a planet in the way. So say we want to use troposcatter...what are the additional losses?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.mike-willis.com/Tutorial/PF9.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mike Willis has a great article on troposcatter&lt;/a&gt;, which includes all sorts of empirical models and stuff. However, it's nicely summarized by this graph:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ceqyq.gif&quot; alt=&quot;Troposcater excess path losses with a 30cm dish&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are losses &lt;em&gt;in addition to&lt;/em&gt; the ideal case we just calculated. For our example of 150km, we can see losses of about 62dB. That brings the minimum EIRP to 123dBm, or again assuming our 40dBi antennas, transmitter power of 43dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Certainly feasible, even after adding margins for noise. With higher gain antennas, on the edge of possibility with consumer equipment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-19T18:06:51.557" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1499" PostTypeId="5" CreationDate="2014-02-19T21:49:49.300" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2014-02-19T21:49:49.300" LastActivityDate="2014-02-19T21:49:49.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1500" PostTypeId="4" CreationDate="2014-02-19T21:49:49.300" Score="0" Body="Questions related to writing software (programming) for Amateur Radio purposes." OwnerUserId="13" LastEditorUserId="76" LastEditDate="2016-10-29T19:18:39.960" LastActivityDate="2016-10-29T19:18:39.960" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1501" PostTypeId="1" CreationDate="2014-02-20T02:34:10.773" Score="10" ViewCount="783" Body="&lt;p&gt;When learning, teaching oneself, or training a class in Morse Code sending using a hand key, how can acceptable quality be scored (other than the letters being correct terms of dot-dash sequence)?  There a big difference between the dots being a bit shorter than the dahs at widely varying WPM between characters and words, and nice perfect 3:1 timing at an exact 13 WPM, etc.  What objective metric should be used to determine a &quot;passing score&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Objective metric requested because many humans are too good at &quot;hearing&quot; the expected message even if there were errors or near errors in the coding.  And it's not hard to measure key open/closure timings to millisecond precision for use in any objective scoring algorithm.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Was there a metric used for acceptability quality in any country back when Morse Code sending was tested as required part of a license exam?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-02-20T02:48:19.987" LastActivityDate="2016-09-21T18:04:35.923" Title="Scoring quality of Morse Code &quot;fist&quot;?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1502" PostTypeId="2" ParentId="1501" CreationDate="2014-02-20T12:51:56.733" Score="6" Body="&lt;p&gt;One quantification would be to measure &lt;a href=&quot;http://en.wikipedia.org/wiki/Jitter&quot; rel=&quot;noreferrer&quot;&gt;jitter&lt;/a&gt;. Ideal Morse code is synchronized to a clock of dits. Wikipedia describes (emphasis mine):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The duration of a dash is three times the duration of a dot. Each dot or dash is followed by a short silence, equal to the dot duration. The letters of a word are separated by a space equal to three dots (one dash), and the words are separated by a space equal to seven dots. &lt;em&gt;The dot duration is the basic unit of time measurement in code transmission.&lt;/em&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A computer decoder could then &lt;a href=&quot;http://en.wikipedia.org/wiki/Clock_recovery&quot; rel=&quot;noreferrer&quot;&gt;recover a clock from this rhythm&lt;/a&gt;. When a transition between on and off is detected, this is compared to the clock. Any error is fed back to the clock synchronization algorithm, and additionally the magnitude of the error is recorded.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One can then take all of these errors and analyze them through any number of statistical means. I'd suggest the &lt;a href=&quot;http://en.wikipedia.org/wiki/Standard_deviation&quot; rel=&quot;noreferrer&quot;&gt;standard deviation&lt;/a&gt; as a general figure of merit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you break the jitter into error during what type of rhythmic unit you can get specific about what aspects of the rhythm are bad. For example, jitter in word spaces is not so bad as jitter in dit timing. You can adjust your scoring metric accordingly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the decoder also tracks the sending speed, you can analyze that statistically to determine to what extent the sender increased or decreased speed, while possibly maintaining a good rhythm.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-20T12:51:56.733" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1503" PostTypeId="1" CreationDate="2014-02-20T15:07:56.080" Score="9" ViewCount="418" Body="&lt;p&gt;I understand that steel is &lt;a href=&quot;https://ham.stackexchange.com/questions/1388/effect-of-different-metals-for-antenna-elements&quot;&gt;not a good material for antenna wire&lt;/a&gt;, but let's consider that I'm using the wire for purely structural support, or I am &lt;a href=&quot;https://ham.stackexchange.com/questions/1391/is-copper-clad-steel-a-good-material-for-wire-antennas/1393#1393&quot;&gt;cladding it with copper&lt;/a&gt; to address the RF conductivity issues.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, which material is more suited to being strung between two supports? It seems to me there is a balance between at least two main concerns:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the wire should be strong, so it doesn't break&lt;/li&gt;&#xA;&lt;li&gt;the wire should be light, so it has to support less of its own weight&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;To a lesser extent, cost may be a factor, although both steel and aluminum are affordable enough that it may not be an issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What material properties are relevant to this application? (Remember: purely &lt;em&gt;structural&lt;/em&gt; concerns, not &lt;em&gt;electrical&lt;/em&gt;.) Can we put some numbers and proper engineering to it?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-09-19T12:09:59.930" Title="Is steel or aluminum structurally a better material for catenaries?" Tags="&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1504" PostTypeId="1" CreationDate="2014-02-20T16:33:14.967" Score="10" ViewCount="910" Body="&lt;p&gt;I was looking over the product page for the K3 (dreaming I know) and noticed that they offer a variety of crystal filters.  Some are 5-pole and some are 8-pole, other than price, what is the difference and what is meant by &quot;pole&quot; in this context?&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-02-20T17:40:47.137" Title="What is meant by &quot;poles&quot; when discussing filters?" Tags="&lt;receiver&gt;&lt;filter&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1505" PostTypeId="2" ParentId="1504" CreationDate="2014-02-20T17:09:55.993" Score="8" Body="&lt;p&gt;&quot;Pole&quot; comes from the &lt;a href=&quot;http://en.wikipedia.org/wiki/Laplace_transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;Laplace transform&lt;/a&gt;, or it's discrete (for digital filters) equivalent, the &lt;a href=&quot;http://en.wikipedia.org/wiki/Z-transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;Z-transform&lt;/a&gt;. Without delving into the mathematics of it, these transforms enable a filter designer to express the response of a filter in terms of some number of &lt;em&gt;poles&lt;/em&gt; and &lt;em&gt;zeros&lt;/em&gt; on the &lt;a href=&quot;http://en.wikipedia.org/wiki/Complex_plane&quot; rel=&quot;nofollow noreferrer&quot;&gt;complex plane&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using these transforms simplifies many tasks of the filter designer, such as guaranteeing stability, or designing a filter to optimize some aspect such as minimum group delay, minimal overshoot, steepest roll-off, etc. There are many &lt;a href=&quot;http://en.wikipedia.org/wiki/Filter_%28signal_processing%29#Classification&quot; rel=&quot;nofollow noreferrer&quot;&gt;common filter designs&lt;/a&gt;, such as &lt;a href=&quot;http://en.wikipedia.org/wiki/Butterworth_filter&quot; rel=&quot;nofollow noreferrer&quot;&gt;Butterworth&lt;/a&gt; or &lt;a href=&quot;http://en.wikipedia.org/wiki/Elliptic_filter&quot; rel=&quot;nofollow noreferrer&quot;&gt;elliptic&lt;/a&gt;, which cover common goals, and these are usually described in terms of poles and zeros.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The practical application for the ham is this: the more poles or zeros a filter has, or the higher the filter's &lt;em&gt;order&lt;/em&gt;, the steeper the roll-off can be. An an example, here's the frequency response for a number of Butterworth low-pass filters with different numbers of poles:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/6Z3ZU.png&quot; alt=&quot;butterworth frequency response&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The numbers by the lines, 1 through 5, denote the order of the filter. For a Butterworth filter, the order is also equal to the number of poles. As we add more poles, the roll-off becomes steeper. Again just for Butterworth filters, the roll-off is 6dB/octave for each pole, so a 6-pole filter would have a roll-off of 36dB/octave, and an 8-pole filter would be 48dB/octave. Other filter designs can achieve a steeper roll-off at the expense of some other property, such as &lt;a href=&quot;http://en.wikipedia.org/wiki/Filter_%28signal_processing%29#Terminology&quot; rel=&quot;nofollow noreferrer&quot;&gt;ripple&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The number of poles and zeros is also the minimum number of reactive components (capacitors, inductors) that would be required to implement the filter. So, more poles and zeros means more components, and more cost.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-02-20T17:16:21.603" LastActivityDate="2014-02-20T17:16:21.603" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1506" PostTypeId="2" ParentId="1504" CreationDate="2014-02-20T17:40:47.137" Score="0" Body="&lt;p&gt;A pole is a mathematical representation of the feedback (amount and phase) in a linear system.  This feedback can be passive (as in an LC or physically tuned circuit), or active (as in a regenerative receiver).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The more poles (or feedback paths) a circuit has, the more complicated or precisely shaped it's frequency response can be, or can be made to be by modifying the locations of the poles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More poles can be (but are not necessarily) better in producing a desired filter frequency response, but are often more expensive, not only because they may require more passive elements (or feedback paths) per pole, but also because the precision requirements may be higher when trying to use more poles more tightly bunched in a complex plane (Z or Laplace) graph of their location to produce some desired response.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-02-20T17:40:47.137" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1507" PostTypeId="1" AcceptedAnswerId="1508" CreationDate="2014-02-20T20:03:09.867" Score="10" ViewCount="403" Body="&lt;p&gt;Per &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1103&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.103&lt;/a&gt;, one is responsible for the proper operation of one's station, which of course includes that no unlicensed person uses it to transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have heard suggestions (no link handy, sorry) of taking actual physical security measures such as keeping HTs and critical components with oneself or in locked boxes, or inserting &lt;a href=&quot;http://en.wikipedia.org/wiki/Key_switch&quot; rel=&quot;nofollow noreferrer&quot;&gt;key-switches&lt;/a&gt; in the power connections to transmitters.  While effective and not infeasible, this seems like overkill to me outside of the presence of children or other unreasonable people.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there “good amateur practice” about a sufficient standard of prevention? Is it sufficient for me to rely on my judgement that the people I live with wouldn't do such a thing, nor permit guests to?&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-09-20T14:18:18.623" LastActivityDate="2017-09-20T14:18:18.623" Title="Do I need to actually lock up my station?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;security&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1508" PostTypeId="2" ParentId="1507" CreationDate="2014-02-20T20:26:47.923" Score="8" Body="&lt;p&gt;That depends largely on your environment.  If you have a separate room, and guests, children, and others are unlikely to enter, and more unlikely to touch anything if they do enter, then it's probably fine to simply leave your radio on and tuned into your preferred frequency 24/7 with the key or mic on the desk.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you need to leave it in the living area with a multitude of children and guests around who have little social conditioning that tells them not to touch things that aren't theirs, you'll probably want to switch your output to the dummy load, turn the transmitter to receive only, turn it off, and put away or otherwise hide the key, microphone and other controls as you are able, and turn off the power strip.  It would take some knowledge to set up the station so it would transmit, and at that point you might as well have that person tested and then you won't have to worry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you could lock it up behind a door if you had significant concerns about this, but I haven't yet run across anyone that felt this level of security was necessary for the purposes of preventing unlicensed transmissions.  Usually the lock and key people would put their equipment under was primarily due to concerns of theft for thousands of dollars of radio equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do have any specific concerns, describe your environment more specifically in terms of location, traffic, people who might have access to it.  You'll probably receive may ideas on how to secure your station while still keeping it easy for you to use.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-20T20:26:47.923" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1509" PostTypeId="1" AcceptedAnswerId="1512" CreationDate="2014-02-21T00:23:47.370" Score="9" ViewCount="11623" Body="&lt;p&gt;If I know how fast a satellite is moving through space, how can I calculate the doppler shift for the pass?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8832" LastEditDate="2017-05-25T01:14:03.477" LastActivityDate="2019-04-08T08:01:10.980" Title="Calculating Doppler Shift for satellites" Tags="&lt;satellites&gt;&lt;doppler&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1511" PostTypeId="2" ParentId="989" CreationDate="2014-02-21T08:26:20.980" Score="2" Body="&lt;p&gt;Surface oxidation will lead to two effects impacting antenna performance&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) building a dielectric layer between radiating (or passive element) and air - here I concur with @Phil Frost that the effect is neglectible (except maybe at microwave frequencies)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) an oxide layer will change the surface of the radiator, i.e. the surface will become more rough. Knowing that the current density in a conductor is maximum near its surface (-&gt; &lt;a href=&quot;http://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow&quot;&gt;skin effect&lt;/a&gt;) this can be noticed - especially on higher frequencies. I have seen myself on frequencies of &gt;= 430MHz that polishing aluminium rods (and let the polished surface passivate by air oxidation which is a good protection) did improve the performance of my self built antennas.  For HF antennas (&amp;lt;= 30 MHz) I couldn't find any significant effect though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) Corroded connection points of course always impose a danger and such connection points should be regularly inspected, maintained and protected ... not only cable/radiator joints, but also soldering spots within baluns etc. as everywhere, where two different metals meet in moist conditions (air humidity, etc.) local elements may form and acellerate corrosion up to the point of permanent damage.&lt;/p&gt;&#xA;" OwnerUserId="765" LastActivityDate="2014-02-21T08:26:20.980" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1512" PostTypeId="2" ParentId="1509" CreationDate="2014-02-21T10:15:10.000" Score="6" Body="&lt;p&gt;The doppler shift $\Delta f$ is function of the relative velocity $\Delta v$ (a scalar quantity) and the emitted frequency $f_0$, see &lt;a href=&quot;http://en.wikipedia.org/wiki/Doppler_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;the relevant wikipedia page&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you know how the relative velocity (either at one instant in time or as a function of time), it's just a matter of using the formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/math/7/c/5/7c54c79c0ecc2aaa26cc046d8d7a2a95.png&quot; alt=&quot;doppler shift formula&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't known the relative velocity, then you need to calculate it. For that you need the ingredients &lt;a href=&quot;https://ham.stackexchange.com/users/9/adam-davis-kd8oas&quot;&gt;Adam Davis KD8OAS&lt;/a&gt; enumerated in his comment.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;You need much more than the speed to find this.&#xA;The orbital elements of a satellite, your location, and the time and date, plugged into a satellite tracking program will do the work for you. Doing it by hand may be interesting, once, but it isn't trivial.&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Note that usually we measure $\Delta f$ with a radio, an &lt;a href=&quot;http://en.wikipedia.org/wiki/Software-defined_radio&quot; rel=&quot;nofollow noreferrer&quot;&gt;SDR&lt;/a&gt; and an accurate clock, compute $\Delta v$ and then try to figure out the satellites' orbit by guessing which one fits best the observed $\Delta v$.&lt;/p&gt;&#xA;" OwnerUserId="766" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-24T21:39:52.247" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1513" PostTypeId="2" ParentId="574" CreationDate="2014-02-21T22:40:24.890" Score="5" Body="&lt;p&gt;20m is the &quot;go-to&quot; band for long haul comms without a huge antenna, but it is by no means the only one.  I've had 5000mi contacts on 20m, 17m, and 10m (using only 100W transmit power).  With more space for antennas, 80m and 40m have even more potential for long distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;unconditional access&quot; is the hard one.  There is no one band that will do that for you all the time.  It all depends on the atmospheric conditions.  For instance, 10m is only good during the daytime, and 20m is best during the daytime, and I wouldn't expect long haul comms out of it at night.  To pick 3 bands, 10,20 and 40m would work if you learned how propagation works.  You can also build (from speaker wire) an antenna that will work pretty well on all three of those bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;low power&quot; means something special in the ham radio world.  If you mean 5W transmit power, then you need to drop the voice mode from your requirements.  Morse code could do that.  Or if you can use a computer with it, JT-65 or PSK31 would work also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's going to sound like the catch-all answer, but find a local club.  Find some used gear.  My first radio (3 years ago) was a 1986 model Kenwood TS-430S.  That, plus the tuner cost me only 325 from a local guy.  Great radio.  add in power supply and antenna fixins and I was under $500 with a wire antenna laying on top of my shingle roof.&lt;/p&gt;&#xA;" OwnerUserId="308" LastActivityDate="2014-02-21T22:40:24.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1514" PostTypeId="1" AcceptedAnswerId="1955" CreationDate="2014-02-22T03:37:38.513" Score="7" ViewCount="298" Body="&lt;p&gt;Can a regenerative shortwave receiver (especially an old vintage unshielded tube or transistor model) connected to a wire antenna generate HF interference?  If so, what are some ways to prevent one from generating such interference (but still receive)?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are some inexpensive ways (if any) to check to make sure that any radiated power from an old receiver (designed well before Part 15) is below legal limits (in the U.S. on amateur HF and broadcast shortwave bands)?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-07-05T19:58:55.550" Title="Regenerative receiver interference?" Tags="&lt;receiver&gt;&lt;testing&gt;" AnswerCount="1" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1515" PostTypeId="1" AcceptedAnswerId="1516" CreationDate="2014-02-22T03:45:58.243" Score="9" ViewCount="1763" Body="&lt;p&gt;What is the difference between software demodulation of an IQ signal between wideband FM and narrowband FM?  Both seem to look at the 2nd difference in unwrapped phase angles of IQ samples.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="29" LastEditDate="2014-02-22T16:03:13.227" LastActivityDate="2014-02-23T15:24:05.407" Title="How does SDR demodulation differ between wideband and narrowband FM?" Tags="&lt;modes&gt;&lt;software-defined-radio&gt;&lt;fm&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1516" PostTypeId="2" ParentId="1515" CreationDate="2014-02-22T16:46:30.617" Score="8" Body="&lt;p&gt;There are actually three different distinctions one could mean by referring to “narrowband” FM.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Wideband FM in this context generally refers to &lt;a href=&quot;http://en.wikipedia.org/wiki/FM_broadcasting#Modulation_characteristics&quot; rel=&quot;noreferrer&quot;&gt;the type of FM used for broadcast stations&lt;/a&gt; — those picked up by consumer FM receivers — as opposed to that used by two-way communications, including amateur transceivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are right that there is no fundamental difference between them in how the &lt;em&gt;frequency modulation&lt;/em&gt; is demodulated via DSP. In both, the difference between the instantaneous frequency of the signal from some nominal carrier frequency is proportional to the modulating (audio) signal. The distinction is in the &lt;em&gt;maximum deviation&lt;/em&gt;, which is closely related to the occupied bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is, if you modulated either type of FM transmitter with a signal at, say, 50% of maximum input level, the wideband FM signal would have a much larger deviation for the same signal. The advantage of this is that wideband FM has higher fidelity and picks up less noise, because the larger instantaneous frequency changes are less easily affected by noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could in principle demodulate either type of FM with the exact same demodulator with the same settings; however, the wideband FM would come out louder because of the larger deviation. In practice, you also need a &lt;em&gt;filter&lt;/em&gt; before the demodulator which removes all the noise or other signals which would interferes with the instantaneous-frequency demodulation; this is what actually makes the biggest difference. To a narrowband receiver, a wideband signal is extremely over-deviating; the frequency repeatedly moves entirely out of the filter passband, so that all but the zero-crossings of the signal are replaced by noise. To a wideband receiver, a narrowband signal is extremely quiet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An additional difference in practice, not inherently related to the deviation and bandwidth, is that wideband FM signals may include stereo or other additional information. Stereo is actually added &lt;em&gt;to the modulating signal&lt;/em&gt; — that is, the FM modulation is unchanged. The “pilot tone” and stereo difference signal are added to the mono audio but shifted to a frequency high enough that they do not conflict with the audio frequencies and a typical mono receiver will not reproduce them. &lt;a href=&quot;http://en.wikipedia.org/wiki/File%3aRDS_vs_DirectBand_FM-spectrum2.svg&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia has a nice plot of what you might find in a broadcast FM signal&lt;/a&gt; — this is an “audio” spectrum, so you will not see these things laid out on a waterfall display.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Another “wide vs. narrow” distinction you might hear about: there are two different maximum deviations (5 kHz and 2.5 kHz) that have been used for two-way radios — in the US, the FCC required a shift to the narrower bandwidth to enable using more channels in the same spectrum; this event was called “narrowbanding”. Amateur equipment is under no such requirement and to my knowledge still typically uses the wider (5 kHz) deviation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In radio software I have seen these distinct modes being cryptically labeled &quot;NFM1&quot; vs. &quot;NFM2&quot;, or &quot;FM&quot; vs. &quot;NFM&quot;, whereas broadcast FM is usually &quot;WFM&quot;.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Finally, &lt;a href=&quot;http://en.wikipedia.org/wiki/Frequency_modulation#Modulation_index&quot; rel=&quot;noreferrer&quot;&gt;in the theory of modulation&lt;/a&gt;, FM is called wideband if the maximum deviation significantly exceeds the highest modulating frequency, and narrowband if the highest modulating frequency significantly exceeds the maximum deviation. By “modulating frequency” we mean the frequencies present in the modulating signal (the audio signal). This relationship affects the effective occupied bandwidth of the signal, and therefore the choice of low-pass filter used to select the channel before demodulating it.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-02-23T15:24:05.407" LastActivityDate="2014-02-23T15:24:05.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1517" PostTypeId="1" AcceptedAnswerId="1528" CreationDate="2014-02-22T23:30:15.747" Score="8" ViewCount="2071" Body="&lt;p&gt;Is the bandwidth of an LCR resonant circuit independent of the capacitance, if the inductance and its series resistance are kept the same, and the Q is high? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This question and the calculation associated with it were originally posted by a radio amateur Anthony G3LAA, who deserves credit for spotting it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At resonance the reactances of L and C are the same and Q is equal to that reactance divided by the series R of the inductor. If we take Q equal to f0/B where B is the bandwidth, and substitute the usual formulae for Q and the resonant frequency f0 in terms of L, C and R,then C cancels out and we are left with B proportional to 1/L. This is true, for all practical purposes (fapp) at moderate frequencies for both series and parallel circuits, and implies that changing the C in the LCR circuit, although this changes the resonant frequency, the bandwidth remains constant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realise that there are a lot of simplifying assumptions in the formulae, both electrical and  mathematical, but, fapp, this looks correct to me. Please, am I right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has an obvious practical advantage in, say, a TRF receiver, with fixed inductance and a variable capacitor to do the tuning, keeping the bandwidth constant over the tuning range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The following is added in response to @Phil Frost's comment, thanks.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the maths — I assume that the formulae for $Q$, $\omega_0 = 2\pi f_0$ and bandwidth, are familiar enough not to need explanation, except that I use $B$ for bandwidth and brevity. I also accept that the formulae depend on many simplifying assumptions, but, fapp, they are good enough, for high $Q$, above about 10.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Q = \frac{1}{\omega_0RC} = \frac{\omega_0L}{R}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reactances equal at resonance, $Q$ is  reactance over $R$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\omega_0=\frac{1}{\sqrt{LC}} \tag{1}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Substituting for $\omega_0$ in each $Q$ formula we get:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Q=\frac{\sqrt{LC}}{RC} = \frac{L}{R} \cdot \frac{1}{\sqrt{LC}}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both of these simplify to&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Q=\frac{1}{R}\sqrt{\frac{L}{C}} \tag{2}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For bandwidth $B$ (frequency difference at half power level) we have $Q=\omega_0/B$ or &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$B=\frac{\omega_0}{Q} \tag{3}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Substituting in (3) for $\omega_0$ from (1) and $Q$ from (2) we finally get &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$B = \frac{1}{\sqrt{LC}}\cdot R\cdot\sqrt{\frac{C}{L}}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which simplifies to $B=R/L$    i.e. Bandwidth is independent of the capacitor value over the range of resonant frequencies for the inductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this correct? I now think so and will give that as an answer&lt;/p&gt;&#xA;" OwnerUserId="297" LastEditorUserId="297" LastEditDate="2014-02-25T16:22:10.597" LastActivityDate="2014-02-25T16:22:10.597" Title="Is the bandwidth of an LCR resonant circuit independent of the capacitance?" Tags="&lt;frequency&gt;&lt;impedance&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1519" PostTypeId="1" CreationDate="2014-02-23T21:58:43.433" Score="8" ViewCount="695" Body="&lt;p&gt;The concept of antenna gain is pretty important for calculation of link budget and is something I've had contact with. I know that it tells me how focused the waves emitted by the antenna are and I know how to read antenna gain charts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I don't know is how to calculate antenna gain for a given antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what are the general steps required in order to calculate antenna gain? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it matters, I'd like to calculate gain of a J-pole antenna, but I'd like to keep this question general, if possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE:&lt;/strong&gt; Just to be clear, what I really want to know is how to actually do the calculations, not just how to use already calculated results. I do expect the &quot;perfect&quot; answer to be extremely long and complicated. Because of that, I'm willing to accept answers which list the necessary steps and provide information in which direction I should do research next for the required steps.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="76" LastEditDate="2015-12-15T21:54:57.963" LastActivityDate="2015-12-15T21:54:57.963" Title="How would I calculate antenna gain?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1520" PostTypeId="2" ParentId="1519" CreationDate="2014-02-24T10:03:27.683" Score="3" Body="&lt;p&gt;Interestingly, while in an ideal world a J-Pole will perform exactly like a half-wave dipole (as it is one), in reality the configuration of your build makes gain incredibly difficult to calculate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w8ji.com/end-fed_vertical.htm&quot; rel=&quot;nofollow&quot;&gt;This great page at w8ji.com&lt;/a&gt; shows field charts for J-Poles with small differences in build where the low angle gain can vary by 5dB. They do state though:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;None of this means the J-pole won't work, have a low SWR, and make&#xA;  contacts. It simply shows the pattern is unpredictable because the&#xA;  feedline, mast, and grounding significantly affects performance.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So you should work under the assumption that your J-Pole will be not quite as good as a half-wave dipole and go with that.&lt;/p&gt;&#xA;" OwnerUserId="50" LastActivityDate="2014-02-24T10:03:27.683" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1521" PostTypeId="2" ParentId="1519" CreationDate="2014-02-24T12:35:58.153" Score="7" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;So what are the general steps required in order to calculate antenna gain?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In the general case, calculating the gain requires solving &lt;a href=&quot;http://en.wikipedia.org/wiki/Maxwell%27s_equations&quot;&gt;Maxwell's equations&lt;/a&gt;, for whatever antenna geometry you have.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's exceptionally hard, and no one does it without the assistance of a computer, except for very simple antennas, such as dipoles. For these simple antennas, you can find the solutions at places like &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot;&gt;antenna-theory.com&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For arbitrary antennas, the solution usually involves breaking the antenna into a large number of smaller conducting elements connected together, then using the &lt;a href=&quot;http://en.wikipedia.org/wiki/Boundary_element_method&quot;&gt;boundary element method&lt;/a&gt; to solve the underlying equations. A number of popular implementations are based on &lt;a href=&quot;http://en.wikipedia.org/wiki/Numerical_Electromagnetics_Code&quot;&gt;NEC&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gain can also be determined empirically. In practice, this is how it's frequently done, because it is more accurate. The antenna is placed in an &lt;a href=&quot;http://en.wikipedia.org/wiki/Anechoic_chamber&quot;&gt;anechoic chamber&lt;/a&gt; and fed with a known power. A field strength meter is then moved around the antenna, and these readings compared to the theoretical field strength at the same distance of an isotropic radiator. The ratio of these is the antenna gain.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-24T12:35:58.153" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1522" PostTypeId="1" AcceptedAnswerId="1523" CreationDate="2014-02-24T23:02:12.290" Score="3" ViewCount="100" Body="&lt;p&gt;I found some pages on info for satellites, and I got different results. Some said to shift the transmit frequency as well as the receive, some said to keep the transmit the same, but shift the receive during the pass, I am confused on what I should do. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is one for UO-14&#xA;&lt;img src=&quot;https://i.stack.imgur.com/4YikL.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and here is one for SO-50&#xA;&lt;img src=&quot;https://i.stack.imgur.com/4N5TY.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice one of them shifts the receive frequency as well as the transmit, and the other only shifts the transmit. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-02-25T00:31:22.843" Title="Transmitting Offset for sats" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1523" PostTypeId="2" ParentId="1522" CreationDate="2014-02-25T00:31:22.843" Score="5" Body="&lt;p&gt;The reason you don't need to shift one frequency is that the Doppler shift for the 144MHz band, for a satellite in this orbit, is only about 2-3kHz, which is within the range needed to make contact without adjusting. You can, and you'll get better results if you do, but to make satellite operation easy many do not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 440MHz band, however, experiences a Doppler shift of 10kHz, which means that the beginning and end of the pass will fall outside the bandwidth allocated if you don't adjust.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The higher the frequency, the greater the Doppler shift. It's relative to the frequency.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-25T00:31:22.843" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1524" PostTypeId="1" AcceptedAnswerId="1526" CreationDate="2014-02-25T00:44:50.243" Score="14" ViewCount="2748" Body="&lt;p&gt;I assume that anyone who has a G5RV or G5RV junior in their attic has done so with ceramic spacers, and has zigzag or dog-leg installations, or otherwise has contorted the antenna to fit up there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My worry is how can I satisfy my own and my XYL (wife)'s concerns about RF in our house, especially in the bedrooms immediately below the attic, where all of us sleep?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What do I need to know, and what do I need to measure to know if any harmful RF levels would exist in the area 12 feet below the attic?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that other questions here cover using radios or Oscilliscopes to measure and observe decreases in RF in the shack, how can I establish reasonably easily that levels not more than 1/10th of the level that could cause harm, are present in my house?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if high levels can cause GFCI breakers in my outlets to trip, how high would such levels be, compared to the levels that could cause damage to people?  Is there any way to know?&lt;/p&gt;&#xA;" OwnerUserId="643" LastEditorUserId="643" LastEditDate="2014-02-25T01:44:55.887" LastActivityDate="2014-02-25T20:31:51.523" Title="If I install a G5RV in my attic how could I be certain there are not harmful levels of RF in the shack, or my kids bedroom?" Tags="&lt;antenna&gt;&lt;safety&gt;" AnswerCount="2" CommentCount="7" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1525" PostTypeId="2" ParentId="1524" CreationDate="2014-02-25T02:31:56.660" Score="3" Body="&lt;p&gt;The &lt;a href=&quot;http://www.arrl.org/rf-exposure&quot; rel=&quot;nofollow&quot;&gt;ARRL RF Exposure page&lt;/a&gt; has a lot of useful resources. It has links to a number of articles and external websites that provide some good info. If you happen to have a copy of the ARRL Handbook, the Safety chapter has a section that covers RF safety.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Between 1.34-30MHz, the FCC maximum permissible exposure (uncontrolled exposures/general population) for power density is 180/f&lt;sup&gt;2&lt;/sup&gt; mW/cm&lt;sup&gt;2&lt;/sup&gt; and 0.2 mW/cm&lt;sup&gt;2&lt;/sup&gt; between 30-300 MHz, where f is the frequency in MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for measuring the field strengths, it's probably not something you'll be able to do yourself without some specialized equipment. There are companies that can do this for you, but if you're not running more than 100 W, it's probably not worth the expense. This &lt;a href=&quot;http://hintlink.com/power_density.htm&quot; rel=&quot;nofollow&quot;&gt;RF safety calculator&lt;/a&gt; looks like it would be useful to see how close you might be to any limits. &lt;/p&gt;&#xA;" OwnerUserId="73" LastEditorUserId="218" LastEditDate="2014-02-25T20:31:51.523" LastActivityDate="2014-02-25T20:31:51.523" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1526" PostTypeId="2" ParentId="1524" CreationDate="2014-02-25T03:51:37.780" Score="12" Body="&lt;p&gt;If you want to be &lt;em&gt;certain&lt;/em&gt;, you will need calibrated electric and magnetic field probes and a spectrum analyzer. If you had that equipment, I doubt you would ask this question, so let's assume you &lt;em&gt;don't&lt;/em&gt; have it, and you don't care to drop thousands of dollars to get it. How can you be &lt;em&gt;pretty sure&lt;/em&gt; that exposure is safe, without expensive test equipment?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First we have to define &lt;em&gt;safe&lt;/em&gt;. Since this forum is about Amateur Radio, and not medical research, let's use the FCC's definition of safe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC has determined that amateur operators need not give any special consideration to RF safety if the transmitter power is below a certain level. At these relatively low transmitter powers, it's just really hard to encounter a dangerous field, no matter how close you get. &lt;a href=&quot;http://www.arrl.org/fcc-rf-exposure-regulations-the-station-evaluation&quot;&gt;The ARRL gives a full table&lt;/a&gt;, but all bands 15m and below are good at 100W PEP or less (limits are even higher on lower bands). The limit for 12m is 75W, and 10m is 50W PEP. That covers the usual operating range for a G5RV.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you exceed those limits, you may very will still be safe, but you have to do some analysis. Here's a simple way to do it: the maximum power density for 3MHz to 30MHz is 180mW per square centimeter, divided by the frequency in MHz squared.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can estimate the power density by making some simplifying assumptions. If we leave a big margin, we can still be pretty sure we are within safe limits despite our gross simplifications. First, let's assume that power is radiated equally along the antenna's length, and that you are close enough that we should consider it as a line source, not a point source. If you put 100W into it, then for any cylinder centered on that antenna, there is 100W passing through it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The half-size G5RV, being smaller, will have higher power density. It's 15.5m long. Let's say you are 3m away from it, and you are feeding it with 100W. The area of a cylinder (without the ends) 15.5m in length and 3m in radius is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 2 \pi \cdot 3\mathrm m \cdot 15.5m = 292 \mathrm m^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your 100W of transmitter power is spread over this cylinder, so the power density is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \require{cancel}&#xA;\frac{100\cancel{\mathrm W}}{292 \cancel{\mathrm m^2}}&#xA;\frac{1 \cancel{\mathrm m}}{100 \mathrm{cm}}&#xA;\frac{1 \cancel{\mathrm m}}{100 \mathrm{cm}}&#xA;\frac{1000\mathrm{mW}}{1\cancel{\mathrm W}}&#xA;= 0.0342 \mathrm{mW}/\mathrm{cm} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's call the top end of 10m an even 30MHz. The maximum safe power density is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{180}{30^2} = 0.2\mathrm{mW}/\mathrm{cm}^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you are 7.6dB below the FCC limit for uncontrolled exposure. I'd call it safe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that this is a gross simplification. Factors that make our estimation less safe include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;power isn't actually radiated equally all over the antenna. There will be hot spots, and cold spots.&lt;/li&gt;&#xA;&lt;li&gt;with the antenna in your attic, you aren't even in the far field of the antenna. Calculating the actual fields is really hard.&lt;/li&gt;&#xA;&lt;li&gt;ground reflections, and also any wiring in your house, may reflect, distort, or focus the field, making more hot spots.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Factors that provide additional safety margin to our estimate include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the antenna doesn't radiate like the worst-case cylinder: some power goes towards the sides also.&lt;/li&gt;&#xA;&lt;li&gt;exposure limits are higher for lower frequencies (at 7 MHz: 3.6 milliwatt per square centimeter).&lt;/li&gt;&#xA;&lt;li&gt;SSB power is usually measured in PEP, while exposure limits are set by average power over 30 minutes. SSB has a duty cycle around 20%.&lt;/li&gt;&#xA;&lt;li&gt;Regardless of the mode you use, you probably don't transmit all the time, further reducing duty cycle.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-25T03:51:37.780" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1527" PostTypeId="1" CreationDate="2014-02-25T14:03:29.917" Score="4" ViewCount="1429" Body="&lt;p&gt;I'm interested in an RF field strength meter that doesn't have to be lab quality, but still gives enough information about the RF field to know if an area exposed to RF is above the &lt;a href=&quot;http://www.arrl.org/rf-radiation-and-electromagnetic-field-safety&quot; rel=&quot;nofollow noreferrer&quot;&gt;safety limits suggested by the ARRL&lt;/a&gt; and others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the simpler designs available has no information about accuracy or calibration.  Can the following design be calibrated, or is the circuit only good for relative measurements?  The only circuit description I have follows the schematic:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/cuTI3.gif&quot; alt=&quot;Schematic of simple RF field strength meter. A dual input FET is fed RF from an antenna which is connected to an inductor/capacitor to select frequency range.  The output of the FET is rectified and fed to an ammeter.&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A radio field signal strength indicator is very usefull for determine radiation patterns of transmitters antennas. An ancillary antenna must be put close to main transmitter antenna. The received signal is applied to L1,L2 and C2, this allows the field indicator circuit to adjust to the same frequency as the transmitter. With the coils values from the radio signal indicator wiring schematic, the frequency band is 6 to 60MHz. A pair of headphones can be connected to hear the transmission. The total impendance of the headphones has to be at least 2.2Kohm.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-02-25T17:25:14.760" Title="How would this RF field strength meter be calibrated?" Tags="&lt;equipment-design&gt;&lt;calibration&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1528" PostTypeId="2" ParentId="1517" CreationDate="2014-02-25T16:07:34.910" Score="0" Body="&lt;p&gt;I am now convinced that the maths is correct, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you @Kevin, for tidying it all up. I was going to transfer the maths here as an answer, but I will leave it in the question&lt;/p&gt;&#xA;" OwnerUserId="297" LastEditorUserId="297" LastEditDate="2014-02-25T16:14:27.970" LastActivityDate="2014-02-25T16:14:27.970" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1529" PostTypeId="2" ParentId="1527" CreationDate="2014-02-25T17:25:14.760" Score="2" Body="&lt;p&gt;In theory, if you can expose this device to a known field, you should be able to calculate some constants which allow you to convert the measured current (in μA) to a power density (in power per area, such as mW per cm&lt;sup&gt;2&lt;/sup&gt;). Power is proportional to the square of current. T1 introduces some unknown gain, and the filters have some unknown loss. The antenna has some &lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_aperture&quot; rel=&quot;nofollow&quot;&gt;aperture&lt;/a&gt;. The power density is the power received by the antenna, divided by the aperture of the antenna. All the variables you don't know (the circuit's impedance, the antenna aperture, T1's gain, filter losses, etc) can all be lumped into a general &lt;a href=&quot;http://en.wikipedia.org/wiki/Quadratic_equation&quot; rel=&quot;nofollow&quot;&gt;quadratic equation&lt;/a&gt; of the form:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{power density} = aI^2 + bI $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $I$ is the current displayed on the meter, and $a$ and $b$ are some constants you must determine through calibration. You could determine them by exposing the device to a handful of known fields, recording the measured current, then performing a &lt;a href=&quot;http://en.wikipedia.org/wiki/Polynomial_regression&quot; rel=&quot;nofollow&quot;&gt;quadratic regression&lt;/a&gt; with a spreadsheet program to find the values for $a$ and $b$ which best fit the measurements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The trouble is coming up with a &lt;em&gt;known field&lt;/em&gt;. You could transmit into some antenna that is easily modeled (say, a dipole) a known power, then calculate (by the antenna model) what the power density should be at some distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, &lt;a href=&quot;http://www.voacap.com/antennas/squeezing-decibels-out-of-dipole/&quot; rel=&quot;nofollow&quot;&gt;modeling with EZNEC&lt;/a&gt; suggests that a half-wave dipole a half-wavelength above ground has between 8.6 dBi of gain for &quot;very good ground&quot; to 6.8 dBi for &quot;very poor ground&quot;, in the direction of maximum gain. This is broadside to the dipole, at about 20 degrees elevation. We can then calculate the power density at some distance with the &lt;a href=&quot;http://en.wikipedia.org/wiki/Inverse-square_law&quot; rel=&quot;nofollow&quot;&gt;inverse square law&lt;/a&gt;. For our example:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;we are &lt;strong&gt;100m&lt;/strong&gt; away,&lt;/li&gt;&#xA;&lt;li&gt;we are putting a &lt;strong&gt;20W&lt;/strong&gt; carrier into the antenna, and,&lt;/li&gt;&#xA;&lt;li&gt;we estimate the dipole's gain is around &lt;strong&gt;7 dBi&lt;/strong&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It's important to note that we need to be many wavelengths away, for two reasons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;We must be in the &lt;a href=&quot;http://www.antenna-theory.com/basics/fieldRegions.php&quot; rel=&quot;nofollow&quot;&gt;far field&lt;/a&gt; for the predictions of our antenna modeling to be accurate.&lt;/li&gt;&#xA;&lt;li&gt;The inverse square law only holds for things that are far enough away that they appear to be an infinitely small, single point.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A measurement distance of 100m might be sufficient for a 10m dipole, but for 160m, I'd want to be much farther away. As a rule of thumb, I'd stick to 10 wavelengths or more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the math. First convert the gain into a multiplicative value:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 7\mathrm{dB} = 10^{7/10} \approx 5 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://en.wikipedia.org/wiki/Equivalent_isotropically_radiated_power&quot; rel=&quot;nofollow&quot;&gt;EIRP&lt;/a&gt; is then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 20\mathrm W \cdot 5 = 100\mathrm W $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 100m, that 100W will be spread out over an area equal to the surface area of a sphere with radius 100m (this is the inverse square law). That sphere's area is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 4\pi (100\mathrm m)^2 \approx 125663 \mathrm m^2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power density is then the EIRP divided by this area:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{100 \mathrm W}{125663 \mathrm m^2} = \frac{0.000796 \mathrm W}{\mathrm m^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Converting to the more usual unit of mW/cm&lt;sup&gt;2&lt;/sup&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \require{cancel}&#xA;\frac{0.000796 \cancel{\mathrm W}}{\cancel{\mathrm m^2}}&#xA;\frac{1000 \mathrm{mW}}{\cancel{\mathrm W}}&#xA;\frac{1 \cancel{\mathrm{m}}}{100 \mathrm{cm}}&#xA;\frac{1 \cancel{\mathrm{m}}}{100 \mathrm{cm}}&#xA;= \frac{0.0796 \mathrm{mW}}{\mathrm{cm^2}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the trouble: this method is only as good as your model, and the model isn't very good. It might get you within an order of magnitude at best.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, if this calibration is dependent on a model for its accuracy, you might as well just model the antenna in question, the one which you want to measure for safety. Then you can guess what its fields are directly, and skip the building of the probe, and the calibration, and you won't be any less accurate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even so, a probe &quot;calibrated&quot; in this manner can still be useful. Its readings will always be off by some multiplicative constant, so it can be used for comparing one antenna to another, or measuring the radiation pattern of an antenna, or measuring the effect of other station changes (upgrade feedline, install a balun, new transmitter, etc).&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-25T17:25:14.760" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1530" PostTypeId="1" AcceptedAnswerId="7688" CreationDate="2014-02-25T17:38:07.557" Score="6" ViewCount="6271" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_aperture#Aperture_and_gain&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia says&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;It can be shown that the aperture of a lossless isotropic antenna, which by definition has unity gain, is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ A_{\mathit{eff}} = \frac {\lambda^2}{4 \pi}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;We also see this emerge as a &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; term in the &lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;Friis transmission equation&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {\frac {P_{r}}{P_{t}}}=G_{t}G_{r}\left({\frac {\lambda }{4\pi R}}\right)^{2} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This would suggest that longer wavelength antennas are more efficient collectors of electromagnetic energy. Why is this? Wikipedia says it can be shown. Show me.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-06-07T00:19:39.443" Title="Why is antenna aperture a function of wavelength?" Tags="&lt;antenna&gt;&lt;math&gt;" AnswerCount="6" CommentCount="7" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1531" PostTypeId="1" AcceptedAnswerId="1547" CreationDate="2014-02-25T17:58:19.100" Score="1" ViewCount="205" Body="&lt;p&gt;I have an opportunity to purchase one or more of these &lt;a href=&quot;http://sine.ni.com/nips/cds/view/p/lang/en/nid/206676&quot; rel=&quot;nofollow&quot;&gt;24 bit, 4 channel, 102ksps USB ADCs&lt;/a&gt;, but before I do I want to understand how difficult they would be to use with existing SDR software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any windows SDR software packages known to connect to National Instruments input devices without extra work?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, is there SDR software that has an API or similar so one can easily add their own analog input drivers to attach the SDR software to custom or unsupported hardware?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-03-02T09:26:19.593" Title="SDR software support for National Instruments USB-4431 ADC?" Tags="&lt;software-defined-radio&gt;&lt;equipment&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1532" PostTypeId="1" AcceptedAnswerId="1533" CreationDate="2014-02-25T19:31:22.363" Score="2" ViewCount="3220" Body="&lt;p&gt;If I have a 2-meter 1/4 wave ground plane antenna with 1/4 wave radials bent down at approximately 45 degrees, what kind of performance in terms of SWR and gain pattern can I expect when using it on the 70cm band, relative to its performance on the 2 meter band?&lt;/p&gt;&#xA;" OwnerUserId="207" LastActivityDate="2014-02-25T20:53:27.303" Title="What is the theoretical performance of a 2m 1/4 wave ground plane antenna when used at 70cm?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;vertical-antenna&gt;&lt;70cm-band&gt;&lt;2m-band&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1533" PostTypeId="2" ParentId="1532" CreationDate="2014-02-25T20:53:27.303" Score="2" Body="&lt;p&gt;Let's assume that this antenna you describe, when operated at 145 MHz, has an SWR of 1:1, and behaves like an ideal antenna. At 145 MHz, the 1/4 wave vertical, plus the image antenna formed by the ground plane, make it effectively like a 1/2 wave dipole. It will have a free-space radiation pattern like this, for an antenna oriented vertically along the Z-axis:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/pzuat.jpg&quot; alt=&quot;0.5 WL antenna pattern&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At three times this frequency (435 MHz), the antenna will be resonant again. That means its impedance is unchanged, so if you had a 1:1 SWR at 145 MHz, you will have a 1:1 SWR again at 435 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the radiation pattern is different, because now it's not a 1/2 wavelength dipole, but a 1 1/2 wavelength dipole. The radiation pattern looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/2q6VZ.jpg&quot; alt=&quot;1.5 WL antenna pattern&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the latter case, at 435 MHz, the maximum gain is the same as it was at 145 MHz. However, the lobes are narrower, and higher elevation. There's a secondary lobe around the horizon, but it's even narrower, and about 4 dB below the main lobes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These images are from &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna-theory.com&lt;/a&gt;, which has a good deal more to say on the issue. Everything there about dipoles is also relevant to verticals, which are just dipoles where half of the dipole is formed by an image antenna through the ground plane.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-02-25T20:53:27.303" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1534" PostTypeId="2" ParentId="1519" CreationDate="2014-02-25T22:40:25.373" Score="0" Body="&lt;p&gt;Calculating the gain is very complicated as it usually involves solving differential equations there are software packages that can do that for you. I personally use 4nec2 &lt;a href=&quot;http://www.qsl.net/4nec2/&quot; rel=&quot;nofollow&quot;&gt;http://www.qsl.net/4nec2/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="788" LastEditorUserId="788" LastEditDate="2014-02-26T15:32:31.237" LastActivityDate="2014-02-26T15:32:31.237" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1535" PostTypeId="1" AcceptedAnswerId="1537" CreationDate="2014-02-25T23:23:57.637" Score="9" ViewCount="8627" Body="&lt;p&gt;I'd like to install an outdoor dual band VHF/UHF base station antenna, a simple pole antenna like the &lt;a href=&quot;http://www.cometantenna.com/products.php?CatID=1&amp;amp;childID=4&amp;amp;famID=5&quot; rel=&quot;noreferrer&quot;&gt;Comet GP-1&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in an area where lightning is rare, but not unheard of. Should I drive ground rods into the ground for antenna/RF grounding? The antenna itself has several small ground radials, so I'm assuming that a good ground will aid performance, but don't know if using the existing building ground is &quot;good enough&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in a multi-unit building which may complicate this since my understanding is that any antenna ground system should be bonded to the building ground to prevent differing ground potentials (and the bonding should be via a dedicated ground wire directly to the building ground, not through a ground conductor in the building wiring), however my building ground rod is in a separate structure. The service entrance is in a closet in the back of a garage structure, then it goes under  a sidewalk and my front yard and then into a service panel in my kitchen in the middle of the house (either under or through the cement slab). There's no apparent grounding electrode for the living unit, and even if there was, there's no  easy way to run a ground wire from the antenna to it since I'd either have to go around a neighbor's unit or over the roof to reach it. It is possible that the service panel is grounded to the slab rebar or to a ground electrode that's not visible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My housing complex looks something like the diagram below (though there are more housing units than what I've drawn), where I'm in unit 2 and would mount the antenna outside a room on the back side of the unit, while the  service entrance comes in from the garage on the other side, The &quot;V&quot; shows the location of the service panel inside the unit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/VP626.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since I'll be using it with a 12VDC mobile transceiver, I could conceivably keep the tranceiver isolated from ground, leaving the antenna &amp;amp; transceiver ground completely separate from the building ground, but that seems quite unsafe if there is a difference in ground  potential between the back yard and front yard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the best practice for grounding this antenna?&lt;/p&gt;&#xA;" OwnerUserId="790" LastEditorUserId="790" LastEditDate="2014-02-26T01:33:12.600" LastActivityDate="2019-08-15T13:31:37.317" Title="Grounding VHF base station antenna" Tags="&lt;grounding&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1536" PostTypeId="2" ParentId="1535" CreationDate="2014-02-26T11:50:16.343" Score="-1" Body="&lt;p&gt;Given what you have presented, &lt;strong&gt;yes&lt;/strong&gt;, put a ground rod down and bond the mast to it.&#xA;It would also be a good idea to attach a ground wire from the radio (one of the mounting screws will do) to this same ground rod.&#xA;Your power supply should have a 3 pin plug on it for connection to the building AC; one of these pins (usually the round one) should be the &quot;safety&quot; ground running back to the distribution panel and its earth ground. You should have no trouble here unless you mount your radio to the power supply (keep them isolated from each other).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There should be &lt;em&gt;no&lt;/em&gt; potential difference between your new ground and the building service ground. If you are qualified to use a AC volt meter you can easily check this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many articles on the net about grounding; what you are trying to create is a &lt;em&gt;single point ground&lt;/em&gt; for your system. At VHF and UHF this is not as critical as at HF frequencies (read up on &lt;em&gt;ground loops&lt;/em&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is always a good idea, if bad weather is in the area, to disconnect the antenna feed line from the radio and isolate it or ground the center pin of the coax to your new station ground. Keep in mind that if your antenna is the tallest thing in the area it may / will become a &lt;em&gt;lightning rod&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="438" LastEditorUserId="76" LastEditDate="2014-02-26T16:18:45.193" LastActivityDate="2014-02-26T16:18:45.193" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1537" PostTypeId="2" ParentId="1535" CreationDate="2014-02-26T12:33:57.287" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Should I drive ground rods into the ground for antenna/RF grounding?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Probably not&lt;/em&gt;. What you are likely to accomplish is this: (diagram from &lt;a href=&quot;http://www.w8ji.com/station_ground.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JZnHt.jpg&quot; alt=&quot;lightning hits power lines&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the lightning hits the antenna, have the same problem in the other direction. The important thing to realize is that the current from a lightning strike is so huge that it will go through &lt;em&gt;all&lt;/em&gt; the grounds, and if one of those paths is through your equipment, expect something to be broken.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might even be making things worse by adding a ground (&lt;em&gt;B&lt;/em&gt;) to your station. Now your radio is part of the safety ground for your house's electrical system, &lt;em&gt;even if you disconnect the feedline (A)&lt;/em&gt;. Don't do that!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Grounding the antenna won't improve its performance. The important thing is to eliminate &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;common-mode currents&lt;/a&gt; in your antenna system, perhaps &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;with a balun&lt;/a&gt;. Once you've done that, there won't be any need to ground the antenna for performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A proper lightning protection scheme requires that you take &lt;em&gt;all&lt;/em&gt; cables entering your station, including the feedline, AC mains, ethernet, telephone, and anything else, and passing them through a common ground point which is bonded &lt;em&gt;really well&lt;/em&gt; with the Earth (read: multiple ground rods, wide, short copper strap). With only one ground connection, there's no path &lt;em&gt;through&lt;/em&gt; your equipment, only &lt;em&gt;around&lt;/em&gt; it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is costly and time consuming, and given your specific situation (relatively small VHF antenna on what I assume isn't an especially large tower, in a region with rare lightning) it may be difficult to justify the expense and effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't add more grounds (such as &lt;em&gt;B&lt;/em&gt; in the diagram above), then you can be reasonably protected by &lt;a href=&quot;https://ham.stackexchange.com/q/1451/218&quot;&gt;disconnecting the feedline&lt;/a&gt;. Your station at least won't be any more vulnerable than any other device you leaved plugged into mains, like your TV.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-02-26T17:36:12.560" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1538" PostTypeId="2" ParentId="51" CreationDate="2014-02-27T01:42:45.000" Score="17" Body="&lt;p&gt;There's a lot that can be said about lightning protection, but it usually boils down to doing &lt;em&gt;all&lt;/em&gt; of these things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;make good, low impedance connections to Earth&lt;/li&gt;&#xA;&lt;li&gt;bond all Earth connections together with a low impedance path&lt;/li&gt;&#xA;&lt;li&gt;have only a &lt;em&gt;single&lt;/em&gt; point of entry to protected equipment&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;A real problem when discussing lightning protection is that people will consider only some of these things, and the result is sometimes worse than doing nothing.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;make good, low impedance connections to Earth&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Just about everyone understands this one. You want long rods in the ground, at least 8 feet. Multiple rods, if you can, about as far apart as they are deep. Lightning currents from a big direct strike can be in excess of 100,000 amperes, so you need &lt;em&gt;fat&lt;/em&gt; conductors so they aren't vaporized by the current. Lighting is also an extremely fast pulse, which means it contains a lot of high-frequency energy, and you should think about it like RF current. Wide strapping is better than round conductors (&lt;a href=&quot;http://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin effect&lt;/a&gt;) and you should make the path of your conductor as straight and short as possible to minimize resistance and inductance.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;bond all Earth connections together with a low impedance path&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;This one is frequently neglected. The current from a strike is so huge that it won't simply all go into the closest grounding rod can find. The Earth itself isn't a low impedance conductor, so even when lightning strikes a point in an empty field, significant voltage gradients can be observed significant distances away from the strike point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w8ji.com/lightning_strikes.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI&lt;/a&gt; has a great example of this, where a tree was struck, and some 20 feet away, arced back out of the ground to travel through a Beverage antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consequently, if you have multiple connections to Earth, or even things &lt;em&gt;close&lt;/em&gt; to Earth, lightning currents &lt;em&gt;will&lt;/em&gt; find a way to those points, even if that means flowing through your station equipment, arcing across water pipes, HVAC ducting, or even through wood or concrete in your home, which aren't great insulators. Bonding all the grounds together with heavy wire gives the current an intentional place to go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most building and fire codes &lt;em&gt;require&lt;/em&gt; that all grounds are bonded with very heavy wire or strap, for this reason.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;have only a &lt;em&gt;single&lt;/em&gt; point of entry to protected equipment&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Perhaps the most neglected point of all. If there are multiple points of entry, that means lightning current can enter at one point, and exit at another. As discussed in the previous point, lightning currents are so huge that they make significant voltage gradients almost everywhere, including between the two points of entry to your station. Where there are voltage gradients, there are currents, and where there are currents, things break.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A very common situation in amateur stations is to have a grounding rod at the mast or tower, where the feedline enters the shack, or both. &lt;a href=&quot;http://www.w8ji.com/images/Lightning/lightningpwrlines.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI provides a great diagram&lt;/a&gt; of a &lt;strong&gt;poor&lt;/strong&gt; grounding system: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/IgqBh.jpg&quot; alt=&quot;poor station ground configuration&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I highly recommend reading through the rest of W8JI's lightning and grounding information. Lots of diagrams, pictures, and good advice. On this topic: &lt;a href=&quot;http://www.w8ji.com/ground_systems.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ground systems&lt;/a&gt;, &lt;a href=&quot;http://www.w8ji.com/house_ground_layouts.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;House ground layouts&lt;/a&gt;, and &lt;a href=&quot;http://www.w8ji.com/second_floor_grounding.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Second floor grounding&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When lightning strikes the power lines, some of this current will go to ground through the additional ground(s) at the tower or shack entrance. After passing through your equipment and frying it, of course. Strikes on the tower cause the same problem, in the other direction. This is a situation where a naïve attempt at protection has made things worse, virtually &lt;em&gt;guaranteeing&lt;/em&gt; equipment damage when a strike occurs. Even a nearby strike might introduce enough of a voltage between the grounds to cook your equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Worse, in some setups, disconnecting the feedline leaves this extra ground (B) still connected, violating the popular &quot;wisdom&quot; that disconnecting the feedline in a storm protects your equipment!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So what can you do?&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;the ideal approach&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Ground the base of your tower or mast with a large field of radials and a lot of ground rods, spaced over a wide area, bonded together with wide copper strap. Bond the shields of all coax feedlines to this. Should lightning strike the mast, this will provide a low impedance ground to take a big share of the current. It may also be useful to reduce ground losses if you want to use the mast as a radiator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inspect the ground where your electrical, CATV, and phone service enter the building and ensure it's in good shape and a sufficiently low impedance. Remember lightning can strike the utility lines, too. Again, you want this to be a low impedance ground so it takes a good part of the strike current, diminishing the load on the other components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Surround your entire house in wide copper strap, with a hefty ground rod every eight feet or so. The copper strap effectively puts all the ground rods in parallel, lowering the ground impedance. The ring around the house also acts as a sort of 2-dimensional Faraday cage, reducing the electric potential difference between any two points on the ground within the ring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bond tower and house ground systems together with wide copper strap, so that any current caused by a voltage between them favors that strap over your feedlines. Make sure any utility grounds (electric, telco, etc) are also part of this system of grounds. This is often required by fire codes because it reduces the chances of an electrical arc between these two ground systems, which might be especially likely if there's a good conductor that goes most of the way but not quite all the way between the grounds, for example a disconnected feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Every&lt;/em&gt; cable that enters your shack, including the mains wiring, any control lines up the tower for rotators and such, ethernet cables for a home network, &lt;em&gt;everything&lt;/em&gt;, enters the shack through a big, fat copper plate that's connected with a wide, short, straight connection to the ground running around the house. Each of these cables go through protection devices such as gas discharge tubes or MOVs. Conductors that should be grounded (feedline shields, AC safety ground, etc) are bolted directly to the grounding panel. By making such a single point of entry, you ensure all the protected equipment stays at the same electric potential.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a setup like this, you can confidently leave your feedlines connected in a storm, and survive direct strikes to the antennas. In fact, your house is probably &lt;em&gt;less&lt;/em&gt; likely to be damaged by lighting than ordinary residential construction. A direct strike may cause some damage to exterior components, burning insulation or melting thin-gauge wires, but equipment inside is quite safe.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;more modest approach&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Most people will not want to invest the time or money to install a protection scheme that extensive. If you don't have a tall tower, or you live in an area where lightning is not frequent, it may be difficult to justify such expenditures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case, it's better to think about what you &lt;em&gt;shouldn't&lt;/em&gt; do. Don't create an extra ground. It's better to address &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;common-mode currents&lt;/a&gt; with &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;baluns&lt;/a&gt; and proper antenna design. If you must have a ground (such as a vertical installed at ground level), then consider the ground part of the antenna, not the station, and be sure to disconnect it in storm conditions.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-04-07T23:53:51.210" LastActivityDate="2020-04-07T23:53:51.210" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="1539" PostTypeId="1" AcceptedAnswerId="1540" CreationDate="2014-02-27T04:03:37.170" Score="6" ViewCount="2359" Body="&lt;p&gt;I've read that the Friis transmission equation can be &lt;a href=&quot;https://ham.stackexchange.com/a/1487/218&quot;&gt;applied to calculate path loss in ideal space&lt;/a&gt;. However, I'd like to better understand the factors that define it and what it represents, and &lt;em&gt;why&lt;/em&gt; it is the equation it is.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-04-29T01:32:22.833" Title="What does the Friis transmission equation represent and how is it derived?" Tags="&lt;math&gt;&lt;path-loss&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1540" PostTypeId="2" ParentId="1539" CreationDate="2014-02-27T04:03:37.170" Score="6" Body="&lt;p&gt;Let's imagine that there are two antennas, entirely in free space. There is no Earth or any other object near enough to affect propagation. Let's also assume that these antennas are far enough apart that the antennas interact only by their &lt;a href=&quot;http://en.wikipedia.org/wiki/Near_and_far_field&quot; rel=&quot;nofollow noreferrer&quot;&gt;far fields&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To start, let's assume that both antennas are isotropic, meaning that they radiate equally in each direction. If we supply a pulse of energy to such an antenna, this energy will spread out as a sphere, to infinity, at the speed of light. It also means that if we supply a constant power to such an antenna, then for any sized sphere centered on that antenna, the power passing through that sphere is equal to the power being fed to the antenna.&lt;sup&gt;1&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we are interested in the power received by an antenna at distance $r$ from the transmitting antenna, then all the transmitted power will be spread across a sphere of radius $r$ by the time it reaches the receiving antenna. The area of that sphere is $ 4 \pi r^2 $. The transmit power $P_t$ divided by that area gives us:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_t \over 4 \pi r^2 \tag{1} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This number has units $\mathrm W/\mathrm m^2$ and is a &lt;em&gt;power flux density&lt;/em&gt; or &lt;a href=&quot;http://en.wikipedia.org/wiki/Irradiance&quot; rel=&quot;nofollow noreferrer&quot;&gt;irradiance&lt;/a&gt;. A watt is one joule per second, so a power flux density of $1\mathrm W/\mathrm m^2$ means that every second, one joule of energy passes through an area of one square meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Isotropic antennas can't exist&lt;sup&gt;2&lt;/sup&gt;, and even a dipole has some gain&lt;sup&gt;3&lt;/sup&gt;. Assuming the receiving antenna is in the direction of maximum gain, this multiplies the power flux density, so if the transmitting antenna's gain is $G_t$, the equation becomes&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {P_t \over 4 \pi r^2} G_t \tag{2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This gives us the power flux density at the receiving antenna, but how much of this power is received? The &lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_aperture&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna aperture&lt;/a&gt; answers that question. Let's call the aperture of the receiving antenna $A_r$. The power received ($P_r$) is then&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_r = {P_t \over 4 \pi r^2} G_t A_r \tag{3} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Effective aperture $A$ and gain $G$ are related by&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A = {\lambda^2 \over 4 \pi} G \tag{4} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Substituting this into equation 3 gives us&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_r = {P_t \over 4 \pi r^2} G_t {\lambda^2 \over 4 \pi} G_r $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simplified:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_r = P_t G_t G_r \left({\lambda \over 4 \pi r}\right)^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or rewritten to use decibels:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{r(\mathrm{dB})} =&#xA; P_{t(\mathrm{dB})}&#xA; + G_{t(\mathrm{dB})}&#xA; + G_{r(\mathrm{dB})}&#xA; + 20 \log_{10} \left({\lambda \over 4 \pi r}\right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since wavelength is a function of frequency and the speed of light ($\lambda = c/f$), the equation can also be written:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{r(\mathrm{dB})} =&#xA; P_{t(\mathrm{dB})}&#xA; + G_{t(\mathrm{dB})}&#xA; + G_{r(\mathrm{dB})}&#xA; + 20 \log_{10} \left({c \over 4 \pi r f}\right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, we can factor out the constant ${c \over 4 \pi}$ and write that as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{r(\mathrm{dB})} =&#xA; P_{t(\mathrm{dB})}&#xA; + G_{t(\mathrm{dB})}&#xA; + G_{r(\mathrm{dB})}&#xA; + 147.6&#xA; - 20 \log_{10} (rf) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$r$ is the distance between antennas in meters, and&lt;/li&gt;&#xA;&lt;li&gt;$f$ is the frequency in Hz.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This formula is essential to the calculation of &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budgets&lt;/a&gt;, and gives the best case path loss. It's then easier to consider other sources of loss as separate factors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: this means you can build a &lt;a href=&quot;http://en.wikipedia.org/wiki/Dyson_sphere&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dyson sphere&lt;/a&gt; around a star, capturing all of its energy.&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;2: at least, not ones that emit coherent radiation. The sun can be (approximately) isotropic because the light (a kind of electromagnetic radiation) it emits is not coherent.&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;3: 1.62, or 2.15 dBi, for a half-wave dipole.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-04-29T01:32:22.833" CommentCount="0" CommunityOwnedDate="2014-02-27T04:10:48.327" ContentLicense="CC BY-SA 3.0" />
  <row Id="1541" PostTypeId="2" ParentId="1530" CreationDate="2014-02-27T06:33:27.283" Score="2" Body="&lt;p&gt;This is simpler than the Friis equation makes it out to be.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The longer wavelength isotropic antenna is bigger, and aperture measures the effective electrical size of the antenna as a radiator. It is no surprise that the electrical size of an antenna that is physically larger is also larger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Half-wave Dipoles have a constant gain, but are similarly larger at longer wavelengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Friis equation is a particular algebraic expression of a conservation-of-energy equation, in a theory where all radiated energy is either received or radiated into space in a sphere. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Gains in the Friis equation are generally lambda-dependent.  Once again, it is common radio wisdom that smaller wavelengths, higher frequencies, require smaller elements for yagis or smaller reflectors for dishes to have the same gain.  Thus if the antenna size stayed constant then as frequency increases, and lambda decreases, the gain should rise.  This suggests gain depends on some inverse or perhaps inverse power of lambda.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, a the gain of a parabolic reflector dish of, say 3m diameter, will depend on the frequency and thus lambda.  &lt;a href=&quot;http://en.wikipedia.org/wiki/Parabolic_antenna&quot; rel=&quot;nofollow&quot;&gt;Wikipedia:Parabolic Reflector&lt;/a&gt; notes that the gain scales as 1/lambda^2.  The Friis equation needs the gain of both antennas (receiving and transmitting), and so with dishes the transmit power received would scale as &#xA;lambda^-2 * lambda^-2 * lambda^2  = lambda^-2 which provides a very different impression of what frequencies are best.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is important to realize the Friis equation is a free space theory where the signal can spread out in a sphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It neglects the Earth, and with it all absorption or reflection by terrain, multipath reflections which can interfere constructively or destructively resulting in hot spots and dead zones, changes of media (e.g. trees, clouds), and various engineering requirements which may play a role at very low or high frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, in the parabolic reflector example, we could move from microwaves to lasers to reduce lambda and increase power received according to the Friis equation. But this may not work out.  Why? Aiming is much more critical with the laser, which relateds to the change in gain with a misaligned receive or transmit antenna. The parabolic antenna must now be a parabolic mirror of good quality instead of, say, stressed wire screening.  And, a solid object such as a tree or bird is known to block a laser beam while a microwave might still be received.  &lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2014-02-27T07:33:10.363" LastActivityDate="2014-02-27T07:33:10.363" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1542" PostTypeId="1" CreationDate="2014-03-01T06:57:26.103" Score="6" ViewCount="747" Body="&lt;p&gt;When using coherent CW, how is the receiver frequency and/or Morse Code dot clock synchronized to the transmission precisely enough to allow for synchronous decoding?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-09-18T01:51:30.503" Title="Coherent CW synchronization?" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1543" PostTypeId="2" ParentId="1507" CreationDate="2014-03-01T10:19:38.793" Score="1" Body="&lt;p&gt;As a licensee, you are being trusted to use your best judgement of the situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you &lt;em&gt;need&lt;/em&gt; to lock up your station?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look at the FCC enforcement actions in &lt;a href=&quot;http://transition.fcc.gov/eb/AmateurActions/&quot; rel=&quot;nofollow&quot;&gt;http://transition.fcc.gov/eb/AmateurActions/&lt;/a&gt; you will notice that most of the actions are warnings.  I would think that if you had children, and your child was found talking on the radio without your supervision or a license, you would (a) realize that you had better educate your child, and (b) could go to the expense of locking things up as a good faith response to a warning from other hams or the FCC.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;People who are fined either had multiple warnings or are usually alleged to have done something egregiously wrong, such as interfere with a genuine distress call or transmit profanity at children or organized nets.  When fines are given out, they tend to be many thousands of dollars.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please note that this is not intended as legal advice.  I am not a lawyer and I do not know your particular situation. This is a general observation from the tone of the FCC enforcement website and my 25 years as a ham. The tone of enforcement could always change in the future. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How to lock up?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A used, enclosed 19-inch equipment rack can often be found fairly cheap.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A friend of mine has an enclosed rack cabinet about 7 feet tall in his garage. The cabinet encloses two HF radios, a VHF all mode, a UHF all mode, amps for VHF and UHF, a tuner, a rotor control, a 50Ah 12V battery, various switchwork, and a solar charge controller. It also has a keyboard and flat monitor in a slide out drawer.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And.. I believe it has a lock on the front.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most people, though, don't go to this extreme.  One advantage is that it is not too obvious what might be in the cabinet when it is locked, although I suppose a locked cabinet with wires going inside might still look interesting to a thief.&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2014-03-02T00:31:24.673" LastActivityDate="2014-03-02T00:31:24.673" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1544" PostTypeId="2" ParentId="1542" CreationDate="2014-03-01T12:52:29.810" Score="8" Body="&lt;p&gt;According to &lt;a href=&quot;https://web.archive.org/web/20140210065600/http://www.njqrp.org/ccw/n2apb-wb9flw/n2apb-wb9flw.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Coherent CW ...&#xA;&quot;The More You Know About a Signal,&#xA;the Easier it is to Copy&quot;&lt;/a&gt; by&#xA;Peter Eaton, WB9FLW and&#xA;George Heron, N2APB:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Coherent software has several other convenient features in addition to auto-tune. It has a fine tuning aid that measures the incoming 800 Hz audio signal (with 0.1 Hz resolution!), and a frame-phasing tracking loop that determines if the SNR would be better had the window ended 1 cycle (1.25 ms) earlier or 1 cycle later. The program adjusts the 100 ms processing frame slightly forward or backward depending on the trend of the signal over time. Thus, once synchronization has been established, Coherent is able to adjust the phasing as necessary to maximize the SNR, further reducing the need for rig stability and frequency standards. All that's necessary is a reasonably stable transceiver (or a DDS VFO, as in our case), the Sigma-Delta interface board and a computer.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is a form of &lt;a href=&quot;http://en.wikipedia.org/wiki/Clock_recovery&quot; rel=&quot;nofollow noreferrer&quot;&gt;clock recovery&lt;/a&gt;, as used in many digital modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The clock is set to 100ms intervals, by definition of the protocol. To begin, the receiver arbitrarily starts its clock, so the receiver and transmitter are clocked at the same speed but some arbitrary phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For each 100ms interval, the receiver actually calculates &lt;em&gt;three&lt;/em&gt; correlations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;one aligned with the current clock&lt;/li&gt;&#xA;&lt;li&gt;one slightly ahead of the clock&lt;/li&gt;&#xA;&lt;li&gt;one slightly behind the clock&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The output of each of these correlations is a number from 0 (no carrier detected at all, space) to 1 (only carrier detected, mark). Of course in the presence of noise, the actual numbers are somewhere between those extremes, and the difference between the mark and space values gives you some idea of the &lt;a href=&quot;http://en.wikipedia.org/wiki/Signal-to-noise_ratio&quot; rel=&quot;nofollow noreferrer&quot;&gt;SNR&lt;/a&gt;. For example, if the SNR is very poor, a space might be 0.02 and a mark might be 0.06. If the SNR is very good, a space might be 0.02 and a mark 0.99.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking back at the past few periods, we can then ask, would the SNR be better if the clock phasing were shifted forwards or backwards? If so, then we shift the timing a little bit. Eventually synchronization is reached.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frequency synchronization is more obvious. They don't really say how the incoming frequency is measured, but a likely technique is &lt;a href=&quot;http://en.wikipedia.org/wiki/Autocorrelation&quot; rel=&quot;nofollow noreferrer&quot;&gt;autocorrelation&lt;/a&gt; of the signal. This gives you a direct measurement of the predominant frequency of the signal, and the difference of this to the correlation filter (800 Hz in the quoted design) gives you a frequency error signal. This error signal is usually low-pass filtered to prevent excessive wandering due to noise, and then by adjusting the receiver's tuning we can drive the frequency error to zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not described in the excerpt above, but another trick is used to eliminate the requirement for exact phase coherence between receiver and transmitter. The receiver actually correlates the received signal with two filters, which differ by a 90 degree phase shift. This guarantees that whatever the relative phase of the stations, the signal will be received. This is not unlike using a circularly polarized antenna to receive a linearly polarized transmission: it doesn't matter if the transmission is polarized vertically, horizontally, or something in-between: it will be received equally well by the circularly polarized antenna. The cost is a 3dB loss, but the gain is the lack of requirement for phase coherence, which is difficult to implement without impracticably stable components, or a second channel for synchronization.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-09-18T01:51:30.503" LastActivityDate="2018-09-18T01:51:30.503" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="1545" PostTypeId="1" CreationDate="2014-03-02T01:47:48.023" Score="2" ViewCount="315" Body="&lt;p&gt;I am building a simple antenna from this article &lt;a href=&quot;http://www.repeater-builder.com/antenna/pdf/2m-pvc-beam-antenna-qst-april-1993.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;7db for 7 bucks.&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I am confused on the measurements for the antenna:&#xA;&lt;img src=&quot;https://i.stack.imgur.com/psQoW.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;It looks like there are two pieces of 18 inch PVC pipes connected to a T fitting.&lt;/p&gt;&#xA;&lt;p&gt;Wouldn't the spacing in the T fitting vary based on the size of the PVC pipe? I have 3/4 inch pipe. Would it work for this?&lt;/p&gt;&#xA;&lt;p&gt;Second, where exactly do I place the director and the reflector beams? Is it just as far out as the drill can possibly go without cutting into the edge of the pipe?&lt;/p&gt;&#xA;&lt;p&gt;I guess it is fine them not telling me for the reflector beam, but for the director, there is no measurement from the driven element. &lt;em&gt;How far should I place the director from the driven element?&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-02-16T18:14:28.707" Title="Measurement Confusion" Tags="&lt;yagi&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1546" PostTypeId="2" ParentId="1545" CreationDate="2014-03-02T02:28:26.147" Score="1" Body="&lt;p&gt;The first thing to remember is that if you are off by 1/4&quot; or 1/2&quot; from the perfect measurement, it's not the difference between working and not working. It might be slightly less efficient...or not.  There are so many variables in antenna performance that even building &lt;em&gt;exactly&lt;/em&gt; to spec may not mean you get the same results.  You may get better, or worse. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, the article specifies drilling the holes 1/4&quot; or 1/2&quot; from the end of the PVC.  PVC is a little brittle, so I would lean towards the 1/2&quot; mark.  Next you don't need the measurement of the director to the driven element.  Place the director at the end of the boom (minus 1/2&quot;).  The driven element is measured off the reflector in this design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, the article was also talking about 3/4&quot; pipe, so everything should work out fine.  Last thing to know is that PVC will break down over time in UV light, not a big deal, it would take a few years, but it will get chalky and then (more) brittle.  Options are to paint it or to not worry about it.  If you are still in the hobby by that time, you will likely have replaced the antenna anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, you can use a boom that's longer than specified to give you a little more meat to drill on.  If it were 2&quot; longer on both ends, it would not affect the performance of the antenna at all.  Though you would have to measure the location of the director as if the boom half were still 18&quot; as shown.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-03-02T02:28:26.147" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1547" PostTypeId="2" ParentId="1531" CreationDate="2014-03-02T09:26:19.593" Score="0" Body="&lt;p&gt;I suggest you take a look at &lt;a href=&quot;http://gnuradio.org/redmine/projects/gnuradio/wiki&quot; rel=&quot;nofollow&quot;&gt;GNU Radio&lt;/a&gt;, it has a large following and is open source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They already have an extensive list of hardware support.&#xA;&lt;a href=&quot;http://gnuradio.org/redmine/projects/gnuradio/wiki/Hardware&quot; rel=&quot;nofollow&quot;&gt;http://gnuradio.org/redmine/projects/gnuradio/wiki/Hardware&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="659" LastActivityDate="2014-03-02T09:26:19.593" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1548" PostTypeId="2" ParentId="1449" CreationDate="2014-03-02T09:30:55.190" Score="2" Body="&lt;p&gt;Well, for one thing it keeps our spectrum in use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Otherwise, some corp or gov entity may swoop down and try and take a band away from us, like 1.2Ghz and repurpose it for wireless broadband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That I believe is the single most important side benefit of Amateur Radio Contesting.&lt;/p&gt;&#xA;" OwnerUserId="659" LastEditorUserId="659" LastEditDate="2014-03-02T17:03:37.897" LastActivityDate="2014-03-02T17:03:37.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1549" PostTypeId="2" ParentId="1480" CreationDate="2014-03-02T23:28:46.350" Score="3" Body="&lt;p&gt;Depending on what you're testing, The safest bet is through a SWR meter into a 50 OHM dummy load, or an attenuator into a spectrum analyzer.&lt;/p&gt;&#xA;" OwnerUserId="659" LastActivityDate="2014-03-02T23:28:46.350" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1550" PostTypeId="2" ParentId="1420" CreationDate="2014-03-02T23:34:54.283" Score="2" Body="&lt;p&gt;I found both of these papers that may help you out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://web.archive.org/web/20140304134741/http://library.utem.edu.my/index2.php?option=com_docman&amp;amp;task=doc_view&amp;amp;gid=4754&amp;amp;Itemid=208&quot; rel=&quot;nofollow&quot;&gt;Bowtie Microstrip Antenna Design&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://web.archive.org/web/20140304134859/http://www.intechopen.com/download/get/type/pdfs/id/14714&quot; rel=&quot;nofollow&quot;&gt;Methods to Design Microstrip Antennas for &#xA;Modern Applications&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="659" LastEditorUserId="565" LastEditDate="2014-03-05T21:35:07.957" LastActivityDate="2014-03-05T21:35:07.957" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1551" PostTypeId="1" CreationDate="2014-03-03T01:51:07.783" Score="9" ViewCount="2184" Body="&lt;p&gt;I'm thinking of building some helical antennas for satellite work. I want to know which way to wind them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If satellites are spinning randomly, how can we know if they are left hand or right hand polarized or&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Which way do I wind my antenna&lt;/em&gt; &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2018-04-11T18:34:35.583" LastActivityDate="2018-04-11T18:34:35.583" Title="Are satellites Left or Right hand circularly polarized?" Tags="&lt;antenna&gt;&lt;satellites&gt;&lt;circular-polarization&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1552" PostTypeId="2" ParentId="1425" CreationDate="2014-03-03T01:53:18.333" Score="1" Body="&lt;p&gt;I figured it out:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For the weird beeping, it was just a bad mike, and I had to replace that.&lt;/li&gt;&#xA;&lt;li&gt;For the spurious transmissions, I should've specified I was on a SLA battery, and the battery was running low&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-03-03T01:53:18.333" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1553" PostTypeId="2" ParentId="1551" CreationDate="2014-03-03T13:44:35.173" Score="4" Body="&lt;p&gt;Circular polarisation is not caused by the spin of the satellite. The reason for circular polarisation is to make the orientation of the satellite irrelevant. If you were running a linearly polarised antenna and the orientation of the satellite was 90 degrees off, you could get end up with an effectively infinite loss whereas you can always pick up a circular polarised signal with a circular polarised antenna of the same direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a clockwise polarisation but the satellite is sending an anticlockwise signal (both as viewed from the same end) you will need to change polarisation - which you can do with a crossed yagi setup (you effectively reverse 90 degree phase by feeding to one side or other of one yagi set)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can't do that with a helical antenna - so you would need two if you want to pick up clockwise and anticlockwise signals.&lt;/p&gt;&#xA;" OwnerUserId="50" LastEditorUserId="50" LastEditDate="2014-03-04T15:39:53.737" LastActivityDate="2014-03-04T15:39:53.737" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1555" PostTypeId="2" ParentId="1449" CreationDate="2014-03-03T15:00:16.180" Score="2" Body="&lt;p&gt;I have an indirect answer, one that surprised me this past weekend during the ARRL contest. This particular contest was for DX contacts. North America to DX stations, and vice versa. The end result was 40+ new countries/bands in my log in just two days.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my answer would be; encouraging contacts between stations that otherwise would not make an effort to study propagation, rotate beams, stay up at odd hours. I worked Japan from the East Coast (US) on 10 meters, with just 100 Watts barefoot and a piece of wire hanging off my rooftop - a contact that has been hitherto impossible for me.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2014-03-03T15:00:16.180" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1556" PostTypeId="1" CreationDate="2014-03-03T15:48:43.183" Score="8" ViewCount="223" Body="&lt;p&gt;The &lt;a href=&quot;http://en.wikipedia.org/wiki/International_Cometary_Explorer&quot;&gt;ICE/ISEE-3 spacecraft&lt;/a&gt;, launched in 1979, is due to pass by the earth in August, 2014.  It was commanded to power down completely years ago, but it appears to have failed to do so, and while it could be re-tasked to perform another mission studying the sun, the equipment to command it was retired in 1999, and no one appears to be interested in funding a new mission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is still transmitting, though, and &lt;a href=&quot;http://www.planetary.org/blogs/emily-lakdawalla/2014/02070836-isee-3.html&quot;&gt;one article suggests&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I wonder if ham radio operators will be able to pick up its carrier signal -- it's meaningless, I guess, but it feels like an honorable thing to do, a kind of salute to the venerable ship as it passes by.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What is the frequency, modulation, and polarization of its signal?&lt;/li&gt;&#xA;&lt;li&gt;What will I need to receive it, in terms of how sensitive a receiver or antenna system will be required as it passes?&lt;/li&gt;&#xA;&lt;li&gt;When is the 24 hour window of time when it is nearest the earth going to occur?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-03-04T17:49:35.130" Title="What will I need to receive the ICE/ISEE-3 transmitter?" Tags="&lt;antenna&gt;&lt;satellites&gt;&lt;frequency&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1557" PostTypeId="2" ParentId="1556" CreationDate="2014-03-03T22:37:53.263" Score="2" Body="&lt;p&gt;From a &lt;a href=&quot;http://mdkenny.customer.netspace.net.au/ISEE-3.pdf&quot; rel=&quot;nofollow&quot;&gt;specifications document&lt;/a&gt;, here's the transponder info:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Transponder A: 2090.66 MHz RHCP uplink, command or ranging&#xA;2270.40 MHz RHCP downlink, telemetry or ranging &#xA;&#xA;Transponder B: 2041.95 MHz LHCP uplink, command&#xA;2217.50 MHz LHCP downlink, telemetry &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;In addition a transmitter/receiver on those frequencies (Tricky), you'd need a reasonably large dish for transmitting/receiving, and the appropriate way to modulate/demodulate the signal. The polarization is circular, left hand. This is in the high bands, pretty close to the Amateur 13cm band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The day of closest approach is August 10, not sure exactly when the &quot;24 hour window&quot; will start. Obviously the higher gain, the further away communication will happen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one was going to do something useful, however, one would need to act sooner than later. And that would require an enormous dish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wouldn't be surprised if a few hams hear the spacecraft pass by Earth, but for right now, hearing it is limited to world class EME stations. I suspect quite a few people will hear it as time goes on, and some might even have the ability (But not authority) to transmit before too long. Hopefully something can happen!&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-03-04T17:30:01.307" LastActivityDate="2014-03-04T17:30:01.307" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1558" PostTypeId="1" CreationDate="2014-03-03T23:14:18.393" Score="3" ViewCount="960" Body="&lt;p&gt;So I just learned that a satellite does not send out a circularly polarized signal, it just switches orientation slowly when it topples through space.  I thought that because they were spinning, the signal would be circularly polarized. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What exactly is circular polarization? &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2018-04-11T18:34:20.273" LastActivityDate="2018-04-11T18:34:20.273" Title="What is Circular Polarization?" Tags="&lt;satellites&gt;&lt;circular-polarization&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1559" PostTypeId="2" ParentId="1558" CreationDate="2014-03-04T00:12:17.377" Score="2" Body="&lt;p&gt;The spinning happens the same as the frequency. So a 144 MHz signal is spinning 144 million times per second.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-03-04T00:12:17.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1560" PostTypeId="2" ParentId="1558" CreationDate="2014-03-04T12:26:54.227" Score="9" Body="&lt;p&gt;First, consider that everywhere, there is an electric field. For every point in space, this field defines a vector that describes the direction and magnitude of force that would be experienced by a mobile test charge at that point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, the mobile charges are electrons in our antenna. Radio works by creating waves in the electric field.&lt;sup&gt;1&lt;/sup&gt; These waves propagate through free space until they reach the receiving antenna and cause the electric charges in it to move. Our receivers then detect, amplify, and demodulate this current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Linear polarization exists when at some point, the direction of the electric field alternates between one direction, then the opposite direction. The frequency of this oscillation is the frequency of our radio signal. For a vertically polarized signal, the electric force alternates between up and down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can have force in any direction, but it's convenient to break it down into two components: horizontal and vertical. Just like any point on a plane can be described with an X and Y coordinate, any direction can be described by some amount of horizontal and vertical direction, added together. For example, a 45 degree angle is equal parts horizontal and vertical. This is a form of &lt;a href=&quot;http://mathworld.wolfram.com/VectorAddition.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;vector addition&lt;/a&gt;, where the vectors are orthogonal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Circular polarization is what you get when you have both a horizontal and vertical component, but oscillating in quadrature. That is, which a 90 degree phase shift between them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/x9uhq.png&quot; alt=&quot;circular polarization&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how when the blue line is at a maximum, the green line is at zero. Put mathematically, one of these lines is tracing $\sin(t)$, and the other is tracing $\cos(t)$. &lt;a href=&quot;https://www.wolframalpha.com/input/?i=parametric%20graph&amp;amp;a=*C.parametric%20graph-_*Calculator.dflt-&amp;amp;f2=cos%28u%29&amp;amp;f=ParametricPlotCalculator.xfunction%5Cu005fcos%28u%29&amp;amp;f3=sin%28u%29&amp;amp;f=ParametricPlotCalculator.yfunction%5Cu005fsin%28u%29&amp;amp;f4=2*pi&amp;amp;f=ParametricPlotCalculator.upperrange1_2*pi&amp;amp;f5=0&amp;amp;f=ParametricPlotCalculator.lowerrange1%5Cu005f0&amp;amp;f6=u&amp;amp;f=ParametricPlotCalculator.variable1%5Cu005fu&amp;amp;a=*FVarOpt.1-_**-.***ParametricPlotCalculator.variable2-.*ParametricPlotCalculator.lowerrange2-.*ParametricPlotCalculator.upperrange2--.**ParametricPlotCalculator.zfunction---.*--&quot; rel=&quot;nofollow noreferrer&quot;&gt;If you plot these functions&lt;/a&gt;, you get a circle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were a movable charge (say, a mobile electron in an antenna) in this field, you would experience a force pushing you in a circle: first up, then to the right, then down, then to the left, then up again. The magnitude of the force remains the same throughout; only the direction changes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why if you receive a circularly polarized signal with any linearly polarized antenna you get a 3dB loss. A 3dB loss is a halving of power. If you had a vertically polarized antenna, then you are receiving only the blue portion, and not the green portion at all. That is, the green (horizontal) component just pushes the charge in the dipole to the side, and that doesn't result in any current at the feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The win is that the orientation of your antenna doesn't matter. If it's horizontal instead of vertical, it's still just a 3dB loss. If it's at 45 degrees, still just 3dB. This is really great if the satellite is spinning, otherwise you'd get fading as it spins an your polarizations align and unalign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To avoid the 3dB loss, you can use circular polarization on each end. The cost is a more complicated antenna. In this case it's important that each end uses the same sense, right-hand or left-hand. If they are different, the result is the same as trying to link between a horizontal and vertical polarization: extreme attenuation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: also the magnetic field, &lt;a href=&quot;https://ham.stackexchange.com/q/1608/218&quot;&gt;which is always orthogonal to the electric field and the direction of propagation&lt;/a&gt;.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-03-21T12:56:42.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1561" PostTypeId="2" ParentId="1551" CreationDate="2014-03-04T13:26:23.567" Score="4" Body="&lt;p&gt;It is not the spinning of the satellite that polarizes the signal. Rather, it is that a circularly polarized signal can be rotated without affecting the signal which makes circular polarization desirable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not the case with linearly polarized signals: if the two are cross-polarized (one is vertical, the other is horizontal, for example), then the link will be extremely poor. As the satellite spins through aligned polarization and cross-polarization, you get deep spin fading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no standard for which way satellites are polarized. Some are right-handed, some are left-handed. Sometimes the difference comes down to which was easier to build. Some satellites aren't circularly polarized at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you build a right-hand antenna, this will work with circularly polarized satellites of the same sense, and also with linearly polarized signals with a 3dB loss. It won't work very well at all with an opposite-sense circular polarization on the other end. If you wanted to work left-hand circular polarization, you either need another antenna, or you need a different kind of antenna where the polarization can be switched. Helical antennas can't do this, but crossed yagis can.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-03-04T13:26:23.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1562" PostTypeId="2" ParentId="1556" CreationDate="2014-03-04T17:49:35.130" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;When is the 24 hour window of time when it is nearest the earth going to occur?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The last fix NASA had on it was in 2008, 6 years ago.  The position and velocity at that time have been entered into the JPL Horizons software so we can predict its future location with as much accuracy as can be provided by very old data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On August 9th, 2014 at 19:12UTC, the spacecraft is predicted to be as close to Detroit Michigan as it will ever be this year, at 0.002729086 AU, which is just over 408,000 kilometers away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However this is expected to change somewhat as the spacecraft nears earth and better information is collected about its location, direction, and speed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To find this same information for your specific location, go to the &lt;a href=&quot;http://ssd.jpl.nasa.gov/horizons.cgi#top&quot; rel=&quot;nofollow&quot;&gt;HORIZONS Web-Interface&lt;/a&gt;, and set up the parameters as follows:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Current Settings&#xA;   Ephemeris Type [change] :    OBSERVER&#xA;      Target Body [change] :    ISEE-3_ICE [-111]&#xA;Observer Location [change] :    Detroit, MI ( 83°02'57.1''W, 42°19'48.0''N )&#xA;        Time Span [change] :    Start=2014-08-09, Stop=2014-08-10, Step=1 m&#xA;   Table Settings [change] :    defaults&#xA;   Display/Output [change] :    default (formatted HTML)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;When searching for the &lt;code&gt;Target Body&lt;/code&gt; you can simply enter &lt;code&gt;-111&lt;/code&gt; and it will find the ISEE-3_ICE spacecraft. Change &lt;code&gt;Observer Location&lt;/code&gt; to your location. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Click &lt;code&gt;Generate Ephemeris&lt;/code&gt; to request the information, and it will provide a lot of information, one part of which is a table of data similar to the following:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;**************************************************************************************************************&#xA; Date__(UT)__HR:MN     R.A._(ICRF/J2000.0)_DEC  APmag  S-brt            delta      deldot    S-O-T /r    S-T-O&#xA;**************************************************************************************************************&#xA; 2014-Aug-09 19:08 *   15 47 41.30 -33 18 20.8   n.a.   n.a. 0.00272908956976  -0.0036236 104.7734 /T  75.0775&#xA; 2014-Aug-09 19:09 *   15 47 46.27 -33 18 35.3   n.a.   n.a. 0.00272908828363  -0.0027886 104.7905 /T  75.0604&#xA; 2014-Aug-09 19:10 *   15 47 51.23 -33 18 49.8   n.a.   n.a. 0.00272908733324  -0.0019495 104.8075 /T  75.0433&#xA; 2014-Aug-09 19:11 *   15 47 56.20 -33 19 04.3   n.a.   n.a. 0.00272908672019  -0.0011066 104.8246 /T  75.0263&#xA; 2014-Aug-09 19:12 *   15 48 01.15 -33 19 18.8   n.a.   n.a. 0.00272908644605  -0.0002596 104.8417 /T  75.0092&#xA; 2014-Aug-09 19:13 *   15 48 06.11 -33 19 33.3   n.a.   n.a. 0.00272908651242   0.0005912 104.8587 /T  74.9922&#xA; 2014-Aug-09 19:14 *   15 48 11.07 -33 19 47.7   n.a.   n.a. 0.00272908692087   0.0014460 104.8757 /T  74.9752&#xA; 2014-Aug-09 19:15 *   15 48 16.02 -33 20 02.1   n.a.   n.a. 0.00272908767299   0.0023048 104.8927 /T  74.9582&#xA; 2014-Aug-09 19:16 *   15 48 20.96 -33 20 16.5   n.a.   n.a. 0.00272908877035   0.0031675 104.9097 /T  74.9412&#xA; 2014-Aug-09 19:17 *   15 48 25.91 -33 20 30.9   n.a.   n.a. 0.00272909021455   0.0040341 104.9267 /T  74.9242&#xA; 2014-Aug-09 19:18 *   15 48 30.85 -33 20 45.3   n.a.   n.a. 0.00272909200714   0.0049046 104.9437 /T  74.9073&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The column that provides the distance to the target is &lt;code&gt;delta&lt;/code&gt;, in &lt;a href=&quot;http://en.wikipedia.org/wiki/Astronomical_unit&quot; rel=&quot;nofollow&quot;&gt;Astronomical Units&lt;/a&gt;, which is about the distance between the Earth and Sun.  An easy method to find the closest location is to copy this table into a spreadsheet program and find the minimum value of that column.  The &lt;code&gt;deldot&lt;/code&gt; is the speed of the spacecraft relative to your location, if negative it is traveling towards you, positive and it's traveling away from you.  Due to the rotation of the earth, you may find that there is more than one 'pass' that brings you as close as you'll ever be to this spacecraft, so you can't rely on that alone to tell you the single closest moment of approach, but you can look at the transitions from negative to positive to give you the two closest moments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have the closest delta, you can use an online converter to do the math for you: &lt;a href=&quot;https://www.google.com/search?q=0.00272908644605au%20in%20km&quot; rel=&quot;nofollow&quot;&gt;0.00272908644605au in km&lt;/a&gt; is 408,266 kilometers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is an explanation of this table's other values after the table which would help one to know where to point their antenna, consult your local astronomer for help with these.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-03-04T17:49:35.130" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1563" PostTypeId="1" CreationDate="2014-03-04T18:26:02.293" Score="5" ViewCount="1566" Body="&lt;p&gt;On the article &quot;&lt;a href=&quot;http://www.repeater-builder.com/antenna/pdf/2m-pvc-beam-antenna-qst-april-1993.pdf&quot; rel=&quot;nofollow&quot;&gt;7db for 7 bucks&lt;/a&gt;&quot;, which is an article about building a simple three element 2M yagi, they stated that vertically polarizing the antenna is better for FM work, and horizontally polarizing the antenna is better for SSB and CW work.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;You'll notice that my antenna is vertically polarized.  This is best for FM work.  If you want to use this antenna for 2-meter SSB and CW, just assemble the boom so the elements are &lt;em&gt;parallel&lt;/em&gt; to the ground, not perpendicular.  &lt;sub&gt;&lt;sup&gt;(&quot;7dB for 7 Bucks&quot;, Nathan Loucks, QST, April 1993, p54)&lt;/sup&gt;&lt;/sub&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Why is this?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="9" LastEditDate="2014-03-04T19:02:32.627" LastActivityDate="2014-03-04T19:02:32.627" Title="Why is optimal polarization different for fm as to SSB/CW" Tags="&lt;antenna&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1564" PostTypeId="2" ParentId="1563" CreationDate="2014-03-04T18:59:18.177" Score="4" Body="&lt;p&gt;This is really a mixed question. It's not the mode that dictates the polarization.  It's the situation in which that mode is used that dictates it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM is typically only used at VHF and above frequencies where we have enough bandwidth to use it.  VHF/UHF being line of sight is the choice for local work either simplex or via a repeater.  For obvious reasons, mobile antennas are all vertical. Therefore all the repeaters also use vertical antennas.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since it's line of sight and you aren't bouncing off the ionosphere, the polarization of the signal stays vertical.  Hence, working FM, vertical is the way to go. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's not to say you can't work horizontally, but you'll give up a lot of strength.  Of course you could setup a QSO with someone else also going horizontally and it would work just fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By contrast, SSB and CW work is mostly in the HF and low VHF range where vertical antennas are less likely to be a good idea. There are some folks that work VHF SSB, but that's pretty rare, at least in my area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At HF frequencies, you are going to get some hop and the polarization gets randomized by the ionosphere on the hop. So, for HF work, the polarization you start with doesn't matter.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-03-04T18:59:18.177" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1566" PostTypeId="2" ParentId="1449" CreationDate="2014-03-05T14:14:06.037" Score="3" Body="&lt;p&gt;Contesting improves operator skills as detailed in &lt;a href=&quot;https://ham.stackexchange.com/questions/1000/what-skills-will-i-learn-from-contesting&quot;&gt;this link&lt;/a&gt; the OP has in the question. Better trained/skilled operators make ham radio operators more valuable to the community if/when they need our services for communications be that public service or emergency service.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-03-05T14:14:06.037" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1567" PostTypeId="1" AcceptedAnswerId="1568" CreationDate="2014-03-05T22:22:51.460" Score="9" ViewCount="2074" Body="&lt;p&gt;If I only want to receive radio signals and not transmit, are there any differences in the way I design the antenna I need to use, or is it the same either way? I was going to pick up &lt;a href=&quot;http://hakshop.myshopify.com/products/software-defined-radio-holiday-promotion&quot;&gt;a Realtek RTL2832U&lt;/a&gt; and use it as an SDR, but it has an antenna that I would like to improve. (Approx range: 25MHz-1700MHz)&lt;/p&gt;&#xA;" OwnerUserId="815" LastEditorUserId="76" LastEditDate="2015-12-15T21:56:46.397" LastActivityDate="2015-12-15T21:56:46.397" Title="Antenna RX vs. TX" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1568" PostTypeId="2" ParentId="1567" CreationDate="2014-03-06T01:34:20.437" Score="7" Body="&lt;p&gt;Most of the issues are already covered in this previous answer by Phil Frost to “&lt;a href=&quot;https://ham.stackexchange.com/questions/1058/is-there-a-simple-diy-antenna-suitable-for-hf-receive-only/1066#1066&quot;&gt;Is there a simple, DIY, antenna suitable for HF receive only?&lt;/a&gt;”:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Receive antennas are the easiest thing ever. You just need two things:&lt;/p&gt;&#xA;  &#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;something that conducts electricity&lt;/li&gt;&#xA;  &lt;li&gt;another thing that conducts electricity&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;  &#xA;  &lt;p&gt;… Don't worry about tuning, or impedance matching. This also will increase the fraction of the energy received by your antenna coupled to the receiver, but again, once you have enough to overcome the receiver's noise, more is of absolutely no help.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;…&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;If you really must worry about something, worry about getting your antenna away from noise sources. …&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As covered there, most characteristics of the antenna don't matter if you are not transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you are interested in the VHF/UHF (rather than HF) frequencies which those receivers cover, there are a couple more concerns.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Polarization matters, because it is not randomized by the ionosphere. You will want your antenna to be vertically or horizontally polarized depending on what signals you want to receive. In the amateur radio bands, most VHF/UHF signals are vertically polarized.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Location matters. At these frequencies signals are much closer to propagating like light — you want a clear path from the transmitter to your antenna, if possible. For strong transmitters like FM broadcast stations and amateur repeaters, this is less of an issue.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Finally — this is equally applicable to HF but more practical at higher frequencies — if you are seeking to receive weak signals, it is helpful to have a &lt;em&gt;directional&lt;/em&gt; antenna pointed at the source. The most common amateur uses for directional antennas at VHF are satellite communications and direction-finding.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So, get a piece of wire of roughly the right length for the band you think you'll be most interested in (again: doesn't matter much), mount it vertically as high in the air as you feel like arranging, hook it up to the center contact of your receiver's antenna port, and there you go. Or if you want to buy something premade, buy a “scanner” antenna, because those are intended for receive-only use and wide bandwidth.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-03-06T01:34:20.437" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1572" PostTypeId="1" AcceptedAnswerId="1573" CreationDate="2014-03-07T15:59:28.420" Score="4" ViewCount="411" Body="&lt;p&gt;I know single sideband is much better than FM for weak signal receiving. I know that SSB is just like AM, but with the unneeded parts removed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For weak signal propagation, like EME and aurora, would reception on AM or SSB be better?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-03-07T17:32:40.933" Title="AM vs SSB weak signal" Tags="&lt;propagation&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1573" PostTypeId="2" ParentId="1572" CreationDate="2014-03-07T17:32:40.933" Score="7" Body="&lt;p&gt;I don't think anyone would be transmitting AM for weak signal work unless they were just fooling around.  You'd get the same effect by cutting your power by 3/4s.  In AM the carrier consumes 1/2 the power with the rest split between the side bands.  So, SSB is not only more efficient use of spectrum, it's more effective use of your power.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-03-07T17:32:40.933" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1575" PostTypeId="5" CreationDate="2014-03-08T01:20:20.727" Score="0" Body="" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-03-08T01:20:20.727" LastActivityDate="2014-03-08T01:20:20.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1576" PostTypeId="4" CreationDate="2014-03-08T01:20:20.727" Score="0" Body="Impedance is the measure of the opposition that a circuit presents to an alternating current when a voltage is applied.  This is a force of much interest to the radio amateur especially surrounding the connection to antennas." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-03-08T01:20:20.727" LastActivityDate="2014-03-08T01:20:20.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1577" PostTypeId="5" CreationDate="2014-03-08T01:24:07.293" Score="0" Body="&lt;p&gt;The Yagi-Uda antenna was invented in 1926 by Shintaro Uda of Tohoku Imperial University, Sendai, Japan, with the collaboration of Hidetsugu Yagi, also of Tohoku Imperial University. Hidetsugu Yagi attempted wireless energy transfer in February 1926 with this antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yagi published the first English-language reference on the antenna in a 1928 survey article on short wave research in Japan and it came to be associated with his name. However, Yagi always acknowledged Uda's principal contribution to the design, and the proper name for the antenna is, as above, the Yagi-Uda antenna (or array).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Yagi was first widely used during World War II for airborne radar sets, because of its simplicity and directionality. Despite its being invented in Japan, many Japanese radar engineers were unaware of the design until very late in the war, partly due to rivalry between the Army and Navy. &lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-03-08T01:24:07.293" LastActivityDate="2014-03-08T01:24:07.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1578" PostTypeId="4" CreationDate="2014-03-08T01:24:07.293" Score="0" Body="The common name for a Yagi-Uda array antenna, a directional antenna consisting of a dipole (the driven element), a reflector and zero or more directors.  The more directors, the more gain and the narrower the beam." OwnerUserId="164" LastEditorUserId="164" LastEditDate="2014-03-08T01:24:07.293" LastActivityDate="2014-03-08T01:24:07.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1579" PostTypeId="1" CreationDate="2014-03-09T05:33:22.633" Score="6" ViewCount="526" Body="&lt;p&gt;I just got an old brass key at a hamfest, and it appears to be in pretty good mechanical condition, aside from some dirt and dust. Taking it apart, the key (apologies for not knowing the exact terminology) is held in place by two cups with four ball bearings in each cup (see picture below). The grease in the cups has long since turned into some sort of solid and I would like to replace it, however I haven't been able to figure out what I need to use. What kind of grease do I need to use for a Morse key?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/rQNHf.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="18" LastEditDate="2014-03-09T15:15:30.033" LastActivityDate="2017-03-18T14:12:10.343" Title="Morse Code Key Grease" Tags="&lt;cw&gt;&lt;repair&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1580" PostTypeId="2" ParentId="1579" CreationDate="2014-03-09T07:52:02.357" Score="4" Body="&lt;p&gt;I would suggest that these were probably designed to run dry or very lightly oiled (ie: no grease) and that some previous owner took it upon them self to &quot;fix it&quot; using the wrong grease. There will most certainly not be such a thing as a grease specific to Morse keys. (So a quick internet search for &quot;precision bearing lubricant&quot; will give you more info than this site).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;I would first clean them thoroughly with a solvent to remove all old contaminants (even WD40 if you have nothing else). Then use a very light oil primarily for rust protection (assuming the bearings themselves are not brass) and should not use &quot;grease&quot;.&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You really don't want any noticeable lubricant build up. You may even decide to oil it well but then dry of the components with a shop cloth (which doesn't leave any fibers behind, unlike a paper towel). This would leave only a microscopic film of oil filling small surface irregularities within the cups/bearings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Grease isn't really necessary when these bearings aren't actually seeing any serious mechanical load (rotation/torque), there is no need to facilitate heat transfer, etc. Grease is intended for application with serious work being done such as machinery/automobiles, etc and facilitates repeated rotation and torque loads, heat transfer, noise control, and rust prevention. A Morse key in your ham shack should not require any of this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you are an engineer, I would expect some precision in your wording:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The grease in the cups has long since turned into some sort of abrasive&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Grease will not &quot;turn into&quot; an abrasive (as in it won't naturally degrade into an abrasive on its own). It may collect abrasives (ie: dirt/sand/etc), but this does require significant exposure to undesirable contaminants. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Old grease/oil will easily clean out with a solvent, however &quot;abrasives&quot; may be more stubborn. You may need to try using a syringe with a needle to create a little precision pressure washing with your solvent to displace contaminants caked in the corners. You may also need a precision scraper if you have dried/caked contaminants in the bearing cups.&lt;/p&gt;&#xA;" OwnerUserId="608" LastActivityDate="2014-03-09T07:52:02.357" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1581" PostTypeId="1" AcceptedAnswerId="1582" CreationDate="2014-03-09T14:02:37.743" Score="3" ViewCount="104" Body="&lt;p&gt;I am wanting to setup a simplex path that is 7KM from base to base in relatively flat ground. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I estimate the path loss, and what do the numbers mean when I find them?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am wanting to do it at the 2 meter band, and there are houses and buildings in between &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My latitude is 39.76256409 , longitude is -104.86949757, and my friends latitude is 39.73935726 and longitude is -104.95158389&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We will probably use cheap easy-to-build 7db yagis on the roof (3 stories or so) if that will work &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2014-03-09T14:47:11.460" LastActivityDate="2014-03-10T11:53:48.953" Title="Estimate Path Loss" Tags="&lt;simplex&gt;&lt;path-loss&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1582" PostTypeId="2" ParentId="1581" CreationDate="2014-03-09T15:52:11.720" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How can I estimate the path loss&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The answer seems to be to pick one from a catalog of available path-loss models and apply the formula.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here, I'd try using the &lt;a href=&quot;http://en.wikipedia.org/wiki/Hata_Model_for_Urban_Areas&quot; rel=&quot;nofollow&quot;&gt;Hata model for urban areas&lt;/a&gt;. The model was originally made for portable cellular systems, so it uses a bit different terminology.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula is not so complicated:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$L_{50}&#xA;=69.55&#xA;+26.16 \cdot \log_{10}f&#xA;-13.82 \cdot \log_{10}h_b&#xA;-C_h&#xA;+(44.9-6.55 \cdot \log_{10}h_b) \log_{10}d$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and for 2 m band the correction factor is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ C_h = 8.29(\log_{10}(1.54 \:h_m))^2 - 1.1 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and   &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$f$ is the frequency in MHz&lt;/li&gt;&#xA;&lt;li&gt;$h_{b}$ is the height of the base station antenna in meters  &lt;/li&gt;&#xA;&lt;li&gt;$h_{m}$ is the height of the mobile station antenna in meters  &lt;/li&gt;&#xA;&lt;li&gt;$d$ is the distance between the base antenna and mobile receiver&#xA;antenna in kilometers&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;what do the numbers mean when I find them?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Basic formula for power at the receiver is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{rx} = P_{tx} - P_L $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$P_{rx}$ is the power received, and&lt;/li&gt;&#xA;&lt;li&gt;$P_{tx}$ is the transmit power, and&lt;/li&gt;&#xA;&lt;li&gt;$P_{L}$ is all losses (path loss, feedline loss, etc).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The Hata model I've shown here will provide path-loss estimate for 50% of locations on the diameter of the circle with center in the &quot;base station&quot; and radius $d$. I personally, as a rough guide, would just use that number as $P_L$. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now let's try to calculate the number. I'll take the frequency to be 145.5 MHz, which is a bit below the optimal range for the use of this model. The given height is 3 stories plus roof, so I'll round that to 10 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, the correction factor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;C_h &amp;amp;= 8.29\left(\log_{10} \left(1.54 \cdot \frac{10 \ \mathrm{m}}{1 \ \mathrm{m}}\right)\right)^2 - 1.1 \\&#xA;    &amp;amp;= 10.6 \ \mathrm{dB}&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, the main formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ L_{50}&#xA;=69.55&#xA;+26.16 \cdot \log_{10}\left(\frac{145.5 \ \mathrm{MHz}}{1 \ \mathrm{MHz}}\right)&#xA;-13.82 \cdot \log_{10}\left(\frac{10 \ \mathrm{m}}{1 \ \mathrm{m}}\right)&#xA;-10.6&#xA;+\left(44.9-6.55 \cdot \log_{10}\left(\frac{10 \ \mathrm{m}}{1 \ \mathrm{m}}\right)\right) \log_{10}\left(\frac{7 \ \mathrm{km}}{1 \ \mathrm{km}}\right) $$&#xA;$$L_{50}=69.55+56.58-13.82-10.6+38.35 \cdot 0.85 $$&#xA;$$L_{50}=134.3 \ \mathrm{dB}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what does this number give us and how is it helpful?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antennas are given as 7 dB Yagi, so I'll take that to be 7 dBi and I'll assume that you have 10 m of say RG-8 coaxial cable (a calculator gives me 0.5 dB loss for that) and that you're transmitting at 35 W. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transmitter &lt;a href=&quot;http://en.wikipedia.org/wiki/Equivalent_isotropically_radiated_power&quot; rel=&quot;nofollow&quot;&gt;EIRP&lt;/a&gt; would be then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$P_{tx}&#xA;=10 \cdot \log_{10}\left(\frac{35\mathrm W}{1\mathrm W}\right)&#xA;+7-0.5&#xA;=21.94\:\mathrm{dBW}&#xA;=51.94\:\mathrm{dBm}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our estimate of path loss is 134.3 dB and we have a same Yagi at the receiver plus same coax losses. This gives us received power of:&#xA;$$P_{rx}=51.94-134.3+7-0.5=-75.86 \ \mathrm{dBm}$$&#xA;which should be above S9 at the receiver, if my calculations are correct and the S-meter is properly calibrated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope that my description of the process will let you do your own more exact calculations and help you a bit.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="218" LastEditDate="2014-03-10T11:53:48.953" LastActivityDate="2014-03-10T11:53:48.953" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1583" PostTypeId="1" CreationDate="2014-03-09T18:23:33.467" Score="-2" ViewCount="121" Body="&lt;p&gt;I'd like to create a multiband MIMO ad-hoc wireless network.  Can I turn on every GPS, WIFI and Bluetooth radio of a mobile device and synchronize data transfers at extreme speeds between a small, short-range network of devices? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Software would intelligently select bytes for transfer at appropriate times estimating time of arrival on each spectrum with prioritization based on initial synchronization testing. Is this possible? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this possible with a multi-antenna and multiband cellphone like a jailbroken iPhone A1533 or even A1530?&lt;/p&gt;&#xA;" OwnerUserId="826" LastEditorUserId="9" LastEditDate="2014-03-10T20:59:46.660" LastActivityDate="2014-03-10T21:54:30.300" Title="multiband mimo ad-hoc wireless connections from different spectrums" Tags="&lt;diy&gt;&lt;receiver&gt;&lt;transceiver&gt;&lt;modification&gt;&lt;mimo&gt;" AnswerCount="1" CommentCount="7" ClosedDate="2014-03-11T04:26:46.200" ContentLicense="CC BY-SA 3.0" />
  <row Id="1584" PostTypeId="1" AcceptedAnswerId="1585" CreationDate="2014-03-10T01:47:08.200" Score="5" ViewCount="1120" Body="&lt;p&gt;Where do you apply for a license to operate on the LTE radio spectrum for amateur radio in the USA? Can this amateur license be used to operate a cell phone independent of a carrier?&lt;/p&gt;&#xA;" OwnerUserId="826" LastEditorUserId="76" LastEditDate="2014-03-10T03:57:17.253" LastActivityDate="2019-03-05T15:23:58.350" Title="Where to apply for an amateur LTE radio license in the USA?" Tags="&lt;license&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1585" PostTypeId="2" ParentId="1584" CreationDate="2014-03-10T03:15:09.573" Score="13" Body="&lt;p&gt;An amateur radio license only grants privileges on the amateur bands. You would need a different type of license to use other bands. The cell companies pay a premium for the license for their spectrum, and they are almost certainly not interested in relicensing it (if they even could).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moreover, LTE is just a protocol, so there is no dedicated spectrum for LTE in general. Each company that uses LTE uses their own spectrum, which differs per carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So no, an amateur radio license does not let you run your own cell phone independently of carriers. It grants you privileges to use certain modes (voice, Morse code, etc) on well defined spectrum, but does not grant privileges for what you're asking about.&lt;/p&gt;&#xA;" OwnerUserId="253" LastActivityDate="2014-03-10T03:15:09.573" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1586" PostTypeId="1" AcceptedAnswerId="1587" CreationDate="2014-03-10T17:55:45.710" Score="14" ViewCount="7410" Body="&lt;p&gt;I just moved, and I want to change my registered address with my call-sign. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Is there a form or something somewhere that I can fill out?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Do I have to mail it, or can I turn it in to the FCC or something electronically?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Does it cost anything?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What will happen if I fail to get my address updated for a while? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2014-03-12T09:07:51.053" LastActivityDate="2020-01-29T14:13:37.900" Title="How do I change my registered address with the FCC?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1587" PostTypeId="2" ParentId="1586" CreationDate="2014-03-10T18:00:36.633" Score="9" Body="&lt;p&gt;Here is the link that describes how to update your FCC information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?id=amateur&amp;amp;job=cft&amp;amp;page=cft_change_address&quot;&gt;http://wireless.fcc.gov/services/index.htm?id=amateur&amp;amp;job=cft&amp;amp;page=cft_change_address&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do mine on the website and I have not been charged for it.  Within a few weeks a new copy of your license with the new address will arrive in the mail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for not updating in a timely manner, if you do something that requires the FCC to contact you and they are unable to is when it's time to worry.  I believe fines start around $2700 for that but I may be wrong.&lt;/p&gt;&#xA;" OwnerUserId="746" LastActivityDate="2014-03-10T18:00:36.633" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1588" PostTypeId="2" ParentId="1583" CreationDate="2014-03-10T21:14:40.527" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Can I turn on every GPS, WIFI and Bluetooth radio of a mobile device and synchronize data transfers at extreme speeds between a small, short-range network of devices?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This question has several parts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Which radios in a typical mobile device can both transmit and receive?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically they'll have Wifi, Bluetooth, CDMA/GSM, and LTE for recent devices.  The other radios, GPS, for instance, are receive only and can't be used for communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Can these radios be used for device to device communications?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, with limitations.  For instance the cellular radios are often developed to transmit and receive in different portions of allocated spectrum, and tuned for that use to make the hardware development easier - smaller filters are usable where it is known that a receiver won't have to deal with the transmitter's power at the received frequency on the same device, for instance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Can I program the phone, perhaps jailbroken, to use these radios?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some limited ways, yes, but the actual software the radio modules run is not open and easy to reprogram.  The phone's software, hidden as it is, is much more accessible to the average programmer than the radio baseband processor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trying to get the cellular module to talk to another nearby device with a cellular module, if the hardware makes it possible, may still be impractical or impossible depending on your knowledge and skills at programming radio baseband processors. You typically won't even be able to get complete datasheets for these modules without NDA's and promises of large orders from Broadcom and other chipset manufacturers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Can I attain extreme speeds using these radios?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No more than they were designed for.  Mobile devices are extraordinarily &lt;em&gt;efficient&lt;/em&gt; in cost, space, and energy usage.  They are designed &lt;strong&gt;exactly&lt;/strong&gt; for the communications they intend to carry, and nothing else.  You aren't going to magically squeeze more speed out of the wifi than it was designed for with &quot;custom programming&quot; or by somehow coupling them with synchronized multi-band radio communications.  If your wifi chipset was designed for 108Mbps, the bluetooth for 263kbps, and the LTE for 1.1mbps, then you'll get, at most, 109Mbps total aggregate data transmission out of them, adding them together.  &quot;Synchronization&quot; isn't going to allow you to double or triple the bluetooth throughput magically.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Software would intelligently select bytes for transfer at appropriate times estimating time of arrival on each spectrum with prioritization based on initial synchronization testing. Is this possible?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Sure, but for short distances it won't matter.  Trying to synchronize the radios down to the bit timing might not be possible anyway, but even if it isn't, synchronization isn't an issue if you packetize everything.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is this possible with a multi-antenna and multiband cellphone like a jailbroken iPhone A1533 or even A1530?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Anything is possible given enough time and resources.  If you want to accomplish this without a team of engineers and access to all the datasheets and existing code of these devices in the next few years, though, I posit that it is practically impossible to fully accomplish your goal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as &quot;extreme speeds&quot; newer devices are coming out with 802.11ac, which can attain what most people would refer to as &quot;extreme speeds&quot; starting at 433Mbps, and going up to 1.6Gbps per device.  Further, these don't require any jailbreaking, hacking, or amateur radio licensing at all, these devices will talk directly to one another in short range situations using standard TCP/IP and have been FCC device licensed for consumer use.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides, the one fast radio, wifi, on these devices is two orders of magnitude faster than &lt;em&gt;all&lt;/em&gt; the other radios on the device put together.  Hacking the device and somehow adding them together will increase your communications speed by 1-2% over simply using the one wifi radio. I don't think there's any value in pursuing this investigation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure what you're trying to accomplish, but I hope this provides some direction for you in achieving your goal.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2014-03-10T21:54:30.300" LastActivityDate="2014-03-10T21:54:30.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1589" PostTypeId="1" AcceptedAnswerId="1592" CreationDate="2014-03-11T02:45:05.377" Score="16" ViewCount="2941" Body="&lt;p&gt;If I wanted a FCC Amateur license, is this going to cost me anything?  That includes tests, application fees, filing fees, and anything else but hardware.&lt;/p&gt;&#xA;" OwnerUserId="831" LastEditorUserId="8717" LastEditDate="2020-08-30T01:08:06.143" LastActivityDate="2020-08-30T01:08:06.143" Title="Does a FCC amateur license cost money?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1590" PostTypeId="2" ParentId="1589" CreationDate="2014-03-11T03:42:41.340" Score="3" Body="&lt;p&gt;Typically yes. The only fees paid are given to the test administrator. Sometimes you'll find administrators that will volunteer to perform testing without fees, making the whole process free.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no licensing fee, application fee, or regulatory fee. The only fee you might have to pay is a nominal testing fee.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-03-11T03:42:41.340" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1591" PostTypeId="2" ParentId="1589" CreationDate="2014-03-11T08:21:05.900" Score="4" Body="&lt;p&gt;In 2014 it costs $15 (sometimes less) for taking a license test with your ARRL VEC (Volunteer Examiner Committee). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;http://www.arrl.org/what-to-bring-to-an-exam-session&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/what-to-bring-to-an-exam-session&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A license is good for 10 years and renewal directly through the FCC is costless.&lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2014-03-11T08:21:05.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1592" PostTypeId="2" ParentId="1589" CreationDate="2014-03-11T12:14:25.393" Score="12" Body="&lt;p&gt;Fees to obtain a license are set by and payable to the &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=licensing_5&amp;amp;id=amateur&quot; rel=&quot;noreferrer&quot;&gt;volunteer examiner coordinator&lt;/a&gt;. They are typically small to free, and limited by &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/retrieveECFR?gp&amp;amp;n=47y5.0.1.1.6&amp;amp;r=PART#47:5.0.1.1.6.6.159.13&quot; rel=&quot;noreferrer&quot;&gt;§97.527&lt;/a&gt; to reimbursement &quot;for out-of-pocket expenses incurred in preparing, processing, administering, or coordinating an examination for an amateur operator license.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some VECs and their fees:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/arrl-vec-exam-fees&quot; rel=&quot;noreferrer&quot;&gt;ARRL: \$15&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.w5yi.org/exam_locations_ama.php&quot; rel=&quot;noreferrer&quot;&gt;W5YI: \$14&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://glaarg.org/&quot; rel=&quot;noreferrer&quot;&gt;GLAARG: \$5&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There are many other VECs (14 in total, at time of writing), each with their own fee. Some of the smaller VECs are branches of local Ham clubs and don't charge any fee at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most filings you'd have to do over the life of the license (for example, &lt;a href=&quot;https://ham.stackexchange.com/q/1586/218&quot;&gt;address changes&lt;/a&gt;, renewals) are free to file with the FCC. Most can be done online through the FCC's &lt;a href=&quot;http://wireless.fcc.gov/uls/index.htm?job=home&quot; rel=&quot;noreferrer&quot;&gt;Universal Licensing System&lt;/a&gt; (ULS), so you don't even need to pay for a stamp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Prior to September 3, 2015, &lt;a href=&quot;http://www.arrl.org/vanity-call-sign-fees&quot; rel=&quot;noreferrer&quot;&gt;vanity call signs cost \$16.10&lt;/a&gt; per 10 year license period, but now even those are free.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-08-29T01:26:35.360" LastActivityDate="2017-08-29T01:26:35.360" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1593" PostTypeId="1" AcceptedAnswerId="1594" CreationDate="2014-03-11T16:13:06.723" Score="10" ViewCount="4112" Body="&lt;p&gt;Ok, so I'm looking to inject some computer generated CW into a little handheld rig by wiring direct into the mic input line. What sort of voltage is expected on this input, are we talking uV, mV or even Volts?&lt;/p&gt;&#xA;" OwnerDisplayName="user521" LastEditorUserId="76" LastEditDate="2016-10-29T18:51:26.547" LastActivityDate="2016-10-29T18:51:26.547" Title="What is the expected microphone input voltage level of a handheld transceiver?" Tags="&lt;diy&gt;&lt;ht&gt;&lt;microphone&gt;&lt;audio-interface&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1594" PostTypeId="2" ParentId="1593" CreationDate="2014-03-11T17:49:26.683" Score="3" Body="&lt;p&gt;In general you are talking volts.  But it's different for each make of radio and even different models of the same brand.  You might want to start researching &lt;a href=&quot;http://homepage.ntlworld.com/rg4wpw/date.html&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;, the link contains a vast amount of information about microphone pinouts and links to even more information.  I know you mentioned you are hacking what's probably a cheap Chinese HT, but this source will give you some idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, connecting the computer directly to the radio, without some form of isolation is a Bad Idea (tm).  It's doable for short tests, but you'll introduce noise and the possibility of ground loops, etc.  They make cheap audio transformers for just such a purpose, plus they are useful for my next point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PC speakers and mics are generally very low impedance, like 4 or 8 Ohms.  Radio mikes are all over the place on impedance, but frequently 600 Ohms.  So you'll need a transformer to match that anyways, once you determine the impedance of the microphone, you can select the right value.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="29" LastEditDate="2014-03-21T10:02:44.950" LastActivityDate="2014-03-21T10:02:44.950" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1595" PostTypeId="2" ParentId="1593" CreationDate="2014-03-11T19:34:07.533" Score="3" Body="&lt;p&gt;A very simple adaptor can be built as follows:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/AEoIh.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can increase R1 to lower the signal level at the microphone output, or decrease R1 to raise the signal level. While some use potentiometers to make adjustments easier, I've found they are a frustrating source of noise and failure in such circuits, and suggest that, if used, they should be used only to find an appropriate level, then measured and replaced with a fixed resister. C1 can be between 1uF and 4.7uF for audio level signals, but if you're trying to pass very high frequency signals you might stay on the lower end of that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While C1 will help reduce ground loop problems, you may still experience them, particularly if the radio is located far from the computer, or attached to a different power source than the computer. The use of an audio isolation transformer can be helpful with this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance matching isn't necessary since the microphone impedance is significantly larger than the speaker output, and we're not trying to transfer significant power.  The only worry one might consider is whether the speaker output will be damaged with a high impedance.  My experience with most PC sound cards suggests that there's nothing to worry about, but you can place a low value resister in parallel with this circuit on the speaker output if it concerns you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The values as suggested will probably provide more volume than needed.  This only drops about 30dB, whereas I'd expect a 40dB drop is needed for a speaker output to microphone input.  However, this is intentional, and allows further volume control to occur on the computer. Again, increase R1 by doubling it each time if you find this too &quot;loud&quot;. A 1Mohm resistor in R1 would give about a 40dB drop.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-03-11T19:34:07.533" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1596" PostTypeId="1" AcceptedAnswerId="1601" CreationDate="2014-03-11T20:00:24.097" Score="10" ViewCount="5006" Body="&lt;p&gt;I don't recall ever seeing an RC oscillator driven RF transmitter or receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What prevents people from choosing RC oscillators in RF design?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2019-05-07T22:22:14.463" Title="Why prefer LC oscillators rather than RC oscillators in RF design?" Tags="&lt;oscillator&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1597" PostTypeId="1" CreationDate="2014-03-11T20:46:53.660" Score="2" ViewCount="1466" Body="&lt;p&gt;Reading a &lt;a href=&quot;https://groups.google.com/forum/#!topic/rec.radio.amateur.homebrew/P64BnNdc3dc&quot; rel=&quot;nofollow&quot;&gt;discussion on low parts count transmitters&lt;/a&gt;, I came across this description, which lacked schematics and build instructions:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Re: PROJECT 14: THE WORLD'S SMALLEST TRANSMITTER&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Are y'all forgetting the Fireball transmitter?&lt;br&gt;&#xA;  Battery, key, dip relay, xtal oscillator at 29.060, antenna.&lt;br&gt;&#xA;  I think this about as minimalist as anyone could go.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Grover&lt;br&gt;&#xA;  WT6P&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The part that is confusing me is the &quot;dip relay&quot; - a quick search suggests it may be shorthand for a DPDT (double pole, double throw) relay.  But in the RF world there's something called &quot;dip tuning&quot; so I'm confused as to whether the terminology is related.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How would one use the above components to make a CW transmitter?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2019-04-07T19:26:33.760" Title="What is a &quot;dip relay&quot; and how does one use it to build a transmitter?" Tags="&lt;transmitter&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1598" PostTypeId="1" AcceptedAnswerId="1605" CreationDate="2014-03-12T01:27:19.897" Score="3" ViewCount="167" Body="&lt;p&gt;So sometimes I hear people trying to get into a repeater with pure noise, and no audible audio on their transmission. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the repeaters that require a PL tone, how can the PL tones get through all of that noise if I can barely get DTMF through with a bit of white noise?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2014-03-12T09:03:57.210" LastActivityDate="2014-03-13T13:50:14.783" Title="How do PL tones make it through so much noise?" Tags="&lt;fm&gt;&lt;tone-squelch&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1600" PostTypeId="2" ParentId="1597" CreationDate="2014-03-12T05:04:56.473" Score="5" Body="&lt;p&gt;This design could be using the key to control a tiny relay (possibly inside a Dual Inline Package) to connect and disconnect a tiny low power oscillator from the antenna feed.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-03-12T15:50:36.517" LastActivityDate="2014-03-12T15:50:36.517" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1601" PostTypeId="2" ParentId="1596" CreationDate="2014-03-12T11:15:54.053" Score="10" Body="&lt;p&gt;I'm going to discuss &lt;em&gt;filters&lt;/em&gt; and not &lt;em&gt;oscillators&lt;/em&gt;, because the reasons are pretty much the same. An oscillator is just a filter with enough gain to put it on the edge of stability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It certainly is possible to use RC filters in RF design, and sometimes you do see them in non-critical filters, especially those that don't require a steep filter or high power handling, such as AC coupling between stages. Reasons you might not want to use inductors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;They are expensive to manufacture&lt;/li&gt;&#xA;&lt;li&gt;Real inductors have significant non-ideal properties&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;saturation current&lt;/li&gt;&#xA;&lt;li&gt;series resistance&lt;/li&gt;&#xA;&lt;li&gt;inter-winding capacitance (for transformers, a special case of inductor)&lt;/li&gt;&#xA;&lt;li&gt;leakage inductance&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Resistors and capacitors also have non-ideal properties (lead inductance) and aren't free, but the magnitude of these problems is less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reasons you might want to include inductors in your circuits:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A LC circuit has two &lt;a href=&quot;https://ham.stackexchange.com/questions/1504/what-is-meant-by-poles-when-discussing-filters&quot;&gt;poles&lt;/a&gt;, where an RC filter has only one. You can get two poles with two RC circuits, but often that's just more components.&lt;/li&gt;&#xA;&lt;li&gt;An inductor's impedance increases with frequency, while a capacitor's inductance decreases with frequency. For many filter topologies you need both kinds of impedance (for example, a &lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_tuner#Pi_network&quot; rel=&quot;noreferrer&quot;&gt;Pi network&lt;/a&gt;). You can simulate an inductor from a capacitor and an inductor using a circuit called a &lt;a href=&quot;http://en.wikipedia.org/wiki/Gyrator#Application:_a_simulated_inductor&quot; rel=&quot;noreferrer&quot;&gt;gyrator&lt;/a&gt;, but this has additional disadvantages:&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The simulated inductance must have some resistance also, limiting &lt;a href=&quot;http://en.wikipedia.org/wiki/Q_factor&quot; rel=&quot;noreferrer&quot;&gt;Q factor&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;It increases complexity, and requires an op-amp capable of RF operation, which can be hard or expensive at higher frequencies&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Related to the previous point, if you have a capacitive impedance (such as all RC filters have), and you want to transform that to a purely resistive impedance (usually, 50Ω), then you need an inductor. Try playing with a &lt;a href=&quot;http://www.fourier-series.com/rf-concepts/smithchart.html&quot; rel=&quot;noreferrer&quot;&gt;Smith chart&lt;/a&gt; to see why.&lt;/li&gt;&#xA;&lt;li&gt;Resistors convert electrical energy to heat, where (ideal) inductors do not. Obviously you wouldn't want anything turning your transmit energy into heat instead of electromagnetic radiation.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-03-12T11:24:01.170" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1602" PostTypeId="1" CreationDate="2014-03-12T20:01:44.697" Score="3" ViewCount="656" Body="&lt;p&gt;What kind of circuit can be constructed and/or could be used to convert audio containing Morse Code sounds (say from an old practice tape, or from computer generated audio) into key, switch or relay closures that can be connected to a generic simple CW transmitter's key input terminals to transmit that code?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-03-12T22:09:28.697" Title="Audio Morse Code to CW converter?" Tags="&lt;cw&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1603" PostTypeId="2" ParentId="1596" CreationDate="2014-03-12T20:44:00.547" Score="2" Body="&lt;p&gt;The transient response of an RC circuit driven to oscillation by negative feedback generates a much higher proportion of harmonics than a similar LC circuits response.  These harmonics have to be either filtered out with additional circuitry, or the oscillation needs a significant amount of post-processing (such as using it to clock an SDR or a digital synthesizer), in order to produce a clean enough waveform to meet legal requirements for RF transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PLLs in receivers may or may not need as clean a waveform, depending on the receiver design.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-03-12T20:44:00.547" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1604" PostTypeId="2" ParentId="1602" CreationDate="2014-03-12T21:48:42.267" Score="5" Body="&lt;p&gt;First, I'd start by separating the idea into smaller logical parts. I'd have an audio input section, a detection section that would test to see if we actually have a Morse code tone and a section that would trigger the output device. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the input section, I'd place some sort of galvanic isolation that would separate the input jack from the part connected to the transmitter. A small audio transformer could be useful here. Also series capacitors for AC coupling would be a good idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the detection part, I'd use a dual operational amplifier as the main device. I'd use one op-amp as a band-pass filter that would only select frequency range used on the tape and another wired as a comparator. There's a calculator for bandpass filters &lt;a href=&quot;http://www.sengpielaudio.com/calculator-filter.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.  I'm not sure what level would be good for the comparator, so I'd experiment here or maybe even use two fixed resistors and a potentiometer to set sensitivity level. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The output from the comparator would go into the section that would drive the relay. &lt;a href=&quot;http://www.electronics-tutorials.ws/transistor/tran_7.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt;'s a tutorial on how to connect a MOSFET as a switch. The relay would then key the transmitter. For the diodes, I'd use Schottky type &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a rough sketch of the circuit:&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/ekUsh.png&quot; alt=&quot;Morse code audio key&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ucc would whatever voltage is available and can trigger a relay. Op-amp probably wouldn't matter too much, but it would need to work at the voltage used for relay. Some tweaking will probably be needed in case relay noise upsets the op-amps. Also tweaking the gain of the OP1 circuit might be helpful, depending on the input signal level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A program like &lt;a href=&quot;http://audacity.sourceforge.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Audacity&lt;/a&gt; can be used to get the frequency of the Morse code tones for band-pass filter design. One more consideration is the relay used. It should be rated for large number of switches, so perhaps a reed relay could be used here.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2014-03-12T22:09:28.697" LastActivityDate="2014-03-12T22:09:28.697" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1605" PostTypeId="2" ParentId="1598" CreationDate="2014-03-13T13:50:14.783" Score="5" Body="&lt;p&gt;As Michael noted, a repeater's CTCSS system is looking for a very specific frequency with a very low deviation (typically 10% or less) as low as about 40 dB down.  What you are hearing is of course the whole audio range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The decoder in a CTCSS system is based on a very narrow bandpass filter which passes the desired CTCSS tone. There is a balance between a tone that can be quickly recognized and one that can intrude on the audio.  The higher the frequency of the tone, the faster the hardware can recognize it and open the transmit, but the more likely you'll notice it.  On the other hand a very low tone consequently takes longer to be recognized and you risk missing a syllable or two off the beginning of a transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These days most amateur radio repeater controller manufacturers offer an audio delay option - this delays the repeated speech audio for a selectable number of milliseconds before it is retransmitted. During this delay period, the CTCSS decoder has enough time to recognize the right tone. This also keeps two transceivers in close proximity to each other (say two people with HTs) from creating an annoying impromptu oscillator. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;References:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Wikipedia - &lt;a href=&quot;http://en.wikipedia.org/wiki/Continuous_Tone-Coded_Squelch_System&quot; rel=&quot;noreferrer&quot;&gt;Continuous Tone-Coded Squelch System&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;WA6ILQ - &lt;a href=&quot;http://www.repeater-builder.com/tech-info/ctcss/ctcss-overview.html&quot; rel=&quot;noreferrer&quot;&gt;A Historical and Technical Overview of Tone Squelch Systems&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-03-13T13:50:14.783" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1606" PostTypeId="1" AcceptedAnswerId="1758" CreationDate="2014-03-14T15:15:47.070" Score="7" ViewCount="720" Body="&lt;p&gt;Amateur radio enthusiasts have slices of spectrum at every magnitude of spectrum MF and above, but in the US none are below MF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why are there no spectrum allocations below 160M?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-05-03T12:10:11.773" Title="Why are there no amateur allocations in the LF and VLF spectrum?" Tags="&lt;united-states&gt;&lt;frequency&gt;&lt;vlf&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1608" PostTypeId="1" CreationDate="2014-03-14T15:40:45.427" Score="8" ViewCount="6413" Body="&lt;p&gt;I've read in several places that the electric field is 90 degrees orthogonal to the magnetic field, and both are orthogonal to the direction of the wave from a transmitting antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What causes this? Are there &lt;em&gt;any&lt;/em&gt; cases where this might not be true, or are the fields &lt;em&gt;always&lt;/em&gt; 90 degrees to each other?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-12-04T22:51:39.470" Title="Why is the electric field orthogonal to the magnetic field from an antenna?" Tags="&lt;antenna&gt;&lt;propagation&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1610" PostTypeId="1" AcceptedAnswerId="1611" CreationDate="2014-03-14T17:50:25.503" Score="13" ViewCount="2005" Body="&lt;p&gt;An easy &lt;a href=&quot;http://byonics.com/tdoa/&quot; rel=&quot;noreferrer&quot;&gt;TDOA design by Byonics&lt;/a&gt; was published with the following schematic:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/VxP5H.png&quot; alt=&quot;Two dipole antennas with a diode switcher controlled by a microcontroller feeding a radio&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It appears that the antennas are switched at a rate of 640Hz, which allows a 640Hz tone to be heard in the radio when the antennas are not in phase.  When the antennas are equidistant from the RF source, the tone goes away, so by turning the antenna and finding the null you can determine the direction of the source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://byonics.com/tdoa/&quot; rel=&quot;noreferrer&quot;&gt;author's description&lt;/a&gt; further explains:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Note that the transmitter being on that perpendicular line means that it could either be directly ahead, or directly behind. You would need to move some distance along the line of the antennas and take another bearing to determine which direction the transmitter actually was. In the next version, &lt;strong&gt;when the audio from the receiver is fed back into the chip and analyzed, it will be able to tell if the signal is coming from the left or right&lt;/strong&gt; when the tone is present, and light the appropriate LED. &lt;sub&gt;&lt;sup&gt;(emphasis added)&lt;/sup&gt;&lt;/sub&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;With the radio's audio going into the microcontroller, and the antennas out of phase with the source, what is the microcontroller looking for, or how would it tell, whether the signal is coming from the right or the left of the dipole array?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2014-04-05T22:44:10.180" LastActivityDate="2019-12-26T22:35:38.853" Title="How would a time-difference-of-arrival receiver with two antennas know which side the signal is from?" Tags="&lt;receiver&gt;&lt;theory&gt;&lt;direction-finding&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1611" PostTypeId="2" ParentId="1610" CreationDate="2014-03-14T18:46:48.320" Score="16" Body="&lt;p&gt;When the tone is present, it is because the antennas are out of phase. One antenna's signal will be leading the other; which one is leading depends on which one is closer to the transmitter (provided that the antennas are less than 1/2 wavelength apart, so that the phase difference will always be less than 180°).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When we switch from the lagging signal to the leading signal (for example), the phase of the switched signal jumps ahead; equivalently, the &lt;em&gt;frequency&lt;/em&gt; of the signal increases for an instant and then returns to normal. The same but inverted applies to switching from the leading signal to a lagging signal. The output of a FM receiver is determined by the frequency of the input, so we get a result like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/UBfcS.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The green waveform is the switch control and the blue waveform is the demodulated signal (the frequency deviation). After audio-frequency filtering on the output, we get a more ordinary tone, though with a delay introduced by the filter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/4REOw.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the time delays of the arriving signal are the other way around, then the phase shifts are opposite, and the audio signal is negated — or, equivalently, phase shifted by 180°.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, to distinguish between left and right (that is, left signal leading vs. right signal leading) one need merely compare the phase of the audio signal to the phase of the switching signal; there are only two possible results (except when the audio tone is absent and the phase is therefore undefined).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the exact phase difference found will depend on all delays in the system, including in the external receiver; but that would be simple to calibrate for.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I have built a simulation of this system using &lt;a href=&quot;https://gnuradio.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;GNU Radio&lt;/a&gt;, and used it to produce the plots shown and confirm that the technique can produce a reliable left/right indication (at least for an unmodulated input). Here are the &lt;a href=&quot;https://switchb.org/kpreid/2014/df-tdoa/tdoa.grc&quot; rel=&quot;nofollow noreferrer&quot;&gt;GNU Radio Companion file&lt;/a&gt; and &lt;a href=&quot;https://switchb.org/kpreid/2014/df-tdoa/tdoa.py&quot; rel=&quot;nofollow noreferrer&quot;&gt;generated Python program&lt;/a&gt; (GNU Radio 3.7+ required). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/qDnRb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that while the RF sections of this simulation use complex (analytic) signals, there is nothing in those sections which would make a difference from the results obtained by using real signals at a nonzero IF as usual analog RF electronics do.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;On the other hand, in the perpendicular direction, it is not possible to distinguish the front and back sides; there is a fundamental ambiguity due to the symmetry of the antenna array. No direction finding system can distinguish between directions in which its antennas are symmetrical; the asymmetry which allows the discrimination described here comes from the switching of the antennas rather than their shape.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-12-26T22:35:38.853" LastActivityDate="2019-12-26T22:35:38.853" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="1612" PostTypeId="2" ParentId="1608" CreationDate="2014-03-14T19:24:43.770" Score="8" Body="&lt;p&gt;The short answer is no, there are no cases where radio waves would not have orthogonal magnetic and electric fields.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In physics, a radio wave, indeed all EM radiation is called a &lt;a href=&quot;http://en.wikipedia.org/wiki/Transverse_wave&quot; rel=&quot;nofollow&quot;&gt;transverse wave&lt;/a&gt;, meaning, by definition, that the oscillations of the waves are perpendicular to the direction of energy transfer and travel. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The electric and magnetic parts of the field stand in a fixed ratio of strengths in order to satisfy the two Maxwell equations that specify how one is produced from the other. These $\mathbf{E}$ and $\mathbf{B}$ (in physics the magnetic part uses B for some reason, I'll maintain that convention to make it easier for the physics folks to correct any errors) fields are also in phase, with both reaching maxima and minima at the same points in space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;OK, so we know this much already, but &lt;strong&gt;&lt;em&gt;why&lt;/em&gt;&lt;/strong&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ask &lt;a href=&quot;http://en.wikipedia.org/wiki/James_Clerk_Maxwell&quot; rel=&quot;nofollow&quot;&gt;James Clerk Maxwell&lt;/a&gt;; his electromagnetic wave equation is a second-order partial differential equation that describes the propagation of &lt;a href=&quot;http://en.wikipedia.org/wiki/Electromagnetic_wave&quot; rel=&quot;nofollow&quot;&gt;electromagnetic waves&lt;/a&gt; through a medium or in a vacuum. It is a &lt;a href=&quot;http://en.wikipedia.org/wiki/Wave_equation#Scalar_wave_equation_in_three_space_dimensions&quot; rel=&quot;nofollow&quot;&gt;three-dimensional form of the wave equation&lt;/a&gt;. The homogeneous form of the equation, written in terms of either the electric field E or the magnetic field B, takes the form:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;\left(\nabla^2 - { \mu\epsilon } {\partial^2 \over \partial t^2} \right) \mathbf{E} = \mathbf{0}&#xA;\\&#xA;\left(\nabla^2 - { \mu\epsilon } {\partial^2 \over \partial t^2} \right) \mathbf{B} = \mathbf{0}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$c = {1 \over \sqrt {\mu\epsilon} }$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Speed_of_light&quot; rel=&quot;nofollow&quot;&gt;speed of light&lt;/a&gt; in a medium with permeability ($\mu$), and permittivity ($\epsilon$), and ∇&lt;sup&gt;2&lt;/sup&gt; is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Vector_Laplacian&quot; rel=&quot;nofollow&quot;&gt;Laplace operator&lt;/a&gt;.  In a vacuum, &lt;em&gt;c&lt;/em&gt; = 299,792,458 meters per second, which is the speed of light in free space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that's the general theory, this can be solved for the plane wave case (the one we are interested in):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given a plane defined by a unit normal vector: $\mathbf{n} = { \mathbf{k} \over k }$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then planar traveling wave solutions of the wave equations are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\mathbf{E}(\mathbf{r}) = E_0 e^{ -i \mathbf{k} \cdot \mathbf{r} }$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\mathbf{B}(\mathbf{r}) = B_0 e^{ -i \mathbf{k} \cdot \mathbf{r} }$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;strong&gt;&lt;em&gt;r&lt;/em&gt;&lt;/strong&gt; = &lt;em&gt;(x, y, z)&lt;/em&gt; is the position vector (in meters).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These solutions represent planar waves traveling in the direction of the normal vector &lt;strong&gt;&lt;em&gt;n&lt;/em&gt;&lt;/strong&gt;.  If we define the z direction as the direction of &lt;strong&gt;&lt;em&gt;n&lt;/em&gt;&lt;/strong&gt;. and the x direction as the direction of &lt;strong&gt;&lt;em&gt;E&lt;/em&gt;&lt;/strong&gt;., then by &lt;a href=&quot;http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction&quot; rel=&quot;nofollow&quot;&gt;Faraday's Law&lt;/a&gt; the magnetic field lies in the y direction and is related to the electric field by the relation $\scriptstyle c^2{\partial B \over \partial z} \,=\, {\partial E \over \partial t}$.  Because the divergence of the electric and magnetic fields are zero, there are no fields in the direction of propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://newton.physics.uiowa.edu/~rmerlino/6Fall10/29006_L30.pdf&quot; rel=&quot;nofollow&quot;&gt;The Production of EM waves&lt;/a&gt; (physics lecture notes) &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Electromagnetism&quot; rel=&quot;nofollow&quot;&gt;Wikipedia&lt;/a&gt;, your first stop shop for math that blows your head off&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://books.google.com/books?id=BRgHAAAAQBAJ&amp;amp;pg=PA715&amp;amp;lpg=PA715&amp;amp;dq=Why%20is%20the%20electric%20field%20orthogonal%20to%20the%20magnetic%20field%20from%20an%20antenna?&amp;amp;source=bl&amp;amp;ots=6PjfZUIQPZ&amp;amp;sig=RscxycSKpoYFY93A3J8SKc_b9Kw&amp;amp;hl=en&amp;amp;sa=X&amp;amp;ei=RVcjU7OqHcac0AGawoCACg&amp;amp;ved=0CDQQ6AEwATgU#v=onepage&amp;amp;q=Why%20is%20the%20electric%20field%20orthogonal%20to%20the%20magnetic%20field%20from%20an%20antenna?&amp;amp;f=false&quot; rel=&quot;nofollow&quot;&gt;College Physics, Volume 2&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="164" LastEditorUserId="76" LastEditDate="2014-03-17T01:05:08.993" LastActivityDate="2014-03-17T01:05:08.993" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1613" PostTypeId="1" CreationDate="2014-03-14T21:45:46.940" Score="3" ViewCount="243" Body="&lt;p&gt;In a slide on calculating link budget, detrimental effects to a link included “Radio pollution (selectivity, blocking, IP3)”.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What is radio pollution? &lt;/li&gt;&#xA;&lt;li&gt;Specifically, what are selectivity, blocking, and IP3 in connection with radio pollution? &lt;/li&gt;&#xA;&lt;li&gt;Do all major forms of radio pollution fall into one of those three, or are there other forms of radio pollution one should be aware of?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2014-03-15T01:12:00.060" LastActivityDate="2014-03-17T00:44:05.823" Title="What is radio pollution?" Tags="&lt;jargon&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1614" PostTypeId="2" ParentId="1579" CreationDate="2014-03-14T21:58:13.063" Score="1" Body="&lt;p&gt;Once cleaned up, a simple light oil, such as 3-in-1 household oil, is sufficient.  There is no need to use a real grease or heavy oil, but a light oil will prevent oxidation, reduce wear, and make the action a little smoother than dry bearings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that while this isn't a big piece of machinery, depending on the materials involved and how much and how fast you use your key, you can wear the bearings or bearing surfaces out. Further the bearings are often only used in a very small range, back and forth, rather than completing circles.  If you do use it heavily, spinning the bearings around a bit every so often may help you avoid wear patterns that could make the key feel loose, sticky, or hard to adjust.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on previous usage you may already be dealing with these issues.  They are relatively minor, though, and the key is certainly usable, but be aware that some keys feel worse or more difficult to adjust than others due to this type of wear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as cleaning this up, a heavy duty degreaser should take care of it.  Don't use anything abrasive. If you are picky, consider keeping the bearings in order and putting them back in the same order they came out.  Depending on the age of the key and usage patterns, this can make a difference, though in most cases it doesn't.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-03-14T21:58:13.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1615" PostTypeId="2" ParentId="1613" CreationDate="2014-03-15T00:38:18.223" Score="5" Body="&lt;p&gt;“Selectivity, blocking, and IP3” are three properties of a receiver's ability to receive the desired signal in the presence of other signals at &lt;em&gt;different&lt;/em&gt; frequencies. Thus it would seem this document is referring to all such signals as “pollution”, presumably on the grounds that they are manmade signals as opposed to “natural” noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I am not aware of a matching accepted definition of “radio pollution”; insofar as the term is defined it seems to refer to &lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_spectrum_pollution&quot; rel=&quot;nofollow&quot;&gt;signals occurring outside of appropriate spectrum allocations&lt;/a&gt;, which is largely not relevant to this.)&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Selectivity_(electronic)&quot; rel=&quot;nofollow&quot;&gt;&lt;em&gt;Selectivity&lt;/em&gt;&lt;/a&gt; refers to the receiver's ability to “select” the desired signal by filtering out others not at the intended frequency; insufficient selectivity means receiving the adjacent signals as well as the desired signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;http://www.radio-electronics.com/info/rf-technology-design/receiver-overload/blocking.php&quot; rel=&quot;nofollow&quot;&gt;&lt;em&gt;Blocking&lt;/em&gt;&lt;/a&gt; is a phenomenon where strong nearby signals cause an apparent reduction in the strength of the desired signal. The (lack of) susceptibility of a receiver to this effect is quantified as &lt;em&gt;blocking dynamic range&lt;/em&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Third-order_intercept_point&quot; rel=&quot;nofollow&quot;&gt;&lt;em&gt;$IP_3$&lt;/em&gt;, or &lt;em&gt;third-order intercept point&lt;/em&gt;&lt;/a&gt;, is a measure of the strength of &lt;em&gt;third-order intermodulation products&lt;/em&gt;. &lt;a href=&quot;https://en.wikipedia.org/wiki/Intermodulation_product&quot; rel=&quot;nofollow&quot;&gt;Intermodulation products&lt;/a&gt; appear as unwanted signals at frequencies with a specific relationship to actual signals; third-order products are particularly of interest because their frequency is close to the original signals; for input signals at frequencies $f_1$ and $f_2$, third-order products occur at $2f_1 - f_2$ and $2f_2 - f_1$.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So, what they said very elliptically was that you should consider, in your link budget calculation, the effects of the other signals in the environment on the imperfections of your receiver.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Do all major forms of radio pollution fall into one of those three, or are there other forms of radio pollution one should be aware of?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Going by this apparently idiosyncratic definition, the other case you would be concerned with is where the unwanted signal is &lt;em&gt;at&lt;/em&gt; your chosen frequency, in which case none of the above receiver properties are relevant since as far as it's concerned it is the wanted signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a completely different problem, which is mostly independent of a link budget (unless you, say, use your budget calculation to determine that your signals will be much stronger than the unwanted signal, e.g. by using high-gain (directional) antennas between your link endpoints).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-03-17T00:44:05.823" LastActivityDate="2014-03-17T00:44:05.823" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1616" PostTypeId="2" ParentId="1589" CreationDate="2014-03-15T13:44:37.637" Score="2" Body="&lt;p&gt;Not always.  &lt;a href=&quot;http://larcmdorg.doore.net/vec/index.php?pg=teams&quot; rel=&quot;nofollow&quot;&gt;Laurel VEC&lt;/a&gt; does not require a fee.  They test at Hamvention, too!&lt;/p&gt;&#xA;" OwnerUserId="678" LastActivityDate="2014-03-15T13:44:37.637" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1617" PostTypeId="2" ParentId="1608" CreationDate="2014-03-17T00:50:37.317" Score="2" Body="&lt;p&gt;For radiated fields, the electric field (&lt;strong&gt;E&lt;/strong&gt;) and (&lt;strong&gt;H&lt;/strong&gt;) are always perpendicular. No one knows why this is more than we know any other physical law, but so far as anyone can demonstrate, it's always true. As WPrecht says, Maxwell's equations require electromagnetic waves to be this way. There's also simpler, albeit less complete mathematical explanation: the &lt;a href=&quot;http://en.wikipedia.org/wiki/Poynting_vector&quot; rel=&quot;nofollow noreferrer&quot;&gt;Poynting vector&lt;/a&gt;. This vector is simply the cross-product of &lt;strong&gt;E&lt;/strong&gt; and &lt;strong&gt;H&lt;/strong&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \mathbf{S} = \mathbf{E}\times\mathbf{H} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This vector &lt;strong&gt;S&lt;/strong&gt; represents the direction of energy transfer, so it follows that if the energy is radiating away, then the electric and magnetic fields must be mutually perpendicular to this, by the definition of the &lt;a href=&quot;http://en.wikipedia.org/wiki/Cross_product&quot; rel=&quot;nofollow noreferrer&quot;&gt;cross product&lt;/a&gt; operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can gain some intuition into why this is true by considering the fields around a dipole. Say the dipole is vertical. The electric field lines are vertical, because the voltages are different along the length of the dipole. Meanwhile, current is flowing through the dipole, and current through a conductor makes magnetic field lines in concentric circles around that conductor. The result looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/b52bP.png&quot; alt=&quot;fields around dipole antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Here they've used &lt;strong&gt;B&lt;/strong&gt; for the magnetic field instead of &lt;strong&gt;H&lt;/strong&gt;. &lt;a href=&quot;http://en.wikipedia.org/wiki/Magnetic_field#Relation_between_H_and_B&quot; rel=&quot;nofollow noreferrer&quot;&gt;There's a difference&lt;/a&gt;, but it will send us off on a tangent. Without compromising the understanding of this particular problem you can consider them to be the same.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see, the fields are perpendicular, and they stay that way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you think more about it, all moving electric charges, not just those in wires, create an associated magnetic field. This includes the &lt;a href=&quot;http://en.wikipedia.org/wiki/Displacement_current&quot; rel=&quot;nofollow noreferrer&quot;&gt;displacement currents&lt;/a&gt; involved in radiation. And really, &lt;em&gt;create&lt;/em&gt; might be the wrong word, because time-variant magnetic fields are also associated with electric fields (see &lt;a href=&quot;http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction&quot; rel=&quot;nofollow noreferrer&quot;&gt;Faraday's law&lt;/a&gt;). That magnetic fields can create electric fields and electric fields can create magnetic fields is what allow these two to self-propagate indefinitely in free space. Of course you can have electric fields with no magnetic field (capacitors) or magnetic fields with no electric fields (inductors), but these don't radiate (in the ideal case). So, the perpendicular arrangement of the fields in a dipole isn't coincidence: it's what makes it an effective antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-03-17T00:50:37.317" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1618" PostTypeId="1" AcceptedAnswerId="1619" CreationDate="2014-03-20T13:59:10.620" Score="8" ViewCount="1002" Body="&lt;p&gt;For context, I'm brand new, with nothing but an HT &amp;amp; 19&quot; dual band (2m/70cm) whip on it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While I'll likely go with a magnetically mounted vertical antenna, I've been thinking of other more covert options.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, could I do a 1/2 wave dipole mounted along the roof? A 2m dipole is just a little over 3 feet and would easily fit along the edge or middle. I'd need to insulate it, I'm sure, but would that work or be worth the effort? What about vertically along a door frame?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bumper is already insulated. Even if the car body reflects the RF in one direction, could I then combine one in the front and one in the back bumper?&lt;/p&gt;&#xA;" OwnerUserId="864" LastEditorUserId="76" LastEditDate="2014-03-20T16:24:00.170" LastActivityDate="2014-03-21T12:01:35.260" Title="Is a VHF antenna on a vehicle's body a bad idea?" Tags="&lt;antenna&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1619" PostTypeId="2" ParentId="1618" CreationDate="2014-03-20T19:19:39.807" Score="6" Body="&lt;p&gt;A horizontal VHF dipole above a (presumably metallic) car roof is not a good idea. Because the car roof is relatively large relative to wavelength, and is a good conductor, you will get a lot of RF current in it through capacitive and inductive coupling. This isn't a bad thing in itself, but because the geometry of your car isn't designed as an antenna, the result will be difficult to predict and probably not very good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's one problem: if we think of the car roof as an infinite conductive plane (just a rough approximation of reality), it will make an &lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;image antenna&lt;/a&gt;. If your dipole is very close to the roof, then this image antenna will cancel most of your antenna's radiation. As you get it higher you will get less cancellation, but most of the radiation will be up, towards the sky. &lt;a href=&quot;https://ham.stackexchange.com/a/487/218&quot;&gt;When you get it to half a wavelength high, then this is no longer a problem&lt;/a&gt;, but then why not just use a mag-mount vertical, which is just as tall? For a vertical, the ground plane and resulting image antenna is a good thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course your car isn't an infinite plane. RF currents will flow all over the car body, and probably you will get a lot of radiation from &lt;a href=&quot;http://www.antenna-theory.com/antennas/aperture/slot.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;slot antennas&lt;/a&gt; formed by seams in the car body. The trouble is we don't know what they will be. They probably won't offer a good match to your 50Ω coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the polarization could be anything. By convention, FM on VHF uses vertical polarization. If you happen to radiate with horizontal radiation, you will only be heard by most people through paths that rotate your polarization. In practice, this means a loss on the order of 30dB. Radiation from your car body probably won't be entirely horizontal, so it may not be so bad, but most likely, it won't be so good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another issue may be the electronics in your car. With the dipole laying against the car body (anywhere), the coupling between the dipole and the car body is so good you might as well have soldered the feedline directly to the car body and skipped the dipole. It's obvious then how much RF current is in the car body, and all the wiring attached to it. Automotive electronics are usually pretty robustly engineered, but I'm not sure I'd trust them to work with an RF transmitter hooked up to them.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-03-21T12:01:35.260" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1620" PostTypeId="1" AcceptedAnswerId="1644" CreationDate="2014-03-22T03:34:29.590" Score="2" ViewCount="410" Body="&lt;p&gt;I was just reviewing the manual of my Yaesu FT-897D to remind myself of useful functions I might have forgotten about, and I found the programmable function keys, which can be set to any of “All Multi Function , all Menu Item, MONI, Q.SPL, TCALL, ATC and USER” (sic).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MONI, Q.SPL, TCALL, and ATC are explained elsewhere, more or less, but what is &lt;strong&gt;USER&lt;/strong&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried assigning it to a button and it operates as a toggle, but doesn't have any obvious effect. The only mentions of “USER” in the manual are in reference to the USER-L/USER-U digital sub-modes which seem to be independent.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-03-26T11:33:59.713" Title="What does the “USER” programmable key function do on the Yaesu FT-897D?" Tags="&lt;transceiver&gt;&lt;yaesu&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1621" PostTypeId="1" CreationDate="2014-03-22T20:49:47.973" Score="3" ViewCount="136" Body="&lt;p&gt;I just got licensed a few weeks back and have been connecting with repeaters on my 2m/7cm HT. My plan is to get a mobile antenna for use in the car and make an antenna for home operation. While those will let me connect with more repeaters and nets locally, it's not really changing what I do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With conversations I've overheard and had I get the feeling that the realm of amateur radio is &lt;em&gt;huge&lt;/em&gt;, but when I ask others what to do next, the most common response is &quot;it depends on what you want to do.&quot; I get that, but I'm not really sure what you &lt;em&gt;can&lt;/em&gt; do. Kind of a catch-22.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, here's my two-part objective question: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are specific areas that some people get into within amateur radio?&#xA;And what is the first/next step to get into those areas if it sounds interesting to me?&lt;/p&gt;&#xA;" OwnerUserId="864" LastEditorUserId="76" LastEditDate="2014-03-22T22:15:57.460" LastActivityDate="2014-03-24T14:19:49.203" Title="What are specific areas that some people get into within amateur radio?" Tags="&lt;education&gt;" AnswerCount="1" CommentCount="5" ClosedDate="2014-08-12T20:10:05.633" CommunityOwnedDate="2014-05-20T03:54:54.467" ContentLicense="CC BY-SA 3.0" />
  <row Id="1622" PostTypeId="2" ParentId="1621" CreationDate="2014-03-22T23:08:28.050" Score="12" Body="&lt;p&gt;Here's a taxonomy of some things hams do. It can hardly be complete, but hopefully it covers both the broad areas and some &lt;em&gt;examples&lt;/em&gt; of very particular activities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(“And what to do next” for each activity would be far too much for one answer; I suggest that if any of these things interest you to ask about them individually.)&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Local communications:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Talking with your friends / acquaintances / random strangers&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...while stuck in traffic&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Public service&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Event communications support&lt;/li&gt;&#xA;&lt;li&gt;Emergency communications (“emcomm”) and preparation/practice&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Ham emergency organizations (US: ARES/RACES)&lt;/li&gt;&#xA;&lt;li&gt;Coordinating with local public safety&lt;/li&gt;&#xA;&lt;li&gt;Formal traffic handling&lt;/li&gt;&#xA;&lt;li&gt;Physical preparedness (getting yourself and your radio out of or into a situation)&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Making contacts:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Contacting as many people/countries/entities as you can&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...under a time limit (contesting)&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Field Day&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;...or not (awards)&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Making technically challenging contacts&#xA;&lt;ul&gt;&#xA;&lt;li&gt;via or to satellites&lt;/li&gt;&#xA;&lt;li&gt;DX (long distance)&lt;/li&gt;&#xA;&lt;li&gt;Unusual propagation (EME, aurora, meteor scatter, etc.)&lt;/li&gt;&#xA;&lt;li&gt;QRP (reduced transmit power)&lt;/li&gt;&#xA;&lt;li&gt;using extremely high frequencies&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Making contacts from strange places&#xA;&lt;ul&gt;&#xA;&lt;li&gt;formally: DXpeditions, SOTA&lt;/li&gt;&#xA;&lt;li&gt;informally: from that hill you just hiked up&lt;/li&gt;&#xA;&lt;li&gt;while in an airplane&lt;/li&gt;&#xA;&lt;li&gt;after jumping out of an airplane&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Technical: designing or building your own...&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;antennas&#xA;&lt;ul&gt;&#xA;&lt;li&gt;for gain, bandwidth, efficiency, stealth, size, or parts cost&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;receivers, transmitters, or transceivers&lt;/li&gt;&#xA;&lt;li&gt;digital mode interfaces/software&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Inventing a new digital mode&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;software-defined radios&#xA;&lt;ul&gt;&#xA;&lt;li&gt;RF/ADC/DAC hardware&lt;/li&gt;&#xA;&lt;li&gt;DSP software&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...running on a normal computer with a RF peripheral&lt;/li&gt;&#xA;&lt;li&gt;...running on a dedicated FPGA/DSP chip in an all-in-one unit&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;test equipment&lt;/li&gt;&#xA;&lt;li&gt;automation/integration (computer control, remote control, etc.)&lt;/li&gt;&#xA;&lt;li&gt;power supplies, cases, cabling, mounting&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...all together as a &quot;go box&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Communication not between two people:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;long-distance radio-controlled aircraft&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...with onboard &quot;first-person view&quot; cameras&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;direction finding to locate hidden transmitters (“transmitter hunting”, “DFing”, “foxhunting”)&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...that are hidden for the purpose&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...in urban areas and sought from a car&lt;/li&gt;&#xA;&lt;li&gt;...in wilderness areas and sought on foot&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...as a formalized sport (“ARDF”, “radiosport”, “radio orienteering”)&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;...that are interfering with communications&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...accidentally&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...and helping the responsible party fix it&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;...maliciously&#xA;&lt;ul&gt;&#xA;&lt;li&gt;...and notifying the relevant authorities&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;APRS&#xA;&lt;ul&gt;&#xA;&lt;li&gt;position tracking (transmitting GPS position data, not DF)&lt;/li&gt;&#xA;&lt;li&gt;weather stations&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-03-24T14:19:49.203" LastActivityDate="2014-03-24T14:19:49.203" CommentCount="2" CommunityOwnedDate="2014-03-24T14:19:49.203" ContentLicense="CC BY-SA 3.0" />
  <row Id="1623" PostTypeId="1" AcceptedAnswerId="1635" CreationDate="2014-03-23T02:19:34.150" Score="2" ViewCount="2746" Body="&lt;p&gt;In USA, is it legal to hear police or ATC (air traffic control) frequency?&lt;/p&gt;&#xA;" OwnerUserId="881" LastActivityDate="2014-03-24T15:44:49.037" Title="In USA, is it legal to hear police or ATC frequency?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="2" CommentCount="6" ClosedDate="2014-03-25T09:58:41.937" ContentLicense="CC BY-SA 3.0" />
  <row Id="1625" PostTypeId="1" CreationDate="2014-03-23T16:48:29.233" Score="3" ViewCount="953" Body="&lt;p&gt;I have a bunch of high-wattage 50 ohm resistors lying around, but they are wirewound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I use them as a dummy load for transmitters 144 MHz and down, how bad would that be? Since they probably will be an inductive load, could I use capacitors to cancel out the inductance?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Probably better that I get some non-wirewound resistors, but I'm just wondering how bad it would be for the radio.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-03-23T20:06:03.130" LastActivityDate="2014-03-23T20:06:03.130" Title="Using wirewound resistors in a dummy load" Tags="&lt;equipment-design&gt;&lt;impedance&gt;&lt;dummy-load&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1626" PostTypeId="2" ParentId="1625" CreationDate="2014-03-23T17:17:23.913" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I use them as a dummy load for transmitters 144mhz and down, how bad would that be?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's just a mismatched load, and the consequences are the same as for a mismatched antenna. Check your transmitter's manual for the degree of mismatch it can handle and any applicable warnings. Modern transmitters typically have self-protection circuits and will not be harmed, but may automatically reduce power or shut off.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Since they probably will seem like an inductive load, could I use capacitors to cancel out the inductance?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, but it would be canceled out at a specific frequency only (and nearly canceled in a region around it) and would have some capacitive or inductive reactance elsewhere. That is, you now have a dummy load with a small bandwidth. If you want to use it on a particular band, or if the transmitter is capable of handling the SWR resulting from the mismatch, then this isn't a problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For comparison, if you instead construct your dummy load from non-inductive resistors, then you can use it at any frequency whatsoever equally well, at least ideally. In practice, there's always some stray inductance and/or capacitance and there will be limits — this is why manufactured dummy loads have specified frequency ranges.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-03-23T18:46:35.150" LastActivityDate="2014-03-23T18:46:35.150" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1627" PostTypeId="2" ParentId="1623" CreationDate="2014-03-23T17:28:12.453" Score="1" Body="&lt;p&gt;If you are a licensed amateur radio operator, using your Part 97 gear, the answer is an unequivocal &quot;yes&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/files/file/pr91-36.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/files/file/pr91-36.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="39" LastActivityDate="2014-03-23T17:28:12.453" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1628" PostTypeId="1" AcceptedAnswerId="1629" CreationDate="2014-03-23T18:06:11.587" Score="12" ViewCount="4313" Body="&lt;p&gt;I bought a ham radio antenna mounting kit for my car that includes ~16' of coax. One end has a trunk lip NMO antenna mount, the other end has a re-solderable PL-259.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I asked the sales person if it is best to shorten the coax after installation to only the length required to reach the radio transceiver and they said &quot;I would just leave it, the length is already optimized for maximum efficiency at the factory&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've heard of this before (mostly from CB Radio installers) but don't actually know if this is true or understand &lt;strong&gt;why/if there is an optimum feedline length for VHF/UHF FM use&lt;/strong&gt; (vs Citizen's Band AM HF). I intend to be setup for both VHF/UHF but will operate primarily on 2M VHF and so any trade-offs should be optimized for the 2M band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My SWR on 2M at my club's repeater frequency is 1.7. Would shortening the length change the SWR or only change the losses incurred due to the SWR?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a nice space in the trunk, normally used for a sub-woofer if you purchased an optional &quot;premium stereo&quot; with the car - in my case this space sits empty. I plan to keep the radio transceiver body in the trunk with the remote head unit up front. This would allow me to keep the antenna feedline shorter and make for an aesthetically clean installation. This would also allow the antenna feedline length to be something around 5-6ft if shortening it would be beneficial (although I could just coil up the unused ~10ft or so).&lt;/p&gt;&#xA;" OwnerUserId="608" LastActivityDate="2020-10-08T01:39:35.437" Title="Is there an optimum Antenna Feedline Length for mobile installations?" Tags="&lt;mobile&gt;&lt;feed-line&gt;&lt;coaxial-cable&gt;&lt;vhf&gt;&lt;2m-band&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1629" PostTypeId="2" ParentId="1628" CreationDate="2014-03-23T18:36:50.923" Score="13" Body="&lt;p&gt;In the absence of common-mode currents, then the optimum feedline length is 0, because a longer feedline only increases your feedline losses. These losses are due to the resistance of the wire, dielectric losses, etc. and are specified in dB per unit length in the coax datasheet. At VHF and up, these losses can be significant even at car lengths, especially with less expensive or smaller feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you do have &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;common-mode currents&lt;/a&gt;, then the feedline is effectively part of the antenna. Changing its length does the same thing as changing the length of the antenna: it can alter the radiation efficiency and impedance (and thus SWR) of the antenna. Even in this case, it's hard to say just what the &quot;optimum length&quot; is, because feedlines tend to be routed to, around, or near other conductive objects (like the radio chassis, and through the negative power supply lead, the car body), and these too will alter the operation of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's nothing special about CB: it's still just radio, and a properly designed and installed station still has no significant common-mode currents, and the feedline should still be a short as possible. The issue is that CB operators have more interest in superstition than a proper understanding of RF engineering. A popular CB antenna is a vertical which is installed with no ground plane, or an insufficient ground plane. In this case, &lt;a href=&quot;https://ham.stackexchange.com/q/601/218&quot;&gt;the feedline acts like the missing half of the dipole&lt;/a&gt;, so the feedline length absolutely is essential to the operation of the antenna. While you can indeed &quot;tune&quot; your &quot;antenna&quot; in this case by altering the feedline length, this is usually &lt;em&gt;bad advice&lt;/em&gt;. &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;Addressing the common-mode current problem&lt;/a&gt;, rather than fiddling with feedline length until you happen to get a good antenna, usually yields a more robust and predictable result.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-03-24T12:00:32.163" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1631" PostTypeId="1" CreationDate="2014-03-24T03:26:41.417" Score="5" ViewCount="306" Body="&lt;p&gt;It always confused me why 100 watts out of your transmitter could radiate 200 watts coming from a high-gain antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is the term gain used instead of directionality?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-03-24T12:54:04.693" Title="Why is gain used?" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1632" PostTypeId="2" ParentId="1631" CreationDate="2014-03-24T04:45:11.137" Score="1" Body="&lt;p&gt;I'll leave the more technical explanations up to someone else, but here's hopefully a good-enough explanation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My assumption is that you know, but just in case, let's start with what &quot;gain&quot; is. Gain in the example you've presented represents a &lt;em&gt;focusing&lt;/em&gt; of power (e.g. 3dBi, or it doubled). There are lots of analogies that I could paint, but let's go with an explosion, since it will try to radiate its power in all directions similar to a basic &quot;perfect&quot; antenna. If you put a cannon ball next to a certain amount of gun powder, both suspended in air, and ignite the powder, it will push the cannon ball some. Put them both on the ground, and the same amount of gunpowder will push the cannon ball even more because the ground is directing the force to go only out and up instead of in all directions. Put them both in a cannon, and the ball will go significantly farther than either because all of the force is being allowed to go in only one direction. Remember, you have the same amount of gun powder in each case, but the effective force on the ball is different because of how the explosion was focused.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gain, then, is a relative description of how much radiation is being directed or focused, and therefore how much more effective power it has. To get the &lt;em&gt;relative&lt;/em&gt; value (dBi), we usually compare antennas to a perfectly omnidirectional one (similar to the gun powder suspended in air). So an antenna with 3dBi will have double the power in the most powerful direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes, for some people, knowing how much it's focused is enough by itself, sometimes the direction the power is focused in is implied by the antenna type, but sometimes it could be purposefully not given to make the antenna sound better than it is--or to make it sound better to a larger group of people.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, knowing &lt;em&gt;both&lt;/em&gt; the gain and direction is probably the most useful when choosing the right antenna for your needs, but knowing just one or the other is only giving part of the story.&lt;/p&gt;&#xA;" OwnerUserId="864" LastActivityDate="2014-03-24T04:45:11.137" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1633" PostTypeId="2" ParentId="1631" CreationDate="2014-03-24T05:17:16.813" Score="6" Body="&lt;p&gt;The directional antenna doesn't actually radiate 200 Watts, it just focuses the actual mere 100 Watts so that along some optimal directional axis, a receiver would see same power as if an imaginary 200 watt transmitter using an imaginary isotropic antenna were instead the source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which makes it easier to categorize the radiated power from that &quot;high gain&quot; antenna in that optimal direction using just one number, instead of 2 or more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An additional 100 Watts isn't created, more like taken away from other less optimal directions in the antenna's radiation pattern.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-03-24T05:17:16.813" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1634" PostTypeId="2" ParentId="1631" CreationDate="2014-03-24T12:27:10.133" Score="6" Body="&lt;p&gt;I'm going to assume you mean &lt;a href=&quot;http://www.antenna-theory.com/basics/directivity.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;directivity&lt;/a&gt;, not directionality. Then:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why is the term gain used instead of [directivity]?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;These are two related but different things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gain measures the ratio of input electrical power to output electromagnetic radiation (or the reverse, for receiving). It is a spherical function, that is: an antenna has gain defined for any direction, azimuth and elevation. When we discussing just &quot;gain&quot; as a single number and not a function, it's usually understood that we mean &lt;em&gt;maximum&lt;/em&gt; gain: the gain of the antenna in the direction of peak sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the law of conservation of energy, a passive antenna (one without any amplifier or other source of energy) can't have an &lt;em&gt;average&lt;/em&gt; gain greater than 1. The only way it can radiate more energy in one direction is to radiate less energy in another direction. The total power output remains the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Directivity is a measure of the extent to which an antenna does this. If the gains are normalized such that the peak gain is 1, then directivity is 1 divided by the average gain over all directions. An &lt;a href=&quot;http://en.wikipedia.org/wiki/Isotropic_radiator&quot; rel=&quot;nofollow noreferrer&quot;&gt;isotropic&lt;/a&gt; antenna, one that radiates equally in all directions&lt;sup&gt;1&lt;/sup&gt;, has a directivity of 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's possible to have a high directivity, low gain antenna. Simply build a very lossy, very directional antenna. This antenna might have a peak gain of -10dBi. The average gain might be -60dBi. That is, it receives and transmits much better in one direction, and thus has a high directivity, but even in that direction it's very poor. In practice we might actually call this device a dummy load or a heater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To build a high gain, low directivity antenna you must have an amplifier. An amplifier with a low directivity antenna could be considered a high gain, low directivity system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that we can point our antennas appropriately, then peak gain is a useful number for the calculation of a &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt;. We might then care about directivity if we consider all energy received from unintended directions as &quot;noise&quot;: then maximizing directivity will minimize noise. Conveniently, if we can make a passive antenna more directional without also making it less efficient, then we maximize both peak gain and directivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: A coherent isotropic radiator does not exist. Even a dipole radiates more in some directions than others.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-03-24T12:54:04.693" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1635" PostTypeId="2" ParentId="1623" CreationDate="2014-03-24T15:44:49.037" Score="3" Body="&lt;p&gt;In the US the answer is generally yes, you can listen to such transmissions, but local and federal laws may have some restrictions on what you can do with information gained from listening activities, and in some very specific circumstances you aren't allowed to listen at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the time the restrictions only come into play when you divulge information you gained from listening to certain transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But there are also restrictions that disallow intercepting transmissions for one's personal gain, such as operating a taxi service, listening to the competitor's dispatcher, and acting on that information to gain a business advantage.  Alternately, there are restrictions on trying to obtain for-pay services without paying for them in certain circumstances, such as pay-tv, hold music services, and so forth even if they do not encrypt their transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While it's generally believed that listening to cellphone conversations is illegal, that is not generally true, and is not federally mandated. However, if you sell scanners you must restrict them from receiving in the cellular bands, for instance.  Also there are specific harsh penalties for divulging information you may learn from cellular transmissions. This makes it difficult to listen to them, or profit from listening, but doesn't necessarily make it directly illegal to listen to them.  There are additional restrictions on decoding digital transmissions, which may make it illegal with today's systems.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Local laws often make it illegal to listen to law enforcement transmissions in connection with a crime.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, Supreme Court rulings, FCC rules, federal laws, and local laws are open to some interpretation. The legality of listening to a particular transmission will depend on more information than you've provided.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.fcc.gov/guides/interception-and-divulgence-radio-communications&quot; rel=&quot;nofollow&quot;&gt;http://www.fcc.gov/guides/interception-and-divulgence-radio-communications&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-03-24T15:44:49.037" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1636" PostTypeId="1" CreationDate="2014-03-24T17:32:39.287" Score="4" ViewCount="3211" Body="&lt;p&gt;While researching how best to install my mobile amateur radio in my car, I didn't understand &#xA;&lt;a href=&quot;https://ham.stackexchange.com/q/1628/608&quot; title=&quot;Is there an optimum Antenna Feedline Length for mobile installations?&quot;&gt;if there was optimum Antenna Feedline Length for mobile installations?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Understanding that this is caused when common-mode currents make the feedline part of the antenna, I want to know &lt;strong&gt;if effectively grounding the antenna mount (coax shield) to the vehicle body will help mitigate common mode currents with mobile antenna installations?&lt;/strong&gt; (Effective meaning metal to metal under the trunk lip, and maybe an extra ground strap from trunk to car chassis.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My feedline does run inside the vehicle along the body panels, so it is definitely not a good place to work as a radiator element and I certainly wish to shorten the feedline and obtain the best SWR reading possible. I am using a small 1/4 wave 2M VHF antenna that also doubles as a 5/8 wave UHF antenna (primarily for the shorter height for underground parking).&lt;/p&gt;&#xA;" OwnerUserId="608" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-12-05T23:15:29.230" Title="Does effective grounding of mobile (vehicle) antenna mounts address common-mode currents?" Tags="&lt;mobile&gt;&lt;feed-line&gt;&lt;grounding&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1637" PostTypeId="1" CreationDate="2014-03-24T23:55:45.347" Score="9" ViewCount="5801" Body="&lt;p&gt;I would like to build my own HF (1.8 - 30 MHz) SWR meter, however I'm not sure how I can calibrate the meter without an accurate power source. I'm targeting a power capacity of 150 W so I can use it with my HF radio. However, my test equipment at hand does not include a directional wattmeter, and I wouldn't trust the power meter on my radio when the radio is turned off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a number of precision RF sources, but most of those don't exceed 1W in output power. I can get a good 100W+ 50Ω load, spectrum analyzers, and oscilloscopes, but nothing that I would really consider &quot;power RF&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I calibrate or validate my meter without an accurate power source or accurate directional wattmeter?&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="76" LastEditDate="2017-04-26T18:38:28.763" LastActivityDate="2017-04-26T18:38:28.763" Title="How can I calibrate a SWR meter?" Tags="&lt;diy&gt;&lt;measurement&gt;&lt;calibration&gt;&lt;swr-meter&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1638" PostTypeId="1" CreationDate="2014-03-25T02:47:18.973" Score="1" ViewCount="219" Body="&lt;p&gt;I'm starting to research building a multi-band antenna in the 1.9 gigahertz range.&#xA;I see them offered on wireless routers, and they use them in cellular sites.&#xA;Can anyone provide a reference or quick explanation of how they are constructed? Or, is it hype altogether, and the antennae are really only cut for one frequency, but the other frequencies have mediocre SWR?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the HF band, I've build and used trap dipoles that are multi-band, but I have the feeling that in the SHF range there may be a better/different approach.&lt;/p&gt;&#xA;" OwnerUserId="887" LastEditorUserId="76" LastEditDate="2014-03-25T03:03:57.253" LastActivityDate="2014-03-25T03:03:57.253" Title="Designs for a multi band vertical/collinear antenna for the 1.9 gigahertz range" Tags="&lt;antenna&gt;&lt;uhf&gt;" AnswerCount="0" CommentCount="3" ClosedDate="2014-03-25T21:15:52.913" ContentLicense="CC BY-SA 3.0" />
  <row Id="1639" PostTypeId="5" CreationDate="2014-03-25T10:04:19.870" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-03-25T10:04:19.870" LastActivityDate="2014-03-25T10:04:19.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1640" PostTypeId="4" CreationDate="2014-03-25T10:04:19.870" Score="0" Body="Tone squelch, or CTCSS (Continuous Tone-Coded Squelch System) is a mechanism by which the presence of a specific frequency in the transmitted audio is used to open a receiver squelch, rather than relying simply on the presence of a strong enough signal." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-03-25T10:04:19.870" LastActivityDate="2014-03-25T10:04:19.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1641" PostTypeId="2" ParentId="1492" CreationDate="2014-03-25T17:54:15.330" Score="4" Body="&lt;p&gt;After looking through things for quite some time, and asking around, I was able to find the following, assuming that I can get a copy of the signed certificate from somewhere. There is some more information at this &lt;a href=&quot;http://www.kd7uiy.com/2014/04/a-trusted-qsl-library-for-java.html&quot; rel=&quot;nofollow&quot;&gt;blog article&lt;/a&gt;, and this &lt;a href=&quot;https://github.com/kd7uiy/trusted-qsl&quot; rel=&quot;nofollow&quot;&gt;GitHub site&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The log file is done in a format called &lt;a href=&quot;http://www.rickmurphy.net/trustedqsl.org/&quot; rel=&quot;nofollow&quot;&gt;GAbbI (Global Amateur Interchange)&lt;/a&gt;. This file format is similar to ADIF, but not quite identical.&lt;/li&gt;&#xA;&lt;li&gt;The signature is performed using X.509 certificate handling.&lt;/li&gt;&#xA;&lt;li&gt;The station data is a field in the GAbbI format. &lt;/li&gt;&#xA;&lt;li&gt;The file is then gzipped, and uploaded to ARRL.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Bottom line is, following the specification given through the linked site is the best bet to getting this to work. X.509 is a standard library, and the GAbbI format is close enough to ADIF that it should be relatively easy to parse through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few things to note that are different from the GAbbI spec:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;All of the data for signing is upper case.&lt;/li&gt;&#xA;&lt;li&gt;The order of fields for the signed data is: CA_PROVINCE, CQZ, GRIDSQUARE, IOTA, ITUZ, US_COUNTY, US_STATE, BAND, BAND_RX, CALL, FREQ, FREQ_RX, MODE, PROP_MODE, QSO_DATE, QSO_TIME, SAT_NAME. Note that station comes first, then QSO data. &lt;/li&gt;&#xA;&lt;li&gt;There are several undocumented fields, including CA_PROVINCE, US_STATE, SIGNDATA, and SIGN_LOTW_V1.0. SIGNDATA is the data signed for the LOTW signature, SIGN_LOTW_V1.0 is the LOTW signature itself. CA__PROVINCE and US_STATE are the Canadian Province and US state.&lt;/li&gt;&#xA;&lt;li&gt;SIGN_LOTW_V1.0 has a :6 after the number of digits. I suspect this is related to the base 64 output.&lt;/li&gt;&#xA;&lt;li&gt;The max space per row is actually 64, not 72 as specified.&lt;/li&gt;&#xA;&lt;li&gt;The character count includes line breaks, and if there is any line breaks, it also counts the last line break. For a single line, it doesn't count the final line break.&lt;/li&gt;&#xA;&lt;li&gt;The signature is signed as SHA1withRSA.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-04-30T18:27:48.840" LastActivityDate="2014-04-30T18:27:48.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1642" PostTypeId="1" AcceptedAnswerId="1643" CreationDate="2014-03-26T03:38:15.530" Score="5" ViewCount="112" Body="&lt;p&gt;47 CFR § 97.507 states that:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(a) Each telegraphy message and each written question set administered to an examinee must be prepared by a VE holding an Amateur Extra Class operator license. A telegraphy message or written question set may also be prepared for the following elements by a VE holding an operator license of the class indicated:&lt;/p&gt;&#xA;&lt;p&gt;(1) Element 3: Advanced Class operator.&lt;/p&gt;&#xA;&lt;p&gt;(2) Elements 1 and 2: Advanced or General Class operators.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;If a VE team has (hypothetically) one Extra class VE and two Generals, cat the team administer all the elements or just the Technician test? Does the answer change if the Extra does all the work of generating the exams?&lt;/p&gt;&#xA;" OwnerUserId="125" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-03-26T11:16:17.407" Title="Must all three VEs hold the required licence class to &quot;prepare&quot; an examination, or just one?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;volunteer-examiners&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1643" PostTypeId="2" ParentId="1642" CreationDate="2014-03-26T11:16:17.407" Score="3" Body="&lt;p&gt;This answer is for valid for the US only:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;47 CFR § 97.507 addresses the preparation of the telegraphy message or the question set.  It does not directly address the testing session itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;47 CFR § 97.509 addresses the testing session.  Paragraph (b) states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(b) Each administering VE must:&lt;/p&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;(1) Be accredited by the coordinating VEC;&lt;/p&gt;&#xA;    &#xA;    &lt;p&gt;(2) Be at least 18 years of age;&lt;/p&gt;&#xA;    &#xA;    &lt;p&gt;(3) Be a person who holds an amateur&#xA;    operator license of the class specified&#xA;    below:&lt;/p&gt;&#xA;    &#xA;    &lt;blockquote&gt;&#xA;      &lt;p&gt;(i) Amateur Extra, Advanced or General Class in order to administer a Technician Class operator license examination;&lt;/p&gt;&#xA;      &#xA;      &lt;p&gt;(ii) Amateur Extra or Advanced Class in order to administer a General Class operator license examination;&lt;/p&gt;&#xA;      &#xA;      &lt;p&gt;(iii) Amateur Extra Class in order to administer an Amateur Extra Class operator license examination.&lt;/p&gt;&#xA;    &lt;/blockquote&gt;&#xA;    &#xA;    &lt;p&gt;(4) Not be a person whose grant of an amateur station license or amateur operator&#xA;    license has ever been revoked or suspended.&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Since all three VEs will need to sign section 2 of form NCVEC 605 then it would make sense that all 3 VEs would hold an operator license of the class indicated it 47 CFR § 97.509.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also found this in the [Volunteer Examiner Manual][1] published by the ARRL:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The three or more VEs required to oversee the separate examination area must each hold the appropriate class of FCC license as well as ARRL VE accreditation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So again, it seems that if you want to administer a test, you would need 3 VEs that hold an operator license of the class indicated it 47 CFR § 97.509.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[1]: &lt;a href=&quot;http://www.arrl.org/files/file/VEs/VE%20Manual%20Web%20FINAL%202013.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/files/file/VEs/VE%20Manual%20Web%20FINAL%202013.pdf&lt;/a&gt;, page 46.&lt;/p&gt;&#xA;" OwnerUserId="892" LastActivityDate="2014-03-26T11:16:17.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1644" PostTypeId="2" ParentId="1620" CreationDate="2014-03-26T11:33:59.713" Score="3" Body="&lt;p&gt;This is from post &lt;a href=&quot;https://groups.yahoo.com/neo/groups/FT897/conversations/messages/35317&quot; rel=&quot;nofollow&quot;&gt;35317&lt;/a&gt;, Jan 7, 2012 in the Yahoo Group for the FT-897:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;With reference to my post in December I have since had a word from Yaesu that the USER setting for menu items 65 to 70 is reserved for future use and not to be used. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="892" LastActivityDate="2014-03-26T11:33:59.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1645" PostTypeId="1" AcceptedAnswerId="1647" CreationDate="2014-03-26T17:47:01.060" Score="7" ViewCount="1531" Body="&lt;p&gt;Is it SSB or NFM or other type of modulation?&lt;/p&gt;&#xA;" OwnerUserId="353" LastEditorUserId="218" LastEditDate="2014-03-27T19:07:01.070" LastActivityDate="2014-03-27T19:07:01.070" Title="What should be the modulation when transmitting APRS signal?" Tags="&lt;modes&gt;&lt;aprs&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1646" PostTypeId="1" AcceptedAnswerId="1671" CreationDate="2014-03-26T18:12:36.970" Score="25" ViewCount="9148" Body="&lt;p&gt;I was reading about EchoLink and came across this rule under &quot;&lt;a href=&quot;http://echolink.org/access_policies.htm&quot;&gt;Access Policies&lt;/a&gt;&quot;:  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;2. No &quot;SWL&quot; (listen-only) access is permitted.  EchoLink is a two-way system by design, and there is no mechanism to validate listen-only stations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm pretty sure that by &quot;SWL&quot; they mean unlicensed/public access, but I'm not entirely sure, as I've read in several forum threads that it isn't appreciated when you connect to an repeater/node and don't identify or say something. I suppose this is because the EchoLink system announces when a remote user connects through the system, but doesn't necessarily announce the call of the connected station.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So is there any reason why I shouldn't use EchoLink to &quot;just listen&quot;? Or is this just a misconception/misunderstanding on my part?&lt;/p&gt;&#xA;" OwnerUserId="63" LastEditorUserId="63" LastEditDate="2014-03-26T23:59:19.013" LastActivityDate="2021-04-07T10:21:13.140" Title="Is &quot;just listening&quot; on EchoLink considered bad etiquette?" Tags="&lt;procedure&gt;&lt;echolink&gt;&lt;etiquette&gt;" AnswerCount="5" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1647" PostTypeId="2" ParentId="1645" CreationDate="2014-03-26T21:08:28.603" Score="9" Body="&lt;p&gt;APRS is a data transmission protocol and is independent of the underlying connection details. So there is no required modulation for the protocol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, the common implementation of APRS is FM modulated 1200 baud &lt;a href=&quot;http://en.wikipedia.org/wiki/AFSK#Audio_FSK&quot;&gt;AFSK&lt;/a&gt; in the 2m band.  Several major vendors like Yaesu and Kenwood support the protocol with built in functionality for APRS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There have also been implementations of the APRS protocol over &lt;a href=&quot;http://en.wikipedia.org/wiki/AX.25&quot;&gt;AX.25&lt;/a&gt; and &lt;a href=&quot;http://en.wikipedia.org/wiki/PSK31&quot;&gt;PSK31&lt;/a&gt; on HF frequencies as well.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-03-26T21:08:28.603" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1649" PostTypeId="1" AcceptedAnswerId="1658" CreationDate="2014-03-27T13:25:28.373" Score="4" ViewCount="1247" Body="&lt;p&gt;I fairly frequently get SWL reports via eQSL. I'm never quite sure what I should do with them. I know that eQSL has SWL capabilities, but I can never tell if I'm actually stating that a contact was one way, or two ways. What should I do? Here's the text, with the call changed (#= number, *= letter).&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;IZ####SWL   26Mar2014&#xA;Cfm ur QSO with IK#*** R-19 PSE QSL Vy 73 de Claudio &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="13" LastEditorUserId="76" LastEditDate="2014-03-30T21:27:43.377" LastActivityDate="2014-03-30T21:27:43.377" Title="How to mark SWL contacts on eQSL?" Tags="&lt;logging&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1650" PostTypeId="2" ParentId="1649" CreationDate="2014-03-27T13:39:52.210" Score="1" Body="&lt;p&gt;You just confirm them like you do regular contacts (check them and move to archive). The text on regular contacts states, &quot;This confirms our &lt;strong&gt;2-way&lt;/strong&gt; SSB QSO&quot;, so since the text on SWL contacts, it's all good.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-03-27T13:39:52.210" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1651" PostTypeId="1" AcceptedAnswerId="1653" CreationDate="2014-03-28T09:02:37.527" Score="1" ViewCount="139" Body="&lt;p&gt;Let's say I have three dipoles, one is resonant at some frequency and is matched at the antenna, the second is shortened with loading coals and is also matched at the antenna, the third is shortened but has no loading coils and is also matched at the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Supposing that all three are matched to 50 ohms and I use a short (ish) piece of coax to the antenna, how would they perform with regard to efficiency, gain, etcetera?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Assuming at least a half wavelength above ground at the same location, only one antenna installed at a time.&lt;/p&gt;&#xA;" OwnerUserId="135" LastEditorUserId="76" LastEditDate="2015-12-15T23:40:27.110" LastActivityDate="2015-12-15T23:40:27.110" Title="Comparing antenna effeciency" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;efficiency&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1652" PostTypeId="1" CreationDate="2014-03-28T12:55:43.647" Score="1" ViewCount="701" Body="&lt;p&gt;I have that problem currently with my HF transceiver: no power output at all in SSB and CW, no matter which band / Frequency, but everything is ok in AM, FM and RTTY...&#xA;There is also a big difference in current consumptions on TX: only about 4A in (not working) SSB and CW, about 20A in (working) AM, FM and RTTY...&#xA;Where should I look for the failure?&lt;/p&gt;&#xA;" OwnerUserId="899" LastEditorUserId="218" LastEditDate="2014-03-28T13:17:41.963" LastActivityDate="2014-04-02T07:45:19.233" Title="What denotes no RF output in SSB and CW?" Tags="&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2014-05-01T18:52:26.060" ContentLicense="CC BY-SA 3.0" />
  <row Id="1653" PostTypeId="2" ParentId="1651" CreationDate="2014-03-28T14:11:05.010" Score="3" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_efficiency&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna efficiency&lt;/a&gt; can be defined as the ratio of the radiation resistance to the total resistance of the antenna (radiation resistance, plus ohmic resistance of the antenna, plus ground losses, etc), normalized to the feedpoint impedance. If radiation resistance is the only resistance in the antenna, then it's 100% efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{efficiency} = \frac{R_\text{radiation}}{R_\text{radiation} + R_\text{ohmic} + R_\text{ground}+R_\text{any other kind}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Performing this calculation can be tricky since there are so many potential sources of loss which may not be thought of as a &quot;resistance&quot;, but can be expressed as such. Dielectric losses are a good example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Loading coils and matching networks are significant only to the extent that they introduce additional loss. Sources of loss might include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;resistive losses in the coils&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Magnetic_hysteresis&quot; rel=&quot;nofollow noreferrer&quot;&gt;magnetic hysteresis&lt;/a&gt; losses in the core material of inductors&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Dielectric_loss&quot; rel=&quot;nofollow noreferrer&quot;&gt;dielectric losses&lt;/a&gt; in capacitors&lt;/li&gt;&#xA;&lt;li&gt;unintentional near-field coupling to nearby lossy materials (mast, trees, etc)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Shortening the antenna tends to decrease the radiation resistance. This doesn't make the antenna less efficient itself: it just makes other losses more significant, since they are now a greater fraction of the effective total resistance of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It doesn't matter much if you use loading coils or &quot;some sort of matching network&quot;. Loading coils &lt;em&gt;are&lt;/em&gt; a matching network. If you take the loading coils out, your matching network, if at the feedpoint near where the loading coils would have been, will be an inductance of similar value. What matters is the losses you introduce with whatever matching technique you use. You can make very good loading coils that introduce no significant losses (fat, low resistance wire around a low-loss core like air), or you can make very poor coils that turn your antenna into a heater (very thin wire around a lossy iron core).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shortening a dipole has a very small effect on the radiation pattern. As the dipole becomes shorter, it becomes less like a half-wave dipole and more like a &lt;a href=&quot;http://www.antenna-theory.com/antennas/shortdipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hertzian dipole&lt;/a&gt;. Wikipedia provides &lt;a href=&quot;http://en.wikipedia.org/wiki/Dipole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;a nice graphical comparison of radiation patterns&lt;/a&gt;, with the half-wave dipole as a solid line, and the Hertzian dipole as a dashed line:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/PlRpR.png&quot; alt=&quot;comparison of dipole radiation patterns&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see, the half-wave dipole has a marginally higher &lt;a href=&quot;http://en.wikipedia.org/wiki/Directivity&quot; rel=&quot;nofollow noreferrer&quot;&gt;directivity&lt;/a&gt;, but they are close enough that for most practical concerns they can be considered identical.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-03-28T23:34:52.247" LastActivityDate="2014-03-28T23:34:52.247" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1654" PostTypeId="2" ParentId="1430" CreationDate="2014-03-28T23:02:36.620" Score="-1" Body="&lt;p&gt;Perhaps a better way to phrase the question is: What is the simplest antenna with which you can make DX contacts?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in southern California. Since last November, I have been using a 65-foot (21.3-meter) end-fed wire and a counterpoise consisting of five long wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna and counterpoise go to a balun outside of my shack. The balun feeds the signal into a 6-foot (2-meter) length of coax that goes to my antenna tuner. I use this arrangement to keep RF out of the shack and to keep the antenna from picking up RF noise from the house wiring and the shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My transmit power is usually 70 to 100W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus far, I have logged QSOs with the Island of Jersey, Sicily, Poland, France, and Germany on PSK31. Using CW, I have had QSOs with Japan, South Korea, Alaska, Yukon Territory (Canada).&lt;/p&gt;&#xA;" OwnerUserId="901" LastActivityDate="2014-03-28T23:02:36.620" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1655" PostTypeId="2" ParentId="1469" CreationDate="2014-03-29T21:31:11.330" Score="11" Body="&lt;p&gt;Requirements:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Less than $100&lt;/li&gt;&#xA;&lt;li&gt;Commercially available&lt;/li&gt;&#xA;&lt;li&gt;Better reception than stock antenna&lt;/li&gt;&#xA;&lt;li&gt;Excellent portability&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Recommendations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Nagoya NA-771&lt;/li&gt;&#xA;&lt;li&gt;Nagoya NA-701&lt;/li&gt;&#xA;&lt;li&gt;Tram 1185 (Vehicle)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Nagoya NA-771&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/CEVoY.png&quot; alt=&quot;Nagoya NA-771&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Cost: $11 on Amazon.com as of March 2014&#xA;Length: 396mm&#xA;Weight: 37g&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;h2&gt;Nagoya NA-701&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Q1l9q.png&quot; alt=&quot;Nagoya NA-701&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Cost: $10 on Amazon.com as of March 2014&#xA;Length: 211mm&#xA;Weight: 40g&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;h2&gt;Tram 1185&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/3wE8L.png&quot; alt=&quot;Tram 1185&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Cost: $16 (+7 for adapter) on Amazon.com as of March 2014&#xA;Length: 19 inches with magnet mount&#xA;Will require SMA female to UHF female RF adapter which is &#xA;$7 on Amazon.com as of March 2014&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/goYIB.png&quot; alt=&quot;Tram 1185&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any one of these would serve you well and all meet your requirements. You could even purchase all 3 and still be under the $100 budget!!!&lt;/p&gt;&#xA;" OwnerUserId="905" LastEditorUserId="905" LastEditDate="2014-03-31T06:28:17.087" LastActivityDate="2014-03-31T06:28:17.087" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1658" PostTypeId="2" ParentId="1649" CreationDate="2014-03-30T16:05:11.933" Score="0" Body="&lt;p&gt;The To line in the details will include a phrase something like &quot;Confirming SWL reception of JT65 QSO&quot;. If you see something like that, then you know you can correctly mark it, assuming that the contact info is in your log, of course.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-03-30T16:05:11.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1660" PostTypeId="1" AcceptedAnswerId="1661" CreationDate="2014-04-01T03:21:25.310" Score="5" ViewCount="2456" Body="&lt;p&gt;What is the difference between a scanner and a receiver?&lt;/p&gt;&#xA;" OwnerUserId="353" LastEditorUserId="76" LastEditDate="2015-01-06T22:53:06.057" LastActivityDate="2016-06-06T19:35:29.860" Title="What is the difference between a scanner and a receiver?" Tags="&lt;receiver&gt;&lt;jargon&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1661" PostTypeId="2" ParentId="1660" CreationDate="2014-04-01T04:05:31.640" Score="8" Body="&lt;p&gt;&lt;strong&gt;A scanner is a specialized receiver&lt;/strong&gt; with features for effectively monitoring many frequencies, classically by tuning to each in rapid succession (scanning) and stopping when a signal is found, then continuing when the signal ends. The scan function can of course be disabled to use it as a receiver for a single channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Scanners as commonly discussed are typically used to monitor the communications of public safety services (police, fire department, etc.) because those organizations use many two-way radios on many channels transmitting intermittently. Modern scanners may include the ability to monitor “trunked” radio systems, which have a centralized control channel containing frequency allocations which the individual users' radios automatically follow; this is a feature which is generally unique to scanners as opposed to other types of receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, scanning is also an incidental feature on many digitally controlled receivers or transceivers — not what they're sold for, but a convenient extra.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;On amateur radio transceivers, scanning is useful to efficiently monitor many memorized local repeaters or simplex frequencies, or to continuously sweep across a HF band rather than having to spin the big knob by hand.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Car stereos have scan functions, which you can use when you're out of your usual area to find stations. In addition to an actual scan button, there's probably a function to find the next adjacent station, skipping over dead channels — this is also based on scanning.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-10-20T14:30:43.033" LastActivityDate="2014-10-20T14:30:43.033" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1662" PostTypeId="2" ParentId="1430" CreationDate="2014-04-01T06:09:41.890" Score="2" Body="&lt;p&gt;Tom N6BT reports accomplishg &quot;Worked All Continets&quot; on 10m CW using 120 watts and an incandescent light bulb as an antenna.&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2014-04-01T06:09:41.890" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1663" PostTypeId="1" CreationDate="2014-04-01T13:11:07.693" Score="3" ViewCount="608" Body="&lt;p&gt;I have bought the two devices in the image. The 100MHz Upconverter with a SMA connector is used to upconvert HF/MF signal for RTL-SDR to demodulate. I found that there is signal from the antenna (tested by using another radio), but I can detect no signal when connecting to upconverter. I think I have connected them wrongly. May you advice the way of connection?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The model of Antenna Loop is Degen 31MS. The up convertor information is located at &lt;a href=&quot;https://code.google.com/p/opendous/wiki/Upconverter&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://code.google.com/p/opendous/wiki/Upconverter&lt;/a&gt;  Mine is using 100MHz v1.0 version.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My method to connect is to try to use a small wire to connect the &quot;hole&quot; of SMA connector with the audio plug. I have tried to contact with different part of that audio plug, still no luck.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/OaaHX.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="353" LastEditorUserId="77" LastEditDate="2014-04-02T01:44:12.973" LastActivityDate="2014-04-02T13:13:52.297" Title="How to connect this Active Antenna Loop and 100MHz Upconverter?" Tags="&lt;hf&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="1664" PostTypeId="1" AcceptedAnswerId="1668" CreationDate="2014-04-01T21:34:19.587" Score="3" ViewCount="1301" Body="&lt;p&gt;I'm considering buying a vertical HF antenna (Such as the &lt;a href=&quot;http://www.cushcraftamateur.com/Product.php?productid=R-8&quot; rel=&quot;nofollow&quot;&gt;Cushcraft R8&lt;/a&gt;), and a tripod antenna stand, such as the &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-1918&quot; rel=&quot;nofollow&quot;&gt;MFJ-1918&lt;/a&gt;, and setting it up on my back porch when I'm operating (Which won't be all of the time. Is this a feasible idea, and if not, can you suggest an alternative? Also, what should I be aware of with such a set up (Weather related, for instance)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My plan is to set this up during contests and other periods where I'm wanting to make a lot of contacts, and take it down during the rest of the time. I'm planning on running the wires underneath the porch, but I'd like no visibility above the porch when I'm not operating ideally, and fairly minimal work to set up the mounting point. Odds are pretty good that I'll occasionally have it up overnight, but not for extended periods.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-04-02T12:54:32.077" Title="Antenna Tripod for a vertical antenna" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1665" PostTypeId="1" AcceptedAnswerId="1677" CreationDate="2014-04-02T06:15:30.177" Score="3" ViewCount="918" Body="&lt;p&gt;What are some softwares that can decode CW, AX25, RTTY, PSK etc? Hope that the softwares provided are freeware or open source.&lt;/p&gt;&#xA;" OwnerUserId="353" LastEditorUserId="353" LastEditDate="2014-04-03T01:35:43.700" LastActivityDate="2014-04-04T03:57:07.210" Title="Some softwares that can decode CW, AX25, RTTY, PSK etc" Tags="&lt;software&gt;" AnswerCount="2" CommentCount="5" ClosedDate="2014-05-03T11:20:00.477" ContentLicense="CC BY-SA 3.0" />
  <row Id="1666" PostTypeId="2" ParentId="1652" CreationDate="2014-04-02T07:45:19.233" Score="0" Body="&lt;p&gt;Ok, sorry for the lack of information (I'm the one who asked the question, but now I've signed up and I'm logged in). My TRX is Icom IC-751 (not the &quot;A&quot; version).&#xA;The SWR/ALC/Power... meter indicates zero (&quot;0&quot;) as soon as I push the PTT in SSB or CW.&#xA;The mic gain is set to max., the RF out is set at least on 10W everytime. What I've done until now: I've checked and new aligned the PLL, checked some voltages according to the service manual (widely available in internet) on the PLL board, logic board and a few on the main board. Everything seems to be ok, the RX is also very good on all bands, in all modes.&#xA;I'm not really sure if I really have to measure all the check points from the service manual, or I should limit the troubleshooting to the main board and (maybe) the RF board and that's why I have asked for some tips. &#xA;I'm not sure if I'm allowed to attach the pdf file of the service manual for the IC-751 here but, as we know, it is easy to find it on the net.&lt;/p&gt;&#xA;" OwnerUserId="924" LastActivityDate="2014-04-02T07:45:19.233" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1668" PostTypeId="2" ParentId="1664" CreationDate="2014-04-02T12:54:32.077" Score="0" Body="&lt;p&gt;My thoughts have improved, thanks to the ideas largely in the comments, to this.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The tripod should work for the start of a base, but it alone will not be good enough. Guide wires attached to the corner of the deck should be sufficient to keep the antenna vertical.&lt;/li&gt;&#xA;&lt;li&gt;A grounding wire placed under the deck should be kept in such a way that it can be attached to the mast of the antenna when it is in use.&lt;/li&gt;&#xA;&lt;li&gt;The antenna comes in 3 sections. I'm going to set up a storage location such that I can easily and safely store the antenna, without complete disassembling. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I still have a few details to work out, but I'm convinced this should work. Thanks for the input!&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-04-02T12:54:32.077" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1669" PostTypeId="2" ParentId="1663" CreationDate="2014-04-02T13:13:52.297" Score="2" Body="&lt;p&gt;Looking at the Google site you posted, it looks like this is the expected setup, so there probably isn't any gross incompatibilities, but I think you skipped looking at the large vector network analyzer graphs on the first page.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The upconverter is attenuating the signal by between 10dB and 76dB depending on the frequency.  Remember that dB is a logarithmic measure of the ratio of the signal strengths ($10 log_{10}$ $\frac{R_{output}}{R_{input}}$ in this case); therefore a 10dB attenuation means the output signal is $\frac{1}{10}$ as strong as the input signal and at 76dB attenuation, the signal would be less than $\frac{1}{1,000,000}$ as strong. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So assuming the input signal is something off the air that may not be that strong to start with and adding in the losses for the connectors and cabling, etc, the signal is probably below the detection threshold of the SDR.  Seems like an RF preamp might be called for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, the FAQ at the bottom mentions this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Why not add an amplifier to overcome the 10dB conversion loss? :&lt;/strong&gt; Since the &lt;a href=&quot;http://en.wikipedia.org/wiki/Noise_figure&quot; rel=&quot;nofollow&quot;&gt;Noise Figure&lt;/a&gt; of an RF system is most dependent on the Noise Figure of the first elements in the signal chain, it does make sense to place an &lt;a href=&quot;http://en.wikipedia.org/wiki/Low_noise_amplifier&quot; rel=&quot;nofollow&quot;&gt;LNA&lt;/a&gt; at the antenna port. I just wasn't sure if most users would have their Upconverter at their antenna.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-04-02T13:13:52.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1670" PostTypeId="2" ParentId="1183" CreationDate="2014-04-02T16:49:11.800" Score="0" Body="&lt;p&gt;You can vertically separate the two receiver vertically, one directly on top of the other.  The transmitter are very ineffective at transmitting directly above or below. Almost all the power is horizontal to the antenna. The next thing is to also use the 5Ghz band 802.11N/AC of WIFI if possible on one of the routers to further reduce interference. If you have to use 2.4 802.11B/G for both you can manually pick two channels that are the farthest apart in frequency.  &lt;/p&gt;&#xA;" OwnerUserId="925" LastActivityDate="2014-04-02T16:49:11.800" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1671" PostTypeId="2" ParentId="1646" CreationDate="2014-04-02T20:10:04.283" Score="21" Body="&lt;p&gt;The full access policy states (my &lt;strong&gt;&lt;em&gt;emphasis&lt;/em&gt;&lt;/strong&gt;):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;No &quot;SWL&quot; (listen-only) access is permitted.  EchoLink is a two-way system by design, and &lt;strong&gt;&lt;em&gt;there is no mechanism to validate listen-only stations&lt;/em&gt;&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The last part is key.  You can't use the echo link system without being a validated licensed amateur.  You logistically can not listen to this system without also being allowed to talk on it.  Contrast that with &quot;traditional&quot; short wave listeners.  Anyone can buy a radio and listen without being licensed to talk on it and there is no way technologically that you can prevent them from listening.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My interpretation of the policy is &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;We don't support a way for a non licensed station to listen only.&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I don't think that they mean that you aren't allowed to connect and not talk.  I hear stations connect to nodes regularly without saying anything.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps the policy would be clearer if it were written this way:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;No &quot;SWL&quot; (listen-only) &lt;strong&gt;&lt;em&gt;capability is supported&lt;/em&gt;&lt;/strong&gt;. EchoLink is a two-way system by design, and there is no mechanism to validate listen-only stations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="47" LastActivityDate="2014-04-02T20:10:04.283" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1672" PostTypeId="1" CreationDate="2014-04-02T23:29:53.140" Score="7" ViewCount="592" Body="&lt;p&gt;I work in an office building about 3 miles from my apartment. I live in a medium sized city in the US.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have thought about getting a pair of walkie talkies for communicating when the cell phone services are not working (I have experienced this), but from what I understand one should not expect to get more than 1 mile on those in a city.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is: What are realistic options for communicating during an emergency over a range of about 3 miles? I would like this to be a handheld option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By realistic I mean something that wouldn't cost more than $500 to establish.&lt;/p&gt;&#xA;" OwnerDisplayName="user926" LastEditorUserId="218" LastEditDate="2014-04-03T01:00:43.220" LastActivityDate="2014-05-14T20:34:07.163" Title="Options for family short range communication in an emergency" Tags="&lt;ht&gt;&lt;emergency&gt;&lt;frs&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1673" PostTypeId="2" ParentId="1672" CreationDate="2014-04-02T23:52:04.243" Score="2" Body="&lt;p&gt;There's 3 potential solutions to this.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Ham Radio. Granted you need a license, but it's free, so long as you take and pass a somewhat simple test. You could get several good radios for about \$140 each, or decent ones around \$35. They would easily work at the range of 3 miles. If you just want cell redundancy service, then these would work excellent via repeaters, where the range can be quite a bit further (I've talked with my HT to people as far as 40 miles away). &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.fcc.gov/encyclopedia/general-mobile-radio-service-gmrs&quot; rel=&quot;nofollow&quot;&gt;GMRS&lt;/a&gt;- This is very similar to FRS (Family Radio Service, most walkie-talkies fall in this category), but has 10 times the power, and thus should work about 3 times further. You do need a license to use this service, but it is inexpensive (\$85). You can buy a pair of radios for around \$60. This would be well in your budget. See also &lt;a href=&quot;http://en.wikipedia.org/wiki/General_Mobile_Radio_Service&quot; rel=&quot;nofollow&quot;&gt;Wikipedia&lt;/a&gt;. You would not need a license for emergency communications. Many of these radios are dual FRS/GMRS radios. Legally you can only use 0.5 W (FRS) without the GMRS license, but in an emergency you are allowed to use more.&lt;/li&gt;&#xA;&lt;li&gt;CB Radio- This should work fine as well, and doesn't require a license. The radios start around \$50, maybe a bit more for backup power systems as well. This system is crowded, and heavily abused, but is an option.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I would recommend the amateur radio approach, as it is the most robust, doesn't require an expensive license, and will definitely get you what you need.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-04-03T01:12:02.450" LastActivityDate="2014-04-03T01:12:02.450" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1674" PostTypeId="1" AcceptedAnswerId="2231" CreationDate="2014-04-03T01:28:53.597" Score="2" ViewCount="350" Body="&lt;p&gt;I just bought my first WRT54G (V3), and wanted to build a mesh network (Using the Broadband-ham firmware, &lt;a href=&quot;http://www.broadband-hamnet.org/&quot; rel=&quot;nofollow&quot;&gt;http://www.broadband-hamnet.org/&lt;/a&gt; , which as I understand is based on OpenWrt). I wasn't paying careful enough attention, and downloaded the firmware for the WRT54G v1, and burned it. I'm unable to get to any online documentation, and have been working my way though troubleshooting this. Here's what I can figure out.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;I can get the router into safe mode. I can't figure anything from there that's useful I can do, but I've done it.&lt;/li&gt;&#xA;&lt;li&gt;The router accepts pings on 192.168.1.1, giving a TTL code 100 if I start from the beginning, and 64 if in safe mode.&lt;/li&gt;&#xA;&lt;li&gt;I have this hooked up to a Windows 7 machine. I've tried using the TFTP software, but while it occasionally looks like it's trying to erase the firmware. It stays there for a few seconds, then it looks like it times out, and tries again.&lt;/li&gt;&#xA;&lt;li&gt;I've tried rebooting this while running a large loop on tftp.&lt;/li&gt;&#xA;&lt;li&gt;I've tried TFTP also when running in safe mode.&lt;/li&gt;&#xA;&lt;li&gt;I found that the error being reported is &quot;Code pattern is incorrect&quot;. Any idea what that means?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Any ideas about what else to try? I feel like I've almost got it figured out, but that last 10% is killing me... Thanks!&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-02-01T19:47:00.270" Title="Linksys WRT54G turned in to a brick" Tags="&lt;microwave&gt;&lt;mesh-network&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1675" PostTypeId="2" ParentId="1674" CreationDate="2014-04-03T13:42:31.897" Score="1" Body="&lt;p&gt;Ah, the mesh is taking the area by storm.  We had a demo at our club last month and folks are working on getting a few of these and starting up some nodes.  Flashing the router is probably the trickiest part. Fortunately, the Linksys routers have a long history of being reprogrammed and therefore there is a lot of info on this topic.  I would suggest starting with the excellent wiki at &lt;a href=&quot;http://www.dd-wrt.com/&quot; rel=&quot;nofollow&quot;&gt;DD-WRT.com&lt;/a&gt; that has a long article on &lt;a href=&quot;http://www.dd-wrt.com/wiki/index.php/Recover_from_a_Bad_Flash&quot; rel=&quot;nofollow&quot;&gt;unbricking&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="164" LastEditorUserId="1579" LastEditDate="2014-10-20T12:19:24.603" LastActivityDate="2014-10-20T12:19:24.603" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1676" PostTypeId="2" ParentId="412" CreationDate="2014-04-03T17:19:12.697" Score="2" Body="&lt;p&gt;You can build a special rig that will give you direction finding capability with a standard radio here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/1610/how-would-a-time-difference-of-arrival-with-two-antennas-know-which-side-the-sig&quot;&gt;How would a time-difference-of-arrival receiver with two antennas know which side the signal is from?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It works by switching between two antennas, located less than a wavelength apart.  If the two antennas are exactly the same distance from the transmitter, then the signal is undistorted into the radio, and you know the transmitter is perpendicular to the line between the antennas.  If the antennas aren't the same distance, then switching between the two introduces a phase modulation, which, on an FM receiver, results in a tone on top of the demodulated transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use this to locate the direction of the transmitter, move a mile, then do it again, and you'll locate the transmitter to within a very small area.  Then walk toward it with this setup and you'll soon find the offending transmitter.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-04-03T17:19:12.697" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1677" PostTypeId="2" ParentId="1665" CreationDate="2014-04-03T17:33:42.703" Score="3" Body="&lt;p&gt;MultiPSK will decode most of those, however AX25 itself is not a modulation scheme, it works at the data link layer, and doesn't specify the physical layer.  More importantly, other applications go on top of AX25 so decoding AX25 by itself isn't that useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While many &quot;all-in-one&quot; programs like MultiPSK exist, you may find better results with individual programs for individual modulation schemes, depending on your exact needs.  If you're just casually using them, they might be good enough, but if you're going for a specific use, feature, or need, then you may find specific programs for the one or two schemes you actually use will often have better support for that scheme.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-04-03T17:33:42.703" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1678" PostTypeId="2" ParentId="1665" CreationDate="2014-04-04T03:57:07.210" Score="5" Body="&lt;p&gt;fldigi is multi-platform and will decode many digital modes and has some rig control features available. Check at &lt;a href=&quot;http://www.w1hkj.com/Fldigi.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.w1hkj.com/Fldigi.html&lt;/a&gt; for more information.&lt;/p&gt;&#xA;" OwnerUserId="308" LastActivityDate="2014-04-04T03:57:07.210" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1679" PostTypeId="1" AcceptedAnswerId="1681" CreationDate="2014-04-04T04:40:02.817" Score="3" ViewCount="2380" Body="&lt;p&gt;My brother and I just got our technician class license. We live close enough to each other that we can use simplex on 2 meters or 440. How do we go about choosing the best frequency to use?&lt;/p&gt;&#xA;" OwnerUserId="905" LastEditorUserId="29" LastEditDate="2014-04-04T18:03:10.167" LastActivityDate="2014-04-04T18:03:10.167" Title="Choosing simplex frequency as a technician" Tags="&lt;united-states&gt;&lt;uhf&gt;&lt;vhf&gt;&lt;band-plan&gt;&lt;simplex&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1680" PostTypeId="2" ParentId="1679" CreationDate="2014-04-04T13:10:15.997" Score="2" Body="&lt;p&gt;The &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow&quot;&gt;ARRL band plan&lt;/a&gt; shows:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A band  plan refers to a voluntary division of a band to avoid interference between incompatible modes.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Listen through the simplex range of frequencies from the chart. Listen some more. If the frequency(ies) you choose are not in use, by all means throw your call out with &quot;Is this frequency in use?&quot; a few times - then go ahead and talk if no one else is using that frequency.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2014-04-04T13:10:15.997" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1681" PostTypeId="2" ParentId="1679" CreationDate="2014-04-04T13:20:05.660" Score="5" Body="&lt;p&gt;Ron points to the band plan and that's where you should start.  I've redacted it somewhat to the bands most appropriate for simplex work.  Note that depending on where you are, there might be large chunks of the repeater frequencies unused.  Or you could live between two major metropolitan areas like me where there are NO unallocated repeater pairs...If they are unallocated, you could work simplex there, just listen first.  I've included the simplex calling frequencies, areas around them often contain traffic (depending again on where you are).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2m&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;144.90-145.10    Weak signal and FM simplex (145.01,03,05,07,09 are widely used for packet)&lt;/li&gt;&#xA;&lt;li&gt;146.40-146.58    Simplex&lt;/li&gt;&#xA;&lt;li&gt;146.52   National Simplex Calling Frequency&lt;/li&gt;&#xA;&lt;li&gt;147.42-147.57    Simplex&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;70 cm&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;432.10   70-cm calling frequency&lt;/li&gt;&#xA;&lt;li&gt;432.10-432.30    Mixed-mode and weak-signal work&lt;/li&gt;&#xA;&lt;li&gt;432.40-433.00    Mixed-mode and weak-signal work&lt;/li&gt;&#xA;&lt;li&gt;445.00-447.00    Shared by auxiliary and control links, repeaters and simplex (local option)&lt;/li&gt;&#xA;&lt;li&gt;446.00   National simplex calling frequency&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-04-04T13:20:05.660" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1683" PostTypeId="5" CreationDate="2014-04-04T15:34:09.063" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2014-04-04T15:34:09.063" LastActivityDate="2014-04-04T15:34:09.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1684" PostTypeId="4" CreationDate="2014-04-04T15:34:09.063" Score="0" Body="Voice over IP is an umbrella term for technologies that enable two-way streaming of voice transmissions over an IP (Internet Protocol) link, as used on the Internet." OwnerUserId="174" LastEditorUserId="29" LastEditDate="2014-04-04T19:09:20.033" LastActivityDate="2014-04-04T19:09:20.033" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1685" PostTypeId="1" AcceptedAnswerId="1689" CreationDate="2014-04-06T21:04:08.357" Score="12" ViewCount="4270" Body="&lt;p&gt;I recently put up a fan dipole for 80/40/20/10. I'm looking for a way to share this antenna with a receive-only SDR and my shack transceiver. Obviously I can just switch this antenna between the two manually, but I was hoping there was a way to have both hooked up at the same time without transmitting into my SDR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a practical, cost effective way to accomplish this? It would be great to have a waterfall display of the entire band while I'm going at it.&lt;/p&gt;&#xA;" OwnerUserId="135" LastEditorUserId="76" LastEditDate="2015-12-15T22:02:48.250" LastActivityDate="2015-12-15T22:02:48.250" Title="Share antenna between receiver and transceiver?" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;antenna-system&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1686" PostTypeId="2" ParentId="1685" CreationDate="2014-04-07T15:36:12.230" Score="-3" Body="&lt;p&gt;For receiving, just a coaxial splitter should work, nothing fancy, just lead the antenna to both radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For transmitting, that is a different story, and bandpass filters are required, but on receive, interference should not be a problem. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-04-07T15:36:12.230" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1687" PostTypeId="1" CreationDate="2014-04-07T15:46:00.323" Score="3" ViewCount="685" Body="&lt;p&gt;I am going to do a simple SIMPLEX all-star node, using the URIx USB radio interface, which I just got. I have a Kenwood TM-241A transceiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was told the speaker out jack is not sufficient:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The goal is access to output not influenced by the radio squelch or&#xA;  volume controls.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I was also told that there are high-pass filters in many radios which will eliminate most CTCSS, so I can't use the CTCSS_DET pin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does the Kenwood tm-241a have a place in it I can find with discriminator out, which I could solder some audio wires to?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2016-10-29T18:57:39.370" LastActivityDate="2016-10-29T18:57:39.370" Title="Kenwood TM-241A direct discriminator out" Tags="&lt;diy&gt;&lt;equipment-design&gt;&lt;kenwood&gt;&lt;audio-interface&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="1688" PostTypeId="2" ParentId="1685" CreationDate="2014-04-07T17:41:13.980" Score="4" Body="&lt;p&gt;Without serious isolation, you will smoke the SDR the first time you transmit.  Typical (i.e., cheap) coax switches &lt;em&gt;suck&lt;/em&gt; at isolation.  If you are lucky it'll be 30 dB down.  That's still enough to smoke the SDR easily unless you are QRP.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only way that comes to mind is to make a relay that drops out the SDR when you key up your rig.  Most rigs have a signal line to key an amp up, you can use this signal to drive the relay.  Basically the inverse of the amp keying circuit.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-04-07T17:41:13.980" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1689" PostTypeId="2" ParentId="1685" CreationDate="2014-04-08T02:13:27.327" Score="8" Body="&lt;p&gt;Back in the olden days, before transceivers took over, the transmitter and receiver were separate units, and the receiver had to be protected from the transmitter. The solution then, as now, is an electronic T/R switch. One approach is an RF sensor that triggers a relay; the MFJ-1708 is one example. A more sophisticated approach uses an active element to isolate the receiver. Used to be a vacuum tube, and if you do a Google search you'll find lots of DIY TR switch projects for vintage radio fans.&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2014-04-08T02:13:27.327" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1692" PostTypeId="2" ParentId="1430" CreationDate="2014-04-09T15:29:23.927" Score="0" Body="&lt;p&gt;A magnetic loop antenna (magloop antenna for short) (&lt;a href=&quot;http://www.alexloop.com/&quot; rel=&quot;nofollow&quot;&gt;example&lt;/a&gt;) can be a good choice for high efficiency in a small size if it is designed well. &lt;/p&gt;&#xA;" OwnerUserId="956" LastEditorUserId="291" LastEditDate="2014-04-10T09:56:54.157" LastActivityDate="2014-04-10T09:56:54.157" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1693" PostTypeId="1" CreationDate="2014-04-10T11:17:55.193" Score="2" ViewCount="438" Body="&lt;p&gt;As advertised on websites of large manufacturers like &lt;a href=&quot;http://www.analog.com/en/rfif-components/rfif-amplifiers/adl5531/products/product.html&quot; rel=&quot;nofollow&quot;&gt;&lt;strong&gt;Analog Devices&lt;/strong&gt;&lt;/a&gt; And &lt;a href=&quot;http://www.ti.com/product/ths9001&quot; rel=&quot;nofollow&quot;&gt;&lt;strong&gt;Texas Instruments&lt;/strong&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am aware of the difference between an IF stage and an RF stage, however, I was curious if there was any any other differences. Say I have a 50-500MHz IF gain block, is it OK to either use it in a 200MHz IF stage of a Tx system, or (and this is my question) use it in a 200MHz RF stage of another system?&lt;/p&gt;&#xA;" OwnerUserId="801" LastEditorUserId="801" LastEditDate="2014-04-11T09:24:55.460" LastActivityDate="2014-07-01T02:17:10.893" Title="What is the difference between Rf Gain Blocks &amp; IF Gain Blocks?" Tags="&lt;amplifier&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1695" PostTypeId="1" CreationDate="2014-04-10T17:19:44.070" Score="16" ViewCount="17702" Body="&lt;p&gt;I have a Baofeng UV-5R HT radio that I have been using for about a month now and I really like it because it was very inexpensive and portable. It currently has the stock antenna on it and I have noticed that if I'm in more rural areas, I sometimes have trouble hitting some of the repeaters that are past 10-15 miles away. I've heard that an aftermarket antenna is a good way to get a little more transmitting range out of an HT, but I don't want to spend a lot of extra money on a radio that cost me $30. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After looking around, I have been thinking about getting the Nagoya NA-701 or NA-702 to replace the antenna (I know a lot of people recommend the NA-771, but it's just a little too long for me on such a small radio). A lot of people seem to feel that these antennas provide a good balance between performance, portability, and price for the Baofeng radios (plus they have a female SMA connector), but after looking some of the actual dB comparisons people have done I am not totally convinced that these antennas are much better than the stock antenna, since the numbers are so close. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/inzQE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/inzQE.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone know if there's any real noticeable difference (specifically in regards to transmitting) between the performance of the stock antenna and these Nagoyas? I like the size and price but if I'd have to go to something like the 771 to get any significant advantage, I think I would just save my money and accept the limitations of the stock antenna.&lt;/p&gt;&#xA;" OwnerUserId="962" LastEditorUserId="8832" LastEditDate="2017-09-26T01:53:06.587" LastActivityDate="2017-12-19T05:55:40.020" Title="Are there any real advantages to an aftermarket NA-701 over the Baofeng stock antenna?" Tags="&lt;antenna&gt;&lt;ht&gt;&lt;baofeng&gt;&lt;uv-5r&gt;" AnswerCount="8" CommentCount="8" FavoriteCount="1" ClosedDate="2017-12-19T14:13:12.910" ContentLicense="CC BY-SA 3.0" />
  <row Id="1697" PostTypeId="1" AcceptedAnswerId="1698" CreationDate="2014-04-14T17:13:41.917" Score="2" ViewCount="119" Body="&lt;p&gt;We all know that in general commercial activities are not welcome on amateur radio bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One thing that somewhat related to that came up in a discussion I had with some operators:&lt;br&gt;&#xA;Is it ethical to accept money for printing and sending QSL cards in return for mentioning a public or private enterprise on the card itself? Say for example &quot;X is friend of radio amateurs!&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to my sense of ethics, that would fit withing &quot;commercial activities&quot;, but some of the people disagreed, so I'm not so sure myself.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2014-04-14T18:50:52.837" Title="Is it ethical to accept sponsorship for QSL cards?" Tags="&lt;qsl-card&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1698" PostTypeId="2" ParentId="1697" CreationDate="2014-04-14T18:15:47.743" Score="6" Body="&lt;p&gt;It isn't that commercial activities are &lt;em&gt;unwelcome&lt;/em&gt; or &lt;em&gt;unethical&lt;/em&gt;, on amateur bands. Rather, it's that they are &lt;em&gt;illegal&lt;/em&gt;. The relevant rules in the USA are in &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.1.159.1&quot; rel=&quot;nofollow&quot;&gt;§97.1   Basis and purpose&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(a) Recognition and enhancement of the value of the amateur service to the public as a voluntary &lt;em&gt;noncommercial communication service&lt;/em&gt;, particularly with respect to providing emergency communications&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.1.159.2&quot; rel=&quot;nofollow&quot;&gt;§97.3   Definitions&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(4) Amateur service. A radiocommunication service for the purpose of self-training, intercommunication and technical investigations carried out by amateurs, that is, duly authorized persons interested in radio technique solely with a personal aim and &lt;em&gt;without pecuniary interest&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.2.159.7&quot; rel=&quot;nofollow&quot;&gt;§97.113   Prohibited transmissions&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(3) Communications in which the station licensee or control operator has a &lt;em&gt;pecuniary interest&lt;/em&gt;, including communications on behalf of an employer, with the following exceptions:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;While I'm not sure of the relevant legislation in your native Serbia, it's a fair bet that it's similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, these regulations are about the communications you make on the air. The FCC has no authority over what you put in the mail. It's a fair extrapolation of the intent expressed in §97.1 and elsewhere that the FCC's concern is commercial interests using the amateur service as a free alternative to commercial spectrum which would otherwise require an expensive license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many activities that &lt;em&gt;do&lt;/em&gt; have some pecuniary interest, related to amateur radio, but not taking place on the air. For example, &lt;a href=&quot;http://www.hamvention.org/&quot; rel=&quot;nofollow&quot;&gt;hamfests&lt;/a&gt; and &lt;a href=&quot;http://www.cq-amateur-radio.com/&quot; rel=&quot;nofollow&quot;&gt;magazines&lt;/a&gt;. Would anyone argue that these are unethical? I doubt it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, I don't see any argument for making a paid endorsement on a QSL card any different than &lt;a href=&quot;http://www.business.ftc.gov/documents/bus71-ftcs-revised-endorsement-guideswhat-people-are-asking&quot; rel=&quot;nofollow&quot;&gt;any other paid endorsement&lt;/a&gt;. Indeed, that can be an ethical minefield, but whether it's on your QSL card or your blog is largely irrelevant.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-04-14T18:39:20.997" LastActivityDate="2014-04-14T18:39:20.997" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1699" PostTypeId="2" ParentId="1697" CreationDate="2014-04-14T18:50:52.837" Score="3" Body="&lt;p&gt;As with many purely ethical questions, there is no canonical answer.  In the US, as far as my reading of the rules go, sponsorship is not illegal.  Most of the code of conduct type things I have seen (e.g., &lt;a href=&quot;http://www.dx-code.org/&quot; rel=&quot;nofollow&quot;&gt;DX Code of Conduct&lt;/a&gt;) are also silent on the issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;QSL cards are ancillary to the radio hobby and basically outside the purview of the rules.  The rules about commercial activity are about keeping the amateur airwaves focused on one-to-one conversation, not broadcast advertisements.  The cards are only going to specific people after you've made contact with them and then not over the air.  I don't see a conflict here with the rules are about commercial endeavors.  In fact, some of these amazing pictures undoubtedly serve (mostly unintentionally) to boost tourism.  I certainly have a few cards with views I would like to see in person :)&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-04-14T18:50:52.837" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1700" PostTypeId="1" AcceptedAnswerId="1701" CreationDate="2014-04-14T19:21:13.667" Score="10" ViewCount="2118" Body="&lt;p&gt;How does a tiny surface-mount &quot;chip antenna&quot; for the 2.x thru 5.x GHz frequency bands work?  What allows such a tiny item to radiate or receive RF with some amount of efficiency?  What allows a chip antenna's radiation pattern to be (somewhat?) non-directional compared to a wire antenna?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2015-12-15T21:57:16.460" LastActivityDate="2015-12-15T21:57:16.460" Title="How does a &quot;chip antenna&quot; work?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1701" PostTypeId="2" ParentId="1700" CreationDate="2014-04-15T18:16:03.287" Score="8" Body="&lt;p&gt;The chip antennas use some material, usually ceramic, that has high permittivity and low losses. In a medium having high permittivity, the wavelength is shorter than in the free space. This way the antenna &quot;sees&quot; the structure that is comparable in the size to the wavelength in the medium, while being very small compared to the free space wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While receiving, the antenna efficiency is not very crucial parameter since less efficient antenna receive less signal but also less noise from the environment. Thus the signal to noise ratio is the same at the output of the antenna. See the related questions:&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/382/what-is-the-relationship-between-swr-and-receive-performance&quot;&gt;What is the relationship between SWR and receive performance?&lt;/a&gt; and &lt;a href=&quot;https://ham.stackexchange.com/questions/1243/if-two-antennas-of-50-and-377-have-vswr-11-then-which-one-is-more-efficien&quot;&gt;If two antennas of 50 Ω and 377 Ω have VSWR=1:1, then which one is more efficient?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, small antennas tend to be less directive: for example, large dishes have higher gain than Yagis that, in turn, have higher gain than dipoles. Based on empirical googling, the chip antenna manufacturers seem to promise gains approximately in the range of 0...3 dBi. However, with high permittivity substrate you can achieve large gains as well: &lt;a href=&quot;http://iopscience.iop.org/1347-4065/53/4S/04EL09/article&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://iopscience.iop.org/1347-4065/53/4S/04EL09/article&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-04-16T04:26:27.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1702" PostTypeId="1" AcceptedAnswerId="1717" CreationDate="2014-04-16T13:05:11.043" Score="13" ViewCount="3453" Body="&lt;p&gt;We just had snow and ice overnight and my wire dipole was coated in ice. Why does the ice covering negatively affect the SWR of the antenna?&lt;/p&gt;&#xA;" OwnerUserId="152" LastEditorUserId="76" LastEditDate="2014-05-23T18:30:59.143" LastActivityDate="2017-02-14T13:46:59.373" Title="Why does ice on a wire dipole affect the SWR?" Tags="&lt;antenna&gt;&lt;impedance&gt;&lt;dipole&gt;" AnswerCount="4" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1703" PostTypeId="2" ParentId="1702" CreationDate="2014-04-16T15:43:06.713" Score="1" Body="&lt;p&gt;The increasing SWR means that some of the transmitted power is reflected back to your transmitter. There are several possible explanations for the effect:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The ice is not completely dry and it partially short circuits (through some resistance) the two arms of your dipole. This way the impedance seen at the feed port of the antenna is lower than it is meant to be making the matching worse.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The feed port and the dipole arms are properly insulated from the melting ice but there is still some conductance in the ice layer: this prevents the radiated field from being transmitted to the free space increasing the power reflected towards the transmitter. This would more or less correspond to a situation where you have a (poorly) conducting box around your antenna.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The third possible explanation is related to the reactive near fields surrounding the antenna (see the image below). The impedance of a dipole is determined by the radiation resistance, capacitance between dipole arms, and the inductance of the dipole wire. &lt;a href=&quot;https://ham.stackexchange.com/questions/1243/if-two-antennas-of-50-and-377-have-vswr-11-then-which-one-is-more-efficien/1245#1245%20%28See%20my%20answer%20to%20a%20related%20question%29&quot;&gt;(See my answer to a related question)&lt;/a&gt;. If you coat your dipole with ice ($\epsilon \approx 3$) the capacitance between the dipole arms is increased dragging the resonance frequency lower.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;It is not easy to say what is the correct explanation for this specific case. If you can plot the SWR as function of frequency with and without the ice and see a clear shift in the resonance frequency, number three would be my suspect. If the ice is near melting and the SWR is poor at all frequencies, the explanation 1 would be my guess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/c/c5/Felder_um_Dipol.svg/259px-Felder_um_Dipol.svg.png&quot; alt=&quot;Field around a dipole&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/File:Felder_um_Dipol.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://en.wikipedia.org/wiki/File:Felder_um_Dipol.svg&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-04-16T15:43:06.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1704" PostTypeId="2" ParentId="1702" CreationDate="2014-04-16T15:43:22.593" Score="0" Body="&lt;p&gt;Assuming we aren't worried about water intrusion into the center insulator or any of the feedline connections, any of which could raise the SWR, the increased SWR is probably due to water ice acting as an insulator on the wire antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This, of course, detunes the antenna.  The dielectric constant of normal wire insulation (polyethylene) is about 2.1 whereas water has a dielectric constant of about 5. This means the antenna is suddenly too long for the intended frequency because the velocity factor of the conductor is now higher than it was when the antenna was cut.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-04-16T15:43:22.593" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="1705" PostTypeId="2" ParentId="1695" CreationDate="2014-04-17T01:58:09.237" Score="9" Body="&lt;p&gt;Yes, the baofeng stock antenna is the worst antenna I have ever used. I have both.  The range on my 5W BaoFeng UV-5R, with the stock antenna is about 3 KM with direct line of sight and no obstacles, and get terrible audio reports and am unable to hit a repeater accurately any more than 2 km away.  With the NA-701, I get about 5 KM distance, with better audio reports, and no problems hitting repeaters 3-5 KM away.  Going up to a decent car-mobile antenna gets me up to 8 KM, and with a Yagi I can go 10+ KM at a cost of being highly directional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am only talking about my own personal results putting out 5 watts, on 2 meter simplex (no repeaters to help you out).  If you just want to hit the repeater and you live right underneath your favorite one, then perhaps you might like the stock antenna, but in my opinion it's rubbish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I spent $7.00 on a better antenna. Suit yourself.&#xA;I got slightly better results on 70 cm band with the rubber ducky, but still nothing good.  As a 2 HT rig, with the stock antenna, you had better expect serious limitations in your range. Your mileage may vary.  Again, dBi don't lie, the rest is opinion.&lt;/p&gt;&#xA;" OwnerUserId="643" LastEditorUserId="643" LastEditDate="2014-05-02T13:45:29.537" LastActivityDate="2014-05-02T13:45:29.537" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1706" PostTypeId="1" AcceptedAnswerId="1707" CreationDate="2014-04-17T22:39:24.323" Score="10" ViewCount="1662" Body="&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/R0s1X.jpg&quot; alt=&quot;Awesome Antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The description on the antenna says it is used for satellite communication, but it was taken in 1984. Is this an antenna style that is still in use? What is it called? What kind of gain should be expected? Is this a style used primarily or only for communications in space? It appears to be a Yagi style antenna strapped to a parabolic, but I've never seen anything like this, so that conclusion may be completely wrong. Any information or links would be awesome.&lt;/p&gt;&#xA;" OwnerUserId="815" LastEditorUserId="70" LastEditDate="2014-06-14T19:21:27.080" LastActivityDate="2017-05-16T23:36:38.410" Title="What kind of antenna has a spiral connected to a reflector like this picture?" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1707" PostTypeId="2" ParentId="1706" CreationDate="2014-04-17T23:54:18.337" Score="8" Body="&lt;p&gt;This is a &lt;a href=&quot;http://www.antenna-theory.com/antennas/travelling/helix.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;helical antenna&lt;/a&gt; (&lt;a href=&quot;http://en.wikipedia.org/wiki/Helical_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia link&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Configured in &lt;em&gt;axial mode&lt;/em&gt;, these are commonly used in microwave satellite communications (below a few GHz) where you need high gain and circular polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The circular metal part behind acts as a reflector element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not only used for space communications. You find similar antennas for directional data links (using WiFi or similar modes).&lt;/p&gt;&#xA;" OwnerUserId="830" LastEditorUserId="9493" LastEditDate="2017-05-16T23:36:38.410" LastActivityDate="2017-05-16T23:36:38.410" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1708" PostTypeId="2" ParentId="1706" CreationDate="2014-04-18T08:02:38.293" Score="7" Body="&lt;p&gt;I've built a helical antenna for 430-440MHz receive from mostly ordinary household items. It was sufficient to receive the FO-29 downlink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dimensions of the helix are determined by the center frequency. I think the helix you posted is larger in circumference than mine, and thus would have a lower center frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/9PpF8.jpg&quot; alt=&quot;436MHz Helix Antenna for use with Amateur Radio Satellites&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe gain is a bit lower than a yagi of the same length, but the helix is circularly polarized and so spin fading in satellite service is not an issue as it would be if a yagi or quad were used.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I chose a center frequency of 436MHz which gives wavelength of 68.8cm. From my notes I see that the design choices were 1.1 wavelengths for the helix circumference (75.7cm), and turn spacing to circumference ratio of ~0.23 (turn spacing 17.5cm). A generalization of Pythagoras' theorem can be used to give the wire length per helix turn as $\sqrt{75.7^2+17.5^2}=77.7\text{cm}$. I used white solid insulated 12 gauge copper wire marked every 1/3 of a turn with a bit of black wire tape to assist in attaching to the 3 supports. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These choices were influenced by various articles I had read on-line, but unfortunately I did not keep these links and the design notes are on notebook paper.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the reflector you need a circular metal plate, such as a pizza pan and to support the wire helix of radius ~12cm I used three bamboo poles arranged in an equilateral triangle with ~21cm side length.  Turn spacing is about ~17.5cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bamboo is an irregular material.  It is not straight, although you can find &quot;approximately straight&quot; pieces.  The bandwidth of the helix is wide and the design fairly tolerant of error, allowing for somewhat imprecise construction. &#xA;To increase the strength and rigidity of the support it is necessary to form some triangles with additional bamboo pieces.  It becomes almost like making bamboo triangular tower.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A helix antenna does not present 50 ohms without a tuning or matching section. &#xA;I remember reading somewhere that other builders had successfully used 1&quot; copper&#xA;strap, 1/4 wavelength, at an adjustable (but close) height above the reflector. &#xA;Create a few threaded holes in the reflector using a tap and then you can use plastic bolts and scrap plastic (like a consumer discount card) to hold the copper strap at an adjustable height.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;See also the &lt;a href=&quot;http://qrz.com/db/KI6CQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRZ page for KI6CQ&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2014-05-22T01:12:50.880" LastActivityDate="2014-05-22T01:12:50.880" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1710" PostTypeId="1" CreationDate="2014-04-18T14:25:01.530" Score="3" ViewCount="1503" Body="&lt;p&gt;I am thinking about putting up a 70cm repeater up on my High School, where they have a very tall roof. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the time It is ready to put it up, I want to make sure a frequency is reserved for the repeater. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Who do I contact / where can I get a frequency coordinated for the repeater?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am located in Denver, Colorado, USA.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2014-05-08T14:56:48.940" LastActivityDate="2019-11-20T07:00:31.773" Title="How do I get a coordinated frequency assigned for my repeater?" Tags="&lt;united-states&gt;&lt;repeater&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1711" PostTypeId="2" ParentId="1256" CreationDate="2014-04-18T16:03:59.270" Score="0" Body="&lt;p&gt;CWCOM by MRX software, &lt;a href=&quot;http://www.mrx.com.au/d_cwcom.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.mrx.com.au/d_cwcom.htm&lt;/a&gt; can be used with a straight or iambic key.. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do not have a 9 pin serial port ( as most laptops do not ).. you will need to buy a USB to Serial Adapter cable...( Like this ...  &lt;a href=&quot;https://h10003.www1.hp.com/digmedialib/prodimg/lowres/c00618023.jpg&quot; rel=&quot;nofollow&quot;&gt;https://h10003.www1.hp.com/digmedialib/prodimg/lowres/c00618023.jpg&lt;/a&gt; ) can be found on ebay . and also a DB9 plug or socket ( depending on the one on the adapter) to connect your key to it.  It is pretty straight forward. but you might need to set the COMPORT number in devices. There is a good &quot;help&quot; page provided . You do not need a ham licence to use it.  It works in Windows up to WIN 7 32 bit... 64 bit windows is tricky. It can be made to work on Linux OS... I did get it to work on Linux Mint 16 &lt;/p&gt;&#xA;" OwnerUserId="982" LastActivityDate="2014-04-18T16:03:59.270" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1713" PostTypeId="2" ParentId="1710" CreationDate="2014-04-18T18:47:42.880" Score="3" Body="&lt;p&gt;I see you're from the United States based on your call sign, so let me answer the question for the US first, and then let me give a few indicators as to how you might do this across the world. In the United States, repeater frequencies are coordinated by a body known as the &lt;a href=&quot;http://nfcc.us/&quot; rel=&quot;nofollow&quot;&gt;National Frequency Coordination Council&lt;/a&gt;. Visiting their web site, you can find a frequency coordinator for your given state. Talk to the frequency coordinator, and make sure you are operating on the correct frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for outside of the United States, you need to either consult your government, or look for a similar frequency coordination council.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-04-18T18:47:42.880" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1714" PostTypeId="5" CreationDate="2014-04-18T21:27:31.267" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-04-18T21:27:31.267" LastActivityDate="2014-04-18T21:27:31.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1715" PostTypeId="4" CreationDate="2014-04-18T21:27:31.267" Score="0" Body="Use this tag for questions relating specifically to the amateur radio UHF allocation around 430 MHz." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-04-18T21:27:31.267" LastActivityDate="2014-04-18T21:27:31.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1716" PostTypeId="1" AcceptedAnswerId="1745" CreationDate="2014-04-19T02:06:34.517" Score="8" ViewCount="185" Body="&lt;p&gt;I'm working on tracking down some 2m repeater interference, and I have identified that the offending signal is a spur transmission on a commercial pager service (that lands right on our repeater input frequency). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How would I identify regulations that the commercial transmitter should be observing, to verify that their equipment is operating properly, or what are the regulations for a commercial transmitter? (For the purposes of this question, I'm located in the USA)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To measure the spur signal, I plan on using a spectrum analyzer to measure the relative magnitude from the fundamental frequency to the spur. I will use an antenna to observe the signal from off-site. Are there potential issues with this method?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm interested in this approach out of curiosity on whether this is a viable option, not because it is currently necessary.&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="76" LastEditDate="2020-02-15T17:02:03.970" LastActivityDate="2020-02-15T17:02:03.970" Title="Identifying regulations for interfering stations" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;rfi&gt;&lt;repeater&gt;&lt;spectrum-analyzer&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1717" PostTypeId="2" ParentId="1702" CreationDate="2014-04-19T12:14:19.803" Score="3" Body="&lt;p&gt;A heavy coating of ice or snow is likely to short the feedpoint of the antenna. Compare:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/KgdBy.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fKgdBy.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if the wires and feedpoint are protected by insulation and the ice isn't directly touching, a thick coating of ice will make a tube around the wires, and the resulting capacitive coupling is a low impedance at RF. (ANT3)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Snow or ice isn't a great conductor, but it's a much better conductor than the air or PTFE insulator that was between the halves of the antenna. Clearly the antenna impedance, and thus the SWR, will be affected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The change in temperature, dielectric constant, and other things mentioned in other answers do affect the antenna impedance, but not to a very significant degree. I'd wager that 80% of the times you sit down in the morning after a storm to find the SWR is all messed up, it's because there's water in the feedpoint. The other 20% of the time, it's because the antenna is sagging into a tree or the ground or broken from the additional weight.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-04-19T12:21:42.193" LastActivityDate="2014-04-19T12:21:42.193" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1718" PostTypeId="1" CreationDate="2014-04-20T13:10:24.683" Score="0" ViewCount="6939" Body="&lt;p&gt;Small lot, must go vertical.&lt;br&gt;&#xA;Which antenna will preform better, with less noise, good DX.&#xA;Cushcraft R9, &lt;strong&gt;NO&lt;/strong&gt; ground radials.  Or, 43' &lt;strong&gt;with&lt;/strong&gt; ground radials.&lt;/p&gt;&#xA;" OwnerUserId="988" LastEditorUserId="70" LastEditDate="2014-04-21T13:42:23.847" LastActivityDate="2016-06-17T19:20:14.683" Title="Vertical Antennas: Compare Cushcraft R9, no radials to 43 foot vertical with ground radials" Tags="&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1719" PostTypeId="2" ParentId="1718" CreationDate="2014-04-20T20:14:45.847" Score="1" Body="&lt;p&gt;&lt;strong&gt;31 foot R9&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;+&lt;/strong&gt;: work parts of 80m and ham bands 40m-6m without a tuner&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;-&lt;/strong&gt;: 25 lbs, top heavy, requires guys, complex assembly compared to simple vertical.  Probably mediocre on 80m compared to dipole, inverted V, or full size vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;43 foot vertical with radials&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;+&lt;/strong&gt;: theoretically superior on 40m (7Mhz), with &quot;enough&quot; radials.  Should be good on higher frequencies when used with an autotuner at the antenna.  Easy to understand and assemble.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;-&lt;/strong&gt;:  Requires autotuner for higher bands.  Might be difficult to tune on exact even harmonics.  Probably mediocre and perhaps not tunable on 80m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Additional Info:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The benefit of the R9 is that you will be able to work various bands from 80m through 6m without an autotuner.  The R9 does use shortened radials and other parts that protrude horizontally.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Cushcraft R9 claims it will &quot;work&quot; all ham bands 6m-80m.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking at the &lt;a href=&quot;http://www.cushcraftamateur.com/Downloads/index.php?productid=R-9&amp;amp;filename=R-9.pdf&amp;amp;company=cushcraft&quot; rel=&quot;nofollow&quot;&gt;R9 assembly instructions&lt;/a&gt;,  here are some facts about the design that you should consider:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;multiple loading coils, capacitance hats, and shortened radials are used to present a reasonable SWR on the different bands.  It is more complex to assemble than the 43 foot vertical but will work more bands without an autotuner.&lt;/li&gt;&#xA;&lt;li&gt;It is only 31 feet tall, but weighs 25 lbs&lt;/li&gt;&#xA;&lt;li&gt;It can not perform as good as a 1/4 wave on 40m (7Mhz) or 80m (3.5-4Mhz) because it is not 1/4 wave long.  &lt;/li&gt;&#xA;&lt;li&gt;It has a top heavy, wind catching section.  &lt;/li&gt;&#xA;&lt;li&gt;The manual requires guying to achieve an 80mph wind survival rating&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Eham only had 7 reviews, with some satisfied and dissatisfied customers.  See &lt;a href=&quot;http://www.eham.net/reviews/detail/11280&quot; rel=&quot;nofollow&quot;&gt;http://www.eham.net/reviews/detail/11280&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 43 foot vertical with ground radials could be an excellent 1/4 wave vertical antenna for 7Mhz/40m.  It may be usable on higher frequency bands with an antenna tuner, though it could be hard to tune on exact even harmonics in the 14Mhz and 28Mhz bands because exact 1/2 wave verticals have very high impedance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible to have a 43 foot vertical made of lightweight nested aluminum poles or as a wire laid out on a set of thin nested plastic or fiberglass poles and it will not weigh 25 lbs and will not be top heavy and might not need guying.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Other Options&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use a vertical dipole cut for ~20m that also works on all higher HF frequencies.  It is a half wave antenna with the vertical radiator cut in the middle and fed with ladder line.  The ladder line goes into a balun just outside the home to run coax under a door frame, and is matched with the autotuner in the radio a few feet away. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also use an 80m spiral wound antenna. This is a low bandwidth design that needs a tuner and/or antenna measurements to get good results.  Like all shortened antennas it is mediocre, but I have worked Europe with it from the southeast US.  Wind ~1/2 wavelength of wire (~130 feet) on a fiberglass pole and add a capacitance hat on top.  I used about 16-20 feet of 2 inch fiberglass and inserted toothpicks every 0.75=3/4 inches to help space the turns.  Got this design from an ARRL Antenna book.   &lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2014-04-20T20:26:23.097" LastActivityDate="2014-04-20T20:26:23.097" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1721" PostTypeId="1" CreationDate="2014-04-21T23:38:37.587" Score="1" ViewCount="987" Body="&lt;p&gt;What is the proper way to calculate or determine the amount of time between words (the key up of the last character of one word to the key down of the first character of the next word) when using Farnsworth timing?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When using the answered time for 18 WPM characters sent at 5 WPM overall, will this calculated time result in exactly 5 canonical &quot;words&quot; sent every minute?  Or more? Or less?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do hand key and paddle operators determine this inter-word delay time in actual over-the-air practice?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-04-21T23:50:06.023" LastActivityDate="2014-04-22T18:14:48.957" Title="Spacing between words in CW using Farnsworth timing?" Tags="&lt;procedure&gt;&lt;cw&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1722" PostTypeId="1" AcceptedAnswerId="2110" CreationDate="2014-04-21T23:49:49.163" Score="5" ViewCount="435" Body="&lt;p&gt;What are some characteristics, when sending CW, of a &quot;bad fist&quot;?  How bad can it get, typically, and still manage to communicate the message text sent to a human operator on the receiving end?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Contra-wise, what (slight?) variations from machine generated Morse Code are still considered as having a &quot;good fist&quot; (for a human operator)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or does machine generated Morse code have some characteristics of a bad fist as well?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-04-23T18:16:42.183" LastActivityDate="2014-09-10T22:21:15.573" Title="Characteristics of a &quot;bad fist&quot;?" Tags="&lt;procedure&gt;&lt;cw&gt;" AnswerCount="3" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="1724" PostTypeId="2" ParentId="1721" CreationDate="2014-04-22T18:14:48.957" Score="1" Body="&lt;p&gt;First of all, let's look at the best source I can find, &lt;a href=&quot;http://www.arrl.org/files/file/Technology/x9004008.pdf&quot; rel=&quot;nofollow&quot;&gt;ARRL's QEX article&lt;/a&gt; relating the desire to use Farnsworth for the W1AW broadcasts. Of interest is this quote:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;There is no standard for Farnsworth Timing.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That withstanding, here's the general rule:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The character speed should be at 18 WPM minimum. A standard word is 60 Morse units of measurement, 1 dit or spacing between characters. &lt;/li&gt;&#xA;&lt;li&gt;The characters are spaced out further than normal. Typical spacing is 3 Morse units, equivalent to a Dah.&lt;/li&gt;&#xA;&lt;li&gt;The words are spaced out. I would apply the same factor that is done to the characters to the words. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;In theory, the 5 canonical words should be sent out in exactly 1 minute with 18 WPM. I think some algorithms do this slightly differently, but that's okay too.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-04-22T18:14:48.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1725" PostTypeId="1" CreationDate="2014-04-23T14:49:40.270" Score="1" ViewCount="79" Body="&lt;p&gt;I know that some amateur radio are using some frequencies that are reflecting on the ionosphere to transmit data over super long distances. I am wondering if it is possible, without an insane lot of power and with relatively portable antenna (on a reduced model of boat that would be about 2*3 meters) to transmit data in this way over at least 7500 kilometers ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT : Finally, the boat might be smaller : 1.6 meters on 0.6 meters. This boat might have an AI so I think that it wouldn't be that problematic if the connection was lost at some moments. The minimum of data to transmit is instructions for the boat to tell it where to go, but it would be great to transmit photos and videos. I am not a licensed amateur radio operator.&lt;/p&gt;&#xA;" OwnerUserId="1000" LastEditorUserId="1000" LastEditDate="2014-04-23T18:29:37.523" LastActivityDate="2014-04-23T18:29:37.523" Title="What is the best solution to transmit data by the ionosphere over at least 7500 km?" Tags="&lt;ionosphere&gt;" AnswerCount="1" CommentCount="3" ClosedDate="2014-05-01T00:17:52.680" ContentLicense="CC BY-SA 3.0" />
  <row Id="1726" PostTypeId="2" ParentId="1725" CreationDate="2014-04-23T15:13:40.280" Score="2" Body="&lt;p&gt;With your project, is it necessary to always have the ability to communicate? Or can you batch up your data and wait for the conditions to be suitable and transmit back a batch of data? A little more information about your project and the type of data you wish to transmit may be helpful in answering this question (or even determining if amateur radio is suitable at all). Consider &lt;a href=&quot;https://ham.stackexchange.com/posts/1725/edit&quot;&gt;editing your question&lt;/a&gt; to include more detail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF propagation varies dramatically from non-functional to miraculous depending on all sorts of conditions: time of day, solar activity, weather, etc. You can compensate for less than perfect conditions with more power, better antenna, more directional antennas, antenna elevation, etc. But its hard to make any recommendation without knowing more about your project.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are you already a licensed amateur radio operator? If not, I'd highly suggest you begin the process! You will start learning about radio functionality including propagation and can start experimenting with various radios and antennas.&lt;/p&gt;&#xA;" OwnerUserId="608" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-04-23T15:13:40.280" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1727" PostTypeId="1" AcceptedAnswerId="1728" CreationDate="2014-04-24T05:56:29.437" Score="3" ViewCount="544" Body="&lt;p&gt;As I own a PL-660, I saw a &lt;a href=&quot;http://www.it9ybg.altervista.org/index_files/Tecsun.htm&quot; rel=&quot;nofollow&quot;&gt;post&lt;/a&gt; that 455kHz IF signal can be obtained by connecting a wire to the board.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wonder, if I can tune to any signal by using this IF signal by SDR? And what are some common usage of this signal?&lt;/p&gt;&#xA;" OwnerUserId="353" LastEditorUserId="353" LastEditDate="2014-04-24T14:19:53.473" LastActivityDate="2014-04-24T14:19:53.473" Title="How can I use the 455kHz IF signal?" Tags="&lt;equipment-design&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1728" PostTypeId="2" ParentId="1727" CreationDate="2014-04-24T12:27:16.030" Score="4" Body="&lt;p&gt;Your radio, as most modern radios, is a &lt;a href=&quot;http://en.wikipedia.org/wiki/Superheterodyne_receiver&quot; rel=&quot;nofollow&quot;&gt;superheterodyne receiver&lt;/a&gt;. These receivers work by first converting the intended signal to a fixed intermediate frequency (IF, 445kHz in your case) then demodulating that. This is in contrast to a &lt;a href=&quot;http://en.wikipedia.org/wiki/Direct-conversion_receiver&quot; rel=&quot;nofollow&quot;&gt;direct conversion&lt;/a&gt; receiver, which demodulates the signal directly, without first converting it to an IF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The superheterodyne design has a number of advantages, mostly due to the fact that much of the filtering and demodulation is done at a single frequency and so does not need to be tunable. For example, this allows crystal filters to be used, which can be very stable but can't be tuned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since whatever frequency to which you tune your receive is first converted to the IF, which is always the same frequency, if you can feed the IF to as SDR, then the SDR can see anything you can tune on the receiver. Essentially, you are replacing the demodulator of your receiver with an SDR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantage here is that many cheaply available SDRs lack all the filters or the tuning range necessary to get the band coverage available in many receivers. Using an SDR at the IF allows one to use the radio for tuning, but use the SDR for demodulation.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-04-24T12:27:16.030" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1729" PostTypeId="1" AcceptedAnswerId="1742" CreationDate="2014-04-24T22:15:14.533" Score="8" ViewCount="3758" Body="&lt;p&gt;When I was at a local radio club today, I witnessed a bit unusual response by a station calling CQ using &lt;strong&gt;BPSK31&lt;/strong&gt;, that is to say phase-shift keying, not the regular A1A telegraphy, on the 20 meter band.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The communication looked something like this:&lt;br&gt;&#xA;&lt;code&gt;CQ CQ CQ DE XYZ1ABC CQ CQ CQ DE XYZ1ABC PSE K&lt;/code&gt;&lt;br&gt;&#xA;&lt;code&gt;XYZ1ABC DE ABC2XYZ KN&lt;/code&gt; -- our reply&lt;br&gt;&#xA;&lt;code&gt;ABC2XYZ DE XYZ1ABC SK SK&lt;/code&gt; -- their reply  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After a minute or so of pause, the station called CQ again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rest of the guys at the club weren't sure what the other station meant by SK so we interpreted it as not being interested in a contact and moved on. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Objectively looking, the other station had no reason why not to be interested: Looking at the last few months of the log, there weren't any contacts with it. It wasn't calling DX or any specific territory and the distance was reasonably large, in the range of 3000 km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is: Is the interpretation of &lt;code&gt;SK&lt;/code&gt; as used here correct? Is there some standard response to such a reply?&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2016-08-30T14:02:06.723" LastActivityDate="2016-08-30T23:27:15.833" Title="What does sending SK after calling CQ mean?" Tags="&lt;digital-modes&gt;&lt;procedure&gt;" AnswerCount="7" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1730" PostTypeId="1" AcceptedAnswerId="1749" CreationDate="2014-04-24T23:19:32.157" Score="3" ViewCount="189" Body="&lt;p&gt;What is the largest, and what were the dimensions of the largest amateur radio designated satellite in Earth orbit as of, or up until, 2014 other than the International space station.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2014-05-01T20:14:38.010" LastActivityDate="2014-05-01T20:14:38.010" Title="What is the largest amateur satellite in orbit through 2014?" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1735" PostTypeId="2" ParentId="1729" CreationDate="2014-04-25T19:40:53.567" Score="2" Body="&lt;p&gt;When I have seen &lt;code&gt;SK&lt;/code&gt; used in CW it's meant &lt;code&gt;Straight Key&lt;/code&gt;.  Those whacky guys like to talk to other whacky guys, I guess :)&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-04-25T19:40:53.567" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1736" PostTypeId="2" ParentId="1729" CreationDate="2014-04-25T20:03:44.307" Score="4" Body="&lt;p&gt;SK generally means &quot;silent key&quot; meaning the conversation is over.  &lt;/p&gt;&#xA;" OwnerUserId="308" LastActivityDate="2014-04-25T20:03:44.307" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1737" PostTypeId="1" AcceptedAnswerId="1739" CreationDate="2014-04-26T04:50:07.883" Score="8" ViewCount="1194" Body="&lt;p&gt;When I took my Technician test some 20 years or so ago, we had to memorize the phonetic alphabet, which I think is the same one used in the military. I was taught that it was international, similar to morse code. It used words such as &quot;Mike&quot; for the letter &quot;M&quot; and &quot;Juliet&quot; for the letter &quot;J&quot; and &quot;Zulu&quot; for the letter &quot;Z&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On VHF, I hear these used almost exclusively, but I recently passed my General class exam and started getting on HF and listening to both local and DX stations use words like &quot;Mary&quot; for &quot;M&quot; and &quot;Japan&quot; for &quot;J&quot; and &quot;Zed&quot; for &quot;Z&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there really a standard or do people just make up their own? It has caused me quite a bit of confusion since I hear stations use words like &quot;Japan&quot; and I am not sure if they are using phonetics or whether they are actually in Japan.&lt;/p&gt;&#xA;" OwnerUserId="687" LastActivityDate="2015-04-16T15:03:21.240" Title="Is there a &quot;proper&quot; phonetic alphabet to use with voice communications?" Tags="&lt;procedure&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1738" PostTypeId="2" ParentId="1737" CreationDate="2014-04-26T05:43:49.100" Score="4" Body="&lt;p&gt;The FAA and ICAO document a standard phonetic alphabet to be used for all aviation radio communication.  See: &lt;a href=&quot;http://en.wikipedia.org/wiki/NATO_phonetic_alphabet&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/NATO_phonetic_alphabet&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-04-26T05:43:49.100" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1739" PostTypeId="2" ParentId="1737" CreationDate="2014-04-26T10:19:05.060" Score="8" Body="&lt;p&gt;There are two standard phonetic alphabets, the NATO/ICAO alphabet, and the Western Union alphabet. A table can be found &lt;a href=&quot;http://www.osric.com/chris/phonetic.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; of them. The one that should be used is the NATO/ICAO alphabet, it's what is desired for emergency communications, traffic passing, etc, but occasionally the Western Union can be good to give your call sign if desired. The military phonetic alphabet is also commonly used, and in fact is probably more common than the Western Union, although there are &lt;a href=&quot;http://usmilitary.about.com/od/theorderlyroom/a/alphabet.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;multiple military versions&lt;/a&gt;. Here's yet another &lt;a href=&quot;http://www.sckans.edu/~sireland/radio/code.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;commonly used list&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reference, NATO is the Alpha-Bravo-Charlie, and that is the one that you should learn if anything. Learn to recognize the other ones at least, as you will hear plenty of them. And remember &lt;a href=&quot;http://xkcd.com/927/&quot; rel=&quot;nofollow noreferrer&quot;&gt;how multiple standards are created&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Uxxph.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-04-26T10:19:05.060" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1741" PostTypeId="2" ParentId="1737" CreationDate="2014-04-28T06:47:21.777" Score="2" Body="&lt;p&gt;Check Ethic and Operating Procedures for the Radio Amateur (&lt;a href=&quot;http://www.ham-operating-ethics.org/files/1-Eth-operating-EN-IARU-R1-V3-CORR-2011.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.ham-operating-ethics.org/files/1-Eth-operating-EN-IARU-R1-V3-CORR-2011.pdf&lt;/a&gt;). Page 65 shows international spelling and phonetic alphabet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That one you should use when making contacts World wide. However, no one will object if you use some other spelling standard as long as it is doing it's job - making other side better understand. For example, it is not good to use &quot;Canada&quot; instead of &quot;Charlie&quot;, as &quot;Canada&quot; sounds like having &quot;K&quot; as the first letter. For people who do not speak English natively that is confusing. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes, when other operator has hard time to get your spelling it is good to use different spelling, as different sounding might better get through noise. I noticed that sometimes people have problems recognizing &quot;Tango&quot; in my call as it sounds soft, so if I have to repeat I try using &quot;Tokio&quot; which sounds more harsh and seems to help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, if you know spelling in mother language of operator you are in QSO with, that could really help, not just in making better understanding, but people generally like to find out that others are speaking their language. That is a good way to make people remember you and to start friendship.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2014-04-28T06:47:21.777" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1742" PostTypeId="2" ParentId="1729" CreationDate="2014-04-28T06:53:48.390" Score="4" Body="&lt;p&gt;I guess that means other operator was just rude. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If contact with you was not interesting for him, he should show respect by exchanging report and making quick contact, as, maybe, contact might be important for you.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2014-04-28T06:53:48.390" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1743" PostTypeId="2" ParentId="936" CreationDate="2014-04-28T15:18:53.450" Score="2" Body="&lt;p&gt;I would opt for the &quot;solder and shrink&quot; and just go on with it. Like you I worried about this problem and decided to do some &quot;basic research&quot; while I had access to proper instruments. What I found was that the use of &quot;dirty patches&quot;, &quot;wrong impedance connectors&quot; and even unshielded joints (twisting the shield braid into a single conductor) made no measurable difference in signal. &#xA;&lt;strong&gt;Note to all who are about to flame me&lt;/strong&gt;: If you disagree, TRY IT before you judge! Do the tests yourself and post the results!&lt;/p&gt;&#xA;" OwnerUserId="1015" LastActivityDate="2014-04-28T15:18:53.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1744" PostTypeId="2" ParentId="1687" CreationDate="2014-04-28T15:48:14.477" Score="2" Body="&lt;p&gt;Typically a good place to get discriminator audio is the &quot;high&quot; end of the squelch control.   Unfortunately the TM-241A does not have a conventional squelch control, making it necessary to tap onto the board itself. &#xA;Pin 9 of IC1, an MC3372, is the output of the discriminator. If you can locate and solder to this pin it should give you the desired signal.&#xA;If at all possible you should check the signal with a scope before soldering to it.&lt;/p&gt;&#xA;" OwnerUserId="1015" LastEditorUserId="1015" LastEditDate="2014-05-08T20:52:46.963" LastActivityDate="2014-05-08T20:52:46.963" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1745" PostTypeId="2" ParentId="1716" CreationDate="2014-04-29T04:00:45.830" Score="2" Body="&lt;p&gt;Your method of measuring the spur signal is perfectly acceptable, and perhaps the best method for this scenario. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Search the FCC database for the transmitter owner that you suspect is on the frequency that's causing the problem. Contact them given the information within the database. In my experience, groups are responsive to requests to clear up any superfluous signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If they respond malignantly to your request, it's time to contact the FCC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that the spur could be a mixing problem with more than one signal involved. For example, 152 MHz and 159 MHz could result in a 145 MHz spurious signal.&lt;/p&gt;&#xA;" OwnerUserId="1019" LastActivityDate="2014-04-29T04:00:45.830" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1747" PostTypeId="2" ParentId="1372" CreationDate="2014-04-30T05:04:06.557" Score="-1" Body="&lt;p&gt;The licence is a legal document..  A binding contract.  A person has to be 18 to sign a binding legal contract.  Very valid reasons.&lt;/p&gt;&#xA;" OwnerUserId="1010" LastActivityDate="2014-04-30T05:04:06.557" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1748" PostTypeId="1" AcceptedAnswerId="1750" CreationDate="2014-04-30T16:08:06.770" Score="3" ViewCount="2007" Body="&lt;p&gt;Are the bands really that different in characteristics where JT65 works better for VHF, and JT9 for HF? The claim comes from the &lt;a href=&quot;http://www.physics.princeton.edu/pulsar/K1JT/wsjtx.html&quot; rel=&quot;nofollow&quot;&gt;WSJT website&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;JT65 was designed for EME (“moonbounce”) on the VHF/UHF bands and has also proved very effective for worldwide QRP communication at HF; in contrast, JT9 is optimized for HF and lower frequencies.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="13" LastEditorUserId="29" LastEditDate="2014-04-30T21:36:28.293" LastActivityDate="2019-08-04T03:48:24.030" Title="What makes JT65 preferable for VHF, and JT9 for HF" Tags="&lt;hf&gt;&lt;digital-modes&gt;&lt;vhf&gt;&lt;jt65&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1749" PostTypeId="2" ParentId="1730" CreationDate="2014-04-30T19:09:54.647" Score="1" Body="&lt;p&gt;According to my sources, the 3 biggest Amateur Radio satellites (By Radar Cross Section) are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;International Space Station&lt;/li&gt;&#xA;&lt;li&gt;Oceansat 1- Had a small Amateur Radio payload&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/AO-40&quot; rel=&quot;nofollow&quot;&gt;AO-40&lt;/a&gt; Dedicated Amateur Radio satellite.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-04-30T20:31:16.140" LastActivityDate="2014-04-30T20:31:16.140" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1750" PostTypeId="2" ParentId="1748" CreationDate="2014-04-30T21:52:18.843" Score="1" Body="&lt;p&gt;According to Wikipedia, &lt;a href=&quot;https://en.wikipedia.org/wiki/JT65#JT65&quot; rel=&quot;nofollow noreferrer&quot;&gt;JT65&lt;/a&gt; uses 65-tone MFSK (Multiple Frequency-Shift Keying), whereas &lt;a href=&quot;https://en.wikipedia.org/wiki/JT65#JT9&quot; rel=&quot;nofollow noreferrer&quot;&gt;JT9&lt;/a&gt; uses 9-tone FSK (Frequency-Shift Keying); probably hence the numerals in the respective names.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By only ever transmitting exactly one out of a set of fewer tones, it would appear intuitively that JT9 would be better suited to the variable signal strength commonly found in ionospheric propagation; there are fewer possibilities, and on the receiver side you only need to identify the &lt;em&gt;one&lt;/em&gt; tone that is currently being transmitted. Similar to &lt;a href=&quot;https://ham.stackexchange.com/q/1598/29&quot;&gt;how CTCSS tones can make it through noise so well&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, JT65 probably achieves a higher data transmission rate but would seem to put higher requirements on the &lt;em&gt;stability&lt;/em&gt; of the received signal strength, as one would see on VHF and up where the major propagation mode is line of sight (with a reflector thrown in for good measure in e.g. the case of EME).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it would appear not to be so much JT65 being preferred for VHF, as JT65 being better suited for line of sight links and JT9 being optimized for ionospheric propagation links. In the vast majority of cases, this simplifies to a rule of thumb of &quot;use JT65 for VHF and up, and JT9 on HF&quot;.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-04-30T22:03:12.410" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1752" PostTypeId="1" AcceptedAnswerId="1754" CreationDate="2014-05-01T18:50:23.680" Score="6" ViewCount="305" Body="&lt;p&gt;I'm interested in stacking a pair of circularly polarized &quot;crosshair&quot; antennas. Do I construct such as both antennas are in phase with one another then match the two signals in phase via the coax line, &lt;em&gt;i.e.&lt;/em&gt; equal length, or should I rotate one by say 180 degrees then use the coax to provide a phase shift? I'm new to RF but pretty eager to learn.&lt;/p&gt;&#xA;" OwnerUserId="1030" LastEditorUserId="76" LastEditDate="2015-12-15T23:59:21.973" LastActivityDate="2015-12-15T23:59:21.973" Title="How to stack circular polarised antennas" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;phased-array&gt;&lt;circular-polarization&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1753" PostTypeId="1" AcceptedAnswerId="1767" CreationDate="2014-05-02T05:08:03.200" Score="3" ViewCount="474" Body="&lt;p&gt;Constraints of various kinds preclude any investment in a rig at present; so I find myself pondering the means to get back on the band piece-meal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say I were successful in an attempt to throw together a DDS/VFO. &#xA;Say further a good deal longer down the line I plan to acquire a commercial rig.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could I use my VFO with a commercial rig?&#xA;Is there any advantage to a facility as mentioned above?&lt;/p&gt;&#xA;" OwnerUserId="5" LastActivityDate="2014-05-05T20:25:16.243" Title="Can an external VFO be injected into a commercial rig?" Tags="&lt;transceiver&gt;&lt;oscillator&gt;&lt;vfo&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1754" PostTypeId="2" ParentId="1752" CreationDate="2014-05-02T11:03:11.363" Score="4" Body="&lt;p&gt;The important thing is that the antennas are in phase. That is, at the instant the electric field is pointing up on one antenna, it's pointing up on the other antenna. Otherwise, they won't add constructively. In the worst case, they are 180 degrees out of phase and they &lt;em&gt;cancel&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keeping the antennas in phase can be accomplished any number of ways. If the coax length to each antenna is equal, the phase shift introduced by the feedline will be equal, so the antennas will be in phase as long as you don't rotate either one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to rotate one to  be ahead 180 degrees in phase, you could compensate by adding an extra half-wavelength (at the appropriate velocity factor for your cable) of feedline, which adds 180 degrees of delay. The result would be a net zero phase shift, so the antennas would still be in phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note this isn't much different from stacking linearly polarized antennas. One way to think of it is that you have a stack of horizontally polarized antennas, and another stack of vertically polarized antennas, and they just happen to be on the same booms and be 90 degrees out of phase. &lt;a href=&quot;https://ham.stackexchange.com/questions/1558/what-is-circular-polarization&quot;&gt;That's all circular polarization is&lt;/a&gt;, and stacking doesn't fundamentally change the picture.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-05-02T11:03:11.363" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1755" PostTypeId="1" AcceptedAnswerId="1757" CreationDate="2014-05-03T03:09:38.790" Score="27" ViewCount="72256" Body="&lt;p&gt;I am rather new to HF operation and have recently purchased my first HF rig. I have read about bands being &quot;open&quot; and &quot;closed&quot; based on various conditions including time of day. As I have been listening, I have been bouncing around all the bands from 80 meters through 6 meters, but I am not sure which are better for me to try to make contacts on. I have heard that certain bands are more appropriate for daylight operation and others are better at night, but which are which?&lt;/p&gt;&#xA;" OwnerUserId="687" LastEditorUserId="13" LastEditDate="2014-05-03T10:30:39.990" LastActivityDate="2014-05-03T11:22:52.413" Title="Which HF bands are best during the day and which are better at night?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="1756" PostTypeId="2" ParentId="1755" CreationDate="2014-05-03T10:28:48.790" Score="13" Body="&lt;p&gt;In general, the shorter wavelength HF bands are better during the day, and the longer wavelength ones at night. Although that depends a bit on what you want to do, and like all things propagation, it's subject to change. Let me try and give a rough mode of operations. Also take a look at the chart from &lt;a href=&quot;http://www.eham.net/newham/bands&quot;&gt;eham&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;6m- Randomly opened, in random directions. I think this happens more in the day, but I'm not a 6m expert. Strictly speaking this is VHF, not HF, but it's often included on HF rigs.&lt;/li&gt;&#xA;&lt;li&gt;10m- This is more consistently opened, especially in times of higher solar activity. Evening tends to be the best time, at least that's what I've found, but this is a daytime band.&lt;/li&gt;&#xA;&lt;li&gt;12-17m- These are traditional daytime bands, usually opened. The longer the band in this window, the more reliable it is, and the more likely it is opened night or day.&lt;/li&gt;&#xA;&lt;li&gt;20m- Can be opened day or night. This is the most reliable band for dx.&lt;/li&gt;&#xA;&lt;li&gt;40m- Daytime is opened in a &quot;local&quot; area, give or take 500 km or more with a good set up. Night time opened worldwide.&lt;/li&gt;&#xA;&lt;li&gt;80m- Similar to 40, but even more extreme.&lt;/li&gt;&#xA;&lt;li&gt;160m- This one is only opened at night, and tends to be a more local area. Not unlike 6 meters, strictly speaking this is MF rather than HF, but it's often included on HF rigs.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13" LastEditorUserId="29" LastEditDate="2014-05-03T11:10:48.337" LastActivityDate="2014-05-03T11:10:48.337" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1757" PostTypeId="2" ParentId="1755" CreationDate="2014-05-03T11:22:52.413" Score="25" Body="&lt;p&gt;HF propagation over long distances is by &lt;a href=&quot;http://en.wikipedia.org/wiki/Skywave&quot; rel=&quot;noreferrer&quot;&gt;skywave propagation&lt;/a&gt;, the reflection and refraction of radio waves between Earth's surface and the &lt;a href=&quot;http://en.wikipedia.org/wiki/Ionosphere&quot; rel=&quot;noreferrer&quot;&gt;ionosphere&lt;/a&gt;. The ionosphere is a consequence of radiation from the sun ionizing Earth's atmosphere, so it changes significantly with time of day and &lt;a href=&quot;http://solarscience.msfc.nasa.gov/SunspotCycle.shtml&quot; rel=&quot;noreferrer&quot;&gt;sunspot activity&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although time of day is just one of many variables, here is a simplified model of the ionosphere:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/wqRCM.png&quot; alt=&quot;ionosphere day vs night&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The F layer is mostly responsible for the refraction of radio waves back to Earth, preventing them from escaping to space. The other layers interact in other ways. During the day, the D layer forms, and the F layer splits into F1 and F2 layers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The D layer is present during the day and is a good absorber of radio waves, increasing losses. Higher frequencies are absorbed less, so higher bands (20m to 10m or so) tend to perform better. Above the &lt;a href=&quot;http://en.wikipedia.org/wiki/Critical_frequency&quot; rel=&quot;noreferrer&quot;&gt;critical frequency&lt;/a&gt;, the ionosphere is unable to refract the signal back to Earth and it escapes to space. The critical frequency during the day is in the neighborhood of 6m: depending on the space weather, 6m way work for skywave, or it may not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During the night we need not contend with D layer absorption, but the critical frequency is lower, so higher frequencies can not support skywave propagation. This can be observed on a &lt;a href=&quot;http://www.spacew.com/www/fof2.html&quot; rel=&quot;noreferrer&quot;&gt;map of critical frequency&lt;/a&gt;: see that the critical frequency is typically lowest around dawn, when the ionosphere has been in the dark the longest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, very rough rule of thumb:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;20m, being in the middle, works to some extent day or night.&lt;/li&gt;&#xA;&lt;li&gt;Lower frequency bands work best at night.&lt;/li&gt;&#xA;&lt;li&gt;Higher frequency bands work best during the day.&lt;/li&gt;&#xA;&lt;li&gt;The farther from 20m you get in either direction, the more pronounced these effects are.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Of course, given that space weather is just as variable as Earth weather, there are exceptions to these rules every day.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-05-03T11:22:52.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1758" PostTypeId="2" ParentId="1606" CreationDate="2014-05-03T11:41:07.880" Score="1" Body="&lt;p&gt;See the &lt;a href=&quot;http://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf&quot; rel=&quot;nofollow&quot;&gt;US allocation of frequencies&lt;/a&gt; for the source data for some of this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Right now, the current users of VLF/LF are either maritime mobile, radio navigation, time frequencies, or aeronautical use. There are a few stations that have experimental privileges, as &lt;a href=&quot;http://www.arrl.org/lf-low-frequency&quot; rel=&quot;nofollow&quot;&gt;ARRL mentions&lt;/a&gt;. The bandwidth for these bands drops dramatically, often only a few kilohertz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As &lt;a href=&quot;http://en.wikipedia.org/wiki/2200-meter_band&quot; rel=&quot;nofollow&quot;&gt;Wikipedia&lt;/a&gt; mentions, the reason why the 2200 band isn't available in the United states is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;On May 14, 2003, however, the FCC declined to grant these privileges&#xA;  citing concerns over potential interference with power line&#xA;  communications (PLC) systems operating unlicensed under Part 15 used&#xA;  by electrical utilities to control the power grid. But the FCC added&#xA;  that amateurs wishing to experiment with 136 kHz communications may&#xA;  apply for a Part 5 Experimental License or operate under Part 15&#xA;  regulations for this part of the electromagnetic spectrum.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;See also the &lt;a href=&quot;http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-03-105A1.pdf&quot; rel=&quot;nofollow&quot;&gt;FCC ruling directly&lt;/a&gt;, which specifically states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;While we agree that amateur experimentation in the 135.7-137.8 kHz and&#xA;  160-190 kHz portions of the LF spectrum could serve to increase the&#xA;  pool of individuals having knowledge of LF transmissions, we conclude&#xA;  that such operations would pose the potential for harmful interference&#xA;  to systems protecting and controlling the national power grid.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-05-03T12:10:11.773" LastActivityDate="2014-05-03T12:10:11.773" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1759" PostTypeId="1" CreationDate="2014-05-03T13:31:49.993" Score="1" ViewCount="2471" Body="&lt;p&gt;While researching &lt;a href=&quot;https://ham.stackexchange.com/a/1758/13&quot;&gt;this answer&lt;/a&gt;, I came across information that indicates that a many good Low Frequency/ Very Low Frequency antennas are loops, with high directionality and good overall characteristics. Can the same thing be easily done with HF signals, of having **some size of a loop with an appropriate amount of antenna coiled together? **&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example is this image from &lt;a href=&quot;http://en.wikipedia.org/wiki/File:Loop_antenna.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/UQxXX.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-11-21T14:53:28.813" Title="How to make a loop antenna for HF?" Tags="&lt;antenna&gt;&lt;hf&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1760" PostTypeId="2" ParentId="1759" CreationDate="2014-05-03T15:16:56.543" Score="2" Body="&lt;p&gt;Specifically, the antenna in your picture is a &lt;a href=&quot;http://www.antenna-theory.com/antennas/smallLoop.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;small loop&lt;/a&gt;. This is quite distinct from the &lt;em&gt;resonant loop&lt;/em&gt;, where the circumference of the loop is equal to the wavelength. Resonant loops are essentially &lt;a href=&quot;http://www.antenna-theory.com/antennas/foldeddipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;folded dipoles&lt;/a&gt; that happen to be round.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, these antennas work at HF also. There are some reasons you may want to do so, but first let's examine the advantages of a small loop at ULF. Their applicability to HF is then apparent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly the obvious: it's small. When the wavelength is several hundreds of meters or more, a practical antenna is going to be electrically small.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we just want small, why not a &lt;a href=&quot;http://www.antenna-theory.com/antennas/shortdipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;short dipole&lt;/a&gt;? This is certainly possible, and since the short dipole is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Duality_%28electrical_circuits%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;electrical dual&lt;/a&gt; of the small loop, the two should be very similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because at ULF, &lt;a href=&quot;http://en.wikipedia.org/wiki/Ground_wave_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;ground wave&lt;/a&gt; is a significant mode of propagation, and ground wave works very much better in vertical polarization, ULF transmissions are most usually vertically polarized. While short dipoles and loops have the same pattern, the nulls point in different directions: for vertically polarized antennas a dipole's nulls are up and down, while for a small loop they are in two directions on the horizon. Thus, with a loop you can null noise, while you can't with a dipole. Thus, the &quot;high directionality&quot; of a loop, even though it's really not any better than a dipole when considered in three dimensions and free space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At HF, size may be less of a concern. Also, since the usual propagation is &lt;a href=&quot;http://en.wikipedia.org/wiki/Skywave&quot; rel=&quot;nofollow noreferrer&quot;&gt;skywave&lt;/a&gt;, where the ionosphere randomly rotates polarization, we are not restricted to vertically polarized antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beware, there are many popular small loop designs among amateurs, and &lt;a href=&quot;http://www.w8ji.com/magnetic_receiving_loops.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;many of them are of rather poor design&lt;/a&gt; because they unbalance the antenna, and consequently &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;the feedline becomes as much of the antenna as the loop&lt;/a&gt;. There's some folk wisdom among amateurs that HF loops are somehow quieter, but the reason is that &lt;a href=&quot;https://ham.stackexchange.com/a/608/218&quot;&gt;they are different, not magic&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-05-03T15:58:49.630" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1761" PostTypeId="1" AcceptedAnswerId="1762" CreationDate="2014-05-03T20:00:10.407" Score="10" ViewCount="6030" Body="&lt;p&gt;As I listen, I often hear stations calling &quot;CQ contest&quot;. When I hear stations respond, they seem to do so with a specific set of information. I recognize the call sign and a signal report but there are often other pieces of information that seem to be standard that I don't recognize. When I hear a CQ contest call I am not sure how to respond.&lt;/p&gt;&#xA;" OwnerUserId="687" LastEditorUserId="29" LastEditDate="2014-05-03T20:07:11.420" LastActivityDate="2014-05-04T18:03:10.430" Title="What is a CQ contest and what is the proper way to respond to a CQ contest call?" Tags="&lt;procedure&gt;&lt;contest&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1762" PostTypeId="2" ParentId="1761" CreationDate="2014-05-03T20:32:28.550" Score="7" Body="&lt;p&gt;A &quot;CQ Contest&quot; is simply a limited CQ, just like someone can call CQ some-specific-area or CQ any-member-of-a-particular-club. I don't think I've heard this variant on SSB, but I imagine in some contests it may be beneficial to actually specify the contest in question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During a contest, there is usually a specific set of information to exchange. &lt;strong&gt;The exact information to be exchanged varies with the contest.&lt;/strong&gt; This can be &lt;em&gt;for example&lt;/em&gt; a serial number, signal report, Maidenhead locator, state/province/county/etc. (usually according to some sort of list of codes), or almost anything else, or a combination of several of these.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to participate, &lt;strong&gt;you must know what the specific exchange is for the contest that the other station is calling CQ for.&lt;/strong&gt; &lt;em&gt;If you don't know what the exchange is and what yours should be, don't respond to a CQ Contest call.&lt;/em&gt; The only exception I can think of is if the remote station is calling repeatedly but not getting any answer; in that case, you might respond with something brief like &quot;W9ABCD, ABC1DE what's the exchange?&quot;, substituting the correct call signs. If it's simply a serial number (or something similar that you know right away) and signal report, you can jump right in and figure out later where to send the logs. Don't ask such a question on the air if the remote station is working stations; you almost certainly &lt;em&gt;will&lt;/em&gt; annoy everyone involved. If the exchange is only a signal report and a serial number, by listening to a few exchanges you should be able to figure that out quickly enough; if it's anything much more involved you'll probably need to look it up somewhere anyway. If the remote station is weak, it may be beneficial to listen to a few exchanges anyway in order to establish the remote station's transmitted exchange before you try to contact it yourself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A contest QSO is just like any other QSO, only in fast-forward mode. A typical phone contest QSO might go something like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W9ABCD transmits: &lt;em&gt;W9ABCD CQ contest&lt;/em&gt;&lt;br&gt;&#xA;N5EFGH transmits: &lt;em&gt;N5EFGH&lt;/em&gt;&lt;br&gt;&#xA;W9ABCD transmits: &lt;em&gt;N5EFGH five-nine, one-four-zero&lt;/em&gt;&lt;br&gt;&#xA;N5EFGH transmits: &lt;em&gt;Five-nine, zero-one-eight&lt;/em&gt;&lt;br&gt;&#xA;W9ABCD transmits: &lt;em&gt;Roger, contest&lt;/em&gt;&lt;br&gt;&#xA;...at which point some other station hopefully responds to W9ABCD, and N5EFGH writes down the QSO in the log and moves on to work the next one. Working a contest by scanning the bands and working stations encountered is called &lt;em&gt;search and pounce,&lt;/em&gt; by the way. By only giving the absolute bare necessities, a strong-signal contact can be over in a few seconds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that to save time, the signal report for any audible contest signal is usually 59 (or 599 on CW and digital modes). That means that you'll normally only need to write down the exchange received (since you know your own transmitted exchange).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On non-phone modes, the exact traffic will obviously differ slightly from the above example, but the general idea remains the same: getting the particular contest's exchange well, &lt;em&gt;exchanged,&lt;/em&gt; as quickly and efficiently as possible.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-05-04T18:03:10.430" LastActivityDate="2014-05-04T18:03:10.430" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1764" PostTypeId="1" AcceptedAnswerId="1768" CreationDate="2014-05-05T11:25:04.090" Score="10" ViewCount="1797" Body="&lt;p&gt;I'm looking for a simple way to impedance match an array of two 50 Ω antennas so that when they are combined they appear as one 50 Ω load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assume that both antennas are identically constructed, are in phase with one another, and have the same VSWR very close to 1. The frequency the antennas are tuned to is 2.4 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a simple “rule of thumb” method that I could use that requires little equipment?&lt;/p&gt;&#xA;" OwnerUserId="1030" LastEditorUserId="76" LastEditDate="2017-04-27T20:42:23.923" LastActivityDate="2017-04-27T20:42:23.923" Title="How to combine two 50 Ω antennas such that they appear as one 50 Ω load?" Tags="&lt;antenna-construction&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1765" PostTypeId="2" ParentId="1014" CreationDate="2014-05-05T17:42:50.747" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Are there any existing codecs or modes, or are hams experimenting with&#xA;  modes that provide better than telephone/radio quality sound?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Here in Canada it's pretty much only D-Star you hear about.  Some hams in USA are experiencing with P25 I think, but only in conventional mode (no trunking).  Both technologies use vocoders from DVSI inc, respectively AMBE and IMBE/AMBE+2 chips.  I think right know Yaesu is coming with a new digital technology (12.5 kHz C4FM FDMA modulation) which looks like a P25 ham adaptation.  According &lt;a href=&quot;https://groups.yahoo.com/neo/groups/YaesuDMR/conversations/topics/49&quot; rel=&quot;nofollow&quot;&gt;to this post&lt;/a&gt;, they are using AMBE+2 too.  D-Star sound quality is terrible in comparison of P25.  P25 sounds a bit better than telephone when properly configured but lesser than analog FM or radio (you're talking about AM/FM radio I guess?), especially with background noises (sirens, music, chatter, etc).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Are the newer digital modes Icom and others coming out with better&#xA;  than telephone/radio quality?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;None that I'm aware of.  I work with D-Star and P25 and Tetra.  The two latters having the best quality/intelligibility to my ear.  D-Star being to worst.  The use of proprietary technology (DVSI vocoders) in D-Star and Yaesu's digital gear makes many radio amateurs angry because it's not aligned with the &quot;openness&quot; philosphy shared in ham communities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know there is a new codec, open source, named Opus that could be used in ham radios, but I don't know if anyone checked it seriously as an alternative to DVSI proprietary vocoders.&lt;/p&gt;&#xA;" OwnerUserId="465" LastEditorUserId="29" LastEditDate="2014-05-06T07:29:00.080" LastActivityDate="2014-05-06T07:29:00.080" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1767" PostTypeId="2" ParentId="1753" CreationDate="2014-05-05T20:25:16.243" Score="3" Body="&lt;p&gt;This falls under the heading of &quot;Depends on the Commercial Rig&quot;... Some commercial Ham gear is equipped with a connection for external VFO, so for those it's a &quot;plug and play&quot; solution. For other gear it would depend on your ability to find the correct spot in the signal chain to inject the signal from your VFO. I know of hams who have built a DDS VFO and added it to old crystal controlled commercial VHF radios to get a very nice, rugged, rig. &#xA;Things to be aware of if you go this route are that the VFO frequency will need to be offset from the receive frequency (by the 1st IF freq.). Also, VHF/UHF rigs may also need the VFO to run at a sub multiple of the &quot;tuned&quot; frequency. (Common practice in crystal controlled rigs is to multiply the crystal frequency with analog multipliers.)&#xA;Most of the DDS kits around have this ability built into the controller firmware.&lt;/p&gt;&#xA;" OwnerUserId="1015" LastActivityDate="2014-05-05T20:25:16.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1768" PostTypeId="2" ParentId="1764" CreationDate="2014-05-06T18:05:41.107" Score="9" Body="&lt;p&gt;The canonical solution to this problem is a &lt;a href=&quot;http://en.wikipedia.org/wiki/Wilkinson_power_divider&quot; rel=&quot;noreferrer&quot;&gt;Wilkinson power divider&lt;/a&gt;. There are of course other &lt;a href=&quot;http://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers#Power_dividers&quot; rel=&quot;noreferrer&quot;&gt;power dividers&lt;/a&gt;, but the Wilkinson is easy to fabricate, provides good isolation between the output ports, and is lossless when the output ports are equal and in phase, which is true for an ideal antenna array.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to make one of these yourself, you'd probably do it with coax. However, it's easier to illustrate with microstrip:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/HEV8z.png&quot; alt=&quot;microstrip power divider&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P1 would be connected to your transmitter, and P2 and P3 to your antennas. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Between P1 and P2, and also between P1 and P3, are quarter-wavelength transmission lines having an impedance of $\sqrt 2 \cdot Z_0$. For your case that works out to $\sqrt 2 \cdot 50 \Omega = 70.7\Omega $. 75 ohm coax is close enough and easier to find.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Between P2 and P3 is a resistor that's twice the characteristic impedance. For your case, that's $100\Omega$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Made with coax, it looks something like this (click for bigger version):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/File:Wilkinson_divider.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dvVhJ.png&quot; alt=&quot;coax power divider&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although it's not impossible to fabricate this sort of thing yourself, doing so at 2.4 GHz is a bit of a trick, especially if you don't have test equipment. 2.4 GHz is a very popular band, and this is a very common device, so you won't have any difficulty finding a pre-made solution for purchase.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-05-06T18:05:41.107" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1769" PostTypeId="2" ParentId="1636" CreationDate="2014-05-07T12:08:42.913" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Does effective grounding of mobile (vehicle) antenna mounts address common-mode currents?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. Well, not really. It might help, incidentally. Any 1/4 wave antenna is only half an antenna, and the other half is your car. The antenna designer made some assumptions about your car and how you'd use it to complete the antenna: if you violate those assumptions then you have a different antenna than the one that was designed, which may or may not be worse in any number of facets of performance, including common-mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, the antenna designer probably assumed that the car is made of sheet metal. If you put a 1/4 wave vertical on a car with fiberglass body panels, you absolutely will have significant common-mode currents because &lt;a href=&quot;https://ham.stackexchange.com/a/604/218&quot;&gt;the feedline is the other half of the antenna&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consequently, the best advice is probably to install the antenna according to the manufacturer's instructions. Many mobile antennas are compromise designs, so by deviating from these instructions it may be possible to make an improvement, but it's also just as possible to make things worse. Without all the details it's hard to say which will happen.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My feedline does run inside the vehicle along the body panels, so it is definitely not a good place to work as a radiator element [...]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is not necessarily the right conclusion. The feedline will be capacitively coupled quite well to the body panels, and the body panels can be decent radiators. RF currents &lt;em&gt;want&lt;/em&gt; to radiate. If you don't absorb that energy in a loss somewhere, it will radiate, eventually. Indeed, it's more ideal if all the energy is radiated from your antenna as designed and there are no common-mode currents, but if that's not completely what happens I suspect the consequences are not as bad as you imagine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bigger problem, if there is one, is probably that some of the radiating structure comes close to electronics in your car resulting in noise when receiving. Remember &lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_%28electromagnetism%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;reciprocity&lt;/a&gt;: if it's transmitting well, it also makes a good receiver. But, this is already a big problem in mobile installations: the RF noise from the electronics tends to find its way everywhere, thanks to the metal car. It's not like the antenna is on a tower in a rural area far away from noise sources. It's practically attached to a noise source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With this in mind, there's an easy experiment you can do which will answer your question better than any musing over theory we can do here. Set up your radio so you can listen to or otherwise measure the noise received. Then, temporarily attach some proposed modification to the antenna system, be it a ground strap or whatever. Can you measure an improvement? If so, you've confirmed your modification reduces noise, perhaps by moving the radiating structures of the car farther away from noise sources. Repeat the experiment listing to some desired signal to be sure you are just reducing noise and not just killing the antenna performance (a dummy load is very quiet, also). If your tested modification reduces noise and increases signal, it is a good modification, and will have an equal improvement on your transmissions, by reciprocity.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-05-07T12:08:42.913" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1770" PostTypeId="2" ParentId="1710" CreationDate="2014-05-07T16:43:12.390" Score="1" Body="&lt;p&gt;Contact the CCARC.net folks - they run the repeater coordination here in Colorado. That said, my understanding is that there are no available allocations in either the 2m or 440 bands, except for some room for digital (MotoTRBO or DSTAR) modes. That said, reach out to them, their web page lists  &lt;a href=&quot;http://www.ccarc.net/wordpress/coordination-support/&quot; rel=&quot;nofollow&quot;&gt;http://www.ccarc.net/wordpress/coordination-support/&lt;/a&gt; as the place to go to request a coordination.&lt;/p&gt;&#xA;" OwnerUserId="55" LastActivityDate="2014-05-07T16:43:12.390" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1771" PostTypeId="2" ParentId="1759" CreationDate="2014-05-07T18:22:42.993" Score="-1" Body="&lt;p&gt;I have built a magnetic loop that tunes 15m - 40m and am quite happy with it.  As stated they are not magic, but have the advantage of being small and rejecting nearby E-field noise.  Small is important if you are unfortunate enough to live in an area that is not friendly towards antennas.  The radiation resistance of a small loop is low, so to get decent results you have to keep the ohmic losses to an absolute minimum.  This means high quality conductors and very low loss capacitors, such as vacuum variables.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do a google search for 'helically loaded magnetic loop', this is the design I built.  I am very happy with its performance and you will find a lot of others with similar experiences.  It's not cheap to build but the results are worth it and it handles the full legal limit.  The Q is extremely high so an additional benefit is you effectively have a narrow bandpass filter right out at your antenna.  The noise floor is consistently several S units below that of my dipole.  Don't skimp and use a cheap capacitor, you'll be disappointed :-)  &lt;/p&gt;&#xA;" OwnerUserId="555" LastActivityDate="2014-05-07T18:22:42.993" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1772" PostTypeId="1" CreationDate="2014-05-07T18:31:06.360" Score="4" ViewCount="105" Body="&lt;p&gt;Many HF circuits posted in my copy of the ARRL manual (1972 edn - Yes, it's a vintage) appear to use a toroidal former with a coil. The same applies to HF circuits posted on the internet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I recall - a toroidal former is to be preferred over a linear former when &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;space is at a premium&lt;/li&gt;&#xA;&lt;li&gt;coil emi is to be avoided&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Apart from these above - &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Under what circumstance would a non-toroidal former lend itself to HF?&lt;/p&gt;&#xA;" OwnerUserId="5" LastActivityDate="2014-05-07T22:52:01.680" Title="Under what circumstance does non-toroid former lend itself to HF?" Tags="&lt;diy&gt;&lt;inductor&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1773" PostTypeId="2" ParentId="1772" CreationDate="2014-05-07T22:52:01.680" Score="3" Body="&lt;p&gt;HF or not, toroidal transformers are pretty great. They'd be the only kind anyone would use were it not for:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Fabrication cost. They are hard to wind with automated machines, since you have to somehow pass the end through the middle multiple times. Try winding one without ever letting go of the wire to see the problem.&lt;/li&gt;&#xA;&lt;li&gt;They have a lossy core.&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Ferrite materials become lossier with increasing frequency and at some point become totally useless.&lt;/li&gt;&#xA;&lt;li&gt;Even at HF, ferrite materials have some loss, which can be problematic for power components.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;While you could wind a toroidal transformer on a very low-loss material (like air, or something magnetically like it), then there wouldn't be a high-permeability core completing a magnetic circuit. Leakage inductance would thus be higher, so there's reduced justification for the increased cost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You pretty much summarized the advantages of a toroid core. So, you might use something other than a toroid core when those advantages don't outweigh these disadvantages. Examples:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;loading coils for antennas. Here you don't care much about leakage inductance, since &quot;leakage&quot; is a desirable property in antennas.&lt;/li&gt;&#xA;&lt;li&gt;UHF inductors. Ferrite materials are poor performers at high frequencies. Fortunately, higher frequencies require less inductance to achieve the same reactance, so higher frequencies need ferrite cores less.&lt;/li&gt;&#xA;&lt;li&gt;high-power inductors for baluns or matching networks. A ferrite core of sufficient size to keep losses acceptably low might be prohibitively expensive.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-05-07T22:52:01.680" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1774" PostTypeId="2" ParentId="1492" CreationDate="2014-05-08T23:30:36.543" Score="1" Body="&lt;p&gt;I'm one of the TrustedQSL developers. We currently have a C library (tqsllib) that you could link against with JNI, but we don't have a Java port of it and aren't really planning to do one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most people writing code against LoTW to use the command-line interface to TQSL, explained here: &lt;a href=&quot;http://www.arrl.org/TrustedQSL/tQSL-help/cmdline.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/TrustedQSL/tQSL-help/cmdline.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you decide to do one, feel free to shoot us an email. Be warned - the spec is pretty annoying and if you're trying to make a full-featured application you'll have to deal with creating station locations, which is worse. (The relevant fields are specified in an XML config file that the ARRL provides...)&lt;/p&gt;&#xA;" OwnerUserId="303" LastActivityDate="2014-05-08T23:30:36.543" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1776" PostTypeId="1" CreationDate="2014-05-10T22:26:34.923" Score="4" ViewCount="859" Body="&lt;p&gt;So I recently bought a pair of Wouxun KG-UV6D. We don't have the license required to operate outside of PMR frequencies, but that's fine, as we will be using these for airsoft. The programming of 8 standard PMR frequencies used is pretty straight forward, but for some reason, I am experiencing &quot;spillover&quot;. &#xA;The channels I am programming into them are these:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;PMR 1:446,00625&lt;/li&gt;&#xA;&lt;li&gt;PMR 2:446,01875   &lt;/li&gt;&#xA;&lt;li&gt;PMR 3:446,03125&lt;/li&gt;&#xA;&lt;li&gt;PMR 4:446,04375   &lt;/li&gt;&#xA;&lt;li&gt;PMR 5:446,05625   &lt;/li&gt;&#xA;&lt;li&gt;PMR 6:446,06875   &lt;/li&gt;&#xA;&lt;li&gt;PMR 7:446,08125   &lt;/li&gt;&#xA;&lt;li&gt;PMR 8:446,09375&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;But when I have one set to 446,00625 and the other to 446,01875, if I send with the 446,01875-radio, the other radio will pick up a lot of static noise. &#xA;So far, I have tried setting squelch level to the least tolerant level, and channged the bandwidth from wide to narrow, but it is still picking up the static. &#xA;Aside from that, the static seems to interfere with my laptop, randomly interacting with my media keys (fan boost, bluetooth etc.). I have set the step to 6.25K, and I will not be using this radio to access any repeaters. Also, I need to send with a TXP of 0.5, but seeing as the radio only has HIGH (4W) and LOW (1W), I stick to the low setting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am programming manually, and I am very, very green to radios. What am I doing wrong?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: I made a short demonstrational video of what this interference sounds like:&#xA;&lt;a href=&quot;https://www.youtube.com/watch?v=TE7MekFMx-o&quot; rel=&quot;nofollow&quot;&gt;https://www.youtube.com/watch?v=TE7MekFMx-o&lt;/a&gt; - Take note that I am on the wrong frequencies in this video: I misread 446.- for 466.-&lt;/p&gt;&#xA;" OwnerUserId="1054" LastEditorUserId="1054" LastEditDate="2014-05-11T20:55:21.180" LastActivityDate="2017-03-09T04:11:19.037" Title="Wouxun KG-UV6D PMR frequency &quot;spillover&quot;" Tags="&lt;uhf&gt;&lt;frequency&gt;" AnswerCount="2" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="1777" PostTypeId="2" ParentId="1637" CreationDate="2014-05-11T12:07:58.380" Score="3" Body="&lt;p&gt;There are many ways you could calibrate. For measuring SWR, try this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Attach a 50Ω dummy load to your transmitter. The SWR should be 1:1. Then, attach two 50Ω dummy loads in parallel, giving you an effectively 25Ω load. The SWR should be 2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems you also want to measure power, and not just SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have some attenuators available, you can put them on your transmitter's output until you are within the acceptable range for your spectrum analyzer. Then measure the power for that, and add to the measured power the power absorbed by the attenuators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, you could transmit into the dummy load, then measure the voltage with the scope (provided it has sufficient bandwidth), and calculate the power from $P=V_{RMS}^2/50\Omega$. If you use a high impedance probe (&quot;high&quot; meaning anything $\gg 50\Omega$) then the scope won't affect the measurement much. 50Ω in parallel with 10kΩ is still 50Ω, within your measurement error.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-05-11T12:07:58.380" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1778" PostTypeId="1" CreationDate="2014-05-11T19:08:30.400" Score="1" ViewCount="3692" Body="&lt;p&gt;I just got my new Icom 7100, and while I'd love to operate it locally, there are just too many things near me that get interfered with from RF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, one solution is to remotely control it - I have some suitable QTH's for the transceiver and antennas all of which have access to internet. I can piece a machine together to run windows, linux, whatever is necessary to get this working.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any software recommendations?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's nice to note that the 7100 has a usb connection which allows me to obtain two sound interfaces - one &quot;microphone&quot; and one &quot;speaker&quot; on the Icom. I'm not familiar with CAT control, but apparently I can also send commands over USB too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is this software Icom makes (RS-BA1), but I would have to wait for it to ship (who the hell still sells CDs of software!?) In addition, I'm sure there are some free and open implementations, I just can't seem to find them.&lt;/p&gt;&#xA;" OwnerUserId="1055" LastEditorUserId="1246" LastEditDate="2015-02-01T19:47:30.577" LastActivityDate="2015-02-01T19:47:30.577" Title="Remote control for Icom IC-7100" Tags="&lt;remote-control&gt;&lt;icom&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1779" PostTypeId="2" ParentId="1776" CreationDate="2014-05-11T20:53:55.510" Score="1" Body="&lt;p&gt;The issue is natural, and specific to cheaper grade radios. Changing the squelch tolerence and putting a small distance between the radios (6-8 meters) nullifies the interference.&lt;/p&gt;&#xA;" OwnerUserId="1054" LastActivityDate="2014-05-11T20:53:55.510" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1780" PostTypeId="2" ParentId="1637" CreationDate="2014-05-12T17:11:24.827" Score="1" Body="&lt;p&gt;Mike Bryce covered a 3:1 dummy load in QST, in Feb 2013, this will NOT give you an accurate input power reading, but WILL generate a known SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The technique uses a 150 ohm resistive load creating an SWR of 3:1, with enough current/watt capacity, and an adequate heat-sink, so you do not overload the dummy load's thermal limits, when you transmit from the desired transmitter.  Your SWR meter can be calibrated while you have your transmitter keyed and attached to this 3:1 dummy load. I believe there is no reactance or inductance involved in this dummy load, it's purely a resistive load, but at the &quot;wrong&quot; resistance, which SHOULD creating a 3.0 readout on a properly calibrated SWR meter.  I would think even a tiny amount of transmitter power (say 0.5 to 1.0 watts at HF) should work admirably.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://connection.ebscohost.com/c/articles/85802751/three-one-dummy-load&quot; rel=&quot;nofollow&quot;&gt;http://connection.ebscohost.com/c/articles/85802751/three-one-dummy-load&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="643" LastActivityDate="2014-05-12T17:11:24.827" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1781" PostTypeId="2" ParentId="1695" CreationDate="2014-05-13T13:54:10.627" Score="3" Body="&lt;p&gt;I have a UV-5R, and both the 771 and the 701. Those antennas were the best decisions I ever made. I was having trouble hitting repeaters 1-2 km away when I was indoors. With the 771, I could hit 70cm repeaters from up to 6 km away on a good day. The stock antenna is good for nothing, throw it out and buy yourself a real antenna.&lt;/p&gt;&#xA;" OwnerUserId="170" LastActivityDate="2014-05-13T13:54:10.627" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1782" PostTypeId="1" AcceptedAnswerId="1802" CreationDate="2014-05-14T01:30:21.277" Score="3" ViewCount="12235" Body="&lt;p&gt;Does anyone know what the spacing between elements on a beam antenna should be? I built a 146 MHz 3 element beam following instructions, and the spacing was 16&quot; between the driven element and the reflector and 20&quot; between the driven element and the director. I was just wondering how you determine the proper spacing between elements; is there any set formula you use to determine boom length, element spacing, etc. that you can use to design a yagi? If anyone can tell me, I would really appreciate it.&lt;/p&gt;&#xA;" OwnerUserId="1056" LastEditorUserId="76" LastEditDate="2015-12-15T22:00:45.540" LastActivityDate="2016-03-06T22:01:54.703" Title="Spacing between elements on a Yagi antenna" Tags="&lt;antenna&gt;&lt;yagi&gt;&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1786" PostTypeId="2" ParentId="1722" CreationDate="2014-05-14T20:26:44.147" Score="1" Body="&lt;p&gt;A bad fist in CW usually refers to improper keying, such as slurring the definition between dots and dashes, so it is harder to copy. Also, varying speed of CW dramatically and accidentally adding in characters that shouldn't be there are examples of a bad fist. &#xA;            Usually machine generated CW is good quality, since it is all programmed, but errors in software or components can result in sloppy machine generated CW.&lt;/p&gt;&#xA;" OwnerUserId="1056" LastActivityDate="2014-05-14T20:26:44.147" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1787" PostTypeId="2" ParentId="1672" CreationDate="2014-05-14T20:34:07.163" Score="0" Body="&lt;p&gt;Alternatively, you could use MURS (multi use radio service). There are no licensing fees     ( unlike gmrs) and no licenses needed. MURS radios can have up to 2 watts of output, and should be able to cover 3 miles fine. &#xA;                  Of course, getting a ham license is probably the best idea. you get many more frequencies, and the technician test is pretty easy.&lt;/p&gt;&#xA;" OwnerUserId="1056" LastActivityDate="2014-05-14T20:34:07.163" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1788" PostTypeId="2" ParentId="1695" CreationDate="2014-05-14T21:18:15.553" Score="2" Body="&lt;p&gt;The rubber ducky antennas supplied with handheld radios are not very efficient radiators. The reason they are used is that they are small and portable.Better antennas are bigger and will get much better performance, but are less portable. A quarter wavelength antenna improves your transmitted signal a lot, and isn't that much longer. Alternatively, just connecting a quarter wavelength wire to the outside ( shield) of the stock antenna's connector where it connects to the radio will improve the swr ratings by a good bit.&lt;/p&gt;&#xA;" OwnerUserId="1056" LastEditorUserId="1056" LastEditDate="2014-05-15T15:28:05.197" LastActivityDate="2014-05-15T15:28:05.197" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1789" PostTypeId="1" AcceptedAnswerId="1795" CreationDate="2014-05-15T01:57:11.727" Score="2" ViewCount="137" Body="&lt;p&gt;I have seen that there are times where reception isn't very good on a radio, but as soon as the hand is approached as much as possible to the antenna (with or without direct contact to the actual antenna), the signal improves a lot, as if the body worked as an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been told that a piece of metal or tin foil could be used in the same way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there other methods (for instance using some liquid to try and improve even more, maybe better than just water for this) that anybody knows of to improve reception in this way?&lt;/p&gt;&#xA;" OwnerUserId="1069" LastActivityDate="2014-05-15T18:10:06.300" Title="Capacitance methods (antenna extensions, whole body as antenna) for receiving better" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1790" PostTypeId="1" CreationDate="2014-05-15T02:22:08.797" Score="4" ViewCount="360" Body="&lt;p&gt;A resonant circuit is typically composed of some resistance and reactance, the latter being provided by inductors and capacitors. The resonant frequency being calculated as the inverse square of their product.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is therefore possible to attain resonance by varying the capacitance, inductance, or both. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the design phase, is there a rule-of-thumb guideline on which parameter (capacitance/inductance) one should vary whilst aiming for a range of values?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2014-05-19T15:59:39.350" LastActivityDate="2014-05-19T15:59:39.350" Title="Should the capacitance or inductance be varied to achieve resonance?" Tags="&lt;diy&gt;&lt;equipment-design&gt;&lt;impedance&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1791" PostTypeId="2" ParentId="1790" CreationDate="2014-05-15T11:03:53.767" Score="0" Body="&lt;p&gt;You can vary both the capacitance and the inductance, or either one. For varying inductance, I like using an air core tapped inductor and a multiple position switch to allow you to adjust inductance without using a slug. A combination of a variable inductor to do the major tuning and a variable capacitor to do the minor tuning works pretty well. &lt;/p&gt;&#xA;" OwnerUserId="1056" LastEditorUserId="1056" LastEditDate="2014-05-15T14:58:05.453" LastActivityDate="2014-05-15T14:58:05.453" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1792" PostTypeId="2" ParentId="1790" CreationDate="2014-05-15T12:34:07.943" Score="2" Body="&lt;p&gt;To vary the inductance you would normally use a cored inductor that is settable in some way, this is generally more lossy than an air wound inductor and would thus have a lower Q. Variable inductors also aren't that common.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To vary the capacitance you would either need a variable capacitor (or varactor that can be varied with voltage), physically variable capacitors are hard to get exactly on frequency however (in my experience at least).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short, I would say vary the capacitance just because physically variable capacitors are easier to find and varying it electronically is easy using varactors.&lt;/p&gt;&#xA;" OwnerUserId="135" LastActivityDate="2014-05-15T12:34:07.943" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1793" PostTypeId="2" ParentId="1789" CreationDate="2014-05-15T15:03:15.450" Score="0" Body="&lt;p&gt;Antenna performance can change based on position and composition of nearby objects, as you observed. A conducting or magnetic object nearby can decrease antenna performance by raising the swr. If your antenna doesn't perform well most of the time, you may want to move it or replace it, as it may be affected by nearby objects or may not be the right length for the frequency you are using. Variable inductors and capacitors can be used to tune an antenna that is not working well, but changing the antenna or position of the antenna would be easier, if it helps.&lt;/p&gt;&#xA;" OwnerUserId="1056" LastActivityDate="2014-05-15T15:03:15.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1794" PostTypeId="2" ParentId="1790" CreationDate="2014-05-15T15:06:02.227" Score="2" Body="&lt;p&gt;I'm not an analog electronics guy, but I heard this on the Internet...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=vi24SpKYYoQ&quot; rel=&quot;nofollow&quot;&gt;This video by W2AEW: &quot;Basics of Capacitor &amp;amp; Inductor self-resonance, parasitics, etc.&quot;&lt;/a&gt; does not discuss &lt;em&gt;variable&lt;/em&gt; inductances or capacitances, but does cover practical concerns for obtaining a given resonant frequency by selecting values of inductors and capacitors. Roughly summarized, the issue is that components are non-ideal:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;They have tolerances: they are not exactly the intended value.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;They have parasitics: all wires have resistance, capacitors have a little inductance in their leads, inductors have a little capacitance between their turns, etc. The effects of this increase with frequency.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Therefore, if your &lt;em&gt;designed&lt;/em&gt; capacitance or inductance is &lt;em&gt;too small&lt;/em&gt;, it will be swamped by the imperfections in the actual circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W2AEW didn't actually say this, but it seems to me that one should therefore choose “balanced” values so that the chosen inductance is large compared to the parasitic inductance, and simultaneously the chosen capacitance is large compared to the parasitic capacitance. I could be wrong there; according to the video there could be and have been whole chapters of books written on the subject. So maybe you want to find one of those.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-05-15T15:06:02.227" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1795" PostTypeId="2" ParentId="1789" CreationDate="2014-05-15T18:10:06.300" Score="1" Body="&lt;p&gt;The ways your body, or a piece of metal, or any thing else with magnetic or electrical properties different from air can interact with an antenna are complex and numerous. Let's take your example, you moved your hand around an antenna, and the reception got better. Why could this be?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your body is reasonably conductive, especially to high-frequency current. By placing anything conductive near the antenna, it becomes part of the antenna through mutual inductance and capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The new antenna (the antenna proper + your body) has different characteristics which may be better or worse than the antenna proper alone. It will likely have a different radiation pattern than before, which may be more sensitive in the direction of the signal, or less sensitive in the direction of noise. Either will improve the signal-to-noise ratio, which is the limiting factor in most wireless communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your body can also absorb, reflect, and refract radio waves. &lt;a href=&quot;http://en.wikipedia.org/wiki/Multipath_interference&quot; rel=&quot;nofollow&quot;&gt;Multipath interference&lt;/a&gt; can be a problem for wireless communications. By putting your body in the path somewhere, you may eliminate one mode of propagation which was interfering destructively. Or, you may enable a mode which will interfere constructively. Thus, you make the signal better or worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Small devices tend to have smaller than optimally sized antennas. Your body, some part of it, or something else might be a more efficient antenna than the device's antenna, and by coupling to it (again, through mutual capacitance and inductance) you might make a more efficient antenna overall. Of course it's just as possible that you make a less efficient antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to &lt;em&gt;predict&lt;/em&gt; what body positions or materials might improve the signal, that's hard. You could solve &lt;a href=&quot;http://en.wikipedia.org/wiki/Maxwell%27s_equations&quot; rel=&quot;nofollow&quot;&gt;Maxwell's equations&lt;/a&gt;, taking into account the electrical properties and geometry of everything between and near the transmitting and receiving devices. Of course, that's absurdly hard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason it's so easy to improve reception by waving your hand on or near an antenna is that you can very quickly try &lt;em&gt;a lot&lt;/em&gt; (you might say &lt;a href=&quot;http://en.wikipedia.org/wiki/Zeno%27s_paradoxes&quot; rel=&quot;nofollow&quot;&gt;infinitely many&lt;/a&gt;) possibilities, and if you can get some immediate feedback on what's working (by listening to the signal, for example), your brain quite naturally finds the optimal configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for what materials besides your body might work, just about anything conductive will do something. Your body works well because it's quite large and easy to control accurately. Waving something conductive around your antenna, you can probably find a configuration that works better in a particular position, receiving a particular station, at a particular time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to find some material or technique that consistently or universally improves reception, that's called antenna design. For example, a &lt;a href=&quot;http://en.wikipedia.org/wiki/Yagi-Uda_antenna&quot; rel=&quot;nofollow&quot;&gt;Yagi-Uda antenna&lt;/a&gt; has some pieces of metal of a particular size in a particular geometry which consistently make the antenna directional, being less sensitive in some directions and more sensitive in others. If you point it at the station you want to receive, it works better than a non-directional antenna almost always.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-05-15T18:10:06.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1797" PostTypeId="1" AcceptedAnswerId="1798" CreationDate="2014-05-16T20:22:16.103" Score="3" ViewCount="418" Body="&lt;p&gt;Can two FM radios transmit two separate PL tones, and be received by two radios with matching PL tones? Or will the receivers hear a mix of the two, or nothing at all?&lt;/p&gt;&#xA;" OwnerUserId="80" LastActivityDate="2014-05-19T17:14:40.523" Title="Can two FM radios transmit two separate PL tones at the same time, and be received by two radios with matching PL tones?" Tags="&lt;fm&gt;&lt;tone-squelch&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1798" PostTypeId="2" ParentId="1797" CreationDate="2014-05-16T21:07:12.570" Score="8" Body="&lt;p&gt;Assuming that the two transmitters operate at the same carrier frequency, and that the receivers receive similar power from each transmitter, then the FM signals will suffer &lt;em&gt;destructive interference&lt;/em&gt; and the demodulated signal will be heavily distorted. PL tone, which is part of the transmitted signal, will also be lost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one of the RF signals gets to the receiver with much more power than the other transmission, then there is FM &lt;em&gt;masking&lt;/em&gt;, where the stronger signal prevails and the weaker signal is undetected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You cannot expect to receive a nice mix of the two transmitted signals in FM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S. this is why aviation VHF uses AM and not FM. In AM, all received signals add up in the demodulated audio, so you can hear all signals at once.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2014-05-16T21:07:12.570" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1799" PostTypeId="2" ParentId="1790" CreationDate="2014-05-17T09:16:56.507" Score="-1" Body="&lt;p&gt;In the old days, the 1920th, there existed a device called variometer, that consisted of two coils connected in series, where one coil was inside the other and which could be rotated. In this way the inductance of the system could be changed.&lt;/p&gt;&#xA;" OwnerUserId="1076" LastActivityDate="2014-05-17T09:16:56.507" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1802" PostTypeId="2" ParentId="1782" CreationDate="2014-05-18T17:19:19.753" Score="7" Body="&lt;p&gt;It would be nice to think that there is simple formula or algorithm that one could plug the frequency and desired gain into, and out would come the required element spacings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reality is that the math is difficult - requiring the solution of many simultaneous equations - and the results may still not absolutely mirror reality due to variations in materials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most Yagi-Uda designs are based on empirical methods and often use pre-tested models such as those by the NIST and DL6WU.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The spacing of the reflector and the first director are usually the most critical. Multiple directors usually end up with around 0.4 wavelength spacing. Small amounts of improvement in gain can be obtained by playing with the spacing of the directors - however, it is generally not worth the effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can obtain a copy of the ARRL Antenna Book, chapter 18 will likely be helpful.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, the following resources may also be informative:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.qsl.net/vk2kfj/DL6WU.html&quot;&gt;DLRWU Yagi Design Page&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.k7mem.com/Electronic_Notebook/antennas/yagi_vhf_help.html&quot;&gt;K7MEM VHF/UHF Yagi Design Help&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a few more that I would like to include, but I do not have enough reputation points.&lt;/p&gt;&#xA;" OwnerUserId="1080" LastActivityDate="2014-05-18T17:19:19.753" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1804" PostTypeId="1" AcceptedAnswerId="1815" CreationDate="2014-05-19T13:21:56.410" Score="11" ViewCount="35792" Body="&lt;p&gt;How (and why) does a Gamma match work, when used on the driven element of a Yagi antenna? As shown here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/qBS6r.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(source: &lt;a href=&quot;http://www.iw5edi.com/ham-radio/?2-element-yagi-for-10-meters-band,49&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.iw5edi.com/ham-radio/?2-element-yagi-for-10-meters-band,49&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The article describes a 10 meter Yagi where the driven element is one continuous conductor and not the classic dipole-halves driven by 50 ohm coax. I have seen other designs where Gamma matches were used on split folded dipole elements joined on the far end. Clearly capacitance is the key, but I don't understand how it can work efficiently.&lt;/p&gt;&#xA;" OwnerUserId="152" LastEditorUserId="8717" LastEditDate="2020-11-09T04:14:29.393" LastActivityDate="2020-11-09T04:14:29.393" Title="What is a Gamma match in the context of the driven element of a Yagi antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;&lt;impedance-matching&gt;&lt;yagi&gt;" AnswerCount="7" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="1805" PostTypeId="2" ParentId="1804" CreationDate="2014-05-19T16:20:52.427" Score="0" Body="&lt;p&gt;For a continuous conductor driven element, like the one in the article, the gamma match is basically a variable capacitor that is used to tune out any inductance from the (unbalanced) feeding of the antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the article states, the center of the driven element is a zero voltage point, so it's OK to ground the boom there and feed the braid side of the coax there (remember RF is AC, not DC).  Attaching the other side of the coax further out on the element is going to create an impedance problem, of course, but that's what the match is for.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The major drawback of the gamma match is that it's &lt;em&gt;there&lt;/em&gt; on the boom of the Yagi, in the air and therefore, inconvenient to adjust.  You'll only want to use such a matching system where the SWR bandwidth of the resulting antenna is wide enough for your purposes. So you won't need to mess with it once the antenna is tuned initially.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could replace the gamma match with a variable capacitor of the appropriate range.  This is common in other types of antenna (e.g., loops) where the bandwidth is narrow and you need to tweak it up as you tune.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-05-19T16:20:52.427" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1806" PostTypeId="2" ParentId="1797" CreationDate="2014-05-19T17:14:40.523" Score="0" Body="&lt;p&gt;The subaudible &quot;PL&quot; tone is only there to control the receiver's squelch circuit.  If the tones don't match, the receiver stays muted.  Once the squelch is opened, the received FM signals continue to behave as they normally would.  &lt;/p&gt;&#xA;" OwnerUserId="1087" LastActivityDate="2014-05-19T17:14:40.523" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1807" PostTypeId="1" CreationDate="2014-05-20T01:04:13.417" Score="2" ViewCount="4903" Body="&lt;p&gt;I have 2 Boafeng UV-82 radios. I programmed the frequencies using Chirp. When I try to access the repeaters in channel mode I cannot connect. When I switch to frequency mode and turn off the duplex offset, I can access the repeater. In channel mode I cannot talk to the other handheld. In frequency mode, I can talk to the other handheld. I made sure the T-CTCS frequency for the tone is set according to the repeater data. Any thoughts on how to fix the problem?&lt;/p&gt;&#xA;" OwnerUserId="1088" LastActivityDate="2019-11-20T07:31:04.137" Title="Baofeng uv-82 will not transmit in channel mode?" Tags="&lt;transceiver&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1810" PostTypeId="1" AcceptedAnswerId="1837" CreationDate="2014-05-21T00:49:25.357" Score="4" ViewCount="343" Body="&lt;p&gt;How do you know which coaxial cable to choose for your application? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance;&#xA;I require a cable that has a 50ohm impedance, an operating frequency of 2.4GHz, length of 100mm, and needs to be semi rigid to support the elements of the antenna I am going to make. &#xA;Requires a RP-SMA connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is going to be used on a video transmitter if that is of importance&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be a suitable cable and why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Previously I have used RG316 then gained rigidity with wire strapped to the outer. &lt;/p&gt;&#xA;" OwnerUserId="1030" LastEditorUserId="1030" LastEditDate="2014-05-21T13:45:40.803" LastActivityDate="2014-05-29T11:29:21.017" Title="How to choose a coaxial cable" Tags="&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1811" PostTypeId="1" AcceptedAnswerId="1812" CreationDate="2014-05-21T02:10:30.043" Score="1" ViewCount="337" Body="&lt;p&gt;My Kenwood has &quot;split&quot; and &quot;rit/xit&quot;. Is the &quot;split&quot; mode suitable for operating a split for a DX pileup situation, where a station is listening &quot;3 up&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm confused about which of the larger or smaller frequencies on my screen, or the letters A and B, is the receive and which is transmit, in split mode?  How do I know which is my receive and which is my transmit in RIT/XIT mode?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I the only one who reads the manual and is left without a clue here? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In split mode I have no idea if the larger frequency value is both my listen and transmit frequency and I have to press A/B, talk, then press A/B again, or what? &lt;/p&gt;&#xA;" OwnerUserId="643" LastEditorUserId="643" LastEditDate="2014-05-22T20:10:59.257" LastActivityDate="2014-05-22T20:10:59.257" Title="How do you operate an &quot;up 3&quot; split dx station with a Kenwood TS570 or similar HF radio?" Tags="&lt;kenwood&gt;&lt;equipment-operation&gt;&lt;split-frequency&gt;&lt;ts570s&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1812" PostTypeId="2" ParentId="1811" CreationDate="2014-05-21T13:09:46.870" Score="1" Body="&lt;p&gt;I'm looking at a TS-570 manual right now.  This is pretty standard split operations.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Select the transmit VFO (press A/B to choose), set the transmit frequency as desired (in your case, operating freq +3).  Then press A/B to select the receive VFO and set the operating frequency.  THEN push the split button. When you transmit, your transceiver will essentially automatically switch VFOs for you, transmit, and switch back.  You should see the frequency change when you transmit, then go back when you finish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/OKr9d.png&quot; alt=&quot;PTT button up and down affect on Split display&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="308" LastEditorUserId="643" LastEditDate="2014-05-21T17:54:01.410" LastActivityDate="2014-05-21T17:54:01.410" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1813" PostTypeId="1" CreationDate="2014-05-21T19:42:46.457" Score="3" ViewCount="422" Body="&lt;p&gt;My friend and I want to see if we can Ham radio between San Jose, CA and Bangalore, India. We're beginners and are going to be using handheld radios. Are there any networks of repeaters, that could connect us, or could you suggest a resource to find them.&lt;/p&gt;&#xA;" OwnerUserId="1102" LastEditorUserId="218" LastEditDate="2014-05-29T01:47:10.543" LastActivityDate="2014-05-30T17:15:44.447" Title="Is it possible to radio between America and India?" Tags="&lt;ht&gt;&lt;repeater&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1814" PostTypeId="2" ParentId="1813" CreationDate="2014-05-21T20:01:35.363" Score="1" Body="&lt;p&gt;The only way this would work would be to use a longer wavelength, 6M at the minimum, but more likely 15-20m. HTs don't come in that size.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as using repeaters, you might be able to find one that connects over the internet. I'm doubtful that such a thing exists, but it might.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="18" LastEditDate="2014-05-30T17:15:44.447" LastActivityDate="2014-05-30T17:15:44.447" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1815" PostTypeId="2" ParentId="1804" CreationDate="2014-05-21T20:44:21.857" Score="13" Body="&lt;p&gt;A gamma-match serves a triple purpose:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;As a small diameter wire parallel and in close vicinity with the main radiating element, it will carry only a fraction of the main element current while being exposed to the same electrical field strength. This turns it in &lt;strong&gt;an effective up-transformer of the antenna input impedance&lt;/strong&gt;.&lt;/li&gt;&#xA;&lt;li&gt;It also forms together with the main radiating element &lt;strong&gt;a closed wire stub&lt;/strong&gt;, adding inductance to the antenna input impedance. If this is not required for matching, the additional inductance can be cancelled out with a lumped capacitor in series.&lt;/li&gt;&#xA;&lt;li&gt;Not shown on your figure but on the picture below: The sheath of the coaxial feed-line is connected to the center of the main radiating element. When properly connected, a gamma-match also serves as a balanced to unbalanced converter or &lt;strong&gt;balun&lt;/strong&gt;.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;All these functions are highly desirable for matching the unbalanced characteristic impedance of the coaxial feed-line to the much lower balanced impedance of a Yagi-antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/0NCMp.jpg&quot; alt=&quot;gamma-match detail&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2017-10-26T16:29:55.260" LastActivityDate="2017-10-26T16:29:55.260" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1818" PostTypeId="1" CreationDate="2014-05-22T01:49:17.213" Score="4" ViewCount="619" Body="&lt;p&gt;How important is it to maintain a consistent Morse Code WPM keying speed when transmitting CW?  I occasionally hear operators slow way down when sending RST and location info, and then later identifying at double speed from the rest of the QSO.   Is this common, sub-optimal or optimal practice?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does slowing down WPM (dot speed) help when one hears condition deteriorating?  Or is repeating info at the prior faster WPM better?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2016-09-21T20:21:37.863" Title="Consistency of Morse Code/CW sending speed" Tags="&lt;cw&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1819" PostTypeId="1" CreationDate="2014-05-23T14:25:31.900" Score="8" ViewCount="395" Body="&lt;p&gt;I will give the magmount antenna as an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The vertical element to the antenna is very critical, cut to a certain wavelength, often added with some loading coils, or a little spiral to make everything perfect for the specific frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other part of the antenna is a random car, just a chunk of metal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On a dipole, both elements are equally important, both acting together to make the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why on the magmount, and other antennas like AM towers is the ground or counterpoise not as important?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can this be switched around, lets say I used the center coax as the RF ground, and the exterior coax as the vertical element, would this work equivalently?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-05-28T17:10:30.543" LastActivityDate="2014-05-30T16:14:00.117" Title="Why is an RF ground not as critical as the other, and can they be used backwards?" Tags="&lt;grounding&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1820" PostTypeId="1" CreationDate="2014-05-23T14:28:45.623" Score="7" ViewCount="2816" Body="&lt;p&gt;I have built a simple ground plane antenna for 70cm with a connector, 4 radials, and one vertical element. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RF ground is connected to the radials, and the RF is connected to the vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It got me thinking, can the actual earth be used, because AM towers use it? IF I went outside, connected one end to a deep ground rod, and the other end to the vertical element, would the radiation be the same? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is using the earth as an RF ground frequency specific, for example, don't use it above 30MHz?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2019-04-13T20:39:59.853" LastActivityDate="2019-04-14T06:17:48.940" Title="Using Earth as an RF ground" Tags="&lt;grounding&gt;&lt;earth&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1821" PostTypeId="1" AcceptedAnswerId="1824" CreationDate="2014-05-23T14:40:14.707" Score="10" ViewCount="1302" Body="&lt;p&gt;What is the fastest legal WPM I can use for my repeater's Morse code identification?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am in the USA.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="218" LastEditDate="2014-05-29T01:43:48.350" LastActivityDate="2014-05-29T01:43:48.350" Title="Fastest Speed allowed for CW FM repeater ID in USA" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;cw&gt;&lt;repeater&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1823" PostTypeId="1" AcceptedAnswerId="1864" CreationDate="2014-05-24T00:48:00.857" Score="4" ViewCount="315" Body="&lt;p&gt;What frequency should I use to try and make meteor scatter contacts on 2m FM tonight, with a nice meteor storm coming?&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="76" LastEditDate="2014-06-03T17:40:55.343" LastActivityDate="2014-06-06T08:31:04.507" Title="2 m meteor scatter FM voice freq?" Tags="&lt;propagation&gt;&lt;vhf&gt;&lt;dx&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1824" PostTypeId="2" ParentId="1821" CreationDate="2014-05-24T00:54:01.973" Score="15" Body="&lt;p&gt;20 wpm.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;§97-119:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) The call sign must be transmitted with an emission authorized for&#xA;  the transmitting channel in one of the following ways:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(1) By a CW emission. When keyed by an automatic device used only for&#xA;  identification, the speed must not exceed 20 words per minute;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-05-24T00:54:01.973" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1825" PostTypeId="2" ParentId="1818" CreationDate="2014-05-24T17:56:24.687" Score="6" Body="&lt;p&gt;I think slowing down for critical information and speeding up for non-critical info is mirroring the way we communicate in non-ham situations.  For example,  when we spell out a word or name phonetically for someone we are slowing down to ensure correct comprehension of our intended message.  An example of speed-up for non-critical information would be those legal statements at the end of some advertisements on radio and TV.  As a CW operator I've always appreciated it when the operator at the other end speeds up the identification portions once we've established contact at a comfortable, slower speed. &lt;/p&gt;&#xA;" OwnerUserId="1114" LastEditorUserId="1114" LastEditDate="2014-05-24T18:04:21.213" LastActivityDate="2014-05-24T18:04:21.213" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1826" PostTypeId="1" CreationDate="2014-05-26T03:30:56.030" Score="5" ViewCount="323" Body="&lt;p&gt;Higher frequencies have a higher energy, simply stated by &lt;a href=&quot;http://en.wikipedia.org/wiki/Planck_constant&quot; rel=&quot;noreferrer&quot;&gt;Planck's constant&lt;/a&gt;. When I am transmitting 100 watts on 500 kHz, and transmitting 100 watts on 5 GHz, is there an energy difference in the wave?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="218" LastEditDate="2014-05-29T12:36:42.303" LastActivityDate="2014-08-13T12:46:51.383" Title="Energy vs power in transmitters" Tags="&lt;physics&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1828" PostTypeId="2" ParentId="1820" CreationDate="2014-05-26T13:44:09.563" Score="-3" Body="&lt;p&gt;Properly grounding an antenna using a ground rod deep into the earth will provide a much better ground than the radials (aka ground planes.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radials act as a pseudo ground and provide other advantages as well. By bringing the ground higher up will help project the signal further distances and simultaneously help with sporadic RF interference with neighbouring electronics. Depending upon the location of the antenna it will also provide resistance for lightning strikes.&lt;/p&gt;&#xA;" OwnerUserId="1119" LastActivityDate="2014-05-26T13:44:09.563" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1829" PostTypeId="2" ParentId="1819" CreationDate="2014-05-26T13:51:12.737" Score="-3" Body="&lt;p&gt;When you use a magnetic mount antenna the metal ground plane underneath (usually the vehicle) is extremely important to the signal. The better the ground plane the further the signal will travel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for your question about the coaxial cable, this is extremely important as well. The coaxial cable sheath is used to bounce/reflect the RF energy all the way down the line. Without it, the RF power would most entirely be lost. Therefore using the ground sheath for the vertical element would result in a pretty much a complete loss of transmit power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coaxial cable is also engineered to have a specific impedance at the frequency you are transmitting. This impedance match ensures the maximum transfer of your signal to the antenna with minimal losses. Again, using the ground sheath for the transmit versus ground would result in a very bad impedance mismatch to the antenna.&lt;/p&gt;&#xA;" OwnerUserId="1119" LastActivityDate="2014-05-26T13:51:12.737" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1830" PostTypeId="2" ParentId="1826" CreationDate="2014-05-26T17:16:52.033" Score="4" Body="&lt;p&gt;Higher frequencies of electromagnetic radiation have higher energy &lt;em&gt;per photon&lt;/em&gt;; “the wave” you transmit is made up of huge numbers of (coherent) photons — for example, at 5 GHz, 100 watts corresponds to $10^{25}$ photons per second. Therefore, the individual photons' energy is not all that relevant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the same power (energy per time), count and frequency are inversely proportional; at a higher frequency, there are fewer photons emitted, each carrying more energy. We can derive this from the &lt;a href=&quot;https://en.wikipedia.org/wiki/Planck_constant&quot; rel=&quot;nofollow&quot;&gt;Planck relation&lt;/a&gt; which contains Planck's constant ($ν$ = frequency):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$E_{\text{photon}}=hν$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a relation of &lt;em&gt;individual photon energy&lt;/em&gt; $E_{\text{photon}}$ to frequency; to consider multiple photons we need to take further steps. First, let's relate a total energy by defining $n$ such that $nE_{\text{photon}}$ is the total energy of the transmission, and then using the Planck relation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$E_{\text{transmission}} = nE_{\text{photon}} = nhν$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, the example you asked about is in &lt;em&gt;power&lt;/em&gt;, not &lt;em&gt;energy&lt;/em&gt;, so we need to introduce time; dividing both sides by a time interval $t$ gives us:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$P_{\text{transmission}} = \frac{E_{\text{transmission}}}{t} = \frac{n}{t}hν$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that $\frac{n}{t}$ is the &lt;em&gt;rate&lt;/em&gt; of photons per time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then if we divide by $hν$ and rearrange we get:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\frac{P_{\text{transmission}}}{h\nu} = \frac{n}{t}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Plugging in your example values gives us values for $\frac{n}{t}$ of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\frac{100\, \mathrm{watts}}{h \cdot 5\,\mathrm{GHz}} \approx 3\cdot 10^{25} \text{ photons per second}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\frac{100\, \mathrm{watts}}{h \cdot 500\,\mathrm{kHz}} \approx 3\cdot10^{29} \text{ photons per second}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if we want to find out the energy-per-photon of your transmission, the total power is irrelevant and we simply use the Planck relation by itself:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$h \cdot 5 \,\mathrm{GHz} \approx 3.3×10^{-24} \,\mathrm{J}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$h \cdot 500 \,\mathrm{kHz} \approx 3.3×10^{-28} \,\mathrm{J}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is everything that Planck's constant tells us about the properties of your transmissions.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;However, these figures are almost irrelevant to the practice of radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often in discussions of the energies of photons the topic is photons of much higher individual energies, which become significant; for example, by being absorbed by individual atoms at specific energies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The photons in the &quot;radio&quot; portion of the electromagnetic spectrum are comparatively so low-energy that these “quantum” effects are not usually of interest, as opposed to the net effect of many coherent photons making up a field which pushes electrons around in antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The “energy in the wave” (provided we define such a quantity, either by choosing a duration in time or a volume of space) is entirely independent of the frequency of the wave.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-07-07T18:01:46.830" LastActivityDate="2014-07-07T18:01:46.830" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1831" PostTypeId="2" ParentId="1813" CreationDate="2014-05-27T05:41:02.280" Score="2" Body="&lt;p&gt;You should consider whether the Internet Radio Linking Project (&lt;a href=&quot;http://www.irlp.net/&quot; rel=&quot;nofollow&quot; title=&quot;IRLP&quot;&gt;IRLP&lt;/a&gt;) could eventually meet your goals.  There are currently a dozen or more IRLP nodes for the 2M, 70cm and higher bands in the San Jose, CA area.  However, there are currently no IRLP nodes listed as active in India according to the &lt;a href=&quot;http://www.irlp.net/&quot; rel=&quot;nofollow&quot;&gt;www.irlp.net&lt;/a&gt; site.  It's possible that there is a country/region-specific regulatory issue that is preventing nodes in India.  If there is no regulatory roadblock then you and your friend could maybe be the ones to establish an IRLP node in Banglore and put India on the IRLP map.&lt;/p&gt;&#xA;" OwnerUserId="1114" LastActivityDate="2014-05-27T05:41:02.280" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1832" PostTypeId="2" ParentId="1820" CreationDate="2014-05-27T06:38:15.893" Score="1" Body="&lt;p&gt;Be aware that connecting your antenna to a good solid earth, and then connecting your radio gear to that antenna, and to the mains electricity supply &lt;em&gt;can&lt;/em&gt; be a hazard in the event of a mains electrical fault.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some properties in some parts of the world are wired using a 'protective multiple earth' (PME) system, and bringing a 'real' earth into the shack can provide a hazard if there is a mains electrical fault. (Basically, if the neutral wire becomes loose &lt;em&gt;and&lt;/em&gt; there is a live-to-chassis type of short, then full mains current would flow through your antenna cable. Not likely to happen, but potentially very dangerous if it did. What WERE they thinking?!? My old house in the UK used to be wired like this until I rewired it myself.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check out this page &lt;a href=&quot;http://en.wikipedia.org/wiki/Earthing_system&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Earthing_system&lt;/a&gt; and find out (really find out) how your property is wired, before bringing an earth into your shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I gather from your user profile that you are in the US, and I don't know if PME has ever been common practice in the US - but where safety is involved I would always recommend checking first.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-05-27T06:38:15.893" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="1833" PostTypeId="2" ParentId="1006" CreationDate="2014-05-27T10:47:39.673" Score="7" Body="&lt;p&gt;If you're used to dealing with protocols between chips, like UART, SPI and I2C, then APRS will feel quite strange. Whereas if you've been involved with CAN, Ethernet, USB at the low level, then APRS will seem quite familiar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not as simple as 1200Hz means 0, and 2200Hz means 1. There are two things which make it different, firstly bit-stuffing, and secondly NRZI encoding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Bit-Stuffing&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reasons that will become clear in a moment, you're not allowed to transmit more than 5 1s in a row. If you want to transmit more than five 1s in a row, you'll have to stuff extra 0s to break up the string of 1s.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/p5TCA.png&quot; alt=&quot;Bit Stuffing&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;NRZI&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Non-Return to Zero inverted is an alternative way to encode a bit stream. Surprisingly, it's the change from one frequency to the next which encodes 0 and 1. Between each 1/1200th of a second, if the frequency changes, that's a 0, and if it doesn't change, that's a 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take your original bit stream. Imagine turning all the 0s into edges, and all the 1s into not-edges, like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/dX9Zn.png&quot; alt=&quot;APRS encoding&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then join up the edges, like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/1rz8V.png&quot; alt=&quot;APRS encoding&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The receiver uses the frequency changes to synchronise itself to the incoming bit stream. It needs to do this fairly often to make sure it stays synchronised. This is the reason that a long string of 1s isn't allowed. A long string of 1s means a long time without any frequency changes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more information on implementing APRS, there's a good set of blog posts on &lt;a href=&quot;http://hugosprojects.wordpress.com/&quot; rel=&quot;noreferrer&quot;&gt;Hugo's Projects&lt;/a&gt; which goes into detail about all of the implementation issues.&lt;/p&gt;&#xA;" OwnerUserId="1122" LastActivityDate="2014-05-27T10:47:39.673" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1834" PostTypeId="2" ParentId="1820" CreationDate="2014-05-29T00:28:34.830" Score="3" Body="&lt;p&gt;AM broadcast stations do &lt;em&gt;not&lt;/em&gt; use the Earth as ground for the antenna. To the contrary, they go through great expense laying huge radial fields precisely to avoid ground currents in the Earth. See these &lt;a href=&quot;http://www.qsl.net/k9ez/wtmjsite.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;pictures of WTMJ on qsl.net&lt;/a&gt;. Here's one of them:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/18xU8.jpg&quot; alt=&quot;tower base with radials&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look closely, there is a copper mesh all around the antenna base. Around the base perimeter, there is a wide copper strap. You can't see the radials directly in this picture, but there are &lt;em&gt;a lot&lt;/em&gt; of them: typically 120. They are attached to the copper strap around the perimeter. You can see a couple empty spools on which the radial wire was probably delivered (and by my estimation, there are many more such spools not in this picture).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Broadcast stations don't want antenna currents in the ground because the ground is not a great conductor. Resistive and magnetic losses in the ground would divert a significant fraction of electrical energy into warming the ground, but that energy would better be spent radiating a signal. When broadcasting at tens or hundreds of kilowatts, the associated currents can be quite huge, and the losses can get really big, really fast according to &lt;a href=&quot;http://en.wikipedia.org/wiki/Joule_heating&quot; rel=&quot;nofollow noreferrer&quot;&gt;Joule's law&lt;/a&gt;: $P = I^2 R$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An AM broadcast station will also have ground rods, but these are not for the operation of the antenna, and under normal operating conditions carry only negligible, ideally zero current. Their purpose is &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;lightning protection&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You &lt;em&gt;can&lt;/em&gt; operate a vertical antenna without radials, and it is sometimes expedient to do so. It is however quite inefficient. Keep your radials, or use an antenna such as a dipole or loop which does not require a ground plane to operate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-07-10T18:57:43.307" LastActivityDate="2018-07-10T18:57:43.307" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="1835" PostTypeId="2" ParentId="1826" CreationDate="2014-05-29T01:41:59.827" Score="5" Body="&lt;p&gt;If the birthrate in Canada is 400 thousand babies per year, and the birthrate is Russia is 1680 thousand babies per year, is there a population difference in the nations?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just as birthrate is a rate of stuff (births), &lt;a href=&quot;http://en.wikipedia.org/wiki/Power_%28physics%29&quot;&gt;power&lt;/a&gt; is a rate of &lt;a href=&quot;http://en.wikipedia.org/wiki/Energy&quot;&gt;energy&lt;/a&gt;. A &lt;a href=&quot;http://en.wikipedia.org/wiki/Watt&quot;&gt;watt&lt;/a&gt; is one &lt;a href=&quot;http://en.wikipedia.org/wiki/Joule&quot;&gt;joule&lt;/a&gt; per second, by definition. The frequency is irrelevant. To answer your question we need to know about &lt;em&gt;time&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you transmit 100 watts on 500 kHz for 1 second, and 100 watts on 5 GHz for 1 second, then each has transmitted the same energy:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 100 \mathrm W \cdot 1 \mathrm s = 100 \mathrm J $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It doesn't matter what the frequency is, or even that this is electromagnetic power. It could have been &lt;a href=&quot;http://en.wikipedia.org/wiki/Power_%28physics%29#Mechanical_power&quot;&gt;mechanical power&lt;/a&gt;. 100 watts of any kind for one second is 100 joules.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If by &quot;the wave&quot;, you mean &quot;per cycle&quot;, then our notion of time is something else.  At 500 kHz ($500\cdot 10^3 \text{cycles}/\mathrm s$), each cycle is one 500,000th of a second, or 2 microseconds. Transmitting at 100W, each cycle then carries the energy:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 100 \mathrm W&#xA;\left ( \frac{1 \mathrm s}{500\cdot 10^3 \: \text {cycle}} \right )&#xA;= \frac{100 \mathrm W \cdot 2 \mu \mathrm s}{\text{cycle}}&#xA;= \frac{200 \mu \mathrm J}{\text{cycle}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 5GHz ($5\cdot 10^9 \text{cycle}/\mathrm s$):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 100 \mathrm W&#xA;\left ( \frac{1 \mathrm s}{5\cdot 10^9 \: \text {cycle}} \right )&#xA;= \frac{100 \mathrm W \cdot 0.0002 \mu \mathrm s}{\text{cycle}}&#xA;= \frac{0.02 \mu \mathrm J}{\text{cycle}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, the energy per cycle at higher frequencies is less, which makes sense because there are more of them per unit time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Kevin Reid explains, Planck's constant relates to the energy of individual photons, which is relevant to quantum physicists, but not to amateur radio operators.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-05-29T12:34:05.630" LastActivityDate="2014-05-29T12:34:05.630" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1836" PostTypeId="1" AcceptedAnswerId="1838" CreationDate="2014-05-29T04:57:35.430" Score="6" ViewCount="508" Body="&lt;p&gt;I know that in the short wavelength region, where parabolic antennas are used, the aperture can be increased simply by making the dish larger, as is the case with the radio telescopes. But how to do this in the RF? If I make a half wave dipole larger, its resonant frequency decreases. The other way I can imagine is to make an array of antennas working in phase, but in this case it gets more directional with larger number of elements. Is there a way to increase antenna aperture without making it directional?&lt;/p&gt;&#xA;" OwnerUserId="1129" LastEditorUserId="76" LastEditDate="2015-12-15T22:24:03.287" LastActivityDate="2017-07-07T20:05:22.973" Title="How to increase antenna aperture?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1837" PostTypeId="2" ParentId="1810" CreationDate="2014-05-29T11:29:21.017" Score="4" Body="&lt;p&gt;Your primary concerns are likely to contain:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Characteristic impedance ($Z_0$). This is usually dictated by the other components in your system and is usually $50\Omega$ for amateur radio applications. $75\Omega$ components are also not difficult to find due to their widespread application in TV. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Loss. At a given frequency, a given cable will have some loss figure, usually given in units of decibels per unit length. Losses increase with frequency, so a cable that might work fine at 960 kHz wouldn't be much more than a heater at microwave frequencies. Because loss is proportionate to length, at shorter lengths a lossier cable may be more acceptable.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Power handling. Several things limit this. One is loss as above: losses become heat, and excessive heat will damage the cable. The cable must also be able to withstand the voltages associated with the power without suffering dielectric breakdown.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Physical characteristics. Do you need a cable rated for direct burial? UV exposure? If you need a tight bend radius, you probably need a smaller diameter cable. Flexible or rigid? Will the cable need to withstand repeated bending from handling, or is it in a permanent installation? Will people potentially step on the cable? Compatibility with connectors can be a concern: clearly you will not be attaching an SMA connector directly to a 2-inch hardline. Fortunately, coax cables tend towards standard dimensions and thus compatibility with connectors is usually not difficult. For example, there are many cables that have the same physical dimensions as, and accept the same connectors as RG-58.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Cost. The materials and manufacturing techniques used to achieve any of these desirable properties cost something. A good engineer is one that selects the cheapest solution which performs acceptably.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Availability. Can you buy it at the electronics store at the corner, or must it be ordered? Is it in stock? Is it sold by the foot or by the spool?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;With these concerns in mind, decide which are most important for your application, then browse distributor and manufacturer catalogs until you find something acceptable. The catalog will specify a few key parameters such as loss at a couple frequencies, basic construction, cost, and size. Pick a few candidates and then read the datasheets, which specify all the parameters in much more detail. Frequently they will also contain helpful information such as compatible connectors, applications to which the cable is especially well suited, etc. Then make your choice.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-05-29T11:29:21.017" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1838" PostTypeId="2" ParentId="1836" CreationDate="2014-05-29T18:12:36.500" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there a way to increase antenna aperture without making it directional?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not really. You can make the antenna more efficient by reducing losses, but since antennas are usually designed for minimum loss already, there is probably no significant gain to be made in this direction unless you are starting with an electrically small or poorly designed antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio telescopes do operate &quot;in the RF&quot;, so what applies to them also applies to any other antenna. Increasing the dish size does increase the effective aperture. It also increases directionality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you didn't know it already, effective antenna aperture ($A_\text{eff}$) and gain ($G$) are essentially two ways of specifying the same thing. They are related by the equation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ G = \frac {4 \pi A_\text{eff} } { \lambda^2 } $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming our antennas are already as efficient as we can make them, then we can't increase the aperture, or equivalently, gain, without also increasing directionality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's why. Consider you have a 1W transmitter. If you send that power equally in all directions, then you have an &lt;a href=&quot;http://en.wikipedia.org/wiki/Isotropic_radiator&quot; rel=&quot;nofollow&quot;&gt;isotropic radiator&lt;/a&gt; which has by definition a gain of 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's just say you found a way to increase the gain of this isotropic radiator without also increasing its directionality. That is, it has a gain greater than unity, but still sends energy equally in all directions. Were you to construct such a device, I would surround it with a &lt;a href=&quot;http://en.wikipedia.org/wiki/Dyson_sphere&quot; rel=&quot;nofollow&quot;&gt;Dyson sphere&lt;/a&gt;, which would capture all of the energy it transmitted. If your device had a gain of 2, then the 1W transmitter would be emitting 2W of power for my Dyson sphere to capture. I could then use the output of that Dyson sphere to power another instance of your device, giving me 4W. I could go on cascading instances of this device and obtain limitless power. It's a perpetual motion machine, so probably is impossible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By &lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_%28electromagnetism%29&quot; rel=&quot;nofollow&quot;&gt;reciprocity&lt;/a&gt;, it can be seen that the same thing is true when receiving. I can make an antenna array which has some greater gain in some direction, but it must necessarily have less gain in some other direction for some given phasing configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you provide a way to vary the phasing of the antenna, such as combining the signals from each element independently and dynamically in software, rather than in hardware, then you can pick the best phasing for a particular signal which might come from any direction. However, this requires that &quot;best&quot; is defined and measured dynamically. Modern radio communication systems do this, for example &lt;a href=&quot;http://en.wikipedia.org/wiki/MIMO&quot; rel=&quot;nofollow&quot;&gt;MIMO&lt;/a&gt; in &lt;a href=&quot;http://en.wikipedia.org/wiki/IEEE_802.11n-2009&quot; rel=&quot;nofollow&quot;&gt;802.11n&lt;/a&gt;. However, it adds complexity to the system, and I guess might be considered as &quot;cheating&quot; as far as your question is concerned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, you can provide an additional source of energy as an amplifier. This adds gain to all directions, so you could say it increases antenna aperture. Because you must supply the amplifier with additional energy, it is not a perpetual motion machine. While we use amplifiers all the time, we don't usually consider this as increasing gain or aperture because that way of thinking isn't very useful. If the antenna directionality is not increased, than the amplifier increases noise as well as signal. That is, the &lt;a href=&quot;http://en.wikipedia.org/wiki/Signal-to-noise_ratio&quot; rel=&quot;nofollow&quot;&gt;signal to noise ratio&lt;/a&gt; remains the same.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-05-29T18:12:36.500" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1840" PostTypeId="2" ParentId="1819" CreationDate="2014-05-30T16:14:00.117" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Why on the magmount, and other antennas like AM towers is the ground or counterpoise not as important?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It &lt;em&gt;is&lt;/em&gt; important. For example, if you try to put a magmount on a fiberglass car, it won't work very well. It won't work well on a bicycle, either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the ground plane (roof of car, radials under antenna, etc) to work well, it must approximate an infinite plane of perfectly conductive material. Of course, we don't have infinitely conductive materials, but any reasonably conductive metal is a good enough approximation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We also don't have infinite planes. However, as the distance away from the feedpoint increases, the electric and magnetic field strengths decrease. Rule of thumb: the ground plane should extend at least a quarter-wavelength in all directions. Beyond this distance there isn't much current or voltage, so the ground plane becomes less significant. You can extend it farther if you want, but you get diminishing returns in efficiency and only small changes to antenna parameters like feedpoint impedance and resonant frequency.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Can this be switched around, lets say I used the center coax as the RF ground, and the exterior coax as the vertical element, would this work equivalently?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes and no, depending on the details of the situation. &lt;a href=&quot;https://electronics.stackexchange.com/q/73375/17608&quot;&gt;Voltage is a relative measurement between two points&lt;/a&gt;, and electrically &lt;a href=&quot;https://electronics.stackexchange.com/questions/56210/what-is-ground-and-what-does-it-do&quot;&gt;what we choose to call &quot;ground&quot; is arbitrary&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a magmount antenna on a car, were you to switch the center and shield connections, nothing much changes. The vertical element still oscillates at an AC voltage relative to the body of the car, which is the other half of the antenna. However, this mostly works because the car is &lt;a href=&quot;http://en.wikipedia.org/wiki/Floating_ground&quot; rel=&quot;nofollow noreferrer&quot;&gt;floating&lt;/a&gt;. It runs on a battery and is on insulating tires, and is not connected to anything else except through some small, mostly negligible capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to try this at a station where the ground plane is not a floating car body but rather radials firmly connected to Earth, then maybe bad things would happen, depending on how things are connected. For example, it's common to have the chassis connected to Earth. If you flip the shield and center connections where the radio meets the feedline you have a problem: the chassis of the radio is connected to Earth, and the center pin on the radio's antenna connector is also connected to Earth (because it's connected to the shield of the feedline, which goes to the antenna's radials). Thus, the thing between your radio's output isn't the antenna, but two points on the ground. Probably not what you wanted.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2014-05-30T16:14:00.117" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1841" PostTypeId="1" CreationDate="2014-05-30T18:09:32.843" Score="6" ViewCount="304" Body="&lt;p&gt;&lt;a href=&quot;http://www.businessinsider.com/social-network-ham-radio-2014-5&quot;&gt;This article&lt;/a&gt; mentions the Ham Shack aboard the ISS. From the picture it looks like a small very light rig like a Yaesu FT-817. What radio(s) do the astronauts use when they talk to Hams and School-age kids (with help from licensed hams) on earth?&lt;/p&gt;&#xA;" OwnerUserId="643" LastEditorUserId="643" LastEditDate="2014-05-30T18:38:04.060" LastActivityDate="2014-07-28T20:41:41.943" Title="What rig or rigs are onboard the ISS?" Tags="&lt;equipment&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1842" PostTypeId="2" ParentId="1841" CreationDate="2014-05-30T18:36:58.400" Score="3" Body="&lt;p&gt;According to Wikipedia and ISSFANCLUB, in 2011, they had a Kenwood TM-D700 UHF/VHF rig, and also an Ericcson UHF/VHF rig.  When the Kenwood had problems, they switched for a while to the Ericcson backup unit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Amateur_Radio_on_the_International_Space_Station&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Amateur_Radio_on_the_International_Space_Station&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://issfanclub.com/node/35931&quot; rel=&quot;nofollow&quot;&gt;http://issfanclub.com/node/35931&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="643" LastActivityDate="2014-05-30T18:36:58.400" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1844" PostTypeId="1" CreationDate="2014-06-01T01:10:39.653" Score="4" ViewCount="936" Body="&lt;p&gt;I have mounted mobile verticals (mag mounts) on my bicycle, but I have learnt that a bike does not have a good RF ground because there is nothing close to a plane. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without wasting too much more space, what is a better antenna I can use for 2m/ 70cm on my bicycle? &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-06-02T00:12:59.890" Title="Bicycle mobile antenna" Tags="&lt;mobile&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1845" PostTypeId="1" CreationDate="2014-06-01T21:15:44.767" Score="9" ViewCount="5374" Body="&lt;p&gt;So, I key up on a repeater to see if it works, or to see what cool courtesy tone they are using. I don't do anything else. Is it illegal or bad ham radio etiquette to just key up for a second, key down, and not do anything else?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where: USA, CO, VHF/UHF REPEATERS&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-06-01T21:33:50.733" LastActivityDate="2019-10-07T14:11:46.627" Title="Is it illegal to key up and not identify?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;procedure&gt;&lt;repeater&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1846" PostTypeId="1" CreationDate="2014-06-01T21:19:38.297" Score="3" ViewCount="787" Body="&lt;p&gt;What is the closest antenna ever made to an isotropic antenna? That is, has the same gain in every direction in free space?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-06-02T12:24:04.480" Title="Closest antenna to an isotropic?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="7" ClosedDate="2014-06-03T17:24:01.780" ContentLicense="CC BY-SA 3.0" />
  <row Id="1847" PostTypeId="2" ParentId="1845" CreationDate="2014-06-01T21:33:01.047" Score="6" Body="&lt;p&gt;Yes, because you have transmitted but not identified. Whether there is a repeater listening to your transmission is irrelevant.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-06-01T21:33:01.047" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1849" PostTypeId="2" ParentId="1845" CreationDate="2014-06-01T23:45:11.970" Score="5" Body="&lt;p&gt;As per the etiquette part of the question, the general consensus is to not simply key up for a second.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don’t want to engage in conversation, but simply want to see if you can access a certain repeater, simply say your call and 'testing'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a signal report from another amateur, state that in plain English. Example: 'This is [your callsign], can someone give me a signal report?'&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="1135" LastEditDate="2014-06-01T23:59:44.347" LastActivityDate="2014-06-01T23:59:44.347" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1850" PostTypeId="2" ParentId="1844" CreationDate="2014-06-02T00:07:38.333" Score="1" Body="&lt;p&gt;The ground plane for a 2m or 70cm vertical would be sufficiently provided by the bicycle's frame. I however would try to hard-wire the mag mount with a cable to the frame. Even a simple alligator clip would suffice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For better performance you could try the J-Pole design, which doesn't require the bike to provide it's ground plane. Here is one design for 2m:&#xA;&lt;a href=&quot;http://vk2fmdb.blogspot.com.au/2012_08_01_archive.html#6475312433642669543&quot; rel=&quot;nofollow&quot;&gt;http://vk2fmdb.blogspot.com.au/2012_08_01_archive.html#6475312433642669543&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you start operating HF from a bicycle you may need to check out some ground tuned circuits to provide a virtual ground.&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="1135" LastEditDate="2014-06-02T00:12:59.890" LastActivityDate="2014-06-02T00:12:59.890" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1851" PostTypeId="2" ParentId="1845" CreationDate="2014-06-02T01:11:36.383" Score="23" Body="&lt;p&gt;Bad etiquette and illegal. Bad etiquette because anyone else scanning the repeater will hear your useless silence, and illegal by &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.2.159.10&quot; rel=&quot;noreferrer&quot;&gt;§97.119&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§97.119   Station identification.&lt;/p&gt;&#xA;&lt;p&gt;(a) Each amateur station, except a space station or telecommand station, &lt;strong&gt;must transmit its assigned call sign on its transmitting channel at the end of each communication&lt;/strong&gt;, and at least every 10 minutes during a communication, for the purpose of clearly making the source of the transmissions from the station known to those receiving the transmissions. &lt;strong&gt;No station may transmit unidentified communications or signals&lt;/strong&gt;, or transmit as the station call sign, any call sign not authorized to the station.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-10-03T15:36:59.420" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="1852" PostTypeId="1" AcceptedAnswerId="1960" CreationDate="2014-06-02T01:51:52.557" Score="3" ViewCount="136" Body="&lt;p&gt;As an extreme example, take mobile HF antennas. These can have very low feedpoint impedances, maybe as low as $6\Omega$. The ideal impedance of a quarter/wave vertical is $36\Omega$, but electrically lengthening it makes the impedance go down. How's that work?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-06-19T16:36:51.880" LastActivityDate="2014-08-05T21:51:43.500" Title="How does inductive base loading cause low feedpoint impedance in verticals?" Tags="&lt;impedance&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1854" PostTypeId="2" ParentId="1846" CreationDate="2014-06-02T12:24:04.480" Score="2" Body="&lt;p&gt;An isotropic antenna &lt;em&gt;can not exist&lt;/em&gt;. Asking how &quot;close&quot; we can get doesn't really make sense. It's like asking how close we can get to any other impossible thing, like creating &lt;a href=&quot;http://en.wikipedia.org/wiki/Perpetual_motion&quot; rel=&quot;nofollow noreferrer&quot;&gt;perpetual motion&lt;/a&gt;. Can we say one thing is &lt;em&gt;closer&lt;/em&gt; to violating the laws of thermodynamics than another? No: all things ever observed obey these laws, no exceptions. Likewise, all antennas ever observed obey &lt;a href=&quot;http://en.wikipedia.org/wiki/Maxwell%27s_equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;Maxwell's equations&lt;/a&gt;, so none can be isotropic. Not even a little bit. No exceptions known to science.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do Maxwell's equations forbid isotropic antennas? I'll explain by analogy. Imagine a ball with some hair on it. Is there any way to comb this hair flat on the ball such that there is not at least one tuft?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/qFS3r.png&quot; alt=&quot;hairy ball&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There isn't. This is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Hairy_ball_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;hairy ball theorem&lt;/a&gt;, which states &quot;there is no nonvanishing continuous tangent vector field on even-dimensional n-spheres.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, imagine that the hairs are the electric or magnetic field radiating from your antenna. We are looking for a vector field on a sphere, so the &quot;tuft&quot;, where the hair sticks straight out, is a vector of zero magnitude. This is a point where there is no radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why does the hairy ball theorem apply? Because electromagnetic waves are &lt;a href=&quot;http://en.wikipedia.org/wiki/Transverse_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;transverse waves&lt;/a&gt;. This is why the tufts count as vectors of zero magnitude and not as vectors sticking out: the &lt;em&gt;only&lt;/em&gt; direction the lines of force can go in a field that you want to radiate away from that sphere are tangential to the sphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Contrast this with sound waves, which are &lt;a href=&quot;http://en.wikipedia.org/wiki/Longitudinal_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;longitudinal waves&lt;/a&gt;. For these, the lines of force must be perpendicular to the sphere, and an isotropic radiator is easily realized: just make the hair stick straight out everywhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the consequence of this is that any antenna must not radiate it at least one direction. Beyond that, arbitrary radiation patterns are possible, but none of them are close to isotropic.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-06-02T12:24:04.480" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1855" PostTypeId="2" ParentId="1706" CreationDate="2014-06-03T02:10:12.620" Score="1" Body="&lt;p&gt;This is an axial mode helix with gain of about 10 dBi. It produces right hand or clockwise polarization.  Circular polarization will fight fade over long paths much better than linear.  However, circular to linear links will experience a 3 dB loss.&lt;/p&gt;&#xA;" OwnerUserId="1149" LastEditorUserId="2988" LastEditDate="2017-05-13T18:47:30.490" LastActivityDate="2017-05-13T18:47:30.490" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1856" PostTypeId="1" AcceptedAnswerId="1869" CreationDate="2014-06-03T02:36:56.633" Score="2" ViewCount="316" Body="&lt;p&gt;I've had this suggested to match 50 ohm coax to a lower feedpoint impedance, like a vertical, especially mobile shortened verticals. What's it called?&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/eVGvb.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2feVGvb.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(CircuitLab has no symbol for an inductor with a tap, but you get the idea)&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2017-04-28T18:01:48.113" LastActivityDate="2017-04-28T18:01:48.113" Title="What is this matching technique called?" Tags="&lt;antenna&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1858" PostTypeId="2" ParentId="1463" CreationDate="2014-06-04T03:13:04.120" Score="1" Body="&lt;p&gt;Try using the Friis equation for questions such as this. See &lt;a href=&quot;http://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Friis_transmission_equation&lt;/a&gt; for more information.&lt;/p&gt;&#xA;" OwnerUserId="1157" LastActivityDate="2014-06-04T03:13:04.120" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1859" PostTypeId="1" AcceptedAnswerId="1865" CreationDate="2014-06-04T11:05:37.707" Score="7" ViewCount="40071" Body="&lt;p&gt;I want to use an end-fed wire antenna, but what would be the best length of wire for the 20m and 40m bands?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to work this out?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is assuming a tuner will be used.&lt;/p&gt;&#xA;" OwnerUserId="1131" LastEditorUserId="76" LastEditDate="2017-01-19T00:28:29.223" LastActivityDate="2019-06-19T08:58:47.080" Title="End-fed wire antenna lengths" Tags="&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;" AnswerCount="7" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1860" PostTypeId="2" ParentId="1859" CreationDate="2014-06-04T14:27:45.920" Score="0" Body="&lt;p&gt;Yes, it is possible to even make very far contacts on random wire antennas.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.sparkbangbuzz.com/easy-ten/easy-ten.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;See this site&lt;/a&gt; for information about the worlds simplest transmitter circuit,and how he was able to hear it from more than 10 miles away on less than 10 milliwatts with a wire outside his window going to trees.&lt;/p&gt;&#xA;&lt;p&gt;Just put a variable capacitor (300pf or so) in series with the antenna and tune around for maximum power output without swamping the oscillator.&lt;/p&gt;&#xA;&lt;p&gt;I enjoy connecting random wires to my bicycle mobile antenna, which consists of a 10 foot long PVC pipe.&lt;/p&gt;&#xA;&lt;p&gt;For the best length, question I say use a 3/8th wave wire; a good compromise between the low impedence quarter wave, and high impedance half wave.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-06-04T14:43:06.533" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1861" PostTypeId="2" ParentId="1859" CreationDate="2014-06-04T22:33:34.243" Score="0" Body="&lt;p&gt;The OP's question may have been edited, but I didn't read the word 'random' in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, with such a broad term as 'wire antenna', the 'best length of wire' depends on what you want to use it for. Some wire antennas with a vertical polarisation like a quarter wave vertical have to have lower take-off angles than a horizontally polarized like a dipole made from wire strung up between the trees in a back yard. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To calculate the lenghts: a rule of thumb for a dipole wire antenna length is: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;dipole length (in feet) = 468 / f (MHz)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that will be 32.96 feet for a dipole on 20m (each leg 16.48 feet) and 65.92 feet total length for a 40m dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a Loop antenna the length also depends on the shape of the loop (Triangle, Rectangular, Square, Round) but start with a full wavelength for the band you wish to work on and tune from there. With a loop antenna I also found that a loop resonant on 40m it will tune up on 80, 20, 15 and 10m but I recently changed to half the size (1 wave length on 20m) and it no longer tunes up on 15 and 10.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An excellent receive antenna for the lower bands is the &lt;a href=&quot;http://www.w0btu.com/Beverage_antennas.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Beverage antenna&lt;/a&gt;. If you have the space to put one (or more) up you will notice that this antenna is very directional and very low noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have found wire antennas to be a great (and often low cost) way to experiment with antenna designs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You mentioned you already have a tuner, so your antenna designs will not have to be 100% perfect, another reason to just have a go at it.&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="8717" LastEditDate="2017-06-30T20:11:25.460" LastActivityDate="2017-06-30T20:11:25.460" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1862" PostTypeId="1" AcceptedAnswerId="1883" CreationDate="2014-06-05T19:42:41.100" Score="5" ViewCount="115" Body="&lt;p&gt;In order to track skydivers/BASE-jumpers with &lt;a href=&quot;http://www.flysight.ca/&quot; rel=&quot;noreferrer&quot;&gt;flysight&lt;/a&gt; I am looking for a one-way radio system to transmit the location data.  System needs the following specifications:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Frequency:          Not important, preferable legal (Europe)&#xA;Bandwidth           1000 bytes per second (at least)&#xA;Range:              4000 meters&#xA;Line of Sight       Yes &#xA;Latency             As little as possible&#xA;Mobile Coverage     Not available&#xA;Transmitter&#xA;    - Location      Air&#xA;    - Movement      Moving, up to 200 km/h horizontal groundspeed&#xA;                    vertical distance: closing towards receiver during operation&#xA;    - Interface     USB or serial&#xA;    - Weight        As little as possible&#xA;    - Size          As small as possible&#xA;Receiver&#xA;    - Location      Ground&#xA;    - Movement      Stationary during operation, movable by car&#xA;    - Interface     Not important, what ever works&#xA;    - Weight        Not important, movable by car&#xA;    - Size          Not important, movable by car&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Any suggestions?&lt;/p&gt;&#xA;" OwnerUserId="1163" LastEditorUserId="76" LastEditDate="2014-06-05T20:25:34.113" LastActivityDate="2014-06-11T23:48:45.637" Title="LOS One-way radio system, 4km with at least 1000bytes/s" Tags="&lt;digital-modes&gt;&lt;equipment-design&gt;" AnswerCount="2" CommentCount="13" ContentLicense="CC BY-SA 3.0" />
  <row Id="1863" PostTypeId="1" AcceptedAnswerId="1867" CreationDate="2014-06-06T00:41:01.317" Score="3" ViewCount="1280" Body="&lt;p&gt;Take for example, the &lt;a href=&quot;http://www.dxengineering.com/parts/hsr-4btv&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hustler 4BTV&lt;/a&gt;. It has traps formed by an inductor, covered by a sleeve that's connected at the lower end, and the upper end is covered by a non-conductive cap:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/VJvT3.gif&quot; alt=&quot;sleeve trap diagram&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://hamuniverse.com/hustlerbtvtrapcalibration.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;tuning instructions&lt;/a&gt; for this antenna advise the installer to move the sleeve up or down relative to the coil it covers, rather than adjusting the length of the intermediate elements. What's the electrical explanation for why this effects a change in resonant frequency?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2016-07-12T14:00:37.317" LastActivityDate="2016-07-12T14:00:37.317" Title="How does adjusting the sleeve on antenna traps tune an antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1864" PostTypeId="2" ParentId="1823" CreationDate="2014-06-06T03:14:25.733" Score="2" Body="&lt;p&gt;There's not a FM calling frequency for this sort of thing.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM requires good signals, and meteor scatter is very weak and intermittent when it exists at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The meteor scatter crowd is mostly digital now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most have all mode (SSB) radios hooked to their computer through some kind of sound card A/D interface and are using the &lt;a href=&quot;http://www.physics.princeton.edu/pulsar/K1JT/&quot; rel=&quot;nofollow&quot;&gt;free WSJT software&lt;/a&gt; written by Nobel prize winning physicist Joe Taylor K1JT.  This software has esoteric modes that can deal with short lived paths or very weak signals in meteor scatter, and very weak slow signal modes for EME, and below the noise HF propagation.  The messages exchanged are very short, typically only callsigns, R's, or maybe a single number for a report.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is an online hangout for Meteor Scatter Enthusiasts at &lt;a href=&quot;http://www.pingjockey.net/cgi-bin/pingtalk&quot; rel=&quot;nofollow&quot;&gt;Ping Jockey&lt;/a&gt;.  &lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2014-06-06T08:31:04.507" LastActivityDate="2014-06-06T08:31:04.507" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1865" PostTypeId="2" ParentId="1859" CreationDate="2014-06-06T14:10:39.877" Score="2" Body="&lt;p&gt;The length doesn't matter much. If you make it the right length, then it will present a good match to your feedline, but if you have a tuner, and either place it near the antenna or use a low-loss feedline, then that doesn't matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible to get really unlucky and pick a wire length that's outside of your tuner's range. What these lengths are depend on your tuner and also the wire's surroundings and also the ground system. Odds are that most lengths are fine though, so the easiest solution is to pick a length based on something else (like, the room you have available) and if you get unlucky, roll the dice again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, if the wire is too short, then it won't be a very effective radiator. If the wire is longer than half a wavelength, then making it longer doesn't make it any more effective. Making it shorter than half a wavelength doesn't suddenly stop making it working either, so if you don't have enough space to put up a full half-wavelength that's fine, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fact is, if you can effectively couple RF current into something that's large relative to the wavelength and is a good conductor, you get an antenna. The bigger problem with end-fed antennas is subtle: it's actually only half the antenna. The ground is the other half, and I don't mean Earth. I mean whatever is attached to the other half of the feedline. If you are using a tuner that has just one wire coming out of it, then the other half is the tuner's chassis, and whatever is connected to it. If you are concerned about making a good antenna, my advice would be to &lt;a href=&quot;http://www.w8ji.com/long_wire_antenna.htm&quot; rel=&quot;nofollow&quot;&gt;learn more about end-fed antennas work, and interact with ground&lt;/a&gt;, before worrying about length.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-06-06T14:10:39.877" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1866" PostTypeId="1" AcceptedAnswerId="1868" CreationDate="2014-06-07T11:58:46.223" Score="6" ViewCount="670" Body="&lt;p&gt;Here's a problem: you buy a fancy new vertical for a fair bit of coin, but there's no coax connector on the thing. There are just screw terminals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/rN7ZP.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need to attach coax to it, but in such a way that the coax termination is protected from the elements so you don't get water wicking into the shield. How do you accomplish that?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-06-09T11:44:16.643" LastActivityDate="2019-06-12T10:50:08.790" Title="Weather-proofing antenna connections" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;coaxial-cable&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1867" PostTypeId="2" ParentId="1863" CreationDate="2014-06-08T02:21:00.043" Score="6" Body="&lt;p&gt;The trap is an LC parallel circuit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZDDnO.png&quot; alt=&quot;capacitor and inductor in parallel&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At some frequency, the inductive and capacitive reactances are equal, and the trap looks like a very high impedance. No significant current can flow through this impedance, and the rest of the antenna is effectively disconnected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the sleeve is adjusted up, more of it overlaps the top section of the trap, increasing the capacitance. Now the trap isn't precisely resonant, and starts to look more like a series capacitor. This electrically lengthens the antenna, effectively making the rest of the antenna a capacitive hat, making it resonate at a lower frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adjusting the sleeve down has the opposite effect: it reduces capacitance and now the trap looks more like a series inductor. This is not like a loading coil: adding series inductance at the &lt;em&gt;top&lt;/em&gt; electrically shortens the antenna, making it resonate at a higher frequency. This is not something you ordinarily see since people usually want to make a small antenna work as a bigger one, not the other way around.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/1eAix.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f1eAix.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With these kinds of adjustments, you can get a very large change in resonant frequency without moving the trap very far, but it's not without disadvantages. Since current is no longer flowing in a quarter-wave section, it won't behave like a quarter-wave antenna. The feedpoint impedance and radiation pattern will be different. There are most likely higher losses as well, since currents are flowing through more metal, increasing resistive losses. The magnitude of these problems is proportional to the distance from resonance the trap has been adjusted.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-06-08T02:21:00.043" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1868" PostTypeId="2" ParentId="1866" CreationDate="2014-06-09T15:52:34.603" Score="6" Body="&lt;p&gt;What I have done once for a dipole was use a SO-239 panel receptacle with a solder cup to make my own &quot;coax to two wire&quot; adapter. For example, I used something like &lt;a href=&quot;http://www.mouser.com/ProductDetail/Amphenol/83-1R-SO-239/?qs=anVall655kREaYeTUBymuQ==&amp;amp;gclid=CjkKEQjwttWcBRCuhYjhouveusIBEiQAwjy8IPZlwQjiVm7idde-fLHXPgfICS_ZxSBiP9-ZSuhSDVTw_wcB&quot; rel=&quot;nofollow noreferrer&quot;&gt;this part&lt;/a&gt; from Mouser. That way, I had a whole piece of coax running to the antenna that could be weatherproofed, and then an exposed section that just had regular wire soldered to the receptacle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/izJpf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/izJpf.jpg&quot; alt=&quot;picture of a panel-mounted coax connector&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I would try to fasten the &quot;panel&quot; side to the ground terminal somehow, and then run wire from the center conductor to the &quot;positive&quot; terminal of the antenna. The center insulator would need to be weatherproofed as well, but it should be a lot easier than weatherproofing coax braid.&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="22" LastEditDate="2017-05-17T00:15:03.243" LastActivityDate="2017-05-17T00:15:03.243" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1869" PostTypeId="2" ParentId="1856" CreationDate="2014-06-09T20:15:01.820" Score="1" Body="&lt;p&gt;This is commonly called a &quot;Tapped Loading Coil&quot;, and combines the functions of loading coil and RESONANT transformer. Typically used with a shortened vertical antenna, the impedance of the coil is selected to cause the antenna to be resonant on the desired frequency. The position of the tap is then adjusted to match the impedance of the transmitter to the resonant antenna circuit. &lt;/p&gt;&#xA;" OwnerUserId="1015" LastEditorUserId="1015" LastEditDate="2014-06-10T16:50:05.437" LastActivityDate="2014-06-10T16:50:05.437" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1870" PostTypeId="1" CreationDate="2014-06-10T18:33:38.453" Score="4" ViewCount="2398" Body="&lt;p&gt;I've been asked to specify an amateur radio for a project which is very general purpose in nature, including HF, VHF, and UHF bands. Cost and user friendliness is a concern, so I wanted to avoid multiple radios and additional complexity when multi-band radios are available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A quick check shows that the FT-817ND fits the requirements, but I must now assert that it is the best fit for the requirements, and not merely a good fit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do Kenwood, Icom, or other manufacturers have a combined HF/VHF/UHF radio?&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2014-12-02T00:22:11.693" LastActivityDate="2014-12-02T00:22:11.693" Title="What radios compare favorably with the FT-817ND?" Tags="&lt;transceiver&gt;" AnswerCount="2" CommentCount="5" ClosedDate="2014-07-14T13:35:46.193" ContentLicense="CC BY-SA 3.0" />
  <row Id="1871" PostTypeId="2" ParentId="1463" CreationDate="2014-06-10T21:16:23.540" Score="-1" Body="&lt;p&gt;Your question is unanswerable with out detailed information, most of which is not obtainable.&#xA;There are many issues that limit the distance on 802.11 &quot;WiFi&quot; communications, some of which are: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The transmitter power of the devices AT BOTH ENDS of the link&lt;/li&gt;&#xA;&lt;li&gt;The antenna system gain at both ends of the link&lt;/li&gt;&#xA;&lt;li&gt;The ambient RF noise level at both ends of the link&lt;/li&gt;&#xA;&lt;li&gt;The &quot;timeout&quot; value set in software at both ends of the link&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Having higher transmit power at one end will only help if the ambient RF noise level at the OTHER end of the link is high because both ends must hear the other for communication to occur. Having a 1 watt transmitter at one end and a cell-phone at the other won't (usually) give you any better results than the 50 milliwatts or so out of a normal access point. Note also that &quot;bi-directional amplifiers&quot; seldom give any better response (except in the case where the amp is located at the antenna and is used to overcome feed line losses).&#xA;Antenna gain is one thing under your control that WILL help out, since a high antenna helps receive as much as it helps transmit power. Better antennae make better links!&#xA;The ambient RF noise level &quot;is what it is&quot; and is seldom under your control.&#xA;The &quot;timeout&quot; value is the amount of time the system waits before giving up on a reply to a message and is usually set low enough that it will be the &quot;hard limit&quot; on how far you can make a link work. It is, with rare exception, not something that you can get access to. The actual value varies by device and almost never published for consumer devices.&#xA;Experimentation is about your only way to get an answer. Beg, borrow, or buy a wireless router or access point that can connect to an external antenna. B, b, or b a high gain antenna. Connect them together and place them on a high point, turn on your wifi, turn off your Mobile Network connection, dial up Pandora and start walking. When you stop hearing music that's as far as it works.&lt;/p&gt;&#xA;" OwnerUserId="1015" LastActivityDate="2014-06-10T21:16:23.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1872" PostTypeId="1" CreationDate="2014-06-10T22:20:53.147" Score="6" ViewCount="307" Body="&lt;p&gt;I have been a ham not quite long enough to experience field day. I have been excited for the weekend ever since I heard about it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I looked at the ARRL site for field days in my location, and found a few I could visit. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I currently don't have HF capabilities yet due to cost of being a teenager, but I wish I still could enjoy the fun. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the day like exactly if I attend one of the ones listed on the ARRL, and will I need to find some equipment before? I might be able to get an HF rig from my friend's house if I need it because he left for a month and he just has it sitting there, but the rig is far from &quot;really good&quot; and does not have tiny filters to block all unwanted signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BTW I'm in the USA if that's important, although field day is a worldwide activity.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-06-11T19:09:39.167" LastActivityDate="2017-06-03T16:59:34.757" Title="What exactly is field day, and do I need equipment?" Tags="&lt;united-states&gt;&lt;contest&gt;&lt;field-day&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1876" PostTypeId="2" ParentId="1870" CreationDate="2014-06-11T15:38:53.633" Score="0" Body="&lt;p&gt;The Icom &lt;a href=&quot;http://www.eham.net/reviews/detail/11080&quot; rel=&quot;nofollow&quot;&gt;IC-7100&lt;/a&gt; has a similar level of band coverage, and while it's significantly more expensive has features that may make it worth the cost difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Elecraft &lt;a href=&quot;http://www.eham.net/reviews/detail/10271&quot; rel=&quot;nofollow&quot;&gt;Kx3&lt;/a&gt; goes to 6M, and has an optional 2M add-on as well.  It wouldn't cover 70CM, and the cost is also higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Wouxun quad band &lt;a href=&quot;http://www.eham.net/reviews/detail/11587&quot; rel=&quot;nofollow&quot;&gt;UV-950P&lt;/a&gt; mobile covers 10M, 6M, 2M, and 70CM.  Not the full HF range, but depending on the requirements it might fit.  Notably it's significantly less expansive, and has two receivers and transmitters, allowing more flexibility. Note that this only supports FM transmission, no typical SSB modes on HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TYT &lt;a href=&quot;http://www.eham.net/reviews/detail/11746&quot; rel=&quot;nofollow&quot;&gt;TH9800&lt;/a&gt; also covers 10M, 6M, 2M, and 70CM. Again, while it may receive AM, it can only transmit FM, and doesn't receive SSB or other typical HF modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without a better list of requirements, it's difficult to suggest other solutions, but the above are comparable to the FT-917ND in that they support HF, VHF, and UHF operation.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2014-06-11T16:07:48.727" LastActivityDate="2014-06-11T16:07:48.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1877" PostTypeId="2" ParentId="1870" CreationDate="2014-06-11T18:41:03.147" Score="2" Body="&lt;p&gt;There is no FT-917ND; you're probably referring to the FT-817ND. I own one and its peak output is 5 watts and you can modify it to put out a little more — up to 10 watts, I think, but I haven't metered it. Just hold down ABC and turn it on to get the system menu and do the mod.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would say if you don't mind an external battery the FT-857D is a great alternative because you have up to 100 watts of output, but shorter battery life or heavier batteries. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as a QRP (low power) radio goes, not much beats the FT-817ND. Just make darn sure you have a good antenna and learn what a 'counterpoise' is because that's a critical part of any vertical or unbalanced antenna and it's the difference between a great signal and no signal. For example, if you're using a telescopic vertical antenna, you need to connect a wire that is around 15 feet long to the GND screw on the radio and run it straight out laid across the ground. The length will vary depending on which frequency you're on. This makes a huge difference because the wire (which is a counterpoise) forms a capacitive ground and is the other half of the vertical antenna.&lt;/p&gt;&#xA;" OwnerUserId="1191" LastEditorUserId="76" LastEditDate="2014-06-11T19:03:37.427" LastActivityDate="2014-06-11T19:03:37.427" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1878" PostTypeId="2" ParentId="899" CreationDate="2014-06-11T18:51:23.857" Score="1" Body="&lt;p&gt;The shield prevents (or greatly reduces) influence of the electric field component of the received signal, making the loop effectively a &quot;pure magnetic&quot; antenna. Shielding makes the antenna &quot;quieter&quot; than an unshielded loop or whip antenna by preventing the capacitive coupling of localized noise sources. It is particularly effective in shielding against the intrusion of impulse noise from power line arcs, light dimmers, fluorescent lights and television &quot;buzz&quot;.&lt;/p&gt;&#xA;" OwnerUserId="1015" LastActivityDate="2014-06-11T18:51:23.857" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1879" PostTypeId="2" ParentId="1872" CreationDate="2014-06-11T19:33:06.673" Score="2" Body="&lt;p&gt;The field day location finder usually has info about the group running the local field day op.  Get in contact with them about participating, see if they have any needs you can help with (sometimes it's not gear that is needed).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last time I went to a field day location, they had a station for each band/mode they were operating on, and when I walked up they pointed me at the 20m SSB station, walked me through their logging software, and turned me loose.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ping the locals and see what the situation is.&lt;/p&gt;&#xA;" OwnerUserId="308" LastActivityDate="2014-06-11T19:33:06.673" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1880" PostTypeId="2" ParentId="1872" CreationDate="2014-06-11T20:06:12.237" Score="3" Body="&lt;p&gt;In addition to what @rhaig said, a field day group can have a Get-On-The-Air (GOTA) station, for use by unlicensed operators or newly-licensed hams, overseen by an experienced ham/instructor (the Control Operator of the station).&lt;/p&gt;&#xA;" OwnerUserId="105" LastEditorUserId="152" LastEditDate="2014-06-12T20:25:26.227" LastActivityDate="2014-06-12T20:25:26.227" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1881" PostTypeId="2" ParentId="1807" CreationDate="2014-06-11T20:55:57.743" Score="1" Body="&lt;p&gt;It sounds like you may have the offset (either direction or distance) configured incorrectly.  I would suggest you try to locate your state's repeater council's web site to see what the official frequency, tone, and off-set are. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Though there are standard offsets for repeaters on UHF and VHF, they can be configured by the trustee of the repeater, so if you can't connect then you might need to double check your info.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 de N5JLC&lt;/p&gt;&#xA;" OwnerUserId="313" LastActivityDate="2014-06-11T20:55:57.743" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1882" PostTypeId="2" ParentId="1862" CreationDate="2014-06-11T22:19:28.963" Score="0" Body="&lt;p&gt;Amateur radio doesn't have a convenient off the shelf solution for you. Typical packet radio modems support up to 9,600 bits per second, which, after overhead, will be less than 960 bytes per second. Even if you use a faster modem, typical off the shelf radios have limited channel bandwidth that would prevent your required data rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should be able to find 2.4Ghz transmitters at will handle the data rate, and with a power a loftier and the proper use of antennas you should be able to have the distance and data rate needed. A lightweight, small, low power solution will require a good bit of investigation and integration, and you'll need a proper amateur radio license and will have to follow the regulations for the area you are using this in, but you should be able to do what you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look for high altitude balloon projects for inspiration. Most of those are low data rate links, but some have experimented with high data rat links for images and video as well.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-06-11T22:19:28.963" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1883" PostTypeId="2" ParentId="1862" CreationDate="2014-06-11T23:48:45.637" Score="4" Body="&lt;p&gt;There are a number of commercially available RF data modems that operate within the amateur radio spectrum for hobby use particularly with RC (remote controlled) hobby aircraft. However, I believe your specific ITU Region imposes additional output power limitations which will make this challenging at 4 km distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://rfdesign.com.au/downloads/RFD900%20DataSheet.pdf&quot; rel=&quot;nofollow&quot;&gt;RFD900&lt;/a&gt; developed by an Australian company is sold in the USA by &lt;a href=&quot;http://store.jdrones.com/jD_RD900_Telemetry_Bindle_p/rf900set01.htm&quot; rel=&quot;nofollow&quot;&gt;jDrones&lt;/a&gt; for hobby RC use and will support ranges up to 40km and data rates up to 250 kbps! However please note these specs are inversely related and subject to the limitations of your antenna system and the environment (more speed closer, slower data rate further away). Line of sight open air 4 km should be no problem at all with the data rates you are talking about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This particular model outputs 1 watt in the 902 Mhz to 928 Mhz frequency range otherwise known as the &lt;a href=&quot;http://en.wikipedia.org/wiki/33-centimeter_band&quot; rel=&quot;nofollow&quot;&gt;33cm band&lt;/a&gt; in &lt;a href=&quot;http://en.wikipedia.org/wiki/ITU_region&quot; rel=&quot;nofollow&quot;&gt;ITU Region 2 (Americas)&lt;/a&gt;. However, it appears this band is not allocated in Europe (ITU Region 1) and may exceed your maximum output power limits - so you may not be able to use this specific model of hobby radio modem in your location. This is simply the only one I know because I am in Canada.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For Europe you should look for a comparable model in the 70cm (433 Mhz) band such as the &lt;a href=&quot;http://store.openpilot.org/modems/23-oplink-mini.html&quot; rel=&quot;nofollow&quot;&gt;PipX&lt;/a&gt; (only 100 mw). However the additional limitation on output power may limit operational range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In that case you may need to look into building an antenna tracker for use with a &lt;a href=&quot;http://en.wikipedia.org/wiki/Yagi-Uda_antenna&quot; rel=&quot;nofollow&quot;&gt;highly directional antenna such as a yagi&lt;/a&gt;. This involves transmitting the GPS co-ordinates down the link and having the antenna tracker point the antenna straight at the target. This may be somewhat experimental if you are moving at 200 km/h - I think you will need to custom build your antenna tracker, perhaps taking into account the average falling speed and any latency in the motor controller and anticipating the targets future position.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Eitherway, experimentation is part of the hobby of amateur radio! So if you do decide to take this on, publish your project progress somewhere for all to enjoy.&lt;/p&gt;&#xA;" OwnerUserId="608" LastActivityDate="2014-06-11T23:48:45.637" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1884" PostTypeId="2" ParentId="1872" CreationDate="2014-06-12T14:55:39.143" Score="5" Body="&lt;p&gt;Field Day is an emergency preparedness exercise/ contest that is held the last full weekend of June each year in the United States and Canada. It is sponsored and maintained by ARRL. Points are awarded in a variety of ways, but the general idea is that the station should be set up in short order, operate only on emergency power, and a number of other activities related to emergency preparedness. You could operate on VHF only, but most of the action will be on HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a number of ways to participate. Some people participate as individuals, but most people participate in clubs. I strongly suggest you find a local club that is participating, and go join them. You shouldn't need any equipment, although there usually is a talk in frequency available if that helps, so a mobile rig can be useful, along with an HT. You've already found the list of clubs participating, feel free to join one of them. Or if you have a club you've participated with in the past, then find their field day site. If you are a new operator, there is a station that most clubs will have called a GOTA station, where there will be someone who will help you to get on the air. There might also be sign ups to operate one of the main stations. You can also sit as a secondary operator, helping to log the contacts and otherwise helping out. You might want to contact the club, or look at their website for more information ahead of time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reference, here's my club, if you're in the area, feel free to stop by and say hi! Most of the club listings will look pretty similar to this one.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;K4LRG&#xA;Loudoun Amateur Radio Group&#xA;38668 Sierra Lane&#xA;Lovettsville, VA&#xA;GOTA: YES&#xA;Talk-in: TBD&#xA;Contact: Norm Styer&#xA;540-338-2584&#xA;ai2c@earthlink.net&#xA;www.k4lrg.org&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-06-12T14:55:39.143" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1885" PostTypeId="5" CreationDate="2014-06-12T15:35:11.503" Score="0" Body="" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-06-12T15:35:11.503" LastActivityDate="2014-06-12T15:35:11.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1886" PostTypeId="4" CreationDate="2014-06-12T15:35:11.503" Score="0" Body="Field Day is an emergency preparedness/ contest run by ARRL in the United States and Canada the last full weekend of June each year." OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-06-12T15:35:11.503" LastActivityDate="2014-06-12T15:35:11.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1887" PostTypeId="1" AcceptedAnswerId="1889" CreationDate="2014-06-12T18:04:08.233" Score="6" ViewCount="277" Body="&lt;p&gt;Looking around for a VFO online, I see most kits/manufacturers make it a point to mention the waveform. Sinusoidal is a fundamental shape, whereas others (sawtooth, square) are a composite. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recall reading online (can't remember where it was) that a VFO with a composite waveform is actually better than one with a pure sinusoid. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Does the VFO signal necessarily have to be a sinusoid? &lt;/li&gt;&#xA;&lt;li&gt;Does the remark about a VFO with a composite signal ring true?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2014-06-12T18:30:10.893" LastActivityDate="2014-07-08T04:39:58.167" Title="Does the waveform of the VFO necessarily have to be sinusoidal?" Tags="&lt;equipment-design&gt;&lt;oscillator&gt;&lt;vfo&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1888" PostTypeId="1" AcceptedAnswerId="1893" CreationDate="2014-06-12T19:20:47.943" Score="1" ViewCount="444" Body="&lt;p&gt;As we saw many design for this Yagi feed point. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Q1 .&lt;/strong&gt; Which one would be the best resonator / driven? &#xA;Gamma match, T-match, delta match, folded dipole, quad, loop? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Q2.&lt;/strong&gt; And what is the reason if people use such design instead of another design? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question apply for VHF band. Narrow bandwidth preferred. Design complexity and economical cost are doesn't matter. Highest gain is the main goal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far, I've build &lt;code&gt;Super Boomer&lt;/code&gt;, &lt;code&gt;Special ZL&lt;/code&gt; and &lt;code&gt;T-match&lt;/code&gt;. And actually, I don't know which one is better. I only have a home brew RF strength meter here, and it seems they radiate the same strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it's come to my mind that these driven things are big enigma to me. &lt;/p&gt;&#xA;" OwnerUserId="1196" LastEditorUserId="76" LastEditDate="2015-12-15T23:52:42.703" LastActivityDate="2015-12-15T23:52:42.703" Title="What is the best resonator in Yagi antennas?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vhf&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1889" PostTypeId="2" ParentId="1887" CreationDate="2014-06-12T20:57:51.610" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Does the VFO signal necessarily have to be a sinusoid?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Absolutely not. For each frequency component on a mixer's inputs, it produces at the output the sum and difference of those frequency components. Of course, if one of the inputs is sinusoidal, then it has just one frequency component. However, if there are more frequency components it still works.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does the remark about a VFO with a composite signal ring true?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Sure. &lt;a href=&quot;http://en.wikipedia.org/wiki/Joseph_Fourier&quot; rel=&quot;nofollow&quot;&gt;Joseph Fourier&lt;/a&gt; proved that any periodic function can be decomposed into a (possibly infinite) number of sinusoidal components, each with some amplitude and phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, a &lt;a href=&quot;http://en.wikipedia.org/wiki/Square_wave&quot; rel=&quot;nofollow&quot;&gt;square wave&lt;/a&gt; consists of some fundamental frequency, plus all its odd harmonics. A &lt;a href=&quot;http://en.wikipedia.org/wiki/Sawtooth_wave&quot; rel=&quot;nofollow&quot;&gt;sawtooth wave&lt;/a&gt; has even and odd harmonics. Each of these harmonics will generate mixing products, just as if you fed in a sine wave at that harmonic frequency. This can be used to an advantage in some designs, as long as the filtering is such that the mixing products from the other harmonics don't cause issues.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-06-12T20:57:51.610" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1890" PostTypeId="2" ParentId="1453" CreationDate="2014-06-12T22:02:23.357" Score="2" Body="&lt;p&gt;In my app “iSDR”, I approached SDR by the book, or more correctly &lt;em&gt;books&lt;/em&gt;, using &lt;a href=&quot;http://fftguru.com/&quot; rel=&quot;nofollow&quot;&gt;“An Introduction to Signal Processing and Fast Fourier Transform (FFT)&quot; by Kevin J. McGee&lt;/a&gt; and &lt;a href=&quot;http://www.dspguide.com/&quot; rel=&quot;nofollow&quot;&gt;&quot;The Scientist and Engineer's Guide to Digital Signal Processing&quot; by Steven W. Smith, Ph.D.&lt;/a&gt; (which is available on-line for free). The old QST series of articles titled &lt;a href=&quot;http://www.arrl.org/software-defined-radio&quot; rel=&quot;nofollow&quot;&gt;&quot;A Software-Defined Radio for the Masses&quot; parts 1-4 by Gerald Youngblood, AC5OG&lt;/a&gt; was also very helpful. Taking bits and pieces from all of the above, iSDR implements CW receive as follows.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The baseband I and Q signals are fed one into each side of a complex FFT. The FFT results are then shifted to bring the desired center frequency bin (minus the CW offset) to the zero position (DC). Then a pre-calculated frequency-domain sinc (brick wall) filter is applied to the contents of the FFT. The inverse-FFT function is then applied giving back the time-domain shifted and filtered audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doing the filtering in the frequency domain is very efficient since most of the calculations are performed ahead of time. So this approach even allowed the old Apple iPod touch second generation device to do a convincing (if suboptimal) job of demodulating CW, SSB, and AM signals. CW is the simplest, since CW signals simply &quot;fall right out&quot; of the above approach without any additional massaging of I and Q.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If any of the terms used in the second paragraph sound like mathematical gobbledygook, take a look through the references in the first paragraph. The math isn't simple, but it is extremely powerful. The few steps described in the second paragraph result in a remarkably sharp and clear receiver. iSDR provides a very usable CW filter as narrow as 100 Hz, and could easily be made narrower, except that centering it on the signal of interest becomes a challenge.&lt;/p&gt;&#xA;" OwnerUserId="1197" LastEditorUserId="1197" LastEditDate="2014-07-11T23:10:03.650" LastActivityDate="2014-07-11T23:10:03.650" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1891" PostTypeId="1" AcceptedAnswerId="1892" CreationDate="2014-06-13T09:32:15.437" Score="14" ViewCount="15972" Body="&lt;p&gt;I've seen many Chinese HTs (Baofeng, Puxing, Wouxun, QuanSheng etc.) using the so-called &quot;Kenwood connector&quot;, which has a 2.5 mm TRS connector and a 3.5 mm TRS connector. It looks something like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/0AXfp.jpg&quot; alt=&quot;Kenwood connector&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen it used for serial ports, speakers, microphones, PTT devices and similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is: What's the exact pinout of this connector?&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2021-04-26T19:36:54.000" Title="What's the pinout for &quot;Kenwood&quot; 2.5mm TRS/3.5 mm TRS connector?" Tags="&lt;connectors&gt;&lt;kenwood&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1892" PostTypeId="2" ParentId="1891" CreationDate="2014-06-13T11:37:47.500" Score="15" Body="&lt;p&gt;This is the one I use for my Baofeng UV-5R.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/XZddX.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2014-06-13T11:37:47.500" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1893" PostTypeId="2" ParentId="1888" CreationDate="2014-06-13T19:07:37.603" Score="1" Body="&lt;p&gt;If your only concern is maximum gain, then &lt;em&gt;any&lt;/em&gt; of the techniques you mention could be considered &quot;best&quot;. They are all very good at what they do, they just do it in different ways. If your field strength meter is showing all the antennas producing a similar field strength at a similar distance and input power, then that's proof that they are all equally good, if radiating a strong and efficient field is your goal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The choice of which techniques to use is largely based on factors other than performance. For example: a delta match can match only resistive loads, whereas a gamma match can also match capacitive loads. But, the gamma match is more difficult and costly to manufacture. The delta match works with a balanced feeder (ladder line), whereas the gamma match works with an unbalanced feeder (coax).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As another example: a simple dipole radiator is easy to manufacture. A folded dipole has four times the impedance of the equivalent dipole. The parasitic elements of a Yagi tend to lower the feedpoint impedance, so increasing it with a folded dipole might be good. But if you already have some other matching technique, then maybe the folded dipole is useless complexity.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-06-16T11:23:24.707" LastActivityDate="2014-06-16T11:23:24.707" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1897" PostTypeId="1" CreationDate="2014-06-17T01:32:07.067" Score="2" ViewCount="462" Body="&lt;p&gt;We moved into a new house, and I noticed these wires sticking up for some sort of tent thing for shade. &#xA;&lt;img src=&quot;https://i.stack.imgur.com/9n2fB.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/WBZdm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/tI18g.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•I tested the wires to the 3rd prong in the outlet, and it showed a DC dead short to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•The wires are a DC short to each other&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am new to antennas for HF, and my first antenna will be a dipole. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could I use these to my advantage, maybe as a ground plane over the dipole, or even trying to make it a vertical with the wires as a ground plane?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or is it just rubbish, and should I try to keep my dipole as far away from them as possible. I know the AM towers have to be very careful by insulating all of the sections of their guy wires from each other. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-06-17T17:37:31.977" Title="Will these wires affect antenna performance negitavely?" Tags="&lt;antenna&gt;&lt;grounding&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1898" PostTypeId="1" CreationDate="2014-06-17T05:15:19.883" Score="9" ViewCount="1518" Body="&lt;p&gt;A quick follow-up to &lt;a href=&quot;https://ham.stackexchange.com/a/619/5&quot;&gt;this answer&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;...  If the impedance mismatch is large, you risk damaging your radio, particularly on the lower frequencies ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm sorry to be so dense, but uh why is the risk of damage to the Tx due to an antenna mismatch greater at lower frequencies? Is it merely that the wavelength is longer?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2017-04-26T17:16:19.247" LastActivityDate="2017-04-26T17:16:19.247" Title="Why is the risk of damage to a transmitter due to a mismatched antenna at lower frequencies greater?" Tags="&lt;antenna&gt;&lt;impedance&gt;&lt;antenna-tuner&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1899" PostTypeId="2" ParentId="1804" CreationDate="2014-06-17T15:05:36.087" Score="18" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Clearly capacitance is the key&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Capacitance is just one part of it. The gamma match in your question is three things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;A sort of folded dipole, performing an impedance step-up&lt;/li&gt;&#xA;&lt;li&gt;A parallel shorted transmission line stub, adding shunt inductance&lt;/li&gt;&#xA;&lt;li&gt;A series capacitance&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;An equivalent circuit is:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/s6rSu.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fs6rSu.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let's say we have some antenna with a feedpoint impedance of $(15+j0)\Omega$. On a &lt;a href=&quot;http://en.wikipedia.org/wiki/Smith_chart&quot; rel=&quot;noreferrer&quot;&gt;Smith chart&lt;/a&gt;, we have this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/v33BN.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our goal is to move that dot to the middle of the circle. How does a gamma match accomplish that?&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;sort of a folded dipole&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;The first point is probably the hardest to understand. Consider that in a &lt;a href=&quot;http://www.antenna-theory.com/antennas/foldeddipole.php&quot; rel=&quot;noreferrer&quot;&gt;folded dipole&lt;/a&gt;, the impedance is four times that of an ordinary dipole because the antenna current flows in both legs of the dipole, but only half of it in the leg where the feedpoint is. Since current is halved while radiation resistance remains essentially unchanged, impedance is quadrupled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider the gamma match: the same condition exists. Some of the current flows through the main antenna element, and some of it through the gamma bar, and this provides the same sort of impedance step-up. In fact, if you move the shorting strap all the way to the end of the antenna, it's exactly a folded dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically, the gamma match is constructed to give an even more than 4:1 impedance step-up. By making the gamma bar smaller than the main element, the gamma bar will take an even smaller share of the total current. Even less current means a higher impedance transformation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In terms of the equivalent circuit, the size of the gamma bar influences where the autotransformer formed by L1 and L2 is tapped. Here's the effect on the Smith chart:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/AnrV7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;a parallel shorted transmission line&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;The gamma bar running parallel to the antenna element make a &lt;a href=&quot;http://en.wikipedia.org/wiki/Twin-lead&quot; rel=&quot;noreferrer&quot;&gt;twin-lead transmission line&lt;/a&gt;. It's &lt;a href=&quot;http://en.wikipedia.org/wiki/Stub_%28electronics%29#Short_circuited_stub&quot; rel=&quot;noreferrer&quot;&gt;shorted stub&lt;/a&gt;, and less than $\lambda/4$ long, so it looks like an inductor. The position of the shorting bar determines the inductance, the value of L1+L2 in the equivalent circuit above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the shorting bar is moved all the way to the end of the antenna, then the &lt;a href=&quot;http://en.wikipedia.org/wiki/Susceptance&quot; rel=&quot;noreferrer&quot;&gt;susceptance is zero&lt;/a&gt;, and has no effect on the feedpoint impedance. As the shorting stub is moved closer to the feedpoint, it makes the susceptance larger, as if L1+L2 were becoming smaller inductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With parallel inductance added, our Smith chart looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/IjlHp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;a series capacitance&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;The capacitor is formed by the aluminium tube, with the gamma rod inside it, insulated by plastic. This is an optional feature of the gamma match, and it's not always present, or configured exactly this way. But with it, we can do this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/KCq2f.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mission accomplished.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As configured, C1 and L1+L2 form a step-down L network. It's also possible to trim the antenna to be a bit short, in which case it will provide some capacitance, but on the other side of the inductance. In this case, you get a step-up L network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since antenna can also be tuned to be exactly resonant (present a purely resistive feedpoint impedance), you don't technically need to add any inductance or capacitance: just the transformation from the first point is sufficient and you could have an ordinary a folded dipole. However this frequently isn't done in practice since adjustment of the impedance transformation requires changing the diameter of either the gamma bar or the antenna element, which is tricky.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also the case that the gamma match works somewhat as a balun. If it steps up the impedance seen looking in from the coax, by reciprocity it also steps down the impedance looking in the other direction back into the differential mode of the coax. The common-mode is left alone but is now a relatively higher impedance. So, it might be more desirable to step-up too much, then step-down with the L network. Even so, for an antenna with high directivity some additional common-mode suppression may be necessary: combined with the gamma match it may be even more effective. &lt;a href=&quot;http://myweb.tiscali.co.uk/g8hqp/radio/gammamatch.pdf&quot; rel=&quot;noreferrer&quot;&gt;G8HQP provides a more complete explanation&lt;/a&gt; with all the math if you want more detail.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-05-04T00:43:43.130" LastActivityDate="2018-05-04T00:43:43.130" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="1900" PostTypeId="2" ParentId="1897" CreationDate="2014-06-17T17:37:31.977" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I am new to antennas for HF, and my first antenna will be a dipole.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The wires look pretty big, so unless you can place your antenna a couple wavelengths away from them, they are going to couple to your antenna in some significant way. The farther away you can place your antenna (relative to wavelength), the less coupling. You might also be able to significantly reduce the coupling by orienting the dipole to be orthogonal (not parallel) to the direction of the wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That the dipole couples with the wires isn't horrible in itself. For example, a &lt;a href=&quot;http://en.wikipedia.org/wiki/Yagi-Uda_antenna&quot; rel=&quot;nofollow&quot;&gt;Yagi-Uda&lt;/a&gt; array utilizes parasitic coupling between wires to great advantage. Your wires probably aren't so carefully placed, so it's hard to say exactly what the outcome will be. You probably won't get an awesome beam antenna, but to the extent that the wires don't introduce additional loss, the RF energy will be radiated somehow, anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first consequence you will probably notice is that the feedpoint impedance isn't anything like what you'd expect from a dipole. This isn't an insurmountable problem; you just might need some kind of matching network at the feedpoint to get a good match to your feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can't avoid interaction with the wires, then you might as well consider using one of them as an antenna. Just about anything works as an antenna if you can get it to match the feedline reasonably well. People have used rain gutters, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect your challenge in making these wires act as a good antenna will be isolating it from the lossy ground. You will have many of the same challenges faced with &lt;a href=&quot;http://www.w8ji.com/long_wire_antenna.htm&quot; rel=&quot;nofollow&quot;&gt;end-fed antennas&lt;/a&gt;. Keep in mind also that the connection to ground for these things may involve some part of your home's wiring, and you probably want to keep RF out of there to avoid tripping GFCIs, receiving all the noise from electronics in your home, among other issues.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-06-17T17:37:31.977" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1901" PostTypeId="1" AcceptedAnswerId="6237" CreationDate="2014-06-17T23:07:02.863" Score="3" ViewCount="1300" Body="&lt;p&gt;In a few days I'm expecting to mount a Cushcraft R7000 multi-band (HF) vertical antenna on top of a metal mast that will be attached to the outside wall of a large metal shed. The aim is to have the base of the antenna stick out above the roof of the shed and so have an unobstructed signal path in any direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This particular antenna doesn't need a system of ground radials but instead uses a matching network, part of which is provided by a set of seven 49&quot; (124.5cm) long steel rods that stick out in the horizontal plane (like a bottom-placed capacity hat).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/uBXNM.png&quot; alt=&quot;R7000 matching network&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The documentation mentions to horizontally space the antenna sixty-six (66) feet from any surrounding metal, but I couldn't find any information on the amount of clearance above a steel sheet roof. I'm thinking of leaving a space of about 3 feet between the roof and the capacity rods but that figure is just pulled out of a hat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At what distance above a metal roof will the capacity bottom-hat of the antenna's matching network not experience a significant disturbance in a) resonance, b) take-off angle and c) perhaps any other main factors I didn't mention here?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be nice to know if the antenna would be similarly resonant in the car-park where it could be easily tuned as well as on top of the shed.&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2016-05-27T03:56:53.187" Title="recommended capacity bottom-hat clearance above metal roof" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;vertical-antenna&gt;&lt;installation&gt;&lt;capacitance&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1903" PostTypeId="1" AcceptedAnswerId="1907" CreationDate="2014-06-18T20:48:16.110" Score="8" ViewCount="2151" Body="&lt;p&gt;It is pretty well established that &lt;a href=&quot;https://ham.stackexchange.com/q/830/29&quot;&gt;folded dipoles have much greater acceptable-SWR bandwidth than ordinary dipoles&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Antenna_efficiency#Definition&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radiation efficiency&lt;/a&gt; is simply the quotient of radiated power to the antenna feedpoint input power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Seeing that folded dipoles are able to achieve the greater bandwidth &lt;a href=&quot;https://ham.stackexchange.com/q/919/29&quot;&gt;without introducing a designed-as-lossy element&lt;/a&gt; (a technique not unheard of with large-bandwidth antennas), &lt;strong&gt;what is the effect on radiation efficiency of using a folded dipole as opposed to a regular dipole?&lt;/strong&gt; Are there any considerations affecting folded dipoles that would not affect a regular dipole antenna erected in the same physical location which would have a noticable impact on the radiation efficiency?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the purpose of this question, assume otherwise identical conditions; identical height over ground, identical ground, identical possible parasitic elements, identical feedline, etc. Also, note that I am not asking about the radiation pattern of the folded dipole; I am &lt;em&gt;only&lt;/em&gt; concerned with the antenna's radiation efficiency here, unless some other factor has a noticable impact on the radiation efficiency as compared to a regular dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;A great answer&lt;/em&gt; would look at this from both the perspective of a same-wire-length antenna (meaning approximately double the folded dipole's physical length) as well as a same-physical-space antenna (meaning effectively half the radiator length).&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2018-10-31T22:28:21.337" Title="What sort of radiation efficiency can one expect from a folded dipole?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;efficiency&gt;&lt;folded-dipole&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1904" PostTypeId="5" CreationDate="2014-06-18T20:57:28.143" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-06-18T20:57:28.143" LastActivityDate="2014-06-18T20:57:28.143" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1905" PostTypeId="4" CreationDate="2014-06-18T20:57:28.143" Score="0" Body="Use this tag for questions that relate to the efficiency of a system or a component. The efficiency is the amount of useful work performed by the system or component (in radio applications, typically its output power), divided by the total amount of energy provided to the same." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-06-18T20:57:28.143" LastActivityDate="2014-06-18T20:57:28.143" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1907" PostTypeId="2" ParentId="1903" CreationDate="2014-06-19T12:12:08.063" Score="5" Body="&lt;p&gt;For all practical purposes, the radiation efficiency of a folded dipole versus an ordinary dipole is the same. Consider, they are essentially the same antenna.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/v3w3r.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fv3w3r.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only difference is that in the folded dipole, we've replaced the feedpoint with a short. Since the &lt;a href=&quot;http://en.wikipedia.org/wiki/Th%C3%A9venin%27s_theorem&quot; rel=&quot;noreferrer&quot;&gt;Thévenin equivalent resistance&lt;/a&gt; of a voltage source is 0Ω, this doesn't make a lick of difference to the currents in the antenna. The currents are the same, the fields are the same. Everything is the same, except that the voltage source now sees only half the current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So then, what is there that could affect radiation efficiency? There is nothing. There might be some difference in ohmic losses, depending on if you allow the folded dipole to have twice as much copper or not, but this is a very small contributor to loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More significant for terrestrial antennas is ground losses in the Earth, but having established that the fields around a dipole and a folded dipole are the same, how could the losses be different? They aren't. The same reasoning applies to any other kind of loss.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-06-19T12:12:08.063" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1908" PostTypeId="2" ParentId="1898" CreationDate="2014-06-19T15:33:16.403" Score="1" Body="&lt;p&gt;I'm aware of no such risk. A SWR of 3:1 on 7MHz is just as bad as a VSWR of 3:1 on 144MHz. There are other things that change with frequency that might contribute to this misconception, however:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF radios typically do not operate at such high power as HF radios. Ultimately, high SWR damages the radio when the final stage is made to operate outside its voltage or current limits. A bigger transmitter means more power to make higher voltages and currents when SWR is high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, low frequency antennas have a narrower bandwidth. If we take a simple antenna such as a dipole and scale it up in every dimension to decrease the frequency, the &lt;a href=&quot;http://www.antenna-theory.com/definitions/fractionalBW.php&quot; rel=&quot;nofollow&quot;&gt;fractional bandwidth&lt;/a&gt; remains the same, but since the center frequency is lower, the bandwidth, in terms of the difference between upper and lower frequencies with an acceptable SWR, is less. Thus on low bands it's harder to keep a low SWR across the band.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-05-09T19:46:23.753" LastActivityDate="2016-05-09T19:46:23.753" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1909" PostTypeId="1" AcceptedAnswerId="1912" CreationDate="2014-06-21T07:27:59.097" Score="3" ViewCount="1220" Body="&lt;p&gt;I'm considering getting an after-market antenna for my new 2 m/70 cm HT and am trying to decide which of the two antennas I should get. My primary reason for considering an alternative antenna is improved RX/TX performance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both antennas in their specifications on the manufacturers web-site say following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maximum power: 10 W, gain 2.15 dBi, 1/4 wave on 2m, 1/2 wave on 70 cm, both have appropriate connector and impedance, both have specified SWR as less or equal to 1:1.5. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only difference between them is that one antenna is 19 cm long and the other antenna is 36 cm long. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After doing some research on the internet, I've noticed that a large number of HT antennas have extremely similar technical specifications, with only difference being the antenna length. I've also read very vague and general descriptions saying that longer HT antenna==better HT antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So how do I determine which antenna is better based on provided information?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, I want to keep the question as general as possible, so I didn't mention models until now, but they are Diamond SRH-701S and Diamond SRH-536.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2019-11-06T21:51:24.967" Title="How do I determine which HT antenna is better based on their very similar catalogue descriptions?" Tags="&lt;antenna&gt;&lt;ht&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1910" PostTypeId="2" ParentId="1909" CreationDate="2014-06-21T12:38:20.787" Score="5" Body="&lt;p&gt;All other things being equal, a longer HT whip will outperform a shorter whip. The shorter length is &lt;em&gt;probably&lt;/em&gt; because of a larger loading coil, which &lt;em&gt;could&lt;/em&gt; result in loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The gain numbers from most antenna manufacturers should be taken with a grain of salt. They use wild assumptions when calculating it. In most cases HT whips are so cheap, one could buy both (or several) and simply try them all out to find the best performance for the given band/frequency/repeater.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2014-06-21T12:38:20.787" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1912" PostTypeId="2" ParentId="1909" CreationDate="2014-06-21T23:07:23.457" Score="6" Body="&lt;p&gt;Catalog descriptions are bogus. What they are describing are characteristics of monopole antennas in general, not either &lt;em&gt;specific&lt;/em&gt; model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly, they can't both be 1/4 wave antennas at the same frequency but also be different lengths. A 1/4 wave at 145 MHz is about 49 cm. Neither one is a 1/4 wave antenna,. What they probably are is &lt;em&gt;electrically&lt;/em&gt; a 1/4 wave, made electrically longer than they physically are with a loading coil. The more loading, the shorter the antenna, and everything else being equal, the less efficient the radiator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They also both quote gain as 2.15 dBi. This is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Dipole_antenna#Half-wave_dipole&quot; rel=&quot;noreferrer&quot;&gt;theoretical gain of a half-wave dipole in free space&lt;/a&gt;. An ideal quarter-wave monopole is equivalent to a dipole, and has the same gain. It doesn't sound like they made any actual measurement of either antenna's gain. These antennas have &lt;em&gt;significant&lt;/em&gt; deviation from the ideal models: they have loading coils, they are over (lossy) Earth, and they lack a ground plane that's anything close to ideal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Absent accurate specifications from the manufacturer or vendor, it's true of all antennas that longer is better, up to the point that the antenna is self-resonant. To make it shorter requires the addition of reactive components that don't contribute to radiation and must necessarily introduce additional loss if constructed of real materials.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-06-21T23:07:23.457" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1913" PostTypeId="1" AcceptedAnswerId="1959" CreationDate="2014-06-22T14:04:54.467" Score="9" ViewCount="219" Body="&lt;p&gt;PL tones have very specific odd numbers with a decimal place like 103.5 or 107.2 or 88.5. The only PL tone that does not have this decimal is the 100.0 hertz tone. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why don't they just use integers with a standard increment of lets say 10 hertz so it would just be 100, 110, 120 etc. instead of the random numbers?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-07-06T16:26:37.107" Title="Why are PL tones strange numbers?" Tags="&lt;tone-squelch&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1914" PostTypeId="1" AcceptedAnswerId="1916" CreationDate="2014-06-22T14:14:14.857" Score="5" ViewCount="634" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/1900/218&quot;&gt;I have heard&lt;/a&gt; that it is possible to feed single wire like a dipole from the center-point without actually making two separate wires. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How would I do this, what impedance would I expect to see, and what matching technique should I use to keep it at 50 ohms. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would expect a very low impedance because of a DC short, with wires right next to each other but I know that changes with RF.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-06-23T20:10:39.833" Title="How to center-feed a single wire dipole?" Tags="&lt;dipole&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1915" PostTypeId="2" ParentId="1913" CreationDate="2014-06-22T21:09:30.870" Score="7" Body="&lt;p&gt;The &lt;em&gt;ratio&lt;/em&gt; between PL tones is roughly constant. From a &lt;a href=&quot;http://wiki.radioreference.com/index.php/Continuous_Tone-Coded_Squelch_System&quot;&gt;list of PL tones&lt;/a&gt;, you can calculate the ratio between each frequency, which turns out to be about 1.035 (with some exceptions, not sure why).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using a constant &lt;em&gt;ratio&lt;/em&gt; rather than a constant &lt;em&gt;difference&lt;/em&gt; avoids two different tones being exact multiples of each other. If you used a constant difference of 10 Hz, then you would have both 100 Hz and 200 Hz which would tend to interfere with each other, as a detector will be more reliable when the target tones are not integer multiples of each other. With the constant ratio scheme, that won't happen.&lt;/p&gt;&#xA;" OwnerUserId="1183" LastEditorUserId="29" LastEditDate="2014-06-23T07:50:05.437" LastActivityDate="2014-06-23T07:50:05.437" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1916" PostTypeId="2" ParentId="1914" CreationDate="2014-06-23T20:10:39.833" Score="2" Body="&lt;p&gt;There are several ways to do this, but given your &lt;a href=&quot;https://ham.stackexchange.com/q/1897/218&quot;&gt;previous question&lt;/a&gt;, we can reasonably assume that:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;your wires won't be resonant at your desired frequency&lt;/li&gt;&#xA;&lt;li&gt;you desire operation on a number of bands anyway&lt;/li&gt;&#xA;&lt;li&gt;even if your wires &lt;em&gt;were&lt;/em&gt; resonant, there are several nearby parallel wires that are going to alter the impedance from a theoretical dipole&lt;/li&gt;&#xA;&lt;li&gt;you aren't going to dig up your patio to install a counterpoise, nor do you have much more space to install a new antenna or extend the existing wires&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Given all of this, I think your easiest solution would be to pick one of those wires, and place another wire closer and parallel to it, shorting it on the ends. This makes a &lt;a href=&quot;http://www.antenna-theory.com/antennas/foldeddipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;folded dipole&lt;/a&gt;, which does have a center feed, but which does not require that you cut the existing wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/FaIDV.jpg&quot; alt=&quot;folded dipole&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The unbroken conductor is your existing wire; the parallel wire with the feedpoint is a wire you add. Keep them roughly parallel with some non-conductive spacers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inherent in a folded dipole is an impedance step-up, since only some of the current flows in the half with the feed. If you make the wire you add smaller, then you get a greater impedance step-up. If you make the wire you add equal in diameter, then you get a 4:1 step-up. For &quot;fat&quot; wire you could use just the shield of some cheap coax. Flat braided wire could work also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd run this, via ladder-line, to a tuner. This will allow you load up your wires on just about any band and get reasonable performance. Ladder line works better than coax in this application since it has much lower loss and is cheaper, and the SWR on the transmission line could be pretty high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option would be a delta match. Simply take your ladder line feed and cut it down the middle for some length. Then attach the two ends at some points centered on the wire:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/n99ke.gif&quot; alt=&quot;delta match&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;a href=&quot;http://www.radio-electronics.com/info/antennas/yagi/yagi-feed-impedance-matching.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;image source&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can think of this working as an autotransformer, with the dipole being a single-turn, straight inductor. By adjusting the connection points you can get different feed impedances. This was, back in the day, a very popular way to feed a half-wave dipole with 600-ohm ladder line. Find the best arrangement by experimentation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option, since you seem to have multiple parallel wires: connect the ends of some of them together, making a loop. Leave a gap in one of the wires you add for the feedpoint. Or, feed it with a delta, as above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, don't make a loop. Just connect one end, forming a &quot;U&quot;. Now you can make a center-fed, bent dipole.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-06-23T20:10:39.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1917" PostTypeId="1" CreationDate="2014-06-24T13:51:36.110" Score="1" ViewCount="576" Body="&lt;p&gt;I have obtained permission by the Rocky Mountain Radio League to link my AllStar linking system node to their repeater via RF or on the input frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since they have such a long tail, they will stop the transmitting tone immediately so I can base the operation on the tone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a simplex link, I would just have the radio programmed to transmit and receive on two separate frequencies just like anyone else would link in to the repeater. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With full duplex, someone on the internet link could still talk even when the repeater is transmitting something (maybe an announcement etc.), but the disadvantage is that the remote link has too much control and trolls could come in and just double with everybody.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I go with a simplex link, or go with the extra efforts of another radio and some sort of filter (duplexer, diplexer, band reject, band pass, high pass, low pass don't know which one)&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="218" LastEditDate="2014-06-24T14:22:54.490" LastActivityDate="2017-01-07T20:25:12.493" Title="VOIP link to repeater- simplex or duplex?" Tags="&lt;repeater&gt;&lt;internet&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1918" PostTypeId="1" AcceptedAnswerId="1920" CreationDate="2014-06-24T16:53:35.400" Score="8" ViewCount="3573" Body="&lt;p&gt;Looking to get a (highly recommended) NAGOYA NA-771 37cm &quot;Dual band (2M/70cm) handheld antenna&quot; for my Baofeng UV-5R. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If my math is correct - this is about a half-wavelength antenna for 70cm, but doesn't seem to correlate to anything for 2m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does this mean? Is it really good for 70cm but no so much for 2m, or am I misunderstanding the principals/construction of this antenna. (Also, it's just a handheld antenna, so it's not a &quot;dipole&quot; nor does it have an evident &quot;ground&quot; - so I might not just understand what it &quot;is&quot;). &lt;/p&gt;&#xA;" OwnerUserId="1243" LastActivityDate="2014-06-24T19:57:44.430" Title="How does a Dual Band Handheld Antenna work?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1919" PostTypeId="2" ParentId="1918" CreationDate="2014-06-24T17:25:56.073" Score="3" Body="&lt;p&gt;I don't have one, but I have similar antennas.  What &quot;it&quot; is is slightly more metal than the stock antenna.  Reviews on this antenna are mixed and some comments state there are counterfeit Nagoya antennas out there.  Why someone would want to counterfeit something with a margin this low is beyond me.  Never the less many folks feel this improves performance over the stock unit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My guess would be that it uses coil in the base to get 1/4 wave on 2m and bypasses it for 1/2 wave on 70cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What this means for you is impossible to predict.  VHF/UHF being largely line of sight, things like terrain, power, repeater siting and power all factor into the kind of reception you will get. I wouldn't trust the dB rating on anything like this.  For one thing, at least my UV-5R didn't state the gain of it's stock antenna, so it's hard to know if this is an improvement.  It probably is, but at $14, you may as well get one and do a test in your environment.  If it sucks, return it.&lt;/p&gt;&#xA;" OwnerUserId="164" LastActivityDate="2014-06-24T17:25:56.073" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1920" PostTypeId="2" ParentId="1918" CreationDate="2014-06-24T19:50:14.300" Score="9" Body="&lt;p&gt;A half-wave dipole, or a quarter-wave monopole, are resonant on their fundamental frequencies and all odd harmonics thereof. 2m and 70cm have that harmonic relationship, 70cm being approximately the first odd harmonic of 2m:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 144 \mathrm{MHz} \cdot 3 = 432 \mathrm{MHz} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, an antenna that looks like a half wavelength on 2m will look like 1.5 wavelengths on 70cm. Although the radiation pattern is different, the antenna impedance is the same, and so will provide a good match to the radio in either case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that handheld antennas are usually monopole antennas, like a vertical. They are approximately equivalent to a dipole of twice the length. There is no obvious ground plane as there is with a vertical because mobile antennas usually sacrifice performance for size. See &lt;a href=&quot;https://ham.stackexchange.com/questions/495/how-do-handheld-antennas-work-without-ground&quot;&gt;How do Handheld antennas work without ground?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For further reading, I suggest &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna-theory.com&lt;/a&gt;, which expands on some math and shows diagrams of radiation patterns under various conditions.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-06-24T19:57:44.430" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1921" PostTypeId="1" AcceptedAnswerId="3598" CreationDate="2014-06-26T13:47:12.147" Score="15" ViewCount="22112" Body="&lt;p&gt;Let's say I have a repeater. Knowing all of the information about antenna height and gain in each direction, as well as power, how can I create a map similar to this map I saw of a repeater in Illinois? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/dkhvU.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Free options are always better!&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="1246" LastEditDate="2015-02-14T18:42:10.380" LastActivityDate="2015-02-14T18:42:10.380" Title="How do I make a RF propagation map for a repeater?" Tags="&lt;propagation&gt;&lt;repeater&gt;&lt;map&gt;&lt;repeater-coverage&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1922" PostTypeId="2" ParentId="1921" CreationDate="2014-06-26T16:24:45.150" Score="7" Body="&lt;p&gt;&lt;a href=&quot;http://www.qsl.net/kd2bd/splat.html&quot;&gt;SPLAT!&lt;/a&gt; is an RF Signal Propagation, Loss, And Terrain analysis tool for the electromagnetic spectrum between 20 MHz and 20 GHz. It is free and open source, and there are builds for Windows and Mac if you don't want to compile from source on linux yourself. I haven't used it, so I can't speak to ease of use, but it should generate propagation maps based on elevation models and RF propagation characteristics.  However it will probably not generate nice map imagery as above since it cannot integrate Google maps or a similar mapping source.  Perhaps it can output KML files for use with Google Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two groups have made free simple web interfaces for SPLAT!:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://splat.ecok.edu/ecuindex.html&quot;&gt;http://splat.ecok.edu/ecuindex.html&lt;/a&gt; (generates image and KML for Google Earth viewing)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://splat.wa7uhf.com/&quot;&gt;http://splat.wa7uhf.com/&lt;/a&gt; (??? Not responding at the moment)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The image in your question was generated from &lt;a href=&quot;http://cloudrf.com/&quot;&gt;CloudRF&lt;/a&gt; - a web service based largely on SPLAT!.  CloudRF does have a web interface for generating such maps, and does have a free trial, which may meet your needs without installing and learning SPLAT!. Since CloudRF is built on SPLAT! and thus subject to the open source license SPLAT! was released under, the server &lt;a href=&quot;https://github.com/Cloud-RF&quot;&gt;backend is largely opensource&lt;/a&gt;.  I believe the map shown was generated using the Keyhole Radio package, which is a client side helper that uses Google Earth along with the CloudRF servers to generate such maps from KML files generated by CloudRF.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2014-06-26T16:32:17.847" LastActivityDate="2014-06-26T16:32:17.847" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1923" PostTypeId="2" ParentId="1270" CreationDate="2014-06-26T20:48:27.030" Score="12" Body="&lt;p&gt;Were the contacts on the day of a major contest?  Chances are that some other station with a callsign close to yours was operating and several operators misread his call as yours.  I, too, get the occasional QSL card or eQSL for a time when I wasn't operating (and they are usually during a major contest).  Unless you have definitive proof that someone else was operating with your call sign, at most you might want to return a NIL (Not In Log) response to the operators requesting the confirmation.&lt;/p&gt;&#xA;" OwnerUserId="1254" LastActivityDate="2014-06-26T20:48:27.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1924" PostTypeId="1" AcceptedAnswerId="1926" CreationDate="2014-06-27T22:30:16.643" Score="4" ViewCount="301" Body="&lt;p&gt;I'm in charge of our Field Day satellite communication, and I'm going to try and do this via SSB on one of the SSB satellites. I know they invert the signal, but is the convention to transmit on USB and receive on LSB, or the other way around?&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-06-28T06:13:18.097" Title="For Linear Transponder satellites, do I transmit on USB or LSB?" Tags="&lt;satellites&gt;&lt;ssb&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1925" PostTypeId="2" ParentId="1804" CreationDate="2014-06-28T05:54:58.557" Score="1" Body="&lt;p&gt;Consider, the impedance presented by any antenna element that's close to resonant varies along its' length from near zero at the boom to near infinity at the tip. Moving the tap allows you to select any impedance you desire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The tap rod has inductance, and the series capacitor allows you to neutralize this inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short, a gamma match has two adjustments; the position of the tap on the driven element (which varies impedance), and the variable capacitor in series with the inductance of the tap (which tunes out reactance). &#xA;With these two adjustments you can match any antenna that's anywhere close to resonant to any feedline impedance you want.&#xA;That's why I LOVE gamma matches!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I have seen only one antenna that had no capacitor, and it would only match at one frequency. The wrong frequency, as it turns out.)&lt;/p&gt;&#xA;" OwnerUserId="1015" LastEditorUserId="1015" LastEditDate="2014-06-28T06:01:06.997" LastActivityDate="2014-06-28T06:01:06.997" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="1926" PostTypeId="2" ParentId="1924" CreationDate="2014-06-28T06:13:18.097" Score="3" Body="&lt;p&gt;From what I've read (no practical experience yet!), the convention is that whoever is receiving on the downlink should be working on USB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So fist step is to identify if the satellite is inverting or not.&lt;br&gt;&#xA;If it's inverting, you transmit on LSB and receive on USB. If it's not inverting, you both transmit and receive on USB.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2014-06-28T06:13:18.097" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1927" PostTypeId="2" ParentId="1898" CreationDate="2014-06-28T14:40:53.893" Score="4" Body="&lt;p&gt;Another phenomenon that might play into the impression that HF transmitters are more susceptible to damage from high VSWR is feedline loss. Feedline loss increases as frequency increases. So at HF frequencies the power reaching the antenna feedpoint is higher due to lower feedline losses, and for the same reason the signal reflected back from the antenna feedpoint toward the transmitter is also higher when it reaches the transmitter. But at VHF frequencies the same feedline will absorb more of the signal going in both directions: making the feedline more effective as a dummy load. So for two antennas, one HF and the other VHF with identical VSWR measured at the antenna feedpoints, using identical feedlines, the VHF transmitter will see a lower VSWR at its antenna connector. This effect will be more apparent for higher-loss feedlines (e.g., coax cable) and less apparent for low-loss feedlines (ladder line, air-dielectric cables, etc.)  &lt;/p&gt;&#xA;" OwnerUserId="1197" LastActivityDate="2014-06-28T14:40:53.893" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1928" PostTypeId="2" ParentId="1826" CreationDate="2014-06-28T15:55:24.983" Score="0" Body="&lt;p&gt;To describe electromagnetic &lt;em&gt;wave&lt;/em&gt; behavior it is necessary to use &lt;a href=&quot;http://en.wikipedia.org/wiki/Maxwell&amp;#39;s_equations&quot; rel=&quot;nofollow&quot;&gt;Maxwell's equations&lt;/a&gt;. Note that &lt;a href=&quot;http://en.wikipedia.org/wiki/James_Clerk_Maxwell&quot; rel=&quot;nofollow&quot;&gt;James Clerk Maxwell&lt;/a&gt; published these equations in 1865, long before any concept of quantum mechanics was put forth. His equations are part of classical electromagnetism, and do not involve photons or quantum theory, and don't require any knowledge of the particle nature of electromagnetism. But these equations are fundamental to describing the wave nature of radio waves. Note that working with them requires using &lt;a href=&quot;http://en.wikipedia.org/wiki/Partial_differential_equation&quot; rel=&quot;nofollow&quot;&gt;partial differential equations&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{eqnarray} &#xA;\nabla \cdot \vec{E} &amp;amp;=&amp;amp; \frac{\rho}{\epsilon_0}\\ &#xA;\nabla \cdot \vec{B} &amp;amp;=&amp;amp; 0 \nonumber \\ &#xA;\nabla \times \vec{E} &amp;amp;=&amp;amp; - \frac{\partial B}{\partial t} \nonumber \\ &#xA;\nabla \times \vec{B} &amp;amp;=&amp;amp; \mu_{0}\vec{J} + &#xA;\mu_{0}\epsilon_{0}\frac{\partial E}{\partial t} &#xA;\end{eqnarray}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maxwell's equations describe mathematically how electromagnetic waves carry energy as they travel: it results from the energy density associated with both the electric field $\begin{equation} \vec{E} \end{equation}$ and the magnetic field $\begin{equation} \vec{B} \end{equation}$ components of electromagnetism. The rate of energy transport per unit area relates directly to your wave question, and can be derived with help from Maxwell's equations. The mathematical concept for energy flow in electromagnetic waves is known as the &lt;a href=&quot;http://en.wikipedia.org/wiki/Poynting_vector&quot; rel=&quot;nofollow&quot;&gt;Poynting vector&lt;/a&gt;; which involves taking a cross product of the $\begin{equation} \vec{E} \end{equation}$ and $\begin{equation} \vec{B} \end{equation}$ components of the radio wave. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation} \vec{S} = \frac{{\vec{E} \times \vec{B}}}{{\mu _0 }} \end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the answer to your question comes down to whether the Poynting vector for otherwise-identical radio waves differs for a 500 kHz wave versus a 5 GHz wave. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A Google search will turn up &lt;a href=&quot;http://www.physicsforums.com/showthread.php?t=402264&quot; rel=&quot;nofollow&quot;&gt;a number of debates&lt;/a&gt; on the issue amongst physics aficionados, and I am relying on what appears to be the general consensus of that group. Based on their arguments, the answer appears to be YES, the Poynting vector contains a frequency-dependant term by virtue of the oscillating field components. So at various instants of time (shorter than the period of a cycle) the magnitude of the Poynting vectors might differ between waves of two different frequencies. However, taken in aggregate, averaged over multiple cycles, the net flow of energy averages out to be the same regardless a wave's frequency. Thus the short-term result does not violate the &lt;a href=&quot;http://en.wikipedia.org/wiki/Conservation_of_energy&quot; rel=&quot;nofollow&quot;&gt;law of the conservation of energy&lt;/a&gt; in the long term.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since most radio amateurs are not physicists, the practical answer is: &quot;there is no difference&quot;. Our senses (particularly our ears) react only to actions lasting much much longer than the cycle period of a 5 GHz wave. Even our radio equipment generally extracts information at much lower bit rates than the carrier frequency being received. So from a practical standpoint radio operators observe and care only about the aggregate. But from a theoretical standpoint there is a subtle difference. Perhaps there is, or will be found, a practical or academic application for that subtle distinction. But regardless, I think yours was an excellent question!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;POWER AND ENERGY&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is easy to confuse a definition with a mathematical model. To illustrate, suppose one asks about &quot;power dissipation in a resistor at room temperature versus as the temperature approaches absolute zero.&quot; Without much thought one might quote:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;P = I^{2}R\,&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although we learned this relationship as &lt;a href=&quot;http://simple.wikipedia.org/wiki/Joule&amp;#39;s_laws&quot; rel=&quot;nofollow&quot;&gt;Joule's Law&lt;/a&gt;, and it is very useful for &lt;a href=&quot;http://www.allaboutcircuits.com/vol_1/chpt_2/4.html&quot; rel=&quot;nofollow&quot;&gt;estimating power dissipation in electronic circuits&lt;/a&gt;, when we apply it using the nominal room-temperature resistance value of a circuit component, it provides only an &lt;a href=&quot;http://www.allaboutcircuits.com/vol_1/chpt_2/6.html&quot; rel=&quot;nofollow&quot;&gt;approximation of the power dissipated&lt;/a&gt;. Joule's Law as stated above is of little use in understanding how power is dissipated in materials as temperature varies - an obvious reality if you consider a resistor made of a superconductive material. That doesn't mean Joule's Law is wrong. It just means that it needs to be applied appropriately, to answer questions to which it applies. $P = I^{2}R$ simplifies the calculation of power dissipation by ignoring the physics describing how electrons actually travel and interact with the materials through which they move.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, the equation defining the &lt;a href=&quot;http://en.wikipedia.org/wiki/Joule&quot; rel=&quot;nofollow&quot;&gt;joule&lt;/a&gt;: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;J = W\cdot\ s\,&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While that definition works fine for converting between power and energy, it does not in any way explain how electromagnetic energy is carried, either in waves or in particles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Waves are complicated things to describe mathematically. The math involved in describing electromagnetic waves goes well beyond algebra, or even basic calculus. Although radio amateurs may never need to work with Maxwell's Equations, valuable insight into wave behavior can be gained from examining the results of physicists' work. It is quite remarkable that the mathematical underpinnings for electromagnetism predate the invention of the &lt;a href=&quot;http://en.wikipedia.org/wiki/Thomas_Edison&quot; rel=&quot;nofollow&quot;&gt;first commercially practical incandescent light bulb&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;OF PARTICLES AND WAVES&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;An energy difference in the wave&quot; pertains to the wave nature of electromagnetism, not the particle (photon) nature of that energy. But the question also mentions Planck's constant, which applies to the quantum nature of light. Therein lies a paradox. In physics the concepts of &lt;a href=&quot;http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality&quot; rel=&quot;nofollow&quot;&gt;wave particle duality&lt;/a&gt; and the &lt;a href=&quot;http://www.open.edu/openlearn/science-maths-technology/science/physics-and-astronomy/physics/paradox-wave-particles&quot; rel=&quot;nofollow&quot;&gt;duality paradox&lt;/a&gt; have been the subject of much debate and study, but in the amateur radio community not so much.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question acknowledges that radio waves are electromagnetic energy, and that electromagnetic energy can appear as particles (photons) or as waves. The wave particle duality paradox makes it necessary to address waves and particles separately because we never observe the wave and particle natures of energy at the same time. Sometimes radio energy looks like particles, and sometimes it looks like waves, but it never looks like particles and waves at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A previous answer addressed the energy associated with each particle of light. As a practical matter, you may never observe the effects of the different energies of electromagnetic particles of different frequencies. That difference in energy between particles of different frequency can be observed experimentally in the &lt;a href=&quot;http://en.wikipedia.org/wiki/Photoelectric_effect&quot; rel=&quot;nofollow&quot;&gt;photoelectric effect&lt;/a&gt; - where in a carefully crafted experiment you might observe that some loosely-bound electrons get &quot;knocked free&quot; from the surface of a metal by 5 GHz photons, but not by 500 kHz photons even if you use a transmit power of 5000 GW! But your question addresses waves, not photons. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The approach taken in this answer (Maxwell's Equations) relies on &lt;a href=&quot;http://en.wikipedia.org/wiki/Classical_electromagnetism&quot; rel=&quot;nofollow&quot;&gt;classical electromagnetism&lt;/a&gt;, not quantum theory. But since quantum physics has a 100-year history of correctly predicting results in carefully conducted experiments designed to disprove it, we would be foolish to carelessly dismiss its results as not relevant. So some history might be in order to help illustrate why it is not appropriate to utilize quantum concepts to address the question that has been posed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the latter part of the 19th century classical physics had done such an excellent job of describing observed phenomena that it was widely believed that nothing new was left to be discovered. There were some pesky experimental results (the &lt;a href=&quot;http://en.wikipedia.org/wiki/Photoelectric_effect&quot; rel=&quot;nofollow&quot;&gt;photoelectric effect&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/Black-body_radiation&quot; rel=&quot;nofollow&quot;&gt;black body radiation curves&lt;/a&gt; to name but two) but they too would surely be explained in terms of classical physics in due time. Now, one-hundred-twenty-some-odd years later, we know that never did happen. Instead, quantum mechanics and relativity theory turned physics on its head. Adherents of classical theories worked feverishly to explain experimental results using the old ideas, but the new theories not only explained results that confounded classical theory, the new theories predicted never-observed phenomena (orbit of mercury, quantum entanglement, to name but two) that cemented the newer theories as accurate and reliable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what about classical electromagnetic theory? Are electromagnetic waves only to be understood as particles and quantized energy? The answer is no. Planck's relation does not describe waves, and is useless for providing insight into how waves operate. Maxwell's equations still do an excellent job of describing electromagnetic wave behavior, just as they did over 150 years ago. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If both classical and quantum equations work for their respective domains, then which equation should you then use? Here enters the largely misunderstood concept of wave-particle duality. Wave–particle duality is an ongoing conundrum in modern physics, and there are various explanations for it that involve particles and waves, only waves, neither-wave-nor-particle, and more. But for the question at hand, namely &quot;...is there an energy difference in the wave?&quot; we need only address the wave behavior. This is actually stated in the question. Thus it is just fine, actually mandatory, that we use the equations that describe the wave: Maxwell's famous equations. We can feel confident in this approach, in part, because based on the results of much experimentation, we do not observe electromagnetic particle behavior at the exact same instant at which we observe wave behavior - we need only deal with the equations that fit our task at hand. Quantum theory is relevant! But not in the context of the question asked.&lt;/p&gt;&#xA;" OwnerUserId="1197" LastEditorUserId="1197" LastEditDate="2014-08-13T12:46:51.383" LastActivityDate="2014-08-13T12:46:51.383" CommentCount="14" ContentLicense="CC BY-SA 3.0" />
  <row Id="1930" PostTypeId="2" ParentId="615" CreationDate="2014-06-29T00:46:13.160" Score="0" Body="&lt;p&gt;A few comments regarding elements of your question(s) that I haven't seen addressed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think of the antenna wire and the feedline leading from your radio to the antenna feedpoint as all being part of your antenna system. Each component contributes to the overall efficiency of the antenna system. If the antenna system is designed to be efficient (low-resistance wires and low-loss feedline), and the impedance it presents at the radio's antenna connector closely matches the impedance the radio is designed to feed (typically 50 ohms resistive), then there isn't any need for an antenna tuner. In fact, an antenna tuner under those conditions would only add resistive losses to the overall antenna system making it less efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding &quot;Does a tube based HF transmitter need an antenna tuner?&quot; the answer is sometimes. Obviously if the antenna system is like the one described in the previous paragraph, no, no antenna tuner should be used. But when the impedance presented to the transmitter by the antenna system differs sufficiently from 50 ohms, a tuner might be required in order to avoid high currents (and associated heating) in the final output stage of the transmitter. Tube-type transmitters tend to be quite robust, in terms of the amount of heat their finals can dissipate without being destroyed, and thus can tolerate greater mismatches at full output power. Modern solid-state rigs automatically throttle back their power in order to prevent their more delicate transistors from being destroyed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Multi-band antennas can be designed to present reasonable antenna system impedances across many bands. No antenna tuner is required for such antennas when they are used within their designed bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A well-designed quality antenna system is an excellent substitute for an antenna tuner. And a good substitute for an SWR meter when evaluating antenna matching across a band of frequencies is an antenna analyzer, such as those popularized by MFJ and others. In fact such analyzers are often much more convenient for that purpose, and provide more useful data than a simple SWR meter. &lt;/p&gt;&#xA;" OwnerUserId="1197" LastEditorUserId="1197" LastEditDate="2014-06-29T19:10:02.910" LastActivityDate="2014-06-29T19:10:02.910" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1931" PostTypeId="2" ParentId="1275" CreationDate="2014-06-29T15:07:52.653" Score="6" Body="&lt;p&gt;SLA cells are dead easy to recharge, improvising a charger may be as easy as a set of jumper cables. Lithium ion's require active charging circuitry and the failure mode can be catastrophic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, the new LiFePO₄ batteries seem to combine the best of both, energy density comparable to lithium ion with the saftey and easy charging of lead acid.&lt;/p&gt;&#xA;" OwnerUserId="1262" LastActivityDate="2014-06-29T15:07:52.653" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1932" PostTypeId="2" ParentId="1693" CreationDate="2014-06-30T14:25:39.557" Score="2" Body="&lt;p&gt;Aside from their operating frequency, for all practical purposes, there is not much difference between the internal schematics of RF and IF amplifiers. But you will find that components designed for use as IF amplifiers have characteristics that are better optimized for their intended use, and likewise for RF amplifiers. So if you are planning to use a component in an RF stage, you might want to pay more attention to a component's dynamic range, isolation, noise figure, input/output impedance, and other parameters that might be especially important in that application. An RF component is more likely to be better optimized for your needs in an RF stage. Analogously for an IF amplifier component. But if a component's parameters (including cost) are all a good match for your circuit design, then pay no attention to the RF versus IF label that the manufacturer has attached to it.&lt;/p&gt;&#xA;" OwnerUserId="1197" LastActivityDate="2014-06-30T14:25:39.557" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1933" PostTypeId="1" AcceptedAnswerId="1934" CreationDate="2014-07-01T00:55:15.367" Score="6" ViewCount="5075" Body="&lt;p&gt;I just got a Yaesu FT-60R handheld, along with the MH-37A4B earpiece. After having it around for a couple days, I think I'd like to be able to connect standard headphones to it, so as to be able to listen privately without carrying around an extra accessory.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see that the pinout for the 4-contact combined &quot;MIC/SP&quot; jack is known, though not in the manual, and there is a a first-party adapter cable (CT-44). However, this doesn't tell me without buying/building whether it's possible to use it in the way I want; specifically:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If I connect only headphones to the FT-60, using an appropriately wired adapter, can I still use the &lt;em&gt;internal&lt;/em&gt; microphone and PTT switch to transmit&lt;/strong&gt;, or will just having a plug inserted cut out the internal mic?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I haven't tested this out because I don't have a bare 4-contact plug to experiment, and I hear that plugging in headphones with a standard 3-contact plug results in misbehavior.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T18:44:24.040" LastActivityDate="2016-11-10T16:35:43.257" Title="Using standard headphones with the Yaesu FT-60?" Tags="&lt;ht&gt;&lt;equipment-design&gt;&lt;yaesu&gt;&lt;equipment&gt;&lt;audio-interface&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1934" PostTypeId="2" ParentId="1933" CreationDate="2014-07-01T00:55:15.367" Score="4" Body="&lt;p&gt;I've done some tests with what I have available (now including the CT-44 adapter).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the MH-37A4B Earpiece/Microphone connected, the internal microphone can still be used: whichever mic has its PTT switch pressed will provide transmit audio and the other will not. Furthermore, the external microphone is open-circuit when its PTT is not pressed. Therefore, &lt;strong&gt;yes, given an appropriate adapter&lt;/strong&gt; one can use headphones without a microphone plugged into the FT-60.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connecting stereo headphones (64Ω impedance) into the jack directly did indeed result in misbehavior as reported elsewhere on the Internet, including a nonfunctional keypad or being stuck in transmit mode; presumably due to mis-connection of the mic line. Using an appropriately wired cable such as the CT-44 solves this problem, but produces mono (left channel only) audio since it has a mono jack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, loud thumps were heard when the radio is switched on or when it unmutes (due to an offset of 3 V DC when unmuted, 0 V when muted). These are also present but considerably milder on the internal speaker or earpiece accessory presumably due to their frequency response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have solved the above problems by building an adapter to stack onto the CT-44, which provides stereo audio and a blocking capacitor (which is an adequate but not ideal fix for the thumps). It could also be built together with a 4-pole plug and no CT-44, but the FT-60's 4-pole jack has slightly different dimensions than the standard smartphone-headset-style 4-pole plug and will not make proper contact with one.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-11-10T16:35:43.257" LastActivityDate="2016-11-10T16:35:43.257" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1935" PostTypeId="2" ParentId="1693" CreationDate="2014-07-01T02:17:10.893" Score="0" Body="&lt;p&gt;Again - I am not an expert on such things, but my understanding of the basic differences between an RF stage amplifier and an IF stage amplifier, is that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;An RF stage amplifier needs to amplify all the frequencies in the current band, to allow tuning across the whole band.&lt;/li&gt;&#xA;&lt;li&gt;An IF stage amplifier is used where the signals from the current band have been downconverted (or upconverted) to a single fixed frequency (the IF), and one of the main jobs of the IF amplifier is to remove unwanted frequencies outside of an extremely narrow band of frequencies, centred on the IF.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So to answer the original question, if the amplifier block is specifically designed to be a 200MHz IF amplifier, check what the bandwidth of the amplifier is at that frequency. if it really is an IF amplifier block, it could easily have a bandwidth of +/- 10kHz or less (so allowing 190-210MHz through, with a fairly sharp cutoff outside that range).&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-07-01T02:17:10.893" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1936" PostTypeId="1" CreationDate="2014-07-01T09:27:50.973" Score="7" ViewCount="692" Body="&lt;p&gt;I am currently doing a project in the area of optical inter-satellite communication (GEO-LEO).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using a optical carrier of 281 THz, and the Doppler shift corresponding to it is ±7 GHz. I introduced this Doppler shift in the transmitted signal $S$ as an offset like &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ S \cdot e^{j 2 \pi f_\mathrm{doppler}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the receiver, I am using a Costas Loop as a demodulator. I have to do Doppler shift compensation to recover the signal. Guess, I have to add an offset compensator in the local oscillator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anybody help me in doing this?&lt;/p&gt;&#xA;" OwnerUserId="1267" LastEditorUserId="8832" LastEditDate="2017-05-25T01:14:31.230" LastActivityDate="2017-05-25T01:14:31.230" Title="Doppler Shift Compensation in Inter Satellite Communication" Tags="&lt;receiver&gt;&lt;satellites&gt;&lt;frequency&gt;&lt;oscillator&gt;&lt;doppler&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1938" PostTypeId="2" ParentId="644" CreationDate="2014-07-01T15:35:28.530" Score="4" Body="&lt;p&gt;Isn't one building a vertical dipole when they make a 'tiger tail' for their HT?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For an example and plans see this:&#xA;&lt;a href=&quot;http://www.hamuniverse.com/htantennamod.html&quot; rel=&quot;nofollow&quot;&gt;http://www.hamuniverse.com/htantennamod.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1269" LastActivityDate="2014-07-01T15:35:28.530" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1940" PostTypeId="1" AcceptedAnswerId="1946" CreationDate="2014-07-01T16:40:23.227" Score="2" ViewCount="1074" Body="&lt;p&gt;My club is considering doing digital modes next year for Field Day. There are a few issues that we are discussing, including:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What modes are most commonly used?&lt;/li&gt;&#xA;&lt;li&gt;How many contacts could be made?&lt;/li&gt;&#xA;&lt;li&gt;What is the best set up for a digital station? Multi-band?&lt;/li&gt;&#xA;&lt;li&gt;What mode will give the least interference with CW operations, but the most contacts?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;In other words, we are trying to figure out how to set up a good digital station, and looking for some feedback along these lines. As Field Day is fresh in everyone's minds, I thought I'd ask and see what we can do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To add a bit of information, I'm thinking primarily of HF modes, with some thought as to typical VHF modes. We haven't tried yet, because the club is worried about a low number of contacts for a potentially large amount of work. We aren't thinking of doing anything like meteor scatter, at least not at this time, just standard HF communication, with a chance of VHF with standard propagation modes.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2014-07-01T20:51:26.133" LastActivityDate="2015-06-18T17:16:28.543" Title="Digital modes on Field Day" Tags="&lt;digital-modes&gt;&lt;field-day&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1941" PostTypeId="2" ParentId="644" CreationDate="2014-07-01T22:48:37.123" Score="8" Body="&lt;p&gt;A dipole is twice as long as the equivalent monopole. However if the size of a dipole isn't a problem, then certainly it's possible to use one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Michael Kjörling mentions, you want (by convention) a vertically polarized antenna on VHF, not horizontal as the &quot;T&quot; you have drawn would be. But that's no problem -- we can make a vertical dipole also. The tricky bit is just getting the feedline into the middle in such a way that the feedline doesn't mess up the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a trivial solution: run the feedline &lt;em&gt;inside&lt;/em&gt; the antenna. Such a thing can easily be constructed from a piece of coax:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ESOI7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The design is quite simple: cut a piece of coax to the length of a dipole. Then, strip the shield off half of it. If you want to be fussy, you might cut the coax-side of the dipole a bit short, since the HT body effectively makes it a bit longer. If you don't do this, you are effectively feeding the dipole a little off center, so the feedpoint impedance will be a bit higher. Not a big deal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This design exploits a thing usually undesired in coax-fed dipoles: common-mode currents on the &quot;feedline&quot;. You don't &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;need a balun&lt;/a&gt; with this design, because the common-mode currents on the feedline are very intentionally half the dipole. Normally we don't want the feedline to be part of the antenna. Here, it &lt;em&gt;is&lt;/em&gt; the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, you could argue this design is a case of an &lt;a href=&quot;http://www.antenna-theory.com/definitions/infinite.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;infinite balun&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To support the coax, you might attach it to a fiberglass rod with some heat-shrink tubing, or use semi-rigid coax that doesn't need additional support.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Thanks to a &lt;a href=&quot;https://ham.stackexchange.com/questions/644/handheld-dipoles#comment3463_655&quot;&gt;comment by user2338215&lt;/a&gt;, I have a great &lt;a href=&quot;http://martybugs.net/wireless/rubberducky.cgi&quot; rel=&quot;nofollow noreferrer&quot;&gt;example of commercial antennas built this way&lt;/a&gt;. They are 2.4 GHz antennas, where even a full-length dipole is really small.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/uyHnq.jpg&quot; alt=&quot;inside of a 2.4 GHz antenna. Each part is a quarter-wavelength&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This antenna is so small that the feedline even extends up into the body. You can see here that the shield has been removed from the final quarter-wavelength of the line (that's one half of the dipole), and the other half of the dipole is made by a sleeve folded back over the feedline. You can construct the same thing by folding the coax shield back over itself, although the cable jacket makes for a relatively lossy dielectric.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a kind of &lt;a href=&quot;http://www.antenna-theory.com/definitions/bazooka.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;sleeve or bazooka balun&lt;/a&gt;. The sleeve plus the coax shield make a coaxial transmission line. Usually they are shorted on the end at the left, which has the effect of making the sleeve not radiate. But they can be shorted on the other end (as in this picture), and then the sleeve does radiate, which is exactly what's desired in this case.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-07-10T21:11:36.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1942" PostTypeId="2" ParentId="1778" CreationDate="2014-07-03T00:08:02.267" Score="1" Body="&lt;p&gt;I am the author of the free-ware DXLab Suite, one component of which -- Commander -- provides transceiver control that supports the IC-7100. However, Commander is not designed for remote control. The two applications most frequently used applications for that purpose are &lt;a href=&quot;http://www.trx-manager.com/&quot; rel=&quot;nofollow&quot;&gt;TRX-Manager&lt;/a&gt; and &lt;a href=&quot;http://www.ham-radio-deluxe.com/&quot; rel=&quot;nofollow&quot;&gt;Ham Radio Deluxe&lt;/a&gt; . Neither is free, but both offer a free trial. User reviews are available &lt;a href=&quot;http://www.eham.net/reviews/detail/680&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;http://www.eham.net/reviews/detail/3498&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="88" LastEditorUserId="218" LastEditDate="2014-07-03T11:13:50.567" LastActivityDate="2014-07-03T11:13:50.567" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1943" PostTypeId="1" AcceptedAnswerId="1952" CreationDate="2014-07-03T16:48:20.167" Score="1" ViewCount="1604" Body="&lt;p&gt;A fellow amateur here in VU-land reported the display on his 570 died.&#xA;Apparently the 570 has a proprietary computer interface called RCP-2 ; &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Are all features on the rig available on the RCP-2?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5" LastActivityDate="2015-02-27T15:20:37.240" Title="Can the TS-570 be fully controlled over RCP-2?" Tags="&lt;kenwood&gt;&lt;remote-control&gt;&lt;ts570s&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1944" PostTypeId="1" CreationDate="2014-07-03T20:02:49.670" Score="-3" ViewCount="190" Body="&lt;p&gt;Has anyone actually seen a visible radio wave? If so please comment. I am just wondering if it has ever been recorded before. or if its something that was left out of NEETS or is maybe top secret.  &lt;/p&gt;&#xA;" OwnerUserId="1276" LastEditorUserId="1246" LastEditDate="2015-03-08T21:26:31.787" LastActivityDate="2015-03-08T21:26:31.787" Title="Visible radio wave propagation" Tags="&lt;propagation&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="0" ClosedDate="2014-07-06T14:40:09.777" ContentLicense="CC BY-SA 3.0" />
  <row Id="1945" PostTypeId="2" ParentId="1944" CreationDate="2014-07-03T20:31:19.227" Score="4" Body="&lt;p&gt;By definition radio waves are not part of the visible electromagnetic spectrum. &lt;/p&gt;&#xA;" OwnerUserId="1274" LastActivityDate="2014-07-03T20:31:19.227" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="1946" PostTypeId="2" ParentId="1940" CreationDate="2014-07-03T20:32:11.773" Score="2" Body="&lt;p&gt;The number of contacts will depend much on the band conditions. But to get a feel for the number of points you might gain for your efforts, you might take a look at what participants in 2012/2013/2014 managed to achieve. Here's one sample: &lt;a href=&quot;http://k8bxq.org/node/7&quot; rel=&quot;nofollow&quot;&gt;http://k8bxq.org/node/7&lt;/a&gt;&#xA;To gauge the rate of growth in popularity (to get an idea of the prospects for next year) take a look at the ARRL's FD results, where you'll find totals for digital contacts over the years:&#xA;&lt;a href=&quot;http://www.arrl.org/files/file/ContestResults/2012/2012-FD-QST-V3.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/files/file/ContestResults/2012/2012-FD-QST-V3.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each contact counts the same as a CW contact (x2) but you don't need someone with CW skills, and digital operating skills are a good bit easier to learn than CW... so a digital station might provide a bonus in terms of available skilled operators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll need to take the same precautions to avoid receiver desense and related strong-signal issues, as with other modes. But many digital modes can perform effectively at low power, so they can be less prone to inter-station interference on FD. Additionally, many of the digital modes are more immune to interference, and are less likely to be troubled by the CW ops. With care, and adequate antenna separation, you might find that the CW and digi-station can share the same band without serious issues - which can be a real bonus when only one band seems to be open on FD.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PSK31 has been around for a very long time, works great with low power and high noise, is very straightforward to use, works great on HF, and should definitely be one of the modes you'll want to use. But if you can be flexible, you'll find that changing to another mode after exhausting all the PSK31 ops on a particular band can help boost your numbers. With a computer running a flexible digi-mode app you will have your choice of virtually any of the HF digi-modes available at your digi station - so plan to use them all! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might find this blog to be of interest: &lt;a href=&quot;http://www.w4cn.org/about-ham-radio/digital-modes&quot; rel=&quot;nofollow&quot;&gt;http://www.w4cn.org/about-ham-radio/digital-modes&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FB OM GL FD&lt;/p&gt;&#xA;" OwnerUserId="1197" LastActivityDate="2014-07-03T20:32:11.773" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1948" PostTypeId="2" ParentId="1944" CreationDate="2014-07-04T01:57:01.377" Score="8" Body="&lt;p&gt;There are visible radio waves. We call them 'light'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can see a whole range of frequencies of these waves, translated by our brains into something we call 'colours'.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-07-04T01:57:01.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1949" PostTypeId="1" AcceptedAnswerId="1958" CreationDate="2014-07-04T07:59:42.687" Score="4" ViewCount="1276" Body="&lt;p&gt;Consider a biquad antenna used for receiving, not for sending. They are typically built with each side having a length of $\lambda / 4$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a biquad antenna was built with a side length of $\lambda / 2$ or even $\lambda$, would this give better results (for receiving)? If yes, how much better?&lt;/p&gt;&#xA;" OwnerUserId="1277" LastEditorUserId="76" LastEditDate="2015-12-15T23:34:04.707" LastActivityDate="2015-12-15T23:34:04.707" Title="Does a larger Biquad antenna give better results?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1950" PostTypeId="1" CreationDate="2014-07-04T22:37:24.587" Score="-4" ViewCount="820" Body="&lt;p&gt;Could please someone state the open radio bands in which one could transmit:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;freely&lt;/li&gt;&#xA;&lt;li&gt;or with Ham Radio license&lt;/li&gt;&#xA;&lt;li&gt;and in what max power in each band&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;between 400 MHz to 4.4 GHz. The purpose of this is to deploy a radar using SDR hardware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or at least point me towards an official manual.&lt;/p&gt;&#xA;" OwnerUserId="409" LastEditorUserId="8573" LastEditDate="2019-05-09T22:47:32.337" LastActivityDate="2019-05-19T09:53:53.187" Title="Amateur Bands (400 MHz to 4.4 GHz)" Tags="&lt;legal&gt;&lt;europe&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="1951" PostTypeId="2" ParentId="1950" CreationDate="2014-07-04T23:05:53.577" Score="3" Body="&lt;p&gt;You have a few choices in the ISM bands:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;433mhz (only in Europe) &lt;/li&gt;&#xA;&lt;li&gt;903mhz (only in the US)&lt;/li&gt;&#xA;&lt;li&gt;2.4GHz (worldwide)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Power and antenna rules vary, but the &lt;a href=&quot;http://www.afar.net/tutorials/fcc-rules/&quot; rel=&quot;nofollow&quot;&gt;FCC lists them for the US&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for with a ham radio license, it depends on what you mean by 'free'. There are certainly high power ham bands, but you still must abide by the rules of ham operators such as no encryption or musical broadcasts etc so they are not free in that sense. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.arrl.org/graphical-frequency-allocations&quot; rel=&quot;nofollow&quot;&gt;ARRL lists ham bands for the US&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not sure what the regulations are when it comes to homebrewing something to communicate on the ISM bands, building equipment that interferes on them is okay, as their original allocation was to give things like microwaves that inherently transmit a known frequency to use. Intentionally using it for communication is a newer thing and subject to its own restrictions.&lt;/p&gt;&#xA;" OwnerUserId="1262" LastEditorUserId="218" LastEditDate="2014-07-05T03:13:08.607" LastActivityDate="2014-07-05T03:13:08.607" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1952" PostTypeId="2" ParentId="1943" CreationDate="2014-07-05T16:42:18.493" Score="1" Body="&lt;p&gt;That software appears to mimic all the controls of the rig. As it is free, it's worth trying it out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a useful list of alternatives here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.dxzone.com/catalog/Software/Radio_Control/&quot; rel=&quot;nofollow&quot;&gt;http://www.dxzone.com/catalog/Software/Radio_Control/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1283" LastEditorUserId="1246" LastEditDate="2015-02-27T15:20:37.240" LastActivityDate="2015-02-27T15:20:37.240" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1953" PostTypeId="1" AcceptedAnswerId="1961" CreationDate="2014-07-05T17:54:46.533" Score="4" ViewCount="1386" Body="&lt;p&gt;I was building the superhet receiver for ham radio. But I seem to have got stuck at the demodulation stage. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Suppose the person is transmitting SSB signal (20m band) at 14.250 MHz carrier frequency. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Let the speech signal occupy 1KHz bandwidth. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;So the RF signal using Upper Side Band is 14.251 MHz. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I take intermediate frequency of 455 KHz.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;So my Local oscillator is set to 14.251 + 0.455 = 14.706 MHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Now at the demodulator, the 455 KHz wave is needed to be demodulated. For this particular example, the oscillator frequency I need to inject in demodulator is 456 KHz (to recover 1 KHz speech).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly, am I going wrong somewhere till now?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, in real situation, I would not be knowing this much information. The only thing I would be knowing is that my Mixer oscillator is set to 14.706 MHz. So the Rf freq must be 14.251 MHz. Now here is the problem:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This 14.251 MHz could be a 14.250 MHz carrier with 1 KHZ sideband or it can be a 14.249 MHz carrier with 2 KHz sideband or any other pair of values. So how do I demodulate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, how do I know what frequency to inject in the demodulator? Do I just keep tuning the oscillator attached to the demodulator until the combination is struck? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If yes, then wouldn't finding any random person over this  wide range of band quite painful; First you set the Mixer oscillator to some value and then you keep tuning the demodulating oscillator over the entire 3 or 4 KHz bandwidth until you find someone?&lt;/p&gt;&#xA;" OwnerUserId="1284" LastEditorUserId="63" LastEditDate="2014-07-14T13:07:53.653" LastActivityDate="2014-07-14T13:07:53.653" Title="SSB demodulation" Tags="&lt;receiver&gt;&lt;frequency&gt;&lt;oscillator&gt;&lt;ssb&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1954" PostTypeId="2" ParentId="1953" CreationDate="2014-07-05T18:50:43.470" Score="2" Body="&lt;p&gt;I would suggest looking at a couple of sites:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.radio-electronics.com/info/rf-technology-design/superheterodyne-radio-receiver/basics-tutorial.php&quot; rel=&quot;nofollow&quot;&gt;http://www.radio-electronics.com/info/rf-technology-design/superheterodyne-radio-receiver/basics-tutorial.php&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://users.tpg.com.au/users/ldbutler/Superhet.htm&quot; rel=&quot;nofollow&quot;&gt;http://users.tpg.com.au/users/ldbutler/Superhet.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Looking at Figure 4 on this second site shows that the RF front end and the local oscillator have a ganged tuning capacitor. The difference in frequency between the two circuits is equal to the IF. Without that front-end selectivity, the mixer would be producing multiples of every signal arriving at the antenna, at equal levels.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;At the IF stage, you can decide on the selectivity by adding band-pass circuits (e.g. 3kHz for SSB and 500Hz for CW).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For SSB demodulation, you also need to inject a carrier with another oscillator (the Beat Frequency Oscillator). There's another useful description and diagram on this page:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.9h1mrl.org/ukrae/arc_cd/full/html/c5-1-2.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.9h1mrl.org/ukrae/arc_cd/full/html/c5-1-2.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Going back to your example, your demodulator will always be set to the IF of 455kHz, and does not need to vary. The output of the demodulator is audio/speech/morse code/etc.&lt;/p&gt;&#xA;" OwnerUserId="1283" LastActivityDate="2014-07-05T18:50:43.470" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1955" PostTypeId="2" ParentId="1514" CreationDate="2014-07-05T19:58:55.550" Score="1" Body="&lt;p&gt;An HF regenerative receiver needs to be oscillating in order to receive morse code and single-sideband transmissions. Therefore it will radiate RF from the receiving antenna. This signal can be reduced if there is an RF amplifier before the detector stage. If you have another radio that can tune the same frequencies, then you should be able to hear the carrier wave emitted from an oscillating regenerative receiver. With a suitable portable radio, you might be able to check if the signal is travelling beyond your property.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Early valve receivers could radiate as much as one watt of power - whilst this may not sound a lot, many radio amateurs regularly converse around the world at that power using morse code and digital modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if the radio is just used for AM reception, then it should not be oscillating.&lt;/p&gt;&#xA;" OwnerUserId="1283" LastActivityDate="2014-07-05T19:58:55.550" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1956" PostTypeId="2" ParentId="1917" CreationDate="2014-07-05T21:46:09.870" Score="1" Body="&lt;p&gt;I would go for the simplex option because there's no need to be able to TX at the same time as RXing if it's on a repeater.&lt;/p&gt;&#xA;" OwnerUserId="1285" LastActivityDate="2014-07-05T21:46:09.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1957" PostTypeId="2" ParentId="135" CreationDate="2014-07-05T22:30:47.863" Score="9" Body="&lt;p&gt;I would echo the point mentioned by N8WRL: &quot;Why do I operate CW? It is a blast!&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm actually re-learning morse and realising I've been missing out on a lot of fun over the years.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In terms of learning and training, it feels some way between learning a musical instrument and learning a new language. It is an excellent way to stimulate the brain - an investigation into morse-related neuroplasticity can be found here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ncbi.nlm.nih.gov/pubmed/20346399&quot; rel=&quot;noreferrer&quot;&gt;http://www.ncbi.nlm.nih.gov/pubmed/20346399&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;You never know when it will be needed&quot;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.cq2k.com/about_morse_code/Medical_Uses_of_Morse_code.htm&quot; rel=&quot;noreferrer&quot;&gt;http://www.cq2k.com/about_morse_code/Medical_Uses_of_Morse_code.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is morse code still in use? We know it is technically efficient, is good for the brain, but many people use morse because it's really fun!&lt;/p&gt;&#xA;" OwnerUserId="1283" LastActivityDate="2014-07-05T22:30:47.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1958" PostTypeId="2" ParentId="1949" CreationDate="2014-07-06T15:24:48.863" Score="3" Body="&lt;p&gt;You need some theory to answer this - it's not entirely simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider that each quad loop really consists of 2 dipoles, with the ends connected together (at the corners of the quad). So, each quad loop really acts as two dipoles located parallel to each other. (The reflected loop, in a similar way, consists of two of these 'pseudo-dipoles').&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you then consider what would happen if you would &lt;em&gt;extend&lt;/em&gt; the dipole to double its length: Instead of one dipole (which has low impedance at its center), you'd have two dipoles, which have a very high impedance at the center - almost impossible to feed (thousands of Ohms). But it would still be possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's not so interesting is that a large part of the field irradiated by the dipoles would cancel each other (because they're too close), so you would probably 'feel' a slight improvement, but not nearly what you'd expect from such an effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: Modified the text slightly to - hopefully - make it less confusing thanks for the remark, Phil). Making use of the edit, do note that if you'd extend the sides to 3/4$\lambda$ you'd actually get 3 dipoles and low impedance. But again, the gain won't be what you'd expect, as, again, parts will cancel. Moreover, if you'd think about using the biquad as a feed for a parabola, you'd be covering a much larger part of the useful area.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2014-07-07T19:01:48.290" LastActivityDate="2014-07-07T19:01:48.290" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1959" PostTypeId="2" ParentId="1913" CreationDate="2014-07-06T15:41:15.287" Score="5" Body="&lt;p&gt;Greg Hewgill's answer is correct, but merits a slight explanation.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Constant (percentual) relations mean that the Q-factor of the detector for the tones remains constant. Most detector chips (like the old NE567) and algorithms are designed for a single Q, and the frequency changes don't change the Q.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Distortion is quite normal in electronics — low tones like these are no exception. In fact, they are more sensitive than others as the audio channel was designed for higher (voice) frequencies. A side effect of distortion is what is called &lt;em&gt;intermodulation&lt;/em&gt;: new frequencies being generated by the presence of two (or more) other signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if the subtones were 100, 105 and 110 Hz, then the second harmonic of 105 (210) minus the first (100Hz) could conceivably generate a difference of 210 &amp;minus; 100 = 110 Hz, which would be the next subtone, and could possibly trigger some detector. This cannot happen with the actual tone.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You may have noticed that the DTMF basic tones are &lt;em&gt;also&lt;/em&gt; organized in a similar way — for the same reasons. In fact, the musical notes on any instrument are like this, because our ears discern differences in a similar way to detectors — constant Q.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I am not sure why the separation was chosen to be 1.035, but the exceptions are very probably because the tones which are near multiples of 60 and 50 Hz are shunned because of mains frequency interference, which can filter into the signal via power supply issues/microphone cables, etc.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="76" LastEditDate="2014-07-06T16:26:37.107" LastActivityDate="2014-07-06T16:26:37.107" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1960" PostTypeId="2" ParentId="1852" CreationDate="2014-07-06T21:48:11.853" Score="2" Body="&lt;p&gt;The ideal $36\Omega$ comes from the fact that a vertical is 1/2 dipole (so 1/2 of $72\Omega$). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you shorten a dipole (shorter than 1/2$\lambda$, the resistive part of the antenna will lessen, and the antenna will get more capacitive. You could see this on a Smith chart, or from the impedance formulas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, if you eliminate the capacitive part, by adding an inductor in series you get only the resistive part. Remember, a capacitor + inductor in series, at resonance are a short-circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a catch though: if the resistive part is so low, the resistance of the inductor (copper!) will start heating up because of the high currents, and you'll loose part of your power through heat, unless you use really thick wire.&#xA;The same, high, current must also be managed by the ground-plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's also why AM stations, which can only afford a fraction of the tower they'd need, have to use a really effective ground-plane to handle such large currents. ELF stations are build near large - preferably salty - water surfaces to have a reflector able to handle 1000's of A.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This reasoning is slightly simplified to make it clear enough to make it understandable, I hope.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-07-06T21:48:11.853" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1961" PostTypeId="2" ParentId="1953" CreationDate="2014-07-06T22:07:45.423" Score="4" Body="&lt;p&gt;To understand better, I'd suggest you follow this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) If you have an AM transmitter at 10.000 MHz (let's use simple numbers). If someone whistles in the microphone, at, say, 1kHz, two sidebands will appear, at&#xA;9.999MHz and 10.001 MHz (and a carrier at 10.000MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) If you convert the AM tx into USB, and transmit at 10.000 MHz, the whistler will appear at 10.001 MHz (only). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) If you want to &lt;em&gt;hear&lt;/em&gt; the whistle at 1kHz, you will have to insert a carrier at 10.000 MHz again. Any other frequency will change the tone of the whistle. (This is how direct conversion works).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4) So, if you IF is 0.5 MHz (again simple numbers), your tuning oscillator should be 9.500 MHz, resulting in the whistler being at 0.501 MHz. You would then need a carrier inserted at 0.500 MHz to get the whistle correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;5) The voice passband should ideally be around 0.3 to 2.5 kHz, so you IF filter should pass from 0.5003 to 0.5025 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not overly complicated - in a superhet receiver, you will have a carrier oscillator at 0.500MHz, a tuning oscillator which varies in the range 0.5 MHz below the desired band, and the filter as described in  5).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And yes, tuning SSB is not easy - you have to be at less than 100 Hz (!) of the correct frequency to have an enjoyable voice reception. The problem isn't so much with a one-note whistler, but if (s)he whistles a melody, all notes will be off, making it sound very strange.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that 'demodulating' SSB is just mixing frequencies, just like mixing from 10.000 to 0.500 MHz - an SSB demodulator is just a mixer.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-07-06T22:07:45.423" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1962" PostTypeId="1" CreationDate="2014-07-07T17:01:57.787" Score="6" ViewCount="211" Body="&lt;p&gt;Some places, like embassies and military bases, are considered US soil, even if not traditional. Can one operate with a US call sign in such situations, and how should it be done?&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-07-07T21:33:30.263" Title="Operating on foreign US soil" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1963" PostTypeId="1" AcceptedAnswerId="1965" CreationDate="2014-07-07T20:45:04.237" Score="5" ViewCount="156" Body="&lt;p&gt;We just finished our Field Day operations, and we're having a disagreement on whether we qualify for the &lt;em&gt;Alternate Power&lt;/em&gt; bonus. Our 1A (single transmitter, emergency power) station was completely solar powered for the duration of Field Day, which seems like it should qualify us for the bonus, but the wording of &lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2014/2014%20Rules.pdf&quot; rel=&quot;nofollow&quot;&gt;the 2014 rules&lt;/a&gt; makes it sound like it must be a separate effort from the main system.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;7.3.8. Alternate Power:&lt;/strong&gt; 100 bonus points for Field Day groups making a minimum of five QSOs  without using power from commercial mains or&#xA;  petroleum driven generator. This means an  &quot;alternate&quot; energy source&#xA;  of power, such as solar, wind, methane or water. This includes&#xA;  batteries charged by natural means (not dry cells). The natural power&#xA;  transmitter counts as an additional transmitter. If you do not wish to&#xA;  increase your operating category, you should take one of your other&#xA;  transmitters off the air while the natural power transmitter is in&#xA;  operation. A separate list of natural power QSOs should be submitted&#xA;  with your entry. &lt;strong&gt;Available to Classes A, B, E, and F.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Can a 1A station qualify for the &quot;Alternate Power&quot; bonus?&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="76" LastEditDate="2014-07-07T21:37:59.587" LastActivityDate="2014-07-07T22:39:24.357" Title="Can a 1A Field Day station qualify for the &quot;Alternate Power&quot; bonus?" Tags="&lt;contest&gt;&lt;field-day&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1964" PostTypeId="2" ParentId="1962" CreationDate="2014-07-07T21:33:30.263" Score="6" Body="&lt;p&gt;I can find no indication that a US-issued amateur licensed would in itself grant you the right to operate on such fringe places. &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.1.159.3&quot;&gt;§97.5 (a)&lt;/a&gt; reads:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(a) The station apparatus must be under the physical control of a person named in an amateur station license grant on the ULS consolidated license database or a person authorized for alien reciprocal operation by §97.107 of this part, before the station may transmit on any amateur service frequency from any place that is:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(1) Within 50 km of the Earth's surface and at a place where the amateur service is regulated by the FCC;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(2) Within 50 km of the Earth's surface and aboard any vessel or craft that is documented or registered in the United States; or&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(3) More than 50 km above the Earth's surface aboard any craft that is documented or registered in the United States.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;An embassy is not 50 km above the Earth's surface, nor is it a vessel or craft. So the question then becomes: is an embassy a &lt;em&gt;place where the amateur service is regulated by the FCC&lt;/em&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a bit tricker to answer. The &lt;a href=&quot;http://www.fcc.gov/what-we-do&quot;&gt;FCC's web page &quot;What We Do&quot;&lt;/a&gt; reads:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Federal Communications Commission regulates interstate and international communications by radio, television, wire, satellite and cable in all 50 states, the District of Columbia and U.S. territories.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Now, I am by no means an expert in international law, but I'm guessing that even if the US does exercise extraterritoriality in the case of embassies and whatnot, they are not claimed as US territories per se, and the US is not going to jeopardize its diplomatic relationships by letting some ham set up a high power station that disrupts local communications. Likewise military bases are not keen to attract negative attention, and commanding officers don't require a law to justify making your life miserable. In either case, you will probably be asked, then made by force to stop or leave, &lt;a href=&quot;http://xkcd.com/651/&quot;&gt;regardless of how vehemently you argue with the authorities&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fortunately, there are plenty of places that have signed &lt;a href=&quot;http://www.arrl.org/bilateral-reciprocal-agreements&quot;&gt;reciprocal agreements&lt;/a&gt; with the US which would permit one to operate in a foreign country ordinarily. If your goal is radio operation, and not a legal challenge, this is the way to go.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-07-07T21:33:30.263" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1965" PostTypeId="2" ParentId="1963" CreationDate="2014-07-07T21:57:54.950" Score="4" Body="&lt;p&gt;Of course you get the 100 points. You only used one transmitter, so there wasn't an issue of using more than your classification allowed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What the next-to-last sentence of that paragraph is getting at, somewhat sloppily, is operations that only used alternate power briefly to make their 5 QSOs. For example, our group was 2A, using two transmitters full time under emergency power from a generator. For about an hour we took one of those transmitters off the emergency power and connected it to solar-charged batteries for the Alternate Power bonus. If we had kept going with two transmitters and added an alternate power transmitter we would have been using three transmitters, violating our 2A classification.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: the reason for pointing out that it counts as a transmitter is that some transmitters don't count. Neither the GOTA transmitter nor a transmitter used for satellite communications counts as a transmitter for determining the category.&lt;/p&gt;&#xA;" OwnerUserId="105" LastEditorUserId="105" LastEditDate="2014-07-07T22:39:24.357" LastActivityDate="2014-07-07T22:39:24.357" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1966" PostTypeId="2" ParentId="1887" CreationDate="2014-07-08T04:33:50.803" Score="2" Body="&lt;p&gt;A small extra bit of information... Even though many VFO circuit descriptions, as you say, make it a point mentioning the 'cleanliness', by far most mixer circuits then proceed to convert the sine wave into something horrible :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mixers, in order to function as such, must be non-linear. Ideally, they should multiply both input signals, and produce neat sum and difference frequencies. In practice however, most mixers only approximate that behavior. An extreme example, is the digital mixer which just inverts the input signal (using analog switches) at the pace of a digital signal (the VFO).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Phil told you, many harmonics are present, so it's up to the designer to include the necessary tricks to avoid those extra frequencies having a bad effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More important than the harmonic content of the VFO, is something more difficult to measure. As most analog sine oscillators use amplifiers (transistors or integrated circuits) to oscillate, thermal effects in those semiconductors introduce modulation onto the carrier frequency. This makes the VFO not generate one clear sine, but rather an AM and FM modulated one. Depending on many factors, the Q factor of the resonator being probably the most important one, this noise can cause much more problems than harmonics.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2014-07-08T04:39:58.167" LastActivityDate="2014-07-08T04:39:58.167" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1967" PostTypeId="1" CreationDate="2014-07-08T09:48:54.517" Score="5" ViewCount="249" Body="&lt;p&gt;I browse ebay.com for used rigs in good condition and approaching my shoe-string and ... There appear to be a decent quantity of boat anchors out there - FT-101, TS-520, TR-4 to name just a few.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By definition, a boat-anchor would date to the 1970s/1980s. Are there any MTTF/MTBF/MTTR data on the typical tubes used in one of these beautiful rigs? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know it's a difficult question to answer because in all probability the answer would be 'It depends'. An old Ekco acquired by my grand-dad back in the early 1930s was still working in 2008 until it got water-logged - and later stuff dating to the 1950s/1960s are &lt;em&gt;still&lt;/em&gt; in excellent trim!&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2017-11-11T00:07:06.047" LastActivityDate="2017-11-11T00:07:06.047" Title="Are there an MTTF/MTBF/MTTR data on the typical tubes used in the FT-101/TS-520?" Tags="&lt;electronics&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1969" PostTypeId="2" ParentId="1967" CreationDate="2014-07-08T20:52:16.320" Score="5" Body="&lt;p&gt;The original RCA specs for &lt;a href=&quot;http://www.n6wk.com/kenwood/12BY7A%20GE.pdf&quot; rel=&quot;nofollow&quot;&gt;12BY7&lt;/a&gt; and &lt;a href=&quot;http://www.n6wk.com/kenwood/6146B%20RCA.pdf&quot; rel=&quot;nofollow&quot;&gt;6146&lt;/a&gt; did not disclose estimated lifetime of the tubes. An average tube has a lifetime of 2,000-4,000 hours, sometimes much-much more depending on usage. Given a low transmit duty cycle on CW/SSB  (compared to prolonged TX with digital modes), and the radio is properly tuned and maintained, the tubes may last a lifetime. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have Kenwood TS-520 made 35 years ago. It has three original 6146A and two 12BY7A tubes. It's still in great shape just starting showing its age - the driver tube doesn't drive well on 10m anymore and so the output power on 10-15m bands is lower. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tune-up is a good time to check your rig for maintenance requirements. As K4EAA &lt;a href=&quot;http://www.k4eaa.com/tune-up.htm&quot; rel=&quot;nofollow&quot;&gt;explains here&lt;/a&gt; :&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Notice how much drive is available.  A fresh 12BY7A will provide more drive than necessary to swing the ALC Meter through its range, even on 10M.  Low drive on any band shows that the driver tube is probably falling off in emission.  It will continue to function for a while, but you might consider replacing it in the near future.&#xA;  Watch for falling drive level as the rig is keyed for a few seconds.  A 12BY7A near the end of its life will fall off in drive within a few seconds or so of key-down.  If you see your drive fall as you are watching, that tube is positively ready for retirement. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Check the sharpness of the dip in CW Mode.  A broad, shallow dip means the finals are nearing the end.  You will notice reduced power output as well, most noticeable on the higher bands. &#xA;  Check for falling plate current under key down conditions.  Just like the driver tube, final tubes at the end of their useful life will jump to full Ip and then quickly start falling off.  When you spot this, they are ready for recycling. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The HV position of the meter reads the plate voltage applied to the finals.  The Kenwood hybrids utilize a voltage doubler circuit in the HV power supply, and aging High Voltage capacitors can result in low output.  To check for this possibility, monitor the HV as you key the rig.  It is normal to see perhaps 10% drop in HV when keyed.  Anything much in excess of this might indicate failing capacitors. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Don't buy these hybrid / tube radios to use for digital modes&lt;/strong&gt; - e.g. PSK31, RTTY - &lt;strong&gt;as the tubes won't like it. For CW / SSB you're okay.&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other issue with these rigs is VFO drift - your frequency will drift while the radio warms up. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other parts that may require eventual replacement are electrolytic capacitors in the power supply and relays. The band / mode switches (contacts) may become oxidized with time and need clean-up / replacement too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The replacement tubes are available sometimes on ebay. K4EAA has spare driver tubes for sale: &lt;a href=&quot;http://www.k4eaa.com/parts.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.k4eaa.com/parts.htm&lt;/a&gt; as well as some good info on using boat anchors properly. There is more info and manuals available from: &lt;a href=&quot;http://www.n6wk.com/kenwood&quot; rel=&quot;nofollow&quot;&gt;http://www.n6wk.com/kenwood&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1296" LastEditorUserId="1296" LastEditDate="2014-07-09T13:45:17.397" LastActivityDate="2014-07-09T13:45:17.397" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="1970" PostTypeId="2" ParentId="1953" CreationDate="2014-07-09T12:34:28.103" Score="0" Body="&lt;p&gt;An image might help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/mMr6y.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You begin with your baseband signal, some voice going from (almost) 0 Hz up to 1 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, when this is AM modulated at 14.250 MHz, we get a carrier at that frequency, then two sidebands above and below it that are just like the baseband signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, this is USB, so the carrier and the lower sideband have been removed (somehow) by the transmitter. So really, all we have is the baseband signal, shifted up by 14.250 MHz. Our goal is now to shift it back down. However, remember where the carrier was. Where the carrier was corresponds to what we want to eventually be 0 Hz when we demodulate the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you mix this with an LO at 14.706 MHz. You can think of this as AM again, only the sidebands are very much more spread apart. The result is the last figure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;carrier&quot; frequency of the signal, the part that we eventually want to land at 0 Hz, is now at&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ | f_1 - f_2 | = |14250 - 14706| = 456 \mathrm{kHz} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The upper end, which eventually should end up at 1 kHz, is at&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ | f_1 - f_2 | = |14251 - 14706| = 455 \mathrm{kHz} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually at this point, after going through the IF filters, you would mix again with a 456 kHz BFO, and that will take the lower sideband you generated in the first mixing stage and convert it back down to baseband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The audio bandwidth (you specified 1 kHz in your example) isn't really relevant, except to the filtering you do. If the audio bandwidth had been 4 kHz, then the BFO would still be at 456 kHz. The only difference is that the image you generated in the first mixing step would extend farther down, and you'd want a wider filter to accommodate that.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-07-09T12:39:47.477" LastActivityDate="2014-07-09T12:39:47.477" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1971" PostTypeId="1" AcceptedAnswerId="1981" CreationDate="2014-07-11T00:54:42.360" Score="7" ViewCount="127" Body="&lt;p&gt;I'm looking at making a portable system that can transmit BPSK31. I have a limited power budget, so I'm looking at trying to make my final power amplifier as efficient as possible. From my understanding, you can't use a plain non-linear amplifier (e.g. Class C or E) because BPSK31 isn't a constant envelope signal. The amplitude drops to zero on bit changes, and that behavior prevents splatter on bit changes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to efficiently amplify BPSK31, or am I stuck with an inefficient final amplifier?&lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2014-07-14T14:15:36.397" Title="Efficient BPSK31 amplification" Tags="&lt;digital-modes&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1974" PostTypeId="2" ParentId="749" CreationDate="2014-07-13T03:38:03.660" Score="1" Body="&lt;p&gt;Check out the ham swapmeets for a used AEA 10 meter Dx handy, I pickup one at the Williams AZ hamfst for a $100, very well made worked several states including Hawaii, converting a CB walkie talkie would not be that worth while as these radios operate in the Am mode, my honest opinion I would avoid the radios made in China as I feel their quality control is not that good, and if the radio is defective where will you get it fixed ? Ship it back to China ? The Japanese radios are far better made ! Check ot the potable FT-817ND &lt;/p&gt;&#xA;" OwnerUserId="1307" LastActivityDate="2014-07-13T03:38:03.660" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1975" PostTypeId="1" CreationDate="2014-07-13T05:53:12.577" Score="10" ViewCount="597" Body="&lt;p&gt;So I build an antenna, tune it with the SWR and make it look great for a 50 ohm load. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That does not determine if it is good at getting a signal out or not, it could just be a 50 ohm dummy load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With my completed home-brew antenna, what is the best way to determine if the signal power is actually &quot;getting out&quot;, and not just eaten up by inefficiencies in the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a big problem and I never think my antennas work &quot;good enough&quot; compared to an already built antenna.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2015-12-15T22:07:29.803" LastActivityDate="2020-12-31T21:30:14.120" Title="How to determine if my antenna is an effective radiator?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1977" PostTypeId="2" ParentId="1975" CreationDate="2014-07-13T13:18:28.813" Score="3" Body="&lt;p&gt;Do you make contacts with the home-brew antenna? If the answer is yes, it works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have another antenna for that band, signal comparison should be straightforward. On the receive of course, and remote stations are often happy to help with signal reports as you switch between antennas and transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you have other local hams that you can talk to separately, say with a HT? They can give you their receive strength for other (distant) stations on your antenna band, and you match frequency and see if you are also getting the same S-level as your friend gets on (presumably) a known good antenna. And both can try to call the remote station with the same power, and compare the reports you each receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A field strength meter may help to identify antenna signal strength as you walk around it (finding the &quot;lobes&quot;), obviously only works in a horizontal plane.&lt;/p&gt;&#xA;" OwnerUserId="152" LastActivityDate="2014-07-13T13:18:28.813" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1978" PostTypeId="1" CreationDate="2014-07-13T22:09:35.963" Score="4" ViewCount="3000" Body="&lt;p&gt;Using a RTL2832U USB dongle, I set up GNU Radio to produce a constellation plot of APRS traffic on 144.8 MHz. The result is what I expected:&#xA;&lt;img src=&quot;https://i.stack.imgur.com/Euvzi.png&quot; alt=&quot;144.8 MHz APRS Qt constellation on Gnu Radio Companion&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far, so good. Why not try the same thing using the wx GUI instead of the Qt version I had used ? Here are the results... The constellation plot does not look the same at all and it is nothing like the clean QAM constellation I had expected and obtained using the Qt GUI:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/2quCk.png&quot; alt=&quot;144.8 MHz APRS wx constellation on Gnu Radio Companion&quot;&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/UCnyE.png&quot; alt=&quot;144.8 MHz APRS wx constellation on Gnu Radio Companion&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone explain why the wx GUI's constellation plot does not behave as I expect ? Is it simply a case of different default settings and naive user expectations ?&lt;/p&gt;&#xA;" OwnerUserId="1291" LastEditorUserId="4076" LastEditDate="2020-04-26T13:35:24.770" LastActivityDate="2020-04-26T13:35:24.770" Title="Why doesn't GNU Radio Companion's wx Constellation Plot doesn't give me the clean QAM constellation I get from its Qt sibling?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;rtl-sdr&gt;&lt;modes&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1979" PostTypeId="2" ParentId="1975" CreationDate="2014-07-14T00:50:47.080" Score="8" Body="&lt;p&gt;If you have a field strength meter, then you can use that. You can also use a 2nd radio, on a 2nd antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, consider &lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot;&gt;reciprocity&lt;/a&gt;: anything you to do increase your transmit gain also increases your receive gain equally. So actually you don't need a 2nd radio, you can use someone else's.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simply find a station that's transmitting, tune it in, and measure its strength. With a more efficient antenna, the received power of that station will be greater, and any efficiency gains (or losses) work for transmitting too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's easiest if you can find a station transmitting something with more or less constant power, like CW, AM, or most digital modes. SSB is tricky because the transmitted power depends on how loudly the operator is talking. If there's a commercial AM broadcast station handy, that could be a good target.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Getting an accurate measurement is somewhat complicated by the fact that S meters on many radios doesn't mean a thing. Usually the S meter simply indicates the AGC level. How does AGC level correlate to the received power? It's different on every radio, and may or may not be useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A cheap SDR like the Softrock or RTL2838 can be useful here. Typically these feed the host computer with data at a fixed RF gain, and then you just need software that can give you a good measurement of power. Most software has some scale on the waterfall or spectrum that will do the job.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-07-14T00:50:47.080" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1980" PostTypeId="2" ParentId="1978" CreationDate="2014-07-14T01:21:37.427" Score="6" Body="&lt;p&gt;There are a lot of things wrong here. Neither plot looks correct.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;There is no way that Qt plot is realistic for anything but a signal generator. Where's the noise?&lt;/li&gt;&#xA;&lt;li&gt;Where are the three missing constellation points in the Qt plot?&lt;/li&gt;&#xA;&lt;li&gt;APRS isn't QAM (it's AFSK over FM), so I'm not sure why you are expecting QAM.&lt;/li&gt;&#xA;&lt;li&gt;You don't have any filters, clock recovery, or really demodulation of any kind between the source and the sink. Normally you do all that stuff before the constellation such that each sample (and thus, each dot) corresponds to one symbol.&lt;/li&gt;&#xA;&lt;li&gt;From the parameters, it looks like WX sink has some clock recovery, but I doubt it's doing anything useful. I doubt it's syncing up with your intended signal. Usually you still need to do some filtering and decimation to at least get it in the right ballpark. The clock recovery is only intended to compensate for slow phase drift. It doesn't know nearly enough to demodulate the signal. For example, how does it know the symbol rate?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-07-14T01:21:37.427" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1981" PostTypeId="2" ParentId="1971" CreationDate="2014-07-14T13:52:31.213" Score="2" Body="&lt;p&gt;There is a way, but you don't end up with an amplifier that you can connect to an ordinary rig. The trick is to &lt;a href=&quot;http://en.wikipedia.org/wiki/Polar_modulation&quot; rel=&quot;nofollow&quot;&gt;express the signal as phase and amplitude&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider: with an ordinary non-linear amplifier (such as typical for FM use, for example) you can manipulate phase (and thus, also frequency), but the amplitude is fixed by the amplifier's supply voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What if you vary the supply voltage? You then have a way to also manipulate amplitude. If you can manipulate phase and amplitude, then you can express anything that can be expressed in I/Q representation -- the only difference is that you are doing it in polar coordinates instead of Cartesian coordinates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you have the problem of making an efficient &quot;amplifier&quot;, the output of which is the power supply for the class C amplifier. However, since the amplitude variations are much slower in this polar domain (for PSK31, only 31.25 Hz), this is a substantially easier problem. A switch-mode power supply can do the task.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems pretty simple, so you might wonder why everyone doesn't use amplifiers like this. The trouble lies in &lt;a href=&quot;http://www.circuitdesign.info/blog/2008/08/challenges-of-polar-modulation/&quot; rel=&quot;nofollow&quot;&gt;implementation details&lt;/a&gt;. However, if you are designing for the specific case of PSK31, then you can take specific knowledge of the modulation into account for your design. Also, PSK31 is such a simple and slow scheme, the challenges are much less than they would be if we were trying to make an amplifier for a cellular phone or Wi-Fi radio.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-07-14T14:15:36.397" LastActivityDate="2014-07-14T14:15:36.397" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1982" PostTypeId="1" AcceptedAnswerId="1983" CreationDate="2014-07-15T15:00:33.413" Score="2" ViewCount="314" Body="&lt;p&gt;I guess my question is as follows: if I find FSPL (there will be no buildings or anything blocking/diffracting), can I figure out how far the signal can be transmitted if the receiver gain, loss and sensitivity as well as the transmission power and gain/loss is known.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All I really know is the &lt;strong&gt;frequency&lt;/strong&gt; of the RF (around 730 MHz), the &lt;strong&gt;TX Power&lt;/strong&gt; (6dBm), the &lt;strong&gt;antenna gain&lt;/strong&gt; (-21 dB), &lt;strong&gt;RX Sensitivity&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since I cannot really find FSPL (free-space path loss) because you need the distance transmitted for that, I am kind of at a loss (no pun intended) as to how to find the possible transmitted distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, is there a way to figure out (based on a receiver's loss/gain and sensitivity) what minimum value (I guess dBm) would be needed for a signal to be decipherable? (I have heard that 3 dB or dBm or what ever measures this is a good assumption...)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, I know &lt;code&gt;RX power = TX power + gains - losses&lt;/code&gt; and FSPL is a loss (which has distance built into the formula). Since &lt;code&gt;**FSPL** (dB) = 20log(**distance**) + 20log(**frequency**) + 32.45&lt;/code&gt; (for kilometers) that means that &lt;code&gt;distance = 10^(**FSPL** (db) - 20log(**frequency**) - 32.45)/20&lt;/code&gt;. The problem is that there is no way to find the FSPL value in the second equation because in order to find that, you need the &lt;em&gt;distance&lt;/em&gt; which is what we are trying to find in the first place!! So, you would be able to solve the initial equation (with RX power = TX power + gains - losses) equal to distance, but you would have no way of finding th FSPL value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;----edit----&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks for your help, Phil! It turns out we cannot even estimate the distance because the TX power outputted can not truly be found.&lt;/p&gt;&#xA;" OwnerUserId="1314" LastEditorUserId="76" LastEditDate="2014-07-16T17:32:41.820" LastActivityDate="2014-07-16T17:32:41.820" Title="Find RF transmission distance" Tags="&lt;propagation&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1983" PostTypeId="2" ParentId="1982" CreationDate="2014-07-15T16:01:34.147" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;there will be no buildings or anything blocking/diffracting&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Really? What about the ground? Unless you are in space, you will need to incorporate some kind of path model into your calculations. The &lt;a href=&quot;https://electronics.stackexchange.com/q/120806/17608&quot;&gt;two-ray ground reflection model&lt;/a&gt; is one simple option.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The problem is that there is no way to find the FSPL value in the second equation because in order to find that, you need the distance which is what we are trying to find in the first place!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes there is. Use &lt;a href=&quot;http://en.wikipedia.org/wiki/Algebra&quot; rel=&quot;nofollow noreferrer&quot;&gt;algebra&lt;/a&gt;. You can take your path loss (based on the &lt;a href=&quot;https://ham.stackexchange.com/questions/1539/what-does-the-friis-transmission-equation-represent-and-how-is-it-derived&quot;&gt;Friis transmission equation&lt;/a&gt;) and solve for $d$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;G_\text{FSPL} &amp;amp;=&#xA;  20 \log_{10}(d_\text{km})&#xA;  + 20log_{10}(f_\text{MHz})&#xA;  + 32.45 \\&#xA;\log_{10}(d_\text{km}) &amp;amp;=&#xA;  (G_\text{FSPL} - 20log_{10}(f_\text{MHz}) - 32.45)&#xA;  / 20 \\&#xA;d_\text{km} &amp;amp;= 10^{&#xA;  (G_\text{FSPL} - 20log_{10}(f_\text{MHz}) - 32.45)&#xA;  / 20}&#xA;\end{align}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, you merely need to calculate a &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt; to determine how much you can afford in path loss. Replace $G_\text{FSPL}$ with this number and solve the equation, and you now have the distance beyond which your path losses are too much.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-07-15T16:01:34.147" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="1985" PostTypeId="1" CreationDate="2014-07-17T02:36:24.037" Score="0" ViewCount="673" Body="&lt;p&gt;It's either math or magic. It seems like the only thing that will explain operation are complex formulas. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a child were to ask &quot;how does an antenna work&quot; what should one say, it magically changes electricity into invisible photons? &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="873" LastEditDate="2021-02-10T12:57:33.960" LastActivityDate="2021-02-11T14:43:28.290" Title="Explain how an antenna works to an 18 year old" Tags="&lt;antenna&gt;&lt;education&gt;&lt;children&gt;" AnswerCount="9" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1986" PostTypeId="2" ParentId="1985" CreationDate="2014-07-17T12:28:04.797" Score="3" Body="&lt;p&gt;You know how sound waves let me talk to you? You can't see them, but you can hear them. Light is similar, you can send it from a lightbulb or flashlight, and receive it with your eyes and cameras, but you can't hear it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas use electromagnetic waves. You can't hear or see them, but antennas can send and receive them.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-07-17T12:28:04.797" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1987" PostTypeId="2" ParentId="1503" CreationDate="2014-07-17T18:03:54.980" Score="0" Body="&lt;p&gt;This might help :&#xA;&lt;a href=&quot;http://www.aflglobal.com/Products/Aluminum-Clad-Steel/Guy-Wire/Type-M-Guy-Wire-Alumoweld-Aluminum-Clad-Steel.aspx&quot; rel=&quot;nofollow&quot;&gt;Type M® Guy Wire - Alumoweld Aluminum-Clad Steel&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1334" LastEditorUserId="218" LastEditDate="2014-07-21T11:14:20.903" LastActivityDate="2014-07-21T11:14:20.903" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1988" PostTypeId="2" ParentId="1985" CreationDate="2014-07-17T21:17:13.100" Score="2" Body="&lt;p&gt;Maybe compare an antenna with an electric heater or incandescent bulb? If you feed the heater with electricity, you can 'feel' the radiation. Similar for a light bulb, where you can 'see' the radiation (and feel it, if you're not careful).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a less correct, but more visual approach: stick a pole in water and move it - you'll see the waves irradiated by the movement. Hey, you can even see the standing waves there, and reflections.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-07-17T21:17:13.100" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1991" PostTypeId="2" ParentId="1985" CreationDate="2014-07-20T04:36:39.407" Score="1" Body="&lt;p&gt;Radio waves travel at the speed of light, and although the electrical current that generates the magnetic and electric fields travel almost as fast, the fields have already escaped so the transmitter cannot change them, only make new fields. It's like once you have said something, you cannot take it back. Dropping a stone in water causes waves to travel away from the spot where the stone was dropped, but dropping another stone cannot change the waves that have already escaped.&lt;/p&gt;&#xA;" OwnerUserId="1341" LastEditorUserId="218" LastEditDate="2014-07-20T15:39:19.597" LastActivityDate="2014-07-20T15:39:19.597" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1992" PostTypeId="2" ParentId="1503" CreationDate="2014-07-20T04:48:44.380" Score="1" Body="&lt;p&gt;Power cables typically have Aluminium conductors enclosing a steel core. 'nuf said? The Aluminium stretches with time, thus changing the tuning, work hardens and can crack, as does steel but at a greater rate, expands more with change in temperature, and although I have no experience with this, becomes brittle at higher temperatures (Read that as 'less cold') than steel. Copper antenna wires need to be pre-stretched to harden the copper, but I don't believe that works for Aluminium. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another concern is the cross-section, or outer diameter of the conductor as this effects the band-width of the tuning. Thicker conductors have a greater bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Light Aluminium power conductors with a steel core be good if a suitable size is available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check your local electrical cable supplier for catenary rated cables. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have known of hams using discarded coax used in television stations for the copper plated steel core, but mostly for the outer sheath as a thick conductor, and low weight. (NB: the impedance doesn't matter, we're using the sheath.)&lt;/p&gt;&#xA;" OwnerUserId="1341" LastActivityDate="2014-07-20T04:48:44.380" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1993" PostTypeId="1" AcceptedAnswerId="1994" CreationDate="2014-07-20T07:15:41.030" Score="6" ViewCount="301" Body="&lt;p&gt;I'm wading through some schematics for a direct conversion I-Q SDR receiver, and there is an L-C band-pass filter on the input. Each inductor is specified by an inductance, a toroidal core material, a wire gauge (AWG), and a number of turns. I understand that this is all the information that is required to replicate the exact specified inductor (and all the values check out), and I know I could replicate the part described in the schematic. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I would like to avoid manually building a component like an inductor if I can ( because of logistics and personal enjoyment). While I can certainly select an inductance value from a menu on Digikey, there is more to inductors than just the value. I suspect the self-resonant frequency (SRF) needs to be well above the frequency of interest, and the Q of the inductor should be high, but past that I'm not sure what is important.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What problems am I going to run into if I switch from hand-wound toroidal inductors to a &quot;store-bought&quot; inductor such as &lt;a href=&quot;http://www.digikey.com/product-detail/en/AIML-1206-R56K-T/535-11688-1-ND/2782903&quot;&gt;this one&lt;/a&gt;?&lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2014-08-03T03:28:22.647" Title="Replacing hand-wound inductors with store-bought versions" Tags="&lt;diy&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1994" PostTypeId="2" ParentId="1993" CreationDate="2014-07-20T12:32:40.873" Score="3" Body="&lt;p&gt;I'm going to say a lot of stuff that could go wrong, but really, don't be discouraged. I think mostly ham equipment is built with self-wound inductors because cores and magnet wire is cheap and easy to source. Take apart a cell phone and you may not find a single wound inductor on it. None of the problems to follow are insurmountable, if they are even problems at all. Of course, it always depends on the application and circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are right to care about the self-resonant frequency and Q. Generally a high SRF and Q is good, but in some circuits it may be a problem merely that they are &lt;em&gt;different&lt;/em&gt;, if the design already compensates for the non-ideal components of the self-wound part. Probably not an issue except in the most critical filters, and probably nothing that can't be fixed by adjusting a capacitor or resistor to compensate. This is why high SRF and Q are desirable: you can always make them lower by adding parts, but you can't make them higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All ferrite-cored inductors get lossier with increasing frequency. Generally, ferrites for low frequencies can provide a higher permeability (thus increasing inductance per turn), but as frequencies increase so do losses, necessitating lower loss ferrite materials with a lower permeability. &lt;a href=&quot;https://ham.stackexchange.com/questions/1159/how-does-one-read-a-ferrite-datasheet&quot;&gt;How does one read a ferrite datasheet?&lt;/a&gt; gives some insight into the parameters of the ferrite itself. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, also check the intended frequency of operation for your considered chip inductor. If the datasheet doesn't say otherwise, you can assume that the test frequency is near the top of frequencies for which the part is suited. You could go a little higher if you don't much care about losses or Q. If you go a lot higher you might as well buy a resistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other problems you might encounter, generally:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Reduced power handling&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The smaller surface area of a chip inductor makes it less able to radiate heat, and its smaller mass makes it heat more quickly for a given power. Probably a non-issue for receive filters, maybe an issue for transmit filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Lower saturation current&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again driven by smallness, chip inductors will typically have less ferrite material per ampere-turn of wire in it, which increases inductance per physical size, but decreases saturation current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides the possibility of outright saturating the core, you can probably measure higher non-linear distortion in a chip inductor with the right equipment. This is because saturation isn't a hard wall, but something that sets in gradually. The less magnetized the core is, the more linear it is. If the core is made smaller but inductance is held constant, the core must be more magnetized, and thus less linear. The difference may be slight, and not important for many applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Higher ohmic losses&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The smaller size of surface mount components usually dictates smaller conductors, which have higher resistance, and thus higher loss and lower Q.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;More leakage&lt;/strong&gt; (in some designs)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some, but not all chip inductors do not have a closed magnetic circuit. This can lead to mutual inductance with others on the board, making transformers where you don't want them. Read the datasheet to see what you are getting. The example you provided says it is &quot;magnetically shielded&quot;, suggesting a closed magnetic circuit.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-07-20T12:32:40.873" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1995" PostTypeId="1" AcceptedAnswerId="1997" CreationDate="2014-07-20T18:00:36.093" Score="1" ViewCount="458" Body="&lt;p&gt;Example, a recent contest offered a multiplier for &quot;All 50 states&quot;.  I presume that means I have to get all 50 states to get the multiplier.  However, nowhere does it list what to multiply by?  I'm very confused and googling around just hasn't been any help.  I've been just submitting my logs only claiming the QSOs and never a multiplier because I have no idea when I'm eligible to claim one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;edit&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example of unclear contest rules: &lt;a href=&quot;http://ncjweb.com/NAQP-Rules.pdf&quot; rel=&quot;nofollow&quot;&gt;http://ncjweb.com/NAQP-Rules.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="102" LastEditorUserId="102" LastEditDate="2014-07-21T11:32:44.277" LastActivityDate="2014-07-21T13:04:57.303" Title="How do contest multipliers work?" Tags="&lt;contest&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="1996" PostTypeId="2" ParentId="1995" CreationDate="2014-07-21T04:11:05.490" Score="2" Body="&lt;p&gt;Well, you have to check the particulars of &lt;em&gt;each&lt;/em&gt; contest. Almost all of them are different.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Some contests give a multiplier for the number of bands you worked a station on&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some contests give a multiplier for the number of different states or countries or continents you worked on.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some even provide incentives to contact with members of the organizing club.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So, your contest may have offered a multiplier per state - I don't think you needed all states.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-07-21T04:11:05.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="1997" PostTypeId="2" ParentId="1995" CreationDate="2014-07-21T04:21:17.150" Score="2" Body="&lt;p&gt;Usually if a contest says there are multipliers for &quot;all 50 states&quot; (and we have to assume this is US States? Without specifying a country or the actual contest we have to guess), that would mean that you would get one multiplier for each State worked (although what about DC? Presumably doesn't count as a mult?).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would mean that the maximum number of multipliers would be 50 - one for each state worked.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again - please specify more information. When saying &quot;in a recent contest&quot;, it doesn't hurt to say which one it was :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are asking how multipliers work generally, they are numbers that you collect as you are going. When you have worked out the score (you will get a number of points for contacts as specified in the rules of the contest), and the number of multipliers (again, specified in the rules of the contest), you multiply the numbers together to give you your final score.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Update&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Since you have now posted an example, I will quote from that PDF: &quot;Multiply total valid contacts by the sum of the number of multipliers worked on each band.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means that each 'valid contact' (defined in the PDF) is worth one point. The total number of contacts would then be multiplied by the number of multipliers &lt;strong&gt;on each band&lt;/strong&gt;, where the allowed bands are &quot;160, 80, 40, 20, 15, 10 meters only, except no 160 meters for the RTTY contest&quot;. The number of multipliers per band is given as 63 (50 states and 13 Canadian provinces). This gives a total number of 378 possible multipliers (6 bands x 63 states/provinces), and 315 for the RTTY contest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you worked 10 stations on all 6 bands, but they were all in the same state/province, you would have 60 valid contacts and 6 multipliers, giving 360 points.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, the cheat's way of doing all this is to use the EXCELLENT contest logging software by N1MM, where you enter each QSO as you work them, and it does the scoring for you.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2014-07-21T13:04:57.303" LastActivityDate="2014-07-21T13:04:57.303" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="1998" PostTypeId="1" CreationDate="2014-07-21T05:35:25.360" Score="1" ViewCount="273" Body="&lt;p&gt;I have a radio with a really horrible squelch. When the knob is all the way to most sensitive, the squelch has problems, the noise is not constant, the noise comes on and goes off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the antenna is disconnected, I hear the noise when the squelch is at the most sensitive point. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I connect the antenna, this noise goes away, and the squelch has major problems, because I can not turn it to least sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is going on? Why would connecting an antenna make the squelch deactivate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The squelch is for VHF, the Alinco DR-600 radio&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2016-10-29T18:53:43.147" LastActivityDate="2016-10-29T18:53:43.147" Title="Squelch sensitivity decreased when antenna is connected" Tags="&lt;equipment-operation&gt;&lt;alinco&gt;&lt;squelch&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="1999" PostTypeId="2" ParentId="1985" CreationDate="2014-07-21T17:17:21.783" Score="2" Body="&lt;p&gt;Say you have a positively charged object, and a negatively charged object. They will be attracted together, like opposite poles of a magnet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if you pull these two objects apart, there will exist an electric field between them. If you were to place an infinitesimal test charge somewhere around your separated charged objects, you'd find if the test charge is positive, then it will be attracted to your negatively charged object, and repelled from the positively charged object.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your two objects have been in the same position, with the same charge, for an infinite amount of time, then as we get farther away from them the force experienced by the test charge is weaker, but it never goes away. That is, for &lt;em&gt;any&lt;/em&gt; point in space, no matter how far, we can calculate some force that will be experienced by the test charge. If we were to calculate the direction and magnitude of the force that would be experienced by the test charge for every possible location in space, this is the &lt;em&gt;electric field&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what if your two charged objects &lt;em&gt;move&lt;/em&gt;? Now the electric field will be something else. If we instantly reversed the positions of your two charged objects, then the electric field around them would be more or less the same, except in the opposite direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the field can't change instantly -- that would &lt;a href=&quot;http://en.wikipedia.org/wiki/Special_relativity#Causality_and_prohibition_of_motion_faster_than_light&quot; rel=&quot;nofollow&quot;&gt;violate causality&lt;/a&gt;. Instead, the new field propagates outward at the speed of light. If you are very close to these charged objects, then the field would seem to change instantly. If you are one light-year away, then the field you observe at your location reflects how the charged objects were one year ago.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, consider a simple dipole antenna. It has two halves. Our transmitter sucks electrons out of one side (making it positively charged) and shoves electrons in the other side (making it negatively charged). It is very much like the two charged objects above. An electric field begins to propagate out...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And then, the transmitter changes direction, and now the charges of each half of the dipole are reversed. This change in the field is also propagating outwards. This reversing of charges continues at whatever our transmit frequency is. If it is 7 MHz, then the charges reverse 7000000 times per second. If you are not moving relative to the antenna, then at one instant the electric field is pointing one way, and then shortly later the electric field is pointing the other way. The wavelength is the distance traveled by light in the time it takes for the antenna to go through one of these oscillations. It's how far the change in the electric field will have propagated by the time we start another cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, we said the electric field allows us to predict the force that an imaginary test charge would experience at that point. What if the test charge isn't imaginary? Like, the mobile electrons in a receiving antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not surprisingly, the charge in the receiving antenna experiences a force. Because the antenna is a good conductor, this makes a current in the antenna, which the receiver can then amplify and demodulate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For further reading, I highly recommend &lt;a href=&quot;http://web.mit.edu/8.02t/www/802TEAL3D/visualizations/guidedtour/Tour.htm&quot; rel=&quot;nofollow&quot;&gt;A Visual Tour of Classical Electromagnetism&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-07-21T17:17:21.783" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2000" PostTypeId="2" ParentId="135" CreationDate="2014-07-22T08:53:28.260" Score="-1" Body="&lt;p&gt;Morse code needs to be known as it is the lowest common denominator for emergency situations.&lt;/p&gt;&#xA;&lt;p&gt;I am aware that there are radio installations for use in emergencies in nuclear fallout situations and the most likely signal to get through will be Morse [although whether it's detectable over any background radiation is another question].&lt;/p&gt;&#xA;" OwnerUserId="1350" LastEditorUserId="1350" LastEditDate="2021-01-20T13:08:58.617" LastActivityDate="2021-01-20T13:08:58.617" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="2001" PostTypeId="1" CreationDate="2014-07-22T12:37:44.770" Score="10" ViewCount="6121" Body="&lt;p&gt;Say the deck is stacked.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm out in the country with an all-band QRP home-brew rig, &lt;strike&gt;and an active antenna.&lt;/strike&gt; Or say ship-wrecked and marooned on that desert island. The battery only has enough juice for say 1-min Tx, and 30-min Rx. The Sun is at the bottom of cycle so conditions may be bad.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I need to get that priority message out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I find out what bands are open? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just a quick note to the comments about the scenario being totally unrealistic. An amateur radio expedition from VU was caught unawares when that Boxing Day tsunami hit the Andaman Island chain in the Indian Ocean. Unlike a team that goes out after the event, when the expedition went out they didn't know what they were going to have to handle. &lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2014-10-23T17:53:40.803" LastActivityDate="2014-10-23T17:53:40.803" Title="How do I find out what bands are open?" Tags="&lt;propagation&gt;&lt;procedure&gt;&lt;emergency&gt;" AnswerCount="4" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="2002" PostTypeId="1" CreationDate="2014-07-22T19:37:16.603" Score="1" ViewCount="123" Body="&lt;p&gt;Apologies, this may be off topic.  Ham radio operators are the probably the only community that might have used Handicode.  Back in 2002, a company &quot;Microsystems Software&quot; made a DOS program that allowed a morse code keyer to be used as an input device for a computer.  They appear to be long out of business, as their website is down, and the internet wayback archive only contains references to Cyber Patrol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm trying to create a similar device for a blind user that used to own one. The first step is to  track down a copy of the documentation so I can reproduce the extended morse code characters, such as &lt;kbd&gt;ALT&lt;/kbd&gt;, &lt;kbd&gt;CTRL&lt;/kbd&gt;, and &lt;kbd&gt;SHIFT&lt;/kbd&gt;.&lt;/p&gt;&#xA;" OwnerUserId="1353" LastEditorUserId="5222" LastEditDate="2015-09-04T11:41:45.367" LastActivityDate="2015-09-04T11:41:45.367" Title="Where can I find documentation on Handicode?" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="6" ClosedDate="2014-08-05T10:48:22.790" ContentLicense="CC BY-SA 3.0" />
  <row Id="2004" PostTypeId="2" ParentId="2001" CreationDate="2014-07-22T20:10:02.703" Score="2" Body="&lt;p&gt;If the deck is stacked, then the best bet is to play the odds. Evenings, check 20 Meters &amp;amp; below. Days, check 20 Meters &amp;amp; above. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can scan for beacons on 20, 10 and 6M to be alerted to band openings. But if you were truly on a desert island with one shot, I would head for 20M band when the terminator is rolling by, and hope for the best. &lt;/p&gt;&#xA;" OwnerUserId="1356" LastEditorUserId="13" LastEditDate="2014-07-27T10:12:45.420" LastActivityDate="2014-07-27T10:12:45.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2005" PostTypeId="2" ParentId="135" CreationDate="2014-07-22T20:14:00.803" Score="11" Body="&lt;p&gt;Because it's fun to send and receive messages by Morse code!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's something that can be done without any specialized equipment for sending and receiving. It's a shared historic experience.  It's a challenge, and a skill that is fun to learn. It puts you into a special &quot;club,&quot; setting you apart from those non-CW capable hams.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But mostly, it's just fun.&lt;/p&gt;&#xA;" OwnerUserId="1356" LastActivityDate="2014-07-22T20:14:00.803" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2006" PostTypeId="2" ParentId="1998" CreationDate="2014-07-23T00:13:27.863" Score="2" Body="&lt;p&gt;There seems to be quite a bit of confusion. First you should tell us if the squelch is for a VHF/UHF set, or some HF equipment. They are very different!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;strong&gt;VHF or UHF squelch&lt;/strong&gt; works by detecting the disappearance (or at least lessening) of noise. That means you can't turn the knob clockwise for increasing sensitivity. The 'most sensitive' point is the point where the squelch is just on (below) the limit between letting the noise pass or not. If you connect an antenna, when the squelch is just open (i.e. lets the noise pass), it can happen that it then closes because of the extra noise coming in. It's just doing its job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An &lt;strong&gt;HF squelch&lt;/strong&gt; on the other hand, generally works by measuring the signal strength. Its most sensitive point is also between 0 and max, but increasing the noise with the connection of an antenna, generally tends to 'open' the squelch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In both cases, the 'most sensitive' point is the limit between opening and closing the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; As you update the question to specify it's a VHF radio, a 'de-activation' of the squelch (i.e. the passing of the noise), may indicate that some specific frequencies are &lt;em&gt;absent&lt;/em&gt; from the antenna noise, which makes the squelch think that there is a valid signal on the input. This could be something like electric noise (possibly from fluorescent tubes), or some other source. Could be even some broadband signal such as an oscillation.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2014-07-24T03:44:42.187" LastActivityDate="2014-07-24T03:44:42.187" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2007" PostTypeId="2" ParentId="135" CreationDate="2014-07-23T01:32:00.450" Score="10" Body="&lt;p&gt;I love Morse code for these reasons:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;It's fun.&lt;/li&gt;&#xA;&lt;li&gt;There is something satisfying about pulling a really weak signal out from the noise just 10s of Hz away from another really strong semi-local signal, and making a decent contact with someone halfway around the planet with less than 100W.&lt;/li&gt;&#xA;&lt;li&gt;I can put headphones on and operate in the living room while the XYL is watching TV (think: condo in the city), and neither of us is disturbed by the other. I'm busy calling CQ DX (from here in Thailand you can get quite a lot of responses when the conditions are right) while she's watching some awful soap on TV - and we're both happy!&lt;/li&gt;&#xA;&lt;li&gt;Speaking of condos in the city - with a compromised antenna and reduced power, you can STILL work the world with a little help from the propagation gnomes if you use Morse code.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Reason 1 is the main one though :)&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-07-23T01:32:00.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2008" PostTypeId="2" ParentId="2001" CreationDate="2014-07-23T01:42:52.887" Score="0" Body="&lt;p&gt;Since you have set the conditions so that there is no way to actually check (think: cluster, solar reports, propagation alerts - all on the internet) then you are stuck with guessing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's day time try 20m or 15m. If it's night, 40m and 80m. Around dawn or dusk, try 40m and 20m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be aware that these will likely get you contacts quite a long way away though! The person you spoke to might be literally half way round the world, and not be much help to you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes you don't want the propagation to be TOO good!&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-07-23T01:42:52.887" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2009" PostTypeId="2" ParentId="2001" CreationDate="2014-07-23T11:43:31.230" Score="7" Body="&lt;p&gt;If you are stuck on an island and have only enough battery for one minute of transmitting, the important thing isn't that propagation is good, but that someone hears you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use your 30 minutes of receive time to find an area of some band that is very busy, with very many very strong signals. By &lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot;&gt;reciprocity&lt;/a&gt;, the better you can hear them, the better they can hear you, and having many people on frequency increases your odds.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-07-23T11:43:31.230" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2010" PostTypeId="1" AcceptedAnswerId="2014" CreationDate="2014-07-23T19:56:34.353" Score="6" ViewCount="1430" Body="&lt;p&gt;Long time ham operator here, new to this particular challenge - &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a software defined radio transceiver that I'd like to try and use to make contacts on HF, in particular 20-meters. Tuning within the 20-meter band is no problem but &lt;a href=&quot;http://www.nooelec.com/store/hackrf.html&quot; rel=&quot;noreferrer&quot;&gt;the transmitter&lt;/a&gt; only puts out about 0.05 watts! Great for the lab but arguably not enough power to make any reasonable contacts. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to amplify the signal up to at least 10 watts, 50 would be perfect if possible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being that I may need two amplifiers I am concerned about noise and keeping the signal clean on the way up to the desired output power. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A typical linear amplifier won't even trigger unless the input power is at least 1-5 watts and so this is why I think I may need a two-step amplifier chain, although I'd like to just have a single amplification stage if possible.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I'm looking for help coming up with a solution, perhaps specific amplifier(s) that I should use to get to the desired output power, based on your experience. &lt;/p&gt;&#xA;" OwnerUserId="1238" LastEditorUserId="218" LastEditDate="2014-07-23T21:12:57.823" LastActivityDate="2014-07-23T21:26:56.360" Title="Suggested method for boosting 0.05 watt transmitter up to 10+ watts?" Tags="&lt;software-defined-radio&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2011" PostTypeId="1" AcceptedAnswerId="2012" CreationDate="2014-07-23T19:59:31.093" Score="3" ViewCount="634" Body="&lt;p&gt;A lot of &quot;big antenna&quot; pictures show these very tall masts being used to hold up a variety of other HF antennas.  The mast itself is almost always conductive, though, and I'm wondering why they aren't using it as an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;AM stations use masts as antennas, so certainly this is done in the industry, but why do hams rarely, if ever, use the mast as an antenna? Are there examples of DIY mast-as-antenna designs?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-09-04T21:14:44.117" Title="Why isn't the mast an antenna?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2012" PostTypeId="2" ParentId="2011" CreationDate="2014-07-23T21:11:14.787" Score="5" Body="&lt;p&gt;Plenty of hams do use their towers as antennas:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.eham.net/articles/10631&quot; rel=&quot;nofollow&quot;&gt;Methods to Shunt Feed a Tower&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://boringhamradiopart.blogspot.com/2009/04/shunt-feeding-short-tower-on-80-and.html&quot; rel=&quot;nofollow&quot;&gt;Shunt-Feeding a Short Tower on 80 and 160m&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.qsl.net/w9rb/webdoc9.htm&quot; rel=&quot;nofollow&quot;&gt;A Lowband Antenna that is Almost Free&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The magic words for Google are &quot;shunt fed tower&quot;. Shunt feeds are most common, since most masts are grounded, and you can't series-feed an antenna if it's grounded at the base.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There certainly are towers that are isolated from ground, and are series fed, but securely attaching a tower to ground without connecting it has obvious disadvantages to cost and complexity. Consequently you will probably encounter them only among the most avid 160 and 80 meter users. &lt;a href=&quot;http://www.w8ji.com/transmitting%20antennas.htm&quot; rel=&quot;nofollow&quot;&gt;W8JI&lt;/a&gt; is a good example. For higher frequencies, a quarter-wave vertical can more cheaply just be a tube, since the structural demands are less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for why people put HF antennas on top of their towers that could be perfectly good HF radiators: usually the antennas at the top are directional: Yagis, quads, etc. Feeding the tower gets you an omnidirectional antenna which is great for broadcast, but not for DX hunting.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-07-24T01:02:55.093" LastActivityDate="2014-07-24T01:02:55.093" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2014" PostTypeId="2" ParentId="2010" CreationDate="2014-07-23T21:26:56.360" Score="5" Body="&lt;p&gt;There is nothing especially unusual about this situation: a modulator in most radios will output only some very tiny power which then goes through multiple amplification stages. You just don't have all the stages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Building a little amplifier to take your 50 mW and amplify it enough to drive a typical linear amplifier could be a fun little homebrew project, but if you are looking for a kit, try the &lt;a href=&quot;http://www.tapr.org/kits_pw.html&quot; rel=&quot;noreferrer&quot;&gt;TAPR PennyWhistle&lt;/a&gt;. It's designed for the HPSDR, which just like your SDR has a very low power output. The PennyWhistle design is also greatly simplified by the lack of any output filtering: the assumption is that it will feed another amplifier stage which will be followed by filtering to remove any harmonic distortion introduced by the amplifier. It has 19 dB (about 80x) of gain, so with your 50 mW drive, will output about 4W, which should be enough to drive another amplifier. &lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-07-23T21:26:56.360" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2015" PostTypeId="2" ParentId="2002" CreationDate="2014-07-24T03:57:26.673" Score="0" Body="&lt;p&gt;You did find &lt;a href=&quot;http://www.abledata.com/abledata.cfm?pageid=113583&amp;amp;top=0&amp;amp;productid=92481&amp;amp;trail=0&quot; rel=&quot;nofollow&quot;&gt;this page&lt;/a&gt;, and &lt;a href=&quot;http://resopedia.emv.org.hk/resopedia/rslpdf/87.pdf&quot; rel=&quot;nofollow&quot;&gt;this page&lt;/a&gt; didn't you? It seems an awfully costly solution. Isn't the blind person able to use a normal keyboard?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, there are a few programs that take code, even from tapping one key, which produce ASCII output. At least in Linux, it would not be difficult to redirect the commands to the shell to be executed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: I'd suggest that using a USB mouse and connect to one of the buttons would be an interesting solution. Depending on the dexterity, one could even imagine a sidesweeper with two buttons. As I mentioned before, there are a few open-source programs available on the 'net, which should be adaptable to that. And directing the output to a sound generator or even speech synth, and use the text for commands should not be too difficult.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some promising links:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://morse-rss-news.sourceforge.net/&quot; rel=&quot;nofollow&quot;&gt;http://morse-rss-news.sourceforge.net/&lt;/a&gt; (uses mouse as keyer, source code is available on Sourceforge)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://sourceforge.net/projects/morsecodees/&quot; rel=&quot;nofollow&quot;&gt;http://sourceforge.net/projects/morsecodees/&lt;/a&gt; (seems promising, should investigate more)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This page has lots of morse decoders:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://radio.linux.org.au/?sectpat=morse&quot; rel=&quot;nofollow&quot;&gt;http://radio.linux.org.au/?sectpat=morse&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2014-07-26T00:39:51.907" LastActivityDate="2014-07-26T00:39:51.907" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2016" PostTypeId="1" CreationDate="2014-07-24T20:35:41.033" Score="4" ViewCount="4156" Body="&lt;p&gt;I'm looking for a dual band base station antenna, and find that many of them have short radials around the base.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the specifics of my installation, I need to remove them.  However, it is being mounted in a way that the antenna penetrates the flat metal roof of the structure (a solid, single sheet of metal about 20'x8').  I can mount it so the roof is at the same location as the radials would have been.  I might still attach the radials, in fact, and have copper mesh on the lower side of the roofing metal sheet to contact the radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will this impair performance?  Do the radials need to be left alone, or are they simply the grounding mirror for the antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I get rid of them, or do I need to have the sheet metal contact the antenna at the base where they attach?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radials would be on the bottom, and are grounded to the mounting point, and presumably to the coax shield.  I'm looking at the Diamond X50A at the moment, but there are many with essentially the same design. The &lt;a href=&quot;http://www.diamondantenna.net/pdfdocs/X50A%20Instructions.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;instructions&lt;/a&gt; don't provide any help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/1rHhz.jpg&quot; alt=&quot;enter image description here&quot;&gt; &lt;img src=&quot;https://i.stack.imgur.com/hYdae.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="218" LastEditDate="2014-07-27T11:08:58.940" LastActivityDate="2014-09-08T14:51:27.090" Title="Can I ignore the radial elements of a 2m/70cm antenna if it's on a metal roof?" Tags="&lt;antenna&gt;&lt;grounding&gt;&lt;vertical-antenna&gt;&lt;radial&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="2017" PostTypeId="1" AcceptedAnswerId="2019" CreationDate="2014-07-24T23:16:34.817" Score="2" ViewCount="1296" Body="&lt;p&gt;I'm going to be installing an ATAS-120A screwdriver antenna at the corner of a metal roof building, without radials going out over 270 degrees of the plane it's on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will this significantly change the omnidirectional nature of this antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will it significantly change the transmit and receive performance?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-07-25T10:27:37.880" Title="What are the effects on an ATAS-120A screwdriver antenna with a limited ground plane?" Tags="&lt;antenna&gt;&lt;grounding&gt;&lt;radial&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2018" PostTypeId="2" ParentId="1412" CreationDate="2014-07-24T23:28:51.030" Score="2" Body="&lt;p&gt;Answering my own question: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, the question was ambiguous, as it does not differentiate between (1) the bandwidth required to transmit the information, (2) the bandwidth required for the typical operator to copy the signal in realistic RF conditions, and (3) the bandwidth actually used by the transmitter, which are really 3 different bandwidths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second (bandwidth required for human copy) is actually called out in an old CCIR/ITU recommendation, where the bandwidth specified is to pass the 3rd or 5th harmonic of the baseband dot modulation rate for human copying, or a bandwidth in Hz of about 4 times the character WPM.  (See: &lt;a href=&quot;http://life.itu.int/radioclub/rr/ap01.htm&quot; rel=&quot;nofollow&quot;&gt;http://life.itu.int/radioclub/rr/ap01.htm&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last bandwidth is often falsely calculated.  Every sharp transient of an RF carrier produces local wide-band noise in the frequency domain.  If the transients are exactly periodic, this wide-band signal will actually cancel out except at exact harmonics of the transition rate.  However, real Morse Code (especially Farnsworth timed) is not exactly periodic.  So this analysis is inaccurate.  The actual spectrum generated is thus mostly created from the envelope (roughly the rise/fall time) of the carrier produced by the transmitter, and nearly completely independent of the WPM (except perhaps when sending repeated 555 RST's at extremely high WPM's).  2 to 5 mS rise times seem to be common, taking up around roughly 125 to 350 Hz in bandwidth between the 40 dB rolloff points.  (See: &lt;a href=&quot;http://www.eham.net/articles/16649&quot; rel=&quot;nofollow&quot;&gt;http://www.eham.net/articles/16649&lt;/a&gt;), with the code WPM only varying this bandwidth used by a few percent.  A typical 500 Hz CW audio filter would allow for this plus some drift in carrier and receiver LO frequency as well as manual tuning error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first bandwidth is related to the theoretical bandwidth required using optimally modulated (e.g. likely Gaussian pulse shaped) dots/dashes, where the minimum bandwidth in Hz required to transmit the information content can be as low as 1.2 times the synchronized dot WPM (there is a slight variability given that Morse Code is a variable length encoding).  But without the signal harmonics (3rd or 5th as per CCIT/ITU), a human can't hear the signal redundancy provided by hearing the onset and end of each dot or dash, so few operators might be able to do this in actual practice.  So this narrow bandwidth is only useful with computer(DSP)-mediated Synchronous Morse Code modulation/demodulation.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2014-07-24T23:37:31.347" LastActivityDate="2014-07-24T23:37:31.347" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2019" PostTypeId="2" ParentId="2017" CreationDate="2014-07-25T10:27:37.880" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Will this significantly change the omnidirectional nature of this antenna?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. For 270 degrees of azimuth, you have no ground plane. Or another way of looking at it: you are missing 3/4ths of your radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There will still be some radiation in every direction, but you may find that there is significantly less radiation in the direction where you have no ground plane, and the take-off angle in that direction will be higher as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The picture is additionally complicated by the fact that you do have a sort of &quot;ground plane&quot; even where there is no roof: the Earth. There will be significant capacitance between the vertical element and the Earth, meaning Earth is going to pick up some of the ground plane's job. The Earth is very lossy, so this can't do anything good for antenna efficiency, and Earth is also not at the base of the antenna, so the feedpoint impedance will probably not be what it would otherwise be.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on how you route the feedline, that may appear to the antenna as a radial (there being no better options around), and you may have to do something about the resulting common-mode currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's hard to quantify exactly what the result will be, since it will depend on your particular geometry and Earth conditions. If you have access to some modelling software you could find out, but in any case it's safe to say the result will be less than ideal. It will work, however, as any number of sub-optimally mounted mobile antennas demonstrate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-07-25T10:27:37.880" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2021" PostTypeId="1" AcceptedAnswerId="2022" CreationDate="2014-07-27T16:21:34.683" Score="5" ViewCount="1534" Body="&lt;p&gt;I don't have conditions for installation of a fixed 2 m/70 cm antenna at home, so I'm thinking of using a mobile magnetically mounted antenna on a conductive plate instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is: What are the rules of thumb for getting ground plane dimensions for a mobile antenna beyond &quot;the bigger, the better&quot;? &lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="76" LastEditDate="2015-12-15T23:32:24.443" LastActivityDate="2015-12-15T23:32:24.443" Title="How to calculate or estimate surface area of required ground plane for a mobile antenna?" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;antenna-theory&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2022" PostTypeId="2" ParentId="2021" CreationDate="2014-07-27T23:56:28.560" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What are the rules of thumb for getting ground plane dimensions for a mobile antenna beyond &quot;the bigger, the better&quot;?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There isn't one. An monopole antenna does not reach ideal performance until the ground plane is infinite, and the ground plane can be arbitrarily reduced in size and it will still work in theory (although at some point in practice, the feedline, or the Earth, becomes a better ground plane than the ground plane).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are making a mobile installation, then you don't have a lot of space, and you must necessarily make some compromises. However much space you have, make it that big.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you must have a rule of thumb, a quarter wavelength is good. By this point you have most of the possible performance. If you want to be obsessive, you can go out to 1.5 wavelengths, which is typical of commercial AM broadcast stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quarter-wave radials are also resonant (provided you don't bury them, or otherwise detune them), which assures that the radials have a low impedance. A low impedance is necessary for the ground plane to function as an effective counterpoise. Resonance is by no means necessary, however. Whatever impedance the radials have, it is halved each time the number of radials is doubled, so it ends up low anyway if you have many radials. If you don't have radials but instead a solid plane, this is equivalent to a very high number of radials so impedance will be low unless it is very tiny.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-07-27T23:56:28.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2023" PostTypeId="2" ParentId="1841" CreationDate="2014-07-28T20:41:41.943" Score="3" Body="&lt;p&gt;The official ARISS web site &lt;a href=&quot;http://www.ariss.org/contact-the-iss.html&quot; rel=&quot;nofollow&quot;&gt;documents the current equipment&lt;/a&gt; as follows (scroll down for the headline &lt;strong&gt;Radios, Modes and Antennas on the ISS&lt;/strong&gt;):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The ISS amateur radios are Ericsson MP-X handheld radios, a Kenwood TM&#xA;  D700 and a Kenwood D710.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The crew is currently able to use these radios to operate on the 2 m and 70 cm bands. Voice, packet radio and SSTV are the operational modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also a brand new &quot;Ham Video&quot; DVB-S digital television transmitter for the 2.4 GHz amateur radio band. The transmitter is being taken into use right now (July 2014) according the &lt;a href=&quot;http://www.ariss.org/news.html&quot; rel=&quot;nofollow&quot;&gt;news page of the official site&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2014-07-28T20:41:41.943" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2025" PostTypeId="1" AcceptedAnswerId="2026" CreationDate="2014-07-29T11:09:14.857" Score="2" ViewCount="219" Body="&lt;p&gt;I've recorded what I believe packet radio signal. I tried few decoding tools on windows to no avail. Can anyone please have a look at this &lt;a href=&quot;https://www.youtube.com/watch?v=c8uVEQMPkrA&quot; rel=&quot;nofollow&quot;&gt;youtube video&lt;/a&gt; and tell me how to decode this signal or what it is?&lt;/p&gt;&#xA;" OwnerUserId="1388" LastEditorUserId="76" LastEditDate="2014-08-08T04:10:11.817" LastActivityDate="2014-09-06T21:25:35.950" Title="What is this signal I've recorded?" Tags="&lt;packet&gt;&lt;signal-identification&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2026" PostTypeId="2" ParentId="2025" CreationDate="2014-07-29T17:21:11.293" Score="1" Body="&lt;p&gt;That is &lt;a href=&quot;http://en.wikipedia.org/wiki/POCSAG&quot; rel=&quot;nofollow&quot;&gt;POCSAG&lt;/a&gt; (Post Office Code Standardization Advisory Group). Typically used by numeric and text pagers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia also has a &lt;a href=&quot;http://en.wikipedia.org/wiki/File:Pocsag-simple-stardado.ogg&quot; rel=&quot;nofollow&quot;&gt;sample&lt;/a&gt; of the audio that you can compare against. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some have used &lt;a href=&quot;http://www.raspberrypi.org/forums/viewtopic.php?t=45142&quot; rel=&quot;nofollow&quot;&gt;rtl_fm combined with multimon-ng&lt;/a&gt; to decode POCSAG. A snippet from this site shows: &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rtl_fm -N -o 4 -A lut -s 22050 -C -f 148.397M - | multimon-ng -t raw -a POCSAG512 -a POCSAG1200 -a POCSAG2400 -f alpha /dev/stdin&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="1238" LastActivityDate="2014-07-29T17:21:11.293" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2027" PostTypeId="1" AcceptedAnswerId="2031" CreationDate="2014-07-29T19:13:09.650" Score="3" ViewCount="1999" Body="&lt;p&gt;Has anyone had experience, or knows from first principles, whether installing a G5RV or dipole BELOW a &quot;lightning-rod&quot; in such a manner would serve as a means of discouraging direct lightning strikes onto your dipole:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;A &quot;lightning rod&quot; is some distance above the highest point of the G5RV, and has a ground wire that avoids coming near to the dipole.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Such that the &quot;lightning rod&quot; is connected to a ground wire which goes directly to its own ground-rod which has been attached to its own dedicated ground-spike.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;With some hope that lightning, should it strike above your QTH, would hit the &quot;rod&quot; above the G5RV and most of the current would travel down the ground wire.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The lightning rod is about 5 feet above the dipole, and is supported from below by fiberglass pole.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;There are no other antenna towers or tall metal objects within 100 feet of the above.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The antenna wire and antenna coax  do not come within 4 feet of the ground wire, the air gap is intended to discourage lightning jumping from the lightning rod to the antenna.  The ground wire is installed with a sloping section to avoid coming near to the G5RV or dipole.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Is the above a reasonable thing? Is it worth doing?  Assume that the G5RV or dipole has a lightning arrestor attached to its coax feed line in the usual manner, and that this &quot;lightning rod&quot; is a secondary protective feature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a sample scenario for the sake of criticism/critique:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/sTBE9.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="643" LastEditorUserId="643" LastEditDate="2014-07-30T13:14:07.697" LastActivityDate="2015-01-18T18:51:26.520" Title="Adequate lightning protection for sloped dipole or G5RV?" Tags="&lt;antenna&gt;&lt;equipment-protection&gt;&lt;lightning&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2028" PostTypeId="2" ParentId="809" CreationDate="2014-07-29T19:57:38.580" Score="2" Body="&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/KaELm.jpg&quot; alt=&quot;NW Digital Radio DV3000&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The DV3000 from NW Digital Radio provides the AMBE Vocoder.  One person has modified &lt;a href=&quot;https://github.com/szechyjs/dsd&quot; rel=&quot;nofollow noreferrer&quot;&gt;Digital Speech Decoder (DSD)&lt;/a&gt; to use it instead of reverse engineered library, it is also supported by other solutions such as G4KLX's DummyRepeater.  An AMBEServer, (Raspberry Pi + DV3000) on your LAN would provide Vocoding to a SDR if the proper protocol and modulation components were available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The UDRX-440 is a band limited SDR which will provide GMSK modulation and use the DV3000 internally to provide D-STAR Digital Voice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://nwdigitalradio.com/category/dv3000&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://nwdigitalradio.com/category/dv3000&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1390" LastEditorUserId="1879" LastEditDate="2015-03-08T21:26:22.503" LastActivityDate="2015-03-08T21:26:22.503" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2029" PostTypeId="2" ParentId="2016" CreationDate="2014-07-30T16:28:59.577" Score="1" Body="&lt;p&gt;Those radials look too small to be a ground plane for 2m. They may be a capacity hat to decouple the coax feedline from the antenna. That would be true if the antenna inside the radome is a vertical dipole rather than a ground plane vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would leave those on the antenna and keep them a reasonable distance from the metal roof, as much as a wavelength if you can manage it. Luckily, that is only six feet on 2m.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2014-07-30T16:28:59.577" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2030" PostTypeId="2" ParentId="2027" CreationDate="2014-07-30T20:13:02.620" Score="1" Body="&lt;p&gt;That will not help enough. Lightning spreads out as it gets near to the ground. It also doesn't really conduct along the ground rod, it can jump back and forth to other objects. So you would get a lot of energy into the antenna. It is no problem for lightning to jump five feet. It has already jumped all the way from the clouds!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My neighbor growing up was a ham and worked on lightning arrestors for GE, so this information is really from him. He said the lightning pulse is so fast that the impedance of a straight wire is too much. You could see a pattern of scorch marks where lightning had jumped from a lightning rod grounding strap to the house and back to the strap every few feet.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2014-07-30T20:13:02.620" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2031" PostTypeId="2" ParentId="2027" CreationDate="2014-07-30T21:24:11.087" Score="3" Body="&lt;p&gt;I suspect this scheme will do little or nothing to decrease the chance of damage to your equipment in the case of a lighting strike.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the sake of argument, let's just presume that it does work as you expect: lighting always strikes the rod, which has a dedicated conductor to a dedicated ground rod, and all of that is sufficiently isolated from everything else that no arcing occurs. Your situation is something like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/CjjQa.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fCjjQa.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We've made a bunch of assumptions but you still have a problem. Lighting happens when the charge imbalance between Earth and a cloud becomes so great that the voltage difference is enough to ionize the air and establish a conductive channel. Electric charge then travels over this channel to equalize the charge imbalance. That electric charge doesn't just need to get to the ground: it needs to spread out over the whole Earth. If it didn't, then there would be a spot on the ground where the lighting struck that would have a severe excess or lack of charged particles. It's like dumping a huge bucket into a pool: the water spreads out over the entire pool to minimize the gravitational potential of the water.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, Earth is anything but a great electrical conductor. That's why we need radials for ground plane antennas if we don't want them to be lossy. The impedance of the Earth between your connections to ground is represented by R2, R3, and R4.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, you have many kiloamperes of current flowing through an Earth that is a little bit resistive. Do you see the problem? Do you think most of that electric charge will go through R3, or your radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, one important aspect of effective lighting protection: have exactly &lt;em&gt;one&lt;/em&gt; ground. You can have multiple ground rods, but you should tie them together with a low impedance path, but any equipment you want to protect should have exactly &lt;em&gt;one&lt;/em&gt; connection to this system of grounds. Remember to consider non-obvious paths through your electrical outlet, feedline, Ethernet cable, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, those assumptions we made are probably not good ones. Having a lighting rod up high reduces, but does not eliminate the odds of a strike on things below it, and it's very likely lighting will arc to anything and everything even many feet away from your lighting rod system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest you check out &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt; for other important aspects of effective lightning protection.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-07-31T15:28:05.627" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="2032" PostTypeId="1" CreationDate="2014-07-30T21:24:27.477" Score="6" ViewCount="2662" Body="&lt;p&gt;I remember not long ago seeing a lot of chatter in the ham community about large-scale &quot;Broadband over Powerline&quot; (BPL) systems causing harmful interference across several bands. Does similar interference happen with SOHO &quot;Ethernet over Power&quot; (usually called &quot;HomePlug&quot;) networks?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HomePlug networking is a convenient way to extend home computer networks, when WiFi is impractical or undesired, without having to run cables across the house. However, I would not want to recommend this to anyone if it is a known RFI offender.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If these devices are known to cause RFI, is there anything the end-users can do to reduce or eliminate their impact without having to actually replace them?&lt;/p&gt;&#xA;" OwnerUserId="201" LastActivityDate="2017-03-28T19:00:45.567" Title="Do ethernet-over-power adapters interfere with radios?" Tags="&lt;rfi&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2033" PostTypeId="2" ParentId="2032" CreationDate="2014-07-31T05:04:27.777" Score="3" Body="&lt;p&gt;There has been an ongoing debate about this in the UK, where the system is called PLT for &quot;Power Line Telecommunication&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See articles on &lt;a href=&quot;http://www.theregister.co.uk/&quot; rel=&quot;nofollow&quot;&gt;The Register&lt;/a&gt; (slightly sarcastic tech news site) for more on the subject. Two such examples are &lt;a href=&quot;http://www.theregister.co.uk/2012/08/20/plt_rsgb/&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;http://www.theregister.co.uk/2011/04/13/bbc_plt/&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;. Of course the general feeling the manufacturers are trying to engender is one of the Luddite radio hams being stuck in their ways and trying to stand in the way of progress, and my feeling is that they are succeeding in this goal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has been proven to exceed the level of radio emissions allowed by the relevant EU regulations, but equipment is still being manufactured, sold, installed and used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, it interferes with HF. No, the regulatory bodies don't seem to care.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-07-31T05:04:27.777" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="2034" PostTypeId="1" AcceptedAnswerId="2035" CreationDate="2014-07-31T17:25:41.773" Score="14" ViewCount="1357" Body="&lt;p&gt;I need some recordings of CW / Morse code for use in a project.  Most of what I find is either nonsense (it just exists for the 'sound of CW', but doesn't contain a message) or is generated by a computer.  Where can I find some audio of real CW operators?  I've been scanning the HF bands but have only found beacons, which are obviously computer controlled.&lt;/p&gt;&#xA;" OwnerUserId="850" LastEditorUserId="218" LastEditDate="2014-08-01T02:33:03.473" LastActivityDate="2021-01-11T04:20:49.223" Title="Where can one find recordings of Morse code, generated by humans and not machines?" Tags="&lt;cw&gt;" AnswerCount="6" CommentCount="1" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2035" PostTypeId="2" ParentId="2034" CreationDate="2014-07-31T22:37:20.150" Score="11" Body="&lt;p&gt;Try to find the allocated amateur radio band plans for your country. You will notice that there are reserved sections of the band plan that are for CW only. Usually they are in the first few kHz (i.e. lowest frequency) for the band you're interested in. For instance, in Australia the CW portions for common HF bands are:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;band  ~freq   CW portion&#xA;160m  1.8MHz   1810 -  1840&#xA;80m   3.5MHz   3500 -  3535&#xA;40m     7MHz   7000 -  7030&#xA;20m    14MHz  14000 - 14070&#xA;15m    21MHz  21000 - 21070&#xA;10m    28MHz  28000 - 28200&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;(These could all differ a bit from country to country)&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/vlk0E.jpg&quot; alt=&quot;Australian band plan for 40 metre band&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;(Australian band plan for 40 metre band)&#xA;Source: &lt;a href=&quot;http://www.wia.org.au/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.wia.org.au/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Then, using the websdr page as AndrejaKo suggested you should be able to tune in to some CW and hear live what is being transmitted.&lt;/p&gt;&#xA;&lt;p&gt;On the websdr website in a waterfall display, CW appears as a thin, interrupted line, like the one below..&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/qPFnN.jpg&quot; alt=&quot;waterfall of websdr&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;Alternatively (and similar to websdr), you can now also visit &lt;a href=&quot;http://kiwisdr.com/public/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://kiwisdr.com/public/&lt;/a&gt; There, many stations have been brought online using OpenWebRX and a BeagleBone Black shield called KiwiSDR.&lt;/p&gt;&#xA;&lt;p&gt;I should add that nowadays many people prefer an electronic 'keyer', a microcontroller-based device that corrects slight timing issues otherwise heard when using straight keys. If you're looking for hand-generated (straight key) CW transmissions you may have a hard time finding any these days.&lt;/p&gt;&#xA;&lt;p&gt;Alternatively.. Learn the Code! For most people it's not too hard to learn how to send Morse. A simple 1kHz sine generator (kit) with a home-built key and a CW decoding program is all you need to get started.&lt;/p&gt;&#xA;&lt;p&gt;Now, audibly READING the code... That's a different story.. :-)&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="1135" LastEditDate="2021-01-11T04:20:49.223" LastActivityDate="2021-01-11T04:20:49.223" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="2036" PostTypeId="2" ParentId="2034" CreationDate="2014-08-01T04:44:53.930" Score="1" Body="&lt;p&gt;Have a look here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.vlf.it/parmigiani/saq_eng.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.vlf.it/parmigiani/saq_eng.htm&lt;/a&gt;  (look for 'Example')&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and do a search on youtube for transmissions of the SAQ transmitter, which is an antique VLF transmitter (17.2 kHz!). Several times each year, they crank up the transmitter, and send a test message. Many people are always listening, and frequently publish the reception reports on youtube or dedicated mailing lists.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Appropiately, the transmitter is operated with a manual keyer!&#xA;Here's an example of a longer message:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.youtube.com/watch?v=tMNIpW94IE4&quot; rel=&quot;nofollow&quot;&gt;http://www.youtube.com/watch?v=tMNIpW94IE4&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could probably contact the author for the complete recording too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another edit - just found a PDF with the description of the transmitter - yes! it's electromechanical!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.nsarc.ca/hf/saq.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.nsarc.ca/hf/saq.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2014-08-01T04:55:13.660" LastActivityDate="2014-08-01T04:55:13.660" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2037" PostTypeId="1" CreationDate="2014-08-01T19:35:14.393" Score="6" ViewCount="830" Body="&lt;p&gt;I'm looking at a RF transformer filter design that appears to be using the primary-side transformer inductance as part of a second-order band-pass filter (first schematic). This isn't the only filter in the design, but I believe I have isolated it properly. The center frequency is approximately 14MHz. My understanding is that the transformer is providing the inductance necessary for the filter as well as presenting the load impedance in parallel.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/R8sgh.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fR8sgh.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I'd like to use a generic &quot;pulse&quot; transformer, like those used in Ethernet or ADSL modems, but those have much higher winding inductances that make it practically impossible to design as part of a HF resonant circuit (e.g. 100µH or more). To compensate for that, I would need to add a separate inductor to get the effective parallel inductance to be correct (as shown in the second schematic). This eliminates the economy of the transformer acting as the inductor, but what else do I lose? &lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/PoE10.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fPoE10.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As requested, I went ahead and simulated the circuit using LTSpice, assuming a perfect magnetic coupling. The -6dB is due to the source impedance of the source. &lt;em&gt;As modeled,&lt;/em&gt; the simulation results are identical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/yh1Uh.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="18" LastEditorUserId="18" LastEditDate="2014-08-03T15:11:22.743" LastActivityDate="2014-08-03T15:11:22.743" Title="Resonant RF Transformer Substitution" Tags="&lt;equipment-design&gt;&lt;filter&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2038" PostTypeId="2" ParentId="2037" CreationDate="2014-08-01T20:40:43.260" Score="2" Body="&lt;p&gt;It seems an excellent idea. The only possible problem I could imagine, is maybe the internal capacitance of the 1:1 pulse transformer -I've seen numbers in the order of 30 - 50 pF. This isn't a problem in non-resonant (ethernet) apps, but you might have to adjust your 220 pF to compensate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just found another datasheet with only 15pF inter-winding capacitance.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-08-01T20:40:43.260" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2039" PostTypeId="2" ParentId="1993" CreationDate="2014-08-03T03:28:22.647" Score="0" Body="&lt;p&gt;And the biggest problem of all: losing that little grain-of-sand inductor in the shack carpeting. Tip: check the vacuum cleaner bag.&lt;/p&gt;&#xA;" OwnerUserId="1197" LastActivityDate="2014-08-03T03:28:22.647" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2040" PostTypeId="2" ParentId="2034" CreationDate="2014-08-04T05:33:55.633" Score="4" Body="&lt;p&gt;Wait for a Straight Key Night (&lt;a href=&quot;http://www.arrl.org/straight-key-night&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/straight-key-night&lt;/a&gt;) to record from the CW portion of HF bands.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-08-04T05:33:55.633" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2041" PostTypeId="1" CreationDate="2014-08-05T19:35:59.570" Score="3" ViewCount="11327" Body="&lt;p&gt;I'm a new ham. The past few days, I've had a few nearby passes of the International Space Station. As it was going overhead, I managed to record what I believe to be 1200 baud AFSK transmissions from it (AX.25) - from it's 145.825MHz Packet Radio downlink. I have an audio file of one. I am trying to figure out how to decode it and haven't had any luck. I've tried QTMM from SourceForge (playing the recording into my computer microphone) - but got no decode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an audio file which has three distinct burst of what appear to be data (with very little noise during these bursts). Both nights, these burst only occurred while the station was nearest to me. Thus, I'm positive I have good audio - just can't figure out how to demodulate!&lt;/p&gt;&#xA;" OwnerUserId="1243" LastActivityDate="2016-01-20T19:34:16.330" Title="How can I decode an AFSK 1200 baud audio clip? (ISS)" Tags="&lt;digital-modes&gt;&lt;packet&gt;" AnswerCount="4" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="2042" PostTypeId="2" ParentId="2041" CreationDate="2014-08-05T19:54:20.720" Score="6" Body="&lt;p&gt;Audio which sounds perfectly fine can be noisy or distorted (notably, by FM deemphasis) enough to prevent digital decoding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At a minimum, you should get rid of the microphone step and feed your audio directly into the demodulator program.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't say what OS you're using, but I have had success demodulating APRS messages using &lt;a href=&quot;https://github.com/EliasOenal/multimon-ng&quot; rel=&quot;noreferrer&quot;&gt;multimon-ng&lt;/a&gt;. It can be set to accept raw input (16-bit at 22050 Hz); you can use an audio editor (such as the free &lt;a href=&quot;http://audacity.sourceforge.net/&quot; rel=&quot;noreferrer&quot;&gt;Audacity&lt;/a&gt;) to convert your recording.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Note that multimon-ng will take the AFSK audio signal and give you text-format AX.25 messages, but it will not actually parse the APRS content into human-readable text except as APRS has some readable fields already; you would need another program to handle that. At least you'll be able to see if the messages are recoverable at all.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-08-06T14:23:46.287" LastActivityDate="2014-08-06T14:23:46.287" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2043" PostTypeId="2" ParentId="2034" CreationDate="2014-08-06T01:14:26.313" Score="3" Body="&lt;p&gt;Another source of hand-keyed CW is the SKCC ( &lt;a href=&quot;http://www.skccgroup.com&quot; rel=&quot;nofollow&quot;&gt;http://www.skccgroup.com&lt;/a&gt; ) 40m calling frequency at 7.050 MHz where you can hear code from straight keys most evenings (US). There is even more activity during their monthly sprints starting at 0000 UTC the fourth Wednesday of each month (Tuesday evening the US).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding CW analysis, you might be interested in the thread which roughly starts here &lt;a href=&quot;http://ag1le.blogspot.com/2013/01/towards-bayesian-morse-decoder.html&quot; rel=&quot;nofollow&quot;&gt;http://ag1le.blogspot.com/2013/01/towards-bayesian-morse-decoder.html&lt;/a&gt; . It goes on for over a year but contains excellent insights in several aspects if CW timing, noise reduction and decoding techniques.&lt;/p&gt;&#xA;" OwnerUserId="1157" LastActivityDate="2014-08-06T01:14:26.313" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2044" PostTypeId="1" CreationDate="2014-08-07T02:08:15.390" Score="2" ViewCount="148" Body="&lt;p&gt;I hear of channels at, for instance, 4625kHz and I want to check them out but the only radio I have is the one in my car which only goes up to 1710kHz.  What kind of radio do I need to listen to channels above that?  P.S. I know nothing about HAM radio;  I just wanted advice from hams.  Thank you.&lt;/p&gt;&#xA;" OwnerUserId="1415" LastActivityDate="2014-08-08T02:57:05.703" Title="How can I listen to channels above 1710kHz?" Tags="&lt;receiver&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2045" PostTypeId="1" CreationDate="2014-08-07T03:01:07.167" Score="3" ViewCount="110" Body="&lt;p&gt;I was thinking about all the different modulation methods and something came to my head. After seeing up converters that convert HF to VHF for SDR (software defined radio) dongles to be able to listen, I thought, &quot;why not use up converted audio?&quot;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;With appropriate filters to take out the highs and lows, it would only take up 4000 hertz max according to the telephone standards. That's less than AM!&lt;/li&gt;&#xA;&lt;li&gt;Simple receive, just down convert until its at the AF band.&lt;/li&gt;&#xA;&lt;li&gt;Better chance Aliens will be able to figure it out because it is just up-converted RAW audio. (Kinda joking with that one)&lt;/li&gt;&#xA;&lt;li&gt;And if nothing else, for example: bad spectrum efficiency, hard to pick up with any noise, etc., I certainly want to try it just for fun!&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So would it work out at all, and if so how well?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="218" LastEditDate="2014-08-07T11:48:03.557" LastActivityDate="2014-08-07T11:48:03.557" Title="Up converted audio transmission" Tags="&lt;modes&gt;&lt;ssb&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2046" PostTypeId="2" ParentId="2045" CreationDate="2014-08-07T03:17:37.810" Score="4" Body="&lt;p&gt;Yes, this is a workable modulation. In fact, it's used all the time on HF; what you have described is &lt;em&gt;precisely&lt;/em&gt; &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation&quot; rel=&quot;nofollow&quot;&gt;single-sideband (SSB)&lt;/a&gt; modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The usual choice of filtering is for an occupied bandwidth of 3 kHz rather than 4 kHz, but that's just a parameter; the principle is the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason it's called single sideband is that if you use the simplest possible analog electronics to perform the upconversion (&lt;em&gt;mixing&lt;/em&gt;), the transmission has two redundant sidebands above and below the carrier frequency (&lt;em&gt;double sideband&lt;/em&gt;), rather than just one; the lower sideband also has the audio signal, but mirrored in frequency. This is wasteful of power and bandwidth, so single sideband is preferred, but significantly more complex to implement in analog electronics. (In a SDR, you've in a sense already paid the complexity cost in the generic hardware; the DSP to demodulate SSB is just as simple as that for AM.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-08-07T03:53:55.980" LastActivityDate="2014-08-07T03:53:55.980" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2047" PostTypeId="2" ParentId="2044" CreationDate="2014-08-07T03:41:23.340" Score="5" Body="&lt;p&gt;The type of radio you are looking for is a &lt;em&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Shortwave_radio&quot; rel=&quot;noreferrer&quot;&gt;shortwave&lt;/a&gt; receiver&lt;/em&gt;. The most common types are portable battery-powered radios, looking much like a portable FM radio but with more controls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides the additional frequency range, another feature to look for is support for &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation&quot; rel=&quot;noreferrer&quot;&gt;&lt;em&gt;single sideband&lt;/em&gt; (SSB)&lt;/a&gt; reception, in addition to the familiar AM and FM modes. Nearly all shortwave &lt;em&gt;broadcasting&lt;/em&gt; stations are AM, but if you are interested in other signals such as amateurs' transmissions, you will definitely want SSB capability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that at these low frequencies, large antennas are useful. Reception can often be improved by stringing a simple wire in the air and connecting one end to the antenna jack, if any, or the end of the stock telescoping antenna.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-08-07T03:41:23.340" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2051" PostTypeId="1" CreationDate="2014-08-07T13:02:19.397" Score="8" ViewCount="1863" Body="&lt;p&gt;What is a fixed digital message forwarding system? I noticed this on the lower end of the 222MHz allocation in the US but it's not explained on the band chart:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/cLeqE.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="76" LastEditDate="2014-08-07T17:05:39.427" LastActivityDate="2016-03-16T11:57:55.930" Title="What is a fixed digital message forwarding system?" Tags="&lt;digital-modes&gt;&lt;jargon&gt;&lt;band-plan&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2052" PostTypeId="2" ParentId="2051" CreationDate="2014-08-07T13:55:59.027" Score="6" Body="&lt;p&gt;That's a lot of words for &lt;a href=&quot;http://info.aprs.net/index.php?title=Digipeater&quot; rel=&quot;noreferrer&quot;&gt;digipeater&lt;/a&gt;. These are stations that listen for digital messages, record them in temporary storage, then re-transmit them. This particular allocation is on a secondary basis, with the primary allocation going to &lt;a href=&quot;http://en.wikipedia.org/wiki/Automated_Maritime_Telecommunications_System&quot; rel=&quot;noreferrer&quot;&gt;AMTS&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;message forwarding system&amp;quot; is defined in &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.1.159.2&quot; rel=&quot;noreferrer&quot;&gt;§97.3&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(32) Message forwarding system. A group of amateur stations participating in a voluntary, cooperative, interactive arrangement where communications are sent from the control operator of an originating station to the control operator of one or more destination stations by one or more forwarding stations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;A &amp;quot;fixed station&amp;quot; isn't defined in §97 anywhere that I can find, but &lt;a href=&quot;http://www.merriam-webster.com/dictionary/fixed%20station&quot; rel=&quot;noreferrer&quot;&gt;Merriam-Webster provides a definition&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;a permanently located radio transmitting station used for communicating with similar stations&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&amp;quot;Digital&amp;quot; in practice probably means 1200 baud AFSK &lt;a href=&quot;http://en.wikipedia.org/wiki/AX.25&quot; rel=&quot;noreferrer&quot;&gt;AX.25&lt;/a&gt;. However, there's no clear definition I can find, so if you wanted to stray outside this (for example, what about digital voice?) you probably end up in a grey area. Definitions might include various mentions of &amp;quot;digital&amp;quot; in the emissions designators in &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=2b906b35446294e0217659ff50cc8ea2&amp;amp;node=47:1.0.1.1.3.3.216.1&amp;amp;rgn=div8&quot; rel=&quot;noreferrer&quot;&gt;Title 47 §2.201&lt;/a&gt;. Or, &amp;quot;digital&amp;quot; might mean the definition of &amp;quot;data&amp;quot; again from &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.1.159.2&quot; rel=&quot;noreferrer&quot;&gt;§97.3&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(2) Data. Telemetry, telecommand and computer communications emissions having (i) designators with A, C, D, F, G, H, J or R as the first symbol, 1 as the second symbol, and D as the third symbol; (ii) emission J2D; and (iii) emissions A1C, F1C, F2C, J2C, and J3C having an occupied bandwidth of 500 Hz or less when transmitted on an amateur service frequency below 30 MHz. Only a digital code of a type specifically authorized in this part may be transmitted.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The specific FCC regulations for 219-220 MHz are &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.4.159.2&quot; rel=&quot;noreferrer&quot;&gt;§97.303 (l)&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(l) In the 219-220 MHz segment:&lt;/p&gt;&#xA;&lt;p&gt;(1) Use is restricted to amateur stations participating as forwarding stations in fixed point-to-point digital message forwarding systems, including intercity packet backbone networks. It is not available for other purposes.&lt;/p&gt;&#xA;&lt;p&gt;(2) Amateur stations must not cause harmful interference to, and must accept interference from, stations authorized by:&lt;/p&gt;&#xA;&lt;p&gt;(i) The FCC in the Automated Maritime Telecommunications System (AMTS), the 218-219 MHz Service, and the 220 MHz Service, and television stations broadcasting on channels 11 and 13; and&lt;/p&gt;&#xA;&lt;p&gt;(ii) Other nations in the fixed and maritime mobile services.&lt;/p&gt;&#xA;&lt;p&gt;(3) No amateur station may transmit unless the licensee has given written notification of the station's specific geographic location for such transmissions in order to be incorporated into a database that has been made available to the public. The notification must be given at least 30 days prior to making such transmissions. The notification must be given to: The American Radio Relay League, Inc., 225 Main Street, Newington, CT 06111-1494.&lt;/p&gt;&#xA;&lt;p&gt;(4) No amateur station may transmit from a location that is within 640 km of an AMTS coast station that operates in the 217-218 MHz and 219-220 MHz bands unless the amateur station licensee has given written notification of the station's specific geographic location for such transmissions to the AMTS licensee. The notification must be given at least 30 days prior to making such transmissions. The location of AMTS coast stations using the 217-218/219-220 MHz channels may be obtained as noted in paragraph (l)(3) of this section.&lt;/p&gt;&#xA;&lt;p&gt;(5) No amateur station may transmit from a location that is within 80 km of an AMTS coast station that uses frequencies in the 217-218 MHz and 219-220 MHz bands unless that amateur station licensee holds written approval from that AMTS licensee. The location of AMTS coast stations using the 217-218/219-220 MHz channels may be obtained as noted in paragraph (l)(3) of this section.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-08-07T14:07:14.743" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2054" PostTypeId="2" ParentId="2044" CreationDate="2014-08-08T02:57:05.703" Score="1" Body="&lt;p&gt;This radio : &lt;a href=&quot;http://www.radioshack.com/product/index.jsp?productId=2634485&quot; rel=&quot;nofollow&quot;&gt;http://www.radioshack.com/product/index.jsp?productId=2634485&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Costs $40 or so, and covers the following frequencies:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&quot;FM Band&quot; 87.5-108.1MHz&lt;/li&gt;&#xA;&lt;li&gt;Medium Wave (&quot;AM band&quot;) 520-1710kHz&lt;/li&gt;&#xA;&lt;li&gt;Shortwave 2.3-26.1 MHz (these are the shortwave bands you are interested in)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Hope this helps.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-08-08T02:57:05.703" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2057" PostTypeId="1" AcceptedAnswerId="2058" CreationDate="2014-08-14T01:15:41.977" Score="6" ViewCount="264" Body="&lt;p&gt;Electromagnetic Exposure wise, does Amateur radio (Particularly 1.8 to 440 megahertz) induce a health risk due to RF radiation? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other than the Maximum Permissible Exposure (MPE) limits, which will cause RF burns etc., are there any studies that show long term usage of radio being bad for you?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8717" LastEditDate="2019-04-13T14:37:17.027" LastActivityDate="2019-04-13T14:37:17.027" Title="Does amateur radio induce a health risk?" Tags="&lt;rf-power&gt;&lt;equipment-operation&gt;&lt;safety&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2058" PostTypeId="2" ParentId="2057" CreationDate="2014-08-14T01:34:23.233" Score="6" Body="&lt;p&gt;Sure, there are &lt;a href=&quot;http://www.dirtyelectricity.org/health-issues.shtml&quot; rel=&quot;noreferrer&quot;&gt;plenty&lt;/a&gt;. Unfortunately, they all seem to be &lt;a href=&quot;http://lessemf.com/&quot; rel=&quot;noreferrer&quot;&gt;selling&lt;/a&gt; &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/145023822X&quot; rel=&quot;noreferrer&quot;&gt;something&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Electromagnetic_radiation_and_health#Radio_frequency_fields&quot; rel=&quot;noreferrer&quot;&gt;The&lt;/a&gt; &lt;a href=&quot;https://yourlogicalfallacyis.com/burden-of-proof&quot; rel=&quot;noreferrer&quot;&gt;scientific&lt;/a&gt; &lt;a href=&quot;http://www.cancer.org/cancer/cancercauses/radiationexposureandcancer/radiofrequency-radiation&quot; rel=&quot;noreferrer&quot;&gt;consensus&lt;/a&gt; &lt;a href=&quot;http://hps.org/hpspublications/articles/powerlines.html&quot; rel=&quot;noreferrer&quot;&gt;is&lt;/a&gt; &lt;a href=&quot;http://www.epa.gov/radtown/power-lines.html&quot; rel=&quot;noreferrer&quot;&gt;quite&lt;/a&gt; &lt;a href=&quot;http://www.niehs.nih.gov/health/topics/agents/emf/&quot; rel=&quot;noreferrer&quot;&gt;clear:&lt;/a&gt; &lt;a href=&quot;http://www.who.int/mediacentre/factsheets/fs193/en/&quot; rel=&quot;noreferrer&quot;&gt;no&lt;/a&gt; &lt;a href=&quot;http://en.wikipedia.org/wiki/Mobile_phone_radiation_and_health&quot; rel=&quot;noreferrer&quot;&gt;known&lt;/a&gt; &lt;a href=&quot;http://transition.fcc.gov/oet/rfsafety/rf-faqs.html#Q5&quot; rel=&quot;noreferrer&quot;&gt;risk&lt;/a&gt;, beyond the obvious risk of being cooked which MPE limits are set to avoid.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-08-14T01:54:35.317" LastActivityDate="2014-08-14T01:54:35.317" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="2059" PostTypeId="1" CreationDate="2014-08-14T22:24:49.897" Score="2" ViewCount="90" Body="&lt;p&gt;In &lt;a href=&quot;http://www.wia.org.au/members/contests/rdcontest/&quot; rel=&quot;nofollow&quot;&gt;the rules for the Australian Remembrance Day Contest&lt;/a&gt;, I read:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Use of skimmer like technology with a bandwidth greater than 3 KHz is not allowed.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What is considered for 'skimmer like technology' here? Are we talking about a CW decoding device or perhaps a panadapter (waterfall display of a range of frequencies)?&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="29" LastEditDate="2014-08-15T11:15:43.300" LastActivityDate="2014-08-16T00:06:18.093" Title="What is &quot;skimmer like technology&quot; as named in the rules for the Australian Remembrance Day Contest?" Tags="&lt;contest&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2060" PostTypeId="2" ParentId="2059" CreationDate="2014-08-16T00:06:18.093" Score="3" Body="&lt;p&gt;I take it to mean any automated cw decoder with a receiving bandwidth of larger than 3khz is disallowed. Using one for small frequency ranges is fine, the problem is that users who can see a broad swath of spectrum and have automatic decoding over that whole spectrum have an unfair advantage over those using more traditional techniques, so this is meant to level the playing field a bit.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2014-08-16T00:06:18.093" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2063" PostTypeId="1" AcceptedAnswerId="2064" CreationDate="2014-08-17T15:05:15.337" Score="6" ViewCount="580" Body="&lt;p&gt;I want to learn about software defined radio and how wireless transmission work in general. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I started messing around with SDRSharp and a little antenna I bought. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I figured I would start looking at known frequencies like local radio stations. Some I can get to come in clear by messing with the digital noise reduction but this station (one of the strongest in my area) has a ton of background noise that I can't seem to filter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ideas? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/6OPxy.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1453" LastActivityDate="2014-08-17T16:50:58.783" Title="SDR - FM Radio station interference" Tags="&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2064" PostTypeId="2" ParentId="2063" CreationDate="2014-08-17T16:50:58.783" Score="6" Body="&lt;p&gt;The interfering harmonics are spaced at around 15.5 kHz. Do you have an old (CRT) TV set nearby? That may be the source, since TV line frequency is 15.625 Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, look for other interfering electronics, such as compact fluorescent lights or other switched-mode power supplies (your own PC?).&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2014-08-17T16:50:58.783" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2065" PostTypeId="2" ParentId="2032" CreationDate="2014-08-18T07:34:25.820" Score="2" Body="&lt;p&gt;Short answer: Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Longer answer: Homeplug devices use HF frequencies (0-30 MHz) to transport data. Active networks cause a lot of noise, idle networks will cause a recognizable ticking sound. &quot;Good&quot; homeplug devices have specific notches for air traffic control, shortwave broadcast and amateur frequencies. I have tested this myself with a Devolo interface and visualized the results with Gqrx at &lt;a href=&quot;http://idefix.net/~koos/newsitem.cgi/1384984155&quot; rel=&quot;nofollow&quot;&gt;To my shame as a radio amateur I must admit I still use a PLC (ethernet over powerline) connection in my home network&lt;/a&gt; (the devices are now gone). A clear notch for the 20 meter band, but serious amounts of noise outside that band.&lt;/p&gt;&#xA;" OwnerUserId="1456" LastActivityDate="2014-08-18T07:34:25.820" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2069" PostTypeId="2" ParentId="2057" CreationDate="2014-08-20T14:10:53.503" Score="2" Body="&lt;p&gt;There are some indications that RF has ill effects on humans, at least in certain configurations or environments.  Here are a few references taken from the top search results from Google Scholar.  It looks like there's a lot of debate on this issue, and support for both sides.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://aje.oxfordjournals.org/content/128/5/1175.short&quot; rel=&quot;nofollow&quot;&gt;aje.oxfordjournals.org/content/128/5/1175.short&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://onlinelibrary.wiley.com/doi/10.1002/bem.10162/full&quot; rel=&quot;nofollow&quot;&gt;onlinelibrary.wiley.com/doi/10.1002/bem.10162/full&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://link.springer.com/article/10.1007/BF00051295&quot; rel=&quot;nofollow&quot;&gt;http://link.springer.com/article/10.1007/BF00051295&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://aje.oxfordjournals.org/content/127/1/50.short&quot; rel=&quot;nofollow&quot;&gt;aje.oxfordjournals.org/content/127/1/50.short&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My personal &lt;em&gt;opinion&lt;/em&gt; is that cell phones are safe, though I don't put mine in my hip pocket or otherwise in close proximity to the soft, permeable tissue of my testicles, nor do I sleep with a phone near my head.  I also hold the &lt;em&gt;opinion&lt;/em&gt; that amplifiers and things like that should be a meter or so away from the body, even the legs, where though there are no major organs, blood constituents are produced in the bone.  I also recommend using external antennas for even handhelds, if they're used more than once in awhile.  There was an old article on this topic written by a ham / medical doctor, I think in the ARRL magazine, but I don't remember the name of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that RF decreases at the inverse square of the distance of propagation.  Pushing the source a little away from you makes a big difference in the amount of energy that permeates your tissue.&lt;/p&gt;&#xA;" OwnerUserId="850" LastEditorUserId="850" LastEditDate="2014-08-20T15:09:46.437" LastActivityDate="2014-08-20T15:09:46.437" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2070" PostTypeId="1" CreationDate="2014-08-21T13:10:37.337" Score="2" ViewCount="1639" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wfFZD.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;1&lt;/a&gt;What is the likely &lt;strong&gt;antenna loss&lt;/strong&gt; for this (coil hidden inside rubber ducky)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1 to 1.5 inches coil antenna, when placed vertically over 4 to 6 inches each side square ground plane &lt;/p&gt;&#xA;&#xA;&lt;p&gt;as compare with a proper 0.25 wavelength wrip antenna placed over ground plane 0.5 wavelength square?   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without access to network analyzer, what tools and how one can calculate the impedance? How to calculate matching network to match it to 50 ohm transmitter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/wfFZD.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I refers to these type of coil antenna as in lower right of this photo as originally designed for walkie talkie. 70cm band is about 10% off the walkie talkie freq. Presumably, one can start by cutting a few percent length and start tuning from there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: Here is dimension and photo of actual antenna on hand. The long 'end' (end of 8.5mm segment) is the feeding point to be soldered to PCB. The end of 28.0mm segment is not-connected.  The antenna coil will be 'vertically mounted' on copper pcb acting as ground plane. The ground plane will only be 100mm, smaller than the ideal 0.25 wavelength, due to size restriction. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT2: @K7PEH Feed point is the end of the straight-segment (leftmost in photo). Wire diameter 0.58mm. Coil diameter is 4.23mm. Coil 27 turns. Total wire length 359mm. Appreciate if you may enter data, save screen dump step-by-step in a words file and email me the work flow file so that I can learn. Specifically, how is the antenna specification entered as 'segments' into the program. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/KMAM2.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/TODFG.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="1473" LastEditDate="2014-11-29T01:01:40.713" LastActivityDate="2015-01-28T01:45:34.967" Title="How much loss for 1 to 1.5 inch Coil (rubber ducky) Antenna at 70cm band?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="2071" PostTypeId="1" AcceptedAnswerId="2073" CreationDate="2014-08-21T17:50:05.580" Score="2" ViewCount="1814" Body="&lt;p&gt;Which PC or Linux software would I use for programming a Boefeng UV-5RE Plus?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How would I make a programming cable to connect to USB/Serial conversion board (ebay FTDI board, size of finger)?&lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="1246" LastEditDate="2014-12-12T22:54:44.133" LastActivityDate="2016-08-15T10:41:59.430" Title="Programming software for Boefeng UV-5RE Plus" Tags="&lt;uv-5r&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2072" PostTypeId="2" ParentId="1105" CreationDate="2014-08-21T19:18:59.157" Score="1" Body="&lt;p&gt;Following  on from the  difficult  question&lt;br&gt;&#xA;When is a  door  not  a  door ? ....When its a JAR&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All  Ham data  modes that  pass  via SSB tx audio channel  are grouped under the  heading  of J2D.. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How the  audio is  generated or decoded is of no interest  or than  is shares the  same generic title 'Spread Spectrum'  which , now  covers 'all aspects' of data processing  of this type , the  FCC  classed the  test modes  as  J2D , just  the  same as  Olivia , MFSK , JT65  WSPR, pactor or  any  other  audio  based  system &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nonsense based round  secrecy issues are flawed , as the  same  program's  are  available to all  stations, try decoding Olivia  , without the  correct  software , not possible , it therefore must be a  secret code ,  use any of the  available packages and it decodes  , therefore  its not  a secret  code... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So when is a mode  secret and SS ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ans  Not  when  everyone  has the  same software  and it  passes  via  SSB sound  channel&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simple &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So can we  all  get  back to  qrp  dxing on the  same  qrg  again ?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To quote the  part-97 &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC issued STA to test Spread Spectrum , for Ros and Chip64 &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look up the FCC website you'll see the interesting thing about the STA is the Emission Designator classification that was used - J2D &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modes which that have that designation are by the FCC's own definition NOT &quot;SS emissions&quot;. J2D modes are already permitted on HF. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This sounds like people have been doing what we have done, taken SS to mean an abbreviation for Spread Spectrum when in fact the FCC's definitions are clear that the two are not the same. J2D is not SS (SS emissions would be specified as JXX) J2D is covered under the Section 97.3 Federal definition for Data. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you know the FCC regulates Amateur Radio transmissions by what might be called &quot;Content Type&quot;. The definitions for CW, Voice, Image, Data, SS etc are all in Section 97.3 at &lt;a href=&quot;http://www.gpo.gov/fdsys/pkg/CFR-2011-title47-vol5/xml/CFR-2011-title47-vol5-sec97-3.xml&quot; rel=&quot;nofollow&quot;&gt;http://www.gpo.gov/fdsys/pkg/CFR-2011-title47-vol5/xml/CFR-2011-title47-vol5-sec97-3.xml&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Data definition says: &#xA;(2) Data. Telemetry, telecommand and computer communications emissions having (i) designators with A, C, D, F, G, H, J or R as the first symbol, 1 as the second symbol, and D as the third symbol; (ii) emission J2D; and (iii) emissions A1C, F1C, F2C, J2C, and J3C having an occupied bandwidth of 500 Hz or less when transmitted on an amateur service frequency below 30 MHz. Only a digital code of a type specifically authorized in this part may be transmitted.&lt;/p&gt;&#xA;" OwnerUserId="1476" LastActivityDate="2014-08-21T19:18:59.157" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2073" PostTypeId="2" ParentId="2071" CreationDate="2014-08-21T23:45:14.130" Score="5" Body="&lt;p&gt;I use chirp (&lt;a href=&quot;http://chirp.danplanet.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://chirp.danplanet.com&lt;/a&gt;) to program it's memories. A simple USB-UART chip like this &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/bi7Xu.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;..is all that I use to connect to the pc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With regards to pinouts, use:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/FcS3U.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above schematic shows connectivity for the UV-5R and the UV-3R. You can safely leave out the UV-3R stuff..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Courtesy of: &lt;a href=&quot;http://www.uv3r.com/uv5r.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.uv3r.com/uv5r.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2014-08-21T23:45:14.130" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2074" PostTypeId="1" CreationDate="2014-08-22T06:09:48.537" Score="6" ViewCount="5518" Body="&lt;p&gt;I saw on YouTube that some software, with another brand transceiver, can command the transceiver to scan a range of frequencies and display a running waterfall display of scanned results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can such a setup work with a Baofeng UV-5RE Plus transceiver?&lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="76" LastEditDate="2014-10-21T00:06:47.453" LastActivityDate="2017-08-22T00:12:35.027" Title="Is there any PC remote control software for the Baofeng UV-5RE Plus?" Tags="&lt;transceiver&gt;&lt;software&gt;&lt;uv-5r&gt;&lt;baofeng&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2075" PostTypeId="1" CreationDate="2014-08-22T06:20:00.870" Score="3" ViewCount="15142" Body="&lt;p&gt;I bought a Baofeng UV-5RE Plus, which presumably is an improved version of the basic UV-5.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is lots of information online on the UV-5. Any idea where I can find out what are the differences and new functions for this plus model?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where can I get a good manual?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I check the firmware version that is installed? For example, by pressing some key during power-up?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any other 'special function' that is activated by, for example, pressing some key during power-up?&lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="1579" LastEditDate="2014-10-23T22:38:15.473" LastActivityDate="2020-03-11T13:25:16.653" Title="Difference between Boefeng UV-5RE Plus and UV-5" Tags="&lt;transceiver&gt;&lt;uv-5r&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2076" PostTypeId="1" CreationDate="2014-08-22T08:53:58.783" Score="5" ViewCount="512" Body="&lt;p&gt;Since the factory manual is simple and basic, is it possible to use the Baofeng UV-5RE to do these things?&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Listen to FM radio, while scanning 2m and 70cm bands in the background (as in hiking)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Set the scan low and high limit, via keypad and/or PC software, so that scanning only takes place within ham bands (instead full transceiver freq range).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Scan 2m and 70cm 'simultaneously'. Does the radio have multiple (FM/UHF/VHF) receivers inside, or can it jump quickly between frequencies and appear to be 'simultaneously' receiving multiple bands?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What can the PC software do that cannot be done with keypad programming? According to some online posts, &quot;NAME&quot; and &quot;AMI&quot; functions are available. Are there others?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="76" LastEditDate="2016-10-29T19:17:59.343" LastActivityDate="2016-10-29T19:17:59.343" Title="Boefeng UV-5RE scanning capability" Tags="&lt;transceiver&gt;&lt;baofeng&gt;&lt;uv-5r&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2077" PostTypeId="1" CreationDate="2014-08-23T06:49:02.710" Score="1" ViewCount="99" Body="&lt;p&gt;Where can I find HAM forum, newsgroup, discussion, chat room, etc., either formal or light hearted, apart from this one? &lt;/p&gt;&#xA;" OwnerUserId="1473" LastActivityDate="2014-08-23T19:33:31.843" Title="Where can I find HAM forum, newsgroup, etc?" Tags="&lt;diy&gt;" AnswerCount="2" CommentCount="1" ClosedDate="2014-08-27T13:56:20.670" ContentLicense="CC BY-SA 3.0" />
  <row Id="2078" PostTypeId="2" ParentId="2077" CreationDate="2014-08-23T19:26:04.173" Score="2" Body="&lt;p&gt;QRZ.com has forums, news postings, classifieds and similar to what you are looking for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;radioreference.com has forums, news, and similar with lots of Amateur discussion, but is not strictly Amateur specific. You can learn a lot from this site.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many more to be found on the Google and you are likely to find some that are more appealing to you than others.&lt;/p&gt;&#xA;" OwnerUserId="1485" LastActivityDate="2014-08-23T19:26:04.173" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2079" PostTypeId="2" ParentId="2077" CreationDate="2014-08-23T19:33:31.843" Score="2" Body="&lt;p&gt;International newsgroups: rec.radio.amateur.* and there are regional newsgroups related to amateur radio.&#xA;Google+ also has some amateur radio related 'communities'.&lt;/p&gt;&#xA;" OwnerUserId="1456" LastActivityDate="2014-08-23T19:33:31.843" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2080" PostTypeId="1" CreationDate="2014-08-24T10:54:11.047" Score="7" ViewCount="4459" Body="&lt;p&gt;I'm hoping to take the exam in the fall. My question is, does it matter whether I do so in the US or Canada?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to operate the radio at my school in Canada, but I do get the chance to come the US, so I can potentially take the exam there. I'm just wondering if there's any chance the exam is easier in the US or if the license granted in the US is potentially more powerful?&lt;/p&gt;&#xA;" OwnerDisplayName="user1488" LastActivityDate="2021-04-24T14:31:01.147" Title="Amateur Radio License: USA or Canada, does it matter?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;canada&gt;" AnswerCount="7" CommentCount="1" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2081" PostTypeId="1" CreationDate="2014-08-24T16:36:36.067" Score="5" ViewCount="461" Body="&lt;p&gt;I regularly practice Morse with a friend on 2m NFM by holding our tone generators, which we also use for personal practice, close to the microphone. We send text by CW, read it back, and discuss how we are doing and how can improve our &quot;fists&quot;. However we have to turn the volume up on the tone generator so loud it is annoying to others in the house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We would like to build  a circuit that allows us to inject the tone directly into the microphone lead, and use earphones to listen to both CW and voice. I have seen circuits for this but they all include a tone generator, we would like to keep that separate. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please has anyone advice on how to go about this, the design parameters to work to, and what pitfalls there might be?&lt;/p&gt;&#xA;" OwnerUserId="297" LastActivityDate="2014-08-25T03:57:32.640" Title="Circuit to send MCW on 2m FM" Tags="&lt;cw&gt;&lt;vhf&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2082" PostTypeId="2" ParentId="2080" CreationDate="2014-08-24T18:11:58.507" Score="5" Body="&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/foreign-licenses-operating-in-u-s&quot; rel=&quot;noreferrer&quot;&gt;The ARRL's information&lt;/a&gt; may help you:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Foreign amateurs who wish to operate in the US and are not US licensees or citizens may do so in one of three ways:&#xA;&lt;ul&gt;&lt;li&gt;If the country of which you are a citizen and an amateur licensee has entered into a &lt;a href=&quot;http://www.arrl.org/reciprocal-permit-faqs&quot; rel=&quot;noreferrer&quot;&gt;&lt;i&gt;multilateral operating agreement&lt;/i&gt;&lt;/a&gt; with the US, CEPT or IARP&lt;b&gt;, &lt;/b&gt;no additional permit is required -- simply bring your CEPT or IARP documentation when you visit the US. Identify your station by the US call district identifier, such as W3/G1ABC. Use &quot;W&quot; and the number of the FCC call letter district in which you are operating followed by a slash and your home call sign (plus any other CEPT or IARP requirements). Amateurs must be a citizen of the country in which they are licensed. Check these links for a list of the US call districts shown &lt;a href=&quot;http://www.arrl.org/files/file/call_district_map.JPG&quot; rel=&quot;noreferrer&quot;&gt;graphically&lt;/a&gt; or for a text listing. And make sure to check the current information with the &lt;a href=&quot;http://wireless.fcc.gov/services/amateur/about/recoperating.html&quot; rel=&quot;noreferrer&quot;&gt;FCC&lt;/a&gt;. This is intended for short visits.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;ul&gt;&lt;li&gt;&lt;i&gt;Or&lt;/i&gt;, if your country of citizenship and amateur license share a bilateral &lt;a href=&quot;http://www.arrl.org/reciprocal-permit&quot; rel=&quot;noreferrer&quot;&gt;&lt;i&gt;Reciprocal Operating Agreement&lt;/i&gt;&lt;/a&gt; &lt;i&gt;with the US&lt;/i&gt;, the FCC allows foreign amateurs to operate with no permit. Simply carry your foreign amateur license and proof of your citizenship in that country. Identify using &quot;W&quot; and the number of the FCC call letter district in which you are operating followed by a slash and your non-US call sign, e.g. W3/G1ABC). Amateurs must be a citizen of the country in which they are licensed. Check these links for a list of the US call districts shown &lt;a href=&quot;http://www.arrl.org/files/file/call_district_map.JPG&quot; rel=&quot;noreferrer&quot;&gt;graphically&lt;/a&gt; or for a text listing.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;ul&gt;&lt;li&gt;If your country of citizenship and amateur license is &lt;i&gt;not &lt;/i&gt;named in &lt;a href=&quot;http://www.arrl.org/reciprocal-permit&quot; rel=&quot;noreferrer&quot;&gt;lists of countries&lt;/a&gt; that have such agreements with the US, then no operating agreement is in effect between the US and that country--and &lt;i&gt;operation is not possible in the US based on your home license&lt;/i&gt;. Should you wish to seek such an agreement between your home country and the US for the future, you may want to contact your national Amateur Radio society to request that they contact the responsible government official to request such an agreement with the US. US citizenship is &lt;i&gt;not &lt;/i&gt;required to obtain a &lt;a href=&quot;http://www.hello-radio.org/&quot; rel=&quot;noreferrer&quot;&gt;US license&lt;/a&gt;&lt;b&gt;, &lt;/b&gt;but a US mailing address is. Once a person is prepared to take the US license examinations, licensing is possible in as little as a few days to a week. &lt;i&gt;If a US license is held, no other reciprocal operating authority may be used for operation in the US&lt;/i&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="1491" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-08-24T18:46:57.207" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2083" PostTypeId="2" ParentId="2081" CreationDate="2014-08-24T19:07:44.983" Score="4" Body="&lt;p&gt;Broadly speaking, this is the same kind of problem as connecting it to a computer's sound output for digital-mode operation. The exact circuit you will need &lt;strong&gt;depends on the specific characteristics of the microphone input of your model of transmitter&lt;/strong&gt;, but it will likely need these characteristics:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Attenuation&lt;/strong&gt;: your tone generator's output is meant to supply power to a speaker or headphones, whereas a microphone input expects a very small signal collected from sound waves (unless the type of microphone used has a built-in amplifier). This is exactly the same as in RF: connecting a transmitter's output to a receiver's input is likely to destroy the receiver unless you attenuate.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Impedance matching&lt;/strong&gt;: likely not a serious issue in itself since you are not trying to transfer power efficiently, but the impedance of the connected devices will affect the design of the attenuator.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Isolation&lt;/strong&gt;: If your tone generator is battery-powered, this is not necessary. If it is powered by an AC adaptor or USB or some such, you will want to make sure you're not creating a ground loop with your transmitter; this usually takes the form of capacitors in series with the input and/or output lines. This may also be needed if the transmitter supplies DC bias power to the microphone (I don't know if this is common for amateur radio microphones, but some kinds of audio systems do this).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you want advice on a specific circuit to build, you'll need to provide more information in your question:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Specifications of transmitter microphone input (microphone type, impedance); may be found in the manual.&lt;/li&gt;&#xA;&lt;li&gt;Signal level of tone generator output.&lt;/li&gt;&#xA;&lt;li&gt;Impedance of tone generator output.&lt;/li&gt;&#xA;&lt;li&gt;Power source of tone generator.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-08-24T19:07:44.983" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2084" PostTypeId="2" ParentId="2080" CreationDate="2014-08-25T02:12:43.560" Score="2" Body="&lt;p&gt;In order to get a licence in the US, I believe it is now a requirement (since 2000 or so) to have a US Social Security Number. I used to have a US Extra Class licence that I got in 1995, that I could not renew when it expired in 2005 for that reason (I am a UK citizen and do not have a US SSN).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reading the answer provided by GrantB, you can see that in order to use a reciprocal licence in the US, you need to have a licence in your country of citizenship unless you are operating under a CEPT or an IARP licence - this might also be the rule in other countries where you may wish to operate in the future, so it may be advantageous to have a licence in your country of citizenship anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The short answer is: assuming that you are a Canadian citizen, you should probably get a Canadian licence anyway. If you qualify to apply for a US licence (i.e. if you have a US SSN) then you might want to apply for a US licence also for convenience, especially if you spend a lot of time in the US.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-08-25T02:12:43.560" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2085" PostTypeId="2" ParentId="2081" CreationDate="2014-08-25T03:57:32.640" Score="1" Body="&lt;p&gt;Google for a device called a VOX (voice operated switch) and you may end up with a design that:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;a) automatically keys up the transmitter using the PTT line (check your radio's schematic)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;b) keeps the radio in transmit mode inbetween dots and dashes&lt;/p&gt;&#xA;&#xA;&lt;p&gt;c) automatically un-keys the transmitter after the last tone has been sent&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your tone generator has relatively high output you may wish to look for a line-out (close to 1V peak-to-peak) operated vox rather than a vox for an electret microphone.&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2014-08-25T03:57:32.640" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2086" PostTypeId="2" ParentId="1105" CreationDate="2014-08-26T10:40:22.783" Score="0" Body="&lt;p&gt;If it fits into SSB bandwidth it is not spread spectrum, and it does fit.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2014-08-26T10:40:22.783" CommentCount="0" CommunityOwnedDate="2014-08-26T10:40:22.783" ContentLicense="CC BY-SA 3.0" />
  <row Id="2087" PostTypeId="2" ParentId="2001" CreationDate="2014-08-26T10:47:59.257" Score="1" Body="&lt;p&gt;Try WSPRNet. It shows real time data of number of WSPR beacons on all ham bands.&#xA;&lt;a href=&quot;http://wsprnet.org/drupal/wsprnet/map&quot; rel=&quot;nofollow&quot;&gt;http://wsprnet.org/drupal/wsprnet/map&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also use WSPR to listen and see what can be heard or even make beacon to see who can hear you.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2014-08-26T10:47:59.257" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2090" PostTypeId="2" ParentId="2074" CreationDate="2014-08-29T07:48:23.080" Score="-2" Body="&lt;p&gt;No, these radios are dirt cheap and quite frankly are made quite poorly.&#xA;You'll never see pc control on such a cheap radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only way it's ever been done on one of these 'ricebox' radios is to remove the cpu and build your own interface.&lt;/p&gt;&#xA;" OwnerUserId="1508" LastActivityDate="2014-08-29T07:48:23.080" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2091" PostTypeId="2" ParentId="2041" CreationDate="2014-08-29T07:51:45.063" Score="0" Body="&lt;p&gt;If you are on windows... go with QTMM &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://sourceforge.net/projects/qtmm/&quot; rel=&quot;nofollow&quot;&gt;http://sourceforge.net/projects/qtmm/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Play it in Audacity and make the output the input of qtmm&lt;/p&gt;&#xA;" OwnerUserId="1508" LastActivityDate="2014-08-29T07:51:45.063" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2092" PostTypeId="2" ParentId="2025" CreationDate="2014-08-29T07:55:45.417" Score="1" Body="&lt;p&gt;PDW in windows will do just fine... no need to grab a linux box (unless you have one setup).&#xA;Certainly much easier than some rtl_fm/multimon setup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.discriminator.nl/pdw/index-en.html&quot; rel=&quot;nofollow&quot;&gt;http://www.discriminator.nl/pdw/index-en.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1508" LastEditorUserId="29" LastEditDate="2014-09-06T21:25:35.950" LastActivityDate="2014-09-06T21:25:35.950" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2093" PostTypeId="1" AcceptedAnswerId="2168" CreationDate="2014-08-29T16:34:02.900" Score="4" ViewCount="2785" Body="&lt;p&gt;I own this simple CB Radio: &lt;a href=&quot;http://www.cbforumas.lt/upload/manuals/alan/alan_42_um.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.cbforumas.lt/upload/manuals/alan/alan_42_um.pdf&lt;/a&gt;&#xA;I would like to connect its 2.5mm microphone jack and my computer's 3.5mm audio out jack. I have tried simple adapters and cables, but they fail, because the 2.5mm jack requires a push to talk microphone. I'm not unfamiliar with soldering, but which contact layout do I have to use for the 2.5mm jack and what do I have to connect to what do make this work?&lt;/p&gt;&#xA;" OwnerUserId="1223" LastEditorUserId="76" LastEditDate="2016-10-29T18:44:12.440" LastActivityDate="2016-10-29T18:44:12.440" Title="How to hook up my computer's audio output to my CB Radio?" Tags="&lt;connectors&gt;&lt;citizens-band&gt;&lt;audio-interface&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2094" PostTypeId="2" ParentId="2093" CreationDate="2014-08-29T17:16:25.597" Score="1" Body="&lt;p&gt;If you want to record into the computer, you need to connect the Transceiver 3.5 jack to the 2.5 mm jack on the computer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to send computer audio to the microphone input, you need to do the inverse, but take into account that very possibly, the microphone input of the transceiver is combined with the PTT switch. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you should connect a capacitor in series with the microphone line, in the order of 100nF to maybe 1 uF or so. The positive side of the capacitor, in case you use an electrolytic cap, should probably point to the transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, very probably, you'll have to attenuate the audio from the computer in order not to saturate the input. &lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2014-08-29T17:27:09.517" LastActivityDate="2014-08-29T17:27:09.517" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2095" PostTypeId="1" CreationDate="2014-08-29T23:46:42.423" Score="4" ViewCount="1304" Body="&lt;p&gt;On many of the DX sites, one will find many variables for solar weather to include flux, A, K, sunspots, etc… I’d like to know how to read those and know what to look for. As I understand it, the sun’s activities affect the ionosphere which affects HF propagation in so many ways. I also hear of interplanetary magnetic fields, solar winds, terrestrial conditions, etc… more than I know what to do with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I’d like to be able to do is factor for myself what the band conditions are like, or will be like at a future time and know what conditions to take into account, aside from the general practice of knowing what bands are good at what times of the day or night. There’s also the fact that it takes me some effort to get my antenna’s out. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realize this can be pretty broad and too much to put in a single post, and I’m also sure it will likely take considerable practice and time to learn, so I’m hoping for a summary about the process overall (i.e., how to make the decision that at X time, conditions will be great to GOTA), and I’ll break it down and study each topic individually from there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any help much appreciated.&lt;/p&gt;&#xA;" OwnerUserId="1433" LastActivityDate="2020-01-12T02:16:50.543" Title="How does one know when band conditions are optimal and what factors to consider?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;space-weather&gt;&lt;weather&gt;&lt;ionosphere&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2097" PostTypeId="2" ParentId="2095" CreationDate="2014-08-30T18:52:55.393" Score="1" Body="&lt;p&gt;If you want to get a more automated prediction, look for propagation prediction software (many available on the 'net) and plug in the data. Of course, it's still useful to know the basics, such as how the ionosphere works (see ARRL handbook), to understand what the programs do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And very important: Even if you take into account all of the data you have available, you cannot rely on the numbers alone. Several factors are near to random, such as short-lived magnetic solar storms, or comet-trails. Others are global, and might not be directly applicable for your location. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even all the wisdom from classic books such as Kenneth Davies' Ionospheric Radio (300+ pages!) cannot predict instantaneous behaviour - only what's 'expected'. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you decide what you want to do and want the tech background, consult the chapter on propagation in the ARRL Handbook; for the juicy details, see the above book. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd say you are approaching the problem the wrong way. You should probably decide first &lt;em&gt;what&lt;/em&gt; you want to do, say eg. making contacts on the 10m band, and then find out which elements influence that goal. &lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="8717" LastEditDate="2020-01-11T18:13:12.493" LastActivityDate="2020-01-11T18:13:12.493" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="2098" PostTypeId="2" ParentId="22" CreationDate="2014-08-31T02:23:27.287" Score="2" Body="&lt;p&gt;In addition, there is an exception for radio antennas that are microwave dishes 1 meter or less.  47 CFR § 1.4000.&lt;/p&gt;&#xA;" OwnerUserId="1514" LastActivityDate="2014-08-31T02:23:27.287" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2102" PostTypeId="2" ParentId="464" CreationDate="2014-09-02T05:34:57.443" Score="1" Body="&lt;p&gt;VHF FM Radios are commonly used for packet radio via digipeaters and nodes on frequencies around 145.01 MHz.  DSTAR and Yaesu's new System Fusion radios are also digital modulation transmitted over FM radios.  In some localities, other soundcard modes are used on VHF/UHF FM radios, such as the SSTV net on 145.51 MHz FM in Sacramento CA &lt;a href=&quot;http://www.n6na.org/nets/sstv-net&quot; rel=&quot;nofollow&quot;&gt;http://www.n6na.org/nets/sstv-net&lt;/a&gt;  Such nets allow owners of common FM transceivers to get experience with these modes.  I use the rear data connector on my Yaesu FT-8800R for soundcard modes with a SignaLink USB and also with my packet TNC.&lt;/p&gt;&#xA;" OwnerUserId="1520" LastActivityDate="2014-09-02T05:34:57.443" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2103" PostTypeId="1" CreationDate="2014-09-03T03:07:05.130" Score="3" ViewCount="2063" Body="&lt;p&gt;Could an attacker use a simple USB SDR dongle, as long as it is capable of transmitting within a certain range, to jam frequencies?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I saw Lady Ada build the WaveBubble which is basically a dual-band, tunable RF jammer. The difficulty of construction was very high though. I'm aware this is against FCC regulations. It's a hypothetical question.&lt;/p&gt;&#xA;" OwnerUserId="1522" LastActivityDate="2014-09-05T18:33:08.130" Title="Jamming with USB SDR" Tags="&lt;software-defined-radio&gt;&lt;noise&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2104" PostTypeId="2" ParentId="2095" CreationDate="2014-09-03T13:13:12.237" Score="1" Body="&lt;p&gt;Here is a useful site for both long-term (monthly) and near-term propagation conditions.&#xA;&lt;a href=&quot;http://propagation.hfradio.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://propagation.hfradio.org/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For VHF and UHF skip conditions (just in case you are interested) try here:&#xA;&lt;a href=&quot;http://www.dxinfocentre.com/tropo.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.dxinfocentre.com/tropo.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1523" LastEditorUserId="8631" LastEditDate="2020-01-12T02:16:50.543" LastActivityDate="2020-01-12T02:16:50.543" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="2105" PostTypeId="2" ParentId="2095" CreationDate="2014-09-03T23:46:51.900" Score="2" Body="&lt;p&gt;Quick and easy propagation forecast tools are at VOACAP Online &lt;a href=&quot;http://www.voacap.com/prediction.html&quot; rel=&quot;nofollow&quot;&gt;http://www.voacap.com/prediction.html&lt;/a&gt;&#xA;and &lt;a href=&quot;http://www.voacap.com/coverage.html&quot; rel=&quot;nofollow&quot;&gt;http://www.voacap.com/coverage.html&lt;/a&gt; for area coverage.&#xA;Required are the transmitter and receiver positions, transmitter power, mode, antenna types, date and sunspot number.  It does not consider the effects of geomagnetic ionospheric disturbances.&#xA;The website has reference material on the the art and science of ionospheric propagation prediction.&lt;/p&gt;&#xA;" OwnerUserId="1520" LastActivityDate="2014-09-03T23:46:51.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2106" PostTypeId="2" ParentId="22" CreationDate="2014-09-04T10:24:03.860" Score="4" Body="&lt;p&gt;You are referring to the OTARD rule -- Over The Air Reception Devices. OTARD does pre-empt lease restrictions and does not apply only to those owning the property.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It does not apply to antennas used for AM/FM radio, Amateur Radio, Citizens Band radio or Digital Audio Radio Services. &lt;a href=&quot;http://www.fcc.gov/guides/over-air-reception-devices-rule&quot; rel=&quot;nofollow&quot;&gt;The FCC has an extensive FAQ on OTARD&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="1528" LastActivityDate="2014-09-04T10:24:03.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2107" PostTypeId="1" AcceptedAnswerId="2111" CreationDate="2014-09-04T15:54:42.393" Score="0" ViewCount="100" Body="&lt;p&gt;Assume I have rotators that are able to move an antenna in different dimensions.  For example, on the x, y, and z axis.  I want to automatically move the antenna to its optimal physical orientation, using a home-made system.  The system knows the frequency we want to turn to, so it shouldn't get confused by stronger signals on other frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to know if sequentially tuning each axis in this way will result in the most efficient orientation of the antenna.  For example, tune the 'x' axis until the signal strength is the highest on that axis, then tune subsequent axis the same way.  Each axis is only tuned once.&lt;/p&gt;&#xA;" OwnerUserId="850" LastEditorUserId="850" LastEditDate="2014-09-04T22:40:32.513" LastActivityDate="2014-09-05T00:14:39.407" Title="If the desired frequency is known, can an antenna tuner tune its 'x' different dimensions sequentially for maximum gain?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2108" PostTypeId="1" AcceptedAnswerId="2114" CreationDate="2014-09-04T20:39:42.763" Score="2" ViewCount="342" Body="&lt;p&gt;I bought a Chinese-made handheld radio with detachable antenna. I programmed it for FRS/GMRS frequencies, but its output is about 3W. Is it illegal? If it is, why and how would anyone find out?&lt;/p&gt;&#xA;" OwnerUserId="1533" LastEditorUserId="76" LastEditDate="2014-09-05T19:23:25.343" LastActivityDate="2014-09-05T19:23:25.343" Title="Transmitting on FRS using a chinese handheld radio" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;frs&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2014-09-06T21:11:41.340" ContentLicense="CC BY-SA 3.0" />
  <row Id="2109" PostTypeId="2" ParentId="2011" CreationDate="2014-09-04T21:14:44.117" Score="2" Body="&lt;p&gt;The tower is the antenna for the Hy Gain AV-18HT Hytower &lt;a href=&quot;http://www.hy-gain.com/Product.php?productid=AV-18HT&quot; rel=&quot;nofollow&quot;&gt;http://www.hy-gain.com/Product.php?productid=AV-18HT&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1520" LastActivityDate="2014-09-04T21:14:44.117" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2110" PostTypeId="2" ParentId="1722" CreationDate="2014-09-04T22:23:21.003" Score="6" Body="&lt;p&gt;Some characteristics that make code harder to copy:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The dahs are are too short compared to the dits.&lt;/li&gt;&#xA;&lt;li&gt;Not enough space between words.&lt;/li&gt;&#xA;&lt;li&gt;Not enough space between characters.&lt;/li&gt;&#xA;&lt;li&gt;An out-of-place pause when sending a word (as when thinking of how to spell a word).&lt;/li&gt;&#xA;&lt;li&gt;Incorrect number of dits (for example, sending b or n instead of d)&lt;/li&gt;&#xA;&lt;li&gt;Sending a correction with insufficient pauses between the error, the error indicator (eight dots, a question mark, whatever) and the correction.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It's been my experience that most hard-to-copy code has timing errors, and the most damaging of those errors are of spacing.&lt;/p&gt;&#xA;" OwnerUserId="628" LastEditorUserId="628" LastEditDate="2014-09-04T22:37:00.080" LastActivityDate="2014-09-04T22:37:00.080" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2111" PostTypeId="2" ParentId="2107" CreationDate="2014-09-05T00:14:39.407" Score="2" Body="&lt;p&gt;Simple answer: Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More complex answer: No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio propagation is complex. In particular, a desired signal may be received by multiple paths. That means there are multiple directions in which the antenna may point and get improved reception. Some paths are better than others, so there's probably just one direction which is best, but without trying &lt;em&gt;all&lt;/em&gt; the directions, you can't know for sure if you've found the absolute best direction, or just a local peak of a sub-optimal path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fortunately, it's usually pretty easy to try all the directions, and in very many situations there may not be significant paths in significantly different directions from the best one. Thus the simple answer, &quot;yes&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also the additional problem that in some situations (HF, especially) the path is constantly changing. What the best path is now is different from what it will be in 30 seconds, so the best we can manage with a mechanically rotated antenna is to orient it in the direction that's pretty good most of the time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further complicating the issue is that orienting the antenna for maximum received signal power is not necessarily optimal for communication. What we are actually trying to optimize is the signal-to-noise ratio, so we also want to minimize received noise. That is, in some situations it may be more advantageous to aim a null at the noise, rather than aim a peak at the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Very complicated answer: Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Interestingly, for electronically phased antennas (that is, an array of antennas where each element is fed an independent signal), there exists an algorithm which can find the best (electronically selected) orientation of the antenna array if we know what the signal should be. Frequently this is achieved by periodically transmitting a synchronization signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This method is called &lt;a href=&quot;http://www.antenna-theory.com/arrays/weights/mmse.php&quot; rel=&quot;nofollow&quot;&gt;minimum mean square error weighting&lt;/a&gt;. If we know what the signal should be, then we can look at what was actually received by each antenna and calculate weights for each antenna that most closely approximate the expected signal. This is very much like &lt;a href=&quot;http://en.wikipedia.org/wiki/Regression_analysis&quot; rel=&quot;nofollow&quot;&gt;regression analysis&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-09-05T00:14:39.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2113" PostTypeId="1" AcceptedAnswerId="2227" CreationDate="2014-09-05T11:59:58.417" Score="5" ViewCount="8364" Body="&lt;p&gt;I have an R820T DVB dongle and the rtl_sdr software on a linux computer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can listen to various frequencies using the gqrx software which uses the rtl_sdr library as a device driver for the USB-attached dongle. I also (obviously) get the spectrum scope and waterfall display of adjacent channels.  Thus, the hardware and software is functional at some level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I notice there is a separate program in the rtl_sdr bundle also called &quot;rtl_sdr&quot; that can record a slice of spectrum onto the hard drive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is an excerpt from the usage reminder generated by running rtl_sdr with no parameters:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rtl_sdr, an I/Q recorder for RTL2832 based DVB-T receivers&#xA;&#xA;Usage:   -f frequency_to_tune_to [Hz]&#xA;    [-s samplerate (default: 2048000 Hz)]&#xA;    [-d device_index (default: 0)]&#xA;    [-g gain (default: 0 for auto)]&#xA;    [-p ppm_error (default: 0)]&#xA;    [-b output_block_size (default: 16 * 16384)]&#xA;    [-n number of samples to read (default: 0, infinite)]&#xA;    [-S force sync output (default: async)]&#xA;    filename (a '-' dumps samples to stdout)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;For a test, I wanted a loud continuous narrow band FM voice signal, so I attempted to record the local national weather service transmitter on 162.55 Mhz with &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rtl_sdr -f 162550000 -g35 -s 1000000 test1.dat&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I note that this also records the 1 Mhz sample around 162.55 Mhz. Large files are made quickly.  A few minutes netted about 300 MB. I've noticed he R820T is finicky and won't always set low sample rates, and once again this is only to produce a test file.  If I wanted to leave it run all night on some other frequency range, I would consider finding a smaller sample rate.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once recorded, what program plays these files?  Although gqrx has an option to play an I/Q sample file, it doesn't seem to play files made with rtl_sdr.  I get a blank waterfall and no audio when attempting to play the file in gqrx. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ideas? &lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2014-10-14T05:05:40.033" LastActivityDate="2014-11-02T19:01:21.987" Title="How to play spectrum recordings made with rtl_sdr in gqrx?" Tags="&lt;rtl-sdr&gt;&lt;linux&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2114" PostTypeId="2" ParentId="2108" CreationDate="2014-09-05T18:24:04.153" Score="1" Body="&lt;p&gt;Yes, transmitting with that kind of power is illegal. The max power you may transmit with would be 1/2 of a watt (0.5 watt - 500mw). Their are other factors that make it illegal as well such as the bandwidth you are using while transmitting, spurious emissions, not having a license to transmit on GMRS, and using a detachable antenna. The radio is also most likely not FCC approved. Their are multiple ways you could be &quot;caught&quot;. Mainly telling others, interfering with local police / ems / other services, or by a Amateur Radio operator listening (or anyone with a scanner). You could be tracked down via RDF and fined or possibly imprisoned if purposely interfering with other services.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do not recommend using your radio for FRS / GMRS services.&lt;/p&gt;&#xA;" OwnerUserId="1540" LastActivityDate="2014-09-05T18:24:04.153" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2115" PostTypeId="2" ParentId="2103" CreationDate="2014-09-05T18:33:08.130" Score="1" Body="&lt;p&gt;As I have said in my first post if someone / something is jamming radio services they may &quot;enlist&quot; help of hams using RDF to locate and eliminate the source. The FCC does not play around when important services are being jammed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer to your question: Yes, as long as the device being used as a jammer has enough power to transmit over the target it will be effectively jammed.&lt;/p&gt;&#xA;" OwnerUserId="1540" LastActivityDate="2014-09-05T18:33:08.130" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2116" PostTypeId="1" AcceptedAnswerId="2118" CreationDate="2014-09-05T22:11:27.893" Score="5" ViewCount="3414" Body="&lt;p&gt;There is only one alphabet in Morse code, so is there a recognised way to indicate a capital letter?&lt;/p&gt;&#xA;" OwnerUserId="297" LastActivityDate="2014-09-16T06:32:47.733" Title="How are capital letters sent in Morse code?" Tags="&lt;cw&gt;&lt;encoding&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2117" PostTypeId="2" ParentId="2113" CreationDate="2014-09-05T22:54:28.870" Score="2" Body="&lt;p&gt;I haven't really tried this, so beware!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I thought the output, as recorded in the file, would actually be the samples in a certain format. So I tried to look it up, and found this page:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://sdr.osmocom.org/trac/wiki/rtl-sdr#rtl_sdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://sdr.osmocom.org/trac/wiki/rtl-sdr#rtl_sdr&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the bottom of the page is a flow diagram for gnu-radio, which takes the contents of the archive, and de-interlaces it (the interlacing is the trick use by the rtl_sdr recorder to record alternatively I and Q).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apparently the samples are stored as unsigned bytes in the original file, and this flow-chart alternatively sends one byte to the top chain or the bottom chain. They are first converted to float, then -127 is added to convert them into signed values. Finally, after some scaling, they are recombined into a complex signal, which would probably be the signal you'd receive from the dongle in the first place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the flow-chart, they save the complex output to a *.cfile format, but I think you could actually input the complex signal into the original receiver to decode it again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/MY9Uq.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you original idea was to record the audio, it would probably be more useful to send the receiver audio to a wav_file sink. That way you simply record it as audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: The scaling ('8m') is multiplying the samples from -128 to +127, into normalized float values, between -1.0 and +1.0. 8m means 0.008, which is (more or less 1/128)&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-09-05T22:54:28.870" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2118" PostTypeId="2" ParentId="2116" CreationDate="2014-09-06T02:31:19.860" Score="4" Body="&lt;p&gt;There is no upper/lower case differentiation in Morse code; just the alphabet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a &lt;a href=&quot;http://www.npr.org/blogs/thetwo-way/2013/06/14/191690435/u-s-navy-approves-use-of-lower-case-letters&quot; rel=&quot;nofollow&quot;&gt;reference&lt;/a&gt; to the military recently approving lowercase letters for navy messaging. Use of uppercase-only dates from days of Morse code communications.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2014-09-06T02:31:19.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2119" PostTypeId="2" ParentId="2116" CreationDate="2014-09-06T02:34:28.077" Score="4" Body="&lt;p&gt;There is no officially recognised way to distinguish between uppercase and lowercase characters in Morse code. When you look at old telegrams printed on paper strips they would all be in capitals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/uhR8w.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2014-09-06T02:34:28.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2120" PostTypeId="2" ParentId="6" CreationDate="2014-09-06T08:38:48.183" Score="-2" Body="&lt;p&gt;I modified mine for the 2.4ghz section of the ham band but you actually can use encrpytion on there same as DStar radios. The military has been modifying wlan gear available over the counter for military frequencies. I use my wifi router modified to 2.2ghz at first than finally got different parts soldered in to make it use 1.2ghz&lt;/p&gt;&#xA;" OwnerUserId="1541" LastActivityDate="2014-09-06T08:38:48.183" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2122" PostTypeId="1" CreationDate="2014-09-06T17:25:13.977" Score="3" ViewCount="178" Body="&lt;p&gt;Sometimes, when I am trying to make contacts, I call out on a bunch of repeaters due to low activity on individual repeaters. I usually call out, wait 10 seconds, then change repeater. Is there a specific length I should wait to see if anyone is on the repeater before changing frequency and trying out another repeater?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2014-09-06T21:42:58.847" LastActivityDate="2014-09-06T21:42:58.847" Title="After I call out &quot;Monitering&quot; how long should I wait until I switch frequency?" Tags="&lt;procedure&gt;&lt;repeater&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2123" PostTypeId="2" ParentId="2122" CreationDate="2014-09-06T21:42:08.580" Score="5" Body="&lt;p&gt;This would depend on local practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally speaking, I'd wait &lt;strong&gt;at least&lt;/strong&gt; for the repeater's sign-off notification (or carrier drop-out if it has a long output carrier hold), then preferably a little longer before moving on to another repeater or frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not everyone can drop what they are doing and grab the microphone right away, so &lt;strong&gt;ten seconds is pretty short.&lt;/strong&gt; Now, imagine that they also have their radio set to scan a handful of repeaters or they have more than one radio, and might have to stop the scan or see which radio the transmission was received on. Even an experienced operator might need a second or two just for that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, if when you do get a response you normally get it within 2-3 seconds, then waiting for 10 seconds may be plenty. But I for one wouldn't count on it.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2014-09-06T21:42:08.580" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2124" PostTypeId="1" CreationDate="2014-09-06T22:11:00.827" Score="1" ViewCount="260" Body="&lt;p&gt;I have decent circuit knowledge and would like to get into some homebrew operating, specifically voice. Would the KN-Q7A be a good place to start? If so can I just get the parts and do the circuit myself? Or should I buy the kit?&lt;/p&gt;&#xA;" OwnerUserId="1544" LastActivityDate="2014-09-07T15:28:15.127" Title="KN-Q7A - A good place to start?" Tags="&lt;diy&gt;&lt;transceiver&gt;" AnswerCount="2" CommentCount="1" ClosedDate="2014-09-17T18:46:46.947" ContentLicense="CC BY-SA 3.0" />
  <row Id="2125" PostTypeId="2" ParentId="2124" CreationDate="2014-09-07T13:17:03.053" Score="0" Body="&lt;p&gt;On the last two questions, I once harbored ambitions of building all my own stuff from scratch. Kits are much easier.&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2014-09-07T13:17:03.053" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2126" PostTypeId="2" ParentId="2124" CreationDate="2014-09-07T15:22:35.660" Score="1" Body="&lt;p&gt;I just read the description of those kits, and I like the concept a lot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;About the only criticism I have, is that the kits only covers 20 kHz (30 kHz on 20m) because of the crystal pulling trick they use. I would find it extremely frustrating not to be able to tune the entire band. But that is just me!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, the mixer (NE602) is used as oscillator, and removing the crystal and inserting a signal from a DDS signal generator will solve that perfectly (there are several kits on the market for DDS oscillators). So, you can start with the original kit, and later replace the VXO by an external, digital VFO. That way, you can tune the entire band!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The circuit looks very well thought out!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the question whether to gather the parts yourself, I have the impression you'd have a hard time to beat the price (and the convenience).&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2014-09-07T15:28:15.127" LastActivityDate="2014-09-07T15:28:15.127" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2127" PostTypeId="1" AcceptedAnswerId="2128" CreationDate="2014-09-07T16:55:09.047" Score="10" ViewCount="4167" Body="&lt;p&gt;I have a couple of Baofeng UV-5R radios. I have a profile in Chirp that works great on one of them, and I foolishly pushed that profile straight over to a UV-5R without checking firmware versions. Chirp crashed, and now the radio won't receive.  I've tried resetting it to factory settings, downloading the factory settings in chirp, and then importing a csv of my channel configs, but it still doesn't make noise when I transmit. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have noticed that it &lt;em&gt;does&lt;/em&gt; receive when I hold the MONI button, but there's no indication of reception if I don't hold that button down.  It appears to behave like the squelch setting is too high, but it's currently set to 3. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For what it's worth, the radio still transmits just fine. &lt;/p&gt;&#xA;" OwnerUserId="1547" LastEditorUserId="873" LastEditDate="2014-09-08T08:22:20.063" LastActivityDate="2020-12-12T17:53:03.123" Title="How do I troubleshoot a Baofeng UV-5R that won't receive?" Tags="&lt;ht&gt;&lt;baofeng&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2128" PostTypeId="2" ParentId="2127" CreationDate="2014-09-08T02:41:01.163" Score="10" Body="&lt;p&gt;I did a bit more reading, and it seems that the new version of the firmware meant I needed to use a different chirp profile.  The solution that worked for me was to find a factory image from a radio with the firmware version I have (which Chirp reported), then import my channels via csv, and clone that resulting image onto the radio. &lt;/p&gt;&#xA;" OwnerUserId="1547" LastActivityDate="2014-09-08T02:41:01.163" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2129" PostTypeId="5" CreationDate="2014-09-08T08:25:54.710" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-09-08T08:25:54.710" LastActivityDate="2014-09-08T08:25:54.710" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2130" PostTypeId="4" CreationDate="2014-09-08T08:25:54.710" Score="0" Body="Baofeng is a manufacturer of radio equipment. Use this tag for questions relating specifically to Baofeng products." OwnerUserId="29" LastEditorUserId="76" LastEditDate="2017-03-23T16:44:41.297" LastActivityDate="2017-03-23T16:44:41.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2131" PostTypeId="1" CreationDate="2014-09-08T10:29:19.320" Score="1" ViewCount="585" Body="&lt;p&gt;In our collective building lot we have an underground parking, in which a company recently changed a functional garage door system, since then the reception is a lot worse than before. (Like it doesn't open even when you stand 5 meters away from the antenna.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The entrance to the parking is like a rectangular tunnel. &#xA;The antenna inside the parking, is a single wire antenna, is 5 meters away from the garage door, 5 centimeters away from the tunnel wall and 50 centimeters from the ceiling, and &lt;strong&gt;pointing alongside the road&lt;/strong&gt;, towards the metallic garage door.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to remember my physics lessons, about electromagnetic waves in rectangular guides, and it seems to me that the antenna should be pointing up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone explain to me &lt;strong&gt;the rationale of making the antenna pointing the way it points?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[edit] adding information : the frequency used is 868.3 Mhz. (Before it was 29.960 Mhz). I measured the emitted power of my remote 50cm away using some USRP with a +3DB log periodic antenna, and it reads a power level of about -70dB (No idea, if that's enough, but my car key on 433.92Mhz in the same setup reads at about -68dB, and works really good)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[edit] I know in open air that single wire antenna emits best when pointed upwards, but here I'm wondering whether the fact of being in an &lt;strong&gt;underground (probably armed concrete)&lt;/strong&gt;, would explain the &lt;strong&gt;alongside the road&lt;/strong&gt; orientation, (that why I was evoking 'rectangular wave guides')&lt;/p&gt;&#xA;" OwnerUserId="1549" LastEditorUserId="1549" LastEditDate="2014-09-08T16:55:17.117" LastActivityDate="2014-09-09T16:35:09.277" Title="In which direction should single wire antenna in underground parking be pointed?" Tags="&lt;antenna&gt;&lt;propagation&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2132" PostTypeId="2" ParentId="2131" CreationDate="2014-09-08T14:16:30.293" Score="1" Body="&lt;p&gt;(short version of the below answer: direction probably doesn't matter, talk to someone at the garage)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This sounds like the antenna was installed by someone whose main concern was NOT functionality.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Much better reception (regardless of frequency) would be if it pointed vertically (either &quot;up&quot; or &quot;down&quot; is equivalent) or perpendicular to the road instead of alongside it.  Radio waves propagate off the broadside of the antenna, not the ends/tips... so to get 2 antennas talking to each other optimally, their &quot;sides&quot; should be pointed at each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regardless, the metal garage door is certainly attenuating/degrading the signal; how much DOES depend on the frequency.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, the super short distances involved between you and the antenna should make all of this for naught... if you haven't already checked the battery in your remote control, then the problem will lay somewhere in 1) the antenna, 2) it's connection to the transmission line, 3) the transmission line's connection to the receiver, or 4) all of the above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 868 MHz, roughly 35 cm wavelength, the relative size of the tunnel won't act as a wave guide, but the walls will simply absorb the energy, or reflect it back to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your description of the antenna being oriented &quot;alongside the road&quot; seems to mean that the broadside of the antenna is parallel to the wall and the ceiling, perpendicular to the garage door.  If so, that's the &lt;strong&gt;worst&lt;/strong&gt; orientation possible for the person trying to activate the opener from the door.  It should be realigned parallel to the garage door.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While the &quot;legal&quot; portion of your question was edited out before I read it, your best bet will be to have a civil... no, downright friendly... conversation with the attendant or whomever you can find at the garage to see how to fix it.  I've personally found an approach along the lines of, &quot;hey, am I doing something wrong with my remote?  I can't seem to get it to work, show me what I'm doing wrong&quot; is VERY effective.  When someone else finds they can't get your remote to work, they'll tell you it's not just you and be interested to work toward fixing it.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2014-09-09T16:35:09.277" LastActivityDate="2014-09-09T16:35:09.277" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2133" PostTypeId="2" ParentId="2016" CreationDate="2014-09-08T14:51:27.090" Score="2" Body="&lt;p&gt;You can remove them and instead attach the shield of the transmission line to the actual roof!  It will make a great ground-plane, probably much better than the radials that are currently attached.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, connecting a copper mesh will work too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will definitely want &lt;em&gt;something&lt;/em&gt; though, as you'll be giving up some power and efficiency if you just leave it off completely. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example: next time you have a 2 meter HT with a rubber-duck in your hand, grab a 19-inch (doesn't need to be exact) piece of wire and connect it to the shield/outside of the antenna connector with an alligator clip or similar... basically, you've made it a dipole.  You can then test just how much the signals improve/degrade with &amp;amp; without that single wire.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2014-09-08T14:51:27.090" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2134" PostTypeId="1" CreationDate="2014-09-08T21:03:30.277" Score="0" ViewCount="184" Body="&lt;p&gt;Is it possible? I know it depends on legal issues; it is just for testing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will &quot;transmit&quot; from RPI &lt;a href=&quot;https://www.youtube.com/watch?v=CBb8BN0dqoQ&quot; rel=&quot;nofollow&quot;&gt;(Raspberry pi as fm transmitter)&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="1554" LastEditorUserId="76" LastEditDate="2014-09-08T22:36:38.623" LastActivityDate="2014-09-08T22:50:46.443" Title="audio amplifier as fm amplifier possible?" Tags="&lt;amplifier&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2135" PostTypeId="2" ParentId="2134" CreationDate="2014-09-08T21:24:39.570" Score="3" Body="&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An audio amplifier is not designed to have the bandwidth to amplify RF — it will not pass or amplify signals much greater than audible frequencies, which would require significantly different design. In fact, if it &lt;em&gt;did&lt;/em&gt; amplify RF, it would be a potential source of RF interference by amplifying incidental noise on the input.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you did find an amplifier to use, then you should also use a &lt;a href=&quot;http://en.wikipedia.org/wiki/Band-pass_filter&quot; rel=&quot;nofollow noreferrer&quot;&gt;band-pass filter&lt;/a&gt; for the desired output frequency, placed between the amplifier and the antenna. This is always a good idea, but especially necessary in this case because the Pi being used in this way produces a &lt;a href=&quot;http://en.wikipedia.org/wiki/Square_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;square wave&lt;/a&gt;, which by definition has harmonics — signals at multiples of the original frequency; e.g. starting from 100 MHz, also 300 MHz, 500 MHz, 700 MHz. If you amplify those too, you interfere with frequency bands unrelated to the one you wanted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it is likely that adding any amplification at all would be illegal even if your original transmission isn't, because unlicensed transmissions are limited to very low power. &lt;a href=&quot;https://ham.stackexchange.com/questions/1016/what-are-the-us-rules-about-unlicensed-low-power-transmissions&quot;&gt;Here's a question about the power limits in the US, for example.&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-09-08T22:50:46.443" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2136" PostTypeId="2" ParentId="1985" CreationDate="2014-09-09T19:16:07.883" Score="2" Body="&lt;p&gt;An antenna is similar to a lightbulb.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lightbulbs spit out photons at a wavelength we can see.  These are roughly in the range of 400 to 900 nanometers... a SUPER short wavelength compared to our everyday experiences.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A radio wave emits the same photons, at a much larger wavelength, for example about 3 meters when looking at the FM broadcast dial in the US.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to generate radio waves, a property that can be referred to as resonance (think about 2 tuning forks that resonate with each other when just the first is struck) greatly controls what wavelength of photons/EMR an antenna of a particular size might be able to spit out and detect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Over-simplistically, the radios that the antennas are plugged into convert voices (or data) into on/off patterns that the antenna &amp;amp; radio on the other side knows how to convert back into voices (or data).  In reality, there's MUCH more to the encoding of information than just on/off patterns, but it's a reasonable analogy.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2014-09-09T19:16:07.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2137" PostTypeId="2" ParentId="1985" CreationDate="2014-09-10T15:47:12.580" Score="1" Body="&lt;p&gt;I like to think of a resonant antenna like a guitar string that vibrates at a given frequency that you can hear. Tighten/shorten the string, the pitch/frequency increases; loosen/lengthen the string, the pitch decreases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly for a resonant antenna like a dipole: shorten the wire, the resonant frequency increases (wavelengths become shorter); lengthen the wire, the resonant frequency decreases (wavelengths become longer).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This doesn't describe how or why the RF leaves the antenna and propagates through the air, and maybe it's not an entirely correct comparison to make (the guitar string is vibrating air molecules that carries the sound to your ear, but the RF doesn't vibrate the air to carry itself), but since we're talking about different frequencies on the electromagnetic spectrum there's probably some truth in part of this explanation. At least it's a comparison with something that someone would be more familiar with so it helps understand the concept.&lt;/p&gt;&#xA;" OwnerUserId="252" LastActivityDate="2014-09-10T15:47:12.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2138" PostTypeId="2" ParentId="1722" CreationDate="2014-09-10T22:21:15.573" Score="2" Body="&lt;p&gt;The worst offenders earning &quot;bad fist&quot; have one or more of three major problems (in my opinion and I admit some of this is repeat of above):&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Poor spacing of dahs, that is too short mostly or changing the length which used to be a popular &quot;swing&quot; to a fist back in the 50s/60s.  Such as a CQ with a very long dah in the first part of the letter C with a shorter dah later as in daaaah-di-dah-dit.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;run-on words, that is, no spacing between.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Chirp.  I can't stand chirp.  Not a fist problem but I say get that rig fixed.  Not as common today with solid-state radios as this used to often be caused by poor voltage regulation in the older tube radios but I still hate it and won't answer a call with chirp.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2014-09-10T22:21:15.573" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2142" PostTypeId="2" ParentId="2080" CreationDate="2014-09-12T20:22:47.650" Score="6" Body="&lt;p&gt;There are advantages and disadvantages to each.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you have citizenship in either country? U.S. citizens are prohibited from transmitting in the U.S. using a foreign license. As well, Canadian citizens are prohibited from transmitting in Canada using a foreign license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What sort of privileges are you looking for? I don't think there's much difference between the U.S. Technician license and the Canadian Basic license. Both are essentially VHF/UHF and above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you qualify for the Canadian Basic with Honours license (80% or more on the Basic test), you will have more privileges on HF than the U.S. Technician license does. The Canadian Basic with Honours covers more or less the same frequencies on HF that the U.S. Extra license covers. Power limits are lower, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will need the Canadian Advanced license to set up a repeater in Canada or build your own radios. In the U.S., you can do that with any class of license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Either way, you will need a local address. The U.S. system allows you to have a call outside your call area (so you could have a vanity KG2 call in the 7 call area); Canada requires that you have a call located in your call area (so you will have to have VE3 / VA3 in Ontario, for instance). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Canadian callsigns are good for life, U.S. callsigns are good for 10 years and then must be renewed (currently free of charge).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Canadian Basic test is 100 questions from a pool of 960. You need 70% to pass, 80% for Basic with Honours. If you don't get Honours when you first take the test, you can take it again. The Canadian Advanced is 50 questions from a pool of 540. The U.S. Technician is 35 questions from a pool of 420; the U.S. General (which will give you HF) is 35 questions from a pool of 450; the U.S. Extra is 50 questions from a pool of 750. All pools in both the U.S. and Canada are multiple choice.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2018-08-20T02:59:35.753" LastActivityDate="2018-08-20T02:59:35.753" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="2143" PostTypeId="2" ParentId="1985" CreationDate="2014-09-13T20:24:19.483" Score="0" Body="&lt;p&gt;One way I have explained to kids (and to myself) is to imagine a jump rope tied to a tree or a post.  You start moving it up and down, soon it makes a nice wave.  If you continue to move it up and down, it continues to keep waving.  That is a radio transmitting into a wire.  Now if the rope were dipped in lots and lots of paint, each time the wave peaked, imagine the paint color flinging off straight up into the sky in a wave form.  That's kind of what the excited electrons do in the wire, they are so small, they simply fling an image of themselves out into space in the form of photons or light particles.  The analogy breaks down after a while, but it is also easy to use this example to teach the principle of a standing wave. Maybe not the most elegant, but for non scientific types it bridges the concepts when too much technical jargon might turn them off. Apologies to the purists.  JP&lt;/p&gt;&#xA;" OwnerUserId="1572" LastActivityDate="2014-09-13T20:24:19.483" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2144" PostTypeId="1" AcceptedAnswerId="2179" CreationDate="2014-09-14T16:26:49.980" Score="3" ViewCount="202" Body="&lt;p&gt;I picked up this 0-80 dB switched RF attenuator at a flea market, with no part number or other useful markings other than the knob settings. I've tested it and confirmed that it works, but there's one thing I'm uncertain about which I don't have the theory to be certain of and can't test non-destructively:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there potentially &lt;strong&gt;a difference between &quot;input&quot; and &quot;output&quot; ports&lt;/strong&gt;, or is it symmetric? In particular, would there possibly be better or worse &lt;strong&gt;maximum power handling&lt;/strong&gt; capability depending on which way around it's connected? If there is a difference, how can I tell which port is which? (They aren't labeled.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm interested in answers which are either general, for all reasonable designs of attenuators, or specific to this unit if you should happen to recognize it. (I have used Google Image Search to try to find things which look like this specific model and haven't succeeded. According to the seller, it was likely an internal module from equipment made by HP.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's unlikely that there's a significant difference, then I'm happy to go ahead and use it as I intend (testing transmitters hooked up to receivers with no antennas involved, no more than 5 watts, not continuous) but if it matters I'd like to use it properly and have less chance of burning it out. (This was cheap, but apparently comparable new units are in the hundreds of dollars.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/pZxpY.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-09-25T14:25:55.617" Title="Would a switched RF attenuator be (a)symmetric?" Tags="&lt;equipment-design&gt;&lt;rf-power&gt;&lt;testing&gt;&lt;electronics&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2145" PostTypeId="1" CreationDate="2014-09-14T21:58:47.380" Score="1" ViewCount="138" Body="&lt;p&gt;Trying to tune a Firestik antenna connected to Magnum 257 on my '98 Jeep Wrangler. Having trouble with SWR reading as it is reading too high (~4) after I set needle on FWD and then switch back to REF. I'm only using it as a CB radio for now and am getting high SWR REF readings on both Ch 40 &amp;amp; 1. Any ideas? Should I just cut the transmit power knob down as far as it will go on the Magnum 257? &lt;/p&gt;&#xA;" OwnerUserId="1577" LastEditorUserId="76" LastEditDate="2014-09-15T02:15:37.327" LastActivityDate="2014-11-17T02:41:51.653" Title="Magnum 257 &amp; Firestik 3' Tuning" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;&lt;citizens-band&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2146" PostTypeId="1" CreationDate="2014-09-14T23:40:42.757" Score="6" ViewCount="10897" Body="&lt;p&gt;I have two buildings. Building A has wifi (2.4GHz) infrastructure, Building B doesn't. One side of building B can pick up the wifi signal from building A. I want to passively extend the signal through to the rest of building B, using two antennas and a short piece of coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Supposing I put a decent directional antenna (24dBi) in building B, pointing at a WAP in building A, then joined that to an omnidirectional antenna with a short (50cm) piece of coax. In this scenaria, for the omni antenna, would it be better to have a large (e.g. 12-15 dBi) antenna, or a small one (~7 dBi) (assuming the smaller one can still cover the range of the building)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am aware an active repeater would be better, but I'd like to get some thoughts on this scenario.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Background reading: &lt;a href=&quot;https://web.archive.org/web/20141026222347/http://www.netscum.com:80/~clapp/wireless.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://web.archive.org/web/20141026222347/http://www.netscum.com:80/~clapp/wireless.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1578" LastEditorUserId="13649" LastEditDate="2018-11-22T16:36:26.447" LastActivityDate="2018-11-22T16:36:26.447" Title="Wifi passive repeater (antenna to antenna connection)" Tags="&lt;antenna&gt;&lt;repeater&gt;&lt;wifi&gt;" AnswerCount="5" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="2147" PostTypeId="2" ParentId="526" CreationDate="2014-09-15T04:29:12.433" Score="1" Body="&lt;p&gt;I have used an old satellite dish to make a 2m slot antenna, and it works pretty well. Basically, you just need to cut a slot in the dish to the appropriate length, and hook up the feed line on either side of the slot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find one example of a slot antenna in a satellite dish here: &lt;a href=&quot;http://w6nbc.com/articles/20xx-dishslot.pdf&quot; rel=&quot;nofollow&quot;&gt;http://w6nbc.com/articles/20xx-dishslot.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user1580" LastActivityDate="2014-09-15T04:29:12.433" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2148" PostTypeId="2" ParentId="1985" CreationDate="2014-09-16T05:03:23.647" Score="0" Body="&lt;p&gt;Two things and maybe getting back to the five year old's view of the world.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;A tuning fork. the sound waves/vibrations from one tuning fork, when struck, radiate out bumping one molecule into another until reaching the other tuning fork. when the lengths of the elements are the same the energy of the wave is absorbed by the second tuning fork where it then begins to emit the same sound/vibration as the first one.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A soap bubble and the ring used to blow it. They have a relationship. if you use the same size ring you can catch a bubble. If it is not similar enough the bubble pops.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Electro Magnetic Mechanics are not quite the same as either of these structures but this helps communicate a handle that can lead to better understanding.&lt;/p&gt;&#xA;" OwnerUserId="1587" LastActivityDate="2014-09-16T05:03:23.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2149" PostTypeId="1" CreationDate="2014-09-16T06:28:24.333" Score="6" ViewCount="246" Body="&lt;p&gt;I want to hold a fox-hunt in a relatively public location, such as a park or college campus. The fox that I've built uses an ammo can with a rubber duck antenna. It occurred to me that this combination makes for a somewhat suspicious package. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My plan is to hide the fox so that it isn't readily visible to regular a passerby, but I'm concerned that I'll look like a terrorist or the fox will look like a bomb. How can I identify/decorate/etc... a fox to make it less suspicious, but still not easily visible? &lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2017-01-15T02:11:56.957" Title="How do I keep the bomb squad from winning a foxhunt?" Tags="&lt;fox-hunt&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2150" PostTypeId="2" ParentId="2116" CreationDate="2014-09-16T06:32:47.733" Score="0" Body="&lt;p&gt;You can spell out CAPITAL LETTER then provide the letter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;example: SPELLING FOLLOWS - CAPITAL LETTER W THE LETTER O THE LETTER W&lt;/p&gt;&#xA;" OwnerUserId="1587" LastActivityDate="2014-09-16T06:32:47.733" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2152" PostTypeId="2" ParentId="2149" CreationDate="2014-09-16T18:25:32.183" Score="3" Body="&lt;p&gt;In my club we do many things to make sure the fox is not stolen / thought it was a bomb / hide it. Here are a few things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our main fox is inside one of those old surplus 50 cal. ammo cans. It is pretty large making it very visible. A good thing about though is it is (custom) painted with a camo pattern that fits our area quite nicely. We also have someone ALWAYS watching it from a good distance away. Lastly on the actual fox we have a printed paper telling what it is, that it is being watched, and basically a warning telling people to not touch it. On the fox we have a BNC connector. Not sure if your fox is a soldered antenna or just connected via some type of RF connector but if it is consider getting a (if you use a bnc connector) BNC to BNC &quot;extension&quot; cable. This will help with signal tremendously and add many options to how / where you can hide it. Also another antenna trick would be using some type of directional antenna pointing at a metal / RF reflective object. This will scatter the signal and make it look like it is coming from somewhere else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now to the actual hiding.. The best place for a ammo can is deep in brushes right off a trail / walking area. (Don't want to make it too hard to get to). In my club we have hidden it in many other places though including hanging it in a tree, in a car, inside buildings (make sure you get permission!!), using a long cable to place the antenna 20 - 30 ft away from the fox burying the coax underground as it goes (this works well since you can just have the antenna sticking up which is much smaller than the ammo can and harder to find BUT may get stepped on). We also thought about burying the whole ammo can underground but our fox already had over-heating issues so we didn't. You could do this as long as your fox had very good cooling or is very low power. For future fox hunts we have considered putting the fox inside a backpack and have someone *NOT IN THE CLUB wear it and sit on a park bench. We have also thought about a moving fox but we decided against it due to being nearly impossible (at-least at our skill level).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some other ideas I myself have thought of is placing the fox inside either the fireplace or the on one of the support beams on the covers (if your local park(s) have them). Also (if funds allow) buy / make a new fox that is small enough to fit inside a coke can or other small objects that you can usually find on the ground. (Warning: May get thrown away if park or area maintenance pass by.. hide in a good spot).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is all I have.&lt;/p&gt;&#xA;" OwnerUserId="1540" LastActivityDate="2014-09-16T18:25:32.183" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2153" PostTypeId="1" CreationDate="2014-09-17T10:56:58.000" Score="2" ViewCount="126" Body="&lt;p&gt;I was recently scanning through the short-wave frequencies and stumbled upon a series of repeating tones, which then cut to classical music and then a woman speaking French (unconfirmed). Later I was unable to locate anything but static on that frequency.&lt;/p&gt;&#xA;&lt;p&gt;I recorded the brief moment on my phone and the &lt;strong&gt;recording can be listened to &lt;a href=&quot;https://soundcloud.com/shortsurrey/11970khz-13092014-2059&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; (SoundCloud).&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I am aware that numbers stations exist and are known to start with repeating tones, &lt;a href=&quot;http://en.wikipedia.org/wiki/Lincolnshire_Poacher_(numbers_station)&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Lincolnshire Poacher&lt;/a&gt; is known for this - though this beacon seemed to be ending on one, not beginning.&lt;/p&gt;&#xA;&lt;p&gt;Am I just confusing a commercial station's opening signals for something more? The UK Shipping Forecast is always lead into by a musical score for people to listen for when tuning in and perhaps this is just a similar method.&lt;/p&gt;&#xA;&lt;p&gt;What is frustrating is that the tones played in the beacon are somewhat recognisable but I cannot place where they are from.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;h1&gt;&lt;strong&gt;Details:&lt;/strong&gt;&lt;/h1&gt;&#xA;&lt;p&gt;&lt;strong&gt;Frequency:&lt;/strong&gt; 11970khz&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Date &amp;amp; Time:&lt;/strong&gt; 13/09/2014 - 20:59 (DD/MM/YYYY - HH-MM)&lt;/p&gt;&#xA;" OwnerUserId="1594" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-04-22T17:45:14.180" Title="Is this beacon the tail end of a 'Numbers Station' broadcast?" Tags="&lt;signal-identification&gt;&lt;beacon&gt;&lt;swl&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2154" PostTypeId="1" AcceptedAnswerId="2193" CreationDate="2014-09-17T14:16:34.310" Score="2" ViewCount="1641" Body="&lt;p&gt;I live in India and would like to know whether it is legal to listen to on the air transmissions there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that transmitting is allowed only in limited frequencies and strictly require a HAM license here. But does it apply for reception also?&lt;/p&gt;&#xA;" OwnerUserId="1595" LastEditorUserId="873" LastEditDate="2014-09-25T08:24:26.680" LastActivityDate="2015-10-29T09:15:46.990" Title="Are there legal restrictions on radio reception in India?" Tags="&lt;legal&gt;&lt;receiver&gt;&lt;india&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2155" PostTypeId="2" ParentId="2153" CreationDate="2014-09-17T17:37:27.860" Score="4" Body="&lt;p&gt;After catching it again today, at 19:30 BST on 5.90mhz I looked it up on &lt;a href=&quot;http://www.shortwaveschedule.com/&quot; rel=&quot;nofollow&quot;&gt;shortwaveschedule&lt;/a&gt;. It seems to be the lead-in call for Radio Romania International.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mystery solved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The introductory music &amp;amp; beacon can also be heard on &lt;a href=&quot;https://www.youtube.com/watch?v=pVMGnMT5FXU&quot; rel=&quot;nofollow&quot;&gt;this old recorded broadcast from 2011&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="1594" LastEditorUserId="1594" LastEditDate="2014-09-17T17:54:30.293" LastActivityDate="2014-09-17T17:54:30.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2156" PostTypeId="2" ParentId="2154" CreationDate="2014-09-17T18:05:50.380" Score="-1" Body="&lt;p&gt;In some countries, such as England, you need a license just to use a TV, so I suppose there might be something similar in India. That said, there might also be military and government transmissions that are not legal to listen to.  Sniffing cellular data or eavesdropping on cordless phones might violate privacy laws. Most laws around the world regarding what you can receive govern decrypting or descrambling a secured signal, and not reception of the signal itself. As far as amateur bands go, you can listen all you want without a license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might check here &lt;a href=&quot;http://en.wikipedia.org/wiki/Amateur_radio_in_India&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Amateur_radio_in_India&lt;/a&gt; and here &lt;a href=&quot;http://www.hamradio.in/amateur_radio/&quot; rel=&quot;nofollow&quot;&gt;http://www.hamradio.in/amateur_radio/&lt;/a&gt; for more information specific to India.&lt;/p&gt;&#xA;" OwnerUserId="1597" LastEditorUserId="-1" LastEditDate="2014-09-24T16:50:17.057" LastActivityDate="2014-09-24T16:50:17.057" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2157" PostTypeId="2" ParentId="1105" CreationDate="2014-09-17T22:23:10.620" Score="0" Body="&lt;p&gt;Your lucky  anyone is actually posting on the  issue ,  links etc  below &lt;/p&gt;&#xA;&#xA;&lt;p&gt;J2D is audio  via  sound channel  ,  the  SS  the  part 97 is  directed  at  is base band [base  band  = ultra wide  band ]and even  defines the  PN number  generators taps to  ensure commonality.. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;1 Spread Spectrum   in a modern sense covers  now  as a group  heading  all  aspects of  data  processing and  bandwidth  is a design choice , just as Olivia  has various b/w options , still  uses  DSSS  Direct Sequence Spread Spectrum  , referring  to  the  Pseudo random number generator used to add redundancy to  the  data , nothing wrong  with  that  , been in use  for  10/15 years  now the  world  over .  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;2 ROS uses  modern techniques , that  utilise  Spread Spectrum  techniques within audio  bandwidths, offering  the  next  generation , low s/n high data  rate and multi qso access .   DSSS and  CDMA  , CDMA  as in  mobile  phones  allows  multiple  simultaneous access  to the  same  qrg , hence the  number of  qso's showing  on 14.103 , providing  the  MOST EFFICIENT USE OF BANDWIDTH  of  and  HAm data  mode , A topic that is dear to  the  congested band  uses in the  US ?  the  answer is  already in use  WW &lt;/p&gt;&#xA;&#xA;&lt;p&gt;3 The  SS  trials  ran  with  no  problems , however  due to  external  off  shore usa , influences , the  end  game was  never played  out  and the  situation  remains  frozen  in time .. if ever the  subject is  raised , the  flow  of nonsense reaches levels  that  even broke the yahoo  data  group , its owner posting  'Thanks for all  the  fish' as a last gasp for  reality , linked to the  number 42 &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/news/fcc-grants-special-temporary-authority-for-amateur-spread-spectrum-experiments&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/news/fcc-grants-special-temporary-authority-for-amateur-spread-spectrum-experiments&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1476" LastActivityDate="2014-09-17T22:23:10.620" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2158" PostTypeId="2" ParentId="2145" CreationDate="2014-09-18T01:51:49.293" Score="1" Body="&lt;p&gt;Start with a basic inspection of the coax, connectors, and antenna. Unless it is a shunt fed antenna or uses a tapped loading coil, you should find no continuity between center pin and shield on the coaxial connector when checked with an ohmmeter. If there is a short in the connector or coax your SWR will be abnormally high. I have found this several times after pulling my hair out over SWR. &#xA;Without any other equipment, the best way to tell how to tune it will be to sweep thru the channels and see if you are able to tell which direction is resonant point is (higher or lower than the CB band apparently). Plot on a piece of paper the SWR on all the channels and see which end of the band the SWR is trending lower. The resonant point should be that direction also. If the SWR is lower towards channel 1, the antenna is electrically long, shorten it. If the SWR is lower towards channel 40, your antenna is electrically short, lengthen it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also very advisable to place the meter inline at the antenna to tune it properly first. Then check it with the meter at the radio to determine if standing waves are present due to problems in the transmission line (coax).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good guide can be found at www.firestik.com/Tech_Docs/Setting_SWR.him&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Running higher than rated power can also skew results unless the meter you are using is designed for more than 4W, just saying)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;~Jonathan&lt;/p&gt;&#xA;" OwnerUserId="1485" LastActivityDate="2014-09-18T01:51:49.293" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2159" PostTypeId="1" AcceptedAnswerId="2164" CreationDate="2014-09-18T07:55:17.983" Score="3" ViewCount="289" Body="&lt;p&gt;I'm trying to figure out how SSB transmitters manage to get rid of the images created when mixing up audio frequencies. For example, when mixing a 1KHz signal with a 7MHz one you will end up with two signals, one at 7.001Mhz and one at 6.999Mhz. Creating a filter with such a narrow cutoff sounds infeasible so how is it done?&lt;/p&gt;&#xA;" OwnerUserId="135" LastEditorUserId="1579" LastEditDate="2014-10-20T20:00:05.430" LastActivityDate="2014-10-20T20:00:05.430" Title="SSB modulation image rejection" Tags="&lt;ssb&gt;&lt;transmitter&gt;&lt;mixer&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2160" PostTypeId="1" AcceptedAnswerId="15716" CreationDate="2014-09-18T08:01:17.273" Score="1" ViewCount="2620" Body="&lt;p&gt;I am a software engineer and a noob to radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to find out the location where a radio signal is intercepted? That is, the location where somebody is eavesdropping on my wireless communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't believe this can be done if the receiver is not transmitting back, but I would like some expert advice. &lt;/p&gt;&#xA;" OwnerUserId="1595" LastEditorUserId="76" LastEditDate="2014-09-18T16:42:03.457" LastActivityDate="2019-11-30T02:34:00.847" Title="Is there a way to find out the location where a radio signal is intercepted?" Tags="&lt;receiver&gt;&lt;direction-finding&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2161" PostTypeId="2" ParentId="2160" CreationDate="2014-09-18T16:41:00.820" Score="6" Body="&lt;p&gt;It is possible &lt;em&gt;in principle&lt;/em&gt; to detect a receiver.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Almost all designs of receivers have a &lt;em&gt;local oscillator&lt;/em&gt; (LO), which oscillates at the same frequency as the carrier frequency of the signal it is receiving, or at some close offset to it. The signal from the LO can leak back out the antenna. However, in a well-designed receiver this leakage is minimized and will always be immensely weaker than the signal from a transmitter.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A receiving antenna collects radio waves — electromagnetic energy. It therefore casts a shadow: if the receiver is between you and the transmitter, the signal will be weaker than if the receiver wasn't present. However, this effect will most likely be very much smaller than the effects of other large objects in the area that are not even radio devices (buildings, metal objects, landscape, etc.).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;These effects are very small and unlikely to be usable for good location purposes, or even to tell whether there's a receiver at all. Even using equipment designed for the purpose, locating a radio that is &lt;em&gt;transmitting&lt;/em&gt; is tricky and requires readings taken at multiple locations, experience interpreting them, and guesswork; it will be essentially impossible for the orders-of-magnitude-weaker effects I've described above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're talking about unlicensed digital communication systems like WiFi and Bluetooth, an additional complication will be other devices unrelated to yours actively using the same channel frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, a hypothetical eavesdropper can be farther away than you might think: use of a directional antenna accurately pointed at the transmitter increases the received signal power, allowing it to be received from much farther away. Never believe any claims about how some wireless signal has a &lt;em&gt;maximum&lt;/em&gt; range; it always depends on antennas and environmental conditions. (For a popular computer-security story on this, look up the “Bluetooth sniper rifle”.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-09-18T16:41:00.820" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2162" PostTypeId="2" ParentId="356" CreationDate="2014-09-18T21:25:11.300" Score="2" Body="&lt;p&gt;Complete rules are here &lt;a href=&quot;http://www.arrl.org/files/file/Regulatory/Part%2097%20-%2004-28-2011.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/files/file/Regulatory/Part%2097%20-%2004-28-2011.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MY understanding of it is &quot;transmissions that are intended to be one-way&quot;, i.e., broadcasting. Singing &quot;Happy Birthday&quot; to another ham operator would be directed at that other ham, not the general public or anyone in range of the transmitter. That said, I am not sure what is meant by &quot;music from a phone emission&quot;, unless that is a roundabout way of saying that you can't put your microphone up to your Walkman playing Bon Jovi, but you yourself could sing provided its not intended to be one way to a general audience. One thing I remember from my exam study was that if you are making a phone call through an autopatch and you get put on hold and it has the &quot;on hold music&quot; that you have to disconnect the call; even though you yourself are not playing music, you're still allowing it (incidentally) to be transmitted. &lt;/p&gt;&#xA;" OwnerUserId="1597" LastActivityDate="2014-09-18T21:25:11.300" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2163" PostTypeId="2" ParentId="2041" CreationDate="2014-09-19T11:02:16.243" Score="1" Body="&lt;p&gt;I had a problem with APRS reception from ISS too. It seems I got frequency shift in received data. Slowing down by 2% (deduced from looking at the spectrum - ymmv) in Audacity helped some, but then I found software with adjustable frequency on site by UZ7HO here: &lt;a href=&quot;http://uz7.ho.ua/packetradio.htm&quot; rel=&quot;nofollow&quot;&gt;http://uz7.ho.ua/packetradio.htm&lt;/a&gt; and there is soundmodem application (file sm2ch57.zip). I set up baud rate to 1200 and then frequency as to have the most packets received. Around 1750 Hz in my case. &#xA;I got packets decoded with recording both through cable onto my digital voice recorder and with it next to my scanner. But I plugged it through line-in for recording on computer in both cases. My computer gives off a hellish amount of interference at frequencies in 2m band so plugging scanner directly was not an option.&lt;/p&gt;&#xA;" OwnerUserId="1609" LastActivityDate="2014-09-19T11:02:16.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2164" PostTypeId="2" ParentId="2159" CreationDate="2014-09-20T19:29:42.407" Score="3" Body="&lt;p&gt;Well, there are two relatively simple methods and one slightly more complicated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the analog world, SSB signals are created in two ways: The filter method and and phasing method. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;The filter method&lt;/strong&gt; does just what you suggested - a very selective&#xA;filter eliminates one sideband. Using piezoelectric crystals, filters&#xA;can be made what can do that. Mostly between 4 and 12 MHz, combining&#xA;crystals can form a nice filter that just passes the audio band (or&#xA;so). As the frequency of the crystal filter is not easy to change, this is done at a fixed frequency (frequently 9 MHz) and the resulting SSB signal is then mixed up or down.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;The phasing method&lt;/strong&gt; is more difficult to explain, and needs some math to do it properly. Basically, both the RF and the audio signal are split into two parts, which are 90 degrees out-of-phase. Then one of the audio signals is modulated onto one of the RF signals to produce DSB (Double sideband). Same for the other audio/RD pair. Adding the two will eliminate one of the sidebands (subtracting eliminates the other one :)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The more complicated way&lt;/strong&gt;, and which needs a fast processor, implements the phasing method purely by algorithms with both signals converted to digital. The phase shifting of the audio is accomplished with an algorithm called the Hilbert Transform, which creates two output signals with 90° phase shift.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The graphics are not too good here:&#xA;&lt;a href=&quot;http://www.daenotes.com/electronics/communication-system/ssb-transmission&quot; rel=&quot;nofollow&quot;&gt;http://www.daenotes.com/electronics/communication-system/ssb-transmission&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This one's much better and mentions some of the math:&#xA;&lt;a href=&quot;http://www.dsprelated.com/showarticle/176.php&quot; rel=&quot;nofollow&quot;&gt;http://www.dsprelated.com/showarticle/176.php&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the actual presentation of the phasing method. It's frequently called the 'third method' (It's old though - uses vacuum tubes :) :&#xA;&lt;a href=&quot;http://www.h4.dion.ne.jp/~ja5fp/weaver.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.h4.dion.ne.jp/~ja5fp/weaver.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2014-09-20T19:35:13.937" LastActivityDate="2014-09-20T19:35:13.937" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2165" PostTypeId="1" AcceptedAnswerId="2166" CreationDate="2014-09-22T13:00:31.563" Score="9" ViewCount="1476" Body="&lt;p&gt;If I built a machine that went far away, say a buoy, would I be allowed to use ham radio frequencies to transmit telemetry data back to its base station, if I used my call sign? This is for personal research, not commercial applications.&lt;/p&gt;&#xA;" OwnerUserId="850" LastEditorUserId="76" LastEditDate="2015-05-01T18:35:38.853" LastActivityDate="2015-05-01T18:35:38.853" Title="Using ham radio bands for telemetry" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;hf&gt;&lt;station-identification&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2166" PostTypeId="2" ParentId="2165" CreationDate="2014-09-22T18:47:43.033" Score="4" Body="&lt;p&gt;I don't see why not as long as you followed the regulations for ID and transmission mode.  There are beacons, satellites, balloons and more transmitting telemetry.  Beyond the laws I would recommend following the band plans for where to transmit and pay attention to where the signals from your buoy would reach.  For example, the lower end of the 70cm band isn't part of the allowed spectrum in Canada so when I go much farther North I have to pay attention and not transmit on some frequencies I can use in the US.&lt;/p&gt;&#xA;" OwnerUserId="1616" LastActivityDate="2014-09-22T18:47:43.033" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2167" PostTypeId="2" ParentId="2146" CreationDate="2014-09-22T21:10:40.577" Score="1" Body="&lt;p&gt;You'll get an awful lot of signal loss from trying to do this.  A wifi AP can lose something like 30 dB of power between the wired section and the air.  Picking up a signal and then retransmitting it will probably lose at least that much, plus the loss in the original signal (originally sent from an omni antenna).  You probably won't notice much improvement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if you get a cheap active wifi repeater and attach a directional antenna, this could work quite well.  Even more so if you install an identical one near the original building.  (There's no reason you can't have two APs in that building.)  Two repeaters will cost you not much money, but give vastly better coverage, reliability, and speed.&lt;/p&gt;&#xA;" OwnerUserId="1621" LastActivityDate="2014-09-22T21:10:40.577" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2168" PostTypeId="2" ParentId="2093" CreationDate="2014-09-23T03:51:35.893" Score="2" Body="&lt;p&gt;Most connector plugs make contact at 3 points:&lt;br&gt;&#xA;1 Tip (pointy bit),&lt;br&gt;&#xA;2 Sleeve (opposite the tip), and&lt;br&gt;&#xA;3 Ring (between tip and sleeve).&lt;br&gt;&#xA;Depending on the rig, two of these will carry audio. One of the audio lines also goes to the Push To Talk switch, with the other side of that switch having the third wire. When you push the switch, you short those lines together.&lt;br&gt;&#xA;If you can't get a schematic for your radio, you'll need to figure out which is what.&lt;p&gt;&lt;br&gt;&#xA;Buy a 2.5mm plug, a 3.5mm socket, and some wire.&lt;br&gt;&#xA;Put the plug in your CB, try shorting pins on it, until you activate the transmit.&lt;br&gt;&#xA;Take it out, permanently wire up the short, then add connections to the 3.5mm socket.&lt;p&gt;&#xA;Presto! Audio through, PTT remanently on. Everyone gets annoyed at you because you &quot;hog&quot; the airwaves.&lt;/p&gt;&#xA;" OwnerUserId="1610" LastActivityDate="2014-09-23T03:51:35.893" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2170" PostTypeId="2" ParentId="2165" CreationDate="2014-09-23T04:13:16.940" Score="2" Body="&lt;p&gt;Make sure you follow the regulations on 'unattended operation'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if you are going to be floating a buoy into the sea, be aware that you may end up transmitting from the territory of another country, at which point your transmission could well be very illegal. If you ended up floating a 'message in a bottle' beacon that made its way to North Korean waters, for example, you could create an international incident!&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-09-23T04:13:16.940" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2171" PostTypeId="2" ParentId="2165" CreationDate="2014-09-23T14:46:55.337" Score="0" Body="&lt;p&gt;I would say that it is probably legal, but depending on the country in which you operate it, there might be restrictions on unattended transmitters. In Switzerland, for example, only amateur radio clubs (and not &quot;private&quot; operators) are allowed to operate an unattended station (e.g., repeater, beacon, etc.) -- if you're member of a club, and the club is ok with that, then no problem (but of course the station has to identify itself with the club's callsign). So, although it is probably legal, you should check if there are any specific restrictions on operating unattended stations in your country.&lt;/p&gt;&#xA;" OwnerUserId="614" LastActivityDate="2014-09-23T14:46:55.337" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2172" PostTypeId="1" AcceptedAnswerId="2210" CreationDate="2014-09-23T17:32:40.563" Score="6" ViewCount="779" Body="&lt;p&gt;What is the best omni-directional antenna design for any RC flying objects?&#xA;Many times I've lost signal and my copter falls due to lost signal. (Using default antenna).&#xA;Since the receiver and transmitter position will be in different altitude, I can not imagine what is the best antenna design for this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am thinking about the receiver would use their default antenna, and the transmitter will use DIY omni antenna, is by this way it can control better?&lt;/p&gt;&#xA;" OwnerUserId="1196" LastEditorUserId="218" LastEditDate="2014-09-30T22:10:00.260" LastActivityDate="2014-10-08T03:47:31.310" Title="2.4 GHz Antenna for RC copter" Tags="&lt;antenna&gt;&lt;uhf&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2173" PostTypeId="1" AcceptedAnswerId="2197" CreationDate="2014-09-23T22:32:31.237" Score="5" ViewCount="178" Body="&lt;p&gt;I am a radio amateur licenced in Canada and a member of a local club station. At a recent meeting, someone asked me whether they could operate at the station if they did not have a radio licence. I am aware that, in general, an unlicenced individual can operate an amateur station with the supervision and presence of a licenced operator, but I am not sure how this rule specifically applies to club stations.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is an unlicenced individual permitted to operate radio equipment at a club station if supervised by a licenced club member?&lt;/li&gt;&#xA;&lt;li&gt;Assuming that an unlicenced individual can use a club station under supervision, which callsign do they use to identify on the air - that of the club station, or that of the licenced supervisor?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="1579" LastEditorUserId="29" LastEditDate="2014-09-24T07:09:23.157" LastActivityDate="2014-09-29T15:00:54.870" Title="Can unlicensed users operate at a Canadian club station?" Tags="&lt;legal&gt;&lt;canada&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2174" PostTypeId="1" AcceptedAnswerId="2177" CreationDate="2014-09-24T02:46:36.597" Score="4" ViewCount="4028" Body="&lt;p&gt;Geographical restrictions exist for various frequencies in terms of usage in the &lt;strong&gt;United States of America&lt;/strong&gt; as stipulated in &lt;a href=&quot;http://www.law.cornell.edu/cfr/text/47/97.303&quot; rel=&quot;nofollow&quot;&gt;47 CFR 97.303&lt;/a&gt;.  What are the restrictions, if any remain, in terms of geography where you cannot use all or part of the 70cm band?  I thought there was an ARRL map that showed this once upon a time but I cannot locate it.  The relevant US regulation just defines things by metes, bounds, and lines that I'm having a hard time conceptualizing.&lt;/p&gt;&#xA;" OwnerUserId="406" LastEditorUserId="29" LastEditDate="2014-09-24T13:10:18.070" LastActivityDate="2017-05-26T20:17:15.230" Title="What are the geographical restrictions in using the 70cm band in the United States of America?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;70cm-band&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2175" PostTypeId="5" CreationDate="2014-09-24T11:19:10.207" Score="0" Body="" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-09-24T11:19:10.207" LastActivityDate="2014-09-24T11:19:10.207" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2176" PostTypeId="4" CreationDate="2014-09-24T11:19:10.207" Score="0" Body="Questions relating to the remote control of radio equipment, including transceivers, rotators, and tuners, as well as remote control of equipment used specifically to facilitate radio communications." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-09-24T11:19:10.207" LastActivityDate="2014-09-24T11:19:10.207" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2177" PostTypeId="2" ParentId="2174" CreationDate="2014-09-24T16:21:12.390" Score="6" Body="&lt;p&gt;Canada does not include 420-430 MHz in their band plan for 70cm, so the restriction is in place to prevent interference to Canadian radio services. There are also a few other geographical restrictions that are made explicit. This excerpt from FCC Part 97.303(m) — In the 70 cm band:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(1) No amateur station shall transmit from north of Line A in the 420-430 MHz segment. See §97.3(a) for the definition of Line A.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(2) Amateur stations transmitting in the 420-430 MHz segment must not cause harmful interference to, and must accept interference from, stations authorized by the FCC in the land mobile service within 80.5 km of Buffalo, Cleveland, and Detroit. See §2.106, footnote US230 for specific frequencies and coordinates.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Here's a rough representation of &quot;Line A&quot; on the map (&lt;a href=&quot;http://www.hamradioschool.com/t1a06-interference-in-70-cm-band/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hamradioschool.com/t1a06-interference-in-70-cm-band/&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/BOHWG.jpg&quot; alt=&quot;FCC 97.3 Line A&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is additional information on the quiet zone info at: &lt;a href=&quot;http://www.micronetcom.com/quiet_zones.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.micronetcom.com/quiet_zones.html&lt;/a&gt; in Section E. &quot;420-450 MHz band&quot;.&lt;/p&gt;&#xA;" OwnerUserId="1579" LastEditorUserId="6742" LastEditDate="2017-05-26T20:17:15.230" LastActivityDate="2017-05-26T20:17:15.230" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2178" PostTypeId="2" ParentId="2172" CreationDate="2014-09-25T00:27:08.233" Score="2" Body="&lt;p&gt;A ground plane antenna might be what you want here; according to this post (&lt;a href=&quot;http://www.rcgroups.com/forums/showthread.php?t=1333382&quot; rel=&quot;nofollow&quot;&gt;http://www.rcgroups.com/forums/showthread.php?t=1333382&lt;/a&gt;), which also includes a detailed tutorial with pictures, the multiple grounded elements change the propagation pattern of the antenna and send the signal upward. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This sort of design is good for both the transmitter and the receiver, and can be cut for 2.4 GHz without much trouble (the elements will be about an inch each). I'll paraphrase and adapt the tutorial's building instructions for the substrate-type antenna (built on a small piece of protoboard) here:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Calculate the quarter-wave length of each element as (2808/f) inches or (71323/f) millimeters, where f is the frequency in MHz you want to operate on.&lt;/li&gt;&#xA;&lt;li&gt;Cut several pieces of wire at this length to use as your elements. You can use any gauge wire you have available (low gauge is typically better as it is sturdier - 12 AWG is my recommendation). Cut any number of pieces you want, between 4 and 9. 5 is a good number because the construction is easy while still having a good radiation pattern.&lt;/li&gt;&#xA;&lt;li&gt;Solder all but one of your quarter-wave wires to a common point in the center of a small piece of protoboard (onto the copper side). The wires should be spaced an equal angle apart (e.g. for four wires, they should be joined to make an 'X'). &lt;/li&gt;&#xA;&lt;li&gt;Drill a small hole in the substrate as close to the solder point as possible, large enough to pass the coaxial cable's center conductor through. &lt;/li&gt;&#xA;&lt;li&gt;Strip the insulation off your coaxial cable, pass the center conductor through the bottom of the board, and solder the last quarter-wave element to the center conductor so the wire rests directly above the solder point. Then solder the cable's shield to the solder point on the substrate.&lt;/li&gt;&#xA;&lt;li&gt;Measure all the elements to be sure they are exactly the length you calculated above, as measured from the center of the antenna, and trim if necessary (especially check the center one since you have joined it to a second wire).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The author's notes indicate that this antenna performs well when the four center conductors are supporting the antenna at a 120-degree angle from the ground plane (this is why you use low-gauge wire here, for strength).&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-09-25T00:27:08.233" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2179" PostTypeId="2" ParentId="2144" CreationDate="2014-09-25T01:40:04.503" Score="2" Body="&lt;p&gt;From &lt;a href=&quot;http://urgentcomm.com/mag/radio_demystifying_rf_attenuators&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://urgentcomm.com/mag/radio_demystifying_rf_attenuators&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;...[A]ttenuators are symmetrical, provided the input and output impedances are&#xA;  the same. In applications where attenuators are used as impedance-matching&#xA;  devices, they are not symmetrical.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A typical attenuator circuit will be a purely resistive network - for example, this pi-network for a balanced attenuator:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/o5CNy.jpg&quot; alt=&quot;Pi-Type balanced attenuator&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since both cables coming out of your attenuator are identical and use the same connector, we expect Z1 and Z2 (the impedance seen &quot;looking into&quot; each cable) to be equal. What makes things interesting in your case is where the variable resistor (controlled by the knob) is connected. In that case, the most likely design for your attenuator is this T-type network:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/v8f3J.jpg&quot; alt=&quot;T-Type balanced attenuator&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case the most likely location for the variable resistor is at component Rp, so no matter how the attenuator is connected, both Z1 and Z2 are symmetric and Rp performs exactly the same function in the circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To summarize, for this particular case there should be no difference with respect to how your attenuator is connected - either &quot;direction&quot; will be fine. In general, it will depend on the input impedance at each connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: The answer so far assumes ideal components, but for a real attenuator the power rating of each resistor is important as well. For a mass-produced attenuator, the most likely case is that the power rating is symmetric as well (although presumably unknown). This is because of the &quot;economy of scale&quot;: using two identical resistors in a circuit is cheaper and easier to design (you only have to do power calculations once but you can use the circuit twice) than using two resistors intentionally chosen to have different power ratings. For this specific attenuator, since it may have been manufactured as a bespoke (one-off) system and not sold commercially, this may not necessarily apply, but it is still the most likely case for the same reason (it's easier to design the circuit that way).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Image credit: &lt;a href=&quot;http://en.wikipedia.org/wiki/File:Pi_type_balanced_attenuator_circuit.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://en.wikipedia.org/wiki/File:Pi_type_balanced_attenuator_circuit.jpg&lt;/a&gt;, &lt;a href=&quot;http://en.wikipedia.org/wiki/File:T_type_balanced_attenuator_circuit.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://en.wikipedia.org/wiki/File:T_type_balanced_attenuator_circuit.jpg&lt;/a&gt;)&lt;/p&gt;&#xA;" OwnerUserId="1579" LastEditorUserId="1579" LastEditDate="2014-09-25T14:25:55.617" LastActivityDate="2014-09-25T14:25:55.617" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2180" PostTypeId="1" AcceptedAnswerId="2196" CreationDate="2014-09-25T04:16:16.377" Score="10" ViewCount="255" Body="&lt;p&gt;Until I can get an HF rig, I've been using my HT through a local repeater IRLP node. I've successfully made a few contacts doing that, but I recently noticed that Palmer Station in Antartica has an IRLP Node (#8838) listed. I tried making a contact, but it kept saying &quot;connection error&quot; and disconnected. The last time, I heard someone, but too scratchy to understand shortly before it disconnected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, is it accept to call that node without a prior arrangement, or it is reserved for the private use of the Hams living there?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it is, is there any special procedure for doing such a contact?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did verify that their local time was 10 am - 12 pm during the time I was trying to make contact.&lt;/p&gt;&#xA;" OwnerUserId="1534" LastEditorUserId="29" LastEditDate="2014-09-25T08:18:02.713" LastActivityDate="2014-09-29T14:23:59.957" Title="Is calling the Palmer Station (Antarctica) via IRLP without prior arrangements acceptable practice?" Tags="&lt;internet&gt;&lt;dx&gt;&lt;etiquette&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2181" PostTypeId="1" AcceptedAnswerId="2182" CreationDate="2014-09-25T16:10:04.027" Score="5" ViewCount="302" Body="&lt;p&gt;I want to establish a microwave link (1.2GHz) between two stations using antennas with a directional radiation pattern. The stations have a clear line of sight to each other. Each antenna is attached to a half-duplex transceiver operating at relatively low power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antennas are too far apart to align &quot;by eye&quot;, what's a good procedure to use that is applicable in general for aligning this type of antenna system? I want to align the antennas for best reception (maximum signal intensity, low error rate) at each station when the other transmits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assume there is a licensed operator present at each station who can manually operate the transceivers, and that the operators can communicate with each other in real time (with cell phones). Additionally, the transceivers are software-defined radio devices, so it is very easy to get FFT/waterfall displays from them, as well as test with non-standard signals. However, a procedure that uses a common modulation scheme to align (e.g. narrowband FM voice) would be preferred.&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-09-25T17:18:42.370" Title="What is a general procedure for aligning directional antennas?" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2182" PostTypeId="2" ParentId="2181" CreationDate="2014-09-25T17:18:42.370" Score="4" Body="&lt;p&gt;&lt;strong&gt;Use a map and a compass.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Really. It doesn't have to be more involved than that. As long as we are talking about line of sight propagation, that should be close enough to get you well within the ballpark unless this is about &lt;em&gt;hugely&lt;/em&gt; directional antennas (as in, beam widths of perhaps 10° or narrower in the horizontal plane), and even if that's the case, it gets you a start.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pull out a map (it can be digital or paper-based), mark the two antenna locations, and determine the magnetic bearing between them. For what can be reliably achieved on UHF, I'd probably just use a straight ruler and not worry about things like great circle propagation. Then, bring a compass to each location and aim the antennas in roughly the correct direction: as good as you can, but not fretting over half a degree. Make a test transmission, note the signal strength, adjust one of the antennas by some reasonable fraction of the beam width in either direction, try it again, rinse and repeat until you hit peak signal strength. Mark the exact antenna direction somehow in case someone bumps it, go back in and have a cup of your hot beverage of choice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to save time and the remote station can transmit continuously, after doing the coarse general-direction aiming you can even simply have the remote station transmit (using a fixed-power fixed-frequency mode; I would suggest a continuous carrier in CW mode, technically N0N) then gradually aim for the strongest received signal. When you are done, switch roles such that the receiving station becomes the transmitting station, and perform the process all over again. All you would need for that is a reliable means of measuring the received signal strength to sufficient precision.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2014-09-25T17:18:42.370" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2183" PostTypeId="1" AcceptedAnswerId="2245" CreationDate="2014-09-25T22:54:19.207" Score="7" ViewCount="142" Body="&lt;p&gt;Some of the members at my local radio club are interested in working with D-Star. Since the equipment is very expensive, it was proposed that the club purchase and operate one rig collectively. Is there any precedent for registering a club station's callsign on the D-Star network for use by its members? What would be the potential consequences for operating in this manner? I don't know whether D-Star would be treated different from other transmission modes, hence the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that we are not setting up a D-Star repeater, only a terminal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the purposes of regulatory laws, we are located in Canada.&lt;/p&gt;&#xA;" OwnerUserId="1579" LastEditorUserId="29" LastEditDate="2014-09-26T12:33:36.367" LastActivityDate="2014-10-21T15:09:13.150" Title="Can club stations register callsigns on the D-Star network?" Tags="&lt;legal&gt;&lt;digital-modes&gt;&lt;canada&gt;&lt;d-star&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2184" PostTypeId="5" CreationDate="2014-09-26T02:56:54.907" Score="0" Body="&lt;p&gt;D-STAR is a packet radio-based system that uses digital transmission modes to encode and send voice and data. D-STAR repeaters can be linked over the Internet to provide coverage across wide geographical areas. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition to repeaters, D-STAR also uses Internet-only connection points known as a &quot;reflector&quot;. Reflectors allow several repeaters to be linked so that when one user transmits into the repeater, their voice is broadcast to all linked repeaters as well as anyone connected to and listening on the reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Almost all D-STAR compatible equipment is sold by Icom. For more information, Icom offers a general introduction and some background material on their website: &lt;a href=&quot;http://www.icomamerica.com/en/products/amateur/dstar/dstar/&quot; rel=&quot;nofollow&quot;&gt;http://www.icomamerica.com/en/products/amateur/dstar/dstar/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also possible to connect to the D-STAR system over the Internet without a radio with the use of a device called a &quot;DV Dongle&quot;. This device is sold at &lt;a href=&quot;http://www.dvdongle.com&quot; rel=&quot;nofollow&quot;&gt;http://www.dvdongle.com&lt;/a&gt; and contains the proprietary voice codec chip used in D-STAR radios. The dongle can be used with the DVTool software available from &lt;a href=&quot;http://opendstar.org/tools/&quot; rel=&quot;nofollow&quot;&gt;http://opendstar.org/tools/&lt;/a&gt; in order to connect to D-STAR repeaters and reflectors without using a radio.&lt;/p&gt;&#xA;" OwnerUserId="1579" LastEditorUserId="1579" LastEditDate="2014-09-30T22:24:29.897" LastActivityDate="2014-09-30T22:24:29.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2185" PostTypeId="4" CreationDate="2014-09-26T02:56:54.907" Score="0" Body="Amateur radio operation on the Internet-enabled D-STAR digital voice and data protocol." OwnerUserId="1579" LastEditorUserId="1579" LastEditDate="2014-09-26T21:08:43.593" LastActivityDate="2014-09-26T21:08:43.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2186" PostTypeId="1" CreationDate="2014-09-26T03:13:54.417" Score="3" ViewCount="1062" Body="&lt;p&gt;I am a new HAM trying to design a small, cheap 2m receiver.  I've been looking up different circuits and homebrew tutorials, but the closest I seem to find to what I'm looking for seems to always use a MK484 chip.  That chip covers 150 kHz to 3 MHz.  I'm only licensed as a Technician at the moment and can't use any bands within that range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a chip out there that fits into a simple, one chip circuit, but reaches 144 MHz?  If not, is there a homebrew design out there you could recommend?  If not, where do I start?&#xA;I'm looking for something simple to get me started.&lt;/p&gt;&#xA;" OwnerUserId="1631" LastEditorUserId="873" LastEditDate="2014-09-26T07:51:43.250" LastActivityDate="2014-09-26T07:51:43.250" Title="2m Homebrew Receiver - Chip for frequency" Tags="&lt;diy&gt;&lt;receiver&gt;&lt;equipment-design&gt;&lt;vhf&gt;&lt;2m-band&gt;" AnswerCount="2" CommentCount="2" ClosedDate="2014-09-26T08:04:30.980" ContentLicense="CC BY-SA 3.0" />
  <row Id="2187" PostTypeId="2" ParentId="2186" CreationDate="2014-09-26T03:56:43.327" Score="-1" Body="&lt;p&gt;Try a Google search for &quot;2m receiver chip&quot; or &quot;receiver chip 144MHz&quot;. Then refine your search to Images - you should see thumbnail pictures of schematics.&lt;br&gt;&#xA;After that, it's a matter of browsing for a circuit that looks small &amp;amp; simple...&#xA;&lt;a href=&quot;http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/RX_144MHz_FM_PU2XJE.gif&quot; rel=&quot;nofollow&quot;&gt;like&lt;/a&gt; &lt;a href=&quot;http://taha.islam-piers.org/circuits/2M-Circuits/modified-ckt-with-squelch.htm&quot; rel=&quot;nofollow&quot;&gt;these&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="1610" LastActivityDate="2014-09-26T03:56:43.327" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2188" PostTypeId="2" ParentId="2186" CreationDate="2014-09-26T05:34:03.520" Score="1" Body="&lt;p&gt;The Si4460 chipset may help you with some low power stuff and alternatively small USB-based SDR receivers like the R820T could be of use..&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2014-09-26T05:34:03.520" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2189" PostTypeId="2" ParentId="34" CreationDate="2014-09-28T19:58:42.850" Score="3" Body="&lt;p&gt;I think there might be confusion between RF ground, counterpoise, and electrical safety grounding.  I am going to restrict my answer to RF ground (but, the word counterpoise is often used for the same thing).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a perfectly balanced antenna, such as a Dipole at its resonant frequency, there is no need for an RF ground since no current would flow to the RF ground (like I said, in a perfect balanced antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a perfectly unbalanced antenna, such as a 1/4-wave vertical, an RF ground (aka counterpoise) is absolutely necessary to &quot;complete&quot; the antenna and make it whole.  As they say, the ground image of your quarter wave antenna is the &quot;other half&quot; of the antenna and current will flow in this ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why a quarter wave antenna needs some sort of RF ground counterpoise made of conductors to make this current flow less lossy.  Just relying on the ground itself results in a very lossy other half of your vertical and thus definitely not as efficient.  In general, the more you can make the ground a good conductor (more radials, etc.) then the more efficient your antenna will be.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given these two extremes, the need for an RF ground depends on all kinds of situations where the actual individual antenna geometry, height above ground, other nearby conductors, and so on come into play.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your dipole antenna is not balanced for example, then common-mode current will flow down your feed line and radiate or enter into your shack and cause other problems.  Making sure that your equipment is well grounded may help eliminate some of this RFI but it is best to eliminate the common-mode currents using an RF choke at the antenna feed point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In summary, for good balanced antennas such as dipoles, Yagis, and similar geometries, RF grounding should not be necessary.  If you have an unbalanced antenna like a vertical or a single long-wire antenna, or an inverted-L, or similar then a ground plane (RF ground) is required for efficient operating.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2014-09-28T19:58:42.850" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2190" PostTypeId="2" ParentId="2154" CreationDate="2014-09-28T22:08:37.333" Score="1" Body="&lt;p&gt;The &lt;a href=&quot;http://www.wpc.dot.gov.in/DocFiles/Sublegislation/GSR_526.doc&quot; rel=&quot;nofollow&quot;&gt;Wireless Telegraph Act 1973&lt;/a&gt; says: “&lt;strong&gt;The receiving apparatus of any wireless telegraph shall not be used for any unauthorized reception or interception of wireless telegraph communications&lt;/strong&gt;”. I suspect this is more to do with listening in to police or aircraft radio (for which &lt;a href=&quot;http://news.bbc.co.uk/2/hi/uk_news/england/bristol/somerset/8528476.stm&quot; rel=&quot;nofollow&quot; title=&quot;Two UK plane-spotters arrested in India … charged with intercepting communications&quot;&gt;two UK plane-spotters [were] charged with intercepting communications&lt;/a&gt; in 2010) rather than listening to amateur transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Act is quite similar to the UK law, which still forbids listening to unauthorized transmissions (UK guidance: &lt;a href=&quot;http://stakeholders.ofcom.org.uk/enforcement/spectrum-enforcement/guidance&quot; rel=&quot;nofollow&quot; title=&quot;Guidance on Receive-Only Radio Scanners&quot;&gt;Guidance on Receive-Only Radio Scanners&lt;/a&gt;). I &lt;em&gt;suspect&lt;/em&gt; you'll be okay listening to amateur radio as an &lt;a href=&quot;http://www.dxing.com/swlintro.htm&quot; rel=&quot;nofollow&quot; title=&quot;SWL&quot;&gt;SWL&lt;/a&gt;, but I don't know for sure.&lt;/p&gt;&#xA;" OwnerUserId="90" LastActivityDate="2014-09-28T22:08:37.333" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2192" PostTypeId="1" AcceptedAnswerId="2194" CreationDate="2014-09-29T02:49:26.503" Score="2" ViewCount="86" Body="&lt;p&gt;In Canada do I need an Advanced license to use a D-Star DVAP hotspot?&lt;/p&gt;&#xA;" OwnerUserId="1427" LastEditorUserId="1579" LastEditDate="2014-09-30T08:56:30.450" LastActivityDate="2014-09-30T08:56:30.450" Title="In Canada do I need an Advanced license to use a DVAP?" Tags="&lt;legal&gt;&lt;canada&gt;&lt;d-star&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2193" PostTypeId="2" ParentId="2154" CreationDate="2014-09-29T05:08:12.687" Score="2" Body="&lt;p&gt;Two things here. Per the 1984 amendment to the Amateur Service Act vide. &lt;a href=&quot;http://www.wpc.dot.gov.in/DocFiles/Para%202%20a.doc&quot; rel=&quot;nofollow&quot;&gt;GSR#1225/84&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;An SWL licence is required to use a communications receiver. This is available 'upon request' from the WPC for a nominal fee&lt;/li&gt;&#xA;&lt;li&gt;&lt;strike&gt;&lt;em&gt;Caveat Emptor&lt;/em&gt; This category of licence may have been superseded by a later amendment made in 2009/2010; let me ask around and get back to you&lt;/strike&gt; &lt;/li&gt;&#xA;&lt;li&gt;The &lt;a href=&quot;http://www.wpc.dot.gov.in/DocFiles/Para%202%20b.doc&quot; rel=&quot;nofollow&quot;&gt;2009/2010 amendment to the Amateur Service act&lt;/a&gt; indeed does away with the SWL category. The former 'low privilege' categories namely Grade.II, Grade.II (restricted - VHF/UHF only), and SWL are now amalgamated into a newly created 'Restricted' category. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;IMHO this means you may not listen in. But don't take my word for it (+: &lt;a href=&quot;http://wpc.gov.in/content/11_1_ContactUs.aspx&quot; rel=&quot;nofollow&quot;&gt;phone the WPC/Amateur Section&lt;/a&gt; (the number is listed on the WPC website)&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="5" LastEditDate="2014-10-06T04:03:22.760" LastActivityDate="2014-10-06T04:03:22.760" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2194" PostTypeId="2" ParentId="2192" CreationDate="2014-09-29T13:24:44.933" Score="1" Body="&lt;p&gt;The DVAP hotspot uses (or at least can be configured to use) simplex operation. This means that both your radio and the DVAP hotspot use the same frequency to transmit and receive. If you are operating with the DVAP in simplex mode, it does not count as a repeater and so &lt;strong&gt;an Advanced Qualification is not necessary.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-09-29T13:24:44.933" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2195" PostTypeId="2" ParentId="1367" CreationDate="2014-09-29T14:02:12.323" Score="4" Body="&lt;p&gt;The KX3 receiver is a software defined radio SDR. The IF filters are made in the software. Since software IF filters are steeper than crystal filters the crystal filters are not necessary anymore. Another advantage is that SDR IF filter width is  continuous adjustable. But band filters and audio filters are still LC filters like in the past. That has not changed. The IF of the KX3 is at audio frequencies. It is not really direct conversion but it is similar. These audio frequencies are fed to usually a soundcard and then the computer does the IF filtering demodulation etc. &#xA;The KX3 is the first software defined radio that does not require a external computer. It’s a great radio. I ‘m never gonna sell it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More info: &lt;a href=&quot;http://en.wikipedia.org/wiki/Software-defined_radio&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Software-defined_radio&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1639" LastEditorUserId="1639" LastEditDate="2014-09-29T14:14:11.017" LastActivityDate="2014-09-29T14:14:11.017" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2196" PostTypeId="2" ParentId="2180" CreationDate="2014-09-29T14:23:59.957" Score="3" Body="&lt;p&gt;So far as I can tell, it's perfectly acceptable to use the Palmer IRLP node, but realize that it might not be connected all the time. It is probably a similar situation to the ISS, you just frequently won't get a response.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-09-29T14:23:59.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2197" PostTypeId="2" ParentId="2173" CreationDate="2014-09-29T15:00:54.870" Score="3" Body="&lt;p&gt;I forwarded this question to the Radio Amateurs of Canada Regulatory Advisor and received an interpretation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To summarize as direct responses to my original questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Yes, an unlicenced individual can use equipment at a club station if supervised by a qualified operator.&lt;/li&gt;&#xA;&lt;li&gt;A non-qualified operator should use the call sign an authorized operator would use when operating the station. For a club station, this would generally be the club station call sign.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Excerpts from the interpretation (paraphrased):&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;em&gt;Regarding the first question, about whether an unlicenced individual can operate under supervision.&lt;/em&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The Industry Canada regulatory document RIC-3 contains the following comment:&lt;/p&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;&lt;strong&gt;1.5 Non-Qualified Persons&lt;/strong&gt;&lt;/p&gt;&#xA;    &#xA;    &lt;p&gt;Non-qualified persons may use an amateur radio station provided a qualified operator is in attendance to perform the control functions. &lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;  &#xA;  &lt;p&gt;[T]here is no distinction as to the type of station, so &lt;strong&gt;this applies to &#xA;  clubs as well as personal stations.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;em&gt;Regarding the second question, about identification.&lt;/em&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;...I didn't find any Industry Canada guidelines. Certainly &lt;strong&gt;the non-qualified operator should use the call sign an authorized operator would use when operating the station.&lt;/strong&gt;&#xA;  This is usually the club station call sign when operating the club station.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;That is what I have seen done on field days at &quot;Get-On-The-Air&quot; stations,&#xA;  at stations in museums and science centres, as well as stations operating&#xA;  with a club or RAC call sign for contests.&#xA;  The call sign was not changed when different radio amateurs took turns supervising.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;[T]he move away from licensing...to certifying radio amateurs left the status of station call signs a little more murky.&#xA;  I am not aware of any firm rules on this so you can use common sense.&#xA;  If your practice is for the ham operating the club station to sometimes use their own call this could be an option when a ham is supervising non-qualified operators.&#xA;  However, &lt;strong&gt;the club call sign is always correct.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(thanks to Glenn MacDonnell VE3XRA for providing this interpretation)&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-09-29T15:00:54.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2198" PostTypeId="1" CreationDate="2014-09-29T20:21:26.867" Score="4" ViewCount="218" Body="&lt;p&gt;I am designing an antenna for a device and was hoping to gain some insight in the correct design direction for the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The Idea:&lt;/strong&gt; A receiver &amp;amp; antenna that fits in a 6&quot; diameter by 3&quot; deep cylinder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Known:&lt;/strong&gt; Frequencies range from 162.400 to 162.550 MHz. The signal will not be coming directly from the top or bottom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Goals:&lt;/strong&gt; Design the “best” antenna I can given my knowledge of the direction the signal will be coming from, the size constraint of the enclosure and the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any advice, recommendations, and/or help would be greatly appreciated. I am specifically interested in the physical layout/design of the antenna.(For example coil wire cylinder)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Thoughts:&lt;/strong&gt; My gut feeling is to enclose the maximum area possible with the antenna. From my initial research the length is not as important as I had previously thought which lead me to start to ponder this even more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/PSb0g.png&quot; alt=&quot;enter image description here&quot;&gt;&#xA;&lt;strong&gt;Notes:&lt;/strong&gt; I like math if you are so inclined :)&lt;/p&gt;&#xA;" OwnerUserId="1640" LastActivityDate="2014-09-30T23:49:14.463" Title="Antenna Design for specific directions" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;physics&gt;&lt;loop-antenna&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2199" PostTypeId="2" ParentId="2198" CreationDate="2014-09-29T22:25:51.817" Score="0" Body="&lt;p&gt;Try a rubber ducky antenna. Heavily loaded vertical whip like you see on handheld transceivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/LQ92t.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2014-09-29T22:25:51.817" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2200" PostTypeId="2" ParentId="2198" CreationDate="2014-09-30T00:18:55.790" Score="2" Body="&lt;p&gt;Given the shape and desired band, I think what you want is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Loop_antenna#Small_loops&quot; rel=&quot;nofollow&quot;&gt;small loop antenna&lt;/a&gt;. This would simply be a coil of wire wound in the shape of your cylinder, preferably with a capacitor wired in parallel to make it resonant at the desired frequency and match impedance to the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Small loops have the type of radiation pattern you are looking for (in the plane of the loop). What makes it a “small&quot; loop is that it is small, both in radius and total length of wire, compared to the wavelength; we can see that a radius of 3 inches (0.07 m) is smaller than your wavelength of 1.85 m but I don't know whether it'd be better to make it even smaller than that. If the loop is too large, comparable to the wavelength, it will have the opposite of the pattern you desire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Small loops are inefficient antennas not suitable for transmitting, which is why transmitters don't use them to avoid having long antennas sticking out, but since you are receiving that doesn't matter unless your desired signals are particularly weak.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are commonly seen as antennas for AM broadcast receivers, either as external wire loops on a frame (oriented vertically to have some directionality; in your case, you would orient the loop horizontally because you are asking for an omnidirectional pattern), or very small internal “loopstick” antennas (wire coiled around a ferrite rod).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Disclaimer: I have made no systematic study of antenna theory; I have never built a small loop antenna; there's probably some caveats I haven't mentioned. I'm writing this answer because I haven't seen a better one yet and I'm reasonably confident the basic idea is OK.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-09-30T23:49:14.463" LastActivityDate="2014-09-30T23:49:14.463" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2202" PostTypeId="1" AcceptedAnswerId="2203" CreationDate="2014-09-30T10:55:52.603" Score="2" ViewCount="3025" Body="&lt;p&gt;I am using a crystal to transmit morse codes, and I am using Kenwood radio receiver to obtain the signal. It receives the signal with a lot of noise, though we can figure out the morse code sound. I want to convert this signal into a series of 0s and 1s so that i can use a code to convert the signal to human readable text.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone please help, or should I use some other alternative to convert the noisy morse code sound file into decoded text file, please suggest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NOTE:- I do want to know the steps behind, so that i can write the code myself.&lt;/p&gt;&#xA;" OwnerUserId="1641" LastEditorUserId="1641" LastEditDate="2014-09-30T16:16:34.620" LastActivityDate="2017-09-23T16:27:01.850" Title="Decoding the Morse code" Tags="&lt;cw&gt;&lt;kenwood&gt;&lt;software&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2203" PostTypeId="2" ParentId="2202" CreationDate="2014-09-30T16:27:03.240" Score="7" Body="&lt;h2&gt;If you would like to decode Morse code with an existing program:&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;My personal recommendation is &lt;a href=&quot;http://www.w1hkj.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fldigi&lt;/a&gt;, which is a software modem that runs on most major operating systems, including Windows and Linux. Fldigi has a modem for &quot;CW&quot; (Continuous Wave), which can both send and receive Morse code. The program uses your sound card to communicate with your radio. To receive and decode Morse code, you would connect your receiver's audio output to your computer's microphone port. Then Fldigi will be able to listen to the Morse code sounds and can decode the transmission for you.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;If you would like to write your own program to decode Morse code:&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;You will need to read about some digital signal processing techniques to do this. Ultimately there are a few different ways to approach the problem. Let's assume you already have some way of getting audio from your receiver into your computer (maybe you have pre-recorded some transmission and saved it to disk, or maybe you are doing this in real time by reading sound input data).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your first goal is to implement some kind of algorithm to detect the presence or absence of the carrier frequency (which is being turned off and on in order to send Morse code). You should learn about something called the Discrete Fourier Transform (DFT); &lt;a href=&quot;https://ccrma.stanford.edu/~jos/st/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this online textbook&lt;/a&gt; is a lot of material, but if you are interested in digital signal processing and working with radio or audio signals on your computer, you will get a lot out of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple explanation of the DFT is that it takes a sequence of audio samples and tells you the amplitude (and phase) of certain frequencies of your signal. For your application, you can calculate the DFT over your sample buffer and then look for the output value that corresponds to the frequency of the Morse code tone. If the value corresponds to a large amplitude then you know the carrier frequency was present in your sample. If the value you see corresponds to a small amplitude then the carrier was not present. This will allow you to detect the Morse code sound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simpler way to do this is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Goertzel_algorithm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Goertzel algorithm&lt;/a&gt;. The Goertzel algorithm is essentially a single tone detector. It calculates only one frequency component of the DFT. If you know ahead of time what the audio frequency of your Morse code tone will be, you can implement a Goertzel filter that will detect the presence or absence of that tone (as illustrated in &lt;a href=&quot;http://www.embedded.com/design/real-world-applications/4401754/Single-tone-detection-with-the-Goertzel-algorithm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this white paper&lt;/a&gt;). However this is a more advanced way to do it, although it is more efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have detected the presence or absence of the Morse code sound, you will need an algorithm to figure out whether a dot or a dash is being sent. One algorithm to do this is that used by the &lt;a href=&quot;http://wwwhome.cs.utwente.nl/~ptdeboer/ham/rscw/algorithm.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;RSCW program&lt;/a&gt;. The disadvantage of this algorithm is that it does not tolerate poorly sent code. It will do well when detecting Morse code that is sent by a machine, but humans cannot send with perfect timing and so this algorithm may not do well. However it is a place to start and maybe you will think of some ways to improve it, or come up with something yourself depending on the results you get from the carrier detection step.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Writing a Morse decoder from scratch is challenging, especially if you have never done digital signal processing before. However it is a rewarding experience and will teach you a lot about DSP and integrating software with radio. If you have some programming experience, you should not have any trouble finding libraries for audio input and DFT in your favourite language.&lt;/p&gt;&#xA;" OwnerUserId="1579" LastEditorUserId="10402" LastEditDate="2017-09-23T16:27:01.850" LastActivityDate="2017-09-23T16:27:01.850" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2206" PostTypeId="2" ParentId="2146" CreationDate="2014-10-02T12:32:03.470" Score="1" Body="&lt;p&gt;Passive repeaters can and do work but require some experimentation.  Since there are large losses, you may have to use several beam antennas to make it work.  Why not have a separate transmitter for building A and beam a signal (on a different channel) over to building B and then redistribute Bs signal with a high gain antenna?  Since Bs coverage is only in one corner of the building, why not use another beam antenna to illuminate the rest of B?  An omni wouldn't make much sense to me in that case.&lt;/p&gt;&#xA;" OwnerUserId="1652" LastActivityDate="2014-10-02T12:32:03.470" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2207" PostTypeId="2" ParentId="2172" CreationDate="2014-10-03T20:45:44.863" Score="1" Body="&lt;p&gt;The &quot;best&quot; antenna depends strongly on the relative orientation of the transmitter and receiver. Since any RC craft is constantly and rapidly changing orientation, there is no antenna that will work well for the entire flight. A dipole, ground plane antenna, loop, or any other basic antenna will all perform about the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two reasons one antenna can not work in all orientations:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly, a truly &lt;a href=&quot;http://en.wikipedia.org/wiki/Isotropic_radiator&quot; rel=&quot;nofollow&quot;&gt;isotropic antenna&lt;/a&gt; can not exist. This means that any antenna you can build will have at least one null, a direction in which it does not radiate. When your craft is in the transmitter's null (or the transmitter is in the receiver's null), you may lose the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, transverse waves such as EM radiation used in radio all have a &lt;a href=&quot;http://en.wikipedia.org/wiki/Polarization&quot; rel=&quot;nofollow&quot;&gt;polarization&lt;/a&gt;. When these polarizations are orthogonal, no power transfer occurs between transmitter and receiver. Again, signal is lost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution is to have &lt;em&gt;multiple&lt;/em&gt; antennas, in different orientations. This is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_diversity&quot; rel=&quot;nofollow&quot;&gt;antenna diversity&lt;/a&gt;. If the receiver or transmitter have a number of antennas available, each in a different orientation, thus radiating in different directions, with different polarizations, then it's possible to select the one that is best at each instant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, this means your communications system has some way to determine what is &quot;best&quot;. This can be done, for example, if periodically the transmitter sends a known synchronization sequence. The receiver can then analyze signals from each antenna, and using a method like &lt;a href=&quot;http://en.wikipedia.org/wiki/Regression_analysis&quot; rel=&quot;nofollow&quot;&gt;regression analysis&lt;/a&gt;, calculate coefficients for each antenna that result in the best fit to the expected synchronization signal. The received signals from each antenna are then multiplied by these coefficients and added, and the result is used to recover the message. In the context of antenna arrays, this is called &lt;a href=&quot;http://www.antenna-theory.com/arrays/weights/mmse.php&quot; rel=&quot;nofollow&quot;&gt;minimum mean square error weighting&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern wireless communications protocols, such as &lt;a href=&quot;http://en.wikipedia.org/wiki/IEEE_802.11n-2009&quot; rel=&quot;nofollow&quot;&gt;802.11n&lt;/a&gt; or &lt;a href=&quot;http://en.wikipedia.org/wiki/LTE_Advanced&quot; rel=&quot;nofollow&quot;&gt;LTE Advanced&lt;/a&gt; do this. Usually it goes by the name of &lt;a href=&quot;http://en.wikipedia.org/wiki/MIMO&quot; rel=&quot;nofollow&quot;&gt;MIMO&lt;/a&gt;, which is, in essence, what I described. MIMO also includes some more advanced techniques like &lt;a href=&quot;http://en.wikipedia.org/wiki/Spatial_multiplexing&quot; rel=&quot;nofollow&quot;&gt;spatial multiplexing&lt;/a&gt; for increased data rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, no commodity RC system does this to my knowledge. As such you may be left to  implement it yourself.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-10-03T20:45:44.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2209" PostTypeId="2" ParentId="2146" CreationDate="2014-10-04T16:25:49.587" Score="3" Body="&lt;p&gt;Trying to extend coverage in this fashion isn't worth doing. Even with highly directional antennas, most of the power transmitted doesn't end up in the receiver. Thus, your &quot;repeater&quot;, which is really two antennas joined by coax, has very little power available to transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can do some math.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's assume that your buildings are 40m apart, and your transmit power is 20 dBm (the legal maximum on 2.4 GHz in the US). Let's further assume that you have 24 dBi antennas on the Wi-Fi AP and your repeater. We can use the &lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;Friis transmission equation&lt;/a&gt; to calculate how much of that power is received by the repeater:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 20 \:\mathrm{dBm}\&#xA; + 24 \:\mathrm{dBi} \&#xA; + 24 \:\mathrm{dBi} \&#xA; + 147.6 \&#xA; - 20 \log_{10}(40\:\mathrm m \cdot 2.4 \:\mathrm{GHz}) \&#xA; = -4 \:\mathrm{dBm}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, assuming no losses in your repeater, it makes the 20 dBm transmitter look like a -4 dBm transmitter. Or put another way, the repeater introduces 24 dB of loss. By &lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;reciprocity&lt;/a&gt;, this loss works in the other direction as well: how ever much power is received by the repeater from the clients, the AP will see it as 24 dB less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides that loss, which is substantial but maybe not impossible, you have a new problem. While the AP might hear the nodes in the external building, other nodes won't. This is called the &lt;a href=&quot;http://en.wikipedia.org/wiki/Hidden_node_problem&quot; rel=&quot;nofollow noreferrer&quot;&gt;hidden node problem&lt;/a&gt;, and will result in transmit collisions which seriously degrade the performance of your network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To solve your problem, best is to run Ethernet to the building, and install an AP. If Ethernet is not possible, then use a cross-band Wi-Fi repeater. They are available for $100 at any big-box electronics store, where they are usually called a &quot;range extender&quot;. You are going to spend at least that on antennas and coax for your passive repeater solution, which will not work as well.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Regarding which omni-directional antenna is better, it's impossible to say, generally. An &lt;a href=&quot;http://en.wikipedia.org/wiki/Isotropic_radiator&quot; rel=&quot;nofollow noreferrer&quot;&gt;isotropic antenna&lt;/a&gt; has exactly 0 dBi gain, by definition. However, such an isotropic antenna can not be physically realized, the closest we can come is a dipole, which is 2.15 dBi in free space. Of course, the presence of the Earth or anything else conductive around the antenna changes that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, any antenna with higher gain works by being more directional. Remember that the antenna's radiation is a three-dimensional function. An &quot;omnidirectional&quot; antenna radiates equally in all directions in one dimension (typically, azimuth), but this says nothing about how it radiates at different angles of elevation. Thus, an antenna that is still &quot;omnidirectional&quot; but quotes a higher gain is either:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;an outright lie by Chineese marketing departments, or&lt;/li&gt;&#xA;&lt;li&gt;radiating more horizontally, and less up or down.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Depending on the orientation of your antenna, and the location of your radios, this could be good or bad. What you want to do is minimize radiation in directions where you don't want coverage, which will in turn maximize radiation in directions where you do want coverage. Which antenna achieves that depends on your particular environment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-10-04T19:58:46.350" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2210" PostTypeId="2" ParentId="2172" CreationDate="2014-10-05T17:44:28.000" Score="3" Body="&lt;p&gt;Wow... The simplest antenna (not entirely that simple :) for your use is the quadrifilar helicoidal antenna (abbreviated QFH or QHA). This antenna has a few characteristics which are important to you:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It radiates in a very wide angle (over 180 degrees) &lt;/li&gt;&#xA;&lt;li&gt;It has circular polarization (which makes the position of the RC plane irrelevant)&lt;/li&gt;&#xA;&lt;li&gt;It doesn't have a 'dead' spot above it, like the groundplane&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Note that both the transmitter and the receiver have to be fitted with the same antenna type (and the 'twist' should be the same, i.e. both should be left- or right-hand circularity).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have a look at: &lt;a href=&quot;http://jcoppens.com/ant/qfh/index.en.php&quot; rel=&quot;nofollow&quot;&gt;http://jcoppens.com/ant/qfh/index.en.php&lt;/a&gt;  There's a calculator to design one for you. There are also a couple of references for more information. I just noticed that the link to the photos is missing - I'll update the page in a moment. Here's a link to pictures of a Vaisala GPS QFH antenna for 1.6 GHz: &lt;a href=&quot;http://jcoppens.com/ant/qfh/index.en.php&quot; rel=&quot;nofollow&quot;&gt;http://jcoppens.com/ant/qfh/index.en.php&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2014-10-08T03:47:31.310" LastActivityDate="2014-10-08T03:47:31.310" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="2211" PostTypeId="1" AcceptedAnswerId="2212" CreationDate="2014-10-06T14:48:01.157" Score="3" ViewCount="634" Body="&lt;p&gt;I am living in crowed area of a city. It is impossible for me to set up an antenna outside the apartment. I receive signal inside the room.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a funcube dongle pro+ and some RTLSDR, the picture shows the antenna I am using:&#xA;&lt;img src=&quot;https://i.stack.imgur.com/4vkzG.jpg&quot; alt=&quot;http://imgur.com/iT8iVCf&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any suggestion on improving the reception by using other antenna of similar size or amplifier?&lt;/p&gt;&#xA;" OwnerUserId="353" LastEditorUserId="1579" LastEditDate="2014-10-21T19:11:04.907" LastActivityDate="2014-10-21T19:11:04.907" Title="Idea for better reception in crowded city" Tags="&lt;antenna&gt;&lt;receiver&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2212" PostTypeId="2" ParentId="2211" CreationDate="2014-10-06T18:20:49.423" Score="6" Body="&lt;p&gt;You have a tough problem, because you are surrounded by many noise sources.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, you should make sure that you have eliminated &lt;strong&gt;your own apartment's noise&lt;/strong&gt;, because it is likely to interfere no matter what antenna you use.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Try shutting off all electronic equipment (including e.g. fluorescent or LED lights, and power adapters plugged into the wall) in your apartment, and use a laptop &lt;strong&gt;on battery power with no other equipment connected&lt;/strong&gt; for receiving. If this cuts down the noise to a worthwhile degree, then you can start looking for individual problematic devices. In some cases, placing ferrite beads on cables connected to the noisy equipment can help (make sure they are appropriate for filtering the frequencies of the noise).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The computer the dongle is attached to can itself be a source of noise. Try using a different computer. Try connecting the dongle to a self-powered USB hub instead of directly from the computer, and move it away from the computer.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Now, if your primary noise sources are not nearby, here are some antenna-based approaches for getting more signal and less noise:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Use a &lt;strong&gt;directional antenna pointed at the transmitter&lt;/strong&gt;, thus attenuating all noise sources which don't happen to be in the same direction as the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This requires you to know where to point the antenna — if you're trying to receive transmissions from moving vehicles, for example, it will not help. It will also not work as well indoors since the surrounding building will affect the effective pattern.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Use an antenna which is significantly better at receiving the desired signal &lt;em&gt;frequency&lt;/em&gt; than other frequencies — that is, have the antenna act as a &lt;strong&gt;filter&lt;/strong&gt;. Your receiver hardware already contains a filter to suppress signals outside the band you tune to, but no filter is perfect, so you will always get some out-of-band leakage. Using an appropriately tuned antenna also improves the antenna's efficiency at collecting the desired signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you specify &quot;30-400 MHz&quot;, which is a very wide band, this implies an antenna which is &lt;em&gt;adjustable&lt;/em&gt;, tunable, in some way. A telescoping whip as seen on portable FM radios is a common example of such an antenna; a telescoping whip with an adjustable loading coil is even narrower; there are also loop antennas which are tuned by variable capacitors, and many other possible designs. (The antenna you have is a fixed-length whip with a fixed loading coil.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a tunable antenna and a SDR receiver, there is a simple way to determine when you have it adjusted correctly: watch the noise floor of the spectrum and adjust until it is at a &lt;em&gt;maximum&lt;/em&gt; — ideally, there should be a visible hump with a peak at your desired frequency and dropping off elsewhere, but whether you can actually see the hump on-screen depends on the bandwidth of the antenna being smaller than the bandwidth of your spectrum plot. (Yes, it sounds funny to be tuning for maximum noise, but the antenna doesn't distinguish in-band signal from in-band noise, so we're also tuning for maximum signal.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, using a tunable antenna is somewhat in conflict with the above option of using a directional antenna, because directional antennas have more complex shapes with multiple dimensions that must be adjusted for the desired frequency, else they will not have the expected radiation pattern.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Receive the noise and subtract it.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This method is good when there is a single, known noise source, and works by using a secondary antenna which is set up to receive the noise source better than your primary antenna. The signal from this antenna is then subtracted from the main antenna's signal (or rather, added but opposite in phase), thus removing that specific noise source. This requires equipment to provide phase and amplitude adjustments to obtain good cancellation — &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-1026&quot; rel=&quot;nofollow&quot;&gt;the MFJ Enterprises MFJ-1026 is an example&lt;/a&gt; (I am not recommending this product).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This method is fundamentally the same thing as building a specialized directional antenna optimized for not receiving the noise source, but more modular and adjustable.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2014-10-08T01:34:10.243" LastActivityDate="2014-10-08T01:34:10.243" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2213" PostTypeId="1" AcceptedAnswerId="2214" CreationDate="2014-10-07T16:55:24.797" Score="4" ViewCount="3771" Body="&lt;p&gt;I am trying to receive a station, but I can only barely hear it through the noise. Will doing anything that increases the signal from my antenna help, such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;using a more sensitive antenna&lt;/li&gt;&#xA;&lt;li&gt;adding a preamplifier&lt;/li&gt;&#xA;&lt;li&gt;installing a shorter or higher quality feedline&lt;/li&gt;&#xA;&lt;li&gt;improving SWR, thus reducing losses&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-10-11T13:25:17.667" Title="Can I improve reception with a more sensitive antenna / preamplifier / better feedline?" Tags="&lt;receiver&gt;&lt;noise&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2214" PostTypeId="2" ParentId="2213" CreationDate="2014-10-07T16:55:24.797" Score="7" Body="&lt;p&gt;These things will significantly help under one condition: the RF noise floor is below the receiver's noise floor. This is almost never the case on HF, where low-noise amplifiers are easy and atmospheric noise is high. On VHF and UHF the natural noise floor is lower, and low-noise receivers are more expensive, so it is possible but not guaranteed. It will depend on the quality of your receiver, and noise in that particular location and frequency. The 2.4 GHz ISM band, for example, is &lt;em&gt;full&lt;/em&gt; of man-made noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a simple test: compare the noise floor with a dummy load versus an antenna connected. If the noise floor is higher with the antenna connected, then the RF noise floor is higher than the receiver noise floor, and a more sensitive antenna will not significantly help. In this case you need to investigate ways of increasing the signal to noise ratio in other ways, such as by increasing transmitter power or installing directional antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we think of the radio's output as the combination of three components:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The desired signal, free of any noise&lt;/li&gt;&#xA;&lt;li&gt;RF noise received by the antenna. This could be atmospheric noise, interfering stations, or noise from electronics, powerlines, etc.&lt;/li&gt;&#xA;&lt;li&gt;Noise generated internally by the receiver. That is, thermal noise in its resistors, its amplifiers, etc.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;We might think that the radio is contributing noise in all circumstances, and if we can boost the noise and signal from the antenna, then the radio's noise becomes relatively less significant, and SNR is improved. However, when the RF noise floor is above the receiver's noise floor, that improvement will be negligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is that RF noise and the receiver's noise are &lt;a href=&quot;http://en.wikipedia.org/wiki/Uncorrelated&quot; rel=&quot;nofollow noreferrer&quot;&gt;uncorrelated&lt;/a&gt;, like random white noise. As I will demonstrate, even if the RF noise is just a little above the receiver noise, because of the way uncorrelated noise adds, the receiver's noise will make very little contribution to the total noise. As such, there is very little to be gained by reducing the receiver's noise, or equivalently, making the antenna &quot;louder&quot;.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Orly? Show Me The Math.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Uncorrelated noise powers simply add:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_1 + P_2 = P_\text{total} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But in this context our noise power is probably specified in dBm. To add these, we must first convert them to plain milliwatts (without the decibel), add, then convert back to dBm:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 10 \log_{10}\left( 10^{P_\text{1(dBm)}/10} + 10^{P_\text{2(dBm)}/10} \right) = P_\text{total(dBm)} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for example, if the receiver noise floor is -96 dBm and the RF noise floor is 6 dB above that (-90 dBm), then the total noise floor is effectively:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 10 \log_{10}\left( 10^{-90\:\mathrm{dBm}/10} + 10^{-96\:\mathrm{dBm}/10} \right) = -89.03\:\mathrm{dBm} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the receiver's noise, which was only 6 dB below the RF noise, increased the total noise floor from -90 to -89.03, or by 0.97 dB. Not a terribly big deal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An equivalent, and perhaps more intuitive way to think about it is this: uncorrelated noise amplitudes (that is, RMS voltage or current) add like orthogonal vectors:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/XVrGc.png&quot; alt=&quot;adding vectors&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Geometrically, we can see that as the RF noise becomes greater than the receiver noise, the triangle gets increasingly thin, and the total noise isn't much longer than the RF noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mathematically, that's:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ E_\text{total} = \sqrt{E_1^2 + E_2^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And we can convert between dBm ($P_\text{dBm}$) and RMS volts ($E_\text{RMS}$), assuming a 50Ω impedance, with:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA; E_\text{RMS} &amp;amp;= \sqrt{&#xA;  0.001\:\mathrm{W}&#xA;  \cdot 50 \:\Omega&#xA;  \cdot 10^{P_\text{dBm}/10}&#xA;}\\&#xA;&amp;amp;= \sqrt{0.05\:\mathrm V^2} \cdot 10^{P_\text{dBm}/20} \\&#xA;&amp;amp;\approx 0.2236\:\mathrm V \cdot 10^{P_\text{dBm}/20}&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;P_\text{dBm} &amp;amp;= 10 \log_{10}\left(&#xA;  E_\text{RMS}^2 / (0.001\:\mathrm W \cdot 50 \:\Omega)&#xA;\right)\\&#xA;&amp;amp;= 20 \log_{10}(E_\text{RMS}) - 10 \log_{10}(0.05\:\mathrm V^2) \\&#xA;&amp;amp;\approx 20 \log_{10}(E_\text{RMS}) + 13.01&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One might still say that even this small improvement is an improvement, and is worth doing. However, there are two circumstances where that would be a bad idea:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly, if you are increasing your antenna sensitivity by adding a preamplifier, this preamplifier will introduce noise of its own. Unless the preamplifier's &lt;a href=&quot;http://en.wikipedia.org/wiki/Noise_figure&quot; rel=&quot;nofollow noreferrer&quot;&gt;noise figure&lt;/a&gt; is lower than that of your receiver, or your receiver lacks sufficient gain to bring the RF noise floor above the receiver noise floor, then you are making things worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, increasing the signal+noise from the antenna by any means in many situations &lt;em&gt;decreases&lt;/em&gt; &lt;a href=&quot;http://en.wikipedia.org/wiki/Dynamic_range&quot; rel=&quot;nofollow noreferrer&quot;&gt;dynamic range&lt;/a&gt;. This is especially a concern with SDRs that are recently popular, because they have such a wide receive bandwidth. Consider that at some point, this signal in an SDR ends up at an analog to digital converter. Say it's a 16 bit converter. If the noise floor is high (because the antenna is so sensitive), then the least significant of these bits contain nothing but noise, and are essentially wasted. Furthermore, you approach overloading the converter and running into &lt;a href=&quot;http://en.wikipedia.org/wiki/Clipping_(audio)&quot; rel=&quot;nofollow noreferrer&quot;&gt;clipping&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-10-11T13:25:17.667" LastActivityDate="2014-10-11T13:25:17.667" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2215" PostTypeId="1" AcceptedAnswerId="2249" CreationDate="2014-10-07T21:24:15.190" Score="2" ViewCount="3856" Body="&lt;p&gt;On my car's LW receiver, I have a severe case of alternator whine, especially when the headlights are on. It has become worse over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have read that capacitors might help.&#xA;However, two things remain unclear to me:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Of what value should these capacitors be?&lt;/li&gt;&#xA;&lt;li&gt;Where in the vehicle should these be installed? A schematic drawing would be very much appreciated.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="250" LastEditorUserId="76" LastEditDate="2017-07-09T17:33:13.173" LastActivityDate="2017-07-17T14:01:25.170" Title="How to eliminate alternator whine?" Tags="&lt;mobile&gt;&lt;rfi&gt;&lt;capacitance&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2216" PostTypeId="1" CreationDate="2014-10-08T21:24:50.263" Score="2" ViewCount="135" Body="&lt;p&gt;Morse Code is defined by most dictionaries in terms of sequences of short and long signals.  What would be the most common or most descriptive terminology for un-timed written or printed code, where the encodings are not longer or shorter?  (I would like to differentiate this written form from actual CW, as calling both Morse Code could be confusing in some situations, such as when describing good/bad methods of transcription.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Examples of written code include encoding using UTF8 or ASCII 45 and 46 (both 1 character in length), or using the two phonetic terms &quot;dit&quot; and &quot;dah&quot; (both 3 characters in length).&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2014-10-11T21:36:41.883" Title="Terminology for written &quot;CW-like&quot; Code?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2218" PostTypeId="2" ParentId="2216" CreationDate="2014-10-08T21:33:04.770" Score="0" Body="&lt;p&gt;Perhaps &lt;em&gt;&lt;a href=&quot;https://en.wiktionary.org/wiki/digital&quot; rel=&quot;nofollow noreferrer&quot;&gt;digital&lt;/a&gt; code&lt;/em&gt; might be an appropriate term?&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;digital&lt;/strong&gt; (not comparable)&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Having to do with digits (fingers or toes); performed with a finger.&lt;/li&gt;&#xA;&lt;li&gt;Property of representing values as discrete numbers rather than a continuous spectrum.&lt;/li&gt;&#xA;&lt;li&gt;Of or relating to computers or the Information Age.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This neatly encompasses an allusion to actual CW which is traditionally performed by moving your finger.&lt;/p&gt;&#xA;" OwnerUserId="1183" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-10-08T21:33:04.770" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2220" PostTypeId="2" ParentId="2216" CreationDate="2014-10-11T21:36:41.883" Score="1" Body="&lt;p&gt;You could perhaps name it a &lt;em&gt;transcription&lt;/em&gt; or &lt;em&gt;written representation&lt;/em&gt;, or something similar. Maybe it has a specific name (e.g., related to the paper tapes where Morse code was transcribed in the early days of telegraphy), but I failed to find it&lt;/p&gt;&#xA;" OwnerUserId="614" LastActivityDate="2014-10-11T21:36:41.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2221" PostTypeId="2" ParentId="221" CreationDate="2014-10-12T00:09:47.173" Score="3" Body="&lt;p&gt;I've included Locator based calculations in PyHamTools - an open source python Library, which is easy to use:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's as easy as this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;from pyhamtools.locator import calculate_distance, latlong_to_locator&#xA;locator1 = latlong_to_locator(48.52, 9.375)&#xA;locator2 = latlong_to_locator(-32.77, 152.125) &#xA;distance = calculate_heading(locator1, locator2)&#xA;print(&quot;%.1fkm&quot; % distance)&#xA;16466.4km&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;For more examples and the documentation check out:&#xA;&lt;a href=&quot;http://pyhamtools.readthedocs.org/en/latest/index.html&quot; rel=&quot;nofollow&quot;&gt;http://pyhamtools.readthedocs.org/en/latest/index.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1689" LastEditorUserId="1689" LastEditDate="2014-10-15T23:49:28.687" LastActivityDate="2014-10-15T23:49:28.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2222" PostTypeId="1" AcceptedAnswerId="2225" CreationDate="2014-10-13T03:51:49.697" Score="2" ViewCount="1215" Body="&lt;p&gt;I have two 50 ohm characteristic impedance cables of which I need to shorten their length to compact my design. (put everything in to a box)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cables I need to shorten are the GPS &amp;amp; GSM antenna cables.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do not know if I can cut it from 12cm off the antenna and join it to the 50 ohm characteristic impedance . Currently each is about 3.5m. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neither antennas have a LNA nor a SAW filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I cut it off near the receiver and solder it to the 50ohm characteristic impedance cable coming off from my PCB, would that create any problems? &lt;/p&gt;&#xA;" OwnerUserId="1694" LastActivityDate="2014-10-13T17:39:05.237" Title="How to shorten the length 50 ohm characteritic impedance antenna cable" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;coaxial-cable&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2223" PostTypeId="2" ParentId="2222" CreationDate="2014-10-13T04:16:59.083" Score="2" Body="&lt;p&gt;The length of a coaxial cable does not affect its impedance. If you cut a piece of 50 ohm cable anywhere, both pieces will be 50 ohm cables. For a uniform transmission line, the characteristic impedance is not a function of length; it will only depend on parameters such as the radii of the conductors and the type of insulation or dielectric used between the conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;References: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Characteristic_impedance&quot; rel=&quot;nofollow&quot;&gt;Characteristic impedance (Wikipedia)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.allaboutcircuits.com/vol_2/chpt_14/3.html&quot; rel=&quot;nofollow&quot;&gt;Characteristic impedance and transmission lines (AllAboutCircuits)&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-10-13T04:16:59.083" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2224" PostTypeId="2" ParentId="2222" CreationDate="2014-10-13T07:00:05.273" Score="2" Body="&lt;p&gt;You would just be rotating around the smith chart, so the SWR as such will not change, just the angle of your impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just cut the transmission line and shorten it. The transmission line loss will cause more problems than the eventual impedance change.&lt;/p&gt;&#xA;" OwnerUserId="1695" LastActivityDate="2014-10-13T07:00:05.273" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2225" PostTypeId="2" ParentId="2222" CreationDate="2014-10-13T16:39:18.177" Score="3" Body="&lt;p&gt;A 50Ω cable is still a 50Ω cable, regardless of length. &quot;50Ω&quot; refers to the &lt;a href=&quot;http://en.wikipedia.org/wiki/Characteristic_impedance&quot; rel=&quot;nofollow&quot;&gt;characteristic impedance&lt;/a&gt;, which is a function of the dielectric used in the cable, and its cross-sectional geometry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the problem: the solder joint you might make between two transmission lines won't have a 50Ω characteristic impedance. If you do it you will want to keep your connection as short as possible. Even then, by introducing this discontinuit, you will be introducing &lt;a href=&quot;http://en.wikipedia.org/wiki/Reflections_of_signals_on_conducting_lines&quot; rel=&quot;nofollow&quot;&gt;reflections on the cable&lt;/a&gt; which causes additional loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe that's a problem, and maybe not. Depends on how efficient you need the transmission line to be. If you are just receiving you could try it and see. If you are also transmitting you could still try it and see, but depending on how robust your transmitter is it might be damaged. Probably it won't.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, you could join the cables with connectors. Coaxial connectors are designed to maintain the same characteristic impedance through the connection, avoiding the reflection problem.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-10-13T17:39:05.237" LastActivityDate="2014-10-13T17:39:05.237" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2226" PostTypeId="1" CreationDate="2014-10-13T22:22:37.557" Score="5" ViewCount="1186" Body="&lt;p&gt;I have a &lt;a href=&quot;http://www.rfstuff.com/manuals/805Dman.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kenwood TK-805D&lt;/a&gt; commercial radio, which I am using for UHF ham operation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For repeater usage, with AllStar, IRLP, and Echolink, I need a DTMF mic for it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did a search on the internet, and found this pinout:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/AYeWB.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The diagram claims that the radio has an 8v potential at pin 1, but I measured 12 instead. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://highfields-arc.co.uk/constructors/micwiring/k/kwt/kwt19.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;This link&lt;/a&gt; displays a confusion between knowing if it is 12v or 8v output, and says from different sources, mixed data is shown. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am looking at a &lt;a href=&quot;https://web.archive.org/web/20141013221846/http://www.ebay.com/itm/KAWAMALL-DTMF-6Pin-Mic-For-Kenwood-TK-7360-TK8360-TKR730-TKR-830-TKR-740-TKR-840-/121439698322?pt=US_Radio_Comm_Antennas&amp;amp;hash=item1c465ebd92&quot; rel=&quot;nofollow noreferrer&quot;&gt;particular DTMF mic found on eBay,&lt;/a&gt; which claims it works on 6-pin Radios, but doesn't have the TK-805 on the list. Weirdly, it has the TK-760 on the list, which is on the pinout diagram above. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would the mic above work? If not, is there any other mics at a reasonable price that would work, if not, I have some adjustable voltage regulators that I could calibrate for 8 volts, and solder it in at the 12v pin. Would one of those work?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="22" LastEditDate="2014-12-01T23:58:49.363" LastActivityDate="2021-01-23T01:45:42.150" Title="Is the Kawamall DMTF 6pin microphone usable with the Kenwood TK-805D radio?" Tags="&lt;kenwood&gt;&lt;microphone&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2227" PostTypeId="2" ParentId="2113" CreationDate="2014-10-14T05:02:24.617" Score="1" Body="&lt;p&gt;The recording in rtl_sdr can be played in gqrx by following the below procedure carefully:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Either &lt;strong&gt;A&lt;/strong&gt; or &lt;strong&gt;B&lt;/strong&gt;: &lt;strong&gt;(A)&lt;/strong&gt; Create a gnu radio program with the flowchart posted by @jcoppens above.  A copy can be found at the rtl-sdr site, but as &lt;a href=&quot;https://stackoverflow.com/questions/25587959/bin-to-cfile-flowgraph-for-grc-3-7-2-1/25655984#comment41364278_25655984&quot;&gt;mentioned on Stack Overflow, the rtl-sdr .grc file uses obsolete modules and must be rewritten&lt;/a&gt; in the new gnu radio companion (30 min to 1 hour work) &lt;strong&gt;OR&lt;/strong&gt; &lt;strong&gt;(B)&lt;/strong&gt; Compile and use the &lt;a href=&quot;https://gist.github.com/DrPaulBrewer/917f990cc0a51f7febb5&quot; rel=&quot;nofollow noreferrer&quot;&gt;Linux GCC program I wrote for rtlsdr-to-gqrx conversion&lt;/a&gt;.  &lt;/li&gt;&#xA;&lt;li&gt;Make a SDR recording with rtl_sdr and &lt;strong&gt;take note of the actual sample rate&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;Run the conversion mentioned in step #1.  Note:  the output .cfile will be more than 4x the size of the input .raw file. &lt;/li&gt;&#xA;&lt;li&gt;Start gqrx, go to the &quot;Configure I/O Devices&quot; dialog&lt;/li&gt;&#xA;&lt;li&gt;Set the &quot;Device String&quot; to read the .cfile generated in step 3 and set the rate from step #2&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;IMPORTANT&lt;/strong&gt;: Set the &quot;Sample Rate&quot; box immediately below the device string  to the rate from step #2.  This seems redundant (the rate is also in device string) but apparently is not (as of October 2014).  If left blank, the sample rate will be set to something you might not want (I suspect 96k) and override the device string setting &lt;em&gt;even though the line appears blank&lt;/em&gt;.  Leaving this line blank can lead to slow audio.&lt;/li&gt;&#xA;&lt;li&gt;Click the &quot;Power&quot; button in gqrx and playback will begin.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="70" LastEditorUserId="-1" LastEditDate="2017-05-23T12:37:22.373" LastActivityDate="2014-10-17T04:24:15.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2229" PostTypeId="2" ParentId="2076" CreationDate="2014-10-14T07:43:52.433" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;1) listen to FM radio, while scanning 2 meters and 70cm bands at background (as in hiking)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;nope (and only 1 band scanning at a time)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;2) set scan hi and low limit, via keypad and/or pc software, so that scan within ham band only (instead full transceiver freq range)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;nope, but you can limit the ranges using chirp&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;3) scan 2m and 70cm 'simultaneously'. Does it has one or two or three (U V FM) real receiver inside only? Or, it can jump quickly between freq and appear to be 'simultaneous'?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;nope. Internally there's only one VFO, so even dual watch is just hopping between bands, not listening on both simultaneously&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;4) what the pc software can do where keypad programming cannot? Seem NAME, ANI are some, from web posts reading, what others?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;using chirp you can set the frequency range (even down to 200mhz / up to 599mhz, but the radio won't work well and you can even burn the PA by txing there)&#xA;setting cross band repeater on memories (to work satellites)&#xA;These are the two more useful on top on my head right now&lt;/p&gt;&#xA;" OwnerUserId="1701" LastEditorUserId="29" LastEditDate="2014-10-14T08:48:34.800" LastActivityDate="2014-10-14T08:48:34.800" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2230" PostTypeId="1" AcceptedAnswerId="2236" CreationDate="2014-10-17T22:19:02.577" Score="10" ViewCount="593" Body="&lt;p&gt;I spent a bit of time researching SDRs, mostly looking into the possibility of building an all-FPGA-based TRX. There are a lot of commercial ready solutions; some are cheap, some not, but they all tend to be operating from 50/70 MHz frequency range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am a complete newbie in RF processing and what escapes me is: if the circuitry is able to process a 50 MHz signal, why can't it do the same with lower frequencies? Is it some physics limitation? I guess it must be — otherwise everyone would advertise an operatiing range from DC to X MHz. Or is operating on lower frequencies uninteresting to everybody except hams?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is TRX specific — not RX only.&lt;/p&gt;&#xA;" OwnerUserId="1719" LastEditorUserId="76" LastEditDate="2014-10-20T19:01:11.167" LastActivityDate="2015-07-12T20:24:10.007" Title="Why are commercial SDRs so limited in operating frequency?" Tags="&lt;hf&gt;&lt;software-defined-radio&gt;&lt;transceiver&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2231" PostTypeId="2" ParentId="1674" CreationDate="2014-10-18T00:00:36.920" Score="5" Body="&lt;p&gt;After a long time pondering about this, I realized the trick. The first problem is that I had a version 3v of the router, and I installed the &lt;code&gt;3g&lt;/code&gt; version of the software. That doesn't work at all. I should have used the file &lt;code&gt;bbhn-1.1.2-wrt54g-2.4-squashfs.bin&lt;/code&gt; instead of &lt;code&gt;bbhn-1.1.2-wrt54g3g-2.4-squashfs.bin&lt;/code&gt; (For the latest, probably something different for the older version).&#xA;As for fixing the problem, the solution involved was the following&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Set up a fixed IP address on a computer.&lt;/li&gt;&#xA;&lt;li&gt;Run &lt;code&gt;&quot;ping -t 192.168.0.1&quot;&lt;/code&gt;, which will continually ping the router.&lt;/li&gt;&#xA;&lt;li&gt;Reboot the router, holding the reset button.&lt;/li&gt;&#xA;&lt;li&gt;If you see a message with &lt;code&gt;&quot;TTL=100&quot;&lt;/code&gt;, you've hit the mark! Otherwise, keep trying.&lt;/li&gt;&#xA;&lt;li&gt;Run the &lt;code&gt;tftp&lt;/code&gt; program, available in a few places on the Internet.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;All in all, this recovery process worked, and I'm (Only 6 months late...) able to get the mesh network up. Now, to figure out some applications for it...&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="1246" LastEditDate="2015-02-01T19:47:00.270" LastActivityDate="2015-02-01T19:47:00.270" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2232" PostTypeId="2" ParentId="2174" CreationDate="2014-10-18T00:07:01.707" Score="1" Body="&lt;p&gt;There are additional power output restrictions in California (around Beale AFB) and in Cape Cod, where the AF have PAVE PAWS radar installations that also use 70cm. The restrictions AFAIK are only mutual agreements with local ham operators and clubs (particularly clubs running 70cm repeaters), and have not been formalized as part of the FCC regulations. Here's an article here for more info: &lt;a href=&quot;http://www.arrl.org/news/new-70-cm-coordination-agreement-reached-for-new-england&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/news/new-70-cm-coordination-agreement-reached-for-new-england&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="252" LastActivityDate="2014-10-18T00:07:01.707" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2234" PostTypeId="1" AcceptedAnswerId="3586" CreationDate="2014-10-18T15:46:00.073" Score="1" ViewCount="139" Body="&lt;p&gt;Is there a way to log contacts over a mesh network, using TQSL/ LOTW/ EQSL/ etc? If so, how should it be logged.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-03-09T05:29:04.387" Title="Logging a contact over a mesh network" Tags="&lt;logging&gt;&lt;mesh-network&gt;&lt;lotw&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2236" PostTypeId="2" ParentId="2230" CreationDate="2014-10-19T15:47:50.517" Score="5" Body="&lt;p&gt;Largely it has to do with filtering and bandwidth. An ADC requires an &lt;a href=&quot;http://en.wikipedia.org/wiki/Anti-aliasing_filter&quot; rel=&quot;nofollow&quot;&gt;anti-aliasing filter&lt;/a&gt; to remove all input frequency components that are more than half the sample rate. Otherwise, these higher frequency components get aliased onto lower harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, if I have a 40 kHz ADC, it should be able to handle at its input anything from 0 to 20 kHz. If I should feed it 25 kHz, it will appear as 15 kHz...not what you want in a radio. The anti-aliasing filter removes everything above 20 kHz so this does not happen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I have that same 40 kHz ADC, but I want to handle radio frequencies above 20 kHz, I need to introduce a &lt;a href=&quot;http://www.radio-electronics.com/info/rf-technology-design/mixers/rf-mixers-mixing-basics-tutorial.php&quot; rel=&quot;nofollow&quot;&gt;mixer&lt;/a&gt;. This is a device that shifts one band of frequencies to another. So, if I want to work in the 40 meter band, I need a mixer that converts frequencies around 7 MHz down to 0 - 20 kHz for my ADC. However, my mixer will again require filters to avoid &lt;a href=&quot;http://en.wikipedia.org/wiki/Intermodulation&quot; rel=&quot;nofollow&quot;&gt;intermodulation&lt;/a&gt; and aliasing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All of this is equally applicable to transmitting -- the process is identical, except in the other direction. However, some stages of the transmitter must handle high power, which makes the filters larger and more costly. This is why it can seem easier to find a receiver with coverage of more bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So greatly simplified, the coverage of an SDR, or in fact, any radio, is determined by what filters it includes. As an example, take a look at the &lt;a href=&quot;http://fivedash.com/index.php?main_page=product_info&amp;amp;products_id=6&quot; rel=&quot;nofollow&quot;&gt;SoftRock RX Ensemble&lt;/a&gt;, which includes filters for four bands, and by changing the component values, can be built to cover LF or HF. With a sufficient selection of filters it becomes possible to cover the entire RF spectrum, but this would be expensive.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-10-22T21:55:08.197" LastActivityDate="2014-10-22T21:55:08.197" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2237" PostTypeId="1" CreationDate="2014-10-19T20:39:35.890" Score="2" ViewCount="96" Body="&lt;p&gt;I was reading &lt;a href=&quot;https://ham.stackexchange.com/questions/1660/what-is-the-difference-between-radio-scanner-and-receiver&quot;&gt;What is the difference between radio scanner and receiver?&lt;/a&gt; and I saw that it said that the scanner continues on scanning after a radio transmission is over.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I find a frequency that I want to listen to, can I tell the scanner to stay put even after the transmission ends?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that is the case, then what becomes the difference between a scanner and a receiver with a &quot;scanning&quot; feature?&lt;/p&gt;&#xA;" OwnerUserId="1724" LastActivityDate="2014-10-21T16:21:20.053" Title="How does a scanner work" Tags="&lt;receiver&gt;" AnswerCount="2" CommentCount="2" ClosedDate="2014-10-24T08:49:50.573" ContentLicense="CC BY-SA 3.0" />
  <row Id="2238" PostTypeId="1" CreationDate="2014-10-19T20:47:54.083" Score="1" ViewCount="8689" Body="&lt;p&gt;I saw here &lt;a href=&quot;http://www.radioreference.com/apps/db/?ctid=442#cid-15933&quot; rel=&quot;nofollow&quot;&gt;Table of broadcasting stations&lt;/a&gt; that there is a mode called DMR (under Atlanta Technical College). What is DMR and if I buy a scanner (I am thinking about the Icom IC-R6) could I listen to those stations?&lt;/p&gt;&#xA;" OwnerUserId="1724" LastEditorUserId="29" LastEditDate="2014-10-20T08:27:05.817" LastActivityDate="2014-10-21T22:40:20.373" Title="What is DMR and can I listen to it?" Tags="&lt;receiver&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2239" PostTypeId="1" CreationDate="2014-10-19T21:23:44.880" Score="1" ViewCount="301" Body="&lt;p&gt;I am considering purchasing the Icom IC-R6. One of the determining factors, and my questions is, can it can receive &lt;a href=&quot;http://www.radioreference.com/apps/db/?ctid=442#cid-15933&quot; rel=&quot;nofollow&quot;&gt;FMN&lt;/a&gt; (I believe that is narrowband FM)?&lt;/p&gt;&#xA;" OwnerUserId="1724" LastEditorUserId="29" LastEditDate="2014-10-20T08:26:46.127" LastActivityDate="2014-10-20T08:26:46.127" Title="Can the IC-R6 scanner receive NFM" Tags="&lt;receiver&gt;&lt;fm&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2240" PostTypeId="2" ParentId="2239" CreationDate="2014-10-19T22:39:35.807" Score="2" Body="&lt;p&gt;From the &lt;a href=&quot;http://www.icomamerica.com/en/products/receivers/handheld/r6/specifications.aspx&quot; rel=&quot;nofollow&quot;&gt;ICOM IC-R6 specifications&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Mode: AM, FM, WFM&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&quot;FMN&quot; is indeed short for &quot;Narrowband FM&quot;, so this scanner, which receives &quot;FM and WFM&quot;, will pick up such a station perfectly fine. (WFM here stands for &quot;Wideband FM&quot;, which is typically used by commercial broadcast radio.)&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-10-19T22:39:35.807" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2241" PostTypeId="2" ParentId="2238" CreationDate="2014-10-20T00:20:44.123" Score="3" Body="&lt;p&gt;DMR stands for Digital Mobile Radio. It is a digital voice and data protocol that can be used unlicenced or commercially. You can peruse &lt;a href=&quot;http://www.etsi.org/website/document/technologies/leaflets/digitalmobilradio.pdf&quot; rel=&quot;nofollow&quot;&gt;a standards document&lt;/a&gt; if you like. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the major issues preventing you from using just any scanner from tuning to DMR is that &lt;a href=&quot;http://www.dvsinc.com/press/PR20063.htm&quot; rel=&quot;nofollow&quot;&gt;the vocoder being used is AMBE&lt;/a&gt;, which is proprietary. Your scanner, in addition to needing support for digital voice, must have an AMBE codec chip in order for you to be able to decode (and, by extension, listen to) the audio data. (The ICOM IC-R6, sadly, supports neither. You will have to find a different product, such as a DMR handheld, if you are interested in receiving this mode.)&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-10-20T00:20:44.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2242" PostTypeId="2" ParentId="2230" CreationDate="2014-10-20T08:04:35.127" Score="1" Body="&lt;p&gt;What I've found is: a lot of the SDR designs are sending data. A fair amount of it, too.&lt;br&gt;&#xA;The bandwidth of a signal increases when it sends more / faster information, and the bandwidth of HF signals is rather limited.&lt;br&gt;&#xA;Higher bands have more space, and the added incentive of &quot;License free&quot; bands at 433 / 900MHz seems to be taking the focus off shortwave. &lt;p&gt;&#xA;&lt;strong&gt;Edit&lt;/strong&gt; Example: Analog have a page on SDR's. Their &lt;a href=&quot;http://www.analog.com/static/imported-files/overviews/Software-Defined-Radio-Solutions-From-ADI.pdf&quot; rel=&quot;nofollow&quot;&gt;overview&lt;/a&gt; lists transceivers with a bandwidth of up to 56MHz covering &quot;most licensed and unlicensed bands&quot;. That's a huge bandwidth, and incredibly convenient - but it comes at a price. The minimum useable frequency is 70 MHz.&lt;br&gt;&#xA;While I'm happy nobody is trying to send video from their toy drone helicopter at 20MHz, I &lt;em&gt;would like&lt;/em&gt; to see more SDR designs that cater to HF. For receivers AND transmitters. With so many people using the unlicensed ISM bands, however, I suspect shortwave is becoming a niche market.&lt;/p&gt;&#xA;" OwnerUserId="1610" LastEditorUserId="1610" LastEditDate="2014-10-21T20:45:05.993" LastActivityDate="2014-10-21T20:45:05.993" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2243" PostTypeId="2" ParentId="2237" CreationDate="2014-10-20T09:01:06.913" Score="1" Body="&lt;p&gt;A scanner is simply a receiver that has the ability to automatically scan frequencies. Most transceivers and receivers have this feature. For example, your car stereo can likely scan for stations, but you can also manually tune the receiver with the knob.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transceivers and receivers that are not &quot;scanners&quot; would have only a tune knob that you must manually control to change frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, yes, you can stop a scanner if you wish to continue to listen to a specific frequency.&lt;/p&gt;&#xA;" OwnerUserId="606" LastActivityDate="2014-10-20T09:01:06.913" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2244" PostTypeId="2" ParentId="2230" CreationDate="2014-10-20T20:57:15.040" Score="1" Body="&lt;p&gt;Another difference is FCC approval. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Approval involves a rigorous set of requirements that are applied to the device's frequency range, transmit capability, spurious emissions, and more. Its not easy and is very strict. Anything not FCC approved falls under the category of experimental / test equipment. &lt;/p&gt;&#xA;" OwnerUserId="1238" LastActivityDate="2014-10-20T20:57:15.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2245" PostTypeId="2" ParentId="2183" CreationDate="2014-10-21T15:09:13.150" Score="1" Body="&lt;p&gt;After consulting with a Canadian D-STAR gateway operator, I have learned that &lt;strong&gt;yes, club stations can register callsigns on D-STAR.&lt;/strong&gt; Operating in this manner would be no different than operating a club station over the air with a non D-STAR radio or using a D-STAR device with a personal callsign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The one caveat to this is that if the club in question wishes to run a D-STAR repeater, it needs to be registered under a unique callsign, and cannot be shared with the callsign assigned to the D-STAR terminal. This would require the club to register a second callsign for use with the repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Thanks to Eric Meth VE3EI for helping provide this information)&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-10-21T15:09:13.150" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2246" PostTypeId="2" ParentId="2237" CreationDate="2014-10-21T16:21:20.053" Score="-1" Body="&lt;p&gt;A Scanner is a basically a receiver with extra bells and whistles. It can automatically scan frequencies and stop at a busy one, and it can be programmed with your favorite public service frequencies. Think of it a wide range receiver with scanning and memory functions. See also: &lt;a href=&quot;http://en.wikipedia.org/wiki/Scanner_%28radio%29%20%22Scanner(radio)%20Wikipedia&quot; rel=&quot;nofollow&quot; title=&quot;Scanner(radio) Wikipedia&quot;&gt;http://en.wikipedia.org/wiki/Scanner_%28radio%29&lt;/a&gt; and &lt;a href=&quot;http://radioreference.com&quot; rel=&quot;nofollow&quot; title=&quot;www.radioreference.com&quot;&gt;http://www.radioreference.com&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1372" LastActivityDate="2014-10-21T16:21:20.053" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2247" PostTypeId="2" ParentId="2238" CreationDate="2014-10-21T22:40:20.373" Score="1" Body="&lt;p&gt;You might be able to listen to DMR using scanner, if the scanner itself is appropriate, that is to say how simple it is to get to the output signal produced by the scanner's discriminator. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The catch is that you'll need to use a computer to decode the DMR signal and to give you useable output. There is software, like for example &lt;a href=&quot;http://wiki.radioreference.com/index.php/Digital_Speech_Decoder_%28software_package%29&quot; rel=&quot;nofollow&quot;&gt;Digital Speech Decoder&lt;/a&gt; which are capable of providing you with decoded DMR. DSD is commonly used for scanning together with RTL-SDR dongles and it works fine for decoding DSD in that use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I myself have no experience with IC-R6, so I cannot provide good recommendation about its suitability, but the specifications I managed to find on the Internet make me skeptical of its out-of-the-box suitability due to mentions of &quot;low-pass filter&quot;. Baseband width of DMR signal is a bit wide and I fear that it could be wider than the passband of the IC-R6's low-pass filter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I can see, it is possible to obtain the unfiltered output from the IC-R6's discriminator itself, but I don't know how complex the modification would be.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2014-10-21T22:40:20.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2248" PostTypeId="1" AcceptedAnswerId="2260" CreationDate="2014-10-22T01:52:02.627" Score="7" ViewCount="342" Body="&lt;p&gt;A while ago I was using a software radio receiver to perform some antenna analysis. I left the spectrum display on while disconnecting the cable and noticed that when the cable was disconnected I could see a very large spike in the frequency component at the center frequency of the display (where the receiver was tuned). I changed the center frequency several times and noticed the same spike appeared regardless of where I tuned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some time later I reconnected a cable and accidentally tuned to a frequency that was completely &quot;out of spec&quot; for the antenna I was using. The same spike appeared at the center of the display; I tuned around to several nearby frequencies and found that the spike stayed put. It disappeared when I moved back to a frequency at which the antenna was designed for operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What is the nature of that spike&lt;/strong&gt; and why does it appear when tuned to a frequency at which the antenna is not resonant, as well as when the antenna is disconnected?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: Here are some screenshots of the spike I'm referring to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/aLd3a.png&quot; alt=&quot;FFT tuned&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an FFT of the received spectrum through an antenna tuned for the 2M band. Everything is nice and flat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/gI6VX.png&quot; alt=&quot;FFT detuned&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an FFT of the spectrum through the same antenna but at a completely unworkable operating frequency. The middle is a bit noisy but still shows the spike at the center frequency well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NcS8y.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the FFT at the same frequency, but with no antenna connected. The spike is clearly visible here, and this is what I'm interesting in learning about.&lt;/p&gt;&#xA;" OwnerUserId="1579" LastEditorUserId="1579" LastEditDate="2014-10-25T03:52:15.130" LastActivityDate="2014-11-02T05:23:37.437" Title="Center frequency spike on software radio for mismatched/disconnected antenna" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2249" PostTypeId="2" ParentId="2215" CreationDate="2014-10-22T03:08:57.330" Score="4" Body="&lt;p&gt;The most important and simplest thing you can do to eliminate alternator whine is run a separate set of power cables directly from the cars battery terminals to the radio. Making sure you include the proper rated fuses links on both leads immediately after the battery terminal connection. (the fuses are for safety and should be on both the positive and negative leads)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doing that should solve a good portion of your issue. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should also make sure the antenna is properly grounded to the vehicles body. If it is mounted on a trunk lid you will need to add a ground connection from the body to the lid. As the hinges don't offer a solid ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly you can buy a noise filter to put in the power leads just before the connection to the radio. This can be purchase at your every day electronics shack or automotive store. make sure you purchase a filter that can handle the load your radio will put on it.&lt;/p&gt;&#xA;" OwnerUserId="1735" LastActivityDate="2014-10-22T03:08:57.330" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2250" PostTypeId="2" ParentId="2075" CreationDate="2014-10-22T17:53:48.817" Score="4" Body="&lt;p&gt;The main differences with these units is FIRMWARE! The firmware can be checked by powering off the unit and holding the &quot;3&quot; key down as you power it on. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This number however does not always reflect the true firmware version and I recommend using CHIRP and a programming cable to find the firmware listed on your exact radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reference I recommend you check out the yahoo groups page for Baofeng UV-5R.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a ton of information listed there for users. &lt;/p&gt;&#xA;" OwnerUserId="1737" LastActivityDate="2014-10-22T17:53:48.817" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2253" PostTypeId="1" AcceptedAnswerId="2254" CreationDate="2014-10-24T12:02:52.450" Score="2" ViewCount="115" Body="&lt;p&gt;With barely no knowledge in this field, I would like to render &lt;a href=&quot;http://www.tp-link.fr/products/details/?model=TL-ANT2409A&quot; rel=&quot;nofollow&quot;&gt;my antenna&lt;/a&gt; used with Bluetooth BLE devices more directional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to shield the antenna with different kind of metals with no luck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there someone to point a way in order to render my antenna directional? Perhaps surounding with something?&lt;/p&gt;&#xA;" OwnerUserId="1746" LastEditorUserId="218" LastEditDate="2014-10-24T21:36:06.757" LastActivityDate="2014-10-24T21:36:06.757" Title="How can I render my 2.4GHz antenna directional?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2254" PostTypeId="2" ParentId="2253" CreationDate="2014-10-24T18:33:45.400" Score="5" Body="&lt;p&gt;The antenna you link to appears to be directional (9dBi) already. If you can figure out where the main lobe of the antenna points (the specifications didn't seem to specify), you may simply try to aim more accurately.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An effective metal structure, in the manner I think you suggest, would probably be a fair-size satellite dish. 2.4GHz is around 12cm wavelength, so a dish would need to be several multiples of that, perhaps a meter or so diameter if I remember well enough. Anything smaller would be subject to diffraction and the radiation would just bend around the metal, perhaps even just reducing the overall radiated power due to losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other modifications would require you to accurately space some sort of parasitic element to accurately re-radiate with the right phase. (Think of an outdoor TV antenna, or Yagi antenna) It may be easier to buy another antenna or build from scratch as you need to know more details about the antenna you already have, like its input impedance and radiation pattern, which changes when you put stuff around it.&lt;/p&gt;&#xA;" OwnerUserId="1748" LastActivityDate="2014-10-24T18:33:45.400" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2255" PostTypeId="1" CreationDate="2014-10-25T00:45:04.873" Score="2" ViewCount="1186" Body="&lt;p&gt;Is it possible to transfer data at a high rate, like 1-2 Mbps, on 0.5 - 30 MHz?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From Shannon's Theorem, with a bandwidth of just 300 kHz it is possible to reach 1.5 Mbps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to use these bands because of longer ranges and lower losses in urban areas, but I do not know why these bands are not used for Wi-Fi connections. What is the problem with operating like this?&lt;/p&gt;&#xA;" OwnerUserId="1742" LastEditorUserId="1579" LastEditDate="2014-10-26T08:42:20.093" LastActivityDate="2014-10-26T08:42:20.093" Title="High data rate on HF &amp; MF bands" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;propagation&gt;&lt;rf-power&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2256" PostTypeId="2" ParentId="1296" CreationDate="2014-10-25T02:10:49.877" Score="2" Body="&lt;p&gt;Just ran across this web site for commercial covert antennas &lt;a href=&quot;https://sti-co.com/project/covert-bumper-antenna-2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://sti-co.com/project/covert-bumper-antenna-2/&lt;/a&gt; -- this one is a bumper mount configuration.  Note there are TWO antennas, in diagonally opposite corners of the vehicle.  If you are using repeaters (as opposed to simplex) this might be a viable option.  The company has many other hidden and covert antennas.  Good luck!&lt;/p&gt;&#xA;" OwnerUserId="1751" LastEditorUserId="4665" LastEditDate="2021-02-01T22:50:10.403" LastActivityDate="2021-02-01T22:50:10.403" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="2257" PostTypeId="1" AcceptedAnswerId="2258" CreationDate="2014-10-25T02:18:05.860" Score="12" ViewCount="19018" Body="&lt;p&gt;I'm listening to (or let's say I'm trying to participate in) a contest (or perhaps Field Day), using SSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I noticed that a station would, after completing a contact, sometimes say “CQ” and sometimes say “QRZ”. In either case, other stations then reply with their callsigns. What's the difference, and &lt;em&gt;when should I&lt;/em&gt; attempt contact?&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-11-28T21:19:22.573" Title="What's the difference between saying “CQ” or “QRZ” in a contest?" Tags="&lt;procedure&gt;&lt;contest&gt;&lt;jargon&gt;&lt;phone&gt;&lt;etiquette&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2258" PostTypeId="2" ParentId="2257" CreationDate="2014-10-25T02:18:05.860" Score="11" Body="&lt;p&gt;This became clear to me after a bit of time to think, but it wasn't at all clear on initially jumping in. It helps to know the formal definitions of the codes used:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;CQ&lt;/strong&gt; is “Calling any station”. The station is asking for (new) contacts from anyone.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;QRZ?&lt;/strong&gt; is “Who is calling me”. The station is asking for a calling station to repeat their callsign. Only a station &lt;em&gt;which has already attempted to contact them&lt;/em&gt; should speak at this time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my observations of actual contests, QRZ seems to be &lt;strong&gt;commonly used&lt;/strong&gt; to mean “Someone other than the station I just worked, please call”, but while trying to research this answer I found &lt;a href=&quot;http://www.arrl.org/files/file/DXCC/Eth-operating-EN-ARRL-CORR-JAN-2011.pdf&quot;&gt;one document&lt;/a&gt; claiming that it is appropriate only for “could not copy previous call” and not for “I want someone else from the pileup now” — but I also found a bunch of other mutually contradictory advice.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-10-25T02:18:05.860" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2259" PostTypeId="2" ParentId="2257" CreationDate="2014-10-25T02:46:29.927" Score="6" Body="&lt;p&gt;During contests, a popular station (say DX) has a pileup with lots of stations trying to make contact.  A station will often merely say QRZ for picking up someone from the pileup.  Thus, in this I am agreeing with the previous answer but with the following comment.  I believe that this method of saying QRZ is now so popular in this pileup situation (that is, commonly done by many) that it has actually changed the use of QRZ over the years from its original intent of not fully copying a call sign or questioning the caller to repeat his call sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether it is correct to use QRZ in this way -- makes no difference -- this is what people are doing.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2014-10-25T02:46:29.927" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2260" PostTypeId="2" ParentId="2248" CreationDate="2014-10-25T15:02:28.607" Score="1" Body="&lt;p&gt;That is probably &lt;a href=&quot;http://en.wikipedia.org/wiki/Pink_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;1/f noise&lt;/a&gt;. This is noise where each octave has equal power. At lower frequencies, each octave is narrow, and thus has more power per unit frequency. It is ubiquitous in every electrical circuit, and in fact a great many physical processes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This will always appear at the center of your FFT, regardless of where the radio is tuned, as the center of the FFT always corresponds to the frequency of your receiver's VFO input to the mixer. For example, if the VFO is tuned to 900 MHz, then a 900.01 MHz signal will appear at 900.01 - 900 MHz = 10 kHz, after mixing. 900 MHz appears at 0 Hz after mixing, the lowest frequency possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1/f noise is present in all electronics, and this is why you observe it even with no antenna connected. It can originate in the components that comprise the gain stages of the receiver like resistors and transistors, and noise so generated then goes on to be amplified and made visible in the FFT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Better, and usually more expensive engineering can reduce noise like this, but in your particular case it would have negligible benefit. If you compare the scale on the left, this noise is significantly below the RF noise floor when you have an antenna connected. Consequently, &lt;a href=&quot;https://ham.stackexchange.com/a/2214/218&quot;&gt;you will realize very little benefit from reducing the noise&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-10-25T15:02:28.607" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2261" PostTypeId="2" ParentId="2255" CreationDate="2014-10-25T16:24:36.303" Score="4" Body="&lt;p&gt;There are many reasons not to use low frequencies such as below 30 MHz. Here are just a few:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) It is prohibited by law. These frequencies are assigned to other services. 2.4GHz is a shared service... Even your microwave oven cooks there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) They need large antennas to function. The shortest antenna at 30 Mhz, which still is effective, is about 5 meters long (while at 2.4GHz it only needs 6-7 cm).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) Shannon's limit isn't (a limit, I mean): the formula $C=B\log_2(1+\frac{S}{N})$ just says that you can send more info over the same bandwidth if you improve the $\frac{S}{N}$ ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4) Then, you should realize that if you want to be at Shannon's C rate, you have to have the channel for yourself. No other users can use the same frequency. If you realize that 2.4 GHz is a jungle with probably 100s of simultaneous users...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you want to improve your channel capacity (C), you should concentrate on improving the S/N ratio, which is much easier to do at 2.4 or 5.2 GHz than at 0-30 MHz&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-10-25T16:24:36.303" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="2262" PostTypeId="2" ParentId="2255" CreationDate="2014-10-25T17:34:14.153" Score="4" Body="&lt;p&gt;There are several reasons the low bands are not used for high data throughput:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The problem is at HF frequencies, a 300kHz bandwidth is a lot of spectrum. At MF frequencies it's a whole lot of spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1a. If you look at &lt;a href=&quot;http://upload.wikimedia.org/wikipedia/commons/4/45/United_States_Frequency_Allocations_Chart_2003_-_The_Radio_Spectrum.jpg&quot; rel=&quot;nofollow&quot;&gt;this spectrum chart&lt;/a&gt; you will see that 300kHz covers more that 10 assigned services at MF and covers most of 4 services at HF.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;From a legal standpoint (most countries have laws governing spectrum usage) you would not be authorized to transmit over such a wide chunk of spectrum.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;2a. To be legal you would have to lease the spectrum and even if you could get the governing agency to lease all that spectrum to you, you couldn't afford it.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you decided to ignore the legal aspect and forge ahead(see point 4 however), remember MF frequencies travel great distances via ground-wave propagation and HF frequencies bounce of the ionosphere and travel around the world.  A 300kHz signal would cause a lot of people interference. Someone would hunt you down and stick a pin in your COAX. [tic]&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You would have to design and build a transmitter/receiver and antenna system capable of transmitting/receiving such a broad signal on those frequency bands which would be impractical.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I hope this clears things up a bit.&lt;/p&gt;&#xA;" OwnerUserId="1744" LastEditorUserId="1744" LastEditDate="2014-10-25T18:53:31.723" LastActivityDate="2014-10-25T18:53:31.723" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2263" PostTypeId="1" CreationDate="2014-10-25T20:17:46.757" Score="3" ViewCount="1809" Body="&lt;p&gt;What is the longest possible range on the 40-meter band by ground wave? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A reference said we can achieve 150 miles at 8 MHz with only a 100 watt transmitter. It also says on 160 meters, the ground wave may extend to more than 900 kilometers. Is this really possible?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ips.gov.au/Category/Educational/Other%20Topics/Radio%20Communication/Intro%20to%20HF%20Radio.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.ips.gov.au/Category/Educational/Other%20Topics/Radio%20Communication/Intro%20to%20HF%20Radio.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1742" LastEditorUserId="1579" LastEditDate="2014-10-26T19:29:33.310" LastActivityDate="2014-10-26T19:29:33.310" Title="Longest achievable ground wave range on 40-meter bands" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="0" ClosedDate="2014-12-02T00:05:40.873" ContentLicense="CC BY-SA 3.0" />
  <row Id="2264" PostTypeId="2" ParentId="2263" CreationDate="2014-10-25T20:44:52.853" Score="2" Body="&lt;p&gt;If you read the document again you will see they were referencing nautical miles over water. Distance over land is greatly reduced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to answer your question, yes this is true.&lt;/p&gt;&#xA;" OwnerUserId="1744" LastActivityDate="2014-10-25T20:44:52.853" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2265" PostTypeId="2" ParentId="2257" CreationDate="2014-10-26T03:16:07.807" Score="6" Body="&lt;p&gt;As said by other answerers, it's typically the station announcing 'I'm ready for more contacts at this time.' It doesn't necessarily have to be a DX station, but any station that is attracting a lot of traffic during contests. It is kind of informal usage, as Kevid Reid mentioned, the official QRZ definition is 'who is calling me?', and CQ means 'calling all stations'. The contest station will usually only use CQ if they're not getting responses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically, when a contest station says QRZ, you should reply by saying your callsign &lt;em&gt;once&lt;/em&gt;, and quickly, especially if there is a pile-up. If the operator heard you, he will repeat back your callsign, and/or parts of it if he/she only caught part of it. It is considered very rude to repeat your callsign many times. One of the worst examples I've heard was after a DX station said QRZ, a station responded with their callsign and 'I know you're hearing me, just answer and I'll stop calling!' and 'I'm just going to keep calling until you answer me!'&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This just causes more irritation to those trying to communicate, especially when the operator is talking over those who are in communication. So best practice is to say your callsign once. If you're having trouble getting through, patience is the best way to get the contact. Just keep trying, saying your callsign once immediately after they say 'QRZ' Don't be discouraged if you hear stronger, clearer stations first. They'll get serviced, and the station will get around to you. They often want to make the contact as much as you do, so they'll be on the air for a while until the pile-up dies down!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feel free to say your callsign after either CQ or QRZ. The best thing to do is to listen for a while, and notice which stations are being responded to. Sometime operators will prematurely respond with their callsign, without waiting to hear if the other station has finished broadcasting. It's about %80 timing and %20 luck!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, as always, good luck and 73!&lt;/p&gt;&#xA;" OwnerUserId="1755" LastActivityDate="2014-10-26T03:16:07.807" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2266" PostTypeId="2" ParentId="2263" CreationDate="2014-10-26T19:28:51.290" Score="2" Body="&lt;p&gt;The longest achievable groundwave range is about 40,075 km, or in other words, the circumference of the Earth. There is no longer possible path over the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, there is no upper limit to how far radio waves can propagate, though there is a limit on distance imposed by the geometry of the earth. This holds for any mode of propagation, including ground wave. It also holds for any frequency, including the 40m band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All electromagnetic radiation becomes progressively weaker with distance according to the inverse square law. At some point it becomes too weak to be detected, but this can always be compensated by using a more sensitive detection method, or increasing the transmitter power. As such, there is no limit without defining additional constraints.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-10-26T19:28:51.290" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2267" PostTypeId="1" CreationDate="2014-10-26T21:19:29.480" Score="3" ViewCount="119" Body="&lt;p&gt;I would like to swap out my 2300h to a 400dr. Would rather not swap out dc power cable. Are the cables the same or is there an adapter for make it possible? &lt;/p&gt;&#xA;" OwnerUserId="1706" LastEditorUserId="76" LastEditDate="2016-04-22T18:45:47.647" LastActivityDate="2016-04-22T18:45:47.647" Title="Are the Icom 2300 h and Ftm 400dr DC cables interchangable?" Tags="&lt;mobile&gt;&lt;dc-power&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2268" PostTypeId="1" CreationDate="2014-10-27T02:43:52.717" Score="4" ViewCount="351" Body="&lt;p&gt;I'm a beginner who's nearly half a year from receiving my ham license in India. I want to start with HF radio and wish to build my own rig. Currently I have looked and multiple designs using the ad9860 module. Also I live in a city and know very little about antenna design. Can someone guide me to the next level? Thanks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&#xA;About myself.&lt;br&gt;&#xA;*Currently Second Year Computer Engineering Student&lt;br&gt;&#xA;*Fairly competent with practical electronics having built a Morse code oscillator with an arduino.&lt;br&gt;&#xA;*&lt;b&gt;NOT&lt;/b&gt; looking to buy a rig, but &lt;b&gt;WANT&lt;/b&gt; to build one.&lt;/p&gt;&#xA;" OwnerUserId="1758" LastEditorUserId="8717" LastEditDate="2020-10-26T20:13:06.560" LastActivityDate="2020-11-17T11:56:16.367" Title="Recommendations for starting out with HF for an amateur" Tags="&lt;antenna-construction&gt;&lt;hf&gt;&lt;india&gt;" AnswerCount="2" CommentCount="10" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2269" PostTypeId="1" CreationDate="2014-10-27T05:22:08.517" Score="3" ViewCount="93" Body="&lt;p&gt;I used nylon rope from the nearest hardware store to stay the centre-mast on my inverted-vee for the 20. The centre-pole is a long long looong bamboo. The trouble is rain here really isn't friendly to nylon; a year - 2 years at most. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham rope/Kevlar/Dacron are beyond my means. A brother operator advised against using MS/GI wire citing both corrosion and distortion in the propagation pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The net lists any number of towers (I believe most of these are high-quality aluminium). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How much distortion would aluminium wire stays for the centre-pole on my inverted-vee cause?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="76" LastEditDate="2015-12-15T23:31:34.927" LastActivityDate="2015-12-15T23:31:34.927" Title="How much distortion would aluminium wire stays for the centre-pole on my inverted-vee cause?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;inverted-vee&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2270" PostTypeId="2" ParentId="2269" CreationDate="2014-10-27T11:46:11.133" Score="3" Body="&lt;p&gt;Maybe a little, maybe a lot. It depends on the particular geometry of that wire. Your best bet would be to either build it and see, or use some simulation like NEC to predict what will happen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But consider: aluminium wires supporting the center of the antenna are not that different from the conductive feedline that's already there. Provided your wire runs right down the middle of the antenna, and the &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;dipole is properly balanced&lt;/a&gt;, then your added wire will have very little effect, just like the ideal balanced feedline running up to the ideal dipole. This is because the electric field around the dipole is perpendicular to the line of symmetry, so any conductor along the line of symmetry will have no electric field along its length. No electric field, no current, no radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course reality is usually a little more complicated. Still, this is a well-solved problem: AM broadcast towers have metal guy wires that must be isolated from the antenna. You can use egg insulators or &lt;a href=&quot;http://www.w8ji.com/detuning_towers.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;tuned sections&lt;/a&gt; to help accomplish this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further consider, aluminium is a good conductor, so losses will be low, so if your wires become part of the antenna, so what? If the resulting antenna + wire stays is still an effective radiator, hasn't your goal been accomplished?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could even &lt;em&gt;intentionally&lt;/em&gt; make the stays part of the antenna, and make yourself a sort of fan dipole. Try cutting the guys at a length to cover some band your current antenna does not, and connecting it in parallel. This could be considered a variation on the fan dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, there is no particular reason to avoid steel if it's just for mechanical support. Steel is cheaper, has higher tensile strength per unit cost, and stretches less. There are plenty of steel cables acceptable for outdoor service. Any metal you use for a wire is going to potentially carry current, so you might as well pick one on its mechanical merits. Unless you are doing the fan dipole thing, or otherwise managed to get very significant currents on the stays, steel's lower RF conductivity is not a problem. Consider: towers are steel, and the guys on professional AM broadcast stations are steel.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-10-28T01:42:51.460" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2271" PostTypeId="1" CreationDate="2014-10-27T15:03:43.893" Score="5" ViewCount="2408" Body="&lt;p&gt;I have  10 watt CB radio system &amp;amp; 0.64 lambda monopole antenna , I think it has a 5 dBi gain .&lt;/p&gt;&#xA;&#xA;&lt;p&gt;what is the maximum acheivable  range by ground wave in an urban area ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I want  to increase my range  without increase the system’s power , can I make  10 elements antenna  array  and get another 10 dB gain above my 5 dBi ?&lt;/p&gt;&#xA;" OwnerUserId="1742" LastActivityDate="2014-10-29T16:46:40.533" Title="maximum acheivable range on CB radio by ground wave?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;digital-modes&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="6" ClosedDate="2014-11-05T09:18:49.917" ContentLicense="CC BY-SA 3.0" />
  <row Id="2272" PostTypeId="1" CreationDate="2014-10-27T22:04:09.453" Score="6" ViewCount="1781" Body="&lt;p&gt;What documented protocol or API does WebSDR use to stream audio over the internet?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm interested in capturing a WebSDR audio stream using a small embedded device which has lots of audio DSP capability, good internet access (TCP/UDP network sockets, raw http, etc.), but no (HTML/JS) browser or Java/JVM runtime.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2017-01-14T09:41:23.523" Title="What protocol or API does WebSDR use to stream audio?" Tags="&lt;software-defined-radio&gt;&lt;software&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2273" PostTypeId="2" ParentId="2272" CreationDate="2014-10-28T17:56:52.730" Score="5" Body="&lt;p&gt;The &quot;HTML5&quot;-compatible (not using Java applets) audio interface for WebSDR uses audio samples streamed over a WebSocket connection — this can be seen from the JS client files it downloads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the author of WebSDR has indicated that they do not wish the software used in ways other than via the provided web client (in &lt;a href=&quot;http://websdr.org/faq.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;their FAQ&lt;/a&gt; and even in a comment in &lt;a href=&quot;http://websdr.ewi.utwente.nl:8901/websdr-sound.js&quot; rel=&quot;nofollow noreferrer&quot;&gt;the very JS file I'm speaking of&lt;/a&gt;!) so I recommend that you do not pursue this project without asking the author, as they might well consider it abuse of their service for you to connect with an alternate client.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you merely want a remote radio receiver and not specifically to use the hardware of existing WebSDR installations, there are several open-source possibilities. If you're interested in that option, I suggest &lt;a href=&quot;https://ham.stackexchange.com/questions/ask&quot;&gt;asking about it as a separate question&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-10-28T17:56:52.730" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2274" PostTypeId="2" ParentId="2271" CreationDate="2014-10-29T16:46:40.533" Score="4" Body="&lt;p&gt;First, a &quot;ground wave&quot; is difficult to estimate since it is so dependent on all kinds of things, most importantly frequency and second the conductivity of the ground (or, water).  Buildings in an urban area can result in diffraction of the ground wave among buildings that can create strange areas of signal strength and signal weakness that are virtually impossible to predict without actual experiment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The previous similar question (noted in the comments) is different from this one in frequency.  So, I will answer for the US CB frequency (just under 28 MHz).  For a 28 MHz signal, with all other features ignored, is about 5 to 7 miles (or, 8 to 11 km).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is actually three different types of propagation considered as ground wave and they behave quite differently from each other which makes guessing at distance for ground wave to be even more difficult.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Tropospheric Bending Ground Wave&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;This is a ground wave that travels in the atmosphere and ground itself is somewhat independent of the nature of the ground.  It is included here because Tropospheric Bending has similar propagation to ground wave.  This type of propagation is most notable in VHF and above frequencies so not much use to CB frequencies.&lt;/p&gt;&#xA;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;Direct Line-of-Sight Ground Wave&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;This is similar to above in that the ground effects are not pertinent other then the fact that curvature of the surface of the earth limits the effective line-of-sight success.  But, this is the most likely type of propagation the OP will see useful in an urban setting for CB (along with benefits of diffraction).  For actual distance coverage, line of site computations can be estimated using either of the following approximate formula:&#xA;$$&#xA;D_\text{miles} = 1.415 \sqrt{H_\text{feet}}\\[2ex]&#xA;D_\text{km}= 4.124\sqrt{H_\text{meters}}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $H$ is the height of the transmitting (or, receiving) antenna.  By including both transmitting and receiving antennas and computing for overlap of the two distance results you can determine the longer line-of-site propagation path available.&lt;/p&gt;&#xA;&#xA;&lt;ol start=&quot;3&quot;&gt;&#xA;&lt;li&gt;Low-Frequency Surface Wave&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I say &lt;em&gt;low-frequency&lt;/em&gt; since this type of ground wave, that actually uses the conductivity features of the ground are most effective at lower frequency, or MF (~2 MHz) and under.  This is the method used for submarine communications where propagation is measured in the 1000s of miles for the super low frequency.  Note that in this case, since frequency is so low, actual information transmission is very slow, measured at only a few characters per second in some cases.  Surface wave propagation for super low frequency requires humongous antennas so it is not a practical solution for hobbyists.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2014-10-29T16:46:40.533" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="2276" PostTypeId="1" CreationDate="2014-10-30T02:02:23.827" Score="12" ViewCount="9177" Body="&lt;p&gt;&lt;strong&gt;How can I continuously discharge static from my end-fed antenna?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My &lt;a href=&quot;http://www.elecraft.com/k2_page.htm&quot; rel=&quot;noreferrer&quot;&gt;Electraft K2/100&lt;/a&gt;'s &lt;a href=&quot;http://www.elecraft.com/kat100/kat100_page.htm&quot; rel=&quot;noreferrer&quot;&gt;autotuner&lt;/a&gt; (&lt;a href=&quot;http://www.elecraft.com/manual/KAT100%20man%20rev%20C.pdf&quot; rel=&quot;noreferrer&quot;&gt;schematics&lt;/a&gt;) has an SWR bridge using two 1N5711 pin diodes.  These diodes get blown if any static builds up on the antenna.  I've replaced them four times now.  It's nice that I can replace them, but I'd rather not buy diodes in bulk.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I keep the antenna disconnected when I'm not using it, but sometimes forget to disconnect it when I'm done.  Plus, static can build up when operating--rain puts a terrific static charge on the antenna.  So I need some kind of protection from static.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've read that I can use a resistor or coil between the antenna and ground to bleed off static, but I don't know what to build or buy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My antenna is end-fed wire slung out of a tree and run through a small hole in the wall.  There's just a few feet of feed line between the rig and the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RF ground is a ground rod just on the other side of the wall and connected to a jumper cable wire also poked through the wall.  The jumper cable connects to a copper pipe mounted to the bench.  Connected to the ground pipe are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The rig's ground lug&lt;/li&gt;&#xA;&lt;li&gt;The tuner's ground lug&lt;/li&gt;&#xA;&lt;li&gt;One side of the balun&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The ground rod is not connected to the house's electrical ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The AC ground is connected only to the station's linear power supply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna, RF ground, and feedline all meet at a 1:1/4:1 switchable balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rig outputs 100W on 80M-10M, but I operate mostly on 40M and 30M.&lt;/p&gt;&#xA;" OwnerUserId="628" LastEditorUserId="628" LastEditDate="2014-11-10T18:27:12.367" LastActivityDate="2014-12-31T16:48:43.390" Title="Protect rig from static charge on antenna" Tags="&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;equipment-protection&gt;" AnswerCount="3" CommentCount="9" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2278" PostTypeId="2" ParentId="1196" CreationDate="2014-10-30T12:26:51.820" Score="3" Body="&lt;p&gt;One of the earlier SDR models, the HPSDR, had/has a single receive board: the &quot;Mercury&quot;. It used a single high-speed ADC. Details are &lt;a href=&quot;http://openhpsdr.org/mercury.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;here.&lt;/a&gt;&lt;br&gt;&#xA;Once the RF is sampled and fed into an FPGA, it typically gets split into I and Q streams anyway. If you have a 120Msps ADC, for example, you could mix with a 30MHz SINE signal (0, 1, 0, -1, repeat) and a 30MHz COSINE signal (1, 0, -1, 0, repeat). &lt;p&gt;&#xA;Benefits? Well for starters, you've halved the number of ADCs and associated amps, physical filters, etc. You still have them - but now they need to be implemented &lt;em&gt;In Code&lt;/em&gt; in the FPGA. Separate I and Q channels also tend to have distortion problems around DC.&lt;p&gt;&#xA;Drawbacks? You have to write more code. Some of that code (the complex exponential) can be quite hard to do well. &lt;strong&gt;Edit:&lt;/strong&gt; Another expense-related problem: your single ADC now has to be twice as fast. This can &lt;em&gt;significantly impact&lt;/em&gt; ADC cost, and even the circuit design. &lt;p&gt;&#xA;As for your idea of looking at 100 - 150MHz: this is where &lt;em&gt;oversampling&lt;/em&gt; comes in. If you sample a 60MHz signal with a 100MHz ADC, the Nyquist effect makes it &quot;look like&quot; a 40MHz signal, ie. reflected around the half-sample rate. A 90MHz signal will &quot;look like&quot; a 10 MHz signal. What would a 101 MHz signal look like...?&lt;br&gt;&#xA;It would look like a 1 MHz signal. This is oversampling.&lt;p&gt;&#xA;Looking at a bandwidth of (up to) half the sample rate, while technically possible, is pushing things a bit. In practice, for the conditions you specified, I'd use ADCs rated at 160Msps (or higher), and expect data between 60 - 10MHz. Such ADCs don't come cheap, so I'd probably consider a single ADC version to start with.&lt;br&gt;&#xA;Also note how the frequency band got &quot;reversed&quot; by using the Nyquist oversampling. This can impact decoding analog TV (color burst in wrong location), SSB (LSB becomes USB), and commercial FM (stereo information in secondary signal).&lt;/p&gt;&#xA;" OwnerUserId="1610" LastEditorUserId="8573" LastEditDate="2019-07-31T18:44:43.657" LastActivityDate="2019-07-31T18:44:43.657" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="2279" PostTypeId="2" ParentId="2272" CreationDate="2014-11-01T11:44:39.420" Score="1" Body="&lt;p&gt;The FAQ makes no mention of third party clients, and the JS file merely has standard boilerplate about being able to distribute that file unmodified.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are already clients for other platforms (eg. glsdr, isdr)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I say to the OP, go for it.. The protocol is very simple, controlled from basic HTTP GET commands.  5 minutes on tcpdump should get you everything you need.&lt;/p&gt;&#xA;" OwnerUserId="1783" LastActivityDate="2014-11-01T11:44:39.420" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2280" PostTypeId="2" ParentId="2276" CreationDate="2014-11-01T22:14:32.033" Score="3" Body="&lt;p&gt;As hotpaw2 mentioned already, a basic search yields a wealth of information about RF chokes and bleeder resistors. Mainly, you need to decide what you're ready to set up. For a bleeder resistor, somewhere around 10k$\Omega$ up to 1M$\Omega$ seems appropriate. Make sure the power rating is high enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The nice thing about an RF choke is that it can have a relatively lower resistance to ground for static charges, and a high impedance for RF power. I would guess an old transformer might even work, it just needs a few hundred millihenries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://hpfriedrichs.com/radioroom/bleeder/rr-bleeder.htm&quot; rel=&quot;nofollow&quot;&gt;http://hpfriedrichs.com/radioroom/bleeder/rr-bleeder.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1748" LastActivityDate="2014-11-01T22:14:32.033" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2281" PostTypeId="1" CreationDate="2014-11-02T04:26:42.030" Score="9" ViewCount="3771" Body="&lt;p&gt;Besides WebSDR, what remote Software-Defined-Radio stations (for shortwave or amateur bands) might be available for open public access over the internet?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What protocols do these SDR stations use to stream data over the internet?  Do any of these SDR stations use open source or published standard APIs for control and data?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-05-04T06:04:19.823" Title="Remote SDR on the internet other than WebSDR?" Tags="&lt;software-defined-radio&gt;&lt;internet&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2282" PostTypeId="2" ParentId="2248" CreationDate="2014-11-02T05:23:37.437" Score="0" Body="&lt;p&gt;The fact that the spike is present, with no antenna connected, inducates it is a product of the receiver chain. Since it happens bang on the frequency you have tuned, implies the DC or low frequency attributes of the system are causing this.&lt;br&gt;&#xA;While you show an FFT at 2m with antenna connected, you don't show 2m without antenna. However, even at 900MHz there seems about 20dB difference when antenna is removed.&lt;br&gt;&#xA;As other have commented, there comes a point where increasing sigmal into a receiver adds noise as well, for no overall gain. You first picture is showing such a setup, where levels are high enough to &quot;mask&quot; potential distortion caused by receiver performance. The other pictures, where antenna performance is poor (or disconnected) expose the limits of the receiver.&lt;/p&gt;&#xA;" OwnerUserId="1610" LastActivityDate="2014-11-02T05:23:37.437" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2283" PostTypeId="2" ParentId="2268" CreationDate="2014-11-02T15:43:40.080" Score="2" Body="&lt;p&gt;I strongly suggest that you begin with a one-band radio kit. There are several manufacturers and the cost is likely to be quite reasonable even with shipping. The main reasons are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;to get on the air as quickly as possible. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Even a little experience with real-world operations will likely&#xA;change your view on what you want from a radio.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The main obstacle to successful operating is likely to be antenna&#xA;design and location. Time spent in this area will yield much more&#xA;performance improvement than reworking radio designs.  Local issues,&#xA;especially QRM/QRN may lead you to change your thinking about HF&#xA;entirely.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A 20 m or 15 m CW-only transceiver would be my recommendation for an in-city location. Antenna length and noise levels both increase at longer wavelengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A local college may have a ham club with useful equipment and assistance. A good SWR meter or even an antenna analyzer could be really useful. Being able to test your new radio with an existing, low-SWR antenna would give you confidence that the radio works and some experience with tuning.&lt;/p&gt;&#xA;" OwnerUserId="1785" LastEditorUserId="76" LastEditDate="2014-11-03T02:09:09.277" LastActivityDate="2014-11-03T02:09:09.277" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2285" PostTypeId="1" CreationDate="2014-11-02T22:05:32.213" Score="8" ViewCount="10804" Body="&lt;p&gt;I just obtained a really old packet TNC and hooked it up to the computer, and it appears to work. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a standard packet calling frequency on 2 meters? I would like to see if there is packet activity in my area, and if I can start some operation.  Also, is there much packet activity on other bands like 1.25 m, 70 cm, 23 cm, 33 cm, etc.?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My QTH is Denver, CO, USA.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2014-11-05T18:16:23.707" LastActivityDate="2020-08-25T17:25:16.667" Title="What frequencies should I listen to for packet radio?" Tags="&lt;united-states&gt;&lt;packet&gt;" AnswerCount="5" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2286" PostTypeId="1" CreationDate="2014-11-02T23:52:04.807" Score="8" ViewCount="2012" Body="&lt;p&gt;In the following diagrams, a microphone pinout is shown for several radios which have DTMF mics that work with them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is DTMF sent to the radio without a pin designated &quot;DTMF&quot;? Is it through the microphone audio, or is it through the up/down pins, which are used only when the radio is not transmitting? Or is there some other way to send DTMF?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/qJ8Ky.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-11-03T02:30:58.917" Title="How are DTMF tones sent through a mic?" Tags="&lt;microphone&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2287" PostTypeId="2" ParentId="2286" CreationDate="2014-11-03T02:30:58.917" Score="9" Body="&lt;p&gt;DTMF is an &lt;strong&gt;audio-frequency based&lt;/strong&gt; signaling system that sends tone pairs as audible frequencies,. Most DTMF microphones send the tones as though they were ordinary &lt;strong&gt;microphone audio&lt;/strong&gt; to be transmitted, so in the diagrams you have shown, the tones will use the same &quot;MIC AUDIO&quot; or &quot;TX AUDIO&quot; path as when you are talking into the mic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(And if you're interested in &lt;em&gt;what&lt;/em&gt; those audio frequencies are, &lt;a href=&quot;https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling&quot;&gt;Wikipedia's page on DTMF&lt;/a&gt; shows the full tone matrix and a few other details about the signaling system.)&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-11-03T02:30:58.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2288" PostTypeId="2" ParentId="2285" CreationDate="2014-11-03T02:42:32.500" Score="2" Body="&lt;p&gt;Have a look at the &lt;a href=&quot;http://www.iaru-r2.org/documents/explorer/files/Plan%20de%20bandas%20%7C%20Band-plan/R2%20Band%20Plan%202013.pdf&quot; rel=&quot;nofollow&quot;&gt;IARU Region 2 Band Plan&lt;/a&gt;. Most of the frequencies marked &quot;all modes&quot; or &quot;DM&quot; (digital mode) may be used for packet radio, although there does not seem to be a single designated packet calling frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally a packet radio frequency is coordinated between operators in the area, since one frequency can be shared by several TNCs. In this case the frequency is standardized &lt;em&gt;ad hoc&lt;/em&gt; and won't necessarily be the same everywhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should be able to get a good picture of packet activity by listening on these digital-mode bands and seeing what is going on. (A spectrum analyzer or software receiver may help you identify activity visually and allow for faster tuning to frequencies of interest.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think most of the packet activity on 70cm and higher bands is point-to-point or &quot;backbone&quot; links between larger sites (similar to a trunked repeater system). This might be due to range issues (APRS uses 2m almost exclusively, if I recall correctly). I have not seen any packet activity in my region (southern Ontario) on any of the higher bands so I can't comment directly on whether packet is really being used on these bands, and if so for what purpose.&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-11-03T02:42:32.500" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2289" PostTypeId="2" ParentId="2276" CreationDate="2014-11-04T14:49:34.253" Score="4" Body="&lt;p&gt;A resistor works. A coil works too. Even a very large resistor is sufficient to dissipate a little static. The advantage of a coil is that it can afford some additional lighting protection, shunting some of the strike current to ground at the antenna so surge protection farther down the feedline has to deal with less. A coil can do this because a significant portion of the strike current is at lower frequencies. A resistor, on the other hand, will probably just be vaporized before it can do much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can calculate the loss (and thus, the necessary power rating) of the resistor knowing the feedline impedance and transmitter power. For example, with a 100W transmitter and a 50Ω antenna feedpoint, we can figure the RMS voltage at the feedpoint is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ E = \sqrt{PR} \\&#xA;70.7\:\mathrm V = \sqrt{100\:\mathrm W \cdot 50\:\Omega} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we had a 10kΩ resistor, then the loss would be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P = E^2 / R \\&#xA;0.5\:\mathrm W = (70.7\:\mathrm V)^2 / 10000\:\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note this is an approximate solution that is valid only if the resistor is much larger than the feedpoint impedance. We probably want at least a 1W resistor here, but more would not hurt. Using a larger resistance (say, 1MΩ) reduces the resistor power. We can also see that the power goes up with the square of voltage. If you have a 1kW station, you will need a very much larger resistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can make a coil easily enough by winding some solid wire around a suitable form, then removing the form. A soda can works, but it's not especially critical. You will want to add enough inductance that it doesn't significantly change your antenna tuning. For lower bands you need more inductance. If the inductance is too low, then you will need to shorten the antenna, thus making it capacitive. This is actually a useful thing for mobile antennas, but I digress...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A lighting arresters will also by nature provide protection against static build-up. Their datasheets should provide a clamping voltage or a turn-on voltage. When they are working, they guarantee that the voltage between the feedline conductors will never be much greater than this. If this voltage is also below the threshold that damages your radio, you're golden. If you do install a lighting arrester, do be sure to &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;install it correctly&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-12-31T13:56:48.700" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2290" PostTypeId="2" ParentId="2285" CreationDate="2014-11-05T21:35:07.950" Score="7" Body="&lt;p&gt;You could tune to 144.390 FM on a 2m rig and see if you can pick up some APRS. This would require some software to decode packets (such as arpx for Linux). Just make sure you're not setting yourself up as a Digipeater until you find out what the network structure is in your area and whether there is a requirement at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;National APRS frequencies:&#xA;&lt;img src=&quot;https://i.stack.imgur.com/Ubzco.jpg&quot; alt=&quot;national APRS frequencies&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should also be able to see APRS activity on sites like aprs.fi for your area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/iTEJS.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://aprs.fi/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://aprs.fi/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="1135" LastEditDate="2016-09-04T01:09:11.857" LastActivityDate="2016-09-04T01:09:11.857" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2291" PostTypeId="1" AcceptedAnswerId="2296" CreationDate="2014-11-06T19:29:16.957" Score="5" ViewCount="875" Body="&lt;p&gt;Is possible to make small HF microstrip or helical antenna by using high permittivity dielectric material like SrTiO3 ?&lt;img src=&quot;https://i.stack.imgur.com/criLR.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1742" LastActivityDate="2015-05-13T00:41:06.040" Title="Is possible to make small HF microstrip or helical antenna by using high permittivity dielectric material?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;rf-power&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2292" PostTypeId="2" ParentId="2291" CreationDate="2014-11-07T03:36:08.533" Score="3" Body="&lt;p&gt;Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://en.wikipedia.org/wiki/Duality_%28electricity_and_magnetism%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;electrical dual&lt;/a&gt; of an antenna loaded with a high permittivity material is the &lt;a href=&quot;http://radio-timetraveller.blogspot.com/2011/01/unassuming-antenna-ferrite-loopstick.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;loopstick antenna&lt;/a&gt;. Loopstick antennas are common in portable AM receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/mqwQ3.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna consists of some turns around a high permeability core. This core effectively multiplies the magnetic field by aligning its own magnetic domains with the magnetic field due to the current in the coil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Likewise, a material with a high dielectric constant, or &lt;a href=&quot;http://en.wikipedia.org/wiki/Permittivity&quot; rel=&quot;nofollow noreferrer&quot;&gt;permittivity&lt;/a&gt;, can be used similarly to multiply the electric field. This can be used to construct an antenna with an &lt;a href=&quot;http://en.wikipedia.org/wiki/Antenna_aperture&quot; rel=&quot;nofollow noreferrer&quot;&gt;effective aperture&lt;/a&gt; much larger than would otherwise be attainable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because these antennas are electrical duals, what is true about the loopstick antenna will be analogously true of a dielectrically loaded antenna. Like the loopstick, an antenna loaded with a high permittivity material will have a reactive impedance, though it will be capacitive rather than inductive. Like the loopstick, or indeed any small antenna, as size goes down, so does operating bandwidth. And like the loopstick, the properties of your antenna will be limited by the dielectric material.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-11-07T03:36:08.533" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2294" PostTypeId="1" AcceptedAnswerId="2295" CreationDate="2014-11-08T21:58:51.807" Score="3" ViewCount="990" Body="&lt;p&gt;I have an old PK-232 packet TNC which is spitting out APRS data from 144.390 to the serial port. I have confirmed this with minicom and see all sorts of data with lat long etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to view this on a map. I have centos 5 linux. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any linux APRS clients that will take data from the serial port, and put it on a map or something? &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="13615" LastEditDate="2018-11-17T16:23:16.043" LastActivityDate="2018-11-17T16:23:16.043" Title="Linux APRS client" Tags="&lt;aprs&gt;&lt;software&gt;&lt;linux&gt;&lt;tnc&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2295" PostTypeId="2" ParentId="2294" CreationDate="2014-11-09T00:20:03.590" Score="8" Body="&lt;p&gt;Xastir is most likely what you want. &lt;a href=&quot;http://xastir.org/index.php/Major_Features#SUPPORTED_TNC.27s:_DARN_NEAR_EVERYTHING.21&quot; rel=&quot;noreferrer&quot;&gt;http://xastir.org/index.php/Major_Features#SUPPORTED_TNC.27s:_DARN_NEAR_EVERYTHING.21&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;YACC - Yet Another APRS Client is also a newer choice. I have not personally tried it.&#xA;&lt;a href=&quot;http://www.ka2ddo.org/ka2ddo/YAAC.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.ka2ddo.org/ka2ddo/YAAC.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="178" LastEditorUserId="178" LastEditDate="2014-12-08T17:06:41.850" LastActivityDate="2014-12-08T17:06:41.850" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2296" PostTypeId="2" ParentId="2291" CreationDate="2014-11-09T22:04:17.283" Score="1" Body="&lt;p&gt;Yes, you can!&#xA;Most of us have two arrays of these as the rods and cones in the retinas of our eyes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/mYXmW.jpg&quot; alt=&quot;A rod and cone of the retina&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The permittivity of the dielectric even does not need to be that high.&#xA;I used high-density polystyrene $(\epsilon_r=2.55)$ to build a &lt;a href=&quot;http://hamwaves.com/antennas/diel-rod.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;10GHz dielectric rod antenna&lt;/a&gt; with a measured gain of 20.5dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/FLB6f.jpg&quot; alt=&quot;10GHz dielectric rod antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dielectric rod antennas support the propagation of a surface wave along the rod. At the end of the rod, this surface wave will interfere with the space wave, also launched by the feeder. Together this creates the large directivity of this type of antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you understand dielectric rod antennas, you will also understand long Yagi-Uda antennas because the space between the Yagi elements can be regarded as an &lt;a href=&quot;https://en.wikipedia.org/wiki/Artificial_dielectrics&quot; rel=&quot;nofollow noreferrer&quot;&gt;artificial dielectric&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="250" LastEditDate="2014-11-09T22:09:27.697" LastActivityDate="2014-11-09T22:09:27.697" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2297" PostTypeId="1" AcceptedAnswerId="2298" CreationDate="2014-11-10T08:01:54.660" Score="8" ViewCount="877" Body="&lt;p&gt;I was recently reading an interesting &lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf&quot;&gt;article&lt;/a&gt; from the ARRL to get a better understanding of the SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following case is still unclear:&#xA;A low loss feed-line with an impedance that doesn't match the antenna's impedance and the receiver's impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case a large part of the signal should &quot;bounces&quot; back and forth into the feed-line due to the impedance mismatch. At this point the article states that: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The energy bounces&#xA;  back and forth inside the cable until it’s all&#xA;  radiated by the antenna for a lossless transmission line. An important point to realize&#xA;  is that with extremely low loss transmission&#xA;  line, no matter what the SWR, most of the&#xA;  power can get delivered to the antenna.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I understand that during each &quot;bounce&quot;, due to the impedance mismatch, some amount of energy will be transmitted and the rest reflected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't understand how this transmitted power could be useful. After &quot;bouncing&quot; back and forth the part of the signal that will be transmitted will probably be out of phase with the signal sent by the transmitter. Even if by any luck the reflected signal and the signal currently sent by the transmitter happened to be in phase, the information conveyed wouldn't be the same. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to me, even if almost of the power is transmitted, due to the high SWR most of this power should be just noise and don't improve the quality of the transmission in any case. But it's not what the article seems to explain. What did I miss ? &lt;/p&gt;&#xA;" OwnerUserId="1816" LastActivityDate="2018-11-22T15:47:58.880" Title="What happens in a low loss feed-line with a high SWR" Tags="&lt;feed-line&gt;&lt;transmission-line&gt;&lt;impedance&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2298" PostTypeId="2" ParentId="2297" CreationDate="2014-11-10T13:56:13.043" Score="7" Body="&lt;p&gt;For many modulations, the modulation is very slow compared to the propagation delay of the feedline. For example, SSB is typically limited to no more than 4 kHz. That corresponds to a wavelength of of 75 km. As long as the feedline is significantly shorter than this, then the delay due to the feedline is negligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may be easier to understand intuitively in a digital case. For example, PSK31 sends 31.25 symbols per second. 31.25 Hz corresponds to 9600 km, meaning by the time you are sending a bit, the previous bit is 9600 km away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This breaks down for very high-speed modulations. For example, &lt;a href=&quot;http://en.wikipedia.org/wiki/8VSB&quot; rel=&quot;nofollow noreferrer&quot;&gt;8VSB&lt;/a&gt; modulation used by HDTV broadcasts transmits 10.76 million symbols per second, equivalent to a 29 meter wavelength. At these speeds, a feedline is long enough to introduce significant delay, which could come out looking like &lt;a href=&quot;http://en.wikipedia.org/wiki/Multipath_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;multipath distortion&lt;/a&gt;. Then again, TV channels are 6 MHz wide. Most amateur transmissions are several orders of magnitude narrower. Protip: don't operate your commercial TV broadcast station with a poorly matched feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But for most amateur transmissions, we can consider the transmission as a pure sine wave, which is a reasonable approximation given the timescales dictated by the length of the feedline and the modulation. Then, it helps to visualize what a &lt;a href=&quot;http://en.wikipedia.org/wiki/Standing_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;standing wave&lt;/a&gt; in the feedline looks like. &lt;a href=&quot;http://commons.wikimedia.org/wiki/File:Standing_wave_2.gif#mediaviewer/File:Standing_wave_2.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;From Wikipedia&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://commons.wikimedia.org/wiki/File:Standing_wave_2.gif#mediaviewer/File:Standing_wave_2.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wmiMs.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we regard the transmitter to be on the left and the antenna to be on the right, then the blue wave represents the transmitted wave, and the red wave the reflected wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now here's the thing to realize: this particular image depicts a &lt;em&gt;complete&lt;/em&gt; standing wave on a &lt;em&gt;lossless&lt;/em&gt; transmission line. In this case, we are delivering 0 power to the antenna, the VSWR is infinite, and the transmitter's finals are probably about to explode. This doesn't happen in practice because our antennas always accept at least &lt;em&gt;some&lt;/em&gt; of the power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, only &lt;em&gt;some&lt;/em&gt; of the power is reflected back, and the result is a &lt;em&gt;partial standing wave&lt;/em&gt;. &lt;a href=&quot;http://www.acs.psu.edu/drussell/Demos/SWR/SWR.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dan A Russel has a page of great animations&lt;/a&gt;, like this one:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ukfVt.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a &lt;em&gt;partial&lt;/em&gt; standing wave, we can see that the envelope (outlined by the dotted lines) does not reach 0 amplitude at the nodes. In this case, some power is transferred. This is also a good visualization of VSWR: it is the ratio of the voltage amplitude at the antinodes (envelope maximums) to the voltage amplitude at the nodes (envelope minimums).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice also that the reflected wave might arrive back at the transmitter in any phase, depending on the length of the feedline and the antenna's reflection coefficient. It may or may not be in phase, but it will be a &lt;em&gt;constant&lt;/em&gt; phase, not just noise. By adding an antenna tuner we can reflect the reflected wave back at the antenna, and adjust the phase of this re-reflected wave to be whatever we want, within the limits of the tuner's capabilities of course.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-09-21T17:07:27.827" LastActivityDate="2015-09-21T17:07:27.827" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2299" PostTypeId="1" AcceptedAnswerId="2302" CreationDate="2014-11-10T17:31:24.157" Score="4" ViewCount="838" Body="&lt;p&gt;I am a high school student and am making a project on FM receiver for class 11. I am following this circuit diagram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/61gCI.gif&quot; alt=&quot;Schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The L2 in this diagram is a 22µH RF Choke. The part listed in the &lt;a href=&quot;http://www.somerset.net/arm/fm_only_one_transistor_radio.html&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;website&quot;&gt;website&lt;/a&gt; has the configuration provided below in its &lt;a href=&quot;http://www.mouser.com/ds/2/54/70f_series-62652.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;datasheet&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;L= 22uH +/-5%&#xA;Q= 51&#xA;Test Freq.= 2.5 MHz&#xA;SRF= 13&#xA;DCR Max.=2.28 Ohm&#xA;I, DC= 229 mA&#xA;Dim. A Max.= 0.16 inch&#xA;Dim. B +/-0.03= 0.25 inch&#xA;Core Material= iron&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I know how to make inductors but some properties such as the thickness of the copper wire (in SWG), whether enameled or not, no. of turns to use and the diameter and length of the inductor is confusing me. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And as an additional note can u please mention the number of turns in the L1 and the thickness of the copper wire to be used that will be suitable for the circuit diagram. &lt;/p&gt;&#xA;" OwnerUserId="1776" LastActivityDate="2014-11-11T06:14:53.593" Title="How to make an inductor?" Tags="&lt;receiver&gt;&lt;fm&gt;&lt;inductor&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2300" PostTypeId="2" ParentId="2294" CreationDate="2014-11-10T21:02:42.127" Score="4" Body="&lt;p&gt;You could use Aprx or Direwolf and configure the client as a Receive-only iGate. You can then assist in sending some directly received data to APRS-IS (the Internet side of APRS) and see the data appear on sites like www.aprs.fi&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will need a password to be able to log to aprsis but this is trivial once you have a callsign and google for aprs password calculator.&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2014-11-10T21:02:42.127" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2301" PostTypeId="1" CreationDate="2014-11-10T21:35:54.353" Score="5" ViewCount="1843" Body="&lt;p&gt;We live full time in our RV. We are at an RV park for the winter. They just knocked on my door and asked what kind of antenna I have on top of my RV. I told them it's a small ham radio antenna that I use only for monitoring at this time.  I was told that it has to come down because the Internet people couldn't figure out what is wrong with the service and decided it has to be my antenna. It is 1.2GHz and the internet company is at 3.2GHz. Could the antenna interfere with the Wi-Fi?&lt;/p&gt;&#xA;" OwnerUserId="1820" LastEditorUserId="1579" LastEditDate="2014-11-11T15:02:03.373" LastActivityDate="2014-12-04T02:45:12.070" Title="Can my small ham radio antenna interfere with WiFi in my RV park?" Tags="&lt;antenna&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2302" PostTypeId="2" ParentId="2299" CreationDate="2014-11-11T06:14:53.593" Score="1" Body="&lt;p&gt;First thing first: Whenever you make an inductor, wire must be insulated for the working voltage of the circuit or higher. Otherwise, you get shorted turns and your inductor turns into jut normal conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, since you're high-school student, my advice would be to just use one of the calculators for coil inductance and get the results from there. One I used to use is &lt;a href=&quot;http://hamwaves.com/antennas/inductance.html&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;. Most of the calculators I've seen work a bit backwards from what you need: You give them physical properties of your coil, and they give you back inductance.  &lt;a href=&quot;http://coil32.narod.ru/calc/multi_layer-en.html&quot; rel=&quot;nofollow&quot;&gt;Here&lt;/a&gt; is one that will let you enter inductance and will give you number of turns needed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, it's the best to just buy the recommended part, but I fully understand that it may be difficult or impossible to source that component in reasonable amount, in reasonable time-frame and for reasonable price. Therefore, some experimentation may be needed if you must manufacture the part by yourself. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, the math behind the calculators is quite complex, so I do not consider it reasonable to calculate all properties of an inductor by hand. Still, there's &lt;a href=&quot;http://en.wikipedia.org/wiki/Inductor#Inductance_formulae&quot; rel=&quot;nofollow&quot;&gt;this&lt;/a&gt; formula sheet at Wikipedia that has some useable formulas for inductance calculations. It can be very useful for tweaking the input parameters of calculators. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2014-11-11T06:14:53.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2303" PostTypeId="2" ParentId="2301" CreationDate="2014-11-11T06:48:00.590" Score="2" Body="&lt;p&gt;A receiving antenna as you describe it couldn't be a source of interference.  You should ask the internet company to provide  concrete data on the suspected interference to hopefully pinpoint the time and place the offending device is emanating the interfering signal.  Good luck on solving the interference!&lt;/p&gt;&#xA;" OwnerUserId="1114" LastActivityDate="2014-11-11T06:48:00.590" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2304" PostTypeId="1" CreationDate="2014-11-11T07:09:33.480" Score="1" ViewCount="339" Body="&lt;p&gt;I am trying to design and build an antenna + LNA board.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna: &lt;a href=&quot;http://www.yageo.com/documents/recent/An_FR4_1690_2405_0.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.yageo.com/documents/recent/An_FR4_1690_2405_0.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;LNA: &lt;a href=&quot;http://www.avagotech.com/docs/AV02-1237EN&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.avagotech.com/docs/AV02-1237EN&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is specced to run at 168 MHz.  In the LNA documentation it provides a suggested circuit for a 500 MHz signal.  The suggested circuit is below.  My Antenna feeds into the left, and my output is on the right.  In building the board following the suggested circuit, only my trace between my antenna and the start of the LNA circuit and the trace between the end of the LNA circuit and my output SMA are 50 ohm traces.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/vaAAz.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My Question is basically why isn't this working?  Am I missing some vital piece of information I have no considered?  Given that the circuit is designed for 500 MHz I would expect lesser performance with a 168 MHz signal, however I am unable to pick up any signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My test setup consists of an RF generator with an antenna attached, and a network analyzer with this antenna design attached. These two components sit a few feet apart. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe all of my soldering connections are correct, and I have confirmed that the board is receiving the appropriate amount of power. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An Image of My board.  Dimensions are roughly 1.5&quot;x1.25&quot;  and all of my components are 0204 size.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/0dCQ7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to recap, I receive no signals on this board even when I am blasting on my RF source right next to it.  I have tested other antennas to verify that the broken piece is indeed this new antenna design.  Could the mismatch between the frequency used to build the recommended circuit and the frequency my board is running at really eliminate all signals?  Or is there some aspect of antenna design that this novice is glossing over?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any thoughts would be appreciated!&lt;/p&gt;&#xA;" OwnerUserId="1822" LastEditorUserId="76" LastEditDate="2016-04-15T17:49:23.667" LastActivityDate="2016-04-15T17:49:23.667" Title="Antenna + LNA Design Questions" Tags="&lt;antenna&gt;&lt;lna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2305" PostTypeId="1" CreationDate="2014-11-11T14:09:05.523" Score="2" ViewCount="172" Body="&lt;p&gt;If someone has a high SWR, obviously their signal will not make it out as far due to reflections. However, they will still be able to hear relatively well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have noticed for receive, a high SWR may cause the signal to fade a small amount, but nothing compared to transmit. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does SWR fit into the law of reciprocity?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2014-12-01T15:46:22.827" Title="Reciprocity and SWR" Tags="&lt;antenna&gt;&lt;transmission-line&gt;&lt;impedance&gt;" AnswerCount="2" CommentCount="1" ClosedDate="2014-12-02T00:03:58.967" ContentLicense="CC BY-SA 3.0" />
  <row Id="2306" PostTypeId="1" CreationDate="2014-11-11T14:20:51.893" Score="4" ViewCount="299" Body="&lt;p&gt;Humans are asynchronous receivers, they can pick up words at any time, even if spread out, can combine into a sentence. Data rates are as fast as someone can hear/talk/copy code.&lt;/p&gt;&#xA;&lt;p&gt;All of the fast digital modes are Synchronous, example the HF digital voice has a lag between someone talking and their voice getting out because of the initial sync code.&lt;/p&gt;&#xA;&lt;p&gt;On a particular &lt;a href=&quot;http://en.m.wikipedia.org/wiki/AN/PRC-148&quot; rel=&quot;nofollow noreferrer&quot;&gt;radio Wikipedia page&lt;/a&gt;, it claimed these data rates:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;AM/FM Synchronous: 12/16 kbit/s&lt;/p&gt;&#xA;&lt;p&gt;AM/FM Asynchronous: Below 4800 Baud&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;What aspect of digital technology allows the data rate to be much faster if the transmission is synchronous.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2014-11-18T12:26:04.830" Title="Asynchronous vs. Synchronous data transmission speed" Tags="&lt;digital-modes&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2307" PostTypeId="2" ParentId="2305" CreationDate="2014-11-11T15:35:14.007" Score="0" Body="&lt;p&gt;High SWR on the transmitter means that less power gets radiated. Received SNR (signal to noise ratio) is degraded.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;High SWR on the receiver side means that both signal + noise reaching the antenna are equally attenuated when reaching the receiver. As long as you are still above the receiver's sensitivity, the SNR is practically unaffected.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2014-11-11T15:35:14.007" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2309" PostTypeId="1" CreationDate="2014-11-11T19:16:29.830" Score="4" ViewCount="1098" Body="&lt;p&gt;Recently I bought a telescopic antenna, model AL-800:&#xA;&lt;a href=&quot;http://www.pryme.com/index.php?l=product_detail&amp;amp;p=2155&quot; rel=&quot;nofollow&quot;&gt;http://www.pryme.com/index.php?l=product_detail&amp;amp;p=2155&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is 863mm (34 inches) long when fully extended. When retracted, it is 785mm long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will adding, for example, 4 ground radials increase the transmitting ability?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm thinking about using it as a portable base antenna that could be fit inside a backpack or fixed to a roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What do you think? Is there any reason for doing this? If yes, will using 1/4-wavelength radials be fine, like 4 radials that are each 17cm long?&lt;/p&gt;&#xA;" OwnerUserId="1827" LastEditorUserId="1579" LastEditDate="2014-11-12T08:13:39.657" LastActivityDate="2016-04-19T19:37:06.060" Title="Counterpoise for telescopic antenna AL-800 as a portable/base antenna on 70cm?" Tags="&lt;antenna&gt;" AnswerCount="4" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2310" PostTypeId="2" ParentId="2304" CreationDate="2014-11-13T04:01:26.177" Score="1" Body="&lt;p&gt;Is there any way to independently test the two parts of the circuit -- the antenna and the amplifier?&#xA;Perhaps use a 1 megaohm through-hole resistor to directly connect your RF source to the big &quot;antenna feed&quot; pad, completely bypassing the antenna, to test the amplifier section?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It appears to me that the version 1.1 circuit board has a ground pour covering most of the board.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While a ground pour is almost always a good thing for almost every PCB,&#xA;and some board-mount antennas &lt;em&gt;require&lt;/em&gt; a ground plane under them to work properly,&#xA;the ground plane can interfere with a few board-mount antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know enough about antenna design to know just by looking whether a particular antenna &lt;em&gt;must&lt;/em&gt; have a ground plane or must &lt;em&gt;not&lt;/em&gt; have a ground plane, so I always look at the data sheet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The data sheet &lt;a href=&quot;http://www.yageo.com/documents/recent/An_FR4_1690_2405_0.pdf&quot; rel=&quot;nofollow&quot;&gt;Yageo ANT2405F001R0169A datasheet&lt;/a&gt; doesn't specifically say in words anything about a ground plane.&#xA;It does have a &quot;evaluation board&quot; figure -- I don't see any copper underneath the antenna in that figure, so perhaps this is the kind of antenna that must &lt;em&gt;not&lt;/em&gt; have a ground plane under it to work properly?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this were my board, I would also measure with a multimeter and confirm that all 3 ground pins on the chip are actually connected to ground.&#xA;Because that's the kind of mistake I often make on the first prototype :-).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;p.s.:&#xA;That datasheet seems to indicate that antenna has a very sharp peak around 169 MHz (one-six-nine).&#xA;Do you see any difference when you test at one-six-nine vs. one-six-eight?&lt;/p&gt;&#xA;" OwnerUserId="1830" LastActivityDate="2014-11-13T04:01:26.177" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2311" PostTypeId="2" ParentId="1695" CreationDate="2014-11-13T18:09:31.750" Score="-2" Body="&lt;p&gt;I have the 771, works great, longer antenna, smaller loading coil, better efficiency. If you need further range, add a tiger tail. 771 is a whip, so its flexable.&lt;/p&gt;&#xA;" OwnerUserId="1837" LastActivityDate="2014-11-13T18:09:31.750" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2312" PostTypeId="2" ParentId="2301" CreationDate="2014-11-14T00:00:50.883" Score="2" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;A receiving antenna will not cause interference to the Internet company's antenna. It may block some of the Internet company antenna signal if is placed too close, but to cause interference your antenna would have to be emitting RF. Maybe its not your 1.2 GHz receiving antenna. Maybe its all the broadcast antennas on the other vehicles parked in the RV park. Doubtful, but just as ludicrous as the explanation given to &quot;They&quot; by the Internet people.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If the Internet company is claiming your antenna is causing interference they must show you, here I am presuming that you are a licensed ham, through instrumentation that your receiving antenna is the cause of the company's antenna interference problem.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="1840" LastEditorUserId="29" LastEditDate="2014-11-14T12:28:48.047" LastActivityDate="2014-11-14T12:28:48.047" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2315" PostTypeId="1" CreationDate="2014-11-14T04:33:03.057" Score="3" ViewCount="136" Body="&lt;p&gt;i was studying SSB demodulation and learned that a carrier is added to the SSB signal to make sure that envelope detection is possible. I came across a problem to find the percentage of power saved in this type of modulation if the modulation index is .5. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to derive the expression, % saving = (Useful power ) / Total power&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However i am not able to reach the final expression given in the answer. Please help !&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/wydb6.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1841" LastEditorUserId="1290" LastEditDate="2014-11-16T19:23:48.897" LastActivityDate="2014-11-16T19:23:48.897" Title="Power efficiency of SSB-Large carrier" Tags="&lt;ssb&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2316" PostTypeId="2" ParentId="2315" CreationDate="2014-11-14T13:51:43.143" Score="1" Body="&lt;p&gt;I think there is quite a bit of confusion in your question, which could have led to not being able to solve it. The Power Saving you obtain is certainly not in %. For that there should be a factor 100 around. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;learned that a local carrier&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is done in the receiver ('local'), so I'm not sure if you are really talking about a 'local' carrier. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;SSB &lt;em&gt;is&lt;/em&gt; (or &lt;em&gt;was&lt;/em&gt;?) transmitted at times with a carrier, to allow detection even in AM receivers, but then the carrier is not local.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula you mention, is that the correct solution or the one you arrived at?&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-11-14T13:51:43.143" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2317" PostTypeId="2" ParentId="2301" CreationDate="2014-11-14T14:57:41.867" Score="1" Body="&lt;p&gt;Maybe, but it's pretty unlikely. Usually, interference is caused by transmissions, but you aren't transmitting. A receiving-only antenna has the possibility of absorbing or phase-shifting other transmissions which happen to pass by.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an extreme example of this, consider a &lt;a href=&quot;http://en.wikipedia.org/wiki/Yagi-Uda_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yagi-Uda antenna&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://commons.wikimedia.org/wiki/File:Montreal-tower-top.thumb2.jpg#mediaviewer/File:Montreal-tower-top.thumb2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IlYqq.jpg&quot; alt=&quot;yagi antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such an antenna has only driven element. We could consider it as one transmitting antenna carefully placed around some number of receiving antennas which absorb and re-emit the transmitted signal in a specific way to create a directional antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As another extreme example, consider &lt;a href=&quot;http://en.wikipedia.org/wiki/Chaff_%28countermeasure%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;chaff&lt;/a&gt; used to interfere with radar transmissions. It is nothing more than a bunch of antennas blown into the air, yet they can really ruin your day if you are trying to make an airplane explode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, we don't know the exact geometry of your antenna relative to the ISP's antenna, but we do know that your antenna is for 1.2 GHz while the ISP is at 3.2 GHz. As 3.2 GHz is very near the third harmonic of 1.2 GHz, and center-fed dipoles or monopoles are also resonant on all their odd harmonics, your antenna is resonant at the ISP's frequency which means it will interact more strongly with the ISP's signal than some random object like an RV.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your antenna is very close to the ISP's, then you could accidentally have a Yagi-Uda antenna, with the two antennas interacting very strongly and giving some directionality to the ISP's antenna that isn't intended. If your antenna is less close, then the effects would be milder, with the effects largely limited to paths that pass through or near your antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the very small wavelength at these frequencies, and the size of an RV park, it's reasonable to assume your antenna falls in the &quot;less close&quot; category, which is why I'm very doubtful there's actually a problem. If the conclusion that your antenna was the problem was reached by some technician with 4 hours of training that did nothing more than plug a black box into the ISP's equipment and observe a red light on the thing, then it's almost surely an ignorant attempt to reassign blame. Most techs have very little knowledge of how to fix anything, so all they really can do is assign blame. Sometimes their test black box finds a problem at the ISP so they blame someone internally who fixes the problem. In all other cases they tend to blame the customer so they can leave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if the ISP sends out a real RF engineer, and he can make a creditable conclusion that your antenna is problematic, you shouldn't rule it out as an impossibility. Incidentally, this real RF engineer should also be quite capable of working with you to resolve the problem to your mutual satisfaction, which probably involves nothing more than a couple minor modifications to your station. After all, getting many antennas to work together (even with many of them transmitting!) is something RF engineers do &lt;em&gt;all the time&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/F9Z4U.jpg&quot; alt=&quot;antenna tower&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://sarixe.deviantart.com/art/Radio-Antenna-Tower-110402272&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Radio Antenna Towerby sarixe&lt;/em&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-11-18T12:36:42.527" LastActivityDate="2014-11-18T12:36:42.527" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2318" PostTypeId="1" AcceptedAnswerId="2320" CreationDate="2014-11-14T22:46:33.093" Score="11" ViewCount="1439" Body="&lt;p&gt;I've heard that APRS is only allowed for non-commercial use. I was thinking of a building a weather station that uploads data via APRS (so far, non-commercial). If I then include data from that weather station on a website with advertisements, is it commercial use (and thus not allowed)? If that is not commercial use, what would be an example of commercial use?&lt;/p&gt;&#xA;" OwnerUserId="1845" LastEditorUserId="1845" LastEditDate="2014-11-16T17:02:11.243" LastActivityDate="2019-02-23T14:59:54.507" Title="When is APRS use considered commercial?" Tags="&lt;united-states&gt;&lt;aprs&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2319" PostTypeId="1" CreationDate="2014-11-16T14:37:17.307" Score="3" ViewCount="43" Body="&lt;p&gt;Looking for a good place to find out what contest or events are going at the present.&lt;/p&gt;&#xA;" OwnerUserId="1847" LastActivityDate="2014-11-16T20:58:16.587" Title="How can I find out what ham radio events or contest are going on?" Tags="&lt;contest&gt;" AnswerCount="1" CommentCount="0" ClosedDate="2014-11-17T09:30:30.817" ContentLicense="CC BY-SA 3.0" />
  <row Id="2320" PostTypeId="2" ParentId="2318" CreationDate="2014-11-16T19:43:55.980" Score="8" Body="&lt;p&gt;There is no rule specific to APRS; the relevant regulations do not care about what mode, protocol, etc. you are using. From &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=9c74c897993f8e8f42eaa5f1fbbaf5a2&amp;amp;node=se47.5.97_1113&amp;amp;rgn=div8&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.113&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;§97.113   Prohibited transmissions.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) No amateur station shall transmit:&lt;/p&gt;&#xA;  &#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;&lt;p&gt;Communications specifically prohibited elsewhere in this part;&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;&lt;strong&gt;Communications for hire or for material compensation&lt;/strong&gt;, direct or indirect, paid or promised, except as otherwise provided in these rules;&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Communications in which &lt;strong&gt;the station licensee or control operator has a pecuniary interest&lt;/strong&gt;, including communications on behalf of an employer, with the following exceptions:&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;...&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;I am not a lawyer. This is not legal advice. This is speculation based on a layman's understanding. If you actually need a reliable answer, consult a lawyer.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These rules prohibit what you are proposing, because you are making transmissions which in which you have a pecuniary interest: your site, from which you profit via advertisements, would be of less value if you did not have the weather station transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if you are only doing one of the two things:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If you have a weather station transmitting and no one's paying you to do it, there is no pecuniary interest, so the transmission is not prohibited.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you are receiving APRS and displaying the data on a web site, you are not transmitting, so §97.113 does not apply. In fact, the well-known APRS data site &lt;a href=&quot;https://aprs.fi/&quot; rel=&quot;nofollow noreferrer&quot;&gt;aprs.fi&lt;/a&gt; contains ads.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-02-23T14:59:54.507" LastActivityDate="2019-02-23T14:59:54.507" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="2321" PostTypeId="2" ParentId="705" CreationDate="2014-11-16T20:07:13.593" Score="2" Body="&lt;p&gt;The &lt;a href=&quot;http://www.cqcontest.eu/&quot; rel=&quot;nofollow&quot;&gt;PG7V HF Contest Calendar&lt;/a&gt; is also a nice one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the meantime, I have put up a &lt;a href=&quot;http://hamwaves.com/contests/en/index.html&quot; rel=&quot;nofollow&quot;&gt;web page linking to all the calendars&lt;/a&gt; mentioned in these answers.&lt;/p&gt;&#xA;" OwnerUserId="250" LastActivityDate="2014-11-16T20:07:13.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2322" PostTypeId="2" ParentId="2306" CreationDate="2014-11-16T20:43:10.497" Score="3" Body="&lt;p&gt;Wikipedia is plain bonkers. The &lt;a href=&quot;http://www.thalescomminc.com/datasheets/Thales%20MBITR.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;manufacturer's data sheet&lt;/a&gt; is more enlightening:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Waveforms/Modes of Operation&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Implemented and Planned&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;AM/FM&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Non-secure voice&lt;/li&gt;&#xA;  &lt;li&gt;Non-secure narrowband voice (FM)&lt;/li&gt;&#xA;  &lt;li&gt;&lt;strong&gt;12 and 16 kbps secure voice&lt;/strong&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;strong&gt;12 and 16 kbps secure synchronous data&lt;/strong&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;strong&gt;Secure asynchronous data to 4800 bps&lt;/strong&gt;&lt;/li&gt;&#xA;  &lt;/ul&gt;&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;[...]&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;ANDVT&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Secure narrowband voice (LPC-10, MELP Vocoders)&lt;/li&gt;&#xA;  &lt;li&gt;&lt;strong&gt;Secure 2400 bps synchronous data&lt;/strong&gt;&lt;/li&gt;&#xA;  &lt;/ul&gt;&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Notice it says &quot;bps&quot; and &quot;kbps&quot; which mean &quot;(kilo) bits per second&quot;. There is no &quot;&lt;a href=&quot;http://en.wikipedia.org/wiki/Baud&quot; rel=&quot;nofollow noreferrer&quot;&gt;baud&lt;/a&gt;&quot; anywhere in the spec sheet. Whoever wrote that Wikipedia article must not know &lt;a href=&quot;https://stackoverflow.com/q/20534417/1574959&quot;&gt;the difference&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, we can't infer from any of this that synchronous communications are faster than asynchronous communications. All we can infer is that this particular radio implements a number of modes. Some are fast, and some are slow. Some are synchronous, and some are asynchronous. You can even see that the &lt;em&gt;slowest&lt;/em&gt; data listed in the datasheet is ANDVT, and it is described as &quot;synchronous&quot;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-05-23T12:37:22.373" LastActivityDate="2014-11-18T12:26:04.830" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2323" PostTypeId="2" ParentId="2319" CreationDate="2014-11-16T20:58:16.587" Score="1" Body="&lt;p&gt;This is an excellent resource:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.hornucopia.com/contestcal/&quot; rel=&quot;nofollow&quot;&gt;http://www.hornucopia.com/contestcal/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1150" LastActivityDate="2014-11-16T20:58:16.587" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2324" PostTypeId="1" AcceptedAnswerId="2328" CreationDate="2014-11-17T05:31:56.293" Score="1" ViewCount="1992" Body="&lt;p&gt;I'm throwing together bits-and-pieces towards my rig on a less than shoestring budget. It is possible to apply a take-off from the key and use it to drive a piezo-buzzer. Of course, there won't be any tone control locally. But I can live with that, or use a divider from ground to provide minimal tone control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does the side-tone oscillator serve any purpose other than allowing the operator to listen to the code being transmitted?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="218" LastEditDate="2014-11-17T14:14:13.897" LastActivityDate="2014-11-18T01:08:22.923" Title="Do I really need a side-tone oscillator?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2325" PostTypeId="1" CreationDate="2014-11-17T06:53:31.807" Score="2" ViewCount="306" Body="&lt;p&gt;Many suggestions on the Internet for a &quot;starter&quot; HF long wire, suggest running a wire in the attic. My (South Australian) roof has a 30 degree pitch, and what little space remains contains air conditioner ducting. Not to mention the steel roof on the carport... &lt;p&gt;&#xA;Can I use that aircon ducting to my advantage, as a counterpoise wire? I thought the general idea of running a wire at height was to get &lt;strong&gt;away&lt;/strong&gt; from ground: that is just not going to happen here.&lt;br&gt;&#xA; If I can't take advantage of the earthed ducting, how far above it should I try to get?&lt;/p&gt;&#xA;" OwnerUserId="1610" LastActivityDate="2014-11-18T01:45:16.477" Title="Air conditioner duct as counterpoise?" Tags="&lt;hf&gt;&lt;wire-antenna&gt;&lt;counterpoise&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2326" PostTypeId="2" ParentId="2324" CreationDate="2014-11-17T20:51:45.017" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;http://www.thefreedictionary.com/side+tone&quot; rel=&quot;nofollow&quot;&gt;side tone&lt;/a&gt;&lt;br/&gt;&#xA;  n&lt;br/&gt;&#xA;  1. (Telecommunications) sound diverted from a telephone microphone to the earpiece so that a speaker hears his own voice at the same level and position as that of the respondent&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;sub&gt;Collins English Dictionary – Complete and Unabridged © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003&lt;/sub&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is of course referring to the more familiar sidetone in a telephone, but the sidetone in a CW transmitter is defined analogously. So by definition, the sidetone oscillator has no purpose other than to make audible what is being transmitted. I suppose some radio designs may have some other use for an audio frequency oscillator for which the sidetone oscillator can be dual-purposed, but there is no general reason this must be so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would also note that if you have a piezo buzzer that produces a tone from DC, then &lt;a href=&quot;http://www.aurelienr.com/electronique/piezo/applic.pdf&quot; rel=&quot;nofollow&quot;&gt;it contains an oscillator&lt;/a&gt;. Thus, you haven't really eliminated the sidetone oscillator, you've just used the one in the buzzer. If it's cheap and otherwise meets your requirements, then I can think of no reason not to use this solution.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-11-17T20:51:45.017" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="2327" PostTypeId="2" ParentId="2325" CreationDate="2014-11-17T21:07:11.970" Score="1" Body="&lt;p&gt;You could just use the ducting in lieu of the wire. Anything conductive makes an antenna to some degree. For example, &lt;a href=&quot;http://www.sgcworld.com/raingutterinstall.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;gutters&lt;/a&gt;. I wouldn't suggest putting more than 10W into your ducting unless you want to find out how your air handler deals with RF current, but the same advice would apply to a wire running in close proximity to your ductwork also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do run a separate wire, the ducting is going to be a &quot;counterpoise&quot; whether you deliberately make it so or not. Unless you deliberately install a more effective counterpoise (like a ground plane, or the other half of a dipole) and make sure that antenna is &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;properly balanced&lt;/a&gt;, then the counterpoise is going to be whatever conductive things are nearby, like the feedline, the earth, your electrical wiring, and your ductwork.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-11-17T21:07:11.970" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2328" PostTypeId="2" ParentId="2324" CreationDate="2014-11-18T01:08:22.923" Score="3" Body="&lt;p&gt;I am assuming two things in my answer and both may be wrong assumptions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Your shoe-string budget rig is a transceiver, probably QRP, maybe even single band.&lt;/li&gt;&#xA;&lt;li&gt;Rig is CW only (typical of small shoe-string budget rigs).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Thus, do you really need a side-tone oscillator so that you can listen to your own sending (assuming CW).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my opinion, the answer is yes.  I learned CW when I was 9 years old (or, 58 years ago) and today, my main operating mode that I use every day, is CW.  My copy speed is a comfortable 20 to 24 wpm error free but I can do contests up to 35 wpm and copy call signs (usually) at 38 to 40 wpm.  But, one thing I can't do is send without using a side tone so that I can hear what I send.  I assume you are just beginning at CW so therefore, I am pretty sure you can't effectively send without hearing what you send.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You ask if you can use a buzzer or some external oscillator.  Answer is yes you can.  Now, whether there would be interference in driving two separate circuits from a single switch (that is, using your single telegraph key with the transmission as well as separate side tone oscillator depends on the circuits themselves.  A high-impedance interface to the side-tone oscillator should be safe (~10 times higher than the impedance of the keying circuit of the transmitter unless that impedance is also high).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will be missing a nice feature of the built-in side tone oscillator and that is the ability to zero-beat a signal.  Actually, there are people who can do this accurately without a side-tone generator but I can't (though, haven't tried in years).  But, if you are a beginner at CW, then maybe zero beating a signal is not the most important feature.  If you were to participate in CW traffic nets (as I do) then the net control would often require zero beat (or, ask for it).  They will send out QNZ which means &quot;Zero Beat your frequency with mine&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you fail to zero beat a signal it is possible that you may not be heard if you send to him (or, her).  The reason is that he may have squeezed down his filters to a point that you have to be very close to his frequency in order to be heard.  For example, when I am on the hunt for CW stations, I keep my filter fairly wide at 1 KHz.  But, once the QSO starts I narrow down my filter to anywhere between 200 and 400 Hz.  If you are more than 400 Hz away in that situation then I probably would not hear you.  Now, I use a K3 that has nice sharp roofing filters: 200 Hz, 400 Hz, 1000 Hz, 1800 Hz, and 2700 Hz.  Note that my rig does not do AM since I took out my 6000 Hz AM filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I said, my rig is an Elecraft K3 and it has a nifty feature.  It can do a zero beat on the incoming signal by the mere push of a button (called the Spot button).  I also have an LED display that shows how far off (low or high side) from center frequency that the signal is which is kind of nice.  And, I have the P3 pan adapter that allows me to sort of zero beat visually on the screen.  Nice rig but often never a first rig.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2014-11-18T01:08:22.923" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2329" PostTypeId="2" ParentId="2325" CreationDate="2014-11-18T01:45:16.477" Score="3" Body="&lt;p&gt;If you run a wire up in your attic, all other conductors such as ducting, house wiring, gutters, and so on are part of your antenna system.  You want to avoid near-field capacitive coupling as your losses will definitely go up in that case.  Therefore, a wire antenna close to other conductors that run parallel to the antenna conductor is not good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am a big fan of numerical modeling of antennas.  I model every single wire antenna I have ever built in the last 10 years using NEC2 (National Electromagnetics Code).  Actually, I bought the license for NEC4 and use that a lot but NEC2 is free and can easily be run on PC Windows, Mac OS X, or any Linux or Unix platform (assuming you build it yourself, source is available).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With NEC2, you can actually model the antenna wire as well as other near by conductors whether they be wire or metal ducting (typically modeled as a mesh).  Doing it up right means spending time creating the model but you can learn a lot about an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens when you have nearby conductive surfaces?&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;If they are close, you can have greater losses.&lt;/li&gt;&#xA;&lt;li&gt;Your matching impedance can be changed (important for resonant antennas).&lt;/li&gt;&#xA;&lt;li&gt;Your propagation pattern will very likely be changed in creating nulls and&#xA;higher gain lobes where you least expect them.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Items 2 and 3 are determined when you model with NEC2 and NEC4.  I mean, that is the principle reasons I do modeling is to calculate the matching impedance and to determine the location of nulls and higher gain lobes and take off angle and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get started with NEC2 you can acquire the free version of EZNEC software available from ARRL.  Or, you can possibly get a 30-day trial from the EZNEC vendor W7EL (at &lt;a href=&quot;http://www.eznec.com&quot; rel=&quot;nofollow&quot;&gt;http://www.eznec.com&lt;/a&gt;).  Or, you can go to &lt;a href=&quot;http://nec2.org&quot; rel=&quot;nofollow&quot;&gt;http://nec2.org&lt;/a&gt; or merely google NEC2.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2014-11-18T01:45:16.477" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2330" PostTypeId="2" ParentId="2075" CreationDate="2014-11-18T03:02:08.063" Score="5" Body="&lt;p&gt;See &lt;a href=&quot;https://baofengtech.com/pdf/CompareChart.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;This Chart&lt;/a&gt; at BaofengTech.com.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Really the UV-5RE is just a cosmetic variant of the UV-5R.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to your firmware version you should check out &lt;a href=&quot;http://baofengtech.com/firmwareguide&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page&lt;/a&gt; at Baofengtech.com. Sadly it is not very helpful with your firmware version:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;BFB297, BFB298&#xA;  Unknown Changes&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;But it is still a great reference.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastEditorUserId="16480" LastEditDate="2020-03-11T13:25:16.653" LastActivityDate="2020-03-11T13:25:16.653" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="2332" PostTypeId="2" ParentId="1038" CreationDate="2014-11-18T09:22:18.833" Score="1" Body="&lt;p&gt;&lt;em&gt;I&lt;/em&gt; and &lt;em&gt;Q&lt;/em&gt; are somewhat confusing to me, too. I came up with a mental picture, which may help...&lt;br&gt;&#xA;Consider a piston, in a motor. If you took a flash photo, and the piston was all the way up (or down) it's fairly easy to figure out the position of the crank.&lt;p&gt;&#xA;But- what if the piston is &lt;strong&gt;Half-way&lt;/strong&gt; up? Is the piston moving down (intake or power stroke), or moving up (compression or exhaust stroke)?&lt;p&gt;&#xA;If you had a &lt;strong&gt;second&lt;/strong&gt; piston, &lt;em&gt;attached to the same crank position&lt;/em&gt;, you could figure out which phase the motor is at.&lt;p&gt;&#xA;How does this compare to electronics?&lt;br&gt;&#xA;Well, when you sample a waveform at a given rate, you get those magnitudes. They will vary, depending on the relative ratio between the signal frequency, and the sample frequency. BUT - is the radio signal faster, or slower?&lt;br&gt;&#xA;The &lt;strong&gt;Second&lt;/strong&gt; sample is like that second piston: it helps you determine if the original signal was faster (upper sideband) or slower (lower sideband). If this &lt;em&gt;changes with time&lt;/em&gt; then the frequency is changing, i.e.. you have an FM signal.&lt;p&gt;&#xA;As to whether they can be demodulated &quot;easily&quot;...There are those who have done it. If you just take their code / designs, it's remarkably easy. Understanding &lt;em&gt;why&lt;/em&gt; it works depends on your definition of &quot;easy&quot;.&lt;/p&gt;&#xA;" OwnerUserId="1610" LastActivityDate="2014-11-18T09:22:18.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2333" PostTypeId="2" ParentId="2309" CreationDate="2014-11-18T18:16:04.900" Score="3" Body="&lt;p&gt;The 'inventions' done to make an antenna are generally considered a trade secret by the manufacturers. I found out how my dual band works, when it got crushed after traveling in the cargo hold of an airplane. It's not simple coils... So simulating it in nec is not a simple task.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When used with an HT, all antennas assume that the user has the antenna in his hand, and the body will act as a (bad) 'counterpoise'. Of course, if you want to improve the situation, and make the use more independent of the user's position and 'pose', a groundplane would help. If nothing else, it will reduce the RF current to the hand of the operator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, I'd think twice about adding 3 (or 4) pointy things to the antenna, which will mostly be traveling at or near eye-height. It seems like an invitation for lawsuits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that you groundplane will only work at 70cm. If you want them to work on 2m too, you'll have to add radials for that frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And a final note: if you &lt;em&gt;only&lt;/em&gt; want 70 cm, think about looking for a J-pole based design, or a vertical dipole, Neither needs a groundplane, and move the high current node up in the antenna.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-11-18T18:16:04.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2334" PostTypeId="2" ParentId="2309" CreationDate="2014-11-19T21:49:10.667" Score="1" Body="&lt;p&gt;Many handheld antennas are just a 1/4 wave whip. In this case, &lt;a href=&quot;https://ham.stackexchange.com/q/495/218&quot;&gt;the counterpoise is your body, the radio, and anything else around&lt;/a&gt;. Obviously this is a less than optimal design, and adding a more deliberate and efficient counterpoise can only help, although it comes at the cost of making the antenna bigger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A better counterpoise can come in many forms, like a ground plane, a &lt;a href=&quot;http://www.hamuniverse.com/htantennamod.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;tiger tail&lt;/a&gt;, or a &lt;a href=&quot;https://ham.stackexchange.com/a/1941/218&quot;&gt;vertical dipole&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, the manufacturer seems to provide about zero information on the design of this particular antenna, so it's difficult to determine if this is applicable or not. One bit of information we have is the length: 34 inches. This is pretty close to a half-wavelength at 2m, which might suggest that it is already a vertical dipole of some sort. If this is the case, then adding pieces to the antenna isn't going to make it more effective: it's going to mess it up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are wondering about 70cm also, there's probably no magic there. Because &lt;a href=&quot;https://ham.stackexchange.com/q/1918/218&quot;&gt;70cm is the third harmonic of 2m&lt;/a&gt;, an ordinary 2m dipole also works for 70cm.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2014-11-19T21:49:10.667" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2335" PostTypeId="2" ParentId="2304" CreationDate="2014-11-20T13:38:09.740" Score="0" Body="&lt;p&gt;At 160 Mhz, there are no &lt;em&gt;great&lt;/em&gt; problems with lengths of paths, so I'm guessing that is not the problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, I cannot find any feedthroughs (through holes) to the other side of the board, so you must be sure that all the grounds on the board are connected together. As far as I can see, there &lt;em&gt;are&lt;/em&gt; a few areas that don't have connection to others. Are you sure all grounds are connected together? A grounded plane on the other side of the board is nearly always a good idea, even if just used to connect all grounds together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Did you check if there is a voltage drop on the 240$\Omega$ resistor? If there is no drop, then your LNA isn't consuming any current. If the drop is too large, there might be a short between VCC and ground.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-11-20T13:38:09.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2336" PostTypeId="1" AcceptedAnswerId="2340" CreationDate="2014-11-20T15:01:42.257" Score="5" ViewCount="864" Body="&lt;p&gt;What happens if all CTCSS tones are transmitted at once? Would it trip all radios listening on that frequency?&lt;/p&gt;&#xA;" OwnerUserId="170" LastActivityDate="2015-07-21T20:49:29.817" Title="Would it be possible to transmit all CTCSS tones at once?" Tags="&lt;tone-squelch&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2337" PostTypeId="1" AcceptedAnswerId="2338" CreationDate="2014-11-20T16:40:57.940" Score="6" ViewCount="1907" Body="&lt;p&gt;I have had some conflicting experiences relating to the effect of night time (ionosphere, temperature, etc.) on propagation.  Perhaps it is related to the frequency of what I was working with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Several years ago I troubleshot a Wi-Fi network in the desert.  Every night at a variable time (but early on in the night, say 10PM) the network would go down.  I fixed this problem by using directional antennas.  This was a ~2.45 GHz system.  So it seems the received power, or at least SNR, decreased with night.  One person I asked about it thought that it was due to increased noise (due to reflection of many other signals off the ionosphere at night).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Last night I looked at a broadcast FM station.  The power was pretty high.  I  just checked it out again during the day and the receive power was at least 5 dB less.  This was ~85 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So there are conflicting results.  One signal propagates better at night, another worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Question:&lt;/strong&gt; What things affect VHF/UHF signal propagation at night?&lt;/p&gt;&#xA;" OwnerUserId="850" LastEditorUserId="76" LastEditDate="2014-11-20T19:24:27.067" LastActivityDate="2014-11-20T19:24:27.067" Title="Effect of night on VHF/UHF propagation" Tags="&lt;propagation&gt;&lt;vhf&gt;&lt;uhf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2338" PostTypeId="2" ParentId="2337" CreationDate="2014-11-20T17:59:09.977" Score="4" Body="&lt;p&gt;When we have a large temperature spread here (day/night) I start looking for new repeaters on vhf/uhf.  The gradient will usually form a temperature inversion that is pretty efficient at scattering radio signals, sometimes in very pronounced ways.  Before digital tv it wasn't uncommon to be watching a station and have another 100's of miles away completely take over the channel (with digital tv you just get a blank screen).  It's called tropospheric ducting, and could have been your culprit seeing as how temperatures differ quite a bit in an environment like the desert.  In your case it could have brought in noise from other distant wifi transmitters that blocked the signals you were trying to receive, and then disappeared when the inversions went away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moisture can also affect (attenuate) frequencies in the GHz so that may have been an issue between sites.  When you installed directional antennas you boosted the SNR by focusing all of your RF towards the desired receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ionospheric propagation at night doesn't typically work for any freq over about 10mhz so that is most likely not your issue.  It's fascinating stuff to learn about! &lt;/p&gt;&#xA;" OwnerUserId="1864" LastActivityDate="2014-11-20T17:59:09.977" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2340" PostTypeId="2" ParentId="2336" CreationDate="2014-11-20T22:50:54.850" Score="8" Body="&lt;p&gt;You could get several different results, depending on exactly how the receiver recognizes the expected tone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a small amount of web research, it sounds like the usual methods are either a filter passing only the expected tone, or a frequency counter which determines the frequency of the tone in the signal which is then compared with the expected tone frequency.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If the receiver uses a filter to detect the tone, then its squelch will open, because it doesn't care about any other part of the frequency content of the signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If the receiver uses a frequency counter to detect the tone, then if all the tones are close enough to equal strength, the counter will not have a valid output, just as if there was no tone at all (only noise) in the relevant frequency range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there is likely to be some non-flat frequency response somewhere along the way, so one particular tone will win and the squelch will open only if that tone is the one the receiver is expecting.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;You will also run into issues transmitting all the tones at once — your audio signal will have high peaks as the tones beat against each other, and you will have to keep the total amplitude low to avoid over-deviating/distorting — quite likely low enough that the individual tones aren't strong enough to be recognized as CTCSS tones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I thought I'd see what the actual result is, so I wrote a program with GNU Radio to synthesize the combination of all tones listed on &lt;a href=&quot;http://en.wikipedia.org/wiki/Continuous_Tone-Coded_Squelch_System#List_of_tones&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia's page&lt;/a&gt;. In order to prevent the output from clipping (analogous to overdeviating in an analog FM signal), I had to set the amplitude of the individual tones to 0.05 (-26 dB), which is significantly below the 0.15 (-16 dB) level that Phil Frost's answer said is normal for CTCSS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/cXX3k.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;#!/usr/bin/env python&#xA;&#xA;from gnuradio import gr, blocks, analog&#xA;&#xA;sample_rate = 44100&#xA;tones = [67.0, 69.3, 71.9, 74.4, 77.0, 79.7, 82.5, 85.4, 88.5, 91.5, 94.8, 97.4, 100.0, 103.5, 107.2, 110.9, 114.8, 118.8, 123.0, 127.3, 131.8, 136.5, 141.3, 146.2, 150.0, 151.4, 156.7, 162.2, 167.9, 173.8, 179.9, 186.2, 192.8, 199.5, 206.5, 213.8, 221.3, 229.1, 237.1, 245.5, 254.1, 159.8, 165.5, 171.3, 177.3, 183.5, 189.9, 196.6, 203.5, 210.7, 218.1, 225.7, 233.6, 241.8, 250.3]&#xA;duration = 10&#xA;gain = 0.05&#xA;&#xA;t = gr.top_block()&#xA;sum = blocks.add_ff()&#xA;out = blocks.wavfile_sink(&quot;out.wav&quot;, 1, sample_rate, 16)&#xA;t.connect(&#xA;    sum,&#xA;    blocks.head(gr.sizeof_float, int(sample_rate * duration)),&#xA;    out)&#xA;for i, tone in enumerate(tones):&#xA;    t.connect(&#xA;        analog.sig_source_f(sample_rate, analog.GR_SIN_WAVE, tone, gain),&#xA;        (sum, i))&#xA;&#xA;t.run()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-07-21T20:49:29.817" LastActivityDate="2015-07-21T20:49:29.817" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2341" PostTypeId="2" ParentId="2285" CreationDate="2014-11-21T00:27:14.140" Score="3" Body="&lt;p&gt;The Colorado Council of Amateur Radio Clubs (CCARC)&#xA;&lt;a href=&quot;http://www.ccarc.net/images/CCARC_FUP_144MHz_revB.pdf&quot; rel=&quot;nofollow&quot;&gt;2 Meter Frequency Use Plan&lt;/a&gt; states that &#xA;144.900 - 145.100 MHZ should be used for Packet communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;144.390 MHZ is also used Nationwide for APRS.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;h2&gt;Colorado Council of Amateur Radio Clubs (CCARC) 2 Meter Frequency Use Plan - 144.000 through 148.000 MHz&lt;/h2&gt;&#xA;  &#xA;  &lt;p&gt;Frequency (MHz) Usage&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;144.000 - 144.050 CW/EME&lt;/li&gt;&#xA;  &lt;li&gt;144.050 - 144.100 CW Weak Signal&lt;/li&gt;&#xA;  &lt;li&gt;144.100 - 144.275 CW and SSB Weak Signal&lt;/li&gt;&#xA;  &lt;li&gt;144.275 - 144.300 Propagation Beacons&lt;/li&gt;&#xA;  &lt;li&gt;144.300 - 144.500 Satellite/OSCAR&lt;/li&gt;&#xA;  &lt;li&gt;144.500 - 144.900 FM Repeater Inputs&lt;/li&gt;&#xA;  &lt;li&gt;&lt;strong&gt;144.900 - 145.100 Weak Signal, FM Simplex, Digital/Packet&lt;/strong&gt;&lt;/li&gt;&#xA;  &lt;li&gt;145.100 - 145.500 FM Repeater Outputs&lt;/li&gt;&#xA;  &lt;li&gt;145.500 - 145.800 Miscellaneous and Experimental Modes&lt;/li&gt;&#xA;  &lt;li&gt;145.800 - 146.000 Satellite/OSCAR&lt;/li&gt;&#xA;  &lt;li&gt;146.010 - 146.370 FM Repeater Inputs&lt;/li&gt;&#xA;  &lt;li&gt;146.400 - 146.580 FM Voice Simplex&lt;/li&gt;&#xA;  &lt;li&gt;146.610 - 147.390 FM Repeater Outputs&lt;/li&gt;&#xA;  &lt;li&gt;147.420 - 147.570 FM Voice Simplex&lt;/li&gt;&#xA;  &lt;li&gt;147.600 - 147.990 FM Repeater Inputs&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2014-11-21T00:27:14.140" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2342" PostTypeId="2" ParentId="2336" CreationDate="2014-11-21T02:37:45.033" Score="2" Body="&lt;p&gt;No, you can't. Based on the particular method the receiver uses to decode CTCSS, multiple tones may or may not be recognized. But that's moot, because you can't transmit all the tones anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CTCSS adds a low frequency tone to the baseband input to the FM modulator. Standards vary, but the amplitude of this tone is around 15% of the deviation. The amplitude needs to be high enough to allow for reliable detection above the noise floor, while low enough to allow the intended transmission (your voice, etc) to also be modulated without overdeviating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's just use round numbers to make the math easy and say the deviation is 10 kHz. That means the CTCSS tone will be responsible for deviation of 1.5kHz, leaving the other 8.5 kHz of deviation available for the intended transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you transmit two tones, you've doubled the power of the CTCSS tones. The deviation also increases, leaving less headroom for the intended transmission. Still workable, I suppose. Presuming of course that the decoder will recognize this as valid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if you transmit &lt;em&gt;all&lt;/em&gt; the tones, there just isn't enough deviation left to transmit all the tones at the specified power. When you add the power of all the tones together, you won't even be able to transmit them without overdeviating. You could reduce the power of the tones to avoid overdeviating, but then whatever tone happens to be the right one at the decoder will no longer be strong enough to be detected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you can transmit a horribly distorted signal, or a tone too weak to be detected.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-11-21T02:37:45.033" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2343" PostTypeId="1" AcceptedAnswerId="3660" CreationDate="2014-11-21T02:38:28.400" Score="6" ViewCount="913" Body="&lt;p&gt;I am considering buying a Byonics TinyTraK4 to connect to my Kenwood TM-281a to do APRS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I am wondering if I should instead buy a separate radio (I am considering a Baofeng UV-5R) as well and connect the TT4 to it instead of the TM-281A.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My fear is that with the TT4 connected to the TM-281, I will no longer be able to use the it for other communications unless I disconnect the TT4.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to use the Kenwood for normal communications even while the TT4 is connected to it?&lt;/p&gt;&#xA;" OwnerUserId="1246" LastEditorUserId="1246" LastEditDate="2015-02-06T01:12:23.250" LastActivityDate="2015-02-26T01:09:53.837" Title="Can I still use my Kenwood TM-281A for normal communications even while I have a TinyTrak4 connected for APRS use?" Tags="&lt;aprs&gt;&lt;kenwood&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2346" PostTypeId="1" CreationDate="2014-11-23T18:54:31.030" Score="3" ViewCount="383" Body="&lt;p&gt;Just going through the RF oscillator listed on &lt;a href=&quot;http://sm0vpo.altervista.org/blocks/osc7m00.htm&quot; rel=&quot;nofollow&quot;&gt;SM0VPO's web-site&lt;/a&gt;. I replaced C1 by a reverse biased 6A8, and used an E-core transformer pulled out of a Compact Fluorescent Lamp instead of an inductor for the 40m bad. In all probability, she wont' swing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if she does, is there a hack to find out the frequency without using an oscilloscope, or digital frequency counter? &lt;/p&gt;&#xA;" OwnerUserId="5" LastActivityDate="2014-11-23T20:13:58.290" Title="How can I tell the frequency without an oscilloscope, or frequency counter?" Tags="&lt;frequency&gt;&lt;oscillator&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2347" PostTypeId="2" ParentId="2346" CreationDate="2014-11-23T20:13:58.290" Score="3" Body="&lt;p&gt;You &lt;em&gt;can&lt;/em&gt; use a radio receiver that has appropriate coverage, but the catch is that you have to sweep across the entire frequency range the oscillator might be oscillating at — you're limited to the bandwidth of the radio's filters, so you can't get an immediate answer like a frequency counter would give you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, you need to make sure the signal is getting to your radio. Since you don't know anything about the signal characteristics, not having a scope (and I wouldn't trust an AC voltmeter to read properly at RF), you don't want to plug it into the antenna port. Instead, just place &lt;a href=&quot;https://ham.stackexchange.com/a/1272/76&quot;&gt;a small, insulated antenna&lt;/a&gt; near the oscillator.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The best type of radio for this purpose is one with some kind of spectrum display (&quot;panadapter&quot;, SDR, whatever) — the wider the better. Tune it to where you hope the oscillator is oscillating, then look for peaks on the spectrum. Turn the oscillator off and check that the peak disappears, to confirm that it isn't some other signal. If you don't see anything, change the tuning step by step (by just less than the bandwidth of the display) so you get a look at the entire plausible band.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you have a CW or SSB receiver, use its “scan” feature and listen for a continuous tone with no modulation, confirming it as above. Once you've found a tone, here's how to get the exact frequency if you need it:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If you have a CW receiver with a tuning indicator or &quot;spot tone&quot;, use it to find the frequency exactly.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you have only a SSB receiver, tune until the tone goes inaudibly low-frequency.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you're stuck with an AM or FM receiver, listen for silence instead of static. (Don't forget to open the squelch so you can hear the static!) You won't be able to make a precise measurement this way.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Once you have determined a frequency using this procedure, you have the additional problem that you may have found a harmonic of the original signal. Therefore, check frequencies which are 1⁄2, 1⁄3, 1⁄4, 1⁄5, etc. of the one you found.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, this procedure is immensely tedious (depending on how fast you can scan the spectrum), and won't help if the oscillator's frequency is outside of your receiver's coverage. Depending on your personal value of time vs. money it may well be a better idea to buy or build a frequency counter (or oscilloscope).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-11-23T20:13:58.290" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2349" PostTypeId="1" AcceptedAnswerId="2350" CreationDate="2014-11-24T00:11:11.037" Score="1" ViewCount="1229" Body="&lt;p&gt;I recently purchased the &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B009MAKWC0&quot; rel=&quot;nofollow&quot;&gt;Baofeng UV-5RA&lt;/a&gt;. I am trying to set up dual watch mode so that I can receive one frequency, and be able to transmit on another frequency when I key the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I enabled TDR and set TDR-AB to B. When I am on frequency A and key the radio, it still transmits on A not B. I followed the instructions &lt;a href=&quot;http://brianbdonaldson.com/docs/Programming%20the%20Baofeng%20UV.pdf&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt; and apparently it is a bug? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone else had this problem before? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I think this has something to do with the upgraded firmware? Can someone confirm &lt;a href=&quot;http://forums.radioreference.com/budget-entry-level-transceivers/296079-baofeng-uv-5r-vs-uv-b5.html#post2233901&quot; rel=&quot;nofollow&quot;&gt;this&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="1878" LastEditorUserId="1878" LastEditDate="2014-11-24T22:11:51.320" LastActivityDate="2014-11-25T22:55:14.513" Title="Baofeng UV-5R Split mode" Tags="&lt;baofeng&gt;&lt;uv-5r&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2350" PostTypeId="2" ParentId="2349" CreationDate="2014-11-25T22:55:14.513" Score="1" Body="&lt;p&gt;It is due firmware. Apparently Baofeng is getting rid of that menu option. &lt;/p&gt;&#xA;" OwnerUserId="1878" LastActivityDate="2014-11-25T22:55:14.513" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2351" PostTypeId="1" AcceptedAnswerId="2355" CreationDate="2014-11-26T05:37:50.660" Score="6" ViewCount="1342" Body="&lt;p&gt;Please don't downvote just for the title, I'm not trolling, and honestly looking for an answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not directly involved with Amateur Radio, but have friends who are. They're always by the book. The book is right. period. With amateur radio, if you even ask whether something is within the rules, you get shot down and threatened with government reports. I've seen this in person, even on &lt;a href=&quot;https://ham.stackexchange.com/questions/2318/when-is-aprs-use-considered-commercial?newreg=1dec0e22e42f41019ed7995528bddee2&quot;&gt;this very forum.&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If you do it, please tell me your call sign and station location so I can file a complaint with the FCC. I'm certain they will come after you. If you want a free wireless link, try a part 15 device like Wi-Fi. Or do what everyone else does: &lt;i&gt;pay for commercial wireless data&lt;/i&gt;. This kind of abuse is precisely what the regulations aim to forbid. What if I'm a radio broadcaster, and I want a remote feed? Maybe I'll use ham radio to link back to the transmitter (so far, non-commercial), then I'll re-transmit it with ads. Yeah, right.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To me, that comes across as extremely hostile. The question is a fair one in my mind. The difference between &quot;legal&quot; and &quot;potentially illegal&quot; is so minute, and the reaction is entirely disproportional, but from my experience, the norm!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most hobbies aren't nearly as strict. If you want to use 80 grit sandpaper instead of 60, or drive 110 instead of 100, no one cares. Absolutely no one would report you to a federal agency for not wearing a mask painting, or using a double instead of an int. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm intrigued by amateur radio, but scared of attitudes like the one above. Could someone explain why these attitudes exist?&lt;/p&gt;&#xA;" OwnerUserId="1882" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-12-22T12:18:38.870" Title="Why are Amateur Radio operators so obsessed about and hostile towards violation of the rules?" Tags="&lt;jargon&gt;&lt;transmission&gt;" AnswerCount="3" CommentCount="6" ClosedDate="2014-12-02T00:04:47.277" ContentLicense="CC BY-SA 3.0" />
  <row Id="2352" PostTypeId="1" AcceptedAnswerId="2366" CreationDate="2014-11-26T05:54:04.170" Score="2" ViewCount="77" Body="&lt;p&gt;A quick follow-up to &lt;a href=&quot;https://ham.stackexchange.com/questions/2346/how-can-i-tell-the-frequency-without-an-oscilloscope-or-frequency-counter&quot;&gt;How can I tell the frequency without an oscilloscope, or frequency counter?&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My supply is a transformer plucked from a dead power adapter rated for 1.5A. This is rectified cap-filtered, then Vo manipulated through an LM317 with a pair of 1k linear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I plan to tap the capacitor output to power the oscillator, and use the 317 output to bias the varactor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does the varactor bias supply have to be distinct from Vcc?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-11-28T20:42:04.533" Title="Does the varactor bias supply have to be independent of Vcc?" Tags="&lt;power-supply&gt;&lt;varicap&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="2353" PostTypeId="1" CreationDate="2014-11-26T07:52:10.127" Score="4" ViewCount="84" Body="&lt;p&gt;Why the value of intermediate frequency (IF) of amplitude modulation (AM) is 455 kHz? Why not another value?&lt;/p&gt;&#xA;" OwnerUserId="1884" LastActivityDate="2014-11-26T07:52:10.127" Title="Why the value of IF of AM is 455 kHz?" Tags="&lt;am&gt;" AnswerCount="0" CommentCount="6" FavoriteCount="1" ClosedDate="2014-12-02T00:03:09.040" ContentLicense="CC BY-SA 3.0" />
  <row Id="2354" PostTypeId="2" ParentId="2351" CreationDate="2014-11-26T19:16:48.703" Score="2" Body="&lt;p&gt;I've only been a licensed ham since 1997, but having worked for 30+ years in a technical field with lots of engineers of various disciplines, I've observed a lot of the &quot;passionate responsiveness&quot; you mention.  I think this &quot;black and white&quot; thinking is a common trait of individuals that populate the technical/engineering world and it seems to be a similar thing in the ranks of the Amateur Radio community.  Don't let it scare you!  Excluding the occasional bad apple (every community has one), you're going to find that hams are some of the most ingenious, problem solving people you'll ever meet.  That passion for &quot;getting things just right&quot; leads to improvements and discoveries that benefit the community as a whole and eventually the &quot;advancement of the radio art&quot;.   &lt;/p&gt;&#xA;" OwnerUserId="1114" LastActivityDate="2014-11-26T19:16:48.703" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2355" PostTypeId="2" ParentId="2351" CreationDate="2014-11-26T22:13:16.297" Score="7" Body="&lt;p&gt;I think there are two parts to this; why are they so &quot;anal&quot; /strict / uptight   about the rules?   why are they so hostile / aggressive / generally unpleasant?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first part I think is due to something that most people don't appreciate.  The Ether (if you'll excuse the name) is a shared resource.  The rules are there to try to let us all use it as effectively as possible.  If people don't follow them it is easy for a few people to cause a lot of inconvenience to many others.  Because they had to show an understanding of this principle in order to be granted a licence, most hams (excuse again pls) try to adhere to the rules and expect / exhort others to do the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some hams overreact to other peoples failure to follow the rules.  Partly this is simply a personality factor.  In other areas this appears - road rage affects some drivers, while most people just ignore bad driving by others; on the forums such as this, some people overreact in ludicrously offensive ways to posts they think are at fault in some way.  The distance created by radio, the internet or being in separate sealed cabins has a slightly disinhibiting effect on people, so that they are more likely to vent their spleen in these situations than they would in normal personal contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since hams may have spent a lot of time and effort to gain their licence and a lot more time, effort and money setting up their station (as the jargon has it), this quite literally ups the ante.  They have a lot invested in this activity and it is hardly surprising that their reaction to ignorant, inconsiderate or even malicious interference is exacerbated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And of course it is the people who have got excited about an issue who are most likely to respond to you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also play Bridge and although most people one plays against are pleasant, courteous, even convivial, at every club I've been to there are always some who cannot get through an evening without being unnecessarily aggressive, offensive or just unpleasant.  Now you can hardly think of a more genteel environment, but this sort of behaviour still happens.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this answer is acceptable, as I see now that it does not conform to the forum standards, in that it expresses opinions and does not cite sources.  If required I can cite sources for the rules, but most other matter is based on my experience as a radio amateur since 1976 and as a human being since 1949.&lt;/p&gt;&#xA;" OwnerUserId="1890" LastEditorUserId="1890" LastEditDate="2014-11-26T22:18:36.327" LastActivityDate="2014-11-26T22:18:36.327" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2356" PostTypeId="1" CreationDate="2014-11-27T08:59:05.503" Score="8" ViewCount="238" Body="&lt;p&gt;I have read in a paper that ground acts as reflector for radio signals in 434 MHz band. Why is that the case?&lt;/p&gt;&#xA;" OwnerUserId="1891" LastActivityDate="2014-12-27T17:06:15.053" Title="Ground influence on 434 MHz radio signal" Tags="&lt;propagation&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2357" PostTypeId="1" CreationDate="2014-11-27T10:11:37.727" Score="5" ViewCount="120" Body="&lt;p&gt;I have a device of copper and iron (about 8 kg) which looks like two shell inductors joined so that there is some coupling but high leakage. The windings seem to be identical.  Each is a single continuous winding with 4 intermediate taps.  I did not see this in use, but when I got it the two windings were linked at one end. The equipment it came from was powered, I think, from normal 240 VAC mains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's just my curiosity, but I can't fathom what it might do.  Since the windings were linked, it does not provide isolation. If it is a transformer or common mode choke, why so little coupling? If it is two independent auto transformers or chokes, isn't the coupling a problem?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone seen one at work anywhere?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/wDnw1.jpg&quot; alt=&quot;Shows outer shell &amp;amp; 2 windings&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZKGrg.jpg&quot; alt=&quot;shows taps: bottom taps linked&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1890" LastEditorUserId="76" LastEditDate="2015-02-25T03:21:23.553" LastActivityDate="2015-02-25T03:24:24.153" Title="Stacked shell inductor — what's its function/use?" Tags="&lt;electronics&gt;&lt;power-supply&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2358" PostTypeId="2" ParentId="2351" CreationDate="2014-11-27T15:03:42.013" Score="8" Body="&lt;p&gt;As has been mentioned, many radio amateurs tend to be in the types of fields where various forms of rules are the name of the game. Electricity always behaves the same. So does a computer (assuming it is working correctly, it simply executes one instruction after another; it doesn't deviate or take initiatives of its own). And so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there is another reason as well which I think is important but that no one has touched on. You point out that:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Most hobbies aren't nearly as strict. If you want to use 80 grit sandpaper instead of 60, or drive 110 instead of 100, no one cares. Absolutely no one would report you to a federal agency for not wearing a mask painting, or using a double instead of an int. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you use 80 grit sandpaper instead of 60 grit, nobody else is affected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you drive above the speed limit, well, others might be affected, or they might not. It depends very much on the situation. (Also note that some countries are &lt;em&gt;very&lt;/em&gt; strict about speed limits, &lt;a href=&quot;https://en.wikipedia.org/wiki/Autobahn#Traffic_laws_and_enforcement&quot; rel=&quot;noreferrer&quot;&gt;&lt;em&gt;including&lt;/em&gt;&lt;/a&gt; &quot;&lt;a href=&quot;https://en.wikipedia.org/wiki/Autobahn#Speed_limits&quot; rel=&quot;noreferrer&quot;&gt;no speed limit on Autobahn&lt;/a&gt;&quot; Germany.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use a &lt;code&gt;double&lt;/code&gt; (floating-point) type variable where an &lt;code&gt;int&lt;/code&gt; (integer) would do just fine, most won't care because most won't (or even won't be able to) realize, and those who do realize will likely know whether it matters or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the flip side, the radio spectrum is constantly under &quot;attack&quot; from different directions. Commercial operators want slices out of the radio spectrum which is allocated, in many cases, on &lt;em&gt;primary&lt;/em&gt; basis to amateur radio (that is, other spectrum uses are outright prohibited, or other spectrum users &lt;em&gt;must&lt;/em&gt; accept interference from amateur radio stations). &lt;strong&gt;Amateur radio licenses are not handed out to anyone who asks and pays; an amateur radio license is a privilege that comes after proving your ability to handle the rights that come with it.&lt;/strong&gt; (Basically no other radio spectrum users get to use homebrew equipment, decide on their own the transmission mode, transmission bandwidth, exact frequency, transmitter location, etc.; for just about every radio service &lt;em&gt;except&lt;/em&gt; amateur radio, such things are stated in the permit document. Amateur radio operators have a &lt;em&gt;huge&lt;/em&gt; amount of leeway in this regard.) Part of that is proving your knowledge of relevant regulations, radio theory, and operating practice; the exact examinations vary by country, but they cover largely the same subject areas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What amateur radio does have, is very generally written regulations which sets the boundaries for how we (amateur radio licensees) are allowed to use the spectrum. (One of those boundaries is that amateur radio is non-commercial in nature.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;A commonly held opinion is that if we in general start accepting people going outside of those already very permissive regulations, the commercial operators in particular will be able to point toward that practice and use that as an argument for taking over portions of the spectrum that is currently allocated to amateur radio.&lt;/strong&gt; Some of that spectrum could easily be quite valuable to commercial entities, and much of it is allocated on a primary or shared-primary basis to amateur radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;By asking of each other to strictly adhere to the rules that do exist, we reduce the risk of commercial entities being able to point to rampant rules violations as an argument for reducing the freedom of and spectrum allocations to radio amateurs.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2014-12-01T09:46:59.987" LastActivityDate="2014-12-01T09:46:59.987" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2359" PostTypeId="2" ParentId="2356" CreationDate="2014-11-27T16:23:05.863" Score="2" Body="&lt;p&gt;Radio waves reflect from the ground because the ground is a big, flat surface that's conductive enough. It reflects for the same reason that a mirror reflects light.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a simplified explanation, let's assume the ground is an infinite, flat, perfectly conductive plane. As a wave approaches the ground, the conductivity of the ground constrains the electric field to 0 (you can't develop a voltage if there's no resistance to work against).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mechanism is identical to a wave reflecting off a short at the end of a transmission line, except the wave is free to move in all three dimensions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For illustration, I'm going to borrow an animation from &lt;a href=&quot;http://www.acs.psu.edu/drussell/Demos/SWR/SWR.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dan Russel's excellent page on wave reflection&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/TrpVV.gif&quot; alt=&quot;wave reflection into a short&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An analogous system which might be more intuitive is a string incident upon a free boundary, like a massless ring sliding without friction on a rod. The lack of friction or mass is analogous to the lack of resistance or inductance in an electrical material. Dan Russel says it better than I can:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The animation [...] shows a wave train moving toward the right, incident upon a free boundary. A free boundary means that there is no force to limit the displacement. Mathematically, this results in the string having zero slope at the boundary.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This limit means the wave can't penetrate the material, nor can the material absorb the wave. The energy must go somewhere, and the only solution given these constraints is reflection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, this shows a wave orthogonal to a plane, reflecting back in the same direction from which it came, forming a standing wave. But if the wave is at an oblique angle (as is more usually the case with radio waves and the ground), then we can think of the wave as separate and independent horizontal and vertical components. Only the vertical component is reflected, because it is perpendicular to the ground. The horizontal component continues unchanged. Just like an ordinary mirror, which works the same way, but at a much higher frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And of course, the ground isn't perfectly conductive, so some fraction of the radio wave will be absorbed. And the ground is also not perfectly flat, so the reflection is distorted to some degree.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Still, it's reflective enough at most radio frequencies to significantly alter propagation. See for example the &lt;a href=&quot;http://en.wikipedia.org/wiki/Two-ray_ground-reflection_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;two-ray ground reflection model&lt;/a&gt; and &lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;image antennas&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-11-27T16:23:05.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2360" PostTypeId="1" CreationDate="2014-11-28T01:20:31.563" Score="4" ViewCount="679" Body="&lt;p&gt;For Thanksgiving, I changed the courtesy beep to a turkey noise on my repeater/node. Some other people did it so I thought it was fine. Someone however told me that it did not follow part 97 FCC. Is this true? &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="1183" LastEditDate="2014-11-28T02:04:33.457" LastActivityDate="2014-12-15T13:05:09.503" Title="Is it legal to use animal noise courtesy beep?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;repeater&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2361" PostTypeId="2" ParentId="2360" CreationDate="2014-11-28T02:36:40.957" Score="5" Body="&lt;p&gt;I can find no regulations on courtesy tones whatsoever in part 97, nor any prohibition on transmission of animal noises or having fun. Maybe there's a rule that could be construed... Nope. I got nothing.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-11-28T02:36:40.957" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2362" PostTypeId="1" CreationDate="2014-11-28T03:57:57.300" Score="1" ViewCount="758" Body="&lt;p&gt;What it the optimal number of wave lengths of RG-8X coax to connect my Icom IC V80 HT to a 50 ohm &lt;a href=&quot;http://www.jetstream-usa.biz/product_info.php?products_id=71568&quot; rel=&quot;nofollow&quot;&gt;Jetstream JTBM270 Yagi&lt;/a&gt; (3 elements 2m/5 elements 70cm)? Odd or even number thereof?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will running the coax through a steel mast inside an abandoned cast iron sewer vent pipe affect my signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna has type N connector and HT has BNC.&lt;/p&gt;&#xA;" OwnerUserId="1894" LastEditorUserId="1246" LastEditDate="2014-12-08T00:30:18.653" LastActivityDate="2014-12-08T00:30:18.653" Title="Multi-part question. correct length of rg-8x coax to connect 2 meter HT to 50 ohm yagi" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2364" PostTypeId="2" ParentId="2362" CreationDate="2014-11-28T13:07:47.893" Score="2" Body="&lt;p&gt;If the antenna is operating correctly, the length of the feedline and the material around the feedline (vent pipe, etc) are irrelevant. This is because coax is designed to contain the electric field in the dielectric between the center conductor and the shield. With no electric field outside of it, what happens outside the cable is irrelevant. This is why coax has supplanted twin-lead in most applications: you can attach coax directly to a metal tower, bury it in the ground, or feed it through a wall with no effect on the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, we must ensure current balance at the feedpoint for this to be true. Current balance means that the current into one half of the antenna equals exactly the current out of the other half of the antenna at all times. The &lt;a href=&quot;http://en.wikipedia.org/wiki/Charge_conservation&quot; rel=&quot;nofollow noreferrer&quot;&gt;law of charge conservation&lt;/a&gt; ultimately requires that all the current goes somewhere, and if we aren't keeping the currents on the antenna elements equal and opposite, then the feedline will make up the difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To ensure current balance in situations like these we use a balun. This is already covered in detail for dipoles in &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt;. The driven element of your Yagi is a resonant dipole, so this applies to your antenna just the same way. Note though that an insufficient balun in a Yagi is especially bad, because it makes the feedline part of the radiating antenna structure. You want a Yagi because it's directional, but the feedline as an antenna is anything but directional. Common-mode currents will destroy the performance of your Yagi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did some brief research on your particular antenna, and I couldn't find any information on whether it has a balun or not. So, you might be interested in &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;How to detect common-mode currents or “RF in the shack”?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-11-28T13:07:47.893" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2365" PostTypeId="1" CreationDate="2014-11-28T13:38:54.663" Score="1" ViewCount="151" Body="&lt;p&gt;In my search to identify the stations I can (barely) hear on my small shortwave setup, I discovered the &lt;a href=&quot;http://www.hfcc.org&quot; rel=&quot;nofollow&quot;&gt;HFCC&lt;/a&gt;. They have a tool that takes your location and UTC time, and provides a list of stations that are aimed at my part of the world (ITU zone). the list is sorted by hours of transmission, and lives &lt;a href=&quot;http://www.hfcc.org/schedule/&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;p&gt;&#xA;This is very nice, but it's not what I'm after. I'd like a list of &lt;strong&gt;all&lt;/strong&gt; broadcasters, on the air at the time I search. I'd like to be able to sort this list, by frequency or by range to Tx station.&lt;p&gt;&#xA;Obviously, this is a matter of setting up a query of the HFCC database files. Before I risk re-inventing the wheel, I'm asking: has anyone else made a database app that uses the HFCC data?&lt;p&gt;&#xA;&lt;strong&gt;Edit&lt;/strong&gt;: This question has been declared &quot;off topic&quot; So I'm amending the question.&lt;br&gt;&#xA;What techniques are used to maintain a log (or database) of stations received?&lt;br&gt;&#xA;I'm still just starting, so the international broadcasters are easier to chase (known transmit times, known location - range &amp;amp; bearing easy to calculate). Whatever log I use, should be &lt;em&gt;expandable&lt;/em&gt; for when I get the equipment (and license) to transmit.&lt;br&gt;&#xA;Do people still exchange cards when they make a contact, or has that practice fallen out of favor?&lt;/p&gt;&#xA;" OwnerUserId="1610" LastEditorUserId="76" LastEditDate="2016-10-29T19:17:35.397" LastActivityDate="2016-10-29T19:17:35.397" Title="International Broadcast - database programs?" Tags="&lt;hf&gt;&lt;software&gt;&lt;transmitter&gt;&lt;international-operating&gt;" AnswerCount="1" CommentCount="7" ClosedDate="2014-11-28T23:06:00.647" ContentLicense="CC BY-SA 3.0" />
  <row Id="2366" PostTypeId="2" ParentId="2352" CreationDate="2014-11-28T20:42:04.533" Score="0" Body="&lt;p&gt;No, you can derive the bias from Vcc just fine. You will want to make sure the bias voltage is well-regulated and low-noise, since any error or noise will be manifest in the tuning of your radio. Nothing that can't be accomplished by a voltage regulator and a bit of filtering, however.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-11-28T20:42:04.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2367" PostTypeId="2" ParentId="2070" CreationDate="2014-11-28T21:11:19.010" Score="1" Body="&lt;p&gt;Answer of sorts (or, not an answer at all) to questions about rubber ducky antenna.  This follows the comments dialog above as this post is too large for a mere comment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I volunteered to run the NEC2 calculation for this antenna and after the OP provided more details I started doing back of the envelop computations since I am away from my main computer for a few days (where I have NEC2/NEC4 and my Mathematica solution modules).  I did a simple reactance calculation of the coil itself at the designated frequency of 462 MHz which is open for FRS/GMRS operations that I think is associated with the rubber ducky antenna of the HT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The inductance is approximately $0.43\,\mu H$ and the resulting inductive reactance $X_L$ is:&#xA;$$&#xA;X_L = 2\,\pi \, f\, L = 2\times 3.14\times 462\times0.43 = 1248\, ohms\qquad \text{(rounded)}&#xA;$$&#xA;This rather large impedance means that this rubber-ducky (for it to work at all) has high capacitive coupling to the HT and even probably to the person holding it which naturally form part of the antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, I posted some questions on NEC2 distribution list and one answer (from the creator of EZNEC, who is a Guru/Wizard with NEC2 and NEC4) provided these comments (quoted directly from his e-mail):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not practical to model with NEC-2 for several reasons:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The &quot;ducky&quot; is only a part of the antenna system. At least as important, and likely more important, is the person holding the radio which can have a major impact on the pattern. Whatever the current flowing into the base of the &quot;ducky&quot;, an equal amount of current flows along the outside of the radio and the person holding it. This current causes radiation just as the current on the &quot;ducky&quot; does, but from a much larger &quot;antenna&quot;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;My experience is that modeling an inductively loaded antenna as a wire with one or more ideal inductive loads doesn't provide accurate results. I believe this is because the current changes significantly from one end of the actual loading inductor to the other, while currents are the same at the ends of idealized loads. Even using multiple loads doesn't do as well as modeling the actual inductor as a helix.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;NEC-2 requires that wires be spaced at least several diameters apart. A typical &quot;ducky&quot; helix has turns spacing closer than this, making modeling the inductor portion of the antenna as a helix questionable.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;NEC-2 doesn't take into account proximity effect, which might be significant with closely spaced helix turns. Presuming you're trying to evaluate the efficiency of the &quot;ducky&quot;, this means that the efficiency shown by the model will be overly optimistic even if you use realistic values for wire resistivity.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;NEC-2 has no way to account for the dielectric surrounding a &quot;ducky&quot;. This will alter the resonance of the antenna in a way not predicted by the program.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Sorry, there are just some things that can't be practically modeled with NEC-2. This is one of them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;End of Quote.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, sorry to say that when I get back home I will probably not try to model this antenna as I volunteered to do.  Hopefully though, there is sufficient content in this answer to give the OP more information to make judgements or decisions regarding the rubber-ducky antenna.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2014-11-28T21:11:19.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2368" PostTypeId="2" ParentId="2365" CreationDate="2014-11-28T22:55:24.877" Score="0" Body="&lt;p&gt;&lt;a href=&quot;http://www.radioexplorer.com.ru/en/&quot; rel=&quot;nofollow&quot;&gt;Radio Explorer&lt;/a&gt; purports that it can use the HFCC data directly (but I haven't tried it, because I use another tool named &quot;eibiview&quot;). Give it a spin and verify if it gives you what you need. &lt;br&gt; &lt;br&gt; Some other resources that might be useful to you are the listings from &lt;a href=&quot;http://www.eibispace.de/&quot; rel=&quot;nofollow&quot;&gt;eibi&lt;/a&gt; and &lt;a href=&quot;http://www.geocities.jp/binewsjp/&quot; rel=&quot;nofollow&quot;&gt;AOKI&lt;/a&gt;. ebiview can process these lists and also present you with what you require (or something close). eibiview can be downloaded at the eibi website above.&lt;/p&gt;&#xA;" OwnerUserId="1761" LastActivityDate="2014-11-28T22:55:24.877" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2369" PostTypeId="1" CreationDate="2014-12-01T02:53:45.413" Score="4" ViewCount="417" Body="&lt;p&gt;I have set up an AllStar link system to a repeater depicted in the picture below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/bLogP.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The repeater is under NØMHU's call, and my node is under me, KDØWHB. With permission, I service EchoLink and AllStar to the machine for wide coverage access. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am curious, who is responsible for what if someone who does not ID gets on and potentially performs illegal action? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Scenario 1)&lt;/strong&gt; Illegal transmitter gets on Eldorado, and transmits through my QTH node to another node remotely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Scenario  2)&lt;/strong&gt; Illegal transmitter gets on a node I am linked to, and it gets aired on Eldorado.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Scenario 3)&lt;/strong&gt; Non-liscensed ham manages to get on an EchoLink account (or the AllStar web transceiver) and transmits to Eldorado, and a remote node I am linked to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Who is responsible for what? With any of those scenarios, is my call held responsible?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;A control operator needs to be listening at all time to make sure nothing illegal happens where your node is responsible from a local transmission.&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Someone told me that. (yes, the same guy from prev. question) Is that true? Will I be responsible for someone getting on my node and doing &quot;bad stuff&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know all of the repeater rules, but it gets complicated with my weird setup.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="1246" LastEditDate="2014-12-06T02:53:59.430" LastActivityDate="2014-12-06T02:53:59.430" Title="What am I responsible for on my link?" Tags="&lt;repeater&gt;&lt;echolink&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2370" PostTypeId="2" ParentId="2369" CreationDate="2014-12-01T14:54:14.033" Score="2" Body="&lt;p&gt;Foremost, remember that the FCC regulates &lt;em&gt;stations&lt;/em&gt; and their &lt;em&gt;emissions&lt;/em&gt;. The FCC does not care about the internet or how things work. They care about what comes out of your station, regardless of how that happened.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, good amateur practice would dictate that regardless of where the regulations place the responsibility, if your equipment is being used even indirectly for illegal transmissions, you know about it, and you can do something about it, you should. Failure to conform to &quot;good amateur practice&quot; can be in itself illegal (&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?rgn=div5&amp;amp;node=47:5.0.1.1.6#se47.5.97_1101&quot; rel=&quot;nofollow&quot;&gt;§97.101&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(a) In all respects not specifically covered by FCC Rules each amateur station must be operated in accordance with good engineering and good amateur practice.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is the &quot;don't be a dick&quot; rule.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Scenario 1) Illegal Transmitter gets on Eldorado, and transmits through my QTH node to another node remotely.&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;You are not transmitting anything in this case, so it's hard to imagine how you might be violating anything. You should probably expect a call from other people operating linked stations though, because you are creating the problem of the next scenario for someone else. These internet linking systems work only because everyone participating in them assumes more responsibility for their proper operation than the regulations require. Without that cooperation, the entire system would not work.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Scenario 2) Illegal transmitter gets on a node I am linked to, and it gets aired on Eldorado&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;That it gets aired on Eldorado is irrelevant (although, may additionally create problems for Eldorado's control operator): just that you've transmitted it is sufficient. As the control operator of your station, you are responsible for what you transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Presumably, your station qualifies as an &lt;em&gt;auxiliary station&lt;/em&gt; which is allowed to be &lt;em&gt;automatically controlled&lt;/em&gt;. Definitions are in (&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?rgn=div5&amp;amp;node=47:5.0.1.1.6#se47.5.97_13&quot; rel=&quot;nofollow&quot;&gt;§97.3&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(6) &lt;em&gt;Automatic control&lt;/em&gt;. The use of devices and procedures for control of a station when it is transmitting so that compliance with the FCC Rules is achieved without the control operator being present at a control point.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(7) &lt;em&gt;Auxiliary station&lt;/em&gt;. An amateur station, other than in a message forwarding system, that is transmitting communications point-to-point within a system of cooperating amateur stations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If an illegal transmission made it into the link system and you retransmitted it, automatic control has failed. Fixing it is your responsibility. &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?rgn=div5&amp;amp;node=47:5.0.1.1.6#se47.5.97_1109&quot; rel=&quot;nofollow&quot;&gt;§97.109   Station control (d)&lt;/a&gt; applies:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;When a station is being automatically controlled, the control operator need not be at the control point. Only stations specifically designated elsewhere in this part may be automatically controlled. Automatic control must cease upon notification by a District Director that the station is transmitting improperly or causing harmful interference to other stations. Automatic control must not be resumed without prior approval of the District Director.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The widespread adoption of Echolink and Allstar is tacit acknowledgement that the access control mechanisms those systems offer are sufficient to prevent illegal operation. You won't get in any trouble if some guy abuses your transmitter one time, as long as reasonable steps are taken to stop it.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Scenario 3) Non-Liscensed ham manages to get on an EchoLink account (or the AllStar web transceiver) and transmits to Eldorado, and a remote node I am linked to&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;This is similar to scenario 2: automatic control has failed and you are responsible. The fact that Eldorado received the illegal transmission from your station doesn't change your responsibility.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;In all cases, although an auxiliary station is permitted to be automatically controlled, that doesn't mean you should set it up and forget it. There are social expectations of responsibility above and beyond what the regulations require.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can make arrangements to control your station either by radio or by internet, I would suggest doing so. This allows you to &lt;em&gt;remotely control&lt;/em&gt; the station in the case that automatic control fails. It might also make it possible for you to give other people the authority to shut down the station in the case a problem occurs when you are not around.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further reading from ARRL:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/voip-faq&quot; rel=&quot;nofollow&quot;&gt;VoIP FAQ&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/auxiliary-station-faq&quot; rel=&quot;nofollow&quot;&gt;Auxiliary Station FAQ&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-12-01T14:59:55.930" LastActivityDate="2014-12-01T14:59:55.930" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2371" PostTypeId="2" ParentId="2305" CreationDate="2014-12-01T15:46:22.827" Score="-2" Body="&lt;p&gt;Now if you think of a RF transistor that has 5 ohms of input impedance and the gain of the transistor is about 20dB over the specified band when the input is matched to 5 ohms. SWR, the measure of the reflected wave will be high because you are measuring it with a 50 ohms network analyzer but you will get the highest transmission(S21).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be more precise if the device does not have active components(passive) ====&gt; Bad SWR, Bad Transmission. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand if the device has active components you can't say anything by looking just at the SWR.&lt;/p&gt;&#xA;" OwnerUserId="1906" LastActivityDate="2014-12-01T15:46:22.827" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="2372" PostTypeId="1" CreationDate="2014-12-01T19:25:09.113" Score="4" ViewCount="1811" Body="&lt;p&gt;I was wondering if I made an antenna from a Rohn 25G tower, would it have the same resonant frequency as a pole of the same height (assuming guys are insulated)? Also with the Rohn antenna, the waves would be both vertically and horizontally polarized, right?&lt;/p&gt;&#xA;" OwnerUserId="1817" LastActivityDate="2015-01-16T22:46:05.510" Title="Does antenna width/shape affect resonant frequency like length does?" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;&lt;polarization&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2373" PostTypeId="2" ParentId="2372" CreationDate="2014-12-01T19:56:13.580" Score="2" Body="&lt;p&gt;Yes, width and shape are relevant. It's mathematically simpler to assume that antennas are infinitesimally thin, however, and usually this is close enough to true that it makes a reasonable simplifying assumption.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.antenna-theory.com/antennas/broaddipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna-theory.com has a good article on &quot;thick&quot; dipoles&lt;/a&gt;, summarized by this graph:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.antenna-theory.com/antennas/broaddipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/G1LHg.jpg&quot; alt=&quot;dipole bandwidth vs thickness&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here, &quot;A&quot; is the thickness of the dipole, and the length of each dipole is 1.5m. As you can see, as the dipole gets thicker, the resonant frequency goes down and the bandwidth goes up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this is only but one of many variables in actual antenna construction that might change the resonant frequency. The effect of thickness is minor enough for reasonable thicknesses that it's best to initially make the antenna bit long, and then trim or otherwise tune it by actual measurement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the support structure of your tower is probably very small relative to the wavelength at which you intend to operate it, it will behave almost identically to a solid bar of metal of similar outside dimensions. It will not make your signal horizontally polarized.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-12-01T19:56:13.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2374" PostTypeId="2" ParentId="1319" CreationDate="2014-12-01T20:57:23.283" Score="-1" Body="&lt;p&gt;Linear Amplifiers are generally used in communication systems because you dont want to give different gains to different input power drives. All of the amplifiers are non-linear after some point(saturation). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amplifier types are, based on the biases;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Class-A,AB,C,D,G,... and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Linear amplifiers generally!! consume more power than non-linear amplifiers because of their class-A nature and they have to be biased in the middle of the I-V diagram.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just keep in mind something like this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Linear amplifier - RADAR, Communication.&#xA;Non-linear amplifier - Jamming, DF systems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way making a linear amp is harder than making a non-linear one.:)&lt;/p&gt;&#xA;" OwnerUserId="1906" LastActivityDate="2014-12-01T20:57:23.283" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="2375" PostTypeId="2" ParentId="2301" CreationDate="2014-12-02T01:27:10.387" Score="0" Body="&lt;p&gt;Your microwave antenna isn't affecting WiFi in any way, since the frequencies are differentiated enough to be irrelevant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An early contributor pointed out &quot;NIMBY&quot; and your conspicuous tall antenna is the latest source of blame for problems. The rest of the RV park residents are unable or even too lazy to figure out the real problem, and superstitiously blaming the new guy makes them feel better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Did &quot;their issues stop occurring when you shut down your radio shack&quot;? You already answered &quot;no&quot;.&lt;/p&gt;&#xA;" OwnerUserId="1910" LastEditorUserId="1579" LastEditDate="2014-12-04T02:45:12.070" LastActivityDate="2014-12-04T02:45:12.070" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2376" PostTypeId="2" ParentId="2372" CreationDate="2014-12-03T21:53:15.393" Score="-1" Body="&lt;p&gt;For any antenna type shape and dimensions are very important parameters. If you want to have both horizontal and vertical polarization simultaneously with your antenna, the antenna must be dual polarized or slant polarized. Slant polarization with this kind of antenna can be performed by tilting it 45 degree to the ground.&lt;/p&gt;&#xA;" OwnerUserId="1917" LastEditorUserId="1917" LastEditDate="2014-12-17T22:30:38.150" LastActivityDate="2014-12-17T22:30:38.150" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2377" PostTypeId="2" ParentId="1702" CreationDate="2014-12-03T22:01:00.153" Score="1" Body="&lt;p&gt;Ice and water has very big dielectric permittivity. If the antenna is in a dielectric, so the resonance frequency changes with the square root of it. So for ice the dielectric permittivity may change due to its density. Water has dielectic permittivity of 80. So the antenna resonance frequency changes with the ratio 1/squareroot (80). It doesn't guarantee that the antenna works well at the new frequency, because 80 is very high permittivity wich can create high reflection, but it works better at this frequency. That's why the antenna doesn't work when it has ice on it. &#xA;It is not about the change of antenna length or anything else because of temperature. If you want to solve this problem you must have heat resistance wires on it in order not to have ice on it. &lt;/p&gt;&#xA;" OwnerUserId="1917" LastActivityDate="2014-12-03T22:01:00.153" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2378" PostTypeId="2" ParentId="1319" CreationDate="2014-12-03T22:03:49.427" Score="3" Body="&lt;p&gt;Actually, any amplifier is non-linear but has a linear region. The linear region is  a region of power input to the amplifier. If you use the amplifier at an appropriately low power level, it works as linear in this region. You can find the linear region in the datasheet for the amplifier.&lt;/p&gt;&#xA;" OwnerUserId="1917" LastEditorUserId="76" LastEditDate="2014-12-03T23:41:32.970" LastActivityDate="2014-12-03T23:41:32.970" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2379" PostTypeId="2" ParentId="2309" CreationDate="2014-12-04T22:26:21.330" Score="3" Body="&lt;p&gt;Try a practical test as follows.  Find a consistantly-readable but weak station (like a medium-distance repeater) and note the signal strength when you hand-hold the antenna on a handie, possibly at arms' length.  Then place the handie and antenna on the centre of a car roof and note the difference in signal strength (if any).  That will indicate if the antenna would benefit from a ground plane.  Some types (like an end-fed half-wave dipole) will not generate strong ground currents (if correctly matched) whereas a quarter-wave monopole does benefit from a ground plane.  The antenna gain is suspiciously similar to that of a quarter wave monopole on 70 cm IF the units are dBi.  In that case I wonder if the top (retractable) section is the radiator and the &quot;bulge&quot; at the top of the fixed section is a coil acting like a choke.  This is pure speculation...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My guess is that radials will not be much help.  If you do use them, then try braid instead of wire, or a metal sheet, and pay lots of attention to making an excellent ground connection at the antenna base.  If you don't, then resistive losses will kill the potential gains.&lt;/p&gt;&#xA;" OwnerUserId="1919" LastActivityDate="2014-12-04T22:26:21.330" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2380" PostTypeId="2" ParentId="1608" CreationDate="2014-12-04T22:51:39.470" Score="2" Body="&lt;p&gt;The two fields do not have to be orthogonal, and in the diagram posted they are in fact NOT orthogonal everywhere  (for example, what do E and H do near the ends of the antenna?).  Orthogonal E and H field are the property of a propagating EM wave in free space.  Around an antenna, within a few wavelengths distance, there are &quot;near field&quot; or &quot;Fresnel&quot; regions in which there are non-propagating waves.  These waves do not have necessarily orthogonal fields.  More detail can be found in a reference text such as Antenna Theory by Balannis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note also that the fields may be orthogonal and out of phase with each other.  You might see this from a circularly-polarised antenna.&lt;/p&gt;&#xA;" OwnerUserId="1919" LastActivityDate="2014-12-04T22:51:39.470" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2381" PostTypeId="2" ParentId="830" CreationDate="2014-12-04T23:44:29.623" Score="4" Body="&lt;p&gt;It may help to consider  the two arms of the folded dipole as end-shorted (ROUGHLY quarter-wave) sections of 300 ohm transmission line.  Any current which attempts to flow in opposite directions on the two conductors in each arm will not radiate (which is why the transmission line works - the two currents generate opposing fields). Only a &quot;common-mode&quot; current can radiate. Looking to either side of the antenna from the centre point, the impedance for differential mode currents across the two conductors is very high (because each arm acts to transform the short at its far end into a high impedance at the centre).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider the feed point changing voltage differentially.  If one side of the feed rises in voltage and (say) a current flows out, then the voltage and current on the opposite (folded section) conductor must follow it (differential currents are cancelled out!). The antenna is balanced and very nearly resistive near its centre, so the other feed point drops in voltage and pulls in a current of the same magnitude.  This current is flowing in the same direction along the antenna as the current from the other feed-point (just as in a regular, non-folded dipole).  Again, the transmission line effect forces the voltage and current in the conductor opposite to the second feed point to follow,, and this current is in the same direction as for the other arm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are effectively TWO current modes operating.  A transmission-line mode (which does not radiate) and an antenna-like, radiative mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should be noted that this concept should have the two arms slightly too short for an efficient half-wave radiator, since the two quarter-wave sections of line would have to be cut accounting for the velocity factor of the line (typically 0.85 or so). Some designs (like ARRL) make the antenna length similar to tat of a simple dipole but add shorting bars slightly in-board of the ends at the points which are electrically a quarter-wave along each arm from the feed point.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The original question asked about why the bandwidth is &quot;wider&quot; for a folded dipole than for a single-wire dipole.  There are probably two effects to consider.  The reactance shows a very sharp dip at resonance, but the resistive impedance is high (near 300 ohms), and varying with frequency.  The combined complex impedance magnitude normalised to 300 ohms does not change so fast. The &quot;non-radiative&quot; mode tends to cancel the reactance changes. The reason may also be that the effective diameter of the folded dipole is increased compared to the single wire system.  A &quot;fatter&quot; effective wire has a lower Q (its resonance is less sharp), and its effective bandwidth is wider. This effect is used on, for example, &quot;caged&quot; dipoles whose (non-folded) arms are made from multiple wires spaced with hoops.  &lt;/p&gt;&#xA;" OwnerUserId="1919" LastActivityDate="2014-12-04T23:44:29.623" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2382" PostTypeId="2" ParentId="1903" CreationDate="2014-12-04T23:57:03.247" Score="0" Body="&lt;p&gt;Beg to differ.  The effective conductor radius is increased to something like half the wire spacing.  That means that there is less loss.  An alternative view is that the impedance transformation properties of the antenna imply that less current flows on either conductor than would be the case for an single-wire dipole.  The resistance of the wires is therefore of relatively less concern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Practically speaking, the differences are indeed small, specially at HF, but they become more important at VHF or UHF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the receive side, the susceptibility to noise can be different I believe.&lt;/p&gt;&#xA;" OwnerUserId="1919" LastActivityDate="2014-12-04T23:57:03.247" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2383" PostTypeId="2" ParentId="1636" CreationDate="2014-12-05T23:10:17.753" Score="1" Body="&lt;p&gt;There are several issues to be considered here.  First, does the antenna type naturally want to sit over a ground plane (for example, in order to radiate effectively or at all)?  An end-fed half-wave antenna for example would not need (or maybe even &quot;want&quot; a ground plane, and would generate only a very small ground-plane current if mismatched slightly.  Some mobile antennas from Japan are advertised as being &quot;no ground plane&quot; types because they are designed in this way.  Other antennas, such as a quarter wave monopole or a 5/8 wave monopole (with base loading coil) DO want to sit on a ground plane in order to generate a good (or just the expected) radiation pattern.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second point is that to which you refer, i.e.  the issue of a poorly-matched antenna generating current on the outside of the coaxial cable shield.  If this is the situation, and especially if the &quot;natural&quot; feed-point impedance is low, then make every possible effort to sort out the mis-match.  This will have the most beneficial effect.  A tool such as the mini-VNA can help with diagnosis and measurement. Remember to resonate the antenna first, and then to adjust the impedance matching.  If the match cannot be improvedthen it is worthwhile attempting to &quot;kill&quot; the current on the coaxial cable outer shield.  Grounding is one way, but it is very hard to do.  You need an RF ground with very low inductance.  The mis-match current must &quot;want&quot; to flow down the ground connection much more than it wants to flow on the outside of the feeder cable. Especially for VHF / UHF, use short, wide straps, NOT wire, and even if you can make a good connection to a panel, some car panels are actually not well bonded to each other as far as RF currents go.  If you need the ground plane for reasons of radiation efficiency, then the plane must be about half a wave-length in diameter to begin to be effective (or at HF as big as you can get!).  At VHF and especially at UHF, a single aluminium roof rack bar can act as a ground &quot;plane&quot; and has the advantage of being drillable without affecting the paintwork of the vehicle!   When you have made your best attempt at grounding, consider adding a choke to the cable close to the feed-point.  This could be a small coil of coax held with cable ties, or wrapped around a ferrite rod, or a few turns of coax through a ferrite or iron-dust toroid, or one of those handy &quot;snap-on&quot; ferrites that come in two halves and close around the cable to make a tube.  This will reduce the braid outer current, make the transceiver happier (less RF flying about near the radio) and also reduce unwanted couplings and variabilities in matching performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, if grounding is impractical, consider installing a quarter-wave resonant wire (or wires, or even a quarter-wave helical antenna) extending from the mounting point ground and orthogonal to the whip.  This acts as a resonant &quot;trap&quot; which will soak up quite a bit of the mismatch current by trying to simulate a ground &quot;plane&quot; (albeit poorly!).  If this approach is not practical, and you cannot drill into the centre of the car roof, then a capacitive RF ground might be the answer - basically if you can make a good RF ground connection at the antenna base and attach that to a conductive plate or foil that is then held very close to the car body panel, the effective impedance will drop (although it will remain reactive).  This is a good way to &quot;try&quot; the effect of grounding in fact - try using aluminium foil smoothed out and taped over the roof for example.  I should warn that this technique is only really effective at VHF and UHF, not so good at HF.&lt;/p&gt;&#xA;" OwnerUserId="1919" LastEditorUserId="1919" LastEditDate="2014-12-05T23:15:29.230" LastActivityDate="2014-12-05T23:15:29.230" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2384" PostTypeId="2" ParentId="2318" CreationDate="2014-12-06T01:29:42.013" Score="0" Body="&lt;h2&gt;This is not only legal but &lt;em&gt;highly prevalent&lt;/em&gt; throughout the amateur community today, especially with APRS.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;What you are referring to is essentially hosting an online logbook. You will log some traffic previously transmitted in some format over amateur radio and display it publicly online.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to help pay for website hosting (presumably) you wish to show ads on your website. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ads on your website give you pecuniary interest in your WEBSITE but not the original APRS transmissions! Any amateur could already intercept your weather data with their own amateur radio gear and decide to view, collect and republish your weather data! Therefore the transmissions themselves are open and freely available to any amateur. If you want to get even more technical even an unlicensed individual could listen to your APRS packets and collect your weather data as no transmission is required to gather APRS packets (as opposed to other digital modes which do require both stations to transmit).&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Real World Examples&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;For a very similar example to what you are proposing, take a look at &quot;&lt;a href=&quot;http://aprs.fi/&quot; rel=&quot;nofollow&quot;&gt;aprs.fi&lt;/a&gt;&quot; which aggregates (&quot;logs&quot;) APRS location data online - &lt;strong&gt;&lt;em&gt;APRS.fi has google ads everywhere!&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another APRS website doing the same thing is &lt;strong&gt;&lt;a href=&quot;http://www.openaprs.net/&quot; rel=&quot;nofollow&quot;&gt;OpenAPRS.net&lt;/a&gt; - ALSO has web ads and explicit offers to purchase advertising.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking outside of digital mode logging, you could look at &lt;strong&gt;QRZ.com (yup lots of ads)&lt;/strong&gt; which hosts some QSO logging software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How about &lt;strong&gt;ARRL.org - yup lots of ads&lt;/strong&gt; even on the LOTW login page the banner has a yaesu sponsor notice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could go on for quite sometime enumerating the numerous other amateur radio websites which have ads on them, but if the ads are only on the web (never transmitted on the air) they only provide pecuniary interest for your online activities - not your on air activities. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Weather Station reports are an important and intentionally designed component of APRS. Use it to the maximum of your capabilities!&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;UPDATE: Answering the original question better - When would APRS use be commercial?&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;APRS (or any transmission) is commercial when either the content is for commercial purposes or you are being paid to make the transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the first example regarding content, this could be making transmissions for a business or coordinating commercial activities. For example if you owned a plumbing company and installed APRS tracking on all your plumber's vehicles in order to facilitate better dispatching - that would be commercial use as the transmission is intended to facilitate business operations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Likewise if the content of the transmission is of a more obvious commercial nature that would of course be commercial. For example you could not transmit an APRS message that read &quot;Sale on Products at my store! Come visit my store!&quot;. That would of course be transmissions with commercial intent and pecuniary interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the second example, if you are being paid for the transmission. This really stems from old times when it cost money to send a message (ie: &quot;telegram&quot;) to friends/family, but still applies today. I can't pay you to send a message across country for me. You cannot receive remuneration for making the transmission.&lt;/p&gt;&#xA;" OwnerUserId="608" LastEditorUserId="608" LastEditDate="2014-12-06T23:19:52.830" LastActivityDate="2014-12-06T23:19:52.830" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2385" PostTypeId="2" ParentId="525" CreationDate="2014-12-06T21:04:02.173" Score="2" Body="&lt;p&gt;There is another reason to be wary... Electronic ballast manufacturers sell them in all shades. I recently bought a batch of them, one of which broke down quite quickly. Being the electronics engineer, I dismantled the ballast and checked. And noticed that several components where missing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I considered this enough motive to draw the circuit and noticed that the missing parts were:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;about filtering RF interference&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;and protective circuitry (in fact, only a $0.02 diode) which switches off the oscillator if one of the filaments of the tube was bad, thus avoiding potential electronic component breakdown.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So I took all the ballasts back to the seller and selected one, only slightly more costly, and never looked back. They've been doing their job for over 6 years now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Conclusion, buy a reputable brand... even if it's slightly more costly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A note about the RFI itself: It will probably not be the electronics themselves that cause the RFI. The oscillator and choke use ferrite cores which are quite autoshielding. The real culprit for the RFI is the cabling in the tube mounting apparatus (and not to forger the tube itself).&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-12-06T21:04:02.173" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2386" PostTypeId="2" ParentId="2357" CreationDate="2014-12-07T10:13:51.660" Score="0" Body="&lt;p&gt;Is it possible that there is an iron-lamination core running through the centre of both coils?  If that is the case then in fact there is a very good magnetic circuit around the outside of the frame as long as both coils are driven in-phase. The central &quot;cross-bar&quot; will not then contribute much to the magnetics I would guess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are you able to guess / measure the tapping ratios? &lt;/p&gt;&#xA;" OwnerUserId="1919" LastActivityDate="2014-12-07T10:13:51.660" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2387" PostTypeId="2" ParentId="2362" CreationDate="2014-12-07T22:09:49.547" Score="1" Body="&lt;p&gt;The photo on the manufacturer's web site suggest that the beam uses a gamma-match arrangement.  The cable shield grounds to the boom, whilst the central conductor is routed on a bar parallel to the driven element and connects to the latter at some distance out from the centre via a series capacitance.  Matching is carried out by adjusting the distance out from the centre at which the contact to the driven element is made and the series capacitance value (which resonates against the inductance of the feed-point).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my experience this form of connection is well balanced, and a good match can be obtained with a little effort.  It is best to start with this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no &quot;optimum&quot; length of cable for a well-matched antenna.  As you are operating at UHF and VHF, the only optimum length is zero - more cable simply gives more loss...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Running your cable inside the mast and then inside a pipe will actually help by adding shielding (and won't hurt at all) but you may want to prevent any imbalance currents running on the steel or (worse) on the iron (rusty joints may act as rectifiers and give harmonics!).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although this is probably overkill, it may be worthwhile just as a safety measure to add either a coil of coaxial cable just after the feed-point or some (clip-on?) ferrites around the cable.  The coil might be (say) 6 or 8 turns of the coax wound on a 3-inch to 4-inch plastic pipe segment.  Either scheme adds some inductive impedance to prevent any accidental outer-braid current from flowing.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might be able to test whether or not you have a problem by trying to detect any &quot;squint&quot; in the antenna's beam pattern (which is often caused by the unwanted radiation coming from an &quot;outer-braid&quot; current).  Mount the antenna clear of obstructions; then, using a beacon or similar constant and &quot;good strength&quot; distant station, swing the antenna and look for two equally sharp &quot;nulls&quot; in signal which should occur at equal angles from the direction of maximum signal strength. Both nulls should be similar: the same loss of signal over thee same angular range.  The maximum signal should occur when the boom points at the station (unless you have hills and buildings around!). Then make a temporary choke in the coax - coil up a few turns (say 6) at 4 to 6 inch diameter just below the feed point and hold them in place with plastic (!) cable ties.  Repeat the beam pattern test.  If the direction of maximum signal changes, and the two nulls become more similar and more symmetrical about the direction of maximum signal, then you had a problem and you have just fixed it.  If there is little or no change (or things deteriorate), you probably did not have a problem in the first place. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One last (probably obvious) point: I am assuming that the antenna will be used for horizontal polarisation.  The antenna balance would be seriously compromised if it were mounted fro vertical polarisation on a steel mast!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck experimenting...&lt;/p&gt;&#xA;" OwnerUserId="1919" LastActivityDate="2014-12-07T22:09:49.547" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2388" PostTypeId="2" ParentId="2267" CreationDate="2014-12-08T04:26:59.900" Score="1" Body="&lt;p&gt;Yes, the cables for both the IC-2300 H and the FTM-400DR are both plasic &quot;T&quot; connectors and so it is possible to swap out the radios without changing the power cables.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.randl.com/shop/catalog/product_info.php?cPath=15_8170&amp;amp;products_id=67399&quot; rel=&quot;nofollow&quot;&gt;JetStream JTPC-33M 9.5’ &quot;T&quot; Connector Power Cord&lt;/a&gt;&#xA;  works quite well.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2014-12-08T04:26:59.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2389" PostTypeId="1" AcceptedAnswerId="2426" CreationDate="2014-12-08T14:08:58.453" Score="2" ViewCount="154" Body="&lt;p&gt;Does a good impedance match imply good balance and lack of common-mode currents?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does a poor impedance match imply poor balance and excessive common-mode currenst?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2017-04-26T17:26:41.847" LastActivityDate="2017-04-26T17:26:41.847" Title="How is impedance matching related to balance and common-mode currents?" Tags="&lt;equipment-design&gt;&lt;theory&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2390" PostTypeId="1" AcceptedAnswerId="2391" CreationDate="2014-12-09T12:41:14.103" Score="5" ViewCount="7564" Body="&lt;p&gt;This is &lt;a href=&quot;http://www.belden.com/techdatas/english/9223.pdf&quot; rel=&quot;noreferrer&quot;&gt;Belden 9223&lt;/a&gt;. It is a 50-ohm coaxial cable, velocity factor 0.56&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ij6S5.png&quot; alt=&quot;coax&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;This is &lt;a href=&quot;http://www.belden.com/techdatas/metric/8524.pdf&quot; rel=&quot;noreferrer&quot;&gt;Belden 8524&lt;/a&gt;. It is a 22 AWG hookup wire. No velocity factor in the datasheet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/RURvo.png&quot; alt=&quot;hookup wire&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Why does the coax datasheet have a velocity factor, while the hookup wire datasheet does not?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-12-10T03:00:35.603" Title="What is the velocity factor of a wire?" Tags="&lt;antenna-construction&gt;&lt;theory&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2391" PostTypeId="2" ParentId="2390" CreationDate="2014-12-09T14:53:39.500" Score="7" Body="&lt;p&gt;A coaxial cable is a transmission line by itself, and therefore the velocity factor is known. It depends on the dielectric properties, geometry, and conductivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A single wire is not a transmission line. You need a return path for the current, and that will most probably be a second wire somewhere, or a ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the geometry and dielectrics around the two conductors is unknown, and thus the velocity factor is unknown.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2014-12-09T14:53:39.500" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2393" PostTypeId="2" ParentId="2390" CreationDate="2014-12-09T18:17:52.983" Score="4" Body="&lt;p&gt;Velocity factor is a property of electromagnetic wave propagation, not wire. A transmission line (like coax) is a conduit for an electromagnetic wave in itself, so the velocity factor can be defined. In fact, the velocity factor can be derived from the lumped model of a transmission line:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Av64m.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fAv64m.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Following the usual simplifying assumptions of a lossless transmission line, R and G become insignificant. If $L$ and $C$ are inductance (henry) and capacitance (farad) per meter, then the velocity of propagation in a transmission line is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ v = \frac{1}{\sqrt{LC}} \tag{1} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The velocity factor is just this relative to the velocity of propagation in a vacuum: $v/c$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A very similar equation is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Characteristic_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;characteristic impedance&lt;/a&gt; of the transmission line:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_0 = \sqrt{\frac{L}{C}} \tag{2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, if we know any two of:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;characteristic impedance,&lt;/li&gt;&#xA;&lt;li&gt;capacitance per unit length, or&lt;/li&gt;&#xA;&lt;li&gt;inductance per unit length&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;then we can calculate the velocity factor. Let's try it for Belden 9223, which specifies in the datasheet:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_0 = 50\:\Omega \\&#xA;C = 37\:\mathrm{pF}/\mathrm{ft} = 1.21 \cdot 10^{-10}\:\mathrm{F/m} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So by equation (2):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;50\Omega &amp;amp;= \sqrt{\frac{L}{ 1.21 × 10^{-10} }} \\&#xA;50^2 &amp;amp;= \frac{L}{ 1.21 × 10^{-10} } \\&#xA;L &amp;amp;= 3.03 \cdot 10^{-7}\:\mathrm{H}/\mathrm{ft}&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And then by equation (1):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;v &amp;amp;= \frac{1}{\sqrt{( 3.03 \cdot 10^{-7} )( 1.21 × 10^{-10} )}} \\&#xA;v &amp;amp;= 165289256 \:\mathrm{m/s}&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus the velocity factor is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ v/c = 165289256 / 299792458 = 0.55 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The datasheet says 0.56. I attribute the discrepancy to rounding error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what about a single wire? What values do we use for L and C?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That depends on the geometry of the wire. In the case of coax, the wave is propagating within the dielectric between the center conductor and the shield. This dielectric has a known geometry and composition, so the manufacturer can specify a velocity factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a wire, the wave will be propagating between the wire, and something else. Maybe the ground. Maybe another wire. Maybe the same wire some distance away, as in the case of a dipole. Are you stretching the wire in a straight line, or winding it into a coil? The capacitance will be depend on the permittivity of the space containing the electric field. Is it air? A tree? Because there are so many variables, a wire datasheet can not possibly specify a velocity factor. And while we might measure one, we must be careful to specify what propagation mode we are talking about, and the conditions under which it was measured.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-12-09T18:17:52.983" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2395" PostTypeId="2" ParentId="2390" CreationDate="2014-12-10T03:00:35.603" Score="0" Body="&lt;p&gt;Have a look here: for &lt;strong&gt;inductance&lt;/strong&gt; &lt;a href=&quot;http://chemandy.com/calculators/round-wire-inductance-calculator.htm&quot; rel=&quot;nofollow&quot;&gt;http://chemandy.com/calculators/round-wire-inductance-calculator.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$L=0.002\times l[ln{\frac{4.0\times l}{d}}-1.0+\frac{d}{2.0\times l}+\frac{\mu_r\times T(x)}{4.0}]$ (in $\mu H$)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This formula is an approximation, and $T(x)$ can be had in several degrees of precision, one value for $T(x)$ is shown in the referenced article.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For &lt;strong&gt;capacitance&lt;/strong&gt; we have a similarly complicated formula (&lt;a href=&quot;http://en.wikipedia.org/wiki/Capacitance&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Capacitance&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$C=\frac{2 \pi \epsilon l}{\Lambda}[1+\frac{1}{\Lambda}(1-ln(2))+\frac{1}{\Lambda^2}(1+(1-ln(2))^2-\frac{\pi^2}{12})+O\frac{1}{\Lambda^3}]$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unluckily, most of my basic electronics textbooks were lost in a flood, many years ago, and I've spent most of my career in the digital world. Never felt the necessity to buy the books again - I spent more than my share on computer books. I might be able to access the mentioned papers at the university, but it'll take a few days - we're in the exams.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As in the inductance case, I suspect 'O' is again some magic constant...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\Lambda$ is just the ln(l/a) where l is the length, and a the radius.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Though self-inductance of a wire is relatively understood, capacitance of a 'lone' conductor is more mysterious. It helps if you think about what capacitance represents from another point of view: even if alone in in the universe, adding another electron to the conductor still takes some work, because you have to re-distribute the ones already on the conductor. After all, having the same sign, they don't like each other.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2014-12-10T03:00:35.603" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2396" PostTypeId="1" AcceptedAnswerId="2397" CreationDate="2014-12-10T03:42:50.320" Score="2" ViewCount="208" Body="&lt;p&gt;I am not terribly interested in hearing about whether or not EMF/RF is hazardous to ones health (as this is frequently discussed in my house).&#xA;&lt;p&gt;&#xA;What I would like to know is; how much EMF/RF does an average scanner emit?&#xA;&lt;p&gt;&#xA;&lt;strong&gt;Edit:&lt;/strong&gt; I would be using this in my house - near my bed for example.&lt;/p&gt;&#xA;" OwnerUserId="1938" LastEditorUserId="1938" LastEditDate="2014-12-24T20:35:02.337" LastActivityDate="2014-12-24T20:35:02.337" Title="How much EMF does a typical scanner put out?" Tags="&lt;receiver&gt;&lt;emergency&gt;&lt;safety&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2397" PostTypeId="2" ParentId="2396" CreationDate="2014-12-10T14:21:28.757" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What I would like to know is; how much EMF/RF does an average scanner emit?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No more than your TV, electric lights, or phone charger. In fact, quite possibly less. Certainly far less than your cell phone, laptop, or Xbox controller, all of which contain intentional transmitters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A scanner does not emit anything intentionally because it does not transmit. There are, of course, &lt;em&gt;unintended&lt;/em&gt; emissions, but then this is true of any electrical device. It is especially true of modern, high speed digital electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most jurisdictions have some authority which limits the maximum permissible unintended emissions for devices. For example, in the USA this is the FCC. To sell a product, a manufacturer must submit a prototype to an &lt;a href=&quot;http://en.wikipedia.org/wiki/Electromagnetic_compatibility#EMC_testing&quot; rel=&quot;nofollow&quot;&gt;electromagnetic compatibility (EMC) testing facility&lt;/a&gt; which measures the very small, unintended emissions of the product. The results are sent to the FCC which must certify the device before it can be sold.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you want to know more specifically how much EMF your scanner might emit, check out the regulations in your jurisdiction.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="1579" LastEditDate="2014-12-10T18:59:09.737" LastActivityDate="2014-12-10T18:59:09.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2398" PostTypeId="2" ParentId="2396" CreationDate="2014-12-11T02:37:41.263" Score="1" Body="&lt;p&gt;As mentioned earlier, the answer is along the lines of &quot;not much at all&quot;, and &quot;about the same as your TV set&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But remember that in the UK they have TV detector vans (to detect people watching TV without a TV licence. Yes, this is real - see &lt;a href=&quot;http://en.wikipedia.org/wiki/Television_licensing_in_the_United_Kingdom#Detection_technology&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Television_licensing_in_the_United_Kingdom#Detection_technology&lt;/a&gt;) that are rumoured to operate by detecting unintentional emissions by a TV receiver - especially around the local oscillator and IF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most common radio receivers are &quot;superhet&quot; receivers that work by mixing a locally-generated signal with a received signal and generating an intermediate frequency from these. This is then optionally mixed down still further to a lower IF, and finally converted to baseband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apparently, TV detector vans work by looking for the IF and local oscillator, rather than other electrical signals generated within a TV (such as flyback transformers etc. in a CRT TV), because other signals would also be generated by a computer monitor that does not receive TV signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, there have been reports that TV detector vans are a ruse, to frighten people to buy a TV licence.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2014-12-11T02:37:41.263" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2399" PostTypeId="1" AcceptedAnswerId="2404" CreationDate="2014-12-11T14:35:13.103" Score="5" ViewCount="1101" Body="&lt;p&gt;I've built &lt;a href=&quot;http://www.aa5tb.com/coupler.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;AA5TB's antenna coupler&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/zmjIo.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I left out C2 because I didn't understand why I would need it - why would I? It works fine without.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, when I started tuning for a 5W 20m transceiver, the LED was on all the time. I then measured with a multimeter the AC voltage over the LED, and tuned to its minimum, about 3.2V~. The maximum was about 4.2V~. I was thinking of changing R4 and/or R5 so that these extremes are  a bit lower. Is that the right way to do this? I'm worried, because I'd say the resistance of the whole R4-R5-D2 circuit should be about 51 Ohm, like the other resistors. Or would adding C2 resolve this issue?&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorUserId="76" LastEditDate="2015-12-15T22:23:17.973" LastActivityDate="2015-12-15T22:23:17.973" Title="Adapting an antenna coupler" Tags="&lt;transceiver&gt;&lt;electronics&gt;&lt;antenna-tuner&gt;&lt;20m-band&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2400" PostTypeId="1" AcceptedAnswerId="2405" CreationDate="2014-12-11T16:10:06.887" Score="8" ViewCount="668" Body="&lt;p&gt;I've built &lt;a href=&quot;http://www.aa5tb.com/coupler.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;AA5TB's antenna coupler&lt;/a&gt; for a 5W 20m transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning was kind of difficult because my transceiver has buttons for sending a dot and a dash, but no tuning mode, so I couldn't have the transmitter on permanently to tune easily. I had to tweak it a bit to make it do this. I also have a 7.017MHz calibrated transmitter. Would it be okay to put the transceiver in receive mode, on 14.034MHz, hold that calibrated transmitter close to the antenna, and tune until the signal is the loudest (or, until the LED doesn't light / the voltage measured over D2 is in its minimum)? So in other words: can I tune the antenna when not transmitting?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/zmjIo.gif&quot; alt=&quot;x&quot;&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorUserId="76" LastEditDate="2016-07-12T14:01:02.633" LastActivityDate="2016-07-12T14:01:02.633" Title="Antenna tuning while receiving" Tags="&lt;transceiver&gt;&lt;antenna-tuner&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2401" PostTypeId="2" ParentId="2399" CreationDate="2014-12-11T17:16:29.127" Score="0" Body="&lt;p&gt;The actual values of R4 and R5 are not important; what is important is their ratio, since in this configuration they are acting as a voltage divider. If you have a pretty good idea of what the &quot;correct&quot; tuning for your transmitter should be, try this: replace either R4 or R5 with a variable resistor or potentiometer. Adjust the potentiometer for maximum voltage across the LED when your transmitter is correctly tuned, and minimum voltage across the LED when poorly tuned or mismatched. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Capacitor C2 is not essential and can be left out. C2 has a &quot;damper&quot; effect on the LED; it slows down the rise and fall of voltage across the diode. This does two things: it protects the LED against large transient voltages, and it keeps the LED lit for a longer period of time after the voltage has fallen to zero (e.g. between CW symbols). However, C2 doesn't interact with the rest of the circuit, so adding it would likely not resolve the issue you are having.&lt;/p&gt;&#xA;" OwnerUserId="1579" LastActivityDate="2014-12-11T17:16:29.127" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="2402" PostTypeId="1" CreationDate="2014-12-11T17:50:12.967" Score="1" ViewCount="89" Body="&lt;p&gt;I was wondering if it would be worth it to engage some of the hotels south of the strip to see if they would allow us to put a repeater on one of the buildings there.  Just wondering as the Marriott, Caesars Palace and New York New York block the repeaters installed north of the strip.   Basically, what does the signal quality look like south of the strip?  I may have a hotel that would consider putting up a repeater if the community provides enough feedback for it.&lt;/p&gt;&#xA;" OwnerUserId="2946" LastActivityDate="2014-12-16T17:39:51.137" Title="What does the current signal look like just south of Las Vegas?" Tags="&lt;repeater&gt;&lt;range&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ClosedDate="2014-12-22T11:00:42.837" ContentLicense="CC BY-SA 3.0" />
  <row Id="2403" PostTypeId="2" ParentId="1903" CreationDate="2014-12-11T21:53:31.567" Score="-3" Body="&lt;p&gt;The folded dipole antenna has lower efficiency than a standard dipole antenna. The efficiency is a factor of both radiation efficiency and impedance matching. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation efficiency of a folded dipole is lower than that of a standard dipole. This is because it is folded; between the two parallel wires of the structure, there is a capacitive effect. This means some part of the electromagnetic energy is stored between these two parallel wires. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance of a folded dipole also differs from a standard dipole, but the impedance can be matched by using a matching network or a transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;About the capaticitive energy stored in parallel wire, you can think about a typical explanation of a dipole antenna. If there are two plates parallel, then it acts like a capacitance and if you put them like a dipole antenna, the rods of the antenna gets + and - poles. Then the antenna radiates. That's because the electric field is not stored between two plates, but the field vector is between one pole to another pole. This provides an antenna to radiate. For example, if the angle between two rods are 120 degrees, then it is more like a capacitance then a standart dipole antenna. And a capacitance means the energy is stored in the capacitance. This is a well known principle in small antenna and mobile phone antenna design. In a transmission line, the electric field vectors are between the two plates, and energy is still stored between the plates. &lt;/p&gt;&#xA;" OwnerUserId="1917" LastEditorUserId="1917" LastEditDate="2014-12-18T22:43:23.270" LastActivityDate="2014-12-18T22:43:23.270" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="2404" PostTypeId="2" ParentId="2399" CreationDate="2014-12-12T13:20:52.570" Score="1" Body="&lt;p&gt;C2 removes the AC component across the LED, and prevents the LED from being on when the antenna is matched to 50 ohms. You say the circuit works anyway -- probably at QRP levels it's not bright enough to see. I bet if you try it in a dark room, or with a higher power transmitter, you will see it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, consider how this circuit works. Here's a simplified version which makes the antenna impedance more explicit, and lacks any sort of visible indicator:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/oaBSI.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2foaBSI.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a &lt;a href=&quot;http://en.wikipedia.org/wiki/Wheatstone_bridge&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wheatstone bridge&lt;/a&gt;. V1 is your transmitter, and the antenna is the resistor of unknown value ($R_{ant}$).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think of it this way: $R_1$ and $R_3$ form a voltage divider, and $R_2$ and $R_{ant}$ form another. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;D1, C1, and R5 make a peak detector. If $R_{ant} &amp;lt; R_3$, then on the positive cycle of V1, the voltage at A is greater than the voltage at B, and C1 charges through D1 to the peak difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If $R_{ant} &amp;gt; R_3$, then on the negative cycle of V1, the voltage at B is more negative than at A, and again C1 charges through D1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if $R_{ant} = R_3$ (50Ω, our target impedance), then there is no voltage between A and B, and so D1 can never be forward biased, and so C1 can have no voltage across it, except for a small AC component via R5. The &lt;a href=&quot;http://en.wikipedia.org/wiki/RC_time_constant&quot; rel=&quot;nofollow noreferrer&quot;&gt;time constant&lt;/a&gt; of C1 and R5 make a filter with a cutoff frequency of&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ f_c = \frac{1}{2\pi R C} = \frac{1}{2 \pi (10\:\mathrm k\Omega) (10\:\mathrm{nF})} \approx 1600\:\mathrm{kHz} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is so low far below the frequency of V1 that we can consider the AC component of the voltage across C1 to be zero. Instead, it appears across R5.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now, look back to your circuit with the LED. It is connected across R5, which has some RF voltage across it all the time. When C1 is charged because the antenna isn't 50Ω then there is additionally some DC component, and it's really this DC component that we are interested in. Remember, a capacitor looks like a low impedance at higher frequencies, so by adding C2, you are effectively shunting any RF current around the LED, so that the LED sees only the DC component.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An alternate solution to this problem is to connect the LED across C1, like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/hBwQH.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fhBwQH.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For that matter, why bother with two diodes when you already have one? An LED doesn't make a great RF rectifier, but I bet it works well enough at HF in this application. In fact, with one less diode drop of voltage I bet it's even more sensitive. We don't really need the capacitor since an LED flickering at 14 MHz looks just the same:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/5Jkzb.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f5Jkzb.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adjust the value of R4 to get the right LED brightness for your transmitter power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One might ask why AA5TB's design is the way it is, and I'm guessing it's because &lt;a href=&quot;http://www.gqrp.com/resistive_swr_bridge.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;that's how someone else did it&lt;/a&gt;, and the design was just copied with minor modifications. R4 and R5 together used to be a potentiometer. The arrangement of connected the LED to ground instead of point B (thus requiring C2) is probably because the LED used to be a meter. If you have a meter with a metal casing, and you are building this in a metal box, it may be easier to connect the meter to ground than to isolate it from the enclosure. With an LED you have no such restrictions.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-12-13T14:57:59.100" LastActivityDate="2014-12-13T14:57:59.100" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2405" PostTypeId="2" ParentId="2400" CreationDate="2014-12-12T13:47:59.613" Score="3" Body="&lt;p&gt;You can tune by receiving, generally. When your antenna is tuned, then SWR losses are minimized. By &lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_%28electromagnetism%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;reciprocity&lt;/a&gt; this minimizes receive losses also, so you can just listen to noise and tune for maximum received noise level. In fact, with more complicated tuners that have more adjustments, this is usually the first step so that you can be in the right ballpark and avoid subjecting your transmitter to a really horrible match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your proposed method of coupling another transmitter to this particular tuner has a couple of problems, though. Firstly, this device doesn't really measure SWR, but instead is an impedance bridge which determines if the antenna impedance is 50 ohms. See the &lt;a href=&quot;https://ham.stackexchange.com/a/2404/218&quot;&gt;explanation of how the circuit works&lt;/a&gt; in another question, and it should be obvious how this won't work without the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, if you put your calibrated transmitter &quot;very close&quot; to the antenna, then it will be coupling to the antenna in the &lt;a href=&quot;http://en.wikipedia.org/wiki/Near_and_far_field&quot; rel=&quot;nofollow noreferrer&quot;&gt;near field&lt;/a&gt;, which has significantly different characteristics than the far field, which is what you care about for radio communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, tuning is frequency dependent, so a 7.017MHz transmitter isn't of much help for tuning 14.034MHz. You could probably find a way to make your transmitter generate a 2nd harmonic and filter that out, and then you'd have 14.034MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a much simpler idea: try increasing C1. If you increase it enough, it will be able to power D2 through the period between the dashes. You can also try increasing R4, which will make the LED less bright, but discharge C1 more slowly. To get an idea of the values you need, consider the &lt;a href=&quot;http://en.wikipedia.org/wiki/RC_time_constant&quot; rel=&quot;nofollow noreferrer&quot;&gt;time constant&lt;/a&gt; of R4 and C1, which you want to be on the order of the spacing between the dashes, which is around 60ms for 20 WPM. So:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 1\:\mathrm k \Omega \cdot C_1 = 60\:\mathrm{ms} \\&#xA;C_1 \approx 60 \:\mu \mathrm F $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The disadvantage of this modification is that the LED indicator will be less responsive to your adjustments.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-12-12T13:47:59.613" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2407" PostTypeId="2" ParentId="2360" CreationDate="2014-12-15T00:44:46.837" Score="-1" Body="&lt;p&gt;I think 97.133(b) speaks to this really.  &quot;An amateur station shall not engage in any form of broadcasting, nor may an amateur station transmit one-way communications...&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Broadcasting is loosely defined as something for the benefit or entertainment of the listening audience and not a two way communication.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is ambiguous to say the least, but I probably wouldn't play the turkey call to be safe.  Just my opinion of how I read it.&lt;/p&gt;&#xA;" OwnerUserId="2953" LastEditorUserId="218" LastEditDate="2014-12-15T13:05:09.503" LastActivityDate="2014-12-15T13:05:09.503" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2408" PostTypeId="2" ParentId="2360" CreationDate="2014-12-15T04:59:07.627" Score="2" Body="&lt;p&gt;Imagine you are working at FCC HQ.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC receives 1000s of complaints each day, such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;too much profanity on television&lt;/li&gt;&#xA;&lt;li&gt;firefighters' repeater is being jammed by some weirdo named Big Jack&lt;/li&gt;&#xA;&lt;li&gt;truck stop sells monster CB amps&lt;/li&gt;&#xA;&lt;li&gt;talk radio has too many republicans/democrats&lt;/li&gt;&#xA;&lt;li&gt;internet should/shouldn't be regulated&lt;/li&gt;&#xA;&lt;li&gt;big media company wants to buy all the little media companies&lt;/li&gt;&#xA;&lt;li&gt;ham wants morse code to be required again&lt;/li&gt;&#xA;&lt;li&gt;smugglers are using GMRS channel Z84 along the border&lt;/li&gt;&#xA;&lt;li&gt;brazilians pirates have hacked milcom satellite uplinks&lt;/li&gt;&#xA;&lt;li&gt;university jams students' cell phones so they won't ring in class&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Only some of these fall within the jurisdiction of the FCC, and their power to do anything about it.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is &quot;turkey call courtesy beep&quot; going to make the cut on this list?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think so, as it is a trivial matter that harms no one and doesn't indicate a serious violation of the regulations. Even if it were technically a violation of some rule when twisted sufficiently, I doubt it even merits a warning letter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But don't take my word for it.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can &lt;a href=&quot;http://transition.fcc.gov/eb/&quot; rel=&quot;nofollow&quot;&gt;search past FCC enforcement actions&lt;/a&gt; to find out.&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2014-12-15T05:10:44.573" LastActivityDate="2014-12-15T05:10:44.573" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2409" PostTypeId="1" AcceptedAnswerId="2413" CreationDate="2014-12-15T11:09:33.097" Score="8" ViewCount="148" Body="&lt;p&gt;I've seen many contests define mobile as something like being able to legally move and broadcast. Well, using an HT while walking I can legally move. Does this count as mobile contacts for a contest?&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2014-12-16T22:20:31.757" Title="Is using an HT and walking considered mobile?" Tags="&lt;contest&gt;&lt;ht&gt;&lt;mobile&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2410" PostTypeId="2" ParentId="2409" CreationDate="2014-12-16T17:08:46.607" Score="0" Body="&lt;p&gt;When I hear people operating portable, they are usually outside and walking or biking through town with an HT.  More often then not they are also outside their QTH's grid square.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2014-12-16T17:08:46.607" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2411" PostTypeId="2" ParentId="2402" CreationDate="2014-12-16T17:39:51.137" Score="0" Body="&lt;p&gt;Because your question is about information for such a small geographical area, I would suggest contacting one of these organizations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.lvrac.org/index.html&quot; rel=&quot;nofollow&quot;&gt;Las Vegas Radio Amateur Club&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hxo.com/&quot; rel=&quot;nofollow&quot;&gt;Las Vegas Repeater Association (LVRA)&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.narri.org/&quot; rel=&quot;nofollow&quot;&gt;NARRI - NEVADA AMATEUR RADIO REPEATERS, INC&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You could also join the &lt;a href=&quot;https://groups.yahoo.com/neo/groups/lvrac/info&quot; rel=&quot;nofollow&quot;&gt;Las Vegas HAM Radio Reflector Yahoo Group&lt;/a&gt; and ask your question there.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2014-12-16T17:39:51.137" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2412" PostTypeId="1" CreationDate="2014-12-16T19:09:13.630" Score="3" ViewCount="167" Body="&lt;p&gt;I have a radio (Flex-1500) that has low level transverter outputs. They can be configured as either a common or split-if.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also have a DEMI transverter that can easily be wired up for common or split-if.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any advantages or disadvantages in using one configuration versus the other?&lt;/p&gt;&#xA;" OwnerUserId="2962" LastEditorUserId="76" LastEditDate="2017-08-17T23:19:32.090" LastActivityDate="2017-08-17T23:19:32.090" Title="Transverter common versus split-if connections" Tags="&lt;vhf&gt;&lt;transverter&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2413" PostTypeId="2" ParentId="2409" CreationDate="2014-12-16T22:20:31.757" Score="7" Body="&lt;p&gt;Insofar as there is an agreed-upon definition of the term “mobile” (and “portable”, which is closely related/confusable and so I'm covering it here), this is how I have most frequently seen the terms used &lt;em&gt;when people are being precise about it&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Portable&lt;/strong&gt;: A station set up in a temporary location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you've parked a radio on a picnic table and strung a wire antenna to a tree, you're operating portable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some contexts there may be the additional implication of being a significant distance from your home location.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Mobile&lt;/strong&gt;: A station which is &lt;em&gt;capable&lt;/em&gt; of being operated &lt;em&gt;while in motion&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most common type of “mobile” is a station installed in a car/truck. For other means of transportation, you usually hear it qualified as “pedestrian mobile”, “bicycle mobile”, “maritime mobile”, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've never seen anyone say that pedestrian mobile isn't a kind of mobile. So, to the first question you asked, &lt;em&gt;Is using an HT and walking considered mobile&lt;/em&gt;, I say “yes”. (And practically, however you're labeled, you've taken on the &lt;em&gt;limitations&lt;/em&gt; of a mobile station — small antenna, no earth ground, battery power, etc.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;But in any specific actual contest — if the rules aren't clear, ask for clarification. It's the opinion of the contest organizers that actually matters.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-12-16T22:20:31.757" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2414" PostTypeId="1" AcceptedAnswerId="2416" CreationDate="2014-12-17T18:07:30.463" Score="3" ViewCount="2385" Body="&lt;p&gt;I'm working on a system (theoretical at the moment) whereby I wish to receive data from multiple sources all transmitting at the same time. I've read that a helical antenna is capable of this. I'm also aware that multiplexing can be used if the sample rate required to receive each signal is small enough that the you could effectively switch between the different signals. Is this the process that is referred to when I've read about helical antennas or are they otherwise beneficial when receiving multiple signals?&lt;/p&gt;&#xA;" OwnerUserId="529" LastEditorUserId="8573" LastEditDate="2020-03-11T13:24:57.303" LastActivityDate="2020-03-16T23:52:26.717" Title="How to receive a signal from multiple sources simultaneously (helical antenna)" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;digital-modes&gt;&lt;software-defined-radio&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="2415" PostTypeId="2" ParentId="2414" CreationDate="2014-12-17T18:53:22.030" Score="3" Body="&lt;p&gt;There is nothing special about a helical antenna that makes it more suited to receiving multiple signals simultaneously than any other kind of antenna. In fact one might argue the opposite: a helical antenna is directional, and if your sources are in many directions this will make it difficult or impossible to receive all of them at once.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To receive multiple sources, you will, by definition, do some kind of &lt;a href=&quot;http://en.wikipedia.org/wiki/Multiplexing&quot; rel=&quot;nofollow&quot;&gt;multiplexing&lt;/a&gt;. What you describe, &quot;switching between the different signals&quot;, sounds like &lt;a href=&quot;http://en.wikipedia.org/wiki/Time-division_multiplexing&quot; rel=&quot;nofollow&quot;&gt;time-division multiplexing&lt;/a&gt;. There are many other kinds, where multiple sources might be differentiated based on:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;time,&lt;/li&gt;&#xA;&lt;li&gt;frequency,&lt;/li&gt;&#xA;&lt;li&gt;location,&lt;/li&gt;&#xA;&lt;li&gt;polarization,&lt;/li&gt;&#xA;&lt;li&gt;any of these in combination,&lt;/li&gt;&#xA;&lt;li&gt;and many more.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Wikipedia has a &lt;a href=&quot;http://en.wikipedia.org/wiki/Multiplexing#Types_of_multiplexing&quot; rel=&quot;nofollow&quot;&gt;more detailed summary&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-12-17T18:53:22.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2416" PostTypeId="2" ParentId="2414" CreationDate="2014-12-17T18:57:35.247" Score="9" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm working on a system (theoretical at the moment) whereby I wish to receive data from multiple sources all transmitting at the same time. I've read that a helical antenna is capable of this.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm afraid you're misinformed. &lt;strong&gt;No single antenna, no matter what the design,&lt;/strong&gt; can be better than another at receiving multiple signals at once. A receiving antenna doesn't know anything about &quot;one signal&quot; or &quot;two signals&quot;; it just collects radiation and turns it into current in the feed line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are ways in which you might optimize the antenna for your particular purpose, but they will depend on details you haven't given. In particular, are the “multiple sources” you refer to at fixed locations? If so, you can use a directional antenna, designed to have more gain in those particular directions. However, this only improves signal-to-noise ratio; it does not help separate the signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use &lt;strong&gt;two separate directional antennas&lt;/strong&gt; pointed at the two sources, then you can receive them independently by having two separate receivers, of course. (Connecting two directional antennas to one receiver &lt;a href=&quot;https://ham.stackexchange.com/questions/4905/connect-two-receiving-antennas-to-the-same-radio/4907#4907&quot;&gt;is just making one more complex directional antenna&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm also aware the multiplexing can be used if the sample rate required to receive each signal is small enough that the you could effectively switch between the different signals.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A high sample rate in a software-defined radio can help with receiving multiple signals, but it's not a matter of “switching”. The sample rate determines the maximum &lt;em&gt;bandwidth&lt;/em&gt; — the size of the slice of the RF spectrum that you receive. If you are trying to receive two signals &lt;em&gt;at different frequencies&lt;/em&gt;, then you can receive them with a single SDR device, programmed appropriately, if they are close enough together to fall simultaneously within the receive bandwidth, like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;                 |Signal1|        |Signal2|&#xA;                 |       |        |       |&#xA;                 |       |        |       |&#xA;   | &amp;lt;----------------------- Receiver bandwidth ----------------------&amp;gt; |&#xA;   |             |       |        |       |                              |&#xA;   |             |       |        |       |                              |&#xA;---+-------------+-------------+-------------+-------------+-------------+---&#xA;162.40        162.42        162.44    ^   162.46        162.48        162.50 MHz&#xA;                                      |&#xA;                                      |&#xA;                             Receiver LO frequency&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This is not helpful if the two signals you want to receive are at the &lt;em&gt;same&lt;/em&gt; frequency. But if they are, they are probably transmitting in bursts or using some other type of multiplexing to avoid interfering with each other. What you do at the receiver entirely depends on what the transmitters are doing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might wish to ask a different question (posted separately, please): tell us &lt;em&gt;about the signals you want to receive&lt;/em&gt; (what are they, are you making the transmitters or do they already exist, etc), and ask how to build a receiver for that.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is this the process that is referred to when I've read about helical antennas or are they otherwise beneficial when receiving multiple signals?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you edited your question to include links to what you've read about helical antennas, I might be able to explain what they're actually saying.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-06-01T20:20:45.123" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2417" PostTypeId="1" CreationDate="2014-12-19T22:20:07.530" Score="1" ViewCount="257" Body="&lt;p&gt;Preferably something that could transmit LED lights, like patterns. After that I'd like to advance to audio and video. But for the basic radio transmitting and receiving how difficult of a job would that be? and what tools and parts would I need? I've worked on a off with electronics for about a year so I know about capacitors, resistors, transistors,transformers, arduinos, basic C and Python Programming. I think I could do this job but could use some guidance and information.&lt;/p&gt;&#xA;" OwnerUserId="2974" LastEditorUserId="1246" LastEditDate="2014-12-23T21:27:48.513" LastActivityDate="2014-12-24T15:43:11.017" Title="How difficult is it to build a basic transmitter and receiver" Tags="&lt;receiver&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2421" PostTypeId="1" CreationDate="2014-12-22T04:13:07.007" Score="2" ViewCount="1699" Body="&lt;p&gt;For two meters, a 5/8th wave antenna has the best omni gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I think the lobe is very low takeoff and not good for mountain work. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is best for the mountains on a mobile? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, I know not much is going to get over mountains at 144Mhz and above but I want to know what will work best?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•For repeaters on mountains&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•And for simplex to other vehicles in repeater &quot;dead zones&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Terrain at 39.501419 , -106.15162650000002&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Time for the Constraints&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•The antenna has to magnetically mount to the roof of a vehicle, which is a van. I have a very strong Tri-magnet mount. (unless someone can think of a different way without manipulation of the vehicle in any way).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•The antenna can not take up much horizontal space due to bicycles on the roof nearby. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;•By much I mean nothing more than a 10cm by 10cm block horizontally at the base and up to the height of a bicycle. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;•The antenna can not be taller than the street regulations for traffic lights, power lines, etc (obviously)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•Weight does not matter&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•The antenna should not pop off the roof&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•I want to optimize for best signal strength to other stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•Power I will be running - 50 watts&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•Band- Primarily VHF, but maybe a bit of UHF. Optimize for high performance in VHF. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;•Max speed of vehicle will be 60 Mph on a highway stretch, so wind strain should be taken in consideration, but not importance (as long as the antenna doesn't fall off). &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2014-12-22T15:32:15.190" LastActivityDate="2015-01-06T16:57:23.867" Title="Best mobile antenna for the mountains" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2423" PostTypeId="2" ParentId="899" CreationDate="2014-12-22T14:43:37.897" Score="4" Body="&lt;p&gt;A &quot;shielded loop antenna&quot; is a very misleading name. It isn't an antenna, with a shield. It's an antenna made from a shield, with a feedline inside it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's commonly stated that the shield blocks electric fields and not magnetic fields. But that's false: it's &lt;a href=&quot;https://ham.stackexchange.com/q/2455/218&quot;&gt;physically impossible&lt;/a&gt;. That's not to say that a shielded loop antenna has no merit beyond an unshielded loop antenna, though. The &quot;shield&quot; makes an excellent, broad-band, low-loss, easily fabricated balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's an &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;analogous problem with dipoles&lt;/a&gt; also. If we want to feed a dipole with coax, we need a balun to prevent common-mode currents on the feedline, because if there are common-mode currents on the feedline, the feedline is part of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could build a magnetic loop antenna like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/tBfrS.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2ftBfrS.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feedline is balanced, and the antenna is symmetrical. Like a dipole with a balanced feeder, there are no common-mode currents and the feedline will not radiate, provided the surroundings are also reasonably symmetrical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But we want a coax feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is only one place to connect the coax that won't result in common-mode currents: immediately opposite the feedpoint. If we do this, then any common-mode currents will cancel at the feedpoint. With any other arrangement, common-mode currents can couple into the feedpoint, so the feedline will be part of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/d84DQ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But then how do we get the end of the coax to the feedpoint? The solution: make the antenna from tubing, and run the feedline &lt;em&gt;inside&lt;/em&gt; the antenna. Because RF currents travel on the surface of the antenna, what happens inside the antenna is irrelevant to the operation of the antenna. Electrically, it looks like an ordinary loop antenna made from fat wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/CgMmN.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://books.google.com/books?id=PPyDQXAd09kC&amp;amp;lpg=PA260&amp;amp;dq=natural%20balun&amp;amp;pg=PA260#v=onepage&amp;amp;q=natural%20balun&amp;amp;f=false&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Modern Antenna Design&lt;/em&gt; by Thomas A. Milligan&lt;/a&gt; describes this as a &lt;em&gt;natural balun&lt;/em&gt; (though, I've never seen that terminology used elsewhere):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A natural balun feeds the coax through a loop antenna to the feed point where the outer shield is split and the center conductor jumps the gap to connect to the outer shield of the coax. At this point the currents flow on to the outer shield and radiate. By moving an equal distance along the coax until the two halves meet, we can connect the feed coax and not have current flow down the outside. The currents flow in opposite directions along the loop and cancel at the connection. From a circuit point of view, the connection point is a virtual short circuit to the balanced mode &lt;a href=&quot;https://ham.stackexchange.com/q/3591/218&quot;&gt;similar to a folded balun&lt;/a&gt; at its connection point. In a similar manner, on a folded dipole we can connect the feed coax to the middle of the shorted dipole and form a natural balun.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If we simplify the construction a bit and double the coax shield as the tubing, this type 2(d) from the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As it is, this design has a coax feed and no problems with common-mode currents. However, if one wants to add a capacitor to resonate the antenna at the operating frequency, or a matching network, one must be careful to preserve the current balance of the antenna. The ARRL design is notably horrible at this. However, we are getting away from the topic of the question, so I will suggest reading &lt;a href=&quot;http://www.w8ji.com/magnetic_receiving_loops.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI on small magnetic loops&lt;/a&gt; for a more detailed discussion.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-02-09T16:37:57.243" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="2426" PostTypeId="2" ParentId="2389" CreationDate="2014-12-24T05:44:12.653" Score="3" Body="&lt;p&gt;The two are separate figures, so one does not imply the other. A good match doesn't imply no common mode currents, and no common-mode current does not imply a good match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are somewhat connected - a change to the common mode currents will probably change the impedance match. But the other way doesn't have to apply - imagine soldering a small capacitor across the feedpoint. No change to common-mode currents, but the impedance match changes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So these are both important considerations in an antenna design, but they are addressed separately, and with different techniques. Common mode currents are tackled by keeping things symmetrical, the addition of a choke or balun, or changing the antenna shape entirely.  Then impedance matching is done by trimming (both sides of the antenna) and addition of matching components.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2014-12-24T05:44:12.653" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2427" PostTypeId="2" ParentId="2421" CreationDate="2014-12-24T10:05:39.927" Score="3" Body="&lt;p&gt;If very high angle coverage is important to you, go for a 1/4 wave monopole antenna, mounted in the middle of the roof. A magnetic mount should be fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 5/8 wave vertical antenna has more gain than a a 1/4 wave vertical only up to an elevation of about 15 degrees, and drops away quickly above 25 degrees. There's a diagram &lt;a href=&quot;http://www.astrosurf.com/luxorion/qsl-antenna.htm&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bicycles on the roof will not help at all. Having a 10cm x 10cm clear area around the antenna isn't enough. You need to keep an upright bicycle at least 1 m away to avoid major interference with patterns. Can you move the antenna elsewhere on the vehicle? If you must use the radio and the bicycles, you could extend the antenna through the bicycles on a pole. If you do this, it must then be a &quot;ground independent&quot; antenna, something with radials that stick out the sides. The pole won't be an acceptable ground plane by itself.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2014-12-24T10:05:39.927" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2428" PostTypeId="2" ParentId="2417" CreationDate="2014-12-24T11:49:26.473" Score="2" Body="&lt;p&gt;Take a look at &quot;Experimental Methods in RF Design&quot; from the ARRL, that will get you started in how to design and build radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A recent copy of the &lt;a href=&quot;http://www.arrl.org&quot; rel=&quot;nofollow&quot;&gt;ARRL&lt;/a&gt; Handbook is also a must.&lt;/p&gt;&#xA;" OwnerUserId="2962" LastActivityDate="2014-12-24T11:49:26.473" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2429" PostTypeId="2" ParentId="2417" CreationDate="2014-12-24T15:43:11.017" Score="3" Body="&lt;p&gt;If you're interested in RF experimentation and you prefer to work in a virtual environment, try GNURadio.  It runs in linux, and has the basic virtual components to build a variety of RF systems, including basic FM/AM transceivers.  There are many online tutorials to get you started with the basics, and you don't need a lab or any parts.  You just need a laptop and some time.  When you want to implement your designs in reality, look at getting a cheap SDR (Software defined radio).  They typically plug into the USB port of your computer, and can be purposed for almost anything (within the limitations of the SDR itself, of course!)&lt;/p&gt;&#xA;" OwnerUserId="2990" LastActivityDate="2014-12-24T15:43:11.017" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2430" PostTypeId="1" CreationDate="2014-12-24T16:23:50.937" Score="4" ViewCount="122" Body="&lt;p&gt;I have a TenTec 506 HF transceiver that uses a Digilent chipKIT UNO32 microcontroller. My PC running Teraterm (serial connection) or the MPIDE monitor is connected to the microcontroller's mini B USB port to read frequency, RIT, voltage, etc. I would like to replace the USB cable (USB A to USB mini B) that runs between the TenTec's controller and my PC with inexpensive USB wireless devices or Bluetooth.&#xA;Can anyone suggest devices that will allow me do this? &lt;/p&gt;&#xA;" OwnerUserId="2983" LastEditorUserId="76" LastEditDate="2016-10-29T19:05:52.067" LastActivityDate="2016-10-29T19:05:52.067" Title="How can I establish a wireless link between my PC and TenTec 506 / chipKIT UNO32 using USB port?" Tags="&lt;hf&gt;&lt;diy&gt;&lt;transceiver&gt;&lt;computer-control&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2431" PostTypeId="2" ParentId="2430" CreationDate="2014-12-25T02:14:19.430" Score="1" Body="&lt;p&gt;I don't have any specific model recommendations, but I once saw that there existed simple dongles which convert between Bluetooth serial and RS-232 serial. If you connected such a device to the microcontroller, then after you pair your PC with the dongle you will have a standard serial device on the PC you can point your control programs at.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, to do this you would have to modify the Uno32 board by cutting the traces between the microcontroller and the USB interface chip (nets &lt;code&gt;U1RX/SDI1/RF2&lt;/code&gt; and &lt;code&gt;U1TX/SDO1/RF3&lt;/code&gt; in &lt;a href=&quot;http://www.digilentinc.com/Data/Products/CHIPKIT-UNO32/ChipKIT%20Uno32_bysa_c_sch.pdf&quot; rel=&quot;nofollow&quot;&gt;this schematic&lt;/a&gt;, if it matches the model you have) and wiring in a serial connector, and probably including a RS232-to-3.3V-logic level converter. (Or maybe there are 3.3V-logic Bluetooth serial modules suitable for direct wiring in, which would save some parts.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I expect that a wireless connection which substituted the USB cable rather than bypassing USB would be more expensive and/or require more specialized driver software, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, I haven't actually done much research on this — this is just an idea off the top of my head that should be feasible.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2014-12-25T02:14:19.430" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2432" PostTypeId="1" CreationDate="2014-12-26T01:20:49.237" Score="4" ViewCount="196" Body="&lt;p&gt;I have heard that it is possible to connect certain flip-phones to external devices via their Micro USB port and, through the USB port, send the NMEA location Data from their internal GPS to an external device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am wondering if it would be possible to use a GPS and Micro USB equipped flip-phone in this way to receive the GPS NMEA location data for an APRS station.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastEditorUserId="76" LastEditDate="2019-03-13T01:45:56.443" LastActivityDate="2019-03-13T01:45:56.443" Title="Using a flip-phones GPS NMEA data for the GPS in an APRS station" Tags="&lt;aprs&gt;&lt;gnss&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2434" PostTypeId="1" AcceptedAnswerId="2441" CreationDate="2014-12-28T10:30:00.863" Score="7" ViewCount="3249" Body="&lt;p&gt;I've built a radio receiver and I'm wondering how the demodulation works here. I think it's done by T1 and T2 (I've used BC547 instead of BF494, they're quite similar), but I'd like to know more about it.&lt;img src=&quot;https://i.stack.imgur.com/ogbb4.jpg&quot; alt=&quot;small fm radio circuit schematic&quot;&gt;&#xA;Source: &lt;a href=&quot;http://www.electroschematics.com/5150/tiny-fm-radio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.electroschematics.com/5150/tiny-fm-radio/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="3002" LastEditorUserId="218" LastEditDate="2014-12-28T19:23:19.530" LastActivityDate="2017-09-04T03:40:55.087" Title="How is the FM-signal demodulated in my receiver?" Tags="&lt;receiver&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2435" PostTypeId="1" AcceptedAnswerId="2437" CreationDate="2014-12-29T03:44:24.597" Score="4" ViewCount="440" Body="&lt;p&gt;Full disclosure, I'm a little dyslexic.&#xA;Concepts that are easy to most people usually seem ambiguous to me. &#xA;I also have a had time expressing myself through writ so please&#xA;forgive me if this seems like an odd question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been reading my ARRL hand book and many items on the internet&#xA;in an attempt to form a good working understanding of antennas.&#xA;I think I may have finally grasped it but I want to check it against a human&#xA;who can give me and clear answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll post a hypothetical:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say I have a stationary dipole and my antenna analyzer gives me a reading&#xA;of 100 +j12 Ω at it's resonant frequency.&#xA;I want to match it to my 50Ω unbalanced feed line so I place both a&#xA;capacitor that gives -j12Ω at the resonant frequency, and a 1:2 balun at the&#xA;feed point.&lt;br&gt;&#xA;Now lets say I want to go off the resonant frequency, this will change the reactive component of the impedance and my conjugate -j12Ω will no longer perfectly match the antenna. But, will the 1:2 balun still correct for the &#xA;resistive portion of the impedance just as it did at resonance?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think what I'm trying to ask is, will the resistive impedance change with frequency as the reactive impedance does? That seems like such a simple question&#xA;but I have not been able to find a clear answer to it which leads me to believe It's a bad or meaningless question like &quot;whats the color of the number two&quot;.&#xA;I honestly can't tell.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;.&lt;/p&gt;&#xA;" OwnerUserId="3008" LastActivityDate="2014-12-29T14:52:52.207" Title="Resistive impedance with frequency" Tags="&lt;antenna&gt;&lt;impedance&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2436" PostTypeId="2" ParentId="2435" CreationDate="2014-12-29T07:35:48.053" Score="1" Body="&lt;p&gt;Yes, you are correct: both resistive (real) and reactive (imaginary) part of the antenna impedance change as function of frequency. However, near the resonance of the dipole the reactive part changes much more rapidly than the resistive part.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See also: &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow&quot;&gt;http://www.antenna-theory.com/antennas/dipole.php&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is slightly off-topic but might help to understand the phenomenom: Near the next resonance, where the length of the dipole is approximately one wavelength, the resistive, or real, part of the impedance is much larger but again the reactive part reaches zero at one frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the tips of the dipole the current is at its minimum (current cannot go outside the dipoles arms so it gradually goes to zero) and the voltage or electric field is at its maximum (all the charge is packed to the end). At the feeding point, $\lambda/2$ away from the tip, the current is at its minimum and the voltage at its maximum. High voltage and small current corresponds to high impedance, thus the real part of the impedance must be high.&lt;/p&gt;&#xA;" OwnerUserId="194" LastActivityDate="2014-12-29T07:35:48.053" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2437" PostTypeId="2" ParentId="2435" CreationDate="2014-12-29T14:52:52.207" Score="3" Body="&lt;p&gt;If you antenna were actually a &lt;em&gt;resistance&lt;/em&gt;, then the impedance would not change with frequency. Resistance is anything that obeys Ohm's law:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ V = I R $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A real example that you may encounter is a dummy load. These are just a $50\Omega$ resistor, which provides a $(50 + 0j)\Omega$ over a broad range of frequencies (ideally, all frequencies).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas are not just a simple resistance. Rather, they are a complex impedance. Antennas are complex to analyze, so let's first consider a simpler circuit, the &lt;a href=&quot;http://en.wikipedia.org/wiki/LC_circuit&quot; rel=&quot;nofollow noreferrer&quot;&gt;LC circuit&lt;/a&gt;. Here's one such circuit:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/7xBYG.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f7xBYG.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrical_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance&lt;/a&gt; of this circuit? Well, the impedance of a capacitor is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_C = -j\frac{1}{\omega C} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And an inductor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_L = j \omega L $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\omega$ is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Angular_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;angular frequency&lt;/a&gt;, which is just $\omega = 2\pi f$. It's just a different way of expressing frequency that doesn't require the equations to contain a $2\pi$ term all over the place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Series impedances add, so the impedance of this series circuit is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ -j\frac{1}{\omega 50\cdot 10^{-9}} + j \omega 10.3\cdot 10^{-9} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we pick some frequency, we can simplify this more. Let's try $f=10\:\mathrm{MHz}$, or equivalently $\omega=2\pi 10\:\mathrm{MHz} \approx 62831853$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;-j\frac{1}{62831853 \cdot 50\cdot 10^{-9}} + j 62831853 \cdot 10.3\cdot 10^{-9} \\&#xA;= -j0.3183 + j0.6472 \\&#xA;= (0+j0.3289) \Omega&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we try again at 7 MHz, we get a slightly different answer. I won't write out all the math, but the answer is $(0-j0.0017)\Omega$. In fact, if we pick just the right frequency, then the impedances of the capacitor and the inductor cancel, and the circuit looks like a dead short. But only at that one frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is what we are doing when we tune the antenna: by adjusting the length of the antenna or changing the operating frequency, we are trying to find the point where the reactive components (capacitance and inductance) of the antenna cancel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But wait, what antenna looks like a dead short? Any effective antenna will have another impedance in the circuit, the radiation resistance&lt;sup&gt;1&lt;/sup&gt;. If electrical power is the product of current and voltage, then we need to both move a current, and move it against some voltage, to do work. If we are radiating energy, then against what is the transmitter working? Radiation resistance is that thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation resistance looks like a resistor to the transmitter, but unlike a resistor it doesn't get hot because the energy is radiated away. Calculating the radiation resistance in general involves solving &lt;a href=&quot;http://en.wikipedia.org/wiki/Maxwell%27s_equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;Maxwell's equations&lt;/a&gt; for your antenna and all the space around it. That's hard, but we can find solutions for common antenna types. For example, &lt;a href=&quot;http://www.antenna-theory.com/antennas/shortdipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna-theory.com gives the radiation resistance of a short dipole&lt;/a&gt; as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ R_{rad} = 20\pi^2 \left(L\over\lambda\right)^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is for a &lt;em&gt;short&lt;/em&gt; dipole, which is one that is less than a tenth of a wavelength long, which allows us to make the simplifying assumption of constant current throughout the entire antenna. Usually we use half-wave dipoles which are not short so this simplification does not apply, and the equation is more complex&lt;sup&gt;2&lt;/sup&gt;. However, notice there is a wavelength ($\lambda$) term in the equation, which means radiation resistance is frequency dependent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, as you can see, every term that goes into calculating an antenna impedance is frequency dependent. Even though the real part of the complex impedance is sometimes called the &quot;resistive&quot; part, this means it looks like a resistance at that one frequency. It does not mean it is a resistance, which is frequency independent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: I suggest not reading the Wikipedia article on radiation resistance. It's horrible, and I just removed two really wrong statements from it.&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;2: Antenna modelling programs like EZNEC work by breaking the antenna into a bunch of short segments and analyzing each segment individually, which is why this is a useful model.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2014-12-29T14:52:52.207" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2438" PostTypeId="1" AcceptedAnswerId="2439" CreationDate="2014-12-29T21:42:26.650" Score="6" ViewCount="616" Body="&lt;p&gt;A strong (100 kW) local FM transmitter causes interference to or overloading of receivers in the VHF/UHF bands. It seems like a single, properly chosen, capacitor could make an effective passive high-pass filter. I would like the filter to pass 200 MHz and up effectively, while suppressing 108 MHz and below. I'm assuming that this doesn't require a particularly challenging filter slope. I envision using this in-line with a 50 Ω coax. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using a filter design app, I put in a cutoff frequency of 160 MHz, and an R of 50 Ω, and got a capacitance of 20 µF. So far, so good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question is: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Will this work? Is there an easier way? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;What type of capacitor is appropriate for this application?&lt;/strong&gt; Should it be a ceramic, mica or film type or what? I need it to be useable to frequencies up to around 600 MHz. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;With this question, I am thinking of over-the-air TV reception as well as amateur radio and scanner reception. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know specific FM traps are available, but those are band-stop filters. Shouldn't a high-pass filter be easier and have lower insertion loss as long as I don't care about anything below the cutoff frequency? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;BTW, I didn't see much in the way of commercial products to do this. I am looking for something competitive with a $5-10 Radio Shack FM trap.&lt;/p&gt;&#xA;" OwnerUserId="1497" LastEditorUserId="76" LastEditDate="2014-12-30T01:28:23.383" LastActivityDate="2014-12-31T05:06:19.160" Title="Choosing capacitor for high-pass filter with cutoff of about 160 MHz" Tags="&lt;equipment-design&gt;&lt;rfi&gt;&lt;filter&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2439" PostTypeId="2" ParentId="2438" CreationDate="2014-12-30T00:27:20.767" Score="3" Body="&lt;p&gt;While that would work somewhat, it won't work great. What you are describing, with a single resistor and capacitor, is a first-order filter. Such a filter has a &lt;a href=&quot;http://en.wikipedia.org/wiki/Roll-off#First_order_roll-off&quot; rel=&quot;nofollow noreferrer&quot;&gt;roll-off&lt;/a&gt; of approximately 6dB per octave. This means for each halving of the frequency, attenuation is increased by 6dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say you design your filter to have a a cut-off frequency of 200 MHz. The FM broadcast band ends at 108 MHz, approximately one octave below that. Consequently, you will get an attenuation of about 6 dB. That's not much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a common engineering problem that steeper filters are harder at higher frequencies. If we wanted to separate 8 MHz from 100 MHz, that's still a difference of 92 MHz as in your example, but we'd have approximately four octaves to make the transition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that you are looking for a simple solution, and you are experiencing problems from just one station, I would suggest using a &lt;a href=&quot;http://www.microwaves101.com/encyclopedias/quarter-wave-tricks&quot; rel=&quot;nofollow noreferrer&quot;&gt;quarter-wave stub&lt;/a&gt; of transmission line as a filter. Advantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;you can make it from coax or twin-lead, which you probably already have&lt;/li&gt;&#xA;&lt;li&gt;attenuation can be very good -- with a loss-less transmission line, attenuation is theoretically infinite&lt;/li&gt;&#xA;&lt;li&gt;it's easy to tune (just need a pair of wire cutters)&lt;/li&gt;&#xA;&lt;li&gt;it's easy to fabricate&lt;/li&gt;&#xA;&lt;li&gt;it will work at any frequency that can be reasonably handled by your transmission line&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Disadvantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;it will also notch all the odd harmonics, so if you tune the notch to be at 108 MHz, there will also be notches at 324 MHz (108*3), 540 MHz (108*5) and so on.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The theory of operation is a little magic but simple: if you are looking at something through a quarter wavelength of transmission line, you see the conjugate impedance of the thing at the end. For your purposes, what matters is that if at the end of the transmission line there is a short, then it looks open. If the end is open, then it looks like a short.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/SJU89.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fSJU89.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, it only looks like a short or an open at the frequency where the stub is a quarter-wavelength long or an odd harmonic thereof. To other frequencies, it looks like some other complex impedance, which means it will change the impedance of your antenna, but this is &lt;a href=&quot;https://ham.stackexchange.com/q/382/218&quot;&gt;probably not a big problem for a receive-only application&lt;/a&gt;. If it is a problem, you will need a more complex filter -- even your simple RC filter has this problem. Again, the merit of this approach is simplicity, not perfection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyhow, now you have either a short or an open which you can insert into your circuit. To make a notch filter, you have two options:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;put a short in parallel&lt;/li&gt;&#xA;&lt;li&gt;put an open in series&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It's easier to tune if you opt for a stub that's open at the end, because you can just cut it. So this is going to look like a short, so we want to put it in parallel, which will effectively short out the antenna for frequencies where the stub is a quarter wavelength:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Axpo1.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fAxpo1.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A further advantage of this approach is that the stub can be added with a T-adapter. You can also just strip the transmission line and solder it together. Don't forget to weatherproof the connections if its outside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just for completeness, you can also use a series stub, which effectively disconnects the antenna:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/HIn5U.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fHIn5U.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The two work identically, so choose whichever one is easier to fabricate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whichever you pick, fabrication is pretty easy. Calculate the wavelegnth of the problematic transmitter, then cut a piece of transmission line that is a quarter of this. Remember to lengthen the transmission line according to the velocity factor. For example, if the offending station is at 108 MHz, and the velocity factor is 66%:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;\lambda = c / 108\:\mathrm{MHz} = 2.78\:\mathrm m\\&#xA;2.78\:\mathrm m / 4 = 0.694 \:\mathrm m \\&#xA;0.694\:\mathrm m / 0.66 = 1.05\:\mathrm m&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning is critical, and it's easier to make it shorter than longer, so cut it a bit longer than this, then keep trimming off little bits until you get maximum attenuation of the problematic station.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2014-12-30T00:27:20.767" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2441" PostTypeId="2" ParentId="2434" CreationDate="2014-12-30T15:57:18.690" Score="8" Body="&lt;p&gt;Essentially, it is an FM to AM converter, followed by an AM detector, followed by an audio amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The heart of this circuit is C1 and L. Together, these make a &lt;a href=&quot;http://en.wikipedia.org/wiki/LC_circuit#Parallel_LC_circuit&quot; rel=&quot;noreferrer&quot;&gt;parallel LC circuit&lt;/a&gt;. At resonance, this looks like a very high (for ideal components, infinite) impedance. Away from resonance, the impedance decreases and becomes more inductive or capacitive.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NyzoD.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fNyzoD.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our circuit will mostly be operating at or very near resonance, so the reactive part of the impedance is negligible. Instead, we can think of the parallel LC circuit as a variable resistor, the resistance of which varies with frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might see where this is going: if we can design an amplifier and use this LC circuit to set the gain, then changes in frequency change the gain, and thus, the amplitude. Then we'd have an FM to AM converter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;T1 and T2 form that amplifier. Specifically, they are a &lt;a href=&quot;http://en.wikipedia.org/wiki/Regenerative_circuit&quot; rel=&quot;noreferrer&quot;&gt;regenerative circuit&lt;/a&gt;. Regenerative circuits use positive feedback to increase gain beyond what would be possible with a single active device. They are very much like oscillators. Like &lt;a href=&quot;http://en.wikipedia.org/wiki/Electronic_oscillator&quot; rel=&quot;noreferrer&quot;&gt;oscillators&lt;/a&gt;, they require feedback with a 360° (or equivalently, 0°) phase shift. Unlike an oscillator, we want the gain to be less than 1 (but very close). If it's more than 1, then we have an oscillator and we've actually made a transmitter.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/UNxnR.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fUNxnR.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's consider what the AC signal from the antenna does to this circuit. When the antenna voltage rises, T2 turns on more, lowering its collector voltage (that's an inversion, or a 180° phase shift). This in turn decreases the base current of T1, increasing T1's collector voltage (another 180°). Thus, these two transistors form a positive-feedback amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The gain depends on LC. Near resonance, LC is a very high impedance and gain is at a maximum. Away from resonance, LC is a lower impedance and the gain decreases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This forms an FM -&gt; AM converter: at resonance (tuned to the center frequency of the station) amplitude is at a maximum, and as the carrier deviates away from this center, the amplitude decreases. Other stations are far enough away from resonance that the gain is very low, and they have very little effect on the circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From here on out it works just like an AM radio. The output of the oscillator (taken off the base of T2) can only sink current and not source it: this provides the rectification. That rectification in combination with C2 and R1 forms an envelope detector. IC1 is just an audio amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And there you have it. A dead-simple, direct-conversion, regenerative FM receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2014-12-30T17:33:04.013" LastActivityDate="2014-12-30T17:33:04.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2442" PostTypeId="2" ParentId="2438" CreationDate="2014-12-31T05:06:19.160" Score="3" Body="&lt;p&gt;Mini-circuits is the place for filters and other RF gadgetry. See &#xA;&lt;a href=&quot;http://www.minicircuits.com/products/filters_coax_high.shtml&quot; rel=&quot;nofollow&quot;&gt;http://www.minicircuits.com/products/filters_coax_high.shtml&lt;/a&gt; for their high pasd catalogue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, the BHP-250+ BNC connectorised high pass filter. It has -40 dB at 100 MHz, -20 dB at 150 MHz and -3 dB at 205 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These little filters can only carry about 1 Watt, so would only be useful for a receiver, not a transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MC do also make an FM band filter which is a band stop device with very sharp edges.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The benefit of buying something built up is that it's performance will stay reasonably constant over temperature and time. You need a fairly high order filter to get many dB between 108 and 200 MHz, and these can be sensitive to component drift.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2014-12-31T05:06:19.160" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2443" PostTypeId="2" ParentId="2276" CreationDate="2014-12-31T05:42:07.290" Score="1" Body="&lt;p&gt;You need to keep the antenna discharged, or be sure to discharge it, before connecting it to the tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A problem I've experienced happens when there is any sudden static discharge into the antenna connector. This could be from plugging in a long wire or piece of coax which was charged up, or from some isolated, conductive object sparking over to the antenna wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difficult thing about this spark is that it is fairly high current and voltage, but also &lt;em&gt;very high frequency&lt;/em&gt;. The impulse may be only a few ns long, effectively a pulse of RF energy extending to 100 MHz. So it will be transmitted through the blocking capacitors, and &lt;em&gt;not shunted to ground by inductors or resistors&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is essential to prevent this from happening, with bleeder resistors, inductors and shorts, &lt;em&gt;before&lt;/em&gt; the voltage builds up in the first place. So it's about grounding the antenna and nearby metallic objects, not adding protection to the tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would also help to use a semiconductor or gas discharge clamping component. &lt;a href=&quot;http://www.dxengineering.com/parts/ppr-is-50ux-c0&quot; rel=&quot;nofollow&quot;&gt;Here&lt;/a&gt; is one that specifically addresses the problem, saying&#xA;&quot;... even &quot;floating&quot; antennas that are not DC grounded. With PolyPhaser DC Blocked protectors, any slow voltage build up from wind driven rain, snow or dust, will not get to the equipment. As the protector reaches threshold for turn-on in a dc blocked circuit, it will go into a momentary soft turn-on as the gas barely ionizes and bleeds the static charge to ground.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this to work the protector must be exposed directly to the antenna and its static voltage; a balun, tuner or switch might defeat it.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2014-12-31T16:48:43.390" LastActivityDate="2014-12-31T16:48:43.390" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2446" PostTypeId="1" AcceptedAnswerId="2457" CreationDate="2015-01-01T20:35:55.830" Score="5" ViewCount="192" Body="&lt;p&gt;I brought an rtl-sdr USB  stick to a foreign country.  I am listening with gqrx, and I am surprised to find audio (e.g. television or radio) up and down the spectrum, up to 600, 700 and 800 MHz ranges.  I haven't experienced this in the States.  I can tune up and down several MHz (between say 7 and 20 MHz) and come across the same and different signals at what seem like multiples (I don't have to fine-tune, just tune several MHz at a time.)  They are all WBFM signals  What might cause this?&lt;/p&gt;&#xA;" OwnerUserId="850" LastActivityDate="2015-01-03T21:24:29.073" Title="Images up and down the spectrum" Tags="&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2447" PostTypeId="1" CreationDate="2015-01-02T07:02:44.537" Score="1" ViewCount="49" Body="&lt;p&gt;Is it feasible to determine what sort of modulation is used for a given signal by looking at the spectrum / FFT?  Does software like this exist?&lt;/p&gt;&#xA;" OwnerUserId="850" LastActivityDate="2015-01-02T09:28:38.120" Title="Determining modulation by spectrum" Tags="&lt;modes&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2448" PostTypeId="2" ParentId="2447" CreationDate="2015-01-02T09:28:38.120" Score="1" Body="&lt;p&gt;You can definitely identify many of them by eye, have a look at:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.sigidwiki.com/wiki/Signal_Identification_Guide&quot; rel=&quot;nofollow&quot;&gt;http://www.sigidwiki.com/wiki/Signal_Identification_Guide&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for software that does it automatically, I'm not sure anything like that exists. If you find something, please let us know.&lt;/p&gt;&#xA;" OwnerUserId="135" LastActivityDate="2015-01-02T09:28:38.120" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2449" PostTypeId="1" CreationDate="2015-01-02T11:38:14.507" Score="10" ViewCount="739" Body="&lt;p&gt;I am interested in learning about digital modes using 2m and Linux.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a couple of older 2m rigs (HTX-212 and an old Yaesu) with no additional hardware, like a TNC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What current resources exist for hardware setup and software configuration for this type of operation?&lt;br&gt;&#xA;I am also willing to consider the use of a Sound Card interface, but everything I have found so far refers specifically to the SoundBlaster cards and Crystal cards of olde.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would software defined radio be a better option for what I am attempting to experiment with?&lt;/p&gt;&#xA;" OwnerUserId="3028" LastActivityDate="2015-01-02T13:33:44.047" Title="Getting Started with Digital Modes on VHF on Linux" Tags="&lt;digital-modes&gt;&lt;software-defined-radio&gt;&lt;vhf&gt;&lt;2m-band&gt;&lt;linux&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2450" PostTypeId="2" ParentId="2449" CreationDate="2015-01-02T11:46:36.697" Score="0" Body="&lt;p&gt;All you need is a way to hook your sound card up to your radio (both line in and out), that's pretty easy for most rigs. It's generally good practice to use an interface with isolation but many people (including myself) manage to get by without it. Apart from WSPR and APRS there isn't much digital going on on 2m though (not in my area at least). Have a look at XASTIR and FLDIGI.&lt;/p&gt;&#xA;" OwnerUserId="135" LastActivityDate="2015-01-02T11:46:36.697" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2451" PostTypeId="2" ParentId="2449" CreationDate="2015-01-02T13:33:44.047" Score="6" Body="&lt;p&gt;2m isn't a good band if you want to do anything digital. Digital modes just aren't very popular on 2m. I think the only digital activity you are likely to find is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;D-STAR&lt;/li&gt;&#xA;&lt;li&gt;APRS&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;D-STAR uses GMSK, but the data for voice transmitted on that channel relies on a proprietary codec called AMBE. Any software that can encode or decode it is almost surely illegal, especially if you didn't pay for it. You could purchase something like a &lt;a href=&quot;http://www.dvdongle.com/DV_Dongle/Home.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;DV Dongle&lt;/a&gt; which has an AMBE ASIC in it. You could also just buy an Icom radio. But that's not much of a learning experience, and probably not what you had in mind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;D-STAR has a data mode which isn't based on anything proprietary, but aside from a talk at Hamvention, I've never run across anyone actually using it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;APRS is easy to find, but it uses an ancient AFSK modulation. It's horribly slow and inefficient in terms of power and bandwidth for what it does. It might be fun to play with, but you won't learn much about good engineering or modern technology from it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w1hkj.com/Fldigi.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fldigi&lt;/a&gt; is great software for digital modes on Linux, but here's the real problem: nearly all 2m rigs are capable of only FM operation. They don't have a &lt;a href=&quot;https://ham.stackexchange.com/questions/1319/what-is-a-linear-rf-amplifier&quot;&gt;linear amplifier&lt;/a&gt;, which rules out a huge class of modulations, but also the &quot;data&quot; input goes through the FM modulator. For some digital modulations, it's possible to design an audio input which will go through an FM modulation and end up transmitting the right thing on the air, but most software isn't designed to work this way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sure, you can connect some PSK31 software into the audio input of an FM radio, and get it back at the audio output of some other FM radio and even send messages, but what you are sending over the air isn't PSK31, it's FM with PSK31 in it. All the nice things about PSK31, like narrow bandwidth, are lost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fldigi, as well as most other digital mode software, is designed to be connected to an SSB radio. This is because &lt;a href=&quot;https://ham.stackexchange.com/questions/2045/up-converted-audio-transmission&quot;&gt;SSB is basically a null modulation&lt;/a&gt;: all it does is take the audio input, and shift everything up to wherever the radio is tuned. You can modulate or demodulate anything through SSB because it doesn't change the signal except by shifting it in frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice: if you want to learn about digital modes, and you don't have an HF rig, get a cheap SDR kit. The cheapest one I know of is the &lt;a href=&quot;http://fivedash.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;SoftRock&lt;/a&gt;. You will have no difficulty finding digital activity, day or night, on 20m.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-01-02T13:33:44.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2452" PostTypeId="1" AcceptedAnswerId="2453" CreationDate="2015-01-02T14:38:25.853" Score="2" ViewCount="158" Body="&lt;p&gt;As a purely theoretical question, what would it be like if wireless computer networking equipment was redesigned and allowed to operate at some other band than the unlicensed ISM band which is presently used? Some other band means in this context a &quot;better&quot; band, as in some licensed band considered to be &quot;better&quot; than the ISM band. E.g. the cellular band used for cell phones, which are allowed to transmit at higher power levels. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not a question regarding the politics or cost involved in licensing these bands and it should be ignored completely for this question to try keep things more simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By wireless networking I mean the typical 802.11* variants, which of course would have to be redesigned at the physical layer to work with a different band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By &quot;what it would be like&quot; I mean:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A) What would the end result in difference in theoretical bandwidth be?&lt;/li&gt;&#xA;&lt;li&gt;B) How would it affect power savings in terms of better SNR?&lt;/li&gt;&#xA;&lt;li&gt;C) How is MIMO affected? Is MIMO more easy to implement and exploit on some radio bands than others?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For A) I'm assuming that using the Shannon-Hartley theorem would work:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$C = Blog_2(1 + \dfrac{S}{N})$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If only I knew what bandwidth $B$ to pick and what the electrical engineering considerations to take into account would be. I'm assuming that you could use a very wide arbitrary band just to improve your theoretical results, but it would be costly engineering wise? Just to answer a theoretical question like this, how would you even determine what frequency range would be &quot;realistic&quot; in this context? Would you simply have to pick some arbitrary range, which also renders the question itself meaningless? If this is the case, then simply assume that the cellular frequencies were suddenly available for use, or even all of the UHF band if that is easier to answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for the S/N ratio, I'm assuming that when moving away from the ISM band, it becomes more safe (without getting into the debate regarding possible harm from cell phones), and simply increasing the transmission power would also allow for higher bandwidth. However it would also cause more noise for everyone else?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;B) I'm assuming this is directly related to A, as some frequency ranges have different properties in terms of transmittance, absorption and reflectance? In addition there would probably be interference from other devices on some bands which are strictly speaking not intended as radio transmitters, e.g. microwave ovens for the ISM band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;C) For this, I don't know. I know MIMO is a big and essential part of the physical layer for modern WLANs, but I don't know how it relates to different frequency bands. Is part of the reason MIMO is used simply that the transmission power is so limited on ISM, and that the band has other limitations/issues to deal with?&lt;/p&gt;&#xA;" OwnerUserId="3029" LastActivityDate="2015-01-02T18:08:27.093" Title="ISM band bandwidth compared to other bands for theoretical WLAN use, performance?" Tags="&lt;theory&gt;&lt;wifi&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2453" PostTypeId="2" ParentId="2452" CreationDate="2015-01-02T17:25:28.623" Score="1" Body="&lt;p&gt;You don't need to ask this as a theoretical question, because it already exists. The &lt;a href=&quot;http://en.wikipedia.org/wiki/13-centimeter_band&quot; rel=&quot;nofollow&quot;&gt;13-centimeter band&lt;/a&gt; overlaps the 2.4 GHz ISM band used by Wi-Fi. A licensed amateur can operate Wi-Fi equipment on the standard channels at a higher power, or operate on channels outside of the ISM band (but still in the amateur band allocation) if the equipment supports it. Consumer equipment usually does not (without hardware modifications), but a lot of professional hardware does, as there are commercial licenses that grant RF privileges beyond the ISM limitations also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Plenty of people have done exactly this. See &lt;a href=&quot;http://www.broadband-hamnet.org/&quot; rel=&quot;nofollow&quot;&gt;HSMM&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for what effect this has, the Shannon-Hartley theorem is indeed the right tool to model the ideal behavior, which isn't far off from real behavior. Operating at a higher power increases the $S/N$ term (by increasing $S$), allowing a higher channel capacity to be sustained over a long distance, or being more able to overpower noise (be it natural or man-made).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moving outside of the ISM band also increases the $S/N$ term, but instead by reducing $N$, simply because there are so many unlicensed Wi-Fi APs, cordless phones, and microwave ovens operating in the ISM band. Moving out of the ISM band, you avoid a whole ton of man-made interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bandwidth ($B$) refers to the channel bandwidth, and this will be defined by the modulation. For example, Wi-Fi uses 20 MHz or 40 MHz channels depending on device configuration. PSK31 requires about 31 Hz, SSB about 4 kHz, and the FM used on amateur VHF about 15 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regulations permitting, you can make the bandwidth as large as you want. If you can maintain the same signal-to-noise ratio, then the Shannon-Hartley theorem says that you can have increased channel capacity. However, increasing the channel bandwidth also increases noise power. If you double the bandwidth, then there is twice as much noise power within that bandwidth. If you don't also double your transmit power, you are decreasing the signal-to-noise ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you make the bandwidth wide enough, you will need to significantly redesign the antenna, filters, and other components. There are a class of modulations that work in this mode. Check out &lt;a href=&quot;http://en.wikipedia.org/wiki/Ultra-wideband&quot; rel=&quot;nofollow&quot;&gt;ultra-wideband&lt;/a&gt; (UWB) and &lt;a href=&quot;http://en.wikipedia.org/wiki/Spread_spectrum&quot; rel=&quot;nofollow&quot;&gt;spread-spectrum&lt;/a&gt; (SS). You will also have to solve the problem of how multiple users can share the wide swatch of spectrum you are now monopolizing, and if you read about UWB and SS you will see they each have different techniques for accomplishing that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MIMO is a complex collection of techniques, and as such it's difficult to point to any one reason why it's used. It's certainly not the case that MIMO is useful only in power-limited ISM bands. As a counter-example, modern radar uses &lt;a href=&quot;http://en.wikipedia.org/wiki/Phased_array&quot; rel=&quot;nofollow&quot;&gt;phased arrays&lt;/a&gt; instead of mechanically steered antennas, and these are some of the highest power transmitters in the world that &lt;a href=&quot;http://en.wikipedia.org/wiki/Boeing_YAL-1&quot; rel=&quot;nofollow&quot;&gt;don't qualify as weapons&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The techniques in MIMO are also applicable to any frequency. Shifting wireless networking to any other frequency would only affect MIMO to the extent that it affects radio communication in general. For example, if frequency is high enough, &lt;a href=&quot;http://en.wikipedia.org/wiki/Radio_propagation#Absorption&quot; rel=&quot;nofollow&quot;&gt;Earth's atmosphere becomes quite absorbent&lt;/a&gt;, and radio communication becomes difficult.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-01-02T18:08:27.093" LastActivityDate="2015-01-02T18:08:27.093" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2454" PostTypeId="2" ParentId="1105" CreationDate="2015-01-03T06:02:34.340" Score="2" Body="&lt;p&gt;FYI, several years ago I emailed a person at the FCC about this question.  I forgot her name but she was the person that replaced Riley Hollinsworth. She replied and said clearly to me that she considered it illegal.  She did not say that the FCC considered it SS and officially declared it illegal, she simply said that the author of ROS said it was SS, and therfore she was taking him at his word, and therefor it is illegal. I think she is wrong,  but you will really have to convince me this mode is SO GOOD that the benefits of using it outweigh the risks.&lt;/p&gt;&#xA;" OwnerUserId="3031" LastEditorUserId="218" LastEditDate="2015-01-05T19:50:37.397" LastActivityDate="2015-01-05T19:50:37.397" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2455" PostTypeId="1" AcceptedAnswerId="2456" CreationDate="2015-01-03T15:17:35.287" Score="3" ViewCount="335" Body="&lt;p&gt;Take, for example, a &lt;a href=&quot;https://ham.stackexchange.com/questions/899/what-does-the-addition-of-a-shield-to-a-small-loop-accomplish&quot;&gt;shielded loop antenna&lt;/a&gt;. It is &lt;a href=&quot;https://ham.stackexchange.com/a/1878/218&quot;&gt;often&lt;/a&gt; &lt;a href=&quot;https://ham.stackexchange.com/a/2424/218&quot;&gt;claimed&lt;/a&gt; that the antenna is inside the shield, and the shield blocks electric fields from reaching the antenna, while allowing magnetic fields to pass through to the antenna. This in turn reduces noise in environments heavy in electrostatic noise, the argument goes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this physically possible? Can a shield block time-varying electric fields while allowing time-varying magnetic fields to pass unchanged?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2020-09-05T11:50:02.987" Title="Is it possible to make a shield that blocks time-varying electric fields, but not time-varying magnetic fields?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2456" PostTypeId="2" ParentId="2455" CreationDate="2015-01-03T15:17:35.287" Score="4" Body="&lt;p&gt;No, it's not possible. Anything that is good at blocking time-varying electric fields will also be good at blocking time-varying magnetic fields of a similar frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First let's consider a vertically polarized, radiated wave incident upon a conductive plane:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/A2Ws5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since this wave is vertically polarized, the electric field vector points alternatively up and down. Because it's a radiated wave, it's also accompanied by a magnetic wave, in phase, but horizontal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The varying electric field will pull the charge carriers in the conductive plane up and down, along with the field. Assuming an infinite, perfectly conductive plane, the electric field won't penetrate the plane at all, because the charges in the plane rearrange themselves to cancel the electric field. This is the principle behind a &lt;a href=&quot;http://en.wikipedia.org/wiki/Faraday_cage&quot; rel=&quot;nofollow noreferrer&quot;&gt;Faraday cage&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But wait...the charges in the plane are moving with the field. That's a current, right? And when there's a current in a conductor, there's an associated magnetic field, right? The current is vertical, and the magnetic field is concentric with the current, so it will be in the horizontal plane. So is the magnetic field associated with the electric field incident upon the plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you &lt;a href=&quot;http://en.wikipedia.org/wiki/Maxwell%27s_equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;do the math&lt;/a&gt;, as it turns out, these magnetic fields cancel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;OK, but what if it isn't a radiated wave, but just a magnetic wave incident upon the plane? Maybe there is a solenoid nearby, which we are driving with an alternating current. Will the plane block that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, it will. The time-varying magnetic field will induce &lt;a href=&quot;http://en.wikipedia.org/wiki/Eddy_current&quot; rel=&quot;nofollow noreferrer&quot;&gt;eddy currents&lt;/a&gt; in the plane which cancel the magnetic field. &lt;a href=&quot;http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction&quot; rel=&quot;nofollow noreferrer&quot;&gt;Faraday's law of induction&lt;/a&gt; explains these eddy currents. It is this very same effect that is responsible for &lt;a href=&quot;http://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin effect&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w8ji.com/skindepth.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI has a good experimental demonstration of this&lt;/a&gt;. He puts a connector in a copper sheet and drives it with a signal generator. He then probes the electric and magnetic fields at increasing distances on the front and then around the back of the sheet. For both the electric and magnetic fields, the field weakens with increasing distance, and by the time he gets around to the back of the sheet, directly behind the connector, neither the electric nor magnetic fields are measurable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems odd, because a sheet of copper has no particularly obvious magnetic properties, and classically we think of separate magnetic forces and electric forces. How can a copper sheet have any effect on the magnetic force? When Maxwell made his equations, he didn't know either: it was just experimentally found to be true.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The development of special relativity provided more insight. &lt;a href=&quot;https://www.youtube.com/watch?v=1TKSfAkWWN0&quot; rel=&quot;nofollow noreferrer&quot;&gt;The magnetic force is really just the consequence of special relativity and the electric force in a moving frame of reference&lt;/a&gt;. So you see, there really isn't a magnetic force. There's only an electric force, and special relativity. Knowing this, it is intuitively less surprising that a sheet of copper, which has obvious electrical properties, can have magnetic properties.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-03T15:17:35.287" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2457" PostTypeId="2" ParentId="2446" CreationDate="2015-01-03T21:24:29.073" Score="4" Body="&lt;p&gt;Sounds like the receiver is being overloaded by a strong station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those inexpensive RTL receivers work by feeding the RF into a quadrature mixer to downconvert the frequency, and then into a pair of analog to digital converters (ADCs). At that point the data are processed by computer software that does all the filtering and demodulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those ADCs have a limited range: 0 is only so small, and 0xFFFF (for a 16 bit ADC) is only so big. Any input outside of this range gets &lt;a href=&quot;http://en.wikipedia.org/wiki/Clipping_%28audio%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;clipped&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clipping is what we call it in the time domain, where it looks like someone clipped off the tops and bottoms of all the peaks with scissors. In the frequency domain, this generates a bunch of harmonic images. Here's a spectogram of a 40 Hz sine wave that has been clipped:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZU6q7.jpg&quot; alt=&quot;spectrogram of clipped 40 Hz sine wave.&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see here that the 40 Hz signal is repeated at each odd harmonic:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;120 Hz (40*3)&lt;/li&gt;&#xA;&lt;li&gt;200 Hz (40*5)&lt;/li&gt;&#xA;&lt;li&gt;280 Hz (40*7)&lt;/li&gt;&#xA;&lt;li&gt;etc...&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This is the same harmonic progression as a &lt;a href=&quot;http://en.wikipedia.org/wiki/Square_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;square wave&lt;/a&gt;. This makes sense: if you clip a sine wave enough, it becomes a square wave. The spectogram above has a logarithmic frequency scale. On a linear frequency scale, the harmonics look evenly spaced:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/kBLFJ.jpg&quot; alt=&quot;spectogram of square wave&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SDRs have particular difficulty with this problem because their input bandwidth is so large. A wider input bandwidth means more power is making its way to the ADC. When there's too much power, you get clipping. Your software may be tuned to a 15 kHz channel somewhere in the spectrum, but the filtering that selects that one channel happens &lt;em&gt;after&lt;/em&gt; the ADC. A much wider bandwidth (as wide as the sample rate of the ADCs) reaches the ADCs. Thus, even if the very strong station isn't the one you are listening to, it can still overload the ADC and cause clipping, which causes harmonic distortion all across the input bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can address this problem by attenuating the RF input until the distortion goes away. More sophisticated radios have automatic gain control (AGC) which does this automatically, but the RTL is built to be cheap, not sophisticated. You can then run into a problem where you've eliminated the distortion, but now weaker stations are attenuated so much that they are below the receiver's noise floor and are thus unreceivable. This is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Desensitization_%28telecommunications%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;desensitization&lt;/a&gt;. The range between the noise floor and clipping is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Dynamic_range&quot; rel=&quot;nofollow noreferrer&quot;&gt;dynamic range&lt;/a&gt;, and is sometimes specified as a figure of merit for receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A better solution is to use a higher resolution ADC. If you had a 16 bit ADC, you could only go up to 0xFFFF. With a 32 bit ADC, you can go up to 0xFFFFFFFF. That means the peak signal can be higher before you run into clipping. See &lt;a href=&quot;https://ham.stackexchange.com/q/607/218&quot;&gt;SDR sampling bandwidth - do the bits per sample matter?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-01-03T21:24:29.073" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2458" PostTypeId="1" AcceptedAnswerId="2464" CreationDate="2015-01-03T22:58:19.250" Score="6" ViewCount="190" Body="&lt;p&gt;I have just started playing with SDR so I downloaded the relevant &lt;a href=&quot;https://thersgb.org/services/bandplans/html/rsgb_band_plan_jan_2014-1.htm&quot; rel=&quot;noreferrer&quot;&gt;amateur band plan&lt;/a&gt; for my location, the UK.  Tuning around I found things like POCSAG/FLEX pagers as expected and amateur radio (e.g. FM repeaters) at frequencies matching the band plan.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However I also found some signals just above 145.8Mhz, which I noticed from the band plan is reserved in the UK:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;145.806-146.000, 12 kHz, All Modes - Satellite exclusive&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I am using an Ettus SDR and a &lt;a href=&quot;http://www.universal-radio.com/catalog/hamantht/4002.html&quot; rel=&quot;noreferrer&quot;&gt;Comet SMA703&lt;/a&gt; antenna, which is designed for 144/400/1200Mhz.  However, with this tiny antenna I was not expecting to receive anything from space, especially indoors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example of the signal is shown below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/PzRmI.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a few more similar signals just a little higher up:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JgFU6.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some seem to be a fixed tone, some sound like they might be morse code when using the CW-U mode in gqrx.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been looking for around 30 minutes and none have shifted in frequency or disappeared.  I had a look at a &lt;a href=&quot;http://www.ne.jp/asahi/hamradio/je9pel/satslist.htm&quot; rel=&quot;noreferrer&quot;&gt;satellite list&lt;/a&gt; and used &lt;a href=&quot;http://www.satsignal.eu/software/wxtrack.htm&quot; rel=&quot;noreferrer&quot;&gt;WXtrack&lt;/a&gt; to see what was overhead, but nothing seemed likely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anybody tell me what these signals are likely to be?&lt;/p&gt;&#xA;" OwnerUserId="1727" LastActivityDate="2015-01-21T21:08:24.940" Title="Identifying signals in the satellite exclusive band" Tags="&lt;satellites&gt;&lt;signal-identification&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2459" PostTypeId="1" AcceptedAnswerId="2461" CreationDate="2015-01-04T00:27:01.660" Score="8" ViewCount="499" Body="&lt;p&gt;I am using the &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/087259811X&quot; rel=&quot;nofollow&quot;&gt;ARRL General Class License Manual 7th Ed.&lt;/a&gt; which was published April 25, 2011.&#xA;However, I know that the National Conference of Volunteer Examiner Coordinators (NCVEC) recently released the &lt;a href=&quot;http://ncvec.org/page.php?id=364&quot; rel=&quot;nofollow&quot;&gt;2015 General Class question pool&lt;/a&gt;. Does this mean that the ARRL manual is obsolete and I will have to get a new edition?&lt;/p&gt;&#xA;" OwnerUserId="1246" LastEditorUserId="76" LastEditDate="2018-04-27T21:03:57.023" LastActivityDate="2018-04-27T21:03:57.023" Title="Am I studying obsolete information?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2460" PostTypeId="2" ParentId="2459" CreationDate="2015-01-04T00:44:57.397" Score="1" Body="&lt;p&gt;Broadly speaking, the rules don't change fast. The question pool revision just means that you will be asked a somewhat different set of questions on the same material. The material in the book that is about the rules, as opposed to being specifically test study material, should be largely up-to-date.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, perhaps someone with more information could answer with whether there have been any changes to the actual regulations that would affect the contents of the book.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-01-04T00:44:57.397" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2461" PostTypeId="2" ParentId="2459" CreationDate="2015-01-04T02:35:54.960" Score="11" Body="&lt;p&gt;The question pools are available online from NCVEC:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.ncvec.org/downloads/Final%20Element%203%20Pool.txt&quot;&gt;2011 pool&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.ncvec.org/downloads/2015-2019%20General%20Class%20Question%20Pool.txt&quot;&gt;2015 pool&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I downloaded these and ran them through &lt;a href=&quot;http://unixhelp.ed.ac.uk/CGI/man-cgi?diff&quot;&gt;&lt;code&gt;diff&lt;/code&gt;&lt;/a&gt;. These are the big changes I noticed:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Section G3E, which is about digital operating procedure, is significantly changed. There isn't anything especially new technology-wise there, but the question pool is quite different. Additionally, there are new questions related to digital modes peppered throughout other sections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Subelements G4 and G5 have many new or rewritten electrical engineering questions. These questions are largely about electrical engineering. The fundamentals of electricity haven't changed, but the question pool has. As long as you are studying the underlying knowledge, and not trying to memorize the answers, you should be fine here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beyond that, there's a lot of rewording and clarification and other insignificant stuff. There are some new questions here and there, but not a lot, and they all cover the same body of knowledge covered by other questions. As always, about 70% of them can be answered with common sense.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;G2B02 (B)&lt;br&gt;&#xA;  What is the first thing you should do if you are communicating with another amateur station and hear a station &#xA;  in distress break in?&lt;br&gt;&#xA;  A. Continue your communication because you were on the frequency first&lt;br&gt;&#xA;  B. Acknowledge the station in distress and determine what assistance may be needed&lt;br&gt;&#xA;  C. Change to a different frequency&lt;br&gt;&#xA;  D. Immediately cease all transmissions&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;For the most part, I'd think the old study guide should be fine. The new pool does not go into effect until July 1, 2015. I couldn't find any online practice tests (ARRL, eHam.net, QRZ, and dozens of others offer them for free) using the new 2015 pool, but I bet by July they will be updated. I'd suggest running through that several times before you take the real test, and if you run into any problems with the new questions, remember that you can always get the current question pool online.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-04T02:35:54.960" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2462" PostTypeId="2" ParentId="899" CreationDate="2015-01-04T14:08:36.530" Score="2" Body="&lt;p&gt;This is extensively and accurately covered in &lt;a href=&quot;http://www.w8ji.com/magnetic_receiving_loops.htm&quot; rel=&quot;nofollow&quot;&gt;a great page by W8JI&lt;/a&gt;. It starts:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;h2&gt;Small Receiving Loops&lt;/h2&gt;&#xA;  &#xA;  &lt;p&gt;Small loops are often referred to as &quot;magnetic radiators&quot;. Folklore claims a small &quot;shielded&quot; loop antenna behaves like an electrical sieve or filter, sorting &quot;good magnetic signals&quot; from &quot;bad electrical noise&quot;. &#xA;  Nothing is further from the truth! At relatively small distances a small magnetic loop is more sensitive to electric fields than a small electric field probe.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="218" LastEditDate="2015-01-04T15:30:35.287" LastActivityDate="2015-01-04T15:30:35.287" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2463" PostTypeId="2" ParentId="2458" CreationDate="2015-01-04T14:53:45.500" Score="2" Body="&lt;p&gt;LED and CFL lights are a known nuisance to hams. It could possibly be one or some equally non-EMC conscious electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ukqrm.org.uk/lighting.php&quot; rel=&quot;nofollow&quot;&gt;http://www.ukqrm.org.uk/lighting.php&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="3036" LastEditorUserId="1246" LastEditDate="2015-01-21T21:08:24.940" LastActivityDate="2015-01-21T21:08:24.940" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2464" PostTypeId="2" ParentId="2458" CreationDate="2015-01-04T15:46:15.530" Score="9" Body="&lt;p&gt;I'm guessing many those signals are just noise. A fixed tone carries no information, so there would be no reason for a satellite (or anything else) to transmit it intentionally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The noise could be from an oscillator in some nearby electronics, or even from within the receiver itself. The noise may not even be at the frequency it appears in the waterfall: nonlinearities and &lt;a href=&quot;http://en.wikipedia.org/wiki/Intermodulation&quot;&gt;intermodulation&lt;/a&gt; can make signals appear at frequencies where they actually are not. Sometimes you can identify these spurious signals by changing the LO frequency of your receiver and noticing how the signals move. For some, you may see them move by something other than the change in the LO. For example, if you tune the LO down by 100Hz, the signal may move by 300Hz.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-01-05T12:58:03.733" LastActivityDate="2015-01-05T12:58:03.733" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2465" PostTypeId="1" AcceptedAnswerId="2466" CreationDate="2015-01-04T22:47:12.123" Score="3" ViewCount="277" Body="&lt;p&gt;I heard that it is illegal to put IRLP linking onto a repeater on 2 meters in the USA.  I was wondering if this was actually the case.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-01-12T13:30:54.313" Title="Is it legal to put IRLP on a 2 meter repeater?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;2m-band&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2466" PostTypeId="2" ParentId="2465" CreationDate="2015-01-04T23:29:52.310" Score="6" Body="&lt;p&gt;The &lt;a href=&quot;http://www.arrl.org/voip-faq&quot; rel=&quot;nofollow&quot;&gt;ARRL has addressed this in detail&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;h2&gt;Is It Legal?&lt;/h2&gt;&#xA;  &#xA;  &lt;p&gt;By Brennan Price, N4QX and ARRL General Counsel Chris Imlay, W3KD&lt;/p&gt;&#xA;  &#xA;  &lt;h2&gt;What Part 97 regulations govern VoIP-assisted Amateur Radio?&lt;/h2&gt;&#xA;  &#xA;  &lt;p&gt;All of them or none of them, depending on whether you're asking about the &quot;VoIP-assisted&quot; or the &quot;Amateur Radio&quot; part of VoIP-assisted Amateur Radio. Follow this link for a PowerPoint presentation on VoIP by Mike Goldberg, K1LJN.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Many callers to the ARRL's Regulatory Information Branch over the last few years have focused on the novelty of the Internet when asking questions about the legal uses of certain systems. Such focus is misdirected. Part 97 does not regulate systems; it regulates stations. The Commission doesn't care what a ham has feeding his or her station; it cares that the station--not the Internet, but the station--is properly operated. And all the rules that apply to any Amateur Radio station apply to one that retransmits audio fed to it by VoIP.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The gist of it is this: it's not illegal. All the FCC cares about is your station, and what you transmit. If your transmissions come from the internet instead of a microphone, more power to you. Just be sure those transmissions comply with the regulations like everything else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It does not matter if the protocol you use on the internet is encrypted or not. Part 97 regulates the RF emissions from your station, not what you do on the internet.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-01-12T13:30:54.313" LastActivityDate="2015-01-12T13:30:54.313" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2467" PostTypeId="2" ParentId="2465" CreationDate="2015-01-05T00:12:12.823" Score="-1" Body="&lt;p&gt;While Part 97 regulates the station and what you transmit, there is still the &quot;no encryption or other privacy techniques may be used&quot; provision (HOW you transmit). As such, VoIP utilizing any encrypted data protocol would probably not be legal.&lt;/p&gt;&#xA;" OwnerUserId="3038" LastActivityDate="2015-01-05T00:12:12.823" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2468" PostTypeId="2" ParentId="946" CreationDate="2015-01-05T11:15:23.890" Score="2" Body="&lt;p&gt;Thinking back, the systems in a hamsat are very similar to a repeater system we had when I staffed a boy scout camp. Like Pete said, it saves you space because duplexers are huge and expensive. We had four business frequencies at our disposal, so we set up one VHF and one UHF in the repeater. It was a two-way system, so you could transmit on the VHF frequency and the repeater will broadcast at UHF, or you could transmit at UHF and the repeater will output VHF. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It was very simply one or two power supplies connected to standard base radios, which fed into each other with an audio cable and an auto-transmit circuit, something like VOX. We stored these radios in a small back room on a shelf. You walk into the repeater room expecting to see a big setup of wires and boxes everywhere, but it was actually just a small PSU box, two small stacked radio boxes, and a couple cables linking the two and the antennas. The whole thing couldn't have taken up more than one or two cubic feet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's very space-efficient and cost-efficient. You don't need any sort of computer, nor do you need a duplexer, nor are your radios terribly expensive. &lt;/p&gt;&#xA;" OwnerUserId="3040" LastActivityDate="2015-01-05T11:15:23.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2469" PostTypeId="1" AcceptedAnswerId="2470" CreationDate="2015-01-05T12:28:39.730" Score="6" ViewCount="2470" Body="&lt;p&gt;(I promise there will be a question in this wall of text. I'm just giving context.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been wanting to try my hand at building my own antenna system for the last few weeks and in doing research, a number of questions came up. In particular, matching transmitters, feed lines and antennas in order to create a fully balanced system. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.comportco.com/~w5alt/antennas/notes/ant-notes.php?pg=7&quot; rel=&quot;noreferrer&quot;&gt;This site, run by W5ALT&lt;/a&gt;, gives a great overview on why different systems need to be impedance matched in order to function properly, as well as consequences of improper impedance matching. I therefore understand why a balun would be used for coax feeding a balanced dipole, both for balance and impedance purposes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also went about researching different antennas for portable use. Stackexchange led me to the October 1984 QST article on a full-wave delta loop. One of these setups (see following image, part B) describes a 450-ohm ladderline going into a 100-ohm feed point on the loop. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NQDiW.jpg&quot; alt=&quot;W1FB (B) full-wave loop scheme&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.iw5edi.com/ham-radio/?full-wave-loop-antenna,164&quot; rel=&quot;noreferrer&quot;&gt;On this site&lt;/a&gt;, the author says to NOT use a balun between the 50- or 75-ohm coax feedline and the 100-ohm feed point: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Don't use a Balun on this Antenna! On a horizontally oriented loop you can feed a corner, center of a side or anywhere it is unimportant. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I also have a folded dipole fed directly by ladderline (Cobra Ultralite Sr.) that functions quite well (I busted through a pileup for a Portuguese contest; it can't be that bad). It is fed by 50-ohm coax from a tuner into a 1:4 balun to the ladderline. From various sources on the internet, the &lt;a href=&quot;http://www.radio-electronics.com/info/antennas/dipole/feed-impedance.php&quot; rel=&quot;noreferrer&quot;&gt;typical impedance of a resonant dipole is roughly 73 ohms&lt;/a&gt;. A folded dipole will &lt;a href=&quot;http://www.radio-electronics.com/info/antennas/dipole/folded_dipole.php&quot; rel=&quot;noreferrer&quot;&gt;increase this impedance to the square of the number of parallel elements&lt;/a&gt; (for the ultralite sr. with 3 parallel elements, I calculate 9 * 73 = 657 ohms impedance). The feedline could very well be 600-ohm ladderline (I am not sure; the line is not marked with impedance). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;So my question is this:&lt;/strong&gt; in particular, why does the W1FB full-wave loop design &lt;em&gt;not&lt;/em&gt; require some form of a transformer between the 450-ohm ladderline and the 100-ohm antenna? My research tells me it's obvious that having matched impedance would allow more efficient power transfer from the feedline to the antenna. Is it because ladderline is balanced? Is that kind of impedance mismatch allowable? Is it a rule that you don't need a balun for ladderline? Is it purely a choice by the designer? I'm familiar with the subject of electronics, but I'm certainly no electrical engineer, so the theory behind this just seems to contradict practical examples. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks for any and all help. I've been trying to find a reason for this for days and nothing seems logical to me.&lt;/p&gt;&#xA;" OwnerUserId="3040" LastEditorUserId="218" LastEditDate="2015-01-05T15:25:15.260" LastActivityDate="2015-01-06T05:59:46.227" Title="Impedance Matching Different Feedlines" Tags="&lt;impedance&gt;&lt;balun&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2470" PostTypeId="2" ParentId="2469" CreationDate="2015-01-05T16:15:58.737" Score="2" Body="&lt;p&gt;It doesn't make sense because people on the internet are wrong or misinformed, present conflicting information, or just plain don't know what they are talking about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance mismatches aren't the end of the world. An impedance mismatch does not, in itself, cause power loss. It causes power to be &lt;em&gt;reflected&lt;/em&gt;, at which point it will go in the other direction until it's either absorbed or encounters another impedance mismatch which reflects it back at the antenna. When it gets back to the antenna, some of that power is radiated, and the rest of it reflects back and forth again until its all radiated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, if you had a lossless transmission line, impedance mismatches wouldn't matter at all. Each parcel of power would just reflect back and forth until it's radiated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can't have lossless transmission line, but we can keep losses very low. One way is to buy good coax. Good coax is expensive. Another way is to use ladder line. For the cost, ladder line has lower loss than coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Interestingly, a piece of transmission line can be used as a transformer. If that transmission line is 1/4 wave long, it's called a &lt;a href=&quot;http://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer&quot; rel=&quot;nofollow noreferrer&quot;&gt;quarter-wave transformer&lt;/a&gt;, and it makes whatever's at the end of it look like the conjugate impedance. That's part of what's going on in some of these antennas, but there's a problem...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whenever you hear someone say &quot;don't use a balun&quot;, you should be thinking:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;they may not have a good understanding of RF engineering, and&lt;/li&gt;&#xA;&lt;li&gt;the feedline is actually part of the antenna&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole?rq=1&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt;. You absolutely can feed a dipole without a balun, but you have to understand that if you do it, the coax is as much of the antenna as the balun. This means anything you read about dipoles (like, their radiation pattern, feedpoint impedance, etc) does not apply. It doesn't necessarily mean it's a bad antenna, it's just some other kind of antenna which might be good or bad. Since the geometry of the feedline is different at each station, it doesn't mean anything. It just means you don't know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be especially dubious when you hear &quot;don't use a balun&quot; in combination with &quot;multi-band antenna&quot;. One way to make a multi-band antenna is to design the antenna such that there are a lot of common-mode currents on the feedline, thus making the feedline in effect a &lt;a href=&quot;http://www.w8ji.com/long_wire_antenna.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;long-wire antenna&lt;/a&gt;. The &quot;antenna&quot; is really just a distraction: the feedline does most of the radiating. There are &lt;a href=&quot;http://www.w8ji.com/e-h_antenna.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;quite a few antennas that dubiously work this way&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope that addresses your concerns enough. I can't really explain every question you have (that would be an entire book on antenna design), but regardless there are some good lessons to be learned here:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the internet can be wrong,&lt;/li&gt;&#xA;&lt;li&gt;especially when hams are writing about antennas,&lt;/li&gt;&#xA;&lt;li&gt;your intuition about things not making sense is well-founded, and&lt;/li&gt;&#xA;&lt;li&gt;the best way to learn how things really work involves a good deal of skepticism.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-01-06T00:35:44.727" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="2471" PostTypeId="2" ParentId="2469" CreationDate="2015-01-05T17:47:48.980" Score="1" Body="&lt;p&gt;Your question: &quot;...in particular, why does the W1FB full-wave loop design not require some form of a transformer between the 450-ohm ladderline and the 100-ohm antenna?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Actually, a lot of horizontal delta loops and square loops are operated without an impedance transformation.  This is because a single impedance transformation is usually not the best solution when an antenna is used for multiple bands and often delta and square loops are considered multi-band antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used a 80-meter full wave delta loop for years operating on 80 through 10 meters.  When I say 80-meter full wave delta loop I mean that I had a full wavelength of wire up in the air as the delta loop.  I fed it (one foot from a corner as it was physically better to do that way) using 450-ohm window-style ladder line.  At the point that the transmission line was brought into my &quot;shack&quot; I used a 1:1 Balun to go from to coax.  My coax run using LMR400 (low loss) was about 10 feet to my antenna tuner.  Such an antenna tuner is a necessity with a multi-band antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This was an excellent wire antenna and it performs very well.  At higher frequencies (than 80) it has lobes of higher gain on it (nulls too of course) so if positioned correctly you can have a nice high-gain antenna.  My models using NEC4 showed lobes of gain up to 9:1 over the isotropic ground free Dipole radiator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a lot of debate on the balun transformer whether it should be 1:1, 4:1, 6:1, and so on.  The reason I chose 1:1 is that it leaves the matching job to my antenna tuner rather than trying to solve it in the balun transformer itself which would only be good for a single band anyway (if at all).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would still be using the delta loop if it were not for the fact that I had to cut down one of the 90 foot tall cedar trees that was used as one of the anchor points.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2015-01-05T18:37:27.763" LastActivityDate="2015-01-05T18:37:27.763" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2472" PostTypeId="2" ParentId="2469" CreationDate="2015-01-05T21:56:48.427" Score="0" Body="&lt;p&gt;Agree 110% that a balun is required, otherwise you have half a loop, and half a strange monopole, with lots of current on the cable, in the shack etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Balun goes where you change from Balanced to Unbalanced, and it can be a choke, not a transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The choice 70' of 450 ohm line is odd. The open wire line is great, low loss and cheap, but 70' is exactly a quarter wave in 80m, so it'll transform the supposed 100 ohms into maybe 1600 ohms. Too high for the 4:1 balun. Rather use an even multiple of 70', so the impedance has returned to something near 100 ohms. Of course if it's a multi band antenna, it's much more complicated and needs hours of simulation.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-01-06T05:59:46.227" LastActivityDate="2015-01-06T05:59:46.227" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="2473" PostTypeId="2" ParentId="2459" CreationDate="2015-01-06T16:25:10.697" Score="2" Body="&lt;p&gt;The 2011 pool is valid and will be used for tests given through June 30, 2015. On July 1, 2015, the new pool goes into effect for the next four years. If you plan to take the test before July 1, use the current, 2011, test pool.&lt;/p&gt;&#xA;" OwnerUserId="3048" LastActivityDate="2015-01-06T16:25:10.697" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2475" PostTypeId="1" AcceptedAnswerId="2479" CreationDate="2015-01-06T16:49:02.310" Score="10" ViewCount="1607" Body="&lt;p&gt;Sometimes I see &lt;a href=&quot;http://en.wikipedia.org/wiki/Dynamic_range&quot; rel=&quot;noreferrer&quot;&gt;dynamic range&lt;/a&gt; mentioned as a figure of merit for an SDR. For example, I know that the &lt;a href=&quot;https://ham.stackexchange.com/q/607/218&quot;&gt;bits per sample&lt;/a&gt; used by the analog to digital converter can affect the dynamic range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why do I care about dynamic range? What happens when I don't have enough of it? Can I have too much of it? Does dynamic range have special significance or importance for an SDR compared to a traditional analog receiver?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2017-11-16T04:57:28.567" LastActivityDate="2017-11-16T04:57:28.567" Title="Why is dynamic range relevant for an SDR?" Tags="&lt;software-defined-radio&gt;&lt;equipment-design&gt;&lt;dynamic-range&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2476" PostTypeId="2" ParentId="2421" CreationDate="2015-01-06T16:57:23.867" Score="0" Body="&lt;p&gt;I'd suggest a good 1/2 wave antenna. You lose a bit of gain relative to a 5/8, but you'll have a good bit more than a 1/4. Also, 1/2s don't need a groundplane, while 1/4s do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you get one with traps in it (most do) it will work nicely on 70cm in addition to 2m. At ~1m long, you shouldn't have any trouble clearing traffic lights, wires, and even most parking structures. You also shouldn't have any trouble with a larger single-mag mount. I used to have my 5/8 on a single-mag on the trunk of my Camry and it could handle 70mph road speeds plus wind with no issues.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BTW, A 5/8 is just a 1/2 with that extra 1/8 added to intentionally shape the beam closer to the horizon as most people don't usually care to hit stations that much higher in elevation.&lt;/p&gt;&#xA;" OwnerUserId="619" LastActivityDate="2015-01-06T16:57:23.867" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2477" PostTypeId="1" AcceptedAnswerId="2480" CreationDate="2015-01-06T17:02:45.017" Score="12" ViewCount="9903" Body="&lt;p&gt;I'd like to try my hand at building a few antennas for VHF/UHF use.  I'm going to be going approximately from established designs, but obviously the final result will require some tuning.  I don't currently own either an SWR meter or antenna analyzer.  Is an SWR meter good enough for what I want to do, or will an antenna analyzer be necessary for this?  What are the benefits of an antenna analyzer in such situations?&lt;/p&gt;&#xA;" OwnerUserId="1343" LastEditorUserId="76" LastEditDate="2017-05-05T20:36:37.347" LastActivityDate="2020-08-28T03:18:49.567" Title="Is an antenna analyzer necessary for building antennas?" Tags="&lt;antenna-construction&gt;&lt;swr-meter&gt;&lt;antenna-analyzer&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="2478" PostTypeId="2" ParentId="2477" CreationDate="2015-01-06T18:00:45.080" Score="3" Body="&lt;p&gt;I couldn't live without my two antenna analyzers -- I may even get a VNA (vector network analyzer) although that is not necessary for simple antenna analysis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I own both the MFJ 259B and the Autek Research RX Vector Analyst VA1.  Although both do roughly the same thing, they have a few different features and I will touch on a few of those.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides digital readout, the MFJ 259B also has an analog SWR meter which greatly helps in finding resonant spots on an antenna using a frequency sweep.  You can watch if you are getting close or drifting away much easier than with digital readout.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can measure capacitance and inductance with both but the MFJ259B does not give you the sign of the reactance.  That is, negative for capacitance and positive for inductance.  You can determine the sign merely by doing a small shift in frequency and seeing which direction the reactance swings (lower for capacitance if frequency shifts upward for example).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Autek VA1 though includes the arithmetic sign of reactance so it is just slightly easier if you want a capacitance versus inductance readout.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, whether you are building antennas for resonance or cutting transmission line to be a transformer, the use of either of these two analyzers makes it gut simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Postscript:  I forgot to mention whether an SWR meter is any good?  Well, it can tell you when you are really bad but it does not really help enough in my opinion.  After all, a 50-ohm resistant dummy load gives an SWR of 1:1 but that does not say it is a good antenna.  Also, by knowing the R and X values of the reactance, you are able to determine where problems might lie with an antenna.  Remember that resonance is where it is purely resistive so $X=0$ or close to zero. &lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-01-06T18:00:45.080" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="2479" PostTypeId="2" ParentId="2475" CreationDate="2015-01-06T19:42:11.090" Score="9" Body="&lt;h3&gt;Signal strength and dynamic range&lt;/h3&gt;&#xA;&lt;p&gt;Generally speaking, dynamic range is the ratio between the strongest and weakest signal that can be received. In a digital signal, the dynamic range is determined by the number of bits per sample: the strongest signal is one which uses the full range of the sample values, and the weakest signal is one which uses only two adjacent values (one bit change).&lt;/p&gt;&#xA;&lt;p&gt;In a software-defined radio, the &lt;em&gt;analog&lt;/em&gt; signal level fed into the analog-to-digital converter must be adjusted (either manually or by an AGC) to make best use of the available dynamic range:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If the analog signal is too strong, then the logically corresponding digital values are not representable in the numeric range of the samples, and the ADC will substitute the maximum or minimum possible output; this is known as &lt;strong&gt;clipping&lt;/strong&gt;, which from a signal processing perspective is an extreme form of nonlinearity.&lt;/p&gt;&#xA;&lt;p&gt;If you have clipping, it can be observed as the appearance of spurious signals which are copies of actual signals in the received band at different frequencies.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If the analog signal is too weak, then its presence will not manage to make even one bit of difference in the digital output. More practically, well before the one-bit point you will be losing information due to the digital sample values being too coarse-grained to accurately represent the signal. This can be thought of as a source of noise, called &lt;strong&gt;quantization noise&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/yc4Xn.png&quot; alt=&quot;&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;The above image shows a sampled (50 samples) and quantized (5 bits) sine wave with different amplitudes, showing each of the above effects. Note in particular how even the relatively nice-looking sine on the left has slightly irregular points (because the sine function's real-number values get rounded to the closest representable value): this is an example of quantization noise.&lt;/p&gt;&#xA;&lt;h3&gt;Why dynamic range matters for SDRs&lt;/h3&gt;&#xA;&lt;p&gt;Given the above, it might sound like you can have an AGC that keeps the input signal at just the right level, and not need very much dynamic range.&lt;/p&gt;&#xA;&lt;p&gt;This would be true, except that in a software-defined radio of the kind we're interested in, &lt;strong&gt;the signal into the ADC is much wider bandwidth than the individual signals we want to demodulate!&lt;/strong&gt; This additional bandwidth is what allows you to get the “waterfall” or “panadapter” display characteristic of SDRs (because you're actually digitizing a wide band of RF), but it means that the analog signal coming into our ADC contains lots of RF power which is not any one signal we want to demodulate — it includes a large amount of noise, and possibly many intentional signals, some of which may be very strong compared to the desired signal.&lt;/p&gt;&#xA;&lt;p&gt;The best analog gain setting is determined by the &lt;em&gt;total RF power&lt;/em&gt; coming into the ADC (from the tuner and analog filter, if present). This fixes the “strong” end of the scale of possible digital signal levels, leaving the “weak” end determined by dynamic range. Therefore, the more dynamic range we have, the less quantization noise is present in narrow-band signals (which are more or less weak compared to the overall signal), allowing them to be received more clearly.&lt;/p&gt;&#xA;&lt;p&gt;You can also improve reception with the same dynamic range by using a narrower analog filter, thus reducing the input power and allowing more gain to be applied to it without clipping — if your SDR hardware has a usefully adjustable filter.&lt;/p&gt;&#xA;&lt;p&gt;The extreme case of using a narrower filter is using one just as wide as a single signal you want to receive. The disadvantage is you don't have any spectrum view while you're doing that — you can only receive that one signal.&lt;/p&gt;&#xA;&lt;h3&gt;Direct answers&lt;/h3&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Why do I care about dynamic range? What happens when I don't have enough of it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Signals you want to receive disappear into the (quantization) noise floor.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Can I have too much of it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;As a user of a SDR, no, except as it affects the price tag. As a designer, additional sample bits:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;require additional computation (significant for embedded systems; probably moot if you're using a general-purpose machine for your DSP since the samples will likely be expanded into 32-bit integers or floats for computation),&lt;/li&gt;&#xA;&lt;li&gt;require a higher-performance (expensive) ADC, and&lt;/li&gt;&#xA;&lt;li&gt;may be worthless due to noise received by the antenna (if the electromagnetic noise floor is higher than the quantization noise floor when the gain is set optimally) or noise getting into the system between the gain-control stage and the ADC (the low bits are always noise).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Does dynamic range have special significance or importance for an SDR compared to a traditional analog receiver?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Strictly speaking, no — it is not being software-defined that makes dynamic range matter, but the wide bandwidth. However, if by SDR you mean something with a waterfall display, then yes, it does (as described above).&lt;/p&gt;&#xA;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2015-05-07T03:59:12.750" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2480" PostTypeId="2" ParentId="2477" CreationDate="2015-01-06T20:45:12.067" Score="10" Body="&lt;p&gt;I've not personally built antennas from scratch, but I appreciate &lt;a href=&quot;http://www.rigexpert.com/index?s=aa1000&quot; rel=&quot;noreferrer&quot;&gt;my antenna analyzer&lt;/a&gt; just for being a good instrument — making the invisible aspects of my antenna system visible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Compared to using a SWR meter for the purpose, an antenna analyzer:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Displays more information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A SWR meter still gives you &lt;em&gt;enough&lt;/em&gt; information, in the sense that you can try things until they move towards 1:1 SWR, but it's a one-dimensional measurement: if you tried to adjust an antenna using it you're doing a “hotter colder” search, trying things until it improves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna analyzer will tell you resistance and reactance independently, which allows you to more directly understand the problem. For example, you can have an exactly resonant antenna, which simply has the wrong magnitude of impedance (you need an impedance transformer). On a SWR meter this can show up as the SWR having a minimum point but remaining well above 1:1. (That minimum point &lt;a href=&quot;//ham.stackexchange.com/questions/2482/whats-the-difference-between-minimum-swr-and-resonance&quot;&gt;is not necessarily the resonant point&lt;/a&gt;.) On an antenna analyzer, you can immediately see that you've got R = 34 Ω instead of 50 Ω (or whatever), and build that correction into your balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;High-end antenna analyzers can also give you measurements at multiple frequencies — either as a graph or individual readings at selected frequencies. A graph allows you to easily obtain measurements in the opposite direction — not “how suitable is this antenna at this frequency?”, but “what frequencies is this antenna good for?”, as well as other RF-electronics measurements like finding the resonant frequency of a circuit or the upper frequency limit of a ferrite choke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ALlnX.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the above picture: my RigExpert AA-600 antenna analyzer displaying an impedance graph (it can also compute SWR from the same data). You can see directly from this graph that whatever it's connected to is resonant at the frequency at the middle of the graph (reactance crosses zero) and at that point has a resistance (and also magnitude of impedance) of 100 Ω.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Lets you use less transmitted power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To measure the impedance of your antenna, no matter what instrument you use, you need a signal generator — a transmitter — somewhere. An antenna analyzer has a low-power signal generator built in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use a SWR meter, you have to use a separate one; if you use your regular transceiver for the purpose, you're limited to its lowest power setting, which might be a few watts! Even if you have a lower power transmitter, it might not be sufficient to show a reading on the SWR meter, which has scales for much higher power levels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By comparison, my antenna analyzer's output falls within FCC Part 15 emissions limits, so I'm much less likely to interfere with anyone else (and don't have to stop to identify myself, either).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-12-12T21:10:01.483" LastActivityDate="2015-12-12T21:10:01.483" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2481" PostTypeId="2" ParentId="2477" CreationDate="2015-01-06T21:51:25.373" Score="4" Body="&lt;p&gt;An antenna analyzer is not necessary. Sure, it's handy. A VNA is even handier. For this equipment you're looking at something like $50 USD for a NanoVNA, up to many thousands of dollars for a lab grade VNA. If you just want to know if you need to trim a bit off a wire dipole or not, and simply get on the air without toasting your transmitter, none of these things are &lt;em&gt;necessary&lt;/em&gt;. While there's a certain joy in being able to measure and quantify exactly how things are operating and make it all &amp;quot;just so&amp;quot;, radios are in fact quite forgiving. An AC current &lt;em&gt;wants&lt;/em&gt; to radiate. In fact, there's an &lt;a href=&quot;http://en.wikipedia.org/wiki/Electromagnetic_compatibility&quot; rel=&quot;nofollow noreferrer&quot;&gt;entire industry around making things &lt;em&gt;not&lt;/em&gt; radiate&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;If you wonder how to make an antenna without these tools, you need only look to the recent past. It wasn't that long ago that we did not have solid state electronics, and test equipment like we have today was either very expensive, or nonexistent. Most of the methods used in those days to measure antenna impedance involve putting an antenna in some kind of &lt;a href=&quot;http://en.wikipedia.org/wiki/Bridge_circuit&quot; rel=&quot;nofollow noreferrer&quot;&gt;bridge&lt;/a&gt; and comparing it against a known impedance.&lt;/p&gt;&#xA;&lt;p&gt;Here's one example of a dead-simple approach:&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/zmjIo.gif&quot; alt=&quot;&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;You can read &lt;a href=&quot;https://ham.stackexchange.com/questions/2399/adapting-an-antenna-coupler/2404#2404&quot;&gt;the full question&lt;/a&gt; for an explanation of how it works. It's not particularly sophisticated, but if you just need to trim your antenna until it's not a horrible match to 50 ohms, it will work just fine. If you have an SWR meter, you can also just adjust for minimum SWR and accomplish the same thing. Note you don't need the matching section (L1, L2, and C3) if you just want to measure impedance.&lt;/p&gt;&#xA;&lt;p&gt;If you want to take the sophistication up a notch, you can use a &lt;a href=&quot;http://en.wikipedia.org/wiki/Grid_dip_oscillator&quot; rel=&quot;nofollow noreferrer&quot;&gt;grid dip meter&lt;/a&gt;. You can find them at any hamfest, or used on eBay or whatnot for some tens of dollars. Just a few decades ago, these were state of the art antenna test equipment. The physical laws that govern their operation have not changed, and they work as just well today.&lt;/p&gt;&#xA;&lt;p&gt;As another step up, you can consider any number of &lt;a href=&quot;http://www.ebay.com/bhp/impedance-bridge&quot; rel=&quot;nofollow noreferrer&quot;&gt;used impedance bridges&lt;/a&gt; which are similar in concept to the schematic above, but have adjustable and calibrated inductors and capacitors so you can measure the complex impedance of the antenna. This is in effect what an antenna analyzer does, the only difference being that the antenna analyzer will automatically adjust the knobs for you, and maybe measure impedance at a range of frequencies at a push of button.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-08-28T03:18:49.567" LastActivityDate="2020-08-28T03:18:49.567" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="2482" PostTypeId="1" AcceptedAnswerId="2483" CreationDate="2015-01-06T21:59:16.897" Score="9" ViewCount="4719" Body="&lt;p&gt;Is the point of minimum SWR equivalent to resonance? Exactly what does resonance mean, anyway?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2017-05-06T23:05:06.397" LastActivityDate="2017-05-06T23:05:06.397" Title="What's the difference between &quot;minimum SWR&quot; and &quot;resonance&quot;?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;impedance&gt;&lt;jargon&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="2483" PostTypeId="2" ParentId="2482" CreationDate="2015-01-07T01:34:24.783" Score="4" Body="&lt;p&gt;Good questions.  But, I think another question to add is:  What is more important, SWR or resonance?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that this is the &quot;Amateur Radio&quot; forum, I think answers that are most meaningful to amateur radio operators are more justified in this discussion.  The reason I say this is that resonance and SWR as testified by several exchanges and questions are debatable things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I operate regularly on 80, 40, 30, 20, 15, 12, and 10 meter bands.  I sometimes visit 17 meters once in a great while.  But, given all those bands and the frequencies I operate NONE of my antennas are resonant.  That is because true resonance is at a single frequency for a given antenna (e.g. Dipole).  But, if the SWR is within reasonable limits or it handled by an antenna tuner (aka match coupler) then the antennas are very effective even when not resonant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several definitions of resonance.  In general, if the antenna impedance at a given frequency is purely resistive, with zero reactance (or, near zero) then that antenna can be considered resonant at that frequency.  This resistance is not usually the same as the typical 50-ohm output of a transmitter.  In fact, a perfect dipole (with no ground effects) has a radiation resistance of approximately 71 ohms.  Thus, this perfect resonant antenna does not have a SWR of 1:1 because the resistance is not 50 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, SWR is important too for two different reasons.  First, to protect the PA circuits of a solid state transmitter (or, amplifier).  Reflected voltage can destroy the output transistors so low SWR helps protect the solid-state circuitry.  Most modern transmitters (transceivers) have protection circuits to roll back power to safe levels when the SWR is too high.  My own Elecraft K3 starts this when faced by an SWR at a little over 2:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second reason SWR is important is to limit the losses in transmission line between the transmitter/transceiver/receiver and the antenna.  The higher SWR causes the losses to increase  There are calculators available on-line (and the ARRL TransmissionLine application) to compute the losses given the input and load SWR or actual $R+jX$ impedance.  I have written my own in Mathematica.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition, SWR is often an indicator of problems in an antenna system.  Monitoring SWR is something that should be done by ham operators as it will show problems.  One afternoon I was preparing for a CW Traffic Net schedule and did a quick key down merely to look at my SWR.  It spiked with the alert beep sounding plus red LED lights blinking.  I looked out into the back yard and saw that my 80 meter dipole was laying on the ground.  One of my anchor point ties had failed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Minimum SWR (as asked in the question) has nothing to do with resonance (by itself).  If I tune up on the 160 meter band using my 80 meter dipole I can find a minimum SWR and that minimum is on the order of 250:1 or so.  My tuner is good but it can't handle that wide of an SWR.  But, a resonant antenna should have a low SWR and likely at the likely minimum at the resonant frequency.  But, as I mentioned earlier for the dipole, this low SWR will not usually be 1:1 as the actual radiation resistance for the antenna is almost always not the same as the 50 ohms expected by the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, when I am building antennas, managing and designing for minimum SWR across the frequencies I want to operate is the most important thing.  Minimum SWR is hopefully under 3:1 for most of a band but even my 80 meter dipole has a higher SWR at the high end of the band (3.9 MHz) with an SWR about 5:1 (my tuner matches this with no problems but I do have to pay for that higher SWR in the transmission loss to the antenna which is the reason I use LMR400 low loss coaxial cable.  One of my Mathematica programs will do a full 3 to 30 MHz sweep (all frequencies in 20 KHz steps) of my antennas I am designing (in concert with solutions produced by NEC4) and I compute the SWR, smooth interpolate it, and then plot the results.  Visually I can see all the low SWR (under 3:1) spots for a given length of wire of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2015-01-09T15:11:11.620" LastActivityDate="2015-01-09T15:11:11.620" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="2484" PostTypeId="2" ParentId="2482" CreationDate="2015-01-07T01:58:51.030" Score="3" Body="&lt;p&gt;&lt;em&gt;Resonance&lt;/em&gt; is at a particular frequency where reactance is zero, and thus current and voltage are in phase. To illustrate, here's a plot of the feedpoint resistance, (R) reactance (X), and &lt;a href=&quot;https://en.wikipedia.org/wiki/Complex_number#Polar_form&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance magnitude&lt;/a&gt; (|Z|)  of my backyard trap vertical on 30 meters: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/m4hLV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/m4hLV.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how at resonance the resistance is not 50Ω, so the SWR here is something higher than 1:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's another resonance around 10.62 MHz, but here the resistance is off the chart. As we'll see in the next chart, although the antenna is resonant here, the SWR is very bad.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are the same data, but plotted as SWR:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kFihZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kFihZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The minimum of the SWR dip is not quite at the same frequency as resonance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(You can also see that I need to go out there and tune this antenna!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;a href=&quot;http://en.wikipedia.org/wiki/Smith_chart&quot; rel=&quot;nofollow noreferrer&quot;&gt;Smith chart&lt;/a&gt; is a nice way to visualize both impedance and SWR on the same chart. Here are the same data again:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Kc8k9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Kc8k9.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The horizontal line in the middle represents all the resonant points, that is, all the points where reactance is zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The very center of the chart represents 50+0jΩ, and a 1:1 SWR. SWR is measured by the distance from the center, and that bullseye in the middle represents an SWR of 1.6 or better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And you can see the curve gets &lt;em&gt;a little bit&lt;/em&gt; closer to the center just a bit away from resonance. The difference is small enough to barely matter in practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also see the curve continue around until it hits the middle line again: that's the other resonance with a bad SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's possible to have an antenna which dips into that 1:6 SWR circle from above or below, and never crosses the 0 reactance line at all. With self-resonant dipoles and verticals the resonant impedance is a decent match and will be near the center, but with other kinds of antennas there might be a matching network involved which creates a very different trajectory through the Smith chart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The addition of a feedline also changes the picture. As the feedline length varies, the impedance at any one frequency rotates about the center of the Smith chart. The SWR of that point remains constant, but for each half-wavelength of feedline added, the point makes a full rotation. So it's possible with the right length feedline to make &lt;em&gt;any&lt;/em&gt; impedance resonant. It's also possible to take any resonant impedance which is not a perfect match and make it non-resonant.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-09-30T14:59:41.717" LastActivityDate="2016-09-30T14:59:41.717" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3478" PostTypeId="1" CreationDate="2015-01-07T17:08:50.323" Score="6" ViewCount="402" Body="&lt;p&gt;I noticed something fairly interesting today, under certain operating conditions my FT857D will exceed the power limit, the highest I saw it go was around 150W! This happened when the power was set to 8W or below on 20m 17m 15m 10m etc (but not VHF/UHF). Strangely, 80m and 40m works as expected. I was working PSK31 and adjusting the Digi Gain when I noticed this first. With the output set to 8W or lower increasing the Digi Gain kept increasing the output power. At first I wrote this off to my tuner giving me a wrong value but then I noticed the current draw from my power supply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This was not only when doing digital, I saw the same behavior on AM. When set to 5W the output could be as high as 40W. I'm really glad I saw this in the shack and didn't take this radio for QRP operation as I was planning. Has anyone seen something like this before?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;These results were confirmed when operating into a dummy load. It seems to be an ALC problem. On 40m the ALC works as expected, on 20m the ALC level is noticeably lower and the power a bit over what I set it. On 10m the ALC doesn't seem to kick in at all and the power output is 130W+.&lt;/p&gt;&#xA;" OwnerUserId="135" LastEditorUserId="135" LastEditDate="2015-01-10T11:22:15.293" LastActivityDate="2015-07-23T17:07:25.663" Title="Yaesu exceeding power limit under certain conditions" Tags="&lt;rf-power&gt;&lt;yaesu&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3481" PostTypeId="2" ParentId="615" CreationDate="2015-01-09T20:19:39.770" Score="1" Body="&lt;p&gt;Question by OP:  did older tube based transmitters need an antenna tuner?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back before the mid-1970s the antenna tuner was a more rare part of the ham radio equipment.  This is because the Pi-network output of the tube based transmitter acted as an antenna tuner as you did your load/tune work to tune up the PA to match the load (the antenna).  Thus, in a way, it was an antenna tuner but it was never called that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first antenna tuner I saw was in the early 1960s and it was the balanced line tuner by E.F. Johnson called the Matchbox Tuner.  This antenna tuner was designed for multi-band wire antennas (such as doublets, loops) fed by open-wire ladder line (often 600 ohm ladder line).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During my early Novice days as a ham and my rebel days prior (starting in the 6th grade) as a bootleg CW operator (circa 1958-1959), I never had an antenna tuner, never had an SWR meter (didn't even know what SWR meant), and I operated quite a few DX stations on 40 watts of power and a crude non-resonant (on anything) dipole up in the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, tubes were definitely more robust than transistors with respect to dealing with high-SWR but that was not the main reason that tube-based transmitters worked without (separate) tuners -- basically the Pi-network was their tuner.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2015-02-18T03:46:35.107" LastActivityDate="2015-02-18T03:46:35.107" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3482" PostTypeId="2" ParentId="615" CreationDate="2015-01-09T20:44:24.197" Score="0" Body="&lt;p&gt;OP Question:  Given the above assumptions, what I would like to know&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How can I transmit without an antenna tuner?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There is no law requiring an antenna tuner.  Most solid-state rigs can handle a mismatch up to about 3:1 SWR.  Above 3:1 there is usually severe fold-back of output power (most modern solid state rigs) to protect the PA from damage.  Fold-back usually begins around 2:1 though and I know it does in my own Elecraft K3.  However, by the time the mismatch is 3:1, so much power is folded-back that you are probably operating a QRP (even under 5 watts) station so you should get QRP credit (assuming you were transmitting 100 watts to begin with).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, you can have a perfect dipole and still have high-SWR problems.  Case in point.  My 80-meter dipole (part of 80/40 fan dipole) has a 1.7:1 SWR at 3.57 MHz.  I designed this antenna to operate best on the low-end of 80.  My penalty is that the SWR gets worse as I go up in frequency such that by the time I am tuned to 3.9 MHz, the SWR is about 4.5:1 which is not that good (though easily corrected by an antenna tuner).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, my low SWR antenna at 3.57 is no where close to low SWR at 3.9 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, my 30-meter dipole (operates 10.1 to 10.15 MHz band) is almost flat across the band.  SWR at 10.105 MHz is 1.28:1, at 10.125 MHz it is 1.33:1, and at 10.145 MHz it is 1.38:1.  So, I can (and do) use my 30-meter dipole without any antenna tuner switched into the transmission line circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, by careful design (and testing after it is in the air) of a dipole antenna and trimming or extending wire legs as needed for your desired frequency, you can have an antenna that has no need for an antenna tuner.  Alternative methods exist in using transmission line transformers but this is often more problematic (in my opinion) and it does not really change the bandwidth of lower SWR you have to operate safely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My examples are drawn here from my own experience with wire antennas because those are the most popular and they are my favorite.  I do a lot of portable operations, especially when on birding photography trips with my wife (the photographer) I will set up a portable station out in the middle of nowhere using (usually) wire antennas I launch into trees with a sling shot.  My SWR is NEVER good in these situations.  I have no intent or attempt to create a low SWR resonant antenna.  Instead, I make sure my transmission line is reasonable efficient and short (under 50 feet) to limit the losses.  My rig most of the time is an Elecraft KX3 though I also use a KX1 and the Norcal 40A.  Mode is always CW.  Power is always QRP.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-01-09T20:44:24.197" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3483" PostTypeId="1" AcceptedAnswerId="3484" CreationDate="2015-01-11T00:52:49.613" Score="3" ViewCount="1125" Body="&lt;p&gt;I received my license and built and tested my first CW transceiver. I've spent the last weeks learning Morse code. Now, time has come to make the first contact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what is a typical CW contact? When you've found each other, what information is typically communicated and in what order? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or isn't there something like a format? &lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorUserId="29" LastEditDate="2015-01-12T21:05:21.583" LastActivityDate="2015-01-12T21:05:21.583" Title="CW contact content" Tags="&lt;cw&gt;&lt;procedure&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3484" PostTypeId="2" ParentId="3483" CreationDate="2015-01-11T03:27:53.033" Score="7" Body="&lt;p&gt;Didn't you need to study basic contact procedure for your license? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, my advice for situations such as these is simple: Listen! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you have a transceiver, just listen and try to find QSOs where you can hear both sides of the conversation, listen to them, copy down all information they send and try to analyze it. This will help you familiarize yourself with local operating customs, so you'll have a good answer for your immediate location. There's also &lt;a href=&quot;http://websdr.ewi.utwente.nl:8901/&quot;&gt;this&lt;/a&gt; SDR site, whose receiver shouldn't be too far away from you (in SW terms at least). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want some &quot;generic&quot; advice, look up QSO templates. You mentioned that you practiced code, so you should already be a bit familiar with them. If you aren't, do practice them! It will make things much easier than if you haven't.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you get the basic template, the rest is just listening. Some people may want to just &quot;rubber stamp&quot; QSOs, other people may want to have longer conversations, so that's something that you need to prepare for by listening. This way, you can get to know the locals who are often on the band, before actually establishing communication with them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you really want another one of those QSO templates, I'll try to provide one with comments along the way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;QRL?&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then you want for a while, to see if you're emitting on a frequency that's already in use. If there's no response, move to next step.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;QRL?&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once again, ask if the frequency is in use and listen for a couple of tens of seconds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;QRL?&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If nobody responds, you can start calling CQ. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;CQ CQ CQ DE YU1NKA YU1NKA YU1NKA K&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Point of the CQ is to draw attention to yourself and not to the fact that you're calling CQ. What the other side wants to hear is your callsign. Depending on your callsign, it might be a bit difficult to copy on the first try. Then wait for a while and see if anyone is responding. If not, call again. Repeat this step until someone does respond, but do keep in mind that you need to leave enough time between your calls for someone to actually respond. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let's assume that someone heard the CQ and wants to respond. He'll go something like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;YU1NKA DE AA1BBB AA1BBB K&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Important point for the other guy is to send your callsign, so that you can recognize that he's talking to you and to send his callsign, so that you can copy it. Some people may send callsign only once, or they may do it several times. After that, there's the end of relation sing. Some people send K, some send KN, some may send AR. In any case, these procedural signs are send without a space between letters, that is, as if they are just one letter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this point, the &quot;connection&quot; is established and it's up to you to respond. So here's my example again:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;AA1BBB DE YU1NKA GM OM TNX FER CALL UR 599 599 QTH BELGRADE BELGRADE BT NAME ANDREJA ANDREJA BT HW CPY? AR AA1BBB DE YU1NKA KN&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in this part, it's important to send the procedural information, such as report, location and name, which are usually send in that order. The BT (sometimes written as =) prosign is often used as a sort of spacer between different sections of a QSO. I've seen some people use full stop there as well, but BT is a bit faster to type. Note some abbreviations used here as well. O is quire a bit longer than E, so in some cases such short-hands are used as a from of &quot;TXT speak&quot; which allows faster sending. Often, in the report, letters will be used instead of numbers. There's a whole set of equivalences between letters and numbers, but the most popular seems to be N for 9, so you may see report sent as 5NN. Near the end of relation, you should ask for the same procedural information from the other side. Sometimes, just HW? is used to ask for report. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then the other side will reply something like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;YU1NKA DE AA1BBB R GD OM UR RPRT 5NN 5NN BT QTH EXAMPLETOWN EXAMPLETOWN BT NAME BOB BOB AR YU1NKA DE AA1BBB KN&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With this part, the formal start of the conversation is over. Do note the R used here. It's used to show that you copied whole previous relation. Now you can talk about whatever you want, if the other side is also interested. Some people may skip this part.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;AA1BBB DE YU1NKA R BLA BLA MY TRX IS BLA BLA MY ANT IS BLA BLA BLA WX IS BLA BLA BLA I LIKE WRITING HAM.SE ANSWERS AT 4 AM IN THE MORNING BLAH BLAH BLAH AR BK&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people may just send BK at the end of a relation instead of sending full callsigns. Just keep in mind how often you're required to identify yourself when you're doing something like this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, there's the conclusion part. In this part, you usually send best wishes, wish for another QSO soon, wish for good DX or something like that and you  end the conversation. Sometimes people may throw in a word or two in the language used in the country of the person you're talking to, if you happen to know them. Also it may be a good place to negotiate sending of QSL cards, if that's something you're into.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the end would look like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;AA1BBB DE YU1NKA R OK TNX DR BOB FER ALL BT WILL SEND QSLL VIA BURO BURO BT HPE TO CU AGN ES ALL BEST FER U ES UR FAMILY IN 2015 BT TNX FER QSO 73 SK AA1BBB DE YU1NKA CL&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here again, we have R, to show that whole last relation came through. Next, I mention that I'll send my QSL card (do note QSLL) through QSL bureau and I wish all the best in the new year and thank for the QSO. In the end, we have 73, which is commonly used. Then there's the procedural part. I send SK, meaning that I'm ending the conversation and I send CL, meaning that I'm closing down my station. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other side will provide a similar transmission. Sometimes, at the very end, people will send E E and E after the final official relation. Sometimes other people listening to the conversation may also send E E as well as a sort of informal greeting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some interesting sites I've noticed:&lt;br&gt;&#xA;&lt;a href=&quot;http://fistsna.org/pdfdocs/A%20BASIC%20CW%20OPERATING%20MANUAL.pdf&quot;&gt;http://fistsna.org/pdfdocs/A%20BASIC%20CW%20OPERATING%20MANUAL.pdf&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://www.skccgroup.com/member_services/beginners_corner/&quot;&gt;http://www.skccgroup.com/member_services/beginners_corner/&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://zs6ez.org.za/tutorial/cw-qso.htm&quot;&gt;http://zs6ez.org.za/tutorial/cw-qso.htm&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also this book about Morse Code theory and background: &#xA;&lt;a href=&quot;http://www.tasrt.ca/bookdown.html&quot;&gt;http://www.tasrt.ca/bookdown.html&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this helps somehow and good luck with CW QSOs!&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2015-01-11T03:27:53.033" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3485" PostTypeId="2" ParentId="3483" CreationDate="2015-01-11T14:59:14.687" Score="2" Body="&lt;p&gt;CW contacts have largely the same format as other contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nearly always exchanged:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;call sign&lt;/li&gt;&#xA;&lt;li&gt;signal report (RST format)&lt;/li&gt;&#xA;&lt;li&gt;location&lt;/li&gt;&#xA;&lt;li&gt;name&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In a contest, it's usually just call signs and a &quot;signal report&quot; which is always 599, and usually a location or any other information which might be relevant to the contest (like multipliers for mobile operation, etc).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Friendlier contacts usually include topics that hams seem to enjoy talking about:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;station description&#xA;&lt;ul&gt;&#xA;&lt;li&gt;antenna&lt;/li&gt;&#xA;&lt;li&gt;transmit power&lt;/li&gt;&#xA;&lt;li&gt;radio&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;the weather&lt;/li&gt;&#xA;&lt;li&gt;insightful, deep, personal remarks, like your age and what you ate for breakfast&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you want a longer QSO, just keep elaborating on these things. Talk about whatever is most important to you. If you are old, talk about your age and how long you've been a ham. Maybe make some remarks about how things were in the stony ages so everyone understands how much experience you have. If you are a gear head, talk about all the expensive station equipment you have and how great it is. Be sure to take turns so the other person can brag about what's important to them, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to sound like a real ham, be sure to use these as much as possible:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;FB: &quot;fine business&quot;, or &quot;uh-huh, yeah.&quot;&lt;/li&gt;&#xA;&lt;li&gt;OK: just &quot;OK&quot;. Used when you need a fresh semantically null filler because &quot;FB&quot; is getting a bit played out.&lt;/li&gt;&#xA;&lt;li&gt;OM: &quot;old man&quot;. Because literally, most hams are old men. Used to make sure all women and anyone young feels excluded from the community.&lt;/li&gt;&#xA;&lt;li&gt;YL: &quot;young lady&quot;. If you must acknowledge a woman, use this to indicate that you imagine that she's young and attractive, thus again making sure women are at least uncomfortable.&lt;/li&gt;&#xA;&lt;li&gt;TNX: &quot;thanks&quot;. Be sure to thank the other person for each and every transmission.&lt;/li&gt;&#xA;&lt;li&gt;HI (usually repeated): Contrived, symbolic laughter. Everyone is entitled to thinking they have a good sense of humor.&lt;/li&gt;&#xA;&lt;li&gt;R: &quot;message received&quot;. Be sure to send it at least three times near the start of each and every transmission so the other person knows you understood them, even when conditions are really good and you've already exchanged 599 signal reports.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Also be sure to know all the &lt;a href=&quot;http://en.wikipedia.org/wiki/Prosigns_for_Morse_code&quot; rel=&quot;nofollow&quot;&gt;prosigns&lt;/a&gt; and &lt;a href=&quot;http://en.wikipedia.org/wiki/Q_code&quot; rel=&quot;nofollow&quot;&gt;Q codes&lt;/a&gt;. Use them as much as possible. If you can use two or three redundantly, even better. Bonus points for using the ones designed for the wireless telegraph days which have only tangential relevance to amateur operation.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-01-11T16:43:29.873" LastActivityDate="2015-01-11T16:43:29.873" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3486" PostTypeId="2" ParentId="3483" CreationDate="2015-01-11T18:09:40.390" Score="1" Body="&lt;p&gt;Another answer more geared to contests or DX hunting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Contests are designed to be fast and short and with CW, they are very fast at times.  If you like CW, this is a great place to learn to copy at faster rates.  My regular CW dialog is at 20 to 25 wpm but during a contest it is 30+ wpm and sometimes up to 40 wpm.  Learning to copy a call sign at 40 wpm usually comes quickly in a contest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, typically, a contester looking for contacts starts with a special CQ:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CQ CQ CQ TEST DE K7PEH&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where the TEST is short for Contest (it is not saying I am testing here).  To respond to a contest you never use the other's call sign.  Let's say that W7IZ (a friend of mine) wants to reply.  His reply is merely:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W7IZ&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, usually once and only once if you are in a pileup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then when K7PEH comes back to you he will give his exchange right away.  Say the exchange is just RST plus state (assuming US):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W7IZ 5NN WA&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often they do not even include their own call sign (takes too much time).  You reply to that by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;TU 5NN OR &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, you can if you want add your call sign at the end but by that time the contester has probably left you go to pick up the next station.  TU is the more common way of saying Thank you or QSL as it is faster than TNX and it is faster than QSL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Last night was the North American QSO Party CW contest.  The exchange was name and state (for US participants at least).  A lot of abbreviations are used on names.  For example, if the contesters name is GEORGE, he will likely only send the first parts, like GEO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used to hate contests but now I am motivated by CW contests for two reasons:  (1) a way to pick up QSLs on DX or other rare QTH; and, (2) a means to stretch my skills at copying fast CW.  I have never sent in my logs for a contest -- I don't care about the competing thing.  I do upload to LOTW for others to use as credit though.  But, I am lazy and I don't upload as often as I should.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Addendum:  Above where I say that TEST is used with CQ in a contest I should clarify or expand.  TEST is not always used, sometimes some abbreviation for the contest is used.  Such as in the North America contest last night, the CQ CQ CQ NA was used where NA was used in place of TEST.  Often the NA or TEST (or whatever) also comes after the call sign such as in:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CQ CQ CQ DE K7PEH TEST&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, sometimes, different people working the same contest will use different things such as in the NA contest you also heard some saying TEST and others saying NA QP (for QSO Party).  In a state QSO Party, you will here something like WA QP if it is Washington state.  Actually, the official Washington State QSO party is named Salmon Run so the letters SR are used instead of WA QP.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2015-01-11T18:38:31.313" LastActivityDate="2015-01-11T18:38:31.313" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3487" PostTypeId="1" CreationDate="2015-01-11T21:55:27.343" Score="5" ViewCount="6943" Body="&lt;p&gt;I have been using Chirp to try to program my Baofeng UV-5R but have been having one problem after another. I was wondering if there was an alternative to Chirp and RT-Systems programming software for use in programming my UV-5R.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2020-07-12T13:46:40.127" Title="HT programming software alternative to Chirp and RT-Systems" Tags="&lt;ht&gt;&lt;software&gt;&lt;baofeng&gt;&lt;uv-5r&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3488" PostTypeId="1" AcceptedAnswerId="3491" CreationDate="2015-01-11T22:18:19.910" Score="2" ViewCount="1279" Body="&lt;p&gt;I am trying to find a convenient place to store my Baofeng UV-5R, I believe the most convenient place to store it would be on its charger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was wondering if storing the UV-5R with its battery still installed, on the unplugged charger with its wall-wart power supply removed would drain the battery or have any negative effect on it.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2017-04-04T01:13:03.310" Title="Storage of a Baofeng UV-5R" Tags="&lt;uv-5r&gt;&lt;baofeng&gt;&lt;battery&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3489" PostTypeId="2" ParentId="316" CreationDate="2015-01-12T01:46:18.847" Score="0" Body="&lt;p&gt;I listen for SO-50 quite often, but being relatively weak, it does pose problems with reception/AOS.&#xA;I heard a late night pass last night, but even with a good GaAsFET preamp, the downlink was noisy. My service monitors have tunable GaAsFET amplifiers built for the receiver section for UHF and VHF. I heard SO-50, but LOS came fast, and the display showed I dropped out of the window at -100 dBm. Of course, using only the Android download, I have to assume that particular pass was not optimal to me, in DM43.&#xA;I rebuilt a destroyed commercial Yagi and was able to 'adjust' its dimensions to force it to play at 436.800+/-.&#xA;Since there are no others I am aware of that are active in satellites, I am all alone. I sure miss UO-14 and AO-51. Now, all the cubesats are packet birds or CW/SSB.which is fine, but some can't swing the costs of the radios and live, so these FM birds are the only way to get into sat-comms. &lt;/p&gt;&#xA;" OwnerUserId="4078" LastActivityDate="2015-01-12T01:46:18.847" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3491" PostTypeId="2" ParentId="3488" CreationDate="2015-01-12T16:41:56.420" Score="4" Body="&lt;p&gt;&lt;a href=&quot;http://batteryuniversity.com/learn/article/how_to_store_batteries&quot; rel=&quot;nofollow&quot;&gt;Battery University&lt;/a&gt; has some general information on storing batteries. Relevant points:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Storing a Li-ion battery in a discharged state will permanently damage it&lt;/li&gt;&#xA;&lt;li&gt;Storing a Li-ion battery at 100% charge is less than optimal&lt;/li&gt;&#xA;&lt;li&gt;around 40% charge is optimal for storage&lt;/li&gt;&#xA;&lt;li&gt;Lower temperatures are better&lt;/li&gt;&#xA;&lt;li&gt;Freezing is bad&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Leaving the battery connected to the radio or the charger might discharge it slowly due to leakage currents. Normally manufacturers try to minimize this, but there is always some leakage in solid-state devices. Given the cheapness of Baofeng, I doubt they put much engineering into this aspect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that cold temperatures are favorable, the refrigerator would be a good place. Put in in a sealed, heavy plastic bag to buffer against moisture. To avoid problems with condensation, don't open the bag or use the battery until it's had time to come back to ambient temperature. Definitely avoid any place in the sun or that gets hot like a car.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-12T16:41:56.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3492" PostTypeId="2" ParentId="2234" CreationDate="2015-01-13T20:53:36.470" Score="0" Body="&lt;p&gt;LoTW/TQSO doesn't require frequency (Just the band) so it doesn't matter if it is SSFH.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most logbook apps also don't require frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just checked my logbook and it only has 3 modes Phone, CW or DIG. So it would be 12cm digital.&lt;/p&gt;&#xA;" OwnerUserId="4083" LastEditorUserId="29" LastEditDate="2015-01-14T10:53:57.660" LastActivityDate="2015-01-14T10:53:57.660" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3493" PostTypeId="1" AcceptedAnswerId="3499" CreationDate="2015-01-13T21:05:52.520" Score="1" ViewCount="70" Body="&lt;p&gt;Does anyone know the forwarding protocol used by FBB?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am working on a program in C# and looking for the protocol to make compressed forwarding etc.&lt;/p&gt;&#xA;" OwnerUserId="4084" LastEditorUserId="4084" LastEditDate="2015-01-13T21:44:22.287" LastActivityDate="2015-01-14T18:16:48.983" Title="What is the forward protocol for FBB?" Tags="&lt;packet&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3496" PostTypeId="1" AcceptedAnswerId="3498" CreationDate="2015-01-14T16:39:36.320" Score="7" ViewCount="2044" Body="&lt;p&gt;Back in the 1960s during my Novice days I operated on the 40-meter band only with 4 different quartz crystals that determined my transmitting frequency with my Eico 720 CW transmitter.  I had heard about other old-timers who would shave (or something, not sure of the actual act) the crystals to shift the frequency by small amounts, maybe up to 10 KHz (or, back then it was 10 KC).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone done this and if so do you know how it was done.  Did they change the dimensions merely by sanding or something or did they actually cut the crystal.  At that time, most of the quartz crystals were in a packaging known as FT243 and this packaging allowed the crystal to be taken apart by unscrewing the package sides and removing them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Today, I have a number of old-style FT243 quartz crystals that I would like to experiment with just for the fun of it but I would like to know more about the process before I start.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Note: none of the tags are specifically fitting that I can tell so I picked two that might hint].&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="8717" LastEditDate="2019-12-05T20:17:32.843" LastActivityDate="2019-12-05T20:17:32.843" Title="Shaving Quartz Crystal for New Frequency" Tags="&lt;cw&gt;&lt;oscillator&gt;&lt;military-surplus&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3497" PostTypeId="2" ParentId="3496" CreationDate="2015-01-14T16:48:23.327" Score="6" Body="&lt;p&gt;It is the thickness of the crystal that primarily determines its operating frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When crystals are manufactured, they are gradually ground down in a special fixture. The operator monitors the process by keeping a shortwave radio nearby, which picks up the electrical noise created by the stress of the grinding action on the crystals, which is relatively narrowband noise centered on the resonant frequency. When this gets to be slightly &lt;em&gt;above&lt;/em&gt; the target frequency, the grinding process is halted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next step is to plate electrical contacts on the newly-ground faces of the crystal so that it can be mounted in a holder. The thickness of this plating affects the final frequency (thicker plating reduces the frequency), and this is how the final calibration of each crystal is accomplished.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to adjust (lower) the crystal frequency after it has been completed, you can try adding additional mass to the contact areas. I don't know any easy way to raise the frequency.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2015-01-14T16:48:23.327" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3498" PostTypeId="2" ParentId="3496" CreationDate="2015-01-14T16:49:18.510" Score="5" Body="&lt;p&gt;didn't do it, but back in the day stumbled across &lt;a href=&quot;http://www.qsl.net/n6ev/ft243.txt&quot; rel=&quot;nofollow&quot;&gt;this&lt;/a&gt;, and thought it might be on-topic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: inserted original text below. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;To: Multiple recipients of list  From:&#xA;  carreiro@netcom.com (Paul Carreiro) Subject: Help in FT-243 Grinding&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Greetings fellow boatanchorites!&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I need help from all the BA gurus out there practiced in the&#xA;  mysterious art of grinding FT-243 type surplus crystals to operate in&#xA;  the ham bands.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I have had some success bringing crystals down in the 6.8 to 6.9 MHz&#xA;  range up into the 40 meter band using dry &quot;ultra fine&quot; grade&#xA;  sandpaper.  Some have resulted in fine CW tones, others seem to be&#xA;  chirpy and have rather lousy short term stability as the transmitter&#xA;  is keyed ( &amp;lt;1/2 second of instability).  I realize this instability is&#xA;  a characteristic sound of the era, but some of these crystals seem to&#xA;  be overly unstable and are just about unusable for CW work.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;So, I'd like to call on the collective experience of all you OTs out&#xA;  there, to help pass on this magical, little understood, and quite&#xA;  possibly lost art of grinding surplus FT-243 type crystals into the&#xA;  ham bands.  What were all the tricks of the trade back then?  Are&#xA;  there any new fangled products on the market that would make this task&#xA;  easier or more accurate?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I also have some general questions on the subject:   Is there a limit&#xA;  in how far you can change the frequency of a crystal?   Seems my&#xA;  attempts at bringing crystals up from 6.7 MHz and below up into   the&#xA;  7.0 MHz range have all resulted in very chirpy output signals.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I've heard that you can alter the frequency slightly up or down by&lt;br&gt;&#xA;  changing the spring tension inside the crystal.  If so, does more&#xA;  tension   lower or increase the frequency?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;What's the best trick to keep from overshooting your desired&#xA;  frequency?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Also, is there a frequency or section in the 40 meter band that is the&#xA;  hang out for Vintage/Classic gear?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Incase you're curious, I'm using these crystals in Johnson Viking&#xA;  Valiant, WRL Globe Chief 90A and Allied Knight T60 transmitters.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Thanks in advance for any and all help! 73 from a young pup trying to&#xA;  get the old dogs to teach me some new tricks.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Paul,  N6HCS carreiro@netcom.com&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;==========================================================================&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;From: &quot;Hal R. Waite&quot;  Subject: Re: Help in FT-243&#xA;  Grinding&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Try tooth paste or better yet tooth powder in a heavy water slurry&#xA;  on a glass plate.  Using light pressure from the second finger (the&#xA;  one that is used for signaling) and a circular motion, grind each of&#xA;  the straight outer edges lightly.  Then clean off and dry.  If you&#xA;  overshoot, a small amount of pencil lead rubbed on the center of the&#xA;  crystal face will either lower the frequency or cause it to fail to&#xA;  oscillate.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;This takes a light touch and a bit of practice.  Avoid grinding the&#xA;  center of the crystal face.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Hal  K4GFI/7  halwaite@netcom.com&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;========================================================================&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;From: &quot;Roberta J. Barmore&quot;  Subject: Re: Help in&#xA;  FT-243 Grinding&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Hi!    [Fair warning--most of what I'm going to say is hearsay, culled&#xA;  from old magazines rather than actual experience.  At least one fellow&#xA;  who posts to the list has ground his own xtals from &lt;em&gt;scratch,&lt;/em&gt; and I'm&#xA;  hoping he'll have additional comment--oh, Gordon???]&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;On Fri, 4 Aug 1995, Paul Carreiro wrote:&lt;/p&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;I have had some success bringing crystals down in the 6.8 to 6.9 MHz range&#xA;    up into the 40 meter band using dry &quot;ultra fine&quot; grade sandpaper.  Some have&#xA;    resulted in fine CW tones, others seem to be chirpy. [...etc. ...]&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;  &#xA;  &lt;p&gt;Based on what I've read, any grade of sandpaper is too&#xA;  rough--scouring power for big jumps, toothpaste for small ones &amp;amp; final&#xA;  grinding on the larger changes.  You can also get grinding paste in&#xA;  various grades at hardware stores, though most of what I see is in a&#xA;  waxy base for buffing-wheel work.    You've got to keep both of the&#xA;  large surfaces parallel and flat!  Work on a slab of plate glass (try&#xA;  junk shops, glass stores, and/or any telescope hobbyists you&#xA;  know--don't take a used lens grinding glass, though, it's not flat any&#xA;  more), and for small rocks, consider grinding a bit of thick brass&#xA;  flat and using it to push on the crystal with.  If it goes inactive,&#xA;  grind gently at the corners.    Cleanliness is &lt;em&gt;vital.&lt;/em&gt; before putting&#xA;  it back in the holder, wash your hands, rinse the crystal; set it down&#xA;  on a &lt;em&gt;clean&lt;/em&gt; and soft surface, wash your hands again, put on gloves&#xA;  and clean it with something that'll zap any oil, like 1,1,1&#xA;  trichlorethane (&quot;Carbo-clor&quot;) or possibly &lt;em&gt;denatured&lt;/em&gt; alchol.  (With&#xA;  older rocks, &quot;cleaning the crystal&quot; was a regular thing). Wash your&#xA;  hands before you start, too, and don't touch your face or hair while&#xA;  thinking what to do.  (A dab of denatuared or trichlor will de-oil&#xA;  your hands, though it doesn't do the skin any good [yessiree, that's&#xA;  why I'm a hand model now, ha!] and may be hazardous--EPA and kin&#xA;  aren't very keen about trichlor). B&lt;/p&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;I've heard that you can alter the frequency slightly up or down by&#xA;      changing the spring tension inside the crystal.  If so, does more tension&#xA;      lower or increase the frequency?&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;  &#xA;  &lt;p&gt;More tension, higher freq--within limits!  Saw mention of this and&#xA;  other tricks, like adding a shunt trimmer condenser, in an old CQ just&#xA;  the other day.  (Naturally I can't find it now).  The article mostly&#xA;  concerned making 'em tweakable--the best trick was an FT-243 version&#xA;  of the old vari-gap &quot;rubber crystals,&quot; for which purpose it was&#xA;  suggested the best type of tension spring was made of a retangular&#xA;  plate with a half-circle bend in the center and the long sides bent&#xA;  flat with a 1/8&quot; radius half-circle cut-out in the center of the long&#xA;  sides (end view like an omega, looking at the short sides; top view, a&#xA;  sort of fat H, wider than it is tall).  Drill and tap the cover plate&#xA;  in the center, run a screw into the tapped hole, and you have a&#xA;  tweakable xtal.  Tweak too far and it may break; that's at your risk&#xA;  and no liability on the part of the writer is implied or assumed.&#xA;  Offer void where prohibited. :)&lt;/p&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;What's the best trick to keep from overshooting your desired frequency?&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;  &#xA;  &lt;p&gt;Go slow, check often.  Most GDOs will work for xtal checking--tune&#xA;  it in on your receiver to check freq.  If you run up the meter&#xA;  sensitivity, a good crystal will give a &lt;em&gt;lot&lt;/em&gt; of deflection.  A&#xA;  five-prong or octal tube socket and some plugs that'll fit the coil&#xA;  jacks on the GDO make a nice test fixture. (A five-prong socket can be&#xA;  wired to fit both &quot;doorknob&quot; and FT-243 rocks, a trick I saw for the&#xA;  first time last week and am now finding in a lot of places--tie pins 3&#xA;  &amp;amp; 4 together, and use pin two for the other connection).    If you&#xA;  like fiddlin' measurements, buy a cheap micrometer; measure the&#xA;  thickness, check freq; grind a bit and check &amp;amp; measure again.  By the&#xA;  third iteration, you'll be able to plot a fair curve correlating&#xA;  thickness and freq, which will hold pretty close for other crystals of&#xA;  the same type and range.  Still need to fire it up and &lt;em&gt;see&lt;/em&gt; in the&#xA;  last stages, especially if you're trying to hit a specific freq. &#xA;  (There are ways to fake up a micrometer, with a well-calibrated dial&#xA;  and fine-theaded hardware, a Depression-era trick; using a real mike&#xA;  is probably just as cheap nowadays).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Hope that's of some use.    73,    --Bobbi&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;=========================================================================&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;From: &quot;Ray L. Mote&quot;  Subject: Re:  Xtal Grinding&lt;/p&gt;&#xA;  &#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;&lt;p&gt;Bon Ami powdered cleanser makes a good grinding paste.  Been using that for over 30 years now.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;The plate glass out of the front of an &lt;em&gt;old&lt;/em&gt; (BA-era) TV set makes a good grinding surface.  Just spread the paste on the glass and have&#xA;  at it&#xA;  &lt;em&gt;very&lt;/em&gt; gently with a circular motion.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;&lt;strong&gt;&lt;em&gt;N E V E R&lt;/em&gt;&lt;/strong&gt; try to grind both sides of a crystal using this technique!  Put a bit of permanent ink or whatever on one side before&#xA;  starting, to show you which side &lt;em&gt;not&lt;/em&gt; to grind on each attempt.&#xA;  (Translation:  always grind the same side.)&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Never tried grinding the edges.  Will have to let those with experience talk about it.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;I've never had decent results more than 5-7 Kc away, if I remember correctly.  (Yeah, I've got Crumbling Mind Syndrome like a lot of&#xA;  other folks.)&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;There were a number of articles written on this topic in QST, CQ, 73, etc.  If you can get next to a CD-ROM version of &quot;From Beverages&#xA;  Through Oscar&quot;, you might do a search on XTAL and grinding.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;  &#xA;  &lt;p&gt;==========================================================================&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;From: &quot;nuusers&quot;  Date:          Sat, 5 Aug&#xA;  1995 21:56:37 EST Subject:       Re: Help in FT-243 Grinding&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Back in 1969 I was interested in making a xtal filter for 455 Kc&#xA;  (oh,oh, I mean 455 Khz) and an old timer showed me how to &quot;edge grind&quot;&#xA;  old military xtals.  The ones I used had a lead fused to the each side&#xA;  of the thin material.  It worked great...in fact an other old timer&#xA;  gave me about 100 of the xtals...I think they worked in the SCR-522&#xA;  sets but there fundamental freq. was 400-500 Kc range...to build him a&#xA;  I.F. filter...&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;On the presure type (FT453 I think) xtals, the secret is to take your&#xA;  time...use 100, 200, 300, and 400 grit NON EMBEDDING grinding compound&#xA;  (Clover brand).  The only place I have ever seen it for sale is&#xA;  machine tool and gun smith supplies.  Do not use valve grinding&#xA;  compound as it is an imbedding type!!  You take it down fast with 100&#xA;  then go to 200 and finish polish with 300 and 400.  You use a flat&#xA;  plate glass piece to grind on.  Once you are finished you let the xtal&#xA;  soak in for about a week in old developing solution that has been used&#xA;  a lot...this silver plates it.  Take the xtal out of solution with&#xA;  cotton gloves so as not toget grease or rub off the coating.  Take a&#xA;  clean piece of plate glass and put white tooth paste on the glass and&#xA;  rub the coating off the edges.  There is also a trick for measuring&#xA;  activity and frequency with a sig gen, vtvm and a freq meter...but I&#xA;  can't remember off hand...good luck!!!&#xA;                              73,&#xA;                              Steve, KD1DT&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;=======================================================================&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;From: wendler@tomcat.adc.ray.com (John Wendler) Subject: Crystal&#xA;  Grinding&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;In re: Crystal Grinding... Bobbi's summary looked pretty good, from&#xA;  what I remember reading. I remember also seeing something about using&#xA;  Hydroflouric Acid as an etchant, but would discourage anyone from&#xA;  pursuing this option unless they are a trained chemist operating in a&#xA;  proper lab with proper garb.  HF is absorbed through the skin and goes&#xA;  to the bone.  All reports indicate that this is extremely painful.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I looked into crystals at one point from a professional perspective;&#xA;  checked into the books and talked with some colleagues who make the&#xA;  world's lowest phase noise SAW devices.  Suffice to say that&#xA;  cleanliness, proper processing, and good materials are all necessary&#xA;  to go for &quot;world class.&quot;  For well made crystals, the differences in&#xA;  performance between nitrogen atmosphere, ambient atmosphere, vacuum,&#xA;  in a cold weld or resistance weld or a glass package are all very&#xA;  noticeable. The presence of a gas will dampen the vibrations,&#xA;  decreasing the Q. Contaminents will settle on a crystal, lowering the&#xA;  frequency and the Q; this can be part of the aging characteristics or&#xA;  a deliberate tuning strategy. Pencil lead, anyone? How about water&#xA;  vapor from the atmosphere, and dust in the package?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;You can guess where WWII crystals end up in the general scheme of&#xA;  things, as well as crystals for microprocessors, etc that are cranked&#xA;  out by the million. We are fortunate that we do not require world&#xA;  class for amateur application!&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;One book had a calculation of the acceleration that an atom on the&#xA;  surface of the crystal suffers... I seem to remember ~1,000,000 G.&#xA;  Deflections were on the order of an atomic diameter, if the memory&#xA;  hasn't completed faded this morning.  I would certainly expect the&#xA;  lead to move around over the long term, thus changing the frequency&#xA;  slightly.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I hope this background gives a little insight into why tuning with a&#xA;  pencil can sometimes cause problems, both long and short term, as well&#xA;  as why some of the old style crystals might require periodic cleaning&#xA;  as Bobbi mentioned.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A common cleaning process in many semiconductor fabs (for grease&#xA;  removal) is (was? EPA?) some kind of Trichloro for grease removal,&#xA;  followed by methanol for Trico removal, followed by de-ionized water&#xA;  for methanol residue removal.  The DI water is then baked off. I used&#xA;  something similar to this while preparing samples (electronic, not&#xA;  insectile) for a scanning electron microscope. (There! I got mention&#xA;  of a hollow state device into this post, so it's partially&#xA;  legitimized!)&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;You may want to consider distilled water from the supermarket for the&#xA;  final clean up of your crystal.  I know that I would not use the water&#xA;  from my faucet to clean it; it's loaded with iron!&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;BTW, you may want to check your can of Tuner Cleaner/Degreaser&#xA;  ingredients; my can will double for the Trichloro and alcohol steps&#xA;  above, even though the ingredients are not exact.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;73 es GL John&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;======================================================================&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;From: &quot;Roberta J. Barmore&quot;  Subject: Re: Xtal&#xA;  Grinding&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Hi!    I'd like to expand on the following, for the benefit of the&#xA;  younger folks.  (It's just a good thing my rheumatiz' isn't actin' up,&#xA;  Sonny! )&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;On Sat, 5 Aug 1995, Ray L. Mote wrote:&lt;/p&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;ol start=&quot;3&quot;&gt;&#xA;    &lt;li&gt;&lt;strong&gt;&lt;em&gt;N E V E R&lt;/em&gt;&lt;/strong&gt; try to grind both sides of a crystal using this&#xA;    technique!&lt;/li&gt;&#xA;    &lt;/ol&gt;&#xA;  &lt;/blockquote&gt;&#xA;  &#xA;  &lt;p&gt;Occurs to me it's might not be clear &lt;em&gt;why&lt;/em&gt; this is so--you see, if&#xA;  we want our xtal to be a good one, both sides need to be &lt;em&gt;parallel&lt;/em&gt;&#xA;  (if not, you can end up with a dead'un--or worse) and remain at the&#xA;  original angle to the crystalline structure of the quartz.  In&#xA;  particular, the AT-cut is a bit fussy; you can think of this common&#xA;  cut as a way to combine the frequency vs. temperature characteristics&#xA;  of the ol' X and Y-cut rocks, which are opposite in sign but of&#xA;  differing slopes.  [Real Engineering and Science types among us will&#xA;  know I'm glossing over a lot in that assertion, but it covers the&#xA;  gross effects].  Get too far off, you've got a drifty rock, and the&#xA;  poor feller with a super-solid-state-Whizbang Wonder xcvr will &lt;em&gt;not&lt;/em&gt;&#xA;  be able to follow you; he doesn't know from drift.    A hardware-store&#xA;  micrometer might be very useful for checking parallelism, especially&#xA;  if you plan to do a lot of crystals.  (At what they're getting for 'em&#xA;  new, moving the surplus ones is pretty attractive!)    There's also&#xA;  some things having to do with surface smoothness that come into play,&#xA;  and saving at least one of the original surfaces helps keep the rock&#xA;  active--might be wise to put the side you've been grinding against the&#xA;  plate that's got a spring right back of it; last time I opened up a&#xA;  junk FT-243-type holder, there was only a spring on one side.  (Dunno&#xA;  if they're all that way).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Oh, the flattish metal spring I mentioned in an earlier post can be&#xA;  found in some types of mil-surplus crystal holders.  (I found the&#xA;  article).  Interested parties can e-mail me for details &amp;amp; such. Think&#xA;  it was the March '62 CQ.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A source tells me Petersen is looking to get back into crystals for&#xA;  ham gear.  Anyone know for sure?  Can't seem to find their number....&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;73,    --Bobbi&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;========================================================================&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;From: swheaton@www.tyrell.net (Sheldon Wheaton) Subject: Re: Help in&#xA;  FT-243 Grinding&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I've ground quite a few xtals for my use in the Antique Wireless&#xA;  Association's annual CW QSO contests (Rig is 1939 vintage reproduction&#xA;  6L6-809). A couple of my comments on the subject:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;For a given type of &quot;cut&quot; (direction of XTAL lattice molecular&#xA;  alignment), the fundamental frequency is inversely proportional to the&#xA;  thickness. Most FT-243 xtals are &quot;AT&quot; cut. The formula is listed in&#xA;  many early (1930's) ARRL handbooks. Using this formula, and a good&#xA;  micrometer, you can make some rough cuts without having to assemble&#xA;  the crystal every time.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Keep your eye out for old xtal grinding kits at hamfests. I have some&#xA;  with different &quot;grits&quot; of grinding powder. Not sure what it is, but&#xA;  looks &amp;amp; feels about like talcum powder, except gray in color.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;If the xtal is not ground with both sides parrallel, you may end up&#xA;  with two or more different &quot;fundamental&quot; frequencies! Not good.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Sometimes an otherwise good xtal that worked fine, but won't oscillate&#xA;  or does so erratically after the last grind that moved it only 5 kc or&#xA;  so, can be made to work correctly by slightly &quot;beveling&quot; all four&#xA;  edges on both sides (8 edges total). This procedure is documented in&#xA;  many books of the 30's. It usually doesn't need to be a visible bevel,&#xA;  just a few &quot;strokes&quot; with the compound.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I have best luck with a figure 8 motion for grinding. Some grinding&#xA;  kits have a flat piece with a pentagon shaped, shallow cut-out, with&#xA;  inwardly curved edges, which will make the quartz piece move around in&#xA;  an impressive &quot;Spiro-graph&quot; type motion, but I haven't had much luck&#xA;  with this item.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;gud luck &amp;amp; 73, Sheldon KC0CW swheaton@tyrell.net&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;========================================================================&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;From: morgan@speckle.ncsl.nist.gov (Roy Morgan) Subject: Re: Help in&#xA;  FT-243 Grinding&lt;/p&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;Greetings fellow boatanchorites!&lt;/p&gt;&#xA;    &#xA;    &lt;p&gt;I need help from all the BA gurus out there practiced in the mysterious art&#xA;    of grinding FT-243 type surplus crystals to operate in the ham bands.&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;  &#xA;  &lt;p&gt;Here are some short notes on your questions:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;-use wet finest possible wet-dry emery paper, or fine carborundum or even toothpaste on a piece of glass.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;-activity goes up and down as you grind the frequency upwards.  You may have just gotten to a poor spot on most of your crystals because&#xA;  of the distance you moved the frequency.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;-activity at/near a frequency depends on thickness/width ratio  so activity can sometimes be restored by grinding the edge(s) of the&#xA;  crystal.  Frequency will likely got up as you grind the edge.  Do a&#xA;  LITTLE at at time.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;-a crystal in a holder with some dust will act strange, if it oscillates at all, so be CLEAN when assembling.  Handy things to have&#xA;  are: acetone or alchohol, clean - the kind you might get at the paint&#xA;  store may not be too clean (and ventilation!), little soft brush from&#xA;  the art store, blower like a bulb-type solder sucker or baby nose&#xA;  syringe ...&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;-increasing spring pressure in the holder will usually increase frequency, I think.  beware of cracking the thing.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;-a bit of pencil lead or solder rubbed on the flat surface will lower the frequency by making it heavier, and doing this may help you&#xA;  predict what will happen if you grind the edges.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;-capacitance of the oscillator circuit may affect the activity of a crytal you've ground.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;I'm intersted in making up a &quot;standard&quot; oscillator circuit - I have a&#xA;  handbook giving lots of tube circuits.  I'd be glad to cooperate on&#xA;  this project if you'd like.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;-- Roy -- Roy Morgan / Tech A-266 / NIST / Gaithersburg  MD 20899 (National Institute of Standards and Technology,  formerly NBS)&#xA;  301-975-3254 Fax: 301-948-6213 Internet: morgan@speckle.ncsl.nist.gov&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;========================================================================&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;From: Andy Wallace  Subject: xtal grinding monitor --&#xA;  someone TRY THIS.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Also in the '49 Hints and Kinks book is a method (page 88) of&#xA;  monitoring the frequency of a quartz crystal DURING GRINDING.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Take a flat piece of aluminum or copper about 6&quot; square, and connect&#xA;  it to your receiver antenna post using a short lead. Place the plate&#xA;  glass on which the grinding is being done on this sheet. You can tune&#xA;  in the crystal frequency on the receiver by the scratches you hear as&#xA;  the crystal is being ground.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;This is the first time I've ever heard of something like this, but I&#xA;  assume the laws of physics and piezoelectricity allow this to work.&#xA;  'scuse me, I have to go take apart a picture frame and find some PC&#xA;  board material!  But seriously, would someone on the List volunteer to&#xA;  try this? Fascinating...&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;--Andy wallace@mc.com&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;P.S. The H+K book also recommends automotive valve grinding compound&#xA;  for speedy xtal grinding. Hmm...I smell some new Novice xtals coming&#xA;  on, maybe even for 80m.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2015-01-15T14:17:57.607" LastActivityDate="2015-01-15T14:17:57.607" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="3499" PostTypeId="2" ParentId="3493" CreationDate="2015-01-14T18:16:48.983" Score="1" Body="&lt;p&gt;I don't know anything about it myself, but a quick web search shows there seems to be &lt;a href=&quot;http://www.f6fbb.org/protocole.html&quot; rel=&quot;nofollow&quot;&gt;documentation here&lt;/a&gt; of the forwarding protocol.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-01-14T18:16:48.983" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3500" PostTypeId="1" AcceptedAnswerId="3501" CreationDate="2015-01-15T21:26:03.527" Score="6" ViewCount="1932" Body="&lt;p&gt;I am just trying to understand the nitty gritty of using decibels and absolute measurements in dBm. I see them referred to routinely in RF, and using reference sheets I can understand enough to make sense of gains and losses, but I would like instead to acquire a much better understanding for myself, being able to convert and calculate freely (without the need for reference sheets) between any power or dB value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I understand that dB is merely a ratio of measurement. But if, for example, a component under test had 20W at its input and 15W at its output and there is an overall loss of 5W, how would that be worked out and expressed in a ratio of dB?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trying to work it out I did:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;20W (in) = 10log10(20W/1W) = 13dB(W)&#xA;15W (out) = 10log10(15W/1W) = 11.76dB(W)&#xA;so, component power loss = 13dB(W) – 11.76dB(W) = 1.24dB(W)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;However, I can see that I am merely subtracting absolute measurements still and not determining the dB ratio of power transfer efficiency or loss. If so, then what would be the equivalent dB ratio for this example?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition, I am able to convert 13dB(W) back to watts with:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;10 to the power of (13/10) or 10^1.3 = 19.95W&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;and so too for 11.76dB(W):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;10^1.176 = 14.997W&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;but for 1.24dB(W):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;10^0.124 = 1.33W&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;which does not appear correct, as I expected instead a value of ~ 5W, for which 1.24dB(W) represents between 13dB(W) and 11.76dB(W), so I unsure where I am going wrong. If someone could let me now I would sure appreciate the insight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, what would it mean to say a receiver has a receive level of -45dBm?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it right to conclude that such a receiver is capable of extracting information from signals received at -45dBm less power than what they (signals) were originally transmitted at? Or actually it just occurred to me that since 45dBm is an absolute value that it perhaps means that the receiver could receive signals as low as -45dBm or:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;10^(-45/10) = 0.0000316mW&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;and still be able to extract the information transmitted so long as the S/N ratio is adequate? Which if that was the case then, if one transmits a signal with 20W or 43dBm of power, then the signal could be attenuated by up to 88dBm:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;43dBm - -45dBm = 88dBm&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;and still be detected adequately enough by the receiver in question so that the original information sent is received?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope I have explained my questions well enough to be easily understood.&lt;/p&gt;&#xA;" OwnerUserId="4097" LastActivityDate="2015-02-04T16:43:21.450" Title="decibels as ratio and dBm as absolute values" Tags="&lt;rf-power&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3501" PostTypeId="2" ParentId="3500" CreationDate="2015-01-15T22:04:29.493" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Trying to work it out I did:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;20W (in) = 10log10(20W/1W) = 13dB(W)&#xA;15W (out) = 10log10(15W/1W) = 11.76dB(W)&#xA;so, component power loss = 13dB(W) – 11.76dB(W) = 1.24dB(W)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Your error is merely in the units, not in the calculation. Taking the difference of two dBW (or any two absolute dB values &lt;em&gt;using the same reference level&lt;/em&gt;) gets you dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to think of this algebraically, you could use the definition&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$x\,\mathrm{dBW} \equiv x\,\mathrm{dB} + (1\,\mathrm{dBW})$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $(1\,\mathrm{dBW})$ can be treated as a funny-named constant we don't need to assign any numerical value to, much like &lt;em&gt;any other unit symbol&lt;/em&gt; — except that we're adding, not multiplying, it, because logarithms transform multiplications to additions (basic property: $\log(a\cdot b) = \log a + \log b$). If we transform the above to non-logarithmic form, we get the trivial and obvious equation&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$y\,\mathrm{W} = y \cdot (1\,\mathrm{W})$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the above definition for dBW, your calculation becomes:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;\begin{align}&#xA;&amp;amp;\phantom{{}={}} 13\,\mathrm{dBW} - 11.76\,\mathrm{dBW} \\&#xA;&amp;amp;= (13\,\mathrm{dB} + (1\,\mathrm{dBW}) - (11.76\,\mathrm{dB} + (1\,\mathrm{dBW})) \tag{change notation}\\&#xA;&amp;amp;= 13\,\mathrm{dB} - 11.76\,\mathrm{dB} + (1\,\mathrm{dBW}) - (1\,\mathrm{dBW}) \tag{reorder terms}\\&#xA;&amp;amp;= 13\,\mathrm{dB} - 11.76\,\mathrm{dB} \tag{$x - x = 0$} \\&#xA;&amp;amp;= 1.24\,\mathrm{dB} \tag{compute}&#xA;\end{align}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;However, I can see that I am merely subtracting absolute measurements still and not determining the dB ratio of power transfer efficiency or loss. If so, then what would be the equivalent dB ratio for this example?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The result of the subtraction &lt;em&gt;is&lt;/em&gt; a ratio expressed in dB; you've just mislabeled it as being absolute.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In addition, I am able to convert 13dB(W) back to watts … but for 1.24dB(W):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt; 10^0.124 = 1.33W&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;  &#xA;  &lt;p&gt;which does not appear correct, as I expected instead a value of ~ 5W&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The 1.24 value is dB, not dBW, so treating it as an absolute value does not get you the answer relative to the original power level you measured. (However, there is a meaning to the figure 1.33 W: it's the amount of power in that would be required to get 1 W of power out. You can check this against simply computing ratios with no logarithms.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, logarithms are simply a computational convenience. If you have a calculation starting in watts and ending in watts, then you can do the intermediate work in dBW and dB (adding and subtracting) or in power and ratios-of-power (multiplying and dividing) and get the same answer. If you don't get the same answer, you made an error in setting up the formulas.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Finally, what would it mean to say a receiver has a receive level of -45dBm? … Or actually it just occurred to me that since 45dBm is an absolute value that it perhaps means that the receiver could receive signals as low as -45dBm … then, if one transmits a signal with 20W or 43dBm of power, then the signal could be attenuated by up to 88dBm:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, you have this right, except that it's “attenuated by up to 88 dB”, not dBm.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-02-04T16:43:21.450" LastActivityDate="2015-02-04T16:43:21.450" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3502" PostTypeId="1" AcceptedAnswerId="3511" CreationDate="2015-01-16T02:40:20.047" Score="12" ViewCount="1998" Body="&lt;p&gt;For an antenna to work, doesn’t charge have to flow through it? A current must be present. To me it indicates it must be a circuit, but how is a dipole a circuit?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If they are not circuits, then how does charge flow in them?&lt;/p&gt;&#xA;" OwnerUserId="4096" LastEditorUserId="76" LastEditDate="2015-12-15T21:48:53.073" LastActivityDate="2015-12-15T21:48:53.073" Title="Are antennas circuits?" Tags="&lt;antenna&gt;&lt;theory&gt;&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="3503" PostTypeId="1" AcceptedAnswerId="3506" CreationDate="2015-01-16T02:56:34.977" Score="5" ViewCount="152" Body="&lt;p&gt;So at any given time, electromagnetic waves of many different frequencies are flooding the space around me. I have a little 2 meter radio. Are not all these electromagnetic waves exciting the electrons in the antenna at the same time?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's just go out on a limb and say the only RF reaching my radio is 2 meters. Let's just say frequency 146.120 and 146.805. If the radio is getting hit with both these frequencies at the same time, how is the antenna providing the voltages for just the one frequency that it is tuned to? It doesn't but then I'm not understanding how an antenna can receive multiple frequencies at the same time. Seems it would be just a jumble.&lt;/p&gt;&#xA;" OwnerUserId="4096" LastActivityDate="2015-01-16T14:18:26.250" Title="How is RF a radio receives just not a mishmash of eletromagnetic energy?" Tags="&lt;antenna&gt;&lt;theory&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3504" PostTypeId="2" ParentId="3502" CreationDate="2015-01-16T04:37:19.593" Score="3" Body="&lt;p&gt;&lt;strong&gt;The idea that a closed circuit — a loop — must be present for current to flow is a simplified description, which is only true for simple DC circuits.&lt;/strong&gt; It's a simplification that works because in the DC case, if there is no complete circuit and yet current is flowing, then charge is accumulating somewhere, and the electric field from that excess of charge will oppose the current, increasing to the exact point at which the current stops.&lt;sup&gt;†&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, in the AC case — and RF is AC, or perhaps “beyond AC” depending on how you classify things — the current is expected to reverse, and therefore those accumulations of charge can go away again, so the system can pass through repeating cycles of charging and discharging. The common circuit component in which this happens is a &lt;strong&gt;capacitor&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The movement of charge in a dipole antenna is &lt;em&gt;somewhat&lt;/em&gt; like that in a capacitor, with “the rest of the universe” substituting for the space between the capacitor plates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like in a capacitor, no charges actually move from one half of the antenna to the other (except indirectly through the rest of the circuit). Instead, the charges &lt;em&gt;bunch up&lt;/em&gt; in the antenna, forming a positive excess on one half and a negative excess on the other. In a receiving antenna, the energy to push the charges together comes from the incoming wave. In a transmitting antenna, it comes from the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the wave continues through the rest of its cycle, the antenna discharges and charges in the opposite polarity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, the rest of the circuit connected to a receiving antenna “sees” an oscillating voltage corresponding to the original wave.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;†&lt;/sup&gt; Actually, it'll increase a little bit further and reverse — sloshing back and forth a bit until it settles down. This is due to &lt;em&gt;inductance&lt;/em&gt;. But that doesn't matter for the rest of this answer.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-11-20T05:12:13.533" LastActivityDate="2015-11-20T05:12:13.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3505" PostTypeId="1" CreationDate="2015-01-16T05:34:24.347" Score="2" ViewCount="1366" Body="&lt;p&gt;This question comes from doing some research into small magnetic loop antennas for HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For transmitting, these antennas are often designed with a big, variable, air (or vacuum) tuning capacitor (e.g. &lt;a href=&quot;https://en.wikipedia.org/wiki/Variable_capacitor#Butterflyhttps://en.wikipedia.org/wiki/Variable_capacitor#Butterfly&quot; rel=&quot;nofollow noreferrer&quot;&gt;butterfly-style&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that the currents and voltages in a loop when transmitting are fairly big and every bit of loss in the loop would quickly add to a less efficient antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To increase the efficiency of these loop antennas for transmitting, wouldn't it be better to reduce the internal resistance of the tuning capacitor and have the plates made from silver plated material or copper instead of (what I most often see) aluminium?&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="366" LastEditDate="2016-11-26T18:12:33.187" LastActivityDate="2017-08-15T01:06:10.733" Title="Why are variable capacitor plates made from aluminium?" Tags="&lt;loop-antenna&gt;&lt;efficiency&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3506" PostTypeId="2" ParentId="3503" CreationDate="2015-01-16T06:06:00.413" Score="3" Body="&lt;p&gt;&lt;strong&gt;Filters.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A filter is a circuit which is designed to react differently depending on the frequency. Every real (not mathematically ideal) circuit element does this to some degree, but filters are designed to have a very specific &lt;em&gt;frequency response&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a &lt;em&gt;very&lt;/em&gt; loose and incomplete high-level schematic of a simple radio receiver:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/zT24s.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fzT24s.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see, the filter has four terminals: two for the input from the antenna, and two for the output to the demodulator. (In practice, they might more likely share a single ground bus for both input and output sides, for a total of three terminals.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The effect of the filter is that the part of the signal coming from the antenna which has the desired frequency passes through — as if the wires on the left were connected to the wires on the right — and the rest of it does not — as if the wires on the left were either shorted together or disconnected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Filters can be made out of various components, but most commonly inductors and capacitors. Introductions to electronic circuits often say something like “capacitors pass AC and block DC; inductors block AC and pass DC&quot;. This is true, but simplified; there is not just “AC” but the entire spectrum of possible frequencies, and the higher the frequency the &lt;em&gt;more&lt;/em&gt; the capacitor will pass it and the inductor will block it. If you put an inductor and capacitor in parallel or in series, you get a circuit with a &lt;em&gt;resonant frequency&lt;/em&gt; — a specific frequency (actually a small range of frequencies) which it will pass (or block) much more than other frequencies. That's the simplest filter. Additional complexity in filter design gets you &quot;sharper&quot; filters that are better at passing what you want and blocking what you don't want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition, the antenna itself has frequency-varying characteristics and therefore acts as a filter. This is why there are different size antennas for different frequency ranges.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The above is a very simple picture. The main thing that I've omitted (besides e.g. amplifiers, which every radio but a “crystal radio” has in order to produce an audible output volume) is &lt;em&gt;tuning&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One approach to tuning is to adjust the filter's resonant frequency (or &lt;em&gt;passband&lt;/em&gt;) to the frequency you want to receive. Early receivers (see &lt;em&gt;crystal radio&lt;/em&gt; and &lt;em&gt;tuned radio frequency (TRF) receiver&lt;/em&gt;) did use this technique. However, it is difficult to make a filter that is both adjustable and sharp enough to be good at receiving one station and not also an adjacent one (it has poor &lt;em&gt;selectivity&lt;/em&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, modern radios (starting with the &lt;em&gt;superheterodyne&lt;/em&gt; design) internally generate a signal at a particular offset from the desired frequency (the &lt;em&gt;local oscillator&lt;/em&gt; (LO)) which is combined with the signal from the antenna (&lt;em&gt;mixed&lt;/em&gt;) in such a way as to produce a copy of the radio signal at a fixed frequency (&lt;em&gt;intermediate frequency&lt;/em&gt; (IF), equal to the offset between the LO and the input) which is then filtered using a sharp non-adjustable filter before being passed to the demodulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Originally, the local oscillator was an adjustable filter (usually containing a variable capacitor and a fixed inductor) and amplifier connected in a positive feedback loop — the filter selects the particular frequency and the amplifier keeps the signal oscillating. (Here, the filter doesn't need to be especially sharp because it's handling only the fed-back signal — which will quickly settle on &lt;em&gt;only&lt;/em&gt; the resonant frequency.) Modern radios instead use digital circuits to generate the local oscillator signal, via digital-to-analog converters (DAC) and phase-lock loops (PLL); this allows very precise tuning under computer control.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-01-16T06:06:00.413" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3507" PostTypeId="2" ParentId="3503" CreationDate="2015-01-16T14:18:26.250" Score="0" Body="&lt;p&gt;Ever blow in an empty bottle? Why is it that you hear just one tone, and not airy noise like you get when you blow on most other things?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why, when you pluck a string on a guitar, do you get a clear tone?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer is &lt;em&gt;resonance&lt;/em&gt;. An empty bottle is a resonant system, specifically a &lt;a href=&quot;http://en.wikipedia.org/wiki/Helmholtz_resonance&quot; rel=&quot;nofollow&quot;&gt;Helmholtz resonator&lt;/a&gt;. Resonant systems are everywhere. Consider musical instruments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radios operate on a similar principle, except the resonator is made of electrical components, not mechanical ones. A very simple electrical resonator is the &lt;a href=&quot;http://en.wikipedia.org/wiki/LC_circuit&quot; rel=&quot;nofollow&quot;&gt;LC circuit&lt;/a&gt;. When we make a resonant system with the intent of separating some frequencies from another, we call it a filter. Modern radios can have much more complex filters, but a simple LC circuit is good enough for a simple radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, the antenna does receive a jumble of electromagnetic energy. However, the resonance of the receiver, like the empty bottle, makes the radio particularly sensitive to just a narrow range of frequencies. All the other frequencies are still there, but because the radio is not sensitive to those frequencies they are much, much quieter, like background noise.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-16T14:18:26.250" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3508" PostTypeId="1" AcceptedAnswerId="3509" CreationDate="2015-01-16T14:23:41.457" Score="8" ViewCount="606" Body="&lt;p&gt;A transmission line does not radiate when the spacing between the two wires is very small when compared to the wavelength, but the transmission line begins to radiate when the spacing between the lines becomes comparable to the wavelength of the signal. Why is this?&lt;/p&gt;&#xA;" OwnerUserId="4101" LastEditorUserId="218" LastEditDate="2015-01-20T13:27:08.167" LastActivityDate="2015-01-20T13:27:08.167" Title="Why must twin-lead conductor spacing be small to avoid radiation?" Tags="&lt;antenna&gt;&lt;feed-line&gt;&lt;theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3509" PostTypeId="2" ParentId="3508" CreationDate="2015-01-16T15:54:02.950" Score="5" Body="&lt;p&gt;Twin-lead transmission lines don't radiate because the opposite fields from each conductor cancel, but when the spacing is far apart this does not happen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, let's consider the magnetic field around an infinite, straight conductor with uniform current throughout. In this image, the conductor is just right of center, and the current is coming straight out of the page.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JqjTi.png&quot; alt=&quot;field from one conductor with uniform current&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now let's add next to it another conductor, with the current going the other way:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/QYGAJ.png&quot; alt=&quot;fields from two conductors with opposite uniform current&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Add these fields together, and you get:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/GG5Kb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For distances far away relative to the conductor spacing, the fields are equal but opposite, so when added together they cancel. Radiation is, by definition, a field that extends to infinity. If there are no fields far away, then it can't be radiating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, we made an assumption of &lt;em&gt;uniform&lt;/em&gt; current. When the spacing between the conductors is small, this is a mostly true assumption. Although the current isn't exactly uniform, we must travel many multiples of the conductor spacing before there's any appreciable change in phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, when the conductor spacing is large, then this is no longer true. Remember, the current is reversing direction periodically, and if we look at the field from just one conductor this means the field is alternating between clockwise and counterclockwise swirl. The changes to this field only propagate at the speed of light, so if we zoom the graph out to be a wavelength wide or more, we'd see those changes propagating away as waves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/k7Ut8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the image above, the wavelength appears to be approximately four units. Now if we add that second conductor, two units away, we get this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/lSykz.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how the fields don't cancel. They don't cancel because on the scale of the conductor spacing (which is not small relative to the wavelength) there can be significant changes in phase. Thus, there are regions of constructive interference where the fields don't cancel. These regions extend out to infinity, and thus, the feedline radiates.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Images were generated with &lt;a href=&quot;http://kevinmehall.net/p/equationexplorer/vectorfield.html&quot; rel=&quot;noreferrer&quot;&gt;a Javascript vector field grapher by Kevin Mehall&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-01-20T13:08:45.073" LastActivityDate="2015-01-20T13:08:45.073" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3510" PostTypeId="2" ParentId="3505" CreationDate="2015-01-16T19:27:51.237" Score="2" Body="&lt;p&gt;I'm not familiar with the practical design of such antennas (so consider this answer a placeholder until someone more knowledgeable comes along), but here are some speculations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The &lt;em&gt;current density&lt;/em&gt; in the capacitor plates is much lower than in the connections to the capacitor, because (in a typical air-variable) there are many plates, and within each plate the current spreads out from the shaft (seeing a larger cross-sectional area) and decreases (because part of the capacitor area is behind it now). Therefore, there is less current flowing per volume of metal and thus less resistance loss.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The plates must be stiff compared to their mass, so that mechanical shock will not change the spacing of the plates or short them out. The materials you propose might be inferior to aluminum for this purpose (I haven't looked up the info needed to verify this).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;My understanding is that variable capacitors for amateur use are typically bought used or otherwise scrounged — and their original use was likely not in a transmitting loop, and doesn't care about resistance as much. Building capacitors to spec for this purpose would be quite expensive.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-01-16T19:27:51.237" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3511" PostTypeId="2" ParentId="3502" CreationDate="2015-01-17T01:56:56.750" Score="15" Body="&lt;p&gt;What do you mean by &quot;circuit&quot;? Do you mean there's a loop of conductor from one side of a battery to the other, possibly with some other conducting components along the way? How about this circuit?&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/6h5hx.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f6h5hx.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a circuit here? There certainly isn't any way to follow a line from one side of the battery to the other. Each half connects to opposite plates of the capacitor, and those plates are separated by an insulator. Yet, if you flip that switch repeatedly, the LED will blink. Clearly there's some current flowing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we pull the plates of the capacitor apart, it's still a capacitor. It capacitance will decrease, but it's still a capacitor. Just a smaller one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we squish the plates into long, thin tubes or wires, it's still a capacitor. Capacitance may decrease still more due to the smaller area of the plates, but it's still a capacitor. The circuit now is looking something like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/r1gjO.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fr1gjO.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What if we now pull the ends of the capacitor apart?&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/UWA2u.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fUWA2u.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yep, it's a dipole antenna. Lose the LED and the resistor, and flip the switch a few million times per second, and you have a transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not illustrated here is also the inductance of the antenna. All circuits have inductance, which you can realize if you follow a similar argument but with an inductor instead of a capacitor, and start straightening the coil into a straight line. The inductance decreases, but it never goes away. Usually we don't draw the inductance because it's small enough to be negligible in a simple circuit that blinks an LED. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, antennas have capacitance and inductance. They also have resistive losses (unless they are made of superconductors) and &lt;a href=&quot;http://en.wikipedia.org/wiki/Radiation_resistance&quot; rel=&quot;noreferrer&quot;&gt;radiation resistance&lt;/a&gt;. Putting all these together, antennas can be modeled as an &lt;a href=&quot;http://en.wikipedia.org/wiki/RLC_circuit&quot; rel=&quot;noreferrer&quot;&gt;RLC circuit&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-17T01:56:56.750" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3512" PostTypeId="2" ParentId="3500" CreationDate="2015-01-17T02:27:03.053" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Trying to work it out I did:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;20W (in) = 10log10(20W/1W) = 13dB(W)&#xA;15W (out) = 10log10(15W/1W) = 11.76dB(W)&#xA;so, component power loss = 13dB(W) – 11.76dB(W) = 1.24dB(W)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Here's your problem: the answer is 1.24 dB, not 1.24 dB(W).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why? Subtraction of logarithms corresponds to division. You end up with watts in the numerator and denominator which cancel, leaving you with a unitless ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formally:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \log(a) - \log(b) = \log\left({ a \over b }\right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you do $ 13\:\mathrm{dB(W)} - 11.76\:\mathrm{dB(W)} $, you are actually doing:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \require{cancel}&#xA;{&#xA;  \left(10^{13\over 10}\right)\cancel{\mathrm W}&#xA;  \over \left(10^{11.76 \over 10}\right)\cancel{\mathrm W}&#xA;}&#xA;= {19.95 \over 14.10 }&#xA;= 1.33&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can convert 1.33 to decibels:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 10 \cdot \log(1.33) = 1.24\:\mathrm{dB} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This also raises a point of common practice: since you are calculating a &lt;em&gt;loss&lt;/em&gt;, it's conventional to arrange the calculation so that the result expressed in decibels is &lt;em&gt;negative&lt;/em&gt;. A negative number in decibels corresponds to a fraction less than 1. Example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 11.76\:\mathrm{dB(W)} - 13\:\mathrm{dB(W)} = -1.24\:\mathrm{dB} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More generally:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{power out} \ -\  \text{power in} = \text{loss or gain in decibels} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which, if you think about the identity above, is equivalent to&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {\text{power out} \over \text{power in}} = \text{loss or gain as a ratio} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This makes the ratio not 1.33 as calculated above, but 1/1.33 or 0.752. This allows us to calculate losses in watts by multiplication. If we were to put 100W into this system, for example...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 100\:\mathrm W \cdot 0.752 = 75.2 \:\mathrm W $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;...we'd get 75.2W out.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="29" LastEditDate="2015-01-18T14:51:59.643" LastActivityDate="2015-01-18T14:51:59.643" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3513" PostTypeId="1" AcceptedAnswerId="3519" CreationDate="2015-01-17T12:34:14.823" Score="5" ViewCount="763" Body="&lt;p&gt;I tried making a CQ on 20 m, 14.060 MHz (the QRP CQ frequency) and parallel to that I had a WebSDR on my computer just to keep an eye on the band. I saw someone responding on the WebSDR, which is rather close to my hometown; however, I couldn't hear him on my receiver and the signal on the WebSDR was too vague to copy. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What should I do in such a situation (apart from improving my receiver)? Should I just send my CQ sequence again and hope the other side understands that I can't hear him, and stops trying or increases power? Or should I send another sequence to say that I know there is someone, but I can't copy him?&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorUserId="76" LastEditDate="2015-01-17T16:02:25.403" LastActivityDate="2015-01-18T19:10:57.460" Title="What if someone responds to my CQ, but I can't hear him?" Tags="&lt;cw&gt;&lt;procedure&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3514" PostTypeId="2" ParentId="3513" CreationDate="2015-01-17T20:11:12.567" Score="5" Body="&lt;p&gt;Well I'd say that there is definitely nothing wrong with just continuing to call CQ. After all, if you didn't have the SDR hearing the other station, you wouldn't know that the other guy is there calling you, so there must not be any had feelings for your lack of response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My practical experience here is mostly related to SSB contests, but I think it could apply in your case as well. Normally, when I'm calling CQ and think that I hear another station answering, but I'm not sure, I'd reply with QRZ or partial callsign, if available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually it would be something like &lt;code&gt;QRZ? de MYCALL&lt;/code&gt; or &lt;code&gt;Question mark Question Mark One Alpha Question mark, this is MYCALL&lt;/code&gt;, depending on how well I copied the sign. This way, you may indicate that you did hear something and ask the other station to fill in the blanks. One problem with the QRZ part is that some users may use QRZ instead of CQ and this way the hint may be misunderstood, so do try to send partial callsign if available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do reply, and using SDR determine that the other station copied your reply, but is still too weak for you to copy, you may want to make it known to other station that the signal is too  weak to be workable. I can't think of a widely-used Q-code to indicate very weak signal, but some things you could try would be sending QRK 1 and then QRS PSE. QRK is the code for signal readability, with 1 being the lowest grade and QRS is invitation to increase output power. Another alternative that comes to mind would be to send QSA 1 and QRO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The procedure usually lasts until one of the sides of this potential QSO runs out of nerves or if the required contact data are successfully transferred. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do determine that reading the other station is too difficult, do try to make it known to other stations. Send something like sorry, too weak and continue  calling CQ in hope that someone else may respond. &lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2015-01-17T23:46:22.580" LastActivityDate="2015-01-17T23:46:22.580" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3515" PostTypeId="2" ParentId="2034" CreationDate="2015-01-17T21:42:39.637" Score="2" Body="&lt;p&gt;There are some recordings here of ships and coast stations from the 'olden days' &lt;a href=&quot;http://coastradio.info/recordings.html&quot; rel=&quot;nofollow&quot;&gt;http://coastradio.info/recordings.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4108" LastEditorUserId="218" LastEditDate="2015-01-19T12:53:37.203" LastActivityDate="2015-01-19T12:53:37.203" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3516" PostTypeId="2" ParentId="3513" CreationDate="2015-01-17T22:13:34.883" Score="1" Body="&lt;p&gt;That is an interesting questions.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only thing I would suggest is ask them to increase power if possible.  However if you are not hearing them on your receiver odds are they will not be able to add enough power to copy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also send a message of no copy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you didn't have the WebSDR, then you won't even know someone is calling you.  This is the case 100s of times a day.&lt;/p&gt;&#xA;" OwnerUserId="4083" LastActivityDate="2015-01-17T22:13:34.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3517" PostTypeId="2" ParentId="3513" CreationDate="2015-01-17T22:26:45.277" Score="0" Body="&lt;p&gt;Consider how much power you are sending. Assuming you are sending QRP as well, you may be at the limit of effective range and he may be only barely able to copy your signal — a clue of propagation conditions. I think I would assume a miss as no signal on receiver and try again.&lt;/p&gt;&#xA;" OwnerUserId="4109" LastEditorUserId="76" LastEditDate="2015-01-18T19:10:57.460" LastActivityDate="2015-01-18T19:10:57.460" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3518" PostTypeId="1" AcceptedAnswerId="3520" CreationDate="2015-01-18T04:32:00.470" Score="8" ViewCount="4555" Body="&lt;p&gt;Living in an apartment, I'm struggling to get good antennas set up, especially for HF.  Worse yet, I'm not allowed external antennas (but am willing to try something low profile on the balcony), my apartment is built with stucco (with the &quot;chicken wire&quot; embedded in it), and my window frames are all aluminum.  I have a balcony, but it's got a low (3') wall made of stucco inside and out (2 layers of mesh!) topped with a metal railing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried a dual-hamstick dipole for 20M, but was placing it only 24&quot; over the balcony floor, and this is below the edge of the wall.  Tuning it was basically impossible, though I eventually could get 2:1 at one frequency.  The balcony is about 4 feet deep and 10 feet long, and there is another floor above mine (so no roof access, and there's poured concrete above).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So how far away does metal have a significant impact on my antennas?  I'm assuming it's design- and frequency-dependent, but I'm looking for resources that can help me figure out approximate clearances that are needed.  Mostly I'd like to work at 20M, 10M, and 2M.  (My balcony is way too small to think about 40M and lower.)&lt;/p&gt;&#xA;" OwnerUserId="1343" LastEditorUserId="76" LastEditDate="2016-07-12T14:01:37.230" LastActivityDate="2019-11-25T13:50:46.270" Title="How far does an antenna need to be from metal to avoid problems?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3519" PostTypeId="2" ParentId="3513" CreationDate="2015-01-18T05:30:17.120" Score="6" Body="&lt;p&gt;Sending simply &quot;?&quot; is sufficient to request the station send his call again. If you want to be a little more verbose, &quot;QRZ?&quot; means &quot;who is calling me?&quot;. If you can copy part of the call you can also respond with the unknown parts replaced with question marks: &quot;AC8? DE MYCALL&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are working the QRP calling frequency you should expect most of your contacts to be difficult, and making repeated attempts isn't unusual. HF conditions can change rapidly, and sometimes all you need to do is wait a minute. It's not uncommon to send key information (names, calls, locations, RST signal reports) 3 or 5 times if conditions are poor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you just can't make it work, you can try to communicate that. &quot;QRN&quot; (I'm troubled by natural noise), &quot;QRM&quot; (I'm troubled by man-made interference) and &quot;QSB&quot; (I'm troubled by fading) can help you communicate your specific problem, though if conditions are poor it may be futile. In the case of another interfering station, you might &quot;QSY&quot; (change frequency) to some clear frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, you can just keep calling CQ. It's not unusual on HF to be unable to make a contact. No one will be offended. The other station will infer that you can't copy their transmissions and either giver up or increase power, aim a directional antenna, or otherwise attempt to improve conditions.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-18T05:30:17.120" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3520" PostTypeId="2" ParentId="3518" CreationDate="2015-01-18T11:30:01.203" Score="2" Body="&lt;p&gt;It sounds like any antenna you can build in this situation is going to be a compromise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Distances are going to be relative to wavelength, so an HF antenna will be more difficult than VHF or UHF. For the antenna to be really in the clear, two wavelengths is a good rule of thumb. You can probably get as close as a quarter wavelength and still make things work with some adjustments to the tuning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use the metal parts of your structure as part of the antenna, if that makes things easier. For example, I bet a 2m whip on the corner of the balcony could work well enough, with the metal railing being the ground &quot;plane&quot;. It's far from ideal of course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF is going to be tricky, no way around it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-18T11:30:01.203" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3521" PostTypeId="2" ParentId="3502" CreationDate="2015-01-18T14:49:05.407" Score="1" Body="&lt;p&gt;Yes, an antenna can be part of a circuit, but it's not as simple as the usual resistors, capacitors, diodes, etc. that you're used to. You need a different set of tools to understand how an antenna works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This distinction is sometimes referred to as &quot;lumped&quot; vs &quot;distributed&quot; elements. In circuits, the elements are either lumped elements (resistors, capacitors, inductors, transistors, etc) or have lumped ports (transmission lines). Distributed elements are modeled by using Maxwell's equations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a physicist's perspective, everything you need to know about electronic circuits is contained in Maxwell's equations. You could apply them to simple resistive DC circuits and, after a lot of grungy math, come up with simple equations that describe the behavior of those circuits. But you'd hate it. So we use the &quot;lumped matter discipline&quot; -- if we assume that we can treat circuit elements as discrete lumps of matter, that the magnetic flux around each lump doesn't change, that the charge inside each lump doesn't change, and that the circuit elements are much smaller than the wavelength of the signals that we're dealing with, then we can simplify Maxwell's equations down to Kirchoff's laws, Ohm's law, and the various other tools that you've learned to use for analyzing circuits. For an antenna, the third assumption obviously doesn't hold; neither does the first. So the usual tools for circuit analysis don't apply, and you have to fall back to more basic, but more complex, tools.&lt;/p&gt;&#xA;" OwnerUserId="105" LastEditorUserId="4241" LastEditDate="2015-02-13T17:17:11.813" LastActivityDate="2015-02-13T17:17:11.813" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3523" PostTypeId="1" CreationDate="2015-01-18T18:53:58.450" Score="10" ViewCount="5150" Body="&lt;p&gt;My shack is on a second story, really far away from the house ground. To run a ground from my equipment to the outside/ground is a run of at least 60-75 feet. The antenna is at least 100 feet away as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I ground this system? I cannot reach the house ground. I can ground the antenna at its base; can I run a ground from the shack to the outside to a rod? Do I tie all my equipment to one point and bring this ground wire to the outside? What wire should I use?&lt;/p&gt;&#xA;" OwnerUserId="4113" LastEditorUserId="76" LastEditDate="2015-01-18T19:32:34.760" LastActivityDate="2018-12-22T11:22:52.040" Title="Grounding a second-story shack with an outdoor antenna" Tags="&lt;grounding&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3524" PostTypeId="2" ParentId="3523" CreationDate="2015-01-19T01:00:39.240" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How do I ground this system?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Don't. You can't, anyway. Whatever connection you make will be long enough that it will be more of an antenna than a ground. But don't worry, you don't really need a ground anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why would you need a ground? One reason is lightning protection, but that's probably not what you hand in mind, and it's more complicated than running some wires to some dirt. You should &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;read more about it in a separate question&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other reason is to give common-mode currents some place to go. Due to &lt;a href=&quot;http://en.wikipedia.org/wiki/Charge_conservation&quot; rel=&quot;noreferrer&quot;&gt;the law of charge conservation&lt;/a&gt;, any common-mode current must be accompanied an opposite current somewhere else in the universe, and usually that thing is the Earth. By grounding the feedline somewhere, you short out these currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it's really better if you just have no common-mode currents in the first place. Anywhere there's common-mode current on your feedline, it's radiating. And by &lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_%28electromagnetism%29&quot; rel=&quot;noreferrer&quot;&gt;reciprocity&lt;/a&gt;, that means it's also receiving. In effect, it's part of the antenna, and usually that's not what you expect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, by not having a good way to ground your station, you are forced to confront the source of the problem, which is what everyone should be doing anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Put &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;baluns on your antennas if they need them&lt;/a&gt;. With a properly current-balanced antenna, you won't have any significant common-mode currents due to your transmissions, so you won't have any problems with RF in the shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that done, you will probably be in better shape than most stations that run a wire to a rod in the dirt without any thought. For further reading, I suggest &lt;a href=&quot;http://www.w8ji.com/rfi_rf_grounding.htm&quot; rel=&quot;noreferrer&quot;&gt;W8JI's article on station grounding&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-01-19T01:55:09.507" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3525" PostTypeId="1" CreationDate="2015-01-21T07:09:50.330" Score="2" ViewCount="273" Body="&lt;p&gt;I'm using a square loop antenna on the rooftop of approximately 15 square meter area.&#xA;I use it to communicate with a group of mobile VHF radios using a station room.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Right now I'm planning to build in the same building a separate radio room that will use a different frequency, and I'm wondering, can a second station with a different frequency use the same antenna, or do I need a separate antenna for it to work?&lt;/p&gt;&#xA;" OwnerUserId="4122" LastActivityDate="2015-03-08T02:18:54.373" Title="Using square loop VHF antenna for two different stations/frequency?" Tags="&lt;diy&gt;&lt;vhf&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3526" PostTypeId="1" AcceptedAnswerId="3530" CreationDate="2015-01-21T15:34:01.943" Score="1" ViewCount="512" Body="&lt;p&gt;Should I or should I not replace an aluminum wire (defective) with a copper wire on a &lt;a href=&quot;http://www.hy-gain.com/Downloads/index.php?productid=LP-1010A&amp;amp;filename=LP-1010A.pdf&amp;amp;company=hygain&quot; rel=&quot;nofollow&quot;&gt;Hy-Gain LP-1010&lt;/a&gt; log periodic ham radio antenna which is made entirely of aluminum with stainless fasteners?  There is a wire connecting each element to the boom. This is a 14 element antenna requiring 28 paired wires.&lt;/p&gt;&#xA;" OwnerUserId="4126" LastEditorUserId="2988" LastEditDate="2015-01-25T01:34:11.533" LastActivityDate="2015-02-27T15:20:28.453" Title="Copper Wire connecting log periodic elements to boom" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="12" ContentLicense="CC BY-SA 3.0" />
  <row Id="3528" PostTypeId="2" ParentId="3505" CreationDate="2015-01-21T17:07:29.297" Score="1" Body="&lt;p&gt;Aluminum is cheap, lightweight, stiff, and easy to shape -- properties that pretty much trump any question of its electrical characteristics in this application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also very inert, forming a non-conductive oxide layer that greatly improves the long-term stability of the capacitor.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2015-01-21T17:07:29.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3529" PostTypeId="2" ParentId="3526" CreationDate="2015-01-21T17:33:33.343" Score="1" Body="&lt;p&gt;I don't think such connections have anything to do with its function as an antenna. I think they're just there to make sure there's a DC path to ground for dissipating static electricity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, I would not recommend using copper for these connections, because the copper will corrode, long term, and the galvanic interaction between the two metals will accelerate any corrosion. Stick with aluminum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can get short lengths of aluminum wire by buying a few feet of heavy-gauge power wire (the type used at the service entrance) at a hardware store and pulling individual strands out of it.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2015-01-21T17:33:33.343" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3530" PostTypeId="2" ParentId="3526" CreationDate="2015-01-22T05:43:35.423" Score="3" Body="&lt;p&gt;The wire is probably tinned copper, not aluminium, but the material is not critical to the function of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could replace it with any other wire of similar thickness, but keep the length and shape of the wire exactly the same (within 1 or 2 cm) to avoid affecting the antenna design itself.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take all the usual corrosion precautions at the junction: lightly sand the aluminium immediately before installing the wire. Use stainless steel fasteners. Apply a bit of grease to the joint. You should probably read up some more on best practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While you're at it, check, clean and tighten all joints between pipes and to wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your sudden loss of signal might be the antenna, or something else. A problem with an LPDA is easiest to see in the VSWR; at frequencies near the resonant length of the faulty element the VSWR will shoot up. Test it at both ends of each band and see that it performs as expected. If you have a long feedline, you can do some maths to find the VSWR at the antenna, from the VSWR in the shack.&#xA;In my experience you can test an HF LPDA on the ground, just pointing it up to the sky, or even lying flat on the ground if you have fairly dry soil. Keep it away from long metal objects of course. It won't give exactly the same result as on the tower, but surprisingly close, and good enough for fault finding.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-01-22T05:43:35.423" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3531" PostTypeId="1" CreationDate="2015-01-23T20:21:40.630" Score="9" ViewCount="3917" Body="&lt;p&gt;How does a so-called slot antenna work?  How can one construct one?  What might be the radiation pattern and efficiency compared to a wire antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, if a small slot antenna &quot;works&quot; at mobile phone cellular and radar frequencies, would a very large hole with proper (slot) dimensions in a large enough building (barn, aircraft hanger, office tower) work for some HF bands?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2015-12-15T22:25:02.300" LastActivityDate="2015-12-15T22:25:02.300" Title="How does a slot antenna work?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3532" PostTypeId="2" ParentId="3531" CreationDate="2015-01-24T13:26:38.457" Score="5" Body="&lt;p&gt;If we cut a hole in an infinite conducting plane, and feed it with a voltage source across the center, we get a slot antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/HOh2v.png&quot; alt=&quot;slot antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the slot is between the sides of the voltage source, the currents must travel around the slot. These currents traveling over a large distance are what make it an antenna and not a Faraday screen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Babinet%27s_principle&quot; rel=&quot;noreferrer&quot;&gt;Babinet's principle&lt;/a&gt;, with some refinements from H.G. Booker, relate the slot antenna to a dipole. If, instead of a hole we have a conductor, and we make a very small cut in the center of this conductor so we can put a voltage source across it, we have a dipole. This dipole will be very similar to the slot, except:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;magnetic and electric fields are exchanged,&lt;/li&gt;&#xA;&lt;li&gt;as a consequence of the above, polarization is rotated, and&lt;/li&gt;&#xA;&lt;li&gt;the feedpoint impedance is different.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The impedance of the slot antenna ($Z_S$) is related to the equivalent dipole ($Z_D$) by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_S Z_D = { \eta^2 \over 4} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\eta$ is &lt;a href=&quot;http://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;noreferrer&quot;&gt;the impedance of free space&lt;/a&gt;, about 120πΩ. So if the impedance of a long, thin, half-wave dipole is about 72Ω, then a long, thin slot has an impedance of about:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {(120\pi\:\Omega)^2 \over 4\cdot72\:\Omega } \approx 493\:\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the slot is made wider, this is equivalent to making a dipole thicker, and it has the same effect: increased bandwidth and decreased length at resonance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, we don't make slot antennas out of infinite conducting planes since infinite planes are so hard to find. A sheet that was many wavelengths big, such that there was negligible current far away from the slot, would be a good approximation. However there wouldn't be much point to it: the equivalent dipole would be smaller. Perhaps most of the slot antennas of this type are undesired, such as interruptions in the ground plane of a PCB, or undesired holes in something that should be acting as a shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For slots that are made to be intentional antennas, they are usually slots in a &lt;a href=&quot;http://www.antenna-theory.com/antennas/aperture/slottedWaveguide.php&quot; rel=&quot;noreferrer&quot;&gt;waveguide&lt;/a&gt; or &lt;a href=&quot;http://www.antenna-theory.com/antennas/aperture/slot2.php&quot; rel=&quot;noreferrer&quot;&gt;a box&lt;/a&gt;. Of course this changes the radiation pattern and the impedance, and the feed is not a voltage source directly across the sides but provided by the currents in the waveguide, but the basic mechanism of how they work remains the same.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-24T13:26:38.457" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3533" PostTypeId="2" ParentId="514" CreationDate="2015-01-25T10:36:56.210" Score="-1" Body="&lt;p&gt;IC-2GAT has a spec to 16V operation.&#xA;Suggest it might run well on 4 lithium batteries - battery pack for a helicopter or car.&#xA;11.1V 3 cells or 14.8V 4 cells.&#xA;The BP4 battery pack took AA size dry cells - 4 of these could be replaced with Lithium.  Use a electric model charger of some sort.  14500 Li Battery same size as AA.&lt;/p&gt;&#xA;" OwnerUserId="4147" LastEditorUserId="29" LastEditDate="2015-01-25T12:34:06.993" LastActivityDate="2015-01-25T12:34:06.993" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3534" PostTypeId="2" ParentId="3523" CreationDate="2015-01-25T13:56:45.903" Score="4" Body="&lt;p&gt;The misconception about grounding is widespread. In the real world outside of hobbies, grounding is an art depending on each situation and location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have no grounds running down my 3rd floor condo, but I do have solid point-to-point grounding systems for two consoles of radio and computer gear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do not depend on your house power wiring grounding pin/points as they are often loosely connected, corroded or simply not on the same common grounding points.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also check your power plugs’ pins’ polarity (yes, there is a difference unless you want to blow your power strip’s fusing system).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I run grounding straps to a common grounding node: a length of metal braided wire and a terminal block cheaply purchased from a hardware store. That has done the trick up to power levels of 600-1.2 kW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck, and experiment, as grounding is not an exact science no matter how many articles regurgitate the old wives tales about grounding everything to the outside grounding point - a 1830 ham byline too often quoted by newbies writing on these blogs.&lt;/p&gt;&#xA;" OwnerUserId="4148" LastEditorUserId="76" LastEditDate="2015-01-25T15:38:02.830" LastActivityDate="2015-01-25T15:38:02.830" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3535" PostTypeId="2" ParentId="3487" CreationDate="2015-01-25T16:06:01.633" Score="4" Body="&lt;p&gt;How about the software made by Baofeng for the UV-5R?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.miklor.com/uv5r/UV5R-Software.php&quot; rel=&quot;nofollow&quot;&gt;http://www.miklor.com/uv5r/UV5R-Software.php&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used it and works fine when you figure out how to put it into English mode. The instructions for that are on the link, in the middle of the page.&lt;/p&gt;&#xA;" OwnerUserId="4149" LastActivityDate="2015-01-25T16:06:01.633" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="3536" PostTypeId="2" ParentId="221" CreationDate="2015-01-25T21:33:11.003" Score="0" Body="&lt;p&gt;In Javascript, I didn't find a grid square library with Google, though obviously there is existing code on several related ham mapping websites.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I coded up &lt;a href=&quot;https://gist.github.com/DrPaulBrewer/4279e9d234a1bd6dd3c0&quot; rel=&quot;nofollow&quot;&gt;HamGridSquare.js&lt;/a&gt; based in part on K6WRU's answer above.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It passes his tests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The function definitions are MeteorJS framework compatible and supports various  inputs. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A call to &lt;code&gt;latLonFromGridSquare()&lt;/code&gt; can have two numeric or string parameters &lt;code&gt;(lat,lon)&lt;/code&gt; or a single parameter that is an array or object with numeric, string, or function properties &lt;code&gt;([lat,lon])&lt;/code&gt; &lt;code&gt;({lat: nnn, lon: nnn})&lt;/code&gt; &lt;code&gt;({lat: latGetterFunc, lon: lonGetterFunc})&lt;/code&gt;.  The latter should be compatible with the LatLon objects created by Chris Veness' LatLon JS library.  Chris' LatLon library provides a way to calculate distances and bearings.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;// HamGridSquare.js&#xA;// Copyright 2014 Paul Brewer KI6CQ&#xA;// License:  MIT License http://opensource.org/licenses/MIT or CC-BY-SA&#xA;//&#xA;// Javascript routines to convert from lat-lon to Maidenhead Grid Squares&#xA;// typically used in Ham Radio Satellite operations and VHF Contests&#xA;//&#xA;// Inspired in part by K6WRU Walter Underwood's python answer&#xA;// http://ham.stackexchange.com/a/244&#xA;// to this stack overflow question:&#xA;// How Can One Convert From Lat/Long to Grid Square&#xA;// http://ham.stackexchange.com/questions/221/how-can-one-convert-from-lat-long-to-grid-square&#xA;//&#xA;&#xA;latLonToGridSquare = function(param1,param2){&#xA;  var lat=-100.0;&#xA;  var lon=0.0;&#xA;  var adjLat,adjLon,GLat,GLon,nLat,nLon,gLat,gLon,rLat,rLon;&#xA;  var U = 'ABCDEFGHIJKLMNOPQRSTUVWX'&#xA;  var L = U.toLowerCase();&#xA;  // support Chris Veness 2002-2012 LatLon library and&#xA;  // other objects with lat/lon properties&#xA;  // properties could be getter functions, numbers, or strings&#xA;  function toNum(x){&#xA;    if (typeof(x) === 'number') return x;&#xA;    if (typeof(x) === 'string') return parseFloat(x);&#xA;    if (typeof(x) === 'function') return parseFloat(x());&#xA;    throw &quot;HamGridSquare -- toNum -- can not convert input: &quot;+x;&#xA;  }&#xA;  if (typeof(param1)==='object'){&#xA;    if (param1.length === 2){&#xA;      lat = toNum(param1[0]);&#xA;      lon = toNum(param1[1]);&#xA;    } else if (('lat' in param1) &amp;amp;&amp;amp; ('lon' in param1)){&#xA;      lat = toNum(param1.lat);&#xA;      lon = toNum(param1.lon);&#xA;    } else if (('latitude' in param1) &amp;amp;&amp;amp; ('longitude' in param1)){&#xA;      lat = toNum(param1.latitude);&#xA;      lon = toNum(param1.longitude);&#xA;    } else {&#xA;      throw &quot;HamGridSquare -- can not convert object -- &quot;+param1;&#xA;    }&#xA;  } else {&#xA;    lat = toNum(param1);&#xA;    lon = toNum(param2);&#xA;  }&#xA;  if (isNaN(lat)) throw &quot;lat is NaN&quot;;&#xA;  if (isNaN(lon)) throw &quot;lon is NaN&quot;;&#xA;  if (Math.abs(lat) === 90.0) throw &quot;grid squares invalid at N/S poles&quot;;&#xA;  if (Math.abs(lat) &amp;gt; 90) throw &quot;invalid latitude: &quot;+lat;&#xA;  if (Math.abs(lon) &amp;gt; 180) throw &quot;invalid longitude: &quot;+lon;&#xA;  adjLat = lat + 90;&#xA;  adjLon = lon + 180;&#xA;  GLat = U[Math.trunc(adjLat/10)];&#xA;  GLon = U[Math.trunc(adjLon/20)];&#xA;  nLat = ''+Math.trunc(adjLat % 10);&#xA;  nLon = ''+Math.trunc((adjLon/2) % 10);&#xA;  rLat = (adjLat - Math.trunc(adjLat)) * 60;&#xA;  rLon = (adjLon - 2*Math.trunc(adjLon/2)) *60;&#xA;  gLat = L[Math.trunc(rLat/2.5)];&#xA;  gLon = L[Math.trunc(rLon/5)];&#xA;  return GLon+GLat+nLon+nLat+gLon+gLat;&#xA;}&#xA;&#xA;testGridSquare = function(){&#xA;  // First four test examples are from &quot;Conversion Between Geodetic and Grid Locator Systems&quot;,&#xA;  // by Edmund T. Tyson N5JTY QST January 1989&#xA;  // original test data / citations by Walter Underwood K6WRU&#xA;  // last test and coding into Javascript from Python by Paul Brewer KI6CQ&#xA;  var testData = [&#xA;    ['Munich', [48.14666,11.60833], 'JN58td'],&#xA;    ['Montevideo', [[-34.91,-56.21166]], 'GF15vc'],&#xA;    ['Washington, DC', [{lat:38.92,lon:-77.065}], 'FM18lw'],&#xA;    ['Wellington', [{latitude:-41.28333,longitude:174.745}], 'RE78ir'],&#xA;    ['Newington, CT (W1AW)', [41.714775,-72.727260], 'FN31pr'],&#xA;    ['Palo Alto (K6WRU)', [[37.413708,-122.1073236]], 'CM87wj'],&#xA;    ['Chattanooga (KI6CQ/4)', [{lat:function(){ return &quot;35.0542&quot;; }, &#xA;                              lon: function(){ return &quot;-85.1142&quot;}}], &quot;EM75kb&quot;]&#xA;  ];&#xA;  var i=0,l=testData.length,result='',thisPassed=0,totalPassed=0;&#xA;  for(i=0;i&amp;lt;l;++i){&#xA;    result = latLonToGridSquare.apply({}, testData[i][1]);&#xA;    thisPassed = result===testData[i][2];&#xA;    console.log(&quot;test &quot;+i+&quot;: &quot;+testData[i][0]+&quot; &quot;+JSON.stringify(testData[i][1])+&#xA;                &quot; result = &quot;+result+&quot; expected= &quot;+testData[i][2]+&#xA;                &quot; passed = &quot;+thisPassed);&#xA;    totalPassed += thisPassed;&#xA;  }&#xA;  console.log(totalPassed+&quot; of &quot;+l+&quot; test passed&quot;);&#xA;  return totalPassed===l;&#xA;}&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="70" LastActivityDate="2015-01-25T21:33:11.003" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3537" PostTypeId="1" CreationDate="2015-01-26T04:00:54.737" Score="5" ViewCount="2626" Body="&lt;p&gt;What is the best (or standard) way to get coax from the radio in the car to the outside of the car without smashing it and damaging the line? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I just put it through the door crack, it seems to look pretty bad and I don't want to damage my new magmount.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2015-01-28T12:45:22.867" LastActivityDate="2015-01-28T13:35:16.237" Title="How to feed coax from inside car?" Tags="&lt;mobile&gt;&lt;coaxial-cable&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3538" PostTypeId="2" ParentId="3496" CreationDate="2015-01-26T04:56:00.153" Score="2" Body="&lt;p&gt;I only scanned that whole quote.  I have my father's W9EHS SK, FT crystal grinding equipment.  It has two special grinding compounds and the two plates.  One of the plates has a rosette-like shaped indent that helps guide the blank in the figure 8 pattern. There is a special FT holder that allowed easy insertion and removal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At times, the edges had to be ground, usually to stop unwanted modes. An acid was also used, IIR to finish it off and, I think&amp;lt; help prevent some spurious modes or possible start-up problems.  I've forgotten much about those crystals...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern crystals are quite a bit different, though operating to the same principles.  I didn't know these FT crystals were AT cut and I only have some design using modern, mostly AT cut crystals, but some other cuts as well as the tuning fork (Statek) types.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe I am the first to have a synthesized 2 meter hand held back in the 70's and had to learn about crystals for a work project that led to that PLL synthesizer.&lt;/p&gt;&#xA;" OwnerUserId="4150" LastEditorUserId="218" LastEditDate="2015-01-26T12:24:21.863" LastActivityDate="2015-01-26T12:24:21.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3539" PostTypeId="2" ParentId="3500" CreationDate="2015-01-26T06:36:04.523" Score="1" Body="&lt;p&gt;When you use this stuff on the job, it becomes second nature...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope these other ways to look at in general help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thing to remember is that dB is only used to represent a &lt;em&gt;ratio of two powers&lt;/em&gt;. That is the definition.  A &lt;strong&gt;bel&lt;/strong&gt; is a ratio of power of 10 to 1; after Alexender Graham Bell. That is why the B is capital and the d is not.&#xA; (see note below)  A decibel is one tenth of a bel. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A ratio means that you divide one by the other (when expressing power in watts).  The reference is on the bottom (denominator) of the ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That 5 W difference between input and output is not a ratio of 5 W to anything, so converting it to dB makes no sense, it is a &lt;strong&gt;difference&lt;/strong&gt;, not a ratio. I can't think of a time when the actual amount lost is expressed that way.  We usually use -1.25 dB or express it as an efficiency of 75%. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We only say that there is 1.24dB of loss (actually 1.2499, or 1.25), we (engineers) also can say that it has a &quot;gain&quot; of -1.25 dB.  These represent &lt;strong&gt;ratios&lt;/strong&gt; of 1.33 and 0.75 respectively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You subtracted in the reverse order you should have.  When calculating the difference of two things you subtract the reference from your number. Since we usually reference the output to the input, the difference is &lt;em&gt;minus 5&lt;/em&gt; watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please note the following: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;20 to 15 watts is a loss of 5 W, but a ratio of 0.75  and -1.25 dB.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;1 W to 0.75 W is a loss of 0.25 W, but a ratio of 0.75  and -1.25 dB.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Going to dB allows you to add or subtract numbers when looking at gains and losses..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;absolute&quot; versions are still ratios referenced to a known power that is shown by the last letter: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;dBm references a mW&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;dBW reference is a watt&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;TV engineers use dBk = reference to a kW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Note:&lt;/em&gt;  For the pedants, we do use dB to represent voltages (and sometimes currents) in places like OP-Amp designs, where the powers are not being calculated. The powers and impedances are totally ignored in many cases.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this &lt;em&gt;is improper&lt;/em&gt; use of dB .&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Double however, those of us who do that know what we mean and that makes it OK.  This is because there are places where only the voltages matter and powers are unimportant, and using dB is still useful in the grand scheme.&lt;/p&gt;&#xA;" OwnerUserId="4150" LastEditorUserId="4150" LastEditDate="2015-01-27T22:33:02.617" LastActivityDate="2015-01-27T22:33:02.617" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3540" PostTypeId="2" ParentId="3537" CreationDate="2015-01-26T12:34:02.247" Score="2" Body="&lt;p&gt;Best would be to cut a hole in the car and feed the coax through that. There are antenna mounts designed to bolt to a car body panel and take care of structurally supporting the antenna and forming a weatherproof seal. NMO mounts are pretty common for VHF antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't want to modify your car in any way, use a section of small diameter coax to slip through the rubber seal around a door or trunk if your feedline is too fat. You can use small connectors like SMA to connect it to your feedline. Just be sure the connections are appropriately weatherproofed to avoid getting water in the feedline.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-01-28T13:35:16.237" LastActivityDate="2015-01-28T13:35:16.237" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3541" PostTypeId="2" ParentId="3537" CreationDate="2015-01-26T17:24:21.470" Score="1" Body="&lt;p&gt;The other alternative is to go through the trunk, which often has easier access than other locations on the car.You can usually get access to the trunk from most modern cars, and that would allow you to have easy access.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-01-26T17:24:21.470" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3542" PostTypeId="1" AcceptedAnswerId="3544" CreationDate="2015-01-26T17:06:36.413" Score="4" ViewCount="240" Body="&lt;p&gt;I have a 20m CW transceiver with an option for a wide or a narrow filter. When the narrow filter is selected, a crystal ladder filter is used in the intermediate frequency filter, between two mixers. When the wide filter is selected, this crystal filter is bypassed and there exists a direct link (that is, only a capacitor) between the two mixers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use the wide filter to search for signals by rapidly increasing frequency from 14.000MHz to 14.075MHz. When I found a good signal, I tune it to have the right pitch, and switch to the narrow filter to have less noise and other signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two frequencies I can tune into to find this pitch that is convenient to listen on, with a difference of about twice the pitch frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I noticed that when I use the lower frequency, when I switch to the narrow filter, the signal is weaker than when using the higher frequency, to the point that only very clear signals can be copied. Can this be explained theoretically, and will this happen with any transceiver, or is it more likely that this is specific to this transceiver?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My explanation would be that the higher frequency, yielding a stronger signal on the narrow filter, is the carrier frequency. The other frequency would be the carrier minus twice the pitch frequency, which is then much weakened by the crystal filter. If the filter is bypassed though, the next mixer outputs both the sum and the complement of its inputs, so the two signals are equally strong. Is this correct?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RX module is from &lt;a href=&quot;http://kd1jv.qrpradio.com/&quot; rel=&quot;noreferrer&quot;&gt;KD1JV&lt;/a&gt;'s ATS 3B. I'm not sure if there's copyright on it, but the idea is quite straightforward: RF enters the first mixer, an NE602, together with the output of a DDS. Then the output of the mixer passes through the (4.9152MHz) crystal ladder filter (or not) and goes to the next mixer, a second NE602, together with the output of a controllable oscillator (with a trimmer cap), to adjust the pitch.&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorDisplayName="user885" LastEditDate="2015-01-26T19:01:02.003" LastActivityDate="2015-01-26T20:10:26.687" Title="Listening below the carrier frequency gives a weaker signal than above the carrier frequency - why?" Tags="&lt;transceiver&gt;&lt;cw&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="3543" PostTypeId="1" CreationDate="2015-01-26T18:40:26.353" Score="2" ViewCount="115" Body="&lt;p&gt;I'm a hobbyist and I'm currently thinking about building a CubeSat. I'm currently designing PCBs, casing, etc. I was wondering what variables are involved with sending data to and from 250 km - 350 km orbit using a frequency of 2.4 GHz and how I should calculate how far the signal will reach.&lt;/p&gt;&#xA;" OwnerUserId="4151" LastEditorUserId="76" LastEditDate="2015-01-26T19:43:00.950" LastActivityDate="2015-02-10T10:13:35.487" Title="Transmitting to and from low earth orbit?" Tags="&lt;propagation&gt;&lt;satellites&gt;&lt;uhf&gt;&lt;range&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2015-02-14T18:41:22.103" ContentLicense="CC BY-SA 3.0" />
  <row Id="3544" PostTypeId="2" ParentId="3542" CreationDate="2015-01-26T18:55:49.453" Score="2" Body="&lt;p&gt;The behavior you see is completely expected with the receiver design you describe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without either additional filtering or quadrature signals, the output of a mixer always contains both the sum and difference of the input frequencies. Therefore, the receiver you have described processes the signal as follows (all variable names are made up and probably nonstandard):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Assume there is an input signal at frequency $X$ (as well as other signals that aren't the one you're tuning to).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Your DDS VFO produces a reference signal at $Y$ which, when properly tuned, is approximately $X - I$ (where $I$ is the intermediate frequency of 4.9152 MHz).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;First mixer combines these signals to $X+Y$ and $\lvert X-Y\rvert$. $X+Y$ is far out of band (~18 MHz for your description) and either there is a low-pass filter to remove it (which doesn't need to be particularly sharp) or it can just be disregarded because it won't be made audible by later stages (I'm not sure). $X-Y$ is approximately $I$.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Crystal filter at frequency $I$ removes everything not close to $I$, thus selecting the signal of interest $X-Y$.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Second oscillator (BFO) produces a reference signal at frequency $I + P$ where $P$ is the pitch you actually hear.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Second mixer combines these signals to $X-Y+(I+P)$ and $\lvert X-Y-(I+P)\rvert$. The first is at RF, the second is at audio frequencies, so only the second will be reproduced by the speaker.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Now work out the consequences of this. Suppose you're tuned exactly on frequency: $Y = X - I$. Then the output of the second mixer is&#xA;$$&#xA;\lvert X-Y-(I+P)\rvert = \lvert X-(X-I)-(I+P)\rvert = \lvert I-(I+P)\rvert = \lvert -P\rvert = P&#xA;$$&#xA;so you hear the pitch the BFO is set for. If $Y$ is a little bit different then the pitch is a little bit different — all of these frequency changes are &lt;em&gt;linear&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Suppose you're instead tuned $2P$ too low: $Y = X - I - 2P$. Then the output of the second mixer is&#xA;$$&#xA;\lvert X-Y-(I+P)\rvert = \lvert X-(X-I-2P)-(I+P)\rvert = \lvert I+2P-(I+P)\rvert = \lvert P\rvert = P&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is, you hear the same pitch. However, since $X - Y$ is farther from $I$ in this case, the crystal filter will attenuate it much more. If the crystal filter is bypassed, this effect does not occur and the two cases are symmetric.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you have can be described as a &lt;em&gt;double-sideband (DSB)&lt;/em&gt; receiver, which is a SSB receiver without the filtering that selects between USB and LSB. When you add the crystal filter, it's like a lower-sideband SSB phone receiver, except that a SSB receiver would have a wider filter for the 3 kHz voice bandwidth rather than a narrow filter trying to select a single CW signal, and the VFO is calibrated so that it shows $Y \pm P$ (plus or minus depending on selected sideband) instead of $Y$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to tune your receiver to a SSB phone (voice) signal, then (assuming the VFO &amp;amp; filters go that high and there's enough audio bandwidth to hear anything intelligible at all) you would hear a difference between the two frequencies: using the higher frequency (lower sideband reception), the spectrum will be reversed (garbled voice) whereas the lower frequency will preserve the spectrum and sound reasonable (if overly filtered).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-01-26T20:10:26.687" LastActivityDate="2015-01-26T20:10:26.687" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3545" PostTypeId="2" ParentId="3537" CreationDate="2015-01-27T00:40:33.420" Score="1" Body="&lt;p&gt;Best position for an antenna is the middle of the roof, if you remember your ARRL Technician exam. You can route your cable from somewhere in the dash, to the center or B pillar. From there you can probably use the crevices to get the coax out.&lt;br&gt;&lt;br&gt;You just mentioned coax, so I'm assuming you will be using standard RG-58. It's the typical coax used in many installations. I'm using it too but I have now started mixing it with RG-174. It is a smaller diameter and very flexible coax. It can fit into some areas more nicely but given it's size it can be easily destroyed or frayed (i.e. jammed between two metal objects). RG-174 can be used to replace your standard RG-58, just mind the crevices that it has to enter. Use extra care when routing. Use cable protectors liberally, you can use the ones used for the car's internal wiring or get a new one that will carry only the coax.&lt;br&gt;&lt;br&gt;Another option will be to use a &quot;through window cables&quot;. A through window cable is a very flat piece of cable with connectors at each end. It is available in 50 ohms if you require correct it. Amateur radio antenna manufacturers have this item in their catalogs. Watch your power output when using through window cables so as not to exceed the ratings.&lt;/p&gt;&#xA;" OwnerUserId="1761" LastActivityDate="2015-01-27T00:40:33.420" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3546" PostTypeId="1" AcceptedAnswerId="3547" CreationDate="2015-01-27T00:48:14.677" Score="3" ViewCount="1833" Body="&lt;p&gt;I'm planning to build the &lt;a href=&quot;http://www.wa5vjb.com/references/Cheap%20Antennas-LEOs.pdf&quot; rel=&quot;nofollow&quot;&gt;WA5JVB Cheap LEO Yagi&lt;/a&gt;, which is basically a 2M and a 70cm yagi on the same beam for handheld or tripod use.  I'm thinking to do a 3-element 2M and a 5-element 70cm design, and I'd like to make the entire thing no more than 36&quot; long.  Each antenna is individually ~20&quot;, which obviously won't fit in 36&quot;.  Can I place the director of the 2M antenna ahead of some of the elements of the 440?  Ideally, this would be between D1 and D2 on the smaller yagi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure how much impact the variously sized pieces of metal would have on each other, my biggest concern is that the 2M director would act as a reflector in front of the 70cm driven element.  If this isn't possible, I'll probably just build the 2 + 5 pictured to keep it portable.&lt;/p&gt;&#xA;" OwnerUserId="1343" LastActivityDate="2015-01-27T16:46:43.560" Title="Dual-band yagi on single beam: element positioning" Tags="&lt;antenna-construction&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3547" PostTypeId="2" ParentId="3546" CreationDate="2015-01-27T16:46:43.560" Score="2" Body="&lt;p&gt;You can't just mix the antennas together without doing a lot of work in simulation to make all the interaction work properly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you suspected, the longer 2m elements will upset the 70cm antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, as they are completely separate antennas on the same boom, if you tilt one so they are 90 degrees apart, they will not interact at all, and you can squeeze them onto a shorter boom. In other words, looking from the front, they form a cross.&#xA;This won't be as easy to handle or store, so you might want to find a way to fold the elements of the 2m antenna.&#xA;Make sure that no elements touch or get too close. Keep the baluns apart too, perhaps one forward and one backward.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simulating antennas is fun, but it's a long journey, quite a lot of work for one yagi. The easy-to-use packages cost more than a car, and the free ones are harder to learn. My advice is to start with a published design from a reputable source and build it carefully.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-01-27T16:46:43.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3549" PostTypeId="2" ParentId="3525" CreationDate="2015-01-29T20:50:13.290" Score="1" Body="&lt;p&gt;Yes, the same antenna can be used for two radios. Case in point: full duplex repeaters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one of the radios is a transmitter, then you must somehow direct that transmitter power into the antenna, and not into the other receivers (which would deafen them, or cook them). If all you have are receivers the problem is somewhat simplified because you need to deal with power in only one direction, the power is very low, and each receiver already has a filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will probably use some combination of duplexers, diplexers, power splitters, and other gadgets to accomplish your goal. The specifics depend on the particulars of the situation, such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How far separated are the stations in frequency or time?&lt;/li&gt;&#xA;&lt;li&gt;How much isolation is necessary?&lt;/li&gt;&#xA;&lt;li&gt;How much loss is acceptable?&lt;/li&gt;&#xA;&lt;li&gt;What's the transmit power?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-29T20:50:13.290" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3550" PostTypeId="1" AcceptedAnswerId="3552" CreationDate="2015-01-29T21:45:53.317" Score="2" ViewCount="645" Body="&lt;p&gt;What are some online resources that can be used for finding an HT package? &lt;/p&gt;&#xA;" OwnerUserId="4160" LastEditorUserId="4160" LastEditDate="2015-02-03T19:24:58.753" LastActivityDate="2015-02-03T19:24:58.753" Title="Starter package?" Tags="&lt;ht&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="7" ClosedDate="2015-02-02T16:44:29.030" ContentLicense="CC BY-SA 3.0" />
  <row Id="3551" PostTypeId="1" CreationDate="2015-01-30T03:50:58.930" Score="0" ViewCount="228" Body="&lt;p&gt;I bought an LDG AT-100Pro via CheapHam. Supported equipment: Yaesu FTDX3000D, ZS6BKW multiband antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I bought this as an improvement over the FTDX's internal tuner. The LDG does a great job tuning bands the Yaesu's tuner already tunes. (Yes, I disabled the internal tuner when using the LDG.) However, the LDG will not tune any portion of 80m/75m and will not tune the low end of 10m. It will tune 40m, 20m, 17m and 12m beautifully where the SWR is less than 1.7:1. Big deal; the Yaesu internal tuner already does that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I have the tuner work all of 10m and more of 80m?&lt;/p&gt;&#xA;" OwnerUserId="4175" LastEditorUserId="76" LastEditDate="2015-01-30T22:46:33.950" LastActivityDate="2015-01-30T22:46:33.950" Title="Understanding needed with LDG AT-100Pro" Tags="&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3552" PostTypeId="2" ParentId="3550" CreationDate="2015-01-30T04:45:55.580" Score="4" Body="&lt;p&gt;I am a new Ham (K7BED) and only transmitted for the second time, today. I want to say to purchase a low cost HT (such as a Baofeng UV-5/5R/5RA/whatever) but that was what I did and it was a waste of money and nothing but frustration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just went out today to a local Amateur Radio shop and picked up an Alinco DJ-500T and so far I love it! When comparing the two radios side by side my contact today said that the Alinco wins by far for voice clarity and volume. Plus the Alinco is NOT ridiculously hard to program.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Right now I have the standard antenna on the Alinco.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will repeat what I've seen other's mention and that is to buy a low cost (100-200 dollars, stackexchange can't use dollar signs in answers apparently) dual-band HT such as from Alinco, Yaesu, Kenwood (though I've not found a dual-band Kenwood for under $300 or so new), Icom, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I went to &lt;a href=&quot;http://www.aesham.com/ham-radios-handheld-multiband/&quot; rel=&quot;nofollow&quot;&gt;AES web store&lt;/a&gt; (just one example of many online stores) and browsed through what they have. The first Japanese radio (though it is produced in China I think) was the Alinco DJ-500T for $129.99, then the Yaesu FT-60R which is a little bit bigger and didn't fit my hand as well when I looked at both in-store today. I preferred the Alinco mainly because it fit better in my hand, but also because I saw a video online showing how to manually program the Alinco and I thought it made more sense than the Yaesu.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can, definitely purchase a non-knock-off Diamond or other higher-end antenna for your HT, though honestly I am not unhappy with the stock antenna of this Alinco.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also want to invest in a AA battery pack if the radio you choose has one available for purchase. The Alinco DJ-500T does not have such an accessory available for purchase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also want to invest in a magmount antenna for your car or vehicle. And you may want to consider purchasing extra batteries so that you will never have a dead battery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also consider purchasing the ARRL Repeater Directory or sign up on repeaterbook.com and print off your local repeaters and those that are in the areas you travel in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may want to check into any local ARES/RACES groups and repeater groups as well, as you will find many local Hams who could definitely become your mentors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have yet to see a &quot;starter set&quot; for Ham Radio equipment, but if you decide to purchase from one specific vendor, either online or in-store, I'm sure they can hook you up with the things you will need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know there is a Diamond X50 antenna which usually would be firmly mounted to a pole in your yard for VHF and UHF reception for a VHF/UHF capable transceiver in your home (base station/portable/HT acting as base) if you don't plan on going mobile with the HT. That is just about $100 most places I think.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that as a newbie Ham Radio can be very confusing, and honestly I am still quite confused by many things but I am only a few months into being licensed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All that being said, you will definitely need to be licensed before you transmit for the first time. And the Volunteer Examiners can become your mentors as well. They will have a lot of good advice for you. I live in a tiny population town but I have met a lot of great Hams here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I would go into radio shops (such as Ham Radio Outlet if they have actual storefronts, Universal Radio, American Electronic Supply, and I'm sure there are other small outfits all over the USA and other countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are licensed as a Technician I'd definitely suggest a dual-band HT that handles VHF and UHF (144mhz band and 440m mhz band) and you wanted to spend the money up front you could go with a mobile or portable transceiver that also does the 50mhz (6 meter) band. If you do plan on quickly getting licensed as a General or Extra feel free to purchase equipment that can handle all modes, and HF + 6M + 2M + 70cm and higher if you want. But you will also need to factor in cost for the antennas and connectors and installation, plus antenna analyzers and other equipment you will need.&lt;/p&gt;&#xA;" OwnerUserId="4177" LastEditorUserId="1246" LastEditDate="2015-02-01T13:54:20.933" LastActivityDate="2015-02-01T13:54:20.933" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3553" PostTypeId="2" ParentId="3551" CreationDate="2015-01-30T05:32:42.600" Score="2" Body="&lt;p&gt;Different tuners have different impedance ranges that they can cope with. The quickest clue to this is the shortest wire that they can tune at some low frequency - some require 10m of wire at 80m, some will tune 5m. There's not much you can do about the tuner range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the tuner is not completely democratic about all forms of high SWR - some are easier to tune than others. It's possible that if you shift the impedance from one side of the chart to the other, it might have a better chance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can alter the impedance seen by the tuner by adding (or removing) some coax. If the SWR isn't too high, this might move the impedance into a range that the tuner can cope with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try 1/8, 1/4 or 3/8 wavelengths. Half a wavelength is too much, the impedance is back where it started. Remember the velocity factor of your coax, which is 0.66 for solid PE.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For 80m you could start with 5 or 6 m of coax, and see if it helps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 10m the same piece of coax will be at least a full wavelength, but probably a bit more or less, so it is likely to shake up the impedance there too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moving the tuner closer to the antenna has the same effect, but has the added benefit of reducing the amount of high-swr coax, which will reduce the losses. Ideally the tuner would be right at the antenna, after the balun. Some tuners have a remote control for this purpose, a small box with the same buttons and LEDs. You can easily build this box.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-01-30T06:23:00.023" LastActivityDate="2015-01-30T06:23:00.023" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3554" PostTypeId="1" CreationDate="2015-01-30T15:33:57.903" Score="4" ViewCount="400" Body="&lt;p&gt;What is the difference between the Yaesu (say FT DX 5000) and Icom (say IC 7700) noise blankers? I understood that the Yaesu NB is an analogue one while Icom uses a digital solution.&lt;/p&gt;&#xA;" OwnerUserId="4178" LastEditorUserId="8832" LastEditDate="2017-08-20T21:22:40.693" LastActivityDate="2018-07-17T01:42:53.580" Title="What is the difference between Yaesu noise blanker (analog IF) and Icom noise blanker (perhaps digital)" Tags="&lt;hf&gt;&lt;equipment-design&gt;&lt;yaesu&gt;&lt;icom&gt;&lt;noise-blanker&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3555" PostTypeId="5" CreationDate="2015-01-30T23:02:48.980" Score="0" Body="&lt;p&gt;An International manufacturer of radio equipment, Based in Japan.  Their products include equipment for radio amateurs, pilots, maritime applications, land mobile professional applications and scanning enthusiasts. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.icomamerica.com/en/&quot; rel=&quot;nofollow&quot;&gt;Icom America&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1246" LastEditorUserId="1246" LastEditDate="2015-02-01T13:54:38.393" LastActivityDate="2015-02-01T13:54:38.393" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3556" PostTypeId="4" CreationDate="2015-01-30T23:02:48.980" Score="0" Body="An International manufacturer of radio equipment, Based in Japan.  Their products include equipment for radio amateurs, pilots, maritime applications, land mobile professional applications and scanning enthusiasts." OwnerUserId="1246" LastEditorUserId="1246" LastEditDate="2015-02-01T13:54:31.517" LastActivityDate="2015-02-01T13:54:31.517" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3557" PostTypeId="1" AcceptedAnswerId="3561" CreationDate="2015-01-31T09:00:58.133" Score="1" ViewCount="132" Body="&lt;p&gt;I was wondering if it is possible to measure the capacitance of a gamma rod using an L/C meter. I tried to measure one by clipping one of the alligator clips on the outer aluminum tube and the other one on the inner core of an insulated piece of RG213 which used inside the aluminum tube but the meter showed 0. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I doubled checked the meter by measuring couple of &quot;normal&quot; capacitors and it measured them without any difficulties&lt;/p&gt;&#xA;" OwnerUserId="2999" LastActivityDate="2015-01-31T22:13:55.963" Title="Is it possible to measure the capacitance of a gamma rod? Gamma match" Tags="&lt;capacitance&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3558" PostTypeId="2" ParentId="3554" CreationDate="2015-01-31T16:02:44.063" Score="1" Body="&lt;p&gt;I am not familiar with those two rigs but generally speaking from my experience, analog noise blankers are separate analog circuits while the digital rigs integrate digital noise blanking into the existing DSP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is kind of an apple vs. orange kind of thing. Some people prefer one ofter the other. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For me, I prefer the warm analog. It seems richer to my ear. Digital has a tendency to be a bit too clean. It almost flattens the audio. The bands are supposed to have some spirt!&lt;/p&gt;&#xA;" OwnerUserId="4187" LastActivityDate="2015-01-31T16:02:44.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3559" PostTypeId="1" AcceptedAnswerId="3560" CreationDate="2015-01-31T18:20:01.593" Score="3" ViewCount="9826" Body="&lt;p&gt;Is it possible to measure RF voltages with a multimeter? I have a multimeter which can measure AC voltages up to 600V RMS, but I'm not sure because I don't know if it assumes the signal to be 50Hz, or at least not several MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to know the RMS value of the voltage on my antenna. When measured with my multimeter, it shows it's beyond 600V~ RMS. When I measure just before my last inductors I have about 350V~ RMS. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a scope which goes up to 400V peak-to-peak on the screen (I'm not sure about its maximum ratings), but I'm reluctant to try, because I'm not sure if the measurements of my multimeter are correct, and I wouldn't like to damage my scope.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So: is it likely that a simple, common multimeter can measure RF voltages? I've seen &lt;a href=&quot;http://jdtechsales.com/measure-rf-voltages-with-a-multimeter/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this circuit&lt;/a&gt; which suggests that it's not possible and you have to put something in between the RF  and the multimeter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/3CeU4.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, they're rectifying the RF voltage, so they in fact measure with the DC input. My multimeter has an AC input - it's unclear to me if a circuit as this one is still needed in that case.&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastActivityDate="2015-01-31T21:42:12.300" Title="Measuring RF voltages with a multimeter" Tags="&lt;measurement&gt;&lt;voltage&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3560" PostTypeId="2" ParentId="3559" CreationDate="2015-01-31T21:42:12.300" Score="1" Body="&lt;p&gt;For an ideal meter, sure, it's possible. However, most multimeters are not designed to work at RF. There are all sorts of problems: what effect does the input capacitance have on the measurement? What's the characteristic impedance of the leads? Most multimeters don't take these things into account because the only AC voltage they are designed to measure is 60 or 50Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rectifying circuit in your question is a good solution. Note that you don't really need to use coaxial cable: since the output is DC, it hardly matters what kind of cable you use. The &quot;cable&quot; might just be the leads of your multimeter. You can also stick a sensitive analog meter (something on the order of microamps) directly on a circuit like this and get a decent RF detector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With an ideal rectifier, what you will measure with the meter (set to DC) is the peak-to-peak voltage of the RF input. Of course, no matter what diode you use, it will be anything but ideal at RF. There is at least the forward voltage drop of the diode to take into account (which can be reduced by using a Schottky or germanium diode). Real diodes also have capacitance, and all the components are going to have some inductances, and these reactances are going to filter the input signal in a way which may or may not be significant for your frequency of interest. However, if all you care about is a qualitative measurement of the input, a simple diode rectifier is quite sufficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also worth mentioning because it's not always obvious, but if you have a receiver, that can make a valuable piece of test equipment. A cheap SDR (like the SoftRock kits) coupled with the audio card of a computer makes a pretty decent RF frequency analyzer. If you also have an RF signal generator of known power (check eBay), then you can also calibrate your test equipment to give quantitative measurements.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-01-31T21:42:12.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3561" PostTypeId="2" ParentId="3557" CreationDate="2015-01-31T21:54:46.180" Score="2" Body="&lt;p&gt;Sure, if your L/C meter is designed to work at those capacitances. The capacitance of a gamma rod isn't much -- it's probably measured in pF. The lowest range of the inexpensive L/C meter I have from eBay is 200pF, which is fine for most of the capacitors in my parts drawer, but not so great for RF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also keep in mind: if you are making connections with long alligator clips, these are going to have inductance and capacitance in addition to the gamma rod. Depending on how well the clips chomp down they may add significant resistance, too. Unless you take some very special care to keep those leads short or compensate for them, you are going to introduce so much stray reactance with the leads that any measurement you obtain won't be of much use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, anything designed to measure the reactances typical at RF stops being called an &quot;L/C meter&quot; and starts being called an &quot;antenna analyzer&quot; or a &quot;network analyzer&quot;. So, while it certainly is possible to measure the capacitance of a gamma match, it's probably not possible to do it with something marketed as an &quot;L/C meter&quot;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-01-31T22:13:55.963" LastActivityDate="2015-01-31T22:13:55.963" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3562" PostTypeId="1" CreationDate="2015-02-01T01:51:06.047" Score="3" ViewCount="214" Body="&lt;p&gt;I would like to test the range of my two HTs by myself while still operating legally. Anyone have any ideas of how I can accomplish this? The only way I could come up with was feeding audio into one at a fixed location with loop of my call sign. It is hard find an exact answer on this but it seems to me like I would operating out of compliance because I am not physically at my station.&lt;/p&gt;&#xA;" OwnerUserId="4188" LastEditorUserId="76" LastEditDate="2015-02-01T03:14:51.580" LastActivityDate="2015-02-18T12:33:41.633" Title="Signal Range Test With One Person" Tags="&lt;legal&gt;&lt;procedure&gt;&lt;ht&gt;&lt;range&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3563" PostTypeId="2" ParentId="3562" CreationDate="2015-02-01T02:52:53.450" Score="1" Body="&lt;p&gt;It might not be legal to transmit unattended, depending where you live. It's also not ideal to transmit continuously; bad manners, and an HT will overheat pretty quickly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll often hear hams using &lt;em&gt;voice keyers&lt;/em&gt; I'm contests, to save them the effort of calling CQ. This would work, but think about what happens when someone responds saying you're in the way, or interrupting them, and you're not there to turn it if.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rather do the transmitting yourself, and find a way to make an unattended receiver. This would always be legal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few ideas would be to: use a voice-activated sound recorder, or an app on a phone, then you would announce your location when you transmit. Or for more immediate feedback and less driving, find a way of calling your house, perhaps your phone or Skype could be set to auto-answer, so you can hear the received audio immediately.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be aware that at the limit of the radio's range, the signal is very sensitive to how you hold the radio. (well, always, but it doesn't matter if the signal is strong). An experienced operator will swing the antenna around while receiving, to find the clearest position. Then freeze in that position when answering. So if you're transmitting blind, I recommend that you try at least four positions of the transmitter, at each location you drive to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's quite likely that your licence conditions specify that you may: Communicate with other amateur stations, and Make Test Transmissions. It's an experimental hobby, so go for it!&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-02-01T02:52:53.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3564" PostTypeId="2" ParentId="3554" CreationDate="2015-02-01T10:56:54.767" Score="-2" Body="&lt;p&gt;In my understanding it has to do with the way we &quot;intervene&quot; on the Intermediate Frequency (IF) of our receivers- which is actually the mixing of the carrier signal with a local oscillator in order to get the difference frequency which holds the actual &quot;information&quot;- which is amplified on the next stage. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, in the analog option we change the frequency of the oscillator a bit in order to filter out the frequency portion of the carrier that interferes with the portion that has the actual information we prefer to listen to. The IF DSP filtering does exactly the same with digital precision and methods, thus more accurately.&lt;/p&gt;&#xA;" OwnerUserId="2999" LastActivityDate="2015-02-01T10:56:54.767" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3565" PostTypeId="1" AcceptedAnswerId="3566" CreationDate="2015-02-01T23:48:32.243" Score="6" ViewCount="4758" Body="&lt;p&gt;In various topics on repeaters, IRLP, D-Star and EchoLink, I see people refer to these 'nodes' (for lack of a better word) as &lt;em&gt;reflectors.&lt;/em&gt; A quick Internet search for these terms comes up with all sorts of ambiguities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've always called my local 2m FM voice repeater a repeater, not a reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are these terms simply interchangeable, or is there a functional difference between a repeater and a reflector?&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="76" LastEditDate="2015-02-02T00:03:43.020" LastActivityDate="2017-01-07T20:09:27.323" Title="“Repeater” vs. “reflector”" Tags="&lt;repeater&gt;&lt;jargon&gt;&lt;reflector&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3566" PostTypeId="2" ParentId="3565" CreationDate="2015-02-02T00:11:19.880" Score="5" Body="&lt;p&gt;According to Wikipedia for IRLP:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;IRLP connections are of two types: node to node, and node to reflector. Stations wishing to communicate with 3 or more nodes at the same time may accomplish this by connecting to what is called an IRLP Reflector. Reflectors are a type of conferencing system. Most reflectors on the network have 10 channels (0-9) with channel 0 being the main channel. Each reflector has a unique 4 digit node number in the range of 9000-9999. The first 3 digits consist of the reflector number, while the fourth digit represents the channel number. As of April 2007, there are 20 operational reflectors (including Echo Reflector 9990, which digitally records and plays back transmissions for testing purposes). Since most reflectors have 10 channels, there are approximately 200 unique reflector channels available for use.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Internet_Radio_Linking_Project&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia: Internet Radio Linking Project&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In IRLP a reflector is a computer based server which connects 2 or more &quot;nodes&quot; (A node is a Repeater connected to a computer or a IRLP computer connected to a radio operating simplex.) together via server to create kind of &quot;conference room&quot;.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-02-02T00:11:19.880" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="3568" PostTypeId="1" CreationDate="2015-02-04T18:55:18.813" Score="3" ViewCount="186" Body="&lt;p&gt;I want to make a contact with a ham who is far away (&gt;10,000km). How would I intelligently plan a scheduled contact to maximize possible success?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assumptions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Both stations have optimized their configuration for each band (maximum power, good antenna, capable of trying both long and short path azimuths)&lt;/li&gt;&#xA;&lt;li&gt;Both stations are capable of multiple HF bands, without a requirement that it be on one specific band (e.g. I don't need this contact just for a 80m phone award)&lt;/li&gt;&#xA;&lt;li&gt;I want to maximize the signal to noise ratio&lt;/li&gt;&#xA;&lt;li&gt;We have an accurate time reference for coordination (e.g. GPS clock)&lt;/li&gt;&#xA;&lt;li&gt;We are trying to make a voice (SSB) contact&lt;/li&gt;&#xA;&lt;li&gt;We can have written correspondence&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;How should I select a time, band, and frequency to maximize the chance for success? Is there any procedure or protocol that would help?&lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2015-02-07T04:24:39.837" Title="Setting up an HF Schedule" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3569" PostTypeId="2" ParentId="3568" CreationDate="2015-02-04T20:24:23.077" Score="2" Body="&lt;ol&gt;&#xA;&lt;li&gt;Eliminate all times and bands which are not acceptable.&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/1755/218&quot;&gt;Select a band appropriate for the time of day and seasonal sunspot activity&lt;/a&gt;. It's pretty easy to scout which bands might be good: if you can hear other stations in similar areas at similar times, it's good. Tools you can use in this endeavor are &lt;a href=&quot;http://www.ncdxf.org/beacon/intro.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;beacons&lt;/a&gt; and &lt;a href=&quot;https://ham.stackexchange.com/q/332/218&quot;&gt;receivers streaming to the internet&lt;/a&gt;. There are even &lt;a href=&quot;http://www.reversebeacon.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;projects which perform this experiment constantly and publish the results&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;(optional) Make alternate plans in case your primary plans don't work out, involving different bands, at different times.&lt;/li&gt;&#xA;&lt;li&gt;Hope for the best, then repeat until it works.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-02-04T20:30:36.813" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3570" PostTypeId="1" AcceptedAnswerId="3571" CreationDate="2015-02-04T22:55:21.177" Score="0" ViewCount="84" Body="&lt;p&gt;I have the following example taken from the &quot;ARRL General Class Manual&quot;, 7th Ed, 4-4.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Here's a practical application. Suppose you are using an antenna feed line that has a signal loss of 1dB. You can calculate the amount of transmitter power that's actually reaching our antenna and how much is lost in the feed line.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;$$\text{Percentage Power} = 100\% \times \log^{-1}\left({-1\over10}\right) = 100\% \times \log^{-1}(-0.1) = 79.4\%$$&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I think I'm missing something extremely trivial. In my calculator, I get&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 10^{-.1} = 9.9 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have inverse log on my calculator but $ 10^{x} $ should be the same, no?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I'm missing the point with multiplying by 100% — that makes no sense to me. Either way I'm not sure how doing something to 9.9 with 100% gets me 79.4%.&lt;/p&gt;&#xA;" OwnerUserId="4096" LastEditorUserId="76" LastEditDate="2015-02-04T23:07:10.397" LastActivityDate="2015-02-04T23:07:10.397" Title="Getting the wrong answer from percentage power/transmit power calculation" Tags="&lt;math&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3571" PostTypeId="2" ParentId="3570" CreationDate="2015-02-04T23:05:18.203" Score="2" Body="&lt;p&gt;You have entered the formula in your calculator wrong. $10^{−0.1} ≈ 0.794$, as the book indicates. If you got $9.9$, then more likely you entered $10 - 0.1$ instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 100% part is merely about explicitly converting &lt;em&gt;multipliers&lt;/em&gt; to &lt;em&gt;percentages&lt;/em&gt;, that is, $0.794 \times 100\% = 79.4$. (I don't care for that notation myself, and would rather define $\%$ such that $0.794 = 79.4\%$, period.) It's just a reminder that if you want a percentage value instead of a multiplier you have to multiply by 100.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-02-04T23:05:18.203" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3572" PostTypeId="1" AcceptedAnswerId="3573" CreationDate="2015-02-05T01:55:58.477" Score="0" ViewCount="3017" Body="&lt;p&gt;What kind of cable would be suitable for wiring an &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-564B&quot; rel=&quot;nofollow&quot;&gt;MFJ-564B Iambic CW Paddle&lt;/a&gt; to an Icom IC-718?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have heard that you can just use a length of old electric guitar cord but I was not sure what to do.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-02-05T03:04:31.187" Title="Wiring a CW paddle" Tags="&lt;cw&gt;&lt;icom&gt;&lt;wiring&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3573" PostTypeId="2" ParentId="3572" CreationDate="2015-02-05T02:18:17.467" Score="2" Body="&lt;p&gt;I always use stereo patch cables for connecting my paddles.  The have the right number of conductors, three.  Almost all stereo patch cables have two conductors and braided shield which is your third conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This works nicely with the standard 1/4 inch stereo phone plug expected by the 718.  You can go down to Radio Shack (before all the stores close) or your other favorite supplier of such things and buy yourself a 6 foot stereo cable with one end attached to stereo 1/4 inch plug. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Only issue it to make sure you wire the TRS (tip-ring-sleeve) to the right conductors and the IC-718 manual tells you how to do that.  You should not need to rewire the actual 1/4 inch plug, just make sure that tip and ring are connected to the right spots on the paddle.  The sleeve is almost always the ground braid attachment (but, double check with continuity tester anyway).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One minor little thing is that these patch cables use small and fragile wires so you need to be careful when hooking up.  Probably solder on some nice lugs for hooking to screw attachments on the paddle.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I like best of these cables is that they are usually very flexible and that is nice on a crowded desktop.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-02-05T02:18:17.467" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3574" PostTypeId="2" ParentId="3572" CreationDate="2015-02-05T03:04:31.187" Score="3" Body="&lt;p&gt;Assuming your question is literally &lt;em&gt;what kind of cable&lt;/em&gt; and not &lt;em&gt;what connectors do I need&lt;/em&gt;, the answer is: it doesn't matter. Use what is at hand, or what will lay nicely on your desk, or what looks good, or what's cheap at the store, as long as it has two (for a key) or three (for a paddle) conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A CW key or paddle is just a switch or pair of switches, nothing more, acting as part of a simple DC circuit. This is the least demanding application for wire or cable that exists. (Exception: Some very old transmitters had high voltage on the keying circuit. In this case, the cable's insulation must be adequate.) You definitely don't need to worry about impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that an electric guitar cable as you mentioned is &lt;strong&gt;not&lt;/strong&gt; suitable for this case, because it has only &lt;em&gt;two&lt;/em&gt; conductors and contacts, whereas a paddle requires &lt;em&gt;three&lt;/em&gt; contacts (one common and two for the two switches). If you want to start with a prebuilt audio cable assembly, use a cable with a TRS (stereo) 1/4&quot; plug. Or, use a 1/8&quot; (a.k.a. 3.5 mm) plug together with a size adapter (these are readily available); this might be useful later if you use a different rig which uses the smaller plug.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether you use bulk cable or a preassembled cable, you will need to strip, separate, and solder the wires on the other end to the solder terminals on the MFJ paddle. (Some cables might have very fine wires that are hard to solder by hand or would break with use; if you build from scratch you can choose cable that doesn't have this problem.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-02-05T03:04:31.187" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3575" PostTypeId="1" AcceptedAnswerId="3576" CreationDate="2015-02-05T05:00:20.767" Score="9" ViewCount="24811" Body="&lt;p&gt;I've just started studying for my HAM license a couple of weeks ago, so please excuse me if this is a remedial question...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have the &lt;em&gt;Canadian Amateur Radio Basic Qualification Study Guide&lt;/em&gt; (which I'm finding is terribly hard to understand). Their explanations of just about everything appear to be missing pertinent information that allow the reader to connect the dots and consequently I'm struggling to understand what they're explaining... anyway, the book discusses a formula which supposedly allows you to determine the bond between frequencies and their band - i.e. the calculation in the book tells me that 300 / Wavelength = Frequency... where one is to assume that 300 is a rough simile of the speed of light in millions of meters per second. The book suggests the resultant frequency is approximately (within some unexplained tolerance) the middle of the bandwidth for that band plan. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm noticing that using this formula for many bands the resulting frequency doesn't fall within the suggested frequency range for that plan and where they do, many don't fall within any discernible tolerance of the middle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;20m band = 300 / 20 = 15.000 MHz, whereas the book suggests the frequency band falls between 14.000 - 14.350 MHz. (Clearly 15.000 MHz falls outside that range)&lt;/li&gt;&#xA;&lt;li&gt;2m band = 300 / 2 = 150.000 MHz, whereas the book suggests the frequency band falls between 144.000 - 148.000 MHz.&lt;/li&gt;&#xA;&lt;li&gt;33cm band = 300 / 0.33m = 909.091 MHz, a long way from the middle of the suggested frequency band of 902.000 - 928.000 MHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Even if I substitute the more accurate (according to Google) measurement of c being 299,792,458 m/s, I arrive at 14.990 MHz for 20m, still not within the frequency band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly I'm missing something, can someone explain what I'm not understanding?&lt;/p&gt;&#xA;" OwnerUserId="4201" LastEditorUserId="29" LastEditDate="2015-02-05T08:39:44.773" LastActivityDate="2020-04-09T04:42:42.663" Title="How can you calculate the frequencies for each band?" Tags="&lt;frequency&gt;&lt;band-plan&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="3576" PostTypeId="2" ParentId="3575" CreationDate="2015-02-05T05:47:49.130" Score="12" Body="&lt;p&gt;$$ \frac{c}{ \text{frequency}} = \text{wavelength}$$&#xA;$$ \frac{c}{ \text{wavelength}} = \text{frequency}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above relation is a fact of physics. It's true unconditionally (provided you are using consistent units, e.g. wavelength in meters and $c$ in meters per second); it's how you convert between two different ways of measuring a wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency limits, and names, of the bands are not physics; they were invented by humans. The frequency limits are a matter of the regulations that divide up the radio spectrum among many users. The limits of the amateur bands are semi-arbitrary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The common names for the bands (&quot;20 m&quot;, &quot;2 m&quot;, and so on) are simply &lt;strong&gt;the closest round number to the actual wavelengths&lt;/strong&gt;. (In your example of 33 cm, note that 32 and 34 cm would be outside the band entirely. 33 is the best two-digit approximation.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What your book &lt;em&gt;should&lt;/em&gt; have told you is not that you can use the above relation to find the limits of the band, but that &lt;strong&gt;given that you already know the bands and frequencies, you can use it to find &lt;em&gt;which&lt;/em&gt; band a frequency belongs to, or vice versa&lt;/strong&gt;, because while the band names do not always fall in the frequency limits, the correct band/frequency will always be the &lt;em&gt;closest&lt;/em&gt; match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, $300/143 ≈ 2.098$, so we can conclude that 143 MHz is in the 2 m band &lt;em&gt;if it is in an amateur band at all&lt;/em&gt;, which it &lt;em&gt;isn't&lt;/em&gt; (but e.g. 145 MHz is).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to know the limits of bands, you must memorize them; there are no shortcuts. The relationship between wavelength and frequency can, however, be used to match up those limits to the wavelength-names of the bands.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-02-05T16:06:03.417" LastActivityDate="2015-02-05T16:06:03.417" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="3577" PostTypeId="1" CreationDate="2015-02-05T15:52:45.387" Score="10" ViewCount="5003" Body="&lt;p&gt;I am attempting to design an antenna for a 162.4 MHz omni receive only application and am confident it is going to be difficult if not impossible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have very tight specs on space(6&quot; diameter by 3&quot; deep cylinder) so the first antenna I came across was a quarter wave antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;162.4MHz length is 17.291 inches. Given my enclosure height this is not going to work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next antenna to look at is the rubber ducky. From wiki I find, &quot;Rubber ducky antennas are typically 4% to 15% of a wavelength long; that is, 16% to 60% of the length of a standard quarter-wave whip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So 17.291 inches in the quarter wave becomes 17.291*(.16)=2.76656 inches in the rubber ducky. Now I know having antenna this small will hurt the range terribly, but it meets the size requirement. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I am attempting to understand how to design such an antenna. I have access to some equipment and will attempt to acquire the tools I need, but I lack the design flow to accomplish this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently I have access to a spectrum analyzer w/ tracking and can get signal to noise ratio(SNR) and Received signal strength indicator (RSSI) values.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have no issues with the impedance matching and am purely focused on how to design the physical antenna for my design. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any suggestions or information would be greatly appreciated on how to go about designing a rubber ducky.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Additional information:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I was looking to choice an antenna type:&#xA;&lt;a href=&quot;https://electronics.stackexchange.com/questions/131323/antenna-design-for-specific-directions&quot;&gt;https://electronics.stackexchange.com/questions/131323/antenna-design-for-specific-directions&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can Rubber ducky be modeled:&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/2070/how-much-loss-for-1-to-1-5-inch-coil-rubber-ducky-antenna-at-70cm-band&quot;&gt;How much loss for 1 to 1.5 inch Coil (rubber ducky) Antenna at 70cm band?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Details:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The enclosure is made from PLA plastic.&lt;/li&gt;&#xA;&lt;li&gt;Other then a ground place the diameter of the enclosure it will be in&#xA;free space.&lt;/li&gt;&#xA;&lt;li&gt;There is a AC power cable running out of the top of the enclosure.&lt;/li&gt;&#xA;&lt;li&gt;The receiver circuit board is inside the volume.&lt;/li&gt;&#xA;&lt;li&gt;The orientation of the cylinder is 3&quot; vertical &amp;amp; 6&quot; horizontal&lt;/li&gt;&#xA;&lt;li&gt;The direction of the signals will be horizontal.&lt;/li&gt;&#xA;&lt;li&gt;I can ideally cope with a directional design, but this is not&#xA;prefered.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="1640" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-02-15T19:19:14.023" Title="How to design a rubber ducky antenna" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;equipment-design&gt;&lt;wire-antenna&gt;" AnswerCount="1" CommentCount="6" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3578" PostTypeId="2" ParentId="3575" CreationDate="2015-02-05T17:45:51.163" Score="5" Body="&lt;p&gt;The names make a kind of sense if you take into account the history behind them. Look at this pattern of names and lower end of the allocation:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;80m: 3.5MHz&lt;/li&gt;&#xA;&lt;li&gt;40m: 7.0MHz&lt;/li&gt;&#xA;&lt;li&gt;20m: 14MHz&lt;/li&gt;&#xA;&lt;li&gt;10m: 28MHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Note how the frequencies and canonical names are related by multiples of two. 80m is almost perfectly named: the allocation goes from 75.0m to 85.7m. Sure, as you go up in frequency it gets less perfect: 20m is closer to 21 meters. But these are nice, round numbers. There being no other bands allocated at the time, there wasn't any particular reason to be more specific.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of note, those bands have been allocated for a very long time, internationally allocated by the ITU in 1927.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;15m was allocated in 1947. Clearly that can't be rounded to 10m or 20m because those names are already taken. 14m would be a more accurate name, but 15 is a &quot;rounder&quot; number, being a multiple of 5.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;30m, 17m, and 12m are the &lt;a href=&quot;http://en.wikipedia.org/wiki/WARC_bands&quot; rel=&quot;nofollow&quot;&gt;WARC bands&lt;/a&gt;, allocated more recently in 1979. 12m couldn't be 10m because that name was taken. 30m is a round number that's close enough that wasn't already used. 17m is actually closer to 15m, but that name was also already taken. I suppose it could have been 16m. Maybe you can dig up the notes from 1979 to figure out why it wasn't. My guess: someone wanted some free space between 15m. You will notice that 12m is right on the money: the actual allocation is from 12.00m to 12.05m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;60m is relatively new, being allocated in the US in 2002. I don't think the ITU allocates it internationally. Though it's actually around 55m, 60 is a nice round number and there wasn't already a band called that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And that's all the HF bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The VHF bands are pretty accurate:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;300/50MHz = 6.00m&lt;/li&gt;&#xA;&lt;li&gt;300/144MHz = 2.08m&lt;/li&gt;&#xA;&lt;li&gt;300/225MHz = 1.333m&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'll forgive you for questioning the last one, because you are Canadian and you use the metric system. Had Canadians named it, they would have called it 133cm. But this band first encountered amateur use in the US, where fractions with powers of two are preferred&lt;sup&gt;1&lt;/sup&gt;. So this is the &quot;1¼-meter band&quot;. Of course at the time the band was named, Canada wasn't using the metric system either. So maybe not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you go up the spectrum, the names continue to be pretty accurate. Eventually, people tend to stop calling them by wavelength. &quot;Four-forty&quot; is a colloquial name for &quot;70 centimeters&quot; in some places. No one has a &quot;13 centimeter&quot; Wi-Fi access point. They have a 2.4GHz access point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: Someone needs to tell Ikea this, because &lt;a href=&quot;http://www.ikea.com/ms/en_US/customer_service/assembly/O_P_Q/P40121585.pdf&quot; rel=&quot;nofollow&quot;&gt;their manuals (page 9)&lt;/a&gt; frequently have measurements like &quot;95 2/3 inches&quot;. No one has a ruler marked in thirds of inches. I guess no one has a ruler marked in fourths of meters either, so maybe this is Ikea's revenge.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-02-06T13:20:37.910" LastActivityDate="2015-02-06T13:20:37.910" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="3579" PostTypeId="1" AcceptedAnswerId="3584" CreationDate="2015-02-05T23:16:02.133" Score="5" ViewCount="290" Body="&lt;p&gt;I'm fairly new to amateur radio, and I've been using &lt;a href=&quot;http://websdr.ewi.utwente.nl:8901/&quot; rel=&quot;noreferrer&quot;&gt;a web-based SDR tool&lt;/a&gt; in addition to my own radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using this SDR tool shows a &lt;em&gt;lot&lt;/em&gt; of activity lower down on the spectrum, such as this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/YbJlZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I tune into it I hear a lot of odd sounds, some sound like data, others are just one long unbreaking tone, for example:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;~20KHz - Very high pitch sound, sounds like data.&lt;/li&gt;&#xA;&lt;li&gt;~59KHz - Beeping, varies between single beep and double beep occasionally.&lt;/li&gt;&#xA;&lt;li&gt;~61KHz to 63KHz - High pitched, also sounds like data.&lt;/li&gt;&#xA;&lt;li&gt;~66KHz - Another type of beeping, also sounds like data.&lt;/li&gt;&#xA;&lt;li&gt;~400KHz - Morse code, but then will start making a continuous tone.&lt;/li&gt;&#xA;&lt;li&gt;~278Khz - Constant tone&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I've tried searching the internet for information but don't get many relevant links. So what are these stations and where are coming from?&lt;/p&gt;&#xA;" OwnerUserId="4205" LastEditorUserId="218" LastEditDate="2015-02-06T02:26:22.200" LastActivityDate="2017-04-24T08:40:03.357" Title="What are the continuous transmissions at the lower end of the spectrum?" Tags="&lt;signal-identification&gt;&lt;vlf&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3580" PostTypeId="1" AcceptedAnswerId="3583" CreationDate="2015-02-06T01:08:13.163" Score="2" ViewCount="1237" Body="&lt;p&gt;What would the radiation pattern look like if I used a 1/4th wave 2 meter mag-mount antenna on 70cm with an HT.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastEditorUserId="1246" LastEditDate="2015-02-06T03:43:34.627" LastActivityDate="2015-02-06T03:43:34.627" Title="Radiation pattern for a 1/4th wave 2 meter antenna used on 70cm" Tags="&lt;ht&gt;&lt;2m-band&gt;&lt;70cm-band&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3581" PostTypeId="2" ParentId="3525" CreationDate="2015-02-06T02:06:22.107" Score="-1" Body="&lt;p&gt;you can use the same antenna.The antenna have it's frequency range.&#xA;You just need change the channels of your VHF Radio's frequency to avoid conflict.&lt;/p&gt;&#xA;" OwnerUserId="4206" LastEditorUserId="218" LastEditDate="2015-02-06T02:10:48.530" LastActivityDate="2015-02-06T02:10:48.530" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3583" PostTypeId="2" ParentId="3580" CreationDate="2015-02-06T02:19:34.170" Score="1" Body="&lt;p&gt;&lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna-theory.com provides some nice images&lt;/a&gt; of the ideal case. A half-wave dipole in free space along the vertical has a radiation pattern like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/pCAxy.jpg&quot; alt=&quot;1/2 wave dipole radiation pattern&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 1/2 wave antenna on 2m is a 3/2 wave antenna on 70cm. That radiation pattern looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/YUJOo.jpg&quot; alt=&quot;3/2 wave dipole radiation pattern&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you are not using a dipole, but a vertical. A vertical on an ideal ground plane has an identical pattern to a dipole, but with the lower half removed. On a ground plane of limited size and conductivity, some of the low angle radiation is lost, but otherwise the pattern is pretty much the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a mobile installation, the ground plane can be very far from ideal, and the radiation pattern will depend more on the ground &quot;plane&quot; than the antenna, so the actual pattern will not resemble these images at all.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-02-06T02:29:33.200" LastActivityDate="2015-02-06T02:29:33.200" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3584" PostTypeId="2" ParentId="3579" CreationDate="2015-02-06T13:25:46.253" Score="6" Body="&lt;p&gt;If you zoom in on these signals, there are labels describing what the stations are. Example, many of the signals around 20kHz are military:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/w4kHN.png&quot; alt=&quot;waterfall around 20kHz&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you mouse over the labels, it will expand them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can zoom with the mouse wheel or with the controls in the &quot;Waterfall view&quot; section.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-02-06T13:25:46.253" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3585" PostTypeId="2" ParentId="3568" CreationDate="2015-02-07T04:14:24.037" Score="4" Body="&lt;p&gt;This is actually quite a standard question that any non-hobby HF user will have, so there is good software to help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend starting with &lt;a href=&quot;http://voacap.com/prediction.html&quot; rel=&quot;nofollow&quot;&gt;VOACAP online&lt;/a&gt; to make predictions for the best bands and times to try. VOACAP makes a prediction based on the typical conditions at a particular sunspot number, not the exact conditions right now. It is really for planning, equipment selection, frequency choice when setting up an HF link. You can download it to run on your computer, but the web version is really easy to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there is great real-time information available from &lt;a href=&quot;http://wsprnet.org/drupal/wsprnet/map&quot; rel=&quot;nofollow&quot;&gt;WSPRnet&lt;/a&gt;, which plots propagation right now. Have a look around and see how it works, you can quite easily try a particular band and time window. You can also run a listening station yourself without too much trouble, to see what you can hear. WSPR is even more sensitive than CW, so it works long before phone. If you're anywhere near a large population centre though, there will be plenty of users close enough to you.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-02-07T04:24:39.837" LastActivityDate="2015-02-07T04:24:39.837" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3586" PostTypeId="2" ParentId="2234" CreationDate="2015-02-07T04:40:17.573" Score="1" Body="&lt;p&gt;I'm not sure you can or should log contacts that were not directly between your stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Contacts through repeaters, packet reflectors, mesh networks, IRLP, echolink etc. don't really count as a measure of your skill and station.&#xA;Satellites are an exception though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://gvarc.us/GVARCFrames/Technical/w2rs/QSLing.htm&quot; rel=&quot;nofollow&quot;&gt;W2RS says here&lt;/a&gt;:  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;QSLs are generally not exchanged for contacts made through repeaters (other than orbiting satellites), nor for those made through such media as Echolink. Such contacts, fun though they are, generally are not valid for operating award purposes.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As LotW is a QSL system for confirming awards and achievements, it's not really appropriate to log contacts made via repeater or mesh.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-02-07T04:52:10.200" LastActivityDate="2015-02-07T04:52:10.200" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3587" PostTypeId="1" AcceptedAnswerId="3590" CreationDate="2015-02-07T14:53:39.043" Score="5" ViewCount="1253" Body="&lt;p&gt;I am making the Printed Yagi-Uda Dipole Array with Balun (that is the full name). I used Antenna Magus to calculate dimensions. I am not sure how to properly connect it to coaxial cable.&lt;BR&gt; Here is what the antenna looks like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/sRojV.png&quot; alt=&quot;Printed Yagi-Uda Dipole Array with Balun&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the Feed Method it states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;Feed Method&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;  &#xA;  &lt;p&gt;The printed Yagi structure requires a balanced feed. Typically,&#xA;  however the antenna is fed using an unbalanced coaxial cable and a&#xA;  balun is required to provide the required balanced feed. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;An integrated balun structure is taken into consideration in the&#xA;  Antenna Magus design procedure and the Antenna Magus export models&#xA;  include a co-planar quarter-wave balun construction. If a coaxial&#xA;  cable is used, the outer conductor is simply soldered along the one&#xA;  line of the balun from the reflector element all the way to the driven&#xA;  element. At this point the inner conductor is extended across the gap&#xA;  of the driven element and soldered onto the opposite arm. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The antenna could be fed using a balanced source or a different balun&#xA;  construction. (Note that for these cases, the balun design will need&#xA;  to be done independently of Antenna Magus, and the co-planar balun&#xA;  structure may need to be removed from the export models for simulation&#xA;  purposes.)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Does the image below show the correct way of connecting coax to the antenna?&lt;/strong&gt;&lt;BR&gt;&#xA;&lt;em&gt;Orange dots are solder spots.&lt;/em&gt;&lt;BR&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/W7oej.png&quot; alt=&quot;Printed Yagi-Uda Dipole Array with Balun Feed method&quot;&gt;&#xA;&lt;BR&gt; &#xA;I do not have much experience making antennas.&lt;/p&gt;&#xA;" OwnerUserId="4213" LastEditorUserId="1246" LastEditDate="2015-02-09T12:57:49.860" LastActivityDate="2015-02-09T12:57:49.860" Title="Connect Printed Yagi-Uda Dipole Array with Balun to coaxial cable correctly" Tags="&lt;antenna-construction&gt;&lt;feed-line&gt;&lt;coaxial-cable&gt;&lt;yagi&gt;&lt;balun&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3588" PostTypeId="1" CreationDate="2015-02-08T10:20:51.157" Score="2" ViewCount="211" Body="&lt;p&gt;in our wireless network we have a variable count of devices. Each device contains one transmitter and receiver. Both receiver and transmitter are working on the same frequency, 433 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To keep the price as low as possible, we are not able to buy more expensive modules which support frequency changes. Thus we have to create kind of time separating mechanism to prevent transmitters to “jam” each other. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is you never know the device cound, and each device doesn't have the same ID each time it is connected to the network – it is set by the owner of the device. Therefore we can not assign the transmission time like $\text{ID} \times ( \text{time between each transmission} + \text{time of transmission} )$. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to determine device count and assign them unique IDs and transmission time?&lt;/p&gt;&#xA;" OwnerUserId="4212" LastEditorUserId="76" LastEditDate="2015-02-10T16:48:14.370" LastActivityDate="2015-02-10T16:48:14.370" Title="Multiple transmitters using same frequency" Tags="&lt;modes&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3589" PostTypeId="2" ParentId="3588" CreationDate="2015-02-08T12:29:13.233" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there a way to determine device count, assign them unique IDs and transmission time?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You could have them all communicate and negotiate this information. That's complex, though. It's more of a computer science problem than a radio one. The issue is that all the nodes have to agree on what their respective slots are, or agree on a leader which will arbitrate channel access. This is a classic &lt;a href=&quot;http://en.wikipedia.org/wiki/Consensus_%28computer_science%29&quot; rel=&quot;nofollow&quot;&gt;distributed consensus problem&lt;/a&gt;, and while it seems simple it's not. What happens, for example, when a node can't hear the leader? Does it then become the leader or elect a new one? What if the former leader is still around, but propagation conditions have changed so just some of the nodes can't hear it? Then you end up with two leaders which each think they are the only one, leading to collisions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consequently, some protocols eliminate the consensus problem by making those decisions static. For example, each node is configured to acknowledge one leader, and if the leader isn't available, then the node just doesn't work. Maybe this is acceptable for you, but by the nature of your question I'm guessing not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, you can just each transmitter listen before transmitting, and not transmit until the channel seems clear. This is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Carrier_sense_multiple_access&quot; rel=&quot;nofollow&quot;&gt;carrier sense multiple access&lt;/a&gt;, or CSMA. It is the method used by Wi-Fi and amateur radio packet. You can still try to reduce collisions through some leader arbitration, as long as you acknowledge that collisions may still occur, due largely to the consensus problem as before. For an example, see &lt;a href=&quot;http://en.wikipedia.org/wiki/IEEE_802.11_RTS/CTS&quot; rel=&quot;nofollow&quot;&gt;802.11's RTS/CTS protocol&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-02-09T16:07:23.353" LastActivityDate="2015-02-09T16:07:23.353" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3590" PostTypeId="2" ParentId="3587" CreationDate="2015-02-08T17:02:59.277" Score="4" Body="&lt;p&gt;I'm no expert on balun designs, but I think they mean to construct a &lt;a href=&quot;http://www.antenna-theory.com/definitions/foldedbalun.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;folded balun&lt;/a&gt;, as follows. The coax's outer conductor is soldered to the same part of the antenna, but it is &lt;em&gt;left on the coax&lt;/em&gt;, not peeled away, so the final balun structure includes a length of the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/pCma7.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The interpretation you proposed in your question is unlikely because if the outer conductor is separated from the coax, attaching it along the length of the trace won't function any differently from a single-point junction.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When soldering, make sure not to melt the dielectric in the coax:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Perform the soldering quickly, so the heat does not spread.&lt;/li&gt;&#xA;&lt;li&gt;Do not use foam-dielectric coax.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-02-08T17:33:13.563" LastActivityDate="2015-02-08T17:33:13.563" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3591" PostTypeId="1" AcceptedAnswerId="3592" CreationDate="2015-02-09T00:49:04.177" Score="6" ViewCount="4820" Body="&lt;p&gt;A folded balun is made from two quarter-wavelength, parallel conductors. A picture is worth a thousand words:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Mv4Xr.png&quot; alt=&quot;folded balun&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some pictures of an actual construction &lt;a href=&quot;http://diydrones.com/profiles/blog/show?id=705844%3ABlogPost%3A1674324&amp;amp;commentId=705844%3AComment%3A1675030&quot; rel=&quot;nofollow noreferrer&quot;&gt;from Gisela &amp;amp; Joe Noci on diydrones.com&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/rDjk3.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/RZay4.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/DcZca.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes they are &lt;a href=&quot;https://ham.stackexchange.com/q/3587/218&quot;&gt;printed on a PCB&lt;/a&gt;, so the quarter-wave sections are not coax but PCB traces.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/pCma7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does this balun work?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="873" LastEditDate="2018-10-24T06:19:00.817" LastActivityDate="2018-10-24T06:19:00.817" Title="How does a folded balun work?" Tags="&lt;antenna&gt;&lt;theory&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="3592" PostTypeId="2" ParentId="3591" CreationDate="2015-02-09T00:49:04.177" Score="8" Body="&lt;p&gt;It's easier to see what's going on with a bit of rearrangement. Imagine this built of tubing:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/5UJjq.png&quot; alt=&quot;antenna and balun of tubing&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feedpoint is still where it would be on a dipole without the balun. The feedpoint sees the dipole as usual (blue).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In parallel with that is a twin-lead transmission line formed by the two parallel sections of the balun (red). This is a &lt;a href=&quot;http://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer&quot; rel=&quot;noreferrer&quot;&gt;quarter-wave section&lt;/a&gt; with a short at the end, so it looks like an infinite impedance. An infinite impedance in parallel with the dipole at the feedpoint doesn't change the impedance the feedpoint sees. The red section might as well not be there at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, there's this green stub on the bottom. It's insignificant to the operation of the antenna because there can be no currents on it. Although there may be currents of the balun (red section), they are equal and opposite, and so at the point where the green stub is, they cancel. So you can't drive a current on the green stub via the feedpoint. Furthermore, because the green stub is symmetrical with respect to the dipole, it will have equal capacitance to either half of the dipole, and so you can't drive a current on the green stub capacitively, either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So there's no way to drive a current on the green stub via the feedpoint. That sounds like exactly what we want in a balun, if the green stub is the coax shield. Trouble is, the feedpoint is up there at the top. How can the shield be connected at the bottom while the feedpoint is at the top? Easy, if it's made from tubing. Just cut a little hole near the feedpoint, and run the feedline inside the tubing. The shield is connected to one half of the dipole at the hole, and the center conductor goes through the hole to feed the other side:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/tJPhf.png&quot; alt=&quot;with feedline inside&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is equivalent to the more usual construction:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/fgNn1.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This uses the coax as the tubing, and since the spacing between the balun halves is usually very small (assuming coax diameters far smaller than the wavelength), not exiting exactly in the center has a negligible impact on performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By running the feedline &quot;inside&quot; the antenna and balun, we have the option of connecting the shield in a location where there can be no common mode current, while connecting the feedpoint somewhere else. A similar trick is used by the &lt;a href=&quot;https://ham.stackexchange.com/q/899/218&quot;&gt;shielded loop antenna&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-02-09T20:25:59.970" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3593" PostTypeId="2" ParentId="3588" CreationDate="2015-02-09T13:30:00.447" Score="1" Body="&lt;p&gt;There are some things to consider before choosing a mechanism. They include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What is the duty cycle of each transmitter and what is the combined duty cycle? How does (average transmit duration for one radio per hour) * (number of radio) compare to one hour?&lt;/li&gt;&#xA;&lt;li&gt;Do all the radios have a similar transmit duration per hour?&lt;/li&gt;&#xA;&lt;li&gt;How often do radios join or leave the net?&lt;/li&gt;&#xA;&lt;li&gt;Is the number of radios in the net constant, or nearly constant? The question does state &quot;&lt;em&gt;we have variable count of devices&lt;/em&gt;&quot;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Assigning fixed slots will be difficult in a net where the number of members keeps changing. It may need frequent reassigning or there may be many slots where no member transmits. Thus wasting bandwidth and possibly slowing down message transmission while a transmitter wait for their slot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the overall bandwidth required is low then it may be better to go for &quot;&lt;strong&gt;Carrier Sense Multiple Access&lt;/strong&gt;&quot; &lt;a href=&quot;http://en.wikipedia.org/wiki/Carrier_sense_multiple_access&quot; rel=&quot;nofollow&quot;&gt;&lt;strong&gt;CSMA&lt;/strong&gt;&lt;/a&gt; or &quot;&lt;strong&gt;CSMA with Collision Detection&lt;/strong&gt;&quot; &lt;a href=&quot;http://en.wikipedia.org/wiki/Carrier_sense_multiple_access_with_collision_detection&quot; rel=&quot;nofollow&quot;&gt;&lt;strong&gt;CSMA/CD&lt;/strong&gt;&lt;/a&gt; networks. These are designed for networks where the membership varies over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CSMA type networks work well when the total amount of messages (ie data) is low compared to the maximum capacity, ie when the number of collisions is relatively low. As the amount of data to be transmitted increases the number of collisions increases. At some point the network may become overloaded and the actual throughput decrease.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Designs for these kinds of network must also consider:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How to handle the detection and possible retransmission of messages that are garbled (corrupted) due to a collision.&lt;/li&gt;&#xA;&lt;li&gt;What happens if a transmitter fails and is continuously transmitting.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4223" LastActivityDate="2015-02-09T13:30:00.447" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3594" PostTypeId="2" ParentId="3591" CreationDate="2015-02-09T19:05:03.337" Score="2" Body="&lt;p&gt;It's possible to make a folded balun on a double-sided PCB, with a track on top of a double-sided PCB. This makes the whole yagi (or dipole or vivaldi) quite easy to fabricate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It looks something like this (terribly not to scale)&#xA;&lt;img src=&quot;https://i.stack.imgur.com/SD7KK.png&quot; alt=&quot;PCB infinite balun&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The short-circuited 1/4 wave stub already helps a lot with matching, it broadens the bandwidth of a dipole nicely. For more difficult matching problems, you can&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;design the yagi for a reasonable feedpoint impedance, of course&lt;/li&gt;&#xA;&lt;li&gt;adjust the length of the driven element&lt;/li&gt;&#xA;&lt;li&gt;adjust the depth of the balun short, by filling it in, or extending it back, which allows you to add some parallel inductance or capacitance&lt;/li&gt;&#xA;&lt;li&gt;use a 1/4 wave open stub to excite the other half of the dipole, which allows you to add some series inductance or capacitance.  The feed will then look like this:&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/HdDsb.png&quot; alt=&quot;extra-credit feedpoint&quot;&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Bear in mind that normal fibreglass PCB is quite lossy, so at GHz frequencies this is not a very efficient antenna. It helps to make only the feed area out of PCB, and the rest out of solid metal, wire, etc., but there's still the transmission line loss, which is much much worse than coax. Going to a Rogers or other low-loss dielectric also helps.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-02-09T19:05:03.337" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="3596" PostTypeId="2" ParentId="3588" CreationDate="2015-02-09T22:36:06.870" Score="1" Body="&lt;p&gt;You need a protocol. Theres no easy way around this without a protocol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By protocol i mean, each radio needs to be at least half-duplex, and negotiate that information on the fly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are going all this long to have a network, you might very well use WiFi modules and have everything solved for you automatically.&lt;/p&gt;&#xA;" OwnerUserId="4225" LastActivityDate="2015-02-09T22:36:06.870" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3597" PostTypeId="2" ParentId="3502" CreationDate="2015-02-09T22:47:29.817" Score="0" Body="&lt;p&gt;Its easier to see an antenna as a ressonator. The antenna ressonates in the frequency that is fundamental to it. Electrons (the charges you refer to) go forward/backwards in the frequency of the fundamental.  And thats simply that.&#xA;Power is transmitted to the air as eletromagnetic waves generated by those electrons accelerating/decelerating (magnetic field) and by the charge up/down of the elements (electric field).&lt;/p&gt;&#xA;" OwnerUserId="4225" LastActivityDate="2015-02-09T22:47:29.817" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3598" PostTypeId="2" ParentId="1921" CreationDate="2015-02-10T01:08:53.750" Score="11" Body="&lt;p&gt;Although much of the main page is not written in English, after you login most of the site is and the RMO Repeater coverage map maker is a wonderful and highly customizable tool even for multi-site repeaters.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;http://www.va3xpr.net/three-easy-steps-to-creating-rf-coverage-maps-like-a-pro/&quot; rel=&quot;noreferrer&quot;&gt;VA3XPR.Net: Three easy steps to creating RF coverage maps like a pro:&lt;/a&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;a href=&quot;http://www.ve2dbe.com/rmonline.html&quot; rel=&quot;noreferrer&quot;&gt;Radio Mobile Online&lt;/a&gt; is a radio wave propagation prediction tool created and maintained by &lt;a href=&quot;http://www.qrz.com/db/ve2dbe&quot; rel=&quot;noreferrer&quot;&gt;Roger Coudé, VE2DBE&lt;/a&gt;, which is dedicated for use by the ham radio community. As indicated on the Radio Mobile Online website, it uses digital terrain information and a mathematical model to simulate radio transmissions between two fixed sites or between a fixed site and a mobile. The digital terrain information comprises three databases: ground elevation, land cover, and population density, which combined total 200 GB of information.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ol2kg.jpg&quot; alt=&quot;va3xpr example map&quot;&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;To generate an RF coverage map using Radio Mobile Online, all you need to do if follow the three easy steps below.&lt;/p&gt;&#xA;  &#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;Create an account with Radio Mobile&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;  &#xA;  &lt;p&gt;Go to the Radio Mobile Online website and create a free account. You can do this by providing your name or callsign and email address. Once you enter this information, you will receive your password to enter the site via the email address you provided during registration.&lt;/p&gt;&#xA;  &#xA;  &lt;ol start=&quot;2&quot;&gt;&#xA;  &lt;li&gt;Plot your transmitter location&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;  &#xA;  &lt;p&gt;Once you have created your account and logged into Radio Mobile Online, you will now seen a menu on items on the left side of the page. Before we can create any RF coverage maps, we first need to define the location of the transmitter that we want to determine coverage for. To do this, simple select the “New Site” option in the menu.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Uv2rg.jpg&quot; alt=&quot;create new site&quot;&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Create a Site&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;You will now see a map of the world and a red pin on it. There are two mays to plot your location on map – either by directly entering the latitude and longitude into the fields provided or by iteratively moving the pin on the map and zooming in until you locate the pin on your desired location. You can switch the map to Ssatellite view if you want to see the actual building or tower that you want to set as your transmitter location. Once you have placed the pin at your desired location, click “Submit”&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/94jgf.jpg&quot; alt=&quot;locate pin at tx site&quot;&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Site map plot&lt;/p&gt;&#xA;  &#xA;  &lt;ol start=&quot;3&quot;&gt;&#xA;  &lt;li&gt;Create a RF coverage map&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;  &#xA;  &lt;p&gt;Once you have defined your transmitter location, it is now time time create a RF coverage map for that location. To do this, select the “New Coverage” option in the menu. You will now see a number of data fields that you’ll need to complete with some already containing default values. An explanation of each of these is below.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Centre Site – this is the location of your transmitter. Select your location using the pull down menu.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Antenna Height – this is the height of your antenna above the ground at that specific location. Please note that this is in metres and if you want to convert your height in feet, divide the value by 3.2808 (i.e. 100 ft = 30.48 m).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Antenna Type – this is the type of antenna that you will be using at the transmitter location. Unless you’ll be using an antenna with an offset gain, you should just use the default omnidirectional, or “Omni” setting.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Antenna Azimuth – this is the direction that your antenna will be pointing, with 0° being north. This value is only important if you are using an antenna with an offset gain value, as it would not have any impact for an omnidirectional antenna.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Antenna Tilt – this is the angle of radiation of your antenna with 0° point towards the horizon. Some antennas have a higher gain value point slightly upwards or downwards, so this setting can be used to address this.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Antenna Gain – this is the amount of gain for your specific antenna. To find out the gain value for your antenna, you may need to check the specifications that are published for it by the manufacturer. Please note that the value for this field is in dBi (isotropic) – if your antenna has a dBd (dipole) value, you can covert dBd to dBi by adding 2.15 dBi (i.e. 5 dBd = 7.15 dBi).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Mobile Antenna Height – this is the height of the receiving antenna on the mobile station that will be used to determine your coverage area. Again, please note that this is in metres and if you want to convert your height in feet, divide the value by 3.2808 (i.e. 10 ft = 3.48 m).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Mobile Antenna Gain – this is the gain of the receiving antenna on the mobile station that will be used to determine your coverage area. Please note that the value for this field is in dBi (isotropic) – if your antenna has a dBd (dipole) value, you can covert dBd to dBi by adding 2.15 dBi (i.e. 5 dBd = 7.15 dBi).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Frequency – this is the frequency that your transmitter will use. Radio Mobile Online allows frequencies to be used within amateur radio bands from 10 MHz to 250 GHz.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;TX Power – this is the power output of your transmitter in Watts.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;TX Line Loss – this is the power loss in your feed line cable between the transmitter and antenna at your transmitter location. The longer the feed line, the higher this value will be. To find the value, you should check with the cable manufactures specification for your feed line and calculate the total loss based upon the length of your cable. For added precision, you can also include the power loss in your connectors as well.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;RX Line Loss – this is the signal loss of the feed line for your receiving station in dBi.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;RX Threshold – this is the lowest signal level that the coverage map will display. While most radios have better receive sensitivity than this, this value will provide a good indication for coverage for all radios, including older one with less sensitive receivers.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Required Reliability – this figure displays the reliability to which the coverage is likely to experience. For more accurate coverage maps, you can increase this value, however the resulting coverage area will less.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Maximum Range – this value defines the limit of the coverage analysis. If you expect coverage beyond 100 km, then increase this value to show coverage beyond 100 km. Please note that if you want to convert from miles to kms, multiply by 1.6 (i.e. 100 mi = 160 km).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Once you have entered all of this information, Radio Mobile Online will begin generating the RF coverage map for your transmitter location. Depending on the details entered and the time of day to which you have requested the RF coverage map to be generated, it may take anywhere from a few minutes to 20 minutes to produce the coverage map. Once it’s complete, a map will appear displaying your RF coverage area. To save this RF coverage map, click “Add to my coverages”.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;One important note for coverage maps being generated in major cities is that Radio Mobile Online does not have building information included in its database, so the coverage maps it produces will not reflect the impact of buildings on the signals proportion. The result of this will be coverage maps that are not representative of the actual signal levels that a users may experience, especially in urban areas.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;So there you go – you’re now on your way to creating professional looking RF coverage maps that can be used to determine how good that proposed repeater site will be that can shared with friends or posted online.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="1246" LastEditorUserId="1246" LastEditDate="2015-02-10T02:12:06.557" LastActivityDate="2015-02-10T02:12:06.557" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3599" PostTypeId="1" CreationDate="2015-02-10T05:54:36.983" Score="2" ViewCount="4819" Body="&lt;p&gt;My &lt;em&gt;Canadian Amateur Radio Basic Qualification Study Guide&lt;/em&gt; tells me that my antenna length is specific to the wavelength I wish to broadcast on and gives a formula that equates to antenna length = half the desired wavelength. In a number of places it also suggests that the length of the antenna must support a standing wave of the radiated frequency &lt;em&gt;exactly&lt;/em&gt; in its length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the propagation effects of the atmosphere, I'm guessing that I am going to need to chop and change between bands in order to talk to people locally and around the world depending on the time of day, phase of the moon and whether it's raining in Helsinki while my Uncle Bob is having his coffee in Copenhagen. Will I need different length antennas to be able to do this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a handheld Yaesu VX-7R radio which appears to do okay on multiple bands, but I clearly don't change the antenna to flick between them. My bedside clock radio also doesn't require a different length antenna for each frequency... so all of my practical experience of radio (which admittedly is virtually nil) tells me that I'm not understanding what the book is telling me. Can I broadcast to higher frequencies using an antenna designed for the 160m band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone clarify what my book means when it says &quot;exactly in its length&quot;?&lt;/p&gt;&#xA;" OwnerUserId="4201" LastEditorUserId="4201" LastEditDate="2015-02-10T13:36:35.993" LastActivityDate="2017-03-02T19:19:42.827" Title="How does the antenna length affect signal transmission/receipt in different bands?" Tags="&lt;antenna&gt;&lt;band-plan&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3601" PostTypeId="2" ParentId="3599" CreationDate="2015-02-10T07:01:20.870" Score="0" Body="&lt;p&gt;Using the 70cm band as an example, The respective frequencies are 420-450 MHz, yielding wavelengths between 71.4 &amp;amp; 66.7 cm. This varies from +2% to -5% of the nominal 70cm wavelength. Fitting an antenna to the nominal frequency/band plan suffices for frequencies in said band plan.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While I'm not sure about the antenna length being half that of the nominal wavelength, my 2m/70cm handheld txer antenna is about a sixteenth (2^-4) wavelength long for the 2m band, and a quarter (2^-2) wavelength long for the 70cm band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure what &quot;exactly in its length&quot; means.&lt;/p&gt;&#xA;" OwnerUserId="4226" LastActivityDate="2015-02-10T07:01:20.870" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3603" PostTypeId="2" ParentId="3599" CreationDate="2015-02-10T12:46:37.567" Score="2" Body="&lt;p&gt;It sounds like your study guide is conflating a few issues, and oversimplifying others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly, in antenna engineering, there are concepts of &lt;em&gt;physical&lt;/em&gt; length and &lt;em&gt;electrical&lt;/em&gt; length. Physical length is measured with a ruler, and is pretty straightforward.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Electrical&lt;/em&gt; length how long the antenna seems to the currents travelling in them. For example, a vertical is typically a 1/4 wavelength long, but because there's a ground plane below it which makes an &lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;image antenna&lt;/a&gt;, electrically it looks like a 1/2 wavelength. There are also ways to &quot;electrically lengthen&quot; an antenna, for example &lt;a href=&quot;http://en.wikipedia.org/wiki/Loading_coil&quot; rel=&quot;nofollow noreferrer&quot;&gt;loading coils&lt;/a&gt; and capacity hats&lt;sup&gt;1&lt;/sup&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that these concepts of &quot;length&quot; don't apply to all antenna types. For wire antennas it makes sense, but what about a &lt;a href=&quot;http://www.antenna-theory.com/antennas/fractal.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;fractal antenna&lt;/a&gt; or a &lt;a href=&quot;http://www.antenna-theory.com/antennas/aperture/vivaldi.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Vivaldi antenna&lt;/a&gt;? These antennas aren't long thin wires, so it's not clear how any concept of &quot;length&quot; would unambiguously apply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More generally, it is usually the objective to make the antenna system match the &lt;a href=&quot;http://en.wikipedia.org/wiki/Characteristic_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;characteristic impedance&lt;/a&gt; of the feedline (usually but not always 50 ohms), either by making the antenna &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrical_resonance&quot; rel=&quot;nofollow noreferrer&quot;&gt;resonant&lt;/a&gt; and selecting an antenna type with the desired &lt;a href=&quot;http://en.wikipedia.org/wiki/Radiation_resistance&quot; rel=&quot;nofollow noreferrer&quot;&gt;radiation resistance&lt;/a&gt; (50 ohms), or by adding a &lt;a href=&quot;http://en.wikipedia.org/wiki/Impedance_matching&quot; rel=&quot;nofollow noreferrer&quot;&gt;matching network&lt;/a&gt; to adjust the antenna impedance to match. The reason we care about impedance matching for transmitters is to &lt;a href=&quot;http://en.wikipedia.org/wiki/Maximum_power_transfer_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;maximize power transfer&lt;/a&gt; from the transmitter to the antenna. For receivers, &lt;a href=&quot;https://ham.stackexchange.com/q/382/218&quot;&gt;this is less important&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Regarding changing frequencies for different propagation conditions, this is true on HF, where the ionosphere plays a significant role in propagation. Ionospheric conditions &lt;a href=&quot;https://ham.stackexchange.com/q/1755/218&quot;&gt;vary by time of day&lt;/a&gt; as well as &lt;a href=&quot;https://ham.stackexchange.com/q/125/218&quot;&gt;solar activity&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On VHF and UHF, this is not a concern, because the ionosphere is mostly transparent at these frequencies&lt;sup&gt;2&lt;/sup&gt;. Rather, propagation is by &lt;a href=&quot;http://en.wikipedia.org/wiki/Line-of-sight_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;line-of-sight&lt;/a&gt;, and the difficulties you encounter are largely due to obstructions (buildings, mountains, etc) being in the way. There is some difference in how &lt;a href=&quot;https://ham.stackexchange.com/q/793/218&quot;&gt;particular frequencies can penetrate obstructions&lt;/a&gt;, but mostly propagation on VHF and UHF is predictable and consistent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: I haven't included a link to capacity hats because I couldn't find a good reference. Beware of sites on antennas written by hams (like this one): hams love to talk about antennas with authority, but few of them are qualified to do so (including me). Remember that it's &lt;em&gt;amateur&lt;/em&gt; radio.&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;2: notable exception: &lt;a href=&quot;https://ham.stackexchange.com/q/1497/218&quot;&gt;troposcatter&lt;/a&gt;.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-02-10T12:46:37.567" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="3604" PostTypeId="1" CreationDate="2015-02-10T14:07:49.653" Score="3" ViewCount="809" Body="&lt;p&gt;Here is my goal: To be able to talk to my friend using packet even when He or I are not there using a saving to TNC technique. We live only a few miles away from each other, and have a good signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would love to be indicated when I have a message awaiting, therefore, I can get right to the terminal and reply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have the MFJ-1270B, and it has 5 LED lights on it DCD PTT STA CON PWR. I am assuming the STA light might have something to do with a message awaiting because it is the only one that hasn't been used yet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does the 1270B support BBS? If so, what commands would my friend use to send a message to me and SAVE it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to do this as simply as possible, and just want to be able to Text over ham radio simple messages where we can have notifications (like the LED on the TNC) when we get a message directly to our calls. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am giving my friend the PK232 and I know that one is capable of BBS and has an indicator light, but I just picked up the MFJ 1270B at the hamfest and don't know much about it. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-04-09T21:08:22.953" Title="How to setup packet BBS?" Tags="&lt;packet&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3605" PostTypeId="1" AcceptedAnswerId="3608" CreationDate="2015-02-11T06:27:47.407" Score="3" ViewCount="526" Body="&lt;p&gt;I'm building a trap dipole for the high HF bands, 10 / 12 / 15 / 17.&lt;br&gt;&#xA;So far what I've got in the air is:    &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The 10 meter section (4.92 meters, 16.14 feet, resonant at 29Mhz)  &lt;/li&gt;&#xA;&lt;li&gt;The 10 meter traps (8pF cap in parallel with a 4µH inductor, resonant at ≈28Mhz)  &lt;/li&gt;&#xA;&lt;li&gt;The 12 meter section (80 cm, 31.5 inch)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;                8pF/4µH                             8pF/4µH&#xA;             ----{10M}------------{Balun}------------{10M}----&#xA;            0.4M        2.46M        ║       2.46M          0.4M&#xA;                                     ║&#xA;                                     ║ 30.4M coax&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Now take a look at the output from my antenna analyzer:&#xA;&lt;img src=&quot;https://i.stack.imgur.com/LoWTG.png&quot; alt=&quot;What my SARK110 sees&quot;&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whhaaaat... Well, I'm happy with the 10 meter resonant point (given by M1)&#xA;but what the heck happened next? I read somewhere that traps would electrically shorten all subsequent dipole sections, but i'm not sure what to make of this. Why would the 12 meter section be so far out of tune. Any ideas?  &lt;/p&gt;&#xA;" OwnerUserId="3008" LastEditorUserId="3008" LastEditDate="2015-02-12T01:03:02.077" LastActivityDate="2015-02-12T15:46:37.207" Title="Trap dipole tuning up on the wrong band" Tags="&lt;hf&gt;&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="3606" PostTypeId="1" CreationDate="2015-02-11T14:05:32.133" Score="10" ViewCount="929" Body="&lt;p&gt;If I insert some impedance (like a loading coil, or a trap) at the base of a monopole antenna, the effect on the feedpoint impedance is easy to predict: the impedance is in series with the antenna, so whatever the feedpoint impedance was, the added impedance (Z) is added to it. See ANT1:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/XJT2D.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fXJT2D.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what happens as that impedance is moved away from the feedpoint, as in ANT2? The impedance is still in series with the antenna, but must be subject to some impedance transformation as seen by the feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can we characterize this impedance transformation? Can we put some math to it?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8832" LastEditDate="2017-02-24T03:18:46.813" LastActivityDate="2017-05-29T12:26:19.023" Title="How does an antenna transform impedances along its length?" Tags="&lt;antenna&gt;&lt;impedance&gt;&lt;theory&gt;&lt;measurement&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3607" PostTypeId="2" ParentId="2" CreationDate="2015-02-11T22:20:33.527" Score="1" Body="&lt;p&gt;Besides monitoring spotting sites for KH stations, you might try contacting when you know there are a lot of Hawaiian stations working the band and where they are working it.  Two sources to consider.  One is the Ohana Net which is on the air regularly on the 20 meter band and I hear them all the time (but, I am in Washington state).  They have a web site where you should be able to find the times of their net schedule.  I think they are Saturday mornings: &lt;a href=&quot;http://www.ohananetradio.com&quot; rel=&quot;nofollow&quot;&gt;http://www.ohananetradio.com&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another source is the Hawaii QSO Party which does not occur in 2015 until August (at least it is in the future for 2015).  I think it is August 22nd but check their web site which is at: &lt;a href=&quot;http://www.hawaiiqsoparty.org&quot; rel=&quot;nofollow&quot;&gt;http://www.hawaiiqsoparty.org&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might e-mail some of the KH stations you can find on these web sites to set up a schedule.  I remember in my days to fulfill my WAS I was lacking Rhode Island.  After several years of missing it, I finally arranged a schedule with a guy in Rhode Island and then added my 50th state.  So, schedules work even though they might be the last resort.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-02-11T22:20:33.527" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3608" PostTypeId="2" ParentId="3605" CreationDate="2015-02-12T15:46:37.207" Score="2" Body="&lt;p&gt;Traps require that the sections that follow them to be shortened because they look like loading coils. We can demonstrate this by calculating the impedance of your trap at 28MHz and 24.9MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://en.wikipedia.org/wiki/LC_circuit#Impedance_2&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance of a parallel LC circuit&lt;/a&gt; is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z(\omega) = &#xA;-j \left( 1 \over C \right)&#xA;\left( \omega \over \omega^2 - \omega_0^2 \right )$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$\omega = 2 \pi f$&lt;/li&gt;&#xA;&lt;li&gt;$\omega_0 = 1 / \sqrt{LC}$&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So for your trap:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \omega_0 = {1 \over \sqrt{4\:\mathrm{\mu H} \cdot 8\:\mathrm{pF}}} = 176776695 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the resonant frequency in radians per second; if we divide by 2π we see that it's 28.13MHz as expected. We can then calculate the impedance at the relevant frequencies:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z(28\:\mathrm{MHz}\cdot 2 \pi) = j73.6\:\mathrm k\Omega \\&#xA;Z(24.9\:\mathrm{MHz}\cdot 2 \pi) = j2.89\:\mathrm k\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of 28MHz, the trap is a high impedance, and this serves to reduce the current on the section past the trap to some negligible level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 24.9MHz the impedance is much lower, but it's not nothing. Additionally, it is no longer a quarter-wave down the antenna, but something less. Because this impedance is purely imaginary and positive, it's an inductive impedance. We can divide the &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrical_reactance&quot; rel=&quot;nofollow noreferrer&quot;&gt;reactance&lt;/a&gt; (the imaginary part of &lt;a href=&quot;http://en.wikipedia.org/wiki/Electrical_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance&lt;/a&gt;) by ω to get an effective inductance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {2.89\:\mathrm k\Omega \over 2 \pi \cdot 24.9\:\mathrm{MHz}} = 18.5\:\mathrm{\mu H} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, at 24.9MHz (and just that one frequency), the trap looks just like a 18.5μH inductor. Just like a loading coil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the coil is not at the base of the antenna but closer to the tip, its effect on the feedpoint impedance somewhat diminished. &lt;a href=&quot;https://ham.stackexchange.com/q/3606/218&quot;&gt;I don't know the exact math&lt;/a&gt;, although you can find loading coil calculators around the net. Normally we use a loading coil when we don't have room for a full-sized antenna, but here we are reasoning in the opposite order: because you have a loading coil, your antenna can't be full-size.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-02-12T15:46:37.207" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3609" PostTypeId="1" AcceptedAnswerId="3615" CreationDate="2015-02-12T21:11:49.240" Score="3" ViewCount="4159" Body="&lt;p&gt;If I am going to use a Kenwood TM-D710G for APRS, will I need to leave one of the VFOs on the APRS frequency of 144.390 MHz, or does the TM-D710G have a 3rd VFO built-in specifically for APRS use?&lt;/p&gt;&#xA;" OwnerUserId="1246" LastEditorUserId="76" LastEditDate="2015-02-14T18:49:39.487" LastActivityDate="2015-03-05T09:46:28.023" Title="Setting up a Kenwood TM-D710G for APRS" Tags="&lt;aprs&gt;&lt;kenwood&gt;&lt;equipment-operation&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3610" PostTypeId="1" AcceptedAnswerId="3611" CreationDate="2015-02-13T00:29:19.647" Score="3" ViewCount="8025" Body="&lt;p&gt;How would I go about converting from Baud to Bits per Second (bps) and then from Bits per Second to Bytes per Second (Bps)?&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-02-14T18:46:40.510" Title="Conversion from Baud to Bits per Second and then to Bytes per Second" Tags="&lt;math&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3611" PostTypeId="2" ParentId="3610" CreationDate="2015-02-13T01:50:36.963" Score="12" Body="&lt;p&gt;&lt;em&gt;Baud&lt;/em&gt; is another name for &lt;em&gt;symbols per second&lt;/em&gt; (a unit of &lt;em&gt;symbol rate&lt;/em&gt;), so you can't convert between it and the others (which are units of &lt;em&gt;bit rate&lt;/em&gt;) without knowing &lt;em&gt;how many symbols are in use&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;em&gt;symbol&lt;/em&gt; is the smallest unit of a digital modulation. For example, suppose we're doing on-off keying (also known as CW): the signal can be either present or absent, so there are two symbols. If we were to also use two intermediate amplitudes between &quot;off&quot; and &quot;full power&quot;, that would make a total of four symbols. (Digital modulations in amateur radio use frequency-shift keying (e.g. RTTY, JT65/JT9) but this is easier to picture to start with.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Using more than two symbols allows you to encode more bits per symbol, which allows for more efficient use of bandwidth for a given data rate.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the conversion, suppose there are $M$ symbols. Then each symbol can be used to encode $\log_2 M$ bits. Inversely, for a whole number of bits $N$, then you need $2^N$ different symbols to encode all those bits in one symbol. Thus the conversion between baud and bits per second is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;1\,\mathrm{baud} = N\,\mathrm{b/s} \\&#xA;\text{ or } \\&#xA;1\,\mathrm{baud} = \log_2M\,\mathrm{b/s}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The conversion between bits per second and bytes per second is, in practice, much simpler: there are 8 bits ($\mathrm{b}$) in a byte ($\mathrm{B}$).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;1\,\mathrm{B/s} = 8\,\mathrm{b/s}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Historically, the word “byte” was used to refer not to exactly 8 bits, but to the smallest addressable unit of memory in computers, or the size of one character. This is not different in practice, because 8 bits per byte is now essentially universal practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one wants to be entirely unambiguous, the word &quot;octet&quot; refers to a unit of eight bits only. In some countries this is commonly used, giving abbreviations for data sizes like “Mo” instead of “MB”.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;As an example, let's combine the above two facts:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;A data rate of 2 kilobytes per second is equal to 16 kilobits per second.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If we were to send this data using only two symbols, the symbol rate would be equal to the bit rate: 16 kilobaud.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If we were to send this data using 256-QAM, a modulation which has 256 distinct symbols (used for digital TV, for example), then each symbol encodes $\log_2{256} = 8$ bits, or one byte, meaning that the symbol rate is 2 kilobaud.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-02-14T18:46:40.510" LastActivityDate="2015-02-14T18:46:40.510" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3612" PostTypeId="1" CreationDate="2015-02-14T06:25:42.730" Score="1" ViewCount="976" Body="&lt;p&gt;How do hams deal with the privacy and security concern of your station location (usually a home) having the information published for everyone to see? It seems hams do not have proper concern for information shared and the security implications thereof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, I hear things like hams talking about being mobile and driving and also talking about their base stations etc. OK you're mobile and you have an expensive radio at home you were just talking about. What's the address? Let's check the FCC website and get it. This is mostly concerning for more local bands like 2m or 70cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are often big social media pushes about being careful who share information with because people see you post a picture from being on vacation then ransack your home. In HAM radio, you have no idea who might be listening. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact the FCC publishes the data as public information baffles me. Why is it public information? Only the FCC needs it right?&lt;/p&gt;&#xA;" OwnerUserId="4096" LastActivityDate="2015-02-18T00:45:47.587" Title="Why does the FCC publish station address information?" Tags="&lt;fcc&gt;&lt;security&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3613" PostTypeId="2" ParentId="3612" CreationDate="2015-02-14T18:03:10.590" Score="4" Body="&lt;p&gt;It's actually your mailing address that gets listed, not your station location, however for most hams they are the same.  You can, however, have a P.O. Box listed instead of a physical location, if you want.  (See &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?node=se47.5.97_123&amp;amp;rgn=div8&quot; rel=&quot;nofollow&quot;&gt;97.23&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to the security aspect: I really doubt there are a lot of thieves listening on the ham bands for who's got an expensive radio to go steal.  Ham gear is hard to sell if you don't know what it is, and so few and far between that stealing laptops &amp;amp; TVs from any random house is probably a far better bet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: The address is useful for sending QSL cards.  Self-policing via DF may play a role, but reporting the location of bad behavior to an official observer should be sufficient even if you can't turn it back into a callsign.  (And consider many violators are either not licensed or not at their station location.)&lt;/p&gt;&#xA;" OwnerUserId="1343" LastEditorUserId="1343" LastEditDate="2015-02-14T21:18:48.793" LastActivityDate="2015-02-14T21:18:48.793" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3614" PostTypeId="1" CreationDate="2015-02-14T18:08:29.333" Score="3" ViewCount="1516" Body="&lt;p&gt;I have an MFJ-934 tuner/artificial ground for my MFJ-1699 multi-band vertical (stuck on a balcony, so limited HF antenna options), and I'm wondering if there's any downside to the counterpoise starting in the shack and then running outside to the balcony rather than at the base of the antenna itself.  I live in an area with a lot of noise, and I'm trying to do whatever I can to get the noise level down, and it seems an effective counterpoise should help.  So, is it okay to have a counterpoise that starts 20' from the antenna, and why or why not?&lt;/p&gt;&#xA;" OwnerUserId="1343" LastEditorUserId="1343" LastEditDate="2015-02-18T00:32:44.007" LastActivityDate="2015-02-18T00:32:44.007" Title="Counterpoise from artificial ground vs base of antenna" Tags="&lt;antenna&gt;&lt;grounding&gt;&lt;counterpoise&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3615" PostTypeId="2" ParentId="3609" CreationDate="2015-02-14T18:15:37.290" Score="1" Body="&lt;p&gt;I don't own a D710 myself, but I was looking at buying one, so this is from my understanding of the manual: no, the D710 does not have a dedicated APRS VFO.  If you look at page PACKET-2 of the D710 manual, it describes selecting which &quot;band&quot; (A or B) is used as the data band.&lt;/p&gt;&#xA;" OwnerUserId="1343" LastActivityDate="2015-02-14T18:15:37.290" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3616" PostTypeId="1" CreationDate="2015-02-14T20:17:20.697" Score="3" ViewCount="167" Body="&lt;p&gt;Is typical background RF plus radio receiver electronics noise (wide-band audio) closer to white noise or pink (1/f) noise?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it depend on the demodulation scheme (AM/FS/SSB/etc.), if any, currently configured or the band being tuned?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2015-02-15T17:25:29.677" Title="Color of radio noise?" Tags="&lt;noise&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3618" PostTypeId="2" ParentId="3616" CreationDate="2015-02-15T13:51:40.840" Score="3" Body="&lt;p&gt;There is no single answer to your question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Atmospheric noise varies over the RF spectrum. It's generally true that the natural RF noise power is higher at lower frequencies, but to call it something like &quot;pink noise&quot; would be inaccurate. For example, lightning is a significant contributor to noise on HF, and it comes in &quot;crashes&quot; as you might expect. There are also regions of higher or lower noise due to the varying absorptive capability of the atmosphere at some frequencies, or due to astronomical noise sources (like the sun) which emit more strongly at some frequencies than others. Of course man-made noise enters into it too: for example the 2.4 GHz ISM band is &lt;em&gt;very&lt;/em&gt; noisy due to the proliferation of microwave ovens, Wi-Fi access points, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, noise over the RF spectrum as a whole doesn't fit any simple mathematical model. However, many communications are band-limited, and within the passband of a typical communications channel the variations from one end to the other are not much, so it's a good approximation to call it white noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now concerning receiver noise, there are several kinds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every component in the receiver generates &lt;a href=&quot;http://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise&quot; rel=&quot;nofollow&quot;&gt;thermal noise&lt;/a&gt;, which is like white noise. This is noise due to the thermal movement of charge carriers in the receiver, and the only way to avoid it is to cool the radio to absolute zero. Radio astronomers have radios that are cooled to reduce thermal noise, but the radios most mortals use are not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, there is &lt;a href=&quot;http://en.wikipedia.org/wiki/Flicker_noise&quot; rel=&quot;nofollow&quot;&gt;flicker noise&lt;/a&gt;, also called 1/f noise or pink noise. There are many physical mechanisms that generate this kind of noise, but it's ubiquitous.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below some frequency, the flicker noise is stronger than the thermal noise, and the converse is true above that frequency. So whether the noise at some point in the receiver is closer to pink or white, or some combination thereof, depends on the relevant frequency at that point. For example, after demodulation, the signal has been mixed down to baseband and so the frequencies are much lower, so the pink noise becomes more relevant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, there's &quot;other&quot; noise in the receiver: noise from digital components, power line hum, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do all of these noise sources combine together into the signal you hear from the receiver? It depends on many factors. In a simple demodulation scheme like SSB, the RF spectrum is just shifted down into audio range, ideally through a filter with a flat passband. Thus, white noise in the RF input becomes white noise at the audio output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM is not so simple. &lt;a href=&quot;https://books.google.com/books?id=coQ6ac-fh6QC&amp;amp;lpg=PA237&amp;amp;ots=qDFZvETe1f&amp;amp;dq=fm%20noise%20distribution&amp;amp;pg=PA237#v=onepage&amp;amp;q=fm%20noise%20distribution&amp;amp;f=false&quot; rel=&quot;nofollow&quot;&gt;FM leads to a different demodulated noise spectral density function&lt;/a&gt;, and you have &lt;a href=&quot;http://claessonedwards.com/index.php?option=com_content&amp;amp;view=article&amp;amp;id=72&amp;amp;Itemid=89&quot; rel=&quot;nofollow&quot;&gt;pre-emphasis&lt;/a&gt; further coloring things. The pre-emphasis is designed to approximately cancel the noise distribution introduced by the demodulation, so you end up with approximately white-ish noise in the end, but this is only approximately true, and it varies by the particular pre-emphasis standard you are using.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Digital modulations can use even more exotic filters which are more concerned about time-domain behavior, so they can color the noise in complex ways. &lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-02-15T17:25:29.677" LastActivityDate="2015-02-15T17:25:29.677" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3619" PostTypeId="2" ParentId="3614" CreationDate="2015-02-15T15:32:26.370" Score="2" Body="&lt;p&gt;The downside of having your counterpoise in the shack is that it will be much closer to all the noise in your shack: your computers, powerlines, and so on. The counterpoise, and everything between it and the antenna, is every bit as much of the receiving structure as the &quot;antenna&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also there will be stronger RF fields near your shack. This may or may not be a problem, depending on the sensitivity of your devices and your transmitter power. With a 10W transmitter, you are almost surely fine. At 100W, you are probably OK. At 2KW, you are almost surely going to have problems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's always better, if you can, to have an intentional, deliberate &quot;counterpoise&quot;, like radials under a vertical, or a dipole where the counterpoise is the 2nd half of the dipole. It's also better if you can put the antenna on a tower, on a mountain, far away from any noise. But you have to work with what you have, and if you are stuck on a balcony or simply don't have room for those things, compromises are necessary.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-02-15T15:32:26.370" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3620" PostTypeId="1" CreationDate="2015-02-15T18:46:21.860" Score="5" ViewCount="979" Body="&lt;p&gt;Why is it that some frequencies transmitted at some known direction are reflected back to earth, yet others transmitted at the same direction, power and polarity pass through into space with no reflection?&lt;/p&gt;&#xA;" OwnerUserId="4201" LastEditorUserId="76" LastEditDate="2015-02-15T20:46:53.463" LastActivityDate="2015-02-15T22:02:17.613" Title="Why does the ionosphere reflect some frequencies and not others?" Tags="&lt;propagation&gt;&lt;frequency&gt;&lt;physics&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3621" PostTypeId="2" ParentId="3577" CreationDate="2015-02-15T19:19:14.023" Score="3" Body="&lt;p&gt;The rubber duck antennas are monopole antennas that have their length of wire turned into a helix. The helical shape allows you to cram the same length of wire into a smaller volume, just as you correctly noticed. The &quot;rubber duck&quot; comes from the fact that these helices are often sealed in rubbery stuff to keep the shape intact and the water out. Monopole, GP (ground plane), and quarter wave antenna all refer to the same basic idea of replacing the other hand of a dipole antenna with a ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see a few challenges in your design: the height of 3&quot; is really litle for the intended wavelength and you also want to put your electronics PCB into the same container. The antennas do not generally like conductive parts near them as the electric field generated by the antenna is coupled into the conductor such as your PCB. The same goes for your AC cabling: it might negatively affect the performance of your antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normal design flow would probably go as follows: first you get an idea of how the antenna should look like, then you simulate it with 3D electromagnetic simulation tools, optimize it and later include a conductor sheet to represent the receiver PCB and a short length of conductor pole to act as the AC cable. In this case, however,  I would go experimenting: with your measuring equipment you can hack together a working prototype very quickly and find out if the result is good enough for your application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And finally to the real content: I would try to do a dipole antenna that has a 90 degree turn in the middle and whose arms have been shortened by wrapping them as coils (just as they do in the rubber duck antennas). The antenna arms would be in horizontal plane of your enclosure. The 90 degree turn in the middle will prevent you from having any radiation nulls in horizontal plane. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope that the size of your receiver is relatively small part of your box, otherwise the following won't work. Does your receiver PCB have a coaxial connector or are you going to solder the antenna leads directly onto the receiver? In either case:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;take a coaxial connector that can be connected to your VNA and your receiver&lt;/li&gt;&#xA;&lt;li&gt;take two little over $\lambda/4$ (20&quot;) wires that keep their shape but can be formed with hand.&lt;/li&gt;&#xA;&lt;li&gt;roll the your antennas around of a plastic pipe with 2-3&quot; diameter so that you will end up with a helix that a) fits inside the box, b) is as long as possible&lt;/li&gt;&#xA;&lt;li&gt;solder the arms of your dipole to the coaxial connector to 90 degree angles.&lt;/li&gt;&#xA;&lt;li&gt;Connect the connector to your VNA and hope that you see a dip in S11 somewhere below your intended frequency.&lt;/li&gt;&#xA;&lt;li&gt;shorten the helices with wire cutters one piece at a time as long as your dip is close to the intended frequency. Make both arms equally long.&lt;/li&gt;&#xA;&lt;li&gt;connect your device into the receiver and hope for the best.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This is a workflow I would try, it might not work for you, depending on your application, signal strenght requirement, and especially the size of your receiver. Let us know how it went.&lt;/p&gt;&#xA;" OwnerUserId="194" LastActivityDate="2015-02-15T19:19:14.023" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3622" PostTypeId="2" ParentId="3620" CreationDate="2015-02-15T21:35:43.570" Score="4" Body="&lt;p&gt;Skywave propagation is closely related to &lt;a href=&quot;http://en.wikipedia.org/wiki/Total_internal_reflection&quot; rel=&quot;nofollow noreferrer&quot;&gt;total internal reflection&lt;/a&gt;. This is easily demonstrated with visible light (which is also electromagnetic radiation) through a block of acrylic:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/lLU3r.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Total internal reflection occurs when the angle of incidence is above a critical angle, which is a function of the refractive indexes of the two materials:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \theta_c = \arcsin\left( n_2 \over n_1 \right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the angle of incidence decreases beyond the critical angle, some of the incident wave is refracted and passes though the interface, and less of it is reflected. Obviously for terrestrial communication we want to maximize the reflected part and minimize the refracted part. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can observe total internal reflection and refraction with something as simple as a glass of water. At some angles, it will look like a mirror. At others, it's almost transparent. For communication, we want it to look like a mirror, or as close as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This reflection (or not) occurs at the interface between any two materials with a different index of refraction. This might seem like it should apply to optics but not to radio propagation, but the disconnect isn't one of physics, but one of terminology. For non-magnetic materials with &lt;a href=&quot;http://en.wikipedia.org/wiki/Permeability_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;relative permeability&lt;/a&gt; of 1, then the &lt;a href=&quot;http://en.wikipedia.org/wiki/Wave_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;wave impedance&lt;/a&gt; ($Z$) and &lt;a href=&quot;http://en.wikipedia.org/wiki/Refractive_index&quot; rel=&quot;nofollow noreferrer&quot;&gt;refractive index&lt;/a&gt; ($n$) are simply related by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z = Z_0 / n $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;...where $Z_0$ is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance of free space&lt;/a&gt;. Wave impedance is simply the square root of the ratio of permeability ($\mu$) to permittivity ($\epsilon$)&lt;sup&gt;1&lt;/sup&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z = \sqrt{\mu \over \epsilon} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Refractive_index#Relations_to_other_quantities&quot; rel=&quot;nofollow noreferrer&quot;&gt;Another way to define the index of refraction&lt;/a&gt; is in relation to the relative permeability and relative permittivity of a material:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ n = \sqrt{\epsilon_r \mu_r} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for any material with a permittivity different than free space, (like the ionosphere) this material will also have a refractive index different than that of air (or vacuum, which is very close to that of air), and thus, reflection can occur. We don't necessarily need &lt;em&gt;total&lt;/em&gt; internal reflection, though that certainly makes things easier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer your question of why this doesn't occur for all frequencies, there are several reasons, but one is that refractive index (or permittivity) depend on frequency. In optics this is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Dispersion_%28optics%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;chromatic dispersion&lt;/a&gt; but the concept applies to lower frequencies of electromagnetic waves as well. A prism illustrates the effect clearly:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/UhzjZ.png&quot; alt=&quot;prism&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The separation of colors is due to each frequency component of white light being refracted to a different degree, due to the frequency dependency of the refractive index.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the refractive index of the ionosphere varies by frequency, at higher frequencies the refractive indexes of the ionospheric layers is such that there isn't enough reflection from the ionosphere for good communication. Most of the incident wave from the transmitter just passes through the ionosphere and is lost to space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, this is just but one thing relevant to ionospheric propagation. The actual picture is more complex because the ionosphere is not cleanly separated from the rest of the atmosphere like a block of acrylic. Nor is the ionosphere homogeneous: it consists of many layers which are constantly undulating. In addition, the ionosphere can absorb radiation as well as reflect or refract it. But the main point still stands: the refractive index, and other properties such as absorption, are frequency dependent, and thus, only at some frequencies is reflection sufficient for communication.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: the equations can also be derived for magnetic materials. Here are some &lt;a href=&quot;http://www2.ph.ed.ac.uk/~playfer/EMlect13.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;lecture notes with more detail&lt;/a&gt;.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-02-15T22:02:17.613" LastActivityDate="2015-02-15T22:02:17.613" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3623" PostTypeId="1" CreationDate="2015-02-15T22:39:04.830" Score="2" ViewCount="608" Body="&lt;p&gt;I have a NMO mount antenna- 1/2 wave on 2 meters. I am going to stick it on top of a PVC pipe which is 5 feet tall. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since this is a bicycle mobile antenna, I do not have the option of large radials out in every direction. Would it work to have a 1/2 wave radial sticking straight down like a vertical dipole? &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-02-16T00:38:51.463" Title="Vertical dipole as a mobile antenna counterpoise?" Tags="&lt;antenna-construction&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3624" PostTypeId="2" ParentId="3623" CreationDate="2015-02-16T00:38:51.463" Score="1" Body="&lt;p&gt;If your antenna is already a 1/2 wave long, it's quite likely already a vertical dipole. Resonant dipoles are a 1/2 wave long. Resonant verticals are a 1/4 wave and make the other half as the image antenna created by the ground plane. In this case, adding another wire probably isn't going to do much of anything, since the antenna was probably designed to work without a ground plane anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If what you have is in fact a 1/4 wave vertical, then adding another 1/4 wave, co-linear wire makes it a dipole. That will indeed work, and it will work very well.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-02-16T00:38:51.463" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3625" PostTypeId="2" ParentId="756" CreationDate="2015-02-16T16:04:04.817" Score="1" Body="&lt;p&gt;Replace the 1K resistor (on the collector) with another transistor. Bias it to the operating point and add a condenser mic to its base.&lt;/p&gt;&#xA;" OwnerUserId="4255" LastActivityDate="2015-02-16T16:04:04.817" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3627" PostTypeId="1" AcceptedAnswerId="3632" CreationDate="2015-02-16T18:44:01.880" Score="3" ViewCount="1079" Body="&lt;p&gt;I have some &lt;a href=&quot;http://www.radioshack.com/enercell-12v-12ah-sla-battery-w-f2-terminal-250-tabs/2301219.html#.VON09DbN8hE&quot; rel=&quot;nofollow noreferrer&quot;&gt;12V, 12Ah Enercell batteries from RadioShack&lt;/a&gt;, RS part number 2301219. As far as I can tell these are AGM SLA batteries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I picked up &lt;a href=&quot;http://www.harborfreight.com/12-volt-deluxe-battery-maintainer-and-float-charger-61911.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this 3-stage charger&lt;/a&gt; from Harbor Freight and as far as I can tell it's charging the batteries (which were probably on the shelf for years and not touched).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The goal is to build a portable 12V (and hopefully 36Ah) battery box. I've wired the batteries in parallel:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NNsaw.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fNNsaw.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The batteries need 14.5-14.9V (max 3.6A) for &quot;normal charging&quot; and 13.6-13.8V (max 1.8A) for &quot;trickle charging&quot;. The packaging says not to use automotive or marine chargers. So for single batteries, the only thing I've found has been something like &lt;a href=&quot;http://www.powerstream.com/lead-acid-12V-5A.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this charger from PowerStream&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will I harm these batteries by only charging them on a trickle charger? If I hook these up to my 15A MFJ power supply for a short period of time, would that hurt these batteries?&lt;/p&gt;&#xA;" OwnerUserId="1097" LastEditorUserId="218" LastEditDate="2015-02-17T17:11:24.610" LastActivityDate="2015-03-05T03:22:33.447" Title="Will I harm batteries by only trickle charging them, or connecting them to a power supply?" Tags="&lt;diy&gt;&lt;battery&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3628" PostTypeId="2" ParentId="3609" CreationDate="2015-02-16T23:34:54.200" Score="2" Body="&lt;p&gt;I am setting up a B2000, a TH-D72 and a 710GA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best practice is to set the APRS freq to 144.39 MHz in &lt;strong&gt;Band B&lt;/strong&gt; then configure the data band of the TNC to &lt;strong&gt;B-Band&lt;/strong&gt;. You can lock it as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Kenwood has &quot;In Depth&quot; Manuals for each model for APRS.&lt;/p&gt;&#xA;" OwnerUserId="114" LastEditorUserId="76" LastEditDate="2015-02-18T00:39:17.083" LastActivityDate="2015-02-18T00:39:17.083" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3631" PostTypeId="2" ParentId="3612" CreationDate="2015-02-17T21:29:40.437" Score="0" Body="&lt;p&gt;Compare FCC &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=1674a953c43c2e10ce77e864a8024380&amp;amp;node=se47.5.97_1103&amp;amp;rgn=div8&quot; rel=&quot;nofollow&quot;&gt;§97.103&lt;/a&gt; to &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&amp;amp;SID=1674a953c43c2e10ce77e864a8024380&amp;amp;r=SECTION&amp;amp;n=se47.5.97_1105&quot; rel=&quot;nofollow&quot;&gt;§97.105&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC really likes to separate the concept of station license from operator license.  See how all the other services work, like marine or radar, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If&lt;/strong&gt; you “have to” separate the concepts, then you need a way to ID the station, and I can't think of a better way than its location.  Ditto the op, because people have similar names and it's either address or something even worse like SS number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If&lt;/strong&gt; the FCC only issued op licenses, &lt;strong&gt;and&lt;/strong&gt; there was a way to prove to a local cop etc. that the op license matched your driver's license info that's better than SS number or address, then I'd be surprised, but if it existed then that scheme would work.  Forcing FCC field offices to issue fedgov standard photo IDs would work, but oh the agony for all involved...&lt;/p&gt;&#xA;" OwnerUserId="4260" LastEditorUserId="76" LastEditDate="2015-02-18T00:45:47.587" LastActivityDate="2015-02-18T00:45:47.587" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3632" PostTypeId="2" ParentId="3627" CreationDate="2015-02-17T22:01:12.270" Score="2" Body="&lt;p&gt;You're not getting answers for multiple reasons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) Batteries are a science but its surrounded by marketing and astrological tradition (concrete floors, blah blah)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) If something bad happens they are destroyed or blow up the house or start a fire and no one wants to get involved in that mess.  I guess I'm just crazy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) You're using stuff from mainland China, not exactly legendary for reliability.  So the charger you have is spec'd by its manual which I downloaded and read, to output never higher than 13.2 volts to float... and from &lt;a href=&quot;http://www.powerstream.com/SLA.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.powerstream.com/SLA.htm&lt;/a&gt; its impossible to outgas explosive hydrogen unless the voltage at room temp (it varies with temp) is around 14.5 volts, so all good there, and most SLA recombinators won't vent until about C/3 charge rate and your Chinese charger theoretically only outputs 0.75 amp so its safe on any battery larger than about 3 amphours and you're at 36.  So you've got a factor of safety of more than a volt and over ten times the capacity, so IF it works to it's written specs, THEN you're totally safe.  At 3/4 amp rate, and 36 theoretical aH capacity, thats going to take more than two days to charge a completely dead battery, but it'll get there eventually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most effective way to kill a SLA is over volt it causing plate corrosion, and cheap 1970s car chargers don't voltage limit because flooded cell batteries from 1970 can have distilled water added when they outgas (unlike a SLA).  So the battery mfgr covers all bases by saying &quot;don't use a car charger&quot;  But per the specs your modern trickle charger even worst case should be very safe if you compare it to typical SLA battery mfgr specs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With no current limiting directly wiring the MFJ supply would just try to supply like 100 amps and blow a fuse if the battery is low.  If it doesn't blow a fuse and you do draw 15 amps (which it won't, for reasons beyond this discussion) then thats about C/2 charge rate and the recombinators in SLAs are usually rated to handle C/3 (optimistically) so you'll pop the vent and leak some acid and get to buy new batteries, which is annoying.  In summary, no, don't wire it directly to a power supply without some kind of circuitry in between, like a charger or charge controller type gadget.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The powerstream charger looks awesome and would make a great charger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other news &quot;which were probably on the shelf for years and not touched&quot; lead acid cells die by abuse (not a problem here) cycles (not a problem) or old age (oh oh thats a problem).  You only get &quot;less than a decade&quot; starting the instant acid hits lead back in the factory.  Just saying if it sat on the shelf for five years already, they don't really have that long to live anymore.  So on one hand if they die &quot;soon&quot; it's probably not your fault, and on the other hand if you do something bad to them they were going to the recycler soon enough anyway so you've not got much to lose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway 73, best of luck, de N9NFB K&lt;/p&gt;&#xA;" OwnerUserId="4260" LastActivityDate="2015-02-17T22:01:12.270" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3633" PostTypeId="2" ParentId="3606" CreationDate="2015-02-17T22:12:49.323" Score="1" Body="&lt;p&gt;Question 1) you can characterize it by going all smith chart on it, plot your first example as starting at 50R feedline and move thru your trap and then the antenna to end up, yes, at the vector addition of them, pretty much.  Plot the second as a short antenna (whatever the length) then based on where-ever you end up on the smith chart, figure the response of your trap at that input (and that input won't be 50R) and plot the trap on the smith chart, then finally from the output of the trap on the smith chart draw the other half of your antenna.  See where you end up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SOME trap and filter designs are fairly insensitive to abuse of input and output impedance, some are really sensitive, so funky things might happen when you feed an optimistically 50 ohm ckt with non 50 ohm source and load.  Also your &quot;second half of antenna&quot; is not being fed with resistive 50 ohm feedline impedance like the first half.  None the less, usually survivable situation.  Just saying it could be big fun under specific circumstances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question 2) Yeah good luck there.  You're asking a very general question about which entire antenna modeling books have been written and whole finite element analysis programs like ANSYS have been designed, so the answer is going to be the size of a textbook or a computer DVD.  Maybe someone who's bored with some modeling software could answer a very specific question, maybe.&lt;/p&gt;&#xA;" OwnerUserId="4260" LastEditorUserId="218" LastEditDate="2015-02-18T01:03:28.203" LastActivityDate="2015-02-18T01:03:28.203" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3634" PostTypeId="2" ParentId="3562" CreationDate="2015-02-17T22:32:33.043" Score="2" Body="&lt;p&gt;tomnexus answer is excellent, as a practical matter when fooling around with microwave gear I would point a camcorder at a wall clock in a spot where it can hear the RX quite well and then hit record on the camcorder and take off for an hour driving around with a transmitter, and making a paper log of Exactly where I was and what I was doing at 16:27 or whatever.  Sync your wall clock and your watch or whatever.  Later, come home and watch the video.  Hopefully you'll have something interesting to listen to on the recording as you correlate what you hear on the recording with your detailed log matching the recorded wall clock time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I regret to report I never ran into problems like getting ranges so high that a mere one hour camcorder recording limited my data taking LOL.  This is a small timer's strategy and those guys with 1500 watts and 200 foot towers probably cannot use this specific technique.  But it would probably work with HTs?&lt;/p&gt;&#xA;" OwnerUserId="4260" LastEditorUserId="218" LastEditDate="2015-02-18T12:33:41.633" LastActivityDate="2015-02-18T12:33:41.633" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3635" PostTypeId="2" ParentId="2482" CreationDate="2015-02-17T22:52:04.997" Score="1" Body="&lt;p&gt;Most folks will describe resonant as zero reactance, a pure resistive load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All antennas are resonant at multiple frequencies.  You can load up a quarter wave vertical as a 3/4 wave, a 5/4 wave, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately practically no pieces of metal have a 50 ohm resistive component when they're resonant so depending on design there will be a matching network and if its &quot;funky&quot; enough of a matching design you can run an antenna such that the minimum SWR is not the resonant freq.  And matching networks are almost never broadband, so the piece of wire might load up as a quarter wave and as a nine-quarters wave, but the matching networks are hard to build like that giving a 50 ohm feedline impedance across that range of freqs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a practical matter trying to do something a bit extreme like tune a small mobile antenna to work on 40 meters is likely to involve a relatively large inductor parallel to the capacitive antenna and its possible the freq where X=0 is not going to be the lowest SWR freq of the antenna.  Assuming no measurement error of course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another fun way to get weird results involves unbalanced conditions that also result in feedline radiation.  So your feedline is part of the antenna system, even if you didn't intend it, and the results can be weird.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally the difference is really small rounding to zero so just adjust for lowest SWR and call it good.  Its a situation that could happen, but you're not likely to run into it very often and even when you do, it usually doesn't matter other than being really confusing.&lt;/p&gt;&#xA;" OwnerUserId="4260" LastEditorUserId="1246" LastEditDate="2015-02-24T20:20:53.517" LastActivityDate="2015-02-24T20:20:53.517" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3638" PostTypeId="2" ParentId="1891" CreationDate="2015-02-20T03:03:15.880" Score="10" Body="&lt;p&gt;Here is a Diagram from page 11 of &lt;a href=&quot;http://radiodoc.github.io/uv-5r/#&quot; rel=&quot;noreferrer&quot;&gt;The (Chinese) Radio Documentation Project's Baofeng UV-5R Manual&lt;/a&gt; PDF: &lt;img src=&quot;https://i.stack.imgur.com/BMmRJ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-02-20T03:03:15.880" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3639" PostTypeId="1" CreationDate="2015-02-21T01:17:51.290" Score="3" ViewCount="1109" Body="&lt;p&gt;I want to build an low power transceiver on 33cm or 23cm (or 2 meters, but not recommended because of all the other activity interfering with my stuff) I would like to use FM and just have enough power for the nearby block to receive, kind of like a FRS radio but maybe even less power. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any very simple circuits out there that will allow me to do this? I am thinking something really simple like the micro power FM broadcast transmitters. I would like to be able to fit it into something close to handheld and the reason I don't want to use 70cm is because my &lt;a href=&quot;http://www.amsatnet.info/#node&quot; rel=&quot;nofollow&quot;&gt;half-duplex AllStar repeater link&lt;/a&gt; will cause desensitization on that band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will link this up with a Simplex AllStar node so I can transceive around the house. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-02-21T22:16:03.497" Title="Simple FM low power UHF transmitter circuit" Tags="&lt;diy&gt;&lt;transceiver&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3641" PostTypeId="2" ParentId="3639" CreationDate="2015-02-21T18:40:53.620" Score="3" Body="&lt;p&gt;Microwave design is often far from simple, since stuff starts to behave significantly differently from how it would at HF or even VHF. Parasitics and the like become a serious problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, there are two designs I know of off the top of my head:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's &lt;a href=&quot;http://electroschematics.com/wp-content/uploads/2008/12/24-ghz-signal-generator.jpg&quot; rel=&quot;nofollow&quot;&gt;this one based on the MAX2750 VCO&lt;/a&gt;. You'd need to vary the input into TUNE with the audio output, and you would get an frequency-modulated signal out of K1. It's for 13 cm though; I believe Maxim make an alternative part for the 23 cm band as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also &lt;a href=&quot;http://www.dutch.nl/bdj/23cmfm/23cmfm.html&quot; rel=&quot;nofollow&quot;&gt;PE1JPD's design&lt;/a&gt; which, while more complex, is a complete transceiver, and about as simple in terms of two-way communications at 1 GHz as you're going to get.&lt;/p&gt;&#xA;" OwnerUserId="1542" LastEditorUserId="76" LastEditDate="2015-02-21T22:16:03.497" LastActivityDate="2015-02-21T22:16:03.497" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3643" PostTypeId="1" CreationDate="2015-02-21T21:04:54.453" Score="5" ViewCount="13203" Body="&lt;p&gt;For reflector antennas, I see a number called aperture efficiency. What does it mean?&lt;/p&gt;&#xA;" OwnerUserId="1917" LastEditorUserId="76" LastEditDate="2015-12-15T23:41:46.877" LastActivityDate="2019-10-14T08:46:08.550" Title="What is the aperture efficiency of an antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-reflector&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3644" PostTypeId="2" ParentId="3643" CreationDate="2015-02-22T01:09:59.087" Score="4" Body="&lt;p&gt;The aperture efficiency of a horn or reflector antenna is the ratio of the effective aperture to the physical aperture.  The formula usually looks like:&#xA;$$&#xA;\epsilon_{ap} = \frac{A_e}{A_p}&#xA;$$&#xA;The aperture efficiency is a dimensionless number usually reported as a percentage and $A_e$ is the effective aperture and $A_p$ is the physical aperture.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For horn and reflector antennas, the aperture efficiency is typically in the range of 50 to 80 percent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume the OP understands antenna aperture.  The effective aperture is usually less than the physical aperture because the $E$-field is not uniform across the physical aperture.  The effective aperture and physical aperture are specific to each kind (with size dimensions) of horn and reflector antennas.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2015-02-22T02:59:23.977" LastActivityDate="2015-02-22T02:59:23.977" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3645" PostTypeId="1" CreationDate="2015-02-22T09:51:07.933" Score="3" ViewCount="591" Body="&lt;p&gt;I am using the Kenwood TM-V71A as an EchoLink link station. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I try to play our weekly bulletin, which has a duration longer than 10 minutes, the TOT cuts the transmission short. I do understand that the 10 minute maximum might be a precaution to overheating in the maximum power setting. However, I am transmitting with 10 W only, and would like to be able to transmit our bulletin in full length. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to accomplish this with this rig?&#xA;More precise: Is it possible to modify the device to work in the intended way?&lt;/p&gt;&#xA;" OwnerUserId="4270" LastEditorUserId="4270" LastEditDate="2015-03-02T16:24:46.237" LastActivityDate="2015-03-02T16:24:46.237" Title="How can I disable the TOT time out timer of the TM-V71A?" Tags="&lt;kenwood&gt;&lt;equipment-operation&gt;&lt;echolink&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3646" PostTypeId="1" CreationDate="2015-02-22T15:36:48.690" Score="3" ViewCount="582" Body="&lt;p&gt;I have a blind friend who can't put anything outside, and is restricted to antennas near the window in his apartment. Luckily he lives closer to the top, which helps with range a little bit. He has a VoIP linked repeater at his apartment and while I was range testing, I had little success getting in to it from anywhere greater than a mile from the apartment. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently, he has a 5/8*5/8 magmount 70cm antenna on some copper strips on the windowsill but I wouldn't think that is a very good ground plane. I am thinking of building an antenna for him to attempt to improve performance for his apartment repeater, I am thinking about wire antennas I could hang up or something. Does anybody have any suggestions?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-02-23T10:10:50.520" Title="70cm antenna for an apartment" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;repeater&gt;&lt;wire-antenna&gt;&lt;repeater-coverage&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3647" PostTypeId="2" ParentId="3646" CreationDate="2015-02-22T16:09:38.600" Score="2" Body="&lt;p&gt;A 70cm halfwave dipole is only 35cm long. That's a bit over a foot. Just do it!&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2015-02-22T16:09:38.600" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3648" PostTypeId="2" ParentId="3526" CreationDate="2015-02-22T17:39:27.997" Score="1" Body="&lt;p&gt;I've home-brewed several LPDA HF antennas, each one bigger than the last. I don't think it would be a problem replacing with same gauge/length of copper stranded. Another place to look for poor connections on the Hy-Gain LPDA, are joints along the small diameter phasing line. A pair of them run the full length of the boom and the short wires connect the tubes to the elements. I know of a TH-11 that had that problem, corrosion in the joints. Same style of feed/phasing lines. Match/SWR went crazy!!!  I cleaned the joints up, used some conductive compound, reassembled the antenna, and was back in business.&lt;/p&gt;&#xA;" OwnerUserId="4280" LastEditorUserId="1246" LastEditDate="2015-02-27T15:20:28.453" LastActivityDate="2015-02-27T15:20:28.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3649" PostTypeId="2" ParentId="3646" CreationDate="2015-02-23T10:10:50.520" Score="1" Body="&lt;p&gt;For an omnidirectional antenna, books will often suggest a 5/8 wavelength vertical antenna for lowest angle of radiation and highest gain (as compared to an ideal antenna, isotropic). The issue with using a vertical or dipole antenna indoors is much of the energy is radiated inside the room and depending on the building/room construction, the signals might pass through (albiet attenuated a bit) or it might not pass thru and be just wasted.&lt;br&gt; &lt;br&gt;You need to shift your focus to other antenna designs, directional antennas. They are designed to have high forward gain, but very low backward (and side) gain. Remember the front-to-back ratio in the exams? You will probably benefit more from a directional antenna (i.e. an Uda-Yagi) pointed out the window but herein lies a problem. Repeaters are really meant to use omnidirectional antennas, using a directional antenna make your system relatively deaf to other signals comming from other directions. This is a big compromise for your repeater system.&lt;br&gt; &lt;br&gt;I suggest you also study the use of antenna modelling SW (i.e. &lt;a href=&quot;http://hamsoft.ca/pages/mmana-gal.php&quot; rel=&quot;nofollow&quot;&gt;MMANA&lt;/a&gt;, NEC, MININEC) so that you can understand what the antenna is designed to do and customize the antenna to fit your needs.&lt;/p&gt;&#xA;" OwnerUserId="1761" LastActivityDate="2015-02-23T10:10:50.520" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3650" PostTypeId="2" ParentId="3643" CreationDate="2015-02-23T14:43:24.003" Score="2" Body="&lt;p&gt;The aperture efficiency tells you what percentage of the power incident upon the antenna is available at the feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The concept of &quot;power incident upon the antenna&quot; is a bit weird. So let's take a step back, and consider something more visible, like a sheet of paper. At any time there's some amount of light hitting this sheet of paper. We can increase the light hitting the paper by making the paper bigger, or by shining brighter lights at it. More specifically, all the light hitting the sheet of paper is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Luminous_intensity&quot; rel=&quot;nofollow&quot;&gt;luminous intensity&lt;/a&gt; measured in &lt;a href=&quot;http://en.wikipedia.org/wiki/Candela&quot; rel=&quot;nofollow&quot;&gt;candelas&lt;/a&gt;. The brightness of the light at the paper is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Luminance&quot; rel=&quot;nofollow&quot;&gt;luminance&lt;/a&gt;, which is luminous intensity per unit area, measured in candelas per square meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The candela is a photometric unit: it takes into account only &lt;em&gt;visible&lt;/em&gt; (by humans) electromagnetic radiation. The analogous unit which takes into account &lt;em&gt;all&lt;/em&gt; electromagnetic radiation is familiar: it's the &lt;a href=&quot;http://en.wikipedia.org/wiki/Watt&quot; rel=&quot;nofollow&quot;&gt;watt&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now consider a receiving reflector or horn antenna. Depending on the transmitter's power, gain, and distance, there will be some &lt;a href=&quot;http://en.wikipedia.org/wiki/Irradiance&quot; rel=&quot;nofollow&quot;&gt;irradiance&lt;/a&gt; at the receiving antenna, measured in watts per square meter. This irradiance, multiplied by the area of the reflector (assuming it's pointed in the right direction) gives you a power in watts, the theoretical power intercepted by the antenna. The ratio of the actual power at the feedpoint to this theoretical power is the aperture efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is another number, the &quot;effective aperture&quot;, which is the area we come up with if we run this calculation in reverse: start with the actual power at the feedpoint, and then calculate the area required to intercept that much power from the transmitter. The effective aperture is another way of expressing gain:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A_\text{eff} = {G \lambda^2 \over 4\pi} \tag{1} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$A_\text{eff}$ is the effective aperture,&lt;/li&gt;&#xA;&lt;li&gt;$G$ is the gain (as a unitless ratio, not in dB), and&lt;/li&gt;&#xA;&lt;li&gt;$\lambda$ is the wavelength.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If $A_\text{phys}$ is the physical aperture, for example the area of the reflector, then aperture efficiency is simply the ratio:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ e_a = {A_\text{eff} \over A_\text{phys}} \tag{2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which we can combine with equation 1 to be expressed in terms of gain rather than effective aperture:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ e_a = {G \lambda^2 \over 4 \pi A_\text{phys}} \tag{3} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or if your gain is expressed in decibels and you have frequency, not wavelength:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ e_a = {10^{G_\text{dB}/10}\: c^2 \over 4 \pi \: A_\text{phys} \: f^2} \tag{4} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, let's find &lt;a href=&quot;https://www.andovercg.com/store/Cisco-Wireless/Cisco-AIR-ANT3338-Aironet-2-4GHz-21dBi-Dish-Antenna-p9683.html?gclid=Cj0KEQiAvKunBRCfsum9z6fu_5IBEiQAu4lg4rDSyqDXlcVFRvfPYVn0Gl9SZ2jy4d4iA_9QabTDWFgaAsSF8P8HAQ&quot; rel=&quot;nofollow&quot;&gt;an arbitrary antenna on the internet&lt;/a&gt; with specifications:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;2.4 GHz&lt;/li&gt;&#xA;&lt;li&gt;24 inch diameter (0.2235 square meters area)&lt;/li&gt;&#xA;&lt;li&gt;21 dBi&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Thus by equation 4, the aperture efficiency of this antenna is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ e_a = {&#xA;  10^{21\mathrm{dBi}/10}\: c^2&#xA;\over&#xA;  4 \pi \: 0.2235\:\mathrm{m}^2 \:&#xA;  (2.4\:\mathrm{GHz})^2&#xA;} = 70\% $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is, 70% of the power hitting that 24 inch reflector is available at the feedpoint, while the other 30% is lost. The losses could be due to:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the feedhorn and its support structure shadowing the dish&lt;/li&gt;&#xA;&lt;li&gt;diffraction around the edges of the dish&lt;/li&gt;&#xA;&lt;li&gt;less than perfect focus and reflectivity of the dish&lt;/li&gt;&#xA;&lt;li&gt;inefficiencies of the feedhorn itself&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-02-23T14:53:08.390" LastActivityDate="2015-02-23T14:53:08.390" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3651" PostTypeId="2" ParentId="2482" CreationDate="2015-02-23T22:02:30.603" Score="3" Body="&lt;p&gt;The antenna impedance is $R+jX$ where $R$ denotes the real part and $X$ denotes the imaginary part of the impedance. Resonance means the imaginary part is exactly zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most antenna designs do not have an impedance of exactly 50 Ω, and their resonance is somewhere close to 50 Ω. For example the resonance may be at 40 Ω, but the minimum SWR may be at $(45+5j) \,Ω$, which is closer to 50 Ω as seen on a Smith chart.&lt;/p&gt;&#xA;" OwnerUserId="1917" LastEditorUserId="76" LastEditDate="2015-02-25T03:28:53.853" LastActivityDate="2015-02-25T03:28:53.853" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3652" PostTypeId="1" CreationDate="2015-02-23T23:09:05.157" Score="5" ViewCount="765" Body="&lt;p&gt;So a very experienced friend of mine is making a portable suitcase kit with Yaesu FTL-2001 (VHF), Yaesu FTL-7002 (UHF) and DX-720D duplexer* plus power supply and other miscellaneous gear. FTL-2001 and FTL-7002 are connected to inputs of DX-720D and the output is connected to the antenna socket on the suitcase. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Originally, the coaxial jumpers were installed inside of the suitcase so that they fit as neatly as possible. Later on, he decided to change one of the jumpers so that it is of same length as the other jumper because &quot;cables going to a duplexer need to be of same length&quot;. He couldn't provide me a better explanation than this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This set off my WARNING! SUPERSTITION alarm, since it seems to look a lot like &lt;a href=&quot;https://ham.stackexchange.com/q/1628/77&quot;&gt;this&lt;/a&gt; question. Furthermore, to me it seems a bit strange that the same length would be very critical, since the transcievers are operating on different bands. I've read some resources about cavity duplexers where jumpers of length corresponding to certain wavelength fraction are recommended, but I haven't seen anywhere this recommendation of having same length even if the frequency bands are different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;So my question is&lt;/strong&gt;: Is there actually any real reason to have coaxial jumpers of same physical length for connection to a duplexer? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;*Note: this unit is referred to as duplexer on various websites that sell it, but it only has fixed low-pass and high-pass filters from what I see, so perhaps term &lt;code&gt;diplexer&lt;/code&gt; would be a better fit.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-02-24T20:33:24.843" Title="Why exactly would cable lengths to a duplexer matter?" Tags="&lt;feed-line&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3653" PostTypeId="1" AcceptedAnswerId="3655" CreationDate="2015-02-24T02:37:06.817" Score="2" ViewCount="2024" Body="&lt;p&gt;I purchased a baofeng car charger for my little UV5Rv2 HT. It was advertised to work with the radio, so I didn't think much of it. It turns out, all it does is pass my car electrical system voltage through to the base charger! Looking at the base charger, I see it accepts 10&amp;nbsp;V input DC and outputs 8.4&amp;nbsp;V DC and 400&amp;nbsp;mA current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I thought I could solder a little resistor inline the charger to add additional resistance to produce a lower voltage. It seems this would work for a fixed load, understanding that my car would produce approximately 14.5&amp;nbsp;V output while running.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So $$ 10 = 0.4 \cdot R $$ produces $$ {10 \over .4} = 25 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the resistance of the charger is approximately 25 $\Omega$, which is maybe where I'm going wrong somewhere, because if I measure resistance across the + and - terminal of the base station while plugged in, I get 10.56 M$\Omega$. Ignoring that and moving on, I need to figure out what the resistance should be for a 400&amp;nbsp;mA load creating a 4.5 voltage drop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$ 4.5 = 0.4 \cdot R $ gives me ${4.5 \over .4} = 11.25$. So I figured putting a $11.25\ \Omega$ resistor inline the positive terminal of the car charger might give me the voltage drop I wanted. This is not the case however. So knowing I have a constant load of 14.5&amp;nbsp;V and a 400&amp;nbsp;mA load, how do I calculate the size resistor I should be putting inline to drop 4.5&amp;nbsp;V to hopefully get to approximately 10&amp;nbsp;V?&lt;/p&gt;&#xA;" OwnerUserId="4096" LastEditorUserId="366" LastEditDate="2016-11-26T18:11:48.583" LastActivityDate="2016-11-26T18:47:43.280" Title="Why doesn't adding a resistor inline to a 12 V car charger change output voltage" Tags="&lt;electronics&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3654" PostTypeId="2" ParentId="3653" CreationDate="2015-02-24T03:09:31.737" Score="2" Body="&lt;p&gt;The charger, which accepts 10V on its input and produces 8.4V on its output, is a voltage regulator. A voltage regulator is designed to hold its output voltage constant over possibly varying input voltage and almost certainly varying current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;400mA&quot; on the charger is most likely not the current it outputs all the time, but the maximum current it could output while still meeting its other specifications. The actual current drawn will depend on the load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the base charger is a voltage regulator (quite possibly with some additional battery charging circuitry), attempting to lower the input voltage by adding a series resistor is unnecessary. Let it function as designed.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-02-24T03:09:31.737" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3655" PostTypeId="2" ParentId="3653" CreationDate="2015-02-24T05:25:56.907" Score="5" Body="&lt;p&gt;&lt;strong&gt;You can't use a fixed resistor&lt;/strong&gt; to control the input the voltage for an arbitrary electronic device, only one which is a &lt;strong&gt;passive&lt;/strong&gt; load, such as a resistor, or an LED. (Note that even a simple LED invalidates your Ohm's-law-based reasoning, because it does not have a fixed value of $R$, though it can still be handled with a resistor.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A battery charger is not passive — it contains a control system providing the appropriate voltage and/or current for each of the stages of charging (which depend on the particular battery chemistry).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you say your “base charger” is marked as having an 8.4 V output, this means it is quite possibly not a charger &lt;em&gt;per se&lt;/em&gt; at all, but a power supply for a charging circuit built into the radio. And the 400 mA figure is not the expected output but rather the &lt;em&gt;maximum&lt;/em&gt; output. (Hint: No device can &lt;strong&gt;ever&lt;/strong&gt; have an output which is both a fixed current and a fixed voltage. It's physically impossible.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether the device is a power supply (power adapter) or a battery charger, in either case it is going to be &lt;em&gt;regulated&lt;/em&gt; — it contains circuits which produce the target output voltage (or current) regardless of the input voltage (within the designed limits). The input &lt;em&gt;power&lt;/em&gt; will be maintained, determined by the demands of the load on the output; if the input voltage is lower, more current will be drawn to compensate; if it is higher, then less current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The result of inserting a resistor in series with a too-high voltage input is that the device will see a too-high voltage whenever it is drawing little current (you can calculate this; just look at $V_\text{across resistor} = IR$ when $I=0$) — and this will happen initially before things are fully powered on, and finally when the battery charge is complete. If there's a protection circuit, this could trip it; if not, and the voltage exceeds the rated voltage of the components, it could damage the device or cause it to misbehave temporarily.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-02-24T05:25:56.907" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3656" PostTypeId="2" ParentId="3652" CreationDate="2015-02-24T20:33:24.843" Score="1" Body="&lt;p&gt;Ham radio is pretty much the intersection of EE and murphys law.  In more detail:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no electrical reason but there is an excellent practical reason with feedlines such that if you need a 49 foot cable and a 50 foot cable, murphys law is you'll inevitably find a way to install the 50 foot cable in place of the 49 foot cable leaving a surprising amount of slack and then try to install the 49 foot cable in place of the 50 footer and end up 12 inches short.  Very annoying when something like this happens, especially if you have to remove 15 zip ties and rerun both cables thru conduit.  All the flexible coax sections on my antennae were precisely my height such that accidents like that can't happen when up in the air, not physically possible to mix up the cable lengths because they're all the same.  At a commercial site I visited it was SOP to permanently label cables with their length, which helps both with mixups and with later TDR testing if necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can totally see a practical use like that getting Urban Legended into a duplexer in a suitcase needs equal length feedlines.  If you do accidentally connect the wrong TX to the wrong duplexer port you probably have enough cable slack to fix it without specifically needing to cut to precisely equal length.&lt;/p&gt;&#xA;" OwnerUserId="4260" LastActivityDate="2015-02-24T20:33:24.843" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3657" PostTypeId="2" ParentId="3645" CreationDate="2015-02-24T20:48:25.480" Score="1" Body="&lt;p&gt;You have two questions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First answer is no, page 70 of the manual, the menu option is TOT and default as you've noticed is 10 and the options are 3, 5, or 10 minutes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second answer is you could rig up some array of 555s or a microcontroller such that it unkeys for half a second every nine minutes and nobody's going to notice but the rig TOT will reset.&lt;/p&gt;&#xA;" OwnerUserId="4260" LastActivityDate="2015-02-24T20:48:25.480" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3658" PostTypeId="2" ParentId="2357" CreationDate="2015-02-24T21:09:39.757" Score="4" Body="&lt;p&gt;This is likely a &lt;strong&gt;ferroresonant transformer&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.electroncoil.com/ferroresonant_transformers.php&quot; rel=&quot;nofollow&quot;&gt;http://www.electroncoil.com/ferroresonant_transformers.php&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hammondmfg.com/CVR.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.hammondmfg.com/CVR.htm&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.oltronix.nl/en/ferroresonant-principle&quot; rel=&quot;nofollow&quot;&gt;http://www.oltronix.nl/en/ferroresonant-principle&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you wanted a surge protector, a motor-generator would work pretty well.  Is there a way to get rid of the moving parts of a MG?  Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most transformers are fairly linear, until you reach a magnetic flux that saturates or they overheat. If you resonated a winding on a transformer and intentionally made it magnetically saturate just at normal voltage output, then if a power surge hit it would try to output a higher voltage but its in saturation so nope; worst case is the output gets some square wave harmonics and of course the transformer would heat up a little.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This transformer is fairly useless without the specs and wiring diagram and the capacitor that resonates the winding.  It's easy to repurpose a regular transformer but CVTs are black magic even with the docs so you've basically got a piece of scrap metal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually one winding is a little larger than the other; yours are almost identical.  Odd.  Other than that, looks like a google image search for “ferroresonant transformer”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's one under my desk right now.  They're only about 90% efficient, plenty of heat.  Also they're heavy.  And they always hummmmm.  Thats why you don't see many.&lt;/p&gt;&#xA;" OwnerUserId="4260" LastEditorUserId="76" LastEditDate="2015-02-25T03:24:24.153" LastActivityDate="2015-02-25T03:24:24.153" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3660" PostTypeId="2" ParentId="2343" CreationDate="2015-02-26T01:09:53.837" Score="0" Body="&lt;p&gt;No, this would not be possible unless you were to program a PIC chip to switch the radio to the call channel, which would be set to the &lt;code&gt;144.930 MHZ&lt;/code&gt; APRS frquency when it heard an APRS brap from the TT. It would then have to switch the radio back when the APRS had been sent. Still, It would be VERY tricky because the PIC would only be switching the radio when it heard the APRS, not before. So, unless you could have the TT start transmitting but wait one second to send the APRS so the PIC could switch the TT, it would not work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, how could the TT know when you were keying the mike?&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-02-26T01:09:53.837" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3661" PostTypeId="2" ParentId="3653" CreationDate="2015-02-26T14:56:37.503" Score="0" Body="&lt;p&gt;The way one typically charges lithium-ion batteries, which I believe the Baofeng radios use, is via a constant current circuit. The circuit adjusts the input voltage to meet the desired current level in essence. All a resistor will do is make it that much harder to get the correct power in to the system, but it won't actually detract from the current going in to the battery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, the circuit isn't simply a resistor, but is a transformer, something in practice a good deal more complex. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would measure the output of the circuit, see if it is reasonably close to the desired output, and if it seems to work, then leave it alone. If you really want to do something more controlled, you'll need to buy a 13 to 10V DC transformer, a simple resistor won't do.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="218" LastEditDate="2015-02-27T12:06:56.380" LastActivityDate="2015-02-27T12:06:56.380" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3663" PostTypeId="1" AcceptedAnswerId="3664" CreationDate="2015-02-26T18:21:17.913" Score="4" ViewCount="259" Body="&lt;p&gt;I just barely learned that IMAP is a protocol that allows you to read and respond to emails without using the internet. Would it be possible to use this application for packet radio and if so, how? I am using the Ubuntu 14.10 operating system. &lt;/p&gt;&#xA;" OwnerUserId="1861" LastEditorUserId="1246" LastEditDate="2015-03-02T02:50:25.823" LastActivityDate="2018-03-18T16:11:19.767" Title="Can IMAP email be used for packet radio?" Tags="&lt;packet&gt;&lt;internet&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3664" PostTypeId="2" ParentId="3663" CreationDate="2015-02-26T19:24:12.440" Score="2" Body="&lt;p&gt;IMAP is a protocol for transferring email, nothing more, nothing less.  It typically uses TCP/IP as the underlying protocol, but it &lt;em&gt;could&lt;/em&gt; be routed over something else (like packet radio).  If you wanted to, you could &lt;a href=&quot;http://www.tldp.org/HOWTO/AX25-HOWTO/x1194.html&quot; rel=&quot;nofollow&quot;&gt;configure TCP/IP over AX.25&lt;/a&gt; but I don't know if anyone else is doing it, so you'd probably need to run your own mailserver on the other end as well.  (You could even configure that mailserver to bridge to the internet, but keep in mind that you'd be responsible for any incoming traffic that made it onto amateur frequencies!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you can't do is use Thunderbird to interact with any typical packet BBS or mailbox systems, they work with different protocols.  So essentially, what you ask is possible, I'm just not sure if it's useful.&lt;/p&gt;&#xA;" OwnerUserId="1343" LastActivityDate="2015-02-26T19:24:12.440" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="3665" PostTypeId="1" CreationDate="2015-02-27T16:39:33.300" Score="4" ViewCount="1470" Body="&lt;p&gt;I'm looking to start building various antenna tuning circuits, but I'm limited by my parts inventory. I have pots and mag wire for winding inductors and a nice spectrum of fixed-value capacitors, but I have no high-voltage parts, nor variable parts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The instructions I find online for mag loop antennas, in particular, require high-voltage variable capacitors. I'm still grappling with the theory to understand exactly what voltages are involved, but tuner circuits I'm finding around the web also involve variable caps/inductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where do I find these parts for sale, or are they reasonable to build at home? I've been to a couple of local swap meets, but they're almost entirely PC parts, software, and manuals from the 90s. No vintage radios that I could find to pirate parts from.&lt;/p&gt;&#xA;" OwnerUserId="1607" LastActivityDate="2015-06-30T13:40:25.323" Title="Where does one find high-voltage variable capacitors and inductors for RF?" Tags="&lt;diy&gt;&lt;antenna-construction&gt;&lt;antenna-tuner&gt;" AnswerCount="2" CommentCount="5" ClosedDate="2015-07-01T11:54:26.900" ContentLicense="CC BY-SA 3.0" />
  <row Id="3666" PostTypeId="2" ParentId="3665" CreationDate="2015-02-27T17:18:52.780" Score="0" Body="&lt;p&gt;They are not cheap, but they can be found.&#xA;&lt;a href=&quot;http://www.ebay.com/itm/Vacuum-Variable-Capacitor-10kV-10-500pF-HAM-RADIO-NOS-/391061938848?pt=LH_DefaultDomain_0&amp;amp;hash=item5b0d1ba2a0&quot; rel=&quot;nofollow&quot;&gt;http://www.ebay.com/itm/Vacuum-Variable-Capacitor-10kV-10-500pF-HAM-RADIO-NOS-/391061938848?pt=LH_DefaultDomain_0&amp;amp;hash=item5b0d1ba2a0&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This guy as a lot of good info on mag loops. I plan on coping his design one day. &lt;a href=&quot;http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4307" LastActivityDate="2015-02-27T17:18:52.780" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3667" PostTypeId="2" ParentId="3665" CreationDate="2015-03-01T13:38:47.467" Score="0" Body="&lt;p&gt;Bob VE3UK is a machinist and makes some really nice butterfly capacitor components which he sells pretty much at cost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He runs the Magnetic Loop Antennas Yahoo group.  If you join that group you'll find a lot of information on Mag Loops and their components.  Look him up on QRZ.COM for more of his info.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Yahoo group is here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://groups.yahoo.com/neo/groups/MagLoop/info&quot; rel=&quot;nofollow&quot;&gt;https://groups.yahoo.com/neo/groups/MagLoop/info&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4130" LastEditorUserId="218" LastEditDate="2015-04-01T11:36:25.060" LastActivityDate="2015-04-01T11:36:25.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3668" PostTypeId="1" CreationDate="2015-03-03T07:53:39.063" Score="9" ViewCount="11325" Body="&lt;p&gt;How does one go about building a portable repeater for use at events? Preferably at low cost, and with a minimum of bulky parts (so it's travel friendly).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously you'd need a pair of radios to handle RX and TX, taking into account that the TX radio will probably have an above-average duty cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd imagine you'd also some sort of controller to add courtesy tones / send out a station ID. I know there's some commercial options out there, but most of them look rather expensive (thousands of dollars, US), and not terribly small. I'd like to imagine that most of this work could be done with a specially equipped Raspberry Pi?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there's the issue of antennas. I know you can use a duplexer to share a single antenna, but I think those are also large and expensive. Can you make due with two antennas, given sufficient separation? Any other options?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anything else I'm missing?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;As a bonus consideration: My primary purpose would be for amateur radio, but it would be awesome if it could be somehow reconfigurable to work as a repeater for GMRS purposes (legally, in the US). There's very little information out there about GMRS repeaters, which is rather surprising.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="304" LastEditorUserId="873" LastEditDate="2015-06-10T12:26:49.193" LastActivityDate="2015-07-10T01:02:39.407" Title="Building a portable event repeater" Tags="&lt;diy&gt;&lt;repeater&gt;" AnswerCount="4" CommentCount="4" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3670" PostTypeId="2" ParentId="718" CreationDate="2015-03-04T16:04:32.713" Score="-1" Body="&lt;p&gt;I think instead of saying that you can &quot;load up anything conductive&quot; or that the tuner makes the transmitter think that the random wire antenna is resonant, it's better to say that the tuner converts the impedance at the end of the random wire to 50 ohms, which is the impedance that the transmitter wants to see. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, what AB3RY says about random wires is correct. I used a random wire antenna on 80m for a while. The tuner was on a window sill in my shack, and I could run up to 25W before the RF in the shack got to be too much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason to have the tuner in the shack is so that it can be easily adjusted, BUT if you had an automatic antenna tuner and could locate it some distance from the shack, then RF in the shack would not be such a big problem. Several companies make remote antenna tuners that come in weatherproof enclosures.&lt;/p&gt;&#xA;" OwnerUserId="42" LastActivityDate="2015-03-04T16:04:32.713" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3671" PostTypeId="2" ParentId="3627" CreationDate="2015-03-05T03:22:33.447" Score="0" Body="&lt;p&gt;I have several &quot;to go&quot; boxes using these exact same 12 aH Radio Shack batteries.  I use Tidy Cat 35 # plastic litter containers with a handle.  Ideal.  Each container has 4 - 12 aH batteries connected in parallel.  Theoretically 48 aH capacity @ 12.72 volts after charging with a Schumacher SEM-1562A maintainer.  This maintainer is rated at 1.5 amps, so with 4 Enercells connected in parallel the charge rate is 0.375 amps per battery.  I would not exceed a 0.5 amp charging rate on a single battery.  It's my understanding that these are AGM batteries and therefore do not &quot;off gas&quot; during charging.  I think that if you hook them up to the 15 amp MFJ power supply you could fry them.  Make sure that you use 10 gauge wire or larger to limit voltage loss when the batteries are put to use, and I wouldn't discharge them to any lower than 70% of the rated 12 aH.  So if you had 3 batteries in parallel you would recharge the batteries when you've used 3.6 aH x 3 = 10.8 aH, or a voltage of 11 volts, whichever comes first.  I use Windy Nation watt meters to monitor voltage and the cumulative aH load with my portable ham gear.  &lt;/p&gt;&#xA;" OwnerUserId="4326" LastActivityDate="2015-03-05T03:22:33.447" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3672" PostTypeId="2" ParentId="3609" CreationDate="2015-03-05T09:46:28.023" Score="1" Body="&lt;p&gt;It only has two VFOs, band A and band B.  You'll need to pick one of them for APRS.  I have memory slots configured for APRS frequencies in the regions I visit (144.800 is APRS-EU, there is also 430.5125 on 70cm in the Netherlands I call APRS-NL).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Kenwood has a nice &quot;APRS lock&quot; feature.  You can configure it to just lock PTT so you don't accidentally start transmitting voice on the APRS frequency, but you can also configure it to lock turning the TNC off accidentally or changing the frequency.  I usually lock all three except when I'm in the Netherlands where I can often hear 70cm beter than 2m and switch between them.&lt;/p&gt;&#xA;" OwnerDisplayName="user4328" LastActivityDate="2015-03-05T09:46:28.023" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3673" PostTypeId="1" AcceptedAnswerId="3674" CreationDate="2015-03-06T16:09:51.410" Score="3" ViewCount="139" Body="&lt;p&gt;When I tried to enter frequencies in my 2 meter YAESU, it was already programmed for 144.000 MHz as the primary. WHY?&lt;/p&gt;&#xA;" OwnerUserId="4333" LastActivityDate="2015-06-03T16:42:59.343" Title="Why is 2 meter pre-programed?" Tags="&lt;2m-band&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3674" PostTypeId="2" ParentId="3673" CreationDate="2015-03-06T16:34:54.497" Score="2" Body="&lt;p&gt;You'll have to be more specific about what “the primary” is (give your radio model and the exact words/labels it uses in your question) for a more definite answer, but most likely it's simply that 144.000 MHz is the lowest frequency that is part of the 2-meter band (&lt;a href=&quot;http://en.wikipedia.org/wiki/2-meter_band&quot; rel=&quot;nofollow&quot;&gt;this is true worldwide&lt;/a&gt;), so it's a reasonable place to start for a VFO which has got to have &lt;em&gt;some&lt;/em&gt; frequency to be on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that you should not actually transmit on 144.000 MHz, because it &lt;em&gt;is&lt;/em&gt; the lower band edge, and so the lower sideband of your signal would extend outside of the band.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-03-06T22:17:41.253" LastActivityDate="2015-03-06T22:17:41.253" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3675" PostTypeId="1" AcceptedAnswerId="3676" CreationDate="2015-03-07T09:29:21.243" Score="12" ViewCount="9069" Body="&lt;p&gt;I'm new to electronics and telecommunication at all, I having trouble with understanding the difference between 2, 3 and 4 radials, as I've searched online I've learned that I can use only 1 radial(and it makes sense) but when using 2, 3 or 4 its to supply a counterpoise to the ground(&lt;strong&gt;balance?&lt;/strong&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other source talked about 2 radials:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The object of the two radials is to produce a canceling signal in the&#xA;  horizontal plane. They do this by being driven together. However, they&#xA;  must radiate a canceling field. That means they must be matched to&#xA;  radiate.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Is the above quote also apply to 4 radials and anyway what is true is it only for &lt;strong&gt;balance&lt;/strong&gt; or &lt;strong&gt;canceling&lt;/strong&gt; maybe I'm confused and its about both, if anyone can help me make sense from all I will be very thankful.&lt;/p&gt;&#xA;" OwnerUserId="4335" LastActivityDate="2018-01-29T13:31:54.387" Title="What is the effect of using different number of radials with ground plane antenna" Tags="&lt;antenna&gt;&lt;radial&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3676" PostTypeId="2" ParentId="3675" CreationDate="2015-03-07T13:58:35.613" Score="16" Body="&lt;p&gt;An ideal vertical doesn't have radials: it's half a dipole sitting upon a perfectly conductive, infinite plane. Under these idealized conditions, its radiation pattern is identical to a dipole's radiation pattern that's been sliced in half (like a bagel), and the vertical's feedpoint impedance is exactly half that of a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RLkhN.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RLkhN.png&quot; alt=&quot;the radiation pattern of an ideal vertical is just like a dipole, missing the bottom half.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the plane under the vertical deviates from this ideal, the effect is generally that radiation at low angles is reduced, and the antenna becomes less efficient due to resistive losses in the ground. This happens if the ground plane isn't very conductive (like dirt), or if it isn't infinitely long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some simulated results to illustrate, thanks to &lt;a href=&quot;https://ham.stackexchange.com/users/4306/jsh&quot;&gt;JSH&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GmKl1.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GmKl1.png&quot; alt=&quot;simulated radiation patterns over ground planes of varying quality&quot;&gt;&lt;/a&gt;&#xA;&lt;em&gt;&lt;a href=&quot;http://www.hamradio.me/wp-content/uploads/2016/01/40m_MonoPole_SXC.png&quot; rel=&quot;noreferrer&quot;&gt;http://www.hamradio.me/wp-content/uploads/2016/01/40m_MonoPole_SXC.png&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More radials, and longer radials, moves you closer to the ideal. Less radials, or shorter radials, moves you closer to a dummy load. If you have no radials at all then the feedline will be the radial and you end up with something not unlike a dipole (albeit a very oddly shaped one).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With just two radials, then if you view the antenna from one side (perpendicular to the radials), you have a pretty good ground plane to the left and to the right. But if you walk 90 degrees around the antenna so that the radials are coming at you, there are no radials at all to the left and the right, and consequently in those directions you'll get less radiation. Such an antenna isn't perfectly omnidirectional, but it can be good enough. A mag-mount on a balcony railing is essentially this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have three radials, the pattern is more or less omnidirectional. Of course this is still very far from an ideal, infinite ground plane, but modeling and empirical evidence have shown that if the radials are elevated (to minimize interaction with the ground) and trimmed to resonant lengths, the results are for practical purposes very good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your radials are in the ground, then 16 is sufficient to have a good ground plane. The lengths don't matter too much since they will be detuned by the ground anyway. Anything longer than a quarter-wave is good.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-01-28T03:15:27.500" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="3677" PostTypeId="1" CreationDate="2015-03-08T12:09:09.090" Score="1" ViewCount="363" Body="&lt;p&gt;I'm trying to demodulate an AFSK signal. My device uses 1200 baud rate and 1200/600Hz as mark/space. I tried using almost every software for demodulation, but nothing worked. Most recently, I tried QTMM AFSK1200 Decoder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is &lt;a href=&quot;https://i.stack.imgur.com/FBzBs.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;my signal plot&lt;/a&gt; and &lt;a href=&quot;https://drive.google.com/file/d/0B91ypjGxJDvdSHJua0s4OW5KbTQ/view?usp=sharing&quot; rel=&quot;nofollow noreferrer&quot;&gt;the audio recording&lt;/a&gt;. I received this signal in FM mode with my radio which is connected through usb port with the PC.&lt;/p&gt;&#xA;" OwnerUserId="4337" LastEditorUserId="76" LastEditDate="2015-03-14T01:13:51.930" LastActivityDate="2015-06-01T18:29:57.380" Title="AFSK signal will not decode" Tags="&lt;digital-modes&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3678" PostTypeId="2" ParentId="3677" CreationDate="2015-03-08T12:57:24.180" Score="1" Body="&lt;p&gt;That does not sound like 1200 baud AFSK, which is probably why you can't demodulate it with your software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is 1200 baud AFSK as used in amateur radio:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://commons.wikimedia.org/wiki/File:AFSK_1200_baud.ogg&quot; rel=&quot;nofollow&quot;&gt;http://commons.wikimedia.org/wiki/File:AFSK_1200_baud.ogg&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.kb9ukd.com/digital/packet12.wav&quot; rel=&quot;nofollow&quot;&gt;http://www.kb9ukd.com/digital/packet12.wav&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Note the first of these is compressed (.ogg), so probably can not be demodulated. The 2nd, however, is not compressed, so you can feed it to your software as a test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how these have a narrower frequency range. They sound vaguely vocal. The squawk at the start of each packet, which is used for synchronization, is also very distinctive. The squawk consists of an alternation between the two tones at 1200 baud.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your sample has a much wider frequency range. It has a &quot;windy&quot; quality to it. There's no audibly discernible squawk at the the beginning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.kb9ukd.com/digital/&quot; rel=&quot;nofollow&quot;&gt;KB9UKD has many more samples of other digital modulations&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-03-08T12:57:24.180" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3679" PostTypeId="1" CreationDate="2015-03-08T16:48:16.543" Score="3" ViewCount="24198" Body="&lt;p&gt;Is this secure if I was talking to another Baofeng UV-5R+?&lt;/p&gt;&#xA;" OwnerUserId="4338" LastEditorUserId="873" LastEditDate="2017-12-01T04:45:49.607" LastActivityDate="2020-05-20T07:14:08.680" Title="Can a Baofeng UV-5R+ be used on FRS, GMRS, and MURS?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;frequency&gt;&lt;security&gt;&lt;murs&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3680" PostTypeId="1" CreationDate="2015-03-09T21:27:36.943" Score="3" ViewCount="2190" Body="&lt;p&gt;Would it be feasible to set up a SSB or AM 2 meter repeater? I want to set up an AllStar full duplex node and like the idea of AM because stations can double without issues. SSB works for weaker signals and it takes up less bandwidth. The circuitry is also way simpler. Just set up a PL tone on the repeater so interference does not get through. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it work?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="10431" LastEditDate="2017-10-01T15:04:39.497" LastActivityDate="2017-10-01T15:04:39.497" Title="Would it be feasible to set up a SSB or AM 2 meter repeater?" Tags="&lt;repeater&gt;&lt;ssb&gt;&lt;am&gt;" AnswerCount="6" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3682" PostTypeId="2" ParentId="3680" CreationDate="2015-03-09T22:45:19.837" Score="7" Body="&lt;p&gt;(This is a purely theoretical answer; I have no experience in repeater building. Sorry.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The components of a repeater are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;an antenna,&lt;/li&gt;&#xA;&lt;li&gt;a duplexer,&lt;/li&gt;&#xA;&lt;li&gt;a transmitter and a receiver,&lt;/li&gt;&#xA;&lt;li&gt;and a repeater controller.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The antenna and duplexer are passive devices and aren't affected by what modulation you're using. The repeater controller is on the audio side of the radios, not the RF side. So there is no fundamental reason this can't work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, using a CTCSS tone together with SSB modulation would not work. This is because SSB causes an audio frequency shift if the transmitter and receiver are not exactly on frequency (as they never are), so the tone sent by a user of the repeater will not be recognized by the repeater controller unless the tuning is exact to within a few Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(With AM, the carrier provides the frequency reference. With FM, as normal VHF repeaters use, the audio frequency is not related to the RF frequency.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are various other coded squelch (&lt;em&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Selective_calling&quot; rel=&quot;noreferrer&quot;&gt;selective calling&lt;/a&gt;&lt;/em&gt;) systems available, some of which &lt;em&gt;might&lt;/em&gt; do better than CTCSS, but many of them are only a burst at the beginning of the transmission and thus assume the signal has a carrier which the repeater can use to know when to &lt;em&gt;stop&lt;/em&gt; repeating, which is not true of SSB.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Incidentally, there &lt;em&gt;are&lt;/em&gt; existing repeaters, of a sort, which can use SSB/AM. There is a device called a linear translator, or linear transponder, which is &lt;em&gt;completely&lt;/em&gt; mode-independent: it receives a certain band, frequency shifts it to another band, amplifies, and retransmits it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These systems can be used with any mode you care to transmit at them. The cost is that since they are not demodulating, they don't have any sort of intelligent handling of the signal (such as tone squelch, timeout, etc.).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Linear transponders are most often found on amateur radio &lt;em&gt;satellites&lt;/em&gt; (those that do not carry FM repeaters instead). Because the satellite has very limited power available, it is polite to use SSB, CW, or other power-efficient modes as opposed to AM or FM.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-03-10T18:51:18.617" LastActivityDate="2015-03-10T18:51:18.617" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3683" PostTypeId="1" CreationDate="2015-03-10T00:13:12.447" Score="6" ViewCount="260" Body="&lt;p&gt;What is the history on the term “lid” when referring to a telegrapher’s capability? How did it originate and what is the significance if any of each letter?&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-06-23T08:27:35.133" Title="History and significance of term &quot;lid&quot;" Tags="&lt;cw&gt;&lt;jargon&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3684" PostTypeId="1" CreationDate="2015-03-10T17:45:30.600" Score="1" ViewCount="268" Body="&lt;p&gt;I was recently reading an article where they mentioned about abandoned microwave towers being replaced by fiber optics. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I understand microwave technology is better at speeds, is cost effective and is easy to install as compared to fiber optics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My Question: Why was the superior microwave technology replaced by fiber optics?&lt;/p&gt;&#xA;" OwnerUserId="4351" LastActivityDate="2015-03-11T16:24:13.867" Title="why fiber optics replaced microwave" Tags="&lt;microwave&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2015-03-11T16:52:36.473" ContentLicense="CC BY-SA 3.0" />
  <row Id="3685" PostTypeId="1" AcceptedAnswerId="3686" CreationDate="2015-03-11T10:30:38.027" Score="3" ViewCount="289" Body="&lt;p&gt;Is it possible for a sub GHZ frequency (Say 300 Mhz) can be used for space communication for small satellites such as a cubesat? What are the advantages and disadvantages for this.&lt;/p&gt;&#xA;" OwnerUserId="460" LastActivityDate="2017-08-03T16:21:24.287" Title="Can sub GHZ frequency can be used in space communciation?" Tags="&lt;satellites&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3686" PostTypeId="2" ParentId="3685" CreationDate="2015-03-11T13:17:33.417" Score="4" Body="&lt;p&gt;Most cubesats communicate in a combination of VHF and UHF for both &lt;a href=&quot;http://www.dk3wn.info/p/?page_id=29535&quot; rel=&quot;nofollow noreferrer&quot;&gt;uplink and downlink&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Advantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Better link budget (lower free-space attenuation).&lt;/li&gt;&#xA;&lt;li&gt;Cheaper ground station (radio equipment, cables, antennas).&lt;/li&gt;&#xA;&lt;li&gt;Lots of support worldwide in amateur bands (144 and 430 MHz bands).&lt;/li&gt;&#xA;&lt;li&gt;No need for directional antennas (and fine attitude control) on the spacecraft.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Disadvantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Limited bandwidth (in the order of 10 kbps maximum).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Only a few cubesats have S or X band downlinks, and always as high-bandwidth extension to the main TT&amp;amp;C downlink.&lt;/p&gt;&#xA;" OwnerUserId="830" LastEditorUserId="9800" LastEditDate="2017-08-03T16:21:24.287" LastActivityDate="2017-08-03T16:21:24.287" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3687" PostTypeId="2" ParentId="3685" CreationDate="2015-03-11T16:03:24.590" Score="3" Body="&lt;p&gt;Certainly possible. 300 MHz is not a very low frequency for satellites. There are a great many amateur satellites operating on the 2m band, around 145.8 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Going much lower, there are allocations for satellites on the 10 meter band, from 29.3 to 29.51 MHz. There are fewer amateur satellites operating here, but they do exist.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, early in space exploration history, HF was used regularly for communications. For example, Yuri Gagarin in &lt;a href=&quot;http://en.wikipedia.org/wiki/Vostok_1&quot; rel=&quot;nofollow&quot;&gt;Vostok 1&lt;/a&gt; sent several reports via HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF for space communication has the same advantages and disadvantages as it does for terrestrial communication, more or less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The big advantage: HF supports skywave propagation, so you may get propagation beyond line of light. There are layers of the ionosphere that are high enough to still be above some low Earth orbits. For example, Vostok 1's orbit varied between 168 and 327 km; the F layer is around 300 km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, lower frequencies require less sophisticated technology, generally. Of course this is becoming less of a concern in modern times since microwave radios are commodity items now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The big disadvantage of HF is that antennas are larger and frequency allocations are more expensive and less available. As an example, the 70cm amateur allocation in the US goes from 420 to 450 MHz and is 30 MHz wide. You could fit the entire HF spectrum in that. Commercial availability of spectrum is similarly rarer at lower frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, high-speed communications are more difficult at HF due to the higher fractional bandwidth required. As an extreme example, &lt;a href=&quot;http://en.wikipedia.org/wiki/Extremely_low_frequency&quot; rel=&quot;nofollow&quot;&gt;ELF communications&lt;/a&gt; can take several minutes to send just a few characters.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-03-11T16:03:24.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3688" PostTypeId="2" ParentId="3684" CreationDate="2015-03-11T16:24:13.867" Score="5" Body="&lt;p&gt;Microwave technology isn't superior. That's why it's abandoned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Optical links are &lt;em&gt;much&lt;/em&gt; faster. A single, inexpensive fiber optic cable easily delivers a bitrate of 1000 Mb/s, while a bundle of fibers designed for telecommunications can deliver over 10,000,000 Mb/s. For comparison, a modern high-speed microwave link like &lt;a href=&quot;https://www.ubnt.com/airfiber/airfiber5x/&quot;&gt;AirFiber&lt;/a&gt; manages a maximum of about 500 Mb/s, subject to a sufficiently noise-free environment and low-loss path. Of course abandoned microwave links are older and much slower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Installing a fiber optic cable doesn't require licensing any radio spectrum. RF spectrum is a very limited and economically valuable resource, and you either have to pay a ton of money to get exclusive access, or deal with sharing a few limited, congested allocations with a lot of other people. On the other hand, there's a lot of dirt in which we haven't buried cables yet, and it's relatively inexpensive to purchase rights to bury a cable which is then exclusively yours.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Microwave links are subject to interference from other users on the same frequency, natural noise, and so on. Someone might decide to build a tall building in your path and you can't stop them. At some frequencies, fog and atmospheric haze can significantly degrade the path. Optical cables are relatively robust, perhaps being subject only to the occasional ill-placed backhoe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Microwave has one big advantage over fiber: it's fast and cheap to install. Put a radio on a tower at one end, and a radio on another tower and the other end and you are good to go. Burying a cable over a similar distance is relatively expensive. But given how valuable communications have become in modern times, the higher installation cost of fiber is offset by the advantages listed above for a great many applications.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-03-11T16:24:13.867" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3689" PostTypeId="2" ParentId="623" CreationDate="2015-03-12T08:04:00.410" Score="7" Body="&lt;p&gt;Before getting my ham license I used MURS on my baofeng with no problems because there is simply no MURS traffic in my area. If I were still an unlicensed operator then I would still be using MURS with my baofeng UV-5R. But once you get the Technician license the penalties go way up (or at least the enforcement) and a ham doesn't need to use MURS anyway. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;GMRS is a whole different story. Although there is almost never any GMRS traffic in my area, there is a licensed local GMRS operator who has nothing better to do than monitor the GMRS only channels of bubble pack radios and rudely scold unlicensed users. While I appreciate his zeal, I think he goes about things the wrong way. Instead of yelling and threatening unlicensed users, usually teenage kids, he should be trying to get them licensed so that he'd have someone to talk to! I think he's the main reason GMRS is dead in this area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I chose to get my Technician license solely because it was way cheaper than getting a GMRS license. And I'm glad I did because it gave me access to local repeaters and taught me a ton about VHF radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't recommend using a Baofeng radio on FRS frequencies because technically its illegal. But if you stay on the FRS only frequencies, 467.562 for example (not 462.562 as you stated), then I doubt anyone will notice. The FRS only frequencies are Channels 8 thru 14 on the bubble pack radios.&lt;/p&gt;&#xA;" OwnerUserId="4357" LastEditorUserId="1246" LastEditDate="2015-03-13T16:05:22.727" LastActivityDate="2015-03-13T16:05:22.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3690" PostTypeId="2" ParentId="3679" CreationDate="2015-03-12T08:49:50.727" Score="5" Body="&lt;p&gt;Yes &amp;amp; No. The Baofeng is capable of transmitting on FRS/GMRS &amp;amp; MURS. But its not legal to do so (except maybe on GMRS with a license). And no frequency is &quot;secure&quot; as in &quot;private&quot; with any handheld radio that I've ever seen. PL tones, (aka Privacy Codes) are not private at all. This is a popular misconception promoted by manufacturers of those bubble-pack radios found at walmart. PL tones, privacy codes, CTCSS, whatever label you want to put on it, do NOTHING to prevent other radios from hearing your conversations. They merely prevent YOU from hearing other radios that are not using the same tone you are using. If you turn off CTCSS on your baofeng, then you will hear every radio on the frequency you are using that are within range, REGARDLESS of which tone they may be using. So much for privacy.&lt;/p&gt;&#xA;" OwnerUserId="4357" LastActivityDate="2015-03-12T08:49:50.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3692" PostTypeId="1" AcceptedAnswerId="3693" CreationDate="2015-03-12T11:59:19.280" Score="16" ViewCount="5351" Body="&lt;p&gt;Free space path loss is calculated as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \left( 4 \pi df \over c \right)^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The presence of $f$ in this equation means that losses increase with increasing frequency, so there's an inherent advantage in lower frequencies, right?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-12-04T05:49:35.977" Title="Is free space path loss dependent on frequency?" Tags="&lt;propagation&gt;&lt;math&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="3693" PostTypeId="2" ParentId="3692" CreationDate="2015-03-12T11:59:19.280" Score="21" Body="&lt;p&gt;Mathematically yes, the value of that equation increases with frequency. However, that's not to say there's some physical mechanism for frequency-dependent attenuation in free space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rather, the frequency term is in the equation due to the assumption of unity gain antennas at each end. A larger antenna is required to get the same gain at a lower frequency. This &lt;a href=&quot;https://ham.stackexchange.com/a/7688/218&quot;&gt;larger antenna collects energy from a larger area&lt;/a&gt;, and thus the loss between them is less, even though the attenuation in free space happens at the same rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To do a fair comparison, let's compare two similarly sized antennas. Let's compare a 2.4 GHz antenna with a 5 GHz antenna, each a parabolic dish antenna with a 5 meter reflector diameter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can approximate &lt;a href=&quot;http://en.wikipedia.org/wiki/Parabolic_antenna#Gain&quot; rel=&quot;noreferrer&quot;&gt;the gain of these antennas&lt;/a&gt; with the the equation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ G = {4\pi A f^2 \over c^2}e_A \tag{1}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$A$&lt;/span&gt; is the area of the reflector,&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is the frequency, in Hz&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$c$&lt;/span&gt; is the speed of light in m/s, and&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$e_A$&lt;/span&gt; is the &lt;a href=&quot;https://ham.stackexchange.com/q/3643/218&quot;&gt;aperture efficiency&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If we assume an aperture efficiency of 80%, then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ G_\text{2.4GHz} \approx 41\:\mathrm{dBi} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ G_\text{5GHz} \approx 47\:\mathrm{dBi} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, despite these antennas being the same size, the 5 GHz antenna has about 6dB more gain. Does this compensate for the higher free space path loss at 5 GHz?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's do the math. Assuming a constant gain receiving antenna in any case, the power received will be proportional to the transmitting antenna's gain (from equation 1), multiplied by the reciprocal of the free space path loss (equation from the question):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \require{cancel}&#xA;\left({4\pi A f^2 \over c^2}e_A\right) \left( c \over 4 \pi df \right)^2 \\&#xA;\&#xA;\left({\cancel{4\pi} A \cancel{f^2} \over \cancel{c^2}}e_A\right)&#xA;\left( \cancel{c^2} \over (\cancel{4 \pi} d)(4 \pi d) \cancel{f^2} \right) \\&#xA;\&#xA;{A \: e_A \over 4 \pi d^2} \tag 2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice that this equation is just the area of the reflector and the aperture efficiency divided by the surface area of a sphere with radius &lt;span class=&quot;math-container&quot;&gt;$d$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, &lt;a href=&quot;http://en.wikipedia.org/wiki/Irradiance&quot; rel=&quot;noreferrer&quot;&gt;irradiance&lt;/a&gt; is proportional to the &lt;a href=&quot;http://en.wikipedia.org/wiki/Inverse-square_law&quot; rel=&quot;noreferrer&quot;&gt;inverse-square&lt;/a&gt; of distance, regardless of frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the 5 GHz antenna will have a smaller beam width, thus focusing the transmitted power over a smaller area. This means the 5 GHz case will have a higher irradiance than the 2.4 GHz case, assuming the antenna is optimally aimed. If the receiving antenna has an &lt;em&gt;equal effective aperture&lt;/em&gt; (rather than a constant gain) at any frequency, the receiving antenna will then be subject to a greater &lt;a href=&quot;http://en.wikipedia.org/wiki/Radiant_flux&quot; rel=&quot;noreferrer&quot;&gt;radiant flux&lt;/a&gt; with increasing frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in summary:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The definition of &lt;em&gt;free space path loss&lt;/em&gt; describes the loss between two unity gain antennas, not the rate at which free space attenuates electromagnetic radiation.&lt;/li&gt;&#xA;&lt;li&gt;Electromagnetic radiation &quot;spreads out&quot; according to the inverse square law, regardless of frequency.&lt;/li&gt;&#xA;&lt;li&gt;The definition of &lt;em&gt;unity gain&lt;/em&gt; is frequency dependent: lower frequencies correspond to a larger aperture.&lt;/li&gt;&#xA;&lt;li&gt;Higher frequency antennas generally allow for a tighter beam within a given physical size.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-04-22T14:21:53.817" LastActivityDate="2019-04-22T14:21:53.817" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="3694" PostTypeId="2" ParentId="4" CreationDate="2015-03-12T12:02:09.213" Score="2" Body="&lt;p&gt;There is not any such listing, as the definitions for CQ zones are a bit ambiguous. The official definitions can be found at the &lt;a href=&quot;http://www.cq-amateur-radio.com/cq_awards/cq_waz_awards/cq_waz_list.html&quot; rel=&quot;nofollow&quot;&gt;CQ Magazine WAZ award definition&lt;/a&gt;. Areas like the ocean aren't covered, otherwise it's a fairly simple geography lookup to get the areas defined.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-03-12T12:02:09.213" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3695" PostTypeId="2" ParentId="425" CreationDate="2015-03-13T13:53:10.420" Score="-4" Body="&lt;p&gt;With respect to the issue of iron ore creating propagation problems, I have noticed the same problem where I live, which has high concentration of iron ore, for cell phone signals and sirus XM satellite reception  in my car.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My theory is that, iron being a good conductor, better than air, if the ore is located between the transmitter and receiver, some portion of  the signal takes the path of better conductivity, the iron ore, and less signal strength is received at the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, assuming the validity of that hypothesis, what to do? Well, I got a signal amplifier for the house. For the car we just tolerate it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How about driving an iron rod into the ground to pick up the diverted portion of the signal?&lt;/p&gt;&#xA;" OwnerUserId="4369" LastEditorUserId="1246" LastEditDate="2015-03-17T16:18:39.440" LastActivityDate="2015-03-17T16:18:39.440" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3696" PostTypeId="1" CreationDate="2015-03-13T17:28:06.200" Score="4" ViewCount="594" Body="&lt;p&gt;I would like to mount a self tuning antenna, ATAS-120, matched with the FT-857D transceiver. I would like to make this pair function on an ARGO 8x8 amphibious vehicle with a polyethylene body.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a metal frame the engine and drive-train is attached to and I would run an independent ground from the antenna to the frame. Will this function properly? &lt;/p&gt;&#xA;" OwnerUserId="4371" LastEditorUserId="76" LastEditDate="2015-03-14T01:12:28.343" LastActivityDate="2015-04-16T11:32:16.137" Title="How should I mount a mobile antenna on a vehicle with a non-conductive body?" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3697" PostTypeId="2" ParentId="3696" CreationDate="2015-03-13T23:38:08.433" Score="2" Body="&lt;p&gt;I think the question is how the frame will act as a counterpoise.  You might consider adding some 450 Ω ladder line, cut to the lengths of the bands of interest, and run them up and down the sides of the argo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not an argo owner, but I live on a sailboat.  What I did is roughly follow the information given on &lt;a href=&quot;http://www.ropeantenna.com/&quot; rel=&quot;nofollow&quot;&gt;ropeantenna.com&lt;/a&gt; about counterpoises.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've put a DC block between the rudder post and the antenna tuner and this is my ground (to sea water); then from the antenna tuner up along the sides of the boat I've run 450 Ω ladder line up and down each side.  My system, a Kenwood 480 with a SGC-230 auto tuner, works well.&lt;/p&gt;&#xA;" OwnerUserId="4372" LastEditorUserId="76" LastEditDate="2015-03-16T20:21:33.097" LastActivityDate="2015-03-16T20:21:33.097" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3698" PostTypeId="2" ParentId="425" CreationDate="2015-03-14T14:13:14.307" Score="3" Body="&lt;p&gt;Probably not much effect from iron in the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF communications are very sensitive to the ionosphere and other natural effects. Predictions are difficult, and only give a probability, never a guarantee. Real data are thin on the ground, and you know that the plural of anecdote is not data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF propagation happens mostly in the air, and by reflection off the ionosphere. The ground only gets involved at the antenna, and possibly if you are using ground wave propagation. Ground wave is more an MF thing, AM radio etc, above a few MHz it is only good for a few km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation pattern and efficiency of an antenna are affected by the ground constants, and the low-angle radiation, so important for long range HF, is particularly sensitive. No matter how far the signal will travel, the only ground that counts is the patch around each antenna. The size of the patch varies, but it's generally only some wavelengths in radius. In reasonable ground, all the RF conduction happens in the first few metres, so don't worry about what is being mined far below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The two ground parameters, conductivity and permittivity, vary widely between locations, but in general, the &quot;richer&quot; the soil, the &quot;better&quot; the ground. So fertile farmland is much better than a desert. This effect is well studied.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The richness of the ground depends on its water content, the geological type of rock etc, and the minerals. Most ground is of course silicon dioxide, sand, which is an insulator. The size of the grains, and the other minerals, are what change its performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Iron oxide is not conductive, so along with the SiO2, AlO2 etc, would make up the inert part of the ground. Salts and water dominate that conductive parts of the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To study this further, try to investigate the effect of various minerals on the ground permittivity and conductivity. This is where the hard data lies. Stories about good and bad reception, or even careful measurements of &quot;how good the signals are&quot;, have too many confounding factors, and are not going to lead to useful conclusions.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-03-14T14:13:14.307" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3700" PostTypeId="1" CreationDate="2015-03-16T19:31:41.533" Score="1" ViewCount="85" Body="&lt;p&gt;Let's say everyone has general liscense classes and can erect antennas to whatever can fit on the human body. What would be the best frequency to talk locally in an area with lots of buildings and man made objects in the way including metal, brick, cement, dirt, wood, and all other RF degrading city material. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frequency range: 1hz - Ultraviolet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mode: AM, FM or SSB whatever works best for voice communications- no morse.&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-03-16T19:31:41.533" Title="Best frequency for very local dense building chat" Tags="&lt;antenna&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2015-04-01T19:35:22.567" ContentLicense="CC BY-SA 3.0" />
  <row Id="3702" PostTypeId="1" AcceptedAnswerId="3742" CreationDate="2015-03-16T20:44:29.533" Score="2" ViewCount="3758" Body="&lt;p&gt;I have this Baofeng UV-B6 (the same as B5), and after using CHIRP a few times, transmission stopped working. In fact, it starts transmitting, but no voice is sent whatsoever — dead carrier. RX works without any issues.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried with restoring default settings (CHIRP backup), &lt;a href=&quot;http://www.miklor.com/UVB5/UVB5-Recovery.php&quot; rel=&quot;nofollow&quot;&gt;by using &quot;recovery&quot; image&lt;/a&gt;, even resetting the radio to factory settings (menu + power on), and got no result. Still nothing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems to me like the radio itself thinks that external mic is plugged in, so it overrides the built-in microphone. That's how I would've described the situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone know how to fix this issue? More important — is it worth fixing it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;&#xA;Here's the video tutorial on how to fix this issue (read the accepted answer): &lt;a href=&quot;https://www.youtube.com/watch?v=7BrGo1-uW3k&quot; rel=&quot;nofollow&quot;&gt;https://www.youtube.com/watch?v=7BrGo1-uW3k&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1464" LastEditorUserId="1464" LastEditDate="2015-03-25T21:40:08.843" LastActivityDate="2021-05-20T04:09:09.433" Title="Baofeng UV-B6 transmits no audio" Tags="&lt;ht&gt;&lt;baofeng&gt;&lt;transmission&gt;&lt;equipment-troubleshooting&gt;&lt;microphone&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3703" PostTypeId="1" AcceptedAnswerId="3705" CreationDate="2015-03-17T15:05:33.653" Score="2" ViewCount="158" Body="&lt;p&gt;We are trying to make a VLF geophysics device for our graduate project and we need two ferrite rod antennas (desired length is 6&quot;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Searching on the internet, we have found two ferrite rod suppliers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first one:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;&lt;a href=&quot;http://www.stormwise.com/page26.htm&quot; rel=&quot;nofollow&quot;&gt;Stormwise&lt;/a&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;2000u Monster Ferrite Rods &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;Length:&lt;/strong&gt; 6 inch&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;Diameter:&lt;/strong&gt; 0.845 inch&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;Price:&lt;/strong&gt; $24&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;And the second one is a local supplier:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Length:&lt;/strong&gt; 3.93 inch&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;Diameter:&lt;/strong&gt; 0.314 inch&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;Price:&lt;/strong&gt; $1&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;We do not have experience and knowledge about antennas and their materials. The guy in the local supplier said that you can butt splice the coils to get 150 mm length and that diameter only affects the number of wire turns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the advice accurate? Can you explain why the price is so different? Might it be due to the material quality or something else?&lt;/p&gt;&#xA;" OwnerUserId="4382" LastEditorUserId="76" LastEditDate="2015-03-17T15:42:44.453" LastActivityDate="2015-03-17T15:56:16.347" Title="Ferrite Rod Price Differences" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;vlf&gt;&lt;ferrite&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3704" PostTypeId="1" CreationDate="2015-03-17T15:37:13.383" Score="4" ViewCount="2475" Body="&lt;p&gt;I have dual stacked crossed yagi antenna. How can I practically measure the gain of the antenna combination?&#xA;I know that this can be done in an &lt;a href=&quot;http://en.wikipedia.org/wiki/Anechoic_chamber&quot; rel=&quot;nofollow&quot;&gt;anechoic chamber&lt;/a&gt;. But this is not feasible for me (transportation and cost).&#xA;Please guide me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is designed to work in the 430-440 MHz band.&#xA;I have a spectrum analyzer and network analyzer with me. If I wish to maintain a weekly of of the antenna gain, what can I do?&#xA;Also while testing how much does the position of reference antenna matter? For testing at the same position, won't the yagi antenna cause interference in power received by reference antenna?&lt;/p&gt;&#xA;" OwnerUserId="4383" LastEditorUserId="76" LastEditDate="2020-02-15T17:01:02.053" LastActivityDate="2020-02-15T17:01:02.053" Title="How to measure gain of an antenna?" Tags="&lt;antenna&gt;&lt;yagi&gt;&lt;antenna-analyzer&gt;&lt;spectrum-analyzer&gt;" AnswerCount="1" CommentCount="6" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3705" PostTypeId="2" ParentId="3703" CreationDate="2015-03-17T15:56:16.347" Score="4" Body="&lt;p&gt;&quot;Ferrite&quot; is not a fungible material. There are many kinds of ferrite materials, each with very different properties. To make a comparison, you need the material datasheets, which answer questions like:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What is the relative permittivity?&lt;/li&gt;&#xA;&lt;li&gt;What is the loss at the frequencies you intend to use them?&lt;/li&gt;&#xA;&lt;li&gt;What is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Curie_temperature&quot; rel=&quot;nofollow noreferrer&quot;&gt;Curie temperature&lt;/a&gt; of the material?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You can see &lt;a href=&quot;https://ham.stackexchange.com/q/1159/218&quot;&gt;How does one read a ferrite datasheet?&lt;/a&gt; for an example of some of the parameters listed on a typical datasheet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without datasheets for each material, it's impossible to make any fair comparison of price between the two options. It may even be that the material is not suitable for your application.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-03-17T15:56:16.347" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3706" PostTypeId="1" CreationDate="2015-03-17T19:25:55.507" Score="2" ViewCount="552" Body="&lt;p&gt;I've been scouring the internet for the answer and my question is never directly answered, usually there is a bunch of technical jargon.  It is not that I am unwilling to learn, because I want to, but I don't want to focus on the wrong subset of radio skills.  The only prerequisite I have is distance/range/coverage whichever is the correct terminology.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to know which form of radio reliably provides at minimum 10 miles of coverage from base to vehicle and from vehicle to base?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edits: The terrain is mainly urban though there are tall trees. In fact it's a rural town so the buildings don't get much higher than two stories. The trees are way taller but arent dense.&#xA;The town is on the water if that also helps!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I intend to use this keep in contact with truck drivers to keep in contact with base. I'll be operating in a third world environment so there is increased risk of accident along routes.&lt;/p&gt;&#xA;" OwnerUserId="4386" LastEditorUserId="4386" LastEditDate="2015-03-19T17:48:13.587" LastActivityDate="2015-04-21T22:45:45.670" Title="Should I use ham or cb radio?" Tags="&lt;propagation&gt;&lt;citizens-band&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="1" ClosedDate="2015-04-22T13:05:45.760" ContentLicense="CC BY-SA 3.0" />
  <row Id="3707" PostTypeId="2" ParentId="3706" CreationDate="2015-03-17T20:02:01.507" Score="0" Body="&lt;p&gt;Which? None! :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In almost all cases, what you're going to get is going to depend on very large amount of factors and no good general answer can be provided. Is the area urban, is it empty fields, are there going to be other users and so on. That's the reason why you can't find a direct answer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, I'll try to focus on the main problem I see with your question: &#xA;To me it seems that you consider the technical parts of CB radio and HAM radio different. They are not. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio is radio and it doesn't matter how you call it.&lt;br&gt;&#xA;What is different is operating culture in some areas and allowed uses for the bands. Propagation part is going to be the same and it is what you should study, if you're mostly interested in just getting a connection. This should allow you to narrow down the acceptable modes of communication and then you'll be able to make an informed decision if for your purpose ham or CB or maybe some other radio service are the most suitable option.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2015-03-17T20:02:01.507" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3709" PostTypeId="1" CreationDate="2015-03-17T23:41:23.063" Score="0" ViewCount="182" Body="&lt;p&gt;For example, Diamond makes the &lt;a href=&quot;http://www.diamondantenna.net/x700hna.html&quot; rel=&quot;nofollow&quot;&gt;X700HNA&lt;/a&gt; which is stated as a 4x5/8 vertical on 2m.  Does this just mean that it is 20/8 wavelength long vertical?  Or is there some magic to phasing the 5/8 segments?  I'm familiar with colinear dipoles, but they normally have some sort of phasing connector (typically looks like a &quot;hairpin&quot; in my experience).  Maybe that's just hidden inside the fiberglass, but I'd be curious if anyone has any idea what might be inside an antenna like this.&lt;/p&gt;&#xA;" OwnerUserId="1343" LastActivityDate="2015-03-18T00:43:54.890" Title="How does a multi-element vertical work?" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3710" PostTypeId="2" ParentId="3709" CreationDate="2015-03-18T00:18:15.693" Score="1" Body="&lt;p&gt;It's probably a &lt;strong&gt;coaxial collinear&lt;/strong&gt; antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each segment of the antenna contains two coaxial conductors (inner and outer). At each joint, the inner conductor of one segment is electrically connected to the outer of the next, and vice versa. The center conductor in each segment forms the phasing line for the two adjacent segments, and does not radiate since it is shielded.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typical designs of such an antenna specify half-wavelength segments, not 5/8, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible to construct such an antenna by taking cut sections of coaxial cable and inserting the center of each under the shield of the next (while separating or insulating the shields from each other); this is a popular “homebrew” receiving antenna design for some applications.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-03-18T00:43:54.890" LastActivityDate="2015-03-18T00:43:54.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3711" PostTypeId="1" AcceptedAnswerId="3712" CreationDate="2015-03-18T00:59:13.413" Score="15" ViewCount="2399" Body="&lt;p&gt;I am studying for my FCC General Class license, and question/answer &lt;code&gt;G4A02&lt;/code&gt; reads as follows:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Q:&lt;/strong&gt; What is one advantage of selecting the opposite or &quot;reverse&quot; sideband when receiving CW signals on a typical HF transceiver?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;A:&lt;/strong&gt; It may be possible to reduce or eliminate interference from other signals.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I am studying from the &lt;em&gt;ARRL General Class License Manual (Seventh Edition)&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't understand how this is possible. If the signal is being transmitted on the upper sideband, how does switching to receive on the lower sideband eliminate interference? As I understand it, that would eliminate everything from the upper sideband, and I would hear nothing from the upper sideband &lt;em&gt;including&lt;/em&gt; the CW signal I'm trying to listen for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The referenced page from the Q/A explains this concept thusly: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;...&lt;br&gt;&#xA;  &lt;em&gt;Reverse Sideband&lt;/em&gt; controls allow the operator to switch between receiving CW signals above the displayed carrier frequency (USB) and below it (LSB). This can help avoid nearby signals causing interference by placing them on the other side of the carrier frequency where filtering rejects them.&lt;br&gt;&#xA;  ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I do not understand. &lt;strong&gt;How does this work?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="4388" LastEditorUserId="76" LastEditDate="2018-04-27T21:34:47.990" LastActivityDate="2018-04-27T21:34:47.990" Title="How does selecting the opposite sideband when receiving CW on HF reduce interference?" Tags="&lt;hf&gt;&lt;cw&gt;&lt;filter&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3712" PostTypeId="2" ParentId="3711" CreationDate="2015-03-18T01:18:59.460" Score="18" Body="&lt;p&gt;CW signals are not “transmitted on the upper sideband”, nor the lower one. A CW signal is approximately &lt;em&gt;at a single frequency&lt;/em&gt; (with only the additional bandwidth required to allow the key-up and key-down transitions).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the standard method of &lt;em&gt;receiving&lt;/em&gt; a CW signal is identical in structure to a single-sideband receiver. The local oscillator (LO) of the receiver is set to a frequency &lt;em&gt;not quite equal&lt;/em&gt; to the CW signal, and the difference between the incoming CW and the LO is the audio tone you hear. Let's say for concreteness that the difference is 800 Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that frequency shifting were all that was going on, then you would hear many CW signals (from both sidebands) at different pitches, so there is a very narrow filter to select just the one signal. That filter will select either the frequency +800 Hz from the LO (upper sideband) or the one &amp;minus;800 Hz from the LO (lower sideband).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For convenience, a modern transceiver does not display the LO frequency (as it does in single-sideband mode) but rather the LO frequency offset by 800 Hz, so that you know the actual frequency of the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you switch from upper-sideband reception to lower-sideband reception, then you (or your receiver's CPU, more likely) should simultaneously change the LO frequency to be 1600 Hz (double the offset) higher, so that (if you were perfectly tuned to start with) you'll hear the same signal at the same pitch as before.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference this makes is that signals &lt;em&gt;not&lt;/em&gt; exactly at the 800 Hz offset frequency will be flipped around that midpoint: an unwanted signal within the filter passband that was at (relative) 1200 Hz will now be at 400 Hz, and you might find that lower-pitched sound less troublesome. Or, if your receiver's filters are not perfectly symmetrical for this purpose, the unwanted signal could be actually attenuated.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;If you have a receiver already, listen to CW and SSB signals using both CW and SSB modes, tune around, and try to get a feel for what's going on. CW mode is just SSB mode with a narrower filter and the offset display.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Note that when you switch between CW and SSB mode, your receiver might preserve the actual LO frequency (thus changing the displayed frequency), or preserve the displayed frequency (thus changing the LO frequency and the pitch of what you hear).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-03-18T01:18:59.460" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3713" PostTypeId="1" CreationDate="2015-03-18T10:00:49.480" Score="5" ViewCount="1539" Body="&lt;p&gt;I have a licence since I was 14 which is exactly half of my life, but honestly with the advent of the internet I somehow lost interest and sold my equipment. &#xA;Now I really start to think, I should dive into it again, but I don't want to spend a lot of money to buy some equipment to talk to strangers - because this really can be done online.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The technical part is now becoming more interesting. So I would like to build a simple transceiver with my kids as a project for next vacation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a 100MHz oszilloscope a standard multimeter and a decent soldering station (though I cannot solder BGA parts).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 100MHz bandwith of the oszilloscope probably limits myself to short wave, but that is fine. &#xA;I would prefer SSB because I can't morse - but I could learn that, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, since this is really just for fun and to learn something a QRP transceiver is fine with me (and a bad SWR probably won't kill the tx while tuning the antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in Germany so a supplier there or in Europe would be preferred.&lt;/p&gt;&#xA;" OwnerUserId="4390" LastActivityDate="2015-10-01T03:54:27.013" Title="What is an cheap and easy to build kit for a sw ssb transceiver?" Tags="&lt;diy&gt;&lt;transceiver&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="5" ClosedDate="2015-07-03T10:43:29.300" ContentLicense="CC BY-SA 3.0" />
  <row Id="3714" PostTypeId="1" CreationDate="2015-03-18T12:28:27.743" Score="3" ViewCount="538" Body="&lt;p&gt;Reading about a 'necklace' coil inducing a strong alternating audio current (using an LM386 f.i.) into a magnet inserted in the ear canal set me thinking. The problem is that the magnet has to be inserted in very close proximity to the eardrum, so removing it can be a problem. Would it be possible to make use of a 27 MHz AM transmitter to induce a strong signal into the tank circuit of a tiny crystal set? That crystal set could be built with some ingenuity into a wireless crystal earpiece. The transmitter would use a 'necklace' loop antenna to induce the signal, containing the audio.&lt;/p&gt;&#xA;" OwnerUserId="4392" LastEditorUserId="4408" LastEditDate="2015-04-24T05:14:56.757" LastActivityDate="2016-04-24T23:22:25.100" Title="Crystal set as wireless earphone" Tags="&lt;receiver&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3715" PostTypeId="2" ParentId="683" CreationDate="2015-03-18T12:59:33.403" Score="0" Body="&lt;p&gt;When I was not licensed I helped in a contest with taking logs, also as a newbie that helped me train my ear on weak ssb stations. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would recommend to try a similar approach, because this allows you to have more kids actually help. If everyone takes notes you can later compare these to weed out mistakes.&lt;/p&gt;&#xA;" OwnerUserId="4390" LastActivityDate="2015-03-18T12:59:33.403" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3716" PostTypeId="1" AcceptedAnswerId="5163" CreationDate="2015-03-18T13:24:30.140" Score="5" ViewCount="457" Body="&lt;p&gt;I have been having problems with the knock off of Icom microphone so I figured I would bite the bullet and get a new Icom microphone, since the original is out of production. I found that HM-133 looks like a good candidate to replace it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not what would you suggest?&lt;/p&gt;&#xA;" OwnerUserId="4083" LastEditorUserId="218" LastEditDate="2015-03-18T15:37:03.553" LastActivityDate="2020-04-05T16:37:48.843" Title="Will Icom HM-133 work on IC-2800H" Tags="&lt;vhf&gt;&lt;microphone&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3718" PostTypeId="1" AcceptedAnswerId="9756" CreationDate="2015-03-19T10:36:33.057" Score="4" ViewCount="487" Body="&lt;p&gt;I have a transceiver working in the 435 MHz ham band. I want to test my uplink capability by communicating with satellites operating in this band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any digital satellites which I can use for this purpose?&lt;/p&gt;&#xA;" OwnerUserId="4397" LastEditorUserId="76" LastEditDate="2015-03-19T19:32:32.397" LastActivityDate="2018-01-14T21:35:42.943" Title="Are there any satellites with 435 MHz uplink?" Tags="&lt;satellites&gt;&lt;uhf&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3719" PostTypeId="2" ParentId="3704" CreationDate="2015-03-20T13:02:56.460" Score="2" Body="&lt;p&gt;Measuring received power is pretty straightforward. Set up a receiving antenna some distance away. Make it at least 10 wavelengths, but even farther is better. Make sure the receive antenna has the same polarization. Transmit a carrier at a fixed power. Read the received power at the receive antenna with your spectrum analyzer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's more convenient, you can also run this test in the other direction, transmitting with some other antenna, and receiving with the Yagi. Due to &lt;a href=&quot;http://en.wikipedia.org/wiki/Reciprocity_%28electromagnetism%29&quot; rel=&quot;nofollow&quot;&gt;reciprocity&lt;/a&gt;, the results you obtain will be identical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This doesn't tell you gain unless your spectrum analyzer is calibrated and you know the gain of your receiving antenna. Without the tightly controlled conditions of an anechoic chamber you probably can't know the receiving antenna's gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, what you can do is perform the same test again and compare the results. If you are testing modifications to the Yagi you can compare the received power before and after the modification and quantity the change. You can also replace the Yagi with a reference antenna like a dipole for comparison.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you receive twice the power with your Yagi versus the reference dipole, then you know the Yagi has 3 dB more gain than the dipole. While this isn't exactly a carefully calibrated, quantitative measurement of antenna gain, it is an objective way to validate that you have indeed constructed an effective antenna, that your Yagi is better than a $1 dipole, or that some modification or adjustment you've made to the Yagi has made a measurable improvement.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-03-20T17:09:02.417" LastActivityDate="2015-03-20T17:09:02.417" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3720" PostTypeId="1" CreationDate="2015-03-20T13:15:29.350" Score="5" ViewCount="330" Body="&lt;p&gt;Here we have a cubesat which operates in VHF/UHF. Communication with it (from a ground station perspective) is done with an Icom Radio. Would it be possible to replace it with a cheaper BAOFENG?&lt;/p&gt;&#xA;" OwnerUserId="4405" LastEditorUserId="4405" LastEditDate="2015-04-20T13:48:14.523" LastActivityDate="2019-12-10T17:06:35.903" Title="BAOFENG UV-5R for cubesat communication on lab, does it work?" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;baofeng&gt;&lt;icom&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3721" PostTypeId="2" ParentId="3714" CreationDate="2015-03-20T16:11:26.903" Score="1" Body="&lt;p&gt;It is certainly possible to build a 27 MHz receiving crystal set small enough to fit in the ear. A 27 MHz crystal has both effective series inductance and parallel capacitance so it could serve alone as the tank circuit. Another &quot;crystal&quot; is the diode detector that demodulates the AM and a third piezoelectric crystal converts the detected voltage to sound. That eliminates your bulky magnet! However more ingenuity is needed to couple adequate RF signal into the receiver and you probably want some kind of tuning control, which could be a tiny variable capacitor in parallel with the 27 MHz crystal.&lt;/p&gt;&#xA;" OwnerUserId="4408" LastActivityDate="2015-03-20T16:11:26.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3722" PostTypeId="2" ParentId="1232" CreationDate="2015-03-20T16:27:26.067" Score="1" Body="&lt;p&gt;Having built an HF receiver you should have little difficulty making a small crystal oscillator in a metal box. It is battery powered, oscillates at 1, 5 or 10 MHz and radiates only from a small stub antenna. Use it to test any HF receiver. The receiver will pick up the harmonics of the crystal frequency; thus you can both check both the receiver frequancy calibration and compare its sensitivity with another receiver+antenna combination. You will need to add an audio frequency modulator to the oscillator to obtain an audible buzz if the HF receiver has only AM detection. But please remember to turn your little transmitter OFF when not actually testing.&lt;/p&gt;&#xA;" OwnerUserId="4408" LastActivityDate="2015-03-20T16:27:26.067" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3726" PostTypeId="2" ParentId="3706" CreationDate="2015-03-21T19:58:49.637" Score="1" Body="&lt;p&gt;Another limiting factor: the license conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio communication is generally restricted by the licensing authority in each country, to testing, technical evaluation and discussion about the hobby, 'remarks of a personal nature' and safety and emergency messages. It can't be used for commercial purposes, or to pass messages for others. Messages may not be in code. Even a discussion between friends about politics is not strictly according to the rules.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Except for emergency situations, amateur stations may only speak to other licensed amateur stations.&#xA;Both the operator and the station are licensed, though licensed operators can use each others' stations if they state this and give both callsigns. Only licensed operators may speak into the microphone, except for some exceptions for education, school kids, scouts and so on, and only with permission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So unless the drivers are all licensed, driving in their personal capacity and communicating only about personal or technical matters, amateur radio isn't the solution.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-03-21T19:58:49.637" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3727" PostTypeId="1" CreationDate="2015-03-21T21:13:38.997" Score="3" ViewCount="2140" Body="&lt;p&gt;What kinds of configurations should I try when trying to make the physically smallest 2.4 GHz (ISM band) antenna that is significantly directional front-to-back.  &quot;Smallest&quot; meaning in in cm maximum dimension.  &quot;Significant&quot; meaning quickly measurable as above above typical ISM band noise floors when turning the antenna around.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2015-03-24T15:59:35.590" Title="How to build the smallest directional antenna (ISM band)?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="11" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3728" PostTypeId="1" AcceptedAnswerId="3731" CreationDate="2015-03-22T11:06:23.423" Score="6" ViewCount="1128" Body="&lt;p&gt;I'm planning to build a 5W PWR/SWR meter very similar to &lt;a href=&quot;http://www.davesergeant.com/tx.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this design by G3YMC&lt;/a&gt;, but with two meters:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/oRsLC.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to put it in this metal box, and use the box as ground. However, the bottom of the box would then also be ground, and I may accidentally touch it. Would that be a problem? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or does that depend on how I will use it? For now I'll use it for 40m/20m, up to 5W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/BAYdr.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorUserId="76" LastEditDate="2017-04-26T17:27:03.383" LastActivityDate="2017-04-26T17:27:03.383" Title="Can I touch the ground of a PWR/SWR meter?" Tags="&lt;diy&gt;&lt;rf-power&gt;&lt;measurement&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3729" PostTypeId="1" CreationDate="2015-03-22T14:43:01.250" Score="6" ViewCount="1398" Body="&lt;p&gt;I want to make a application with my Raspberry Pi along with a XBee module. I am going to use it in public places and in my own home.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question is, do I need a radio licence (UK) to use the XBee in my home and/or in public places? I want to know this before I even buy a XBee (won't be until later). When this is in public it will be a two-way communication between me and my friend.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;People complaniing that my friend is wrong and needs to do his test again don't need to any more. He didn't hear that I was talking about the zigbee/xbee he just thought it was transmitting data via FM radio waves. Sorry about the confusion.&lt;/p&gt;&#xA;" OwnerUserId="4413" LastEditorUserId="873" LastEditDate="2015-06-10T12:26:45.120" LastActivityDate="2015-06-10T12:26:45.120" Title="Do you need a radio licence to use ZigBee/Xbee?" Tags="&lt;legal&gt;&lt;license&gt;&lt;united-kingdom&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3730" PostTypeId="2" ParentId="3729" CreationDate="2015-03-22T20:46:38.313" Score="0" Body="&lt;p&gt;I'm not from the UK, but stumbled upon the following thread regarding the same issue you're asking about, so make sure to read it, might come in handy:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.avrfreaks.net/forum/zigbee-legal-issues-uk-need-advice&quot; rel=&quot;nofollow&quot;&gt;http://www.avrfreaks.net/forum/zigbee-legal-issues-uk-need-advice&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1464" LastActivityDate="2015-03-22T20:46:38.313" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3731" PostTypeId="2" ParentId="3728" CreationDate="2015-03-23T00:01:56.493" Score="5" Body="&lt;p&gt;There's no problem with what you're proposing, usually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of your other equipment probably has exposed metal connected to “ground”. If it's not causing trouble, this won't either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if you have the problem known as “RF in the shack” — your transmitter's RF coming back to you on the outer shield of your feedline — then the metal will be RF-hot, but you should fix the problem rather than trying to insulate this particular piece of equipment.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-03-23T00:01:56.493" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3733" PostTypeId="2" ParentId="3720" CreationDate="2015-03-23T04:57:06.153" Score="4" Body="&lt;p&gt;The usability of the Baofeng (or any radio with &gt; 1Hz frequency step) will depend on the frequency and mode that you are using. If you use a 12.5kHz frequency step size you will never be able to tune to 435.345 MHz (FM mode) frequency, for example. You have to change your frequency step size to 5 kHz or 2.5 kHz to tune it. &lt;br&gt;&lt;br&gt;Notice though that the Baofeng has a tunable step size as documented in the specification you linked (Page 11). 2.5/5/6.25/10/12.5/25kHz frequency step sizes are sufficient for FM mode communications with a satellite.&lt;/p&gt;&#xA;" OwnerUserId="1761" LastEditorUserId="8573" LastEditDate="2019-12-10T17:06:35.903" LastActivityDate="2019-12-10T17:06:35.903" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="3735" PostTypeId="2" ParentId="3720" CreationDate="2015-03-23T20:17:52.277" Score="1" Body="&lt;p&gt;You should also take into consideration the mode. If the spacing, as the other answer suggests to consider, is not an issue, will the Baofeng actually use a mode compatible with the CubeSat? I don't know anything about your CubeSat, but keep in mind that a Baofeng will only work on FM, not LSB or USB. It also lacks the host of other features the IC910 offers, specifically for satellite use.&lt;/p&gt;&#xA;" OwnerUserId="4419" LastActivityDate="2015-03-23T20:17:52.277" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3736" PostTypeId="1" CreationDate="2015-03-23T22:21:21.803" Score="2" ViewCount="253" Body="&lt;p&gt;Let's say my entire house is 5 stories underground with a lead nuclear sheild and no radio waves get out. Given that no interference will be made, am I allowed to transmit on any frequency (not only ham band) in the faraday cage house?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess a more practical situation, can I transmit whatever I want in an RF anechoic chamber? Or does the FCC &quot;own&quot; every point in space for all frequencies. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-03-23T23:41:11.550" Title="Can I use any frequency In a faraday cage?" Tags="&lt;legal&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2015-03-24T20:28:33.537" ContentLicense="CC BY-SA 3.0" />
  <row Id="3737" PostTypeId="2" ParentId="3736" CreationDate="2015-03-23T23:41:11.550" Score="2" Body="&lt;p&gt;The FCC (Federal Communications Commission) does not &quot;own&quot; space in some divine way, instead it is the US agency that issues licences for transmissions at certain powers and certain frequencies, and it may act to interdict unlicensed transmissions that cause interference to receivers of permitted transmissions (and radio astronomers). The questioner asks about radio frequency equipment that is so thoroughly screened that there is no transmission and that would be no concern of the FCC. In the case of frequencies that went unused after the change of analog TV signal to digital the FCC have expressly relinquished control.&#xA;&lt;a href=&quot;http://www.cnet.com/news/fcc-opens-free-white-space-spectrum/&quot; rel=&quot;nofollow&quot;&gt;http://www.cnet.com/news/fcc-opens-free-white-space-spectrum/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However the activities described if discovered would likely attract negative attention from authorities in countries with little or no tradition for amateur radio, notably Iran, Yemen and North Korea.&lt;/p&gt;&#xA;" OwnerUserId="4408" LastActivityDate="2015-03-23T23:41:11.550" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3738" PostTypeId="2" ParentId="3727" CreationDate="2015-03-24T15:59:35.590" Score="4" Body="&lt;p&gt;(Sorry about the long delay)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna that might meet your requirements is called the HB9CV. It's an array with two dipoles about 1/4 wave apart, driven with the correct current that they add in-phase in the forward direction, and completely out of phase in the backward direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Getting the currents to do this isn't trivial, because they interact with each other, but Mr Baumgartner, HB9CV, designed this neat way of doing it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I built mine for the 2 m amateur band, 15 years ago, after some optimisation in NEC. It worked well, had a sharp null which produced a nice &quot;Crunch&quot; of static in the receiver as I rotated the null past the direction of the source. Searching now on the net, I can find instructions but no simulated patterns, so here they are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 3D pattern, which looks cute but doesn't really tell you anything:&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/bIgbG.png&quot; alt=&quot;3D pattern&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And a 2D cut at Theta=90, on the horizon, which looks great:&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/vK6If.png&quot; alt=&quot;2D cut on Theta=90&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A compact antenna can't really have high gain, or a narrow beam in the front, but it can have this deep null. The one above is over 30 dB deep, in simulation, in practice you won't achieve this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the layout of the antenna, I made it with soldered copper water pipe:&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/SNGog.png&quot; alt=&quot;HB9CV for 145 MHz&quot;&gt;&lt;br&gt;&#xA;Dimensions are in m, for 145 MHz, so you could scale these down by about 16.8 times for 2450 MHz.  But it will get very fiddly making the antenna out of piping, so I proposed you make it on a PCB, like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/PkLzm.png&quot; alt=&quot;HB9CV on PCB&quot;&gt;&lt;br&gt;&#xA;The two colours represent the copper on the two sides of the PCB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is obviously an incomplete design, I can't simulate it on PCB for you, so there will be some more research, design and trial and error required to get it working.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The final size is reduced slightly by the PCB, if I remember correctly, to about 80% for the dipole lengths, and say 90% for the spacings. So the final PCB will be about 50 x 50 mm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope that is small enough for you!&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-03-24T15:59:35.590" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3739" PostTypeId="2" ParentId="3729" CreationDate="2015-03-25T06:07:47.420" Score="2" Body="&lt;p&gt;If I am not wrong, XBee works at 2.4&amp;nbsp;GHz, which is a free band used worldwide. You do not need a license to use this frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there are some other frequencies which need a license. I would still recommend you to search the country-specific frequencies free to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/ISM_band&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/ISM_band&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4423" LastEditorUserId="366" LastEditDate="2015-04-01T11:52:25.973" LastActivityDate="2015-04-01T11:52:25.973" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3740" PostTypeId="2" ParentId="1052" CreationDate="2015-03-25T12:53:50.697" Score="7" Body="&lt;p&gt;I'm trying to find a better source, but according to &lt;a href=&quot;http://apps.fcc.gov/ecfs/document/view;jsessionid=5JyTP1QGSSdmyghc65ChZ22gwVhnSGby4JNQNJWhmXJyQzzC0jSM!-1221852939!-1969853125?id=7021034054&quot; rel=&quot;noreferrer&quot;&gt;this letter&lt;/a&gt; from Boeing petitioning the FCC in 2011, an experimental license is technically required to operate even within a Faraday cage, although they have an unofficial policy of permitting such actions. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Finally, the Commission should codify its policy of permitting entities to conduct experiments within RF enclosures, such as anechoic chambers or Faraday cages, without an experimental license.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This makes sense as someone would have to complain before the FCC was involved. And such a chamber should be able to reduce the RF power going out to almost nothing, making the odds that someone complains very miniscule. Still, it could happen. If you use low power in such a device, you probably will be fine.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2015-04-07T18:35:32.487" LastActivityDate="2015-04-07T18:35:32.487" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3742" PostTypeId="2" ParentId="3702" CreationDate="2015-03-25T17:33:57.267" Score="1" Body="&lt;p&gt;Usually this happens when you accidentally bend the inside of the jack (inside the radio) with the programming cable (or speaker mic) plug. In general you have to carefully open the radio and bend the contacts back down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.miklor.com/&quot; rel=&quot;nofollow&quot;&gt;Miklor&lt;/a&gt; has some instructions on opening the radio. There are also some videos of opening the radio on YouTube.&lt;/p&gt;&#xA;" OwnerUserId="4430" LastEditorUserId="76" LastEditDate="2015-03-25T18:29:42.670" LastActivityDate="2015-03-25T18:29:42.670" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3743" PostTypeId="1" CreationDate="2015-03-25T19:59:14.963" Score="2" ViewCount="293" Body="&lt;p&gt;I have a custom digital transceiver and will like to communicate with digital satellites in the UHF band. It might be fun to try different protocols other than commonly used (like AX.25) as well!&lt;/p&gt;&#xA;" OwnerUserId="4383" LastEditorUserId="4383" LastEditDate="2015-03-27T19:47:22.423" LastActivityDate="2017-04-27T07:43:31.380" Title="Are there any satellites in UHF that do not use AX.25? Which of them are in working state? Is the communication to them open?" Tags="&lt;digital-modes&gt;&lt;satellites&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="3745" PostTypeId="1" AcceptedAnswerId="3746" CreationDate="2015-03-25T21:56:33.203" Score="2" ViewCount="160" Body="&lt;p&gt;I'm trying to set up sdrSharp on my PC using a NooElec nesdr mini for the receiver.  I've read a bunch of setup instructions which all suggest using &lt;a href=&quot;http://zadig.akeo.ie/&quot; rel=&quot;nofollow&quot;&gt;Zadig&lt;/a&gt; to install the usb drivers for the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, whenever I plug the nesdr into my usb port I receive an error &lt;code&gt;Power Surge on Hub&lt;/code&gt; after which my computer disconnects the port which means I can't install the drivers for that device.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone run into this?  Any suggestions?&lt;/p&gt;&#xA;" OwnerUserId="4431" LastActivityDate="2015-03-25T22:05:34.743" Title="Power surge on hub when using NooElec nesdr mini" Tags="&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3746" PostTypeId="2" ParentId="3745" CreationDate="2015-03-25T22:05:34.743" Score="2" Body="&lt;p&gt;Sounds like you have a defective device with an internal short or other flaw causing it to draw too much current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RTL dongles are fairly high power (note how warm they get), but should be well under the 500 mA USB current limit; I run two of them from a single bus-powered hub. (I measured the draw of some a while ago, but I don't have records on on that handy.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obtain a replacement or second dongle (lots of uses for them anyway!) and test it. If the second one doesn't fail, then you probably got a defective unit. If it does, you evidently have a particularly picky USB port.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-03-25T22:05:34.743" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3747" PostTypeId="2" ParentId="221" CreationDate="2015-03-26T01:14:33.217" Score="5" Body="&lt;p&gt;This helped me.  For anyone that needs it, here is a port to Java:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;public class Location {&#xA;&#xA;  String latlon;&#xA;  String maidenhead;&#xA;&#xA;  public Location(String p1, String p2) {&#xA;    float lat = -100.0f;&#xA;    float lon = 0.0f;&#xA;    try {&#xA;      lat = Float.parseFloat(p1);&#xA;      lon = Float.parseFloat(p2);&#xA;&#xA;      maidenhead = latLonToGridSquare(lat, lon);&#xA;    } catch (Exception e) {&#xA;      // TODO Auto-generated catch block&#xA;      e.printStackTrace();&#xA;    }&#xA;  }&#xA;&#xA;  public Location(float lat, float lon) {&#xA;    try {&#xA;      maidenhead = latLonToGridSquare(lat, lon);&#xA;    } catch (Exception e) {&#xA;      // TODO Auto-generated catch block&#xA;      e.printStackTrace();&#xA;    }&#xA;  }&#xA;&#xA;  private void gridSquareToLatLon(String grid) {&#xA;&#xA;  }&#xA;&#xA;  public String latLonToGridSquare(float lat, float lon) throws Exception{&#xA;    float adjLat,adjLon;&#xA;    char GLat,GLon;&#xA;    String nLat,nLon;&#xA;    char gLat,gLon;&#xA;    float rLat,rLon;&#xA;    String U = &quot;ABCDEFGHIJKLMNOPQRSTUVWX&quot;;&#xA;    String L = U.toLowerCase();&#xA;&#xA;    // support Chris Veness 2002-2012 LatLon library and&#xA;    // other objects with lat/lon properties&#xA;    // properties could be getter functions, numbers, or strings&#xA;&#xA;&#xA;    if (Float.isNaN(lat)) throw new Exception(&quot;lat is NaN&quot;);&#xA;    if (Float.isNaN(lon)) throw new Exception(&quot;lon is NaN&quot;);&#xA;    if (Math.abs(lat) == 90.0) throw new Exception(&quot;grid squares invalid at N/S poles&quot;);&#xA;    if (Math.abs(lat) &amp;gt; 90) throw new Exception(&quot;invalid latitude: &quot;+lat);&#xA;    if (Math.abs(lon) &amp;gt; 180) throw new Exception(&quot;invalid longitude: &quot;+lon);&#xA;&#xA;&#xA;    adjLat = lat + 90;&#xA;    adjLon = lon + 180;&#xA;    GLat = U.charAt((int) (adjLat/10));&#xA;    GLon = U.charAt((int) (adjLon/20));&#xA;    nLat = &quot;&quot;+(int)(adjLat % 10);&#xA;    nLon = &quot;&quot;+(int)((adjLon/2) % 10);&#xA;    rLat = (adjLat - (int)(adjLat)) * 60;&#xA;    rLon = (adjLon - 2*(int)(adjLon/2)) *60;&#xA;    gLat = L.charAt((int)(rLat/2.5));&#xA;    gLon = L.charAt((int)(rLon/5));&#xA;    String locator = &quot;&quot;+GLon+GLat+nLon+nLat+gLon+gLat;&#xA;    return locator;&#xA;  }&#xA;}&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And here is the JUnit test case:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;import static org.junit.Assert.*;&#xA;&#xA;import org.junit.After;&#xA;import org.junit.AfterClass;&#xA;import org.junit.Before;&#xA;import org.junit.BeforeClass;&#xA;import org.junit.Test;&#xA;&#xA;public class LocationTest {&#xA;  @Test&#xA;  public void testLatLonToGridSquare() {&#xA;    Location loc = new Location(48.14666f,11.60833f);&#xA;    System.out.println(loc.maidenhead);&#xA;    assertEquals(loc.maidenhead, &quot;JN58td&quot;);&#xA;&#xA;    loc = new Location(&quot;-34.91&quot;,&quot;-56.21166&quot;);&#xA;    System.out.println(loc.maidenhead);&#xA;    assertEquals(loc.maidenhead, &quot;GF15vc&quot;);&#xA;&#xA;    loc = new Location(38.92f,-77.065f);&#xA;    System.out.println(loc.maidenhead);&#xA;    assertEquals(loc.maidenhead, &quot;FM18lw&quot;);&#xA;&#xA;    loc = new Location(-41.28333f,174.745f);&#xA;    System.out.println(loc.maidenhead);&#xA;    assertEquals(loc.maidenhead, &quot;RE78ir&quot;);&#xA;&#xA;    loc = new Location(41.714775f,-72.727260f);&#xA;    System.out.println(loc.maidenhead);&#xA;    assertEquals(loc.maidenhead, &quot;FN31pr&quot;);&#xA;&#xA;    loc = new Location(37.413708f,-122.1073236f);&#xA;    System.out.println(loc.maidenhead);&#xA;    assertEquals(loc.maidenhead, &quot;CM87wj&quot;);&#xA;&#xA;    loc = new Location(35.0542f,-85.1142f );&#xA;    System.out.println(loc.maidenhead);&#xA;    assertEquals(loc.maidenhead, &quot;EM75kb&quot;);&#xA;  }&#xA;}&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="4432" LastEditorUserId="76" LastEditDate="2015-03-26T03:47:31.997" LastActivityDate="2015-03-26T03:47:31.997" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3752" PostTypeId="1" CreationDate="2015-03-27T23:16:05.543" Score="2" ViewCount="1116" Body="&lt;p&gt;I'm looking to buy a shortwave to listen to either solely at home or perhaps if possible in a vehicle when traveling. What should I look for when looking them over?  I recall many years ago the ability to listen to Quito Ecuador from South Central Canada, as well as many Russian propaganda stations. I had purchased a radio from a Garage sale WWII vintage all tube, but boy did it work well (after it warmed up)!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm sure today's radios are very good, but would rather some of you experts tell me about things to look for. &lt;/p&gt;&#xA;" OwnerUserId="4449" LastEditorUserId="76" LastEditDate="2015-03-27T23:51:55.253" LastActivityDate="2020-01-12T20:28:21.843" Title="What should I look for in a modern portable shortwave radio?" Tags="&lt;hf&gt;&lt;mobile&gt;&lt;swl&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3753" PostTypeId="2" ParentId="3752" CreationDate="2015-03-28T23:20:47.063" Score="2" Body="&lt;p&gt;To me, a good portable shortwave radio is:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Battery Powered with built-in charger.&lt;/li&gt;&#xA;&lt;li&gt;Hand-held with telescoping antenna (removable for external antenna).&lt;/li&gt;&#xA;&lt;li&gt;Speaker plus headphone attachment.&lt;/li&gt;&#xA;&lt;li&gt;Very wide coverage, preferably DC to Daylight (or, 0.15 to 3000+ MHz).&lt;/li&gt;&#xA;&lt;li&gt;Many memory channels for storage.&lt;/li&gt;&#xA;&lt;li&gt;Frequency scanning (programmable) with memory stored bands.&lt;/li&gt;&#xA;&lt;li&gt;Dual-watch VFO.&lt;/li&gt;&#xA;&lt;li&gt;Multiple tuning steps, direct entry frequency.&lt;/li&gt;&#xA;&lt;li&gt;Reasonable Light weight.&lt;/li&gt;&#xA;&lt;li&gt;Highly sensitive receiver across all bands.&lt;/li&gt;&#xA;&lt;li&gt;Multiple modes: CW, SSB, AM, FM, WFM&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Actually, I am describing my &lt;a href=&quot;http://icomamerica.com/en/products/receivers/handheld/r20/default.aspx&quot; rel=&quot;nofollow&quot;&gt;Icom IC-R20&lt;/a&gt; hand-held portable receiver.  It is excellent.  I take it every with me in addition to taking along my portable transceiver (Elecraft KX3).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I highly recommend the IC-R20 although it is a bit pricey but worth it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Late Comment Edit:  I need to add one &quot;negative&quot; to the IC-R20 radio.  Though this less than &quot;best&quot; feature does not bother me, it did bother a friend of mine to the point that he declared he would not buy an IC-R20.  Since the radio is hand-held portable, it has a single speaker.  Not only that, but that the headphones (at least on mine) are mono, not stereo.  Thus, if you want to listen to your favorite FM music stereo station, you are out of luck, hearing one mono only.  Therefore, if FM music is what you want in a portable shortwave radio, you may not want the IC-R20.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2015-03-29T20:04:24.617" LastActivityDate="2015-03-29T20:04:24.617" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3754" PostTypeId="1" CreationDate="2015-03-30T15:24:56.090" Score="3" ViewCount="173" Body="&lt;p&gt;I am trying to receive beacon from the analog satellites and observe its power on signal analyzer.I am using a 15dB gain and LNA with a 40dB gain. I am trying satellites like Ho-68(-81.64 dB at 56 deg elevation), JUGNU(-95 at 50 deg elevation), CO-57 etc. What should be the value of received power? Does anyone have any reference values?&lt;/p&gt;&#xA;" OwnerUserId="4456" LastEditorUserId="29" LastEditDate="2015-03-31T09:51:48.467" LastActivityDate="2015-03-31T09:51:48.467" Title="How much RF power should I expect to receive from a satellite?" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3755" PostTypeId="1" CreationDate="2015-03-30T19:53:24.007" Score="3" ViewCount="839" Body="&lt;p&gt;I built a little USB dongle I put on my radio. This dongle interfaces audio and PTT to my radio so it can use AllStar link. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is interference. When the radio transmits, I heard a high pitch squeal as well as a lower frequency hum that is not present in the audio when the radio was not transmitting. I shielded the device and put RF chokes on every pin in and out of the device, and that fixed the squeal, but there is still a lower pitch hum coming through the audio port. I confirmed it wasn't the power supply by giving the radio a dead key without the audio in. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What steps can I take to find the problem with the RF interference and eliminate the noise on the transmitters audio?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="4408" LastEditDate="2015-04-24T05:14:53.540" LastActivityDate="2015-06-11T22:00:18.683" Title="Steps for eliminating RF interference" Tags="&lt;rfi&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3757" PostTypeId="2" ParentId="3754" CreationDate="2015-03-30T21:27:24.063" Score="4" Body="&lt;p&gt;You can calculate the answer with the &lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;Friis transmission equation&lt;/a&gt;. The great thing about space communications is that the path is very close to free space, so even highly idealized calculations are pretty accurate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to &lt;a href=&quot;http://www.pe0sat.vgnet.nl/satellite/amateur-radio-satellites/ho-68/&quot; rel=&quot;nofollow noreferrer&quot;&gt;some information on HO-68&lt;/a&gt;, its CW beacon transmits with a power of 200 mW (or 23 dBm). I don't see any information on its antenna gain, but it's probably not much, so we can just assume a gain of 1. It might be more: a free space dipole has a gain of 1.5. But it could also be less: it's unlikely its antenna is aligned precisely to your station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From that same information it looks like HO-68's altitude is in the neighborhood ot 1200 km. Of course the distance is greater for anything but an overhead pass, so you can use some tracking software to calculate a more accurate number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using those numbers as examples, we can calculate the transmitted power, less free space path loss as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 23\:\mathrm{dBm} + 147.6 - 20\log_{10}(1200\:\mathrm{km} \cdot  435.79\:\mathrm{MHz}) \approx -124 \:\mathrm{dBm} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding your receive antenna gain (15 dB) brings this up to -109 dBm. You will want to make sure this is above the noise floor of your test equipment, otherwise you will measure nothing but noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding the LNA gain of 40 dB then brings it up to -69 dBm, which is approximately the power you'd expect to measure. It's probably safe to bet that's within 10 dB of reality, which must also take into account the alignment and gain of the satellite's antenna, cable losses, etc.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-03-30T21:27:24.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3759" PostTypeId="2" ParentId="3752" CreationDate="2015-03-31T23:40:01.860" Score="1" Body="&lt;p&gt;I was an SWL (Shortwave Listener)/ BCL (Broadcast Listener) before I got my ham license. So I hope I can give you an idea of what might work in your scenario. Shortwave (SW) is from 3MHz to 30MHz. Most shortwave radios focus on these bands. As with any other radio, you want a selective and sensitive radio, but there will always be tradeoffs specially in mass market SW radios. Also, a good radio can be made better with a good external antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most ham equipment can be used for SWL/BCL. They all have the pros mentioned by @K7PEH. Except maybe for portability, as most are intended for tabletop (station) use. Portable/mobile units exists. They are capable of transmitting/receiving on the amateur ham bands and receive on other frequencies. Just remove the mic so as not to inadvertantly transmit on the ham bands if you don't have an amateur radio license. All these extra features make them more complex and expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there are wideband receivers. Same pros as mentioned by @K7PEH above. They are receive only. The frequency coverage is wider than typical ham radios! IC R-20 (hand held), AOR AR-8200 (hand held), AOR AR-8600 (table top) comes to mind. These are the do-all radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, there are dedicated SW radios. These focus mostly on the shortwave bands and the lower bands LW, MW (AM broadcast bands), but might cover the air band (to monitor airport controll tower to airplane communications), and maybe WX (weather channels in the US). These will have limited filtering options, FM, AM, SSB. Some have limited frequency step size, but for normal SW listening 5KHz is enough (9KHz/10KHz if you want to listen to AM broadcast). Fixed rod antenna (for local FM, and SW) and probably a small internal ferrite bar antenna (for LW, MW). Some do have 3.5mm jacks where one can plug a longwire antenna. Most run off batteries, and some come with internal chargers too. These are quite portable, but might lack the necessary connections/adapters to run off the car battery. As you can see, they are quite feature packed given the low price (as compared to a dedicated wideband receiver or ham radio).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dominating SW radios are now China-made, these manufacturers have released new radios almost every year (or 2-3 years), but it doesn't mean these are new design because some design changes are cost cutting changes thus undermining the overall performance of the radio. Even the US branded SW radios are rebranded Chinese radios. On the other hand Sony has not updated it's SW radio lineup for at least a decade. As a point of reference, I still have an analog Sony ICF SW-23 (pocket size), and the newer the Degen DE-1103 (book size) and Tecsun PL-380 (pocket size, larger and wider than the Sony). The Degen and Tecsun are digital SW radios from China.&lt;/p&gt;&#xA;" OwnerUserId="1761" LastActivityDate="2015-03-31T23:40:01.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3760" PostTypeId="2" ParentId="3752" CreationDate="2015-04-01T01:16:58.103" Score="1" Body="&lt;p&gt;Chinese-made radios under various brand names have been mentioned. A low-price example is Philips AE3350 which has 12 bands (9 SW, MW, LW, FMmono). While good enough for listening on the broadcast bands this little analog radio has a remarkable defect: the OFF switch doesn't disconnect the batteries (two AA cells)! It took me a while to understand how the radio could deplenish perfectly good alkaline batteries every time I put it away for a few weeks. My tip is to glue the switch in ON position and to turn OFF when needed by pushing a thin slab of plastic between the battery cells.&lt;/p&gt;&#xA;" OwnerUserId="4408" LastActivityDate="2015-04-01T01:16:58.103" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3762" PostTypeId="2" ParentId="1379" CreationDate="2015-04-02T09:46:42.167" Score="7" Body="&lt;p&gt;È grave •-••- (ex) (French) or&#xA;È grave or ••-•• (el) (Italian)&#xA;Ë diaresis or ••-•• (el)&#xA;Ę hook or ••-•• (el) (Polish)&#xA;É acute ••-•• (el) (French, Spanish) or&#xA;É acute or -••-• (xe)&#xA;Here's a list of Morse Code characters with diacritics I've been able to compile from various sources:                   (Two letters in parentheses means combination of letter codes)&lt;br /&gt;&#xA;ÃO ••-•- (ua) (Portuguese)&lt;br /&gt;&#xA;Ã tilde or   •--•- (ak)&lt;br /&gt;&#xA;Á acute or   •--•- (ak)&lt;br /&gt;&#xA;Å corona or  •--•- (ak)&lt;br /&gt;&#xA;À grave or   •--•- (ak)&lt;br /&gt;&#xA;Â circumflex •--•- (ak)&lt;br /&gt;&#xA;Ä umlaut or       •-•- (aa)&lt;br /&gt;&#xA;Ą hook or         •-•- (aa) (Polish)&lt;br /&gt;&#xA;Æ Scandinavian or •-•- (aa)&lt;br /&gt;&#xA;Ç cedille         •-•- (backward C) or&lt;br /&gt;&#xA;Ç cedille or      -•-•• (ce) (French, Portuguese, Turkish)&lt;br /&gt;&#xA;Ć acute or        -•-•• (ce) (Polish)&lt;br /&gt;&#xA;Ĉ circumflex      -•-•• (ce) (Esperanto)&lt;br /&gt;&#xA;Č caron -•--• (kn) (Croatian)&lt;br /&gt;&#xA;CH ---- (mm) (French, Spanish, Portuguese, German)&lt;br /&gt;&#xA;CZ ---• (oe) (Polish)&lt;br /&gt;DŽ --•-• (gn) (Croatian)&lt;br /&gt;&#xA;Ð eth ••--• (ep) (Icelandic, Faroese)&lt;br /&gt;&#xA;Ð stroke ••-•• (id) (Croatian)&lt;br /&gt;&#xA;È grave •-••- (ex) (French) or&lt;br/&gt;&#xA;È grave or ••-•• (el) (Italian)&lt;br/&gt;&#xA;Ë diaresis or ••-•• (el)&lt;br/&gt;&#xA;Ę hook or ••-•• (el) (Polish)&lt;br/&gt;&#xA;É acute ••-•• (el) (French, Spanish) or&lt;br/&gt;&#xA;É acute or -••-• (xe)&lt;br /&gt;&#xA;Ê circumflex -••-• (xe) (French)&lt;br /&gt;&#xA;Ğ breve --•-• (gn) (Turkish)&lt;br /&gt;&#xA;Ĝ circumflex --•-• (gn) (Esperanto)&lt;br /&gt;&#xA;Ĥ circumflex ---- (mm) (Esperanto) (new) or&lt;br /&gt;&#xA;Ĥ circumflex -•--• (kn) (Esperanto) (old)&lt;br /&gt;&#xA;I dotless   •-••- (lt) (Turkish)&lt;br /&gt;&#xA;Ï diaeresis -••-- (dm)&lt;br /&gt;&#xA;Ì grave or   •---• (je) (Italian)&lt;br /&gt;&#xA;Ĵ circumflex •---• (je) (Esperanto)&lt;br /&gt;&#xA;LJ              •---• (je) (Croatian)&lt;br /&gt;&#xA;Ł slash •-••- (lt)&lt;br /&gt;&#xA;NJ      or --•-- (gm) (Croatian)&lt;br /&gt;&#xA;NY      or --•-- (gm) (Hungarian)&lt;br /&gt;&#xA;Ń acute or --•-- (gm) (Polish)&lt;br /&gt;&#xA;Ñ tilde    --•-- (gm) (Spanish)&lt;br /&gt;&#xA;ÕES or          ---• (oe) (Portuguese)&lt;br /&gt;&#xA;Ó acute or      ---• (oe)&lt;br /&gt;&#xA;Ò grave or      ---• (oe) (Italian)&lt;br /&gt;&#xA;Ö umlaut or     ---• (oe)&lt;br /&gt;&#xA;Ô circumflex or ---• (oe)&lt;br /&gt;&#xA;Ø Scandinavian  ---• (oe)&lt;br /&gt;&#xA;Ś acute •••-••• (sb) (Polish)&lt;br /&gt;&#xA;Ş hook •--•• (pe) (Turkish)&lt;br /&gt;&#xA;Ș comma or ---- (mm) (Romanian)&lt;br /&gt;&#xA;Š caron    ---- (mm)&lt;br /&gt;&#xA;Ŝ circumflex •••-• (sn) (Esperanto)&lt;br /&gt;&#xA;SZ -•-•- (ct) (Polish)&lt;br /&gt;&#xA;ß ess-tzet •••--•• (sz) or&lt;br /&gt;&#xA;ß ess-tzet ••• ••• ss&lt;br /&gt;&#xA;Þ thorn •--•• (pe) (Icelandic)&lt;br /&gt;&#xA;Ü umlaut or  ••-- (ut)&lt;br /&gt;&#xA;Ù grave or   ••-- (ut) (Italian)&lt;br /&gt;&#xA;Ŭ breve or   ••-- (ut) (Esperanto)&lt;br /&gt;&#xA;Û circumflex ••-- (ut) (French)&lt;br /&gt;&#xA;Ž caron or --••- (zt) (Croatian)&lt;br /&gt;&#xA;Ź acute --••- (zt) (Polish)&lt;br /&gt;&#xA;Ż dot --••-• (zn) (Polish)&lt;br /&gt;&#xA;¿ inverted question mark ••-•- (ua) (Spanish)&lt;br /&gt;&#xA;¡ inverted exclamation point --•••- (za) (Spanish)&lt;br /&gt;&lt;/p&gt;&#xA;" OwnerUserId="4478" LastEditorUserId="13" LastEditDate="2015-11-18T23:29:41.293" LastActivityDate="2015-11-18T23:29:41.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3764" PostTypeId="1" CreationDate="2015-04-04T18:34:17.763" Score="3" ViewCount="73" Body="&lt;p&gt;I would like to decode de-interleaved demodulated 4FSK symbols that were transmitted using the CML FX919B chip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The datasheet only gives the following information:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Forward Error Correction&lt;/strong&gt; In transmit mode, the FX919B uses a Trellis Encoder to translate the 96 bits (12 bytes) of a 'Header',&#xA;  'Intermediate' or 'Last' Block into a 66-symbol sequence which&#xA;  includes FEC information. In receive mode, the FX919B decodes the&#xA;  received 66 symbols of a block into 96 bits of binary data using a&#xA;  'Soft Decision' Viterbi algorithm to perform decoding and error&#xA;  correction.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;Interleaving&lt;/strong&gt; The 66 symbols of a 'Header', 'Intermediate' or 'Last' block are interleaved by the modem before transmission to give&#xA;  protection against the effects of noise bursts and short fades. In&#xA;  receive mode, the FX919B de-interleaves the received symbols prior to&#xA;  decoding.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Would this be possible?&#xA;All C++ code I found on the web that decodes similar FEC methods, requires  polynomials that I can't find in the datasheet, and most of them only work for 2-level symbols, not four as in 4FSK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where would I start, trying to do this?&lt;/p&gt;&#xA;" OwnerUserId="4489" LastEditorUserId="76" LastEditDate="2015-04-04T20:25:51.060" LastActivityDate="2015-04-04T20:25:51.060" Title="CML FX919B Forward Error Correcting" Tags="&lt;digital-modes&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3766" PostTypeId="1" CreationDate="2015-04-06T13:26:44.077" Score="1" ViewCount="72" Body="&lt;p&gt;I have selected XStream RF modules due to their price and their range (7 miles). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am part of a car team and hence need to transmit and receive data between the car and the ground station (follower); hence I need to know the procedure to connecting the module to our SBC (BeagleBone black) and also needed to know what I need to buy to receive this data being transmitted by the car. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any new suggestions about the mode of communication would be appreciated (min. range: 1.5 miles).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PS: I am a beginner in radio communication so any material shared would be appreciated. &lt;/p&gt;&#xA;" OwnerUserId="4494" LastEditorUserId="76" LastEditDate="2015-04-07T03:19:47.590" LastActivityDate="2015-05-14T05:49:43.390" Title="How do I integrate XStream RF modules with any microcomputer (Rasp Pi, Beaglebone)?" Tags="&lt;diy&gt;&lt;digital-modes&gt;&lt;uhf&gt;&lt;electronics&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3768" PostTypeId="1" CreationDate="2015-04-07T12:07:31.727" Score="1" ViewCount="192" Body="&lt;p&gt;I need to make shallow (max 2m) underwater wireless sensor network. Data payload is about 10kB/s. I know that VLF band (~3-30kHz) could be the best solution for that, but because of time-to-market I cannot make hardware and software from the ground up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe someone could share experience in this field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible in the 100-900MHz band to send 10kB/s from one device to another - from 2m underwater to over a dozen cm from water surface? Maybe some IC for ultrasonic communication exist? Other ideas?&lt;/p&gt;&#xA;" OwnerUserId="4502" LastEditorUserId="218" LastEditDate="2015-04-09T16:22:33.200" LastActivityDate="2015-04-27T14:19:15.570" Title="Shallow underwater wireless sensor network" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3769" PostTypeId="1" CreationDate="2015-04-07T21:16:11.193" Score="1" ViewCount="57" Body="&lt;p&gt;In the Friis transmission equation, can you please explain the significance of the factor&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\left(\frac{\lambda}{4\pi R}\right)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and what it helps us achieve? Specifically in terms of path loss.&lt;/p&gt;&#xA;" OwnerUserId="4506" LastEditorUserId="76" LastEditDate="2015-04-07T21:47:01.193" LastActivityDate="2015-04-07T21:47:01.193" Title="Interpreting the Friis transmission equation" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;theory&gt;" AnswerCount="0" CommentCount="5" ClosedDate="2015-04-22T13:06:02.910" ContentLicense="CC BY-SA 3.0" />
  <row Id="3770" PostTypeId="1" CreationDate="2015-04-07T23:02:02.680" Score="5" ViewCount="20737" Body="&lt;p&gt;I am trying to decide whether or not I should use a CTCSS (Continuous Tone-Coded Squelch System) or a DCS (Digital Coded Squelch) for my mini repeater I just set up. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the advantages of using a DCS over a CTCSS? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am in an area with a lot of RF noise, and I think DCS may help keep some of that noise out. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which method will pick up a weaker signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What factors should I consider when choosing the squelch method? &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="9493" LastEditDate="2018-03-13T01:28:50.030" LastActivityDate="2018-03-13T01:38:28.567" Title="Advantages of using Digital Code Squelch" Tags="&lt;rfi&gt;&lt;tone-squelch&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3771" PostTypeId="1" CreationDate="2015-04-07T23:32:22.610" Score="10" ViewCount="12858" Body="&lt;p&gt;All tests are performed in Carrier Squelch mode on all radios without any sub-audible tone or digital squelch involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Scenario 1: The Baofeng handheld radio Keys up. Another Baofeng is listening. When the transmitting Baofeng un-keys, the receiving baofeng does not hear any squelch tail, and has a smooth un-key.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Scenario 2: The Baofeng handheld radio Keys up. A different brand radio is used to receive. When the Baofeng un-keys, the squelch tail is heard through the speaker of the other radio. I have tested this on Kenwood, Alinco, and ICOM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Scenario 3: A different brand radio keys up. The Baofeng is listening. When the radio un-keys, I hear the squelch tail through the Baofeng speaker. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is it that Baofeng uses to eliminate squelch tails on the radios where no other brand inhibits this property? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have confirmed it is NOT chicken burst (ending the PL tone early) , or reverse burst (phasing the PL tone 180 degrees) , and there is something special about the Baofeng radio's &quot;End-Of-Transmission&quot; squelch tail eliminator. &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2016-10-29T18:54:14.460" LastActivityDate="2017-05-29T05:33:24.490" Title="How does the baofeng radio eliminate squelch tail?" Tags="&lt;baofeng&gt;&lt;squelch&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3772" PostTypeId="2" ParentId="1379" CreationDate="2015-04-08T09:25:00.863" Score="1" Body="&lt;p&gt;The Greek language is a little bit special because of the diphthongs (two successive letters producing a different sound when they appear together) which get mapped to a single symbol in Morse code. For more information (including Cyrilic) please see: &lt;a href=&quot;http://en.wikipedia.org/wiki/Morse_code_for_non-Latin_alphabets&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/Morse_code_for_non-Latin_alphabets&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="471" LastActivityDate="2015-04-08T09:25:00.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3773" PostTypeId="1" CreationDate="2015-04-08T17:17:18.697" Score="0" ViewCount="360" Body="&lt;p&gt;What are ALL the potential signal loss mechanisms between the output of the earth station antenna and the input of the satellite receiver. With a bit of explanation for each if possible please.&lt;/p&gt;&#xA;" OwnerUserId="4506" LastEditorUserId="29" LastEditDate="2015-04-09T07:07:57.437" LastActivityDate="2015-04-09T16:14:21.850" Title="What are the signal loss mechanisms between a ground station antenna and a satellite receiver?" Tags="&lt;propagation&gt;&lt;theory&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3774" PostTypeId="1" CreationDate="2015-04-08T22:33:01.813" Score="3" ViewCount="605" Body="&lt;p&gt;What determines the optimum frequency range for the transmission of signals in a system that's transmitting electromagnetic signals between an antenna on the surface of the earth and an orbiting satellite antenna.&lt;/p&gt;&#xA;" OwnerUserId="4506" LastEditorUserId="76" LastEditDate="2015-12-15T23:42:03.567" LastActivityDate="2015-12-15T23:42:03.567" Title="What determines the optimum frequency range for the transmission of signals?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;satellites&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3775" PostTypeId="2" ParentId="3774" CreationDate="2015-04-08T23:44:57.970" Score="3" Body="&lt;p&gt;Many factors, and since your question is so broad, a broad answer follows:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal bandwidth (amount of information per second) will determine a minimum carrier frequency. In practice, the modulated signal should have a bandwidth of not more than say 1% of the carrier frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, at lower carrier frequencies, you need to consider antenna size (which can be too large for a satellite), and ionospheric effects (mostly in HF range).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Commercial satellites communicate in the microwave range (L band, all the way to the K bands and above).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At high carrier frequencies, atmospheric attenuation becomes a problem. Also clouds and rain provide attenuation in the K bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Small amateur radio satellites normally operate in UHF and VHF, but those frequencies allow for a very small bandwidth (1200 or 9600 bits per second).&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2015-04-08T23:44:57.970" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3778" PostTypeId="2" ParentId="3773" CreationDate="2015-04-09T15:49:31.093" Score="1" Body="&lt;h1&gt;polarization loss&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;If the polarization of the two antennas are not identical, and they rarely are, then there's some loss. For linear polarization on each end:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_r \propto \cos(\theta) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$P_r$ is the received power, and&lt;/li&gt;&#xA;&lt;li&gt;$\theta$ is the angle difference between the antennas.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If each antenna is circularly polarized in the same sense, then there is no loss, regardless of angle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If each antenna is circularly polarized in opposite senses, then loss is theoretically infinite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one antenna is circularly polarized (either sense -- it doesn't matter) and the other is linear, then there is a fixed 3 dB loss regardless of the rotation of the antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While polarization loss can theoretically be infinite, in practice &quot;infinite&quot; means around -30 dB since no real antenna is exactly linearly or circularly polarized, and reflections off other objects (the ground, the satellite's solar panels, etc) mean at least some of the received energy is in a different polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Faraday_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;Faraday rotation&lt;/a&gt; can alter the polarization of the signal as it passes through the atmosphere, introducing polarization loss.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;directional loss&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Antenna gains are usually given in their direction of maximum gain. This is only valid for calculations if the antennas are aligned perfectly, which is rarely the case. The difference from the maximum, on-axis gain and the actual gain could be considered a &quot;loss&quot; in the calculation of a link budget.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The value of this loss depends on the particular antenna's pattern.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;multipath interference&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Although this isn't as much of a problem as it can be for terrestrial communication, there's at least the ground to consider. For highly directional antennas the ground reflections can be negligible unless the satellite is very near the horizon. For less directional antennas a simple but effective model for this loss is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Two-ray_ground-reflection_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;two-ray ground reflection model&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on the geometry of the satellite, there can potentially be significant reflections on that end, also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on how the geometry works out, this can be a gain, not a loss.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;atmospheric absorption&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;The atmosphere &lt;a href=&quot;http://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)&quot; rel=&quot;nofollow noreferrer&quot;&gt;absorbs electromagnetic radiation&lt;/a&gt;. The absorption is frequency dependent. It also depends on the position of the satellite: when the satellite is overhead the path must go though less atmosphere than when the satellite is at the horizon. The atmosphere changes with the weather, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fortunately, satellite communication frequencies are selected in regions of the electromagnetic spectrum where absorption is usually negligible.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;atmospheric reflection&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;The atmosphere can also reflect electromagnetic energy as well as absorb it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At VHF and higher frequencies, the reflection is very slight and diffuse. This can be exploited for terrestrial communications and is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Tropospheric_scatter&quot; rel=&quot;nofollow noreferrer&quot;&gt;troposcatter&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At HF, reflection from the atmosphere can be very significant. When used for terrestrial communications, this is called &lt;a href=&quot;http://en.wikipedia.org/wiki/Skywave&quot; rel=&quot;nofollow noreferrer&quot;&gt;skywave propagation&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to calculate these losses for purposes of space communication, you can research these propagation modes, keeping in mind what is a &quot;loss&quot; for terrestrial communication is energy that made it past the atmosphere, which is good for space communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Space weather can exacerbate these issues, sometimes severely.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;inverse square law&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Radio communications, just like light and all other forms of electromagnetic radiation, are subject to the &lt;a href=&quot;http://en.wikipedia.org/wiki/Inverse-square_law&quot; rel=&quot;nofollow noreferrer&quot;&gt;inverse square law&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_r \propto {1 \over r^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $r$ is the distance between the receiver and transmitter. In other words, for each doubling of the distance, power is divided by 4.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;other&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Of course, we can't enumerate every possible source of loss. Possibly significant:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;birds landing on the antenna&lt;/li&gt;&#xA;&lt;li&gt;airplanes flying in the way&lt;/li&gt;&#xA;&lt;li&gt;ice on the antenna&lt;/li&gt;&#xA;&lt;li&gt;heavy clouds&lt;/li&gt;&#xA;&lt;li&gt;dust storms&lt;/li&gt;&#xA;&lt;li&gt;trees&lt;/li&gt;&#xA;&lt;li&gt;wind messing with antenna alignment&lt;/li&gt;&#xA;&lt;li&gt;space weather and its many effects on the atmosphere&lt;/li&gt;&#xA;&lt;li&gt;supervolcanos&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h1&gt;summary&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Path losses for practical space communications are almost entirely a function of the inverse square law, antenna gain, and antenna alignment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Multipath interference can be a problem sometimes, if the antennas are not sufficiently directional to be isolated from nearby reflective surfaces (notably the ground).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other sources of loss are small under normal conditions and complex to calculate. For amateur needs it's sufficient to add a few dB of margin in the link budget to account for these things. People investing millions of dollars in launching satellites perform extensive studies of space weather and other stochastic factors and calculate an acceptable margin based on a specified probability of failure.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;further reading&lt;/h1&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;What is a link budget, and how do I make one?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;What does the Friis transmission equation represent and how is it derived?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/3692/218&quot;&gt;Is free space path loss dependent on frequency?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-04-09T16:14:21.850" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3779" PostTypeId="2" ParentId="3604" CreationDate="2015-04-09T20:57:10.607" Score="3" Body="&lt;p&gt;I didn't see anything in the manual that would indicate the MFJ 1270B would support packet BBS natively. You would need some external hardware to do that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find a scan of the manual online here:&#xA;&lt;a href=&quot;http://www.repeater-builder.com/mfj/pdfs/mfj-1270b-tnc-manual.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.repeater-builder.com/mfj/pdfs/mfj-1270b-tnc-manual.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to that doc, the STA LED &quot;is normally low and goes high only when this TNC has unacknowledged packets in its transmit buffer.&quot;&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2015-04-09T21:08:22.953" LastActivityDate="2015-04-09T21:08:22.953" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3780" PostTypeId="1" CreationDate="2015-04-10T23:45:37.493" Score="2" ViewCount="264" Body="&lt;p&gt;I have a Yaesu FTDX-1200.  There is a feature that allows storage of 3 sets of frequency for each of the band selection buttons.&#xA;I tried pressing store and then the band button but it does not seem to store the current frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do you program these buttons?&lt;/p&gt;&#xA;" OwnerUserId="4519" LastEditorUserId="76" LastEditDate="2016-10-29T18:09:03.380" LastActivityDate="2016-10-29T18:09:03.380" Title="Yaesu FTDX-1200 how to load band stack register" Tags="&lt;yaesu&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3782" PostTypeId="1" CreationDate="2015-04-11T12:53:28.097" Score="4" ViewCount="2657" Body="&lt;p&gt;I know I have probably experienced multi-path propagation on FM modes when I was working a repeater in the grand canyon and in the mountains. How can I identify when I am getting multi-path, and what does it sound like while using frequency modulation?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2015-04-11T14:57:02.873" LastActivityDate="2017-06-01T08:02:21.307" Title="What does multi-path sound like on FM?" Tags="&lt;propagation&gt;&lt;fm&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3783" PostTypeId="1" CreationDate="2015-04-11T18:07:33.660" Score="5" ViewCount="5370" Body="&lt;p&gt;I would like to make a dipole antenna. This particular antenna is used for reception only; no transmission is involved. I would like to receive as much power as possible by this antenna as it is used in energy harvesting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I read that a length of 1.25 λ (i.e. each leg length is 5/8 λ) has more gain. To match it with a load, I need to create a matching circuit. So, what is the impedance of a 1.25 λ length dipole antenna?&lt;/p&gt;&#xA;" OwnerUserId="4524" LastEditorUserId="76" LastEditDate="2015-12-15T22:29:26.547" LastActivityDate="2015-12-15T22:29:26.547" Title="What is the impedance of a 1.25 λ dipole antenna?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;impedance&gt;&lt;antenna-theory&gt;&lt;dipole&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3784" PostTypeId="2" ParentId="3783" CreationDate="2015-04-11T18:38:10.470" Score="2" Body="&lt;p&gt;The impedance is double that of a 5/8 wave monopole, which is well studied, there's lots of information out there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the ARRL Antenna Compendium:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;The input impedance of a 5/8-wave whip above a ground plane 1/2 wavelength or more in diameter has a resistive component close to 50 ohms, and a capacitive reactance that depends considerably on the whip diameter, typically in the range of 50 to 150 ohms.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The impedance of your 1.25 wavelength dipole will be about 100 -j100 to -j300 Ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two comments on this choice of antenna:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;higher gain only means more power if you aim the antenna at the source. If you're harvesting in general, rather use a low gain antenna.&lt;/li&gt;&#xA;&lt;li&gt;this is a fairly narrow band antenna, so only really useful if you know the frequency of the signal you are harvesting. Its impedance will change quickly with frequency, and the matching inductors change the other way.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-04-11T18:38:10.470" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="3785" PostTypeId="1" CreationDate="2015-04-11T19:50:33.720" Score="2" ViewCount="1216" Body="&lt;p&gt;I don't seem to be able to find the data to enter a 4:1 current balun in the 4nec2 software. Has anyone found or written one?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am building a 75 Ω fed OCFD and need to model the radiated patterns, but I have no data for 4nec to add a balun.&lt;/p&gt;&#xA;" OwnerUserId="4527" LastEditorUserId="8717" LastEditDate="2019-11-05T21:38:14.533" LastActivityDate="2019-11-05T21:38:14.533" Title="Is there a 4:1 current balun model for 4nec2?" Tags="&lt;antenna&gt;&lt;balun&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3786" PostTypeId="2" ParentId="3768" CreationDate="2015-04-11T20:06:43.850" Score="1" Body="&lt;p&gt;For just 2 m range, how about a low frequency magnetic field, not radio waves*?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have a coil in each device, and drive a current into it at (say) 22 kHz for 0 and 44 kHz for 1.&lt;br&gt;&#xA;Receiving would use the same coil, or one with more turns, connected to an audio amplifier, automatic gain control, and some sort of detector. Even straight into your micro, depending on what it has.&lt;br&gt;&#xA;The self-resonance of each coil should be high, at least 100 kHz, and the inductance low enough that you can get reasonable current into it without unreasonable voltage. There's no gain from resonance, you don't want a high Q coil here at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This principle is used by heart rate monitors, which work (badly) under water. And I can relate some childhood experiments with a coil around the room, connected to an audio amplifier in place of the loudspeaker, and a search coil picking up the music anywhere nearby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fresh water will have almost no effect on your magnetic fields. Seawater, I don't know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Its quite easy to experiment, with a scope and a signal generator or oscillator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;.* &lt;em&gt;In fact all changing magnetic fields create a changing electric field, and hence an electromagnetic wave, but here we are in the near field where the magnetic field of a loop is dominant.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-04-11T20:06:43.850" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3787" PostTypeId="2" ParentId="3785" CreationDate="2015-04-11T20:18:39.077" Score="1" Body="&lt;p&gt;I don't know 4nec2, just regular NEC. A balun isn't a NEC primitive, it would have to be modelled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the 4:1 part of it, this is just maths done outside of the simulation itself. You simply double the applied voltage (if that matters for actual total power), and divide the impedance by 4 afterwards. Impedance makes no difference to patterns, so you could ignore that part if you're just after patterns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the current balun, you need to know the choke impedance of the balun. Connect a feed cable to the side of the antenna which will take the braid of the coax. Load the last segment of the coax (braid) with a load equal to the balun common mode impedance. If you don't have a figure, try about 1000 Ohms resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As always with NEC, rather use long thin segments that obey the rules, than try to exactly model the shape of things. For example at 14 MHz your coax wire will have segments about 1 m long. Don't stress that the balun is really only 25 cm long, just load the last 1 m segment. Making tiny, accurate segments will just make it worse.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-04-11T20:18:39.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3789" PostTypeId="2" ParentId="3782" CreationDate="2015-04-11T22:15:19.537" Score="-1" Body="&lt;p&gt;Multi-path distorts FM reception like this&#xA;&lt;a href=&quot;https://www.youtube.com/watch?v=sFQ5IUUQfOw&quot; rel=&quot;nofollow&quot;&gt;https://www.youtube.com/watch?v=sFQ5IUUQfOw&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4408" LastActivityDate="2015-04-11T22:15:19.537" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3790" PostTypeId="2" ParentId="3782" CreationDate="2015-04-12T11:50:42.570" Score="2" Body="&lt;p&gt;Multi-path doesn't make any sound itself, and if the environment is constant, you'll never notice it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you will notice is the &lt;em&gt;fading&lt;/em&gt; caused by multi-path, if you move (or the reflector moves) which causes a regular drop in the RF signal strength. When FM is demodulated, this drop results in an increase in the background noise heard, so it sounds like a rising hiss, or a repeating shhp sound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It generally repeats as you move, every half-wavelength or so. Walking around, it's an irritating fading on the signal. Driving, it's a fluctuation that even becomes a fast flutter or buzz as you move.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the mountains, you are more likely to be shielded from the direct path to the repeater, so your propagation depends more on the reflected paths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How to tell? Unless you're talking to a satellite or aeroplane, the signal you hear always contains some reflected components. The question is whether they're strong enough to cause significant cancellation of each other. They can only cancel completely if they're the same strength.  So if you move your receive antenna by a few wavelengths, and you can detect a significant change in audio quality, then you have significant multi-path propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM receivers produce clean audio as soon as the RF SNR is over (say) 10 dB, and there's no change as it rises after that. So if you have a strong signal (60 dB above noise) and good cancellation (99%) then you could still be 20 dB above noise, which won't cause any change in the audio quality.  So you can only tell multipath by listening, if the signal is weak to begin with.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-04-12T11:50:42.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3791" PostTypeId="2" ParentId="830" CreationDate="2015-04-12T16:01:25.840" Score="8" Body="&lt;p&gt;The increased bandwidth of a folded dipole is almost entirely due to the extra thickness. Two parallel elements behave as a thicker single element. There is a small contribution too from the combination of the reactances of the transmission-line mode and radiator-mode acting in opposite directions.&lt;/p&gt;&#xA;" OwnerUserId="4529" LastActivityDate="2015-04-12T16:01:25.840" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3792" PostTypeId="1" CreationDate="2015-04-12T21:06:37.853" Score="2" ViewCount="1231" Body="&lt;p&gt;My house is vinyl sided with aluminum around the windows. But will the inverted vee tune? will it adversly effect the radiation pattern of the G5RV ?&lt;/p&gt;&#xA;" OwnerUserId="4530" LastActivityDate="2015-07-23T03:13:07.887" Title="will my G5RV Jr. work/tune beside the house" Tags="&lt;antenna&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3793" PostTypeId="2" ParentId="3792" CreationDate="2015-04-12T22:13:10.573" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;But will the inverted vee tune?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Probably. If the G5RV is up in the air (and not, for example, stapled to a metal gutter or something else absurd), the metal around you windows will, at worst, have a minor effect on the tuning. It's unlikely to be anything that won't be compensated by the tuner.  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Will it adversly effect the radiation pattern of the G5RV?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The G5RV already has a largely omnidirectional pattern that has lobes and nulls which move around depending on the frequency and how it's installed. It's possible that metal frames around your windows might change the pattern, but since the pattern is already so variable with frequency and installation specifics, such changes would not be &quot;adverse&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most important thing is to get the antenna in the air. A half wavelength is best. The reason: &lt;a href=&quot;https://ham.stackexchange.com/a/487/218&quot;&gt;the ground significantly affects the radiation pattern&lt;/a&gt;. Of course, a G5RV is usually operated at many frequencies, but it can be mounted at the optimal height only for one frequency. Such are the compromises with a multiband antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-04-12T22:13:10.573" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3796" PostTypeId="1" CreationDate="2015-04-13T19:29:40.267" Score="6" ViewCount="711" Body="&lt;p&gt;I have been told by someone that my repeater is not allowed to have a slash r on the end of transmission because that is an identifier for the Russian Federation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Almost every repeater locally uses that, for example KDØWHB/R. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I allowed to use the /R identifier at the end of my repeaters call-sign?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&#xA;I found this site, and it claims that R is not allowed for repeater usage &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://w3beinformed.org/id45.html&quot; rel=&quot;noreferrer&quot;&gt;http://w3beinformed.org/id45.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2015-04-14T12:29:39.373" LastActivityDate="2015-04-14T12:29:39.373" Title="Is it legal to use an R identifier for my repeater in the USA?" Tags="&lt;legal&gt;&lt;repeater&gt;&lt;station-identification&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3797" PostTypeId="2" ParentId="3796" CreationDate="2015-04-13T22:53:10.307" Score="5" Body="&lt;p&gt;In the USA (based on your callsign) I know the FCC specifies /KT, /AG, /AA and /AE because they are in the US callsign group. According to the FCC (97.119):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;If an indicator is self-assigned, it must be included before, after, or both before and after, the call sign. No self-assigned indicator may conflict with any other indicator specified by the FCC Rules or with any prefix assigned to another country.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it sounds like technically you could argue that you should never sign /R (for repeater), or /M (for mobile - since M belongs to the UK) or /MM (for maritime mobile - since MM corresponds to Scotland).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The consensus here:&#xA;&lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?topic=32949.0&quot; rel=&quot;nofollow&quot;&gt;http://www.eham.net/ehamforum/smf/index.php?topic=32949.0&lt;/a&gt;&#xA;is that the FCC rule is badly written. If you're really concerned, you could sign /R. or /RPT, since that is not a prefix assigned to another country.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on the ITU article 19, I think you could also make the argument that R is not a prefix - that R0-R9 are prefixes. (&lt;a href=&quot;http://life.itu.ch/radioclub/rr/art19.htm&quot; rel=&quot;nofollow&quot;&gt;http://life.itu.ch/radioclub/rr/art19.htm&lt;/a&gt; 19.68). After all, a foreign station in the US can't just transmit VE1RAC/W, they need to transmit VE1RAC/W7.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2015-04-13T22:59:01.760" LastActivityDate="2015-04-13T22:59:01.760" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3798" PostTypeId="1" CreationDate="2015-04-14T15:21:09.580" Score="4" ViewCount="1029" Body="&lt;p&gt;I would like to chose an inductor to make a matching circuit. Operating frequency is 6.1 GHz. I am more concerned with self resonance frequency and Q of an inductor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would an inductor with SRF &gt; 7 GHz and Q &gt; 10 be okay at above frequency?&lt;/p&gt;&#xA;" OwnerUserId="4524" LastEditorUserId="218" LastEditDate="2015-04-15T12:07:11.457" LastActivityDate="2016-03-30T18:02:13.100" Title="How to choose right inductors for a matching circuit" Tags="&lt;rfi&gt;&lt;capacitance&gt;&lt;inductor&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3799" PostTypeId="1" CreationDate="2015-04-15T04:21:24.220" Score="4" ViewCount="1746" Body="&lt;p&gt;Is there any software similar to &lt;a href=&quot;http://gpredict.oz9aec.net/&quot; rel=&quot;nofollow&quot;&gt;Gpredict&lt;/a&gt; but which can be used without a GUI and can control rotor Az/EL and radio doppler shift? I'm using Linux in particular, especially Ubuntu 14.04.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently, I can control rotors and radio via Gpredict's interface, but it requires manually selecting the satellite and tracking it. I want to script this process — provide &lt;a href=&quot;http://en.wikipedia.org/wiki/Two-line_element_set&quot; rel=&quot;nofollow&quot;&gt;TLE&lt;/a&gt; files and satellite to track and automatically record the downlink (mainly CW beacons) so that I can track multiple satellites without issuing manual commands for each one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, I'm looking for a command-line interface to Gpredict.&lt;/p&gt;&#xA;" OwnerUserId="4539" LastEditorUserId="76" LastEditDate="2016-10-27T19:08:40.733" LastActivityDate="2016-10-27T19:08:40.733" Title="Command-line satellite tracking software" Tags="&lt;satellites&gt;&lt;software&gt;&lt;gpredict&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3800" PostTypeId="2" ParentId="3783" CreationDate="2015-04-15T12:03:44.297" Score="3" Body="&lt;p&gt;If you want a closed-form function, &lt;a href=&quot;http://en.wikipedia.org/wiki/Dipole_antenna#Detailed_calculation_of_dipole_feedpoint_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia gives those&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{align}&#xA;R &amp;amp;= \frac{Z_m}{2 \pi \sin^2(kL/2)} \Big\{&#xA;  \gamma + \ln(kL) - \operatorname{Ci}(kL) + \tfrac{1}{2}\sin(kL) \big[\operatorname{Si}(2kL)- 2\operatorname{Si}(kL)\big] \\&#xA; &amp;amp;\qquad\qquad\qquad\qquad + \tfrac{1}{2}\cos(kL)\big[ \gamma + \ln(kL/2) + \operatorname{Ci}(2kL) - 2\operatorname{Ci}(kL) \big]&#xA;\Big\} \\&#xA;X &amp;amp;= \frac{Z_m}{ 4 \pi \sin^2(kL/2)} \Big\{&#xA;  2 \operatorname{Si}(kL) + \cos(kL)\big[ 2 \operatorname{Si}(kL) - \operatorname{Si}(2kL) \big] \\&#xA; &amp;amp;\qquad\qquad\qquad\qquad - \sin(kL)\big[ 2 \operatorname{Ci}(kL) - \operatorname{Ci}(2kL) - \operatorname{Ci}(2ka^2/L) \big]&#xA;\Big\}&#xA;\end{align}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not even going to try to explain those equations since they are so hairy. Easier, and more insightful is to see a graph of the equations (from the same Wikipedia article):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/G8ftt.png&quot; alt=&quot;dipole impedance as function of length&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In theory, a 5/8 monopole has an impedance of something like $(75-425j)\:\Omega$, and the impedance of a dipole is twice that of the equivalent monopole, so $(150-850j)\:\Omega$. Eyeballing that on the graph looks about right.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the thing to note here is that around 1.25λ, the slope of both the real and imaginary components of the impedance is pretty steep, meaning small changes in length make large changes in impedance. Also note that this graph is valid only for a conductor diameter of 0.001λ. Thicker or thinner conductors can also make a significant difference. The sensitivity of the impedance to these parameters explains the variance in the numbers given by various sources.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consequently, to successfully build this antenna you will need some way to measure the impedance and adjust accordingly.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-04-15T12:03:44.297" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="3801" PostTypeId="2" ParentId="3782" CreationDate="2015-04-15T12:37:43.127" Score="6" Body="&lt;p&gt;Multipath distortion can be problematic on fast digital modulations since the receiver sees multiple copies of the transmitted signal, each delayed by some appreciable fraction of a symbol. For example, digital TV uses a symbol rate of something like 4 million symbols per second. That means each symbol is about 250 nanoseconds long, which corresponds to a distance of about 75 meters at the speed of light. Thus, if one path is 75 meters longer than another, the receiver will actually be receiving the previous symbol at the same time as the current signal. This introduces obvious complications in decoding the digital signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM voice, however, is relatively slow. It's not digital so we don't have a symbol rate, however we can say that the highest frequency components in the baseband signal (your voice) are somewhere around 4kHz. 1/4000 seconds corresponds to about 75,000 meters at the speed of light. Any path that's 75,000 meters longer will be significantly attenuated from the direct path, so any audible distortion due to multipath propagation on FM voice is insignificant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, still significant for FM voice is the effect multipath has on the effective antenna pattern. Consider a simple case where the receiver sees the direct path, and also a reflection off a building near the transmitter. We could consider the building as a second transmitting antenna, transmitting the same signal with some delay and attenuation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on the position of the receiver, and the resulting path length to the two transmitting sources, the source phases might be equal, resulting in constructive interference and a stronger received signal, or the phases might be opposite, resulting in destructive interference and a weaker received signal. As the receiver moves in a circle around the two sources, the path lengths and thus the phase delay to each source change, and thus the receiver will encounter alternating regions of constructive and destructive interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Effectively, the transmitter's antenna pattern has been modified to have a large number of narrow lobes. These are called &quot;grating lobes&quot; in the context of phased arrays:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/MBBLI.jpg&quot; alt=&quot;Typical antenna pattern with grating lobes&quot;&gt;&#xA;&lt;em&gt;&lt;a href=&quot;http://commons.wikimedia.org/wiki/File:Typical_antenna_pattern_with_grating_lobes.jpg#/media/File:Typical_antenna_pattern_with_grating_lobes.jpg&quot; rel=&quot;noreferrer&quot;&gt;&quot;Typical antenna pattern with grating lobes&quot; by Mr. PIM at the English language Wikipedia. Licensed under CC BY-SA 3.0 via Wikimedia Commons&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how between the 5 large peaks, there are very many smaller peaks. Depending on the multipath geometry, there might be very many such peaks, and the receiver might not need to move very far from being in one of the peaks to one of the nulls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And this is what most amateurs mean when they talk about &quot;multipath&quot; on FM. It's especially noticeable when operating from a moving vehicle where the mobile station might go through many of these peaks per second. When conditions conspire to make the nulls very deep, and the mobile station is at the edge of the repeater's coverage, the station can alternate between hitting the repeater and not. The resulting sound is sometimes called &quot;picket-fencing&quot;, because it sounds like a station is moving past a picket fence where the individual pickets intermittently occlude the station.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-04-15T12:37:43.127" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3802" PostTypeId="2" ParentId="3799" CreationDate="2015-04-15T13:26:01.770" Score="3" Body="&lt;p&gt;&lt;a href=&quot;http://www.qsl.net/kd2bd/predict.html&quot; rel=&quot;nofollow&quot;&gt;Predict&lt;/a&gt; is the option that comes to mind. It is console based (no GUI), and provides a &lt;em&gt;server mode&lt;/em&gt; where you can request data via UDP messages to a running predict server.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It uses hamlib for rotor control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;N.B.: predict &lt;em&gt;does not&lt;/em&gt; provide transceiver control. You can get the current Doppler (normalized to 100MHz) via UDP queries, so you will need some extra scripting to control your transceiver having this information. I'm personally trying this out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Predict is very stable (I've had an instance running for months).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can install it directly from your package manager.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2015-04-15T13:26:01.770" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3804" PostTypeId="2" ParentId="3696" CreationDate="2015-04-16T11:32:16.137" Score="1" Body="&lt;p&gt;Any &lt;a href=&quot;http://www.antenna-theory.com/antennas/monopole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;monopole antenna&lt;/a&gt; such as the ATAS-120 is designed with the assumption that it will be mounted on a ground &lt;em&gt;plane&lt;/em&gt;. The geometry of the ground plane is important. At radio frequencies, a sheet of metal such as the roof of a metal car is reflective, just like a mirror. Because the ground plane is reflective, an &lt;a href=&quot;http://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;image antenna&lt;/a&gt; is formed below the monopole, making it look like a &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;dipole&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/F6TvX.png&quot; alt=&quot;monopole image antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&quot;&lt;a href=&quot;http://commons.wikimedia.org/wiki/File:Monopole_and_image_antenna.svg#/media/File:Monopole_and_image_antenna.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;Monopole and image antenna&lt;/a&gt;&quot; by Chetvorno - Own work. Licensed under &lt;a href=&quot;http://creativecommons.org/publicdomain/zero/1.0/deed.en&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Creative Commons Zero, Public Domain Dedication&quot;&gt;CC0&lt;/a&gt; via &lt;a href=&quot;//commons.wikimedia.org/wiki/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikimedia Commons&lt;/a&gt;.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna is mounted on anything other than a plane, then there is no &quot;mirror&quot;, so you have no image antenna. Consequently, you no longer have a monopole antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't have a conductive plane available, an alternate solution is to forget the monopole and just make a dipole. This could be two ATAS-120 antennas, each making half of the dipole. If you could figure out some way to mount such an arrangement, it would behave similarly to one ATAS-120 on a ground plane, except it would have twice the feedpoint impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course it would also be twice as big, and you'd somehow have to interface to two autotuners. So for practical reasons, this might not be the best approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you take your proposed approach of running a ground lead to the base of the antenna, that might work, but it's important to understand what you are doing. You are essentially making a dipole, with one half being the ATAS-120, and the other half being that ground lead plus the car body at the end of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The issue here is that we don't know much about the geometry of this ground lead or the car frame. In theory, you just have a funny shaped dipole, and there's no reason it couldn't be an antenna. But in practice, there are many difficult to answer questions. What will the resulting feedpoint impedance be? Will the autotuner still be able to function effectively? The easiest way to answer this question is to try it and see.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another approach, if you don't have a conductive roof, is to make one. You can install radials on your roof just as radials are installed in the ground for HF verticals. Run the radials to the edge of the roof, and install as many as you can, I'd say at least 16. The result will look, electrically, very much like the antenna was mounted on a metal body car.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-04-16T11:32:16.137" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3805" PostTypeId="1" AcceptedAnswerId="3809" CreationDate="2015-04-16T12:57:35.593" Score="2" ViewCount="465" Body="&lt;p&gt;I saw that Oona Räisänen uses C and Perl to process digital signals:&#xA;&lt;a href=&quot;https://github.com/windytan&quot; rel=&quot;nofollow&quot;&gt;https://github.com/windytan&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I was wondering if there is any book (or ebook) about how to use programming to process digital signals. I mean, I have read a lot of books about theory of digital signal processing, such as the Oppenheim books, but I feel that there is a gap between that theory and how to do it using a computer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At my university, we use Matlab but I think that it is not practical since it can't generate binaries (or at least, not easily). So, I was wondering if there is any book but using Perl, Python, C, Java or so.&lt;/p&gt;&#xA;" OwnerUserId="1454" LastEditorUserId="76" LastEditDate="2015-04-16T16:35:20.663" LastActivityDate="2016-10-24T11:00:03.887" Title="How to process signals captured using a SDR?" Tags="&lt;software-defined-radio&gt;&lt;software-development&gt;" AnswerCount="1" CommentCount="8" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3806" PostTypeId="2" ParentId="1737" CreationDate="2015-04-16T15:03:21.240" Score="0" Body="&lt;p&gt;If you're looking for a printable phonetic alphabet, you can download a nice PDF at &lt;a href=&quot;http://www.outsideopen.com/alphabet/&quot; rel=&quot;nofollow&quot;&gt;http://www.outsideopen.com/alphabet/&lt;/a&gt;&#xA;The poster includes morse code, semaphores and shipping flags.&lt;/p&gt;&#xA;" OwnerUserId="4545" LastActivityDate="2015-04-16T15:03:21.240" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3807" PostTypeId="2" ParentId="3771" CreationDate="2015-04-16T20:06:28.013" Score="10" Body="&lt;p&gt;According to the &lt;a href=&quot;http://www.miklor.com/COM/kc9hi/5RMenus.html&quot;&gt;detailed menu descriptions on the Miklor site&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;35 - STE&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Transceiver - Squelch Tail Elimination&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;This function is used eliminate squelch tail noise between UV-5Rs that&#xA;  are communicating directly (no repeater). Reception of a 55 Hz or&#xA;  134.4 Hz tone burst mutes the audio long enough to prevent hearing any squelch tail noise.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Note: When enabled and T-DCS is set to OFF the radio sends a 55 Hz&#xA;  tone for about 1/4 second when the PTT key is released.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Note: When enabled and T-DCS is not set to OFF the radio sends a 134.4 Hz tone for about 1/4 second when the PTT key is released.  &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Note: Set to OFF before communicating through a repeater.      &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Note: Recommended setting is OFF&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="4472" LastActivityDate="2015-04-16T20:06:28.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3808" PostTypeId="2" ParentId="749" CreationDate="2015-04-17T00:54:47.777" Score="2" Body="&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NqFv2.jpg&quot; alt=&quot;Simplex 10M AM HT&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;About as simple as a half-watt can get.&lt;/p&gt;&#xA;" OwnerUserId="4548" LastActivityDate="2015-04-17T00:54:47.777" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3809" PostTypeId="2" ParentId="3805" CreationDate="2015-04-17T05:23:35.827" Score="2" Body="&lt;p&gt;This may not be a direct answer to the question but since a comment suggested a book, let me suggest some others that I have in my library.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, what I think is the most practical for hands-on programming:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;DSP Software Development Techniques for Embedded and Real-Time Systems&quot; by Robert Oshana and published by Newnes.  My copy is copyrighted 2006 and I am not sure if there are any other editions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This book (above) is more geared to the professional engineer who is doing DSP that may be embedded in microprocessor based systems as a lot of care is given to memory use and other concern for other limited processing resources.  For a student project it would be helpful but not really a real beginner book.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another, also mentioned in the comment by @AndrejaKo is the Richard Lyons book &quot;Understanding Digital Signal Processing&quot;.  This is more like a text book covering the mathematical foundation of DSP as well as the theory of digital filters, digital sampling, and so on.  It has a good chapter on Quadrature Signals that might be fitting for some SDR applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another book similar in content to the Lyons book is one by Steven W. Smith with the title &quot;Digital Signal Processing -- A Practical Guide for Engineers and Scientists&quot;.  Not really into the details of programming though.  I am only mentioning it because I have it but I recommend the Lyons book over this one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, an introductory book on what DSP is all about from a amateur radio viewpoint is a publication of the ARRL called &quot;Digital Signal Processing Technology&quot; by Doug Smith, KF6DX.  It has a slim bit of stuff on ham radio transceiver design using DSP (partial SDR mostly if I remember correctly).  But, not as much as I would like.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In summary, these are all reasonably good books but the best for programming is the first book I mentioned by Oshana and even that does not address ham radio type applications (or, maybe that is not the interest of your question).&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-04-17T05:23:35.827" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3812" PostTypeId="5" CreationDate="2015-04-18T23:21:22.163" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2015-04-18T23:21:22.163" LastActivityDate="2015-04-18T23:21:22.163" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3813" PostTypeId="4" CreationDate="2015-04-18T23:21:22.163" Score="0" Body="A voluntary, not regulated, division of an amateur radio band into sections for specific modes or types of operation." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-04-22T13:08:18.533" LastActivityDate="2015-04-22T13:08:18.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3814" PostTypeId="1" CreationDate="2015-04-19T09:08:02.547" Score="2" ViewCount="889" Body="&lt;p&gt;I use 2.4GHz receivers for flying my RC planes via FPV. &#xA;So i can get best reception i use multiple antennas on multiple video receivers.&#xA;I have a diversity controller that uses noise in the video signal to decide which receiver output i will be viewing. The problem with this arrangement is that the signal can switch from a less noisy receiver to a more noisy one and then back again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many examples of diversity that use a RSSI output from the HF module to control the switching. However the brand i use doesnt have this output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was wondering if there is a way to add this functionality to my receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally i need an output between 0 and 5V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone else encountered this problem and come up with a good solution?&lt;/p&gt;&#xA;" OwnerUserId="1030" LastActivityDate="2015-04-22T22:07:47.140" Title="How to measure received signal strength, using DIY circuit" Tags="&lt;diy&gt;&lt;rssi&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3815" PostTypeId="1" AcceptedAnswerId="3817" CreationDate="2015-04-19T11:26:33.707" Score="3" ViewCount="1602" Body="&lt;p&gt;I would like to get hands-on experience with Fldigi. What setup is recommendable?&lt;/p&gt;&#xA;" OwnerUserId="4555" LastEditorUserId="9450" LastEditDate="2019-07-04T15:40:58.300" LastActivityDate="2019-07-04T15:40:58.300" Title="What rig should I start with when trying to get hands-on experience with Fldigi?" Tags="&lt;digital-modes&gt;&lt;software&gt;&lt;equipment&gt;&lt;fldigi&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="3816" PostTypeId="2" ParentId="3815" CreationDate="2015-04-19T12:23:10.963" Score="1" Body="&lt;p&gt;The rig only matters a little, more important is getting a good interface to your computer, and making sure that interface can support your rig. The two most common interfaces are SignaLink and the RigBlaster Pro, although there are other options. Basically you figure out how you want to connect the interface to your radio, and then you connect the interface to your computer via USB. I prefer to have one that has an aux port in the back. Most radios have the ability to do some kind of interfacing with this, although some may require you to set the radio in that mode to begin with.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-04-19T12:23:10.963" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3817" PostTypeId="2" ParentId="3815" CreationDate="2015-04-19T12:24:13.277" Score="4" Body="&lt;p&gt;Nearly any SSB HF rig will do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need some way to get audio out of the receiver and into your computer, and out of your computer and into the transmitter. Most modern transceivers provide some kind of connection for this. In a pinch, you can use the headphone and microphone connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also convenient (through not necessary) if Fldigi can key the radio for you. With some fiddling, you can usually rig up something that uses one of the control lines on a serial port to control a relay or optioisolator to key the radio. Methods vary based on the radio, so just search the internets for a rig you are considering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even better is to get a rig which supports control over a serial connection. Fldigi uses &lt;a href=&quot;http://hamlib.sourceforge.net/manuals/1.2.15/index.html&quot; rel=&quot;nofollow&quot;&gt;hamlib&lt;/a&gt;, so anything supported by hamlib will work. Usually there's a serial port on the back of the radio, and if you don't have a serial port on your computer a USB cable can be had for $20 or so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Get the list of supported radios by running &lt;code&gt;rigctl -l&lt;/code&gt;. Your version might be different, but I get:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Rig #  Mfg                    Model                   Version         Status&#xA;    1  Hamlib                 Dummy                   0.5             Beta&#xA;    2  Hamlib                 NET rigctl              0.3             Beta&#xA;  101  Yaesu                  FT-847                  0.5             Beta&#xA;  103  Yaesu                  FT-1000D                0.0.6           Alpha&#xA;  104  Yaesu                  MARK-V FT-1000MP        0.0.5           Alpha&#xA;  105  Yaesu                  FT-747GX                0.4.1           Beta&#xA;  106  Yaesu                  FT-757GX                0.4.1           Beta&#xA;  107  Yaesu                  FT-757GXII              0.4             Stable&#xA;  109  Yaesu                  FT-767GX                1.0             Stable&#xA;  110  Yaesu                  FT-736R                 0.3             Stable&#xA;  111  Yaesu                  FT-840                  0.1             Untested&#xA;  113  Yaesu                  FT-900                  0.1             Untested&#xA;  114  Yaesu                  FT-920                  2010-08-23      Stable&#xA;  115  Yaesu                  FT-890                  0.1             Stable&#xA;  116  Yaesu                  FT-990                  0.2.1           Alpha&#xA;  117  Yaesu                  FRG-100                 0.4             Beta&#xA;  118  Yaesu                  FRG-9600                0.2             Untested&#xA;  119  Yaesu                  FRG-8800                0.2             Untested&#xA;  120  Yaesu                  FT-817                  0.5.1           Beta&#xA;  121  Yaesu                  FT-100                  0.4.1           Beta&#xA;  122  Yaesu                  FT-857                  0.4             Beta&#xA;  123  Yaesu                  FT-897                  0.3.3           Beta&#xA;  124  Yaesu                  FT-1000MP               0.1.1           Beta&#xA;  125  Yaesu                  MARK-V Field FT-1000MP  0.0.5           Alpha&#xA;  126  Yaesu                  VR-5000                 0.2             Alpha&#xA;  127  Yaesu                  FT-450                  0.22.1          Beta&#xA;  128  Yaesu                  FT-950                  0.22.2          Stable&#xA;  129  Yaesu                  FT-2000                 0.22.1          Stable&#xA;  130  Yaesu                  FTDX-9000               0.22.1          Untested&#xA;  131  Yaesu                  FT-980                  0.1             Alpha&#xA;  132  Yaesu                  FT-DX5000               0.22            Alpha&#xA;  133  Vertex Standard        VX-1700                 1.1             Alpha&#xA;  201  Kenwood                TS-50S                  0.8             Untested&#xA;  202  Kenwood                TS-440                  0.8.0.6.1       Alpha&#xA;  203  Kenwood                TS-450S                 0.8.1           Beta&#xA;  204  Kenwood                TS-570D                 0.8.2           Stable&#xA;  205  Kenwood                TS-690S                 0.8.1           Beta&#xA;  206  Kenwood                TS-711                  0.8.0.6.1       Untested&#xA;  207  Kenwood                TS-790                  0.8.2           Alpha&#xA;  208  Kenwood                TS-811                  0.8.0.6.1       Untested&#xA;  209  Kenwood                TS-850                  0.8.1           Beta&#xA;  210  Kenwood                TS-870S                 0.8.0           Beta&#xA;  211  Kenwood                TS-940S                 0.8.0.6.1       Alpha&#xA;  213  Kenwood                TS-950SDX               0.8             Beta&#xA;  214  Kenwood                TS-2000                 0.8.4           Beta&#xA;  215  Kenwood                R-5000                  0.6.1           Alpha&#xA;  216  Kenwood                TS-570S                 0.8.1           Stable&#xA;  217  Kenwood                TH-D7A                  0.5             Alpha&#xA;  219  Kenwood                TH-F6A                  0.5             Beta&#xA;  220  Kenwood                TH-F7E                  0.5.1           Beta&#xA;  221  Elecraft               K2                      20120615        Beta&#xA;  222  Kenwood                TS-930                  0.8             Untested&#xA;  223  Kenwood                TH-G71                  0.5             Beta&#xA;  224  Kenwood                TS-680S                 0.8.1           Beta&#xA;  225  Kenwood                TS-140S                 0.8.1           Beta&#xA;  226  Kenwood                TM-D700                 0.5             Beta&#xA;  227  Kenwood                TM-V7                   0.5             Beta&#xA;  228  Kenwood                TS-480                  0.8.5           Untested&#xA;  229  Elecraft               K3/KX3                  20120615        Beta&#xA;  230  Kenwood                TRC-80                  0.8             Alpha&#xA;  231  Kenwood                TS-590S                 0.8.1           Beta&#xA;  232  SigFox                 Transfox                20111223        Alpha&#xA;  233  Kenwood                TH-D72A                 0.5.1           Alpha&#xA;  234  Kenwood                TM-D710                 0.5             Untested&#xA;  302  Icom                   IC-1275                 0.7             Beta&#xA;  303  Icom                   IC-271                  0.7             Untested&#xA;  304  Icom                   IC-275                  0.7.1           Beta&#xA;  306  Icom                   IC-471                  0.7             Untested&#xA;  307  Icom                   IC-475                  0.7.1           Beta&#xA;  309  Icom                   IC-706                  0.7.1           Untested&#xA;  310  Icom                   IC-706MkII              0.7.1           Untested&#xA;  311  Icom                   IC-706MkIIG             0.7.2           Stable&#xA;  312  Icom                   IC-707                  0.7             Untested&#xA;  313  Icom                   IC-718                  0.7.1           Beta&#xA;  314  Icom                   IC-725                  0.7.1           Stable&#xA;  315  Icom                   IC-726                  0.7             Stable&#xA;  316  Icom                   IC-728                  0.7             Untested&#xA;  319  Icom                   IC-735                  0.7.1           Beta&#xA;  320  Icom                   IC-736                  0.7             Untested&#xA;  321  Icom                   IC-737                  0.7             Untested&#xA;  322  Icom                   IC-738                  0.7             Untested&#xA;  323  Icom                   IC-746                  0.7.1           Beta&#xA;  324  Icom                   IC-751                  0.7.1           Beta&#xA;  326  Icom                   IC-756                  0.7.1           Alpha&#xA;  327  Icom                   IC-756PRO               0.7             Untested&#xA;  328  Icom                   IC-761                  0.7.1           Stable&#xA;  329  Icom                   IC-765                  0.7             Stable&#xA;  330  Icom                   IC-775                  0.7.1           Untested&#xA;  331  Icom                   IC-781                  0.7.1           Untested&#xA;  332  Icom                   IC-820H                 0.7             Alpha&#xA;  334  Icom                   IC-821H                 0.7             Alpha&#xA;  335  Icom                   IC-970                  0.7             Untested&#xA;  336  Icom                   IC-R10                  0.7             Untested&#xA;  337  Icom                   IC-R71                  0.7             Untested&#xA;  338  Icom                   IC-R72                  0.7             Untested&#xA;  339  Icom                   IC-R75                  0.7             Beta&#xA;  340  Icom                   IC-R7000                0.7.0           Alpha&#xA;  341  Icom                   IC-R7100                0.7.0           Untested&#xA;  342  Icom                   ICR-8500                0.7.1           Beta&#xA;  343  Icom                   IC-R9000                0.7.1           Alpha&#xA;  344  Icom                   IC-910                  0.7.1           Beta&#xA;  345  Icom                   IC-78                   0.7             Untested&#xA;  346  Icom                   IC-746PRO               0.7             Stable&#xA;  347  Icom                   IC-756PROII             0.7             Alpha&#xA;  351  Ten-Tec                Omni VI Plus            0.2             Beta&#xA;  352  Optoelectronics        OptoScan535             0.3             Beta&#xA;  353  Optoelectronics        OptoScan456             0.3             Beta&#xA;  354  Icom                   IC ID-1                 0.7             Untested&#xA;  355  Icom                   IC-703                  0.7             Untested&#xA;  356  Icom                   IC-7800                 0.7.2           Untested&#xA;  357  Icom                   IC-756PROIII            0.7.1           Beta&#xA;  358  Icom                   IC-R20                  0.7             Untested&#xA;  360  Icom                   IC-7000                 0.7.2           Beta&#xA;  361  Icom                   IC-7200                 0.7             Beta&#xA;  362  Icom                   IC-7700                 0.7.1           Stable&#xA;  363  Icom                   IC-7600                 0.7             Beta&#xA;  364  Ten-Tec                Delta II                0.1             Untested&#xA;  365  Icom                   IC-92D                  0.7             Untested&#xA;  366  Icom                   IC-R9500                0.7.1           Untested&#xA;  367  Icom                   IC-7410                 0.7             Untested&#xA;  368  Icom                   IC-9100                 0.7             Untested&#xA;  369  Icom                   IC-RX7                  0.7             Untested&#xA;  401  Icom                   IC-PCR1000              0.8             Beta&#xA;  402  Icom                   IC-PCR100               0.8             Beta&#xA;  403  Icom                   IC-PCR1500              0.8             Beta&#xA;  404  Icom                   IC-PCR2500              0.8             Beta&#xA;  501  AOR                    AR8200                  0.6.1           Alpha&#xA;  502  AOR                    AR8000                  0.6.1           Beta&#xA;  503  AOR                    AR7030                  0.4.1           Beta&#xA;  504  AOR                    AR5000                  0.6.1           Beta&#xA;  505  AOR                    AR3030                  0.4             Untested&#xA;  506  AOR                    AR3000A                 0.5             Beta&#xA;  508  AOR                    AR2700                  0.6             Untested&#xA;  513  AOR                    AR8600                  0.6.1           Beta&#xA;  514  AOR                    AR5000A                 0.6             Alpha&#xA;  515  AOR                    AR7030 Plus             0.1             Beta&#xA;  516  AOR                    SR2200                  0.1             Beta&#xA;  605  JRC                    NRD-525                 0.1             Alpha&#xA;  606  JRC                    NRD-535D                0.6             Stable&#xA;  607  JRC                    NRD-545 DSP             0.6             Beta&#xA;  801  Uniden                 BC780xlt                0.3             Untested&#xA;  802  Uniden                 BC245xlt                0.3             Untested&#xA;  803  Uniden                 BC895xlt                0.3             Untested&#xA;  804  Radio Shack            PRO-2052                0.3             Untested&#xA;  806  Uniden                 BC250D                  0.3             Untested&#xA;  810  Uniden                 BCD-396T                0.3             Alpha&#xA;  811  Uniden                 BCD-996T                0.3             Alpha&#xA;  812  Uniden                 BC898T                  0.3             Untested&#xA;  902  Drake                  R-8A                    0.5.1           Beta&#xA;  903  Drake                  R-8B                    0.5             Untested&#xA; 1004  Lowe                   HF-235                  0.3             Alpha&#xA; 1103  Racal                  RA6790/GM               0.1             Untested&#xA; 1105  Racal                  RA3702                  0.1             Alpha&#xA; 1204  Watkins-Johnson        WJ-8888                 0.2             Untested&#xA; 1402  Skanti                 TRP8000                 0.2             Untested&#xA; 1404  Skanti                 TRP 8255 S R            0.1             Untested&#xA; 1501  Winradio               WR-1000                 0.6             Untested&#xA; 1502  Winradio               WR-1500                 0.6             Untested&#xA; 1503  Winradio               WR-1550                 0.6             Untested&#xA; 1504  Winradio               WR-3100                 0.6             Untested&#xA; 1505  Winradio               WR-3150                 0.6             Untested&#xA; 1506  Winradio               WR-3500                 0.6             Untested&#xA; 1507  Winradio               WR-3700                 0.6             Untested&#xA; 1601  Ten-Tec                TT-550                  0.2             Beta&#xA; 1602  Ten-Tec                TT-538 Jupiter          0.6             Beta&#xA; 1603  Ten-Tec                RX-320                  0.6             Stable&#xA; 1604  Ten-Tec                RX-340                  0.3             Untested&#xA; 1605  Ten-Tec                RX-350                  0.1             Untested&#xA; 1607  Ten-Tec                TT-516 Argonaut V       0.2             Stable&#xA; 1608  Ten-Tec                TT-565 Orion            0.5             Beta&#xA; 1609  Ten-Tec                TT-585 Paragon          0.3             Beta&#xA; 1611  Ten-Tec                TT-588 Omni VII         0.3             Alpha&#xA; 1612  Ten-Tec                RX-331                  0.1             Beta&#xA; 1613  Ten-Tec                TT-599 Eagle            0.4             Untested&#xA; 1701  Alinco                 DX-77                   0.7             Beta&#xA; 1801  Kachina                505DSP                  0.3             Alpha&#xA; 1901  Hamlib                 RPC rig                 0.3             Beta&#xA; 2201  TAPR                   DSP-10                  0.2             Alpha&#xA; 2301  Flex-radio             SDR-1000                0.2             Untested&#xA; 2303  DTTS Microwave Society DttSP IPC               0.2             Alpha&#xA; 2304  DTTS Microwave Society DttSP UDP               0.2             Alpha&#xA; 2401  RFT                    EKD-500                 0.4             Alpha&#xA; 2501  Elektor                Elektor 3/04            0.4             Stable&#xA; 2502  SAT-Schneider          DRT1                    0.2             Beta&#xA; 2503  Coding Technologies    Digital World Traveller 0.1             Untested&#xA; 2506  AmQRP                  DDS-60                  0.1             Alpha&#xA; 2507  Elektor                Elektor SDR-USB         0.3.1           Stable&#xA; 2508  mRS                    miniVNA                 0.1             Alpha&#xA; 2509  SoftRock               Si570 AVR-USB           0.2             Beta&#xA; 2511  KTH-SDR kit            Si570 PIC-USB           0.2             Beta&#xA; 2512  FiFi                   FiFi-SDR                0.5             Beta&#xA; 2513  AMSAT-UK               FUNcube Dongle          0.2             Beta&#xA; 2514  N2ADR                  HiQSDR                  0.2             Untested&#xA; 2601  Video4Linux            SW/FM radio             0.2.1           Beta&#xA; 2602  Video4Linux2           SW/FM radio             0.2.1           Alpha&#xA; 2701  Rohde&amp;amp;Schwarz          ESMC                    0.1             Alpha&#xA; 2702  Rohde&amp;amp;Schwarz          EB200                   0.1             Untested&#xA; 2801  Philips/Simoco         PRM8060                 0.1             Alpha&#xA; 2901  ADAT www.adat.ch       ADT-200A                1.36            Beta&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-04-19T12:24:13.277" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3818" PostTypeId="1" AcceptedAnswerId="3822" CreationDate="2015-04-19T19:49:20.057" Score="2" ViewCount="135" Body="&lt;p&gt;I'm reading Rec. ITU-R M.1172 and its precise definition of Q-code QSD is &quot;Are my signals mutilated?  Your signals are mutilated.&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I've seen, QSD is usually used to check if keying is defective, but this is the first time I've seen word &quot;mutilated&quot; used to describe defectiveness. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is: Is there any deeper meaning to mutilated other than defective here?&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2015-04-20T20:54:18.467" Title="What exactly is meant by &quot;mutilated&quot; in sense of QSD?" Tags="&lt;procedure&gt;&lt;q-codes&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3819" PostTypeId="1" CreationDate="2015-04-20T01:05:11.633" Score="6" ViewCount="5529" Body="&lt;p&gt;I have an account/profile on &lt;a href=&quot;http://aprs.fi&quot; rel=&quot;noreferrer&quot;&gt;aprs.fi&lt;/a&gt;, and now I am trying to use &lt;a href=&quot;http://aprsdroid.org/&quot; rel=&quot;noreferrer&quot;&gt;APRSdroid&lt;/a&gt;, which requested my credentials. Can I use the password from aprs.fi for it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am unable to register/submit my application through TQSL because my country is not on the list. I will investigate that in more detail, but at this point I just wonder if aprs.fi and APRS-IS are the same thing, because I read that the former pulls data from the latter.&lt;/p&gt;&#xA;" OwnerUserId="290" LastEditorUserId="76" LastEditDate="2015-04-20T01:16:07.417" LastActivityDate="2015-04-23T21:26:55.263" Title="Do aprs.fi and APRS-IS use the same credentials?" Tags="&lt;aprs&gt;&lt;software&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3821" PostTypeId="2" ParentId="3818" CreationDate="2015-04-20T15:44:35.993" Score="1" Body="&lt;p&gt;Back in the day, it wasn't uncommon for the key to directly switch the transmitter. Transistors didn't exist, and why would you use a relay when you already have a perfectly good switch under your fingers?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also back in the day, it wasn't uncommon to transmit with a whole ton of power. Building a bigger transmitter is technologically less challenging than building a more sensitive receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the full power of a very large transmitter going through your key -- you might imagine what happens. Between mechanical wear from sending all those telegrams, and arcing from using a key to switch many kilowatts of transmitter power (probably with no attempt to suppress the inductive arcing), the key contacts inevitably get mutilated. Imagine what a resistive, scratchy, intermittent switch contact does to your signal. &quot;Mutilated&quot; seems like as apt an adjective than any.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These days the switching is done with relays or transistors, so if you encounter &quot;QSD&quot;, the most likely explanation is that you have traveled back in time to the early 20th century.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-04-20T15:44:35.993" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3822" PostTypeId="2" ParentId="3818" CreationDate="2015-04-20T20:54:18.467" Score="1" Body="&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Q_code&quot; rel=&quot;nofollow&quot;&gt;Wikipedia&lt;/a&gt; explains this with a second option for QSD. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is my keying defective? [AP13] or Are my signals mutilated? [AP14]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So essentially it means, is your keying having some kind of an issue. This could be the result of a defective keyer. Essentially it means is there something going on that's cutting off the signal?&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-04-20T20:54:18.467" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3823" PostTypeId="2" ParentId="3819" CreationDate="2015-04-20T22:17:46.247" Score="7" Body="&lt;p&gt;&lt;strong&gt;The aprs.fi passwords can not be used when logging in to the APRS-IS servers. aprs.fi and APRS-IS are two different things.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The APRS-IS network consists of roughly a hundred servers distributed around the world, run by a large team of volunteer server operators. APRS-IS requires the use of the passcode number for logging in and sending data to the APRS-IS network. APRSdroid and most other APRS applications connect to the APRS-IS for sending and receiving APRS data. APRSdroid simply gives your passcode to an APRS-IS server when logging in. The passcode is a static number calculated from the callsign, and it cannot be changed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're using APRSdroid, you can &lt;a href=&quot;https://aprsdroid.org/passcode/&quot; rel=&quot;nofollow&quot;&gt;get a passcode from the APRSdroid team&lt;/a&gt;. It may take a short while for them to respond, as explained on the &lt;a href=&quot;https://github.com/ge0rg/aprsdroid/wiki/Frequently-Asked-Questions&quot; rel=&quot;nofollow&quot;&gt;FAQ&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some APRS-IS servers also accept TLS/SSL connections, as an experimental feature, in which case you can use an amateur radio certificate, together with your private RSA key, to log in. The TQSL app can be used to request such a certificate from the &lt;a href=&quot;http://www.arrl.org/logbook-of-the-world&quot; rel=&quot;nofollow&quot;&gt;ARRL Logbook Of The World&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;aprs.fi is a web site, which connects to the APRS-IS network just like APRSdroid itself does, collects APRS data, and stores it in a large database. aprs.fi has its own user database, with usernames and passwords. Each aprs.fi user may choose their own password, and it can also be changed afterwards.&lt;/p&gt;&#xA;" OwnerUserId="129" LastEditorUserId="129" LastEditDate="2015-04-20T22:46:09.967" LastActivityDate="2015-04-20T22:46:09.967" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3824" PostTypeId="1" CreationDate="2015-04-21T00:45:09.260" Score="5" ViewCount="613" Body="&lt;p&gt;So if I were to build a simple AM radio transmitter just using say, my Arduino, an oscillator, and wire for an antenna  (this is all crude I know, but work with me here) and use it to transmit data collected or what have you, how do I receive and decode this signal? I understand if I'm using say an MP3 player and the same idea I could just tune in to the frequency of the oscillator on a modern AM radio, but I want to send and receive data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I get the basics of the transmitter side, but I don't grasp the receiver side as well. I'd also prefer to only receive the signal I sent out, so only receive on the 1.2 MHz channel, or what have you, if that's possible. What I'm saying is I don't want a tunable receiver, rather just a receiver fit for the transmitter's exact frequency, in a perfect world.&lt;/p&gt;&#xA;" OwnerUserId="4560" LastEditorUserId="4408" LastEditDate="2015-04-24T05:14:48.897" LastActivityDate="2015-04-24T05:14:48.897" Title="Receive Data on Specific Frequency" Tags="&lt;diy&gt;&lt;digital-modes&gt;&lt;equipment-design&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3827" PostTypeId="2" ParentId="3824" CreationDate="2015-04-21T13:31:25.847" Score="4" Body="&lt;p&gt;Sending data is not so different from sending audio. You just have to come up with some kind of &lt;a href=&quot;http://en.wikipedia.org/wiki/Symbol_rate#Symbols&quot; rel=&quot;nofollow noreferrer&quot;&gt;symbol&lt;/a&gt; which represents one or more bits of data. For example, you could encode your data by speaking &quot;1&quot; or &quot;0&quot; into a microphone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://xkcd.com/257/&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LQ5wQ.png&quot; alt=&quot;xkcd: Code Talkers&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Someone at the other end listens to the audio and types in the numbers, and boom, you are sending data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you probably want something easier for electronics to encode and decode so you can replace the humans with electronics. So maybe you say a 1000 Hz tone is a &quot;1&quot;, and a 2000 Hz tone is a &quot;0&quot;. Now you have invented &lt;a href=&quot;http://en.wikipedia.org/wiki/Frequency-shift_keying#Audio_FSK&quot; rel=&quot;nofollow noreferrer&quot;&gt;AFSK&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or maybe you realize this is using a lot of transmitter power and radio bandwidth to send not very much information. You realize that you can detect the presence of an AM carrier, even if there's no tone but just silence. So you decide that to transmit a 1, you transmit a carrier, and to transmit a 0, you transmit nothing at all (the absence of a carrier). Now you have invented &lt;a href=&quot;http://en.wikipedia.org/wiki/On-off_keying&quot; rel=&quot;nofollow noreferrer&quot;&gt;on-off keying&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are just two of many possible &lt;a href=&quot;http://en.wikipedia.org/wiki/Modulation#Digital_modulation_methods&quot; rel=&quot;nofollow noreferrer&quot;&gt;digital modulation methods&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for the other part of your question about tuning, it doesn't really matter, nor does making a non-tunable receiver simplify things very much. You still need to design an oscillator or a filter (the two are very similar, electronically) at some particular frequency. If you don't need to tune, then the design of this component might be a little simpler, but all the other bits of the receiver are the same, and those other bits are most of the work.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-04-21T13:31:25.847" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3828" PostTypeId="2" ParentId="3706" CreationDate="2015-04-21T22:45:45.670" Score="1" Body="&lt;p&gt;I have done both and strongly prefer Amateur (Ham) Radio. More reliable, less noise, wider choice of equipment, antennas, transmission modes, etc... The licences no longer require code although I suggest you learn it and use it. It was the world's first use of digital communications. Great with local, state, national, and international clubs and organized groups. Participate in emergency communications to assist your local community. Storm tracker and watchers everywhere and once trained you can participate too! Do it now!Have fun!&lt;/p&gt;&#xA;" OwnerUserId="4574" LastActivityDate="2015-04-21T22:45:45.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3829" PostTypeId="1" AcceptedAnswerId="3830" CreationDate="2015-04-22T00:13:44.487" Score="4" ViewCount="6508" Body="&lt;p&gt;In &lt;a href=&quot;http://www.nsw.wicen.org.au/technical/projects/coaxial-folded-dipole-antenna&quot; rel=&quot;nofollow&quot;&gt;http://www.nsw.wicen.org.au/technical/projects/coaxial-folded-dipole-antenna&lt;/a&gt;, the guy is using a 50 ohm coax cable to build a folded dipole antenna and claims that this will enable use at 50 ohm (I assume the required matching impedance).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, from my understanding, the impedance of a folded dipole is based on the theoretical radiation resistance of a dipole (73 ohm) multiplied by 4 since folded. This is roughly 300 ohm and does not depends on the cable itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is that correct?&lt;/p&gt;&#xA;" OwnerUserId="4575" LastActivityDate="2019-01-29T05:47:53.920" Title="Coaxial Folded Dipole Antenna Matching Impedance" Tags="&lt;impedance&gt;&lt;folded-dipole&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3830" PostTypeId="2" ParentId="3829" CreationDate="2015-04-22T05:42:56.337" Score="5" Body="&lt;p&gt;The site above depicts a regular dipole, with a simple matching system.&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/PmxHS.png&quot; alt=&quot;Antenna in question&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, a bit about dipole impedance. The impedance of a dipole is 73 Ohms at resonance, but away from the resonant frequency the impedance is different. At frequencies lower than resonance, i.e. when the antenna is too short, it is capacitive, and its resistance is lower.&lt;br&gt;&#xA;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Smith_chart&quot; rel=&quot;nofollow noreferrer&quot;&gt;Smith Chart&lt;/a&gt; is the usual way of plotting this. 50 ohms is in the middle, short circuit on the left, open circuit is on the right.&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/YX7F1.png&quot; alt=&quot;Dipole on smith chart&quot;&gt;&lt;br&gt;&#xA;If it makes more sense, you can see them on a regular X-Y chart.&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/9cmDN.png&quot; alt=&quot;Dipole on x-y chart&quot;&gt;&lt;br&gt;&#xA;It's fairly simple to choose a point where the impedance is 50 -j something ohms. Then to match the antenna, only a series inductor is required. Please excuse my wobbly inductors.&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/ScE8f.png&quot; alt=&quot;Antenna with inductors&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now a bit about the stubs.&lt;br&gt;&#xA;The impedance of a short-circuited coaxial cable, like this:&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/PDEe7.png&quot; alt=&quot;Short circuit stub&quot;&gt;&lt;br&gt;&#xA;is given by the equation  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$Zin = j * Z_0 * tan(\beta x)$&lt;br&gt;&#xA;where  $\beta = 2 \pi / \lambda$&lt;br&gt;&#xA;and $Z_0$ is the impedance of the line, in this case $50 \Omega$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can also be done on the Smith chart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The two short-circuited stubs each need to contribute about 80 ohms of reactance, so they will be a bit over 1/8 of a wavelength long. They're further contracted by the velocity factor of the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The inductive reactance cancels the antenna capacitive reactance, resulting in a perfect 50 Ohm match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's how it works. Now for some comments about the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, about bandwidth: The capacitance of the antenna and inductance of the stubs both change over frequency. The antenna gets more capacitive at frequencies below resonance, requiring more inductance to match, but the inductance of the stub &lt;em&gt;drops&lt;/em&gt; at lower frequencies. This leads to a reduced bandwidth from this antenna, as compared to one matched with a transformer or some other way. Note the narrow VSWR curve on the left. In fact, if your radio could tolerate a VSWR of 2:1 or more, you'd be better off &lt;em&gt;not&lt;/em&gt; using any coax stub to match it.&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/FcDln.png&quot; alt=&quot;Bandwidth plot&quot;&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This makes me think this isn't such a great choice of antenna - the ham bands are already wide enough that a regular dipole isn't perfectly matched across the band, so this one will be even narrower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, about the balun: The site doesn't mention any Balun. This is a huge problem!! The feed cable of these antennas will carry current, perhaps half as much as the antenna itself, and so the VSWR will be affected by the length of the cable, the equipment connected to it, the ham moving around in the shack, everything. This is just bad practice. With any antenna design, the balun should be the first problem you solve, and then worry about the matching.&lt;br&gt;&#xA;&lt;a href=&quot;https://ham.stackexchange.com/a/555/2988&quot;&gt;See this very comprehensive answer&lt;/a&gt; for more about why you need a balun when connecting an dipole to coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, the impedance of a dipole like this will only be $50 \Omega$ in free space. An antenna is &lt;em&gt;never&lt;/em&gt; in free space, unless it's hanging off a cubesat. The supporting mast, or just the feedline, will affect its impedance.  A good design starts by considering those effects, mechanical support, grounding for static, safety and lighting, then the balun, and finally the matching.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-04-22T20:48:30.960" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="3831" PostTypeId="2" ParentId="3814" CreationDate="2015-04-22T22:07:47.140" Score="1" Body="&lt;p&gt;Something is inadequate in the way your diversity controller weighs &quot;noise&quot; if it changes in directions that increase subjective noise. You might construct a video signals comparator that applies a more appropriate test; that might be the strength of the sync pulse if you have peak-power sync pulses. Also it may reduce disruption to arrange gradual mix changes between video sources instead of cuts, though there would likely be some ghosting during the mixes, due to unequal propagation delays.&lt;/p&gt;&#xA;" OwnerUserId="4408" LastActivityDate="2015-04-22T22:07:47.140" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3832" PostTypeId="1" AcceptedAnswerId="3848" CreationDate="2015-04-23T09:14:29.823" Score="2" ViewCount="1966" Body="&lt;p&gt;How do you cancel a D-STAR user registration from one local repeater and re-register with a &lt;em&gt;different&lt;/em&gt; local repeater?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't seem to find any documentation on this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Background:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;D-STAR requires that users first register their callsign with a local repeater in order to route traffic across the D-STAR network. This is done via web server, run by the operator of said local repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you've registered with any one repeater, that registration becomes valid for every other repeater in the world. The US Trust database is used to share registrations amongst D-STAR repeaters, as well as keep track of the last known repeater for each callsign (so that direct traffic can be routed correctly).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given this, it's not surprising that there's not much demand for moving a registration; it would seem most folks just register once and leave things as-is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, my understanding is that it's still best to register with the repeater used most frequently, since that's the default used for routing messages to you if your radio hasn't been heard for awhile. (For example, if a friend is trying to contact you directly, and you haven't transmitted in a very long time, the message may get routed to your home repeater.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just can't find any way to actually do this.&lt;/p&gt;&#xA;" OwnerUserId="304" LastEditorUserId="304" LastEditDate="2015-04-23T09:21:05.857" LastActivityDate="2016-08-02T22:09:51.147" Title="How can I change my &quot;home&quot; registration server for D-STAR?" Tags="&lt;d-star&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3833" PostTypeId="2" ParentId="3770" CreationDate="2015-04-23T10:32:52.917" Score="6" Body="&lt;p&gt;DCS (aka DSQ/DPL) provides a &lt;em&gt;slightly&lt;/em&gt; larger range of codes to pick from compared to CTCSS. This means less chance that a nearby station will accidentally overlap with yours.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically, DCS gives you 83 codes, whereas CTCSS gives you somewhere between 26-50 squelch tones depending on the radio -- manufacturers have added extra codes over time. For compatibility, you're probably best sticking to the original 26. Here's a list:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.repeater-builder.com/tech-info/pl+dpl.html&quot; rel=&quot;nofollow&quot;&gt;http://www.repeater-builder.com/tech-info/pl+dpl.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Fun fact: Technically DCS has enough address space to support 512 codes, but the majority of those are disallowed in order to prevent false positives because of the way the DCS protocol works. So 83 is what we're stuck with.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, those 26-ish tones vs 83 codes are the biggest difference. Practically speaking though, there's a few other considerations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;CTCSS is compatible with older (cheaper) equipment. DCS didn't come around until much later, so it's not uncommon to find radios on eBay that only support CTCSS.&lt;/li&gt;&#xA;&lt;li&gt;CTCSS is a bit more forgiving to implement, since it requires less bandwidth. Again, mostly an issue with older radios.&lt;/li&gt;&#xA;&lt;li&gt;CTCSS is purely analog, so if you're building a radio from scratch it would probably be easier to implement. Decoding a DCS signal obviously requires a digital processor.&lt;/li&gt;&#xA;&lt;li&gt;DCS is less likely to trigger accidentally. Some CTCSS tones share harmonics with the local power grid, for example. Also, some old/cheap radios with noisy/slow circuits can accidentally trigger adjacent CTCSS tones, so some guides recommend only using ever-other tone.&lt;/li&gt;&#xA;&lt;li&gt;DCS is much less common on the amateur bands, which further reduces the chances of a collision if you use DCS.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;That said, the range is about the same for both. And neither will behave differently in the face of RF noise, since the squelch is either completely open or closed at any given time.&lt;/p&gt;&#xA;" OwnerUserId="304" LastEditorUserId="304" LastEditDate="2015-04-24T02:32:35.027" LastActivityDate="2015-04-24T02:32:35.027" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3834" PostTypeId="1" CreationDate="2015-04-23T16:27:26.960" Score="7" ViewCount="1575" Body="&lt;p&gt;Which equipment would be good for broadcasting a WiFi SSID the longest possible range? We're making an orienteering race in a forest and would place a sender somewhere high over the trees, transmitting a WiFi signal into the forest. The SSID should be picked up by the participants with a regular smartphone, but no actual communication is needed. The message will be written in the SSID itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone guide me to which antenna or equipment would be most applicable and give the longest range possible? We don't expect omni-directional functionality, but could perhaps purchase several of the same antennae to widen the transmit angle.&lt;/p&gt;&#xA;" OwnerUserId="4582" LastEditorUserId="13" LastEditDate="2015-05-03T01:04:20.410" LastActivityDate="2021-05-02T08:30:35.940" Title="Broadcasting a WiFi SSID long-distance" Tags="&lt;antenna&gt;&lt;equipment&gt;&lt;transmission&gt;&lt;wifi&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3835" PostTypeId="2" ParentId="3834" CreationDate="2015-04-23T17:56:42.173" Score="7" Body="&lt;p&gt;Assuming you are in the US (sorry if I'm wrong, but you didn't specify!), normal WiFi falls under Part 15 regulations which &lt;a href=&quot;https://ham.stackexchange.com/questions/1016/what-are-the-us-rules-about-unlicensed-low-power-transmissions&quot;&gt;limit the radiated field strength, not the transmit power&lt;/a&gt;. This means that, assuming the transmitter is not underpowered, you cannot legally increase the range using directional antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Supposing you did so anyway, hooking up multiple directional antennas to the same transmitter will split the input power among those antennas, so you're back to where you started.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are your available legal options:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Make sure the WiFi AP you use actually transmits the maximum legal power and has an antenna with a suitable pattern. (In particular, a so-called “high-gain omnidirectional” antenna will radiate mostly in the horizontal plane and less in the &quot;up/down&quot; directions, which might be good for the range or bad if your terrain is not flat or the antenna isn't oriented properly.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Use multiple APs arranged in a large circle. This only extends your range by the radius of the circle. (Multiple APs in the same location would increase the total power radiated but not in a way useful for communication since they're not coordinated.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Obtain an amateur radio license, which will allow you to transmit more power. The 2.4 GHz ISM band used by WiFi overlaps with an amateur radio band, so you can use stock WiFi equipment together with directional antennas and/or power amplifiers, provided that you:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;include your assigned callsign in the SSID&lt;/li&gt;&#xA;&lt;li&gt;configure the device to use a channel which is in the amateur band, rather than autoselecting&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I haven't done this myself, so I can't advise on the exact details of doing this, but it's fairly popular so you should be able to find information easily.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This &lt;strong&gt;does not&lt;/strong&gt; require the other participants to obtain a license.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-04-23T17:56:42.173" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3836" PostTypeId="2" ParentId="3819" CreationDate="2015-04-23T21:26:55.263" Score="4" Body="&lt;p&gt;To get a passcode for the APRS-IS on APRSdroid you do not necessarily have to contact the APRSdroid Developer team. You can use any one of several APRS-IS passcode generators available on the web as web based or Windows based applications .  Just enter your callsign, press enter and a APRSIS passcode will appear with which you can login to the APRS-IS in APRSdroid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a list of just a few web based APRSIS passcode generators:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://apps.magicbug.co.uk/passcode/&quot; rel=&quot;nofollow&quot;&gt;APRS Passcode Generator - Magicbug&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://callpass.kf5jwc.us&quot; rel=&quot;nofollow&quot;&gt;KF5JWC.us-APRS passcode generator&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.george-smart.co.uk/wiki/APRS_Callpass&quot; rel=&quot;nofollow&quot;&gt;APRS Callpass - George Smart's Wiki&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Here is a list of a few downloadable Windows based applications:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://blog.eagleflint.com/software-downloads/aprs-is-passcode-generator/&quot; rel=&quot;nofollow&quot;&gt;APRS-IS Passcode Generator - EagleFlint | Soar&lt;/a&gt; (Needs to be installed to run.)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.n8zak.com/files/index.html&quot; rel=&quot;nofollow&quot;&gt;N8ZAK's APRS Passcode Generator&lt;/a&gt; (Portable Windows command line application)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-04-23T21:26:55.263" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3838" PostTypeId="2" ParentId="3768" CreationDate="2015-04-26T17:01:33.710" Score="1" Body="&lt;p&gt;For very short distance communication in salty water consider conduction. An audio frequency carrier can be transmitted as a current from surface level to sea bed. The propagation is omnidirectional and loss is high, but test and development would be quick.&lt;/p&gt;&#xA;" OwnerUserId="4408" LastActivityDate="2015-04-26T17:01:33.710" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3839" PostTypeId="2" ParentId="3768" CreationDate="2015-04-27T14:19:15.570" Score="1" Body="&lt;p&gt;Using very low frequency (electro) magnetic fields make it difficult to get a data rate of 10kbps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what about using the 500nm band (blue light)? &#xA;Attenuation of visible light (in clean water) is lowest for blue colored light.&lt;br&gt;&#xA;It should be low enough to do data communication at distances of 2m even if the water is not very clean.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As transmitters you can use blue LEDs.&lt;/p&gt;&#xA;" OwnerUserId="1642" LastActivityDate="2015-04-27T14:19:15.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3840" PostTypeId="1" CreationDate="2015-04-27T18:08:31.890" Score="2" ViewCount="277" Body="&lt;p&gt;I'm designing a drone(UAV) as a hobbyist, and radio communications is not my strong point. I will be transmitting waypoints from a portable control station and receiving video(a low frame rate is ok). I'm trying to decide what frequency I should use. I want to get a range of about 1 - 2 miles with not a lot of power. Are there power to range benefits from using different frequencies? At the moment I'm thinking about using 2.4Ghz is this suitable for my needs? Thanks!&lt;/p&gt;&#xA;" OwnerUserId="4594" LastActivityDate="2018-10-15T13:04:59.137" Title="Is 2.4Ghz good for an UAV?" Tags="&lt;frequency&gt;" AnswerCount="3" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="3841" PostTypeId="2" ParentId="3840" CreationDate="2015-04-28T14:14:17.033" Score="2" Body="&lt;p&gt;The frequency you choose is largely irrelevant with respect to range, at least within the range of frequencies you are likely to choose for this kind of application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Size limitations (and probably licensing requirements) will probably dictate VHF or UHF, and so you will be using &lt;a href=&quot;http://en.wikipedia.org/wiki/Line-of-sight_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;line-of-sight propagation&lt;/a&gt;. Regardless what frequency you select, electromagnetic radiation is subject to the same &lt;a href=&quot;http://en.wikipedia.org/wiki/Inverse-square_law&quot; rel=&quot;nofollow noreferrer&quot;&gt;inverse square law&lt;/a&gt;. That is, in the absence of obstructions, 2.4 GHz radiation &quot;travels just as far&quot; as that of any other frequency you might reasonably choose for radio communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;What is a link budget, and how do I make one?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/3692/218&quot;&gt;Is free space path loss dependent on frequency?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;What does the Friis transmission equation represent and how is it derived?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-04-28T14:49:37.457" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="3843" PostTypeId="2" ParentId="1313" CreationDate="2015-04-29T05:38:11.403" Score="-1" Body="&lt;p&gt;I have used an app called &lt;a href=&quot;https://play.google.com/store/apps/details?id=org.jfedor.morsecode&quot; rel=&quot;nofollow&quot;&gt;Morse Code Reader&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It works well for me!&lt;/p&gt;&#xA;" OwnerUserId="4600" LastEditorUserId="13" LastEditDate="2015-08-29T00:01:04.300" LastActivityDate="2015-08-29T00:01:04.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3845" PostTypeId="1" CreationDate="2015-04-29T07:17:16.820" Score="2" ViewCount="354" Body="&lt;p&gt;I have recently heard about recording video games' binary codes from radio programmes  which was quite popular several decades ago. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The computer name was ZX Spectrum. The general idea behind the process was that you had to turn on recording when the radio program started. The whole radio program sounded like a high-pithced noise to human ear but overall it could be decoded to a binary file and run by ZX Spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to learn about the technology which made this cool process work. As @hotpaw2 mentioned in the comment, it might be quite interesting to learn something about &lt;b&gt;the modulation scheme&lt;/b&gt; and &lt;b&gt;protocols used to transfer the programs over RF&lt;/b&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lately, I learnt some basics about the signal modulation schemes, so I think I am capable of understanding general ideads behind this technology.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are these modulation schemes and protocoles used in this particular technology? Why it usually took over 15-20 minutes to &lt;i&gt;transmit&lt;/i&gt; the whole program over RF.&lt;/p&gt;&#xA;" OwnerUserId="4602" LastEditorUserId="4602" LastEditDate="2015-04-30T10:57:32.680" LastActivityDate="2015-04-30T10:57:32.680" Title="How did recording ZX Spectrum games from radio work?" Tags="&lt;modes&gt;&lt;transmission&gt;" AnswerCount="0" CommentCount="8" ClosedDate="2015-04-29T09:30:23.987" ContentLicense="CC BY-SA 3.0" />
  <row Id="3847" PostTypeId="2" ParentId="135" CreationDate="2015-04-30T21:44:38.433" Score="7" Body="&lt;p&gt;It was all I could afford when I was a kid. AM and SSB gear was expensive and still is! Stuck with it because: Signals are stronger, More of a challenge, and a CQ gets answered faster. Great people on CW.  &lt;/p&gt;&#xA;" OwnerUserId="4612" LastActivityDate="2015-04-30T21:44:38.433" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3848" PostTypeId="2" ParentId="3832" CreationDate="2015-05-01T06:21:28.663" Score="2" Body="&lt;p&gt;It has been about a year since I have administered a US Trust System gateway, but I believe you would need to contact the administrator of the old gateway; they would delete you from the gateway, and then you can register with the newer gateway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although it is a guideline, I wouldn't think it is a necessity to move your registration.  Since we do not run the US Trust system on our gateway locally, I'm registered with a US Trust gateway a few hours away.&lt;/p&gt;&#xA;" OwnerUserId="4613" LastEditorUserId="76" LastEditDate="2015-05-01T17:38:08.890" LastActivityDate="2015-05-01T17:38:08.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3849" PostTypeId="2" ParentId="1270" CreationDate="2015-05-01T18:52:33.583" Score="2" Body="&lt;p&gt;One time is an error, multiple times seems on purpose. Report it to the FCC in case they violate any laws or frequency uses. &lt;/p&gt;&#xA;" OwnerUserId="4615" LastActivityDate="2015-05-01T18:52:33.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3850" PostTypeId="2" ParentId="3792" CreationDate="2015-05-01T18:57:54.650" Score="0" Body="&lt;p&gt;I have a G5RV in my attic. That is also a possibility. It works fine as long as it does not contact any duct work or other metal.&#xA;In your case, the amount of metal is minimal and should not present a big problem. If the house was also aluminum it would be a bigger issue.&#xA;Happy operating. 73's Marty, KB4MG&lt;/p&gt;&#xA;" OwnerUserId="4615" LastActivityDate="2015-05-01T18:57:54.650" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3851" PostTypeId="2" ParentId="1270" CreationDate="2015-05-02T06:57:18.970" Score="-1" Body="&lt;p&gt;Wait until you actually witness it yourself. It will look bad on you if you falsely report. I would just listen and if and when you hear it, report it to the FCC.&lt;/p&gt;&#xA;" OwnerUserId="4616" LastEditorUserId="4616" LastEditDate="2015-05-05T04:48:54.360" LastActivityDate="2015-05-05T04:48:54.360" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3852" PostTypeId="1" CreationDate="2015-05-02T07:18:13.270" Score="2" ViewCount="1154" Body="&lt;p&gt;I have a little MFJ QRP CW 20m rig that I plan to turn into a portable kit for SOTA peaks. I have everything figured out except for the antenna. I am wanting to make a dipole. However, I was wondering, is a Balun really necessary for this? This is all I plan to use this antenna for. (This one band, with QRP)&lt;/p&gt;&#xA;" OwnerUserId="4616" LastActivityDate="2015-05-05T14:13:28.810" Title="Do I need a Balun for a single band QRP antenna?" Tags="&lt;hf&gt;&lt;cw&gt;&lt;dipole&gt;&lt;balun&gt;&lt;20m-band&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3853" PostTypeId="2" ParentId="3852" CreationDate="2015-05-02T15:44:03.750" Score="7" Body="&lt;p&gt;You don't &lt;em&gt;need&lt;/em&gt; a balun, in that it will work and it won't hurt you. But your antenna will not work as well as it ought to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you are transmitting, the effect of a balun used to connect a coax (unbalanced) feed line to a dipole (balanced) antenna is to &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole/555#555&quot;&gt;prevent the RF from the transmitter from returning down the outside of the feed line&lt;/a&gt; and go entirely into the antenna instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't do this, then your feed line is effectively part of your antenna. This changes the pattern and means it has a part close to ground — so you've put up an antenna that is not the shape you intended, isn't resonant where you intended, is more lossy, and is partly made up of the transceiver, your body, and any other connected equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two things you &lt;em&gt;don't&lt;/em&gt; need to worry about as much because you're QRP portable:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;You are not transmitting enough power to be dangerous. If you were, then the issue is that the RF returning down the feed line would make the case of your transceiver (and anything else sharing the same ground) “hot”, possibly causing RF burns when you touch it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, you're not transmitting very much power, so you probably want to make sure every watt is getting out as well as it ought — which means you don't want it going places that aren't efficient antennas, which means using a balun.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you were not on battery power, then noise coming from the power line could come in on the ground, up the outside of the coax, down the inside, and into your receiver. Even so, any noise sources among your equipment will interfere more than they would if you had a balun, but I'd guess they're unlikely to be strong enough to make things worse.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;It is also common to include impedance matching in the construction of a balun. This conceptually a completely separate function, but if you're building a balun (other than the simple choke type) you might as well include it; typical amateur equipment is designed for a 50 Ω impedance whereas resonant dipoles have impedance around 70-73 Ω depending on surroundings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance matching prevents the transmitter from being exposed to high SWR, reduces losses in transmitting (assuming that the balun is located at the antenna end of your feed line, not the transceiver end), and acts to some degree as a band-pass filter for received signals. Again, none of this is necessary, but it all helps.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-05-05T14:13:28.810" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3854" PostTypeId="1" AcceptedAnswerId="3856" CreationDate="2015-05-02T19:26:41.800" Score="2" ViewCount="3293" Body="&lt;p&gt;I have an older FM Radio with a telescoping antenna.  Is it possible to convert that to work with an FM dipole antenna to get better reception? Such as &lt;a href=&quot;http://amzn.com/B000EIOQBM&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;this one&quot;&gt;this one&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Preferably without any soldering. (I'm not able to do that yet)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a picture of the inside of the radio: &#xA;&lt;img src=&quot;https://i.stack.imgur.com/sPdYr.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="4619" LastEditorUserId="4619" LastEditDate="2015-05-05T19:18:31.407" LastActivityDate="2015-05-05T19:20:18.463" Title="Can I convert a telescoping antenna radio to work with an FM Dipole?" Tags="&lt;antenna&gt;&lt;fm&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3855" PostTypeId="1" AcceptedAnswerId="4946" CreationDate="2015-05-02T21:39:37.797" Score="3" ViewCount="597" Body="&lt;p&gt;I have designed a dual band WIFI antenna (2.4-2.5GHz and 5.1-5.7GHz). In 2.4GHz it's completely omnidirectional but with negative gain and in 5.6GHz it's somehow  directional but with very good positive gain. why is this?? Where have I been wrong? &lt;img src=&quot;https://i.stack.imgur.com/6pSs4.jpg&quot; alt=&quot;the dual band S11&quot;&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/Bjihh.jpg&quot; alt=&quot;3D Polar gain at 2.4GHz&quot;&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/Q2sU0.jpg&quot; alt=&quot;3D Polar gain at 5.6GHz&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="4621" LastEditorUserId="4621" LastEditDate="2015-05-03T08:14:13.827" LastActivityDate="2015-06-02T20:32:20.643" Title="WIFI Antenna Design" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wifi&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3856" PostTypeId="2" ParentId="3854" CreationDate="2015-05-03T02:27:07.183" Score="1" Body="&lt;p&gt;Connect one conductor of the dipole's feed line in place of the antenna on the radio. (It may be removable by a screw. If not, shorten the telescoping antenna as much as it goes and gently clamp the wire onto it instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other conductor should go to the circuit ground of the radio. Try the first one of these you can find:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A provided antenna ground terminal (GND, ⏚) is best.&lt;/li&gt;&#xA;&lt;li&gt;If the radio's case is metal attach it to that.&lt;/li&gt;&#xA;&lt;li&gt;Otherwise try other case screws. (&lt;strong&gt;Avoid any other electrical connectors&lt;/strong&gt; like the radio's audio output; this could cause damage, especially as many “FM dipole antennas”, including the one you showed, are &lt;em&gt;folded dipoles&lt;/em&gt; where there is DC continuity through the antenna.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Listen to a weak station while you experiment to notice whether there are any results.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-05-05T19:20:18.463" LastActivityDate="2015-05-05T19:20:18.463" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3857" PostTypeId="1" AcceptedAnswerId="3863" CreationDate="2015-05-03T16:24:30.607" Score="1" ViewCount="492" Body="&lt;p&gt;I am going to build a QRP morse code transceiver. Due to money, I am only going to build one, for one band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I plan on taking the QRP transceiver backpacking where I will wire the antenna in a tree. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will be operating from South America, and I am starting the process of building the QRP rig. I am thinking about building for either 40 meters or 20 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;Given the constraints&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•Two Watts&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•Small antenna  (wire strung in a tree)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•CW operation&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•Probably more in the early morning and late afternoon/evening because we will be hiking during the day&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•Very portable for lightweight hiking &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Which band should I go with:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•40 meters&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•20 meters&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or another band&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, I am only choosing one band &lt;em&gt;for now&lt;/em&gt;, I may expand later, but I only have the money for one band QRP at this point in time.&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-05-04T13:11:27.933" Title="Which band for portable, backpacking operation" Tags="&lt;qrp&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="3858" PostTypeId="5" CreationDate="2015-05-03T16:24:51.963" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2015-05-03T16:24:51.963" LastActivityDate="2015-05-03T16:24:51.963" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3859" PostTypeId="4" CreationDate="2015-05-03T16:24:51.963" Score="0" Body="Low power operation, Typically 5 watts or less" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2015-05-04T15:24:16.193" LastActivityDate="2015-05-04T15:24:16.193" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3860" PostTypeId="1" CreationDate="2015-05-03T16:37:10.900" Score="9" ViewCount="354" Body="&lt;p&gt;6 meters seems to be a place where when the conditions are right, repeaters may interfere with each other from far distances, but when the conditions are normal, repeaters are similar to 2 meters. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the advantage of installing repeaters on 6 meters? &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-05-03T23:52:29.623" Title="Advantage of 6 meter repeaters" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3861" PostTypeId="2" ParentId="3860" CreationDate="2015-05-03T23:52:29.623" Score="7" Body="&lt;p&gt;6m works better than 2m when dealing with terrain. For direct line of site, any of the VHF or UHF repeaters will work essentially equally well. Their significant difference comes when one is dealing with obstacles. The larger the wavelength, the more ground effect there will be, which essentially allows the radio wave to hug the ground and thus be propagated further. 6m repeaters are thus more popular in mountainous areas. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Incidentally, UHF does a better job of going through a building. The reason is, the signal can find smaller holes than the VHF can (To oversimplify it). There are a lot of little quirks in the different bands, which is why there are so many bands available to Amateurs, to learn all of these quirks and maximize communication possibilities.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-05-03T23:52:29.623" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3863" PostTypeId="2" ParentId="3857" CreationDate="2015-05-04T13:11:27.933" Score="6" Body="&lt;p&gt;20 meters. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This assumes you're wanting to work back to the States or into Europe.  If your primary interest is local in South America, then I'd go with 40 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An advantage is the ease of dealing with a smaller antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;While not a single-band radio, I'd seriously consider one of the KD1JV rigs.  Occasionally available as kits, but now commercially available built from LNR Precision.  I have a two-band MTR, as well as a six-band ATS3b.  Very compact and very nice performers. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;GL!&lt;/p&gt;&#xA;" OwnerUserId="4628" LastActivityDate="2015-05-04T13:11:27.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3864" PostTypeId="2" ParentId="3855" CreationDate="2015-05-04T16:19:18.350" Score="1" Body="&lt;p&gt;Decibels measure &lt;em&gt;ratios&lt;/em&gt;. It looks like the horizontal line in your graph is around -10 dB. That translates to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ -10\:\mathrm{dB} = 10^{-10/10} = {1 \over 10} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In English, &quot;-10 decibels&quot; means &quot;one tenth&quot;. So, one tenth of what? There is nothing in the graphs you have provided to say.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So when your graphs indicate negative gain, this means &quot;radiation in that direction is some fraction of radiation in that direction compared to some reference which is not specified.&quot; Which may or may not mean you've done anything wrong, depending on what that reference is.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-05-04T16:19:18.350" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="3865" PostTypeId="2" ParentId="3855" CreationDate="2015-05-04T19:28:31.497" Score="1" Body="&lt;p&gt;The gain seems to be low in one of the plots, it looks like the peak is about -5 dB (dBi I suppose). The matching of your antenna looks reasonable, so your antenna is absorbing power within the two bands. The pattern also looks like that of a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So where is the power going? Do you have any lossy elements in the simulation? Any printed circuit boards, real metal conductors, lossy dielectrics, or is it all perfect conductors and insulators?  If there's anything with loss, that is where the power is going. Ff you can get HFSS to plot the structure losses or dissipation, that might tell you where it is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think -5 dBi is very surprising at 5 GHz if you've used real materials in the simulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps post a picture of the simulation model and we can see where the power might be going.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-05-04T19:28:31.497" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="3866" PostTypeId="2" ParentId="425" CreationDate="2015-05-05T01:35:00.147" Score="-3" Body="&lt;p&gt;I live in the same type of area. At the bottom of a Canon and I think the iron ore is above me in the hills or I am in the middle of it, but I have terrible propagation on 11M and it even spreads out to 15M and 10M. But 11M is far the worse. At times, I can go days with nothing but static, and don't be telling me about the flip flop of the seasons. I am retired and my radio is on from 5 am to 9pm 365 days a year. I know all about the changing times. This is something else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the next thing to look at is one of two things, the geomagnetic storm influence on the iron, and now I am wondering about the churning magma under the Yellowstone Super Volcano. I hear it is becoming more active and closer to the surface this year, and so is my propagation getting worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just my 2 cents worth. But if you do not live in one of these areas, please stop muddying the waters with your guesses. ;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have since found some evidence of the Iron Ore culprit here in my little canyon. I have made a short video of what mine looks like and these rocks are laying around here on the ground anywhere there is alluvial gravel on the surface. I suspect they came out of layers above my location. Hopefully, this will add some insight to the problem, and in passing, my propagation has never gotten any better, since last posting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=lge6WRF8BXM&quot; rel=&quot;nofollow&quot;&gt;https://www.youtube.com/watch?v=lge6WRF8BXM&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4631" LastEditorUserId="4631" LastEditDate="2016-01-24T19:52:58.293" LastActivityDate="2016-01-24T19:52:58.293" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="3867" PostTypeId="2" ParentId="3792" CreationDate="2015-05-05T20:14:16.587" Score="2" Body="&lt;p&gt;I make contacts all over the US with a home brew multi-dipole very similar to the G5RV using 200 mW out to about 8 watts.  One day I went out and it had fallen down onto the roof, was dangling partly onto the gutter, etc. and I was still &quot;getting out&quot;.  I saw some changes in the SWR (but was still able to tune it), which is why I went outside to look at it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Go for it!  One fun experiment to try is run it awhile in one configuration, then go change something - bend one leg around, change the Vee angle - and try it some more.  Great antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take notes and pay attention to the difference when it has rained, etc.  You'll be surprised how much antennas are changing all the time anyway.  Good luck!&lt;/p&gt;&#xA;" OwnerUserId="4285" LastEditorUserId="218" LastEditDate="2015-05-06T17:54:28.413" LastActivityDate="2015-05-06T17:54:28.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4867" PostTypeId="1" CreationDate="2015-05-06T17:14:32.860" Score="11" ViewCount="2172" Body="&lt;p&gt;I am planning a trip with a large group in 6 weeks. We will be spread out in small groups on a trail in a mostly desert plateau landscape perhaps 5 miles apart, but mostly in a straight line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm new to amateur radio, but I have been studying and I intend to take the test for my technician license next week. I have just ordered a Baofeng uv 5r and a Nagoya NA-771. My initial plan was to just change out the antenna on the radio and clip the radio to the side of the backpack, but I've been thinking about it and wondering if there would be sufficient advantage to make it worth mounting the antenna to the backpack frame, or even possibly mounting two with about 16 inches of separation to make my transmissions slightly more directional in front of and behind me. There is a repeater in the 70cm band 10-20 miles from where we will be hiking, but we will only use that if needed to call for emergency help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like with 5 watts, and the distances involved, I probably don't need to worry, but there will be no cell coverage, so I want to make sure I'm prepared. Would it be worth mounting on the backpack? Should I just add a rat tail on the radio and call it good?&lt;/p&gt;&#xA;" OwnerUserId="2957" LastEditorUserId="76" LastEditDate="2015-12-15T22:13:03.260" LastActivityDate="2018-09-29T15:53:00.613" Title="While backpacking, is it worth mounting the antenna to the backpack frame (above my head)?" Tags="&lt;antenna&gt;&lt;united-states&gt;&lt;2m-band&gt;&lt;70cm-band&gt;&lt;antenna-system&gt;" AnswerCount="6" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4868" PostTypeId="2" ParentId="4867" CreationDate="2015-05-06T17:52:48.490" Score="2" Body="&lt;p&gt;&lt;em&gt;Will getting the antenna higher and in the clear improve things?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Probably.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;How much?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something between &quot;some&quot; and &quot;not at all&quot;. It depends on what's in your pack and the very specific geometry involved. The easiest way to quantify the change is to try it and see.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Is it worth doing, given the necessary work, and the inconvenience of having an antenna sticking above your head which will smack into trees and poke people in the eye when you take off the pack?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Only you can decide.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-05-06T17:52:48.490" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4870" PostTypeId="2" ParentId="3834" CreationDate="2015-05-07T17:42:26.493" Score="2" Body="&lt;p&gt;So...A couple of things here:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;According to &lt;a href=&quot;http://www.afar.net/tutorials/fcc-rules&quot; rel=&quot;nofollow&quot;&gt;FCC regulations&lt;/a&gt;, a fixed point-to-point link can actually broadcast well above the 30 dbm rule. In fact, you can go up to 52 dbm EIRP.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In order to get that high, you will need to regulate the output power of your router. You can do this digitally in the router settings or by putting in-line attenuation at the output of the transmitter. You can buy them from Mini-Circuits online. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A high power antenna increases the range by concentrating the power into a narrow beam which covers a smaller area, which is measured in dbi (decibels-isotropic). You can buy them &lt;a href=&quot;http://www.l-com.com/wireless-antenna-24-ghz-wifi-antennas?cmp=LM2&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The only tricky part is that you may have to buy antenna adapters in order to connect the output of your router to the antenna itself. The output of the router is typically reverse polarity, so you will have to check that. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you set up a point-to-point link, your devices can receive the SSID without connecting, so you can still tx at a higher power level.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Hope this helps!&lt;/p&gt;&#xA;" OwnerUserId="4640" LastActivityDate="2015-05-07T17:42:26.493" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4871" PostTypeId="1" CreationDate="2015-05-08T08:17:01.503" Score="-1" ViewCount="422" Body="&lt;p&gt;I want to design a steerable beam array antenna which has 15 dBi directivity using uniform fed infinitesimal dipole elements at 1GHz frequency occupying physical aperture.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Considering that phases of elements have beam shift of 20 degrees, which type of array antenna I should chose? End fire or broad side? Any other type?&lt;/p&gt;&#xA;" OwnerUserId="4621" LastEditorUserId="7798" LastEditDate="2016-06-25T15:28:52.140" LastActivityDate="2017-02-18T07:58:43.833" Title="Choosing a type of array antenna" Tags="&lt;antenna-construction&gt;&lt;phased-array&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="4872" PostTypeId="1" CreationDate="2015-05-09T06:49:44.593" Score="0" ViewCount="1224" Body="&lt;p&gt;Is it possible to buy a cheap transceiver chip with similar functionality to the RDA1846?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm looking for something else, because I'm wary of buying a probably counterfeit chip on AliExpress, and I got a message after I ordered RDA1846 on that site from another seller: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Dear friend, you take a picture of RDA1846S this product has been discontinued. Trouble you cancel the order&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="4648" LastEditorUserId="76" LastEditDate="2015-05-15T15:22:21.300" LastActivityDate="2015-05-15T15:22:21.300" Title="Chip with price and functionality to the RDA1846?" Tags="&lt;baofeng&gt;&lt;electronics&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4873" PostTypeId="1" AcceptedAnswerId="4875" CreationDate="2015-05-09T07:57:22.490" Score="-1" ViewCount="1371" Body="&lt;p&gt;i have a uhf radio I want to wire a cigarette lighter plug to so it can be removed from the car and be put into another car is the possible or not plz help me with this matter&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is just a standed uniden uhf radio 12v dc and it draws 2 to 3 amps I think the only accessory on the lighter socket is a gps&lt;/p&gt;&#xA;" OwnerUserId="4649" LastEditorUserId="-1" LastEditDate="2015-05-10T16:09:20.060" LastActivityDate="2015-07-25T22:13:01.733" Title="I want to wire a cigarette lighter plug to the back of my uhf radio to make it portable can I do this" Tags="&lt;uhf&gt;&lt;installation&gt;&lt;wiring&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4874" PostTypeId="2" ParentId="1270" CreationDate="2015-05-10T15:25:51.033" Score="2" Body="&lt;p&gt;I agree, don't report till you witness it. Keep your logs but don't claim the contacts in case the FCC contacts you. It works as testimony that you didn't make the contacts. There are several possibilities here. The person has a call close to yours and was not pronouncing it well. Or, the receiving stations didn't copy well and went to web for correction and got yours. or, they were trolls, heard you on the air logged you and then asked for add to your log, hoping you wouldn't catch it. I check my log... if they are not there, I don't add them and they get nothing,if I find an error I fix it. If it's a troll they get nothing. If a bootlegger, you've contemporaneous evidence that it's not you.&lt;/p&gt;&#xA;" OwnerUserId="4653" LastEditorUserId="4653" LastEditDate="2015-05-11T00:29:37.110" LastActivityDate="2015-05-11T00:29:37.110" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4875" PostTypeId="2" ParentId="4873" CreationDate="2015-05-11T03:10:36.173" Score="1" Body="&lt;p&gt;Yes this is possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A standard car cigarette lighter socket is rated at up to 10A and 100W, so you have plenty of leeway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another question when moving from one car to another, is what to do about an antenna.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-05-11T03:10:36.173" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="4876" PostTypeId="2" ParentId="4872" CreationDate="2015-05-11T03:43:06.617" Score="1" Body="&lt;p&gt;There is a REALLY cheap chip that has all the functionality of the rda1846, and is in fact is 100% compatible, with the same pinout and power requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is ... the rda1846: &lt;a href=&quot;http://www.aliexpress.com/store/product/single-chip-transceiver-for-Walkie-Talkie-RDA1846-new-and-original/715898_694516758.html&quot; rel=&quot;nofollow&quot;&gt;http://www.aliexpress.com/store/product/single-chip-transceiver-for-Walkie-Talkie-RDA1846-new-and-original/715898_694516758.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You say you want a 'cheap' chip, well this one is pretty cheap!&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-05-11T03:43:06.617" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="4877" PostTypeId="1" AcceptedAnswerId="4880" CreationDate="2015-05-12T07:25:16.767" Score="1" ViewCount="399" Body="&lt;p&gt;How does SDR resolution translate to audio resolution when using an FM demodulation algorithm?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example: using a 8-bit/2.048 Mhz IQ stream, what is the maximum audio sample rate and bit depth that can be generated from a +/-75kHz mono WFM signal with 20kHz audio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are the steps of a basic FM conversion algorithm. My question is, what effect does each step have on the bit depth of the result of the step:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Step 1 - Decimate down to the relevant bandwidth (150khz). Doing so reduces the sample rate but increases the bit depth.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Step 2 - Take the arctan of the resulting IQ samples. The combination of the I and Q parts further increases the bit depth of the current data.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Step 3 - Use a differentiator to get the final audio result. I am not sure how this affects the resolution, but since no data is combined, I suspect there would be no change.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Step 4 - Further decimate the audio to desired sample rate (48khz presumably). Would result in further increase in bit depth, but not by much.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In each step, combinations of data result in more data possibilities, eg:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Average 2 and 3 to get 2.5&lt;/li&gt;&#xA;&lt;li&gt;Arctan(I/Q) provides N^2 possibilities, though not all are unique&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Wikipedia has an explanation of the effect of oversampling on bit depth. But I am not sure about the arctan and differentiator processes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you for your expertise&lt;/p&gt;&#xA;" OwnerUserId="4659" LastEditorUserId="4659" LastEditDate="2015-05-13T16:50:52.313" LastActivityDate="2015-05-13T17:53:49.247" Title="WFM SDR and Audio resolution" Tags="&lt;modes&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4878" PostTypeId="1" CreationDate="2015-05-12T11:48:47.373" Score="2" ViewCount="269" Body="&lt;p&gt;When amateur radio operators associated with the national weather service &quot;close the net&quot; on a repeater and request only severe weather reports on that frequency, what FCC ruling is in effect, given that this is an amateur radio band?&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2015-05-12T14:21:11.337" Title="What FCC rule allows Skywarn and other spotters to restrict repeater use?" Tags="&lt;united-states&gt;&lt;repeater&gt;&lt;emergency&gt;&lt;fcc&gt;&lt;weather&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4879" PostTypeId="2" ParentId="4878" CreationDate="2015-05-12T14:21:11.337" Score="5" Body="&lt;p&gt;There is &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1205&quot; rel=&quot;noreferrer&quot;&gt;§97.205&lt;/a&gt;, which regulates repeater stations:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(e) Ancillary functions of a repeater that are available to users on the input channel are not considered remotely controlled functions of the station. Limiting the use of a repeater to only certain user stations is permissible.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So if the net is on a repeater, the repeater's control operator can decide who can and can not use the repeater, for pretty much any reason. For example, there are some repeaters that are made available only to paying members.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1403&quot; rel=&quot;noreferrer&quot;&gt;§97.403&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;No provision of these rules prevents the use by an amateur station of any means of radiocommunication at its disposal to provide essential communication needs in connection with the immediate safety of human life and immediate protection of property when normal communication systems are not available.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Interpreted somewhat broadly, this can be understood to mean that if the safety of human life is threatened, you can do just about anything you want. Asking people &lt;em&gt;not&lt;/em&gt; participating in Skywarn activities to move to a different frequency certainly seems reasonable, and even if there isn't a law requiring it, it's hard to imagine why someone would not comply with such a request.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, Skywarn nets are &lt;a href=&quot;http://en.wikipedia.org/wiki/Amateur_radio_net#Formal_operation&quot; rel=&quot;noreferrer&quot;&gt;directed nets&lt;/a&gt;, which have some structure which may not be regulated, but is at least convention. In particular, there is a net control station who coordinates who can talk and in what turn. Skynet isn't the only such net: there are other directed nets with the purpose of passing third-party traffic and other such activities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Willfully disregarding the net control station would not be good amateur practice, and so would violate &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1101&quot; rel=&quot;noreferrer&quot;&gt;§97.101&lt;/a&gt;(a):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(a) In all respects not specifically covered by FCC Rules each amateur station must be operated in accordance with good engineering and good amateur practice.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;And also in the same section:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(d) No amateur operator shall willfully or maliciously interfere with or cause interference to any radio communication or signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Where &quot;interference&quot; is defined in &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_13&quot; rel=&quot;noreferrer&quot;&gt;§97.3&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(23) &lt;em&gt;Harmful interference&lt;/em&gt;. Interference which endangers the functioning of a radionavigation service or of other safety services or seriously degrades, obstructs or repeatedly interrupts a radiocommunication service operating in accordance with the Radio Regulations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-05-12T14:21:11.337" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4880" PostTypeId="2" ParentId="4877" CreationDate="2015-05-12T15:03:55.633" Score="0" Body="&lt;p&gt;If all you want to know is what limit is placed on fidelity by the sample format of the SDR, there is a much simpler answer. Sample rate limits the frequency components the digital signal can represent, and the bit depth relates to quantization noise. If we can sample the entire bandwidth of the RF channel, and the quantization noise isn't a significant component of all the noise, then the digitization process isn't significantly degrading the fidelity of the demodulated signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 2048 kHz, the sample rate in the example you gave is more than sufficient to cover a 200 kHz wide FM channel. So we are good on that front by a wide margin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 8-bit samples, the quantization noise is more than it would be with a more precise sample. But as long as the quantization noise is several decibels below the analog noise floor (which is itself a sum of RF noise and electrical noise in the receiver, among other things), then digitization adds only negligible noise to the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Oversampling will not help you reduce quantization noise unless your SDR has an analog filter to reduce the bandwidth of the signal at the ADC's input. Indeed, the 2048 kHz bandwidth of the IQ samples is far in excess of the 200 kHz of an WFM channel. But if you aren't doing the filtering before reaching the ADC, that excess bandwidth contains information about other stations and noise outside the channel rather than extra information about the channel you wish to receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you did have an analog filter, then you are oversampled by a factor of at least 8x. Every 4x oversampling effectively adds one bit, so you could reasonably convert your incoming 8-bit samples to 10-bit samples. With quiet electronics and proper application of noise shaping and dithering in the ADC you might even do a little better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Practically speaking, you'd probably convert your samples to 16 bits at this point since that's convenient for most processors and it guarantees rounding error in the subsequent calculations are buried in the noise floor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this point, if the quantization noise is still not a few decibels below the analog noise floor, all the processing that follows is irrelevant. The signal has irreversibly been degraded. Once noise becomes mixed with signal, there's nothing that can be done to unmix it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-05-13T17:53:49.247" LastActivityDate="2015-05-13T17:53:49.247" CommentCount="12" ContentLicense="CC BY-SA 3.0" />
  <row Id="4881" PostTypeId="2" ParentId="3755" CreationDate="2015-05-12T21:56:04.277" Score="2" Body="&lt;p&gt;Your problem could easily be a ground loop.  In this scenario, your computer and your radio are at different RF or DC potentials, and current is flowing on the ground line of your audio or PTT connections between the computer and the radio; the flowing current causes noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So how to diagnose whether you have a ground loop?  One way could be to power both the computer and the radio with batteries, which would break ground loops that go through the power lines.  If the noise is reduced, then that would make a ground loop look like the problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many &quot;sound card&quot; interfaces between radios and computers eliminate ground loop issues through complete galvanic isolation.  In other words, there is no direct electrical connection between the computer and the radio.  The audio goes through an isolation transformer, the PTT goes through an optical isolator (an LED and a phototransistor in the same component package), and the grounds of the radio and computer aren't connected.  You could try that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another possibility could be common-mode currents on your antenna feedline coupling noise into the radio.  If that were the case, then you'd likely hear the same noise when using a microphone to key the radio though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet another possibility could be RF getting into your circuit through incomplete shielding.  You say the box is shielded, which is good, but are you using shielded cables?  Twisted-pair might not be enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2015-05-12T21:56:04.277" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4882" PostTypeId="2" ParentId="2291" CreationDate="2015-05-12T22:59:13.137" Score="0" Body="&lt;p&gt;It certainly seems to be possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This &lt;a href=&quot;http://www.michigancmes.org/papers/sarabandi17.pdf&quot; rel=&quot;nofollow&quot;&gt;recent paper&lt;/a&gt; mentions physically small inverted-F high dielectric-constant (e=10.2) HF antennas, although it covers another approach (it describes an HF antenna running at frequencies of the order of 20-30 MHz which is only 15cm x 15cm and weighs under 20 grams, but doesn't use high dielectric-constant material. Interesting in its own right, although I think it's rather narrow-band). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note, though, that the paper says the high dielectric-constant HF antenna will have losses of around -33dBi &quot;due to ohmic and dielectric losses&quot;, but claims slightly more cheerfully that its own design is 6dB better than that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Almost all of the commercial interest in high dielectric-constant antennas is at UHF and above, because these days that's where the money is. Still fertile ground for the committed experimenter, though. If you find a way to run Top Band from a small apartment, I'll be in the queue...&lt;/p&gt;&#xA;" OwnerUserId="4666" LastEditorUserId="218" LastEditDate="2015-05-13T00:41:06.040" LastActivityDate="2015-05-13T00:41:06.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4883" PostTypeId="1" CreationDate="2015-05-13T06:03:36.543" Score="2" ViewCount="174" Body="&lt;p&gt;I have designed a receiver for FSK reception in 434 MHz ISM band. For this I used USRP1 and GNU Radio. Now, I would like to measure performances of my receiver. For this purposes I did following:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;I transmit over cable using signal generator a bunch of 10000 frames with pseudorandom data, with output power of signal generator as a parameter.&lt;/li&gt;&#xA;&lt;li&gt;I have a sort of lookup table since the device is not able to measure absolute power, but rather relative to ADC full scale. So, the lookup table consisted of abosulte input power and gain as an input parameters while the output parameter is relative power. I obtained this lookup table with signal generator. The relative power is calculated by squaring magnitude of the complex baseband signal followed by averaging, which would basically lead to RMS value.&lt;/li&gt;&#xA;&lt;li&gt;I measured relative noise power with antenna port terminated with 50 ohms. (Procedure same as above squaring and averaging)&lt;/li&gt;&#xA;&lt;li&gt;Next, I combine data from 1), 2) and 3). I calculated SNR as relative signal power - relative noise power. For such calculated SNR, I plot PER and BER. BER is derived with: &lt;span class=&quot;math-container&quot;&gt;$ \text{BER} = 1 - \sqrt[n]{1-\text{PER}} $&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;With this I get that my PER goes close to zero at around 20dB SNR value, which is too much in my opinion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, was my approach correct and are those values normal?&lt;/p&gt;&#xA;" OwnerUserId="1891" LastEditorUserId="4076" LastEditDate="2020-04-26T13:39:16.647" LastActivityDate="2020-04-26T13:39:16.647" Title="FSK real world application BER" Tags="&lt;receiver&gt;&lt;digital-modes&gt;&lt;uhf&gt;&lt;gnuradio&gt;&lt;snr&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="4884" PostTypeId="1" CreationDate="2015-05-13T11:16:54.050" Score="2" ViewCount="248" Body="&lt;p&gt;Can someone explain to me exactly how a quarter-wave transmission line transformer is put into action? I mean, how does it operate and what values are usually taken into consideration, calculation wise?&lt;/p&gt;&#xA;" OwnerUserId="4506" LastEditorUserId="76" LastEditDate="2015-05-13T15:30:17.693" LastActivityDate="2015-05-13T15:30:17.693" Title="Quarter Wave Transmission Line transformer" Tags="&lt;impedance&gt;&lt;theory&gt;&lt;transmission-line&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4885" PostTypeId="1" CreationDate="2015-05-13T11:33:17.020" Score="3" ViewCount="2478" Body="&lt;p&gt;What is the process of stub impedance matching and what are the elements included in the calculations relevant to it?&lt;/p&gt;&#xA;" OwnerUserId="4506" LastEditorUserId="830" LastEditDate="2015-05-13T17:56:54.143" LastActivityDate="2015-05-16T14:52:49.173" Title="Stub impedance matching" Tags="&lt;impedance&gt;&lt;transmission-line&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4887" PostTypeId="2" ParentId="4884" CreationDate="2015-05-13T14:47:39.107" Score="2" Body="&lt;p&gt;A quarter-wave transmission line makes some load appear to the source on the other end look like the load's dual impedance. The most common case is that the impedance at the end is a short or an open, and the quarter-wave transmission line makes it look to the source (V1 or V2) as the opposite:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/e1Hod.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fe1Hod.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is pretty weird. In the case of V1, it looks like it's connected to a short: a huge (theoretically infinite) current flows. But if you stick an ohmmeter on the same terminals where V1 is connected, it will tell you there's no connection between them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of V2, it looks like it's connected to nothing: no current flows. Yet if you measure with your meter again, it will tell you there's a dead short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since it seems like this is logically impossible, it bears mentioning that a short &quot;looks like&quot; an open (or vice versa) &lt;em&gt;only at equilibrium&lt;/em&gt;. If you were able to slow time such that the speed of light were observable, you'd see that in both cases, which V1 is initially connected, some current does flow. Once that initial wave has reached the end of the transmission line, and then reflected back (maybe several times), does the system reach equilibrium.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the more general case, the load on the right end doesn't have to be a short or an open: it can be any impedance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/File:Quarter_wave_impedance_transformer.svg#/media/File:Quarter_wave_impedance_transformer.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/en/thumb/d/dc/Quarter_wave_impedance_transformer.svg/1200px-Quarter_wave_impedance_transformer.svg.png&quot; alt=&quot;Quarter wave impedance transformer.svg&quot;&gt;&lt;/a&gt;&lt;br&gt;&quot;&lt;a href=&quot;http://en.wikipedia.org/wiki/File:Quarter_wave_impedance_transformer.svg#/media/File:Quarter_wave_impedance_transformer.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Quarter wave impedance transformer&lt;/a&gt;&quot; by Courtesy Spinningspark at Wikipedia. Licensed under &lt;a href=&quot;http://creativecommons.org/licenses/by-sa/3.0/&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Creative Commons Attribution-ShareAlike 3.0&quot;&gt;CC BY-SA 3.0&lt;/a&gt; via &lt;a href=&quot;//en.wikipedia.org/wiki/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$Z_\text{in}$ is the impedance something will see, looking into the transmission line,&lt;/li&gt;&#xA;&lt;li&gt;$Z_0$ is the &lt;a href=&quot;http://en.wikipedia.org/wiki/Characteristic_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;characteristic impedance&lt;/a&gt; of the transmission line, which is commonly $50\:\Omega$, and&lt;/li&gt;&#xA;&lt;li&gt;$Z_L$ is the impedance of the load at the end.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These three parameters are then related by the equation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {Z_\text{in} \over Z_0} = {Z_0 \over Z_L} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since these are complex numbers the math can be a little unintuitive, so some consequences, in plain English:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;inductors look like capacitors&lt;/li&gt;&#xA;&lt;li&gt;capacitors look like inductors&lt;/li&gt;&#xA;&lt;li&gt;small resistors look like big resistors&lt;/li&gt;&#xA;&lt;li&gt;big resistors look like small resistors&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-03-10T09:42:50.217" LastActivityDate="2015-05-13T14:47:39.107" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4888" PostTypeId="2" ParentId="4885" CreationDate="2015-05-13T15:06:00.447" Score="3" Body="&lt;p&gt;&quot;Stubs&quot; are sections of transmission line which are usually less than a half-wavelength long and either shorted or open on one end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The two connections on the other end look like two terminals on a lumped impedance which can be either an inductor or a capacitor, depending on the length of the stub.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a short-circuited stub, the impedance is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ j Z_0 \tan\left({2\pi\over\lambda}l\right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$j$ is the imaginary unit,&lt;/li&gt;&#xA;&lt;li&gt;$Z_0$ is the characteristic impedance of the transmission line,&lt;/li&gt;&#xA;&lt;li&gt;$\lambda$ is the wavelength, and&lt;/li&gt;&#xA;&lt;li&gt;$l$ is the length of the line (in the same units as the wavelength).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;An open-circuited stub is the same but negative:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ -j Z_0 \tan\left({2\pi\over\lambda}l\right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is thus possible to construct a stub which has the same effect as any reactive component at a particular frequency. A distinct advantage is that stubs are in some cases more easily fabricated than capacitors or inductors, for example at microwave frequencies where transmission lines are easily fabricated on PCBs.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-05-13T15:06:00.447" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4889" PostTypeId="2" ParentId="4883" CreationDate="2015-05-13T15:28:23.593" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The relative power is calculated by squaring magnitude of the complex baseband signal followed by averaging, which would basically lead to RMS value.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To get an RMS value, you would need to then take the root of this result. That is, I understand your description as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{1}{n} \left( x_1^2 + x_2^2 + \cdots + x_n^2 \right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;but RMS is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \sqrt{ \frac{1}{n} \left( x_1^2 + x_2^2 + \cdots + x_n^2 \right) } $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If $x_1 \cdots x_n$ are the magnitudes of your samples, then the result of this expression is like an RMS &lt;em&gt;voltage&lt;/em&gt;, and then of course power is proportional to the square of that, which would be equivalent to not taking the square in the first place. So you may have it right, but the wording is a bit ambiguous so I'd double-check it.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I calculated SNR as relative signal power - relative noise power.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;After converting the powers to decibels, I hope.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Other than those things, which may not be problems anyway, your process sounds reasonable to me. Your results might be valid or there might be any number of things that went wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So rather than guess, I'll suggest a way you might validate your empirical measurements: generate some AWGN in GNUradio, and make the same experiment in a purely simulated environment. If the results are pretty close to your real-world measurements, it's pretty likely they are correct. If not, you can investigate more.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-05-13T15:28:23.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4890" PostTypeId="2" ParentId="3766" CreationDate="2015-05-14T05:49:43.390" Score="2" Body="&lt;p&gt;The xstream provides an rs232 connection controlled via AT commands. You will need to use a dialer and control it directly. If you have never worked with modems before, look up general info on the &quot;Hayes AT command set&quot; and have a look at the &lt;a href=&quot;http://www.tldp.org/LDP/nag2/x-087-2-serial.devices.html&quot; rel=&quot;nofollow&quot;&gt;Linux serial guide.&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That should be enough to figure it all out.&lt;/p&gt;&#xA;" OwnerUserId="4679" LastActivityDate="2015-05-14T05:49:43.390" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4893" PostTypeId="1" AcceptedAnswerId="4895" CreationDate="2015-05-15T13:45:20.773" Score="5" ViewCount="1407" Body="&lt;p&gt;Let's say there's a transmitter far away, and I'm going to receive the transmitted signal. To keep things simple let's further say the transmitted signal is a pure, unmodulated sine wave. Further, let's say the electric field generated by that distant transmitter, at the point where my receive antenna is to be installed, has an intensity of 1 mV/m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that I can now install an ideal, lossless dipole, how much power would be received by this dipole? How does the received power vary with length, ie a half-wave dipole versus a shorter dipole?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-01-17T11:03:13.093" Title="How does power received by a dipole relate to electric field intensity?" Tags="&lt;antenna&gt;&lt;rf-power&gt;&lt;math&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4894" PostTypeId="2" ParentId="1313" CreationDate="2015-05-15T14:09:50.540" Score="1" Body="&lt;p&gt;You can download many free applications to convert a digital sound of morse or any other digital mode into text. My favorite is the last free version before it was sold, of &lt;a href=&quot;http://www.iw5edi.com/software/ham-radio-deluxe-5-download-links&quot; rel=&quot;nofollow&quot;&gt;Ham Radio Deluxe&lt;/a&gt;, and use the Digital Master 780 application inside the main program.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Install it, open DM-780 and set the Program Options to read the sound from almost any source your soundcard can hear, such as Line In to get the sound from the MP3 file. You can also open a window to one of the SDR websites, tune the digital radio in to a good frequency with CW or one of the digital modes come in and then set the Program Options to read from Line In, and decode to your hearts content. &lt;/p&gt;&#xA;" OwnerUserId="4631" LastActivityDate="2015-05-15T14:09:50.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4895" PostTypeId="2" ParentId="4893" CreationDate="2015-05-15T15:02:02.437" Score="7" Body="&lt;p&gt;There are a lot of ways to approach this problem, but here's one: we can calculate the power density of that field, and determine the area from which the antenna captures power, and multiply them together.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Calculating the power density&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;If we know the electric field to be 1 mV/m, and the transmitting antenna is distant, then the magnetic field must be related by the &lt;a href=&quot;http://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance of free space&lt;/a&gt;: $376.7\:\Omega$. So, the magnetic field must be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {1\:\mathrm{mV} \over \mathrm m }&#xA;\cdot {1 \over 376.7\:\Omega}&#xA;= {2.655\:\mathrm{\mu A} \over \mathrm m } $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Multiplying these two together, we can calculate the power density:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {1\:\mathrm{mV} \over \mathrm m }&#xA;\cdot {2.655\:\mathrm{\mu A} \over \mathrm m }&#xA;= {2.655\:\mathrm{nW} \over \mathrm m^2 } $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, there is 2.655 nW passing through an area of a square meter perpendicular to the transmitting antenna. &lt;a href=&quot;http://en.wikipedia.org/wiki/Poynting%27s_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;Poynting's theorem&lt;/a&gt; is the formal basis for this calculation, but since we know we are dealing with a radiated field (in the far-field of the transmitting antenna), we know the electric and magnetic fields are in phase and so we can simplify the calculations substantially.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Calculating the effective aperture&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Now that we know the power density, we just need to know the area from which the dipole will collect power. We'll have to approach this part of the problem backwards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We know that the free-space gain of a dipole is 2.15 dBi or 1.64. The area from which an antenna collects energy is called &lt;a href=&quot;https://ham.stackexchange.com/q/3643/218&quot;&gt;effective aperture&lt;/a&gt; ($A_\mathrm{eff}$), and it has a simple relation to gain (G):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A_\mathrm{eff} = {G \lambda^2 \over 4 \pi} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if we set $G = 1.64$ we get the effective aperture of a free-space half-wave dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {1.64 \lambda^2 \over 4 \pi } = 0.1305\:\mathrm m^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, a dipole half a meter long ($\lambda = 1\:\mathrm m$) collects power from an area of $0.1305\:\mathrm{m^2}$. With decreasing frequency the half-wave dipole gets bigger, and consequently collects more power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to know the power we'd see at the antenna terminals, we just multiply these two numbers together:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {2.655\:\mathrm{nW} \over \mathrm m^2 }&#xA;\cdot 0.1305\:\mathrm{m^2}&#xA;= 346.4\:\mathrm{pW} = -64.60\:\mathrm{dBm} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this point, you may wonder why we use the &lt;em&gt;free-space&lt;/em&gt; dipole gain. Don't dipoles over ground have more gain? And the reason is simple: the question specified that the electric field strength at the point where the receiving antenna was to be installed. Any constructive interference due to reflections from the ground would have already been taken into account by this measurement.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Effective aperture of a shorter dipole&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Amazingly, it's almost the same as a half-wave dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you begin with an ideal half-wave dipole and then keep shortening it, the thing you are left with in the limiting case where the dipole is infinitesimally short is called a &lt;a href=&quot;http://en.wikipedia.org/wiki/Dipole_antenna#Hertzian_dipole&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hertzian dipole&lt;/a&gt;. Amazingly, this infinitesimally short dipole has a free-space gain of 1.5 (where the half-wave dipole was 1.64). Thus, it collects power from a slightly smaller area, but not smaller by much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can this be, when we know practically that really small antennas don't work well? Well, as the antenna becomes smaller, the radiation resistance approaches zero. Thus, it becomes increasingly difficult to make an &lt;a href=&quot;http://www.antenna-theory.com/basics/gain.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;efficient antenna&lt;/a&gt; with real materials since the resistance of the wire used to make the antenna becomes much larger relative to the radiation resistance.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Putting it all together&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;With a bit of algebra we can combine all of this into one equation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_\mathrm{ant} = { E_E^2 \ G \lambda^2 \over 4\pi Z_0 }&#xA;\approx { E_E^2 \ G \lambda^2 \over 4734 } $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$P_\mathrm{ant}$ is the power at the antenna terminals,&lt;/li&gt;&#xA;&lt;li&gt;$E_E$ is the electric field intensity ($\mathrm{V/m}$),&lt;/li&gt;&#xA;&lt;li&gt;$G$ is the gain of the antenna (1.64 for a half-wave dipole),&lt;/li&gt;&#xA;&lt;li&gt;$\lambda$ is the wavelength, and&lt;/li&gt;&#xA;&lt;li&gt;$Z_0$ is the impedance of free space ($376.7\:\Omega$).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-05-15T15:02:02.437" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4896" PostTypeId="1" CreationDate="2015-05-15T18:49:09.230" Score="2" ViewCount="165" Body="&lt;p&gt;Does anyone know the protocol compatibility with regard to DAB and Low Delay AAC codecs? Is AAC-LD data or AAC-ELD data compatible with AAC and AAC+ decoding. Or how likely is it that an AAC/AAC+ decoder would have built-in compatibility for the Low Delay codecs?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simpler question behind the question: Is it possible to use DAB+ to broadcast audio without the latency of the traditional AAC+ codec?&lt;/p&gt;&#xA;" OwnerUserId="4659" LastActivityDate="2018-10-12T09:02:06.637" Title="DAB/DAB+ and AAC-LD/AAC-ELD" Tags="&lt;jargon&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4897" PostTypeId="1" CreationDate="2015-05-15T19:07:31.240" Score="4" ViewCount="127" Body="&lt;p&gt;I would like to ask you what it means when it is written that a transmitter has 10 dBm power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does that mean that 10 dBm is provided to the antenna, or that 10 dBm is measured at particular frequency at the receiving side?&lt;/p&gt;&#xA;" OwnerUserId="1891" LastEditorUserId="76" LastEditDate="2015-05-21T23:59:03.333" LastActivityDate="2015-05-21T23:59:03.333" Title="What does radiation power mean?" Tags="&lt;rf-power&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4898" PostTypeId="2" ParentId="4897" CreationDate="2015-05-15T20:26:22.523" Score="5" Body="&lt;p&gt;This means that the transmitter output power (to the antenna) is 10 dBm (which is $10^{1.0}\, \rm{mW} = 10\, \rm{mW}$).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally this is valid at the rated output impedance. If the transmission line or antenna are not matched to the transmitter output impedance, less power will be effectively irradiated by the antenna.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2015-05-15T20:26:22.523" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4900" PostTypeId="2" ParentId="4885" CreationDate="2015-05-16T11:21:06.473" Score="0" Body="&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/QJJyg.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Quarter wave impedance transformer and quarter wave stub&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The input impedance Zin  of a length of coax depends on four factors: 1) its characteristic impedance, Z0, which is independent of the RF frequency;  2) its load impedance, Zload and 3) its length in terms of wavelength, the latter both at the fourth factor: the frequency of the applied RF. Note in all this that the wavelengths are in terms of the reduced velocity of RF in the feeder. The formula relating these is complex, but one simple case is often used, however note that this formula applies only to quarter wavelength lines:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;                 Zin  = Z0²  / Zload&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Basic principle is that, since a  1/4 wave length of transmission line obeys this formula, it is useful in two different ways.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first is a quarter wave stub. This is connected across the feeder line, and and acts as a filter, at the frequency it is a 1/4 wavelength of. There are two cases:  the first is if the far end, is an open circuit, Zload is infinite, then Zin  is zero, and we have a notch filter at that frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have not seen any mention of  a use for the second case, a short circuited stub: its input impedance would be infinite, with no effect on the transmission around its 1/4 wavelength frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second use is a  &lt;strong&gt;quarter wave matching transformer&lt;/strong&gt;. &lt;img src=&quot;https://i.stack.imgur.com/Mkzap.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the formula we see that we can match Zin  to Zload by a line with a suitable Z0. This has applications when we want to match a fixed load impedance, e.g. the input impedance of an antenna, to a fixed feeder impedance, say that of a transmission line, by inserting into the line a quarter wavelength of a different transmission line with a specially chosen characteristic impedance. That is, by having a mismatch at both ends, you choose a line impedance so that the two end impedances are the ones in your circuit. This is difficult with coax because there are only a few fixed values of Z0 to choose from. It can be more easily be applied to parallel lines, because their impedance can be changed by altering the diameter and spacing, and in microwave applications where the line is in the copper of a double sided printed circuit. For example, in the  figure, a short  50 Ohm microstrip transmission line is matched to a square patch antenna (impedance typically 200 Ohms or more) via the thinner 1/4 wavelength microstrip line with a Z0 chosen to make the match.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(images courtesy of Wikipedia)&lt;/p&gt;&#xA;" OwnerUserId="297" LastEditorUserId="297" LastEditDate="2015-05-16T14:52:49.173" LastActivityDate="2015-05-16T14:52:49.173" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4902" PostTypeId="2" ParentId="3668" CreationDate="2015-05-17T01:11:06.903" Score="0" Body="&lt;p&gt;A guy on youtube built one:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=VMkULsNU2_A&quot; rel=&quot;nofollow&quot;&gt;https://www.youtube.com/watch?v=VMkULsNU2_A&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;His VHF/UHF repeater is built into a waterproof pelican case:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;4X Yaesu FT-60R radios&lt;/li&gt;&#xA;&lt;li&gt;Radio-Tone repeater controller &lt;/li&gt;&#xA;&lt;li&gt;Some assembly required.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="643" LastActivityDate="2015-05-17T01:11:06.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4903" PostTypeId="1" CreationDate="2015-05-17T02:38:28.457" Score="6" ViewCount="1295" Body="&lt;p&gt;I have two HT's that I bought from Baofeng for emergency use and I don't have a license. I was wondering: is it perfectly legal in the USA for me to be monitoring police and weather channels without a license so long as I don't transmit on any frequency?&lt;/p&gt;&#xA;" OwnerUserId="4700" LastEditorUserId="218" LastEditDate="2015-05-17T15:31:49.057" LastActivityDate="2015-05-24T16:44:01.423" Title="Is it legal to monitor police and weather channels without a license?" Tags="&lt;united-states&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4904" PostTypeId="1" AcceptedAnswerId="4909" CreationDate="2015-05-17T02:58:10.997" Score="6" ViewCount="958" Body="&lt;p&gt;I passed my Technician exam today and my grandma, who's been a ham for decades, suggested that I could try to get my grandpa's call sign. He passed away several years ago, but his FCC registration is still marked active, expiring later this year. From what I've read, this would probably be surmountable by making the right kind of notification to FCC and then making a vanity request for it. But here's the rub: it's a KH6???, which I've read are reserved for pacific island addresses. That makes sense since he probably lived in Hawaii when he got it (and I grew up there), though he kept it for decades after moving to Oregon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any sort of familial transfer process that could get that call assigned to me in California?&lt;/p&gt;&#xA;" OwnerUserId="4699" LastEditorUserId="873" LastEditDate="2015-05-18T05:24:31.460" LastActivityDate="2015-05-19T23:23:06.893" Title="Is it possible to transfer an area-specific call sign from a deceased relative?" Tags="&lt;united-states&gt;&lt;fcc&gt;&lt;callsign&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="4905" PostTypeId="1" AcceptedAnswerId="4907" CreationDate="2015-05-18T09:48:12.770" Score="9" ViewCount="12064" Body="&lt;p&gt;I have built a 1090 MHz ADS-B antenna roughly following &lt;a href=&quot;https://www.youtube.com/watch?v=TkUYdCPFXXs&quot; rel=&quot;noreferrer&quot;&gt;some video instructions&lt;/a&gt;. It appears to work reasonably.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, because of how it is placed, it captures signals for more or less a half of the sky. So I would like to build another and put it on the other side of the house to receive from the other half. Is there some proper way to attach the two antennas to the same receiver (possibly connecting them via some impedance matcher or whatever is needed)? Or do I really need to put two receivers in operation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(beside the practical answer itself, I am also curious of the explanations)&lt;/p&gt;&#xA;" OwnerUserId="1654" LastEditorUserId="76" LastEditDate="2015-12-15T23:41:30.560" LastActivityDate="2019-10-31T02:06:06.557" Title="Connect two receiving antennas to the same radio" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;antenna-system&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4906" PostTypeId="2" ParentId="4904" CreationDate="2015-05-18T15:25:31.623" Score="1" Body="&lt;p&gt;Vanity call signs are covered by &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_119&quot; rel=&quot;nofollow&quot;&gt;§97.19&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(3) A call sign shown on a license canceled pursuant to §97.31 of this part is not available to the vanity call sign system for 2 years following the person's death, or for 2 years following the expiration of the license grant, whichever is sooner. If, however, a license is canceled more than 2 years after the licensee's death (or within 30 days before the second anniversary of the licensee's death), the call sign is not available to the vanity call sign system for 30 days following the date such action is taken. The following applicants are exempt from this 2-year period:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;[...]&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(ii) An applicant who is the spouse, child, grandchild, stepchild, parent, grandparent, stepparent, brother, sister, stepbrother, stepsister, aunt, uncle, niece, nephew, or in-law of the person now deceased or of any other deceased former holder of the call sign, provided that the vanity call sign requested by the applicant is from the group of call signs corresponding to the same or lower class of operator license held by the applicant as designated in the sequential call sign system&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There is no restriction on the numeral in the call sign according to region. As the &lt;a href=&quot;http://www.arrl.org/vanity-call-signs&quot; rel=&quot;nofollow&quot;&gt;ARRL puts it&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;First, the FCC does not limit the Vanity call sign choice numeral (0-9). For example, you can be a W1-land addressee, and have a W6 (California) type call if you so desire.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Also, aside from a very few FCC-limited choices, Extra class licensees can choose virtually any vacant but valid US call sign -- FCC call sign Groups A, B, C or D. Although Advanced class licensees cannot seek the special 1x2, 2x1 or 2x2 (beginning with letter &quot;A&quot;) Extra class type call signs, they can seek a 2x2 or 1x3 call sign (beginning with prefix N, K or W), or a 2x3 call sign (beginning with prefix letter K or W) -- FCC call sign Groups B, C or D. General or Technician class licensees can seek a 1x3 call sign (beginning with prefix N, K or W), or 2x3 call sign (beginning with prefix letter K or W) -- FCC call sign Groups C or D. Novice licensees also have access to the Vanity program. Novices can seek a 2x3 call sign (beginning with prefix letter K or W) of their choice -- FCC call sign Group D.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=call_signs_3&amp;amp;id=amateur&amp;amp;page=1&quot; rel=&quot;nofollow&quot;&gt;FCC excludes a few calls from vanity assignments&lt;/a&gt;, none of which seem to apply to &quot;KH6???&quot;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;KA2AA-KA9ZZ, KC4AAA-KC4AAF, KC4USA-KC4USZ, KG4AA-KG4ZZ, KC6AA-KC6ZZ, KL9KAA- KL9KHZ, KX6AA-KX6ZZ;&lt;/li&gt;&#xA;  &lt;li&gt;Any call sign having the letters SOS or QRA-QUZ as the suffix;&lt;/li&gt;&#xA;  &lt;li&gt;Any call sign having the letters AM-AZ as the prefix (these prefixes are assigned to other countries by the ITU);&lt;/li&gt;&#xA;  &lt;li&gt;Any 2-by-3 format call sign having the letter X as the first letter of the suffix;&lt;/li&gt;&#xA;  &lt;li&gt;Any 2-by-3 format call sign having the letters AF, KF, NF, or WF as the prefix and the letters EMA as the suffix (U.S Government FEMA stations);&lt;/li&gt;&#xA;  &lt;li&gt;Any 2-by-3 format call sign having the letters AA-AL as the prefix;&lt;/li&gt;&#xA;  &lt;li&gt;Any 2-by-3 format call sign having the letters NA-NZ as the prefix;&lt;/li&gt;&#xA;  &lt;li&gt;Any 2-by-3 format call sign having the letters WC, WK, WM, WR, or WT as the prefix (Group X call signs);&lt;/li&gt;&#xA;  &lt;li&gt;Any 2-by-3 format call sign having the letters KP, NP or WP as the prefix and the numeral 0, 6, 7, 8 or 9;&lt;/li&gt;&#xA;  &lt;li&gt;Any 2-by-2 format call sign having the letters KP, NP or WP as the prefix and the numeral 0, 6, 7, 8 or 9;&lt;/li&gt;&#xA;  &lt;li&gt;Any 2-by-1 format call sign having the letters KP, NP or WP as the prefix and the numeral 0, 6, 7, 8 or 9;&lt;/li&gt;&#xA;  &lt;li&gt;Call signs having the single letter prefix (K, N or W), a single digit numeral 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and a single letter suffix are reserved for the special event call sign system.&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Of course the transfer happens more or less at the pleasure of the FCC, so the only way to know for sure is to &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=cft&amp;amp;id=amateur&amp;amp;page=cft_get_call_sign&quot; rel=&quot;nofollow&quot;&gt;make the application&lt;/a&gt; and see.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-05-19T00:54:50.497" LastActivityDate="2015-05-19T00:54:50.497" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="4907" PostTypeId="2" ParentId="4905" CreationDate="2015-05-18T17:55:40.773" Score="9" Body="&lt;p&gt;Yes, you can do this. There are two issues: connecting it to the radio, and the effect on reception. The latter might be problematic enough that using two receivers is actually a better option.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Connecting two antennas to the radio&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;If you simply connect two antennas in parallel, the math is just like connecting two resistors in parallel: the impedance is halved. This is in principle a problem, because there will be losses due to the mismatch reflecting some received power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The “correct” thing to do is use a &lt;em&gt;power combiner&lt;/em&gt; (a.k.a. power divider (when used in the other direction) or “splitter” in TV-cable-land). This device has three ports with equal impedances, one of which goes to your receiver and the others go to the two antennas. Since you're using 75 Ω TV coax for your antenna, you might as well get one sold for TV/cable/satellite use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, not using one might not matter much, or might even improve things, because there's a very good chance that your antenna is not actually well matched to your receiver already (because your antenna's resonant frequency is not 1090 MHz, or the antenna has a resistive impedance not equal to the receiver's or coax's impedance). I recommend trying things and seeing what happens. Or if you have access to an antenna analyzer, start measuring.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Effect on reception (radiation pattern)&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;What you're doing is building an &lt;em&gt;array antenna&lt;/em&gt;. When the signals from the two antennas meet, the waves are summed, and this means there can be either constructive or destructive interference (stronger or weaker resulting signal). Which one you get depends on the &lt;em&gt;phase&lt;/em&gt; of the signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your antennas literally saw exactly half the sky, then there would be no problem. But in practice, they will overlap in coverage — a transmitter (aircraft) can be in the view of both antennas at once. In this case, if the signals from both antennas are &lt;em&gt;in phase&lt;/em&gt;, you will receive a good signal; if they are &lt;em&gt;out of phase&lt;/em&gt; (more or less), you will receive a weaker signal than if you had only one of the two antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to make sure the signals are in phase in this case, the coax from the two antennas to the combiner must be of equal length, plus or minus complete wavelengths. A wavelength at 1090 MHz is 27.5 cm; but this must be adjusted for the velocity factor of the coax, so the easiest thing is to use identical lengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were building a array antenna in free space, then the antenna will have a highly uneven pattern with many nulls (directions of almost no reception), as the varying distance to the two antennas from the transmitter changes the phase, but insofar as your house blocks the signal from arriving at more than one antenna at a time it will cause a more uniform pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can in principle use antenna modeling software to determine the pattern to expect and adjust it to be omnidirectional, but it would be very, very hard to create a sufficiently accurate model of your house.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Using two receivers&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;If you're using RTL-SDR dongles or similarly cheap receivers, using two receivers is &lt;strong&gt;highly likely to be a better option&lt;/strong&gt;. Using two receivers:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;avoids the possibility of the two antennas canceling each other out.&lt;/li&gt;&#xA;&lt;li&gt;avoids signal loss from the length of coax needed to cross your house (coax which has low loss at 1 GHz is expensive and bulky).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The disadvantage of separate receivers (besides needing software to combine the data streams in this particular application) is that if the transmitter &lt;em&gt;is&lt;/em&gt; in sight of both antennas, you don't get the SNR benefit from receiving a stronger combined signal.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-05-19T15:17:11.410" LastActivityDate="2015-05-19T15:17:11.410" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="4908" PostTypeId="2" ParentId="4903" CreationDate="2015-05-18T19:40:37.870" Score="3" Body="&lt;p&gt;Yes, That is perfectly legal, just as long as you &lt;strong&gt;DO NOT transmit&lt;/strong&gt; on those frequency's. It will be just the same as if you were using any scanner, which you could not transmit with even if you wanted to.&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-05-18T19:40:37.870" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4909" PostTypeId="2" ParentId="4904" CreationDate="2015-05-19T05:12:55.213" Score="7" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there any sort of familial transfer process that could get that call assigned to me in California?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;br&gt;There are 3 types of vanity call sign requests:&#xA;&lt;br&gt;&lt;em&gt;Primary station preference list&lt;/em&gt;&#xA;&lt;br&gt;&lt;em&gt;Close relative of former holder&lt;/em&gt;&#xA;&lt;br&gt;&lt;em&gt;Former primary station holder&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your case you can apply for &quot;Close relative of former holder&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, vanity calls can not be assigned outside specific call areas but there seems to be an exception when the request type is &quot;&lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?id=amateur&amp;amp;job=call_signs_3&amp;amp;page=5&quot; rel=&quot;noreferrer&quot;&gt;By Close Relative of Former Holder Now Deceased&lt;/a&gt;&quot;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Request Types: By Close Relative of Former Holder Now Deceased&lt;/strong&gt; &lt;br&gt;&lt;br&gt; For&#xA;  your primary station, you may request a call sign that was previously&#xA;  assigned to the primary, secondary, repeater, auxiliary link, control&#xA;  or space station of your now-deceased spouse, child, grandchild,&#xA;  stepchild, parent, grandparent, stepparent, brother, sister,&#xA;  stepbrother, stepsister, aunt, uncle, niece, nephew, or in-law. An&#xA;  &quot;in-law&quot; is limited to a parent, stepparent, sibling, or step-sibling&#xA;  of a licensee's spouse; the spouse of a licensee's sibling,&#xA;  step-sibling, child, or stepchild; or the spouse of a licensee’s&#xA;  spouse’s sibling or step-sibling. When so requesting for your primary&#xA;  station: &lt;br&gt;&lt;br&gt; - You may request the former call sign of a close relative now&#xA;  deceased even though it has been unassigned for less than two years.&#xA;  Upon the death of the holder, a call sign is assignable immediately to&#xA;  an otherwise eligible primary station of a close relative once it has&#xA;  been cancelled from the database. &lt;br&gt;&lt;br&gt; - You must be an Amateur Extra Class&#xA;  operator to request a Group A call sign. &lt;br&gt;&lt;br&gt; - You must be an Amateur Extra&#xA;  or Advanced Class operator to request a Group B call sign. &lt;br&gt;&lt;br&gt; - You must be&#xA;  an Amateur Extra, Advanced, General, Technician Plus, or Technician&#xA;  Class operator to request a Group C call sign. &lt;br&gt;&lt;br&gt; - You must be an Amateur&#xA;  Extra, Advanced, General, Technician Plus, Technician or Novice class&#xA;  operator to request a Group D call sign. &lt;br&gt;&lt;br&gt; &lt;strong&gt;- Your mailing address does not&#xA;  have to be in a Region designated in the sequential system for the&#xA;  call sign requested. A call sign requested by a close relative of&#xA;  former holder now deceased may be in any Region.&lt;/strong&gt; &lt;br&gt;&lt;br&gt; - You must show your&#xA;  relationship to the deceased person exactly as listed in the&#xA;  instruction, i.e., &quot;child&quot;, &quot;niece&quot; or &quot;in-law&quot;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;More &lt;a href=&quot;http://wireless2.fcc.gov/helpfiles/licensemanager/commonQuestions.html#eligible1&quot; rel=&quot;noreferrer&quot;&gt;answers to Frequently Asked Questions here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On a separate note, normally &lt;em&gt;vanity calls can not be assigned outside call areas&lt;/em&gt;. Normal, in which you were neither a relative of the deceased previous owner of the call nor actual previous owner of the call, applications fall under the &quot;&lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=call_signs_3&amp;amp;id=amateur&amp;amp;page=3&quot; rel=&quot;noreferrer&quot;&gt;Primary station preference list&lt;/a&gt;&quot; category.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Q: My mailing address is in (one of the 48 contiguous states). May I request a Group A call sign designated in Amateur Station Call Sign Systems for Navassa Island?&lt;/strong&gt;&#xA;  &lt;br&gt;A. No. You do not have an address on Navassa Island where you can receive mail delivery by the United States Postal Service (&quot;USPS&quot;). As a operating aid for ?the amateur service community, certain places such as Navassa Island are designated small blocks of unique call signs. In the Memorandum Opinion and Order, 10 FCC Rcd 11135 (1995), the FCC decided to limit the assignability of call signs designated for these places to preclude the possibility of the call signs becoming quickly depleted. &lt;strong&gt;Therefore, Amateur Station Call Sign Systems provides that for Alaska, Hawaii, and the Caribbean and Pacific Insular Areas, only licensees having a mailing addresses where mail delivery by the USPS can be received in the specific state, commonwealth or island can request a call sign designated for that specific state, commonwealth or island.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;br&gt;&lt;br&gt;72 es GL in the application!&lt;/p&gt;&#xA;" OwnerUserId="1761" LastEditorUserId="1761" LastEditDate="2015-05-19T23:23:06.893" LastActivityDate="2015-05-19T23:23:06.893" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4910" PostTypeId="2" ParentId="1379" CreationDate="2015-05-20T02:01:38.833" Score="1" Body="&lt;p&gt;I found this one for Thai characters on Wikipedia, in Thai. Unfortunately there is not an English Language version of this page, because they put the information in the &quot;Morse Code&quot; entry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://th.wikipedia.org/wiki/%E0%B8%A3%E0%B8%AB%E0%B8%B1%E0%B8%AA%E0%B8%A1%E0%B8%AD%E0%B8%A3%E0%B9%8C%E0%B8%AA#.E0.B8.A3.E0.B8.AB.E0.B8.B1.E0.B8.AA.E0.B8.A1.E0.B8.AD.E0.B8.A3.E0.B9.8C.E0.B8.AA.E0.B8.A0.E0.B8.B2.E0.B8.A9.E0.B8.B2.E0.B9.84.E0.B8.97.E0.B8.A2&quot; rel=&quot;nofollow&quot;&gt;http://th.wikipedia.org/wiki/%E0%B8%A3%E0%B8%AB%E0%B8%B1%E0%B8%AA%E0%B8%A1%E0%B8%AD%E0%B8%A3%E0%B9%8C%E0%B8%AA#.E0.B8.A3.E0.B8.AB.E0.B8.B1.E0.B8.AA.E0.B8.A1.E0.B8.AD.E0.B8.A3.E0.B9.8C.E0.B8.AA.E0.B8.A0.E0.B8.B2.E0.B8.A9.E0.B8.B2.E0.B9.84.E0.B8.97.E0.B8.A2&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Thai writing system is 100% phonetic. It has 44 consonants and 32 vowels. The consonants are separated into three groups (with some duplication of the same sound in the same group), and it's interesting to note that the Thai language morse code does away with the duplication of sounds within the same group, so some morse symbols represent several letters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many vowels are compounds of other symbols, and it looks like they break all the vowels into their components for the sake of sending them in morse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, there are some markers for tone, or to indicate vowel length.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-05-20T02:01:38.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4912" PostTypeId="1" CreationDate="2015-05-21T20:16:03.963" Score="3" ViewCount="1220" Body="&lt;p&gt;I'm looking for the protocol used by Kenwood's TS-590S antenna tuner port. I've worked as far as I can with Kenwood's tech support. They know what the pins are labeled, but don't have any information on the protocol used to control the tuner.&lt;/p&gt;&#xA;" OwnerUserId="4207" LastEditorUserId="8832" LastEditDate="2017-02-05T05:31:20.527" LastActivityDate="2017-02-05T05:31:20.527" Title="TS-590 Antenna Tuner Protocol" Tags="&lt;kenwood&gt;&lt;antenna-tuner&gt;&lt;remote-control&gt;" AnswerCount="0" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="4913" PostTypeId="2" ParentId="4897" CreationDate="2015-05-21T20:25:45.077" Score="1" Body="&lt;p&gt;The power rating is at the output of the transmitter at the rated frequency. Feedline, impedance mismatch, antenna efficiency, directivity and gain and other losses &amp;amp; gains will affect the Effective Isotropic Radiated Power (EIRP). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;EIRP is a measure of power output of the antenna in reference to a theoretical antenna that radiates power equally in all directions in free space.&lt;/p&gt;&#xA;" OwnerUserId="4207" LastActivityDate="2015-05-21T20:25:45.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4914" PostTypeId="2" ParentId="4867" CreationDate="2015-05-21T20:41:02.540" Score="3" Body="&lt;p&gt;If you are worried about range the best thing you can do is get a full sized antenna that you can remotely mount, either on your backpack or elsewhere, and feed it with a short feed line (pigtail). The rubber ducky antennas that come with HT's are very lossy. There are several 2m/440 antennas that can break down with a small allen wrench, so that you could use the ducky most of the time and only have the larger antenna hooked up when you are planning to be further apart, or you are trying to reach the repeater. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The phased array you mention would be something that you could try, but it takes some doing to get it just right. I wouldn't slap that together and hope it works. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The nice thing about Amateur Radio is that you can try all kinds of things. My son is creating a walking stick that contains a break-down 6-meter moxon antenna, complete with balun, for use when he is hiking in Alaska with his 6m/2m/440 HT. I plan to outfit my small sailboat with a VX-7R and a 1/4 wave vertical on the top of the mast to shoot 6m to my car, and then cross-band repeat from there to 2 meters at 50 watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The options for what you can do are endless. The options for what will work and work well in a pinch are fewer, but very rewarding when you find them.&lt;/p&gt;&#xA;" OwnerUserId="4207" LastActivityDate="2015-05-21T20:41:02.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4915" PostTypeId="1" CreationDate="2015-05-23T17:23:07.573" Score="3" ViewCount="1383" Body="&lt;p&gt;I want to build a simple circuit, preferably only a few transistors which simply activates when it hears a low level audio, and deactivates when the audio signal does not exist anymore. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;No pre-delay and no after delay is needed or wanted. I just want a circuit to activate simply when it hears the packet from my sound card. &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8832" LastEditDate="2017-02-25T23:12:56.873" LastActivityDate="2017-04-14T06:10:38.423" Title="Ideas for a simple VOX circuit for packet?" Tags="&lt;diy&gt;&lt;packet&gt;&lt;audio-interface&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4916" PostTypeId="1" CreationDate="2015-05-24T02:12:46.890" Score="1" ViewCount="201" Body="&lt;p&gt;While researching a DIY digital video streaming solution for an outdoor quad-rotor project, I've noticed that a lot of the popular digital transceivers seem to be limited to 63mW transmit power:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/zigbee-mesh-module/xbee-zb-module#specs&quot; rel=&quot;nofollow&quot;&gt;http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/zigbee-mesh-module/xbee-zb-module#specs&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/zigbee-mesh-module/xbee-digimesh-2-4#specs&quot; rel=&quot;nofollow&quot;&gt;http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/zigbee-mesh-module/xbee-digimesh-2-4#specs&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://wireless.murata.com/datasheet?/RFM/data/dnt2400c.pdf&quot; rel=&quot;nofollow&quot;&gt;http://wireless.murata.com/datasheet?/RFM/data/dnt2400c.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://wireless.murata.com/datasheet?/RFM/data/dnt900dk_manual.pdf&quot; rel=&quot;nofollow&quot;&gt;http://wireless.murata.com/datasheet?/RFM/data/dnt900dk_manual.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;(sorry, newbs can't post too many links)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My original guess was that it was a legislation issue, but the last module (that operates on 900MHz unlike the other 2.4GHz ones) has the following message in the datasheet:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;Selectable 1, 10, 63, 250, 500 or 1000 mW transmit power with a firmware interlock of 63 mW maximum for 500 kb/s operation&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That would suggest that something in the underlying physics breaks down above 63 mW for high bitrates. Is that the case, or is it just a combination of coincidence and poorly written datasheets (the third module is rated for 63 mW on its datasheet, but 100 mW on its specs page)?.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;About me:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm an established programmer with a decent understanding of physics (albeit I'll admit to skipping quite a few electrical engineering classes) so as long as you keep it below line integrals and wave functions (the quantum type), I should be able to follow.&lt;/p&gt;&#xA;" OwnerUserId="4732" LastEditorUserId="1761" LastEditDate="2015-05-25T12:29:55.277" LastActivityDate="2015-07-22T08:27:49.683" Title="Why are many FHSS / DSSS transcievers limited to 63 mW?" Tags="&lt;legal&gt;&lt;diy&gt;&lt;digital-modes&gt;&lt;rf-power&gt;&lt;uhf&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="4917" PostTypeId="1" CreationDate="2015-05-24T02:43:27.937" Score="3" ViewCount="948" Body="&lt;p&gt;Does anyone here have experience connecting one exciter radio to a pair of identical amplifiers each connected to identical cables connected to identical antennas?  Let's suppose we are talking about 2m FM and the pair of identical 4 element Yagi beam antennas are stacked vertically at 1 wavelength (WL) apart (center to center spacing).  Should I expect the Tx performance of this to be better than that of the same stack fed by only one amplifier (which is the normal way to do it)?  What problems could and may arise with the dual amp?  If there is a phase difference in them is there an easy way to fix that such as adding a short piece of coax cable to one of the antennas?  If that works on Tx, will it possibly mess up the Rx slightly?  What are the chances that 2 identical amps (same make same model), will have the same phasing and will work from the same input signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To me it seems there is no benefit to doing this on Rx (vs. a normal stack with just 1 amp) but there is a possible 3dB to be gained on Tx.  Also, if someone has a pair of identical 100 watt amps and they want to Tx with 200 watts, they wouldn't have to sell their 100 watt amps and then buy a 200 watter.  It would be a good conversation piece on the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also what is the best way to test the dual amp setup to make sure it is working?  Would a Field Strength (FS) meter suffice?  Does it matter much if the stack is side by side vs. one above the other as far as for testing purposes?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another interesting question is can a comparison be done with the single amp setup simply by powering down the 2nd amp?  Suppose the amps are 5W in and 100W out and they are both being &quot;hit&quot; with 5W on their inputs.  Then with 1 amp off, it will be about 105 watts (assuming they are in perfect phase) vs. 200W with both amps on (also assuming perfect phase).&lt;/p&gt;&#xA;" OwnerUserId="1652" LastEditorUserId="1652" LastEditDate="2015-05-24T03:39:33.657" LastActivityDate="2015-08-18T17:47:12.410" Title="2 antennas and 2 amplifiers connected to same exciter radio" Tags="&lt;antenna&gt;&lt;2m-band&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4918" PostTypeId="2" ParentId="3714" CreationDate="2015-05-24T06:56:40.917" Score="1" Body="&lt;p&gt;Having seen your question, I can not leave it without cautioning you against &amp;quot;experimenting&amp;quot; with putting things into the ear canal.&lt;/p&gt;&#xA;&lt;p&gt;If you cause an ear infection, depending on the health care system in your locality, you could find yourself having to pay thousands of dollars for treatment.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.drugs.com/cg/ear-foreign-body-inpatient-care.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.drugs.com/cg/ear-foreign-body-inpatient-care.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Be good, and if you can't be good, BE CAREFUL.&lt;/p&gt;&#xA;" OwnerUserId="4733" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2015-05-24T06:56:40.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4919" PostTypeId="2" ParentId="3683" CreationDate="2015-05-24T07:55:09.123" Score="1" Body="&lt;p&gt;KD8NXH, GE OM,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you say, there are many answers. I was licensed about 44 years ago which might make me a &quot;novice&quot; HIHI. In the absence of a definitive definition, I usually resort to &quot;which one appeals to me the most, personally&quot;. As an avid collector in my youth of tin containers for storing small parts, I quite like this one from Rod (SK RIP) and Jeff Dinkins AC6V &lt;a href=&quot;http://www.ac6v.com/73.htm&quot; rel=&quot;nofollow&quot;&gt;ORIGIN OF HAM SPEAK -  FACT, LEGENDS AND MYTHS???&lt;/a&gt; They write, &quot;Certainly, the term LID came from land-line telegrapher slang. (LID was a reference to use of a tobacco can lid on the sounder to aid a poor operator in copying Morse.) This one may be true. It wouldn't be the first time that a group adopted a term originally meant as an insult to serve as a slang term for themselves.&quot; :-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Incidentally, I still have many of my old 1970's tobacco tins somewhere. According to &lt;a href=&quot;https://www.etsy.com/uk/listing/183597634/lloyds-old-holborn-blended-virginia&quot; rel=&quot;nofollow&quot; title=&quot;to this Etsy seller, my tobacco tins could be worth about £5 &amp;#40;US $9.25&amp;#41;&quot;&gt;this Etsy seller, my tobacco tins could be worth about £5 (US $9.25)&lt;/a&gt; - I should start looking for them!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73'S ES GD DX DE MART G8EAD&lt;/p&gt;&#xA;" OwnerUserId="4733" LastActivityDate="2015-05-24T07:55:09.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4920" PostTypeId="2" ParentId="4903" CreationDate="2015-05-24T16:44:01.423" Score="3" Body="&lt;p&gt;In some states it is not legal to have a scanner in your car.  See &lt;a href=&quot;http://www.fireline.org/scanlaws/scanner5.html&quot; rel=&quot;nofollow&quot;&gt;http://www.fireline.org/scanlaws/scanner5.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In these states, it's &lt;em&gt;not&lt;/em&gt; legal to have a ham radio in your car unless you have a ham license because police will consider it to be a scanner..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apparently it's even a problem for hams that do have a license: &lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?topic=17576.0;wap2&quot; rel=&quot;nofollow&quot;&gt;http://www.eham.net/ehamforum/smf/index.php?topic=17576.0;wap2&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4735" LastActivityDate="2015-05-24T16:44:01.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4921" PostTypeId="1" CreationDate="2015-05-25T01:47:11.973" Score="5" ViewCount="133" Body="&lt;p&gt;I just installed a mobile CB (Uniden) into my Jeep. When the key is in auxiliary (car off, accessories on) and the squelch turned all the way down, no S/RF lights are illuminated and the background noise is relatively low. When I start the car, I can hear engine noise and the first of three S/RF lights light up (while the CB is receiving). If I turn the squelch up to block it out, operating the windshield washer (spray pump) can break squelch. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/RI3jK.jpg&quot; alt=&quot;S/RF Number 1 light illuminated at engine idle&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm new to amateur radio and CB. Is this normal? When I first installed the radio a few days ago, this was not happening. &lt;/p&gt;&#xA;" OwnerUserId="4738" LastEditorUserId="4738" LastEditDate="2015-06-01T20:39:56.220" LastActivityDate="2015-06-01T20:39:56.220" Title="OK for S/RF light to be illuminated at engine idle?" Tags="&lt;mobile&gt;&lt;rfi&gt;&lt;citizens-band&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="4925" PostTypeId="2" ParentId="1807" CreationDate="2015-05-25T21:24:27.340" Score="0" Body="&lt;p&gt;In short the unit is defective, despite rather called UV-82 or UV-82L the unit is defective. I have purchased and configured many Baofeng UV-82 units including the GT-3TP. of the 19+ UV-82 units I have programmed, I too have encountered that same problem a couple times. If you are using the chirp software and are copying and pasting the memory frequencies from a working unit in Channel mode, and still not able to transmit in channel mode then You know it's NOT a user programming error. I have successfully copied and pasted my fleet Memory Range before and after recognizing a brand new purchased defective units. again you have a defective unit, stop wrecking your brain re-programming that unit over and over thinking you missed a step, configured incorrectly or done something wrong. :-)&lt;/p&gt;&#xA;" OwnerUserId="4745" LastActivityDate="2015-05-25T21:24:27.340" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4926" PostTypeId="1" AcceptedAnswerId="4935" CreationDate="2015-05-26T14:25:18.473" Score="3" ViewCount="2064" Body="&lt;p&gt;Is there a morse code for a hash character? If so, what is that morse code? My thoughts where that there is morse code for an @ but why not for a #?&lt;/p&gt;&#xA;" OwnerUserId="4749" LastEditorUserId="76" LastEditDate="2015-05-26T21:05:47.273" LastActivityDate="2015-05-29T14:05:28.227" Title="Morse code for hash (#)" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="4927" PostTypeId="1" AcceptedAnswerId="4929" CreationDate="2015-05-27T05:13:36.693" Score="1" ViewCount="120" Body="&lt;p&gt;Is it wise to use my call sign as SSID on 802.11x spectrum. I wish to be known.&#xA;My question more pointently is, is it common for amateurs to ID on shared common wifi frequencies.&lt;/p&gt;&#xA;" OwnerUserId="436" LastEditorUserId="436" LastEditDate="2015-06-01T04:44:38.043" LastActivityDate="2015-06-01T04:44:38.043" Title="Amateur licenced operation and wifi" Tags="&lt;wifi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4929" PostTypeId="2" ParentId="4927" CreationDate="2015-05-27T08:09:14.353" Score="0" Body="&lt;p&gt;You can use anything at all as the SSID for a wifi network. Absolutely anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it wise? I don't think it is unwise - in theory you and only a handful of other people will ever see your SSID, and most of them won't know what a KB1DMR is.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-05-27T08:09:14.353" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4931" PostTypeId="2" ParentId="4921" CreationDate="2015-05-28T01:44:35.177" Score="5" Body="&lt;p&gt;If your car uses petrol (gasoline) rather than diesel, then the ignition system can potentially generate a lot of noise because of the high-voltage system used to generate the sparks that ignite the fuel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Electric motors such as those used in the windscreen washer pump and/or wipers (or electric windows, etc.), can also generate noise. This would mean that when you operate the motorised devices, the noise will show on the radio as extra 'hash', and will eventually break squelch if it reaches a high enough level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All of this noise can get in through the power system (electrical noise), or can be received as electromagnetic radiation across a broad range of frequencies (RF noise). Any electrical noise can be reduced by using choke filters on the power supply to the radio, and RF noise is better eliminated at source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer the question &quot;is it OK for the S/RF light to be illuminated at engine idle?&quot;, the answer is that it's not completely unexpected in a noisy environment, but it's something you can probably do something about. The first thing to do (as suggested in a comment to your question) is to disconnect the antenna from the back of the radio, and see if any (even a small amount) of the noise is present when no antenna is connected. If so, then you're in luck, and some choke filters on the power leads where they enter the radio might be able to stop the problem. If not, you have the more difficult task of trying to reduce the noise generated by the multiple systems within your Jeep, at source.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-05-28T01:44:35.177" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4932" PostTypeId="1" CreationDate="2015-05-28T18:29:46.470" Score="2" ViewCount="11808" Body="&lt;p&gt;I'm very new to walkies and radios, and I know next to nothing. My friends and I bought a box of Baofeng 888s radios (which apparently also go by quite a few other names and manufacturers) and I'm having trouble getting them to communicate with my walkie of another brand (Midland LXT650, specifically). The problem is, when they're on the same channel, neither one picks up any chatter from the other. The Baofeng works with the other ones of its model, and the midland one works with every run of the mill department store radios I've tried it with in the past. After researching, I found out about CTCSS and DCS; I'm pretty sure the privacy is the issue. Perhaps it's the default privacy for the baofeng models? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes, I can get the radios to receive odd sound from each other, but no voice. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realize this must be pretty vague, but if there is any advice or hint you can give me, I'd really appreciate it! Also, if I left out any important info, please let me know. Thanks!&lt;/p&gt;&#xA;" OwnerUserId="4760" LastEditorUserId="6113" LastEditDate="2016-02-08T00:02:05.297" LastActivityDate="2017-03-19T10:05:06.010" Title="Trouble communicating between Baofeng and Midland walkies" Tags="&lt;united-states&gt;&lt;baofeng&gt;&lt;tone-squelch&gt;&lt;frs&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4933" PostTypeId="2" ParentId="4932" CreationDate="2015-05-28T20:44:03.113" Score="0" Body="&lt;p&gt;Several things can prevent a radio from breaking squelch. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first thing I would do is to manually break squelch (with the &quot;monitor&quot; button), so that you can monitor the channel. If you can't hear anything, hear only static, or only a tone then you need to verify that the radios are set to the same mode, frequency and modulation. Both should be Narrowband FM buy default, but I'm not sure if they have other options because I don't own either of them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you can hear voice using the monitor function then it is just a matter of turning off all of the squelch features until you find the one that is affecting you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On a Yaesu I had the &quot;Battery Saver&quot; mode interfere with communication. It was set to 10 seconds, so it only monitored the channel every 10 seconds. If a broadcast happened in the middle, I wouldn't hear it at all, and even a long broadcast would chop off the first bit (up to 10 seconds worth). &lt;/p&gt;&#xA;" OwnerUserId="4207" LastActivityDate="2015-05-28T20:44:03.113" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="4934" PostTypeId="2" ParentId="3714" CreationDate="2015-05-29T12:03:00.070" Score="1" Body="&lt;p&gt;Seems like a good idea to me.  Using a crystal earpiece avoids inserting anything &quot;into&quot; the ear that worries MartinRH - at least no more than you would with Walkman earworms etc.&#xA;The reciever does not need to be tuneable, as you make the transmitter necklace tuneable.&#xA;The only limitation that I see to miniaturisation, is there needs to be some element which receives the signal.  Without an antenna this is usually the coil, so even if you can have a complete tuned cct with a crystal, I think you need to have a coil to act as antenna.&lt;/p&gt;&#xA;" OwnerUserId="1890" LastActivityDate="2015-05-29T12:03:00.070" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4935" PostTypeId="2" ParentId="4926" CreationDate="2015-05-29T14:05:28.227" Score="8" Body="&lt;p&gt;There isn't one. Why? Because it's not defined &lt;a href=&quot;https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.1677-1-200910-I!!PDF-E.pdf&quot;&gt;in the standard&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;#&quot; isn't the only symbol in common computer use which is not defined in Morse code. For example, Morse code can't distinguish upper and lower case letters. Nor does it have codes for any of &lt;code&gt;{*^&amp;amp;_&lt;/code&gt;. The reason is likely that Morse code is intended to be memorized and decoded by a human, and each additional code makes that harder. How much harder would it be if instead of the 26 basic letters, a little punctuation and a few prosigns, you had to learn 128 codes for the entire basic ASCII character set? Or, 113,021 codes to cover all of &lt;a href=&quot;http://en.wikipedia.org/wiki/Unicode#Versions&quot;&gt;Unicode 7&lt;/a&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's also not forget that Morse code predates ASCII by about 130 years and its intended application is sending telegrams.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course there are modern encodings which are more similar to modern computer technology. For example, PSK31 can encode all 127 characters of basic ASCII. And there are any number of digital modulations which just send arbitrary strings of bytes, so with a suitable encoding like UTF-8, you can encode any character in Unicode, just like a modern web page.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-05-29T14:05:28.227" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4936" PostTypeId="2" ParentId="1469" CreationDate="2015-05-31T07:44:16.323" Score="2" Body="&lt;p&gt;Yes you can try Nagoya with good results.  I was thinking you can also try a slim jim antenna found on ebay.  This antenna has high marks with unbelievible performance.&lt;/p&gt;&#xA;" OwnerUserId="4772" LastActivityDate="2015-05-31T07:44:16.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4937" PostTypeId="1" CreationDate="2015-06-01T13:29:25.340" Score="3" ViewCount="1506" Body="&lt;p&gt;I would like to know how to transmit a voice message from my PC by software, to my HT radios at a specific channel. My radios are Baofeng BF-A5.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you know of software to deal with it?&lt;/p&gt;&#xA;" OwnerUserId="4776" LastEditorUserId="76" LastEditDate="2015-06-01T19:28:42.847" LastActivityDate="2015-06-03T14:03:21.700" Title="How can I send a voice message from my PC to HT radios?" Tags="&lt;ht&gt;&lt;software&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4938" PostTypeId="1" AcceptedAnswerId="4943" CreationDate="2015-06-01T15:39:58.083" Score="23" ViewCount="50869" Body="&lt;p&gt;I don't have $500 for a radio scanner. If I know the few (analog) frequencies that I would like to listen to, I think one can use the Baofeng UV5R (which doesn't cost much). The only problem is that one accidentally can transmit with this and this isn't allowed unless one has a license. From watching some Youtube videos it seems like one maybe can set the transmitting frequency to the same FRS frequency. That way, if one accidentally, presses the transmit button, then one wouldn't accidentally talk to the police or something.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;My question is whether this is true?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;More generally, what is the best way to prevent accidental transmitting on the Baofeng UV5R?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;(I understand that the best way would be to not even have it, but I don't have money enough right now to buy an expensive scanner.)&lt;/p&gt;&#xA;" OwnerUserId="4777" LastEditorUserId="218" LastEditDate="2015-06-01T15:44:46.153" LastActivityDate="2019-08-17T23:42:34.493" Title="How can I avoid accidentally transmitting with a Baofeng UV-5R?" Tags="&lt;receiver&gt;&lt;baofeng&gt;" AnswerCount="8" CommentCount="3" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="4939" PostTypeId="1" AcceptedAnswerId="4986" CreationDate="2015-06-01T18:30:51.043" Score="2" ViewCount="407" Body="&lt;p&gt;I'm currently experiencing what I think is induced coupling on my ground line. Can someone explain how this is possible?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live on the third floor of an apartment block and my only grounding option is currently the third prong of an ac outlet. I was under the impression that any low freq noise on the ground line would dissipate into the earth, however this is not what I'm experiencing. Any idea why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm thinking perhaps there is some resistance on the ground-line and some rf and ac is taking a shorter path to my shack, instead of taking the longer route to the utility ground. I think this is happening because my apartment building doesn't have a ground rod in place and relies on the the utility companies ground, which is earthed who knows where.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an amp connected to my receiving radio and the utility ground I'm using at the moment is creating audible hum. I figure if I can use a quieter ground then this will improve the fidelity of any audio I want to amplify. Most of the interference is at 50hz (UK), which I guess is being conducted on the ground-line from my some of my neighbors apartments, although there's a lot from various other frequencies too. I plan on using some grounded coaxial cable connected to a rod outside with the intention of shielding any rf's from my hopefully quiet ground.&lt;/p&gt;&#xA;" OwnerUserId="4779" LastEditorUserId="76" LastEditDate="2017-07-09T17:33:05.780" LastActivityDate="2017-07-09T17:33:05.780" Title="Low frequency noise on ground line. Why?" Tags="&lt;rfi&gt;&lt;grounding&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="4940" PostTypeId="2" ParentId="4937" CreationDate="2015-06-01T19:27:20.130" Score="3" Body="&lt;p&gt;All you need to do this is the following components:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;A radio to transmit the message.&lt;/strong&gt; It doesn't have to be the same model as the HTs you want to receive the signal. In fact, it might be overall simpler and cheaper to choose a radio which has a built-in computer interface.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;A “sound card” for your computer&lt;/strong&gt;. It is possible to connect your computer's main audio output to your radio, but this is not to be preferred because you might transmit beeps or other incidental sound effects produced by your computer. Instead, get a “USB audio interface” or “USB sound card” to add an additional audio output to your computer. There are three options here:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Buy a standard USB audio interface and use a separate interface box to connect that to the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The interface box is needed both to adapt the pinouts and potentially to break ground loops or for sorts of electrical issues.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1b. However, some radios may have electrically compatible audio jacks that don't need any interface circuit.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Buy a USB audio interface designed for connecting to radios. These will be more expensive but have built-in isolation. For example, the &lt;a href=&quot;http://www.tigertronics.com/slusbmain.htm&quot; rel=&quot;nofollow&quot;&gt;Tigertronics SignaLink USB&lt;/a&gt; is a very popular model. (It is sometimes accused of having inherent design flaws limiting its performance, but I don't know the details.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some radios have built-in USB audio connections. However, these are likely to be high-end expensive models.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Software to play the message.&lt;/strong&gt; This can be any audio/music program, as long as it lets you select the output audio device to use rather than always using the system default device.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Note that all of this is the same equipment you would be using for some digital modes, such as APRS. In fact, I would strongly recommend that you &lt;strong&gt;look into using the same equipment that people have used for APRS&lt;/strong&gt;, as this is a very popular application for computers hooked to radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two caveats to that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;APRS stations sometimes use separate hardware to do the message encoding/decoding (a “TNC”). Look at setups that use a “software TNC” — you would use your audio player instead of the TNC software.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;APRS stations are often battery-powered. I assume that you're doing this from a fixed station; in which case note that line-powering both the radio and computer may introduce a ground loop issue that wouldn't otherwise be present. This is only a problem if you're using option (1b) above.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Finally, if you get all this set up, you've got all the hardware you need to start operating with APRS, and (if you use an all-mode radio) other digital modes! Check them out!&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-06-01T19:27:20.130" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4941" PostTypeId="2" ParentId="3729" CreationDate="2015-06-02T01:28:05.733" Score="2" Body="&lt;p&gt;According to Wikipedia (which is never wrong?), these devices implement IEEE 802.15.4, which defines among other things the frequencies upon which they operate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/IEEE_802.15.4&quot; rel=&quot;nofollow&quot;&gt;http://en.wikipedia.org/wiki/IEEE_802.15.4&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From that page, there are three radio bands those devices can use: 868-868.6MHz (Europe only), 902-928MHz (North America only) and 2400–2483.5MHz (Worldwide).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The IEEE 802.15.4 standard is licence-free.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As long as the device is not set to use the North America-only band, you should be good to go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do note that the 2400MHz band has quite a few other legitimate (also licence-free) users, such as IEEE 802.11 in various guises (WiFi), Bluetooth, and microwave ovens - in a 'noisy' environment you might want to try using the 868MHz band, if you have that option on your devices.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-06-02T01:28:05.733" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4942" PostTypeId="2" ParentId="4938" CreationDate="2015-06-02T02:39:38.317" Score="1" Body="&lt;p&gt;You can use software to set the channel frequencies individually. Change the channel type to split, and set the transmit offset to 0.000MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's one reference for this process:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://chirp.danplanet.com/issues/211&quot; rel=&quot;nofollow&quot;&gt;http://chirp.danplanet.com/issues/211&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2015-06-02T02:39:38.317" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4943" PostTypeId="2" ParentId="4938" CreationDate="2015-06-02T05:09:06.067" Score="23" Body="&lt;p&gt;It'll be easier just to buy a programming cable and use the free Chirp software to turn off transmit permanently.  I did this, and used my Baofeng as a receiver only before getting my licence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT - When I mean permanently, I mean the radio will not respond to the transmit key being pressed.  If you get your license in future, you can reenable this feature to turn the radio back into a transceiver.&lt;/p&gt;&#xA;" OwnerUserId="4784" LastActivityDate="2015-06-02T05:09:06.067" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4944" PostTypeId="1" CreationDate="2015-06-02T15:35:15.550" Score="3" ViewCount="411" Body="&lt;p&gt;The TS2000 has inbuilt AX.25 support. However, is it possible to use the TNC in a &quot;transparent&quot; mode so that I can view the on-air data without any decoding?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Upon basic searching, I came up with this page (&lt;a href=&quot;http://www.waterfunrental.com/K0SWI/REVIEW/KW/KW_TS2000/KENWOOD%202000%20ALL%20MODELS%20COMMENTS.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.waterfunrental.com/K0SWI/REVIEW/KW/KW_TS2000/KENWOOD%202000%20ALL%20MODELS%20COMMENTS.htm&lt;/a&gt;) which says that TS2000 does not support a &quot;transparent&quot; mode. Is it possible to see the on-air data in some other way?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&#xA;The real purpose is to try creating my own protocol and hence transmitting and receiving raw binary data. - My protocol does not use HDLC flags so I need the direct decoding of AFSK to binary and vice-a-versa.&lt;/p&gt;&#xA;" OwnerUserId="4539" LastEditorUserId="4539" LastEditDate="2015-06-02T18:49:16.487" LastActivityDate="2016-09-07T19:58:37.140" Title="Can I receive raw on-air data using Kenwood TS2000?" Tags="&lt;transceiver&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="4945" PostTypeId="2" ParentId="4867" CreationDate="2015-06-02T16:38:36.450" Score="2" Body="&lt;p&gt;When backpacking with others where regular radio contact is planned, I will typically clip my Yaesu FT-60 to the side of my pack in a way that positions the antenna higher than the top of my head and then use a hand speaker/mic clipped to the shoulder strap where I can easily reach it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to antennas, I pitched the rubber duck that came with my HT and bought a Diamond SRJ77CA 16&quot; antenna. That has made a huge difference in both transmitting and receiving, especially as you get farther apart. &lt;/p&gt;&#xA;" OwnerUserId="4786" LastActivityDate="2015-06-02T16:38:36.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4946" PostTypeId="2" ParentId="3855" CreationDate="2015-06-02T20:32:20.643" Score="1" Body="&lt;p&gt;Just to make it clear - if you're wondering why the directivity changes from one configuration to the other, there is no clear answer. The directivity of an antenna varies a lot, depending mostly on the shape of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're wondering why you have this particular link between directivity and gain, it is actually logical that you would find this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$G = E_{antenna} D$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $E_{antenna}$ is the antenna efficiency (you can look it up on wikipedia). If you have an omnidirectional antenna, you have a lower directivity, and thus a lower gain than for a directive antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This being said, you might also have a different antenna efficiency for those two frequencies, explaining a bigger gap than what you would obtain with only the directivity thing.&lt;/p&gt;&#xA;" OwnerUserId="4787" LastActivityDate="2015-06-02T20:32:20.643" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4948" PostTypeId="1" CreationDate="2015-06-02T23:53:07.577" Score="2" ViewCount="2241" Body="&lt;p&gt;On this quesiton: &lt;a href=&quot;https://ham.stackexchange.com/questions/4938/how-can-i-avoid-accidentally-transmitting-with-a-baofeng-uv-5r&quot;&gt;How can I avoid accidentally transmitting with a Baofeng UV-5R?&lt;/a&gt; I learned how one can avoid accidentally transmitting on a Baofeng UV5R. This can be done using software by setting the trasmit frequency to 0 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My next question is: How can this be done manually?&lt;/p&gt;&#xA;" OwnerUserId="4777" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-06-11T14:47:42.293" Title="How to set trasmit freq. on Baofeng UV5R to 0MHz manually" Tags="&lt;baofeng&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4949" PostTypeId="2" ParentId="4937" CreationDate="2015-06-03T07:26:59.100" Score="0" Body="&lt;p&gt;You haven't really specified anything along the lines of what the purpose of this is, what you hope to achieve, distance communicating, etc., but if you have any 70 cm repeaters in the area that have &lt;a href=&quot;http://www.echolink.org/&quot; rel=&quot;nofollow&quot;&gt;EchoLink&lt;/a&gt; enabled, you can do it that way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EchoLink allows any digital device (computer, mobile phone, tablet etc) to transmit voice via the Internet to the EchoLink repeater which then rebroadcasts it as a radio wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an EchoLink app on my phone.  I can dial into my local repeater and hear myself talking on my radio.&lt;/p&gt;&#xA;" OwnerUserId="4792" LastEditorUserId="76" LastEditDate="2015-06-03T14:03:21.700" LastActivityDate="2015-06-03T14:03:21.700" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4950" PostTypeId="2" ParentId="3673" CreationDate="2015-06-03T16:42:59.343" Score="2" Body="&lt;p&gt;It's just the default setting. You can change it either through the menus or with the software, depending on which model radio you have.&lt;/p&gt;&#xA;" OwnerUserId="4786" LastActivityDate="2015-06-03T16:42:59.343" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4951" PostTypeId="1" AcceptedAnswerId="4956" CreationDate="2015-06-04T13:13:18.313" Score="11" ViewCount="22918" Body="&lt;p&gt;From what I've seen, there are generally two ways to power a mobile radio:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Positive lead to battery, negative lead grounded to chassis&lt;/li&gt;&#xA;&lt;li&gt;Both positive and negative leads to battery&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I know that antennas should be grounded to the chassis, but what about the radio itself? There must be some electrical difference, but I'm not sure what it is and I've seen a lot of contradictory information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the &quot;correct&quot; way to do this? The vehicle is a 2012 Honda Accord.&lt;/p&gt;&#xA;" OwnerUserId="160" LastEditorUserId="76" LastEditDate="2016-10-29T18:06:15.483" LastActivityDate="2021-04-22T20:33:43.423" Title="Should I ground my radio to the chassis or battery for a mobile install?" Tags="&lt;mobile&gt;&lt;grounding&gt;&lt;dc-power&gt;" AnswerCount="5" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4953" PostTypeId="1" AcceptedAnswerId="4958" CreationDate="2015-06-04T14:07:56.980" Score="0" ViewCount="67" Body="&lt;p&gt;Does wireless communications like wifi, where different clients get different data, use different frequencies for each client? Or do they use the same frequency, but with time-divison multiplexing and encryption, so that no client can understand what was meant for another client?&lt;/p&gt;&#xA;" OwnerUserId="4798" LastActivityDate="2015-06-05T06:14:16.877" Title="How does wireless communication like wifi connect to different clients?" Tags="&lt;wifi&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2015-06-15T12:14:00.847" ContentLicense="CC BY-SA 3.0" />
  <row Id="4954" PostTypeId="1" CreationDate="2015-06-04T14:22:44.173" Score="3" ViewCount="676" Body="&lt;p&gt;I am looking to make a simple receive antenna from some wire, and I have some questions about resonance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being that this wire can only be so long (about 3 meters maximum, as it must fit inside my apartment), would cutting it to 2.5 meters be beneficial so it would be at an even harmonic of the ham bands (160 m, 80 m, 40 m, 20 m, 10 m, 1.25 m, and close to 33 cm), or would it be better to just cut it as long as possible?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, if I make it a dipole style antenna, does the other element have to run in the opposite direction of it, or can it run parallel to it?  Does it even have to be in the same plane, or could I run it along another wall?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My receiver is the RTL-SDR with a Ham-It-Up upconverter.&lt;/p&gt;&#xA;" OwnerUserId="4799" LastEditorUserId="76" LastEditDate="2015-06-04T19:07:49.150" LastActivityDate="2015-06-04T19:07:49.150" Title="Receive antenna design for a small apartment" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4955" PostTypeId="2" ParentId="4954" CreationDate="2015-06-04T17:06:55.933" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Would cutting it to 2.5 meters be beneficial so it would be at an even harmonic of the ham bands&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, for most of the bands you've listed. Dipoles are resonant around 1/2λ and odd harmonics thereof: 3/2λ, 5/2λ, 7/2λ, etc. In other words, the dipole needs to be a half-wavelength &lt;em&gt;or longer&lt;/em&gt; to be resonant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But do not fret. A dipole that's too short just means a poor match to the receiver, which may or may not be an issue. See &lt;a href=&quot;https://ham.stackexchange.com/questions/382/what-is-the-relationship-between-swr-and-receive-performance&quot;&gt;What is the relationship between SWR and receive performance?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Also If I make it a dipole style antenna, does the other element have to run in the opposite direction of it, or can it run parallel to it&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The two halves can not be parallel. If you just had two parallel halves of a dipole, you'd have a &lt;a href=&quot;http://en.wikipedia.org/wiki/Twin-lead&quot; rel=&quot;nofollow noreferrer&quot;&gt;twin-lead transmission line&lt;/a&gt;. Transmission lines are designed to not radiate or receive, so they make horrible antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the other half doesn't need to be exactly opposite, either. They just need to go generally in different directions. See the &lt;a href=&quot;http://en.wikipedia.org/wiki/Inverted_vee_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;inverted vee antenna&lt;/a&gt; for a very common way of building a dipole. The arms of the dipole don't need to be straight, either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, my advice for someone in your situation is this: Wire is cheap. Don't fret. Try science. Any HF antenna you try to fit inside is going to be a compromise solution because there simply isn't enough room. Any indoor antenna is also going to pick up a lot of noise from electronics in the house. Theoretical antenna models don't account for that. So just build an antenna, get on the air, and experiment until you find something that works well in your specific environment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-06-04T17:06:55.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4956" PostTypeId="2" ParentId="4951" CreationDate="2015-06-04T17:27:50.797" Score="7" Body="&lt;p&gt;There are two reasons for the advice to run direct to the battery:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Minimize the &lt;em&gt;area enclosed by the power connections&lt;/em&gt;. This reduces both interference picked up by the wiring, and inductance (which is undesirable in power supply connections).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Minimize resistance. A radio can be a fairly heavy load as car &lt;em&gt;accessories&lt;/em&gt; go, so you want to avoid any voltage drop you can, and the chassis may not give you the best conduction to the battery.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Neither of these is a reason to wire specifically to the battery per se, only to avoid using a completely different conductor (the chassis). According to K0BG.com, a site dedicated to mobile amateur radio, &lt;a href=&quot;http://www.k0bg.com/wiring.html&quot; rel=&quot;noreferrer&quot;&gt;some modern cars have electrical systems in which you shouldn't wire direct to the battery terminals&lt;/a&gt;, for example:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The use of these sophisticated subsystems have necessitated the&#xA;  relocation of the ELD to the negative lead of the SLI battery as shown&#xA;  at right (surrounding the battery ground lead), and below right&#xA;  (incorporated in the battery negative connector). The photos are of a&#xA;  2014 Nissan Titan, and 2013 Honda Accord respectively, but other makes&#xA;  are similar such as Ford's F150 shown below at left.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Ford's Battery Monitoring SystemIt should be obvious that transceiver&#xA;  ground connections cannot be made directly to the battery as&#xA;  recommended in the past, as doing so would bypass the BMS. Thus in the&#xA;  examples shown, the negative lead would be attached to the battery's&#xA;  chassis connection point (Titan), or on the ground side of the ELD&#xA;  (Honda).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(Note that the reference to connecting to the chassis is to the point at which the &lt;em&gt;battery&lt;/em&gt; is connected to the chassis, not elsewhere on the chassis.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The article goes on to say, after discussing other possible complications:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The bottom line here is, if in doubt, read your Service Manual, or contact your dealer's service department before undertaking your installation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To summarize:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Learn how your vehicle's electrical system works — specifically, where it is safe to tap for a high-current accessory.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Run a dedicated, fused 2-conductor power cable between that connection point and your transceiver.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-06-09T00:08:31.097" LastActivityDate="2015-06-09T00:08:31.097" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4957" PostTypeId="2" ParentId="3668" CreationDate="2015-06-04T18:40:21.843" Score="0" Body="&lt;p&gt;If it were me, I would want something self-contained.  This example has a repeater, controller and a gateway (this was a potable networkable single site solution for public safety) in a 6u rolling rack chassis we, BridgeCom Systems made.  This would easily house a repeater or mobiles, small battery and all your cables, radios, etc (to a point, lol!).  This would make it easy to move it from one location to another. This could cost as low as $400 and up depending on specs. I see your other questions have been answered.  BridgeCom Systems, Inc (Disclosure, I work at BridgeCom Systems) has answered this question at &#xA;&lt;a href=&quot;http://www.bridgecomsystems.com/collections/bcr-repeaters/products/rolling-case&quot; rel=&quot;nofollow&quot;&gt;http://www.bridgecomsystems.com/collections/bcr-repeaters/products/rolling-case&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="4788" LastEditorUserId="4788" LastEditDate="2015-07-02T13:43:23.313" LastActivityDate="2015-07-02T13:43:23.313" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="4958" PostTypeId="2" ParentId="4953" CreationDate="2015-06-05T06:14:16.877" Score="0" Body="&lt;p&gt;Wifi is packet-based TDMA/CSMA with all users for a given access point using the same frequency.  &lt;/p&gt;&#xA;" OwnerUserId="609" LastActivityDate="2015-06-05T06:14:16.877" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4960" PostTypeId="2" ParentId="137" CreationDate="2015-06-05T21:13:40.860" Score="2" Body="&lt;p&gt;There are also prohibitions against using 462.650, 467.650, 462.700 and 467.700 MHz north of Line A or east of Line C. Note that these are GMRS frequencies (not covered by a regular amateur license). On most GMRS handsets, these frequencies are referred to as &quot;channel 19&quot; and &quot;channel 21&quot;, respectively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=operations&amp;amp;id=general_mobile&quot; rel=&quot;nofollow&quot;&gt;http://wireless.fcc.gov/services/index.htm?job=operations&amp;amp;id=general_mobile&lt;/a&gt; for a description of this restriction. I can't find any specific mention of this in Part 95, but it's something that you must agree to when applying for a GMRS license.&lt;/p&gt;&#xA;" OwnerUserId="4801" LastActivityDate="2015-06-05T21:13:40.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4961" PostTypeId="1" AcceptedAnswerId="4963" CreationDate="2015-06-06T02:22:54.657" Score="9" ViewCount="28309" Body="&lt;p&gt;I tested and passed my Technician's test on Thursday, June 4, 2015. Approximately how long will my license take to appear in the FCC database?&lt;/p&gt;&#xA;" OwnerUserId="4803" LastEditorUserId="76" LastEditDate="2015-06-08T16:53:45.200" LastActivityDate="2019-03-28T05:32:20.847" Title="When will my new license appear in the FCC database?" Tags="&lt;license&gt;&lt;fcc&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4962" PostTypeId="2" ParentId="1469" CreationDate="2015-06-06T23:16:06.663" Score="4" Body="&lt;p&gt;I also have a couple of Baofeng HTs and little budget to work with, and I have 2 go-to antennas and a couple others I use on occasion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The one I would recommend is a &lt;a href=&quot;http://www.eham.net/reviews/detail/1839&quot; rel=&quot;nofollow&quot;&gt;Comet SMA(in my case, BNC with an adaptor)-24&lt;/a&gt;. Performance on 2 meters is similar to a plain 1/4 wave vertical I made out of a bit of wire and a BNC connector, but the Comet's much less awkward than my homebrew and seems more durable. Its performance on 440 is nothing to write home about, but is still significantly better than the factory duck or the 2m 1/4 wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have no personal experience with the Nagoya antennas mentioned here by others, but from what I've read there are quite a few knockoffs floating around Amazon and eBay, so buyer beware. If it costs less than $20-30, it's almost certainly a knockoff. That being said, I have a knockoff Harvest RH-770, which has a similar Nagoya equivalent (NL-770), and it performs even better on 2m than the Comet or the homebrew 1/4 wave, but it's only so-so on 440 and it's awkward and delicate so I'd avoid it as an only antenna because when it inevitably breaks, you're in trouble.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Though it's not directly applicable to your requirements because it's not handheld, I'll mention my other go-to antenna, an &lt;a href=&quot;http://www.eham.net/reviews/detail/9892&quot; rel=&quot;nofollow&quot;&gt;N9TAX dual-band roll-up slim jim&lt;/a&gt; with 16' of coax. This one I hang in a tree or from whatever I can find, as it's happiest with at least 6 feet of free space around it. The higher the better, as it has a low take-off angle, and the results with it 20' in a tree are nothing short of astounding compared to any handheld antenna, both on 2m and on 440. It rolls up small enough to fit in a coat pocket.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each of these can be had for about \$30 and are available with an SMA connector to directly fit your Baofeng radio, but if you want to use more than one I'd advise getting the BNC versions and spend another \$5 for an SMA/BNC adapter so they can be swapped quickly and easily without too much wear and tear to the radio's SMA connector. All 3 of them and an adaptor is still under your \$100 budget, and gives you options for most portable (Comet), most gain (N9TAX), and compromise (RH-770) situations.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastEditorUserId="4452" LastEditDate="2015-06-06T23:21:26.943" LastActivityDate="2015-06-06T23:21:26.943" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4963" PostTypeId="2" ParentId="4961" CreationDate="2015-06-06T23:33:54.063" Score="10" Body="&lt;p&gt;Congratulations!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This depends on the folks that gave you your test (Volunteer Examiners, or VEs), the organization they are working with (ARRL?), and the FCC (if you're in the US). A bottleneck anywhere can make it take up to a couple weeks, but likely you'll have a call sign about a week after the VEs submit your paperwork. Your best bet would be to ask them, though, as they will know if there are local factors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can &lt;a href=&quot;http://wireless2.fcc.gov/UlsApp/UlsSearch/searchLicense.jsp&quot; rel=&quot;noreferrer&quot;&gt;search the FCC license database&lt;/a&gt; with your name to see if you've been assigned a call sign. I have no idea how long it will take for them to (presumably) email your license, as they no longer mail out paper licenses like I got, but once you have a call sign you're legal to operate.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2015-06-06T23:33:54.063" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="4964" PostTypeId="1" AcceptedAnswerId="4965" CreationDate="2015-06-08T03:12:35.570" Score="3" ViewCount="221" Body="&lt;p&gt;From all my reading online it seems LMR-240 and RG-8X are only about .002 inches apart in diameter and most connectors/tools that support one support the other. I'm looking for a crimper and stripper for some LMR-240 I plan on buying and have found a lot that say they will do RG-8X, but fewer that mention LMR-240 specifically. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will RG-8X tools work on LMR-240?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I am considering &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00HDPA4XI&quot; rel=&quot;nofollow&quot;&gt;this crimper&lt;/a&gt; (as well as &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B0012YO78Y&quot; rel=&quot;nofollow&quot;&gt;this other one&lt;/a&gt;) and &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00HDPIG4C&quot; rel=&quot;nofollow&quot;&gt;this stripper&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="63" LastEditorUserId="218" LastEditDate="2015-06-08T11:38:41.587" LastActivityDate="2015-06-08T11:59:10.687" Title="Can I use an RG-8X crimper/stripper on LMR-240?" Tags="&lt;coaxial-cable&gt;&lt;connectors&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4965" PostTypeId="2" ParentId="4964" CreationDate="2015-06-08T11:59:10.687" Score="2" Body="&lt;p&gt;RG-8X is very close to LMR-240, and the two are usually compatible. But the crimpers you list are for RG-&lt;em&gt;8&lt;/em&gt;, not RG-&lt;em&gt;8X&lt;/em&gt;. The two are not the same, not even close. RG-8 is roughly twice the diameter of RG-8X.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To determine the crimper you need, you'll want to find the datasheet for the connectors you will be using. For example, look at &lt;a href=&quot;http://www.amphenolconnex.com/downloads/dl/file/id/4671/172135_customer_drawing.pdf&quot; rel=&quot;nofollow&quot;&gt;Amphenol Connex 172135&lt;/a&gt;. This is described as an &quot;N crimp plug for LMR-240 / RG-8/X cable&quot;. It specifies crimp sizes of 0.255&quot; and 0.100&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Strippers are usually adjustable, so a 0.002&quot; difference will not be a problem. But again, you want tools for RG-&lt;em&gt;8X&lt;/em&gt;, not RG-&lt;em&gt;8&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-06-08T11:59:10.687" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4966" PostTypeId="2" ParentId="4961" CreationDate="2015-06-09T10:07:02.043" Score="0" Body="&lt;p&gt;The processing times will probably vary. It took 1 month for my call to appear on the FCC website. (My exam was conducted by the Volunteer Examineers from Yokohama, Japan)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the e-mail address field in your FCC ULS entry or &lt;a href=&quot;http://www.arrl.org/files/file/ncvec605-3.pdf&quot; rel=&quot;nofollow&quot;&gt;NCVEC QUICK-FORM 605&lt;/a&gt; is filled-up, then an e-mail notification will be sent. The NCVEC QUICK-FORM 605 is the form you fill up prior to taking the exams with your chosen VE.&lt;/p&gt;&#xA;" OwnerUserId="1761" LastActivityDate="2015-06-09T10:07:02.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4967" PostTypeId="1" CreationDate="2015-06-09T17:03:03.050" Score="2" ViewCount="1050" Body="&lt;p&gt;Goal&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am trying to setup an XPR-8300 MotoTRBO repeater ultimately with the goal of joining DMR-MARC.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reasoning&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My area does not have a repeater that's reachable on handhelds.  I got a fairly cheap XPR-8300 off a guy I know.  Not the latest and greatest gear, but should do the job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specific Asks ( The known unknowns ):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where do I even get programming software for the XPR-8300?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone have a preference in what sort of duplexer I should use on this repeater?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone have any suggestions on cheap but affective antennas or antenna suppliers?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Same as above for lightning arresters and antenna supports.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And any other suggestions / warnings ( unknown unknowns )?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've not found too much specific information on existing DMR repeaters on the google.  But if you have a link you know of, or can out google me, I'd love to read the information.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="4820" LastActivityDate="2015-06-09T17:03:03.050" Title="Tips on how to setup a MOTOTRBO XPR-8300 Repeater for DMR Ham operation?" Tags="&lt;digital-modes&gt;&lt;repeater&gt;" AnswerCount="0" CommentCount="2" FavoriteCount="1" ClosedDate="2015-06-15T12:20:23.140" ContentLicense="CC BY-SA 3.0" />
  <row Id="4968" PostTypeId="1" CreationDate="2015-06-09T18:16:05.577" Score="2" ViewCount="570" Body="&lt;p&gt;I have a digital data signal with frequency in the 434-438 MHz band. The data is BFSK modulated with frequency deviation of 9.6 khz, baud rate of 1200 bps. The bandwidth is 25 Khz.&#xA; Is there a way I can receive the above signal on Kenwood TS-2000. The maximum deviation of TS2000 on BFSK mode is 850 Hz. But can I receive the data by using the TS200 in FM mode ? Is the baud rate of 1200 bps supported by TS2000 ?&lt;/p&gt;&#xA;" OwnerUserId="4397" LastEditorUserId="873" LastEditDate="2015-06-10T17:30:42.517" LastActivityDate="2018-02-28T05:07:40.013" Title="Receiving BFSK on Kenwood TS2000 transceiver" Tags="&lt;digital-modes&gt;&lt;kenwood&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4970" PostTypeId="1" AcceptedAnswerId="4997" CreationDate="2015-06-09T20:27:33.260" Score="5" ViewCount="188" Body="&lt;h2&gt;You buy a &quot;20dBi omni&quot; Wifi antenna, operating in the 2.4-2.5GHz band. You note that the expected range is not achieved from this 300mm long antenna. What could be wrong?&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Can someone please tell me whether may approach is correct&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;λ(min) = 300/2500 = 0.12m = 120mm&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dipole length is therefore = 300mm/120mm = 2.5λ =&gt; 0.5λ (neglect '2' since its just a full revolution on smith chart??)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;driven element have  length of = 0.5λ/2 = 0.25λ&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Actual gain of the antenna = 300mm/(0.25λ) = 10dB, therefore antenna in question is not 20dB and therefore thats why doesnt meet expected range. - is this the right way to calculate gain?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;-Thanks.&lt;/p&gt;&#xA;" OwnerUserId="4823" LastEditorUserId="13" LastEditDate="2015-06-15T12:17:06.833" LastActivityDate="2015-06-15T12:17:06.833" Title="Theoretical Wifi antenna not working for the expected range" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;wifi&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4971" PostTypeId="2" ParentId="4970" CreationDate="2015-06-09T23:35:38.657" Score="1" Body="&lt;p&gt;Given the size (30cm) and assuming it is omnidirectional, it is probably a collinear array.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this type of antenna, claiming 20dBi gain is quite exaggerated. You would expect something around 6 to 8 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example of 2.4GHz collinears:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.nodomainname.co.uk/Omnicolinear/2-4collinear.htm&quot; rel=&quot;nofollow&quot;&gt;A 2.4Ghz Vertical Collinear Antenna for 802.11 Applications&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A 20dBi gain is expected from a directional antenna (&quot;cantenna&quot;, helical, patch array), not omni. &lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2015-06-09T23:35:38.657" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4972" PostTypeId="1" CreationDate="2015-06-10T00:25:59.417" Score="6" ViewCount="3862" Body="&lt;p&gt;Has there been any success in transmitting two simultaneous FM signals? I am assuming if the phase is correct, and the signals are identical, it would be possible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That would be really nice if newer repeaters could find a way to broadcast two signals on the same frequency from two different locations, giving extended coverage without sacrificing more coordinated frequencies. RX is already solved with voting receivers, but I haven't heard much on the TX end.  &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2018-07-15T00:03:32.233" Title="Is it possible to have 2 FM transmitters on the same frequency?" Tags="&lt;repeater&gt;&lt;repeater-coverage&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4973" PostTypeId="2" ParentId="4972" CreationDate="2015-06-10T01:34:52.923" Score="1" Body="&lt;p&gt;If you transmit the same FM signal from 2 locations, the receiver will experience a similar effect as FM multipath (when a single FM transmission arrives at the receiver from different paths, mainly due to reflection of the signal). The result is normally a very distorted audio signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Single frequency networks&lt;/em&gt; (SFN) is the term used for multiple repeaters on the same frequency. SFN is possible and is actually used with OFDM transmissions such as digital TV. But, as stated above, it is not possible for FM transmissions.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2015-06-10T01:34:52.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4974" PostTypeId="1" CreationDate="2015-06-10T04:08:15.493" Score="2" ViewCount="273" Body="&lt;p&gt;I want to ask something about the compatibility issue of the sub-1Ghz radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I am using two different RF chips (such as TI's cc1120 and Silicon Labs' si4432; both have FSK modulation), can they communicate with each other?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;update 2015-06-12 (more details)&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have read the datasheets (however I am not a professional communication engineer, so I cannot quite understand all the details...).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, both cc1120 and si4463 have GFSK modulation, they both support the same frequency range, they both can hop frequency in several tens of us. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some chip support FEC and digital encoding, but for compatibility's sake, these features can be disabled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have searched the internet, however haven't found someone do this kind of experiments. Do you guys know someone who has experiences on this? Thanks.&lt;/p&gt;&#xA;" OwnerUserId="4825" LastEditorUserId="4825" LastEditDate="2015-06-12T03:31:07.377" LastActivityDate="2015-06-12T03:31:07.377" Title="Sub-1Ghz radio compatibility" Tags="&lt;digital-modes&gt;&lt;uhf&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4975" PostTypeId="1" CreationDate="2015-06-10T06:44:08.833" Score="4" ViewCount="164" Body="&lt;p&gt;I am doing research on how SSN-like parameters affect HF radio signals. As I can see, effective SSN is a parameter that is derived from SSN or using other parameters. Does anyone know how to calculate effective SSN?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, this file has some parameters: &lt;a href=&quot;ftp://ftp.swpc.noaa.gov/pub/latest/DSD.txt&quot; rel=&quot;nofollow&quot;&gt;ftp://ftp.swpc.noaa.gov/pub/latest/DSD.txt&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;ref &lt;a href=&quot;http://spawx.nwra.com/spawx/ssne.html&quot; rel=&quot;nofollow&quot;&gt;http://spawx.nwra.com/spawx/ssne.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4826" LastEditorUserId="76" LastEditDate="2015-06-10T17:39:46.780" LastActivityDate="2018-10-09T00:45:30.090" Title="Calculating effective SSN (sunspot number)?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;sunspots&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4976" PostTypeId="1" CreationDate="2015-06-10T09:46:53.967" Score="1" ViewCount="153" Body="&lt;p&gt;I'm using an antenna that works in the range from 1 GHz to 3 GHz. I want to match impedances between a cable from the transmitter and the input amplifier and from the output amplifier and the cable to the receiver to get the maximum power and the lossless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found that there is a technique called Bode-Fano equations when you use a wide range of frequencies (1GHz to 3GHz) instead only one frequency, but I don't understand it how could I used it. Can you help me?&lt;/p&gt;&#xA;" OwnerUserId="4827" LastActivityDate="2015-08-11T18:39:53.553" Title="Wideband impedance matching" Tags="&lt;antenna&gt;&lt;impedance&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4977" PostTypeId="2" ParentId="4974" CreationDate="2015-06-10T12:11:21.573" Score="1" Body="&lt;p&gt;In general, you have to read the datasheets in detail to know. Just that they &quot;have FSK modulation&quot; is not enough information to know if they are compatible. FSK is merely a modulation technique, not a complete and precise definition of a protocol. In addition to the RF modulation used, integrated transceivers typically include some digital encoding, FEC, and so on which again must be compatible on both ends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your objective is compatibility among integrated solutions, then it's probably easiest to either:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;stick to one product line of one manufacturer, or&lt;/li&gt;&#xA;&lt;li&gt;look for devices designed to comply with some standard protocol, like ZigBee, WiFi, Bluetooth, etc.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-06-10T12:11:21.573" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4979" PostTypeId="1" CreationDate="2015-06-10T17:33:08.450" Score="4" ViewCount="778" Body="&lt;p&gt;I just got my license a week ago. Installed a new VHF/UHF radio in my car and everything seems to be working great. I've been heard at distant locations and picked up signals from repeaters that are way beyond where I expected to reach. However after programming my radio, I noticed that one VHF frequency in particular, 147.000 MHz, got quite frequent interference (by &quot;interference&quot; what I really mean is that when I leave it in memory scan mode, it often stops on that frequency, picking up a signal with no information in it for a few seconds, and then moves on). I've tried to adjust squelch settings and that doesn't help at all, so it really seems to be detecting something. (Unfortunately avoiding this frequency is not an option, as it is a local repeater frequency.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After about a week I realized a pattern - this happened either whenever my cell phone received a message or whenever the lights lit up on the phone (due to me pressing a button, for example). So it definitely seems like the cell phone is at fault here. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now I'm looking at ways of mitigating the interference from the phone. Granted, I'm not even sure what should be causing the interference. My first instinct is to add a low-pass filter at the location where the antenna wire hooks into the radio, but it seems like what I'd be looking for is something on the order of a 600MHz cutoff low-pass filter and it doesn't seem like ferrite chokes exist at that high frequency (without attenuating the UHF or VHF signal as well).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, I guess it could be some other signal from the phone causing interference, but the pattern seems to suggest it is the RF from the phone (which I believe will either be on the order of 800MHz or 2GHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I imagine I can't be the first person to experience this problem - any advice for a new ham? I'm really just not sure where to start trying to filter this signal - I've looked through catalogs but come up empty on any kind of ferrite core that meets my need.&lt;/p&gt;&#xA;" OwnerUserId="4830" LastEditorUserId="4830" LastEditDate="2015-06-10T18:02:57.637" LastActivityDate="2015-07-16T14:30:44.857" Title="Cellular VHF Interference" Tags="&lt;rfi&gt;&lt;filter&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="4980" PostTypeId="1" CreationDate="2015-06-11T06:40:49.200" Score="3" ViewCount="947" Body="&lt;p&gt;I would like to construct the following &lt;a href=&quot;http://zpostbox.ru/ham_radio_sw_receiver.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;receiver&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JjDDU.gif&quot; alt=&quot;ham-radio&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a fair knowledge about a receiver building blocks. I have previously build small receivers.&lt;br&gt;&#xA;In the description it say:  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The local oscillator ... generates an oscillations with a frequency&#xA;  twice lower than the frequency of received signals.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;How can that be possible and why it is needed?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="786" LastActivityDate="2018-12-05T07:46:05.113" Title="&quot;Local oscillator generates a frequency twice lower than received signals&quot;. Why and how does it work?" Tags="&lt;receiver&gt;&lt;oscillator&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4981" PostTypeId="1" CreationDate="2015-06-11T12:25:29.070" Score="1" ViewCount="136" Body="&lt;p&gt;I have heard that stacking two or more antennas help in increasing the reception gain. Will this be true for transmission? For example, in transmission using double stacked yagis, wouldn't each antenna in the stack receive half of the power fed to the stack?&lt;/p&gt;&#xA;" OwnerUserId="4831" LastEditorUserId="76" LastEditDate="2015-12-15T23:41:15.173" LastActivityDate="2015-12-15T23:41:15.173" Title="Query about double stacked circular polarized yagis" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4982" PostTypeId="1" AcceptedAnswerId="4987" CreationDate="2015-06-11T12:49:26.893" Score="3" ViewCount="5398" Body="&lt;p&gt;I've currently got a long-wire antenna (made from 24 ga. wire recovered from CAT-5) running to a receive only MW/HF radio. It is hung from a tree bough down to a window and looks approximately like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/1uBUH.jpg&quot; alt=&quot;Approximate configuration of my long-wire antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have seen other configurations of wire antennas that recommend a &quot;right-angle&quot; configuration like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/cE3Om.jpg&quot; alt=&quot;Allegedly better configuration of long-wire antenna&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the latter more likely to yield better reception? Does it really matter for receive-only?&lt;/p&gt;&#xA;" OwnerUserId="1097" LastActivityDate="2016-03-26T07:01:21.710" Title="Most effective placement of receive-only long wire antenna?" Tags="&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4983" PostTypeId="2" ParentId="4981" CreationDate="2015-06-11T14:43:09.193" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I have heard that stacking two or more antennas help in increasing the reception gain. Will this be true for transmission? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes! Electromagnetism as it applies to typical antennas has a property called &lt;strong&gt;reciprocity&lt;/strong&gt;, which says that everything works the same when you reverse the directions of motion of the waves (or reverse time, equivalently). Transmission and reception are always symmetrical, as far as the antenna's concerned.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For example, in transmission using double stacked yagis, wouldn't each antenna in the stack receive half of the power fed to the stack?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, but that's okay; all of the power is still being transmitted. If the goal here were to feed more total power in, you could do that by using a bigger amplifier instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The benefits of an antenna array of any sort are, largely, &lt;em&gt;not&lt;/em&gt; because it is able to gather or emit more power than it would otherwise. Rather, it is because the power is more focused in the desired direction — the array has more gain than the individual antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This occurs because the elements of the stacked antenna array are transmitting in phase, so as long as their distances to the receiver are equal — i.e. the array is perpendicular to the direction to the receiver — the signals add up. And they add up to &lt;em&gt;more&lt;/em&gt; than the power &lt;em&gt;in that direction&lt;/em&gt; for a single antenna, because there are many other directions in which they cancel out instead, saving that wasted power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, the array has gain in the direction perpendicular to it. The effect of the individual antennas being Yagis, rather than more omnidirectional antennas, is just to add their own gain; maximum gain in a single direction is obtained by making sure the Yagis' individual beam directions are exactly perpendicular to the line of the array.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-06-11T14:43:09.193" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4984" PostTypeId="2" ParentId="4948" CreationDate="2015-06-11T14:47:42.293" Score="2" Body="&lt;p&gt;This cannot be done manually. The UV-5R does not a allow you to type in channel frequencies outside of the range it is set to.&lt;br&gt;&#xA;So when you program a channel by going into frequency mode - type in the receive frequency 146910 for 146.910 and go to menu item 27 select the memory number you want to save 000 through 127 hit menu again to save the receiving freq. Exit the menu type in or scroll to the transmit frequency. This is where you cannot go beyond the range set for your UV-5R. This range can be changed in software but not through the radio interface. If you type in a number that is outside the range it will just cancel and go back to the number you were on. If you are at the lowest number in the range and hit the down arrow it will wrap up to the highest number in the range. &lt;/p&gt;&#xA;" OwnerUserId="4834" LastActivityDate="2015-06-11T14:47:42.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4985" PostTypeId="2" ParentId="2074" CreationDate="2015-06-11T14:56:57.283" Score="3" Body="&lt;p&gt;No the UV-5R does have a programming cable but it does not do any more that retrieve/store information to the radio. It is possible to build a small device that will listen to the audio output of the radio, send audio to the radio and enable transmit. This however won't allow you to change the frequency on the radio, or any settings &quot;live&quot; to accomplish what you've asked.&lt;/p&gt;&#xA;" OwnerUserId="4834" LastActivityDate="2015-06-11T14:56:57.283" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="4986" PostTypeId="2" ParentId="4939" CreationDate="2015-06-11T15:43:05.790" Score="1" Body="&lt;p&gt;This sounds like a basic ground loop problem. Make sure you don't have multiple paths to ground. Grounding every single piece of equipment, and the antenna sounds like it might be a good and safe idea but is not really good practice. Try several methods of consolidating your grounding method.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We probably need more details but I would guess if you're in the 3rd floor of an apartment you're antenna is probably not outside, or it's at least not outside while you are not operating. In this scenario my guess is that you really don't need a ground for lightning or RF reasons. The electrical ground that's part of the third prong on your electrical cord is probably sufficient. If your receiver doesn't use any high voltages it may not even need the electrical ground. You could try bypassing that and just use the Amp ground and bond the chassis grounds together.&lt;br&gt;&#xA;A basic guide to grounding can be found all over the internet. Here's the ARRL version: &lt;a href=&quot;http://www.arrl.org/grounding&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/grounding&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I should also add that you should use common sense and I take no responsibility if something goes wrong since I do not know your whole setup I may be missing something crucial that would have changed this advice.&lt;br&gt;&#xA;KISS (Keep It Simple Stupid!) Something a professor told me constantly.&lt;/p&gt;&#xA;" OwnerUserId="4834" LastActivityDate="2015-06-11T15:43:05.790" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4987" PostTypeId="2" ParentId="4982" CreationDate="2015-06-11T15:45:07.293" Score="4" Body="&lt;p&gt;If the antenna is sloped upwards towards the end of wire, chances are it works as an effective backbeam. Ie. It receives signals better from opposite direction. This can be enhanced by dropping wire vertically over the branch to the ground . That flat height is ideal for antenna that is purposed to receive as well from front and back. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Naturally the actual pattern will change a lot according to the length of wire and received frequency. At some point antenna will behave omnidirectional, at some point it receives better from the sides of wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For all practical purposes a slight angle doesn't matter anything. &lt;/p&gt;&#xA;" OwnerUserId="4837" LastEditorUserId="4837" LastEditDate="2015-06-11T15:52:29.193" LastActivityDate="2015-06-11T15:52:29.193" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="4988" PostTypeId="2" ParentId="4980" CreationDate="2015-06-11T19:22:33.857" Score="2" Body="&lt;p&gt;Mixing products from the oscillator.&#xA;Best way is to use the oscillator on a higher frequency.&#xA;Example: receiving 10 MHz, mf is say 9 MHz, so the oscillator is on 19 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Demodulation does it´s work on 9 MHz so no [you hope] no mixing problems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also use a oscillator in 1 MHz, mf is 9 MHz bus you see the problem harmonics from the 1 MHz oscillator. 1,2,3,4,5,6,7,8,9,10 &amp;lt;- problem&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also possible if you use a crystal oscillator that it is a thirtieth overtone crystal so in basic the crystal oscillates on 19 MHz but also on a third of the oscillator frequency 6,33 MHz and 12,66 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope you find the error.&lt;/p&gt;&#xA;" OwnerUserId="4838" LastEditorUserId="13" LastEditDate="2015-06-15T12:13:36.903" LastActivityDate="2015-06-15T12:13:36.903" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="4990" PostTypeId="2" ParentId="4968" CreationDate="2015-06-12T17:16:25.750" Score="1" Body="&lt;p&gt;Ashish,  you should be able to receive this using FM.  I'm not sure what the BFSK mode of the TS-2000 is but the data should be visible in FM mode.  You will then have an audio square wave (or rounded if there is some bit shaping).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you feed the audio into a computer soundcard, you should be able to record the data with something like Audacity and see the bits. That will give you confidence that you can demodulate it from there.&lt;/p&gt;&#xA;" OwnerUserId="4432" LastEditorUserId="76" LastEditDate="2015-06-12T19:43:29.417" LastActivityDate="2015-06-12T19:43:29.417" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="4991" PostTypeId="1" CreationDate="2015-06-12T17:35:54.760" Score="3" ViewCount="172" Body="&lt;p&gt;I have written a Software Defined Radio.  I take I/Q audio into the computer at a 192K sample rate and perform a 4096 sample Complex FFT.  I display the spectrum (PSD) to the user so they can pick the signal they want to listen to, and capture the given frequency bin.  So far so good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I copy a set of frequency bins around the selected bin (based on the bandwidth I want) to baseband, following the approach in the QEX article &quot;&lt;a href=&quot;https://www.arrl.org/files/file/Technology/tis/info/pdf/020708qex013.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;SDR For the Masses&lt;/a&gt;&quot; by Youngblood.  I multiply the copied bins with a blackman window whoes width is the same as the bandwidth. I then run an inverse FFT, and FM demodulate using a fast Arctan algorithm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Everything works well, except with some frequency bins I get terrible phase distortion and at some bins it sounds perfect.  I can literally nudge the center bin a few to the right or left and clean up the audio completely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I &lt;a href=&quot;http://www.3db-labs.com/01598092_MultibandFilterbank.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;read that this is an issue associated with copying the bins&lt;/a&gt; to baseband and that only certain bins avoid the issue.  Specifically the paper says: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The mixing precision is limited further by the fact that we don't use complete buffer of output in fast convolution. We use only L samples. We must restrict the mixing to the subset of frequencies whose periods complete in those L samples. Otherwise, phase discontinuities occur. That is, one can only shift in multiples of V bins&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So my question is how do I determine which bins are good?  I have tried many calculations to get &quot;V&quot;, which is the Overlap Factor but can't seem to find an algorithm that sorts the good bins from the bad.  I think it's because V is defined in terms of the filter length and I do not know my filter length&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I can also comment on the alternative approach, which is mixing in the time domain.  I have written a Numerically Controlled Oscillator (NCO) to generate a Complex &quot;carrier&quot; and multiplied it by the I/Q signals thus: &#xA;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;i = i \sin(p) + q \cos (p) \\&#xA;q = q \cos(p) - i \sin (p) &#xA;$$&lt;/span&gt;&#xA;(where &lt;span class=&quot;math-container&quot;&gt;$p$&lt;/span&gt; is the phase accumulator).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This also works well and you get nice clear audio after FM demodulation.  But it needs to be low pass filtered, otherwise you FM demodulate the entire IF.  When I low pass filter it, again it sounds terrible.  Much worse than copying the bins.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding is that a complex signal can be filtered with a linear filter by just filtering the I and Q individually.  I have lots of digital filters working for other audio purposes, but in this case they do not work. I tried IIR filters (because of linear phase response) as well as FIR, but no difference.&lt;/p&gt;&#xA;" OwnerUserId="4432" LastEditorDisplayName="user4168" LastEditDate="2019-01-24T04:20:33.067" LastActivityDate="2019-01-24T04:20:33.067" Title="FFT frequency shift corrupting phase" Tags="&lt;receiver&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="4992" PostTypeId="2" ParentId="4976" CreationDate="2015-06-12T17:38:23.103" Score="1" Body="&lt;p&gt;The Bode-Fano equations are not what you are looking for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a brief read around the net, it seems they are related to the study of the trade off between bandwidth, size and efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an interesting topic, there seem to be some fundamental limits to the size, bandwidth and efficiency of small antennas. This study is mainly interesting and useful when considering small antennas ( \$d&amp;lt;\lambda/2\$, narrow bandwidth (under a few %), and low efficiency (well below 100%).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your antenna is most likely the opposite of most of these - wide band, efficient and probably bigger than half a wavelength - so these might not be directly applicable here.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-06-12T17:38:23.103" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4993" PostTypeId="2" ParentId="4991" CreationDate="2015-06-12T19:42:39.640" Score="2" Body="&lt;p&gt;I don't have a complete understanding of the implications here, but here's a vague gesture in the direction of the answer which might be helpful.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;What you are doing &lt;strong&gt;is filtering&lt;/strong&gt;. And you've defined your filter as a brick-wall in the frequency domain (by copying some bins and ignoring the rest), without regard for the phase or time-domain characteristics. Therefore it's garbage in those ways.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll guess that you should be able to fix the phase response by applying the appropriate phase offsets to each bin, but I don't know what those offsets would look like (likely linear).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FFT-modify-IFFT is a valid implementation strategy for a filter, and it can be more efficient than a straightforward FIR filter while getting the same answer, but you need to actually design a sensible filter (not a rectangular-in-the-frequency-domain one) to use it with.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Here's a question over on Signal Processing Stack Exchange that I think is essentially the same question. The answers aren't all that illuminating for me, though, so I don't know if it'll help you: &lt;a href=&quot;https://dsp.stackexchange.com/questions/10595/what-are-the-problems-with-designing-an-fir-filter-using-fft&quot;&gt;What are the problems with designing an FIR filter using FFT?&lt;/a&gt; The answers suggest that part of the problem with this approach is that it's defining the filter to be perfect at each frequency bin but disregarding its characteristics at the frequencies between the bins.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:47:28.700" LastActivityDate="2015-06-12T19:42:39.640" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="4994" PostTypeId="1" AcceptedAnswerId="4995" CreationDate="2015-06-12T20:41:36.570" Score="9" ViewCount="200" Body="&lt;p&gt;I just bought a SDR dongle that comes with an antenna. The dongle is for DVB-T. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is very small but the specs say that the dongle can go 30Mhz to 850Mhz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From my knowledge of antenna physical size should be 1/4 the size of the wavelength. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can the small antenna scan from 30Mhz to 850Mhz? i thought the size of the antenna would have to be different to accommodate that wide of a frequencies. Unless there is a design of antenna i do not know about and i can not find the answer anywhere on the internet.&lt;/p&gt;&#xA;" OwnerUserId="4849" LastActivityDate="2015-06-14T20:39:27.687" Title="Antenna size for wideband" Tags="&lt;antenna&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4995" PostTypeId="2" ParentId="4994" CreationDate="2015-06-12T21:11:14.470" Score="6" Body="&lt;p&gt;An antenna of the wrong size is just an antenna that is not &lt;em&gt;resonant&lt;/em&gt; at the particular frequency — meaning that each cycle of the radio wave &lt;em&gt;captured by and conducted in the antenna&lt;/em&gt; does not perfectly match phase with the preceding cycle, since that only happens at the specific length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Incidentally, the length of 1/4 wavelength is appropriate for a &lt;em&gt;ground plane&lt;/em&gt; antenna, which you don't exactly have unless you have a ground plane. (Those antennas usually have a magnetic base — stick it on the biggest flat metal object you have handy for better performance.) Other designs of antennas have other required lengths.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the antenna is not resonant, it will be &lt;em&gt;less efficient&lt;/em&gt; at transferring energy from electromagnetic radiation to the feed point (connection to the cable to the dongle), or vice versa. The effect of this for reception is that you will see &lt;em&gt;slightly&lt;/em&gt; stronger signals close to the resonant frequency of the antenna, and weaker signals elsewhere, but the antenna will still work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can be to your benefit — the antenna is acting as a (not very sharp) filter, and filtering out frequencies you &lt;em&gt;don't&lt;/em&gt; want to receive gets you less noise in the signal you &lt;em&gt;do&lt;/em&gt; want. So, if there is a particular frequency range you are interested in more than others, or which typically has weak signals whereas other bands have strong signals not needing any help, then you can improve the situation by using an antenna of the right length for about that frequency (either cut and built to that length, or using a telescoping element).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The place where the resonant frequency really starts to matter is when you are &lt;em&gt;transmitting&lt;/em&gt;, because that's where the inefficiency starts to hurt. When receiving, &lt;a href=&quot;https://ham.stackexchange.com/questions/2213/can-i-improve-reception-with-a-more-sensitive-antenna-preamplifier-better-fe/2214#2214&quot;&gt;it doesn't matter how efficient the antenna is as long as the signal is strong &lt;em&gt;enough&lt;/em&gt; that the ambient noise floor received by the antenna exceeds the receiver's inherent noise floor&lt;/a&gt;. On the other hand, when transmitting, the inefficiency is wasted energy and decreased range. A sufficient mismatch will damage equipment (usually the transmitter's amplifier first) due to heating or excess voltage.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-06-14T20:39:27.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4996" PostTypeId="1" CreationDate="2015-06-13T18:24:30.827" Score="3" ViewCount="9023" Body="&lt;p&gt;I am looking for a simple UHF / VHF transceiver that I can plug into my PC via USB and be able to RX/TX on one channel, using the built in mic... Maybe even record the RX from the freq. &#xA;Everything I was able to find online, were just complicated systems for PC. What should I be looking for, what keywords should I be Searching?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I work in a overnight camp, and we use Person to Person Motorola Radius CP200 to communicate over the grounds. Being that I am at my PC all day, with a headset in my ears anyways, I would like to use my PC. Additional, sometimes I have pre-recorded messages that I would like to broadcast. &lt;/p&gt;&#xA;" OwnerUserId="4851" LastEditorUserId="76" LastEditDate="2016-10-29T19:02:00.750" LastActivityDate="2021-01-06T07:26:13.347" Title="Looking for a UHF / VHF transceiver for PC.`" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;transceiver&gt;&lt;computer-control&gt;" AnswerCount="4" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="4997" PostTypeId="2" ParentId="4970" CreationDate="2015-06-13T21:04:29.777" Score="1" Body="&lt;p&gt;Nice try but that's definitely not how you calculate gain!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gain depends on many things, but first is the number of dipole elements in the stack. You could estimate the gain by guessing the number of half-wave dipoles that fit in the antenna. I suppose in your case a 300 mm antenna would fit four dipoles, to leave space for the top cap, connector and matching at the bottom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then the maximum theoretical gain will be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2 dBi for the first dipole, + 3 dB for each further doubling, so 8 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, each additional antenna also brings some further losses. So it is probably closer to: 1 dBi for one dipole, 3 dBi for two, 5 dBi for 4, 7 dBi for 8.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've never heard of 20 dBi in an omni before. That would require a minimum length of 32 wavelengths, 3 m, and more in practice. It would have an elevation beamwidth of around 1 degree. Not much use having such a flat beam anyway. I think you have a 5 or 6 dBi omni, which should give you about double the range of the little dipole that comes with the router.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-06-15T08:24:13.277" LastActivityDate="2015-06-15T08:24:13.277" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="4998" PostTypeId="1" CreationDate="2015-06-14T11:00:00.417" Score="0" ViewCount="510" Body="&lt;p&gt;I woke up to find a series of &quot;images&quot; on the window of my kitchen slider.&#xA;They were concentric circles.  They appear to be images of a magnetic field.&#xA;I was trying to link a photo of them onto this site, but was not successful&#xA;I will try &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/CHGnI.jpg&quot; alt=&quot;concentric circles&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="4852" LastEditorUserId="786" LastEditDate="2015-06-15T12:18:50.207" LastActivityDate="2015-06-15T12:18:50.207" Title="Strange image of concentric circles…magnetic field?" Tags="&lt;theory&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2015-06-15T12:19:13.593" ContentLicense="CC BY-SA 3.0" />
  <row Id="4999" PostTypeId="2" ParentId="4996" CreationDate="2015-06-14T16:27:28.183" Score="1" Body="&lt;p&gt;There aren't, as far as I know, any radios on the market that are pure computer peripherals and high-power enough to be practical communication tools (as opposed to milliwatt-scale experimental devices) while still being at a reasonable cost for this application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you &lt;em&gt;can&lt;/em&gt; buy or build reasonably is an interface to connect the audio from a standard radio to your PC. The exact details of this interface will depend on the radio model as they are not very standardized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more general information on such interfaces, you could read my previous answer to a similar question, &lt;a href=&quot;https://ham.stackexchange.com/a/4940/76&quot;&gt;How can I send a voice message from my PC to HT radios?&lt;/a&gt; If you've decided you want to do this I suggest looking for products or designs specific for the brand of radio you're already using; if you can't find one then consider a different radio that's easier to interface.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-06-14T16:27:28.183" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5000" PostTypeId="2" ParentId="4998" CreationDate="2015-06-15T03:37:07.830" Score="3" Body="&lt;p&gt;Those look like marks left behind by the suction cup carriers that windows installers use to carry and install plates and complete windows. They became visible because the lighting and condensation was just right.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(And yes, terribly off-topic.)&lt;/p&gt;&#xA;" OwnerDisplayName="user4182" LastActivityDate="2015-06-15T03:37:07.830" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5001" PostTypeId="2" ParentId="1379" CreationDate="2015-06-18T03:05:39.950" Score="1" Body="&lt;p&gt;Here is Korean code.&#xA;there's 26 alphabets codes,&#xA;numbers are same with English.&#xA;&lt;img src=&quot;https://i.stack.imgur.com/IkjvK.png&quot; alt=&quot;korean morse code&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;from &lt;a href=&quot;https://ko.wikipedia.org/wiki/%EB%AA%A8%EC%8A%A4_%EB%B6%80%ED%98%B8&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ko.wikipedia.org/wiki/%EB%AA%A8%EC%8A%A4_%EB%B6%80%ED%98%B8&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4863" LastActivityDate="2015-06-18T03:05:39.950" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5002" PostTypeId="2" ParentId="4996" CreationDate="2015-06-18T03:24:47.977" Score="2" Body="&lt;p&gt;You can do this with a little setup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember you need a Amateur radio licence if you are going to be transmitting. If you are just wanting to try out receiving then you can get a usb tv tuner (for less than $20 on amazon) and use some software like &lt;a href=&quot;http://sdrsharp.com/#sdrsharp&quot; rel=&quot;nofollow&quot;&gt;SDR#Sharp&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are wanting to do transmission:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can get a 1.5w handheld transceiver like &lt;a href=&quot;https://en.wikipedia.org/wiki/Yaesu_VX_series&quot; rel=&quot;nofollow&quot;&gt;https://en.wikipedia.org/wiki/Yaesu_VX_series&lt;/a&gt; reasonably cheap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then you need a special audio cable (4 part 3.5 audio jack to (normal) 3.5 line in|out audio). You can buy them as an accessory, with the radio, on ebay|amazon or solder one up yourself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This will let you wire up the radio to the pc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you need some software. There is lots of ham radio software out there. It depends what you want to do. A lot is free. Some you have to pay for. Google is your friend (or ask another question specifically about software)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may just be able to get away with some simple recording and play back software that comes with your PC, depending on what you want to do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also want/need to use &lt;a href=&quot;https://en.wikipedia.org/wiki/Virtual_Audio_Cable&quot; rel=&quot;nofollow&quot;&gt;https://en.wikipedia.org/wiki/Virtual_Audio_Cable&lt;/a&gt; to route audio around in you pc.&lt;/p&gt;&#xA;" OwnerUserId="972" LastActivityDate="2015-06-18T03:24:47.977" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5003" PostTypeId="2" ParentId="1940" CreationDate="2015-06-18T17:16:28.543" Score="1" Body="&lt;p&gt;You might be surprised at the number of 6 and 2M contacts you can generate using low power and simple antennas. I have been able to do several Grid expeditions to put on the less populated grids for the guys chasing VUCC on 6 and 2 Meteor Scatter. I used my FT897 mobile at 100W (50W on 2) out into a 9 element 2M Yagi and Full wave loop made of wire and a PVC cross. It was not unusual to work stations to 1000 Miles plus with a few contacts at 1300 Miles. I plan on offering my rig to the local club this year as the VHF UHF station.&#xA;You should be able to call CQ on FSK441 (WSJT software) on 50.260 (The 6M FSK441 calling frequency. It is normal practice to set your CQ up so it also contains your RX frequency. When you hear someone answer on the RX frequency you switch to TRX on your RX frequency to keep the calling frequency clear. The CQ message would look like &quot;CQ WQ5S U3 U3&quot; if I wanted to use 50.263 as my RX frequency.&lt;br&gt;&#xA;Before FD you might want to watch some of the activity on the Ping Jockey Chat page and get an idea of how everyone there operates and schedules contacts. The guys there a friendly bunch and would be glad to help someone get started on MS&#xA; 73 and GL&#xA;WQ5S&lt;/p&gt;&#xA;" OwnerUserId="4866" LastActivityDate="2015-06-18T17:16:28.543" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5005" PostTypeId="2" ParentId="4972" CreationDate="2015-06-19T23:43:28.753" Score="4" Body="&lt;p&gt;Yes, it's very possible, and in fact, it's quite commonly done in commercial FM broadcasting, in order to provide full coverage for major metropolitan areas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The key to making it work is to make sure that the &lt;em&gt;modulation&lt;/em&gt; (not the carrier) of two transmitters is time-aligned in the &quot;overlap&quot; region where the signal levels are approximately equal (e.g., within 6 dB). Outside this region, an FM receiver will &quot;capture&quot; one transmitter or the other, but inside this region, it will randomly jump from one to the other. But as long as the modulation is time-aligned, the output of the detector is essentially the same regardless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That isn't to say that there aren't many compromises in such a system. Given the variabilities of terrain, etc., it's impossible to get optimal time alignment in all of the overlap regions. Considerable effort goes into modeling the placement of the transmitters (and to some extent, adjusting their power levels) in order to position the less-well-optimized regions away from high-traffic areas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the distant past (1990s), I worked for a company that sold networking equipment to commercial radio stations, and I designed the part that implemented the required timing control.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastEditorUserId="1459" LastEditDate="2015-06-20T00:57:12.397" LastActivityDate="2015-06-20T00:57:12.397" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5007" PostTypeId="2" ParentId="4972" CreationDate="2015-06-20T15:29:10.713" Score="-1" Body="&lt;p&gt;We should distinguish between ways of having multiple FM transmissions on a single frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CAPTURE EFFECT&#xA;Transmitter frequencies in FM broadcasting networks are allocated relying on the limiters in FM receivers to separate a stronger signal from weaker signal(s). This is a key advantage of FM over AM (that exhibits no capture effect i.e. any interefering signals are heard proportional to their relative strengths) and is well described in Dave Tweed's answer. The chopping effect sometimes heard on a mobile receiver in an area where the desired signal is not strong enough to reliably saturate the limiter has been called the &quot;picket fencing&quot; effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;QUADRATURE SIGNALS&#xA;The I (in-phase) and Q (quadrature- or 90 degree phase) components of a transmitted carrier can be modulated and demodulated without interference, potentially allowing two independant FM transmissions. This works only with a single transmitter antenna because there must be no difference in receive path delays that would change the quadrature phase relationship, and the receiver needs a special synchronous demodulator. This is common practice with QPSK data transmission but unusual for sudio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SUBCARRIER(S)&#xA;Since FM transmitters are usually allowed generous bandwidth (band limiting increases distortion) there is the possibility of adding an ultrasonic sub-carrier to the audio modulation. Broadcast stations add subcarriers for many purposes that include a channel-difference signal for stereo receivers, data broadcasts, transmitter/studio telemetry, reading service for the blind and (now defunct) Muzak distribution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above are continuous multiple FM transmissions on a single frequency. I do not count signal sharing formats such as TDMA (Time- ) FDMA (Frequency- ) or CDMA (Code-Division Multiple Access) that are used in cellular telephony nor OFDM whch is a wide band multi-carrier modulation.&lt;/p&gt;&#xA;" OwnerUserId="4408" LastActivityDate="2015-06-20T15:29:10.713" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5009" PostTypeId="1" CreationDate="2015-06-21T07:29:11.500" Score="6" ViewCount="2629" Body="&lt;p&gt;HF radio can be reflected by the ionosphere, giving very long range communications.&#xA;Why can't VHF / UHF used with ionosphere reflection?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it due to the attenuation of the atmosphere over that distance with VHF / UHF wavelengths?&#xA;Or is it to do with the interaction of the ionosphere at the HF wavelengths (vs the VHF / UHF wavelengths)?&#xA;Or some other reason?&lt;/p&gt;&#xA;" OwnerUserId="972" LastEditorUserId="76" LastEditDate="2015-06-22T14:57:49.983" LastActivityDate="2017-12-01T04:01:56.577" Title="Why can't VHF / UHF be used with ionosphere reflection?" Tags="&lt;propagation&gt;&lt;uhf&gt;&lt;vhf&gt;&lt;theory&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5010" PostTypeId="1" AcceptedAnswerId="5014" CreationDate="2015-06-21T07:47:22.330" Score="9" ViewCount="747" Body="&lt;p&gt;HF transmissions from the ground can be reflected by the ionosphere leading to very long distance propagation. Satellites in low Earth orbit (160 km to 2,000 km)  fly within the ionosphere (60 km  to 1,000 km); with the F layer at 150 km to 500+ km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if a satellite is under, over or in the F layer, do the signals get absorbed, reflected away from the earth, or skim around/under the ionosphere (i.e. propagate a long distance)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would also depend on the incidence angle,  presumably.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason I ask is I am wondering if HF would be useful for in CubeSats, which at UHF frequencies can only downlink/load during short pass windows. HF would probably be a lower bandwidth connection, but the time available, and the more constant connection might outweigh the low bandwidth.  &lt;/p&gt;&#xA;" OwnerUserId="972" LastEditorUserId="972" LastEditDate="2017-11-30T21:06:33.507" LastActivityDate="2017-11-30T21:06:33.507" Title="Can there be (long range) propagation of HF from satellites?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;satellites&gt;&lt;theory&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5012" PostTypeId="2" ParentId="5009" CreationDate="2015-06-21T18:57:25.103" Score="8" Body="&lt;p&gt;The ionosphere typically neither reflects nor absorbs waves with VHF or higher frequencies, but passes them through to space. There are no reflections back to the ground, so there is no useful propagation between stations on the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Tropospheric_propagation#Tropospheric_ducting&quot; rel=&quot;noreferrer&quot;&gt;Tropospheric ducting&lt;/a&gt; is a different propagation mode which does carry VHF signals well, and is actually sought and used for VHF DX contacts. However, it depends on specific weather conditions that do not occur daily, and so is much less a reliable means of communication than the ionosphere.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-06-21T20:37:27.623" LastActivityDate="2015-06-21T20:37:27.623" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5013" PostTypeId="2" ParentId="117" CreationDate="2015-06-21T21:46:20.007" Score="3" Body="&lt;p&gt;Yes, you can convert a CB to a ham band radio. Even an AM radio can be used in the ham bands; a small portion of the 10 meter band is allocated to AM service &lt;a href=&quot;https://en.wikipedia.org/wiki/10-meter_band#AM_sub-band&quot; rel=&quot;nofollow&quot;&gt;(29,000,000 Hz to 29,200,000 Hz).&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't need an amplifier. Many hams work varied countries using a QRP rig. Most QRP rigs are around 5 watts or less. I've heard a few say 10 watts or less is QRP, but on average it is 5 or less, so an unmodified CB is considered QRP. Anyway, anyone who is anyone in radio knows it's not critical to have an amp, when you get the most bang for the buck with a good directional or high gain antenna, which isn't as hard to do at these frequencies than the low bands, due to antenna size.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it takes good engineering techniques to get a CB radio to shift that far from its normal range of operation. Many of the the techs I've talked to say some won't track that far because the VCOs don't like the voltages it takes to go that far and the PLLs used in them don't like it either. So be set up with the equipment to test your mods, till you get it to do what you're attempting to achieve.&lt;/p&gt;&#xA;" OwnerUserId="4882" LastEditorUserId="76" LastEditDate="2015-06-23T03:52:42.323" LastActivityDate="2015-06-23T03:52:42.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5014" PostTypeId="2" ParentId="5010" CreationDate="2015-06-21T22:30:32.097" Score="10" Body="&lt;p&gt;Satellites can and do use HF for communications.&lt;/p&gt;&#xA;&lt;p&gt;The first example would of course be &lt;a href=&quot;https://en.m.wikipedia.org/?title=Sputnik_1&quot; rel=&quot;noreferrer&quot;&gt;Sputnik&lt;/a&gt;, which transmitted at 20 and 40 MHz.&lt;/p&gt;&#xA;&lt;p&gt;Amateurs use HF to communicate with satellites. According to &lt;a href=&quot;http://www.amsat.org/amsat/intro/sats_faq.html#RTFToC5&quot; rel=&quot;noreferrer&quot;&gt;Amsat&lt;/a&gt;,&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;mode A: This mode requires a 2 meter SSB/CW transmitter and a 10 meter SSB/CW receiver...&lt;/p&gt;&#xA;&lt;p&gt;Mode K; This mode requires a 15 meter SSB/CW transmitter and a 10 meter SSB/CW receiver... This mode is unique in that it can be done with a simple HF rig.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;HF has advantages in its smaller Doppler shift, and reduced path loss, allowing omnidirectional antennas to be used more easily.&lt;/p&gt;&#xA;&lt;p&gt;For the physics part of your question: the reflection from a layer of the ionosphere depends on electron density,  frequency and angle of incidence (which changes its effective thickness).&lt;/p&gt;&#xA;&lt;p&gt;At normal incidence, frequencies of below about 7-10 MHz are reflected, higher frequencies pass through. See &lt;a href=&quot;https://en.wikipedia.org/wiki/Ionosonde&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia&lt;/a&gt; for a graph of reflection against height.&lt;br /&gt;&#xA;&lt;a href=&quot;http://www.radio-electronics.com/info/propagation/ionospheric/maximum-lowest-critical-optimum-usable-working-frequency.php&quot; rel=&quot;noreferrer&quot;&gt;This page&lt;/a&gt; gives a great overview; (written with communication in mind, but what isn't reflected is transmitted). The equation for MUF is F_normal / ( sec θ ). So it's only for very long paths, grazing reflection, that the ionosphere ever reflects a 28 MHz signal. It would usually pass straight through the ionosphere, down to a fairly shallow angle.&lt;/p&gt;&#xA;&lt;p&gt;Your last question makes it sound like you hope to use HF from a cubesat when it's &lt;em&gt;over the horizon&lt;/em&gt;, not in &lt;em&gt;line of sight&lt;/em&gt;. This would be highly unusual and would certainly not help with your data rate problem.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;If you choose a frequency which easily penetrates the ionosphere, then it won't bounce around inside, to get to you, it'll just reflect out again.&lt;/li&gt;&#xA;&lt;li&gt;Cubesats have very limited power, HF requires plenty of power to communicate around the world, 10s or 100s of watts.&lt;/li&gt;&#xA;&lt;li&gt;If you're trying to send more data during a pass, then the right solution is to go &lt;em&gt;higher&lt;/em&gt; in frequency, where antenna gains are higher, there's less atmospheric noise, and more bandwidth available. HF modems run at 1200 bps, WiFi runs at 11 Mbps and more.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;That all said, there is &lt;a href=&quot;http://www.arrl.org/news/australian-pico-balloon-piques-ham-radio-interest&quot; rel=&quot;noreferrer&quot;&gt;one tiny balloon project&lt;/a&gt;, launched to fly around the southern hemisphere, that uses HF to phone home. It's only 30 km high, but it transmits just a few mW using wspr, and can be heard around the world, with luck. Bear in mind that it sends nothing but its position and callsign.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2015-06-21T22:48:05.887" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5015" PostTypeId="2" ParentId="117" CreationDate="2015-06-22T03:49:15.057" Score="4" Body="&lt;p&gt;There are some CB-style &quot;11m&quot; multimode (AM/FM/SSB and sometimes even CW) sets that operate in bands at the top of 27MHz, and some of these can be made to work at the bottom of the 10-metre band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These can usually be used legally by licensed amateur operators, as long as they stick to frequencies for which they are licensed, and follow the band plans for that portion of the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is true for the US and European countries. However, it is NOT the case in all countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some countries only allow the import, possession, and use of specific models of radio transmitters/transceivers, and using any other equipment can result in a fine, confiscation of the equipment, and even prison. An example of such a country is Thailand, where I live and am licensed (with a reciprocal licence - 'real' licences are for Thai citizens only). We have to import radios, and have them checked by the Broadcasting regulator before they will issue a licence for the equipment. We also need a licence to operate (the actual radio licence), and a licence for the premises where we will operate. The list of equipment that can be applied for approval does not include any radio equipment with 50MHz capability, so all modern HF sets are not allowed. I use an Icom IC-718, one of the only HF-only sets still sold.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, despite these restrictions, Thailand still manages to have the third-highest number of licensed radio amateurs of any country in the world (behind Japan and the United States of America). Go figure.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-06-22T03:49:15.057" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5017" PostTypeId="1" AcceptedAnswerId="5018" CreationDate="2015-06-23T04:11:56.263" Score="5" ViewCount="373" Body="&lt;p&gt;I've heard two sides to this. On one hand, sites that allow you to send messages into the APRS-IS network, for relay over RF, demand you enter a call, as &quot;only licensed HAMs may cause a message to be relayed over HF&quot;. On the other hand, gateways like SMSGTE and EMAIL will allow non-licensed HAMs to send messages over HF to a HAM, generally when they're replying to a message sent by that HAM. The system I'm designing is somewhere in the middle - incoming APRS messages from a certain call sign are posted to a Twitter account. Then, replies and mentions are relayed back to the HAM, provided the HAM has pre-approved the Twitter user that sent that reply or mention. So, given that this gateway server is a &quot;good citizen&quot;, with conservative rate limits, blocks against spam, etc, it is legal, in the US, for it to relay the replies, mentions and DMs as described?&lt;/p&gt;&#xA;" OwnerUserId="361" LastEditorUserId="873" LastEditDate="2015-06-23T11:42:24.470" LastActivityDate="2015-06-23T11:45:34.543" Title="Is it legal (in the US) for a server on APRS-IS to relay replies from non-HAMS to a HAM?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;aprs&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5018" PostTypeId="2" ParentId="5017" CreationDate="2015-06-23T11:45:34.543" Score="5" Body="&lt;p&gt;What you are referring to is known as &quot;Third Party Communications&quot;. Here is the blurb from the &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=about_2&amp;amp;id=amateur#Third%20Party%20Communications&quot; rel=&quot;noreferrer&quot;&gt;FCC&lt;/a&gt; on third party communications:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Section 97.115 of the Commission's Rules, 47 C.F.R. §97.115,&#xA;  authorizes an amateur station regulated by the FCC to transmit a&#xA;  message from its control operator (first party) to another amateur&#xA;  station control operator (second party) on behalf of another person&#xA;  (third party). No amateur station, however, shall transmit messages&#xA;  for a third party to any station within the jurisdiction of any&#xA;  foreign government whose administration has not made arrangements with&#xA;  the United States to allow amateur stations to be used for&#xA;  transmitting international communications on behalf of third parties.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The following countries have made the necessary arrangements with the&#xA;  United States to permit an amateur station regulated by the FCC to&#xA;  exchange messages for a third party with amateur stations in: Antigua&#xA;  and Barbuda, Argentina, Australia, Belize, Bolivia,&#xA;  Bosnia-Herzegovina, Brazil, Canada, Chile, Colombia, Federal Islamic&#xA;  Republic of Comoros, Costa Rica, Cuba, Dominica, Dominican Republic,&#xA;  Ecuador, El Salvador, The Gambia, Ghana, Grenada, Guatemala, Guyana,&#xA;  Haiti, Honduras, Israel, Jamaica, Jordan, Liberia, Republic of the&#xA;  Marshall Islands, Mexico, Federated States of Micronesia, Nicaragua,&#xA;  Panama, Paraguay, Peru, Philippines, St. Christopher and Nevis, St.&#xA;  Lucia, St. Vincent and the Grenadines, Sierra Leone, South Africa,&#xA;  Swaziland, Trinidad and Tobago, Turkey, United Kingdom (special event&#xA;  stations with call sign prefix GB followed by a number other than 3),&#xA;  Uruguay, and Venezuela. The United Nations also has arrangements with&#xA;  the United States to permit an amateur station regulated by the FCC to&#xA;  exchange messages for a third party with amateur stations 4U1ITU in&#xA;  Geneva, Switzerland, and 4U1VIC in Vienna, Austria.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;No amateur station regulated by the FCC shall transmit messages for a&#xA;  third party to any amateur station located within the jurisdiction of&#xA;  any foreign government not listed above. This prohibition does not&#xA;  apply to a message for any third party who is eligible to be the&#xA;  control operator of the station.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Bottom line, it's only legal to send a third party message to certain countries. It is perfectly legal if you are keeping it to within the United States, and it's risky to do so outside of the US, unless you know exactly where it's going.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not a lawyer, but I would believe the system you described to be legal if the messages were coming from authorized countries, otherwise it would not be considered legal.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-06-23T11:45:34.543" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5019" PostTypeId="1" CreationDate="2015-06-23T17:33:04.447" Score="2" ViewCount="185" Body="&lt;p&gt;I have an old Alinco dual-band radio, the DR-600 &lt;a href=&quot;https://drive.google.com/file/d/0B4diWKEz3YQuMDd6MUxyY1NOUGc/view&quot; rel=&quot;nofollow&quot;&gt;(service manual)&lt;/a&gt; &lt;a href=&quot;http://www.alinco.com/pdf.files/Instruction/Mobile/dr600insweb.pdf&quot; rel=&quot;nofollow&quot;&gt;(manual)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to use this radio for receiving APRS packets. The speaker audio out &lt;em&gt;Works&lt;/em&gt; but there are too many things to go wrong with Squelch, Volume knobs, or filter circuits designed for a speaker with a human ear which make a packet harder to decode with software. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have looked through the service manual, but I don't really see anything that says &quot;Discriminator&quot; or &quot;flat audio&quot; on the schematic. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where is the best place to pull audio for packet use on my Alinco DR-600 mobile transceiver? I would greatly appreciate pointers in the schematic to where I can test for audio sources.&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2016-10-29T18:52:15.117" LastActivityDate="2016-10-29T18:52:15.117" Title="Where to pull audio for packet on an alinco DR-600" Tags="&lt;transceiver&gt;&lt;aprs&gt;&lt;packet&gt;&lt;audio-interface&gt;&lt;alinco&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5020" PostTypeId="1" CreationDate="2015-06-23T22:19:18.783" Score="6" ViewCount="1619" Body="&lt;p&gt;I'm transmitting a simple tone which lasts 50 ms using an FM transmitter. I can see clearly this tone being received on my RTL-SDR device when I look at a spectrum graph (using GQRX).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I need to call a linux kernel function a soon as the tone is received, so I want a real-time solution which processes the signal. I'm thinking the best way would be to have the output stream piped into a shell program of mine via terminal, but I would need this stream to simply be a demodulated amplitude of the signal. I would then call my function when the amplitude has increased by enough of a factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any way to achieve this?&lt;/p&gt;&#xA;" OwnerUserId="4890" LastActivityDate="2015-06-24T01:07:32.673" Title="How to detect a tone on an FM Frequency using an RTL SDR receiver?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;linux&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5021" PostTypeId="2" ParentId="5020" CreationDate="2015-06-23T22:30:55.280" Score="3" Body="&lt;p&gt;If the tone is, or can be made to be, a DTMF tone or one of several other simple tone code protocols, then you could use &lt;a href=&quot;https://github.com/EliasOenal/multimon-ng/&quot; rel=&quot;nofollow&quot;&gt;multimon-ng&lt;/a&gt; to detect it. multimon-ng will output text corresponding to the detected tones. This also means you don't need to program the amplitude criterion. Something like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rtl_fm -f &amp;lt;freq&amp;gt; -s 22050 -M wbfm | multimon-ng -a DTMF -t raw - | &amp;lt;your program&amp;gt;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;where “&lt;code&gt;&amp;lt;your program&amp;gt;&lt;/code&gt;” is a program that waits for some input on stdin and calls the function you need.&#xA; Explanation of the options:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;code&gt;rtl_fm ... -s 22050&lt;/code&gt; sets the audio  rate appropriately for multimon-ng which requires an input sample rate of 22050 Hz.&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;rtl_fm ... -M wbfm&lt;/code&gt; is because you say you're using a &quot;FM car radio” to transmit, by which I assume you mean those low-power transmitters intended for use with a car stereo. Broadcast FM is wideband FM, not the narrowband FM used by amateur / two-way radios. If you were using one of those, it would be &lt;code&gt;-M fm&lt;/code&gt; (or left out as that's the default).&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;multimon-ng ... -a DTMF&lt;/code&gt; tells multimon-ng to decode DTMF only and not try anything else.&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;multimon-ng ... -t raw -&lt;/code&gt; tells multimon-ng to read from stdin rather than opening an audio device.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You may also wish to use the frequency correction PPM, gain, filtering, etc. options to &lt;code&gt;rtl_fm&lt;/code&gt;; that would be a whole other article, and so I just want to point out they exist.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The output of multimon-ng will be one line per detected code with the prefix &lt;code&gt;DTMF:&lt;/code&gt;, like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;DTMF: 1&#xA;DTMF: 2&#xA;DTMF: 3&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;There are several other codes multimon-ng supports that you could use — I suggest researching the codes mentioned in multimon-ng's readme. You could even use &lt;code&gt;MORSE_CW&lt;/code&gt; (Morse code), which doesn't have a specific pitch but does have specific durations of the tones (a lone 50 ms tone would always decode as “E”).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;It would also be reasonable to build this within GNU Radio, which would allow integrating all of the signal processing in one program and more choices of RF hardware. However, it would require considerably more code to set everything up.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-06-24T01:07:32.673" LastActivityDate="2015-06-24T01:07:32.673" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5022" PostTypeId="2" ParentId="5019" CreationDate="2015-06-23T23:53:51.187" Score="1" Body="&lt;p&gt;You may actually &lt;em&gt;want&lt;/em&gt; to use speaker out as it will most likely have the proper de-emphasis (6db/octave). Most APRS signals sent our are with pre-emphasis and tapping from your radio at the flat audio signal may actually do more harm than good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even with a dedicated port for audio out on your radio you probably still have to tune your TNC to the proper signal levels (deviation) anyway so you might as well hook it up to a cro and confirm all looks good.&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="1135" LastEditDate="2015-06-26T00:17:57.027" LastActivityDate="2015-06-26T00:17:57.027" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5023" PostTypeId="1" AcceptedAnswerId="5125" CreationDate="2015-06-25T01:42:56.720" Score="3" ViewCount="949" Body="&lt;p&gt;Why do most radios have a microphone ground as well as a Ground?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have found that simply using one ground and tying the microphone as well as the PTT (and audio out, 5v out or whatever else is in the I/O) to work just fine.   &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2016-10-29T18:50:46.810" LastActivityDate="2017-07-19T09:22:24.840" Title="Mic ground vs ground" Tags="&lt;equipment-design&gt;&lt;microphone&gt;&lt;audio-interface&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5024" PostTypeId="1" CreationDate="2015-06-25T01:49:41.690" Score="5" ViewCount="3576" Body="&lt;p&gt;I am confused when someone says &quot;your audio levels are set right and has good deviation at 3 kHz&quot; when talking about wide-band 25 kHz FM signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First confusion: Why are audio levels measured in kHz? I find it very misleading when you are measuring amplitude values.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second confusion: I understand that FM works by deviating from the carrier frequency and will accept a frequency term for amplitude. Why is it 3 kHz though, not 25 kHz or 12.5 kHz for narrow band FM? I would assume perfect audio is when the transmitter is deviating the entire 25 kHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is one measuring when talking about audio deviation? Why 3 kHz? &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2016-10-29T19:11:01.600" LastActivityDate="2016-10-29T19:11:01.600" Title="What does the term 3 kHz deviation relate to in the FM world?" Tags="&lt;theory&gt;&lt;fm&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5025" PostTypeId="2" ParentId="5024" CreationDate="2015-06-25T02:23:26.787" Score="4" Body="&lt;p&gt;FM works by varying the frequency of the signal around the nominal carrier frequency. Because the frequency is varying, the signal is not a pure sine wave. Therefore, it necessarily has some energy in sidebands as well as the instantaneous frequency. The higher the audio frequency, the more the signal deviates from a sine wave, so the more energy ends up in the sidebands instead of at the instantaneous frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one works out the math, one finds that a FM signal has an infinite bandwidth (sidebands of arbitrarily high frequencies), but the energy drops off quickly as we look farther away, so in practice they are negligible (and may be filtered out).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3 kHz is the &lt;em&gt;deviation&lt;/em&gt; of the signal — the amount the instantaneous frequency differs from the carrier frequency. Because there are sidebands, the occupied bandwidth is larger than the deviation.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;If you have access to a software-defined radio or panadapter, try tuning it to the wideband FM broadcast frequencies. You'll see that even though the bandwidth of the signal is big enough to easily get a high-resolution look, it doesn't look like a single instantaneous frequency but a wide hump. These are the rapidly varying FM sidebands. In particular, when the station is quieter you may be able to distinguish a set of three or more peaks moving in concert — these are the result of the inaudible 19 kHz stereo-encoding “pilot” tone which is always present for a stereo transmitter.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;“Why are audio levels measured in kHz?” Because FM maps the audio signal to frequency changes, so the only absolute measurement of the level &lt;em&gt;on the air&lt;/em&gt; is the change in frequency. Any other way of measuring audio — sound pressure level, AF voltage — is inapplicable because those depend on the characteristics of the transmitter or receiver.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-06-25T04:18:19.967" LastActivityDate="2015-06-25T04:18:19.967" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5026" PostTypeId="1" CreationDate="2015-06-25T04:57:16.140" Score="2" ViewCount="338" Body="&lt;p&gt;I am using 2 array crossed yagi-uda antenna operating at 437.025 MHz. Where and how should I ground it? Should I ground at mast of antenna or to its metallic boom?&lt;/p&gt;&#xA;" OwnerUserId="4894" LastEditorUserId="76" LastEditDate="2015-12-15T23:28:42.717" LastActivityDate="2015-12-15T23:28:42.717" Title="Should I ground a 2 array crossed yagi-uda antenna?" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;grounding&gt;&lt;yagi&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5027" PostTypeId="1" CreationDate="2015-06-25T05:51:06.107" Score="3" ViewCount="94" Body="&lt;p&gt;Background - &#xA;UHF - 434-438MHz&#xA;Two identical crossed Yagi's mounted on rotator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently, I have a low noise preamplifier after combining cables from the two antennas (T connector + matching stub).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm considering adding two separate identical low noise preamplifiers right after each antenna(on the antenna boom itself) and combining their outputs later with a T connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am currently calculating link margin for one antenna + preamplifier till the T connector and directly adding 3dB gain after the T connector (in the post-preamplifier feed line) to add the gain from the second identical antenna system. However, this 3dB gain does not seem to affect my SNR much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I adding the gain from the second antenna at the right place? Is the second system helping at all or should I use just one antenna with a preamplifier immediately after it?&lt;/p&gt;&#xA;" OwnerUserId="4539" LastActivityDate="2016-02-17T22:15:40.970" Title="Link margin calculations with two antennas and two low noise preamplifiers" Tags="&lt;amplifier&gt;&lt;snr&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5028" PostTypeId="1" AcceptedAnswerId="6172" CreationDate="2015-06-25T06:20:45.993" Score="4" ViewCount="931" Body="&lt;p&gt;What will be the effect if I add the insulation between elements and metallic boom of the cross yagi antenna (where elements from outside of the boom, instead of through boom) and in this case boom correction is required?&#xA;If this is not the best way, feel free to suggest another methods for connecting the elements and metallic Boom.&lt;/p&gt;&#xA;" OwnerUserId="4895" LastEditorUserId="13" LastEditDate="2015-06-25T12:00:28.483" LastActivityDate="2016-05-10T08:15:07.310" Title="Cross Yagi Antenna Design" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5030" PostTypeId="2" ParentId="2432" CreationDate="2015-06-25T12:10:01.593" Score="2" Body="&lt;p&gt;This question was answered in part at &lt;a href=&quot;https://stackoverflow.com/q/5501719/544198&quot;&gt;Stack Overflow&lt;/a&gt; for an Android device. As they are getting to be quite inexpensive, I assume it will work for your needs. Here are some parts to your solution:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Use an OTG cable to connect your phone to your other device.&lt;/li&gt;&#xA;&lt;li&gt;The phone needs to run a program called &quot;ShareGPS &quot;, which will communicate the location over USB. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Feel free to look at the question to see a solution for TCP/IP, Bluetooth, etc.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="-1" LastEditDate="2017-05-23T12:37:22.373" LastActivityDate="2015-06-25T12:10:01.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5031" PostTypeId="2" ParentId="5026" CreationDate="2015-06-25T15:23:10.187" Score="3" Body="&lt;p&gt;A Yagi-Uda antenna is a dipole antenna (sometimes folded dipole) with extra parasitic elements. Both the dipole and the parasitic elements are symmetrical; therefore the antenna is balanced; therefore it does not require any connection to ground to perform as designed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may wish to use grounding for protection against lightning or electrostatic buildup, but those are independent of the antenna design and can be done away from the antenna itself. (Lightning protection is a complex topic and must consider the electrical connections and physical layout in the whole station and building.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-06-25T16:46:25.233" LastActivityDate="2015-06-25T16:46:25.233" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5032" PostTypeId="1" CreationDate="2015-06-26T04:55:52.427" Score="7" ViewCount="159" Body="&lt;p&gt;A neighbor ham user recently started doing something that causes very noticeable feedback/buzzing in AM radio as well as any device that uses a wired microphone (such as a gopro with wired mic). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before I approach this individual, I'd like to make sure what the interference is.  Are there any cell apps or other equipment I could use to document (record levels, or at least plot what frequencies and dates/times) the disturbance? &lt;/p&gt;&#xA;" OwnerUserId="4899" LastEditorUserId="8717" LastEditDate="2021-02-13T03:46:33.270" LastActivityDate="2021-02-13T03:46:33.270" Title="Apps and or equipment needed to document local interference?" Tags="&lt;receiver&gt;&lt;rfi&gt;&lt;direction-finding&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5033" PostTypeId="1" AcceptedAnswerId="5035" CreationDate="2015-06-26T10:54:28.720" Score="2" ViewCount="253" Body="&lt;p&gt;I am using a double stacked Yagi-Uda antenna with about 57 Ω impedance. The 50 Ω feed line (coaxial) cables are combined using a tee connector. I observed, at the output of the tee connector, an impedance of about 28 Ω while transmission and hence I used a single short-end stub matching technique to transform this impedance into 50 Ω at the transceiver end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neglecting the practical terms such as attenuation, will this technique still cause reflections at the tee connector output? The wave shall see 28 Ω again from the stub to the tee connector output, so wouldn't there be a reflection again? &lt;/p&gt;&#xA;" OwnerUserId="4831" LastEditorUserId="76" LastEditDate="2017-04-26T17:22:01.060" LastActivityDate="2017-04-26T17:22:01.060" Title="Do stub matching techniques still produce some loss?" Tags="&lt;uhf&gt;&lt;impedance&gt;&lt;transmission-line&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5034" PostTypeId="1" AcceptedAnswerId="5038" CreationDate="2015-06-26T12:38:36.183" Score="3" ViewCount="226" Body="&lt;p&gt;Lets say I want to send some data from the London eye. I decide to mount the antenna at the centre of the wheel point out (normal to the circular plane). It's an omnidirectional antenna so I know there wont be any issue of point specifically, but due to the rotation of the wheel (and hence the antenna) does it cause any serious issue for a receiver on the ground (let say at the base of the wheel)? What if the receiver is moving (in a car driving past the base of the wheel)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, my current understand of how this works is since it doesn't matter where you are located relative to the antenna, it shouldn't matter if the antenna is rotating. However my intuition is that this isn't right! That there would be some issue with the received signal (similar to Doppler maybe?).&lt;/p&gt;&#xA;" OwnerUserId="529" LastActivityDate="2015-06-26T15:49:46.750" Title="Does a rotating source antenna (omi) cause any issue for receiving?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5035" PostTypeId="2" ParentId="5033" CreationDate="2015-06-26T14:44:37.900" Score="2" Body="&lt;p&gt;Yes, you have correctly analyzed the situation, and there will be reflections. But you ask if there will be any &lt;em&gt;loss&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reflections don't cause loss directly; they just traverse the same piece of transmission line many times and the loss in the line adds up. (Or to take a sum-of-all-the-reflections perspective: They cause increased current in the transmission line (relative to what's going in and out the ends), and therefore additional loss due to resistance.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another effect of reflections is to add a time delay to part of the signal, like multipath, &lt;a href=&quot;https://ham.stackexchange.com/q/2297/76&quot;&gt;but this rarely matters&lt;/a&gt;, and it is not loss per se — all the energy in still goes out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, “neglecting the practical terms such as attenuation”, there is no loss, but in practice there is. You can reduce the coax loss by minimizing the length between the stub and tee, of course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would theoretically make sense here is a tee with two 50 Ω ports and one 25 Ω port, but those don't exist since they'd need specialized connectors. Instead, you would build a custom matching circuit which just keeps everything inside as short as possible or, for higher frequencies, has &lt;a href=&quot;https://en.wikipedia.org/wiki/Microstrip&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance-matched PCB traces&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Note that what you're effectively building here is a &lt;em&gt;power divider&lt;/em&gt; (a.k.a. splitter in cable-TV land). Therefore, you could purchase it as a standard part instead of building your own, and it would be already designed to minimize reflections and loss. Then the worst problem you'd have is the 57 Ω - 50 Ω mismatch.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-06-26T14:44:37.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5036" PostTypeId="2" ParentId="5032" CreationDate="2015-06-26T15:05:38.987" Score="3" Body="&lt;p&gt;I think the most important thing to use is a clock. That is, record the times when the interference starts (I know, hard to do at times) and when it ends and even the way it behaves with starts and stops over a period of time. Unless the interference is due to something continuous going on inside the ham's equipment, the interference should not be continuous but have breaks (starts and stops) due to the nature of ham radio communication. Hams still keep log books (usually computer based) so this date and time information is the best evidence for identifying the source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, the second most important thing is a recording of the interference itself. After the ham operator is convinced it is him causing the interference (due to the information of dates and times) he will want to know what it sounds like to give him hints to the problems. It could just be that high power is overwhelming your very poorly engineered electronic equipment. Take no offense, almost all commercial electronic equipment found in homes today is poorly engineered to protect from RFI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When some neighbor approaches me about interference the first thing I ask is when -- that is, the date and time of the interference.  Usually the answer is vague (like, &quot;this morning&quot;) but with one particular neighbor, even the vague answer was sufficient for me to claim that I was not operating.  I actually showed her the detail of my log book to demonstrate my proof that I was not operating at the time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It turned out that this neighbor saw my antenna on my roof so any problems or unusual activity of her TV set (her complaint) were blamed on me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another neighbor complained of my CW signal coming through his stereo system speakers.  Now, I believed this complaint right off because he could almost copy the signal himself being a former (years ago) radio operator in the Navy.  It was only occurring when my power was above 1000 watts and since he was next door likely a near-field interference.  I put a number of ferrite RF chokes on his speaker cables and that solved the problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, today's modern TV sets are fairly immune to RF signals unless they are really close to the signal's near field.  For example, at about the 700 watt level with CW, I can often turn my TV set on (well, I have since fixed that problem).  The problem was the attached DVD player.  The signal came over the DVD player power line plug and then turned on the DVD player.  With my configuration, when the DVD player turns on, the HD TV set automatically turns on and switches to that HDMI port even if there is no DVD in the player.  Fixed again by using about a dozen small wraparound  style ferrite RF chokes on the power cable to the DVD player.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the interference is not due to a local ham radio operator, some other likely sources could be commercial equipment known to be RFI sources like:  Plasma TV sets (some vendor's), Fish Tank heating regulators, Wall-wart style switching type power supplies, Exercise treadmill!!  [Also a light dimmer.  These are notorious for wiping out a section of a band(s)]  My neighbor two doors down from my house has an exercise treadmill that can put a 40/9 signal on my receiver's S-meter.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="-1" LastEditDate="2015-06-29T01:55:20.710" LastActivityDate="2015-06-29T01:55:20.710" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5037" PostTypeId="1" CreationDate="2015-06-26T15:23:40.087" Score="2" ViewCount="186" Body="&lt;p&gt;What should I do with all the cables connecting this to that?&#xA;Coiled, folded, cut-to-length, wound on ferrite?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone have the definitive answer to this?&#xA;My rat's nest is getting more messy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cables I'm talking about are power, USB, RS232, and twisted pair. Basically anything that connects shack equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm both looking for aesthetics, as well as RFI issues. Cutting to length is really not an option as the equipment can be moved. Along with the fact I'm not that good at re-plugging the cables themselves. I was really wondering what people do as a general rule. All the mains electric supply and networks are neat and tidy in their ducting. It's just those pesky usb to rig, or usb to device. I think I'll coil them see if it makes any difference to the RFI. I live in an area where I get between S1 and S5 noise level over the HF bands. Very annoying when signals are normally QRP for my interest. SOTA. But have to make the best of what I've got. Will see if there any other idea's come out of the melting pot. 73&lt;/p&gt;&#xA;" OwnerUserId="4904" LastEditorUserId="13" LastEditDate="2015-06-29T11:56:25.350" LastActivityDate="2015-06-29T11:56:25.350" Title="Computer cables in shack — what to do with them?" Tags="&lt;rfi&gt;&lt;equipment&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5038" PostTypeId="2" ParentId="5034" CreationDate="2015-06-26T15:49:46.750" Score="3" Body="&lt;p&gt;“Omnidirectional antenna” is a bit of a misnomer; there is no antenna which radiates equally in all directions on the sphere. I'm going to assume you mean some kind of monopole or coaxial antenna, i.e. one that has all of its parts in a straight line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In that case, if it is, as you say, &lt;strong&gt;on&lt;/strong&gt; the axis of rotation, then the rotation makes no difference whatsoever. After all, it's rotationally symmetric about that axis. The radiation pattern is also symmetric (in both amplitude and phase) about that axis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to mount the antenna in the same orientation, but not at the center of the wheel, then there would be a very small amount of Doppler shift, since the distance from it to the receiving antenna changes. But the velocity is so small that it would not significantly affect reception — after all, it's slower than a radio in a car on a highway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(For an example of a radio technology which &lt;em&gt;does&lt;/em&gt; make use of significant Doppler shifts due to (effectively) moving antennas, take a look at &lt;a href=&quot;https://en.wikipedia.org/wiki/VHF_omnidirectional_range&quot; rel=&quot;nofollow&quot;&gt;VOR (VHF Omnidirectional Range)&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if you were to mount the antenna in the plane of the wheel instead, there would be major effects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your receiver is in a direction near the plane of the wheel, then the signal will drop out twice per revolution, as the two nulls of the antenna align with the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your receiver is in a direction near the axis of the wheel (e.g. some distance away and looking at it), then it sees the &lt;em&gt;polarization&lt;/em&gt; of the signal rotate. Using a normal, linearly polarized, antenna, the receiver would observe it fade out twice per revolution (as the polarization difference reaches ±90°). If the receiver instead had a circularly polarized antenna, then the signal would be stable but have a consistent 3 dB loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(This last scenario is exactly how communication with amateur satellites, which are usually spinning relative to the earth and have linearly polarized antennas, is best accomplished.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-06-26T15:49:46.750" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5039" PostTypeId="2" ParentId="5032" CreationDate="2015-06-26T20:48:06.850" Score="3" Body="&lt;p&gt;If it is from the ham, I would expect the following characteristics:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be intermittent, only happening for a few seconds to a minute at a time. Hams generally communicate in a conversation with modest length monologues, so the interference will probably come and go a bit like that. Also, it'll probably be only a few hours per day - even if he's retired and plays radio all day, he'll change band or mode and the interference will stop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would either be a series of clicks or crackles, or something like very distorted speech. Buzzing isn't as likely, but it's not impossible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be at shortwave frequencies. If you have an all band shortwave radio, try to isolate it by tuning around these most likely frequencies:&#xA;14.0 to 14.35 MHz, 21.0 to 21.45 MHz, 7.0 to 7.3 MHz.  Do this without extending the antenna, so you only hear strong local signals. Finding a smoking gun there doesn't guarantee that he's the problem, but it is more likely. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It will affect equipment with long wires more than short wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try to find a piece of electronics that is consistently affected, and keep notes about the duration and times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do start out on a friendly tack. Most hams would not like to cause interference even if we're somehow allowed to, we're aware the hobby is a bit fragile and requires careful management of our image. It may be that all of your equipment is just too sensitive to his perfectly legal radio transmissions, but it's also possible he has something wrong, which could land him in real trouble, so he'll probably listen to you.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-06-26T20:48:06.850" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5040" PostTypeId="2" ParentId="5024" CreationDate="2015-06-27T00:51:11.833" Score="1" Body="&lt;p&gt;Since the 12,5 kHz and 25 kHz were mentioned in the question, I think it might be a good idea to have an answer mentioning the &lt;a href=&quot;https://en.wikipedia.org/wiki/Carson_bandwidth_rule&quot; rel=&quot;nofollow&quot;&gt;Carson's rule&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rule is used for approximate calculation of FM bandwidth, which is the kHz number referred to in 12,5 and 25.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ B=2(f_{dev}+f_{mod_{max}})$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that means that our bandwidth doesn't just depend on our deviation, but also on the highest modulating frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually, you'll have some common combinations of maximum modulating frequency and deviation. For example, in 5 kHz systems, it's not uncommon to have a 3 kHz set as maximum audio frequency. From my interpretation of the quote in the question, I'd say that this are the 3 kHz it's talking about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we do the calculation, we get following:&#xA;$B=2(5 \mbox{ }kHz +3 \mbox{ } kHz)=16 \mbox{kHz}$, giving us some space for filter slope and the power outside of the Carson's bandwidth, if we're using the 25 kHz step. If we do calculation for so-called narrow-band, we'd get something like this:$B=2(2,5 \mbox{ }kHz + 2,5 \mbox{ }kHz)=10 \mbox{ }kHz$, giving us extra 2,5 kHz space for imperfections. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here we actually have some other considerations as well. Both transmitter and receiver need to have same audio bandwidth and same deviation in order for the system to work properly. If your deviation is too high, you run the risk of going outside of channel bandwidth and sounding over-modulated. If your deviation is too low, then you'll sound very quiet on reception. Why? Because your spectral lines that represent the tone will be too close together.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2015-06-27T00:56:57.473" LastActivityDate="2015-06-27T00:56:57.473" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5041" PostTypeId="1" CreationDate="2015-06-27T02:00:57.327" Score="2" ViewCount="93" Body="&lt;p&gt;I am interested in expanding my experimentation on visible light communication to Ultraviolet. The properties of visible light are well known because we see it every day, and have receiver equipped permanently. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Through Amateur radio, I have learned about the spectrum below visible wavelength, but I want to dive into higher frequency transmissions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are some common properties of Ultraviolet light (UVA, UVB, UVC) when exposed to the atmosphere, and materials on Earth such as buildings, mountains, clouds, etc.?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I begin experimenting on a budget?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2018-11-01T19:31:31.540" LastActivityDate="2018-11-01T19:31:31.540" Title="Properties of Ultraviolet transmissions" Tags="&lt;optical&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5044" PostTypeId="2" ParentId="5037" CreationDate="2015-06-28T03:21:43.377" Score="1" Body="&lt;p&gt;My priorities are to get cables off the floor so they can't be kicked around, avoid tight bends that alter capacitance in coax and leak signal, and avoid coiling cable that introduces unaccounted inductance.&#xA;To accomplish this, I mount behind my desk something that looks like a coat rack with 2 rows of 1&quot; diameter dowel rods.  I weave excess signal and computer cable loosely back and forth in a W pattern onto it, keeping analog separate from digital.&#xA;DC cables I cut red/black zip cord to length and make new cables when I have to.&#xA;AC cables I am not as concerned about, so just bundle them all together and wrap the whole bundle with a large velcro strap, or put them all in a mesh laundry bag, then hang the bundle off one of the pegs.&lt;/p&gt;&#xA;" OwnerUserId="4912" LastActivityDate="2015-06-28T03:21:43.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5045" PostTypeId="2" ParentId="5041" CreationDate="2015-06-28T12:51:12.373" Score="3" Body="&lt;p&gt;Hams have played with visible light communication for ages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Near-UV is pretty similar to visible light, so you could do the same sort of experiments, you can easily buy good LEDs and photodiodes in the UV range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There might be less ambient noise than in the visible and IR ranges, but there will be more atmospheric absorption.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do a bit of searching for amateur projects that cheap laser pointers, or LEDs, you'll find several of these. Also seatch for an LED-based data transmission project, that extends an ethernet cable over a free space optical link.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-06-28T12:51:12.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5046" PostTypeId="1" AcceptedAnswerId="5047" CreationDate="2015-06-28T22:47:28.310" Score="1" ViewCount="1294" Body="&lt;p&gt;I have found, and the manual agrees, that the Yaesu FT-897 (and presumably the essentially identical FT-857) stores multiple “RF POWER SET” values, for different bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manual simply describes this value as “for the current band”, but I have found that not every band has a separate value. Which bands have separate power values?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like this information so that I can know when I need to change the setting if I am changing bands but want to use the same power, or so that if I have been using high power and want to reset everything to low power to avoid damage to sensitive equipment, I can be sure I have reset it for all bands.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-07-27T14:23:35.010" Title="How many independent power settings does the Yaesu FT-897/857 have?" Tags="&lt;yaesu&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5047" PostTypeId="2" ParentId="5046" CreationDate="2015-06-28T22:47:28.310" Score="2" Body="&lt;p&gt;Empirically, there are four independent power settings.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;HF          0-32.99999 MHz     5-100 W&#xA;50 MHz     33-56               5-100&#xA;VHF        76-164              5-50&#xA;UHF       420-470              2-20&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The frequency ranges shown exceed those in which the FT-897 will transmit, of course, but it will still display a particular one of the four stored values for any given tunable frequency.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-07-27T14:23:35.010" LastActivityDate="2015-07-27T14:23:35.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5048" PostTypeId="1" AcceptedAnswerId="5051" CreationDate="2015-06-29T14:01:13.287" Score="3" ViewCount="81" Body="&lt;p&gt;I am trying to find general difference between radiation patterns of &lt;a href=&quot;https://en.wikipedia.org/wiki/Smart_antenna&quot; rel=&quot;nofollow&quot;&gt;adaptive&lt;/a&gt; and stationary antennas (common difference, calculation difference and any other). I am interesting in any example and better any science publication on this theme. Appreciated any help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could confused by word &quot;stationary&quot;, for this question two things can be applicable &quot;smart antennas&quot; as stationary antennas or even any other antennas (stationary too), and under term &quot;adaptive&quot; I mean &quot;smart antennas&quot; in mobile systems (for example in military systems on wheels).&lt;/p&gt;&#xA;" OwnerUserId="4918" LastEditorUserId="4918" LastEditDate="2015-06-29T18:25:47.160" LastActivityDate="2015-06-30T11:17:03.793" Title="What's the general difference between radiation patterns of stationary and adaptive aerials in mobile communication systems?" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5049" PostTypeId="1" CreationDate="2015-06-29T15:46:47.187" Score="2" ViewCount="328" Body="&lt;p&gt;I've just finished Field Day, and my 4 hours of operating my club's station resulted in about 70 qsos/ hour, no more than 80. Some of the other operators topped 120. How can I improve my QSO rate to get to the level that these other operators have?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically, I'm comparing voice/ voice operators, on the same band and about the same time of day, where one gets lots of qsos, and one not quite as many. We both ran a frequency.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2015-06-29T16:28:31.153" LastActivityDate="2015-07-06T11:46:34.723" Title="How can I speed up my QSO rate for Field Day" Tags="&lt;contest&gt;&lt;field-day&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5050" PostTypeId="2" ParentId="5049" CreationDate="2015-06-29T16:03:29.800" Score="1" Body="&lt;p&gt;QSO speed up...&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Be a part of a club with multiple operators.&lt;/li&gt;&#xA;&lt;li&gt;All QSOs CW.&lt;/li&gt;&#xA;&lt;li&gt;Use automatic computer logging of QSOs (e.g. N1MM Logger)&lt;/li&gt;&#xA;&lt;li&gt;Cheat and use automatic computer macros and copy rather than sending by hand and receiving by ear.&lt;/li&gt;&#xA;&lt;li&gt;Make sure CW speed is 35+ and stick to the lower portions of the bands where others operate at that speed.&lt;/li&gt;&#xA;&lt;li&gt;Most importantly, give up sleep, eating, and bathroom breaks during the entire weekend.&lt;/li&gt;&#xA;&lt;li&gt;Have a short 1x2 or 2x1 call sign.  Send brief CQ, Just &quot;CQ FD DE N1AX&quot; and park on one frequency, do not move around.  Just kidding about the short call sign but it may help.&lt;/li&gt;&#xA;&lt;li&gt;Keep replies to brief minimum exchange, nothing else.  My reply to the above CQ once my call is picked up would be &quot;TU 1B WWA&quot; which translates &quot;Thank you, one operator, class B Western Washington Section (ARRL)&quot;.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2015-06-29T17:51:17.980" LastActivityDate="2015-06-29T17:51:17.980" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5051" PostTypeId="2" ParentId="5048" CreationDate="2015-06-30T11:17:03.793" Score="2" Body="&lt;p&gt;Non-adaptive antennas in mobile systems are usually omnidirectional, meaning they radiate equally in all directions. They can also have directional antennas, if there is some means for getting them to point in the right direction. Usually that means the vehicle on which the antenna is mounted has to stop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adaptive arrays are directional antennas that automatically point themselves in the right direction. This could be determined by the &lt;a href=&quot;http://www.antenna-theory.com/arrays/weights/lms.php&quot; rel=&quot;nofollow&quot;&gt;least mean square (LMS) algorithm&lt;/a&gt;, for example. This algorithm works by finding the coefficients for each array element which minimize the error in some known aspect of the signal, like a sub-carrier, synchronization, or error-correction information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the algorithm is dynamic and statistical, we can't say exactly what the radiation pattern will look like, but generally lobes will be placed in the direction of the desired signal, and nulls in the direction of noise sources. It will maintain this orientation even as the stations move, since the LMS algorithm constantly adjusts the coefficients to compensate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-06-30T11:17:03.793" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5052" PostTypeId="1" AcceptedAnswerId="5053" CreationDate="2015-06-30T15:44:14.997" Score="3" ViewCount="261" Body="&lt;p&gt;I've been using a USRP software-defined radio to try to send an amplitude modulated signal to a very basic receiver, basically just a piece of wire as an antenna, over a very short distance.  The signal, a wav file of me counting to ten, is transmitted clearly enough to be understood by a human, but not by a speech-to-text program.  The received signal is also clearly much higher in frequency than the transmitted signal.  I took FFTs(illustrations provided below) of the sent and received signals and it seems clear to me that the lower frequencies in the signal are not being transmitted as strongly.  The solution I've been trying to work on is adjusting the signal I'm transmitting by amplifying the lower frequencies of the signal and attenuating the higher frequencies using Python to modify the original wav file.  My question is whether this seems like a viable solution or not?  Is it possible to make up for a transfer function that is making it difficult to transmit the low frequency parts of the signal by amplifying those parts of the signal in the file to be transmitted?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.imgur.com/13q897M.png&quot; alt=&quot;fft of signal sent&quot;&gt;&#xA;&lt;img src=&quot;https://i.imgur.com/FrWVJzw.png&quot; alt=&quot;fft of received signal&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the GnuRadio flowchart I'm using for the USRP transmission:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.imgur.com/hH4MtwU.png&quot; alt=&quot;GnuRadio flowchart&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="4923" LastEditorUserId="4076" LastEditDate="2016-01-17T22:26:09.240" LastActivityDate="2016-01-17T22:26:09.240" Title="Losing Low Frequencies in AM transmission" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5053" PostTypeId="2" ParentId="5052" CreationDate="2015-06-30T19:00:50.123" Score="3" Body="&lt;p&gt;You are not making an AM transmission, because you have not added a carrier. Without a carrier, what you have is &lt;em&gt;double sideband&lt;/em&gt; (DSB) modulation, which will not be properly demodulated just by an improvised detector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To create the carrier, &lt;strong&gt;add a constant value&lt;/strong&gt; to the signal (between the Multiply Const and Float To Complex stages).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Constraints:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The carrier should be of greater amplitude than the peak level of the modulating signal, to avoid &lt;em&gt;overmodulation&lt;/em&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You should also make sure that the final signal does not exceed a level of ±1, which would cause it to be clipped (distorted) by the USRP's DAC or a preceding float-to-integer conversion.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Together, these constraints mean that for best dynamic range your carrier should have a value of 0.5, and the input signal, if it had a maximum range of ±1 (which I believe is true for GR WAV sources, but your file may be significantly quieter), should be multiplied by 0.5, so that the resulting signal has a range of 0 to 1.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I would recommend visualizing your signal by adding a GUI FFT Sink in parallel with the UHD sink, to observe that it has the proper spectrum of an AM signal. If you wanted to simulate the effects of quantization and possible clipping, you could do so by converting the signal to short or byte and back before feeding it to the FFT sink.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-06-30T20:40:53.520" LastActivityDate="2015-06-30T20:40:53.520" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5054" PostTypeId="1" AcceptedAnswerId="5055" CreationDate="2015-06-30T21:23:22.863" Score="7" ViewCount="7083" Body="&lt;p&gt;I would like to get involved in ham radio and I'm inclined to study for and take the General exam right away, rather than going for Technician and then upgrading. Are there good reasons not to do this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this course of action is allowed and not ill advised, then does The ARRL General Class License Manual assume a base of knowledge covered in the Technician Class manual, or can the General Class manual stand on its own for someone starting from no ham knowledge?&lt;/p&gt;&#xA;" OwnerUserId="4927" LastEditorUserId="8717" LastEditDate="2020-10-26T20:12:31.587" LastActivityDate="2020-10-26T20:12:31.587" Title="Straight to General license, skipping Technician?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5055" PostTypeId="2" ParentId="5054" CreationDate="2015-06-30T21:38:37.703" Score="8" Body="&lt;p&gt;You can't take the General exam &lt;em&gt;only&lt;/em&gt;, if that's what you're asking. What you can do is take the Technician and General (and Extra, should you so choose) exams in one sitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're going to take an exam at all, there is no reason not to continue to the highest level of examination you expect to be able to pass, unless you want to deliberately limit yourself until you have gained experience. (I haven't heard of anyone actually doing that.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Make sure to let the examiners know you're planning on this, just in case it matters for their scheduling — a General or Extra class test requires Extra class examiners, and of course there is the time taken to administer the second test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, if you initially obtain an Extra class license (I did this), you may be assigned a shorter call sign than you would otherwise — though you can apply for a change, or a specific vanity call sign, later. Shorter call signs are an advantage if you care about how long it takes to speak or send your call sign, such as in a contest. (Technician and General licenses have the same pool of allowed call signs.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;As to your second question, if I recall correctly, the ARRL license books are incremental just like the exams — you would need all of the books up to the level you're studying for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are other study materials besides the ARRL’s, including free ones on the Web — if you think you might be interested in higher levels I encourage you to just try a free practice test (&lt;a href=&quot;https://hamstudy.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;one such site I used&lt;/a&gt;) and decide whether you'd like to learn the material and how.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-05-04T15:04:16.330" LastActivityDate="2020-05-04T15:04:16.330" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="5056" PostTypeId="2" ParentId="5054" CreationDate="2015-07-01T00:31:10.523" Score="-2" Body="&lt;p&gt;There is one good reason not to do this as it is not allowed by the FCC.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Technician, General and Exam liscenses are access to privileges. You must take each exam. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://arrl.org/upgrading-to-a-general-license&quot; rel=&quot;nofollow&quot;&gt;ARRL&lt;/a&gt; quotes: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;&lt;em&gt;To upgrade to General Class, you must already hold a Technician Class&#xA;  license (or have recently passed the Technician license exam).&lt;/em&gt;&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In terms of vanity call signs and what is available you can start here: arrl.org/vanity-call-signs and arrl.org/applying-for-a-vanity-call. Does that help? –  KG5HNZ 8 mins ago   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look at this chart and you'll see why it makes sense to be licensed in the three Classes.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Regulatory/Band%20Chart/Hambands_color.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/files/file/Regulatory/Band%20Chart/Hambands_color.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, there are other rules and regulations that you must be aware of as a holder of a Technician, General and Extra licenses.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When taking the Technician Class Exam, if you pass you are given a chance for free to attempt the General Class exam.  Upon passing the General Class in turn you can take the Extra Class Exam, for free.  This provides you with all privileges that are available to you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen this done and its quite possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Call signs have changed recently, so its best to goto the ARRL site to read up on the changes.  Honestly, just get your license before you start thinking about changing your call sign, that essentially you don't have at the moment.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In terms of vanity call signs and what is available you can start here: arrl.org/vanity-call-signs and arrl.org/applying-for-a-vanity-call.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you feel you are ready for the General Class then try the tech mock exams on the internet and see how you do... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope that helps.&lt;/p&gt;&#xA;" OwnerUserId="4928" LastEditorUserId="13" LastEditDate="2015-07-01T11:56:27.590" LastActivityDate="2015-07-01T11:56:27.590" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5057" PostTypeId="2" ParentId="5054" CreationDate="2015-07-01T02:56:20.977" Score="1" Body="&lt;p&gt;When I was living in the US for a short while in 1995 (for work), I decided to sit the US amateur exams since it was allowed for anyone from anywhere to sit them back then. I am originally from the UK, and held/hold a UK licence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was told that I could take as many exams as I wanted, starting at the Novice and working up the five classes (Novice, Technician, General, Advanced and Extra). My plan was to take as many as they would allow - if I failed one, that would determine which class of licence I would qualify for. I also sat the Morse tests, as those were still required then. For those I did them the other way round - I planned to take the 20wpm first, and if I failed that I would try the 13wpm and finally the 5wpm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They gave the 20 wpm Morse test first, and I managed to scrape by a pass. So that was good - I only needed to take one test. Then I sat the exams in order.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the end of the session, by lunchtime I walked out qualified as an Extra Class ham. I was a happy man :)&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-07-01T02:56:20.977" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5058" PostTypeId="1" CreationDate="2015-07-01T03:23:44.637" Score="2" ViewCount="85" Body="&lt;p&gt;Is there another book I can use to study for my test?&#xA;This ARRL Ham Radio License Manual book (Level 1 ) is HORRIBLE!&#xA;I never had electronics anything in school nor electricity. &#xA;I got through the explanations about frequency even though I am still confused. One paragraph referred to a term that wasn't explained until the next page. DUH.&#xA;Then I got to the electronics section. OMG!!! It's horrible. One unfamiliar term after another after another with limited explanations.&#xA;I have absolutely no idea what this guy is talking about.&#xA;No wonder people get scared away.&#xA;If I can't find another way to learn this (no classes within 400 miles), I am just going to give up.&#xA;I haven't even gotten to the place where I learn how to use my radio yet.&lt;/p&gt;&#xA;" OwnerUserId="4929" LastActivityDate="2015-07-01T03:37:26.117" Title="Beginner: Is there another book?" Tags="&lt;arrl&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2015-07-01T11:55:12.790" ContentLicense="CC BY-SA 3.0" />
  <row Id="5059" PostTypeId="1" AcceptedAnswerId="5087" CreationDate="2015-07-01T03:35:16.300" Score="11" ViewCount="505" Body="&lt;p&gt;I know that the amateur bands are not channelized. I know that anyone can pick an arbitrary frequency and they're not wrong, and you are not obligated to have a calibrated VFO. But if everyone picks frequencies at random during a period of heavy usage, there's likely to be inefficient allocation due to not-quite-wide-enough gaps to fit in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do there exist, then, any &lt;strong&gt;conventions for what frequencies to use, that are more widespread than each individual operator's idea for best practice?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thinking about this once, I said to myself: SSB is 3 kHz wide, so we can divide that neatly into XXX0000, XXX3000, XXX6000 Hz with only a little bit of waste.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More recently while I was operating on Field Day this year, I noticed a lot of people using XXXX500 Hz frequencies, and it occurred to me that if we consider the bandwidth as 2.4 or 2.5 kHz (as it apparently typically is as &lt;em&gt;transmitted&lt;/em&gt;, even if receive filters aren't that sharp) then four channels fit into 10 kHz that way. Is that something people try do? (Reviewing my logs, some but not all of the 500 Hz frequencies fit this pattern.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But trying to spot the pattern this way is an exercise in numerology. Are there any &lt;strong&gt;deliberately promoted, or somewhat accepted, schemes&lt;/strong&gt; for SSB frequency selection?&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-07-03T00:10:20.747" LastActivityDate="2015-07-12T23:06:09.847" Title="Is there a convention for SSB frequency selection?" Tags="&lt;procedure&gt;&lt;ssb&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5060" PostTypeId="2" ParentId="5058" CreationDate="2015-07-01T03:37:26.117" Score="3" Body="&lt;p&gt;I studied for my technician class exam using Gordon West's book:&#xA;&lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/0945053800&quot; rel=&quot;nofollow&quot;&gt;http://www.amazon.com/Technician-2014-2018-manual-HamStudy-software/dp/0945053800&lt;/a&gt;&#xA;It basically just goes through each question in the question pool and explains how to understand the question. I studied for about a month, just memorizing each question and getting a basic understanding. You should also supplement your learning with &lt;a href=&quot;http://www.qrz.com/hamtest/&quot; rel=&quot;nofollow&quot;&gt;QRZ practice tests&lt;/a&gt;. Try to meet other people in your area and ask them lots of questions.&lt;/p&gt;&#xA;" OwnerUserId="4930" LastActivityDate="2015-07-01T03:37:26.117" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5061" PostTypeId="1" AcceptedAnswerId="5141" CreationDate="2015-07-01T04:00:34.527" Score="14" ViewCount="630" Body="&lt;p&gt;Idle curiosity:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are the call signs of amateur radio operators distinct from call signs in all other radio services, such that there can be no ambiguity even if the relevant license and band(s) of operation is disregarded?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If they are not distinct internationally, are they distinct in the United States?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I'm interested primarily in overlap &lt;em&gt;not&lt;/em&gt; the result of an administrative dispute, and between amateurs and a different radio service.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;To be accepted, an answer should be &lt;strong&gt;complete&lt;/strong&gt;, even if this means repeating what has already been said. Citations would be nice, too.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-07-22T00:59:49.177" LastActivityDate="2015-07-22T00:59:49.177" Title="Are amateur radio call signs unique among all radio call signs?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;callsign&gt;" AnswerCount="4" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5062" PostTypeId="1" CreationDate="2015-07-01T12:45:50.907" Score="4" ViewCount="196" Body="&lt;p&gt;For Field Day this year, most stations on the East Coast received a large amount of rain. I've heard our reports at around 2 inches of rain. Being Field Day, we were operating outdoors inside tents, but we still had a few issues with the radios, despite them being protected. The most significant issue was a foot petal that became submerged when water seeped in underneath the tent, which caused not only the foot pedal to stop working, but seemed to cause other issues with the radio, which rather than troubleshoot in the middle of Field Day we switched out the radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can we operate efficiently in a condition where there is a lot of rain? This includes both Field Day and other emergency type situations. &lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-07-02T02:55:24.463" Title="How can I operate in the rain safely?" Tags="&lt;emergency&gt;&lt;field-day&gt;&lt;weather&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5063" PostTypeId="1" CreationDate="2015-07-01T12:53:53.920" Score="3" ViewCount="222" Body="&lt;p&gt;I noticed when operating Field Day this year that during a period of rain, the RF background noise went up as well, from about S2 to S5-6. I was operating inside a tent, with the antenna outside the tent. It got me thinking though, is there things that I can do to a home station to keep the RF noise down during a rainstorm?&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-07-06T11:28:23.093" Title="Rain and RF noise" Tags="&lt;noise&gt;&lt;weather&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5064" PostTypeId="1" AcceptedAnswerId="5065" CreationDate="2015-07-01T16:01:37.703" Score="3" ViewCount="236" Body="&lt;p&gt;I am trying to engineer my first antenna to get on the air. I need to hit a repeater 50 miles away at a lower elevation than me so that I can use its IRLP nodes. Would this mean I am looking for low angle radiation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;25 feet up with an HT  in the clear and a rubber duck antenna and I can hear just the faintest crackle. I believe that a rhombic would be a cheap, interesting, and clear way of getting my signal to the repeater. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will it need to be vertically polarized, considering everyone else will be? I started working on the design, here are some preliminary radiation maps before optimization. I just wanted to confirm that I had the correct polarization for the job. ANY tips regarding rhombics would be appreciated as I am new to the hobby and will probably learn a few things the hard way on this project :D&#xA;&lt;img src=&quot;https://i.stack.imgur.com/44ZcX.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;* Note that the scale on the perimeter of the chart is shifted 90 degrees for some reason, I didn't see this at first. *&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/6sr7F.png&quot; alt=&quot;Horizontal Plane&quot;&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/axgAJ.png&quot; alt=&quot;General Orientation&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="4932" LastEditorUserId="4932" LastEditDate="2015-07-01T19:09:44.193" LastActivityDate="2015-07-01T19:09:44.193" Title="Rhombic Polarization Question, provided radiation maps" Tags="&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;2m-band&gt;&lt;polarization&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5065" PostTypeId="2" ParentId="5064" CreationDate="2015-07-01T18:34:06.310" Score="1" Body="&lt;p&gt;Some information, since you asked for comments:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) your rhombic isn't working properly. It shouldn't have a double beam like that, it should have a single forward beam. Something about the proportions is wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can and should design a rhombic from formulas, and only simulate at the end. It's a well understood antenna, there is good design data for it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It needs a termination resistor at the end away from your feed. It's not showing in your model. This needs to be non-inductive, which is tricky for 2m, possibly made of a hundred quarter-watt resistors in series and parallel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) as they are usually built, rhombics are horizontally polarised. The repeater is almost certainly vertical. You need to tilt it up on edge to make it vertical. The masts that support it, both the the middle and at the front, must be non-conductive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) You're simulating over a ground plane, which is appropriate for HF because it's so intimately involved in the antenna fields. For a VHF antenna 25' up, the ground doesn't matter. You should remove the ground and simulate the antenna in free space. The ground will get involved later, a hundred metres away, but it affects all antennas equally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4) consider a yagi instead. The main features of rhombics are their simple construction, limited number of supports, and wide bandwidth to cover many bands. This makes them attractive for HF when you have a lot of space. They have reasonably good gain, but nothing like a yagi. Do some digging for information about the gain of a yagi and compare. For example, you can easily make a yagi for 2m from an old broomstick and some fencing wire / welding rods, that will give you about 10 dBi, which is at least 13 to 16 dB more than your handheld antenna yields. If you want a lot of gain, look up the Rope Yagi, which can be made very long.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-07-01T18:34:06.310" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5066" PostTypeId="1" CreationDate="2015-07-01T18:53:04.103" Score="2" ViewCount="457" Body="&lt;p&gt;I am currently working on a student project that involves having a UAV fly an orthogonal path over a series of transmitters -- taking in data (through an arduino-based system for data processing).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is -- I can't seem to decide on the right antenna(s, if more are required) in order to efficiently receive these signals (from these various trackers and transmitters in the canopy). A suggestion was to use a series of omni-directional whip aerial antenna linked to a single receiver. Most of the recording would be done on board. The drone should theoretically fly a .5 grid over the canopy area, sweeping for signal strength throughout the channels (operating in the 142 - 150 MHz range).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately,  I am a bit directionless in the area of hardware -- what receiver and corresponding antenna would be optimum for logging signal strength over a forested area. I've looked into smaller Yaesu receivers, but I am a bit clueless in regards to what antenna attachment to look into -- perhaps a series of omnidirectional whip antennas linked to a receiver. An alternative was also taking a Baofeng radio and hacking the thing. The bird itself would be reasonably high above the canopy, but I'm told that the rule of thumb is basically to be able to sweep the area as far as possible while maintaining a good gauge of signal strength from each transmitter beneath the canopy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would any of you be able to point me in the right direction in terms of hardware? I work mostly on the software end, so this is a rather new horizon for me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="4936" LastEditorUserId="4936" LastEditDate="2015-07-04T04:14:44.783" LastActivityDate="2015-07-04T04:14:44.783" Title="VHF antenna / receiver suggestion for a UAV" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;transceiver&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5067" PostTypeId="2" ParentId="3713" CreationDate="2015-07-01T19:18:47.147" Score="2" Body="&lt;p&gt;I think this is a very legit question — a search only returns an array of stuff that are marketing blurbs, out of date links, and flame wars about CW and the old days.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I built an Elecraft K2 (serial #1067) ~14yrs ago and they are still made today! It was a very enjoyable experience and it still performs very well. The nice thing is that you can start QRP with basic features and add kits to make it full-featured. There are extensive materials that explain the theory of each part of the design and build process, and a mailing list that is &lt;em&gt;very&lt;/em&gt; active.&lt;/p&gt;&#xA;" OwnerUserId="4925" LastEditorUserId="76" LastEditDate="2015-07-01T20:23:03.867" LastActivityDate="2015-07-01T20:23:03.867" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5068" PostTypeId="1" AcceptedAnswerId="5070" CreationDate="2015-07-01T21:40:56.410" Score="2" ViewCount="292" Body="&lt;p&gt;So I'm trying to understand how radiation pattern are calculated and it's going well (so far!). I've come across a bit of an issue when it comes to the following situation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we have a omnidirectional antenna and then place some reflective material collinear with the direction of the radiation (so if the antenna was a flag pole, the material could be like a flag) does the reflective material interfere with the radiated signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now intuitively I would say no, since the material is collinear with the radiation then it can not reflect the radiation in any way, I understand that the material couldn't be infinitely thin so there would be a small section of reflected/absorbed radiation, but that would be pretty tiny.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So where am I going wrong in my understanding here? I've found another forum where someone says this isn't how it works, but not why.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="529" LastActivityDate="2017-10-19T13:46:33.713" Title="Can you place reflective material near to an antenna without interfering with the radiation pattern?" Tags="&lt;antenna&gt;&lt;radiation-pattern&gt;&lt;antenna-reflector&gt;&lt;reflector&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5069" PostTypeId="2" ParentId="1099" CreationDate="2015-07-01T23:29:15.093" Score="1" Body="&lt;p&gt;A lot of people in the United States refer to the 70 cm band as “440”, because that’s pretty close to where the repeaters in the 70 cm band start.&lt;/p&gt;&#xA;" OwnerUserId="775" LastEditorUserId="76" LastEditDate="2015-07-02T14:07:06.663" LastActivityDate="2015-07-02T14:07:06.663" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5070" PostTypeId="2" ParentId="5068" CreationDate="2015-07-01T23:38:52.383" Score="3" Body="&lt;p&gt;If the only thing the material did was &quot;reflect&quot;, and it was like a flag on a vertical antenna, then I guess it wouldn't have any effect on the radiation pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that no such material exists.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One problem is that for a material to &quot;reflect&quot;, it has to be many (at least 10, say) wavelengths long. Any less than this, and effects like &lt;a href=&quot;https://en.wikipedia.org/wiki/Diffraction&quot; rel=&quot;nofollow&quot;&gt;diffraction&lt;/a&gt; will be significant, and so the material won't behave very much like an ideal reflector. There are &quot;reflectors&quot; that are less than many wavelengths long, such as the elements of a &lt;a href=&quot;https://en.wikipedia.org/wiki/Yagi-Uda_antenna&quot; rel=&quot;nofollow&quot;&gt;Yagi antenna&lt;/a&gt;, but these work by being tuned to very specific sizes, and that's probably not what you had in mind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another problem is that any material that you might consider for this purpose (like metal), will have &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity&quot; rel=&quot;nofollow&quot;&gt;conductivity&lt;/a&gt; and &lt;a href=&quot;https://en.wikipedia.org/wiki/Permeability_(electromagnetism)&quot; rel=&quot;nofollow&quot;&gt;permeability&lt;/a&gt; significantly different than that of air. The electromagnetic radiation an antenna produces is the result of mutually perpendicular electric ($\vec E$) and magnetic ($\vec B$) fields. In the case of a vertical antenna, the electric field is vertical, and the magnetic field horizontal, concentric with the antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Felder_um_Dipol.jpg#/media/File:Felder_um_Dipol.jpg&quot; rel=&quot;nofollow&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/d/da/Felder_um_Dipol.jpg&quot; alt=&quot;Felder um Dipol.jpg&quot;&gt;&lt;/a&gt;&lt;br&gt;&quot;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Felder_um_Dipol.jpg#/media/File:Felder_um_Dipol.jpg&quot; rel=&quot;nofollow&quot;&gt;Felder um Dipol&lt;/a&gt;&quot; by Averse - http://de.wikipedia.org/wiki/Datei:Felder_um_Dipol.jpg. Licensed under &lt;a href=&quot;http://creativecommons.org/licenses/by-sa/3.0/&quot; rel=&quot;nofollow&quot; title=&quot;Creative Commons Attribution-Share Alike 3.0&quot;&gt;CC BY-SA 3.0&lt;/a&gt; via &lt;a href=&quot;https://commons.wikimedia.org/wiki/&quot; rel=&quot;nofollow&quot;&gt;Wikimedia Commons&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Were you to put a metal &quot;flag&quot; on this antenna, it would be coplanar with the electric field. Metals are very conductive (that's what gives them their shiny appearance), and so they will have a very significant effect on that electric field, which in turn affects the radiation pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Put more generally, your line of thought seems to be based on reasoning that works with mirrors and visible light. But even though visible light and radio waves are electromagnetic radiation which differ only in wavelength, this turns out to be very significant. Visible light has a wavelength on the order of 500 nm, whereas the radiation from a 2.4 GHz Wi-Fi has a wavelength of approximately 125,000,000 nm, or approximately 250 thousand times bigger. If you could make your bathroom mirror 250 thousand times smaller you'd find intuition breaks down, and you will start seeing effects not usually seen in everyday life simply because they are so small.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-07-01T23:38:52.383" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5071" PostTypeId="1" AcceptedAnswerId="5073" CreationDate="2015-07-02T01:44:10.980" Score="2" ViewCount="217" Body="&lt;p&gt;I am trying to learn about how to talk to satellites and the ARISS via ham radio. What I am wondering is if there is an audio feature I can access for the azimuth. In the sun, I cannot really see the images on the laptop that well, so this would be helpful. I use Gpredict for a satellite tracking program. Any suggestions are always helpful, thank you very much in advance. &lt;/p&gt;&#xA;" OwnerUserId="1861" LastEditorUserId="76" LastEditDate="2016-10-27T19:08:14.920" LastActivityDate="2016-10-27T19:08:14.920" Title="Is there an audio feature for Gpredict?" Tags="&lt;satellites&gt;&lt;software&gt;&lt;antenna-rotator&gt;&lt;gpredict&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5072" PostTypeId="2" ParentId="5062" CreationDate="2015-07-02T02:55:24.463" Score="2" Body="&lt;p&gt;Generally, keep equipment higher up and sheltered from the elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The comment above about being unsympathetic to the desire for a foot-switch is not far off the mark too. A foot-switch is a comfort, and (as you have discovered) Field Day is not about comforts. If it's dry and pleasant out then sure, use a foot-switch. If it starts getting damp, unplug it and live with the reality that life is sometimes cold and wet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When it rains heavily, keep electrical equipment dry at all costs. Keep batteries higher up (on a desk) and protected from water, while allowing some of that horrible cold air to circulate around them (lead-acid batteries can give off explosive hydrogen when under heavy current loads). Be especially careful if you are using a generator - it might be weatherproof, but the 110v it generates is going to cause some problems if it starts finding itself submerged. If you do use a generator, make sure it is weatherproof, and keep it on a table outside. Run the 110v lines high up, and drop them down to the equipment that needs it. There are reasons why the electrical utility companies tend to take this approach. All outlets inside should be high up and kept dry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep yourself and the team warm and dry - there is no point in being miserable through the exercise. And keep your spirits up! If you follow these guidelines, you can enjoy the experience, and will probably be doing a lot better than the other teams in similar conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Always try to enjoy the predicament, and remember that you are doing this out of choice, for fun. It will help you get more from the whole event.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-07-02T02:55:24.463" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5073" PostTypeId="2" ParentId="5071" CreationDate="2015-07-02T03:27:00.260" Score="4" Body="&lt;p&gt;&lt;strong&gt;I just wrote you one.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the things Gpredict can do is control antenna rotators (via the &lt;em&gt;hamlib&lt;/em&gt; driver library). In this case, you're the rotator, but hamlib can't handle that (as far as I know), so instead we'll use a program that pretends to be hamlib (more precisely, pretends to be &lt;code&gt;rotctld&lt;/code&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Setup instructions&lt;/strong&gt; (I'm going to assume you're on a unixy system and somewhat comfortable with it; if not I recommend finding someone to help you in person):&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Install &lt;a href=&quot;https://twistedmatrix.com/trac/&quot; rel=&quot;nofollow&quot;&gt;Twisted&lt;/a&gt;, a Python library I used. It should be available through your favorite package manager as well as from their site.&lt;/li&gt;&#xA;&lt;li&gt;Install some text-to-speech software if you don't have any already.&lt;/li&gt;&#xA;&lt;li&gt;Change the line &lt;code&gt;COMMAND = 'say'&lt;/code&gt; in my program to refer to whatever command your text-to-speech software uses (I hear &lt;code&gt;espeak&lt;/code&gt; and &lt;code&gt;spd-say&lt;/code&gt; are some other names; &lt;code&gt;say&lt;/code&gt; is the command on Mac OS X).&lt;/li&gt;&#xA;&lt;li&gt;In Gpredict, go to Edit → Preferences → Interface → Rotators → Add New. Put in some name or other and leave the rest of the settings alone.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Usage instructions:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Start my program.&lt;/li&gt;&#xA;&lt;li&gt;In the &quot;module options&quot; menu accessed by the little button in the upper-right corner of the main window, select Antenna Control. In the Antenna Control window:&lt;/li&gt;&#xA;&lt;li&gt;Set the Cycle and Tolerance values to control how often it speaks.&lt;/li&gt;&#xA;&lt;li&gt;Click the Engage button.&lt;/li&gt;&#xA;&lt;li&gt;Choose your target and click the Track button.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The program:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;#!/usr/bin/env python&#xA;&#xA;import os&#xA;from twisted.internet import protocol, reactor, endpoints&#xA;from twisted.protocols.basic import LineReceiver&#xA;&#xA;COMMAND = 'say'&#xA;&#xA;class RotctlEmulator(protocol.Protocol):&#xA;    def __init__(self):&#xA;        self.az = 0.0&#xA;        self.el = 0.0&#xA;        self.__line_receiver = LineReceiver()&#xA;        self.__line_receiver.delimiter = '\n'&#xA;        self.__line_receiver.lineReceived = self.__lineReceived&#xA;&#xA;    def dataReceived(self, data):&#xA;        self.__line_receiver.dataReceived(data)&#xA;&#xA;    def __lineReceived(self, line):&#xA;        if line == 'p':&#xA;            self.transport.write('%.6f\n%.6f\n' % (self.az, self.el))&#xA;        elif line.startswith('P'):&#xA;            _p, azstr, elstr = line.split()&#xA;            new_az = float(azstr)&#xA;            new_el = float(elstr)&#xA;            self.transport.write('RPRT 0\n')&#xA;            self.update(new_az, new_el)&#xA;        else:&#xA;            print 'unrecognized:', line&#xA;&#xA;    def update(self, new_az, new_el):&#xA;        # round to degrees&#xA;        new_az = int(round(new_az))&#xA;        new_el = int(round(new_el))&#xA;&#xA;        if self.az != new_az or self.el != new_el:&#xA;            os.spawnlp(os.P_NOWAIT, COMMAND, COMMAND, '%s %s' % (new_az, new_el))&#xA;        self.az = new_az&#xA;        self.el = new_el&#xA;&#xA;class Factory(protocol.Factory):&#xA;    def buildProtocol(self, addr):&#xA;        return RotctlEmulator()&#xA;&#xA;endpoints.serverFromString(reactor, 'tcp:4533:localhost').listen(Factory())&#xA;reactor.run()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-07-02T03:52:26.243" LastActivityDate="2015-07-02T03:52:26.243" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5074" PostTypeId="2" ParentId="1099" CreationDate="2015-07-02T10:34:52.570" Score="1" Body="&lt;p&gt;The 2m band is sometimes referred to as the 144MHz band, and the 3rd harmonic of that is 432MHz. I have heard the 23cm band referred to as the 1296MHz band, too - for the same reason (3rd harmonic of 432MHz and 9th harmonic of 144MHz).&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-07-02T10:34:52.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5075" PostTypeId="2" ParentId="1228" CreationDate="2015-07-02T14:51:47.423" Score="2" Body="&lt;p&gt;TM-V71A firmware update Ver.2.00 (May 16, 2008) added microphone sensitivity to the Menu (No. 111) so that MCP-2A is not needed to change it.&lt;/p&gt;&#xA;" OwnerUserId="4939" LastActivityDate="2015-07-02T14:51:47.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5076" PostTypeId="2" ParentId="3713" CreationDate="2015-07-02T15:13:29.313" Score="2" Body="&lt;p&gt;A few years ago I built an &lt;a href=&quot;http://ea3gcy.blogspot.com/2013/04/egv-40-cw-qrp-40m-transceiver.html&quot; rel=&quot;nofollow&quot;&gt;ILER-40 ssb transceiver.&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It basically meets all of your criteria, its cheap, easy to build and it comes from Spain. I discovered this kit after having some really bad luck trying to build another kit called the bitx-20, I worked on it for over a year before it even kind of worked....then one day it died for no reason. But the ILER-40 kit is really great, I put it together in two afternoons and was talking to canada the next day on a random wire. Since then I have made dozens of contacts over the United States and Canada. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would recommend also buying the DDS kit which gives you a digital readout and more accurate tuning. The K2 is also a great radio but it is a bit more complicated and is very expensive. I think the ILER is a good radio to start getting back into things, then you could try the K2 or K3 if you wanted a really high performance rig.&lt;/p&gt;&#xA;" OwnerUserId="4930" LastEditorUserId="76" LastEditDate="2015-10-01T03:54:27.013" LastActivityDate="2015-10-01T03:54:27.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5077" PostTypeId="1" CreationDate="2015-07-02T16:24:05.797" Score="4" ViewCount="152" Body="&lt;p&gt;I am in a Kenwood TK805D and a Kenwood TM241A to interface some of the hidden inner circuitry with the outside world so I can use the radios to do more than just talk on (ex. AllStar node, cross band repeater, packet radio, and much more.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I have found the place where I need to interface wires, but I am having trouble interpreting the abbreviations on the schematic. Can anybody help? Below are some connectors where I am looking into interface:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I obviously understand some of them, for example Mic is microphone input, but some (especially the single digit letters) are confusing including E and B, which I am thinking is battery. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;On the &lt;a href=&quot;http://file:///Users/skylerfennell/Desktop/TM-241%20Service%20Manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kenwood TM241A&lt;/a&gt;&lt;/strong&gt; (svc manual)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ROf9d.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;On the &lt;a href=&quot;http://www.rfstuff.com/manuals/805Dman.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kenwood TK805D&lt;/a&gt;&lt;/strong&gt;(svc manual)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/mIXic.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can Anybody help interperet the pinouts of the particular connectors?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-07-22T04:01:56.337" Title="Help with readings on schematic" Tags="&lt;diy&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5080" PostTypeId="2" ParentId="1099" CreationDate="2015-07-02T23:55:13.730" Score="-2" Body="&lt;p&gt;The reason it is called the 70 cm band is because the approximate wavelength of an RF signal in that band is 70 cm. If  you recall, wavelength in m = frequency in MHz / 300.  432/ 300 is about 0.7m or 70 cm.&lt;/p&gt;&#xA;" OwnerUserId="42" LastActivityDate="2015-07-02T23:55:13.730" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5081" PostTypeId="2" ParentId="5063" CreationDate="2015-07-02T23:58:44.697" Score="1" Body="&lt;p&gt;Not really. You can try using the noise reducer control on your radio, but if the noise is really bad, it won't be that effective. Most of the noise you're talking about was due to lightning near where you were operating. Not much you can do about that.&lt;/p&gt;&#xA;" OwnerUserId="42" LastActivityDate="2015-07-02T23:58:44.697" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5082" PostTypeId="2" ParentId="5061" CreationDate="2015-07-03T00:01:01.400" Score="0" Body="&lt;p&gt;Yes. In the U.S., for example, you won't find a callsign in another service with the same formats as an amateur radio callsign. While I'm not 100% sure for other countries, I'd guess it was the same there as well.&lt;/p&gt;&#xA;" OwnerUserId="42" LastActivityDate="2015-07-03T00:01:01.400" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5083" PostTypeId="2" ParentId="5059" CreationDate="2015-07-03T00:03:46.533" Score="0" Body="&lt;p&gt;For normal, i.e. not contest operations, the convention is to try to be at least 3 kHz from the nearest station. During contests, however, that convention is regularly violated, and whatever interference such operation may cause is chalked up to there being a contest in progress. Contest operators learn to deal with such interference.&lt;/p&gt;&#xA;" OwnerUserId="42" LastActivityDate="2015-07-03T00:03:46.533" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5084" PostTypeId="1" AcceptedAnswerId="5085" CreationDate="2015-07-03T02:15:09.463" Score="12" ViewCount="573" Body="&lt;p&gt;While I was operating on 40 m for Field Day, I noticed a higher SWR than when I first set my antenna tuner for the band. This happened, of course, because I was in a different part of the band, but I hadn’t done enough HF operation to expect the result automatically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;80 m is famously so wide that the phone segment of it gets called “75 meters” because the difference matters for antenna design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’ve heard that what matters for antenna and electronic design is the relative bandwidth — the ratio of the low and the high ends. I’d like to see what this ratio is for &lt;em&gt;all&lt;/em&gt; of the amateur bands, and just how much of an outlier 80 m is or isn't.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="873" LastEditDate="2015-07-22T02:35:05.790" LastActivityDate="2016-05-03T06:25:22.527" Title="What are the relative bandwidths of the amateur bands?" Tags="&lt;united-states&gt;&lt;hf&gt;&lt;bandwidth&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5085" PostTypeId="2" ParentId="5084" CreationDate="2015-07-03T02:15:09.463" Score="10" Body="&lt;p&gt;The usual figure used in this context is, apparently, &lt;em&gt;fractional bandwidth&lt;/em&gt;, defined as the bandwidth divided by the center frequency, and therefore having a range of 0 to 2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;\text{fractional bandwidth}&#xA;\,=\, \frac{f_{\text{max}} - f_{\text{min}}}{f_{\text{center}}}&#xA;\,=\, 2\frac{f_{\text{max}} - f_{\text{min}}}{f_{\text{max}} + f_{\text{min}}}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that definition, and using the United States band edges, here are the fractional (and absolute) bandwidths of all amateur bands:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/XQtzE.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This chart was generated using a &lt;code&gt;gnuplot&lt;/code&gt; program which can be found in the source of this answer.&lt;/p&gt;&#xA;&#xA;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-07-21T21:04:11.470" LastActivityDate="2015-07-21T21:04:11.470" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5086" PostTypeId="2" ParentId="5066" CreationDate="2015-07-03T07:02:48.853" Score="1" Body="&lt;p&gt;First of all, the antenna on the aircraft needs to have a good radiation pattern downward. This rules out a whip, though a horizontal dipole may work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the polarisation of the source is unknown, for most reliable detection you need a circularly polarised antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This could be a pair of dipoles fed 90 degrees out of phase, called a turnstile antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It could also be a pair of loops, which have the advantage of a wider radiation pattern. The two loops fed 90 degrees out of phase are called an eggbeater antenna. It will be about 50 cm in diameter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency range you list is quite broad,you'll struggle to cover it in one go. Surely you know what the transmitters are set to? A standard two-element yagi for animal tracking will be a very narrow band antenna, just a few MHz, so no-one would set the collar transmitters all over the place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last antenna you might consider would be a quadrafilar helix, as used for GPS and iridium phones, and many satcom applications. A QHA for your frequencies might be 0.6 m tall, 0.3 m diameter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both the quadrafilar helix and the eggbeater are commonly constructed by amateurs for receiving weather satellites, in a very similar frequency band, so you might find good information on building them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One last idea - it might be lighter and lower wind resistance to just use two receivers, connected to two dipole antennas, one in each polarisation, and combine their detection results in software later.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-07-03T07:02:48.853" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5087" PostTypeId="2" ParentId="5059" CreationDate="2015-07-04T04:04:17.730" Score="4" Body="&lt;p&gt;I am not sure I understand the question but I will attempt to answer a part of what you are asking.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Thinking about this once, I said to myself: SSB is 3 kHz wide, so we can divide that neatly into XXX0000, XXX3000, XXX6000 Hz with only a little bit of waste.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No one does that.   When you choose a particular frequency for SSB, you usually will look for empty space and that means probably at least 3 KHz distant from other signals.  But, not always.  As previously stated, if the band is crowded, such as during contests, this 3 KHz rule goes out the window.  On modern radios today, many SSB operations will work with filters narrowing down their operating window to maybe 2 KHz.  I sometimes have operated at 1.8 KHz since I have a 1.8 KHz roofing filter on my Elecraft K3.  Yes, you can understand SSB at 1.8 KHz and it is not quality but who cares for SSB work especially in a contest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often I will arrange schedules with some buddies for late night 80 meter SSB chats.  For some unusual reason, we have a habit of picking 3767 KHz or something like that.  I like the odd numbers because it allows some kind of distance from a lot of regularly scheduled things that have a tendency to chew up the 1 KHz 0 digit (e.g. 3760, 3770, 3780,...).  And, if not the 0 mark, they go for the 5 KHz intervals (e.g. 3760, 3765, 3770, 3775,...).  So, regularly scheduled nets that can crowd the 80 meter band usually end up on the 0 and 5 1 KHz digit place so I avoid those for my schedules which are not regular.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, when you make a schedule, you always inform the other party (parties) that if not found on such-and-such frequency, scan up 5 to 10 KHz and down 5 to 10 KHz looking.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, no one that I know of has ever planned or thought of channelizing the bands into 3 KHz chunks.  No one would obey that rule anyway so it is probably a waste of time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On CW though or other digital modes, anything goes because the average signal width is much less than 1 KHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my experience, on the 80 meter band, in the evening hours, no matter where you pick your frequency you are probably stepping on someones skirt or right on top of them.  You raise QRL? to find if anyone is there but their answer may not be heard by you even though you may be heard by them so you may likely stomp on them anyway.  This is especially true in the range 3900 to 3990 KHz.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-07-04T04:04:17.730" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5088" PostTypeId="1" CreationDate="2015-07-06T08:51:42.083" Score="3" ViewCount="317" Body="&lt;p&gt;I want to generate an FSK signal with a radio. My first idea is to generate an audio in which the high level is a 1 and the low level is a 0:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/rXjch.png&quot; alt=&quot;Audio generated by MATLAB&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This audio is then modulated by the radio with FM. In theory I think it should work, as FSK is just modulating the binary packet, but I see that programs like MixW generate an audio completely different from what I generated:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/AiFzp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the proper way to generate an audio which will input a radio to obtain an FSK modulation?&lt;/p&gt;&#xA;" OwnerUserId="4951" LastActivityDate="2015-07-22T03:57:00.450" Title="How to generate FSK with Matlab and radio" Tags="&lt;software-defined-radio&gt;&lt;fm&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5089" PostTypeId="2" ParentId="5059" CreationDate="2015-07-06T10:49:30.953" Score="2" Body="&lt;p&gt;The answer to your question is no. There is not any internationally recognised standard of channelisation on the amatuer radio HF bands when operating SSB. There is a suggested band plan to keep different modes separated and give priority for specific usage but this is only a &quot;gentleman's agreement&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The standard accepted &quot;good conduct&quot; is to ensure that your transmission is at least 3KHz away from any other that you can hear to avoid causing interference.&lt;/p&gt;&#xA;" OwnerUserId="4952" LastActivityDate="2015-07-06T10:49:30.953" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5090" PostTypeId="2" ParentId="5061" CreationDate="2015-07-06T10:57:51.247" Score="0" Body="&lt;p&gt;I believe that all Amatuer Radio call signs are unique to the service and are not issued for use with another licensed service.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Saying that, there is nothing stopping you naming a boat &quot;M0LMK&quot; and using it as a call sign on the marine bands (if you hold a licence) but it won't be an official call sign.&lt;/p&gt;&#xA;" OwnerUserId="4952" LastActivityDate="2015-07-06T10:57:51.247" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5091" PostTypeId="2" ParentId="3668" CreationDate="2015-07-06T11:04:03.230" Score="2" Body="&lt;p&gt;You can simplify this a lot if you can set up and use a cross band repeater instead of an in band unit (licence dependent).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Units like the Yaesu FT-8800 have a cross band repeat mode built in as standard and will just need a single antenna and a power supply or battery.&lt;/p&gt;&#xA;" OwnerUserId="4952" LastActivityDate="2015-07-06T11:04:03.230" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5092" PostTypeId="2" ParentId="5063" CreationDate="2015-07-06T11:28:23.093" Score="0" Body="&lt;p&gt;Magnetic loops are resistant to RF noise so may be a good choice in a wet environment. Also, using coaxial fed antennas instead of ladder line will reduce rain related issues.&lt;/p&gt;&#xA;" OwnerUserId="4952" LastActivityDate="2015-07-06T11:28:23.093" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5093" PostTypeId="2" ParentId="5049" CreationDate="2015-07-06T11:39:22.490" Score="0" Body="&lt;p&gt;The secret to packing in the QSO's on SSB voice is all down to operator efficiency which can only be gained for experience. You need to go fast but not too fast, be consistent and concise with your information and tell your contact exactly what you need from them. Don't engage in chat and don't encourage your contact to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find having a small crib sheet works well with all the information that you need right in front of you. Call sign, locator, what you are doing (brief details if it is a special event) and somewhere your contact can go for more information (QRZ page or other website).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also cheat (like I do sometimes) and record your QSO's and play them back later to log but always remember, it's quality not quantity that counts! As long as you are having fun it doesn't matter how many contacts you make.&lt;/p&gt;&#xA;" OwnerUserId="4952" LastActivityDate="2015-07-06T11:39:22.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5094" PostTypeId="2" ParentId="5049" CreationDate="2015-07-06T11:46:34.723" Score="0" Body="&lt;p&gt;There are definitely a few techniques that can be used to improve the speed of a SSB QSO in a contest environment. Some of it comes down to experience. Some of the keys are:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Find a clear frequency and call CQ, especially if you have a relatively powerful station.&lt;/li&gt;&#xA;&lt;li&gt;There is a rhythm to how often you should call CQ. Keep it short, and wait about 3-4 seconds before calling again.&lt;/li&gt;&#xA;&lt;li&gt;Picking out all of the calls that are calling you can be quite difficult. Try to pay careful attention, and you'll have some success. This is the biggest area which takes time to get the call right.&lt;/li&gt;&#xA;&lt;li&gt;Keep QSOs as short as possible. If you get a good call, it should it something like you calling CQ, hear a call, repeat the call you heard with your exchange, them returning with their exchange, and you concluding theirs while calling out for the next person. If there's a weak signal, some repeats might be required, but try to stick to that pattern.&lt;/li&gt;&#xA;&lt;li&gt;Remove unneeded phrases like &quot;Please Copy&quot;, &quot;Good luck in the contest&quot;, etc. You can sometimes use shorter phrases. If you keep the QSO short, then you'll encourage people to keep trying to talk with you, and not just give up on you.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;To get a really high rate, the secret is to follow these tips, and practice picking out calls. The really skilled people can even call one, then remember the second call and get back to the second person after the first qso by returning their call.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-07-06T11:46:34.723" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5095" PostTypeId="2" ParentId="4982" CreationDate="2015-07-06T12:01:39.890" Score="0" Body="&lt;p&gt;The sloper configuration will yield more omnidirectional reception with a bias toward the direction of the slope. A horizontal configuration will have some nulls towards the ends of the antenna and will work well for signal sources broadside on. For a non bias omnidirectional antenna you could try adding a support in the centre and creating an &quot;Inverted V&quot; style  layout.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also try feeding the antenna from the tree end and connecting back to your receiver with coax cable (75ohm or 50ohm) which will reduce the amount of electrical noise that is being picked up from the house.&lt;/p&gt;&#xA;" OwnerUserId="4952" LastActivityDate="2015-07-06T12:01:39.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5096" PostTypeId="2" ParentId="5009" CreationDate="2015-07-06T12:05:21.723" Score="2" Body="&lt;p&gt;Maximum Usable Frequency changes with time of day, season, solar radiation and many other factors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best resource I have found for checking the current MUF and other conditions is here... &lt;a href=&quot;http://www.hamqsl.com/solar.html&quot; rel=&quot;nofollow&quot;&gt;http://www.hamqsl.com/solar.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4952" LastActivityDate="2015-07-06T12:05:21.723" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5097" PostTypeId="1" CreationDate="2015-07-06T15:01:49.067" Score="2" ViewCount="272" Body="&lt;p&gt;I currently have a Kenwood TM-V71A 2m/70cm transceiver that I would like to connect to my Macbook to transmit morse code, using the cocoaModem software. Aside from the cables needed to connect the radio to the Macbook and possibly an external USB sound card, I'm wondering what I need in order to connect a CW keyer to the computer. I don't want to generate CW with the computer, I just want to transmit CW myself with a keyer such as the MFJ 564 iambic dual paddle. Most 2m radios (mine included) do not have a jack into which you can plug a CW keyer, thus my need to connect through the computer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I understand, the paddle does not generate a tone by itself, and it seems to connect through a 1/4&quot; phone plug. Would I need to build my own tone generator circuit that is controlled by the keyer and outputs audio into the microphone jack of the computer? Or would I be able to generate a tone from software and plug the keyer directly into the microphone jack? I'd prefer to buy a tone generator circuit (if one is needed), but I'm not opposed to building one myself from a kit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you for any help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: The other question only applies to Windows as far as software goes, but does refer to 'code practice oscillators', which I think is what I need in order to connect the keyer to the microphone jack and generate an audible tone.&lt;/p&gt;&#xA;" OwnerUserId="4953" LastEditorUserId="4953" LastEditDate="2015-07-07T02:09:52.830" LastActivityDate="2015-07-07T02:09:52.830" Title="How can I connect a CW keyer to my Mac and transmit CW on VHF?" Tags="&lt;cw&gt;&lt;vhf&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2015-07-07T02:08:29.070" ContentLicense="CC BY-SA 3.0" />
  <row Id="5098" PostTypeId="1" AcceptedAnswerId="5100" CreationDate="2015-07-07T03:52:37.380" Score="5" ViewCount="413" Body="&lt;p&gt;I know that except in the perfectly matched case, transmission lines transform impedances along their length; if I measure the impedance at the other end of my feed line, or even with a short jumper between my antenna analyzer and the antenna, I won't be reading the true impedance of the antenna (or other device at the end of the line).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Will the impedance transformation ever make an actual mismatch “look good” (1:1 SWR)?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-07-22T03:45:17.753" Title="Will measuring SWR through a feed line mislead me?" Tags="&lt;impedance&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5099" PostTypeId="2" ParentId="5098" CreationDate="2015-07-07T03:52:37.380" Score="3" Body="&lt;p&gt;&lt;strong&gt;No,&lt;/strong&gt; the SWR will remain high (in fact, constant) no matter how much line there is between the meter/analyzer and the antenna, assuming the line is matched to the meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An argument that this must be the case, skipping the math:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Instead of considering the impedance of the antenna and how it is transformed along the feed line towards the transmitter or meter, work from the other direction. The transmitter has a standard 50 Ω (or whatever) impedance, and the feed line also has a &lt;em&gt;characteristic&lt;/em&gt; impedance of 50 Ω, so we know the impedance observed at the other end of the line itself must be 50 Ω.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Therefore, if the antenna feed point has an impedance other than 50 Ω, there is a mismatch at that junction. During transmission, this mismatch will, as mismatches do, reflect some of the signal, which will propagate all the way back down the feed line, and be observable at the transmitter end.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Therefore, if we substitute the analyzer for the transmitter, it will detect the mismatch.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;You won't see the same &lt;em&gt;complex impedance&lt;/em&gt; as you would without the line in the way, but you'll see the same SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a caveat here: the feed line has some loss, and that loss will tend to make the mismatch look less bad because it absorbs power in both directions, resulting in less reflection. But if you have a significant amount of such loss, then you have a worse problem than bad SWR.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;If you did want to compensate for the effect of the transmission line, or generally to visualize this situation, the tool for that is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Smith_chart&quot; rel=&quot;nofollow&quot;&gt;Smith chart&lt;/a&gt;. On a Smith chart, for this purpose:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The center point corresponds to the characteristic impedance, and all other points to different impedances.&lt;/li&gt;&#xA;&lt;li&gt;Distances from the center correspond to SWR.&lt;/li&gt;&#xA;&lt;li&gt;Adding a length of transmission line corresponds to rotating by an angle about the center of the chart.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-07-07T03:52:37.380" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5100" PostTypeId="2" ParentId="5098" CreationDate="2015-07-07T11:20:10.137" Score="4" Body="&lt;p&gt;In an ideal world, if the characteristic impedance of your transmission line matches the system impedance (usually 50Ω), then adding or removing lengths of transmission line just moves the complex impedance around a constant-SWR circle. So you may get a different impedance (it may look capacitive instead of inductive, etc), but the SWR will always be the same, regardless of how much transmission line is between your meter and the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the real world is not ideal. Firstly, if the transmission line is lossy, that will make the SWR better. It does so because the transmission line absorbs some of the transmitted energy, and then absorbs again the reflected wave. No reflected wave means 1:1 SWR. Absorbing all the energy is one way to reduce the reflected wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, there are a great many amateur antenna designs which, intentionally or not, &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;use the feedline as part of the antenna&lt;/a&gt;. These antenna currents on the feedline are called &lt;em&gt;common-mode currents&lt;/em&gt;. When they exist, the feedline is very much part of the antenna, and changing the feedline length can change the impedance of the antenna, just like changing the length of any of the other antenna elements would. For this reason and many others, good antenna designs do not have significant common-mode currents.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-07-07T11:20:10.137" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5101" PostTypeId="1" AcceptedAnswerId="5103" CreationDate="2015-07-08T11:03:49.110" Score="9" ViewCount="1696" Body="&lt;p&gt;I don't really get it. How is it possible to just send upper or lower side of a band (SSB USB/LSB):&#xA;&lt;img src=&quot;https://i.stack.imgur.com/uoJG4.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And how is it possible to send anything without the carrier wave!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I have misunderstood anything I am sorry because I am new to this and would like a answer.&lt;/p&gt;&#xA;" OwnerUserId="4968" LastEditorUserId="5087" LastEditDate="2015-08-10T17:39:41.550" LastActivityDate="2017-05-07T14:15:52.903" Title="What does a SSB signal look like?" Tags="&lt;ssb&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5102" PostTypeId="2" ParentId="5101" CreationDate="2015-07-08T12:42:43.897" Score="4" Body="&lt;p&gt;Let's start with voice, just to show what it looks like. Voice doesn't have a &quot;carrier wave&quot;. It simply contains the up and down level of the voice. Where the sound wave is 0 is effectively the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typical AM signals take this signal, and modulate it with the carrier wave. Thus, the signal has a large peak at the peak of the carrier wave, and a relatively small part of the signal is everything else. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Okay, so how does SSB actually work then? Imagine that the signal contains signals that go both above and below the base value. Let's say you are broadcasting a tone, with amplitude X. The tone will have some signals with value X, and some with value -X, with a sinusoidal wave between the two.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the figure you showed isn't really what is transmitted in SSB. Rather, it is a rectified sin wave, such that half of it is shown at 0, and the other half shown above. As sound doesn't really change that much over the frequency of sound waves, this is an acceptable way to show the signal. The carrier wave is then the part of the signal at 0. As that isn't really important, just not sending the 0 part of the signal removes a significant part of power that doesn't add much to the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bottom line, this chart from &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation#/media/File:SSB_bandform.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt; shows how the various modes work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/rP0Jf.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-07-08T12:42:43.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5103" PostTypeId="2" ParentId="5101" CreationDate="2015-07-08T16:11:25.343" Score="5" Body="&lt;p&gt;It looks like you are confused about what these graphs represent. Here's the diagram you used in the question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/uoJG4.gif&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Probably, this diagram is intended to be interpreted with the horizontal axis being time, and the vertical axis representing voltage or current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using that same representation, then SSB looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/onLV2.png&quot; alt=&quot;sine wave&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For comparison, AM looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/onLV2.png&quot; alt=&quot;sine wave&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and FM looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/onLV2.png&quot; alt=&quot;sine wave&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, they all mostly look the same. Why? In these images, we can only see about 5 cycles of the carrier. While the carrier is modulated somehow, the highest frequencies in the baseband signal (your voice) are usually much lower than the carrier frequency. So although the amplitude or frequency may be changing, we can't see any significant changes over such a short span of time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These images, because the X axis represents time, are said to be &lt;em&gt;time domain&lt;/em&gt; representations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, one thing we know from &lt;a href=&quot;https://en.wikipedia.org/wiki/Fourier_analysis&quot; rel=&quot;noreferrer&quot;&gt;Fourier analysis&lt;/a&gt; is that we can also represent any periodic signal in the &lt;em&gt;frequency&lt;/em&gt; domain. We can represent that graphically by making the Y axis frequency instead of time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To illustrate, we can look at a square wave in the time domain ($f$), and see how it can be represented in the frequency domain ($\hat f$):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Fourier_transform_time_and_frequency_domains_(small).gif#/media/File:Fourier_transform_time_and_frequency_domains_(small).gif&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/7/72/Fourier_transform_time_and_frequency_domains_%28small%29.gif&quot; alt=&quot;Fourier transform time and frequency domains (small).gif&quot;&gt;&lt;/a&gt;&lt;br&gt;&quot;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Fourier_transform_time_and_frequency_domains_(small).gif#/media/File:Fourier_transform_time_and_frequency_domains_(small).gif&quot; rel=&quot;noreferrer&quot;&gt;Fourier transform time and frequency domains (small)&lt;/a&gt;&quot; by &lt;a href=&quot;//commons.wikimedia.org/wiki/User:LucasVB&quot; rel=&quot;noreferrer&quot; title=&quot;User:LucasVB&quot;&gt;Lucas V. Barbosa&lt;/a&gt; - Own work. Licensed under Public Domain via &lt;a href=&quot;https://commons.wikimedia.org/wiki/&quot; rel=&quot;noreferrer&quot;&gt;Wikimedia Commons&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We don't usually use square waves in radio communications because they have power spread over a wide range of frequencies. A square wave at 1 MHz also has energy at all the odd harmonics, 3 MHz, 5 MHz, 7 MHz, and so on. This would cause a lot of interference, since each station is typically allocated just a small channel in which to transmit. Broadcast FM, for example, is allocated a channel 200 kHz wide, and all their transmitted power has to fit in that. For example, from 89.7 MHz to 89.9 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consequently, most transmissions look more or less like sine waves, since a sine wave has all its power at exactly one frequency. Then we vary the amplitude or frequency of this wave to carry information, but at a relatively slow rate compared to the frequency of the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you understand the concept of looking at signals not as a function of time, but as a function of frequency, then it is easy to say what SSB looks like: it looks just like the baseband signal (your voice), but shifted up in frequency to wherever the transmitter is tuned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, a whistle is approximately a pure sine wave. So if you whistle at 1kHz into the microphone, and the transmitter is tuned to 1MHz, then what you will see transmitted is a pure sine wave at 1.001 MHz (1 MHz + 1 kHz). If you make no sound at all, then nothing is transmitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you get two people whistling at different frequencies, say 1 kHz and 2 kHz, then what you will see is the sum of two sine waves, one at 1.001 MHz and another at 1.002 MHz. Because these two frequencies are so close together, if we view it on any timescale where we can see the individual oscillations of the transmitter, it will just look like a sine wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it doesn't really make much sense to think about what SSB looks like in the time domain, and consequently, most of the graphics you see represent the signal in the frequency domain.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-07-08T16:11:25.343" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5104" PostTypeId="1" AcceptedAnswerId="5107" CreationDate="2015-07-08T17:07:24.900" Score="6" ViewCount="914" Body="&lt;p&gt;Which is the minimal information I should require to confirm/QSL a reception report I receive ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know the report must contain my callsign, time, date and band where I was listened. Is it also a requirement to indicate the callsign of the other participant in the QSO ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am receiving some QSLs without this last info. This makes sometimes difficult to confirm if the listener actually heard me. For example, In those occasions I stay the full day glued to my rig, without other information, any time would match. &lt;/p&gt;&#xA;" OwnerUserId="1308" LastActivityDate="2015-07-22T03:18:02.620" Title="Minimal info on a SWL QSL" Tags="&lt;qsl-card&gt;&lt;swl&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5105" PostTypeId="2" ParentId="5061" CreationDate="2015-07-08T19:03:05.067" Score="0" Body="&lt;p&gt;Haven't looked lately, but some years ago I did find an exception to &quot;... you won't find a callsign in another service with the same format as an amateur radio callsign...&quot;. At that time, and perhaps yet, stations experimenting with &quot;weird&quot; propagation modes or which were in some other way unconventional were given callsigns in the series KA6Xxx, where xx ran from AA through ZZ.&lt;/p&gt;&#xA;" OwnerUserId="4971" LastActivityDate="2015-07-08T19:03:05.067" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5106" PostTypeId="1" CreationDate="2015-07-08T22:58:23.373" Score="10" ViewCount="1006" Body="&lt;p&gt;Consider a typical source -&gt; transmission line -&gt; load (i.e. TX-&gt;transmission line-&gt;antenna) arrangement and assume that the load is not matched to the transmission line characteristic impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's always possible to select a length of transmission line that transforms the load impedance, X+jY, into a pure resistance, R+j0, at the source (where R is not equal to the characteristic impedance of the transmission line). This can be illustrated by moving around a constant VSWR circle on the Smith Chart - starting from any random load impedance, you can always arrive at a pure resistance at the source end of the line&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is: would there any advantage in doing that - i.e. does a source prefer to see a mismatched resistive load rather than a mismatched load with a reactive component?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a specific example, take a normalised characteristic impedance, Zo = 1+j0, a source with the same matched output impedance, and assume we have a mismatched load impedance of 0.5+j. Initially assume a line of length equal to an integer number of half-wavelengths so that the source sees 0.5+j. Now change the length of the line (i.e. move around a constant VSWR circle starting from 0.5+j) until we reach a pure resistance of about 0.24+j0. Would the source, with output impedance 1+j0, prefer to see 0.24+j0 or 0.5+j (or, perhaps, no preference)?&lt;/p&gt;&#xA;" OwnerUserId="4940" LastEditorUserId="4940" LastEditDate="2015-07-08T23:38:40.000" LastActivityDate="2017-10-06T17:07:41.273" Title="Is there an optimum transmission line length for maximum power transfer?" Tags="&lt;transmission-line&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5107" PostTypeId="2" ParentId="5104" CreationDate="2015-07-09T02:06:24.833" Score="2" Body="&lt;p&gt;Usually when listening to DX on the bands, a listener will note the DX station as well as the station the DX station is working. Without this information it can be difficult for the DX station to look up their own transmission in their log.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, the other day I heard a weak station on 17m CW - ET3AA, quite rare, and difficult to work from here (Thailand). He was not particularly busy, and was rather weak. I heard him going through a few contacts, but I only really heard the prefixes of the stations he was working (UA4, DL, G), as I was trying to work him myself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was lucky that he heard my weak signals after about 45 minutes, but if I had completely failed to work him after an hour, and sent him an SWL QSL card instead saying &quot;I heard you on 18MHz at 1430Z on 2015-07-07&quot;, he might have thought &quot;yeah, I was on 18MHz at that time, that's a good one&quot;. But conversely he might have thought &quot;you heard me? So who was I working??&quot; and not send a QSL in response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a QSL sent to an amateur DX station, I would expect to see as a minimum: The DX Callsign, Date, Time, Frequency Band (or better yet, actual frequency), Mode and Station Worked by the DX station. Without that the DX station can not usually guarantee that they were actually heard at that time/date/frequency/mode, as they can't cross-check it with their own log.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One exception to this is if a DX station is calling CQ and you hear them - if you were to send an SWL QSL to them, they might not even HAVE a log entry for what frequencies/dates/times/modes they call CQ. Most logging software these days is all about QSOs, and not so much about procedural stuff like &quot;station on/off times&quot; or &quot;calling CQ&quot; or &quot;started/stopped packet software on 2m&quot; or whatever. Back in the days of paper logs, such things were regularly logged.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-07-09T02:06:24.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5108" PostTypeId="1" AcceptedAnswerId="5120" CreationDate="2015-07-09T08:06:34.830" Score="5" ViewCount="547" Body="&lt;p&gt;why does the receiver needs to add a carrier signal to the SSB signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am new to ham radio and can't so much.&lt;/p&gt;&#xA;" OwnerUserId="4968" LastActivityDate="2018-09-06T10:29:48.853" Title="Why needs a carrier signal on receiver (SSB)" Tags="&lt;ssb&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5109" PostTypeId="1" CreationDate="2015-07-09T13:19:35.520" Score="0" ViewCount="86" Body="&lt;p&gt;&lt;a href=&quot;https://i.imgur.com/oUAjfr5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.imgur.com/oUAjfr5.png&quot; alt=&quot;Circuit&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see, one of inputs of a XOR gate is connected to the output of the same XOR gate. Each time when the output is &quot;true&quot; it influences its input and it makes the gate change output to &quot;false&quot;. But when the output is &quot;false&quot; it's redirected to input and makes the gate change output to &quot;true&quot;.&lt;/p&gt;&#xA;" OwnerUserId="4974" LastEditorDisplayName="user885" LastEditDate="2015-07-10T12:01:16.993" LastActivityDate="2015-07-10T12:01:16.993" Title="What would happen if I created this circuit?" Tags="&lt;electronics&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2015-07-09T15:51:50.820" ContentLicense="CC BY-SA 3.0" />
  <row Id="5110" PostTypeId="2" ParentId="5108" CreationDate="2015-07-09T14:13:08.423" Score="5" Body="&lt;p&gt;You need to add a carrier in order to perform &lt;a href=&quot;https://en.wikipedia.org/wiki/Envelope_detector&quot; rel=&quot;noreferrer&quot;&gt;envelope detection&lt;/a&gt;, which is the standard detector in most applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If no carrier is added, the signal envelope is centered around 0, so the detected output is full-wave rectified. The carrier adds a DC component to avoid the zero crossing of the envelope.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2015-07-09T14:13:08.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5111" PostTypeId="2" ParentId="5109" CreationDate="2015-07-09T14:58:49.000" Score="3" Body="&lt;p&gt;As a purely logic circuit, it is unstable and has no solution as is noted in your question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, logic gates have a propagation delay and a non-linear transfer characteristic. Delay in CMOS chips depends on load capacitance and supply voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is &lt;a href=&quot;http://www.ti.com/lit/ds/symlink/cd4030b.pdf&quot; rel=&quot;nofollow&quot;&gt;an example (PDF)&lt;/a&gt;, where propagation delay can be around 50ns to 200ns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you will probably get an oscillator if you build this circuit. Or, depending on construction and the actual chip, you may end up operating in the linear range of the transfer characteristic (just like an op-amp configured as a voltage follower), so the output may be a stable voltage midway between 0 and Vdd.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2015-07-09T14:58:49.000" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5112" PostTypeId="2" ParentId="5108" CreationDate="2015-07-09T16:24:19.830" Score="4" Body="&lt;p&gt;As Juancho already mentioned, adding a carrier to the signal is needed for envelope detection, one particular demodulation technique (which can be seen as locally converting the signal to an AM, or more precisely &lt;em&gt;vestigial sideband&lt;/em&gt;, signal).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, &lt;em&gt;any&lt;/em&gt; SSB reciever, no matter how it is designed, &lt;em&gt;must&lt;/em&gt; in some sense have a signal at the carrier frequency (or an intermediate frequency and the carrier frequency ± the IF). This is because the demodulator must, one way or another, translate the SSB signal from its original carrier frequency to zero (putting the “sideband” into audio frequencies), and in order to perform that translation, whether in electronics or in software, one must produce a signal at the frequency one is translating the signal by.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(At least, I haven't heard of any methods that don't have that as a component, and it's hard to see how something else could work — what defines the tuning frequency, if not a signal at that frequency or a known offset of it?)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-07-09T16:24:19.830" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5113" PostTypeId="2" ParentId="3668" CreationDate="2015-07-10T01:02:39.407" Score="0" Body="&lt;p&gt;You can build a repeater using 2 Motorola CDM radios and a RICK box.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ebay.com/itm/MOTOROLA-REPEATER-RICK-HLN3333-/301682707188?pt=LH_DefaultDomain_0&amp;amp;hash=item463db0caf4&quot; rel=&quot;nofollow&quot;&gt;http://www.ebay.com/itm/MOTOROLA-REPEATER-RICK-HLN3333-/301682707188?pt=LH_DefaultDomain_0&amp;amp;hash=item463db0caf4&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;see this youtube&#xA;&lt;a href=&quot;https://www.youtube.com/watch?v=WpNIwV9S4Bw&quot; rel=&quot;nofollow&quot;&gt;https://www.youtube.com/watch?v=WpNIwV9S4Bw&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4976" LastActivityDate="2015-07-10T01:02:39.407" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5115" PostTypeId="1" CreationDate="2015-07-11T12:20:45.120" Score="6" ViewCount="1204" Body="&lt;p&gt;I have heard about many lightning protection strategies in the shack, but nobody mentioned the lightning dissipator. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The lightning dissipator consists of many small spikes and prevents a strike by slowly discharging through each little spike. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/4DtXq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would seem to be much more advantegous to a radio amateur because it would try to prevent lightning, not advocate, and even better, it will slowly discharge the to-be-strike so lightning won't get anywhere else. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is price an issue? I don't think so, becuase this seems like a fairly cheap solution just consisting of many metal spikes bonded to ground. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So are any amateurs using dissipators? Are they known to work? Should I consider for my shack?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-07-22T02:56:13.587" Title="Lightning Dissipators" Tags="&lt;lightning&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5116" PostTypeId="2" ParentId="5115" CreationDate="2015-07-11T14:00:59.480" Score="4" Body="&lt;p&gt;Seems mythical. For example, &lt;a href=&quot;http://www.practical-sailor.com/blog/-11222-1.html&quot; rel=&quot;nofollow&quot;&gt;this article&lt;/a&gt; discusses in a fair amount of detail why this doesn't work for sailboats. Land-based antennas face the same issues.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Some people believe that by constantly discharging the charge build-up&#xA;  on an object, the magnitude of the charge imbalance can be controlled&#xA;  and kept to a level where a lightning strike will not occur.&#xA;  Continuous dissipation of static charge potentials is used in every&#xA;  electronics laboratory that works with sensitive integrated circuits&#xA;  and transistors. The workers wear wristbands of conductive material&#xA;  that are connected to the room’s electrical ground. Charges bleed off&#xA;  before they reach levels that might destroy the electronics.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Unfortunately, what works in a laboratory, with very modest static&#xA;  charge quantities, does not work in nature. Let’s look at the facts that &#xA;  govern the charge dissipation approach to undoing what Thor wants to&#xA;  do—blast us with a lightning bolt&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="105" LastActivityDate="2015-07-11T14:00:59.480" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5117" PostTypeId="2" ParentId="5115" CreationDate="2015-07-12T07:05:56.980" Score="2" Body="&lt;p&gt;These alternative air termination systems are a triumph of marketing over physics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll quote what I can easily find on the net, you will find a lot more with a bit of digging.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These statements are quite reserved, but the meaning is clear - there is no evidence that there is any system that works to dissipate, preferentially attract or repel lightning. The only proven solution is an air terminal on every exposed corner, and a downconductor system to carry the strike to ground.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;STATEMENT OF CIGRE TASK FORCE 33.01.03 &#xA;  “LIGHTNING INTERCEPTION”&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;• The components of the Task Force during the meeting held in Milano on May 18th 1995, have examined the problem related with the use of non conventional lightning air terminals (e.g. Early Streamer Emission).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;• From the discussion it arise that up to now there is neither sufficient &#xA;  theoretical analysis, nor substantial field data which support conclusive improvement in interception efficiency of these kinds of devices with respect to the conventional ones (metallic air terminals).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;• Main technical reasons&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;– 1 – Even if a streamer from a non conventional active terminal can be launched at an earlier time than a streamer from a conventional air terminal, once launched, it will require the same conditions of field strength to propagate as for a leader from a conventional air terminal.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;– 2 - The assumed constant velocity of 106 m/s for upward leader propagation is in &#xA;  contrast with the field records which show an initial channel speed of about 0.04 &#xA;  to 0.2 106 m/s and it increases as the gap between the upward and downward &#xA;  leaders diminishes.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;CIGRE 95 SC 33 (WG 01) 17 IWD, 24th May 1995&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;• The members of the Working Group during the meeting held in South Africa on 23rd and 24th of May 1995, have examined the problems related to the use of non-conventional lightning air terminals (e.g. Early Streamer Emission, ESE, terminals).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;• From the discussion it was concluded that up to now there is neither sufficient theoretical analysis nor substantial field data which support claims of significant improvement in interception efficiency of these kinds of devices, with respect to the conventional ones (metallic air terminals).&#xA;  Furthermore, the theoretical basis for the Early Streamer Emission technology appears technically incorrect for the following reasons:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;– 1 - Even if a streamer from a non-conventional terminal can be initiated at an earlier time than a streamer from a conventional air terminal, once initiated it will require the same field strength to propagate as a leader from a conventional terminal.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;– 2 - The assumed constant velocity of 106 m/s for the upward leader propagation is in contradiction with the available data for both natural lightning and long laboratory sparks which show an average velocity of one order of magnitude lower.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;• Therefore the early initiation of streamers cannot be translated into an increased length of the ESE terminal as compared with the conventional one.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;• In conclusion, at this time, any use of such non-conventional lightning protection technology cannot be supported by CIGRE WG &#xA;  33.01 “Lightning”.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-07-12T07:58:03.893" LastActivityDate="2015-07-12T07:58:03.893" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5118" PostTypeId="1" CreationDate="2015-07-12T17:07:22.127" Score="5" ViewCount="201" Body="&lt;p&gt;I'm new to radio, and I'm trying to get into the electronics aspect of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was wondering if it was at all possible to build your own transmitter, receiver, etc. (basic radio components) as good beginner project.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've searched the Internet for tutorials, but the links have either made it seem too complicated or they aren't actually simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyways, if you all could refer me to some beginner material, that would be great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, if my question is too vague, let me know and I can edit it. I'm new to the whole Stack Exchange too.&lt;/p&gt;&#xA;" OwnerUserId="4986" LastActivityDate="2015-07-13T22:18:02.103" Title="New to Amateur Radio" Tags="&lt;electronics&gt;" AnswerCount="2" CommentCount="1" ClosedDate="2015-07-14T18:06:10.167" ContentLicense="CC BY-SA 3.0" />
  <row Id="5119" PostTypeId="2" ParentId="5118" CreationDate="2015-07-12T19:58:36.407" Score="3" Body="&lt;p&gt;Most hams don't build their own transmitters and receivers, more's the shame.  But it is quite possible, depending on your skill level and determination.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest rigs (the place to start first, of course) are generally what are called &quot;QRP&quot; (low power) radios.  You can find a lot of information through the ARRL web: &lt;a href=&quot;http://www.arrl.org/qrp-low-power-operating&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/qrp-low-power-operating&lt;/a&gt; and also at the ARRL bookstore.  You can buy QRP radios in kit form, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you haven't looked into ARRL, I recommend you check out &lt;a href=&quot;http://www.arrl.org/what-is-ham-radio&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/what-is-ham-radio&lt;/a&gt;, and consider joining the League.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-07-12T19:58:36.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5120" PostTypeId="2" ParentId="5108" CreationDate="2015-07-12T20:07:35.063" Score="3" Body="&lt;p&gt;The SSB signal needs to be converted to the audio range so that you can hear the modulation normally.  The carrier that you inject acts as a frequency reference, defining the translation of each RF frequency to an audio frequency (after detection).   If you are transmitting a 1 kHz tone at 14,200 kHz, upper sideband, you are sending a single frequency, 14,201 kHz.  The receiver needs to inject 14,200 kHz &quot;carrier&quot; so that you will end up with 1 kHz audio after detection.  &lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-07-12T20:07:35.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5121" PostTypeId="2" ParentId="2230" CreationDate="2015-07-12T20:24:10.007" Score="0" Body="&lt;p&gt;There are commercial amateur transceivers that offer &quot;direct digital conversion&quot; (DDC) using fast samplers (&gt;100 MHz) and FPGA processing.  You might check &lt;a href=&quot;http://www.flexradio.com/amateur-products/flex-6000-signature-series/&quot; rel=&quot;nofollow&quot;&gt;Flex Radio Systems 6000 series&lt;/a&gt;.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also the ANAN series of radios (eg ANAN-100D) from &lt;a href=&quot;https://apache-labs.com/&quot; rel=&quot;nofollow&quot;&gt;Apache Labs&lt;/a&gt;.  These products are fully open sourced, so you can get schematics and listings to see what is involved in making a full featured SDR system. Hint: It's not simple!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Filters are an issue.  On the Rx side, you want to reject possible out of band interference.  (Anti-aliasing, too, but that's relatively simple to do.)  On the Tx side you need to be sure that harmonics are well filtered.  That means low pass filters for every octave of frequency (or so).&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-07-12T20:24:10.007" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5122" PostTypeId="2" ParentId="5068" CreationDate="2015-07-12T20:44:53.833" Score="2" Body="&lt;p&gt;If the transmitted signal induces any currents in the &quot;sheet&quot;, the sheet will affect the radiation pattern.  One simple argument: if you run a wire parallel to the &quot;flag pole&quot;, there will be induced currents.  They may be small (if the wire is not resonant) but there will be some current.  (Think of how a yagi antenna works with its &quot;parasitic&quot; elements.)  The sheet can be approximated as a superposition of many wires. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Non-conducting (dielectric) obstacles also will change the pattern.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-07-12T20:44:53.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5123" PostTypeId="2" ParentId="5104" CreationDate="2015-07-12T21:00:05.353" Score="2" Body="&lt;p&gt;There are no rules about SWL cards.  Why do we have SWL cards at all?&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;to report reception, signal strength, etc. to the transmitting station to let them know how well they are getting out.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;to request a QSL card in reply, signifying the SWL has accurately heard the transmission and to thank him/her for the SWL card.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;An SWL card should give enough data to accurately identify the sender and the transmission.  At a minimum, time, date, frequency, and call sign.  It helps to include the call sign of the other ham, too, along with any other particulars - operating mode and any special information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The whole business is a courtesy.  Nobody needs to send an SWL card, and a station does not need to confirm it with a QSL.  So, be polite and helpful!&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-07-12T21:00:05.353" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5125" PostTypeId="2" ParentId="5023" CreationDate="2015-07-12T21:21:52.070" Score="5" Body="&lt;p&gt;The problem you could run into is RF feedback into the sensitive mic input. This is particularly a problem if you run &quot;QRO&quot; - high power.  It is best to use shielded multi-conductor cable, with the shield being used as the return for the PTT control.  The mic output (signal and ground) are separately carried to the mic input connector, where the mic &quot;ground&quot; may actually terminate at the (sensitive) mic amplifier internally.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This way, any RF currents (or possible 60 Hz AC pickup) are carried by the shield ground, which is generally terminated directly at the case of your radio, and they are kept away from the low-level audio amplifiers.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-07-12T21:21:52.070" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5126" PostTypeId="2" ParentId="2412" CreationDate="2015-07-12T21:29:00.743" Score="2" Body="&lt;p&gt;Both systems work.  One problem with the common connection is that, if you screw up your transmit switching somehow, there is the potential to send your transceiver's Tx output into the transverter's Rx output, and that might fry something. (But probably not if the levels are really low.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's probably also an extra relay in the circuit that could slow down T/R switching a little.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand with the common setup, you only need one coax cable.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-07-12T21:29:00.743" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5127" PostTypeId="2" ParentId="5059" CreationDate="2015-07-12T23:06:09.847" Score="2" Body="&lt;p&gt;There is no standard, but I note that many SSB stations transmit on an even kHz.  I suppose this is just for tuning convenience for those who have accurately calibrated digital VFOs.  It's very easy to scan the band with a 1 kHz step on many rigs.  It means you don't have to fine tune if you're talking with someone who also has accurate frequency setting.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using 1 kHz steps with ~2.4 kHz bandwidth means there aren't likely to be big gaps in spectrum usage.  (Besides, plenty of people do not use 1 kHz &quot;channels&quot;.) Sure you could pack people more efficiently with a finer step size, but when you consider variable propagation (the &quot;hidden transmitter&quot; problem), things work reasonably well.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-07-12T23:06:09.847" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5128" PostTypeId="1" CreationDate="2015-07-13T22:15:39.793" Score="1" ViewCount="471" Body="&lt;p&gt;I recently built a sound card packet TNC and it is working fine under my standard laptop power supply when I hook it into the wall. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I plug my computer in via a car inverter (12VDC to 120VAC), however, the radio will transmit hum with it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried an isolation transformer through the audio out, but that minimally helped solve the problem. Other then getting a pure sine wave inverter, what other things can I try?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2015-07-14T01:55:50.573" LastActivityDate="2015-10-20T04:47:47.793" Title="Inverter noise on my signal" Tags="&lt;rfi&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5129" PostTypeId="2" ParentId="5118" CreationDate="2015-07-13T22:18:02.103" Score="1" Body="&lt;p&gt;I would strongly reccomend reading the book &lt;a href=&quot;http://www.qsl.net/k0iye/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Crystal Sets to Sideband&lt;/a&gt; by Frank Harris K0IYE.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This book should get you started in the process of homebrewing radios and starts out with a very basic easy to build circuits to complicated radio projects up to the present stuff he is working on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live not to far, and met him. His entire station is homebrew including a 10-80 meter SSB/CW/AM transceiver, power supply, morse key, antenna tuner, antenna etc. It was quite amazing!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is an image of his homebrew radios:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/xbtIZ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-07-13T22:18:02.103" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5130" PostTypeId="2" ParentId="352" CreationDate="2015-07-13T23:48:21.033" Score="14" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/353/29&quot;&gt;That's&lt;/a&gt; a pretty good answer but I can add some more details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The exact formula for path loss is $$ 20 \times \log_{10}\left( 4 \times \pi \times \frac{d}{\lambda{}} \right) $$ $ 20 \times \log_{10}\left(4\times\pi{}\right) \approx 21.98$, and that's where the '22' comes from.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your receiver specs give a minimum signal strength, then the analysis above is pretty much all you need. But in a more general link budget you have to compute the required receive power yourself from the data rate, the type of modulation and coding, and the receiver system noise temperature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most power-efficient modulation/coding method in use is rate 1/6 turbo coding over BPSK (binary phase shift keying). This is a very popular deep space signal; it's being used by New Horizons at Pluto, for example. This particular signal requires a minimum $E_b/N_0$ of about 0 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is $E_b/N_0$? It's the received energy per bit divided by the received noise power spectral density in watts/Hz. This also has units of energy, so the ratio is dimensionless. It's usually expressed in decibels. The famous Shannon Limit says it's impossible to make a system operate error-free at an $E_b/N_0$ below -1.6 dB even if you can use infinite bandwidth. So you can see that we're pretty close to the theoretical limit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then you add the data rate, also expressed in decibels (with respect to 1 bps). For example, 1000 b/s would be 30 dB(bps), so your New Horizons signal would require a $P/N_0$ of at least 0 + 30 = +30 dB, where P is received power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That just leaves us with $N_0$. In space communications, noise is usually expressed as a temperature T since everything above absolute zero generates thermal noise. The big 70m dish at the NASA Deep Space Network sites has a noise temperature of 17.5 kelvins (I looked it up). To get N0, you multiply T by Boltzmann's constant, 1.38e-23 J/K or -228.6 dBW/Hz-K. So 17.5K is an $N_0$ of -216.2 dBW/Hz (or dBJ, same units).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you have what you need to compute P, the required receive power. It is simply -216.2 dBW/Hz + 30 dB-Hz = -186.2 dBW or -156.2 dBm. That's not much, but it's still hard to generate all the way from Pluto!&lt;/p&gt;&#xA;" OwnerUserId="4992" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-07-14T12:14:34.107" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5131" PostTypeId="2" ParentId="5077" CreationDate="2015-07-15T02:22:09.167" Score="1" Body="&lt;p&gt;E is &quot;earth&quot;, better known in north America as &quot;ground&quot;.&#xA;A1 and A2 are audio lines, as evidenced by connection to the volume control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the rest, I can only guess. &#xA;CK for &quot;clock&quot;&#xA;EN for &quot;enable&quot;&#xA;TX for &quot;transmit&quot;&#xA;DT for &quot;data&quot;&#xA;SQ for &quot;squelch&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to study the circuit at the other end of these wires, it would help fill in the missing bits.&lt;/p&gt;&#xA;" OwnerUserId="4998" LastActivityDate="2015-07-15T02:22:09.167" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5132" PostTypeId="2" ParentId="5106" CreationDate="2015-07-15T21:22:49.880" Score="1" Body="&lt;p&gt;If you assume an ideal 50ohm source and look at max power transfer, you're probably right. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Things are less straight forward with real world parts. Consider these two points.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No PA or antenna is matched perfectly to 50ohm, especially across frequency and harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unlike gain and vswr contours, power contours are not circles. They often resemble the shape of a cat eye. Traveling on a circle won't keep you on a constant power contour.&lt;/p&gt;&#xA;" OwnerUserId="4609" LastActivityDate="2015-07-15T21:22:49.880" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5133" PostTypeId="1" AcceptedAnswerId="5136" CreationDate="2015-07-15T17:22:57.080" Score="3" ViewCount="2182" Body="&lt;p&gt;My lady and I were driving on the interstate recently when we noticed an unusual phenomenon. We were listening to the radio (an FM signal), and only over a couple of bridges did we entirely lose our signal. I had some ideas explaining this but I'm not sure, so I am asking for your help. What caused this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To clear things up a bit:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It happened over three bridges in a thirty mile stretch. Each was over a river (not sure if that matters for reasons of over-water architecture or aquatic radio effects), but we crossed several other bridges that did not cause this phenomenon.&lt;/li&gt;&#xA;&lt;li&gt;Our signal was excellent the whole drive except on these few bridges, when it suddenly disappeared (white noise) and reappeared immediately after crossing.&lt;/li&gt;&#xA;&lt;li&gt;The bridges were concrete with no supports from above, no street lights, etc. There was no difference in obstructions above the vehicle for the entire drive.&lt;/li&gt;&#xA;&lt;li&gt;I have spent a lot of time driving with the radio on and have never experienced such a loss of signal with no explainable obstruction. I can only assume that the construction of these few bridges is unique.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5005" OwnerDisplayName="Sam Fahey" LastEditorUserId="4987" LastEditDate="2015-07-16T15:59:12.983" LastActivityDate="2018-12-27T08:41:00.907" Title="Why did I lose my FM radio signal?" Tags="&lt;propagation&gt;&lt;rfi&gt;" AnswerCount="4" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5134" PostTypeId="2" ParentId="4979" CreationDate="2015-07-16T05:09:10.090" Score="1" Body="&lt;p&gt;I wouldn't be surprised to hear such interference to an HT laying by the phone; neither would I be surprised at interference from outside sources (e.g. electronic pumps at gas station).  That the phone is strong enough to be picked up by a radio with an antenna on the roof (or at least outside the cabin) is more surprising to me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While there are many things that can affect this kind of interference, consider installation details: where are the radio &amp;amp; antenna mounted, how do you have power run, is there any other chassis grounding (is the radio bonded to metal on the car, or screwed into plastic), length &amp;amp; placement of extra coax, etc.  Also, where do you usually lay your phone, and what effect does putting it different places have -- that might clue you into the ingress point for the RFI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm thinking that a low-pass filter may not do much regardless. Whatever the nature of the interference, it's probably not enough to downright overload the receiver, but rather is actually carrying a pattern that includes a frequency in the neighborhood of what you're trying to receive.  Or, perhaps it's a frequency that's skipping the front-end, maybe going right through the case of the radio, and hitting an IF stage; in that case, you'd have a hard time keeping it out unless you encased the entire radio...so I'm sure there's a better way. &lt;/p&gt;&#xA;" OwnerUserId="5004" LastEditorUserId="9" LastEditDate="2015-07-16T14:30:44.857" LastActivityDate="2015-07-16T14:30:44.857" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5135" PostTypeId="2" ParentId="5128" CreationDate="2015-07-16T14:49:44.300" Score="1" Body="&lt;p&gt;Well, you can always get a pure sine wave inverter, which -&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Other then getting a pure sine wave inverter, what other things can I try?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Ah.  So you understand the problem and why it's happening, and are hoping for an easier/cheaper solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One option is to get a laptop power supply that uses the vehicle power. These are relatively inexpensive, and may not only resolve the problem, but be more efficient overall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's a low power requirement and a high power AC inverter, you could use a high power isolation transformer between the inverter and the laptop power supply.  This will act as a huge filter and force the signal to be more of a sine wave, cutting out a lot of the higher frequencies.  Could also damage the inverter, and this isolation transformer will heat up quite a bit as it's being abused.  Follow that with a &lt;a href=&quot;http://www.digikey.com/product-search/en/filters/power-line-filter-modules/&quot; rel=&quot;nofollow&quot;&gt;power line filter&lt;/a&gt; and you might resolve the problem, though at a significant cost in money, weight, and efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beyond that, though, there aren't any magic tricks you can use to get rid of the hum without further investigation.  You may be able to add ferrites along all the power lines and signal paths, isolators to avoid ground noise, etc, but the signal is very strong and won't be easily removed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try to characterize the noise - it is a single frequency, is it broadband, what is the signal level? If it's a typical cheap modified sinewave inverter, you're going to have a lot of high power harmonics, it won't be a simple fix or filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have that information, ask for the specific methods to filter that type of noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My expectation, though, is that you'll find it's cheaper and easier to simply use the right power supply in the first place, than to use the existing equipment and stack filters, isolators, etc on top of it.&lt;/p&gt;&#xA;" OwnerUserId="9" LastEditorUserId="9" LastEditDate="2015-07-16T15:10:20.747" LastActivityDate="2015-07-16T15:10:20.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5136" PostTypeId="2" ParentId="5133" CreationDate="2015-07-16T16:04:58.150" Score="2" Body="&lt;p&gt;The likely source of this problem is not that the FM signal went away, but that it was overwhelmed by a local interference (RFI) source.  Certain electrical systems, like high-intensity lighting, can generate a lot of &quot;white noise&quot; in the VHF range, including the FM broadcast band.  It is quite possible that the bridges' lighting system (or some other electrical system) was active when you drove over.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You did not say what time of day was involved.  You might notice whether the lights were on.  The RFI problem would be worse for weaker FM signals.  You might try tuning in other, more local (stronger) FM stations to see if they can get through the radio noise.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-07-16T16:04:58.150" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5137" PostTypeId="2" ParentId="5128" CreationDate="2015-07-17T03:09:25.973" Score="0" Body="&lt;p&gt;Do try grounding the laptop chassis to the radio chassis. Not via the sound card ground, find a solid earth like the screws of the VGA connector or a USB plug chassis. Use a heavy enough wire to keep the residual voltage to a minimum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most likely way for the noise to get in is thst the laptop chassis has some high frequency potential with respect to the car chassis. The isolation transformer is a good idea, but why force it to cope with a high voltage, high frequency noise between the windings? Any stray capacitance will cause the common mode voltage to become differential mode, unless it's a very fancy transformer you're looking for trouble.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A solid earth connection is quick to try out and might just help.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-07-17T06:05:39.477" LastActivityDate="2015-07-17T06:05:39.477" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5138" PostTypeId="1" CreationDate="2015-07-19T20:01:19.123" Score="3" ViewCount="3021" Body="&lt;p&gt;I've been fighting to get chirp working with my father's baofeng radios. The only computer that he has access to has Win 7 installed. The manufacturer drivers won't work with win7. I tried using the profilic drivers (did the whole install, etc.) and haven't had any success. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Chirp is giving the following error message: could not open port : [Error 3] The system cannot find the path specified.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any help is appreciated.&lt;/p&gt;&#xA;" OwnerUserId="5017" LastActivityDate="2019-05-24T11:39:43.653" Title="Baofeng UV-5r drivers for win7" Tags="&lt;baofeng&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5139" PostTypeId="2" ParentId="5138" CreationDate="2015-07-20T15:02:56.877" Score="4" Body="&lt;p&gt;Drivers are not required for the radio, but for the USB cable, as it has to provide a serial port via USB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A long workaround could be:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Download a Linux distro that can run from a USB drive in persistent mode, like Ubuntu.&lt;/li&gt;&#xA;&lt;li&gt;Download and install CHIRP on Linux.&lt;/li&gt;&#xA;&lt;li&gt;Let Linux handle it for you.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm saying this because in my case it worked right away on Linux without any problem.&lt;/p&gt;&#xA;" OwnerUserId="5018" LastEditorUserId="76" LastEditDate="2015-07-21T21:32:20.170" LastActivityDate="2015-07-21T21:32:20.170" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5141" PostTypeId="2" ParentId="5061" CreationDate="2015-07-22T00:37:02.283" Score="5" Body="&lt;p&gt;In most countries, they are unique.  But in the United States, there is an overlap between Aircraft (which are assigned N-numbers based on the &quot;International Radiotelegraph Convention&quot; in Washington in 1927) and amateur radio callsigns.  See &lt;a href=&quot;https://en.wikipedia.org/wiki/Aircraft_registration&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia article&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;There is a unique overlap in the United States with aircraft having a single number followed by two letters and radio call signs issued by the Federal Communications Commission to Amateur Radio operators holding the Amateur Extra class license. For example, N4YZ is, on the one hand, a Cessna 206 registered to a private individual in California, while N4YZ is also issued to an Amateur Radio operator in North Carolina.&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So the answer is: almost, but not 100%.&lt;/p&gt;&#xA;" OwnerUserId="5025" LastActivityDate="2015-07-22T00:37:02.283" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5142" PostTypeId="2" ParentId="5084" CreationDate="2015-07-22T01:49:45.913" Score="3" Body="&lt;p&gt;Here is a chart I made. Hope you find it useful. The numbers are approximate and it depends on your exact method of calculation. I use percentages because that information is easier to find or calculate. This chart is the average percentage using the center frequency (I also have numbers related to each band edge). A lot of people quote a &quot;good&quot; or &quot;well designed&quot; or &quot;average&quot; antenna as having about 10% bandwidth, but it varies a LOT with the exact antenna type in use. The &quot;notoriously wide&quot; bands are 160M, 80M, 10M (despite the smaller numbers), and I would add 6M and 70Cm.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt; 160M 10.55%&#xA;  80M 13.39%&#xA;  60M  1.36%&#xA;  40M  4.2%&#xA;  30M   .49%&#xA;  20M  2.47%&#xA;  17M   .55%&#xA;  15M  2.12%&#xA;  12M   .4%&#xA;  10M  5.9%&#xA;   6M  7.7%&#xA;   2M  2.74%&#xA;1.75M  2.7%&#xA; 70Cm  6.9%&#xA; 33Cm  2.84%&#xA; 23Cm  4.73%&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="5026" LastEditorUserId="76" LastEditDate="2015-07-22T02:44:42.547" LastActivityDate="2015-07-22T02:44:42.547" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5145" PostTypeId="1" CreationDate="2015-07-22T02:54:04.507" Score="5" ViewCount="2612" Body="&lt;p&gt;I want to setup a TCP/IP link between my friends house 7km away from me on 70cm. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;1200 Baud is a bit slow, and we are looking into something with a faster data rate. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know normal audio does not work for 9600 baud packet. What are the requirements?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a bunch of Motorola Radius SM50 UHF wideband commercial radio's and I am wondering if they would work? They have direct discriminator out on the back. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2016-08-04T17:08:00.690" Title="Requirements for 9600 baud" Tags="&lt;digital-modes&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5146" PostTypeId="2" ParentId="5115" CreationDate="2015-07-22T02:56:13.587" Score="0" Body="&lt;p&gt;It is my opinion and experience that lightning DOES NOT CARE what you put in its way. It destroys EVERYTHING that tries to conduct the HUGE amount of energy in the lighting. It can be diverted to a lower resistance path, but it STILL has too much energy to contain or control it without MASSIVE equipment made just for that purpose. (a lightning lab for example).&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T02:56:13.587" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5147" PostTypeId="2" ParentId="5108" CreationDate="2015-07-22T03:03:03.447" Score="1" Body="&lt;p&gt;As mentioned there are several way to demodulate SSB, but ALL of them that I am aware of need a &quot;REFFERENCE&quot; frequency (the carrier). How else will you differentiate between the various audio frequencies? How will you know if it is 100Hz or 1Khz or 10Khz? ONLY by refference to the carrier frequency can you properly demodulate SSB signals!&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T03:03:03.447" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5148" PostTypeId="2" ParentId="5106" CreationDate="2015-07-22T03:10:43.433" Score="1" Body="&lt;p&gt;Unless the load and source are matched to the transmission line there will ALWAYS  be SOME loss due to missmatch at one or both ends. The amount of loss can vary GREATLY, but will ALWAYS be present to some extent. Therefore foe MAXIMUM power transfer, MATCH THE LINE to BOTH the source AND the load! Otherwise accept whatever loss is incurred. If the source, line, and load are matched the line lenght is only a concdern because of the increasing LINE LOSS (resistive) with longer lines. SO the complete answer is MATCH all components and use the SHORTEST LINE POSSIBLE for maximum power transfer!&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T03:10:43.433" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5149" PostTypeId="2" ParentId="5104" CreationDate="2015-07-22T03:18:02.620" Score="2" Body="&lt;p&gt;The more information the better. A well designed card will give MORE THAN ENOUGH information to properly confim the contact or what was heard. To little information is poor communication at best and WORTHLESS at its worst.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T03:18:02.620" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5150" PostTypeId="2" ParentId="5101" CreationDate="2015-07-22T03:28:46.933" Score="1" Body="&lt;p&gt;The simple answer is that the baseband (voice) modulates the carrier and the result is 2 BANDS of frequencies added above and below the carrier (carrier +/- the voice). The amplitude (shape seen in typical illustrations) of these waves correspond to the baseband. The higher frequencies (USB) AND the lower frequencies (LSB) BOTH have the same but opposit shape and BOTH contain the SAME informtion (baseband/audio). Separating the upper or lower SIDSEBANDS does NOT remove that information. It is then sent as a narrower (more efficient) band of frequencies (compared to the carrier and BOTH sidebands) and can be demodulated and recover ALL of the baseband (voice) info.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T03:28:46.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5152" PostTypeId="2" ParentId="5088" CreationDate="2015-07-22T03:57:00.450" Score="1" Body="&lt;p&gt;The whole idea is to use 2 (or more for MFSK) tones to modulate the signal. As long as the tones are the correct frequencies it works. You can use standard tones and no need for special equipment to detect the tones or use non-standard tones and make your own detectors. Either way works. I had a schematic when I was younger (about 40 years ago) that used opamps configured as cascaded Butterworth filters to do the job. it then went to a Timex/Sinclair 1000 computer with A whopping 2K of memory and the program encoded and decoded it for you. You could tune them to ANY frequency you wanted, but the parts used were for the standard frequencies.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T03:57:00.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5154" PostTypeId="2" ParentId="3606" CreationDate="2015-07-22T04:53:51.667" Score="0" Body="&lt;p&gt;As stated just do the vector math at each junction. There are releatively simple programs that do just that and are pretty accurate.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T04:53:51.667" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5155" PostTypeId="2" ParentId="5027" CreationDate="2015-07-22T05:22:29.617" Score="0" Body="&lt;p&gt;Use of 2 preamplifiers should be done symetrically. The usual reason to place the amplifier closer to the antenna is to avoid amplifying noise induced into the feed line and thus increase the S/N ratio BEFORE the extra noise is added improving the overall signal quality. If the end result is the same signal level it makes no difference except for the possible S/N ratio improvement.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T05:22:29.617" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5157" PostTypeId="2" ParentId="3792" CreationDate="2015-07-22T05:35:43.363" Score="0" Body="&lt;p&gt;The simple answer is that ANYTHING will tune, but the pattern and efficiency are the real problems. We need more specific information to truly answer the questions. Too much metal in close proximity to the antenna WILL distort the pattern and change the feedpoint impedance/SWR. An antenna simulator can accurately simulate virtually any situation if you take the time to model it correctly and accurately. Among other things, it can model nearby structures of metal or conductive materials as well as the antenna itself. Some of us have these programs and can model it for you if it would really help. But please don't ask and waste someone's time when you already know the results.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastEditorUserId="5026" LastEditDate="2015-07-23T03:13:07.887" LastActivityDate="2015-07-23T03:13:07.887" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5158" PostTypeId="2" ParentId="5033" CreationDate="2015-07-22T05:45:33.673" Score="0" Body="&lt;p&gt;There is ALWAYS SOME loss when adding coax ANYWHERE! Inthis case the solution is to use 1/4 wave (or odd multiples of 1/4 wave) lengths of 75 Ohm coax from the antennas to the T to make a &quot;coax transformer&quot;, thus reducing the loss and removing the need for the stub. This the &quot;standard&quot; way to connect 2 50 ohm antennas to a 50 ohm radio.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T05:45:33.673" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5159" PostTypeId="2" ParentId="5028" CreationDate="2015-07-22T05:48:55.400" Score="0" Body="&lt;p&gt;ANY time you change the mounting method the lengths need to be recalculated. You can google &quot;element correction factor&quot; and trust that their formula is correct or use an antenna simulator to do it for you. It is usually just a few percent (2%???) BUT IT WILL MAKE A DIFFERENCE!&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T05:48:55.400" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5161" PostTypeId="2" ParentId="4871" CreationDate="2015-07-22T06:06:21.067" Score="0" Body="&lt;p&gt;The type of array you use will affect mostly the GAIN and DIRECTIVITY. ANY antenna can be used in an array. It just depends on your goals and what is best for the situation. Broadside or endfire? It depends if you want vertically/horizontally wide or narrow patterns and how broad of a main lobe. Spacing and phasing will also affect the pattern.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T06:06:21.067" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5162" PostTypeId="2" ParentId="5145" CreationDate="2015-07-22T06:53:18.217" Score="1" Body="&lt;p&gt;The following solution has been tried many times and is simple to do. No special connections and very little effort. This has been done by replacing the original antenna from a wireless modem and the reported distances can be modest or huge. Many have used cheap but effective home built antennas or wave guides with horns. Coffee cans and potato chip cans have been used effectively. Some claim distances of more than 20-40 Km and one claimed they would get much more distance, but only with super careful attention to many details. If you have the space a small dish can even be used. You can make the dish too. Be sure to look at the rules where you live. There is likely a legal limit to the ERP (effective radiated power).&lt;/p&gt;&#xA;" OwnerUserId="5026" LastEditorUserId="13" LastEditDate="2015-07-27T13:18:23.923" LastActivityDate="2015-07-27T13:18:23.923" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5163" PostTypeId="2" ParentId="3716" CreationDate="2015-07-22T08:15:00.500" Score="2" Body="&lt;p&gt;As a general rule if the pins match it will work. They are usually a standard configuration. The real question is the quality.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T08:15:00.500" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5164" PostTypeId="2" ParentId="4916" CreationDate="2015-07-22T08:27:49.683" Score="2" Body="&lt;p&gt;Most likely they are complying with the ERP limits imposed by the government. The different powers could have to do with the gain of the antenna at different frequencies.&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T08:27:49.683" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5166" PostTypeId="2" ParentId="3478" CreationDate="2015-07-22T09:15:50.810" Score="-1" Body="&lt;p&gt;You &lt;strong&gt;might&lt;/strong&gt; already know this but you need to remember &lt;strong&gt;how&lt;/strong&gt; you are measuring the power. Thre is a difference between, peak, PEP, average, etc. Maybe you are comparing your measured Peak power to the rating of the radio measured in average power???&lt;/p&gt;&#xA;" OwnerUserId="5026" LastActivityDate="2015-07-22T09:15:50.810" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5168" PostTypeId="2" ParentId="5145" CreationDate="2015-07-22T23:44:17.910" Score="3" Body="&lt;p&gt;In fact, it appears 9600 baud will work on narrowband FM. Here is a description from Amsat of &lt;a href=&quot;http://www.amsat.org/amsat/articles/g3ruh/109.html&quot; rel=&quot;nofollow&quot;&gt;a 9600 baud packet modem which used a bandwidth of 4800 Hz&lt;/a&gt; and &lt;a href=&quot;http://www.jrmiller.demon.co.uk/products/mod96.html&quot; rel=&quot;nofollow&quot;&gt;its board&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to the Amsat article, the design is used in many devices including:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;PacComm Inc: NB-96&lt;/li&gt;&#xA;&lt;li&gt;Kantronics: DE-9600&lt;/li&gt;&#xA;&lt;li&gt;MFJ: MFJ-9600 &lt;/li&gt;&#xA;&lt;li&gt;Tasco: TMB-965&lt;/li&gt;&#xA;&lt;li&gt;Symek: TNC2-H&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;(These were from 1988 when the article was written; here are &lt;a href=&quot;ftp://ftp.tapr.org/general/9600baud/96man2x0.txt&quot; rel=&quot;nofollow&quot;&gt;some slightly more modern instructions&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Packet is AX.25, which Linux routes natively. &lt;a href=&quot;http://www.tldp.org/HOWTO/AX25-HOWTO/x1194.html&quot; rel=&quot;nofollow&quot;&gt;Here's an AX.25 howto&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="76" LastEditDate="2015-07-26T19:15:43.533" LastActivityDate="2015-07-26T19:15:43.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5170" PostTypeId="2" ParentId="3478" CreationDate="2015-07-23T17:07:25.663" Score="6" Body="&lt;p&gt;Think of the &quot;power&quot; setting on the radio as more of a guideline than a rule. It should be more or less accurate, given reasonable inputs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Few radios actually measure the output power and adjust gain to achieve the desired power. More likely, the power setting simply adjusts the gain of the radio's power amplifier with no feedback whatsoever.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally, ALC keeps the input power to the power amplifier at the appropriate level. However, the ALC is probably just measuring peak voltage of the input signal and adjusting gain based on that. It's simpler to implement a peak detector than it is to measure true RMS voltage, and usually this works fine enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's probably happening is this: when you turn the digital gain up, you are &lt;a href=&quot;https://en.wikipedia.org/wiki/Clipping_(audio)&quot; rel=&quot;noreferrer&quot;&gt;clipping&lt;/a&gt; at some stage. Once you start clipping, increasing the gain adds more power in harmonics, but does not increase the peak voltage of the signal. Because the ALC circuitry is looking at the peak voltage, it doesn't decrease the gain to compensate for this additional power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For digital modes, you really don't want this to happen. That power in the harmonics means you are occupying more bandwidth than intended: it wastes your transmitter's power and interferes with nearby stations. Here are some waterfall &lt;a href=&quot;http://www.eham.net/articles/12626&quot; rel=&quot;noreferrer&quot;&gt;examples of PSK31 from an eham.net&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a good signal, with no visible distortion:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fk7oC.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fk7oC.png&quot; alt=&quot;psk31 signal with no distortion&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And here's one with extreme distortion:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SKoGh.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SKoGh.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See how the signal has &quot;echos&quot; above and below the center frequency? That's harmonic distortion caused by clipping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To properly set your levels for digital operation, you want to adjust your digital gain and/or computer's audio output level so that the ALC just barely kicks in, then back it off a tad. You don't want ALC working at all, since the variable attenuation provided by ALC is equivalent to multiplying your signal with some other function, and this can introduce additional distortion which degrades your signal quality.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-07-23T17:07:25.663" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5171" PostTypeId="2" ParentId="5145" CreationDate="2015-07-24T21:34:03.050" Score="2" Body="&lt;p&gt;In addition to what user3486184 said and the direct discriminator on the back, you'll need direct access to the modulator too.  A good way to test whether it all works is to fire up a sound card packet program.  Once you can make reliable connections with that (that's your Network Layer 2) you can move up the stack to TCP/IP.&lt;/p&gt;&#xA;" OwnerUserId="5045" LastActivityDate="2015-07-24T21:34:03.050" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5172" PostTypeId="1" CreationDate="2015-07-24T21:51:41.213" Score="1" ViewCount="178" Body="&lt;p&gt;The maximum data rate on UHF is 56kbaud. This is well over most &quot;high-speed&quot; 9600 baud transmissions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to use two receivers at one site, and two transmitters (vice versa when the packets come back) to double the baud rate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transmiter/receiver pairs would obviously have to be on different frequencies to avoid doubling. &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="873" LastEditDate="2015-07-31T22:56:29.040" LastActivityDate="2015-07-31T22:56:29.040" Title="Using two radios for a faster data rate" Tags="&lt;united-states&gt;&lt;digital-modes&gt;" AnswerCount="3" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="5173" PostTypeId="2" ParentId="5172" CreationDate="2015-07-25T21:59:07.147" Score="0" Body="&lt;p&gt;Yes, you would need to conform to local regulations (ex. in the US you are often required to transmit your callsign at regular intervals), but if you had software on both sides that could do load balancing, there is no technical reason why it could not be accomplished.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps look into protocols and compression for higher data rates? :)&lt;/p&gt;&#xA;" OwnerUserId="5046" LastActivityDate="2015-07-25T21:59:07.147" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5174" PostTypeId="2" ParentId="5138" CreationDate="2015-07-25T22:07:19.387" Score="1" Body="&lt;p&gt;You might have some luck with Zadig: &lt;a href=&quot;http://zadig.akeo.ie/&quot; rel=&quot;nofollow&quot;&gt;http://zadig.akeo.ie/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a Windows tool for replacing installed drivers with generics compatible with common devices. If the baofeng cable is just be a serial-USB adapter, it might work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, I bought a cable from Amazon that was DOA. Most are cheaply manufactured, it might just be a bad cable.&lt;/p&gt;&#xA;" OwnerUserId="5046" LastActivityDate="2015-07-25T22:07:19.387" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5175" PostTypeId="2" ParentId="4873" CreationDate="2015-07-25T22:13:01.733" Score="0" Body="&lt;p&gt;Many vendors sell &quot;batteries&quot; which are just cigarette (&quot;accessory port&quot;) lighter plugs on one end and a battery-shaped connector on the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They're perfect for cars.&lt;/p&gt;&#xA;" OwnerUserId="5046" LastActivityDate="2015-07-25T22:13:01.733" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5177" PostTypeId="1" AcceptedAnswerId="5178" CreationDate="2015-07-28T11:02:13.803" Score="2" ViewCount="377" Body="&lt;p&gt;If I have two SDRs like the BladeRF and I want to use one as a signal generator and connect them together do I have to attenuate the connections? &lt;/p&gt;&#xA;" OwnerUserId="5061" LastActivityDate="2015-07-28T18:34:15.867" Title="Connecting two SDRs together for one to act as a signal generator" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5178" PostTypeId="2" ParentId="5177" CreationDate="2015-07-28T14:38:54.883" Score="3" Body="&lt;p&gt;It depends on the specifications of the particular hardware, but in most cases &lt;strong&gt;yes, you must use an attenuator.&lt;/strong&gt; Specifically, you want to compare the &lt;em&gt;maximum transmit power&lt;/em&gt; (how much power the transmitter can produce) to the &lt;em&gt;maximum receive power&lt;/em&gt; (the incoming power above which the receiver will be damaged).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, at a glance the bladeRF web site doesn't give these specifications, so &lt;strong&gt;for the purposes of this answer I'll use the published figures for the &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/HackRF-One&quot; rel=&quot;nofollow noreferrer&quot;&gt;HackRF One&lt;/a&gt; instead,&lt;/strong&gt; but you’ll have to obtain the specs for your own hardware. The maximum transmit power in that case is given as 15 dBm (decibels relative to one milliwatt; i.e. 31 milliwatts). The maximum receive power is given as -5 dBm. Since we have them in the form of decibels, we can subtract the latter from the former to conclude there is a &lt;strong&gt;20 dB&lt;/strong&gt; gap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that for this example you should use an attenuator of &lt;strong&gt;at least&lt;/strong&gt; 20 dB to avoid hardware damage. You may need even more attenuation than that to avoid distortion of the received signal, as the point of hardware damage is likely above the point of &lt;a href=&quot;https://ham.stackexchange.com/a/2479/76&quot;&gt;clipping&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You &lt;em&gt;could&lt;/em&gt; use less attenuation by configuring your devices properly. For example, you can decrease transmit amplifier gain or send lower-amplitude samples, and you can also decrease or shut off receive amplification. But this is running the risk of hardware damage due to software misconfiguration — do you really want to take that chance? (However, using transmit power controls to avoid clipping on the receive side or to simulate a weaker signal is reasonable.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For my own testing purposes, I am using a 0-80 dB manually-variable attenuator I picked up at a flea market. I find it quite useful and recommend you obtain a similar device if you can (new ones can be fairly expensive, however).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;While you asked about software-defined radios, everything here is applicable to any other type of radio. Two notes on the subject:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;For higher-power transmitters, transmit power may be given in watts. Convert to dBm, $10\cdot\log_{10}\left(\tfrac{P}{0.001 W}\right)$, and remember that transmit power may be poorly calibrated and exceed the specified value.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If your receiver does not have maximum receive power specs, you can start with sensitivity specs instead; you'll want to apply &lt;em&gt;more&lt;/em&gt; than that signal, but how much more is needed until the signal is adequately received will have to be determined by experiment. This is where a &lt;em&gt;variable&lt;/em&gt; attenuator is handy.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-07-28T18:34:15.867" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5179" PostTypeId="1" AcceptedAnswerId="6259" CreationDate="2015-07-29T14:09:11.707" Score="6" ViewCount="802" Body="&lt;p&gt;I'd like to experiment with amateur video transmission in a setup halfway between ATV and SSTV. 480 lines of B&amp;amp;W image would be sufficient with 10 FPS, and I'm interested in both digital and analog methods.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd prefer if I wouldn't have to buy new hardware, I was thinking about using my HackRF as a transmitter and my RTL-SDR stick as the receiver, but that'd probably require building (buying?) an appropriate amplifier for former.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has there been any similar projects in ham radio? Could DVB-T be used with reduced parameters, thus smaller bandwidth? Any tips and/or links are appreciated!&lt;/p&gt;&#xA;" OwnerUserId="5068" LastEditorUserId="5046" LastEditDate="2015-08-01T06:53:26.620" LastActivityDate="2016-06-04T10:44:53.317" Title="Video transmission between ATV and SSTV" Tags="&lt;diy&gt;&lt;modes&gt;&lt;rtl-sdr&gt;&lt;sstv&gt;" AnswerCount="1" CommentCount="6" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5180" PostTypeId="2" ParentId="5172" CreationDate="2015-07-29T23:20:52.903" Score="1" Body="&lt;p&gt;What you're talking about is called &quot;Link aggregation.&quot;  It's done all the time in the LAN/WAN industry, but I hadn't heard of it being done on ham radio (which isn't to say it isn't being done.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And for hb9tst, the reason for the 56k limit is the FCC.  Part 97 limits the data rate to 56k baud on 70cm (the band the questioner is using.)&lt;/p&gt;&#xA;" OwnerUserId="5045" LastActivityDate="2015-07-29T23:20:52.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5181" PostTypeId="1" CreationDate="2015-07-30T03:04:17.103" Score="6" ViewCount="382" Body="&lt;p&gt;In the US, the common (though not universal) repeater offsets are ±600 kHz in the 2m band and ±5 MHz in the 70cm band.  &lt;strong&gt;How and why did these offsets come to be standard for amateur repeaters?&lt;/strong&gt;  The minimum simplex channel spacing is much less than the repeater offset convention.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, spacing between FRS channels and GMRS channels, both near the 70cm band, is 25 kHz.  Is there a reason why a smaller interval is undesirable, or a larger interval is advantageous?&lt;/p&gt;&#xA;" OwnerUserId="1693" LastEditorUserId="1693" LastEditDate="2015-07-31T19:54:26.737" LastActivityDate="2017-01-07T20:29:04.377" Title="What is the reason/origin of conventional US repeater offsets?" Tags="&lt;united-states&gt;&lt;repeater&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5183" PostTypeId="1" CreationDate="2015-07-30T09:59:43.713" Score="2" ViewCount="2459" Body="&lt;p&gt;I want to get to know about the satellite communication at 8000-10000 km,&#xA;During that, I come across the VHF and UHF.&#xA;In that I am facing problem for deciding the frequency band for communicating with the satellites at 8000 to 10000 km height from the earth surface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please help me and give some important links which will help me for better understanding of the VHF and UHF, Also suggest me which frequency band is most suitable for this height for uplink and downlink.&lt;/p&gt;&#xA;" OwnerUserId="4895" LastEditorUserId="4665" LastEditDate="2017-04-09T15:34:51.083" LastActivityDate="2017-04-09T15:34:51.083" Title="Which Frequency Band(VHF/UHF) is most useful for satellite in MEO?" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;satellites&gt;&lt;frequency&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5184" PostTypeId="2" ParentId="5172" CreationDate="2015-07-30T13:32:22.600" Score="0" Body="&lt;p&gt;Yes it possible it's called MIMO technology (Multiple Input Multiple Output) used for 3G and above standards and new WIFI norms&lt;/p&gt;&#xA;" OwnerUserId="5072" LastActivityDate="2015-07-30T13:32:22.600" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5185" PostTypeId="2" ParentId="5181" CreationDate="2015-07-30T17:02:28.753" Score="6" Body="&lt;p&gt;Repeaters need to receive and transmit at the same time. The offset needs to be large enough to make it possible for the filters  to separate the transmit and receive frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my opinion 600 kHz is a very narrow spacing, it results in filters that are enormous, usually six cavities each 150 x 500 mm. Even so, they have several dB of loss in both bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;5 MHz is much more reasonable, the filters can be made much smaller by helical loading of the coaxial elements inside. This lowers the Q somewhat, but with the larger spacing, it's much easier. A filter for a 5 MHz spacing might be 1/2 the length and diameter, and probably with less loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reducing the offset below 600 kHz would be very difficult, the filters would be unstable over temperature changes, and the losses would be enormous.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the reason - I suspect - 600 kHz was chosen is because the amateur band is only 2 MHz wide in many countries. 600 allows some repeaters and some simplex traffic, space, etc. Possibly the lower parts of the band (144.0 -  144.5) were already allocated for CW,  SSB and so on, so when FM came along, the repeaters needed to squeeze into the top 1.2 MHz.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-08-01T05:18:54.953" LastActivityDate="2015-08-01T05:18:54.953" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5187" PostTypeId="2" ParentId="4917" CreationDate="2015-08-01T18:43:24.797" Score="0" Body="&lt;p&gt;My sense is that with two amps, you will be faced with a phasing issue.  You could conceivably correct for that with a short piece of coax, but then you've just reduced the bandwidth of your system.  If it were me, I would just get one amp with twice the power.  That would simultaneously reduce complexity, improve efficiency (power out/power in) and cost.&lt;/p&gt;&#xA;" OwnerUserId="5045" LastActivityDate="2015-08-01T18:43:24.797" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5188" PostTypeId="1" AcceptedAnswerId="5190" CreationDate="2015-08-01T20:17:36.387" Score="2" ViewCount="173" Body="&lt;p&gt;Planning to travel out of state, I decided to try using echolink to connect with my local repeater. I validated my callsign and successfully connected to the test server. I decided to try connecting to KE6TZG by searching for the callsign in the app, but I couldn't find it. There were no stations in search results for KE6TZG but when I searched for KE6 I got a list of some local stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to kpra.net the node is &quot;idle&quot; which I assume means it is empty and available. I would be connecting though 3g/4g or WiFi, though I would not have router setting access so I would need to go through a relay server, would that cause the problem? Thanks&lt;/p&gt;&#xA;" OwnerUserId="5083" LastActivityDate="2015-08-01T20:42:21.567" Title="Echolink for Android not showing repeater node" Tags="&lt;echolink&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5189" PostTypeId="2" ParentId="5181" CreationDate="2015-08-01T20:30:05.363" Score="3" Body="&lt;p&gt;Was going to comment, but don't have enough rep on the ham site yet.&#xA;This discussion offers a few tidbits regarding history/reasoning behind the 600kHz split and other oddities of the 2m band:&#xA;&lt;a href=&quot;https://forums.qrz.com/index.php?threads/history-of-vhf-repeater-splits.26321/&quot; rel=&quot;nofollow&quot;&gt;https://forums.qrz.com/index.php?threads/history-of-vhf-repeater-splits.26321/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5004" LastActivityDate="2015-08-01T20:30:05.363" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5190" PostTypeId="2" ParentId="5188" CreationDate="2015-08-01T20:42:21.567" Score="0" Body="&lt;p&gt;The node is reported as currently offline.&#xA;&lt;a href=&quot;https://www.repeaterbook.com/repeaters/echolink/node_status.php?node=KE6TZG-R&amp;amp;type=search&quot; rel=&quot;nofollow&quot;&gt;https://www.repeaterbook.com/repeaters/echolink/node_status.php?node=KE6TZG-R&amp;amp;type=search&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The notes on the repeater at RepeaterBook do say that incoming connections are restricted.&lt;/p&gt;&#xA;" OwnerUserId="5004" LastActivityDate="2015-08-01T20:42:21.567" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5192" PostTypeId="2" ParentId="221" CreationDate="2015-08-03T15:19:53.363" Score="2" Body="&lt;p&gt;I didn't see any answers that had the extended square as referenced in the &lt;a href=&quot;https://en.wikipedia.org/wiki/Maidenhead_Locator_System&quot; rel=&quot;nofollow&quot;&gt;Wikipedia&lt;/a&gt; article. My Clojure implementation &lt;a href=&quot;https://gist.github.com/damionjunk/f799a10e5bfbb678d8bd&quot; rel=&quot;nofollow&quot;&gt;(GitHub Gist Here)&lt;/a&gt; encodes the fourth and fifth pairs.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;(defn to-maidenhead&#xA;  [lat long]&#xA;  (let [long (-&amp;gt; long (+ 180) (/ 2))&#xA;    lat  (-&amp;gt; lat (+ 90))&#xA;    funs [#(* 10 (mod % 1)) #(* 24 (mod % 1)) #(* 10 (mod % 1)) #(* 24 (mod % 1))]&#xA;    cars [\A \0 \a \0 \a]]&#xA;    (map (fn [geo]&#xA;       (map (fn [n car] (char (+ (int car) n)))&#xA;            (reductions (fn [n fun] (fun n))&#xA;                        (/ geo 10)&#xA;                        funs)&#xA;            cars))&#xA;     [long lat])))&#xA;&#xA;(def to-maidenhead-str (comp #(apply str %) #(apply interleave %) to-maidenhead))&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;A simple bit of testing:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;(comment&#xA;&#xA;  (apply str&#xA;    (apply interleave&#xA;      (to-maidenhead 36.165926 -86.723285)))&#xA;&#xA;  ;; =&amp;gt; &quot;EM66pd39et&quot;&#xA;&#xA;  (and&#xA;    (= &quot;EM66pd39et&quot; (to-maidenhead-str 36.165926 -86.723285))&#xA;    (= &quot;OF86cx76ql&quot; (to-maidenhead-str -33.014673 116.230695))&#xA;    (= &quot;FD54oq44oh&quot; (to-maidenhead-str -55.315349 -68.794971))&#xA;    (= &quot;PM85ge79vh&quot; (to-maidenhead-str 35.205535 136.56579)))&#xA;&#xA; ;; =&amp;gt; true&#xA;&#xA;&#xA; ;; Just a simple test at various coordinates around the globe.&#xA; ;; Maidenhead Locator taken from http://no.nonsense.ee/qth/map.html&#xA;&#xA;)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="5091" LastActivityDate="2015-08-03T15:19:53.363" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5193" PostTypeId="2" ParentId="119" CreationDate="2015-08-04T10:59:51.203" Score="5" Body="&lt;p&gt;I hold an Amateur Extra licence from the United States and have moved to the United Kingdom. I sent an application to Ofcom for a Full reciprocal licence and received the following response.&lt;/p&gt;&#xA;&lt;p&gt;I can operate for three months for free, then £20 each six months for an indefinite length. I plan on arguing my case as the United States does not issue Harmonized Amateur Radio Examination Certificates (HAREC) but there is past precedent for the UK issuing Full licences to US Amateur Extras.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Ofcom have not been able to issue you with  an Amateur Full reciprocal because your licence needs to be part of the T/R 61-02 arrangement.  You can certainly operate up to three months at a time the UK when visiting under the T/R 61-01 licence that you hold.&lt;/p&gt;&#xA;&lt;p&gt;The options are to apply for a Temporary Reciprocal Licence which would cost £20 and would only be valid for 6 months with the requirement to renew each time at the administrative cost of £20&lt;/p&gt;&#xA;&lt;p&gt;Therefore, if you are residing here for a while, it would seem a better option to simply sit the Amateur Full licence examination via the Radio Society of Great Britain and issue a licence free of charge online once you have passed.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="4818" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2015-08-04T10:59:51.203" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5194" PostTypeId="1" AcceptedAnswerId="5897" CreationDate="2015-08-07T15:58:34.250" Score="5" ViewCount="428" Body="&lt;p&gt;I've recently started looking into APRS, and can easily receive some APRS signals from my station - however, I can't seem to decode them using QTMM or any similar software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this because they're too weak / noisy, or am I doing something else wrong? I presume it's picking up an APRS envelope but failing a checksum or something similar - if there's any way to just get partial packet data I'd be interested in that as well.&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="65" LastEditDate="2016-03-10T16:10:54.667" LastActivityDate="2016-03-10T16:10:54.667" Title="Decoding weak APRS signals" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5195" PostTypeId="1" AcceptedAnswerId="5196" CreationDate="2015-08-07T18:20:06.647" Score="3" ViewCount="1305" Body="&lt;p&gt;I have a Kenwood TM-V71A dual-band radio that I have attempted to use to listen to the FM repeater on the SO-50 satellite. I'm using a home-made dual-band yagi antenna made out of coat hangers, that I built from these instructions: &lt;a href=&quot;http://www.amateurradio.bz/4_dollar_satellite_antenna.html&quot; rel=&quot;nofollow&quot;&gt;http://www.amateurradio.bz/4_dollar_satellite_antenna.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tested out the antenna by listening to some local repeaters and weather frequencies and it seems to work fine for that. I double-checked that I'm using the right downlink frequency for the satellite, and that I have the correct time and direction info from pass predictions obtained here: &lt;a href=&quot;http://www.amsat.org/amsat-new/tools/predict/index.php&quot; rel=&quot;nofollow&quot;&gt;http://www.amsat.org/amsat-new/tools/predict/index.php&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't even bothered trying to transmit yet, because I can barely get a receive signal from SO-50. When I attempt to listen to a satellite pass, at approximately the halfway point where the satellite is at maximum elevation, I can hear a clear signal for about 5-10 seconds, and then nothing for the rest of the pass. This has happened several times now. On passes with low elevation (less than 20 degrees from horizon), I hear nothing at all. On passes with high elevation (45-70 degrees from horizon), I will get a few seconds of signal, right around the middle of the pass.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what am I doing wrong? I'm pretty sure I've built the antenna correctly, and have the correct pass times. I started out using the directional information, but now I basically just spin in circles at all different angles, trying to get any signal whatsoever. I also rotate the antenna for different polarizations. The times that I do get a few seconds of signal, it may end up being from the totally wrong direction than what the pass prediction said.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I need to be at a much higher elevation than ground-level in my back yard? What else could be going wrong? Are there other satellites that I can try? It seems to me that SO-50 is the only operational FM voice repeater (aside from the ISS, which isn't always in voice mode, if I understand correctly).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you for any help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I had been adjusting for Doppler shift at first, but then left it at the centre frequency, as it did not seem to be making a difference. However, the chart provided by Pete NU9W was very helpful in making me realize the problem. I think my radio isn't sensitive enough to adjust for Doppler shift properly. It will only change the frequency by 25 kHz at a time, and the chart suggests adjusting by 5 kHz at a time. In my case, I can be 5 kHz off centre, or 30 kHz off in either direction. Since 30 kHz is too far off, it would explain why I only hear something in the middle of the pass.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT 2: I figured out how to change the step frequency on my radio to 5 kHz instead of 25 kHz. I will try using this setting and see if I can adjust for Doppler shift better next time.&lt;/p&gt;&#xA;" OwnerUserId="4953" LastEditorUserId="4953" LastEditDate="2015-08-09T22:47:58.487" LastActivityDate="2015-10-04T15:46:40.190" Title="Why can I barely hear the SO-50 satellite?" Tags="&lt;satellites&gt;&lt;uhf&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5196" PostTypeId="2" ParentId="5195" CreationDate="2015-08-07T19:02:06.547" Score="3" Body="&lt;p&gt;It sounds like you're not adjusting for Doppler shift. Just like the sound of a car horn, which is higher pitched when the car is coming toward you than when it's going away, the signal from the satellite is at a higher frequency when it's coming toward you than when it's going away. When the satellite is close to the horizon at the start of the pass it's coming toward you, so the frequency you see is higher; at the end of the pass it's going away, so the frequency is lower. When it's overhead you see it at its actual frequency. You have to adjust for these frequency changes during the pass. &lt;a href=&quot;http://www.amsat.org/wordpress/wp-content/uploads/2014/01/Work_FM_Sats-20131010.pdf&quot; rel=&quot;nofollow&quot;&gt;Here's a link&lt;/a&gt; to a page with suggested frequencies (scroll down).&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2015-08-07T19:02:06.547" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5197" PostTypeId="1" AcceptedAnswerId="5199" CreationDate="2015-08-08T09:57:23.483" Score="10" ViewCount="535" Body="&lt;p&gt;Why does AM have sidebands? Isn't the whole point of AM to broadcast on ONE frequency and ONLY change the amplitude?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3MGAZ.gif&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3MGAZ.gif&quot; alt=&quot;AM wave.&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the picture there is only ONE frequency and the amplitude changes, so why got AM sidebands? And why can't AM work without the sidebands? After all it's only the amplitude we need.&lt;/p&gt;&#xA;" OwnerUserId="5115" LastEditorUserId="13" LastEditDate="2015-08-10T17:38:33.723" LastActivityDate="2015-08-10T17:38:33.723" Title="Why does AM have sidebands?" Tags="&lt;modes&gt;&lt;ssb&gt;&lt;am&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5198" PostTypeId="2" ParentId="2281" CreationDate="2015-08-08T16:10:38.560" Score="4" Body="&lt;p&gt;The question specifies &quot;SDR&quot;, but if all you want is to listen to signals in a distant location, you might try &lt;a href=&quot;http://www.globaltuners.com/&quot; rel=&quot;nofollow&quot;&gt;http://www.globaltuners.com/&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="5116" LastEditorUserId="76" LastEditDate="2015-08-09T00:38:16.657" LastActivityDate="2015-08-09T00:38:16.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5199" PostTypeId="2" ParentId="5197" CreationDate="2015-08-08T17:07:21.157" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;In the picture there is only ONE frequency and the amplitude changes&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Ah, but this actually causes a second frequency component, the one that you wish to transmit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/czOd1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/czOd1.png&quot; alt=&quot;Modulated wave&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Please excuse my rudimentary paint skills.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is this second, implicit frequency which combines with the AM carrier to then form a strong carrier signal in the centre of the spectrum, and a couple of sidebands that are mirrored in either direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Intuitively it can be quite difficult to understand, however there is a &lt;a href=&quot;https://physics.stackexchange.com/questions/10463/understanding-the-cause-of-sidebands-in-amplitude-modulation&quot;&gt;relatively simple mathematical explanation&lt;/a&gt; (if you understand basic trigonometry) which shows this is the case.&lt;/p&gt;&#xA;" OwnerUserId="65" LastEditorUserId="-1" LastEditDate="2017-04-13T12:40:15.020" LastActivityDate="2015-08-08T17:07:21.157" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5203" PostTypeId="1" CreationDate="2015-08-09T07:57:25.510" Score="4" ViewCount="385" Body="&lt;p&gt;Question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What are the most effective audio tone frequency(s) and pattern(s) used in direction finding in the world of amateur radio?&lt;/strong&gt; Also: Is there a specification for the tones that amateur radio fox hunt transmitters use, and if so, is it designed with effectiveness in mind?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Supplemental Discussion:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am designing a Fox-hunt transmitter for the 70-cm band. I'm developing it to produce a range of tones in sequence, such as 440 Hz for 500 ms, 740 for 300 ms, 2200 Hz for 300 ms, etc. These are square-wave tones generated on a microcontroller and fed to a FSK transceiver module which is configured for direct modulation. The transceiver is configured for 5 kHz deviation. Thus, when an amateur radio HT is tuned to the FM center frequency, the tones can be heard. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The prime design goal is for this to be heard as far away as possible, which means making the signal as unique and identifiable as possible for a human listener. This basically means finding the best signal-to-noise ratio in the audible spectrum, the signal being the tone(s) and the noise being the background static present at the given tone frequency. According to &lt;a href=&quot;https://en.wikipedia.org/wiki/Equal-loudness_contour&quot; rel=&quot;nofollow&quot;&gt;this&lt;/a&gt; document, the human ear is most attuned to tones around 3 kHz at the threshold of hearing. Thus, it would make sense to use 3 kHz tones exclusively. However, as I have experimented with white noise mixed with various tones (using Audacity), it seems that the range from 300 Hz to 2 kHz is more conducive for identifying the tone from the background noise. Thus I'm somewhat stumped. I've found a few videos of Fox-hunt transmitters in action, but these offer no consensus on tones or pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is one precedent I am aware of which does define a set of parameters for radio direction finding: Aircraft Emergency Location Transmitters. According to &lt;a href=&quot;https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf09186.html&quot; rel=&quot;nofollow&quot;&gt;Industry Canada RS-287 Section 5.3(a)&lt;/a&gt;, 121.5 MHz aircraft radio distress beacons sweep down from between 1600 Hz and 300 Hz, covering no less than 700 Hz of this range. The document does not reference any research or reason for the range chosen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am also familiar with the Emergency Alert System's dual-tone alert, which is the combination of 853 Hz and 960 Hz sine waves. This irritating tone gets your attention, but I'm not sure if it is relevant to radio, and as it is a composite tone, generating it with my microcontroller will add more complexity to the system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;References:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Equal-loudness_contour&quot; rel=&quot;nofollow&quot;&gt;Wikipedia: Equal-loudness contour&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Hearing_range#Humans&quot; rel=&quot;nofollow&quot;&gt;Wikipedia: Hearing range&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=unIBO1lClzE&quot; rel=&quot;nofollow&quot;&gt;YouTube video showing 1.2 kHz tones for a Fox-hunt Tx&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Radio_beacon_of_distress_on_121,5_MHz.ogg&quot; rel=&quot;nofollow&quot;&gt;WikiCommons: 121.5 MHz ELT Beacon&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf09186.html&quot; rel=&quot;nofollow&quot;&gt;Industry Canada RSS-287&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Emergency_Alert_System&quot; rel=&quot;nofollow&quot;&gt;Wikipedia: Emergency Alert System&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5120" LastActivityDate="2017-04-25T17:35:27.327" Title="Audio tones and patterns used for fox-hunt transmitters?" Tags="&lt;fox-hunt&gt;&lt;direction-finding&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5204" PostTypeId="2" ParentId="5203" CreationDate="2015-08-10T12:02:08.827" Score="1" Body="&lt;p&gt;I would make something discrete, as sudden changes are easier to detect than large ones. Stick into the middle of the hearing range (Many Hams are older, and tend to lose the extreme hearing range with time). I would choose a random sweep of tones in the 1000-1500 Hz range, changing the tone 2-5 times per second (Random time intervals might also work). This should give a pretty good indicator of what the signal is, and make it easy to find.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't forget to identify the station every 10 minutes as required.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2015-09-09T14:01:57.323" LastActivityDate="2015-09-09T14:01:57.323" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5205" PostTypeId="1" AcceptedAnswerId="5207" CreationDate="2015-08-10T16:34:45.920" Score="2" ViewCount="2892" Body="&lt;p&gt;What is the mix of a received frequency 27 MHz and a oscillator frequency of 27.001 MHz?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I expect the mix of them would be 1 KHz.&lt;/p&gt;&#xA;" OwnerUserId="5115" LastEditorUserId="5115" LastEditDate="2015-08-11T12:04:40.950" LastActivityDate="2015-08-11T12:04:40.950" Title="Mix of Sine waves with different frequencies" Tags="&lt;frequency&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5206" PostTypeId="2" ParentId="5205" CreationDate="2015-08-10T17:29:06.747" Score="0" Body="&lt;p&gt;When you mix two sine waves with different frequencies you get four frequencies in the result: the two that are coming in, the sum of the two, and their difference. So with 27 MHz and 27.001 MHz you'd see 27MHz, 27.001 MHz, 54.001 MHz (27 + 27.001), and .001 MHz (27.001 - 27). For a radio receiver you'd typically run that mixed-up output throw a low-pass filter so that all you see is the difference frequency, 1 kHz.&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2015-08-10T17:29:06.747" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5207" PostTypeId="2" ParentId="5205" CreationDate="2015-08-11T02:41:52.417" Score="1" Body="&lt;p&gt;If you simply add two sine waves together, it's a linear operation and you do not get mixing.  So you would see only the 27.000 and 27.001 MHz components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to get the sum or difference frequencies, you have to &quot;mix&quot; them in a non-linear device, like a diode or a switching transistor.  Then you will get components at .001 MHz (the difference), 54.001 (the sum), as well as some left over power at the original 27.000 and 27.001 frequencies.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Actually, you will get even more frequencies than these as &quot;higher order&quot; mixing products, like 2x27.000 - 27.001 = 26.999 MHz and many other combinations, as well as the harmonics (double, triple, etc.) of 27.000 and 27.010. (But the high order mixing products are probably going to be weaker.)&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-08-11T02:41:52.417" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5209" PostTypeId="1" CreationDate="2015-08-12T05:20:53.043" Score="3" ViewCount="1957" Body="&lt;p&gt;Has anyone tested the new ICOM ID-51A Plus with regular repeaters (i.e. analog)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm looking to quickly find the nearest repeater (and sign on with a PL code!) with like 1 or 2 clicks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is that possible with this radio?&lt;/p&gt;&#xA;" OwnerUserId="1463" LastEditorUserId="1463" LastEditDate="2015-08-27T13:33:31.027" LastActivityDate="2019-11-04T18:50:42.623" Title="Does the ICOM ID-51A's repeater search work with non-D-STAR repeaters?" Tags="&lt;repeater&gt;&lt;ht&gt;&lt;d-star&gt;&lt;icom&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5210" PostTypeId="1" CreationDate="2015-08-12T14:45:09.447" Score="3" ViewCount="1220" Body="&lt;p&gt;I've built a 2 meter ground plane antenna that works pretty well for RX and has a decent SWR on 2 meters with my Alinco.  However, I'm experimenting with SDR quite a bit and would really like to build something for weak signals, especially CW and RTTY at less than 50 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To that end, I was thinking of building a large dipole, but I'm getting advice that says that an ungrounded end fed wire run up the side of the house would likely perform far better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, is this true?  Second, if it is true, why is it true?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Note:&lt;/em&gt; I am planning to use this antenna for &lt;em&gt;RX ONLY&lt;/em&gt;, so I'm not really concerned about frequency matching on the length of the wire or dipole arms.&lt;/p&gt;&#xA;" OwnerUserId="5137" LastEditorUserId="76" LastEditDate="2017-01-19T00:29:03.303" LastActivityDate="2017-01-19T00:29:03.303" Title="Dipole versus ungrounded end fed for HF RX" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="5211" PostTypeId="1" AcceptedAnswerId="11608" CreationDate="2015-08-13T13:36:27.720" Score="4" ViewCount="2349" Body="&lt;p&gt;Clearly, building a Yagi tuned for 2 meters will likely have the best &lt;em&gt;directional&lt;/em&gt; performance.  Putting that aside, I'm trying to get information on what antenna type will have the best overall performance in the 2 meter band in an NFM mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a 5/25 watt 2 meter FM transceiver that I'm currently using.  I've been experimenting with a ground plane antenna that I built with 4 radials.  Just using it here in the office (rather than up high and outside) reception seems &quot;ok&quot;.  SWR is currently 3:1, but I'm not using it for TX at the moment.  I'm also hesitant to try to tune it since I'm not sure if the ground plane radials are too long... or too short. :)  I'm afraid that I could make things worse by trimming them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm on a bit of a budget, so I'm currently building gear.  In your experience (or if you can back it up with some theory), which type of antenna would provide the best overall (non-directional) performance?  Building a dipole is definitely within my capabilities.  I'm sure I can handle a j-pole too... but I'd rather not end up in an endless cycle of antenna building. :)  I'd rather build the thing just once!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Update&lt;/strong&gt;: Just for clarification, &quot;working ok&quot; means that I'm reading a signal off of a repeater that's 43 miles away in Hartford, CT with the antenna sitting on the floor of my office.  Perhaps I just need to scale up, tune it and get it up above my roof.&lt;/p&gt;&#xA;" OwnerUserId="5137" LastEditorUserId="5137" LastEditDate="2015-08-13T19:57:17.690" LastActivityDate="2018-07-20T23:40:34.770" Title="Ideal antenna type for FM 2 meters?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5212" PostTypeId="1" AcceptedAnswerId="5218" CreationDate="2015-08-13T13:44:43.820" Score="4" ViewCount="3925" Body="&lt;p&gt;I've built a ground plane antenna with a 19.5&quot; vertical and 4 20&quot; radials.  Currently, at 147.135 MHz my SWR is 3:1, clearly not ideal (and even bad for the transmitter!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm reluctant to start snipping radials because I really don't know if the problem is that they are too long or too short.  How can I figure this out?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My thought is that I could measure SWR at 142 MHz and again at 149 MHz and that this should tell me, based on the difference, if they are too long or two short or if, possibly, simply changing the radial down angle will help, but I have no idea how to interpret the differences.&lt;/p&gt;&#xA;" OwnerUserId="5137" LastEditorUserId="76" LastEditDate="2017-05-06T23:04:35.090" LastActivityDate="2017-05-06T23:04:35.090" Title="Tuning/trimming a ground plane antenna" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;vhf&gt;&lt;measurement&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5213" PostTypeId="1" AcceptedAnswerId="5220" CreationDate="2015-08-13T15:09:30.567" Score="5" ViewCount="1425" Body="&lt;p&gt;First, I'm very new to SDR.  This may turn out to be really obvious.  I just want to verify my thoughts before I spend more dollars.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a USB dongle with the RT28xx in it.  Works great.  Side by side I have a 35 year old Azden 2 meter receiver.  What I'm noticing is that the Azden seems to be able to pull in somewhat weak signals while the SDR doesn't even register a signal in the waterfall view.  This is true even when I hook the SDR dongle up to the same antenna that I've got on the Azden.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To my mind there are two possible issues.  First, the noise in the dongle is so high that the signal is way below the noise floor.  Second, the dongle simply does't have the sensitivity to pull out the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm leaning toward option 1 (noise in the dongle) and I see some 30 to 50  dollar shielding arrangements for the dongles.  From my description of what I'm seeing, would any experts agree that 1 is the more likely option?&lt;/p&gt;&#xA;" OwnerUserId="5137" LastEditorUserId="76" LastEditDate="2017-07-09T17:21:16.967" LastActivityDate="2017-07-09T17:21:16.967" Title="Noise &amp; shielding, SDR Dongle" Tags="&lt;rfi&gt;&lt;rtl-sdr&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5214" PostTypeId="2" ParentId="5213" CreationDate="2015-08-13T18:32:36.867" Score="3" Body="&lt;p&gt;“Sensitivity” isn't all that well-defined. Insofar as it is, you might as well just think in terms of noise, because there is &lt;em&gt;always&lt;/em&gt; a noise floor and it's &lt;em&gt;always&lt;/em&gt; what determines the weakest signal you can receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most direct way to deal with noise is to &lt;strong&gt;make the signal stronger than the noise.&lt;/strong&gt; This means improving your antenna:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;making it more efficient&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;a full-sized antenna containing no lossy elements&lt;/li&gt;&#xA;&lt;li&gt;tuned specifically for the band you wish to receive&lt;/li&gt;&#xA;&lt;li&gt;away from obstructions, metallic or otherwise&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;moving it to a better location&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;away from local noise sources&lt;/li&gt;&#xA;&lt;li&gt;away from obstructions lying between it and the transmitter&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;making it more directional, pointed towards the transmitter&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This helps with almost everything. If you've done that and it isn't enough, let's start considering the categories of noise:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Noise that is from outside sources and picked up by your antenna, because it's propagating just like the wanted signal.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You can't do anything about this other than use a directional antenna to avoid picking up noise that's not in the direction of the transmitter. And that means you have to pick a frequency and build the antenna for it, and aim it.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Noise that is generated by your own electronic equipment and &lt;em&gt;picked up by the antenna&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You can reduce this by moving your antenna (and receiver) farther away from it.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Noise that is generated by your own equipment and radiates through the unshielded case.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;As you note, this could be fixed by a shielded case. But it's often not the worst problem or the easiest to solve.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Noise that is conducted from your computer to the rtl-sdr device along the USB cable.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Shielding can't help with this.&lt;/li&gt;&#xA;&lt;li&gt;Try a different type of computer — brands vary widely.&lt;/li&gt;&#xA;&lt;li&gt;Disconnect/shut off all other peripherals — in particular cases I have seen power adapters, Ethernet ports, Thunderbolt ports, and &lt;em&gt;built-in speakers!&lt;/em&gt; be major noise sources that can be avoided. (Internal radios such as Wi-Fi and Bluetooth are usually comparatively clean, because they're actually designed to be.)&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Phase noise, from the internal oscillator's imperfection. This can be improved by hardware modifications.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Internal analog noise from the RTL chip etc., and &lt;a href=&quot;https://ham.stackexchange.com/questions/2475/why-is-dynamic-range-relevant-for-an-sdr/2479#2479&quot;&gt;quantization noise&lt;/a&gt;, from the limited resolution of the ADC. These are not really very similar, but they are both addressed by&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Setting the hardware gain controls properly, so that almost the full dynamic range of the ADC is used. (&lt;strong&gt;Do not&lt;/strong&gt; use the built-in AGC (automatic gain control) — in my experience it always sets the level too high.) Turn AGC &lt;em&gt;off&lt;/em&gt;, tune to a known signal, and adjust gain until the &lt;em&gt;height difference&lt;/em&gt; between the signal peak and the noise floor is &lt;em&gt;largest&lt;/em&gt; — this corresponds to maximum SNR.&lt;/li&gt;&#xA;&lt;li&gt;For quantization noise only, &lt;em&gt;increase the sample rate&lt;/em&gt; (as long as your computer can handle it; 2.4 MHz is the usual recommendation for RTL-SDR). This reduces quantization noise via &lt;em&gt;oversampling&lt;/em&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Given that you are comparing two receivers with the same antenna and getting unsatisfactory performance from one, my recommendations are to do the following, as detailed above:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Make sure the gain control is set optimally.&lt;/li&gt;&#xA;&lt;li&gt;Increase the sample rate to 2.4 MHz if it isn't already.&lt;/li&gt;&#xA;&lt;li&gt;Shut off/disconnect all unnecessary computer peripherals; try a different computer.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-08-13T19:00:11.967" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5215" PostTypeId="2" ParentId="5212" CreationDate="2015-08-13T18:50:59.173" Score="4" Body="&lt;p&gt;If you take SWR measurements at a range of frequencies and plot them (or just watch the SWR reading as you change frequency), you should get a graph with one or more valleys of low SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally, if you find the ratio between the valley's actual position and where you want it to be, and trim or rebuild-bigger the antenna according to that ratio (or rather, the reciprocal of it — note that physical lengths go with &lt;em&gt;wavelength&lt;/em&gt;, not frequency!), then the resulting antenna will be spot on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, it won't be exact because you're not building an exactly scaled antenna — your feed-point components and your wire diameter will be staying constant. But you can aim for a little bit too big, then trim it down until the SWR stops dropping.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The above procedure will get you minimum SWR for that antenna design. But remember that you can have a resonant antenna that still has the wrong resistance (i.e. not 50 Ω, assuming you're using normal equipment and coax). Resizing the antenna will &lt;em&gt;not&lt;/em&gt; change the resistance — you have to change the shape or add a matching network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest way to figure this out is to use an antenna analyzer that can read out the resistance value. Find that minimum SWR point, then look at the resistance (or the magnitude of the impedance — which is the same here).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also tell from the shape of the SWR graph. A matched antenna will have a very sharp valley that hits 1:1 SWR. One with a different resistance will have a broader valley that does &lt;em&gt;not&lt;/em&gt; ever reach 1:1.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-08-13T18:50:59.173" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5216" PostTypeId="2" ParentId="5183" CreationDate="2015-08-13T18:58:45.780" Score="1" Body="&lt;p&gt;I'm not going to try to address the &quot;Whys&quot; (since I'm not competent to do so) but you may find the following useful.  This is from the &lt;a href=&quot;http://www.esa.int/Our_Activities/Telecommunications_Integrated_Applications/Satellite_frequency_bands&quot; rel=&quot;nofollow&quot;&gt;European Space Agency&lt;/a&gt;.  There's also a really nice graphic to go with it on the site:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;L-band (1-2 GHz) Global Positioning System (GPS) carriers and also&#xA;  satellite mobile phones, such as Iridium; Inmarsat providing&#xA;  communications at sea, land and air; WorldSpace satellite radio.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;S-band (2–4 GHz) Weather radar, surface ship radar, and some&#xA;  communications satellites, especially those of NASA for communication&#xA;  with ISS and Space Shuttle. In May 2009, Inmarsat and Solaris mobile&#xA;  (a joint venture between Eutelsat and Astra) were awarded each a 2×15&#xA;  MHz portion of the S-band by the European Commission. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;C-band (4–8 GHz) Primarily used for satellite communications, for&#xA;  full-time satellite TV networks or raw satellite feeds. Commonly used&#xA;  in areas that are subject to tropical rainfall, since it is less&#xA;  susceptible to rainfade than Ku band (the original Telstar satellite&#xA;  had a transponder operating in this band, used to relay the first live&#xA;  transatlantic TV signal in 1962).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;X-band (8–12 GHz) Primarily used by the military. Used in radar&#xA;  applications including continuous-wave, pulsed, single-polarisation,&#xA;  dual- polarisation, synthetic aperture radar and phased arrays. X-band&#xA;  radar frequency sub-bands are used in civil, military and government&#xA;  institutions for weather monitoring, air traffic control, maritime&#xA;  vessel traffic control, defence tracking and vehicle speed detection&#xA;  for law enforcement.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Ku-band (12–18 GHz) Used for satellite communications. In Europe,&#xA;  Ku-band downlink is used from 10.7 GHz to 12.75 GHz for direct&#xA;  broadcast satellite services, such as Astra.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Ka-band (26–40 GHz) Communications satellites, uplink in either the&#xA;  27.5 GHz and 31 GHz bands, and high-resolution, close-range targeting radars on military aircraft.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="5137" LastActivityDate="2015-08-13T18:58:45.780" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5217" PostTypeId="2" ParentId="5211" CreationDate="2015-08-13T19:27:54.303" Score="4" Body="&lt;p&gt;Fundamental questions in a choice of antenna design are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Does it have the proper polarization (vertical, horizontal, or circular)?&lt;/li&gt;&#xA;&lt;li&gt;Does it have the proper radiation pattern?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Some secondary issues are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Will the antenna be small enough for the space available, at the desired frequency?&lt;/li&gt;&#xA;&lt;li&gt;How will it be mechanically supported, without interfering with the electrical properties?&lt;/li&gt;&#xA;&lt;li&gt;Will nearby objects interfere with it, or assist it (e.g. car roof as ground plane)?&lt;/li&gt;&#xA;&lt;li&gt;What type of matching network will it require?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The &lt;strong&gt;mode&lt;/strong&gt; does not matter at all. The &lt;strong&gt;frequency&lt;/strong&gt; only matters as it affects the size and therefore what is feasible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You've said you want to do 2 meter FM, and that means that you will want &lt;strong&gt;vertical polarization&lt;/strong&gt;. (This mainly means you don't want to build a horizontal dipole, which is a shame because it's really simple. Vertical dipoles work fine, but you need a horizontal structure to keep the feed line running away perpendicularly, which is why it's rarely done.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This leaves you with a wide variety of vertical antenna designs — ground plane (with radials, or mounted on a metal roof), J-pole, bazooka dipole, coaxial collinear, et cetera. These can all work; it's largely a matter of what you want to build.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, one factor we haven't yet addressed is the radiation pattern. You said “non-directional”, but there's no such thing as a truly omnidirectional (&lt;em&gt;isotropic&lt;/em&gt;) antenna. Any so-called omnidirectional vertical antenna will in fact have a null pointing directly upward. In between directly up and horizontal, the pattern depends on the antenna design, as well as how high above the earth it is. What you want depends on the environment you're in and how stably actually-vertical your antenna is: if you have it mounted in a fixed location &lt;em&gt;with an unobstructed horizontal view&lt;/em&gt; then you can benefit from using a higher-gain antenna (more horizontal, less vertical pattern).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Overall: Don't worry about it too much. Given that you're &lt;em&gt;building&lt;/em&gt; your antenna, it's likely much more important to pick a design that you can build accurately and tune easily (because small variations in length can matter a lot for VHF).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-08-13T19:27:54.303" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5218" PostTypeId="2" ParentId="5212" CreationDate="2015-08-14T06:02:11.310" Score="5" Body="&lt;p&gt;My trick is instead of cutting, rather &lt;em&gt;extend&lt;/em&gt; the whip first, and see if the SWR gets better or worse. Extend it 1/2&quot; with a bit of wire wrapped around it and sticking out. If the SWR gets better, then you made it too short in the first place. If it gets worse, you can start trimming.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember you should only measure SWR when you are away from the antenna - anyone within 1 or 2 m of the antenna will change the SWR and confuse you as you tune.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need to bend the radials down at 45 degrees to be able to match it properly. The length of the radials isn't as critical as the length of the whip, rather just bend them up and down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lots of small steps is the key, not one big jump. Enjoy the antenna tuning!&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-08-14T06:02:11.310" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5219" PostTypeId="1" AcceptedAnswerId="5227" CreationDate="2015-08-14T14:10:03.610" Score="4" ViewCount="756" Body="&lt;p&gt;The section &lt;a href=&quot;http://www.dummies.com/how-to/content/operating-your-ham-radio-in-an-emergency.html&quot; rel=&quot;nofollow&quot;&gt;Operating Your Ham Radio in an Emergency&lt;/a&gt; from &lt;em&gt;Ham Radio For Dummies&lt;/em&gt; recommends using an &quot;emergency autopatch&quot; to reach the emergency services when reporting an emergency from an amateur radio transmitter:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol start=&quot;3&quot;&gt;&#xA;  &lt;li&gt;State clearly that you are making an emergency autopatch (a feature&#xA;  that allows you to make a telephone call from your repeater) and then&#xA;  activate the autopatch system.&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;If you cannot activate the repeater's autopatch, you may ask another&#xA;    repeater user to activate it for you. Or, on HF or VHF, you can ask&#xA;    for someone to make an emergency relay to 911. In this case, report&#xA;    all the necessary material and then stand by on frequency until the&#xA;    relaying station reports to you that the information is relayed and&#xA;    the call is complete.&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;  &#xA;  &lt;ol start=&quot;4&quot;&gt;&#xA;  &lt;li&gt;&lt;p&gt;Dial 911 and when the operator responds, state your name and that you are reporting an emergency via amateur radio.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Follow the directions of the operator from there.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;If the operator asks you to stay on the line, do so and ask the other&#xA;    repeater users to please stand by.&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;  &#xA;  &lt;ol start=&quot;6&quot;&gt;&#xA;  &lt;li&gt;When the operator finishes, release the autopatch and announce that you released the autopatch.&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Apparently autopatches (aka &quot;phone patches&quot;?) are &lt;a href=&quot;http://www.arrl.org/phone-patch-guidelines&quot; rel=&quot;nofollow&quot;&gt;common in the USA&lt;/a&gt;, but searching the Web has turned up scant information about them in, for example, the UK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That makes me wonder: are they legal in the UK, and if so, where can I find out more about how they are regulated and used there?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Likewise for other jurisdictions.&lt;/p&gt;&#xA;" OwnerDisplayName="user5147" LastEditorDisplayName="user5147" LastEditDate="2015-08-14T23:39:41.840" LastActivityDate="2015-08-17T06:49:16.633" Title="Repeater autopatch (&quot;phone patch&quot;): which countries use this?" Tags="&lt;repeater&gt;&lt;emergency&gt;&lt;phone&gt;&lt;united-kingdom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5220" PostTypeId="2" ParentId="5213" CreationDate="2015-08-15T00:39:48.940" Score="4" Body="&lt;p&gt;While the other answer is quite detailed, this one is much shorter and specific:  I purchased and installed an aluminum RF shield for the dongle.  The noise floor is significantly lower as a result!  I was able to drop it even further by adding a ferrite bead to the USB cable.  (I was already using a 10' extension to get it away from the computer.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Update:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Watching the waterfall display while adding a ferrite bead to the USB cable and to the feed line where it immediately enters the dongle also reduced the noise visibly.  Note that this was not a &lt;em&gt;huge&lt;/em&gt; visible difference, but seeing a visible intensity change, even minor, in the background noise can really make a difference when looking for weak signals (which is what I do).&lt;/p&gt;&#xA;" OwnerUserId="5137" LastEditorUserId="5137" LastEditDate="2015-08-17T21:05:04.193" LastActivityDate="2015-08-17T21:05:04.193" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5221" PostTypeId="2" ParentId="5209" CreationDate="2015-08-15T16:03:53.380" Score="3" Body="&lt;p&gt;Is case anyone is curious, yes...it does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simply push the middle button and a repeater list comes up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is simple to set up, as can be seen from this HOWTO guide&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.dstarinfo.com/Data/Sites/1/GalleryImages/FullSizeImages/id-51-beginner.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.dstarinfo.com/Data/Sites/1/GalleryImages/FullSizeImages/id-51-beginner.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1463" LastActivityDate="2015-08-15T16:03:53.380" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5224" PostTypeId="1" AcceptedAnswerId="5225" CreationDate="2015-08-16T10:12:52.613" Score="7" ViewCount="1290" Body="&lt;p&gt;In terms of radio transmission, three major issues seem to arise for various sensitive transmissions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Others do not gain access to the content of the message&lt;/li&gt;&#xA;&lt;li&gt;Others cannot determine the location of the sender&lt;/li&gt;&#xA;&lt;li&gt;Others cannot block (jam) message channels&lt;/li&gt;&#xA;&lt;li&gt;Others do not know a message is being sent at all&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;In terms of amateur radio and non-amateur radio in different bands (if this is applicable) and different protocols/specifications (if this is applicable), how well does frequency hopping (without encryption) address each of these issues both in terms of avoiding the accidental observer, deliberate amateur (not as in amateur radio but amateur as in non-professional) observer, and determined professional government/authority observer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;BONUS:&lt;/strong&gt; How well does frequency hopping work in these matters when combined with encryption?&lt;/p&gt;&#xA;" OwnerUserId="5160" LastEditorUserId="8573" LastEditDate="2018-12-10T01:43:32.967" LastActivityDate="2018-12-10T01:43:32.967" Title="Is frequency hopping a viable solution for privacy and security without encryption?" Tags="&lt;modes&gt;&lt;security&gt;" AnswerCount="4" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="5225" PostTypeId="2" ParentId="5224" CreationDate="2015-08-16T20:40:09.767" Score="7" Body="&lt;blockquote&gt;&#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;Others do not gain access to the content of the message&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In the US amateur radio service, transmitting “messages encoded for the purpose of obscuring their meaning” is prohibited by &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1113&quot;&gt;§97.113&lt;/a&gt; and specifically for spread-spectrum (SS) by &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1311&quot;&gt;§97.311&lt;/a&gt;. I would imagine other jurisdictions have similar rules which prohibit such transmissions and/or require that hopping patterns etc. be published.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll leave the detailed question of whether it is useful for this purpose when legal to others who are more familiar with the technical aspects of spread-spectrum modulation. Some remarks from general principle follow.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol start=&quot;2&quot;&gt;&#xA;  &lt;li&gt;Others cannot determine the location of the sender&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No method can give you this as an absolute guarantee. Someone can always take a wide-band receiver and a directional antenna and look for where the received power is higher. All that spread-spectrum gets you here is requiring the receiver to have a wider bandwidth, therefore being unable to filter out unrelated signals from other radiators, making it harder to find the transmitter at a longer distance.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol start=&quot;3&quot;&gt;&#xA;  &lt;li&gt;Others cannot block message channels&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Spread-spectrum techniques increase the power requirements of jamming, because the jammer must decrease the SNR sufficiently across the entire bandwidth and not just a narrow band.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol start=&quot;4&quot;&gt;&#xA;  &lt;li&gt;Others do not know a message is being sent at all&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This falls into the same category as point 2; as you move away from the transmitter, a spread-spectrum transmission will apparently disappear into the noise floor sooner, but if you are close enough a transmission is obvious no matter what the frequency.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For the “accidental observer” as you put it, not attempting to decode spread-spectrum transmissions, they will receive the SS transmission as a (possibly imperceptible) increase in the noise floor. Thus, spread-spectrum signals are indeed unlikely to be accidentally received (or interfered with).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-08-16T20:40:09.767" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5226" PostTypeId="2" ParentId="5224" CreationDate="2015-08-16T23:36:33.077" Score="0" Body="&lt;p&gt;I am not an expert. However, I am aware of &lt;a href=&quot;http://www.youtube.com/watch?v=Ru8RshSVkGI&quot; rel=&quot;nofollow&quot;&gt;Mike Ossmann's work on sniffing Bluetooth&lt;/a&gt; and &lt;a href=&quot;http://www.youtube.com/watch?v=A-kJ3AXp9cI&quot; rel=&quot;nofollow&quot;&gt;Mike Ryan's work on sniffing Bluetooth Smart&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of those two technologies:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Others do not gain access to the content of the message&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;False.&lt;/strong&gt; Others may well be able to gain access to the content of the message, unless the message is encrypted with a strong cipher and a strong key that remains unknown to the attacker.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Others cannot determine the location of the sender&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;See answer by Kevin Reid AG6YO.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Others cannot block message channels&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;See answer by Kevin Reid AG6YO.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Others do not know a message is being sent at all&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;False.&lt;/strong&gt; Certainly, if one can access the content of the message, that's a pretty good indicator that a message was sent!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the general case, the answer to those questions is likely to depend on factors such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;protocol used;&lt;/li&gt;&#xA;&lt;li&gt;transmit power;&lt;/li&gt;&#xA;&lt;li&gt;bandwidth utilisation;&lt;/li&gt;&#xA;&lt;li&gt;directionality of source;&lt;/li&gt;&#xA;&lt;li&gt;background noise profile and level;&lt;/li&gt;&#xA;&lt;li&gt;etc.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerDisplayName="user5147" LastActivityDate="2015-08-16T23:36:33.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5227" PostTypeId="2" ParentId="5219" CreationDate="2015-08-17T06:49:16.633" Score="1" Body="&lt;p&gt;Phone patches (&lt;a href=&quot;https://en.wikipedia.org/wiki/Autopatch&quot; rel=&quot;nofollow&quot;&gt;autopatches&lt;/a&gt;) are not legal in the UK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The restriction is largely because a phone patch allows you to contact non-licensed people using amateur radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, in an actual emergency, anyone can transmit anything on any frequency - but in a non-emergency situation there are strict restrictions on 'third-party traffic' (i.e. passing messages or voice from non-licensed people over amateur radio). In the UK, some club stations are allowed to pass third-party traffic, and at special events this is also sometimes permitted. This is usually done using a NoV (Notice of Variation) on the licence used by the club or individual during a special event.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-08-17T06:49:16.633" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5228" PostTypeId="1" CreationDate="2015-08-17T19:40:12.513" Score="3" ViewCount="856" Body="&lt;p&gt;I am looking for a website that has the satellite footprint as well as the downlink freq. I just got a 2m/70cm handheld and want to see what I can pick up.&lt;/p&gt;&#xA;" OwnerUserId="5163" LastEditorUserId="8573" LastEditDate="2019-12-10T17:07:11.373" LastActivityDate="2020-09-08T17:09:22.183" Title="Website for satellite down/uplink frequencies and live footprint?" Tags="&lt;satellites&gt;&lt;2m-band&gt;&lt;70cm-band&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="5230" PostTypeId="2" ParentId="5228" CreationDate="2015-08-18T12:36:50.840" Score="5" Body="&lt;p&gt;&lt;a href=&quot;http://www.n2yo.com&quot; rel=&quot;noreferrer&quot;&gt;n2yo.com&lt;/a&gt; is a wonderful resource for keeping track of all of the orbiting satellites. It has many resources for tracking info to enter into tracking software and other places. It also shows a live google map of the location of each satellite.:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/t6p1T.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/t6p1T.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.amsat.org/&quot; rel=&quot;noreferrer&quot;&gt;amsat.org&lt;/a&gt; also has a wealth of information about contacting and tracking the satellites including uplink and downlink information and tips.: &#xA;&lt;a href=&quot;https://i.stack.imgur.com/uzuhp.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uzuhp.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1246" LastActivityDate="2015-08-18T12:36:50.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5231" PostTypeId="2" ParentId="4917" CreationDate="2015-08-18T17:47:12.410" Score="3" Body="&lt;p&gt;Combining multiple power amplifiers is a standard technique for generating high power from a number of lower-power components.  You feed all amplifiers with the same input (split the input with transformers or other devices) and combine amplifiers through transformers.  For example, 4 25 Watt amplifiers will give you an equivalent 100 Watt amplifier.  (These would typically be fixed-tuned, broadband amplifiers, run from a single power supply.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You would run into problems when you try to combine amps that have to be retuned for changes in operating frequency, like many HF SSB linear amps.  It would be hard to get the tuning just right, so that all amps are pulling their share of the load.  Furthermore, if you run one amp at a lower level (or off) the transformer combiner is likely to push reverse power into that amp, or even into the exciter -- not a great idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So making a big amp by combining outputs of smaller amps can work if the smaller amps are well matched and operated under similar conditions. Otherwise, things get tricky.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using multiple amps to drive multiple antennas should not be a problem if the antennas are not coupled to each other.  Two yagis in a stack would be somewhat coupled, but one yagi pointing north and another pointing east would mostly uncoupled.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-08-18T17:47:12.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5232" PostTypeId="2" ParentId="1545" CreationDate="2015-08-19T00:39:12.903" Score="1" Body="&lt;p&gt;One thing to note with the original article is that the schematic conflicts with the picture of the completed aerial - you'll note that the driven element(s) is clearly closer to the director (shorter) than the reflector in the snapshot. I actually built it as per the picture as that is what would have been tested and I can say that the Yagi works really well with 1&quot; PVC. I rivetted the elements to the boom with a single rivet per element. No more loose elements. Very happy with this design and a flat 1:1 SWR across the 2 metre band with excellent directivity (F/B).&lt;/p&gt;&#xA;" OwnerUserId="5169" LastActivityDate="2015-08-19T00:39:12.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5233" PostTypeId="1" CreationDate="2015-08-19T09:45:49.053" Score="2" ViewCount="178" Body="&lt;p&gt;I am building a wideband dual band omni for school. My antenna is about 2m long. The antenna length basically has two sections (divided by ports) - from 0 - 1.8m (This length is for 20-180MHz) and from 1.8m - 2m (This length is for 500-3000MHz). I have two edge ports feeding each section i.e. port at 0m and port at 1.8m.&lt;/p&gt;&#xA;&lt;p&gt;I have managed to match for 20-180MHz band, but am struggling for the other band, is there a way to make sure that &amp;quot;port 2&amp;quot; doesnt see the impedance below it - i.e. impedance seen by port1.&lt;/p&gt;&#xA;&lt;p&gt;How can i go about matching for the other port?&lt;/p&gt;&#xA;&lt;h1&gt;N.B This is all being done in a simulation package &amp;quot;Feko&amp;quot;&lt;/h1&gt;&#xA;" OwnerUserId="4823" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-10-26T20:56:32.253" Title="Dual Band Antenna Matching" Tags="&lt;antenna-theory&gt;&lt;wire-antenna&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5236" PostTypeId="2" ParentId="5224" CreationDate="2015-08-20T16:14:54.083" Score="4" Body="&lt;p&gt;Frequency hopping is more typically considered an ECCM measure. That is to say that a transciever that continuously cycles frequencies in accordance with some &quot;hop set&quot; is more difficult to jam than a single-channel radio system. In and of itself, it doesn't constitute proper encryption of your signal -- you are still transmitting data in plain text. It would make it more difficult for unmatched hardware to receive your signal in its entirety, but considering the narrow bands of spectrum you're allowed to operate on with an amateur license I'd be extremely concerned about inadvertently causing interference as your radio hops across the spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've only really seen freqhop implemented on the VHF spectrum as an ECCM measure, and other matched radios designed to talk on that net need carefully matched radio time (a time drift of as little as a second would cause a radio to fall out of net).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would not obscure that you're sending a signal at all -- on the contrary, a frequency hopping radio would, to me, be quite notable and draw my attention. If your objective is to prevent your signal from being received by third party stations, the tried and true solution is to use a directional antenna. This also wouldn't run afoul of any FCC regulations and would actually help mitigate interference, in my opinion.&lt;/p&gt;&#xA;" OwnerUserId="1575" LastActivityDate="2015-08-20T16:14:54.083" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5238" PostTypeId="1" AcceptedAnswerId="5239" CreationDate="2015-08-22T06:30:53.997" Score="0" ViewCount="70" Body="&lt;p&gt;A radio receiver needs $1 \textrm{ nW}/\textrm{m}^2$ of power density function, how far away from a 1-watt point source will it continue to work?&lt;/p&gt;&#xA;" OwnerUserId="5183" LastActivityDate="2015-08-22T11:00:32.040" Title="Power Density Function" Tags="&lt;rf-power&gt;&lt;transmission&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5239" PostTypeId="2" ParentId="5238" CreationDate="2015-08-22T10:45:06.480" Score="0" Body="&lt;p&gt;So we have a point source, so it has no gain and radiates evenly in all directions. The result of that is that our waves will look like a sphere. Then we will have the receiver antenna into which those waves will impact. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AzudV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AzudV.png&quot; alt=&quot;Point transmitter emitting waves&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That antenna has its own effective aperture (in the illustration, I used parabolic antenna, because the effect is most obvious with it), which is the area into which the waves from the transmitter impact. The part that impacts the Rx antenna will be received. In this problem, we don't have specifics of the Rx antenna, but we are given density of the power at the needed distance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So how do we calculate power density? We simply take the formula for the surface of a sphere, $$P_s=4 \pi r^2 $$ Next, we spread out our 1 watt over that surface, so we have density of $$P_d=\frac{P_{Tx}}{P_s}=\frac{1\mbox{ }W}{4 \pi r^2}$$ Our problem says that $P_d=\frac{1\mbox{ } nW}{m^2}$, so we just need to solve the equation for $ r $ to get the final solution.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2015-08-22T11:00:32.040" LastActivityDate="2015-08-22T11:00:32.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5240" PostTypeId="1" AcceptedAnswerId="5343" CreationDate="2015-08-22T15:24:25.553" Score="9" ViewCount="3867" Body="&lt;p&gt;I've found all sorts of info concerning digital modes, sound samples, spectrum samples, but nobody ever cites what speed a given digital mode can reach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could anyone tell me more about that, or point me somewhere where I can find this kind of info, possibly in terms of kbps?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, what could be the maximum achievable transfer rate on short waves, specifically?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit:&lt;/strong&gt; I thought that given the premises in first paragraph, it was clear that the heart of the question was about knowing the actually achievable transfer limits using known and used modes, not just understanding theoretical limits...  (which is still a precious contribute though). &#xA;Since it seems this did not come off so clear to some people, so I'm specifying it here and in title too. &lt;/p&gt;&#xA;" OwnerUserId="5184" LastEditorUserId="5184" LastEditDate="2015-09-27T04:02:49.980" LastActivityDate="2016-08-01T17:12:11.500" Title="What transfer rates are actually achievable using known digital modes?" Tags="&lt;digital-modes&gt;" AnswerCount="6" CommentCount="6" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5241" PostTypeId="1" CreationDate="2015-08-24T02:01:01.547" Score="0" ViewCount="45" Body="&lt;p&gt;A 50 ohm match can be tricky outside a transmitter to match. One has to deal with ensuring the antenna , coax, and all connectors are all equal or close to the output impedance of the radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let alone the external connections, is impedance matching as tricky when dealing with PCB layout, and internal components? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does impedance only matter on the final amplifier stage because low power reflections won't make much of a difference in efficiency?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have found circuits to build simple radio transmitters. If only a schematic is given, and no board layout, or construction notes are provided, how can I ensure the impedances are matched throughout the internal circuitry of the radio, so all the power goes to the external connector?&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-08-24T05:15:59.003" Title="Impedances inside transmitter?" Tags="&lt;impedance&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5242" PostTypeId="2" ParentId="5241" CreationDate="2015-08-24T05:15:59.003" Score="3" Body="&lt;p&gt;If you are building a device from a schematic, then the issue of impedance matching between various parts of the circuit has already been addressed by the designer. Interconnections between circuit components are generally extremely short in terms of the wavelength of the RF energy that they are carrying, especially at HF. Because of this, as long as interconnections in the circuit are kept as short as reasonably possible, there is no need to impedance match the connections between circuit elements. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not true when working at very high frequencies like VHF,  UHF,  and microwave frequencies. In devices designed for those frequencies, printed circuit boards are often designed using special techniques such as striplines or waveguides that do transmit RF energy at a specific impedance. &lt;/p&gt;&#xA;" OwnerUserId="5188" LastActivityDate="2015-08-24T05:15:59.003" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5243" PostTypeId="2" ParentId="5210" CreationDate="2015-08-24T05:26:47.790" Score="1" Body="&lt;p&gt;Yes, a single piece of wire connected to the antenna socket of the receiver can be an effective receive antenna for many frequencies. A so-called random wire antenna doesn't need to be any more complicated than that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the spatial pattern of best reception will vary with frequency as the length of the antenna in terms of the wavelength changes. If there are particular frequencies or directions where you would like to optimize your reception, then you may want to consider a more sophisticated antenna such as a doublet or dipole  &lt;/p&gt;&#xA;" OwnerUserId="5188" LastActivityDate="2015-08-24T05:26:47.790" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5244" PostTypeId="1" CreationDate="2015-08-24T07:34:41.257" Score="1" ViewCount="916" Body="&lt;p&gt;I have a Baofeng UV-82HP that I want to use to TX and RX to a TeamSpeak Server. For this I'm going to use a dedicated computer, for both the client and server that has a sound card (ASUS Xonar Essence STX) that is not used by the OS or any other applications (so, there will be no spurious transmissions.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to take the computer audio, and put that through the radio's accessory Microphone Port. That's a simple 3.5mm TRRS from the Radio's MIC port into the Line-In of the Sound Card.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to take the audio from the radio via the radio's accessory Speaker Port, and put that into the microphone for the sound card. From the Speaker Port I'm using a 2.5mm TRRS to 3.5mm TRRS adapter, then 3.5mm TRRS to the Line-In for the Sound Card.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is when I complete the connection from the radio's accessory Speaker Port to the Sound Card's Line-In, it causes the radio to transmit. This happens even with the radios's accessory Microphone Port unplugged. It does not happen when the 2.5mm TRRS to 3.5mm TRRS adapter by it's self on the Speaker Port.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/GSMOz.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fGSMOz.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 2 Pin Kenwood uses a TRS style for both Speaker and Mic, should I use a TS for the Speaker to bypass the PTT functionality of the circuit?&lt;/p&gt;&#xA;" OwnerUserId="5189" LastActivityDate="2015-08-29T13:57:22.843" Title="2-Pin Kenwood to Sound Card (Beofeng UV-82HP &amp; ASUS Xonar Essence STX)" Tags="&lt;receiver&gt;&lt;baofeng&gt;&lt;transmitter&gt;&lt;wiring&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5245" PostTypeId="1" AcceptedAnswerId="5254" CreationDate="2015-08-24T12:18:09.947" Score="6" ViewCount="1674" Body="&lt;p&gt;I have a Tecsun PL-600 and when I can receive clear signals, and they come through just fine on headphones, and through the speaker. If I'm trying to receive RTTY or fax, when I connect the radio to my computer the signal becomes inaudible because a huge amount of interference comes through. It only happens when connecting the radio to the computer, so I assume it's something to do with interference going into the radio through the audio cable. But I have no clue if that's even possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any way to stop the interference that happens and what is causing it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.dropbox.com/s/9g9ktggra9bugxq/nice.mp3?dl=0&quot; rel=&quot;noreferrer&quot;&gt;Here&lt;/a&gt;'s a signal recorded with my phones microphone, using the radio's speaker. The signal is coming through very loud and clear.&#xA;&lt;a href=&quot;https://www.dropbox.com/s/48a5irkau00d3gg/noise.mp3?dl=0&quot; rel=&quot;noreferrer&quot;&gt;Here&lt;/a&gt;'s when I have the radio plugged into the computer and I used the computer to record the audio directly through the input. Be warned that both the audio clips are quite loud, especially the one with the noise.&lt;/p&gt;&#xA;" OwnerUserId="5191" LastEditorUserId="5191" LastEditDate="2015-08-24T20:20:39.147" LastActivityDate="2015-08-27T16:33:09.807" Title="How to stop interference on shortwave radio when connecting to a computer" Tags="&lt;hf&gt;&lt;rfi&gt;" AnswerCount="3" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="5248" PostTypeId="2" ParentId="5240" CreationDate="2015-08-24T20:00:17.587" Score="2" Body="&lt;p&gt;It really is a function of the bandwidth of the signal which is driven by the speed. Lower-speed, lower-bandwidth signals take up &quot;less space&quot; on the air and are on HF while higher-speed, wider signals are on VHF and higher. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lower-speed modes also tend to be more resilient in the face of varying band conditions, as found on HF. VHF and higher tend to be more stable but much more local as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a great resource: &lt;a href=&quot;http://wb8nut.com/digital/&quot; rel=&quot;nofollow&quot;&gt;http://wb8nut.com/digital/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="359" LastActivityDate="2015-08-24T20:00:17.587" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5249" PostTypeId="2" ParentId="5245" CreationDate="2015-08-24T20:16:48.693" Score="0" Body="&lt;p&gt;You may have to take steps to isolate the computer signal from the radio. Here is a nice guide that focuses on PSK31 and transceivers but it will work for any mode and receive-only.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.wa1wa.net/filespdf/pskhandbook.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.wa1wa.net/filespdf/pskhandbook.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are also commercial products if you want to go that route.&lt;/p&gt;&#xA;" OwnerUserId="359" LastActivityDate="2015-08-24T20:16:48.693" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5250" PostTypeId="2" ParentId="5240" CreationDate="2015-08-24T20:21:25.370" Score="6" Body="&lt;p&gt;You are looking for the &lt;a href=&quot;https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;Shannon-Hartley theorem&lt;/a&gt;. Borrowing Wikipedia's summary, because it's better than what I can come up with:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In information theory, the Shannon–Hartley theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The Shannon-Hartley theorem states that the theoretical maximum bandwidth of a communications channel can be stated as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ C = B \log_2{\left( 1 + \frac{S}{N} \right)} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $C$ is the channel capacity in bits per second, $B$ is the bandwidth of the channel in Hz, $S$ is the average received signal power over the bandwidth, $N$ is the average noise power received over the bandwidth, and $S$ and $N$ are in the same unit (here, watts, or a multiple thereof). Notice that no communications channel in practice (not even a crystal-clear FM transmission or studio CD recording) is completely free of noise, so you will always have a $N &amp;gt; 0$. The theorem does &lt;em&gt;not&lt;/em&gt; state how to achieve this channel capacity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It follows from this that if you know the bandwidth, the signal strength received and the noise level, you can compute the maximum theoretical data rate. Transmission frequency does not enter into the picture, although it could place a practical limit on the achievable transmission bandwidth because antennas for lower frequencies tend to be more narrow-band due to employing various forms of matching networks which are not needed when antenna sizes are a considerable fraction of a full-sized antenna for the transmission frequency range employed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that this allows you to compute the &lt;em&gt;maximum theoretical&lt;/em&gt; data rate at which transmission is &lt;a href=&quot;https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem#Noisy_channel_coding_theorem_and_capacity&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;somehow possible practically without errors&lt;/em&gt;&lt;/a&gt;. This data rate will not always be achievable in practice, and in fact a lot of transmission mode research has gone into getting as close to the theoretical maximum data rate as possible. A transmission actually at the Shannon-Hartley limit would most likely look like white noise across the transmission bandwidth unless you know what to look for; compare &lt;a href=&quot;https://en.wikipedia.org/wiki/Ultra-wideband&quot; rel=&quot;nofollow noreferrer&quot;&gt;ultra-wideband&lt;/a&gt;, or the signals used by late-generation &lt;a href=&quot;https://en.wikipedia.org/wiki/Modem#V.34.2F28.8k_and_33.6k&quot; rel=&quot;nofollow noreferrer&quot;&gt;dial-up telephone modems&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since a large factor in the equation is the received signal-to-noise (S/N) ratio, you can increase the achievable transmission rate within a given bandwidth &quot;simply&quot; by increasing transmitter output power, or antenna gain. Conversely, in situations where bandwidth is extremely limited, such as on 136 kHz, &lt;a href=&quot;https://en.wikipedia.org/wiki/2200-meter_band#Technical_issues&quot; rel=&quot;nofollow noreferrer&quot;&gt;the transmission bandwidth is reduced by reducing the data rate&lt;/a&gt;. In situations where signal is hard to come by, such as in communication with faraway space probes or again on 136 kHz, &lt;a href=&quot;https://physics.stackexchange.com/a/13232/14091&quot;&gt;the data rate is reduced&lt;/a&gt; in order to match the available S/N ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia has &lt;a href=&quot;https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem#Examples&quot; rel=&quot;nofollow noreferrer&quot;&gt;several examples applying the theorem&lt;/a&gt; that you may be interested in.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="-1" LastEditDate="2017-04-13T12:40:15.020" LastActivityDate="2015-08-24T20:52:58.263" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5251" PostTypeId="2" ParentId="5209" CreationDate="2015-08-26T07:49:27.007" Score="4" Body="&lt;p&gt;What do you mean by &quot;regular repeaters&quot;? Do you mean analog repeaters?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't found a list of analog repeaters built into the ID-51A, no. But I found this site that will give you the nearest several hundred repeaters to a given location (enter your city/state and click the button). You get them in CSV format which maybe is used by Icom's programming software?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.dstarinfo.com/RepeaterDownloads.aspx&quot; rel=&quot;nofollow&quot;&gt;http://www.dstarinfo.com/RepeaterDownloads.aspx&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, even once you import that list I don't know if you can search by location. It may just fill the memory with those repeater frequencies and text labels.&lt;/p&gt;&#xA;" OwnerUserId="5205" LastActivityDate="2015-08-26T07:49:27.007" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5253" PostTypeId="2" ParentId="5245" CreationDate="2015-08-27T00:15:24.153" Score="2" Body="&lt;p&gt;Have you considered placing an &lt;a href=&quot;http://denethor.wlu.ca/pc300/optoisolators/analogoptoisolatorintroduction.pdf&quot; rel=&quot;nofollow&quot;&gt;analog optical isolator&lt;/a&gt; in line?&lt;/p&gt;&#xA;" OwnerUserId="1264" LastActivityDate="2015-08-27T00:15:24.153" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5254" PostTypeId="2" ParentId="5245" CreationDate="2015-08-27T16:33:09.807" Score="2" Body="&lt;p&gt;I listened to your samples and I can say that I've never heard interference that sounded like wind on a microphone before. It doesn't sound like typical RFI, but it still could be. It doesn't sound like clipping either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regardless, some things worth trying (including those already mentioned in other answers, to be complete) are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Change the antenna&lt;/strong&gt;; in particular, use an external antenna which is either &lt;strong&gt;balanced&lt;/strong&gt; (dipole) and has a balun, or is &lt;strong&gt;grounded&lt;/strong&gt; (actual earth ground at the spot, not electrical service ground) at the feed point. This helps prevent conducted noise from your equipment from being received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(If you set up a outdoor antenna, grounded or otherwise, then I recommend either disconnecting it whenever there may be a thunderstorm, or doing further research on effective ground systems. This is a nontrivial problem.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Improving &lt;em&gt;or removing&lt;/em&gt; equipment grounding&lt;/strong&gt;, where by the latter I mean &lt;strong&gt;running on batteries instead of AC adapter&lt;/strong&gt;. Removing grounding may be useful if you have a &lt;em&gt;ground loop&lt;/em&gt; problem rather than an RFI problem per se. First, if you live in an older building, make sure that the electrical outlets are actually grounded. Then, try these four configurations — just to be complete:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Computer and radio grounded. (Ideally, this would be best, but depending on the equipment it could result in ground loop noise.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use a multimeter to confirm that the radio's power adapter has continuity between the AC earth pin and the (-) terminal of the DC plug (identified by the symbol on the radio's input and possibly on the adapter itself). If it's not grounded, you could try replacing it with one that is, but there might be something “interesting” about the radio circuit and I'd instead think about grounding at the antenna jack instead.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Computer and radio ungrounded, running off battery power. (This requires a laptop computer or similar, of course.) If you get less noise here, then it could be a ground loop or it could be noise from the AC power adapter of one or both devices.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Computer grounded, radio ungrounded. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Computer ungrounded, radio grounded. This is likely to be the worst case, but if it &lt;em&gt;doesn't&lt;/em&gt; add more noise, then your problem is something else.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Use a different audio interface.&lt;/strong&gt; Get a decent quality USB audio interface/sound card (different words for the same thing) and use its input instead. (Make sure it has a line-level input, not a microphone input.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Use an isolation device&lt;/strong&gt; — which could be an optical isolator, as already mentioned, or a 1:1 transformer — in the audio line. I note that some of the designs in that PDF do not isolate ground, which may or may not be a good idea.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-08-27T16:33:09.807" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5255" PostTypeId="1" AcceptedAnswerId="5256" CreationDate="2015-08-28T00:04:56.770" Score="9" ViewCount="803" Body="&lt;p&gt;I am a bit new to the radio scene, so excuse me for any ignorance that may follow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I saw on a website that you could mod the Yaesu FT-270r so that you can increase its transmission range outside of 144 MHz. I have no plans on transmitting outside of  FCC designated MURS frequencies. (I am not a licensed ham operator.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it be legal and/or OK to transmit on MURS with this mod on this radio? I'd rather find out know then start transmitting on MURS and get in trouble with the FCC for doing so if it is illegal.&lt;/p&gt;&#xA;" OwnerUserId="5216" LastEditorUserId="76" LastEditDate="2015-08-28T01:38:02.513" LastActivityDate="2015-08-28T01:49:37.470" Title="Is a modded Yaesu FT-270r acceptable to use on MURS frequencies?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5256" PostTypeId="2" ParentId="5255" CreationDate="2015-08-28T01:49:37.470" Score="6" Body="&lt;p&gt;&lt;em&gt;I am not a lawyer, and this is not legal advice. I'm also not particularly familiar with MURS, and generalizing from other information.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Multi-Use_Radio_Service#Eligibility&quot;&gt;According to Wikipedia&lt;/a&gt;, MURS (as many other US unlicensed radio services do) requires the use of &lt;strong&gt;type accepted&lt;/strong&gt; equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Terminology note: &lt;em&gt;radio services&lt;/em&gt; are CB, FRS, GMRS, MURS, amateur, commercial, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that the only radios you can use on MURS are those which the FCC approves for use on MURS. So, no, your modded radio cannot legally be used. (Modified equipment is only useful on the amateur bands or otherwise on frequencies which &lt;em&gt;you have been granted a specific a license to use&lt;/em&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And in these services which require type-accepted equipment, FCC generally only approves equipment &lt;em&gt;which cannot be used for licensed services&lt;/em&gt; — the widely understood rationale being that they don't want to trust the users of the type-accepted equipment not to use the other functions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, there is no radio which you can legally use in the US which allows transmitting on both amateur frequencies and unlicensed service frequencies.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-08-28T01:49:37.470" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5257" PostTypeId="1" CreationDate="2015-08-28T23:23:57.173" Score="9" ViewCount="2664" Body="&lt;p&gt;I have a few baofeng UV5R handhelds sitting around that only transmit, the receiver is damaged. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I would like to do with these is build a foxhunt transmitter. Sure, I could set it to low power (1 watt) and put it through a less efficient antenna, where it will radiate less ERP wise, but it will still get quite hot and waste the battery. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anybody know of any way to decrease these Chinese handhelds transmit power below 1 watt? Maybe destroy the final amplifier? Give it less voltage on the input? Change resistor values? I don't care if I fry the radio in the process, I have nothing else to do with it.&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2017-05-22T10:25:37.737" Title="Baofeng low power mod" Tags="&lt;diy&gt;&lt;baofeng&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5258" PostTypeId="2" ParentId="5244" CreationDate="2015-08-29T13:57:22.843" Score="1" Body="&lt;p&gt;I have had this problem before. The circuits need to be isolated from each other. Either install capacitors in series with the audio or an isolation transformer (better option). An isolation transformer might also keep RF out of the audio signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, where you have the 10uf capacitor, place another one between the other wire of the audio jack and the PTT switch.&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-08-29T13:57:22.843" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5259" PostTypeId="1" AcceptedAnswerId="5260" CreationDate="2015-08-30T19:07:44.747" Score="10" ViewCount="968" Body="&lt;p&gt;If I were to implement a remote computer control system using amateur radio, would using hashes (such as md5, sha-*, etc...) for authentication be permissible under the United States rules?&lt;/p&gt;&#xA;" OwnerUserId="1246" LastEditorUserId="873" LastEditDate="2015-08-31T03:02:59.200" LastActivityDate="2015-12-01T22:35:56.923" Title="Are hashes (such as md5) legal in the US" Tags="&lt;united-states&gt;&lt;digital-modes&gt;&lt;fcc&gt;&lt;remote-control&gt;&lt;encryption&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5260" PostTypeId="2" ParentId="5259" CreationDate="2015-08-30T20:04:31.533" Score="11" Body="&lt;p&gt;Yes, they are. Generally speaking, authentication is legal, obfuscating is not legal. So you could do a cryptographically signed hash that would be legal in the United States to transmit over Amateur Radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's worth mentioning that &lt;a href=&quot;http://rsaxvc.net/blog/2014/2/1/Encryption%20and%20Amateur%20Radio.html&quot;&gt;there is some debate&lt;/a&gt; as to how legal a cryptographically signed hash would be. I believe it would be legal, so long as it was a signature, intended to ensure that the message came from a particular person.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MD5 type hashes are definitely legal, they merely provide a signature of data already sent, and are used to ensure the data that was sent is correct.&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2015-08-31T19:56:47.073" LastActivityDate="2015-08-31T19:56:47.073" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5261" PostTypeId="1" AcceptedAnswerId="5263" CreationDate="2015-08-31T18:01:16.023" Score="2" ViewCount="642" Body="&lt;p&gt;Is it possible to create a circuit to hear (through earphones) or show (with an LED) the direction of a radio source? What does a really simple circuit look like and how does it work? How does the frequency of the radio source affect this circuit and antenna? Is it possible to locate WiFi, Bluetooth or ZigBee/XBee with this approach?&lt;/p&gt;&#xA;" OwnerUserId="5229" LastEditorUserId="76" LastEditDate="2015-08-31T20:29:40.707" LastActivityDate="2015-08-31T20:54:40.170" Title="antenna circuit to hear or show radio direction" Tags="&lt;direction-finding&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5262" PostTypeId="2" ParentId="5261" CreationDate="2015-08-31T19:32:52.760" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it possible to create a circuit to hear(earphones) or show(with an LED) the direction of a radio source? How does a really simple circuit looks like and how does it work?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Virtually any receiver, connected to any antenna, will work. With some knowledge of the antenna pattern, and a receiver that can indicate the received signal strength, then one can infer how the antenna is oriented relative to the source.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How does the frequency of the radio source affects this circuit and antenna?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In a lot of ways. The size of an antenna is proportional to wavelength, so while you might be able to use a hand-held parabolic dish at 5 GHz, the same wouldn't be possible at 5 MHz since the frequency is 1000 times lower, and consequently the wavelength and antenna 1000 times larger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, the frequency will dictate the kinds of components you can use. It's quite easy to make a radio that will work at low frequencies like 20 MHz, and this can be accomplished with ordinary, discrete components and a soldering iron. As frequency increases this becomes increasingly impracticable and you'll need to use fabricated components like MMICs.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it possible to locate wifi, bluetooth or zigbee/xbee with this aproach?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, provided you have a receiver that can operate at those frequencies.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-08-31T19:32:52.760" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5263" PostTypeId="2" ParentId="5261" CreationDate="2015-08-31T20:54:40.170" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it possible to create a circuit to hear (through earphones) or show (with an LED) the direction of a radio source?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. There are basically two different types of direction finding techniques:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;You can simply change the orientation of your antenna and observe whether this makes the received signal weaker or stronger. This has the advantage of working with any radio receiver, as long as either&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the receiver displays some indication of the received signal strength, or&lt;/li&gt;&#xA;&lt;li&gt;your antenna is sufficiently directional (e.g. a Yagi or loop antenna) that it makes the signal strength drop enough to make the signal vanish under the noise. (In fact, when using a loop antenna, it is normal to look for that point, the &lt;em&gt;null&lt;/em&gt;, because it is easier to hear the absence of the signal than when it is at maximum strength.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This method is commonly used by amateur radio operators who do it for fun, on foot (this goes under a number of names: foxhunting, T-hunting, radiosport); their equipment typically consists of a handheld transceiver, a Yagi or loop antenna, and a variable attenuator (to avoid overload when too close).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You can use a direction-finding receiver; this requires &lt;em&gt;at least two antennas&lt;/em&gt; (or an antenna with multiple outputs, depending on how you look at it), connected to a receiver with multiple inputs, which compares the signal amplitude and phase to derive the direction information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio operators who do direction-finding in their vehicles (either as a sport or to locate interferers) often use the so-called “Doppler direction finder” design, which can give an indication of direction on LEDs, uses an array of four antennas, and passes through to an ordinary FM receiver to also listen to the signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Aircraft used to have an &lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_direction_finder#Automatic_direction_finder_.28ADF.29&quot; rel=&quot;nofollow noreferrer&quot;&gt;automatic direction finder (ADF)&lt;/a&gt; as standard equipment. These may work on either of the above principles. They are not typically used for navigation today, having been replaced by VOR and GPS.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What does a really simple circuit look like and how does it work?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In general, any design for a radio receiver which has either an audio (if the signal is continuous, anyway) or signal-strength output can be used together with a directional antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/1610/how-would-a-time-difference-of-arrival-receiver-with-two-antennas-know-which-sid&quot;&gt;Here's another question on this site which happens to have a schematic of one two-antenna design&lt;/a&gt; for a specialized receiver, and my answer discusses how it works and includes results of a simulation.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How does the frequency of the radio source affect this circuit and antenna?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Very loosely speaking, radio works the same at all frequencies. In practice,&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Lower frequencies are more likely to propagate long distances, pass through walls, refract around obstacles, and otherwise complicate direction finding. Higher frequencies act more like visible light, making it more straightforward to locate them &lt;em&gt;if&lt;/em&gt; you can receive them.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Lower frequencies require larger antennas, making moving antennas less practical to use.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it possible to locate WiFi, Bluetooth or ZigBee/XBee with this approach?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, but because these are packet protocols you will practically need receivers for the purpose, which can recognize the quick bursts and distinguish them from noise. You will also need the receiver to report the signal strength (RSSI); I understand this is commonly available but I haven't worked with this sort of packet radio hardware so I can't give any details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In principle, you should be able to connect a standard module to a tiny directional antenna, write software to ask it for the RSSI of every packet it receives, and be ready to go. The trickiest part will be fabricating the correctly sized and correctly matched antenna (more or less depending on what test gear you have available).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-08-31T20:54:40.170" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5264" PostTypeId="1" AcceptedAnswerId="5265" CreationDate="2015-09-01T02:36:50.487" Score="4" ViewCount="734" Body="&lt;p&gt;Can I use my wireless ethernet card with GNU Radio? I have a Broadcom BCM4311 mini PCIe, and Debian / Kali 2.0 Linux.&lt;/p&gt;&#xA;" OwnerUserId="5202" LastEditorUserId="4076" LastEditDate="2020-04-26T13:34:46.433" LastActivityDate="2020-04-26T13:34:46.433" Title="Can a WLAN device be used with GNU Radio?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;wifi&gt;&lt;linux&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5265" PostTypeId="2" ParentId="5264" CreationDate="2015-09-01T03:22:25.030" Score="3" Body="&lt;p&gt;No. Most radio peripherals will not pass raw RF samples to or from the host computer, but only fully decoded packets. I'm not familiar with that particular card, but I'm sure if it had such capabilities people would be talking about it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The so-called “RTL-SDR” TV tuner device &lt;em&gt;does&lt;/em&gt; have this mode of operation, which is why it is so popular for cheap SDR receiver applications.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-09-01T03:22:25.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5270" PostTypeId="1" CreationDate="2015-09-02T17:05:31.153" Score="5" ViewCount="232" Body="&lt;p&gt;We know that the primary source of interference at HF is atmospheric noise. Thus, all else being equal, the strength of heard noise is a fair indicator of RX system performance (such as in adjusting an antenna tuner for maximum noise while receiving, in lieu of transmitting and measuring SWR), since the noise is received from all over and is not local interference which it would be useful to remove.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Suppose that we &lt;strong&gt;leave the frequency, antenna tuner, antenna orientation, etc. unchanged, but observe a change in received noise power.&lt;/strong&gt; Does this reliably indicate a corresponding change in propagation conditions, or does the absolute level of atmospheric noise change independent of propagation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, if (I'm not making any contacts and) my radio is quieter than it was an hour ago, is it time to change bands?&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-09-02T19:24:38.987" Title="Does a low amount of atmospheric noise reliably indicate a lack of propagation?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;noise&gt;&lt;physics&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5271" PostTypeId="2" ParentId="5270" CreationDate="2015-09-02T19:24:38.987" Score="2" Body="&lt;p&gt;First of all, noisier or quieter, if you haven't made any contacts, it's probably time to change bands, regardless of anything else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to the meat of your question, what does a quieter actually mean? Basically, it means one or more of the sources of RF noise has quieted down. What are these sources of noise? Well, here's a few:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Aurora Borealis (Northern Lights)&lt;/li&gt;&#xA;&lt;li&gt;Thunderstorms (Mostly noticed in spikes on the air). Note, these could be far away.&lt;/li&gt;&#xA;&lt;li&gt;Local Electronic Interference- This will peak when people are awake, and die down during the quiet times of the day. It will also peak if you are receiving interference from a distance. The distance is relatively rare, mostly local RF noise is relatively close. Going out to a farm outside of the city will reduce your noise to almost nothing.&lt;/li&gt;&#xA;&lt;li&gt;Solar activity- The sun setting or a sun spot quieting down could cause this. If the Sun just set, it will almost certainly get quieter.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I'm sure I could come up with a list of other things, but the bottom line is, the band quieting down could very well be a good thing for making more contacts.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-09-02T19:24:38.987" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5272" PostTypeId="2" ParentId="5240" CreationDate="2015-09-03T00:12:43.640" Score="-1" Body="&lt;p&gt;Basically the higher the baud rate the greater the frequency bandwidth required. The degree of shift of the FSK signal affects the required bandwidth as well. In practical terms, 300 bd is the norm for HF, 1200 bd is the norm for VHF, 9600 baud on UHF not so common but is used with satellites and there is talk about 19kbd as well but not very common. It's all about the bandwidth allowed by the spectrum administrators. Generally they don't like you using more than 5kHz on voice frequencies on HAM bands. A TV Channel is 7 MHz wide.&lt;/p&gt;&#xA;" OwnerUserId="5244" LastActivityDate="2015-09-03T00:12:43.640" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5273" PostTypeId="1" CreationDate="2015-09-03T02:54:14.383" Score="4" ViewCount="4276" Body="&lt;p&gt;5.8 GHz NTSC video transmitters are popular for FPV (first person view) model aircraft flying. However, because the 5.8 GHz band (5725 to 5875 MHz) is also available for ISM (unlicensed) use, it's not clear to me at what point I need a license to operate a transmitter of some given power. I've seen &lt;a href=&quot;http://www.afar.net/tutorials/fcc-rules/&quot; rel=&quot;nofollow noreferrer&quot;&gt;a table&lt;/a&gt; that says I can transmit up to 1 W (30 dBm) with a low-gain (6 dBi) antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Isn't the ham power limit for 1.3 GHz and up 1 W anyways? What does having a ham license do in ISM bands?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reference:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;           GHz :  5.650       5.725          5.850    5.875      5.925&#xA;      ISM Band :                |&amp;lt;------ 100 MHz ------&amp;gt;|&#xA;ITU Region 1/3 :    |&amp;lt;------------------ 275 MHz -----------------&amp;gt;|&#xA;ITU Region   2 :    |&amp;lt;-------- 200 MHz -------&amp;gt;|&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="5100" LastEditorUserId="5100" LastEditDate="2019-02-06T16:17:43.277" LastActivityDate="2019-02-06T16:17:43.277" Title="What's the unlicensed power limit for 5.8 GHz (5 cm) transmissions?" Tags="&lt;united-states&gt;&lt;fcc&gt;&lt;shf&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="5274" PostTypeId="2" ParentId="5273" CreationDate="2015-09-03T03:44:18.127" Score="4" Body="&lt;p&gt;According to &lt;a href=&quot;http://www.afar.net/tutorials/fcc-rules&quot; rel=&quot;nofollow&quot;&gt;this site&lt;/a&gt;, the maximum allowed for non-licensed (&quot;Part 15&quot;) equipment is 1W to the antenna, and the maximum EIRP is 4W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For point-to-point links, the limit is higher, and the site mentions that on 5.8GHz the maximum allowed would be 53dBm EIRP (30dBm transmitted plus 23dBi gain of the antenna), which is 200W EIRP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For licensed radio amateurs, I could not find any limit other than the 1,500W regular maximum power limit. Restrictions to transmitting as a 'radio ham' on the amateur bands that overlap with the ISM bands are those of the amateur radio licence. This includes the requirement to send an ident every 10 minutes and the end of the transmission in a mode that can be read by any radio amateur, if you transmit anything at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC point us at &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.1.157.1&quot; rel=&quot;nofollow&quot;&gt;this link&lt;/a&gt; for the latest Part 97 regulations (the regulations that govern amateur radio), and looking in there it states that 1,500W is the maximum unless otherwise stated, and there is no other statement indicating a lower power requirement for the higher bands, unless the operator holds a Novice licence.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="13" LastEditDate="2015-09-03T13:26:12.517" LastActivityDate="2015-09-03T13:26:12.517" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5275" PostTypeId="2" ParentId="5273" CreationDate="2015-09-03T05:07:39.780" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Isn't the ham power limit for 1.3 GHz and up 1 W anyways? What does having a ham license do in ISM bands?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is the latest version of the table. Updated 2014 but I can't see the PDF (the text on the site is not formatted properly) because the FCC is updating the website.&#xA;&lt;a href=&quot;https://www.fcc.gov/document/5-ghz-u-nii-ro&quot; rel=&quot;nofollow&quot;&gt;https://www.fcc.gov/document/5-ghz-u-nii-ro&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From FCC 14-30 linked above:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The U-NII-3 band is allocated on a primary basis to the Radiolocation Service for Federal operation, and is allocated on a secondary basis to the Amateur Radio Service for non-Federal operation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Actually having a ham license makes it more difficult because we are secondary users of the band. If somebody is causing interference to us, we have to adjust. If we are causing interference to others, we have to adjust out equipment so as not to cause/create said interference. The license doesn't have any effect on the maximum Transmit Power that we can use.&lt;/p&gt;&#xA;" OwnerUserId="1761" LastEditorUserId="1761" LastEditDate="2015-09-03T05:12:57.050" LastActivityDate="2015-09-03T05:12:57.050" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5277" PostTypeId="2" ParentId="5228" CreationDate="2015-09-03T16:11:16.267" Score="2" Body="&lt;p&gt;If you're just using the antenna that comes with the HT, don't get your hopes up. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only FM sat is Saudi-Sat 50, and its transmitter outputs 200mw. It will be very difficult, if not impossible, to hear that bird without a directional antenna. In some conditions, you may be able to hear a &quot;moment of something&quot; from SO50, and perhaps pick up the digital signals from NOAA satellites as they go overhead. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are plans online for building a hand held directional antenna out of anything meta from a wooden stick with arrow shafts, and even using an old tape measure. It is not all that difficult and it's rewarding. In fact, it is very fun to build something and have it work as intended, especially if you don't have the funds to afford the gear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Arrow antenna makes an inexpensive handheld dual band yagi that's perfect for working sats. I've used it to work stations on SO50 and will use it for the FOX sat booked to launch in October 2015&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider that only 1 (and soon to be 2) birds are FM, which is the mode common for HTs. The rest are sideband, CW (morse code) or digital modes like PSK, FSK,GFSK, and APRS. The latter modes require a computer and soundcard interface with the radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An ideal and a more expensive enterprise would be to setup an array of large 2 meter and 70cm yagis on your roof with a computer controlled azimuth/elevator rotor (Yaesu G5500,) signal pre-amplifier(SSB Electronics,) and  low-loss coax like Heliax or a short run of LMR400. You'd need a great radio with dual receive on 2m and 70cm so you can monitor the downlink while transmitting to ensure you're making it into the bird.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;All told, I priced such a satellite station described above between $5,000 and $6,500 USD including the ICOM IC9100 which is one of the best satellite radios money can buy since its all band all mod with a built in tnc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A bonus would be that you could use a modest satellite station to work the big boys who do Earth-Moon-Earth communications; however, you'll likely need 200 to 400 watts of output power to be heard so prepare to shell out some cash for a VHF amplifier. &lt;/p&gt;&#xA;" OwnerUserId="5248" LastActivityDate="2015-09-03T16:11:16.267" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5279" PostTypeId="1" CreationDate="2015-09-04T12:10:04.653" Score="3" ViewCount="6211" Body="&lt;p&gt;Why is BPSK preferable over BFSK? On what parameters this comparison is based? What are the advantages of BPSK?&lt;/p&gt;&#xA;" OwnerUserId="4894" LastEditorUserId="76" LastEditDate="2015-09-04T14:20:34.897" LastActivityDate="2015-09-05T21:17:42.637" Title="Comparision between BFSK and BPSK" Tags="&lt;modes&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5280" PostTypeId="2" ParentId="5279" CreationDate="2015-09-05T21:17:42.637" Score="2" Body="&lt;p&gt;In general, FSK modulations tend to be worse than comparable linear modulations by several criteria. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FSzhN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FSzhN.png&quot; alt=&quot;BER curve from AtlantaRF link budget presentation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I couldn't find a nice picture for this, so the one above from AtlantaRF will have to do, but in telecommunications literature, you have these bit error rate versus per bit signal to noise ratio graphs for various modulation schemes. One thing you always see in those graphs is that you need higher $E_{b}/N_{0}$ for same BER in FSK compared to PSK. In amateur radio, (clean) power is often relatively limited and getting more with less is respected, giving advantage to PSK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One big advantage of FSK is that we don't need clean power for it! It can work with very non-linear power amplifiers, so a set power level is easier to reach with FSK than it is with PSK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, we have the spectral efficiency as well. FSK is less spectrally efficient compared to PSK with same number of modulation levels.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, for non-coherent orthogonal FSK, the null-to-null bandwidth is $B=(M+1)R_{s}$, while for PSK (which is same as for non-coherent DPSK as used in say BPSK31) it's $2R_{s}$, so in binary case, we have $3R_{b}$ compared to $2R_{b}$ for BPSK. If number of modulation levels increases, FSK starts to lose very quickly, since in PSK case, bandwidth does not depend on number of modulation levels. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2015-09-05T21:17:42.637" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5281" PostTypeId="2" ParentId="5210" CreationDate="2015-09-06T18:49:22.273" Score="4" Body="&lt;p&gt;An end fed wire may not necessarily work BETTER for reception, but it should be effective and it is much simpler to put up. You might pick up a bit more hash noise from local RFI sources with an ungrounded configuration though, due to common mode currents induced on the outer shield of the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feeding the wire through an isolation transformer, and grounding the end of the secondary winding opposite the antenna wire, and then also grounding the shield of the feedline at some distance from the antenna where the feedline enters your house would help reduce noise, and provide more safety for your equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other good configurations for reception of weak signals might be:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Run the wire close to the ground (6ft) with a counterpoise wire on&#xA;the ground beneath, and then short the FAR end to the counterpoise&#xA;wire through a large resistor and feed the two wires at the other&#xA;end via a matching transformer and ground the shield of the feedline&#xA;where it enters your house.&lt;/li&gt;&#xA;&lt;li&gt;A fairly small loop of wire with a tuning capacitor at the point opposite the feedpoint, fed via a matching transformer. The loop can be rotated for best signal pickup or to null out local noise sources.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5258" LastActivityDate="2015-09-06T18:49:22.273" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5282" PostTypeId="1" CreationDate="2015-09-06T23:34:00.193" Score="6" ViewCount="4124" Body="&lt;p&gt;I know that the national calling frequency is 146.520. Everywhere I go, it does not give a DUP or TSQ. I am not trying to be or, ask a crazy question but is there or not.&lt;/p&gt;&#xA;" OwnerUserId="5259" LastEditorUserId="76" LastEditDate="2015-09-08T15:04:54.997" LastActivityDate="2020-04-02T01:19:49.883" Title="Is the National Calling Frequency actually used?" Tags="&lt;united-states&gt;&lt;2m-band&gt;&lt;simplex&gt;" AnswerCount="5" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5283" PostTypeId="2" ParentId="5282" CreationDate="2015-09-07T00:13:40.183" Score="6" Body="&lt;p&gt;146.520 MHz is the national calling frequency for FM voice.  It's a &quot;simplex&quot; frequency, meaning that you call on this frequency and then listen for a reply on the same frequency.  (It is &quot;national&quot; in the US, but that does not guarantee that many people are actively monitoring this frequency! YMMV)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're interested in other modes, there are other more-or-less standard frequencies, like 144.200 for SSB voice. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check &lt;a href=&quot;http://www.arrl.org/band-plan&quot;&gt;http://www.arrl.org/band-plan&lt;/a&gt; for frequencies and sub-bands for various amateur bands and operating modes.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-09-07T00:13:40.183" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5285" PostTypeId="1" CreationDate="2015-09-07T23:33:33.933" Score="5" ViewCount="621" Body="&lt;p&gt;I see several products that operate in the 5.8 GHz range that specifically mention a Ham license is required for their use.  For example, the page for &lt;a href=&quot;http://www.getfpv.com/lumenier-tx5g2r-mini-200mw-5-8ghz-fpv-transmitter-with-raceband.html&quot; rel=&quot;noreferrer&quot;&gt;this video transmitter&lt;/a&gt; specifically mentions&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The use and operation of this type of product in the USA and many other countries may require a license and some countries may forbid its use entirely. In the USA, you will need a &quot;HAM&quot; amateur radio license.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What's the current USA regulation for this band?  Where can I find a the definitive statement for this?&lt;/p&gt;&#xA;" OwnerUserId="5270" LastEditorUserId="76" LastEditDate="2015-09-07T23:52:38.023" LastActivityDate="2015-09-08T00:40:30.187" Title="What are the rules for proper use of the 5.8G (5cm) band?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;shf&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5286" PostTypeId="2" ParentId="5285" CreationDate="2015-09-08T00:05:08.737" Score="5" Body="&lt;p&gt;&lt;em&gt;Disclaimer: I am not a lawyer and this is not legal advice. The interpretation of the regulations I am giving is based entirely on the reasoning I have seen other hams make in discussing how to operate properly.&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;There is no one set of rules for the particular band. Rather, there are two entirely separate general regimes:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=beeb54a8902866dd523d66af29f34284&amp;amp;mc=true&amp;amp;node=pt47.1.15&amp;amp;rgn=div5&quot; rel=&quot;noreferrer&quot;&gt;Title 47 Part 15&lt;/a&gt;, for &lt;em&gt;unlicensed&lt;/em&gt; operations — which is what the page is telling you is not applicable here. I don't know what the specific reason is, but the usual one is that the transmission is too powerful.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=beeb54a8902866dd523d66af29f34284&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5&quot; rel=&quot;noreferrer&quot;&gt;Title 47 Part 97&lt;/a&gt;, which defines the amateur radio service and what may be done under an amateur radio license.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;For amateur radio operators, most bands are broadly similar; there are no unusual rules that apply specifically to the 5 cm band. There are specific rules,&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(1) Amateur stations transmitting in the 5.650-5.725 GHz segment must not cause harmful interference to, and must accept interference from, stations authorized by other nations in the mobile except aeronautical mobile service.&lt;/p&gt;&#xA;&lt;p&gt;(2) Amateur stations transmitting in the 5.850-5.925 GHz segment must not cause harmful interference to, and must accept interference from, stations authorized by the FCC and other nations in the fixed-satellite (Earth-to-space) and mobile services and also stations authorized by other nations in the fixed service. In the United States, the use of mobile service is restricted to Dedicated Short Range Communications operating in the Intelligent Transportation System.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;but these are similar to rules in other bands except for the details of what you're supposed to avoid interfering with. In practice, you are unlikely to need to do anything in particular to comply.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Practically: I assume you don't currently have an amateur radio license. Study for and obtain one, and you'll learn what you need to be doing in general sufficiently to use the particular band you have in mind.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2015-09-08T00:40:30.187" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5288" PostTypeId="1" CreationDate="2015-09-09T21:32:22.900" Score="2" ViewCount="156" Body="&lt;p&gt;I have a project idea. It uses a pair of RF transmitter and receiver. The application is a little complicated since it involves motion, typically the speed of a vehicle going on local or even better on highway. I'm wondering if the transmitter and receiver like these can still work under that condition. Supposed both car A and car B have a pair of transmitter and receiver each. Can car A send messages to car B and vice versa?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.sparkfun.com/products/10534&quot; rel=&quot;nofollow&quot;&gt;RF Link Transmitter - 434MHz&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.sparkfun.com/products/10532&quot; rel=&quot;nofollow&quot;&gt;RF Link Receiver - 4800bps (434MHz)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, what different kind of products can achieve this?&lt;/p&gt;&#xA;" OwnerUserId="5275" LastEditorUserId="76" LastEditDate="2015-09-09T22:01:43.720" LastActivityDate="2017-11-30T21:20:04.527" Title="Can RF work while it's in motion?" Tags="&lt;propagation&gt;&lt;uhf&gt;&lt;mobile&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5289" PostTypeId="2" ParentId="5288" CreationDate="2015-09-09T21:59:38.087" Score="5" Body="&lt;p&gt;The effect of motion is to cause &lt;a href=&quot;https://en.wikipedia.org/wiki/Doppler_effect&quot; rel=&quot;noreferrer&quot;&gt;Doppler shift&lt;/a&gt; in the received signal. This changes both the carrier frequency and the symbol rate. However, because the speed of propagation of the wave — an electromagnetic wave — is the speed of light, this effect is &lt;em&gt;very small&lt;/em&gt; for terrestrial conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A link between a fixed station and a vehicle moving at, let's say, 60 miles per hour, will observe a Doppler shift of order of magnitude $10^{-9}$. Multiply that by 433 MHz and you get 433 &lt;em&gt;milli&lt;/em&gt;hertz. The effect on the symbol rate is also tiny. These values are likely smaller than the temperature-dependent frequency error in the modules' local oscillators!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, no, you don't need to worry about the motion of the vehicles. Your biggest problem is likely to be range. (Be prepared to, for example, mount the module and antenna outside the car, ideally in the center of the roof.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-09-09T21:59:38.087" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5290" PostTypeId="1" CreationDate="2015-09-10T09:58:47.800" Score="5" ViewCount="3104" Body="&lt;p&gt;I live in Japan. Japanese houses are very narrow, but I want to try 160 m band.&lt;br&gt;&#xA;Is there good antenna for 160 m band?&lt;br&gt;&#xA;I want to operate HF (160m～10m) bands. Now I use vertical antenna (40,&#xA;30,20,15,10m).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want a low band (under 40m) antenna. Low band antennas is small in Japan. &#xA;So I have to make it. Is there the antenna that it is small, and production is easy?&lt;/p&gt;&#xA;" OwnerUserId="1450" LastEditorUserId="1450" LastEditDate="2015-09-11T23:23:52.380" LastActivityDate="2015-09-17T17:29:27.297" Title="Is there good antenna for 160m Band?" Tags="&lt;antenna&gt;&lt;hf&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5291" PostTypeId="2" ParentId="5290" CreationDate="2015-09-10T10:36:10.363" Score="1" Body="&lt;p&gt;The cheapest solution for the 160m band is probably a magnetic loop antenna, but do be aware that these antennas are optimised for small space and low cost, and NOT for performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A magnetic loop is an extremely high-Q antenna with a very tight bandwidth (think ~5kHz on the 160m band), but they are tunable. The gain of such an antenna will be anything from 0dBi to -20dBi (that is to say they are not very efficient).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it will allow you to get on the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The usual warnings about the high voltages present on a magnetic loop antenna apply here, especially if you put any power into it! Do not install one where people can get close to it while you are transmitting.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example of a magnetic loop antenna is &lt;a href=&quot;http://home.alphalink.com.au/~parkerp/projects/projmag.htm&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck!&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-09-10T10:36:10.363" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5295" PostTypeId="1" AcceptedAnswerId="5297" CreationDate="2015-09-11T14:41:55.890" Score="2" ViewCount="2275" Body="&lt;p&gt;I'm interested in listening to the local EMS/Fire transmissions around here and was wondering if I have to configure the CTCSS/PL tones on the radio in order to hear those transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that a PL tone is used to create sub-banding in the same frequency to basically subdivide a single frequency into about 38 private &quot;channels&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens if I don't configure a PL tone on my radio? Will I be able to hear all transmissions on that frequency even if some particular group is using a specific PL tone? I'm using a Baofeng UV-5RB.&lt;/p&gt;&#xA;" OwnerUserId="5295" LastActivityDate="2015-09-12T08:20:18.763" Title="Receiving without configuring CTCSS" Tags="&lt;tone-squelch&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5296" PostTypeId="2" ParentId="5295" CreationDate="2015-09-11T15:04:32.713" Score="0" Body="&lt;p&gt;Basically yes, most radios will open the squelch for all activity if a RX tone isn't specified. Your assumption that you can hear EMS/Fire transmissions is flawed however. Most of these services use TETRA which encrypts all traffic, so even if you could tune to these with your radio, which you might not be able to, you won't hear anything legible. &lt;/p&gt;&#xA;" OwnerUserId="135" LastActivityDate="2015-09-11T15:04:32.713" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5297" PostTypeId="2" ParentId="5295" CreationDate="2015-09-11T16:36:11.013" Score="4" Body="&lt;p&gt;Your understanding of tone squelch is wrong. Tone squelch is simply an &lt;em&gt;extension&lt;/em&gt; to the squelch system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally, the squelch opens whenever the received signal is stronger than the squelch threshold.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a tone squelch (and I use that term broadly here to refer to CTCSS, DCS and any other possible, similar schemes) configured for receive squelch, the squelch opens only if the received signal is strong enough &lt;em&gt;and&lt;/em&gt; the configured tone is present in the demodulated audio. (The tone is filtered out before the audio is fed to the speaker or headphones; hence &quot;subaudible&quot; in the context of the radio transmission.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All the issues with &lt;a href=&quot;https://en.wikipedia.org/wiki/Capture_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;FM capture&lt;/a&gt; and so on remain exactly the same with or without tone squelch, so you do not get any additional &quot;channels&quot;. (Also consider &lt;a href=&quot;https://ham.stackexchange.com/q/1797/29&quot;&gt;Can two FM radios transmit two separate PL tones at the same time, and be received by two radios with matching PL tones?&lt;/a&gt;) All that happens is that you can filter out some of the transmissions that you are not interested in. This is particularly useful in situations where the received signal is relatively weak, as you can leave the signal strength squelch turned all the way down and rely on the tone squelch to only open for useful transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that said, &lt;strong&gt;we can answer your question:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If tone squelch is not configured on the receiver, practically any FM receiver will open the squelch whenever the received signal is strong enough, regardless of the presence of any particular subaudible tone or code, because it is not filtering based on any particular subaudible tone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, if you do not set up tone squelch on your radio, or your radio does not support tone squelch (applies primarily to older equipment), &lt;strong&gt;you should be able to hear all transmissions as they sound on the air.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It isn't entirely uncommon that radios allow separate tone squelch for transmit and receive. This can be useful, for example, if your local repeater input is tone squelch operated (to reduce interference) but it does not re-transmit the tone on the repeater's transmit (output) side.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-09-12T08:20:18.763" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5299" PostTypeId="1" CreationDate="2015-09-11T21:39:25.567" Score="2" ViewCount="326" Body="&lt;p&gt;What restrictions exist for non-HAMs in the 5.8 GHz band in the USA?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Context: these types of popular video transmitters (&lt;a href=&quot;http://www.getfpv.com/fpv/5-8ghz-600mw-9ch-a-v-transmitter-receiver-combo.html&quot; rel=&quot;nofollow&quot;&gt;600 mW&lt;/a&gt;, &lt;a href=&quot;http://www.getfpv.com/fpv/altituderc-nano-25mw-5-8ghz-fpv-video-transmitter.html&quot; rel=&quot;nofollow&quot;&gt;25 mW&lt;/a&gt;) commonly used for FPV piloting.  Any requirements to have a HAM license to use either of these units?&lt;/p&gt;&#xA;" OwnerUserId="5270" LastEditorUserId="873" LastEditDate="2015-09-13T02:43:58.157" LastActivityDate="2016-01-21T04:40:38.503" Title="What restrictions exist for non-HAMs in the 5.8 GHz band?" Tags="&lt;united-states&gt;&lt;diy&gt;&lt;rf-power&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5301" PostTypeId="2" ParentId="345" CreationDate="2015-09-13T15:34:07.933" Score="2" Body="&lt;p&gt;If I say best regards to you it would be 73. If I and in a group or a net there are many people hence 73's, plural. It originated from code, person to person, singular. IMO, best regard(s) , Jerry W5JRY &lt;/p&gt;&#xA;" OwnerUserId="5303" LastActivityDate="2015-09-13T15:34:07.933" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5302" PostTypeId="2" ParentId="5282" CreationDate="2015-09-14T05:16:10.987" Score="0" Body="&lt;p&gt;Yes it is used, but it depends on your area. I include it in my set of scanned frequencies, and have made 3 or 4 contacts over the past few months. &lt;/p&gt;&#xA;" OwnerUserId="5306" LastActivityDate="2015-09-14T05:16:10.987" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5303" PostTypeId="2" ParentId="5282" CreationDate="2015-09-14T14:32:57.320" Score="3" Body="&lt;p&gt;I have my VHF rig in my pickup truck set to 146.52 MHz all of the time when I am driving.  In an hour's time I would guess I hear maybe 3 or 4 copyable signals.  My main use is to help someone out by answering questions that are asked (frequently, traffic snarls and/or other travel related things of mobile operators).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, not long ago I was stuck in traffic (south of Tacoma, Washington on I-5) and so I raised up a question on 146.52.  Another guy, traveling in the opposite direction (south-bound) had just passed the accident causing the backup that was about 2 1/2 miles north from my location.  We chatted he got out of range for easy which I am guessing was about 7 to 10 miles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not uncommon for ham radio operators who normally operate HF to have their VHF rig set to 146.52 whether in a vehicle or at home.  In a large city, you can use the simplex 146.52 traffic to ask advice on restaurants or routes or directions and usually pick someone up.  Not as predictable as a repeater but it is a lot easier than programming in your repeater tone while driving in other cities.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-09-14T14:32:57.320" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5304" PostTypeId="1" AcceptedAnswerId="5317" CreationDate="2015-09-15T10:50:52.500" Score="4" ViewCount="60" Body="&lt;p&gt;I'm going to be starting the Foundation course in the next few weeks, and have been offered an initial practical assessment at a member's shack to save time for the club during the course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The call to be made is on 2m with a QSY, so I'm wondering how that will pan out and what to expect?&lt;/p&gt;&#xA;" OwnerUserId="5313" LastActivityDate="2015-09-18T11:02:41.550" Title="UK Foundation - initial practical assessment, what to expect?" Tags="&lt;united-kingdom&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5305" PostTypeId="1" CreationDate="2015-09-15T12:39:42.333" Score="9" ViewCount="1976" Body="&lt;p&gt;For marine VHF (156~162 MHz), the most commonly used antenna is a 1/2-wave dipole or a collinear array in the form of a fibreglass rod. Collinear arrays are used to increase gain in some antennas. Dipoles/collinear arrays by their nature do not need a groundplane. This much I gather.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, another popular type - especially with the sailing crowd - is the stainless steel whip antenna. Also supposedly a 1/2-wave antenna, it is roughly 1 m long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following page has examples of both types of antennas - AV7M is a fibreglass rod dipole, and AV53BIS3 is a stainless steel whip: &lt;a href=&quot;http://www.comrod.com/category.php?categoryID=129&quot; rel=&quot;noreferrer&quot;&gt;http://www.comrod.com/category.php?categoryID=129&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further examples of stainless steel whips specifically:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.scan-antenna.com/product/vhf23&quot; rel=&quot;noreferrer&quot;&gt;http://www.scan-antenna.com/product/vhf23&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.glomex.it/shop/prodotti/diporto-antenne-marine/antenne-vhf/ra106slspb.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.glomex.it/shop/prodotti/diporto-antenne-marine/antenne-vhf/ra106slspb.html&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.pacificaerials.co.nz/Marine/P6001VHF10mStainlessSteelAntenna.aspx&quot; rel=&quot;noreferrer&quot;&gt;http://www.pacificaerials.co.nz/Marine/P6001VHF10mStainlessSteelAntenna.aspx&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://shakespeare-ce.com/marine/wp-content/uploads/sites/4/2015/04/5240-r_5241-r_0.pdf&quot; rel=&quot;noreferrer&quot;&gt;http://shakespeare-ce.com/marine/wp-content/uploads/sites/4/2015/04/5240-r_5241-r_0.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;According to the datasheet and other information available on this type of antenna, the stainless steel whip is an end-fed dipole, and does not need any external ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following page describes the concept of an end-fed dipole: &lt;a href=&quot;http://www.aa5tb.com/efha.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.aa5tb.com/efha.html&lt;/a&gt;&#xA;The cylindrical base of the VHF whip then, it can be assumed, contains the LC matching circuit/balun(?) described.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We learn that the antenna doesn't work without a &quot;counterpoise&quot; - and it seems reasonable to assume that the VHF whip is in fact constructed similarly to Figure 15.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further reading-up on counterpoises brings much confusion about their nature: &lt;a href=&quot;http://www.antennex.com/shack/Dec06/cps.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.antennex.com/shack/Dec06/cps.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With this in mind:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;While several of the whip antennas referenced above are described as DC-open, whereas &quot;Figure 15&quot; is DC-shorted, is it possible that they are of a &quot;Figure 15&quot;-similar design? If not, then what are they?&lt;/li&gt;&#xA;&lt;li&gt;What is the nature of the (probably misnamed) &quot;counterpoise&quot; in &quot;Figure 15&quot; et al (which then, presumably, consists of the antenna's cylindrical brass base, feedline, and the radio equipment)? What is its role in allowing the standing wave/electrons-on-the-move in the radiating element to excite the E-field and, well, radiate?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Would also much appreciate references to literature that explains the physics of antennas in general and these types in particular, with sound scientific base without going deeply into the maths.&#xA;Have had a hard time finding quality literature among the seemingly vast quantities of &quot;black magic&quot; antenna cookbooks.&lt;/p&gt;&#xA;" OwnerUserId="5314" LastEditorUserId="5314" LastEditDate="2015-09-19T07:42:26.113" LastActivityDate="2019-06-14T19:38:05.590" Title="Marine VHF whip antennae - what are they?" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5306" PostTypeId="1" CreationDate="2015-09-16T18:25:15.487" Score="4" ViewCount="178" Body="&lt;p&gt;Overseas hams can join RSGB from their site for 51 GBP, which today is about 79 USD.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;USA hams can also join through the ARRL for 75 USD.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming the $4 is not a factor, are there any advantages to joining directly with RSGB in terms of membership benefits and discounts, access to RadCom Plus, etc.&lt;/p&gt;&#xA;" OwnerUserId="2962" LastEditorUserId="873" LastEditDate="2015-09-17T10:49:07.613" LastActivityDate="2016-05-11T18:55:14.237" Title="Best way for US ham to join RSGB" Tags="&lt;united-states&gt;&lt;arrl&gt;&lt;rsgb&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5308" PostTypeId="1" CreationDate="2015-09-17T15:04:46.790" Score="3" ViewCount="1037" Body="&lt;p&gt;I want to know this omnidirectional antenna's maximum distance:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;gain 15 dBi&lt;/li&gt;&#xA;&lt;li&gt;frequency 2400 GHz&lt;/li&gt;&#xA;&lt;li&gt;power 50 watts&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5327" LastEditorUserId="76" LastEditDate="2015-09-17T15:08:50.393" LastActivityDate="2015-09-17T15:15:08.030" Title="maximum distance omnidirectional antenna" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;wifi&gt;&lt;loop-antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5309" PostTypeId="2" ParentId="5308" CreationDate="2015-09-17T15:15:08.030" Score="3" Body="&lt;p&gt;&lt;strong&gt;Antennas don't have ranges.&lt;/strong&gt; The maximum range of a link is determined by many factors in addition to the information you have about the antenna, among them:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the power output of the transmitter (not the power rating of the antenna)&lt;/li&gt;&#xA;&lt;li&gt;the minimum usable signal of the &lt;em&gt;receiver&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;the strength of interfering signals&lt;/li&gt;&#xA;&lt;li&gt;the amount and type of obstacles (e.g. trees, building walls) between the two antennas&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The only information you need about the antenna is its gain &lt;em&gt;in the relevant direction&lt;/em&gt; (an “omnidirectional” antenna necessarily has less gain than a directional one).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have gathered enough information, you can do a &lt;em&gt;link budget&lt;/em&gt; calculation to model the expected performance. Have a look at the answers to this question: &lt;a href=&quot;https://ham.stackexchange.com/questions/352/what-is-a-link-budget-and-how-do-i-make-one&quot;&gt;What is a link budget, and how do I make one?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-09-17T15:15:08.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5310" PostTypeId="1" CreationDate="2015-09-17T16:14:05.920" Score="3" ViewCount="194" Body="&lt;p&gt;I am (KB3IFP) going on a 400 mile bike ride in the middle of West Virgina with 0 access to cell reception. I have a 2 meter handheld and a small book of all the US repeaters. I like to 'check-in' every evening/morning so my family knows I am OK. I could buy a Delorme GPS with texting capabilities via sat but what's the fun in that? My brother is K3OD and he has a HF station back in Pittsburgh. Is there a way to have my brother use Echolink to monitor a freq/channel using Echolink and record any messages I transmit? Am I thinking of this all wrong? What would you do?&lt;/p&gt;&#xA;" OwnerUserId="5328" LastActivityDate="2015-12-12T17:15:21.247" Title="Can I leave voice messages via Echolink using my 2-meter handheld?" Tags="&lt;2m-band&gt;&lt;echolink&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5311" PostTypeId="2" ParentId="5290" CreationDate="2015-09-17T17:29:27.297" Score="0" Body="&lt;p&gt;You can modify your vertical to work on 160m. Small antennas are always a compromise in performance, but they do work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might research mobile antennas, intended for operation from a vehicle. These have similar restrictions on size, and so they usually use two methods, or both in combination, to make the antenna appear longer electrically than it is physically.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Capacity or capacitance hats&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;These come in a lot of styles, but the idea is to put spokes or something similar at the top of the antenna to increase the capacitance to ground at the tip of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's an example &lt;a href=&quot;http://www.k0bg.com/caphats.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;from K0BG&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.k0bg.com/caphats.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OMcN6.jpg&quot; alt=&quot;vertical antenna with capacitance hat&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are all kinds of variations, but anything that makes the antenna thicker accomplishes the same thing. Increasing the thickness at the top has more effect than increasing it at the bottom. See the &lt;a href=&quot;https://en.wikipedia.org/wiki/T-antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;T-antenna&lt;/a&gt; for an antenna where the capacitance hat is most of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Loading coils&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;As you might guess from &lt;a href=&quot;https://en.wikipedia.org/wiki/Duality_(electrical_circuits)&quot; rel=&quot;nofollow noreferrer&quot;&gt;duality&lt;/a&gt;, it's possible to electrically lengthen an antenna (and thus, make it physically smaller), with inductance also. This is accomplished by putting an inductance somewhere along the length of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a homemade loading coil &lt;a href=&quot;https://www.flickr.com/photos/jonathancharles/3967628132&quot; rel=&quot;nofollow noreferrer&quot;&gt;by KC7FYS&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.flickr.com/photos/jonathancharles/3967628132&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JIPoB.jpg&quot; alt=&quot;loading coil&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Putting the coil near the base of the antenna is more effective at electrical lengthening than putting the same coil near the tip. But the current is higher at the base than the tip, so the closer the coil is to the base, the higher the losses, and thus the lower the antenna efficiency. Likewise, a bigger coil will electrically lengthen the antenna more, but losses will be higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So as usual, placement and sizing of the loading coil is a compromise between size and performance. A lot of designs end up putting the coil somewhere around the middle of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;These aren't the only options&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;There are a lot of ways to make antennas and this is just one. As Scott Earle says, a magnetic loop antenna is an equally valid solution. People do all sorts of things: just about any conductor can be made into an antenna. People have used rain gutters, metal fences, metal roofs, or just random wires strung around wherever they can fit them. If you can match your radio's impedance, and keep losses low, it will work as an antenna!&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-09-17T17:29:27.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5312" PostTypeId="2" ParentId="5310" CreationDate="2015-09-17T18:01:16.550" Score="0" Body="&lt;p&gt;I haven't used EchoLink myself, but from listening while other people are using it on the local repeater, and reading the web site, it seems that EchoLink does &lt;em&gt;not&lt;/em&gt; have any kind of store-and-forward messaging capability, only real-time communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could use it to talk directly with your brother if he is available at the same time, but you would be limited to repeaters which have functioning EchoLink nodes.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I'm not aware of anything commonly available that will let you pass on &lt;em&gt;voice&lt;/em&gt; messages, but I have two suggestions for alternatives:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Ask people to relay your messages home.&lt;/strong&gt; (You could do formal radiograms, even.) This sort of thing is not done often in these days of the Internet and cell phones, but some people will very much enjoy helping your message along. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Use APRS.&lt;/strong&gt; You can transmit APRS messages which contain your current location and whatever text you want; wherever there is APRS digipeater/IGate coverage, your messages will be passed to the Internet (e.g. on &lt;a href=&quot;http://aprs.fi/&quot; rel=&quot;nofollow&quot;&gt;http://aprs.fi/&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This does require some more hardware, but I hear it can be as simple as your HT, your smartphone, and an audio interface cable.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-09-17T18:01:16.550" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5313" PostTypeId="1" AcceptedAnswerId="5314" CreationDate="2015-09-18T00:01:06.350" Score="5" ViewCount="270" Body="&lt;p&gt;For example, the &lt;a href=&quot;http://www.qrp-labs.com/ultimate3/u3s.html&quot; rel=&quot;noreferrer&quot;&gt;Ultimate3S kit info&lt;/a&gt; page says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Produces 250mW RF output on 30m (lower output on higher bands)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Would bands &quot;higher&quot; than 30m mean:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;bands with higher &lt;em&gt;frequency&lt;/em&gt; e.g. 20m/17m/15m?&lt;/li&gt;&#xA;&lt;li&gt;bands with higher &lt;em&gt;wavelength&lt;/em&gt; e.g. 40m/80m/160m?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It seems like an ambiguous way to refer to the &quot;height&quot; of a &lt;em&gt;band&lt;/em&gt; rather than either its frequency or wavelength directly, so whenever I see this usage I am uncertain.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2015-09-18T02:57:17.570" Title="What do hams mean when they refer to &quot;higher bands&quot;" Tags="&lt;jargon&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5314" PostTypeId="2" ParentId="5313" CreationDate="2015-09-18T00:24:46.967" Score="5" Body="&lt;p&gt;In &lt;em&gt;this&lt;/em&gt; case, they probably mean higher frequency. Two pieces of evidence:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;One typically says “&lt;strong&gt;longer/shorter&lt;/strong&gt; wavelength”, not “higher/lower wavelength”.&lt;/li&gt;&#xA;&lt;li&gt;Lower power output at higher frequencies is common, because components' and circuits' characteristics are generally worse at higher frequencies.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;But there are also opposite terms, like “top band” for 160 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would personally avoid saying things like “higher bands” exactly because of this ambiguity; perhaps instead “higher-frequency bands”.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-09-18T02:57:17.570" LastActivityDate="2015-09-18T02:57:17.570" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5315" PostTypeId="5" CreationDate="2015-09-18T01:02:37.050" Score="0" Body="&lt;p&gt;The Radio Society of Great Britain is the national radio society of the United Kingdom of Northern Ireland and Great Britain, founded in 1913.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://rsgb.org/&quot; rel=&quot;nofollow&quot;&gt;http://rsgb.org/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2015-09-18T14:57:49.113" LastActivityDate="2015-09-18T14:57:49.113" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5316" PostTypeId="4" CreationDate="2015-09-18T01:02:37.050" Score="0" Body="For questions regarding the Radio Society of Great Britain (RSGB)" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2015-09-18T14:57:45.123" LastActivityDate="2015-09-18T14:57:45.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5317" PostTypeId="2" ParentId="5304" CreationDate="2015-09-18T11:02:41.550" Score="3" Body="&lt;p&gt;I can answer this question myself at this point as I've just completed the practical last night.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;@AndrejaKo provided a perfect example of the whole exercise in his video clip. Thanks also to the Essexham channel for that information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It was simply a matter of:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Calling CQ on the VHF calling frequency 145.500.&lt;/li&gt;&#xA;&lt;li&gt;Finding a clear frequency, checking it's clear then reporting that back to correspondent on calling frequency, requesting a QSY (frequency change) to the new frequency (using their call sign first each time before your own)&lt;/li&gt;&#xA;&lt;li&gt;Checking signal reports and QTH (location) with correspondent on new frequency and then finally clearing the frequency&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You get an almost scripted sheet from your instructor, if you're lucky, as per the video and my own experience, and then you are guided through the call. It's just to show you can use the controls on a basic VHF set.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you've been listening to any ham calls at all you'll be familiar with the format of the conversations. I went first, my associate second. I have been listening in for a year or more so was quite comfortable, if a little nervous at my first contact. He got through it just fine with no prior experience, obviously with a few more nerves from being bombarded by dozens of new and unfamiliar terms. But went over no trouble.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope that helps any new hams-to-be in the future.&lt;/p&gt;&#xA;" OwnerUserId="5313" LastActivityDate="2015-09-18T11:02:41.550" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5318" PostTypeId="1" AcceptedAnswerId="5332" CreationDate="2015-09-18T13:50:31.483" Score="3" ViewCount="516" Body="&lt;p&gt;I'm running Chirp on Linux Mint 17.2 and for some reason when I try to program anything in 400mhz-480mhz range I get the error.&#xA;&quot;Error setting memory: Frequency 453.66250 is out of supported range&quot; &#xA;When I download from the Radio it has channels like 456.525000 so is there any reason I shouldn't be able to program something like 453.66250 or 460.25000&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to Download and Upload to the Radio I do have to run chirp as root.&#xA;Could this be the problem?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also have this issue when trying to program the channel manually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks,&lt;/p&gt;&#xA;" OwnerUserId="5332" LastEditorUserId="76" LastEditDate="2016-10-29T19:17:12.517" LastActivityDate="2016-10-29T19:17:12.517" Title="Baofeng UV5RA Unable to Program anything in 400-480 Bands" Tags="&lt;baofeng&gt;&lt;uv-5r&gt;&lt;radio-programming&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5319" PostTypeId="2" ParentId="2174" CreationDate="2015-09-20T05:57:42.870" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Canada does not include 420-430 MHz in their band plan for 70cm, so the restriction is in place to prevent interference to Canadian amateurs.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Actually, this is to prevent interference to non-amateur fixed and mobile comms; the treaty/arrangement text is available with a simple search.  WHY Canada went and did this is another matter I haven't been able to find.  This is also why the FCC justified removing 420-430 from ham use in 3 US border cities around the Great Lakes, since hams were already absent there due to their being within Line-A's boundaries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also text about interference to US radars on the band (just like the comment above), with the Concrete, North Dakota radar mentioned by name several times and Alaska a couple of times.  Lines B and D are not often mentioned on this side of the border, but are very important to the US NTIA. (I believe Industry Canada regulates everything over there rather than having two agencies do it like we do here, which seems pretty dumb on our part--but then again, you can never have enough alphabet soup agencies, right?)&lt;/p&gt;&#xA;" OwnerUserId="5342" LastActivityDate="2015-09-20T05:57:42.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5320" PostTypeId="1" CreationDate="2015-09-20T23:15:35.973" Score="3" ViewCount="298" Body="&lt;p&gt;I want to understand the theory behind how &lt;em&gt;link margin&lt;/em&gt; or &lt;em&gt;fade margin&lt;/em&gt; is decided? If I have to have a point to point UHF voice communication link from ground to aircraft, for example, with a reliability of 95%, how is the link margin decided? What is acceptable link margin for these links? Are there any standards for these?&lt;/p&gt;&#xA;" OwnerUserId="5349" LastEditorUserId="5046" LastEditDate="2015-09-26T19:46:03.593" LastActivityDate="2016-01-01T12:42:06.323" Title="Acceptable link margin for voice communication in uhf band" Tags="&lt;propagation&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5321" PostTypeId="2" ParentId="4932" CreationDate="2015-09-21T12:41:52.203" Score="1" Body="&lt;p&gt;The best way to use a Baofeng to communicate with any walkie talkie is to:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Find the frequency. Make sure you are on the right frequency by transmitting from the midland walkie talkie to your Baofeng. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Run a tone decoder. In the option &quot;R-CTCS&quot;, the bafeng has a tone decoder by pressing either the # button or the * button. When the tone decoder is running, you should see the CT icon flashing. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Transmit on your walkie talkie, give a long dead carrier. This will give the boafeng time to search through any CTCSS tone. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Once the radio finds it, remember that tone, and put it on the T-CTCS menu option. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Now test both ways by transmitting on the baofeng and the walkie talkie. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Its might illegal in your country to transmit out of band on your specific frequency the Baofeng. Use caution.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2015-09-21T12:47:41.627" LastActivityDate="2015-09-21T12:47:41.627" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5322" PostTypeId="2" ParentId="5305" CreationDate="2015-09-21T15:42:06.733" Score="6" Body="&lt;p&gt;Without having one of these antennas to disassemble (perhaps destructively), I can't tell you exactly how they are constructed. But maybe I can address some of your underlying concerns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly, &lt;em&gt;counterpoise&lt;/em&gt;. In one sense, this is an elevated screen of wires designed to take the place of Earth. This sense developed with the Marconi antenna (what we'd probably call a &quot;vertical&quot;) in the late 19th century.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the other sense, &lt;em&gt;counterpoise&lt;/em&gt; is the &quot;other half&quot; of the antenna. If charge is being removed from the antenna, then it is being added to the counterpoise, and vice versa. This must be so, due to the law of &lt;a href=&quot;https://en.wikipedia.org/wiki/Charge_conservation&quot; rel=&quot;noreferrer&quot;&gt;charge conservation&lt;/a&gt;. In this sense, the counterpoise may be the Earth, or radials, or the other half of the dipole, or the feedline, mast, tower, or whatever else may be connected or capacitively coupled to the antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people will tell you that one of these senses is wrong, but the fact is that &quot;counterpoise&quot; has no rigorous definition: you have to figure it out by context.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the trouble with end-fed dipoles is this: if you are putting charge into the antenna from the end, where are you getting the charge from? In a vertical we can take it from the ground and put it into the antenna, and in a center-fed dipole we take it from one half and put it into the other. But with an end-fed dipole, there's no &quot;other&quot; thing: there is no &lt;em&gt;counterpoise&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, the feedline or mast will become the counterpoise. Since you probably didn't intend for the feedline to have RF current all over it, you might want to do something about that. &lt;a href=&quot;http://www.w8ji.com/end-fed_1_2_wave_matching_system_end%20feed.htm&quot; rel=&quot;noreferrer&quot;&gt;W8JI has a pretty good article on the subject&lt;/a&gt;. In summary, you may want to isolate the feedline with a transformer, but if you don't, it's not the end of the world. 25W transmit power probably isn't enough to cause arcing or RF burns no matter what you do. Without disassembling an antenna it's hard to say exactly what the feed and matching arrangement is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it is pretty safe to assume that in all cases, the feedpoint impedance is high, and we need some way to make it lower to match 50 ohms. If the impedance is already purely resistive, then a transformer with the right turns ratio will do the trick.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But we can also accomplish a step-down in impedance with either:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;a parallel inductor + a series capacitor, or&lt;/li&gt;&#xA;&lt;li&gt;a series inductor + a parallel capacitor.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/BKwDg.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fBKwDg.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's easy to see how this works on a &lt;a href=&quot;http://www.fourier-series.com/rf-concepts/smithchart.html&quot; rel=&quot;noreferrer&quot;&gt;Smith chart&lt;/a&gt;: if we start at 1000 ohms (the green dot) then there are two ways we can get to 50 ohms (the center):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wUccJ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wUccJ.png&quot; alt=&quot;smith chart&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, making the antenna a little too long, or a little too short, will introduce a reactive component to the feedpoint impedance. So it very well may be that a clever antenna designer can use this to take place of one of the components, and then achieve an acceptable match with just one other component.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-09-21T15:42:06.733" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5323" PostTypeId="2" ParentId="5033" CreationDate="2015-09-21T17:17:54.883" Score="3" Body="&lt;p&gt;Wherever there is an impedance discontinuity, there are reflections. So indeed, even with your stub there are still reflections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the goal of a matching network, be it stubs, discrete components, or anything else, is to confine these reflections and the energy they contain to the smallest area possible. By reducing the amount of transmission line with reflections (and thus, a VSWR greater than 1:1), we minimize the loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stubs do this (when they are the right length) by creating another reflection that cancels the initial reflection. So the stub operates with an increase VSWR (and thus, greater current, and greater loss), but since the stub is in practice less than a quarter wavelength long, the loss isn't much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Compare this to the case with no stubs: the entire transmission line from the transmitter to the antenna operates at a high VSWR. Since this feedline is usually pretty long, this can add up to a lot of loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With discrete components the problem is the similar: that reflected energy is cancelled by reactive energy alternately stored and released in either the magnetic field of a coil, or the electric field of a capacitor. This flow of energy into and out of these reactive components is subject to loss when we use real components, but this loss is ostensibly less than the loss that would occur were that energy to travel the whole length of the feedline multiple times.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-09-21T17:17:54.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5324" PostTypeId="2" ParentId="5224" CreationDate="2015-09-22T23:05:17.023" Score="0" Body="&lt;p&gt;Just to try a contradictory answer: If each &quot;hop&quot; is well below the RF noise floor at your location, both in RF power, bandwidth, and duration, even for directional antenna pointed at you from outside your secure zone, and the time and frequency of all the hops are well separated and known only to the sender and receiver (such as via a long one-time pad), and the data rate is low enough such that information can be determined to exist and thus received (due to a sufficiently/highly redundant encoding scheme) only after a period much longer than the attention span of anyone DF-ing you, then (4) and (2) can be met, implying (1) as well, but (3) can still be violated by anyone raising the entire RF noise floor above what Shannon's law allows for your chosen low data rate.  Which could be a neighbor turning on their vacuum cleaner and/or old microwave oven.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the long one-time pad and custom encoding scheme is essentially equivalent to encryption.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2015-09-22T23:19:42.610" LastActivityDate="2015-09-22T23:19:42.610" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5325" PostTypeId="1" CreationDate="2015-09-23T13:07:25.337" Score="1" ViewCount="288" Body="&lt;p&gt;I need to determine the correct sidelobe envelope for various VSAT antennas. Given the radiation pattern (this one, for example &lt;a href=&quot;http://www.gdsatcom.com/vsat/technical_docs/patterns/6000-023.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.gdsatcom.com/vsat/technical_docs/patterns/6000-023.pdf&lt;/a&gt;), how can I determine whether it is &lt;strong&gt;29-25 log theta&lt;/strong&gt; or &lt;strong&gt;32-25 log theta&lt;/strong&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is my understanding that it depends on the off-axis angle (theta), but I don't know how it can be calculated. I think I've also seen somewhere that it depends on the azimuth and elevation, but I don't see how exactly they influence the off-axis angle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking forward to your answers!&lt;/p&gt;&#xA;" OwnerUserId="5359" LastActivityDate="2015-11-22T17:48:18.660" Title="Determining the correct sidelobe envelope" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5326" PostTypeId="1" CreationDate="2015-09-23T13:22:15.560" Score="3" ViewCount="1970" Body="&lt;p&gt;I need to determine the Peak Envelope Power for the VSAT station. Given that the modulation is not AM, would it be correct to assume that the PEP will be the same as transmitter power?&lt;/p&gt;&#xA;" OwnerUserId="5359" LastActivityDate="2017-02-25T01:26:53.053" Title="Peak Envelope Power (PEP) = Transmitter Power?" Tags="&lt;rf-power&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5327" PostTypeId="2" ParentId="5325" CreationDate="2015-09-23T17:02:16.787" Score="1" Body="&lt;p&gt;I haven't seen a description like that before, but it looks to me like it's just giving you a piecewise function for the envelope — that is, first you find the range in which the off-axis angle is in, then you compute the value using the formula for that range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, you would use the formula $ 29 - 25 \log \theta$ whenever $\theta$ is between 26.3 and 48 degrees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In these plots, they would not be using “azimuth” and “elevation” in the sense of the absolute orientation of the antenna, but rather to mean the off-axis angle in a specific direction (horizontal or vertical, respectively).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-09-23T17:02:16.787" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5328" PostTypeId="2" ParentId="5320" CreationDate="2015-09-23T22:07:32.540" Score="1" Body="&lt;p&gt;It all starts by determining the &lt;a href=&quot;https://en.wikipedia.org/wiki/Link_budget&quot; rel=&quot;nofollow&quot;&gt;link budget&lt;/a&gt;. According to your model and your system characteristics (i.e., bandwidth, frequency band, bit rate, antennas, etc.), the link may have different kinds of behaviors. For instance, the motion of the aircraft will produce Doppler effect, which might be important for high frequencies (e.g. S-band). Anyway, a Doppler effect combined with specular reflections of the radio wave on the communication environment results in a time varying communication channel, commonly described by its &lt;a href=&quot;https://en.wikipedia.org/wiki/Coherence_time_(communications_systems)&quot; rel=&quot;nofollow&quot;&gt;coherence time&lt;/a&gt;. Time varying channels are also referred to as fading channels. On the other hand, you may also encounter atmospheric effects, which come from the interaction of the radio wave with the particles on the atmosphere (so it depends on the frequency and the altitude of the spacecraft). So again, everything depends on your model. Sometimes these effects can be neglected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you can describe the behavior of the channel, then you can define a worse case scenario and determine the required link margin in order to cope with the fading events. The fading statistics of typical channels are known, so you can compute the probability of having a fading event larger than X dB. Having that, you can design your system to achieve a certain availability objective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ITU provides recommendations for the design of radio links. You may take a look at the ITU-R P.618-7 to get an idea (it is for an Earth-Space communication system), but possibly you may find something closer to your application.&lt;/p&gt;&#xA;" OwnerUserId="5362" LastActivityDate="2015-09-23T22:07:32.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5330" PostTypeId="2" ParentId="5318" CreationDate="2015-09-24T12:25:53.973" Score="0" Body="&lt;p&gt;I noticed this issue was solved on &lt;a href=&quot;http://chirp.danplanet.com/issues/2859&quot; rel=&quot;nofollow&quot;&gt;the Chirp issues forum&lt;/a&gt;, however without instructions. I might recommend posting what you did here, as the Baofeng family of radios has quirks that cause this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, just to offer insight, running something as root in Linux is akin to running programs as administrator in Windows. Root is the superuser, and should be the ONLY one on your system with permissions to make changes to it. Otherwise any user profile would be able to mess about willy nilly, which has obvious security concerns. &lt;/p&gt;&#xA;" OwnerUserId="5355" LastActivityDate="2015-09-24T12:25:53.973" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5332" PostTypeId="2" ParentId="5318" CreationDate="2015-09-24T14:29:29.003" Score="1" Body="&lt;p&gt;I ended up working with someone from chirp who took an image file from my radio and modified it to work. He said that my radio had been setup with an image for the 220 model radio. This was the second radio he'd done this for in 10 days. I'm not sure how someone would go about making the changes themselves. &lt;/p&gt;&#xA;" OwnerUserId="5332" LastActivityDate="2015-09-24T14:29:29.003" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5333" PostTypeId="1" AcceptedAnswerId="5432" CreationDate="2015-09-24T22:49:25.097" Score="2" ViewCount="128" Body="&lt;p&gt;I've been monitoring a signal locally on 159.150mhz (which is allocated for &quot;Civil Defense&quot;). I believe that this frequency is for the local tornado sirens and I would like to be able to decode the transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anybody have any ideas on what this signal could be and the steps I could take to decode it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the signal: &#xA;&lt;a href=&quot;https://soundcloud.com/spencer-neitzke/159-150a&quot; rel=&quot;nofollow&quot;&gt;Recording 1&lt;/a&gt;,&#xA;&lt;a href=&quot;https://soundcloud.com/spencer-neitzke/159-150b&quot; rel=&quot;nofollow&quot;&gt;Recording 2&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5366" LastEditorUserId="29" LastEditDate="2015-09-25T22:46:46.167" LastActivityDate="2015-10-22T14:24:58.877" Title="Identifying Local Signal" Tags="&lt;vhf&gt;&lt;signal-identification&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5334" PostTypeId="1" CreationDate="2015-09-25T03:19:13.443" Score="2" ViewCount="396" Body="&lt;p&gt;I am looking to get a handheld radio that does digital. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Requirements&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•The most open-source, tweak-able system that I can mess around with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•The lower end price wise&lt;/p&gt;&#xA;&#xA;&lt;p&gt;•A system that actually gets used, something that I will be able to talk to other digital friends on. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like every company has their own system, so which mode should I go with?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2015-09-26T21:59:47.217" LastActivityDate="2015-09-28T14:29:02.320" Title="Which Digital voice mode?" Tags="&lt;digital-modes&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5335" PostTypeId="1" CreationDate="2015-09-25T04:24:41.240" Score="1" ViewCount="255" Body="&lt;p&gt;I understand that half-wave dipole antenna, which is in far-field, impedance is around 73 ohms. If I keep same antenna in near-fied at distnace lambda/2 from the 1.25 lambda length tranmiter?&lt;/p&gt;&#xA;" OwnerUserId="4524" LastActivityDate="2015-09-25T04:24:41.240" Title="What will be antenna impedance of a dipole antenna when it is kept lambda/2 away from the transmitter" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;electronics&gt;" AnswerCount="0" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5336" PostTypeId="2" ParentId="5333" CreationDate="2015-09-25T06:33:59.403" Score="0" Body="&lt;p&gt;The first one sounds like standard 1200bps packet radio (AFSK). The second one sounds similar, but using slightly different frequencies.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-09-25T06:33:59.403" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5337" PostTypeId="2" ParentId="5334" CreationDate="2015-09-25T16:39:13.147" Score="1" Body="&lt;p&gt;Answer: It all depends.  No one system is clearly &quot;better&quot; technically and cost-wise IMO.  It's a network thing.  You need to know what your neighbor hams are adopting and (probably) go with that.  If you're the first in your area, you won't have anyone to talk to! At minimum, you need at least one active repeater in your area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Actually, the incompatibility of VHF digital systems is a pretty good reason to stick with tried and true analog FM, and save your cash until the dust settles, if it ever does.  In many areas, VHF activity is rather low.  It's a shame if the relatively small number of active users is split up into incompatible &quot;walled gardens&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, a digital system linked through the internet can open up the whole world to your handheld device.  Your choice!&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-09-25T16:39:13.147" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5338" PostTypeId="1" CreationDate="2015-09-26T17:31:57.883" Score="2" ViewCount="2084" Body="&lt;p&gt;I'm looking for the smallest/thinnest UHF or VHF two-way radio under $100. So far I've found:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Baofeng/Pofung UV-5R (current solution)&lt;/li&gt;&#xA;&lt;li&gt;Baofeng/Pofung BF-888S (102m x 51mm x 11.35mm)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.dhgate.com/product/new-radio-walkie-talkie-kst-k-888-uhf-400/250919228.html&quot; rel=&quot;nofollow&quot;&gt;KST K-888 (122mm x 55mm x 23mm)&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.aliexpress.com/item/MINI-Walkie-Talkie-TP-03-Single-Frequency-Single-Band-UHF-400-470MHz-2W-16CH-Portable-Two/32379893989.html?currencyType=USD&amp;amp;src=google&amp;amp;albch=shopping&amp;amp;acnt=708-803-3821&amp;amp;isdl=y&amp;amp;aff_short_key=UneMJZVf&amp;amp;albcp=206813665&amp;amp;albag=14156629225&amp;amp;slnk=&amp;amp;trgt=56128534817&amp;amp;plac=&amp;amp;crea=en32379893989&amp;amp;netw=&amp;amp;device=c&amp;amp;mtctp=&amp;amp;gclid=CKfyjZiclcgCFUJufgodEAsGOw&quot; rel=&quot;nofollow&quot;&gt;MINI TP-03 (86mm x 20mm x 46mm)&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Does anyone know of a smaller/thinner radio? Any recommendation for or against a listed radio would also be appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Note:&lt;/strong&gt; I haven't been able to find reliable dimensions for the BF-888S. Above are the &quot;official&quot; dimensions, but a YouTuber measured them to be 110mm × 50mm × &lt;strong&gt;32mm&lt;/strong&gt;, almost three times as thick.&lt;/p&gt;&#xA;" OwnerUserId="5046" LastActivityDate="2015-10-07T01:14:17.717" Title="Smallest / Thinnest UHF/VHF Mobile Transceiver under $100" Tags="&lt;transceiver&gt;&lt;ht&gt;&lt;mobile&gt;&lt;baofeng&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5339" PostTypeId="1" AcceptedAnswerId="5345" CreationDate="2015-09-27T16:25:00.080" Score="2" ViewCount="174" Body="&lt;p&gt;My brother (in Ohio) just passed his Technician test. We both have UV-5R equivalent radios. I have my General (in Colorado). Without physical modifications to our radios,  can we have a QSO? I've been looking into things like IRLP, but that looks like I'd have to lose my speaker. &lt;/p&gt;&#xA;" OwnerUserId="4171" LastEditorUserId="76" LastEditDate="2015-09-28T03:46:09.230" LastActivityDate="2015-10-04T15:37:06.040" Title="Colorado to Ohio with UV-5R" Tags="&lt;repeater&gt;&lt;vhf&gt;&lt;uv-5r&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5340" PostTypeId="1" AcceptedAnswerId="6031" CreationDate="2015-09-27T23:45:31.007" Score="6" ViewCount="332" Body="&lt;p&gt;I picked up a random piece of RF hardware at a flea market. I'd like to know what these unusual connectors on it are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The jack is flat on its face except for the gold ring. Inside the gold ring appear to be fingers gripping the central pin (which does not extend out of the connector). The plug's center contact is a helical spring which presses flat against the gold ring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The diameter of the threads is 17.4 mm outside the jack and 16.2 mm inside the plug (slightly larger than N or UHF connectors). The insulating gap is 11.8 mm and the outer diameter of the gold ring is 7.43 mm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ttscy.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ttscy.jpg&quot; alt=&quot;(oblique view)&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/8tcDF.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8tcDF.jpg&quot; alt=&quot;(face on)&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/US6aS.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/US6aS.jpg&quot; alt=&quot;(view into plug)&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The plug is actually an adapter to a BNC jack (which does suggest the possibility that these are not standard connectors at all); here's a picture of them fitted together:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uq5mU.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uq5mU.jpg&quot; alt=&quot;(assembled)&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The entire unit has two of these connectors, one N connector, and what looks like a mechanically tuned stub for somewhere above 900 MHz. I haven't been able to clearly determine any of its functionality yet.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-04-11T13:52:38.147" Title="What is this large, flat microwave coaxial connector?" Tags="&lt;connectors&gt;&lt;microwave&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5341" PostTypeId="2" ParentId="5339" CreationDate="2015-09-27T23:57:16.650" Score="0" Body="&lt;p&gt;There's no way to contact each other directly under normal conditions, as you probably realize.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Indirectly, you can use Internet-linked repeaters, such as with Echolink or IRLP.  One of you needs to find a local repeater that can link to a repeater in the other's area.  You would have to ask the repeater owners how to set that up.  Your two radios are each talking with local repeaters that happen to be cross-linked through the Internet.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With Echolink, you can hook up computer-to-computer, with no radios at all.  Sort of audio Skype for hams.  I suppose you're not looking for that!&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-09-27T23:57:16.650" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5342" PostTypeId="2" ParentId="5339" CreationDate="2015-09-28T13:37:55.500" Score="-1" Body="&lt;p&gt;Not really, not with those radios. The UV-5R is a VHF/UHF radio, and at those frequencies, radio propagates primarily via &lt;a href=&quot;https://en.wikipedia.org/wiki/Line-of-sight_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;line of sight&lt;/a&gt;. With the Earth being curved as it is, there's no way you could directly communicate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wanted a radio contact between Colorado and Ohio, you'll want HF. HF supports &lt;a href=&quot;https://en.wikipedia.org/wiki/Skywave&quot; rel=&quot;nofollow noreferrer&quot;&gt;skywave propagation&lt;/a&gt;, and so can travel worldwide in the right conditions. Colorado two Ohio should be a piece of cake on 20m most days.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could find some repeaters, one in Colorado, and one in Ohio, which are linked via the internet. Check out the &lt;a href=&quot;http://status.irlp.net/?PSTART=5&amp;amp;country=2&quot; rel=&quot;nofollow noreferrer&quot;&gt;IRLP repeater directory&lt;/a&gt;. If you can each hit one of these repeaters, then usually there's some DTMF incantation you send to tell the repeater to link. Talk to the club that operates the repeater to get the details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, if you wanted to make a contact over 1210 miles of data network, with radios providing the last 5 miles, you could use a couple of these, with a lot less fuss:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Bcl1r.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Bcl1r.jpg&quot; alt=&quot;it&amp;#39;s a cell phone.&quot;&gt;&lt;/a&gt;&lt;br/&gt;&#xA;&lt;em&gt;Rico Shen &lt;a href=&quot;http://www.gnu.org/copyleft/fdl.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;GFDL&lt;/a&gt;, &lt;a href=&quot;http://creativecommons.org/licenses/by-sa/3.0/&quot; rel=&quot;nofollow noreferrer&quot;&gt;CC-BY-SA-3.0&lt;/a&gt; or &lt;a href=&quot;http://creativecommons.org/licenses/by-sa/2.5/tw/deed.en&quot; rel=&quot;nofollow noreferrer&quot;&gt;CC BY-SA 2.5 tw&lt;/a&gt;, via Wikimedia Commons&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-09-28T13:37:55.500" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5343" PostTypeId="2" ParentId="5240" CreationDate="2015-09-28T14:21:45.513" Score="3" Body="&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/8VSB&quot; rel=&quot;nofollow&quot;&gt;8VSB&lt;/a&gt;, as used ATSC digital television, has a gross bit rate of 32 Mbit/s in a 6 MHz channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/IEEE_802.11ac&quot; rel=&quot;nofollow&quot;&gt;802.11ac&lt;/a&gt;'s fastest mode (1024-QAM) is capable of a gross bit rate of 1300 Mbit/s in a 160 MHz channel in each spatial stream, with up to 8 spatial streams. (I don't think any 8x8 MIMO APs are on the market yet, but surely someone's tried it in the lab.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are just two examples of ubiquitous digital modes which achieve high bit rates. There are undoubtedly modes used in scientific, military, and experimental applications which are orders of magnitude faster.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no upper physical limit besides that provided by the &lt;a href=&quot;https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem&quot; rel=&quot;nofollow&quot;&gt;Shannon-Hartley theorem&lt;/a&gt;. As long as I can do any of:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;buy more spectrum,&lt;/li&gt;&#xA;&lt;li&gt;transmit with a higher power,&lt;/li&gt;&#xA;&lt;li&gt;use a more directional antenna to reduce received noise, or&lt;/li&gt;&#xA;&lt;li&gt;put the receiver and transmitter closer together,&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;then I can cram more bits into the æther. The reason it's not done in practice is that at some point there ceases to be a need (do most people have a need for Wi-Fi that's faster than their wired network?) or it becomes more economically feasible to run a wire.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-09-28T14:21:45.513" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5344" PostTypeId="2" ParentId="5334" CreationDate="2015-09-28T14:29:02.320" Score="1" Body="&lt;p&gt;The only open-source digital voice mode with any significant adoption on the ham bands I'm aware of is &lt;a href=&quot;https://freedv.org/tiki-index.php&quot; rel=&quot;nofollow&quot;&gt;FreeDV&lt;/a&gt;. It's used with some regularity on HF, and some people are working on a constant envelope modem &lt;a href=&quot;http://www.rowetel.com/blog/?p=3856&quot; rel=&quot;nofollow&quot;&gt;for VHF use&lt;/a&gt;. The voice codec used is &lt;a href=&quot;http://www.rowetel.com/blog/?page_id=452&quot; rel=&quot;nofollow&quot;&gt;codec2&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-09-28T14:29:02.320" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5345" PostTypeId="2" ParentId="5339" CreationDate="2015-09-28T14:32:19.877" Score="2" Body="&lt;p&gt;As has already been said, your radios won't be able to contact each other directly outside of extremely unusual propagation conditions. So I'm going to address how “things like IRLP” work, since I see some confusion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea of IRLP, EchoLink, phone patches, and other such systems is that instead of just two radios:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/U4sCH.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fU4sCH.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;there is another radio, &lt;em&gt;not yours in this case&lt;/em&gt;, which transfers the audio signal to an Internet or telephone connection. That other radio is usually a repeater. Thus, the way things work in this case is:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/lKvci.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2flKvci.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You do &lt;em&gt;not&lt;/em&gt; need any special hardware. The case where you would is if you were trying to set up a linking node of your own — something which communicates on RF &lt;em&gt;and&lt;/em&gt; the Internet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All you &lt;em&gt;need&lt;/em&gt; is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;you both to be in range of repeaters which have compatible linking system.&lt;/li&gt;&#xA;&lt;li&gt;your HTs and their &lt;a href=&quot;https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling&quot; rel=&quot;nofollow noreferrer&quot;&gt;DTMF&lt;/a&gt; keypads, which are used to activate the link.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I can't advise you on exactly how to use the link, as I haven't used such systems myself. I would suggest that you ask the regular users of the repeater how to use it (and when it's polite to, and so on, since you would be occupying it for a while).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-09-28T15:14:24.830" LastActivityDate="2015-09-28T15:14:24.830" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5346" PostTypeId="2" ParentId="23" CreationDate="2015-09-28T16:15:59.637" Score="3" Body="&lt;p&gt;You might want to use a roll up antenna called the DBJ-2 from Ed Fong.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;See: &lt;a href=&quot;http://edsantennas.weebly.com/&quot; rel=&quot;nofollow&quot;&gt;http://edsantennas.weebly.com/&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a J-pole antenna.  I use one with my hand held and it works great!  If you email Ed I think you can get your sma female connector installed on it when it is built.  I think the antenna is about $28.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm using one with my radio shack HTX-202 radio.  I was told that my signal was clear with no noise.  It was a great improvement over the short antenna I was using.  So I'm talking from South San Jose to a Stanford repeater with no problems.  I like the thin coax that comes with the roll up antenna.  I just hang up the antenna from a book shelf and it dangles down to my desk.  Works like a champ.&lt;/p&gt;&#xA;" OwnerUserId="5379" LastActivityDate="2015-09-28T16:15:59.637" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5347" PostTypeId="1" CreationDate="2015-09-29T19:20:16.853" Score="1" ViewCount="55" Body="&lt;p&gt;To transfer maximum power from the secondary coil to the load, I need to find secondary coil impedance. My load impedance 5 - J365. I would design a matching circuit between load and secondary coil, if I know secondary coil transformer source impedance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone please share your thoughts?&lt;/p&gt;&#xA;" OwnerUserId="4524" LastEditorUserId="4524" LastEditDate="2015-10-01T23:00:40.687" LastActivityDate="2015-10-01T23:00:40.687" Title="Transformer secondary coil impedance" Tags="&lt;transceiver&gt;&lt;rf-power&gt;&lt;impedance&gt;&lt;electronics&gt;" AnswerCount="0" CommentCount="5" ClosedDate="2015-10-01T16:54:58.607" ContentLicense="CC BY-SA 3.0" />
  <row Id="5348" PostTypeId="2" ParentId="5338" CreationDate="2015-10-01T18:04:44.150" Score="2" Body="&lt;p&gt;The Baofeng UV-3R and UV-3R+ are both quite a bit smaller than the UV-5R or BF-888S.  The UV-3R+ uses the same programming cable as your UV-5R, if that matters to you.&lt;/p&gt;&#xA;" OwnerUserId="5396" LastActivityDate="2015-10-01T18:04:44.150" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5349" PostTypeId="1" CreationDate="2015-10-01T21:50:59.410" Score="2" ViewCount="968" Body="&lt;p&gt;I've recently obtained a Quad Loop antenna for 2 m and 70 cm that's fed through gamma match, as shown in the picture:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FVI8C.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FVI8C.jpg&quot; alt=&quot;Photo of gamma match section in YZ plane&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The shorter metal bars are connected to the hot side of the BNC, while the longer assembly is connected to the ground of the BNC. Screws are made of dielectric material.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a photo of the whole antenna:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/jb2Fs.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jb2Fs.jpg&quot; alt=&quot;Photo of the antenna in XY plane]&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's drawing of the whole antenna. The connector and matching section is on top of the parallelogram part of the antenna and is on the left side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Azmcd.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Azmcd.png&quot; alt=&quot;Diagram of the antenna with matching section and connector shown in XY plane&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wWlSC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wWlSC.png&quot; alt=&quot;Diagram of the antenna with matching section and connector shown in YZ plane&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On these (not to scale!)diagrams, the BNC connector in in red, the antenna assembly that connects to the connector's ground side is in black, the assembly that connects to the connector's hot side is in orange, the screws are in brown. The orange and black parts are not directly connected, it's just that I don't know how to draw good 3D shapes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The instruction manual says that I'm supposed to adjust the distance between the two parts and then secure both parts with screws when correct distance has been determined. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is: How do I adjust the distance using an SWR meter? More explicitly, how do I determine if I should increase or decrease the distance between the two components? Is there a rule of thumb, like the rule for short/long dipoles, for this case? How do I take into account two bands? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: Link to the manual was requested in comments, so &lt;a href=&quot;http://www.wimo.com/download/fensterq.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; it is. &lt;a href=&quot;http://www.hummelmasten.de/index.php?id=52&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt;'s the manufacturer's webpage about the antenna, but it only provides specifications, such as mass, wind load, radiation angles and so on. Since the manual is on German only, here's a translation:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Assembly and adjustment  &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The attachment of the antenna is possible in all polarization modes on&#xA;  a smooth, non-conductive surface with the two suckers. The window pane&#xA;  offers the best HF position! A suspension at the corner (diamond&#xA;  shape) often brings good results. SWR setting: Unscrew the plastic&#xA;  isolator screws, change the plate spacing and turn the screw back in.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Description  &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The antenna is a full-wave loop (quad-loop), available as monoband&#xA;  antenna for 2m or 70cm, or as a duo antenna for both bands. The gain&#xA;  is about 1 dBD. The individual parts are connected via fatigue-free&#xA;  special joints. One of the connections is a metal push button so that&#xA;  the antenna can be very small. The SWR adjustment is easy to make with&#xA;  a plastic screw. The antennas are attached to the window pane with two&#xA;  oversized suckers; Depending on the suspension, operation is possible&#xA;  either with horizontal or with vertical polarization.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Photo of the connector:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/8hneG.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8hneG.jpg&quot; alt=&quot;Image of the center connector&quot;&gt;&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are 3 versions of the antenna that I have: 2 m version, 70 cm version and the dual-band version. The sections marked as 70 cm and 2 m on the image are the sections that appear on the mono-band versions of the antenna. They are connected to the center pin of the BNC connector. The big frame is connected to the ground of the BNC.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2017-06-15T14:50:04.467" LastActivityDate="2017-06-16T00:25:17.410" Title="Is it possible to determine if I'm adjusting gamma match in correct direction with an SWR meter and if yes, how?" Tags="&lt;antenna-construction&gt;&lt;2m-band&gt;&lt;70cm-band&gt;&lt;loop-antenna&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="5350" PostTypeId="1" AcceptedAnswerId="5351" CreationDate="2015-10-01T23:17:59.827" Score="6" ViewCount="181" Body="&lt;p&gt;The regulations that govern Amateur Radio in the United States are often described as Part 97.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What statute are they a part of? Where can I find other parts of the same law?&lt;/p&gt;&#xA;" OwnerUserId="3043" LastEditorUserId="8573" LastEditDate="2018-12-13T18:53:49.470" LastActivityDate="2018-12-13T18:53:49.470" Title="What is Part 97 a part of?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="5351" PostTypeId="2" ParentId="5350" CreationDate="2015-10-01T23:17:59.827" Score="6" Body="&lt;p&gt;The full name is 47 CFR (Code of Federal Regulations) 97. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find other parts that radio transmissions are regulated by &lt;a href=&quot;https://www.fcc.gov/encyclopedia/rules-regulations-title-47&quot; rel=&quot;nofollow noreferrer&quot;&gt;on the FCC's website&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="3043" LastEditorUserId="3043" LastEditDate="2016-12-05T23:33:22.577" LastActivityDate="2016-12-05T23:33:22.577" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5352" PostTypeId="2" ParentId="986" CreationDate="2015-10-02T03:44:45.357" Score="0" Body="&lt;p&gt;220mhz is supported by the RDA1846S chip used in many HT designs. Hobbypcb has the Radio Shield RS-UV3 that supports 2m, 1.25m and 70cm. Yes all the radio manufacturers can make 1.25m but the market is smaller than the whole market.  That's why a chip like this should help get the bigger players not to have excuses in adding 1.25m. So please keep asking and hopefully they will listen. In the meantime Chinese radio manufacturers are supporting 1.25m. &#xA;KM4ESU &lt;/p&gt;&#xA;" OwnerUserId="5397" LastActivityDate="2015-10-02T03:44:45.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5353" PostTypeId="2" ParentId="5333" CreationDate="2015-10-03T00:04:57.553" Score="0" Body="&lt;p&gt;Many affordable USB Software Defined Radios (SDRs) may be able to help you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.adafruit.com/products/1497&quot; rel=&quot;nofollow&quot;&gt;https://www.adafruit.com/products/1497&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You would likely need a free tool called &quot;Zadig&quot; to get the drivers working. And there are many blogs such as &lt;a href=&quot;http://www.rtl-sdr.com/&quot; rel=&quot;nofollow&quot;&gt;http://www.rtl-sdr.com/&lt;/a&gt; which offer reviews of software tools for decoding various signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It wasn't clear from your question what sort of setup you're using to capture the signals, but getting them into the computer would likely be the first step to decoding them.&lt;/p&gt;&#xA;" OwnerUserId="5046" LastActivityDate="2015-10-03T00:04:57.553" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5354" PostTypeId="1" CreationDate="2015-10-03T19:07:05.317" Score="1" ViewCount="297" Body="&lt;p&gt;I just started an Amateur Radio Club at our High School (KE0FXH)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our school is not a technical school (it is an arts school) and I am trying to find activities to get students interested in ham radio and technology.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far, I ran a foxhunt, we built a mini repeater out of two old wideband 440 radios and a raspberry pi, and I plan on experimenting with packet for all of the kids who are interested in computers. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What other projects / activities make good ham radio clubs?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am the only kid there in the 4-6 member club who has electronic experience, and I am thinking along the lines of basic electronics for ham radio. The budget is also very limited, its an entirely student funded club plus whatever donations we get.  &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-10-03T19:07:05.317" Title="Activities for High School ham radio club" Tags="&lt;diy&gt;" AnswerCount="0" CommentCount="1" ClosedDate="2015-10-03T19:19:11.777" ContentLicense="CC BY-SA 3.0" />
  <row Id="5355" PostTypeId="1" CreationDate="2015-10-03T23:54:12.880" Score="3" ViewCount="280" Body="&lt;p&gt;I recently bought a Techsun PL-660 radio and it picks up virtually nothing on SW. I fear I may have a dud.&lt;/p&gt;&#xA;" OwnerUserId="5411" LastEditorUserId="76" LastEditDate="2015-10-04T00:58:46.977" LastActivityDate="2018-03-06T18:03:26.673" Title="What are some shortwave radio stations I ought to reliably receive in New Hampshire?" Tags="&lt;hf&gt;&lt;receiver&gt;&lt;swl&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5356" PostTypeId="5" CreationDate="2015-10-04T01:01:00.360" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-10-04T01:01:00.360" LastActivityDate="2015-10-04T01:01:00.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5357" PostTypeId="4" CreationDate="2015-10-04T01:01:00.360" Score="0" Body="Questions about the practice of, and legal requirement to, identify your transmissions using your call sign." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-10-04T01:01:00.360" LastActivityDate="2015-10-04T01:01:00.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5358" PostTypeId="2" ParentId="532" CreationDate="2015-10-04T13:08:07.897" Score="1" Body="&lt;p&gt;I have had my two dipoles up now for 3 years with .105 trimmer line. I just inspected them and there is no sign of wear; still strong with no sign of deterioration. I think I should get at least 8-10 years from the .105 gauge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just make sure it is secured to the insulator. I wrap it twice through the hole, then tie one knot, then wrap. Finally use tie wraps and high quality electrical tape.&lt;/p&gt;&#xA;" OwnerUserId="5414" LastEditorUserId="76" LastEditDate="2015-10-06T22:04:29.580" LastActivityDate="2015-10-06T22:04:29.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5359" PostTypeId="1" CreationDate="2015-10-04T15:31:41.933" Score="5" ViewCount="16377" Body="&lt;p&gt;I have a headphone and a cellphone that has built-in FM radio, and the headphone acts as the radio antenna.&#xA;but my problem is the radio stations I listen to are very far from my place,&#xA;good thing there are some position where the sound is very clear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have 5 favorite station whom I listen to which are at the same place (that means they're all far from me) and I often switch to each one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BAD THING is... each station has its OWN &#xA;position for it to give a clear sound so if I want to &#xA;switch to another frequency then I need to change the position to another which is very exhausting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wanna know if there is still hope to fix this thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I listen using the headphone's speaker not in loudspeaker (just saying).&lt;/p&gt;&#xA;" OwnerUserId="5417" LastEditorUserId="76" LastEditDate="2017-06-07T19:47:55.853" LastActivityDate="2019-08-12T21:18:24.963" Title="How to improve reception with a headphone-cord antenna?" Tags="&lt;antenna&gt;&lt;receiver&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5360" PostTypeId="2" ParentId="5339" CreationDate="2015-10-04T15:37:06.040" Score="3" Body="&lt;p&gt;Use the satellite SO-50 when it passes over. You need nothing more than what you have now, although improved antennas would help tremendously.&lt;/p&gt;&#xA;" OwnerUserId="5418" LastActivityDate="2015-10-04T15:37:06.040" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5361" PostTypeId="2" ParentId="5195" CreationDate="2015-10-04T15:46:40.190" Score="0" Body="&lt;p&gt;If that antenna is built properly it is fine. I have worked so-50 down to about 16 degrees with an antenna just like that and a 5w handheld. I would also bet doppler shift is your issue. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember to move the antenna slowly once you hear some signal, very small adjustments are all that it takes to go from nearly full quieting to just noise. Good luck - it does take a few tries to get it right.&lt;/p&gt;&#xA;" OwnerUserId="5418" LastActivityDate="2015-10-04T15:46:40.190" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5362" PostTypeId="2" ParentId="5359" CreationDate="2015-10-04T16:14:03.217" Score="2" Body="&lt;p&gt;I don't have one of that style of receiver (headphone cord as antenna) to test with, but here's what comes to mind as easy to do:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Get a headphone splitter / 3.5 mm Y cable.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you have an extension/patch cable you can plug into the splitter, you can use that; if you have access to parts, get a 3.5 mm plug with no cable, and a length of plain wire, and attach the wire to the ring (ground/outside shell) contact of the plug.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Plug in your headphones and the extra wire into the two jacks of the splitter, and the splitter into the radio.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The extra wire should have some effect on the reception. Rearrange it, hang it up high in the air (vertically), and so on until you get reception you find adequate for all stations. Remember that your body also has an effect, so try to hang it up somehow and step away before evaluating the result. (You can change the effective length of the wire without cutting it by tightly coiling the free end.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Once you have a result you like, tie down the wire so it'll stay where you put it and you're done.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The positioning of the headphone cord will still have an effect on reception, but hopefully it will be lesser, and may be more like missing just one of the five stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What we're doing here is creating a second antenna. By moving it away from your body, it should function better, hopefully picking up all five stations strongly enough for your receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, for the best results we would want a carefully designed antenna, but we'd need to know the characteristics of the receiver input and possibly build a matching network for it, and I figure that's more trouble than you're looking for. After all, the most straightforward way to get better reception is to get a radio with a proper antenna (or antenna jack).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-10-04T16:14:03.217" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5363" PostTypeId="1" CreationDate="2015-10-04T07:16:42.600" Score="1" ViewCount="99" Body="&lt;p&gt;I have a Drake transceiver. I want to replace the valves in the final output stage. The valve in question is a 6jb6.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was told by elmers that the valves need to be preheated (cooked) before replacement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the logic behind this, and is it essential?&lt;/p&gt;&#xA;" OwnerDisplayName="vu3uno-kk" LastEditorUserId="76" LastEditDate="2015-10-04T20:07:47.530" LastActivityDate="2015-10-04T23:43:51.083" Title="Is preheating required before replacing an old valve?" Tags="&lt;amplifier&gt;&lt;repair&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5364" PostTypeId="2" ParentId="5363" CreationDate="2015-10-04T23:43:51.083" Score="2" Body="&lt;p&gt;The process is called degassing.  This is done to prevent arcing in high voltage transmitting (power amplifier) tubes.  It is not as important for lower voltage tubes but I am sure if done correctly no harm should result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To degas you preheat the tube when it has been inactive or in storage for a long period of time.  Residue of gas is removed or absorbed by getters (elements such as zirconium placed in the tube to absorb gasses). As a result of degassing, the cathode regains its optimal emission. If that is omitted, there is a greater risk of arcing (flashover) between anode and other internal connections.  Preheating can be done using the tube's heater filaments for a period of time prior to applying high voltage to the anode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a number of resources on the Internet that describe the methods and why it needs to be done.  I myself have actually never done it.  See W8JI's web site: www.w8ji.com.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-10-04T23:43:51.083" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5365" PostTypeId="1" CreationDate="2015-10-05T14:31:34.287" Score="3" ViewCount="948" Body="&lt;p&gt;Theoretically free space loss is independent of the height of the transmitting and receiving antenna.&#xA; However when link loss is calculated in ground to air v/UHF communication, the link loss varies with the airborne receiving  height of the antenna.&#xA; With transmitting antenna on ground at constant height, as the receiving antenna height increases, the losses are reduced. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to know what is the reason for decrease in losses as the receiving antenna height increases. This phenomena is observed as per various propagation models.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can one please explain the actual physics behind this ?&lt;/p&gt;&#xA;" OwnerUserId="5349" LastActivityDate="2015-10-27T13:56:12.873" Title="Why link losses are more as the antenna height decreases in ground to air communication, in v/UHF bands?" Tags="&lt;path-loss&gt;" AnswerCount="4" CommentCount="3" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5366" PostTypeId="2" ParentId="5365" CreationDate="2015-10-05T17:11:11.460" Score="0" Body="&lt;p&gt;An easy way to think of it uses an analogy and a laser, a target, and an apple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you point a laser at an apple, you see the point on the apple, and the target never sees the laser.  If you increase the altitude of the laser, the point eventually passes the apple and shines to the laser.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a nice way to imagine the &lt;em&gt;radio horizon&lt;/em&gt;.  The radio horizon is the point at which your signal is blocked by the earth.  The higher your antenna is, the further out this point it.&lt;/p&gt;&#xA;" OwnerUserId="5404" LastActivityDate="2015-10-05T17:11:11.460" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5367" PostTypeId="1" CreationDate="2015-10-05T20:57:44.097" Score="4" ViewCount="876" Body="&lt;p&gt;I am designing a 1.25-wavelength dipole antenna with the 4nec2 software. What I noticed is that the input impedance of antenna is changing greatly when I change the number of segments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How many segments should I choose?&lt;/p&gt;&#xA;" OwnerUserId="4524" LastEditorUserId="8717" LastEditDate="2019-11-05T21:36:07.670" LastActivityDate="2019-11-05T21:36:07.670" Title="Correct number of elements in 4nec2 antenna simulation" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5368" PostTypeId="2" ParentId="5359" CreationDate="2015-10-05T23:09:01.800" Score="1" Body="&lt;p&gt;I always try to get a headphone or earbuds that have long cables. The longer the cable, the better the reception. It also helps to stretch the cable as much as you can if the cables are sort of bunched up. Also, for me on my MP3 player, reception is best once the screen turns off. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the unique areas, there's really not much you can do. I'd try to get to the highest ground possible and test my luck there. Hope this helps!&lt;/p&gt;&#xA;" OwnerUserId="5425" LastActivityDate="2015-10-05T23:09:01.800" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5369" PostTypeId="1" CreationDate="2015-10-06T00:07:32.417" Score="1" ViewCount="165" Body="&lt;p&gt;Measurement 20dbm + 20 db attenuator, what is the actual power of rf source&lt;/p&gt;&#xA;" OwnerUserId="5349" LastActivityDate="2015-11-05T02:12:55.167" Title="If i measure a rf source as 20 dBm in spectrum analyser inline with 20db attenuator, what is the actual power generated by rf sorce" Tags="&lt;measurement&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5370" PostTypeId="2" ParentId="5365" CreationDate="2015-10-06T00:52:14.063" Score="4" Body="&lt;p&gt;&lt;strong&gt;&lt;em&gt;UNDER CONSTRUCTION!!!&lt;/em&gt;&lt;/strong&gt;&lt;br&gt;&#xA;A this answer is in need of a considerable edit, so please do not take it into account until it has been fixed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems to me as if you're referring to the &lt;a href=&quot;https://en.wikipedia.org/wiki/Two-ray_ground-reflection_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;two-ray&lt;/a&gt; propagation model, sometimes called signal ground bounce problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The concept is relatively simple: You have one ray going from the antenna to the receiver and you have another ray going from the antenna into ground, bouncing off it and then reaching the receiver. Changing antenna heights and distance will affect the influence of the reflected wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JHqy1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JHqy1.png&quot; alt=&quot;Ground bounce illustration&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the reflected signal is received by the receiver, the electrical fields add together as complex numbers, so we get something like:&#xA;$$E_{Rx}=E_{LOS}+E_{NLOS}=E_{LOS}e^{j(\phi+kd_{LOS})}+E_{NLOS}e^{j(\phi+kd_{NLOS}) } \qquad(0)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the two paths are of different length, it will take different time for the signal to cross them and this will create phase difference between the two signals. Since the carrier frequency is much higher than the information frequency, there will not be a significant difference between wavefronts that are integer number of wavelengths away from one another. The result is that, depending on the phase difference, the direct and reflected signals can add up or they can cancel out. The phase difference depends on the differences in distances traveled, so we need to go to the derivation for traveled distances. Do note that the reflected path will have greater free-space attenuation, but usually this effect is considered to be minor and not taken into account. Also it is assumed that ground distance is greater than the height difference between antennas and that ground reflection coefficient is -1. I'll point out when we take this into consideration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The classical derivation for length differences uses triangles for calculation of path lengths. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the line-of-sight path, the triangle is created by the top of Tx antenna, the top of Rx antenna and by the virtual ground, so we get the purple triangle here:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/nGAXl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nGAXl.png&quot; alt=&quot;LOS path triangle&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This gives us formula for the line-of-sight path:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$d_{LOS}=\sqrt{ ({h_{Rx}-h_{Tx}})^2+d^2} \qquad(1)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then for the non-line-of-sight path we have following triangle and formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SwZn8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SwZn8.png&quot; alt=&quot;non-LOS triangle&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formula for distance is:&#xA;$d_{NLOS}=\sqrt{ ({h_{Rx}+h_{Tx}})^2+d^2} \qquad(2)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, we need the formula for the difference of those two distances. It's simply:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$d_{\Delta}=\sqrt{ ({h_{Rx}+h_{Tx}})^2+d^2}-\sqrt{ ({h_{Rx}-h_{Tx}})^2+d^2}\qquad(3)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So our answer is hidden somewhere in this formula for difference of distances. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further derivation makes this very obvious, so let's take a look at it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, we re-write the formula by taking ground distance outside of the square roots:&lt;br&gt;&#xA;$d_{\Delta}=d(\sqrt{ (\frac{h_{Rx}+h_{Tx}}{d})^2+1}-\sqrt{ (\frac{h_{Rx}-h_{Tx}}{d})^2+1})\qquad(4)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, we apply Taylor series approximation to the formula, so we take $(1+x)^n=1+nx \qquad(5)$ so we get:&#xA;$d_{\Delta}=d(\frac{1}{2}({ (\frac{h_{Rx}+h_{Tx}}{d})^2+1})- \frac{1}{2}({ (\frac{h_{Rx}-h_{Tx}}{d})^2+1}))\qquad(6)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$d_{\Delta}=\frac{d}{2}(({ (\frac{h_{Rx}+h_{Tx}}{d})^2+1})- ({ (\frac{h_{Rx}-h_{Tx}}{d})^2+1}))\qquad(7)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$d_{\Delta}=\frac{d}{2}(({ \frac{h_{Rx}^2+2h_{Rx}h_{Tx} + h_{Tx}^2}{d^2}+1})- ({ \frac{h_{Rx}^2-2h_{Rx}h_{Tx} + h_{Tx}^2}{d^2}+1}))\qquad(8)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$d_{\Delta}=\frac{d}{2}({ \frac{h_{Rx}^2+2h_{Rx}h_{Tx} + h_{Tx}^2}{d^2}+1}- { \frac{h_{Rx}^2-2h_{Rx}h_{Tx} + h_{Tx}^2}{d^2}-1})\qquad(9)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$d_{\Delta}=\frac{d}{2}({ } { \frac{+4h_{Rx}h_{Tx} }{d^2}})\qquad(10)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We finally get:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$d_{\Delta}= { \frac{2h_{Rx}h_{Tx} }{d}}\qquad(11)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So we now should use this in the received electrical field equation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$E_{Rx}=E_{LOS}|1-e^{jk\frac{2h_{Rx}h_{Tx} }{d}}|\qquad(12)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Received power density is:&lt;br&gt;&#xA;$$S_{Rx}=\frac{E_{Rx}^2}{Z_{F0}}=\frac{E_{LOS}^2}{Z_{F0}}|1-e^{jk\frac{2h_{Rx}h_{Tx} }{d}}|^2\qquad(13)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This gives us received power of:&#xA;$P_{Rx}=S_{Rx}A_{eff}=\frac{E_{LOS}^2}{Z_{F0}}{|1-e^{jk\frac{2h_{Rx}h_{Tx} }{d}}|}^2\frac{\lambda^2}{4 \pi}\qquad(14)$, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I'll have to do a bit of handwaving and magically introduce the formula for power density of a plane wave at distance d:&lt;br&gt;&#xA;$$S_{d}=\frac{E_{LOS}^2}{Z_{F0}}=\frac{P_{LOS}}{4d^2 \pi}\qquad(15)$$&#xA;which gives us transmitted power of:&#xA;$$P_{LOS}=\frac{E_{LOS}^2}{Z_{F0}}{4d^2 \pi}\qquad(16)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now finally we can get to the path loss formula. For some reason I do not fully understand, it's defined as ratio of radiated and received power. Since that's a bit counter intuitive for me, I'll use inverse of path loss instead. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So:&lt;br&gt;&#xA;$$\frac{1}{L}=\frac{P_{Rx}}{P_{LOS}}= \frac {\frac{E_{LOS}^2}{Z_{F0}}{|1-e^{jk\frac{2h_{Rx}h_{Tx} }{d}}|}^2\frac{\lambda^2}{4 \pi}}    {\frac{E_{LOS}^2}{Z_{F0}}{4d^2 \pi}}={(\frac{\lambda}{4 \pi d})}^2{|1-e^{jk\frac{2h_{Rx}h_{Tx} }{d}}|}^2\qquad(17)$$&#xA;Some trigonometry gives us:&#xA;$$\frac{1}{L}={(\frac{\lambda}{4 \pi d})}^2 2(1- \cos(k\frac{2h_{Rx}h_{Tx} }{d}))\qquad(18)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This cosine is important, because due to it, we have the behavior which we can see for example in Rec. ITU-R P.528-3 figure 1-1 b) below radio-horizon distance. We have a small part where we have almost free-space propagation, then we have a wobbly part and then we have rapid drop until we come to the radio-horizon, after which we have even more rapid drop. The free-spaceoid part is before we actually get effects of ground bounce, then we have area with both constructive and destructive interference and then we have part where drop normalizes a bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also worth mentioning that in many calculations, the cosine is simplified even further, but in this case, I believed that it might not always be justified, so I left it unsimplified. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Entire $\frac{2h_{Rx}h_{Tx} }{d}\qquad(19)$ expression takes into account the height behavior, so I first do not believe that just simply increasing the antenna height will in all cases be helpful. I think that, using the abovementioned ITU recommendation as an example, we just tend to notice that behavior due to plotted data points. I did some calculations and for say distance of 800 km, one antenna height of 10 km and other antenna height going from 1.5 m to 10 km I made a plot of changing height of one antenna versus the path loss. As  it can be expected from the formula, the function is periodic and has positive and negative peaks. Do note that my calculations are a bit over-optimistic, since I only used the path loss formula and did not pay attention to the rest of the stuff included in the recommendation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3j25U.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3j25U.jpg&quot; alt=&quot;Loss versus antenna height from 1.5 m to 10 km&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a zoomed version of the plot, where we can see heights from 1.5 m to 400 m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/is7TU.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/is7TU.jpg&quot; alt=&quot;Loss versus antenna height from 1.5 m to 400 m&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So all plotted values in the ITU rec are near the peak and one above the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let me try to sum this up:&#xA;If we fix one antenna height and the ground distance and let the other antenna move up and down, we have lower loss due to two effects: With increase of height, the reflected signal has greater free -space loss, which is a small contribution, and due to change of antenna heights we change the phase difference, which has major contributions on the loss.  &lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2015-10-26T15:22:05.497" LastActivityDate="2015-10-26T15:22:05.497" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="5371" PostTypeId="2" ParentId="5369" CreationDate="2015-10-06T02:11:02.403" Score="2" Body="&lt;p&gt;40 dBm - 20 dB  = 20 dBm&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So your input is +40 dBm (10 Watts).&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-10-06T02:11:02.403" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5372" PostTypeId="2" ParentId="5365" CreationDate="2015-10-06T02:18:44.717" Score="0" Body="&lt;p&gt;The two-ray issue would cause an interference pattern as seen at different elevation angles.  (See info on &lt;a href=&quot;https://en.wikipedia.org/wiki/Lloyd&amp;#39;s_mirror&quot; rel=&quot;nofollow&quot;&gt;Lloyd's Mirror&lt;/a&gt;)  This might or might not affect you (or even help you), depending on your exact geometry (launch angle).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Real grounds are lossy.  I would expect greater ground losses as your antenna is closer to the ground.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-10-06T02:18:44.717" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5373" PostTypeId="2" ParentId="5359" CreationDate="2015-10-06T04:14:09.110" Score="3" Body="&lt;p&gt;Plug in a USB cable, and stretch it out in the opposite direction as the headphones cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or place the phone on a large metal object - a stove, car, sheet of tinfoil - and extend the headphone cord away from that object.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Headphone cords are used as an antenna by separating the wires from the phone body, at radio frequencies, with inductors, or a small cross-over network or diplexer if you like.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately although the headphone wires are a good length, very close to a quarter wave in fact, the other half of the antenna is the phone body, which is still quite small. This can be improved a lot with the USB cable, which doesn't need to be plugged into anything else, or by the capacitive coupling to the large metal object.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-10-06T04:14:09.110" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5374" PostTypeId="2" ParentId="5367" CreationDate="2015-10-06T04:22:54.733" Score="1" Body="&lt;p&gt;Generally in NEC2, 10 segments per wavelength is good, so 12 or 13 segments depending on where you want your feed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you are doing better than just  following the rule, investigating the effect of the number of segments!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd suggest trying 4, 6, 8, 10, 15, 20, 30 segments per wavelength and comparing the results. The impedance should be pretty constant from 10 to 30. If not, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Watch out for all the other rules too.  Segment length to diameter - they must not be too fat; Length to length ratios - joining long and short segments; radius step changes, joining at too narrow an angle so they overlap too much; small loops are difficult in NEC, etc etc.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-10-06T04:22:54.733" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5375" PostTypeId="1" AcceptedAnswerId="5376" CreationDate="2015-10-06T11:58:48.593" Score="9" ViewCount="326" Body="&lt;p&gt;I want to find out why, say in a GSM/cellular system, a base station can be up to 50 watts however the mobile units can be only 100mw (for example).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Surely if the base station ever uses 50w to reach a mobile at long range, the mobile will have no chance to transmit back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that on a base station receiver tech is perhaps more sophisticated / bigger and better then on a mobile unit, but why would there be such a large difference in max power? - why not limit the base stations to 5 watts or such?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: Only using GSM as an example, but question stands for any technology. Here is what I think I know already:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Difference between a 1W mobile and 50W base station is 17 dB.&lt;/li&gt;&#xA;&lt;li&gt;Base Station Diversity can add up to 5-6 dB gain, which would balance a 1W mobile to a ~4w basestation&lt;/li&gt;&#xA;&lt;li&gt;MIMO is on both sides, so this would be roughly equal gain and so would probably not be relevant in this topic (although the BTS with its larger antennas + better spacing may be able to get a few more dB gain).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Is the antenna technology in the base station that much better - they are larger, higher, and directional...&lt;/p&gt;&#xA;" OwnerUserId="5427" LastEditorUserId="5427" LastEditDate="2015-10-07T07:43:51.263" LastActivityDate="2015-10-07T07:43:51.263" Title="Why bother to have a high power base station when mobile units are generally low-power?" Tags="&lt;rf-power&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5376" PostTypeId="2" ParentId="5375" CreationDate="2015-10-06T14:49:00.063" Score="6" Body="&lt;p&gt;The link is actually balanced, because the base station receiver has &lt;em&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/Antenna_diversity&quot;&gt;diversity gain&lt;/a&gt;&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2G and 3G cellular systems use two antennas at the base station (for each coverage direction). They are either spaced a few metres apart, or more commonly, +45 and -45 degree polarisation, in the same housing. With two antennas and two receivers, the base station has a much greater probability of receiving the handset, above some threshold. If one antenna is in a null, the other might not be.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The base station also transmits from one of the antennas. Your phone doesn't have two antennas, so can't use diversity to increase its probability of receiving the signal. But the base station transmits a lot more power, and this compensates somewhat for the lack of diversity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The phone is about 1W, but if it's close to the base station, it may be instructed to turn down its power, to save battery and to balance all the mobile signals at the base station receiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Diversity is related to MIMO, but is not the same thing. A diversity receiver &lt;em&gt;selects&lt;/em&gt; the best signal from the two antennas. A MIMO receiver &lt;em&gt;combines&lt;/em&gt; the two signals in the optimum way.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-10-07T06:19:42.917" LastActivityDate="2015-10-07T06:19:42.917" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="5377" PostTypeId="1" CreationDate="2015-10-06T16:52:19.287" Score="8" ViewCount="749" Body="&lt;p&gt;I am trying to find near field mutual coupling affects between two antennas - one being transmitter and other being receiver. The receing antenna is fed with very little voltage (I think, if I don't feed any source, then nec tool inserts default source). The problem I see is that nec tool does not show input impedance of individual antennas. Both antennas are kept half-wave length apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/P5cMX.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/P5cMX.png&quot; alt=&quot;Impedance&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/M72cu.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/M72cu.png&quot; alt=&quot;physical dimensions&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0OyFS.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0OyFS.png&quot; alt=&quot;sources&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4524" LastEditorUserId="8717" LastEditDate="2019-11-05T21:40:39.013" LastActivityDate="2019-11-05T21:40:39.013" Title="Simulating two antennas (transmitter and receiver) using 4nec2 tool" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;antenna-modeling&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5378" PostTypeId="1" AcceptedAnswerId="5379" CreationDate="2015-10-06T19:03:36.910" Score="3" ViewCount="2334" Body="&lt;p&gt;I volunteer with the local search and rescue group as a team medic and a radio operator. The team is new and recently decided to go with the Garmin 64st as our go-to GPS units. Those of us with licenses use the cheaper Baofeng UV-5R and BF-8HP radios. I was volun-told to look into pairing our GPS to the radios for APRS use. I’ve searched around and haven’t found any definitive information, although from what I could find, I gather that NMEA is needed on the GPS to make it work, which our units do have. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to know if it’s possible to use the two together, and if so, how.&lt;/p&gt;&#xA;" OwnerUserId="5428" LastEditorUserId="76" LastEditDate="2019-03-13T01:46:04.017" LastActivityDate="2019-03-13T01:46:04.017" Title="How do I connect a GPS receiver to a radio for APRS?" Tags="&lt;baofeng&gt;&lt;aprs&gt;&lt;gnss&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5379" PostTypeId="2" ParentId="5378" CreationDate="2015-10-06T20:26:02.903" Score="1" Body="&lt;p&gt;&lt;em&gt;Disclaimer: I have no experience with any of the below matters; I'm just writing an explanation of what I've heard.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neither your radio nor your GPS unit knows how to encode APRS packets. Therefore you will need to add a device which does, and will also perform the other control/interface functions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, a hardware device which encodes and AFSK-modulates (and in cases other than this, also decodes) APRS packets is known as a TNC, or a tracker for the specific case of sending position reports.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's an example of a product that you could use: &lt;a href=&quot;http://www.byonics.com/tinytrak/&quot; rel=&quot;nofollow&quot;&gt;Byonics TinyTrak3&lt;/a&gt;. &lt;strong&gt;I am not recommending this product;&lt;/strong&gt; it's just one that I remember people talking about (I haven't personally used such devices).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since your radios don't know about APRS and don't have an external control interface, you will necessarily be transmitting your position reports on the same frequency as your voice communication (unless you're using a separate radio for APRS). This isn't a critical problem (and CTCSS can be used to mute the data packets for listeners), it just means a little more activity, and that your packets won't go onto the regular APRS network unless you set up your own digipeater or IGate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that one of the features of the product I linked is “Burst after voice / Send Position Now input”. This means you get to control the timing of the packet versus your other use of the radio, which is appropriate here, as opposed to a completely autonomous system that transmits position reports automatically and does nothing else with its radio.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-10-06T20:26:02.903" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5380" PostTypeId="2" ParentId="5338" CreationDate="2015-10-07T01:14:17.717" Score="2" Body="&lt;p&gt;In some countries the Baofeng UV-82 can be found and it is preferable to the UV-5R and clones, as it has 1 extra watt output power, and it is an evolution of the UV-5R&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check this link: &lt;a href=&quot;https://baofengtech.com/comparechart&quot; rel=&quot;nofollow&quot;&gt;https://baofengtech.com/comparechart&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5430" LastActivityDate="2015-10-07T01:14:17.717" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5382" PostTypeId="2" ParentId="615" CreationDate="2015-10-08T04:10:20.950" Score="-4" Body="&lt;p&gt;You Can transmit on an unknown system ???? not very well! nor with any Real power . Simple answer to this is ! buy an SWR meter Or TUNER with ONE built in.  The tuner can be switched out if the VSWR is below 1.3 and you use 100 W or less. TUBE AMPS AND radios are more forgiving but still require a tuner to Get the signal into the wire to be heard. .&#xA;Signals NEED a resonant Antenna system to be heard you cannot simply RUN FORM 3.5 to 3.995 without A tuner the antenna length Varies by 8 meters in the length of each of its 2 Elements. same on 40 meters the Length required at one end is too much for a single antenna to comprehend under a 2.5 to 1 VSWR A:though you will learn how to Achieve a Better limit than 2:1 20 M is about the Longest Wavelength you  can compromise your antenna on CB and one half of the 10 Meter Band can be covered without a tuner. VHF UHF are Ok BUT you ALWAYS need a SWR meter Capable of Accurate reading at HF VHF UHF no one meter will do it all. &#xA; Ham Radio IS an Expensive Hobby if you don't have money to spare for these Items Don't start. Cut your antennas For the longest frequency of the band its for. NOT mid band and PLEASE USE A TUNER its a Great HARMONIC filter ( TVI filter) &#xA; VE7IBV (Advanced Class 25 year)       &lt;/p&gt;&#xA;" OwnerUserId="5441" LastActivityDate="2015-10-08T04:10:20.950" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5384" PostTypeId="1" CreationDate="2015-10-08T22:09:57.190" Score="5" ViewCount="129" Body="&lt;p&gt;the literature talks about PIM occuring with two or more carriers:  can it not happen in a single carrier antenna?  e.g. creating second harmonic (2*f)?&lt;/p&gt;&#xA;" OwnerUserId="5448" LastActivityDate="2016-01-06T20:21:15.127" Title="Can PIM occur with one carrier?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5385" PostTypeId="1" CreationDate="2015-10-09T16:18:46.083" Score="4" ViewCount="2175" Body="&lt;p&gt;I was an ARRL VE years ago. The info about ARRL VEs says that you remain a VE and the only way one will be dropped is loss of license. However, years ago to be a valid VE one would have to have a current date sticker on one's badge. Am I still a VE? Do I need the date sticker?&lt;/p&gt;&#xA;" OwnerUserId="5452" LastEditorUserId="1362" LastEditDate="2016-08-28T21:57:31.637" LastActivityDate="2016-08-28T21:57:31.637" Title="What is my VE status?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;arrl&gt;&lt;volunteer-examiners&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5386" PostTypeId="2" ParentId="5385" CreationDate="2015-10-09T17:31:41.760" Score="6" Body="&lt;p&gt;For general info, check &lt;a href=&quot;http://www.arrl.org/volunteer-examiners&quot;&gt;http://www.arrl.org/volunteer-examiners&lt;/a&gt;.  It will point you to a PDF manual for ARRL VEC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;http://www.arrl.org/files/file/VEs/VE%20Manual%20Web%20FINAL%202014.pdf&quot;&gt;http://www.arrl.org/files/file/VEs/VE%20Manual%20Web%20FINAL%202014.pdf&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;Once accredited as an examiner in the ARRL/VEC’s program, your&#xA;  accreditation credentials will be good until your FCC license&#xA;  expires.&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Also&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;ARRL accreditation renewal is automatic for ARRL VEs who maintain a&#xA;  current address, contact phone number and/or email address on file at&#xA;  the VEC office &lt;strong&gt;and have participated at an exam session within the&#xA;  past 5 years&lt;/strong&gt;. &lt;em&gt;(Emphasis added.)&lt;/em&gt; Renewal stickers, extending the ARRL VE’s accreditation&#xA;  expiration date, are issued and should be placed on your credentials.&#xA;  By issuing automatic accreditation renewals, the ARRL/VEC can ensure&#xA;  that the needs of our VEs are met; as well as the amateur radio&#xA;  community. After 5 years of inactivity, your VE accreditation will be&#xA;  placed on hold until you contact the VEC office. Depending on the&#xA;  amount of time that has passed, you may be required to reapply. No&#xA;  one's accreditation will be permanently revoked solely because of his&#xA;  or her inactivity, because many factors can contribute to a VE’s&#xA;  activity level.&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you want to reactivate your credential, contact the VEC office vec@arrl.org or call (860) 594-0300.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-10-09T17:31:41.760" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5387" PostTypeId="1" AcceptedAnswerId="5388" CreationDate="2015-10-09T17:57:00.820" Score="4" ViewCount="352" Body="&lt;p&gt;I was recently asked to explain why a &quot;carrier injection oscillator&quot;, or CIO is needed in an SSB receiver but not in a transmitter. This is the explanation I gave, and I would be grateful for comments on its validity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find the usual diagrams confusing, and a verbal explanation better so here is a basically correct, but very simplified explanation. An SSB transmission is derived from an AM signal within the transmitter, which (AM) is produced by mixing the audio with the carrier. If the audio is a single tone, say 1 kHz, and the carrier is 1 MHz, we get  the carrier 1 Mhz and the mixer products, 1 Mhz -1kHz and 1MHz + 1kHz, or 1.000, 0.999 and 1.001 Mhz, all transmitted and received. An SSB transmitter does the same but with a filter that removes all RF frequencies except just those of one sideband, so we may get just 1.001 MHz, the upper sideband, transmitted. To get the original signal back the original carrier, 1 MHz is mixed with this, and among the multitude of mixer products we pick out the three we want, and we have the same as the original AM. &quot;1 MHz is mixed with this&quot; is what is meant by &quot;carrier injection&quot;, and it needs an oscillator, a CIO, to produce it. Note the the CIO is necessary in the receiver only, not in the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;ANSWERED&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks to the answer from Kevin Reid, I have amended the text, and this is now my explanation. I have tried to avoid too much detail:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was recently asked to explain why a &quot;carrier injection oscillator&quot;, or CIO is needed in an SSB receiver but apparently not in an SSB transmitter. This is my explanation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find the usual diagrams confusing, and a verbal explanation easier to follow, so here is a basically correct, but very simplified explanation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, for SSB, both the receiver and the transmitter require RF oscillators. They may be called different things in the two cases, but they are playing essentially the same role: defining the carrier frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In an AM transmitter the signal is produced by mixing the audio, from some external source such as a microphone, with a carrier which is produced by an RF oscillator within the transmitter. From the mixer, if the audio is a single tone, say 1 kHz, and the carrier is 1 MHz, we get the carrier 1 Mhz and the mixer products, 1 Mhz -1kHz and 1MHz + 1kHz, or 1.000, 0.999 and 1.001 Mhz: all these are transmitted and received. The detector stage of the receiver removes the RF components to leave the audio signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An SSB transmission is derived from an AM signal within the transmitter, with an additional filter that removes all RF frequencies except just those of one sideband, so, in the case cited, we may get just 1.001 MHz, the upper sideband, transmitted. To get the original signal back in the receiver the original carrier, 1 MHz, is mixed with this, and among the multitude of mixer products we pick out the three we want, and we have the same as the original AM for the detector stage. &quot;1 MHz is mixed with this&quot; is what is meant by &quot;carrier injection&quot;, and it needs an oscillator, a CIO, to produce it. Note that the oscillator is called the CIO only in the receiver: in a transmitter it is called the RF oscillator, or VFO if the transmitter is tuneable.&lt;/p&gt;&#xA;" OwnerUserId="297" LastEditorUserId="297" LastEditDate="2015-10-11T16:03:08.530" LastActivityDate="2018-09-06T09:22:32.870" Title="Is this simple description of SSB correct?" Tags="&lt;receiver&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5388" PostTypeId="2" ParentId="5387" CreationDate="2015-10-09T20:07:58.443" Score="5" Body="&lt;p&gt;Your description is not wrong, but your premise is. In the system you describe, both the receiver and the transmitter require oscillators at 1 MHz. They may be called different things in the two cases, but they are playing essentially the same role: &lt;em&gt;defining the carrier frequency&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;In the transmitter, the oscillator's frequency is &lt;em&gt;added&lt;/em&gt; (in the frequency domain) to the audio signal, producing an RF signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In the receiver, the oscillator's frequency is &lt;em&gt;subtracted&lt;/em&gt; from the received RF signal, producing an audio signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In practice, SSB receivers and transmitters both have more than one oscillator — one &lt;em&gt;variable-frequency oscillator&lt;/em&gt; (VFO) plus one or more fixed &lt;em&gt;intermediate frequency&lt;/em&gt; (IF) oscillators. This is not fundamental to the modulation, but rather a technique to make implementing the required filtering more practical.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;If you are receiving AM rather than SSB you can avoid having any oscillator in the receiver at all, in favor of a variable filter, as used in crystal or &lt;a href=&quot;https://en.wikipedia.org/wiki/Tuned_radio_frequency_receiver&quot; rel=&quot;noreferrer&quot;&gt;TRF&lt;/a&gt; receivers. However, this is the opposite of your claim. (It is possible because the carrier present in the transmitted signal essentially replaces the function of the local oscillator in the receiver.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-10-09T20:07:58.443" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5390" PostTypeId="1" AcceptedAnswerId="5452" CreationDate="2015-10-11T08:26:10.200" Score="3" ViewCount="128" Body="&lt;p&gt;I got my foundation licence and a Baofeng. Just curious if it's in the license boundaries that I could make a little Morse weather station?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be controlled by computer and transmit once every 5/10 minutes, with my call sign of course.&lt;/p&gt;&#xA;" OwnerUserId="5163" LastEditorUserId="76" LastEditDate="2015-11-02T16:14:58.263" LastActivityDate="2016-03-10T14:51:19.073" Title="UK 2m Morse Simplex" Tags="&lt;legal&gt;&lt;united-kingdom&gt;&lt;automation&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5391" PostTypeId="1" CreationDate="2015-10-11T15:37:00.943" Score="3" ViewCount="581" Body="&lt;p&gt;I'm a new operator (since Thursday) and I'm just curious how folks here log participation in a net. There is a twice a day social net here I've been participating in occasionally. Do I log everyone who participates, just the operator, or just the repeater it happens on?&lt;/p&gt;&#xA;" OwnerUserId="5458" LastEditorUserId="873" LastEditDate="2015-10-19T22:41:38.507" LastActivityDate="2015-10-19T22:41:38.507" Title="What is the proper way to log participation in a net?" Tags="&lt;united-states&gt;&lt;logging&gt;&lt;net&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5392" PostTypeId="2" ParentId="5391" CreationDate="2015-10-11T17:45:11.843" Score="4" Body="&lt;p&gt;[Assuming US Rules]  Since the FCC relaxed the rules regarding logging -- that is -- you do not have to maintain a log -- you can choose to develop and use your own practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am part of a CW traffic net and I once asked the group how many log the nightly fifteen minute net QSOs.  Answer, only one other person besides myself.  One other out of about 12 other individuals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for me, I log everything just because it is something to do in between my time with the paddle.  I am very rarely on with SSB so in a CW net you are often sitting there merely listening.  But, I only log the contact between myself and the net control operator.  If I take traffic then I log the traffic handled and the destination.  If I pass traffic I do the same and the operator's call sign who took the traffic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes while mobile I am involved in a simplex 2-meter QSO.  Often, answering questions about traffic or asking such questions.  I never log these.  I also do a lot of portable work, CW on my KX3 or KX1, and I log those using a digital voice recorder and then transcribe to log later.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-10-11T17:45:11.843" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5394" PostTypeId="2" ParentId="5391" CreationDate="2015-10-12T12:59:44.307" Score="5" Body="&lt;p&gt;Logging is not required by the FCC, but there are several reasons to do it anyway:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Keeping a personal record, like a diary, of your activity on the air. You can include other things like weather, equipment conditions, etc.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You need a log to submit for most contests.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You need a log if you want to exchange QSLs with the other operator, to confirm date, time, frequency, etc.  You might get a QSL request from the other fellow and need to confirm the contact using your log.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A log and QSLs (paper or electronic like Logbook of the World or eQSL) are needed if you want to get an award like Worked All States, DXCC, etc.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you have an RFI (interference) problem with neighbors, it's helpful to have a log of your operation.  That way, you can often say that the neighbor's problems happened when you were not on the air -- or at least you will know what bands and modes are causing trouble.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So typically for a local net, you're not likely to need a log, although you might want to keep some record of the people you've talked to, just to remember names if nothing else.  And, if the other guy is not logging the contact, there's no great need for you to do it either.  (No QSL is likely.)&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-10-12T12:59:44.307" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5395" PostTypeId="2" ParentId="5183" CreationDate="2015-10-13T01:40:38.750" Score="3" Body="&lt;p&gt;Satellite communication works from around 30 MHz to 40,000 MHz. Once you are out of Earth's atmosphere, it doesn't really matter how much higher you get since there isn't anything out there to alter your signal's propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the lower bound, the same phenomena responsible for making skywave propagation on HF possible also make the same frequencies ill-suited to space communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the upper bound, &lt;a href=&quot;http://www.rfcafe.com/references/electrical/atm-absorption.htm&quot; rel=&quot;nofollow&quot;&gt;absorption from atmospheric oxygen and water&lt;/a&gt; make the atmosphere sufficiently opaque that communication is not feasible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Absorption by water gets worse with increasing frequency, making frequencies above 11 GHz or so susceptible to &lt;a href=&quot;https://en.wikipedia.org/wiki/Rain_fade&quot; rel=&quot;nofollow&quot;&gt;rain fade&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice most of these concerns are overshadowed by the limited availability of spectrum. For commercial concerns frequency selection is dominated by cost and availability. Amateur operators of course have to stick to the allocations given to them, with 2m and 70cm being popular choices.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-10-13T01:40:38.750" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5397" PostTypeId="1" CreationDate="2015-10-13T23:08:44.733" Score="5" ViewCount="294" Body="&lt;p&gt;I am doing research on near-field harvesting. In my situation the transmitting antenna is a dipole antenna operating at 2.45 GHz and its length is 14 cm long.  I am trying to find how far near-field reactive region extends from the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I noticed that there are two kinds of formulas – one for  very short antennas  (i.e. $\lambda/(2\pi)$) and other for longer antennas ($0.62 \sqrt{(D\cdot D\cdot D)/\lambda}$). Here are my questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;In my situation, do I have to use the second formula to find near-field reactive region boundary? &lt;/li&gt;&#xA;&lt;li&gt;If I have to harvest within the reactive field of the transmitting antenna, can I use a dipole antenna or do I have to use a coil?&lt;/li&gt;&#xA;&lt;li&gt;If I can use a dipole antenna within the reactive region for harvesting, how would I find its impedance?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="4524" LastEditorUserId="76" LastEditDate="2015-12-15T22:24:34.853" LastActivityDate="2020-09-06T07:25:36.260" Title="How far the near-field reactive region extends from the transmitting antenna?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;wire-antenna&gt;&lt;antenna-theory&gt;&lt;microwave&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5398" PostTypeId="1" CreationDate="2015-10-14T15:19:09.603" Score="3" ViewCount="369" Body="&lt;p&gt;First off, very new to ham radio.  I wanted to track my High altitude balloon using APRS, and after loosing that payload in a mature cornfield for 2 months, decided to add a micro-fox from Byonics to find it if it couldn't easily be seen.  So, I need some pointers for finding this kind of fox.  Can I actually do it without a yagi antenna, and hope to find it?  It will not be &quot;hidden&quot; by clever humans, but fall randomly and be covered by super bright duct tape.  I have already gone over budget and would like to avoid purchasing an $80 antenna, but just don't have the skills or equipment at this time to make one. Using my Baofeng UVR-5a can I use body fade, aluminum can tube, make a trashcan lid shield? etc?  While testing yesterday I was having a lot of difficulty getting body fade or a tube wrapped in foil to work.  It sounds simple, but I am missing something, and the only video tutorial I could find on body fade was just some adorable baby boy scouts doing an easter bunny hunt, and not a tutorial at all. Sorry if any of this sounds silly, I just need a little advice on this strange fox hunt activity.  Thank you so much.&lt;/p&gt;&#xA;" OwnerUserId="5474" LastActivityDate="2015-10-15T00:35:40.190" Title="Fox Hunting w/o yagi to find a lost High altitude balloon payload" Tags="&lt;antenna&gt;&lt;aprs&gt;&lt;yagi&gt;&lt;fox-hunt&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5399" PostTypeId="2" ParentId="5398" CreationDate="2015-10-14T16:33:24.900" Score="2" Body="&lt;p&gt;Would this help?  A cheap and simple yagi that's been used for fox-hunting before. &#xA;&lt;a href=&quot;http://www.arrl.org/files/file/ETP/The%20tape%20measure%20antenna.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/files/file/ETP/The%20tape%20measure%20antenna.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a youtube vid from AmateurLogic.tv&#xA;&lt;a href=&quot;https://youtu.be/PqTH42NRMck?t=30m8s&quot; rel=&quot;nofollow&quot;&gt;https://youtu.be/PqTH42NRMck?t=30m8s&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as the payload you lost - does it currently have the micro-fox installed?  If so, have you tried taking a 2m HT out to the field to see if it's still transmitting and the battery hasn't run out?&lt;/p&gt;&#xA;" OwnerUserId="717" LastEditorUserId="717" LastEditDate="2015-10-14T16:43:16.377" LastActivityDate="2015-10-14T16:43:16.377" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5401" PostTypeId="2" ParentId="5398" CreationDate="2015-10-14T22:08:40.907" Score="1" Body="&lt;p&gt;If the reason you're having trouble with body fade is that you can hear the signal no matter what, then you need to make the signal &lt;em&gt;weaker&lt;/em&gt;, so that you can hear the difference in how well your receiver is picking it up. To do this properly, you use an attenuator between the radio and antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But of course, that's also equipment you need to buy or make (a basic attenuator is just a resistor network between two connectors). You might be better served by getting a Yagi or loop antenna first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Serious foxhunters have both directional antennas and attenuators; the attenuator is needed when you are very close to the fox such that the signal is loud and clear even when your antenna has its null pointed at the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you really want to try with improvised equipment and the signal is strong, try using a terrible antenna:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Remove the antenna entirely. The antenna socket, and leakage through the case, will still pick up some signal.&lt;/li&gt;&#xA;&lt;li&gt;Use an antenna of the wrong length. You can use a piece of wire, provided that you have a way to attach it to the antenna socket without damaging the contacts (such as a &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00D2L2RBE&quot; rel=&quot;nofollow&quot;&gt;coaxial to binding post adapter&lt;/a&gt;, which is generally handy for experimentation).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-10-14T22:08:40.907" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5402" PostTypeId="2" ParentId="5397" CreationDate="2015-10-15T01:36:04.430" Score="1" Body="&lt;p&gt;I would say the near field would be no more than about 28cm max.&lt;br&gt;&#xA;You could use a dipole or a coil, but the dipole would be more efficient.&lt;br&gt;&#xA;If you wanted to find the impedance of a dipole in the reactance region, go for EZNEC.  No way you'll find an analyzer in tat high a frequency.&lt;/p&gt;&#xA;" OwnerUserId="5404" LastActivityDate="2015-10-15T01:36:04.430" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5404" PostTypeId="1" AcceptedAnswerId="5406" CreationDate="2015-10-16T14:14:06.470" Score="5" ViewCount="906" Body="&lt;p&gt;I'm looking at designing a communication system using very low power transmitter (0.1 W) and operating in the 400 Mhz range. For my uses I think a quarter wave whip antenna would work well, so I've calculated the length of the antenna to be 187.5 mm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far so good (I hope). Now I'm looking at how light I can make this antenna. My understanding is that an antenna of this sort is essentially just a bit of wire of the appropriate length (187.5 mm), but I can't figure out if there's a minimum thickness of the wire. The only limitation I can think of is a thinner wire has higher resistance and hence will heat more quickly (causing more noise). Is this really the limitation? I've never seen a very thin whip antenna and I fear there may be a reason behind this.&lt;/p&gt;&#xA;" OwnerUserId="529" LastEditorUserId="76" LastEditDate="2015-12-15T23:27:40.700" LastActivityDate="2015-12-15T23:27:40.700" Title="Minimum thickness of whip antenna" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5405" PostTypeId="1" CreationDate="2015-10-16T15:00:52.923" Score="4" ViewCount="4766" Body="&lt;p&gt;So I'm really trying to get to grips with antenna radiation patterns, and more importantly things that are to close to the antenna that might interfere. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've downloaded Qantenna and 4NEC2 to try and model my antenna and see what I can do, however neither of these programs allow you to 'make' an antenna (as far as I can tell) they require you to import an NEC file. Is there a free piece of software that will make a NEC file for a simple quarter wave whip antenna?&lt;/p&gt;&#xA;" OwnerUserId="529" LastEditorUserId="8717" LastEditDate="2019-11-05T21:43:04.963" LastActivityDate="2019-11-05T21:43:04.963" Title="How to produce a NEC antenna file (and what software to use it with)?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wire-antenna&gt;&lt;antenna-modeling&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5406" PostTypeId="2" ParentId="5404" CreationDate="2015-10-16T16:01:47.317" Score="3" Body="&lt;p&gt;At such a low power, durability is probably more of a concern than anything else. A few simplifying assumptions and quick calculations will demonstrate this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance of a quarter-wave whip is highest at the tip and lowest at the base. That is to say, the current is lowest at the tip, and highest at the base. So if we can demonstrate that the wire gauge is sufficient at the base, where current is highest, then it should be sufficient for the rest of the antenna, also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given your transmit power:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P = 0.1\:\mathrm W $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the impedance of a quarter-wave vertical at its base:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ R = 36\:\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And Joule's first law:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P = I^2 R $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can solve this system of equations for $I$ and figure out what the current at the antenna base must be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 0.1\:\mathrm W = I^2 \cdot 36\:\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{0.1\:\mathrm W}{36\:\Omega} = I^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \sqrt{\frac{0.1\:\mathrm W}{36\:\Omega}} = I $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 0.053\:\mathrm A = I $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the question is now how small a wire can you use to carry (at maximum) 53 mA. You can look at a &lt;a href=&quot;http://www.powerstream.com/Wire_Size.htm&quot; rel=&quot;nofollow&quot;&gt;wire gauge chart&lt;/a&gt; and see the answer is &quot;pretty damn small&quot;, especially considering we calculated the current at the maximum and it is less everywhere else in the wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's another way you might approach the problem: you can calculate (again referencing a wire gauge chart) the resistance of some proposed wire. Then compare that resistance to the $36\:\Omega$ radiation resistance of a whip to get an estimation antenna efficiency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{antenna efficiency} = \frac{36\:\Omega}{36\:\Omega + \text{resistance of wire}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I say estimation, because to properly apply this formula you must transform all the impedances to the impedance they would have at the feedpoint, but remember since the impedance is at a minimum at the feedpoint, were you to go through the trouble of doing that you would end up with a smaller resistance and a higher efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And so you can look at this and see that even if your wire has a $1\:\Omega$ resistance, you still have at least a 97% efficient antenna. And a wire that's a quarter-wave long at 440 MHz and has a resistance of 1 ohm is a really thin wire.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-10-16T16:01:47.317" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5407" PostTypeId="2" ParentId="5405" CreationDate="2015-10-16T16:14:05.557" Score="1" Body="&lt;p&gt;First, I have never used Qantenna so I can't comment on that.  I have used 4NEC2 before and you should be able to enter your antenna description easily.  Maybe I don't understand what you mean by &quot;make&quot; an antenna.  You should enter the geometry of the antenna which is essentially the cartesian coordinates of the end points of each wire segment and some information about the wire itself.  Also, you use this information to describe other features such as the all important feed point location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is other software too such as the $oftware product EZNEC and the Apple Mac software called cocoaNET by W7AY.  Merely googling these items will find them for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used NEC2 and NEC4 for years. I prefer NEC4 ($300 license from Livermore Labs) because it has more accurate modeling of ground and ground level conductors and a few other features.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With NEC4, I use the Mathematica package as the front-end for all data preparation and graphical display of results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Preparing the input data file describing the antenna geometry is very simple.  A simple dipole or a vertical consists of no more than about 3 or maybe 4 data lines to describe the geometry and the feed point and execution requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The documentation for NEC2 contains all you need to understand how to do this and it contains many examples of antenna geometry and execution styles.  You can find the documentation at the web site: &lt;a href=&quot;http://www.nec2.org&quot; rel=&quot;nofollow&quot;&gt;http://www.nec2.org&lt;/a&gt; and you will want to download the User Guide.  The other guides are more useful if you are going to modify the source for NEC2.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-10-16T16:14:05.557" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5408" PostTypeId="1" CreationDate="2015-10-16T20:01:22.590" Score="7" ViewCount="195" Body="&lt;p&gt;If I have a load Z_L and a length of transmission line with impedance Z_0 I know how to compute the impedance at the input to the transmission line (using smith chart or using telegraph equation).  But now suppose I attach a 4:1 Unun to the (input) end of this, what do I do here? Just divide the complex impedance at that point by 4? Is there some phase factor?&lt;/p&gt;&#xA;" OwnerUserId="5296" LastEditorUserId="5296" LastEditDate="2015-10-17T05:56:18.467" LastActivityDate="2016-02-17T03:48:05.843" Title="What exactly does an unun do to the impedance of a transmission line?" Tags="&lt;impedance&gt;&lt;transmission-line&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5409" PostTypeId="1" CreationDate="2015-10-17T23:41:08.867" Score="2" ViewCount="262" Body="&lt;p&gt;I have a situation where I need to find receiving antenna impedance when it’s $\lambda/2$ distance from the transmitting antenna. Both are dipole antennas. Is it possible with EZNEC?&lt;/p&gt;&#xA;" OwnerUserId="4524" LastEditorUserId="8717" LastEditDate="2019-11-05T21:30:09.250" LastActivityDate="2019-11-05T21:30:09.250" Title="How do I simulate a receiving antenna in EZNEC simulation tool?" Tags="&lt;antenna-construction&gt;&lt;propagation&gt;&lt;wire-antenna&gt;&lt;wifi&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="5411" PostTypeId="1" CreationDate="2015-10-18T11:05:23.123" Score="1" ViewCount="283" Body="&lt;p&gt;Is this text correct?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use it when helping people to study for their Licence, and get a lot of indignant scorn for my assertion &quot;It is important to realise, that, after the first brief flutter, no energy is transferred back from the load&#xA;to the source, that is there is no more reflection of energy when it settles down to the steady state.&quot; I hope that here I can get endorsement or at least a fully thought out rebuttal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Standing waves: reflections and impedances of a radio frequency feeder&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an overview in non-mathematical terms. Eye-crossers and tea-dotters will complain that I&#xA;have been too ready to say “always”, and have not gone into all the ifs and buts. I don't apologise&#xA;for this: you will not have to unlearn anything you read here if you then go on to study the subject&#xA;more deeply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When an RF signal is applied to a transmission line, such as a co-ax cable, by a &quot;source&quot;, usually&#xA;the output stage of a transmitter, the front of it rushes down the line at the speed of light (somewhat&#xA;slower than in a vacuum) until it reaches a point where the impedance changes, typically at a&#xA;connection to an Antenna Matching Unit, the &quot;load&quot;. Unless the match of the AMU to the line is&#xA;exact, the wave front, or part of it, is reflected back towards the source, where it will again be&#xA;reflected towards the load end. This to and fro', between more and more mixed up waves, bangs&#xA;about for a brief moment until it fades out and everything settles to a steady state, with RF energy&#xA;being transferred from the source to the load. Since RF is just very rapid alternation, there is an RF&#xA;variation of voltage along the cable, and a corresponding current in and out of each end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is important to realise, that, after the first brief flutter, no energy is transferred back from the load&#xA;to the source, that is there is no more reflection of energy when it settles down to the steady state.&#xA;However in the mathematical analysis of the situation, it is convenient and common to express&#xA;things in terms of forward and reflected waves as though they exist as separate entities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What the resulting steady state is depends (all else being equal) entirely on the impedance of the&#xA;load. If the load impedance matches the line impedance, happy, happy state, there is no reflection at&#xA;switch on, and the voltage and current measured at any point on the line is the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From now on I am talking about the steady state after the start up transient has settled down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When there is a mismatch, measuring the voltage (it's more difficult to measure the current) at any&#xA;point will show a rhythmic variation, if the line is long enough, with equal values of voltage at&#xA;distances equal to the wavelength of the RF in the line. This is the standing wave. It is a wave in&#xA;space, along the line, not a wave in time like voltage and current. It has peaks and troughs at fixed&#xA;points along the line, and the height of these can vary, from a slight ripple if the match to the load is&#xA;almost exact, to an extreme where the voltage troughs are zero and the peaks are very high. I will&#xA;come back to this again later.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is important to realise that the peaks are not a steady value, but a wildly oscillating voltage, and&#xA;the “peak” is a measure of its amplitude, r.m.s. or whatever. Also a reminder that all this happens in&#xA;the standing wave at the frequency of the applied RF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As well as the voltage standing wave there is a current standing wave within the line, with its&#xA;troughs where the voltage peaks are, and vice versa. Compare the standing wave with a child's&#xA;swing: at the ends (momentarily stationary = zero current I) the swing is at its height (high Voltage&#xA;V); as it swings past the bottom the height (V) converts to speed (I), and so on. Just like the&#xA;stationary wave in the line, the swing is going nowhere, but it is full of speed and energy.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/1yuwk.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;See this Standing Wave diagram&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At any point on the line the ratio of voltage to current at that point, taking account of the phase&#xA;differences, gives the impedance of the line at that particular point. This is important: the impedance&#xA;varies from point to point along the line, and this is a static condition: the troughs and peaks do not&#xA;move; and it has serious consequences especially for the transmitter end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's worth repeating that the steady state depends (all else being equal) entirely on the impedance of&#xA;the load. A first consequence of this is that the standing wave is &quot;anchored&quot; at the load end. What&#xA;happens at the source end then depends on the length of the line, that is how many wavelengths of&#xA;the standing wave, or parts of a wavelength, it carries, working back from the load. Then, it is the&#xA;ratio of voltage to current, at the source end that determines the load on the transmitter, and it's also&#xA;worth repeating that what the transmitter sees as the load on its own output terminals, at its end of&#xA;the line, depends on the length of the line, and the load on the far end, and the frequency, and&#xA;nothing else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two special cases of mismatch at the load end are a short circuit and an open circuit. In the short&#xA;circuit case there can be no voltage across that end, it is at a trough of the voltage standing wave,&#xA;and at the peak of the current standing wave, so there is a large current in and out of whatever it is&#xA;that forms the short circuit. At an open circuit end no there can be no current, and the situation is&#xA;reversed, it's a voltage peak and a (zero) current trough. For a load impedance between these&#xA;extremes there is both a current in the load, and a voltage across it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Considering now the transmitter at the&#xA;source end of a mismatched line, once&#xA;again the phase of the standing wave at&#xA;this end is determined by the length of&#xA;the line. In the worst case, on a line that&#xA;is a number of half wavelengths long,&#xA;with a short circuit at the end of it, then&#xA;the load end is at a voltage trough, zero&#xA;voltage in this case, and a current peak.&#xA;Looking back at the transmitter, it too is&#xA;at a point where it has a short circuit as&#xA;its immediate load, with possible&#xA;damage to its output amplifier&#xA;transistors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is strange, but true, that if the load end is open circuit, and the line is an odd number of quarter&#xA;wavelengths long, (in the diagram imagine the end being moved a quarter wavelength closer to the&#xA;transmitter, to the first current trough, i.e. the line is cut to a shorter length) the same situation will&#xA;occur, with the transmitter again seeing a short circuit as its load. How can this happen? With no&#xA;current out of the far end, yet a very heavy current at the transmitter end? Well, that current is just&#xA;back and forth between the troughs and the peaks as they oscillate, and in the end getting nowhere,&#xA;like the child's swing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the transmitter is at a voltage peak, this again can have serious consequences: the instantaneous&#xA;peak voltage is much higher than that generated within the transmitter, and can damage the output&#xA;transistors by exceeding their maximum voltage rating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We see from the above that the input impedance Zin of a length of coax depends on four factors: its&#xA;characteristic impedance, Z0, which decides the match to the load, and is determined by its&#xA;construction, and is independent of the RF frequency; its load impedance, Zload and its length in&#xA;terms of wavelength, the latter both at the frequency of the RF, the fourth factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula relating these is complex, but two simple cases are often used: Zin = Zload if the line is a&#xA;whole number of wavelengths long; and another formula commonly quoted is Z0² = Zin × Zload but&#xA;note that this last formula applies only to quarter (or multiples of a quarter) wavelength lines. See&#xA;articles on quarter wave stubs and impedance transformers for applications of these formulae.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Many thanks to everybody who has commented on this, it has been a lively discussion. Most of the comments are on my assertion about (un)real reflected energy. Please note the paragraph &quot;This is an overview ...&quot;. I did not want to go too deeply into it, I really intended it to give some background about how a transmitter is affected by the load on the end of a feeder, at an elementary and easily digested level. I don't yet see any need to change anything.&lt;/p&gt;&#xA;" OwnerUserId="297" LastEditorUserId="297" LastEditDate="2015-10-21T16:18:20.210" LastActivityDate="2015-10-21T16:18:20.210" Title="There is no reverse flow of energy in a mismatched transmission line, is this correct?" Tags="&lt;theory&gt;&lt;transmission-line&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5412" PostTypeId="1" CreationDate="2015-10-19T00:14:37.613" Score="1" ViewCount="1761" Body="&lt;p&gt;I'm hoping to set up a ham radio in my small apartment, to operate on the 2 meter band. I just picked up my general license and I don't know where to start or what equipment go get.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a picture of my balcony. I'm hoping someone can give me some ideas for an antenna that might fit nicely here. I'm currently looking at the MFJ-1622 &amp;amp; the MP-1. Can anyone offer some advice, or another alternative? Bonus question, if you have advice regarding other equipment I may need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in the northern part of Austin Texas, and off to the left in this picture is the direction towards downtown. Which is convenient that my balcony is facing this way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SlWB3.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SlWB3.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Or22g.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Or22g.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5496" LastEditorUserId="5496" LastEditDate="2015-10-19T03:33:07.483" LastActivityDate="2015-10-19T03:33:07.483" Title="Antenna for small balcony" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5413" PostTypeId="2" ParentId="5412" CreationDate="2015-10-19T01:45:46.897" Score="2" Body="&lt;p&gt;Those balcony railings look like stucco, which has a metal mesh inside, so you will probably need to treat them as RF obstacles and place the antenna well clear of them or use an antenna that can work directly above a semi conductive surface, like a quarter wave ground-plane (with radials). You're in a similar position to David KF4MDV &lt;a href=&quot;https://ham.stackexchange.com/q/3518/76&quot;&gt;who asked a question about a similar balcony&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You say you want to operate on 2 meters, but both of the antennas you mentioned are designed to also operate on HF. This means that they will be more expensive, heavier, and might be less weatherproof (I'm not familiar with the specific designs) than a dedicated 2 m antenna. On the other hand, if you want to get into HF and want to have less total equipment and be able to experiment with adjustments, they could be good choices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also live in an apartment with a balcony, but my balcony is wood, which makes it much less problematic. I would personally suggest obtaining a 2 meter (or 2 m/70 cm) ground-plane type antenna, with horizontal radials, and mounting it just above the edge of your railing, in the middle horizontally. This should minimize the effect any metal in your building has on the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above advice is if you want to optimize your 2-meter antenna. If you're in easy reach of everyone you want to talk to on 2 m then you might find that the HF/VHF verticals you mentioned are good enough and will give you additional options.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't forget to think about how you will actually mount the antenna. Even if the antenna you buy comes with a clamp, it will likely be too small to fit on those railings, and could damage them if it did fit. You will probably want to get some kind of stand to sit behind the railing to mount the antenna on, and it will need to be guyed or weighed down for stability. How exactly to do this depends on what materials you can find locally and care to work with (wood, PVC pipe, metal pipe, angle iron, etc.).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-10-19T01:45:46.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5415" PostTypeId="1" CreationDate="2015-10-19T14:45:35.107" Score="2" ViewCount="248" Body="&lt;p&gt;I'm looking into purchasing a mobile radio (&lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00I53VUEY&quot; rel=&quot;nofollow&quot;&gt;TYT TH-9800&lt;/a&gt;) for my Jeep Wrangler. I am hoping to be able to use it in my apartment as well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since I'm going to need a power supply for this, I think it would be great to pick one up that can double as a variable lab supply (since I don't yet own one and would like to use it for tinkering and other projects).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The non-variable one recommended was&#xA;&lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B0002D6KOU&quot; rel=&quot;nofollow&quot;&gt;http://www.amazon.com/23-Amp-Desktop-Switching-Power-Supply/dp/B0002D6KOU&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you suggest a power supply that might be a good choice for this? Will I need special cables to connect my mobile radio to my PS?&lt;/p&gt;&#xA;" OwnerUserId="5496" LastEditorUserId="76" LastEditDate="2016-04-22T18:50:35.847" LastActivityDate="2016-04-22T18:50:35.847" Title="Ham Variable Lab Power Supply" Tags="&lt;mobile&gt;&lt;power-supply&gt;&lt;dc-power&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5417" PostTypeId="2" ParentId="5411" CreationDate="2015-10-19T18:18:35.683" Score="4" Body="&lt;p&gt;I'm afraid that it is not correct that there is no energy transfer back to the source after an initial period.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wherever you have a mismatch on a transmission line, there is a reflection (at least partial) back to the source.  A percentage of power is &quot;actually&quot; reflected back.  It can be separated from the transmitted power using a suitable device like a hybrid.  When the reflected wave comes back to the source, it can be absorbed if it is terminated at Zo (eg 50 ohms).  A typical transmitter does not provide a 50 ohm load to returning power, however, so there is a (partial) reflection of energy back in the forward direction.  There is an infinite series of partial reflections back and forth, fading away as power is transferred to the load or lost in the transmission line.  In the end, a fraction of the transmitter's power is ultimately transferred to the antenna.  The fraction not transferred ends up partly as heat due to transmission line loss and partly as heat dissipation in the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is useful, as you suggest, to consider the &quot;time domain&quot; situation, such as when you transmit a very short pulse (much shorter than the propagation time of the transmission line).  You can &quot;watch&quot; the reflection at the far end and the series of &quot;internal&quot; reflections in the transmission line.  In the end (neglecting the wide bandwidth required), you should see just the same power transfer and loss as you would with CW waves. (A sine wave can be thought of as a sum of multiple short pulses if you like.)&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-10-19T18:18:35.683" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5418" PostTypeId="2" ParentId="5411" CreationDate="2015-10-19T22:16:29.893" Score="2" Body="&lt;p&gt;I think your description is fairly reasonable, with one exception: I would change it to say that&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the &lt;em&gt;net&lt;/em&gt; energy transfer is forward, not reverse, and&lt;/li&gt;&#xA;&lt;li&gt;don't try argue the point of whether there is a “reverse flow” at all.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Energy is not a substance, it's a quantity&lt;/strong&gt;. I would say that there &lt;em&gt;is no meaningful difference between&lt;/em&gt; “energy only moves from the source to the load” and “the forward flow is slightly larger than the reverse”. They are simply two different models of the exact same situation. You can't put a label on a piece of energy and say where &lt;em&gt;that&lt;/em&gt; energy ended up.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-10-21T14:47:16.700" LastActivityDate="2015-10-21T14:47:16.700" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5419" PostTypeId="1" AcceptedAnswerId="5421" CreationDate="2015-10-19T22:43:38.757" Score="3" ViewCount="157" Body="&lt;p&gt;So, from what I hear, the FCC has done away with mailing out paper certificates.  The way I read the regs, I'm required to have an official paper certificate either on my person or at the station I'm operating.  I know I can print out copies from online, but those are clearly marked as &quot;copy&quot; and are not considered official.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What do I have to do in order to transmit legally once my renewal goes through?&lt;/p&gt;&#xA;" OwnerUserId="102" LastEditorUserId="76" LastEditDate="2015-10-20T00:41:17.967" LastActivityDate="2015-10-20T23:47:40.140" Title="Renewing, how do I transmit legally with the new certification process (USA)?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5420" PostTypeId="2" ParentId="5411" CreationDate="2015-10-20T12:22:30.740" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;It is important to realise, that, after the first brief flutter, no energy is transferred back from the load to the source, that is there is no more reflection of energy when it settles down to the steady state.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If there were no more reflection, then the transmitter could not distinguish between a mismatched load and an infinitely long transmission line. But of course this is not the case, so I think your statement is demonstrably wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can say that the transmitter is putting energy into the system at some rate (the transmit power), and the antenna and losses are taking it out at exactly the same rate. But that's just an obvious consequence of the law of conservation of energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also say that if you had a lossless transmission line, and a transmitter capable of ideal operation into any impedance without damage, that all the transmit power ends up in the antenna eventually. And for moderate mismatches and operation on HF where feedline losses are typically low, this is approximately true in practice, also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also say that it is sometimes a valid engineering simplification to not concern ourselves with the forward versus reflected power, and instead just think of the impedance at the load, transformed by rotation according to the length of the transmission line. The operative word here is &lt;em&gt;sometimes&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you can't say &quot;there is no more reflection&quot;. As Martin Ewing points out, we can at any time extract the reflected power with a hybrid. We can measure it with an SWR meter. We can transmit an impulse and see the reflection in the time domain. So it's demonstrably happening.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps this is the issue: &quot;reflection&quot; is inherently a time domain concept. So if we are thinking about the &quot;steady state&quot;, we are thinking about sinusoids and the frequency domain. There can't be &quot;reflections&quot; in the frequency domain, because a reflection requires a concept of time and the frequency domain has none. So is there a frequency domain equivalent of reflection in the time domain? There is: in a mismatched system there will be variations in group delay with respect to frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is that a problem? It depends. See &lt;a href=&quot;https://ham.stackexchange.com/q/2297/218&quot;&gt;What happens in a low loss feed-line with a high SWR&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-10-20T12:22:30.740" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="5421" PostTypeId="2" ParentId="5419" CreationDate="2015-10-20T17:11:55.563" Score="2" Body="&lt;p&gt;Which part of the regulations talk about the paper certificate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I didn't read every word but I searched part 97 for the words paper, person, certificate etc and didn't find any reference to it.&lt;/p&gt;&#xA;" OwnerUserId="4979" LastActivityDate="2015-10-20T17:11:55.563" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5422" PostTypeId="2" ParentId="5419" CreationDate="2015-10-20T23:47:40.140" Score="4" Body="&lt;p&gt;You need to register with the &lt;a href=&quot;http://wireless.fcc.gov/uls/index.htm?job=home&quot; rel=&quot;nofollow&quot;&gt;ULS&lt;/a&gt; (Universal Licensing System) which is part of the FCC's web site.  You can print a copy of your license which states 'official copy'.&lt;/p&gt;&#xA;" OwnerUserId="5252" LastActivityDate="2015-10-20T23:47:40.140" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5423" PostTypeId="2" ParentId="5415" CreationDate="2015-10-20T23:48:52.537" Score="2" Body="&lt;p&gt;I agree with the comment by @Johnny -- you should get fixed voltage for the ham equipment and separate lower amperage for the tinkering needs.  If you are just tinkering with solid-state circuits that might need 3, 5 or 12 volts than consider one of those cheap industrial multi-voltage fixed supplies.  These are switching power supplies with regulated voltage outputs typically 5 volts and 12 volts.  If you need something else like 3 volts than do like I do, I use D-cell batteries that I keep there on my tinkering bench.  You can pick up these types of supplies for about \$15 to \$25 on Ebay or Amazon.  &lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="29" LastEditDate="2015-10-25T14:07:48.420" LastActivityDate="2015-10-25T14:07:48.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5424" PostTypeId="2" ParentId="5415" CreationDate="2015-10-20T23:57:29.237" Score="0" Body="&lt;p&gt;powerwerx.com has a 30 amp variable desktop power supply (SKU:SPS-30DM) which has a switch to set as single voltage or as variable.  It's also very small and won't take up much room on your desk.&#xA;For cables, I always change mine to Anderson powerpoles.  You can get them from the same site.  You need to be handy with a crimper to make the cables, but you should be able to buy a cable ready-made for your radio.&lt;/p&gt;&#xA;" OwnerUserId="5252" LastActivityDate="2015-10-20T23:57:29.237" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5426" PostTypeId="1" CreationDate="2015-10-21T13:54:07.610" Score="2" ViewCount="892" Body="&lt;p&gt;I came across &lt;a href=&quot;http://users.telenet.be/on4qz/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;QSSTV&lt;/a&gt; today. It's a relatively new Linux program for SSTV and DRM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The config suggests that it can use a number of different external radios as transmitters. What I'd really like to try (as mentioned in this post: &lt;a href=&quot;https://ham.stackexchange.com/questions/5179&quot;&gt;Video transmission between ATV and SSTV&lt;/a&gt;), is send images from a HackRF One, initially, to a nearby RTL-SDR dongle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, neither the Hack RF One, or RTL-SDR are listed in the radio setup page (which appears to use &lt;strong&gt;Hamlib&lt;/strong&gt; as a source).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone had success with the above, either with QSSTV, Hamlib (maybe with a different program), or even with GNU Radio Companion?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Indeed, is there much in the way of SDR SSTV/DRM experimentation?&lt;/p&gt;&#xA;" OwnerUserId="5388" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-10-21T14:46:38.480" Title="QSSTV/Hamlib and RTL-SDR/HackRF One" Tags="&lt;rtl-sdr&gt;&lt;linux&gt;&lt;sstv&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5427" PostTypeId="2" ParentId="5411" CreationDate="2015-10-21T14:00:35.033" Score="2" Body="&lt;p&gt;It's true that if the transmitter is sending a pure sine wave which began infinitely long ago, and will continue on forever, then we can take the mismatched load impedance, rotate it the appropriate amount according to the length of the transmission line, and arrive at some impedance that the transmitter sees. And, from the transmitter's perspective, this long transmission line plus the mismatched load is indistinguishable from a lumped impedance right at its output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, this is exactly true:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/YtZ57.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fYtZ57.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a simplification we can make in some circumstances. The problem with your statement is you neglect the conditions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;it must be a pure sine wave&lt;/li&gt;&#xA;&lt;li&gt;that began forever ago&lt;/li&gt;&#xA;&lt;li&gt;and continues forever into the future&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Of course, such a signal contains zero information, and real communications are never like that. Real transmissions modulate a carrier over time. Or we can say the same thing in the frequency domain: real transmissions aren't just one frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, we can't reduce the entire system to just one impedance that the transmitter sees. For a complete analysis we must think about the &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_response&quot; rel=&quot;nofollow noreferrer&quot;&gt;frequency response&lt;/a&gt; of the system over the entire range of frequencies present in the signal. We can depict the frequency as a &lt;a href=&quot;https://en.wikipedia.org/wiki/Bode_plot&quot; rel=&quot;nofollow noreferrer&quot;&gt;Bode plot&lt;/a&gt; which shows the changes in magnitude and phase present in a system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a feedline and an antenna, we want the magnitude to be unity, or as close as possible across the entire channel. Less than unity would be a loss, and more than unity would violate energy conservation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But magnitude is only half the frequency domian: we must also consider phase. If we have a transmission line, all frequencies will be delayed by some constant amount of time. Higher frequencies will advance more in phase during this time than low frequencies, so the phase plot will be a straight line, although perhaps slanted. We say such a frequency response has &lt;a href=&quot;https://en.wikipedia.org/wiki/Linear_phase&quot; rel=&quot;nofollow noreferrer&quot;&gt;linear phase&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since we care only that the phase response is linear, but any amount of delay is acceptable, it is common to differentiate the phase response with respect to frequency to arrive at the &lt;a href=&quot;https://en.wikipedia.org/wiki/Group_delay_and_phase_delay&quot; rel=&quot;nofollow noreferrer&quot;&gt;group delay&lt;/a&gt;. If the phase response is linear, the group delay will be flat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And group delay has a intuitive explanation: it is the delay introduced to the amplitude envelopes of the frequency components of the signal. And it makes sense that we want the group delay to be flat: our signal consists of many frequency components, and we want them all delayed by the same amount so they arrive at the receiver at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what happens to the group delay if the load is not matched to the transmission line? It stops being flat, meaning some of the frequency components of the signal arrive after others. This interferes with demodulation of the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For SSB and CW this is rarely a problem: these modulations work over a very narrow channel. Over this small range of frequencies it is hard to get enough group delay variation to significantly degrade intelligibility. But for high-speed modulations such as used in TV broadcasting or Wi-Fi, this can very much be a problem. &lt;a href=&quot;https://books.google.com/books?id=V8Lk2ghPl7IC&amp;amp;lpg=PA793&amp;amp;ots=b0VoECxIR1&amp;amp;dq=fm%20broadcast%20group%20delay&amp;amp;pg=PA793#v=onepage&amp;amp;q=fm%20broadcast%20group%20delay&amp;amp;f=false&quot; rel=&quot;nofollow noreferrer&quot;&gt;Even commercial FM broadcasters work to minimize variations in group delay&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, a mismatched load can be a real problem. Now getting back to your original statement:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;It is important to realise, that, after the first brief flutter, no energy is transferred back from the load to the source, that is there is no more reflection of energy when it settles down to the steady state.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As it turns out, all this explanation of frequency response and group delay is just saying that there are reflections, in different terms. The feedline and antenna are a linear time-invariant (LTI) system. If I were to transmit an impulse and measure the reflections that came back over time, I would know the &lt;a href=&quot;https://en.wikipedia.org/wiki/Impulse_response&quot; rel=&quot;nofollow noreferrer&quot;&gt;impulse response&lt;/a&gt; of the system. And through the mathematics of &lt;a href=&quot;https://en.wikipedia.org/wiki/Fourier_analysis&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fourier analysis&lt;/a&gt; and the &lt;a href=&quot;https://en.wikipedia.org/wiki/LTI_system_theory&quot; rel=&quot;nofollow noreferrer&quot;&gt;properties of all LTI systems&lt;/a&gt;, I can calculate the frequency response knowing just the impulse response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, it does not matter if we think about reflections in the time domain, or variations in group delay in the frequency domain. They can mathematically be demonstrated to be the same thing. So you can not say that there is no reflection. And, you can not simplify a mismatched load to a simple impedance, though that may be a valid approximation &lt;em&gt;under some circumstances&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-10-21T14:00:35.033" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5429" PostTypeId="2" ParentId="5426" CreationDate="2015-10-21T14:46:38.480" Score="2" Body="&lt;p&gt;The signal interface with traditional hardware radios (such as those controlled by hamlib) is through an audio device (sound card). A glance at QSSTV's manual looks like it works that way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SDR programs generally output the demodulated audio &lt;em&gt;to&lt;/em&gt; an audio device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, what you need is a loopback audio device, one which is used as an output by your main program (e.g. gqrx) and an input by QSSTV. I believe that most Linux audio systems have the capability to create such devices, but I'm not familiar with the specifics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also just use an audio cable from a line-out to a line-in (not necessarily on the same computer), of course, if that's more convenient.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-10-21T14:46:38.480" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5430" PostTypeId="1" CreationDate="2015-10-22T09:52:02.680" Score="2" ViewCount="114" Body="&lt;p&gt;I am searching for a single chip/small board solution for quadrature demodulation to sample IQ signals with an integrated ADC for DC-50Mhz frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason for that is that I found &lt;a href=&quot;http://hiqsdr.com/images/7/7c/HiQTRX_V24T_B.pdf&quot; rel=&quot;nofollow&quot;&gt;this sdr transceiver&lt;/a&gt; and I was wondering if sampling could be performed on a single chip with IQ outputs&lt;/p&gt;&#xA;" OwnerUserId="1719" LastActivityDate="2015-10-22T11:44:48.960" Title="quadrature demodulator on a chip" Tags="&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5431" PostTypeId="2" ParentId="5430" CreationDate="2015-10-22T11:44:48.960" Score="1" Body="&lt;p&gt;As far as I'm aware, there are no ICs that perform just quadrature demodulation. If you did this, you'd no longer have an SDR as there would be no software, and having discarded the constraint of reprogrammability, there's usually a simpler hardware solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, demodulation is commonly performed in FPGAs or DSPs in these situations, yielding the advantages of dedicated hardware (as opposed to performing it on a desktop computer), while retaining the programmable nature of SDRs. In the schematic you link, the very large IC in the middle is an FPGA. It's common in wideband SDRs like this for the FPGA to be responsible only for filtering some narrow band(s) out of the received signal and sending them, via ethernet, elsewhere for further processing. &lt;a href=&quot;http://openhpsdr.org/&quot; rel=&quot;nofollow&quot;&gt;HPSDR&lt;/a&gt; and &lt;a href=&quot;http://sdrstick.com/&quot; rel=&quot;nofollow&quot;&gt;SDRstick&lt;/a&gt; are other SDRs intended to work this way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you could also add another DAC, audio amplifier, and speaker and program the FPGA to perform your desired demodulation directly. The radios by &lt;a href=&quot;http://www.elecraft.com/&quot; rel=&quot;nofollow&quot;&gt;Elecraft&lt;/a&gt; are an example.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-10-22T11:44:48.960" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5432" PostTypeId="2" ParentId="5333" CreationDate="2015-10-22T12:53:42.863" Score="2" Body="&lt;p&gt;If you can record a waterfall plot of the signal (the easiest way is via a cheap sub $20 &lt;a href=&quot;http://www.rtl-sdr.com/rtl-sdr-quick-start-guide/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTL-SDR&lt;/a&gt; dongles, as @user3431540 mentions), you might have some luck identifying the signal visually via the brilliant &lt;a href=&quot;http://www.sigidwiki.com/wiki/Signal_Identification_Guide&quot; rel=&quot;nofollow noreferrer&quot;&gt;Signal Identification Wiki&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here for example is a waterfall plot for APRS:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/O1nD2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O1nD2.jpg&quot; alt=&quot;APRS waterfall plot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, some software may even allow you to create waterfall plots from recorded sounds, or by placing your computer mic next to the radio speaker.&lt;/p&gt;&#xA;" OwnerUserId="5388" LastEditorUserId="5388" LastEditDate="2015-10-22T14:24:58.877" LastActivityDate="2015-10-22T14:24:58.877" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5433" PostTypeId="1" CreationDate="2015-10-22T21:41:32.327" Score="1" ViewCount="108" Body="&lt;p&gt;I built a node for my friend out of a baofeng BF-888s UHF transceiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am powering the radio with a voltage regulator, and a few caps with a wall wart power supply. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio will transmit fine when there is a dummy load on the output, but when there is an antenna installed on the SMA connector, the radio will fail to transmit even though the transmit LED is on. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a nearby receiver, the transmitter is heard only if I cover my hand over the antenna in a certain way, and even then, there is crazy 60hz hum on the transmit signal overloading the audio. &lt;strong&gt;This 60 hz hum is not due to the lack of filter caps, the hum is not present with the dummy load on the antenna output.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried putting an inductor in series with the positive lead of the power input, but that did not help. I powered the radio on battery, and it helped with the 60hz noise, but the radio would still not transmit until I cover the antenna with my hand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I shielded the entire radio with aluminum foil, and that did help only if I touched my hand to the aluminum foil. I don't want aluminum foil over the whole radio for the final configuration, however. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transceiver is plugged into with a USB sound card, and strange enough, even when the card is umplugged from my computers USB port, and manually cause the radio to transmit, the problem still exists. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course I could move the antenna far away with a coax extension, but then I could not have a compact portable node. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is causing the radio to not transmit, any tips on eleminating RFI while keeping the transmit antenna near the radio? &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-10-29T17:18:12.717" Title="Transmitter won't transmit with antenna installed" Tags="&lt;rfi&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5434" PostTypeId="2" ParentId="5320" CreationDate="2015-10-23T10:23:30.253" Score="1" Body="&lt;p&gt;If you have to estimate the loss that your signal will face whilst propagating to your receiver you perform a link budget for your design.Ignoring antenna gains/losses we generally have, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;  P_{TX} = P_{RX} + L_{TOTAL} + L_{MARGIN}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $P_{TX}$ is the transmit power, $P_{RX}$ is the minimum recieve power you need, $L_{TOTAL}$ is an estimate of the total link loss and $L_{MARGIN}$ (link margin) is the difference you want between the the recieve sensivity and the actual recieve power.$L_{MARGIN}$ is the &lt;strong&gt;additional losses&lt;/strong&gt; your scheme can withstand over and above standard losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and &#xA;$$&#xA;  L_{TOTAL} = L_{PATH} + L_{SLOW} + L_{FAST}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $L_{PATH}$ is the path loss, $L_{SLOW}$ is the slow fading loss and $L_{FAST}$ is the fast fading loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The term &quot;fading margin&quot; is not consistently used, it can be used to either mean i) the link margin ($L_{MARGIN}$) or ii) the total estimated loss due to fading ($L_{TOTAL}$).$L_{MARGIN}$ is chosen at the designers discretion, if $L_{MARGIN}$ is 0 then the average BER will be $10^{-9}$, a higher value of $L_{MARGIN}$ will lead to a lower (and hence better) BER.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$L_{TOTAL}$ is computed by individually computing and summing up $L_{PATH}$,$L_{SLOW}$ and $L_{FAST}$.If you do not know how these individual components are computed then you might want to ask separate questions about how to calculate each type of loss.&lt;/p&gt;&#xA;" OwnerUserId="5515" LastEditorUserId="5515" LastEditDate="2016-01-01T12:42:06.323" LastActivityDate="2016-01-01T12:42:06.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5435" PostTypeId="2" ParentId="5365" CreationDate="2015-10-23T11:30:55.813" Score="1" Body="&lt;p&gt;The reason loss generally goes down when the height of a receiver is increased is because channel fading is usually reduced because the increase in reciever height enables the propagating LOS signal to avoid more obstacles and travel further, hence reaching the receiver with higher power.This then increases the ratio of the power received in the direct line-of-sight path to the total power received via indirect scattered paths (i.e improves the Rician K-factor) and results in a less hostile channel being realised.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, the path loss will reduce with increasing height of the receiving antenna and it will do that a rate of about -20dB/decade so the losses can be significant if the height is changed very drastically but the most important factor will most likely be whether or not distance between the transmitter and receiver ($d$) is within or outside the radio horizon distance ($d_{hr}$).If $d &amp;gt; d_{hr}$ then there is no LOS path (giving us the worst case value of $K = 0$) making the channel very hostile.The height of the airbourne reciever determines the radio horizon which in turn will detemine where the &quot;knee&quot; (i.e the point in the link loss graph where the link loss starts it's short term rapid decrease) of the link loss graph will be.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To illustrate this, I will refer you to figure 1.5-a and figure 1.5-b from the same &lt;a href=&quot;https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.528-3-201202-I!!PDF-E.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU document&lt;/a&gt; that was linked earlier and compare the $h_2 = 1000$m and $h_2 = 10000$m (which is about plane cruising height) graphs.Lets take $h_1$ to be about 30m for both cases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a ground transmitter we have $d_{hr} \approx 3.57 \sqrt{h_2}$ [&lt;a href=&quot;https://en.wikipedia.org/wiki/Line-of-sight_propagation#Radio_horizon&quot; rel=&quot;nofollow noreferrer&quot;&gt;link&lt;/a&gt;] so $d_{hr}$ is about 112km for $h_2$ = 1000m and 358km for $h_2$ = 10000m.Note that the knee's of the graphs start at about these points.Lets look at the graph at d = 300km (which is after the knee of the first graph but before the knee of the second graph).At 1000m the link loss is about 190dB but at 10000m the link loss is about 135dB, a difference of 55dB.The height has changed by one decade and so the contribution of path loss to this total change in link loss is of order 20dB.The rest of the 35dB loss has come about because of the loss in LOS transmission resulting in a more hostile channel.So even though the height of the receiver has changed by a factor of 10, the path loss was not the biggest loss.That is the point I was essentially trying to bring forward.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1WC61.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1WC61.png&quot; alt=&quot;ITU Pic&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5515" LastEditorUserId="5515" LastEditDate="2015-10-27T13:56:12.873" LastActivityDate="2015-10-27T13:56:12.873" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5436" PostTypeId="2" ParentId="5355" CreationDate="2015-10-23T16:48:07.210" Score="1" Body="&lt;p&gt;The primary factory controlling SW reception is your antenna.  Find the antenna antenna input (marked 'FM and SW Antenna') and connect it to a wire of at least 50 feet in length (longer is better); route the wire outside of your house, if possible.  Ideally, it should be mounted high up in the air, on poles, to get it away from the earth.    The antenna wire can be bare or insulated, but try to keep it away from  metallic objects, transformers, electric wires, etc.  The wire should be mounted using insulators, so it can't lose signal to ground. If it goes outside, use an insulated wire where it comes into contact with walls, windows, etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to pull in more signals, try a high-performance receiving antenna.   You could consider a magnetic loop antenna like the Wellbrook Loop, or the W6LVP Loop.  They cost more, but are outstanding antennas.   I use a Wellbrook Loop with my KiwiSdr; it covers 10kHz to 30MHz. &lt;/p&gt;&#xA;" OwnerUserId="5516" LastEditorUserId="5516" LastEditDate="2018-03-05T15:38:18.347" LastActivityDate="2018-03-05T15:38:18.347" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5437" PostTypeId="1" CreationDate="2015-10-23T17:10:40.320" Score="9" ViewCount="2175" Body="&lt;p&gt;I would like to lift a 5/8 wave wire vertical for 160m, using a drone, over my lovely saltwater swamp. The thing must be powered from the ground, capable of being left aloft for a couple of hours while I work DX, and capable of hovering in position with windspeeds of up to 20 kph. IT should also be resistant to RFI from a strong RF (KW) field. Has anyone tried this yet? &lt;/p&gt;&#xA;" OwnerUserId="5516" LastActivityDate="2016-11-18T01:24:02.063" Title="Drones for lifting verticals?" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5438" PostTypeId="1" CreationDate="2015-10-23T21:12:51.913" Score="3" ViewCount="1573" Body="&lt;p&gt;With only pen and paper, is it possible to calculate the ideal Q-factor for e.g. a dipole antenna, loop etc, given a frequency?&lt;/p&gt;&#xA;" OwnerUserId="5520" LastEditorUserId="76" LastEditDate="2015-12-15T22:31:54.330" LastActivityDate="2016-08-28T21:10:02.583" Title="Is it possible to calculate the Q factor for an antenna type, given a frequency?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;bandwidth&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5439" PostTypeId="1" CreationDate="2015-10-24T17:52:45.017" Score="1" ViewCount="388" Body="&lt;p&gt;Is it possible to give approximate answers about what an antenna is capable of? There are a lot of formulas out there, but every single one I found is based on actual measurement; input, output, SWR etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I want to build a dipole for 450 MHz. What can I expect in bandwidth, Q-factor, impedance matching, SWR?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there some kind of standard chart board for different antennas regarding the specs mentioned above? Like standard values you can expect if the construction is not that bad.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example: A Vivaldi antenna produced by amateurs is often around 50% radiation efficiency with an SWR of 10:1 due to the equipment used in the construction.&lt;/p&gt;&#xA;" OwnerUserId="5520" LastEditorUserId="76" LastEditDate="2015-12-15T23:41:01.673" LastActivityDate="2020-03-09T10:43:15.893" Title="Bandwidth, Q-factor, Radiation Eff calculations" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;antenna-theory&gt;&lt;bandwidth&gt;&lt;efficiency&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5440" PostTypeId="2" ParentId="5437" CreationDate="2015-10-25T03:49:57.350" Score="7" Body="&lt;p&gt;You ask “has anyone tried this”. I'm just back from Pacificon 2015 where &lt;a href=&quot;http://www.sonic.net/~n6gn/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Glenn Elmore, N6GN&lt;/a&gt;, gave a talk on exactly this topic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He found that using a helium balloon is not practical for lifting antennas on all but the very calmest of days, since the wind will blow it away from vertical, and as well the helium will leak away quickly enough to make keeping it aloft expensive (though there was some discussion of better balloons).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem with actively supporting the antenna using a quadcopter (or dirigible balloon) is battery life — “a couple of hours” is pushing the limits of what is possible with a drone that is free flying and &lt;em&gt;not&lt;/em&gt; also supporting an antenna. (The bigger the battery, the more power spent supporting the weight of that battery.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;N6GN's latest work is on powering the quadcopter using RF energy sent up the feed line, on a different band than is being used for communications. I encourage you to &lt;a href=&quot;http://www.sonic.net/~n6gn/&quot; rel=&quot;nofollow noreferrer&quot;&gt;visit his site and read about his work&lt;/a&gt;, since he's working on exactly what you're looking for.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-11-18T01:24:02.063" LastActivityDate="2016-11-18T01:24:02.063" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5441" PostTypeId="2" ParentId="5439" CreationDate="2015-10-25T05:04:38.393" Score="2" Body="&lt;p&gt;Actual realistic and therefore useful antennas are not described by simple analytic formulas where you just plug in various parameters to compute a solution.  Also, these other features such as bandwidth, impedance matching, SWR is not computed from simple formulas for such antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They can be computed from a numerical modeling program that performs a numerical solution for the antenna.  This is what the free program called NEC2 does.  You provide an input file describing the geometry of the antenna and one or more other commands to describe excitation and and frequency of operation and then run the program to produce results.  NEC2 will produce tables (aka arrays) of numbers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Application programs such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;EZNEC (read about at &lt;a href=&quot;http://eznec.com&quot; rel=&quot;nofollow&quot;&gt;http://eznec.com&lt;/a&gt;),&lt;/li&gt;&#xA;&lt;li&gt;4nec2 (located at &lt;a href=&quot;http://www.qsl.net/4nec2/&quot; rel=&quot;nofollow&quot;&gt;http://www.qsl.net/4nec2/&lt;/a&gt;),&lt;/li&gt;&#xA;&lt;li&gt;Apple Mac program CocoaNet (available at &lt;a href=&quot;http://www.w7ay.net/site/Applications/cocoaNEC/index.html&quot; rel=&quot;nofollow&quot;&gt;http://www.w7ay.net/site/Applications/cocoaNEC/index.html&lt;/a&gt;)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Can all give you graphical output of various kinds of results including antenna impedance, SWR, and antenna Gain at given angles of elevation and azimuth, and other interesting things.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think any of these will compute the Q-Factor for the simple reason that nobody cares to know the Q-Factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With EZNEC for example, the SWR plot that is given will tell you for a given operating frequency what the SWR is for nearby frequencies above and below the operating frequency.  From this you can easily see the window of operation for the 2:1 (typical cutoff) SWR points below and above thus showing the bandwidth.  Note that you can compute the bandwidth for the entire band, say 3.5 to 4.0 MHz for 80-meter band, or whatever for any antenna you model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also model transmission line with some of the programs I have mentioned or you can treat the transmission line separately using some of the other available programs such as TLW made available by ARRL.  Just google &quot;ARRL TLW&quot; and you should find a description and how to obtain it.  It is freely distributed as part of the annual publication of the ARRL Handbook.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used all of the applications cited above but I prefer to use NEC4 (a newer and improved version of NEC2) along with the Mathematica application as the UI front-end.  Mathematica Home Edition costs about \$300 or so, the NEC4 license was \$300 when I acquired it several years ago.  But, you need to &quot;program&quot; your own graphics displays of the result data produced by NEC2 or NEC4 yourself -- that is what Mathematica does best.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want web resources to learn more about antennas than google is your friend.  Start with the ARRL if you are a member, if not then buy their Handbook or maybe also their Antenna Handbook.  For 2016 there is a brand new version of the Antenna Handbook published.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get the answers you are looking for though, learn NEC2 and learn how to model simple dipole antennas and interpret the results.  The NEC2 User Guide tells you all you need to know.  See &lt;a href=&quot;http://www.nec2.org&quot; rel=&quot;nofollow&quot;&gt;http://www.nec2.org&lt;/a&gt; and download the User Guide.  You can also download the Theory and the Program Description to learn more about NEC2.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2015-10-27T16:13:27.413" LastActivityDate="2015-10-27T16:13:27.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5442" PostTypeId="1" CreationDate="2015-10-26T13:04:10.343" Score="2" ViewCount="428" Body="&lt;p&gt;I was playing with HDSDR+ExtIO and &lt;a href=&quot;http://www.ettus.com/product/details/USRPPKG&quot; rel=&quot;nofollow&quot;&gt;Ettus USRP1&lt;/a&gt; to track a BPSK signal. In the end I successfully heard the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I would like to see the data, I mean the raw data (HEX values). For that I tried &lt;a href=&quot;http://sourceforge.net/projects/fldigi/files/&quot; rel=&quot;nofollow&quot;&gt;fldigi&lt;/a&gt; in which I just selected BPSP-31 under PSK (in the Op Mode menu).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've used a cable to forward audio from speaker to mic and I saw something in the waterfall but cannot get any data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which things should I check? (Any lower level tutorial?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know the source operates at 1200bps (symbol rate) but I'm not aware of line coding, preamble (, et cetera) at this moment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, i successfully experimented to decode some public BPSK sounds:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Got the message &quot;CQ CQ CQ de EA2BAJ EA2BAJ EA2BAJ&#xA;PSE K&quot; for &lt;a href=&quot;http://www.nonstopsystems.com/radio/radio-sounds.html&quot; rel=&quot;nofollow&quot;&gt;this&lt;/a&gt;. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Got the message &quot;The quick brown fox jumps over the lazy dog 1234567890&quot; for &lt;a href=&quot;http://www.sigidwiki.com/wiki/Phase_Shift_Keying_(PSK)&quot; rel=&quot;nofollow&quot;&gt;this&lt;/a&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5524" LastEditorUserId="9450" LastEditDate="2019-07-04T15:38:28.403" LastActivityDate="2019-07-04T15:38:28.403" Title="BPSK raw data aquisition with HDSDR and FLDIGI" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;&lt;satellites&gt;&lt;modes&gt;&lt;fldigi&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5443" PostTypeId="2" ParentId="5442" CreationDate="2015-10-26T13:41:37.600" Score="0" Body="&lt;p&gt;I did something similar a year or so ago. Eventually I ended up creating a GnuradioCompanion block in python that would take the output after being demodulated and converted it to a binary stream.&lt;/p&gt;&#xA;" OwnerUserId="135" LastActivityDate="2015-10-26T13:41:37.600" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5445" PostTypeId="1" AcceptedAnswerId="5458" CreationDate="2015-10-27T15:07:01.823" Score="6" ViewCount="1208" Body="&lt;p&gt;Let's say a transmitting station is using a 8W radio with a J pole antenna. The cable connecting the radio to the antenna is RG-58A/U and is 25ft long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 144.075MHz, the attenuation of the cable is 1.5dB. At 8W, the power from the radio is 9.03dB. Assuming no losses other than cable losses, the antenna is getting 7.53dB, or 5.66W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's now say the receiving station, 4 miles away, has the same setup (8W radio, J pole, and RG-58A/U). Assuming the gain of the two J pole antennas is 2.15dBi, and using the Friis transmission equation, the receiving antenna is receiving 1.733e-8W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the cable losses of the receiving station being 1.5dB (1.41W), and the antenna receiving 1.733e-8W, it appears the received signal will never make it to the receiving station's radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Me and my buddy have this setup with Baofeng BF-F8HP radios. If we are both using J pole antennas, we cannot communicate with each other. If one of us is using a J pole and the other is using the stock rubber ducky, the rubber ducky user can &lt;strong&gt;receive&lt;/strong&gt; the J pole user's transmissions. I'm assuming the reason we cannot communicate with each other if we are both using J poles is because of the cable losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this correct? If so, is there a way around this?&lt;/p&gt;&#xA;" OwnerUserId="5526" LastEditorUserId="5526" LastEditDate="2015-10-27T15:29:13.350" LastActivityDate="2019-09-06T20:24:22.890" Title="What is the minimum signal strength I need to receive?" Tags="&lt;transceiver&gt;&lt;baofeng&gt;&lt;2m-band&gt;&lt;transmission-line&gt;&lt;path-loss&gt;" AnswerCount="4" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5446" PostTypeId="1" CreationDate="2015-10-27T18:29:26.427" Score="2" ViewCount="363" Body="&lt;p&gt;I have a setup in which &lt;a href=&quot;https://github.com/wb2osz/direwolf&quot; rel=&quot;nofollow&quot;&gt;Direwolf&lt;/a&gt; is used in conjunction with a Baofeng radio to basically send data (AFSK). My app connects to the TCP server provided by Direwolf, send him some data which then is forwarded to the PC speaker. The PC speaker is connected to the Baofeng MIC and so it works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it be possible to replace Direwolf by HDSDR? So HDSDR forwards the data to the Baofeng radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;May I provide more information?&lt;/p&gt;&#xA;" OwnerUserId="5524" LastActivityDate="2017-05-27T09:08:23.610" Title="Can HDSDR perform the work of Direwolf?" Tags="&lt;digital-modes&gt;&lt;modes&gt;&lt;software-defined-radio&gt;&lt;baofeng&gt;&lt;software&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5447" PostTypeId="2" ParentId="5445" CreationDate="2015-10-28T17:04:04.700" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;At 8W, the power from the radio is 9.03dB.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;With the cable losses of the receiving station being 1.5dB (1.41W), and the antenna receiving 1.733e-8W, it appears the received signal will never make it to the receiving station's radio.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This seems to be the crux of your misunderstanding. You can't convert watts into decibels, or decibels into watts. A decibel expresses a ratio of two things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of losses at the receiver, it expresses the ratio of the received power (before losses) to the output power (after losses).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of dBi, it expresses the ratio of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Radiant_intensity&quot; rel=&quot;nofollow&quot;&gt;radiant intensity&lt;/a&gt; of a given antenna in its direction of maximum gain to the same of a hypothetical antenna which radiates equally in all directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of dBm, it expresses the ratio of some power to 1mW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if your transmitter is 8W (that is, 8000mW), we can convert that into dBm:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \require{cancel}&#xA;\frac{8\:\mathrm W}{1\:\mathrm{mW}}&#xA;= \frac{8000\:\cancel{\mathrm{mW}}}{1\:\cancel{\mathrm{mW}}}&#xA;= 10 \cdot \log_{10}(8000)\:\mathrm{dBm}&#xA;= 39\:\mathrm{dBm}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how this is a ratio, and it is a unitless number because the unit (mW) cancelled in the second step. We add the &quot;m&quot; to &quot;dB&quot; to remember that the denominator is 1 mW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can convert 39 dB back into a ratio:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 10^\frac{39}{10} = 7943 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This ratio is telling us that something is 7943 times bigger than something else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;m&quot; at the end of &quot;dBm&quot; reminds us that this is the proportion of some quantity &lt;em&gt;in relation to 1 mW&lt;/em&gt;, so to get back to the original quantity we must multiply by 1 mW:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 7943 \cdot 1\:\mathrm{mW} = 7941\:\mathrm{mW} \approx 8\:\mathrm W $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The discrepancy is just rounding error. Really 8 W is closer to 39.03089986991944 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your receiver losses are 1.5 dB, then we can calculate the corresponding ratio (and I'll use &lt;em&gt;negative&lt;/em&gt; 1.5 dB, because it's a &lt;em&gt;loss&lt;/em&gt;):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 10^{-1.5 \over 10} = 0.71 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that's a ratio: to get to some quantity we have to multiply it by something. In this case we are comparing the power delivered to the receiver to the power received by the antenna. So if the antenna was receiving 0.01 mW, then we'd do this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 0.71 \cdot 0.01\:\mathrm{mW} = 0.0071\:\mathrm{mW} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With this in mind, try your calculations again, and I think you will get a more sensical answer.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-10-28T17:05:57.297" LastActivityDate="2015-10-28T17:05:57.297" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="5448" PostTypeId="1" AcceptedAnswerId="5454" CreationDate="2015-10-28T18:12:29.307" Score="4" ViewCount="3521" Body="&lt;p&gt;I was expecting to see an AFSK option in the Fldigi &quot;Op Mode&quot; menu (as there is one option for CW, i.e.), why isn't it there?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, I want to get the data send according to &lt;a href=&quot;https://ham.stackexchange.com/questions/5446/can-hdsdr-perform-the-work-of-direwolf&quot;&gt;this&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="5524" LastEditorUserId="9450" LastEditDate="2019-07-04T17:00:26.297" LastActivityDate="2019-07-04T17:00:26.297" Title="Why there is no AFSK in FLDIGI" Tags="&lt;digital-modes&gt;&lt;modes&gt;&lt;fldigi&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="5450" PostTypeId="1" AcceptedAnswerId="5451" CreationDate="2015-10-28T23:13:00.537" Score="3" ViewCount="7311" Body="&lt;p&gt;What &lt;strong&gt;file format&lt;/strong&gt; does the &lt;a href=&quot;https://greatscottgadgets.com/hackrf/&quot; rel=&quot;nofollow&quot;&gt;HackRF One&lt;/a&gt; &lt;strong&gt;expect on the command line&lt;/strong&gt;, using the &lt;code&gt;-t&lt;/code&gt; option with &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/Software-with-HackRF-Support#hackrf-tools&quot; rel=&quot;nofollow&quot;&gt;hackrf_transfer&lt;/a&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, how would I &lt;strong&gt;create or convert&lt;/strong&gt; that format from a standard WAV file?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was expecting the following to transmit a 36 second wav file:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;hackrf_transfer -t test.wav -f 145500000 -p 1 -a 1 -x 47&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it just quits (without intervention, despite what it says) after 1 second or so, with the following:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;call hackrf_sample_rate_set(10000000 Hz/10.000 MHz)&#xA;call hackrf_baseband_filter_bandwidth_set(9000000 Hz/9.000 MHz)&#xA;call hackrf_set_freq(145500000 Hz/145.500 MHz)&#xA;call hackrf_set_amp_enable(1)&#xA;call hackrf_set_antenna_enable(1)&#xA;Stop with Ctrl-C&#xA; 3.7 MiB / 1.000 sec =  3.7 MiB/second&#xA;&#xA;User cancel, exiting...&#xA;Total time: 1.00032 s&#xA;hackrf_stop_tx() done&#xA;hackrf_close() done&#xA;hackrf_exit() done&#xA;fclose(fd) done&#xA;exit&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="5388" LastEditorUserId="76" LastEditDate="2016-10-29T19:08:28.807" LastActivityDate="2016-10-29T19:08:28.807" Title="HackRF One — Expected 'hackrf_transfer -t' file format and its creation?" Tags="&lt;software-defined-radio&gt;&lt;hackrf&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5451" PostTypeId="2" ParentId="5450" CreationDate="2015-10-28T23:23:17.487" Score="4" Body="&lt;p&gt;Outside of the &lt;code&gt;-w&lt;/code&gt; receive options, &lt;code&gt;hackrf_transfer&lt;/code&gt; always deals in 8-bit signed IQ samples, raw with no file headers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You must also make sure that the sample rate of the data matches the sample rate specified on the command line and is a rate supported by the HackRF hardware. WAV files contain the sample rate information in a header, but raw files have no place to put it, and in RF signals it can be undesirable for programs to attempt automatic sample rate conversion anyway.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Modulation&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Before considering converting a WAV file, you need to ensure you actually have RF (IQ) samples, not audio; that is, it must be &lt;em&gt;modulated&lt;/em&gt;. If you got the recording from another program which explicitly says it produces IQ output, then that's fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have audio data, and the signal is intended to be fed to a single-sideband (SSB) transmitter, such as most HF digital modes, then you can use it anyway, but you will get double-sideband (DSB) transmission — two copies of the signal, one with the spectrum inverted. This may be adequate for testing purposes, but don't make a habit of it as you're wasting bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have audio data which is intended to be modulated as FM (such as an AFSK APRS packet, for example), then you will need to modulate it. This can be done fairly easily given the right tools, as I will describe below.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Conversion&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;I recommend that you install &lt;strong&gt;GNU Radio&lt;/strong&gt;. While it is primarily intended for real-time processing, and can in fact talk directly to the HackRF One, it can also be used to convert files.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In GNU Radio's graphical tool, &lt;strong&gt;GNU Radio Companion&lt;/strong&gt;, you can design a &quot;flow graph&quot; to read a file, write a file, and do any particular conversions along the way, such as for your case:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WeChN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WeChN.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here we take the two “stereo” channels of the WAV file (which GNU Radio automatically converts to floats in the &amp;minus;1 to +1 range), put them in alternating left-right-left-right sequence, resample it from an assumed rate of 44.1 kHz to 2 MHz (that being the minimum supported by the HackRF One), rescale to &amp;minus;127 to +127, and write to the raw output file (which will have the same sample rate as the input file).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you needed to perform modulation (as I described above) as well, that would be just another block or two in this chain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, GRC does have some limitations — for example, this has the filenames hardcoded into it. But GRC generates (overly verbose) Python programs which you can then clean up into something reasonable, or write from scratch once you're familiar with the vocabulary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a lot to learn to use GNU Radio effectively, but it is a very useful tool for SDR experimentation, if with some rough edges, and I recommend it.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-11-02T00:02:40.017" LastActivityDate="2015-11-02T00:02:40.017" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="5452" PostTypeId="2" ParentId="5390" CreationDate="2015-10-28T23:27:27.900" Score="1" Body="&lt;p&gt;My understanding of the rules is that your idea would be perfectly legal. According to the &lt;a href=&quot;https://services.ofcom.org.uk/amateur-terms.pdf&quot; rel=&quot;nofollow&quot;&gt;OFCOM terms&lt;/a&gt; (PDF file): &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;10(1) The Licensee may conduct Unattended Operation of Radio Equipment&#xA;  provided that any such operation is consistent with the terms of this&#xA;  Licence. Additional restrictions which apply to the Unattended&#xA;  Operation of Beacons are specified in Schedule 2 to this Licence.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Basically, as long as you conform to the normal rules (correct band, power, stating your call sign regularly, etc) it's acceptable.&lt;/p&gt;&#xA;" OwnerUserId="5388" LastActivityDate="2015-10-28T23:27:27.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5454" PostTypeId="2" ParentId="5448" CreationDate="2015-10-29T11:28:40.283" Score="7" Body="&lt;p&gt;Fldigi is largely intended for HF operation. From &lt;a href=&quot;http://www.w1hkj.com/beginners.html&quot;&gt;the beginner's guide&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Fldigi is a computer program intended for Amateur Radio Digital Modes operation using a PC (Personal Computer). Fldigi operates (as does most similar software) in conjunction with a conventional HF SSB radio transceiver, and uses the PC sound card as the main means of input from the radio, and output to the radio.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;AFSK, as used by APRS and packet radio, is not very popular on HF. A few people do it for sure, but having tried it personally I can tell you it's not a very robust mode with all the noise and fading in a typical HF channel. Since the mode is typically deployed with no FEC at all, it's usual for any HF packet frequencies to be clogged with nothing but retransmit attempts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fldigi is also focused on &quot;chat&quot; modes, like PSK31. Again from the beginner's guide:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In this context, we are talking about modes used on the HF (high frequency) bands, specifically chat modes, those used to have a regular conversation in a similar way to voice or Morse, where one operator talks for a minute or two, then another does the same. These chat modes allow multiple operators to take part in a net.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So I suspect the reason you do not find AFSK in Fldigi is that it's neither popular (or really effective) on HF, and it's not a chat mode.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-10-29T11:28:40.283" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5456" PostTypeId="2" ParentId="5433" CreationDate="2015-10-29T17:18:12.717" Score="1" Body="&lt;p&gt;You are probably getting the 60 Hz tone through your power supply OR the computer. Try the radio with a battery.  If no hum, then the problem is with your power supply. If still present, remove connection to computer and see if hum still present.&lt;/p&gt;&#xA;" OwnerUserId="5252" LastActivityDate="2015-10-29T17:18:12.717" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5457" PostTypeId="1" AcceptedAnswerId="5459" CreationDate="2015-10-29T19:23:37.817" Score="8" ViewCount="1162" Body="&lt;p&gt;I am currently studying for my amateur radio license. Until I'm licensed, I'm trying to use a Sony ICF-SW7600GR receiver to listen in on amateur radio &quot;phone&quot; transmissions. No matter what I do, however, I can't seem to locate any amateur radio conversations. Everything I manage to tune into is a broadcast, usually some news, music, or religious broadcasts. Since this receiver covers all MF and HF amateur bands, I really expected to pick up something. I've dialed directly into frequencies set aside for &quot;phone&quot; in Region 1 (I'm in Prague, Czech Republic), searched LSB under 10 MHz, USB above 10 MHz, normal AM, utilized the external SW antenna, dialed in directly to local stations, tried with and without synchronous detection, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe everyone is using FM or PM while my receiver only picks up AM? &lt;/p&gt;&#xA;" OwnerUserId="5540" LastEditorUserId="5540" LastEditDate="2015-11-03T16:06:11.917" LastActivityDate="2017-11-20T00:41:31.343" Title="Why do I only hear broadcasts from 150 kHz to 29.999 MHz?" Tags="&lt;hf&gt;&lt;receiver&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5458" PostTypeId="2" ParentId="5445" CreationDate="2015-10-29T20:33:49.210" Score="1" Body="&lt;p&gt;I ended up switching from a &lt;strong&gt;25ft&lt;/strong&gt; RG-58A/U cable with &lt;strong&gt;F connectors&lt;/strong&gt; on each end to an &lt;strong&gt;18ft&lt;/strong&gt; RG-58A/U cable with &lt;strong&gt;PL-259&lt;/strong&gt; connectors on each end. I can now receive, using my J-pole, my buddy's signal when he is transmitting with his J-pole. However, there is &lt;strong&gt;a lot&lt;/strong&gt; of noise. This fixed the reception issue, but I'm still experimenting to figure out what the minimum signal strength is required at the RF input of my radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the answer to &quot;What is the minimum signal strength I need to receive?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://baofeng.perm.ru/data/soft/Baofeng_UV-5R_receiver_sensitivity.pdf&quot; rel=&quot;nofollow&quot;&gt;Baofeng Sensitivity&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5526" LastEditorUserId="5526" LastEditDate="2015-11-10T17:54:16.000" LastActivityDate="2015-11-10T17:54:16.000" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5459" PostTypeId="2" ParentId="5457" CreationDate="2015-10-29T20:50:44.847" Score="12" Body="&lt;p&gt;It doesn't sound like you're doing anything wrong. Most likely, you are simply only hearing strong stations; broadcasters put much more power into their transmissions than amateurs are legally allowed to, so you can hear them over a much wider range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Advice on the practice of listening:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;For finding signals, first of all, &lt;strong&gt;always use SSB&lt;/strong&gt;. Even if it's the wrong mode to demodulate the signal correctly, you will hear &lt;em&gt;something&lt;/em&gt; (often including a strong carrier tone), because SSB is just turning a slice of the RF spectrum into audio regardless of what it contains. The only way you can miss hearing a signal using SSB is if the signal is much wider bandwidth than 3 kHz (so that it sounds like just an increase in the noise floor). Once you have found something, you can try other modes to receive it correctly.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Try tuning to the CW band segments (using a CW mode if you have it, otherwise SSB), rather than phone. Even if you don't know Morse code, CW signals are much easier to pick out of the noise by ear, so you can tell whether you're receiving anything.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Make sure you're listening at the right time. Broadly speaking, propagation is better at night, so not only will you receive better, but more people will be transmitting. You should be able to hear the broadcasters more clearly as well. When you're studying for your license, read about the ionosphere and other kinds of propagation effects, and figure out when you should be listening to what band.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Advice on improving your reception:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;You may have local noise sources which interfere with reception. They won't necessarily sound like anything other than the usual hiss of noise. Shut off all the electrical devices in your home temporarily and see whether they make a difference. (Instead of listening for signals you can't hear yet, listen for how clear the broadcasters are.) Or, especially if you're in an apartment building with many close neighbors, you could try going out to a park or other location with very little electronics.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Make sure you have a decent antenna. Since you are receiving, not transmitting, this is not critical, but it helps. According to some reviews, your model of radio comes with a reel of wire in addition to the telescoping antenna; use it. There are two basic approaches:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;“Long wire”: Make your antenna wire as long as you can reasonably fit in the space you have. (Keep it away from large metal objects.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Make it resonant on the band of interest. In particular, make it about 1/4 wavelength long, or possibly an odd multiple (3/4, 5/4, and so on). (Coiling up the free end will make it effectively shorter without needing to cut the wire.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Maybe everyone is using FM or PM while my receiver only picks up AM?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Nobody uses FM on HF, because it is a waste of bandwidth. But if they did, then you could still hear it. Specifically:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;An AM receiver tuned exactly on a FM signal will produce silence (&lt;em&gt;not&lt;/em&gt; noise).&lt;/li&gt;&#xA;&lt;li&gt;An AM receiver tuned slightly off the FM signal will produce decent audio, with excess noise.&lt;/li&gt;&#xA;&lt;li&gt;A SSB receiver tuned to an FM signal will produce a distorted sound which will still be recognizable as being voice-like (due to the timing of speech sounds), and possibly a tone from the carrier.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-10-29T20:50:44.847" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5460" PostTypeId="1" AcceptedAnswerId="5461" CreationDate="2015-11-01T19:56:32.813" Score="1" ViewCount="239" Body="&lt;p&gt;I just joined the community, and I got a communication question. Based on searches most relevant questions were posted in this community, so I hope I can get a proper answer!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EMT, first responders, and ambulance life support use radio communications for emergency crisis management. Can anybody point me to more detailed information about the frequency bands/channels they use, the bandwidth, etc? Seems like they also have multiple levels of priorities associated with them, with multiple level of reliability. Is there any technical documentation that I can use?&lt;/p&gt;&#xA;" OwnerUserId="5555" LastEditorUserId="5555" LastEditDate="2015-11-02T14:18:25.863" LastActivityDate="2015-11-02T14:18:25.863" Title="EMT radio communications" Tags="&lt;united-states&gt;&lt;procedure&gt;&lt;frequency&gt;&lt;emergency&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5461" PostTypeId="2" ParentId="5460" CreationDate="2015-11-01T21:01:13.443" Score="4" Body="&lt;p&gt;I wanted to add a comment but I don't have enough reputation. I think this is a broad question and will depend on your particular location of interest. I would start checking, specially if you are located in USA, &lt;a href=&quot;http://www.radioreference.com/apps/db/?coid=1&quot; rel=&quot;nofollow&quot;&gt;http://www.radioreference.com/apps/db/?coid=1&lt;/a&gt; for the frequencies, type of stations, access code tones, transmission mode, and description of use for EMS/Fire frequencies in any county in the U.S. Hope it helps.&lt;/p&gt;&#xA;" OwnerUserId="5114" LastActivityDate="2015-11-01T21:01:13.443" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5463" PostTypeId="2" ParentId="5460" CreationDate="2015-11-02T06:08:33.103" Score="1" Body="&lt;p&gt;If you are located in the US, then locate the local ARES group working in your area.  ARES is Amateur Radio Emergency Service and it is a volunteer organization created by the ARRL (see &lt;a href=&quot;http://arrl.org&quot; rel=&quot;nofollow&quot;&gt;http://arrl.org&lt;/a&gt;) that works with local government and non-government emergency services such as EMT, Fire, Rescue, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A local ARES volunteer would be a good person to ask your question.  They should know all of the important frequencies, repeaters, and other communications channels for various services.  Note that these are not open to you (usually) to use for communication but you can listen in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a &quot;Ham&quot; license then you could join such groups.  You may be able to volunteer without having a ham (amateur radio) license although I do not know about that.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-11-02T06:08:33.103" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5464" PostTypeId="1" CreationDate="2015-11-02T12:09:37.513" Score="4" ViewCount="226" Body="&lt;p&gt;I'm trying to decode a BPSK 1200 (with no success). In this endeavor I tried both &lt;a href=&quot;http://uz7.ho.ua/packetradio.htm&quot; rel=&quot;nofollow&quot;&gt;SoundModem&lt;/a&gt; and &lt;a href=&quot;http://members.casema.nl/b.ubbels/Warbler.htm&quot; rel=&quot;nofollow&quot;&gt;Warbler&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The scenario here is the following: Ettus receiver + HDSDR with speaker plugged into mic via an audio cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Warbler and SoundModem both do the same job or are there little differences?&lt;/p&gt;&#xA;" OwnerUserId="5524" LastActivityDate="2018-09-05T21:01:31.253" Title="Warbler vs SoundModem" Tags="&lt;digital-modes&gt;&lt;modes&gt;&lt;software-defined-radio&gt;&lt;satellites&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5465" PostTypeId="1" CreationDate="2015-11-02T14:12:42.037" Score="9" ViewCount="192" Body="&lt;p&gt;(Sorry, I don't know if this is the right forum for this question, but maybe someone will know the answer. If not, which StackExchange forum could be more suitable?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Me and a few friends of mine are planning to build a remote controlled balloon probe. As there already were many projects involving stratosphere flights, we are rather trying to go just a few kilometers high, but establish a permanent data connection. The problem is that where I live (Germany), operating quite much any RF module with sufficient range is illegal for people without a radio license, which we happen not to have.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So instead of that we are thinking of connecting a RasPi to a 3G dongle and transmit our data over a TCP connection. But how high does the signal of cell towers usually reach? I have read very contrary opinions about this. And how good is the quality of a connection up there? Is it sufficient to send greater chunks of data like low-res pictures? Maybe it might be important that mobile connections in airplanes have the additional problem of needing to change cell towers very frequently because of the high moving speed, which would not be the case in a slow-moving balloon probe.&lt;/p&gt;&#xA;" OwnerUserId="5561" LastEditorUserId="76" LastEditDate="2015-11-03T23:53:16.817" LastActivityDate="2020-01-11T20:29:01.560" Title="Can cellular radio be used for communication with a balloon?" Tags="&lt;mobile&gt;&lt;uhf&gt;&lt;internet&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5466" PostTypeId="1" CreationDate="2015-11-02T15:41:06.123" Score="3" ViewCount="332" Body="&lt;p&gt;I've come across plenty of resources for programmatically transmitting SSTV images and/or broadcasts (including &lt;a href=&quot;https://ham.stackexchange.com/users/5068/dnet&quot;&gt;dnet's&lt;/a&gt; &lt;a href=&quot;https://github.com/dnet/pySSTV&quot; rel=&quot;nofollow noreferrer&quot;&gt;pySSTV&lt;/a&gt;/&lt;a href=&quot;https://github.com/dnet/unixsstv&quot; rel=&quot;nofollow noreferrer&quot;&gt;UnixSSTV&lt;/a&gt; and &lt;a href=&quot;https://github.com/windytan&quot; rel=&quot;nofollow noreferrer&quot;&gt;Oona Räisänen's&lt;/a&gt; &lt;a href=&quot;https://github.com/windytan/slowrx&quot; rel=&quot;nofollow noreferrer&quot;&gt;slowrx&lt;/a&gt;), but none yet for it's error corrected, higher quality cousin: &lt;a href=&quot;https://en.wikipedia.org/wiki/Digital_Radio_Mondiale&quot; rel=&quot;nofollow noreferrer&quot;&gt;DRM&lt;/a&gt; (aka &lt;a href=&quot;http://www.g6hoq.com/easypal.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;EasyPal or Digital SSTV&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do useful open code libraries or examples exist? Such as for GRC, high level code(such as Python) or Linux libraries?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(&lt;em&gt;Note&lt;/em&gt;: I'm interested in the use of DRM for the transmission of data and images)&lt;/p&gt;&#xA;" OwnerUserId="5388" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-05-03T06:21:13.157" Title="DRM/Easypal/Digital SSTV programatic generation resources?" Tags="&lt;sstv&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5467" PostTypeId="2" ParentId="5466" CreationDate="2015-11-02T15:52:18.263" Score="0" Body="&lt;p&gt;For GRC I have only come across:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/kit-cel/gr-drm&quot; rel=&quot;nofollow&quot;&gt;GR-DRM&lt;/a&gt; / &lt;a href=&quot;https://github.com/fewu/gnuradio_drm&quot; rel=&quot;nofollow&quot;&gt;GNU Radio DRM&lt;/a&gt; GRC Examples. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Both are audio only and I do not have personal experience of the use / respective pros and cons.&lt;/p&gt;&#xA;" OwnerUserId="5388" LastEditorUserId="5388" LastEditDate="2015-11-03T11:00:03.227" LastActivityDate="2015-11-03T11:00:03.227" CommentCount="0" CommunityOwnedDate="2015-11-02T15:52:18.263" ContentLicense="CC BY-SA 3.0" />
  <row Id="5468" PostTypeId="1" AcceptedAnswerId="5469" CreationDate="2015-11-02T17:24:39.840" Score="3" ViewCount="5696" Body="&lt;p&gt;When should I use one polarization over the other on 2 meters?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've looked at the radiation patterns for horizontal dipole and seen how it changes based on mounting height. I haven't been able to find any information on how the vertical dipole radiation pattern changes with mounting height.&lt;/p&gt;&#xA;" OwnerUserId="5526" LastActivityDate="2015-11-14T04:54:55.887" Title="2 Meter horizontal or vertical dipole polarization?" Tags="&lt;antenna&gt;&lt;2m-band&gt;&lt;vertical-antenna&gt;&lt;dipole&gt;&lt;polarization&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5469" PostTypeId="2" ParentId="5468" CreationDate="2015-11-02T17:50:38.180" Score="4" Body="&lt;p&gt;For VHF, choice of polarization is not up to your desired radiation pattern, but who you want to be able to communicate with. In HF, the ionosphere causes random rotation of your signal's polarization, but in all line-of-sight communication, VHF or higher, there is no such rotation and a polarization mismatch can result in no signal at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should use vertical polarization if you wish to communicate with existing FM mobile and repeater stations, because they also use vertically polarized antennas (by convention, and because quarter-wave verticals are much more convenient than other types of antennas on vehicles and handhelds).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, you should use horizontal polarization if you are attempting 2 meter SSB or other types of DX/weak-signal work. Again by convention, but the convention arises because (if I understand correctly) horizontal dipoles typically have more gain, and because a horizontal dipole is a simple, efficient freestanding antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to be able to communicate with both types of stations using a single antenna, you &lt;em&gt;can&lt;/em&gt; use a diagonally or circularly polarized antenna, as a compromise which has a reliable small amount of loss in either case. However, such antennas are more directional than a vertical (at least as much as a horizontal dipole) and thus require pointing.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-11-02T17:50:38.180" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5470" PostTypeId="1" AcceptedAnswerId="5476" CreationDate="2015-11-02T18:07:08.920" Score="2" ViewCount="720" Body="&lt;p&gt;Consider the radiation pattern of a horizontal dipole mounted at a height of 1.75λ. Is it possible for a receiving station's antenna to be mounted at a certain height such that the radiation of the transmitting station misses the receiving antenna completely?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1SUW0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1SUW0.png&quot; alt=&quot;Horizontal Dipole Radiation Patters&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5526" LastActivityDate="2015-11-03T18:24:43.473" Title="Horizontal dipole radiation gaps" Tags="&lt;2m-band&gt;&lt;dipole&gt;&lt;polarization&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5472" PostTypeId="1" CreationDate="2015-11-03T08:08:20.477" Score="3" ViewCount="173" Body="&lt;p&gt;I have a 900Mhz transmitting antenna that is being received by one receiving antenna at the moment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to add a second (and possibly third, fourth, etc) antenna to increase the signal strength. Receiving antenna array size is somewhat a constraint, so I want to fit as many receiving antennas together as possible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that I'll have to do a bit of work to combine the signals, but I want to know, in theory, what is the spacing limit between each antenna in order to maximize signal power reception?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the moment, I'm using antennas with a gain of 5dbi. So each antenna has an &lt;a href=&quot;http://www.antenna-theory.com/basics/aperture.php&quot; rel=&quot;nofollow&quot;&gt;effective capture area&lt;/a&gt; of 276cm^2. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I place two (or more) antennas within the effective area of another antenna so that the effective areas overlap, and still receive an increase in signal strength?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What is the optimal spacing between antennas and their effective areas in order to maximize signal reception?&lt;/strong&gt; &lt;/p&gt;&#xA;" OwnerUserId="5569" LastEditorUserId="76" LastEditDate="2015-12-15T23:33:16.797" LastActivityDate="2015-12-15T23:33:16.797" Title="Antenna proximity limit to increasing signal strength via additional receiving antennas?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5473" PostTypeId="1" CreationDate="2015-11-03T11:24:43.240" Score="1" ViewCount="314" Body="&lt;p&gt;Are there any software TNC's (like &lt;a href=&quot;http://uz7.ho.ua/packetradio.htm&quot; rel=&quot;nofollow&quot;&gt;SoundModem&lt;/a&gt;) for Linux?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is limited to the ones which deal with BPSK1200 (used by cubesat projects).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For some cases &lt;a href=&quot;http://members.casema.nl/b.ubbels/Warbler.htm&quot; rel=&quot;nofollow&quot;&gt;Warbler&lt;/a&gt; will suffice.&lt;/p&gt;&#xA;" OwnerUserId="5524" LastEditorUserId="5524" LastEditDate="2015-11-04T11:41:26.633" LastActivityDate="2015-11-09T17:04:04.370" Title="Software TNC's for Linux? (targeted to BPSK1200)" Tags="&lt;digital-modes&gt;&lt;modes&gt;&lt;software&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5474" PostTypeId="2" ParentId="5473" CreationDate="2015-11-03T14:22:50.823" Score="0" Body="&lt;p&gt;&lt;a href=&quot;http://paclink-unix.sourceforge.net/&quot; rel=&quot;nofollow&quot;&gt;Paclink&lt;/a&gt; is a Linux adaptation of &lt;a href=&quot;http://www.winlink.org/&quot; rel=&quot;nofollow&quot;&gt;WinLink&lt;/a&gt; and might be a good place to start. As might the &lt;a href=&quot;http://tnc-x.com/TNCPi.htm&quot; rel=&quot;nofollow&quot;&gt;TNC-Pi project&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="5388" LastActivityDate="2015-11-03T14:22:50.823" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5475" PostTypeId="2" ParentId="5472" CreationDate="2015-11-03T16:12:01.983" Score="1" Body="&lt;p&gt;If you combine the signals from multiple antennas, you are not just collecting more power from any direction. &lt;strong&gt;A higher gain antenna is &lt;em&gt;always&lt;/em&gt; more directional;&lt;/strong&gt; this is a fundamental property of receiving &lt;em&gt;coherent&lt;/em&gt; radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that's not acceptable, because the transmitting antenna is moving, then you need multiple receivers (a.k.a. a &lt;strong&gt;diversity receiver&lt;/strong&gt;) as well as multiple antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that is acceptable, because the transmitting antenna is fixed or you can point the receiving antenna at it, then you are likely better off using a standard design for high-gain antennas (such as the Yagi-Uda antenna) rather than designing an array from scratch.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-11-03T16:12:01.983" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5476" PostTypeId="2" ParentId="5470" CreationDate="2015-11-03T18:24:43.473" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it possible for a receiving station's antenna to be mounted at a certain height such that the radiation of the transmitting station misses the receiving antenna completely?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In theory yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But in practice not entirely. Real dipoles are not mounted over infinitely large, perfectly flat, perfectly conductive planes, so the nulls will not be so deep as these idealized images suggest. Furthermore, there's likely more than one path between transmitter and receiver, taking into account reflections off mountains, trees, buildings, ionospheric changes, feedline radiation, etc. In practice there are dozens of things which make the path work (or not), and many of them are constantly changing or difficult to predict. Antenna height is just one factor.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-11-03T18:24:43.473" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5477" PostTypeId="2" ParentId="5473" CreationDate="2015-11-03T21:30:57.457" Score="1" Body="&lt;p&gt;Soundmodem (the original from Thomas Sailor) is still (Debian Jessie) available for Linux. I used it recently with aprx to create a software TNC with a generic USB sound card for APRS purposes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;apt-get install soundmodem&lt;/code&gt;&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2015-11-03T21:30:57.457" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5478" PostTypeId="1" CreationDate="2015-11-03T21:55:35.350" Score="2" ViewCount="182" Body="&lt;p&gt;I'm trying to determine the best way to operate a model rocket tracking beacon.  There's various vague details on modes of operating in part 97, and equally vague descriptions in the 70cm band plan, and I was hoping someone could bring some clarity to the topic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For now, I'm looking at using just a basic transmitter that can send a tone at regular intervals; since both weight and space are at a premium in a rocket, the simpler, the better.  97.215 covering telecommand of a model craft seems close other than this transmission will be generated by the craft and not used to control it.  Some of the telemetry regulations seem close except at this point with just a basic transmitter, it's more of a beacon, there's no actual telemetry data.  It's a bit like a fox hunt, but the transmitter isn't capable of identification (making the rules under 97.215 attractive).  It's definitely somewhat beacon-like, but it's not a propagation beacon.  What rules cover this type of operation?  The transmitter has a max of 100mW power, and the antenna is just a short piece of wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second part of this question is about frequency choice.  The arrl band plan (which Arizona uses with some small exceptions that don't seem to apply to this) has some vague categories, none of which seem to fit exactly.  Given the power level, weak signal work would seem to be the closest.  Although in general, if I pick a frequency that's not in use in the area combined with the 100mW transmit power, there should be few issues here as long as I stay inside the 70cm ham band I believe.&lt;/p&gt;&#xA;" OwnerUserId="5575" LastEditorUserId="76" LastEditDate="2015-11-03T22:20:36.983" LastActivityDate="2015-11-05T22:02:16.930" Title="model rocket locater" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;automation&gt;&lt;beacon&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5479" PostTypeId="2" ParentId="1584" CreationDate="2015-11-04T06:22:53.527" Score="-2" Body="&lt;p&gt;Actually LTE standard could be adapted for Amateur for certain bands Amateur radio has some packet switching radios where you can connect to the internet but like Ham radio it is so slow. If Ham radio wants to survive into the 21st century we need to get it away from these old gray haired men and give it new life. Get the internet working at very high speeds. LTE advanced can go as high as 3GIG Amateur has 1.2GHZ band and 440 we could use those bands and implement LTE. You can't sell the service but provide it for free to other Ham radio operators. &lt;/p&gt;&#xA;" OwnerUserId="5579" LastActivityDate="2015-11-04T06:22:53.527" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5480" PostTypeId="2" ParentId="5472" CreationDate="2015-11-04T15:37:35.720" Score="1" Body="&lt;p&gt;It sounds like you will need to simulate various configurations in something like EZNEC or another product.  Trial and error is king here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally I would recommend 1/2 wavelength, but in this case you may want to just simulate trial and error.&lt;/p&gt;&#xA;" OwnerUserId="5404" LastActivityDate="2015-11-04T15:37:35.720" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5481" PostTypeId="2" ParentId="5437" CreationDate="2015-11-04T15:41:12.717" Score="0" Body="&lt;p&gt;Ditch the drone idea, that's going to be way too expensive.  You're better off getting a bunch of PVC pipe, sticking it in the mud, and guying it every 25 feet.&lt;/p&gt;&#xA;" OwnerUserId="5404" LastActivityDate="2015-11-04T15:41:12.717" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5482" PostTypeId="2" ParentId="5472" CreationDate="2015-11-05T11:31:40.330" Score="0" Body="&lt;p&gt;The spacing between antennas has to be at least $\lambda/2$ where $\lambda$ is the wavelength.The key to using a diversity scheme is that the fading channels between the transmitter's antenna  and the receiver antennas should  be as independent as possible so the greater the distance between the receive antennas the better.Recieve diversity does not improve received signal strength, it just improves the receiver's sensitivity and in thus doing improve link performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that you have 1 transmitter and 2 receivers (i.e  a single-input single output SIMO system), there are two options you can use to demodulate at the receiver:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) You can independently demodulate the two symbols, average them and choose the most likely transmitted symbol.This option will double the processing time at the receiver or will use twice as many resources at the recievers so it isn't the most ideal option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) What is commonly done is that there is channel estimation done at the receiver (this commonly done by using pilot symbols and the LMS algorithm) and those the channel estimates are used to multiplex the symbols at the receiver to create the decision variable, $Z$.The decision variable, Z, can then be used for demodulation.i.e&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;   \mathbf{y = H}x + \mathbf{n}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;  Z = \mathbf{H^Hy} = \left( \sum_{n = 1}^N |h_n|^2 \right)x + \mathbf{H^Hn} = \left( \sum_{n = 1}^N |h_n|^2 \right)x + \mathbf{\hat{n}}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\mathbf{y} = [y_0 ,y_1]$ is the received symbol vector for the received symbols at receiver 0 and receiver 1, $\mathbf{H} = [h_0 , h_1]^T$ is the channel estimates for the different fading channels to the reciever, $x$ is the transmitted symbol and $\mathbf{n} = [n_0 , n_1]$ is the noise vector.The operation $\mathbf{H^H}$ is the Hermitian transpose of the vector $\mathbf{H}$ and is equivalent to performing a transpose and then taking the complex conjugate (i.e $\mathbf{H^H = (H^*)^T} $). As the equation shows, a divesity gain of order $N$ can be achieved using this method.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;General diagram of a SIMO scheme:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0f5DU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0f5DU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5515" LastEditorUserId="5515" LastEditDate="2015-11-05T14:31:40.053" LastActivityDate="2015-11-05T14:31:40.053" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5483" PostTypeId="2" ParentId="5478" CreationDate="2015-11-05T22:02:16.930" Score="1" Body="&lt;p&gt;If you don't have identification, then it's probably not a ham band item. The only exception to that rule is model aircraft controllers, and that is only for 6m, specific frequencies, and still doesn't apply. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You probably want a &lt;a href=&quot;https://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf&quot; rel=&quot;nofollow&quot;&gt;Part 15 device&lt;/a&gt;. See the FCC rules, but basically you can make up to 5 without FCC approval (Conditions apply) for non-commercial use.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-11-05T22:02:16.930" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5485" PostTypeId="1" CreationDate="2015-11-06T12:37:14.063" Score="3" ViewCount="181" Body="&lt;p&gt;To track and receive some data from satellites, or should I say cubesats - which are kind of popular these days, which is the minimum investment? What's cheapest/easiest satellite to begin with? Besides a laptop which equipment do I need?&lt;/p&gt;&#xA;" OwnerUserId="5524" LastActivityDate="2015-12-18T21:10:24.143" Title="Low cost satellite (cubesat) tracking station" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5486" PostTypeId="1" CreationDate="2015-11-06T17:56:58.437" Score="1" ViewCount="169" Body="&lt;p&gt;&lt;a href=&quot;http://websdr.org/&quot; rel=&quot;nofollow&quot;&gt;WebSDR&lt;/a&gt; is a Software-Defined Radio receiver connected to the internet. &lt;a href=&quot;http://websdr.suws.org.uk/WebSDR-Presentation.pdf&quot; rel=&quot;nofollow&quot;&gt;Here&lt;/a&gt; is being said &quot;OK for HF but no good for VHF / UHF&quot;. I was thinking to use it for cubesat reception but given that the antennas as fixed I guess It will not work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could WebSDR be used for cubesat reception? To be more specific I would like to listen to VHF BPSK1200.&lt;/p&gt;&#xA;" OwnerUserId="5524" LastActivityDate="2015-12-08T20:23:40.947" Title="Track cubesat with webSDR, is is feasible?" Tags="&lt;software-defined-radio&gt;&lt;satellites&gt;&lt;software&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5487" PostTypeId="1" CreationDate="2015-11-06T19:13:59.643" Score="2" ViewCount="81" Body="&lt;p&gt;Will a directional antenna guarantee longer reception periods then a &lt;a href=&quot;https://ham.stackexchange.com/questions/2211/idea-for-better-reception-in-crowded-city&quot;&gt;standard antenna&lt;/a&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;May I ask for the specs for one of this directional antennas to use with RTL-SDR?&lt;/p&gt;&#xA;" OwnerUserId="5524" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-11-08T20:07:23.940" Title="Directional antenna for FUNcube reception" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5488" PostTypeId="2" ParentId="5487" CreationDate="2015-11-08T20:07:23.940" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Will a directional antenna guarantee longer reception periods then a standard antenna?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Provided it's pointed in the right direction, and of the right polarity, then a more directional antenna will have higher gain and allow you to successfully demodulate the signal at a lower threshold than had you used a less directional antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course the issue with satellites is the things are always moving, so getting them pointed in the right direction can be difficult. So you have a design compromise to make: do you want it to be able to receive weaker signals, or be less critical of aiming?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;May I ask for the specs for one of this directional antennas to use with RTL-SDR?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The RTL-SDR does not require any special antenna. Any antenna with the right connector, and designed to operate at your desired frequency, should work fine.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-11-08T20:07:23.940" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5489" PostTypeId="2" ParentId="5486" CreationDate="2015-11-08T20:20:59.090" Score="1" Body="&lt;p&gt;That presentation says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Most websdr cover HF and VHF using sound cards&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Only 96 KHz band coverage&lt;/li&gt;&#xA;  &lt;li&gt;Just like Softrock&lt;/li&gt;&#xA;  &lt;/ul&gt;&lt;/li&gt;&#xA;  &lt;li&gt;OK for HF but no good for VHF / UHF&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The operative statement is &lt;em&gt;only 96 KHz band coverage&lt;/em&gt;. This is fine on HF, since 96 KHz is a good chunk or all of many HF bands. But with increasing frequency, the bands tend to get bigger. For example here the 2m band goes from 144 to 148 MHz: that's 4,000 KHz wide. The 23cm band goes from 1240-1300 MHz: that's 60,000 kHz wide: enough to fit the entire HF spectrum!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you can see the issue: with &quot;most&quot; web SDR implementations using a sound card SDR which has a receive bandwidth of only 96 KHz, only a very small fraction of any VHF band can be covered. It's not any problem of WebSDR per se, just the receivers that are sometimes used with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can find a WebSDR which covers your frequency of interest, and has enough sensitivity to receive the satellite you'd like to track, there's no particular reason it would not work.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-11-08T20:20:59.090" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5490" PostTypeId="1" CreationDate="2015-11-09T11:06:02.110" Score="2" ViewCount="218" Body="&lt;p&gt;Is it possible to use an Ettus &lt;a href=&quot;http://www.ettus.com/product/details/USRPPKG&quot; rel=&quot;nofollow&quot;&gt;USRP1&lt;/a&gt; (or &lt;a href=&quot;http://www.ettus.com/content/files/kb/07495_Ettus_B100_DS_Flyer_HR_4.pdf&quot; rel=&quot;nofollow&quot;&gt;B100&lt;/a&gt;) instead of &lt;a href=&quot;http://www.funcubedongle.com/?page_id=1201&quot; rel=&quot;nofollow&quot;&gt;Funcube Dongle&lt;/a&gt; to receive cubesat signals?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Ettus ones are more expensive.&lt;/p&gt;&#xA;" OwnerUserId="5524" LastEditorUserId="4637" LastEditDate="2015-11-10T18:02:31.507" LastActivityDate="2016-01-14T01:00:01.030" Title="Ettus USRP1 (or B100) instead of Funcube Dongle" Tags="&lt;software-defined-radio&gt;&lt;satellites&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5491" PostTypeId="2" ParentId="5490" CreationDate="2015-11-09T14:03:11.163" Score="2" Body="&lt;p&gt;Yes. You'll want to get the daughterboard covering the band(s) you want to receive. And since both the Funcube Dongle and the USRP radios are &lt;em&gt;sofware defined&lt;/em&gt; radios, you'll need in each case appropriate software which is compatible with your hardware, and capable of demodulating the signal you wish to receive.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-11-12T12:20:10.553" LastActivityDate="2015-11-12T12:20:10.553" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5492" PostTypeId="1" CreationDate="2015-11-09T15:20:28.817" Score="2" ViewCount="400" Body="&lt;p&gt;Given the following specs of a directional antenna:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;VHF yagi antenna – 12dBic gain, switchable RHCP - LHCP&#xA;VHF Low Noise Amplifier (NF: 0.8dB)&#xA;Frequency range: 144-146MHz&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;(Is this description enough to characterize the antenna?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What will be the specs of a fixed antenna capable to receive the same signal (~145.8 MHz, cw and BPSK1200)?&lt;/p&gt;&#xA;" OwnerUserId="5524" LastEditorUserId="76" LastEditDate="2016-04-15T17:46:28.320" LastActivityDate="2016-04-15T17:46:28.320" Title="Replace directional antenna by fixed antenna" Tags="&lt;antenna&gt;&lt;satellites&gt;&lt;vhf&gt;&lt;lna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5493" PostTypeId="1" CreationDate="2015-11-09T15:42:17.853" Score="2" ViewCount="109" Body="&lt;p&gt;What are the specs of the &lt;a href=&quot;https://ham.stackexchange.com/questions/2211/idea-for-better-reception-in-crowded-city&quot;&gt;FUNcube Dongle antenna&lt;/a&gt;? I mean, how to fully describe only the antenna?&lt;/p&gt;&#xA;" OwnerUserId="5524" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2015-11-19T12:51:41.010" Title="FUNcube Dongle antenna specs" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;&lt;satellites&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5495" PostTypeId="2" ParentId="5492" CreationDate="2015-11-09T18:51:15.623" Score="1" Body="&lt;p&gt;Whether you can use an omnidirectional antenna to replace a directional antenna depends entirely on&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the minimum signal-to-noise ratio required by the receiver, and&lt;/li&gt;&#xA;&lt;li&gt;the amount of noise arriving from directions other than the wanted signal.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Without this information, your question does not have a yes-or-no answer. And if you are going to go to the effort of collecting the second piece of information you might as well just replace the antenna with your proposed alternative and see what the results are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Presumably you are attempting to receive a signal from a satellite. An appropriate omnidirectional antenna for the purpose — one which does not have a null pointing upward, as a vertical does — would be a “turnstile” or “eggbeater” type antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The presence of an LNA at the antenna feed point is largely independent of the choice of antenna — you can think of it just as well as being part of the receiver. And as I mentioned to start, the input signal-to-noise ratio is the key characteristic. If there is too much noise, the LNA will do you no good. A directional antenna avoids your receiving unnecessary noise.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-11-09T18:51:15.623" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5496" PostTypeId="2" ParentId="5492" CreationDate="2015-11-09T18:54:23.833" Score="2" Body="&lt;p&gt;These specifications mean:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;VHF yagi antenna&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This tells you the general kind of antenna it is: a &lt;a href=&quot;https://en.wikipedia.org/wiki/Yagi-Uda_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yagi&lt;/a&gt; intended to operate at &lt;a href=&quot;https://en.wikipedia.org/wiki/Very_high_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;VHF&lt;/a&gt;: &quot;very high frequency&quot;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;12dBic gain&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This means that in the antenna's direction of maximum gain, it will receive 12dB more power than a theoretical circularly polarized antenna which receives power equally from all directions. It means that if the antenna is pointed directly at the satellite, and the satellite also has a circularly polarized antenna, you can add 12dB to your &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt;. (If the satellite does not have a circularly polarized antenna, you can add only 9dB: there's a 3dB penalty for not having circular polarization on both ends).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;switchable RHCP - LHCP&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This means that the polarization of the antenna can be switched between right-handed circular and left-handed &lt;a href=&quot;https://ham.stackexchange.com/q/1558/218&quot;&gt;circular polarization&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;VHF Low Noise Amplifier&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This means the antenna contains an integrated amplifier. Amplifiers require power, so you'll want to read about how that power is supplied to make sure it's compatible with the rest of your system. It might have a separate power supply that you just plug into the wall. Or, it may have some arrangement to be powered over the feedline.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;NF: 0.8dB&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Noise_figure&quot; rel=&quot;nofollow noreferrer&quot;&gt;noise figure&lt;/a&gt; of the amplifier. It is telling you that the amplifier degrades the signal to noise ratio by 0.8dB. An ideal amplifier that added no noise would have a noise factor of 0dB.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Frequency range: 144-146MHz&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is telling you the frequencies over which the antenna is designed to work well.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What will be the specs of a fixed antenna capable to receive the same signal (~145.8 MHz, cw and BPSK1200)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Antennas do not &quot;know&quot; what kind of signal they are receiving. That is, they don't care what the modulation is. So there are quite a lot of antennas which could have similar capabilities. Hopefully with the explanation of the specifications above you can better understand how a different antenna might be more or less suitable to your needs.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-11-09T18:54:23.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5498" PostTypeId="1" AcceptedAnswerId="8891" CreationDate="2015-11-13T10:12:52.273" Score="3" ViewCount="5260" Body="&lt;p&gt;Okay so I saw these walkie talkies on eBay that I want to buy but I live in Japan and I am not sure if they are legal. I did some research but couldn't figure out if they are or not. I am very much a beginner when it comes to walkie talkies etc. so any help would be very much appreciated.&#xA;Here is the walkie talkie specs:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;BAOFENG UV-3R &#xA;VHF/ UHF  DUAL-BAND TWO WAY RADIO&#xA;Frequency Range: 136-174 / 400-470MHz&#xA;Output Power: 2 Watts&#xA;99 Channels + 1 Emergency Channel&#xA;50 CTCSS and 104 CDCSS&#xA;Built-in VOX Function&#xA;1750Hz Brust Tone&#xA;FM Radio (87.0MHz-108.0MHz)&#xA;25KHz/12.5KHz Switchable&#xA;Channel Step: 5/6.25/12.5/25KHz   &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Here are some more:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Frequency Range&#xA;VHF136-174 UHF 400-470MHz (Dual Band)&#xA;Operating Voltage: 3.7V&#xA;Operating Temperature: -30c~+60c&#xA;Battery: (Li-ion)&#xA;Antenna Impedance: 50 ohm&#xA;Transmitter &#xA;RF Power Output: UHF:2W/  &#xA;FM Noise: 65dB&#xA;Adjacent Channel Power:45dB/42dB&#xA;&#xA;Receiver&#xA;Spurious response rejection: 60dB&#xA;Receiver current: 400mA&#xA;Standby Current: 75mA&#xA;&#xA;Band:   UHF / VHF&#xA;Frequency Range:    VHF136-174 UHF 400-470MHz (Dual Band)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I hope these do work. Here is the link to the page.&#xA;&lt;a href=&quot;http://www.ebay.com.au/itm/351398723510&quot; rel=&quot;nofollow&quot;&gt;http://www.ebay.com.au/itm/351398723510&lt;/a&gt;&#xA;I thought it best to ask here before I buy because I don't want to get myself or my Dad in trouble with the law.&lt;/p&gt;&#xA;" OwnerUserId="5616" LastEditorUserId="76" LastEditDate="2015-11-13T18:38:45.597" LastActivityDate="2021-05-15T02:29:29.603" Title="Are these walkie talkies legal in Japan?" Tags="&lt;legal&gt;&lt;ht&gt;&lt;japan&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5499" PostTypeId="2" ParentId="996" CreationDate="2015-11-13T12:41:29.747" Score="2" Body="&lt;p&gt;I've been doing some experimentation as well and met the same issue. The way I've been dealing with it is to use a CW tag before and after the mode (as well as sometimes alongside my data mode). In it I put my callsign, and a tiny url (as its morse)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;e.g. if my experiment data was at google.com, i nip to tinyurl and get a tinyurl: &lt;code&gt;http://tinyurl.com/2tx&lt;/code&gt;, so I would transmit:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;[CALLSIGN]    EXPERIMENT SEE - HTTP TINYURL COM 2TX    [CALLSIGN]&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;and hopefully people understand that without the punctiaton. The page itself is generally a blog page containing information on what I'm doing - not necessarily anywhere you can download a file to decode or instructions, but importantly I put a contact form or a way of getting in touch if I'm causing interference. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I currently pre-code the audio files that I transmit, and can overlay that morse alongside the data blob so it goes out like a margin notes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rules (in the UK) say you can't transmit secret codes, and the essence of my work not being public isn't that I'm being secret, just that I'm not ready to publish the source (thats arguably an interpretation). In practice it wouldn't take long for someone to analyse and decode the message as mine are all PSK based of underlying data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Software testing with generated noise etc is good, but doesn't always let you test reality. I probably do 99% of my tests with just audio connections between overplayed with static etc, which lets me tinker without having to make real radio connections between people.&lt;/p&gt;&#xA;" OwnerUserId="5199" LastActivityDate="2015-11-13T12:41:29.747" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5500" PostTypeId="2" ParentId="5498" CreationDate="2015-11-13T15:48:47.423" Score="1" Body="&lt;p&gt;These cover a broad range, and would not be legal in all of the bands. (I'm assuming you are a licensed ham, BTW) From my research (See &lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?topic=28252.5;wap2&quot; rel=&quot;nofollow&quot;&gt;eham forms&lt;/a&gt;) it seems that the bands are both smaller in Japan, and don't permit repeaters in the 2m band. Of particular note is that the 70 cm band, which does allow repeaters, is much smaller, namely 430-440 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, I would recommend buying one made for Japan, because it sounds like repeater offsets and other information are different in Japan than the US. You might be able to find a downloadable software upgrade that will configure the UV-3R to transmit only on the allowed Japanese frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are not licensed, then in the US you could operate on FRS radio. These radios are not configured in a legal FRS in the United States (They have to only be able to transmit on FRS frequencies). In Japan, there is no FRS radio, so normal walkie-talkies are illegal there as well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bottom line, I wouldn't take them, or any walkie-talkie, unless you are a licensed amateur radio operator, and even in that case, be careful!&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2015-11-13T15:48:47.423" CommentCount="15" ContentLicense="CC BY-SA 3.0" />
  <row Id="5501" PostTypeId="2" ParentId="5468" CreationDate="2015-11-14T04:54:55.887" Score="2" Body="&lt;p&gt;I've always heard (but am unable offhand to quote authoritative research or provide an explanation of why this is so) that an advantage of horizontal for weak signal work is that a lot of man-made noise tends to be better received with vertical polarization than with horizontal.  Thus, all else being equal, you will have better performance (i.e. a better SNR at the receiver) with horizontal.  As a side benefit, if you are operating on frequencies that are usually used vertically, interference between you and other users is reduced; thus, not only are you giving yourself an advantage, but you are arguably being a good neighbor at the same time!&lt;/p&gt;&#xA;" OwnerUserId="5004" LastActivityDate="2015-11-14T04:54:55.887" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5502" PostTypeId="2" ParentId="1367" CreationDate="2015-11-14T22:48:46.583" Score="7" Body="&lt;p&gt;As Phil Genera says, the KX3 uses a different type of receiver that requires a different kind of filter. A traditional superheterodyne receiver, which is what you'd find in most older radios, uses a mixer to convert the desired signal to a fixed IF of say 10.7MHz and then uses a very narrow bandpass filter at that frequency to select only that signal. Crystal filters are particularly well suited here because they're extremely narrow, stable bandpass filters - far narrower and more stable than can be achieved with LC bandpass filters. Ceramic filters are very similar but cheaper, less narrow, and less stable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The KX3 doesn't work like that. It's a quadrature direct conversion receiver - instead of converting the signal to IF, it converts it to a pair of I and Q signals at around audio frequencies, and then uses a pair of lowpass filters to filter out all the other frequencies, which can easily be implemented as standard LC filters. (Though looking at the schematic, those aren't the only filters - there's also some active filtering in the following amplifier stages. See the capacitors in the op-amp feedback loops? Those turn the amplifiers into additional low-pass filters. This is a very common and effective way of filtering audio-frequency signals.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also a subsequent software filtering stage that's far sharper and more adjustable than the hardware filters, but this isn't specific to direct conversion designs - there are modern ham transceivers out there that use traditional superheterodyne receivers with a standard IF filter, followed by adjustable software filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you might ask, &lt;a href=&quot;https://ham.stackexchange.com/questions/850/how-is-the-if-for-a-superhet-selected&quot;&gt;why use such a high intermediate frequency&lt;/a&gt; if it makes constructing filters harder? Image rejection. The mixer doesn't just convert our desired frequency to the IF, it also does the same with an image frequency exactly twice the IF away from the frequency we want. Since we can't make tunable RF filters that are anywhere near as narrow as our fixed-frequency IF filter, we have to make the IF high enough that we can stop the image frequency reaching the mixer using a relatively wide input filter. Using separate I and Q signals makes it possible to distinguish signals at the desired and image frequencies and makes direct conversion practical, but only if all the stages after the IQ conversion are done in software rather than hardware. &lt;/p&gt;&#xA;" OwnerUserId="5622" LastEditorUserId="8573" LastEditDate="2019-07-31T18:44:54.223" LastActivityDate="2019-07-31T18:44:54.223" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="5503" PostTypeId="2" ParentId="5437" CreationDate="2015-11-15T00:57:43.983" Score="1" Body="&lt;p&gt;Use a balloon on calm days and a kite on windy days.&lt;/p&gt;&#xA;" OwnerUserId="5623" LastActivityDate="2015-11-15T00:57:43.983" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5504" PostTypeId="1" AcceptedAnswerId="5508" CreationDate="2015-11-15T22:50:36.880" Score="6" ViewCount="397" Body="&lt;p&gt;I would like to build an antenna for receiving NOAA weather satellites. They're receivable at around 137.5 Mhz. I'm a total new to amateur radio stuff. I know that it's not legal to communicate as private person on several frequency areas- so I would like to know if it's legal to &quot;listen-only&quot; to those satellites on this frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm here because I haven't found any sources proofing that it's legal or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it matters, I live in Germany.&lt;/p&gt;&#xA;" OwnerUserId="5630" LastActivityDate="2015-11-16T16:37:12.537" Title="Weather Imaging with NOAA satellites - legal?" Tags="&lt;legal&gt;&lt;satellites&gt;&lt;vhf&gt;&lt;weather&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5505" PostTypeId="2" ParentId="5504" CreationDate="2015-11-16T01:11:49.043" Score="5" Body="&lt;p&gt;Here in the US, it is perfectly legal for you to listen and &quot;download&quot; the satellite data.  Since the data is created by a public agency, it is considered to be in the public domain and not subject to copyright.  On this website at &lt;a href=&quot;http://www.weather.gov/disclaimer&quot;&gt;http://www.weather.gov/disclaimer&lt;/a&gt;, you can find the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;The information on National Weather Service (NWS) Web pages are in the public domain, unless specifically noted otherwise, and may be used without charge for any lawful purpose so long as you do not: 1) claim it is your own (e.g., by claiming copyright for NWS information -- see below), 2) use it in a manner that implies an endorsement or affiliation with NOAA/NWS, or 3) modify its content and then present it as official government material. You also cannot present information of your own in a way that makes it appear to be official government information.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a lot more information there that you should read.  I am not a lawyer, but I would assume that with the information being in the public domain and with Germany being a Berne Convention signatory, you should be just fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might want to contact your country's copyright office and make sure, but I use the weather fax as transmitted on HF all the time here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73,&#xA;Sean KD5COL&lt;/p&gt;&#xA;" OwnerUserId="5631" LastActivityDate="2015-11-16T01:11:49.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5507" PostTypeId="1" CreationDate="2015-11-16T11:56:30.973" Score="1" ViewCount="221" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3xmPV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3xmPV.png&quot; alt=&quot;Ultimate 3s PCB&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In &lt;strong&gt;basic terms&lt;/strong&gt;, using an &lt;a href=&quot;http://www.qrp-labs.com/ultimate3.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ultimate3S Beacon&lt;/a&gt; (above) as an example, what do the various toroidal components do exactly? How do they accomplish this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In construction terms, does it matter if the wound wires touch or overlap? Or does only the number of 'wraps' matter?&lt;/p&gt;&#xA;" OwnerUserId="5388" LastActivityDate="2015-11-17T17:21:37.777" Title="Toroidal inductor and transformer basics" Tags="&lt;electronics&gt;&lt;filter&gt;&lt;inductor&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5508" PostTypeId="2" ParentId="5504" CreationDate="2015-11-16T16:37:12.537" Score="5" Body="&lt;p&gt;Here in EU it's perfectly legal to receive transmission on any frequency. Additional restrictions may apply if the transmission is not mean to be public, for example encrypted Wi-Fi networks or government agencies radios. (source: Telekommunikationsgesetz (TKG) § 89).&lt;/p&gt;&#xA;" OwnerUserId="5636" LastActivityDate="2015-11-16T16:37:12.537" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5510" PostTypeId="2" ParentId="5507" CreationDate="2015-11-16T19:48:39.667" Score="1" Body="&lt;p&gt;Inductors act analogously to a flywheel for electrical current. That is, they want to keep the current steady. To increase or decrease the current requires &lt;a href=&quot;https://en.wikipedia.org/wiki/Work_(physics)&quot; rel=&quot;nofollow&quot;&gt;work&lt;/a&gt;, like speeding or slowing a flywheel requires work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are the &lt;a href=&quot;https://en.wikipedia.org/wiki/Duality_(electrical_circuits)&quot; rel=&quot;nofollow&quot;&gt;electrical dual&lt;/a&gt; of capacitors: capacitors do for voltage what inductors do for current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In RF applications, inductors (like capacitors) are frequently used as components in filters which accept or reject signals by frequency. They are also used in constructing oscillators, which electrically are really just specialized filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transformers are effectively two or more inductors that share the same core. As the name suggests, they can be used to &quot;transform&quot; impedances by some ratio, analogously to how a gearbox transforms mechanical impedances. This has application in &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_matching&quot; rel=&quot;nofollow&quot;&gt;impedance matching&lt;/a&gt;. Since the two halves of the transformer aren't connected by any wire, transformers also provide &lt;a href=&quot;https://en.wikipedia.org/wiki/Galvanic_isolation&quot; rel=&quot;nofollow&quot;&gt;galvanic isolation&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A nice property of toroidal inductors and transformers, versus other shapes, is that the magnetic field lines are almost entirely contained within the toroid. This means they less susceptible to perturbations from other nearby components, and generate less such perturbations themselves. The downside is they are more expensive, since it takes a complicated machine to wind them. If they are being wound by hand this is much less of a concern, which is why toroidal inductors are popular in kits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manner in which the wires go through the toroid does not matter too much. It's fine if the wires touch: although the wire may look bare, it's actually coated in an insulating enamel. However, it is best to keep the turns as uniformly spaced and snug as possible.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2015-11-17T17:21:37.777" LastActivityDate="2015-11-17T17:21:37.777" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5512" PostTypeId="1" CreationDate="2015-11-17T02:19:14.207" Score="1" ViewCount="34" Body="&lt;p&gt;Given a number of mobile clients, is it possible to find a spot to place a wifi ap to optimize the reception for said clients?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use FSPL equation to calculate the signal from the clients' position:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{FSPL(dB)} = 20\log_{10}(d) + 20\log_{10}(f) + k $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For d,f in meters and kilohertz, respectively, k becomes -87.55.&#xA;For d,f in meters and megahertz, respectively, k becomes -27.55.&#xA;For d,f in kilometers and megahertz, respectively, k becomes 32.45.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Free-space_path_loss&quot; rel=&quot;nofollow&quot;&gt;https://en.wikipedia.org/wiki/Free-space_path_loss&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any help appreciated&lt;/p&gt;&#xA;" OwnerUserId="5638" LastEditorUserId="13" LastEditDate="2015-11-18T23:12:32.573" LastActivityDate="2015-11-18T23:12:32.573" Title="Find optimal position to place antenna" Tags="&lt;wifi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5515" PostTypeId="2" ParentId="5512" CreationDate="2015-11-17T17:16:22.697" Score="2" Body="&lt;p&gt;If we assume that each client has a similar antenna, and is working on the same frequency, then we can simplify the math by simply stating that the signal strength, in decibels, falls off linearly with distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are then various ways you might decide what the &quot;best&quot; compromise in placement is, but one is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Centroid#Of_a_finite_set_of_points&quot; rel=&quot;nofollow&quot;&gt;centroid&lt;/a&gt;, which minimizes the sum of squared Euclidean distances to each client.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course given pathological cases it won't work so well. Consider if you have 10 clients in your home, and one on the moon, the centroid will be somewhere in cislunar space, and you'll end up with a WiFi AP that doesn't work for any of the clients.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, real world conditions make this mathematical solution purely academic. Practical applications must consider:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;reflection off objects&lt;/li&gt;&#xA;&lt;li&gt;attenuation from walls&lt;/li&gt;&#xA;&lt;li&gt;interference from other APs&lt;/li&gt;&#xA;&lt;li&gt;noise from other electronic devices&lt;/li&gt;&#xA;&lt;li&gt;antenna directionality and polarization&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These effects make the idealized free-space path loss significantly different from the real loss. And in practice, and &lt;em&gt;especially&lt;/em&gt; on the crowded 2.4 GHz band, avoiding interference is at least as critical as getting a good signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, AP placement is done by picking a location which seems pretty close to most of the clients, but which is also clear of walls and other obstructions, and which is physically accessible for the installation. Then measurements of signal quality are made in situ, and adjustments are made as necessary.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-11-17T17:16:22.697" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5516" PostTypeId="2" ParentId="5485" CreationDate="2015-11-18T20:38:36.690" Score="2" Body="&lt;p&gt;With as little as about £20 you can get going. For a starter you can try to listen to the CW beacons of cubesats like UKube-1. They are in good old morse code and usually transmitting in the 2m amateur band. I built the cheapest tracking yagi out of an old venetian blind and used an RTL-SDR dongle as the receiver.&#xA;Here are two articles I wrote about the subject:&lt;br&gt;&#xA;&lt;a href=&quot;http://www.spaceportscotland.org/news.asp?intent=viewstory&amp;amp;newsid=63498&quot; rel=&quot;nofollow&quot;&gt;Tracking UKube-1&lt;/a&gt; &lt;br&gt;&#xA;&lt;a href=&quot;http://www.spaceportscotland.org/index.asp?pageid=571655&quot; rel=&quot;nofollow&quot;&gt;Low budget satellite tracking&lt;/a&gt; &lt;br&gt;&lt;/p&gt;&#xA;" OwnerUserId="5644" LastActivityDate="2015-11-18T20:38:36.690" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5517" PostTypeId="2" ParentId="5408" CreationDate="2015-11-19T01:45:27.337" Score="1" Body="&lt;p&gt;This is not a complete answer so I am not going to mark it, but I just did some testing with an MFJ-911 4:1 balun with fixed resistances connected to the output. (Metal oxide resistors). Using an antenna analyzer I got results consistent with assuming that the impedance was just 1/4 the resistance I connected, with no additional phase factor other then what I expected due to the cable connecting the balun to the analyzer. &lt;/p&gt;&#xA;" OwnerUserId="5296" LastActivityDate="2015-11-19T01:45:27.337" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5520" PostTypeId="2" ParentId="5493" CreationDate="2015-11-19T12:51:41.010" Score="2" Body="&lt;p&gt;It appears that you provide your own antenna for the FUNcube (but this isn't explicitly stated anywhere I can find on their web site).  If you want to know the specs for the specific antenna the person in the post you link to used, you should probably ask him directly.&lt;/p&gt;&#xA;" OwnerUserId="5643" LastActivityDate="2015-11-19T12:51:41.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5521" PostTypeId="1" AcceptedAnswerId="5537" CreationDate="2015-11-20T03:28:24.847" Score="1" ViewCount="1040" Body="&lt;p&gt;I'm getting started with my first (very basic) HF rig and for convenience and the experience I'd like to try an &lt;a href=&quot;http://www.aa5tb.com/efha.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;End Fed Half Wave&lt;/a&gt; antenna. Typical designs for a &quot;matchbox&quot; in this case include somewhere between a 6:1 and 10:1 turns ratio around a toroid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Winding my own toroids is a new experience (though I guess I've built electromagnets and germanium radios as a kit) and I'm still pretty unfamiliar with the conventions. I understand that ferrites come in a &lt;a href=&quot;https://ham.stackexchange.com/questions/1159/how-does-one-read-a-ferrite-datasheet&quot;&gt;variety of specifications&lt;/a&gt; beyond just size — permeability, flux density, etc. I need to learn more about these for winding &lt;em&gt;inductors&lt;/em&gt; themselves, but how relevant are they for &lt;em&gt;transformers&lt;/em&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, on the first link there's one short reference &quot;the torroid [sic] is actually larger than a T-50-2&quot;. In &lt;a href=&quot;http://pages.suddenlink.net/wa5bdu/efhw.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this build&lt;/a&gt; &quot;the toroid is a T130-2 core&quot;. I really don't know what those numbers mean to begin with, but I get the impression I could wind the right number of turns around pretty much any size/shape ferrite and get something that would work? Would certain options be less efficient? Or simply effect the maximum working power? What factors should I pay attention to, and what can I ignore for these purposes?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-19T00:29:43.643" Title="Do a toroid's specs matter much in an antenna matching transformer?" Tags="&lt;antenna-tuner&gt;&lt;ferrite&gt;&lt;end-fed-antenna&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5522" PostTypeId="1" AcceptedAnswerId="5529" CreationDate="2015-11-20T04:59:43.263" Score="6" ViewCount="2654" Body="&lt;p&gt;I'm having trouble understanding what seems to be the fundamental principle behind baluns (and probably other related topics).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps some of my confusion comes from an audio background, where one has &quot;balanced&quot; and &quot;unbalanced&quot; cabling in a way that is easier for me to understand: an unbalanced cable is simply a signal and ground wire, while a &lt;em&gt;balanced&lt;/em&gt; cable actually has a ground wire and &lt;em&gt;two&lt;/em&gt; conductors whose voltages are opposite. Balanced cables are used — it is said — so that external interference that raises the voltage across the cable as a whole does not affect the &lt;em&gt;difference&lt;/em&gt; between the two signal lines. [Although now I'm questioning why just the two wires of an unbalanced cabled can't be measured &quot;differentially&quot; too…]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now in ham radio lore, it seems a ladder line usually would serve as a balanced transmission line while a coax is unbalanced. But in both there's just two conductors. And in both cases, according to Kirchhoff's current law, the current entering one conductor of either type of line should equal the current exiting the other conductor…right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet I read things like &lt;a href=&quot;https://ham.stackexchange.com/a/543/1362&quot;&gt;this&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;you need equal and opposite currents in coax to make it not radiate&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;And even the wide-spread term:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;shield-current-induced noise&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(Isn't there always current going through the shield?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, in &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this handbook on RFI&lt;/a&gt;, in a section that seems relevant if I could only understand it:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Several cable defects (essentially manufacturing tolerances) certainly can and do convert this &quot;common mode&quot; antenna current to a differential signal (that is, a voltage between the signal conductors), but that is rarely the most powerful coupling mechanism.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(Isn't there also always a voltage between the inner conductor and the coax shield?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is it about coax that makes it different than ladder line as far as signal &quot;balance&quot; goes? And what makes coax radiate in some circumstances but not others? It seems the reasons that coax would radiate (namely: current in the shield, or a voltage between the two conductors) are &lt;em&gt;always&lt;/em&gt; present — whether or not there's a balun or choke, or open or short or perfect load, at the end of it.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2015-11-25T14:15:32.700" Title="Understanding coax radiation and &quot;current on the shield&quot;" Tags="&lt;rfi&gt;&lt;coaxial-cable&gt;&lt;transmission-line&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5523" PostTypeId="2" ParentId="5340" CreationDate="2015-11-20T05:21:42.443" Score="1" Body="&lt;p&gt;Could this be an &lt;a href=&quot;https://en.wikipedia.org/wiki/APC-7_connector&quot; rel=&quot;nofollow&quot;&gt;APC-7 connector&lt;/a&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to &lt;a href=&quot;http://ecee.colorado.edu/~kuester/Coax/connchart.htm&quot; rel=&quot;nofollow&quot;&gt;this reference&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The APC-7 (Amphenol Precision Connector - 7 mm) offers the lowest reflection coefficient and most repeatable measurement of all 18 GHz connectors. … This is a sexless (hermaphrodite) design and is the preferred connector for the most demanding applications, notably metrology and calibration. …&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The pictures I can find do have a similarity to yours, though it's hard to tell especially not having encountered them personally.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2015-11-20T05:21:42.443" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5524" PostTypeId="1" CreationDate="2015-11-20T08:15:16.917" Score="3" ViewCount="674" Body="&lt;p&gt;I want to build a simple amplifier using those Mitsubishi modules (like the RA30H1317M or other RA parts). I know this might seem like a very obvious question, but I am unable to find the answer after searching a while.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When using a linear amplifier with a transceiver, is the transceiver still connected to the antenna when not transmitting or is it essentially disconnected and needs a &quot;special&quot; type of amplifier that will leave it connected so it can receive through the amplifier properly?&lt;/p&gt;&#xA;" OwnerUserId="1817" LastActivityDate="2015-11-21T00:07:07.063" Title="Receiving through a linear amplifier" Tags="&lt;antenna&gt;&lt;transceiver&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5525" PostTypeId="2" ParentId="1367" CreationDate="2015-11-20T08:53:54.977" Score="0" Body="&lt;p&gt;Selecting a set of crystals with almost the same frequency requires one to test many more crystals than the required number for that circuit. For example, to select a set of five crystals one would have buy at least 20 and test each one.&lt;/p&gt;&#xA;" OwnerUserId="5657" LastActivityDate="2015-11-20T08:53:54.977" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5526" PostTypeId="2" ParentId="759" CreationDate="2015-11-20T11:29:17.713" Score="1" Body="&lt;p&gt;Last time, almost ten years ago, I used W5YI's service to renew my license.  I hate most computerized data base systems and the endless hoops you have to jump through to get them to work.  The small fee I paid to W5YI back then was worth every penny to me in terms of avoided aggravation and frustration.  You can bet that I will be using their services again in a few more months!&lt;/p&gt;&#xA;" OwnerUserId="5660" LastEditorUserId="76" LastEditDate="2015-11-20T15:22:02.923" LastActivityDate="2015-11-20T15:22:02.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5527" PostTypeId="2" ParentId="5524" CreationDate="2015-11-21T00:07:07.063" Score="7" Body="&lt;p&gt;Every linear amplifier designed to work with a transceiver has a bypass circuit which switches the antenna between the amplifier and transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When transmitting, the transceiver connector is connected to the input of the amplifier, subsequently the output to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When receiving, the amplifier circuit is disconnected and the antenna is connected directly to the transceiver connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The switching can be done by relays or some kind of electronic RF switches. Many linear amplifiers have the feature to detect the carrier and switch to transmit mode if they detect the transceiver output. Alternatively a separate line to activate the transmitter can be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've looked into the data sheet of RA30H1317M and I don't see any bypass circuit feature. You have to implement it by yourself.&lt;/p&gt;&#xA;" OwnerUserId="5636" LastActivityDate="2015-11-21T00:07:07.063" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5528" PostTypeId="2" ParentId="5522" CreationDate="2015-11-21T03:39:43.453" Score="1" Body="&lt;p&gt;One point to make is that at radio frequencies, the &lt;strong&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow&quot;&gt;skin effect&lt;/a&gt;&lt;/strong&gt; is important.  That is, the RF currents are present only on the surfaces of conductors -- actually in a thin layer whose depth (the &quot;skin depth&quot;) gets lower as frequency goes up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the picture is that an ideal coaxial cable has a current +I on the surface of the inner conductor and a current -I on the &lt;strong&gt;inner&lt;/strong&gt; surface of the shield. (at any give location and moment of time) From the &lt;strong&gt;outside&lt;/strong&gt; of the coax, you don't see any electric or magnetic fields -- they are contained inside the shield.  [Shields aren't perfect, so in reality there is some leakage.]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the (balanced) antenna is fed with a balun that transforms the impedance correctly, the power is transmitted on the inside of the coax and all is well. The shield (outside) stays at ground potential, and there no outside current flow. But if the antenna or balun is not symmetrical, the current will divide between the inside and the outside of the coax shield.  On transmit, this means that your coax is radiating power and distorting the radiation pattern of your antenna and possibly getting into TVs or other equipment in nasty ways.  On receive, it means that noise from household appliances, the power line, etc.  can couple &lt;strong&gt;into&lt;/strong&gt; the coax and make extra noise in your receiver. (Shield leakage has a similar effect.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Balanced open wire lines or ladder lines have some of the same problems, although the electric and magnetic fields are not confined as nicely as in coax.  If the antenna is symmetrical (balanced) and the balanced lines are really balanced (no nearby conductors like drain spouts, for example), the current on one leg is +I and on the other it is -I.  This means that the fields cancel out when seen from a good distance (many times the conductor spacing), and there is little if any radiation from the feed line itself.  If the antenna or feed line are imbalanced, the feed line will radiate on transmit and noise will be coupled into the feed line on receive.  That is the same problem as with coax lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The big advantage of balanced lines is low attenuation, so they can operate OK with fairly high SWR.  Coax is usually easier to work with, since you can route it as needed without worrying so much about nearby structures, etc.  Balanced lines have to be accurately spaced with wire separation a small fraction of a wavelength.  Coax is generally used at very high frequencies, because balanced lines with very narrow spacings are hard to construct.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2015-11-21T03:39:43.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5529" PostTypeId="2" ParentId="5522" CreationDate="2015-11-21T13:38:28.037" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Perhaps some of my confusion comes from an audio background, where one has &quot;balanced&quot; and &quot;unbalanced&quot; cabling in a way that is easier for me to understand: an unbalanced cable is simply a signal and ground wire, while a balanced cable actually has a ground wire and two conductors whose voltages are opposite.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's not entirely accurate. What makes a balanced audio connection &quot;balanced&quot; is that there are two connections, and each has &lt;em&gt;equal impedance&lt;/em&gt; (to each other, and the wire's surroundings). It's not about having equal and opposite voltages, or currents. See &lt;a href=&quot;https://electronics.stackexchange.com/q/95803/17608&quot;&gt;What makes a “balanced” audio signal?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And that's why simply measuring the two wires of an unbalanced audio cable isn't useful. It's how unbalanced audio equipment works: the shield is ground, and the signal is the difference between ground and some other wire. But since the &lt;em&gt;impedance&lt;/em&gt; of the wires are not equal, noise picked up from external sources isn't necessarily common-mode, and so isn't rejected by the difference amplifier.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And in both cases, according to Kirchhoff's current law, the current entering one conductor of either type of line should equal the current exiting the other conductor…right?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I think you misunderstand the KCL, which says that the sum of all current entering a node is equal to the sum of all current exiting a node. A &quot;node&quot; is any place wires connect on a schematic. Unless you short the two wires of a transmission line together somewhere (which would make it pretty worthless as a transmission line), they don't necessarily share a common node, so the KCL isn't of much help.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;you need equal and opposite currents in coax to make it not radiate&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Radio transmissions work by detecting changes in the electromagnetic fields from a distant source. So to radiate, we need to make electromagnetic fields which extend to infinity (though they will necessarily get weaker with distance according to the &lt;a href=&quot;https://en.wikipedia.org/wiki/Inverse-square_law&quot; rel=&quot;nofollow noreferrer&quot;&gt;inverse square law&lt;/a&gt;). By &lt;a href=&quot;https://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;reciprocity&lt;/a&gt;, we also know that something good at transmitting will be good at receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So conversely, if we can show that the electromagnetic fields don't extend to infinity, then we can't be radiating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So consider that we have a short section of coax. At this very instant, there is an excess of electrons on the shield:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dTevQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dTevQ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and an excess of electron holes on the center conductor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/foNCp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/foNCp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've drawn electrons as blue, and electron holes as red. And the arrows represent the electric field. If you were a positive electric charge floating about, the arrows point in the direction you'd feel a push. You'd be attracted to the shield, because positive charges are attracted to the negative charge of electrons. And likewise, you are repelled from the center conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you get farther away, the push you feel becomes less, but it never fully goes away. These fields extend to infinity, so if we can make these electric fields oscillate, we'd probably have a good antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there are exactly as many electrons as there are electron holes in this diagram. Consequently, the fields are equal in magnitude: they are just opposite in direction. So if you put the two together:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ID2Mk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ID2Mk.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the electric field exists only inside the coax. A floating positive charge outside the coax simultaneously feels a push and a pull that are equal. That is, it doesn't feel anything at all. The field does not extend to infinity: the coax does not radiate (or receive, by reciprocity).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice these extra electrons and electron holes are there as a result of the RF current on the transmission line. When the currents are equal and opposite as they are here, we call these &lt;em&gt;differential-mode currents&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the currents weren't exactly equal and opposite, then we can factor out some amount of current that's the difference. We call that &lt;em&gt;common-mode current&lt;/em&gt;. Since the electric charge associated with this portion of the current isn't cancelled by an equal but opposite amount of charge, the associated fields extend to infinity and the transmission line radiates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also by reciprocity, if only common-mode currents radiate, then anything &lt;em&gt;received&lt;/em&gt; by the transmission line (and not by the antenna at the end) will &lt;em&gt;also&lt;/em&gt; be common-mode. That may seem odd, but just keep it in mind. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Let's say I divide all the currents on some coax into three components:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/142xq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/142xq.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$I_a$ is the current on the center conductor.&lt;/li&gt;&#xA;&lt;li&gt;$I_b$ is the portion of current on the shield which is equal and opposite $I_a$. These are the differential-mode currents.&lt;/li&gt;&#xA;&lt;li&gt;$I_c$ is whatever current is left over: the common-mode current. It can be of any direction or magnitude, independently of $I_a$ and $I_b$.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Notice that $I_c$, the common-mode current, is on the outside of the shield. There's no provision for a common-mode current on the center conductor, because it can't happen (for RF currents, anyway).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is &lt;a href=&quot;https://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin effect&lt;/a&gt;. Normally we talk about skin effect as causing the RF current to flow on or near the outer surface of a solid conductor. However, the electric and magnetic fields responsible for skin effect can reach across the dielectric of the coax as well: any common-mode current on the center conductor will create eddy currents that cancel the center conductor's current, replacing it with a current on the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, notice that $I_b$, the shield's half of the differential-mode current, is drawn on the inside of the shield. That's because the charges associated with this current are attracted to the opposite charges associated with the current on the center conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And this is how ultimately common-mode noise is rejected in a coax system. When eventually this coax terminates at a receiver, that receiver will be in a metal box. And that metal box functions as an extension of the coax shield. Common-mode currents will continue to flow around the &lt;em&gt;outside&lt;/em&gt; of the metal box, because of skin effect, and because they don't have an opposite charge on the center conductor to draw them to the inside. So consequently, these common-mode currents can't enter any of the receiver circuitry inside the box.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, all of this is true only to the extent that the shield is a perfectly solid, perfect conductor. Real shields have some resistance, and making flexible coax requires thin foil or a braid, which isn't ideal. That's what the other is talking about when he writes of &quot;shield-current-induced noise&quot;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2015-11-25T14:15:32.700" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5531" PostTypeId="1" AcceptedAnswerId="5533" CreationDate="2015-11-23T02:30:07.877" Score="8" ViewCount="848" Body="&lt;p&gt;Today I noticed that a piece of RG-58 that's feeding a Beverage antenna for HF was in two pieces. On further inspection it turned out to be cut. On further inspection I think it's actually chewed by some animal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the risk of this post being deleted for being vastly off-topic I think that some fellow hams out there have also come in very close contact with nature's hungry cable chewers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone of you identify whether this was malicious or just a rodent of sorts?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fTMag.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fTMag.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cable is out in a paddock with spikey shrubs and grass. No cattle around but I did see a horse at one stage. Plenty of mice and falcons too. I live on the East Coast of Australia so it could be cockatoos but the cut marks don't look obvious to me.&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="873" LastEditDate="2015-11-24T04:24:50.453" LastActivityDate="2016-12-02T06:33:15.953" Title="What chewed my coax" Tags="&lt;coaxial-cable&gt;&lt;environment&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5533" PostTypeId="2" ParentId="5531" CreationDate="2015-11-23T19:46:50.653" Score="2" Body="&lt;p&gt;This looks like a relatively clean cut.  I would say mice or other rodents.  You can deter then by getting a cat, or maybe mouse traps.  Snakes also work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While this does involve coax, this sounds more like a question for an SE that deals with animal identification (not sure if there is one).&lt;/p&gt;&#xA;" OwnerUserId="5404" LastActivityDate="2015-11-23T19:46:50.653" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="5534" PostTypeId="5" CreationDate="2015-11-24T06:31:30.237" Score="0" Body="&lt;p&gt;This tag is for when the question involves the environment, location or general situation, rather than specific equipment or a person or people.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2015-12-14T17:34:03.170" LastActivityDate="2015-12-14T17:34:03.170" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5535" PostTypeId="4" CreationDate="2015-11-24T06:31:30.237" Score="0" Body="For questions that concern the environment, rather than equipment or an operator of the equipment." OwnerUserId="873" LastEditorUserId="873" LastEditDate="2015-12-14T17:34:00.027" LastActivityDate="2015-12-14T17:34:00.027" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5536" PostTypeId="1" CreationDate="2015-11-24T16:37:29.590" Score="1" ViewCount="4017" Body="&lt;p&gt;What kind of wire is best to use for connecting a FM radio to the antenna?&#xA;&lt;a href=&quot;http://www.wikihow.com/Make-an-FM-Antenna&quot; rel=&quot;nofollow&quot;&gt;This article&lt;/a&gt; doesn't say what kind of wire is used.&lt;/p&gt;&#xA;" OwnerUserId="5684" LastEditorUserId="76" LastEditDate="2015-11-24T21:56:42.057" LastActivityDate="2016-01-22T16:07:40.273" Title="What kind of wire is best to use for connecting a FM radio to the antenna?" Tags="&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5537" PostTypeId="2" ParentId="5521" CreationDate="2015-11-24T18:40:15.313" Score="2" Body="&lt;p&gt;Transformers &lt;em&gt;are&lt;/em&gt; inductors. They just happen to have mutual inductance with another inductor. Like inductors, they also have self-capacitance, and so a resonant frequency. They also have loss, and consequently some maximum power handling ability which if exceeded causes the transformer to fail by overheating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, any parameter which is relevant to an inductor might also be relevant to a transformer. There is no general way to say what parameters are relevant or not: to answer that question requires some understanding of the circuit in question, and its operation and requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, you'll need to consider the magnetizing inductance of the transformer. This is the inductance that the transmitter sees looking into the transformer as a result of the transformer itself. You can measure it by leaving the secondary disconnected and measuring the transformer as an inductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your end-fed dipole example, this magnetizing inductance appears in parallel with the antenna. There are two ways to approach this problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One way is to make sure the magnetizing inductance is an impedance much greater than 50Ω (50Ω being, hopefully, the impedance of the antenna, as seen by the transmitter). This will mean that the magnetizing inductance has negligible effect on the overall impedance seen by the transmitter. (If that doesn't make sense, consider the impedance of a 1kΩ resistor: what happens if you add a 1MΩ resistor in parallel?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's not practical to obtain a sufficiently high inductance, then a capacitor can be added in parallel with the transformer to make a &lt;a href=&quot;https://en.wikipedia.org/wiki/LC_circuit#Parallel_LC_circuit&quot; rel=&quot;nofollow&quot;&gt;parallel LC circuit&lt;/a&gt;, which at resonance has a very high impedance. The interwinding capacitance of the transformer also effectively contributes parallel capacitance, so it's possible to design a transformer which is self-resonant and does not require an additional capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another way to deal with the magnetizing inductance is to incorporate it into the design of the circuit. If you needed an inductor anyway, perhaps as part of a filter or a matching network, then you can put the primary of an appropriately designed transformer there instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what does this mean for your end-fed dipole example? What things might we change, and what effect would they have in that application?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could increase the number of turns, while maintaining the same turns ratio. This will increase magnetizing inductance, which might be good since we want that impedance to be high. More turns will also increase the interwinding capacitance. But more turns will also increase the magnetic flux through the core, eventually hitting the limit of saturation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could use a different material. But we'd want to consider the losses inherent in that material, its permeability and the effect that will have on the magnetizing inductance, and its maximum flux density and how that will impact the peak current the transformer can handle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The physical size of the core is also a concern. A larger core spreads the magnetic flux through it through more area, and so can handle more magnetic flux (and consequently, current and power) before reaching saturation. A larger core also has more area to lose heat from losses to its surroundings, and more thermal mass to absorb transient power peaks, and so can handle more power.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-11-24T18:40:15.313" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5538" PostTypeId="2" ParentId="5536" CreationDate="2015-11-24T21:54:45.193" Score="0" Body="&lt;p&gt;&lt;strong&gt;That article is terribly written&lt;/strong&gt;, because it doesn't tell you how to construct the dipole part of the antenna and the pictures make it look like you're modifying something that already exists, but it does tell you what to use: &lt;strong&gt;300 Ω twin-lead&lt;/strong&gt;. This is a standard cable for connecting TV antennas (though less common than coaxial cable these days) and should be easy to find at stores that sell TV antenna components.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Also, this is not answering the question you asked, but if you are building an antenna design that uses a &lt;em&gt;single&lt;/em&gt; strand of wire, not twin-lead, then the type of wire basically doesn't matter except for non-electrical properties (whether it is strong enough, whether it will corrode outdoors).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-11-24T21:54:45.193" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5539" PostTypeId="1" CreationDate="2015-11-25T10:23:14.743" Score="2" ViewCount="186" Body="&lt;p&gt;I'm looking at using a 1/4 wave whip antenna for a transmitter. If possible I'd like to cover the antenna in very thin (0.02 mm) &lt;a href=&quot;http://www.dupont.com/content/dam/assets/products-and-services/membranes-films/assets/DEC-Kapton-HN-datasheet.pdf&quot; rel=&quot;nofollow&quot;&gt;aluminised kapton&lt;/a&gt; for reasons unrelated to the radio system; to be clear the Kapton will not be directly touching the antenna, it will be about 3 cm away. I have a feeling that although this material is very thin there is a significant possibility that I will end up with a very different radiation pattern than a typical 1/4 wave omnidirectional antenna if I surround the antenna in Kapton. I'm just not sure how to go about investigating this? I'd like to be able to predict the effect (either reduction in received signal - putting some extra factor in my link budget - or change in radiation pattern) but I have no idea where to start with this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the governing principal in this scenario?&lt;/p&gt;&#xA;" OwnerUserId="529" LastEditorUserId="529" LastEditDate="2015-11-25T16:21:24.703" LastActivityDate="2016-01-26T05:07:32.413" Title="Would a covering like aluminised kapton effect antenna radiation pattern?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5540" PostTypeId="2" ParentId="5539" CreationDate="2015-11-25T21:02:12.753" Score="1" Body="&lt;p&gt;Yes it will probably have a profound effect on your radio signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was once involved in an experimental evaluation of some reflective window coating, to see if it would attenuate cell phone radio waves. This is a partially transparent shiny adhesive coating which can be applied to existing windows to make them more like mirror glass.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The results were fairly good, the coating reduced the radiation by up to 30 dB compared to uncoated glass.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I would assume for a starting point, that any shiny metallic coating on plastic or glass is fairly conductive to RF and block the signal, even if if the plastic is not touching it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit after re-reading your question: if the metallised foil is a cylinder, concentric to the 1/4 wave antenna, shorter than the antenna, and not touching the metal groundplane, then its only effect will be to slightly detune the antenna. If you are able to measure the antenna impedance, you can just cut it for the right frequency again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Last edit: car windscreens sometimes include a metallic coating to help reject solar radiation. This coating is so thin it doesn't make the windscreen noticeably shiny at all, but it still affects radio reception. For example, a GPS receiver doesn't work through such a windscreen.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2015-11-27T04:46:15.273" LastActivityDate="2015-11-27T04:46:15.273" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5542" PostTypeId="1" CreationDate="2015-11-28T07:16:08.270" Score="1" ViewCount="89" Body="&lt;p&gt;Does any one know or have a frequency chart with Australian Emergency services?&lt;/p&gt;&#xA;" OwnerUserId="5707" LastActivityDate="2015-11-28T10:38:27.123" Title="Australian Police Radio Frequency" Tags="&lt;frequency&gt;&lt;emergency&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2015-11-30T02:02:56.223" ContentLicense="CC BY-SA 3.0" />
  <row Id="5543" PostTypeId="2" ParentId="5542" CreationDate="2015-11-28T10:38:27.123" Score="0" Body="&lt;p&gt;Unless you listen to country Police on HF you are unlikely to be able to hear anything - most states have gone digital now, and APCO25 encrypted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They're no fun...&lt;/p&gt;&#xA;" OwnerUserId="5705" LastActivityDate="2015-11-28T10:38:27.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5544" PostTypeId="1" AcceptedAnswerId="5551" CreationDate="2015-11-28T14:16:26.060" Score="1" ViewCount="41" Body="&lt;p&gt;I am planning to set up an ESP8266 mesh network. If node A receives beacons from node B, does this mean node B can receive beacons from node A? Assume they are the same (same antenna, ...)&lt;/p&gt;&#xA;" OwnerUserId="5693" LastActivityDate="2015-11-30T01:41:08.590" Title="Can I always see the other module?" Tags="&lt;wifi&gt;&lt;range&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5545" PostTypeId="2" ParentId="2477" CreationDate="2015-11-29T04:12:05.720" Score="2" Body="&lt;p&gt;I've been a ham since 1963 and have built all my own antennas.  Yagi beams—wire beams—loops—verts, etc.   Back in those days all you had was a SWR bridge and maybe a grid dip meter.  The most important thing, I think, is a booklet or some kind of articles on  antenna design.  They will give you accurate lengths and feed line info that should get you up and running in no time.  There's plenty of info on the internet, although my personal favorite source is Bill Orr, W6SAI; his antenna books and very entertaining antenna articles in CQ magazine circa 1970's are great. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My first antenna was made of electric  fence wire and a second hand hunk of RG-58 in an inverted vee configuration.  It is supremely simple to build.  One support pole, one hunk of 50 ohm coax, balun or not, 120 degree spread between the legs, gives you 50 ohms. Make it about three feet longer than formula and trim it to resonance using an el cheapo used (\$10) SWR bridge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A used grid dip meter (\$30.00) will let you get the resonant frequency—not necessary here—and a used (\$30.00) noise bridge will let you deal with impedance issues, but is not necessary with simple antennas like this.  Simple antennas are easy to build and work well.  Height is a big plus.  Just get in there and klutz around until it works.  You can build anything easily with the three pieces of test gear mentioned here and they will do a lot more things than help set up antennas. Simplicity is bliss.&lt;/p&gt;&#xA;" OwnerUserId="5715" LastEditorUserId="13" LastEditDate="2015-12-14T22:09:59.727" LastActivityDate="2015-12-14T22:09:59.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5546" PostTypeId="2" ParentId="5259" CreationDate="2015-11-29T09:21:55.377" Score="0" Body="&lt;p&gt;While some of this discussion ventures into cryptography terminology, your understanding of it may not automatically mean that the FCC will see it the same way. A hash is a one-way cryptographic function, and as such, it cannot be &quot;decoded&quot; on the other end with a password (or key). This is clearly not obfuscation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, if this hash is sent out in the open as a &quot;signature&quot;, there is no guarantee that someone else cannot intercept it and send it from his or her own station later. One way to prevent that is to have a list of one-time strings shared in advance, out of band (off-air). Once a string is used, it is scratched off by both parties. (You can automate this process with an OTP mobile app based on just one pre-shared string. These strings are strictly used for authentication, and can change every few seconds. Nobody can predict the next one without access to the secret string. They also only take a few digits, so they do not look suspicious as &quot;obfuscation&quot;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The vague area comes from encrypting a hash with a private key. As the name of the process implies, it is actual encryption, since you use the recepient's public key that derived from his private key, and your private key remains secret. The purpose of Public Key Cryptography is in fact, would satisfy the FCC's definition of obfuscation, because the process hides the meaning of the message from those who intercept the transmission. That would be a clear violation of FCC rules.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition, someone intercepting the message would not immediately know that your string is &quot;just a hash signature&quot;; you may be accused of sending an AES-256 encrypted string, which is actually two-way encryption, and as such, &quot;obfuscation&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rules were most likely not written with all these technicalities in mind, so the best bet is to keep it safe and minimize cyphertext traffic.&lt;/p&gt;&#xA;" OwnerUserId="3038" LastActivityDate="2015-11-29T09:21:55.377" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5547" PostTypeId="1" CreationDate="2015-11-29T09:27:49.580" Score="11" ViewCount="42182" Body="&lt;p&gt;I am reading about wireless networks basics. I found three terms I cannot find exact definition for: channel, frequency band, frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone give exact definitions for them?&lt;/p&gt;&#xA;" OwnerUserId="5716" LastEditorUserId="873" LastEditDate="2017-06-07T01:23:43.143" LastActivityDate="2019-02-04T14:17:03.400" Title="What is the difference between channel &amp; frequency &amp; band in RF?" Tags="&lt;frequency&gt;&lt;jargon&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5548" PostTypeId="2" ParentId="5547" CreationDate="2015-11-29T14:47:04.940" Score="4" Body="&lt;p&gt;A channel is a generally accepted stopping point - somewhere that we know other people or devices will be listening. For example, in the United States, amateurs get access to 5 distinct channels on the 5 MHz band. Or your WiFi router uses several channels, but most of those channels overlap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A frequency band is a range of frequencies. They're usually referred to by the wavelength (e.g. 40 meters is the band from 7000 KHz to 7300 KHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A frequency is the reference point for tuning your transceiver. Depending on how you're communicating, you'll be using far more than that single frequency, but when people mention a frequency, that's what they're referring to - where you should set your transceiver.&lt;/p&gt;&#xA;" OwnerUserId="5087" LastEditorUserId="5087" LastEditDate="2015-11-30T14:14:44.983" LastActivityDate="2015-11-30T14:14:44.983" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5549" PostTypeId="2" ParentId="5547" CreationDate="2015-11-29T16:33:18.850" Score="1" Body="&lt;p&gt;Even though this is an amateur &quot;ham&quot; radio forum, the OP's question seems to be about how these terms are used for wireless networks or maybe also in the field of telecommunication system engineering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A channel has a more defined meaning in telecommunications and generally implied the use of specific modulation/demodulation schemes (e.g. FSK, PSK, etc.) and also specific management of control parameters and channel performance.  This is all done to ensure quality communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whole books in telecommunications engineering are written about channels and how to use them effectively for digital (usually) communications.  Topics such as phase distortion, attenuation distortion, level control, channel capacity, equalization are all topics associated with channels in telecommunications engineering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, in ham radio, the use of the term channel is rare and about the only times I have heard it mention by someone it is referring to the US Citizens Band channels.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-11-29T16:33:18.850" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5550" PostTypeId="2" ParentId="5547" CreationDate="2015-11-29T17:22:04.517" Score="16" Body="&lt;p&gt;If you don't know what a &lt;strong&gt;frequency&lt;/strong&gt; is, you need to read up on waves-in-general and radio waves. But the other two terms can be defined in terms of frequency; frequencies are the “natural” thing and everything else are things people invented on top of that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;strong&gt;frequency band&lt;/strong&gt;, or &lt;strong&gt;band&lt;/strong&gt;, is a range of frequencies with a specific least frequency and greatest frequency. Generally bands are used to describe some relevant range:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A radio is capable of operating within some band of frequencies; outside that band its performance will not meet specification or it will be incapable of tuning there.&lt;/li&gt;&#xA;&lt;li&gt;The legal limits on transmissions are defined in terms of many bands; when people say &quot;the 2.4 GHz band&quot; they mean the &lt;a href=&quot;https://en.wikipedia.org/wiki/ISM_band&quot; rel=&quot;noreferrer&quot;&gt;ISM band&lt;/a&gt; that extends from 2.400 GHz to 2.500 GHz, which is purely a legal definition and has no technical significance other than that devices may be internally restricted to operate in those bounds.&lt;/li&gt;&#xA;&lt;li&gt;When a signal is actually transmitted, we can talk about the band of that signal, that is, the range of frequencies which have significant/useful signal power on them. This usage is where the terms &quot;in-band&quot; and &quot;out-of-band&quot; come from. (The &lt;em&gt;bandwidth&lt;/em&gt; of a signal is the size of the band, the lowest frequency subtracted from the highest frequency.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Channel&lt;/strong&gt; has two different meanings:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Usage of a band can be &lt;strong&gt;channelized&lt;/strong&gt;, which means that the radios which transmit on it do not pick frequencies arbitrarily but stick to a certain step size (e.g. 10 KHz for CB radio, so frequencies like 27.105, 27.115, 27.125 MHz). This makes it easier for a receiver to match a transmitter, and allows more efficient use overall as there are no wasted narrow gaps between signals. If you want to see a spectacular example of precise channelization, take a look at broadcast FM radio: stations with added &lt;a href=&quot;https://en.wikipedia.org/wiki/HD_Radio&quot; rel=&quot;noreferrer&quot;&gt;HD Radio digital signals&lt;/a&gt; transmit right up to the limits of their channel.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In communications theory, the &lt;strong&gt;channel&lt;/strong&gt; is the medium that carries the signal. This is a different kind of word than the others because it's an abstraction that is not about frequency, but it is like the above in that to look at an RF channel you ignore everything outside of the frequency range that defines the channel. Within that range, you care about the effects on the signal — loss, noise, multipath, fading, etc. — and those effects are frequency-dependent on a larger scale and possibly even within the channel.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-06-06T20:17:18.050" LastActivityDate="2017-06-06T20:17:18.050" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5551" PostTypeId="2" ParentId="5544" CreationDate="2015-11-30T01:41:08.590" Score="2" Body="&lt;p&gt;Generally, in the absence of environmental RF noise at either end, if you have two identical systems then if node 1 can hear node 2, then node 2 should be able to hear node 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you can imagine a situation where you are upstairs in a house and people are sitting watching TV downstairs and you can hear them talking fairly quietly between themselves - you could be shouting quite loudly but they would not hear you because of the sound of the TV.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same would apply in a WiFi network where node 1 has a lot of local noise (nearby microwave oven, BlueTooth devices, anything that uses frequencies at or near the 2.4GHz or 5GHz that it is using), then node 2 might be able to hear node 1 perfectly clearly but node 1 would not hear anything above the local noise.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-11-30T01:41:08.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5552" PostTypeId="2" ParentId="5547" CreationDate="2015-11-30T02:16:12.610" Score="2" Body="&lt;p&gt;For regulatory purposes, a frequency is usually used to refer to a carrier frequency, which has a specific meaning related to the mode of transmission (for example, in an SSB transmitter the carrier frequency is in theory never actually transmitted, but in a morse code CW transmitter it is the only frequency ever transmitted).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A frequency band is a range of frequencies with a lower and upper limit. If the regulations state that you must only transmit signals within a specified band, then you must make sure that your transmitted signals never go outside that range of frequencies - again, very easy to determine when transmitting CW, not so easy with SSB, AM or FM (requires knowledge of the bandwidth of the transmitted signal on each side of the carrier).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 'channel' is an agreed-upon set of specific frequencies with additional information included in the agreement. For example, in the amateur 2m and 70cm bands, a portion of the band is 'channelised' and set aside for repeaters. These repeaters use specific spot frequencies for both their inputs and outputs, and have certain other requirements regarding mode (FM), deviation (for example, max. 3kHz) and other requirements for CTCSS tones and the like.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-11-30T02:16:12.610" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5554" PostTypeId="1" CreationDate="2015-12-01T21:31:52.000" Score="4" ViewCount="392" Body="&lt;p&gt;I am looking for a communication solution with the following requirements:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;wireless&lt;/li&gt;&#xA;&lt;li&gt;unidirectional, point to point&lt;/li&gt;&#xA;&lt;li&gt;low power (li-ion battery powered, should operate at least one hour on the single charge)&lt;/li&gt;&#xA;&lt;li&gt;low baudrate data transfer (cca 40 - 80 bauds)&lt;/li&gt;&#xA;&lt;li&gt;long distance, in the terrain covered by the forest, behind the small hill. One km sholud be enough but more is better&lt;/li&gt;&#xA;&lt;li&gt;using free band within EU&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;What technologies should I check? Are there any existing modules for this? I would like to connect it to Arduino.&lt;/p&gt;&#xA;" OwnerUserId="5731" LastEditorUserId="5731" LastEditDate="2015-12-01T21:38:53.563" LastActivityDate="2016-06-20T18:36:51.867" Title="Low power long distance wireless data communication" Tags="&lt;digital-modes&gt;&lt;receiver&gt;&lt;transmitter&gt;&lt;europe&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5555" PostTypeId="2" ParentId="5259" CreationDate="2015-12-01T22:35:56.923" Score="1" Body="&lt;p&gt;Please see:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;§97.309   RTTY and data emission codes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(a) Where authorized by §§97.305(c) and 97.307(f) of the part, an amateur station may transmit a RTTY or data emission using the following specified digital codes:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(1) The 5-unit, start-stop, International Telegraph Alphabet No. 2, code defined in ITU-T Recommendation F.1, Division C (commonly known as “Baudot”).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(2) The 7-unit code specified in ITU-R Recommendations M.476-5 and M.625-3 (commonly known as “AMTOR”).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(3) The 7-unit, International Alphabet No. 5, code defined in IT--T Recommendation T.50 (commonly known as “ASCII”).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(4) An amateur station transmitting a RTTY or data emission using a digital code specified in this paragraph may use any technique whose technical characteristics have been documented publicly, such as CLOVER, G-TOR, or PacTOR, for the purpose of facilitating communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(b) Where authorized by §§97.305(c) and 97.307(f), a station may transmit a RTTY or data emission using an unspecified digital code, except to a station in a country with which the United States does not have an agreement permitting the code to be used. RTTY and data emissions using unspecified digital codes must not be transmitted for the purpose of obscuring the meaning of any communication. When deemed necessary by a Regional Director to assure compliance with the FCC Rules, a station must:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(1) Cease the transmission using the unspecified digital code;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(2) Restrict transmissions of any digital code to the extent instructed;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(3) Maintain a record, convertible to the original information, of all digital communications transmitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[54 FR 25857, June 20, 1989, as amended at 54 FR 39537, Sept. 27, 1989; 56 FR 56172, Nov. 1, 1991; 60 FR 55486, Nov. 1, 1995; 71 FR 25982, May 3, 2006; 71 FR 66465, Nov. 15, 2006; 80 FR 53753, Sept. 8, 2015]&lt;/p&gt;&#xA;" OwnerUserId="5252" LastActivityDate="2015-12-01T22:35:56.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5556" PostTypeId="2" ParentId="5554" CreationDate="2015-12-01T23:11:36.830" Score="2" Body="&lt;p&gt;RFM12B or RFM69CW sounds like what you want. Operates in the ISM band. There's sketches available for Arduino and with a decent yagi antenna you should be able to reach that far.&lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2015-12-01T23:11:36.830" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5557" PostTypeId="1" AcceptedAnswerId="5558" CreationDate="2015-12-02T03:43:02.183" Score="5" ViewCount="815" Body="&lt;p&gt;I have gathered what is basically a &lt;a href=&quot;http://www.hamradiofun.com/yoyodeluxe.html&quot; rel=&quot;nofollow&quot;&gt;Yo-Yo Tenna&lt;/a&gt; using some Camco laundry reels and a spool of cheap speaker wire split in half (pretty much exact duplicate of &lt;a href=&quot;https://www.ar15.com/archive/topic.html?b=10&amp;amp;f=22&amp;amp;t=675149&quot; rel=&quot;nofollow&quot;&gt;this build&lt;/a&gt; as it turns out). I've got a bit of equipment to measure the amount of noise the antenna absorbs to help tune it up, but I'm wondering more from a theoretical/antenna-design standpoint: what happens RF-wise as I roll the reels up?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is, the idea of these antennas is simply a &quot;wind up&quot; dipole: two lengths of wire that can each be coiled up. Not only does this make the antenna nicely portable, but as the description of the &lt;a href=&quot;http://www.hamradiofun.com/yo-yo-vee.htm&quot; rel=&quot;nofollow&quot;&gt;Yo-Yo Vee&lt;/a&gt; claims:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Simply adjust bands or SWR by winding/unwinding the reels!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I've seen this to be true with my own setup too, I can unwind way less than the 100ft of each leg and get a higher frequency resonance. But what happens with the wound ends of the wire? Won't they form something of an inductor hanging out at each end? How would that inductance be expected to affect the efficiency and radiation pattern of the resulting antenna?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="76" LastEditDate="2015-12-15T23:27:24.493" LastActivityDate="2017-04-13T21:42:37.297" Title="What happens to the &quot;Yo-Yo Tenna&quot; when you coil up its ends for use on higher frequencies?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;&lt;inductor&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5558" PostTypeId="2" ParentId="5557" CreationDate="2015-12-02T04:39:54.113" Score="4" Body="&lt;p&gt;I'm not certain of this answer, but this is my approximate understanding:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, the coiled-up ends form inductors at the ends of the antenna. But the ends of the antenna are the part of it where (almost) no current flows, only voltage builds up! Therefore no current flows through the inductor, and so the inductance has no effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if you're wondering why the extra length of wire doesn't still result in a “long” antenna due to the propagation time through it — well, the &lt;em&gt;mutual inductance between the turns of the coil&lt;/em&gt; acts to couple the signal into all turns simultaneously, rather than it passing through the full length of the wire, so the signal enters the coil and immediately has effectively hit the end of the wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(But I think those are just two descriptions of the same thing, not two separate issues.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-12-02T04:39:54.113" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5559" PostTypeId="2" ParentId="1368" CreationDate="2015-12-02T07:03:38.017" Score="1" Body="&lt;p&gt;You might take a look at the &lt;a href=&quot;http://www.al7fs.us/AL7FS2.html&quot; rel=&quot;nofollow&quot;&gt;Pixie 2&lt;/a&gt;-style transceivers, even if you need to leave the key plug disconnected for lack of license or desire to transmit. They are a very simple circuit, and if you'd like there are even kits available for import via online auction sites at extremely low prices (e.g. search eBay for &quot;qrp pixie&quot;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A post on &lt;a href=&quot;http://kb2hsh.blogspot.com/2014/12/the-chinese-pixie-2-qrp-transceiver.html&quot; rel=&quot;nofollow&quot;&gt;The Chinese Pixie 2 QRP Transceiver&lt;/a&gt; gives a little more history of the design (and also mentions some slightly more complicated alternatives), and Circuit Swamp's &lt;a href=&quot;http://www.circuitswamp.org/projects/pixie2.html&quot; rel=&quot;nofollow&quot;&gt;Pixie 2 Transceiver&lt;/a&gt; page offers a bit more explanation of the circuit itself. It is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Direct-conversion_receiver&quot; rel=&quot;nofollow&quot;&gt;direct conversion receiver&lt;/a&gt; in this case fed by a simple oscillator circuit, mixed with the incoming signal using a transistor, and then amplified by a common IC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my experience, it was a fairly easy build — my kids helped &quot;pick&quot; the components while I did the soldering to PCB included with the kit we bought, but it should be simple enough to breadboard too. Especially with a mismatched antenna (100ft of wire thrown out the window) it picked up more local AM stations than it did 40m signals, but even under those circumstances we could still hear occasional Morse code at various pitches.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2015-12-02T07:08:58.293" LastActivityDate="2015-12-02T07:08:58.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5563" PostTypeId="1" AcceptedAnswerId="5565" CreationDate="2015-12-03T23:59:29.030" Score="8" ViewCount="14032" Body="&lt;p&gt;I have a 10m dipole and am going to feed it with 50 ohm unbalanced feed line (coax).  My understanding is the feed point of this style antenna is about 50-75 ohms, and since it is a balanced antenna I'm thinking I need some type of balun.  I'm wondering:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is a 1:1 current balun the same as a choke?&lt;/li&gt;&#xA;&lt;li&gt;Are they the exact same devices internally, or are they different internally and just perform the same function?&lt;/li&gt;&#xA;&lt;li&gt;If they are different, do they both keep common mode current off the feed line?&lt;/li&gt;&#xA;&lt;li&gt;If they are the same, why are there two different names?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5620" LastEditorUserId="8717" LastEditDate="2021-03-11T21:30:57.490" LastActivityDate="2021-03-11T23:10:23.030" Title="How is a 1:1 current balun different from a choke?" Tags="&lt;dipole&gt;&lt;coaxial-cable&gt;&lt;impedance&gt;&lt;balun&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="5564" PostTypeId="2" ParentId="5563" CreationDate="2015-12-04T00:18:55.787" Score="3" Body="&lt;p&gt;The name &lt;em&gt;choke&lt;/em&gt; refers to the electrical component, whereas the name &lt;em&gt;1:1 current balun&lt;/em&gt; refers to the job it is doing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's more than one way to construct a balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are purposes for a choke that are not baluns.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-12-04T00:18:55.787" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5565" PostTypeId="2" ParentId="5563" CreationDate="2015-12-04T03:29:14.490" Score="5" Body="&lt;p&gt;Baluns are designed to be transformers (like 1:1 4:1, 6:1, etc.) or choke baluns, and both.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For an antenna, the purpose of a choke balun is to create a high-impedance to common mode currents that would flow on the outside of coaxial cable shielding.  These common mode currents can cause all kinds of problems such as RF in the shack, matching problems, and others.  So, minimizing common mode currents is a good thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common mode currents arise when you are coupling a balanced antenna to an unbalanced line (usually).  For example, connecting coax cable to a dipole antenna.  You can use either a 1:1 balun or a choke balun at the feed point of the antenna or where the balanced part of the system meets the unbalanced part.  The choke balun usually does the same thing as a regular 1:1 current balun but adds the high impedance path to the common mode currents too.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the names Choke Balun and regular current balun are somewhat interchangeable as both are used to do the same thing in ham radio&#xA;antenna matching: matching coax to balanced antenna and minimizing common mode currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently, on my 80-meter dipole, I run 450 ohm ladder line to a 4:1 Current Balun and the remaining 20 feet or so is coax into the shack.  In this application, I experimented with both a 4:1 and a 1:1 balun to find the best match and overall SWR on my bands of choice I use with this antenna: 80, 40, 30.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the same antenna, I have used my own custom made choke balun made from coax turns through 6 toroids -- about 7 turns of coax through all 6 toroids.  This worked very effectively except for one thing.  This balun was heavy and often would be a factor in my antenna coming down in a wind storm so I replaced it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, in answer to your question specifics: (1) they do not always perform the same function but sometimes they do; (2) A regular current balun internally is very much like a transformer where as a choke balun usually focuses on multiple turns through toroids to provide high-impedance to common mode currents; (3) the names are different and some people distinguish between one thing and another by the names and others do not.  It is usually not a big deal from my experience unless you are buying something but then you look at the data sheet to understand the balun better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The image below is of one of my custom made choke baluns.  This is an older one that used only five toroids.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9tCrp.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9tCrp.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following image shows one of my current baluns, a 1:1 5 KW balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rS4MW.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rS4MW.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2015-12-04T03:49:17.010" LastActivityDate="2015-12-04T03:49:17.010" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5567" PostTypeId="2" ParentId="3680" CreationDate="2015-12-05T09:20:18.537" Score="3" Body="&lt;p&gt;I find the idea of an SSB repeater quite challenging.&#xA;A repeater has noteworthy the function of allowing communication between points which are mutually inaccessible along the direct line.&#xA;A repeater has not the function of giving the word (the channel) to one sole participant a time (sic!). I greatly prefer the convivial chat in SSB on the HF bands to the scholarly sequenced conversation in FM on 2m and above!&#xA;Therefore, the SSB repeater would just be a continuously operating frequency translator, installed at a high place, which takes in a first, lower frequency band, e.g. a 12kHz channel at 434MHz, and gives it out, transposed and amplified, in a higher frequency band, e.g. at 439MHz.&#xA;For putting this in place, two problems must be solved:&#xA;1) to achieve an amplification of 90dB without feed-back, and&#xA;2) to achieve steep (rectangular!) channel filtering to avoid crosstalk.&#xA;The solution to the problem is in the combination of a digital I/Q receiver at the first, lower frequency, e.g. based on the Realtek RTL2832U chip, with digital filtering, amplification and processing to isolate the 12kHz baseband signal, and reemitting the baseband signal at the second, higher frequency with the help of an I/Q switching modulator, followed by a HF amplification stage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantages of passing through the baseband are a) the distribution of the necessary gain stages between three different frequency levels, reducing possible internal feedback problems, and b) the ease of realizing a very steep and phase-linear filter window for the 12kHz channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantages of digital signal processing are the ease of realizing time-delayed phase-linear FIR filters and the total avoidance of external feedback by an appropriate combination of time-delay between input and output signal, and high-pass filter cutting off all low-frequency signals beyond the time delay of the signal processing chain. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Input and output frequency may be in the same, or preferably in different bands.The operation on the repeater is as ordinary operation, but in duplex.The repeater processes any type of analog or digital input signal and any type of modulation to the frequency-translated output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remains the question whether such repeaters are admissible after all, because they work in continuous operation, monopolizing one channel (the emission channel) from the band.However, this might be worth the value of providing a real chatting option in SSB or CW via a repeater. Furthermore, if there is no activity on the input channel, the output is silent, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, HAM radio is an experimental discipline, and this would certainly be a field of new experience, which is worth the effort!&lt;/p&gt;&#xA;" OwnerUserId="5755" LastEditorUserId="76" LastEditDate="2015-12-05T15:10:17.327" LastActivityDate="2015-12-05T15:10:17.327" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5568" PostTypeId="1" CreationDate="2015-12-05T19:03:13.423" Score="2" ViewCount="3243" Body="&lt;p&gt;Why are some frequencies 5 digits like 51344 and some six or seven digits long like 158.7600?&lt;/p&gt;&#xA;" OwnerUserId="5759" LastEditorUserId="76" LastEditDate="2015-12-06T14:36:56.810" LastActivityDate="2021-02-06T17:31:50.483" Title="Frequencies as 5 digits and 6 or 7 digits" Tags="&lt;united-states&gt;&lt;transceiver&gt;&lt;mobile&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5569" PostTypeId="1" CreationDate="2015-12-05T19:59:23.723" Score="0" ViewCount="235" Body="&lt;p&gt;I'm a new ham and have only used 2m/70cm so far. I have recently completed a QRP CW setup: a YouKits HB-1B transceiver and a simple wire dipole. I haven't made any contacts yet, and I'm wodering if the radio is even working. A SWR meter shows power to the antenna when keying, but an HF radio nearby is only registering clicks. My question is twofold: how far away would a HF-SW radio have to be from the transmitting antenna to hear a clear groundwave CW signal on 40m, and is there a better way for me to test my rig if I still haven't made any contacts? &lt;/p&gt;&#xA;" OwnerUserId="5760" LastActivityDate="2015-12-09T23:30:19.503" Title="Testing my HB-1B QRP CW Transceiver on 40m" Tags="&lt;cw&gt;&lt;wire-antenna&gt;&lt;qrp&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5570" PostTypeId="2" ParentId="5568" CreationDate="2015-12-05T20:38:44.173" Score="5" Body="&lt;p&gt;It depends mainly on the culture using the frequency, the frequency value itself and how important is each part of the frequency.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the lower frequency ranges, it's not uncommon to give the frequency in kilohertz. For example, the broadcast radio station I'm listening to right now is on frequency of 7375 kHz (or 7.375 MHz), that is to say the carrier is on 7375 kHz and the signal goes 5 kilohertz above and below and stations are places on a grid with 5 kHz steps.&lt;br&gt;&#xA;If I was talking to community of short-wave listeners, they would immediately understand what 7375 means, since the modulation type and bandwidths are standardized, so there's no reason to go into details. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were listening to say amateur single sideband transmission, radio-telegraphy or modern digital modulation schemes, I would use more significant digits, like for example 7015.1 kHz. In such cases, the bandwidth itself is smaller (2.7 kHz in case of SSB or 300 Hz in case of telegraphy), so adding more significant digits makes sense. If you'd say go to 7015 instead of 7015.1, you'd be listening to a different station. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, in higher frequency bands, the frequency itself is higher, so we need more digits to represent the number itself. For example, I could be listening to another shortwave radio station at 11670 kHz and because the frequency itself is higher, I need one more digit to represent it, even though the rest of the information is the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When we move up even higher, again the number of actually used digits will depend on the modulation type, field and channel spacing. Let's take a look at the frequency you provided of 158.7600. My guess would be that this is 158.76 MHz and that whatever service is using this frequency, they're using frequency modulation with most likely 12,5 kHz step. How did I decode this: First, you used the US tag in the question. This tells me I can try to use US traditions for writing frequencies. Next, we have 3 digits to the left of the decimal separator and 4 to the right. Looking at the left side of the number itself, I can see that it's very close to the VHF frequency ranges used for businesses in the US. This is a hint that the measurement unit is most likely megahertz. On the right side, we have decimal places. If you're using 12,5 kHz channel spacing, you would need 4 significant digits to express the center frequency of the channel itself. We have four significant digits. So everything fits. Since we already know more or less where we are, then no more digits are needed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do note that the number of digits used itself depends on the culture and regulations used. For example, if using 25 kHz channel spacing, we would need only 3 significant digits to the right of the decimal point. Until recently, 25 kHz channel spacing was common, so only 3 digits on the right side were used.&lt;br&gt;&#xA;In some cultures, you can have reminders of previous traditions as well. For example aviation used 50 kHz channel spacing, then moved to 25 kHz. With 50 kHz channel raster, you only need 2 digits to the right of decimal separator, but they kept saying only two even when they switched to 25 kHz spacing because the third digit can be either 5 or 0 and the first two are enough to identify if the third is going to be 0 or 5. So for example, in aviation field, frequency of 119.975 MHz would be represented as 119.97. Since everything else is well-known, there's no need to say 119.97 MHz or 199.975 MHz.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2015-12-05T20:38:44.173" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5573" PostTypeId="1" AcceptedAnswerId="5574" CreationDate="2015-12-06T15:31:17.007" Score="0" ViewCount="76" Body="&lt;p&gt;I go camping to France every year. There is a wifi station at 200 metres from where I camp, but I don't have a direct line of sight (it's on a slope). I can put a shoebox at the base station, but I prefer not to. I am willing to write the software myself. There is no cell reception and I don't have a HAM licence. How can I transmit data from and to the station?&lt;/p&gt;&#xA;" OwnerUserId="5693" LastActivityDate="2015-12-06T16:15:46.070" Title="Transmit data without line of sight - Legal, fast, cheap and error corrected" Tags="&lt;wifi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5574" PostTypeId="2" ParentId="5573" CreationDate="2015-12-06T16:15:46.070" Score="0" Body="&lt;p&gt;I'm not familiar with the regulations in France, but if they are similar to the US, then an amateur radio license would not help you, because the traffic of a typical internet connection (HTTPS encrypted data, most notably) would be illegal to transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that's the case, and considering your question purely as a matter of using unlicensed WiFi gear:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Putting equipment at the base station would not help you (much), since it's under the same restrictions as the existing equipment. Instead, what you would have to do is &lt;strong&gt;find an accessible location which has line of sight to both you and the base station.&lt;/strong&gt; There you would place a WiFi repeater (also known as an extender) and a battery sufficient to power it.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The repeater will need to be configured with the SSID of the target network. It must be a model which works with arbitrary networks; many will only work with access points of the same brand. (Or at least, that was the case some years ago; I haven't researched the current state of WiFi much.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You will need a battery with sufficient capacity to power the repeater over the time it is operating. If the repeater location is inaccessible (so that you're not turning it off when you're not using it) then this may be a serious problem. Check the specifications of the equipment for its current draw before buying, and test it before your camping trip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will also need to supply the repeater with the proper voltage. This can be done by using a battery with the proper voltage (possibly composed of several cells/batteries wired in series), or by using a DC-DC converter (power adapter). The converter adds inefficiency but also adds regulation, allowing proper operation over a much larger voltage range and therefore use more of the capacity of the battery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most likely you will want to use a single 12 volt battery and a matching adapter, as that is a common voltage due to its use in cars. However, you should not use a car battery as they can spill acid and are not designed for complete discharge, in addition to being very heavy. A better choice would be a &lt;a href=&quot;https://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery&quot; rel=&quot;nofollow&quot;&gt;lithium iron phosphate&lt;/a&gt; battery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will also need a battery charger designed for the type of battery.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-12-06T16:15:46.070" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5575" PostTypeId="1" CreationDate="2015-12-06T17:32:11.850" Score="2" ViewCount="189" Body="&lt;p&gt;Currently trying to figure out what type of digital mode I'm listening to. I've purchased a Vaisala Radiosonde RS-92AM. It's a meteorological device usually attached to below a weather balloon. I've been trying to use SondeMonitor to decode what should be SGP encoded data (&lt;a href=&quot;https://www.youtube.com/watch?v=Mz2id1cBmjs&quot; rel=&quot;nofollow&quot;&gt;An example of what SGP sounds like&lt;/a&gt;). &lt;a href=&quot;https://soundcloud.com/joshua-ferrara/sdrsharp-20151206-172313z-402666khz-af&quot; rel=&quot;nofollow&quot;&gt;I've linked what I recorded from the device here&lt;/a&gt; which doesn't sound like SGP. I've done research on google but haven't found anything useful.&lt;/p&gt;&#xA;" OwnerUserId="5767" LastEditorUserId="76" LastEditDate="2015-12-08T16:42:32.157" LastActivityDate="2016-01-07T17:37:52.153" Title="What type of digital mode is this?" Tags="&lt;digital-modes&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5577" PostTypeId="2" ParentId="5575" CreationDate="2015-12-08T04:09:04.620" Score="1" Body="&lt;p&gt;Actually, that does sound very much like the same kind of signal, but with a lot of noise on top of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you recorded sounds like it was taken from an FM receiver with a very low signal strength, so there is a lot of white noise on the signal. With some low-pass filtering on the audio and some kind of white noise filtering, you could get it to sound a lot more like the one in the YouTube link.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2015-12-08T04:09:04.620" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5578" PostTypeId="1" CreationDate="2015-12-08T13:58:39.203" Score="6" ViewCount="325" Body="&lt;p&gt;I was able to demodulate a signal I've recieved in gnuradio. Here you can see my flowgraph:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ArU0j.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ArU0j.png&quot; alt=&quot;Flowgraph&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But now I would like to be able to send data as well. But how should I modulate my data? As you can see I've demodulated with Quadrature Demod -&gt; Hilbert -&gt; Complex to Mag.&#xA;To my understanding the reversing would be AM Mod -&gt; something -&gt; GFSK Mod. Is that correct? And if so what could I use as a reverse Hilbert filter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&#xA;Here's the wave I get after the Complex to Mag:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/4OVZ3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4OVZ3.png&quot; alt=&quot;Wave4&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5772" LastEditorUserId="4665" LastEditDate="2020-11-04T16:32:46.450" LastActivityDate="2020-11-04T16:32:46.450" Title="What kind of modulation is this?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5579" PostTypeId="2" ParentId="5578" CreationDate="2015-12-08T16:38:16.237" Score="8" Body="&lt;p&gt;The Hilbert block in GNU Radio creates an &lt;a href=&quot;https://en.wikipedia.org/wiki/Analytic_signal&quot;&gt;analytic signal&lt;/a&gt; from a real-valued one by applying the Hilbert transform to create the Q (imaginary, quadrature) component.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Complex to Mag block then discards the phase information in that analytic signal, keeping only the amplitude. Generally speaking, this is AM demodulation. This further agrees with your Add Const later on which is subtracting the offset resulting from the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you're then taking the output of that as the digital signal, it would be called &lt;em&gt;amplitude shift keying&lt;/em&gt; (ASK) rather than AM. If the lower amplitude is in fact zero (I can't tell from the flow graph), then you have &lt;em&gt;on-off keying&lt;/em&gt; (OOK).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming it's OOK, the corresponding modulator would be a kHz signal source multiplied by your (repeated to have more than one sample-per-symbol) data bits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would then go into the opposite of a Quadrature Demod, which is a VCO. (No conversions to complex are needed.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This combination of OOK with an audio-frequency carrier put into another modulator is commonly known as &lt;em&gt;MCW&lt;/em&gt; (modulated continuous wave), though the term is more often used in the context of Morse code signals than other digital signals.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-12-08T16:38:16.237" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5580" PostTypeId="1" AcceptedAnswerId="5581" CreationDate="2015-12-08T17:06:48.213" Score="2" ViewCount="240" Body="&lt;p&gt;I was going through a datasheet of an HPE M210 802.11n Access Point. According to the specs it has 2 internal antennas and supports 2 x 3:2 MIMO. My question are:&#xA;1) is it actually possible to have 3 receivers given that there are only 2 antennas&#xA;2) in this particular case 2 x 3:2 MIMO consists of only 2 radio chains, right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you in advance&lt;/p&gt;&#xA;" OwnerUserId="5774" LastActivityDate="2015-12-08T17:15:01.420" Title="Is it possible to have 2 x 3:2 MIMO with 2 antennas?" Tags="&lt;antenna&gt;&lt;mimo&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5581" PostTypeId="2" ParentId="5580" CreationDate="2015-12-08T17:15:01.420" Score="0" Body="&lt;p&gt;I'm not familiar with the description &quot;2 × 3:2 MIMO&quot;, but to answer your first part,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;1) is it actually possible to have 3 receivers given that there are only 2 antennas&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, absolutely. One receiver connected to each antenna, and one receiver connected to both. (As long as they are receiving and not transmitting, and the right sort of dividers/combiners are used for the interconnections, they will not interfere with each other). Each receiver is connected to a different combination of antenna elements and will therefore have a different pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, given an antenna array with $n$ elements, any subset of those elements could potentially be useful, so you have the &lt;a href=&quot;https://en.wikipedia.org/wiki/Power_set&quot; rel=&quot;nofollow&quot;&gt;powerset&lt;/a&gt; of combinations or $2^n - 1$. (Minus one because having &lt;em&gt;no&lt;/em&gt; antennas connected is of course not useful.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-12-08T17:15:01.420" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5582" PostTypeId="1" CreationDate="2015-12-08T20:24:04.680" Score="5" ViewCount="1935" Body="&lt;p&gt;For HF operating, &lt;strong&gt;I am considering running a ladder line from the ATU just inside a window, through the window&lt;/strong&gt; (squeezing it between the window and the window frame; not actually through the glass), and &lt;strong&gt;out to a dipole suspended outside.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am interested in all amateur HF bands, 3.5 MHz to 28 MHz, but can absolutely live without 1.8 MHz, and can live without 24 and 28 MHz in a pinch. The idea is to try to avoid having to drill a hole to route a coax cable through. The window frames are made of wood, so coupling should not be a problem there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't yet considered the exact height and length of the dipole, but the plan is to make it a simple center fed dipole as long and high as I can make it, with a bleeder resistor across the feedpoint to help bleed off static. The ladder line would ideally extend to the feedpoint of the antenna, minimizing the number of joints that could break.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feed between the ATU and the transceiver would be a short coax patch cable (think half a meter of RG-58 or something like that, mostly depending on what exactly I have in my junkbox).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some computer equipment, including a powered 2.1 speaker set and a USB hub, within a meter or so from where, based on my current (very rough draft) ideas, the feedline would pass. I don't need to have the speakers turned on while transmitting, but it would be a bummer if for example the computer starts acting up due to RFI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Hence my questions&lt;/strong&gt; (two, but highly related):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Am I insane for even considering a setup like this?&lt;/li&gt;&#xA;&lt;li&gt;What do I need to watch out for? Any particular things that can come back and bite me if I'm not aware of them, and how to mitigate those?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Particularly when answering the latter, please consider me essentially a beginner; it's been long enough since I had to actually worry about these things that the things you would mention to a beginner is probably a good place to start.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="76" LastEditDate="2015-12-15T22:21:49.963" LastActivityDate="2015-12-15T22:21:49.963" Title="Running ladder line through window from inside shack to outside dipole antenna - what to watch out for?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;feed-line&gt;&lt;dipole&gt;&lt;antenna-system&gt;" AnswerCount="3" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5583" PostTypeId="2" ParentId="5582" CreationDate="2015-12-08T21:42:25.523" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Am I insane for even considering a setup like this?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What do I need to watch out for? Any particular things that can come back and bite me if I'm not aware of them, and how to mitigate those?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Avoid running the ladder line parallel to any conductive material for any &quot;larger&quot; fraction of your shortest operating wavelength.  By &quot;larger&quot; I guess 10 percent or larger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, try to avoid 90 degree bends in the ladder line or loops.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-12-08T21:42:25.523" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5584" PostTypeId="2" ParentId="5582" CreationDate="2015-12-08T22:03:11.473" Score="1" Body="&lt;p&gt;I haven't done this myself, but I've heard about people doing it without trouble.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You specify that your window frames are wood, so that's not a problem. However, modern insulated (double-glazed) windows may have metal as part of the seal on the glass (it would be visible looking in through the glass). If you have this, make sure the ladder line doesn't run parallel to the frame on the inside or outside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Twisting your ladder line also helps reduce radiation and coupling to nearby metal.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The second issue is interference with the speakers and other electronic equipment. (Even if the effects are minor, you'll likely want to get them entirely cleaned up if you get into digital modes!) In priority:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Make sure that you have a suitable balun either built in to, or in addition to, your antenna tuner. (I've heard rumors that some tuners with balanced outputs have baluns that aren't actually very effective.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Ground the antenna tuner: connect its ground terminal to the shortest path to earth ground you can get. If everything else is perfect, this is unnecessary, but it will help. (Note: All else being equal, making only this connection likely &lt;em&gt;decreases&lt;/em&gt; lightning safety. Either do your research for a complete grounding system, or &lt;strong&gt;disconnect your antenna, and the additional ground, for any storm.&lt;/strong&gt;)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Finally, if you can separate equipment, do so. (Move that USB hub!) Try to have one side of the room for your digital signals and the other for your RF signals.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Add ferrite chokes to all the cables in the room/house. This is a last resort because it is better to stop the signal getting out (of your feed line) than to stop it getting in (to everything else), but it may be necessary if you are getting interference not from your feed line but &lt;em&gt;your antenna&lt;/em&gt;, i.e. the signal you're actually intending to transmit.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-12-10T19:18:54.290" LastActivityDate="2015-12-10T19:18:54.290" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5585" PostTypeId="1" AcceptedAnswerId="5586" CreationDate="2015-12-09T17:25:13.893" Score="8" ViewCount="2289" Body="&lt;p&gt;I understand why a &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Dummy_load&quot;&gt;dummy load&lt;/a&gt; is used, but (aside from it getting hot) how do I know if it's doing it's job and doing it's job well?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my specific case, I'm using a &lt;a href=&quot;https://greatscottgadgets.com/hackrf/&quot;&gt;Hack RF One SDR&lt;/a&gt; and a &lt;a href=&quot;http://www.amazon.co.uk/gp/product/B00SV39VEE/ref=as_li_tl?ie=UTF8&amp;amp;camp=1634&amp;amp;creative=19450&amp;amp;creativeASIN=B00SV39VEE&amp;amp;linkCode=as2&amp;amp;tag=mophosandphot-21&quot;&gt;Souked SMA Dummy Load 50 Ohm&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="5388" LastActivityDate="2015-12-09T18:24:09.477" Title="How do I know if my dummy load is working?" Tags="&lt;dummy-load&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5586" PostTypeId="2" ParentId="5585" CreationDate="2015-12-09T18:24:09.477" Score="8" Body="&lt;p&gt;A dummy load, or terminator, consists of a non-inductive power resistor (or multiple resistors in series and parallel) and a heat sink, both rated for the maximum power to be dissipated.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The simplest test on a dummy load you can perform is to &lt;strong&gt;measure it with an ohmmeter&lt;/strong&gt; — it should be 50 Ω (or whatever the specified impedance is). Wiggle the connections while you're doing this to make sure it does not have an intermittent open circuit — I've found this to be a problem with some cheap terminators.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The above test tells us that it is 50 Ω at DC, or 0 Hz. It is possible that its impedance will be something else at higher frequencies; if it is, this is a design flaw (or limitation), because this impedance is affected by the geometry of the conductors between the resistor and the input connector. If you wanted to test this property, you would want an &lt;strong&gt;antenna analyzer&lt;/strong&gt; which can sweep over the relevant frequency range and report the impedance or SWR, which you would check for being reasonably close to 50 Ω.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you already have a transmitter, then you can in principle use a &lt;em&gt;SWR meter&lt;/em&gt; combined with the transmitter, but most SWR meters that are sold separately are not sensitive enough for this little power to produce any reading at all. Additionally, the entire point of using a dummy load at all in this low-power situation is to avoid impedance-mismatch reflections damaging the transmitter (or triggering protective power fold-back), and if you need to test the dummy load then you in principle don't know whether there will be reflections or not, so it's not a safe test. In theory.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A dummy load should have the expected impedance, but so does an antenna. The difference between a dummy load and an antenna is that the dummy load mostly does not radiate. To test this characteristic, you would &lt;strong&gt;use a receiver&lt;/strong&gt; to determine the radiated signal strength — ideally one with a signal strength meter (S-meter or RSSI). (You could use a &lt;em&gt;field strength meter&lt;/em&gt; for calibrated results, but if you have that specialized gear...)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that there will always be &lt;em&gt;some&lt;/em&gt; radiation — if not from the dummy load, then from the transmitter. No shielding is perfect. (And the HackRF One has no shielding, anyway.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The final characteristic of a dummy load is power handling capability. To test this, increase transmit power until you smell smoke, then buy a replacement!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you're not going to manage that with the HackRF One. I wouldn't even expect any noticeable warmth.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-12-09T18:24:09.477" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5587" PostTypeId="2" ParentId="5569" CreationDate="2015-12-09T23:30:19.503" Score="1" Body="&lt;p&gt;Call CQ, preferably using a keyer, and see if you are spotted by the Reverse Beacon Network.&lt;/p&gt;&#xA;" OwnerUserId="1590" LastActivityDate="2015-12-09T23:30:19.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5588" PostTypeId="2" ParentId="5310" CreationDate="2015-12-10T12:05:49.103" Score="1" Body="&lt;p&gt;Yes, you can leave voice messages with your radio, &lt;strong&gt;if&lt;/strong&gt; the EchoLink server you connect to (via RF) has the &lt;a href=&quot;http://www.svxlink.org/&quot; rel=&quot;nofollow&quot;&gt;svxlink&lt;/a&gt; server daemon running on a Linux system. This can be done with any DTMF capable radio.&lt;/p&gt;&#xA;" OwnerUserId="5784" LastEditorUserId="76" LastEditDate="2015-12-12T17:15:21.247" LastActivityDate="2015-12-12T17:15:21.247" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5590" PostTypeId="2" ParentId="5582" CreationDate="2015-12-10T19:32:22.037" Score="0" Body="&lt;p&gt;In theory, any material with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Relative_permittivity&quot; rel=&quot;nofollow&quot;&gt;relative permittivity&lt;/a&gt; or &lt;a href=&quot;https://en.wikipedia.org/wiki/Relative_permeability&quot; rel=&quot;nofollow&quot;&gt;permeability&lt;/a&gt; in the space within a few multiples of the conductor spacing of the ladder line will alter the characteristic impedance of your ladder line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will that be a problem? It's not likely. You already have a tuner so you are equipped to deal with whatever impedance may appear at the end of the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The window frame might be lossier than air, but since the transmission line is running through it for only a very small distance (relative to HF wavelengths), it's unlikely to have any practical consequence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But don't just believe me, try science! You can use your radio's S meter to measure the power received from a signal. If the window frame is introducing loss, you should see that when the window is shut on the feedline, the S meter indicates less received power, because some of it is being lost in the window frame. So find some CW or AM station (because these modulations, unlike SSB, have a more or less constant power) and compare for yourself the received power under various conditions.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2015-12-10T19:32:22.037" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5591" PostTypeId="1" CreationDate="2015-12-10T20:19:30.707" Score="0" ViewCount="1470" Body="&lt;p&gt;I have this Baofeng and I want listen to my school radios. The problem is that I want to find the CTCSS tone for the fun of it, but when I scan the tones on the Baofeng it cycles through but does not stop on one. I know that the school uses a little 35 Watt repeater but the input frequency does not yield any tone when I scan it. Do you think the school uses a non-standard CSCSS tone? Also, could they be using a DCS tone? Thanks!&lt;/p&gt;&#xA;" OwnerUserId="5787" LastActivityDate="2016-04-13T05:44:05.177" Title="Baofeng not finding CTCSS tone" Tags="&lt;ht&gt;&lt;baofeng&gt;&lt;tone-squelch&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5592" PostTypeId="2" ParentId="5465" CreationDate="2015-12-10T20:34:41.083" Score="2" Body="&lt;p&gt;I am by no means an expert, but here's my point of view on this. Cellphones get their data by a Cell Tower, and if you have ever been on a plane there is little to no reception once you are in the air. The reason this happens is because the cell towers are horizontally directional so that they can get the most range from the smallest amount of power possible. They don't waste RF by sending it up. I know it's not the answer your looking for, but I hope it helps!&lt;/p&gt;&#xA;" OwnerUserId="5787" LastEditorDisplayName="user4168" LastEditDate="2019-01-21T02:23:22.013" LastActivityDate="2019-01-21T02:23:22.013" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="5593" PostTypeId="2" ParentId="5465" CreationDate="2015-12-10T20:40:37.323" Score="1" Body="&lt;p&gt;Clearly not possible if you try to reach a certain altitude. Why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because antennas of cell phones are made -by design- to &quot;spread&quot; the signal on a horizontal plan.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are to high in the sky, you cannot listen, nor speak to cellular antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Turn your chance on VHF spectrum instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No chance to make a world-around balloon with no repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Planes are using a local cell repeater itself, then forward traffic through plane-to-land special uplink or plane-to-sat special uplink.&lt;/p&gt;&#xA;" OwnerUserId="454" LastEditorUserId="13" LastEditDate="2015-12-14T00:58:35.903" LastActivityDate="2015-12-14T00:58:35.903" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5599" PostTypeId="2" ParentId="221" CreationDate="2015-12-14T22:30:25.710" Score="7" Body="&lt;p&gt;My first post in SO. Here's a C version... made this for an Arduino project.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;void calcLocator(char *dst, double lat, double lon) {&#xA;  int o1, o2, o3;&#xA;  int a1, a2, a3;&#xA;  double remainder;&#xA;  // longitude&#xA;  remainder = lon + 180.0;&#xA;  o1 = (int)(remainder / 20.0);&#xA;  remainder = remainder - (double)o1 * 20.0;&#xA;  o2 = (int)(remainder / 2.0);&#xA;  remainder = remainder - 2.0 * (double)o2;&#xA;  o3 = (int)(12.0 * remainder);&#xA;&#xA;  // latitude&#xA;  remainder = lat + 90.0;&#xA;  a1 = (int)(remainder / 10.0);&#xA;  remainder = remainder - (double)a1 * 10.0;&#xA;  a2 = (int)(remainder);&#xA;  remainder = remainder - (double)a2;&#xA;  a3 = (int)(24.0 * remainder);&#xA;  dst[0] = (char)o1 + 'A';&#xA;  dst[1] = (char)a1 + 'A';&#xA;  dst[2] = (char)o2 + '0';&#xA;  dst[3] = (char)a2 + '0';&#xA;  dst[4] = (char)o3 + 'A';&#xA;  dst[5] = (char)a3 + 'A';&#xA;  dst[6] = (char)0;&#xA;}&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="5806" LastEditorUserId="5806" LastEditDate="2015-12-16T21:24:06.333" LastActivityDate="2015-12-16T21:24:06.333" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5601" PostTypeId="5" CreationDate="2015-12-15T20:41:05.907" Score="0" Body="&lt;p&gt;This tag is for questions about antenna theory — the relationship between the electromagnetic properties of an antenna and the material structure.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-12-15T20:41:05.907" LastActivityDate="2015-12-15T20:41:05.907" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5602" PostTypeId="4" CreationDate="2015-12-15T20:41:05.907" Score="0" Body="Designing antennas, selecting antennas for specific applications, properties of a given antenna design." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-12-15T20:41:05.907" LastActivityDate="2015-12-15T20:41:05.907" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5603" PostTypeId="5" CreationDate="2015-12-15T22:12:21.300" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-12-15T22:12:21.300" LastActivityDate="2015-12-15T22:12:21.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5604" PostTypeId="4" CreationDate="2015-12-15T22:12:21.300" Score="0" Body="The system composed of an antenna and a feed line, and possibly also an RF ground connection, antenna tuner, balun, phasing device, et cetera." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2015-12-15T22:12:21.300" LastActivityDate="2015-12-15T22:12:21.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5605" PostTypeId="1" AcceptedAnswerId="5654" CreationDate="2015-12-18T00:05:53.600" Score="3" ViewCount="3365" Body="&lt;p&gt;Can I use the inside conductor of coax to radiate RF energy?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My in-laws have some sort of attic antenna installed many years ago for broadcast reception, which I would love to temporarily co-opt for MW/HF reception, and/or QRP transmission on 40 meters. I'm assuming the antenna itself is designed for the VHF/UHF television bands, but there's a tantalizing amount of feedline leading up to it — at least relative to the weather conditions outside to operate a proper antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I'd like to use the feedline as an antenna, does it make much difference if I connect to the outer shield versus the inner conductor? Seems intuitively that the outer shield should work just fine as a long wire. But will the center conductor also serve just as well? In this case, does the outer &quot;shield&quot; still serve as such, or would it just sort of re-radiate the signal like a director element might? I am assuming there is no earth grounding on the far end of the coax, that it simply is connected to a VHF/UHF antenna in the attic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess my question boils down to: if the outer braid of a coax is &lt;em&gt;not&lt;/em&gt; grounded, does it still shield the inner conductor? Trying to answer this question myself, I can see it going both ways:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;yes, the shield always works as a &lt;a href=&quot;https://en.wikipedia.org/wiki/Faraday_cage&quot; rel=&quot;nofollow&quot;&gt;Faraday cage&lt;/a&gt; around the wannabe &quot;antenna&quot; inside it&lt;/li&gt;&#xA;&lt;li&gt;no, when the center conductor near a section of braid has a lot of electrons it will repel the electrons on the inside of the shield so they migrate to the outside of the shield and then cause radiation from there&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Bonus: what happens if I short the inner and outer conductors and then feed &lt;em&gt;that&lt;/em&gt; as an antenna?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="76" LastEditDate="2015-12-18T00:37:45.080" LastActivityDate="2016-01-04T20:39:58.367" Title="Using inner conductor of a coax feedline as an antenna" Tags="&lt;antenna-theory&gt;&lt;wire-antenna&gt;&lt;coaxial-cable&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5606" PostTypeId="2" ParentId="5405" CreationDate="2015-12-18T11:57:08.803" Score="4" Body="&lt;p&gt;It is true that 4nec2 is a bit non-intuitive when it comes to creating a new antenna, but it is easy to start from scratch and create anything, without the need to import.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4nec2 provides 4 different methods to edit the antenna model and you can find them on the Settings menu. By default, the 'Nec Editor (new)' is selected but you can change it to 'Geometry edit' which uses a 3d antenna creation tool but it is quite hard to use. Selecting either of the two first options means that you are quite comfortable to use directly NEC2 commands.&#xA;Under the Edit menu there is the option 'Input (.nec) file' and clicking on this option opens the editor you have previously selected on the Settings menu.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest to leave the 'Nec Editor (new)' selected and try to work the geometry of your antenna using 3d coordinates.For this example make sure you have selected this option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is how to create a model for a vertical whip antenna. note: this is just the procedure not that the model will be the one that will serve 100% your purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;the tricky part is that 4nec2 does not have a 'create new' option.So, create an empty text file with any editor (e.g notepad) and save it where you prefer using the .nec extension. eg: vertical_whip.nec you don't have to put anything on this file yet.just an empty file.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;now on 4nec2 select 'File-&gt;Open 4nec2 in/out file' and open the empty file you just created (e.g the vertical_whip.nec).You will notice that 4nec2 will start a new antenna project.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now select 'Edit-&gt;Input (.nec) file' and you will be presented with a spreadsheet like screen, and the 'Geometry' tab will be selected. This is where you enter the antenna geometry. Let's enter the geometry of the vertical whip and make use of the symbols on 4nec2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The length of a vertical quarter wave whip (in feet) is given by the formula length = 234/F , where F is the frequency in Mhz.So to make our life easier we will use a few symbols.Go to 'Symbols' tab and enter the following symbols ont he first column 'Symbols and equations', one on each row:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;F=144&lt;/p&gt;&#xA;&#xA;&lt;p&gt;L=234/F&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(in this example I use 144Mhz for frequency but since we use it in a symbol we can move the design at any frequency)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;make sure that at the bottom of the tab under section 'Scaling' the 'Feet' radio button is selected (because all the dimensions in the model will be in feet)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now switch to 'Geometry' tab and click on the first row and first column and from the drop down select 'wire' to add the antenna element. on the second column (Tag) just enter 1 as this is the first wire on the model.on the 'Segs' enter 11 and then enter the following (X,Y,Z) pairs:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;X1=0,Y1=0,Z1=0&#xA;X2=0,Y2=0,Z2=L &#xA;Radius=0.001&lt;/p&gt;&#xA;&#xA;&lt;p&gt;this will create a vertical wire of length L centered at the axis and at height 0 feet from ground&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Move to 'Source/Load' tab and click on the first row on the first column and select 'current source'. The next two parameter define where to place the feedpoint of the antenna. We need it to be on Tag 1 (our first and only wire) on segment 1 (which is the lower end of the antenna). Enter 1 on 'Real' and 0 on 0 on 'Imag' and you are done here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Move to 'Freq/Ground' and enter F on the frequency box, so that the frequency is taken from our symbols.on the 'Environment' section select 'Real ground' and also select 'Good' on ground type below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Select 'File-&gt;Save' to save the model and you can close the editor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4nec2 will update the geometry of the antenna and the 'Geometry' window will display your antenna.If it is not visible just press F3, or if the window is visible and the geometry was not updated just select 'View-&gt;reset' on the geometry window.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;you can now model your antenna by pressing F7 and selecting 'far field pattern'. The Frequency should already be set to 144Mhz.Click on the 'Generate' button and you should see the antenna pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that this is not necessarily the best way to model a vertical antenna  but it is a good start to create models from scratch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Make sure you read 4nec2 help files and also the 4 parts article on starting modelling with nec.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://wireless.ictp.it/school_2005/download/nec2/nec_part1.pdf&quot; rel=&quot;nofollow&quot;&gt;http://wireless.ictp.it/school_2005/download/nec2/nec_part1.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I cannot post more than 2 links so this is the first part and the rest is just changing the file name to nec_part2.pdf,nec_part3.pdf,nec_part4.pdf)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this helps you to get started.&lt;/p&gt;&#xA;" OwnerUserId="5818" LastEditorUserId="13" LastEditDate="2015-12-18T14:01:21.763" LastActivityDate="2015-12-18T14:01:21.763" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5607" PostTypeId="2" ParentId="5378" CreationDate="2015-12-19T00:00:37.887" Score="3" Body="&lt;p&gt;If you're OK with using a smart phone instead of a regular GPS, you can use:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://aprsdroid.org&quot; rel=&quot;nofollow&quot;&gt;APRSdroid&lt;/a&gt; with a &lt;a href=&quot;http://www.mobilinkd.com&quot; rel=&quot;nofollow&quot;&gt;Bluetooth TNC&lt;/a&gt; for an Android phone&lt;/li&gt;&#xA;&lt;li&gt;PocketPacket with an audio level converter you make yourself with an iOS device.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5820" LastActivityDate="2015-12-19T00:00:37.887" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5608" PostTypeId="1" CreationDate="2015-12-19T23:34:07.013" Score="3" ViewCount="473" Body="&lt;p&gt;I am about to purchase a Baofeng HT.  I have one I am thinking of using primarily in work truck.  I can't really drill holes or have antenna be too obvious.  On Amazon I found a 2 meter 70cm 2m dipole.  I am guessing it would have to be mounted vertically. It seems like it clips to inside of window.  I know it is not optimal but would it be better than stock ducky?  Has anyone used this antenna or have any ideas about really discreet antenna?&#xA;73 Joe&lt;/p&gt;&#xA;" OwnerUserId="5824" LastEditorUserId="873" LastEditDate="2015-12-23T15:56:47.040" LastActivityDate="2016-03-22T17:50:11.363" Title="2 meter dipole of work vehicle" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;vhf&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5609" PostTypeId="2" ParentId="5608" CreationDate="2015-12-20T00:39:49.070" Score="1" Body="&lt;p&gt;I intended on writing a comment but took up too much space.  I think your question is ripe for opinions and suggestions rather than answers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I think if I were you I would operate first with just the antenna that comes with the HT before you decided you need something different from that.  A case in point.  I can generally reach all points of interest (a couple of repeaters in the area) with my HT without using a separate antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, in my pickup truck I also have a Yaesu FT-7800 (2m/70cm) rig and it has an external dual band (2m/70cm) antenna that has a easy to install and easy to remove antenna mount (screw clamp, no need for drilling holes).  It works fine too.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It really depends on who you are talking to (simplex or duplex/repeater) and where they are located and any obstructions (hills, buildings, mountains) that might be in the way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, my mobile 2m/70cm antenna is a Comet SBB-5NMO (i.e. with an NMO mount).  My clamp on mounting (supporting NMO mount) is also from Comet and model number CP-5NMO.  No, these are not the cheapest possible antenna solutions but I usually never go for cheapest.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2015-12-20T00:39:49.070" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5610" PostTypeId="2" ParentId="5608" CreationDate="2015-12-20T01:05:02.910" Score="1" Body="&lt;p&gt;If the antenna is small enough to fit on the inside of your window, then it must be a “shortened” antenna — a true 2-meter-band dipole is about 1 meter (1/2 wavelength) long. This means it will be relatively inefficient — just like the “rubber duck” antenna that would be supplied with your handheld. It will have the advantage of being closer to being outside the vehicle than wherever you're holding or mounting the HT, but that's not a whole lot of benefit, and it only works well on one side of the vehicle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would advise not bothering with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want an effective antenna which can be temporarily mounted, get a magnet-mount quarter-wave antenna for the roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a better antenna which stays inside the vehicle, get a quarter-wave flexible whip antenna, such as the &lt;a href=&quot;http://www.cometantenna.com/amateur-radio/ht-antennas/chinese-ht-antennas/&quot; rel=&quot;nofollow&quot;&gt;Comet SMA-24J&lt;/a&gt;. This will not give you great performance since it's surrounded by the metal of the vehicle, but since it's on the HT itself you can always stop and step outside to improve the situation.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-12-20T01:05:02.910" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5612" PostTypeId="1" CreationDate="2015-12-21T08:07:16.050" Score="0" ViewCount="86" Body="&lt;p&gt;What is the required signal-to-noise ratio of a AX5042 transceiver IC?&lt;/p&gt;&#xA;" OwnerUserId="4894" LastEditorUserId="76" LastEditDate="2015-12-23T15:58:04.423" LastActivityDate="2016-02-21T20:00:45.900" Title="What is the required signal-to-noise ratio for a AX5042 transceiver?" Tags="&lt;electronics&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5614" PostTypeId="2" ParentId="5457" CreationDate="2015-12-21T22:41:37.480" Score="2" Body="&lt;p&gt;If your antenna is hanging down the side of the building that may be your very problem!  Most DXing on HF is done on horizontal antennas.  If yours is vertical then you be getting only a sliver sized cross section of the horizontal signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The station you did pick up may be driving a vertical antenna.  The cheapest way to test this is to put up a horizontal dipole and see if it increases or decreases the reception of the known signal from the vertical antenna. (Always power down your rig before changing the antenna.)  Don't forget to tune your antenna.  If you have an antenna tuner or just a SWR meter then you're good to go.  If not then be as exact as you can in measuring your wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can tape it to the walls of your apartment near the ceiling for a temporary setup.&lt;/p&gt;&#xA;" OwnerUserId="5834" LastActivityDate="2015-12-21T22:41:37.480" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5615" PostTypeId="1" CreationDate="2015-12-22T10:27:18.650" Score="1" ViewCount="70" Body="&lt;p&gt;I have used Kenwood TS-2000 to receive BFSK signals with 3.3 khz deviation operating the TS-2000 in FM mode. Can we receive similar signals but whose BFSK deviation is 9.6 Khz using either the TS-2000 or the ICOM IC-910H transceiver? Do these transceivers support this large deviation? &#xA;Also what are the software that can be used to decode the AF tones obtained from these transceivers?&lt;/p&gt;&#xA;" OwnerUserId="4397" LastActivityDate="2015-12-22T10:27:18.650" Title="Receiving BFSK with 9.6 khz deviation on TS-2000 / ICOM(IC-910H) in FM mode" Tags="&lt;kenwood&gt;&lt;fm&gt;&lt;icom&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5616" PostTypeId="2" ParentId="5612" CreationDate="2015-12-23T19:46:12.320" Score="1" Body="&lt;p&gt;A manufacturer will specify the receiver sensitivity at a particular bit transmission rate and not the minimum signal-to-noise ratio (SNR) required for the receiver to demodulate.This is because the receive sensitivity is the most important specification needed when designing wireless systems, not the minimum SNR.So when you are performing a link budget, you have to make sure that the power that reaches your receiver is at least equal to the receive sensitivity if you want to maintain a good BER.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The receive sensitivity is the minimum signal power that should reach the receiver for there to be &quot;successful demodulation&quot;.Successful demodulation is usually defined as there being a BER of at least $10^{-9}$ but a manufacturer can chose to specify a receive sensitivity relating to another BER value (if this is done then that BER is explicitly stated).&lt;/p&gt;&#xA;" OwnerUserId="5515" LastActivityDate="2015-12-23T19:46:12.320" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5617" PostTypeId="1" CreationDate="2015-12-23T21:51:11.957" Score="1" ViewCount="177" Body="&lt;p&gt;I have a Realistic STA-78 AM/FM Stereo receiver I recently rescued from my grandmother's attic. It hadn't been played in a while, but it appears everything is in working order except the FM dial. It's an old-style scrolling dial, and receives FM stations but the signal is shifted by +1.4 to 1.5 Mhz. The AM stations are fine, with no noticeable offset. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anybody have any suggestions for a fix?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;update:&lt;/strong&gt; It appears the stations are becoming more accurate over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;update 2:&lt;/strong&gt; Originally I had plugged in some small FM wires to the base of the radio, even though it has a built-in antenna.  Like previously mentioned, the FM slowly corrected itself with those FM wires.  But I recently started having problems with the AM, where it would either only come out of the right speaker, or if it would come out of the left speaker, it was extremely quiet.  Additionally, the AM stations were shifted over.  In an effort to rectify the problem, I unplugged the FM tuner wires.  Now, the AM works perfectly fine, but the AM is again shifted up, about the same amount as it was originally (a little less now, closer to 1.3 Mhz up from usual).  As Nate said, it could be capacitors.  I'll have it checked soon to see if that's a problem.  In the mean time, any other ideas as to the cause?  Thanks&lt;/p&gt;&#xA;" OwnerUserId="5843" LastEditorUserId="5843" LastEditDate="2016-04-26T22:09:12.747" LastActivityDate="2016-04-26T22:09:12.747" Title="Reception for FM stations is offset, but AM stations aren't" Tags="&lt;receiver&gt;&lt;fm&gt;&lt;am&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5618" PostTypeId="2" ParentId="5617" CreationDate="2015-12-23T22:06:09.960" Score="3" Body="&lt;p&gt;While I wouldn't rule out old capacitors or whatnot, if it's anything like some of the radios I've played with through the years, the solution might be a simple mechanical one: can you open it up enough so that you can hold the dial from moving while gently nudging the linkage from the FM circuit tuning mechanism until it lines up?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2015-12-23T22:06:09.960" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5619" PostTypeId="1" AcceptedAnswerId="5621" CreationDate="2015-12-23T22:18:53.333" Score="9" ViewCount="1098" Body="&lt;p&gt;I am winding an EFHW matchbox and many of the designs I've found (including the diagram provided with the kit I bought) include a sort of &quot;twist&quot; when winding them:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uFL5R.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uFL5R.jpg&quot; alt=&quot;EFHW toroid example&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Image taken from &lt;a href=&quot;http://pa-11019.blogspot.com.au/2012/04/149-transformer-for-endfed-antennas-35.html&quot; rel=&quot;noreferrer&quot;&gt;this post&lt;/a&gt; and similar can be seen &lt;a href=&quot;http://www.ebay.com/itm/181945438397&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;https://pa3hho.wordpress.com/end-fed-antennes/multiany-band-end-fed-english/&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;http://vk3il.net/projects/efhw-matching-unit/&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding is that the section where the two green turns go with the initial red turns is called a &quot;bifilar&quot; winding and some recommend twisting the two wires together for that part — its own topic that I can research a bit more on my own.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what is the trick where the red winding crosses across the middle and then continues winding? Does it have a name? Does it count as a turn — or a &quot;negative turn&quot;? (In the diagram I have linked there are drawn 8+7 turns labeled as 2x7…but I suspect this is just a mistake.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why would the toroids be wound this way in two groups instead of just a simple total number of windings spread evenly around? When is this technique useful?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2015-12-24T11:37:06.243" Title="What's this &quot;crossover&quot; toroid winding called and what is its purpose?" Tags="&lt;physics&gt;&lt;toroid&gt;&lt;transformer&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5621" PostTypeId="2" ParentId="5619" CreationDate="2015-12-24T11:37:06.243" Score="5" Body="&lt;p&gt;This is a magnetic flux transformer, not a transmission line transformer. It works by flux coupling just like a mains power transformer. So the bifilar part isn't too special, nothing like a transmission line transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a regular flux transformer, the position of the winding doesn't really matter, only the number of turns. At RF though there is the concern about capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First concern is the inter-turn capacitance, which might make the coil resonant and stop working as a transformer. The best you can do is keep the number of turns small, and spread them out evenly. Of course fewer turns means more flux, so there's a trade-off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second concern is about the capacitance from one end of the winding to the other. A 64:1 transformer will have a very high impedance at the high voltage end, and any capacitance to the ground end of the winding will tend to load the high impedance end. This transformer might transform to an impractical 3200 ohms, but quite likely the capacitance from live to ground will be less than that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you follow the wire, the reverse winding only reverses direction on the core, it keeps going the same way through and out, so it keeps developing more voltage at each turn. The reverse winding is a neat trick to keep the windings spread out, keep them going in the same direction, and keep the high voltage, high impedance end of the transformer far away from the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know it's name, but I'm sure it will have one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Recommended reading: &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/1884932185&quot; rel=&quot;noreferrer&quot;&gt;Jerry Sevik - Transmission Line Transformers&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2015-12-24T11:37:06.243" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5622" PostTypeId="1" CreationDate="2015-12-24T19:58:39.830" Score="1" ViewCount="218" Body="&lt;p&gt;I'm hoping this question is okay to ask here. While this question is not strictly amateur radio related, I think this is the best community to ask.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://imgur.com/a/k5RTx&quot; rel=&quot;nofollow noreferrer&quot;&gt;I'm looking for any information on this.&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I have no real information on it other that the pictures I have provided.&lt;/p&gt;&#xA;" OwnerUserId="5849" LastEditorUserId="8717" LastEditDate="2019-12-05T20:06:25.980" LastActivityDate="2019-12-05T20:06:25.980" Title="I need help identifying what I believe is a military radio" Tags="&lt;electronics&gt;&lt;military-surplus&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5623" PostTypeId="1" CreationDate="2015-12-25T06:18:30.617" Score="0" ViewCount="287" Body="&lt;p&gt;Can the Motorola GTX 800MHz mobile or handheld be modified to operate on the 33cm  902MHz US ham band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know the GTX 900 MHz version can and requires a filter change if you want to receive towards the bottom of the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, what is required for the modification? I assume a change of front end filter, and hex editing of the software, is there anything else?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, are there any parts in this radio that are useful in this band or should I not bother with these radios? I have a few that I got off eBay dirt cheap for 900MHz before I realized I needed the 900MHz version. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2015-12-30T23:43:40.500" Title="Motorola GTX 800 for ham band" Tags="&lt;33cm-band&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5624" PostTypeId="2" ParentId="221" CreationDate="2015-12-25T17:56:08.763" Score="1" Body="&lt;p&gt;Have a Look at numpy.meshgrid&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://docs.scipy.org/doc/numpy-1.10.0/reference/generated/numpy.meshgrid.html&quot; rel=&quot;nofollow&quot;&gt;http://docs.scipy.org/doc/numpy-1.10.0/reference/generated/numpy.meshgrid.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5853" LastActivityDate="2015-12-25T17:56:08.763" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5625" PostTypeId="2" ParentId="5605" CreationDate="2015-12-25T22:57:37.110" Score="0" Body="&lt;p&gt;A rule of thumb is that if there is any impedance mismatch anywhere beyond (e.g. at least a fraction of a wavelength) your (matched) feed point, then it can be used as an antenna. Just make sure your antenna tuner can handle it (drive with very low power until you know it can). For example, the ends of a dipole are severely mismatched even though the feed point is matched without an antenna tuner, and that's why it radiates. Of course, it may not radiate in the direction you want. Shorting the inner &amp;amp; outer conductors is also OK as long as the above still holds.&lt;/p&gt;&#xA;" OwnerUserId="5855" LastEditorUserId="5855" LastEditDate="2015-12-26T01:33:09.063" LastActivityDate="2015-12-26T01:33:09.063" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5629" PostTypeId="1" AcceptedAnswerId="5630" CreationDate="2015-12-27T18:17:19.740" Score="2" ViewCount="68" Body="&lt;p&gt;I would like to know what are all the licensing options available to get started with Ham in India.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in Hyderabad, India any pointers towards local groups would be great.&lt;/p&gt;&#xA;" OwnerUserId="5732" LastEditorUserId="76" LastEditDate="2015-12-29T03:50:22.240" LastActivityDate="2015-12-29T03:50:22.240" Title="Licensing options in India" Tags="&lt;license&gt;&lt;india&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5630" PostTypeId="2" ParentId="5629" CreationDate="2015-12-27T18:58:10.333" Score="1" Body="&lt;p&gt;Licensing and tests vary per country.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio in India:&#xA;&lt;a href=&quot;https://en.wikipedia.org/wiki/Amateur_radio_in_India&quot; rel=&quot;nofollow&quot;&gt;https://en.wikipedia.org/wiki/Amateur_radio_in_India&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Licensing in India:&#xA;&lt;a href=&quot;https://en.wikipedia.org/wiki/Amateur_radio_licence_categories_in_India&quot; rel=&quot;nofollow&quot;&gt;https://en.wikipedia.org/wiki/Amateur_radio_licence_categories_in_India&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I couldn't find any practice test questions for the Indian tests, but there are a lot of questions free on-line and in book form for the U.S. tests. You might figure out the equivalent U.S. test of the license you are interested in and practice with those questions. I imagine they are similar.&lt;/p&gt;&#xA;" OwnerUserId="5855" LastActivityDate="2015-12-27T18:58:10.333" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5631" PostTypeId="1" CreationDate="2015-12-28T14:14:59.960" Score="0" ViewCount="233" Body="&lt;p&gt;I am designing a Class-E power amplifier in UHF band using ADS. Now I have 20dBm fundamental output power with 13% PAE, which is low for this class of PA. The problem is that I have  thermal dissipation and DC power consumption and harmonics. How can I reduce these? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qvp6V.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qvp6V.jpg&quot; alt=&quot;Schematic of the designed PA&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CeYZh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CeYZh.jpg&quot; alt=&quot;Results obtained&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4621" LastEditorUserId="76" LastEditDate="2016-04-22T18:51:56.823" LastActivityDate="2016-04-22T18:51:56.823" Title="How can I reduce power consumption and thermal dissipation in power amp?" Tags="&lt;amplifier&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5633" PostTypeId="1" CreationDate="2015-12-28T19:27:21.130" Score="0" ViewCount="214" Body="&lt;p&gt;I am having this issue and cant seem to find a solution. I am running a Yaesu vx6r radio, I have had it for about 6 years. Today, I fired it up, as I had just built a 5 element 70cm yagi for satellite down links and what not. But I tried to key up a local repeater and well nothing. I made sure the the tone (103.5) was correct, and that the shift settings are correct. I put on my stock antenna, and still nothing (unusual as I can normal hit this repeater just fine)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So i went and put together my Icom, and got set up on two meters, it too could not hit a local two meter repeater. But i went to a simplex band, and I could listen and hear myself on both radios. But no repeaters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I checked the tone, and shift points. they are all fine. anything else to look at? It seems like both radios are having this issue. I just got back into radio, could I be missing something?&lt;/p&gt;&#xA;" OwnerUserId="5874" LastActivityDate="2016-01-14T22:48:38.283" Title="Radio wont RX or TX on repeaters. Fine in simplex" Tags="&lt;repeater&gt;&lt;yaesu&gt;&lt;icom&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5634" PostTypeId="1" AcceptedAnswerId="5635" CreationDate="2015-12-29T01:59:42.707" Score="1" ViewCount="830" Body="&lt;p&gt;I've been doing mostly HF for the last 20 years and just recently installed a 2m/70cm mobile rig in my shack for base station work. I like to work FM simplex and repeaters when the HF bands are not cooperating, and would like to build a beam for those bands. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What negative or positive impacts would a circular polarized beam have for terrestrial communications? An uneducated assumption would be that it would work well for both repeater work (vertical polarized) and SSB/CW (horizontal polarized). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I'm also interested in having one antenna that I can use for satellite work in the future if the compromise is small)&lt;/p&gt;&#xA;" OwnerUserId="606" LastEditorUserId="76" LastEditDate="2015-12-29T02:55:02.223" LastActivityDate="2015-12-29T02:55:02.223" Title="VHF / UHF - Terrestrial Circular Polarized Antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;uhf&gt;&lt;vhf&gt;&lt;circular-polarization&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5635" PostTypeId="2" ParentId="5634" CreationDate="2015-12-29T02:54:35.930" Score="1" Body="&lt;p&gt;Circular polarization can be seen as half horizontal and half vertical polarization. Therefore, between a circularly polarized antenna and a linearly polarized antenna, half the signal will be lost (-3 dB gain).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only disadvantages of a circularly polarized antenna are that loss and the additional complexity (phasing, mechanical structure, weight). If you're OK with that, go right ahead!&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2015-12-29T02:54:35.930" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5636" PostTypeId="2" ParentId="3718" CreationDate="2015-12-29T18:47:21.780" Score="2" Body="&lt;p&gt;From &lt;a href=&quot;http://amsat-uk.org/2015/10/07/fox-1a-launch/&quot; rel=&quot;nofollow&quot;&gt;Amsat UK&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Fox-1A frequencies, see &lt;a href=&quot;http://www.amsat.org/wordpress/wp-content/uploads/2015/05/FoxOperatingGuide_May2015_Hi.pdf&quot; rel=&quot;nofollow&quot;&gt;Operating Guide&lt;/a&gt; to set up your rigs memory channels:&lt;br&gt;&#xA;  435.180 MHz FM Uplink 67 Hz CTCSS PL tone required&lt;br&gt;&#xA;  145.980 MHz FM Downlink&lt;br&gt;&#xA;  Note: If your rig has selectable FM filters use the wider filter for 5 kHz deviation 25 kHz channel spacing.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="5882" LastEditorUserId="76" LastEditDate="2015-12-31T01:06:42.567" LastActivityDate="2015-12-31T01:06:42.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5637" PostTypeId="1" AcceptedAnswerId="5642" CreationDate="2015-12-29T22:12:32.527" Score="0" ViewCount="2589" Body="&lt;p&gt;Just looking for some general advice for in-car radio mounting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my previous vehicle (06' Ford focus ZX3), I simply screwed the metal brackets into the dash which worked fine for an old beater car.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I have a 2014 Nissan Xterra X and want to be a bit more careful, especially since I have a loan to pay off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone have any experience with this situation? I just want a non-permanent solution that wouldn't void any warranties. No drastic modifications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I currently have a Baofeng UV5R+, Uniden BC880 CB, and a Uniden BC355n Scanner. I plan on replacing the Baofeng handheld with a small Yaesu or Kenwood Dual-band mobile unit at some point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a picture of what my interior looks like for an example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8g8GF.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8g8GF.jpg&quot; alt=&quot;Xterra Interior&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5023" LastActivityDate="2016-09-16T04:02:02.587" Title="In Vehicle Mounting recommendations" Tags="&lt;mobile&gt;&lt;installation&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5639" PostTypeId="2" ParentId="5623" CreationDate="2015-12-30T23:43:40.500" Score="2" Body="&lt;p&gt;It is virtually impossible to modify a 800 MHz GTX to transmit on the ham bands. To start with, the 800 MHz radios transmit a 5 MHz signal, while the 900 MHz devices transmit a 2.5 MHz signal. This is not something that can be configured, it's hard wired.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, the filters for both receive and transmit for the 800 MHz GTX are all wrong, and even if you modified the Motorola code plug with a hex editor, the radio would still be deaf and dumb on 900.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've found the 800 MHz variants of these radios are good for spare parts - knobs, antenna jacks, buttons, speakers - but not much else.&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2015-12-30T23:43:40.500" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5641" PostTypeId="2" ParentId="5637" CreationDate="2016-01-01T10:21:01.920" Score="0" Body="&lt;p&gt;Not sure just how much of a foot-print your rig will have but there looks like there is some space in of the gear lever.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the past I made a block of wood - to fit that type of space and then using my rig's Brackets - attached the brackets to the wood. This fixed the rig/wood together but allowed me to move the unit in and out of the vehicle easily.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that will not work - you may be able to mount the rig against the centre console - either on your (or the passengers side).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I also hate drilling holes in plastic - some velcro strips may be sufficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power and Antenna in both of these areas are quite easy as you will have access to the carpets. I would then look for a rubber grommet that will accommodate the power/antenna cables.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck with the installation.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2016-01-01T10:21:01.920" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5642" PostTypeId="2" ParentId="5637" CreationDate="2016-01-02T01:17:53.667" Score="1" Body="&lt;p&gt;Sometimes doing the right mount means getting the right rig.  I am not familiar with the rigs you plan to install but when I decided to install a mobile rig in my truck, I studied my options before buying the rig and made my decision on what fits best.  In my case, it was two rigs:  HF Transceiver and VHF/UHF FM Transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I figured my favored  configuration was to use my cup holder (between the seats) and a cup holder radio mount.  Since I can see the entire range of the console unit between the two front seats, not sure if this method applies.  Here is a photo of the kind of mount:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/KsEJy.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KsEJy.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Indeed, that is an Icom 706 in the image which is the HF radio I ended up getting because of the removable head piece (like shown).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My VHF/UHF rig is the Yaesu FT-7800R (no longer available new) and it would share the same space but no mounted, it just laid around some place convenient (such as the storage box between the seats) since I never had to look at it and could use the mic buttons to switch memory cells of favored frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I liked about my solution is that absolutely no holes in plastic parts (see below, some holes drilled) and nothing permanent placed anywhere up front -- not even sticky tape.  Only one cord for each radio followed under the carpet to the rear seat of my pickup truck (crew cab so extra space) and the main base unit of each radio sat under the seat with access to antennas and power -- nothing visible or in the way of any other activity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The photo below shows under the rear seat of the crew cab extension on my Chevy Silverado (2004) pickup truck.  This particular photo only shows the base unit for the Icom 706 but the Yaesu is about the same size and sits right next to it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1tx66.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1tx66.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the photo you can see my power distribution boxes from cables that run from the battery in the front of the truck, through the firewall (an opening already existed there) and then under and along side the main frame of the truck and then up through the floor to the distribution boxes which support fuses.  Since this photo was taken (about 7 years ago) I have installed a fused West Mountain Radio Anderson Power Pole distribution box making it more convenient to add and remove equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, there to the lower right of the distribution box is a UHF extender about 2 inches long that goes through the floor of the cab and provides for PL-259 adapter hookup under and in the truck for the main HF antenna coax.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-01-02T01:17:53.667" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5643" PostTypeId="2" ParentId="5457" CreationDate="2016-01-02T05:43:58.140" Score="0" Body="&lt;p&gt;The Sony ICF-SW7600GR does not support SSB. You need to use a radio such as the Tecsun PL880 which has the option to listen to SSB signals also. Using this radio you could listen to AM stations. As Kevin explained, buy/build a better antenna also.&lt;/p&gt;&#xA;" OwnerUserId="5900" LastEditorUserId="76" LastEditDate="2016-01-02T22:39:25.310" LastActivityDate="2016-01-02T22:39:25.310" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5646" PostTypeId="1" CreationDate="2016-01-02T13:52:12.443" Score="3" ViewCount="1640" Body="&lt;p&gt;On page 2-9 of the ARRL Ham Radio License Manual, it discusses how in SSB one of the side bands and the carrier are suppressed to conserve power and bandwidth. Given the explanation of how AM works, however, it seems like a receiver would need the carrier in order to determine the various frequencies in the SSB; it would need the offset distance from the carrier to understand what frequency the rightmost or leftmost sidebands represent. Are SSB receivers just guessing, looking for the cluster of sidebands and assuming the leftmost is some low phone frequency?&lt;/p&gt;&#xA;" OwnerUserId="5540" LastEditorUserId="29" LastEditDate="2016-01-06T19:14:14.977" LastActivityDate="2016-01-06T19:14:14.977" Title="In SSB how do receivers calculate the frequency offset without a carrier?" Tags="&lt;receiver&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5647" PostTypeId="2" ParentId="5646" CreationDate="2016-01-02T15:29:27.657" Score="7" Body="&lt;p&gt;No, the receiver does not try to determine a carrier frequency, &lt;em&gt;you&lt;/em&gt; do. When receiving SSB, you must adjust the VFO (main frequency control), not just until you hear a signal, but also to adjust to match the suppressed carrier frequency by ear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Slightly-off SSB signals have a distinct sound, which is not just being too low or high in pitch, because the human voice contains harmonics. For some fundamental audio frequency $f$ you have $f, 2f, 3f, …$ in some proportions, but if the VFO is offset by some amount $\delta$, the demodulated audio will have $f + \delta, 2f + \delta, 3f + \delta, …$ which do not make up the same wave shape and therefore sound funny.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In principle a receiver could attempt to automatically tune in the way you describe, but this would only work at high signal-to-noise ratios (strong signals). Doing it manually takes advantage of your human skill at recognizing human speech.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll quickly understand this for yourself once you have a receiver in your hands — and learn why people care about the feel of the VFO knob.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-01-02T15:29:27.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5649" PostTypeId="2" ParentId="5605" CreationDate="2016-01-03T03:33:51.960" Score="-1" Body="&lt;p&gt;The inner conductor is shielded by the outer. I you want to use coax as an antenna, then it's easier to use the outer conductor. Given a ground plane the outer conductor of coax measured to 1/4 wavelength of the frequency can make a good transmitting antenna.&lt;/p&gt;&#xA;" OwnerUserId="5906" LastActivityDate="2016-01-03T03:33:51.960" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5652" PostTypeId="1" AcceptedAnswerId="5663" CreationDate="2016-01-04T03:29:08.873" Score="4" ViewCount="932" Body="&lt;p&gt;So I found these rules:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(2)&#xA;  No&#xA;  amateur&#xA;  station&#xA;  shall&#xA;  transmit&#xA;  from&#xA;  those&#xA;  portions&#xA;  of&#xA;  Texas&#xA;  and&#xA;  New&#xA;  Mexico&#xA;  that&#xA;  are&#xA;  bounded&#xA;  by&#xA;  latitudes&#xA;  31°41&#xA;  ′&#xA;  and&#xA;  34°30&#xA;  ′&#xA;  North&#xA;  and&#xA;  longitudes&#xA;  104°11&#xA;  ′&#xA;  and&#xA;  107°30&#xA;  ′&#xA;  West;&#xA;  or&#xA;  from&#xA;  outside&#xA;  of&#xA;  the&#xA;  United&#xA;  States&#xA;  and&#xA;  its&#xA;  Region&#xA;  2&#xA;  insular&#xA;  areas.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(3)&#xA;  No&#xA;  amateur&#xA;  station&#xA;  shall&#xA;  transmit&#xA;  from&#xA;  those&#xA;  portions&#xA;  of&#xA;  Colorado&#xA;  and&#xA;  Wyoming&#xA;  that&#xA;  are&#xA;  bounded&#xA;  by&#xA;  latitudes&#xA;  39° and&#xA;  42° North&#xA;  and&#xA;  longitudes&#xA;  103°&#xA;  and&#xA;  108° West&#xA;  in&#xA;  the&#xA;  following&#xA;  segments:&#xA;  902.4–902.6&#xA;  MHz,&#xA;  904.3–904.7&#xA;  MHz,&#xA;  925.3–925.7&#xA;  MHz,&#xA;  and&#xA;  927.3–927.7&#xA;  MHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;But I can't find exactly what the government needs 30MHz of bandwidth for, especially in the middle of New Mexico.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the reason for this restriction?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="29" LastEditDate="2016-01-05T15:26:43.940" LastActivityDate="2016-02-04T19:43:51.637" Title="Why is 900MHz restricted in some areas in the US?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;33cm-band&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5654" PostTypeId="2" ParentId="5605" CreationDate="2016-01-04T14:03:14.817" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;if the outer braid of a coax is not grounded, does it still shield the inner conductor?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Can I use the inside conductor of coax to radiate RF energy?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You can, but you might as well use the shield.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;what happens if I short the inner and outer conductors and then feed that as an antenna?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Basically the same thing. The currents end up on the shield.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The purpose of the shield, in ordinary operation, is to assure that there are no electromagnetic fields outside the cable. All the energy being transferred in coax, in ordinary operation, exists in an electromagnetic field exclusively between the center conductor and the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This works because usually the shield is grounded. If you wanted to launch a voltage step down a coax transmission line, you'd connect a voltage source to the shield and the center conductor:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/9UfKi.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f9UfKi.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the instant the button (SW1) is pressed, the voltage source (V1) will pump electric charge into the center conductor and out of the shield. It will pump however much charge is necessary to maintain a difference in electric potential of 1V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the voltage source &lt;a href=&quot;https://en.wikipedia.org/wiki/Charge_conservation&quot; rel=&quot;nofollow noreferrer&quot;&gt;can neither create nor destroy electric charge&lt;/a&gt;, the charge removed from the shield must exactly equal the charge put into the center conductor. &lt;em&gt;Current&lt;/em&gt; is amount of charge moved per second, so this means the center conductor and shield have &lt;em&gt;equal but opposite currents&lt;/em&gt;. The shield current, and the center conductor current each have an associated magnetic field. But because they are equal but opposite, for any position outside the cable, they cancel. (The same is true for the electric field).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wanted to connect the voltage source to just the center conductor, you are left with the question of where the other end of the voltage source connects. Probably you will use Earth. So you end up with this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/UaShj.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fUaShj.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the instant you press the switch, V1 begins pumping charge out of Earth, and into the center conductor. The current on the center conductor is now positive and increasing. That current is accompanied with a concentric magnetic field which is growing, and that growing concentric magnetic field will reach the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When it does, &lt;a href=&quot;https://en.wikipedia.org/wiki/Eddy_current&quot; rel=&quot;nofollow noreferrer&quot;&gt;eddy currents&lt;/a&gt; will be induced in the shield. These eddy currents will cancel the current in the center conductor and reinforce the current on the shield, especially on the outer surface of the shield. This is known as &lt;a href=&quot;https://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin effect&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This only happens at the instant the switch is pressed. Eventually V1 moves enough charge to make its 1V difference and reaches a steady state. There are still currents and magnetic fields, but they aren't changing. Without a changing magnetic field, there are no eddy currents, so there's no skin effect so the current can flow on the center conductor. So, skin effect is relevant only for AC or RF currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for radio applications, the current ends up on the shield anyway, and you end up making a field between Earth and the &quot;shield&quot;, which isn't really shielding anything. Maybe if you want to use the feedline as an antenna this is good for you.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;That's the theoretical explanation. There are also some practical concerns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This feedline probably connects to some television receiver's enclosure, which is probably in turn connected to the safety ground on the electrical cord, which is in turn connected to a grounding rod at your electrical meter. So you will end up with this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/SoBzS.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fSoBzS.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can still make an antenna out of this: it's called a &lt;a href=&quot;http://www.vias.org/radioanteng/radio_antenna_engineering_02_03_04.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;shunt fed antenna&lt;/a&gt;. But it's not how your typical long-wire antenna is set up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, your home's wiring is directly connected to just about every noise source in your home. You may find that it does not make a very quiet antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-01-04T20:39:58.367" LastActivityDate="2016-01-04T20:39:58.367" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5655" PostTypeId="1" AcceptedAnswerId="5656" CreationDate="2016-01-04T19:10:43.600" Score="3" ViewCount="1335" Body="&lt;p&gt;Devices I need to hook up to roof-mounted antennas in my truck.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Scanner - 25Mhz-800Mhz (mostly listen to FD/EMS on 2m and 70cm)&lt;/p&gt;&#xA;&lt;p&gt;Handheld HAM (possibly upgrading to mobile unit) - 2m/70cm&lt;/p&gt;&#xA;&lt;p&gt;CB Radio - 27Mhz&lt;/p&gt;&#xA;&lt;p&gt;stock FM radio - 88Mhz-108Mhz&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I know at least the CB needs to be fairly long but I'd like to shorten the overall height of my vehicle (2014 Nissan Xterra) so I don't keep knocking into stuff.&lt;/p&gt;&#xA;" OwnerUserId="5023" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-01-06T04:10:25.797" Title="What is the minimum length antenna I can use with my vehicle setup?" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;citizens-band&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5656" PostTypeId="2" ParentId="5655" CreationDate="2016-01-04T21:14:04.790" Score="3" Body="&lt;p&gt;There is no minimum length; all else being equal, a shorter antenna (with the proper loading/matching) is just less efficient. Antenna efficiency is not a critical issue if the antenna is not being used for transmitting (and you do not have strong noise sources inside your vehicle). Therefore, you primarily need to concern yourself with transmitting antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your CB antenna is likely to remain the tallest no matter what you do. I would recommend investigating shortened CB antennas first, and worrying about the others only if you succeed in making it shorter than them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will have to make your own tradeoff between length and performance.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-01-04T21:14:04.790" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5659" PostTypeId="1" AcceptedAnswerId="5660" CreationDate="2016-01-05T12:41:50.323" Score="2" ViewCount="876" Body="&lt;p&gt;I was thinking of getting a retractable antenna for my Baofeng UV-82 8W HT. I found a &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00SCI0BRO&quot; rel=&quot;nofollow&quot;&gt;Nagoya NA771R&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What are the dos and don'ts for using such a retractable antenna with a HT? &lt;/li&gt;&#xA;&lt;li&gt;Should it always be fully extended while Rx and Tx?&lt;/li&gt;&#xA;&lt;li&gt;Will it offer additional benefit over the default rubber ducky?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I have had '59' rated QSOs on VHF bands using the rubber ducky with stations about 20-30kms away w/o repeaters. &lt;/p&gt;&#xA;" OwnerUserId="1723" LastEditorUserId="29" LastEditDate="2016-01-05T15:43:21.170" LastActivityDate="2016-01-06T01:48:04.707" Title="What are the dos and don'ts when it comes to retractable antennae for HTs?" Tags="&lt;antenna&gt;&lt;ht&gt;&lt;collapsible-antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5660" PostTypeId="2" ParentId="5659" CreationDate="2016-01-05T15:24:58.577" Score="3" Body="&lt;p&gt;The biggest &lt;strong&gt;do&lt;/strong&gt; is to &lt;strong&gt;follow the manufacturer's instructions.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't immediately locate any sort of instruction sheet for this particular antenna, but given that using it is &lt;em&gt;slightly&lt;/em&gt; more involved than just connecting it to your radio's antenna connector, something like that should be included with it. (You could also just contact your local Nagoya reseller and ask.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With collapsible antennas, you need to take care to not break it; the joints between sections present a breakage risk that is not present in antennas that have a fixed physical length. Fixed length antennas can be made as basically a flexible piece of wire; retractable antennas need to be much more rigid to support their own weight, particularly in odd orientations which are common with HT operating. &lt;strong&gt;In many cases&lt;/strong&gt; this can make a full-length, fixed-length flexible antenna a better choice than a collapsible, rigid antenna because the former is better able to handle the moderate abuse portable antennas often are put through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&quot;More antenna&quot; (fully extended) is rarely a problem &lt;em&gt;when receiving&lt;/em&gt;. The sweet spot for feedpoint impedance is an odd number of quarter wave lengths (1/4, 3/4, 5/4, ...) assuming a reasonable ground plane; the physical length that this corresponds to depends on the specific construction of the antenna.&lt;/li&gt;&#xA;&lt;li&gt;&quot;Less antenna&quot; (collapsed) &lt;em&gt;should not&lt;/em&gt; be a significant problem &lt;em&gt;when receiving&lt;/em&gt;. At worst, the received signal strength will be reduced vis-a-vis a larger antenna.&lt;/li&gt;&#xA;&lt;li&gt;Antenna length is much more critical &lt;em&gt;when transmitting&lt;/em&gt; because the impedance matching becomes more important.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It doesn't really matter very much if the antenna/radio impedance mismatch causes 99% of the signal received by the antenna to be reflected back into the antenna rather than being transferred to the radio (your received signal strength would be 20 dB down, which isn't great but probably not that much worse than most rubber duck antennas), but it matters a whole lot if 99% of the signal transmitted by the radio is reflected back into the radio (that's 4.95 W out of 5 W, going in a direction it doesn't belong)!&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Shortened antennas are always a compromise. 1/4 wavelength with a good ground plane is almost always the best you can strive for mounted on a HT. However, if a shortened antenna gives good enough results for you (as in, you are able to hear everyone you want to hear, and can raise everyone you need to and/or hear), then you won't magically be getting &lt;em&gt;more use&lt;/em&gt; out of your radio when getting a better antenna. In really extreme situations, it could raise your noise floor, making picking out stations &lt;em&gt;more&lt;/em&gt; difficult.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A more efficient antenna may allow you to operate using a lower power output setting (as in, you might be able to work the same stations with good results on 500 mW as with 5 W into the rubber duck antenna), which will help conserve some battery power. However, due to the transmission duty cycle commonly being very low in amateur radio, this isn't going to make a very big difference; I would expect a few percent longer operating time out of being able to reduce transmitter power by 10 dB, at best. In other words, this should not be your deciding factor.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2016-01-05T15:38:49.640" LastActivityDate="2016-01-05T15:38:49.640" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5661" PostTypeId="5" CreationDate="2016-01-05T15:44:24.300" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2016-01-05T15:44:24.300" LastActivityDate="2016-01-05T15:44:24.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5662" PostTypeId="4" CreationDate="2016-01-05T15:44:24.300" Score="0" Body="For questions about antennas that are designed to have their length physically changed in response to changing operating needs." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2016-01-05T20:21:59.397" LastActivityDate="2016-01-05T20:21:59.397" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5663" PostTypeId="2" ParentId="5652" CreationDate="2016-01-05T19:17:15.580" Score="1" Body="&lt;p&gt;The New Mexico restriction covers the &lt;a href=&quot;http://www.wsmr.army.mil&quot; rel=&quot;nofollow&quot;&gt;White Sands Missile Range&lt;/a&gt;.  Colorado and Wyoming also have military installations.  Some 900 MHz frequencies are allowed for amateurs there.  More comments at &lt;a href=&quot;http://www.qsl.net/kb9mwr/projects/900mhz/900users.html&quot; rel=&quot;nofollow&quot;&gt;http://www.qsl.net/kb9mwr/projects/900mhz/900users.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2016-01-05T19:17:15.580" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5665" PostTypeId="2" ParentId="5655" CreationDate="2016-01-06T04:10:25.797" Score="3" Body="&lt;p&gt;To augment my comments above as an answer including photos.  I repeat my comments here:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why would you knock into stuff with a CB antenna? I have an HF, 80-10 meter, screwdriver antenna on my pickup truck. The overall size of the antenna is about the same as an 11-meter CB antenna. The top of that antenna is 11 feet 4 inches from the ground. In the 10 years I have had that antenna on the truck, I have never &quot;knocked&quot; into stuff.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;And,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I live in a neighborhood with lots of trees on the streets and arterials and never once have I hit a tree. I never go to fast food drive-throughs. And, if there is ever a time I need to park in a parking garage I stop and remove my antenna and put it in the back seat -- an operation that takes just about 30 seconds as I have a quick release base mount. Antenna is Hi-Q 80/4 with their quick release base, see hiqantennas.com and go to Accessories and see GCD (giant quick disconnect).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The first photo shows the Hi-Q antenna, center loaded, with the top whip antenna topping out at 11 feet 4 inches from ground.  You can just barely see the whip part of the antenna on top of the center loading coil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/m6RHx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/m6RHx.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second photo shows the quick release base mount and my custom made mounting for shunt coil (which is hidden behind black PVC box).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/55wd5.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/55wd5.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, the third photo shows the shunt coil.  But, this is not my actual shunt coil I use.  This was one of the first experimental coils I built to finally arrive at the perfect match.  I adjusted diameter and number of turns on each coil to achieve the matching characteristics needed for 80 and 40 meter bands.  Thus coil is nothing but a high-impedance (like open circuit) for higher frequency bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/axiJV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/axiJV.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fourth photo shows the VHF/UHF antenna side mounted on the door with a small pass-thru coax cable that passes through the door and the frame cushioned by weatherproof strip.  Overall height is about 9 feet from ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Vx8nJ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Vx8nJ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-01-06T04:10:25.797" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5667" PostTypeId="2" ParentId="5646" CreationDate="2016-01-06T19:08:15.463" Score="0" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/5647/29&quot;&gt;Like Kevin already wrote&lt;/a&gt;, the receiver doesn't &quot;auto-tune&quot; in SSB. In fact, I think the only modes in which there is an appreciable amount of &quot;auto-tuning&quot; or allowance for being significantly off frequency is modes where the absolute transmission frequency offset does not carry any important information; in other words, frequency and phase modulated modes. In amplitude modulation modes, both the absolute offset and the amplitude carries information, and what business does the receiver have deciding what I am listening to?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said; look at a diagram of a SSB (or CW; for our purposes here, they are the same) receiver. (I'm not familiar with the ARRL material, but I would be very surprised if it doesn't have some.) You will see that the VFO setting (either directly or through some other stage, sometimes separately handled) affects the &lt;em&gt;beat&lt;/em&gt; frequency oscillator or BFO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Very basically, &lt;strong&gt;the purpose of the BFO is to &quot;re-inject&quot; the carrier that was suppressed in the transmitter.&lt;/strong&gt; This then allows for easy demodulation of the RF (at this point often IF) signal. If this re-injected carrier is at the wrong frequency relative to the station you want to listen to, then the audio will become distorted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In CW, modern receivers usually offers some means of controlling the (receiver) BFO separate from the (transmitter) tuning VFO. This allows you to change the pitch of the CW signal -- not everyone likes their CW at 700 Hz sharp. This can be termed &quot;beat offset&quot;, &quot;CW pitch&quot; or something similar, but what it really does is affect the frequency difference (offset) between the indicated VFO frequency and the internal BFO frequency. In the good old days of separate transmitters and receivers, it depended on whether the two shared a VFO; if they had separate VFOs, you just tuned them slightly differently and hoped for the best; if they shared a VFO, you basically had a transceiver occupying multiple boxes in your shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;In practice, this means&lt;/strong&gt; that for a SSB signal to sound right, your receiver's BFO frequency needs to be very close to the (suppressed) carrier frequency of the transmitter. (This is most often achieved by simply setting your VFO such that the frequency readout is the same as that on the transmitter, assuming both are frequency-accurate; in real life, you tune until the audio sounds right.) If your BFO is off by more than a few tens of hertz at most compared to the suppressed carrier, then the signal will start to sound funny or even garbled; the audio will start to sound somewhat like Donald Duck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sharp filters can make this effect even more pronounced, when a part of the intended signal falls outside the main passband of the receiver's filter (which is often approximately 300-2700 Hz at -6 dB in SSB).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning a SSB signal accurately will quickly become second nature once you start listening, and absent split/IF shift/beat offset/etc. you will only need to worry about tuning the VFO until the signal sounds right and then you will be right on the other station's transmission frequency. &lt;em&gt;The exact frequency readout at that point is basically unimportant.&lt;/em&gt; (Obviously, as long as you stay within the limits of your transmission license and ultimately ensure that your entire transmitted signal fits within the band limits.)&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-01-06T19:08:15.463" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5668" PostTypeId="2" ParentId="5633" CreationDate="2016-01-06T19:34:17.087" Score="3" Body="&lt;p&gt;Since you say that both radios have the exact same problem, I think we can more or less rule out an outright problem with the radio itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you say that you used to be able to hit this repeater easily, I think we can rule out that you would be too far away from the repeater for the antenna that you are using.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It also seems unlikely that both radios would have had their settings spontaneously changed compared to the previous values. You also specifically state that you have checked the tone and shift.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That does however leave one very real possibility, especially since I don't see you stating anything that answers the question: &lt;strong&gt;is the repeater itself operational?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best course of action at this point might be to contact the people who operate the repeater, or visit the appropriate web site, and check to make sure that the repeater itself is QRV, that they haven't changed the CTCSS tone, that it's still operating on the same frequency pair, or any other major changes since you last were able to use it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Repeaters sometimes do go off the air, either temporarily (due to maintenance or unplanned outages) or permanently (because of everything from lost interest to dissolution of the club operating it to abuse). Frequency or CTCSS changes are sometimes necessary to deal with interference problems.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2016-01-07T10:20:49.423" LastActivityDate="2016-01-07T10:20:49.423" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5669" PostTypeId="2" ParentId="5384" CreationDate="2016-01-06T20:21:15.127" Score="2" Body="&lt;p&gt;It's true the only thing to worry about with just one carrier is harmonics as you and Kevin suggest.  However, when one modulates the carrier we generate a variety of frequencies near the carrier that can play off each other as many little carriers.  The classic check to see how well our radio transmitters keep IMD at bay is the two-tone test.  In theory this two tone test applies to our antenna system as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The likely reason we don't hear more about single-system PIM is those who worry about PIM are generally concerned with PIM generation at sites with many radio services all with strong signals.  Two strong signals into a non-linear junction is no joke and can throw a mix-product signal on top of another radio service.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastActivityDate="2016-01-06T20:21:15.127" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5670" PostTypeId="1" CreationDate="2016-01-05T22:42:58.563" Score="0" ViewCount="220" Body="&lt;p&gt;I have the &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-564B&quot; rel=&quot;nofollow&quot;&gt;MFJ-564B&lt;/a&gt; iambic paddle which I need to wire to the &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-552&quot; rel=&quot;nofollow&quot;&gt;MFJ-552&lt;/a&gt; CW interface. The paddle is stereo (dits/dahs) and the interface is mono (when connected to paddle, only gives DITS). How can I make a connector for it without rewiring my paddle? The paddle works perfectly with my other radios.&lt;/p&gt;&#xA;" OwnerDisplayName="Mic Sherwood" LastEditorUserId="76" LastEditDate="2016-01-07T01:31:28.530" LastActivityDate="2016-02-06T01:54:52.773" Title="CW paddle interface wiring problem" Tags="&lt;diy&gt;&lt;cw&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5671" PostTypeId="2" ParentId="5670" CreationDate="2016-01-05T23:52:48.360" Score="1" Body="&lt;p&gt;As I read the MFJ-522 manual, it appears that you will need a keyer between your paddle and the 522.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your paddle is essentially two switches, and a keyer is an electronic box (MFJ-401D, for example) that makes dots when you close one switch, and dashes when you close the other. The output of the keyer is a single switch contact that could be used to replace a manual key. If your other radios can use the paddle directly, they must have built-in keyers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(This is a very strange use of mono/stereo terminology.)&lt;/p&gt;&#xA;" OwnerDisplayName="Peter Bennett" LastEditorUserId="76" LastEditDate="2016-01-06T21:58:08.083" LastActivityDate="2016-01-06T21:58:08.083" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5672" PostTypeId="1" AcceptedAnswerId="6829" CreationDate="2016-01-07T19:58:56.413" Score="5" ViewCount="3426" Body="&lt;p&gt;I have a Baofeng BL-5L battery for my Baofeng UV-5R transceiver, and I notice that it has a socket on the side:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/8tMjY.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8tMjY.png&quot; alt=&quot;as in the image&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please, what is this socket for?&lt;/p&gt;&#xA;" OwnerUserId="297" LastActivityDate="2019-10-05T07:50:05.880" Title="What is the socket for on this Baofeng BL-5L battery?" Tags="&lt;baofeng&gt;&lt;battery&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5673" PostTypeId="1" CreationDate="2016-01-08T01:16:41.640" Score="2" ViewCount="915" Body="&lt;p&gt;Where can I find the definition of the Q Codes for amateur radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far I could only find &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;ITU-R M.1172&lt;br&gt;&#xA;  ANNEX 1&lt;br&gt;&#xA;  Miscellaneous abbreviations and signals to be used&#xA;  for radiocommunications in the maritime mobile service&lt;br&gt;&#xA;  Section I. Q Code&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;But this is about Q codes for maritime telegraphy and most of these make no sense for amateur radio. I have also found definitions of Q/Z Codes for aviation and military usage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has there ever been an official definition of Q Codes for amateur radio and if so, where can I find it?&lt;/p&gt;&#xA;" OwnerUserId="3010" LastEditorUserId="76" LastEditDate="2016-01-08T02:01:29.473" LastActivityDate="2016-08-27T03:44:21.770" Title="Where can I find the definition of the Q Codes as they should be used in amateur radio (CW)?" Tags="&lt;cw&gt;&lt;q-codes&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5674" PostTypeId="2" ParentId="5673" CreationDate="2016-01-08T05:28:32.590" Score="2" Body="&lt;p&gt;There is basically three (somewhat overlapping) lists of Q-codes used in Ham Radio.  The three lists are those used by voice operators (SSB), those used by CW operators, and those used in CW traffic handling nets (QN codes).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A full single &quot;official&quot; list of Q-codes is not useful to the ham radio operator.  What is useful is to know those that are commonly used.  The use of Q-codes is most dominant among CW operators because CW begs the use of abbreviations to limit keying.  Use of Q-codes among voice operators, mostly SSB is also common but the usage is typically more limited to just a handful such as: QSL, QSO, QSB, QRM, QRN, QTH, QSY, QRZ, QRL, QRU, and maybe a few others I am missing.  But, many times a voice operator will merely say something equivalent to the Q-code meaning.  For example, he/she might say &quot;I am being interfered with&quot; instead of &quot;there is QRM&quot; or &quot;there seems to be a slow fade on your signal&quot; rather than saying &quot;some QSB on your signal&quot;. Note that I am listing these as I think of them and obviously the same set is not the common usage of all operators.  But, you can expect to hear these at times among SSB operators.  [By the way, many SSB voice operators would say &quot;QR-Mary instead of QRM or QR-Nancy instead of QRN (atmospherics noise or other non-operator RFI)].&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With CW operators, you can add to the list signals (above) such as QRT, QRV, QSP, QRS (and, less frequently QRQ), QST (by scheduled nets usually).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, within a CW traffic net, the QN signals are common such as: QNI, QNX, QNZ, QNA, QNZ, QND, and a few others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When asking a question via a Q-code in CW it is common practice to include a ?-mark following the Q-code.  For example, a CW operator will check to see if his frequency is clear by sending QRL? meaning &quot;is the frequency busy?&quot;.  An answer of the letter C from someone if the answer is yes, it is busy.  The letter C is a common CW abbreviation meaning Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, in the above lists I did not define these Q-codes because they are very easy to look up.  The ARRL has lists published on their web site plus these Q codes and many more are published on many web sites.  Just Google &quot;Q signals ham radio&quot; or some variation of that and you will find them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also above, I did not list every Q-code known to amateur radio.  Some are never heard.  I am almost 100 percent CW activity and I spend a lot of time on CW traffic nets and I use maybe a dozen total Q codes from the regular Q code lists and the QN codes.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2016-01-08T17:37:19.150" LastActivityDate="2016-01-08T17:37:19.150" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="5676" PostTypeId="1" CreationDate="2016-01-08T10:07:47.663" Score="1" ViewCount="2081" Body="&lt;p&gt;I am having problem charging my Baofeng UV-82HX HT. No sooner do I put up the HT on the charger, it starts showing the error lights - green stable, red flickering. &#xA;I bought this off the shelf in Nov 2015, and have had good QSOs with it, but it has been having this problem since some time now. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=Z2gKXZyhLZU&quot; rel=&quot;nofollow&quot;&gt;https://www.youtube.com/watch?v=Z2gKXZyhLZU&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Right now this is happening every time I charge. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ideas what could be going wrong, or something I can do?&lt;/p&gt;&#xA;" OwnerUserId="1723" LastEditorUserId="76" LastEditDate="2016-01-08T15:48:07.923" LastActivityDate="2017-07-25T22:49:40.513" Title="Baofeng UV82-HX charger problem" Tags="&lt;ht&gt;&lt;baofeng&gt;&lt;battery&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5677" PostTypeId="2" ParentId="5439" CreationDate="2016-01-08T15:22:30.300" Score="2" Body="&lt;p&gt;There are a couple of ways to approximately determine the antenna Q-factor (which is related to the bandwidth) without a full 3D simulation.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;One is to use &lt;a href=&quot;http://www.mathworks.com/matlabcentral/fileexchange/26806-antennaq/content/AntennaQ.m&quot; rel=&quot;nofollow&quot;&gt;this MATLAB script&lt;/a&gt;, which determines the antenna's theoretical bounds from its polarizability. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Another approximation of the Q-factor which is from the 40's is to use the Chu limit&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Q_{\text{Chu}} = \frac{1}{(ka)^3} + \frac{1}{ka}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $k = 2\pi / \lambda$ and $a$ is the radius of the sphere enclosing the antenna.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It is important to note that the first method will give a much better result as it can find the Q-factor for spheroidal shells as well as spherical shells (Chu).&lt;/p&gt;&#xA;" OwnerUserId="5941" LastEditorUserId="76" LastEditDate="2016-01-08T15:47:25.157" LastActivityDate="2016-01-08T15:47:25.157" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5678" PostTypeId="2" ParentId="5672" CreationDate="2016-01-08T17:35:49.703" Score="3" Body="&lt;p&gt;Check point no 6.7 on this page - &lt;a href=&quot;http://www.miklor.com/uv5r/UV5R-FAQ.php#Batteries&quot; rel=&quot;nofollow&quot;&gt;http://www.miklor.com/uv5r/UV5R-FAQ.php#Batteries&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It talks about an extended battery like you have shown here. Also says that it uses a side jack. The port you see here is probably for the side jack.&lt;/p&gt;&#xA;" OwnerUserId="1723" LastActivityDate="2016-01-08T17:35:49.703" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5679" PostTypeId="1" CreationDate="2016-01-08T17:41:15.473" Score="0" ViewCount="144" Body="&lt;p&gt;we are trying to track &quot;DTUsat-2&quot; which transmit at 2.402 GHz using automatic frequency adjustment to compensate for Doppler shift. Our receiver ( a professional one) have the ability to set frequency using PC interface. Is there a software that can write the Doppler shift or frequency into a file that can be read and send to receiver for correction. Or should we write our own software?&#xA;Help is appreciated&lt;/p&gt;&#xA;" OwnerUserId="5943" LastEditorUserId="76" LastEditDate="2016-10-29T19:16:57.263" LastActivityDate="2017-06-24T02:45:15.847" Title="Is there a satellite tracking software with S-band downlink" Tags="&lt;uhf&gt;&lt;software&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5681" PostTypeId="1" AcceptedAnswerId="5682" CreationDate="2016-01-09T10:48:59.233" Score="6" ViewCount="754" Body="&lt;p&gt;I'm pretty new with antenna stuff. I'm not sure how to understand antenna length in relation to lambda with dipole antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a simple dipole antenna is lambda/4, has it a total length of lambda/2 (every pole lambda/4 long) or a total length of lambda/4?&lt;/p&gt;&#xA;" OwnerUserId="5630" LastEditorUserId="76" LastEditDate="2016-01-11T00:03:01.410" LastActivityDate="2016-01-18T17:45:40.157" Title="Antenna length in relation to lambda length" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;jargon&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5682" PostTypeId="2" ParentId="5681" CreationDate="2016-01-09T16:25:01.487" Score="6" Body="&lt;p&gt;Terminology can be ambiguous here; there is no universal standard for how to describe antennas. That said, here are some heuristics:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If someone says, e.g., “a 20-meter dipole”, they mean an antenna which is &lt;em&gt;for the 20-meter band&lt;/em&gt;, i.e. almost 10 meters long from end to end (because a full-size dipole has an electrical length of λ/2).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If someone says the &lt;em&gt;length&lt;/em&gt; of a dipole antenna is some particular value, then they mean the length from one end to the other — the physical space taken up by the antenna — which will be λ/2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the US, if they specify a length in &lt;em&gt;feet&lt;/em&gt;, then they're almost certainly referring to the physical length. I don't know if there are any clues like this in other countries.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;As far as I know, no one ever uses the λ/4 value in discussing dipole antennas, unless they're giving instructions for cutting the wires to the proper length.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-01-09T16:25:01.487" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5683" PostTypeId="1" AcceptedAnswerId="5684" CreationDate="2016-01-10T03:09:30.153" Score="1" ViewCount="1092" Body="&lt;p&gt;Is it possible to set the frequency on a Kenwood TM-D710G via either the PC or COM ports over a Serial connection?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TNC manual does not mention an option to set the frequency, and the PC port seems generally undocumented.  Ideally, I'd like to set this over Linux, but I'm willing to sniff a serial connection on a Windows PC if it's possible from Windows software.&lt;/p&gt;&#xA;" OwnerUserId="5738" LastActivityDate="2018-04-12T16:37:16.580" Title="Is it possible to set the frequency on my Kenwood TM-D710G via Serial Port?" Tags="&lt;kenwood&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5684" PostTypeId="2" ParentId="5683" CreationDate="2016-01-10T05:05:03.237" Score="1" Body="&lt;p&gt;&lt;a href=&quot;http://www.n8gnj.org/2014/02/my-kenwood-tm-d710g-is-finally-usable.html&quot; rel=&quot;nofollow&quot;&gt;This fellow&lt;/a&gt; mentions that he planned to do this:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Install serial cable from TM-D710G in basement to office for a future project - computer control over radio frequency, etc.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;But he may never have been successful. I do not see the TM-D710G listed in any of the &lt;a href=&quot;http://wiki.radioreference.com/index.php/Amateur_Radio_Transceiver_Control&quot; rel=&quot;nofollow&quot;&gt;transceiver control&lt;/a&gt; software lists:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.dxlabsuite.com/commander/&quot; rel=&quot;nofollow&quot;&gt;Commander&lt;/a&gt; doesn't list&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://ham-radio-deluxe.com/supported_radios.html&quot; rel=&quot;nofollow&quot;&gt;Ham Radio Deluxe&lt;/a&gt; doesn't list&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.bonito.net/service/make_radio_list.php3?language=en&amp;amp;R1=LB#HAM&quot; rel=&quot;nofollow&quot;&gt;Bonito RadioCom&lt;/a&gt; doesn't list&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Looks like Kenwood do provide software for programming presets and such, &lt;a href=&quot;http://www.kenwood.com/i/products/info/amateur/mcp_2a.html&quot; rel=&quot;nofollow&quot;&gt;MCP-2A&lt;/a&gt;, while it is &lt;a href=&quot;http://chirp.danplanet.com/issues/1287&quot; rel=&quot;nofollow&quot;&gt;currently not supported&lt;/a&gt; by Chirp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.kenwood.com/i/products/info/amateur/pdf/TM-D710A_E_GA_GE_IDM.pdf&quot; rel=&quot;nofollow&quot;&gt;TM-D710G manual&lt;/a&gt; also lists several cool things you can do over various cables like APRS and EchoLink — between all this and the MCP-2A you'd think it should be possible, but perhaps not! Have you tried contacting their support?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-01-10T05:05:03.237" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5685" PostTypeId="1" CreationDate="2016-01-10T13:28:31.773" Score="1" ViewCount="710" Body="&lt;p&gt;Is there an app that sends random morse code that I can copy to paper, then shows me what was sent for me to check my work? Basically an app that works like the MFJ-418 Code Tutor. All the apps I find have me hunt and peck for keyboard letters as I copy. Doing that on my phone can be awkward and causes errors. I would rather practice copying code to paper as I would off the airwaves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Android app preferred does not need to be free &lt;/p&gt;&#xA;" OwnerUserId="5954" LastActivityDate="2016-01-31T23:04:46.047" Title="Looking for a CW Tutor app" Tags="&lt;cw&gt;" AnswerCount="6" CommentCount="2" ClosedDate="2016-02-01T02:29:24.947" ContentLicense="CC BY-SA 3.0" />
  <row Id="5686" PostTypeId="1" AcceptedAnswerId="5687" CreationDate="2016-01-10T14:31:42.207" Score="1" ViewCount="97" Body="&lt;p&gt;Here, in VU-land, 6M allocation is from 50 MHz through 54 MHz... which is a fair chunk of spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I think about a half-dipole antenna; between 50/54 MHz it's length varies by over a foot ... and I can't imagine an antenna with a 4MHz bandwidth. Is it possible to work on 6M with a simple dipole? What frequency should it be centred upon?&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="29" LastEditDate="2016-01-10T18:48:34.930" LastActivityDate="2016-01-10T18:48:34.930" Title="Antenna for 6M, or Antenna system?" Tags="&lt;antenna&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5687" PostTypeId="2" ParentId="5686" CreationDate="2016-01-10T18:48:18.630" Score="1" Body="&lt;p&gt;&lt;strong&gt;Yes, a dipole for 50 MHz is most definitely possible.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your 6 meter band is 52 ± 2 MHz. 2/52 is just over 0.038. This is the frequency &lt;em&gt;variance&lt;/em&gt; involved: how much, in terms of a center frequency, does the frequency vary the most while remaining within the band edges. You could make this worse by cutting the antenna for one band edge and using it at another, but it doesn't get that &lt;em&gt;much&lt;/em&gt; worse even then.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For comparison, assume 80 meters is 3.5 to 3.8 MHz. That's 3.65 ± 0.15 MHz, where 0.15/3.65 is just over 0.041. If you were to cut an antenna for 3.7 MHz (good for 80 meters SSB) and use it toward the lower end of the band, this effect becomes even more pronounced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In terms of frequency variance between the band edges, 80 meters is actually &lt;em&gt;worse&lt;/em&gt;, despite being far narrower in absolute terms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or consider 23 cm; where I'm at, the allocation there is 1240 through 1300 MHz -- that's a good 60 MHz wide swath of spectrum. (60 MHz isn't even an absurdly wide signal in the microwave range.) However, 30/1270 is less than 0.024, so in terms of frequency variance, this band is actually far &lt;em&gt;narrower&lt;/em&gt; than is 80 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna doesn't care about the absolute frequency of your transmission. Ignoring any nearby obstacles that could throw off the tuning, antenna matching depends entirely on the error in terms of wavelengths.&lt;/p&gt;&#xA;" OwnerUserId="29" LastActivityDate="2016-01-10T18:48:18.630" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5690" PostTypeId="2" ParentId="5681" CreationDate="2016-01-13T01:24:09.650" Score="3" Body="&lt;p&gt;Also, don't get confused if you see actual, physical antenna lengths shorter than theoretical wavelengths/lambdas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the dipole legs are made of real-world components in complex situations, &quot;velocity factor&quot; comes into play which will tweak the numbers slightly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many &lt;a href=&quot;http://www.westmountainradio.com/antenna_calculator.php&quot; rel=&quot;nofollow&quot;&gt;guides&lt;/a&gt; give you nice numbers to make the math easier, but almost always advise that these are starting lengths, almost always longer than needed, so you will trim the antenna to best resonance.&lt;/p&gt;&#xA;" OwnerUserId="5961" LastEditorUserId="76" LastEditDate="2016-01-18T17:45:40.157" LastActivityDate="2016-01-18T17:45:40.157" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5691" PostTypeId="2" ParentId="5490" CreationDate="2016-01-14T01:00:01.030" Score="0" Body="&lt;p&gt;I think the main consideration between a FUNcube Dongle and any sort of high-bandwidth SDR would be drivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;AFAICT all the FUNcube Dongle products present as a USB audio device, plus additional control (via HID most likely). So software written for them would expect to get input from a &quot;sound card&quot;. There are other SDRs similar to this that also present as [or through] audio devices, e.g. the Softrock and Peaberry transceivers. Their control protocols might be different, though, and therefore you still might run into compatibility trouble.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The USRP radios are high-samplerate SDR devices and I suspect have their own custom USB interface, rather than showing up as a soundcard and passing the I/Q samples as if they were &quot;stereo audio&quot;. Since there is no real standard yet for this [at least not on Windows or OS X to my knowledge, there's been at least &lt;a href=&quot;http://palosaari.fi/linux/kernel_sdr_api_requirement_specification.txt&quot; rel=&quot;nofollow&quot;&gt;a start&lt;/a&gt; for Linux], it usually requires specific support built into the app, or at least through a wrapper library like &lt;a href=&quot;http://sdr.osmocom.org/trac/wiki/GrOsmoSDR&quot; rel=&quot;nofollow&quot;&gt;gr-osmosdr&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So unless the software you are trying to use already offers support for Ettus devices, I would expect that you'd have to combine a number of pieces of software: some SDR software like GnuRadio/Gqrx or HD-SDR or SDR# or similar to talk to the dongle, plus a &quot;virtual audio cable&quot; type driver that will take output from the SDR and deliver it as input to the dongle software. But if the dongle software may still be unhappy if it does not have access to the frequency control protocol that would normally be provided by a real FUNcube Dongle.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-01-14T01:00:01.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5693" PostTypeId="2" ParentId="5685" CreationDate="2016-01-14T10:00:23.067" Score="0" Body="&lt;p&gt;You might want to try code practice sound files you can download from the ARRL in a variety of different speeds.  Each sound file comes with a plain-text transcription that you can compare to what you copied when you listened to the file.  The content is a paragraph or two of text, not random characters, but it might still work for you.  They create new practice files every week.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the link:  &lt;a href=&quot;http://www.arrl.org/code-practice-files&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/code-practice-files&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4677" LastActivityDate="2016-01-14T10:00:23.067" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5694" PostTypeId="2" ParentId="749" CreationDate="2016-01-14T14:37:46.110" Score="1" Body="&lt;p&gt;The best little book you can get yourself is &lt;em&gt;How to Make Walkie-Talkies,&lt;/em&gt; a Bernard Babani book by F. G. Rayer. It is simple and you can make everything yourself for 27 MHz and 28 MHz TX and RX, wind your own coils, etc., and using ordinary transistors build a few of the circuits great for experimenting with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also for more serious stuff, books are in French but circuits are good: a set of 4 or more books by Pierre Duranton on CB and ham radio, &lt;em&gt;Émetteurs - récepteurs, Walkies - talkies&lt;/em&gt;.  All make-it-yourself stuff including details of making chokes etc. Best books around. I collected them all over the years and made my first walkie talkies at the age of 11. 50 mW 27 MHz single channel 7 transistor AF115 OC71 types worked OK; short range but they got me into electronics and still going at 58. Enjoy.&lt;/p&gt;&#xA;" OwnerUserId="5984" LastEditorUserId="76" LastEditDate="2016-01-18T17:44:13.550" LastActivityDate="2016-01-18T17:44:13.550" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5695" PostTypeId="1" CreationDate="2016-01-14T16:29:33.240" Score="0" ViewCount="116" Body="&lt;p&gt;Unfortunately, the ISS SSTV transmissions scheduled to the next weekend had to be canceled. Anyway, I'm planning to capture some images and have a doubt. I've been trying to find some answers, but no success this far.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My doubt is: during the days of the transmissions (let's suppose, the next saturday and sunday), do the transmissions usually happen continuously, or they happen at specific times (For instance, at scheduled times or while the Station is passing over specific countries/regions)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Putting it in other words: may I expect that the Station will be transmitting during all the passes over my QTH, or I would have to be a little &quot;lucky&quot; to have the station transmiting something while passing over my location?&lt;/p&gt;&#xA;" OwnerUserId="5985" LastActivityDate="2016-01-26T14:23:46.513" Title="ISS SSTV transmission times" Tags="&lt;satellites&gt;&lt;sstv&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5696" PostTypeId="2" ParentId="5685" CreationDate="2016-01-14T16:39:31.820" Score="1" Body="&lt;p&gt;I've tryed some mobile apps and recorded CW, but I adapted myself better to the &quot;Koch's method&quot; (&lt;a href=&quot;http://www.justlearnmorsecode.com/koch.html&quot; rel=&quot;nofollow&quot;&gt;http://www.justlearnmorsecode.com/koch.html&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Just Learn Morse Code (&lt;a href=&quot;http://www.justlearnmorsecode.com/download.html&quot; rel=&quot;nofollow&quot;&gt;http://www.justlearnmorsecode.com/download.html&lt;/a&gt;) is one of the softwares that implement this method.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm still learning, but making pretty decent progress daily.&lt;/p&gt;&#xA;" OwnerUserId="5985" LastActivityDate="2016-01-14T16:39:31.820" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5697" PostTypeId="2" ParentId="5685" CreationDate="2016-01-14T17:46:37.647" Score="2" Body="&lt;p&gt;From my own experience about 60 years ago and from what other's have said to bolster this same experience, the best CW practice is to listen to on-air CW.  Of course, it is best to learn most of the alphabet by whatever means suits you.  But, as soon as you can start copying fragments of words or maybe just every other character or so, start listening to the actual ham radio CW QSOs that go on every single day and night.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL has practice sessions at different speeds per a schedule that is available on the ARRL web site: &lt;a href=&quot;http://www.arrl.org/w1aw-operating-schedule&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/w1aw-operating-schedule&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequencies used for these ARRL transmissions (from station W1AW) are at 14.0475 or 7.0475 (and others but these handle day and night).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, it is not important to get every single character and sometimes even words can be skipped or ignored.  When I am working a station and running above my comfort speed of about 20 wpm, say 30+ wpm, I miss a lot but not so much that I can't continue with a QSO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, you learn faster by pushing your speed.  If you are comfortable at 5 wpm, listen to someone at 10 to 15 wpm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The CW portion of the bands (low end of the band) are also grouped into the faster and slower areas.  Note that this is not an official grouping but just the typical practice of ham radio operators.  The slower CW operators seem to hang out around the 050+ KHz range (that is, 14.050, or 7.050, etc.) and the faster ones are lower.  But, not always.  You find the reverse too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Day time hours, the 20 and 30 meter bands are best.  At night though, 40 meters is the best and then 80 is good too but not as dense in CW activity as 40 (usually).  And, a lot of the CW traffic on 80 is scheduled CW message handling nets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No, this is not software for an Android but it is a better way to learn CW.  Learning live CW with the usual QRN and QSB (and, even QRM at times) is good for the ear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, I have mentioned various CW code speeds in this message but it is not important that you know the speed you are listening to.  I understand that there are some signals that are way too fast, and way too fast for me.  I can copy a call sign and some stuff at 40 wpm (usually) but I have heard some guys at 60 wpm and it is just a sound blur to me (no dots, no dashes, just almost a buzz).  My Elecraft K3 radio actually will read out the CW speed in wpm and it is very accurate if the sender is an electronic keyed and it gets worse with more poor &quot;fist&quot; in sending by straight key or Vibroplex or whatever.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-01-14T17:46:37.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5698" PostTypeId="2" ParentId="5633" CreationDate="2016-01-14T22:48:38.283" Score="0" Body="&lt;p&gt;Check your antenna and also the feed line between the radio and antenna.  Eliminate one variable at a time.  2 radios, 2 antennas, 2 feed lines(?), one repeater.  Take Michael's advice and check if the repeater has changed or better yet try another repeater.&lt;/p&gt;&#xA;" OwnerUserId="5252" LastActivityDate="2016-01-14T22:48:38.283" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5699" PostTypeId="1" CreationDate="2016-01-15T01:26:23.967" Score="0" ViewCount="206" Body="&lt;p&gt;I am trying to confirm on a Smith chart the matching network for 169MHz frequency using an external PA and and 437Mhz with an external LNA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not able to end at the origin of the Smith chart using the reference design provided.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transmitting and receiving paths have different frequencies:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For 169MHz, I am trying to verify the conversion from 80 ohms to 50 ohms&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For 437MHz, I am trying to verify the conversion from (50+j30) ohms to 50 ohms&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the figure outlined below, could you let me know which lumped elements are used for the matching and which ones are used for decoupling or serve other purposes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YYlpS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YYlpS.png&quot; alt=&quot;reference design&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5989" LastEditorUserId="873" LastEditDate="2018-07-15T00:52:24.063" LastActivityDate="2018-07-15T00:52:24.063" Title="CC1125 reference design matching network using Smith chart" Tags="&lt;impedance&gt;&lt;smith-chart&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5700" PostTypeId="2" ParentId="5536" CreationDate="2016-01-15T04:37:28.600" Score="1" Body="&lt;p&gt;To construct an antenna, the focus should be on the resonant length, not on the wire used. It needs to be conductive; if it's going to be outside, protected against the elements, but if you're using free wire, then you can replace it after it rusts through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas can be either connected directly to a radio, or via some feed mechanism. Depending on which frequencies you're wanting to use (you say FM, but that's not a frequency, it's a mode), you may well find that a simple coat-hanger is more than sufficient.&lt;/p&gt;&#xA;" OwnerUserId="5991" LastEditorUserId="13" LastEditDate="2016-01-22T16:07:40.273" LastActivityDate="2016-01-22T16:07:40.273" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5702" PostTypeId="2" ParentId="3675" CreationDate="2016-01-15T18:33:45.627" Score="6" Body="&lt;h2&gt;Elevated radials not equal to ground plane&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;A common misconception is elevated radials (as counterpoise) perform the role of &quot;ground plane&quot; in an antenna system including dominating the far field effects from real ground over which the antenna resides.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radials perform two roles: a conductive path for the inner shield currents and a method to ensure the radiation from this new path is cancelled in the far field.  Your research is correctly touching on these realities, but let's dig further by examining the two roles.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;A conductive path for inner shield currents&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Almost everyone knows the RF currents within a coaxial transmission line have two equal and opposite polarity components.  The current from the center conductor energizes the monopole... easy enough.  The current on the inside of the shield has many more pathways to follow.  Notably, the outside of the coax can entice the current to flow depending on what impedance it presents to the antenna feedpoint.  If the antenna electrically connects to the mounting structure, it too can entice currents to flow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Enter a single radial...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A conductor trimmed to 1/4 wavelength at the operating frequency is a form of impedance transformer.  Since the free end of the radial is open, it maintains a high impedance by definition.  Following the transformer logic, this high impedance transforms to a low impedance at the other end.  If we connect this Low Z point to the shield/mounting-structure at the feedpoint, it will provide a low impedance and tend to draw a large proportion of the inner shield current to itself.  This radial, thus energized, radiates.  We have solved half the problem with monopoles... namely we have reduced the current flow on the outer transmission line and mounting structure by monopolizing the current flow into the radial with its manufactured low impedance at said feedpoint.  This logic doesn't necessarily hold true if the outer shield of the feedline or mounting structure also presents a Low Z in parallel with the radials, but let's assume for the moment the radials win the &quot;current&quot; battle.  With current flowing upon it, the single radial is free to radiate its energy exactly like the monopole element.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Canceling far field effects by adding another radial...&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;If we add a second radial opposite the first, the same action occurs with both receiving the lion's share of current divided equally between them.  The symmetric orientation of the two radials is such each both radiate, but because their polarities are opposite each other by way of orientation, the far field summation from both is negligible.  It isn't zero, but is so small to be of no consequence so long as the radials are 1/4 wavelength or less.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Two problems solved&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Thus providing two radials, one opposite the other, solves two problems for us: manhandling the shield inner current and ensuring this current doesn't affect the far field of the antenna pattern.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;What tests have to say&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Simulation and direct measurement both confirm just two radials of 1/4 wavelength or less result in almost zero perturbation of the monopole far field radiation pattern leaving the monopole element alone in determining the radiation circular symmetry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note the induction fields (stored energy fields) of each radial are not balanced in the near-field.  Thus it is possible to greatly perturb the far-field balance if one radial is too close to some mounting structure or another conductive object.  With each radial containing half the shield current energy, they are each more sensitive to nearby conductors.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Add more radials&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Continuing the theme, adding more radials almost completely eliminates any microscopic deviation from a pure circular far-field pattern.  Three or four radial monopole antennas are the most popular configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One interesting consequence of adding still more symmetrical radials to the base of a monopole antenna is raising the capacitance between the radials and monopole.  The net effect of this is each radial can now be a bit shorter in length.  See &quot;Hats, Number of Spokes, and Capacitance&quot; and &quot;Two Radials are Enough&quot; in the article about the AHVD antenna for more details...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.hamradio.me/antennas/asymmetrical-hatted-dipole-antenna.html&quot; rel=&quot;nofollow&quot;&gt;http://www.hamradio.me/antennas/asymmetrical-hatted-dipole-antenna.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More radials also means if the energy present in one is perturbed by placing a conductor in its induction fields, the net effect is &quot;out voted&quot; by the numerous non-perturbed radials.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;The consequence of radials&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;One particularly unwanted byproduct of using radials, and one that caught me by surprise when I finally figured it out, is the raising of the elevation angle.  I've suggested above that radials contribute little to no effect on the important far-field pattern in azimuth.  What about elevation.  Measure any classic 1/4 wave ground plane antenna and you will see elevation on the primary lobe.  Look at figure 5 in this web page...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.hamradio.me/antennas/slimjim-vs-traditional-j-pole-antenna.html&quot; rel=&quot;nofollow&quot;&gt;http://www.hamradio.me/antennas/slimjim-vs-traditional-j-pole-antenna.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note the measurements (not simulations) of two monopoles (one over a metal place, the other with four radials).  They both exhibit an upward tilt.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one simulates the radial monopole with a source right on the feedpoint, but without any mast or feedline component, the far field elevation pattern looks like the classic doughnut shape you get from a standalone dipole, less a bit of gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So why the difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you add the feedline outer conductor and/or a mast to the simulation model you wind up tilting the pattern upwards and get agreement with measurements.  The problem is the radials induce currents into the mast/feedline, encourage a mast current and thus tilt the elevation pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This fascinating effect is often erroneously credited to the radials somehow &quot;reflecting&quot; the signal upwards just like a metal sheet, but is in fact due to induced energy on the mast/feedline beneath the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is easy to confirm in any antenna simulation tool.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Conclusion&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Two or more radials shorter than a 1/4 wavelength and arranged symmetrically produce little to no effect on the circularity of the monopole azimuth far field pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radials induce energy to the mounting structure and/or feedline generating the typical up-tilt in the elevation far field pattern.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastEditorUserId="4306" LastEditDate="2016-04-27T03:04:51.107" LastActivityDate="2016-04-27T03:04:51.107" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5703" PostTypeId="2" ParentId="3780" CreationDate="2016-01-16T06:49:47.247" Score="3" Body="&lt;p&gt;The &lt;strong&gt;Triple Band Stack&lt;/strong&gt; will simply remember (store) the last frequency entered or tuned for that band and stack position. Try this:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;pick a band - 40 meters - by pressing [7.0]&lt;/li&gt;&#xA;&lt;li&gt;Tune to a frequency&lt;/li&gt;&#xA;&lt;li&gt;Press [7.0] again and tune to a different freq on 40 meters&lt;/li&gt;&#xA;&lt;li&gt;Press [7.0] again and tune to yet a different freq on 40 meters&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Now, press {7.0} repeatedly and you will cycle through the last 3 tuned (or entered) frequencies on that band. This is the triple band stack — there is no formal store command or button for the triple stack. The [STO] feature is for storing frequencies in Memory/Channel Groups.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Triple Band Stack will not only store the frequency - it will store mode such as LSB or CW. Both VFO A and B have independent Triple Band Stacks!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe this is explained in the manual under “Convenience Features”.&lt;/p&gt;&#xA;" OwnerUserId="6001" LastEditorUserId="76" LastEditDate="2016-01-16T18:12:56.640" LastActivityDate="2016-01-16T18:12:56.640" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5704" PostTypeId="1" CreationDate="2016-01-16T06:58:06.390" Score="0" ViewCount="184" Body="&lt;p&gt;I have a couple of MacBooks.  Using a Trifield EMF meter with radio/microwave capability, if I hold the meter near the laptop (where I understand the wifi antenna is located), I receive blips ranging from 4-10 milligauss.  In Radio/Microwave mode it does blips from 0.1 to about 1.5 mW/cm^2).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The router itself, near its antenna, does movement between about 0.5 to 2.5 (0.5mW/cm^2 to 2.5/cm^2).  No wireless devices are connected, but the wireless antenna is turned &quot;on&quot; (cannot be turned off).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I work in a high security field and am wondering if the wifi is actually transmitting even though it is set to &quot;off&quot; in the operating system.  E.g., due to a root kit or other virus. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can other components in a MacBook cause quick fluctuations of this much?  I would expect it to remain mostly constant if Bluetooth/wifi were not transmitting.  &lt;/p&gt;&#xA;" OwnerUserId="6002" LastEditorUserId="6002" LastEditDate="2016-01-16T07:33:34.907" LastActivityDate="2016-01-30T20:02:43.827" Title="Should a MacBook emit fluctuating EMF when WIFI and Bluetooth are turned off?" Tags="&lt;antenna&gt;&lt;united-states&gt;&lt;digital-modes&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5706" PostTypeId="1" AcceptedAnswerId="5707" CreationDate="2016-01-17T09:50:51.137" Score="0" ViewCount="117" Body="&lt;p&gt;Looking for a list of capture-able &lt;strong&gt;data services&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By browsing some sites I accidentally discovered&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;that it is possible to receive NOAA satellite weather images with DIY receiver (&lt;a href=&quot;http://www.instructables.com/id/Downloading-NOAA-satellite-images-cheaply-and-easi/&quot; rel=&quot;nofollow noreferrer&quot;&gt;link&lt;/a&gt;) or (&lt;a href=&quot;http://www.rtl-sdr.com/rtl-sdr-tutorial-receiving-noaa-weather-satellite-images/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;), and also&lt;/li&gt;&#xA;&lt;li&gt;that it is possible to track the location of aircrafts via &lt;a href=&quot;https://en.wikipedia.org/wiki/Automatic_dependent_surveillance_%E2%80%93_broadcast&quot; rel=&quot;nofollow noreferrer&quot;&gt;ADS-B&lt;/a&gt; (&lt;a href=&quot;http://www.instructables.com/id/Track-Airplanes-with-RTL-SDR-and-ADS-B/&quot; rel=&quot;nofollow noreferrer&quot;&gt;link&lt;/a&gt;)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Exists somewhere &lt;strong&gt;a list&lt;/strong&gt; of other interesting &lt;strong&gt;worldwide data&lt;/strong&gt; &quot;services/signals&quot; which are possible to capture and interpret with some DIY receiver?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(i hope this question fits into the &lt;a href=&quot;https://ham.stackexchange.com/help/on-topic&quot;&gt;on-topic questions&lt;/a&gt; here)&lt;/p&gt;&#xA;" OwnerUserId="6007" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-01-17T19:43:44.740" Title="List of capturable data services (diy)" Tags="&lt;diy&gt;&lt;digital-modes&gt;&lt;receiver&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5707" PostTypeId="2" ParentId="5706" CreationDate="2016-01-17T15:00:45.377" Score="4" Body="&lt;p&gt;No, such a list cannot exist -- there's far too many devices operating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, with something like a software defined radio frontend, you can capture &lt;em&gt;any&lt;/em&gt; signal whose bandwidth is limited enough to be properly digitizable with the given device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means that you can capture WiFi, Bluetooth, GSM, LTE, Wideband FM RDS, narrowband FM squelch signatures, Wireless microphone battery readings, Tetra network control messages, Bus display announcements, your garage door opener, your wireless door bell, your zigbee thermometer, your car keys, your wireless power outlet switch, DVB-T, DVB-S, ATSC, ISDB-T, RC planes, Iridium satellite communications, terrestrial flex pagers, weather balloon data, GPS, Glonass, your wireless home automation bus, distress beacons, RFID emissions,…&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And that's just naming the few things that I've heard someone does with the help of a software radio framework called &lt;a href=&quot;http://gnuradio.org&quot; rel=&quot;nofollow&quot;&gt;GNU Radio&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, you can add &lt;em&gt;any&lt;/em&gt; wireless device to that list. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the closest you'd get to such a list would be the list of official spectrum allocations as maintained by your national authority: FCC in the US, Ofcom in GB, Bundesnetzagentur in Germany. However, that will only tell you what rough kind of application or user may use given spectrum generally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: a few things that you in particular might find interesting; might contain repetitions from above:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://ftp.heanet.ie/mirrors/fosdem-video/2015/devroom-software_defined_radio/sdr_rds_tmc.mp4&quot; rel=&quot;nofollow&quot;&gt;traffic channel on RDS&lt;/a&gt; (there's also a SDR transmitter realization. Don't cause a bullfight in your favourite inner city, though.)&lt;/li&gt;&#xA;&lt;li&gt;Bus stops (I mentioned that, I think)&lt;/li&gt;&#xA;&lt;li&gt;Restaurant Pagers (Balint Seeber has a &lt;a href=&quot;https://www.youtube.com/watch?v=_jJEJUsdQ40&quot; rel=&quot;nofollow&quot;&gt;fun video&lt;/a&gt; of him messing with a restaurant's &quot;food ready&quot; notifiers)&lt;/li&gt;&#xA;&lt;li&gt;The ISEE-3 reboot effort (sometimes when I need a little mood-lightening, I watch &lt;a href=&quot;https://youtu.be/CLPG15HXkv8&quot; rel=&quot;nofollow&quot;&gt;this&lt;/a&gt;)&lt;/li&gt;&#xA;&lt;li&gt;PSK-31 ham radio&lt;/li&gt;&#xA;&lt;li&gt;Emergency/fire department tracking: &lt;a href=&quot;http://www.openmhz.com/scanner&quot; rel=&quot;nofollow&quot;&gt;http://www.openmhz.com/scanner&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Tetra is really an interesting system. There's public transport networks using that, power companies... basically, organizations that need a reliable cellular service to control their off-site devices&lt;/li&gt;&#xA;&lt;li&gt;analog TV teletext (j/k.)&lt;/li&gt;&#xA;&lt;li&gt;Car tire pressure sensors (this sounds odd -- but think about it! You can detect who's home from the comfort of your PC by just checking for their pressure sensor's emissions, for example, you can find out when the DHL guy supposedly stopped in front of your place to drop you a leaflet that you weren't there when he claims to have rung the bell. Which brings me back to your doorbell ;) )&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-01-17T19:43:44.740" LastActivityDate="2016-01-17T19:43:44.740" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5708" PostTypeId="2" ParentId="5699" CreationDate="2016-01-17T15:23:31.377" Score="1" Body="&lt;p&gt;Not having tried to verify this myself, I'd say it wouldn't be very surprising if matching wasn't exact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, on small device TX, engineers nowadays tend to just waste a bit of PA power (they've potentially got plenty, compared to what they're &lt;em&gt;allowed&lt;/em&gt; to transmit, typically) on a non-optimal matching (which implies worse SWVR) in favor of easier design, and better filtering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look at it this way: a 80Ω vs 50Ω mismatch would imply a reflection coefficient of&#xA;&lt;a href=&quot;https://i.stack.imgur.com/vdlBZ.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vdlBZ.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, for your lower frequency, you'd be losing but 23% of energy if you didn't do matching at all. That's not very much, considering the amplifier in that chip won't work constantly efficient at all frequencies; other effects just outshine that mismatch, and if you're not into building the most energy-efficient system possible, you simply wouldn't care.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the 433MHz ISM band, you get frequency-dependent contributions, too, so that's what I'd try to optimize.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-01-17T15:23:31.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5709" PostTypeId="2" ParentId="5631" CreationDate="2016-01-17T15:56:09.577" Score="1" Body="&lt;p&gt;Class-E implies switching a transistor on and off, rather than operating it linearly. This implies a rectangular signal shape, which implies a sinc spectrum, which implies high out-of-band emissions. You counteract that correctly by using High-Q LC filters. Make sure you measure efficiency at the right point -- that is, including these filters, as they convert harmonic energy to in-band energy, if you want so.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-01-17T15:56:09.577" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5710" PostTypeId="2" ParentId="5704" CreationDate="2016-01-18T22:02:40.523" Score="5" Body="&lt;p&gt;We would expect no emissions from a disabled WiFi or BT adapter, but as you suggest, all bets are off if your system is compromised.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your broadband detector is only a crude way to check for emissions, because you have no idea of the frequency involved.  The computer has a lot of digital circuitry and clocks that emit RF energy at low levels -- not just WiFi and BT.  Some devices also have NFC (near-field communications) that you could pick up.  You need a &lt;a href=&quot;https://en.wikipedia.org/wiki/Spectrum_analyzer&quot;&gt;spectrum analyzer&lt;/a&gt; or other more accurate receiver to truly assess what's going on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also check the output as the computer boots up -- before it would activate the WiFi or BT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Very high security installations require &quot;&lt;a href=&quot;https://en.wikipedia.org/wiki/Tempest_%28codename%29&quot;&gt;TEMPEST&lt;/a&gt;&quot; qualified computers, that are specially shielded and RF-suppressed.  With standard computers, it's possible to pick up a screen image or other info using a (fairly nearby) sensitive receiver.&lt;/p&gt;&#xA;" OwnerUserId="4987" LastActivityDate="2016-01-18T22:02:40.523" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5711" PostTypeId="2" ParentId="1394" CreationDate="2016-01-19T11:58:10.217" Score="4" Body="&lt;p&gt;Currently, the best electrical conductivity is reached by materials such as &lt;strong&gt;nanotubes&lt;/strong&gt; or &lt;strong&gt;graphene&lt;/strong&gt;. They also have excellent mechanical properties. Unfortunately, there is still no technology of mass production, and thus we must rely on metals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best metal for this purpose is &lt;strong&gt;silver (Ag)&lt;/strong&gt;. It has the highest conductivity, even better than copper and much better than gold. It is broadly used in Russian military connectors of ShR ШР series. The weakness of silver coated connectors is that they are very sensitive to sulfur (S) compounds, which are present in human sweat (even its vapour) and breath, which produce the worst kind of patina which you can find on silver contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Gold (Au)&lt;/strong&gt; has worse conductivity than silver (still very good) but is free from the above drawbacks:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;no corrosion at all, produces no patina;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;contacts can be touched with bare hands,&lt;/li&gt;&#xA;&lt;li&gt;reliable in humid environments (household, automotive, marine),&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;well known technology for refining and coating with it.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6018" LastEditorUserId="76" LastEditDate="2016-01-19T16:17:00.753" LastActivityDate="2016-01-19T16:17:00.753" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5713" PostTypeId="2" ParentId="5299" CreationDate="2016-01-19T21:43:26.283" Score="1" Body="&lt;p&gt;You should be covered by FCC Part 15 unlicensed use as long as&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For the band 5.725-5.85 GHz, the maximum conducted output power&#xA;     over the frequency band of operation shall not exceed 1 W. In addition,&#xA;     the maximum power spectral density shall not exceed 30 dBm in any&#xA;     500-kHz band.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;FCC 15.407 section covers in more detail. For example you must reduce power when using a directional transmitting antenna..&lt;/p&gt;&#xA;" OwnerUserId="6020" LastActivityDate="2016-01-19T21:43:26.283" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5714" PostTypeId="2" ParentId="2041" CreationDate="2016-01-20T19:34:16.330" Score="2" Body="&lt;p&gt;Just a suggestion, but have you considered the possibility of it being an SSTV transmission? I would download an SSTV decoder and run it through that, using various encoding methods (e.g. Robot32, PD180, etc.) and see what you get.&lt;/p&gt;&#xA;" OwnerUserId="6024" LastActivityDate="2016-01-20T19:34:16.330" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5716" PostTypeId="2" ParentId="5299" CreationDate="2016-01-21T03:33:43.503" Score="0" Body="&lt;p&gt;I believe that in order to comply with licence-free use, all transmitting equipment must be type-approved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One option available for home-built equipment would be to work within the regulations of the amateur radio licence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By this, I mean that if you were going to build some equipment yourself and experiment with it, even with a view to producing it commercially later, then in order to test that it works correctly you would need SOME sort of licence. The amateur licence would serve well for this purpose (self-training, etc.), although it does not of course permit commercial use of the equipment. It would also require that the person/people doing the work would hold the right kind of licence themselves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once developed to the point where you have something that works, you could apply for type approval, but my understanding is that this is a lengthy and costly procedure.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2016-01-21T04:40:38.503" LastActivityDate="2016-01-21T04:40:38.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5719" PostTypeId="1" AcceptedAnswerId="5721" CreationDate="2016-01-23T15:45:01.653" Score="2" ViewCount="3043" Body="&lt;p&gt;I have two high-speed sampling devices that can use UDP (through 1G Ethernet) and PCIe to transmmit their samples, respectively. They are used to record signals I interested. These devices are made by myself so the data format and the software running on OS are easy to be modified. Now I want to use GNU radio to demodulate some signals from the devices in real-time but I don't now the interface and format of GNU Radio. Is it possible to do that? Is it necessary to read or even modify its source code? And which document should I read?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="6040" LastEditorUserId="6040" LastEditDate="2016-01-23T15:51:31.500" LastActivityDate="2016-01-24T02:52:31.490" Title="Can I send samples from the device made by myself to GNU radio?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5720" PostTypeId="2" ParentId="5719" CreationDate="2016-01-23T16:24:41.147" Score="1" Body="&lt;p&gt;GNU Radio does not implement any interface or format itself. That would be the responsibility of some block.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are any number of blocks you might choose. There is a very simple &lt;a href=&quot;https://gnuradio.org/doc/doxygen/classgr_1_1blocks_1_1udp__source.html&quot; rel=&quot;nofollow&quot;&gt;udp_source&lt;/a&gt; which could work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also try to make your SDR compatible with an existing ethernet SDR. A couple you might consider:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://gnuradio.org/redmine/projects/gnuradio/wiki/USRP&quot; rel=&quot;nofollow&quot;&gt;USRP&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.tapr.org/~n5eg/index_files/DCC_2013_Gnuradio_Presentation%20-%20Rev%205.pdf&quot; rel=&quot;nofollow&quot;&gt;HPSDR Metis&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Alternately, you can always &lt;a href=&quot;https://gnuradio.org/redmine/projects/gnuradio/wiki/OutOfTreeModules&quot; rel=&quot;nofollow&quot;&gt;implement your own GNU Radio block&lt;/a&gt;, using whatever network format you want.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-01-23T16:24:41.147" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5721" PostTypeId="2" ParentId="5719" CreationDate="2016-01-23T16:25:11.920" Score="4" Body="&lt;p&gt;Here are several different approaches you can take.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;You can write a GNU Radio source block which knows how to interact with your particular device. This does not require modifying GNU Radio's source code: you can compile your block separately, in which case it is known as an &lt;a href=&quot;https://gnuradio.org/redmine/projects/gnuradio/wiki/OutOfTreeModules&quot; rel=&quot;nofollow&quot;&gt;&lt;em&gt;out of tree module&lt;/em&gt;; here's a tutorial&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This custom source block would be written in C++ (or Python, though there are some restrictions in that case) and gets a thread of its own in which it can do whatever is necessary to obtain samples from the hardware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantage of this method is that you can write methods on the source to control the device and handle special events using stream tags and message ports. The disadvantage is that you're writing more custom code, including the application that uses your block.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You can use one of the existing general-purpose source blocks.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The &lt;a href=&quot;http://gnuradio.org/doc/doxygen/classgr_1_1blocks_1_1udp__source.html#details&quot; rel=&quot;nofollow&quot;&gt;UDP source block&lt;/a&gt; simply takes the content of UDP datagrams and puts them into the GR flow graph. You can use this immediately with your UDP-based device if it has no high-level protocol carried within the datagrams.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You could also have your application open a connection to the device in whatever way, before the flow graph is started, and then use the &lt;a href=&quot;http://gnuradio.org/doc/doxygen/classgr_1_1blocks_1_1file__descriptor__source.html&quot; rel=&quot;nofollow&quot;&gt;file descriptor source&lt;/a&gt;; this works if you have some way to open your device as a file (&lt;code&gt;/dev/something&lt;/code&gt; or a pipe from another process/thread doing the reading). If you use stdin (file descriptor 0) then you don't need extra code inside the process, so you can use GNU Radio Companion, and set up a pipe like &lt;code&gt;./my-device-reader | ./my-grc-flowgraph.py&lt;/code&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If your PCIe device can be made to look like a standard audio device, then you could use the audio source block. I suspect that you would find that audio driver systems aren't designed to work well at the sample rates you want; I just mention this to give another example of ways to use existing source blocks.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The advantage of this method is that you don't have to write as much code, and you might find the generic interfaces useful (e.g. piping your samples into something that's &lt;em&gt;not&lt;/em&gt; written in GNU Radio instead). The disadvantage is that you can't control the device or use any particular features beyond the stream of samples, because the generic source block doesn't know about the features of your device.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If your hardware is mostly like typical software radio peripherals, you could modify &lt;a href=&quot;http://sdr.osmocom.org/trac/wiki/GrOsmoSDR&quot; rel=&quot;nofollow&quot;&gt;gr-osmosdr&lt;/a&gt; to support it. This is of comparable difficulty to writing a custom source block, but has the advantage that your hardware can be used with existing applications that use gr-osmosdr as their generic hardware interface. The disadvantage is that you are limited to gr-osmosdr's interface for controlling the device.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Since you say you can change the hardware's protocols, you can also simply change them to use the same protocol as an existing radio peripheral. This is excellent for compatibility, since no new “driver” software is required at all, but runs the risk of your reimplementation being subtly incompatible (if there is no formal protocol documentation) and may not allow you to add features that the device you are imitating does not have.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-01-24T02:52:31.490" LastActivityDate="2016-01-24T02:52:31.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5725" PostTypeId="1" CreationDate="2016-01-26T05:50:36.047" Score="1" ViewCount="88" Body="&lt;p&gt;I built a OCF HF antenna. The feed line contains a 4:1 balun and a line insolator (choke) per instructions. When checking the radio end of the coax, I get a &quot;grounded&quot; response between the inner wire and outer mesh. Is this a correct circumstance?&lt;/p&gt;&#xA;" OwnerUserId="6059" LastEditorUserId="76" LastEditDate="2016-01-26T15:06:49.867" LastActivityDate="2016-01-26T15:06:49.867" Title="OCF Antenna Feed Line" Tags="&lt;antenna&gt;&lt;antenna-system&gt;" AnswerCount="0" CommentCount="1" ClosedDate="2016-01-27T22:14:07.290" ContentLicense="CC BY-SA 3.0" />
  <row Id="5726" PostTypeId="2" ParentId="5695" CreationDate="2016-01-26T13:07:48.900" Score="2" Body="&lt;p&gt;The SSTV transmissions were originally already scheduled for late December. I'm waiting for them, too. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the past, the ISS was relatively continuously transmitting pictures in a loop, the same 4-5 pictures multiple times with small (some minute long) breaks in between. &#xA;It is very easy to spot the ISS signal in a waterfall, it's quite strong and you will see the Doppler shift/drift very easily. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had really good luck receiving pictures in last April and have recorded 5 absolutely clear images. &lt;/p&gt;&#xA;" OwnerUserId="6061" LastEditorUserId="13" LastEditDate="2016-01-26T14:23:46.513" LastActivityDate="2016-01-26T14:23:46.513" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5727" PostTypeId="2" ParentId="1936" CreationDate="2016-01-26T20:19:48.330" Score="-2" Body="&lt;p&gt;I think the main issue will be targeting the sat. The receiver should handle the flux in frequency based on the carrier. leading the sat target depending on how far the sat is from each other. Geo sync sates are 28k miles and signal takes&#xA;28000 / 186000 seconds to reach earth and twice that to reach back. So you have to lead the target by a few hundred yards before the sat will even pickup the focused signal.&lt;/p&gt;&#xA;" OwnerUserId="5906" LastActivityDate="2016-01-26T20:19:48.330" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5728" PostTypeId="2" ParentId="142" CreationDate="2016-01-26T21:51:46.000" Score="6" Body="&lt;p&gt;I'm not sure what you mean by &quot;M&quot; type, but here are some points to address your question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pros:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Well understood, and very old, design that most know how to work with;&lt;/li&gt;&#xA;&lt;li&gt;Numerous vendors continue to manufacture various connector topologies with the 'UHF Connector' specifications.  Note the PL-259 &amp;amp; SO-239 are but two examples of many compatible part numbers that all mate with each other - the PL-258 is another example;&lt;/li&gt;&#xA;&lt;li&gt;Is somewhat mechanically robust;&lt;/li&gt;&#xA;&lt;li&gt;The ~4 mm center pin is quite large as connector center pins go and provides peace of mind for high power uses below 30 MHz.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Cons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Impedance-bump loss mechanisms become measurable above just 30 MHz and problematic above 50 MHz;&lt;/li&gt;&#xA;&lt;li&gt;Expiration of the original mil standard decades ago leaves interface specifications subject to some silly interpretations (example: the not-quite-compatible 'metric' UHF Connector);&lt;/li&gt;&#xA;&lt;li&gt;Absolutely no mechanical mechanism to deter ingress of moisture into the mating interface;&lt;/li&gt;&#xA;&lt;li&gt;Complete reliance on shell torque for shield path electrical continuity.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The inferior UHF connector continues to appear on ham and CB gear mostly due to market inertia.  At this point, the devil you know is better than the devil you don't.  Folks are simply accustomed in making good use of the UHF Connector where it makes sense to do so: &amp;lt;50 MHz with weatherization treatments applied by the user.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another way to think of this is if ham and CB gear were suddenly made with BNC, TNC or N connectors, the cry heard throughout the land would be deafening..., but fun to observe.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Reference&lt;/h2&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/UHF_connector&quot; rel=&quot;noreferrer&quot;&gt;https://en.wikipedia.org/wiki/UHF_connector&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hamradio.me/connectors/uhf-connector-test-results.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.hamradio.me/connectors/uhf-connector-test-results.html&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4306" LastActivityDate="2016-01-26T21:51:46.000" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5730" PostTypeId="2" ParentId="5685" CreationDate="2016-01-27T09:59:12.207" Score="0" Body="&lt;p&gt;For paper and pen training I recommend &lt;a href=&quot;https://play.google.com/store/apps/details?id=com.wolphi.morsetrainer&amp;amp;hl=en&quot; rel=&quot;nofollow&quot; title=&quot;Morse Trainer for Ham Radio&quot;&gt;Morse Trainer for Ham Radio&lt;/a&gt; from Wolphi LLC. Itt can play random groups of letters (you can use the Koch method), play random QSO like texts - or a text file you choose.&lt;/p&gt;&#xA;" OwnerUserId="5611" LastActivityDate="2016-01-27T09:59:12.207" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5731" PostTypeId="2" ParentId="5257" CreationDate="2016-01-28T15:34:00.810" Score="0" Body="&lt;p&gt;Put a dummy load in stead of the antenna; that will attenuate the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It won't solve your &quot;heating up&quot; problem, nor your &quot;battery drain&quot;, but it will reduce the output EIRP quite a bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I ran a fox hunt with a Baofeng, tested on 1 W, sending out morse (over FM, hihi) every 15 minutes; the battery lasted 16 hours, more than enough for a day's fun.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="76" LastEditDate="2016-01-29T19:08:18.040" LastActivityDate="2016-01-29T19:08:18.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5732" PostTypeId="2" ParentId="5438" CreationDate="2016-01-28T16:34:31.387" Score="1" Body="&lt;p&gt;This is all about definition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, define what is acceptable as maximum VSWR for your particular situation, at a given impedance for a given antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have that you can measure the lowest frequency (call this f1) where the maximum VSWR is measured on that antenna, then you measure the highest frequency (call this f2) that maximum VSWR is reached. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now your Q can be calculated as&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;    f_c = \frac{f_1+f_2}{2} \\&#xA;    Q = \frac{f_c}{f_2-f_1}&#xA;$$&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="76" LastEditDate="2016-01-29T19:07:47.670" LastActivityDate="2016-01-29T19:07:47.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5733" PostTypeId="1" CreationDate="2016-01-29T18:16:15.530" Score="1" ViewCount="219" Body="&lt;p&gt;So I'm looking at building a satellite receiving stations (amateur bands). I know that a station that is transmitting requires grounding of the RF components due to the high power of the transmitter, but do I need to ground my station if I only plan on receiving?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm hoping to learn here, so top answer will explain the rational behind the yes/no. :)&lt;/p&gt;&#xA;" OwnerUserId="529" LastActivityDate="2016-01-30T15:47:34.430" Title="Does a station that's only going to receive require grounding" Tags="&lt;receiver&gt;&lt;grounding&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5734" PostTypeId="2" ParentId="5733" CreationDate="2016-01-29T19:05:05.917" Score="1" Body="&lt;p&gt;Let's first eliminate some reasons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If you have a receiving antenna which is permanently outdoors, then you may want grounding for lightning protection. This is a substantial topic of its own which I am not qualified to describe briefly here. This is largely a separate topic from grounding for RF purposes, though some of the design principles are useful in both cases.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some types of antennas, deliberately or accidentally, have connections to ground as part of their functional structure. Directional, rotatable antennas such as Yagi, log periodic, or dish antennas, as you would use for satellite work, do not.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There are reasons for grounding applicable here: electrical safety and RFI. Electrical safety is not specific to this application; the usual rules apply, and we'll assume that your line voltage power supplies are properly grounded and everything else (your computer, radio, antenna rotator...) is low-voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That leaves RFI (radio frequency interference). We need to think about grounding &lt;em&gt;and shielding&lt;/em&gt;. The purpose of shielding is to prevent noise from entering sensitive circuits or leaving noisy ones. The purpose of grounding is to allow noise which is flowing on some (shield/ground) conductor to preferentially flow to earth rather than into your receiving equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In theory, a receiver does not need a ground at all: if the entire system is enclosed in an impermeable shield, with appropriate filtering at power, antenna, and received-signal-out ports, then grounding has no effect whatsoever.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, anything you can do to reduce the noise power around by redirecting it to earth via a ground connection &lt;em&gt;may&lt;/em&gt; be useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Caveat: your ground connection needs to not have the effect of conducting noise from a noisy component to a quiet one, which can happen if you wire grounds in daisy-chain fashion rather than separate wiring to a single ground bus/plane/chassis. It's also possible for the ground wiring to end up acting as an antenna for other noise; this is reduced by keeping it as short as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, grounding is useful not only for your receiver but also for other electronic equipment which may be &lt;em&gt;producing&lt;/em&gt; noise that would interfere with reception. Of course, you can also “just” shut off that equipment while receiving, which is an easier option for initial troubleshooting.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-01-29T19:05:05.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5735" PostTypeId="1" CreationDate="2016-01-30T00:13:54.480" Score="5" ViewCount="526" Body="&lt;p&gt;I'm working on a 144 MHz antenna using a gamma match. The best result (resonance 50+j0 at 144.400 MHz) I reached is a 10 mm diameter gamma rod, 15 cm long and a capacity of 10 pF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I thought to obtain the 10 pF with a 4 mm rod inside the gamma rod (internal diameter 8 mm). The dielectric is air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since I will use 1 kW I wonder if this configuration (dielectric air, spacing 2 mm) is sufficient for the power I'll use or I have to find a different configuration (having more spacing at the dielectric).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More in general, how can I esteem the maximum power of a gamma match with air dielectric? Is there a rule to decide the minimum better dielectric spacing in function of the power to use?&lt;/p&gt;&#xA;" OwnerUserId="6087" LastEditorUserId="76" LastEditDate="2017-03-08T21:11:01.117" LastActivityDate="2017-03-08T21:11:01.117" Title="Necessary spacing for 1 kW Gamma Match on 144 MHz" Tags="&lt;antenna-construction&gt;&lt;impedance&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5738" PostTypeId="2" ParentId="5733" CreationDate="2016-01-30T15:47:34.430" Score="1" Body="&lt;p&gt;As I am unable to comment on Kevin's great answer, I would add that for any device that you add grounding to, in addition to keeping it short, ensure that you have a solid earth. If you don't have solid connection you will introduce noise, not reduce it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also the problem of potential(voltage) differences between multiple grounds. For example if your device has a 3 wire chassis ground though the electrical which uses single common ground in your primary-mains-service panel, and you add additional grounding to say a cold water pipe that enters the building from the other side. You now have a loop and the effectiveness of one ground over the other will generate a minor current flow between the grounds and though your device. You want to avoid floating grounds where you attach devices to each other and not to a common ground. &lt;/p&gt;&#xA;" OwnerUserId="6092" LastActivityDate="2016-01-30T15:47:34.430" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5739" PostTypeId="2" ParentId="5704" CreationDate="2016-01-30T20:02:43.827" Score="2" Body="&lt;p&gt;I find it very likely that you are picking up the computer itself and not the expected radiators you are listing. If instead of a Spectrum Analyzer which shows a field strength across a range of frequencies, you use a Frequency counter, that could tell what you are seeing with the other meter which is only showing a general field strength. My guess is you are seeing the clock, the frequency will be the core bus frequency. I suggest the clock because its the strongest regular signal emitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, any time you run electricity through unshielded circuit traces your going to get some level of RFI. You could even be picking stuff up off the power adapter since it is also a switching supply, and in a plastic box it isn't really shielded either. The old PC's with 50mhz clocks used to harmonize 'nicely' with bottom end of 6 meteres&lt;/p&gt;&#xA;" OwnerUserId="6092" LastActivityDate="2016-01-30T20:02:43.827" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5740" PostTypeId="1" AcceptedAnswerId="7564" CreationDate="2016-01-31T04:53:04.477" Score="2" ViewCount="1136" Body="&lt;p&gt;The mode of SSB is alive and well. It has relevance for long-distance comms and does not waste spectrum. The orthodox methods of generation are Filter, Phasing and Weaver. These methods can be and are done in DSP or firmware but the fundamentals are the same. The resulting low-level analog RF signal goes to a linear amp possibly via one or more hetrodyning stages. The linear amp has not gotten much more efficient since the 1960s. So the more efficient classes of PA operation are not utilised in practical SSB rigs.  Example FM and its digital cousin FSK are fine running class C or the less-documented class E. It has been said that it's mathematically possible to apply AM and FM to a RF carrier simultaneously to make SSB. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Amateur who said this may be very very old now. When he was in his heyday it would not have been practical but the question is: Can we do this now?&lt;/p&gt;&#xA;" OwnerUserId="6095" LastEditorUserId="8573" LastEditDate="2019-05-03T22:39:33.500" LastActivityDate="2020-07-13T19:09:39.553" Title="SSB Generation. 4th method?" Tags="&lt;ssb&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="5741" PostTypeId="2" ParentId="5740" CreationDate="2016-01-31T05:43:25.460" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;It has been said that it's mathematically possible to apply AM and FM to a RF carrier simultaneously to make SSB.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is true. However, it's equally true of &lt;em&gt;every other modulation&lt;/em&gt; — not just SSB. This is easiest to see from the DSP perspective, where we work with complex-valued signals almost all the time. &quot;AM and FM simultaneously&quot; is just the &lt;em&gt;polar&lt;/em&gt; (rather than Cartesian) breakdown of the complex baseband signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This actually has an application in RF electronics, which is probably the idea you heard about: I've heard it under the name &lt;em&gt;polar amplifier,&lt;/em&gt; and indeed it is theoretically more efficient than an ordinary linear amplifier. The major problems of &lt;em&gt;using&lt;/em&gt; a polar amplifier are generating the nonstandard driving signals and getting the proper phase alignment between the phase control and amplitude control. (&lt;a href=&quot;http://doc.utwente.nl/74708/1/thesis_R_Shrestha.pdf&quot; rel=&quot;nofollow&quot;&gt;Here's a document I just found discussing the design (in Chapter 4); it calls the thing a &quot;polar modulated power amplifier&quot;.&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, as far as I know you could certainly build a complete SSB transmitter this way. It would be a substantial engineering challenge, and it would hopefully be more efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, given that in practice the modulation would be implemented by DSP producing the phase and amplitude signals, and the most straightforward way to do that I can think of is to apply one of the standard methods to convert the real audio to IQ (Cartesian) SSB, then convert to polar, it doesn't seem quite right to call this truly a fourth method of generating SSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Also, in DSP, the filter method and the phasing method are essentially the same thing, and the Weaver method is just breaking up the math into slightly different parts.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-01-31T05:51:34.310" LastActivityDate="2016-01-31T05:51:34.310" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5742" PostTypeId="1" AcceptedAnswerId="5758" CreationDate="2016-01-31T19:03:22.103" Score="5" ViewCount="8020" Body="&lt;p&gt;I have a &lt;a href=&quot;http://nice.kaze.com/pl-660_man_en.pdf&quot; rel=&quot;noreferrer&quot;&gt;Tecsun PL-660&lt;/a&gt; (link is to the manual) has the usual AM/FM radio telescoping internal antenna, and a 1/8th-inch jack for an external shortwave antenna.   There appears to be no facility for attaching to station ground, unless one of the terminals in the 1/8th inch jack can be attached to a station ground.  It has USB/LSB single-sideband modes, as well as AM reception and pretty good general coverage from about 3200 khz up, in AM and SSB, plus commercial AM/FM and air-band coverage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is:  It stands to reason I should get better reception on the 80 meter, 40 meter, 30meter, 20meter ham bands if I build a proper dipole for each, and manually switch them out.  With better quality non-portable amateur radio receivers and transceivers there appears to be a way to ground the radio. Perhaps one of the pins on portable radios is also possibly the station ground pin? Does anybody ground their portable radios when using them for Shortwave listening?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have lost the little bit of wire attached to a headphone jack as shown in the picture here, that makes up the provided shortwave listening antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nzsKp.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nzsKp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm about to experiment and see if I can't get good reception with a home-made replacement, or rather set of replacements, but as dipoles instead of just random-wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I think I know is that:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;That for a particular shortwave band, a dipole for that frequency will be resonant and will thus be ideal for receiving that band.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A coaxial feed, with the jacket of the coaxial feed attached to station ground will be good.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;That it won't take long to figure out which terminal (pin) in the 1/8th-inch 3-pin connector is for the actual antenna.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Things I don't know:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;a. What the impedance of the radio tuner is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;b. What else can be done if I want to improve overall reception quality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;c. I intend to just experiment with wiring up the dipole to the two pins on the headphone jack but I have no idea if the little portable radio is likely to even have both pins connected inside the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone ever made their own antennas for little portable AA battery receivers like the Tecsuns (or Grundigs or other similar units)?&lt;/p&gt;&#xA;" OwnerUserId="643" LastActivityDate="2020-04-25T21:20:42.683" Title="Shortwave Antenna Listening with Portable Receiver Like TECSUN PL-660?" Tags="&lt;antenna&gt;&lt;receiver&gt;" AnswerCount="5" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5743" PostTypeId="2" ParentId="1139" CreationDate="2016-01-31T20:46:54.470" Score="0" Body="&lt;p&gt;You may be asking about what is known as a “&lt;a href=&quot;https://en.wikipedia.org/wiki/Log-periodic_antenna&quot; rel=&quot;nofollow&quot;&gt;log-periodic antenna&lt;/a&gt;.”&lt;/p&gt;&#xA;" OwnerUserId="6096" LastEditorUserId="76" LastEditDate="2016-02-02T16:20:17.827" LastActivityDate="2016-02-02T16:20:17.827" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5744" PostTypeId="2" ParentId="5257" CreationDate="2016-01-31T22:15:03.957" Score="1" Body="&lt;p&gt;As per tomnexus answer above but consider if you can pick up the trace to Q8 and add a variable resistor to lower the bias.&lt;/p&gt;&#xA;" OwnerUserId="6098" LastActivityDate="2016-01-31T22:15:03.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5745" PostTypeId="2" ParentId="5685" CreationDate="2016-01-31T22:18:23.833" Score="1" Body="&lt;p&gt;Before you go for an app try this free website.  lcwo.net&#xA;I found it very useful.&lt;/p&gt;&#xA;" OwnerUserId="6098" LastActivityDate="2016-01-31T22:18:23.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5746" PostTypeId="2" ParentId="5676" CreationDate="2016-01-31T22:21:05.260" Score="1" Body="&lt;p&gt;Have you checked the voltage on the battery because I think it's full.  My UV-82 charger starts blinking like that when the charge is complete.  It is oscillating between charge/no charge state as soon as it sees full voltage on the battery.&lt;/p&gt;&#xA;" OwnerUserId="6098" LastActivityDate="2016-01-31T22:21:05.260" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5747" PostTypeId="2" ParentId="5685" CreationDate="2016-01-31T23:04:46.047" Score="2" Body="&lt;p&gt;The Morse Trainer (&lt;a href=&quot;http://www.wolphi.com/ham-radio-apps/morse-trainer/morse-trainer-manual/&quot; rel=&quot;nofollow&quot;&gt;http://www.wolphi.com/ham-radio-apps/morse-trainer/morse-trainer-manual/&lt;/a&gt;) does exactly what you're looking for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It provides random QSO, the first 20 lessons of the Koch method, and supports Farnsworth method, which I highly recommend because many of us consider it best to listen to the actual character speed at the rate we are attempting to acheive, while increasing the spacing between the letters so the brain can have time to adapt to receiving at slower rates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This has the effect of you not having to relearn (i.e., train your brain to comprehend) the same characters over again when the delivery speed changes - it's not a problem to hear live code slower, just faster.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To surprise yourself, you can dump (paste) random pages from Wikipedia or any other textual source into the app, and even have it randomize that text. That way you have no idea what code you're going to copy.... and of course, the text is displayed, as you stipulated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moving forward, it should be noted that perfectly delivered code is NOT the real world - no one's &quot;fist&quot; is perfect code, so with respect to this phenomena I'll defer to the answer that @k7peh provided: Learn to listen to live code delivered by real people. Again, you'll need to let your brain be trained to copy this code accurately because any morse code tutor program is incapable of delivering this sort of imperfection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Listening to w1aw is good, but an Android app that can tune into, say 20 meters, and offer you the opportunity to get a handle on different fists will go a long way toward getting you back to your morse tutor endeavoring to hear words, rather than characters, and then back to live radio again, where you'll eventually find yourself not even hearing/seeing the characters, but rather, the words themselves, eventually even anticipating the next word before it is sent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One more thing, when switching back and forth between the tutor app for increasing your copying speed and accuracy, and live a live QSO, search in the novice and general portions of the particular band you choose, people there will generally be sending code at a slower rate - this will save you a lot of anguish from missed characters/words.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this helps, and congratulations on your commitment to learning code!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 de kd6ncg&lt;/p&gt;&#xA;" OwnerUserId="6097" LastActivityDate="2016-01-31T23:04:46.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5750" PostTypeId="1" AcceptedAnswerId="5757" CreationDate="2016-02-01T00:12:59.797" Score="0" ViewCount="840" Body="&lt;p&gt;I'm in the midst of constructing a fan dipole for 80, 40, 30, 20 and 10 meters.  I have everything laid out and am about to start cutting wire.  I have an ugly balun (RF choke) wound at the feed point but I'm wondering what I should do for lengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My sense from all of my research is that I should care about the &lt;em&gt;wire&lt;/em&gt; length of the legs in the dipoles.  For instance, each leg of the 40 meter segment will be 32.6 feet in length.  I'm figuring that it's &lt;em&gt;actually&lt;/em&gt; 32.6 feet, including the portion of the wire at the feed point that is loose and comes up to be bundled into the rest of the wires into the feed point.  This would also include the piece that is folded over at the end through the egg insulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The alternative is that the overall linear length is more important, which feels wrong, but, admittedly, antenna calculations are not my strong suit.  :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, should I be calculating linear length end to end from the feed point out or the actual wire length regardless of the way it comes into the feed point or the folded piece at the end for the insulator?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Update&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a followup, I've now built and hoisted the fan dipole.  I have it suspended from the center feed point / RF choke and from the ends at about 40 feet.  It tunes up between 1:1 and 1.6:1 on 80, 40, 30, 20, 17, 15 and 10 meters.  It's a big tangle of wires until you get it into the air but well worth the time and effort if you have the space, IMHO.&lt;/p&gt;&#xA;" OwnerUserId="5137" LastEditorUserId="5137" LastEditDate="2016-02-11T16:53:10.403" LastActivityDate="2016-02-11T16:53:10.403" Title="Which matters most in a fan dipole: Overall linear length or actual wire length?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5752" PostTypeId="1" AcceptedAnswerId="5753" CreationDate="2016-02-01T01:06:23.563" Score="10" ViewCount="1644" Body="&lt;h2&gt;Bens Best Bent Wire&lt;/h2&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;My uncle, who was a Merchant Marine in WWII used to tell me this. He was a ham, and said it would develop my fist musically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was a small child at the time, and through his enthusiasm for all things geeky, especially Ham Radio, he inspired me to pursue technology as both a hobby and vocation - an old crystal AM radio kit was my introduction into the fascinating world of radio propagation and electronics, but information I have on the musically phrased, &lt;strong&gt;&lt;em&gt;&lt;a href=&quot;http://longlist.org/best+bent+wire&quot; rel=&quot;noreferrer&quot;&gt;Bens Best Bent Wire&lt;/a&gt;&lt;/em&gt;&lt;/strong&gt;, is rather sparse I find.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what is the backstory on this, and especially, what is the nature of its endearment to amateur radio, that so many Hams are enamored of?&lt;/p&gt;&#xA;" OwnerUserId="6097" LastEditorUserId="8717" LastEditDate="2021-04-12T23:12:33.273" LastActivityDate="2021-04-12T23:12:33.273" Title="What is the origin, history behind &quot;Ben's Best Bent Wire&quot;?" Tags="&lt;hf&gt;&lt;cw&gt;&lt;jargon&gt;&lt;history&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5753" PostTypeId="2" ParentId="5752" CreationDate="2016-02-01T01:41:14.860" Score="3" Body="&lt;p&gt;The best information I have on this is a single post on an old contesting discussion list about 12 years ago, related to a thread about an issue of TenTec Digest here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://lists.contesting.com/_tentec/2003-08/msg00545.html&quot; rel=&quot;nofollow&quot;&gt;http://lists.contesting.com/_tentec/2003-08/msg00545.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I really wonder if the phrase, widely accepted as a warm up practice with a wonderful ring to it, originated with the military or commercial radio services rather than the amateur radio community.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A bit more background was provided in a &lt;strong&gt;&lt;em&gt;&lt;a href=&quot;https://aa7ee.wordpress.com/2013/03/29/good-ops-bens-best-bent-wire-and-some-new-home-made-qsl-cards/&quot; rel=&quot;nofollow&quot;&gt;blog post by Dave Richards AA7EE&lt;/a&gt;&lt;/em&gt;&lt;/strong&gt;, who infers that this was an inovation by commercial radio operators performed prior to the beginning of their shifts, to loosen up their fists before going on the air.&lt;/p&gt;&#xA;" OwnerUserId="6097" LastActivityDate="2016-02-01T01:41:14.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5754" PostTypeId="1" AcceptedAnswerId="5756" CreationDate="2016-02-01T16:27:13.697" Score="2" ViewCount="1227" Body="&lt;p&gt;I made a 1090Mhz antenna for ADS-B following the instructions from &lt;a href=&quot;http://www.sprut.de/electronic/pic/projekte/adsb/adsb_en.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;sprut.de&lt;/a&gt;.  The antenna looks like below and I made it from the copper centre of some stripped coax:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5OTlA.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5OTlA.gif&quot; alt=&quot;Antenna diagram&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The instructions say:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Now we need a &quot;dummy-ground&quot;, that has to be connected to the shield of the coaxial cable.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Why does this virtual ground / counterpoise need to be connected to the shield?  Will it be slightly less effective or completely useless if left unconnected?&lt;/p&gt;&#xA;" OwnerUserId="1727" LastActivityDate="2016-02-02T17:45:52.973" Title="Why does a counterpoise need to be grounded" Tags="&lt;antenna&gt;&lt;grounding&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5755" PostTypeId="1" CreationDate="2016-02-01T16:39:22.630" Score="1" ViewCount="74" Body="&lt;p&gt;I want to build a system that can transmit data through 2-way radios &lt;strong&gt;as far as possible&lt;/strong&gt;. I use the &quot;line-in&quot; as the input of the baseband signal in the transmitter and use the &quot;audio out&quot; as the output in the receiver. The RF modulation scheme seems to be a &lt;strong&gt;NBFM&lt;/strong&gt; and the bandwidth of their audio input and output are about &lt;strong&gt;2kHz-4kHz&lt;/strong&gt;. The bit rate should be &lt;strong&gt;more than 64bits/s&lt;/strong&gt;. I think there are many systems that work like this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was plan to use &lt;strong&gt;64-MSK with RS code and interleaving&lt;/strong&gt; at first but one of my workmate insist &lt;strong&gt;DSSS+BPSK without any coding&lt;/strong&gt;. Personally, I don't think DSSS is a good choice in this situation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to know who is right? Which one is better and why. Are there any mature schemes that I can choose?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks. &lt;/p&gt;&#xA;" OwnerUserId="6040" LastEditorUserId="6040" LastEditDate="2016-02-02T02:05:44.580" LastActivityDate="2016-02-02T02:05:44.580" Title="Is it suitable to use DSSS in a narrow-band channel for a power-starved system" Tags="&lt;digital-modes&gt;&lt;cw&gt;&lt;fm&gt;" AnswerCount="0" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5756" PostTypeId="2" ParentId="5754" CreationDate="2016-02-01T19:48:03.807" Score="4" Body="&lt;p&gt;It will be mostly useless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every electrical circuit has current flowing in a loop. When a circuit contains an antenna, there are always, in some form, &lt;em&gt;two halves&lt;/em&gt; to the antenna, which have opposite voltages and currents (and the current loop is completed by &quot;empty space&quot;, &lt;a href=&quot;https://ham.stackexchange.com/questions/3502/are-antennas-circuits/3511#3511&quot;&gt;much like in a capacitor&lt;/a&gt;). When you see an antenna that looks like one wire sticking out, there is actually something else forming the other half, usually being whatever the circuit ground is (possibly a metal casing or a power supply ground).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you have there is an unusual form of &lt;em&gt;ground plane antenna&lt;/em&gt;, where a plane of metal (or approximation by wires) is used to form that other half. If you leave it disconnected, then you're removing it from the circuit (except for some very small amount of capacitive coupling) and the coax shield (and, in part, whatever it's attached to) will be pressed into service as the other half of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is undesirable because it means the antenna does not have stable characteristics (depends on metal near the coax), is not overall as far away from obstructions, and because noise from your receiver or other equipment that is conducted along the coax shield will be added to the received signal. (This last effect is not truly eliminated unless you also have a choke/unun at the feed point.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(By the way, the instructions describe as a series of dipole antennas. Note that an ordinary dipole, with a feed point at the midpoint of the wire, does &lt;em&gt;not&lt;/em&gt; require any sort of ground or counterpoise. This antenna has its feed point at one end of the wire.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-02-02T17:45:52.973" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5757" PostTypeId="2" ParentId="5750" CreationDate="2016-02-02T13:56:35.830" Score="2" Body="&lt;p&gt;It doesn't matter much. The tuning of a dipole is affected by many things:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;ground conductivity&lt;/li&gt;&#xA;&lt;li&gt;height above ground&lt;/li&gt;&#xA;&lt;li&gt;feedline placement&lt;/li&gt;&#xA;&lt;li&gt;trees, towers, gutters, etc around the antenna&lt;/li&gt;&#xA;&lt;li&gt;thickness of the wires&lt;/li&gt;&#xA;&lt;li&gt;(unique to fan dipoles) interaction of the multiple wires in the &quot;fan&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;As such, the extra inch or two of wire introduced by a droop in the wires isn't going to introduce any significant change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usual practice is to cut the wires a bit long, measure the antenna impedance (or SWR), then make them shorter until the antenna is sufficiently tuned. This &quot;estimate, measure, adjust&quot; approach is much more practical than trying to account for all the variable factors above.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-02-02T13:56:35.830" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5758" PostTypeId="2" ParentId="5742" CreationDate="2016-02-04T00:12:19.393" Score="4" Body="&lt;p&gt;Receiving is all about signal to noise ratio. If most of the noise is generated outside of the receiver (as it is on most HF bands) then matching the antenna system to the receiver increases the signal and the noise by the same amount so you have no change in the signal to noise ratio. Thats why the mismatched random wire works so well on HF receivers and impedance match is not so important in that case. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF/UHF is a different story because the majority of the noise is usually generated by the internal receiver circuits. In that case matching the antenna system to the receiver input impedance does make a difference because it increases the signal without causing a corresponding increase in noise so the signal to noise ratio improves and you copy better.&lt;/p&gt;&#xA;" OwnerUserId="6116" LastActivityDate="2016-02-04T00:12:19.393" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5759" PostTypeId="1" CreationDate="2016-02-03T16:45:26.743" Score="1" ViewCount="50" Body="&lt;p&gt;My amateur radio uses 1925-3-2 relays on the low pass filter board to select &#xA;bands. This relay is no longer available. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there an alternative I can use? Or something?&lt;/p&gt;&#xA;" OwnerUserId="6128" OwnerDisplayName="Dave nf4r" LastEditorUserId="9493" LastEditDate="2017-10-26T20:59:29.797" LastActivityDate="2017-10-26T20:59:29.797" Title="Relay cross reference for 1925-3-2" Tags="&lt;electronics&gt;&lt;repair&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5760" PostTypeId="1" AcceptedAnswerId="5795" CreationDate="2016-02-04T06:45:54.070" Score="5" ViewCount="396" Body="&lt;p&gt;I am about 870 miles and 16 degrees due west of WWVB at Ft. Collins, CO. WWVB transmits at a frequency of 60 KHz. At this distance I should be getting the signal reflected from the ionosphere. If I assume the ionosphere layer I'm getting the bounce off of is sixty-two miles high and it's a straight line between here and WWVB, using Tangent = Opposite÷Adjacent (T=62÷435), I get an incoming angle of 8.1°. Since I'm 16° away, I'm tilted 8° away from the midpoint between here and WWVB, which gives me an incoming angle of only 0.1°. This seems counterintuitive.&lt;br&gt;&lt;br&gt;The reason I ask this is because I have a so-called atomic clock on my kitchen counter that does not get a signal unless I move it away from the solid patio cover next to the kitchen, but since the signal is at such a low angle, the patio cover shouldn't matter. I only need to move it a few feet for it to get a signal.&lt;br&gt;&lt;br&gt;So is my math right, or am I missing something?&lt;br&gt;&lt;br&gt;&lt;b&gt;Edit:&lt;/b&gt; I'm not sure where I got the 62-mile figure, but a Wikipedia article I found and a PDF state the altitude of the F Layer starts at 93 miles. With that figure plugged into the formula, it gives me an incoming angle of slightly more than 4°, which is probably just enough (can't measure it precisely) for the patio cover to come into play.&lt;/p&gt;&#xA;" OwnerUserId="6118" LastEditorUserId="6118" LastEditDate="2016-02-04T19:22:46.090" LastActivityDate="2016-02-15T15:36:23.373" Title="Incoming angle of radio signal reflected off of ionosphere" Tags="&lt;propagation&gt;&lt;ionosphere&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5761" PostTypeId="1" CreationDate="2016-02-04T15:08:04.090" Score="2" ViewCount="519" Body="&lt;p&gt;I have a Wouxun KG-699E and I am trying to connect it to audio connectors in a PC. Right now, I have connected it by this &lt;a href=&quot;http://www.qsl.net/g4wpw/th78a.jpg&quot; rel=&quot;nofollow&quot;&gt;schematic&lt;/a&gt; (it uses Kenwood-type of headset connector) where instead of external Speaker and external MIC is 3,5mm TRS jacks (only Tip and Sleeve connected). The one from ext. speaker leads to MIC hole in the external soundcard and the one from ext.MIC leads to the speaker hole in the external soundcard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can listen to the signal received by the Wouxun, but when I engage PTT connection it starts to transmit &quot;empty&quot; signal (no voice, just like you hold PTT and don't say anything). Even though I know that there is signal going from soundcard (I have a jack splitter and headphones).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is probably something I missed in the wiring, but I can't figure out what it is. Or, can I use the USB programming cable directly to broadcast/listen to frequency? &lt;/p&gt;&#xA;" OwnerUserId="6122" LastEditorUserId="76" LastEditDate="2016-02-04T18:06:36.600" LastActivityDate="2016-07-01T20:58:20.120" Title="Connecting Wouxun KG-699E to computer sound card audio input/output" Tags="&lt;diy&gt;&lt;ht&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5762" PostTypeId="2" ParentId="3606" CreationDate="2016-02-04T17:47:57.270" Score="-2" Body="&lt;p&gt;Shifting your impedince up or down feed point, i belive changes nth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you imagine the current flows throw the wire,it will face two impedences.one is Z and one is R from the wire itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Putting R Bfore Z or Z BEFORE R wont change nth in a series connection.mathmaticaly speaking.&lt;/p&gt;&#xA;" OwnerUserId="6124" LastActivityDate="2016-02-04T17:47:57.270" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5763" PostTypeId="2" ParentId="5445" CreationDate="2016-02-05T17:43:37.510" Score="3" Body="&lt;p&gt;From the symptoms you state of not being able to hear transmissions from identical setups only 4 miles from each other, and then being able to have one person receive with the rubber duck antenna, it tells me your J-Pole antennas are not behaving ideally on the frequency you choose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider that an antenna like a J-Pole has about a 10MHz bandwidth in the 70cm Ham band.  The rubber duck antenna has a broader bandwidth.  Prove this to yourself by comparing reception of your NOAA weather broadcast station using first the J-pole and then the rubber duck.  I'll bet you can receive it with the rubber duck.  The NOAA broadcast is about 162.5MHz which is far above the 2M Ham band yet the rubber duck will work and very likely the J-pole tuned for the Ham band will not work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider that the two antennas may have their band sweetspot tuned to some frequency 20MHz away from your transmitting frequency as an example.  The antenna itself may contribute a lot of loss.  You begin by looking at your feedline loss but maybe at the transmit frequency you have a very high SWR meaning that most of the power is reflected back from the antenna at your chosen frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Invest in an SWR meter and measure the SWR of your J-pole at your desired frequency.  Compare the two J-Poles.  You should be able to see an SWR between 1.0 and 1.5 and if you see some crazy high SWR &gt;5 then you can blame the J-pole instead of the feedline.  You may be able to &quot;hunt&quot; for a frequency that your J-pole likes by using your SWR meter, meaning a frequency that the J-pole is tuned to work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also consider that any obstructions like trees and houses and especially hills between you and your friend will contribute most of the loss you see.  Fighting this problem by desiring more output wattage can be a losing battle.  If you have reasonable line of sight between the two radios then likely the rubber duck antennas will work for you with only 1 Watt.  You can prove this to yourself by driving to hills that are within line of sight and see how well it works.&lt;/p&gt;&#xA;" OwnerUserId="6113" LastActivityDate="2016-02-05T17:43:37.510" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5764" PostTypeId="2" ParentId="4932" CreationDate="2016-02-05T18:39:26.010" Score="4" Body="&lt;p&gt;The BF-888S radios have a 16-channel knob on the top and no LCD display nor a number keypad.  The BF-888S is marketed all over the world for use mostly in licensed commercial operation or licensed Amateur Radio.  The BF-888S can be programmed to use frequencies in the range of 400 to 470MHz which nicely permits programming the radios for the 70cm Amateur band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being a &quot;world&quot; radio you should not expect them to come from the factory with the USA's FRS and GMRS frequencies pre-programmed.  They come programmed from the factory with some default frequencies that do not match any FRS and GMRS channel frequencies. The Midland radios you mention are marketed in the USA for the un-licensed FRS frequencies and licensed GMRS frequencies.  Find details in the manual for the Midland LTX650 explaining which channels require the GMRS license (most consumers sadly ignore the GMRS license requirement).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The BF-888S can be programmed to receive FRS and GMRS frequencies.  The BF-888S is not legal for transmitting on FRS (having a removable antenna and up to 2 Watts of power) and not legal on GMRS (simply not type-certified by the USA FCC for GMRS use).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good advice in the USA is to get a HAM technician license.  It is a matter of taking a very simple 35 question test which would cost you up to $15 to take.  The license lasts for ten years and can be renewed for free.  Then take the BF-888S radios and program them for your available HAM repeater frequencies and you will be very happy with the BF-888S radios.  The BF-888S radios have very simple operation with no controls other than the 16-channel knob and the volume knob and a push-to-talk button, making them an amazingly good value to use on the 70cm Amateur Radio Band and capable of 2 Watt power.&lt;/p&gt;&#xA;" OwnerUserId="6113" LastEditorUserId="6113" LastEditDate="2016-02-07T16:38:22.860" LastActivityDate="2016-02-07T16:38:22.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5765" PostTypeId="1" CreationDate="2016-02-05T18:42:15.483" Score="2" ViewCount="1063" Body="&lt;p&gt;Some RF receivers accept square wave clock reference (10MHz, 1pps, etc) and others accept sine wave.  Most of the GPS do devices are outputting 10MHz sine wave timing signals.  &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Are there practical or theoretical differences in the way these timing signals will contribute to the accuracy of time-stamped output samples?  Which one is better?&lt;/li&gt;&#xA;&lt;li&gt;What is the best way to convert the sine wave output of the GPS devices to a square wave without impacting accuracy of the timing signal?&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;My goal is to have time-stamped output samples from my receiver/ADC that are as close as possible (&amp;lt;2ns error) to the timing on the GPS do.  Will a conversion ruin this?&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/HackRF-One#external-clock-interface-clkin-and-clkout&quot; rel=&quot;nofollow&quot;&gt;https://github.com/mossmann/hackrf/wiki/HackRF-One#external-clock-interface-clkin-and-clkout&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.aventasinc.com/datasheets/7820Nov132.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.aventasinc.com/datasheets/7820Nov132.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.jackson-labs.com/index.php/products/firefly_iia&quot; rel=&quot;nofollow&quot;&gt;http://www.jackson-labs.com/index.php/products/firefly_iia&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="6132" LastEditorUserId="13" LastEditDate="2016-02-07T14:28:14.417" LastActivityDate="2016-02-07T14:28:14.417" Title="Square wave vs. sine wave timing reference" Tags="&lt;receiver&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5766" PostTypeId="2" ParentId="5765" CreationDate="2016-02-05T19:06:56.967" Score="1" Body="&lt;p&gt;In my experience, instruments that are meant to use a 10MHz reference clock signal input have their own local oscillator of much higher frequency and the 10MHz serves to keep the local oscillator phase locked to the 10MHz signal.  Ultimately then the precision of any timing obtained is up to the precision of the instrument and depends little on the 10MHz signal being either a sine or more like a square wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think of the 10MHz reference input as keeping the local oscillator from drifting at a slow rate like one second per day.  Instead the local oscillator stays locked in phase to the reference input.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most important is when using two separate instruments and having them share a common 10MHz reference signal.  This keeps the two instruments in phase with each other.  Otherwise depending upon the stability of the separate local oscillators there will be some observable drift over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In summary, seeking 2ns resolution, do not look to the 10MHz reference to give you the precision.  Instead the high precision will come from whatever clock is used as the internal local clock in the device.  The benefit of using the 10MHz reference from GPS then is that you are locked to the very stable atomic clocks used in GPS so you will not see your local oscillator drift slowly over days and months and years.&lt;/p&gt;&#xA;" OwnerUserId="6113" LastActivityDate="2016-02-05T19:06:56.967" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5769" PostTypeId="1" CreationDate="2016-02-06T16:00:20.370" Score="3" ViewCount="5863" Body="&lt;p&gt;I can't find my general class license. I want to apply for a vanity call sign (my call sign when I was 16 years old) but I don't know the expiration date of my current license. Is there some way to find the expiration date online?&lt;/p&gt;&#xA;" OwnerUserId="6139" LastEditorUserId="4665" LastEditDate="2016-11-04T17:57:30.543" LastActivityDate="2019-08-06T02:05:56.860" Title="How do I find expiration date of my misplaced US ham license?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5770" PostTypeId="2" ParentId="5769" CreationDate="2016-02-06T16:15:30.257" Score="7" Body="&lt;p&gt;Go to &lt;a href=&quot;http://wireless2.fcc.gov/UlsApp/UlsSearch/searchLicense.jsp&quot; rel=&quot;noreferrer&quot;&gt;the FCC Universal Licensing System (ULS) web site and search for your license&lt;/a&gt;. You can search by call sign, name (in &lt;em&gt;lastname, firstname initial&lt;/em&gt; order), or address (in the advanced search form). It will show you the expiration date and current status.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your license has already expired, you can submit a renewal &lt;a href=&quot;http://www.arrl.org/renewals&quot; rel=&quot;noreferrer&quot;&gt;up to two years afterward&lt;/a&gt;. From a review of the form, it looks like you can combine a renewal with a vanity call sign application, but I'm not sure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If two years has passed since the expiration of your license, you will have to take the Technician exam over again, but &lt;a href=&quot;http://www.arrl.org/exam-element-credit&quot; rel=&quot;noreferrer&quot;&gt;you can get exam credit for your previous General license&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that there is a very good chance that &quot;your call sign when you were 16&quot; has already been claimed by someone else if it is shorter than modern sequential call signs; short vanity call signs are in high demand. The first thing you should do is search for &lt;em&gt;that&lt;/em&gt; call sign in the ULS, even though it's not the one you currently hold, to check if it is available.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-02-06T18:42:00.530" LastActivityDate="2016-02-06T18:42:00.530" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5771" PostTypeId="2" ParentId="5769" CreationDate="2016-02-06T16:19:08.580" Score="3" Body="&lt;p&gt;For licenses in the USA you can go to this site&#xA;&lt;a href=&quot;http://wireless2.fcc.gov/UlsApp/UlsSearch/searchAmateur.jsp&quot; rel=&quot;nofollow&quot;&gt;FCC ULS&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Scroll down the page to the entry for entering your call sign, then scroll to the bottom and click search.  It should find your license no matter if it is current or already expired.  You can click the call sign it finds to see all of the detail including your FRN number you can use to attempt to renew the license.  The license should be good for ten years and you have a two year grace period after that for renewal.  Renewal can be done online and costs nothing.&lt;/p&gt;&#xA;" OwnerUserId="6113" LastActivityDate="2016-02-06T16:19:08.580" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5773" PostTypeId="2" ParentId="5761" CreationDate="2016-02-08T16:06:31.790" Score="0" Body="&lt;p&gt;This is not a DIY solution but I thought I would comment since you are looking for a USB direct to audio. You may want to consider the Tigertronics SingaLink USB, it has a cable to support Kenwood HTs and supports audio sense feature for PTT. I successfully got this working with a Raspberry PI and a Kenwood TH-F6A so I needed the sound card interface. Unfortunately, this solution costs more than the radio.&lt;/p&gt;&#xA;" OwnerUserId="6148" LastEditorUserId="6148" LastEditDate="2016-02-11T22:46:58.593" LastActivityDate="2016-02-11T22:46:58.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5774" PostTypeId="1" CreationDate="2016-02-08T20:25:23.457" Score="1" ViewCount="578" Body="&lt;p&gt;I have a very difficult antenna design/installation challenge. I need to install an VHF antenna (118 to 140 MHz) into &lt;a href=&quot;https://www.google.com/imgres?imgurl=http://windward-performance.com/wp-content/uploads/2012/02/DuckHawk-Poster-20-X-30-Rev2-300-dpi.jpg&amp;amp;imgrefurl=http://windward-performance.com/duckhawk/media-gallery/&amp;amp;h=9000&amp;amp;w=6000&amp;amp;tbnid=z2rgsFXDI25YdM:&amp;amp;tbnh=160&amp;amp;tbnw=106&amp;amp;docid=7rnneNdqgMZfbM&amp;amp;itg=1&amp;amp;usg=__SVUKC2FeHJm9O5-f4pcXdjbpZiw=&quot; rel=&quot;nofollow&quot;&gt;a nearly all carbon fiber glider&lt;/a&gt;. The radio provides 5 watts and 50 ohm, and most signals of interest are vertically polarized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since this is a glider, and aerodynamic efficiency is the highest priority, mounting an antenna external to the hull is not considered an acceptable option. So the options seem to be:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Mount a rubber ducky style antenna in the lower front of the aircraft, below the cockpit center-line, which is the only place on the aircraft that is fiberglass. But the maximum vertical height in this region is only about 5 inches and it there is a carbon fiber bulkhead above and behind this small zone.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Mount a rubber ducky style antenna in the upper half of the cockpit, where the antenna would at least have some line of sight forward, to the sides, and upward. This would at least allow the antenna to be mounted fully vertically.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I've considered a full wave loop around the outside of the fuselage. But my research into this says that even if the antenna is isolated from carbon fiber skin with some dielectric (like Kapton tape), I'll end up with RF coupling and reflections that cancel most of the signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So, with all of this said, I'm wondering if there is an approach I'm missing, or if this is just a bad situation and an electrically short monopole antenna is about the best that could be done.&lt;/p&gt;&#xA;" OwnerUserId="6151" LastEditorUserId="76" LastEditDate="2016-02-08T20:34:25.507" LastActivityDate="2016-02-09T16:41:19.900" Title="Airband VHF antenna challenge" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;mobile&gt;&lt;vhf&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5775" PostTypeId="2" ParentId="5676" CreationDate="2016-02-09T07:29:32.607" Score="2" Body="&lt;p&gt;Try reducing the power and see if that helps.  If it lets you transmit longer then the battery needs to be replaced.  If it shuts off right away at low power then you may have a bad final or other malfunction in the rig itself.  If you suspect the battery after this test try to borrow one and see if it does the same thing rather than buy a new one.  Unless you could use a second battery.  Second option is the 12V battery adapter.  Always a good thing to have for long nights of radio contacts at high power.  It is cheaper than a new battery.&lt;/p&gt;&#xA;" OwnerUserId="5922" LastActivityDate="2016-02-09T07:29:32.607" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5776" PostTypeId="2" ParentId="5761" CreationDate="2016-02-09T07:34:47.957" Score="0" Body="&lt;p&gt;Did you try incresing the output volume on the computer?  Play with the audio controls and see if that changes anything.  You may want to keep the headset on the desk for this until you see if it works and at what sound level.&lt;/p&gt;&#xA;" OwnerUserId="5922" LastActivityDate="2016-02-09T07:34:47.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5777" PostTypeId="2" ParentId="5591" CreationDate="2016-02-09T07:59:49.517" Score="1" Body="&lt;p&gt;They may not be transmitting a tone at all.  I had this with my Baofeng and a local club repeater I wanted to access.  They only receive the tone but do not transmit it because then others would know what it is and could use it without paying dues to the club.  The school may be of the same mind.&lt;/p&gt;&#xA;" OwnerUserId="5922" LastActivityDate="2016-02-09T07:59:49.517" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5778" PostTypeId="1" CreationDate="2016-02-09T08:18:01.247" Score="1" ViewCount="279" Body="&lt;p&gt;I was given a TS-440 that was lightly used.  Being old it does need some work.  This week I am doing the &quot;Button Bounce&quot; fix.  Several of the buttons were bouncing so I pulled the component and cleaned up the pads and disks, then remounted them.  All work well except the scan button.  When I press it and release I get three quick beeps.  If I press and hold it I get one beep on the press and three on the release.  It did this when I got the rig and fixing the bounce problem did not change it.  I know this is not likely to be the pad or disk as I did them all at once the exact same way.  Does anybody know what this might be?  Besides frustrating.&lt;/p&gt;&#xA;" OwnerUserId="5922" LastEditorUserId="76" LastEditDate="2016-02-09T16:26:38.193" LastActivityDate="2016-03-18T15:36:29.140" Title="Kenwood TS-440SAT Button Bounce or error code?" Tags="&lt;kenwood&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5779" PostTypeId="1" CreationDate="2016-02-09T08:23:35.483" Score="0" ViewCount="267" Body="&lt;p&gt;Inside my TS-440 &amp;amp; TS-930 are (former) foam pieces.  They have disintigrated into a pile of dust in the bottoms of the rigs.  I am more than sure that Kenwood does not have fresh stock off these.  Can anyone tell me what type of foam it was and where it was used in each rig?  Maybe even a supplier?&lt;/p&gt;&#xA;" OwnerUserId="5922" LastActivityDate="2017-03-30T13:53:08.397" Title="Kenwood TS-440SAT &amp; TS-930SAT Refurbishing" Tags="&lt;kenwood&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5780" PostTypeId="1" CreationDate="2016-02-09T15:16:05.067" Score="0" ViewCount="280" Body="&lt;p&gt;When I turn the VFO on my Kenwood TS-440 it changes the frequency in 10Hz steps.  One full rotation changes it by 1kHz.  There is a modification (by cutting a diode lead) to change the frequency DISPLAY resolution but not the tuning resolution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am hoping someone has a way to change the VFO by 10x.  So that it moves in 100Hz steps.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would also be content with 1kHz steps if I can then disable the mod once I got close to the desired frequency.  I was thinking an external switch connected to the unused connector (ACC3 is a RCA connector) on the back of the rig would be perfect so no other case modification is performed.&lt;/p&gt;&#xA;" OwnerUserId="5922" LastActivityDate="2016-03-18T17:37:39.253" Title="Kenwood TS-440SAT Change VFO Resolution?" Tags="&lt;diy&gt;&lt;kenwood&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5781" PostTypeId="2" ParentId="5774" CreationDate="2016-02-09T16:24:55.017" Score="0" Body="&lt;p&gt;A duck, with a guide wire to prevent bending, mounted forward of the vertical fin and attached to a counterpoise might do the trick.  Depending on the height of fin you may be able to get a full 1/4 wave with minimal drag.  I suggest forward of the fin for two reasons.  First, The air is going to drag at that point anyway, maybe this will provide a pre-break.  I don't know aeronautics any better than I do brain surgery and you do not want me doing that.  Second, the fin will offer the least signal blockage, only a few degree from the aft area.  The counterpoise should overcome the effects of being so close to the carbon fiber of the fin with a minimal increase in weight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an added thought, a proper 1/2 wave whip antenna can provide up to an 11dB gain and should be about 43.5 inches or 1.1 meters.  The dB gain could also serve to counter the carbon fiber concerns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am very interested in hearing your thoughts, and any others, on these ideas.  Please provide any calculations that may allow me to better visualize the problem and adjust any further thoughts on the matter.  I am intrigued by the idea and would love to work the issue as a good mental exercise, at a minimum.  I know there is an optimal solution.&lt;/p&gt;&#xA;" OwnerUserId="5922" LastEditorUserId="5922" LastEditDate="2016-02-09T16:40:02.400" LastActivityDate="2016-02-09T16:40:02.400" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5783" PostTypeId="2" ParentId="5774" CreationDate="2016-02-09T16:41:19.900" Score="3" Body="&lt;p&gt;I wouldn't worry too much about polarization. If you are 45 degrees off vertical, that's only a -1.5 dB loss, in a theoretical free-space situation. In practice, reflections and absorption from the carbon airframe will alter the polarization anyhow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd consider a &lt;a href=&quot;http://www.antenna-theory.com/antennas/aperture/slot.php&quot; rel=&quot;nofollow&quot;&gt;slot antenna&lt;/a&gt;. This way, the conductivity of the carbon fiber works as part of the antenna, instead of a conductive plane that interferes with the antenna. I'd think the hole in the fuselage where the cockpit attaches would make a dandy slot. You'll probably want to add some copper or aluminium wire or foil around the slot to increase conductivity and reduce losses, since carbon is a relatively poor conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also keep in mind that you aren't limited to quarter wave whips, half wave dipoles, full-wave loops, or other kinds of self-resonant antennas. Just about any wire or loop can be made into an antenna, so I'd focus on making an antenna within the geometry you have, then you can add a matching network to get the right impedance at the feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are just a few ideas. Building a mock-up and then testing performance is usually easier than trying to predict what an antenna will do in complex situations like this. So I'd grab a roll of copper foil and wire and do a couple tests rather than fretting over every detail.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-02-09T16:41:19.900" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5785" PostTypeId="2" ParentId="5760" CreationDate="2016-02-11T00:34:02.310" Score="1" Body="&lt;p&gt;Just wanted to post an answer so that this question wouldn't show up in an unanswered search result.&lt;br&gt;&lt;br&gt;I was using the wrong figures in my calculation. The altitude of the first F layer according to a Wikipedia article &lt;a href=&quot;https://en.wikipedia.org/wiki/Ionosphere&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt; is 150 km (93 mi). Using the correct figure gives me and incoming angle of 12° for a flat plane; subtracting half the angle between here and WWVB (16° total, 8° half) gives me an incoming angle of 4°.&lt;/p&gt;&#xA;" OwnerUserId="6118" LastActivityDate="2016-02-11T00:34:02.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5786" PostTypeId="1" CreationDate="2016-02-12T15:50:54.827" Score="8" ViewCount="654" Body="&lt;p&gt;I'm working on a passively scanned phased array radar project, as a concept and hopefully design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the things that bugs me is that antenna patterning used. The vast majority of radar arrays I've seen employ a hex grid pattern, with a small minority using an orthogonal grid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be the benefits of using a hex grid like this:&#xA; &lt;a href=&quot;https://i.stack.imgur.com/gyNK8.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gyNK8.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As opposed to a square orthogonal grid like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1fbEn.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1fbEn.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6172" LastEditorUserId="6079" LastEditDate="2017-02-21T07:42:12.480" LastActivityDate="2017-02-21T07:42:12.480" Title="Phased Array Pattern" Tags="&lt;phased-array&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5788" PostTypeId="1" CreationDate="2016-02-12T20:58:52.180" Score="3" ViewCount="904" Body="&lt;p&gt;I'm completely new to amateur radio, so please forgive me if this is a silly question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm looking at these devices: &lt;a href=&quot;http://www.ebay.co.uk/itm/391246170894&quot; rel=&quot;nofollow&quot;&gt;Assembled HAM RADIO 40M CW HF QRP Pixie Transmitter Receiver 7.023-7.026MHz DIY on eBay&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I would like to know is how feasible is it to use these CW transceivers to create a (low baud) data connection over, say fifty miles, between two Raspberry Pis?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I appreciate that these transceivers are the absolute cheapest that I could find, but this is the point: I would like this project to be dirt cheap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you know of any links or guides that you could point me at, I would be most appreciative - if you can think of a better, cheaper, way to do this then I'd love to hear about it!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="6175" LastEditorUserId="29" LastEditDate="2016-02-29T10:47:14.727" LastActivityDate="2016-02-29T10:47:14.727" Title="Comms between Raspberry Pis over CW on 40m" Tags="&lt;cw&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5789" PostTypeId="2" ParentId="5788" CreationDate="2016-02-13T00:46:13.887" Score="2" Body="&lt;p&gt;A Raspberry PI (preferrably a model 2) could run &quot;fldigi&quot;, a free open source digital mode software.  You might have to rig up some form of CW keying also&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fldigi can run a multitude of digital modes including CW, PSK and Olivia.  It can also be programmed to transfer email, formatted and pre-canned messages both in keyboard to keyboard and automatic mode. Each transceiver would require a bidirectional  audio interface, such as a low cost USB sound dongle. Pi's only come equipped with audio out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These non-CW modes rquire a SSB transceiver though. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The low cost &quot;Pixie&quot; transceivers only do CW, but could be &quot;keyed&quot; with an cheap transistor using the circuit included in the fldigi documentation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most SSB transceivers are somewhat more expensive, but by using the more advanced digital modes instead of CW, you could greatly improve accuracy and speed in difficult propagation conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might also look at the low cost (~$30) Baofeng (or similar) 2m/70cm HT's that could probably transmit in MT-63 mode with only a microphone and speaker on the Pi held close the the HT. Some FM repeaters might have sufficient bandwidth to give you 50 mile coverage. Otherwise a yagi directional antenna and tower could provide a strong enough signal without a repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;" OwnerUserId="6178" LastActivityDate="2016-02-13T00:46:13.887" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5793" PostTypeId="1" CreationDate="2016-02-14T13:50:12.837" Score="1" ViewCount="237" Body="&lt;p&gt;I listen in a close room.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have &lt;a href=&quot;https://www.google.com.ph/search?q=portable+radio&amp;amp;rlz=1C1CHWA_enPH646PH646&amp;amp;source=lnms&amp;amp;tbm=isch&amp;amp;sa=X&amp;amp;ved=0ahUKEwjtzt3dsffKAhWD5aYKHf4XBkgQ_AUIBygB&amp;amp;biw=1366&amp;amp;bih=643#imgrc=E2lK6Lbf2rE07M%3A&quot; rel=&quot;nofollow&quot;&gt;this&lt;/a&gt; kind of radio, but it doesn't give a clear sound... it has &quot;shhhhhhh&quot; sound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a certain position where it will give out a clear sound but that position is not a good position in the long run.&lt;/p&gt;&#xA;" OwnerUserId="6183" LastEditorUserId="76" LastEditDate="2016-02-14T15:49:52.263" LastActivityDate="2016-02-14T16:26:51.327" Title="How will I improve my portable radio reception" Tags="&lt;antenna&gt;&lt;receiver&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5794" PostTypeId="2" ParentId="5793" CreationDate="2016-02-14T15:59:16.460" Score="2" Body="&lt;p&gt;The noise you hear is most likely the result of the signal being weak inside the room.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to receive the signal better without relocating the radio you need to relocate the antenna — that is, use an add-on antenna. This can be as simple as taking a piece of wire and fastening one (bare) end to the telescoping antenna on the radio, then stringing the rest of it towards and across the space where you get better reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(You can use any kind of wire you have available, but for convenience, thin, stranded is best. Thin so that it is lightweight, stranded so that it is flexible and doesn't break easily. But you might also use solid wire if you need it to stand up by itself instead of being supported at the end, for example.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;@kyukzkie I assume you don't mean for a radio transmitter, but just for &lt;em&gt;transferring&lt;/em&gt; the signal. The type of wire you use doesn't matter electrically. For &lt;em&gt;convenience&lt;/em&gt;, you . And don't bother with aluminum foil shapes or anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, antenna design is complex, but for basic &lt;em&gt;receiving&lt;/em&gt; there's no need to work from theory and you can just try rearranging the wire until something helps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want something more designed than a piece of wire, you can get a piece of wire with a connector on the end and a winder, such as the &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B000023VW2&quot; rel=&quot;nofollow&quot;&gt;Sangean ANT-60&lt;/a&gt;. The clip supplied with it attaches to the end of a standard telescoping antenna, or you can plug it directly into an external antenna jack if your radio has one. (If your radio is genuinely a Kaito KA2100 as the picture you linked, then you will need an adapter to its type of jack.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-02-14T16:26:51.327" LastActivityDate="2016-02-14T16:26:51.327" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5795" PostTypeId="2" ParentId="5760" CreationDate="2016-02-15T15:36:23.373" Score="2" Body="&lt;p&gt;Calculating the angle of an incoming signal traveling via skywave is not nearly so straight forward as you might presume, and there are two primary reasons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ionosphere is highly variable, and also exists not as a single impermeable layer, but rather a diffuse region several hundred kilometers thick. At any given moment, two signals of significantly different frequency will likely appear to 'bounce' from two very different altitudes depending on ionospheric conditions, transmitter antenna characteristics, and frequency of the waves. The height at which the signal appears to reflect is referred to as the &quot;virtual height&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In reality, the signal is refracting over a relatively large physical distance, gradually bending back toward earth as it moves through the ionosphere. The distance over which the refraction takes place is dependent primarily on frequency, with higher frequency requiring a longer path. This means that if you have a 10MHz and a 20MHz transmitter with identical antennas, the 20MHz signal will have a longer single hop range, so long as the maximum usable frequency at the point where your signal meets the ionosphere is greater than 20MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Things are further complicated by the highly variable nature of the ionosphere. Depending on time of day, solar conditions, and the state of the earth's magnetic field, the varying layers of the ionosphere can not only change altitude by more than 50% &lt;a href=&quot;https://www.ngdc.noaa.gov/stp/iono/ionosonde/WP937_2009274.GIF&quot; rel=&quot;nofollow&quot;&gt;over the course of a single day&lt;/a&gt;, but they can even merge with other layers, or almost disappear completely. The F1 and F2 layers merge during local night to form a single layer, and the D and E layers are dramatically weaker or almost absent, for example. The F1 layer might begin at 150km at 10am today, but it could start somewhere above 200km at 10am tomorrow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The exact range of a single hop also depends on takeoff angle from the transmitting station, as a wave with a frequency of 5MHz for example, is likely to return to the earth even if radiated nearly straight up, just as it would if it were radiated at 4 degrees above the horizon. Waves can also make multiple trips between the surface and the ionsphere, and there are times when two short hops can result in good reception, while a single longer hop may not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case, you are well within range of ground wave propagation (nearly the entire continental US is for at least part of the day). At 60KHz, and a whopping 70kW ERP, the night time ground wave range is &gt;1,000 miles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Skywave propagation on VLF is finicky stuff. The ionosphere and the surface of the earth can form a waveguide that a VLF signal propagates along quite well, but this can vary depending on time of day and ionospheric conditions, as sometimes the altitude of the layers is not optimal for a particular frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, if this were indeed a case of skywave 'shadowing' from a porch awning or other object in your home, the size of the shadow would depend on the electrical size of the object that's creating it to the wave that it's blocking. In the case of a 60kHz wave, an object would have to be absolutely &lt;strong&gt;enormous&lt;/strong&gt; to create appreciable attenuation, as the wavelength is almost exactly 3 miles long. That means significant shadowing might require an object to be several hundred feet along at least one axis. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;By comparison, the low end of AM broadcast at 500kHz is about 1 mile, and FM radio at 100MHz is just 3 meters. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moving the object just a foot or two and seeing marked improvement, as you describe in the comments above, all but rules out skywave shadowing on this frequency. It is far more likely that you've got an issue with local radiated or  coupled interference that's rendering your WWVB receiver deaf.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-02-15T15:36:23.373" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5797" PostTypeId="1" CreationDate="2016-02-17T00:20:46.467" Score="3" ViewCount="4353" Body="&lt;p&gt;I've been poking around the internet on how to make a Yagi for my HT. I understand all the math for cutting directors and reflectors to length and placing them at the correct spacing for 146.52 mHz. However, I keep finding different descriptions on how to make the driven element, or worse, no description at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I make the driven element? More importantly, how do I make sure that the antenna is 50 Ohms? Preferably, I'd like to not solder.&lt;/p&gt;&#xA;" OwnerUserId="6099" LastActivityDate="2017-04-20T22:17:20.417" Title="How do I construct the driven element of a yagi?" Tags="&lt;antenna-construction&gt;&lt;2m-band&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5798" PostTypeId="2" ParentId="5797" CreationDate="2016-02-17T02:49:21.227" Score="1" Body="&lt;p&gt;Pulling it off without soldering will be tricky, your only option will probably be to get a chunk of coax with the connectors already on it, cut off a connector, then use bolts and crimp on lugs to connect the coax to the antenna element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're finding multiple descriptions of how to do it because there are multiple ways of doing it depending on the intended use of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;You can feed it directly like a dipole, splitting the driven element in two and connecting one side to the coax shield and one to the center conductor of the coax. It will not be possible to get maximum bandwidth &lt;em&gt;and&lt;/em&gt; maximum gain with this method, though you should be able to get a reasonable compromise that works on all of 2 meters. 70cm would be much trickier.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You can feed it with a gamma match. This gives a wide match and has the advantage of also acting as a balun. They're finicky to make, and would be very difficult to tune without an SWR meter or antenna analyzer&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You can feed it with a hairpin match. Similar problems to the gamma match, but similar advantages.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Personally, I'd recommend finding a design that specifically calls for a directly driven element. Google for NT1K Tape Measure Yagi for a good project write-up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option if you don't need portability would be to ditch the yagi and build a cubical quad instead. There are many calculators available online that give you all the required dimensions, and they tend to be a bit more forgiving on the SWR front. They also provide more gain per element than a yagi, at least until you get out to about 7 elements. They can be made very inexpensively out of PVC or wooden dowel and 1&quot;x1&quot; hardwood lumber for the boom and wooden dowels for the spreaders.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-02-17T02:49:21.227" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5799" PostTypeId="2" ParentId="5778" CreationDate="2016-02-17T14:47:50.427" Score="1" Body="&lt;p&gt;Have you tried this in memory, program, and vfo mode? If there are no memories saved, it may squawk at you because there's nothing to scan. I suspect it will do the same if you try to scan in 'program' mode without the lower and upper frequency limits saved in memory channels 6 and 7 respectively for PG.S-1 and 8 and 9 for PG.S-2, though the manual doesn't say that for sure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would think they would program something generic in to the memories at the factory so that the scan function works right out of the box, but I'm not sure about that. It's also possible that the program scan channels aren't protected and an MCU reset at some point in the past cleared them as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manual doesn't say anything at all about it having an unbounded VFO mode scan, so the beeps might just mean &quot;That doesn't exist&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://inform3.kenwoodusa.com/Manuals/TS-440.pdf&quot; rel=&quot;nofollow&quot;&gt;Here's a link to the manual in case you don't have one&lt;/a&gt;, the bit you want is on Pages 17 and 18.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-02-17T14:47:50.427" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5800" PostTypeId="2" ParentId="5780" CreationDate="2016-02-17T14:59:31.077" Score="2" Body="&lt;p&gt;Just give the knob a good flick in the direction you want to go. The radio automatically switches to 1kHz tuning when the knob is moving at a fast pace.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://inform3.kenwoodusa.com/Manuals/TS-440.pdf&quot; rel=&quot;nofollow&quot;&gt;Manual page 8, paragraph 22&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-02-17T14:59:31.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5801" PostTypeId="2" ParentId="5027" CreationDate="2016-02-17T22:15:40.970" Score="1" Body="&lt;p&gt;I'm guessing by crossed Yagi, you mean two Yagis with a 90 degree phase shift, creating a circularly polarized Yagi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A circularly polarized antenna does not get you any gain. If the other end is linearly polarized, then there's a -3dB &lt;em&gt;loss&lt;/em&gt;. The benefit is the loss is same no matter the orientation -- horizontal, vertical, or something in between.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use circularly polarized antennas on each end, and they are the same sense (right-hand or left-hand), then you avoid the 3dB loss. That's not the same as adding 3dB to your link budget. The link budget would be the same if you used two vertically polarized antennas on each end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were adding a preamplifier to a circularly polarized antenna, I would add it after they have been combined. A couple reasons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the two preamps may have different phase shifts or gain, which would mess up the phasing of your antenna.&lt;/li&gt;&#xA;&lt;li&gt;the impedance the preamp sees (in input or output) might not be 50 ohms, and that may not work so well.&lt;/li&gt;&#xA;&lt;li&gt;the preamp will probably alter the impedance seen by the T, and depending on just what kind of T you have, that may mess it up.&lt;/li&gt;&#xA;&lt;li&gt;again depending on what you are using for the T, the isolation between the antennas may not be great, and this will result in one preamp trying to drive against the output of the other, which could result in oscillations or failure.&lt;/li&gt;&#xA;&lt;li&gt;preamps generate noise, and two preamps generates more noise.&lt;/li&gt;&#xA;&lt;li&gt;preamps cost money, and two preamps cost more money.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-02-17T22:15:40.970" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5802" PostTypeId="1" CreationDate="2016-02-18T01:36:08.963" Score="1" ViewCount="105" Body="&lt;p&gt;Duplexers are very annoying, you have to go up to the site with your service monitor and tune it up just to switch the frequency that it operates at. They are a pain to tune, and are designed to stay on the frequency you wish to operate for a long time. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In many cases, I would find it very advantageous to have a duplexer which would automatically tune to the right frequency. Ex. Full duplex mobile setups, frequency agile repeaters, and full duplex digital links. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are such devices made? I am sure the military has designed something that would do the trick. If so, how do these devices work? Is it simply a motor changing the physical shape of the cavity, or something more complicated? &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8713" LastEditDate="2018-05-30T15:36:12.923" LastActivityDate="2018-05-30T15:36:12.923" Title="Frequency Agile Duplexer" Tags="&lt;duplexer&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5804" PostTypeId="2" ParentId="5802" CreationDate="2016-02-18T14:25:11.373" Score="3" Body="&lt;p&gt;I've got a bit of knowledge of military radio systems. The military is not especially fond of ground based repeater systems, especially in any environment where they would need to be mobile, partially for the reasons you mention. They're bulky, finicky and take time to set up. More importantly though, losing one to enemy action or just bad luck instantly results in chaos as troops a) realize it immediately and react by moving to established contingencies, b) realize it but decide the established contingency is a bad idea for whatever reason and do their own thing c) fail to realize the repeater is dead, and instead spend 30 minutes swearing at their radios. You typically end up with 3 or more groups of people who can talk to the other people in their group...and nobody else, and it takes &lt;em&gt;forever&lt;/em&gt; to get all the ducks back in a row.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On VHF in particular, but also to some extent on UHF, cavities are really the best bang for your buck in almost all scenarios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In theory you could motorize the adjustments on a typical VHF or lower UHF 'can' style duplexer, and build a streaming system that could send the data from a VNA over a network connection to a remote operator who could adjust things accordingly, but that's going to cost thousands (or tens of thousands) of dollars and it sounds like a huge pain in the ass, and it adds more things to the chain that can break. Way cheaper to just pay a tech to go to the site.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option would be to have several duplexers, each tuned to a specific frequency pair, and a coaxial switch to move them in and out of the chain. If you only needed to have 3 or 4 pairs, this would probably still be cheaper, easier, and more reliable than the above remote system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally speaking though, if frequency agility is paramount, cross-band repeat (as used on nearly all hamsats) is far and away the least expensive and least hassle on the repeater end. It just creates a bigger pain in the ass on the user side. With an inexpensive diplexer, you can even use a single antenna for two radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can make the cross-band invisible to the user by having two different locations geographically separated from each other, one for the transmitter, one for the receiver, and use an RF link on a different band (or VOIP) to send received audio to the transmitter site. This way, as far as the user is aware both frequencies in the pair are on the same band, but there's no issue with desense on the receiver. The challenge then becomes creating a roughly symmetrical RX and TX coverage area, otherwise you may have areas where the user can be heard, but can't hear, or can hear the repeater fine, but can't get in to it. Multiple receive sites with a polling system can be a workaround for that.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-02-18T14:25:11.373" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5806" PostTypeId="2" ParentId="5788" CreationDate="2016-02-19T03:01:12.013" Score="0" Body="&lt;p&gt;For one thing you'll need a receiver on each end.  One problem with receiving CW mechanically (I.s., not by humans) is that it's very sensitive to noise.  You'll probably be unhappy with the result.  VHF might be an option in some parts of the country (50 miles is quite a haul for qrp.)  You might be ucky to find a couple digipeaters between end points but if they aren't yours, YMMV.&lt;br&gt;&#xA;But most of all, have fun!&lt;/p&gt;&#xA;" OwnerUserId="5045" LastActivityDate="2016-02-19T03:01:12.013" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5807" PostTypeId="2" ParentId="5788" CreationDate="2016-02-19T09:14:16.670" Score="1" Body="&lt;p&gt;I see no reason why you could not use these devices as some form of low cost CW link - assuming that you can configure fldigi (it's free - and it looks like you are being frugal).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The main issue I would have with this is the &lt;strong&gt;VERY LIMITED&lt;/strong&gt; spectrum they can operate in. Whilst I am UK Ham - I live overseas, and the chance of 2 Khz of the 40M band being free from other users is not realistic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also have propagation issues - in some respects the 60m band could be better with NVIS propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do not see what you have to loose.... sounds like loads of fun/learning/development for absolutely nothing. Wish I had thought of it &lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2016-02-19T09:14:16.670" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5808" PostTypeId="1" AcceptedAnswerId="5813" CreationDate="2016-02-19T19:32:16.857" Score="2" ViewCount="808" Body="&lt;p&gt;I've become very accustomed to the waterfall display on my SDR, especially for digital modes over HF.  I'm thinking about tying into the IF on my IC-718 and connecting to an SDR to add a waterfall to the Icom, but I hesitate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The electronics work isn't the issue.  My hesitation is with regard to what hooking into the IF could do to introduce noise into the IF.  Hence, my question:  What sort of impact would hooking into the IF signal with a short piece of coax have on the overall behavior of the radio?  Are there things that could be done (adding an RF transformer perhaps?) to induce the signal into another wire rather than tying in directly?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My research is telling me that I'd want some sort of a high impedance buffer.  What exactly would that be?  Something like an optoisolator?&lt;/p&gt;&#xA;" OwnerUserId="5137" LastEditorUserId="76" LastEditDate="2016-02-20T00:44:10.563" LastActivityDate="2016-02-20T13:00:28.423" Title="Adding a panadapter via SDR" Tags="&lt;rtl-sdr&gt;&lt;electronics&gt;&lt;modification&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5809" PostTypeId="2" ParentId="5797" CreationDate="2016-02-19T21:33:43.120" Score="0" Body="&lt;p&gt;The easiest way to make a driven element for a hand-made Yagi, without having to solder is to get out a knife+some elec. tape or heat-shrink tubing and make a &lt;a href=&quot;http://www.iw5edi.com/ham-radio/?the-vertical-bazooka-antenna,18&quot; rel=&quot;nofollow&quot;&gt;'bazooka dipole'&lt;/a&gt; antenna from your feedline coax &amp;amp; use that for your driven element.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Advantages:  &#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Quick &amp;amp; easy to make, with absolutely no soldering necessary.  &lt;/li&gt;&#xA;&lt;li&gt;Forms its own balun, so you don't need an impedance-matching network added to your feedline, or your yagi.  &lt;/li&gt;&#xA;&lt;li&gt;If damaged, a 'new' D.E. can be made simply by re-cutting &amp;amp; inverting the same feedine (until the feedline gets too short to be practical, at least).&#xA;&lt;br&gt;&lt;br&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Disadvantages:  &#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Feedpoint impedance is not easily adjusted, so you'll have to be careful to place your elements in an arrangement that closely matches your feedpoint impedance to your coax's characteristic impedance (Antenna simulation programs are available for free download on most platforms to help with this).  &lt;/li&gt;&#xA;&lt;li&gt;Your D.E. won't hold its own shape well, and will most likely need to be supported in order to maintain proper element alignment/spacing.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6066" LastActivityDate="2016-02-19T21:33:43.120" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5811" PostTypeId="1" AcceptedAnswerId="5818" CreationDate="2016-02-20T00:41:12.657" Score="2" ViewCount="273" Body="&lt;p&gt;I'm looking into getting a cheap SDR (perhaps the RTL-SDR RTL2832U) to use as a spectroscope, especially to test the frequency output of Baofeng radios. I currently have reason to believe that one of my radios, on high power in 2m, transmits most of its power below 140 MHz but I'd like to characterize where.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm fine writing software/scripts on Linux to do this, and I've found that there's apparently an rtlsdr toolkit for this. However, I can't find whether or not it can give me an AM-demodulated signal (i.e. I want samples of data within, say, 1 MHz of the specified frequency).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anybody have experience (or software!) doing this? Or have an idea of which devices have which capabilities?&lt;/p&gt;&#xA;" OwnerUserId="4860" LastActivityDate="2016-03-01T03:00:02.657" Title="SDR for Spectroscope" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5812" PostTypeId="1" AcceptedAnswerId="5822" CreationDate="2016-02-20T03:21:31.183" Score="3" ViewCount="153" Body="&lt;p&gt;How far away should I transmit from a rare DX station in RTTY? RTTY itself doesn't take that much bandwidth, but I've heard that I should be spaced 2-3 kHz away. Is that true? Thanks!&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2016-02-24T04:03:34.987" Title="What is the proper spacing away from a rare RTTY station?" Tags="&lt;digital-modes&gt;&lt;bandwidth&gt;&lt;rtty&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5813" PostTypeId="2" ParentId="5808" CreationDate="2016-02-20T13:00:28.423" Score="2" Body="&lt;p&gt;An optoisolator would not likely accomplish what you're wanting here (relatively low feed impedance, with not-so-great linearity).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Op Amps seem to be the generally preferred implimentation for buffer amps now; something like this should work for you:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/LkSgE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LkSgE.png&quot; alt=&quot;Op Amp IF buffer amp&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, if you don't want to directly connect anything to your IF line, you could use a close-coupled parallel wire (like in your SWR meter) to sense the IF signal, then put it through 1-2 amp (LNA) stages before feeding to your SDR.&lt;/p&gt;&#xA;" OwnerUserId="6066" LastActivityDate="2016-02-20T13:00:28.423" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5814" PostTypeId="1" AcceptedAnswerId="5888" CreationDate="2016-02-20T13:40:52.197" Score="0" ViewCount="175" Body="&lt;p&gt;The Navy MARS program was officially decommissioned effective 30 September 2015. What is the state of the other MARS programs (Army and Air Force)? Is it known that they too will be decommissioned in the next few years? &lt;/p&gt;&#xA;" OwnerUserId="810" LastEditorUserId="76" LastEditDate="2016-02-20T15:32:48.350" LastActivityDate="2016-03-09T15:19:47.830" Title="Military Amateur Radio Service (MARS)" Tags="&lt;emergency&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5816" PostTypeId="1" CreationDate="2016-02-21T00:36:20.627" Score="3" ViewCount="844" Body="&lt;p&gt;Are there any software defined receivers capable of receiving Regular FM broadcast band stations and displaying a waterfall of the band from 88 MHz to 107 MHz or a significant portion of that range?&lt;/p&gt;&#xA;" OwnerUserId="6210" LastEditorUserId="76" LastEditDate="2016-02-21T02:52:12.187" LastActivityDate="2018-01-24T22:42:11.300" Title="Any SDR radios that receive FM BCB" Tags="&lt;receiver&gt;&lt;software-defined-radio&gt;&lt;fm&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5817" PostTypeId="2" ParentId="5816" CreationDate="2016-02-21T02:51:49.390" Score="6" Body="&lt;p&gt;Almost every SDR receiver is capable of receiving the FM broadcast band. The ones which can't are typically SDR transceivers designed for specific HF bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The harder part of your requirements is the waterfall of “the band … or a significant portion of that range”. The FM broadcast band is 20 MHz wide, and to display all of it straightforwardly requires delivering that entire bandwidth to the attached computer (I assume you are looking for that type as opposed to a single-box SDR).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When evaluating a receiver, look at the bandwidth (MHz) or sample rate (MSPS), and that tells you approximately how much you will be able to see ay once. (Approximately because there will be band-pass filters which have some rolloff at the edges.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, another option if you are not looking to &lt;em&gt;demodulate&lt;/em&gt; any one station while you are displaying the wide-band waterfall, then you can use software which rapidly steps the receive frequency across the range to construct a composite image. The most well-known tool to do this is &lt;em&gt;rtl_power&lt;/em&gt;, but I understand that it is a non-real-time tool (I could be wrong); I hear from comments that SDR# can do it real-time.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-02-28T15:55:10.813" LastActivityDate="2016-02-28T15:55:10.813" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5818" PostTypeId="2" ParentId="5811" CreationDate="2016-02-21T05:36:55.893" Score="2" Body="&lt;p&gt;You could just use an RTL-SDR and any SDR software (Gqrx, SDR#, etc) that supports it, and manually scroll around 140 Mhz until you see the signal (the RTL-SDR allows you to view 3.2Mhz max at one time). To not pick up other people's transmissions/other noise, use a few inches of 22ga solid wire stuck in the center of the SMA port of the RTL-SDR for a really poor antenna. And most SDR software allows you to demodulate AM or FM or SSB or CW or... :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used this method to see how clean the oscillator in a microcontroller is, with great success.&lt;/p&gt;&#xA;" OwnerUserId="5704" LastActivityDate="2016-02-21T05:36:55.893" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5820" PostTypeId="1" CreationDate="2016-02-23T01:56:56.367" Score="1" ViewCount="1069" Body="&lt;p&gt;I am a newbie in HAM.The transceiver I have in my lab is ICOM IC910 H. My goal is to use it to communicate with our cubesat which uses GMSK. According to the manual, on page 50, there are notes for operating the radio at 9600 bps. In the note, the manual instruct to set AFSK/GMSK output level to some value. My question is does this mean AFSK mode can also be used to receive GMSK signals as there is nowhere else in that manual where the term GMSK is used? Could you elaborate more on the implication of attempting to demodulate GMSK by using AFSK communication chain?&#xA;Regards.&lt;/p&gt;&#xA;" OwnerUserId="6214" LastEditorUserId="873" LastEditDate="2016-02-23T14:51:08.203" LastActivityDate="2016-03-24T15:42:46.487" Title="AFSK and GMSK in ICOM IC910 H" Tags="&lt;digital-modes&gt;&lt;satellites&gt;&lt;icom&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5821" PostTypeId="2" ParentId="5820" CreationDate="2016-02-23T02:30:58.193" Score="1" Body="&lt;h2&gt;Background&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;GMSK is a type of FSK (frequency-shift keying) with specific parameters and pulse shaping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;AFSK is &quot;audio FSK&quot; — that is, taking some choice of analog modulation and using FSK with some audio-frequency carrier frequency (e.g. around 100 Hz to 3 KHz) as the modulating signal.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If the analog modulation chosen is SSB, then this is identical on the air to FSK transmitted without a secondary modulation step (because SSB modulation is essentially just a frequency translation and bandpass filter), assuming the bandwidth of the signal fits within the ≤3 KHz bandwidth of a SSB signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you use FM then the signal on the air is different from a non-AFSK system. Do this only if your satellite is actually using AFSK on FM.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h2&gt;Usage&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;If your cubesat is transmitting GMSK, then you will want to set your radio to SSB mode. Then you will need to connect its output to a separate GMSK demodulator — which could be a computer running suitable software and with a sound card (or dedicated radio interface unit) connected to the radio. To learn about the appropriate connections/devices, read about amateur radio “digital modes”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also: If the radio gives different advice for &quot;1200 baud&quot; vs &quot;9600 baud&quot;, then choose the 9600 option. This minimizes unwanted filtering not suitable for digital signals.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-02-23T02:30:58.193" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5822" PostTypeId="2" ParentId="5812" CreationDate="2016-02-23T19:53:14.560" Score="3" Body="&lt;p&gt;Generally the RTTY Bandwidth is  170 hz, So if the frequency on your transceiver reads 14082.00 Khz  - the lower part of the RTTY signal is at 14082.00 Khz - 170 hz which is 14081.83.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That frequency allocation is being &lt;strong&gt;used&lt;/strong&gt;, now if you have very good filters in your &quot;rig&quot; - then you could in theory operate very very close to this frequency  - i.e. 14082.4 (that would be your Mark... the lower end would be 14082.230) which would leave a theorectical gap of aprox 400 Hz....&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the other station has &lt;strong&gt;No Frequency Variation&lt;/strong&gt; and all the people calling them are also very careful - you will not have any issues.... assuming of course that your HF Transceiver has good Filters and Image Rejection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alas lots of stations just use pure &lt;strong&gt;power&lt;/strong&gt; and literally burn away the edges....&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would I use ? On a non Contest day 500 hz is easily enough - but for CQWW-RTTY ... you will not have any space in the digital allocation - and the quest for &lt;strong&gt;power&lt;/strong&gt; plus &lt;strong&gt;filters&lt;/strong&gt; will become more significant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there is a DX station, and I note that you have said a &lt;strong&gt;rare DX&lt;/strong&gt; station - then there is always the possibility that they will work a split, i.e. receive on 1 frequency and transmit on another (hence most/all(?) modern transceivers have 2 VFOs). The size (gap/distance) of the split is totally down to the DX operators choice, whilst this is very common in CW and SSB modes, it is less common in RTTY from what I have observed. In CW a split of +1-2Khz and SSB +3-5Khz. You however need to ensure that you are keeping your signal inside the allocated band, and (US Bands) adhere to the band plan if applicable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the DX station has been going for several minutes (and the DX Cluster will indicate that clearly) - and they do have a split - respect that. If they are working SIMPLEX (1 Frequency) then my 500hz offset is more than enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some clever ops - deliberately position themselves close to DX stations - so those people who have been trying to get the DX and who can not (lack of Power/Ant/Propagation etc), and who are disappointed/frustrated so they try their luck for another station (just checking there is something coming out of the antenna). &lt;/p&gt;&#xA;" OwnerUserId="4994" LastEditorUserId="4994" LastEditDate="2016-02-24T04:03:34.987" LastActivityDate="2016-02-24T04:03:34.987" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5823" PostTypeId="2" ParentId="3714" CreationDate="2016-02-24T04:10:11.997" Score="1" Body="&lt;p&gt;When I was a little kid I lived about ten miles from AM station WLW near Cincinnati Ohio which is a 50kW station.  I had a crystal radio set and I found I could never tune anything but WLW.  Then after some experimentation I found I could just use the crystal earpiece and the germanium diode across the leads of the earpiece and since WLW had such a dominant signal I needed no tuning circuit at all nor did I need any antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems encouraging that you could attempt what I succeeded to use forty years ago.&lt;/p&gt;&#xA;" OwnerUserId="6113" LastActivityDate="2016-02-24T04:10:11.997" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5824" PostTypeId="1" AcceptedAnswerId="5825" CreationDate="2016-02-24T15:33:14.083" Score="0" ViewCount="135" Body="&lt;p&gt;We are constructing a house on a tiny 30ft by 55ft plot and the construction uses cement bricks and the roof has embedded iron rods. The house has ground + 2 floors and the top floor mostly has two rooms, one of which I plan to use for the shack. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As someone interested in 40m and 20m, I am planning to try putting a fan dipole (if needed, I hope to get some help from the neighbouring house in extending the antenna) and also explore other antenna construction techniques for limited space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any references or considerations on house construction specific to amateur radio operation? I will need to put small ducts through the walls to route the cables. Is there any value in putting a permanent mast with a pulley at the top?&lt;/p&gt;&#xA;" OwnerUserId="6231" LastEditorUserId="218" LastEditDate="2016-02-24T17:48:03.297" LastActivityDate="2016-02-24T18:00:54.197" Title="Amateur Radio shack/antenna considerations during house construction" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5825" PostTypeId="2" ParentId="5824" CreationDate="2016-02-24T18:00:54.197" Score="2" Body="&lt;p&gt;Ideally you want a place to put that antenna in the clear, though getting any HF antenna in the clear on such a tiny lot is going to be tricky no matter how you do it. Not much you can do about it, besides buy a bigger lot. If the antenna is close-ish to your roof, don't worry: it will still work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Masts are always useful. Whether it's permanent or not is really up to you. A pulley at the top makes pulling dipoles up easier, but also think about how you'll service rope and the pulley. You might want to make that a push-up mast, or have some way to tilt it down so you can get at the top of the mast without a tall ladder precariously balanced on your roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also lived on a small lot once, and I installed a trap vertical on the center of the roof, with radials extending to the edge of the roof. I mounted it on a standard rooftoop TV antenna tripod screwed into the roof decking, with three guy wires to be sure the wind wouldn't blow it over. It worked pretty OK, though there was a lot of noise. Such is to be expected in an urban area. There was simply no place to put it that wasn't within 30 feet of my house or a neighbor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can manage it, it would be nice to have the electrical service ground in the same place as you plan to have the antenna feedline enter the house. This will make &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;lightning protection&lt;/a&gt; easier.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-02-24T18:00:54.197" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5826" PostTypeId="1" AcceptedAnswerId="5827" CreationDate="2016-02-24T18:51:09.240" Score="0" ViewCount="43" Body="&lt;p&gt;I'm designing some low loss antenna switches for 160-10 meters, and my current plan is to construct the entire system as continuous 50 ohm microstrip feedlines on 2 sided FR4 PCB. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;All examples that I've been able to find focus on applications above 100MHz, and I'm unable to find any information at all on whether there is a practical or theoretical lower limit to the frequency that such feedlines can operate at.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-02-24T19:05:08.570" Title="Is there a lower limit to the usable frequency for PCB 'stripline' feedline?" Tags="&lt;feed-line&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5827" PostTypeId="2" ParentId="5826" CreationDate="2016-02-24T19:05:08.570" Score="3" Body="&lt;p&gt;Microstrips should in theory work just fine at low frequencies, as Z0 is independent of f. The advantage of microstrip technology becomes clear at high frequency when it is practical, and often easier, to create distributed element matching networks and filters than using lumped elements. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Microstrip&quot; rel=&quot;nofollow&quot;&gt;https://en.wikipedia.org/wiki/Microstrip&lt;/a&gt;&#xA;&lt;a href=&quot;http://www.microwaves101.com/encyclopedias/microstrip-calculator&quot; rel=&quot;nofollow&quot;&gt;http://www.microwaves101.com/encyclopedias/microstrip-calculator&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5944" LastActivityDate="2016-02-24T19:05:08.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5828" PostTypeId="1" CreationDate="2016-02-25T18:19:17.477" Score="8" ViewCount="4880" Body="&lt;p&gt;Studying for a Pivate Pilot's Licence (PPL) and I've hit something in the study material that doesn't make sense to me. Typical of the PPL study material, it's quite shallow, so the full explanation may have been omitted.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;To double the range of a radio wave, you need 4x the power.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I understand this, because of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Inverse-square_law&quot; rel=&quot;noreferrer&quot;&gt;inverse square law&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;To double the range of RADAR you need 16x the power.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is where I'm stuck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a radar system has a range of 3km, the wave must travel 6km, so the received return has 1/36 the power of the transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if I want to double the range of the system, to 6km, the wave must now travel 12km. Without power increase, the return signal has 1/144 the original transmission. To get back to 1/36, I need to multiply by 4. - Twice the range, 4x the power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are my PPL notes wrong, or am I misunderstanding?&lt;/p&gt;&#xA;" OwnerUserId="6236" LastEditorUserId="218" LastEditDate="2016-02-25T20:10:05.120" LastActivityDate="2016-03-11T22:20:43.853" Title="What is the power increase required to double the range of RADAR?" Tags="&lt;rf-power&gt;&lt;range&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5829" PostTypeId="2" ParentId="5828" CreationDate="2016-02-25T19:32:41.430" Score="6" Body="&lt;p&gt;Here's what you are thinking: if the radar station and the target are 1km away, then the distance there-and-back is 2km. If the distance doubles to 2km, then the distance there-and-back is 4km, just twice what it was. So the there-and-back distance also doubles, so you should need only a 4x increase in power, right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the radar target were a flat reflector aimed in just the right direction, this would be true. A target can also employ a &lt;a href=&quot;https://en.wikipedia.org/wiki/Corner_reflector#Radar_corner_reflectors&quot; rel=&quot;noreferrer&quot;&gt;corner reflector&lt;/a&gt;, which works like a mirror but without the aiming requirement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oF2UU.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oF2UU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_\text{received} \propto {P_\text{transmitted} \over 2d^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That $ \propto $ symbol means &quot;proportional to&quot;. The power received is also going to depend on the gain of the antenna, the size of the target (more specifically, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Solid_angle&quot; rel=&quot;noreferrer&quot;&gt;solid angle&lt;/a&gt; &lt;a href=&quot;https://en.wikipedia.org/wiki/Subtended_angle&quot; rel=&quot;noreferrer&quot;&gt;subtended&lt;/a&gt; by the target), etc. But if all the factors (except distance) are held constant, then the relationship of power received to power transmitted will obey this proportionality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A flat target, like a bathroom mirror, forms a &lt;a href=&quot;https://www.khanacademy.org/science/physics/geometric-optics/mirrors-and-lenses/v/virtual-image&quot; rel=&quot;noreferrer&quot;&gt;virtual image&lt;/a&gt; behind it. So the radar station &quot;sees itself&quot; behind the target, twice the distance away. Since in radar the receiver and transmitter are the same station, we can also think of this as the virtual image transmitting to the real station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But most targets aren't mirrors. The power they receive from the radar station isn't reflected back towards where it came from (like a mirror). Aircraft aren't shaped like mirrors. Since the wavelength of radar is many orders of magnitude greater than light, &lt;a href=&quot;https://en.wikipedia.org/wiki/Diffraction&quot; rel=&quot;noreferrer&quot;&gt;diffraction&lt;/a&gt; will also make the target less like an ideal mirror. Given all these variables, it's a reasonable assumption that the power intercepted by the aircraft will be scattered randomly in all directions. That is, it's a &lt;a href=&quot;https://en.wikipedia.org/wiki/Diffuse_reflection&quot; rel=&quot;noreferrer&quot;&gt;diffuse reflector&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rmgb4.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rmgb4.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_\text{received} \propto {P_\text{transmitted} \over d^2 \cdot d^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's one way to think of it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine the radar target isn't passively reflecting, but instead is a transmitter in itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the target doubles its distance to the station, the target must now &quot;transmit&quot; with 4 times the power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But targets aren't transmitters: they are passive reflectors of the power they intercept from the station. So to get 4 times the power at the target which is now twice as far away, you need to multiply the power by 4 again. 4*4 gives you 16.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another example: a mirror can reflect nearly all of the power it receives from a laser pointer back at the source. A white sheet of paper receives the same power from the laser pointer, but that power is diffusely reflected everywhere, and so the power received back at the source is much less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's still not making sense, think about how the reflection off the target affects the divergence of the beam. We can also do better than a flat reflector: we can use a parabolic reflector, with the radar station at the focal point:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/C3RPl.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/C3RPl.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_\text{received} \propto P_\text{transmitted} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As long as the antenna is in the focal point, a parabolic reflector will &lt;em&gt;reverse&lt;/em&gt; the divergence of the beam. Thus, it will make a &lt;a href=&quot;https://www.khanacademy.org/science/physics/geometric-optics/mirrors-and-lenses/v/parabolic-mirrors-and-real-images&quot; rel=&quot;noreferrer&quot;&gt;real image&lt;/a&gt; of the antenna right on top of the actual antenna. &lt;em&gt;All&lt;/em&gt; of the power transmitted (in the direction of the reflector) is received, and there's no distance term at all!&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-02-26T11:59:47.507" LastActivityDate="2016-02-26T11:59:47.507" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5830" PostTypeId="1" AcceptedAnswerId="5831" CreationDate="2016-02-25T21:30:07.670" Score="10" ViewCount="352" Body="&lt;p&gt;I've just written code for the RTL2832 to receive and decode ADS-B packets (very cool!). I had some confusion about what is actually happening:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is the raw data coming from the USB dongle literally samples of the ~1090 MHz wave? Or is the carrier frequency first demodulated (in that case, what actually am I receiving?)&lt;/li&gt;&#xA;&lt;li&gt;What is the relationship between sampling rate and bandwidth? (I've read that it's equal; e.g. 1 MSPS = 1 MHz, but reading about higher end SDR setups doesn't confirm this)&lt;/li&gt;&#xA;&lt;li&gt;Isn't the ADS-B encoding scheme particularly sensitive to phase and sampling frequency differences (like if my receiver is slightly out of calibration)? It seems that if I were sampling just a little faster or slower, that I would have received a much different signal than the one below:&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hBOUz.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hBOUz.png&quot; alt=&quot;ADS-B mode S short packet&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="6237" LastActivityDate="2016-02-26T01:27:07.410" Title="Confusion about SDR" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5831" PostTypeId="2" ParentId="5830" CreationDate="2016-02-25T22:33:45.977" Score="12" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is the raw data coming from the USB dongle literally samples of the ~1090 MHz wave? Or is the carrier frequency first demodulated (in that case, what actually am I receiving?)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's downconverted, not demodulated, using a local oscillator, mixer, and filters. That is, the signal you obtain is the same as if the transmitter had its carrier frequency set to 0 MHz instead of 1090 MHz (ignoring for the moment the fact that negative frequencies don't exist as propagating waves).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the relationship between sampling rate and bandwidth? (I've read that it's equal; e.g. 1 MSPS = 1 MHz, but reading about higher end SDR setups doesn't confirm this)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If your receiver has perfect antialias filtering, you can have bandwidth equal to sample rate (in a quadrature (IQ) system). In practice, your filter lets some out-of-band signals through, so whatever sample rate you pick, you get less usable bandwidth than that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To demonstrate that the filtering is not perfect, find a continuous narrowband signal (e.g. weather radio), then change the hardware frequency gradually. As the signal gets closer to the edge of the receive bandwidth, it will decrease in amplitude — but when it gets to the edge it will &lt;em&gt;wrap around to the other side&lt;/em&gt;, weaker! This is aliasing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you have a situation where &lt;em&gt;you do not need to reject nearby signals or noise&lt;/em&gt; (that is, the signal you want to receive is stronger than everything else nearby in frequency), then you could use all of your sampling rate. But that is an unusual situation, and not robust against interference.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Isn't the ADS-B encoding scheme particularly sensitive to phase and sampling frequency differences (like if my receiver is slightly out of calibration)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In this type of receiver, the phase and exact sample rate of your &lt;em&gt;analog-to-digital converter&lt;/em&gt; is &lt;strong&gt;not&lt;/strong&gt; the same as the phase and &lt;em&gt;symbol rate&lt;/em&gt; of the signal you're receiving. Instead, the software has a a control loop which looks at the incoming signal (knowing its expected properties) and adjusts to match its phase and symbol rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other way (phase-locking the ADC to the digital signal) is possible, but that requires additional hardware to precisely control the local oscillator, and makes the receiver hardware more specific to the characteristics of the particular modulation being received (rather than a general-purpose software-defined radio).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-02-26T01:27:07.410" LastActivityDate="2016-02-26T01:27:07.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5832" PostTypeId="1" AcceptedAnswerId="5835" CreationDate="2016-02-26T01:57:56.070" Score="1" ViewCount="759" Body="&lt;p&gt;I need to demodulate and decode a signal.It is transmitted from a satellite using GFSK. The packets are based on AX.25. Could you recommend any out-of-the-box HAM software packages that could do either GFSK demodulation or AX.25 decoding?&lt;/p&gt;&#xA;" OwnerUserId="6214" LastEditorUserId="873" LastEditDate="2016-02-29T10:50:38.940" LastActivityDate="2016-07-18T09:36:06.440" Title="GFSK Demodulationsoftware" Tags="&lt;digital-modes&gt;&lt;satellites&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5833" PostTypeId="2" ParentId="5816" CreationDate="2016-02-27T02:35:35.083" Score="1" Body="&lt;p&gt;I have had good luck using a software defined radio rig that starts out using one of the European TV USB sticks.  They are often sold as RTL-SDR or as DVB-T USB STICKS. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the right software, you definitely get a waterfall display, and you can receive anything above 70-80 Mhz without any additional hardware  or mods.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use HD-SDR and the SDR# application to tune the radio and give me a waterfall video display plus audio, plus the receiver-controls.  Locally Broadcast FM is so strong that even the little stubby 4 inch tall antenna that comes with the USB-Stick (RTL-SDR) will give you fine reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mine has an HF upconversion board that can be switched in, that was homebrewed by my local amateur radio club, but the unmodified version will work fine with RTL-SDR software, using that board, I can tune HF and VHF. With the upconvertor, I have a more general coverage SDR solution that will tune AM broadcast bands&#xA;and the Amateur HF bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sample hardware: (not vouching for this amazon product, just giving you a screenshot)&#xA;&lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B008S7AVTC&quot; rel=&quot;nofollow&quot;&gt;http://www.amazon.com/NooElec-RTL-SDR-RTL2832U-Software-Packages/dp/B008S7AVTC&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Software sample:&#xA;&lt;a href=&quot;http://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/&quot; rel=&quot;nofollow&quot;&gt;http://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Blog post by me on the PARC Lil Pup upconvertor Plus RTL-SDR build:&#xA;&lt;a href=&quot;http://ve3wpx.blogspot.ca/2014/04/building-sdr-kit-project-lil-pup-build.html&quot; rel=&quot;nofollow&quot;&gt;http://ve3wpx.blogspot.ca/2014/04/building-sdr-kit-project-lil-pup-build.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="643" LastEditorUserId="643" LastEditDate="2016-03-02T18:16:03.133" LastActivityDate="2016-03-02T18:16:03.133" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5834" PostTypeId="2" ParentId="2051" CreationDate="2016-02-27T16:30:16.287" Score="0" Body="&lt;p&gt;I found this definition of data acceptable in the 219 MHz by hams.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(13) A data emission using an unspecified digital code under the&#xA;  limitations listed in §97.309(b) also may be transmitted. The&#xA;  authorized bandwidth is 100 kHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="6246" LastEditorUserId="218" LastEditDate="2016-03-16T11:57:55.930" LastActivityDate="2016-03-16T11:57:55.930" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5835" PostTypeId="2" ParentId="5832" CreationDate="2016-02-27T21:31:23.413" Score="1" Body="&lt;p&gt;This is a bit cobbled together, but sometimes that's the only way to get things done!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.pe0sat.vgnet.nl/decoding/unix-tlm-decoding&quot; rel=&quot;nofollow&quot;&gt;http://www.pe0sat.vgnet.nl/decoding/unix-tlm-decoding&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part of this article refers to Dirweolf, a packet AX.25 modem.  It is an incredible software modem for packet reception.  So for decoding the incoming packet frames, Direwolf may be a good bet.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://github.com/wb2osz/direwolf&quot; rel=&quot;nofollow&quot;&gt;https://github.com/wb2osz/direwolf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dealing with AX.25 is better left to Linux.  Attach Direwolf to the Linux AX.25 network stack via the KISS protocol and it can provide you with decoded frames, though only in a specific format when you use the built in tool set, namely &quot;axlisten&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check out my HALDigital project on Sourceforge if you would like a Linux ax.25 system that is easy to build and configure on a cheap RasberryPi.  The current Beta image is running Rasbian Wheezy for an RPi2, and includes the AX.25 linkage with Direwolf and all the standard utilities.&lt;/p&gt;&#xA;" OwnerUserId="6248" LastActivityDate="2016-02-27T21:31:23.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5836" PostTypeId="2" ParentId="5811" CreationDate="2016-02-29T21:43:10.227" Score="3" Body="&lt;p&gt;If you are concerned about checking for a wide variety of potential spurious emissions, you will want to look into the many software packages for using the RTL-SDR as a spectrum analyzer. The RTL-SDR.com blog has a number of articles on this, e.g. &lt;a href=&quot;http://www.rtl-sdr.com/rtl-sdr-spectrum-analyzer/&quot; rel=&quot;nofollow&quot;&gt;http://www.rtl-sdr.com/rtl-sdr-spectrum-analyzer/&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What these do is programmatically tune across a whole wide range of frequencies and sample the spectrum at each &quot;stop&quot; along the way. So instead of seeing only distortion products in the ~2MHz spectrum around one particular center frequency, you can get a single composite view from the whole tunable range with one of the &quot;spectrum analyzer&quot; helpers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you can manually accomplish something similar simply by tuning to various windows where you might &lt;em&gt;expect&lt;/em&gt; to see spurious signal, e.g. 2x the transmitter frequency and further harmonics, or at various combinations of signal/IF/LO interactions. But scanning through an entire wider range while continuously transmitting might help you catch something you wouldn't have thought to check.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note also that the signal on your handheld transmitter's antenna port will be &lt;em&gt;waaaay&lt;/em&gt; to strong to inject directly into pretty much any receiver, including your SDR. So if you want a direct cable connection, make sure to use an appropriate amount of attenuation. Even picking up the signal via antenna at the same workbench could easily overload the SDR's receiver circuitry and cause a variety of &lt;strong&gt;additional&lt;/strong&gt; signal distortions to show up, which aren't actually emitted by the transmitter itself. Make sure your receiver is not overloaded by your (or any other nearby transmitter!) before considering its output valid.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-02-29T21:43:10.227" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5838" PostTypeId="2" ParentId="5811" CreationDate="2016-03-01T03:00:02.657" Score="1" Body="&lt;p&gt;In addition to easy-to-use software packages suggested, I would also suggest that you consider gnu radio. Gnu radio is a drag and drop sdr framework. It does also allow programming in python and c++ with hundreds of signal processing libraries needed for your application.&lt;/p&gt;&#xA;" OwnerUserId="6214" LastActivityDate="2016-03-01T03:00:02.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5840" PostTypeId="1" AcceptedAnswerId="5842" CreationDate="2016-03-01T17:54:11.363" Score="1" ViewCount="16327" Body="&lt;p&gt;Most antennas for the Baofeng UV-5R have male connectors, but the UV-5R actually has a larger diameter set of threads that look like they'd accept a female connector. Is that true? Is it a female SMA, or some other female connector?&lt;/p&gt;&#xA;" OwnerUserId="6229" LastActivityDate="2017-10-17T23:30:13.850" Title="Does the Baofeng UV-5R accept both male and female SMA connectors?" Tags="&lt;baofeng&gt;&lt;connectors&gt;&lt;uv-5r&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5841" PostTypeId="2" ParentId="5816" CreationDate="2016-03-01T17:54:28.693" Score="2" Body="&lt;p&gt;The HackRF is a relatively inexpensive SDR that is capable of capturing the entire FM broadcast band. It costs around $300 and can sample up to 20MHz of spectrum at a time. It can tune between 1MHz all the way up to 6GHz. &lt;/p&gt;&#xA;" OwnerUserId="170" LastActivityDate="2016-03-01T17:54:28.693" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5842" PostTypeId="2" ParentId="5840" CreationDate="2016-03-01T17:57:52.287" Score="4" Body="&lt;p&gt;No, the UV-5R will not accept a female connector. The threads on the outside are for the nut that mounts the connector to the case.&lt;/p&gt;&#xA;" OwnerUserId="170" LastEditorUserId="1362" LastEditDate="2017-10-17T23:30:13.850" LastActivityDate="2017-10-17T23:30:13.850" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5843" PostTypeId="2" ParentId="5840" CreationDate="2016-03-01T18:55:23.640" Score="8" Body="&lt;p&gt;The Baofeng UV-5R and any other variations in the UV-5R family of radios have an SMA male connector on the radio mating to an SMA female antenna or SMA female adapter.  In the picture I'm holding the anntenna along with the radio so that you can see for yourself which sex connector is on the radio and which is on the antenna. &lt;a href=&quot;https://i.stack.imgur.com/qHH7c.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qHH7c.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6113" LastActivityDate="2016-03-01T18:55:23.640" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5844" PostTypeId="1" AcceptedAnswerId="5845" CreationDate="2016-03-01T21:14:23.017" Score="2" ViewCount="2339" Body="&lt;p&gt;Hy i found this projekt: &lt;a href=&quot;https://github.com/argilo/gr-dsd&quot; rel=&quot;nofollow noreferrer&quot;&gt;gr-dsd&lt;/a&gt; i compiled it and it seems to work so far.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My problem is i don't find any Example just a Youtube Video (www.youtube.com/watch?v=DtkiC_Li_GI) wher it is used.&#xA;Can some One tell me how i have to use this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tryed the folowing:&#xA;osmocom source(hackrf 1) &gt; nfm demod &gt; dsd &gt; audio sink&#xA;I don't know if that is right how is D-STAR Modulated?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My Flow graph looks like this:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Mfms2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Mfms2.png&quot; alt=&quot;sample gr-dsd&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6257" LastEditorUserId="6257" LastEditDate="2016-03-01T22:54:52.037" LastActivityDate="2016-03-01T23:02:09.180" Title="SDR GnuRadio gr-dsd decode D-STAR voice" Tags="&lt;software-defined-radio&gt;&lt;d-star&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5845" PostTypeId="2" ParentId="5844" CreationDate="2016-03-01T21:24:35.713" Score="4" Body="&lt;p&gt;You have the right general idea, but a couple of problems:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;The sample rate entering the DSD block (hence the output of the FM demodulator) &lt;em&gt;must&lt;/em&gt; be 48000 Hz; this is hard-coded in gr-dsd.&lt;/strong&gt; From your screenshot, you have 35k where you need 48k.&lt;/li&gt;&#xA;&lt;li&gt;The deemphasis (a.k.a. tau) of the FM demodulator should be set to None, rather than the default of 75.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In my experience gr-dsd will work for D-STAR. As a development strategy, first build an analog narrow FM receiver, test it on analog radio (e.g. on amateur FM or weather radio) to make sure the filters and rates are correct (you can hear the output, and there is no over/underrun), then add the DSD block to the chain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that it is possible for there to be a digital signal present but no audio to decode. Silence doesn't mean it isn't working; gr-dsd will print text whenever it successfully decodes packets.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-03-01T23:02:09.180" LastActivityDate="2016-03-01T23:02:09.180" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5846" PostTypeId="1" CreationDate="2016-03-02T02:35:27.170" Score="1" ViewCount="297" Body="&lt;p&gt;I was recently gifted the &lt;a href=&quot;http://www.shop.radiowavz.com/DX-40-OCF-SHORT-37-FT-1500w-SSB-PEP-200w-CW-DX40SH.htm&quot; rel=&quot;nofollow&quot;&gt;RadioWavz DX40 Short&lt;/a&gt; sans wire. I have the balun and the wound inductor, but can't find any information as to the proper lengths of wire for this antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can find general information for building OCF dipoles, but this is a special dipole with that inductor doing something that is above my knowledge level.&lt;/p&gt;&#xA;" OwnerUserId="1216" LastEditorUserId="76" LastEditDate="2016-03-02T17:59:46.770" LastActivityDate="2016-03-09T16:37:04.900" Title="What are the wire lengths of the RadioWavz OCF 40m dipole?" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5848" PostTypeId="1" AcceptedAnswerId="5852" CreationDate="2016-03-02T15:21:54.747" Score="3" ViewCount="592" Body="&lt;p&gt;I'm trying to evaluate HF antennas for low angle performance to pick from a list of designs that will fit in my limited space. I'm using 4nec2 to simulate them and compare the patterns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When your simulated antenna has a low radiation efficiency, is the reported gain compared to an isotropic radiator with perfect radiation efficiency, or one with a radiation efficiency the same as your simulated antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's an example to clarify because I'm not sure I'm using the right terminology. I'm comparing two antennas: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Antenna 1 reports 6dBi at 0 degrees azimuth and 10 degrees elevation, and it has a radiation efficiency of 80%. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Antenna 2 reports 6dBi at 0 degreez azimuth and 10 degrees elevation, but it has a &lt;strong&gt;radiation efficiency of only 40%&lt;/strong&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Assuming everything else like ground and feed systems are the same, is the model telling me that the effective radiated power in that specific direction will be the same for both antennas, or will antenna 2 radiate half as much power in that direction because of the lower radiation efficiency?&lt;/p&gt;&#xA;" OwnerUserId="6260" LastEditorUserId="8717" LastEditDate="2019-11-05T21:37:37.523" LastActivityDate="2019-11-05T21:37:37.523" Title="Antenna gain vs. radiation efficiency in 4nec2" Tags="&lt;antenna-theory&gt;&lt;hf&gt;&lt;antenna-modeling&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5849" PostTypeId="2" ParentId="5846" CreationDate="2016-03-02T18:31:25.517" Score="1" Body="&lt;p&gt;It appears that the inductor is used specifically to shorten the long leg of the OCF so that the feedpoint is still in the right place electrically even though the physical size of one leg is different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally OCFs work with roughly a 2:1 ratio for the two legs, but looking at the photos, it appears that they've loaded it such that both legs are now equal. Try two lengths of wire 18.5' long, then split one of them roughly in half and install the inductor. So long as that coil isn't a trap (is there a capacitor in that piece of pipe?), it's unlikely that placement of the inductor is critical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your antenna will look like:&lt;br&gt;&#xA; ----18.5' wire----[balun]---9.5' wire---[coil]---9.5' wire---&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check your SWR. If you're close but not quite, try moving the inductor a little closer or further away from the feed point and see if it dials in.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-03-02T18:31:25.517" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5851" PostTypeId="2" ParentId="5761" CreationDate="2016-03-03T18:21:27.303" Score="1" Body="&lt;p&gt;I wonder if you've accidentally shorted out the speaker to ground? Not all radios use mono jacks, and you might be connecting something when you use a stereo jack that you don't intend.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's what Singalink recommends:&#xA;&lt;a href=&quot;http://www.tigertronics.com/sl_wireht_sep.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.tigertronics.com/sl_wireht_sep.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In particular, the PTT on the ring of the 2.5mm plug might be causing you trouble.&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2016-03-03T18:21:27.303" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5852" PostTypeId="2" ParentId="5848" CreationDate="2016-03-03T21:07:18.117" Score="3" Body="&lt;p&gt;4nec2 takes the radiation efficiency into account when it calculates the gain.  You can see this for yourself by modeling an antenna made of copper and then writing down the gain, and then changing the antenna model to use a lossier material such as iron.  So 6 dBi is 6 dBi no matter what the radiation efficiency of the antenna may be.  To answer your question, both antennas would radiate the same amount of power in that specific direction.  But there is no such thing as a free lunch, so the lower efficiency of the lossier antenna surely shows up in the antenna pattern in the form of lower gain in other directions, even if the peak gain of 6 dBi is the same as the peak gain of the other antenna.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-03T21:07:18.117" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5853" PostTypeId="1" CreationDate="2016-03-03T23:10:01.550" Score="3" ViewCount="1627" Body="&lt;p&gt;I am looking for a recommendation of an inexpensive scanner radio that should be used to locate animals equipped with 433MHz locator beacons. The beacons (based on DRA887TX) will send periodic tones. The radio needs to have the ability to be connected to a Yagi antenna. I was looking at the Baofeng UV5R scanner. Since I never used anything like this I would like to know if this is useable or not.&lt;/p&gt;&#xA;" OwnerUserId="6268" LastEditorUserId="29" LastEditDate="2016-04-15T23:05:35.543" LastActivityDate="2016-04-15T23:05:35.543" Title="Scanner radio for 433MHz locator beacon" Tags="&lt;receiver&gt;&lt;uhf&gt;&lt;beacon&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5854" PostTypeId="2" ParentId="5853" CreationDate="2016-03-04T00:32:31.850" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I am looking for a recommendation of an inexpensive scanner radio that should be used to locate animals equipped with 433MHz locator beacons. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;First, let me clarify some terminology: you don't need a &lt;em&gt;scanner&lt;/em&gt;, just a &lt;em&gt;receiver&lt;/em&gt;. A scanner is a type of receiver which monitors a large range of frequencies, but you know the exact frequency of your beacon.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The beacons (based on DRA887TX) will send periodic tones.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I just looked up &lt;a href=&quot;http://www.dorji.com/docs/data/DRA887TX.pdf&quot;&gt;a datasheet for the DRA887TX&lt;/a&gt; and it says it uses ASK (amplitude-shift keying) modulation. It's not clear what the levels are or if it's actually OOK (on-off keying, like Morse code but not necessarily the same patterns). In any case the behavior will depend on exactly how you use the module in your beacon circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The key point, however, is that this is &lt;em&gt;not&lt;/em&gt; frequency modulation (FM). This means that if you use a FM-only radio such as the Baofeng UV-5R, you will hear &lt;em&gt;silence&lt;/em&gt; when picking up the transmission. Silence is distinguishable from the noise you hear when there is no signal at all, but this isn't exactly pleasant to listen to.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If your beacon is transmitting an audio-frequency wave (pulse train, rather) into the DATA pin of the transmitter module, then you could use an AM receiver to pick up the tone. (&lt;em&gt;Not&lt;/em&gt; a regular &quot;AM radio&quot;, because those cannot receive at 433 MHz). Some other models of handheld radios (e.g. the popular Yaesu FT-60) have this capability.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you are just turning on the transmitter periodically and not doing any actual modulation (this is the simplest circuit design), you will need a receiver suitable for &lt;em&gt;CW&lt;/em&gt; (continuous wave), or &lt;em&gt;SSB&lt;/em&gt; (single-sideband), reception.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So to summarize, you likely need a &lt;em&gt;receiver&lt;/em&gt; (or transceiver) with these specifications:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Frequency coverage&lt;/strong&gt; including 433.92 MHz.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Modes&lt;/strong&gt; including either CW or SSB.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm afraid I'm not personally familiar with what products are available with these specifications that are suitable for the purpose, as opposed to being large and expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Well, you could get an RTL-SDR dongle paired with an Android phone. That's cheap if you have the phone already. Not the best performance, nor battery life, though.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But now that you know what to look for, you can do some research. It's probably also worth looking for information specifically for direction-finding/&quot;fox-hunting&quot;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The radio needs to have the ability to be connected to a Yagi antenna.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Any radio which has an antenna port can be connected to a Yagi antenna. You may need some type of adapter or pigtail cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may wish to consider using a loop antenna as opposed to a Yagi — this is a popular choice among &quot;fox hunters&quot;. It is more compact and allows for getting a much more precise determination of the direction, but you have to listen for the &lt;em&gt;absence&lt;/em&gt; of the signal (null) rather than its presence.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-03-04T00:32:31.850" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5855" PostTypeId="2" ParentId="5853" CreationDate="2016-03-04T06:59:39.803" Score="1" Body="&lt;p&gt;If you want to try and visualise the excellent advice from Kevin, look for &#xA;&lt;a href=&quot;http://www.homingin.com/intlfox.html&quot; rel=&quot;nofollow&quot;&gt;http://www.homingin.com/intlfox.html&lt;/a&gt; &quot;Introduction to ARDF -- Radio-Orienteering&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency may be different but the tools and techniques will be exactly the same.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2016-03-04T06:59:39.803" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5856" PostTypeId="1" AcceptedAnswerId="5857" CreationDate="2016-03-04T19:06:03.413" Score="0" ViewCount="984" Body="&lt;p&gt;What does switching to digital mode on Yaesu Xcvr's (or any other HF radio) actually do?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The documentation states that &quot;specific digital mode selections, which include custom BFO offsets to optimize the receive and transmit passbands for the mode selected&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the context of this question is a friend whom recently purchased an FT-840 HF Xcvr which doesn't have a digital mode selection to speak of.  How can he tune his radio to match the performance of a radio with a digital mode option?  Besides BFO offsets, what else does digital mode do, and how would one mirror that same configuration on a radio without &quot;digital mode&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Page 36: Digital Mode selecion : PSK31-L or PSK31-U&#xA;&lt;a href=&quot;http://www.download.n7tgb.net/yaesu/ft897/ft-897_operating_manual.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.download.n7tgb.net/yaesu/ft897/ft-897_operating_manual.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6274" LastEditorUserId="6274" LastEditDate="2016-03-05T12:21:10.597" LastActivityDate="2017-05-03T03:25:20.307" Title="What is Digital Mode on newer HF Transceivers" Tags="&lt;digital-modes&gt;&lt;modes&gt;&lt;transceiver&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5857" PostTypeId="2" ParentId="5856" CreationDate="2016-03-04T19:15:12.093" Score="3" Body="&lt;p&gt;I can't comment from experience on other Yaesu transceivers, but the &quot;Digital&quot; mode on the &lt;strong&gt;Yaesu FT-857/897&lt;/strong&gt; is basically a second SSB/CW mode. It exists in order to have a separate, configurable group of settings so that you don't have to change your regular settings away from those suitable for SSB phone use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I remember correctly, it includes the following separated settings (adjusted separately vs. other modes) or special settings (adjusted with “digital”-specific menu items):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Upper vs. lower sideband&lt;/li&gt;&#xA;&lt;li&gt;Offset between the displayed frequency and carrier frequency (SSB phone normally displays the carrier frequency; CW displays the center of the passband; the Digital mode lets you set an &lt;em&gt;arbitrary&lt;/em&gt; offset.)&lt;/li&gt;&#xA;&lt;li&gt;DSP filter passband edges&lt;/li&gt;&#xA;&lt;li&gt;IF shift&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If another radio &lt;em&gt;has these settings,&lt;/em&gt; then it can be configured the same way. The &quot;digital mode&quot; is merely a convenience to enable all those settings at once; it does not have any unique capabilities (other than the arbitrary frequency offset) and does not involve anything like a modem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other models or brands of transceivers might use the term differently, such as by actually implementing digital modes (modems) directly in the transceiver.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-05-03T03:25:20.307" LastActivityDate="2017-05-03T03:25:20.307" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5858" PostTypeId="2" ParentId="5856" CreationDate="2016-03-05T08:28:25.570" Score="0" Body="&lt;p&gt;On my Elecraft Digital is called Data - and because the Radio has in-built capabilities to handle &lt;strong&gt;digital&lt;/strong&gt; (Tone Signals) modes, and I suspect that this is the case on some of the higher end-models from Icom, Yaesu and probably Kenwood.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example using the mode PSK-32, you want minimal signal compression (as it causes splatter) - so you need to adjust the Mic-Gain and the Compression of the audio from you transceiver - but if you QSY (Change frequency) to somewhere else and are now in a part of the spectrum (frequency allocation) that allows Voice  - You now want compression, and higher mic-gain (It makes your voice sound better/clearer)... instead of going through the tedious setup routines (as Kevin previously stated) - you just switch modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power settings can differ between CW/SSB and Digital modes - some modes are only wanting to use very very small amount of power J65 - whereas others - RTTY it is Full-Blown linear amplifiers and high gain Yagi's.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most difficult thing regarding digital is interfacing your PC (An Elecraft can send some digital modes using a CW key - assuming you are proficient at CW) to the radio. Once you have accomplished that - then Digital just takes a little time to figure out what mode, software and setup you need.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2016-03-05T08:28:25.570" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5859" PostTypeId="1" CreationDate="2016-03-05T15:47:07.997" Score="2" ViewCount="410" Body="&lt;p&gt;I want to create a sink block in &lt;a href=&quot;http://gnuradio.org&quot; rel=&quot;nofollow&quot;&gt;GNU Radio&lt;/a&gt; which transfers the signal to &lt;a href=&quot;http://www.baudline.com/&quot; rel=&quot;nofollow&quot;&gt;baudline&lt;/a&gt;. My purpose is viewing SDR's received signal online. How should I program this block?&lt;/p&gt;&#xA;" OwnerDisplayName="user6211" LastEditorUserId="76" LastEditDate="2016-03-09T21:38:28.973" LastActivityDate="2019-11-09T08:22:11.303" Title="How link between gnuradio and baudline?" Tags="&lt;software-defined-radio&gt;&lt;software-development&gt;&lt;gnuradio&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5860" PostTypeId="2" ParentId="5859" CreationDate="2016-03-05T16:54:45.977" Score="2" Body="&lt;p&gt;Just use pavucontrol to redirect the audio output from gnuradio to the audio input of baudline, shouldn't take more than a minute. Creating gnuradio blocks is a mission, and that's without integrating with something like baudline, which I don't even think is possible.&lt;/p&gt;&#xA;" OwnerUserId="135" LastActivityDate="2016-03-05T16:54:45.977" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5861" PostTypeId="2" ParentId="5828" CreationDate="2016-03-05T21:39:01.780" Score="0" Body="&lt;p&gt;To (roughly) double the range of radar, you not only need to double the range of the transmitted signal, but double the range of the reflected signal, in order to produce the same received signal level.  A 4X power increase for the returning reflected signal on top of a 4x power increase for the initial transmitted signal thus requires 16X the transmit power for roughly the same received reflected power at double the range.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2016-03-11T22:20:43.853" LastActivityDate="2016-03-11T22:20:43.853" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5862" PostTypeId="2" ParentId="1782" CreationDate="2016-03-06T11:29:52.773" Score="1" Body="&lt;p&gt;The spacing of of the driven element from the reflector of a Yagi antenna is&#xA;$$0.19 \cdot \text{wavelength}$$&#xA;then, the spacing of the driven element from the director element is&#xA;$$0.17 \cdot \text{wavelength}$$&lt;/p&gt;&#xA;" OwnerUserId="6286" LastEditorUserId="76" LastEditDate="2016-03-06T22:01:54.703" LastActivityDate="2016-03-06T22:01:54.703" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5863" PostTypeId="1" CreationDate="2016-03-06T20:16:28.853" Score="1" ViewCount="453" Body="&lt;p&gt;I live in an attic apartment, just acquired a JRC NRD-545, and am somewhat limited to what I can put outside (within reason).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an old folded dipole CB antenna that I might get away with mounting just outside my window.  Comments, suggestions?&lt;/p&gt;&#xA;" OwnerUserId="6287" LastEditorUserId="76" LastEditDate="2016-03-06T22:00:20.890" LastActivityDate="2016-07-05T19:09:34.113" Title="What is an adequate antenna for a JRC NRD-545?" Tags="&lt;antenna&gt;&lt;receiver&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5864" PostTypeId="2" ParentId="5863" CreationDate="2016-03-06T21:59:20.950" Score="1" Body="&lt;p&gt;When only receiving HF, &lt;a href=&quot;https://ham.stackexchange.com/questions/1058/is-there-a-simple-diy-antenna-suitable-for-hf-receive-only&quot;&gt;the design of the antenna does not matter  much&lt;/a&gt;, unless your receiver has notably bad filtering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most valuable characteristic of a receive antenna is being located away from local noise sources and structures that absorb/reflect the signal. The second thing to consider (for HF in constrained spaces) is making it as big as you feasibly can (up to 1/2 wavelength).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I encourage you to &lt;strong&gt;try&lt;/strong&gt; using any and all antennas you have on hand, or can construct from wire and a connector, and compare their performance. (You can't damage a receiver by using the wrong antenna. Unless it's so wrong it touches energized metal.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you say you live in an &lt;em&gt;attic&lt;/em&gt; apartment, unless your roof is metallic, you should try running a wire dipole antenna indoors along the ceiling as close to the ridgeline of the roof as you can reach. This may well be the best antenna you can put up.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-03-06T21:59:20.950" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5867" PostTypeId="1" CreationDate="2016-03-07T12:42:50.287" Score="1" ViewCount="64" Body="&lt;p&gt;Using a 1000 watt (mains, not TPO) transmitter capable of theoretically transmitting on any frequency, would TPO change based on frequency at which we transmit (LF, MF, HF, VHF, UHF,...)? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I mean, is it more expensive in terms of wasted power to transmit on a certain side of the RF spectrum rather than on the other, with the same mains power? And why? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If TPO remains constant, would ERP remain unchanged too at any frequencies, assuming in all cases that no power is reflected back into the transmitter from the antenna, and a neutral antenna gain? &lt;/p&gt;&#xA;" OwnerUserId="5184" LastEditorUserId="76" LastEditDate="2016-03-07T18:15:57.723" LastActivityDate="2019-01-21T01:38:24.603" Title="For a given transmitter mains wattage, is its TPO wattage affected by the transmission frequency?" Tags="&lt;efficiency&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5868" PostTypeId="2" ParentId="5867" CreationDate="2016-03-07T18:06:51.353" Score="3" Body="&lt;p&gt;The first part of your question seems to be about transmitter efficiency.  Engineers designing transmitters must make many design compromises at any frequency.  At frequencies of several gigahertz amplifier and oscillator efficiency drops tremendously, and producing even a 10-Watt signal can be a real achievement.  Speaking very roughly, losses increase as frequency increases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second part of your question is about transmission line and antenna losses.  For open wire line and coaxial cable losses increase with frequency, but at microwave frequencies waveguides become practical, and waveguides can be very efficient.  Again speaking very generally, losses tend to increase as frequency increases.  Of course as the frequency gets lower, the antenna must be larger and higher, and generally more expensive, in order to be efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your question focuses on one factor, power efficiency, but in the real world the designer of a radio system must also be concerned with many other factors: the expense, the size of the equipment, the size of the antenna, the path loss (the loss between the transmitting antenna and the receiving antenna), the noise present in the band that must be overcome in order for the receiver to hear, and so on.  It's difficult to make blanket statements about one part of the radio spectrum being better than other parts without more specifics about the problem.  If the goal is to talk to submerged submarines, then the answer can be a very large antenna and a powerful transmitter at a very low frequency.  If the goal is to inexpensively allow two hikers a mile apart to communicate, then the answer can be a pair of FRS handheld radios.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-07T18:06:51.353" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5873" PostTypeId="1" AcceptedAnswerId="5878" CreationDate="2016-03-08T07:22:03.943" Score="2" ViewCount="1096" Body="&lt;p&gt;Before discovering that connectors can have characteristic impedance, I ordered a bunch of adapters. I've noticed that I'm getting really sub-par performance out of the antennas I'm using and think I may have ended up with some 75-ohm connectors, but I don't have a VHF/UHF SWR meter and it won't be in the budget for a while yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I determine the characteristic impedance of a connector or adapter?&lt;/p&gt;&#xA;" OwnerUserId="6295" LastEditorUserId="76" LastEditDate="2016-03-09T21:38:58.850" LastActivityDate="2016-03-09T21:38:58.850" Title="Measuring Connector Impedance" Tags="&lt;impedance&gt;&lt;connectors&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5875" PostTypeId="1" AcceptedAnswerId="5877" CreationDate="2016-03-08T09:39:57.457" Score="1" ViewCount="147" Body="&lt;p&gt;I am very new to 4Nec2 and need to do a simulation of a half-wave dipole antenna for 433 MHz. I've read a couple of tutorials and I understand most of it so far, still, my simulation doesn't make sense.&#xA;As you can see, the antenna is outside the pattern. Using the editor, I lifted both ends up 1 meter (on the Z-Axis). The pattern is still around the origin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone knows why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/18T7b.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/18T7b.png&quot; alt=&quot;Simulation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6297" LastEditorUserId="8717" LastEditDate="2019-11-05T21:34:33.477" LastActivityDate="2019-11-05T21:34:33.477" Title="4NEC2 - Antenna outside Pattern" Tags="&lt;antenna&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5876" PostTypeId="2" ParentId="5867" CreationDate="2016-03-08T10:42:24.977" Score="0" Body="&lt;p&gt;rclocher3 is correct when it comes to increasing losses as F goes up and lower practical antenna efficiency as F goes down. There is probably a very broad optimum which would be somewhere between 80m and 2m depending on where you live. The method of modulation is also a big factor. For example old analog FM and its digital cousins FSK and PSK don't need a linear amplifier and therefore run in more efficient classes like C or D or E. A class C VHF PA will be more efficient than a class AB HF linear SSB. Full carrier AM can run a class D modulator and a class E final giving mains efficiencies of over 90%. Looking at things this way makes AM not so bad.&lt;/p&gt;&#xA;" OwnerUserId="6095" LastEditorDisplayName="user4168" LastEditDate="2019-01-21T01:38:24.603" LastActivityDate="2019-01-21T01:38:24.603" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="5877" PostTypeId="2" ParentId="5875" CreationDate="2016-03-08T16:38:32.863" Score="4" Body="&lt;p&gt;The displayed radiation pattern is not a physical object in a meaningful spatial relation to the elements of the antenna, it's a graph of data. Consider the meaning of the (polar) coordinates of each:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For the antenna model, $(r, \phi, \theta)$ are coordinates of the antenna structure elements.&lt;/li&gt;&#xA;&lt;li&gt;For the pattern graph, $(\phi, \theta)$ specify a &lt;em&gt;direction&lt;/em&gt; away from the antenna, and $r$ is a &lt;em&gt;gain value&lt;/em&gt;, not a length.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Remember, when you are modeling an antenna like this you are considering the &lt;em&gt;far field&lt;/em&gt; results — the pattern is telling you the radiated power that would pass through a given point &lt;em&gt;infinitely far away&lt;/em&gt; from the physical antenna structure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To make spatial sense of the pattern, if you must, you can think of it like your antenna model is “shrunk to a point”, made infinitely small. And the point it's shrunk to might as well be the coordinate origin, not the center of your entered model, because that's simple and well-defined, and there's no particular guarantee that your antenna model is symmetric to &lt;em&gt;have&lt;/em&gt; a well-defined center.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-03-08T16:38:32.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5878" PostTypeId="2" ParentId="5873" CreationDate="2016-03-08T20:38:01.290" Score="3" Body="&lt;p&gt;You can look at them. The characteristic impedance of a coaxial transmission line or connector is a function of the geometry of the conductors and the dielectric between them. Connectors are standardized, so for a given impedance they have a standard geometry. The pins are usually different sizes, and the amount of plastic dielectric in the connector might be different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The specifics will vary based on the connector of course. A quick image search should turn up plenty of examples, for whatever kind of connector you have. Common ham radio connectors are BNC and N which come in 50Ω and 75Ω flavors. You might also run into a TNC connector, which is really just a BNC with a screw instead of bayonet shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;UHF&quot; or SO-239/PL-259 connectors are also common. They were made in a time where &quot;ultra high frequency&quot; was much lower. They are fine on HF but less than optimal on VHF. They don't come in 50Ω or 75Ω flavors: there's just the one kind. They are basically shielded banana plugs and have a non-constant characteristic impedance throughout their length. Network analyzers didn't exist when they were designed, and that's why they don't work well on the upper parts of the VHF spectrum and above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also measure the impedance with a network analyzer or time-domain reflectometer. But I'm guessing if you don't have an SWR meter, you won't have those things either.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-03-08T20:38:01.290" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5880" PostTypeId="1" AcceptedAnswerId="5881" CreationDate="2016-03-08T22:32:29.283" Score="10" ViewCount="3226" Body="&lt;p&gt;Assuming I have an antenna for receiving GPS signals, can I use it also for transmit — to create a repeater in a tunnel (or some place with no reception)?  &lt;/p&gt;&#xA;" OwnerUserId="5673" LastEditorUserId="76" LastEditDate="2019-03-13T01:49:27.460" LastActivityDate="2019-03-13T01:49:27.460" Title="Can every antenna be used both for transmit and receive?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;gnss&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5881" PostTypeId="2" ParentId="5880" CreationDate="2016-03-08T23:09:03.027" Score="23" Body="&lt;p&gt;&lt;strong&gt;No.&lt;/strong&gt; Many types of antennas may be unsuitable for transmitting.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;A so-called &lt;em&gt;active antenna&lt;/em&gt; contains an integrated low-noise amplifier (LNA) for amplifying weak signals. (&lt;strong&gt;This is very common for GPS antennas.&lt;/strong&gt;) This amplifier cannot pass a signal in reverse, and could be damaged by transmit power levels appearing on its output. It is possible to have an automatic switch to bypass the LNA when transmitting, but this feature would not be designed into an antenna meant for receiving.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some designs of antenna, such as the &lt;a href=&quot;https://en.wikipedia.org/wiki/Beverage_antenna&quot; rel=&quot;noreferrer&quot;&gt;Beverage antenna&lt;/a&gt;, contain resistors or other dissipative elements. If they are used for transmitting, the resistor must be capable of dissipating a certain fraction of the power input to the antenna. This is inefficient since that fraction of power is not transmitted, and requires a resistor which will not be destroyed by the heat.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A receiving antenna may &lt;a href=&quot;https://en.wikipedia.org/wiki/Loop_antenna#Small_loop_receiving_antennas&quot; rel=&quot;noreferrer&quot;&gt;contain a ferrite element&lt;/a&gt;, which allows it to be much more efficient when receiving than its size would otherwise permit, but which will &lt;em&gt;saturate&lt;/em&gt; at any significant power, becoming nonlinear and creating harmonic distortion (as well as heat).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A transmitter requires &lt;em&gt;impedance matching&lt;/em&gt; between the final power amplifier and the antenna. An antenna's impedance varies with frequency, so it has some frequency range over which there is an acceptable match. The same antenna can be used for receiving over a much wider range; antennas used solely for receiving may be deliberately mismatched vs. the intended band to gain other advantages such as being physically small.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna with the wrong impedance at the desired frequency &lt;em&gt;can&lt;/em&gt; be matched using a matching network or &lt;em&gt;antenna tuner&lt;/em&gt; (adjustable matching network), but this is still less efficient because there will be additional losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the least significant problem of all those I have listed: with a good antenna tuner, just about any chunk of metal insulated from other objects can be used as an antenna. The problem comes when non-metallic elements are in circuit as in the other cases.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Since you mention GPS in particular:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You cannot repeat a GPS signal usefully. Or rather, if you did, it would cause your GPS receiver to think it is at the position of the original receiving antenna, not its actual location. (This is because GPS operates by analyzing the combination of signals from multiple satellites, and this combination happens in the receiving antenna.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would also be likely illegal to operate such a transmitter, because you are transmitting on frequencies you do not have permission to and interfering with normal GPS operation.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-07-04T17:26:23.667" LastActivityDate="2016-07-04T17:26:23.667" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="5884" PostTypeId="2" ParentId="4938" CreationDate="2016-03-09T09:04:16.477" Score="2" Body="&lt;p&gt;Using the Chirp software, set the offset for each channel to &quot;off&quot;. Transmit is disabled for that channel.&lt;/p&gt;&#xA;" OwnerUserId="6305" LastEditorUserId="76" LastEditDate="2016-03-09T16:44:03.323" LastActivityDate="2016-03-09T16:44:03.323" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5886" PostTypeId="2" ParentId="5873" CreationDate="2016-03-09T15:09:33.560" Score="2" Body="&lt;p&gt;You mentioned &quot;adapters&quot; in your post.  If you truly mean adapters, in other words, changing a BNC to an SO-239 or something similar, bear in mind that those sorts of adapters, proper impedance or not, present an &quot;insertion loss&quot; to your signal on both transmit and receive.  Avoid using more than one such adapter if at all possible, because these insertion losses add up.&lt;/p&gt;&#xA;" OwnerUserId="6248" LastActivityDate="2016-03-09T15:09:33.560" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5888" PostTypeId="2" ParentId="5814" CreationDate="2016-03-09T15:19:47.830" Score="1" Body="&lt;p&gt;Army and Air Force MARS are very much alive and well, and growing.  There is no reason to believe that either will be decommissioned as the volunteer base continues to grow as well as the customer base.&lt;/p&gt;&#xA;" OwnerUserId="6248" LastActivityDate="2016-03-09T15:19:47.830" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5890" PostTypeId="2" ParentId="5828" CreationDate="2016-03-09T18:41:45.253" Score="0" Body="&lt;p&gt;In addition to Phil Frost's answer. I believe what's missing is a coefficient sigma, which represents the amount of signal returned to the transceiver. Let's assume some units (m and m-squared if you like). Pictured below is a signal that at 1 unit from transmitter, is spread over 1 unit squared of area. At 3 units from the transmitter, covers 9 units squared of area. This is the basic inverse square law. (the intensity is spread over this area - hence the inverse part). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now let's assume sigma is 1 unit square (the amount of signal returned - not necessarily equivalent to surface area of the target as it is also shape dependent - see Phil Frost's answer). The red illustrates a simple application of the same inverse square law and shows that the signal picked up at the point of transmission again will be proportional to 1/r^4.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mistake I made in my original post was assuming that the entire signal is reflected. This was implicit in assuming that the return signal is equivalent to simply extending the signal over the same distance again. This would only be the case if sigma was proportional to r-squared. So if, at r = 3, sigma was 9 units square, then it would be equivalent to continuing the original signal over double the distance. (sigma sits on the top the intensity equation, so it it's proportional to r^2, the remaining r in the denominator is r^2).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To put it another way, if only a single unit square is returned, this unit square is projected onto 9 units square back at r=1 (shown in red). So the intensity is spread of 9 units square of area. If the signal continues to r=5 (same extra distance covered) that single unit square projects onto less than 9 units squared (9 units squared needs to project onto 25, so each can only project onto 25/9 units squared) so the signal here is more intense. (as expected - proportional to 1/r^2 not 1/r^4.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4SaTF.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4SaTF.jpg&quot; alt=&quot;radar return&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope that makes some sense, anyone have any corrections?&lt;/p&gt;&#xA;" OwnerUserId="6236" LastEditorUserId="6236" LastEditDate="2016-03-11T06:02:57.460" LastActivityDate="2016-03-11T06:02:57.460" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5891" PostTypeId="2" ParentId="4938" CreationDate="2016-03-09T18:51:21.417" Score="6" Body="&lt;p&gt;Chirp can only disable Transmitting on pre-programmed memory frequencies, if you select the vfo it will still transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Searching Google for 'uv5r transmit inhibit' yielded this on the fifth hit&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.bytebang.at/Blog/Locking+down+a+Baofeng+UV5R%2B+to+disable+unintentional+TX&quot; rel=&quot;noreferrer&quot;&gt;http://www.bytebang.at/Blog/Locking+down+a+Baofeng+UV5R%2B+to+disable+unintentional+TX&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Within the Uv5R there is a thin rubber pad that pushes against the TX button. This pad can be easily cut of with a sharp knife. After that the TX button on the UV5R does not work any more while the TX circuitry is still untouched.  This means that the TX with the headsed plugged in is still working.&quot;&lt;/p&gt;&#xA;" OwnerUserId="6273" LastActivityDate="2016-03-09T18:51:21.417" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5892" PostTypeId="1" CreationDate="2016-03-10T03:46:38.653" Score="4" ViewCount="4169" Body="&lt;p&gt;I would like to construct a 9:1 unun that connects my QRP transceiver to a random-wire antenna.  The transceiver's antenna connection is an unbalanced BNC jack and the random-wire antenna is, well, a random wire. ;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have several toroidal ferrite cores laying around from disassembled power-supplies and such, but the many websites I've visited that show the construction of the 9:1 unun have not specified what type/mixture/diameter of toroidal core I need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll be operating mostly on 20 and 40 meters HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were to order a toroid just for this purpose, which would be ideal for this application?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the future -- Here is an answer that gives a lot of good information: &lt;a href=&quot;https://ham.stackexchange.com/a/6145/1738&quot;&gt;https://ham.stackexchange.com/a/6145/1738&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1738" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2018-11-01T22:43:49.547" Title="Recommended 9:1 unun core type(s)" Tags="&lt;diy&gt;&lt;wire-antenna&gt;&lt;balun&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5895" PostTypeId="2" ParentId="5390" CreationDate="2016-03-10T14:51:19.073" Score="1" Body="&lt;p&gt;Afraid I have to disagree with the accepted answer and say that no, as a foundation license you are not allowed to do this. The key is in the &quot;additional restrictions&quot; in &quot;schedule 2&quot; of &lt;a href=&quot;http://rsgb.org/main/files/2015/09/EX309-Advance-Reference-Data.pdf&quot; rel=&quot;nofollow&quot;&gt;the license&lt;/a&gt;, as quoted by M6JNY. If you scroll to page 13 in that document, you'll see that no frequencies are allocated for beacon use for foundation license holders.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for the definition of beacon (page 7):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;“Beacon” means automatic transmitting only Radio Equipment which is operated by the Licensee in&#xA;  accordance with Clause 10 and Schedule 2 of this Licence; &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Afraid that definition sounds like it fits!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd (genuinely) love to be proven wrong, as it'd mean I'm able to run these sorts of fun projects with foundation license holders building their own remote stations and the like - but it does seem to be off the cards for now at least.&lt;/p&gt;&#xA;" OwnerUserId="65" LastActivityDate="2016-03-10T14:51:19.073" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5896" PostTypeId="2" ParentId="4938" CreationDate="2016-03-10T15:53:51.757" Score="10" Body="&lt;p&gt;If you haven't seen them, the RTL-SDR dongles are really hard to beat for scanning. They let you see a waterfall display so that you can see visually which frequencies are active. It's wonderful!&lt;/p&gt;&#xA;" OwnerUserId="6295" LastActivityDate="2016-03-10T15:53:51.757" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5897" PostTypeId="2" ParentId="5194" CreationDate="2016-03-10T16:10:42.713" Score="2" Body="&lt;p&gt;I never did manage to decode the signal reliably, which I believe to be a combination of two factors - the radio I was using was attenuating the upper frequency somewhat, and there was some additional interference in the area. APRS also uses AX25 which is hardly the most resilient protocol - at 1200baud, you get a single sine wave oscillation for each bit, so if a slight bit of noise gets in there it's easy to see how the packet can be unreadable - there's not much room for error on the physical layer. FWIW, I've also later read that QTMM isn't the best decoding tool on the block - I didn't try many others since QTMM was so simple and appeared to work for audio clips I found online, but that could be the next port of call if I were to revisit the project.&lt;/p&gt;&#xA;" OwnerUserId="65" LastActivityDate="2016-03-10T16:10:42.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5898" PostTypeId="5" CreationDate="2016-03-10T16:35:22.863" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-03-10T16:35:22.863" LastActivityDate="2016-03-10T16:35:22.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5899" PostTypeId="4" CreationDate="2016-03-10T16:35:22.863" Score="0" Body="Devices for connecting balanced and unbalanced feed lines/antennas. Also covers questions about ununs, unbalanced-to-unbalanced connection." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-03-10T16:35:22.863" LastActivityDate="2016-03-10T16:35:22.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5900" PostTypeId="1" AcceptedAnswerId="5903" CreationDate="2016-03-10T17:20:31.093" Score="3" ViewCount="242" Body="&lt;p&gt;I'm considering hanging a long wire this spring and trying to get my 13 y.o. son interested in radio as a Scouting activity.  Has everything gone to &lt;a href=&quot;https://en.wikipedia.org/wiki/Digital_Radio_Mondiale&quot; rel=&quot;nofollow&quot;&gt;DRM&lt;/a&gt; these days, or is it worth dusting off my HQ-180 and checking the capacitors?&lt;/p&gt;&#xA;" OwnerUserId="1426" LastEditorUserId="76" LastEditDate="2016-03-11T21:46:58.763" LastActivityDate="2018-03-05T15:41:21.440" Title="Are there many analog (AM) shortwave broadcast stations left?" Tags="&lt;hf&gt;&lt;swl&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5901" PostTypeId="2" ParentId="1013" CreationDate="2016-03-10T17:26:51.607" Score="0" Body="&lt;p&gt;I believe the commenter who says that FM and PM are interrelated is correct.  To really understand it, (which I once did but can no longer claim to do!), read something like &lt;a href=&quot;https://books.google.com/books/about/The_Science_of_Radio.html?id=V1GBW6UD4CcC&quot; rel=&quot;nofollow&quot;&gt;The Science of Radio by Paul Nahin&lt;/a&gt; and/or the sort-of-companion text &lt;a href=&quot;https://books.google.com/books/about/The_Electronics_of_Radio.html?id=203BJeFu5qQC&quot; rel=&quot;nofollow&quot;&gt;The Electronics of Radio by David Rutledge&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1426" LastActivityDate="2016-03-10T17:26:51.607" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5902" PostTypeId="1" AcceptedAnswerId="5909" CreationDate="2016-03-10T17:30:06.793" Score="5" ViewCount="4825" Body="&lt;p&gt;Am considering getting my license again after raising kids, and wondering if there is any point in HF operation besides local chats — that is, what is propagation like when there are no sunspots?&lt;/p&gt;&#xA;" OwnerUserId="1426" LastEditorUserId="76" LastEditDate="2016-03-10T17:50:12.387" LastActivityDate="2018-01-08T00:07:04.213" Title="What is propagation like when there are no sunspots?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;dx&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5903" PostTypeId="2" ParentId="5900" CreationDate="2016-03-10T18:13:28.423" Score="4" Body="&lt;p&gt;There are still many AM shortwave stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A great way to find out the state of the spectrum for yourself is to use &lt;a href=&quot;http://websdr.org/&quot; rel=&quot;nofollow&quot;&gt;WebSDR&lt;/a&gt; sites, which let you use many different receivers around the world from your web browser. Many of them are restricted to the amateur bands only, but some have wider coverage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://websdr.ewi.utwente.nl:8901/&quot; rel=&quot;nofollow&quot;&gt;University of Twente WebSDR&lt;/a&gt; in particular has continuous 0-30 MHz coverage. You'll find that its marked broadcast bands are full of AM signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, that's just one location, in the Netherlands. At my home on the west coast of the United States, I have very high local noise, but I can still hear several shortwave AM broadcast stations when propagation conditions are good, and I have not heard any DRM stations at all.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-03-11T17:59:15.613" LastActivityDate="2016-03-11T17:59:15.613" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5904" PostTypeId="2" ParentId="5591" CreationDate="2016-03-10T19:22:42.420" Score="0" Body="&lt;p&gt;It could be no tone, it could be DCS, or it could have an activation tone. It could even be a very, very simple trunking system implemented in an odd way.&lt;/p&gt;&#xA;" OwnerUserId="6295" LastActivityDate="2016-03-10T19:22:42.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5905" PostTypeId="1" AcceptedAnswerId="5907" CreationDate="2016-03-10T21:35:06.423" Score="11" ViewCount="1080" Body="&lt;p&gt;If I start with no current license, can I take all the exams in one sitting to get to Amateur Extra?&lt;/p&gt;&#xA;" OwnerUserId="1426" LastEditorUserId="8717" LastEditDate="2020-10-26T20:11:55.930" LastActivityDate="2021-04-19T21:00:55.537" Title="What is the highest US amateur license I can get in one sitting?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5906" PostTypeId="2" ParentId="5905" CreationDate="2016-03-10T21:42:01.903" Score="4" Body="&lt;p&gt;After you pass an amateur exam, you will receive an CSCE (Certificate of Successful Completion of Examination).  This proves that you have passed the exam.  This ticket also allows you to take the next exam.  In recursion, a new ham &lt;strong&gt;&lt;em&gt;can&lt;/strong&gt; go from having no license to obtaining an Extra &lt;strong&gt;in one sitting...&lt;/em&gt;&lt;/strong&gt; for the same price as your original technician exam.&lt;/p&gt;&#xA;" OwnerUserId="6317" LastEditorUserId="29" LastEditDate="2016-04-01T21:20:27.750" LastActivityDate="2016-04-01T21:20:27.750" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5907" PostTypeId="2" ParentId="5905" CreationDate="2016-03-10T22:49:13.210" Score="14" Body="&lt;p&gt;Yes, you can take all three exams in sequence at the same session and obtain an Extra class license. (I did and had no trouble.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doing this, rather than getting a lower license class and upgrading later, has the small advantage that you will be assigned a shorter sequential call sign (without having to request one when you upgrade), as well as not paying additional exam session fees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I would recommend that you &lt;strong&gt;arrive early, and inform the VEs that you are planning to do this.&lt;/strong&gt; I've heard that in some exam sessions, the examiners qualified to administer the General and Extra exams (that is, ones who themselves hold Extra class licenses) may leave after everyone who came to &lt;em&gt;upgrade&lt;/em&gt; their licenses has taken their single exam, whereas you will be starting only after you finish your Technician exam.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-03-17T22:55:53.907" LastActivityDate="2016-03-17T22:55:53.907" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="5909" PostTypeId="2" ParentId="5902" CreationDate="2016-03-11T00:13:05.193" Score="7" Body="&lt;p&gt;We went through quite an extended sunspot minimum before the current sunspot cycle started, and I well remember what it was like.  10m was open only when there was e-skip, which wasn't very often.  15m had openings from time to time, but when it was open typically you'd only hear stations in one direction, like from South America for instance, and they'd be weak, like S2 on the meter.  It often seemed like 15m was only open during contests, probably because people would be discouraged from even trying the band at other times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, 20m was open during the daytime, and 40m, 80m, and 160m were open at night.  When I started in 2006 I only had a base-model Elecraft K2 with no options, meaning I had just 11 W output to a vertical and Morse code was my only mode.  I had plenty of fun and worked some good DX from my West Coast QTH, including Europe and Africa, but I had to work harder to get the DX than I would now for sure.  A lot of the DX I worked was contest megastations, but I had several memorable contacts with ordinary hams running ordinary stations in faraway places.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we get another sunspot minimum like we had before, then I'd say that there will still be plenty of activity on HF.  If you want to work DX, you'll have to listen harder for grayline propagation (magic!) and unusually good conditions, which actually happen fairly often; pay no attention to the computer program that says Europe is currently impossible, turn on the radio instead and find out for yourself.  Consider using Morse code or a computer mode like PSK31; those modes work much better than SSB when conditions are only so-so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice would be to ignore the grumblers, there will still be plenty to do on HF even if the sunspots vanish for a while.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-11T00:13:05.193" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5910" PostTypeId="1" AcceptedAnswerId="5912" CreationDate="2016-03-11T02:04:19.540" Score="2" ViewCount="134" Body="&lt;p&gt;What type of technical questions are on the FCC Technician Exam? I am asking because I have been reading the FCC Rules as a study guide for the Technician Exam and I don't want there to be any surprises when I go and take the test.&lt;/p&gt;&#xA;" OwnerUserId="6163" LastActivityDate="2016-03-11T02:26:37.017" Title="Technical Questions on the FCC Technician Exam?" Tags="&lt;fcc&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5911" PostTypeId="2" ParentId="5905" CreationDate="2016-03-11T02:13:07.983" Score="2" Body="&lt;p&gt;In 1995, I was living in the US for three months. I bought some study books, read all the question pools and booked myself in to the local test centre. I had planned to take the 20wpm Morse test, and if I failed that then the 13wpm test, and if for some reason I failed that then the 5wpm test. Then I had planned to sit the five exams for Novice, Technician, General, Advanced and Extra classes of licence. As it happened, I scraped a pass in the 20wpm Morse test and passed all of the other exams (the Advanced test was the hardest! The pool was enormous), and came out with pass slips to allow me to apply for an Amateur Extra licence, the highest there is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All in all, it was a good morning's work! The guys at the test centre said I was the first person to manage that at their centre, although they had heard of people doing it before.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did also at that time hold a UK class A licence, otherwise I would have been extremely nervous at the prospect of taking between 6 and 9 tests for a radio licence!&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2016-03-11T02:13:07.983" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5912" PostTypeId="2" ParentId="5910" CreationDate="2016-03-11T02:26:37.017" Score="1" Body="&lt;p&gt;If you want to know exactly what to expect from the test, you can read the test questions; they are public. You can get them &lt;a href=&quot;http://ncvec.org/page.php?id=362&quot; rel=&quot;nofollow&quot;&gt;directly from the source at NCVEC.org&lt;/a&gt;, or you can use a web site designed to help you study the test such as &lt;a href=&quot;https://hamstudy.org/&quot; rel=&quot;nofollow&quot;&gt;HamStudy.org&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The Technician question pool has several sections with technical questions, but they are mainly vocabulary/concepts rather than any sort of, say, calculation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are sections on electronic principles and components, which are easy if you have some familiarity with electric circuits, and study enough about RF to know the difference between an inductor and a capacitor in RF circuits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there are several other areas that will require specific study unless you have a background with which you probably wouldn't be asking this question. You need to learn about radio equipment, modes and propagation, and various jargon specific to amateur operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, the big area that you didn't mention in your question, which is neither regulatory nor exactly technical, is &lt;strong&gt;operating procedures and practices&lt;/strong&gt;. Unfortunately, there is no good way to get this information without reading the question pool or a study guide; nothing else is going to contain all of the information in one place, because it covers a wide variety of topics and some of the questions can be fairly obscure.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-03-11T02:26:37.017" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5913" PostTypeId="1" AcceptedAnswerId="5914" CreationDate="2016-03-11T02:30:41.713" Score="4" ViewCount="346" Body="&lt;p&gt;I know that there are various bands referenced in meters (or cm). My question refers to what exactly the word &quot;meter&quot; is referring to when identifying the 5MHz band? I know that the 60-meter band is 5MHz, and considering that communications on that band can go farther than 60 meters, I am assuming that &quot;meter&quot; refers to the wavelength. Is that assumption correct?&lt;/p&gt;&#xA;" OwnerUserId="6163" LastEditorUserId="4665" LastEditDate="2020-11-04T16:31:43.523" LastActivityDate="2020-11-04T16:31:43.523" Title="What is &quot;Meter&quot; referencing in &quot;60-Meter Band&quot;?" Tags="&lt;propagation&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5914" PostTypeId="2" ParentId="5913" CreationDate="2016-03-11T02:42:18.640" Score="9" Body="&lt;p&gt;That's right, the 5 MHz band has approximately a 60 m wavelength.  Back in the early days of radio people often measured where they were on the airwaves by wavelength rather than frequency.  Nowadays the radio display shows the frequency, but amateurs still refer to bands by their approximate wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wavelength x frequency = speed of light, 2.99792e8 m/s.  Or to put it another way, wavelength = 299.792 / frequency in MHz.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-11T02:42:18.640" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5915" PostTypeId="1" AcceptedAnswerId="5919" CreationDate="2016-03-11T08:05:24.167" Score="1" ViewCount="2008" Body="&lt;p&gt;I am migrating to Australia, and want to find out whether I can carry my Baofeng UV82 HX / HP model there. The model has CE, FCC, ROHS compliance, and a black 'Tick' mark next to these three. &#xA;If the same model is sold in Australia, I believe I can carry it too?&lt;/p&gt;&#xA;" OwnerUserId="1723" LastEditorUserId="76" LastEditDate="2016-03-11T14:56:45.457" LastActivityDate="2016-03-14T12:06:34.580" Title="Baofeng radio allowed in Australia?" Tags="&lt;legal&gt;&lt;baofeng&gt;&lt;australia&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5916" PostTypeId="2" ParentId="5892" CreationDate="2016-03-11T16:39:48.743" Score="0" Body="&lt;p&gt;Seek out retailers who cater to the Ham Radio consumer for information.  For instance, Buxcomm sells toroids which are specifically indexed based upon your intended use.  I am sure that there are other retailers who will provide the same help, and it may be wise to get multiple sources to seek a range of agreement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without your intended frequency range it is difficult to comment on which exact toroidal core material to use, but indications are that a &quot;Type 43&quot; with a mu of 850 is appropriate for 2 through 60 Mhz.  Other manufacturers also use colored lacquer to indentify charactaristics.  A 2 - 30 Mhz toroid may have a red lacquer color (type 2), at least from some manufacturers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, I would suspect that toroids which came from power supplies would not be appropriate as they deal in very low frequency AC.  Thankfully, the Ham specific ones are relatively inexpensive.&lt;/p&gt;&#xA;" OwnerUserId="6248" LastActivityDate="2016-03-11T16:39:48.743" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5917" PostTypeId="2" ParentId="4944" CreationDate="2016-03-11T16:55:17.410" Score="1" Body="&lt;p&gt;As noted in your linked article:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All is not lost, though, as there are two viable workaround solutions.&#xA;  The internal TNC does support KISS mode so all you need is a packet&#xA;  program that supports KISS (many packet programs do) and let the&#xA;  packet program handle the chore for you.  This is by far the simplest&#xA;  and least painfull way of working around the limitations of the&#xA;  internal TNC.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;When using KISS mode, the AFSK modem should send whatever you put into the KISS frame.  There are command codes which must be escaped in the KISS wrapping function of your program, but it is quite simple and I would be happy to supply you with some skeleton Java code which is easily decipherable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you send the KISS frame from your program to the AFSK modem which operates in KISS mode, it will send the HDLC across the link.  Essentially, you will get a stream of bytes to deal with on the receive side.  The receive modem in KISS mode sends those bytes to the controlling program in a KISS wrapper.  So your limitations are few when using KISS and KISS enabled AFSK modems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note also that there are OTHER CODECs out there beside plain old Ma Bell AFSK used in typical packet.  UZ7HO's sound modem makes use of another handful of CODECs, and provides a KISS mode via TCP port which is very convenient for programming.  Similarly, the Direwolf packet modem provides a KISS TCP port as well.  FLDIGI even has some limited support for KISS with many of it's modem CODECs.&lt;/p&gt;&#xA;" OwnerUserId="6248" LastActivityDate="2016-03-11T16:55:17.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5918" PostTypeId="2" ParentId="5913" CreationDate="2016-03-11T21:51:31.127" Score="2" Body="&lt;p&gt;The wavelength also literally defines the length of a full-wave resonant wire antenna -- and specifies where along the wire the voltage will have peaks and valleys!  So it has practical value when constructing an antenna, which is probably why amateurs still use it.&lt;/p&gt;&#xA;" OwnerUserId="1426" LastActivityDate="2016-03-11T21:51:31.127" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5919" PostTypeId="2" ParentId="5915" CreationDate="2016-03-11T23:34:42.793" Score="2" Body="&lt;p&gt;I see from a Google search of &quot;Baofeng UV82 Australia&quot; that the UV82 is sold there.  It's possible that there is a different firmware version for Australia, perhaps to restrict the power level or to keep users out of certain frequencies, but that seems unlikely to me.  Personally I would bring it; there's a small chance that it might be confiscated by Customs, but surely you could afford to buy another if that were to happen.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-11T23:34:42.793" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5920" PostTypeId="1" CreationDate="2016-03-11T23:40:46.140" Score="8" ViewCount="930" Body="&lt;p&gt;From what I've learnt so far, the longer the wave frequency on which you want to transmit or receive, the longer the antenna needed to do so. However my portable receiver other than SW can also receive LW and MW, and is receiving those using its internal (very short!)  antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is that? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is that even possible that the short internal antenna does its work better than the much longer  telescopic antenna that the radio uses for SW? (my radio automatically switches to the internal when on LW MW...) &lt;/p&gt;&#xA;" OwnerUserId="5184" LastEditorUserId="5184" LastEditDate="2016-03-13T06:15:16.360" LastActivityDate="2016-03-14T10:37:41.600" Title="Why a thousand miles long antenna is not needed to receive LW and MW?" Tags="&lt;antenna&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5921" PostTypeId="2" ParentId="5920" CreationDate="2016-03-11T23:56:03.033" Score="1" Body="&lt;p&gt;Electricaly short antennas seem to work fine on RX at these low frequencies .The humble AM car radio is case and point .Sure the little antenna produces less signal but it also produces less noise in proportion.So the Carrier to noise ratio coming in to the radio is roughly the same for both cases.Any low frequency RX that is worth its salt will have enough gain to compensate for this and its internal noise is much less than atmospheric noise .This is why increasing the length of the antenna often does not give a observable reception improvement .Things will actually get worse on some cheap solid state recievers because of poor overload performance.&lt;/p&gt;&#xA;" OwnerUserId="6095" LastActivityDate="2016-03-11T23:56:03.033" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5922" PostTypeId="2" ParentId="5920" CreationDate="2016-03-12T00:15:38.320" Score="1" Body="&lt;p&gt;Antenna efficiency is far more important for transmitting than for receiving.  If the small AM antenna in your transistor radio produces only one thousandth the signal that a 300-foot vertical with 160 radials does, the deficiency is easily made up by the amplifier.  It's nowhere near as easy to increase the power of a transmitter by a thousand times, which is why great care is taken to make AM broadcast antennas as efficient as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The internal AM antenna in your radio works better than the telescoping stick antenna because the internal antenna is either a wire loop with many turns, or a ferrite stick with many turns of wire around it.  The many turns of the internal antenna 'amplify' (in a manner of speaking) the received signal.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-12T00:15:38.320" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5923" PostTypeId="2" ParentId="5920" CreationDate="2016-03-13T13:48:16.520" Score="5" Body="&lt;p&gt;A ferrite stick antenna is a kind of &lt;a href=&quot;http://www.antenna-theory.com/antennas/smallLoop.php&quot;&gt;small loop antenna&lt;/a&gt;, &quot;small&quot; here meaning small retaliative to wavelength. These kinds of antennas can most easily be understood by &lt;a href=&quot;https://en.wikipedia.org/wiki/Electromagnetic_induction&quot;&gt;electromagnetic induction&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The loop acts as a &quot;net&quot; for &lt;a href=&quot;http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/fluxmg.html&quot;&gt;magnetic flux&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;As the magnetic flux changes, an electromotive force (EMF) is induced in the loop.&lt;/li&gt;&#xA;&lt;li&gt;This force pushes the electric charges in the loop around, making a current through the loop and a voltage across the feedpoint which the receiver can detect.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This is the same operating principle behind an electric generator. However, in the case of a loop antenna the changing magnetic field comes not from a nearby moving magnet, but instead from a distant radio transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Electromagnetic induction is formally described by &lt;a href=&quot;http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html&quot;&gt;Faraday's law of induction&lt;/a&gt;. It says EMF ($\mathcal{E}$) is proportional to the rate of change of magnetic flux ($\Phi_B$).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \mathcal{E} = -{{\mathrm d\Phi_B} \over \mathrm dt} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several ways we might increase the magnetic flux through the antenna, thus increasing the EMF and making it easier to build an efficient antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could make the magnetic field strength higher, by increasing the power of the transmitter or getting closer to it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, we can make the loop bigger. A bigger loop captures more flux, like a bigger net.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can also add more turns around the loop. It doesn't matter that both turns are capturing the same area of space. The EMF in each turn adds together, so an antenna with two turns captures twice the magnetic flux as an antenna with one turn of equal diameter. A ferrite stick antenna might have 60 turns, so it captures 60 times the magnetic flux as one turn would.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last thing we can do is to stick a ferrite rod in the loop. The ferrite rod has some interesting magnetic properties that make it work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All ordinary matter has some magnetic properties. For example, every electron &lt;a href=&quot;https://en.wikipedia.org/wiki/Electron_magnetic_moment&quot;&gt;is like a tiny bar magnet&lt;/a&gt;, or a magnetic dipole. In most matter, these magnetic dipoles are arranged in random directions, and so at macroscopic scales there are no interesting magnetic properties.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In &lt;a href=&quot;https://en.wikipedia.org/wiki/Ferromagnetism#Ferromagnetic_materials&quot;&gt;ferromagnetic materials&lt;/a&gt; some of these magnetic dipoles can be reoriented. For example, if a piece of iron is placed in a strong magnetic field, then its magnetic dipoles tend to align with that field, just like a compass aligns with the Earth's magnetic field. The ability of the magnetic dipoles to align is called &lt;a href=&quot;https://en.wikipedia.org/wiki/Permeability_(electromagnetism)&quot;&gt;permeability&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the external field is removed, some of the magnetic dipoles tend to &quot;stick&quot; in their orientation, and you are left with a permanent magnet. This tendency for the magnetic dipoles to stick is called &lt;a href=&quot;https://en.wikipedia.org/wiki/Coercivity&quot;&gt;coercivity&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The interesting property of the ferrite material used in a ferrite antenna is that it has low coercivity and high permeability. So their magnetic dipoles are good at aligning with an external field, but they tend not to get stuck, like a compass needle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So when you stick a ferrite rod in the loop, whichever way the magnetic field from the transmitter is going (remember it's oscillating with the transmitter's frequency), the magnetic dipoles in the ferrite are aligned in the same direction. The fields of the magnetic dipoles add to the external field, and the result is that the magnetic flux through the loop is stronger.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-03-13T13:48:16.520" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="5924" PostTypeId="2" ParentId="5902" CreationDate="2016-03-14T07:59:27.713" Score="4" Body="&lt;p&gt;In a word: miserable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was not active during the last solar minimum, but the one before it was long and full of people complaining about it on USENET, which was still a thing back then. The solar flux index was in the 60s for months at a time, and all you could read in the DX bulletins was how awful things were.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However - HF bands seem to open miraculously during contests, only to appear to close again afterwards, as everyone who would normally be on HF tries their hand at gardening or similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;10m and 12m are for all intents and purposes dead at all times, unless there is some E-layer magic going on. The lower bands are lovely, but activity is all closer by, and there are fewer 'interesting' stations about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have long maintained that we make our own propagation, and that if everyone thinks the bands are dead, then BAM you tune around and there is nobody on! (They are all doing something else, rather than calling CQ. The propagation is still there, but there are no stations to hear.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;'Propagation' is a bit like the economy - when things are 'going well' everyone is borrowing and buying stuff. When things are 'going badly' nobody is buying anything, and you can't borrow money even if you want to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in general, it's a pretty miserable time - and that's on us :)&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2016-03-14T07:59:27.713" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5926" PostTypeId="2" ParentId="5920" CreationDate="2016-03-14T10:37:41.600" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How is that even possible that the short internal antenna does its&#xA;  work better than the much longer telescopic antenna that the radio&#xA;  uses for SW?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;let me try to answer it differently: the &quot;short internal&quot; antenna, even when the summary length of the coils do not even approach the length needed of a stretched dipole, is efficient due to &quot;&lt;strong&gt;L/C resonance&lt;/strong&gt;&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;for every frequency you can find (multiple) coil/capacitor combinations which will be resonant for that frequency. And will work &quot;better&quot; as an antenna compared to a small telescopic antenna for receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;This is also why certain HAMs which want to Tx on such bands are using &quot;magnetic loop antennas&quot; which have the same principle, it is a resonant L/C circuit.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH, Edwin&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-03-14T10:37:41.600" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5927" PostTypeId="2" ParentId="5240" CreationDate="2016-03-14T10:49:19.347" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I thought that given the premises in first paragraph, it was clear&#xA;  that the heart of the question was about knowing the actually&#xA;  achievable transfer limits using known and used modes, not just&#xA;  understanding theoretical limits... (which is still a precious&#xA;  contribute though).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Practically, I have maintained 155Mbps for a while now.&#xA;- digitally&#xA;- achieved&#xA;- maintained long term&#xA;- very little packet loss (sub 0.1%)&#xA;- verified&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using &quot;known and used modes&quot; in the form of 802.11n/wifi&#xA;or if you like: &lt;code&gt;IEEE 802.11n-2009&lt;/code&gt; with &lt;code&gt;64-QAM modulation&lt;/code&gt; on a &lt;code&gt;40MHz-channel-BW&lt;/code&gt; as it is known formally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe the question is a bit &quot;wide&quot; to answer really... you would need to ask the question in reference to which band you use, and which bandwidth you like to use, then you can find protocols to use, or even write your own...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I often thought about increasing bandwidth of PSK by using multiple PSK in parallel... and I actually found someone who implemented this already. Although I forgot the link, I am sure you can search for it.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-03-14T10:49:19.347" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5929" PostTypeId="2" ParentId="5915" CreationDate="2016-03-14T12:06:34.580" Score="1" Body="&lt;p&gt;When Migrating from one country to another, regardless of countries, it is a good idea to contact customs in both countries to ensure that you declare your equipment, and get information about the specifics of import/export details, forms, and procedures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't want any surprises on the day itself.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-03-14T12:06:34.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5930" PostTypeId="1" AcceptedAnswerId="5935" CreationDate="2016-03-14T19:14:11.883" Score="6" ViewCount="6192" Body="&lt;p&gt;Like many new hams, I have just one radio: an inexpensive 2m/70cm FM transceiver.  It doesn't do SSB and it doesn't have a digital input.  If I wire up a connection between the radio and my computer's sound card, are there any digital modes that I could reasonably take advantage of with this hardware?&lt;/p&gt;&#xA;" OwnerUserId="6080" LastActivityDate="2019-05-03T06:02:03.403" Title="Are there any commonly used digital modes that work with an FM transceiver?" Tags="&lt;digital-modes&gt;&lt;fm&gt;" AnswerCount="5" CommentCount="1" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5931" PostTypeId="1" AcceptedAnswerId="5933" CreationDate="2016-03-14T20:25:04.640" Score="5" ViewCount="204" Body="&lt;p&gt;Lets say I can throw a satellite into orbit (I've got a good arm). I'm amateur radio qualified so can I just set it up to transmit on an amateur band and start having fun? Is there anyone I have to register with? Or am I good to go with my own license? Do I need to contact the FCC or something like that?&lt;/p&gt;&#xA;" OwnerUserId="529" LastEditorUserId="76" LastEditDate="2016-03-14T20:59:32.747" LastActivityDate="2016-03-14T21:24:13.340" Title="What are the legal requirements for an amateur radio satellite?" Tags="&lt;legal&gt;&lt;satellites&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5932" PostTypeId="2" ParentId="5930" CreationDate="2016-03-14T20:36:20.917" Score="0" Body="&lt;p&gt;Nearly all common modes will work this way, however because of the way FM is generated and received, you get absolutely no advantage over voice, so it's only useful if you specifically want to transmit data for some reason. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because of the much narrower envelope, a CW signal has between 9 and 12dB advantage over an SSB signal at the same power. Using PC audio to modulate an SSB signal as most digital modes do offers an additional 6dB more than CW, as they can be fantastically narrow. SSB is 2-4kHz wide on average, a clean CW signal should be less than 40Hz wide, and a properly generated JT9 signal may be less than 10Hz wide.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that a 100 watt CW signal will be about equivalent to a 1,000 watt SSB signal, and a JT9 signal will be equal to 2,000 Watts or more on SSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With FM, the envelope does not change width regardless of input, so all modes are equal.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-03-14T20:36:20.917" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5933" PostTypeId="2" ParentId="5931" CreationDate="2016-03-14T21:24:13.340" Score="4" Body="&lt;p&gt;As far as I can tell, the &lt;a href=&quot;http://www.iaru.org/satellite.html&quot; rel=&quot;nofollow&quot;&gt;IARU&lt;/a&gt; attempts to regulate which amateur satellites use which amateur bands to transmit, who in turn coordinates transmission with the ITU. &lt;a href=&quot;http://www.itu.int/en/about/Pages/default.aspx&quot; rel=&quot;nofollow&quot;&gt;Most countries&lt;/a&gt; have signed treaties with the ITU (a UN special agency) to not intentionally cause interference, etc. It looks like there are &lt;a href=&quot;http://www.amsat.org.uk/iaru/&quot; rel=&quot;nofollow&quot;&gt;370 cubesats currently registered&lt;/a&gt; with the IARU.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you plan on transmitting to the satellite, you will also need an amateur radio license (from the &lt;a href=&quot;http://www.arrl.org/&quot; rel=&quot;nofollow&quot;&gt;ARRL&lt;/a&gt; if in the US), the version will depend on the frequency band operated in.&lt;/p&gt;&#xA;" OwnerUserId="5944" LastActivityDate="2016-03-14T21:24:13.340" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5934" PostTypeId="1" AcceptedAnswerId="6089" CreationDate="2016-03-14T21:33:48.163" Score="2" ViewCount="211" Body="&lt;p&gt;Hy just a &quot;stupid&quot; question, I bought a technisat skystar s2 pci card.&#xA;Can any body tell me why this thing has a mac address printed on it? ^^&#xA;And the mac address can even been looked up. (00-08-c9-xx-xx-xx)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to receive/transmitt ethernet packets and if so is it possible to use this data link via atv(HAM TV - Digital).&lt;/p&gt;&#xA;" OwnerUserId="6257" LastEditorUserId="6257" LastEditDate="2016-03-15T16:53:33.750" LastActivityDate="2016-04-21T12:26:13.493" Title="SkyStar S2 has a mac address, for what?" Tags="&lt;receiver&gt;&lt;satellites&gt;" AnswerCount="2" CommentCount="5" ClosedDate="2016-04-29T02:45:51.737" ContentLicense="CC BY-SA 3.0" />
  <row Id="5935" PostTypeId="2" ParentId="5930" CreationDate="2016-03-14T22:35:51.207" Score="4" Body="&lt;p&gt;I interpret your question to mean &quot;what kind of cool digital stuff could I do with my inexpensive HT?&quot;  I can think of two digital activities that people commonly do with inexpensive handheld transceivers: APRS and Winlink 2000.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;APRS is used to send and receive &quot;tactical situation data&quot;.  Most people use APRS to send GPS position reports from their cars, but it can also be used to send short person-to-person text messages, weather data, and all sorts of other things.  (You can see what kind of information people are sending on APRS by pointing your browser at &lt;a href=&quot;http://aprs.fi&quot; rel=&quot;nofollow&quot;&gt;aprs.fi&lt;/a&gt;.)  Winlink 2000 is a way to send and receive short emails over HF, VHF, or UHF: just the thing to help the larger community when disaster strikes.  Both APRS and Winlink 2000 over VHF/UHF are based on AX.25 packet radio, which means that you would need some sort of Terminal Node Controller (TNC).  The TNC is likely to cost more than your handheld, but as ham equipment goes they are considered relatively inexpensive.  I use a Byonics Tiny Trak 4 for APRS; it's reasonably-priced and compact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check out APRS and/or Winlink 2000, and have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-03-15T00:15:04.437" LastActivityDate="2016-03-15T00:15:04.437" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5936" PostTypeId="2" ParentId="5930" CreationDate="2016-03-15T11:43:19.020" Score="0" Body="&lt;p&gt;If you can get audio between the radio and the computer, then there are a number of modes you can use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most common is AFSK, or audio frequency shift keying. This is some discrete number of audio tones, which are then FM modulated just as they would be if you whistled them into the microphone. The pitch of the tone encodes some digital bit or bits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually, AFSK of a particular specification is used to encode the AX.25 protocol, which is then used for APRS and packet radio. Packet was common back in the day, but not so much today.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;AFSK isn't an especially efficient modulation compared to designed-for-digital modulations like &lt;a href=&quot;https://en.wikipedia.org/wiki/Minimum-shift_keying&quot; rel=&quot;nofollow noreferrer&quot;&gt;MSK&lt;/a&gt;. However, any FM radio can trivially be converted for AFSK operation (with an external computer), and you can find other hams using it. The same can not be said for most other modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible to take most digital modes meant to be used on HF SSB, and feed them into the audio input of an FM radio also. Apparently &lt;a href=&quot;https://ham.stackexchange.com/questions/464/2m-or-70cm-fm-mobile-radio-for-digital-mode-operation&quot;&gt;people do this with PSK31&lt;/a&gt;, although this is a horrible use of spectrum since FM-modulated-PSK31 spreads your transmitter power over a much wider bandwidth than PSK31 alone. There's also more noise power in this wider bandwidth, while the energy per bit transmitted is not increased. Consequently, the maximum error-free bitrate for PSK31-over-FM is much less than that of ordinary PSK31, or the theoretical maximum.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-03-15T11:43:19.020" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5937" PostTypeId="2" ParentId="5892" CreationDate="2016-03-15T11:59:01.377" Score="1" Body="&lt;p&gt;Most manufactures that sell ferrite materials will say something about their intended application. HF isn't especially demanding. You'll probably want to avoid anything intended for EMI suppression, since these materials tend to be lossy since the goal is specifically to convert EMI into heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also just search around the internet for people who have built similar things and do what they are doing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having narrowed down the choices, you'll want to &lt;a href=&quot;https://ham.stackexchange.com/questions/1159/how-does-one-read-a-ferrite-datasheet&quot;&gt;read the datasheet&lt;/a&gt; and select a core which&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;has low loss and won't overheat,&lt;/li&gt;&#xA;&lt;li&gt;won't saturate at your maximum transmit power,&lt;/li&gt;&#xA;&lt;li&gt;meets any dimensional constraints you might have, and&lt;/li&gt;&#xA;&lt;li&gt;provides sufficient inductance to not adversely affect the impedance seen by the transmitter.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-03-15T11:59:01.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5939" PostTypeId="2" ParentId="5930" CreationDate="2016-03-16T08:23:13.340" Score="0" Body="&lt;p&gt;Well, there is a difference in regards to &quot;mode&quot; and &quot;encoding&quot; and &quot;modulation&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can &quot;encode&quot; a PSK &quot;mode&quot; on an FM &quot;modulation&quot;, as long as &quot;the other end&quot; is using the same to demodulate and decode, you can make a contact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Certain &quot;modes&quot; will work more efficiently with certain modulations, but it is nowhere written that you MUST use a particular modulation for any modes (with some restrictions and exceptions)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you start using (the example given) PSK on top of an FM modulated signal, you might not get a lot of responses, as there not be a lot of people listening for that mode using that modulation. But let that not stop you ! Experimenting like this can be fun; but for first trials I would urge you to &quot;line up the other end&quot; to ensure you have someone listening, decoding and responding to your signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH,&#xA;Edwin.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-03-16T08:23:13.340" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5941" PostTypeId="2" ParentId="3716" CreationDate="2016-03-16T17:16:26.333" Score="3" Body="&lt;p&gt;There's a great reference for radio and microphone pinout diagrams here: &lt;a href=&quot;http://www.qsl.net/g4wpw/date.html&quot; rel=&quot;nofollow&quot;&gt;www.qsl.net/g4wpw/date.html&lt;/a&gt;.  That site indicates that the IC-2800H is meant to work with the HM-98 rather than the HM-133, but the pinouts are the same, so if nothing else it will work as a microphone with a PTT button.  The fancy buttons on the back are quite different, and who knows if they would work with your radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there's &lt;a href=&quot;http://tinymicros.com/wiki/Icom_HM-133&quot; rel=&quot;nofollow&quot;&gt;this site&lt;/a&gt;, which says there are actually several versions of the HM-133; the oldest is based on the HM-98.  The pictures of the fancy buttons of a couple different versions of the HM-133 look similar, but of course not the same as the HM-98.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did a web search for &quot;Icom HM-98&quot; and found some for sale for US$ 18.95.  That's suspiciously cheap, so it may be a knock-off, but both genuine Icom mics and knockoff Icom mics use electret elements, so a knockoff is likely to sound very similar to a genuine Icom mic anyway.  I'd probably buy one of those and try it out.  If not you could certainly try an HM-133, but the fancy buttons might not work correctly.  Good luck, and let us know what you tried and how it worked in the comments.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-16T17:16:26.333" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5942" PostTypeId="1" AcceptedAnswerId="5946" CreationDate="2016-03-16T20:20:00.793" Score="1" ViewCount="1024" Body="&lt;p&gt;I am using a &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B017AYH5G0&quot; rel=&quot;nofollow&quot;&gt;FS1000a Transmitter and a MX-RM-5V Reciever&lt;/a&gt; for transmitting Sensor Data inside my flat to an Arduino Device. (13 Chars every 10 Seconds) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same Transmitter type is also used for switching wireless power plugs from the Arduino Device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00SO2EV8S&quot; rel=&quot;nofollow&quot;&gt;antennas that are wound&lt;/a&gt; with a diameter of approximately 0.4 cm and the length of the wire seems to be lambda/2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While I can control the power plugs two rooms further with no problems, receiving the sensor data from there is not possible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I already built some antenna-variants (copper wire with lamdba/4 and lamdba/2, normal wire), but nothing seems to work out. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the moment I am using the wound-antennas and placed them all in a vertical position, the baud rate is set to 2000 (1000 made no difference)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe someone can give me an advice how to extend the range of the system? Increasing the voltage of the transmitter is not possible.&lt;/p&gt;&#xA;" OwnerUserId="6346" LastEditorUserId="6346" LastEditDate="2016-03-18T00:09:06.340" LastActivityDate="2016-03-22T12:26:49.590" Title="Better antenna for 433 MHz" Tags="&lt;antenna-construction&gt;&lt;range&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5943" PostTypeId="1" CreationDate="2016-03-17T16:07:49.617" Score="2" ViewCount="137" Body="&lt;p&gt;I am part of a research team looking at the possible effects of EM fields on psychological function. The experiment calls for participants to perform a series of tests while inside a Faraday tent that blocks most of the radio spectrum. We'd like to have the participants perform the same tests inside the tent, but now while being exposed to roughly the same EM fields that are present outside of the enclosure. If we open the door or a panel to allow EM fields inside, then the participants will know. Instead we need the participants to not know whether they are being exposed to ambient EM fields. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our current plan is to link 2 broad spectrum antennas outside the Faraday tent with a matched pair of antennas inside the tent. We'd have a relay switch in the cable to control the on/off function, and a preamp to slightly boost the signal. I'm not convinced this will work though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would you guys recommend? It doesn't have to be a perfect replication, just &quot;good enough.&quot; We're most interested in reproducing the 25MHz-3GHz range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks for your suggestions!&lt;/p&gt;&#xA;" OwnerUserId="6350" LastActivityDate="2016-03-19T05:31:13.607" Title="Reproduce ambient EM fields inside a Faraday cage?" Tags="&lt;antenna&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5945" PostTypeId="2" ParentId="5943" CreationDate="2016-03-17T18:15:48.803" Score="2" Body="&lt;p&gt;Something along those lines might work.  I think you would need to use a spectrum analyzer hooked to a broad-spectrum antenna to analyze your test environment.  You could record a sweep of the ambient spectrum outside the tent, another sweep of the interior of the tent with your &quot;noise repeater&quot; off, and another of the interior with your noise repeater on.  Those results will tell you if your noise repeater works adequately or not.  You might have a problem with the signal being reproduced more accurately at some frequencies than others.  I would think that you would need the data from those scans to include in the writeup of your results.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-17T18:15:48.803" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5946" PostTypeId="2" ParentId="5942" CreationDate="2016-03-17T20:01:11.623" Score="0" Body="&lt;p&gt;I'll begin by saying I do not have any first-hand experience with these transmitter receiver pairs.  But it seemed very interesting to me so I did a little bit of research to learn more about how they can be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My conclusion is that you probably will not see much improvement in the error-rate of data transmission by altering the existing antennas.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;While I can control the power plugs two rooms further with no&#xA;  problems, receiving the sensor data from there is not possible.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The reason that you find success controlling the power plugs is that the message is very simple (on or off) and there is some error checking built into the data protocol.  Also the on or off message is repeated many times with some unique data pattern that can be reliably distinguished from random data meaning that the receiver is smart at ignoring false messages due to random noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly you could transmit data packets at a very slow rate, I'll guess at a rate of a few characters per second by using the same error-tolerant technique used for simple on/off messages.  You'd implement this with some unique code to indicate begin of data and also you'll need to send some sort of error checking code like a CRC after the data character.  The receiver software needs to throw away any characters that are not received with a valid CRC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;http://thegaragelab.com/wireless-communications-433mhz-modules/&quot; rel=&quot;nofollow&quot;&gt;what I found in my research&lt;/a&gt; you need to expect a very high error rate in data transmission of 90% error rate or even worse.  Your only way to conquer such a poor error rate is to repeat the message (or each data character) many times and have the receiver have some logic to know how to ignore erroneously received characters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a code library called &lt;a href=&quot;http://www.airspayce.com/mikem/arduino/RadioHead/classRH__ASK.html&quot; rel=&quot;nofollow&quot;&gt;RadioHead&lt;/a&gt; that has a good protocol already coded so you do not need to begin with nothing.  One comment describing their protocol helps to understand how they solve the noisy data transmission error rate in their code: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does not use the Arduino UART. Messages are sent with a training preamble, message length and checksum. Messages are sent with 4-to-6 bit encoding for good DC balance, and a CRC checksum for message integrity.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You may ask yourself how or why such product can be marketed that are so unreliable as an error rate of worse than 90%.  The reason is they are using frequencies that are assigned to other licensed users.  So the cheap devices you use need to be tolerant of interference and also not interfere with the licensed users.  You need to write a software protocol to be tolerant of interference and already the modules you chose are not going to present much of a problem interfering with licensed users since the modules have a very low 25mW transmit power which is a very tiny level unlikely to bother your next door neighbor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively you could adopt a more expensive transmitter and receiver technology like Bluetooth LE or XBEE where the modules already handle the error checking protocol for you so that you do not need to invent your own software error tolerant protocol.  The modules you have begun to use are very nice for their extremely low price, but like all things in engineering you trade one thing for another.  In this case the low cost brings more complexity in your application.  Keeping the cost down makes sense in mass production but maybe not so much for a single project.&lt;/p&gt;&#xA;" OwnerUserId="6113" LastEditorUserId="6113" LastEditDate="2016-03-19T15:13:45.480" LastActivityDate="2016-03-19T15:13:45.480" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5948" PostTypeId="2" ParentId="5942" CreationDate="2016-03-18T00:59:03.637" Score="0" Body="&lt;p&gt;I think you could improve the sensitivity of the receive antenna by making the antenna a larger loop with more turns, with the axis of the loop pointing at the transmitter.  It would also be possible to increase the efficiency of the transmit antenna, but more difficult, because the transmit antenna's impedance must match the impedance that the transmitter's output circuit expects.  If there is an impedance mismatch power will be reflected back to the transmitter, which would raise the voltage on your output transistor and possibly damage or destroy it.  It is possible to measure the transmitter's characteristic impedance, that is the impedance that the output circuit expects, but to do so would take some radio knowledge and expertise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My practical suggestion would be to experiment with a larger loop with more turns for the receive antenna, or do as Craig suggests and buy a different transmitter and receiver.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-18T00:59:03.637" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5950" PostTypeId="2" ParentId="5943" CreationDate="2016-03-19T05:31:13.607" Score="2" Body="&lt;p&gt;To add to the good answer from rclocher3,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) as you will be looking for a very small effect, (possibly  non-existent) it might help to be able to vary the levels in the tent, from zero to say 100 times ambient. Then you can plot a dose response curve, not just on/off. To do this you'd need quite a large, high gain amplifier, and a step attenuator, adjustable from 0 to 90 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) you must measure the power spectrum - the EM environment can vary by 1000x between places, depending on your proximity to broadcast towers, cell phone masts etc. You don't want that variation clouding the results. No need for a separate measuring antenna, just tap off a fraction of the signal you're injecting, into a spectrum analyser.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) you might find that the external, source environment changes too much over time due to people with phones and wifi devices moving around the experiment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It might just be better to generate controlled signals yourself, with a signal generator. Depending on how much you spend, you can generate quite realistic signals, but even the most basic signal generator would do for a simple pulsed or modulated signal at one frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4) if you deliberately expose people to amplified RF signals you'll need to monitor compliance with safety standards. As a rough guideline, 1 watt into the tent is unlikely to exceed the safety levels, as this is what an average phone produces, against your body. With a 1 watt amplifier, you could prove compliance with only a calculation based on the amplifier specifications and the experimental setup. You might need more power than this to get useful fields at lower frequencies, but then you'll need some professional monitoring for safety. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;5) you will need very broadband antennas, for example the TESEQ CBL6143. In fact you might consider renting an EMC facility for the test, they'd have all the antennas, amplifiers  and the shielded room. But all the equipment can be rented loose, too.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2016-03-19T05:31:13.607" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5952" PostTypeId="1" CreationDate="2016-03-20T04:05:00.297" Score="2" ViewCount="1759" Body="&lt;p&gt;I have a Cobra HG A1500 on a 1998 Ford Ranger. Due to clearance issues I cannot mount it on my roof, so I put it in front of my windshield by the wipers. Will this give me good enough ground plane to communicate with CB? I live in a mountainous area and haven't been able to get a radio check with anyone.&lt;/p&gt;&#xA;" OwnerUserId="6366" LastEditorUserId="218" LastEditDate="2016-03-23T11:16:43.283" LastActivityDate="2016-03-23T17:05:33.700" Title="Is my ground plane good?" Tags="&lt;grounding&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5953" PostTypeId="1" AcceptedAnswerId="12730" CreationDate="2016-03-20T08:38:11.513" Score="3" ViewCount="509" Body="&lt;p&gt;Are plastic predator bird props &lt;strong&gt;any effective at keeping away real birds from our antennas?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I mount such a plastic predator bird with screws or &lt;strong&gt;does it need to wiggle in the wind to be effective?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the latter case, &lt;strong&gt;how do I mount it then?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The props are hollow and have an opening at the bottom which allows them to be filled with sand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pictures or drawings of mounting examples in amateur radio applications are very much welcomed!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AVcYr.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AVcYr.jpg&quot; alt=&quot;plastic owl&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="250" LastActivityDate="2019-01-30T17:49:12.377" Title="Plastic predator bird props --- Are they effective? How to mount them?" Tags="&lt;antenna-construction&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5954" PostTypeId="2" ParentId="5953" CreationDate="2016-03-20T14:35:19.587" Score="4" Body="&lt;p&gt;They've been shown to only be effective when moved frequently, and even then, some of the biggest pest species like grackles and pigeons catch on quickly and they become completely ineffective, especially when actual predators are scarce. We tried to use them in a garden a couple years ago with very little success, even moving them around every few days.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bigger question when using them for antennas is, why? If you have issues with birds building nests in your tower or on top of your beams, other methods of exclusion would probably be far more effective. Fiberglass window screen wrapped around the tower at spots where they might try to nest, such as around the rotor plate, ought to do the trick. A few bamboo kabob skewers taped to your beam in the areas where there are big enough flat spots for a nest, such as where the boom meets the elements should also deter nesting there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're concerned about them sitting on the antenna, you aren't likely to do them any harm, and it's pretty unlikely that less than a dozen good sized birds like pigeons will change the characteristics of the antenna noticeably. If droppings are an issue, that could be a bit trickier, but something like a bit of cloth stuck to a motor that spun a few times intermittently to create motion near their favorite perches should deter them. One of the most effective means we discovered was a motion activated lawn sprinkler, which would obviously be impractical to implement on top of your tower, but you can extrapolate other ways of creating motion and/or noise on queue to scare them off.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-03-20T14:35:19.587" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="5955" PostTypeId="2" ParentId="5952" CreationDate="2016-03-20T14:51:41.917" Score="1" Body="&lt;p&gt;The center of the vehicle on a large flat metal surface is always the best placement for performance, but when that isn't possible, placement at any given point around the periphery of the vehicle has relatively little impact on antenna performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is especially true if all of the various parts of the chassis and body are bonded together electrically. The windshield is electrically pretty small on 11 meters, and there are other conductive paths around the windshield that should mean that performance there isn't radically different than anywhere else on the vehicle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The big issue is that how well various body panels are bonded together varies considerably from panel to panel and from vehicle to vehicle. The door especially, which in this case is going to be a big part of the ground plane, very often has a poor electrical connection to the rest of the vehicle from an RF perspective, because it's constructed to minimize sound conduction, which usually requires isolating mechanical connections with sound deadening (and electrically insulating) material.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would probably be a good idea to run a bit of copper braid from the quarter panel to the chassis under the hood, and from the quarter panel to the door itself, to ensure that it's got a nice low resistance path. This is usually done by running the braid from one of the bolts on the door hinge connected to the chassis, to one of the bolts on the side of the hinge that's connected to the door.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The roof and hood may also be similarly mechanically isolated, so it would be worth using a multimeter to check electrical resistance between the antenna mount and a bit of bare metal on the roof and hood. If they show a resistance of more than a fraction of an ohm, bond them all together in the same way as I described for the door, using the chassis as your common conductor rather than running gobs of copper braid straight from the antenna mount to each body panel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beyond that, bonding the rest of the vehicle together, or locating it at any other point around the vehicle is not likely to get you an improvement in efficiency of more than a few percent, and probably isn't worth the hassle. If you were running a 100 watt HF ham radio, it might be a different story just for mitigation of RFI and protecting the radio, but on a 4 watt CB, it's not something worth sweating over.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-03-20T14:51:41.917" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="5956" PostTypeId="2" ParentId="5952" CreationDate="2016-03-20T14:52:19.603" Score="0" Body="&lt;p&gt;Well I don't really know the car and the specific antenna good enough to give a proper answer, but I can think of several general steps you could take to check if everything is working fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First see if you have any reception with the antenna. Listen to the band at different times of the day and try to see if you can actually hear anything. &#xA;If you know of any regular nets or round tables you should definitely try listening to them and to see if it's working.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, you mentioned clearance issues. My advice would be to actually try to find somewhere an open area where you can park the car and do some experiments. Try placing the antenna right at the middle of the roof and right at the middle of the hood of the car. Check SWR in both locations. I'm no sure if Google is giving me good results for the pictures of the car, but from what I've found, it seems that the hood has greater surface area than the roof of the car, so it should be sort of OK as a ground plane. Try to make some contacts if you can like that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Afterwards, try moving the antenna to a more preferred location and see how things change.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2016-03-20T14:52:19.603" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5957" PostTypeId="1" AcceptedAnswerId="5969" CreationDate="2016-03-21T18:42:28.980" Score="3" ViewCount="355" Body="&lt;p&gt;I own the original Icom ID-51A.  I have the GPS logger logging every 5 seconds to the microSD card.  How do I view this saved track data on my computer?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reference, here's one of my logs (I know it looks like I'm going in circles, I was doing GSAR training that weekend): &lt;a href=&quot;http://www.km4ayu.com/errors/20160320_145218.log&quot; rel=&quot;nofollow&quot;&gt;http://www.km4ayu.com/errors/20160320_145218.log&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feel free to download and process that log, and let me know what you did.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the first several lines of content of that file (plaintext - and the whole thing exceeded the character limit, so just download it from that link above if you want more):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;$GPGGA,205221.743,3320.2409,N,08646.8572,W,1,04,10.5,170.1,M,-29.1,M,,0000*51&#xA;$GPGSA,A,3,23,09,08,07,,,,,,,,,11.5,10.5,4.6*36&#xA;$GPRMC,205221.743,A,3320.2409,N,08646.8572,W,1.64,49.17,200316,,,A*4D&#xA;$GPVTG,49.17,T,,M,1.64,N,3.0,K,A*36&#xA;$GPGGA,205222.743,3320.2939,N,08646.7655,W,1,04,7.4,100.0,M,-29.1,M,,0000*64&#xA;$GPGSA,A,3,23,09,08,07,,,,,,,,,7.8,7.4,2.6*3D&#xA;$GPRMC,205222.743,A,3320.2939,N,08646.7655,W,1.00,49.17,200316,,,A*4B&#xA;$GPVTG,49.17,T,,M,1.00,N,1.8,K,A*3E&#xA;$GPGGA,205223.743,3320.3039,N,08646.7474,W,1,04,7.4,81.6,M,-29.1,M,,0000*52&#xA;$GPGSA,A,3,23,09,08,07,,,,,,,,,7.8,7.4,2.6*3D&#xA;$GPRMC,205223.743,A,3320.3039,N,08646.7474,W,2.11,49.25,200316,,,A*41&#xA;$GPVTG,49.25,T,,M,2.11,N,3.9,K,A*3F&#xA;$GPGGA,205224.743,3320.3077,N,08646.7421,W,1,04,7.4,80.5,M,-29.1,M,,0000*5D&#xA;$GPGSA,A,3,23,09,08,07,,,,,,,,,7.8,7.4,2.6*3D&#xA;$GPRMC,205224.743,A,3320.3077,N,08646.7421,W,0.24,49.25,200316,,,A*48&#xA;$GPVTG,49.25,T,,M,0.24,N,0.4,K,A*35&#xA;$GPGGA,205225.743,3320.3062,N,08646.7444,W,1,04,7.4,87.1,M,-29.1,M,,0000*58&#xA;$GPGSA,A,3,23,09,08,07,,,,,,,,,7.8,7.4,2.6*3D&#xA;$GPRMC,205225.743,A,3320.3062,N,08646.7444,W,0.88,49.25,200316,,,A*48&#xA;$GPVTG,49.25,T,,M,0.88,N,1.6,K,A*30&#xA;$GPGGA,205226.743,3320.2993,N,08646.7560,W,1,04,7.4,102.4,M,-29.1,M,,0000*63&#xA;$GPGSA,A,3,23,09,08,07,,,,,,,,,7.8,7.4,2.6*3D&#xA;$GPRMC,205226.743,A,3320.2993,N,08646.7560,W,1.41,48.98,200316,,,A*49&#xA;$GPVTG,48.98,T,,M,1.41,N,2.6,K,A*30&#xA;$GPGGA,205227.743,3320.2751,N,08646.8022,W,1,05,2.8,116.5,M,-29.1,M,,0000*62&#xA;$GPGSA,A,3,23,27,09,08,07,,,,,,,,3.8,2.8,2.6*35&#xA;$GPRMC,205227.743,A,3320.2751,N,08646.8022,W,1.68,49.11,200316,,,A*4F&#xA;$GPVTG,49.11,T,,M,1.68,N,3.1,K,A*3D&#xA;$GPGGA,205228.743,3320.2493,N,08646.8520,W,1,05,2.8,128.0,M,-29.1,M,,0000*6F&#xA;$GPGSA,A,3,23,27,09,08,07,,,,,,,,3.8,2.8,2.6*35&#xA;$GPRMC,205228.743,A,3320.2493,N,08646.8520,W,0.35,49.11,200316,,,A*43&#xA;$GPVTG,49.11,T,,M,0.35,N,0.7,K,A*31&#xA;$GPGGA,205229.743,3320.2420,N,08646.8655,W,1,05,2.8,130.5,M,-29.1,M,,0000*6B&#xA;$GPGSA,A,3,23,27,09,08,07,,,,,,,,3.8,2.8,2.6*35&#xA;$GPRMC,205229.743,A,3320.2420,N,08646.8655,W,0.21,49.11,200316,,,A*4E&#xA;$GPVTG,49.11,T,,M,0.21,N,0.4,K,A*37&#xA;$GPGGA,205230.743,3320.2406,N,08646.8679,W,1,05,2.8,130.0,M,-29.1,M,,0000*6C&#xA;$GPGSA,A,3,23,27,09,08,07,,,,,,,,3.8,2.8,2.6*35&#xA;$GPRMC,205230.743,A,3320.2406,N,08646.8679,W,0.73,49.11,200316,,,A*4B&#xA;$GPVTG,49.11,T,,M,0.73,N,1.4,K,A*31&#xA;$GPGGA,205231.743,3320.2402,N,08646.8685,W,1,05,2.8,132.0,M,-29.1,M,,0000*68&#xA;$GPGSA,A,3,23,27,09,08,07,,,,,,,,3.8,2.8,2.6*35&#xA;$GPRMC,205231.743,A,3320.2402,N,08646.8685,W,0.29,49.11,200316,,,A*42&#xA;$GPVTG,49.11,T,,M,0.29,N,0.5,K,A*3E&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="5404" LastEditorUserId="76" LastEditDate="2019-03-13T01:48:04.883" LastActivityDate="2019-03-13T01:48:04.883" Title="How to read ID-51A GPS logger data" Tags="&lt;ht&gt;&lt;software&gt;&lt;gnss&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5959" PostTypeId="1" AcceptedAnswerId="5961" CreationDate="2016-03-22T01:25:21.680" Score="6" ViewCount="1228" Body="&lt;p&gt;When attaching a red and black pair of Powerpoles together, which way should I do it to ensure that it will plug into the most number of other people's gear?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When looking from the top of the connector (the side where the &quot;tongue&quot; is not visible) should the red one be on the left or the right when viewed from the front? &lt;/p&gt;&#xA;" OwnerUserId="5577" LastEditorUserId="76" LastEditDate="2016-04-22T18:44:42.077" LastActivityDate="2017-05-28T01:55:11.157" Title="On Anderson Powerpoles, does the red on go on the left or right?" Tags="&lt;connectors&gt;&lt;dc-power&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5961" PostTypeId="2" ParentId="5959" CreationDate="2016-03-22T11:58:18.907" Score="2" Body="&lt;p&gt;They say a picture is worth a thousand words:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GWhw6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GWhw6.png&quot; alt=&quot;Powerpole connector&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Source: &lt;a href=&quot;http://www.arrl.org/files/file/Public%20Service/TrainingModules/Technical/Anderson%20powerpole.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If viewed from the &quot;hood&quot; side where the connector is flat, with the wires going down, and the mating side of the connector up, then the positive side is on the right.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other amateur radio sources that corroborate this orientation:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.ohd3ares.org/equipment/power-poles/&quot; rel=&quot;nofollow noreferrer&quot;&gt;West Central Ohio District 3 ARES&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.qsl.net/ah6rh/am-radio/emcomm/powerpole.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;AH6RH&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.snj-ares.org/anderson_powerpole&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mercer County ARES&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Beware: this is a recommendation, not a standard. Hopefully within amateur radio people observe the ARRL recommendation, but Powerpole connectors are made of individual pieces which can be stacked in any orientation. If you do an &lt;a href=&quot;https://www.google.com/search?q=anderson%20powerpole&amp;amp;tbm=isch&quot; rel=&quot;nofollow noreferrer&quot;&gt;image search&lt;/a&gt; you can find examples where people have assembled them the other way. There's significant potential for an expensive mistake here.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-03-22T12:10:29.917" LastActivityDate="2016-03-22T12:10:29.917" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5962" PostTypeId="2" ParentId="5942" CreationDate="2016-03-22T12:26:49.590" Score="1" Body="&lt;p&gt;Those antennas appear to be a &lt;em&gt;normal mode&lt;/em&gt; &lt;a href=&quot;https://en.wikipedia.org/wiki/Helical_antenna&quot; rel=&quot;nofollow&quot;&gt;helical antenna&lt;/a&gt;. When mounted on a portable radio and encased in plastic to improve durrability, they are known as a &lt;a href=&quot;https://en.wikipedia.org/wiki/Rubber_ducky_antenna&quot; rel=&quot;nofollow&quot;&gt;rubber ducky&lt;/a&gt; antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are essentially &lt;a href=&quot;http://www.antenna-theory.com/antennas/monopole.php&quot; rel=&quot;nofollow&quot;&gt;monopole antennas&lt;/a&gt; which have been made physically smaller by distributing a large degree of self-inductance throughout their length. This smaller size also means reduced efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can get improved efficiency at the expense of larger size by using a quarter-wave monopole or a &lt;a href=&quot;http://www.antenna-theory.com/antennas/halfwave.php&quot; rel=&quot;nofollow&quot;&gt;half-wave dipole&lt;/a&gt; antenna. These are easy to construct as they are simply a straight piece of wire. For 433 MHz, the length of a monopole antenna is about 165 millimeters. For a dipole, make two such wires, each 165mm long, and attach one to the antenna connection, and the other to ground on your radio board.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Craig notes, these radios appear to be more about low cost than robustness, so a more effective antenna may not make them significantly better. Since it is quite easy to make a straight piece of wire, I suggest you give it a try anyway.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-03-22T12:26:49.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5963" PostTypeId="1" AcceptedAnswerId="5964" CreationDate="2016-03-22T13:25:36.997" Score="5" ViewCount="210" Body="&lt;p&gt;I got my amateur license back in the early '80s, primarily for putting it on my resume for an electronics job. Never used it outside of developing my Morse code speed, and once I got my Advanced Class and short call sign, I never used it again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well I'm retired now, and I plan on traveling the US while living long-term in an Airstream RV. Are there any constraints or gotchas I should be aware of when it comes to having no fixed address for years at a time?&lt;/p&gt;&#xA;" OwnerUserId="6377" LastEditorUserId="76" LastEditDate="2016-03-22T15:04:10.493" LastActivityDate="2016-03-22T15:15:51.197" Title="Amateur Radio for a Nomad" Tags="&lt;united-states&gt;&lt;mobile&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ClosedDate="2017-03-29T14:09:03.477" ContentLicense="CC BY-SA 3.0" />
  <row Id="5964" PostTypeId="2" ParentId="5963" CreationDate="2016-03-22T15:08:05.700" Score="6" Body="&lt;p&gt;The only thing you need to do is &lt;strong&gt;make sure you can receive mail at the mailing address on your license,&lt;/strong&gt; because that is part of the obligation of holding a license. It doesn't have to be your ‘residence’ or your true address in any sense; you can put down the address of a friend who'll read it for you and notify you of anything important, and that'll satisfy your obligation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's it! Have fun!&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-03-22T15:08:05.700" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5965" PostTypeId="2" ParentId="5963" CreationDate="2016-03-22T15:15:51.197" Score="6" Body="&lt;p&gt;The relevant regulation is &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_123&quot; rel=&quot;noreferrer&quot;&gt;§97.23&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Each license grant must show the grantee's correct name and mailing address. The mailing address must be in an area where the amateur service is regulated by the FCC and where the grantee can receive mail delivery by the United States Postal Service. Revocation of the station license or suspension of the operator license may result when correspondence from the FCC is returned as undeliverable because the grantee failed to provide the correct mailing address.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So you can be wherever you want, but you need to be able to respond to mail sent to the address registered to your license.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-03-22T15:15:51.197" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5966" PostTypeId="2" ParentId="5959" CreationDate="2016-03-22T15:56:49.697" Score="2" Body="&lt;p&gt;The mnemonic that I use is &quot;red right tongue top&quot;.  (It leaves out &quot;when the connectors are pointed at you.&quot;)  That is to say, when the tongues are up, then the red connector is on the right.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-22T15:56:49.697" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5967" PostTypeId="2" ParentId="5957" CreationDate="2016-03-22T16:28:38.593" Score="1" Body="&lt;p&gt;The first step is to get the file into your computer, either by plugging a USB cable into the radio if that works, or by removing the microSD card from the radio, plugging it into an SD card adapter, and then putting the adapter into your computer.  Then copy or move the file.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you probably were asking about how to handle the file.  The manual seems pretty vague about the file format.  If you're lucky the format will be an open widely-recognized format such as GPX or KML.  If you have Google Earth installed, the first thing I would try is to open the file with that; you might just get lucky.  If that doesn't do it then you'll probably need to do some detective work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a web site &lt;a href=&quot;http://www.gpsvisualizer.com/&quot; rel=&quot;nofollow&quot;&gt;www.gpsvisualizer.com&lt;/a&gt; that is tremendously useful.  That site may be able to recognize the file format right away, and if it does, it will be able to translate to a more useful format.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a program that you can download called &lt;a href=&quot;http://www.gpsbabel.org/&quot; rel=&quot;nofollow&quot;&gt;GPSBabel&lt;/a&gt;.  That software can translate between many different GPS formats.  It can be difficult to use, but it's tremendously powerful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck, and if you figure out how to handle the file format please come back here and let us know how you did it.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-22T16:28:38.593" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="5968" PostTypeId="1" AcceptedAnswerId="5970" CreationDate="2016-03-22T20:18:46.180" Score="4" ViewCount="1065" Body="&lt;p&gt;I'm looking at incoming packets. Here's the beginning of a few messages:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;KF7WXW-9&amp;gt;TU3RTW,WIDE1-1,WIDE2-1:`2D&amp;lt;..&#xA;KX5ONE-9&amp;gt;T5SRPV,WIDE1-1,WIDE2-1:`2E0..&#xA;KX5ONE-9&amp;gt;T5SRSV,WIDE1-1,WIDE2-1:`2E ..&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;So, what to the Txxxxx labels mean? &lt;a href=&quot;http://www.aprs.org/doc/APRS101.PDF&quot; rel=&quot;nofollow&quot;&gt;The APRS spec talks about the destination addresses&lt;/a&gt; (pg13). Is it related to the MIC-E encoding (pg44)? If so, please break down the encoding in your answer.&lt;/p&gt;&#xA;" OwnerUserId="6229" LastActivityDate="2016-03-23T00:53:11.943" Title="What does the APRS 'to'/destination address mean?" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5969" PostTypeId="2" ParentId="5957" CreationDate="2016-03-22T20:21:14.537" Score="5" Body="&lt;p&gt;This is standard NMEA data format.  The GPS is configured to provide the following NMEA strings:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;GPGGA, Essential fix data, time, location, quality of fix, altitude&lt;/li&gt;&#xA;&lt;li&gt;GPGSA, Dilution of precision and active satellites&lt;/li&gt;&#xA;&lt;li&gt;GPRMC, Recommended minimum data: position, velocity, vector, time&lt;/li&gt;&#xA;&lt;li&gt;GPVTG, Velocity and vector&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You'll notice much of the information is redundant, time occurs in many sentences, so does position. The original design of the NMEA communications standard allowed many devices to connect to one common data bus and listen only for those sentences they need, and provide only those sentences they had available.  Some devices didn't calculate vector and velocity, so never provided more than the &lt;code&gt;GGA&lt;/code&gt; and &lt;code&gt;GSA&lt;/code&gt; sentences.  Now almost all GPS units deliver most of the possible GPS sentences, but they are configurable so you can turn some sentences on or off depending on your needs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The essential NMEA API is sentence based.  The $ starts a sentence, and the *xx ends it, with xx being a checksum. Each device has a two letter prefix, &lt;code&gt;GP&lt;/code&gt; for GPS units, and a three letter suffix for the sentence type.  There are further interesting things about the standard, but they are not necessary to understand your data.  See &lt;a href=&quot;http://www.gpsinformation.org/dale/nmea.htm&quot;&gt;http://www.gpsinformation.org/dale/nmea.htm&lt;/a&gt; for more detail, but here's the interpretation of the first four entries, which comprise one data point, of your data:&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;$GPGGA,205221.743,3320.2409,N,08646.8572,W,1,04,10.5,170.1,M,-29.1,M,,0000*51&lt;/h3&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Where:&#xA; GGA          Global Positioning System Fix Data&#xA; 205221.743   Fix taken at 20:52:21.743 UTC&#xA; 3320.2409,N  Latitude 33 deg 20.2409' N&#xA; 08646.8572,W Longitude 8 deg 46.8572' W&#xA; 1            Fix quality: 0 = invalid&#xA;                           1 = GPS fix (SPS)&#xA;                           2 = DGPS fix&#xA;                           3 = PPS fix&#xA;                           4 = Real Time Kinematic&#xA;                           5 = Float RTK&#xA;                           6 = estimated (dead reckoning) (2.3 feature)&#xA;                           7 = Manual input mode&#xA;                           8 = Simulation mode&#xA; 04           Number of satellites being tracked&#xA; 10.5         Horizontal dilution of position&#xA; 170.1,M      Altitude, Meters, above mean sea level&#xA; -29.1,M      Height of geoid (mean sea level) above WGS84 ellipsoid&#xA; (empty)      Time in seconds since last DGPS update&#xA; 0000         DGPS station ID number&#xA; *51          the checksum data, always begins with *&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;h3&gt;$GPGSA,A,3,23,09,08,07,,,,,,,,,11.5,10.5,4.6*36&lt;/h3&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Where:&#xA; GSA      Satellite status&#xA; A        Auto selection of 2D or 3D fix (M = manual) &#xA; 3        3D fix - values include: 1 = no fix&#xA;                                   2 = 2D fix&#xA;                                   3 = 3D fix&#xA; 23,9,8,7,... PRNs of satellites used for fix (space for 12) &#xA; 11.5     PDOP (dilution of precision) &#xA; 10.5     Horizontal dilution of precision (HDOP) &#xA; 4.6      Vertical dilution of precision (VDOP)&#xA; *36      the checksum data, always begins with *&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;h3&gt;$GPRMC,205221.743,A,3320.2409,N,08646.8572,W,1.64,49.17,200316,,,A*4D&lt;/h3&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Where:&#xA; RMC          Recommended Minimum sentence C&#xA; 205221.743   Fix taken at 20:52:21.743 UTC&#xA; A            Status A=active or V=Void.&#xA; 3320.2409,N  Latitude 33 deg 20.2409' N&#xA; 08646.8572,W Longitude 8 deg 46.8572' W&#xA; 1.64         Speed over the ground in knots&#xA; 49.17        Track angle in degrees True&#xA; 200316       Date - 20th of March 2016&#xA; (empty),(empty) Magnetic Variation&#xA; A            Fix type (NMEA 2.3, not included on older receivers):&#xA;                       A=autonomous&#xA;                       D=differential&#xA;                       E=Estimated&#xA;                       N=Not Valid&#xA;                       S=Simulated&#xA; *6A          The checksum data, always begins with *&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;h3&gt;$GPVTG,49.17,T,,M,1.64,N,3.0,K,A*36&lt;/h3&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;where:&#xA;    VTG          Track made good and ground speed&#xA;    49.17,T      True track made good (degrees)&#xA;    (empty),M    Magnetic track made good&#xA;    1.64,N       Ground speed, knots&#xA;    3.0,K        Ground speed, Kilometers per hour&#xA;    A            Fix type (NMEA 2.3, not included on older receivers):&#xA;                       A=autonomous&#xA;                       D=differential&#xA;                       E=Estimated&#xA;                       N=Not Valid&#xA;                       S=Simulated&#xA;    *48          Checksum&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Of course you don't have to use all of these.  A quick way to interpret the data is to load it all into excel as comma delimited, then extract the data you need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course many programs support this data directly.  For instance, Google Earth imports these files using &lt;a href=&quot;https://support.google.com/earth/answer/148095?hl=en&quot;&gt;these instructions, under &quot;Importing GPS Data&quot;.&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a very commonly used GPS data format, so while it may not be immediately obvious, most mapping software will have a way to import and use it.&lt;/p&gt;&#xA;" OwnerUserId="9" LastActivityDate="2016-03-22T20:21:14.537" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5970" PostTypeId="2" ParentId="5968" CreationDate="2016-03-22T22:02:43.317" Score="2" Body="&lt;p&gt;The Txxxxx labels are the Mic-E encoded Destination field.  Let's take the first example, TU3RTW.  If we look up the latitude digits from the table, we get 453247.  Then there is the other information encoded in the six digits.  The first three digits give the message code.  T gives 1 (standard), U gives 1 (standard), and 3 gives 0.  So that's standard message code 110, which means &quot;en route&quot;.  Moving on, R in the 4th digit (rather than 2) means North.  The T in the 5th digit means +100&amp;deg; longitude.  The W in the 6th digit means West.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To sum up, we have a station &quot;en route&quot; at 45&amp;deg; 32.47' North latitude.  Also the station is in the western hemisphere, somewhere west of the 100&amp;deg; West longitude line.  (The rest of the longitude is encoded in the Information field of the message.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-03-23T00:53:11.943" LastActivityDate="2016-03-23T00:53:11.943" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5971" PostTypeId="2" ParentId="5952" CreationDate="2016-03-23T11:33:56.477" Score="1" Body="&lt;p&gt;Mobile antennas are always compromises. No matter where you put the antenna, your ground plane will never be &quot;good&quot;. A good ground plane is flat, and extends out at least a quarter-wavelength in every direction, preferably more. A vehicle simply isn't big enough to make that happen on HF. This is the compromise that must be made for mobile operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question is not if it's &quot;good&quot;, but if it's &quot;good enough&quot;. People have mounted antennas on the trailer hitch, on the lips of the hood or trunk, and on the edge of a door, and had results that were good enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The usual test for determining if it works well enough is to see if you can talk to people with it. But if you can't talk to people, we can't conclude the ground plane is bad. It could be all kinds of things, like no one is around to hear you, or the radio or some other component isn't functioning properly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are things you can do to check, with the right equipment. If you have a directional power meter, you can check that the radio is putting power into the antenna, and that not too much of it is being reflected back. That would rule out most kinds of malfunctions, and suggest the problem is just that no one is around to hear you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately you can find a situation where you know someone will be around to hear you. Find someone else with a CB radio, and do some tests within shouting distance. Then get farther away and see if you get reasonable range.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-03-23T11:33:56.477" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5972" PostTypeId="2" ParentId="5952" CreationDate="2016-03-23T17:05:33.700" Score="0" Body="&lt;p&gt;In my answer to the question I will augment the merged previous answers.  I do not use a CB antenna but I do operate HF 3.5 thru 30 MHz ham bands using a Hi-Q 4/80 Screwdriver antenna mounted on the rear of my pickup truck as shown in the image below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LofIN.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LofIN.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although it is hard to see, above the center loaded coil is the top part of the antenna that extends about 3 feet or so above the coil.  The top of the antenna is 11 feet, 4 inches from ground level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the best performance of this antenna is when operating on the 10-meter band which is similar to the CB band; although, the antenna mentioned by the OP seems to be a major compromise as a CB antenna (and, as Phil Frost says, all mobile antennas are a compromise).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the best performance I have, I have bonded using copper strap conductors in about six spots under the truck -- bonding frame to metal cab and panel parts.  Result -- significantly reduces the noise generated by the truck itself (ignition, computers, alternator, etc.).  And, I assume that it has improved my ground plane but I have no actual experimental proof of that as I failed to do a before and after test as I did with the RFI problems of a mobile rig.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, the ground plane itself of the truck is a significant part of the efficiency of the antenna.  How do I know.  I know because the signal strength (as measured by S-meter) and by cooperating hams during a QSO, is much better for the direction off the front of the Truck rather than the rear and even the sides.  How much better?  About a half S-unit better.  In fact, If I am in a QSO while driving and the other station is off the front of the truck and I make a right hand turn then that signal drops appreciatively.  Indeed, I have lost signals entirely merely by the direction I travel -- it is like rotating a Yagi beam antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mounting dead center of the vehicle is probably the best as mentioned earlier but that is very impractical for many antennas, especially those trying to cover HF frequencies.  Mounting below metal though is also very bad such as mounting in the bed of my pickup truck.  Having a position high and clear from as much metal as practical that is below the antenna is best which justified the position I used on my truck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Performance?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have made QSOs to the Falkland Islands, Indonesia, and other far off DX locations from my truck using this antenna and my Icom IC-706 MkIIg 100-watt rig.  Also, I have contacted Cuba (from Washington State) via mobile CW on three different occasions from my truck.  It works well for North American contacts too.  Most of my operating though and all of the above examples were on 20 meters.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-03-23T17:05:33.700" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5973" PostTypeId="1" AcceptedAnswerId="5974" CreationDate="2016-03-24T00:44:40.650" Score="10" ViewCount="1342" Body="&lt;p&gt;I have a Baofeng GT3-MK3, a great little radio.&#xA;Is it OK to use this on the low output setting for general use without a licence, for things like camping/hiking family use etc, if I used the legal frequencies, i.e. 446 in UK?&lt;/p&gt;&#xA;" OwnerUserId="6388" LastEditorUserId="76" LastEditDate="2016-03-24T01:09:54.970" LastActivityDate="2017-08-27T01:15:43.593" Title="Is Using PMR446 On A Baofeng GT3-MK3 HAM Radio Legal (If on low power)?" Tags="&lt;legal&gt;&lt;baofeng&gt;&lt;united-kingdom&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5974" PostTypeId="2" ParentId="5973" CreationDate="2016-03-24T01:08:35.417" Score="6" Body="&lt;p&gt;Unfortunately not in the eyes of Ofcom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While you can restrict the power usage down to 0.5 Watts, the antenna is removable.  You'll notice that most of the stuff sold on the high-street will have solid antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the PMR frequency use, as part of the &quot;license-free agreement&quot;, apparatus in use must meet the high-street requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Worth noting though, there's not a single Ofcom document out there that mentions removable antennas as a no-go, interpretation of the documentation and relevant citations is all we have to go on.  It's a rather deep rabbit hole reading through all the linked PDF documents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further reading:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Non-ofcom interpretation)&#xA;&lt;a href=&quot;http://www.walkie-talkie-radio.co.uk/information-about-walkie-talkie-radios/two-way-radio-licencing-in-the-uk&quot; rel=&quot;noreferrer&quot;&gt;http://www.walkie-talkie-radio.co.uk/information-about-walkie-talkie-radios/two-way-radio-licencing-in-the-uk&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Ofcom)&#xA;&lt;a href=&quot;http://stakeholders.ofcom.org.uk/binaries/spectrum/spectrum-policy-area/spectrum-management/licence-exempt-radio-use/licence-exempt-devices/Analogue_and_Digital_PMR4461.pdf&quot; rel=&quot;noreferrer&quot;&gt;http://stakeholders.ofcom.org.uk/binaries/spectrum/spectrum-policy-area/spectrum-management/licence-exempt-radio-use/licence-exempt-devices/Analogue_and_Digital_PMR4461.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(UK Interface Requirement 2009)&#xA;&lt;a href=&quot;http://stakeholders.ofcom.org.uk/binaries/spectrum/spectrum-policy-area/spectrum-management/research-guidelines-tech-info/interface-requirements/IR2009.pdf&quot; rel=&quot;noreferrer&quot;&gt;http://stakeholders.ofcom.org.uk/binaries/spectrum/spectrum-policy-area/spectrum-management/research-guidelines-tech-info/interface-requirements/IR2009.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6389" LastActivityDate="2016-03-24T01:08:35.417" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5975" PostTypeId="1" AcceptedAnswerId="5977" CreationDate="2016-03-24T15:27:16.350" Score="0" ViewCount="123" Body="&lt;p&gt;Is there a device, something like a dummy load, that will allow one to test two radio's back-to-back without going over the air?&lt;/p&gt;&#xA;" OwnerUserId="810" LastActivityDate="2016-03-24T20:44:18.140" Title="Testing Radios Back-to-Back without Going Over-the-Air" Tags="&lt;testing&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5976" PostTypeId="2" ParentId="5975" CreationDate="2016-03-24T20:23:34.633" Score="1" Body="&lt;p&gt;Yes. A dummy load. They make horribly inefficient antennas, but when you have two radios on the same table, the path loss is low enough to make up for it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-03-24T20:23:34.633" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5977" PostTypeId="2" ParentId="5975" CreationDate="2016-03-24T20:44:18.140" Score="3" Body="&lt;p&gt;If you use a dummy load on the transmitter, it is likely that there will be enough power and enough leakage from either the load or the transmitter itself to be easily received. This is quite likely for the power levels and shielding quality in amateur equipment (homebrew or commercial).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you had a non-leaky or very low-power transmitter (e.g. the various SDR transceivers recently popular), so that you actually do need to make a connection, then what you need is an &lt;strong&gt;attenuator&lt;/strong&gt;. This is essentially a “pass-through dummy load”: it has two ports and an internal resistance, all properly impedance matched, so you just connect it between the transmitter and the receiver, and the majority of the power goes into the resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An attenuator used for this purpose must have the following specifications:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Enough attenuation (loss) so that the power output of the transmitter is reduced to the safe input level of the receiver, but not so much that the signal is below the noise floor of the receiver.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Like a dummy load, it must be able to dissipate the full power output of the transmitter (the fraction going to the receiver is insignificant).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Attenuators can have either fixed or variable (manually or electrically) attenuation. Variable attenuation is very useful for testing but can be very expensive since they are fairly obscure test gear. &lt;a href=&quot;https://ham.stackexchange.com/questions/2144/would-a-switched-rf-attenuator-be-asymmetric&quot;&gt;I found one for cheap at a flea market&lt;/a&gt; that I am informed probably used to be a component of a larger unit, but absent such luck I would suggest purchasing a fixed one of the appropriate value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is, if the dummy load doesn't work to start with.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-03-24T20:44:18.140" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5978" PostTypeId="1" AcceptedAnswerId="5979" CreationDate="2016-03-25T12:00:54.547" Score="1" ViewCount="625" Body="&lt;p&gt;what happens to the gain of a parabolic antenna, say this, &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00NQGVMSE&quot; rel=&quot;nofollow&quot;&gt;http://www.amazon.com/24dBi-Directional-Booster-Parabolic-Antenna/dp/B00NQGVMSE&lt;/a&gt;, for example if I use it in lower or higher frequencies?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;more specifically: what will be the gain if I use it in 1.1GHz, 1.5GHz, 1.9GHz, 3GHz, 3.5GHz?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;will it even work?&lt;/p&gt;&#xA;" OwnerUserId="6399" LastActivityDate="2016-03-28T14:48:12.117" Title="2.4GHz wifi parabolic antenna frequency response" Tags="&lt;antenna&gt;&lt;wifi&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5979" PostTypeId="2" ParentId="5978" CreationDate="2016-03-25T17:13:35.947" Score="3" Body="&lt;p&gt;The antenna feed is designed for 2.4 GHz, so performance at other frequencies will be not good (unmatched impedance, poor gain).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The parabolic reflector is usable at other frequencies as long as the wavelength is not smaller than the grid spacing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can &lt;a href=&quot;http://www.everythingrf.com/rf-calculators/parabolic-reflector-antenna-gain&quot; rel=&quot;nofollow&quot;&gt;calculate&lt;/a&gt; the &lt;a href=&quot;https://en.wikipedia.org/wiki/Parabolic_antenna#Gain&quot; rel=&quot;nofollow&quot;&gt;gain&lt;/a&gt; of the reflector at other frequencies.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2016-03-25T17:13:35.947" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5981" PostTypeId="2" ParentId="651" CreationDate="2016-03-25T20:27:33.327" Score="0" Body="&lt;p&gt;As explained in my comments above, I think your problem is this:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Airband communications are &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Airband&amp;amp;oldid=709193426#Modulation&quot; rel=&quot;nofollow&quot;&gt;typically Amplitude Modulated&lt;/a&gt;, i.e. &lt;strong&gt;AM&lt;/strong&gt;. (This has nothing to do with the frequency: just because they may be at VHF/UHF megahertz frequencies and close to FM broadcast frequencies, rather than MW  kilohertz frequencies like broadcast AM in the United States, does not matter. Technically speaking, you can use &lt;em&gt;any&lt;/em&gt; modulation at &lt;em&gt;any&lt;/em&gt; frequency, albeit subject to legal/practical restrictions.) They use AM for safety reasons: amplitude modulated signals are able to combine over top of each other. They don't always combine perfectly, but hearing the mess of overlapping AM signals is better better than if using FM, where the strongest signal may simply win and you didn't realize someone else was talking. (See &lt;a href=&quot;https://en.wikipedia.org/wiki/Tenerife_airport_disaster&quot; rel=&quot;nofollow&quot;&gt;Tenerife airport disaster&lt;/a&gt; for an example where sadly it was still not enough to prevent an accident.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Most amateur radio communications on VHF/UHF tend to be frequency modulated, i.e. &lt;strong&gt;FM&lt;/strong&gt;. Other modulation is certainly allowed, and certainly used especially in specialized simplex communications, but far less common in typical use with repeaters and APRS gateways and whatnot.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;All this to say: you need to verify that your receiver can demodulate signals of the type you wish to receive. It looks like the Yaesu VX-3 does support AM, and must be automatically selecting that mode for you. Apparently your VX-6R does &lt;em&gt;not&lt;/em&gt; support AM demodulation, or at least it is not switching over from the usual FM mode, to the necessary AM mode, when you try to listen to the airband transmissions.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-03-25T20:27:33.327" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5982" PostTypeId="2" ParentId="3714" CreationDate="2016-03-25T23:04:27.720" Score="1" Body="&lt;p&gt;You can do this .The coil of your crystal set will act as the receiving antenna .The necklace is your transmitting loop antenna . Your crystal set could be a class E resonant rectifier or some other technology borrowed from wireless charging. Your propagation is in the near field not the far field . 27 MHz is your choice of operating frequency . Sure  crystals are easy to find but it may not be optimum . A lower frequency increases detector efficiency . I think you should experiment with a sig gen so  you will minimise battery drain on your proposed production device .     &lt;/p&gt;&#xA;" OwnerUserId="6095" LastActivityDate="2016-03-25T23:04:27.720" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5984" PostTypeId="2" ParentId="5978" CreationDate="2016-03-26T15:59:58.380" Score="0" Body="&lt;p&gt;For 2.4 ` 2.5GHz antenna. You must be clear that it is a free band antenna. As for 3 Ghz to 3.75Ghz it lies in Paid frequency band. Other than this, For 2.4GHz yes you can use it with all the nearby frequency although it will hinder some of the gain issues but in practical scenario. It will work. &lt;/p&gt;&#xA;" OwnerUserId="6406" LastActivityDate="2016-03-26T15:59:58.380" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5985" PostTypeId="2" ParentId="5880" CreationDate="2016-03-26T16:04:02.743" Score="-3" Body="&lt;p&gt;No issue. You can use it on both ends and the loss is almost negligible.&lt;/p&gt;&#xA;" OwnerUserId="6406" LastEditorUserId="76" LastEditDate="2016-04-04T18:39:49.883" LastActivityDate="2016-04-04T18:39:49.883" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="5986" PostTypeId="2" ParentId="651" CreationDate="2016-03-27T06:22:44.687" Score="3" Body="&lt;p&gt;My experience, with a VX-5R, is that its AM receiver just isn't very good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It will switch into AM mode when you tune into the air band, but because it's really an FM radio, there is no AGC on the AM. Distant aeroplanes sound much softer than near ones. Even if the voice is clear, it's soft.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the squelch opening and faint hum that you hear might actually be a more distant aeroplane. Try turning up the volume and listening carefully for the voice.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2016-03-27T06:22:44.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5987" PostTypeId="2" ParentId="1509" CreationDate="2016-03-27T10:08:33.657" Score="0" Body="&lt;p&gt;I want to add to and correct the previous answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The velocity $v$ is a &lt;strong&gt;vector quantity&lt;/strong&gt;, the scalar quantity is the magnitude of $v$ which is the speed.Also note that the equation is commonly simplified to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;  \Delta f = \frac{\Delta v}{c} f_{carrier} = \frac{\Delta v}{\lambda} = \frac{|| \Delta v|| }{\lambda} \cos \theta = f_m \cos \theta&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\theta$ is the angle of arrival at the transmitter, $f_m$ is the maximum doppler shift (commonly called the doppler spread) and ||$v$|| is the scalar speed the receiver is traveling relative to a stationary transmitter (or vice versa).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The equation shows that $\Delta f$ will vary from $-f_m$ to +$f_m$ as $\theta$ varies making the received frequency vary (this is called frequency dispersion) and contributing to fast fading. If the only thing you know is the speed the satellite is travelling then all you can calculate is $f_m$ which the worst case scenario for $\Delta f$ so if your system is resistant to frequency shifts of up to $f_m$ then your system will operate well.&lt;/p&gt;&#xA;" OwnerUserId="5515" LastEditorUserId="5515" LastEditDate="2016-03-28T10:14:54.570" LastActivityDate="2016-03-28T10:14:54.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5988" PostTypeId="1" CreationDate="2016-03-27T12:16:30.090" Score="1" ViewCount="473" Body="&lt;p&gt;I'm trying to identify this Icom portable radio.&#xA;Unfortunately, the picture is in a quite a bad shape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does someone know the model number?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EPX56.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EPX56.jpg&quot; alt=&quot;Icom radio&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you!&lt;/p&gt;&#xA;" OwnerUserId="6410" LastActivityDate="2016-03-31T01:52:18.180" Title="Identify Icom portable radio" Tags="&lt;icom&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="5989" PostTypeId="2" ParentId="3798" CreationDate="2016-03-28T08:42:11.023" Score="2" Body="&lt;p&gt;As others have pointed out, the discrete components, suchs as capacitors and inductors, start to be quite challenging in higher frequencies. In general, transmission lines tend to have lower losses and higher repeatability around your frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Long story:&lt;/strong&gt; &#xA;While the transmission lines might be better for practical applications, I wanted to share the simulations I did for this problem to help to understand the challenges. Consider a $75 \Omega$ load that you want to match to $50 \Omega$ source. Most practical loads would have also a imaginary component and vary as function off the frequency, but constant resistance will do nicely in this example. One solution, at 6 GHz, would be a 0.25 pF parallel capacitor and a 1 nH series inductor. The left hand side of the figure shows a maximum in the power transmitted to the 75 $\Omega$ load resistance R_load (blue curve) and that the feed impedance is $50 \Omega$ at 6 GHz (green curve). This means that the load got matched at that frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In reality, the 1 nH inductor has also some capacitance between the legs and windings (C1) and some resistive losses (R1). See the right hand side of the figure. Parallel inductor and capacitor in series with your load create a band stop filter: low frequencies cannot pass the capacitor and the circuit seems like inductance. At high frequencies the circuit behaves like a capacitor. In the middle, at the resonance frequency, the impedance is very high and no current can flow through the circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The self resonance frequency found on the datasheet of the inductor corresponds the frequency at which the inductor starts to behave like a capacitor, that is, above the resonance frequency the parasitic capacitance of the inductor is the easier path for the current flowing through the component. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The component values for the better model of inductor can be calculated from the equations. Parallel capacitor from the self resonance frequency:&#xA;$C =  1/((2\pi f_{res})^2L)$. And equivalent series resistance from the Q value: $R = 2\pi f_{res}L/Q$. The simulations show that with all non-idealities taken into account, the matching circuit is quite horrible and also the power delivered to the resistor has dropped significantly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LQWXT.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LQWXT.png&quot; alt=&quot;Left: matching with ideal inductor. Right: Inductor replaced with more realistic one.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The situation can be improved by optimizing the matching network while taking into account the non-idealities of the inductor. The figure below shows one solution: it turned out to be impossible to get the circuit tuned with 0.25 pF parallel capacitor: if the inductor value decreases and SRF is constant, the value of parasitic capacitor gets up and the circuit is newer matched to $50 \Omega$. For practical inductors, this probably would not be the case: by removing turns from otherwise identical inductor the capacitance would actually drop. A few sample inductors from Farnell had tolerances of e.g. 0.5nH $\pm$ 0.2 nH.&lt;a href=&quot;https://i.stack.imgur.com/uTJNW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uTJNW.png&quot; alt=&quot;Re-tuned circuit.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="194" LastEditDate="2016-03-30T18:02:13.100" LastActivityDate="2016-03-30T18:02:13.100" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5990" PostTypeId="2" ParentId="3798" CreationDate="2016-03-28T13:38:50.483" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Would an inductor with SRF &gt; 7 GHz and Q &gt; 10 be okay at above frequency?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Could it be made to work? I suppose. But any discrete inductor at 6 GHz is going to have significant non-ideal behaviors that you will need to model (or empirically measure) to get an accurate match. At the SRF the inductive reactance and capacitive reactance are equal, but this does not mean below the SRF the capacitive reactance is zero, so you'll need to include that in your model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moreover, you'll need to consider how repeatable and stable these parameters are. The answer is usually &quot;not very&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For these reasons (and also cost), transmission line stub matching is usually used at these frequencies. I suggest starting with the &lt;a href=&quot;http://www.fourier-series.com/rf-concepts/smithchart.html&quot; rel=&quot;nofollow&quot;&gt;Smith chart tutorial at fourier-series.com&lt;/a&gt; to get an intuitive understanding of the technique. Then you can research some of the practical considerations and fabrication techniques.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-03-28T13:38:50.483" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5991" PostTypeId="2" ParentId="5978" CreationDate="2016-03-28T14:48:12.117" Score="3" Body="&lt;p&gt;A parabolic antenna consists of two parts:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the parabolic reflector&lt;/li&gt;&#xA;&lt;li&gt;a feed antenna at the reflector's focus&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The feed antenna is commonly a horn antenna, which can have a relatively wide bandwidth, depending on the particular design. You will want to check the antenna's specifications. If the feed antenna won't work at your desired frequency, then you can replace it for one that does and keep the reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The gain of a parabolic antenna is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ G = {4 \pi A f^2 \over c^2} e_A $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$A$ is the area of the reflector in square meters,&lt;/li&gt;&#xA;&lt;li&gt;$f$ is the operating frequency, in Hz&lt;/li&gt;&#xA;&lt;li&gt;$c$ is the speed of light in meters per second, and&lt;/li&gt;&#xA;&lt;li&gt;$e_A$ is the aperture efficiency.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This equation suggests that gain increases with the square of frequency. While this is technically true, it is intuitively misleading. The reason is that the &lt;a href=&quot;https://ham.stackexchange.com/q/3692/218&quot;&gt;free space path loss also increases with frequency&lt;/a&gt;, and as it turns out, the frequency term in the path loss equation cancels the frequency term in the path loss. So for a given power transmitted, the same fraction of power is received at the other end, regardless of frequency. There is no inherent advantage to higher frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you &lt;em&gt;do&lt;/em&gt; get with increasing frequency is a decreased beam width for the same reflector. This has some benefits:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Fresnel_zone&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fresnel zone&lt;/a&gt; is smaller, so trees and terrain in the way is less of a problem&lt;/li&gt;&#xA;&lt;li&gt;The decreased beam width can make it easier to reject interference that is near the same direction as the intended target&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It also has some disadvantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It's harder to aim the antennas&lt;/li&gt;&#xA;&lt;li&gt;Higher frequencies tend not not penetrate buildings, trees, etc. as well&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-03-28T14:48:12.117" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5992" PostTypeId="1" CreationDate="2016-03-28T16:12:52.733" Score="4" ViewCount="321" Body="&lt;p&gt;I currently live in Brazil and our governmental regulatory agency (www.anatel.gov.br) has recently started a public consultation process regarding the allocation, in secondary nature, of part of the 70 cm band to the radiolocation service.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of us amateur radio operators are concerned about this public consultation, fearing the impacts of the proposed band sharing, specially over educational cubesats communications using weak signals in 430-440 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By doing some research we realized that this band sharing actually already exists in many other countries and, in fact, so far we brazilians are enjoying a privileged position on that matter, having the whole band for amateur use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I would like to hear from you guys: do you have or know about some bad experiences about the coexistence of the radiolocation service and any amateur operation on the 70 cm band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moreover: do you have any knowledge of the specifics of the radiolocation service (output power, how often such service is usually activated over a given area and so on)?&lt;/p&gt;&#xA;" OwnerUserId="5985" LastActivityDate="2016-03-29T18:51:53.007" Title="Experiences on a 70 cm band shared with radiolocation service" Tags="&lt;license&gt;&lt;band-plan&gt;&lt;70cm-band&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5993" PostTypeId="2" ParentId="5442" CreationDate="2016-03-28T17:18:02.267" Score="1" Body="&lt;p&gt;So as I understand you, the Ettus USRP1 is a software-defined receiver, and HDSDR+ExtIO is software that you are using to control the receiver.  So the audio comes from HDSDR running on the computer, and the audio cable loops right back to the computer for fldigi to decode?  Interesting!  Do you have a hardware attenuator in the audio circuit?  If not you're probably way, way overdriving the mic input; your problem could be distortion.  The speaker output is a few tenths of a volt perhaps, but the microphone input is expecting millivolts.  Check out the attenuator circuit in the picture in &lt;a href=&quot;http://www.qsl.net/wm2u/interface.html&quot; rel=&quot;nofollow&quot;&gt;this web page&lt;/a&gt;, and any PSK31 tutorial such as &lt;a href=&quot;http://bpsk31.com/&quot; rel=&quot;nofollow&quot;&gt;this one&lt;/a&gt; for advice on adjusting the signal level.  There are some great PSK31 tutorials on YouTube also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were you I'd set things up to receive PSK31 signals successfully first.  Once you do that, then hopefully it shouldn't be too hard to tweak fldigi or some other program to get the raw hex stream you're after.  Have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-28T17:18:02.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5994" PostTypeId="2" ParentId="5992" CreationDate="2016-03-28T17:33:27.023" Score="4" Body="&lt;p&gt;Here in the US ham radio is only a secondary user of the 70cm band, with the primary user being military radar.  That didn't stop ham operators from setting up hundreds of repeaters on the band.  Back in 2007 the US Air Force complained about interference, and the ARRL worked with them to create a plan to reduce the interference (&lt;a href=&quot;http://www.arrl.org/w1aw-bulletins-archive/ARLB013/2007&quot; rel=&quot;nofollow&quot;&gt;article&lt;/a&gt;).  I don't remember hearing anything more about the issue, so hopefully the problem was solved; presumably the ARRL asked the owners of the repeaters involved to reduce power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So we as secondary users of the 70cm band in the US normally use the band without worrying about interfering with the primary user, except for a few repeaters near US Air Force bases.  I hope that you hams in Brazil are able to cooperate successfully with the radiolocation service!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-03-28T17:33:27.023" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5995" PostTypeId="1" CreationDate="2016-03-28T21:13:58.247" Score="5" ViewCount="1232" Body="&lt;p&gt;I just got my Technician's license a few weeks ago and I'm trying to figure out if this is user error or if I need to return my radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding of squelch is that when the received signal strength exceeds the squelch threshold the radio starts playing the audio for whatever it is receiving.  When I have the squelch set to '0' I get a ton of static as well as hearing anyone who is talking from the repeater and the green RX light on my HT lights up solid; as expected.  However, if I set the squelch to '01' then I get nothing at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At first I just assumed that my dinky HT just couldn't get a very strong signal from the repeater and was unable to distinguish the activity from the static.  However, I noticed that sometimes when the squelch was turned up a notch that I would see the green RX light illuminate for significant stretches of time.  If I turn the squelch back down to '0' I was able to confirm that there were actually people talking.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems to me that these signals shouldn't cause the light to illuminate unless the radio is receiving something over the squelch threshold.  This leads me to suspect that when squelch is set to a non-zero value it is failing to actually activate the speaker when the signal is strong enough and I have a faulty device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I missing something here?&lt;/p&gt;&#xA;" OwnerUserId="6421" LastEditorUserId="76" LastEditDate="2016-10-29T18:56:29.763" LastActivityDate="2016-10-29T18:56:29.763" Title="Squelch never seems to &quot;open the gate&quot; on Wouxun KG-UV9D" Tags="&lt;ht&gt;&lt;equipment-troubleshooting&gt;&lt;squelch&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5996" PostTypeId="2" ParentId="5995" CreationDate="2016-03-28T21:44:42.027" Score="4" Body="&lt;p&gt;I'm not familiar with the exact behavior of that model of radio (and the manual was not very helpful), but a &lt;em&gt;possible&lt;/em&gt; explanation in general is that you have CTCSS/DCS squelch enabled, and the repeater is not using the same tone/code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, for this to match the observed behavior it would have to be the case that a squelch setting of '0' disables tone squelch as well as power-based squelch. If that's true, then what you're seeing is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;When you disable squelch entirely, you can hear the signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;When the squelch is on, the RX light is telling you that there is a signal meeting the power squelch criterion (so the receive circuit is active) but it isn't meeting the CTCSS/DCS criterion (so there is no audio).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In order to fix this, you need to make one of two changes to the radio settings. I can't advise you on how to do this because I couldn't make enough sense of the manual at a quick skim.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Disable CTCSS/DCS squelch. Then the squelch will work as you describe in your question.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Enter the CTCSS tone or DCS code actually used by your repeater, so that it can activate the squelch.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-03-28T21:44:42.027" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="5997" PostTypeId="2" ParentId="5988" CreationDate="2016-03-29T18:12:20.143" Score="6" Body="&lt;p&gt;I went to the Icom America Headquarters office in Kirkland to look over the wall of history of a sampling of their amateur radio gear.  This model shown below in the photo is the closest in appearance to the photo posted by the OP.  It is an Icom IC-F3, first released in 1997.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bXqYl.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bXqYl.jpg&quot; alt=&quot;Icom IC-F3&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The OP's image of the HT appears to be a derivative of the IC-F3 called the IC-F3GS.  Here is an image of the IC-F3GS.  It seems to have the right body shape as the OP's photo as well as the up/down arrow design.  Even though the up/down arrow buttons to the left of the screen are hard to make out, if you zoom in the OP's image you will be able to see the buttons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jqY7z.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jqY7z.jpg&quot; alt=&quot;Icom IC-F3GS&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="76" LastEditDate="2016-03-31T01:52:18.180" LastActivityDate="2016-03-31T01:52:18.180" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="5998" PostTypeId="2" ParentId="5992" CreationDate="2016-03-29T18:51:53.007" Score="3" Body="&lt;p&gt;I'm from Serbia, and there we have radio-location service as secondary user in almost whole (both ham and commercial) 70 cm band. In practice, this means ground-based or space-based RADARs. Space-based are following ITU-R SA 1260-1, which being only 15 pages long, I recommend that you read. It contains lots of interoperability information and tells you a bit about what to expect, basically answering in detail your question about power and duty cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now a bit of warning, my knowledge of RADARs comes from university course, not from practical experience, so I might be missing something obvious!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So first of all, space-based systems... I don't think there's too much to worry about you interfering them. They must already be designed (see 1260-1) to work properly if they're exposed to a ground-based RADAR illumination. There's pretty much nothing in amateur radio service that can compete with that level of interference. In addition, the signal from a ham station will basically show up as a sort of clutter and there are already very robust systems in place to deal with that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, the interference that can be coming from them might be a bit troubling in some cases.&lt;br&gt;&#xA;The type of RADARs used there is a so-called synthetic aperture radar. That means that the satellite will have a high-gain antenna pointed at a relatively small area on the ground that will be &quot;scanned&quot; by the RADAR. The satellite will then make a number of successive overflies over the area, each time &quot;shaving&quot; a strip of ground it scanned. The result of that is that the area that is under interference at one time moment will be relatively small and the interference will not last long, since the satellite keeps moving. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NavdQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NavdQ.png&quot; alt=&quot;Illustration of SAR principle&quot;&gt;&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in the picture here, the blue stripes are the &quot;track&quot; the satellite is covering on the ground and the red area is covered by the satellite at any one moment. Afterwards, the data is merged into a single image. When the track is passed, the satellite will, in the next orbit, shift it a bit to the side and repeat the procedure for the next track.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what about signals that can be heard? Well if you want to hear something a bit similar to how it would sound, you can go to say &lt;a href=&quot;http://websdr.ewi.utwente.nl:8901/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://websdr.ewi.utwente.nl:8901/&lt;/a&gt; and on the waterfall look for signals that look like: &lt;code&gt;//////////&lt;/code&gt; or &lt;code&gt;_ _ _ _ _&lt;/code&gt; This would be over-the-horizon radars. Also keep in mind the &quot;Woodpecker&quot; nickname of the Cold-war era system.   That's how they sound.&lt;br&gt;&#xA;The principles of operation are sort of the same, but you can expect much bigger difference in frequency and in pulse repetition period. Normally, the space-borne radars can be running with the peak power of several hundred watts (ITU recommendation used 400 W for some calculations) and can have few pulse repetition frequency of few kilohertz. Also the bandwidth will be several megahertz (ITU uses 6 as example), so you can expect them to be capable of covering big parts of the band. It should be kept in mind that for SAR systems, most of the gain comes from clever waveform design and off-line post-processing and not raw transmit power, so the aren't as bad as more traditional systems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your last part, I never actually heard of anyone reporting interference from space-based SAR systems, so I can only say what the ITU recommendation already says=&gt; The systems are to be run in &quot;campaign&quot; mode with a duty cycle of 10%, but not exceeding 15%. Campaign mode means that the satellite will only scan a certain geographic area at a certain time and when outside of that area, it will switch the sensor off. This limits the possibility of creating interference to weak satellite systems in general. A specific pass might be jammed for a while, but situation should not repeat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my speculation is that you can expect some activity soon after the license is received and then a rapid decrease, after SAR pictures of interesting areas have already been made. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For ground-based systems, if they get allowed, I expect much bigger issues. They will have their few hundred watts on the ground, possibly near your antennas. This will most likely render the 70 cm band unusable to people in the affected area while the system is running, if you're unlucky enough to have a system running in the middle of the band. I haven't found any international documents regarding duty cycle or similar, but in my own opinion, I wouldn't expect the ground based systems to run continuously. They could run for several seconds every few minutes to get the update on the wind changes, but I don't see a reason why to keep them running continuously. This is also confirmed by some reports of interference to repeaters I've heard of. I myself haven't heard much about ground RADAR interference, because, based on reports I did hear of, such systems are only used sporadically in ham and neighboring bands in Serbia.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2016-03-29T18:51:53.007" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6000" PostTypeId="1" CreationDate="2016-03-30T12:44:38.263" Score="2" ViewCount="343" Body="&lt;p&gt;I known you can control the rig with the CI-V interface, but my question is: Once the rig goes to sleep (inactivity timeout) can it be turned back on without having to use the power button on the front?  &lt;/p&gt;&#xA;" OwnerUserId="5045" LastActivityDate="2016-03-30T14:52:41.640" Title="Remote wake up of Icom IC-706Mk2g" Tags="&lt;icom&gt;&lt;remote-control&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6001" PostTypeId="2" ParentId="6000" CreationDate="2016-03-30T14:52:41.640" Score="2" Body="&lt;p&gt;The inactivity timeout is controlled by the auto-power-off menu setting where you can designate the number of minutes, such as 30 minutes, for the radio to be switched off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, this is tantamount to turning the radio off just as if you had pushed (and, held) the power button on the front panel.  It is not some &quot;sleep mode&quot; where functions are still active, such as listening on the CI-V port.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I own an Icom IC-706MkIIG and use it as a mobile rig but I used to have it in my home shack.  I have a habit of keeping the radios on all the time.  Sometimes, not turning them off for weeks, maybe even months, although I never kept track of when I turned power off or how frequently.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, why not disable the auto-off feature and then leave the radio on power all the time.  In idle mode, it is not consuming very much power and may be a reasonable alternative unless you are on some kind of battery backup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounds like you may not have the user guide, it is easily found at the Icom America web site, here is a link: &lt;a href=&quot;http://www.icomamerica.com/en/downloads/default.aspx?category=38&quot; rel=&quot;nofollow&quot;&gt;http://www.icomamerica.com/en/downloads/default.aspx?category=38&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-03-30T14:52:41.640" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6002" PostTypeId="1" AcceptedAnswerId="6003" CreationDate="2016-03-31T02:42:08.947" Score="1" ViewCount="45" Body="&lt;p&gt;Help! I got a PicoStation off of Ebay. When trying to upload the Amateur Radio Emergency Data Network firmware to it, I get &lt;code&gt;Bad firmware update image.&lt;/code&gt; How do I get AREDN running on this?&lt;/p&gt;&#xA;" OwnerUserId="1285" LastActivityDate="2016-03-31T02:42:08.947" Title="Picostation Not Accepting AREDN Firmware" Tags="&lt;microwave&gt;&lt;mesh-network&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6003" PostTypeId="2" ParentId="6002" CreationDate="2016-03-31T02:42:08.947" Score="1" Body="&lt;p&gt;Chances are, you have a Picostation 2. AREDN only supports the Picostation &lt;strong&gt;M2&lt;/strong&gt;. I suggest returning it.&lt;/p&gt;&#xA;" OwnerUserId="1285" LastActivityDate="2016-03-31T02:42:08.947" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6005" PostTypeId="2" ParentId="5953" CreationDate="2016-04-01T16:50:55.773" Score="5" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6UvWQ.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6UvWQ.jpg&quot; alt=&quot;Plastic owl surrounded by pigeons&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This came from &lt;a href=&quot;http://pigeonpatrol.ca/whos-not-afraid-of-the-owl&quot; rel=&quot;noreferrer&quot;&gt;pigeonpatrol.ca/whos-not-afraid-of-the-owl&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2016-04-01T16:50:55.773" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6011" PostTypeId="1" CreationDate="2016-04-03T15:34:19.967" Score="1" ViewCount="1362" Body="&lt;p&gt;I need to disable or block the side key moni(monitor) so others can't hear on my private CTS DTS.  I use a Baofeng UV-5R and a UV-82. Another team that uses the same repeater, but has different CTS DTS codes, can hear when I press the side key moni.&lt;/p&gt;&#xA;" OwnerUserId="6449" LastEditorUserId="8028" LastEditDate="2016-08-02T14:01:39.567" LastActivityDate="2016-08-02T14:01:39.567" Title="Baofeng uv-5r,uv-82. i need disable or block side key moni(monitor) for don´t listen private cts dts" Tags="&lt;baofeng&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6012" PostTypeId="2" ParentId="6011" CreationDate="2016-04-03T21:19:06.487" Score="6" Body="&lt;p&gt;Don't bother.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;CTCSS tones are not an effective privacy mechanism.&lt;/strong&gt; Anyone at all with a FM two-way radio or scanner can receive your transmissions; attempting to prevent this by locking down your radios gives you only the &lt;em&gt;illusion&lt;/em&gt; of privacy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(P.S. This site is for &lt;em&gt;Amateur Radio&lt;/em&gt;, and I'm guessing you're actually a commercial radio user. I'm answering your question anyway because I think it's close enough to being about the technology in general and Baofeng radios are commonly used by amateur license holders as well.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-04-03T21:19:06.487" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6013" PostTypeId="1" CreationDate="2016-04-04T00:42:55.847" Score="5" ViewCount="419" Body="&lt;p&gt;I'm considering buying a new HT radio (Hong Ying HX-860UV Handheld) from China.  The company says the model is approved by the FCC.  Since I can't see it in person (only a photograph), I can't confirm.  How can I be sure they are telling the truth?&lt;/p&gt;&#xA;" OwnerUserId="6450" LastEditorUserId="76" LastEditDate="2016-04-04T00:58:06.923" LastActivityDate="2016-04-04T11:32:31.057" Title="How can I know whether a radio is FCC approved?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6014" PostTypeId="1" AcceptedAnswerId="6315" CreationDate="2016-04-04T03:40:17.397" Score="12" ViewCount="6651" Body="&lt;p&gt;I designed a Yagi antenna using 4nec2, assuming that I would use a non conductive boom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I use an aluminum boom but I insulate the elements from the boom, can I keep the same design? How does it affect performance, in particular SWR?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is a 2m (144-148mhz) designed to be a portable VHF / UHF (not mounted on a mast).&lt;/p&gt;&#xA;" OwnerUserId="5947" LastEditorUserId="5947" LastEditDate="2016-04-04T16:05:26.557" LastActivityDate="2020-03-04T18:55:01.003" Title="Conductive boom vs non conductive boom: what's the difference on a Yagi?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="8" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6015" PostTypeId="1" CreationDate="2016-04-04T03:44:18.600" Score="3" ViewCount="396" Body="&lt;p&gt;Assuming I wanted to reverse engineer 13FSK, what steps would I take to begin reverse engineering it? I have seen tools such as inspectrum and baudline that can help me view the raw signals, but I am unsure as to how to reverse engineer the 13FSK and then build a way to receive and transmit data using 13FSK.&lt;/p&gt;&#xA;" OwnerUserId="6451" LastEditorUserId="76" LastEditDate="2016-04-04T03:51:52.910" LastActivityDate="2018-02-11T18:10:38.390" Title="How to reverse engineer a proprietary FSK protocol" Tags="&lt;software-defined-radio&gt;&lt;modes&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="6016" PostTypeId="2" ParentId="6013" CreationDate="2016-04-04T11:32:31.057" Score="4" Body="&lt;p&gt;The FCC provides a good &lt;a href=&quot;https://www.fcc.gov/engineering-technology/laboratory-division/general/equipment-authorization&quot; rel=&quot;nofollow&quot;&gt;summary of their authorization process&lt;/a&gt; on their website. The manufacturer must get the device tested at an FCC Recognized Accredited Testing Laboratory. The results are then filed with FCC, and the device must be &lt;a href=&quot;https://apps.fcc.gov/oetcf/kdb/forms/FTSSearchResultPage.cfm?switch=P&amp;amp;id=27980&quot; rel=&quot;nofollow&quot;&gt;appropriately labeled and documented&lt;/a&gt;. If you can get a look at that documentation you will find an FCC compliance statement and an FCC ID.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can get the FCC ID of the device, then you can &lt;a href=&quot;https://www.fcc.gov/general/fcc-id-search-page&quot; rel=&quot;nofollow&quot;&gt;search for it in the FCCs database&lt;/a&gt;. In addition to demonstrating that the device has been tested and registered with the FCC, you can also see the test results which includes some interesting performance data about the device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All FCC IDs are prefixed by an FCC Registration Number which indicates the organization making the filing. For well-known companies, it's usually easy enough to find the FRN by a bit of searching. For example, Apple's FRN is &lt;a href=&quot;https://apps.fcc.gov/oetcf/eas/reports/GenericSearchResult.cfm?RequestTimeout=500&quot; rel=&quot;nofollow&quot;&gt;BCG&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately in your case of a cheap Chinese manufacturer, this information is more difficult to find, especially if it is not in fact registered with the FCC. I did a bit of searching, and while I was able to find a few &quot;Hong Ying&quot; registered companies, none of them seemed to be the manufacturer of your radio. Perhaps with a bit more searching, or by obtaining the relevant documentation, you will be able to find the registration.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-04-04T11:32:31.057" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6019" PostTypeId="1" AcceptedAnswerId="6021" CreationDate="2016-04-04T21:06:34.700" Score="4" ViewCount="685" Body="&lt;p&gt;A friend of mine and I live across a lake from each other, and recently we thought it'd be fun to try and connect our computers together somehow across that distance.  Running cable from either side is expensive, difficult (no boat), and probably illegal (or is regulated in some boring way), so we thought radio would be a good approach to the problem.  We're aware that there are people selling products that solve this problem, we'd like to do as much of it ourselves as possible.  While we might be fairly technical when it comes to computers, radio stuff is certainly not our strongsuit.  Thus, we've decided to use this as a project to learn more about the subject.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our goal is to somehow connect our LANs together via radio, as though there was an ethernet cable connecting our switches.  If possible, It'd also be neat to be able to expand the system so that we could relay from his place to, say the beach we go to that I can't see from my house, and maybe from that bridge somewhere further up the lake.  Our houses are in direct visual contact with each other, and my limited knowledge of radio suggests that we might try some sort of a directional antenna.  Other than that, I have no idea how to approach this project.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;While a solid and detailed set of instructions would be lovely, we'd much more prefer an answer that contained resources we could check out to learn more about what we're doing, what solutions to our problem are available, and how we might implement them ourselves.  Learning is the primary goal of this project, after all!&lt;/p&gt;&#xA;" OwnerUserId="6459" LastActivityDate="2016-04-19T13:19:29.010" Title="Bridging LAN over ~1-2km distance" Tags="&lt;antenna&gt;&lt;digital-modes&gt;&lt;diy&gt;&lt;repeater&gt;" AnswerCount="3" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="6020" PostTypeId="2" ParentId="6019" CreationDate="2016-04-04T21:45:27.200" Score="3" Body="&lt;p&gt;This answer hasn't got very many links, but I hope it has a lot of useful keywords for further research.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Technical&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;People often want to do this and are disappointed that it's not practical. The good news is that because you have a clear line of sight, you have many options. (The absence of obstacles is &lt;em&gt;far&lt;/em&gt; more important than the distance.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The typical solution to your problem could be called a &lt;em&gt;point-to-point microwave link&lt;/em&gt;. The equipment consists of a transceiver and dish antenna at each end. You will need to find mounting points for the antennas which are well clear of any trees blocking the direct view, and aim them precisely at each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The “microwave” part of the name just means that it's using frequencies in the 300 MHz - 3 GHz range, much higher than classic broadcast and two-way radio, which is relevant because it allows high bandwidth and small antennas, at the price of the equipment being much more tricky to design and build.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Legal&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;What you are asking for may in fact &lt;em&gt;not&lt;/em&gt; be “Amateur Radio” in the sense of this site's title. The reason for this is that Amateur Radio is a legally defined subset of radio operations: licensed 'amateurs' have permission to freely use a substantial amount of radio spectrum &lt;em&gt;under certain conditions&lt;/em&gt;. Those conditions restrict the content of messages sent, in ways which are incompatible with carrying Internet traffic; most notably, &lt;em&gt;encryption&lt;/em&gt; is prohibited. (I'm most familiar with the U.S. (FCC) regulations but my understanding is that similar rules apply worldwide, via the ITU.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, you have two options:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;You can create a network which uses &lt;a href=&quot;https://en.wikipedia.org/wiki/Internet_Protocol&quot; rel=&quot;nofollow&quot;&gt;IP&lt;/a&gt;, Ethernet, etc. but which is &lt;em&gt;separate&lt;/em&gt; from the Internet. On most modern operating systems, just hooking up a separate Ethernet adapter (via USB, PCI, etc.) to each computer is sufficient to make this work as you want it to. You would then need to avoid using any software which encrypts its traffic to talk to your friend('s computer) — for example you could use HTTP (web browsers and servers) but not HTTPS. (I could comment on how to think about security given this constraint, but that would be a whole other question-and-answer.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You can obtain a license for your particular link. However, this can be expensive, as it is intended for serious commercial use — a little research suggests that the total costs might be in the area of \$1000 - \$3000 in the U.S., for a 10-year license.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-04-04T21:45:27.200" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6021" PostTypeId="2" ParentId="6019" CreationDate="2016-04-05T00:08:40.913" Score="4" Body="&lt;p&gt;My advice here is to avoid the amateur radio service completely and instead go with license-free spectrum, perhaps around 2.4 GHz or 5 GHz. There are more than enough WiFi products that can solve your problems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice for research directions would be to look for let's say parabolic antenna for your band of interest:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/T4vmJ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/T4vmJ.jpg&quot; alt=&quot;TL-ANT5830B from TP-LINK&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA; plus an access point. For access point, my advice would be to look to one of the third-party GNU/Linux distributions for routers and similar equipment. Fro example OpenWRT. Then look for the devices on their supported list and find one you like. OpenWRT and the like will give you more than enough options to fine-tune the WiFi settings you have and will also be able to improve security in the long run. since they actually receive updates, unlike stock firmwares for cheap units. The down-side of this approach is that if you want modern features such as antenna diversity and spatial multiplexing, you'll need two to four antennas per AP, which can get costly. A ballpark price for an antenna could be around USD 50 plus maybe USD 50 to USD 100 for an AP, plus low-loss coaxial cabling and installation costs. Keep in mind that the traditional distance between antennas i  simpler diversity or multiplexing setups should be half of wavelength or odd multiple of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or maybe a combination unit that has both WiFi card and an integrated outdoor directional antenna with sufficient gain could be interesting:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9pI0f.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9pI0f.png&quot; alt=&quot;SXT SA5 ac&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such units will usually have wired Ethernet connection on them and can be powered over Ethernet using standardized PoE or their own proprietary power injectors. They can have several integrated antennas (pictured unit has two), meaning that they can take advantage of antenna diversity or spatial multiplexing in one unit, but it will be a somewhat compromise solution, since quite often, there's very little that can be done to have many uncorrelated antennas in small space. Price could be a bit higher than an access point plus one antenna, but will in general be lower than access point plus two good antennas. The pictured unit goes for around 115€, just to give you a reference point. Also with this type of solutions, you usually completely avoid the coaxial cable loss between the radio and the antenna, since the unit is fed by classical Ethernet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, there's the part where you should calculate how much gain you actually need. You'll often be able to find tables with minimum signal strength needed for various modulation types from WiFi equipment manufacturers in tables such as one on &lt;a href=&quot;http://www.tp-link.us/products/details/cat-37_TL-WA7510N.html#specifications&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; page. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/4uJp0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4uJp0.png&quot; alt=&quot;Speed rates&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should use that information to give yourself a base-line of how much power you need at the receiver.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next step is to take the antenna gain in dBi and subtract the cable loss in dB from it and then repeat the calculation for the receiver. This will give you a sort of let me call it &quot;effective&quot; antenna gain, that you can later on use for different types of calculators. Cable loss is calculated by getting the manufacturer's specification that will list it usually in loss per meter, per foot or per 100 feet/30 meters or per 100 meters and then add the loss of the connectors, if you want to be really picky.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After that, you can go to a Friis calculator such as &lt;a href=&quot;https://www.pasternack.com/t-calculator-friis.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; one and use it to calculate the path loss for your distance and put the info from your equipment such as the gains you calculated previously and the transmitter power. The output will be received power, which needs to be higher than the minimum power needed for the speed you want to use, plus some more decibels  for extra safety margin, just in case of bad weather or similar. If the numbers don't fit, you can try to do trade-offs. You could switch to a higher-gain antenna, but that would be more expensive, you could move to a lower-loss cable, you could try to use a higher-power transmitter, but that can very easily be illegal if you break the local rules and so on. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, there's the part where you should decide which band you want to use. If you want to use regular WiFi bands (meaning cheap equipment), you should do a &quot;site survey&quot; of some sort. Basically, you need to see which channels are free in the area. In general, 2.4 GHz is the band with larger antennas, cheaper APs and is more crowded. The path loss is lower in this band.&lt;br&gt;&#xA;In 5 GHz band, the antennas are smaller, there are more channels and usually much less users (this is VERY important for a good-working link). Also the newest IEEE 802.11 ac standard only works in this band. You'll also have more space for use of wider bandwidth transmissions. The path loss here is usually higher, so you can expect your signal to be around 6-7 dB weaker than in 2.4 GHz band. Equipment is also somewhat more expensive. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With latest AC equipment, you can expect a bit less than 1 gigabit per second speeds with a good WiFi installation, but that can somewhat deteriorate with weather.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, let me remind you to check local regulations on WiFi equipment. In some cases, you might have restrictions on antenna types, antenna gains, EIRP, outdoor installations, so that even though WiFi is in general considered license-free, the your specific application might need registration or license or might be (in the worst case) simply illegal.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2016-04-05T00:15:57.877" LastActivityDate="2016-04-05T00:15:57.877" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6022" PostTypeId="1" AcceptedAnswerId="6023" CreationDate="2016-04-06T02:51:13.973" Score="2" ViewCount="756" Body="&lt;p&gt;I am building a miniature yagi antenna that is made for 2.4ghz. Would a 2.4ghz yagi antenna work for Ham Radio? &lt;/p&gt;&#xA;" OwnerUserId="6466" LastActivityDate="2019-11-06T21:25:54.797" Title="Would a 2.4ghz yagi antenna work for Ham Radio?" Tags="&lt;antenna&gt;&lt;frequency&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6023" PostTypeId="2" ParentId="6022" CreationDate="2016-04-06T13:14:01.780" Score="2" Body="&lt;p&gt;One of the amateur radio bands covers 2390-2450 MHz. A 2.4 GHz antenna should work quite nicely for that band. But it likely wouldn't work on other bands very well, for receiving, and I highly recommend you don't try to transmit on any other band (Except for perhaps with an antenna tuner)!&lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="13" LastEditDate="2016-04-08T13:09:35.720" LastActivityDate="2016-04-08T13:09:35.720" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="6024" PostTypeId="1" CreationDate="2016-04-06T14:27:13.070" Score="4" ViewCount="711" Body="&lt;p&gt;I want to work with amateur, low power, and/or pico satellites. I would like to use an Eggbeater or Turnstile antenna with my UHF 433 MHz radio, since those antennas are very cheap and easy to build and I don't have to care about yagi rotors. The space for the antennas is also limited. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would also like to use an LNA next to the antenna, but I don't know how to bypass the LNA when transmitting. I know I need some sort of switch or relay, but I can't seem to find something useful in Google. I don't mind soldering something and building some filters!&lt;/p&gt;&#xA;" OwnerUserId="4926" LastEditorUserId="76" LastEditDate="2016-04-06T16:42:51.883" LastActivityDate="2016-09-20T03:50:16.183" Title="How to bypass LNA for TX in UHF Antenna?" Tags="&lt;antenna&gt;&lt;satellites&gt;&lt;uhf&gt;&lt;antenna-system&gt;&lt;lna&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6026" PostTypeId="2" ParentId="1134" CreationDate="2016-04-07T22:31:08.140" Score="2" Body="&lt;p&gt;There is a complete list of all Amateur contests at: &lt;a href=&quot;http://www.hornucopia.com/&quot; rel=&quot;nofollow&quot;&gt;http://www.hornucopia.com/&lt;/a&gt;. Some ham contests include a category for SWLs, others don't. Check the contest's rules at this site to see if includes an SWL category.&lt;/p&gt;&#xA;" OwnerUserId="6476" LastActivityDate="2016-04-07T22:31:08.140" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6029" PostTypeId="2" ParentId="6022" CreationDate="2016-04-09T14:00:44.560" Score="1" Body="&lt;p&gt;Absolutely yes.  You can find plans for a Pringles can antenna, which is a yagi inside a Pringles can.  You may have to adjust the size slightly, but it'll work.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An alternative you might consider is a discarded satellite dish.  That would give you more gain (and a larger capture area) at the expense if more directivity.&lt;/p&gt;&#xA;" OwnerUserId="5045" LastActivityDate="2016-04-09T14:00:44.560" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6030" PostTypeId="2" ParentId="1134" CreationDate="2016-04-09T19:38:30.013" Score="1" Body="&lt;p&gt;Absolutely, you can be a SWL (Short Wave Listener). &#xA;Here are some links to be a better SWL:  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.astrosurf.com/luxorion/qsl-cqdx.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.astrosurf.com/luxorion/qsl-cqdx.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6488" LastActivityDate="2016-04-09T19:38:30.013" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6031" PostTypeId="2" ParentId="5340" CreationDate="2016-04-10T02:34:04.543" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/users/4987/martin-ewing-aa6e&quot;&gt;Martin Ewing AA6E&lt;/a&gt; got it right in his comments on the question, which he hasn't posted as an answer yet himself so I'm copying here for the record:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Can't verify the dimensions, but is it possible this is a diode detector? Maybe you can gently pull out the gold piece and find that it's the base of a 1N23 or similar.&lt;/p&gt;&#xA;&lt;p&gt;I'm guessing it's not really a connector, but a spring fixture for holding the diode in place. This could be a simple mixer or power detector, with the (IF) output going out the BNC jack. The diodes have a tendency to burn out with overloads, so it's important to have a way to replace them.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I finally got around to disassembling the thing further, and you are completely correct about this “connector” actually being a diode holder. The gold part does indeed pull out revealing the diode (unfortunately I did not actually try hard enough to confirm this before disassembling the main body).&lt;/p&gt;&#xA;&lt;p&gt;One of the diodes was marked &lt;code&gt;1N416D&lt;/code&gt; (according to the Internet, a &amp;quot;X-S BANDS POINT CONTACT MIXER DIODE&amp;quot;) and the other &lt;code&gt;MA450D&lt;/code&gt; (a varactor diode), so again Martin's theory about this being a mixer or detector fits.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-04-11T13:52:38.147" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6032" PostTypeId="2" ParentId="5902" CreationDate="2016-04-10T02:47:37.637" Score="2" Body="&lt;p&gt;Typically during low/no sunspots radio propagation is bad at higher frequencies but excellent at low frequencies. At the bottom of the sunspot cycle the bands are quieter and signals travel farther down at 80 and 160 metres. And if you're a mediumwave DXer this is also a great time to listen.&lt;/p&gt;&#xA;" OwnerUserId="6489" LastActivityDate="2016-04-10T02:47:37.637" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6033" PostTypeId="2" ParentId="5340" CreationDate="2016-04-10T11:37:54.063" Score="0" Body="&lt;p&gt;Ok, The connector shown above may be a MW connector.. But its only being used to support the BNC connector nothing less nothing more. It has not to do with the device. It is just a connecting a BNC cable and this is basically a cable extender.. &lt;/p&gt;&#xA;" OwnerUserId="6406" LastActivityDate="2016-04-10T11:37:54.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6034" PostTypeId="2" ParentId="1134" CreationDate="2016-04-10T16:21:17.847" Score="1" Body="&lt;p&gt;Most contests welcome logs from SWL especially when you are confirming the qso's and the values that are being sent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have (and continue) to issue ask cards for SWL-ers who confirm qso's I have made either in a contest or in normal mode.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2016-04-10T16:21:17.847" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6035" PostTypeId="1" CreationDate="2016-04-10T17:46:01.733" Score="4" ViewCount="453" Body="&lt;p&gt;How do I build the best antenna for a given VHF frequency given that an optimal design is too large?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am trying to understand the properties of a directional antenna of sub-optimal design.  All the discussions of directional antennas assume optimally sized elements for a specific frequency.  I need to design a directional antenna (Yagi) that is &lt;em&gt;as good as it can be&lt;/em&gt; for a given VHF frequency (say 144 MHz)directional, but approximately 50% of the usual size.  This is a receive-only, direction finding situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously my antenna needs to be a good SWR match.  I presume that it needs to be resonant at the target frequency, and I want to preserve as much efficiency and forward gain as possible.  But the references I consult (ARRL Antenna Book, antenna-theory.com, RGSB publications) generally do not seem to approach the question from this direction. &lt;/p&gt;&#xA;" OwnerUserId="6491" LastEditorUserId="76" LastEditDate="2016-04-10T17:59:34.420" LastActivityDate="2017-07-01T01:24:09.713" Title="Receive directionality of a sub-optimal Yagi" Tags="&lt;antenna-theory&gt;&lt;yagi&gt;&lt;direction-finding&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6036" PostTypeId="2" ParentId="6035" CreationDate="2016-04-11T11:52:38.483" Score="5" Body="&lt;p&gt;A few things to start off with:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;You don't care about efficiency, unless the antenna efficiency is truly abysmal, or your receiver is of very poor quality. Efficiency on the receive side is a measure of how effectively the antenna can couple with the ambient RF field and get that energy to the receiver. Even a receiver of very poor quality will have an extremely large dynamic range, 10s of decibels, and a circuit called an Automatic Gain Control, or AGC. The AGC's job is to increase the amplification in the receiver to make incoming signals strong enough to be effectively received. The AGC typically works by taking the strongest signal on a given frequency, and dialing up the gain until that signal has a specified amplitude at the receiver output. So long as the antenna is efficient enough to couple with the desired frequency sufficiently to bring in a signal that is above the receiver's internal noise floor, the receiver should be able to compensate. This is how a &lt;a href=&quot;http://www.w0btu.com/Beverage_antennas.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Beverage Receiving Antenna&lt;/a&gt; works. While they are highly directional, &lt;s&gt;they are abysmally efficient, &amp;lt;1%, and peak gain can be as low as -20dBi because of this poor efficiency.&lt;/s&gt; The receiver compensates, however.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You don't care about SWR, so long as it isn't incredibly high, like &gt;20:1, for the same reason. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So, what you care about is &lt;strong&gt;directionality&lt;/strong&gt;, which means how well it 'hears' in a given direction compared to how it hears in other or all directions. You &lt;em&gt;don't&lt;/em&gt; care about &lt;strong&gt;directivity&lt;/strong&gt;, meaning how well it hears in a given direction compared to an isotropic radiator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that out of the way, it might be easier to see where you can cut corners here. The physical aperture of the antenna, meaning it's size compared to the size of the wavelength it is receiving, is a big player in antenna efficiency, especially when you're trying to get seriously tiny. Since you don't care about efficiency nearly so much, you can sacrifice aperture and accept the reduction in overall gain and efficiency, in exchange for a small package and good directionality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on your design limitations, you might consider inductive loading of the yagi elements. Just like a dipole or monopole, a yagi can be shortened by adding capacitance or inductance to it's elements to make them electrically longer. You can google for &quot;hamstick yagi&quot; and see an example of this for HF using inductively loaded monopole antennas to create loaded dipole arrays.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case, the one thing you won't be able to reduce very much will be the optimal spacing between the elements. In a typical yagi, maximum front to back and front to side ratio is achieved with the antenna elements spaced out a certain amount, and best SWR is achieved at a different spacing. This is why many yagis use gamma matches or the like to achieve a good match at maximum gain. Since you don't care about the SWR, you should stick with the spacing that would give maximum front to back ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might also consider deviating from the typical yagi shape and use a design that still functions as a yagi, but has a smaller overall footprint. The SteppIR &quot;trombone yagi&quot;, &lt;a href=&quot;http://www.steppir.com/wp-content/uploads/2011/11/DB11-061.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;as seen here&lt;/a&gt; is an example of this. That design yields a roughly 50% reduction in element length, but with no reduction in boom length. Front to back and side rejection are slightly degraded, but not severely, generally &amp;lt;25% with careful design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option would be to consider other directional antenna designs, which would yield a more compact overall package, but resulting in a more 3 dimensional shape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Examples of this would include the Cubical Quad Array, Delta Loop Arrays, or a circular loop array. Like the yagi, however, they will not provide a dramatic reduction in boom length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally there are antennas that work opposite the typical directional array. Rather than having high gain in one direction and low gain in all others, you can use an antenna with 'average' gain all the way around, but with a steep attenuating null in a single direction. Then, rather than trying to find what direction the signal is strongest in, you attempt to put the signal in the null of the antenna so it as weak as possible. These designs can be quite handy for DF work on strong local radiators that would otherwise overwhelm the receiver's AGC circuit. Small &quot;magnetic&quot; loop antennas exhibit this behavior (though they have 2 nulls), as can Moxon antennas when oriented vertically and relatively close to the ground (below 1 wavelength).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A magnetic loop in particular may work well for you, as they can be absolutely tiny, just 1/10th of a wavelength in circumference, on the desired frequency, however they can be quite tricky to design, particularly when they are electrically very small, and when they are operating above 50MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Small receiving array&quot; and &quot;Small directional receiving antenna&quot; would be good terms to google for, as they should give you additional designs I didn't include above.&lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="8717" LastEditDate="2017-07-01T01:24:09.713" LastActivityDate="2017-07-01T01:24:09.713" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6037" PostTypeId="2" ParentId="6035" CreationDate="2016-04-11T13:07:36.700" Score="3" Body="&lt;p&gt;If a full-sized VHF antenna is too big, then look at how people do direction finding on HF. A longer wavelengh means bigger antennas, so HF direction finders have been dealing with the &quot;too big&quot; problem for a long time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The canonical HF direction finding antenna is a &lt;a href=&quot;http://www.antenna-theory.com/antennas/smallLoop.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;small loop&lt;/a&gt;. This antenna is vertically polarized and gives two nulls when the plane of the loop is perpendicular to the source. The nulls are pretty sharp and deep. So instead of finding the direction where the signal strength is strongest, the operator finds the direction where the strength is weakest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a US Navy radio direction finder. Of course if you scale this down to VHF sizes and build it with modern electronics it will be much smaller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lrpnh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lrpnh.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;http://www.angelfire.com/space/proto57/rdf.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;the source&lt;/a&gt; for many more examples.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course this gives two directions. One way to deal with this taking measurements from two locations and triangulating. In one direction the lines implied by the two measurements intersect, and that's where the source is. In the other direction the lines don't intersect so it doesn't matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another solution to the two-direction problem is to add an omnidirectional antenna, making a &lt;a href=&quot;http://www.antenna-theory.com/arrays/main.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;phased array&lt;/a&gt;. The directionality of this array isn't great, but it's enough to figure out in which of the two directions is the source. You can see such a thing as the vertical rod on the right of the direction finder above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your source is horizontally polarized, a vertically polarized antenna won't work especially well. You'll still receive something, but it will be weaker. And much of what you receive will be reflections off objects that rotate the polarization, which will make localizing the source more difficult.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution is simple, albeit not obvious: use a dipole. Loops are historically more common because in the day they were developed, technology for high frequency radio didn't exist. Low frequencies propagate as ground waves, and ground waves work work much better in vertical polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF doesn't propagate as ground waves so this isn't a problem. If your source is horizontally polarized then use a dipole (short, if you like) instead of a loop. The directionality is identical: only the polarization is different. The nulls are in the directions of the ends of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-04-11T19:42:53.160" LastActivityDate="2016-04-11T19:42:53.160" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6038" PostTypeId="2" ParentId="5306" CreationDate="2016-04-11T18:28:54.133" Score="4" Body="&lt;p&gt;I am not sure that you can join RGSB through ARRL.  I'm not finding it on the ARRL website.  Perhaps it was a promotional effort, limited by time in some way.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am a member of both.  I usually renew each year at the RGSB boot at Dayton.  I have not checked lately, but there may be minor savings if you buy RSGB books from ARRL, as some titles may be shipped in bulk.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my opinion, it is well worth joining both, because they each have a different 'feel', and often present a slightly different point of view or emphasis on many topics.  Radio is international by its nature, and I find it useful to know the interests and concerns of our British friends.&lt;/p&gt;&#xA;" OwnerUserId="6491" LastActivityDate="2016-04-11T18:28:54.133" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6039" PostTypeId="1" CreationDate="2016-04-11T21:56:51.510" Score="5" ViewCount="258" Body="&lt;p&gt;I am involved in a precise positioning project that uses &lt;a href=&quot;https://en.wikipedia.org/wiki/Real_Time_Kinematic&quot; rel=&quot;nofollow&quot;&gt;Real Time Kinematic&lt;/a&gt; (RTK) for cm-accurate positioning. We use unattended base stations that provide real-time corrections for mobile rovers. The corrections can be used within a radius of about 10-20 km around a single base station (rover positioning precision degrades with greater radius) and need a data feed of about 1 kB/s. Currently mainly mobile networks (GSM, 3G, LTE) or ISM bands are used to transmit the corrections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is whether ham radio could be potentially used to transmit RTK corrections from either temporary or permanent base station(s) for non-commercial purposes. The RTK corrections would be publicly available for anyone to use with an unlimited number of rovers in given area. Multiple overlapping base stations could be used for greater area coverage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should ham allow the broadcasting I think this may expand globally since 1) it would be very useful public service, 2) receiver equipment would most likely be cheaper (no GSM data etc.) and 3) the range and reliability would be greater than with ISM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The territories of interest are mainly US and EU (but others welcome too). Of course proper amateur radio licenses would be obtained for broadcasting. The frequency and power used has not been defined yet but should allow for a reliable &lt;a href=&quot;https://en.wikipedia.org/wiki/Non-line-of-sight_propagation&quot; rel=&quot;nofollow&quot;&gt;NLOS&lt;/a&gt; propagation.&lt;/p&gt;&#xA;" OwnerUserId="6496" LastEditorUserId="76" LastEditDate="2019-03-13T01:48:42.193" LastActivityDate="2019-03-13T01:48:42.193" Title="Use ham to broadcast GPS RTK correction data" Tags="&lt;legal&gt;&lt;packet&gt;&lt;beacon&gt;&lt;gnss&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6040" PostTypeId="2" ParentId="6039" CreationDate="2016-04-11T23:05:09.357" Score="1" Body="&lt;p&gt;The only precedent that I can think of for using the ham bands for data beacons, where the data has nothing to do with either ham radio or emergency traffic, is weather station data over APRS.  In that case the data is in very short infrequent bursts, and is just being relayed to an internet gateway, rather than being broadcast for general consumption.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You didn't mention what country you're in, but I'll assume that you're in the US, and the rest of my answer is relevant only for that country.  I'm not a lawyer, but I can read &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1203&quot; rel=&quot;nofollow&quot;&gt;Part 97&lt;/a&gt;.  §97.3 defines a beacon as &quot;An amateur station transmitting communications for the purposes of observation of propagation and reception or other related experimental activities,&quot; and broadcasting as &quot;transmissions intended for reception by the general public, either direct or relayed.&quot;  It seems to me that you're talking about a beacon broadcasting data for the general public, rather than to study radio propagation, and so my non-expert take is that what you propose would not be legal.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-04-11T23:05:09.357" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6041" PostTypeId="1" CreationDate="2016-04-11T23:58:26.603" Score="6" ViewCount="6637" Body="&lt;p&gt;I was given about 60 feet of good cable with connections but only need about 20 feet. Can I loop up the end or do I need to cut and put a new connector on?&lt;/p&gt;&#xA;" OwnerUserId="6500" LastEditorUserId="29" LastEditDate="2016-07-25T19:34:20.420" LastActivityDate="2019-04-17T18:32:41.420" Title="I have 60 feet of coax but only need 20 feet; can I loop up the excess?" Tags="&lt;coaxial-cable&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6042" PostTypeId="2" ParentId="6041" CreationDate="2016-04-12T01:03:34.863" Score="2" Body="&lt;p&gt;That depends on what kind of cable it is, the band you'll be using, what your SWR is, how old the coax is, and how demanding your needs are.  If your SWR is less than 2:1, you're using the coax for HF, and you're not concerned about that last dB, then go ahead and try it as-is.  If you're talking about the coax to your 2m antenna that you use to talk to the repeater and your signal is normally full-quieting, then go ahead and try it as-is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the coax has been out in the weather for ten years or more, or if it's a lot thinner than the coax people usually use, or if the coax is marked &quot;75 &amp;ohm;&quot;, then I'd leave it alone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your situation is somewhere in the middle, then give us more details.  73!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-04-12T01:03:34.863" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6043" PostTypeId="2" ParentId="6041" CreationDate="2016-04-12T02:15:45.870" Score="12" Body="&lt;p&gt;There's nothing inherently wrong with “looping up” extra coaxial cable. In fact, a neatly wound coil of coax can function as an air-core choke balun (“ugly balun”) which is useful for some antenna systems when located at the feed point of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only disadvantage is the extra loss in the coax from the extra length. Loss in a coaxial cable, when measured in dB, is &lt;strong&gt;proportional to the length of the cable&lt;/strong&gt;. For example, if your 60 feet of cable has 6 dB of loss as used, then you will have 2 dB if you cut it down or replace it with 20 feet of the same cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Note that this means that the lower loss-per-length the coax has, the less valuable it is to trim it to the right length.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other factors — how much loss a particular length has — are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the type of cable (better quality coax will have less loss since it is designed to), and&lt;/li&gt;&#xA;&lt;li&gt;the frequency of the signal (higher frequencies experience more loss).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you look at the manufacturer's datasheet for the coax (you should be able to look it up from the printing on the side of the cable, if any) will give a table or graph of loss in dB per 100 feet (or some other such standard length) versus frequency. Just multiply/divide to find the actual loss for your length.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;But be sure to think about whether you actually care about the loss:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Loss when transmitting means you're wasting that fraction of your transmitter's power — if the current result is adequate for the contacts you want to make, then don't worry about it, but if the loss is significant then improving the coax is overall cheaper and more efficient than getting a bigger amplifier.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Loss when receiving matters &lt;em&gt;only if&lt;/em&gt; the incoming signal is so weak that the limiting factor is not noise picked up by your antenna but noise internal to your receiver or leaking into it from nearby sources.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;If you have or can borrow an &lt;strong&gt;antenna analyzer&lt;/strong&gt;, you may be able to use it to measure the actual loss in a piece of coax. Hook it up to the analyzer with the other end &lt;em&gt;not connected to anything&lt;/em&gt; — this &lt;em&gt;unterminated&lt;/em&gt; end will reflect the signal back almost perfectly. In this configuration the &lt;em&gt;return loss&lt;/em&gt; (amount of power not reflected back to the analyzer) the analyzer measures will be equal to twice the loss in the cable (because the signal bounced back, so it went across the entire length of the cable twice).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since cable loss is frequency-dependent, set the analyzer's frequency to the highest frequency you plan to use (which should have the most loss), or whichever frequency you wish to measure at.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best to worst test configurations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If your antenna analyzer directly reports return loss (e.g. the higher-end &lt;a href=&quot;http://www.rigexpert.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RigExpert&lt;/a&gt; models do) then you can use that value. Remember, the return loss is the coax loss applied to the signal &lt;em&gt;twice&lt;/em&gt;, so divide the dB value by two.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you only have a SWR value,  you can calculate it from the SWR value using the following formula or &lt;a href=&quot;https://www.microwaves101.com/calculators/872-vswr-calculator&quot; rel=&quot;nofollow noreferrer&quot;&gt;any purpose-made calculator&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;\mathrm{RL} = 20\log_{10}\left(\frac{\mathrm{VSWR}+1}{\mathrm{VSWR}-1}\right)&#xA;$$&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If your analyzer displays the SWR as infinity or off-scale, the loss is &lt;em&gt;too low&lt;/em&gt; to measure. To get a better measurement, you would need an &lt;strong&gt;attenuator&lt;/strong&gt; inserted in line (at either end); this will increase the loss by a known amount, and therefore reduce the SWR into a measurable range. Then subtract the attenuator's loss from the return loss before dividing by two.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If your only measurement instrument is a transmitter with built in SWR meter, don't do this unless you know it's protected against mismatched loads. You will almost certainly need an attenuator, and it will have to be rated for the output power, and the result may be rather inaccurate as these meters are not intended for precision measurements.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-07-11T16:21:35.043" LastActivityDate="2017-07-11T16:21:35.043" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="6044" PostTypeId="1" AcceptedAnswerId="6045" CreationDate="2016-04-12T19:36:05.173" Score="2" ViewCount="256" Body="&lt;p&gt;According to the MRF421 or MRF454 transistor &lt;a href=&quot;http://cdn.macom.com/datasheets/MRF421.pdf&quot; rel=&quot;nofollow&quot;&gt;datasheets&lt;/a&gt;,  used in the AN762 HF amplifiers say that the transistors are &quot;100% tested for load mismatch at all phase angles with 30:1 VSWR&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, in the &lt;a href=&quot;http://www.seboldt.net/k0jd/mot-an762.pdf&quot; rel=&quot;nofollow&quot;&gt;application not&lt;/a&gt;e (page 9), they describe testing the amplifier with varying SWR and noted stable performance up to a 5:1 or 9:1 depending on the model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it safe to operate an amplifier based on this design with an SWR measured between the amp and antenna of say 3:1, or are there other factors involved?&lt;/p&gt;&#xA;" OwnerUserId="5418" LastActivityDate="2016-04-12T23:55:20.420" Title="AN762 Amplifier Transistors" Tags="&lt;hf&gt;&lt;diy&gt;&lt;amplifier&gt;&lt;impedance&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6045" PostTypeId="2" ParentId="6044" CreationDate="2016-04-12T23:55:20.420" Score="4" Body="&lt;p&gt;The tests they are referring to are for amplification characteristics like linearity and stability, not continuous thermal dissipation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, unless you've constructed the thing in such a way that the transistor's thermal dissipation capacity is severely derated, it is very rarely heat that kills finals, at least in the short term. While severe and repeated thermal cycles caused by poor design or execution of the cooling system can cause mechanical stress that eventually cause the amp to fail, it takes exceptionally high temperatures to get the silicon itself to fail while it is operating within normal design parameters. Like, &quot;burn your finger when touching it&quot; high temperatures. When radios do fail from heat, it is quite often not the finals transistors themselves that fail, at least at first. Peripheral components such as capacitors and resistors are much more likely to go severely out of tolerance when temperatures really start to climb, though as those fail, they may take the finals with them as the circuit fails in a less than graceful manner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;High voltage is far and away the most likely killer of PA transistors in the short term. The 'cooking the transistors' scenario that everybody fears is a misconception that likely stems from the fact that high voltage and high temperatures generally occur under similar conditions, poor impedance matching, and high temperatures are usually far easier to spot than a brief arc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Arcing can occur for a couple of reasons. Most often it is a failure in a high Q L/C tank somewhere in the antenna or feed system. Such tank circuits are present in filters, tuners, antenna loading systems, and band traps. If the antenna itself presents a very high impedance, or is simply absent due to an operator error, these high Q, resonant tank circuits can &quot;ring&quot;, inducing &lt;em&gt;very&lt;/em&gt; high voltage within the tank, often on the order of 1kV or more. The result is most often directly observed as a &quot;burned&quot; plate in a variable capacitor inside an antenna tuner, as the plate spacing of air variable capacitors is often the weakest link in the circuit. Many times this arcing is not fatal to the radio when it happens in some component along the transmission line/antenna chain, but it can be under the right circumstances. If this arcing occurs within the radio, or the circumstances of the arc in the feed/antenna chain allow the high voltage to travel directly back to the radio, the finals may be destroyed almost instantly as the high voltage literally burns through delicate internal structures in the transistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a good example of high voltage appearing in high Q resonant circuits in ham radio applications, a magnetic loop antenna is a very good example. Voltage at the tuning capacitor can often exceed 2kV with just 100 watts input, nearly 10 times the typical peak voltage observed within a 50 ohm antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All of that said: Is 3:1 safe for your amp?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In all likelihood, yes, but be generous with the selection of your heat sink, use best practices for construction of filters and matching networks, and include a solid safety margin in voltage and temperature ratings when selecting all components &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reflected power will only be a few watts, and the maximum peak to peak (ignoring potential for ringing) voltage will only be about 100V higher than a 50 ohm load would generate. &lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-04-12T23:55:20.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6046" PostTypeId="2" ParentId="5995" CreationDate="2016-04-13T03:25:41.203" Score="0" Body="&lt;p&gt;Page 28. &lt;a href=&quot;http://www.cbradio.hu/doc/kg-uv9d.pdf&quot; rel=&quot;nofollow&quot;&gt;Manual&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Set RX-CTC to OFF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;TX-CTC should be set to the repeater tone.&lt;/p&gt;&#xA;" OwnerUserId="5418" LastActivityDate="2016-04-13T03:25:41.203" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6047" PostTypeId="2" ParentId="5591" CreationDate="2016-04-13T05:44:05.177" Score="0" Body="&lt;p&gt;Can you determine the repeater input frequency? If so, you could try running the tone scan on the input frequency, this would help in the case that the tone is not output by the repeater.&lt;/p&gt;&#xA;" OwnerUserId="5418" LastActivityDate="2016-04-13T05:44:05.177" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6048" PostTypeId="1" CreationDate="2016-04-13T17:08:07.307" Score="2" ViewCount="209" Body="&lt;p&gt;I am trying to design and build a basic signal detector using MOSFETs because they are more compact than resistors, capacitors, and inductors. I was wondering if anyone here has any suggestions on how I can do this project. The original thought I had was to simply look up a simple Field Strength Meter (attached below) and simply replace the capacitors in the circuit with properly biased MOSFETs so that they can be used effectively as capacitors. This approach seems too naive, if anyone has a more refined approach please feel free to tell me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RCB74.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RCB74.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6508" LastEditorUserId="76" LastEditDate="2016-04-13T18:13:16.800" LastActivityDate="2016-07-18T18:03:07.693" Title="Basic Signal Detector using MOSFETs" Tags="&lt;diy&gt;&lt;equipment-design&gt;&lt;electronics&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6050" PostTypeId="5" CreationDate="2016-04-13T23:17:08.667" Score="0" Body="&lt;p&gt;SWL stands for &quot;Shortwave listening&quot;. Wikipedia has &lt;a href=&quot;https://en.wikipedia.org/wiki/Shortwave_listening&quot; rel=&quot;nofollow&quot;&gt;an article&lt;/a&gt; about the hobby. Could perhaps more broadly refer to any sort of monitoring of DX-friendly bands or lower (MW/LF/VLF) but usually distinguished from &quot;scanner monitoring&quot; on the VHF/UHF bands.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-04-20T17:58:27.207" LastActivityDate="2016-04-20T17:58:27.207" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6051" PostTypeId="4" CreationDate="2016-04-13T23:17:08.667" Score="0" Body="Questions about shortwave listening and similar low-frequency reception activities." OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-04-20T17:58:30.597" LastActivityDate="2016-04-20T17:58:30.597" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6052" PostTypeId="1" CreationDate="2016-04-15T02:44:26.953" Score="1" ViewCount="2847" Body="&lt;p&gt;I have a HackRF, and I'm trying to figure out the best way to decode an On-Off Key digital signal. I'd like to just run a script (specifying the frequency and sample rate) and have it print out the digital signal in binary and/or hex. Does anything like this exist?&lt;/p&gt;&#xA;" OwnerUserId="5960" LastActivityDate="2016-04-15T16:01:43.810" Title="Decode digital signal (On-Off Keying) with SDR" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6053" PostTypeId="1" CreationDate="2016-04-15T04:45:05.013" Score="1" ViewCount="301" Body="&lt;p&gt;I'm designing a circuit which uses the RF6886 amplifier IC. What is the maximum reverse power that the amplifier can sustain? At what reverse power will the amplifier die?&lt;/p&gt;&#xA;" OwnerUserId="5762" LastEditorUserId="76" LastEditDate="2016-04-15T17:29:19.573" LastActivityDate="2016-04-19T13:20:52.687" Title="RF6886 high power amplifier maximum reverse power" Tags="&lt;electronics&gt;&lt;amplifier&gt;&lt;impedance&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6054" PostTypeId="2" ParentId="6053" CreationDate="2016-04-15T12:21:41.293" Score="0" Body="&lt;p&gt;You have, at least, 3 alternatives:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Read the datasheet. They mention SWR 5:1&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Empirical research: Increase the SWR until smoke.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Avoid. Use a matchbox.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6521" LastActivityDate="2016-04-15T12:21:41.293" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6055" PostTypeId="2" ParentId="6052" CreationDate="2016-04-15T15:56:01.137" Score="1" Body="&lt;p&gt;Sorry, I have not fully done this so my answer is not coming from experience. (I.e., I do not know offhand the &lt;em&gt;best&lt;/em&gt; way to do this or have a personal favorite method or anything.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However you might find some good info in &lt;a href=&quot;https://greatscottgadgets.com/sdr/8/&quot; rel=&quot;nofollow&quot;&gt;https://greatscottgadgets.com/sdr/8/&lt;/a&gt; (&quot;Software Defined Radio with HackRF, Lesson 8: On-Off Keying&quot;) or by searching the web for &quot;gnuradio ook&quot; or &quot;gnuradio ask&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you don't necessarily need to use GnuRadio, e.g. &lt;a href=&quot;https://github.com/merbanan/rtl_433&quot; rel=&quot;nofollow&quot;&gt;https://github.com/merbanan/rtl_433&lt;/a&gt; and &lt;a href=&quot;https://github.com/jimstudt/ook-decoder&quot; rel=&quot;nofollow&quot;&gt;https://github.com/jimstudt/ook-decoder&lt;/a&gt; do OOK/ASK decode for many 433MHz/etc. devices albeit via RTL dongles rather than HackRF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some cases, often during preliminary stages reverse engineering where the exact encoding mechanism e.g. Manchester or whatnot is not yet known, I've seen some folks even decode the AM-recorded audio manually by carefully inspecting &quot;the bumps&quot; in Audacity. This is mentioned e.g. in some of the posts listed in &lt;a href=&quot;http://www.rtl-sdr.com/tag/ook/&quot; rel=&quot;nofollow&quot;&gt;http://www.rtl-sdr.com/tag/ook/&lt;/a&gt; or in &lt;a href=&quot;http://forum.arduino.cc/index.php?topic=145341.0&quot; rel=&quot;nofollow&quot;&gt;this thread&lt;/a&gt; or &lt;a href=&quot;http://rayshobby.net/reverse-engineer-wireless-temperature-humidity-rain-sensors-part-1/&quot; rel=&quot;nofollow&quot;&gt;this blog post&lt;/a&gt; both about doing ASK decodes of a temperature sensor.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-04-15T16:01:43.810" LastActivityDate="2016-04-15T16:01:43.810" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6056" PostTypeId="5" CreationDate="2016-04-15T17:37:11.503" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-15T17:37:11.503" LastActivityDate="2016-04-15T17:37:11.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6057" PostTypeId="4" CreationDate="2016-04-15T17:37:11.503" Score="0" Body="Questions about standing-wave ratio (SWR or VSWR) on transmission lines, measuring SWR, reflected power, losses therefrom, transmitter ability to withstand high SWR, etc." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-15T17:37:11.503" LastActivityDate="2016-04-15T17:37:11.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6058" PostTypeId="5" CreationDate="2016-04-15T17:43:47.807" Score="0" Body="&lt;p&gt;A low-noise amplifier (LNA) is an &lt;a href=&quot;/questions/tagged/amplifier&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;amplifier&amp;#39;&quot; rel=&quot;tag&quot;&gt;amplifier&lt;/a&gt; designed to amplify very weak signals while adding a minimum of noise to the output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In &lt;a href=&quot;/tags/antenna-system&quot;&gt;antenna systems&lt;/a&gt;, a LNA may be placed between the antenna and feed line (as opposed to between the receiver and feed line) in order to improve the signal-to-noise ratio found at the receiver after losses in the feed line; this is particularly useful for higher frequencies where losses in transmission lines are significant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the same antenna is to be used for transmitting, a transmit/receive switch must be used to bypass the amplifier when transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Links:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Low-noise_amplifier&quot; rel=&quot;nofollow&quot;&gt;Low-noise amplifier&lt;/a&gt; at Wikipedia&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-15T17:43:47.807" LastActivityDate="2016-04-15T17:43:47.807" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6059" PostTypeId="4" CreationDate="2016-04-15T17:43:47.807" Score="0" Body="Questions about low-noise amplifiers (LNAs) and their application in receiving antenna systems." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-15T17:43:47.807" LastActivityDate="2016-04-15T17:43:47.807" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6060" PostTypeId="5" CreationDate="2016-04-15T17:49:00.240" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-15T17:49:00.240" LastActivityDate="2016-04-15T17:49:00.240" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6061" PostTypeId="4" CreationDate="2016-04-15T17:49:00.240" Score="0" Body="Questions about amplifiers, typically RF power amplifiers. For low-noise amplifiers (LNAs) consider using the &quot;lna&quot; tag." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-15T17:49:00.240" LastActivityDate="2016-04-15T17:49:00.240" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6062" PostTypeId="5" CreationDate="2016-04-15T17:52:35.323" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-15T17:52:35.323" LastActivityDate="2016-04-15T17:52:35.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6063" PostTypeId="4" CreationDate="2016-04-15T17:52:35.323" Score="0" Body="Questions which involve the properties or applications of individual electronic components." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-15T17:52:35.323" LastActivityDate="2016-04-15T17:52:35.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6064" PostTypeId="1" AcceptedAnswerId="6090" CreationDate="2016-04-17T12:06:23.027" Score="2" ViewCount="468" Body="&lt;p&gt;I currently reside in Japan (not on a military base) and I have been interested in purchasing some walkie talkies. I found these on amazon JP&#xA;&lt;a href=&quot;http://www.amazon.co.jp/F-R-C-EXPLORER-%E3%82%A8%E3%82%AF%E3%82%B9%E3%83%97%E3%83%AD%E3%83%BC%E3%83%A9-%E7%89%B9%E5%AE%9A%E5%B0%8F%E9%9B%BB%E5%8A%9B%E3%83%88%E3%83%A9%E3%83%B3%E3%82%B7%E3%83%BC%E3%83%90%E3%83%BC2%E5%8F%B0%E3%82%BB%E3%83%83%E3%83%88-ET-20X/dp/B001238SDU/ref=sr_1_1?ie=UTF8&amp;amp;qid=1460893425&amp;amp;sr=8-1&amp;amp;keywords=walkie%20talkie&quot; rel=&quot;nofollow&quot;&gt;Link&lt;/a&gt; and I was wondering if can I own something like this without a license. Here are the specs.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Transmission and reception frequency: 422.050 ~ 422.300MHz (12.5KHz step) &#xA;&#xA;Types of radio wave: F3E&#xA;&#xA;Transmission output: 10mW &#xA;&#xA;Receiving sensitivity: -14dBμ following (12dB SINAD)&#xA;&#xA;Receiving system: double superheterodyne system&#xA;&#xA;Power supply voltage: DC3.6 ~ 4.5V (AA alkaline batteries × 3 This optional)&#xA;&#xA;Current consumption receiving standby time of about 50mA receive a maximum time of about 140mA during transmission about 70mA&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I assumed that since it was on Amazon Jp that it must be legal in Japan but I thought that I should be safe than sorry. So are these walkie talkies legal and if they are would I need a license? Also do these seem like good quality walkie talkies? Would they have a good range (i.e. a few miles). I couldn't find and info about the distance on that amazon page. &lt;/p&gt;&#xA;" OwnerUserId="5616" LastEditorUserId="5616" LastEditDate="2016-04-18T07:28:33.477" LastActivityDate="2016-04-21T12:41:51.847" Title="Do I need I license to have these walkie talkies in Japan" Tags="&lt;legal&gt;&lt;license&gt;&lt;ht&gt;&lt;japan&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6065" PostTypeId="1" AcceptedAnswerId="6071" CreationDate="2016-04-18T00:29:50.313" Score="3" ViewCount="1794" Body="&lt;p&gt;Anderson PowerPole connector housings can be joined side-to-side using dovetail joints molded into the plastic to make a multi-conductor connector, as seen in the conventional amateur radio 12V power positive/negative configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;How does one &lt;em&gt;separate&lt;/em&gt; the joined connectors, particularly if they have wires attached?&lt;/strong&gt; When experimenting, I found it impossible to separate them by hand. I can think of solutions involving a specifically shaped jig and a vise or hammer, but I'd like to know if there's a way to do this that's more practical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason I'm asking is that I plan to make up a wiring harness which is not strictly symmetric but has something inserted in one half and not the other (e.g. a switch or ammeter). I'd like to be able to later change the wire length, termination, etc. of one side without also replacing the other side.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T17:49:50.327" LastActivityDate="2016-10-29T17:49:50.327" Title="How do I separate dovetailed PowerPole housings?" Tags="&lt;connectors&gt;&lt;dc-power&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6067" PostTypeId="2" ParentId="6065" CreationDate="2016-04-18T16:13:36.223" Score="1" Body="&lt;p&gt;Many Anderson Powerpole connectors have a circular opening for a roll pin to keep the sections from sliding along the dovetail. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a link to page with a image, &lt;a href=&quot;http://www.qsl.net/w2vtm/powerpole.html&quot; rel=&quot;nofollow&quot;&gt;http://www.qsl.net/w2vtm/powerpole.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6539" LastActivityDate="2016-04-18T16:13:36.223" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6068" PostTypeId="2" ParentId="6065" CreationDate="2016-04-18T18:43:39.567" Score="1" Body="&lt;p&gt;They do seperate, just apply brute force, they slide apart the same way they go together, obviously in the opposite direction.   Try tapping one of the connectors from behind with the fronts on your desk, and something like a ruler to hold one of the housings up from the other.  &lt;/p&gt;&#xA;" OwnerUserId="3027" LastActivityDate="2016-04-18T18:43:39.567" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6069" PostTypeId="2" ParentId="5934" CreationDate="2016-04-18T18:54:02.563" Score="0" Body="&lt;p&gt;The DVB-T2 standard specifies (many things and ) an ethernet controler, that's all ...&lt;/p&gt;&#xA;" OwnerUserId="454" LastActivityDate="2016-04-18T18:54:02.563" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6070" PostTypeId="2" ParentId="6065" CreationDate="2016-04-18T23:24:52.987" Score="1" Body="&lt;p&gt;They only go on one way and have to come apart the opposite direction.  Make sure you're pushing and pulling on the right ones, otherwise they'll just lock harder. &lt;/p&gt;&#xA;" OwnerUserId="6178" LastActivityDate="2016-04-18T23:24:52.987" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6071" PostTypeId="2" ParentId="6065" CreationDate="2016-04-18T23:45:22.207" Score="1" Body="&lt;p&gt;Individual PowerPole housings are in fact easy to separate by hand, assuming they are not locked together in some way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason I found it hard is that the first time I experimented with using the dovetail joint, what I used was actually the outer sides of two &lt;a href=&quot;https://powerwerx.com/anderson-powerpole-connectors-30amp-bonded&quot; rel=&quot;nofollow&quot;&gt;pre-assembled ultrasonically welded red/black pairs&lt;/a&gt;. Apparently the welding process also affects the outside surfaces of the connectors, because the individual housings slide together and apart easily whereas the welded ones have rougher, harder-to-slide surfaces.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one &lt;em&gt;were&lt;/em&gt; starting with housings that are jammed or bonded together, then another approach to reusing the parts as described in the question is to remove one or both &lt;em&gt;contacts&lt;/em&gt; (terminals) from the paired housings (which requires a specialized tool or careful use of a tiny screwdriver or such), which does the same job of allowing the two wires to be separated.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T17:48:31.370" LastActivityDate="2016-10-29T17:48:31.370" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6072" PostTypeId="2" ParentId="6019" CreationDate="2016-04-19T07:41:06.677" Score="1" Body="&lt;p&gt;All good answers here: I can only add a little warning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While WiFi in both the 2.4 GHz and 5 GHz bands is &quot;license free&quot; and can be used over longer distances, you may want to look up the legislation in your own area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example: where I live the maximum power output is 100 mW ERP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that if an antenna is used with gain, then the power output of the WiFi units need to be throttled back to ensure power out (with antenna gain) is not exceeding 100 mW ERP. If running longer coax lengths between the unit and antenna, you may want to take coax losses into account as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This of course to stay in the letter of the law. Legislation varies from country to country.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you choose to ignore this, then it is a matter of evaluating the risk of getting caught — completely up to you.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="76" LastEditDate="2016-04-19T13:19:29.010" LastActivityDate="2016-04-19T13:19:29.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6073" PostTypeId="2" ParentId="6053" CreationDate="2016-04-19T07:54:31.727" Score="2" Body="&lt;p&gt;&lt;a href=&quot;http://www.rfmd.com/store/downloads/dl/file/id/29775/rf6886_data_sheet.pdf&quot; rel=&quot;nofollow&quot;&gt;The datasheet&lt;/a&gt; has an interesting table on page 5, which lists VSWR 5:1 for most frequencies, and 3.5:1 for some frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can &lt;a href=&quot;http://www.antenna-theory.com/definitions/vswr-calculator.php&quot; rel=&quot;nofollow&quot;&gt;calculate return power from VSWR&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;VSWR 5:1 would 44.4444% of return power.&lt;/li&gt;&#xA;&lt;li&gt;At a maximum of 34 dBm (which is about 2.5 watts), the maximum return power would be 1.1 watts (at VSWR 5:1).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;However, it is stated as &quot;survival&quot;, so you will have to be more careful then that. Either build a protection circuit, or simply match properly.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="76" LastEditDate="2016-04-19T13:20:52.687" LastActivityDate="2016-04-19T13:20:52.687" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6075" PostTypeId="2" ParentId="6065" CreationDate="2016-04-19T16:01:28.017" Score="8" Body="&lt;p&gt;Firstly, there's a hole for a locking pin in the connectors. The pin prevents the connectors from sliding apart. If there's a pin in there, you'll need to push it out with a punch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xd6lS.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xd6lS.jpg&quot; alt=&quot;roll pin&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there isn't a pin, it's possible the connector was assembled with cyanoacrylate glue. Since the roll pin can sometimes fall out, Anderson recommends glue in applications where this would be a problem. In this case you may not be able to get the connectors apart without damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the roll pin removed, the connectors slide apart. Each side of the connector will have either a groove or a tongue. If one side has a groove, the opposite side will always have a tongue, so you should be able to determine the necessary sliding direction by looking at the connector. An image helps:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zMplC.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zMplC.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there are wires attached to the connector it might be hard to slide connector apart. If the wire is zipline, it may be possible to separate the wires for a few inches so there's enough flexibility to move the connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that's not possible, then you may be able to get the contacts out of the housing. There's &lt;a href=&quot;https://powerwerx.com/powerpole-insertion-removal-extraction-tool&quot; rel=&quot;noreferrer&quot;&gt;a tool for doing this&lt;/a&gt;. If you don't have or don't care to purchase the tool, then you may be able to improvise something similar with a bent piece of metal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The contacts are held in place by an internal spring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0o4UI.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0o4UI.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need to get something around and behind the contact to push up the spring. The spring is what retains the contact: by lifting the spring the contact will be free to slide out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take care to avoid bending the contact when doing this: if the contact is bent it may no longer make solid contact with the mating connector. Where possible I'd advise discarding the old contacts and attaching new contacts.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-04-19T16:01:28.017" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6076" PostTypeId="1" CreationDate="2016-04-19T19:37:01.770" Score="3" ViewCount="127" Body="&lt;p&gt;What statistical or other descriptions exist regarding modeling of an HF-band RF fading channel?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is allow making (as in code my own software) lots of simulated test input signals for an SDR demodulator to allow testing different software demodulation algorithms under different and varying signal and noise levels (etc.), even when not around an HF antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There seem to be channel modeling standards for commercial cellular bands, but I am interested in typical fading in amateur radio HF bands.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2016-04-20T04:37:24.697" Title="RF fading channel model?" Tags="&lt;hf&gt;&lt;software-defined-radio&gt;&lt;testing&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6077" PostTypeId="2" ParentId="2309" CreationDate="2016-04-19T19:37:06.060" Score="0" Body="&lt;p&gt;Simple answer, yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Handhelds use a metal support frame inside the unit as its counterpoise. Using a resonant external wire hanging off the unit aka &quot;tiger tail&quot; allows for much better receive and transmit. For temporary base station use (like while camping), yes it would help to create a ground plane setup, but rather than buy something, can easily make one with solid copper wire onto a SO239-BNC adapter piece.&lt;/p&gt;&#xA;" OwnerUserId="6545" LastActivityDate="2016-04-19T19:37:06.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6078" PostTypeId="2" ParentId="6076" CreationDate="2016-04-20T04:30:31.210" Score="2" Body="&lt;p&gt;Here's a paper from the IEEE antennas and propagation society, describing a channel model and the experimental verification thereof.  Noise will be another whole subject on its own, but the IEEE APS will be a good place to start.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://ieeexplore.ieee.org/xpl/login.jsp?tp=&amp;amp;arnumber=1090438&amp;amp;url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D1090438&quot; rel=&quot;nofollow&quot;&gt;Experimental Confirmation of an HF Channel Model&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The abstract describes the model quite well. Unfortunately to read the whole article and find the coefficients, you need to subscribe, or find it elsewhere.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Specially designed HF ionospheric propagation measurements were made and analyzed to confirm the validity and bandwidth limitations of a proposed stationary HF ionospheric channel model. In the model, the input (transmitted) signal feeds an ideal delay line and is delivered at several taps with adjustable delays, one for each resolvable ionospheric modal component. Each delayed signal is modulated in amplitude and phase by a baseband tap-gain function, and the delayed and modulated signals are summed (with additive noise) to form the output (received) signal. Statistical specifications for the tap-gain functions involved three hypotheses: 1) that each tap-gain function is a complexGaussian process that produces Rayleigh fading, 2) that the tapgain functions are independent, and 3) that each tap-gain function has a spectrum that in general is the sum of two Gaussian functions of frequency, one for each magnetoionic component. Statistical tests were performed on daytime and nighttime measurements confirming the validity of the three hypotheses, and thereby the validity of the model. For practical applications, the model can be considered valid over a bandwidth equal to about one fourth of the reciprocal of the effective (weighted) time spreads on the ionospheric modal components. The model should be useful both in theoretical analyses of communication system performance and for channel simulator designs.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2016-04-20T04:37:24.697" LastActivityDate="2016-04-20T04:37:24.697" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6079" PostTypeId="1" CreationDate="2016-04-20T09:20:00.000" Score="2" ViewCount="203" Body="&lt;p&gt;From what info I've found, it seems a pc parport has a max speed of  ~2meg /sec  ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So transmission on medium wave, to ~160 meters should be possible ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With antenna than possibly a small wire, I would think transmission range would only be a few feet at best ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I've also found info to suggest that trying to program the port under any non real time os is going to yield only a few hundred Khz at best.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, I'm thinking maybe a custom boot program that might be the solution ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've found a few examples of RF / AM, FM transmitting using microcontrollers, and I then wondered if a PC could do something similar with either the parallel, USB or serial ports for either medium wave or ham frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Serial looks too slow, and USB not doable without some kind of USB dev board / custom device, so that leaves the parallel port.&lt;/p&gt;&#xA;" OwnerUserId="6337" LastActivityDate="2016-04-20T09:50:39.707" Title="Is it possible to generate rf by directly programming a pc parallel port?" Tags="&lt;transmitter&gt;&lt;software-development&gt;" AnswerCount="1" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6080" PostTypeId="2" ParentId="6079" CreationDate="2016-04-20T09:50:39.707" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;Is it possible to generate rf by directly programming a pc parallel port?&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, you can.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact any &quot;alternating current&quot; will produce RF, and a &quot;port&quot; (parrallel or other) from a &quot;computer&quot; can do this...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;but... (there is always one, isn't there?) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will have to ensure that you are filtering intermodulation, harmonic's and so on so forth, before the signal will be clean enough to amplify and transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't have to re-invent the wheel either; an article was written on how to transmit FM (and other modes) using a Raspberry-Pi, here: &lt;a href=&quot;http://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-with-just-a-raspberry-pi/&quot; rel=&quot;nofollow&quot;&gt;http://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-with-just-a-raspberry-pi/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not taking away the requirement of filtering, but fear not; someone thought of that as well, see here: &lt;a href=&quot;http://shop.languagespy.com/products/pi-tx-transmitter-kit-for-the-raspberry-pi?variant=11348563589&quot; rel=&quot;nofollow&quot;&gt;http://shop.languagespy.com/products/pi-tx-transmitter-kit-for-the-raspberry-pi?variant=11348563589&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Disclaimer: I have no affiliation with either product/shop/site, and I have not personally used either product; so the obligatory &quot;YMMV&quot; applies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-04-20T09:50:39.707" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6085" PostTypeId="1" AcceptedAnswerId="6094" CreationDate="2016-04-21T05:50:11.663" Score="1" ViewCount="66" Body="&lt;p&gt;In the simplest form, how could thermal resistor noise be described? I've looked up online but just found the calculation part.&lt;/p&gt;&#xA;" OwnerUserId="4506" LastActivityDate="2016-04-21T20:23:54.747" Title="Inquiry regarding thermal resistor noise" Tags="&lt;noise&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6086" PostTypeId="2" ParentId="6085" CreationDate="2016-04-21T09:16:48.127" Score="2" Body="&lt;p&gt;I am a complete novice, so it does not necessarily mean that what I found on is something I understand, especially in terms of application to amateur radio - I would like to figure out how to apply some of the reduction techniques:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;From a set of &lt;a href=&quot;http://engrwww.usask.ca/classes/EE/323/notes_2005/chapter8.pdf&quot; rel=&quot;nofollow&quot;&gt;lecture notes from a college class&lt;/a&gt;:&lt;/strong&gt;&#xA;&quot;Thermal noise is produced by the motion of free electrons in a resistance due to temperature. It is generated even when the resistance is not connected to a circuit but is due to the random fluctuations in charge at either end of the resistance. Thermal noise is often called Johnson noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The noise power in thermal noise is constant per unit of bandwidth across the usable electronic spectrum. Because of this, it is a form of white noise. The maximum noise power available from a thermal noise source is given by the equation:  Pn = kTB&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On pp. 155-191, noise reduction techniques are discussed in detail; the main techniques include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Capacitors&lt;/li&gt;&#xA;&lt;li&gt;Varistors&lt;/li&gt;&#xA;&lt;li&gt;Suppressors&lt;/li&gt;&#xA;&lt;li&gt;Screening tehcniques&lt;/li&gt;&#xA;&lt;li&gt;Grounds, Shields, and Connecting Wires&lt;/li&gt;&#xA;&lt;li&gt;Filters&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;From wikipedia, there is a bit more background:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Johnson–Nyquist noise (thermal noise, Johnson noise, or Nyquist noise) is the electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage. The generic, statistical physical derivation of this noise is called the fluctuation-dissipation theorem, where generalized impedance or generalized susceptibility is used to characterize the medium.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thermal noise in an ideal resistor is approximately white, meaning that the power spectral density is nearly constant throughout the frequency spectrum (however see the section below on extremely high frequencies). When limited to a finite bandwidth, thermal noise has a nearly Gaussian amplitude distribution.&lt;a href=&quot;http://engrwww.usask.ca/classes/EE/323/notes_2005/chapter8.pdf&quot; rel=&quot;nofollow&quot;&gt;1&lt;/a&gt;&quot;&#xA;.......&#xA;Thermal noise is distinct from shot noise, which consists of additional current fluctuations that occur when a voltage is applied and a macroscopic current starts to flow. For the general case, the above definition applies to charge carriers in any type of conducting medium (e.g. ions in an electrolyte), not just resistors. It can be modeled by a voltage source representing the noise of the non-ideal resistor in series with an ideal noise free resistor.&#xA;......&lt;/p&gt;&#xA;" OwnerUserId="6557" LastActivityDate="2016-04-21T09:16:48.127" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6087" PostTypeId="1" CreationDate="2016-04-21T09:29:14.833" Score="3" ViewCount="225" Body="&lt;p&gt;Does anyone know of software and/or techniques to effectively and efficiently to:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Merge contact logging with displaying location information on a digital map; e.g. Google Earth/Map&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I would like to be able, in some fashion, record locations of contacts, and then efficiently turn this into a layered geospatial display on a map.  In practice, this might be a separate layer for the type/power of the rig used to make the contact, and then compare.  Ideally, this information would be exportable to a standard GIS data from; e.g. Google Map/Earth&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Related to the first question:  Are there any best practices, software for also capturing/recording the effective transmission area in a similar manner?&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;That is, if it is reasonably easy, I would like to start recording a station's effective theoretical transmission span (in principle, a circle), and then update and geospatially display effective transmission space (i.e. record deadspaace, where bouncing was effective).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;The first is relatively easy, but the latter is a challenge.&lt;/p&gt;&#xA;&lt;p&gt;If efficient, geospatial visualization would help me learn application, identify interferences, etc. Ideally, one could combine it with other key factors which lend themselves to geospatial display (e.g., recurring weather/tie patterns, etc.), but that is probably too far to reach.&lt;/p&gt;&#xA;" OwnerUserId="6557" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-04-21T20:00:57.887" Title="Contact Logging Software and Geospatial Mapping" Tags="&lt;software&gt;&lt;logging&gt;&lt;map&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6088" PostTypeId="1" CreationDate="2016-04-21T09:44:18.120" Score="1" ViewCount="70" Body="&lt;p&gt;I'm brand new to amateur radio, with no previous relevant technical background, and I, unfortunately, will be unlikely to participate significantly in a local club.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I am trying to learn and grow in a hands-on hobby without &quot;without adult supervision,&quot; so to speak, and would like to remedy that:  I'm way too old to get a Boy Scouts merit badge counselor to help me :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Are there any 'virtual' coaching/tutoring (Elmer) tools?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am thinking more than a standard Q&amp;amp;A-type forum, but an environment where I could schedule focused coaching to assist in station set-up, initial GOTA coaching, etc.&lt;/p&gt;&#xA;" OwnerUserId="6557" LastEditorUserId="76" LastEditDate="2016-04-21T14:05:58.357" LastActivityDate="2016-04-21T15:20:02.553" Title="Are there virtual tools or resources for learning amateur radio on one's own?" Tags="&lt;education&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6089" PostTypeId="2" ParentId="5934" CreationDate="2016-04-21T12:26:13.493" Score="2" Body="&lt;p&gt;Because Skystar card works as a network device. Physical layer is DVB-S signal on 1.2 GHz band comming from parabolic antenna converting from Ku or C band via LNB. Data stream is only downlink (no uplink or packet acknowlegment) and there are used error-correction codes based on Reed-Solomon which help to recover data on reception side (sometimes it is not possible because 10 GHz Ku-band does not &quot;like&quot; heavy rain :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was using this card for reception of Meteosat images via EUMETCAST. Eumetsat distributes satellite data to users via a regular TV satellite (it was Hotbird6, not it is Eurobird9). So on the one frequency, there are many multicast data streams identified via Packet ID (they IP addresses started with 224.223.xxx.xxx). I was using Linux, so there were many virtual ethernet devices for each PID linked binded with Skystar driver and routed to final dummy0 device by smcroute. Special software Tellicast is used for storing files on disk (they are usually encrypted and you need to be registered and have a hardware key) and another software for data decompression and display.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More info about Meteosat reception is on my homepage: &lt;a href=&quot;http://bruxy.regnet.cz/web/meteosat/&quot; rel=&quot;nofollow&quot;&gt;http://bruxy.regnet.cz/web/meteosat/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6558" LastActivityDate="2016-04-21T12:26:13.493" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6090" PostTypeId="2" ParentId="6064" CreationDate="2016-04-21T12:41:51.847" Score="2" Body="&lt;p&gt;From Wikipedia: &lt;a href=&quot;https://en.wikipedia.org/wiki/Personal_radio_service#Japan&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Personal_radio_service#Japan&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;In Japan, a similar service is limited to 10 milliwatts in the 420, 421,   and 422 MHz bands.It is called &amp;quot;Tokutei Shoudenryoku Musen&amp;quot; (&amp;quot;SLPR:Specified Low Power Radio&amp;quot;).&lt;/p&gt;&#xA;&lt;p&gt;422.0500–422.1750 MHz (Business use) 10 mW 11ch 12.5 kHz spacing.&lt;/p&gt;&#xA;&lt;p&gt;422.200–422.300 MHz (Leisure use) 10 mW 9 channels 12 kHz spacing.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Looks pretty legal to me. Enjoy! (There are also similar bands around globe, but because the Radio Frequencies World is divided into regions, there are different bands used in Europe or North America with different power and sometimes other legal constraints.)&lt;/p&gt;&#xA;" OwnerUserId="6558" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-04-21T12:41:51.847" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6091" PostTypeId="2" ParentId="6088" CreationDate="2016-04-21T14:52:38.930" Score="2" Body="&lt;p&gt;As you seem to be in the US you can start learning on your own by preparing the US Ham exams.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Start easy with the Technician Licence, where you don't need to have much technical knowledge, and from there you can go up to General and Amateur Extra.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not in the US but still did the US licences for 'fun' and trained a lot using the Android application &lt;a href=&quot;https://play.google.com/store/apps/details?id=com.iversoft.ham.test.prep&amp;amp;hl=en&quot; rel=&quot;nofollow&quot;&gt;https://play.google.com/store/apps/details?id=com.iversoft.ham.test.prep&amp;amp;hl=en&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This gives you training questions arranged around different themes as well as the correct answer. But instead of just learning the correct answers, use the question to identify themes you don't know much about or don't understand, and then try to learn as much as you can or want about this subject, using wikipedia, books, google or whatever you want. Once you feel confident to have a basic understanding about the field go back and train the questions about it. Repeat if necessary. And then move to the next question pool about another subject.&#xA;I prepared and passed all US Licences using mainly this app as a 'Training plan'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Passing the exams will give you already much theoretical background. But it won't help you much with the 'Hands-on' part to set-up a station.&lt;/p&gt;&#xA;" OwnerUserId="5586" LastEditorUserId="76" LastEditDate="2016-04-21T15:20:02.553" LastActivityDate="2016-04-21T15:20:02.553" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6092" PostTypeId="2" ParentId="6087" CreationDate="2016-04-21T16:42:39.610" Score="1" Body="&lt;p&gt;Ham Radio Deluxe's logger can plot contacts on a map or a globe.  Regarding the second part of your question, in ham radio when talking about effective transmission area, the term that is generally used is &quot;propagation&quot;.  Propagation varies quite a bit depending upon the band; propagation on the nighttime HF bands (160m &amp;ndash; 40m) is quite different from propagation on the daytime HF bands, which is quite different from VHF and UHF, which is quite different from the microwave bands.  There are many software tools for estimating propagation, including free online tools.  Most of the time, for most bands, there are so many variables (the antennas on both ends, the ionosphere, solar weather, the state of the earth's magnetic field, etc.) that a computerized simulation of current propagation conditions is no more than a rough guess.  So I would say that there is generally no good way of recording the effective transmission area.  But take a look at &lt;a href=&quot;http://www.dxmaps.com/spots/map.php?Lan=E&amp;amp;Frec=ALH&amp;amp;ML=M&amp;amp;Map=W2&amp;amp;DXC=N&amp;amp;HF=S&amp;amp;GL=N&quot; rel=&quot;nofollow&quot;&gt;this site&lt;/a&gt;, which shows recent HF contacts on a map; that gives a picture of contacts other people are making now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounds to me that you're going for a graphical way of seeing propagation as a way to gain an initial understanding.  Computer simulations are good for that, just know that they are only estimates.  Real understanding will require book learning and real-world experience also.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-04-21T16:42:39.610" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6093" PostTypeId="2" ParentId="6087" CreationDate="2016-04-21T19:54:34.583" Score="1" Body="&lt;p&gt;Ham Radio Deluxe is a popular package for doing what you want to do as for the first part of the question.  Actually, QRZ.com can do that too via its web site features -- although I have found that at times it contains errors in the geo-location features.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't use Ham Radio Deluxe but I have made use of QRZ.com web site via their call sign lookup features.  There are two pieces of information available.  First, their street address if it is provided (sometimes, it is not provided as a PO Box is used instead).  But, a street address plus city plus state can be used in a Geocoded lookup using features from Google Maps JavaScript support software for locating on a map.  Also, sometimes the Longitude/Latitude is available from QRZ and this can also be used with Google Maps via their JavaScript interface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have written my own Java software (long time ago) to make use of QRZ.com.  This meant requesting their XML result which used to require an elevated registration that costs a small annual fee.  Not sure if that is still true.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, using Java, I would initiate the web URL request, and then parse the results which is not hard to do with Java (XML parse).  Then, I would use the Java and also JavaScript interface to Google Maps.  Java was used to initiate the web request as a client and then parse results for custom display.  Learning how to do this is easy as there are a number of books available to describe the Google Maps software interfaces (via JavaScript).  I would give you the title of the one I used but I gave it away several years ago at my last big book give-away prior to retirement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the second question, you are asking about propagation information and doing something automatically is a bigger task.  There are some resources available though.  For example, the MUF (Maximum Usable Frequency) information available at &lt;a href=&quot;http://www.spacew.com/www/realtime.php&quot; rel=&quot;nofollow&quot;&gt;http://www.spacew.com/www/realtime.php&lt;/a&gt; can be helpful although not totally definitive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, the software that the MUF display is based upon is available, Proplab-PRO, but albeit it cost some $$.  You can find more info at &lt;a href=&quot;http://www.spacew.com/www/skycom.html&quot; rel=&quot;nofollow&quot;&gt;http://www.spacew.com/www/skycom.html&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that I am offering up mainly solutions that require some software effort on your own to make use of in a way that fits your needs but I think these are not bad solutions.  I myself have not used the Proplab software so I cannot say too much about whether it is easy or complex to use.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2016-04-21T20:00:57.887" LastActivityDate="2016-04-21T20:00:57.887" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6094" PostTypeId="2" ParentId="6085" CreationDate="2016-04-21T20:23:54.747" Score="3" Body="&lt;p&gt;Imagine an ordinary gas, like air, inside a room. If the room is perfectly sealed and the air is completely still, we can say that the average motion of all the gas molecules is zero. However, each individual molecule is taking a random path all over, colliding with the walls of the room and other molecules. The only way to get rid of this random motion of each molecule is to cool the gas to &lt;a href=&quot;https://en.wikipedia.org/wiki/Absolute_zero&quot; rel=&quot;nofollow&quot;&gt;absolute zero temperature&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you had a sufficiently sensitive microphone, you'd hear those molecules hitting the microphone. But there are so many molecules hitting the microphone all the time that what you hear is noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same thing happens in electronics, but instead of gas molecules, it's electric charges (in metals, electrons) that are moving around. When electric charges move, that's a current. And by Ohm's law, when there's a current through some resistance, there's also a voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So with a sufficiently sensitive instrument, we can detect the individual electrons moving through the resistor as a result of random thermal motion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power of this noise is a function of temperature. As the resistor heats up, the electrons move around more, so there's more noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For practical calculation at room temperature, the noise power can be calculated in dBm by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ -174 + 10 \log_{10}(\Delta f) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here, $\Delta f$ is the bandwidth of interest, in hertz. For example, single sideband is typically within a 4kHz channel, so at room temperature the noise power within this channel is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ -174 + 10 \log_{10}(4000\:\mathrm{Hz}) = -138\:\mathrm{dBm} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More precisely, noise power in watts can be calculated by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ k_B T \Delta f $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $k_B$ is &lt;a href=&quot;https://en.wikipedia.org/wiki/Boltzmann%27s_constant&quot; rel=&quot;nofollow&quot;&gt;Boltzmann's constant&lt;/a&gt; in joules per kelvin, and the temperature $T$ is in &lt;a href=&quot;https://en.wikipedia.org/wiki/Kelvin&quot; rel=&quot;nofollow&quot;&gt;kelvin&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that these calculations of power assume that the noise is generated by some source impedance (say, a 50Ω antenna), and is going into an &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_matching&quot; rel=&quot;nofollow&quot;&gt;equal impedance&lt;/a&gt;. This is often the case in RF engineering and so works well because we can avoid introducing a resistance term in the equations. When this is not the case, it can be more convenient to calculate the RMS noise voltage, which is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \sqrt{ 4 k_B T R \Delta f } $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Likewise the RMS noise current is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \sqrt{ 4 k_B T\Delta f \over R} $$&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-04-21T20:23:54.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6095" PostTypeId="1" CreationDate="2016-04-21T20:47:21.377" Score="2" ViewCount="86" Body="&lt;p&gt;Is there a way to determine the length of a symbol in a wave? For example, how could I determine the length of a 0 or a 1 in a 2FSK wave?&lt;/p&gt;&#xA;" OwnerUserId="6561" LastActivityDate="2016-04-22T14:46:00.440" Title="How to determine the length of a symbol in a wave?" Tags="&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6096" PostTypeId="2" ParentId="6095" CreationDate="2016-04-21T21:03:32.260" Score="2" Body="&lt;p&gt;Well the procedure itself is not very complicated.&lt;br&gt;&#xA;You'll need following things:  &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Carrier frequency $F_c$ or the period &lt;/li&gt;&#xA;&lt;li&gt;Wavelength $\lambda$ in your environment or the speed of wave in the medium&lt;/li&gt;&#xA;&lt;li&gt;Symbol rate $Rs$&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So let's say we have radio signal in free space (or close to it) with carrier frequency of 7075 kHz (wavelength 42.4028 m) and that we're running say RTTY at 50 Bd.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way to think about the issue is simple: The wave moves one wavelength in one carrier cycle. So to get the length of a symbol, you need to see how many carrier cycles we have during one symbol cycle and multiply the number by the wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This gives us:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ l = \frac{R_s}{F_c} \lambda= 6000\:\mathrm{km} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is same as the wavelength of the symbol rate inside of the medium itself, but the long-way around explanation is mostly there to illustrate the thought process used given the question itself.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="218" LastEditDate="2016-04-22T14:34:01.223" LastActivityDate="2016-04-22T14:34:01.223" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6097" PostTypeId="1" CreationDate="2016-04-22T02:07:01.507" Score="2" ViewCount="385" Body="&lt;p&gt;My understanding of an RSSI reading is that it should equal Tx power - Tx feed loss + Tx antenna gain - pathloss + Rx antenna gain - Rx feed loss. If this is the case, if the radios at either end are identical and have the same Tx power, shouldn't the RSSI experienced at both sides be the same?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a scenario where on one side, the radio is receiving at around -100dB, at at the other side, the RSSI is -85dB. What could be the cause of this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have noted that both of the antennas could benefit from being raised away from the nearby metal roof, but wouldn't that still factor the same in both transmitting and receiving? Also, note that on one end there is an omni directional antenna and on the other end a yagi (same vertical polarisation). Unfortunately I do not have VSWR readings of either side at this stage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;@tomnexus, your answer is insightful. There is some additional information which I have discovered though, which might confuse the matter even more. At this stage I cannot measure the VSWR as the site distant from here - all I have are some computer diagnostic logs which I am reviewing now, and the diagnostic utility doesn't have VSWR readings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio network is in fact a point to multipoint data radio network. Let's say the base (omni antenna) is called &quot;BASE&quot;, and the two remotes are R1 and R2, each with yagis pointing back to the base. They are not near one another. Communication is half duplex, so R1 and R2 can only hear B, not one another.&#xA;BASE's RSSI from R1 is -80dBm. R1's RSSI from BASE is likewise -80dBm. BASE's RSSI from R2 is -85dBm, however R2's RSSI from BASE is -100dBm as explained above.&#xA;The initial thought, seeing that R2 receives from BASE 15dB quieter than vice versa is as you said - bad VSWR at BASE, combined perhaps with the BASE radio automatically turning it's own Tx power down. However, if this were the case, I would expect to see the same phenomenon with RSSI at R1. The odd one out in this picture appears to be R2 alone. Is it ever possible that receive sensitivity is degraded more than its transmit performance? Does this point necessarily to an issue with the radio itself?&#xA;As mentioned before, all antennas are each mounted rather close to the slightly angled roof of a metal shed. Is it at all possible that a radiation pattern or path loss can be influenced differently on Tx than on Rx?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure if it's relevant or not, but the last thing is that the supply voltage at BASE is occasionally dropping slightly - this might be related or not. The nominal voltage for the radios is 13.8VDC, however these radios are commonly used in conjunction with batteries and solar radios and have a fairly wide voltage tolerance (will work properly at &gt;10VDC, shuts down at &amp;lt; 9VDC). I have noted that the supply voltage for the BASE radio is 11.9, and occasionally it simply drops to 11.4 (all along, however, R2 receives at -100dBm). It might be that the power supply/battery combination is not adequately handling the required current draw, but I wonder if this current draw is increased on account of bad VSWR. That still doesn't explain it though. Thanks for you ongoing help. BTW, radios are running at roughly 5W.&lt;/p&gt;&#xA;" OwnerUserId="6564" LastEditorUserId="6564" LastEditDate="2016-04-23T01:18:29.360" LastActivityDate="2016-04-23T01:18:29.360" Title="RSSI on both ends of UHF Point to Point network do not match" Tags="&lt;antenna&gt;&lt;path-loss&gt;&lt;rssi&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6098" PostTypeId="2" ParentId="6097" CreationDate="2016-04-22T04:35:42.897" Score="0" Body="&lt;p&gt;VSWR is one possible explanation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the transmitters are a few watts or more, they probably have a protection circuit that reduces the transmitter power if the VSWR is too high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one antenna had high VSWR, say 5:1, it would introduce a small loss, a few dB, on transmit and receive. However with the protection circuit active, only the transmitter power might be reduced by a further 10 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could test the VSWR, or just add a 6 dB attenuator or a roll of cable in line with the antenna, and see if the RSSI becomes symmetrical. The suspect antenna is on the opposite side to the radio with the low RSSI reading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A second, more subtle effect, could come simply from the output impedance match of the transmitter. While the receiver is likely quite well matched to 50 Ohms, the transmitter might have a low impedance. This wouldn't matter if the antenna match is good. However with a badly matched antenna, you could have an accidental enhancement or reduction in transmission power. This would also be an asymmetrical effect, but probably only 1 or 2 dB.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2016-04-22T04:35:42.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6099" PostTypeId="2" ParentId="1042" CreationDate="2016-04-22T06:09:38.567" Score="3" Body="&lt;p&gt;The &lt;a href=&quot;http://nuand.com/&quot; rel=&quot;nofollow&quot;&gt;bladeRF&lt;/a&gt; is one such SDR radio that supports full duplex, i.e. simultaneous signal transmit and receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The short answer is that in its case, as I suspect in many other cases with a &quot;raw&quot; SDR unit, they could &lt;strong&gt;not&lt;/strong&gt; be used &quot;out of the box&quot; for full-duplex &lt;em&gt;communications&lt;/em&gt;. I.e. the receive circuity &lt;strong&gt;will&lt;/strong&gt; be swamped unless the user takes their own care to prevent this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you take a look at this forum thread, &lt;a href=&quot;https://nuand.com/forums/viewtopic.php?f=6&amp;amp;t=3730&quot; rel=&quot;nofollow&quot;&gt;Cavity Duplexer needed?&lt;/a&gt; you will find the first reply says basically:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the bladeRF isn't a great choice in situations where one would typically use a cavity duplexer, e.g. repeater&lt;/li&gt;&#xA;&lt;li&gt;&quot;using separate RX and TX antennas is entirely doable, especially if the antennas are in each other's nulls and they're operating far enough apart frequency-wise … Filters are, as always, a good investment, but they don't need to be anywhere near as sharp as a cavity&quot; — i.e. you could sort of use it anyway, but you're relying on external arrangements for preventing receiver desense/overload&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Likewise in the case of the Flex radio systems you mention in your question. For example in &lt;a href=&quot;https://community.flexradio.com/flexradio/topics/is_the_6500_be_a_true_full_duplex_radio?topic-reply-list%5Bsettings%5D%5Bfilter_by%5D=all&quot; rel=&quot;nofollow&quot;&gt;Is the 6500 a true 'full duplex' radio&lt;/a&gt; you find answers such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&quot;appears to me the answer is yes... If you have sufficient isolation between your RX and TX antennas&quot;&lt;/li&gt;&#xA;&lt;li&gt;&quot; I am not sure it will be possible with the 6500. With the 6700 you have the two SCUs and a compliment of BPFs for both of them.&quot;&lt;/li&gt;&#xA;&lt;li&gt;&quot;The radio hardware has some capabilities that you would consider full duplex. There are limits to what can or that you would want to do and we have not yet spent any time looking into this. For the immediate future, we are muting receivers when transmitting…&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So again, it's clear that there is no silver bullet inside either the bladeRF or the Flex radio SDRs which handles the tight filtering needed when transmitting near a receiver. The 6700 model radio mentioned in comparison to the Flex unit would possibly be able to serve as a &lt;em&gt;cross-band&lt;/em&gt; repeater with its separate band pass filters, but not within the same band if the TX signal has any significant level of amplification.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;However, this is not to say that having an SDR with full-duplex capability is worthless — especially if you were to use it as test equipment rather than a transceiver. A vector network analyzer like the VNWA3 for example is quite similar to a full-duplex SDR, architecturally speaking. With the right &lt;a href=&quot;https://github.com/adamgreig/bladerf-vna&quot; rel=&quot;nofollow&quot;&gt;software&lt;/a&gt; and perhaps an external bridge or similar, I would think something like the bladeRF could be useful for measuring filters and much much more.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-04-22T06:16:18.320" LastActivityDate="2016-04-22T06:16:18.320" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6100" PostTypeId="2" ParentId="6097" CreationDate="2016-04-22T06:42:22.463" Score="0" Body="&lt;p&gt;The difference in RSSI is easily explained by the two different antennas.  The omni-directional antenna transmits the energy of the radio waves equally in all directions.  (let's assume a 2 dimensional world for now.  ) So think of circles emanating from a single point.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The yagi, on the other had, transmits the same TOTAL energy but loads more of that energy in the direction that it is pointing. It does this because it reflects more of it's total energy in one direction.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence you will receive more energy on the omni if the yagi is pointing at it.   Conversely of the yagi was pointing away from the omni, the omni side would receive less.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Caveat: there is always something else going. Reflected waves can combine in positive or negative ways.  Also even two products that are the same model can be different, given that each component on them is accurate within a range.  etc. etc.    &lt;/p&gt;&#xA;" OwnerUserId="3027" LastActivityDate="2016-04-22T06:42:22.463" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6101" PostTypeId="2" ParentId="6035" CreationDate="2016-04-22T07:57:23.220" Score="-1" Body="&lt;p&gt;I thought the more 3D answer was going to mention fractal&#xA;&lt;a href=&quot;https://www.google.com/search?site=&amp;amp;q=fractal+antenna&quot; rel=&quot;nofollow&quot;&gt;https://www.google.com/search?site=&amp;amp;q=fractal+antenna&lt;/a&gt;&#xA;That's 2 and a half D.&lt;/p&gt;&#xA;" OwnerUserId="6565" LastActivityDate="2016-04-22T07:57:23.220" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6104" PostTypeId="2" ParentId="6097" CreationDate="2016-04-22T13:48:33.257" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;My understanding of an RSSI reading is that it should equal Tx power - Tx feed loss + Tx antenna gain - pathloss + Rx antenna gain - Rx feed loss. If this is the case, if the radios at either end are identical and have the same Tx power, shouldn't the RSSI experienced at both sides be the same?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Your intuition about reciprocity is correct but your understanding of what RSSI means is not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually, the RSSI is nothing more than a measurement of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Automatic_gain_control&quot; rel=&quot;nofollow&quot;&gt;AGC&lt;/a&gt; level. The AGC's job is to adjust the gain of the receiver's amplifiers so the input to the demodulator is at an appropriate level. When the received power goes up, the AGC turns down the gain, and the RSSI goes up. This prevents saturation or clipping in the demodulator, while simultaneously assuring the input level is high enough to overcome the demodulator's internal noise floor, and (for digital receivers) to effectively utilize the DAC's full range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The AGC is just looking at the overall level of the signal coming from the antenna. It doesn't know about demodulation, so it can't distinguish between signal and noise. This is necessarily so, because if the AGC were not to reduce gain in the presence of noise the demodulator would become saturated, causing distortion and effectively more noise. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you see an RSSI associated with a particular packet, this is usually a sample of the AGC level as that packet was being received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, your situation could easily be explained by a noise source which is closer to one station than the other. While the signal between the two stations obeys reciprocity and thus should have identical strength on each end, the higher noise at one station requires the AGC to reduce gain, and thus increase RSSI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also keep in mind that there's no defined unit for RSSI. It's not necessarily in dBm, or even decibels relative to any reference at all. So a difference of 15 in RSSI does not necessarily mean a 15 dB difference in signal strength.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-04-22T13:55:20.697" LastActivityDate="2016-04-22T13:55:20.697" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6105" PostTypeId="2" ParentId="6095" CreationDate="2016-04-22T14:46:00.440" Score="0" Body="&lt;p&gt;Say we are transmitting 50 symbols per second. You begin by transmitting a 1. Then 1/50th of a second later, you are done transmitting that 1. Now how far has the signal propagated since you started transmitting the 1? That's the &quot;length&quot; of the symbol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's simple to calculate, as the signal propagates away at the speed of light. We can just divide the speed of light by the number of symbols per second to get the length of a symbol in meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So with the speed of light being about 300000000 meters per second, and one second per 50 symbols:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\require{cancel}&#xA;{3\cdot 10^8\:\text{meters}\over \cancel{\text{second}}} \cdot&#xA;{1\:\cancel{\text{second}} \over 50\:\text{symbols}}&#xA;= {6000000\:\text{meters} \over \text{symbol}}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is, 6000 km per symbol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll also see this is exactly the same calculation as for converting from frequency to wavelength, but in place of frequency (cycles per second) we use the baud rate (symbols per second).&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-04-22T14:46:00.440" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6106" PostTypeId="5" CreationDate="2016-04-22T18:47:06.687" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-22T18:47:06.687" LastActivityDate="2016-04-22T18:47:06.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6107" PostTypeId="4" CreationDate="2016-04-22T18:47:06.687" Score="0" Body="Questions about DC power supplied to equipment (typically 12/13.8 volts), power distribution, wiring, connectors." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-04-22T18:47:06.687" LastActivityDate="2016-04-22T18:47:06.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6109" PostTypeId="2" ParentId="3496" CreationDate="2016-04-26T00:44:52.793" Score="2" Body="&lt;p&gt;I can second the comments about bon-ami.  Way back 2/3 of the way through the last century, we also used some of the super fine abrasives used for the later stages of grinding amateur telescope mirrors.  Try Googling &quot;Amateur Telescope Making Supplies&quot;  and &quot;Telescope Mirror Blanks&quot; for suppliers.  - W6HPA&lt;/p&gt;&#xA;" OwnerUserId="6578" LastActivityDate="2016-04-26T00:44:52.793" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6110" PostTypeId="2" ParentId="891" CreationDate="2016-04-26T20:36:45.510" Score="3" Body="&lt;p&gt;This is sort of an &quot;it depends&quot; question, and you noted that yourself in your text I believe.  It will take some Q &amp;amp; A with yourself to come to a conclusion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First: What is the &quot;field&quot; situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;a. A literal field?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;b. The side of the road?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;c. A shelter in place situation with no grid mains?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;d. Pure mobile/portable on the move?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second: Based on &quot;First&quot;, one decides what is then appropriate, and whether the situation may be fluid and require &quot;oozing&quot; from one situation to another.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;a. A literal field: Photo-voltaic panel(s) with integrated charge controller to an appropriate battery.  AGM batteries offer the capacity of a lead acid with less weight and less maintenance and less chance of losing your battery due to a tip over where you might lose the fluid.  They also don't emit gasses like wet lead acid (more important for c.).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;b. The side of the road: A mobile set-up with a PV charging backup is ideal, because you can run the engine if you really need to, but can choose to recharge the vehicle battery with the PV.  Not ideal because the vehicle battery is not deep cycle, and you run the risk of stranding yourself until you get enough sun to let her crank again.  Having a second battery, and a deep cycle one either installed with vehicle charging or carried with PV charging is a good move.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;c. A shelter in place situation: This allows you to plan this all out in advance.  A generator is a perfect companion to the deep cycle battery(ies) and the PV charging.  Fuel-sipping, quiet, 2kW Honda generators can run for 8 hours or more on a gallon of gasoline, particularly with a low overall load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;d. Pure mobile/portable:  Pretty much b. above, but if constantly changing position, mobile operation within the vehicle and it's battery makes the most sense, just so long as fuel is abundant, thus your &quot;solution&quot; is carrying fuel, vs. carrying batteries, PV's, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is truly one of those never-ending answers, and I guess there isn't really any sort of truly lightweight power to be had.  Battery technologies improve in size, weight and capacity regularly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were to be forced to choose only one technology, it would be PV and AGM (or Lithium Ion) deep cycle batteries.  None of the answers are terribly convenient, but as long as you have sunshine, you can use the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Third:  Operating requirements/types.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;a. Repeater ops that can be done with hand-helds or low power mobiles?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;b. Simplex ops with HF?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are the two major methodologies that Hams have used for decades.  Using the least power to accomplish the &quot;mission&quot; is your task in this discussion.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Repeater ops make it easy as they are typically very low power, and if you are using ONE repeater, then the antenna is as (or more) important than the power source (and a gain antenna sort of IS a power source).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simplex HF ops are more challenging, but one can usually move more information further, per hop, thus using potentially less power.  The best of the QRP capable HF mobile/portable rigs like the Yaesus are incredibly flexible when coupled with the right software and perhaps a simple Signalink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While this consideration doesn't speak directly to a power source, I think it certainly colors the decision making process.  You could work all day and half the night with one AGM battery in repeater ops.  It might require two or three for HF ops.&lt;/p&gt;&#xA;" OwnerUserId="6248" LastEditorUserId="6248" LastEditDate="2016-04-29T12:46:14.173" LastActivityDate="2016-04-29T12:46:14.173" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6111" PostTypeId="1" AcceptedAnswerId="6162" CreationDate="2016-04-26T22:50:59.433" Score="4" ViewCount="126" Body="&lt;p&gt;I am thinking on what is the practical limit of precision for VHF positioning system (like currently obsolete and gone &quot;Transit&quot; system). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is well known how GPS receivers calculates pseudorange to each satellite to calculate the position of the receiver - GPS transmits PRN signal at 1 MBit, so by just counting the &quot;chips&quot; you can get pseudorange precision down to 1us which is 300m, and by tracking the phase you can get much more precise (ultimately to the point where you are limited by oscillator phase noise and ionospheric delays). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But in VHF we typically don't have bandwidth to transmit 1Mbit PRN signal even if it's below noise level, and one will have to use much lower speed, like 19200. Obviously length of 1 bit at 19200 is extremely long. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question is what is the practical limit on precision of phase tracking of the signal given that it's VHF and bitrate is mere 19200? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to track the phase with ultimate precision by recoding the data with SDR and after decoding the data we go back in history, and try every possible signal start time by maximum SNR using this now known data? It seems that in this case phase resolution will be limited by SDR sample rate and phase precision will be limited by length of the data packet and physical limitations (phase noise, ionosphere, e.t.c).&lt;/p&gt;&#xA;" OwnerUserId="546" LastActivityDate="2016-05-07T13:12:38.140" Title="Pseudorange in VHF band navigation and precision phase tracking" Tags="&lt;software-defined-radio&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6112" PostTypeId="2" ParentId="197" CreationDate="2016-04-27T12:33:53.363" Score="0" Body="&lt;p&gt;Acknowledge that the thread is a bit old, just some information for anyon ending up here with the question regarding dBS9.&#xA;When testing antennas, on must set up a reference system. &#xA;This is usually don by having a Tx/Rx system equipped with equal antennas. Then the signal strength is measured, and the result refereed to as dBref. In the mentioned article this becomes DBS9.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal measured for another antenna will then be compared to this reference. For instance a antenna with a DBS9 of +3 has 3dBm better sensitivity than the referenceat the given frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding dBm and messuring in decibel. Usefull information can be found in an article by Rohde&amp;amp;Schwarz&#xA;&quot;Everything you ever wanted to know about decibels but were afraid to ask… &quot;&#xA;(Google know where to find it)&lt;/p&gt;&#xA;" OwnerUserId="6583" LastActivityDate="2016-04-27T12:33:53.363" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6113" PostTypeId="2" ParentId="490" CreationDate="2016-04-27T13:00:04.197" Score="0" Body="&lt;p&gt;It could be done, but as my understanding there is no easy/default way to do so, yet. theoretically if you create a ip network like 802.x with less protocol overhead and more vocoder performance, you could, sustain multiple conversations within connected units pretty much like IM talk group within one wifi AP range, just with much less bandwidth, here vocoder performance come to play vital role. With advance of semiconductor manufacturing and DSP advance, vocoder are no longer power hungry and too hard to implement.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of recent Bluetooth stack originally designed for IoT already come with all requirements mentioned above. We, HAM, are supposed to be pioneer on vocoders, indeed.&lt;/p&gt;&#xA;" OwnerUserId="6584" LastActivityDate="2016-04-27T13:00:04.197" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6114" PostTypeId="1" CreationDate="2016-04-27T16:10:46.867" Score="3" ViewCount="2290" Body="&lt;p&gt;I have a list of maidenhead grid squares in an Excel sheet that I want to convert to latitude and longitude.  I want to keep it as simple as possible.  Does anyone know of a formula to convert from maidenhead to lat/long?&lt;/p&gt;&#xA;" OwnerUserId="6587" LastEditorUserId="8717" LastEditDate="2018-11-24T14:40:15.403" LastActivityDate="2018-11-24T14:40:15.403" Title="Convert maidenhead grid square to lat/long in Excel?" Tags="&lt;contest&gt;&lt;map&gt;&lt;maidenhead-locator&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="6115" PostTypeId="1" CreationDate="2016-04-27T16:43:59.687" Score="1" ViewCount="2372" Body="&lt;p&gt;&lt;strong&gt;The problem&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a concrete wall between my computer and my router (Linksys E900) which affects my WIFI reception pretty harshly, computer receives signal is at -65 dBm, at this rate i get around 5%~8% packet loss. Without the concrete wall blocking the signal i get around -30 dBm to -45 dBm, which results in only about 1% packet loss. (Tested with desktop and laptop).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Xs2wm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Xs2wm.png&quot; alt=&quot;http://i.imgur.com/AQhodaQ.png&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The idea&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a door in my room, perhaps if I could make my own passive repeater, bending the WIFI's radio wave's path to turn a corner (and go through the door instead of the concrete wall), would my WIFI reception increase significantly? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If this is a good idea, how do I go about making it?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where do I learn the math on how big the repeater needs to be and how to position it? What materials do I need for this? &lt;/p&gt;&#xA;" OwnerUserId="6586" LastEditorUserId="76" LastEditDate="2016-04-27T16:59:37.130" LastActivityDate="2016-04-30T17:21:04.993" Title="Can I build a mini passive repeater to improve my WIFI reception at home?" Tags="&lt;diy&gt;&lt;antenna-theory&gt;&lt;wifi&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6116" PostTypeId="2" ParentId="6115" CreationDate="2016-04-28T09:16:59.617" Score="0" Body="&lt;p&gt;at -65dBm you should not experience that amount of packet loss, however; trusting your measurements are correct, there are a couple of things you might be able to do in order to improve without &quot;building a repeater&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the computer is in a static location, and the router is in a static location (this is usually true in most installs) then you can improve the signal greatly with some handy antenna work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the computer, you should get a WiFi card with an external antenna connector, these are not too expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have an external antenna connector on that card, you can use a directional antenna to point at the router. There are various commercial models, or you can home brew.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But before we go there, a little tip in regards to signals in houses/buildings:&#xA;It is known, and I have positive experience with this, that circular polarized signals have a better penetration-property then linear (Horizontal or Vertical) polarized signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example: I live in a house built in the 18th-century, with 3-foot thick granite walls. I experienced major problems with WiFi distribution, as the signals simply did not travel through the walls. By switching to circular polarized I managed to get reliable WiFi at 2.4GHz throughout the property !&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How did I do this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) changed the antenna on the router to a &quot;RHCP clover leaf antenna&quot; (you can search for this, there are commercial types, but there are plenty of plans for self-build as well)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) changed the antenna on the computers which were in a fixed position to a directional antenna, I choose to built a 5-turn-RHCP-helix.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I now had Right Hand Circular Polarized (RHCP) throughout the property the signals were good enough to use without any &quot;booster/repeater&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I built all antenna's myself, which was a fun project in itself, but I realize that would not be for everyone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Actually &quot;building a repeater yourself&quot;... I imagine that this would be a very complex and precise project, which you should only do if you are very familiar with the internal workings of such. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you cannot get the required signal levels with some handy antenna work, I would suggest that you buy a &quot;WiFi signal booster&quot;, they are really not that expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;YMMV,&#xA;HTH.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-04-28T09:16:59.617" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6118" PostTypeId="2" ParentId="6024" CreationDate="2016-04-28T15:34:32.167" Score="1" Body="&lt;p&gt;If the antennas are cheap and easy to build, why not build two and use one for TX and one for RX, then use a common RF sense antenna switch such as MFJ-1707 to switch between the two.  This allows you to have one coax to your transceiver and two antennas.  Control lines for switching are also accommodated in many of these types of antenna switches.  Typical of these types of switches is to also have auxilliary &quot;switch to ground&quot; ports which you can use for other fun stuff, such as isolating your LNB by de-powering it, assuming the LNB is at the antenna and not at the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, if you enjoy antenna experimentation like I do, it's a nice way to compare different RX and TX antennas for their suitability/gain/performance, etc.&lt;/p&gt;&#xA;" OwnerUserId="6248" LastActivityDate="2016-04-28T15:34:32.167" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6119" PostTypeId="2" ParentId="6115" CreationDate="2016-04-28T20:43:52.603" Score="2" Body="&lt;p&gt;While &lt;a href=&quot;https://en.wikipedia.org/wiki/Passive_repeater&quot; rel=&quot;nofollow&quot;&gt;passive repeaters&lt;/a&gt; do exist, I don't think building one for your apartment would be feasible or useful. As you can see in that article, they are usually quite large.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moreover, a signal of -65 dBm is not excellent, but it's at least good and will work reliably, given no additional problems. So this doesn't really explain your situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In many WiFi receivers, the RSSI, from which that signal level is calculated, is actually a measure of the receiver's &lt;a href=&quot;https://en.wikipedia.org/wiki/Automatic_gain_control&quot; rel=&quot;nofollow&quot;&gt;automatic gain control&lt;/a&gt; (AGC) level. The AGC is responsible for adjusting the gain of the RF amplifier such that the input to the demodulator (the part that decodes the WiFi signal) is at an appropriate level. It's like adjusting the volume on your radio so it's not so loud that it hurts your ears, but also so it's loud enough you can clearly hear it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the AGC responds to noise as well as signal. It can't know the difference, and in fact no receiver can. Were it possible to separate noise from signal then noise wouldn't be a problem because it could just be discarded.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the more likely explanation is that your packet loss is due to noise. Professional WiFi radios provide metrics on things like &lt;a href=&quot;https://en.wikipedia.org/wiki/Cyclic_redundancy_check&quot; rel=&quot;nofollow&quot;&gt;CRC errors&lt;/a&gt; which quantify noise more precisely, and spectrum analyzers can measure noise directly. Some professional-level WiFi radios even have a crude spectrum analyzer built in. But consumer WiFi radios are unlikely to expose these features, so we just have to guess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reducing the noise is the first thing you should try. You might find another channel has less noise. Try using the 5 GHz band if you can: it has more channels, and generally less noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you've done all you can to reduce noise and you still have problems, you can increase the signal. If you can't move the AP closer, then you could try a directional antenna. If that won't work, then a WiFi &quot;range extender&quot; is an active repeater that is pretty cheap. Using such a repeater does mean you will be making roughly twice as much noise for your neighbors, but maybe that doesn't bother you.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-04-28T20:43:52.603" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6120" PostTypeId="1" CreationDate="2016-04-28T20:59:25.053" Score="0" ViewCount="82" Body="&lt;p&gt;I'm curious what kind of directional antennas could fit inside a cell phone, which would require it to be 5mm or less in its longest dimension. I know that the length of a directional antenna is often a critical factor in the gain and directionality of an antenna, so I'm wondering also what frequency would be ideal for that constraint. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in short, what types of directional antennas would be practical at a maximum length of 5mm, and what limitations are necessary with that constraint?&lt;/p&gt;&#xA;" OwnerUserId="6596" LastActivityDate="2016-05-03T07:48:23.200" Title="What parameters are currently possible in a directional antenna less than 5mm long?" Tags="&lt;antenna-construction&gt;&lt;antenna-theory&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6121" PostTypeId="2" ParentId="6120" CreationDate="2016-04-29T10:47:05.037" Score="1" Body="&lt;p&gt;You could look into &quot;Patch Antenna&quot; design.&#xA;Some theory here: &lt;a href=&quot;http://www.antenna-theory.com/antennas/patches/antenna.php&quot; rel=&quot;nofollow&quot;&gt;http://www.antenna-theory.com/antennas/patches/antenna.php&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;however: manufacturing this yourself would be quite challenging I would imagine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[edit due to comments]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hi BT, it seems you asked a different question in the comments.&#xA;I guess the original question: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;what types of directional antennas would be practical at a maximum length of 5mm, and what limitations are necessary with that constraint?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Would be answered by above reference to patch-antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you are asking:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How are these used in mobile devices without being omnidirectional?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This can be broken up in two questions:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;1) How are these used in mobile devices ?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;2) without being omnidirectional ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Answers are simple:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) They are not used in mobile devices, or at least not main-stream, due to size of the patch itself (there are others derived from patch antenna design, already commented below)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) They are directional. But this does not seem to hinder mobile technology. The cell towers seem to have enough directivity/gain/coverage/power to reliably build connections even when the mobile device has a &quot;somewhat directional&quot; antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-05-03T07:48:23.200" LastActivityDate="2016-05-03T07:48:23.200" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6122" PostTypeId="2" ParentId="6114" CreationDate="2016-04-29T10:59:24.430" Score="0" Body="&lt;p&gt;This seems to be impossible doing with a Macro correctly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even when you take the link provided by @tomnexus in the comments and reverse the process, you will not get a precise location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reason is: a Maidenhead locator is a square, and therefore consists of my combinations of lon/lat. Therefore a Macro cannot result in a single lon-lat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I am sure that you can come up with a script/macro with 4 results, which represent ranges:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;lon = (lon_start) to (lon_end)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;lat = (lat_start) to (lat_end)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you please clarify what you are looking for ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[edit 04-May]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not an excel person, but I know a bit of Python 3.x, so here is a script which actually translates Maidenhead to a range of lon/lat... use at your discretion, no warrantees made &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;# -*- coding: utf-8 -*-&#xA;#maiden head to lon/lat&#xA;&#xA;__MH__ = 'HK34wh'&#xA;&#xA;def GetLon(ONE, THREE, FIVE):&#xA;    StrStartLon = ''&#xA;    StrEndLon = ''&#xA;&#xA;    Field = ((ord(ONE.lower()) - 97) * 20) &#xA;    Square = int(THREE) * 2&#xA;    SubSquareLow = (ord(FIVE.lower()) - 97) * (2/24)&#xA;    SubSquareHigh = SubSquareLow + (2/24)&#xA;&#xA;    StrStartLon = str(Field + Square + SubSquareLow - 180 )&#xA;    StrEndLon = str(Field + Square + SubSquareHigh - 180 )&#xA;&#xA;    return StrStartLon, StrEndLon&#xA;&#xA;def GetLat(TWO, FOUR, SIX):&#xA;    StrStartLat = ''&#xA;    StrEndLat = ''&#xA;&#xA;    Field = ((ord(TWO.lower()) - 97) * 10) &#xA;    Square = int(FOUR)&#xA;    SubSquareLow = (ord(SIX.lower()) - 97) * (1/24)&#xA;    SubSquareHigh = SubSquareLow + (1/24)&#xA;&#xA;    StrStartLat = str(Field + Square + SubSquareLow - 90)&#xA;    StrEndLat = str(Field + Square + SubSquareHigh - 90)    &#xA;&#xA;    return StrStartLat, StrEndLat&#xA;&#xA;def main(strMaidenHead = __MH__):&#xA;    if len(strMaidenHead) &amp;lt; 6: strMaidenHead = __MH__&#xA;&#xA;    ONE = strMaidenHead[0:1]&#xA;    TWO = strMaidenHead[1:2]&#xA;    THREE = strMaidenHead[2:3]&#xA;    FOUR = strMaidenHead[3:4]&#xA;    FIVE = strMaidenHead[4:5]&#xA;    SIX = strMaidenHead[5:6]&#xA;&#xA;    (strStartLon, strEndLon) = GetLon(ONE, THREE, FIVE)&#xA;    (strStartLat, strEndLat) = GetLat(TWO, FOUR, SIX)&#xA;&#xA;    print ('Start Lon = ' + strStartLon)&#xA;    print ('End   Lon = ' + strEndLon)&#xA;    print ()&#xA;    print ('Start Lat = ' + strStartLat)&#xA;    print ('End   Lat = ' + strEndLat)&#xA;&#xA;    return strStartLon, strEndLon, strStartLat, strEndLat&#xA;&#xA;#BEGIN&#xA;if __name__ == '__main__':&#xA;    main ()&#xA;    sys.exit ('end of script: '+ os.path.basename(__file__) + os.linesep + 'by: Edwin van Mierlo')&#xA;#END&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-05-04T07:57:44.413" LastActivityDate="2016-05-04T07:57:44.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6123" PostTypeId="2" ParentId="6115" CreationDate="2016-04-30T17:21:04.993" Score="0" Body="&lt;p&gt;Another option that could possibly work. If your wireless modem has the capability of being connected by ethernet cable. Just find a place to put modem where it gets the best signal like near a window and as high as possible.&#xA;Connect the ethernet cable to modem and compute...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a similar thing with my wireless internet stick. I build a metal reflector and cut for it frequency of operation at 2600GHz-4G 14db gain with 25db front to back ratio-great signal.&lt;/p&gt;&#xA;" OwnerUserId="6604" LastActivityDate="2016-04-30T17:21:04.993" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6124" PostTypeId="1" CreationDate="2016-04-30T22:34:03.570" Score="1" ViewCount="292" Body="&lt;p&gt;Im not sure what is true, when I want to calculate it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, the fact is that classic homodyne is used only in receivers. (I'm not talking about quadrature homodyne.) But I can't understand how the spectrum behaves when a theoretical homodyne TX is transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone answer me which one of my propositions are good: A or B?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gHBBI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gHBBI.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6607" LastEditorUserId="76" LastEditDate="2016-05-01T03:42:54.527" LastActivityDate="2016-05-01T03:42:54.527" Title="Homodyne vs heterodyne" Tags="&lt;software-defined-radio&gt;&lt;mixer&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6125" PostTypeId="2" ParentId="6124" CreationDate="2016-05-01T03:41:11.023" Score="2" Body="&lt;p&gt;If I understand your question correctly, you are asking about the inputs and output of the frequency mixer in a direct-conversion transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neither of your pictures is correct, but B is closer to correct. Here is the correct picture:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GjZvY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GjZvY.png&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some facts about frequency mixing that can be used to help see where you went wrong:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Until a filter is added, the output cannot have a &lt;em&gt;partial&lt;/em&gt; copy of the input. Your input signal's spectrum has the shape &lt;code&gt;|\___/|&lt;/code&gt;, so your output signal must be some sort of sum of copies of &lt;code&gt;|\___/|&lt;/code&gt;. But both of your ideas don't: they contain &lt;code&gt;|X|&lt;/code&gt; instead which is something different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your option B does contain &lt;code&gt;|\___/|&lt;/code&gt;, but it also contains &lt;code&gt;/|___|\&lt;/code&gt;, which cannot be made up of complete copies of the input in any way.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Whenever the spectrum is inverted/reflected, it is always about some frequency that in some sense &lt;strong&gt;exists in the system&lt;/strong&gt; — such as a carrier frequency, or zero. When you made the &lt;code&gt;|X|&lt;/code&gt; shape, you instead reflected (part of) the input signal spectrum about the midpoint of the signal. That midpoint doesn't correspond to any signal we're presuming to exist exist, so the signal cannot be reflected about it.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-05-01T03:41:11.023" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6126" PostTypeId="1" CreationDate="2016-05-02T16:40:43.863" Score="0" ViewCount="177" Body="&lt;p&gt;With «green» electricity bills amounting to ever more greenbacks, I am in the process of gradually replacing my incandescent light bulbs with LED light bulbs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, my efforts met with mixed results in terms of radio frequency interference (RFI) caused by certain LED bulb models—brands. This made me cautious to the point of buying only one unit at a time of any unknown brand—model and testing these first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Still, this leaves me with money wasted on unusable LED bulb models.&#xA;This made me wonder whether there is some &lt;strong&gt;online database where amateur radio operators can share their RFI experience with certain LED bulb models?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S.: We are not supposed to make any shopping recommendations on Stack Exchange!&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="76" LastEditDate="2016-05-02T16:51:36.160" LastActivityDate="2016-05-03T07:38:50.660" Title="How can I find out if a particular LED light bulb model is known to cause RFI before buying?" Tags="&lt;rfi&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6127" PostTypeId="2" ParentId="6126" CreationDate="2016-05-02T16:56:00.573" Score="1" Body="&lt;p&gt;One trick I learned so far is to check for &lt;strong&gt;a big series capacitor&lt;/strong&gt; when the base is transparent. Series capacitor fed LED bulbs tend to cause very little RFI if any at all. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, this trick only applies to low power LED light bulbs.&#xA;Almost all high power LED light bulbs tend to have a &lt;strong&gt;switched power supply&lt;/strong&gt; in a white plastic base. It is here where there seems to be a lot of disparity in RFI suppression between different LED bulb models, even within the same brand! You never know into what RFI suppression quality you are buying...&lt;/p&gt;&#xA;" OwnerUserId="250" LastActivityDate="2016-05-02T16:56:00.573" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6128" PostTypeId="1" AcceptedAnswerId="6129" CreationDate="2016-05-02T19:20:23.937" Score="1" ViewCount="2792" Body="&lt;p&gt;I am using an Ettus Research B200 with GNU Radio Companion (GRC) and I would like to transmit two signals at two different frequencies simultaneously.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a simple example, I would like to transmit a sine wave at 915 mhz and another at 916 mhz, both at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequencies are within 2 mhz of each other, so I would imagine that this is possible. Not having any luck messing with GRC to make this work; I'm a total noob to SDR! Which blocks do I need to use in GRC? &lt;/p&gt;&#xA;" OwnerUserId="6615" LastActivityDate="2016-05-02T21:53:40.430" Title="Transmit on multiple frequencies with USRP using GRC" Tags="&lt;software-defined-radio&gt;&lt;frequency&gt;&lt;transmission&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6129" PostTypeId="2" ParentId="6128" CreationDate="2016-05-02T19:35:41.930" Score="5" Body="&lt;p&gt;To transmit two signals at once, just generate the two signals with the appropriate frequency spacing between them, and add them together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With your mentioned frequencies, you might generate the signals at &amp;minus;0.5 MHz and +0.5 MHz, add them together, and transmit with the hardware center frequency set to 915.5 MHz. (You don't have to use the exact midpoint, but doing so allows you to use the lowest sample rate and filter bandwidth.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically to transmit two unmodulated sine waves, in GRC:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Create two Signal Source blocks, complex sine, with their carrier frequencies set to &lt;code&gt;-0.5e6&lt;/code&gt; and &lt;code&gt;0.5e6&lt;/code&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Connect them to two inputs of an Add block.&lt;/li&gt;&#xA;&lt;li&gt;Connect the output of the Add block to your (USRP) sink block with center frequency &lt;code&gt;915.5e6&lt;/code&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you want to use a modulator that produces a baseband signal, you will have to take that baseband signal and frequency-shift it to the desired offset, in place of the signal source which creates the signal at any frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, there's no block that is actually convenient for this purpose; the easiest is the &quot;Frequency Xlating FIR Filter&quot;, which does decimation as well as shifting. Just enter &lt;code&gt;1&lt;/code&gt; for the decimation, &lt;code&gt;[1]&lt;/code&gt; for the filter taps, and it'll do the job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The “Rotator” block does pure frequency shifting, but it needs the shift specified as a complex vector (amount of rotation per sample) so it's not convenient to use.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-05-02T21:53:40.430" LastActivityDate="2016-05-02T21:53:40.430" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="6130" PostTypeId="1" CreationDate="2016-05-03T03:09:39.003" Score="2" ViewCount="1601" Body="&lt;p&gt;I'm a newbie who is attempting to build a half-wave dipole antenna that will be located in the rudder of a sailplane. 123.3 MHz is the most important frequency to me, although it's reasonable to assume that the antenna should be wide-band enough to work adequately down to 118 MHz and up to 136 MHz. Based on these requirements, and based on a whole lot of internet reading, using some copper tape about 1/2 in wide and 45 inches long (0.47 lambda) is a good starting point for a resonant half-wave dipole antenna centered on 123.3 MHz. I would expect this antenna will be around 73 ohms of inductance (more or less because I expect some coupling to the carbon fiber structure of the aircraft). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is, given that I'm feeding this with around 5 watts of power through 50 ohm RG-400 coax, I'm struggling with how to approach matching the inductance and adding a balun between the coax and the antenna? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like a gamma match might be a good choice, but there are a bewildering number of choices here and it's hard to get a handle on where to even get started with this design. It's probably worth mentioning that the rudder is small, thin, and needs to stay very light weight.&lt;/p&gt;&#xA;" OwnerUserId="6151" LastEditorUserId="6079" LastEditDate="2016-05-03T20:29:40.917" LastActivityDate="2016-05-03T20:29:40.917" Title="Balun and impedance matching suggestions for dipole antenna" Tags="&lt;antenna-construction&gt;&lt;vhf&gt;&lt;impedance&gt;&lt;dipole&gt;&lt;balun&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6131" PostTypeId="2" ParentId="5466" CreationDate="2016-05-03T06:21:13.157" Score="1" Body="&lt;p&gt;By programatically you mean through command line and/or scriptable ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was looking for a linux app for DRM digital SSTV compatible with EasyPal and found TXRXAMADRM:&#xA;&lt;a href=&quot;http://pa0mbo.nl/ties/public_html/hamradio/txamadrm/&quot; rel=&quot;nofollow&quot;&gt;http://pa0mbo.nl/ties/public_html/hamradio/txamadrm/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It comes with an executable for sending, one for receiving as well as a GUI wrapping them. Just managed to compile them but couldn't test them yet as i'm waiting for the data cable to connect my transceiver to my PC.&#xA;So i guess you could use directly the tx and rx apps from your scripts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;QSSTV (&lt;a href=&quot;http://users.telenet.be/on4qz/&quot; rel=&quot;nofollow&quot;&gt;http://users.telenet.be/on4qz/&lt;/a&gt;) seems reuing parts of TRXAMADRM as well, but comes only with a GUI.&lt;/p&gt;&#xA;" OwnerUserId="5586" LastActivityDate="2016-05-03T06:21:13.157" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6132" PostTypeId="2" ParentId="5084" CreationDate="2016-05-03T06:25:22.527" Score="2" Body="&lt;p&gt;The bandwidth is often quoted as a percent of the difference between the &quot;center frequency&quot; and the &quot;band edges&quot; or the difference between the &quot;band edges&quot;. Band edge can be defined in several ways (-3Db point, pattern degradation, or some other requirement, to name a few). Because of the mathematical relationship, the lower frequencies (with smaller numbers, in terms of Mhz) are wider due to even a small difference in frequency (at the band edges compared the the center frequency) is a significant percentage of the center frequency so they are at a disadvantage from the beginning. Since 80 Meters has a relatively wide (compared to the center frequency) bandwidth in the USA it is an outlier. Also note that the center frequency method of design is not the best. The geometric mean more closely aligns the results in the band due to the difference between the center frequency and &quot;lower&quot; band edge, compared to the difference between the center frequency and the &quot;upper&quot; band edge. The percentages are NOT the same. Using the geometric mean helps the design work nearer the same at the top and bottom band edges.&lt;/p&gt;&#xA;" OwnerUserId="6620" LastActivityDate="2016-05-03T06:25:22.527" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6133" PostTypeId="2" ParentId="6130" CreationDate="2016-05-03T06:59:37.387" Score="1" Body="&lt;p&gt;&lt;strong&gt;If you truly have 73 as impedance&lt;/strong&gt;, I would not further match this, and connect the coax to it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lets look at VSWR for a 73 Ohm antenna fed with 50 Ohm coax:&#xA;(calculation here: &lt;a href=&quot;http://www.cdt21.com/resources/TechnicalTools/vswr1.asp&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.cdt21.com/resources/TechnicalTools/vswr1.asp&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VSWR is 1:1.46, if you look at reflected power, that would be 3.5%&#xA;(calculation here: &lt;a href=&quot;http://www.antenna-theory.com/definitions/vswr-calculator.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.antenna-theory.com/definitions/vswr-calculator.php&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From your 5W in: 4.825W &quot;going into the antenna&quot;; depending on the antenna efficiency (assuming 100%) then it all would be radiated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the 0.175W which is reflected, some of that will make it back up to the antenna as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to this, I would not worry too much about matching, I would tune/prune your dipole to have lowest VSWR at your transmitter, which would include the coax and influence the plane's body, and get it as low as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you still want to further match, have a look at the Gamma-Match discussion, right here on this site: &lt;a href=&quot;https://ham.stackexchange.com/questions/1804/what-is-a-gamma-match-in-the-context-of-the-driven-element-of-a-yagi-antenna&quot;&gt;What is a Gamma match in the context of the driven element of a Yagi antenna?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-05-03T06:59:37.387" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6134" PostTypeId="2" ParentId="6126" CreationDate="2016-05-03T07:38:50.660" Score="2" Body="&lt;p&gt;I have faced the same, how to know before you purchase, and even if you would know, you could end up with RFI from LED bulbs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One method I have used with reasonable success is to repress RFI right at (or very close to) the bulb on the mains wiring. While RFI is still generated by the bulb, at least the mains wiring is not used as a distribution medium or antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-05-03T07:38:50.660" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6135" PostTypeId="2" ParentId="4980" CreationDate="2016-05-03T11:28:36.230" Score="4" Body="&lt;p&gt;The oscillator may really be running at half of the received frequency. Search for &lt;a href=&quot;https://sites.google.com/site/linuxdigitallab/rf-ham-radio/dc-polyakov-based-first-dc-receiver&quot; rel=&quot;nofollow&quot;&gt;Poliakov mixer&lt;/a&gt; on the web for an example of this.&lt;/p&gt;&#xA;" OwnerUserId="6621" LastEditorUserId="1362" LastEditDate="2016-05-13T19:41:48.707" LastActivityDate="2016-05-13T19:41:48.707" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6136" PostTypeId="1" CreationDate="2016-05-03T15:24:41.330" Score="3" ViewCount="1286" Body="&lt;p&gt;I'm not sure if this is the proper StackExchange site, but you guys know RF and I don't know who else would know better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I take the commuter rail to work every day. I have 60-70% cell phone coverage. I can regain 500 hours of my life per year if I could maintain a reliable data connection all the way in. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've thought of switching carriers to get a hotspot device that supports external antennas, and carrying a 8dBi antenna in my backpack to place on the train table. Then I thought perhaps I can do the same with my cell phone and save that hassle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I looked into the teardown of my device - the LG G5. It has two connections which would become perfectly accessible with some carefully drilled holes in the back cover. See bottom right:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VpxMx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VpxMx.jpg&quot; alt=&quot;LG Motherboard&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would gaining access to these ports, locating an adapter, and hooking up an antenna be effective and/or even possible in this scenario?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could get a soft case with holes drilled in the right places, hot glueing the adapter cable to it for strain relief.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also love the idea of being able to have a 2 foot antenna on a magnet on the top of my car next time I go camping or for a remote roadtrip. &lt;/p&gt;&#xA;" OwnerUserId="6623" LastActivityDate="2016-05-04T16:10:12.130" Title="Would retrofitting an external antenna to a smartphone be feasible?" Tags="&lt;antenna&gt;&lt;diy&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6137" PostTypeId="2" ParentId="6136" CreationDate="2016-05-03T20:46:26.367" Score="0" Body="&lt;p&gt;Remember that the antenna shape factor will interact with the operating frequency of your device. Changing the shape and/or the length may influence the energy and frequency radiated from your device. If you have Spectrum Analyser you may be able to optimise the output power and tweak the antenna shape to yield the MAX output power, or improve on RF power efficiency if you wish. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have you tired to use bi-directional RF amplifier to add on the RF gain and probably change the receiver sensitivity? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that increasing the range or coverage may yield to increasing the data error, if using data communication. So you may get sluggish communication. Unless you have the schematic I wouldn't recommend to tinker with it, unless you don't mind losing it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A word of caution: if you walk with modified RF equipment on you and big brother sees you he may be mad - it did happen to many people though. &lt;/p&gt;&#xA;" OwnerUserId="6625" LastActivityDate="2016-05-03T20:46:26.367" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6138" PostTypeId="2" ParentId="6136" CreationDate="2016-05-03T21:00:54.310" Score="2" Body="&lt;p&gt;From general radio-equipment principles, there's no reason you &lt;em&gt;can't&lt;/em&gt; do this. However, there are many caveats, and it may be impractical without technical information you can't have. Here's the points you should consider:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;It may be illegal to use a device with a modified antenna. This is true of some radio services in the US; I don't know if it's true of cellular radio and you haven't specified a location.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Those connectors may not be antenna ports, but serve some diagnostic purpose, or be for Bluetooth or WiFi antennas rather than cellular antennas. &lt;strong&gt;You need to find this information.&lt;/strong&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;An antenna used for transmitting (as cell phones do) must be impedance-matched to the transmitter. If not, there may be damage to the transmitter. Some degree of mismatch is tolerated (and it is possible that the existing antenna is severely mismatched due to being small) but unless &lt;strong&gt;you have the datasheet for the transmitter chip&lt;/strong&gt; you don't know what its limits are, or even what the optimum impedance is.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If one of those ports is an antenna port and is not &lt;em&gt;normally&lt;/em&gt; occupied by an antenna connector, then it must be the case that you will be connecting your antenna in parallel with the built-in antenna. Connecting two antennas in parallel reduces their impedance (see previous point) and combines their radiation pattern (which is probably not significant if your new antenna is substantially better, but is still worth noting).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-05-04T16:10:12.130" LastActivityDate="2016-05-04T16:10:12.130" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6139" PostTypeId="2" ParentId="6136" CreationDate="2016-05-04T06:37:33.847" Score="2" Body="&lt;p&gt;I would not do this, unless you are prepared to damage your phone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are multiple antennas in a mobile device, examples could be 850 MHz, 1700 MHz, 2100 MHz, 2600 MHz for GSM/3G/4G/LTE.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of those antenna's may be dual-or-multi-band, or MIMO — or other technologies. Simply &quot;connecting an antenna&quot; to an unknown port on a board, may result in damaging the circuit. Besides that, the ports you are mentioning may be there for diagnostics for the manufacturing process of the board/circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some antennas would be for WiFi and GPS as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would not modify your mobile device, unless you have intimate knowledge of the circuitry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you could do is look into a small 12V/battery-powered 3G booster. There are various shops which would sell them; however you will have to carry the booster, the battery, the donor antenna, and the distribution antenna with you on your journey.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a booster from &lt;a href=&quot;http://www.myamplifiers.com&quot; rel=&quot;nofollow&quot;&gt;http://www.myamplifiers.com&lt;/a&gt;, for base install, and it did work for me. But as that is a home install it is a different piece of equipment. There are amplifiers made for mobile installations which run on a 12V supply, but I have no further experience with those.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, in some countries/areas the use of a booster is illegal; you may want to look into this.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="76" LastEditDate="2016-05-04T16:05:01.940" LastActivityDate="2016-05-04T16:05:01.940" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6140" PostTypeId="1" AcceptedAnswerId="6145" CreationDate="2016-05-04T07:04:24.807" Score="24" ViewCount="38151" Body="&lt;p&gt;I would like to add a balun/choke to my dipole for the reasons outlined in &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt;. In the spirit of continued kit and/or DIY building for my ham shack, I set out to investigate how I might best proceed &quot;from scratch&quot;.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Simply wind two conductors together over some sort of core?&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;At &lt;a href=&quot;http://vk6ysf.com/balun_guanella_current_1-1.htm&quot; rel=&quot;noreferrer&quot;&gt;http://vk6ysf.com/balun_guanella_current_1-1.htm&lt;/a&gt; a design is given for a 1:1 current balun that simply wraps a pair of wires around a toroidal core:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/f7yu7.gif&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/f7yu7.gif&quot; alt=&quot;Simple bifilar winding around toroid, unbalanced in and balanced out&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;…or as &lt;a href=&quot;http://vk5ajl.com/projects/baluns.php#current&quot; rel=&quot;noreferrer&quot;&gt;http://vk5ajl.com/projects/baluns.php#current&lt;/a&gt; even shows:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YTgb8.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YTgb8.jpg&quot; alt=&quot;A pair of wires wrapped around a nail&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suppose the air-wound &quot;ugly balun&quot; as demonstrated at &lt;a href=&quot;http://www.hamuniverse.com/balun.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.hamuniverse.com/balun.html&lt;/a&gt; also fits in this same category, unless using coax in place of the bifilar winding somehow changes things?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OMppA.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OMppA.jpg&quot; alt=&quot;Coax wrapped repeatedly around a large-diameter PVC tube&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that's all well and good, I guess.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Two tangled toroids?&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;But then — under the same &quot;Guanella balun&quot; name as the first diagram above, no less! — I find that &lt;a href=&quot;http://www.kn9b.us/guanella-balun&quot; rel=&quot;noreferrer&quot;&gt;http://www.kn9b.us/guanella-balun&lt;/a&gt; presents this diagram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VK2lz.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VK2lz.jpg&quot; alt=&quot;Schematic of a 1:1 current balun using two bifilar windings on two separate toroids&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;…which is to be built using &lt;em&gt;two&lt;/em&gt; toroids resulting in something that looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VZvAu.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VZvAu.jpg&quot; alt=&quot;Current balun using two toroids, assembled in a project box&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any benefit to this dual core balun over the single core type? What is the purpose of this sort of &quot;push-pull&quot; reminiscent design? Is it worth buying two toroids and going to twice the trouble of winding and sorting out which loose ends connect to which others, versus just winding a pair of wires around a rusty bolt, or wrapping some coax around some scrap PVC?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2019-02-20T01:42:57.980" Title="Why are some 1:1 current baluns twice as complicated as others?" Tags="&lt;balun&gt;&lt;toroid&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="6141" PostTypeId="2" ParentId="5735" CreationDate="2016-05-04T07:14:52.183" Score="1" Body="&lt;p&gt;So at 1 kW for a truly resistive impedance of 50 Ω, the voltage would be &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;V = \sqrt{PR} = \sqrt{1000 \cdot 50} = 223.6\,\mathrm{V}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now you need to establish the minimum gap to avoid arcing for 223.6 volts.&#xA;An example calculator online would be &lt;a href=&quot;https://www.cirris.com/learning-center/calculators/50-high-voltage-arc-gap-calculator&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But at 223.6 volts, I believe your 4 mm rod inside an internal-dia-8-mm would be an air gap of 2 mm, which should be sufficient. Then again, maybe not — in case of humidity in the air, which may change the dielectric constant of the air. &lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="76" LastEditDate="2016-05-04T16:01:57.483" LastActivityDate="2016-05-04T16:01:57.483" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6142" PostTypeId="2" ParentId="6140" CreationDate="2016-05-04T07:34:17.063" Score="0" Body="&lt;p&gt;It is all about the choke impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good example overview of the different cores / windings for coaxial baluns would be on this page: &lt;a href=&quot;http://karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow&quot;&gt;http://karinya.net/g3txq/chokes/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would take an expert, which I am not, to answer your specific question, as it is very much dependent on the materials used (what torroid material, what is the wire thickness, the wire coating, the wire material... and so on so forth) and dependent on the exact frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-05-04T09:23:46.390" LastActivityDate="2016-05-04T09:23:46.390" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6144" PostTypeId="2" ParentId="6011" CreationDate="2016-05-04T11:23:07.883" Score="2" Body="&lt;p&gt;CTCSS tones or DTS digital tones, are only for &quot;Receiving intended signals&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a receiver is configured to receive on a frequency with CTCSS or DTS, then the squelch is only opening when the transmitted signal contains the &quot;matching&quot; CTCSS or DTS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a signal is transmitted without the &quot;matching&quot; CTCSS or DTS, then the receiver's squelch will not open, and you will not hear the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if a receiver is configured on a frequency without CTCSS or DTS, then it will receive all signals, including those which have CTCSS or DTS, and the squelch will open.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you are communicating on a frequency with many many users, you can transmit with CTCSS/DTS, and receive with the same CTCSS/DTS, and you will only hear these signals.... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, everyone else; with receivers configured without CTCSS/DTS... will also hear your transmitted signal!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why it is a &quot;false/illusion of privacy&quot; as answered already.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use CTCSS/DTS only if you want to &lt;strong&gt;restrict a receiver to a specific transmitted signal&lt;/strong&gt;, with the understanding that &lt;strong&gt;others can perfectly receive your signal&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-05-04T11:23:07.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6145" PostTypeId="2" ParentId="6140" CreationDate="2016-05-04T16:20:40.087" Score="14" Body="&lt;p&gt;Baluns are a source of &lt;strong&gt;much&lt;/strong&gt; confusion in the hobby, and are probably one of the most common causes of RFI, common mode noise reception, and poor antenna performance. Folks try to shoe-horn a lot of very complex values and characteristics in to a very linear way of thinking, and most of it is just flat wrong.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Starting from the top: That design should in theory work fine, except the website is using a toroid for which I can find almost no tech data, and what little is available in the data sheet suggests it's meant for SMPS transformers and the like. This means it is quite likely to saturate, or potentially just not offer much of any choking impedance at higher frequencies. You &lt;strong&gt;might&lt;/strong&gt; be able to justify using it for 160m, maybe even 80m, but above that, it's almost certainly at best ineffective, and at worst, very inefficient. Even on the lower frequencies, given the type of transformer they're typically used for, I suspect that choking impedance would be quite low.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The counter winding technique is also at best needlessly complicated, and at worst can act to increase parasitic capacitance within the transformer, causing a &lt;strong&gt;reduction&lt;/strong&gt; in performance, not the commonly claimed improvement. W8JI, K9YC, and VK1OD all failed to find any evidence of the supposed elimination of saturation with that winding style, in reality it likely just causes a complex eddy current which may lead to localized saturation in some areas of the toroid but not others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This design with a Type 43 or Type 31 (Amidon, Palomar, or Fair-Rite) T106 core would be fine for 40m and up on QRP, T200 or larger for 100w, especially if you want to operate below 40m). IIRC Type 77 or type 62 is typically recommended for frequencies from 10m to 2 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ditch the counter-winding technique, it's pointless and just complicates things. 14-18 bifilar turns of 18-14awg wire should do the trick for most of HF on the T240 cores.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The second design is a common failure to understand the concept of saturation. Yes, in theory for a 1:1 bifilar current choke, lossy material at the frequency you're using is desirable. Only the common mode current (the current that remains when the equal and opposite current on the two conductors cancel each other out) appears on the core, where it will ideally encounter very high impedance and be dissipated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Random steel has very unpredictable (and almost certainly undesirable) saturation characteristics, and also may have wildly varying impedance across the range of HF frequencies, which means it may work fine on some frequencies, and/or at lower power, but again, at best it's likely to be ineffective on some bands, and at worse it may just turn most of your power to heat. This is particularly the case with an antenna that is anything more than almost perfectly balanced already. Use one of these on a dipole with elements that interact unevenly with surrounding objects or terrain, or worse, on something like an OCF dipole, and that thing will get extremely hot very quickly.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Third is a classic &quot;Ugly balun&quot; or air core solenoid balun. They CAN work, however because capacitance in the coil is quite high (without looking, I believe RG-8X is ~5pF/ft), they are self-resonant tank circuits. This means that they can present quite useful impedance on a couple of bands at most, but otherwise may be all but invisible on other bands. They can be strung together along the coax, but you end up using a lot of extra coax that equates to more loss, and it's far more expensive than just buying a proper toroid for $5.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The final design is a bit of a novelty to me, and is rather puzzling. It's done in the manner of a proper 4:1 current balun, and there's no reason it wouldn't work, but the design is counter-productive. Electrically the two cores are in parallel, acting as two parallel bifilar chokes. Presuming they are identical cores and windings, this will actually &lt;strong&gt;reduce&lt;/strong&gt; choking impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There doesn't seem to be any logical reason to do this unless you're constructing a balun to handle a &lt;em&gt;lot&lt;/em&gt; of power, 500w or more, but then you'd still want them in series, just with less impedance per core. I suspect that the designer has read the technical discussions on why single core 4:1 voltage baluns are not baluns at all, but impedance transformers that provide little, if any, useful feedline isolation, and just took that to mean that you can't achieve isolation in any situation with 1 core. That statement only applies to a 4:1 balun due to the DC short that is present. A 1:1 bifilar winding is more than capable of providing good isolation on a single core on a wide range of frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A single T240-43 with 14awg magnet wire should be more than capable of dissipating the common mode current from even a moderately imbalanced antenna at 500w PEP without issue. The only reasons I can imagine using this final design this would be to compensate for poor component choice (saturation, perhaps) and perhaps it's an attempt to reduce the total current through each choke, or if he were using two different cores (it doesn't look like he is) to provide good choking impedance on two different frequency ranges, but again, they should be in series, not parallel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's another one that seems to needlessly complicate the situation because of a failure to grasp the basic qualities that a choke balun (as opposed to a true isolated winding transformer) should have.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;If you want 1:1, buy the right toroid, use large enough wire, and KISS. Baluns aren't magic. They aren't even really that complicated if you just stop and think about what they're actually supposed to do. Things get a little more complex when you need impedance transformation, but if you stick to the same basic design, it's hard to fail entirely. One bifilar winding per core, and design with parasitic capacitance in mind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the best resources on this matter is the &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;noreferrer&quot;&gt;K9YC RFI Bible&lt;/a&gt;. You can find the 1:1 choke balun I described above, along with many other possible (and experimentally verified) designs, along with a teardown of some of the most popular (and least effective) designs you'll find &quot;in the wild&quot;.&lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="76" LastEditDate="2016-05-04T16:32:41.797" LastActivityDate="2016-05-04T16:32:41.797" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6146" PostTypeId="1" CreationDate="2016-05-04T16:51:49.177" Score="3" ViewCount="2932" Body="&lt;p&gt;I have an inkling of an idea- a modem system communicating over Short-wave. I know that WiMAX already exists, but the difference is that, while WiMAX works on the Gigahertz frequencies, and most concepts for Ham Radio ones think Megahertz frequencies would be ideal, My idea was to make it work on kilohertz, AM, possibly even long-wave frequencies (3Mhz-150KHz). The only thing I have to go on is a Bell 103 300-Baud time code broadcasting from CHU every day.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, can you send Modem signals of a higher quality &amp;amp; baud rate(1200 Baud?) over regular Short-wave and AM broadcast frequencies? If so, how would it work? Is it even legal? Practical?  could it be two way?&lt;/p&gt;&#xA;" OwnerUserId="6635" LastEditorUserId="6635" LastEditDate="2016-05-05T17:00:25.697" LastActivityDate="2016-05-05T18:01:27.760" Title="Can one send data over Short-wave frequencies?" Tags="&lt;mf&gt;&lt;lf&gt;" AnswerCount="1" CommentCount="9" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6147" PostTypeId="1" CreationDate="2016-05-04T20:44:52.147" Score="1" ViewCount="307" Body="&lt;p&gt;If it sounds like a stupid question, it probably is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My mom loves being nosy... When she hears the police siren, an ambulance, firefighters, or something like that, she's the first one to run to the balcony to see what's going on and ask neighbors what happened. She also loves weather stations; give her the &quot;sense&quot; that she knows something that nobody else knows.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, she's not technological.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that said, could someone please give me some advice on buying her a scanner that will let her listen to police, emergency, and those frequencies without needing much technological know-how?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm looking for something that she can turn on and start being nosy. I can do a few modifications if needed since I work with computers, but I know very little about frequencies, scanners, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was thinking of those Uniden scanners, but the cheapest one is about $90 and I've read that it's hard to program and includes virtually no documentation out-of-box.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="6636" LastEditorUserId="4665" LastEditDate="2016-05-07T00:36:51.570" LastActivityDate="2016-07-12T20:53:24.277" Title="Scanner radio purchase advice for someone that's nosy but not technological?" Tags="&lt;antenna&gt;&lt;united-states&gt;&lt;receiver&gt;&lt;frequency&gt;&lt;equipment&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="6148" PostTypeId="5" CreationDate="2016-05-05T15:33:50.573" Score="0" Body="&lt;p&gt;Medium frequency is lower than &lt;a href=&quot;/questions/tagged/hf&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;hf&amp;#39;&quot; rel=&quot;tag&quot;&gt;hf&lt;/a&gt;, and higher than &lt;a href=&quot;/questions/tagged/lf&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;lf&amp;#39;&quot; rel=&quot;tag&quot;&gt;lf&lt;/a&gt; in frequency. The common AM radio broadcast band falls within the MF band.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-05-05T15:33:50.573" LastActivityDate="2016-05-05T15:33:50.573" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6149" PostTypeId="4" CreationDate="2016-05-05T15:33:50.573" Score="0" Body="Medium Frequency: The frequency range from 300 kHz to 3 MHz" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-05-05T15:33:50.573" LastActivityDate="2016-05-05T15:33:50.573" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6150" PostTypeId="5" CreationDate="2016-05-05T15:36:39.730" Score="0" Body="" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-05-05T15:36:39.730" LastActivityDate="2016-05-05T15:36:39.730" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6151" PostTypeId="4" CreationDate="2016-05-05T15:36:39.730" Score="0" Body="Low Frequency: frequencies in the range of 30 kHz–300 kHz." OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-05-05T15:36:39.730" LastActivityDate="2016-05-05T15:36:39.730" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6152" PostTypeId="2" ParentId="6146" CreationDate="2016-05-05T17:34:47.050" Score="8" Body="&lt;p&gt;Modern digital systems communicating over HF (aka short-wave) are legal in the US and practical, and in fact one such system is in routine daily use.  Have a look at the Winlink system.  (The official web site is &lt;a href=&quot;http://www.winlink.org/&quot;&gt;here&lt;/a&gt;, but the &lt;a href=&quot;https://en.wikipedia.org/wiki/Winlink&quot;&gt;Wikipedia article&lt;/a&gt; provides a better general overview.)  It uses the &lt;a href=&quot;https://en.wikipedia.org/wiki/PACTOR&quot;&gt;PACTOR&lt;/a&gt; and &lt;a href=&quot;https://en.wikipedia.org/wiki/Winmor&quot;&gt;WINMOR&lt;/a&gt; modes.  Winlink messages are formatted as email; the Winlink system is connected to the internet (when the internet works), and a Winlink user can choose to send and receive messages via HF, VHF/UHF, or internet.  Because Winlink messages may be sent over a low-bandwidth connection, messages should be short; small attachments are allowed.  Winlink is an excellent tool for emergency communications, and is also often used by mariners at sea.  (An amateur radio license is required.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Digital communication on the HF bands is inherently more difficult than on VHF, UHF, and higher bands, due to noise, fading, and many other issues; the bit rate varies according to the signal-to-noise ratio.  The newer versions of PACTOR offer better performance than WINMOR, but those newer PACTOR modes require an expensive terminal node controller (TNC), whereas WINMOR is free and implemented in software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, digital modes are legal in the US and other countries on the 160m band, which is close to the AM broadcast band and is considered a medium-frequency (MF) band.  But the noise on 160m is generally much higher than on any HF band, so 160m is not generally used for Winlink.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-05-05T18:01:27.760" LastActivityDate="2016-05-05T18:01:27.760" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6153" PostTypeId="1" CreationDate="2016-05-06T01:16:46.660" Score="6" ViewCount="2921" Body="&lt;p&gt;It seems there are almost as many &quot;balun&quot; designs as there are web pages about &quot;baluns&quot;. There's lots of accusations pointed in all directions (&quot;design Z isn't a balun OR a choke&quot;, &quot;design Y is overkill&quot;, &quot;design X could lead to spurious emissions/overheating/loss-of-limbs…&quot;) and given how hard such an ostensibly simple thing seems to be to understand, I'd like to be able to test any balun I might make or purchase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How might I go about measuring a balun or a line choke to see if it will work as intended?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-05-10T11:20:28.907" Title="How to measure a balun for effectiveness?" Tags="&lt;balun&gt;&lt;measurement&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6154" PostTypeId="2" ParentId="6153" CreationDate="2016-05-06T01:16:46.660" Score="2" Body="&lt;p&gt;In the article &lt;a href=&quot;http://www.arrl.org/files/file/QEX_Next_Issue/Nov-Dec_2010/Skelton_QEX_Nov-Dec.pdf&quot; rel=&quot;nofollow&quot;&gt;Measuring HF Balun Performance&lt;/a&gt; the author (Ron Skelton, W6WO) states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Common Mode Rejection Ratio (CMRR) of a balun is defined in professional literature as the ratio of wanted to un-wanted transmitted power&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This sounds like a reasonable start: the claim is that the CMRR is a good measurement of balun performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He continues:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Measurements and calculations of CMRR [Common Mode Rejection Ratio] can be made by directly measuring impedance in the common-mode path, or by observing power flows using a power meter or oscilloscope&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;…but then goes on to say that this is subject to errors due to phase imbalances that would not be detected with simpler methods.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Any balun or line choke can be viewed as a 3-port device.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The unbalanced input would count as the one port, and each of the balanced outputs (referenced to the same ground as the input, afaict) is another port.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He then gives the equation:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;CMRR dB =20*log (S21+S31)/(S21-S31) &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This basically compares the difference in power transfer from the input to each of the outputs (relative to each other).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So to use this technique, one would need at least a 2-port VNA to measure first the signal transfer to the one output, and then the other. Then a calculated graph based on those two plots could be derived using the above formula.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think this method covers all the things that can go wrong with baluns, however. For example, this measurement doesn't seem to tell you anything about the power handling capability of a balun, nor what happens if you exceed it.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-05-06T01:16:46.660" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6155" PostTypeId="2" ParentId="6153" CreationDate="2016-05-06T07:47:21.103" Score="2" Body="&lt;p&gt;&quot;How might I go about measuring a balun or a &lt;strong&gt;line choke&lt;/strong&gt; to see if it will work as intended?&quot; (emphasis added)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Steve Hunt (G3TXQ, SK) has measured many chokes, coaxial toroid wound, coaxial air wound, as well as some bifilar wound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The results of his measurements can be found here: &lt;a href=&quot;http://karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://karinya.net/g3txq/chokes/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the bottom of the page he explains how he measured the chokes, using a two port VNA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/i82Ko.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/i82Ko.png&quot; alt=&quot;VNA setup&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also a good explanation on why resistive chokes (R &gt; X) are better then reactive chokes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used his charts with great success winding my own chokes, using the &quot;black&quot; areas (this is where R &gt; X) of the charts I managed to wind chokes specifically for the bands intended. While in the beginning I did use air-wound-coaxial chokes, the chart is clearly demonstrating that this is not ideal, as they are mostly reactive not resistive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This explanation may not be as scientific as it seems, it would give a good starting point for your own measurements of chokes.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="9621" LastEditDate="2020-05-10T11:20:28.907" LastActivityDate="2020-05-10T11:20:28.907" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="6156" PostTypeId="1" AcceptedAnswerId="6157" CreationDate="2016-05-06T08:54:01.520" Score="1" ViewCount="42" Body="&lt;p&gt;Asking for a friend, of course, this homebrew yagi is probably somewhere between 3 and 6dB gain (not yet analysed) and was aimed about +30 degrees off-center, tilted 10-20 degrees upwards, transmitting 50W on 2m. 'They' were standing side-on, approx. 1.5m away. The over lasted around 1 minute. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen the RF radiation recommendations, which average out the power to at least 6 minutes. If this is the case then the ERP of 100-200W would be much reduced. 'They' would have been standing within the safe-zones, however.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Their eye on the antenna side may also be feeling a dull pain, but that could be psychosomatic :)&lt;/p&gt;&#xA;" OwnerUserId="5313" LastActivityDate="2016-05-06T10:29:04.920" Title="Impact of keying-up in yagi beam 1.5m (or 5ft) away on 2m FM?" Tags="&lt;rf-power&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6157" PostTypeId="2" ParentId="6156" CreationDate="2016-05-06T10:29:04.920" Score="2" Body="&lt;p&gt;Interesting question, my gut feeling tells me that the &quot;dull pain in eye&quot; experienced may not be from RF radiation... but that would be a &quot;gut feeling&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Exposure to RF radiation, and safety of RF radiation is very well documented by the FCC. Realizing that this is US based, and may or may not be applicable for other regions of the world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC FAQ can be found here: &lt;a href=&quot;https://www.fcc.gov/engineering-technology/electromagnetic-compatibility-division/radio-frequency-safety/faq/rf-safety&quot; rel=&quot;nofollow&quot;&gt;https://www.fcc.gov/engineering-technology/electromagnetic-compatibility-division/radio-frequency-safety/faq/rf-safety&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bullitin with formula's to calculate is the OET65, which can be found here: &lt;a href=&quot;https://www.fcc.gov/general/oet-bulletins-line#65&quot; rel=&quot;nofollow&quot;&gt;https://www.fcc.gov/general/oet-bulletins-line#65&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Particular interesting is the example of document &lt;a href=&quot;https://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65.pdf&quot; rel=&quot;nofollow&quot;&gt;https://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65.pdf&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Page 26 of the pdf-document (numbered as Page 21), lists an example of a 100MHz transmission at 10kW ERP power, experienced by someone standing 20 meters from the antenna-mast. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use this to calculate with your own numbers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another nice example would be the graph of &quot;FIGURE-1 Power Density vs. Distance (assumes no surface reflection)&quot; on Page 28 of the pdf (numbered as page 24). Which could be use for preliminary estimations of exposure&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, regulating bodies in various countries would have similar publications, it would be worthwhile checking this at your own discretion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-05-06T10:29:04.920" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6158" PostTypeId="1" AcceptedAnswerId="6159" CreationDate="2016-05-06T13:04:22.813" Score="3" ViewCount="1702" Body="&lt;p&gt;I'm trying to receive VHF airband transmitted from a nearby airport via RTLSDR and having a hard time doing so. Obviously the stock antenna is useless in this situation. I tried building a quarter-wave ground plane antenna but that didn't improve reception much. Only overhead planes are heard well, controller is barely audible, and so is the ATIS frequency. Roof access is also a hard one, so I'm limited by what I can receive from my window.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the important factors when trying to improve VHF airband reception? What will get me the best reception without going crazy with expensive antennas/parts?&lt;/p&gt;&#xA;" OwnerUserId="191" LastActivityDate="2016-05-09T08:13:39.643" Title="Improving VHF airband reception" Tags="&lt;software-defined-radio&gt;&lt;vhf&gt;&lt;rtl-sdr&gt;&lt;airband&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6159" PostTypeId="2" ParentId="6158" CreationDate="2016-05-06T14:36:21.207" Score="4" Body="&lt;p&gt;Controllers and ATIS are transmitting from the ground, so they're always harder to receive because terrain, trees, and buildings are in the way. The best thing you can do to improve your reception is &lt;strong&gt;move your antenna as high off the ground as you can&lt;/strong&gt;, to reduce the density of line-of-sight obstacles. If you can't put it on the roof, at least hang it from the ceiling for a minor improvement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best antenna for your purpose would be a &lt;strong&gt;“high-gain” vertical antenna&lt;/strong&gt;. Such an antenna has a pattern which is more flattened — it has more gain in the horizontal plane at the cost of lesser gain at higher angles. Since your current system performance is unbalanced in the other direction, it should be an overall improvement.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;After setting up the best antenna you can, you want to improve your receiver's &lt;em&gt;signal-to-noise ratio&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;First, make sure you have &lt;strong&gt;set the hardware AGC &lt;em&gt;off&lt;/em&gt;&lt;/strong&gt; (there should be a checkbox for this in whichever software you are using), because the RTL's AGC doesn't work well for these applications (it runs too high). Then find a good setting for the manual gain control (e.g. pick an ATIS station you can barely hear, and listen for the best audio).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Check for local broadband noise sources. Try turning off electrical equipment (including non-incandescent light bulbs!), and watch the spectrum to see if the noise floor (‘everywhere there isn't a signal’) reduces in intensity. Find out if there's a culprit you own and can replace or turn off when you want to listen. &lt;strong&gt;Try a different computer&lt;/strong&gt; in case you have a particularly noisy computer.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you find that there is no significant local noise — in particular, if the noise floor doesn't rise above the level you get with the gain turned all the way down or the antenna disconnected — then you are in the “lucky” position of having a good signal-to-noise ratio but weak signals. This means that you can benefit from &lt;strong&gt;a better receiver&lt;/strong&gt; — in particular one with a higher ADC bit depth than the 8-bit RTL-SDR. This will appear as reducing the receiver's internal noise floor.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Alternatively to the previous option, or if you &lt;em&gt;do&lt;/em&gt; have local noise but can move the &lt;em&gt;antenna&lt;/em&gt; away from it, you can use a &lt;strong&gt;low-noise amplifier (LNA)&lt;/strong&gt;. This is a device which is installed right at the antenna, and amplifies the signal at that point so that it is much stronger than the noise internal to the receiver (or leaking into the receiver from nearby equipment or out-of-band).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-05-06T14:36:21.207" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6160" PostTypeId="1" AcceptedAnswerId="7222" CreationDate="2016-05-07T01:04:35.177" Score="11" ViewCount="3698" Body="&lt;p&gt;In the audio realm, where cable lengths are insignificant compared to the signal wavelength, I would understand an impedance mismatch damaging an amplifier as follows:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take an audio amplifier that can deliver 100 watts of power into an 8 ohm speaker driver. So under normal operating conditions, by &lt;code&gt;P = R * I^2&lt;/code&gt;, there would be 3.5A of current flowing to deliver these 100W. If this amplifier were connected instead to 2 ohm speakers, it would need to pass 7A of current assuming it will still attempt to deliver this same 100W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Viewed even more simply: a 2 ohm load tends to &quot;short circuit&quot; an amp designed for an 8 ohm load. Further to this logic, connecting the same amplifier to a 32 ohm load would not hurt it, as the resulting current would be smaller than expected.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;With radio frequency, we don't really worry about the impedance being &quot;too low&quot; but rather &quot;too mismatched&quot; and we use SWR to represent this mismatch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why in RF is connecting a 500 ohm load i.e. 10:1 SWR, to my amplifier's 50 ohm output, considered equally bad as causing a 10:1 SWR by connecting a 5 ohm load instead?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do the two 10:1 SWR cases cause amplifier failure for different reasons? I wonder if in the 5 ohm case it is just a simple &quot;too much current&quot; like in the audio case, but in the 500 ohm case the transmission line somehow ends up increasing the &lt;em&gt;voltage&lt;/em&gt; beyond what the transistors can handle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it make any difference if we eliminate the transmission line altogether, so that standing waves can't really develop? Would it be okay to connect a high-impedance antenna feedpoint &lt;em&gt;directly&lt;/em&gt; to a transmitter without problems, whereas a low-impedance antenna might still cause an overcurrent condition?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2017-10-05T22:11:00.963" Title="Why does &quot;high SWR&quot; damage transmitters, instead of &quot;impedance mismatch&quot;?" Tags="&lt;electronics&gt;&lt;amplifier&gt;&lt;impedance&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6161" PostTypeId="1" AcceptedAnswerId="6164" CreationDate="2016-05-07T03:29:43.280" Score="2" ViewCount="576" Body="&lt;p&gt;I am unable to autotune on 21Mhz as the SWR is more than 1:3 which is out side the range of the radio. I would like use it only for digital TX with a max. power of 50 watts. Any solution/s?&lt;/p&gt;&#xA;" OwnerUserId="6641" LastActivityDate="2016-08-21T07:38:19.037" Title="Yaesu FT-950 with G5RV lite antenna auto tune problem on 21Mhz" Tags="&lt;antenna&gt;&lt;digital-modes&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6162" PostTypeId="2" ParentId="6111" CreationDate="2016-05-07T11:51:10.240" Score="2" Body="&lt;p&gt;Interesting question, and I'm surprised you haven't had any responses before now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's no fundamental limitation to the time resolution you can achieve, even in a bandlimited channel. Consider a carrier modulated by a continuous 1-kHz sinewave. A DFT can make a very accurate measurement of the phase and amplitude of this modulation. The resolution is limited by the number of samples used in the DFT, and the accuracy is limited by the amplitude and phase noise introduced by the channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming the channel noise has zero mean, then longer DFTs (more samples, longer integration times) give you better results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It isn't difficult to set up a simulation of this kind of system in any sort of math-processing system (e.g., Matlab, octave, numpy, etc.). Generate the signal, add the channel distortions to it, and then do the DFTs on the resulting samples and see what kind of distribution you get in the measurement errors. I would be surprised if you couldn't get down to 1 &amp;micro;s accuracy with &quot;reasonable&quot; noise levels and integration times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to turn this into a complete time-of-flight measurement system, you could add additional tones that carry data that would allow you to resolve the cycle-counting ambiguities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back in the late 1990s, I was doing some experiments trying to determine just how much accuracy I could extract from the time signal transmitted by the Canadian time station CHU. The problem there is that they only transmit 10 cycles of a 1-kHz tone every second (to create an audible &quot;tick&quot;), and the fading/multipath on the HF bands make it impossible to maintain any sort of phase coherency from one burst to the next. It was interesting to watch this on an oscilloscope.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastEditorUserId="1459" LastEditDate="2016-05-07T13:12:38.140" LastActivityDate="2016-05-07T13:12:38.140" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6164" PostTypeId="2" ParentId="6161" CreationDate="2016-05-08T02:36:48.513" Score="1" Body="&lt;p&gt;The traditional &quot;No balun&quot; G5RV design is famous (infamous, more like) for these sorts of quirks, primarily because the claim that it behaves in various different (and universally desirable) ways at different frequencies is a crock. In reality, it has two modes, a balanced dipole when used on a frequency where SWR (and in theory, common mode current) is low (30 and 17m on the Lite), and a sort of Frankenstein vertical (driven by common mode) and dipole (driven by the differential mode) everywhere else. That second mode is unpredictable at best, because the coax shield is just hanging there begging to act as part of the antenna, and the ladderline likes to radiate to varying degrees depending on frequency and severity of imbalance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case, a quick model suggests you've got several hundred ohms of inductive reactance at the junction between the coax and ladderline at 21MHz, which may be more than your tuner can handle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to handle this would be to extend the ladder line to the shack window, or as close as you can get it, place a good quality 2 core 4:1 current balun there, and then run a short length of low loss coax like RG-213 in to the tuner. This should drastically reduce your feedline losses, and generally results in a much broader useful bandwidth overall. In your case, if this model is even remotely close to accurate, you're likely losing more than 50% of your power in the coax run, even if you're using just 50 feet of RG-8X in the current setup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;band aid&quot; solution would be to place a bit of capacitive reactance across the ladderline to counteract the inductive reactance. I'm not sure exactly how much capacitance you might need, as that's going to be highly situation dependent. I would recommend using a variable capacitor at low power to determine how much is necessary to get below 4:1 or so, and then swap the variable capacitor out for a fixed capacitor with at least a 1kV voltage rating when you want to run 15 meters, and remove it otherwise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A final (and maybe optimal) solution, but requiring substantial financial investment, would be to place a remote tuner like an Icom AH-4 or LDG RT-100 at the point where the ladderline from the G5RV ends, and run coax to the tuner. This is probably the best of all worlds, keeping coax loss low, giving maximum bandwidth, making it easy to isolate the coax from the antenna, and eliminating the frustrations of running ladderline long distances.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-05-08T02:36:48.513" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6165" PostTypeId="2" ParentId="6158" CreationDate="2016-05-08T17:09:27.403" Score="0" Body="&lt;p&gt;I live within 5 miles of my local airport, and I could barely hear the tower and ATIS (no airplanes on the ground).  I put up a good external antenna (a discone) and this made all the difference.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck.&lt;/p&gt;&#xA;" OwnerUserId="1158" LastActivityDate="2016-05-08T17:09:27.403" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6166" PostTypeId="1" AcceptedAnswerId="6167" CreationDate="2016-05-08T21:31:14.243" Score="1" ViewCount="196" Body="&lt;p&gt;I'm trying to learn about how SSB modulation works.  My current understanding from reading and looking at spectrum plots from SDR software is that the sound is modulated with the carrier, but only half the carrier wave.  (Alternatively, the sound's 0-point is offset either plus or minus a bit, and then modulated against the half-wave carrier.)  Then, filters are used to remove the actual carrier, resulting in a much more efficient transmission at the expense of some bandwidth.  Is this remotely accurate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, it seems clear that we're only using half of bandwidth.  Does that mean we can use the other half, if we wanted to?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I'm wondering is if it's possible to modulate a signal using both side bands but in a differential mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yJjF7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yJjF7.png&quot; alt=&quot;Differential Signaling&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;(Image from &lt;a href=&quot;https://en.wikipedia.org/wiki/Differential_signaling&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Differential_signaling&lt;/a&gt;.)&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In professional audio applications, audio signal is sent down balanced cables twice, with one side inverted.  When one side is then inverted on the receiving end and added to the other side, any noise that affected both sides in the same way is cancelled out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If both side bands could be used simultaneously by the same transmitter, perhaps the lower side band could have the regular audio signal modulated on it, with the upper side band having the inverted audio signal modulated on it.  Then the receiver could flip one side and add them together, eliminating a lot of noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this sort of modulation exist?  Is it feasible?  If not, what parts of SSB am I not understanding?&lt;/p&gt;&#xA;" OwnerUserId="51" LastActivityDate="2016-05-09T04:48:48.860" Title="SSB Modulation and Differential Signaling" Tags="&lt;modes&gt;&lt;ssb&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6167" PostTypeId="2" ParentId="6166" CreationDate="2016-05-09T01:22:52.410" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;My current understanding from reading and looking at spectrum plots from SDR software is that the sound is modulated with the carrier, but only half the carrier wave.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's — not really accurate. A SSB signal &lt;em&gt;uses half the bandwidth&lt;/em&gt; of a double-sideband (whether AM or DSB-SC) signal, but there's no sense in which it uses &quot;half the carrier&quot; in the modulation process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you're starting from a SDR perspective, let's talk DSP and complex (IQ) signals. Any &lt;em&gt;real&lt;/em&gt; signal, such as that obtained from your microphone, has, from the complex-signal perspective, a spectrum which is &lt;em&gt;symmetric about zero Hz&lt;/em&gt;. &lt;strong&gt;All&lt;/strong&gt; methods of generating a SSB signal are essentially methods of &lt;em&gt;removing&lt;/em&gt; one half of that symmetric signal. Some of them are more like “filter it out” (complex bandpass filter) and some of them are more like “synthesize a signal which cancels out only the unwanted half” (phasing), but they all are taking what is “really” a symmetric signal and making an asymmetric signal out of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Side note: In DSP, there is no reason to think about “carrier waves” as an essential ingredient. Because we can work at &lt;em&gt;complex baseband,&lt;/em&gt; we can work with (de)modulation completely separately from frequency-shifting, whereas electronic circuits largely have to use nonzero “intermediate frequencies”. On the other hand, the “carrier frequency” is meaningful — it's a convenient reference, it's what we shift down from or up to vs. a baseband signal.)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In any case, it seems clear that we're only using half of bandwidth. Does that mean we can use the other half, if we wanted to?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, but:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If you use the other half for an additional independent signal, then you're just transmitting USB and LSB with the same carrier frequency.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you use the other half for the same signal, then you're transmitting DSB-SC (double sideband, suppressed carrier) which is exactly the same as AM without a transmitted carrier wave. DSB-SC has most of the same properties as SSB, but of course does use the double bandwidth.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you use the other half for an inverted (180° phase shifted) signal:&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What I'm wondering is if it's possible to modulate a signal using both side bands but in a differential mode.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not usefully. As you mentioned, differential signaling is a technique to use against “noise that affected both sides in the same way”, but in the case where it's useful, you have two signals at the same frequency traveling on &lt;em&gt;different wires&lt;/em&gt;. Here, you have only one “wire” (empty space), and the two signals you propose are at &lt;em&gt;different frequencies&lt;/em&gt;. And that's the problem: in most cases, the RF noise affecting the upper sideband will not be the same as the noise in the lower sideband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(And because the receiver must receive twice the bandwidth of SSB, it receives additional noise as well, so it has a worse signal-to-noise ratio than doubling the power of a regular SSB signal.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This mode &lt;em&gt;would&lt;/em&gt; help with some types of noise sources — for example, broadband impulses like those a &lt;em&gt;noise blanker&lt;/em&gt; is used against, but that type of noise isn't common enough to motivate modes for its sake.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if you and a friend have open-source SDR transceivers, maybe it's worth experimenting with! Just remember that you're using twice the bandwidth, and don't use it on a crowded band.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-05-09T04:48:48.860" LastActivityDate="2016-05-09T04:48:48.860" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6168" PostTypeId="2" ParentId="6158" CreationDate="2016-05-09T08:13:39.643" Score="0" Body="&lt;p&gt;In my experience it is very hard to receive aviation ground stations if you do not have a good/clear line of sight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some years ago, I did built a 3 element yagi to point at an airport about 10 miles away from my location. This did improve the reception of the ground stations a bit, but was still sketchy at best. In that setup; I did use 2 antenna's and two SDR receivers, one for the Yagi antenna, and one for the omnidirectional antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the end I gave up on trying to improve the reception of ground stations...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-05-09T08:13:39.643" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6169" PostTypeId="2" ParentId="6147" CreationDate="2016-05-09T15:28:21.040" Score="2" Body="&lt;p&gt;If you live in an urban environment, you'll want a scanner that can do trunking.  If you live in a rural environment, then you might not need trunking.  You'll want a scanner that allows you to give each channel a descriptive label.  Don't get a Baofeng ham walkie-talkie; they're very inexpensive, but they make lousy scanners.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't waste your time programming the scanner manually; use software (probably costs extra).  The software can help you research frequencies also.  Buy the scanner and program it, and spend at least a couple weeks playing with it so that you can explain how to use it to your mom.  You'll also want to learn the lingo that the public services use; it can be daunting at first, but there are web sites to help, and once you get the hang of it then it's not so cryptic.  Have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-05-09T15:28:21.040" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6170" PostTypeId="2" ParentId="6161" CreationDate="2016-05-09T16:01:41.583" Score="0" Body="&lt;p&gt;As Hamsterdave suggests, you could use a different antenna that has a lower SWR on 15m, or a remote antenna tuner.  You could also use an external antenna tuner in the shack, which would be lossier but perhaps more versatile.  You'd want one that can be entirely bypassed, because antenna tuners are inherently lossy, and you want to bypass it if you don't need it.  Automatic antenna tuners are certainly popular now, but manual tuners cost a lot less, and they aren't difficult to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;High SWR is bad for transmitters because it creates higher voltages or temperatures at the final amplifier stage.  If you reduce the output power, that of course reduces the voltage and temperature of the final amplifier stage, so your rig may be able to tolerate a higher SWR mismatch if you turn down the power, so you may not have a problem at all at 50 W.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-05-09T16:01:41.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6171" PostTypeId="2" ParentId="6161" CreationDate="2016-05-09T21:06:11.647" Score="0" Body="&lt;p&gt;The usual solution to autotuner problems is to change the length of the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try adding a half wavelength of coax, approx 5 m, to the antenna feed, and see if that helps. You could also try 2.5 or 7.5 m, anything about that long will have some impact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although the VSWR won't change much if you add a bit of cable, the impedance will change completely, from inductive to capacitive, from high to low, or vice versa. You will likely move from a spot where the tuner can't cope, to a better spot where it can match the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While you are at it, do you at least have a coil of coax or some other choke at the base of the G5RV? If not, it might help all bands to have 5 turns about 20-30 cm in diameter, right at the end of the ladder line.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2016-05-09T21:06:11.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6172" PostTypeId="2" ParentId="5028" CreationDate="2016-05-10T08:15:07.310" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;&lt;em&gt;But I want to get know what happen when the elements of the antenna are from outside and insulated from the metallic boom&lt;/em&gt;&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The characteristics of your antenna will change:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;code&gt;R&lt;/code&gt; component of &lt;code&gt;Z&lt;/code&gt; at &lt;code&gt;f&lt;/code&gt; will change&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;X&lt;/code&gt; component of &lt;code&gt;Z&lt;/code&gt; at &lt;code&gt;f&lt;/code&gt; will change&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;VSWR&lt;/code&gt; at &lt;code&gt;f&lt;/code&gt; will change&lt;/li&gt;&#xA;&lt;li&gt;Antenna Resonance &lt;code&gt;f(r)&lt;/code&gt; (where &lt;code&gt;X~~0&lt;/code&gt;) will change&lt;/li&gt;&#xA;&lt;li&gt;directivity/gain-plots, &lt;code&gt;-3dB angles&lt;/code&gt;, will change&lt;/li&gt;&#xA;&lt;li&gt;front/back ratio will change&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;How much all this is changing is cannot be determined unless a lot of very precise detail is documented, and complex simulations are ran. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even then these would be simulations, as the real numbers are actually dependent on the  mounting, height, and other environmental factors.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-05-10T08:15:07.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6173" PostTypeId="1" AcceptedAnswerId="6175" CreationDate="2016-05-11T01:05:24.240" Score="9" ViewCount="358" Body="&lt;p&gt;Is this a recognized SDR technique with a name, or is just a combination of DSP, r/f techniques ?&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;I asked the author, but didn't receive an answer, perhaps because he thought it was &amp;quot;obvious&amp;quot; (not to me, though, an SDR / electronics newbie)&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://forums.parallax.com/discussion/105674/hook-an-antenna-to-your-propeller-and-listen-to-the-radio-new-shortwave-prog/p4&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://forums.parallax.com/discussion/105674/hook-an-antenna-to-your-propeller-and-listen-to-the-radio-new-shortwave-prog/p4&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;See the third post down by Phil Pilgrim  &amp;quot;Attached is a set of traces that may help to explain what's going on in the receiver. .....&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;Is this some modified form of Sigma Delta ADC ? :&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;If we were using this counter as an ADC, we could set its FRQx to 1 and let it count the number of 1s it sees on A3 in a given interval. This count would be proportional to the average signal strength on A3 during that interval. But we're not going to do that. Instead, all we need is that string of 0s and 1s on pin A4. This is shown as signal &amp;quot;ADC&amp;quot; in the middle of the attached image, in magenta.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;More info on the project is in the first post here :&lt;/p&gt;&#xA;&lt;h1&gt;&lt;a href=&quot;http://forums.parallax.com/discussion/105674/hook-an-antenna-to-your-propeller-and-listen-to-the-radio-new-shortwave-prog/p1&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://forums.parallax.com/discussion/105674/hook-an-antenna-to-your-propeller-and-listen-to-the-radio-new-shortwave-prog/p1&lt;/a&gt;&lt;/h1&gt;&#xA;&lt;p&gt;*Now that I've got your attention, here's the theory behind it. Most consumer radios on the market are superheterodynes. In such receivers, the incoming RF signal is &amp;quot;mixed&amp;quot; with a sinewave coming from a tunable local oscillator (LO).&lt;/p&gt;&#xA;&lt;p&gt;Mixing is basically analog multiplication, which produces, in addition to the original RF and oscillator signals, signals which are at both the sum and difference frequencies of the two. The output of the mixer is filtered to a single, fixed, &amp;quot;intermediate frequency&amp;quot; (IF) and then amplified. In AM (amplitude modulation) broadcast radios, which tune from 550KHz to 1600KHz, the IF is usually at 455KHz. So, by varying the frequency of the local oscillator from 1005KHz to 2055KHz, one can obtain a 455KHz difference signal from the mixer for the entire broadcast band. The output of the IF amplifier is then introduced to a &amp;quot;detector&amp;quot;, which rectifies and low-pass filters the IF signal to produce an audio waveform.&lt;/p&gt;&#xA;&lt;p&gt;A receiver similar to the superheterodyne is the direct conversion receiver. In such a receiver the &amp;quot;intermediate frequency&amp;quot; is zero. In other words, the LO is tuned to the exact frequency you want to listen to, and the difference signal is simply the detected audio, which can then be lowpass filtered and amplified. But there's a catch: the local oscillator must not only have the same frequency as the desired signal, it must also have the same phase. To understand this, suppose the incoming RF carrier and the LO were 90° out of phase with each other. When multiplied together, these two signals would effectively cancel each other out, and you'd hear nothing. When they're in phase, the positive swings would multiply, returning positive results, and the negative swings would multiply, also returning positive results. But getting the LO to lock onto an incoming carrier can be tricky — especially if that carrier is weak.&lt;/p&gt;&#xA;&lt;p&gt;One way around this is to have two LOs, 90° out of phase with each other, and two mixers. The idea is, what one LO oscillator misses by having the wrong phase, the other will catch. In fact, the outputs from the two mixers can be combined in such a way that the actual LO phases are irrelevant, so long as they're 90° apart. The formula for doing so is:&#xA;····Audio Amplitude = sqrt(I2 + Q2),&#xA;where I is the output of one mixer (from the &amp;quot;In-phase&amp;quot; LO), and Q is the output of the other mixer (from the &amp;quot;Quadrature-phase&amp;quot; LO).&#xA;Well, that's enough theory to lay the groundwork for the Propeller receiver. I've really glossed over a lot of stuff, but this is a forum post, not a book, and I want to get to the actual hardware and software.*&lt;/p&gt;&#xA;&lt;p&gt;*APPLICATION&#xA;The use of a Propeller counter as the basis for an analog-to-digital converter (ADC) is now well-established. So why not simply attach an antenna to the input of one of these ADCs and see what comes out? Basically, that's what I've done. Here's a schematic:&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/J9k5N.gif&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;The antenna (a wire strung across the ceiling of my shop) is connected, through an inductor to both digital ground and earth ground. I used a 330uH power inductor I found in my junkbox. It actually worked better than the ferrite antenna scavenged from a cheap transistor radio. A bunch of enameled wire wound on a plastic sewing machine bobbin worked almost as well, too. I'm sure Beau Schwabe (i.e &amp;quot;He Who Understands Inductors and Knows What to Do with Them&amp;quot;) can shed a lot more light on the choice of inductors and why one is needed here. I just grabbed what I had until I found something that worked. My &amp;quot;earth ground&amp;quot; consists of the ground clip from my scope attached to the ground stud on the Demo Board. My scope input return ground and its AC protective ground are connected together, thence back to the breaker box and to a metal grounding rod. (By the way, I live in a fringe area for AM reception. If you live in a city with strong AM transmitters, you may not have to go to all this trouble.)&lt;/p&gt;&#xA;&lt;p&gt;The antenna also connects, through a capacitor, to pin A3 of the Propeller. This is the &amp;quot;analog&amp;quot; input terminal. The feedback comes from A4 through a 470K 0805 SMD resistor, which I soldered between pins A3 and A4 right on the chip itself. I've omitted the usual filter caps to Vdd and Vss (Gnd), choosing instead to let the inherent input capacitance of A3 do the filtering. This keeps both the input impedance and frequency response of the ADC high, which is necessary for detecting weak RF signals. During positive swings of an incoming signal, A4 will be sending more 0s than 1s to counterbalance it; during negative swings, more 1s than 0s. One counter can do this, set up in the &amp;quot;positive-with-feedback&amp;quot; special analog mode. Unlike the usual ADC usage, though, we're never going to read this counter again. It's just that string of 1s and 0s fed back from A4 that we're interested in.&#xA;I love the Propeller's counters! I don't know if Chip knew what all could be done with them when he designed them, or if he just had an inkling that, with the right set of features, almost anything could be accomplished. In any event, the counters make ideal local oscillators and mixers! The oscillator part is pretty easy: just configure two counters as numerically-controlled oscillators (NCOs) in quadrature with each other. The frequency will be the frequency of the station you want to tune in. So, if I want to receive KIXI 880 in Seattle, I set up both counters to output 880KHz square waves, 90° out of phase with each other (i.e. PHSB = PHSA + $4000_0000).&lt;/p&gt;&#xA;&lt;p&gt;Now comes the magic part: the mixers. The counters can be configured to count up whenever two inputs satisfy a Boolean conditional. The Boolean equation can be anything you want: AND, OR, NAND, NOR, XOR, you name it. I used XOR. Each &amp;quot;mixer&amp;quot; counter gets two inputs: the feedback from A4 and one of the LO outputs. If the LO output is low when A4 is feeding back 1s, predominantly (i.e. when the antenna signal is low), the counter will count up at a fast clip. Likewise, if LO is high when A4 is feeding back 0s, predominantly, the counter will, again, count up at a fast clip. In other words, the counter will count up faster when an incoming RF signal is in phase with the LO than when it's not. Moreover, the rate at which it counts up will be proportional to the amplitude of that signal. So, to read the amplitude of a signal in phase with the LO, one need only zero the mixer counter, wait awhile, then read it to see how far up it counted. On average, there will be as many increments during the sample period as non-increments, so the mean (average) count will be half the number of system clocks occurring during the same period. Any signal that's out of phase with LO, or of a different frequency, will contribute as many increments as non-increments, thus having no effect on driving the net count away from the mean.&lt;/p&gt;&#xA;&lt;p&gt;Therefore, after each sample period, we can subtract the actual count from the mean count to get the instaneous amplitude of the signal. By doing this for both the I mixer and Q mixer, squaring the individual amplitudes, adding them, and taking the square root, we get the signal's amplitude, which can then be fed to the audio output: another counter in DUTY mode, feeding a lowpass filter. (I used A10 on the Demo board, which has the filtering hardware already in place.)&lt;/p&gt;&#xA;&lt;p&gt;The length of the sample period will affect two things: the audio frequency response and the signal-to-noise ratio. Like most things in life, each of these two desirable qualities increases at the expense of the other, so you have to strike a balance. I got the most pleasing results with a 16KHz sample rate, which yields an 8KHz audio bandwidth. This is about as good as AM radio audio can get anyway, since the stations are spaced 10KHz apart. You can lower the sampling rate to get less static, but the audio starts to sound more &amp;quot;boomy&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;SUMMARY&lt;/p&gt;&#xA;&lt;p&gt;To summarize, the receiver uses six counters (spread over four cogs), as follows: (1) ADC (actually just a digitizing RF amplifier), (2) Local Oscillators in quadrature, (2) Mixers, and (1) Audio Output&#xA;The counters do virtually all the work. There's not a lot of code required, outside of setting up the counters, reading them, and shuffling data between them via the hub. The attached program is configured as a scanner for the AM broadcast band. It increments continuously by 10KHz steps from 550KHz to 1600Khz, pausing at each frequency for three seconds, which is long enough to tell if something's there. It displays the frequency on a TV monitor, via tv_wtext (included). I've also used it for LF reception below the broadcast band with some minor success. As I stated in the intro, it's not a very good receiver — in fact it sounds pretty crappy and noisy. If, like me, you live in a fringe area, you may be disappointed by its performance. But, even then, it does illustrate the capabilities of those amazing Propeller counters. And that, really, was the main point.&#xA;-Phil&lt;/p&gt;&#xA;&lt;p&gt;Update: Owing to advice received from Beau Schwabe, based on his own testing, I've changed some component values. The inductor is now 500uH; the feedback resistor, 10M; the coupling cap, 0.047uF; and the antenna, a 2-meter-long vertical wire. The attached schematic reflects these changes, which did lead to an improvement in performance.*&lt;/p&gt;&#xA;" OwnerUserId="6337" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-12-31T15:39:49.213" Title="Is there a name for the demodulation technique described here using the parallax propeller?" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="6174" PostTypeId="2" ParentId="32" CreationDate="2016-05-11T03:18:59.657" Score="2" Body="&lt;p&gt;i like QRQ (Mac) or RUFZ (Linux) - and whilst they are both designed for high speed CW contests - they are adaptive. You get the call sign correct it goes faster, get it wrong and it goes slower... Which is just what the poster requested. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It does however assume that you know the code already - there is no punctuation in it (except '/') and there are also no &lt;strong&gt;prosigns&lt;/strong&gt; (SK, AR, CL, KN etc). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Very addictive - with each set of 50 calls taking &amp;lt; 5 mins. I try and do 1 or 2 rounds when I have a few minutes spare.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2016-05-11T03:18:59.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6175" PostTypeId="2" ParentId="6173" CreationDate="2016-05-11T15:12:45.223" Score="6" Body="&lt;p&gt;Very interesting (and clever)!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jd7u9.gif&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jd7u9.gif&quot; alt=&quot;block diagram&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, the first counter is being used as a delta-sigma modulator to turn the incoming analog signal into a high-speed string of bits. Then the counters generating the I and Q signals are defining the lower-speed sample rate. Two other counters (labeled &quot;mixer&quot;) are essentially integrating (i.e., low-pass filtering) the high-speed sample data for each output sample period.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the high-speed sample rate is 80 MHz, and the carrier frequency is on the order of 1 MHz, the output samples are counts in the range of 0 to 79, roughly 6 bits of resolution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the sample rate of the output is equal to the carrier frequency, this creates a direct-conversion receiver. The sample clock serves the same function as the local oscillator in an analog receiver. In digital terms, the carrier, along with its sidebands, is being deliberately aliased down to DC, which means that the sidebands become the audio that you can hear. The low-pass filtering of the output (partly in the integrators, and partly in the analog output connection) determines the bandwidth that is being received.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2016-05-11T15:12:45.223" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6176" PostTypeId="2" ParentId="5106" CreationDate="2016-05-11T21:04:08.817" Score="4" Body="&lt;p&gt;Ideally, it doesn't matter where on the constant VSWR circle you are. The transmitter is an ideal voltage source with 0Ω impedance, essentially a short. There's no way to couple power into a short, so whatever power is reflected from the antenna gets reflected back when it reaches the transmitter, so all you need to worry about is the impedance presented to the transmitter, and what effect that will have on the current required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But transmitters are rarely just a voltage source. Usually they have filters at the output to strip off the harmonic distortion created by the amplifier. Even a linear class AB amplifier will generate a little harmonic distortion, enough to require a filter to avoid spurious emissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The filters are designed with a 50Ω load assumed. Since they are passive filters, loading them differently will change the frequency response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's look at the &lt;a href=&quot;http://openhpsdr.org/support/Alexiares/ALEX-P1.1.4-TX%20Sch.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;schematics for the Alex-TX board of HPSDR&lt;/a&gt; for an example. Here's the 20/30m transmit filter. R1 isn't part of the filter, but the impedance seen by the transmitter, which we will vary.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/rgABA.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2frgABA.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the power dissipated in R1 (that is, RF power radiated) as a function of frequency. Shown is what happens at 5, 50, and 500 ohms, normalized to the power that would be expected at a given voltage into a 50Ω load:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VkTjr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VkTjr.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The orange line is a 50Ω load. You can see the filter makes a good low-pass filter, with a steep cutoff above the 20 meter band, effectively suppressing harmonic distortion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, look at the peaks and valleys introduced by the mismatch. One of those peaks in the 5Ω case is at 14 MHz, so on 20 meters it looks like you get an extra 10dB of transmit power with this particular filter and load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That might seem like a good thing, but that power isn't free: it comes from your transmitter. That means the transmitter will be asked to deliver a lot more current, and probably overheat if it lacks appropriate protection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reactive 10:1 SWR cases fall around (9±49j)Ω. Unfortunately, CircuitLab doesn't provide a way to model a complex impedance, but it's basically the same, except the peaks and valleys fall in different places.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's another issue as well: since the filter is made of resonant, reactive components, there is a potential for very high currents or voltages to develop in there if you start messing with the load impedance. So although in these 10:1 conditions the power in the transmitter and the load are identical to the 1:1 case, that doesn't mean the current and voltages within the filter are the same. High currents will overheat or saturate inductors, and high voltages will arc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to answer your question, there usually is a transmission line length which will spin the impedance around to one that will allow the transmitter to deliver full power without overheating. But in practice we don't know the details of the transmitter's design, so there's not really a way to know what that length is.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-05-11T21:04:08.817" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6178" PostTypeId="1" CreationDate="2016-05-12T00:32:42.270" Score="2" ViewCount="107" Body="&lt;p&gt;It is resonate for 22 Mhz haven't had any luck tuning it for 30 Mhz  it is an excellent antenna I feel at the Z is 0 for 22 Mhz  I have given up and think I will just buy a Imax 2000 w/ radials??&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;10 meter&quot; I attempted to build a 1/4 antenna with 8 ground radials 4 feet long with 1/4 wave length of copper coiled around them and are sloped down 55 degrees&lt;/p&gt;&#xA;" OwnerUserId="6670" LastEditorUserId="76" LastEditDate="2016-05-13T22:16:50.570" LastActivityDate="2016-05-13T22:16:50.570" Title="tuning trouble - 1/4 wave 8 elevated ground radials 10 meter" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6179" PostTypeId="2" ParentId="6178" CreationDate="2016-05-12T02:46:59.960" Score="1" Body="&lt;p&gt;From your description, it sounds as if your radials are basically a long inductor, with a resonant 1/4 wave of wire (8'ish) coiled around a noncondcutive form that's much shorter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that's the case, it won't work as is, as you're making the radials electrically longer than 1/4 wave. Basically you've added loading coils to them. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because of this, the radials aren't presenting a low impedance, so the characteristic impedance is off for the whole antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Test it with straight 1/4 wave wire radials. If it tunes, your radials are the problem. You'll need to make them even shorter to get them to resonate on 28MHz with the extra loading.   &lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-05-12T02:46:59.960" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6180" PostTypeId="1" AcceptedAnswerId="6183" CreationDate="2016-05-12T13:07:44.593" Score="1" ViewCount="285" Body="&lt;p&gt;I am looking for ideas to improve my Impedance measurements I perform on my VLF antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to circumstances my VLF experiments are usually &quot;on location / in a field&quot; so I do not have the luxury of a fully stacked workbench.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The setup I have is:&#xA;- a function generator - 4000 Hz output&#xA;- an audio amplifier&#xA;- feedline&#xA;- Antenna&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I consider the feedline part of the antenna system, and I use the following method of determining the Impedance of the antenna system:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Measure the open output voltage of the Amplifier = Vopen&lt;/li&gt;&#xA;&lt;li&gt;Measure the output voltage with a known load (Rload=1000) = Vload&lt;/li&gt;&#xA;&lt;li&gt;Calculate the output impedance of the amplifier Rout = Rload * ((Vopen/Vload)-1)&lt;/li&gt;&#xA;&lt;li&gt;Measure the output voltage with the antenna system = Vant&lt;/li&gt;&#xA;&lt;li&gt;Calculate the antenna system impedance Rant = Rout / ((Vopen - Vant)-1)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I would repeat this process with multiple values of Rload to ensure measurements are accurat; usually I use the following values: 1000 Ohm and 2400 Ohm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This way I can determine/tune the antenna system to come as close to 8 ohm impedance which the amplifier wants to see.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) is this method correct ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) are there better methods given the limitation of being &quot;on location&quot; ?&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-05-13T07:56:39.117" LastActivityDate="2016-05-13T17:48:53.727" Title="Rudementary Impedance measurements for VLF antenna system" Tags="&lt;impedance&gt;&lt;measurement&gt;&lt;vlf&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6181" PostTypeId="2" ParentId="6180" CreationDate="2016-05-12T15:38:00.993" Score="3" Body="&lt;p&gt;Your method only crudely measures the magnitude of the feedline impedance, without taking into account the fact that it is probably a complex value, with a phase shift between voltage and current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the output impedance of most modern audio power amplifiers is very low &amp;mdash; usually way less than an ohm. I'm surprised that you get any useful answers by testing it with 1000&amp;Omega; and 2400&amp;Omega; load resistors. The goal here is not to &lt;em&gt;match&lt;/em&gt; the output impedance of the amplifier, but rather to maximize the power delivered to the antenna without exceeding the amplifier's capability to deliver current (i.e., without driving it into clipping). When an amplifier is &quot;rated for&quot; 4&amp;Omega; or 8&amp;Omega; or whatever, it simply means that its voltage output and current output capabilities both max out at about the same time with loads in that range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be far more interesting to take a portable 2-channel oscilloscope (e.g., a USB device plugged into your laptop) and a current probe along on your field trip so that you can simultaneously measure both the voltage and current at the feedline input &amp;mdash; and also do an instantaneous power calculation, assuming that your scope has the appropriate math features.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2016-05-12T15:38:00.993" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6182" PostTypeId="2" ParentId="6160" CreationDate="2016-05-12T17:28:30.123" Score="3" Body="&lt;p&gt;&lt;em&gt;Since writing this answer, I've learned this explanation isn't entirely accurate. I'm leaving it because it's not entirely wrong, either.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ultimately, it is impedance mismatch (really, too low an impedance) that damages transmitters. The thing to realize is the impedance seen by the final power transistors in the amplifier (the part that usually breaks) isn't the same impedance at the amplifier's terminals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is that amplifiers contain filters on their output to filter harmonic suppression, among other things. These filters are designed with the assumption of a 50Ω resistive load. When that assumption holds, the filter presents the design impedance to the finals, which the designer has determined will not smoke the transistors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the load is not 50Ω, the design conditions are violated and the impedance presented to the finals could be anything. If you get lucky, it will be a high impedance which just means the amplifier can't deliver its full rated power. If you get unlucky, it's a low impedance which draws too much current and overheats the transistors. It's hard to predict where you will get lucky, and where you will get unlucky without knowing the details of the transmitter's filters. Here's an example from &lt;a href=&quot;https://ham.stackexchange.com/questions/5106/is-there-an-optimum-transmission-line-length-for-maximum-power-transfer/6176&quot;&gt;Is there an optimum transmission line length for maximum power transfer?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VkTjr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VkTjr.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a 30/20m filter, so it is intended to pass up to about 14.4 MHz and attenuate all the higher harmonics of that. The orange line shows the case where there's a matched 50Ω load, while the blue and tan lines show  500Ω and 5Ω loads which are two cases of a 10:1 SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how the mismatch introduces peaks in the frequency response. Where these peaks are above the orange line, the amplifier is seeing a lower impedance, thus a higher current and more power. Here's the potential for damage. One of those blue peaks is right at 14 MHz and is about 10dB above the orange line. So on 20 meters, a 100W amplifier is suddenly trying to produce 1000W into a low impedance, which will quickly damage it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are any number of impedances which will result in a 10:1 SWR, and depending on the transmission line you might get any of them. I suggest checking out a &lt;a href=&quot;http://www.fourier-series.com/rf-concepts/smithchart.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Smith chart tutorial&lt;/a&gt; to get familiar with how this works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why SWR is used to quantify the quality of the match: it is independent of transmission line length. For any given SWR, the height of those peaks in the graph above are about the same, and moving around different impedances with the same SWR just changes where they lie. Since you really don't know where they lie in practice, it's just best to avoid high SWR generally.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-02-14T02:10:45.137" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6183" PostTypeId="2" ParentId="6180" CreationDate="2016-05-12T22:26:09.717" Score="4" Body="&lt;p&gt;At 4 kHz you could use your laptop as a rudimentary two-channel oscilloscope.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First find out if it has a useful two-channel input sound card, and find a way of recording a stereo 16-bit WAV and processing it. Octave or Python would work, or you could write your own.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then build a circuit like this, adjusting parameters to suit:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/zOWkj.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fzOWkj.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've chosen to float the laptop and measure current in the live wire, as the laptop is the most likely part of the circuit to be battery powered. Keep the laptop away from the ground and don't connect anything else to it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you may see a graph of Voltage (R) and Current (L) like this:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/oTHGQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oTHGQ.png&quot; alt=&quot;In Phase&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;Meaning your load is purely resistive, or like this:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/MQ0Sf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MQ0Sf.png&quot; alt=&quot;Capacitive&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;Meaning your load is purely capacitive, or like this:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/JvMr8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JvMr8.png&quot; alt=&quot;ComplexLoad&quot;&gt;&lt;/a&gt;&#xA;Which will give both the magnitude and phase relationship of the voltage and current, allowing you to measure your antenna impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should probably calibrate the whole thing - try it out with a 1k resistor instead of the antenna, and check voltage/current readings, then try a modest capacitor and check that you get the right impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've used this method with a high speed 'scope, to measure an unknown impedance at 500 MHz. Results were within 10% of the network analyser figures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PS. For an 8-ohm source and antenna, you'll need a much smaller current sense resistor, perhaps 0.1 ohms. I was still thinking of higher impedances.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2016-05-13T17:48:53.727" LastActivityDate="2016-05-13T17:48:53.727" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6184" PostTypeId="1" CreationDate="2016-05-13T19:42:25.877" Score="7" ViewCount="589" Body="&lt;p&gt;An answer on this question &lt;a href=&quot;https://ham.stackexchange.com/questions/2010/suggested-method-for-boosting-0-05-watt-transmitter-up-to-10-watts&quot;&gt;Suggested method for boosting 0.05 watt transmitter up to 10+ watts?&lt;/a&gt; suggests putting a filterless 19dB amplifier between the HackRF (or similar general-purpose SDR) and a larger amplifier — so only the final stage includes much in the way of filtering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is some caution warranted here for spurious emissions?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as I can tell, the &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/Tips-and-Tricks#sampling-rate-and-baseband-filters&quot; rel=&quot;nofollow noreferrer&quot;&gt;HackRF's own filters&lt;/a&gt; are &lt;em&gt;before&lt;/em&gt; (from a transmit perspective) its RF amplifier stage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The project's &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/Hardware-Components#block-diagrams&quot; rel=&quot;nofollow noreferrer&quot;&gt;block diagrams&lt;/a&gt; aren't very helpful in this regard, but &lt;a href=&quot;http://www.wimo.com/hackrf-sdr_f.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.wimo.com/hackrf-sdr_f.html&lt;/a&gt; has a detailed write up (&quot;After the antenna input two MGA-81 GaAs MMIC amplifiers follow, one serves the input, the other the output path.&quot;) and provides this frontend block diagram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/lXB9H.png&quot; alt=&quot;HackRF frontend block diagram showing MGA81563 amplifier chips as the last step before antenna output&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So after its filtering, the HackRF adds a +14dB gain of its own. After which, we might add something like the &lt;a href=&quot;http://www.tapr.org/kits_pw.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;PennyWhistle&lt;/a&gt;, &lt;a href=&quot;http://www.qsl.net/in3otd/ham_radio/QRPPA2008/QRPPA2008.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRP-PA 2008&lt;/a&gt; or &lt;a href=&quot;http://preview.sitebuilder.com/extern/ecwid-app/ecwid.html?wzId=id1448850183778&amp;amp;wzInstanceId=id1448850183778&amp;amp;wzAppId=ecwid_app&amp;amp;wzAppV=1&amp;amp;wzApiType=app&amp;amp;wzDeviceType=desktop&amp;amp;wzMode=view&amp;amp;storeId=7649462&amp;amp;categoriesPerRow=3&amp;amp;categoryView=grid&amp;amp;tableNumber=20&amp;amp;listNumber=10&amp;amp;gridColumnNumber=4&amp;amp;gridRowNumber=3&amp;amp;wzEncodeParams=eyJ3ekN1cnJlbnRVcmwiOiJodHRwOi8vd3d3LmhmcHJvamVjdHMuY29tLyMhL1NEUi1QUkVBTVAtTU9ERUwtUEEtMTAwLTEwMG13LXRvLTVXLXByZWFtcC1uby1MUEYtRElZLXByb2plY3QvcC81Nzc1OTM5MS9jYXRlZ29yeT0wIiwid3pTaXplIjp7IndpZHRoIjo5NjAsImhlaWdodCI6MTU4NH19#!/SDR-PREAMP-MODEL-PA-100-100mw-to-5W-preamp-no-LPF-DIY-project/p/57759391/category=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;PA-100&lt;/a&gt; to boost the SDR's still-small signal closer to the 5W range — something like another 15–25dB further gain. Finally we might put this through something like the &lt;a href=&quot;http://preview.sitebuilder.com/extern/ecwid-app/ecwid.html?wzId=id1448850183778&amp;amp;wzInstanceId=id1448850183778&amp;amp;wzAppId=ecwid_app&amp;amp;wzAppV=1&amp;amp;wzApiType=app&amp;amp;wzDeviceType=desktop&amp;amp;wzMode=view&amp;amp;storeId=7649462&amp;amp;categoriesPerRow=3&amp;amp;categoryView=grid&amp;amp;tableNumber=20&amp;amp;listNumber=10&amp;amp;gridColumnNumber=4&amp;amp;gridRowNumber=3&amp;amp;wzEncodeParams=eyJ3ekN1cnJlbnRVcmwiOiJodHRwOi8vd3d3LmhmcHJvamVjdHMuY29tLyIsInd6U2l6ZSI6eyJ3aWR0aCI6OTYwLCJoZWlnaHQiOjE1ODR9fQ%3D%3D#!/HF-PackerAmp-V4R6-Kit-all-the-parts-you-need-are-supplied/p/57436769/category=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;HF-Packer&lt;/a&gt; or &lt;a href=&quot;https://www.hobbypcb.com/products/hardrock-50-hf-power-amp&quot; rel=&quot;nofollow noreferrer&quot;&gt;HARDROCK-50&lt;/a&gt; amplifier which provides another ~10dB gain, before the signal finally getting filtered again by that amp's LPF section.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is all this gain going to add more spurious emissions than the power amplifier's LPF section is likely designed to handle? I've been told that one really should filter after every stage of amplification, but in this setup the signal goes through three stages before filtering. Perhaps the &quot;pre-amp&quot; stages are much easier to keep clean/linear, or is that a bit too optimistic?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How could I use the specifications for each of the pre-amp stages to determine all the expected types and levels of spurious emissions they are adding? Do these harmonics compound from one stage to another, i.e. if the input to the external pre-amp is already not clean how do I take that into account when calculating the distortion it will add?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2017-08-08T02:07:07.743" Title="How to calculate if low-pass filtering is sufficient?" Tags="&lt;diy&gt;&lt;software-defined-radio&gt;&lt;amplifier&gt;&lt;filter&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6185" PostTypeId="1" AcceptedAnswerId="6187" CreationDate="2016-05-13T20:35:10.070" Score="5" ViewCount="724" Body="&lt;p&gt;I have a small collection of &quot;software defined RF lab&quot; equipment, notably a &lt;a href=&quot;https://greatscottgadgets.com/hackrf/&quot;&gt;HackRF&lt;/a&gt; and a &lt;a href=&quot;http://sdr-kits.net/VNWA3_Description.html&quot;&gt;VNWA3&lt;/a&gt;. I am almost done building a 35W HF amplifier and once I've done some other testing, would like to look at the spectrum of the final output as a whole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most natural tool for this job would be a spectrum analyzer, of course, but any of my SDR receivers and/or the VNA should be able to handily gather spectrum data as well. The trouble is: all of my equipment is rated for input in the ballpark of 0dBm, i.e. milliwatts or less. It looks like even a &quot;real&quot; spectrum analyzer like the entry-level &lt;a href=&quot;https://www.rigolna.com/products/spectrum-analyzers/dsa800/dsa815-tg/&quot;&gt;Rigol DSA815-TG&lt;/a&gt; has input rated around +20 dBm (100 milliwatts).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In preparation for another project where I want to diagnose a ~5W signal, I bought a handful of SMA attenuators. The larger dB-drop ones have heat sinks and are rated at 5W — so I should be able to connect my &quot;device under test&quot; for this other project directly to my equipment through the attenuators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But how would one go about measuring the spectrum of a 35W signal? Or 1500W and beyond for that matter! I could be mistaken, but I get the impression that that inline attenuators are NOT a common method past a certain power level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How are high-power signals typically measured in a professional RF lab setting? How might I go about characterizing my signals with more typical amateur operator equipment? Say, between my amp and a dummy load and an SDR, what's a good way to connect/couple them so that I can get a known — or at least &quot;known-to-be-safe&quot; — signal level into some spectrum analysis software?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-05-16T14:41:08.850" Title="Recommended way to analyze spectrum output of a high-power amplifier?" Tags="&lt;amplifier&gt;&lt;measurement&gt;&lt;equipment-protection&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6187" PostTypeId="2" ParentId="6185" CreationDate="2016-05-14T01:55:34.303" Score="6" Body="&lt;p&gt;Professional-level dummy loads generally have a &quot;sampling&quot; port that provides a reduced level signal for analysis. You should be able to create something similar.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2016-05-14T01:55:34.303" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6188" PostTypeId="2" ParentId="6185" CreationDate="2016-05-14T06:58:18.353" Score="0" Body="&lt;p&gt;I have used SDR equipment for measurements, and build a little &quot;fuse box&quot; with  two 100mA fuses inside the box (both center as coax shield).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This little box will change impedance, and is not truly 50 Ohm (and I did not spend the time to make it 50 Ohm)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use this box as well on receivers close to TX antenna's where I want to test, but want to avoid blowing anything up in the front end of the receiver, once satisfied that I can remove the fuse box, I remove it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few years ago I blew one of the fuses... not sure what went wrong, but I am glad it was only a fuse. As well as proving that the fuse box worked!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-05-14T06:58:18.353" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6189" PostTypeId="2" ParentId="6185" CreationDate="2016-05-15T02:44:09.330" Score="2" Body="&lt;p&gt;As Dave Tweed says, professionals have equipment for exactly this. But since you are asking I bet you don't have that equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you just want something on the cheap, transmit into a dummy load at full power and put the receiver nearby. There's enough &quot;accidental&quot; coupling you can probably hear the transmitter even without an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The trouble with this is it's not calibrated or reproducible at all, which is important in a professional context. However if you just need to see a spectrum, and you don't need to make accurate quantitative measurements, it's probably good enough.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-05-15T02:44:09.330" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6190" PostTypeId="1" CreationDate="2016-05-15T04:57:30.080" Score="1" ViewCount="192" Body="&lt;p&gt;I have a remote base where stations can log in with DTMF touch pad.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this remote base transmitter need to send out a CW ID?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2017-04-16T15:00:02.233" LastActivityDate="2017-04-16T15:00:02.233" Title="Remote base identification" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;remote-control&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6191" PostTypeId="1" CreationDate="2016-05-15T14:43:26.417" Score="1" ViewCount="232" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WNyHU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WNyHU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a red circle in the picture, What does 1700 number means?&#xA;When I change it to another value seems like it can not decode APRS sound. So what is it(1700 in textbox after ChA label)?&lt;/p&gt;&#xA;" OwnerUserId="6686" LastActivityDate="2016-05-15T14:54:43.443" Title="What is 1700 in SoundModem by UZ7HO?" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6192" PostTypeId="2" ParentId="6191" CreationDate="2016-05-15T14:54:43.443" Score="1" Body="&lt;p&gt;I'm not familiar with the SoundModem program, but APRS uses an AFSK modulation which switches between two tones at 1200 Hz and 2200 Hz. 1700 Hz is exactly halfway between those.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore I would guess that it's setting the demodulator's threshold for discriminating between the two tones. You would change it if you are decoding packets that differ from the APRS standard.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-05-15T14:54:43.443" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6193" PostTypeId="2" ParentId="6190" CreationDate="2016-05-15T18:33:55.610" Score="3" Body="&lt;p&gt;I believe that according to §97.3, logging in to a remote base through the Internet is considered remote control.  Therefore, the amateur logging in is the control operator, and the normal identification rules apply.  The base does not need to identify separately.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, if there's a repeater linked in to the system, such that transmissions are automatically rebroadcast on a different frequency, I think that repeater would need to auto-identify as per usual.  &lt;a href=&quot;http://www.w3beinformed.org/id43.html&quot; rel=&quot;nofollow&quot;&gt;This site&lt;/a&gt; also indicates (search for 'remote base' within that page) that you'd need to approve this entire setup (a remote base accessed through an otherwise publicly-available repeater) with your local frequency coordinator.&lt;/p&gt;&#xA;" OwnerUserId="6446" LastActivityDate="2016-05-15T18:33:55.610" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6194" PostTypeId="2" ParentId="6185" CreationDate="2016-05-16T14:41:08.850" Score="3" Body="&lt;p&gt;As answers already posted show, there are a variety of solutions to this problem.  But, a very simple one is an old timer ham radio operator's &quot;trick&quot;.  Popular back in the late 1950s and 1960s as &quot;the only way&quot; to hook up an oscilloscope (which also usually had low power input needs) to a high power amplifier was to use a regular PL-259 coaxial connector.  You snip off the center conductor pin from the male plug (it doesn't hurt too much if you do it fast) and then hook up to the output of your amplifier.  You do not screw the PL-259 all the way in but fiddle with it to get just the right signal pickup to drive your measuring device.  It capacitively couples with the source.  Works quite nicely but I do admit to never having done it with power as low as 35 watts.  Usually I have had 1000 to 1500 watt amplifiers feeding my oscilloscope.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-05-16T14:41:08.850" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6195" PostTypeId="1" CreationDate="2016-05-16T15:54:46.363" Score="1" ViewCount="145" Body="&lt;p&gt;In his book &quot;Crystal Sets to Sideband&quot;, Frank Harris K0IYE describes using premix oscillators (PMOs) to convert signal from low-frequency LO to a particular ham band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many ham bands are harmonically related, so it could be possible to substitute separate crystal oscillators for each ham band with one high frequency crystal oscillator (say, for 10m band) and some kind of frequency divider(s) to generate frequencies for 20m, 40m, 80m and 160m. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet I've never seen anything like that. Are there any problems with this scheme?&lt;/p&gt;&#xA;" OwnerUserId="6691" LastEditorUserId="6691" LastEditDate="2016-05-16T16:17:11.470" LastActivityDate="2016-05-22T11:37:40.153" Title="Frequency divider in premix oscillator (PMO)" Tags="&lt;diy&gt;&lt;oscillator&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6196" PostTypeId="1" CreationDate="2016-05-16T21:06:39.000" Score="2" ViewCount="890" Body="&lt;p&gt;I just passed both my Technician and General Class license this past weekend, and am now contemplating my first station. To get my feet wet I'm planning on getting a Yaesu FT-7900R Dual band Radio with a yet to be named power supply (probably a Samlex SEC 1223). I plan on installing a DBJ-1 from Ed Fong. He has stated to me: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The antenna is DC grounded so no lighting arrestor is needed.  All you need to do is to make sure the shield is grounded (which I assume it is from the power supply).  Nothing will protector your antenna from a lightning strike.  So yes, if you see a storm coming it would be advised that you disconnect the antenna from you radio. All a lightning arrestor does is to DC ground the antenna which protects your radio with high voltage spikes induced by the lighting.  Our antenna is a DC ground antenna so it already does that.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I plan to operate in this manner for about 6 months or so until I can get my first HF rig. I am setting up my &quot;shack&quot; in a bedroom on the west wall of my house where there is a window and an input for my Fios TV cable comes in from the outside there also.  I want to make sure that my station is properly grounded for the current configuration but also for my future expansion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Outside the wall, there's about 8' to the neighbor's wooden fence, and a fairly big tree on the other side. So I won't be able to just go straight up to the roof with my antenna. I live in North Texas, in the Northwest part of Dallas County, so during the April-May time of year we do get our share of severe thunderstorms with lightning and hail, though in 30 years we've never taken a hit around our area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would you suggest that I do to begin a good grounding system? I do have a computer that I'll be using, the power supply, the FT-7900R and that's pretty much it. I have a surge protector that's plugged into my home 3-wire socket.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have SOME room outside, but not all that much but I COULD drive copper rods close to the house if need be. I've ready all about these very elaborate grounding systems, and I'm honestly not sure I have the room for all those things at my house!&lt;/p&gt;&#xA;" OwnerUserId="6696" LastEditorUserId="76" LastEditDate="2016-05-17T17:47:24.720" LastActivityDate="2016-06-07T14:37:37.977" Title="What would be the easiest and most cost effective ground system for a startup UHF/VHF station" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;grounding&gt;&lt;antenna-system&gt;&lt;lightning&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6197" PostTypeId="2" ParentId="6196" CreationDate="2016-05-16T22:37:45.063" Score="0" Body="&lt;p&gt;and welcome to ham.stackexchange.com!  I can't say that I agree with Mr Fong, because a good lightning arrestor also includes components to block the high voltages resulting from a nearby lightning strike.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perfect protection against a direct lightning hit is probably not possible at your house, but nearby lightning strikes can also do damage, and that's something that you can do something about.  Lightning protection is a compromise, and each ham must decide for him or herself how much is desirable and affordable.  If you asked ten hams what the best compromise is, then you'd probably get ten different answers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my opinion, a good compromise to start with would be to use a good-quality lightning arrestor mounted on the end of a ground rod.  The ground rod should be buried in the ground of course, and also connected to your existing electrical ground rod(s) according to code.  Installing a lightning arrestor would mean that you would need to cut pieces of coax to size and install connectors on the ends, which can be a bit tricky for a beginner; you might want to go to a meeting of your local ham club and ask for some help there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might also want to think about insurance; it wouldn't be a bad idea to ask your insurance agent whether your homeowner's or renter's insurance policy would cover lightning damage.  If not, you could buy coverage for your equipment from the ARRL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck, and have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-05-16T22:37:45.063" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6198" PostTypeId="2" ParentId="6196" CreationDate="2016-05-17T00:26:18.893" Score="6" Body="&lt;p&gt;That statement is wrong on several levels.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The antenna is DC grounded so no lighting arrestor is needed.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A lightning arrester is needed, even if the antenna is DC ground. The arrester's job is to limit the center conductor's voltage to be not very different from the shield. That the antenna is &quot;DC grounded&quot; isn't worth much. Lightning is not DC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, the fact that this antenna works tells us that it's not grounded at high frequencies. The fast pulse that is lightning also has high frequency components, so from the perspective of the lightning, the antenna is in fact not grounded.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All you need to do is to make sure the shield is grounded (which I assume it is from the power supply).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Simply attaching the shield to something else that's grounded in some way isn't going to help at all. Lightning is a very fast pulse, and as such we have to think about it as RF, not DC. A circuitous route to ground is worth very little since the inductance will encourage the lightning current to flow elsewhere.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Nothing will protector your antenna from a lightning strike. So yes, if you see a storm coming it would be advised that you disconnect the antenna from you radio.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Tell that to professional broadcast stations. I'm sure whenever there's a storm, someone goes up the mountain to disconnect the antenna while the station is off air for several hours, right?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All a lightning arrestor does is to DC ground the antenna which protects your radio with high voltage spikes induced by the lighting. Our antenna is a DC ground antenna so it already does that.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's not what they do. Most lightning arresters have a spark gap between the shield and the center conductor. When the center conductor gets too high, the gap sparks, limiting the voltage between the shield and center conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some are DC grounded, which can be good since it prevents static buildup on the antenna. Some are not DC grounded, which is important if the feedline is powering remote equipment with a DC bias. If you look at &lt;a href=&quot;http://www.polyphaser.com/products/rf-surge-protection&quot; rel=&quot;nofollow noreferrer&quot;&gt;lightning protection produces from PolyPhaser&lt;/a&gt; for example, they have both &quot;DC block&quot; and &quot;DC pass&quot; products.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;If you want to protect your station from lightning, see &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if you don't care that much about lightning protection, don't worry about grounding. A ground isn't necessary for a radio to work. Just disconnect the antenna in a storm, and if you are using a vertical, be sure it has radials to provide a &quot;ground&quot; plane.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-05-18T20:56:14.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6199" PostTypeId="1" AcceptedAnswerId="6207" CreationDate="2016-05-17T01:31:28.257" Score="3" ViewCount="133" Body="&lt;p&gt;I have a very old Harvey Wells Z-Match antenna tuner (transmatch) with two outputs on the back for 450 Ω window line. One output is for “medium frequency” and works for 75 and 40 meters. The other output is marked “high frequency” and works for 20 meters and up. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently switching the window line back and forth is a pain, since I have to break out a wrench and unscrew terminals. So I have three questions: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How can I efficiently switch this back and forth?&lt;/li&gt;&#xA;&lt;li&gt;Am I correct in assuming that connecting two antennas at once is a bad idea?&lt;/li&gt;&#xA;&lt;li&gt;Would soldering PowerPole connectors to segments of window line create impedance problems, and are they up to the voltages and currents experienced in a piece of window line?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5577" LastEditorUserId="76" LastEditDate="2016-05-17T20:32:11.830" LastActivityDate="2016-05-17T20:32:11.830" Title="Switching 450 Ω window line" Tags="&lt;electronics&gt;&lt;feed-line&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6200" PostTypeId="1" AcceptedAnswerId="6202" CreationDate="2016-05-17T10:44:05.140" Score="2" ViewCount="1150" Body="&lt;p&gt;I would like to split a coaxial feed line 3 ways, maintaining 50 Ω impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know how to do this 2 ways; you use 1/4 wavelength 75 Ω coax as matching stubs.&lt;br&gt;&#xA;I know how to do this 4 ways; you do 2 way twice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/g5LvO.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/g5LvO.gif&quot; alt=&quot;2 way Matching&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But how do I do this 3 ways, ideally using 50 Ω and 75 Ω cables (as I have them in stock)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to use the 3-way split to feed 3 dipoles in an end-fire-array configuration, on the 70cm band, with a maximum power of 50 W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason for 3 is that there is no room for 4 (4 would be handy), and I would like more gain then 2. Furthermore, three is easily switchable in regards to direction: the middle dipole feed will stay static, while the outer dipoles reverse their phase offset.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="76" LastEditDate="2017-04-26T17:25:35.600" LastActivityDate="2017-04-26T17:25:35.600" Title="3 way coax split / impedance match" Tags="&lt;antenna&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6201" PostTypeId="1" AcceptedAnswerId="6204" CreationDate="2016-05-17T15:14:38.603" Score="6" ViewCount="3968" Body="&lt;p&gt;Sometimes designs call for quarter-wave sections of transmission lines. There are some situations when using actual transmission lines would not be practical:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The necessary characteristic impedance is something not easily obtained&lt;/li&gt;&#xA;&lt;li&gt;A quarter wavelength of transmission line would be too physically large&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Can I accomplish the same thing with lumped elements like inductors and capacitors? If so, how?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-01T14:40:32.213" Title="How can a quarter-wave transmission line transformer be implemented with lumped elements?" Tags="&lt;transmission-line&gt;&lt;transformer&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6202" PostTypeId="2" ParentId="6200" CreationDate="2016-05-17T15:16:35.680" Score="3" Body="&lt;p&gt;The picture in your question is almost a &lt;a href=&quot;http://www.microwaves101.com/encyclopedias/wilkinson-power-splitters&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wilkinson power splitter&lt;/a&gt;. Missing is a 100 ohm resistor between the outputs:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ESnio.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fESnio.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without that resistor there's no isolation between the output ports. You say you are using this to feed an antenna array. The consequence of not having isolation between the ports is that if any of the antenna elements is not a perfect match, that reflected power will show up on the other antenna elements, messing up your phasing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the resistor, if there's a perfect match everywhere, each output is in phase and so there's no voltage across the resistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When there's some reflected power from one of the antennas, half the power goes back through the input, and the other half is dissipated in the resistor. Ideally, none goes out the other output. In practice you can expect 20dB of isolation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you have three antennas. Fortunately, Wilkinson power splitters can be made with any number of ports. This &lt;a href=&quot;http://www.microwaves101.com/encyclopedias/n-way-wilkinson-splitters&quot; rel=&quot;nofollow noreferrer&quot;&gt;article by Microwaves101.com&lt;/a&gt; illustrates the concept well:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1c1xQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1c1xQ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This requires a different impedance 1/4 wave section. Z&lt;sub&gt;0&lt;/sub&gt; is probably 50 ohms, so:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \sqrt{3} \cdot 50\:\Omega = 86.6\:\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you happen to have some 87 ohm coax sitting around, you are good to go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, an equivalent circuit can also be realized with lumped elements. See:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/6201/218&quot;&gt;How can a quarter-wave transmission line transformer be implemented with lumped elements?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.microwaves101.com/encyclopedias/lumped-element-wilkinson-splitters&quot; rel=&quot;nofollow noreferrer&quot;&gt;microwaves101.com: Lumped Element Wilkinson Splitters&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that with an end-fire array there is significant coupling between each element of the array which can make things messy in practice. See the answer by tomnexus.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-05-18T14:59:20.707" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6203" PostTypeId="2" ParentId="6200" CreationDate="2016-05-17T17:35:48.497" Score="3" Body="&lt;p&gt;Go carefully when feeding an end fire array. Unlike a vertical collinear array, the coupling between ports is substantial. Even with a perfect well isolated splitter, you won't get the current distribution and hence patterns that you expect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you need to do is simulate the array in NEC or something, and experiment with the voltage magnitudes and phases on the elements, until you have the current distribution or radiation pattern that you want. Then only can you start to design the feed network - three different transformers and delay lines to achieve the feed voltages you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some end fire arrays are designed for feeding simplicity. The LPDA has a simple transmission line running between elements, they each take some current and the rest flows on down the line. The yagi generally has a zero feed point voltage on all but one of the elements, which is of course easy to feed. There are others, like a yagi with two or three driven elements, the W8JK and the HB9CV with two, but the common theme is that the feedline design is an integral part of the antenna design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried a quick simulation of four cases:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Simple $\lambda/2$ dipole.&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Result: Well matched at 445 MHz. Gain=2.1 dBi.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Three dipoles $\lambda/4$ apart. Fed with $-90^\circ, 0^\circ, +90^\circ$  &lt;em&gt;current&lt;/em&gt; sources.&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Gain = not calculated for current sources, sorry. F/B = 7 dB.&lt;/li&gt;&#xA;&lt;li&gt;Currents on the three are equal, and phases are as requested.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Three dipoles $\lambda/4$ apart. Fed with $-90^\circ, 0^\circ, +90^\circ$ &lt;em&gt;voltage&lt;/em&gt; sources.&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Gain = 8 dBi, F/B = 6 dB.&lt;/li&gt;&#xA;&lt;li&gt;Impedance at ports: Insane. One port 1.5:1, one 3:1, last port has power flowing back from it, SWR is negative, hard to describe.&lt;/li&gt;&#xA;&lt;li&gt;Currents on the back two are equal, almost no current on the front dipole.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Three dipoles $\lambda/4$ apart. Fed with transmission lines: first each dipole has a $\lambda/4$, 86.6$\Omega$ line, which would transform 50$\Omega$ into 150$\Omega$. Then each has a 150$\Omega$ line back to a common source, one zero length, one $\lambda/4$, one $\lambda/2$. This would be the naive phasing to get the end fire effect.&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Gain = 5.6 dBi, F/B = 5 dB.&lt;/li&gt;&#xA;&lt;li&gt;Impedance at port: SWR of 1.5:1.&lt;/li&gt;&#xA;&lt;li&gt;Currents quite mismatched, middle dipole has about 60% of the current of the side two. Phases are about right for end-fire.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The next step, which I can't easily automate, would be to play with the transmission line lengths and impedances to achieve equal current, correct phasing. As a guess, it might pay to split half the power to the middle dipole, and 1/4 to each side one, keeping the -90, 0, 90 phase relationship.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In summary, N-port equal power equal phase splitters are for collinear arrays and perhaps broadside arrays, but for end-fire things get a lot more complicated.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2016-05-17T20:54:49.293" LastActivityDate="2016-05-17T20:54:49.293" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6204" PostTypeId="2" ParentId="6201" CreationDate="2016-05-17T19:02:24.443" Score="6" Body="&lt;p&gt;It can be done! Remember that a transmission line consists of some self-inductance per unit length, and some capacitance per unit length, and the ratio of these determines the line's characteristic impedance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_0=\sqrt{\frac{R+j\omega L}{G+j\omega C}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Intuitively then, a lumped element implementation might look like some series inductance and some parallel capacitance. We need something that's symmetrical, so a pi network&lt;sup&gt;1&lt;/sup&gt; like this should do it:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/geAm9.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fgeAm9.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All we have to do is determine the appropriate values. Since transmission lines work in both directions this arrangement is going to be symmetrical, so C1 = C2. And as it turns out, the values are very elegant: the reactance of the components is equal to the characteristic impedance.&#xA;Put mathematically:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ X_{L1} = Z_0 \\&#xA;X_{C1} = Z_0 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And while we're at it, let's review the formulae for reactance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ X_L = 2 \pi f L \\&#xA;X_C = 1 / (2 \pi f C) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Putting those together, with a bit of algebra, you get:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ L = {Z_0 \over 2 \pi f} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ C = {1 \over 2 \pi f Z_0} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say we want a characteristic impedance of 86.6 ohms so we can realize a &lt;a href=&quot;https://ham.stackexchange.com/a/6202/218&quot;&gt;3-way Wilkinson power splitter&lt;/a&gt;. We'll use the frequency 435 MHz for the middle of the 70cm band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ L = { 86.6\:\Omega \over 2\pi  \cdot 435\:\mathrm{MHz} }&#xA;= 31.5\:\mathrm{nH} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ C = {1 \over 2\pi \cdot 435\:\mathrm{MHz} \cdot 86.6\:\Omega }&#xA;= 4.22 \:\mathrm{pF} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now the circuit with real values, terminated with an 86 ohm load:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/b0OUU.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fb0OUU.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is indeed a quarter-wave transmission line, we should see R1 90 degrees out of phase with the input. Let's run a time-domain simulation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/h2oI3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/h2oI3.png&quot; alt=&quot;voltage&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ut931.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ut931.png&quot; alt=&quot;current&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bingo! The impedance transforming properties of a quarter wave transmission line are also preserved: if the output is open, the source will see a short, and so on. So this circuit can be used in place anywhere that calls for a quarter-wave transmission line.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt; This pi network makes a low pass filter, which can be a nice side-effect since it reduces harmonic distortion.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-05-19T18:27:03.127" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6205" PostTypeId="2" ParentId="6196" CreationDate="2016-05-17T19:11:15.837" Score="0" Body="&lt;p&gt;I think what I have decided to do for the outdoor grounding station is to start with a single copper ground rod (specifically an ERICO 8' .358dia) driven into the ground just outside my &quot;shack&quot;. I'm opting for a Alpha-Delta UCGC that will be put on the rod along with an MFJ-270 lightening arrester. I intend to run a 6ga copper wire from the rod to my meter ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I can gather, I'll then just use RG8X Coax to run from the antenna to the arrester, then another coax inside to my FT-7900R. The Power Supply will have it's own ground wire (not sure what I need there) to go to the grounding station UCGC. I don't know whether I also need a ground from the receiver to the ground rod.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inside, I'll have a surge protector with battery-backup plugged into the wall AC, with all equipment plugged there. Then if a particularly severe storm comes along I can simply pull the antenna on the unit, and pull the surge protector from the wall. &lt;/p&gt;&#xA;" OwnerUserId="6696" LastEditorUserId="76" LastEditDate="2016-05-17T20:27:52.633" LastActivityDate="2016-05-17T20:27:52.633" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6206" PostTypeId="2" ParentId="6199" CreationDate="2016-05-17T19:39:15.967" Score="1" Body="&lt;p&gt;You should be OK using power-pole connectors.  Observe the manufacturer's power rating for the connector.  Don't connect the two antennas. 73, KC2OGR.&lt;/p&gt;&#xA;" OwnerUserId="6701" LastActivityDate="2016-05-17T19:39:15.967" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6207" PostTypeId="2" ParentId="6199" CreationDate="2016-05-17T19:54:18.940" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Would soldering Power-Pole connectors to segments of window line create impedance problems?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;On HF, no. The significance of an impedance mismatch is proportional to its size in relation to wavelength. For HF the wavelength is so much more huge compared to a connector that the impact is negligible.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;are they up to the voltages and currents experienced in a piece of window line?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you are using 450 ohm line, and transmitting with 100 watts, Ohm's law tells us:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ V = \sqrt{ P \cdot R } = \sqrt{ 100\:\mathrm{W} \cdot 450\:\Omega } = 212\:\mathrm V $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's an RMS voltage; the peak voltage is 1.4 times more, or about 300 volts. If you are operating the line with a high VSWR, the voltage could be higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that in mind, read the datasheet for the particular connectors you are considering and see what their limits are.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Am i correct in assuming that connecting two antennas is a bad idea?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Usually, yes. However in some circumstances multi-band antennas are made by connecting multiple antennas to the same feedpoint, fan dipoles for example. Not recommending you try connecting two antennas, just an interesting fact.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How can I efficiently switch this back and forth?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You can just use a switch. Just be sure to check its voltage and current ratings (using Ohm's law) make sure it's rated appropriately. I'd build in a very healthy margin to account for high VSWR and other things which could make voltages and currents higher than in the ideal case. And you might want to take steps to avoid touching the switch when transmitting: RF burns are painful.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-05-17T19:54:18.940" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6208" PostTypeId="2" ParentId="6199" CreationDate="2016-05-17T20:10:43.547" Score="2" Body="&lt;p&gt;I had a similar situation once with window line and I merely used a knife switch (double-pole) to handle the switching duties. Worked quite well. Nice thing about window (or, ladder) line is that it can be easily cut, switched, patched, and so on without too much disturbance. &lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-05-17T20:10:43.547" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6210" PostTypeId="1" CreationDate="2016-05-18T18:43:19.373" Score="3" ViewCount="645" Body="&lt;p&gt;An array of dipoles can be fed to achieve an end-fire pattern.&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/UCpN8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UCpN8.png&quot; alt=&quot;Three dipoles&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;If the phase of the current on each element is equal, the array will have maximum radiation broadside to the array. If the phase of the currents is equal to the physical spacing of the elements, then the array radiates from its end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An attempt to show this is shown here:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/eeepR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eeepR.png&quot; alt=&quot;wavecancellation&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;The three circles represent the dipoles, and the three waves are the electric fields radiated by them. To the right, the waves all add in phase, this is the direction of maximum radiation. To the left, they do not add in phase, and the pattern is smaller. &lt;em&gt;(in fact, with three dipoles, this isn't the optimum phasing for best front-to-back, but for larger arrays this is less important)&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How should such an array be fed, to ensure the currents are as required for end-fire radiation?&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-01-24T04:20:43.877" Title="How to feed an array of dipoles for an end-fire pattern" Tags="&lt;impedance&gt;&lt;dipole&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6211" PostTypeId="1" AcceptedAnswerId="6212" CreationDate="2016-05-19T10:41:46.403" Score="1" ViewCount="145" Body="&lt;p&gt;Suppose you want to make a &lt;a href=&quot;https://ham.stackexchange.com/questions/6201/how-can-a-quarter-wave-transmission-line-transformer-be-implemented-with-lumped&quot;&gt;wilkinson 3-way splitter with lumped components&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the following circuit, you need a 31.5nH inductor&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kn5IG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kn5IG.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The inductor can be wound various ways:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;3 wdg, 1 cm diameter, 2.36 cm long&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;2 wdg, 1 cm diameter, 0.8 cm long&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;3 wdg, 0.5 cm diameter, 0.48 cm long&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;These are examples, you can calculate more variations for this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, given the example of building a wilkinson 3-way splitter with lumped components as described in the link above, for 435 MHz from the same example, for 50 Watts transmit power: &lt;strong&gt;what way should the inductor be constructed ?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;thanks&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-05-19T12:16:55.637" Title="What dimensions to choose when winding your own inductor" Tags="&lt;impedance&gt;&lt;filter&gt;&lt;inductor&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6212" PostTypeId="2" ParentId="6211" CreationDate="2016-05-19T12:16:55.637" Score="4" Body="&lt;p&gt;It boils down to practical issues &amp;mdash; you want to make it as small as possible, but no smaller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power-handling requirements will dictate the wire diameter (to handle the current) and the end-to-end spacing (to handle the voltage). For an air-core coil, you also want the wire to be stiff enough to hold its shape well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will want to wind the coil on some sort of handy form (drill bits are useful for this), so this puts some limits on your choice of inside diameter. The one variable you have the most flexibility with is the length. Indeed, it is possible to tweak the final inductance value after construction by squeezing/stretching the length of the coil a bit.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2016-05-19T12:16:55.637" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6213" PostTypeId="1" AcceptedAnswerId="6216" CreationDate="2016-05-19T16:44:34.780" Score="8" ViewCount="2930" Body="&lt;p&gt;I'm looking at some raw APRS packets over APRS-IS. I'd like to determine which stations heard particular packets, but I'm having trouble understanding how TNC-2 paths work. Here are two examples:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;2016-05-19 05:51:46 PDT: PACCTY&amp;gt;APN390,HEBOWX,KFALLS,OR2*,qAR,STUKEL:&#xA;2016-05-19 05:55:32 PDT: PACCTY&amp;gt;APN390,WIDE1-1,OR2-1,qAR,W7GC-4:&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Can you explain how I can determine the actual path the packet took? Also, how do I differentiate this from the path that the sender, &lt;code&gt;PACCTY&lt;/code&gt; requested?&lt;/p&gt;&#xA;" OwnerUserId="5820" LastEditorUserId="5820" LastEditDate="2016-05-19T21:48:22.110" LastActivityDate="2016-05-25T00:04:44.913" Title="Help understanding path taken by APRS packet" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6214" PostTypeId="2" ParentId="6210" CreationDate="2016-05-19T17:07:50.327" Score="1" Body="&lt;p&gt;Short answer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For an array of dipoles with equal spacing &lt;span class=&quot;math-container&quot;&gt;$d$&lt;/span&gt;, the direction of maximum gain with respect to the end-fire direction (call this &lt;span class=&quot;math-container&quot;&gt;$\theta_0$&lt;/span&gt;) can be obtained using the following equation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\delta = k d\cos(\theta_0)$&lt;/span&gt; where &lt;span class=&quot;math-container&quot;&gt;$\delta$&lt;/span&gt; is the incremental phase difference between adjacent elements, &lt;span class=&quot;math-container&quot;&gt;$kd$&lt;/span&gt; is in radians. (&lt;span class=&quot;math-container&quot;&gt;$k$&lt;/span&gt; is the wave number defined as &lt;span class=&quot;math-container&quot;&gt;$2\pi/\lambda$&lt;/span&gt;). See figure below. NOTE: the angle &lt;span class=&quot;math-container&quot;&gt;$\delta$&lt;/span&gt; in the figure below should be a &lt;span class=&quot;math-container&quot;&gt;$\theta_0$&lt;/span&gt; !!! This is an errata in the edition I took this figure from...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aUolG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aUolG.png&quot; alt=&quot;Figure 1&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Longer Answer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To plot the gain, we first will first need the array factor given by &lt;span class=&quot;math-container&quot;&gt;$\gamma' = k d(\cos\theta-\cos\theta_0)$&lt;/span&gt; where &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt; is the clockwise angle from the end-fire direction (&lt;span class=&quot;math-container&quot;&gt;$\theta_0$&lt;/span&gt; is the direction we want to steer the beam). The array factor is found as &lt;span class=&quot;math-container&quot;&gt;$F_{an}(\gamma')=\frac{\sin^2(N\gamma'/2)}{N^2\sin^2(\gamma'/2)}$&lt;/span&gt;. True gain is found by multiplying the gain of a dipole with the array factor. An example of various &lt;span class=&quot;math-container&quot;&gt;$\theta_0$&lt;/span&gt; for a normalized 10-element array with &lt;span class=&quot;math-container&quot;&gt;$\lambda/2$&lt;/span&gt; spacing is shown below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RG6sJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RG6sJ.png&quot; alt=&quot;Figure 2&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can post more info if there are more questions. The full derivation takes over 10 pages so there is a lot of info I glossed over.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Source: Fundamentals of Applied Electromagnetics, 6th edition, Section 9-9.&lt;/p&gt;&#xA;" OwnerUserId="5944" LastEditorDisplayName="user4168" LastEditDate="2019-01-24T04:20:43.877" LastActivityDate="2019-01-24T04:20:43.877" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="6215" PostTypeId="2" ParentId="4871" CreationDate="2016-05-19T17:23:08.990" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I want to design a steerable beam array antenna which has 15 dBi directivity using uniform fed infinitesimal dipole elements at 1GHz frequency occupying physical aperture.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Array elements cannot be uniformly fed and steerable. Steering is most simply provided by applying a linear phase distribution across elements. Kieth is correct that gain/directivity will be a function of the antenna used as elements of the array, as well as spacing, phasing, and number of elements. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I provided a basic explanation of beam steering &lt;a href=&quot;https://ham.stackexchange.com/questions/6210/how-to-feed-an-array-of-dipoles-for-an-end-fire-pattern&quot;&gt;over here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="5944" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-05-19T17:23:08.990" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6216" PostTypeId="2" ParentId="6213" CreationDate="2016-05-19T21:34:06.360" Score="6" Body="&lt;p&gt;According to the way things work for simple AX.25 packets, the part after &quot;&gt;&quot; is the destination address.  However, the APRS specification commonly repurposes fields, with the goal being to keep the packet as small as possible.  The destination field is like that: most APRS packets are broadcast rather than sent to a specific station, so when an APRS packet isn't meant for a specific station then the destination field is pressed into service to hold something else.  If the &quot;destination&quot; starts with AP, then it's a code that indicates what device or software package sent the packet.  In this case, a &quot;destination&quot; of the pattern APN3xx means that the packet was sent by a Kantronics KPC-3.  (The destination can also be Mic-E encoded, in which case it holds the latitude and part of the longitude of the sending station, plus a few other miscellaneous data flags.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, &lt;code&gt;WIDE1-1&lt;/code&gt; doesn't actually mean that the packet was repeated by a station of that name.  In this case, &lt;code&gt;WIDE1-1&lt;/code&gt; is an instruction for how to repeat the packet, which was part of the packet when it was first sent.  It requests that a &quot;wide&quot; digipeater (one with a wide coverage area, like on a mountaintop) repeat the packet, but only once; if a second &quot;wide&quot; digipeater should hear the rebroadcast packet, then the second digipeater wouldn't repeat it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apparently &lt;code&gt;qAR&lt;/code&gt; is the &quot;Q-construct&quot; that indicates that the packet was was successfully &quot;Igated&quot; to APRS-IS, the APRS internet packet routing system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm reasonably familiar with APRS, but not an expert.  Even so I'll give the second part of your question a go, but I reserve the right to be wrong ;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;PACCTY&amp;gt;APN390,HEBOWX,KFALLS,OR2*,qAR,STUKEL:&lt;/code&gt; This packet was sent by PACCTY using a Kantronics KPC-3.  It was digipeated by HEBOWX, KFALLS, and OR2, and then copied onto APRS-IS, the internet APRS packet network, by STUKEL.  It's unlikely that that exact path was requested by the sender; it's more likely that the original path request was &lt;code&gt;WIDE1-1,WIDE2-1&lt;/code&gt;.  &lt;code&gt;WIDE1-1&lt;/code&gt; is a request for a small home digipeater to rebroadcast the packet.  &lt;code&gt;WIDE2-1&lt;/code&gt; is a request for a high-up digipeaters to rebroadcast.  Each station that rebroadcasts the packet puts its call sign into the path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;PACCTY&amp;gt;APN390,WIDE1-1,OR2-1,qAR,W7GC-4:&lt;/code&gt;  Here we have a packet that was never digipeated before being copied to the internet; we can tell because there is no asterisk.  The original packet was heard by Igate W7GC-4 and copied onto APRS-IS there.  (The packet probably was digipeated, but when multiple copies of a packet are received on APRS-IS, then one is chosen at random to be kept, and the rest are ignored as being redundant.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because this packet was copied to APRS-IS before being digipeated, we have a better look at the original path request.  As I suspected, &lt;code&gt;WIDE1-1&lt;/code&gt; is in there first as an invitation for small home digipeaters to repeat the packet.  Next comes &lt;code&gt;OR2-1&lt;/code&gt;.  That could be a station OR2 with an SSID of &quot;-1&quot;.  But given that the first packet didn't contain &lt;code&gt;OR2-1&lt;/code&gt;, it seems like it is more likely to be an alias.  Maybe it works like &lt;code&gt;WIDE2-1&lt;/code&gt;, but just in Oregon?  I'm not sure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just for grins, let's look again at the first packet and assume that it was sent with &lt;code&gt;WIDE1-1,WIDE2-1&lt;/code&gt; to see how digipeaters modify the packets going through them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;PACCTY&amp;gt;APN390,WIDE1-1,WIDE2-1:&lt;/code&gt; original packet&lt;br&gt;&#xA;&lt;code&gt;PACCTY&amp;gt;APN390,HEBOWX*,WIDE2-1:&lt;/code&gt; packet was heard and digipeated by HEBOWX, which responded to the alias WIDE1 and substituted its own call sign&lt;br&gt;&#xA;&lt;code&gt;PACCTY&amp;gt;APN390,HEBOWX,KFALLS*:&lt;/code&gt; packet was heard and digipeated by KFALLS, responding to the alias WIDE2&lt;br&gt;&#xA;&lt;code&gt;PACCTY&amp;gt;APN390,HEBOWX,KFALLS,OR2*,qAR,STUKEL:&lt;/code&gt; packet was heard and copied to APRS-IS (but not digipeated) by STUKEL&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="76" LastEditDate="2016-05-25T00:04:44.913" LastActivityDate="2016-05-25T00:04:44.913" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6217" PostTypeId="1" CreationDate="2016-05-20T21:48:49.453" Score="0" ViewCount="364" Body="&lt;p&gt;I am using RG 11 coax connected to receive radio. Center wire to one post shield to other post. Can it be used as a long wire antenna by it's self? &lt;/p&gt;&#xA;" OwnerUserId="6721" LastActivityDate="2019-12-11T14:27:16.717" Title="Using cable coax rg 11" Tags="&lt;coaxial-cable&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6218" PostTypeId="2" ParentId="6217" CreationDate="2016-05-21T10:12:09.900" Score="1" Body="&lt;p&gt;It will work after a fashion - like that - but as the &quot;shield&quot; is trying to stop signals reaching the &quot;core&quot; you would be best placing the shield connection to the centre of the receiving plug lead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What length of RG-11 are you using ? As it is not good for HF (&amp;lt;30 Mhz) especially is you have 100 feet or so of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You would probably be best just making a long-wire receive antenna and not worrying about the coax at all.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2016-05-21T10:12:09.900" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6220" PostTypeId="2" ParentId="6217" CreationDate="2016-05-21T14:33:31.133" Score="1" Body="&lt;p&gt;Yes, RG-11 coax can be used as a receiving antenna wire by attaching the braid outer conductor to the antenna connection post on your receiver.  You ignore the inner conductor as it serves no useful purpose in this application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, why?  Why would you want to use a more bulky, less flexible, coaxial cable for receiving antenna when a small thin wire can do the job just as well.  I mean, if you have this coax lying around and if it is in sufficient quantity then sell it on Craigslist and then go out and buy some small gauge wire, say #18, insulated so you can run it anywhere, and string that up in some fashion.  Experiment with position and length of the wire for the receiving bands of your interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use standard home wiring insulated copper wire for all my wire antenna applications -- both transmitting and receiving.  It is strong and gets the job done.  In the US, it is something you find at big box discount stores.  I buy it in the 500 foot spool size.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-05-21T14:33:31.133" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6221" PostTypeId="2" ParentId="6217" CreationDate="2016-05-21T19:56:32.447" Score="1" Body="&lt;p&gt;RG11 can work as well as any other wire as an antenna, but you wouldn't want to connect the shield to one post, with the center conductor to the other post. The reason is that any current which is on the center conductor but which is not matched by an equal and opposite current on the shield migrates to the shield via skin effect. So, you are effectively connecting both posts to the same wire, which won't work especially well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Better would be to connect one post to the shield, and connect the other post to ground, like a cold water pipe. Or really any other metal thing. Be sure to disconnect it in lightning storms. Utilized in this fashion the coax is essentially a fat wire. If you had ordinary wire I'd use that instead, but if you already have the coax, I don't see why not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another thing you can do is remove the outer insulation from a quarter-wavelength section of the coax, then bunch up the shield and fold it over on itself, effectively making a &lt;a href=&quot;http://www.antenna-theory.com/definitions/bazooka.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;sleeve or bazooka balun&lt;/a&gt;. Check out &lt;a href=&quot;https://ham.stackexchange.com/a/1941/218&quot;&gt;this answer&lt;/a&gt; for some more pictures. Utilized this way, you are essentially making a dipole.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-05-21T19:56:32.447" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6222" PostTypeId="2" ParentId="6195" CreationDate="2016-05-22T11:37:40.153" Score="2" Body="&lt;p&gt;Not really a problem – just a technological challenge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The challenge, in almost any case, lies in the fact that per definition, the input is a harmonic of the output of the frequency divider, and since you don't want to have both the &quot;high&quot; input frequency and the &quot;low&quot; output frequency in your LO signal, you'll have to strongly suppress the frequency of the input signal. Now, the input signal has usually a high chance of being relatively powerful – and hence, hard to suppress.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, if you asked me how I'd go about building a flexible LO-generater from a high input frequency, my answer would be:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;use one of the many existing LO synthesizer ICs – they work excellently, there's a lot of code that shows how to use them (e.g. attached to some computer via some I²C bridge) and they really get the job done without requiring you to build a lot of specific filters at exotic frequencies, measure them etc. and are far more flexible than just giving you dividers of your input LO; ask e.g. analog.com or Maxim Integrated about fractional-n or integer-n synthesizers: you can often do stuff like taking a single, arbitrary input oscillator, and generate a nearly arbitrary set of output frequencies with one single device. You can probably even get a free sample IC. High-End devices use these ICs, so it's not a &quot;short cut with drawbacks&quot;. these ICs do not only allow you to generate non-integer factors of your input frequency, but also non-integer &lt;em&gt;multiples&lt;/em&gt; of it – so you could, for example, buy a good 10MHz oscillator, and use it to generate 2.443265 GHz with the accuracy of that 10MHz reference oscillator.&lt;/li&gt;&#xA;&lt;li&gt;if I didn't feel like just getting a part that was built by someone who knows his trade better than I do, I'd just get some 10€-20€ ARM dev board, or whatever microcontroller platform you'd feel most comfortable with, and used the timer units these devices have to generate a set of already pretty adaptive clocks – for example, I have a &lt;a href=&quot;http://www.st.com/content/st_com/en/products/evaluation-tools/product-evaluation-tools/mcu-eval-tools/stm32-mcu-eval-tools/stm32-mcu-nucleo/nucleo-f446re.html&quot; rel=&quot;nofollow&quot;&gt;ST Nucleo-F446RE&lt;/a&gt; board lying around, which I could use to generate a lot of clocks by letting the PWM units count up to values that I can specify via software, at a rate that I specify via software. The oscillator used to make the PWM unit &quot;tick&quot; can be supplied externally, e.g. from a high-quality OCXO if I felt that the simple quartz oscillator on-board of that eval board wasn't sufficiently accurate. These outputs could then either be filtered in an analog fashion (use the excellent &lt;a href=&quot;http://www.analog.com/designtools/en/filterwizard/&quot; rel=&quot;nofollow&quot;&gt;Analog Devices Filter Designer&lt;/a&gt; ) or used to feed a PLL that controls a voltage-controlled oscillator (VCO) – I'd recommend the later. &lt;/li&gt;&#xA;&lt;li&gt;Same idea as 2., but build your own control loop: Use a microcontroller with a timer/PWM unit (the ST ARMs tend to have lots of those) to generate a &quot;system tick&quot;. Either write a piece of software that counts the rising edges of your your VCO, or use a dedicated integrated piece of hardware (again, the ST ARMs have such counters integrated in their timer units). Compare the number of edges that you counted with the &quot;should-be&quot; value (e.g. in 0.1 milliseconds, your VCO should have produced 750 such edges for a 40m=7.5MHz LO) and increase/decrease the control voltage accordingly. &lt;/li&gt;&#xA;&lt;li&gt;In any case, I wouldn't use the still-often-thaught analog &quot;regenerative frequency divider&quot; method to build a frequency divider – you'd need pretty good equipment to verify the quality of its operation, and it's not a fun thing to implement right. Also, although they have the advantage of not generating a square wave with the mentioned sinc-shaped spectrum, they tend to have harmonics all over the place unless you can do fantastic filtering (which usually is more expensive/complicated than just getting another quartz).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Yet I've never seen anything like that. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Look harder: Frequency dividers are everywhere in digital hardware, and even more prominently used in radio electronics. They work well, are part of the ICs I mentioned in 1. above, and are extremely easy to implement if you have digital signals – in fact, it's more likely you'll find a frequency divider that does &lt;/p&gt;&#xA;&#xA;&lt;p&gt;sine signal -&gt; threshold/Schmitt trigger -&gt; counter -&gt; filter / (PLL+VCO) -&gt; sine signal&lt;/p&gt;&#xA;&#xA;&lt;p&gt;than something that works directly on the analog signal&lt;sup&gt;[citation needed]&lt;/sup&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-05-22T11:37:40.153" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6223" PostTypeId="1" CreationDate="2016-05-22T12:25:49.920" Score="1" ViewCount="2510" Body="&lt;p&gt;Is it possible to use an ordinary GMRS/FRS UHF handheld set for data communications? &#xA;I hope to use a Motorola UHF GMRS handheld with a terminal node controller device to for data communication. Are there any terminal node controller devices for this task? &lt;/p&gt;&#xA;" OwnerUserId="6727" LastEditorUserId="76" LastEditDate="2016-05-22T13:44:02.647" LastActivityDate="2016-05-22T17:19:28.350" Title="GMRS/FRS data communication" Tags="&lt;digital-modes&gt;&lt;frs&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6224" PostTypeId="2" ParentId="6223" CreationDate="2016-05-22T16:57:25.503" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it possible to use an ordinary GMRS/FRS UHF handheld set for data communications?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In principle: yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You see, you're talking about voice communication devices. If now, on one end, someone spoke &quot;zero one zero one…&quot;, obviously, you could communicate arbitrary data through that voice-optimized channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In reality, you'd use a device that &lt;em&gt;mo&lt;/em&gt;dulates the data onto audio on one side, and &lt;em&gt;dem&lt;/em&gt;odulates it on the other – a &lt;em&gt;modem&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's modems that actually work over voice channels. See the &lt;a href=&quot;https://en.wikipedia.org/wiki/Acoustic_coupler&quot; rel=&quot;nofollow&quot;&gt;acoustic couplers&lt;/a&gt; that predate the little grey modem boxes that connected everyone and their mom to the internet over telephone lines in the 90s.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, using something that is designed to transport speech as understandably as possible (that does &lt;strong&gt;not&lt;/strong&gt; mean &quot;as close as possible to the original&quot;) to transport data is a pretty bad approach – basically, you're using the wrong transport. That's why telephone line modems went away from the acoustic coupling principle (which put the telephone's speaker/mic and amplifiers in between the data and the telephone line channel) and switched over to modems that used the available channel as efficiently as possible, at the cost of it spectrally no longer looking like voice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you could design a pretty simple e.g. FSK (frequency shift keying) modulator to act as &quot;fake&quot; microphone to your voice communication device, and do the opposite (FSK demodulator as fake speaker) on your receiving end. But frankly: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FM, AM or AM/SSB modulation done by the UHF handset is pretty simple compared to implementing a working modem. So, you're most likely better off just designing an UHF modem directly, and not be limited by the audio-centric behaviour of your handset. In fact, such devices are extremely common – your remote car key, your remote door bell, your wireless temperature sensor going with your kitchen thermometer, all do such things at miniature cost, using freely (and cheaply) available RF modules. You really don't &lt;em&gt;have&lt;/em&gt; to use the large, battery-eating walkie talkie.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that this might not be entirely true for all use cases – if you really only need to transport a few bit ever minute or so, then implementing a short sequence of beep codes would be totally sufficient – just as Morse code is really sufficient if you just need to get a few words across.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-05-22T16:57:25.503" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6225" PostTypeId="2" ParentId="6223" CreationDate="2016-05-22T17:19:28.350" Score="8" Body="&lt;p&gt;The short answer: this is probably technically feasible, but it's not legal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?gp=&amp;amp;SID=4d648ad4de9c24f953726d7e243a95e2&amp;amp;mc=true&amp;amp;tpl=/ecfrbrowse/Title47/47CIsubchapD.tpl&quot;&gt;Part 95 of the Code of Federal Regulations&lt;/a&gt; is where all the rules on personal radio services (which includes FRS, GRMS and amateur services) are found.  §95.631 specifically regulates permitted emission types.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are the relevant passages for GMRS:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;§95.631 (a): &quot;A non-voice emission is limited to selective calling or tone-operated squelch tones to establish or continue voice communications.&quot;&lt;/li&gt;&#xA;&lt;li&gt;§95.631 (e): &quot;No GMRS or CB transmitter shall employ a digital modulation or emission.&quot;&lt;/li&gt;&#xA;&lt;li&gt;§95.631 (f): &quot;No GMRS, CB or R/C transmitter shall transmit non-voice data.&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And for FRS:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;§95.631 (d): &quot;A non-voice emission is limited to selective calling or tone-operated squelch tones to establish or continue voice communications, digital data transmission of location information or text messaging.&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In summary: non-voice transmissions are limited to tone squelch/tone burst for using repeaters, and a very narrow range of location/text data.  It's worth reading the rules to see all the specifics, but I don't think using a TNC would be permitted.  I hope this is helpful!&lt;/p&gt;&#xA;" OwnerUserId="6446" LastActivityDate="2016-05-22T17:19:28.350" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6227" PostTypeId="1" CreationDate="2016-05-23T10:39:51.527" Score="1" ViewCount="80" Body="&lt;p&gt;What electrical circuits can be easily build by someone with basic electrical engineering skills that exemplify the fundamental components of radios, antennas and so on?&lt;/p&gt;&#xA;" OwnerUserId="6718" LastEditorUserId="6446" LastEditDate="2016-05-23T18:33:50.020" LastActivityDate="2016-05-23T18:33:50.020" Title="Practical Resources for the Amateur Radio Student?" Tags="&lt;license&gt;&lt;electronics&gt;&lt;education&gt;" AnswerCount="0" CommentCount="4" ClosedDate="2016-05-23T14:33:08.247" ContentLicense="CC BY-SA 3.0" />
  <row Id="6228" PostTypeId="1" CreationDate="2016-05-23T23:44:49.367" Score="2" ViewCount="944" Body="&lt;p&gt;Please forgive the naive question, as I've been away from the hobby for too long, but want to make sure I do this right.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We just added an addition to our house, and I lost my usual mounting place for my X200a.  I've never had this antenna mast connected to a ground rod for lightning protection before, but I'm wondering if in this new location, I should...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm wondering this because of a few reasons:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The X200a will be several feet lower than it was before (rather than at the apex of my roof, it will be at the bottom of the soffit line right by the gutter, mounted off of a satellite radio mast).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I'm in a very suburban area, near a water tower, and another ham down the street who has many more antennas on his roof, much higher than mine.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Aside from #1 above (below the apex of the roof), we have several trees on our property which are 30-50 feet taller than the house. Yes, trees are not made of a conductive material, I understand that. Just another point of emphasis.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Yes, I know, lightning can strike anywhere and the &quot;you should always ground everything to multiple ground stakes,&quot; etc., but I'm hoping for a productive, realistic answer from here as opposed to what I'd get on other ham forums.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the above - does the X200a really need to be grounded for lightning protection?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;This is a duplicate question of...&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No, it's not a duplicate. I've looked. I know &lt;em&gt;how&lt;/em&gt; to properly ground my equipment. I'm asking &lt;em&gt;if&lt;/em&gt; and &lt;em&gt;why&lt;/em&gt; I should ground my equipment given the above conditions.&lt;/p&gt;&#xA;" OwnerUserId="1556" LastEditorUserId="1556" LastEditDate="2016-05-24T19:46:05.337" LastActivityDate="2020-10-31T14:17:52.777" Title="Diamond X200A Lightning Protection" Tags="&lt;vertical-antenna&gt;&lt;lightning&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6229" PostTypeId="2" ParentId="6228" CreationDate="2016-05-24T00:19:21.833" Score="1" Body="&lt;p&gt;Welcome back to ham radio, and to ham.stackexchange.com!  I don't think your question is naïve at all.  It is however very similar to a &lt;a href=&quot;https://ham.stackexchange.com/questions/6196/what-would-be-the-easiest-and-most-cost-effective-ground-system-for-a-startup-uh&quot;&gt;question that we just debated recently&lt;/a&gt;.  Check out that discussion, and especially the earlier question &lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer your specific question, in my personal opinion having your antenna be lower down on the roof than it was before, and close to some tall trees, a water tower, and another ham's tall antennas, doesn't count for much protection.  I think a good lightning arrestor connected to a good ground system would serve you much better, without costing too much.  But it's your equipment and your health at stake, so do as you see fit.  73!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S. My dad had a station in the Chicago suburbs for 21 years.  He didn't bother with much of a lightning protection system; his shack suffered lightning damage three times from nearby hits.  He had a 40-foot tower though.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-05-24T00:19:21.833" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6230" PostTypeId="2" ParentId="6228" CreationDate="2016-05-24T08:24:04.063" Score="1" Body="&lt;p&gt;Polish professional antennas installation (police, firemen), antenna type 32812 similar in sizes to x200 are mounted like this (sorry, cant find with english description)&#xA;odgromnik - arrestor&#xA;odległość - distance&#xA;długość - length&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GGUP6.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GGUP6.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;EDIT: I do not negate rest of discussion. Problem should be resolved in good, complex way - or not resolved all, i.e. problem of loop ground&lt;/p&gt;&#xA;" OwnerUserId="6323" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-05-24T08:37:41.147" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6233" PostTypeId="1" AcceptedAnswerId="6242" CreationDate="2016-05-25T13:07:31.153" Score="2" ViewCount="1049" Body="&lt;p&gt;I am searching for a 5W effective output power TX amplifier that I can use with my BladeRF to send DVB-T Signals for ATV (33cm band).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone tell me on what things I have to look for when buying an amplifier for this usage, beside minimum input power, bandwidth and frequency?&lt;/p&gt;&#xA;" OwnerUserId="6257" LastEditorUserId="4076" LastEditDate="2016-05-26T12:43:46.167" LastActivityDate="2016-05-28T12:23:17.103" Title="33cm 5W(effective output power) tx amplifier for ATV (HamTV)" Tags="&lt;software-defined-radio&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6234" PostTypeId="1" CreationDate="2016-05-25T18:06:17.930" Score="2" ViewCount="2291" Body="&lt;p&gt;I am communicating about 1000'. Is the orientation of the antennas critical, can a vertical antenna communicate with a horizontal antenna?&#xA;The equipment is spec'd as VHF 148-174MHz and UHF 400-470MHz.&lt;/p&gt;&#xA;" OwnerUserId="6746" LastEditorUserId="-1" LastEditDate="2016-05-26T14:01:05.467" LastActivityDate="2016-05-28T03:40:00.590" Title="Can VHF/UHF antennas have different orientation" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6235" PostTypeId="2" ParentId="6234" CreationDate="2016-05-25T18:31:18.147" Score="4" Body="&lt;p&gt;For line-of-sight communication between two antennas, they must have compatible polarization. Monopole and dipole antennas (as typically used for VHF/UHF communications) emit and absorb waves with a polarization the same as the orientation of the wire/rod.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you mount two such antennas such that, viewed along the line between them, they are perpendicular to each other, then theoretically, you will observe &lt;strong&gt;no signal&lt;/strong&gt; at the receiving antenna. In practice, imperfections in the antenna system and reflections/refractions from nearby objects will result in less than complete loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer your question directly, &lt;strong&gt;no&lt;/strong&gt;, you cannot have one vertical and one horizontal antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You do not have to have both antennas exactly matching, however. For linear polarization, the signal is reduced by a factor of the cosine of the angle, squared. For example, if you have one vertical and one at 45°, then that's a factor of 0.5, or &amp;minus;3 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option is a circularly polarized antenna. With CP on one end and LP on the other, you &lt;em&gt;always&lt;/em&gt; get &amp;minus;3 dB — no less, no more.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-05-25T18:31:18.147" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6236" PostTypeId="2" ParentId="6234" CreationDate="2016-05-26T11:27:31.503" Score="3" Body="&lt;p&gt;Going back to a bit of electromagnetic wave theory:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A (TX) antenna's job is to generate an electromagnetic wave. To do so, the usual way to go is to generate a time-varying electrical field, and let the Maxwell equations do their job (thank Hertz for proving that these equations actually lead to energy propagating through space with finite speed!). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;em&gt;polarization&lt;/em&gt; of an electromagnetic (EM) wave is the axis (or more generally, curve) along which the electric field component of that wave varies. Generally, the magnetic field is perpendicular to that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of simple dipoles, it's pretty easy to see that, since the current travels in a linear &quot;rod&quot;, the magnetic field lines are &quot;circles&quot; around that rod, and since, due to the speed of the light, there are voltage differences along that rod, the electrical field is parallel to that rod. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Antenna_%28radio%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;wikipedia page on antennas&lt;/a&gt; actually has a good animation on that:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/etZrJ.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/etZrJ.gif&quot; alt=&quot;electrical field in dipole&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that there is absolutely &lt;em&gt;no&lt;/em&gt; electrical field perpendicular to this dipole's orientation/polarization!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you put any conductor oriented the same way that the wave is polarized, you'll notice a voltage across its ends, and a current flowing through it – the exact qualities of that conductor as a receive antenna depend on its discrete shape, material, and size relative to wavelength – but if you took the same conductor, rotate it by 90° so that it's now perpendicular to the plane in which the E-field happens, you'll see &lt;em&gt;nothing&lt;/em&gt;. (This fact, by the way, is often exploited by people who need to have two channels on the same frequency; but this leads too far.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A quick geometrical sketch makes it clear that only the dimension of a dipole in parallel to the E-field contributes to the voltages that build across it. &#xA;Hence, these voltages go with cos(θ), and θ being the angle between dipole &quot;axis&quot; and polarization. Power goes quadratic with voltage, and hence, the polarization loss factor is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PLF = cos²(θ)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, whatever you do, make sure your antennas are not 90° (or 270°) degrees offset. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That was for the case where the wave travels directly from TX to RX antenna – as Kevin points out, that's the Line-of-sight (LOS) scenario. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other scenarios, a specific reflection that turns polarization by 90° might be the main path of energy. In that case, you're fine. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A common HAM usage for relatively lower frequency communication is using diffraction in the atmosphere, which often has a gradual &quot;spin&quot; of polarization to it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you, for example, have a GHz wave going through trees, then the leaves will wildly, and quite randomly, scatter the waves, and give you an unpredictable mixture of linearization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, no general answer can be given. You'll have to be able to rotate your antenna, or have two perpendicular antennas to chose from (or combine! In fact, you can, with adequate delay lines, generate/receive any linear polarization with two perpendicularly linear polarized antennas), or be able to live with the LPF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you, however, look at satellite TV, you'll notice that it'll be a good idea to use neither horizontal nor vertical polarization – as it's absolutely unclear which spin the atmosphere will give the ways on their way from satellite to dish. Now, ASTRA et al solve this by simply using circular polarizations. Those are a bit more funky do draw, and antennas typically have some &quot;spiral&quot; shape, but it's one good way to avoid the dilemma you're in. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-05-26T11:27:31.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6237" PostTypeId="2" ParentId="1901" CreationDate="2016-05-27T03:56:53.187" Score="1" Body="&lt;p&gt;The R7000 and 7000+ are NOT quarter wave verticals they are HALF wave verticals( check dimensions you'll see starting 10 meters that its not 8ft=quarter wave , its about 12-13 ft , shortened from 16ft because of the traps)., the spokes at the base are NOT radials they are Counterpoises, 3 feet distance is not enough above metal roof or even an AC unit(I tried my AC unit and could never get ALL bands right), I suggest at least 8 preferably 10 ft above a metal object which Cushcraft exactly suggests if ground mounting the antenna.If u are using a metal roof, thats ur ground right there so we follow manufacturer's guideline=8 to 10ft. &lt;/p&gt;&#xA;" OwnerUserId="6758" LastActivityDate="2016-05-27T03:56:53.187" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6239" PostTypeId="2" ParentId="6228" CreationDate="2016-05-27T16:21:16.137" Score="3" Body="&lt;p&gt;You question seems to boil down to this: &quot;Do I need to be concerned about lightning protection, even though my antenna isn't very high relative to its surroundings?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer is yes. In fact you need to worry about lighting protection even if you have no antenna at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say you have this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/VfSog.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fVfSog.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You have your radios and whatever connected to a great big ground rod near the station. Maybe you attach the ground to the chassis, or maybe it's part of the ground for your antennas. Maybe you even make all the connections with heavy copper strap. Maybe you even have a mesh mat under the floor and the desk. This station is &lt;em&gt;really&lt;/em&gt; grounded.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And there isn't even an antenna. A lightning strike directly on your station is quite unlikely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Safe, right? No. We have failed to model the finite conductivity of the soil between the two ground rods. The situation is more like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/WJd2U.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fWJd2U.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Soil conducts electricity, but not very well, represented by the resistors between the two grounds. Now when lightning strikes nearby, maybe on the ground, maybe a tree, or maybe it hits the power lines, all that charge transferred by the strike needs to go somewhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the strike point, and at the instant the strike occurred, there's an excess of electric charge that was put there by the strike. Like charges repel, and so all this electric charge flies away from the strike point, until it's more or less evenly distributed over the surface of the Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where does it flow? Like all current, wherever it can. The lower the impedance of some path, the more the current will flow there. The soil is pretty resistive, and copper wires that run through your equipment is not. So you are providing the strike current a shortcut through the relatively poor soil conductor which goes through your equipment, probably resulting in damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lightning arrestors won't help you at all with this particular problem. They are essentially spark gaps. Consider, the strike current is driven by a force strong enough to create an arc between the ground and the clouds. A little piece of metal isn't going to stop the current that needs to get from point A to point B.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is &lt;em&gt;why&lt;/em&gt; you must consider lightning protection, no matter what your antenna installation, or indeed, even if you have no antenna at all. You must make sure there is no path between two points in the ground which flows through your equipment. &quot;Properly&quot; grounding your antenna is likely to do exactly this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt; for a more detailed explanation of how to ground your station in such a way that lightning damage is unlikely.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-05-27T16:21:16.137" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6240" PostTypeId="1" CreationDate="2016-05-27T19:07:25.540" Score="6" ViewCount="5142" Body="&lt;p&gt;I'm wrapping up a &quot;home build&quot; of the &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-941EK&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ-941EK antenna tuner kit&lt;/a&gt; and having trouble getting the wattmeter calibrated. I can't use C4 to get the reflected power reading calibrated down to 0 as is supposed to happen. So now I need to figure out what I got wrong, and to do that it would help to figure out how it's supposed to work in the first place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[&lt;strong&gt;UPDATE&lt;/strong&gt;: my theory now is that I fried D1 during initial testing and so I'm &lt;a href=&quot;https://electronics.stackexchange.com/questions/237295/schottky-diode-equivalence-in-rf-wattmeter&quot;&gt;pursuing a fix&lt;/a&gt; for that next. However I'd still appreciate an understanding of this circuit.]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MFJ helpfully provides the full schematic in the kit assembly manual. Here is the meter portion of the circuit. SW3a simply goes to a dummy load during calibration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/v9Rt8.png&quot; alt=&quot;Wattmeter half of MFJ-941EK schematic diagram&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The directional coupler transformer is implemented by routing the conductor from the transmitter plug through the middle of a toroid that had the secondary windings on it already.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bottom half of the circuit seems pretty straightforward. I imagine the diodes D1/D2 are used to &quot;detect&quot; the power (i.e. rectify the RF signal to a DC voltage) on each &quot;output&quot; of the directional coupler and the resistor networks that follow just put it into one of the two selected ranges appropriate for the galvanometers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But how is the coupler itself working? I've watched &lt;a href=&quot;https://www.youtube.com/watch?v=byF1FLdbUiA&quot; rel=&quot;nofollow noreferrer&quot;&gt;How a Directional Coupler in an SWR meter works&lt;/a&gt; a few times in the past; the math makes sense but it still's a bit magic to me. And in this circuit, it's a bit more complicated, and there's only one transformer instead of two. What is the purpose of the circuit (C4/C5/L2/R2) off the center tap of the transformer?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Seems like my problem is that I'm getting a voltage to D1 when there's not actually reflected power. The intended solution is that you simply adjust C4 to make that go away — and I &lt;em&gt;can&lt;/em&gt; increase/reduce the reading — but I can't zero it out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This same circuit is also sold as a commercial product, which MFJ calibrates themselves. So I doubt its simply a matter of sometimes needing &amp;lt;3pF or &gt;10pF from the trimcap; that would cause headaches on their factory floor. The trouble is that not knowing how the circuit is supposed to work, it's hard to track down where things are getting thrown off — whether the toroid got messed up, or whether an out-of-spec component could be throwing it, or what!&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="76" LastEditDate="2017-04-26T17:19:00.060" LastActivityDate="2017-04-26T17:19:00.060" Title="How should this SWR meter's directional coupler work?" Tags="&lt;diy&gt;&lt;rf-power&gt;&lt;electronics&gt;&lt;measurement&gt;&lt;swr-meter&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6241" PostTypeId="2" ParentId="6234" CreationDate="2016-05-28T03:40:00.590" Score="1" Body="&lt;p&gt;The simple answer is:  It depends... on a lot of stuff... power, interference, quality of service requirements, antenna type/height/location/obstacles, antenna system performance- gain, tuning, and yes orientation.  But communicating only a thousand feet over VHF/UHF should generally not be difficult.  In theory it is all critical.  In reality everything has a lot of flexibility and trade offs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Preferably antennas at each location should be the same orientation. Yes it does work much better that way.  However, using a horizontal antenna I've contacted 2-Meter stations with vertical antennas even 17 miles away! &lt;/p&gt;&#xA;" OwnerUserId="6762" LastActivityDate="2016-05-28T03:40:00.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6242" PostTypeId="2" ParentId="6233" CreationDate="2016-05-28T12:23:17.103" Score="5" Body="&lt;p&gt;DVB-T signals are OFDM (orthogonal frequency division multiplexing), which means that you take your symbols, put them in a vector, put that vector through a discrete fourier transform, and get the time-domain signal you want to transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, this is fine and all, but OFDM hence has a high Peak-to-average power ratio. Which means that your amplifier needs to be quite linear across large dynamic range – otherwise, you'll get nonlinearities, which means intermodulation, which means (in OFDM, at least) inter-symbol interference, which means symbol errors, which means bit errors... For means of PAPR reduction in DVB signals, &lt;a href=&quot;http://www.hindawi.com/journals/ijdmb/2010/797393/&quot; rel=&quot;noreferrer&quot;&gt;this paper&lt;/a&gt; might be of interest. The takeaway from that paper is that in an easy 1% of the symbols (i.e. in 1% of your data carrying units), there is a PAPR &gt; 12.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd say that infers a need for a spurious-free dynamic range of at least 20dB for your amplifier. Note that an amplifier rated for an output power $x$ will not be linear close to that power – take away around 9 dB, and you'd typically end up close to the upper edge of your linear range. That means that if you need 5W of power in the linear range, your amplifier would typically be rated $8\cdot 5\,\text W= 40\,\text W$. Note that this is really just a rule of thumb. How conservatively sellers spec their maximum output power or how much the amplifier is designed for maximum single-carrier or broadband transmission, or power efficiency, will play a big role. There's no way around getting some curve or numbers from which you can see how linear an amplifier is, over what range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the HackRF, being very universal, is not a spectacularly &quot;clean&quot; device, which means that your output signal might (will!) contain out-of-band emissions. You should probably counter that with an analog filter, which doesn't have to be overly sharp – just make sure no multiples of your center frequency and no dividers of it make it into the output. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look for impedance matching. I'm not quite sure, but from the top of my head, the HackRF has a nominal output impedance of 50 Ohm. It's probably slightly different for different frequencies, but you'll not lose much with that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Make sure the amplifier is not leaking back too much energy into it's input (input/output isolation). Rule of thumb: Max output power of HackRF - 3dB should be the maximum amount you leak back. Make sure not to start the HackRF in receive mode if the energy leaked into the connector would kill the sensitive input electronics.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-05-28T12:23:17.103" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6243" PostTypeId="1" AcceptedAnswerId="6244" CreationDate="2016-05-28T15:27:40.313" Score="2" ViewCount="384" Body="&lt;p&gt;I am looking for RTTY AFSK specifications. I am a little confused when coding the Baudot code; not the normal characters, but the symbols and numbers.&lt;/p&gt;&#xA;" OwnerUserId="6768" LastEditorUserId="76" LastEditDate="2016-05-28T17:59:06.463" LastActivityDate="2016-05-28T22:16:45.637" Title="How are symbols encoded in RTTY?" Tags="&lt;rtty&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6244" PostTypeId="2" ParentId="6243" CreationDate="2016-05-28T21:33:22.513" Score="8" Body="&lt;p&gt;The 5-bit &lt;a href=&quot;https://en.wikipedia.org/wiki/Baudot_code#ITA2&quot;&gt;Baudot code&lt;/a&gt; only has 32 combinations, so a special trick is used to encode 52 different letters, numbers and special symbols.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The key concept is that the receiver can be in one of two different states or modes, and two of the 32 codes are reserved for putting it into one state or the other. &lt;code&gt;11111&lt;/code&gt; puts it into &quot;letters&quot; mode, while &lt;code&gt;11011&lt;/code&gt; puts it into &quot;figures&quot; mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a few control codes that do the same thing regardless of which mode the receiver is in:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;code&gt;00000&lt;/code&gt; is &quot;null&quot;&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;00010&lt;/code&gt; is line feed&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;00100&lt;/code&gt; is space&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;01000&lt;/code&gt; is carriage return&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The remaining 26 codes are interpreted according to the current mode of the receiver. In &quot;letters&quot; mode, they represent the letters of the alphabet. In &quot;figures&quot; mode, they represent the digits and various special characters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, to transmit &quot;N3AOA&quot;, you would send the following string of codes:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;11111 01100 11011 00001 11111 00011 11000 00011&#xA;LTRS    N   FIGS    3   LTRS    A     O     A&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Does this address your confusion?&lt;/p&gt;&#xA;" OwnerUserId="1459" LastEditorUserId="1459" LastEditDate="2016-05-28T22:16:45.637" LastActivityDate="2016-05-28T22:16:45.637" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6245" PostTypeId="1" AcceptedAnswerId="6246" CreationDate="2016-05-29T09:12:36.907" Score="10" ViewCount="813" Body="&lt;p&gt;If I put my mobile phone in my microwave oven and close its door, &#xA;Should I be able to get incoming calls ?&#xA;Because, I tried it and I was able to get calls, what does it mean?&#xA;Does my microwave oven has a radiation leak?&lt;/p&gt;&#xA;" OwnerUserId="5673" LastEditorUserId="5673" LastEditDate="2017-04-17T19:44:05.730" LastActivityDate="2017-04-17T19:44:05.730" Title="Faraday cage in Microwave oven" Tags="&lt;microwave&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6246" PostTypeId="2" ParentId="6245" CreationDate="2016-05-29T11:31:04.363" Score="16" Body="&lt;p&gt;No, your oven does not have a dangerous leak. It is designed to only contain only the frequency used by the magnetron (2.45 GHz). The frequency bands used by cell phones are very different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In particular, the door &quot;seals&quot; are rather frequency-selective. Instead of trying to maintain a good electrical contact between the door and the rest of the oven box, they are designed as quarter-wave waveguide &quot;traps&quot; that prevent the microwave energy from getting past them. They have little to no effect on cellphone signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;https://skeptics.stackexchange.com/a/5410&quot;&gt;Skeptics.SE&lt;/a&gt; for additional details.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastEditorUserId="-1" LastEditDate="2017-04-13T12:46:46.753" LastActivityDate="2016-05-29T11:31:04.363" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6247" PostTypeId="2" ParentId="6240" CreationDate="2016-05-30T23:54:27.707" Score="2" Body="&lt;p&gt;&lt;strong&gt;Incomplete answer&lt;/strong&gt; — I still haven't figured this one out, but here's some leads/ideas I have so far.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I found a circuit with some similarities on Wikipedia called a &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Hybrid_coil&amp;amp;oldid=598460608#Single_transformer_hybrid&quot; rel=&quot;nofollow noreferrer&quot;&gt;single transformer hybrid coil&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/6KFh3.jpg&quot; alt=&quot;&amp;quot;Single transformer hybrid transformer&amp;quot; schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is described as follows:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;X, Y, and Z share a common ground. As shown at left, signal into W, the 2-wire port, will appear at X and Z. But since Y is bridged from center of coil to center of X and Z, no signal appears. Signal into X will appear at W and Y. But signal at Z is the difference of what appears at Y and, through the transformer coil, at W, which is zero. Similar reasoning proves both pairs, W &amp;amp; Y, X &amp;amp; Z, are conjugates.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In a paragraph &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Power_dividers_and_directional_couplers&amp;amp;oldid=708059548#Hybrid_transformer&quot; rel=&quot;nofollow noreferrer&quot;&gt;referencing this device in the context of directional couplers&lt;/a&gt; it is described a bit differently:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Power at port 1 is split equally between ports 2 and 3 but in antiphase to each other. The hybrid transformer is therefore a 180° hybrid. The centre-tap is usually terminated internally but it is possible to bring it out as port 4; in which case the hybrid can be used as a sum and difference hybrid. However, port 4 presents as a different impedance to the other ports and will require an additional transformer for impedance conversion if it is required to use this port at the same system impedance.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/hwF1b.png&quot; alt=&quot;Schematic: hybrid transformer for a 50 Ω system&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way the secondary windings are connected is significantly different in the MFJ version, however. Two of the &quot;ports&quot; are bridged together with a resistor that is three times the 50ohm characteristic impedance, and the center &quot;port&quot; goes into a bunch of other components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that R2/L2/CC5 form a &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=RLC_circuit&amp;amp;oldid=720848417#Parallel_RLC_circuit&quot; rel=&quot;nofollow noreferrer&quot;&gt;Parallel RLC circuit&lt;/a&gt;, used to &lt;a href=&quot;http://www.electronics-tutorials.ws/accircuits/parallel-circuit.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;vary the impedance&lt;/a&gt; of the so-called &quot;port 4&quot; across frequencies — whether this is to compensate for varying measurment response or simply to maintain a good match I'm not sure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And then I'm still stuck with what C4 is doing, coupling the center tap with the input for some reason.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that these schematics I found seem to be designed more as &quot;power dividers&quot; than &quot;directional couplers&quot; and so maybe that explains why things aren't quite matching up.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Update&lt;/strong&gt;: here's another clue. I found this schematic via &lt;a href=&quot;http://users.tpg.com.au/users/ldbutler/MeasBalLine.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Measurements on Balanced Lines Using the Noise Bridge &amp;amp; SWR Meter&#xA;&lt;/a&gt; by Lloyd Butler VK5BR, first published in &quot;Amateur Radio, July 1992&quot; and the diagram itself attributed to &quot;Amateur Radio, November 1969&quot;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/fUGHG.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The instrument operates by comparing two voltages. One voltage is derived from the voltage across the line and is proportional to (and in phase with) that voltage. The other is derived from the current through the line and is proportional to (and in phase with) that current. One type of instrument uses a loop run along in parallel with a length of the line to inductively couple the current component. The voltage component is capacity coupled into the loop. Most SWR meters are also calibrated in power, and this particular instrument, more often used at VHF/UHF, gives a power reading which varies with frequency. Hence it requires a power versus frequency calibration chart.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;An SWR meter, which is often assembled by the home constructor, makes use of a toroidal current transformer to derive the current sourced voltage component and a resistive voltage divider for the voltage component. A typical circuit taken from Amateur Radio, Nov 1969 (ref 1) is shown in figure 5. Because of the methods used to couple each component, the developed voltages are constant with frequency, and a calibration chart is not required. For this particular circuit, operation to 70MHz is claimed. For further explanation of the SWR meter we will make use of this circuit.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So here we see a very similar usage of two ports off a toroidal transformer. This time however, there is no center tap though and the resistor bridge between them only totals up to 1x the Z0.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-05-31T00:07:29.360" LastActivityDate="2016-05-31T00:07:29.360" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6248" PostTypeId="2" ParentId="1729" CreationDate="2016-06-01T02:10:44.483" Score="2" Body="&lt;p&gt;What you heard was a ceremony and tribute to a silent key&#xA;Silent key is a ham that has passed away , &#xA;The ceremony is called, The Final  Call&lt;/p&gt;&#xA;" OwnerUserId="6778" LastActivityDate="2016-06-01T02:10:44.483" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6250" PostTypeId="2" ParentId="1729" CreationDate="2016-06-01T17:02:56.950" Score="0" Body="&lt;p&gt;&lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?topic=40420.0&quot; rel=&quot;nofollow&quot;&gt;eHam Silent Key&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it wasn't done in a tradional way, at least the way I read it, because if it was a silent key ceremony, where was the silent keys' callsign?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;KC2JLJ&lt;/p&gt;&#xA;" OwnerUserId="6771" LastActivityDate="2016-06-01T17:02:56.950" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6255" PostTypeId="1" AcceptedAnswerId="6271" CreationDate="2016-06-03T21:12:02.273" Score="9" ViewCount="700" Body="&lt;p&gt;I've noticed while reading literature and websites geared towards and written by amateurs and ham radio enthiuasts that frequency bands are commonly referred to by wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In professional environments I have been a part of, we always used frequency (170 MHz) or band name (ie VHF, UHF) to describe the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why do hams prefer wavelength? Is this tradion or convention? Is it more accurate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have seen VHF frequencies referred to by wavelength and UHF frequencies referred to by frequency in the same sentence, thereby lacking consistency.&lt;/p&gt;&#xA;" OwnerUserId="4476" LastEditorUserId="4665" LastEditDate="2016-06-04T03:05:40.173" LastActivityDate="2016-06-13T20:11:09.217" Title="Why do Hams refer to bands by wavelength and not frequency?" Tags="&lt;frequency&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6256" PostTypeId="2" ParentId="6255" CreationDate="2016-06-03T22:03:31.277" Score="2" Body="&lt;p&gt;This is tradition, but also has some utility.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's true that the 2m band is not exactly 150 MHz - but it is useful to refer to the class of radios which will transmit on 144-148 MHz (US) or 144-146 MHz (UK) as 2m radios, rather than by frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It comes down to personal preference and what the audience is expecting. Almost everyone knows 2m means somewhere around 144-148 MHz. Most know that 70 cm is 420-450 MHz or so. Fewer people know that 13cm is 2.4 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Referring to something as &quot;UHF&quot; is also problematic - the PL-259 connector is also known as a &quot;UHF&quot; connector, because when it was created UHF meant above 30 MHz.&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2016-06-03T22:03:31.277" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6257" PostTypeId="1" CreationDate="2016-06-04T01:30:04.610" Score="1" ViewCount="171" Body="&lt;p&gt;I have a collection of medium old (in my opinion) radios such as a ts-440, ft-920, ft-840 and on all of them the vfo/tuning knobs are very stiff and &quot;stutter&quot; when turning. These radios have been in storage for a long time though they otherwise work.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Should I lubricate the shafts?&lt;/li&gt;&#xA;&lt;li&gt;How can I adjust the tension?&lt;/li&gt;&#xA;&lt;li&gt;Is there anything I should be careful of before removing the knobs?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5577" LastActivityDate="2016-06-05T11:11:12.810" Title="How to fix stickey VFO knobs on medium to old radios" Tags="&lt;repair&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6258" PostTypeId="2" ParentId="6255" CreationDate="2016-06-04T04:20:23.053" Score="5" Body="&lt;p&gt;I think that one reason is that talking about the wavelength gives an immediate sense of the scale of the antenna required.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2016-06-04T04:20:23.053" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6259" PostTypeId="2" ParentId="5179" CreationDate="2016-06-04T10:35:23.677" Score="4" Body="&lt;p&gt;So, a teaser first:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With GNU Radio, you can transmit various DVB standards. Here's Alexandru Csete &lt;a href=&quot;https://twitter.com/csete/status/738859910558015488&quot; rel=&quot;nofollow noreferrer&quot;&gt;demoing&lt;/a&gt; his DVB-S2 &lt;a href=&quot;https://twitter.com/csete/status/738860390868717568&quot; rel=&quot;nofollow noreferrer&quot;&gt;transmission&lt;/a&gt;:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/qRtpD.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qRtpD.jpg&quot; alt=&quot;GNU Radio Flow graph&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/QQhpO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QQhpO.jpg&quot; alt=&quot;TV showing video&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see from the FFT Plot generated by the flow graph in the upper picture, some 7MHz of bandwidth would be sufficient for this transmission mode – the HackRF should, like the device Alexandru used, be able to deal with the 10MHz that this flowgraph ran at. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The input is really just an MPEG transport stream file that's compatible with the DVB-S2 specs. You can find a lot of these at W6RZ Ron Economos' &lt;a href=&quot;http://www.w6rz.net&quot; rel=&quot;nofollow noreferrer&quot;&gt;website&lt;/a&gt;, who's the main author behind gr-dtv.  File source doesn't sound that great – but really, MPEG transport streams like this are meant to be streamed, and you can just replace that file in the file source with a named pipe and pipe the output of your MPEG encoder to it, or maybe just the MPEG transport screen you grabbed off the air from another broadcast. Also, because GNU Radio is so flexible, you could just replace the file source e.g. with a UDP source, and let another computer stream MPEG to that, in case your computer isn't up to SDR reception of video, reencoding &lt;em&gt;and&lt;/em&gt; SDR modulation. That's is a handful of things even for fast PC workstations!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm going to go ahead and shamelessly plug GNU Radio here: If you haven't heard about it, it is a Software Defined Radio framework. It's based on the idea of signal processing flow graphs, in which (as you can see in the upper screenshot) you connect blocks that contain functionality to a bigger, useful application. Such blocks can be simple things like &quot;multiply signal with a constant value&quot;, or more complex things like a DVB-S2 modulator, or they can also be hardware interfaces (the &lt;em&gt;osmocom Sink&lt;/em&gt; in the screenshot talks to your SDR device). You're also not limited to existing blocks: writing blocks that do things that aren't possible by combining existing blocks is easy, and there's a whole ecosystem of people writing modules for GNU Radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without further ado: GNU Radio's &lt;a href=&quot;http://gnuradio.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;website&lt;/a&gt; and the &lt;a href=&quot;http://tutorials.gnuradio.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;Guided Tutorials&lt;/a&gt;, which I strongly recommend.&#xA; Generating an FM receiver takes minutes from scratch if you went through them, which shouldn't take too long, either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm fully aware that SSTV with let's say 48kHz of sampling rate isn't really comparable to DVB-S2 with Megahertzes of bandwidth, but to answer your original question:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Could DVB-T be used with reduced parameters, thus smaller bandwidth? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You &lt;strong&gt;can&lt;/strong&gt; configure &lt;code&gt;gr-dtv&lt;/code&gt;'s DVB-T (contained in the standard GNU Radio source code) for smaller bandwidth than what is used in above example, no problem. The lowest standardized (and hence, decodable by anyone) bandwidth is 5 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;DVB-T is an OFDM-based transmission standard, and has a lot of channel coding. That makes a lot of sense, because it's designed to carry high-datarate bitstreams, and thus, by Shannon's Channel Capacity, needs a large bandwidth for a limited SNR. High bandwidth means that the channel response isn't &quot;flat&quot;, ie. attenuation and rotation aren't the same for all frequency within that bandwidth. You need an equalizer to counter that at the receiver – equalizers are hard to do right, and even harder to implement fast, and so standards like DVB, IEEE802.11a/g/n/p (WiFi), LTE… take the channel and divide it into small subchannels with a DFT (the frequencies in the DFT don't cross-talk, hence the &quot;O&quot; in OFDM, Orthogonal Frequency Division Multiplex). That way, you get a lot channels, but each of those is flat, so equalization is really just one independent correction factor per subcarrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you reduce the bandwidth of OFDM a lot, you lose that advantage, and also get into SNR problems (signals within a small bandwidth necessarily have less energy than signals of the same spectral density in a larger bandwidth), so I'm not sure that scaling DVB-T below let's say 2MHz would work.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-06-04T10:44:53.317" LastActivityDate="2016-06-04T10:44:53.317" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6260" PostTypeId="2" ParentId="6255" CreationDate="2016-06-04T12:14:15.377" Score="6" Body="&lt;p&gt;I'd agree with @user3486184's &lt;a href=&quot;https://ham.stackexchange.com/a/6256/4076&quot;&gt;answer&lt;/a&gt;, that this is primarily an effect of tradition. However, what @DaveTweed &lt;a href=&quot;https://ham.stackexchange.com/a/6258/4076&quot;&gt;answered&lt;/a&gt; hit the spot how that tradition came to be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In early radios, you really had not much of a notion of electrical fields doing something periodic at a fixed frequency; these were simple crystal radios, doing nothing but taking the envelope of the (rectified) signal they were fed. They weren't radio frequency selective at all – the channel selection happened by &lt;em&gt;tuning the antenna&lt;/em&gt; (ie. matching its resonant frequency to the channel you want to receive), not the receiver circuit, like in (most) modern radios!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So antenna designers were the people that actually executed the concept of channel selectivity first, hence they got some normative powers :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, if you look at this, you'll notice that for someone who builds frame or long wire antennas, &lt;em&gt;wavelength&lt;/em&gt; is an excellent description of what they'd be designing the antenna for. You can, within boundaries of material effects, usually scale any antenna design to a different frequency/wavelength by just multiplying its dimensions – and hence, someone who was able to build 200m antenna, was instantly also able to build one for 20m. They were the kind of people that build radio receivers that made it to the &quot;living room customer market&quot;, and hence, they decided what as on the frequency selection scale. That was meters.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-06-04T12:14:15.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6261" PostTypeId="2" ParentId="6255" CreationDate="2016-06-04T15:30:17.793" Score="4" Body="&lt;p&gt;When I say: &quot;I was on the air on 15 meters&quot;, everyone will know that I had some contacts with other stations on one or several different frequencies in the range from 21.000 to 21.450 MHz (at least that's the 15m band in Germany).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I say, &quot;I was on the air on 21 Megahertz&quot; instead of 15 meters, someone could think that I were on air on exactly that frequency. You could of course also say &quot;I was on the air on the 21 Megahertz band&quot; but saying that takes longer, so it is easier to say &quot;on 15 meters&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I think it is both a way to keep the description of the band shorter and to clarify that you were on air on a frequency range rather than one frequency only.&lt;/p&gt;&#xA;" OwnerUserId="6781" LastEditorUserId="4665" LastEditDate="2016-06-13T20:11:09.217" LastActivityDate="2016-06-13T20:11:09.217" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6263" PostTypeId="2" ParentId="6257" CreationDate="2016-06-05T11:11:12.810" Score="1" Body="&lt;p&gt;Old plastic can crack into tiny bits, ruining everything; however yours doesn't sound that old.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally, silicone grease applied to moving surfaces is the best; it doesn't degrade plastic, lots of things do degrade plastic. Apply to shafts after removing them if that seems best, don't use too much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although silicone grease (sold for putting on spark plugs among other things) doesn't harm plastics as far as I know, silicone sprays contain nasty solvents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tension adjustments are probably different from radio to radio, think old fashion stringing diagrams.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be careful when loosening and tightening knob screws, the can crack plastic on the way in or out.&lt;/p&gt;&#xA;" OwnerUserId="7795" LastActivityDate="2016-06-05T11:11:12.810" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6264" PostTypeId="2" ParentId="5863" CreationDate="2016-06-05T18:45:43.563" Score="1" Body="&lt;p&gt;You might try using a receiving end fed balun at the end of a 45 ft wire strung by 2 insulators on each side of the wire.  Don't forget a surge protector in line to protect the receiving front end of your JRC NRD-545.  I have a receiving antenna for my Icom IC-746 Pro using regular RG-6U TV Coax fed about 50 ft. between the radio and the antenna.  You have to search for 2 PL259 Male to F female adapters for connecting the TV cable.  The nice thing about this is that it's pretty stealth with 14 AWG black insulated wire.  Also the nice feature is the antenna does not need to be tuned because it's broadband from 50 KHz to 30 MHz.  You might find one on ebay.  I must mention there is book for Receiving Antennas by Joe Carr.    &lt;/p&gt;&#xA;" OwnerUserId="7797" LastActivityDate="2016-06-05T18:45:43.563" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6265" PostTypeId="2" ParentId="6196" CreationDate="2016-06-06T00:45:03.010" Score="0" Body="&lt;p&gt;A few notes on top of the other answers: a few feet of copper/copper-clad-steel to make a ground post is a good idea, a copper or tinned braid into the house from the post is (at HF) a conductor to ground, and a single ground point for your station (I've seen a copper pipe used on the back of a ham station's bench) to strap your rig/DC supplies/lighting arrestors to rounds out grounding. Make sure that you have secure connections between each. A screw clamp with multiple bolts outside and some good pipe clamps inside should ensure you've got a good connection. Definitely inspect the outside connection every couple months.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For some NEC-based advice on conforming to safety standards for antenna installation, &lt;a href=&quot;http://www.reeve.com/Documents/Articles%20Papers/AntennaSystemGroundingRequirements_Reeve.pdf&quot; rel=&quot;nofollow&quot;&gt;this document&lt;/a&gt; is a good resource (also available in the Internet Archive Wayback Machine).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To protect against lightning/static discharge when you're away from your station, a coax switch to choose between your antenna with lighting arrestor and an inside dummy load/cantenna would make disconnect easy. This also makes it more difficult to inadvertently transmit from your station, provided you remember to change from antenna to load at the end of each session. Remember to choose a load that has a short-time rating for your usual transmitter (or amplifier) output power setting and frequency. &lt;/p&gt;&#xA;" OwnerUserId="7798" LastEditorUserId="7798" LastEditDate="2016-06-06T00:53:29.853" LastActivityDate="2016-06-06T00:53:29.853" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6266" PostTypeId="2" ParentId="4980" CreationDate="2016-06-06T01:48:28.347" Score="2" Body="&lt;p&gt;This appears to be a design that uses a harmonic mixer (or a subharmonic mixer, both names are used on the &lt;a href=&quot;https://en.wikipedia.org/wiki/Harmonic_mixer&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia page&lt;/a&gt;).  While these are more commonly used at microwave or millimeter wave frequencies in contemporary equipment, they were probably reasonable, low-cost solutions for these single-conversion receivers. As described in the text, VD1 and VD2 form the mixer for this radio receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a consequence of being a harmonic mixer, the mixer uses a harmonic of the local oscillator, making the local oscillator a subharmonic of the radio frequency being received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A diagram for a microwave-type mixer using this concept shows the anti-parallel diodes seen in the HF mixer in the question's design. This is currently advantageous because generating high-power oscillations &gt;10GHz is difficult and there are applications targeting 60 and 70 GHz with &lt;a href=&quot;http://www.keysight.com/en/pc-2033178/smart-harmonic-mixers?cc=US&amp;amp;lc=eng&quot; rel=&quot;nofollow noreferrer&quot;&gt;test equipment&lt;/a&gt; up to 110 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hV4lw.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hV4lw.gif&quot; alt=&quot;harmonic mixer image from http://www.microwavejournal.com/legacy_assets/FigureImg/AR_5033_fig02_L.gif&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="7798" LastActivityDate="2016-06-06T01:48:28.347" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6267" PostTypeId="1" CreationDate="2016-06-06T02:18:08.507" Score="1" ViewCount="1382" Body="&lt;p&gt;Need to duplicate gqrx settings in rtl_fm command line switches. Review of rtl_fm docs has yielded no joy. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;gqrx configuration:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Freq 156.425 Mhz&lt;/li&gt;&#xA;&lt;li&gt;Filter: Wide&lt;/li&gt;&#xA;&lt;li&gt;Mode: Narrow FM&lt;/li&gt;&#xA;&lt;li&gt;AGC: Fast&lt;/li&gt;&#xA;&lt;li&gt;Squelch: -58.5 dBFS&lt;/li&gt;&#xA;&lt;li&gt;LNB LO: 0Mhz&lt;/li&gt;&#xA;&lt;li&gt;Gain: 10&lt;/li&gt;&#xA;&lt;li&gt;Freq Correction: 0ppm&lt;/li&gt;&#xA;&lt;li&gt;Stream as UDP&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Stream as UDP nice but not required... TIA for your assistance. Project background and details on request...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;----------------Edit--------------&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Details of project follow as requested.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The Project:&lt;/strong&gt;&#xA;The Boot Key Harbor Cruisers Net is a marine vhf net that meets every morning at 0900 in support of the local community of cruising boats here in Marathon. In the winter &quot;season&quot; we can have as many as 300+ boats in the harbor and surrounding area. After discussions with some of the other net-controllers, we decided it would be good to push the broadcast onto the internet so folks not able to participate on the live VHF net due to moving outside the local area or time constraints like a job, can still listen &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Goals and Requirements:&lt;/strong&gt;&#xA;Eventually, we would like to be able to record and push the mp3 encoded files to the internet server unattended. Currently the recordings are started and stopped manualy using the hardware/software listed below. If we can get the physical footprint small enough and operate &quot;headless&quot; we may be able to convince the Marathon City Marina (one of our sponsors) to allow us to hang the system off their tower with an ethernet connection to the public wifi router. To this end, my logic dictates a RasPi2 or 3 running linux and arm compatible software. The low power requirements of the Pi would allow it to run 24/7 with recording and SFTP functions controlled by simple bash scripts. Therefor, we are looking at linux only software that also can be run from the command line only (No gui).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Hardware:&lt;/strong&gt; (Current)&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Standard 1/4 wave loaded VHF whip antenna. Elevation aprox 15'.&lt;/li&gt;&#xA;&lt;li&gt;Rtl-Sdr usb dongle (RTL2832U with 1ppm TCXO). Coupled direct to antenna with PL-259/SMA male adaptor.&lt;/li&gt;&#xA;&lt;li&gt;15' usb cable (no balun)&lt;/li&gt;&#xA;&lt;li&gt;IBM t42 laptop running linux OS&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Software:&lt;/strong&gt; (Installed)&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Navigatrix OS (Debian/Ubuntu 14.04)&lt;/li&gt;&#xA;&lt;li&gt;RTL-SDR (current latest)&lt;/li&gt;&#xA;&lt;li&gt;GnuRadio (current latest)&lt;/li&gt;&#xA;&lt;li&gt;Gqrx (current latest) &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;History, Issues, Current Status:&lt;/strong&gt;&#xA;Initial setup using rtl_fm tested on VHF WX2 (162.4M)with good results. 1Kw station with tall tower located about 25 miles distant. rtl_fm test on Cruisers Net VHF 68 (156.425M) very poor quality do to interfering signal at about 156.125M (See gqrx waterfall screen shot below). Testing using gqrx usuable to good quality despite strong nearby signal. Encoded udp stream as mp3 using | sox and pushed to server via sftp (manual). Usuable gqrx settings as follow:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Filter: Wide&lt;/li&gt;&#xA;&lt;li&gt;Mode: Narrow FM&lt;/li&gt;&#xA;&lt;li&gt;AGC: Fast&lt;/li&gt;&#xA;&lt;li&gt;Squelch: -58.5 dBFS&lt;/li&gt;&#xA;&lt;li&gt;LNB LO: 0Mhz&lt;/li&gt;&#xA;&lt;li&gt;Gain: 10&lt;/li&gt;&#xA;&lt;li&gt;Freq Correction: 0ppm&lt;/li&gt;&#xA;&lt;li&gt;Stream as UDP&lt;/li&gt;&#xA;&lt;li&gt;Freq 156.425M&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Have been unable to duplicate gqrx settings in rtl_fm after numerous tries despite going over the rtl_fm documentation numerous times. While gqrx works as long as I am here to interact with the gui, it is not command line happy as far as scheduled control via bash. Rtl_fm also has another issue with how it handles squelch. When squelch kicks in, it stops output and busts the sox recording pipe. Found a modified version that is supposed to address this issue, plus another that includes outputing a udp stream rather than a raw file, but until I can get the command line switches set up to match the working gqrx config, its kinda a moot point... One thing at a time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[b]Specific Questions:[/b]&#xA;Can anyone help us configure the gqrx command line to the same config as gqrx listed above? Any suggestions as to software we have not tried yet that will meet the requirements of command line operation? Have not tried RTLSharp yet... know it will run on linux under mono, but not sure on raspian.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have read this far, thanks for your patience. You can listen to test recordings on our partial website at bootkeycruisers.net Screen shot of typical gqrx waterfall below (no traffic on target freq).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kF2xe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kF2xe.png&quot; alt=&quot;gqrx screenshot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="7799" LastEditorUserId="4076" LastEditDate="2020-04-26T13:39:59.360" LastActivityDate="2020-04-26T13:39:59.360" Title="Transposing gqrx setup to rtl_fm?" Tags="&lt;gnuradio&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6270" PostTypeId="2" ParentId="4980" CreationDate="2016-06-07T07:23:22.360" Score="0" Body="&lt;p&gt;How does it work? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Its a good question. I will be using example frequencies and not the actual ones used in a real receiver. The Design is called the Superheterodyne receiver and what happens is that you will get EVERY frequency coming in to the arial(assuming that the arial is tuned for all frequencies) so having a tuned arial starts to reduce the frequencies incoming on the input. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next you are interested in say 1500khz frequency (AM signal here for simplicity)&#xA;so you set your local ocillator to either 2400khz or 600khz (difference of 900 khz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The local ocillator is mixed with the incoming signal from the arial which will for our wanted frequency provide the original signals, the sum and the difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1500,600,900,2100&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because your next stage is a Band pass filter tuned to 900khz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;meaning only the difference is passed through to the Audio amplifier stage &#xA;which uses a diode to remove the radio frequency and pass only the audio signal out to the speakers.&lt;/p&gt;&#xA;" OwnerUserId="7803" LastActivityDate="2016-06-07T07:23:22.360" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6271" PostTypeId="2" ParentId="6255" CreationDate="2016-06-07T07:26:34.813" Score="3" Body="&lt;p&gt;Just to add to the answers already given; there used to be a practice to call &quot;CQ 40m&quot; indicating you are indeed on the 40m band, avoiding stations to comeback to your call if your transmitter would have harmonics... say in the 15m band... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This was obviously a long time ago, when filtering harmonics was more difficult, and more difficult to measure/tune when building/operating equipment... and probably license conditions were different then today's.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Still this practice can be heard on the bands today, although modern transmitters would not have harmonics (or should not have harmonics) outside the band. I guess old habits die hard, especially in Amateur Radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess the practice referring to the bands is also a matter of &quot;least effort to indicate&quot;. Which is already discussed in previous answers. Far more practical to say &quot;I had some contacts on the 20m band&quot; is stead of &quot;I had some contacts between 14.000 MHz and 14.350 MHz&quot;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;or band name (ie VHF, UHF) to describe the signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To answer that part of the OP question: the indication of VHF/UHF, and respecively HF would be a too broad indication to be accurately describing the operating band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you would take HF alone, it would be 9 (or 10, or 11 bands) which are included, namely: 80m, 60m, 40m, 30m, 20m, 17m, 15m, 12m, 10m. Some will count the 6m band as HF and some will count the 160m as HF. Although I believe 6m is actually inside VHF and 160m is actually MF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF would have 3, or 4 bands; 6m, 4m, 2m, and some regions will have an allocation at 220MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And so on so forth; so the indicators &quot;VLF, LF, MF, VHF, UHV, and higher&quot; are not suitable for use for Amateur radio to indicate where you are operating, they do have their uses, and are used if a &quot;broad term&quot; is sufficient in the context of what is communicated...&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-06-07T07:33:27.597" LastActivityDate="2016-06-07T07:33:27.597" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6272" PostTypeId="2" ParentId="6196" CreationDate="2016-06-07T14:37:37.977" Score="0" Body="&lt;p&gt;Lived in this house for over 30 years and never experienced a lightning hit at my house and I have a 50ft mast with an old C-Band antenna outside. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After talking to local hams in my area, I'm just going to rely on my regular three-prong ground in my house with a GFI socket. I will have a pass through panel on my window that hooks up the two outside antennas (UHF/VHF and HF loop) to the rig inside. In case of storms, I simply disconnect all inside connections at the window pane. The loop is going to run under the eaves of my house not 60 ft in the air, so no danger of lightning there. The UHF/VHF antenna will extend a mere 5ft over the roof, and I will run a ground to the meter for it. &lt;/p&gt;&#xA;" OwnerUserId="7805" LastActivityDate="2016-06-07T14:37:37.977" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6274" PostTypeId="1" AcceptedAnswerId="6275" CreationDate="2016-06-10T03:57:06.517" Score="7" ViewCount="9667" Body="&lt;p&gt;Doing some study for the ham test, I read a question asking about a certain “national calling frequency”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is a “calling frequency”?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is meant by “calling” in this instance?&lt;/p&gt;&#xA;" OwnerUserId="7818" LastEditorUserId="76" LastEditDate="2016-06-10T14:37:44.770" LastActivityDate="2018-10-06T12:58:34.810" Title="What is a &quot;calling frequency&quot;?" Tags="&lt;frequency&gt;&lt;jargon&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6275" PostTypeId="2" ParentId="6274" CreationDate="2016-06-10T04:19:04.117" Score="8" Body="&lt;p&gt;A calling frequency is a common channel known to all - this is the channel that anyone can jump onto and say Hi! Or a specific person you know may be monitoring this channel, you can call out to them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should you wish to hold a longer conversation, you would use this channel to agree upon which channel you will be switching to.&lt;/p&gt;&#xA;" OwnerUserId="5618" LastEditorUserId="5618" LastEditDate="2016-06-10T19:15:41.153" LastActivityDate="2016-06-10T19:15:41.153" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6276" PostTypeId="1" CreationDate="2016-06-10T17:30:04.553" Score="2" ViewCount="109" Body="&lt;p&gt;What are the &lt;strong&gt;bit per second&lt;/strong&gt; ratings and &lt;strong&gt;signal-to-noise-ratio&lt;/strong&gt; ratings of various modern, popular, good performance and well supported digi-modes for HF low power (0.1 watt) long distance (500 to 10000km) communication? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My brief understanding is that BPS is a trade off for SNR. PSK31 is 31 BPS. JT9 is slower, 13 characters per 50 seconds, but with better SNR rating. &lt;/p&gt;&#xA;" OwnerUserId="1473" LastActivityDate="2016-06-12T07:24:46.800" Title="Transmission speed of modern digi-modes" Tags="&lt;digital-modes&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6277" PostTypeId="1" CreationDate="2016-06-10T18:15:31.197" Score="1" ViewCount="163" Body="&lt;p&gt;Will SDR, like &lt;strong&gt;RTL SDR dongle and Ham it Up&lt;/strong&gt; converter, performing as well as traditional desktop HF receiver for digi-modes, like JT9, for HF low power (0.1 watt) long distance (500 to 10000km) communication?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On paper specification, JT9 signal can be 20 to 30dB lower than noise. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the &lt;strong&gt;sensitivity&lt;/strong&gt; for the above SDR setup in dBm?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will the &lt;strong&gt;noise&lt;/strong&gt; generate by the SDR chip (RFI radiating from chip, do we need foiling it with copper foil?) or the ADC quantization noise (it that 8 bit ADC inside?) make it not suitable for low SNR digi-modes?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Ham it Up has simple front end, will adding &lt;strong&gt;passive LC filter&lt;/strong&gt;, at antenna terminal, help to cut down un-wanted interference, says for 10MHz band?      &lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="4076" LastEditDate="2016-06-12T00:36:10.167" LastActivityDate="2016-06-17T18:38:42.117" Title="SDR dongle and HamitUp for QRP Digi-modes" Tags="&lt;digital-modes&gt;&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6278" PostTypeId="2" ParentId="5554" CreationDate="2016-06-10T18:37:53.473" Score="2" Body="&lt;p&gt;The LoRa standard use spread spectrum technology, provides 20 to 30 dB improvement over traditional modes, when configure at the type of low speed that you require. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some test documented on web shows 20km using 0.1 watt.  These chip work at Global bands, EU, US ISM, 430, 8xx and 9xxMHz&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Adafruit sites as full tutorial for two Arduino libraries &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sigfox is a competing standard, using ultra narrow band&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.adafruit.com/products/3071&quot; rel=&quot;nofollow&quot;&gt;Adafruit&lt;/a&gt;&#xA;&lt;a href=&quot;http://www.hoperf.com/rf_transceiver/lora/&quot; rel=&quot;nofollow&quot;&gt;hopeRF&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1473" LastActivityDate="2016-06-10T18:37:53.473" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6280" PostTypeId="2" ParentId="6274" CreationDate="2016-06-11T03:38:46.137" Score="4" Body="&lt;p&gt;Calling frequencies are defined for specific bands and most common for VHF and UHF and are mode specific (i.e. Weak signal, FM simplex, etc.).  In fact, knowing calling frequencies such as 2-meter simplex calling frequency is a typical question on the Technician license test in the US.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Making contacts on VHF and UHF bands is often more difficult (simplex or also weak signal that is) due to various propagation factors and the size of the band.  So, calling frequencies are well used.  For example, on 2-meters, you can agree to meet someone on 146.52 (2 meter simplex FM calling frequency) and then when contact is made QSY to some other open frequency.  It is not polite to tie up the calling frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I am mobile, the only VHF ops I do is hanging out on the 2-meter calling frequency.  I almost never initiate a call but often reply when someone raises a general call or question about nearby restaurants, gas stations, rest stops, whatever.  Most of my other mobile ops is HF mobile CW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find lists of defined calling frequencies for US operations on the ARRL web page, it is part of the published band plans: &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow&quot;&gt;http://www.arrl.org/band-plan&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-06-11T03:38:46.137" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6281" PostTypeId="1" AcceptedAnswerId="16278" CreationDate="2016-06-11T08:58:05.423" Score="1" ViewCount="3463" Body="&lt;p&gt;If system 1 has 10 dB return loss and system 2 has 20 dB return loss then what is the overall return loss of cascaded system of 1&amp;amp;2 ?  &lt;/p&gt;&#xA;" OwnerUserId="7827" LastActivityDate="2021-02-04T11:56:15.560" Title="How to calculate Return loss of cascaded system?" Tags="&lt;transmission-line&gt;&lt;microwave&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6282" PostTypeId="1" AcceptedAnswerId="6290" CreationDate="2016-06-11T16:55:08.490" Score="1" ViewCount="235" Body="&lt;p&gt;By the FCC rules, if you are in an emergency situation and it's your best chance at survival, you're allowed to TX on any frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what if you're hiking and are monitoring the Search &amp;amp; Rescue frequencies just in case you hear something and you hear that somebody is in dire need of services within a few hundred yards of you but it'll take SAR a long while to get there? Are you allowed to transmit to provide aid in the meantime?&lt;/p&gt;&#xA;" OwnerUserId="4860" LastEditorUserId="76" LastEditDate="2017-04-16T14:59:45.840" LastActivityDate="2017-04-16T14:59:45.840" Title="TXing on another frequency to provide aid in anothers' emergency" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6283" PostTypeId="2" ParentId="6276" CreationDate="2016-06-11T20:37:24.903" Score="2" Body="&lt;p&gt;I can't answer your &quot;bits-per-second in actual usage&quot; question, because I've never worked at HF myself. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My brief understanding is that BPS is a trade off for SNR.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;SNR (Signal-to-Noise Ratio) is what you effectively see on the receiver, not something that you can directly influence by your choice of bps – but they are, indeed strongly linked:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, for a higher bit rate, you need higher bandwidth. Higher bandwidth means that your receive filter needs to be wider. Higher filter bandwidth means higher equivalent noise bandwidth. And noise power in your receive signal is proportional to that bandwidth. So, if you've got to signals, both with a signal power of x Watt, and one is 10 kHz wide, and the other is 10 MHz wide, then the filter bandwidth for the 10 MHz one will necessarily &quot;let through&quot; thousand times the noise, and SNR for the 10 kHz signal (same signal power!) will be 30dB better (=factor of thousand, due to noise being only one thousandst).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I said &quot;Generally, for a higher bit rate, you need higher bandwidth&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does that happen?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, mathematically proven is that you cannot shove arbitrarily much data over any link. That's called the &lt;strong&gt;Channel Capacity&lt;/strong&gt;, and it's actually measured in bits per second!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let us bask in the formulas for a second. However, I need to stress this: &lt;strong&gt;This is a theoretical boundary for what is &lt;em&gt;possible&lt;/em&gt; with a given link. It does not say that any transceiver does actually achieve that rate. However, there's no transceiver that &lt;em&gt;could be faster&lt;/em&gt;.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;C&amp;amp;= B\cdot \log_{2}\left(1+\frac SN\right)\\&#xA;\text{with:}\\&#xA;C:&amp;amp; \text{ the channel capacity}\\&#xA;B:&amp;amp; \text{ bandwidth}\\&#xA;S:&amp;amp;\text{ signal power}\\&#xA;N:&amp;amp;\text{ noise power}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, as you can see, the amount of bits you can push through a channel per second is &lt;em&gt;proportional&lt;/em&gt; to its bandwidth $B$. And also, it goes with the &lt;em&gt;logarithm&lt;/em&gt; of the SNR – which itself only increases linearly with the signal power $S$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's the first takeaway here: &lt;strong&gt;If you want to double the possible bitrate of a link, you can double the bandwidth and double the transmit power to keep SNR constant,or you can just use much much more power&lt;/strong&gt;. That's the reason why non-ham high rate systems have high bandwidth, but rarely much power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;You asked about SNR for a specific HF scenario. So let's roll!&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;TX power: $P_{TX}=0.1\text{ W}$&lt;/li&gt;&#xA;&lt;li&gt;operational frequency: Let's say we're using one of the subbands of the 15m band $f=c_0\cdot\lambda=300\cdot 10^6\frac{\text m}{\text s}\cdot 14.184\text{ m}=21.15\text{ MHz}$, $c_0$ is the speed of light, $\lambda$ our wavelength&lt;/li&gt;&#xA;&lt;li&gt;Bandwidth: highest legal bandwidth (to my knowledge) $B=2.8\text{ kHz}$&lt;/li&gt;&#xA;&lt;li&gt;Distance: Let's do this for $d_0= 500\text{ km}$, or expressed in wavelengths $\lambda$, $\frac{d_0}{\lambda} =35250$.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;We don't know our antennas (yet?), so let's just roll with antenna gains $G_{TX}$ and $G_{RX}$ for the transmit and receive antennas, respectively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, due to free space loss, the power $P_{RX}$ reaching the receiver is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;P_{RX}&amp;amp;= P_{TX}\left(\frac{\lambda}{4\pi d_0}\right)^2\,G_{TX}G_{RX}\\&#xA;&amp;amp;\text{which, in our special case, is, entering numbers}\\&#xA;&amp;amp;=0.1\text{ W} \left(\frac{1}{4\pi 35250}\right)^2\, G_{TX}G_{RX}\\&#xA;&amp;amp;\approx 5.1 \cdot 10^{-13}\text{ W}\,G_{TX}G_{RX}\\&#xA;&amp;amp;\text{this is not handy. Let's put it as dB:}\\&#xA;&amp;amp;\approx -123 \text{ dBW}+ G_{TX}\,[\text{dB}] + G_{RX}\,[\text{dB}]\\&#xA;&amp;amp;=-93 \text{ dBm} + G_{TX}\,[\text{dB}] + G_{RX}\,[\text{dB}]\\&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the receiver, we get a really good filter and filter exactly to $B=2.8\text{ kHz}$. We know that thermal noise power in any receiver is given by&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;P_N &amp;amp;= kBT\\&#xA;\text{with}\\&#xA;P_N:&amp;amp;\text{ noise power}\\&#xA;k:&amp;amp;\text{ Boltzmann's constant}\\&#xA;T:&amp;amp;\text{ absolute system temperature}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I've learned by heart that noise power in 1 Hz is always -174 dBm at room temperature, or&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$P_N = -174\frac{\text{dBm}}{\text{Hz}} + B\,[\text{dBHz}]$$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our $28\text{ kHz}\approx 34.5\text{ dBHz}$, so $P_N=(-174+34.5)\text{ dBm}= -139.5\text{ dBm}$. That allows us to calculate SNR:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;\frac SN &amp;amp;= \frac{P_{RX}}{P_N}\\&#xA;&amp;amp;= -93 \text{ dBm} + G_{TX}\,[\text{dB}] + G_{RX}\,[\text{dB}] &amp;amp;-&amp;amp; -139.5\text{ dBm} \\&#xA;&amp;amp;= 46.5\text{ dB} + G_{TX}\,[\text{dB}] + G_{RX}\,[\text{dB}]\text{.}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So assuming you have no antenna gain whatsoever, i.e. your antenna is an isotropic radiator, you still get an SNR of $\text{SNR}_{500\text{ km}}=46.5\text{ dB}$, which is pretty awesome! (By the way, we're neglecting interference here.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While we're at it, let's derive the Channel Capacity for this case:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;C_{500\text{ km}} &amp;amp;= 2.8\text{ kHz} \log_2 \left( 1+ 46.5\text{ dB}\right)\\&#xA;&amp;amp;= 2800 \frac1{\text s}\log_2 \left( 1+ 10^{4.65}\right)\\&#xA;&amp;amp;\approx 43.25\frac{\text{kb}}{\text s}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, we must assume that the digital mode you want to use also has to work with the 10,000 km link. From the formula for the free space loss above we see that receive power &lt;strong&gt;reduces with the square of distance&lt;/strong&gt;. Since 10,000 km is 20 times the distance of 500 km, the receive power will be &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;P_\text{RX, 10,000 km}&amp;amp;= \frac1{20^2}P_\text{RX, 500 km}\\&#xA;&amp;amp;=\frac1{400}\cdot-93\text{ dBm}\\&#xA;&amp;amp;=-26\text{ dB}-93\text{ dBm}\\&#xA;&amp;amp;=-119\text{ dBm}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So we suffer from a 26 dB worse SNR, i.e. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{SNR}_{10,000\text{ km}}=46.5\text{ dB}-26\text{ dB}= 20.5\text{ dB} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a 20.5 dB SNR, our Channel capacity reduces to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;C_{10,000\text{ km}} &amp;amp;= 2.8\text{ kHz} \log_2 \left( 1+ 20.5\text{ dB}\right)\\&#xA;&amp;amp;= 2800 \frac1{\text s}\log_2 \left( 1+ 10^{2.05}\right)\\&#xA;&amp;amp;\approx 19\frac{\text{kb}}{\text s}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, this is a &lt;em&gt;maximum achievable rate&lt;/em&gt;, and it assumes you do a lot of stuff right: filtering, modulation/demodulation, and channel coding, and even then, it doesn't say &lt;em&gt;how&lt;/em&gt; to build a transceiver that achieves that rate. It's really just a theoretical limite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham systems are –intentionally, and by tradition– not as complex and optimized as commercial communication systems and hence tend to have a much lower spectral efficiency – you'll be happy if you can get more than one kilobit across.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-06-11T21:10:45.463" LastActivityDate="2016-06-11T21:10:45.463" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6284" PostTypeId="2" ParentId="6276" CreationDate="2016-06-12T07:24:46.800" Score="0" Body="&lt;p&gt;Signal to noise ratio rating shows how protocol can cope in bad signal conditions, meaning if this ratio is lower protocol can handle worse signals. Some protocols can handle signals lower than noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bits per second rating shows speed of data transfer protocol can provide. In practice, lower signal to noise ratio is achieved by slowing down data transfer.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-06-12T07:24:46.800" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6285" PostTypeId="2" ParentId="5554" CreationDate="2016-06-12T07:33:02.243" Score="0" Body="&lt;p&gt;For such terrain I guess something in lower frequencies would do better. There are some cheap wireless serial radio modules for Arduino that use 433 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other viable solution is xBee, but it uses higher frequencies, and it is more expensive.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-06-12T07:33:02.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6287" PostTypeId="2" ParentId="6282" CreationDate="2016-06-12T18:04:30.093" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Are you allowed to transmit to provide aid in the meantime?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In this specific instance, one should not change their course of action (transmit out of permissible band) based on judgments here or the threat of FCC reprisal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;FCC rules usually permit during emergencies “any means necessary” to communicate in order to protect life and property.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this a Type Specific/Type Certified question, or one of morality, it may be bordering on &quot;off-topic&quot; for this forum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do what you do, and in an emergency situation Charlie and &quot;legal&quot; opinions rendered from experts here should be the last of your concerns.  To the SAR/First Responder, you'll be somewhere between a big help to a hero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73  KC2JLJ&lt;/p&gt;&#xA;" OwnerUserId="6771" LastEditorUserId="6771" LastEditDate="2016-06-12T18:16:52.520" LastActivityDate="2016-06-12T18:16:52.520" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6288" PostTypeId="2" ParentId="6147" CreationDate="2016-06-12T20:18:20.307" Score="2" Body="&lt;p&gt;You may find &lt;a href=&quot;http://broadcastify.com&quot; rel=&quot;nofollow&quot;&gt;Broadcastify&lt;/a&gt; to be useful as a start for your search, especially if you are not sure whether this is a passing interest or an ongoing one.  They have web-based feeds of scanners all around the USA and in a few other countries. The &lt;a href=&quot;http://www.broadcastify.com/listen/top&quot; rel=&quot;nofollow&quot;&gt;top 50 audio feeds&lt;/a&gt; listing gives you access to the most popular scanners on their list. This gives you access to scanner traffic, including traffic outside of your local area that would be impossible to pick up with a radio tuned to local frequencies.&lt;/p&gt;&#xA;" OwnerUserId="5844" LastActivityDate="2016-06-12T20:18:20.307" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6289" PostTypeId="2" ParentId="6282" CreationDate="2016-06-13T06:44:18.460" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Disclaimer: the following is not legal advice in any juristiction&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In the situation described, common sense need to prevail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are monitoring SAR frequencies, and for that: the SAR agencies are as well. If you hear a distress message to a SAR agency you should relay this in a legal manner: e.g. you contact the SAR agency by cell phone, or on a frequency you are licensed to use. Relay what you have heard, and on what frequency you have heard it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need to keep monitoring the frequency, to establish if a SAR agency tries to contact the distressed party. Please keep in mind that while you may hear the distressed party, you may not hear the SAR agency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the distress signal/message continues, and you have established that no official SAR agency is responding to the signal, you should answer the distress call; identify yourself, get as much information as possible, such as nature of the distress, location, number of people in the party, and any other information. Keep this communications as short as possible, as you are using a frequency you are not licensed to use, and you do not want to interfere with official communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once again, relay this information to the SAR agency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are now the &quot;gateway/relay&quot; for communications and you need to follow the instructions of the SAR agency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep monitoring the frequency, and once in a while... say every 10 minutes, contact the distressed party to ensure them you are in contact with a SAR agency. But ONLY if the SAR agency has not established contact themselves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While doing this, in parrallel, you need to establish if you, or someone in your party can provide assistance to the distressed party. However; make absolutely sure that you are physically able to do so, and not putting yourself or others in harms way !! You do not want to become a second distressed party !&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you approach this in a proffessional manner, keep communications to a minimum on unlicensed frequencies, and follow the instructions of the SAR agency, you will not find a judge which will prosecute you for using unlicensed frequencies.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-06-13T06:44:18.460" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6290" PostTypeId="2" ParentId="6282" CreationDate="2016-06-13T14:37:07.863" Score="4" Body="&lt;p&gt;&lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.403&quot; rel=&quot;nofollow&quot;&gt;§97.403&lt;/a&gt; reads:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;No provision of these rules prevents the use by an amateur station of&#xA;  any means of radiocommunication at its disposal to provide essential&#xA;  communication needs in connection with the immediate safety of human&#xA;  life and immediate protection of property when normal communication&#xA;  systems are not available.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;At least one ARES org. &lt;a href=&quot;http://harriscountyares.org/training/EME/EME-107.pdf&quot; rel=&quot;nofollow&quot;&gt;[PDF]&lt;/a&gt;, and some &lt;a href=&quot;http://www.redwaveradio.com/7_e411a9189fb78b81_1.htm&quot; rel=&quot;nofollow&quot;&gt;other hams&lt;/a&gt;, construe this to mean that in an emergency, you may communicate by any means necessary.  Note that the rule does not specify it has to be your life or property in danger, but does say &quot;when normal communication systems are not available.&quot;  So in the particular case you bring up (overhearing SAR traffic when you are in a position to help faster than they can), you should probably call SAR on the phone first and tell them where you are and that you can help.  Failing that, you could try them on the radio.   Either way, keep your comments short and follow their instructions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this is helpful.&lt;/p&gt;&#xA;" OwnerUserId="6446" LastActivityDate="2016-06-13T14:37:07.863" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6291" PostTypeId="1" AcceptedAnswerId="6292" CreationDate="2016-06-14T12:50:02.490" Score="1" ViewCount="134" Body="&lt;p&gt;I've just added a leisure battery, split relay and circuit swap loom to a newly acquired Mazda Bongo. Also added was a 1000W pure sine wave inverter, hooked up directly to the leisure battery. That's in the glove box. There's room above that for the radio body, as far as I can tell.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rather than feed the radio power cables back through the bulkhead, does anyone know if there are any potential problems with hooking it up in parallel to the inverter, i.e. connecting the + and - to the inverter's terminals?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm assuming it'll power just the same, only putting the inverter cables under more work if both on at the same time - TV and HF radio, perhaps, at a push. The cables are 16mm, ought to be sufficient for the ampage the inverter can theoretically pull (although I'll be running at most 600W through it intermittently).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the leisure battery reads 13.7v-ish when the engine is on, 12.9v when off. Obviously I'd like to run it with it off. The 12.9/12.5v the battery will run at when engine off is within the +/- 15% tolerance of the Yaesu 857d being used, so that shouldn't present too much of a problem, if I'm not mistaken?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further note: I'll enable the auto switch off feature I've heard the 857d has, if and when this installation happens!&lt;/p&gt;&#xA;" OwnerUserId="5313" LastActivityDate="2019-07-31T06:42:52.383" Title="Connecting radio in parallel with inverter in mobile set up" Tags="&lt;mobile&gt;&lt;dc-power&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6292" PostTypeId="2" ParentId="6291" CreationDate="2016-06-14T14:09:52.983" Score="4" Body="&lt;p&gt;There are two things I like to highlight:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) You are thinking of putting the radio in the same glove box as the inverter; hence you may need extra ventilation/circulation to ensure neither equipment will over heat&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) Usually inverters have fuses built into the inverter, which means that the cables between battery and inverter are unfused (fused at the far end). The best practice for mobile radio installs is to fuse as closely to the battery as possible, you divert from this by connecting the radio directly to the inverter terminals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In regards to 1) I would not put the inverter in the glove box, nor would I put the radio in the glove box. I would try to find better locations in the vehicle with more (air-)space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In regards to 2) I would run separate cables from battery to radio, fused as close to the battery as possible. And I would fuse both positive as neutral.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.k0bg.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;K0BG&lt;/a&gt; runs an excellent website with information about mobile installs. I highly recommend a read.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Every transceiver manufacturer, and every vehicle manufacturer, has heretofore recommended &lt;strong&gt;direct to battery connections&lt;/strong&gt; (both positive and negative leads), or to so-called jumps points when the battery is indirectly mounted under a fender well, or trunk area. However, that has changed! All late model vehicles, especially those with EIS (Engine Idle Shutoff), have a battery monitoring system. Typically, these systems use a Hall device to measure battery current drain (Electronic Load Detector). However the wiring is done, it must &lt;strong&gt;not circumvent the ELD&lt;/strong&gt;. A service manual is essential in these cases. As an alternative, your dealer's service manager is a good resource. In any case, both leads should be &lt;strong&gt;fused as close to the power source (SLI battery) as possible.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(emphasis added)&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="8573" LastEditDate="2019-07-31T06:42:52.383" LastActivityDate="2019-07-31T06:42:52.383" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="6293" PostTypeId="1" AcceptedAnswerId="6294" CreationDate="2016-06-14T22:30:55.333" Score="2" ViewCount="2357" Body="&lt;p&gt;I have a big box of air-variable capacitors I inherited and want to see if I can use one of them for a low power magnetic-loop antenna for 30m digital.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How can I figure out if any of them have a high enough maximum voltage?&lt;/li&gt;&#xA;&lt;li&gt;If I do this by trial and error I risk damaging my radio right?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5577" LastActivityDate="2016-06-14T23:05:37.357" Title="How to estimate or measure the max voltage of an air variable capacitor" Tags="&lt;capacitance&gt;&lt;magnetic-loop&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6294" PostTypeId="2" ParentId="6293" CreationDate="2016-06-14T23:05:37.357" Score="3" Body="&lt;p&gt;From the ARRL Handbook...&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Spacing  &#xA;inches ___ V_peak &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;0.015 ___ 1000&lt;/li&gt;&#xA;&lt;li&gt;0.02 ____ 1200&lt;/li&gt;&#xA;&lt;li&gt;0.03 ____ 1500&lt;/li&gt;&#xA;&lt;li&gt;0.05 ____ 2000&lt;/li&gt;&#xA;&lt;li&gt;0.07 ____ 3000&lt;/li&gt;&#xA;&lt;li&gt;0.08 ____ 3500&lt;/li&gt;&#xA;&lt;li&gt;0.125 ___ 4500&lt;/li&gt;&#xA;&lt;li&gt;0.175 ___ 7000&lt;/li&gt;&#xA;&lt;li&gt;0.25 ____ 9000&lt;/li&gt;&#xA;&lt;li&gt;0.35 ___ 11000&lt;/li&gt;&#xA;&lt;li&gt;0.5 ____ 13000&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Also note that these are mere recommendations.  Actual high voltage you will see of course depends on the reactance and input power to the antenna (a little circuit analysis may be in place) along with frequency needed to determine the reactance of the capacitor.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-06-14T23:05:37.357" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6296" PostTypeId="1" AcceptedAnswerId="6297" CreationDate="2016-06-16T03:07:03.107" Score="2" ViewCount="374" Body="&lt;p&gt;If I take my license exam in California, but my residence is in New York, would my call sign still reflect the New York location?&lt;/p&gt;&#xA;" OwnerDisplayName="user7822" LastEditorUserId="8832" LastEditDate="2017-08-31T03:38:10.310" LastActivityDate="2017-08-31T03:38:10.310" Title="How Are US Call Sign Location ID's Assigned?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;location&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6297" PostTypeId="2" ParentId="6296" CreationDate="2016-06-16T03:41:01.193" Score="3" Body="&lt;p&gt;When you fill out the paperwork at the time of taking the test you specify your permanent home address for your license.  Thus, if you take the test in California but use a NY address then you will be assigned a call sign appropriate for your license level for New York which uses the 2 zone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Licenses like for a Technician license are issued usually as a 2x3 call sign and the suffix usually is assigned in alphabetic order.  So, for example, you could be issued something like a KG2XYZ call sign.  I am not sure about the 'G' part of the prefix or where the suffix falls but there are web sites where you can find out what that is because they list the most recently issued licenses for each zone number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want though, after licensed you can request a Vanity call sign and it can be any available and legal US call sign you choose.  A friend I know here in the state of Washington requested a Vanity callsign in the 0 zone because the suffix he wanted was his three kids first name initials.  So he is a zero-callsign in Washington state (zone 7).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you apply for a more advanced license, you can possibly get a 1x3 call sign or maybe even a 2x2 call sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case you are unaware, the different call signs are known by how many letters are before the zone number and how many after.  So, a 1x3 call sign is like mine, K7PEH.  A friend of mine has a 2x2, or KE7FB.  And, another friend of mine is a 1x2, W7IZ.  A 2x3 is something like KD7ZVB or whatever.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-06-16T03:41:01.193" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6298" PostTypeId="1" AcceptedAnswerId="6299" CreationDate="2016-06-16T04:13:09.470" Score="0" ViewCount="2970" Body="&lt;p&gt;According to this sales listing for a 2.4Ghz antenna, it can handle up to 20 watts of power but has an impedance of 50 ohms. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means that (at 20 watts), the input would need to be at more than 50 volts to keep the heat generated to be less than 8 watts&lt;/p&gt;&#xA;&#xA;&lt;p&gt;20 watts / 50 volts = 0.4 amps&lt;/p&gt;&#xA;&#xA;&lt;p&gt;0.4 amps ^ 2 * 50 ohms = 8 watts of heat&lt;/p&gt;&#xA;&#xA;&lt;p&gt;50 volts is enough to shock someone (and that's probably a low estimate)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I missing something here?&lt;/p&gt;&#xA;" OwnerUserId="6668" LastActivityDate="2016-06-16T16:28:16.520" Title="How much voltage is on a typical high power (1000mw) 2.4Ghz WiFi antenna?" Tags="&lt;voltage&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6299" PostTypeId="2" ParentId="6298" CreationDate="2016-06-16T06:48:44.423" Score="3" Body="&lt;p&gt;The answer is &quot;it depends&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It depends on the Antenna design, but lets look at an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A typical (license free / home / consumer) installation of WiFi is 100mW (not a 1000mW as your post indicates)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A typical antenna has a 50 Ohm impedance, and lets take an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a 1/4 wave vertical antenna the voltage distribution has a voltage minimum at feed point, and a voltage maximum at the end. And lets take that this antenna has a perfect Resistance part of the complex Impedance = 50 + 0j Ohm (in practice this may vary a lot)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ohm's Law will show you E = SQRT(P*R) = SQRT(0.1*50) = 2.23 V (at the antenna tip)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is only true for the standard quarter-wave vertical, other antenna designs may have different voltage distribution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna may have a rating of &quot;20 W&quot; but that only indicates the maximum power input possible with that antenna before &quot;things go bad&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will have to check local legislation on what the maximum power is you may run, but as indicated above in many regions of the world this is 100mW (YMMV)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often this is expressed in ERP, so it will take antenna gain into account. Example: If your antenna has a unity gain of 3dB, then you need to ensure that the transmitter (the WiFi Router) is throttled back to 50mW in order to be compliant with a 100mW-ERP legislation. This assumes no cable loss, so the actual calculation will be more complex taking cable loss / connector loss into account.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-06-16T10:47:58.863" LastActivityDate="2016-06-16T10:47:58.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6300" PostTypeId="1" CreationDate="2016-06-16T06:52:17.300" Score="7" ViewCount="7734" Body="&lt;p&gt;I understand that MW broadcast stations use vertical antennas because that polarization works much better for groundwave propagation. But in amateur radio, I would assume the focus for communications on the HF bands would be via ionospheric propagation, where the polarization doesn't matter a great deal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I contemplate what antenna to install next (after a simple inverted-vee hung out a second story window), I am struck by just how many articles/recommendations and even locals are using vertical antennas for HF communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The huge drawback to a vertical seems to be the ground plane required: instead of two light quarter-wavelength wires hung in various fashions across a yard/trees/attic, you instead need a sturdy tower for starters and as the icing on the cake, placement of dozens and dozens of fairly long wires all through your yard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have room for a proper radial system, wouldn't you also have room for a decent loop or inverted vee? What is the attraction of replacing one of the &quot;poles&quot; of a dipole with dozens of almost-as-long radials instead?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2019-10-26T18:47:25.860" Title="What is the attraction of vertical antennas for HF?" Tags="&lt;antenna-construction&gt;&lt;vertical-antenna&gt;" AnswerCount="7" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6301" PostTypeId="2" ParentId="6300" CreationDate="2016-06-16T07:10:05.243" Score="7" Body="&lt;p&gt;Cribbing a few quotes from answers to related questions, here's a start.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://ham.stackexchange.com/a/195/1362&quot;&gt;https://ham.stackexchange.com/a/195/1362&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The primary advantages of vertical antennas are that they are omnidirectional, and with an appropriate ground plane (radials) yield a low radiation angle; this reduces the number of &quot;hops&quot; that HF signals must make to reach their destination.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This makes a lot of sense: a horizontal dipole will have nulls off its ends, whereas the null of a vertical will point up into space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://ham.stackexchange.com/a/494/1362&quot;&gt;https://ham.stackexchange.com/a/494/1362&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;At the lower end of the HF spectrum, the λ/2 height requirement for horizontal antennas can become cumbersome (even though a horizontal phased array may weaken this requirement by allowing somewhat lower heights). A vertical HF antenna can get away with a height of only λ/4.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is something I keep neglecting to consider: that ideally (at least assuming low-angle radiation is the goal) a horizontal antenna needs to be really really high, i.e. twice as high as a vertical for the same band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And of course the good old-fashioned &lt;a href=&quot;https://ham.stackexchange.com/a/555/1362&quot;&gt;https://ham.stackexchange.com/a/555/1362&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;…the coax shield makes just as fine of an antenna as the dipole. It distorts the radiation pattern horribly, but since a dipole wasn't a directional antenna to begin, it hardly matters. It could mean that you get a lot of RF in the shack, but if you are transmitting with 100W this is unlikely to cause any serious problems.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;i.e. sometimes the results of an &quot;antenna&quot; are actually the results of a long leaky feedline plus a generous amount of transmit power. Unless they are operating as loaded end-feds or something, this is the only explanation I can figure out for how HF verticals like the Comet CHA250B might be working in practice with no radials.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-06-16T07:10:05.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6302" PostTypeId="2" ParentId="6300" CreationDate="2016-06-16T08:35:10.613" Score="1" Body="&lt;p&gt;Let me try to answer this part of the question:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If you have room for a proper radial system, wouldn't you also have&#xA;  room for a decent loop or inverted vee? What is the attraction of&#xA;  replacing one of the &quot;poles&quot; of a dipole with dozens of almost-as-long&#xA;  radials instead?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I will answer this from my own experiences, and decisions I made when constructing 3 verticals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have 3 verticals, one 9.6m high (120 radials of 4m), one 4.6m high (120 radials of 2.6m), and one 10m high with a T-top each leg 30m (120 radials of 4m). All of them have an auto-tuner at feed-point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why did I construct these ? -- here is my reasoning:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I don't own the land and was given the use of 3 small plots of land to use.&lt;/li&gt;&#xA;&lt;li&gt;I did not get approval of the land owner to construct anything above 10m hight&lt;/li&gt;&#xA;&lt;li&gt;I did not get approval to go for planning permission for a tower&lt;/li&gt;&#xA;&lt;li&gt;I wanted to cover all HF bands for DX (low angles of radiation)&lt;/li&gt;&#xA;&lt;li&gt;I had enough copper wire for radial for zero cost&lt;/li&gt;&#xA;&lt;li&gt;I wanted the visual impact to be low&lt;/li&gt;&#xA;&lt;li&gt;I had a budget&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Due to this I built verticals, I use them as follows:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;9.6m height: 40m - 15m bands&lt;/li&gt;&#xA;&lt;li&gt;4.6m height: 20m - 10m bands&lt;/li&gt;&#xA;&lt;li&gt;10m-T: 160m - 80m bands (some NVIS properties when used on 40m)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I also experimented with:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;horizontal dipoles at 10m height&lt;/li&gt;&#xA;&lt;li&gt;inverted V center at 10m height&lt;/li&gt;&#xA;&lt;li&gt;loops, long wires, and various others&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I believe a big part of the hobby is experimenting with antenna's, different designs, shapes, materials, and see what works for you, and what doesn't.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question you are asking is &lt;strong&gt;not easy to answer with one single answer, and varies from amateur to amateur&lt;/strong&gt;, with reasoning which varies as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For me: the verticals work, they were cheap to built and if they wouldn't have worked I would have taken them down and built something else for my QTH.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Built, operate try, built something else, rinse and repeat.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-06-16T08:43:33.133" LastActivityDate="2016-06-16T08:43:33.133" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6303" PostTypeId="2" ParentId="6300" CreationDate="2016-06-16T10:20:04.943" Score="2" Body="&lt;p&gt;One obvious answer is that a vertical antenna can be made to work in a very small area. The house where I live is a townhouse in a large city, and has basically no land. It is also close to power lines, and so a tower would be totally out even if I had space for one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you say about how a vertical can take up as much room as a loop, is true if you put all the radials down to make it work very well. But it can also be bolted on the back of a house with just a few bits of metal on the bottom to act as radials. It won't work as well, but if that's all the space you have then a vertical with a poor ground might well be your only choice.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2016-06-16T10:20:04.943" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6304" PostTypeId="1" AcceptedAnswerId="6309" CreationDate="2016-06-16T11:10:03.953" Score="3" ViewCount="75" Body="&lt;p&gt;I recently watched a video of someone making an auroral voice contact, and the received audio had a distinctively raspy and disembodied sound to it. Some CW was audible in the background and it had the same sound to it. I understand that this is characteristic of auroral signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What mechanism causes this kind of distortion when working via aurora?&lt;/p&gt;&#xA;" OwnerUserId="6138" LastActivityDate="2016-06-16T23:07:08.290" Title="What causes the audio distortion when working aurora?" Tags="&lt;propagation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6305" PostTypeId="1" AcceptedAnswerId="6306" CreationDate="2016-06-16T15:27:08.473" Score="4" ViewCount="218" Body="&lt;p&gt;My wife and I are studying for our Technician class licenses. We are thinking about how we could communicate with each other while both of us are at work, she being in Oakland, CA and myself in Pleasant Hill, CA. with several hills and about 15 to 25 miles between us. We are aware that our soon-to-be license type will limit our frequencies and power output. We also have not determined what handheld radios we'll be purchasing and are not looking for recommendations other than best frequency range and wattage output to use for this particular scenario, and if it would be possible to communicate with this distance and geographical features, even for just a few minutes during any part of the year.&lt;/p&gt;&#xA;" OwnerUserId="7851" LastEditorUserId="8573" LastEditDate="2018-05-14T20:48:25.783" LastActivityDate="2018-05-14T20:48:25.783" Title="How can we determine what repeaters to use?" Tags="&lt;license&gt;&lt;ht&gt;&lt;repeater&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="6306" PostTypeId="2" ParentId="6305" CreationDate="2016-06-16T16:11:04.410" Score="3" Body="&lt;p&gt;It sounds like you've gotten the characteristics of HF and VHF+ operating mixed up a bit. If you're going to use VHF/UHF repeaters to communicate, then your &quot;frequencies and power&quot; (and time of day) are almost always irrelevant and you either can communicate or not, with some variation due to weather.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two basic cases for repeater-based communication:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Both of you have a line-of-sight to the same repeater, and are close enough to it. In this case, with your radios appropriately set for that repeater (frequency, split, CTCSS tone), you can simply talk pretty much like simplex.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You each have a line-of-sight to &lt;em&gt;different&lt;/em&gt; repeaters. In this case, you need to find two repeaters which have compatible &lt;em&gt;linking&lt;/em&gt; systems (either part of a specific permanently-linked network, or having a controllable linking system like EchoLink or IRLP). Then you can contact one repeater, and in if needed instruct it to link to another repeater, at which point it's like the two repeaters are now one repeater (everyone hears everyone else).&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Permanently linked repeaters can be treated just like a single repeater with a larger coverage area.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In the case of temporarily linked repeaters, however, you're now occupying two repeaters with your conversation — it's less convenient to share it with others than in the first case, since you can't just stop talking but need to also end the link. There's nothing wrong with doing this if the other repeater users don't mind, though.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In either case, you don't choose a frequency, you use the repeater's frequency. Your transmit power will affect how far you can be from the repeater, but an even better approach is to use a directional antenna pointed at the repeater, as this improves both transmission and reception. Of course, directional antennas are bulky and you may not wish to set one up just for this purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For &lt;strong&gt;you in particular&lt;/strong&gt;, I took a look at RepeaterBook, a user-updated database of repeaters, and found what looks like a good candidate for a single repeater usable by both of you: &lt;a href=&quot;https://www.repeaterbook.com/repeaters/details.php?state_id=06&amp;amp;ID=165&quot; rel=&quot;nofollow&quot;&gt;WA6HAM&lt;/a&gt; which is on a mountain directly between Pleasant Hill and Oakland, CA. There's an intervening hill on the Pleasant Hill side, and the database doesn't say how tall the repeater's tower is, so I can't say for sure whether it'll actually work, but it's worth a try.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-06-16T23:10:51.570" LastActivityDate="2016-06-16T23:10:51.570" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6307" PostTypeId="2" ParentId="6300" CreationDate="2016-06-16T16:24:10.737" Score="1" Body="&lt;p&gt;There are commercially-made verticals that are only 26 feet (8 m) high, that offer decent low-takeoff-angle (DX) performance on eight HF bands (and so-so performance on 80m), assuming that a good radial system has been installed.  By comparison, a horizontally-polarized antenna needs to be up fairly high to have good low-angle performance.  I seem to recall that a height of &amp;lambda;/2 or higher is recommended for dipoles used for DXing; that's often difficult to achieve for 40m and 80m.  By the way, inverted vees have terrible low-angle performance for any direction other than broadside-on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any multi-band antenna is a compromise, but if you ask me horizontally-polarized multi-band antennas are more of a compromise than commercially-made multi-band verticals; G5RV-style antennas typically work well on five or six bands, but have two bands that the antenna isn't designed for at all.  (Let's please not start yet another G5RV debate here.)  Off-center-fed horizontally-polarized antennas can work well, but they make tremendous demands on the balun; when cheap baluns are used, as they often are, then the antenna's performance suffers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my opinion, the best reason to use a vertical is that vertically-polarized antennas and horizontally-polarized antennas complement each other so very well.  When one works poorly, the other often works beautifully.  If you only have a dipole or an inverted-vee up, then I'd advise you to try putting a vertical up also.  You might be surprised at what the vertical can pull in that the dipole or inverted-vee can't.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-06-16T16:24:10.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6308" PostTypeId="2" ParentId="6298" CreationDate="2016-06-16T16:28:16.520" Score="1" Body="&lt;p&gt;This doesn't actually answer your question per se, but I think you have an important misconception: &lt;strong&gt;An antenna is not a resistor.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you know it's not, but in particular, an antenna having a 50 Ω input impedance does not dissipate as much heat as a 50 Ω resistor would for the same input. The majority of the energy is radiated, not converted to heat — that's what makes it an antenna!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna having some particular resistive input impedance means that the electrical characteristics &lt;em&gt;at its input&lt;/em&gt; (that is, how a connected transmitter will be affected by it) are &lt;em&gt;equivalent to&lt;/em&gt; a resistor of the same value, not that it behaves the same way otherwise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Suppose you indeed put 20 W into your 50 Ω antenna. The only thing the 50 Ω number tells you is &lt;em&gt;the ratio between current and voltage on the feed line&lt;/em&gt; — if we work it out then it is 32 V and 632 mA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That same ratio of voltage and current exists at &lt;em&gt;one&lt;/em&gt; place on the antenna: the feed point, where the feed line connects to the antenna element(s). Everywhere else, it will be different, and in no case is it primarily due to the resistance of the metal in the antenna.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-06-16T16:28:16.520" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6309" PostTypeId="2" ParentId="6304" CreationDate="2016-06-16T23:07:08.290" Score="4" Body="&lt;p&gt;The ionized air associated with aurorae functions as a reflector for radio waves. However, the effective position of the reflection for any given path between two stations moves around rapidly and randomly as a function of the solar wind density and the magnetic field fluctuations. This introduces an extreme amount of phase noise into the signal being reflected. It's like trying to see an image in a mirror that's being shaken around.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2016-06-16T23:07:08.290" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6310" PostTypeId="2" ParentId="6277" CreationDate="2016-06-17T00:38:46.007" Score="1" Body="&lt;p&gt;The receive performance of an RTL-SDR with an upconverter will probably not be as good as a &quot;traditional receiver&quot;, for pretty much exactly the three reasons you highlight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't speak authoritatively on sensitivity or noise, but I can think of two strikes against the RTL-SDR dongles in this regard:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;As a cheap USB dongle intended primarily for DVB-T reception, really clean input across the whole spectrum may not have been a design priority. Some companies, for example &lt;a href=&quot;http://www.nooelec.com/store/&quot; rel=&quot;nofollow&quot;&gt;NooElec&lt;/a&gt; market (presumably) higher quality design/manufacturing around the RTL chipset and this may yield an improved experience.&lt;/li&gt;&#xA;&lt;li&gt;The other potential issue is that the RTL chipset uses an only 8-bit analog-to-digital converter (ADC) meaning even if interfering noise sources are solved there's plenty of potential signal lost, that would be above the theoretical minimum receiver noise floor but ends up being &quot;rounded away&quot;.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Some further discussion this can be found at &lt;a href=&quot;https://www.reddit.com/r/RTLSDR/comments/3niyxe/rtlsdr_noise_floor/&quot; rel=&quot;nofollow&quot;&gt;https://www.reddit.com/r/RTLSDR/comments/3niyxe/rtlsdr_noise_floor/&lt;/a&gt; and &lt;a href=&quot;https://groups.google.com/forum/#!topic/ultra-cheap-sdr/8vFptr61TAA&quot; rel=&quot;nofollow&quot;&gt;https://groups.google.com/forum/#!topic/ultra-cheap-sdr/8vFptr61TAA&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also got the other main issue with this setup right: filtering. The fun of these kinds of SDR setups is that you can tune &quot;any&quot; frequency. But the design are usually fairly simple, and if there's much filtering at all it tends to be very wide.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm no seasoned transceiver designer, but my impression is that a good receiver architecture, with the right combo of filters available at all the right stages, is something of an art form — and one of the investments you are paying for with a &quot;traditional&quot; receiver. This is not to say a highly frequency-agile SDR and good filtering are incompatible; rather it's not something to be expected in a $15 DVB-T dongle and a general-purpose upconverter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, I have this exact combo and don't regret purchasing either. Definitely no regrets with the cheap little RTL-SDR which was an incredible value and opened the world of radio up to me. I'm also happy with the Ham it Up as far as delivering on its promises. However just for RTL-SDR usage, I really enjoy the &lt;a href=&quot;http://www.ebay.com/itm/Upgraded-100KHz-1-7GHz-Full-Band-RTL-SDR-USB-Tuner-Receiver-R820T-2832U-Radio-/131492551147&quot; rel=&quot;nofollow&quot;&gt;&quot;100KHz-1.7GHz Full Band RTL-SDR USB Tuner Receiver&quot;&lt;/a&gt; I found later, since it combines the RTL and an upconverter both into a single little package!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But to get back to it: without external filters, all of my &quot;generic SDR&quot; device combinations end up vulnerable to various and sundry imaging/intermodulation/etc. problems. So if you end up trying it — and IMO theres's not a lot to lose in doing so. I think you'll find either device useful for all sorts of &lt;em&gt;other&lt;/em&gt; projects even if this one fails… — plan on adding some filtering of your own before being able to see if the noise/sensitivity are also good enough.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-06-17T18:38:42.117" LastActivityDate="2016-06-17T18:38:42.117" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6311" PostTypeId="2" ParentId="297" CreationDate="2016-06-17T02:02:23.963" Score="0" Body="&lt;p&gt;The Dire Wolf APRS software will do all of this and more. It is a multiport &quot;soundcard&quot; TNC, digipeater, IGate, and APRStt gateway. Runs on Windows or Linux, including the Raspberry Pi. The most recent version generates NMEA style waypoint sentences in multiple formats:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;$GPWPL, NMEA generic with only location and name.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;$PGRMW, Garmin,  adds altitude, symbol, and comment to previously named waypoint.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;$PMGNWPL, Magellan, more complete for stationary objects.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;$PKWDWPL, Kenwood with APRS style symbol but missing comment.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://github.com/wb2osz/direwolf&quot; rel=&quot;nofollow&quot;&gt;https://github.com/wb2osz/direwolf&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="7855" LastActivityDate="2016-06-17T02:02:23.963" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6312" PostTypeId="1" AcceptedAnswerId="6313" CreationDate="2016-06-17T09:44:11.287" Score="3" ViewCount="1828" Body="&lt;p&gt;When studying modulation of radio waves (or of most electromagnetic waves for that matter) I came across this question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Why are FM waves less susceptible to interference than AM waves?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that in FM the frequency has been modulated to carry the signal by superimposing the signal wave to the carrier wave and for AM the amplitude has been varied by a similar process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, what I don't understand is why FM radio waves are less susceptible to interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it because when two waves interfere it is easier to change the amplitude as compared to the frequency, if so why?&lt;/p&gt;&#xA;" OwnerUserId="7857" LastEditorUserId="4076" LastEditDate="2016-06-21T03:10:12.733" LastActivityDate="2016-06-21T03:10:12.733" Title="Why are FM radio waves less susceptible to interference than AM?" Tags="&lt;fm&gt;&lt;microwave&gt;&lt;am&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6313" PostTypeId="2" ParentId="6312" CreationDate="2016-06-17T10:08:35.107" Score="4" Body="&lt;p&gt;The waves (to be correct: the &lt;em&gt;signals&lt;/em&gt;) are exactly as suspectable to noise for both modulations!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's different is the receiver:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the name suggests, Amplitude Modulation (AM) works by taking the input (audio) signal, and using its strength, to modify the amplitude of your carrier wave. The AM receiver hence only has the amplitude of the received signal to recover the original audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In Frequency Modulation (FM), the input signal's amplitude is used to change the &lt;em&gt;frequency&lt;/em&gt; of the carrier wave. The receiver then tries to detect the frequency changes, and reconstruct the original audio signal as the change in frequency observed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The absolute strength of the received signal hence doesn't matter for FM, and is the only thing relevant for AM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, noise as we usually look at it, is &lt;em&gt;additive&lt;/em&gt;, meaning that it changes the receive signal amplitude. Hence, AM is especially badly suited to deal with noisy channels (a &lt;em&gt;channel&lt;/em&gt; in signal theory is everything that happens to a signal between transmitter and receiver).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;&lt;strong&gt;Edit:&lt;/strong&gt; Your questions continue:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I see, and is there a particular reason why noise only seems to affect aplitude? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;physics. Noise is &quot;random&quot; energy that changes the observed voltage with a positive or negative sign. It adds to the signal. Really, just simple addition of voltages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, as I said, this goes for &lt;strong&gt;additive&lt;/strong&gt; noise. There's &lt;em&gt;other&lt;/em&gt; types of noise, but luckily, we're technically able to avoid a lot of those, so you don't have to worry about these (much harder to compensate) types of noise. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If two waves of different frequency superimpose shouldn't the frequency of the resulting wave differ to that of the original one? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. That doesn't happen. There's intermodulation in non-linear components, but that doesn't change the frequency, it merely creates new frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, if you have a strong interferer, your FM receiver might &quot;lock&quot; onto that instead of the station you actually want to listen to. But that's interference, not noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, if Noise power related to signal power (1/SNR) gets too high, your receiver might not be able to estimate the &quot;instantaneous&quot; frequency of the signal within the noise – then you get garbage out. But that implies a really bad reception.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Doesn't interference with noise &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Interference&lt;/em&gt; and &lt;em&gt;Noise&lt;/em&gt; are two different things. Please don't mix the terms. Interference is someone else interfering.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;suggest superposition with waves of all kinds of frequencies?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. Noise is a random process and as such doesn't necessarily have a frequency. Many types (but far from all types!) of noise we consider are modelled to be &lt;em&gt;white&lt;/em&gt;, ie. statistically contain the same amount of energy at all frequencies (if you take the spectrum of a theoretical, inifinitely long observation of noise). But that doesn't mean that your instantaneous noise realization contains a specific set of frequencies. That's the difference between statistics and events: If you have a chance of $10^{-7}$ to win the lottery jackpot of 10 Million € every week, it doesn't mean that you'll get 1€ every week.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-06-17T13:15:48.663" LastActivityDate="2016-06-17T13:15:48.663" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6315" PostTypeId="2" ParentId="6014" CreationDate="2016-06-18T16:38:51.730" Score="10" Body="&lt;p&gt;So, by design, the elements of any Yagi have a zero current going through the center point. That's pretty obvious be symmetry: assuming you excite the &quot;left and right&quot; halves of the driving dipole with exactly opposing voltages, everything should be symmetrical across the plane through the middle of that dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, if you approach that plane from left and right, you should see the same voltage, at any time. If two points have exactly the same potential, no current will flow. That's why Yagis work even if their elements are non-perfectly isolated from a metal boom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The boom correction factor is really just the effect of having a metal object of non-zero left/right dimension in the way of your EM field – that will basically &quot;swallow&quot; a bit of E-field, but that effect should be relatively small for reasonably sized booms. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;SWR will practically not be affected; the couple of millimeters you'd have to add to the driving dipole to compensate for a conductive boom are, from a matching perspective equivalent to using the antenna with a couple 0.001 mismatched cables – you'll be hardly pressed to find a matching circuit that is good enough to make the effect even measurable. Also, remember, you're not going to use that antenna for a CW of &lt;strong&gt;exactly&lt;/strong&gt; the maximum efficiency frequency of that Yagi, but a couple of MHz around; now, &quot;±1.5MHz around the optimal frequency&quot; means your wavelength-to-antenna element ratio is off by around an easy percent, anyway – it's really no use to over-optimize your antenna here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Things like non-perfect impedance, dielectric and ohmic losses, geometry imperfection, non-ideal free space impedance (funny fact: air moisture &lt;em&gt;does&lt;/em&gt; change the $\epsilon_r$ of air) will probably outshadow this.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="76" LastEditDate="2016-06-18T16:44:40.343" LastActivityDate="2016-06-18T16:44:40.343" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6316" PostTypeId="2" ParentId="6048" CreationDate="2016-06-18T16:47:28.983" Score="2" Body="&lt;p&gt;So first of all, using a semiconductor as adjustable capacitance is pretty &quot;normal&quot; – it's typically PIN diodes, though, which you can DC-bias to give them a specific junction capacitance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;PIN diodes are &quot;bad&quot; rectifiers, as they have high forward resistance – the &quot;I&quot; in PIN is for &quot;intrinsic&quot;, and that means undoped semiconductor, which means good isolator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, if you're really doing semiconductors, then you'll inherently have non-linear behaviour. Your crystal radio (which your &quot;tuned antenna-&gt;rectifier&quot; setup is, in fact) will hence have a nonlinear I/U line – which means it could be used as a mixer :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, since it'll be very hard to get things sufficiently exact, and not too lose all accuracy, stability and signal in the inductance, I'd rather go for a simple super-heterodyne receiver in this situation.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-07-18T18:03:07.693" LastActivityDate="2016-07-18T18:03:07.693" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6317" PostTypeId="1" AcceptedAnswerId="6318" CreationDate="2016-06-18T17:48:31.520" Score="1" ViewCount="1585" Body="&lt;p&gt;The constellation diagrams for a 4-ary modulation using PSK (qpsk),MSK ,QAM and OQPSK look alike. How to differentiate them?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;What is the modulation for the constellation diagram in the figure?&#xA;&lt;a href=&quot;https://i.stack.imgur.com/JcXVY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JcXVY.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="7827" LastActivityDate="2020-12-14T04:02:08.420" Title="How to identify type of modulation based on constellation diagram?" Tags="&lt;digital-modes&gt;&lt;modes&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6318" PostTypeId="2" ParentId="6317" CreationDate="2016-06-18T18:20:30.077" Score="4" Body="&lt;p&gt;In general, &lt;em&gt;any&lt;/em&gt; modulation that makes sense to plot on a constellation diagram could be described as a kind of QAM. However, we generally use the term QAM only for modulations that use &lt;em&gt;both&lt;/em&gt; degrees of freedom on the plot (amplitude &lt;em&gt;and&lt;/em&gt; phase).&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If the modulation varies the &lt;em&gt;phase&lt;/em&gt; but not the &lt;em&gt;amplitude&lt;/em&gt; — all the constellation points lie on a circle about the origin — then we call it PSK (phase-shift keying).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If the modulation varies the &lt;em&gt;amplitude&lt;/em&gt;, but not the &lt;em&gt;phase&lt;/em&gt; — all the constellation points lie on a ray from the origin — then we call it ASK (amplitude-shift keying).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So you &lt;em&gt;can&lt;/em&gt; tell QAM from PSK because QAM displays multiple amplitudes as well as multiple phases, whereas PSK has exactly one amplitude.  MSK and OQPSK are subtypes of PSK and you are right to think that you cannot tell them apart on a constellation diagram, but the question you show is not asking you to do so — only to distinguish between ASK, PSK, and QAM.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-06-18T18:20:30.077" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6319" PostTypeId="1" CreationDate="2016-06-18T18:52:52.243" Score="3" ViewCount="840" Body="&lt;p&gt;I'm a math and computer science student, starting to mess around with using amplifiers and antennas to build long-range wifi hardware in my spare time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Calculating the expected power density of a system is easy enough, but--I'd like to measure power density directly. Namely, in the neighborhoods of 2.4 GHz and 5.0 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I went to the Physics department at my university to borrow equipment. They said EMF meters, gauss meters, etc. that work in the 5.0 GHz range are extremely expensive, and suggested I use a normal wifi antenna to measure field strength. I have since downloaded some software that gives me measurements from my laptop's antenna in dBm; I have no way of knowing how accurate those measurements are, however.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, given that I get to choose input wattage on the systems I build and can buy just about any antenna off the Internet as well as the next guy--I'd really, really like it if the meter were capable of measuring power densities in the &quot;you should probably be worried&quot; level ( and above, to some degree ).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any meters out there that measure EMF power in the neighborhoods of 2.4 GHz and 5.0 GHz? Meters that are priced so that one can hope to afford them without the financial backing of an institution?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ninja Edit : I'm perfectly aware of FCC regulations and follow them in my designs. I'm simply looking for tools with which to empirically verify the system &lt;em&gt;is&lt;/em&gt; behaving as expected. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll hit up the EE department and local government for access to testing facilities. &lt;/p&gt;&#xA;" OwnerUserId="7861" LastEditorUserId="7861" LastEditDate="2016-06-18T21:18:00.203" LastActivityDate="2016-06-18T21:18:00.203" Title="Measuring energy density of 2.4 GHz and 5.0 GHz signals" Tags="&lt;rf-power&gt;&lt;wifi&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6320" PostTypeId="1" CreationDate="2016-06-18T19:39:09.237" Score="0" ViewCount="105" Body="&lt;p&gt;Is there an antenna supplier out there that is particularly well known for publishing enough data on their antennas that one can model their antennas' transmission fields in spherical or cylindrical coordinates?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to make mathematical models of several antennas in three-dimensions, using whatever coordinate system, and then use level curves of those equations to calculate power density at various points in space given an input wattage to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These systems will be using 2.4 GHz and 5.0 GHz to transmit ( and receive ).&lt;/p&gt;&#xA;" OwnerUserId="7861" LastActivityDate="2016-06-19T15:36:16.060" Title="Acquiring specs on anntenas so as to mathematically model level curves in their transmission feilds" Tags="&lt;antenna&gt;&lt;wifi&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6321" PostTypeId="2" ParentId="6320" CreationDate="2016-06-18T21:02:03.010" Score="2" Body="&lt;p&gt;Most antenna manufacturers &lt;strong&gt;will&lt;/strong&gt; supply you with measurement data of how much power is radiated in which direction. That is a perfectly normal thing to do, and it's much more likely you'll get one of these measurements that fully describe the far field of your antenna then measurements that suffice to do a simulation. For example, something like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/I8EfA.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/I8EfA.gif&quot; alt=&quot;Radiation pattern, wikimedia, from https://upload.wikimedia.org/wikipedia/commons/a/ae/Patch_antenna_pattern.gif&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;for both the E- and the H-Plane. Having two orthogonal cross-sections of the amount of power radiated in the respective angles fully describes your antenna's directivity. Nothing to simulate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are called &lt;strong&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Radiation_pattern&quot; rel=&quot;nofollow noreferrer&quot;&gt;radiation patterns&lt;/a&gt;&lt;/strong&gt;. When buying non-trivial antennas for use cases where approximate knowledge of the directivity isn't enough, it's expected that the manufacturer has done the measurements necessary to generate them – it's practically impossible to do this at home, without an anechoic chamber and calibrated reference antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You probably won't get exact fabrication data of what you can buy as patch antennas, but you can simply measure them with a ruler – so PCB type antennas should be OK, too, assuming the substrate is well-known (for cost reasons, and because at these frequencies it still works great, it'll be FR-4, anyway).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you're describing is antenna simulation. Such simulations are usually rather complex finite element method simulations, that, by decomposing the antenna geometry and the time or frequency domain into small enough parts can mathematically approximate the antenna's fields well enough. You don't have to re-invent the wheel. There's software out there that does that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a free software, have a lookt at OpenEMS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, if you're really experienced, then your simulations are meaningful. I've rarely seen someone generate a simulation that is closer to measured reality than an educated guess at the first try. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if your goal is to learn how to simulate antennas, start with very basic ones. A dipole, then a rectangular patch, then a patch with receded feedline etc, not with something as overwhelmingly complex to simulate as real-world 3D aperture antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your goal is to get a very good impression of what an antenna will behave like in usage before buying it, than the manufacturer's measurements are way more useful than a simulation.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-06-18T21:02:03.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6322" PostTypeId="2" ParentId="6319" CreationDate="2016-06-18T21:11:43.467" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm a math and computer science student, starting to mess around with using amplifiers and antennas to build long-range wifi hardware in my spare time.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You're potentially breaking the law. In fact, I'm pretty sure you're breaking the law.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;WiFi operates in the ISM bands, which sets a very strong limit on how much power your device might send in any direction, no matter how directive your antenna is. For most regions, you &lt;strong&gt;must not&lt;/strong&gt; send more energy in any direction than what a theoretical antenna, which perfectly distributes power in all directions evenly, would emit when fed with 100mW. Take the same 100mW and feed it to an antenna with gain, and you're breaking the law.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Calculating the expected power density of a system is easy enough, but--I'd like to measure power density directly. Namely, in the neighborhoods of 2.4 GHz and 5.0 GHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, you need measurement equipment, and calibrated microwave equipment doesn't come cheap. I wouldn't let an untrained student anywhere near my calibrated measurement setup. Just too much work and money on the line here.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I went to the Physics department at my university to borrow equipment. They said EMF meters, gauss meters, etc. that work in the 5.0 GHz range are extremely expensive, and suggested I use a normal wifi antenna to measure field strength. I have since downloaded some software that gives me measurements from my laptop's antenna in dBm; I have no way of knowing how accurate those measurements are, however.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;They're straight up unusable. Simple as that. Without an anechoic chamber, you'll have both fading and interference in the ISM bands. You can't do these measurements like this. Also, WiFi cards will tell you how much &quot;WiFi-alike&quot; energy they can detect. Which has pretty much nothing to do with how things are with the antenna. WiFi cards do amazing correction, self-adjusting amplification and other things that make them completely unusable as measurement devices.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Also, given that I get to choose input wattage on the systems I build and can buy just about any antenna off the Internet as well as the next guy--I'd really, really like it if the meter were capable of measuring power densities in the &quot;you should probably be worried&quot; level ( and above, to some degree ).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Did I mention the law? I think I did. To measure the radiation pattern of your antennas, you don't need much power. Cleanly detectable is enough. And for clean detection you'll need a clean room without interference (this is the ISM bands, where everyone is &lt;em&gt;allowed&lt;/em&gt; to interfere) and reflections (these are microwaves. They will show very surprising non-line-of-sight propagation if you do not work in a room with echo-swallowing walls). &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Are there any meters out there that measure EMF power in the neighborhoods of 2.4 GHz and 5.0 GHz? Meters that are priced so that one can hope to afford them without the financial backing of an institution?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Obviously, that depends on your budget. Still, you'd not only need the meter, you'd need an antenna measurement setup, which is a meter, a calibrated transmitter, calibrated reference antennas, calibrated cables, calibrated reference attenuators, calibrated stands, and an anechoic chamber. This will not be affordable to a normal person.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Really, don't try to measure an antenna yourself. Ask someone from the electrical engineering department or a specialized company if you'd ever need to do something like that. They might have an anechoic chamber, and they might have rates at which you can rent that, and rates at which you can pay a technician to conduct the measurement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I really think you should first read up a bit on antenna theory, to be honest. You can analytically understand a lot of the simpler antennas, and for the more complex one, the manufacturer typically delivers measurements.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-06-18T21:11:43.467" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6324" PostTypeId="2" ParentId="6320" CreationDate="2016-06-19T15:36:16.060" Score="0" Body="&lt;p&gt;For wire antennas I do mathematical modeling using NEC4.  NEC4 is version 4 of the National Electromagnetics Code.  It must be licensed from Lawrence Livermore Labs.  I have a licensed copy and the cost was $300 when I obtained my copy 4 years ago.  There is a public free version, older and less accurate with less features known as NEC2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NEC2 and NEC4 are batch programs (written in Fortran, NEC4 is Fortran 90+) and they accept an input antenna description with execution commands dictating the desired simulation and output.  The output is printed numbers, not graphs.  To obtain graphs of output you need to post-process the output data and draw the graphs yourself or use some of the freely available software that does that for you such as 4NEC2, CocoaNET (for Mac computers), and EZNEC (licensed, not free).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use the Wolfram Mathematica application to produce all my graphic output.  This is far more powerful than any of the above cited software but you need Mathematica (Home Edition about 200 or maybe 300 US dollars).  And, you need to learn Mathematica which to some people is a bit of a learning curve to overcome.  But, I create functional representations of all of the output data that not only allows me to plot graphs nicely but I can do Calculus on the functions for finding minimums and maximums or working to do other extended calculations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that NEC2 and NEC4 are useful for wire antennas only or antennas using linear conductors such as aluminum tubing on Yagi antennas.  You can do some mesh network modeling and try your hand at simulating a dish antenna but that is stretching the accuracy depending on the work you are doing.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-06-19T15:36:16.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6325" PostTypeId="1" AcceptedAnswerId="6335" CreationDate="2016-06-20T02:21:31.663" Score="8" ViewCount="4804" Body="&lt;p&gt;A typical gain pattern for a quarter wave ground plane antenna is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GmKl1m.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GmKl1m.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/3675/4647&quot;&gt;Image from a similar question and see watermark.&lt;/a&gt;&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a situation where the signals of interest are below the antenna in elevation (e.g. antenna on a hill/mountain), would mounting the antenna upside down make any difference?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A naive response would be that the antenna's pattern would be unaffected except to be rotated 180 degrees, i.e.:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CQ0Xpm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CQ0Xpm.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An &lt;a href=&quot;https://ham.stackexchange.com/a/5702/4647&quot;&gt;answer to a similar question&lt;/a&gt; seems to imply that the radials on a ground plane antenna don't have as much to do with the pattern as the actual &lt;strong&gt;earth&lt;/strong&gt;. My trials at modeling this with EZNEC resulted in no change based on the antenna's orientation, but I don't trust myself. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, looking at just the plots would lead you to believe that there is zero chance of receiving a signal from below the antenna's elevations. Which also is hard to believe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Searching the internet resulted in many variations of &quot;Try it.&quot; or &quot;It worked for me back in ...&quot;.  I'm looking for more specific reasoning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And in case it matters much for this answer, I am mainly considering the 2m range of frequencies. Also for consideration, height above ground can be assumed to be in the 5 meter range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simplified configuration for clarity:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IJywE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IJywE.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4647" LastEditorUserId="8717" LastEditDate="2019-11-05T19:43:15.213" LastActivityDate="2020-02-18T11:42:02.333" Title="Does mounting a ground plane antenna upside down change the takeoff angle?" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;&lt;antenna-modeling&gt;" AnswerCount="5" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="6326" PostTypeId="2" ParentId="6325" CreationDate="2016-06-20T16:19:23.313" Score="4" Body="&lt;p&gt;If you were to flip the antenna upside-down, ideally with no part of the antenna touching the ground, then your antenna radiation pattern wouldn't change all that much, as you've discovered on EZNEC.  Two things have changed compared to a 'normal' ground-mounted vertical: you've elevated the radials, and you've flipped the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The following explanation may displease physicists as being overly simplified, but I think it's useful for the average ham.  This is ham.stackexchange.com, not physics.stackexchange.com.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By elevating the radials you've changed the way that the antenna works.  Instead of a 1/4 &amp;lambda; monopole mirrored by the ground that you've made highly conductive with your radials, you now have a dipole.  Half of your dipole is the vertical conductor, which creates vertically-polarized radiation.  The elevated radials, which should be tuned to be 1/4 &amp;lambda; long, work to counter-balance the vertical part of the antenna.  (Some people use the word 'counterpoise' for elevated verticals, but that word has been overly used and abused so much that the late L.B. Cebik, W4RNL, argued that the word should be retired.)  Verticals with elevated radials work very well, but because the verticals must be tuned, they are essentially single-band antennas (plus odd harmonics).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you've flipped the antenna.  The pattern of the signal is very similar to a 'normal' ground-mounted vertical because the pattern is the result of a vertically-polarized signal radiated close to the earth and not in free space.  Flipping the antenna but not flipping the earth just doesn't do much to change the pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no particular reason to flip the antenna just because the antenna is on a mountaintop.  Vertically-polarized antennas on mountaintops are common but I've yet to see a flipped one, ha ha.  Antenna modeling is almost always done over an idealized flat earth, but experience shows that the signal from a mountaintop antenna makes it down into the valley.  There is a program called HFTA or HF Terrain Analysis by Dean Straw N6BV, which comes with the ARRL Antenna Book, that can be used to model propagation over actual terrain that isn't perfectly flat, but the software only works with horizontally-polarized antennas.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-06-20T16:19:23.313" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6327" PostTypeId="2" ParentId="5554" CreationDate="2016-06-20T18:36:51.867" Score="0" Body="&lt;p&gt;There are some type of NRF24L01 that are long range 3km+ rated. With a wifi amplifier (it works at 2.4GHz) you could also reach bigger distances.&lt;/p&gt;&#xA;" OwnerUserId="7873" LastActivityDate="2016-06-20T18:36:51.867" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6328" PostTypeId="1" AcceptedAnswerId="6334" CreationDate="2016-06-20T19:35:36.310" Score="3" ViewCount="204" Body="&lt;p&gt;I've built a high impedance buffer out of an op amp on a small piece of perf board. I'm going to attach the input to the first IF on an Icom IC-718 and the output will be pulled out to a jack that I've drilled into the case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that I want to keep stuff as short as possible... but at the same time, there's no super good place to mount the board that I've created. How bad an idea is it to tap into the IF with a piece of RG-174 that's about 6 inches long between the IF and the board? I would tie the shield to ground as close to where I tap the IF as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is my first major modification to an expensive radio beyond repairs and I'm trying really hard to get it right the first time. :)&lt;/p&gt;&#xA;" OwnerUserId="5137" LastActivityDate="2016-06-21T18:38:10.657" Title="RG-174 to pull signal from 1st IF?" Tags="&lt;coaxial-cable&gt;&lt;modification&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="6330" PostTypeId="1" AcceptedAnswerId="6331" CreationDate="2016-06-20T22:33:44.080" Score="1" ViewCount="163" Body="&lt;p&gt;If you have had occasion to open up a transceiver for repair or other reasons, you have seen the thin grey coax that's used to carry signals from one part of the radio to another.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the designation of this coax?&lt;/p&gt;&#xA;" OwnerUserId="5137" LastActivityDate="2016-06-21T09:54:06.197" Title="Type of coax used inside of a transceiver?" Tags="&lt;coaxial-cable&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6331" PostTypeId="2" ParentId="6330" CreationDate="2016-06-21T06:00:48.907" Score="1" Body="&lt;p&gt;There are probably a variety of such miniature coaxial cables used in various radio equipment.  My Elecraft K3 uses a TMP coaxial cable which is about 1/8th inch in diameter.  It is manufactured by a Japanese company but I forgot their name.  I don't think there is one single designation for such cables.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-06-21T06:00:48.907" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6332" PostTypeId="2" ParentId="6325" CreationDate="2016-06-21T07:43:37.640" Score="4" Body="&lt;p&gt;To answer this very graphically:&lt;/p&gt;&#xA;&lt;p&gt;Flipping the diagram geometrically &lt;strong&gt;can't&lt;/strong&gt; work:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0lMC8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0lMC8.png&quot; alt=&quot;Diagrams&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;What you've actually build is kind of a waveguide, consisting of two grounded planes below (earth) and above (virtual earth spanned by radials) your antenna; in this rotation-symmetrical setup, the H-field only exists in horizontal direction, and the E-field between the two planes will only exist vertically.&lt;/p&gt;&#xA;&lt;p&gt;In other words: if we assume the virtual ground plane to be a perfect circle, then this looks like a lot of dipoles standing tightly next to each other between that plane's edge and the ground, being fed with exactly the same signal. Since this, for symmetry reasons, won't have any horizontal gain, the only gain we can have is vertical; but there's no vertical group factor in a group of horizontally shifted dipoles, so this will really just have the radiation pattern of a half-length dipole.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-06-21T07:43:37.640" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6333" PostTypeId="2" ParentId="6330" CreationDate="2016-06-21T09:54:06.197" Score="3" Body="&lt;p&gt;This can't be generally answered. There's quite a lot of characteristics to coax cable that are relevant to its application, and hence, device designers have the choice from a great deal of different cable and connector types. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just to give you an idea of what one would care about, and for which there's pretty much always different choices:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;cable RF impedance ($50\,\Omega$, $75\,\Omega$, …)&lt;/li&gt;&#xA;&lt;li&gt;attenuation of desired frequency per length&lt;/li&gt;&#xA;&lt;li&gt;propagation speed in the dielectric (there's different dielectrics out there!)&lt;/li&gt;&#xA;&lt;li&gt;mechanical aspects such as&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;bendability&lt;/li&gt;&#xA;&lt;li&gt;rigidity&lt;/li&gt;&#xA;&lt;li&gt;tolerance to vibration&lt;/li&gt;&#xA;&lt;li&gt;weight&lt;/li&gt;&#xA;&lt;li&gt;length&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;connectors (there's literally hundreds of different PCB-Coax connection options)&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Cost&lt;/li&gt;&#xA;&lt;li&gt;attenuation&lt;/li&gt;&#xA;&lt;li&gt;all the mechanical aspects above&lt;/li&gt;&#xA;&lt;li&gt;well-matchedness&lt;/li&gt;&#xA;&lt;li&gt;reliability of electrical data&lt;/li&gt;&#xA;&lt;li&gt;expected number of plugging cycles&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;thermal stability&lt;/li&gt;&#xA;&lt;li&gt;tolerance to humidity&lt;/li&gt;&#xA;&lt;li&gt;maximum transportable power / field strength&lt;/li&gt;&#xA;&lt;li&gt;tolerance of all the above things across&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;different points of the same piece of cable&lt;/li&gt;&#xA;&lt;li&gt;different cables from the same production run&lt;/li&gt;&#xA;&lt;li&gt;future production runs&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;long-term availability&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;costs&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-06-21T09:54:06.197" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6334" PostTypeId="2" ParentId="6328" CreationDate="2016-06-21T17:59:51.823" Score="5" Body="&lt;p&gt;So, you say:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I don't care if the signals are delayed. I'm just tapping the line out to a pan adapter. I am most concerned about influencing the existing function of the receiver&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;And that's &lt;em&gt;exactly&lt;/em&gt; what you're going to do with this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your Opamp circuit has a high impedance, which translates into &quot;looks like an open end&quot;. That means that your tapping coax has a very distinct feature: A &lt;a href=&quot;https://en.wikipedia.org/wiki/Reflection_coefficient&quot;&gt;&lt;em&gt;reflection coefficient&lt;/em&gt;&lt;/a&gt; of 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can easily be seen by the &quot;mismatch&quot; equation: The ratio of electric field (voltage!) going through the interface between two transmission lines with different impedances and getting reflect is defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\Gamma = \frac{E^-}{E^+} = \frac{Z_2 - Z_1}{Z_1 + Z_2} $&lt;/p&gt;&#xA;&#xA;&lt;p&gt;with $Z_1$ being the impedance of the transmission line from which the wave comes, and $Z_2$ being the impedance of the second transmission line or the sinking device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case, $Z_2\rightarrow \infty$, and hence&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;\lim_{Z_2\rightarrow \infty} \Gamma &amp;amp;=\lim_{Z_2\rightarrow \infty}  \frac{Z_2 - Z_1}{Z_1 + Z_2}\\&#xA;&amp;amp;= \lim_{Z_2\rightarrow \infty}  \frac{\frac{Z_2}{Z_2} - \frac{Z_1}{Z_2}}{\frac{Z_1}{Z_2} + \frac{Z_2}{Z_2}}\\&#xA;&amp;amp;= \lim_{Z_2\rightarrow \infty}  \frac{1 - \frac{Z_1}{Z_2}}{\frac{Z_1}{Z_2} + 1}\\&#xA;&amp;amp;=\frac{1-0}{0+1}\\&#xA;&amp;amp;=1&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means that &lt;em&gt;all&lt;/em&gt; energy put into that tap line returns to the line you've tapped – which is pretty logical! Where should the energy you &quot;steal&quot; from the original coax go if you don't sink it somewhere? It's pretty clear you'll have a bad SWR in this situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let's look at the wave from your IF line:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It meets the point where you've tapped the original line. Let's assume that you've build a reflection-free splitter here – that's highly unlikely, but it makes things both better for your use case, and easier to understand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the wave enters your 6 inch (really, inches are a terrible unit for RF design – with meters, and hertz, everything can be calculated without converting) line. That's about $d=0.15\text{ m}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, RG-174 has a &lt;em&gt;velocity factor&lt;/em&gt; of 0.66 – meaning that a wave travels with $\frac 23$ of the speed of light in vacuum, which is accurately enough $v_{RG-174}=\frac 23 \, 3\cdot 10^8\frac{\text m}{\text s} = 2\cdot 10^8\frac{\text m}{\text s}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, for the distance between your tapping point, and the end of your RG174, and back, the wave needs &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\Delta t = \frac{2d}{v_{RG-174}} = \frac{0.3\text{ m}}{2\cdot 10^8\frac{\text m}{\text s}}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After that time, the wave will hit the tapping point – and &lt;strong&gt;interfere&lt;/strong&gt; with the original IF!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By adding up a wave and a delayed version, you have built a frequency-selective device – a &lt;em&gt;filter&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, what's relevant here is to know the &lt;em&gt;phase&lt;/em&gt; with which the interference will happen. Let's have a look at that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The phase $\varphi$ of a signal is the delay, measured in full periods $T$ of the signal (and period is related to frequency by $T=\frac1f$; from your comment, $f=70\text{ MHz}$); in other words: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;\Delta \varphi &amp;amp;= 2\pi \frac{\Delta t}{T}\\&#xA;&amp;amp;= 2\pi \frac{\Delta t}{\frac1f}\\&#xA;&amp;amp;= 2\pi \frac{\frac{2d}{v_{RG-174}}}{\frac1f}\\&#xA;&amp;amp;= 2\pi \frac{2df}{v_{RG-174}}&#xA;&amp;amp;\approx 2\pi \cdot 0.1&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, you're overlaying your original IF signal with a 0.1 waveperiods delayed version of itself. That &lt;strong&gt;will&lt;/strong&gt; cancel out specific frequencies, while others will be amplified.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, we could derive the frequency response of the &lt;strong&gt;tapped delay line&lt;/strong&gt; filter you've built – but since that will in practice depend a lot on things that are hard to know beforehand, like reflection coefficient of your tap (since that massively changes impedance of the line, depending on a lot of things), exact length, etc, this would be pretty much in vain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The essence is: don't tap analog coax lines. Simple as that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Get a proper splitter with the correct input impedance, and make sure your opamp circuit is impedance-matched to your transmission line. Everything else will end in significant reflections, interference and frequency-dependent cancelation of signal that is hard to predict and to measure.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-06-21T18:38:10.657" LastActivityDate="2016-06-21T18:38:10.657" CommentCount="18" ContentLicense="CC BY-SA 3.0" />
  <row Id="6335" PostTypeId="2" ParentId="6325" CreationDate="2016-06-21T21:12:30.900" Score="3" Body="&lt;p&gt;An elevated &quot;ground-plane&quot; antenna with tuned radials has, by itself, a pattern much like a dipole doughnut shape (freespace is what I'm talking about at the moment).  Unfortunately we must mount the antenna and feed it with a feedline.  This introduces one or more additional conductors below the radials that demonstrably (via simulation and measurement) draw/induce some power from the radials and flow energy below the antenna.  See figure 5 &lt;a href=&quot;http://www.hamradio.me/antennas/j-pole-antenna-grounding-have-your-j-pole-and-ground-it-too.html&quot; rel=&quot;nofollow&quot;&gt;of this article&lt;/a&gt;.  This seems to cause the slight uptilt you most often see in ground-plane antenna documentation.  The 3 dB beamwidth in the vertical E-plane is still quite enormous with energy both above and below the level of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some purists do mount these things upside down on a tower side bracket when the antenna site is much much higher than the surrounding users of the radio system. Indeed &quot;beam downtilt&quot; in collinear phased array systems is a serious attribute to study for some radio system circumstances... especially for the shorter wavelengths.  Trigonometry helps answer when to consider this approach as I cover &lt;a href=&quot;http://www.hamradio.me/antennas/repeaters-antennas-trigonometry.html&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, the vertical beamwidth of the typical quarter-wave monopole antenna is so big, mounting it upside down is probably not going to make any difference for most circumstances.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastActivityDate="2016-06-21T21:12:30.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6336" PostTypeId="1" CreationDate="2016-06-21T23:11:00.740" Score="2" ViewCount="94" Body="&lt;p&gt;I would like to listen to my own transmitted signal using a second receiver and connecting one into the other could possibly be a bad idea ;-) so How can I safely tap into my transmitted signal without risking melting the receiver?&lt;/p&gt;&#xA;" OwnerUserId="5577" LastActivityDate="2016-06-22T06:20:11.130" Title="How to safely listen to my transmitted signal with a second receiver" Tags="&lt;safety&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6338" PostTypeId="2" ParentId="6336" CreationDate="2016-06-22T03:08:28.837" Score="5" Body="&lt;p&gt;If the receiver is close to the transmitter, and you are transmitting with more than a few milliwatts, just fire up the receiver with no antenna attached. Not having an antenna makes the receiver far less sensitive, but with the path loss being only some feet, it really doesn't need to be very sensitive.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-06-22T03:08:28.837" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6339" PostTypeId="2" ParentId="6336" CreationDate="2016-06-22T06:20:11.130" Score="4" Body="&lt;p&gt;Also, there's a lot of &lt;em&gt;attenuators&lt;/em&gt; out there. Just do the math: If your transmitter is capable of thransmitting let's say 20 dBm, and your receiver has a sensitivity of -90 dBm and a max input of 10 dBm, then your maximum attenuation you could use is ( 20 - (-90) ) dB = 110 dB, and the mininimum necessary is ( 20 - 10 ) dB = 10 dB. &lt;strong&gt;Always go for the higher end&lt;/strong&gt;, since attenuators are practically noise-free, and short output power spikes above what you're expecting could fry your receiver. 60 dB is a common value, so that's what I'd use here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Phil's answer is also pretty perfect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The point I want to stress here is that if you want to&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;safely tap into my transmitted signal without risking melting the receiver&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;you'll need the &quot;melting point&quot; (max. input power) of your receiver, and the amount of &quot;heat&quot; (max output power) of your transmitter. As Phil pointed out, it's pretty unlikely you'll fry your receiver without an antenna attached to its open port (which is, technically, still an antenna, because it's now the interface between the 50 or 75 $\Omega$ line impedance and free space impedance, but a &lt;em&gt;bad&lt;/em&gt; antenna; think of it as miniature horn antenna), but that's just because the efficiency at which such ports pick up energy are pretty small. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-06-22T06:20:11.130" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6340" PostTypeId="1" CreationDate="2016-06-22T14:59:13.577" Score="2" ViewCount="890" Body="&lt;p&gt;I recently obtained an IC-2730E and can't figure out the difference between its squelch options. Unfortunately, the user manual isn't very helpful. The squelch option had 3 types: off, attenuation and S-meter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I could gather, the attenuator is just the normal squelch with an attenuator added in the signal path. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, I'm not really sure what's the difference between the S-meter squelch and the &quot;off&quot; squelch. In practice, they both seem to be doing the same thing, except that the S-meter squelch will show S-levels to which it is set to.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="76" LastEditDate="2016-10-29T18:56:39.847" LastActivityDate="2020-08-09T18:14:22.750" Title="What's the difference between the normal and S-meter squelch in IC-2730?" Tags="&lt;receiver&gt;&lt;fm&gt;&lt;equipment-operation&gt;&lt;icom&gt;&lt;squelch&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6341" PostTypeId="2" ParentId="6340" CreationDate="2016-06-22T16:26:41.893" Score="1" Body="&lt;p&gt;Can't speak from experience with this radio, but I looked at &lt;a href=&quot;http://www.icomuk.co.uk/files/icom/PDF/productManual/IC-2730_ENG_0.pdf&quot; rel=&quot;nofollow&quot;&gt;the manual&lt;/a&gt; and it says about the option that:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Squelch/ATT select      FUNC — SQLTYP&lt;br&gt;&#xA;  Sets to use the S-Meter Squelch or the Attenuator function for the&#xA;  [SQL] control.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The way I would read this is that it does not change the squelch behavior but controls &lt;em&gt;whether the knob changes the squelch level or changes the attenuation&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manual later says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;When you rotate [SQL]S clockwise beyond the center position,&#xA;  [SQL]S becomes an ‘S-meter Squelch’ or ‘Attenuator.’ Select&#xA;  the [SQL]S option in the MENU mode. (p. 14)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I read this as the menu option affects the behavior of the &lt;em&gt;upper range&lt;/em&gt; of the SQL knob, and the lower range is always “regular” squelch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not at all clear to me what “S-meter squelch” as opposed to regular squelch means, however, but it's clear (from the use of the upper range of the SQL knob) that in either case these are functions for dealing with &lt;em&gt;very strong signals&lt;/em&gt;. That is when you would want an attenuator: when the incoming signal is too strong for the receiver to function correctly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One possible explanation is that in the attenuator mode it doesn't increase the squelch level higher but adds attenuation (presumably before the squelch's sensor), but in the S-meter squelch mode it just increases squelch further. But it's really unclear and I'd suggest conducting some experiments with a nearby friend to see how it behaves in the two cases with a strong signal.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-06-22T16:26:41.893" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6342" PostTypeId="1" CreationDate="2016-06-22T17:20:36.477" Score="3" ViewCount="568" Body="&lt;p&gt;I tried but failed to decode WSPR using Tecsun PL-600 receiver that tunes in 1KHz step. I heard tones with good SNR but cannot be decoded. So, I mis-set it somewhere.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Is it correct that transmission is around 10.140200MHz, with a few Hz bandwidth?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What are the four symbol RF frequencies? I seem to read documentation saying that they are 10.140200 + (0_to_3 x 1.4648Hz). I observed WSPR sound card output, using Spectrum Lab software, and they are spreading from 1497 to 1503 Hz, instead of 1500 to 1506Hz. Where did I miss?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;On a 'normal' receiver, should I set the receiver frequency to 10.138700MHz, get audio at 1500Hz and WSPR software will auto search and decode signal around 1500Hz? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;On my receiver, is it correct that audio will be 1200 and 2200Hz, when dialed to 10.138 or 10.139MHz? Will WSPR software auto search to 1200 and 2200Hz? If not, can I set it in the software?  Or, I should vary BFO to make it &quot;back to&quot; 1500Hz?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Are the below tabled calculation of LO and BFO, etc correct? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The receiver only have setting of AM/SSB. It does not have separate setting for USB and LSB.  It has a BFO knob with a 'central click&quot; which got a good zero beat for 10MHz time signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;To get effective USB mode, I believe I should turn it &quot;away from the central click&quot; in order to set BFO to 453.5KHz, right? &lt;/p&gt;&#xA;&#xA;&lt;ol start=&quot;7&quot;&gt;&#xA;&lt;li&gt;If I turn the BFO knob to the &quot;wrong&quot; direction, setting BFO to 456.5KHz, resulting in LSB mode, I will hear similar signal tone, but, the 4 symbols are in &quot;up side down frequency order&quot; and cannot be decoded. Are these right? &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aLLcz.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aLLcz.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1473" LastActivityDate="2016-07-09T21:07:44.170" Title="WSPR RX dial frequency" Tags="&lt;ssb&gt;&lt;wspr&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6343" PostTypeId="5" CreationDate="2016-06-22T17:33:08.740" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2016-06-22T17:33:08.740" LastActivityDate="2016-06-22T17:33:08.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6344" PostTypeId="4" CreationDate="2016-06-22T17:33:08.740" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2016-06-22T17:33:08.740" LastActivityDate="2016-06-22T17:33:08.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6345" PostTypeId="2" ParentId="6342" CreationDate="2016-06-22T19:12:22.587" Score="2" Body="&lt;p&gt;I'm neither an electrical engineer nor a software-defined radio expert, but I have used WSPR, so I'll have a go at answering your question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're correct that WSPR transmissions on 30m are centered around 10.1402 MHz, but the WSPR 2.0 User's Guide says that the passband is about 200 Hz wide since the software will generate tones between 1400 and 1600 Hz, and transceiver frequency drift can add to that.  The screen shots in the User's Guide show a passband of slightly more than 200 Hz wide (see the scale at the right of the waterfall).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most ham radio software for digital modes shows signals in the entire passband sent by the radio, typically 2.7 kHz wide or so, but K1JT's software decodes a much smaller passband, probably with the intention of keeping WSPR signals confined to a small part of the band since there is no need to use a larger passband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had a look at the manual for your Tecsun PL-600, which is quite vague about SSB reception.  I think you're probably right about turning the BFO knob one way for USB and the other way for LSB.  If I were in your situation I would test that theory by tuning the radio to the ham 20m band (14.225 to 14.350 MHz in the US), where USB is the norm, and also to the ham 40m band (7.175 to 7.300 MHz) where LSB is common.  Tuning SSB signals in those two bands will tell you how the BFO knob works, and which way you twist for USB and which way for LSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would suggest that you try W1JT's software before trying that Spectrum Lab software.  If you can successfully decode signals with W1JT's software then you will know that your radio is tuned correctly, that the incoming signal voltage levels are correct, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please keep in mind also that signals from the headphone jack of the radio are at about line level (~ 1 V), but the input level of the sound card in your computer may be at microphone level (millivolts).  If that is the case, then an attenuator is necessary between the radio and the computer.  Some sound cards have a line-level input, in which case an attenuator may not be necessary.  For more details about such an attenuator, do a web search for &quot;ham radio sound card interface&quot;.  Sometimes galvanic isolation (a transformer) is required in the sound card interface in order to prevent ground loop problems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck, and let us know in a comment how things go!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-06-22T19:12:22.587" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6346" PostTypeId="1" CreationDate="2016-06-24T06:29:49.593" Score="0" ViewCount="911" Body="&lt;p&gt;I'm thinking of buying &lt;a href=&quot;https://www.ubnt.com/airmax/powerbeam-ac/&quot; rel=&quot;nofollow noreferrer&quot;&gt;PowerBeam ac&lt;/a&gt;. It's a wireless device to connect two computer networks that are about 25 kilometers apart. But it depended on line-of-sight they say. So is there a cheap way to test for line-of-sight at that distance and frequency? Like a homemade thing or something? &lt;/p&gt;&#xA;" OwnerUserId="7886" LastEditorUserId="873" LastEditDate="2017-05-19T08:04:40.880" LastActivityDate="2017-05-20T16:33:03.700" Title="How to test Line-of-Sight radio at 5GHz at range 25Km or less?" Tags="&lt;mesh-network&gt;&lt;line-of-sight&gt;&lt;shf&gt;" AnswerCount="5" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6347" PostTypeId="2" ParentId="6346" CreationDate="2016-06-24T06:57:17.407" Score="5" Body="&lt;p&gt;5 GHz and 25 km range is &lt;strong&gt;hard&lt;/strong&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's do a quick free space loss calculation: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;a &amp;amp;= \left(\frac{4\pi d}{\lambda}\right)^2\\&#xA;&amp;amp;= \left(\frac{4\pi dc}{f}\right)^2\\&#xA;&amp;amp;= \left(\frac{4\pi \cdot 2.5\cdot 10^4 \text{ m} \cdot 5\cdot 10^9\text{ Hz}}{3\cdot 10^8\frac{\text m}{\text s}}\right)^2\\&#xA;&amp;amp;= \left(\frac{5\pi}{3}10^6\right)^2\\&#xA;&amp;amp;\approx {5.2}^2\cdot10^{12}\\&#xA;&amp;amp;\approx 130\text{ dB}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;130 dB is a lot. Remember, in the ISM band you're normally not allowed to send more than 20 dBm, which leaves you with but -110 dBm at the receiver – not a good thing, considering that thermal noise in a 20 MHz WiFi channel is already $-174 \frac{\text{dBm}}{\text{Hz}}\cdot 20\text{ MHz}= -101\text{ dBm}$, i.e., you'll get ten times the power of the signal in thermal noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, your antenna gains must be very high on both receiver and transmitter side, and hence, your equipment must be very well-aligned. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, adding to the thermal noise mentioned above, you got the receiver's Noise Figure  (NF) – building a low-NF receiver at 5 GHz isn't easy, either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, physics and legislation are stacked against you here: If non-LOS communication over microwave over 25 km would easily work, everyone and their mom would run to use it. But then, the spectrum would be crowded – because each station would &quot;spoil&quot; the spectrum for a 25 km radius. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact that the higher the frequency, the higher the path loss, is the only reason we actually have these large ISM bands in the 2.4 and 5 GHz region.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Directional links in the Gigahertzes are thoroughly common; look for the horizontally pointing dishes (typically encased in white plastic) on larger cell phone towers. However, these are usually run with an explicit license for stationary earth-earth directional links, and hence legally do much more power than your AC router. Now, you could possibly build a similar link yourself with off-the-shelf satellite dishes, but I've got no experience nor appropriate license knowledge on doing so on ham bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, coming back to your original question:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;so is there a cheap way to test for line-of-sight at that distance and frequency? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;well, line-of-sight can be tested by sight! So, good binoculars are your weapon of choice. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I feel like I should also point you to Fresnel zones: it's recommendable to not only have clean LOS, but also a clean first Fresnel zone, to avoid diffracting/reflecting your microwave beam. In other words: this is something to be mounted &lt;em&gt;high&lt;/em&gt; if you want to go the full distance!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aligning those dishes won't be easy, but maybe they come with some straight piece that points exactly parallel to the beam direction, on which you can mount a laser pointer, and tell a friend over the phone to turn the dish until you can see the laser pointer pointing at you.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Another thing to consider: WiFi was never meant to be used over huge distances. It's a carrier-sense system, ie. a station must listen for a predefined time, before it considers the channel free and may device send. That way, the chance of packets colliding in the air is reduced significantly enough to make such systems work without a central instance to coordinate spectrum access in fixed time slots.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is achieved by first sensing, then sending a short &quot;Ready To Send&quot; packet containing the coming packet's length, which the intended receiver detects, and then again waits for a fixed period, to make sure no one missed the original RTS, before replying with a &quot;Clear To Send&quot;. The idea is that all other stations hear at least either the CTS or RTS and know that they need to stay silent for the specified amount of time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if the CTS-&gt;RTS mechanism, being completely superfluous for a fixed length, takes 2 times the sensing period in addition to 160 µs of signal flight, the consequences for throughput are dire, because the channel will be used nearly only for waiting and sensing – a full IEEE802.11n symbol is about 4µs &lt;em&gt;the most&lt;/em&gt;, and there's about 30 of those in a frame; though a couple of frames can be aggregated under 802.11n, the relation of flight time to active data transmission is unnecessarily bad:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your wave has to travel 25 km, it'll be in flight for $\frac{d}{c}= \frac{2.5\cdot 10^4\text{ m}}{3\cdot 10^8\frac{\text m}{\text s}} \approx 80\, \mu\text{s}$. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this scenario, having a system with separate up- and downlink frequencies (FDD), halving the available bandwidth, is significantly more efficient.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-06-24T16:30:41.150" LastActivityDate="2016-06-24T16:30:41.150" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6348" PostTypeId="2" ParentId="6346" CreationDate="2016-06-24T11:06:24.310" Score="1" Body="&lt;p&gt;To add to the already given answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most countries have a 100mW / 20dBm ERP maximum for license free usage of those bands. (You will have to check if this is your case, but chances are)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As this is usually expressed in &quot;ERP&quot; which is &quot;Effective Radiated Power&quot; it will take antenna gains into account. Example by using an antenna with 3dBi gain, you will have to compensate your TX-output power to 50mW, to ensure you comply with legislation. This is probably the single most limiting aspect of what you are asking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However (!!)&#xA;If you can design your system, where you stay within your 100mW ERP for TX, but you somehow can improve your RX by means of an antenna with extreme directional gain, you may have a chance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this to be successful, you need to use devices with separate TX antenna and RX antenna connections, or use of a &quot;Circular Coaxial Coupler&quot; (for the bands you intend to use)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lets use a calculation from another answer already given:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;So we know that path-loss is about 130 dB. &lt;/li&gt;&#xA;&lt;li&gt;We have seen the noise figure at -101 dBm. &lt;/li&gt;&#xA;&lt;li&gt;And we take a maximum of 20 dBm. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;But now we take the RX antenna at 40 dBi (huge parabolic dish).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;20(dBm) - 130(dB) + 40(dBi) = -70dBm for RX with a -101 dBm noise figure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Theoretically this should be possible, but you will have to precisely line up the parabolic dishes, you need to have the correct equipment, and-so-on-so-forth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be a nice experiment if you have the equipment laying around... If you have to buy it all from scratch, then my practical advice is: &lt;strong&gt;25 km is just a little to far for bridging networks with &quot;consumer&quot; equipment and staying within the confines of the law.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;[EDIT] based on the answer already given: regards &quot;Timing&quot;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some equipment may have settings to further control the RTS/CTS and other parameters of the protocol, to enable longer distances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here a typical screenshot of an EnGenius device:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/D1gPK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/D1gPK.jpg&quot; alt=&quot;EnGenius advanced settings&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are various settings which would help longer distances:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Data Rate&quot; - the lower the data rate the longer the distance, experimentation needed&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Transmit Power&quot; - the higher the Transmit Power the longer the distance, this should be as high as (legally) allowed (taking antenna gain, coax/feeder loss, into consideration)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;RTS/CTS Threshold&quot; - the lower the threshold the longer the distance, at a cost of bandwidth, experimentation needed: set as high as possible without collisions. This might require monitoring of re-transmits&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Distance&quot; - this should be set as accuarately as possible, as according to &lt;a href=&quot;http://www.engeniustech.com/resources/Troubleshooting%20EnGenius%20Wifi%20Networks.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; document it affects the ACK timeout on longer links.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Short GI&quot; - should be disabled, this affects the timing between &quot;characters&quot; on the link, and should be set to standard/disabled (timing 800ns) which prevents/avoids collisions within the same character due to reflections. The longer the distance the more risk of reflected signals you have&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Aggregation&quot; - this should &lt;em&gt;probably&lt;/em&gt; be disabled, but experimentation may be needed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obligatory disclaimers:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;other brands may call settings differently&lt;/li&gt;&#xA;&lt;li&gt;EnGenius has different models, not all of them available to consumers&lt;/li&gt;&#xA;&lt;li&gt;I have no affiliation with EnGenius, this is only an example&lt;/li&gt;&#xA;&lt;li&gt;and... ofcourse... YMMV&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-06-27T12:13:40.890" LastActivityDate="2016-06-27T12:13:40.890" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6349" PostTypeId="1" CreationDate="2016-06-24T22:59:06.690" Score="2" ViewCount="1877" Body="&lt;p&gt;I have a CB radio and I occasionally mess with a cheap SDR Dongle I have. I can pick up CB transmissions no problem but would like to be able to broadcast from my SDR. Is there any way to do this? &#xA;I believe that it is a RTL-SDR I have never really been able to figure it out. &lt;a href=&quot;https://i.stack.imgur.com/FylpB.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FylpB.jpg&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the radio is not compatible do you have any recommendations of one that is?&lt;/p&gt;&#xA;" OwnerUserId="7887" LastEditorUserId="7887" LastEditDate="2016-06-24T23:26:08.253" LastActivityDate="2019-08-15T21:10:30.397" Title="SDR CB Transmission" Tags="&lt;software-defined-radio&gt;&lt;citizens-band&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6351" PostTypeId="2" ParentId="6349" CreationDate="2016-06-25T08:42:34.433" Score="5" Body="&lt;p&gt;CB is licensed by rule (like FRS), and CB transmitters must be certified by the FCC (also like FRS).  If the SDR you're using doesn't have an identifying label on it, you're probably not allowed to transmit on CB frequencies (of course, monitoring them is fine).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, aside from the technical question of whether your SDR will transmit in that band, you need to make sure it's FCC-certified.  I did a quick search in the &lt;a href=&quot;https://apps.fcc.gov/oetcf/eas/reports/GenericSearch.cfm&quot; rel=&quot;noreferrer&quot;&gt;FCC OET database&lt;/a&gt;, which is where records of equipment authorization are found.  CB is regulated under Part 95D, and the search page even has a convenient &quot;software defined radios&quot; checkbox.  There were no results with those two criteria.  Unless I'm running the search wrong (if someone else gets a different result, please say so), that means there are currently &lt;strong&gt;no SDRs certified for use on CB channels&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Monitor away, but know that transmitting with uncertified equipment is illegal, and &lt;a href=&quot;http://www.southgatearc.org/news/november/cb_operator.htm&quot; rel=&quot;noreferrer&quot;&gt;the penalties can be quite severe&lt;/a&gt;.  If you don't have one already, maybe you should consider getting an amateur license!  You'll get a lot more flexibility in where you can transmit and the equipment you use.&lt;/p&gt;&#xA;" OwnerUserId="6446" LastActivityDate="2016-06-25T08:42:34.433" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6352" PostTypeId="1" CreationDate="2016-06-25T11:37:31.233" Score="0" ViewCount="157" Body="&lt;p&gt;So I have a 1.5 m by 1.5 m window. Through it, I have a number of spatially separated ~10 cm wide &quot;beams&quot; coming from local repeaters. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It looks something like this:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/RXL5C.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RXL5C.png&quot; alt=&quot;Picture of my window with reception areas marked&quot;&gt;&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Outside of the marked areas, I have absolutely no reception of local repeaters and inside of them, it's relatively good. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I can't use the traditional methods of solving the issue by placing an antenna at the roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So are there any antenna types that could be helpful in this case?&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2016-06-25T14:52:26.770" LastActivityDate="2016-08-09T12:28:27.223" Title="What type 2 m /70 cm antenna to use when I want to receive a number of spacially separated beams?" Tags="&lt;antenna&gt;&lt;vhf&gt;" AnswerCount="2" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6353" PostTypeId="2" ParentId="6352" CreationDate="2016-06-25T14:07:04.997" Score="0" Body="&lt;p&gt;You should be more specific as I am not quite sure if I got it right.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Distance in centimeters does not matter. What matters is beam angles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you should do is to choose location where you want to set antenna. Then measure angles of each repeater using some directional antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Calculate angle between beams of the most left and most right repeater. That angle is minimum beam angle of antenna you need. You may use wider beam antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pay attention that for repeaters you have to use vertical polarization, meaning if you use Yagi antenna it should be set vertically. Yagi antenna charts are usually drawn for horizontal set antenna, you have to take that in count.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-06-25T14:07:04.997" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6354" PostTypeId="1" AcceptedAnswerId="6355" CreationDate="2016-06-25T17:34:02.870" Score="5" ViewCount="104" Body="&lt;p&gt;I recently bought one of the classic USB dongles to experiment with SDR. &#xA;At 460MHz (Europe, CH) I constantly see many digital transmission that use BFSK.&#xA;What is strange to me is that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the frequency spacing is about 9KHz, instead of the much lower values used for example in RTTY (170Hz). Is this a known protocol spacing?&lt;/li&gt;&#xA;&lt;li&gt;The baud rate doesn't look standard to me: 510 baud. What could be an explanation?&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Before sending the actual payload (1140 bits) I see 575 alternating bits. Is that some kind of CSMA?&#xA;The full content is:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101010&#xA;10101010101010101010101010101011&#xA;00000110010110111101010001001111&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001001001001100011011011011000&#xA;10111111010010111110010100011110&#xA;01000011011011000011100110110111&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001000000000000011100010001011&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001010111011000111110011010001&#xA;00001000000000000011100010001011&#xA;111111111111111111&#xA;&lt;/code&gt;&lt;/pre&gt;&lt;/li&gt;&#xA;&lt;li&gt;I see that there is a pattern that repeats every 32bits in the payload. Any guess about the protocol? Is it legal to tx with a proprietary protocol on HAM frequencies?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="7890" LastActivityDate="2016-06-25T23:28:39.967" Title="BFSK with huge spacing, why?" Tags="&lt;rtty&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6355" PostTypeId="2" ParentId="6354" CreationDate="2016-06-25T23:22:50.360" Score="5" Body="&lt;p&gt;Let's see if I can answer your question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shift:&lt;br&gt;&#xA; The usual theory says that we need spacing between frequencies that is at least equal to symbol rate (or 1/2 of symbol rate for coherent detection). This automatically eliminates the 170 Hz spacing we have in some RTTY implementations. This tells us why not 170 Hz, but it doesn't say why 9 kHz. In my opinion, this would be useful shift that could deal nicely with bad carrier. Basically, the actual middle frequency of the BFSK system might not be exactly the one that has been assigned to the system and could easily have some offsets and is likely to drift with time and temperature. At 460 MHz, 1 ppm of drift would be 460 Hz, the entire spacing of a short-wave RTTY system. By using 9 kHz, we have more room for transmitter imperfections. I also believe that it could be very possible that whoever is running the system needs to get at least a 12.5 kHz channel for it. If that's the case, then there's no reason why to be saving up all that spectrum, when you don't have to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Baud rate:&lt;br&gt;&#xA;Well it does look very unusual, but I'd say that the intended rate is perhaps 512 Bd instead of 510 Bd. This would then be very close a usual symbol rate. Since you asked about protocol, I think this is probably &lt;a href=&quot;http://www.sigidwiki.com/wiki/POCSAG&quot;&gt;POCSAG&lt;/a&gt; used for pagers. I'm in Germany right now and the town that I'm in has 3 paging frequencies around 466 MHz. They run BFSK with 9 kHz spacing and 512 Bd is a POCSAG baud rate. There's a POCSAG decoder called &lt;a href=&quot;http://www.discriminator.nl/pdw/index-en.html&quot;&gt;PDW&lt;/a&gt; that you can play around with, to see if it's really POCSAG or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CSMA:&lt;br&gt;&#xA;I don't really think this is CSMA. I mean, we're trying to sense if there's a carrier or not and we won't do that by transmitting directly. To me, this more looks like a synchronization step for the receiver. You measured the symbol rate of 510 Bd. It's relatively easy to add a pre-amble that will synchronize the transmitter's and receiver's symbol clocks together, so that when the actual data transfer starts, the receiver knows the real symbol rate and knows when a new symbol starts. Furthermore, by having a pre-amble, you can train the adaptive filters used in &lt;a href=&quot;https://en.wikipedia.org/wiki/Equalization_(communications)&quot;&gt;receiver equalizer&lt;/a&gt; to the particular channel that we have. This way, receiver can try to compensate for environment effects. This is commonly used in digital wireless technologies today. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;32 bits:&lt;br&gt;&#xA;I'm not really an expert in POCSAG, so I don't know why they have those 32 bits. I think that they can be used as a sort of rudimentary error correction, they can be used to separate parts of message and give knows ending points for say &lt;a href=&quot;https://en.wikipedia.org/wiki/Viterbi_decoder&quot;&gt;Viterbi decoder&lt;/a&gt; and also to update equalizer channel estimation. Finally, I'm pretty sure that 460 MHz is outside of amateur radio bands in Switzerland. &lt;a href=&quot;http://www.ezv.admin.ch/zollinfo_privat/04414/04853/index.html?lang=en&amp;amp;download=NHzLpZeg7t,lnp6I0NTU042l2Z6ln1ad1IZn4Z2qZpnO2Yuq2Z6gpJCDfH93gWym162epYbg2c_JjKbNoKSn6A--&quot;&gt;Here&lt;/a&gt;'s a nice illustrated guide to licensing basics from their government website which says that the 70 cm band is 430 MHz to 440 MHz, like in many parts of the Europe, so 460 MHz would be a commercial part of the band.&lt;br&gt;&#xA;To answer your question more directly, I'm not really sure if proprietary protocols are allowed or not in CH and this is an ongoing debate in ham radio community as a whole, since there are certain interests that are pushing for mutually not-very-open digital voice standards right now. In general case, encryption is banned, but proprietary, or not very known, standards aren't automatically considered encryption. Do note that in some countries POCSAG is explicitly allowed in ham radio. For example, &lt;a href=&quot;http://www.darc.de/fileadmin/filemounts/referate/vus/bandplaene/UHF_Bandplan_70_cm_Mai_2016.pdf&quot;&gt;Germany&lt;/a&gt; has reserved frequencies for POCSAG in 70 cm amateur band. It's at 439.9875 MHz, if I remember correctly.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="77" LastEditDate="2016-06-25T23:28:39.967" LastActivityDate="2016-06-25T23:28:39.967" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6356" PostTypeId="1" CreationDate="2016-06-26T14:08:54.953" Score="1" ViewCount="351" Body="&lt;p&gt;I've just tried making my own J pole antenna. While matching for lowest SWR on the SWR meter, I noticed that my FTM400 didn't show 5 W forward power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hardly saw the reflected power needle move so I increased the power to 20 W just to have a quick peek. There it showed a forward power of about 12 W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On my normal antenna I get 5 W for 5 W input and 20 W for 20 W input, but this has me stumped. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The homebrew is a J pole for 146 MHz and SWR should be in the ballpark. At 20 W I get a SWR of about 1.3.&lt;/p&gt;&#xA;" OwnerUserId="6504" LastEditorUserId="76" LastEditDate="2017-05-05T20:36:58.933" LastActivityDate="2017-05-05T20:36:58.933" Title="Measured forward power less than &quot;usual&quot;" Tags="&lt;antenna-construction&gt;&lt;swr-meter&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6358" PostTypeId="2" ParentId="6356" CreationDate="2016-06-26T18:45:03.210" Score="1" Body="&lt;p&gt;Let's consider this system&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Transmitter --&amp;gt; SWR meter --&amp;gt; Antenna&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;A (V)SWR of 1.3 means that the magnitude of your reflection coefficient $\Gamma$ between your transmitter and your antenna is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$|\Gamma| = \frac{SWR-1}{SWR+1} = \frac{0.3}{2.3}\approx 0.13$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which is pretty good, actually, meaning that but 13% of the field strength your transmitter inserts into the antenna is reflected by the antenna, or that 87% actually reach the antenna!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can convert that into a relation of power inserted and reflected, simply by squaring it – then things look like this: The reflection dampening factor (i.e. how much of your energy is reflected is &#xA;$$a=\frac{1}{|\Gamma|^2}\approx59\approx 17dB$$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, for a power amplifier to reach maximum power output, it must be connected to a device that matches its source impedance $Z_s$. In that case, 0% of power is reflected. In all other situations (e.g. $Z_s=50\,\Omega$, $Z_a\ne50\, \Omega$, output power is below the maximum output. I don't actually know how your device displays forward power – that's something non-trivial to measure – but the fact that we don't have a unity SWR indicates your PA can't sink it's full output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's known that&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;\Gamma &amp;amp;= \frac{Z_s-Z_a}{Z_s+Z_a}\\&#xA;\implies\\&#xA;0.13 &amp;amp;= \frac{|Z_s-Z_a|}{Z_s+Z_a}\\&#xA;0.13(Z_s+Z_a) &amp;amp;= |Z_s-Z_a|\\&#xA;0.13Z_s+0.13Z_a &amp;amp;= |Z_s-Z_a|\\&#xA;0.13Z_s+0.13Z_a &amp;amp;= Z_s - Z_a &amp;amp;\vee&amp;amp;&amp;amp; 0.13Z_s+0.13Z_a &amp;amp;= Z_a - Z_s\\&#xA;-0.87Z_s&amp;amp;=  - 1.13 Z_a &amp;amp;\vee&amp;amp;&amp;amp; 1.13 Z_s &amp;amp;= 0.87 Z_a \\&#xA;Z_a&amp;amp;\approx 0.77 Z_s &amp;amp;\vee&amp;amp;&amp;amp; Z_a &amp;amp;\approx 1.30 Z_s\text{ .}&#xA;\end{align}$$&#xA;I'm going to assum $Z_s = 50\,\Omega$, so your antenna impedance is either $38.5$ or $65.0\,\Omega$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That doesn't really explain the power loss your device is displaying, but it's common for HF measurement devices to not be on identical terms.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-06-26T18:45:03.210" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6359" PostTypeId="2" ParentId="6349" CreationDate="2016-06-26T19:44:05.347" Score="7" Body="&lt;p&gt;An RTL Dongle is Receive-Only. You can't transmit with it.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-06-26T19:44:05.347" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6360" PostTypeId="2" ParentId="5742" CreationDate="2016-06-27T03:25:35.230" Score="0" Body="&lt;p&gt;Find out the input impedance by connecting different versions of unun impedance transformers, 1:1, 1:2, 4:1, 9:1, and seeing how the signal is improving or degrading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;High impedance 500-10000 ohms. Medium impedance 200-500 ohms. Low impedance 25-150 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a given length of wire, as frequency goes up the impedance generally goes down. A quarter-wavelength wire antenna will have an impedance of 35 to 75 ohms, but that length of wire on other frequencies will be high impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think if the radio feeds the antenna input to the gate of a FET transistor frontend, it will have a millon-ohm input impedance. Just try a balun feeding to whip antenna and the negative battery terminal, with alligator jumper wires connected to the high impedance side of the balun.&lt;/p&gt;&#xA;" OwnerUserId="7898" LastEditorUserId="76" LastEditDate="2016-07-02T02:55:13.783" LastActivityDate="2016-07-02T02:55:13.783" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6361" PostTypeId="1" AcceptedAnswerId="6363" CreationDate="2016-06-27T07:34:53.937" Score="0" ViewCount="282" Body="&lt;p&gt;If we consider a basic half wave dipole array does the radiation resistance of array depend on distance between two elements and phase we feed?&lt;/p&gt;&#xA;" OwnerUserId="7827" LastActivityDate="2016-06-30T17:13:51.637" Title="Does antenna array structure effect overall radiation resistance?" Tags="&lt;antenna-theory&gt;&lt;phased-array&gt;" AnswerCount="2" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="6362" PostTypeId="2" ParentId="6356" CreationDate="2016-06-28T10:30:21.027" Score="1" Body="&lt;p&gt;There are various considerations which could influence your measurements.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Antenna height and location&lt;/strong&gt;: compared to your (unspecified) &quot;normal antenna&quot; did you test the J-pole at exactly the same height and location ?&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Feed line&lt;/strong&gt;: did you use the same, or same lengt/type of, feed line ?&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Weather condition&lt;/strong&gt;: did you test in the same weather conditions: temperature, humidity, rain, wind, snow, hale can all influence measurements&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In my experiments with J-poles I have a good range of failures and some successes. This is (IMHO) to do with the fact that a J-pole is an:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Unbalanced&lt;/strong&gt; half-wave radiator&lt;/li&gt;&#xA;&lt;li&gt;with a &lt;strong&gt;balanced&lt;/strong&gt; matching section&lt;/li&gt;&#xA;&lt;li&gt;fed with an &lt;strong&gt;unbalanced&lt;/strong&gt; coaxial cable&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This will cause all kinds of wonderful effects, most common: common-mode. Which may or may not be influencing the measurements you are taking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best results I have established over the years is to use a 4:1 balun, which then needs to be fed &quot;higher&quot; on the matching section to get a 200 Ohm match, combined with a good number of beeds on the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can easily create 4:1 match using something like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jpBpk.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jpBpk.gif&quot; alt=&quot;4:1&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This will at least transform your unbalanced 50 Ohm feed into 200 Ohm balanced, for the balanced matching section of the J-pole. It still is a unbalanced half-wave radiator, nothing you really can do about that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally I have given up on J-poles, while with the above method I had some success, I really think that a standard quarter-wave GP, or a vertical half-wave dipole is much easier and I had better results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;YMMV&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-06-28T10:30:21.027" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6363" PostTypeId="2" ParentId="6361" CreationDate="2016-06-28T16:12:23.517" Score="3" Body="&lt;p&gt;Yes, element spacing and geometry most definitely has an effect on radiation resistance in the real world. Radiation resistance is essentially that part of the signal which is not lost in some other fashion, be it resistance of the elements, the feed line, the ground, etc. In free space, the difference either spacing or phasing make would be miniscule (or possibly zero, I'm limited in my ability to confirm that by the modeling software I use), but when you take in to account the lossy nature of an antenna's surroundings and the system attached to it, the difference can be considerable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The precise way in which the radiation resistance will change, however, is highly situation dependent. Additional elements can effectively increase the physical aperture of the antenna, which can increase radiation efficiency (and necessarily radiation resistance). The spreading of current over a larger physical area can reduce losses in the ground, for instance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of parasitic arrays, the spacing of the elements would determine how effectively the parasitic elements interacted with the driven element, changing the amount of energy they re-radiate. The electrical length of the parasitic elements would also come in to play, as a very high impedance would result in a smaller interaction with the field around it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a driven array such as an LDPA, the degree to which the additional elements changed radiation resistance would depend on their own impedance relative to each other, one element with a very good impedance match and another with a poor impedance match to the transmitter would result in one element radiating a majority of the power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An extreme example of spacing and phasing impacting radiation resistance in driven arrays can be seen in balanced feedline or &quot;ladder line&quot;. If we imagine a theoretically perfect balanced feed line that is terminated with a perfectly matched resistive load on the far end, 100% of the power that is fed in to the feed line will be dissipated by that resistive load. The fields of the two conductors are precisely equal and opposite, perfectly canceling each other, so there can be no radiation, therefore the radiation resistance is zero. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we move this system from our theoretically perfect example to something as close to perfect as we can get in the real world, we can see that the power would be dissipated mostly by the load, as well as some resistance in the conductors, but there would now be a third component. The two conductors are some tiny fraction of a wavelength apart, they are likely very slightly different in length, width, or resistance, and they can't inhabit exactly the same space, so the fields can not perfectly cancel in all directions. Some minute fraction of the power we feed in is now being radiated. The worse the phase match between the two conductors at an arbitrary point along their length, the more power is radiated. The radiation resistance is increasing as you change their relative phase or amplitude at a given point in the length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When it comes to spacing, in our theoretically perfect example, we could move our conductors arbitrarily far apart and as long as the match to the load was still perfect, the radiation resistance would still be zero. If you were to move arbitrarily far away from the two conductors, their opposing fields would appear to occupy the same space, resulting in perfect cancellation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the real world, however, distance between the conductors does have an impact. Because the two conductors must exist in a medium which is not perfectly uniform in all directions, the two conductors will interact unequally with objects around the feed line. This means that a conductive object nearer to one conductor of the feed line not only interacts more strongly with that conductor than the other, resulting in induction of current on the object which is not opposed by any other field and thus can be radiated, it also couples more power out of the nearer conductor, resulting in an imbalance of the feedline, meaning that the feed line itself can now radiate. The radiation resistance has climbed from very nearly zero, to some appreciable fraction of the total system impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The further apart you move the conductors, the more likely you are to have objects that interact strongly with only one conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This same basic idea can be applied to any array, and demonstrates why the effect of phasing and spacing would be so highly dependent on real-world circumstances.&lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="246" LastEditDate="2016-06-28T16:55:24.373" LastActivityDate="2016-06-28T16:55:24.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6365" PostTypeId="1" CreationDate="2016-06-30T02:35:32.570" Score="4" ViewCount="480" Body="&lt;p&gt;Is there any kind of technology similar to ADS-B for trains? I'm aware of HOT/EOT/DPU messages, but as far as I can see these don't allow you to see its location. I'm specifically wondering about the location aspect. Would be particularly nice if I could pick it up with my RTLSDR!&lt;/p&gt;&#xA;" OwnerUserId="7918" LastActivityDate="2016-07-30T15:24:44.193" Title="ADS-B for Trains?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6366" PostTypeId="2" ParentId="6365" CreationDate="2016-06-30T15:17:55.873" Score="1" Body="&lt;p&gt;Yes, there is a technology used by trains for location -- or more correctly, there used to be.  Back in 1985/1986 timeframe, our company licensed a large software system used to implement large-scale, real-time control systems, to a company (Harman Industries) out of Kansas City whose business was building such control systems for trains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The system used transponders and fixed locations with satellite comms -- this was NOT GPS, in fact, this predated GPS.  The advantage that train location had was that the system actually always knew which track the train was on and they new where the track runs across the country side.  The train would pass a known location (e.g. signal tower, switching track, etc.) and then communicate that location whose status would find its way back to the control system that would affect signals and switches on the tracks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The long-haul trucking industry also uses transponders for location management.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Today though, I think everyone uses GPS.  The other day, I used GPS to find my wife who was photographing birds in a wildlife refuge. We were briefly separated and I used FriendFinder on my iPhone to track her location.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2016-06-30T15:23:35.377" LastActivityDate="2016-06-30T15:23:35.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6367" PostTypeId="2" ParentId="490" CreationDate="2016-06-30T15:26:25.460" Score="3" Body="&lt;p&gt;What you describe is exactly how TETRA DMO repeaters work.&#xA;They use 4 time slots on a single frequency, using 25MHz bandwidth. The repeater receives on time slot #1 and transmits on slot #4.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See for instance &lt;a href=&quot;http://tetraforum.pl/doc/The_power_of_TETRA-Direct_Mode_Operation-Selex_Communications_Francesco_Pasquali.ppt&quot; rel=&quot;nofollow noreferrer&quot;&gt;TETRA DMO modes&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="7920" LastEditorUserId="7920" LastEditDate="2017-12-07T14:25:56.377" LastActivityDate="2017-12-07T14:25:56.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6368" PostTypeId="2" ParentId="6361" CreationDate="2016-06-30T17:13:51.637" Score="1" Body="&lt;p&gt;An antenna is effectively a transformer between the impedance of free space (377Ω) and whatever the feedpoint impedance is. For any antenna which has only negligible losses, and no reactive impedance at the feedpoint, the feedpoint impedance is equal to the radiation resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider this model:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/R0HVR.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fR0HVR.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any power put into R1 is radiated. But the impedance of that resistor is transformed by the antenna, represented by the transformer and reactive components. Additionally we have antenna losses. So when we ask what the &quot;radiation resistance&quot; is, really we are asking what R1 looks like from the feedpoint, through whatever impedance transformations the antenna might make.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, we try to tune the reactance of the antenna (represented by C1 and L1) to 0Ω, and R2, which represents losses in the antenna, is negligibly small. So when losses are negligible and the feedpoint impedance has no reactance, then the impedance seen at the feedpoint is also the radiation resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You probably already know that different antennas have different feedpoint impedances. For example, a dipole is about 72Ω, while a vertical is half that, 36Ω.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you introduce arrays, the coupling between the arrays introduces additional reactances into the antenna. This is why Yagis (a passively driven array) usually require some additional matching network or trick (like a folded dipole driven element) to get their feedpoint impedance, and thus radiation resistance close to 50Ω. Actively driven arrays are no different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So essentially, if your antenna requires a matching network, and it's not because you've introduced losses, it's probably because the antenna has changed the radiation resistance in an undesirable way. And if you consider the matching network as part of the antenna, then you've probably changed the radiation resistance to 50Ω.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-06-30T17:13:51.637" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6372" PostTypeId="2" ParentId="6346" CreationDate="2016-07-01T15:44:42.740" Score="1" Body="&lt;p&gt;If you want to calculate the height required for a 25 km radio link. Check out this link.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.everythingrf.com/rf-calculators/line-of-sight-calculator&quot; rel=&quot;nofollow&quot;&gt;http://www.everythingrf.com/rf-calculators/line-of-sight-calculator&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This link gives not visual line of sight but also the radio horizon which is slightly longer. At 5 Ghz with sufficient gain antenna to direct the signal as close to the horizon as possible and height above ground you should be able to establish a good strong link. This should be at both sites. At 5 Ghz the radio noise and interference would be quite low which is a bonus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;40 meters above ground should do it. If you have an unobstructed point to point link you could probably do it on relatively low power.&lt;/p&gt;&#xA;" OwnerUserId="6604" LastActivityDate="2016-07-01T15:44:42.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6373" PostTypeId="2" ParentId="2281" CreationDate="2016-07-01T16:42:19.633" Score="5" Body="&lt;p&gt;OpenWebRX is another way to monitor an SDR online.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://sdr.hu/openwebrx&quot; rel=&quot;noreferrer&quot;&gt;http://sdr.hu/openwebrx&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you go to &lt;a href=&quot;http://sdr.hu/&quot; rel=&quot;noreferrer&quot;&gt;http://sdr.hu/&lt;/a&gt; you can also  see a list of receivers you can listen in to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(As to your other questions, those might be better split out.  These days there exist many ways to handle the needs of a remote monitoring client written for the browser.  I would guess both WebSDR and OpenWebRX use WebSockets to constantly push data to the clients but other than that I'm not sure what you're asking.)&lt;/p&gt;&#xA;" OwnerUserId="841" LastActivityDate="2016-07-01T16:42:19.633" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6375" PostTypeId="1" CreationDate="2016-07-01T22:46:27.217" Score="1" ViewCount="275" Body="&lt;p&gt;I recently got a Kenwood TM-D710G and have been experimenting with using its internal TNC connected to a serial port on my laptop for packet / PBBS operation. I can connect to PBBSes whose callsigns I know, and I can get the TNC to monitor (that is, print to the terminal) most traffic on the channel using the commands:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;MONITOR ON&#xA;MALL ON&#xA;MCON ON&#xA;MCOM ON&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;However, I cannot seem to get the TNC to monitor the 'ID' packets sent by other packet systems. This is a problem when I go to other cities with packet systems on the air whose callsigns I don't know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I use the &lt;code&gt;TRACE ON&lt;/code&gt; command, the TNC does show hex dumps of ID packets, such as the following one from station WU8C:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;a2 a6 a8 40 40 40 e0 ae aa 70 86 40 40 65 03 cd 00 03 00 cc 07 04 00 01 ae aa 70 86 40 40 64 2c 66 30 08 00 00 00 00 00 00 00 2c 66 01 01&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Granted, it is possible to decode these by hand (that one decodes to &quot;QST WU8C...&quot;), but it would be nice not to have to do so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anyone has any hints on how I might get the TNC to decode and display these packets, I'll be very grateful.&lt;/p&gt;&#xA;" OwnerUserId="7935" LastEditorUserId="76" LastEditDate="2016-07-01T22:55:10.943" LastActivityDate="2020-03-19T12:03:15.707" Title="Kenwood D710G TNC Won't Monitor ID Packets?" Tags="&lt;kenwood&gt;&lt;packet&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6377" PostTypeId="2" ParentId="5742" CreationDate="2016-07-02T21:12:01.103" Score="0" Body="&lt;p&gt;Ground terminal is on the 3.5mm antenna jack for PL600. PL660 may use similar circuit. Both units look very similar on the outside. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I experimented with 3 inch wire loop antenna and did successful QRP DF (direction finding) at 14MHz. The telescopic antenna has poor directivity. Once the loop antenna was plugged in, the telescopic antenna was disconnected and now it has good directivity, so, the ground pin was definitely there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe a longer wire, up to 50 meters or even longer, at higher level and away from strong noise source like fluorescence lamp, will improve reception. You may try connect and disconnect the ground terminal at the ant jack to see what changes.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/PorQS.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PorQS.jpg&quot; alt=&quot;PL600&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="1473" LastEditDate="2016-07-03T07:45:35.000" LastActivityDate="2016-07-03T07:45:35.000" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6378" PostTypeId="1" AcceptedAnswerId="6379" CreationDate="2016-07-02T21:33:37.740" Score="5" ViewCount="7067" Body="&lt;p&gt;Are we now at the good or bad portion of the 11 years cycle? What effect are we seeing now? How large (strong/deep) is the effect during the peak and bottom of cycle? What will change in coming years?&lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="1550" LastEditDate="2019-03-05T15:23:51.410" LastActivityDate="2019-03-05T15:23:51.410" Title="Where year 2016 falls in the sun spot cycle for HF propagation?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;sunspots&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="6379" PostTypeId="2" ParentId="6378" CreationDate="2016-07-03T13:31:50.583" Score="6" Body="&lt;p&gt;We're about half way down in the waning years of Cycle 24. We're currently on a 9 day stretch with zero sunspots, the first such stretch since 2010. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the number of sunspots dwindling, we've seen little F layer propagation on frequencies above 25MHz in the last 2 months, and that downward trend is likely to continue. As we approach minimum in 2018(ish), frequencies above 15MHz will only open sporadically and usually thanks to Sporadic E or Trans-equitorial low angle F layer propagation for a couple weeks on either side of the Equinoxes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition to the impact on the higher bands, the mid bands like 20m and 30m will no longer stay open all night, though they will generally continue to produce good DX during the day even at solar minimum. During the minimum of cycle 23, 20 meters rarely failed to open in the afternoon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The lower solar activity actually improves conditions on 160m, 80m, and to some extent 40m, as there will be less D layer absorption, so those bands will open earlier in the evening and stay open later in to the morning than they have in the past few years. They will also experience fewer ionospheric disturbances and geomagnetic storms as solar activity tapers off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This cycle was unusually quiet, and the previous minimum was unusually and unexpectedly protracted, so most predictions regarding the various trends and extremes of cycle 24 have so far proven to be inaccurate. It's difficult to say for sure how deep this minimum is likely to be, or how long it will last, but it is safe to assume that the occasional article that pops up claiming we're entering a new Maunder Minimum or the like are just psuedo-scientific rantings. This cycle caught everyone off guard, and proved just how bad we are at predicting these things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Historically, if we look at the &lt;a href=&quot;https://en.wikipedia.org/wiki/Solar_cycle#/media/File:Sunspot_Numbers.png&quot;&gt;long term trends&lt;/a&gt; we can see that while cycle 24 was quite weak, if we look at the cycles before it, there is a clear cyclic trend that dates back to at least the late 18th century. It would appear we're entering a low point in that larger cycle, but it seems likely that cycle 25 and 26 will rebound somewhat or be about the same. Given the rapid descent from the peak in 2014, however, it seems safe to assume this will be another unusually long minimum.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-07-03T13:31:50.583" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6380" PostTypeId="2" ParentId="6349" CreationDate="2016-07-05T15:07:03.853" Score="0" Body="&lt;p&gt;You can transmit arbitrary data with a hackrf one or a hackrf blue. Both will work with gnuradio. The frequency range is very wide, see &lt;a href=&quot;http://www.rtl-sdr.com/hackrf-initial-review&quot; rel=&quot;nofollow&quot;&gt;http://www.rtl-sdr.com/hackrf-initial-review&lt;/a&gt; . The output signal will need amplification. &lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-07-05T15:07:03.853" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6381" PostTypeId="1" AcceptedAnswerId="6385" CreationDate="2016-07-07T07:13:36.677" Score="2" ViewCount="364" Body="&lt;p&gt;I'd like to get some recordings of typical receiver audio output of HF CW transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to both train my mental copying capabilities and look into improved automatic (software) CW transcribers; hence, typical, humanly induced symbol rate changes are of special interest. Ideally, there'd be a few recordings of similar (the same?) transmission at different RX SNRs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of the audio recording, I'd also take &quot;raw&quot; I/Q, IF or direct sampling recordings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As correctly pointed out in the comments:&#xA;&lt;em&gt;I'm a total novice when it comes to digesting CW.&lt;/em&gt; Which means that I can't tell a well-keyed transmission from a lesser one; I've found it vastly helpful to have reference signals in the past, so I'm really asking for recordings of transmissions of &quot;known&quot; quality, not an information on how to make my own recording (which I can't classify myself). &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-07-08T07:26:41.177" LastActivityDate="2017-06-21T01:39:38.283" Title="CW &quot;training&quot; recordings" Tags="&lt;cw&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6382" PostTypeId="1" CreationDate="2016-07-07T17:59:57.200" Score="9" ViewCount="32787" Body="&lt;p&gt;I have a Baofeng UV-5RA, and I need to know what frequencies on the &quot;channel mode&quot; (what the lady says when you press the &quot;V/M&quot; button on the radio) don't require a ham license. I am in Philadelphia, Pennsylvania. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frequencies: 138.550, 155.700, 157.650, 172.750, 402.225, 402.225, 437.425, 438.500, 453.225, 454.325, 455.425, 456.525, 457.625, 458.725, 459.825, 461.925, 462.225, 463.325, 464.425, 465.525, and 479.975.&lt;/p&gt;&#xA;" OwnerUserId="7965" LastEditorUserId="873" LastEditDate="2016-08-02T14:01:27.973" LastActivityDate="2019-08-11T04:06:09.943" Title="On which of these frequencies can I transmit without a license?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;uhf&gt;&lt;baofeng&gt;" AnswerCount="5" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6383" PostTypeId="2" ParentId="6382" CreationDate="2016-07-07T18:11:40.717" Score="32" Body="&lt;p&gt;&lt;strong&gt;None of them.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You say you are in the United States. In general, all radio transmissions fall into one of three categories:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The &lt;strong&gt;operator&lt;/strong&gt; is allowed to transmit on that frequency (amateur, &quot;business band&quot;, aviation, military, etc.)&lt;/li&gt;&#xA;&lt;li&gt;The &lt;strong&gt;radio&lt;/strong&gt; is allowed to transmit on that frequency (CB, FRS, MURS).&lt;/li&gt;&#xA;&lt;li&gt;The transmissions are very low-power (&quot;Part 15&quot;: WiFi, Bluetooth, lots of other things).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You do not have an amateur or other radio license, the radio is not approved for a specific service that works that way, and it does not meet Part 15 restrictions. Therefore you may not transmit with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I highly recommend getting an amateur radio license — it's cheap and easy, and studying for it will help you understand what you &lt;em&gt;can&lt;/em&gt; do.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="9480" LastEditDate="2017-04-19T16:07:48.487" LastActivityDate="2017-04-19T16:07:48.487" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="6384" PostTypeId="2" ParentId="221" CreationDate="2016-07-07T20:00:37.157" Score="1" Body="&lt;p&gt;The solutions I've seen all seem to be rehashing the same code with little thought to what is actually happening.  I decided to write a solution that solves the general case, making it a simple matter to extend the precision of the result to any length.  Since I am an iOS developer, the solution is in Swift:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;private let upper = &quot;ABCDEFGHIJKLMNOPQRSTUVWX&quot;&#xA;private let lower = &quot;abcdefghijklmnopqrstuvwx&quot;&#xA;public func maidenhead(latitude: Double, longitude: Double) -&amp;gt; String {&#xA;  var lonDegrees: Double = 360&#xA;  var latDegrees: Double = 180&#xA;  var lon = longitude + 180.0&#xA;  var lat = latitude + 90.0&#xA;  var lonRemainder = lon&#xA;  var latRemainder = lat&#xA;&#xA;  func gridPair(divisions: Double) -&amp;gt; (Double, Double) {&#xA;    lonDegrees   = lonDegrees/divisions&#xA;    latDegrees   = latDegrees/divisions&#xA;    lon          = lonRemainder/lonDegrees&#xA;    lonRemainder = lonRemainder%lonDegrees&#xA;    lat          = latRemainder/latDegrees&#xA;    latRemainder = latRemainder%latDegrees&#xA;    return (lon, lat)&#xA;  }&#xA;&#xA;  let (gridLonField, gridLatField)               = gridPair(18)&#xA;  let (gridLonSquare, gridLatSquare)             = gridPair(10)&#xA;  let (gridLonSubSquare, gridLatSubSquare)       = gridPair(24)&#xA;  let (gridLonExtSquare, gridLatExtSquare)       = gridPair(10)&#xA;  let (gridLonSubExtSquare, gridLatSubExtSquare) = gridPair(24)&#xA;&#xA;  return &quot;\(upper[Int(gridLonField)])\(upper[Int(gridLatField)])\(Int(gridLonSquare))\(Int(gridLatSquare))\(lower[Int(gridLonSubSquare)])\(lower[Int(gridLatSubSquare)])\(Int(gridLonExtSquare))\(Int(gridLatExtSquare))\(lower[Int(gridLonSubExtSquare)])\(lower[Int(gridLatSubExtSquare)])&quot;&#xA;}&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="508" LastActivityDate="2016-07-07T20:00:37.157" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6385" PostTypeId="2" ParentId="6381" CreationDate="2016-07-07T22:07:30.883" Score="2" Body="&lt;p&gt;On the computer-assisted side of things, AG1LE has a nice write-up on &lt;a href=&quot;http://ag1le.blogspot.com/2015/11/experiment-deep-learning-algorithm-for.html?m=1&quot; rel=&quot;nofollow&quot;&gt;applying machine learning&lt;/a&gt; to the complex task of adaptive CW recognition (adaptive for the purposes of HF reception). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the same site, the author talks about the &lt;a href=&quot;http://ag1le.blogspot.com/2015/01/morse-learning-machine-v1-challenge.html?m=1&quot; rel=&quot;nofollow&quot;&gt;Morse Learning Machine Challenge&lt;/a&gt;, in which another participant used their own curated recordings to teach the system the difference between signal and noise as well as interruptions and human pauses. The &lt;a href=&quot;https://github.com/Morse-Learning-Machine-Challenge/MLMv1&quot; rel=&quot;nofollow&quot;&gt;GitHub repository for the challenge&lt;/a&gt; contains these training file (under &lt;code&gt;./acidtobi/trainingfiles/&lt;/code&gt;) as well as the source.&lt;/p&gt;&#xA;" OwnerDisplayName="user157" LastEditorDisplayName="user157" LastEditDate="2016-07-09T13:12:44.413" LastActivityDate="2016-07-09T13:12:44.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6386" PostTypeId="2" ParentId="6381" CreationDate="2016-07-07T22:15:54.870" Score="1" Body="&lt;p&gt;Check out &lt;a href=&quot;http://websdr.org&quot; rel=&quot;nofollow&quot;&gt;websdr.org&lt;/a&gt;. There you'll be able to 'tune in' with a web-based java application to stations all over the world. Live. Typically you'll find CW at the bottom of the bands (e.g. around 7.000MHz - 7.030MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These days you probably won't find a lot of (manual) straight keyed CW, it's pretty much all nice and clean (microcontroller based) keyer output. &lt;/p&gt;&#xA;" OwnerUserId="1135" LastActivityDate="2016-07-07T22:15:54.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6387" PostTypeId="1" CreationDate="2016-07-08T08:55:44.893" Score="1" ViewCount="548" Body="&lt;p&gt;I am new in the world of Radio Technology and I would build an idea with Bluetooth 4.0 and want to see the frequency for debugging. So I will need a Spectrum Analyzer, but won't buy one of these. Bluetooth 4.0 works with 2,4GHz and that is now my question. Can I build a Spectrum Analyzer with a wireless antenna and maybe setting the interface in passive mode for this kind of action?&lt;/p&gt;&#xA;" OwnerUserId="7968" LastEditorUserId="76" LastEditDate="2020-02-14T01:21:51.477" LastActivityDate="2020-02-14T01:21:51.477" Title="2,4GHz Spectrum Analyzer with wireless card" Tags="&lt;antenna&gt;&lt;wifi&gt;&lt;spectrum-analyzer&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6388" PostTypeId="2" ParentId="6382" CreationDate="2016-07-08T13:05:35.843" Score="1" Body="&lt;p&gt;Additional to the answer given:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may want to check your local, and country legislation if it is legal to &lt;strong&gt;own&lt;/strong&gt; the device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not in the US and certainly not familiar with all legislation as such, but in my country it would be &lt;strong&gt;illegal to own&lt;/strong&gt; the device without a valid Amateur Radio License.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-07-08T13:05:35.843" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6389" PostTypeId="2" ParentId="6387" CreationDate="2016-07-08T15:25:07.987" Score="2" Body="&lt;p&gt;Probably not. Most radio equipment of this sort only gives access to the demodulated-and-decoded signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The requirements for being an (uncalibrated) spectrum analyzer of this sort are essentially the same as being used for &lt;em&gt;software-defined radio&lt;/em&gt;. So if any particular cheap consumer hardware is usable in the way you want, we would have heard of it as possible SDR equipment. And I haven't heard of any repurposed Bluetooth (or WiFi) devices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you &lt;em&gt;can&lt;/em&gt; do, which is still cheaper than a proper spectrum analyzer, is get a hobbyist SDR device that covers 2.4 GHz, such as the HackRF One or bladeRF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, the primary thing that you lose by not using a real spectrum analyzer is calibration — being able to determine the true power of an observed signal at any frequency. The lower-cost equipment will still be able to show you the presence or absence of a signal, and its strength relative to other signals at the same frequency.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-07-08T15:25:07.987" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6391" PostTypeId="1" CreationDate="2016-07-08T16:59:02.700" Score="-1" ViewCount="1166" Body="&lt;p&gt;I have a friend who has a HAM license and a ham radio, and when he first pushes the button to talk, I hear a &quot;call dialer&quot; sound. It sound like someone is dialing a phone number in. The tone starts in the beginning of the broadcast, it sounds a phone dial tone 3 times, and the same at the end of his transmission. What is this? Thanks!&lt;/p&gt;&#xA;" OwnerUserId="7965" LastEditorUserId="13" LastEditDate="2016-07-08T22:30:57.623" LastActivityDate="2016-07-09T00:28:56.013" Title="Call dialer sound on start/end of transmission?" Tags="&lt;legal&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6392" PostTypeId="1" AcceptedAnswerId="6396" CreationDate="2016-07-08T17:33:03.973" Score="0" ViewCount="176" Body="&lt;p&gt;I am currently getting my EE degree, and I'm trying to build my first antenna for a weather balloon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand with a dipole, you want the feed line perpendicular to the antenna for at least l/4, but what about loop or quad antennas?  It seems like people like to route the wire to the boom, then go perpendicular, then go parallel down the mast, which doesn't make sense to me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the best direction to feed a loop, or more specifically a quad antenna?&lt;/p&gt;&#xA;" OwnerUserId="7972" LastEditorUserId="7798" LastEditDate="2016-07-10T15:59:18.187" LastActivityDate="2016-07-10T15:59:18.187" Title="Feed line direction for Quad antenna" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;&lt;loop-antenna&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6393" PostTypeId="2" ParentId="6391" CreationDate="2016-07-08T17:33:50.027" Score="0" Body="&lt;p&gt;Correcting my first answer after a re-read: It sounds like a &quot;courtesy tone&quot;. I initially thought DTMF tones (like dialing a number) for accessig a repeater, but you mentioned &quot;dial tone&quot; (the steady tone on a land line before you start dialing) and it got me thinking it may just be a courtesy tone. More descriptive detaul would be needed. Or as Kevin said, you could just ask your friend. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given your other recent question, however, I ask with a friendly grin if this &quot;friend&quot; is you trying to understand your radio before you're licensed by keying it a few times. Maybe a shiny new Baofeng handheld? ;-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm sure it's a friend though. :-P&lt;/p&gt;&#xA;" OwnerDisplayName="user157" LastEditorDisplayName="user157" LastEditDate="2016-07-08T17:49:46.560" LastActivityDate="2016-07-08T17:49:46.560" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6394" PostTypeId="2" ParentId="6391" CreationDate="2016-07-08T22:25:16.763" Score="0" Body="&lt;p&gt;I'd be pretty willing to bet you have a Yaesu. Press the button that looks like an atomic symbol. It's used for digital modes, that are almost never used, and this is a frequent issue.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2016-07-08T22:25:16.763" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6395" PostTypeId="2" ParentId="6391" CreationDate="2016-07-09T00:28:56.013" Score="2" Body="&lt;p&gt;Between the clue in your original post (&quot;sounds like someone is dialing a phone number in&quot;) and a more pertinent one in &lt;a href=&quot;https://ham.stackexchange.com/a/6393/1362&quot;&gt;Joshua Nozzi's answer&lt;/a&gt; (&quot;Maybe a shiny new Baofeng handheld?&quot;) that you seem to have acknowledged, my guess would be that Someone Who Isn't You® has accidentally enabled the &lt;a href=&quot;http://support.baofengradio.us/article/105-automatic-number-identification&quot; rel=&quot;nofollow noreferrer&quot;&gt;Automatic Number Identification feature&lt;/a&gt; on the handheld:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In dispatch environments it's common to have a system in place that will allow radios to automatically identify themselves to the dispatcher. This is known as Automatic Number Identification (AIN), or sometimes PTT-ID since the radio sends a data burst containing the ID code at the beginning or end of a transmission. The Baofeng UV-5R uses DTMF signaling to enable ANI implementation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The instructions there describe how to disable it via the PC configuration software, but IIRC it's also configurable through the menu via the handheld's own keypad.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-07-09T00:28:56.013" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6396" PostTypeId="2" ParentId="6392" CreationDate="2016-07-09T11:26:00.030" Score="0" Body="&lt;p&gt;Why doesn't the configuration you described make sense to you?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The whole idea is that you want minimal interaction between current in the loop and current in the feedline. Consider the distribution of the magnetic field around the driven element in a quad antenna. Routing the feedline both radially and then along the axis of the loop are directions that are perpendicular to the field lines of the loop itself, providing zero magnetic coupling and zero induced current, which is exactly what you want.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2016-07-09T11:26:00.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6397" PostTypeId="2" ParentId="6387" CreationDate="2016-07-09T13:43:20.377" Score="1" Body="&lt;p&gt;In addition to what AG6YO &lt;a href=&quot;https://ham.stackexchange.com/a/6389/4076&quot;&gt;said&lt;/a&gt; in his answer (No, a network card is a network card and is built to find networks, not &quot;spurious&quot; power of another standard) – Bluetooth as is is a protocol especially hard to capture with a spectrum analyzer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is very simple: Bluetooth works by jumping through separate, small 1MHz wide channels within a large overall bandwidth (up to 79 MHz IIRC). That hopping happens at up to 1600 hops per second. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, there's specific exceptions to that in the Bluetooth standard: Bluetooth LE only uses a single 1MHz bandwidth – but you only mention you're using Bluetooth 4.0, which is the most recent release of Bluetooth, and contains all low- to extremely high rate-modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the same time, classically, spectrum analyzers work by &quot;tuning&quot; in sequentially on small parts of the spectrum, measuring the power that's passing through a narrow filter (the narrower the filter, the higher the spectral resolution) for a short duration of time, moving on to the next frequency and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, for sweeping spectrum analyzers (SAs), the &lt;em&gt;intercept probability&lt;/em&gt; of bluetooth is &lt;em&gt;really&lt;/em&gt; low. Without a lot of luck and/or  experience, you won't be able to configure your SA to even stand a chance of &lt;em&gt;noticing&lt;/em&gt; bluetooth, let alone debug it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, a spectrum analyzer is clearly not the only device you'd need for bluetooth debugging. As Kevin pointed out, the right choice will be an SDR – something that continously samples what signal is on the air over a large bandwidth, giving it to a computer, so that software there can either generate a visualization of all the spectrum at once (as opposed to SAs, which visualize spectrum in small steps, but with more precision / higher dynamic range), or even try to decipher the Bluetooth communication. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can't restrict how much your Bluetooth system will jump (in general, you can't), however, you will need to cover &lt;em&gt;all&lt;/em&gt; of the aforementioned 80 MHz at once. Which means you'd need an SDR device with at least that bandwidth – and that's just the beginning of your fun, since actually processing let's say 100MS/s isn't going to be easy on any hardware, and even just getting these samples out of the SDR device into e.g. a PC is a costly feat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the 1MHz-only Bluetooth variants, however, the devices mentioned (or basically, most SDRs that cover 2.4GHz) could do the job – a hackRF, the ubertooth, a lot of the more costly USRPs etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That still leaves one question open: What is it that you want to debug? Bluetooth is still a complex standard, and though you can capture a few modes and even extract the raw digital packets from the analog signal, my blind guess is that this kind of approach to understanding what happens between your bluetooth devices might be a bit too low-level to actually help you advance, unless you already know well enough what you're looking for.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-07-09T13:48:39.143" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6398" PostTypeId="2" ParentId="6342" CreationDate="2016-07-09T14:11:58.673" Score="0" Body="&lt;p&gt;Compare with typical ham equipment, this SWL receiver, Tecsun PL-600 &lt;/p&gt;&#xA;&#xA;&lt;p&gt;a) only tunes in &lt;strong&gt;1KHz step&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;b) only has one SSB mode, without &lt;strong&gt;separate USB and LSB&lt;/strong&gt; settings&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Following is how to receive WSPR through adjustment of BFO to get 1500Hz audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The on air signal is 10.140200MHz + (0 to 3) x 1.4648Hz for 4 symbol frequencies.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Set PL-600 dial frequency to &lt;strong&gt;10.140MHz&lt;/strong&gt;, SSB mode, Narrow Bandwidth, BFO first set to central click point then &lt;strong&gt;turned anti-clockwise 70&lt;/strong&gt; degrees.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Adjust audio signal level for 0dB at WSPR, Dial 10.138700 Tx 10.140200 &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Run WSPR 2.12, WSJT-X 1.6.0 and Spectrum Lab V2.90b16. Fine tuned BFO until audio signal was 1500Hz on water fall display.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="1473" LastEditDate="2016-07-09T21:07:44.170" LastActivityDate="2016-07-09T21:07:44.170" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6400" PostTypeId="1" AcceptedAnswerId="6402" CreationDate="2016-07-09T17:00:58.660" Score="3" ViewCount="214" Body="&lt;p&gt;I'm building a magnetic loop antenna and was wondering if the voltage ratings on the vaccuum variable capacitors I have are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;RMS&lt;/li&gt;&#xA;&lt;li&gt;Peak to Peak&lt;/li&gt;&#xA;&lt;li&gt;Peak &lt;/li&gt;&#xA;&lt;li&gt;other?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I have been looking at this wonderful &lt;a href=&quot;http://www.66pacific.com/calculators/small_tx_loop_calc.aspx&quot; rel=&quot;nofollow&quot;&gt;magnetic loop calculator&lt;/a&gt; to help choose a capacitor and it gives the required cap voltage in RMS.&lt;/p&gt;&#xA;" OwnerUserId="5577" LastActivityDate="2016-07-10T09:01:04.653" Title="Are the voltage ratings on Vacuum Variable Capacitors RMS or Peak" Tags="&lt;capacitance&gt;&lt;magnetic-loop&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6401" PostTypeId="2" ParentId="6382" CreationDate="2016-07-09T23:42:03.560" Score="3" Body="&lt;ul&gt;&#xA;&lt;li&gt;There are lots of &quot;radios&quot; for sale on places like EBAY that are not legal to use in the U.S.&lt;/li&gt;&#xA;&lt;li&gt;There are lots of radios of recent manufacture for sale in many places that include the ability to transmit on a wide number of out-of-band frequencies (CB's that do 10M, 10M ham rigs that do 11M (CB), etc.)&lt;/li&gt;&#xA;&lt;li&gt;There are a bunch of cheap radios that are just mega-splatter factories that send all kinds of spurious emissions off frequency and are nearly deaf&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;IMHO: Get or build a well engineered radio, and get a license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That being said: getting a Technician license (In the U.S.) is about three times harder than getting a CPR certificate. &lt;/p&gt;&#xA;" OwnerUserId="7975" LastEditorUserId="7975" LastEditDate="2016-07-27T22:35:00.883" LastActivityDate="2016-07-27T22:35:00.883" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6402" PostTypeId="2" ParentId="6400" CreationDate="2016-07-10T09:01:04.653" Score="1" Body="&lt;p&gt;You raise an interesting point; intuitively, what I'd have thought is that the peak voltage matters – because discharge through the dielectric doesn't happen for any reason but an electrical field strength (at least for vacuum as dielectric, which can have no electric polarization of any kind, being not a material) above the &lt;a href=&quot;https://en.wikipedia.org/wiki/Dielectric_strength&quot; rel=&quot;nofollow&quot;&gt;Schwinger limit&lt;/a&gt; which you will never reach even remotely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, necessarily, your cap doesn't hang in &lt;em&gt;perfect&lt;/em&gt; vaccuum, but let's assume it  happens in a quality of vacuum (gas pressure) that guarantees a breakdown value at least equivalent to that of air (see &lt;a href=&quot;https://en.wikipedia.org/wiki/Paschen%27s_law&quot; rel=&quot;nofollow&quot;&gt;Paschen's Law&lt;/a&gt;), but with negligible polarization losses; then you'd still have around 2.5 MV/m breakdown voltage (probably more).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how I precluded polarization effects – this is my guess why these caps use vacuum instead of just being filled with some inert gas: Without any material to be subject to changing electrical field strength, you can't have molecules/atoms align their electric momentum with the field, which can, when quickly enough changing that field, reduce the breakdown voltage of a capacitor, and lead to energy losses and thus, heating of the dielectric.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For considerations of how much energy will get lost in a material, the RMS voltage is a good measure – same goes for the breakdown voltage reduction. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, as a vacuum cap sees neither of these effects under &quot;earthly&quot; conditions, RMS is not what you need to know – you really just want to know how much voltage you might &lt;em&gt;ever&lt;/em&gt; see, because, as soon as that voltage crosses breakdown voltage, there will be an arc within your cap – and that might become a self-sustaining arc, considering that its heat will possibly vaporize and splutter some of the conductor plates into the vacuum, making it a box of conductive plasma.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-07-10T09:01:04.653" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6404" PostTypeId="1" CreationDate="2016-07-11T07:52:41.507" Score="12" ViewCount="11422" Body="&lt;p&gt;I'm a complete newbie here, and on the Southeast Coast of the USA. I don't even own a ham radio yet. Some &lt;a href=&quot;http://www.theprepperjournal.com/2013/04/22/what-is-a-prepper/&quot; rel=&quot;noreferrer&quot;&gt;&lt;em&gt;preppers&lt;/em&gt;&lt;/a&gt; and I got to talking about a dystopian time of Internet collapse where shortwave radio might be an important factor of survival. This led me to consider joining or starting a packet radio BBS (bulletin board system), unless of course there is something better by now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is what kind of equipment and licenses would I need in order to join and communicate with a packet radio bulletin board system (unless of course something is better/faster now)? Ideally it would be great to interact with other preppers on this system in case some ill-fated dystopian future arrives.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Note my background -- I'm a PHP, C++, Objective C++ coder and a former computer networking engineer who's well aware of the OSI model of several protocols, although not this AX.25 protocol that's used in packet radio. So, feel free to speak technically to me.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="7983" LastEditorUserId="9844" LastEditDate="2018-04-06T21:48:22.267" LastActivityDate="2019-03-04T22:30:26.493" Title="How To Join Packet Radio BBS" Tags="&lt;united-states&gt;&lt;receiver&gt;&lt;transmitter&gt;&lt;packet&gt;" AnswerCount="4" CommentCount="3" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6405" PostTypeId="2" ParentId="6404" CreationDate="2016-07-11T13:59:21.637" Score="2" Body="&lt;p&gt;At a minimum you'll need a Technician class amateur radio license. A VHF/UHF radio capable of APRS (Automatic Packet Reporting System) should be enough to do what you're looking for. No detailed protocol knowledge is needed. I encourage you to look into &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Automatic_Packet_Reporting_System&quot; rel=&quot;nofollow&quot;&gt;APRS&lt;/a&gt;, to which you can pist short messages, location updates, and more.&lt;/p&gt;&#xA;" OwnerDisplayName="user157" LastActivityDate="2016-07-11T13:59:21.637" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6406" PostTypeId="2" ParentId="6404" CreationDate="2016-07-11T17:39:01.173" Score="3" Body="&lt;p&gt;I think you're barking up the wrong tree preparing for the possible dystopian future.  If the internet is unavailable, short-term or long-term, generally the need is to communicate as widely as circumstances allow to get emergency messages in and out.  In times like that, I'd think that you'd want to be able to talk to anybody who can still get on the air.  That would mean either 2m/70cm FM for local communications, or HF SSB for longer range.  If you restrict yourself to digital protocols, then you'll only be able to reach a small fraction of hams.  Also if electricity is scarce, then going analog means that the computer, which generally needs lots more power than the radio, isn't required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But please don't let me discourage you from checking out ham radio in general, and digital modes in particular.  Hams use all sorts of interesting digital technologies.  &lt;a href=&quot;http://www.winlink.org/&quot; rel=&quot;nofollow&quot;&gt;Winlink&lt;/a&gt; is a technology used to send email over VHF/UHF or HF, which makes it very valuable for communications in a local or wide-area emergency.  If there's a digital mode used in a dystopian future without the internet then Winlink is the one most likely to be it, in my opinion.  In order to use Winlink you'll need a &quot;sound card interface&quot; to the radio, which can be home-brewed or purchased.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've always found AX.25 packet to be an interesting protocol, especially because it runs somewhat parallel to various protocols used on the internet.  Unfortunately packet is pretty dead where I live, although it might be alive and well where you are.  &lt;a href=&quot;http://www.aprs.org/&quot; rel=&quot;nofollow&quot;&gt;APRS&lt;/a&gt; is a protocol built on top of packet.  It's meant to share tactical information and short messages, although in practice it's only used to broadcast weather station data and the locations of hams' cars most of the time.  You can see your local APRS activity on &lt;a href=&quot;http://aprs.fi/&quot; rel=&quot;nofollow&quot;&gt;aprs.fi&lt;/a&gt;.  Packet and APRS require a Terminal Node Controller, which is normally a hardware device, although some software can emulate a TNC.  As I mentioned in a comment, I don't know how well software TNCs work, so your mileage my vary.  Some high-end VHF/UHF radios include a built-in TNC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the US, a Technician license is the minimum class of license needed to get on the air; that would get you on VHF and UHF, and a tiny little bit of HF access.  That's a great place to start.  A ham club near you probably offers a license class.  There's lots of information &lt;a href=&quot;http://www.arrl.org/licensing-education-training&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;.  Another good way to prepare for the license exam is to buy a book, and take practice tests online. &lt;a href=&quot;http://www.qrz.com/hamtest/&quot; rel=&quot;nofollow&quot;&gt;This practice test&lt;/a&gt; offers immediate feedback on whether you picked the right answer or not; if you take it frequently, the right answers soon stick in your head.  Your local ham club should be quite helpful, so feel free to just drop in on a meeting, whether you have your license or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck, and have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-07-11T18:04:42.593" LastActivityDate="2016-07-11T18:04:42.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6407" PostTypeId="2" ParentId="6404" CreationDate="2016-07-11T18:43:26.433" Score="10" Body="&lt;h3&gt;A summary of requirements:&lt;/h3&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Licensing: Technician - very minimal requirements&lt;/li&gt;&#xA;&lt;li&gt;Equipment: Transceiver, Terminal Node Controller and terminal&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Transceiver - traditionally a VHF/UHF FM radio&lt;/li&gt;&#xA;&lt;li&gt;Terminal Node Controller - Partly a modem, partly an AX.25 layer manager&lt;/li&gt;&#xA;&lt;li&gt;Terminal - Any serial terminal will do, but most likely you will use a personal computer&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;A bulletin board system to connect with.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Let's break these down a bit.&lt;/p&gt;&#xA;&lt;h3&gt;Licensing&lt;/h3&gt;&#xA;&lt;p&gt;You're in luck here as the technician class license is easy to obtain only requiring minimal study, no code, and learning the basic rules of how to transmit without going outside the allocated frequency privileges.&lt;/p&gt;&#xA;&lt;h3&gt;Transceiver&lt;/h3&gt;&#xA;&lt;p&gt;There are a growing number of ways to pass a digital message or two around, but the traditional meat and potatoes way for AX.25 packet is with a 2m or 440 FM transceiver.  The audio connections marry with the modem IO of the terminal node controller.&lt;/p&gt;&#xA;&lt;h3&gt;Terminal Node Controller (TNC)&lt;/h3&gt;&#xA;&lt;p&gt;You're in luck here as well as in addition to a fairly large used market, new makes and models of packet ready modems are coming online.  I think we have the &lt;a href=&quot;http://www.aprs.org/&quot; rel=&quot;noreferrer&quot;&gt;APRS system&lt;/a&gt; to thank for these recent development efforts.  Some TNCs have both the modem component along with the AX.25 management firmware.  For these all you need is something that can connect to an EIA232 style serial port.&lt;/p&gt;&#xA;&lt;p&gt;Another kind of TNC is the KISS (keep it simple) version that omits some or all of the AX.25 network firmware leaving a much simpler and much cheaper modem in place.  There is still a serial port, but the expectation is a program running on the other end of that serial line will perform the necessary AX.25 network management features.&lt;/p&gt;&#xA;&lt;p&gt;A modern approach is to skip the standalone TNC and connect the transceiver audio directly to a computer soundcard port.  Numerous programs exist that will perform all packet functions (modem and AX.25) within the PC and make the resulting &amp;quot;terminal&amp;quot; text available on some TCP/IP port or virtual serial port.  This is likely an excellent way to initially explore packet radio.&lt;/p&gt;&#xA;&lt;h3&gt;Terminal&lt;/h3&gt;&#xA;&lt;p&gt;At the user end of the above, you have a simple text entry screen with responses typed on your display.  What you actually type here is a learning exercise and a really good resource to learn the basics may be found on this very old, but nonetheless excellent resource...&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.choisser.com/packet/&quot; rel=&quot;noreferrer&quot;&gt;http://www.choisser.com/packet/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;h3&gt;Bulletin Board System (BBS)&lt;/h3&gt;&#xA;&lt;p&gt;Here is where things get a bit difficult.  In the old days, numerous BBS systems were available for hams to connect with and leave messages to each other.  Some are still around, but packet radio fell out of favor after excessive traffic proved too much for AX.25 and the relatively slow data speeds to handle with any practical utility.  You may be in luck and have a local BBS you can connect with and I'm sure the sysop may well allow access for want of users.&lt;/p&gt;&#xA;&lt;p&gt;Several of us in our area are in the planning stages of rolling out a BBS available on a variety of frequencies including HF (shortwave)...&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://vapn.org/&quot; rel=&quot;noreferrer&quot;&gt;Virginia Packet Network&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;We have not made it through a feasibility study yet, but the prepper community is one target &amp;quot;market&amp;quot; for such a system and your very question gives us hope.&lt;/p&gt;&#xA;&lt;p&gt;Note that ham BBS users may interact with the typical BBS system entirely on the command line, sending, receiving and listing, BBS &amp;quot;mail&amp;quot; not unlike modern email concepts.  There are also programs you can run on your local PC that will interact with the BBS behind the scenes, but organize the display and management of the messages on your machine much like a modern email program.  Once such example is &lt;a href=&quot;http://www.outpostpm.org/&quot; rel=&quot;noreferrer&quot;&gt;Outpost Packet Message Manager (PMM)&lt;/a&gt;.  I, for one, love the convenience of Outpost, but relish the fact the straight terminal interaction with the BBS is still possible if a terminal is all you have at the moment.&lt;/p&gt;&#xA;&lt;p&gt;I will add that some of the more expensive standalone TNCs have BBS functionality built in or available as an option.  PBBS is what I believe it is called.  Storage is limited by the amount of memory space and we are talking about values under 100 kbytes or so.  It is, however, an almost plug and play BBS that you and your friends can access and use to store messages.&lt;/p&gt;&#xA;&lt;h3&gt;Caveats&lt;/h3&gt;&#xA;&lt;p&gt;A few good points to know include:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A BBS is &lt;em&gt;infrastructure&lt;/em&gt; and if the SHTF, there is no reason to believe&#xA;someone's BBS will still be there to serve users. The Virginia Packet Network is focusing a great deal on this important aspect, but it can be hard to predict the harsh circumstances of hard times.&lt;/li&gt;&#xA;&lt;li&gt;As stated above we have APRS to thank for a lot of the development of new AX.25 modem products.  One thing to keep in mind is the data send and receive buffers are often quite small.  APRS packets are short enough to survive this, but practical BBS usage with much larger packets may simply not work with modems designed only for APRS.&lt;/li&gt;&#xA;&lt;li&gt;BBS software is in, surprisingly, very active development.  &lt;a href=&quot;http://www.cantab.net/users/john.wiseman/Documents/BPQ32.html&quot; rel=&quot;noreferrer&quot;&gt;BPQ32&lt;/a&gt; is one such example.  Yes it is as quirky as the web site design makes it look.  It works though.  If you decide to try making your own BBS system, BPQ32 is probably the best way to go these days and it is available in both Windows and Linux packages... very cool.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h3&gt;Conclusion&lt;/h3&gt;&#xA;&lt;p&gt;Having a way to pass messages between each other in hard times is important. The fact BBS packet radio interactions are no longer very popular may, in fact, be a good thing since traffic to/from such systems may remain manageable. &amp;quot;Infrastructure&amp;quot; concerns aside, I think you are heading in a good direction.  It is certainly worth a good long look.  We certainly are.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-07-11T18:53:47.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6408" PostTypeId="1" CreationDate="2016-07-12T00:28:31.357" Score="1" ViewCount="186" Body="&lt;p&gt;Is there any practical way to match the output of my PA which is 420 Ω  to my antenna which is 50 Ω at 434MHz?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was thinking about adding  a pi-network and using a VSWR Meter with the output of the pi-network connected to the VSWR Meter and the other end of the VSWR Meter to the antenna, then by trial and error changing components until I get close to 1.00 VSWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a spectrum analyzer but I do not have a Vector Network Analyzer to create the Smith Charts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone know of a better/simpler way?&lt;/p&gt;&#xA;" OwnerUserId="7986" LastEditorUserId="218" LastEditDate="2016-07-13T20:09:00.837" LastActivityDate="2016-07-14T07:03:57.903" Title="Match 420 Ω to 50 Ω" Tags="&lt;impedance&gt;&lt;antenna-system&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6409" PostTypeId="2" ParentId="6408" CreationDate="2016-07-12T16:37:50.867" Score="1" Body="&lt;p&gt;Comment turned into answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can easily buy a 6:1 impedance transformer to do the job. That gets you close -- indeed, for me and my equipment (ham radio that is) it is close enough. I bought a 6:1 transformer for about \$60 or \$70 from DXEngineering maybe 10 years ago. Have since sold it at a ham-fest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am assuming that your question is about amateur &quot;ham&quot; radio in making the following comments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Along the output from your transmitting equipment (PA or whatever) you have multiple opportunities for a mis-match.  This involves the transmission line connected to your equipment, anything in that path such as antenna couplers, and the antenna itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You want to do two things: (1) get the best match practical for the antenna and frequency of operation; and, (2) have the lowest practical loss path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually any SWR under 2:1 meets the needs of (1).  Above 2:1 and especially over 3:1 you definitely need some type of matching solution such as an antenna coupler, transmission line transformer, and so forth.  Most modern amateur radio transceivers will fold back power levels when the SWR seen at its output is above 2:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For item (2) above, you want low-loss transmission line for most if not all of the path from transmitting equipment to antenna.  For my wire antenna covering bands 80, 40, and 30 I use ladder line except for the last 15 feet.  Ladder line is coupled to 50-ohm coax (LMR400) using a 4:1 transforming balun.  The loss on the remaining coax is insignificant even when I operate at QRP levels (which I often do).  I also use an antenna coupler/tuner (Elecraft KAT500).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For my mini-beam antenna (bands 20 - 10 meters) I use LMR400 coax for the entire path because the matching impedance with the antenna itself ranges between 1.1:1 and 1.8:1 (which I consider very good).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note LMR400 coax is not the cheapest coaxial transmission line but it is low loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Very curious about your PA 420 ohm output impedance.  In the last 55 years of ham radio activity, I have never seen any amateur radio equipment, even home brew, that did not have a 50-ohm output impedance.  Again, I am assuming amateur radio as the OP question did not make it clear if it is something else.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="29" LastEditDate="2016-07-13T11:43:47.013" LastActivityDate="2016-07-13T11:43:47.013" CommentCount="12" ContentLicense="CC BY-SA 3.0" />
  <row Id="6410" PostTypeId="1" AcceptedAnswerId="6411" CreationDate="2016-07-13T18:15:05.997" Score="2" ViewCount="250" Body="&lt;p&gt;I have been asked by an Arabic speaker here in UK if it is legal, or desirable, to call CQ in Arabic if his beam is directed that way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please, what answer should I give? Is there a general rule that covers all calls to a foreign country?&lt;/p&gt;&#xA;" OwnerUserId="297" LastEditorUserId="76" LastEditDate="2016-07-13T18:43:20.913" LastActivityDate="2016-07-14T10:23:38.387" Title="Is it all right to call CQ to a foreign country in their own language?" Tags="&lt;legal&gt;&lt;procedure&gt;&lt;united-kingdom&gt;&lt;international-operating&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6411" PostTypeId="2" ParentId="6410" CreationDate="2016-07-14T05:39:38.447" Score="3" Body="&lt;p&gt;It is ok. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hams may use any language they want if both sides agree to use it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If ham calls CQ in Arabic that is invitation to use that language in QSO.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-07-14T05:39:38.447" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6412" PostTypeId="2" ParentId="6410" CreationDate="2016-07-14T06:57:11.683" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;if it is &lt;strong&gt;legal&lt;/strong&gt;, or desirable&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Radio Amateurs may use any language which they can speak. I am not aware that there are any countries where the use of, or the not-use of, a particular language is stipulated in the license. But IANAL, and there are many countries.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;if it is legal, or &lt;strong&gt;desirable&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If the licensed Amateur wants to use his own native language, then the answer is simple; 'yes' it is desirable for that person. Using a language other than English will restrict the CQ, and with that the QSO, to only those who speak the same language. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We will have to understand that there are lots of people, who do not speak English, and will communicate in their own native language. My uncle, PD0FFS(SK) only spoke Dutch, but he still had a lifetime of fun in the hobby. He did try to make some international contacts using &quot;Pigeon English&quot; and sometimes this would work, sometimes it didn't, and sometimes the other party would be rude for not being able to clearly speak English (!!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This rudeness for not-speaking English can still be heard on the bands today, in fact I would believe that it is increasing. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would therefore ask everyone to be courteous for non-native-English speakers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(&lt;em&gt;I will get off my soap-box now&lt;/em&gt;)&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-07-14T06:57:11.683" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6413" PostTypeId="2" ParentId="6408" CreationDate="2016-07-14T07:03:57.903" Score="2" Body="&lt;p&gt;If your output need 420 Ohm (balanced)&#xA;And your antenna is 50 Ohm (unbalanced)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could run a 450 Ohm balanced feeder, which are commercially avaiable for cheap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And put a 9:1 balun at the antenna end, to feed your antenna.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-07-14T07:03:57.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6416" PostTypeId="1" AcceptedAnswerId="6417" CreationDate="2016-07-14T13:43:08.033" Score="3" ViewCount="831" Body="&lt;p&gt;What does &quot;RF in the shack&quot; mean? How does it interfere with devices around coax?&lt;/p&gt;&#xA;" OwnerUserId="7827" LastEditorUserId="76" LastEditDate="2016-07-15T13:56:27.030" LastActivityDate="2016-07-15T13:56:27.030" Title="What do we mean by &quot;RF in the shack&quot;?" Tags="&lt;coaxial-cable&gt;&lt;balun&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6417" PostTypeId="2" ParentId="6416" CreationDate="2016-07-14T14:38:04.073" Score="3" Body="&lt;p&gt;RF in the shack refers to the EM radiation that comes off of the outside of the conductor (usually) of coaxial cable.  Coaxial cable is actually three conductors:  center conductor, inside of the braided shield conductor, outside of the braided shield conductor.  Due to the &quot;skin effect&quot; RF currents are limited to a thin outer layer of a conductor.  This allows for the current to be separate on the inside and outside of the braided shield conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Current on the outside of the shield can easily radiate and even act like an antenna.  Other conductors that are close to this coaxial cable in the shack are affected and you can build up a potential that results in RF &quot;shocks or burns&quot; merely by touching metal objects.  When I was a young kid back in 1961 or 1962 I had such a strong RF in the shack condition that when I keyed down I could light up the florescent lights hanging from the ceiling (my shack was in the garage).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This outer conductive current is known as a &quot;Common Mode&quot; current and is usually produced from an imbalance in the antenna system.  One typical imbalance is connecting coaxial cable directly to a Dipole Antenna.  A Dipole Antenna is a balanced antenna and coaxial cable is unbalanced so that results in currents flowing in Common Mode on the outside of the shield conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution to resolve this problem and eliminate the common mode currents is to use a choke balun between the antenna and the coaxial cable.  Alternatively, you can use balanced transmission like, such as 450 ohm ladder line and that can attach (in the shack to a balanced load antenna tuner which then acts like a choke balun or a current balun (aka choke) which allows you to then attach coaxial line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do use 450-ohm ladder line you will have a mismatch between the Dipole antenna and the transmission line and this mismatch results in reflections.  This is not too much of a problem in itself since ladder line is low-loss however you do have to match this to your transmitting equipment, nominally at 50 ohms, which will require a tuned circuit such as an antenna tuner or coupler circuit.  The variable control of an antenna tuner is much nicer to adjust for match at various frequencies (or, even various bands).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I use an 80-meter dipole antenna on bands 80, 40, and 30 meters.  Most of my transmission line, about 80 feet, is 450 ohm ladder line.  Just outside of the shack it interfaces with the balanced side of a 4:1 transforming balun (from DX Engineering) and then coaxial cable (LMR400) the remaining 15 feet to my KAT500 (Elecraft) antenna tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common mode currents radiate so this is the cause of the primary problems  resulting in both &quot;RF in the shack&quot; but also altered radiation patterns from the interference with the antenna itself.  I have modeled this condition using NEC4 (mathematical modeling software), to observe the actual impact and in a worse case (although, with high power), it can create nulls in your radiation pattern where you don't expect them (on the broadside of a dipole antenna) in certain physical arrangements of the antenna and feed line.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-07-14T14:38:04.073" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6418" PostTypeId="1" AcceptedAnswerId="6419" CreationDate="2016-07-14T15:58:11.083" Score="1" ViewCount="352" Body="&lt;p&gt;how does slotted coax Balun eliminate common current? why the length of the slot should be quarter wavelength?&lt;/p&gt;&#xA;" OwnerUserId="7827" LastActivityDate="2016-07-15T03:31:28.367" Title="how does slotted coax Balun eliminate common current?" Tags="&lt;coaxial-cable&gt;&lt;balun&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6419" PostTypeId="2" ParentId="6418" CreationDate="2016-07-15T03:31:28.367" Score="1" Body="&lt;p&gt;The slotted coax balun is very similar to the folded balun (aka Pawsey stub).  I wrote about the folded balun in my article...&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.hamradio.me/antennas/coax-velocity-factor.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Coax Velocity Factor in Baluns, Does it Matter?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The references at the bottom of the article provide some good quotes to consider.  There are two things to consider for your question: why and where the split balun is shorted back together.&lt;/p&gt;&#xA;&lt;h2&gt;Why the split balun is shorted&lt;/h2&gt;&#xA;&lt;p&gt;Balanis discusses the theory behind matching techniques including the 1/4 Wave Coaxial 1:1 Balun. In particular he describes the purpose of the electrical short of the coax center conductor to shield, is to maintain balance, thereby, ensuring no current flows back to the transceiver on the outside of the coax.  As both halves of the split balun are fed by energy at the feedpoint 180 degrees out of phase, when the currents join at the shorted end, they are in balance and just act like a short between each other with little eagerness to flow current to the third conductor (the mast or feed system).&lt;/p&gt;&#xA;&lt;p&gt;I've built several folded baluns for various tests and do find they put a hard stop on any common mode current that tries to flow back down the feed system and over essentially all frequencies (or at least frequencies well outside the antenna's operation band).  It may well be erroneous to say all common mode current is stopped, but my measurements suggests certainly most is quelled by the, essentially, short across the end of the feed line.&lt;/p&gt;&#xA;&lt;h2&gt;Where the split balun is shorted&lt;/h2&gt;&#xA;&lt;p&gt;If we make the split balun portion much shorter than a quarter-wave at the desired operating frequency, we can see we are simply shorting the feedpoint of the antenna and nothing will work optimally.  However, if we place this short exactly one quarter-wavelength back along the feed system, we can surmise the transformer action of a quarter-wave length of wire will convert the impedance at one end to a different impedance at the other.  The classic example of a quarter-wave wire transformer are the radials and vertical of the classic quarter-wave monopole antenna.  The high impedance present at the end of the radials (because they are in freespace) is converted to a low impedance 1/4, 3/4, 5/4, etc. wavelengths away from the tip.  In this way, the radials present a low impedance (opposite their tip impedance) to the center of the antenna thereby drawing lots of shield current and leaving less to flow back down the antenna mast or feedline.&lt;/p&gt;&#xA;&lt;p&gt;The split or slotted coaxial balun works the same way, but in reverse.  In this case the location where the split balun joins is considered a direct short to each other and the feed system.  This low impedance is converted through the 1/4 wavelength of conductor to a high impedance at the feed point.  In this use, the high impedance presents a strong rejection to the relatively low impedance currents and keeps them from flowing back down the line thus keeping the currents on the intended antenna elements.&lt;/p&gt;&#xA;&lt;p&gt;Balanis summarizes this much better:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;“The parallel auxiliary line need not be made 1/4 wave in length to achieve the balance. It is made 1/4 wave to prevent the upsetting of the normal operation of the antenna.”&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="4306" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-07-15T03:31:28.367" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6420" PostTypeId="1" AcceptedAnswerId="6421" CreationDate="2016-07-15T03:48:51.380" Score="5" ViewCount="7279" Body="&lt;p&gt;A common phrase/word I've seen used in text and I've heard on air in conversation is &quot;hihi&quot; or &quot;hi-hi&quot;. What does this mean and in what contexts is it appropriate to use?&lt;/p&gt;&#xA;" OwnerUserId="7798" LastActivityDate="2020-02-21T14:47:34.473" Title="In amateur radio conversation, what does &quot;hihi&quot; mean?" Tags="&lt;jargon&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6421" PostTypeId="2" ParentId="6420" CreationDate="2016-07-15T03:58:54.287" Score="8" Body="&lt;p&gt;It is ham radio laughter.  HIHI, sometimes HI, other other times HIHI.  It's origins are in CW (aka Morse Code), not voice.  In fact, I believe old-timers might think it is silly to say HiHi or something on SSB or other voice comms when you can merely laugh if something is funny.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, with Morse Code, laughter is not in the alphabet so HIHI gets the job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In Morse code, this is &quot;di-di-di-dit  di-dit&quot; -- and the pattern is supposed to vaguely sound like laughter (I think very vaguely).  I actually never use it even though I have been mostly CW ops for decades and decades.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-07-15T03:58:54.287" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="6422" PostTypeId="2" ParentId="1273" CreationDate="2016-07-15T06:21:24.727" Score="2" Body="&lt;p&gt;Overe here, DX is considered to be long distance QSO, arbitrarily, greater that 2000 km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In Europe we consider any station outside Europe to be DX.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-07-15T06:21:24.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6423" PostTypeId="2" ParentId="1273" CreationDate="2016-07-15T14:55:21.227" Score="5" Body="&lt;p&gt;In the US, DX most often refers to a foreign country no matter how far the distance.  I live near Seattle Washington and the nearest foreign country is Canada, about 100 miles distant from my QTH.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, DX has some specific definitions created in support of various contests and awards.  For example, the DXCC award sponsored by ARRL recognizes a DX contact as a contact with a DX entity outside of your QTH entity.  All recognized DX entities (not necessarily countries) are defined by ARRL for this very purpose.  Also, there are several contests where the contest rules define what DX contacts generate points in the contest.  Often these are the same as the ARRL definitions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, a DX entity is not necessarily a foreign country.  For example, two of the states (Alaska and Hawaii) of the US are DX entities separate from the one I have in Washington state.  Therefore, they qualify to be counted as DX.  Actually, both Alaska and Hawaii are easy everyday contacts for my QTH (near Seattle, WA).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should you answer CQ DX if you are not DX to the caller?  I do that only to offer a signal report and in CW this can be done very fast.  In response, I will say something like &quot;579 WA K7PEH&quot;.  But, I will only do this for someone who is distant from me, such as an east coast QTH trying for DX such as Hawaii or Alaska or Japan, etc.  Some ops get upset if you answer their DX and you are not DX but most will polite respond to your signal.  A typical response to a signal report such as I mentioned earlier is sending just two dots.  In CW, sending two dots (technically the letter I but you are not sending an I) is sort of like a quick way to say &quot;OK&quot;, or &quot;I hear ya&quot;, or even &quot;Bye&quot; (which is a shortened version of &quot;shave and a haircut, two bits&quot;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are calling DX and someone answers who is not DX -- be polite.  You should always know though if they are DX or not merely by their call sign.  All separate DX entities are defined as having recognizable (usually) call signs.  By usually, I mean it is not always easy to know unless you have the DX list in front of you to check.  For example, in the US, Guantanamo Bay, Cuba, is DX (A US entity) but it's call sign prefix of KG4 can easily be mistaken for a QTH in the states representing the number 4 call area now that many call areas are using KG as a prefix in their sequentially assigned call signs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL DX entity list can be found at:&#xA; &lt;a href=&quot;http://www.arrl.org/files/file/DXCC/2016%20DXCC%20Current.pdf&quot; rel=&quot;noreferrer&quot;&gt;ARRL DX CURRENT LIST&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not all DX is DX either.  One example.  I heard a strong DX station (CW) and planned to answer.  I didn't recognize his call sign so I looked up the prefix on my ARRL DX Entity List poster hanging on the wall next to me.  He was South Africa which is a particularly hard DX for my QTH.  But, I listened to his CQ call again and this time heard his slash suffix -- he was operating remote in the state of Arizona.  I answered anyway and we had a nice chat about his vacation visiting near the Grand Canyon.  But, this QSO does not count as true DX for either him or I.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2016-07-15T15:10:05.383" LastActivityDate="2016-07-15T15:10:05.383" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6424" PostTypeId="2" ParentId="4905" CreationDate="2016-07-15T18:53:34.113" Score="5" Body="&lt;p&gt;Rather than two receivers, maybe a switch that selects between antennas could be a cheaper option?  &lt;/p&gt;&#xA;" OwnerUserId="7999" LastEditorUserId="76" LastEditDate="2016-07-15T21:36:47.827" LastActivityDate="2016-07-15T21:36:47.827" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6425" PostTypeId="1" CreationDate="2016-07-15T19:46:28.243" Score="3" ViewCount="426" Body="&lt;p&gt;I use a J Pole for air band (122 MHz). I get superb aircraft reception but a very weak signal from my local airport 20 miles away. Is there a way to set up a yagi, or other gainy directional antenna, pointing at the airport and combine it with the omnidirectional J Pole ?  I assume I'd need to get the impedance back to 50 ohms. Could this be done with a phasing harness ?  Would I be able to mount both antennae on the same mast and have only one feeder coming to the receiver. Help appreciated.&lt;/p&gt;&#xA;" OwnerUserId="8000" LastEditorUserId="218" LastEditDate="2016-07-16T02:38:13.853" LastActivityDate="2016-07-16T02:38:13.853" Title="Combining yagi and J pole for airband" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6426" PostTypeId="2" ParentId="6425" CreationDate="2016-07-15T20:44:27.907" Score="0" Body="&lt;p&gt;Your question is very similar to &lt;a href=&quot;https://ham.stackexchange.com/questions/4905/connect-two-receiving-antennas-to-the-same-radio&quot;&gt;this one&lt;/a&gt;, except decent coaxial cable for the air band is much cheaper than decent coax for 1 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition to the suggestions given in the other question, you might try just mounting the antenna up higher.  Or even just a few feet over, because your antenna could be in a local null.  You've surely experienced local nulls before&amp;mdash;you're sitting at a red light and your FM broadcast band reception is suddenly terrible; then the light turns green, you roll just a few feet away, and the reception is good again.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-07-15T20:44:27.907" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6427" PostTypeId="2" ParentId="6425" CreationDate="2016-07-16T02:37:59.853" Score="1" Body="&lt;p&gt;They can be combined, but if you are thinking by combining them you'll get the best of each antenna, that's not how it works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides signal, each antenna picks up noise. The two combine to be, in effect, a single antenna with a different directional pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A cheap option is to put the two on a switch, and you can then manually select whichever antenna works best for the situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to get more sophisticated, if you have two phase coherent receivers you can write an algorithm which dynamically &lt;a href=&quot;http://www.antenna-theory.com/arrays/main.php&quot; rel=&quot;nofollow&quot;&gt;combines the amplitude and phase of the two&lt;/a&gt; for best reception. Such an arrangement is called an &lt;a href=&quot;https://en.wikipedia.org/wiki/Smart_antenna&quot; rel=&quot;nofollow&quot;&gt;adaptive antenna&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-07-16T02:37:59.853" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6428" PostTypeId="1" CreationDate="2016-07-16T12:06:43.343" Score="2" ViewCount="282" Body="&lt;p&gt;I have a tracking station for UHF band satellites which comprises of a cross yagi of 12 dBi and a wideband LNA of 40 dB Power Gain and 1.3 dB Noise Figure. I observe a Noise floor of about 300 kHz centered at the frequency of 436 MHz on the spectrum analyzer. The floor power varies between -75 and -80 dBm, while the floor at other frequencies is -100 dBm. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried reducing the RBW and VBW of the analyzer, but the floor doesn't change.&#xA;I tested both antenna and LNA separately and couldn't find the reason for this floor. Please help me.&lt;/p&gt;&#xA;" OwnerUserId="4831" LastEditorUserId="76" LastEditDate="2020-02-15T17:01:21.903" LastActivityDate="2020-02-15T17:01:21.903" Title="Strange Noise Floor observed in UHF Band" Tags="&lt;antenna&gt;&lt;noise&gt;&lt;lna&gt;&lt;spectrum-analyzer&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6429" PostTypeId="2" ParentId="6428" CreationDate="2016-07-16T16:31:34.300" Score="0" Body="&lt;p&gt;Are you sure you're not picking up RFI from one of the electronic devices that's part of your station? Some power supplies have offset knobs you can adjust (the RFI will change frequency); SDRs frequently have similar adjustments to move their self-interference if it's in the way (as is common for budget SDRs). You'll have to hunt via process of elimination but I'' betting it's part of your station (including wall warts, inverters, etc.). Adjust or replace the noisy components; try &quot;choking the hell out of&quot; any cables (as an elmer once said to me) with an RFI choke or six. &lt;/p&gt;&#xA;" OwnerDisplayName="user157" LastEditorDisplayName="user157" LastEditDate="2016-07-16T16:37:40.443" LastActivityDate="2016-07-16T16:37:40.443" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6430" PostTypeId="2" ParentId="6428" CreationDate="2016-07-16T21:49:04.790" Score="1" Body="&lt;p&gt;300 kHz channel at 436 MHz sounds a lot like your spectrum analyzer might be seeing that are at twice the frequency – 872 MHz would be a typical 2G cellular network frequency, and 300 kHz might be around the bandwidth of a 2G channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try and tune to your SA to 872 MHz.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-07-16T21:49:04.790" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6433" PostTypeId="1" CreationDate="2016-07-17T20:55:58.593" Score="4" ViewCount="296" Body="&lt;p&gt;If a band allows one watt EIRP and I have an antenna that is 1% effective could I legally run 100 watts into the antenna because only one watt is radiated? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that same antenna also has a gain would I then have to include this as well in the calculation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How about feed line losses, do I then just multiply these factors together?&lt;/p&gt;&#xA;" OwnerUserId="5577" LastEditorUserId="5577" LastEditDate="2016-07-18T16:35:11.487" LastActivityDate="2016-07-23T12:06:45.660" Title="How to calculate effective isotropic radiated power apply to lossy antennas" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6434" PostTypeId="2" ParentId="6433" CreationDate="2016-07-17T22:18:03.820" Score="2" Body="&lt;p&gt;If the antenna &lt;em&gt;gain&lt;/em&gt; is 1%, then yes.&lt;/p&gt;&#xA;&lt;p&gt;If you have a 1% &lt;em&gt;efficiency&lt;/em&gt; antenna, but it's a dipole, then no, as your EIRP would be 1.6 W from the dipole gain of 2 dBi.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Gain&lt;/strong&gt; is the property of the antenna most easily measured at the terminals, and covers the effective performance of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;EIRP is simply the product of the transmitter power and the gain of the antenna, so 100 W into a 0.01× gain antenna is an EIRP of &lt;span class=&quot;math-container&quot;&gt;$100\,\mathrm{W} \cdot 0.01 = 1\,\mathrm{W} $&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Antennas have two relevant properties which make up gain: Directivity (the degree to which the radiation is concentrated in a particular direction) and Efficiency &lt;span class=&quot;math-container&quot;&gt;$\eta$&lt;/span&gt; (the fraction of the total input power that is radiated). &lt;span class=&quot;math-container&quot;&gt;$ Gain = Directivity \cdot \eta$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Feedline losses&lt;/strong&gt; act simply to reduce the transmitter power. So if your feedline loss is 3 dB, then the transmitter power is multiplied by &lt;span class=&quot;math-container&quot;&gt;$10^{-3/10}$&lt;/span&gt; or &lt;span class=&quot;math-container&quot;&gt;$ 0.5 $&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;For example&lt;/strong&gt;: A &lt;a href=&quot;http://www.buddipole.com/buddipole.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;short loaded dipole&lt;/a&gt;, 8.7 ft long, has an efficiency at 7 MHz of about 4%. It has a directivity of about 1.8 dB (a short dipole has slightly less directivity than a 1/2wave dipole).&lt;br /&gt;&#xA;It is fed with a coaxial line with 2 dB of loss.&#xA;With 100 W input, it will produce, &lt;em&gt;at the peak of its radiation pattern&lt;/em&gt; an EIRP of &lt;span class=&quot;math-container&quot;&gt;$$\mathit{EIRP} = 100\,\mathrm{W} \cdot 10^{-2/10} \cdot 10^{1.8/10} \cdot {4 \over 100} = 3.8\,\mathrm{W} $$&lt;/span&gt;.&lt;br /&gt;&#xA;By the way, I like to use &lt;a href=&quot;https://www.google.com/search?q=100+W+*+10%5E(-2%2F10)+*+10%5E(1.8%2F10)+*+(4%2F100)&quot; rel=&quot;nofollow noreferrer&quot;&gt;Google Calculator&lt;/a&gt; for these sorts of things, it knows the constants and calculates with units. &lt;a href=&quot;https://www.google.com/search?q=speed+of+light+%2F+20+MHz&quot; rel=&quot;nofollow noreferrer&quot;&gt;Try it&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;A note about licensing restrictions&lt;/strong&gt;: some countries have a restriction on power into the feedline, and even DC power into the final amplifiers, so study your own regulations. An EIRP limit is rare, I've only seen it on the 600 m band.&lt;br /&gt;&#xA;For example, in South Africa:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;&amp;quot;Carrier wave power&amp;quot;&lt;/strong&gt; means the average power that is supplied by the transmitter to the antenna transmission line and is measured during one radio-frequency cycle in conditions of no modulation;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Transmitter Power Output of Amateur Radio Stations&lt;/strong&gt;&lt;br /&gt;&#xA;The maximum power output of the transmitter, as measured at the antenna port, must not exceed the levels specified in the national radio frequency plan for the relevant licence classes ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-07-23T12:06:45.660" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6435" PostTypeId="2" ParentId="1273" CreationDate="2016-07-18T01:14:09.893" Score="3" Body="&lt;p&gt;One definition of DX is &quot;anything you have not worked&quot;. Someone above said that if you're in Europe then anything outside Europe is considered DX - but that rather depends where you live. If you are on the European side of Istanbul, then the Asian side of Istanbul is certainly not DX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, even if you were in (say) Italy and you called CQ DX and got an answer from Monk Apollo (SV2ASP/A, the only active station in Mount Athos in Greece) you might be EXTREMELY happy about it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also just because a station is not DX to you, it doesn't mean you can't be DX to them! A QRP station in Alaska might be delighted to work someone in Nova Scotia, even though USA to Canada might not usually be considered DX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;DX is generally considered to be anything a long distance away, but if you are not sure about it and you hear a station you want to work calling DX and getting no replies, try giving them a call and see if they answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And you can bet your bottom dollar that if there was a station active in Myanmar or Andaman Islands everyone would be calling them no matter how near or far away they are - I'm HS0ZLW and would be in the pileups with everyone else.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2016-07-18T01:14:09.893" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6436" PostTypeId="1" AcceptedAnswerId="6437" CreationDate="2016-07-18T03:40:54.310" Score="5" ViewCount="159" Body="&lt;p&gt;I have taken two years of high school physics and am very interested in RF communication. I know that electromagnetic waves do not necessitate a medium in order to propagate. Thus, shouldn't I be able to send/receive RF signals even when the signal is apparently blocked by things like mountains? I know most interference is due to incorrectly channelizing the correct wave from its assigned frequency. However, this is not an interference issue, right? Shouldn't there always be a path to the satellite(s)? I am only a rising high school senior, so I apologize if this is ridiculously simple... :)&lt;/p&gt;&#xA;" OwnerUserId="8010" LastEditorUserId="29" LastEditDate="2016-07-18T08:34:26.773" LastActivityDate="2016-07-18T18:43:37.953" Title="If EM waves require no medium, why can't I get service at all times?" Tags="&lt;propagation&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6437" PostTypeId="2" ParentId="6436" CreationDate="2016-07-18T05:58:15.530" Score="3" Body="&lt;p&gt;Electromagnetic waves do not necessitate a medium in order to propagate, but if medium is present it can enhance or degrade radio waves propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In that matter you may recognize not just mountains as media, but buildings too, even atmosphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Satellites usually communicate using very high frequencies, such that require line of sight. Any hard object, including mountains or even buildings may block very high frequency radio-wave. If satellite is &quot;visible&quot; on the sky you can reach it by radio. Atmosphere does not have much influence on very high frequencies so it does not matter if it is cloudy, day, night, winter or summer.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-07-18T05:58:15.530" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6438" PostTypeId="1" AcceptedAnswerId="6450" CreationDate="2016-07-18T09:16:39.487" Score="3" ViewCount="2112" Body="&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Morse_code#Learning_methods&quot; rel=&quot;nofollow&quot;&gt;Koch method&lt;/a&gt; of learning Morse code is based on the idea that you learn characters at full speed, but a reduced set of characters that is expanded over time, instead of learning the full set of characters from the beginning at reduced speed and then increasing speed over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is there a recommended order in which to add characters to the set?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, then what is important when deciding in which order to learn characters?&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="4076" LastEditDate="2016-07-18T09:26:01.780" LastActivityDate="2021-02-17T04:55:06.363" Title="Is there a preferred order for learning Morse code using the Koch method?" Tags="&lt;cw&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6439" PostTypeId="1" CreationDate="2016-07-18T09:30:00.773" Score="2" ViewCount="600" Body="&lt;p&gt;I'm currently facing a little problem with our Yaesu controller. I have done all the calibration and the controller appears to be working fine. Unfortunately, it does so for short duration (a couple of hours maybe). After that, the azimuth control goes askew with an offset of around 15 degrees. Therefore I had to recalibrate it almost every time before I try to communicate with any satellite. Could you please provide advice in case you have encountered a problem like this before? I use GPredict and rotctld for all the control.&lt;/p&gt;&#xA;" OwnerUserId="6214" LastEditorUserId="76" LastEditDate="2016-07-18T13:28:22.150" LastActivityDate="2019-07-28T19:04:00.637" Title="Yaesu G-5400B rotator controller problem" Tags="&lt;yaesu&gt;&lt;equipment-troubleshooting&gt;&lt;antenna-rotator&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6440" PostTypeId="2" ParentId="5832" CreationDate="2016-07-18T09:36:06.440" Score="2" Body="&lt;p&gt;I managed to solve the problem. Basically I implemented the DSP demodulation software in GNU Radio. I then rewrote AX.25 software stack in C++. It is not a very complicated stack and it didnt take a lot of time. &lt;/p&gt;&#xA;" OwnerUserId="6214" LastActivityDate="2016-07-18T09:36:06.440" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6441" PostTypeId="2" ParentId="6438" CreationDate="2016-07-18T16:17:27.060" Score="2" Body="&lt;p&gt;I learned Morse code from cassette tapes sold by the ARRL, in which the characters were at 15 WPM but the characters were spaced at 5 WPM; in other words, the Farnsworth method.  The Koch method has the characters and the spacing at the same speed, which is relatively fast.  Both the Farnsworth and Koch methods introduce the learner to a few characters at a time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would think that there are two considerations involved.  First, the trainers want to introduce the learner to the easy characters, the ones with only one or two dits and dahs, earliest.  The second consideration is that they would like to teach characters that are easy to make into words, because it is more satisfying for the learner to copy complete words than to copy random groups of characters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't done a scientific study, but in my opinion it's more important to make words than it is to teach the &quot;easy&quot; characters.  Personally I remember that for me, some of the longer characters such as P (·--·) were easier to recognize and memorize than some of the shorter characters, such as N (-·).  Of course the International Morse Code is designed around the English language, so that the easier characters are also the some of the most commonly-used characters, so there isn't much of a conflict between the two considerations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regardless of the method used to learn Morse Code, I think the best thing is to get through the awkward phase of learning all the characters as quickly as possible.  It is far more satisfying to use the code in an actual QSO, even at a slow speed, than it is to listen to a tape or use a computer program.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-07-18T16:17:27.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6443" PostTypeId="2" ParentId="6436" CreationDate="2016-07-18T17:15:18.223" Score="1" Body="&lt;p&gt;This is also a Physics question and the OP might consider posting under Physics.SE or at least a portion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Actually, Electromagnetic Waves do require a medium and that medium is in fact called the Electromagnetic Field which is defined for all points in space-time.  The area of physics known as QED (Quantum Electrodynamics) solves the problem of photon interactions with charged particles (e.g. electron) The photon is the quanta of the EM Quantum Field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EM waves propagate in the EM Field and particles (photons) are excitations of the EM Field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that the idea of a &quot;Field&quot; being the medium might be a bit obscure or abstract but it is indeed a reality as far as current Theoretical Physics is concerned.  All forces and quantum particles are defined by quantum fields.  The so called &quot;physics&quot; of the interactions is all in the field itself and fields interacting with other quantum fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The abstract notion of Space-Time and its geometry is also a field and the dynamics of this field are specified by Einstein's General Relativity field equations.  But, it is considered a classical field, not quantum (at least not yet).&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-07-18T17:15:18.223" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6444" PostTypeId="2" ParentId="6436" CreationDate="2016-07-18T18:43:37.953" Score="4" Body="&lt;p&gt;I'd like to answer this from a perspective of high-level principles:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;“Does not require a medium” just means that the wave can pass through vacuum, not that the wave never interacts with anything in its path. If the wave would pass through anything without interaction, &lt;em&gt;then it would pass right through the receiving antenna, too&lt;/em&gt; and it wouldn't be useful for communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are no exceptions in the laws of physics for antennas; there are just arrangements of matter that interact very little (vacuum or air), arrangements that have been designed to interact very strongly (antennas, reflectors), and everything else in between (trees, walls, mountains) which reflect, refract, or absorb the wave to some degree.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-07-18T18:43:37.953" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6445" PostTypeId="1" AcceptedAnswerId="6446" CreationDate="2016-07-18T19:44:14.790" Score="8" ViewCount="2646" Body="&lt;p&gt;My son was asking about some Ethernet cable (Cat 5 unshielded twisted pair), and since he recently passed his Technician exam and we both have &quot;radio stuff&quot; on our minds, I tried to make the analogy between coax transmission lines and the balanced pairs in the wire. I understand they both are used as RF transmission lines, essentially.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This got me thinking: why don't we use twisted pair for antenna feedlines? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As question T9B03 on the FCC exam covers:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why is coaxial cable used more often than any other feedline for amateur radio antenna systems?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The correct answer being &quot;It is easy to use and requires few special installation considerations&quot; and &lt;strong&gt;not&lt;/strong&gt; that &quot;It has less loss than any other type of feedline&quot; — the latter advantage going to balanced line, which is low-loss but does require special considerations particularly to avoid coupling to nearby metallic objects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would twisted pair offer something of best of both worlds? Could it provide lower loss than coax, and still without &quot;special installation considerations&quot;? (Looks like Category 5 cable specifically has a 100ohm characteristic impedance, but that seems easily enough dealt with since you'd need a unbalanced-to-balanced transformer off of most ham equipment anyway, right?)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-11-23T03:28:27.763" Title="Why isn't twisted pair used for feedlines?" Tags="&lt;coaxial-cable&gt;&lt;feed-line&gt;&lt;balun&gt;&lt;transmission-line&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6446" PostTypeId="2" ParentId="6445" CreationDate="2016-07-18T21:04:55.757" Score="8" Body="&lt;p&gt;Balanced lines (of which twisted pair is a special type) really have an upper frequency limit; you can't use them to transport 1 GHz (well, you can, but the smallest variation in direction or distance would have catastrophic effects, and the conductor distance would get &lt;em&gt;pretty small&lt;/em&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can be seen in technical practice: 100 Mbit/s Ethernet (Fast Ethernet) and 1 Gigabit/s ethernet both work with twisted pair, their baudrate being 125 MBaud – and hence, most of their signal energy is contained below ~250 MHz. For higher-rate digital busses, twisted pair, as nice and cheap it is, doesn't do well enough anymore – the typical &quot;cheap&quot; (as in: 16€/m) direct attach copper for the next faster 10GE (10GBase-CR) uses Twinax - which is exactly that, a balanced line within a shielded, well-specified dielectric (same goes for SATA 6b/s, where this picture is from):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qmOKt.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qmOKt.jpg&quot; alt=&quot;https://en.wikipedia.org/wiki/Serial_ATA#/media/File:SATA3-TwinAxCable.jpg&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That way, up to 3.125 Gigabaud are possible. So yeah, for digital baseband, balanced line is used up to the multiples of GHz, but it's not cheaper than coax – in fact, it's the noise immunity considerations of differential signaling that led to the usage of twinax instead of simple coax. For an antenna, simple coax would have the same effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, whenever you see a PCB transport RF signals, you'll find something like a microstrip line, a buried microstrip line, or a pair of differential lines – there you are, balanced lines again. On PCB, this gets easier (and necessary, as there's no chance to build true coax on a PCB), because the dielectric (the PCB substrate) is so mechanically and electrically reliable, and powers typically are limited.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For higher frequencies, losses due to radiation simply take the upper hand in free-swinging balanced line – and coax, with its losses in the dielectric, becomes the better line. If you go for the really high frequencies, or rather the really high powers, you typically drop the (inner) conductor altogether – and use a wave guide.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-07-18T21:04:55.757" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6448" PostTypeId="2" ParentId="6041" CreationDate="2016-07-18T23:16:41.683" Score="2" Body="&lt;p&gt;Unless you are operating VHF and above, abide by the rule of never cutting your coax cable unless you absolutely must for some reason.  What you need today may be 20 feet but a new antenna you might put up next may need 40 feet.  If you are active in ham radio, especially with HF, you will probably have dozens of antennas over the life of your coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a coax attenuation chart showing loss per frequency per cable type.  There are dozens of such charts to be found on the Internet via google.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QR7H8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QR7H8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-07-18T23:16:41.683" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6450" PostTypeId="2" ParentId="6438" CreationDate="2016-07-19T05:59:02.273" Score="2" Body="&lt;p&gt;While testing several CW training application I noticed they use different learning orders. My opinion is that it actually does not matter what order is. Point is to listen each character at full speed and having pauses between characters. I used that method to train new hams back in 80-s with completely different order that is used now and it worked perfectly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer your question fully, LCWO uses this character order in lessons:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;K M U R E S N A P T L W I . J Z = F O Y , V G 5 / Q 9 2 H 3 8 B ? 4 7 C 1 D 6 0 X &lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-07-19T05:59:02.273" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6451" PostTypeId="2" ParentId="135" CreationDate="2016-07-19T06:01:39.693" Score="-2" Body="&lt;p&gt;Using Morse code is a skill, and people like to practice their skills.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-07-19T06:01:39.693" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6452" PostTypeId="1" CreationDate="2016-07-20T04:42:53.330" Score="0" ViewCount="200" Body="&lt;p&gt;I have an old ICOM R-71a receiver that is giving me grief. The problem started off with audio and rf cutting out completely after being on for a few hours. The frequency display would work but nothing else. After shutting off the unit for a while and turning the unit back on then everything would operate as normal then recur later. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now another problem occurs. Now everything below 8 MHz is silent but everything above 8 MHz still works but doesn't seem as sensitive as before. &#xA;This is beginning to annoy me. Any ideas or suggestions on what's going on? I suspect a power supply problem. I have a nice 40 meter vertical antenna that is going to waste.....&lt;/p&gt;&#xA;" OwnerUserId="6604" LastEditorUserId="76" LastEditDate="2016-07-20T15:31:29.293" LastActivityDate="2017-04-18T12:17:16.667" Title="Issue with Icom R-71A" Tags="&lt;icom&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6453" PostTypeId="1" AcceptedAnswerId="6454" CreationDate="2016-07-21T21:31:27.067" Score="1" ViewCount="178" Body="&lt;p&gt;What would be the result of accidentally applying a UHF signal to a VHF power amplifier? Say a 70cm transmission from a dual-band 2 meter / 70 cm radio into a 2 meter PA, assuming the input power is within the PA's specs?&lt;/p&gt;&#xA;" OwnerDisplayName="user157" LastActivityDate="2016-07-21T22:31:52.800" Title="UHF Into VHF Power Amplifier" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6454" PostTypeId="2" ParentId="6453" CreationDate="2016-07-21T22:26:46.077" Score="1" Body="&lt;p&gt;That depends, but generally speaking, your amplifier will just be &quot;too slow&quot; to follow the signal, and you'll just get a mishmash of frequencies at the output. Usually, nothing bad would happen (aside from you emitting at frequencies where that's illegal). Nice thing about having energy at the wrong frequencies is that it stays the same energy, even if somehow converted to something amplifiable by the PA. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It really depends on your device, but some amplifiers might even have an input stage with a moderate low-pass characteristic on purpose – you really don't want to amplify harmonics of the intended signal, anyway, so designing an input stage that has some series resistance followed by a shorting capacity comes pretty easy (or accidentally, actually), and that's only for the better. In this case, your UHF signal will possibly already be canceled when it would reach the main gain stages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that things might look a bit different for very sensitive amplifiers, or in situations where your tone might lead to nonlinearities mixing down energy from formerly out-of-band into your amplifiers operational range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All in all: Be safe. Have filters. In this particular case, having an RC actually is easy enough :)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-07-21T22:31:52.800" LastActivityDate="2016-07-21T22:31:52.800" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6455" PostTypeId="1" AcceptedAnswerId="6458" CreationDate="2016-07-24T17:05:53.053" Score="1" ViewCount="987" Body="&lt;p&gt;I'm developing a type of ground penetrating radar that does not use pulses. It's extremely narrow bandwidth. As narrow as a good crystal can get it. The frequency I'm shooting for initially is somewhere between 150MHz to 900MHz, but that's not set in stone. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I'm wondering what the maximum legal power is for such a device in the United States, California. I don't have any HAM license. I've seen GPR units for sale that produce hundreds of watts, but they produce pulses. My device will not produce pulses and will not modulate the frequency. The signal will initially slowly rise to peak, and from there it will maintain a constant power for about 100 seconds at a fixed frequency, followed by a slow decay when it's done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried googling this. The only thing I find is regarding HAM radios (up to 1500 watt limit). Also there are pulsed GPR units for sale. Perhaps there are less restraints for non-modulating fixed frequency signals. My GPR unit will be slowly rotating. The device will be used far out in rural areas. Perhaps 10 to 200 miles away from any city. I'm guessing that even if the unit exceeds legal power limits there's almost zero chance of being caught since there'll be nobody out there except some hunters and campers and perhaps forest rangers. If caught, then I'm wondering if the authorities will take away my GPR. The GPR unit wouldn't be heard on radios since its at an extremely narrow BW. So the Rangers should be okay. They'll probably be more curious then anything else. At say 300MHz the GPR yagi antenna will be around  7 elements. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any help is greatly appreciated!&lt;/p&gt;&#xA;" OwnerUserId="8049" LastEditorUserId="76" LastEditDate="2016-07-24T20:12:34.737" LastActivityDate="2016-07-26T08:15:13.230" Title="Max legal power with nearly zero BW" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;rf-power&gt;" AnswerCount="4" CommentCount="14" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6456" PostTypeId="2" ParentId="6455" CreationDate="2016-07-24T19:21:32.340" Score="2" Body="&lt;p&gt;If you transmit without a license in a band allocated to a licensed service and/or with unlicensed equipment, you're breaking the law and possibly messing up someone else's communications.  Don't do that.  Even if you're unlikely to get caught, there's a reason the FCC is in charge of frequency allocations: the EM spectrum is a public resource, and no one gets to use it to the exclusion of others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to experiment with new (non-commercial) uses for radio technology, get a ham license – that's what it's for!  The entry-level Technician license is easy to study for with &lt;a href=&quot;https://www.hamradiolicenseexam.com/&quot; rel=&quot;nofollow&quot;&gt;free online tools&lt;/a&gt; or &lt;a href=&quot;http://www.arrl.org/shop/ARRL-Ham-Radio-License-Manual-3rd-Edition/&quot; rel=&quot;nofollow&quot;&gt;inexpensive books&lt;/a&gt;, and you can &lt;a href=&quot;http://www.arrl.org/find-a-club&quot; rel=&quot;nofollow&quot;&gt;find a club near you&lt;/a&gt; that offers license exams.  I'm a newbie myself and have loved the freedom to learn about radio technology by experimentation and from talking with more experienced hams.&lt;/p&gt;&#xA;" OwnerUserId="6446" LastActivityDate="2016-07-24T19:21:32.340" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6457" PostTypeId="2" ParentId="6455" CreationDate="2016-07-24T20:11:53.733" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;So I'm wondering what the maximum legal power is for such a device in the United States, California. I don't have any HAM license.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you do not have an Amateur license then you are limited to “Part 15” operations and a very low output power — 1 watt or less depending on frequency and antenna gain (&quot;citation needed&quot; as they say; I found only unclearly-written sources).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The GPR unit wouldn't be heard on radios since its at an extremely narrow BW. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In general, your question is supposing that your device will interfere less if its frequency is stable and unmodulated. This is false.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While it does mean you are less likely to interfere with any given other user (since you are less likely to be within the channel they're using), it also means that the &lt;em&gt;severity&lt;/em&gt; of the interference is worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, anyone using FM two-way radios (“walkie-talkies”) for communications on the same frequency you're using would be unable to communicate if their signal power is not higher than yours — they would hear only silence. Other modes will display different effects, but there will always be interference.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I don't know for sure whether it is legal to operate a radar in amateur bands at all (since it is not a transmission for &lt;em&gt;communications&lt;/em&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If it is&lt;/strong&gt;, then using an amateur band is actually a better choice than any other portion of the radio spectrum. This is because amateurs are prepared to change frequencies if needed to avoid other users, whereas most other radio services use fixed frequencies. And for this purpose, your narrow bandwidth is advantageous.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you &lt;em&gt;will&lt;/em&gt; need to modulate your signal, because except in the case of radio-control transmissions (model airplanes and cars), you are required to &lt;em&gt;identify yourself&lt;/em&gt; within the transmission. This identification can simply consist of CW / Morse code, i.e. periodically interrupting the signal in a specific pattern.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-07-24T20:11:53.733" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6458" PostTypeId="2" ParentId="6455" CreationDate="2016-07-25T00:47:11.640" Score="4" Body="&lt;p&gt;An amateur &quot;ham&quot; radio license in the US will not allow the kind of transmission you are attempting to do.  Therefore, amateur radio is not your solution path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC regulations &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#47:5.0.1.1.6.1.157.1&quot; rel=&quot;nofollow&quot;&gt;part 97&lt;/a&gt; that covers the Amateur Radio Service dictates precisely the types of transmissions that can be made.  In particular, the purpose is maintain two-way communications between two stations.  At least one station must be a licensed amateur radio station and if the other station is not a licensed amateur radio station then it must fit into a very small category such as special MARS (Military Affiliated Radio Service) station, or possibly a licensed but non-amateur emergency services station where the amateur station is participating in emergency services communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your desired transmission is called one-way in FCC Part 97 regulations and the only valid one-way communications allowed are each explicitly dictated by the regulations.  Operating a ground penetrating RADAR unit is not one of them.  These legal one-way transmissions are allowed for a variety of reasons such as:  brief test signals, transmissions designed to raise a responding licensed station, and a few other reasons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The full detailed list of the legal and and restricted (illegal) transmissions made by an licensed amateur station are covered in paragraphs:  97.111 &quot;Authorized Transmissions&quot;; 97.113 &quot;Prohibited Transmissions&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other specialized one-way transmissions include beacon stations outlined by paragraph 97.203; and a space station 97.207; a space telecommand station as described in 97.211; telecommand of model craft 97.217; and telemetry as described in 97.219.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other than these sections I list here, there is other language such as the opening paragraphs, of FCC 97 that do not allow the type of transmissions you describe for a ground penetrating RADAR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, having said all this about amateur radio regulations, it is possible to obtain a special license for short-term usage of some band of frequencies for scientific experiment usage.  This would be by request to the FCC but I expect the format and content to be specific to the precise needs of the experiment, duration, and so forth.  Definitely not something for some general usage application.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-07-25T00:47:11.640" CommentCount="13" ContentLicense="CC BY-SA 3.0" />
  <row Id="6459" PostTypeId="1" CreationDate="2016-07-25T01:56:06.283" Score="1" ViewCount="54" Body="&lt;p&gt;Can two identical yagi antennas be linked together to improve a cell phone signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea is to put one antenna on the rooftop and the other in the house, and connect the two with feedline but no amplifier. If the rooftop antenna is pointed to the tower and you use the cell phone while in front of the antenna that is in the house, will this provide a signal advantage for duplex and solve the common problem of low signal strength in a house?&lt;/p&gt;&#xA;" OwnerUserId="8053" LastEditorUserId="29" LastEditDate="2016-07-25T19:04:36.870" LastActivityDate="2016-07-25T19:04:36.870" Title="Can two directional antennas be connected without an amplifier to improve reception?" Tags="&lt;propagation&gt;&lt;repeater&gt;&lt;antenna-system&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2016-07-25T20:06:06.347" ContentLicense="CC BY-SA 3.0" />
  <row Id="6462" PostTypeId="1" CreationDate="2016-07-25T07:57:12.337" Score="3" ViewCount="1833" Body="&lt;p&gt;Can someone explain how can get the Lat/Lon of a given Grid square? (the middle of the grid would be the best).&#xA;I've looked at this (that does the &quot;reverse&quot;...from lat/lo to grid&quot;):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/221/how-can-one-convert-from-lat-long-to-grid-square&quot;&gt;How can one convert from Lat/Long to Grid Square?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But i need to do the inverse...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone can explain in step by step?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many thanks!&lt;/p&gt;&#xA;" OwnerUserId="8055" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-03-13T02:35:36.720" Title="How can one convert from Grid Square to Lat/Long?" Tags="&lt;location&gt;&lt;maidenhead-locator&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6463" PostTypeId="1" CreationDate="2016-07-26T05:21:17.360" Score="9" ViewCount="1738" Body="&lt;p&gt;In discussing HF ionospheric propagation, you hear about both &quot;critical&quot; and &quot;maximum usable&quot; frequencies. For example:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Above the critical frequency, the ionosphere is unable to refract the signal back to Earth and it escapes to space. The critical frequency during the day is in the neighborhood of 6m: depending on the space weather, 6m way work for skywave, or it may not.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(from &lt;a href=&quot;https://ham.stackexchange.com/a/1757/1362&quot;&gt;https://ham.stackexchange.com/a/1757/1362&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've found maps for both &lt;a href=&quot;http://www.spacew.com/www/fof2.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;F2-Layer Critical Frequency&lt;/a&gt; and &lt;a href=&quot;http://www.spacew.com/www/realtime.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Maximum Usable Frequency&lt;/a&gt;, and they're quite different — the Maximum Usable Frequency map seems much more &quot;optimistic&quot;, that is, the frequencies are much higher at any given location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's the difference between the two measures?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-07-26T19:36:07.383" Title="What's the difference between &quot;maximum usable&quot; and &quot;critical&quot; frequencies?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;map&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6464" PostTypeId="2" ParentId="6463" CreationDate="2016-07-26T05:21:17.360" Score="7" Body="&lt;p&gt;The maps are related, but as &lt;a href=&quot;http://lists.contesting.com/archives/html/Propagation/2004-10/msg00012.html&quot;&gt;this excellent posting&lt;/a&gt; describes:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The 'critical frequency' is the highest frequency that gets reflected&#xA;  when it is aimed straight up at the ionosphere. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;However:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;…as the angle decreases from vertical the reflected frequency increases.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;And so therefore:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;MUF or MOF is a path dependent value.  It depends not only on the state&#xA;  of the ionosphere but also the path between the end points. […] What you may see for a MUF map is what is often called M3000, or some similar value which is the MUF calculated using a single 3000km hop with that point as the center.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So basically, the critical frequency &lt;em&gt;is&lt;/em&gt; the most pessimistic because it's showing what signals will reflect in the very &quot;worst case&quot; (i.e. straight up) above each particular location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The maximum usable frequency would be estimated based on the expected path the signal would take between two points, and could be significantly better if the expected angle of incidence is more oblique.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-07-26T05:21:17.360" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6465" PostTypeId="2" ParentId="6462" CreationDate="2016-07-26T07:52:03.307" Score="1" Body="&lt;p&gt;if by &quot;Grid&quot; you mean &quot;Maidenhead Locator&quot; then here is a similar &lt;a href=&quot;https://ham.stackexchange.com/questions/6114/convert-maidenhead-to-lat-long-in-excel/&quot;&gt;question&lt;/a&gt;, with some sample Python code as answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The result from the code will be&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Lon = (start_lon) to (end_lon)&#xA;Lat = (start_lat) to (end_lat)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;From that you can easily calculate the &quot;middle&quot; of the square.&#xA;or you can take the code and adapt, here is the code from the above mentioned question/answer:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;# -*- coding: utf-8 -*-&#xA;#maiden head to lon/lat&#xA;&#xA;__MH__ = 'HK34wh'&#xA;&#xA;def GetLon(ONE, THREE, FIVE):&#xA;    StrStartLon = ''&#xA;    StrEndLon = ''&#xA;&#xA;    Field = ((ord(ONE.lower()) - 97) * 20) &#xA;    Square = int(THREE) * 2&#xA;    SubSquareLow = (ord(FIVE.lower()) - 97) * (2/24)&#xA;    SubSquareHigh = SubSquareLow + (2/24)&#xA;&#xA;    StrStartLon = str(Field + Square + SubSquareLow - 180 )&#xA;    StrEndLon = str(Field + Square + SubSquareHigh - 180 )&#xA;&#xA;    return StrStartLon, StrEndLon&#xA;&#xA;def GetLat(TWO, FOUR, SIX):&#xA;    StrStartLat = ''&#xA;    StrEndLat = ''&#xA;&#xA;    Field = ((ord(TWO.lower()) - 97) * 10) &#xA;    Square = int(FOUR)&#xA;    SubSquareLow = (ord(SIX.lower()) - 97) * (1/24)&#xA;    SubSquareHigh = SubSquareLow + (1/24)&#xA;&#xA;    StrStartLat = str(Field + Square + SubSquareLow - 90)&#xA;    StrEndLat = str(Field + Square + SubSquareHigh - 90)    &#xA;&#xA;    return StrStartLat, StrEndLat&#xA;&#xA;def main(strMaidenHead = __MH__):&#xA;    if len(strMaidenHead) &amp;lt; 6: strMaidenHead = __MH__&#xA;&#xA;    ONE = strMaidenHead[0:1]&#xA;    TWO = strMaidenHead[1:2]&#xA;    THREE = strMaidenHead[2:3]&#xA;    FOUR = strMaidenHead[3:4]&#xA;    FIVE = strMaidenHead[4:5]&#xA;    SIX = strMaidenHead[5:6]&#xA;&#xA;    (strStartLon, strEndLon) = GetLon(ONE, THREE, FIVE)&#xA;    (strStartLat, strEndLat) = GetLat(TWO, FOUR, SIX)&#xA;&#xA;    print ('Start Lon = ' + strStartLon)&#xA;    print ('End   Lon = ' + strEndLon)&#xA;    print ()&#xA;    print ('Start Lat = ' + strStartLat)&#xA;    print ('End   Lat = ' + strEndLat)&#xA;&#xA;    return strStartLon, strEndLon, strStartLat, strEndLat&#xA;&#xA;#BEGIN&#xA;if __name__ == '__main__':&#xA;    main ()&#xA;    sys.exit ('end of script: '+ os.path.basename(__file__) + os.linesep + 'by: Edwin van Mierlo')&#xA;#END&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;(for the purists amongst you, no; this is not very 'pythonic', but it does work)&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-07-26T07:52:03.307" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6466" PostTypeId="2" ParentId="6455" CreationDate="2016-07-26T08:15:13.230" Score="0" Body="&lt;p&gt;Let me word this differently:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do NOT have a license, you may NOT transmit and &quot;radar&quot; signal.&#xA;(full stop, no exceptions)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even when you do this in &quot;license free&quot; frequencies/bands. These bands and frequencies, while excempt from license requirements, are still allocated, and only for use for certain services and type-approved-equipment. Which does not cover what you are asking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you have a license, then you are bound by the terms of the license. And for your question; this will be a very specific license. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;IANAL: I do not believe that a Amateur (HAM) Radio license includes permission for transmissions as you describe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In regards to other very valid answers given. Most answers (and comments) refer to &quot;allocations&quot; in the frequency spectrum. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Lets be very clear&lt;/strong&gt;: EVERY FREQUENCY IS ALLOCATED in some form or other; there are NO &quot;free bands&quot; ! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;.... exception below 9KHz, which is in the VLF spectrum, good luck with your radar signal there. Even at that; you are still bound to rules and regulations from local/federal authorities !&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;so, the answer is: sorry, but no.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-07-26T08:15:13.230" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6468" PostTypeId="5" CreationDate="2016-07-27T17:01:28.383" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2016-07-27T17:01:28.383" LastActivityDate="2016-07-27T17:01:28.383" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6469" PostTypeId="4" CreationDate="2016-07-27T17:01:28.383" Score="0" Body="The Maidenhead locator system allows expressing a latitude and longitude as a compact series of letters and numbers, and was adopted in 1980. A Maidenhead locator is typically expressed as two or three groups of two characters each; if higher precision is required, four groups of two characters each can be used. Groups alternate between letters and numbers; for example BL (field), BL11 (square), BL11BH (subsquare), or BL11BH16 (extended square)." OwnerUserId="29" LastEditorUserId="29" LastEditDate="2016-08-02T14:01:22.190" LastActivityDate="2016-08-02T14:01:22.190" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6471" PostTypeId="1" AcceptedAnswerId="6492" CreationDate="2016-07-28T07:01:51.883" Score="13" ViewCount="39680" Body="&lt;p&gt;If a transceiver such as the BaoFeng UV-5R is used to transmit over FRS/GMRS frequencies (unlicensed), it is illegal in the United States due to FCC regulations that state that the power must be &amp;lt;0.5W and that the radio must not have a detachable antenna (the UV-5R is rated up to 5W and has a detachable antenna). Realistically, though, I am wondering if and how the FCC actually enforces this? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, if two people decided to use these as high power &quot;walkie talkies&quot;, and were careful to select unused frequencies, didn't disrupt other peoples' communications, didn't communicate from home/work (i.e. a static location that identified the person transmitting), and changed frequencies regularly, my questions are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) I understand the law, but is it actually enforced? Do they even waste resources trying to catch people doing this if there is no disruption occuring? Are there any documented cases of the FCC actually tracking down and harassing/fining/jailing people for illegal FRS/GMRS transmissions of this sort? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) How would the FCC actually track down this sort of sporadic, non-disruptive transmission from multiple locations? I understand the concept of triangulation of radio signals, but how is this actually achieved on a nationwide scale and in a way that can promptly lead them to the location of the transmission (so that they can fine/arrest someone)? Are there passive monitoring systems in place in urban areas that can automatically/instantly detect illegal transmissions? Black helicopters with FCC agents flying around hunting for illegal walkie-talkie usage? etc :) What does their tracking technology actually look like nowadays, and what kind of capabilities does it have that would enable tracking this type of transmission?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) Are there any sorts of identifying signals (some sort of unique identifier) that handheld transceivers such as these emit while transmitting, that allow for the instant identification of the device? (i.e. something akin to an IMEI # for cell phones)&lt;/p&gt;&#xA;" OwnerUserId="8074" LastEditorUserId="9844" LastEditDate="2018-02-09T13:27:20.973" LastActivityDate="2018-02-25T23:00:55.930" Title="FCC tracking of unlicensed FRS/GMRS transmissions" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;&lt;frs&gt;" AnswerCount="4" CommentCount="8" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6472" PostTypeId="1" CreationDate="2016-07-28T13:03:25.173" Score="1" ViewCount="91" Body="&lt;p&gt;I got my license 25 years ago. I bought a 2-meter ham radio from Radio Shack ($200). I am thinking about renew my license and re-start this hobby. To my surprise, local Radio Shacks no longer carry ham radios. Where do you guys buy them? What brand is good? After 25 years, the price must have come down. I am in Chicago area.&lt;/p&gt;&#xA;" OwnerUserId="8076" LastActivityDate="2016-07-28T13:03:25.173" Title="Where to buy 2 meter ham radio" Tags="&lt;license&gt;" AnswerCount="0" CommentCount="2" FavoriteCount="1" ClosedDate="2016-07-28T14:12:11.623" ContentLicense="CC BY-SA 3.0" />
  <row Id="6473" PostTypeId="1" AcceptedAnswerId="6476" CreationDate="2016-07-28T14:16:54.540" Score="6" ViewCount="548" Body="&lt;p&gt;I have read myself blue, about baluns. Especially 1:1 ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some claim they're only there to balance the unbalanced signal, and that's what's in the name also, but I find several that claims that the main thing at the point of a balun is common mode current attenuation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And from where I stand I agree with both, because both are logical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, when I Google around for baluns I find recipes for ones that do one or the other, never any that do both. Why?&lt;/p&gt;&#xA;" OwnerUserId="6504" LastEditorUserId="29" LastEditDate="2016-07-28T14:48:03.093" LastActivityDate="2016-07-31T13:58:51.720" Title="Why aren't there baluns that do BOTH balanced/unbalanced transformation and common mode current attenuation?" Tags="&lt;balun&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6474" PostTypeId="1" CreationDate="2016-07-28T14:25:54.010" Score="1" ViewCount="1462" Body="&lt;p&gt;End goal: Play about with RTL-SDR in GNURadio Companion&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While following the instructions on &lt;a href=&quot;http://sdr.osmocom.org/trac/wiki/rtl-sdr&quot; rel=&quot;nofollow&quot;&gt;this page&lt;/a&gt;, I've run into errors concerning the Boost C++ libraries. While building the gr-osmosdr blocks to use in GNURadio, cmake fails to complete because it cannot find Boost which is definately installed. Version 1.57.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Last metadata expiration check performed 1:27:21 ago on Thu Jul 28 15:01:40 2016.&#xA;Package boost-1.57.0-6.fc22.x86_64 is already installed, skipping.&#xA;Dependencies resolved.&#xA;Nothing to do.&#xA;Complete!&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Specifically, the error message I receive looks like...&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-- Detecting C compile features - done&#xA;-- Build type not specified: defaulting to release.&#xA;-- Found Git: /usr/bin/git (found version &quot;2.4.11&quot;) &#xA;-- Extracting version information from git describe...&#xA;-- Configuring Boost C++ Libraries...&#xA;-- Could NOT find Boost&#xA;CMake Error at CMakeLists.txt:125 (message):&#xA;  Boost required to build gr-osmosdr&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The code in CMakeLists.txt concerning Boost is...&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;########################################################################&#xA;# Setup boost&#xA;########################################################################&#xA;MESSAGE(STATUS &quot;Configuring Boost C++ Libraries...&quot;)&#xA;&#xA;# Although not required on my system, some users have linking issues without&#xA;SET(BOOST_REQUIRED_COMPONENTS&#xA;    thread&#xA;    system&#xA;)&#xA;&#xA;if(UNIX AND NOT BOOST_ROOT AND EXISTS &quot;/usr/lib64&quot;)&#xA;    list(APPEND BOOST_LIBRARYDIR &quot;/usr/lib64&quot;) #fedora 64-bit fix&#xA;endif(UNIX AND NOT BOOST_ROOT AND EXISTS &quot;/usr/lib64&quot;)&#xA;&#xA;set(Boost_ADDITIONAL_VERSIONS&#xA;    &quot;1.35.0&quot; &quot;1.35&quot; &quot;1.36.0&quot; &quot;1.36&quot; &quot;1.37.0&quot; &quot;1.37&quot; &quot;1.38.0&quot; &quot;1.38&quot; &quot;1.39.0&quot; &quot;1.39&quot;&#xA;    &quot;1.40.0&quot; &quot;1.40&quot; &quot;1.41.0&quot; &quot;1.41&quot; &quot;1.42.0&quot; &quot;1.42&quot; &quot;1.43.0&quot; &quot;1.43&quot; &quot;1.44.0&quot; &quot;1.44&quot;&#xA;    &quot;1.45.0&quot; &quot;1.45&quot; &quot;1.46.0&quot; &quot;1.46&quot; &quot;1.47.0&quot; &quot;1.47&quot; &quot;1.48.0&quot; &quot;1.48&quot; &quot;1.49.0&quot; &quot;1.49&quot;&#xA;    &quot;1.50.0&quot; &quot;1.50&quot; &quot;1.51.0&quot; &quot;1.51&quot; &quot;1.52.0&quot; &quot;1.52&quot; &quot;1.53.0&quot; &quot;1.53&quot; &quot;1.54.0&quot; &quot;1.54&quot;&#xA;    &quot;1.55.0&quot; &quot;1.55&quot; &quot;1.56.0&quot; &quot;1.56&quot; &quot;1.57.0&quot; &quot;1.57&quot; &quot;1.58.0&quot; &quot;1.58&quot; &quot;1.59.0&quot; &quot;1.59&quot;&#xA;    &quot;1.60.0&quot; &quot;1.60&quot; &quot;1.61.0&quot; &quot;1.61&quot; &quot;1.62.0&quot; &quot;1.62&quot; &quot;1.63.0&quot; &quot;1.63&quot; &quot;1.64.0&quot; &quot;1.64&quot;&#xA;    &quot;1.65.0&quot; &quot;1.65&quot; &quot;1.66.0&quot; &quot;1.66&quot; &quot;1.67.0&quot; &quot;1.67&quot; &quot;1.68.0&quot; &quot;1.68&quot; &quot;1.69.0&quot; &quot;1.69&quot;&#xA;)&#xA;&#xA;find_package(Boost COMPONENTS ${BOOST_REQUIRED_COMPONENTS})&#xA;&#xA;if(NOT Boost_FOUND)&#xA;    message(FATAL_ERROR &quot;Boost required to build &quot; ${CMAKE_PROJECT_NAME})&#xA;endif()&#xA;&#xA;ADD_DEFINITIONS(-DBOOST_ALL_DYN_LINK)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Probably just have to point one thing to another. But I don't know which to what.&lt;/p&gt;&#xA;" OwnerUserId="8075" LastActivityDate="2016-07-29T11:13:12.560" Title="gr-osomosdr Could NOT find Boost (C++ libraries)" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6475" PostTypeId="2" ParentId="6471" CreationDate="2016-07-28T19:39:34.557" Score="-1" Body="&lt;p&gt;There are ways to track radio transmissions, however, due to  low power output of hand held devices they would have to be relatively close to track you. I think generally if you aren't causing any interference (using 5 watts or less, not stepping on other peoples transmissions or using unauthorized frequencies) the men in black suits would leave you alone.&lt;/p&gt;&#xA;" OwnerUserId="8077" LastActivityDate="2016-07-28T19:39:34.557" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6476" PostTypeId="2" ParentId="6473" CreationDate="2016-07-28T20:54:23.613" Score="5" Body="&lt;p&gt;There are. I suspect you're confusing a couple of different things when it comes to balance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common mode current is current which appears to flow on both conductors in the feed line with the same polarity and magnitude. If you put RF in to an ideal coax and from an ideal source, the current on the center conductor is precisely equal in magnitude and opposite in phase to the current flowing on the &lt;em&gt;inside&lt;/em&gt; of the coax shield. No current should flow on the exterior of the coax shield at all, and the fields of the current on the two conductors on the inside of the coax cancel, resulting in zero radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any current that does flow on the exterior of the coax shield has no opposing current, as there's no closely coupled conductor for it to induce that opposite current on as there is for the center conductor and the inside of the shield. There is no counteracting field to cancel it, so it can radiate freely. In the case of a received signal and an ungrounded radio, you can imagine that this unopposed signal would cause the entire radio to &quot;float&quot; at the common mode voltage, essentially the signal would enter the receiver through the ground plane of the radio's circuits. This makes it very difficult to filter once it reaches the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a transmitted signal, the exterior of the coax shield appears to be a radiating element or a ground radial, depending on the exact nature of the installation. This is most often the cause of &quot;RF in the shack&quot;. The exterior of the coax is radiating in very close proximity to sensitive electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common mode on balanced line is just the same. It is some voltage that appears to travel on both conductors equally, not opposite in phase as it should be, and the same problems arise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common mode can arise either because of a difference in magnitude between the two conductors in a feed line, or difference in phase between the two. Let's consider an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a symmetrical dipole with perfect balance, fed with ladder line, we know that the voltage on one feed line conductor will be precisely equal in magnitude and opposite in phase to the other. If we were to measure voltage on a single conductor relative to ground at an arbitrary instant in time and point on the ladder line and saw a potential of +100 volts, we would expect to check the spot on the other conductor at the same point in time and place on the ladder line and see -100 volts. Measured relative to each other, the voltage would be 200 volts peak to peak.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now let's pass our ladder line by a big chunk of grounded metal, but let's say that one of the ladder line conductors was much closer to that metal than the other. More power would be coupled out of the conductor that came closer to the metal than the one that was further away. If we measured voltage at some point between the radio and that grounded metal, perhaps now we would see only +75 volts relative to ground on the one that came close to the metal, and still -100 volts on the conductor that was further away. We now have a common mode voltage of -25 volts between the conductors. The field of the wire with lower voltage doesn't have a strong enough field to cancel the entire field from the other conductor, so there is now &quot;excess&quot; field, the feed line can radiate, and if the radio is not well grounded, it will appear to float at -25 volts. This is how RF burns from microphones happen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ok, so now we've got a good picture of common mode and what it is. What do baluns do about it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two basic forms of balun, and it is important not to confuse them: Chokes, and transformers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transformers are less common. They work through magnetic coupling and generally have &lt;strong&gt;isolated windings&lt;/strong&gt;. This means there are separate primary and secondary windings, and no direct path for DC between the two. Any transfer of current between them is via coupling, usually through a core of some kind. Transformers are good for very high efficiency impedance transformation because the cores are very low loss at the frequency you're using, and they're usually designed to resonate at a given frequency. When the differential mode and common mode current meet in the primary, they are essentially added together, resulting in a wave that is once again &quot;clean&quot; and balanced, but with the magnitude of the wave altered by the constructive and destructive interference of the two signals being combined. This is what is meant when it is said that balance is &quot;forced&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When properly designed and installed, &lt;strong&gt;they do provide common mode suppression&lt;/strong&gt;, but at a price. They are generally narrow banded, working best on only a couple of bands. Outside of their resonant window, there is substantial reactance that will make them inefficient and cause SWR issues. They also tend to be more expensive, as the low loss core material is more expensive to make, and it must be physically large because it will carry 100% of the total current between the windings. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can make them wide banded, but only by sacrificing the common mode suppression, as you won't have isolated windings. These are often called &quot;ununs&quot; though that's a terrible term IMO because it implies that it still does...something...with regards to choking or the like. They are, in fact, only impedance transformers (Put a good choke on your EARCHI at the feed point with no radials and it won't tune at all).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second kind of balun, a choke, is much more common and provides both balance and excellent common mode attenuation over a wide frequency range. The trade off is efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Choke baluns work by inducing the current of both conductors on to a single core at the same time. We know that the current is equal and opposite ideally, so if they are wrapped around a toroid side by side, in the same direction, the field they induce on the toroid will also be equal and opposite. This means it will cancel and there will be no net magnetic field in the core. This means that if the system is perfectly balanced, zero current will flow in the toroid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the system is unbalanced, the field of one conductor &quot;wins&quot;, and induces some current on the toroid. This current then has to travel through the toroid between the two conductors. If we use very lossy core material, this current will be turned to heat and disappear from the feed line. Since that induced field is equal to the difference in field strength between the two windings, the signal will once again be balanced when it leaves the balun, though at a loss equal to the ratio of common mode current to differntial mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem with chokes is that heat. If the system is badly unbalanced, considerable heat can be generated by the toroid, and because they aren't particularly efficient shapes or materials for radiating that heat, it can accumulate to a problematic level with only 15 or 20 watts of common mode loss in a large toroid. You can get around this by using several toroids and fewer turns around them, spreading the power dissipation between several toroids, but this gets big, heavy, and potentially pretty expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By using a combination of series and parallel 1:1 chokes, you can accomplish impedance transformation efficiently (assuming reasonable balance in the first place). The fact that they are non-resonant and actually utilize loss rather than avoiding it to the greatest degree possible makes them very wide banded.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;TL;DR&lt;/strong&gt; There is no effective difference between attaining balance and eliminating common mode, but there are two different ways to accomplish balance that are easily described as &quot;transformers&quot; and &quot;chokes&quot;.&lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="246" LastEditDate="2016-07-28T21:03:34.320" LastActivityDate="2016-07-28T21:03:34.320" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6477" PostTypeId="2" ParentId="6474" CreationDate="2016-07-29T11:13:12.560" Score="4" Body="&lt;p&gt;Thanks to @Marcus Müller. It seemed in this instance it was the lack of the devel packages for boost. A simple...&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;$ sudo dnf install boost-devel&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;...did the trick (Well, I mean it moved me on to the next failure).&lt;/p&gt;&#xA;" OwnerUserId="8075" LastActivityDate="2016-07-29T11:13:12.560" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6478" PostTypeId="1" CreationDate="2016-07-29T12:30:21.800" Score="3" ViewCount="694" Body="&lt;p&gt;I'm finally getting to the point of hopefully putting up a HF antenna. The idea is to start with a simple, straight wire dipole using trees as support points. (No traps or coils.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, with the layout of my property and the location of the trees thereon, putting up a fully balanced antenna might be difficult.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not aiming for an antenna that is resonant on any particular frequency to begin with, so will be using an ATU in any case. I'm also going to be operating on most of the HF bands, so the feedline will essentially be random length at least on &lt;em&gt;some&lt;/em&gt; relevant frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm aiming more for local-ish contacts than DX; with what I'm planning to do right now I won't really be able to get the antenna up high enough to get the takeoff angle down far enough for DX anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The general idea for station setup is to have the transceiver, then 50 ohm coax to the ATU (which in turn is just inside the window, and which has a built-in 4:1 balun), then attached to its binding posts balanced ladder line (through the window) which eventually splits into the two legs of the antenna to actually radiate the signal. There will also be a bleeder resistor somewhere along the length of feedline, to help reduce the buildup of static, and a physical/electrical disconnection point between the bleeder resistor and where the feedline enters the house (allowing for true electrical disconnection of the antenna when I'm not on the radio). I'm aware of the need to keep balanced ladder line away from other conductors that it could parasitically couple to (as e.g. &lt;a href=&quot;https://ham.stackexchange.com/a/6476/29&quot; title=&quot;Why aren&amp;#39;t there baluns that do BOTH balanced/unbalanced transformation and common mode current attenuation?&quot;&gt;Hamsterdave illustrated just recently&lt;/a&gt;, though perhaps not quite as extreme).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With such a setup, &lt;strong&gt;which approach is &lt;em&gt;likely&lt;/em&gt; to lead to better operating results, as well as less problems with RFI and friends?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;As much antenna wire in the air as possible, disregarding the relative feedpoint, &lt;em&gt;possibly&lt;/em&gt; leading to an off-center-fed antenna?&lt;/li&gt;&#xA;&lt;li&gt;Keeping the antenna as balanced as possible, even if this means less wire in the air?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Bonus if answers also touch on how the choice is likely to impact antenna tuning (it'd be nice if I don't have to retune every 10 kHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ambient HF noise level, as far as I have been able to determine by completely unscientific testing, is quite low, and I'd love to be able to make the most of that.&lt;/p&gt;&#xA;" OwnerUserId="29" LastEditorUserId="29" LastEditDate="2016-07-29T19:47:56.023" LastActivityDate="2016-07-30T16:02:27.673" Title="Which is better in my situation: Balanced dipole, or as much wire as possible in the air?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;feed-line&gt;&lt;antenna-system&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6479" PostTypeId="2" ParentId="6478" CreationDate="2016-07-29T17:12:46.870" Score="0" Body="&lt;p&gt;I haven't been in your exact situation, but I have friends who have, and I would suggest that the answer is &lt;em&gt;it depends&lt;/em&gt;.  There are many variables involved.  One important variable is the quality of your balun.  Another is the kind of contacts that you'd like to make: local, DX, or both?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's certainly nothing wrong with asking here for suggestions, but a big part of the traditional amateur radio experience is experimenting with antennas to see what works best for you.  I suggest that you put up a dipole (it would actually be a doublet if you don't plan on using it only near its resonant frequency), or an unbalanced doublet, in such a way that you can easily add or remove wire later.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Upon reflection I'll venture an opinion: I would say that the antenna being slightly unbalanced, with the feed point somewhere in the middle third of the antenna, would be unlikely to cause you problems.  Many people run antennas more unbalanced than that, but then the balun becomes more critical, so I wouldn't recommend a more unbalanced antenna for starters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also suggest that you pay attention to mechanical details.  Most importantly, try to keep the ladder line as far away from metal as possible.  You'll want to put up your antenna so that you can easily bring it down temporarily and put it up again; perhaps have the ends of the antenna attached to halyards, i.e. ropes attached to pulleys.  Some sort of strain relief so that the wire doesn't get snapped in a storm would be a good idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think you'll enjoy the process of experimentation much more than just accepting someone else's idea of what antenna would be best.  Have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-07-29T17:12:46.870" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6480" PostTypeId="2" ParentId="6478" CreationDate="2016-07-29T20:29:00.180" Score="3" Body="&lt;p&gt;I think in practice you'll find it doesn't make much difference as long as there's a common mode choke or &quot;current balun&lt;sup&gt;1&lt;/sup&gt;&quot; at the feedpoint. In fact, &lt;a href=&quot;http://www.w8ji.com/windom_off_center_fed.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;if you get it off-center in just the right place&lt;/a&gt; you can get an impedance around 200 ohms on several bands. Even though you'll be using an ATU, there's a limit to how much mismatch they can tune out, and feedline losses go down with decreasing SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the feedline isn't in the middle of the dipole, the impedance between the common mode of the feedline and the two legs of the dipole are unequal, so you end up with common-mode currents on the feedline. This isn't much different from the situation with a coax feedline. Just use a choke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The balun in the ATU does take care of interfacing with the ladder line, but it doesn't do anything about the feed arrangement: you still need a choke up there if you want to prevent common-mode current on the feedline, thus effectively making the feedline part of the antenna. At 100W or less you'll probably not get any RF burns, but it does mean your antenna is within a few feet of noisy electronics like computer monitors and switching power supplies in your shack. Not the best for receive performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A couple more points of note:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the intention in disconnecting your antenna is to protect from lightning damage, you'll need more than a little gap in a switch to do it. See &lt;a href=&quot;http://www.w8ji.com/ground_systems.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI on grounding systems&lt;/a&gt; (The &quot;Isolating or Disconnecting feed lines&quot; section in particular) and &lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your antenna setup is not going to have any effect on RFI with your neighbors except to the extent that you radiate less energy (not usually desirable in an antenna), put it farther from the neighbors, or direct the radiation pattern away from them. Feeding the dipole in the center or not will make no difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have a 1/2 wavelength of wire in the air, more isn't really a benefit.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt; or is it a balbal in this case? Or a unbal? Amateur terminology is so confusing.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-07-29T23:07:21.527" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6481" PostTypeId="1" AcceptedAnswerId="6485" CreationDate="2016-07-30T03:14:10.653" Score="2" ViewCount="6069" Body="&lt;p&gt;Is there a way to calculate bandwidth of an classical dipole antenna having this information:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;center frequency&lt;/li&gt;&#xA;&lt;li&gt;wire velocity&lt;/li&gt;&#xA;&lt;li&gt;wire diameter&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I would disregard antenna height, to simplify.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not targeting high precision calculation, just rough but usable. I need this to be calculated, not measured.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-08-16T14:11:12.150" Title="Calculating bandwidth of antenna?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;bandwidth&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6482" PostTypeId="2" ParentId="6478" CreationDate="2016-07-30T03:39:22.893" Score="0" Body="&lt;p&gt;I would prefer balanced dipole. That would solve some issues by itself. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With unbalanced antenna you would have to use chokes to fix symptoms like RFI, but does not fix unbalanced behavior of antenna so it is better to avoid need to use them. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check &lt;a href=&quot;https://ham.stackexchange.com/questions/6473/why-arent-there-baluns-that-do-both-balanced-unbalanced-transformation-and-comm&quot;&gt;Why aren&amp;#39;t there baluns that do BOTH balanced/unbalanced transformation and common mode current attenuation?&lt;/a&gt; for some explanation about chokes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you plan is to use single antenna and ATU, then I guess using as much wire ass possible is more viable option (I still prefer balanced setup, or closed loop). You will have huge looses anyways so more wire will at least compensate, and radiate more efficiently energy that makes into it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As already suggested, it is possible you will not find solution in first strike. It needs experimentation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would suggest reconsidering idea of using single antenna and think of some kind of multiband antennas or combination, dipole for lower bands and vertical for higher bands.&lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-07-30T03:39:22.893" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6483" PostTypeId="2" ParentId="6481" CreationDate="2016-07-30T15:01:43.033" Score="-2" Body="&lt;p&gt;Bandwidth  of  an antenna  is the frequency range which the  antenna  can  operate  correctly.  The  antenna's  bandwidth  is  the  range in  Hz  that the  antenna  will  exhibit  an  SWR  &amp;lt; 2:1. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bandwidth  can  also  be  described  as  the  percentage  of  the center  frequency  of  the  band:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;BW=100*((FH−FL)/FC)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;(FH  is  the  highest  frequency  in  the  band,  FL  is  the  lowest frequency  in  the  band,  and  FC  is  the  center  frequency  in  the  band.)&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="8085" LastActivityDate="2016-07-30T15:01:43.033" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6485" PostTypeId="2" ParentId="6481" CreationDate="2016-07-30T17:01:37.797" Score="3" Body="&lt;p&gt;Assuming the antenna is in free space, you only need to know the length and diameter of the wire used to construct the dipole. The math is hairy but I wrote a program to do the calculations. Here is the SWR (assuming a 50 ohm source) and feedpoint impedance for a dipole 10 meters long, with a diameter of 2.053mm:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;14.100 MHz: SWR 2.07,  61.3 + j-39.6&#xA;14.130 MHz: SWR 1.98,  61.7 + j-36.8&#xA;14.160 MHz: SWR 1.89,  62.0 + j-34.0&#xA;14.190 MHz: SWR 1.81,  62.4 + j-31.3&#xA;14.220 MHz: SWR 1.73,  62.8 + j-28.5&#xA;14.250 MHz: SWR 1.66,  63.2 + j-25.7&#xA;14.280 MHz: SWR 1.60,  63.5 + j-23.0&#xA;14.310 MHz: SWR 1.54,  63.9 + j-20.2&#xA;14.340 MHz: SWR 1.48,  64.3 + j-17.4&#xA;14.370 MHz: SWR 1.44,  64.7 + j-14.7&#xA;14.400 MHz: SWR 1.40,  65.1 + j-11.9&#xA;14.430 MHz: SWR 1.37,  65.5 + j-9.1&#xA;14.460 MHz: SWR 1.35,  65.8 + j-6.4&#xA;14.490 MHz: SWR 1.33,  66.2 + j-3.6&#xA;14.520 MHz: SWR 1.33,  66.6 + j-0.9&#xA;14.550 MHz: SWR 1.34,  67.0 + j 1.9&#xA;14.580 MHz: SWR 1.36,  67.4 + j 4.7&#xA;14.610 MHz: SWR 1.39,  67.8 + j 7.4&#xA;14.640 MHz: SWR 1.43,  68.2 + j10.2&#xA;14.670 MHz: SWR 1.47,  68.6 + j13.0&#xA;14.700 MHz: SWR 1.52,  69.0 + j15.7&#xA;14.730 MHz: SWR 1.57,  69.4 + j18.5&#xA;14.760 MHz: SWR 1.63,  69.9 + j21.3&#xA;14.790 MHz: SWR 1.69,  70.3 + j24.1&#xA;14.820 MHz: SWR 1.75,  70.7 + j26.8&#xA;14.850 MHz: SWR 1.82,  71.1 + j29.6&#xA;14.880 MHz: SWR 1.89,  71.5 + j32.4&#xA;14.910 MHz: SWR 1.97,  71.9 + j35.1&#xA;14.940 MHz: SWR 2.05,  72.4 + j37.9&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;To calculate the bandwidth we must define what we mean by bandwidth. Let's define it as the range through which SWR is 2:1 or less. In that case, this antenna works from about 14.125 to 14.920 MHz, for a bandwidth of 795 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can express that as a fractional bandwidth:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;{14.125 - 14.920 \over (14.125 + 14.920) / 2} = 5.5\%&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll find that similar dipoles will have a similar fractional bandwidth. For example if I run the numbers for the same wire diameter but now 20 meters long, I find a fractional bandwidth of 5.0%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This decrease in bandwidth is due to the wire diameter being thinner relative to wavelength. A thicker dipole relative to wavelength will have more bandwidth than a thinner one. The bandwidth is actually quite sensitive to the conductor radius.&lt;sup&gt;*&lt;/sup&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if I make a dipole for the 2 meter band from 3/4 copper pipe, the fractional bandwidth goes up to 15% on account of the much smaller wavelength and the much thicker wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you need just a rough calculation, then an estimate of fractional bandwidth is sufficient. Just multiply the center frequency by the fractional bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the source for the program, if you want to do your own calculations:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;#!/usr/bin/python3&#xA;&#xA;from math import sin, cos, log&#xA;from scipy.special import sici&#xA;from scipy.constants import pi, c&#xA;&#xA;def sin2(t):&#xA;    return sin(t)**2&#xA;&#xA;def ci(t):&#xA;    '''cosine integral'''&#xA;    return sici(t)[1]&#xA;&#xA;def si(t):&#xA;    '''sine integral'''&#xA;    return sici(t)[0]&#xA;&#xA;# euler constant&#xA;gamma = 0.577215664901532&#xA;&#xA;# impedance of free space&#xA;Z0 = 376.73031&#xA;&#xA;def R(f, L, a):&#xA;    k = 2*pi*f/c&#xA;&#xA;    return Z0 / (2*pi*sin2(k*L/2)) * (&#xA;        gamma&#xA;        + log(k*L)&#xA;        - ci(k*L)&#xA;        + .5 * sin(k*L) * (&#xA;            si(2*k*L)&#xA;            -2*si(k*L)&#xA;        )&#xA;        + .5 * cos(k*L) * (&#xA;            gamma&#xA;            + log(k*L/2)&#xA;            + ci(2*k*L)&#xA;            - 2*ci(k*L)&#xA;        )&#xA;    )&#xA;&#xA;&#xA;def X(f, L, a):&#xA;    k = 2*pi*f/c&#xA;&#xA;    return Z0 / (4*pi*sin2(k*L/2)) * (&#xA;        2*si(k*L)&#xA;        + cos(k*L) * (&#xA;            2*si(k*L)&#xA;            - si(2*k*L)&#xA;        )&#xA;        -sin(k*L) * (&#xA;            2*ci(k*L)&#xA;            - ci(2*k*L)&#xA;            - ci(2*k*a**2/L)&#xA;        )&#xA;    )&#xA;&#xA;&#xA;def Z(f, L, a):&#xA;    return complex(R(f, L, a), X(f, L, a))&#xA;&#xA;&#xA;def SWR(Z_l, Z_s):&#xA;    reflection_coef = (Z_l - Z_s) / (Z_l + Z_s)&#xA;    return (1 + abs(reflection_coef)) / (1 - abs(reflection_coef))&#xA;&#xA;&#xA;# in Hz&#xA;f_lower = 137e6&#xA;f_upper = 155e6&#xA;step = 750e3&#xA;&#xA;# in meters&#xA;length = 0.942&#xA;diameter = 19.05e-3&#xA;&#xA;# in ohms&#xA;source = complex(50)&#xA;&#xA;f = f_lower&#xA;while f &amp;lt; f_upper:&#xA;    load = Z(f, length, diameter)&#xA;    print('    %6.3f MHz: SWR %4.2f, %5.1f + j%4.1f' % (f/1e6, SWR(load, source), load.real, load.imag))&#xA;    f += step&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;*&lt;/sup&gt; Note how $a$ appears only in the $\mathrm{Ci}(2ka^2/L)$ term, and the cosine integral function asymptotically approaches $-\infty$ at 0.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-08-16T14:11:12.150" LastActivityDate="2016-08-16T14:11:12.150" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6486" PostTypeId="2" ParentId="6481" CreationDate="2016-07-30T19:04:25.117" Score="0" Body="&lt;p&gt;I have used NEC4 to model the antenna parameters used by Phil Frost in his answers.  I am doing this primarily for my own curiosity to see how close or far apart his answers from his algorithm are from the NEC4 modeling of the same antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna being modeled is a center fed dipole, 10-meters total length, with #12 copper wire.  The only difference between the previous answer and mine is that Phil Frost used 3 mm for the diameter of the #12 wire and I am using 2.053 mm which is a value I get from this web-site: &lt;a href=&quot;https://en.wikipedia.org/wiki/American_wire_gauge&quot; rel=&quot;nofollow noreferrer&quot;&gt;American Wire Gauge&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My first run is for a FREE-SPACE solution and the only thing I am showing at this time is the computed SWR plot.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MmDCO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MmDCO.jpg&quot; alt=&quot;20 meter dipole SWR&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The plot is generated from Mathematica using the following procedure:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Run NEC4 on input data to produce solution output file.&lt;/li&gt;&#xA;&lt;li&gt;Scrape output file to produce curated data file.&lt;/li&gt;&#xA;&lt;li&gt;In Mathematica, read curated data file.&lt;/li&gt;&#xA;&lt;li&gt;In Mathematica, create Interpolation Function on data to compute SWR.&lt;/li&gt;&#xA;&lt;li&gt;Plot function.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The data used is the antenna input impedance calculated by NEC4 versus a standard 50-ohm RG-8X coaxial cable made by CableXperts (using their data). The actual data computed is shown in the table below.  The three columns left to right are frequency, real value of impedance, imaginary value of impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0hdUO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0hdUO.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The  above plot shows the SWR minimum of 1.42 at 14.44 MHz.  The minimum is marked by the yellowish-orange horizontal line.  On my SWR plots I always mark the SWR 2:1 horizontal line as the bandwidth that I am interested in is between the intersection points of the SWR curve and the 2:1 SWR horizontal line.  Other people may use other SWRs to determine bandwidth (such as 3:1).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resonant frequency of the antenna is when the impedance is a pure resistance.  This occurs when the reactance, the imaginary value, is zero.  The following plot shows where the reactance crosses the zero value at approximate frequency of 14.475 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/q4yO7.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/q4yO7.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequencies below the resonant frequency have negative reactance values meaning that these are capacitive reactance.  Capacitive reactance indicates that the antenna is too short for those longer wavelengths.  Given that the resonant frequency of 14.475 MHz is outside of the 20-meter amateur band, a better antenna solution would demand a longer antenna than the 10 meters as modeled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following plot shows the SWR of the same physical antenna but this time it is modeled over a real ground profile using a Sommerfeld/Asymptotic solution implemented by NEC4.  The elevation of the antenna over ground is 10 meters.  The key ground parameters are conductivity of 0.004 siemens/meter and a relativity permittivity of 12.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice that the minimum SWR is now slightly lower than before and the frequency where minimum SWR occurs has shifted slightly to a higher value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5rzHj.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5rzHj.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2016-07-30T21:03:01.570" LastActivityDate="2016-07-30T21:03:01.570" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6487" PostTypeId="1" CreationDate="2016-07-31T01:19:50.133" Score="5" ViewCount="810" Body="&lt;p&gt;I am trying to increase my knowledge on software defined radio and according to what I have read its hardware consists of three parts:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Amplifier &lt;/li&gt;&#xA;&lt;li&gt;Tuner&lt;/li&gt;&#xA;&lt;li&gt;ADC&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I just wanted to make sure that my assumption that the filtering and demodulation is done by the computer mathematically is correct.&lt;/p&gt;&#xA;" OwnerUserId="7843" LastEditorUserId="76" LastEditDate="2016-07-31T01:53:22.783" LastActivityDate="2016-08-02T20:43:06.653" Title="Software defined radio demodulation" Tags="&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6488" PostTypeId="2" ParentId="6487" CreationDate="2016-07-31T01:52:43.453" Score="1" Body="&lt;p&gt;No, not all filtering is done in software. The ADC must be preceded by an analog low-pass anti-aliasing filter. This can be considered as being part of the ADC subsystem or part of the tuner subsystem, but it exists in either case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That analog filter is separate from (typically) the much narrower digital filter which passes the signal to be demodulated. There may be more than one such filter depending on the modulation. (Most filtering is done in software because digital filters can have very good characteristics and be adjusted as needed, but the hardware antialiasing filter is a physical necessity.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The demodulation is indeed done entirely in software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also possible to eliminate the hardware tuner component. This requires an ADC with a sampling rate greater than the desired RF frequency, so this is a strategy typically used only by HF SDRs that operate only up to 30-50 MHz. It has the advantage of a simpler, cleaner signal path, and being able to receive at multiple widely-separated frequencies simultaneously, but requires higher performance from the ADC and DSP.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-08-01T16:12:43.287" LastActivityDate="2016-08-01T16:12:43.287" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="6489" PostTypeId="2" ParentId="6487" CreationDate="2016-07-31T06:12:03.750" Score="1" Body="&lt;p&gt;Adding to AG6YO's &lt;a href=&quot;/questions/6487/software-defined-radio-demodulation#6488&quot;&gt;excellent answer&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Software defined radio depends on a signal that is well digitizable by the ADC, and that usually includes amplification in the analog domain. The typical signal chain hence would kind of look like:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Antenna ➔ RX Port ➔ LNA ➔ Mixer ➔ Low/Band pass Filter ➔ ADC ➔ DSP ➔ &#xA;                            ⮤ Synthesizer  -----------------------⭠&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Antenna: Receives EM wave&lt;/li&gt;&#xA;&lt;li&gt;RX Port: well, connect the antenna&lt;/li&gt;&#xA;&lt;li&gt;LNA (Low Noise Amplifier): The first amplifier in a receive chain dominates the noise figure, hence use a low noise one here, and sprinkle in adjustable amplifiers anywhere you see fit further down before the ADC&lt;/li&gt;&#xA;&lt;li&gt;Mixer: Mixes down (and up, and twice up, and...) the receive signal with the local oscillator (LO) as generated by the synthesizer. If it mixes directly to baseband, you get an I/Q &quot;complex&quot; baseband signal (two lines). If it is designed to mix to an IF (intermediate frequency), you just get a single signal. &lt;/li&gt;&#xA;&lt;li&gt;Synthesizer: In essence, a programmable oscillator. Typically uses something like fractional-N techniques to generate a lot of selectable frequencies from a single reference oscillator. Frequency error of these frequencies is defined by the reference's performance. Typically addressed by software running on the computer. &lt;/li&gt;&#xA;&lt;li&gt;Low pass filter: &lt;a href=&quot;http://marcus.hostalia.de/sdra16.pdf&quot; rel=&quot;nofollow&quot;&gt;As per Nyquist&lt;/a&gt; you mustn't have any signal more signal than the ADC can represent unambigously; which means that you need to restrict the bandwidth of the analog signal to half the sampling rate per real channel; usually, if done in baseband, you just use a low pass filter for that with half the sampling rate as stop band edge, though it's also common to see Intermediate Frequency (IF) systems that use a Nyquist-rate band around a non-zero frequency.&lt;/li&gt;&#xA;&lt;li&gt;ADC (Analog to Digital Converter): Samples the signal at discrete times (dictated by the sampling rate $f_\text{sample}$), holds its value at that instant  for as it takes to get a digital reading, sends that reading over to some DSP chain, usually even still on the device&lt;/li&gt;&#xA;&lt;li&gt;DSP (Digital Signal Processing): First of all, there's no ADC with e.g. USB, so you need some silicon to buffer samples on one end and on the other hand put them in to computer bus packets. Then, it's often desirable to do some digital signal processing already on the device. For example:&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;your synthesizer can generate many frequencies, but not &lt;em&gt;all&lt;/em&gt;; hence you still have a frequency offset that you can now get rid of by shifting the signal in frequency domaint (i.e. multiply with $e^{j2\pi f_\text{offset}}$)&lt;/li&gt;&#xA;&lt;li&gt;your ADC runs continuously at 2x 100MS/s for I and Q – so the spectrum your observing is $(-\frac{100\text{ MHz}}2, \frac{100\text{ MHz}}2)$ around the center frequency. Problem is: your transport (e.g. Gigabit Ethernet) cannot possibly transmit that many samples ($100\cdot 10^6 \frac{\text S}{\text s}\cdot \frac{16\text{bit [I]}16+\text{bit [I]}}{\text S}=3.2\frac{\text{ Gb}}{\text s} &amp;gt; 1\frac{\text{ Gb}}{\text s} $)&lt;br&gt;&#xA;You hence have to filter and decimate in the DSP chain already&lt;/li&gt;&#xA;&lt;li&gt;You know your mixer's imperfections (different gains on I and Q), and you want to compensate for those without tasking your computer&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Then comes the interconnect to whatever runs your DSP software – for example, a PC, or a single board computer like the popular Raspberry Pi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They then get a clean sample stream representing a bandwidth &quot;as it was on the air&quot;, and then can demodulate it to their will. Modern PC hardware is quite capable, so for example, you can take a laptop, and with something that sends 25 MS/s over network or USB3, look at all the FM broadcast radio range (87–108 MHz) at once, easily, and just pick arbitrarily many stations at once to demodulate to audio and play/save for later etc. At the same time, you could decipher the &lt;a href=&quot;https://www.youtube.com/watch?v=yNiJRZjLxcQ&quot; rel=&quot;nofollow&quot;&gt;bus sign&lt;/a&gt; information that are present in that spectrum as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the mixer and synthesizer allows, you could tune the same device to 2.4 GHz and reconstruct operation of RC cars, or what your neighbour was typing (which is not really that much of a surprising fact, but makes the round &lt;a href=&quot;https://www.mousejack.com/&quot; rel=&quot;nofollow&quot;&gt;in the media&lt;/a&gt; lately.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or you could receive NOAA weather images, or listen to aircraft transponders, or ship transponders, or just tune in to your friendly ham discussions :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The nice thing about having the ADC sample a relatively high bandwidth is indeed that good filters are expensive – only in the real world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your ADC is not running into any clipping problems, and there's no strong nearby signals that desensitize your analog amplifiers, and let's say you've got a noise floor at -100 dBm/Hz and a CW at -93 dBm, then you'd need a 10 Hz wide filter just to get an SNR of 3dB. Which is pretty complicated and highly specific in analog electronics – but in SDR, you'd just let (if it can do that) the DSP chain give you something very easily processable with a modern CPU, e.g. 0.5MS/s, and then either apply a cascade of decimating filters to further suppress the noise, or just go another route and just estimate the power of that single tone with an algorithm whose job is nothing but to find tones within noise (that could be a so-called parametric spectrum estimator, like ESPRIT).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="76" LastEditDate="2016-08-02T20:43:06.653" LastActivityDate="2016-08-02T20:43:06.653" CommentCount="12" ContentLicense="CC BY-SA 3.0" />
  <row Id="6490" PostTypeId="2" ParentId="6473" CreationDate="2016-07-31T13:58:51.720" Score="1" Body="&lt;p&gt;You could make a balun as a box with an SO-239 connector and two screw terminals, with some wire connecting them. I suppose this works in a sense, though not especially well if you don't want common-mode currents on your transmission lines. Many of the &quot;baluns&quot; in cheap dipole kits are exactly this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, making an &lt;em&gt;effective&lt;/em&gt; balun almost always means also finding a way to connect the two without ending up with excessive common-mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On coax or twin-lead transmission lines operating without common-mode currents, there's a point within them where the electromagnetic fields from the currents in the transmission line cancel. For coax this is the shield, and for twin-lead this is &lt;a href=&quot;https://ham.stackexchange.com/questions/3508/why-must-twin-lead-conductor-spacing-be-small-to-avoid-radiation/3509#3509&quot;&gt;the imaginary point between the two conductors&lt;/a&gt;. Let's call this point &quot;ground&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there are fields at this point, then it must be because there are common-mode currents. So it follows that if we want to connect coax and twin-lead we need to connect ground-to-ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you think about coax this is easy because the shield is something to which you can directly connect something. But with twin-lead it's not so easy, since ground isn't a conductor, it's a space between conductors. Thus, there's no way to connect coax to twin-lead with plain wires that doesn't introduce common-mode currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, &lt;em&gt;all&lt;/em&gt; effective baluns must address common-mode current in one way or another. Some, like an &lt;a href=&quot;https://en.wikipedia.org/wiki/Balun#Autotransformer_type&quot; rel=&quot;nofollow noreferrer&quot;&gt;autotransformer balun&lt;/a&gt;, work only if there weren't common-mode currents on the transmission lines to begin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Others, like a &lt;a href=&quot;https://en.wikipedia.org/wiki/Choke_(electronics)#Common-mode_chokes&quot; rel=&quot;nofollow noreferrer&quot;&gt;common-mode choke&lt;/a&gt;, work by presenting a high (ideally infinite) impedance to common-mode currents. A common-mode choke is a very common balun design, and it is useful on its own even with balanced-to-balanced or unbalanced-to-unbalanced transmission line connections for reducing common-mode currents that might be introduced by some other mechanism.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-07-31T13:58:51.720" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6491" PostTypeId="2" ParentId="5240" CreationDate="2016-08-01T17:12:11.500" Score="3" Body="&lt;p&gt;For what it's worth, I made a graph of a token selection of amateur digital modes with bandwidth vs. frequency (as wavelength) to provide a rough sense of the digital scene.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iNIOx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iNIOx.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This came from our feasibility study for a &lt;a href=&quot;http://vapn.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;new packet system&lt;/a&gt; in the Virginia area.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastActivityDate="2016-08-01T17:12:11.500" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6492" PostTypeId="2" ParentId="6471" CreationDate="2016-08-01T23:14:36.640" Score="10" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Are there any documented cases of the FCC actually tracking down and harassing/fining/jailing people for illegal FRS/GMRS transmissions of this sort?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You can browse the Enforcement Bureau's Field Notices at &lt;a href=&quot;http://transition.fcc.gov/eb/FieldNotices/&quot; rel=&quot;noreferrer&quot;&gt;http://transition.fcc.gov/eb/FieldNotices/&lt;/a&gt;. I did find a few related to FRS violations, e.g. several cases where a company (or even a township water authority!) was using FRS/GMRS for business purposes — even going so far as to set up repeaters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I didn't find a case of enforcement against simply an individual casually using an unlicensed walkie-talkie in an otherwise non-interfering manner. However, if the FCC truly &quot;didn't care&quot; they would change their rules to reflect that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, they have recently (May 26, 2016) issued &lt;a href=&quot;http://transition.fcc.gov/Daily_Releases/Daily_Business/2016/db0526/DA-16-588A1.pdf&quot; rel=&quot;noreferrer&quot;&gt;a Public Notice&lt;/a&gt; warning that &quot;Persons or Businesses Using Authorized Equipment&#xA;In a Manner that Violates Federal Law or the Commission’s Rules&#xA;Are Subject to Enforcement Action&quot;. They don't single out &quot;use an uncertified ham handheld on FRS?&quot; in their examples — and in fact they mostly seem to be targeting the use of &quot;authorized equipment&quot; in &lt;em&gt;un&lt;/em&gt;authorized ways — but it's clear that at least some attention is being paid to the use of &quot;unlicensed&quot; (more properly, &quot;licensed by rule&quot;) spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL for their part, want you to think of the the FCC's notice as applicable in this case. In &lt;a href=&quot;http://www.arrl.org/news/fcc-warns-that-use-of-authorized-equipment-must-comply-with-all-laws-and-rules&quot; rel=&quot;noreferrer&quot;&gt;their news item covering the notice&lt;/a&gt; they add this as their own example: &quot;using an Amateur Radio transceiver on the Family Radio Service.&quot;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How would the FCC actually track down this sort of sporadic, non-disruptive transmission from multiple locations? […] Are there passive monitoring systems in place in urban areas that can automatically/instantly detect illegal transmissions? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Most of the &lt;a href=&quot;https://www.fcc.gov/general/enforcement-primer&quot; rel=&quot;noreferrer&quot;&gt;NAL&lt;/a&gt; documents I've seen are in response to &lt;strong&gt;complaints&lt;/strong&gt;. Even the aforementioned public notice doesn't talk about agency resources being bulked up or anything, but merely &quot;If you have reason to believe that radio frequency equipment is being used […] in a manner that violates the Commission’s rules or the Communications Act, you can file a complaint with the FCC.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The liability letters also provide insight not just into &lt;em&gt;why&lt;/em&gt; enforcement action was taken, but how enforcement is done. For example, &lt;a href=&quot;https://transition.fcc.gov/eb/FieldNotices/2003/DOC-290813A1.html&quot; rel=&quot;noreferrer&quot;&gt;when a GMRS licensee was maliciously interfering with a LMRS licensee&lt;/a&gt;, one of the transmitting antennas involved was tracked down &quot;using a mobile direction finding ('MDF') vehicle&quot; — i.e. they had to send an agent out driving around to find the perp. Perhaps this is merely &lt;a href=&quot;https://en.wikipedia.org/wiki/Parallel_construction&quot; rel=&quot;noreferrer&quot;&gt;parallel construction&lt;/a&gt;, but taking their word for it, means enforcement is not cheap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC does have a &lt;a href=&quot;https://www.fcc.gov/general/high-frequency-direction-finding-center&quot; rel=&quot;noreferrer&quot;&gt;High Frequency Direction Finding Center&lt;/a&gt; which is apparently &lt;a href=&quot;http://www.arrl.org/news/fcc-releases-warning-notices-to-several-radio-amateurs&quot; rel=&quot;noreferrer&quot;&gt;fairly precise&lt;/a&gt; — whether this is true or primarily a &lt;a href=&quot;https://en.wikipedia.org/wiki/Television_licensing_in_the_United_Kingdom#TV_detector_vans&quot; rel=&quot;noreferrer&quot;&gt;Television detector van&lt;/a&gt;-type ruse to keep us honest I couldn't tell you. (It's certainly more plausible in the case of an intentional radiation.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, due to much more limited UHF propagation you would need a lot more listening stations to address this sort of problem. Perhaps there is public information on this, perhaps there is inter-agency involvement NOT part of the public record (the HFDFC is part of a &quot;Homeland Security&quot; bureau…) — whether the feds are as interested in non-hams out hiking with Baofengs, as they are in tracking the cellphones of everyone attending a political protest… your guess is as good as mine…&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Are there any sorts of identifying signals (some sort of unique identifier) that handheld transceivers such as these emit while transmitting?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_fingerprinting&quot; rel=&quot;noreferrer&quot;&gt;Radio fingerprinting&lt;/a&gt; is a thing, for an example of some of the signal characteristics that might be involved check out &lt;a href=&quot;https://www.youtube.com/watch?v=_dV4gLlGbq0&quot; rel=&quot;noreferrer&quot;&gt;Use Real-Time Spectrum Analysis to Characterize a transmitter key-up&lt;/a&gt;. Whether the FCC could or would use this as sufficient evidence for liability, I don't know.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-08-01T23:14:36.640" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6494" PostTypeId="1" CreationDate="2016-08-02T09:44:53.990" Score="3" ViewCount="204" Body="&lt;p&gt;There are many examples of IQ mixers on the internet; all use 90 degree hybrids to split the LO to the mixers with the outputs being combined in-phase. I'm curious, could both mixers be fed an &lt;em&gt;in-phase&lt;/em&gt; LO and a 90 degree hybrid used to combine the signals from the two mixers instead, in a sort of reversed IQ mixer?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RSsId.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RSsId.png&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is such a thing even possible? And if not, why?&lt;/p&gt;&#xA;" OwnerUserId="8094" LastEditorUserId="76" LastEditDate="2016-08-02T13:55:55.697" LastActivityDate="2016-08-02T20:32:22.737" Title="Building an IQ mixer using an in-phase LO splitter" Tags="&lt;electronics&gt;&lt;mixer&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6495" PostTypeId="2" ParentId="6494" CreationDate="2016-08-02T17:46:07.457" Score="1" Body="&lt;p&gt;Sure, this will perform the same function as a 90 deg hybrid -&gt; mixers -&gt; combiner. The diagram you show will perform the rejection in the hybrid, while the other arrangement would perform the rejection in the mixers and combiner. You may be able to achieve better conversion loss / bandwidth / isolation in one vs the other, since components may be easier or harder to design at the RF/IF frequency. Sadly I don't know any rules of thumb on their behavior. Anyone who does please contribute. A third conversion arrangement feeds each mixer with LOs 90 degs out of phase. Others with multiple 90 deg hybrids exist as well. (Maybe I'll do the math when I get some free time...)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A reverse image search shows &lt;a href=&quot;http://www.markimicrowave.com/blog/2013/06/iq-image-reject-and-single-sideband-mixers/&quot; rel=&quot;nofollow&quot;&gt;the source of the image&lt;/a&gt; with a detailed discussion of this topology, although doesn't do much comparison.&lt;/p&gt;&#xA;" OwnerUserId="5944" LastEditorUserId="5944" LastEditDate="2016-08-02T17:55:16.333" LastActivityDate="2016-08-02T17:55:16.333" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6496" PostTypeId="2" ParentId="6494" CreationDate="2016-08-02T20:32:22.737" Score="2" Body="&lt;p&gt;Yes, this will work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, that is nothing but emulating an ADC with twice the sampling rate by using two synchronous ADC of the original rate, delaying one branch of the signal by half a sample clock. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-08-02T20:32:22.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6498" PostTypeId="1" CreationDate="2016-08-03T04:48:14.920" Score="3" ViewCount="448" Body="&lt;p&gt;Any idea what might be causing this signal to appear in the &quot;panadapter&quot; spectrogram of my Omnia SDR around the 40m band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/q7vyM.png&quot; alt=&quot;Waterfall of interfering signal, showing signal spreading and &amp;quot;twisting&amp;quot; within repeated patterns&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/sdfql.png&quot; alt=&quot;Waterfall of interfering signal, emphasizing its periodic nature&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every twenty seconds, I get a strong &quot;focused&quot; signal that then rapidly spreads out its power — like all the power is concentrated at one frequency but then gets &quot;spiralled&quot; out within a certain (relatively narrow) bandwidth. This signal seems somewhat symmetrical, and is repeated every 12kHz or so across my waterfall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Its exact characteristics/&quot;sound&quot; seems to change occasionally — for example tonight it repeated fairly consistently every 20 seconds for a long time, then went quiet for a few minutes, then gave one isolated (and slower) buzz. A few minutes later, it began repeating every 20 seconds again. This sort of thing happened a few months ago too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live near a power substation, and have some neighbors who weld, but neither seem a likely culprit, particularly given the usual streaks of consistent repetition of a shaped signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given its symmetrical and repetitive nature, am I right to suspect there is some sort of intermodulation involved here — i.e. the actual noise source is simply a strong sweep that's getting mixed with something in my SDR? Then what are some ways I could determine its actual frequency and get a better/cleaner look at it? And any guess as to the source based on this information? Might it be some sort of radar, or more likely just somebody's malfunctioning digital panini press?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-08-03T04:54:45.780" LastActivityDate="2016-08-05T16:49:20.740" Title="What might this &quot;spreading&quot; interference be?" Tags="&lt;rfi&gt;&lt;signal-identification&gt;&lt;mixer&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6499" PostTypeId="1" CreationDate="2016-08-03T05:41:52.033" Score="8" ViewCount="4896" Body="&lt;p&gt;There are many anecdotes of hams learning Morse Code at e.g. 5wpm and then &quot;hitting a wall&quot; trying to gradually speed up to 15wpm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;David G. Finley, N1IRZ claims the reason is this:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Morse at 5 wpm and Morse at 15 or 20 wpm are completely different critters, and you don’t want to waste time on the wrong one.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In his essay &lt;a href=&quot;http://www.qsl.net/n1irz/finley.morse.html&quot;&gt;&quot;So You Want To Learn Morse?&quot;&lt;/a&gt; he contrasts the slow &quot;lookup table&quot; of thinking about the individual dits and dahs, versus the faster &quot;reflex&quot; way of learning the whole sounds of letters. If it's not clear, he's in favor of learning the fast/reflex sounds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suppose this is a little akin to the &lt;a href=&quot;https://languagedebates.wordpress.com/category/the-phonics-versus-whole-language-controversy/&quot;&gt;Phonics vs. whole language&lt;/a&gt; debate in teaching English reading skills, and perhaps there's merits to both sides. But I'm willing to accept N1IRZ's claims regarding the superiority of Koch-style methods for learning fast morse code. Makes sense to me and seems to match my experience so far. What I learn of &quot;slow Morse&quot; won't help me with &quot;fast Morse&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I'm wondering, though: is the &quot;flip side&quot; true? If I learn &quot;fast Morse&quot; first, will I still need to learn &quot;slow Morse&quot; separately anyway before I can understand the latter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is, say I go ahead and stop learning the &quot;slow&quot; whole patterns of letters (so as not to &quot;waste time on the wrong one&quot;). I get good at &quot;fast&quot; letter sounds, and can talk to fast keyers. Will I end up unable to hear what someone using &lt;a href=&quot;http://www.qsl.net/w5www/qcode.html&quot;&gt;QRS&lt;/a&gt; is saying? Or does it end up being easier to hear slow Morse as a stre-e-e-tched out version of known sounds, versus being simply overwhelmed by uncountable dashes and dots coming from the other direction?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since N1IRZ claims these are &quot;completely different critters&quot;, that sort of implies I really need to learn them &lt;em&gt;both&lt;/em&gt; to converse fluently with both sets of operators on the bands. But perhaps it is more trivial to understand slow Morse after learning fast?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-08-03T05:49:39.187" LastActivityDate="2016-08-13T02:55:28.633" Title="Should I learn morse at &quot;both&quot; speeds?" Tags="&lt;cw&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6500" PostTypeId="1" CreationDate="2016-08-03T07:50:17.457" Score="2" ViewCount="522" Body="&lt;p&gt;How can I measure/what instrument should I use to identify/measure the RF signal strength in a &quot;noisy&quot; environment?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I want to measure the RF signal strength of my device at a particular spot in a convention hall, while there may be external wireless routers/personal devices emitting 2.4 GHz as noise too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a gadget that can identify the different RF signals in a noisy environment? &lt;/p&gt;&#xA;" OwnerUserId="8108" LastEditorUserId="4076" LastEditDate="2016-08-03T17:58:40.463" LastActivityDate="2016-08-09T21:49:25.253" Title="Measuring a device's 2.4 GHz RF signal in an open field/indoors" Tags="&lt;rfi&gt;&lt;signal-identification&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6501" PostTypeId="2" ParentId="6499" CreationDate="2016-08-03T11:29:58.840" Score="10" Body="&lt;p&gt;No. Stick with higher speeds. Not only will the slower speeds naturally come along with higher speeds (to some extent, you'll have to practice a bit later on), but learning at a slow speed tends to develop bad habits that are very difficult to break later, like &quot;sounding out&quot; the characters as dots and dashes rather than distinct sounds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, finding someone on the air who's actually sending at 5wpm character speed is extremely uncommon. The lowest you might hear commonly is probably close to 10wpm, but most folks send farnesworth these days, with the character speed somewhere north of 10wpm.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-08-03T11:29:58.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6502" PostTypeId="2" ParentId="6499" CreationDate="2016-08-03T11:34:07.237" Score="6" Body="&lt;p&gt;I am not sure if this can count as an answer, but my personal opinion is that 5 wpm Morse code is unusable. It can only serve purpose to pass exam. At that slow speed you have no other way but to count dits and dahs, which is simply wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you plan to use Morse code for radio communication go faster, 12 to 18 wpm is sufficient, if you can go 20 or faster - even better. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will never need 5 wpm, but if you do, you will manage to receive.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-08-03T11:34:07.237" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6503" PostTypeId="2" ParentId="6499" CreationDate="2016-08-03T12:40:51.357" Score="6" Body="&lt;p&gt;The most popular method to learn CW these days is the &quot;Kosh&quot; method, such as is taught at &lt;a href=&quot;http://lcwo.net/&quot; rel=&quot;noreferrer&quot;&gt;lcwo.net&lt;/a&gt;. Essentially, the individual characters should always be sent at a high speed, say, 20 WPM, but spacing between the characters is allowed. If you are going to learn low speeds, this is the only way that I would recommend it. &lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2016-08-03T12:40:51.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6504" PostTypeId="2" ParentId="6500" CreationDate="2016-08-03T13:05:53.613" Score="1" Body="&lt;p&gt;I used MetaGeek Wi-Spy for that purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not cheap solution but it can recognize various signal sources, not only WiFi.&lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="306" LastEditDate="2016-08-09T21:49:25.253" LastActivityDate="2016-08-09T21:49:25.253" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6505" PostTypeId="2" ParentId="6500" CreationDate="2016-08-03T13:53:45.680" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there a gadget that can identify the different RF signals in a noisy environment?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not in &lt;em&gt;general&lt;/em&gt;. One radio's signal is another radio's noise, especially in the case of high-bandwidth digital signals. The problem is essentially the same as wanting one radio to receive every type of signal in the environment. Which is theoretically possible (as long as each modulation is &lt;em&gt;already known&lt;/em&gt; to the radio), but as far as I know not something that's been done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can get a spectrum analyzer, or a SDR receiver, which will give you a plot of power vs. frequency vs. time (waterfall plot). (The difference between the two for this purpose is that a spectrum analyzer is &lt;em&gt;calibrated&lt;/em&gt;, giving measurements in absolute units, and much more expensive.) This will show you the strength of the signals, but it won't let you tell the difference between different protocols or devices (unless you know &lt;em&gt;when&lt;/em&gt; particular devices are transmitting and can match up the timing).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you just want to figure out which channels are least-occupied, or find the signal-to-noise ratio for a particular configuration (have your device transmit, see how far it sticks up above the background), then this is sufficient.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-08-03T13:53:45.680" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6506" PostTypeId="1" AcceptedAnswerId="6511" CreationDate="2016-08-03T16:24:11.770" Score="7" ViewCount="4021" Body="&lt;p&gt;I am trying to listen to FM station using an SDR and GNU radio. I have followed this procedure &lt;a href=&quot;https://i.stack.imgur.com/yTKYW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yTKYW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a reason that the decimation is done gradually? For example would it make a difference if I change audio decimation to 1 in WBFM Receive and change the decimation to 50 in rational resampler block?&lt;/p&gt;&#xA;" OwnerUserId="7843" LastEditorUserId="218" LastEditDate="2016-08-04T14:18:33.907" LastActivityDate="2016-08-04T14:54:36.107" Title="Decimation to listen to FM radio with gnu radio" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6507" PostTypeId="2" ParentId="6499" CreationDate="2016-08-03T17:31:37.717" Score="4" Body="&lt;p&gt;I learned Morse at 5 wpm when I was about 9 and 10 years old.  Listening to CW on my radio and also during my Novice year, my speed increased to about 20 wpm and I was copying in my head with the exception of writing down names of things (name, city name, and other kinds of names that did not fall into easy head copy).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, about 60 years later I am still most comfortable with head copy at about 20 wpm but I can do contests and other short exchanges up to 35 wpm and usually copy a call sign at between 35 and 40 wpm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, and this is the big thing of my statement here.  If the speed is below about 8 to 10 wpm I can't copy in my head anymore and I revert to writing things down.  One reason to write down letters at such slow speed is now that I am an aged ham, I will often forget the first letters of the word before it is finished since it is so slow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Koch method is the way to learn these days but as I have said before on this forum -- get on the air and copy true CW QSOs -- that is the only way to improve that &quot;head copy&quot; in my opinion.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-08-03T17:31:37.717" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6508" PostTypeId="2" ParentId="6506" CreationDate="2016-08-03T17:49:18.277" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;For example would it make a difference if I change Audio Decimation to 1 in WBFM Receive and change the Decimation to 50 in Rational Resampler block?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Why don't you try? GNU Radio lends itself very well to experimentation, and by attaching signal visualizations (mainly, frequency sinks), you could combine your theoretical with your practical knowledge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this will not really work. For frequency modulation, you can't have a input signal bandwidth equal to the output signal bandwidth (decimation is the ratio $\frac{\text{input sampling rate}}{\text{output sampling rate}}$); in &quot;which&quot; spectrum would the modulation take place?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your question shows that you might want to brush up your knowledge on what FM is, and how signals are represented in digital signal processing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen you ask similar question; I'd strongly suggest going through the &lt;a href=&quot;http://tutorials.gnuradio.org&quot; rel=&quot;nofollow&quot;&gt;official guided GNU Radio tutorials&lt;/a&gt;. They really explain a lot of the concepts you're missing here. Also, things like &quot;Great Scott's Gadgets introduction to complex numbers (signals)&quot; is a great starting point for SDR adventures!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-08-03T18:25:26.313" LastActivityDate="2016-08-03T18:25:26.313" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6509" PostTypeId="2" ParentId="6500" CreationDate="2016-08-03T22:29:48.367" Score="2" Body="&lt;p&gt;If you're purely interested in 2.4GHz Wi-Fi signals then I can recommend the free Ekahau Wifi Heatmapper for Windows.&#xA;&lt;a href=&quot;http://www.ekahau.com/wifidesign/ekahau-heatmapper&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ekahau.com/wifidesign/ekahau-heatmapper&lt;/a&gt; Of course this doesn't pick up any non-802.11 signals but may still be of great help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Heatmapper doesn't support GPS in the free version but if you have a floor plan then you just walk around and left-click at corresponding locations where you're walking and the program figures out how the signal fades.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example neighbourhood 2.4GHz Wi-Fi map:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/B3oYf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/B3oYf.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see I first walked around the block (the dark-green line) and then let the program do its thing. It also picked up heaps of other nearby access points (around the edges of the screen) but was unable to properly give them a location on the map.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Super simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, look for a wardriving app for your mobile phone.&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="1135" LastEditDate="2016-08-03T22:56:33.090" LastActivityDate="2016-08-03T22:56:33.090" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6511" PostTypeId="2" ParentId="6506" CreationDate="2016-08-04T14:16:29.467" Score="4" Body="&lt;p&gt;One reason in general to perform decimation in multiple steps is it reduces the computational requirements of the low-pass filtering. To achieve a sharp transition width in the filter requires a longer convolution kernel and thus, more computation. Also the sample rate is very high before decimation, requiring yet more computational power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So generally, we want the sample rate to be as low as possible at each stage. The minimum sample rate will be dictated by the Nyquist Theorem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What we can do instead is use a less sharp filter, then decimate, then another less sharp filter, then decimate again, and so on. There's a further advantage here in that the tails of the filter can extend beyond the output bandwidth such that they alias or &quot;wrap around&quot;, since further filtering and decimation steps will remove that aliasing. The filter just needs to be narrow enough to avoid aliasing into what will eventually be the passband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus by filtering and decimating in multiple stages we can use fast filters where the sample rate is high, and put the more expensive filters with the sharper transition where the sample rate is low.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this particular case, the aim was to get from a sample rate of 20M to 480k. That's a ratio of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 20000000 / 480000 \approx 41.666 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can't decimate by fractional samples, so we must write that as a ratio of integers:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {20000000 \over 480000} = {500 \over 12} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GNU Radio's low-pass filter block can perform decimation but not interpolation, so we can refactor that fraction as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {20000000 \over 480000} = {100 \over 1} \cdot {5 \over 12} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since 5 is prime, that 5/12 fraction can't be refactored any more. We usually don't want to interpolate any more than we need to since that just creates more data that must be processed, so this is the cheapest way to do it. And you'll notice these numbers (100, 5, 12) match the parameters in your blocks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FM demodulator further decimates its audio output after demodulation by a factor of 10 to get 48kHz since this is a common audio rate, and covers the entire range of human hearing.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;would it make a difference if I change audio decimation to 1 in WBFM Receive and change the decimation to 50 in rational resampler block?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This would reduce the sample rate into the WBFM demodulator to 48k. On the plus side, it will require less computational power with the lower sample rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the passband of the low-pass filter upstream is 75k, with a transition of 25k. That means the signal coming out of that filter has a bandwidth of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 2(75 + 25) = 200\:\mathrm{kHz} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, it can't be represented with a sample rate less that 200k. If you were to decimate this to 48k the excess bandwidth would cause aliasing, and you'd be feeding the demodulator garbage.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-08-04T14:54:36.107" LastActivityDate="2016-08-04T14:54:36.107" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6512" PostTypeId="2" ParentId="5145" CreationDate="2016-08-04T16:28:11.477" Score="0" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;1200 Baud is a bit slow, and we are looking into something with a&#xA;faster data rate.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;h1&gt;Exciting times in 'softmodem' development&lt;/h1&gt;&#xA;&lt;p&gt;There are two exciting developments in play currently.  One expands on what can be squeezed out of the normal audio path in an FM transceiver while the other pushes the standard 9600 speed to 19,200 and beyond. Both lean heavily on sound card specifications and, of course, the transceiver's bandwidth and signal path quality.&lt;/p&gt;&#xA;&lt;h3&gt;Regular audio channel - up to 4800 bps&lt;/h3&gt;&#xA;&lt;p&gt;Without going into too many details have a look at this post concerning the UZ7HO Soundmodem soundcard software TNC...&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.tapr.org/pipermail/aprssig/2015-April/044345.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.tapr.org/pipermail/aprssig/2015-April/044345.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;To quote:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;With these latest versions, the Soundmodem can now transmit and receive AX.25 packet on:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Classic 300, 600 or 1200 Hz baud FSK&lt;/li&gt;&#xA;&lt;li&gt;300, 600, 1200 and 2400 baud BPSK&lt;/li&gt;&#xA;&lt;li&gt;2400, 3600 and 4800 baud QPSK&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;...all of which fits into the bandwidth of a normal voice channel of a transceiver. Obviously the required quality of the audio link has to be higher for the QPSK modes, but at least now we have (or soon will have) the option to try.&lt;/p&gt;&#xA;&lt;h3&gt;Direct to discriminator - 9600 bps and beyond&lt;/h3&gt;&#xA;&lt;p&gt;Traditional high speed modes require direct connection to the modulator and discriminator as you know. The G3RUH modem design is the default approach for both 9600 and 19200.  There is one TNC on the market, the SCS Tracker TNC, that, among other amazing feats, can handle both G3RUH speeds.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.p4dragon.com/en/Modems.html#widget4&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.p4dragon.com/en/Modems.html#widget4&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;What this tells us is there is an off the shelf modem ready for you to connect to your SM50 discriminator port and likely get at least 9600 working between you and your friend and perhaps 19200 if the radio and signal path will support it.&lt;/p&gt;&#xA;&lt;p&gt;The more interesting news is the soft-modem developers are examining this in the sound card TNC regime as well. The Direwolf soundmodem software offers such hope in this document in their bleeding edge development area...&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://github.com/wb2osz/direwolf/blob/dev/doc/Going-beyond-9600-baud.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/wb2osz/direwolf/blob/dev/doc/Going-beyond-9600-baud.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is sort of vaporware at the moment, but highlights the required and rather stringent specifications for your sound card device.&lt;/p&gt;&#xA;&lt;p&gt;The active and exciting development of the sound card soft-TNC-modems may help you and your friend continue to up the throughput of your connection as new releases arrive.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I know normal audio does not work for 9600 baud packet. What are the&#xA;requirements?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The requirements include:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Direct-to-discriminator/modulator connections as the voltage from the sound card or hardware TNC directly translates to RF frequency and vice versa - aka direct FM.&lt;/li&gt;&#xA;&lt;li&gt;Sufficient channel bandwidth, from close to DC to whatever it takes to adequately house the waveform. For an excellent demo and explanation of digitization &lt;a href=&quot;http://www.hamradio.me/digital/understanding-digitization.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;go here&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Rock solid transceiver frequency stability... much more so than required for normal voice FM communication. Frequency drift and phase noise have a direct impact on your digital waveform.&lt;/li&gt;&#xA;&lt;li&gt;TX/RX circuitry that can take the harsh beating given to them by the constant back and forth of a typical data link.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I have a bunch of Motorola Radius SM50 UHF wideband commercial radio's&#xA;and I am wondering if they would work? They have direct discriminator&#xA;out on the back.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I am cautiously optimistic these may work.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-08-04T17:08:00.690" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6513" PostTypeId="1" CreationDate="2016-08-04T20:54:41.450" Score="3" ViewCount="638" Body="&lt;p&gt;I know that there are several commercial programs that will decode incoming CW using the computer's sound card, but this is not quite what I need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The specific requirement that I have is to feed the decoded output (in real time) into a memo/text field in another program running on the same computer. In my mind, the easiest way to do this is to have the decoding program generate keyboard messages directed at the receiving program.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The application is for a museum exhibit that allows people to send messages using Morse Code as input. The audio input quality will be very good (generated on-site with an oscillator and wired (non-radio) connections, so having a known frequency and audio level), but the Morse code timing will be poor as the general public will be using this system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm looking for solutions preferably for Windows.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone know of any resources or insights that might help with this problem?&lt;/p&gt;&#xA;" OwnerUserId="4669" LastActivityDate="2017-05-04T12:37:28.540" Title="Looking for a morse code decoder that simulates keyboard input" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6514" PostTypeId="2" ParentId="6498" CreationDate="2016-08-04T21:37:48.103" Score="4" Body="&lt;p&gt;If nobody is able to recognize what kind of signal you're dealing with by looking at your waterfall screen shots, then perhaps your best chance of identifying the signal would be to use old-fashioned RDF (radio direction-finding) techniques.  If you can, consider borrowing a portable battery-powered receiver that can do 40m, and ideally also SSB, like a shortwave broadcast receiver or a Yaesu FT-817, with a portable antenna.  A portable directional antenna like a loop would be ideal; those are fairly rare though, so you'd probably need to make do with a whip antenna.  A whip antenna would obviously attenuate the signal quite a bit compared to a full-sized dipole or vertical, but often the problem with RDF isn't too &lt;em&gt;faint&lt;/em&gt; of a signal, but rather too &lt;em&gt;strong&lt;/em&gt; of a signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's quite possible that the noise is coming from your own house or apartment.  For that matter the problem could be a ground loop; if so, then you shouldn't be able to hear the noise at all in a portable receiver.  Phil Frost also points out that the observed signal could be intermodulation or some other mixing product or other spurious signal generated inside the receiver; in that case, there might be external RFI on a different frequency, or no external RFI at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can hear the RFI in the portable receiver, then try flipping circuit breakers off, one at a time, and see if the noise goes away suddenly; if so, then you know the RFI generator is powered by that circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can establish that the RFI isn't coming from your house, then if you know someone with a 40m yagi, then you might ask him or her which direction the signal seems to be coming from.  If nobody you know has a 40m yagi, it may still be useful to ask other people to listen for the signal because the signal may be weak but coming from someplace close by.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From there, your best bet would probably be to drive around with the portable receiver and see if you can locate the source by using the signal strength as a &quot;hotter/colder&quot; style indicator.  Of course that can be quite a challenge if the signal is intermittent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck!  If you figure out what the noise source is, please let us know.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-08-05T16:49:20.740" LastActivityDate="2016-08-05T16:49:20.740" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6515" PostTypeId="1" CreationDate="2016-08-05T06:28:33.567" Score="4" ViewCount="1250" Body="&lt;p&gt;I'm new to radios. Just bought the mini Eton which has FM/AM/SW and while FM &amp;amp; AM work I have never received a single station on SW1 (5.9 - 10 MHz) or SW2 (11.65 - 18 MHz). Is that normal?   Will shortwave only work in Europe? I'm in Canada now. If it makes any difference I live walking distance to an airport. Does that cause any interference?&lt;/p&gt;&#xA;" OwnerUserId="8121" LastEditorUserId="29" LastEditDate="2016-08-06T21:00:06.743" LastActivityDate="2020-01-11T22:58:56.780" Title="Is it normal for mini shortwave radios to not have any reception in a major city?" Tags="&lt;hf&gt;&lt;receiver&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6516" PostTypeId="2" ParentId="6500" CreationDate="2016-08-05T12:06:44.593" Score="0" Body="&lt;p&gt;You could your mobile/cell phone for free&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally I use Android, and use an app called &quot;WiFi Overview 360&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It will give you a good indication of the various signals and details&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-08-05T12:06:44.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6517" PostTypeId="2" ParentId="6515" CreationDate="2016-08-05T17:33:02.287" Score="2" Body="&lt;p&gt;Shortwave broadcasting isn't as popular as it used to be, thanks to the internet; the BBC World Service stopped broadcasting to North America in 2001.  But there are still many shortwave stations broadcasting to North America.  Here's a &lt;a href=&quot;http://www.primetimeshortwave.com/america.txt&quot; rel=&quot;nofollow&quot;&gt;list&lt;/a&gt; of stations and times in UTC.  During Daylight Saving Time the Eastern time zone is four hours behind UTC and the Pacific time zone is seven hours behind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would suggest to try a bigger external antenna, but the manual for your Eton Mini suggests that there is no external antenna jack.  You could always try stretching a long wire out a window to a tree, and attaching the other end to the whip antenna with an alligator clip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your nearby airport is unlikely to have anything to do with your reception.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-08-05T18:16:20.880" LastActivityDate="2016-08-05T18:16:20.880" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6518" PostTypeId="1" CreationDate="2016-08-05T19:20:40.250" Score="0" ViewCount="111" Body="&lt;p&gt;In a 2-Rx by 2-Tx directional antenna system, say both transmitters are transmitting concurrently as in Fig. The main lobes from the two transmitters overlap. How does this affect the resultant signal received at either receivers ? Any thoughts on this would be greatly appreciated !&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/y4RhF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/y4RhF.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8125" LastActivityDate="2016-08-05T19:59:29.227" Title="Directional antenna overlapping main lobes" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6519" PostTypeId="2" ParentId="6518" CreationDate="2016-08-05T19:59:29.227" Score="4" Body="&lt;p&gt;Free space is (under normal conditions of frequency and power and atmosphere) a &lt;em&gt;linear medium&lt;/em&gt;, so waves propagating in it follow the &lt;a href=&quot;https://en.wikipedia.org/wiki/Superposition_principle&quot;&gt;superposition principle&lt;/a&gt;, so they do not interact just because they occupy the same space. The situation in your diagram is not particularly significant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you do need to consider is the &lt;em&gt;rest&lt;/em&gt; of the radiation pattern of your antennas, specifically the part of TX 1's pattern in the direction of RX 2 and the part of TX 2's pattern in the direction of RX 1. These &lt;em&gt;will&lt;/em&gt; have an effect — hopefully a negligible one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact that the beams cross does not matter; the exact same analysis would apply if they were parallel instead.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-08-05T19:59:29.227" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6521" PostTypeId="2" ParentId="6352" CreationDate="2016-08-06T02:37:44.710" Score="2" Body="&lt;p&gt;I think you'll find this problem isn't so easy to analyze or solve. What you have are not spatially separated beams, at least not in the sense that there's a beam of signal going through those specific areas in your window.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is the same reason why individual atoms &lt;a href=&quot;https://en.wikipedia.org/wiki/Diffraction-limited_system&quot; rel=&quot;nofollow&quot;&gt;can't be imaged by an optical microscope&lt;/a&gt;: diffraction. Anything small relative to the wavelength of light (or RF radiation, which is just a much lower frequency of light) can't be resolved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what you are observing when you stick your antenna in the window and get good reception there isn't that you've placed the antenna in a &quot;beam&quot;. Rather, it's just in that particular spot, you've just happened to find a local maximum in the diffraction pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The orientation of the antenna also plays a role, since unlike visible light from the sun or an ordinary light bulb which is incoherent radiation, radio radiation is mostly &lt;a href=&quot;https://en.wikipedia.org/wiki/Coherence_(physics)&quot; rel=&quot;nofollow&quot;&gt;coherent&lt;/a&gt;. This means (among other things) it has a particular polarization, and if you don't match that polarization with the antenna, you'll experience signal loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This diffraction pattern can be perturbed by anything with electrical properties different from free space anywhere within a few multiples of wavelength. Unfortunately this means it's not feasible to design an antenna that will &quot;catch&quot; all those signals. Remember they aren't really beams anyway. Simply adding an antenna will perturb the system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice? Trial and error, just as you'd adjust a TV antenna. There's no guarantee you'll find one antenna and orientation that works well to receive all the signals.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-08-09T12:28:27.223" LastActivityDate="2016-08-09T12:28:27.223" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6522" PostTypeId="2" ParentId="6515" CreationDate="2016-08-06T07:04:46.653" Score="3" Body="&lt;p&gt;&lt;strong&gt;Get out of town&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It could very well possible that your radio is picking up interference from all kinds of sources around you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can get to a remote spot, at least a couple of miles away from any town/plant/power-line you might receive a lot more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you do, you can build a list of stations/frequencies you can receive, then get back into town, and see if you can receive them there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At that point you can start experimenting with extending your whip with a long wire, as suggested in other answer and comments, to improve your reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;and... welcome to the hobby! Shortwave listening is a great way to start your radio hobby !!&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-08-06T07:04:46.653" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6523" PostTypeId="1" AcceptedAnswerId="6524" CreationDate="2016-08-08T17:14:27.407" Score="1" ViewCount="798" Body="&lt;p&gt;I purchased a Yaesu FT2900,a mobile antenna and mount. The install question is for a 2016 Chevy Cruze.  Is there an easy way to run the power cables from rear of  radio to the forward engine compartment?&lt;/p&gt;&#xA;" OwnerUserId="6567" LastEditorUserId="6567" LastEditDate="2016-08-08T20:43:58.370" LastActivityDate="2016-08-09T02:42:35.057" Title="Mobile Installation in 2016 Chevy Cruze" Tags="&lt;mobile&gt;&lt;installation&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6524" PostTypeId="2" ParentId="6523" CreationDate="2016-08-08T18:00:16.007" Score="1" Body="&lt;p&gt;Welcome to ham.SE, and congratulations on the new mobile rig.  Alan K0BG has an excellent &lt;a href=&quot;http://www.k0bg.com/&quot; rel=&quot;nofollow&quot;&gt;website&lt;/a&gt; that has everything you might need to know about installing a mobile radio and operating mobile.  His &lt;a href=&quot;http://www.k0bg.com/wiring.html&quot; rel=&quot;nofollow&quot;&gt;page about wiring and grounding&lt;/a&gt; recommends drilling a new hole through the firewall, if there isn't a spare hole available, and using a rubber grommet to prevent chafing to the wire, which could start a fire.  He also recommends fuses on both the negative and positive leads to the mobile rig, and connecting the negative lead to the same chassis ground point as the vehicle battery's chassis ground point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While you're perusing Alan's site, also be sure to read his &lt;a href=&quot;http://www.k0bg.com/install.html&quot; rel=&quot;nofollow&quot;&gt;installation notes page&lt;/a&gt;, which has lots of other stuff you'll want to read.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know if you'll consider Alan's recommendations &lt;em&gt;easy&lt;/em&gt;, but if you follow them you'll have peace of mind from knowing that you've done the job right and that the installation will be as safe as possible.  Good luck and have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-08-08T18:00:16.007" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6525" PostTypeId="2" ParentId="6523" CreationDate="2016-08-09T02:28:07.140" Score="0" Body="&lt;p&gt;I agree with the suggestion of Alan's sites for mobile installs.  Actually, Alan has a few photos posted of my installed antennas and rigs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also have a Chevy but it is a Silverado 3/4 ton pickup truck.  I went to a local retail business called &quot;Car Toys&quot;.  It is a chain of stores over west coast states and I think they have a few in Texas and Colorado.  But, that is not the point, the point is that I paid someone to do what I wanted to have done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My install was a 100-watt HF Transceiver, Icom 706 MkIIG, and a Yaesu FT-7800R 2 meter, 70 cm, transceiver.  The job of the Car Toys business was to run new wires from battery to the rear crew cab section of the truck coming in under the floor through a hole drilled by them.  The hole was protected with rubber grommet and after installation a thick liquid plastic stuff was inserted to seal the hole from water.  Current capacity of my wires was 80 amps as I was thinking of also putting in a 350 watt linear but I never did that.  Car Toys, as a business was very skilled in this sort of thing as putting in high-power audio amplifiers was a good part of their business.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also have them drill and install a extension coaxial connector into the floor board that I could hook PL-259 connectors to it for my HF mobile antenna (HiQ 4/80).  I have photos of all aspects of this installation and would be willing to share or even post here if there is interest.  However, this one particular photo shows the main parts:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QqMK8.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QqMK8.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The view is under the seat (which is lifted up and out of the way) of the rear seat of the crew cab of the pickup truck.  The lower part of the photo you see the power distribution units where the red and black wires are connected.  The power cables come up through the floor board where they run along the chassis frame from the engine compartment (the firewall is never pierced).  You can just barely see where the cables come up.  Just to the right of that spot is my coaxial connection for my HF antenna which comes up through the floor.  The coax runs along the chassis frame (inside cable wrap) and to the rear part of the pickup truck bed where it comes up through the bed floor to feed the HF antenna.  The black box you see is the Icom IC-706 transceiver with the control panel remote up front with easy access to driver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since this photo was taken, I have made one other change and that is installing a West Mountain Radio power distribution strip (fused for each circuit) using Anderson Power-pole connectors for all rigs and power needs.  Not shown is that the base unit for my Yaesu 7800R also sits there under the rear seat.  Both rigs are velcro stuck to the carpet so that they will not move around.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition I had grounding straps placed at about 6 key spots on the undercarriage of the truck to make sure that there is solid continuity on all metal parts of the truck as it is important for HF operations.  This is something that Alan (K0BG) emphasizes on his web site.  Probably not as important for VHF/UHF radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back in 2005, total cost was about $400 including the horribly high state sales tax of about 9.6 percent.  This included all high-current capacity cables for power but I supplied the straps used for grounds.  In addition, both battery cables are protected by in-line fuses and a nice power distribution unit was included that is bolted into the floor of my truck under the rear seat in the crew cab.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2016-08-09T02:42:35.057" LastActivityDate="2016-08-09T02:42:35.057" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6526" PostTypeId="2" ParentId="6515" CreationDate="2016-08-09T09:30:49.693" Score="2" Body="&lt;p&gt;Some general advices to listen to SW inside a city:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Fully extend the antenna. AM doesn't need to extend the antenna (it uses an internal ferrite core) and FM usually is so strong in cities that the non-extended antenna works fine. SW however requires an fully extended antenna, and orientation may also play a role, so try to move it around.&lt;/li&gt;&#xA;&lt;li&gt;Get close to the window/balcony. SW reception is worse inside the house. You can also try in a park or something like that in the city.&lt;/li&gt;&#xA;&lt;li&gt;Try to identify any interferences and try to avoid them by moving to another window or moving the antenna around. Electrical interferences are caused by electronic devices (computers, TV...) and motors (A/C units, elevators...). They may sound like a strong buzzing sound that is always present in the whole band or that appears periodically in the band.&lt;/li&gt;&#xA;&lt;li&gt;Try different bands at different times. Lot of transmissions are half an hour or one hour long, so you should sweep the whole band every half an hour to catch everything. Also day/night cycle is very important, so try at different times of the day. In particular, lower bands (SW1 in your radio) should be more active at night while higher bands (SW2) usually are more active at day. But there can be stations at any frequency at any time. Lower band travels longer distances at night and you may receive stations not intended for your region.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In my personal experience, the problem in cities or buildings is not usually that the station is weak, but that the interferences are strong and will mask the weak stations. That is why moving to a window may reduce the interferences while improving the signal. Going to a park should give you an idea of what can be heard in a quieter place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope you are lucky with your reception and please share with us your findings.&lt;/p&gt;&#xA;" OwnerUserId="369" LastActivityDate="2016-08-09T09:30:49.693" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6527" PostTypeId="2" ParentId="6499" CreationDate="2016-08-09T22:45:50.450" Score="1" Body="&lt;p&gt;Do not learn slow Morse. I learned 5 WPM when I was 10. Now I am 62 and still count dits and dahs. I can not unlearn it, I have tried many things.&lt;/p&gt;&#xA;" OwnerUserId="1157" LastActivityDate="2016-08-09T22:45:50.450" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6530" PostTypeId="1" AcceptedAnswerId="6531" CreationDate="2016-08-11T15:41:44.617" Score="6" ViewCount="7100" Body="&lt;p&gt;Receiving the frequency of 97.9 MHz&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YDsiy.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YDsiy.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a Terratec SDR dongle and I am trying to capture a radio frequency. The FFT window shows the frequency range from -500 to 500 KHz. Is there a way to increase this or it depends on the dongle and is fixed? Does it depend on the sampling rate?&lt;/p&gt;&#xA;" OwnerUserId="7843" LastActivityDate="2016-08-11T20:08:29.537" Title="How to choose the right sampling rate and bandwidth for RTL-SDR dongle?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6531" PostTypeId="2" ParentId="6530" CreationDate="2016-08-11T15:51:12.887" Score="7" Body="&lt;p&gt;What the FFT sink shows as frequency axis actually has no basis in &quot;real world signal&quot; – it just takes the sample rate you set (here, you set 1 MHz), and scales the full nyquist bandwidth to that. If you used a different number in the sample rate field of the FFT sink, the spectrum would look absolutely the same, just the frequency axis would have different labels!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's important to understand that in DSP (and in GNU Radio especially), things are always only handled with respect to samples – e.g. a sine with a period of three samples would have frequency $\frac13$, no unit. The spike on the FFT plot would be at $2 \cdot \frac 13= \frac23$ of the axis (factor of two: your Nyquist zone is from $-\frac{f_\text{sample}}{2}$ to $+\frac{f_\text{sample}}{2}$).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's an example to illustrate:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AafuU.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AafuU.png&quot; alt=&quot;relative frequencies&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How that $\frac 13$ relates to real world frequencies is defined by the sampling rate of the analog-to-digital (or digital-to-analog, in TX) converter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you need to increase the observed bandwidth, you need to increase the sampling rate at the dongle! They are identical for complex sampling, like the direct-conversion receiver that the RTL dongle is does. For real-valued sampling, your bandwidth is half the sampling rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RTL dongles support multiple sampling rates. You should simply try – for example, 2 MS/s should work with most dongles. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-08-11T20:08:29.537" LastActivityDate="2016-08-11T20:08:29.537" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6532" PostTypeId="1" AcceptedAnswerId="6535" CreationDate="2016-08-11T17:01:51.140" Score="5" ViewCount="916" Body="&lt;p&gt;I tried searching a lot before, but couldn't find anything about it;&#xA;I have an old TV/FM card from an old computer, I wish to know if it can be used as an Software Defined Radio, and if yes, how?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The one I have is the same as this one:&#xA;&lt;a href=&quot;http://www.itwinkle.com/51askotvfmnt.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.itwinkle.com/51askotvfmnt.html&lt;/a&gt;&lt;br&gt;&#xA;It does even have that wire-antenna shown in the photo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just found out that Stack Exchange had a site for Amateur Radio, so I wanted to ask here, I know someone might answer xD&lt;/p&gt;&#xA;" OwnerUserId="8153" LastActivityDate="2016-08-11T19:01:54.327" Title="Can I use old TV FM card as SDR?" Tags="&lt;software-defined-radio&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6533" PostTypeId="2" ParentId="6532" CreationDate="2016-08-11T17:49:43.117" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Can I use old TV FM card as SDR?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Without loss of generality, no.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Old TV cards typically have dedicated analog demodulators to give you a video signal that then is digitized and sent to the PC. No reconstruction of the original signal can be done, usually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Seriously, though, DVB-T sticks that &lt;em&gt;don't&lt;/em&gt; do that specific TV signal demodulation can be had for a couple of Euros (you're in Brazil, right? Don't know who imports them there, but I'm pretty sure you can directly buy them somewhere), and they will do a pretty decent job :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way: not every new PC (since ca. 2007) even has a PCI interface anymore, that's one of the reasons these TV cards are cheap/for free this often. I, myself, have two cards I've never used for anything.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-08-11T17:58:10.430" LastActivityDate="2016-08-11T17:58:10.430" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6535" PostTypeId="2" ParentId="6532" CreationDate="2016-08-11T19:01:54.327" Score="4" Body="&lt;p&gt;With the limited information provided on that link you posted, I am guessing that the answer would be no.  The DVB-T Dongles from nooelec or RTL-SDR are set up to &lt;strong&gt;receive only&lt;/strong&gt; on a pretty large portion of the radio spectrum.  There is also the option of getting one of the more expensive cards and then purchasing the &quot;ham it up kit&quot; so you would be able to cover the HF channels as well. I have one of the RTL-SDR dongles and it does a pretty amazing job with just the little whips that come with it.  I have regular reception from the public safety channels in my area that are up to 30 miles away.  Pretty amazing for a $20-30 piece of usb ware. You can research more on SDR and these dongles by going to RTL-SDR.com&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope that helps     &lt;/p&gt;&#xA;" OwnerUserId="8154" LastActivityDate="2016-08-11T19:01:54.327" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6536" PostTypeId="2" ParentId="173" CreationDate="2016-08-11T20:16:18.617" Score="1" Body="&lt;p&gt;Three years later:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Currently, there is a solution available using GNU Radio … but it is complicated to set up and keep running.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, you're referring to Nick Foster's &lt;a href=&quot;https://github.com/bistromath/gr-ais&quot; rel=&quot;nofollow&quot;&gt;&lt;code&gt;gr-ais&lt;/code&gt;&lt;/a&gt;, which is a GNU Radio out-of-tree module, and actually, not that hard to set up. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, it's included in current versions of the &lt;a href=&quot;http://gnuradio.org/redmine/projects/gnuradio/wiki/GNURadioLiveDVD&quot; rel=&quot;nofollow&quot;&gt;GNU Radio Live DVD&lt;/a&gt;, and you should be able to just boot that, and run &lt;code&gt;ais_rx&lt;/code&gt;; haven't tried that out lately, because I've installed it directly on my normal system; I've got GNU Radio installed, so the dependencies are already there:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;git clone https://github.com/bistromath/gr-ais&#xA;cd gr-ais&#xA;mkdir build&#xA;cd build&#xA;cmake ..&#xA;make&#xA;make install&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-08-11T20:16:18.617" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6538" PostTypeId="1" CreationDate="2016-08-14T01:23:45.530" Score="9" ViewCount="8504" Body="&lt;p&gt;I'm studying for my Technician license, and listening in to HF, VHF and UHF bands just to get a feel for how to work with frequencies, squelch, antennas, etc.   Had something happen today that I couldn't explain.  I was doing a scan through the 70cm band, running from 400MHz to 480MHz, and at 450.040 I picked up a local AM radio station.  I checked the radio station website and they only broadcast on 1520 KHz.  How did I receive that signal on such a different frequency?  I wasn't even working with a very powerful antenna, just a Baofeng UV5R.  My first thought was that perhaps the local signal was just so powerful it overcame my radio reception.  But if that's the case, why did it happen just on that one frequency?  I was scanning other frequencies through the day and didn't have it happen on any other frequency. I also checked to see if we had any nearby repeaters at that frequency but we don't; nearest frequency for a regional repeater is 444.9750.   Thanks.&lt;/p&gt;&#xA;" OwnerUserId="8164" LastActivityDate="2018-06-16T22:55:56.380" Title="receiving AM radio station on UHF frequency" Tags="&lt;uhf&gt;" AnswerCount="3" CommentCount="6" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6539" PostTypeId="1" CreationDate="2016-08-14T03:06:09.680" Score="0" ViewCount="302" Body="&lt;p&gt;There is this one youtube video I have not been able to find again, where someone with a similar model radio was making replica of the original loop antenna on the back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am wanting to make a replica of this antenna &lt;a href=&quot;https://i.stack.imgur.com/VheyO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VheyO.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be the best way to remake one of these? What kind of gauge wire should I use? Should I add a ground?&#xA;I found the schematics for the radio &lt;a href=&quot;http://www.nostalgiaair.org/Resources/download.asp?FN=%5CM0014914.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Tube Schematic&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8165" LastActivityDate="2016-10-13T20:03:44.970" Title="RCA victor 35x tube radio loop antenna replica?" Tags="&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6540" PostTypeId="2" ParentId="2146" CreationDate="2016-08-14T09:37:52.337" Score="1" Body="&lt;p&gt;My suggestion is to get an Alfa R36 wi-fi router and an Alfa wireless card. The R36 can provide wired/wireless internet in the building which has none. Set it to a channel far apart from the channel used in the building which has internet. Connect the R36 as a client with the USB Alfa card and a yagi. This is seamless, and my setup has never failed. I point the yagi directly toward the remote accesspoint (which has generic omnis). Across 35-40 metres and through a few walls I still pulled 35-40mbit/s. The nice thing about the R36 is that it is an excellent accesspoint on its own, with ethernet port so you can wire it to a switch or other accesspoints. A yagi in the building with internet, pointed at the R36 would be best. Don't use parabolic dish from inside a building to inside another building, the waves get thrown around too much.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-08-14T09:37:52.337" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6541" PostTypeId="1" AcceptedAnswerId="6550" CreationDate="2016-08-14T11:34:38.687" Score="3" ViewCount="120" Body="&lt;p&gt;I just learnt about such a thing as a crystal radio receiver and the following idea came to my mind. I have no background knowledge on electronics nor anything related.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What if battery-less earbuds can be made, picking AM waves from very short range nearby stations such as an antenna plugged in the audio-out of my pc or smartphone or laptop or all 3 of them at the same time, the receiver shall mix them together in this case and differentiate left-right channels for stereo. Not sure if AM would suffice for the 20kHz bandwidth necessary to cover the full audio spectrum but FM would be more complex for little benefit i think?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna would be inside the string that connects the two earbuds for maybe a max of half a meter length. If two antennas (one per earphone) are needed they can both coexist in the same string but it would be thicker.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would be compatible with any standard audio plug and have enough range for an apartment.&lt;/p&gt;&#xA;" OwnerUserId="8167" LastEditorUserId="76" LastEditDate="2016-10-29T18:43:48.753" LastActivityDate="2016-10-29T18:43:48.753" Title="feasibility of wireless passive crystal earphones" Tags="&lt;receiver&gt;&lt;am&gt;&lt;crystal-radio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6542" PostTypeId="2" ParentId="6539" CreationDate="2016-08-14T19:26:25.630" Score="1" Body="&lt;p&gt;Litz wire can be used. Compare with solid copper wire, it is more efficient and higher Q factor, due to skin effect. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;No ground is needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Litz wire is used in modern version which uses ferrite core instead of air core. &lt;a href=&quot;https://i.stack.imgur.com/9SBLE.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9SBLE.jpg&quot; alt=&quot;Modern version&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try search &quot;loop antenna&quot; and you can find more information, like &lt;a href=&quot;https://en.wikipedia.org/wiki/Loop_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia on loop ant&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1473" LastActivityDate="2016-08-14T19:26:25.630" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6543" PostTypeId="1" CreationDate="2016-08-15T05:56:23.710" Score="1" ViewCount="84" Body="&lt;p&gt;I read an article in a magazine or online about a (.gov, I think) site which showed two, four to six character sequences in a mobile phone browser window. The letters from left to right indicated lower to higher precision positioning. As precision decreased, the characters on the right turned red, indicating a best guess accuracy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There wasn't an app to install. It was a web page where you would visit it once while on 4G/WiFi, let it download some data to your phone (I think it was an HTML5 web app), then it could be used offline, so long as you had a GPS signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm going on a trip soon and I'd like to use this app, but I forget what the website was. I saw it within the last year. Does anyone have any clue what the site could be? It could have used maidenhead or MGRS, but I'm not 100% sure.&lt;/p&gt;&#xA;" OwnerUserId="4226" LastActivityDate="2018-11-16T05:27:31.183" Title="Mobile Phone offline maindenhead or mgrs web app" Tags="&lt;aprs&gt;&lt;echolink&gt;&lt;location&gt;&lt;dx&gt;&lt;maidenhead-locator&gt;" AnswerCount="1" CommentCount="4" ClosedDate="2018-11-16T18:47:12.597" ContentLicense="CC BY-SA 3.0" />
  <row Id="6544" PostTypeId="1" AcceptedAnswerId="6549" CreationDate="2016-08-15T06:40:21.690" Score="0" ViewCount="246" Body="&lt;p&gt;I want to use &lt;a href=&quot;http://www.rfmd.com/store/downloads/dl/file/id/29775/rf6886_data_sheet.pdf&quot; rel=&quot;nofollow&quot;&gt;RF 6886 power amplifier&lt;/a&gt; for VHF band design. The datasheet doesn't mention VHF design specifications. Has anyone used the PA for VHF design? If yes then please share your designs.&lt;/p&gt;&#xA;" OwnerUserId="5762" LastEditorUserId="4076" LastEditDate="2016-08-15T12:44:32.093" LastActivityDate="2016-08-15T12:59:50.143" Title="Using RF6886 Power Amplifier for VHF design" Tags="&lt;vhf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6545" PostTypeId="1" AcceptedAnswerId="7427" CreationDate="2016-08-15T09:51:42.227" Score="13" ViewCount="21751" Body="&lt;p&gt;I am curious to know if it is possible to do packet radio on VHF/UHF using the UV-5R... I have seen some invasive hardware hacks, but without modifying the radio itself (firmware, hardware) it's my understanding that you can only toggle send/receive using the 2.5mm/3.5mm TRS ports. &lt;/p&gt;&#xA;" OwnerUserId="7957" LastEditorUserId="76" LastEditDate="2016-10-29T18:48:02.200" LastActivityDate="2020-10-31T04:10:02.810" Title="Is packet radio possible on Baofeng UV-5R and similar HTs?" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;packet&gt;&lt;audio-interface&gt;" AnswerCount="8" CommentCount="1" FavoriteCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6546" PostTypeId="2" ParentId="3488" CreationDate="2016-08-15T10:33:13.207" Score="1" Body="&lt;p&gt;Not on the AC charger, certainly. It generates so much noise on VHF/UHF/Commercial FM for me that I cannot listen to it while it's charging. Try using the 12VDC adapter included in the set connected to a PC PSU instead, This worked for me, no noise any more when my UV-5R is docked.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-08-15T10:33:13.207" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6547" PostTypeId="2" ParentId="1469" CreationDate="2016-08-15T10:38:53.573" Score="1" Body="&lt;p&gt;I use a sainsonic 36cm VHF/UHF antenna. It's light (unlike the Nagoya 40cm I had before) and has perfect reception for my needs. I can hear stations up to 80-100km away if I'm high enough (altitude, not R&amp;amp;R). People shouldn't knock the rubber ducky, it's perfect for critical CAMPING comms. A backup antenna, essentially.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-08-15T10:38:53.573" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6548" PostTypeId="2" ParentId="2071" CreationDate="2016-08-15T10:41:59.430" Score="0" Body="&lt;p&gt;Not to mention that Baofeng more often than not includes a perfectly good FTDI USB data cable with the various UV-5Rs. A lot more handy than a serial adapter that is fragile. I use Chirp as well.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-08-15T10:41:59.430" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6549" PostTypeId="2" ParentId="6544" CreationDate="2016-08-15T12:59:50.143" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The datasheet doesn't mention VHF design specifications.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;VHF is 30-300 MHz. The Chip is only specified for 100 MHz upwards – so the lower part of VHF will definitely work very suboptimally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my first reaction would be: you're trying to use the wrong amplifier for VHF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, assuming you're just considering the 100 – 300 MHz range: As far as I can read the data sheet, I'd say they expect a designer to have access to a network analyzer; the numbers they give for nominal complex input impedance for 430 MHz indicate that if you can design a 100 MHz - 300 MHz line with 50 Ohm impedance, then you should be fine :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the main problem here is that you're in charge of designing a matching circuit, and that for a very wide band (100 - 300 MHz is as much bandwidth than the center frequency of 200 MHz! This means you need a wideband matching circuit). That won't be trivial. To be honest, you should ask their sales people for S-parameters at 100 – 300 MHz if this is your region of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, if you don't have access to calibrated microwave network analyzers, I'd simply estimate a matching inductance value from their 900 and 430 MHz examples, and try with their eval board; not like that you could get perfect matching with a single component over the whole 100-300 MHz band, anyways.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-08-15T12:59:50.143" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6550" PostTypeId="2" ParentId="6541" CreationDate="2016-08-15T16:03:30.040" Score="1" Body="&lt;p&gt;A crystal radio is powered by the incoming signal.  If you've ever listened to one, you'll know that the audio is quite faint, although a purpose-built transmitter could probably be made strong enough to overcome that problem.  Traditional crystal radios receive AM only, and not in stereo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It could be theoretically possible to make a receiver powered by the signal, but it wouldn't be very practical.  You would need a high-power transmitter, which would be against the law in the US and in most other countries.  There would be a tremendous amount of interference for the neighbors, and the problem would be multiplied for people in high-density housing such as a large apartment building.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any way you look at it, a low-powered transmitter such as a Bluetooth transmitter, paired with a battery-powered receiver, is more practical.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-08-15T16:03:30.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6551" PostTypeId="2" ParentId="6545" CreationDate="2016-08-15T16:15:30.333" Score="2" Body="&lt;p&gt;Sure it's possible.  You'll need some sort of Terminal Node Controller (TNC), either one implemented in hardware or software, plus a set of cables that plug into the  2.5 mm / 3.5 mm TRS ports.  If you're using a hardware TNC then you'll need some sort of computer and a serial or USB cable between the computer and the TNC.  I've used a different model HT to send and receive APRS packets with a TinyTrak 4 as my TNC and xastir (APRS software for Linux), and it worked fine.  APRS is a protocol that sends and receives specially-formatted AX.25 packets.  I've heard there are &quot;software TNCs&quot;, i.e. computer programs that generate audio tones to be sent to the radio, but I can't vouch for how well they work, having never tried them.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-08-15T16:15:30.333" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6552" PostTypeId="2" ParentId="6545" CreationDate="2016-08-15T20:39:41.060" Score="8" Body="&lt;p&gt;You sure can. It's been done before with a Baofeng HT, a &lt;a href=&quot;https://www.raspberrypi.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;Raspberry Pi&lt;/a&gt;, a &lt;a href=&quot;https://www.adafruit.com/product/1475&quot; rel=&quot;nofollow noreferrer&quot;&gt;USB sound card&lt;/a&gt;, and some custom cables and some open-source &lt;a href=&quot;https://github.com/wb2osz/direwolf&quot; rel=&quot;nofollow noreferrer&quot;&gt;sound card modem software&lt;/a&gt;. &lt;a href=&quot;http://www.wcares.org/special-interests-3/aprs/aprs-raspberry-pi-virtual-tnc/&quot; rel=&quot;nofollow noreferrer&quot;&gt;This article&lt;/a&gt; explains a step-by-step approach.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://willbradley.name/2015/08/09/aprs-via-rf-cable-for-connecting-aprsdroid-to-a-baofeng-radio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;This article&lt;/a&gt; shows how to create a custom cable for interfacing a Baofeng HT with an Android phone (but should be sufficient for figuring out the wiring for the USB sound card so you can interface with your Raspberry Pi - specifically, you'll probably need to separate the right/left audio from the mic and PTT for the sound card's separate mic/audio jacks). Of course you could use the custom cable and an Android phone or tablet running the APRSdroid software mentioned in that article. There are also ready-made cables like the &lt;a href=&quot;https://baofengtech.com/aprs-k2-trrs-cable&quot; rel=&quot;nofollow noreferrer&quot;&gt;BTECH APRS-K2 TRRS / APRS Cable&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;In the first case, the Raspberry Pi is acting as the TNC; in the latter, the Android and APRSdroid are serving that function.&lt;/p&gt;&#xA;&lt;p&gt;The point of this cable is to connect the input and output audio cables of your computing device (smart phone, raspberry pi or whatever) to the radio. By setting the VOX and squelch settings just right (e.g. &amp;quot;&lt;em&gt;VOX at ~2, Squelch at ~1&lt;/em&gt;&amp;quot;). Then the computer takes the role of the modem and does modulation (for transmitting, triggered by the VOX setting) and demodulation (for receiving, triggered by the squelch setting).&lt;/p&gt;&#xA;&lt;p&gt;I hope this helps.&lt;/p&gt;&#xA;" OwnerDisplayName="user157" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-09-29T18:13:56.600" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6553" PostTypeId="2" ParentId="6538" CreationDate="2016-08-16T07:18:16.707" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;at 450.040 I picked up a local AM radio station&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I am sure you picked up a transmission&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;just a Baofeng UV5R&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;But not with that radio, or at least not AM&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You either:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Picked up a signal which is indeed AM, but then it would not be very distorted as the radio you are using only has FM (de)modulation.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;or:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Picked up something else.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If the audio received was not distorted (so then it must be FM), and clearly the same 'program' as the said AM station on 1520 KHz. Then it is very likely this is a &quot;studio to transmitter link/feed&quot; that you picked up. (as detailed in the comments already)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;But to give you the official answer:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are &lt;strong&gt;not&lt;/strong&gt; picking up an &lt;strong&gt;AM&lt;/strong&gt; transmission originally on &lt;strong&gt;1520 KHz&lt;/strong&gt;, on &lt;strong&gt;450.040 MHz&lt;/strong&gt; with an &lt;strong&gt;Baofeng UV5R&lt;/strong&gt; radio. &lt;em&gt;That would be quite impossible&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;:-)&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-08-16T07:18:16.707" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6556" PostTypeId="1" CreationDate="2016-08-16T13:25:40.267" Score="2" ViewCount="214" Body="&lt;p&gt;I have a modulation mode:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;em&gt;(to be used for a satellite)&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;em&gt;(of a series of AX.25 frames)&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;em&gt;(in the 70 cm band)&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;9.6 kbps&lt;/li&gt;&#xA;&lt;li&gt;Ideally BPSK or QPSK modulation&lt;/li&gt;&#xA;&lt;li&gt;but could be plain FM&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Which I need to describe with an abbreviation from the table of modes recognised by our amateur radio regulator (in South Africa):  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Oo2Ez.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Oo2Ez.png&quot; alt=&quot;Table of mode descriptions&quot;&gt;&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suppose the same would apply to all packet radio operation, really.&lt;br&gt;&#xA;Which mode fits best?&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2016-08-17T07:02:53.440" Title="Which mode describes this modulation scheme" Tags="&lt;digital-modes&gt;&lt;modes&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6557" PostTypeId="2" ParentId="6556" CreationDate="2016-08-16T13:39:46.937" Score="2" Body="&lt;p&gt;After a bit of google:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems &lt;strong&gt;J2D&lt;/strong&gt; describes this mode best.&#xA;The ITU says in &lt;a href=&quot;https://www.itu.int/en/ITU-R/terrestrial/workshops/RRS-13-Americas/Documents/Systems_ClassofEmissions_RRS13.pdf&quot; rel=&quot;nofollow&quot;&gt;this workshop document&lt;/a&gt; that J2D is  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Single-sideband, suppressed carrier with single channel containing quantized or digital information for data transmission&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Types_of_radio_emissions&quot; rel=&quot;nofollow&quot;&gt;Wikipedia has a more detailed table&lt;/a&gt; from which we could construct new mode names, &lt;strong&gt;G1B&lt;/strong&gt; or &lt;strong&gt;G1D&lt;/strong&gt;,  &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;G (phase modulation)&lt;/li&gt;&#xA;&lt;li&gt;1 (single channel containing digital information, no subcarrier)&lt;/li&gt;&#xA;&lt;li&gt;B (Electronic telegraphy, intended to be decoded by machine (radioteletype and digital modes))&lt;br&gt;&#xA;or  &lt;/li&gt;&#xA;&lt;li&gt;D Data transmission, telemetry or telecommand (remote control)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For digital modulation, I'm not sure it's worth separating Phase modulation from Frequency modulation.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2016-08-16T13:39:46.937" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6558" PostTypeId="2" ParentId="6556" CreationDate="2016-08-16T13:39:57.323" Score="1" Body="&lt;p&gt;You can figure it out yourself using this &lt;a href=&quot;https://en.wikipedia.org/wiki/Types_of_radio_emissions&quot; rel=&quot;nofollow&quot;&gt;wiki&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example: &lt;code&gt;BPSK&lt;/code&gt; or &lt;code&gt;QPSK&lt;/code&gt; would be &lt;code&gt;J2B&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[EDIT]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other answer given is &lt;code&gt;J2D&lt;/code&gt; or &lt;code&gt;G1B&lt;/code&gt; / &lt;code&gt;G1D&lt;/code&gt;, which is specifically for Data, and I must agree that is probably a better type indication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is totally dependent on how your protocol is structured, I guess.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-08-16T13:39:57.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6559" PostTypeId="2" ParentId="1172" CreationDate="2016-08-16T17:55:40.807" Score="2" Body="&lt;p&gt;Since OP requires MCU, doesn't have to be extremely sensitive or selective and the 'local' transmitter, one suggestion is&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Use Arduino (Atmel) to control DDS chip to generate 25MHz + - 77.5KHz&lt;/li&gt;&#xA;&lt;li&gt;Use mixer circuit taken out of Hamitup or similar. Simple transitor, FET, MosFet or diode also ok (for local transmitter)  &lt;/li&gt;&#xA;&lt;li&gt;The 25MHz signal, now shifted to 77.5KHz, can be feed to a 'standard DCF77 receiver' (below and also many design on web) which presumably have some degree of band pass filtering in the front end. &lt;/li&gt;&#xA;&lt;li&gt;This setup does not have good image rejection. It will work under specific condition OP requires, local transmitter.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Info DDS and driver &lt;a href=&quot;http://www.ad7c.com/projects/ad9850-dds-vfo&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;&#xA;&lt;a href=&quot;http://www.ad7c.com/projects/ad9850-dds-vfo&quot; rel=&quot;nofollow noreferrer&quot;&gt;DDS2&lt;/a&gt;&#xA;&lt;a href=&quot;http://www.ad7c.com/projects/ad9850-dds-vfo&quot; rel=&quot;nofollow noreferrer&quot;&gt;DDS info&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, to above DDS with Arduino, another suggestion is the &lt;a href=&quot;http://qrp-labs.com/progrock.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;ProgRock&lt;/a&gt; and &lt;a href=&quot;http://qrp-labs.com/images/progrock/progrock.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;(manual here)&lt;/a&gt; which is an interesting solder kit and also fulfills OP's Atmel chip requirement. It uses another DDS chip, Si5351A and outputs square wave instead of sine wave as above chip. Square wave has less favorable spurious response but no problem under OP specified conditions. LPF can be added to make it sine wave. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As OP mentioned building stuff, yet another alternative to consider is to get a HamitUp, removes the oscillator and replace with signal, with suitable level adjustment (no need to be very accurate), from either of the two DDS plan. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After building it, both DDS become a signal generator that you can use it for other task.  Like WSPR and a few other digimode transmitter, just change software. Tie 2 balloons and flew around the Earth &lt;a href=&quot;http://qrp-labs.com/ultimate3/ve3kcl-balloons/ve3kcl-s11.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;S11&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Happy HAM / DIY. Tens of Euro/USD/Stg/etc., in hands of knowledgeable people, can go far. Hope it helps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is plan for a &lt;a href=&quot;http://www.arduinoclub.de/2013/11/15/dcf77-dcf1-arduino-pollin/&quot; rel=&quot;nofollow noreferrer&quot;&gt;standard DCF receiver&lt;/a&gt; with Arduino decode software. &lt;a href=&quot;http://www.pollin.de/shop/dt/NTQ5OTgxOTk-/Bauelemente_Bauteile/Bausaetze_Module/Module/DCF_Empfangsmodul_DCF1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hardware ant with amplifier module&lt;/a&gt;.  Signal from the mixer can be coupled to the antenna rod by 3 turns winding at the far end (away from existing coil) of the ferrite rod &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NUcfq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NUcfq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="1473" LastEditDate="2016-08-17T03:04:02.033" LastActivityDate="2016-08-17T03:04:02.033" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6560" PostTypeId="2" ParentId="6556" CreationDate="2016-08-16T21:12:23.337" Score="0" Body="&lt;p&gt;In our national frequency plan, sub bands reserved for digital data, including packet radio are marked as dedicated for modes A1D, A2D, F1D, F2D, J2D  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A     Amplitude modulation&lt;/p&gt;&#xA;&#xA;&lt;p&gt;F     Frequency modulation   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;J     SSB modulation&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1   One channel containing digital information, no subcarrier&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2   One channel containing digital information, using a subcarrier  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;D   Data transmission  &lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="306" LastEditDate="2016-08-17T07:02:53.440" LastActivityDate="2016-08-17T07:02:53.440" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6561" PostTypeId="2" ParentId="6161" CreationDate="2016-08-17T01:59:20.863" Score="1" Body="&lt;p&gt;An off centre fed dipole is a better bet if you want multi band operation. Just use a good dual core Guanella current balun and a line isolator choke and you'll have no problems.&lt;/p&gt;&#xA;" OwnerUserId="8182" LastEditorUserId="76" LastEditDate="2016-08-18T23:36:32.293" LastActivityDate="2016-08-18T23:36:32.293" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6564" PostTypeId="1" CreationDate="2016-08-18T10:02:19.073" Score="3" ViewCount="516" Body="&lt;p&gt;Does anyone know if it's possible to shift the center frequency of a SAW filter? I'm only talking about 0.1% shift, say from 433MHz to 437MHz. Can it be done or is the center frequency baked into the design during manufacture?&lt;/p&gt;&#xA;" OwnerUserId="8094" LastActivityDate="2016-08-19T09:40:38.393" Title="Tuning a SAW filter?" Tags="&lt;filter&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="6565" PostTypeId="1" AcceptedAnswerId="6566" CreationDate="2016-08-18T12:43:34.983" Score="2" ViewCount="603" Body="&lt;p&gt;I have made a dipole for 40 m, no swr to speak of on 7040 kHz, but I've been told that it should also work on 20 m as it is 20 meters long (2× 9,92 m) but there I get SWR in the 7-9 range. Will this improve if I add a balun to the center?&lt;/p&gt;&#xA;" OwnerUserId="6504" LastEditorUserId="76" LastEditDate="2016-08-18T17:28:05.037" LastActivityDate="2016-08-18T17:28:05.037" Title="Will adding a balun to a full-wave dipole help?" Tags="&lt;antenna-theory&gt;&lt;balun&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6566" PostTypeId="2" ParentId="6565" CreationDate="2016-08-18T15:40:50.617" Score="3" Body="&lt;p&gt;A 1 wavelength dipole will always present a high impedance. Low feedpoint impedance occurs at odd half wave harmonics, so 1 half wave, 3 half waves, etc. A 40m dipole will usually present an acceptable SWR on 15 meters, not 20. A 4:1 balun at the feed point may allow you to tune the antenna on 20 meters, but losses in the coax will be extremely high on both bands then, because of the transformation of the impedance on both 40m and 20m without achieving a perfect match on either. A better bet is to turn it in to a fan dipole by adding a 20 meter element to it, which should give you a nice triband antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, dipoles should always have baluns if at all possible, ideally ferrite toroid 1:1 choke baluns, as these have a wide bandwidth and will keep RFI to a minimum. While single band dipoles will often work without one, they're more prone to causing or receiving RFI and noise due to common mode current on the coax shield.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-08-18T15:40:50.617" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6567" PostTypeId="1" AcceptedAnswerId="6568" CreationDate="2016-08-18T17:59:04.970" Score="6" ViewCount="6781" Body="&lt;p&gt;I've been reading about HInternet a bit, and all explanations I find are detailed technical explanations. &#xA;I have no idea who pays for internet connectivity, where the internet sources from, etc.  Just articles about the frequencies used and prettymuch all that's on the wiki page.  From what I read, I am imagining people connected to a wired internet connection, transmitting that service over long distances with big towers, and also locally with beefed up wifi routers.&lt;br&gt;&#xA;Would users need a HAM license to connect to this?  Would it be free or paid service?  Is my mental image of this correct?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I stumbled upon the concept in search of free/cheap internet for an invention I hope to sell about 4 million of.  If there's a way I can use it, great, if there's a way I can help it grow big (since it seems to need help) awesome.  I just need to figure out what it really is first to see if I can do anything with it.&lt;/p&gt;&#xA;" OwnerUserId="8188" LastActivityDate="2018-10-02T20:49:19.403" Title="What is Hinternet, in simple terms?" Tags="&lt;internet&gt;&lt;mesh-network&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6568" PostTypeId="2" ParentId="6567" CreationDate="2016-08-18T18:23:22.443" Score="3" Body="&lt;p&gt;Eventually someone somewhere would have to provide a connection to the Internet proper to route anything there and back again, yes. In practice, the Hinternet behaves like the Internet but is functional (like a home WiFi network without an active Internet connection) without it in that devices can talk to each other (just not with Internet devices if there's no route out thereto).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to access the Hinternet you do need to be a licensed ham as you're using ham equipment / RF to form your link to the network over which you can then pass data via TCP/IP. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short, the Hinternet refers to the same technologies that power the Internet employed by hams using ham equipment, forming essentially a WiFi network over longer distances with ham radios using Amateur parts of the spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I &lt;em&gt;believe&lt;/em&gt; (but definitely fact-check) a Technician license is all you need to join the fun, which is easy enough (with study) to obtain that at least one new ham between 9 and 12 passes their Tech in my area (Southern Virginia) a month. So go for it! :-)&lt;/p&gt;&#xA;" OwnerDisplayName="user157" LastActivityDate="2016-08-18T18:23:22.443" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6569" PostTypeId="2" ParentId="6567" CreationDate="2016-08-18T20:08:41.520" Score="8" Body="&lt;p&gt;The Hinternet is the &quot;ham internet&quot;.  In the US, and likely in other countries also, several WiFi channels fall into the 13cm ham band; being in the ham band is advantageous because licensed hams can use higher power than non-licensed ISM (industrial, scientific, medical) band users.  So the hinternet generally refers to hams using WiFi gear, often with modified firmware and higher power, to communicate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are restrictions on &lt;em&gt;what&lt;/em&gt; hams can communicate, however.  Hams aren't allowed to pass any messages for commercial use, including advertising.  Hams aren't allowed to broadcast entertainment.  Hams are allowed to pass messages for other people, but if the other people are in other countries then the other countries must explicitly permit such messages.  (Most first-world countries do.)  Hams aren't allowed to encrypt over-the-air messages.  Curse words aren't allowed.  Hams must send their call signs periodically when transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because of these restrictions, hams can't just connect a router on the ham bands running higher power to the regular internet and call it good.  Generally ham radio communication has to be from a ham, to another ham, with the content either generated by the transmitting ham, or at least carefully monitored by the transmitting ham if the content is a recording.  Sorry if this bursts your bubble.  Hams are doing some interesting stuff with this technology though; for instance, hams are reprogramming WRT54G routers to make ad-hoc mesh networks transmitting sound, video, and data.  If this sounds interesting to you, you could get started with just a Technician-class license, which isn't too difficult to earn; we could point you in the right direction.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="8717" LastEditDate="2018-10-02T20:49:19.403" LastActivityDate="2018-10-02T20:49:19.403" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="6570" PostTypeId="2" ParentId="6564" CreationDate="2016-08-19T09:40:38.393" Score="2" Body="&lt;p&gt;As ~430 MHz SAW filters generally have a 3dB bandwidth of 0.2–2 % $f_\text{center}$, tuning them by some 0.1% does seem like a relatively big change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could try to build a small &quot;oven&quot; for your filter to operate in, e.g. by placing a resistor atop of your filter, using that to heat up the filter, and encasing everything in spray foam to make the thing thermically more stable. However, I doubt that will let you get the adjustments you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frankly, when tuning an SAW, you're probably adjusting the wrong part: SAW filters are used &lt;em&gt;because&lt;/em&gt; they are stable. The most common usage in technology is as IF (intermediate frequency) filter. Now, IF signals get generated by  converting an RF signal to that IF; you do that by mixing the RF with a local oscillator at the difference frequency $f_{LO}=f_{RF}-f_{IF}$. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically, these oscillators are adjustable to allow for tuning a receiver to different frequencies – the fact that the SAW stays fixed is an advantage here, not a problem, because you'd normally just tune the LO!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adjusting oscillators is also pretty easy; there's a lot of types of oscillators, but let's identify the more relevant ones here:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;L/C oscillators, Colpitts etc.: You can vary a capacitance or an inductivity; that's most often done mechanically, eg. by turning a screw&lt;/li&gt;&#xA;&lt;li&gt;Adjustable crystal oscillators: These come with an &quot;adjust voltage&quot; pin; you change the voltage applied to that pin, and that changes the frequency. This is often done with control loops, which are used to compare the frequency that the oscillator generates to a frequency normal. For example, assume you have a 900 MHz oscillator that has a factory accurace of 50ppm; it might be $\pm$45 Hz off. But you have a known-to-be-very-good 10 MHz oscillator. You can simply count how many &quot;900 + error&quot; MHz oscillations you see while the 10 MHz oscillator does one – that would be a very simple digital PLL.&lt;/li&gt;&#xA;&lt;li&gt;Integer-N/Fractional-Q synthesizers: In essence: you do the above, but the signal you're generating is derived by frequency multiplying your input frequency normal with an adjustable factor, and then using a bit of algebra to derive a wide range of possible tones on demand. Note that these things aren't &lt;em&gt;continously&lt;/em&gt; adjustable, they can just give you  fine-grained grid of frequencies. This grid is typically finer than the bandwidth of a 400 MHz SAW filter, so that's not really a problem – &quot;we're off by around 200 kHz&quot; translates to &quot;ok, so let's change the the LO frequency by something in the vicinity of 200 kHz; not like a 30 Hz offset would make any difference to a filter of 1MHz bandwidth&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-08-19T09:40:38.393" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6571" PostTypeId="2" ParentId="1172" CreationDate="2016-08-19T17:27:21.310" Score="1" Body="&lt;p&gt;I may be overlooking RF concerns that come into play as you get closer to VHF here, but since you're looking at AM modulation, could you take inspiration from some of the simplest &quot;crystal radio&quot; designs?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These don't even use a &quot;crystal&quot; in the modern sense of crystal oscillator — rather the crystal refers to the &quot;cat's whisker&quot; and galena detector of the earliest designs, usually replaced nowadays by a geranium diode. All the tuning essentially happens in the antenna matching.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea is basically: filter out everything but the desired signal, then use a diode to rectify that to a varying DC signal, which then gets filtered down to just the baseband (sometimes inherently, in the case of a radio earpiece).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So depending on the signal strength of your local station, and the feasibility of implementing a resonant coil with sufficient selectivity at 25MHz to pick out your signal, you might be able to do the rest with a fast enough diode rectifier directly on a microprocessor ADC pin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those might be big contigencies, and maybe what works at 1MHz for kilowatt broadcast stations might not be practical for weaker 25MHz work. If I had to hazard a guess at the first thing to go wrong, it'd be implementing a filter with high enough Q to eliminate the other voltages flying around near your desired station.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-08-19T17:35:01.303" LastActivityDate="2016-08-19T17:35:01.303" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6572" PostTypeId="2" ParentId="6161" CreationDate="2016-08-21T07:38:19.037" Score="1" Body="&lt;p&gt;Don't add half a wavelength of coax. Add a quarter wavelength (at 15m) ideally take the velocity factor of the coax into account.&lt;/p&gt;&#xA;" OwnerUserId="8197" LastActivityDate="2016-08-21T07:38:19.037" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6573" PostTypeId="1" CreationDate="2016-08-21T22:02:55.273" Score="2" ViewCount="715" Body="&lt;p&gt;Is this a good representation of the  sound card SDR systems in which a receiver has a simple hardware detector producing two quadrature audio channels that can be fed to a computer's sound card?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What should I put in ???? box? The first schematic is mine and this is what I understood from listening to a lecture. My problem is that I do not understand how we divide a message signal m to its i and Q components. Is this just by mixing the message signal to quadrature sinusoids or the message signal gets divided into it real and imaginary part (by using Hilbert transform for example) and then goes through the two mixers?&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/tjjYn.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2ftjjYn.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="7843" LastEditorUserId="7843" LastEditDate="2016-08-22T20:28:05.163" LastActivityDate="2016-08-25T07:08:26.757" Title="SDR hardware architecture schematic" Tags="&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6574" PostTypeId="1" AcceptedAnswerId="6579" CreationDate="2016-08-22T02:59:10.840" Score="4" ViewCount="1258" Body="&lt;p&gt;My shack is on the second floor of my home, and I run a single operator, 2 radio contest setup. The two coax runs pass through the wall and drop down to an antenna switch approximately 15 feet from the radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ground system consists of multiple copper ground rods driven in over a fairly wide area, bonded together with 4awg bare copper wire, and the ground then travels up the exterior of the house to the shack via a 1&quot; wide copper braid, also about 15 feet long in total.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coax shields are grounded to the same ground stakes that the antenna switch is grounded to, and there are polyphaser lightning arrestors located at the ground stakes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;K9YC and W8JI both recommend installing common mode chokes as close to the radio as possible, and connected to a low impedance ground line to prevent high power common mode signals from efficiently coupling to nearby electronics. I intend to do so using 1:1 common mode chokes right at the radio coax connector, bonded to the ground line, but neither mention bonding feed line runs together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm trying to determine if there would be any advantage or disadvantage to bonding the shields of both coax runs and the ground line together at the bulkhead panel. On the one hand, this would reduce overall impedance of the ground connection, but on the other, it may provide a route that common mode current appearing on one conductor could bleed over on to the other conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will likely also include common mode suppression within the antenna switch itself, so the line should be fairly well isolated on both ends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I use the bulkhead connectors and bond the lines together at the pass through plate (some 6 feet from the radios and 10 feet from earth), or use grommets to protect the coax as it passes through the hole in the aluminum panel, and bond the coax shield to the ground line only at the radio chassis and the antenna switch?&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-08-22T13:15:00.777" Title="Bonding of Coax shield to RF ground conductor for long ground runs?" Tags="&lt;grounding&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6575" PostTypeId="1" AcceptedAnswerId="6578" CreationDate="2016-08-22T07:38:55.900" Score="2" ViewCount="506" Body="&lt;p&gt;I'm building &lt;a href=&quot;http://www.norcalqrp.org/files/BLTManualPrintVersion-Linked.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;NorCal's / W6JJZ's BLT tuner&lt;/a&gt; (pdf) for use on 40m/20m with a 5W transmitter. I would like to remove the LED and use a small panel meter instead.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I don't have a 1N34A at hand, but I do have a 1N4148. It seems to work fine. What kind of characteristics do I need for D1? Could I use a 1N4148 instead?&lt;/li&gt;&#xA;&lt;li&gt;Would I still need C1? It seems to work fine without.&lt;/li&gt;&#xA;&lt;li&gt;How do I calculate the value of R4?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/DOE6M.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorDisplayName="user885" LastEditDate="2016-08-22T07:45:32.223" LastActivityDate="2016-08-22T13:29:49.547" Title="Adapting an antenna tuner for use with a panel meter instead of an LED" Tags="&lt;electronics&gt;&lt;antenna-tuner&gt;&lt;modification&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6576" PostTypeId="2" ParentId="6573" CreationDate="2016-08-22T08:47:24.673" Score="2" Body="&lt;p&gt;So your picture:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/CZqo6.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fCZqo6.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;is &lt;strong&gt;one of many&lt;/strong&gt; specific implementations of an SDR; what is implied here is that it is a &lt;strong&gt;Direct Conversion Receiver&lt;/strong&gt;/&lt;strong&gt;Quadrature Demodulator&lt;/strong&gt;, which directly brings down the Antenna signal at $f_{RF}$ to (complex) baseband, using the two mixers fed with a cosine and a sine (notice: same frequency, 90° phase difference). (I know this has confused you in the past: The usage of &quot;Demodulator&quot; here has nothing to do with &quot;AM/PSK/QAM modulation&quot;, but with modulation in the mixing sense)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The combination of I and Q signal is called baseband signal. It's called that because it's around 0 Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that the signal that was at exactly $f_{RF}$ on the air ends up on exactly 0 Hz after the mixing, and things that were above $f_{RF}$ end up on positive baseband frequencies, whereas things slightly below end up at negative frequencies – for that to work, to mathematically be able to distinguish between positive and negative frequencies, one must declare I and Q parts of a &lt;em&gt;complex baseband signal&lt;/em&gt; $s(t) = I(t) + jQ(t)$.&#xA;Just like the imaginary axis in the plane of complex numbers is orthogonal to the real axis, the Q axis is orthogonal to the I axis – just that you don't use Pythagoras to prove orthogonality but the infinite integral over the whole space¹. &#xA;&lt;hr&gt; &#xA;Regarding your QSD receiver: It's really just a specific special-purpose implementation of the cosine and sine. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ok, assume you can link the points in time when your ADCs take a sample to your LO frequency. You do so, defining the sampling always to happen exactly when the cosine is 1 or -1 or 0: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VXqdv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VXqdv.png&quot; alt=&quot;Cos and Sine&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;so the sine is also either 0, -1 or 1 when that happens. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, you don't actually need the full oscillator shape, just these three values coming in at the right times. And that's exactly what the logic part above does: When the switch is open, the capacitors pull the input of each opamp to zero, when the switch connecting the input signal to inverting input of an opamp it's -1, and if it connects to the positive input, it's +1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have to stress this: &lt;strong&gt;This is a very special design only useful for the very special case that you only want to sample at an integer factor of the mixing clock, and you have very good control over the phase delay all the connections between components introduce.&lt;/strong&gt; In general, this design is only used if it is impossible to actually use a fully-fledged oscillator for many reasons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've read your other questions on DSP.SE, and this is nothing you'd touch soon, in reality. Yes, there are several ham receivers that work like that beautifully, but to be honest, if I was to demodulate a 10 MHz signal, I'd rather go for the 10 MHz sinusoidal oscillator. Things look different in the multi-GHz case, where getting something to mix reliably is very hard. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹ Orthogonal are things whose dot product is zero. In geometry, the length of this dot product is the projection of some vector A onto a Vector B, i.e. you build a right(-angled) triangle with A the hypotenuse and B containing one cathete/leg, and then you you drop the perpendicular and measure the length. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you project the Y axis onto the X axis, you'll see the projection's length is always zero. So X and Y are orthogonal&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, X and Y are only &quot;normals&quot; under which you  &quot;measure&quot; the position of a point in the plane. You take that point, project it onto the X and onto the Y axis, and get the coordinates. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can do the same for harmonic signals, with another plain: You project that signal $s(t)$ onto $\cos$ and $\sin$ and get the coordinates. In case of your mixer, these would be&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;i_(t) &amp;amp;=  s(t) \cos(2\pi f_{LO} t) \\&#xA;q_(t) &amp;amp;=  s(t) \sin(2\pi f_{LO} t) \\\\&#xA;r(t) &amp;amp;= i(t) + jq(t)&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look at $r(t)$ it describes a function in the complex plane; these are exactly the things you see when you look at one of the classical constellation diagrams!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;As a general advice: Try to not mix up too many concepts; take one textbook and read it from front to back, and get a good understanding of what's happening there. Asking about what the parts of Quadrature Demodulator are and how to understand a QSD circuit in the same question is &lt;em&gt;very&lt;/em&gt; symptomatic of someone who tries to understand stuff by googling words – this will confuse you more than it will help, usually, because you don't get a consecutive, logical introduction to stuff, but will be presented with approaches that only make sense if you fully understood the basics. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-08-22T08:47:24.673" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="6577" PostTypeId="2" ParentId="6575" CreationDate="2016-08-22T09:37:15.843" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I don't have a 1N34A at hand, but I do have a 1N4148. It seems to work fine. What kind of characteristics do I need for D1? Could I use a 1N4148 instead?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That diode has only rectifying jobs - so any diode that can withstand the powers and voltages to expect, and which has a sufficiently low forward voltage, should work. Also, recovery time is critical. If that recovery time is too low, the bandwidth of rectification would drop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;anyway, the 1N34A is a Germanium Diode. Let's call that &quot;Retro&quot;. As far as I can see, your 1N4148 is superior in every single specification, so go for it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Traditionally, Germanium Diodes have a lower forward voltage, something that took silicone technology quite a while to catch up. However:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1N34A (it's impossible to come by a datasheet of that diode that has a U/I curve – strange. Or well, might be due to high production variances!):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yHHOB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yHHOB.png&quot; alt=&quot;1n34a&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1N4148:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2nGU4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2nGU4.png&quot; alt=&quot;1n4148&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At least for the forward current of 5mA, the maximum expected $V_F$ of the 1N4148 seems to be at least 0.2V smaller than that of its germanium competitor.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Would I still need C1? It seems to work fine without.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, C1 is critically important: Together with the differential resistance of D1 and the current sourcing capabilites of the signal passing T1, it builds a low-pass filter, and hence, has the job of averaging. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, with a not-as-retro LED that might be much more photon-efficient at pulsed operation than what might have been available to someone at design time of a circuit that includes a Germanium Diode, this might work without. You still get a better (read: less-noise) output with some 100nF, so keep that. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How do I calculate the value of R4?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;to be honest: This looks like it was chosen due to availability and not due to calculation. Simply measure the voltage over C1 if not connecting any R4, and derive from that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, for your instrumentation, it might be a good idea not to worry about that too much: just replace R4 with a series of three resistors to get a voltage across the middle one, use an opamp to amplify / buffer that so you can drive your instrument without interfering with your signal. Choose the values of these three resistors in a way that ensures the voltage at the top of the middle one won't fry opamp. Using a clamping diode as overvoltage protection might also be a good idea.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-08-22T13:29:49.547" LastActivityDate="2016-08-22T13:29:49.547" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6578" PostTypeId="2" ParentId="6575" CreationDate="2016-08-22T12:57:21.670" Score="3" Body="&lt;p&gt;First, consider how the circuit works. It's a &lt;a href=&quot;https://en.wikipedia.org/wiki/Wheatstone_bridge&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wheatstone bridge&lt;/a&gt;, although you might have to squint and turn your head to see it. Think about how &quot;Tune&quot; is a connection to ground through what should be a 50 ohm impedance. Here it is redrawn a bit:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/bD0WZ.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fbD0WZ.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the antenna is tuned, then R2 and R3 make a voltage divider, and R1 and the antenna make a similar voltage divider. As the input is driven by the transmitter, the nodes between each of these voltage dividers are at the same voltage (because they are each the same voltage divider), and thus there's no voltage across T1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the antenna isn't 50 ohms, then it is not the same voltage divider as R2 and R3, and so there is voltage across T1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bit with the other half of T1 and the LED is essentially an AM detector. Think of it like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/60DZk.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f60DZk.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;D1 rectifies the input: when V1 is at its maximum the diode permits current to raise the voltage of node &lt;em&gt;A&lt;/em&gt; by charging C1. When V1 swings back down the diode is reversed biased so the only path for current out of C1 is through R4 and the LED. So the voltage at A is approximately the peak voltage of the voltage source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course the voltage source is actually the secondary of T1. The winding ratio of T1 helps to generate a higher voltage for the detector so it's better able to overcome the forward voltage of the diodes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The selection of D1 isn't terribly critical. Anything that rectifies will work here. Even a &lt;a href=&quot;https://en.wikipedia.org/wiki/Foxhole_radio&quot; rel=&quot;nofollow noreferrer&quot;&gt;razor blade could work&lt;/a&gt;. Ideally it will have a low forward voltage and a fast recovery time, but if it doesn't it just means it will be harder to light the LED, so you may not be able to tune as precisely. 1N34A is a germanium diode which has a lower forward voltage (around 0.3V) than silicon diodes (around 0.65V). Germanium diodes are an antique item these days. You might have better luck finding a Schottky diode, and it will probably work better too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if a 1N4148 is what you have and it works acceptably, then go with that. Nothing bad will happen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't strictly need C1 either, but it might make the LED brighter. Without C1 the LED will only blink, but with C1 it can charge up and power the LED though the entire AC cycle. You can also think about how C1 lowers the AC impedance of the detector circuit, enabling it to draw more power and thus make the LED brighter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Calculating R4 is pretty noncritical. You want something that's high enough to limit the current through the LED so it doesn't go up in smoke, but low enough that the LED is bright enough to see. Ideally you want the time constant of R4 and C1 to be long relative to the frequency so the capacitor doesn't discharge much between cycles. But the time constant shouldn't be so long the LED continues glowing long after you've reached a good tuning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now it should be apparent how you might adapt this circuit for use with a panel meter. Depending on the kind of meter you have and how sensitive it is, you might even forgo the transformer, and instead put the meter in place of T1's primary in series with a rectifying diode. Otherwise you might play with the winding ratio of T1 to make good use of the meter's range, and you can replace R4 and D2 with the meter.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-08-22T13:25:48.153" LastActivityDate="2016-08-22T13:25:48.153" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6579" PostTypeId="2" ParentId="6574" CreationDate="2016-08-22T13:15:00.777" Score="4" Body="&lt;p&gt;Bond it all together. At both ends, if you can. Effective lighting protection isn't really just about providing a path to ground, though that's part of it. More importantly, &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;lightning protection&lt;/a&gt; is about having &quot;ground&quot; at just one point so &quot;ground over here&quot; can't be 200V different from &quot;ground over there&quot;. This is what you get, for example, when your radio is plugged into a normal AC outlet which goes to the ground at the electrical panel (ground #1), while also being plugged into the antenna (ground #2).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The more effectively you bond all the grounds together, the less potential difference can develop between them, providing better protection. The lightning protector is just there to temporarily ground thing which can not be grounded (like the coax center conductor) in the case of a strike.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bonding the grounds together isn't going to make common mode issues any worse, and if anything will make them better. In fact common mode currents will flow over all your cables whether you connect them or not: that they run parallel means they are inductively and capacitively coupled and so the RF current will &quot;jump&quot; across them even if they aren't connected at DC. This is why for example common mode currents always end up on the outside of coax, even if you try to drive the current on the center.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if your common-mode currents are due to something like driving a vertical without a sufficient ground plane, then those common mode currents want to get to ground to match the current in the vertical. Providing a lower impedance path to ground will thus improve things.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-08-22T13:15:00.777" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6580" PostTypeId="1" CreationDate="2016-08-22T23:19:35.460" Score="4" ViewCount="1523" Body="&lt;p&gt;On a number of fairly modern rigs I've seen that both power leads are fused:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cUyKA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cUyKA.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is this still so?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this have something to do with some vehicles having a ground-positive system or is this simply a forgotten relic that needs to disappear as quick as possible?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the fuse (in the negative lead) needs to go, what would be a safe and proper solution?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Related: &lt;a href=&quot;https://ham.stackexchange.com/questions/300/how-do-i-power-my-radio-in-a-vehicle-mobile-install&quot;&gt;How do I power my radio in a vehicle mobile install?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1135" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-08-22T23:34:39.097" Title="why do some radios have two fuses in the power leads" Tags="&lt;safety&gt;&lt;dc-power&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6581" PostTypeId="2" ParentId="6580" CreationDate="2016-08-22T23:34:39.097" Score="4" Body="&lt;p&gt;According to Alan K0BG's &lt;a href=&quot;http://www.k0bg.com/wiring.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;page about wiring&lt;/a&gt;, the negative lead is fused because of the possibility of a faulty ground elsewhere in the vehicle, which could cause excessive current to flow in the negative lead to the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a diagram from Alan, showing how to properly wire power to the radio:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/rnHOx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rnHOx.jpg&quot; alt=&quot;how to properly wire power to a ham radio in a vehicle&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alan's page about wiring, and the rest of &lt;a href=&quot;http://www.k0bg.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;his site&lt;/a&gt;, are chock-full of excellent advice about mobile ham radio.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-08-22T23:34:39.097" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6582" PostTypeId="1" AcceptedAnswerId="6583" CreationDate="2016-08-23T02:33:32.287" Score="0" ViewCount="2319" Body="&lt;p&gt;I am living in a small compartment, considering setting up an antenna indoors. As my room is so small (3m^2), thinking of putting a dipole antenna with soft wire indoors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If two ends of dipole antenna are pointing to the same direction. Will the signal be cancalled?&lt;/p&gt;&#xA;" OwnerUserId="353" LastActivityDate="2016-08-28T19:23:42.670" Title="Will two ends of dipole antenna pointing to the same direction cancel out the signal" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6583" PostTypeId="2" ParentId="6582" CreationDate="2016-08-23T03:37:33.890" Score="2" Body="&lt;p&gt;From an antenna theory perspective, &lt;strong&gt;if you've bent the wire it isn't a dipole antenna any more.&lt;/strong&gt; You've changed the shape of the antenna away from a dipole, so it will have a different radiation pattern than a dipole. The exact results will depend on what specifically you did.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the results will not be “the antenna no longer works”. &lt;strong&gt;It will just be different,&lt;/strong&gt; and &lt;em&gt;somewhat&lt;/em&gt; less efficient — as is &lt;strong&gt;any&lt;/strong&gt; antenna folded or coiled to fit in a smaller space. But you'll also have pattern changes and losses from putting the antenna indoors — all structures interact with radio waves somewhat, even if they contain no metal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(You can use antenna modeling software to see the results of using a particular shape, but this does not account for the characteristics of the surrounding walls and ceiling.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Practically, don't worry too much about the antenna shape, just spread it out as much as you can. &lt;strong&gt;Bending an antenna to fit inside an apartment is a very common thing to do.&lt;/strong&gt; Remember that the antenna will have a different impedance than an ordinary dipole of the same length, so don't use a pre-designed antenna and expect it to work as intended this way; expect to need to tune it (by trimming the ends, or using an antenna tuner or custom matching network).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also consider, instead of a dipole, a wire loop around the entire perimeter of your ceiling — on the principle that this is the biggest antenna you can put up in your space.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-08-23T03:37:33.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6584" PostTypeId="2" ParentId="6582" CreationDate="2016-08-23T13:18:45.297" Score="2" Body="&lt;p&gt;I too have a small room and can not put my antenna outside or in the attic. My solution was a flag antenna mounted around the room. The flag or pendant antenna when used outdoors is rectangular and supported by two corners often with weights on the other two corner thus the name flag. (sometimes called a pendant) I ran a thin wire around the room below the crown mold. If you google flag antenna you will find several. They use a transformer at the feed and a resistor in the center. The resistor is adjusted to match the antenna to the receiver. This design was developed by the navy in the 1940s for shipboard use and later for portable use. &lt;a href=&quot;https://i.stack.imgur.com/4jqND.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4jqND.jpg&quot; alt=&quot;This is mine. &quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may not be as good as an outdoor antenna but I listen to the net login from a the southeast. Fla,Tenn,Texas and Arkansas. &#xA;I have a 1.2Kohm resistor between the two dots and a 29T:9T transformer wound on a 1/2&quot; yellow toroid. &lt;/p&gt;&#xA;" OwnerUserId="8207" LastEditorUserId="8207" LastEditDate="2016-08-23T13:24:31.243" LastActivityDate="2016-08-23T13:24:31.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6586" PostTypeId="5" CreationDate="2016-08-24T08:23:42.587" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2016-08-24T08:23:42.587" LastActivityDate="2016-08-24T08:23:42.587" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6587" PostTypeId="4" CreationDate="2016-08-24T08:23:42.587" Score="0" Body="A widely used toolkit used to develop software-defined radios and general signal processing applications." OwnerUserId="194" LastEditorUserId="194" LastEditDate="2019-09-29T18:08:56.290" LastActivityDate="2019-09-29T18:08:56.290" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="6588" PostTypeId="2" ParentId="6573" CreationDate="2016-08-25T07:08:26.757" Score="1" Body="&lt;p&gt;In the &quot;???&quot; you'd expect to find a low-pass or band-pass filter. Without one you'd get &lt;a href=&quot;https://en.wikipedia.org/wiki/Aliasing#Sampling_sinusoidal_functions&quot; rel=&quot;nofollow&quot;&gt;aliasing&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's nothing special to separate the &quot;I samples&quot; from the &quot;Q samples&quot; as part of the filter. The distinction between I and Q does not exist until after the mixers, and what makes them different is the 90 degree phase difference between the LO for the two mixers.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-08-25T07:08:26.757" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6589" PostTypeId="2" ParentId="1172" CreationDate="2016-08-25T07:19:51.133" Score="1" Body="&lt;p&gt;I recommend looking at &#xA;&lt;a href=&quot;http://playground.arduino.cc/Code/DCF77&quot; rel=&quot;nofollow&quot;&gt;http://playground.arduino.cc/Code/DCF77&lt;/a&gt;&#xA;and&#xA;&lt;a href=&quot;http://forum.arduino.cc/index.php?topic=102039.0&quot; rel=&quot;nofollow&quot;&gt;http://forum.arduino.cc/index.php?topic=102039.0&lt;/a&gt;&#xA;I plan to build a few units with this and a DS3231 RTC, so they can supply a time array to anything I wish over serial connection. &lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-08-25T07:19:51.133" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6590" PostTypeId="1" CreationDate="2016-08-25T16:54:04.450" Score="2" ViewCount="718" Body="&lt;p&gt;I bought Veronica 1W FM Transmitter online, hooking it up and tuning the radio beside me, I can hear the audio on multiple 'stations' or frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried screwing the vc1 which the seller said changed the frequency, there are in total 4 pots.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is it sending to multiple frequencies, and how can I get it to send to only one frequency?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think's it's this type: &lt;a href=&quot;http://www.electroschematics.com/5/veronica-1w-fm-transmitter/&quot; rel=&quot;nofollow&quot;&gt;http://www.electroschematics.com/5/veronica-1w-fm-transmitter/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8223" LastActivityDate="2016-08-26T12:12:21.483" Title="FM transmitter sending to multiple frequencies" Tags="&lt;frequency&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6592" PostTypeId="2" ParentId="6590" CreationDate="2016-08-26T12:12:21.483" Score="4" Body="&lt;p&gt;So you're clearly seeing signal where there shouldn't be any – this can have different reasons:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Your transmitter actually transmits on frequencies it shouldn't&lt;/li&gt;&#xA;&lt;li&gt;Your receiver sees signal where there isn't actually signal &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Both can again be caused by different things – the Veronica class of transmitters seem to be working with &quot;kind of&quot; two 180° offset intermediate frequencies of half the desired RF carrier. So your transmitter could actually just be leaking those on TX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, your receiver might simply be picking up the strong signal although it's tune somewhere else completely, simply by the fact that the receiver's mixers never &quot;calculate&quot; the frequency difference you wish, but also other linear combinations of RF and IF – you can only counteract that by filtering, but filtering might simply not be sufficient if the input power is so large that things still make it through the filter in sufficient strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then: every active component in both your receiver and your transmitter is potentially a mixer. Fundamental truth of RF design: &lt;strong&gt;every&lt;/strong&gt; nonlinearity produces intermodulations (ie. sum and difference frequencies of the different signal frequencies present at the component). Most don't do that intentionally, and  designers take care to eliminate the effects. However, especially amplifiers get the less linear the more you drive them with an overly strong signal – making them mix different frequencies present. So, suddenly, your receiver's (hypthetical, I don't know your receiver) IF amplifier becomes a mixer for the IF and the remnants of RF that passed through the &quot;intentional&quot; mixer, leading to surprising results.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-08-26T12:12:21.483" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6593" PostTypeId="2" ParentId="6267" CreationDate="2016-08-26T13:50:38.490" Score="4" Body="&lt;p&gt;This will be an incomplete answer to begin with, hoping that collectively we can come up with a workable solution:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Freq 156.425 Mhz&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-f 156.425e6&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Filter: Wide&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;I did not find &quot;Filter&quot; in any online-reference of rtl_fm, unless this is &quot;sample rate&quot;, which can be set by:&lt;/em&gt; &lt;code&gt;-s 12k&lt;/code&gt; &lt;em&gt;for narrow FM&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Mode: Narrow FM&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-M fm&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;AGC: Fast&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;I did not find AGC in any online-reference of rtl_fm&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Squelch: -58.5 dBFS&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-l 58.5&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;(not very clear what values the &lt;code&gt;-l&lt;/code&gt; switch takes, and what this would result in, so this value will need experimentation)&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;LNB LO: 0Mhz&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;LNB is for devices with external block downconverters; it doesn't apply here, so we don't have to account for this&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Gain: 10&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-g 10&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Freq Correction: 0ppm&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-p 0&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Stream as UDP&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Streaming over UDP is not one of the functionalities of the rtl_fm tool versions that are available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can emulate this behaviour, however, by using the output of &lt;code&gt;rtl_fm&lt;/code&gt; e.g. as input to an audio compressor and a network sending program such as &lt;code&gt;n[et]cat&lt;/code&gt;:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Network Streaming&#xA;&#xA;Maybe you have a poor quality wifi link and don't want to send a &#xA;full 1MS/s data stream around. Here is how to make a quick and &#xA;dirty mp3 stream that will average 4KB-8KB/sec for voice channels. &#xA;Other codecs may be swapped in as desired.&#xA;&#xA;On the dongle side:&#xA;rtl_fm ..... | sox -traw -r24k -es -b16 -c1 -V1 - -tmp3 - | socat -u - TCP-LISTEN:8080&#xA;&#xA;On the loudspeaker side:  &#xA;netcat don.gle.ip.adr 8080 | play -t mp3 -&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;Generally, you can get a list of &lt;code&gt;rtl_fm&lt;/code&gt; options by calling it with the &lt;code&gt;-h&lt;/code&gt; flag:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;$&amp;gt; rtl_fm -h&#xA;rtl_fm, a simple narrow band FM demodulator for RTL2832 based DVB-T receivers&#xA;&#xA;Use:    rtl_fm -f freq [-options] [filename]&#xA;    -f frequency_to_tune_to [Hz]&#xA;        use multiple -f for scanning (requires squelch)&#xA;        ranges supported, -f 118M:137M:25k&#xA;    [-M modulation (default: fm)]&#xA;        fm, wbfm, raw, am, usb, lsb&#xA;        wbfm == -M fm -s 170k -o 4 -A fast -r 32k -l 0 -E deemp&#xA;        raw mode outputs 2x16 bit IQ pairs&#xA;    [-s sample_rate (default: 24k)]&#xA;    [-d device_index (default: 0)]&#xA;    [-g tuner_gain (default: automatic)]&#xA;    [-l squelch_level (default: 0/off)]&#xA;    [-p ppm_error (default: 0)]&#xA;    [-E enable_option (default: none)]&#xA;        use multiple -E to enable multiple options&#xA;        edge:   enable lower edge tuning&#xA;        dc:     enable dc blocking filter&#xA;        deemp:  enable de-emphasis filter&#xA;        direct: enable direct sampling&#xA;        offset: enable offset tuning&#xA;    filename ('-' means stdout)&#xA;        omitting the filename also uses stdout&#xA;&#xA;Experimental options:&#xA;    [-r resample_rate (default: none / same as -s)]&#xA;    [-t squelch_delay (default: 10)]&#xA;        +values will mute/scan, -values will exit&#xA;    [-F fir_size (default: off)]&#xA;        enables low-leakage downsample filter&#xA;        size can be 0 or 9.  0 has bad roll off&#xA;    [-A std/fast/lut choose atan math (default: std)]&#xA;&#xA;Produces signed 16 bit ints, use Sox or aplay to hear them.&#xA;    rtl_fm ... | play -t raw -r 24k -es -b 16 -c 1 -V1 -&#xA;               | aplay -r 24k -f S16_LE -t raw -c 1&#xA;      -M wbfm  | play -r 32k ... &#xA;      -s 22050 | multimon -t raw /dev/stdin&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;Others: please comment or directly edit this post to see if we can complete the command-line switches&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;[EDIT 29-Aug-2016]&#xA;our answer to the question is:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Answer 1, gain to be automatic,&lt;/strong&gt; &lt;code&gt;-l&lt;/code&gt; &lt;strong&gt;value need to be determined experimentally:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rtl_fm -f 156.425e6 -s 12k -M fm -l 58.5 &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Answer 2, gain to be set at 10,&lt;/strong&gt; &lt;code&gt;-l&lt;/code&gt; &lt;strong&gt;value need to be determined experimentally:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rtl_fm -f 156.425e6 -s 12k -M fm -l 58.5 -g 10&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-08-29T07:39:57.633" LastActivityDate="2016-08-29T07:39:57.633" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6594" PostTypeId="1" CreationDate="2016-08-27T01:12:02.300" Score="2" ViewCount="3978" Body="&lt;p&gt;Context&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Using a Baofeng UV5RA&lt;/li&gt;&#xA;&lt;li&gt;Would like to transmit on MURS (e.g., 151.880&#xA;MHz) using a CTCSS code for more private discussions&lt;/li&gt;&#xA;&lt;li&gt;All of the online guides talk about &lt;em&gt;scanning&lt;/em&gt; for CTCSS&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Question&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Rather than scanning, is it possible to just &lt;em&gt;explicitly set&lt;/em&gt; both the transmitting radio, as well as the receiving radio, to use one of the 38 tones?&lt;/li&gt;&#xA;&lt;li&gt;If so, how do you choose and set one of these?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Thanks so much for any guidance&lt;/p&gt;&#xA;" OwnerUserId="8228" LastActivityDate="2016-08-28T10:59:42.133" Title="MURS - Set to broadcast and receive on a specific CTCSS code" Tags="&lt;baofeng&gt;&lt;tone-squelch&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6595" PostTypeId="2" ParentId="6582" CreationDate="2016-08-27T01:42:53.510" Score="2" Body="&lt;p&gt;Harold,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer is no. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation pattern simply changes depending on how much is bent and if the ends of a dipole are bent nearer ground or to the side where ground reflection is uniform.  Fine tuning can be done by angle of bend.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a figure in the QSL Bent Dipoles site for “Bent Down Ends”:  The 4NEC2 modeling shows as the bend point is increased to 50% length, gain gradually goes down little more than a half dB.   SWR goes down to a minimum at 60% and rises at 50%.  Shorter than 50% the SWR rises quickly.  The total length of wire necessary to maintain resonance gradually increases up to the 50% bend point then decreases past that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The associated polar graph and 3D picture at the 50% bend point show a typical dipole shape only slightly fatter than a standard dipole. Two other 3D pictures show separately the major horizontal radiation and the smaller amount of vertical radiation from the bent ends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quoting “The modeling software makes it clear that you can bend the ends of a horizontal dipole with very little change in antenna performance, just some retuning is required”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking at another figure: “Dipole, Laterally Bent-ends”, modeling shows that when bending to the same side, the decrease in gain is the same as a bent down dipole. The length of wire to maintain resonance will increase up to around 3% as the bend point approaches 50%.  SWR shows a minimum at 60% bend rising rapidly past 50% bend.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another figure about bending to opposite sides is noticeably different. In this form the gain drops only slightly until bends reach 50% to 30% but does not rise “off-the-map” like same-side antennas.  SWR is lowest when the dipole is 60% long at the bends then rises 30 % and interestingly falls again because the long bends are radiating broadside which skews the RF pattern.  The amount of wire needed increases steadily to over 4% longer as the bend points reduce the dipole to less than 40% length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For fine tuning near 1:1 SWR, changing the angle of bend has the effect of changing the resonant length of the dipole.  With right angle bends in the same direction: Rule&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;If the impedance is greater than 50 Ohms, increase the angle of bend.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If the impedance is less than 50 Ohms, reduce the angle of bend. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The greater the bend the longer you must make the wire to keep in tune...&#xA;2-3% longer for up to a 90 degree bend.  Up to 10 to 15% longer when greater than a 90% bend. Roughly double the % increase for every 30 degrees of bend.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The above information comes from a web site about 4NEC2 modeling of the many ways to bend a dipole for space limited situations. Here is the link.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.qsl.net/kk4obi/Center-fed%20Dipole%20selection.html&quot; rel=&quot;nofollow&quot;&gt;http://www.qsl.net/kk4obi/Center-fed%20Dipole%20selection.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To see the “Bent Dipoles” discussions, figures and 3D pictures mentioned above, select Center-fed bent-end dipoles bent Horizontally or Laterally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider also selecting Folded-end dipoles. And, if you sometimes like to think out-of-the-box, take a look at zig-zag and particularly multi-catenary techniques that are so set-up tolerant yet and perform so well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dick Reid&lt;/p&gt;&#xA;" OwnerUserId="8229" LastEditorUserId="8229" LastEditDate="2016-08-28T19:23:42.670" LastActivityDate="2016-08-28T19:23:42.670" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6598" PostTypeId="1" CreationDate="2016-08-27T12:12:40.980" Score="1" ViewCount="655" Body="&lt;p&gt;What needs to be considered?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which type of antenna(only self-made or reused parts, for example satellite dish) is the best for a long range, high throughput WiFi? How to calculate Antenna size and shape? Which characteristics of the WiFi Module play a role for this application?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Long-Range WiFi for LOS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can share also any results of your own application.&lt;/p&gt;&#xA;" OwnerUserId="8230" LastActivityDate="2016-08-30T22:58:24.307" Title="Best way to make a selfmade Long-Range WiFi Link" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;wifi&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6600" PostTypeId="1" CreationDate="2016-08-28T09:37:51.940" Score="2" ViewCount="148" Body="&lt;p&gt;&lt;a href=&quot;http://vocaroo.com/i/s0fsMOJ82A7k&quot; rel=&quot;nofollow&quot;&gt;http://vocaroo.com/i/s0fsMOJ82A7k&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trying to decipher this morse code if someone can help me. It's 14 characters long and the first lot is Illuminatih I think.&lt;/p&gt;&#xA;" OwnerUserId="8236" LastActivityDate="2016-08-29T21:52:07.687" Title="Morse code help" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6601" PostTypeId="2" ParentId="6600" CreationDate="2016-08-28T10:19:23.860" Score="4" Body="&lt;p&gt;Well, a good starting way to solve this issue is to look up programs that do CW decoding and try out one of them. I'll give an example for decoding in &lt;a href=&quot;https://sourceforge.net/projects/fldigi/?source=directory&quot; rel=&quot;nofollow noreferrer&quot;&gt;FL-DIGI&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So first, you need to enable an audio source that will allow you to record what your loudspeakers are playing. In Windows, for example, this is called Stereo Mix. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next step is to get the FL-DIGI software. Start it up and it will ask you to configure it at first. You can skip the wizard, since you won't be controlling a radio with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, in the Op Mode menu select CW. You'll see two red bars appear in the waterfall display. After that go to configure menu and click on sound card. There, under capture, select Stereo Mix. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you can play your audio. The next step requires a bit of experience, since you'll need to identify the Morse code in the waterfall. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a picture of how it all looks like:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/XpCmL.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XpCmL.jpg&quot; alt=&quot;Morse code decoding&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So click on the Morse code in the waterfall and the two red bars will center on it. Now, use the two arrows next to the number 18 on my picture, to adjust the distance between the bars, so that the bars are as wide as the signal is. This is to ensure proper timing. Otherwise, spaces between words and numbers can be incorrectly decoded. If you aren't getting any decoding, take a look at the squelch setting on the right side. You need to adjust the slider so that the green bar is above the slider when you have code coming in, but below when you don't. This is to ensure that the program isn't trying to decode background noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hopefully, if it all went fine, you'll have a good decode. If it didn't mess around with the decode speed until it comes out fine. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck!&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2016-08-28T10:19:23.860" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6602" PostTypeId="2" ParentId="6594" CreationDate="2016-08-28T10:59:42.133" Score="3" Body="&lt;p&gt;Here on StackExchange we call what you asked an &lt;a href=&quot;https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem&quot;&gt;XY&lt;/a&gt; problem. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're asking how to set up CTCSS, but what you really want is to have privacy. Those are two different things. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First of all, a tiny bit of theory about CTCSS. The name means Continuous Tone-Coded Squelch System. It's not a privacy system, it's a squelch system! It works by sending a tone-code continuously while you're transmitting.&lt;br&gt;&#xA; So here comes the failure of the privacy idea: When it's sending the tone, what the radio is doing is basically &lt;strong&gt;kindly asking&lt;/strong&gt; other radios that do not have that code set on their receive not to open their squelch. If your receiver has no CTCSS code set, you'll hear everything since the squelch will just open. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for more private conversations, you'll need a radio with a scrambler. This won't make your conversations secret, but it will make it a tiny bit harder for other people to listen in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, for your CTCSS question. I don't have a Baofeng right now, so I can't test, but from what I can see, you should go to menu 13, which should be called CTCSS, and set up the code there. There's an explanation for example &lt;a href=&quot;https://hamgear.wordpress.com/2012/04/07/setting-up-and-programming-your-uv-5r/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; in comments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other option would be to get a programming cable and use &lt;a href=&quot;http://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP&lt;/a&gt; to set up channels and CTCCSS codes. &lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="-1" LastEditDate="2017-03-20T10:32:31.393" LastActivityDate="2016-08-28T10:59:42.133" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6603" PostTypeId="2" ParentId="5438" CreationDate="2016-08-28T21:10:02.583" Score="2" Body="&lt;p&gt;There are at least two definitions of Q factor. One is the reciprocial of &lt;a href=&quot;http://www.antenna-theory.com/definitions/fractionalBW.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;fractional bandwidth&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Q = {f_r \over \Delta f} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $ f_r $ is the resonant frequency (or center of the antenna's bandwidth) and $ \Delta f $ is the difference between the upper and lower frequencies of the bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By this definition, it's easy to calculate with pen and paper if you are allowed some empirical data. You might define &quot;bandwidth&quot; as the range of frequencies where the VSWR is better than 2:1 and empirically measure this bandwidth. Then calculating the Q factor is some simple arithmetic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other definition of Q is the ratio of energy stored to energy dissipated per cycle:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Q = 2 \pi {\text{energy stored} \over \text{energy dissipated per cycle}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is &lt;a href=&quot;https://ham.stackexchange.com/q/6481/218&quot;&gt;in theory calculable&lt;/a&gt;, but it's complex enough I don't think any normal person would attempt the calculation with pen and paper.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2016-08-28T21:10:02.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6604" PostTypeId="2" ParentId="5752" CreationDate="2016-08-29T08:00:04.150" Score="6" Body="&lt;p&gt;In the RAF we used &quot;best bent wire&quot; as a test transmission largely because it has a lovely jazz rhythm.  Some put &quot;bens&quot; in front, some put another &quot;bent&quot; on the end, but i you send it a reasonable speed, it does flow rather nicely.  Hope this helps.&lt;/p&gt;&#xA;" OwnerUserId="8244" LastActivityDate="2016-08-29T08:00:04.150" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6605" PostTypeId="2" ParentId="6600" CreationDate="2016-08-29T11:05:18.077" Score="3" Body="&lt;p&gt;Illuminati5643&#xA;Repeated in a loop&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above answer with the digits as 6543 is wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And it is easy to copy it by ear&lt;/p&gt;&#xA;" OwnerUserId="8160" LastEditorUserId="8160" LastEditDate="2016-08-29T21:52:07.687" LastActivityDate="2016-08-29T21:52:07.687" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6607" PostTypeId="2" ParentId="139" CreationDate="2016-08-29T17:13:15.423" Score="4" Body="&lt;p&gt;I share the same pain, I bought into a Home with HOA BEFORE I got interested in HAM.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good reference for ideas for HOA restricted Antennas can be found in the ARRL's book &quot;Small Antennas for Small Spaces&quot;.   It's chalk full of ideas.&#xA;(ARRL:  &lt;a href=&quot;https://www.arrl.org/shop/Small-Antennas-for-Small-Spaces-2nd-Edition/&quot; rel=&quot;nofollow&quot;&gt;https://www.arrl.org/shop/Small-Antennas-for-Small-Spaces-2nd-Edition/&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check YouTube, there are lots of creative ideas that appear to work.&#xA;I myself have purchased a speaker stand and mounted a J-Pole on it and put it out at night or when I need to get on the air.   Seems to work for me pretty well with my HT.  Now to get my IC-7100 up and running. :)  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I saw one where a Ham put an Antenna in a flower pot and decorated it with fake/plastic flower vines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good look.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A fellow like minded Ham&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8250" LastActivityDate="2016-08-29T17:13:15.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6608" PostTypeId="1" CreationDate="2016-08-30T06:07:11.247" Score="1" ViewCount="84" Body="&lt;p&gt;Back in the 90's I received my Tech license. I let it expire. Now many years later and I have the time (Retired) I would like to get back into Ham Radio. Do I need to take the Tech exam again? Or If I show proof that I took the test and received a tech license I can just pay any fees and be reissued a tech license?&lt;/p&gt;&#xA;" OwnerUserId="8257" LastEditorUserId="76" LastEditDate="2016-08-30T14:31:51.927" LastActivityDate="2016-08-30T14:40:52.450" Title="Geting my Tech Licence again" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6609" PostTypeId="1" CreationDate="2016-08-30T06:29:59.537" Score="0" ViewCount="145" Body="&lt;p&gt;I was wondering what the laws are in Japan concerning FM Transmitters. I recently purchased one of eBay (&lt;a href=&quot;http://www.ebay.com/itm/401047827071&quot; rel=&quot;nofollow&quot;&gt;http://www.ebay.com/itm/401047827071&lt;/a&gt;)&#xA;I don't have a license or anything so I would like to know if I can legally use it.&lt;/p&gt;&#xA;" OwnerUserId="5616" LastActivityDate="2016-08-30T07:32:26.767" Title="is fm transmitters legal in japan" Tags="&lt;legal&gt;&lt;fm&gt;&lt;transmitter&gt;&lt;japan&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6610" PostTypeId="2" ParentId="6609" CreationDate="2016-08-30T07:32:26.767" Score="3" Body="&lt;p&gt;Usually these type of questions are not easy to answer precisely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally speaking countries allow certain low-power devices to transmit within the FM-broadcast band, pending type-approval of the device. (e.g. the device must be tested and found to be OK according to specifications)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are resources which can be found on the internet, such as &lt;a href=&quot;http://www.teleconformity.com/index?page=japan&quot; rel=&quot;nofollow&quot;&gt;this&lt;/a&gt;, which lists the following:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;As specified in the Radio Law, Extremely Weak (low) Power Equipment&#xA;  and Receivers must comply with the Japanese Radio Regulations, but do&#xA;  not require registration at MIC. Examples of products requiring&#xA;  performance of compliancy with the emission limits, are FM modulators&#xA;  and radio Receivers. Teleconformity offers Performance Certification,&#xA;  including testing.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You do need to ask yourself how much &quot;authority&quot; these resources have in these cases. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems that there is some sort of &quot;&lt;em&gt;certification&lt;/em&gt;&quot; needed for low power devices, from MIC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could ofcourse contact &lt;a href=&quot;http://www.soumu.go.jp/english/&quot; rel=&quot;nofollow&quot;&gt;MIC&lt;/a&gt; (Ministry of Internal Affairs and Communications) to get further information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;... maybe someone with more specific knowledge about Japanese legislation can give you a more precise answer...&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-08-30T07:32:26.767" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6611" PostTypeId="1" AcceptedAnswerId="6613" CreationDate="2016-08-30T08:18:06.357" Score="8" ViewCount="3910" Body="&lt;p&gt;Brand new Ham. I bought a cheapo UV5 right before I got my call sign. I want to set up a decent 2m/70cm station for starters and I realize that a better radio is important but wanted to knock out the antenna situation first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in HOA hell so no outdoor antennas, and to make matters worse, I am working with a 60 foot length / 36-40 inch height attic space. The good thing is my room/ham shack sits below the largest part of the house so I would only be looking at a — at most — 30 foot run to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any recommendations on DIY or for purchase antennas would be much appreciated. Any recommendations on type of cable to run (RG8/RG8x/LMR-400)? I'm  looking for really good results to get started without a huge investment — I may be dreaming on this one.&lt;/p&gt;&#xA;" OwnerUserId="8258" LastEditorUserId="8258" LastEditDate="2016-08-31T10:41:46.977" LastActivityDate="2018-01-12T15:38:07.700" Title="Antenna for a cramped attic" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;antenna-system&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6612" PostTypeId="2" ParentId="1729" CreationDate="2016-08-30T13:50:37.533" Score="1" Body="&lt;p&gt;As mentioned, it might have been an SKCC member just calling for others.  He might have done better to use the full 'SKCC' acronym to avoid confusion.&lt;br&gt;&#xA;I say this as a rookie CW and new SKCC member.&lt;br&gt;&#xA;The SKCC website mentions 21.050  14.050  7.050 as hot spots for us.  Btw I think paddle keyers refer to SK as signifying 'Slow Keyers' (hi hi)&lt;/p&gt;&#xA;" OwnerUserId="8260" LastActivityDate="2016-08-30T13:50:37.533" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6613" PostTypeId="2" ParentId="6611" CreationDate="2016-08-30T14:29:16.137" Score="5" Body="&lt;p&gt;Your attic is pretty low but not quite low enough to be a problem for installing a vertically polarized 144 MHz antenna. There are two common antenna designs that would suit your case:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Ground plane antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This simply consists of a vertical quarter-wavelength element (stiff wire or rod) sticking up from a horizontal ground plane (sheet metal, as big as you can make it). You can either make it entirely from scratch, or get an antenna intended for vehicles (magnet or through-hole mount) and supply your own sheet metal surface (if you don't have metal supply handy, buy a steel cookie sheet).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Vertical dipole antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This consists of two quarter-wavelength elements, one above the other, fed from the center. Your roof is &lt;em&gt;just&lt;/em&gt; high enough that you'll be able to fit one in in the full height.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most straightforward way to feed a vertical dipole is to run coax &lt;em&gt;horizontally&lt;/em&gt; to the center (feed point); the coax must not just dangle next to the lower element. Alternatively, you can &lt;a href=&quot;https://ham.stackexchange.com/questions/644/handheld-dipoles/1941#1941&quot;&gt;run the feed line inside the antenna, coaxially&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A vertical dipole is an uncommon antenna because it's taller than most and because it either requires a sideways bit sticking out or more complex construction. You'll probably have to make it from scratch, but that's easier since (for the horizontal feed) all you need is plain wire and a way to support the ends and join to the coax in the center.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Ideally, your antenna would be cut to exactly the right length to present a 50 Ω impedance (1:1 SWR) to the radio, but HTs are built to deal with compromise antennas (short ‘rubber duckies’), so it'll work fine, just not quite as efficiently. But if you know a friend with an antenna analyzer, have them bring it over to test while you trim the antenna to length.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;In either case, if you are planning higher-power operation, or in general for best results, you should install a &lt;em&gt;choke balun&lt;/em&gt; at the feed-point (except for the coaxial vertical dipole which does not need one). This ensures that the part of your system which actually radiates/receives is the part in the attic, not the rest of the cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest possible design is simply taking some extra length of cable in your feed line and coiling it into a tight neat helix (use a piece of plastic pipe as a form) as if you were making an inductor. Don't bend coaxial cable too tightly — check the specifications!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Finally, for your choice of coaxial cable: look up its specifications, find the loss (given in dB per some length at a particular frequency), multiply that by the length you'll be using (check your units!), and decide if that loss is acceptable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if you paid the price to install some LMR-400 which specifies loss as 1.5 dB/100 ft at 150 MHz, and your run is 30 feet long, then your actual loss is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;\frac{1.5\,\mathrm{dB}}{100\,\mathrm{ft}} \cdot 30\,\mathrm{ft} = 0.45\,\mathrm{dB}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And to convert that to a power ratio we calculate $10^{-0.45/10} = 0.902$. So however much power your transmitter puts out, you're losing a tenth of it in the coax. That's quite good. If you use lesser coax, you'll have worse results, but even, say, a 3 dB loss is not really a big deal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Note that the actual loss will be worse than this insofar as your SWR is poor, because standing waves mean reflections mean the signal traversing the cable more than once.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-08-31T18:40:34.923" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6614" PostTypeId="2" ParentId="6608" CreationDate="2016-08-30T14:40:52.450" Score="4" Body="&lt;p&gt;&lt;strong&gt;You must retake the examination.&lt;/strong&gt; The relevant regulation is &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=c89c6646e415ced62cde7df69e8f017a&amp;amp;mc=true&amp;amp;node=se47.5.97_1505&amp;amp;rgn=div8&quot; rel=&quot;nofollow&quot;&gt;§97.505&lt;/a&gt;. Unfortunately it is formatted in a table which I can't quote in full neatly, but the relevant part says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(a) The administering VEs must give credit as specified below to an&#xA;  examinee holding any of the following license grants:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;    …&lt;br&gt;&#xA;      (3) Technician Plus; or Technician granted on or after March 21, 1987&lt;br&gt;&#xA;          Expired and beyond the renewal&#xA;  grace period&lt;br&gt;&#xA;                  No credit.&lt;br&gt;&#xA;      …  &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) The administering VEs must give credit&#xA;  to an examinee holding a CSCE for each element the CSCE indicates the&#xA;  examinee passed within the previous 365 days.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if you had held a higher class of license, you would be able to regain your license at that class by only taking the Technician exam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that in any case &lt;strong&gt;you will also be assigned a new call sign.&lt;/strong&gt; If you want your old call sign and it is still available, then you may apply for it as a vanity call sign; this can only be done &lt;em&gt;after&lt;/em&gt; you have your new call sign.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Look at it this way: you have time, and you need to take the exam. You might as well shoot for Extra along the way! Get studying!&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-08-30T14:40:52.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6615" PostTypeId="2" ParentId="606" CreationDate="2016-08-30T18:45:31.923" Score="1" Body="&lt;p&gt;To lower the incoming noise on a dipole antenna, connect a ground wire to the coax fitting at the antenna base. Run it to a ground rod and enjoy hearing stations that were covered up before. This does not drop incoming signals it just gives noise that comes in the shack on the shielding portion of the coax a direct path to ground. Turn off all filters and squelch to get a base line and connect the ground wire and recheck. Made a 2 s unit difference on my rig. Good luck !&lt;/p&gt;&#xA;" OwnerUserId="8264" LastActivityDate="2016-08-30T18:45:31.923" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6616" PostTypeId="2" ParentId="6598" CreationDate="2016-08-30T22:58:24.307" Score="1" Body="&lt;p&gt;A 2.4Ghz parabolic dishes reflect into/from a 12.5cm yagi pointed at the centre. I suppose you could be flexible with the dish diameter, but the yagi must be correctly made ( with reflector and director ), and you can't expect good results long-range with a yagi shorter than one full wavelength. If you are in an area with much traffic on 2.4GHz, use 5GHz instead. Ubiquiti networks used to sell pretty good cards for long-range links, but I suppose you can get by with some Alfa USB cards on the endpoints. Remember to use coax for antenna cables. If you are truly serious about DIY:&#xA;&lt;a href=&quot;http://m.youtube.com/watch?v=WkXsS-kTtPo&quot; rel=&quot;nofollow&quot;&gt;http://m.youtube.com/watch?v=WkXsS-kTtPo&lt;/a&gt;&#xA;&lt;a href=&quot;http://www.instructables.com/id/Wifi-Signal-Strainer-WokFi/&quot; rel=&quot;nofollow&quot;&gt;http://www.instructables.com/id/Wifi-Signal-Strainer-WokFi/&lt;/a&gt;&#xA;&lt;a href=&quot;http://lifehacker.com/5053796/boost-your-wi-fi-signal-with-cooking-strainer&quot; rel=&quot;nofollow&quot;&gt;http://lifehacker.com/5053796/boost-your-wi-fi-signal-with-cooking-strainer&lt;/a&gt;&#xA;Try to keep endpoints using identical operating systems. Tomato *WRT, whichever is most effective. &lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-08-30T22:58:24.307" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6617" PostTypeId="1" AcceptedAnswerId="6619" CreationDate="2016-08-30T23:08:45.213" Score="2" ViewCount="526" Body="&lt;p&gt;Is it possible to jam the jammer signal, to disrupt its jamming of the owned RF signal?&lt;/p&gt;&#xA;" OwnerUserId="8230" LastActivityDate="2016-09-02T07:16:47.853" Title="Can you jam jam?" Tags="&lt;rfi&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6618" PostTypeId="2" ParentId="1729" CreationDate="2016-08-30T23:27:15.833" Score="3" Body="&lt;p&gt;In Morse communication, SK is a so-called prosign - see the entry in  &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Prosigns_for_Morse_code&quot; rel=&quot;nofollow&quot;&gt;wikipedia&lt;/a&gt; - meaning &quot;end of contact&quot;. It's what you normally send when you have finished with another station. The KN you used at the end of your call, meaning &quot;go ahead only&quot; is another such prosign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lots of these morse prosigns are carried over to other modes like digital...but maybe not always used correctly, I suppose.&lt;/p&gt;&#xA;" OwnerUserId="8160" LastActivityDate="2016-08-30T23:27:15.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6619" PostTypeId="2" ParentId="6617" CreationDate="2016-08-30T23:35:21.760" Score="4" Body="&lt;p&gt;This would be something like &lt;a href=&quot;https://en.wikipedia.org/wiki/Active_noise_control&quot; rel=&quot;nofollow&quot;&gt;active noise cancellation&lt;/a&gt; and depending on the nature of the source could be somewhat possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it is not a trivial task.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you imagine trying to cancel out an unmodulated carrier wave, with both the unwanted transmitter and a single receiver you are trying to &quot;unjam&quot; in fixed locations, you simply would need to transmit your own unmodulated carrier at some particular amplitude and phase, such that your &quot;unjamming&quot; signal and the jamming signal cancel out at the receiver.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;However, if the jamming signal is changing unpredictably, you'll need to be able to mimic it — only 180º out of phase — quickly enough to maintain the cancellation at the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, if you are trying to &quot;unjam&quot; multiple (and perhaps mobile!) receivers the problem becomes much harder still: now you have to cause this destructive cancellation not just at a single fixed point, but at multiple points simultaneously. Sort of like causing a &quot;picket fence&quot; effect to the jamming signal, but your job is to control things so the &quot;dead spots&quot; land exactly where you want!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically you're having to design an antenna array with deep nulls in all the right places. To make matters worse, before you can drive those elements of this antenna array which &lt;em&gt;are&lt;/em&gt; under your control (at least one won't be!), you're also having to reconstruct the original transmission to feed into your part.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Can you do this more simply?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, if you can arrange to unjam the interfering signal directly at each receiver, you avoid the need to deal with all the &quot;antenna array&quot; stuff. But then the problem boils down to really the same thing &quot;noise blankers&quot; and &quot;DSP filtering&quot; and whatnot are trying to solve already.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if you can arrange to unjam the interfering signal directly at its source, well, then… bring some wire snips?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-08-30T23:40:43.777" LastActivityDate="2016-08-30T23:40:43.777" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6620" PostTypeId="2" ParentId="5209" CreationDate="2016-08-31T02:38:30.173" Score="2" Body="&lt;p&gt;The ID-51A Plus behaves differently.  Near repeater does NOT work as documented.  I am hacking at it to try to figure it out.  Following the instructions on the above link provides nothing.  The to: is underlined and you cannot use the up down to go to the field to reset it.  Basically you are stuck in a catch where a reset is required to get you out. If someone has the true solution I would like to see it.  Also the Advanced instructions are dumbed down instructions.  The Section 6 in Advanced instructions referenced on page xii in the Basic Instructions is no good. Too bad somebody did not know what they were doing documenting the transceiver.  I am not fond of it because of the poor documentation &lt;/p&gt;&#xA;" OwnerUserId="8267" LastActivityDate="2016-08-31T02:38:30.173" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6621" PostTypeId="2" ParentId="6617" CreationDate="2016-08-31T07:47:24.567" Score="2" Body="&lt;p&gt;While the other answer is all true and well formulated, let me take another approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One definition of &lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_jamming&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;Radio Jamming&quot;&lt;/a&gt; as given by the linked Wiki page is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&quot;any device that deliberately blocks, jams or interferes with authorized wireless communications&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And doing so would be in disregard of our Amateur Radio license conditions, and ethic, therefor we as licensed amateurs should not do this to begin with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the question &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;em&gt;&quot;Is it possible to jam the jammer&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;is an ethical question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe that jamming a jammer will make you a jammer. Therefore we should not try to do this either.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Don't jam&lt;/li&gt;&#xA;&lt;li&gt;Don't jam the jammer&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Some will jam, so then you spin the dial and move somewhere else, we have plenty of spectrum to play with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;[EDIT based on comments]&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some further explanation is needed:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I deliberately did not take a &quot;&lt;em&gt;legal&lt;/em&gt;&quot; definition of &quot;&lt;em&gt;jamming&lt;/em&gt;&quot; as the wording of legislation could differ between jurisdictions. However, we can probably all agree that &quot;&lt;em&gt;jamming&lt;/em&gt;&quot; as a term will be interpreted by most people as a &lt;em&gt;&quot;&lt;strong&gt;deliberate action to disrupt communications&lt;/strong&gt;&quot;&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[opinion] I certainly believe that across the different jurisdictions, the legislation and license conditions will include some wording that &quot;&lt;em&gt;deliberately interfering with signals&lt;/em&gt;&quot; is not allowed. [/opinion]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a HAM is &quot;&lt;em&gt;disrupting communications&lt;/em&gt;&quot; due to malfunctioning equipement, or he simple does not know there are communications on the frequency due to the fact that he doesn't receive the communications at his end (due to propagation or his setup/equipment) then this is QRM, and I would not call it &quot;&lt;em&gt;jamming&lt;/em&gt;&quot;. In such case you would try to solve this in a more HAM-like way, trying to contact the operator to inform him of the situation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the &quot;&lt;em&gt;jamming&lt;/em&gt;&quot; is causing life threatening situations, which you can only think of a few-and-far-in-between situations on Amateur frequencies/allocations:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[opinion] Then I would still believe that &quot;&lt;em&gt;jamming the jammer&lt;/em&gt;&quot; is not the correct action to take.[/opinion]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One could indeed argue that &quot;&lt;em&gt;jamming a jammer&lt;/em&gt;&quot; is not &quot;&lt;em&gt;jamming an authorized signal&lt;/em&gt;&quot;, in which the ethical approach of my previous answer will still prevail as my &lt;em&gt;opinion&lt;/em&gt; on what the expected behaviour of a licensed Radio Amateur shoud display.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore the OP uses the following wording &quot;&lt;em&gt;to disrupt its jamming&lt;/em&gt;&quot; which indicates a deliberate action on the part of the jammer-of-jammers. [opinion] Ethically this is still the wrong action [/opinon]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have never heard, read or otherwise, something like a &quot;&lt;em&gt;jammer of jammers&lt;/em&gt;&quot; to exist in the licensed Amateur Radio world. &quot;&lt;em&gt;proof me wrong&lt;/em&gt;&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I stand by my first answer:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Don't jam&lt;/li&gt;&#xA;&lt;li&gt;Don't jam the jammer&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And add:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;In life threatening situations, follow escalation and notification to&#xA;official institutions. Try to help with the communications which are jammed by relaying the message another way. But do not jam the jammer, as you may risk that your anti-jammer-jamming is actually jamming for the original communications.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And maintain the final:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Spin the dial, don't give a &quot;&lt;em&gt;jammer&lt;/em&gt;&quot; the satisfaction of engagement.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If the OP was in reference to &quot;&lt;em&gt;jamming outside Amateur Radio frequencies&lt;/em&gt;&quot; or &quot;&lt;em&gt;the technical details on how to jam or anti-jam&lt;/em&gt;&quot; then one could consider that this could/would be a topic for:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://electronics.stackexchange.com/&quot;&gt;electronics&lt;/a&gt; as there are questions like this &lt;a href=&quot;https://electronics.stackexchange.com/questions/83292/how-does-rf-anti-jam-technology-work&quot;&gt;example&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://security.stackexchange.com/&quot;&gt;security&lt;/a&gt; as example see this &lt;a href=&quot;https://security.stackexchange.com/questions/41094/strategies-against-jamming-attacks&quot;&gt;question&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2016-09-02T07:16:47.853" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6623" PostTypeId="2" ParentId="6611" CreationDate="2016-08-31T16:34:46.863" Score="2" Body="&lt;p&gt;The antennas that Kevin AG6YO describes are single-band antennas.  If there aren't many 70cm repeaters in your area, then a single-band 2m antenna should work fine.  However, if there are 70cm repeaters where you live, then you might want to think about dual-band antennas.  Antennas designed for 2m will often radiate on the 70cm band with an acceptably-low SWR, but with a poor radiation pattern that avoids the horizon, where the repeaters are.  If both bands are important to you, then you might consider a dual-band antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend a dual-band J-pole antenna as designed by Ed Fong, WB6IQN, described in a &lt;a href=&quot;http://www.work-sat.com/Antennas_files/FONG-DBJ1.pdf&quot; rel=&quot;nofollow&quot;&gt;QST article from February 2003&lt;/a&gt;.  I homebrewed one myself and learned quite a lot about antennas that way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I must warn you though, it's a fairly advanced project for an antenna homebrewer: I had to accurately measure the velocity factor of a transmission line, completely understand the theory behind a J-pole and how this design was made to work efficiently on both bands (oh so clever!), understand the theory of transmission lines including shunts and stubs using Smith charts, and raise and lower the antenna many times while making measurements during construction.  I borrowed an expensive antenna analyzer that works on both bands.  The 2m part was fairly simple to build, but the 70cm part required sub-millimeter precision.  I probably put 10 hours into the build, but as I said I learned quite a lot about antennas doing so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if you just want to get on the air, you can buy one of these antennas from the designer himself on eBay for a very reasonable price: just search for &quot;dual-band J-pole&quot;, and click on the listing that mentions Ed Fong.  By the way, Ed's design is mounted in a PVC pipe.  Of course you could put it in the attic, but also I would think that there are many ways to disguise a PVC pipe outdoors so that neighbors would never suspect that it's an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're curious about the theory, a J-pole antenna is an end-fed vertical dipole.  End-fed dipoles have a high impedance, so the J-pole includes a matching network to make the impedance 50 &amp;ohm;.  Being a vertical dipole, it doesn't need radials or a ground plane.  It should be used with a choke balun, usually made from eight to ten turns of coax around a suitable form, such as a piece of PVC drain pipe 4 inches / 10 cm in diameter.  (Be sure to respect the minimum bending radius specified by the coax manufacturer.)  Because this particular vertical dipole is end-fed, instead of being fed in the middle, the coax doesn't need to be connected perpendicularly to the middle of the antenna; the coax conveniently connects to the end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;People often build (single-band) J-poles out of copper pipe; the antenna then looks like a letter J, that is two parallel vertical lines, one short and one tall, connected at the bottom.  The tall part of the J is the half-wave vertical dipole plus an approximately quarter-wave matching section, and the short part is the &lt;em&gt;nearly&lt;/em&gt; quarter-wave matching stub.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dual-band J-pole makes an excellent 2m and 70cm antenna, but there are lots of other ways you could go.  There are several commercially-made dual-band antennas that would serve you well.  A dual-band antenna made for a car would need a ground plane such as a large piece of sheet metal, so I'd recommend a dual-band antenna designed for home use instead.  If you're determined to homebrew antennas, but you want both bands, but you want a simpler antenna than Ed's design, then you could homebrew two single-band antennas and connect them together with a duplexer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think you're taking the right approach to get the antenna right first, and then worry about getting a better radio later.  Good luck and have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-08-31T16:34:46.863" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6624" PostTypeId="2" ParentId="6617" CreationDate="2016-08-31T17:49:41.880" Score="6" Body="&lt;p&gt;A receiver's objective is to take some message which has had noise added to it, and recover from that the original message. Receivers need to do this even in the absence of jammers since natural sources add noise all the time. Jammers just add more of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this sense, a jammer can't be &quot;jammed&quot;. The jammer does not have the objective of recovering a message hidden in some noise, so there's nothing to jam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That doesn't mean signals can't be made resistant to jamming, however. The game of jamming and counter-jamming is a game about information asymmetry. If the receiver knows something that differentiates the jammer from the legitimate transmitter then it can use that information. For example if a receiver knows the transmitter is to the North and there's a jammer to the East, then the receiver can employ a directional antenna pointed to the North.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Likewise, the more the jammer knows about the intended communication, the more effectively it can disrupt communications. For example, if the jammer knows that the communications are initiated on 146.52 MHz at noon each Monday, this is a lot easier to jam versus a situation where communication could take place on any frequency at any time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's no limit to how much or what kinds of information are relevant in this game. In military applications where malicious jamming is the norm they've been playing this game for a very long time. Simple &lt;a href=&quot;https://en.wikipedia.org/wiki/Spread_spectrum#Invention_of_frequency_hopping&quot;&gt;frequency hopping&lt;/a&gt; techniques saw use in the First World War, and since then it's been an electronic arms race.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-08-31T17:49:41.880" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6625" PostTypeId="1" AcceptedAnswerId="6626" CreationDate="2016-09-01T03:57:46.850" Score="5" ViewCount="3097" Body="&lt;p&gt;Is there an IC out there that implements all, or most all, of a simple FM receiver in the VHF range? I'm interested in doing some experiments with using DTMF over the air for tele-commands and the like, and I'd like to keep the receiver electronics as simple as possible.  The idea is to have a very simple receiver from which I can pipe the audio output to a DTMF decoder IC and then send signals to an Arduino or Raspberry Pi or something of that nature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I may be looking for something like the &lt;a href=&quot;http://www.nxp.com/documents/data_sheet/TDA7000_CNV_2.pdf&quot; rel=&quot;nofollow&quot;&gt;TDA7000&lt;/a&gt; chip but I'm not clear on what frequency range it can support.  It also appears that it may be obsolete / hard to source? I seem to mostly only see ebay vendors selling these.  Is there perhaps a more modern successor this this chip that I should be looking at?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This &lt;a href=&quot;http://www.newark.com/silicon-labs/si4362-b1b-fm/rf-receiver-142mhz-1-05ghz-qfn/dp/49X9779&quot; rel=&quot;nofollow&quot;&gt;Silicon Labs chip&lt;/a&gt; also looks promising and the frequency range is clearly spec'd, and should work for what I want to do, but the problem is that it's only available in a surface mount QFN package, and I'm really not familiar with soldering SMT devices.  Something in a good old fashioned DIP package would be great if something like that exists.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: the more I look at this stuff, the more confused I get.  It looks like a lot of the IC's that are out there that are billed as &quot;RF receivers&quot; assume you're encoding data in FSK or something, and they want to give you decoded data.  Sadly, that's not what I want.  I just want the audio demodulated from FM.    On that front, it appears that there are &quot;receiver&quot; IC's that will demodulate FM and give you audio, but from what I can tell, they all expect to receive as input, an &quot;IF&quot; (Intermediate Frequency) of 10.7mhz or 45mhz or something... which if I'm reading this right, implies you need another circuit - a mixer - in front of the receiver to downconvert the RF.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is starting to seem overly complicated, so I may just drop the idea of looking for an IC to do this stuff and just roll it the old fashioned way. That said, if somebody reading this can point to a nice, simple IC based way (using no more than 2 or 3 IC's preferably, 1 would be better) to go from RF -&gt; demodulated audio, it would be appreciated.  &lt;/p&gt;&#xA;" OwnerUserId="7947" LastEditorUserId="7947" LastEditDate="2016-09-01T22:03:27.053" LastActivityDate="2016-09-03T08:26:53.640" Title="Good FM receiver single-chip IC for simple VHF receiver?" Tags="&lt;receiver&gt;&lt;vhf&gt;&lt;electronics&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6626" PostTypeId="2" ParentId="6625" CreationDate="2016-09-01T17:08:30.980" Score="1" Body="&lt;p&gt;I don't know much about receiver-on-a-chip devices, although both of the chips you mention look promising.  I'd be very surprised if the TDA7000 couldn't handle VHF frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TDA7000 is almost certainly not being manufactured, but I wouldn't let that bother you.  &lt;a href=&quot;https://octopart.com/&quot; rel=&quot;nofollow&quot;&gt;octopart.com&lt;/a&gt; shows two resellers that have the parts in stock, which means that they will be available for a few more years yet in small quantities.  I wouldn't design a product to be manufactured around the chip, but if you're just experimenting then you can expect eBay sellers to have them for a few years longer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Si4362 is carried by the usual distributors, so it's likely still being manufactured.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could attach the Si4362 to a &lt;a href=&quot;http://www.proto-advantage.com/store/product_info.php?products_id=3100112&quot; rel=&quot;nofollow&quot;&gt;DIP adapter&lt;/a&gt;, which would allow you to plug the chip into a 20-pin DIP socket, but you'd still need to solder the chip to the adapter.  Soldering SMT parts by hand is easier than it looks; Adafruit has &lt;a href=&quot;https://learn.adafruit.com/smt-manufacturing/overview&quot; rel=&quot;nofollow&quot;&gt;some great advice&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck, and let us know how you do with a comment.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-09-01T17:08:30.980" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6627" PostTypeId="1" AcceptedAnswerId="6628" CreationDate="2016-09-01T19:04:38.263" Score="1" ViewCount="448" Body="&lt;p&gt;Are the oscillators in SDR hardware (that are used to mix the input to sinusoidal waves) purely digital?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, is the sinusoidal analog signal is created digitally?&#xA; For example getting the sinusoid from $\cos(2\pi kt+ \phi)$ where $k$ is an integer counter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically I am trying to figure out how the frequency of the oscillator of the HackRF One is changed by software.&lt;/p&gt;&#xA;" OwnerUserId="7843" LastEditorUserId="4076" LastEditDate="2016-09-01T20:10:31.037" LastActivityDate="2016-09-01T20:11:50.170" Title="Oscillators inside SDR hardware" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6628" PostTypeId="2" ParentId="6627" CreationDate="2016-09-01T20:03:53.077" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Are the oscillators in SDR hardware (that are used to mix the input to sinusoidal waves) purely digital?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The answer is the same as to your other questions:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The term &quot;SDR&quot; doesn't describe a single device architecture, and hence, all imaginable solutions to the problem of generating a tone for a mixer exist¹. There's SDR devices that have a numerical oscillator (pretty much what you described, though often implemented differently, and there's a lot of ways of doing that), others use PLLs (often with complex fractional-N schemata) to condition a LC oscillator, a quartz or some other source of periodic signal, yet others simply use a very high-frequency digital counter to generate a set of frequency, yet others have adaptable frequency multipliers; I'm sure there's even devices that simply have a bank of oscillators to select from (and combine); other implementations use tricks to avoid explicitly generating an oscillator at all and simply switch transistors on and off. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is impossible to list all potential and actual implementations of oscillators. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Basically I am trying to figure out how the frequency of the oscillator of the HackRF is changed by software.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Now we're talking about a specific device; I recommend referring to the &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki&quot;&gt;HackRF wiki&lt;/a&gt;, especially the page on &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/Hardware-Components&quot;&gt;Hardware Components&lt;/a&gt;; you'll find a link to the &lt;a href=&quot;http://datasheets.maxim-ic.com/en/ds/MAX5864.pdf&quot;&gt;MAX2837&lt;/a&gt; there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I neither want to nor can save you the labour of reading that, but to give you a short breakdown: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The MAX2837 is an integrated mixer/LO generator/amplifier... module. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It contains a Voltage-Controlled Oscillator (VCO), which is controlled by a Phase-Locked Loop (PLL), which derives the desired VCO frequency from the external reference oscillator input, and uses a complex control scheme (selectable fractional-N or integer-N synthesis with selectable harmonics selection filters) to put the VCO at a specific ratio of the reference oscillator's frequency.&#xA;&lt;hr&gt;&#xA;¹ note that &quot;SDR&quot; doesn't even imply any mixing at all! Or, that you can adjust the frequency that is mixed with. That is a speciality of the specific devices you seem to be thinking about, and generalize! &lt;em&gt;Not all SDR devices look like the ones that you seem to be looking at.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-09-01T20:11:50.170" LastActivityDate="2016-09-01T20:11:50.170" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6629" PostTypeId="2" ParentId="6625" CreationDate="2016-09-02T01:49:53.270" Score="1" Body="&lt;p&gt;I think I might have found something.  The Motorola MC3362 is described in the datasheet as:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The MC3362 is a complete FM narrowband receiver from&#xA;  antenna input to audio preamp output. The low voltage dual&#xA;  conversion design yields low power drain, excellent&#xA;  sensitivity and good image rejection in narrowband voice and&#xA;  data link applications.&#xA;  In the typical application (Figure 1), the first mixer&#xA;  amplifies the signal and converts the RF input to 10.7 MHz.&#xA;  This IF signal is filtered externally and fed into the second&#xA;  mixer, which further amplifies the signal and converts it to a&#xA;  455 kHz IF signal. After external bandpass filtering, the low IF&#xA;  is fed into the limiting amplifier and detection circuitry. The&#xA;  audio is recovered using a conventional quadrature detector.&#xA;  Twice–IF filtering is provided internally.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.futurlec.com/Motorola/MC3362Ppr.shtml&quot; rel=&quot;nofollow&quot;&gt;http://www.futurlec.com/Motorola/MC3362Ppr.shtml&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It also covers up to 200mhz.  Sadly these also appear to be somewhat obsolete but Futurlec seems to have a supply of them, and they're in a nice old fashioned DIP package which I like.  (Hey, I'm old-school, so sue me!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think I'll order a couple of these and see if I can do something with them.&lt;/p&gt;&#xA;" OwnerUserId="7947" LastActivityDate="2016-09-02T01:49:53.270" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6631" PostTypeId="1" CreationDate="2016-09-02T18:19:22.693" Score="3" ViewCount="784" Body="&lt;p&gt;I have the mini Eton radio and it has a DC 3V port but I haven't been able to find the official plug. Is using a generic one safe?  How do i know if I found the correct AC adapter?  It goes through 2 AAA's in two days! So I definitely want an alternative power source but safety comes first.&lt;/p&gt;&#xA;" OwnerUserId="8121" LastEditorUserId="1362" LastEditDate="2017-11-10T23:31:38.670" LastActivityDate="2019-07-11T22:00:57.773" Title="Is using a generic DC 3V adapter dangerous to a radio?" Tags="&lt;power-supply&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6632" PostTypeId="2" ParentId="6631" CreationDate="2016-09-02T18:39:00.507" Score="3" Body="&lt;p&gt;A new generic AC adapter that says 3 VDC with the correct plug and the correct polarity should be safe.  Almost all 3 VDC adapters will have the correct polarity; if the polarity were wrong, then the radio probably just wouldn't work.  The trickiest part about finding an AC adapter is usually getting the correct plug, because there is no standard plug for 3 VDC.  Hopefully a local electronics store could help you find the correct AC adapter, if you bring the radio in.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-09-06T17:53:30.427" LastActivityDate="2016-09-06T17:53:30.427" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6633" PostTypeId="2" ParentId="2146" CreationDate="2016-09-02T22:00:29.273" Score="1" Body="&lt;p&gt;a couple of years ago i saw a passive repeater array that was named after the engineer that designed it... now i can't find that article. but a google search for passive repeater array brings up a lot of entries, and it looks like it's very common above 1Ghz to use passive repeaters in many communications systems.  everything from reflective (think of a metal billboard) to antenna-waveguide-antenna systems seem to be abundant.  the one i was thinking about (wish i could remember the name of it) used several dipoles in a line, running through coax to another line of dipoles (like on the other side of a hill, etc..), the idea being, a single dipole-to-dipole repeater has a very small &quot;aperture&quot;, but an array of passive repeaters increases the efficiency by the use of a larger &quot;aperture&quot;.  since 2.4Ghz is such a short wavelength, you could probably fabricate a few arrays on panels of PC board material and connect them with coax cables (you do want to use a good grade of coax, because you really don't want to have a lot of loss in your transmission lines)  and make certain they are all the same length.&lt;/p&gt;&#xA;" OwnerUserId="8280" LastActivityDate="2016-09-02T22:00:29.273" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6634" PostTypeId="2" ParentId="5973" CreationDate="2016-09-03T07:06:49.810" Score="-4" Body="&lt;p&gt;fixed antennas are not abligatory on pmr 446 anymore as long as they dont increase gain i was told personly by ofcom that so regardless of what anyone says its like the story of baofeng s not complying whole top and bottom of it is big companies dont like it so spread crap thats it&lt;/p&gt;&#xA;" OwnerUserId="8281" LastActivityDate="2016-09-03T07:06:49.810" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6635" PostTypeId="2" ParentId="6625" CreationDate="2016-09-03T08:26:53.640" Score="2" Body="&lt;p&gt;another way to do it would be to use a cheaply available RTL-SDR device (like a 5$ DVB-T receiver), and then go software-defined from there. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;rtl_fm can do FM demodulation in the needed frequency bands and multimon-ng can demodulate DTMF tones and signaling and give you the data. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple Raspberry Pi has enough processing power to do something like this. &lt;/p&gt;&#xA;" OwnerUserId="6061" LastActivityDate="2016-09-03T08:26:53.640" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6636" PostTypeId="1" AcceptedAnswerId="6637" CreationDate="2016-09-03T08:41:22.323" Score="4" ViewCount="163" Body="&lt;p&gt;I have a portable radio which serves for FM / MW / SW bands. At nights I can listen to 4-6 international channels from different countries on MW. However, I am unable to tune them at daytime. Is it about my location as a result of earth's spin or there are other reasons that I don't know? Shutting down the radio station at nights comes to my mind but all the stations are from different (meridians) countries.&lt;/p&gt;&#xA;" OwnerUserId="8282" LastEditorUserId="8282" LastEditDate="2016-09-04T08:50:17.567" LastActivityDate="2016-09-04T08:50:17.567" Title="No stations on MW band at daytime" Tags="&lt;propagation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6637" PostTypeId="2" ParentId="6636" CreationDate="2016-09-03T12:04:06.947" Score="5" Body="&lt;p&gt;During the day, the ionosphere is strengthened by direct exposure to the solar wind, making it thicker and lower relative to the Earth's surface. This prevents any sort of skip propagation at MW frequencies, limiting MW propagation to ground wave only, which only covers a limited range from the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At night, the ionosphere is higher and more diffuse, allowing skip propagation to much longer distances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These effects have been known for a long time, which is why most MW stations are required to reduce power at night in order to reduce interference with distant stations on the same frequency. Only designated &quot;clear-channel&quot; stations are permitted to continue to operate at full power.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2016-09-03T12:04:06.947" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6638" PostTypeId="1" CreationDate="2016-09-03T13:38:51.493" Score="1" ViewCount="486" Body="&lt;p&gt;MW reception is often plauged by man made interference these days. Most man made interference comes from small close sources like say a laptop power supply .Is a loop antenna better than a whip when man made noise in the near field is significant ? Is this near field man made noise predominantly electrostatic ? magnetic? Or is it both like the desired far field signal? Loop antennas do work for MW DX but it there more to it than the ability to directionally null out interference?&lt;/p&gt;&#xA;" OwnerUserId="6095" LastActivityDate="2016-09-03T16:07:51.840" Title="Loop Vs Whip for MW DX" Tags="&lt;antenna-theory&gt;&lt;noise&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6639" PostTypeId="1" CreationDate="2016-09-03T14:06:16.600" Score="1" ViewCount="164" Body="&lt;p&gt;So I have an IC-2730, which doesn't have external inputs for packet radio, but it does have optional board for Bluetooth connectivity and there's also an optional Bluetooth headset for it. I'm trying to evaluate feasible it would be to use Bluetooth to transfer say 1200 baud audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, it's been some time since I worked with Bluetooth and I haven't worked with Bluetooth audio at all, so I'm wondering what types of issues I could expect if I try to use Bluetooth to send audio data to the radio.&lt;br&gt;&#xA;I expect that compression could be an issue here. From what I could dig up, the module IC-133 module which implements the Hands-Free Profile, Serial Port Profile and HeadSet Profile.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="76" LastEditDate="2016-10-29T18:43:58.750" LastActivityDate="2016-10-29T18:43:58.750" Title="What issues can I expect when using Bluetooth for packet radio?" Tags="&lt;transceiver&gt;&lt;aprs&gt;&lt;packet&gt;&lt;audio-interface&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6640" PostTypeId="2" ParentId="6638" CreationDate="2016-09-03T16:07:51.840" Score="3" Body="&lt;p&gt;I'm going to assume that by &quot;loop&quot; you mean a &quot;magnetic loop&quot; or a &quot;small loop&quot;. That is, one with a circumference significantly less than the wavelength. Larger loops, with a circumference approximately equal to the wavelength, are more like folded dipoles and behave differently.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is a loop antenna better than a whip when man made noise in the near field is significant?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's impossible to say in the general case. Each will pick up different fields in the near field, so it will depend on what kind of noise is around.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is this near field man made noise predominantly electrostatic? magnetic?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There's a good mix of each.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Loop antennas do work for MW DX but it there more to it than the ability to directionally null out interference?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes and no.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the very near field, a loop has a lower field impedance than a whip, meaning it's more sensitive to magnetic noise. Farther away, but still in the near field, the loop actually has a higher field impedance than a whip, making it more sensitive to electric field noise. And in the far field the impedances are equal, as required by the laws of physics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So which is more effective at avoiding near-field noise really depends on local conditions which are hard to predict.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although loops and whips have identically shaped radiation patterns, those patterns are oriented differently with respect to the antenna's polarization. In each case the free space radiation pattern looks like a doughnut with two nulls. For a vertically polarized whip, the nulls point up and down, but for a vertically polarized loop, the nulls point at the horizon. Of course the presence of ground alters this in a way that depends on the height of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you must have a vertical polarization (as is the case for ground-wave propagation), then the loop gives you nulls pointed in a more useful direction. This certainly can be part of its effectiveness, but as previously mentioned the differing near field impedances can help as well, depending on what kind of noise is around.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-09-03T16:07:51.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6641" PostTypeId="2" ParentId="6639" CreationDate="2016-09-04T08:16:13.833" Score="2" Body="&lt;p&gt;Sounds a lot easier to reverse-engineer the Hand Controller Interface, especially since that comes with a handy RJ45 connector, which would make it cheap to build an adapter that allows you to poke around. Pretty certain that carries raw analog audio on any 2 of the 8 wires :), as they actually sell a mic adapter cable (OPC-589)! (turns out &lt;a href=&quot;http://www.ik8vrq.net/Note/PinOut/opc589.pdf&quot; rel=&quot;nofollow&quot;&gt;somebody did the work, and you can use that info&lt;/a&gt;) (oh furthermore turns out the ICOM manual actually has the pin assignments...)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What issues can I expect when using Bluetooth for packet radio?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Point is that the bluetooth headset profile uses a digital audio compression optimized heavily for speech – and not for preserving the digital audio symbols. It &lt;em&gt;might&lt;/em&gt; work to transmit low-rate data through that, but it would be equivalent to adding  a significant noise source to your system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words: you'd be making your transmission worse without need. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be honest, I'd expect a system that has up to 50W power output to be very cleanly modularized – you can probably easily identify the PA chain when you open it (it's what attaches to the antenna port and has big heat sinks!). Developing something that only generates / demodulates packet radio audio signal pre-distorted to counteract the Bluetooth compression as far as possible sounds a lot more complex than just building your own packet radio/FM modulator and directly piggy-backing that onto your radio :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, if I needed to build something that takes 1200bd of data for transmission wirelessly, I'd go for something like a Pi Zero, a RJ45 connector soldered onto a PCB that would plug directly on top of the Pi Zero and that contains both a 8V/5V voltage converter to power the Pi from the Mic port, and a I²S or USB sound card IC to generate/receive the audio, plus some kind of data connectivity (bluetooth, if you will), plugged in directly to the Pi. That way, I'd have something relatively small, which only transmits the raw data bits over your bluetooth link (no quality loss there), and does the modulation as close as possible to the radio. Of course, you'd need some kind of packet radio audio modem software running on the pi, but there should be something readily available :)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-09-04T08:38:30.713" LastActivityDate="2016-09-04T08:38:30.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6643" PostTypeId="1" CreationDate="2016-09-04T16:36:54.163" Score="1" ViewCount="76" Body="&lt;p&gt;I need to cram the last bits for my exam - I don't know my competence level precisely, but I've passed the US B-license tests a bunch of times. Problem is I'm in Denmark - how should I cram for this so I'm not caught by some EU specific regulation?&lt;/p&gt;&#xA;" OwnerUserId="7957" LastEditorUserId="29" LastEditDate="2016-09-05T20:28:03.957" LastActivityDate="2016-09-05T20:28:03.957" Title="Able to consistently pass the US B license test; what more is needed for a Danish amateur radio license?" Tags="&lt;license&gt;&lt;europe&gt;" AnswerCount="0" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="6645" PostTypeId="1" AcceptedAnswerId="6647" CreationDate="2016-09-05T12:26:18.630" Score="11" ViewCount="2310" Body="&lt;p&gt;I'm a relatively new ham (licensed a couple of years ago, occasional activity on 70cm and 2m, mostly repeaters). I'm looking to extend my ham experience and am interested in digital and packet modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm interested in APRS. The main reason is to update my location when I'm off to wilderness, which is often. But outside of Europe and North America, I see that there are not many APRS digipeaters around. Let's say I want hike for days in Central Asia or the Himalayas. What options do I have? Is there some portable HF rig I can carry? When I'm in some deep narrow valleys, is there any hope of updating my location?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any experience or suggestions will be helpful.&lt;/p&gt;&#xA;" OwnerUserId="213" LastEditorUserId="213" LastEditDate="2016-09-05T21:16:44.473" LastActivityDate="2016-09-07T19:04:46.647" Title="How to do APRS in real wilderness?" Tags="&lt;hf&gt;&lt;ht&gt;&lt;aprs&gt;&lt;repeater-coverage&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6646" PostTypeId="2" ParentId="6645" CreationDate="2016-09-05T20:53:18.140" Score="4" Body="&lt;p&gt;Apart from matured and highly reliable commercial satellite-based services, WSPR can be another 'DIY/experimental' alternative for broadcasting your location from wilderness. See examples for &lt;a href=&quot;http://qrp-labs.com/ultimate3/ve3kcl-balloons/ve3kcl-s11.html&quot; rel=&quot;nofollow&quot;&gt;balloon&lt;/a&gt;, &lt;a href=&quot;http://qrp-labs.com/ultimate3/ve3kcl-balloons/ve3kcl-s2.html&quot; rel=&quot;nofollow&quot;&gt;photo&lt;/a&gt; and &lt;a href=&quot;http://www.qsl.net/zl1rs/oceanfloater.html&quot; rel=&quot;nofollow&quot;&gt;ocean floater&lt;/a&gt;, &lt;a href=&quot;http://www.qsl.net/zl1rs/oceanfloater1.html&quot; rel=&quot;nofollow&quot;&gt;photo&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;WSPR is an very low speed mode with 2x to 3x dB SNR advantage over many other digi-modes. Range of a few hundreds to a few thousands km are possible with a few watts, or less, of HF transmission power. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A global &lt;a href=&quot;http://wsprnet.org/drupal/&quot; rel=&quot;nofollow&quot;&gt;network&lt;/a&gt; of receiving stations are already setup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: If broadcasting position and/or maintaining telecommunication are essential for 'safety' reasons, mature commercial satellite equipment should be used. As said, WSPR is 'DIY/experimental'. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some satellite system uses a large number of LEO (Low Earth Orbit) satellites (Iridium etc.) and would have better coverage probability for partially sky view obstructed locations. Satellites can appear at higher elevation (near Zenith), multiple and time-varying sky positions. If you wait a while, one of the many satellites may move to a position in sky with direct line-of-sight toward you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on where you are on Earth, those use equator geo-sync satellites (Inmarsat etc.) demand &quot;much more openness&quot; sky view as satellite may appear at fixed and lower elevation (toward South and toward horizon) positions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even LEO satellite may have better coverage, no satellite works at too deep and too narrow valleys.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Examples of mature commercial equipment for 'safety' (non DIY/Hobby) uses &lt;a href=&quot;https://www.iridium.com/products/details/gtts-2000b-tracking-and-tracing-system&quot; rel=&quot;nofollow&quot;&gt;1&lt;/a&gt; &lt;a href=&quot;https://www.iridium.com/products/details/guardianmobilityguardian5&quot; rel=&quot;nofollow&quot;&gt;2&lt;/a&gt;  &lt;a href=&quot;https://www.iridium.com/products/details/pivotel-tracertrak-1&quot; rel=&quot;nofollow&quot;&gt;3&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="1473" LastEditDate="2016-09-06T20:22:51.437" LastActivityDate="2016-09-06T20:22:51.437" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6647" PostTypeId="2" ParentId="6645" CreationDate="2016-09-06T17:46:52.313" Score="11" Body="&lt;p&gt;So you want to broadcast your location using backpack-portable equipment from deep in a narrow valley hundreds of miles from civilization.  I'll assume that you would also like the ability to get a message out when necessary.  These are very demanding requirements.  I don't think that there is any inexpensive, 100% reliable way to do what you seem to want, but here are some alternatives to consider.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Option: Morse code QRP (low-power) transceiver&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pros:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Radio, battery, and antenna can be under 1.5 lb / 0.75 kg&lt;/li&gt;&#xA;&lt;li&gt;Radio can be inexpensive if you're willing to homebrew it&lt;/li&gt;&#xA;&lt;li&gt;Simple equipment, therefore hopefully reliable&lt;/li&gt;&#xA;&lt;li&gt;Can hold a conversation, rather than just delivering a simple message&lt;/li&gt;&#xA;&lt;li&gt;Can normally communicate out to about 1000 miles / 1600 km with ease&lt;/li&gt;&#xA;&lt;li&gt;No computer required&lt;/li&gt;&#xA;&lt;li&gt;Very power-efficient&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Cons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Results depend on propagation to some extent&lt;/li&gt;&#xA;&lt;li&gt;Morse code knowledge and QRP skill required&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Option: satellite phone&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pros:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Theoretically works from anywhere&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Cons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Expensive&lt;/li&gt;&#xA;&lt;li&gt;Fragile equipment&lt;/li&gt;&#xA;&lt;li&gt;Battery hog&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Option: PSK31 over HF&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pros:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;No Morse code experience required&lt;/li&gt;&#xA;&lt;li&gt;Easy propagation to about 1000 miles / 1600 km&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Cons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Results depend on propagation to some extent&lt;/li&gt;&#xA;&lt;li&gt;Amateur radio skill required&lt;/li&gt;&#xA;&lt;li&gt;Some sort of computer required; computer is fragile and battery-hungry&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Option: APRS via ISS&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm talking about APRS using the International Space Station's digipeater (or another satellite's). (&lt;a href=&quot;http://www.aprs.org/iss-faq.html&quot; rel=&quot;noreferrer&quot;&gt;more information&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pros:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Potentially send APRS messages from anywhere!&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Cons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Skill required&lt;/li&gt;&#xA;&lt;li&gt;Need a fragile gain antenna&lt;/li&gt;&#xA;&lt;li&gt;Need some sort of computer for satellite pass information and packet generation&lt;/li&gt;&#xA;&lt;li&gt;Difficult for one person to aim the antenna at the satellite and operate the radio at the same time&lt;/li&gt;&#xA;&lt;li&gt;Need to get a short packet out during a very brief satellite pass&lt;/li&gt;&#xA;&lt;li&gt;Depends on a single digipeater in orbit, which may be hopelessly congested&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Option: Personal Locator Beacon (PLB)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.rei.com/learn/expert-advice/personal-locator-beacons.html&quot; rel=&quot;noreferrer&quot;&gt;PLBs&lt;/a&gt; are similar to EPIRBs used at sea: a simple, rugged commercially-made transmitter that is designed to transmit an urgent MAYDAY message.  When a PLB is activated, generally a Search And Rescue (SAR) team is called out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pros:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Reliable and rugged&lt;/li&gt;&#xA;&lt;li&gt;Simple to use&lt;/li&gt;&#xA;&lt;li&gt;No subscription required&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Cons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Can't use it for routine updates&lt;/li&gt;&#xA;&lt;li&gt;If a SAR team responds, the user may be liable for the cost of the rescue attempt&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Option: Satellite Messenger device&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;a href=&quot;https://www.rei.com/learn/expert-advice/personal-locator-beacons.html&quot; rel=&quot;noreferrer&quot;&gt;Satellite Messenger&lt;/a&gt; is a simple commercially-made device that allows the user to send text messages via the Iridium or Globalstar satellite network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pros:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Reliable and rugged&lt;/li&gt;&#xA;&lt;li&gt;Simple to use&lt;/li&gt;&#xA;&lt;li&gt;Can send regular non-emergency updates&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Cons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Subscription is required&lt;/li&gt;&#xA;&lt;li&gt;The &quot;jury is still out&quot; on how well they work, according to the &lt;a href=&quot;https://www.rei.com/learn/expert-advice/personal-locator-beacons.html&quot; rel=&quot;noreferrer&quot;&gt;REI article&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Other options&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;WSPR: I wouldn't choose this option, because there is no good way to send a MAYDAY / SOS&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.winlink.org/&quot; rel=&quot;noreferrer&quot;&gt;Winlink&lt;/a&gt;: I wouldn't choose this one either, because it requires a strong signal, which would require a big battery and larger antenna&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Personally, I would choose the QRP Morse code transceiver (with a PLB or a Satellite Messenger as a backup), but I already have experience with Morse code QRP.  This is a skill, which takes some time to learn, that would need to be acquired and practiced in civilization &lt;em&gt;before&lt;/em&gt; you head out to the middle of nowhere.  But it's the method that uses the simplest equipment and the least power.  By the way, for any of these methods to work reliably you would need to hike out of the narrow, deep valley.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-09-07T19:04:46.647" LastActivityDate="2016-09-07T19:04:46.647" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="6648" PostTypeId="2" ParentId="1628" CreationDate="2016-09-07T03:00:03.183" Score="-3" Body="&lt;p&gt;Data: CB frequency (used) 27.375 Mhz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Considerations: MULTIPLES of 1/4, 1/2. and .64 wavelengths.&lt;br&gt;&#xA; 186,282.398 (speed of light) divided by 27,375,000 = .006804836456;  times 5,280 (ft. / mile)= 35.92953648 Ft. (wavelength);&lt;br&gt;&#xA; 35.92953648 (wavelength) divided by (Pi)  3.141592653 = 11.4372666 Diameter;&lt;br&gt;&#xA; 2 Diameters of  11.43672666 (diameter)  = 22.87345332 (:)  22.87345332 divided by 35.92953648 = .636619771 wavelength (approximates .625/.64 wavelength).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Utilization: Total Length 68.62035996 feet for 1/4, 1/2, and .64 multiples:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;8 waves of 8.577544995 (1/4 wave).&lt;/li&gt;&#xA;&lt;li&gt;6 Diameters of 11.43672666&lt;/li&gt;&#xA;&lt;li&gt;4 waves of 17.15508999 (1/2 wave)&lt;/li&gt;&#xA;&lt;li&gt;3 .64 wavelengths &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;However, the cable length  between the CB Radio and the antenna = 51.46526997 ft. connected to the antenna mount (grounded to the car body). The FACTORY 102&quot; whip makes up for 8.577544995 ft.;  The cable SHIELD  grounded next to the 102&quot; radiator makes the car body mirror 8.577544995 Ground Plane. Add it up: (works great / very low SWR).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;51.46526997 feet rg58u cable, plus&lt;br&gt;&#xA; 8.577544995 radiator ( 102&quot; whip), plus&lt;br&gt;&#xA; 8.577544995 grounded antenna mount( car body mirrored) provides...&lt;br&gt;&#xA; the 68.62035996 feet total length. &lt;/p&gt;&#xA;" OwnerUserId="8300" LastEditorUserId="76" LastEditDate="2016-09-07T04:30:27.693" LastActivityDate="2016-09-07T04:30:27.693" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6649" PostTypeId="1" AcceptedAnswerId="6654" CreationDate="2016-09-08T10:17:52.777" Score="1" ViewCount="233" Body="&lt;p&gt;I have a system with a 1/4 wave whip antenna and above the antenna there is a mess of aluminium they're not connected but are nearby. I would like to figure out what effect this would have on the radiated signal strength but I'm at a complete loss at how to do this. My actually problem is trying to figure out how far away the aluminium needs to be to have a negative effect on received signal&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just to make the situation clear;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;/\/\/\/\&#xA;\/\/\/\/&#xA;\/\/\/\/&#xA;\/\//\/\&#xA;&#xA;&#xA;&#xA;   l&#xA;   l&#xA;   l                                              R&#xA;   l&#xA;   l&#xA;GGGGGGGG&#xA;&#xA;Key: \/ = aluminium&#xA;l = antenna&#xA;G = ground plane&#xA;R = far away receiver (in that approximate direction)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="529" LastActivityDate="2016-09-09T00:27:39.680" Title="How to calculate/estimate the effect of having conductive material nearby an antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vertical-antenna&gt;&lt;radiation-pattern&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6650" PostTypeId="2" ParentId="6649" CreationDate="2016-09-08T10:47:41.913" Score="2" Body="&lt;p&gt;There is modeling software you can use for this. EZNEC and 4nec2 are popular among hams, but they only do wires. You could try modeling the aluminium as a bunch of wires - spacing them, say, 0.05 wl apart. If nothing else, the model might tell you when the effect becomes negligible. Software that handles conducting planes also exists, but is AFAIK fairly pricey. May be you could get a student or trial license?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All antenna modeling software takes some learning, though. So why not just experiment. Another idea is to turn your ground plane upside down. The antenna ground plane would - at least to some extent - shield off the metal.&lt;/p&gt;&#xA;" OwnerUserId="6220" LastEditorUserId="76" LastEditDate="2016-09-08T14:17:16.503" LastActivityDate="2016-09-08T14:17:16.503" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6651" PostTypeId="1" CreationDate="2016-09-08T11:06:12.057" Score="2" ViewCount="312" Body="&lt;p&gt;The loading coils for electrically short MF and HF antennas that I have seen over the decades are all air cored. Ferrites have got better but air has not .Clearly a ferrite cored coil would be smaller but would it have lower losses? How would say a planar core compare to air? Has anyone tried this?&lt;/p&gt;&#xA;" OwnerUserId="6095" LastActivityDate="2016-09-08T12:38:19.123" Title="Highest Q loading Coils" Tags="&lt;hf&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6652" PostTypeId="2" ParentId="6651" CreationDate="2016-09-08T12:34:52.530" Score="4" Body="&lt;p&gt;Air will always have higher Q than ferrite. Air hasn't gotten better, because &lt;em&gt;it can't really get any better&lt;/em&gt;. It's loss tangent is so close to 0 that it is typically just set to zero when calculating Q in most small(ish) coils.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, ferrite has definitely gotten better. With very careful core selection and design, Q might exceed 600 for values useful in RF design(&lt;a href=&quot;http://www.w8ji.com/loading_inductors.htm&quot; rel=&quot;nofollow&quot;&gt;1&lt;/a&gt;). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Calculations will yield insane Q numbers for air core coils, &gt;10,000 in many cases, but practically the ceiling will be somewhere around 1,000 due to shunt capacitance, interaction with other circuit elements, etc. Edge wound coils might do slightly better than that, but you'll be stuck solidly in the low thousands. Regardless, physically large air core coils will always best a ferrite toroid when it comes to Q. The best they can ever hope for is to draw even.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-09-08T12:34:52.530" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6653" PostTypeId="2" ParentId="6651" CreationDate="2016-09-08T12:38:19.123" Score="5" Body="&lt;p&gt;Ferrite has limitations such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;hysteresis losses&lt;/li&gt;&#xA;&lt;li&gt;eddy current losses&lt;/li&gt;&#xA;&lt;li&gt;saturation, limiting maximum current&lt;/li&gt;&#xA;&lt;li&gt;limited heat radiation ability, limiting maximum power&lt;/li&gt;&#xA;&lt;li&gt;nonlinearities, causing harmonic distortion&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;On the plus side for ferrite:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;higher permeability, reducing size&lt;/li&gt;&#xA;&lt;li&gt;also due to permeability, magnetic field is mostly contained within the ferrite, reducing problems like mutual inductance and other undesirable interactions&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Although ferrites have indeed improved, they still have all the losses and limitations above. Air has losses so low they are insignificant for practical radio applications. It doesn't saturate, it's perfectly linear, you don't have to cool it because it has no losses to make it hot. There are resistive losses in the wire, and since the coil is bigger you need more wire. But that's usually easy to solve by using bigger wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because air has no core losses, it will always have a higher Q than ferrite, all else equal.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-09-08T12:38:19.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6654" PostTypeId="2" ParentId="6649" CreationDate="2016-09-08T12:58:04.407" Score="6" Body="&lt;p&gt;In your particular case, I'd note 2 things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The aluminium is directly above the whip, where the antenna's fields are the weakest.&lt;/li&gt;&#xA;&lt;li&gt;Aluminium is a good conductor, so unless there is something about it that will increases losses, it won't decrease the radiated energy. It might change the feedpoint impedance, and it might change the direction in which energy is radiated, but the antenna efficiency must remain the same because there are no significant losses to account for the difference.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;My advice would be to not worry about it too much. Probably the effect is small.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more general rule of thumb:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;anything 10 wavelengths or more away from the antenna is insignificant to the near-field operation of the antenna. It might have other effects by reflecting or redirecting the energy, but then the receiver could be in a Faraday cage too.&lt;/li&gt;&#xA;&lt;li&gt;at 2 wavelengths, things are somewhat significant.&lt;/li&gt;&#xA;&lt;li&gt;below 1 wavelength, things are very significant.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Remember &quot;significant&quot; isn't the same as &quot;bad&quot;. Sometimes it can be good, look at Yagis and horn antennas, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to get more precise than that, some options are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;experience and intuition&lt;/li&gt;&#xA;&lt;li&gt;modelling (EZNEC, 4nec2, ...)&lt;/li&gt;&#xA;&lt;li&gt;empirical measurement&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-09-08T12:58:04.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6655" PostTypeId="2" ParentId="6649" CreationDate="2016-09-09T00:27:39.680" Score="0" Body="&lt;p&gt;Creating a model of your antenna (not too much different than your little diagram) with all nearby associated metal can be done with the NEC2 (or, NEC4) antenna modeling software.  It is the best way to compute the effect of nearby conductors.  In fact, there are no formulas or easy fill-in-the-blanks methods to do this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NEC2 is easy to use but without a nice 3rd party output processing program, such as EZNEC (&lt;a href=&quot;http://eznec.com&quot; rel=&quot;nofollow&quot;&gt;http://eznec.com&lt;/a&gt;) it is hard to make use of the results.  These 3rd party output programs will create graphs to show SWR on the antenna and radiation propagation field and show currents on the antenna (and other things).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a variety of tutorials available that show you how to do this and they are easily found by googling NEC2.  Note, you can probably get a Free Trial Use of EZNEC that will allow you to do the model and display the graphic results.  EZNEC runs on Windows PCs only.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I personally do not use EZNEC although I did years ago.  I use Mathematica as my 3rd party graphic display of result data produced by NEC2.  Technically I use NEC4 but NEC2 should be able to do everything you need to do.  NEC2 is freely available on the Internet, NEC4 is source licensed from Lawrence Livermore Laboratories.  I purchased my single-user license for $300 about five years ago.  Not sure if it is still priced the same though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my own antenna analysis work I always use NEC to produce the model and evaluate the results.  I have found that results of NEC (NEC2 or NEC4) to be very close to actual measurements that I can make on the antenna after I put it up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NEC4 does a better job of ground modeling and much more accurate for conductors close to the ground (inches or under) as you might use with a radial counterpoise for a 1/4 wave vertical.  However, NEC2 is quite adequate for just about all uses being mindful of where the model starts to show weakness.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-09-09T00:27:39.680" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6656" PostTypeId="1" AcceptedAnswerId="6662" CreationDate="2016-09-09T06:13:06.747" Score="1" ViewCount="170" Body="&lt;p&gt;I was studying about the Guanella 1:1 balun and came across the term &quot;choking reactance&quot;. What does this mean? Why does its value need to be large? &lt;/p&gt;&#xA;" OwnerUserId="7827" LastEditorUserId="76" LastEditDate="2016-09-09T14:17:29.440" LastActivityDate="2016-09-09T14:57:56.047" Title="what is choking reactance in TLT?" Tags="&lt;balun&gt;&lt;transmission-line&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6657" PostTypeId="2" ParentId="6656" CreationDate="2016-09-09T07:35:10.470" Score="2" Body="&lt;p&gt;I'm not familiar with the term &quot;guenella&quot;, but:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A choke, in this context, is typically an inductivity with the function of suppressing high frequency signals/noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As inductivity, it has inductive reactance. Think of inductive reactance as the &quot;resistance in effect at a specific frequency $f$&quot;, i.e. $2 \pi f L$, with $L$ the inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, the higher it is, the higher the resistance of the inductance to the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the context of baluns, things might be a bit more complex: Since inductivity is the ability of something to store energy in the magnetic field, and baluns often are pretty much transformers, i.e. devices that convert electrical current to magnetic field change, and back to current, this size is tightly linked to the ability of a transformer to transport energy. I must admit that I'd need &lt;em&gt;a lot&lt;/em&gt; more context to explain why its value would need to be large (a.k.a. slight ciriticism: give more background in your question!)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-09-09T07:35:10.470" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6658" PostTypeId="2" ParentId="5213" CreationDate="2016-09-09T09:51:38.697" Score="0" Body="&lt;p&gt;I can tell you what I did, and it worked pretty well. Since I didn't have copper wrap or a suitable little  steel box, I wrapped my SDR in about 20-30 layers of alu foil. I soldered a copper filament from USB GND to this makeshift shield, wrapped a few turns of copper solid core wire to hold it in place, and then electrical tape. I should have put a mini heatsink on the tiny chips that get pretty hot, and drilled holes for passive airflow. Next I took two of those little antennas that come with the dongles, clipped the wire from one of them, and connected GND to the antenna bit of the clipped one. I just superglued it together, and covered the bases in electrical tape. Nice dipole, much better reception. I should use shielded antenna cable or add ferrite beads, but I'm not that bothered though. The little antennas are worth keeping, since they're easy to solder solid core copper wire onto. Just clip them, and add your desired 1/4, 1/2 or 1/1 wavelengths - lambda = 300/145 = 200cm for VHF, and lambda = 300/433 = 69.3cm for UHF. I would probably need at least 1/2 wavelength to make it worthwhile. &#xA;I use a USB repeater cable to move my dongle far away from my noisy laptop PSU and other things. I believe it's 5M. Not much loss in that. I disable AGC in my SDR software and set it manually, since AGC usually sets gain too high. You should run &lt;code&gt;rtl_test -p&lt;/code&gt; for about ten minutes to get your PPM value. It does vary, apparently due to heat. If I were to do it again, I would heatsink the SDR dongle and drill ventilation holes in it. Hope this is useful.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-09-09T09:51:38.697" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6659" PostTypeId="1" AcceptedAnswerId="6661" CreationDate="2016-09-09T12:32:34.373" Score="5" ViewCount="6493" Body="&lt;p&gt;I live in a small cottage with an unlevelled terrain. My house was built in the lower part of it (left-side), and in the other half of it there is a hill. On top of the hill there's a fairly good plateau where I would like to have my antennas installed, since the place my house was built seems to be too low (my place is surrounded by hills). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the top of this plateau, I can see very from a very big distance, and I'll bet that would be the perfect area for my antennas. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I can't solve is the fact that my antennas would stay just too far apart from my house, where I plan to have my shack put together. There would be necessary a whole lot of cable to reach the antennas -never counted, but as a wild guess - about 350 feet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer I can't seem to find here - and elsewhere - is how much is too much, when it comes down to setting an antenna apart from one's shack? I understand that in order to properly resonate, my entire system, i.e. radio + cable + antenna need to be in harmony and everything has to be thoroughly calculated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To me it seems that's it's just too much cable and it will definitely affect my overall &lt;em&gt;transception&lt;/em&gt; quality, if not entirely cripple the entire system. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are your thoughts on the cable distance? Any workaround for that kind of problem if that is not an option? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm still to take some small QRP equipment and run some tests on the lower part of my cottage, to see if that's an option, should the whole placing the antenna on the topmost part option become void. &lt;/p&gt;&#xA;" OwnerUserId="4239" LastEditorUserId="4239" LastEditDate="2016-09-09T12:40:46.080" LastActivityDate="2016-09-13T15:07:24.000" Title="Distance between antenna and radio" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6660" PostTypeId="2" ParentId="6659" CreationDate="2016-09-09T14:49:24.753" Score="2" Body="&lt;p&gt;If you find the coax losses too high, you could try turning your station into a remote controlled station. A lot of hams do this. They install  interfacing equipment at both ends, and control the station from their computer. Remoterig is one brand of interface, and I am sure there are many others. Some radio vendors also supply remote control heads, if you prefer a radio with knobs. You probably also want to control other equipment - antenna switches, antenna tuner, amplifier(?), etc, so check that the interface can handle that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Strictly speaking, you do not need an IP connection to accomplish this. But I suspect it will be easier to find products which run over IP. In your case, it would be a local network run over wifi or wired Ethernet.&lt;/p&gt;&#xA;" OwnerUserId="6220" LastEditorUserId="6220" LastEditDate="2016-09-09T16:52:59.777" LastActivityDate="2016-09-09T16:52:59.777" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6661" PostTypeId="2" ParentId="6659" CreationDate="2016-09-09T14:49:33.750" Score="7" Body="&lt;p&gt;This isn't nearly as big of an issue as you're thinking.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The answer I can't seem to find here - and elsewhere - is how much is too much, when it comes down to setting an antenna apart from one's shack?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The effect of a longer &lt;em&gt;feed line&lt;/em&gt; between your transceiver and your antenna is increased &lt;em&gt;loss&lt;/em&gt; — the signal will be weaker at the destination.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If you are transmitting, this means that less of the power from your final amplifier (whether built into your radio or external) reaches the antenna and radiates. Thus, the consequence of the loss is exactly the same as if your radio had less power output — not anything inherently bad.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you are receiving, this means that less of the power gathered by your antenna arrives at your receiver. This is problematic if the signal is too weak for the &lt;em&gt;sensitivity&lt;/em&gt; of your receiver (but that is unlikely for HF operation) or if you have sources of interference near your receiver that are stronger than the signal (this is something you can avoid).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The way loss in a transmission line works is that, at a given frequency, over a given length of the cable, a certain proportion of the energy will be lost (dissipated in heat or leaked out). Since this is a ratio, it is easily expressed in dB. For example, Times Microwave LMR-400 (a model of coaxial cable popular for high-end amateur use) &lt;a href=&quot;https://www.timesmicrowave.com/documents/resources/LMR-400.pdf&quot; rel=&quot;nofollow&quot;&gt;specifies that&lt;/a&gt; at 30 MHz (the high frequency end of HF), there will be 0.7 dB of loss in 100 ft of cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to calculate loss for a particular length, you just multiply it (given that it's in dB).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$0.7\,\text{dB} \cdot \frac{350\,\text{ft}}{100\,\text{ft}} = 2.45\,\text{dB}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, with this cable you would have 2.45 dB of loss. &lt;strong&gt;That's not bad at all&lt;/strong&gt; — compared to the average ham's setup, you'll be more than making up for it with your advantageous antenna location and height (assuming you put up a modest tower).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(If you were operating at higher frequencies — VHF or UHF range, say — cable loss becomes &lt;em&gt;much&lt;/em&gt; more of a problem. But here, having a clear line of sight from your antenna makes even more of an improvement.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also do better than coax, for HF operation. If you use &lt;em&gt;ladder line&lt;/em&gt; (two plain wires separated by insulating spacers), you will get less loss at a lower price. The primary disadvantage of ladder line is that it will not work properly if there are nearby conductive objects, but that is not at all a problem for a long outdoor run in open air (not along the ground). It is also not suitable for higher frequencies as the spacing of the wires must be much smaller than the wavelength and consistent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above is assuming perfect SWR — that is to say, if you have an antenna that is built for the frequency band you are operating on. If you want to use many different bands with a single antenna, you will need an “antenna tuner”, and depending on the precise relationships there will be more loss in the section of feed line between the antenna and the tuner. You can reduce this problem by installing a remote-controlled/automatic tuner at the antenna end rather than at your transceiver.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I understand that in order to properly resonate, my entire system, i.e. radio + cable + antenna need to be in harmony and everything has to be thoroughly calculated.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is false. There are badly-designed systems where every part influences the characteristics, but you should avoid that (and they would be nearly impossible to “thoroughly calculate” because you would need more information than you can practically gather and compute for the model). In a properly built system, the only shape and lengths that matter are those of the antenna itself (and its immediate surroundings — which is why you mount an antenna up high to avoid them).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-09-13T15:07:24.000" LastActivityDate="2016-09-13T15:07:24.000" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6662" PostTypeId="2" ParentId="6656" CreationDate="2016-09-09T14:57:56.047" Score="4" Body="&lt;p&gt;A &quot;Guanella balun&quot; is really just a common-mode choke.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JrreI.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fJrreI.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For differential-mode currents, the current on one half of the transmission line is equal but opposite the current on the other half. Likewise, the magnetic fields due to these currents is equal but opposite, so they cancel, and so there's no magnetic field at all. Consequently differential-mode currents see no inductance at all, and pass through as if the choke isn't there at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For common-mode currents the magnetic fields don't cancel, and so the choke looks like an inductor. This is the &quot;choking reactance&quot;, inductance being a specific case of reactance. Ostensibly, we have the feedline where we don't common mode currents to flow (the &quot;wrong&quot; place), and we have some other place we'd like them to flow (the &quot;right&quot; place). For example in a coax-fed dipole, the &quot;right&quot; place is the leg of the dipole attached to the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea with a common-mode choke employed as a balun in this case is to make the impedance seen by the common-mode currents on the feedline significantly higher than the impedance to the &quot;right&quot; place, whatever that is. Consequently most of the current will flow in the &quot;right&quot; place, and very little in the &quot;wrong&quot; place: the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a similar but much simpler situation at DC:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/S3GMo.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fS3GMo.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since R1 is significantly bigger than R2, almost all of the current will flow through R2. The idea with the choke is similar, except instead of resistances we are using reactances which are analogous for AC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in order for this balun to be effective, that impedance seen by common-mode currents, the &quot;choking reactance&quot; due to the transformer, must be significantly higher than the impedance to whatever the other place is where you'd prefer those currents flow.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-09-09T14:57:56.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6663" PostTypeId="2" ParentId="6659" CreationDate="2016-09-09T17:02:35.863" Score="3" Body="&lt;p&gt;My answer builds upon @KevinReidAG6YO's fine answer.  Let's assume that you're talking about HF frequencies, and that you do put the antennas on top of the hill (which is what I think you should do), and that you use LMR 400 coaxial cable with 2.45 dB loss at 30 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two situations to consider: receive and transmit.  For receive, incoming signals will be attenuated, but the noise will be attenuated also.  The signal-to-noise ratio, which is the most important measurement for receiving, will be the same.  The gain in your receiver will easily make up for the lost 2.45 dB.  So you will receive just as well as if your receiver were directly connected to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transmitting is different.  When you transmit, some of your power is lost as heat to the coax, so your signal will be weaker for anyone listening.  But how bad is the problem?  Receivers have meters calibrated in S-units, and the traditional definition of an S-unit is 6 dB.  So if your signal is 2.45 dB weaker than it would be if your transmitter were connected directly to the antenna, people listening will hear a signal 2.45 / 6 &amp;approx; 0.4 S-units weaker than if your transmitter were connected directly to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For most purposes, 0.4 S-units is so small a loss that it's not worth worrying about.  If you did want to worry about it, you could solve the problem by increasing your output power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Contesters and DXers would probably say that 2.45 dB is too much loss, but that is because they are already running the maximum legal power (or a bit more, ha ha), and the 2.45 dB will make enough of a difference that some far-away stations won't be able to hear the signal when propagation is difficult.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact I know a DXer who has his antennas at the top of the hill about 400 feet / 120 m from his house, and he uses cable-TV &quot;hardline&quot; coaxial cable about 3/4&quot; / 2 cm in diameter to the top of the hill, in order to lower the loss.  I understand that the loss of his coaxial cable at HF frequencies is about 1 dB.  He has gone to quite a lot of expense and trouble to save himself about 1.5 dB in coaxial cable loss, but he likes to work stations halfway around the world that have very weak signals.  If your goal isn't to work stations with very weak signals, then 350 feet of LMR-400 to the top of your hill should suit you very well for HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All these coaxial loss calculations assume that the SWR is close to 1:1.  If the SWR is higher, then the loss increases very quickly.  2.45 dB might not be much loss, but if your SWR were 10:1, then the loss might be 20 dB.  That kind of loss is a real problem.   (If you had a 100 W transmitter and 20 dB of loss, then you would be radiating only 1 W.)  For that reason, if you put the antennas on top of the hill you would do well to choose antennas that have SWRs close to 1 already, or use a remote antenna tuner that is close to the antenna, so that the SWR on the coax is close to 1:1.  If the SWR on the coax is close to 1:1, then you won't need to worry at all whether your coax is a certain multiple of wavelengths at a certain frequency.  (If you're curious about why that is, get a copy of the ARRL Antenna Book and read up on transmission lines and Smith charts.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-09-09T17:02:35.863" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6664" PostTypeId="1" AcceptedAnswerId="6668" CreationDate="2016-09-10T19:39:55.890" Score="2" ViewCount="309" Body="&lt;p&gt;I currently have a linked dipole up and running at 40,20,15 and 10M. While I have looked at trapped dipoles the losses discourage me as I wish to use as little power as possible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I now I'm wanting to put in latching relays instead of the banana links, but I'm unsure of what specifications I need. &#xA;As they will be at the end of each dipole,  where the voltage is high and current is low I have guessed that high voltage might be a necessity. &#xA;Hope to get some insights on this, and if it's doable. &lt;/p&gt;&#xA;" OwnerUserId="6504" LastActivityDate="2016-09-12T12:46:20.317" Title="Relay specifications for linked dipole" Tags="&lt;dipole&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6665" PostTypeId="2" ParentId="1804" CreationDate="2016-09-10T22:45:03.897" Score="1" Body="&lt;p&gt;A variation of the gamma match is a coupling loop antenna mutually coupling to the center of a dipole.  A small single turn loop antenna is formed and as a very inductive loop, a series capacitor is inserted between the feedline and the inductor which will become resonant at a LOW impedance. (series resonant tank)  When this is coupled to a solid dipole element, which also a low center impedance, a near 1:1 transformer ratio efficiently couples from the loop antenna into the dipole element.  This loading raises the R value of the resonant loop to the feedline impedance.  A gamma match has some quality of the series resonant tank circuit coupled to a driven element.  In some designs, the match does not tap the element at a distance from the center, but instead is a loop that is only connected at the center point of the element.  In this design, there is only mutual coupling as there is no direct electrical connection.&lt;/p&gt;&#xA;" OwnerUserId="8320" LastActivityDate="2016-09-10T22:45:03.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6666" PostTypeId="1" CreationDate="2016-09-11T17:57:06.063" Score="4" ViewCount="1826" Body="&lt;p&gt;What serial number is referred to in a cq contest? How do I determine that serial number?&lt;/p&gt;&#xA;" OwnerUserId="8319" LastEditorUserId="5222" LastEditDate="2016-09-28T19:46:29.210" LastActivityDate="2021-05-22T14:25:22.740" Title="How to determine a serial number in cq contest?" Tags="&lt;contest&gt;&lt;jargon&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6667" PostTypeId="2" ParentId="6666" CreationDate="2016-09-11T20:23:58.840" Score="3" Body="&lt;p&gt;Serial numbers usually count from 1 to N where 1 is for your first contact of the contest.  Serial numbers are incremented by 1 typically.  But, there is no reason why you cannot start at 577 and increment by 5 if you want unless the rules require you do count in a specific fashion [Recently added update per discussion in comments].&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I actually start at 22 for some reason. All my contests I do are CW and I just like the sound of 22 I guess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, during a contest when the exchange uses serial numbers, the other operator will give you his serial number and you give yours.  Of course the numbers are not the same.  In contesting and submitting your log, serial numbers are usually included to demonstrate a qualified contact.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2016-09-12T17:25:34.927" LastActivityDate="2016-09-12T17:25:34.927" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6668" PostTypeId="2" ParentId="6664" CreationDate="2016-09-12T01:48:05.880" Score="2" Body="&lt;p&gt;Interesting idea. Here's a start: &lt;a href=&quot;https://ham.stackexchange.com/questions/1410/what-is-the-peak-voltage-at-the-tips-of-a-dipole-antenna&quot;&gt;What is the peak voltage at the tips of a dipole antenna?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The conclusion there is for a 100W transmitter and a &quot;normal&quot; dipole, you can expect a peak of about +/-900V relative to ground at the dipole ends. You'll want to pad that with a healthy safety margin. Also keep in mind that power is proportional to the square of voltage, so if you have more than 100 watts that voltage can get very high, very fast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the relays are closed and they find themselves somewhere in the middle of the dipole, they'll have to deal with the current. Current is highest at the feedpoint, so in the worst case, for a 100W transmitter the current is $ \sqrt{100\:\mathrm(W) / 72\:\Omega} = 1.8\:\mathrm A$. In practice lower, since the relay is not at the feedpoint. This is an upper bound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll want to be sure the relays don't switch while transmitting. I'd imagine there'd be some arcing and the contacts would wear out quickly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect the bigger challenge will be controlling the relays, since being on a wire with 100 watts of RF is a little tricky. Not only do you need to get the wires to them to control them, but once you've got the wires there you'll need to devise a way to keep the RF out of the control wires and the relay coils.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've never done this, and I can't find descriptions by anyone who has, but I might try using twin-lead as the antenna element. The common-mode current radiates as a dipole normally would, while you can use the differential mode to control a DPDT relay.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The trouble then is the mechanism to control both common and differential modes from the shack. You don't want to put common-mode RF on the feedline: that would make it an antenna. If only you had a 3rd wire...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use a folded dipole, you can make one. At the center of what would normally be the undriven element is &quot;ground&quot;. You can just attach a wire there. And if &quot;ground&quot; is actually DC +12V, you can use that to control the relay coils.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/PJgna.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fPJgna.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you'll need to impedance match the folded dipole somehow, like a 4:1 balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also avoid running the 3rd wire to the shack if instead you use a DC bias on the coax and separate that from the RF at the feedpoint with a capacitor.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-09-12T12:46:20.317" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6671" PostTypeId="2" ParentId="6666" CreationDate="2016-09-13T18:12:38.310" Score="1" Body="&lt;p&gt;You did say 'cq' contest. Did you mean the CQ WW DX or WPX contest? For CQ WW DX, the message is your CQ Zone: 5 for US east coast, 3 for west coast, 14 for W Europe, etc. For WPX, it is a serial number. The rules state that it starts from 1.&lt;/p&gt;&#xA;" OwnerUserId="6220" LastActivityDate="2016-09-13T18:12:38.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6672" PostTypeId="1" AcceptedAnswerId="6673" CreationDate="2016-09-14T15:47:52.523" Score="7" ViewCount="219" Body="&lt;p&gt;We can measure power in watts, and gain or loss in unitless ratios. So why bother using decibels for these things?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-09-16T15:41:24.937" Title="Why do we use decibels in radio?" Tags="&lt;theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6673" PostTypeId="2" ParentId="6672" CreationDate="2016-09-14T15:47:52.523" Score="12" Body="&lt;p&gt;We use decibels because they are the most intuitive representation when our primary concern is signal quality. Signal quality changes not in proportion to the power added (in watts), but rather to the percentage change. Decibels put &quot;percentage change&quot; on a linear scale which is easy and intuitive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't show you with a radio here, but I can show you with a visual analogy. Your monitor is emitting visible electromagnetic energy. Your eye receives this power just like a radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm going to &quot;transmit&quot; an image, with some added noise. The noise power remains constant, but I'll vary the transmit power. After &quot;receiving&quot; the image, I'll normalize the contrast of the image to make use of all the pixel values between black and white. This is analogous to what AGC does in a radio. Your job is to decode the image.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here it is at my maximum transmit power, which we will say is 100 watts, or equivalently 50 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FBjsu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FBjsu.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The noise is detectable but the image is still quite clear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I turn my power way down to 30dBm or 1 watt:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Xji7N.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Xji7N.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm totally buried in the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now let's explore between these two extremes. I'll show a sequence of 100 images, starting and ending at these extremes. The steps between are each an equal increase in either watts or dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Watts first. I'll go from 1 watt to 100 watts, so each step increases power by about 1 watt.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mFrqc.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mFrqc.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how the image emerges from the noise almost immediately. About 1 second in you can already see individual jelly beans. By the 2nd half there's no noticeable improvement in quality, even though the power is still increasing by 1 watt each frame.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now in dBm. I'll go from 30 to 50dBm, so each step is about 0.2dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/I3PGW.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/I3PGW.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This time the image goes through stages of &quot;I think there could be something in there&quot;, &quot;I can read 'IPI'&quot;, and &quot;Hey, those are jelly beans!&quot; The noise continues to improve up to the end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By taking the logarithm of power we change watts to dBm, and so &quot;percentage change&quot;, the real determinant in signal quality, becomes a more intuitive linear unit. I'll demonstrate with a dilemma: would you rather:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Have 64x antenna gain, while increasing your power from 1 to 2W, or&lt;/li&gt;&#xA;&lt;li&gt;Have 8x antenna gain, while increasing your power from 1 to 100W?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The dilemma is easier in decibels:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Have a 18dB antenna gain, while increasing your power 3dB, or&lt;/li&gt;&#xA;&lt;li&gt;Have a 9dB antenna gain, while increasing your power 20dB?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;It's easy to see 18+3=21 is less than 9+20=29, so option 2 is the better choice. And it's easy to quantify how much better: 29-21=8dB. With experience you'll learn &lt;a href=&quot;https://ham.stackexchange.com/q/6676/218&quot;&gt;what a difference 10dB will make&lt;/a&gt;, and you can know that 8dB is just a bit less than that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;This is a 10dB improvement&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bOinZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bOinZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;a href=&quot;https://i.stack.imgur.com/9y5Nb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9y5Nb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;This is an 8dB improvement&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bOinZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bOinZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;a href=&quot;https://i.stack.imgur.com/TCQWD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TCQWD.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power in watts still has some utility. Heat generated and electrical costs are linearly proportional to watts. And it's more convenient to calculate voltages and currents with power in watts. But at the transmitter's output our primary concern ceases to be electrical engineering and becomes signal quality, and decibel units make more sense.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-09-16T15:41:24.937" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6674" PostTypeId="2" ParentId="5637" CreationDate="2016-09-16T02:13:00.677" Score="1" Body="&lt;p&gt;Tim Seed, comment number two, is spot on.  I used a standard Icom mobile mounting bracket, the MB-4, to mount the entire radio (the ID-880) down there in front of the gear shift, including leaving the control head right on the radio.  The MB-4 merely tips the unit up to a nice viewing angle AND solves the problem that the radio will not quite fit in there down flat.  Obviously it is totally unsafe to be looking down there or touching the control head while driving.  I use the HM-154 NON touch pad mic.  It does have Channel UP &amp;amp; DOWN buttons.. hold and press either to scan.  That allows me to operate a radio that I essentially cannot see while driving.  And I don't use an external speaker, I use the one in the ICOM 880.  I saw that spot in front of the gear shift while dwelling on how my wonderful 2015 factory rock crawler offers no spot other than in front of the gear shift that does not take away from passengers and cargo.   AF7RM   Rich  in Reno.&lt;/p&gt;&#xA;" OwnerUserId="8348" LastActivityDate="2016-09-16T02:13:00.677" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6675" PostTypeId="2" ParentId="5637" CreationDate="2016-09-16T04:02:02.587" Score="1" Body="&lt;p&gt;Even though I have a 4-dr, space is limited for me as well. I only use radios with remote heads. Two heads are mounted up front with the microphone coming up from alongside my seat for one of them. I did drill holes for a Motorola Spectra head although some good double-sided tape would probably have worked. The Kenwood is attached to a spot on the dash with the double-sided tape it came with and it's pretty solid. You can see these at www.n0xmz.com. The radios themselves are in the trunk, mounted to the back of a back seat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We probably won't talk you into it but through-hole NMO really is the only way to go when it comes to antennas. It's waterproof, sturdy, and looks like a professional install. You gotta admit, they look pretty sweet on my car. Lip mounts can bend the trunk's metal and when I used them, I always had problems with water seeping in when there was a good storm. As for the holes, if the day comes where I decide to sell it, I'll do what I did with previous cars and insert some black rubber plugs the fill the holes perfectly (Motorola part # 0580379B46). That's what they do with retired police cars and commercial vehicles. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also recommend checking out www.k0bg.com, especially the photo gallery section. There are over 600 pictures submitted by hams showing off their mobile installs. I think my old Accord is still on there and it had an HF ball mount with an 8' whip. Alan has several in-depth articles on all facets of mobile operation. I highly recommend it to anyone interested in mobile hamming.&lt;/p&gt;&#xA;" OwnerUserId="8350" LastActivityDate="2016-09-16T04:02:02.587" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6676" PostTypeId="1" AcceptedAnswerId="6677" CreationDate="2016-09-16T15:39:59.413" Score="5" ViewCount="353" Body="&lt;p&gt;Say I've calculated that my feedline losses are 3dB, or I'm considering an antenna with 10dB gain, or trying to decide between a transmitter with 10dBm output power versus 16dBm (6dB difference).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand &lt;a href=&quot;https://ham.stackexchange.com/questions/6672/why-do-we-use-decibels-in-radio&quot;&gt;a decibel is a degree of change in signal quality&lt;/a&gt;, similar to a degree of temperature. But how much change? For example, if I increase my antenna gain by 3dB, how much better will that make my signal?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-09-19T16:27:14.800" Title="How big is a decibel?" Tags="&lt;snr&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6677" PostTypeId="2" ParentId="6676" CreationDate="2016-09-16T15:39:59.413" Score="4" Body="&lt;p&gt;Here are some visual examples, corresponding to what you'd see receiving an analog TV transmission. I've picked an image with features of varying detail. Look for:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the letters &quot;IPI&quot;&lt;/li&gt;&#xA;&lt;li&gt;individual jelly beans&lt;/li&gt;&#xA;&lt;li&gt;contrast between the beans, especially the darker ones that are very close in brightness&lt;/li&gt;&#xA;&lt;li&gt;reflections on the beans&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Here are sets of three images side-by-side, each adjacent image some number of decibels apart in signal to noise ratio. Our eyes are good at picking out fine detail in noise, about as good as a well-designed digital mode. So this should give you an intuitive sense of the difference a decibel makes for digital modes, and also slow-scan TV.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Audio samples are past the images, if SSB is more your concern. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;1dB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Gxl8N.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Gxl8N.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/Jmk3U.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Jmk3U.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/af5Pa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/af5Pa.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;1dB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mSRNc.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mSRNc.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/eNvPk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eNvPk.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/YWsSy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YWsSy.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;3dB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CtA3m.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CtA3m.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/iPpPn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iPpPn.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/jD3uM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jD3uM.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;3dB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vIjUN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vIjUN.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/1XUo6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1XUo6.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/6624k.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6624k.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;10dB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3VXF4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3VXF4.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/7J6GW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7J6GW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;10dB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8V0Um.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8V0Um.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/yTU24.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yTU24.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Ears don't work like eyes, so I've also generated some audio samples such as you'd hear for SSB. Again they are normalized to a constant volume like AGC would do. The numbers refer to the noise power, so -48 dB is the highest quality (lowest noise power), and -06 dB is the worst quality (highest noise power)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://bitglue.com/noise_demo/combined-06.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;-06 dB&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://bitglue.com/noise_demo/combined-12.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;-12 dB&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://bitglue.com/noise_demo/combined-18.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;-18 dB&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://bitglue.com/noise_demo/combined-24.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;-24 dB&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://bitglue.com/noise_demo/combined-30.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;-30 dB&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://bitglue.com/noise_demo/combined-36.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;-36 dB&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://bitglue.com/noise_demo/combined-42.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;-42 dB&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://bitglue.com/noise_demo/combined-48.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;-48 dB&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-09-17T14:01:15.233" LastActivityDate="2016-09-17T14:01:15.233" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6678" PostTypeId="2" ParentId="6676" CreationDate="2016-09-16T17:45:20.017" Score="1" Body="&lt;p&gt;If your transceiver has an S-meter, &lt;strong&gt;one &quot;S&quot; has 6dB&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is decibel small? In my sense, yes, &lt;strong&gt;dB is quite small&lt;/strong&gt;: it is difficult to hear a change of 1-5dB in voice quality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 5-10dB change is significant, 15dB or 18dB totally changes conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Few devices in the amateur market can measure a 1dB difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But precise &quot;bookkeeping&quot; of the antenna system is important: the sum contains many small numbers: +7dB antenna gain, -0.5dB lost in UC-1 connector (other name for PL-259) , 20 meters of feedline with -35dB per 100m gives a 7dB loss, another UC-1 connector: In total, this system has an effective -1dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connector power loss like UC-1 (PL-259) are not measurable at home, so take it from literature (most sources give 0.5dB).&#xA;Loss in longer cable can be measured in a good quality amateur testing set, or more simply read it from the manufacturer's data sheet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In reality small changes can add up: increase antenna gain 1.5dB, install a better feedline for 0.3dB/1m, better connectors etc .... and you've made a 6dB improvement. This is a good result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM has a different behavior from SSB: quality is 'good' in a broad central part of scale (hard to distinguish for an untrained ear), a small drop in quality (voice+noise) near the low range, and drastic loss of quality when signal drops more and suddenly voice is totally unreadable under noise.&lt;/p&gt;&#xA;" OwnerUserId="6323" LastEditorUserId="218" LastEditDate="2016-09-17T21:31:34.503" LastActivityDate="2016-09-17T21:31:34.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6679" PostTypeId="1" AcceptedAnswerId="6680" CreationDate="2016-09-17T02:12:38.260" Score="3" ViewCount="4988" Body="&lt;p&gt;New to this particular site on StackExchange and new to amateur radio period so bear with me:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm looking into buying a VHF radio for work related purposes. More specifically the Icom IC-2300H.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been wondering if it was possible to program a VHF radio to run on CB radio frequencies?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've done some searching but didn't find anything on the topic, but I may not be using the correct keywords.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not familiar with the various radio frequencies and types.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not looking to specifically use this radio for the purpose of cb, but just the possibility of.&lt;/p&gt;&#xA;" OwnerUserId="8355" LastEditorUserId="76" LastEditDate="2016-10-29T19:00:50.330" LastActivityDate="2016-10-29T19:00:50.330" Title="Programming VHF To CB" Tags="&lt;vhf&gt;&lt;citizens-band&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="6680" PostTypeId="2" ParentId="6679" CreationDate="2016-09-17T02:31:42.290" Score="3" Body="&lt;p&gt;CB or its close relatives fall into the HF frequency range (covering somewhere around 26 to 28 MHz, depending on country), so anything that accurately calls itself a VHF radio will not transmit (and most likely will not receive) CB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, what you do to answer this kind of question is find the radio's &lt;em&gt;specifications&lt;/em&gt; — either &lt;a href=&quot;http://www.icomamerica.com/en/products/amateur/mobile/2300h/specifications.aspx&quot; rel=&quot;nofollow&quot;&gt;on the web site&lt;/a&gt; or in the user's manual which will often be available as a PDF — and look for the transmit and receive frequency ranges. You can see that this radio's lowest receive frequency is 136 MHz, somewhat below the low end of the 2-meter amateur band. Therefore it cannot receive or transmit on CB frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Another issue is whether it supports the relevant modulation, or &lt;em&gt;mode&lt;/em&gt; — which in this case is also a problem, because this radio supports only FM whereas CB is conventionally AM and sometimes SSB.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also cannot use this radio “for work related purposes” unless you are intending to receive only and not transmit. This is because it will only transmit on the amateur bands, where any use for which you receive compensation is prohibited. Outside the amateur bands, all other frequencies you might legitimately use in the US (I see your location from your profile) require “certified” (formerly “type accepted”) equipment, which in practice means equipment that transmits on that band or frequency &lt;em&gt;only&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-09-17T02:42:11.757" LastActivityDate="2016-09-17T02:42:11.757" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6682" PostTypeId="1" AcceptedAnswerId="6699" CreationDate="2016-09-18T11:37:10.670" Score="0" ViewCount="683" Body="&lt;p&gt;I broke so called 'IF transformer' on my radio. I was just slightly trying to regulate it to follow an instructions that is found on Wikihow page. My aim was to listen to the conversations of pilots from the airport we have near our house. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, I cannot find a transformer with the same size (5.7mm X 5.7mm). The radio still works. How important it is to replace it? I will go to a place where electonic components are sold and I don't know if I should accept if they offer a transformer with slightly bigger size(7.9mm X 7.9mm)?! Maybe I can use wires to mount it to the board?&lt;img src=&quot;https://i.stack.imgur.com/JI5LR.jpg&quot; alt=&quot;![enter image description here&quot;&gt;]&lt;a href=&quot;https://i.stack.imgur.com/JI5LR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;1&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8282" LastActivityDate="2016-09-24T01:26:18.250" Title="Broken IF Transformer (tiny and 455 KHz)" Tags="&lt;repair&gt;&lt;transformer&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6683" PostTypeId="1" CreationDate="2016-09-19T02:56:20.810" Score="6" ViewCount="4162" Body="&lt;p&gt;The large VHF / UHF digital voice communication modes all require the same AMBE vocoder chip from &lt;a href=&quot;http://www.dvsinc.com/&quot; rel=&quot;noreferrer&quot;&gt;dvsinc&lt;/a&gt;. This surface mount chip can be aquired standalone  for a relatively high price or all of the required encode / decode electronics can be preinstalled in the form of various boards such as the DV Mega. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every single product which transmits and receives most mainstream digital voice modes requires one of these chips from the specific manufacturer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This introduces limitations, however. In the case of attempting to run a virtual private server providing an analog to digital DMR bridge using the &lt;a href=&quot;https://github.com/N4IRS/DMRGateway&quot; rel=&quot;noreferrer&quot;&gt;DMRGateway software&lt;/a&gt; , I couldn't procede any farther until I plugged a USB fob with the vocoder chip which is completely impossible on a virtual server. Even if I had a physical computer with USB, price is a large limiting factor in this as well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So basically, at this point, after several hours of research and attempting software packages, there is no way I have found to decode / encode digital voice through the means of software only. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the fact that amateur radio requires unencrypted and usually led by an open-source community, I  am wondering if anybody has even heard if this has been done before, if someone is working on it, or if there are any alternative open-source digital voice modes for VHF and above not requiring a separate vocoder chip?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Small Update:&#xA;Alinco looks like they use an &lt;a href=&quot;http://www.universal-radio.com/catalog/fm_txvrs/20275025.html&quot; rel=&quot;noreferrer&quot;&gt;open source GMSK modem&lt;/a&gt; using the &lt;a href=&quot;https://www.itu.int/rec/T-REC-V.32/en&quot; rel=&quot;noreferrer&quot;&gt;ITU V.32 protocol&lt;/a&gt;. I couldn't really find any other information on this, however. &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2016-09-19T22:49:30.803" LastActivityDate="2016-09-19T22:49:30.803" Title="DMR / DSTAR / P25 Software Encode / Decode" Tags="&lt;digital-modes&gt;&lt;d-star&gt;&lt;digital-voice&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6684" PostTypeId="2" ParentId="6683" CreationDate="2016-09-19T12:38:11.003" Score="5" Body="&lt;p&gt;Here is a link to a presentation by Bruce Perens K6BP two years ago: &lt;a href=&quot;http://algoram.com/dcc2014/AMBE_Exposed.pdf&quot; rel=&quot;noreferrer&quot;&gt;http://algoram.com/dcc2014/AMBE_Exposed.pdf&lt;/a&gt;. Start at &quot;Can Hams Use Software AMBE?&quot; I am not aware of any significant changes since then. There exists a software solution (mbelib), but it is patent encumbered. So much so that the authors are anonymous.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are probably aware of the open voice codec &quot;Codec2&quot; by David Rowe: &lt;a href=&quot;http://www.rowetel.com/?page_id=452&quot; rel=&quot;noreferrer&quot;&gt;http://www.rowetel.com/?page_id=452&lt;/a&gt;. But it doesn't appear to fit your use case.&lt;/p&gt;&#xA;" OwnerUserId="6220" LastActivityDate="2016-09-19T12:38:11.003" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6685" PostTypeId="2" ParentId="6676" CreationDate="2016-09-19T16:27:14.800" Score="1" Body="&lt;p&gt;A decibel is a mathematical measurement of the change in the magnitude of a quantity. It uses a logarithmic scale so that a change of 10 db is an increase of 10 times, while a change of 20 db is an increase of &lt;em&gt;100 times&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula for computing the change in decibels between the original power $P_0$ and the new power $P$ is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$10 \log\left(\dfrac{P}{P_0}\right)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where the logarithm uses base 10. There are some useful relations with decibels that are easy to remember&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;3 dB = 2x&#xA;6 dB = 4x&#xA;7 dB = 5x&#xA;10 dB = 10x&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;and because it is a logarithmic scale, you can use these together so 13 dB = 10 dB + 3 dB = 10x * 2x = 20x.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because decibels measure change relative to some baseline value, to use them to specify absolute values, like a power of 1W, we sometimes use the unit dBm which means &quot;decibels relative to 1 milliwatt&quot;.  So $1\ W = 1000\ mW = 30\ dBm$ because 30 dB = 10 dB + 10 dB + 10 dB = 10 x 10 x 10 = 1000x.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A transmitter with 10 dBm power output puts out 10 dB more than one millwatt, or $10\ mW$.  A transmitter with 6 dB &lt;em&gt;more&lt;/em&gt; power or 16 dBm puts out 4x as much power or $40\ mW$.&lt;/p&gt;&#xA;" OwnerUserId="5188" LastActivityDate="2016-09-19T16:27:14.800" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6687" PostTypeId="2" ParentId="1530" CreationDate="2016-09-21T02:52:29.713" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;This would suggest that longer wavelength antennas are more efficient collectors of electromagnetic energy. Why is this? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I think of it like in optics.  A larger lens will collect more light because more light is incident on the lens.  More photons hit the lens.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A radio antenna is a lens for a different wavelength of light, i.e. radio waves, not visible light.  Therefore, the (electrically) larger the antenna, the more photons are incident on the conductor, the more energy will be collected.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Said differently:&#xA;If you had 2 antennas of the same length, you would collect twice as much energy as a single antenna.  If you had two lenses of the same size, you would collect twice as much light as a single lens.  Instead of 2 antennas, you could have a single antenna of twice the length and collect twice the energy of the original antenna.  Same for the optical lens.&lt;/p&gt;&#xA;" OwnerUserId="8373" LastEditorUserId="8373" LastEditDate="2016-09-28T21:27:23.727" LastActivityDate="2016-09-28T21:27:23.727" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6688" PostTypeId="2" ParentId="1282" CreationDate="2016-09-21T16:44:40.997" Score="1" Body="&lt;p&gt;Good question.  I would say that I operate 1/3 CW and 2/3 SSB, but wish that the ratio was the opposite.  Reminds me of a joke:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;What's ya got for lunch?&quot; - &quot;Baloney sandwich, and I hate baloney.&quot; - &quot;Who makes your lunch?&quot; - &quot;I do.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I like to QSL too, and keep a log.  On review of my log, I see that the 1:2 ratio is true.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wonder what the ratio is with other hams?  The ARRL may do some analysis of their LoTW statistics to get a fuller, more accurate picture.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W3TTT&lt;/p&gt;&#xA;" OwnerUserId="4289" LastActivityDate="2016-09-21T16:44:40.997" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6689" PostTypeId="2" ParentId="6381" CreationDate="2016-09-21T16:53:50.647" Score="0" Body="&lt;p&gt;Try this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://w3ttt.radiostream321.com/&quot; rel=&quot;nofollow&quot;&gt;http://w3ttt.radiostream321.com/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have set up a streaming internet station that reads the news feed from Google, removes all those pesky HTML tags, and sends the text in morse code.  It is great for practice, for two great reasons: 1) because it is news and interesting.  I fantasize that I am a shipboard radio operator in the 1930's.  And 2) it tends to repeat words or phrases, which is good because if you missed something, you get it a few more times, and then get better at it.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And 12 words per minute is a nice speed - not too slow - but relatively easy to achieve.  I think that 12 wpm should be the default CW speed on ham bands.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;W3TTT&lt;/p&gt;&#xA;" OwnerUserId="4289" LastActivityDate="2016-09-21T16:53:50.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6690" PostTypeId="2" ParentId="1818" CreationDate="2016-09-21T17:56:23.060" Score="2" Body="&lt;p&gt;It could be that the sending operator has experience with the type of operator that is receiving, and the experience was that the receiving op &quot;counts dits&quot; in numbers, but can comfortably copy text at a faster speed.  Also, each number is vital, as in a phone number, but one can fill in for misd lttrs.  &lt;/p&gt;&#xA;" OwnerUserId="4289" LastActivityDate="2016-09-21T17:56:23.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6691" PostTypeId="2" ParentId="1501" CreationDate="2016-09-21T18:04:35.923" Score="2" Body="&lt;p&gt;This is exactly a matter of the CW measurement of &quot;weight&quot;.  With this weight measurement, the dahs are shorter or longer.  A longer dah means a heavier weight.  Weight is adjustable in most electronic keyers or Bugs.  Personally, I like a longer dah, a heavier weight to my sending. I use a straight key only.  People who are used to a heavier weight will complain about a lighter weight, and visa versa. The dits are usually less variable, and it usually is not as important if the dits are shorter than normal, but it does matter if the dits are so long that they start to be confused with dahs.  IMHOOP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;...There a big difference between the dots being a bit shorter than the dahs at widely varying WPM ...&quot;&lt;/p&gt;&#xA;" OwnerUserId="4289" LastActivityDate="2016-09-21T18:04:35.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6692" PostTypeId="2" ParentId="1818" CreationDate="2016-09-21T20:21:37.863" Score="4" Body="&lt;p&gt;You've asked two questions.  About whether it is important or not to be consistent in speed when transmitting, I would say that the important thing is to get the information across at a speed comfortable to the receiving operator.  If the operator is not as good at copying numbers, then slowing down the RST is perfectly appropriate.  If the receiving operator is copying the address for the QSL card, then slowing down is appropriate.  It's usually better to get the information across the first time than to send it fast, and then have to repeat.  So I would say that yes, it is appropriate to slow down parts of the QSO to suit the receiving operator.  Like @k6ekb says, it can also be appropriate to speed up the routine parts of the QSO, such as the third or fourth identification of the two stations before an &quot;over&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To illustrate one thing that the sending operator shouldn't do, there was an incident when I was a new operator with US &quot;novice&quot; privileges.  I sent my shaky CQ with a straight key at about 6 wpm, and I was answered by a European station, my first DX!  In my excitement, I probably started sending a little too fast: I was easily capable of sending faster than I could receive.  The other station, which had started at a speed that was comfortable to me, began to send faster and faster, despite my &quot;QRS PSE&quot;.  Soon he was sending about 15 wpm, far faster than I could copy.  In a panic, I &quot;pulled the big switch&quot;, and switched off the transceiver, and abandoned the shack!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding the second question about whether it is better to slow down or repeat when conditions deteriorate, I would say that the answer depends on the conditions, the situation, and the skill of the receiving operator.  I most often experience deteriorating conditions, usually interference and fading, when contesting.  In a contest situation, it's almost always better to repeat the information at the &quot;normal&quot; speed, which is usually about 30 wpm, rather than to send it slowly.  In a contest with QRM and QSB, it seems as though there is clear reception for periods of about one to three seconds; at 30 wpm, that's hopefully enough to copy the entire &quot;payload&quot; (crucial part) of the exchange.  When the other operator sends slowly, I'll often miss one or two crucial characters, and have to ask for several repeats.  So in a contest, if conditions are really bad then repeat the exchange two or three times at normal speed, but only if you're asked for a repeat.  Many contesters have amazingly good ears, and can copy accurately despite conditions that would baffle an average operator.  I hesitate to recommend the same answer for all circumstances, but in general I'd personally lean towards repeating the information at normal speed in bad conditions rather than sending slowly.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-09-21T20:21:37.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6693" PostTypeId="1" AcceptedAnswerId="6696" CreationDate="2016-09-22T23:34:47.990" Score="1" ViewCount="69" Body="&lt;p&gt;I recorded an OOK transmission (of a temperature sensor) and I'm trying to reverse engineer the recording to get the binary out with python.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First I searched for the length of a bit. Therefore I search all zones where the value is high and then mean it to get the sample count of one bit. This works well, and  I can get a bitlength and a bitrate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aT9yG.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aT9yG.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My problem is about the first peak in the preamble. As you see it is much shorter than all other &quot;bits&quot;. All other bits have about the same length.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;what could be a reason behind the a short bit at the beginning, which is just about 1/3 of a &quot;regular bit&lt;/li&gt;&#xA;&lt;li&gt;How to process: should I treat the shortest peak as default bitlength or should I treat this short bit as a regular bit?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8382" LastEditorUserId="76" LastEditDate="2016-09-23T00:02:06.493" LastActivityDate="2016-09-23T17:26:35.563" Title="short bit at beginning of tranmission" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6695" PostTypeId="2" ParentId="6114" CreationDate="2016-09-23T15:37:34.540" Score="4" Body="&lt;p&gt;Assuming for the sake of precision that the particular point in the grid square that you want the exact latitude and longitude for is the midpoint of the 6-character subsquare, this can be done readily with Excel formulas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the 6-character grid square data is in cell A1, in a format similar to AA00aa (i.e. upper-case, then digits, then lower-case), the formula for the latitude (based directly on the Python code posted previously) is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;=(CODE(MID(A1,2,1))-65)*10 + VALUE(MID(A1,4,1)) + (CODE(MID(A1,6,1))-97)/24 + 1/48 - 90&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and the formula for the longitude is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;=(CODE(MID(A1,1,1))-65)*20 + VALUE(MID(A1,3,1))*2 + (CODE(MID(A1,5,1))-97)/12 + 1/24 - 180&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want the latitude and longitude of the southwest corner of the subsquare, just leave out the + 1/48 and + 1/24 terms. Add error-checking, upper- and lower-case conversion, conversion of four-character squares to six-character by adding 'mm', and other embellishments as you see fit.&lt;/p&gt;&#xA;" OwnerUserId="8387" LastActivityDate="2016-09-23T15:37:34.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6696" PostTypeId="2" ParentId="6693" CreationDate="2016-09-23T17:26:35.563" Score="2" Body="&lt;p&gt;Perhaps the reason for the shortness is to not confuse it with actual data.  This short &quot;bit&quot; signals a receiving device to start monitoring for data, and could be ignored as recording of data.  It is essentially a &quot;start recording&quot; marker not relevant to the data.  However, if you are repeating this signal or sending it, then you most likely need to include it to initiate the receiving device to start &quot;listening&quot; for &quot;data&quot;.  But it is not &quot;data&quot; per say.&lt;/p&gt;&#xA;" OwnerUserId="6298" LastActivityDate="2016-09-23T17:26:35.563" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6697" PostTypeId="2" ParentId="6682" CreationDate="2016-09-23T18:54:28.693" Score="3" Body="&lt;p&gt;The transformer is most probably a part of a critical tuned circuit. If the ferrite is broken then the radio keeps working but the filtering is worse.&#xA;There a a number of ways to find a replacement for the transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1: Try to get the technical manual and find the partnumber and supplier (manufacturer)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2: Look for the information on the pcb and try to find that on the internet&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3: Look for the information on the transformer body and try to find that part on the internet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning an if circuit should be done with a sweep generator/ spectrum analizer. Otherwise is is very difficult to find the correct critical tuning position.&#xA;Also a technical manual is to be preferred.&lt;/p&gt;&#xA;" OwnerUserId="8374" LastActivityDate="2016-09-23T18:54:28.693" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6698" PostTypeId="2" ParentId="1282" CreationDate="2016-09-23T21:25:09.813" Score="2" Body="&lt;p&gt;As others have posted, answers to this question would be hard to find.  I would point you towards the SKCC and FISTS membership roles and then do some data analysis comparing SKCC/FISTS members to the age of their license using the FCC database or other resources on-line.  Even then, you are likely to capture a lot of older hams who were away from the hobby for decades during career and family time and may have learned CW back in their youth in the hobby days of yore.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am mostly CW.  I do one thing in SSB and that is to QNI into an evening 80-meter net.  All other activity is CW.  I haven't called CQ in SSB in close to 10 years I think.  But, I call CQ in CW almost every day.  However, my purpose here is to note that in all of my CW contacts I have not run across a new ham that I know of -- most, if not all, are old codgers like myself.  In fact, there are times that now at the age of almost 70 I feel like a youngster compared to the other CW ops I run across some are in their early 90s.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-09-23T21:25:09.813" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6699" PostTypeId="2" ParentId="6682" CreationDate="2016-09-24T01:26:18.250" Score="1" Body="&lt;p&gt;Chances are you can find what you need here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.digikey.com/product-search/en/inductors-coils-chokes/adjustable-inductors/196629?k=toko&quot; rel=&quot;nofollow&quot;&gt;http://www.digikey.com/product-search/en/inductors-coils-chokes/adjustable-inductors/196629?k=toko&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could be you broke the slot without moving the coil core. If that's the case you might be better off to leave it alone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can solder and want to replace it you need a voltmeter and a schematic. Put the voltmeter on the AGC line. Tune to a station. Adjust the core for maximum AGC reading on the meter. If you do replace the transformer you should get an alignment tool or a plastic screwdriver to prevent damaging the new transformer's core.&lt;/p&gt;&#xA;" OwnerUserId="8207" LastActivityDate="2016-09-24T01:26:18.250" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6701" PostTypeId="1" CreationDate="2016-09-24T19:41:23.010" Score="5" ViewCount="611" Body="&lt;p&gt;I just bought a CB and mounted it in my truck. I ran my antenna to the back and was going to stick it to my tool box but it turns out to be aluminum, so I'm thinking of bolting a metal plate to the top so the magnet will stick.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I attach a ground wire to my plate so my antenna will be grounded as well?&lt;/p&gt;&#xA;" OwnerUserId="8397" LastEditorUserId="76" LastEditDate="2016-09-25T00:40:39.673" LastActivityDate="2019-04-19T14:03:02.267" Title="Mounting my antenna" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;citizens-band&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6702" PostTypeId="2" ParentId="6701" CreationDate="2016-09-24T23:15:07.230" Score="3" Body="&lt;p&gt;Many hams who do a lot of mobile HF operating (CB is HF also) take the time to bond many different parts of the vehicle together.  The theory is that your vertical antenna is 1/4 wavelength long electrically, but it's only half the antenna; the other half is the ground plane, through which current must pass for efficient operation.  There's lots of information on Alan K0BG's &lt;a href=&quot;http://www.k0bg.com/bonding.html&quot; rel=&quot;nofollow&quot;&gt;page about bonding&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think you'd need to bond the steel plate inside the toolbox to the toolbox, because the RF current will be mainly flowing on the surface of the aluminum.  (RF currents flow mainly in a thin surface layer of a conductor.) If I were you I would bond the toolbox to the truck, and also bond the bed of the truck to the frame.  Have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-09-24T23:15:07.230" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6703" PostTypeId="1" CreationDate="2016-09-25T10:54:45.343" Score="0" ViewCount="431" Body="&lt;p&gt;The rig I'm possessed of is a homebrew from a fellow ham in a manpack case (GE524).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OBxNe.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OBxNe.jpg&quot; alt=&quot;[U229](http://cryptomuseum.com/crypto/usa/u229/img/300826/011/small.jpg)&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The audio connector is a 5-pin 3-point all-weather bayonet mount from the heritage of the manpack.&lt;/p&gt;&#xA;&lt;p&gt;The trouble is ... the connector provided with the rig has gone walkabout; my elmer is unavailable and the prices posted against this connector online are outrightly beyond my budget.&lt;/p&gt;&#xA;&lt;p&gt;Would there be any suggestions on a substitute for the U229 connector?&lt;/p&gt;&#xA;&lt;p&gt;p.s. More detail about the &lt;a href=&quot;http://www.commandcomponents.net/uploads/4/7/3/1/47311171/8704152.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;U229&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-09-27T06:44:00.657" Title="How to substitute a U229 connector?" Tags="&lt;connectors&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6704" PostTypeId="2" ParentId="6703" CreationDate="2016-09-25T14:16:45.597" Score="1" Body="&lt;p&gt;Here are two &lt;em&gt;generic&lt;/em&gt; (not specific to that connector type) and ugly alternatives:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Measure the critical dimensions of the plug and 3D print a replacement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This might not work at all (not enough strength, fine detail, or wear resistance from the print) and is unlikely to be weatherproof. You'll also need to find suitable contacts and a way to mount them in the new plug.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Remove the connector on the radio and mount a modern replacement (or a similar-vintage one that is more readily available) which can be fit in the existing hole.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-09-25T14:16:45.597" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6705" PostTypeId="2" ParentId="6701" CreationDate="2016-09-25T18:58:42.520" Score="3" Body="&lt;p&gt;You didn't mention if the antenna was a full-sized quarter wave-length or a shorter antenna with a loading coil.  This makes a difference for two different reasons.  I will handle the first reason immediately -- no full sized quarter-wave 11-meter (CB in US) antenna should be mounted with a magnetic mount -- although the &quot;wrongness&quot; of this type of mount suggests it is likely a shorter antenna with a loading coil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming your tool box is mounted just behind the cab of the truck then I believe that your antenna will be below (or mostly below) much of the cab which is a lot of conductive metal.  This is not good for having the best performance from your antenna.  In fact, you can experiment with this easily (especially for magnetic mount) is to try doing tests (signal strength etc.) with the antenna temporarily placed at different locations on your truck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the coil loaded CB antennas I have seen have a center mounted loading coil.  This means that the higher current part of the antenna which produces your strongest radiation, is between the base of the antenna (at the feed point) and the center loaded coil.  This part of the antenna should be clear from as much of the metal of the truck as possible (metal below the antenna is OK).&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-09-25T18:58:42.520" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6706" PostTypeId="2" ParentId="6701" CreationDate="2016-09-26T15:57:07.273" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Should I attach a ground wire to my plate so my antenna will be grounded as well?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I wouldn't bother. The &quot;grounding&quot; of the antenna at DC like a multimeter would measure is irrelevant. You care about the impedance at 27 MHz which is very different. At 27 MHz, a capacitance which has an infinite impedance at DC can be a very low impedance, and a wire of the right length which has very little impedance at DC can have a large impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The capacitive coupling between the steel plate and the toolbox provides a low impedance at 27 MHz. The same is true when the mag-mount antenna is stuck directly to a steel panel of the vehicle with an insulating layer of paint between.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-09-27T13:39:23.723" LastActivityDate="2016-09-27T13:39:23.723" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6707" PostTypeId="2" ParentId="6703" CreationDate="2016-09-27T06:44:00.657" Score="1" Body="&lt;p&gt;I would use classic microphone connectors used for ham radio righs like these &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OzZqy.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OzZqy.jpg&quot; alt=&quot;5 pin connector&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should not be problem ti make metal or plastic rings as adapters to fit the hole.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2016-09-27T06:44:00.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6708" PostTypeId="1" CreationDate="2016-09-27T17:56:30.850" Score="2" ViewCount="687" Body="&lt;p&gt;I have connected my HackRF to my computer that runs Ubuntu and it was working fine until now. It gives me an error:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;FATAL:Failed to open HackRF device(-5) HACKRF_ERROR_NOT_FOUND&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Has anyone had the same experience?&lt;/p&gt;&#xA;" OwnerUserId="7843" LastEditorUserId="76" LastEditDate="2016-10-29T19:08:05.573" LastActivityDate="2016-10-29T19:08:05.573" Title="HACKRF_ERROR_NOT_FOUND" Tags="&lt;software-defined-radio&gt;&lt;hackrf&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6709" PostTypeId="2" ParentId="6708" CreationDate="2016-09-27T22:57:51.047" Score="1" Body="&lt;p&gt;Your problem seems to involve USB permissions under Ubuntu, so perhaps your question would have been better-suited for &lt;a href=&quot;https://askubuntu.com/&quot;&gt;askubuntu.com&lt;/a&gt;.  But you probably didn't know that when you asked, so we shouldn't really hold that one against you ;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, your question seems to be the first one in the &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/FAQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;HackRF FAQ&lt;/a&gt;.  If the advice there were short I would repeat it here, but it isn't, so I won't.  Good luck, I hope their advice helps you solve your problem!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="-1" LastEditDate="2017-04-13T12:25:25.657" LastActivityDate="2016-09-27T22:57:51.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6710" PostTypeId="1" AcceptedAnswerId="6712" CreationDate="2016-09-28T07:36:21.973" Score="0" ViewCount="3709" Body="&lt;p&gt;I need to build two minimalistic antennas for RX/TX at ~433MHz. &#xA;I have insulated solid core copper wire, but I need to make it perfectly straight. I was thinking of using the type of sticks you set next to plants to support them while growing but perhaps there is a better, less ugly way. What do you suggest?&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-09-28T12:41:15.860" Title="DIY 433MHz antennas from copper wire" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6711" PostTypeId="2" ParentId="6708" CreationDate="2016-09-28T07:39:09.263" Score="0" Body="&lt;p&gt;Try using the HackRF as root to determine if it works. Also try adding yourself to the &lt;code&gt;dialer&lt;/code&gt; group in &lt;code&gt;/etc/group&lt;/code&gt; - that works for me with my SDR dongle. What's the &lt;code&gt;dmesg&lt;/code&gt; output when you plug it in?&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-09-28T07:39:09.263" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6712" PostTypeId="2" ParentId="6710" CreationDate="2016-09-28T10:09:09.000" Score="6" Body="&lt;p&gt;Based on the information you have given in the post and comments, the simplest way to construct a &quot;omni&quot; for 433 MHz, is by using an SO239-chassis-connector, and solder/screw the antenna elements directly onto the connector. Make sure the ground-plane elements are bended down, to ensure a close match to 50Ohm impendance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The single-strand/1mm wire will do nicely without supports.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/L73Gh.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/L73Gh.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dimensions can of each of the wire elements would be 300/433/4 (a quarter wavelength), each element would be the same length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Start with somewhat longer elements, and &quot;prune&quot; them until you have the lowest SWR for the intended frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is not what you are looking for, please update your &lt;strong&gt;post&lt;/strong&gt; with more information.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-09-28T10:09:09.000" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="6713" PostTypeId="2" ParentId="6710" CreationDate="2016-09-28T12:41:15.860" Score="2" Body="&lt;p&gt;To straighten single-conductor copper wire, clamp one end in a vice, grab the other end in a pair of lineman's pliers and turn the pliers so that the wire is wrapped around them a bit. Pull to tighten the wire, then hit the wire-end of the pliers with a hammer (going away from the vice). Easier to do than to describe.&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2016-09-28T12:41:15.860" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6714" PostTypeId="1" AcceptedAnswerId="6715" CreationDate="2016-09-29T19:24:34.287" Score="8" ViewCount="1217" Body="&lt;p&gt;What is the result of a contest station not submitting a log for the contest?  Are all the contacts nullified for the other stations that contacted him?  Is it bad form for a non-participating station to contact stations that are participating in a contest?&lt;/p&gt;&#xA;" OwnerUserId="4289" LastEditorUserId="76" LastEditDate="2016-09-29T19:30:50.893" LastActivityDate="2016-09-30T06:15:58.300" Title="What happens if a station did not submit a contest log?" Tags="&lt;contest&gt;&lt;logging&gt;&lt;etiquette&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6715" PostTypeId="2" ParentId="6714" CreationDate="2016-09-30T06:15:58.300" Score="11" Body="&lt;p&gt;In general, it is not a bad thing to work stations in a contest and not submit a log.  In the big popular contests that don't have difficult exchanges, such as the ARRL DX contest or the CQ WPX contest, the majority of participants are casual.  Casual operators are not trying to beat their buddies, or their scores from the year before; they are just there to hand out a few QSOs just for fun, and maybe pick up a new state, province, or DX entity.  The vast majority of casual entrants don't bother to submit their logs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the time comes to judge the contest, the scoring &quot;robot&quot; (computer program) must judge whether a given contact was completed accurately.  If both stations submitted their logs, and the call signs, frequencies, and times match, and the exchanges sent match the exchanges received, then the contact is considered good (assuming that suspicious behavior patterns that might indicate possible cheating are absent).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Things get more complicated for the scoring robot if only one station has logged the QSO.  The robot then looks to see if any other stations logged that station at the same frequency and time.  Often, the call sign has been miscopied; if W1ABC logged VE2XYZ, but VE2XYY submitted a log claiming a QSO at that time with W1ABC, then W1ABC will probably be judged to have made a mistake copying VE2XYY's call sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider the situation in which several stations log a particular call sign, for example K9EFG.  If eight stations reported working K9EFG, but K9EFG didn't submit a log, the most likely reason is that K9EFG worked several stations but didn't submit a log.  Almost all contest robots will give the eight stations the points for having worked K9EFG.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the big prestigious contests email reports to stations that submitted logs after the contest has been scored.  The reports give the station's final score, but also an explanation of points that were subtracted for mistakes, and often even a report of stations that miscopied the station's call sign or exchange.  These reports make excellent feedback, letting the operators know exactly what mistakes they made.  CQ Magazine call their report the &quot;UBN&quot; report, for Unique stations, Bad call signs, and Not-in-log reports.  Of those three situations, a bad call sign or a not-in-log will definitely cost points.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But then there is the interesting situation in which a station logs a particular station that no other station logged; a &quot;Unique&quot; in the CQ Magazine UBN report.  That could be caused by a casual contester making only one QSO, or it could be caused by the operator getting a call sign wrong.  Most contest robots will give the operator the benefit of the doubt for a unique call sign, but it does look somewhat suspicious, which is why it is flagged in the UBN report.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My personal contest etiquette recommendation for casual contesters is to try and work at least two or three stations, so that your call sign won't be unique.  But if you should make a single QSO and then be called away from the shack, don't worry about it; stations actively participating in the contest want your QSO, and are willing to accept the inevitable &quot;uniques&quot; in the UBN report to make QSOs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if you make just a few QSOs in a contest and you are using contest logging software, then I recommend that you submit a log, for two reasons: first, it helps the contest organizers score the contest more accurately, and second, for major contests you will receive the report giving excellent feedback on where improvement is needed.  Most contests give the option to submit a log as a &quot;check log&quot;, which is used to check the accuracy of other logs, but does not get scored for points.  So if you might submit a log but don't want to be embarrassed by being listed near the bottom of the results, then submit your log as a check log.  I don't think stations that submit check logs get feedback reports though.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-09-30T06:15:58.300" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6716" PostTypeId="1" AcceptedAnswerId="6718" CreationDate="2016-09-30T09:58:52.747" Score="1" ViewCount="1022" Body="&lt;p&gt;How does the demodulation done with HackRF? Is the mixed with IF and then the frequency spectrum is shifted to baseband frequency by sampling OR &#xA;the frequency of the mixer in the hardware can be change by the software to the baseband frequency first and then sampled?&lt;/p&gt;&#xA;" OwnerUserId="7843" LastEditorUserId="76" LastEditDate="2016-10-29T19:07:54.497" LastActivityDate="2016-10-29T19:07:54.497" Title="HackRF Hardware" Tags="&lt;software-defined-radio&gt;&lt;hackrf&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6717" PostTypeId="2" ParentId="6716" CreationDate="2016-09-30T12:30:31.270" Score="2" Body="&lt;p&gt;As this is SDR, the HackRF hardware presents the received signal as I/Q to the computer. The actual demodulation is done in software.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-09-30T12:30:31.270" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6718" PostTypeId="2" ParentId="6716" CreationDate="2016-09-30T13:27:58.247" Score="5" Body="&lt;p&gt;The RF architecture of the HackRF One is &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/Hardware-Components#block-diagrams&quot; rel=&quot;nofollow noreferrer&quot;&gt;diagrammed here&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/66mU1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/66mU1.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is a bit elliptical so I'll explain what I read from it (describing the receive-mode operation; transmit is just the reverse). There are &lt;em&gt;two&lt;/em&gt; integrated LO/mixer units:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;One is in the RFFC5072 chip. This is the one that provides the HackRF One's wide tuning range. It mixes the incoming signal to an IF that is within the MAX2837's range. (I don't know whether that's fixed or adjusted for any reason.)&lt;/li&gt;&#xA;&lt;li&gt;The MAX2837 chip then mixes that 2.x GHz IF down to baseband (as well as providing configurable gain and filtering).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The baseband IQ signal from the MAX2837 is then sent to the MAX5864 ADC for conversion to digital samples, which are then sent to the host computer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When transmitting, all of these stages operate in reverse; the MAX5864 works as a DAC instead of an ADC, and the same LOs and mixers are used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The HackRF One does not use &lt;a href=&quot;https://en.wikipedia.org/wiki/Undersampling&quot; rel=&quot;nofollow noreferrer&quot;&gt;bandpass sampling&lt;/a&gt;, as I think you might be asking.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;One of the characteristic features of a receiver using an analog baseband I/Q signal is the “DC offset” or “DC spike”, a spurious signal visible at exactly the center frequency of the received samples. You can see this in any waterfall plot:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1e1jh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1e1jh.png&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is my HackRF One tuned to the FM broadcast band with a mediocre antenna, displayed using my &lt;a href=&quot;https://github.com/kpreid/shinysdr/&quot; rel=&quot;nofollow noreferrer&quot;&gt;ShinySDR&lt;/a&gt; software. You can see the wideband FM signals across the spectrum, and a much narrower unmodulated peak at exactly the center frequency.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-09-30T14:57:33.920" LastActivityDate="2016-09-30T14:57:33.920" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="6719" PostTypeId="1" CreationDate="2016-10-01T08:50:24.733" Score="2" ViewCount="106" Body="&lt;p&gt;Most AM receivers use Envelope detection. Historically this was simple. PLL-based systems are slightly better at low carrier-to-noise levels. Would there be any SNR advantage if each sideband was detected separately?  Would the correlation of the LSB and the USB be useful because the noise in general is not correlated? Could this be better than a PLL at higher carrier-to-noise ratios? Would putting each detected sideband into say each ear of some headphones or Left and right stereo channels give good results by allowing the ear to do some processing?&lt;/p&gt;&#xA;" OwnerUserId="6095" LastEditorUserId="8832" LastEditDate="2017-03-23T10:13:13.547" LastActivityDate="2017-03-23T10:13:13.547" Title="MW AM reception improvements?" Tags="&lt;diy&gt;&lt;am&gt;&lt;dx&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6720" PostTypeId="2" ParentId="6719" CreationDate="2016-10-01T14:31:11.280" Score="5" Body="&lt;p&gt;That's a lot of questions!&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Would there be any SNR advantage if each sideband was detected seperately?&lt;/p&gt;&#xA;&lt;p&gt;Would the correlation of the LSB and the USB be usefull because the noise in general is not correlated?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Well, that's exactly what envelope detection does: It takes advantage of the fact that the correlated signal energy in the two sidebands doubles the detector output, while the uncorrelated noise energy only contributes 1.4×.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Could this be better than a PLL at higher carrier to noise ratios?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;No. Whether or not you use a PLL for synchronous detection is orthogonal to this issue. In general, the overall advantages of using synchronous detection would be far greater than what you're proposing. Besides, how would you &amp;quot;detect the sidebands separately&amp;quot; &lt;em&gt;without&lt;/em&gt; using synchronous detection, or something functionally equivalent to it?&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Would putting each detected sideband into say each ear of some headphones or Left and right stereo channels give good results by allowing the ear to do some processing?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;That is in fact how one AM stereo system works. The effect on a mono signal is that you perceive the signal to be &amp;quot;in the middle of your head&amp;quot;, while the noise is spread out from ear to ear.&lt;/p&gt;&#xA;" OwnerUserId="1459" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-10-01T14:31:11.280" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6722" PostTypeId="2" ParentId="2281" CreationDate="2016-10-02T20:27:41.973" Score="4" Body="&lt;p&gt;To answer my own question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;WebSDR seems to stream demodulated audio via using private (closed) API for control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A couple other possible solutions for streaming remote SDR data over the internet include:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;rtl_tcp : You can build your own remote SDR station with an RTL-SDR (or similar SDR) on a tiny server (Raspberry Pi 3, et.al.), and stream data over the network using the rtl_tcp protocol. See: &lt;a href=&quot;https://github.com/steve-m/librtlsdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/steve-m/librtlsdr&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;OpenWebRX: &lt;a href=&quot;http://sdr.hu/openwebrx&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://sdr.hu/openwebrx&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cloud-SDR: &lt;a href=&quot;http://www.cloud-sdr.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.cloud-sdr.com/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These all seem to use open protocols and/or open source software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.rtl-sdr.com/tag/rsp_tcp/&quot; rel=&quot;nofollow noreferrer&quot;&gt;rsp_tcp&lt;/a&gt; is a rtl-tcp workalike for SDRPlay RSP receivers/devices.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-05-04T06:04:19.823" LastActivityDate="2019-05-04T06:04:19.823" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="6723" PostTypeId="1" AcceptedAnswerId="6725" CreationDate="2016-10-02T21:13:57.443" Score="4" ViewCount="722" Body="&lt;p&gt;Reading this &lt;a href=&quot;http://www.ahars.com.au/wp-content/uploads/2014/05/The-Underestimated-Magnetic-Loop-HF-Antenna-version-1.1.pdf&quot; rel=&quot;nofollow&quot;&gt;interesting piece&lt;/a&gt; on magnetic loop antennas, the author explains that a magnetic loop has great efficiency even at small size, but the the price you pay is very narrow bandwidth. Why is this? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems counter-intuitive (and miraculous) to me that efficiency doesn't suffer, but bandwidth does when antenna size is much much smaller than wavelength. &lt;/p&gt;&#xA;" OwnerUserId="8284" LastActivityDate="2020-04-22T07:20:41.007" Title="Why does an &quot;electrically small&quot; antenna have narrow bandwidth?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;magnetic-loop&gt;&lt;small-loop&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6724" PostTypeId="2" ParentId="6723" CreationDate="2016-10-03T13:42:33.233" Score="0" Body="&lt;p&gt;These antennas rely heavily on the associated inductors or capacitors to attain a reasonable impedance match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This matching condition, much like an L-C resonance, has a high Q and therefore works over a small bandwidth without re-tuning.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2016-10-03T13:42:33.233" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6725" PostTypeId="2" ParentId="6723" CreationDate="2016-10-03T16:55:32.373" Score="12" Body="&lt;p&gt;Short answer: electrically small antennas have a relatively low radiation resistance. With less resistance, the resonance is less damped, meaning a higher &lt;a href=&quot;https://en.wikipedia.org/wiki/Q_factor&quot;&gt;Q factor&lt;/a&gt; and consequently less bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To expand on that a bit, consider a children's playground variety swing. It's essentially a pendulum, and depending on the length of the swing and the mass of the child it will swing at a particular frequency. By shifting one's weight at exactly this frequency, it's possible to get the swing going very high with very minimal (but well-timed) energy inputs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The swing works because the work of each pump adds more energy, while relatively little is lost to friction. Thus with the proper timing, the work from each pump adds to the work of the previous until the swing is very high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the energy lost to friction is low compared to the stored energy, we say the swing has a high Q. The swing will continue swinging for quite a while even if the rider stops pumping. And the timing is very important, so it has low bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now imagine a swing submersed in a very viscous goo. The work of each pump goes almost entirely into the friction, and very little is stored in the swing. If the rider stops pumping the swing stops almost immediately (low Q). And the timing of the pumps hardly matters since all the work is lost to friction (high bandwidth).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dummy load is analogous to this swing in goo: it stores no energy at all, and all the input energy is converted immediately to heat in the resistance. Thus a dummy load has &lt;em&gt;very low Q and very high bandwidth&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something like a resonant dipole is somewhere in the middle of these examples. Instead of alternating between kinetic and potential energy, it alternates between energy stored in a magnetic and electric field. However with each cycle some of this energy is lost to radiation, and this appears at the feedpoint as radiation resistance. This appears to a transmitter as an ordinary resistance just as the dummy load did, but this work is going into radiation, not heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This radiation resistance dampens the resonance, giving this example a &lt;em&gt;moderate Q, and a moderate bandwidth&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the dipole gets shorter it becomes less effective at radiating. Less energy is lost to radiation on each cycle. So if we want to radiate the same power, we must store more energy. A higher stored energy to energy lost ratio means a &lt;em&gt;higher Q, and a lower bandwidth&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-10-03T16:55:32.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6726" PostTypeId="1" CreationDate="2016-10-04T09:03:59.767" Score="3" ViewCount="202" Body="&lt;p&gt;Is there a way to get a professional propagation map for my VHF 50 watt repeater?&lt;/p&gt;&#xA;" OwnerUserId="5999" LastEditorUserId="4665" LastEditDate="2016-10-06T01:37:02.240" LastActivityDate="2016-10-06T01:37:02.240" Title="What is the best way to get propagation VHF map for FM repeater?" Tags="&lt;propagation&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6727" PostTypeId="2" ParentId="6726" CreationDate="2016-10-04T11:17:11.877" Score="2" Body="&lt;p&gt;Not sure about &lt;em&gt;&quot;propagation&quot;&lt;/em&gt; but you can check an estimate of &lt;em&gt;&quot;coverage&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without promoting anything, and with the normal &lt;em&gt;&quot;Your Milage May Vary&quot;&lt;/em&gt; and &lt;em&gt;&quot;There might be others&quot;&lt;/em&gt; disclaimers, the site I use for checking coverage is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.cplus.org/rmw/rmonline.html&quot; rel=&quot;nofollow&quot;&gt;Radio Mobile online&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need to do the following:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;setup a user account (free)&lt;/li&gt;&#xA;&lt;li&gt;setup a base/home location&lt;/li&gt;&#xA;&lt;li&gt;then setup a &quot;coverage&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The free edition of this website will only allow frequency inputs in the HAM/Amateur radio bands.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-10-04T11:17:11.877" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6728" PostTypeId="1" CreationDate="2016-10-04T14:44:38.853" Score="0" ViewCount="78" Body="&lt;p&gt;In some notes on transmitters I have found the statement that &quot;inductive coupling between transmitter amplifier stages reduces the generation of harmonics&quot;, with no further explanation. Can anyone please explain why this is so, or convincingly refute it if it isn't?&lt;/p&gt;&#xA;" OwnerUserId="297" LastActivityDate="2016-10-05T00:08:03.693" Title="How does inductive coupling between transmitter amplifier stages reduce harmonics" Tags="&lt;rfi&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6729" PostTypeId="2" ParentId="6728" CreationDate="2016-10-05T00:08:03.693" Score="3" Body="&lt;p&gt;Absent any other context, I have a couple guesses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A ferrite core in a transformer has losses that increase with frequency, so consequently the higher frequency energy in the harmonics is dissipated as heat in the transformer. Provided of course that the core is not saturated to the point where its non-linear properties introduce more harmonics than are removed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, any real inductor, of any core material, or a transformer winding, has a parasitic capacitance due to the proximity of the windings. The inductance and this capacitance define a self-resonant frequency for the inductor, and above this frequency the inductor presents a capacitive reactance instead of an inductive one. If the transformer is designed such that the harmonics are above the self-resonant frequency, those harmonics will then see a shunt capacitance to ground, effectively low-pass filtering them.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-10-05T00:08:03.693" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6731" PostTypeId="1" CreationDate="2016-10-08T22:12:46.053" Score="0" ViewCount="357" Body="&lt;p&gt;I'm using SDR# and with virtual audio cable sound&#xA;is piped to Wavecom W-CODE. W-code recognizes a frequency on 4&#xA;and 24 MHz as Pactor-II with 100% confidence, but he can't decode in&#xA;terminal text window nothing &quot;0&quot;. This is something that I can't&#xA;understand, because I don't have HAM experience.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They say for Pactor&#xA;that is very adaptive signal used mainly in extreme situation like sea&#xA;(almost never failed). I'm living far away from the sea, and using&#xA;default antenna which came with rtl-sdr dongle, with software gain &quot;0&quot;&#xA;can  catch  signal -30 dB on 24 MHz (don't matter if is day or night).&#xA;To visualize more, with gain &quot;0&quot; and with frequency &lt;a href=&quot;http://www.freqmgrsuite.com&quot; rel=&quot;nofollow&quot;&gt;scanner&lt;/a&gt; in 0-30 MHz band can&#xA;catch just 5 signal during the day. That's mean that source is very&#xA;close or Pactor is very good adaptive signal...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second question would&#xA;be regarding w-code. How come that he can recognize signal with &quot;100%&#xA;confidence&quot;, but can't demodulate the wav file? I also tried with sorcerer and&#xA;MixW, with no luck. Is W-CODE right about Pactor or not?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://1drv.ms/i/s!AgTtpXlIRe8lhC6T94waIWaIGvDW&quot; rel=&quot;nofollow&quot;&gt;Screenshot&lt;/a&gt; that wcode recognize signal as Pactor-II&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I put other files beacuse quota limit under comments!!!&lt;/p&gt;&#xA;" OwnerUserId="8458" LastEditorUserId="8458" LastEditDate="2016-10-12T20:33:45.427" LastActivityDate="2017-02-18T17:07:21.583" Title="Why is this signal recognized as PACTOR II but not decoded?" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;" AnswerCount="2" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="6732" PostTypeId="1" CreationDate="2016-10-09T04:53:45.727" Score="3" ViewCount="885" Body="&lt;p&gt;The service schematic of the Vertex Standard VX-2200 VHF radio shows that the &lt;code&gt;ACC5&lt;/code&gt; and &lt;code&gt;ACC6&lt;/code&gt; pins of the back DB 15-pin connector are connected to pins &lt;code&gt;EXT_TXD&lt;/code&gt; and &lt;code&gt;EXT_RXD&lt;/code&gt; pins on the main processor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can those pins (or some other pins in the same connector) be used to program the radio or do I &lt;em&gt;have to&lt;/em&gt; use the RJ45 connector in the front?&lt;/p&gt;&#xA;" OwnerUserId="8018" LastEditorUserId="76" LastEditDate="2016-10-29T19:00:23.987" LastActivityDate="2017-02-06T21:32:11.040" Title="Is it possible to program the Vertex VX-2200 using the back DB 15-pin connector?" Tags="&lt;equipment-operation&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6733" PostTypeId="1" CreationDate="2016-10-09T13:46:56.387" Score="2" ViewCount="127" Body="&lt;p&gt;I have seen a number of programming cable schematics on the internet, but I couldn't understand very much how they worked. From what I picked from all schematics, it appears the protocol uses the &lt;code&gt;CL_DATA&lt;/code&gt; pin for both RX and TX, and the &lt;code&gt;CL_SW&lt;/code&gt; pin to signal stuff.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I couldn't really understand the protocol that the radio uses. Can someone please explain? What are both the radio and the computer interfaces sending and expecting in each pin?&lt;/p&gt;&#xA;" OwnerUserId="8018" LastEditorUserId="76" LastEditDate="2016-10-29T18:58:16.283" LastActivityDate="2016-10-29T18:58:16.283" Title="What protocol does the Vertex VX-2200/2100 use for programming?" Tags="&lt;electronics&gt;&lt;equipment-operation&gt;&lt;radio-programming&gt;" AnswerCount="0" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6734" PostTypeId="1" CreationDate="2016-10-10T00:00:32.827" Score="5" ViewCount="534" Body="&lt;p&gt;So, I'm relatively new to all this; and I've gotten an ICOM IC-7100 on sale, which looks like an &lt;em&gt;excellent&lt;/em&gt; transceiver … unfortunately, this very specific line shows up in the manual:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The transceiver may not receive well on some frequencies when installed in a hybrid vehicle, or any type of electric vehicle (fuel cell vehicle). This is because vehicle’s electric components such as the inverter system generate a lot of electric noise.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To boot, reading other questions on this site, I came across &lt;a href=&quot;https://ham.stackexchange.com/a/320/8465&quot;&gt;this excellent news&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;… In the worst case, your cigarette lighter may be wired for &quot;chassis ground return&quot;, where [the] current is not being returned through a copper ground wire, but through the car's steel chassis. This is OK for stuff like an AM/FM radio or the cabin lighting, but that same resistance equates to a higher voltage drop with your [radio], which can distort your output signal or even cause devices to sense an &quot;undervolt&quot; condition and shut down.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Taking a look under the hood, so to speak, this is &lt;em&gt;precisely&lt;/em&gt; the situation in my car … except not for a cigarette-lighter port, rather literally for the entire car — of the 50A primary-12V “battery terminals” you're supposed to jump her with, the negative is simply a post on the chassis:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Vj2NO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Vj2NOm.jpg&quot; alt=&quot;positive terminal and instructions&quot;&gt;&lt;/a&gt; &lt;a href=&quot;https://i.stack.imgur.com/PAJtu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PAJtum.jpg&quot; alt=&quot;negative terminal&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, how should I best wire up my transceiver? (I've tried to google up some sort of ‘line noise filter’ for DC power, but 1. they all seem like extremely sketchy products, 2. most of them have lots of ‘this did nothing for me’ reviews, and 3. most of them are rated for small amperages.)&lt;/p&gt;&#xA;" OwnerUserId="8465" LastEditorUserId="76" LastEditDate="2017-07-09T17:32:55.090" LastActivityDate="2017-07-09T17:32:55.090" Title="How can I counter DC-DC inverter noise / ground noise in an electric-vehicle mobile setup?" Tags="&lt;mobile&gt;&lt;rfi&gt;&lt;grounding&gt;&lt;dc-power&gt;&lt;battery&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6735" PostTypeId="2" ParentId="6734" CreationDate="2016-10-10T01:01:48.193" Score="2" Body="&lt;p&gt;Allow me to refer you to Alan Applegate K0BG's excellent &lt;a href=&quot;http://www.k0bg.com/wiring.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;page about mobile radio wiring and grounding&lt;/a&gt;.  That page recommends that you power the radio with a fused negative lead connected to the chassis, and a fused positive lead connected to the main battery.  Here's a picture:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3aT8E.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3aT8E.jpg&quot; alt=&quot;how to wire a mobile radio&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alan's site is chock-full of excellent advice about seemingly every aspect of mobile operating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding your specific question, I'd of course recommend that you don't use the cigarette lighter to power your radio, but you knew that already.  There's nothing stopping you from using the same chassis ground point as the ELD (electronic load detector) in the picture for your fused negative lead.  That way you won't have the steel chassis in your current path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alan also has a &lt;a href=&quot;http://www.k0bg.com/hybrid.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;page on mobile radios in hybrid cars&lt;/a&gt; that specifically confronts the noise in electric cars issue.  (There's no difference between a hybrid and an all-electric car when the hybrid is running on battery power alone, of course.)  That page says that electric and hybrid cars generate &quot;copious&quot; amounts of RFI.  He then goes on to say, &quot;The next question is, can it be tamed? Yes, but it is a herculean task requiring countless hours, and hundreds of dollars spent reducing the RFI to a level compatible with HF operation.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do decide to take on the Herculean task, know that the noise isn't just coming in through the power supply; the electronics generating the three-phase power for the motor generate RFI directly.  So filtering the radio's DC power would only solve one aspect of the problem.  It might be easier to do as Alan suggests and just pull over and stop the car when you want to operate HF.  Good luck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be safe, and enjoy your IC-7100!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-10-11T06:06:27.190" LastActivityDate="2016-10-11T06:06:27.190" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6736" PostTypeId="1" CreationDate="2016-10-10T17:44:31.837" Score="5" ViewCount="148" Body="&lt;p&gt;According to &lt;a href=&quot;https://ham.stackexchange.com/questions/357/is-morse-code-allowed-on-fm/444#444&quot;&gt;this question&lt;/a&gt; MCW (modulated continuous wave) is allowed on large portions of the VHF bands in the U.S.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is using MCW suitable for passing small amounts of digital data between 2 PCs or mobile phones using just air-gapped audio (speaker and mic, no wired connections or acoustic couplers) with generic handheld VHF HT radios?  Are there other standard modes more suitable for this purpose?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If using MCW, what encoding methods (arbitrary digital data to hex characters in Morse Code?) might be legal in the U.S.?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-10-11T13:24:46.053" Title="Air gapped digital communications mode on VHF?" Tags="&lt;united-states&gt;&lt;digital-modes&gt;&lt;cw&gt;&lt;modes&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6737" PostTypeId="2" ParentId="6736" CreationDate="2016-10-11T03:11:14.520" Score="5" Body="&lt;p&gt;Suitable, I suppose, though not especially efficient in terms of spectrum or power. Morse code was never really designed for machine demodulation, so unless you also need the ability to decode by ear, Morse code isn't a great choice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 1200 baud FSK modes used for packet and APRS are something to consider. Normal use involves hooking a PC to the radio's audio input or output via a cable. If you add a speaker and microphone of good fidelity in between it continues to work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the fidelity isn't so great, or it's noisy, you can slow down the baud rate. &quot;Packet&quot; goes down to 300 baud, but if you want FSK slower than that, look at RTTY.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mobile phones in particular present a challenge because the compression they employ is optimized for human voice, and introduces a ton of distortion otherwise. But a sufficiently slow FSK modulation should work fine, and at least as good as morse code.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-10-11T03:11:14.520" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6738" PostTypeId="1" CreationDate="2016-10-11T04:42:45.047" Score="4" ViewCount="97" Body="&lt;p&gt;I found old plans for a quagi that uses copper for the Reflector and Driven Element and any 1/8&quot; metal available for the directors. The general recommendation for antennas is: no steel for the DE. Is it OK to use for the directors, and OK to 'mix' the metals in an antenna? I'm very new to building and ham in general. I might be able to find something besides steel but so far everything non-steel around here is larger than 1/8&quot;.&lt;/p&gt;&#xA;" OwnerUserId="8477" LastEditorUserId="76" LastEditDate="2016-10-11T15:23:03.800" LastActivityDate="2016-10-11T15:23:03.800" Title="Steel Directors with Copper DE" Tags="&lt;antenna-construction&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6739" PostTypeId="2" ParentId="6738" CreationDate="2016-10-11T06:31:07.777" Score="6" Body="&lt;p&gt;It's probably OK to use a different metal for the directors than the driven element, as long as you don't have dissimilar metals touching that would create a galvanic corrosion problem.  But steel is a lousy conductor that would make your antenna less efficient.  If you wanted to know exactly how much less efficient, then you could model the antenna in EZNEC or 4nec2 to find out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're just making an antenna to better reach the local repeater, and you're not concerned with every decibel, then go ahead and try it!  If you're intention is to use the antenna for moonbounce work, in which case you would be concerned with each and every dB, then you're probably better off finding copper, brass, or aluminum rods to use for the directors rather than steel.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My guess would be that the 1/8&quot; diameter recommendation reflects what the antenna designers had on hand; I wouldn't think that a larger diameter would change the specifications of the antenna much.  I don't have much experience building VHF/UHF yagis though.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-10-11T06:31:07.777" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6740" PostTypeId="2" ParentId="6736" CreationDate="2016-10-11T13:18:30.167" Score="3" Body="&lt;p&gt;To add to the answer already given:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would require some experimentation, but you could run an audio modem on each of the computers (one sender, one receiver) then TX/RX the audio from A to B.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example of such audio modem is &lt;a href=&quot;https://github.com/romanz/amodem&quot; rel=&quot;nofollow&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First test is to take the two computes side by side, line up speaker of sender to mic of receiver, and test such package over a simple air-gap without any TX/RX, the following from the documentation:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Calibration&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Connect the audio cable between the sender and the receiver, and run&#xA;  the following scripts:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;On the sender's side:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;~/sender $ export BITRATE=48  # explicitly select high MODEM bit rate (assuming good SNR). &#xA;~/sender $ amodem send --calibrate&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;On thereceiver's side:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;~/receiver $ export BITRATE=48  # explicitly select high MODEM bitrate (assuming good SNR). &#xA;~/receiver $ amodem recv --calibrate&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If BITRATE is not set, the MODEM will use 1 kbps settings (single&#xA;  frequency with BPSK modulation).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Change the sender computer's output audio level, until all frequencies&#xA;  are received well:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;3000 Hz: good signal  &#xA;4000 Hz: good signal  &#xA;5000 Hz: good signal &#xA;6000 Hz: good signal  &#xA;7000 Hz: good signal  &#xA;8000 Hz: good signal  &#xA;9000 Hz: good signal &#xA;10000 Hz: good signal&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Various test modes of this mentioned software exists, to test for SNR, example:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;2015-02-06 18:12:48,198 DEBUG      Prefix OK&#xA;2015-02-06 18:12:48,866 DEBUG        3.0 kHz: SNR = 34.82 dB&#xA;2015-02-06 18:12:48,866 DEBUG        4.0 kHz: SNR = 36.39 dB&#xA;2015-02-06 18:12:48,867 DEBUG        5.0 kHz: SNR = 37.88 dB&#xA;2015-02-06 18:12:48,867 DEBUG        6.0 kHz: SNR = 38.58 dB&#xA;2015-02-06 18:12:48,867 DEBUG        7.0 kHz: SNR = 38.86 dB&#xA;2015-02-06 18:12:48,867 DEBUG        8.0 kHz: SNR = 38.63 dB&#xA;2015-02-06 18:12:48,867 DEBUG        9.0 kHz: SNR = 38.07 dB&#xA;2015-02-06 18:12:48,868 DEBUG       10.0 kHz: SNR = 37.22 dB&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;You can test without TX/RX, then add this in once the you are sucsesfully transferring info over the air-gap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTH, Edwin.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-10-11T13:24:46.053" LastActivityDate="2016-10-11T13:24:46.053" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6741" PostTypeId="1" CreationDate="2016-10-12T15:24:50.550" Score="5" ViewCount="572" Body="&lt;p&gt;I bought a MFJ 1786 Magnetic Loop Antenna, which is made for 10 thru 30 MHz. It is not meant for use on 40 meters. The antenna has its own built in tuner. I have a Yaesu FT-890AT with built in antenna tuner. So my question is: could I tune the loop to a harmonic frequency of the frequency that I wish to work on 40 meters and then tune the Yaesu for the best SWR? Will it work even at somewhat less than optimal? This would allow me to work CW at night.&lt;/p&gt;&#xA;" OwnerUserId="8487" LastEditorUserId="76" LastEditDate="2016-10-12T18:18:02.133" LastActivityDate="2016-10-13T16:03:01.263" Title="Using a loop antenna on a harmonic of the intended antenna frequency" Tags="&lt;antenna-theory&gt;&lt;magnetic-loop&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6742" PostTypeId="1" CreationDate="2016-10-12T17:56:14.670" Score="9" ViewCount="3339" Body="&lt;p&gt;I want to eventually use a CW paddle and built in keyer in my Yaesu FT-890. What are the merits of each style. Single or Dual Paddle. Does it make any difference if I start with say a dual paddle then later use a single paddle? Any disadvantages of switching from the one that I may have learned on?&lt;/p&gt;&#xA;" OwnerUserId="8487" LastEditorUserId="76" LastEditDate="2016-10-12T18:23:09.750" LastActivityDate="2019-06-02T00:22:01.013" Title="Single or Dual Paddle Key?" Tags="&lt;cw&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6743" PostTypeId="2" ParentId="6742" CreationDate="2016-10-12T19:01:18.500" Score="4" Body="&lt;p&gt;Usually (but not always) a dual-paddle key is iambic.  An iambic paddle is one where you can key in characters by using: dashes in one direction of paddle, dots in the other direction, and alternating dots and dashes by squeezing the two paddles.  The alternating dashes and dots begin with the dash if squeezed first on the dash side of the paddle and dots if opposite to that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people will use an iambic paddle and never make use of the squeeze technique of the paddle.  I started this way with my paddle but slowly I taught myself various characters using the squeeze method.  The first character I learned was Q and then I learned Y and then C and other similar characters like K.  In my experience, the longer strings (length four) are easier to learn at first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use a Bengali Magnetic Classic Paddle and it is shown in my avatar image.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-10-12T19:01:18.500" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6744" PostTypeId="2" ParentId="6741" CreationDate="2016-10-12T19:04:19.773" Score="3" Body="&lt;p&gt;Dipoles are resonant on their fundamental frequency, and all odd harmonics. So a dipole resonant at 10 MHz is also resonant at 30, 50, 70 MHz and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the fundamental frequency it takes one cycle for a wave to travel the full length of the antenna and back. At odd harmonics it takes 3, 5, 7, and so on cycles. Only the odd harmonics are considered because on odd numbers the feedpoint in the middle falls on a low impedance point of the antenna. On even numbers the feedpoint is a high impedance and thus presents an extremely poor match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This 10 MHz dipole is not resonant at any frequencies below 10 MHz. The antenna is simply too short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Self-resonant, or full-wave loops are similar, being effectively folded dipoles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the MFJ 1786 is a different beast. It consists of a very small (relative to wavelength) loop, which presents an inductive impedance. A variable capacitor cancels that inductance, and the loop and the capacitor together are resonant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the loop becomes smaller relative to wavelength (in other words, as you move down in frequency), the impedance of the loop becomes more inductive, and thus requires more capacitance to tune it. The higher reactances involved also mean a higher Q, and a higher peak voltage across the capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a practical limit to how small the loop can be. While it's easy enough to make a larger capacitance, it's more difficult to make a capacitor with a sufficiently large capacitance while still withstanding the peak voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna is designed to work down to 10 MHz it will not work at 7 MHz. The variable capacitor in it is not large enough, and if it were, it would not be able to handle the voltage without arcing. So at 7 MHz, the antenna will not present a good match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's possible you can compensate for this with an antenna tuner, but it's unlikely. The match is probably bad enough to be outside the tuner's capabilities.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-10-13T16:03:01.263" LastActivityDate="2016-10-13T16:03:01.263" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6745" PostTypeId="2" ParentId="6742" CreationDate="2016-10-12T19:50:04.107" Score="8" Body="&lt;p&gt;Single-lever paddles have a single lever that generates dots when pressed to one side, and dashes when pressed to the other.  Dual-lever paddles have two paddles, one of which generates dots and the other generates dashes; when connected to a keyer in iambic mode with both levers pressed, a dual-lever paddle generates a stream of alternating dots and dashes.  There are some paddles that look like they have two levers, but the two levers are securely fastened together, so mechanically they are actually single-lever paddles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The single-lever vs iambic debate seems to be perpetually hot.  (There is also the iambic-A vs iambic-B vs ultimatic debate.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The styles of keying a single-lever paddle vs true iambic keying are very different.  Single-lever paddle users generally have an energetic style, because the paddle has to move fast and change directions quickly.  Iambic users generally have a gentler style.  Note that many dual-lever paddle users don't bother to use iambic mode, and are perfectly happy sending as though the paddle had a single lever.  Switching from a single-lever paddle to true iambic mode, or vice-versa, is difficult but can be done.  Most people stick with the method they first learned all their lives.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many articles on the internet that attempt to prove that single-lever is better than iambic for all people in all circumstances, or vice-versa.  The truth is, most people use the keying method that their elmers used.  In my opinion ham radio is a hobby, no one keying method is best for everyone, and people should use the keying method they enjoy most.  For people new to Morse code who don't have elmers, my advice would be to watch videos of people using both methods, try both for yourself, and pick which one feels best. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Single-lever paddle pros:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Almost all competitors in high-speed Morse code competitions (faster than 40 wpm) use single-lever paddles&lt;/li&gt;&#xA;&lt;li&gt;Former &quot;bug&quot; users have an easier time with single-lever paddles&lt;/li&gt;&#xA;&lt;li&gt;Single-lever paddle users can also use a dual-lever paddle when necessary, but may make keying errors until they become accustomed&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Single-lever paddle cons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;More motion, more &quot;work&quot; is required than a dual-lever paddle in iambic mode&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Iambic mode pros:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Less motion is required than a single-lever paddle; &quot;feels more comfortable&quot; or &quot;feels like less work&quot; to people used to iambic&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Iambic paddle cons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Not as accurate at very high speed (faster than 40 wpm, say)&lt;/li&gt;&#xA;&lt;li&gt;More accurate timing is required; a modest amount of regular practice is required to stay proficient&lt;/li&gt;&#xA;&lt;li&gt;People used to iambic have a very difficult time when confronted with a single-lever paddle&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-10-12T19:50:04.107" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6746" PostTypeId="2" ParentId="6742" CreationDate="2016-10-12T23:00:05.240" Score="0" Body="&lt;p&gt;I am sorry, while good answers are given; the posted question screams for another answer...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Straight key&lt;/strong&gt; &lt;em&gt;the one key to rule them all&lt;/em&gt; &lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-10-12T23:00:05.240" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6747" PostTypeId="2" ParentId="6723" CreationDate="2016-10-13T12:27:06.420" Score="0" Body="&lt;p&gt;There is an antenna theorem that might be called the &quot;no free lunch&quot; theorem, and can be summarized as &quot;Antennas: broadband, efficient, and compact: choose any two.&quot;  I may be able to turn up a citation for this theorem if someone else doesn't first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An efficient, broadband antenna is large, e.g. an LPDA or a discone; a broadband, compact antenna will be inefficient, e.g. a 50 Ohm resistor with small wire stubs on the resistor wires; finally, a compact, efficient antenna will be narrowband, e.g. a magnetic loop antenna with thick conductors, or, better still, a small, superconducting magnetic loop.  &lt;/p&gt;&#xA;" OwnerUserId="8495" LastActivityDate="2016-10-13T12:27:06.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6749" PostTypeId="2" ParentId="6742" CreationDate="2016-10-16T01:18:47.627" Score="2" Body="&lt;p&gt;I suggest a dual-paddle iambic keyer cos it's more versatile. &#xA;-- from a veteran CW operator from India, VU2TS, @Ganesh Subramaniam, India&lt;/p&gt;&#xA;" OwnerUserId="8504" LastActivityDate="2016-10-16T01:18:47.627" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6750" PostTypeId="1" AcceptedAnswerId="6751" CreationDate="2016-10-16T18:23:24.677" Score="8" ViewCount="1225" Body="&lt;p&gt;My cubesat team is working on our design for rolled whip antennas to deploy in a UHF turnstile configuration based on this design:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/s0tNa.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/s0tNa.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I would like advice on is the material for the antennas themselves. Spring steel has ideal mechanical properties, but isn't an optimal antenna metal. The material of the one shown is apparently Nitinol shape memory alloy, that will unroll itself when heated. What other metals would you suggest looking into further?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The system characteristics are&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;435 MHz&lt;/li&gt;&#xA;&lt;li&gt;Under 50kHz BW&lt;/li&gt;&#xA;&lt;li&gt;4W max power&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8509" LastEditorUserId="8509" LastEditDate="2016-10-18T05:15:10.253" LastActivityDate="2016-10-18T05:15:10.253" Title="cubesat turnstile antenna material selection" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;satellites&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6751" PostTypeId="2" ParentId="6750" CreationDate="2016-10-17T09:36:05.107" Score="5" Body="&lt;p&gt;As usual, for antennas, the better your material conducts, the higher your antenna efficiency. Hence, go for copper. It has an excellent conductivity per volume (which might or might not be critical in your application), and there's not many metals that will beat its conductivity at all. Steel really isn't good for that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're using suitable frequencies, steel wire with a copper coating might work for a dipole. The frequency will define your skin depth and the losses that a non-perfectly conducting antenna will incur. Definitely sounds like you'd have to just copper-coat some spring steel and try.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another thing: I don't know how stiff the deployed antenna will be, but you &lt;em&gt;are&lt;/em&gt; in the earth's magnetic field, with long ferromagnetic rods; that will excert a torque on your satellite... I can't calculate how much, though, since I know nothing about your antenna sizes, your orbit, your height or anything about the satellite. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, when asking about &quot;what's the perfect material for my antenna&quot;, you should include a lot of factors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;frequency (which I find kind of obvious)&lt;/li&gt;&#xA;&lt;li&gt;bandwidth&lt;/li&gt;&#xA;&lt;li&gt;acceptable loss&lt;/li&gt;&#xA;&lt;li&gt;power&lt;/li&gt;&#xA;&lt;li&gt;mechanical forces&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-10-17T09:36:05.107" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6752" PostTypeId="2" ParentId="6750" CreationDate="2016-10-17T12:16:50.143" Score="3" Body="&lt;p&gt;I think the mechanical properties for proper deployment are much more important than the electrical properties.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The picture appears to show elements that are flat tapes rather than round wires, which is probably a good idea. I'm thinking that if the tape can be given a slightly U-shaped cross-section (like a steel measuring tape), it will be better able to fully straighten itself after deployment, and may allow you to use thinner (lighter) steel stock.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And as Marcus says, plating the steel with copper and/or silver will improve its electrical characteristics without compromising its mechanical characteristics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm trying to figure out the deployment mechanism, but the picture is a bit fuzzy. There are little plastic doors holding the coiled elements in place, with spring-loaded threads holding the doors closed. Are those pairs of SMD resistors designed to heat up and cut the thread for deployment?&lt;/p&gt;&#xA;" OwnerUserId="1459" LastActivityDate="2016-10-17T12:16:50.143" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="6753" PostTypeId="1" AcceptedAnswerId="6755" CreationDate="2016-10-17T15:31:20.643" Score="3" ViewCount="1290" Body="&lt;p&gt;I want to play a bit more with programming side of digital modes. However, a quick Google search turned up lots of software and some general explanations but no open-source library implementing such a code. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I would find a library that encodes and decodes messages from/to plain text to either text output or sound most useful. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was looking particularly at RTTY, FSK and PSK31 as they seem to be the simpler modes around. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone have any experience or useful pointer in this area? &lt;/p&gt;&#xA;" OwnerUserId="1792" LastActivityDate="2019-09-16T00:00:45.047" Title="Open Source Library for Digital Mode" Tags="&lt;digital-modes&gt;&lt;software&gt;&lt;rtty&gt;" AnswerCount="3" CommentCount="7" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6755" PostTypeId="2" ParentId="6753" CreationDate="2016-10-17T17:59:06.987" Score="5" Body="&lt;p&gt;What you describe is Software Defined Radio! Hurray!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, everyone having read my answers knows: I'm a GNU Radio fanboy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GNU Radio has to be understood as the Free&amp;amp;Open-Source LEGO of Software-Defined Radio:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It comes with a huge library of signal processing blocks, which one can combine to build complex applications. Itself, it's not a library to be used to decode any particular standards, but you can download modules that combine GNU Radio blocks to do that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can write your own blocks in C++ or Python, and to build flow graphs out of blocks, you'd typically use Python or a graphical design tool called the GNU Radio companion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FSK, for example, can be astonishingly easy to decode; if you neglect the need for synchronization, a complete FSK decoder might look like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FgCMp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FgCMp.png&quot; alt=&quot;very basic&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which does nothing but convert an input signal stream to a stream of estimates of the current frequency. You'd of course would want to have things like filtering, sanitation, conversion to bits, and packetization, but again, there's already modules that do that for you; see the list at&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://wiki.gnuradio.org/index.php/HamRadio&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wiki.gnuradio.org/index.php/HamRadio&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They've got RTTY, PSK31, and a lot more (FSK is really just a general modulation scheme – there's a lot of modes that use it!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I feel I should mention is that you can, for example, use gr-dtv, the digital TV transmitter library within GNU Radio, to transmit extremely low-bandwidth TV – think of the digital evolution of SSTV, by using gr-dtv with appropriate MPEG transport streams that contain low-rate video and e.g. Codec2 audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to take the chance to highlight a few GNU Radio projects that are of interest in this context, but aren't specifically related to amateur digital modes:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;GQRX is probably the most famous GNU Radio standalone application. It's a spectrum visualizer, and audio demodulator. I don't know from the top of my head whether it does digital modes (it probably doesn't), but it's extremely useful when trying to find a signal in a wide bandwidth receive signal&lt;/li&gt;&#xA;&lt;li&gt;gr-inspector is awesome, in that it allows to estimate signal parameters out of life signals automagically&lt;/li&gt;&#xA;&lt;li&gt;gr-noaa is interesting if you already happen to have a dish and a feed capable of receiving NOAA satellite imagery, or a good helical antenna&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="218" LastEditDate="2019-09-16T00:00:45.047" LastActivityDate="2019-09-16T00:00:45.047" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="6756" PostTypeId="1" AcceptedAnswerId="6757" CreationDate="2016-10-17T19:40:54.810" Score="2" ViewCount="882" Body="&lt;p&gt;I saw some apartment in my county in a very good location (quite close to the beach), however, the rent is very cheap. The apartment is the highest on that building, on top of this building there is a cellular antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is there any danger in living 10 meters from such antenna?&lt;/li&gt;&#xA;&lt;li&gt;Is there any way to measure the transmit power (using some application or device)?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="5673" LastEditorUserId="76" LastEditDate="2016-10-17T20:18:10.957" LastActivityDate="2016-10-18T14:34:40.253" Title="Is it safe to live close to cellular antenna?" Tags="&lt;antenna&gt;&lt;rf-power&gt;&lt;safety&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6757" PostTypeId="2" ParentId="6756" CreationDate="2016-10-17T19:58:13.447" Score="4" Body="&lt;p&gt;Cellular networks are heavily regulated all over the world. Part of these regulations is that there's no amount of power radiated in any inhabitable direction that would pose a risk to the health of any human being.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, there are ways to measure the transmit power, but you'd need to measure that in the antenna cable (and there's no way they'd let you do that). You can measure the field strength at the point where you stand, and that's probably more useful for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, two things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;It's already guaranteed by the fact that the antenna is where it is that it's aligned and powered in a way that makes sure no harm will be done, and someone with a very expensive measurement device measured that after setting up the antenna, anyway.&lt;/li&gt;&#xA;&lt;li&gt;Such measurements require very expensive equipment, a lot of know-how and the chance to measure all relevant usage scenarios: A base station with only a few handsets that are very close will only transmit a tiny fraction of the power it would transmit if it had hundreds of handsets very far away. The power and the direction of base stations are adaptable, and you have no influence whatsoever on that.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So, for me, as a studied electrical engineer: I wouldn't worry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I answered another question on electronics.SE a couple hours back, and there, someone had dug up a magic, passive &quot;ring&quot; of some simple diodes that the seller claims would be able to detect GSM signals – which is total nonsense, as a single cell phone  would under almost no circumstances transmit enough power to light up an LED – that'd be illegal, and also, stupid, because the battery would be empty within minutes. Don't believe people that try to sell you fear about radio waves. Yes, you can cook meals and kill animals with microwave radiation, but for all we know and can scientifically prove (and we've been doing the GSM &quot;experiment&quot; on about 3 to 6 Billion people for about 25 years now) it's not harmful. If you need to worry about something invisible, worry about structural damages to your building. You are very much more likely to die in a building collapse than of cell tower microwave irradiation. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-10-17T19:58:13.447" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6758" PostTypeId="2" ParentId="221" CreationDate="2016-10-17T21:35:20.567" Score="1" Body="&lt;p&gt;Here's the docs on it. &lt;a href=&quot;http://www.qrz.ru/vhf/qth_h.pdf&quot; rel=&quot;nofollow&quot;&gt;http://www.qrz.ru/vhf/qth_h.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And of course you were given this one. &lt;a href=&quot;https://en.wikipedia.org/wiki/Maidenhead_Locator_System&quot; rel=&quot;nofollow&quot;&gt;https://en.wikipedia.org/wiki/Maidenhead_Locator_System&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take a look at&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://aprs.fi/&quot; rel=&quot;nofollow&quot;&gt;http://aprs.fi/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://aprs.fi/page/api&quot; rel=&quot;nofollow&quot;&gt;http://aprs.fi/page/api&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8518" LastActivityDate="2016-10-17T21:35:20.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6759" PostTypeId="1" AcceptedAnswerId="6763" CreationDate="2016-10-18T04:41:30.400" Score="0" ViewCount="970" Body="&lt;p&gt;I'm wondering if it would be more efficient for me to replace several AC/DC adapters (linear, non-switching) with a regulated power supply?  Two of the adapters get very warm and are rated 9 watts input and 3.6 watts (12 volts * 300 ma) output.  So 40% efficiency doesn't seem that good and I don't need the heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or are there good non-RFI producing switching adapters that you could recommend?  How does their efficiency compare?&lt;/p&gt;&#xA;" OwnerUserId="8521" LastEditorUserId="76" LastEditDate="2016-10-18T16:41:13.590" LastActivityDate="2016-10-19T07:20:20.747" Title="Regulated Power Supply vs Class 2 AC/DC Adapters" Tags="&lt;dc-power&gt;&lt;power-supply&gt;&lt;efficiency&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6760" PostTypeId="2" ParentId="6756" CreationDate="2016-10-18T09:23:00.867" Score="2" Body="&lt;p&gt;I think the biggest risk you would take by renting such an appartment is terrible cellular reception. If your provider is one of the providers using the antenna on top of your building, that would most likely imply that an extra tower was needed on that spot. Being right underneath it, you'd have little benefit from the tower above you, apart from reflections...&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2016-10-18T09:23:00.867" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6761" PostTypeId="2" ParentId="6756" CreationDate="2016-10-18T10:45:13.433" Score="1" Body="&lt;p&gt;The only way you can get some real damage from anything microwave is from concentrated RF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like if you saw a radar by your house and decided to lay on top of it for some reason...you won't last very long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are ever in an aircraft hangar and someone forgets to turn off their radar and you start feeling all warm inside its because you are cooking!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think about kitchen microwaves, RF trapped in a box that's it! So as long as the transmissions aren't insanely powerful and concentrated you don't have anything to worry about. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Malfunctioning HPA (high power amplifiers) have been known to fry birds (the flappy ones not satellites), besides the crazy readings, that's a pretty clear sign there is a problem.&lt;/p&gt;&#xA;" OwnerUserId="8522" LastActivityDate="2016-10-18T10:45:13.433" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6762" PostTypeId="2" ParentId="6756" CreationDate="2016-10-18T14:34:40.253" Score="2" Body="&lt;p&gt;The FCC &lt;a href=&quot;http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet56/oet56e4.pdf&quot; rel=&quot;nofollow&quot;&gt;has a bulletin on this&lt;/a&gt;. It says (page 21):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Measurement data obtained from various sources&#xA;  have consistently indicated that &quot;worst-case&quot; ground-level power densities near typical cellular&#xA;  towers are on the order of 1 µW/cm&lt;sup&gt;2&lt;/sup&gt; or less (usually significantly less).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.wolframalpha.com/input/?i=1%20microwatt%20per%20square%20cm&quot; rel=&quot;nofollow&quot;&gt;Wolfram Alpha can put that into perspective&lt;/a&gt; for us:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;1/89th the average solar irradiance at Pluto&lt;/li&gt;&#xA;&lt;li&gt;1/10th ACGIH limit for 10 minute UV light exposure&lt;/li&gt;&#xA;&lt;li&gt;approximately the retinal irradiance from a pyrotechnical flare&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In other words, if you aren't afraid of looking at a fireworks show, 1 µW/cm&lt;sup&gt;2&lt;/sup&gt; shouldn't concern you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another comparison: solar irradiance, at noon, at the equator, on a clear day, is about 100,000 µW/cm&lt;sup&gt;2&lt;/sup&gt; (1 kW/m&lt;sup&gt;2&lt;/sup&gt;). So, the electromagnetic energy you will receive from the cell tower is about five orders of magnitude less than the maximum you could get from the Sun without leaving this planet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's another effect to consider: With your phone in your pocket, or held against your head, the associated field strength on your body can easily be more than the field from a relatively distant cell tower. With the tower so close your phone will run on its minimum power, which might actually mean less RF energy incident on your body overall.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-10-18T14:34:40.253" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6763" PostTypeId="2" ParentId="6759" CreationDate="2016-10-18T16:41:04.820" Score="3" Body="&lt;p&gt;If by “a regulated power supply” you mean specifically a non-switching one as your second paragraph, then “a regulated power supply” and “an AC/DC adapter (linear, non-switching)” are exactly the same thing.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Types of power supplies&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;There are basically only three categories of Things You Plug Into The Wall And Get DC Out:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Unregulated linear power supplies.&lt;/strong&gt; These contain a transformer, a rectifier, and smoothing capacitors. Their voltage output is significantly higher than rated when less than their rated load is applied, and their output has lots of “ripple” (a bit of 120 Hz AC on top of the DC output).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Regulated linear power supplies.&lt;/strong&gt; These add a linear regulator circuit to the above, producing a stable, lower, output voltage. The difference in voltage, times the output current, is dissipated as heat; therefore they are &lt;em&gt;less efficient than&lt;/em&gt; an unregulated supply, and most efficient when under maximum or minimum load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;“Laboratory” linear power supplies may add a current-limiting feature to this design. This is an addition to the &lt;em&gt;control&lt;/em&gt; section but the power-handling components are the same.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Switch-mode power supplies.&lt;/strong&gt; These produce a stable output voltage (or current, as in LED drivers) and do not dissipate heat, but they can produce RFI due to the high switching frequency. A well-designed switching supply will keep the noise inside the box by way of shielding and output filtering capacitors.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Any of these may come in “wall-wart”, “lump on the cable”, or desktop/benchtop form factors. This is determined more by their power rating (and hence their necessary physical size) than anything about their type of functionality, though a linear power supply will be larger and heavier than a switch-mode power supply of the same capabilities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The “Class 2” mentioned in your question title is a &lt;em&gt;safety&lt;/em&gt; standard: it says that the adapter is guaranteed not to produce &lt;em&gt;too much&lt;/em&gt; voltage or current, so that the output will not pose the kinds of safety hazard AC line power does. This means both under normal operation (the maximum output current must not be too high) and possible faults (internal physical protection against the AC input jumping over to the output side).&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Replacing power supplies&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Historically, an electronic device might use an external unregulated linear supply and place the linear regulator on the main circuit board instead. Modern devices may also have linear regulators or switching converters built in, in order to accept variable voltage or to produce multiple lower voltages for internal use. In this case, you could replace a switch-mode power supply with an unregulated linear one, as long as its open-circuit voltage is not too high for the device's input circuit components. This will reduce RFI but increase waste heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is OK to replace a regulated linear power supply with a switch-mode power supply of the same output voltage and current rating, or vice versa. The tradeoff you are making is efficiency versus RFI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not OK to use an unregulated power supply with an electronic device that does not have an internal regulator, as the varying input voltage may be too high unloaded or too low unloaded, causing damage or incorrect operation. It may be OK to use an unregulated power supply with a merely “electrical” low-voltage device having only lamps, motors, and such, but it should be chosen to match the current rating of the power supply to the actual load of the device.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-18T19:09:22.237" LastActivityDate="2016-10-18T19:09:22.237" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6764" PostTypeId="2" ParentId="6753" CreationDate="2016-10-18T19:11:32.553" Score="1" Body="&lt;p&gt;Additionally to the two answers above about GNU Radio and Soundmodem, &lt;a href=&quot;https://github.com/kamalmostafa/minimodem&quot; rel=&quot;nofollow&quot;&gt;minimodem&lt;/a&gt; was brought to my attention. It is a general-purpose software audio FSK modem with the code on GitHub. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you to Marcus and Phil for their quick answers. &lt;/p&gt;&#xA;" OwnerUserId="1792" LastActivityDate="2016-10-18T19:11:32.553" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6765" PostTypeId="2" ParentId="6759" CreationDate="2016-10-19T06:59:13.980" Score="0" Body="&lt;p&gt;A good answer already given; I am taking a slightly different approach. It seems to me that you have two concerns, first the efficiency of the power supplies, and second RFI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So lets take efficiency in terms of $.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming maximum use 24h/day, 1 year. Taking 10.42 cents per kWh (&lt;a href=&quot;https://www.statista.com/statistics/183700/us-average-retail-electricity-price-since-1990/&quot; rel=&quot;nofollow&quot;&gt;source&lt;/a&gt;). And lets take a &quot;&lt;em&gt;loss&lt;/em&gt;&quot; of 5.4 Watts from your details; 9 Watt in, 3.6 Watt out. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lets see what this is in a year:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;0.0054 (kW) * 24 (h) * 365 (d) * 0.1042 = $ 4.93 &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lets take a &lt;em&gt;theoretical&lt;/em&gt; switch mode power supply with an efficiency of 90%, and output of 3.6 Watts, so the &quot;&lt;em&gt;loss&lt;/em&gt;&quot; is 0.4 Watts, and calculate the same for a year:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;0.0004 (kW) * 24 (h) * 365 (d) * 0.1042 = $ 0.37&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As expected it is a big difference in annual cost: about four and a half dollars. However, the more efficient switch mode power supply have to be purchased, and probably/maybe EMI/RFI filtering is needed to clean up interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now the approach of this answer is an economical one:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Taking into account purchase price for the replacement, possible purchase price for EMI/RFI-filters, and the difference of the running cost. &lt;strong&gt;What is it worth to you; running a low-RFI high-loss power supply, versus, a possibly-high-RFI low-loss power supply ?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And I purposely omitted &quot;&lt;em&gt;durability&lt;/em&gt;&quot; in this answer. In my &lt;em&gt;opinion&lt;/em&gt; linear power supplies have a longer life than switch mode power supplies. However I have no data to back up that claim. If that is true then in the economic answer you will have to figure in depreciation of both, and set this off over time/annual.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my &lt;em&gt;experience&lt;/em&gt; over the years, the lower cost switch mode power supplies are prone to failure and high RFI. In regards to RFI: I have had to put filter on both input as well as output of those cheap switch mode power supplies. However I have some more expensive ones, which are OK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One experience I had was with mobile/cell phone chargers. Two exactly the same branded phones (which shall not be named, but which is in the news lately due to burning phones), with the original power supplies, both PSU &lt;strong&gt;exactly&lt;/strong&gt; the same, same print on the casing, same type number and other indicators/writing... except one showed &quot;made in China&quot; the other showed &quot;made in Taiwan&quot;... The one &quot;made in China&quot; had no noticeable RFI (I did not do measurements, other then SDR-waterfall observations), the PSU which was &quot;made in Taiwan&quot; had RFI all over the place, to a point that when the phone was charging I could not operate on HF. So even when you purchase known-good-brand switch mode power supplies, you can get a bad one. The obligatory &lt;em&gt;YMMV&lt;/em&gt; applies here.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-10-19T07:20:20.747" LastActivityDate="2016-10-19T07:20:20.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6766" PostTypeId="1" AcceptedAnswerId="6770" CreationDate="2016-10-19T10:35:40.133" Score="6" ViewCount="1445" Body="&lt;p&gt;This is probably a very simple and stupid question, but I'm getting more confused over time. Perhaps it is a matter of terminology, but a unified resource differentiating and explaining the different interfaces to connect radio with computer (desktop, Mac, mobile phone, GPS devices, etc.) would be very helpful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To start: I have assembled a home-brew cable to connect Kenwood radios with Android/iPhone. The cable has a 3.5 mm audio (in and out) at one end and Kenwood style audio double-jack at the other end. I understand this as a TRRS cable. I've also worked with a programming cable that has USB at one end and Kenwood style audio jack at the other end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've read about TNCs, CAT cables and Wolphi Link interfaces. What is the advantage of one over the other? I want to interface my radio with my smartphone as well as my computer. Both have a 3.5mm audio jack and the computer has a USB interface too. I'd also like to connect the radio to some GPS device, and possibly other devices. I'd also like to program the radio from a computer/phone. I have Yaesu and Kenwood phones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What cables/interfaces should I use? Can I use just one type of cable for different tasks (digital+packet operations and programming), or do I need a different cable for each task?&lt;/p&gt;&#xA;" OwnerUserId="213" LastEditorUserId="76" LastEditDate="2016-10-29T19:06:27.923" LastActivityDate="2019-10-14T01:45:35.150" Title="Confusion about radio-computer interfaces: TNC, CAT, TRRS, Wolphi Link, ...?" Tags="&lt;digital-modes&gt;&lt;audio-interface&gt;&lt;computer-control&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6767" PostTypeId="1" CreationDate="2016-10-19T14:02:41.383" Score="2" ViewCount="219" Body="&lt;p&gt;After detecting the transmitted signal of a garage door opener with SDR, is it correct to assume the first repeating pattern of the signal is preamble?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I only see two one and zeros with equal intervals and after that there is no pattern. Is it correct to assume that those two one and zeros are preamble of the transmitted signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should the preamble always be a repeating pattern and if so why?&lt;/p&gt;&#xA;" OwnerUserId="7843" LastActivityDate="2016-10-19T14:15:05.047" Title="Preamble of a garage door opener" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6768" PostTypeId="2" ParentId="6767" CreationDate="2016-10-19T14:15:05.047" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;After detecting the transmitted signal of a garage door opener with SDR, is it correct to assume the first repeating pattern of the signal is preamble?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It is a reasonable assumption. For very simple things like garage door openers, the lines between preamble and payload might be a bit blurry:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A preamble has the purpose of giving a receiver something &quot;known&quot; to look for. Now, a garage door receiver might simply just be looking for one special kind of signal and open its door if it sees that. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I only see two one and zeros with equal intervals and after that there is no pattern. Is it correct to assume that those two one and zeros are preamble of the transmitted signal?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Maybe! to elaborate:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Should the preamble always be a repeating pattern and if so why?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, not generally, not always.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it makes a lot of sense to have alternating symbols in a preamble. That way, you can easily tell a preamble from e.g. a constant tone interferer, and also, and in practice very importantly, you can use the preamble to get the timing of symbols – since no two oscillators are 100% identical, it's necessary that the receiver &quot;learns&quot; about how long a symbol is by observing the symbol rate of the transmitter.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-10-19T14:15:05.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6770" PostTypeId="2" ParentId="6766" CreationDate="2016-10-19T21:55:25.607" Score="9" Body="&lt;p&gt;First of all, don't feel to overwhelmed! This can be a bit confusing at the start, but once you understand the pattern and historical development, things will get a bit simpler. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So fist of all, you're confusing connectors and cable purposes.  Some cable types for certain purposes have common connectors, but in general, be sure to differentiate between the two. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let's start with the TRRS cable. TRRS is a a connector type, the one used by smart-phones for headphones, with tip, two rings and sleeve. The Kenwood connector has two TRS (tip-ring-sleeve) connectors. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radios using Kenwood connector usually implement a serial port via the Kenwood connector. This serial port is usually used to program frequencies and set the settings for the cable. The USB cable you have will have a USB to serial port chip inside and will use that serial port to communicate with the radio. The other alternative is to use a Kenwood to serial cable that can be used with a real serial port. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same Kenwood connector also implements connection for external loudspeaker-microphone combinations with push-to-talk buttons. There are TRRS to Kenwood cables that can be used with smart-phones to transfer audio from the radio to the smart-phone and from the smart-phone to the radio. Usually, that's done for purposes of &quot;digital modes&quot; or for &quot;packet radio&quot;. Basically, the phone acts as an old-school fax modem and generates audio that is then transmitted by the radio. In this case, usually the radio is set to VOX (voice activated) mode, so that the phone just needs to send audio to the radio. A better solution is to use external hardware to key the radio, but implementing this with a phone can be a bit complicated, so most people don't do it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, you mentioned TNC and CAT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let's go back in time a bit, before the smart phones, in the era of analog telephone modems. Back then, if you wanted to send and receive data over audio lines, you needed an external device to do that. This device would be connected to a computer via a serial port and on the other hand have audio connection over the telephone jack. In Internet world, such devices got the name &quot;analog modems, &quot;fax modems&quot; or just &quot;modems&quot;, but in amateur radio world, they got name Terminal Node Controller. The TNC, in addition to doing modulation/demodulation, would also do a bit of packet processing. So the device would go between your computer (or even just dumb serial terminal!) and your radio and supply radio with suitable audio that would carry the data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fast forward a couple of decades and now we have computers (and telephones!) that can do all the work of a TNC in software and only need the audio connection to the radio. The name TNC however stuck and the cable used to connect the TNC to the radio is called TNC cable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that in usual TNC operation, you set up the radio more-or-less manually and the TNC only receives audio, keys up the radio and sends audio to the radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then we have CAT and CI-IV(old radios)/CI-V(newer radios). The CAT stands for computer aided tuning and CI-V is Communications Interface 5 (4 was the older version) and is the name used by Icom for CAT.&lt;br&gt;&#xA;Basically, the idea here is to remotely control the operation of the radio itself. So the radio has a serial port, you sit in front of a computer connected to the radio and select frequency, mode and other settings of the radio. Keep in mind that this is just settings for the radio and carries no audio signal on its own. Depending on the commands implemented by the radio, you might be able to do the &quot;programming&quot; of the radio as well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you want to do digital modes on a relatively new radio, you need two cables: A &quot;TNC&quot; cable and a CAT cable, one to carry data and the other to carry audio. Some newer radios solve this by having just one USB cable: The radio shows up as a composite USB device consisting of a USB to serial converter and a sound card. You just send the instructions using the serial port and audio using the sound card and that's it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now about the Wolphi Link. This is what they call an &quot;interface&quot;. It's a realization of a TNC (more or less) cable. On one side, you have the 6-pin connector for the radio, then you have the interface itself and on the other side, you have audio connection for the phone. The interface is there to provide some isolation between the radio and the phone, since it can happen that you have RF going over the TNC cable. The device also claims to be able to generate the key signal for the radio, which can be more reliable than just using VOX and will work with VOX-less radios as well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;About the GPS part... There's no sense in connecting a GPS to a dumb radio, pretty much in the same way it's senseless to connect an egg to a radio. On the other hand, with some &quot;smarter&quot; radios, you have a TNC inside of the radio and some radios even have full APRS support (marine radios also have GPS connection for digital selective calling). In this case, it does make sense to connect a GPS receiver to the radio, but from &quot;subsystem&quot; point of view, you're connecting the GPS to the TNC/computer inside of the radio. You'll usually do this using serial port as well or by connecting radio with its own proprietary GPS receiver. If you however want the phone or computer to be the TNC, then you need to connect the GPS to the computer or use phone's GPS. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this answer, I left out the part about software on the phone/computer that's going to drive the radio itself, since I believe that this side of the story is a bit too complicated to be fitted in this answer. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2016-10-19T21:55:25.607" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="6771" PostTypeId="1" CreationDate="2016-10-19T22:22:35.893" Score="1" ViewCount="61" Body="&lt;p&gt;Currently I use a Motorola &lt;a href=&quot;https://www.motorolasolutions.com/content/dam/msi/docs/products/two-way-radios/consumer/mr350-mx-uy-pa-us.pdf&quot; rel=&quot;nofollow&quot;&gt;MR30R&lt;/a&gt; radio in the frequency 20 (462,6750 Mhz) with Interference Eliminator Code 59. I also have a Motorola &lt;a href=&quot;https://www.motorolasolutions.com/content/dam/msi/docs/en-xl/products/two-way-radios-business/portable-radios/on-site-small-business/rva50/RVA50_User_Guide.pdf&quot; rel=&quot;nofollow&quot;&gt;RVA50UL&lt;/a&gt;, according to the manual, the frequency will be available at channel 3, but I am not able to set the interference eliminator code. the manual does not define that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am misreading the manual of the RVA50UL?&lt;/p&gt;&#xA;" OwnerUserId="8534" LastActivityDate="2016-10-19T22:22:35.893" Title="How to connect a motorola RVA50UL with MR350?" Tags="&lt;uhf&gt;&lt;frequency&gt;&lt;tone-squelch&gt;" AnswerCount="0" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6773" PostTypeId="1" CreationDate="2016-10-20T13:24:38.243" Score="3" ViewCount="498" Body="&lt;p&gt;I'm using a 14 element cross Yagi antenna in my system. For my link budget calculations, what antenna noise temperature should I consider? How does this vary with elevation?&lt;/p&gt;&#xA;" OwnerUserId="5762" LastActivityDate="2016-11-20T12:31:31.057" Title="How does the antenna noise temperature vary with antenna elevation?" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;noise&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6774" PostTypeId="1" AcceptedAnswerId="6788" CreationDate="2016-10-20T19:58:48.847" Score="4" ViewCount="1466" Body="&lt;p&gt;I wanted to explore digital modes by connecting a Raspberry Pi via audio cables to a transceiver. However, I realized that thanks to the clock generator, the raspberry pi can produce RF signals directly. Adding a square to sine wave converter, a band pass filter and an amplifier, this could be used as the transmitter. There is good software in &lt;a href=&quot;http://gnuradio.org/&quot; rel=&quot;noreferrer&quot;&gt;GNU Radio&lt;/a&gt; and &lt;a href=&quot;https://github.com/F5OEO/rpitx&quot; rel=&quot;noreferrer&quot;&gt;PiTx&lt;/a&gt;. FM signals can be produced. As far as I can tell it is possible to generate SSB directly on the pi but I haven't understood yet how. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Q1: Is it possible to directly generate SSB on the pi?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the receiver side, things look a bit more tricky. It requires a down converter and a very fast analog to digital converter. The good news is that they appear to be very cheap, e.g. &lt;a href=&quot;http://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/&quot; rel=&quot;noreferrer&quot;&gt;R820T2&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Q2: Would combining a cheap dongle such as the R820T2 enable me to operate in half-duplex mode with the Raspberry Pi?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm mainly interested in playing with the radio, so any band is fine. If I were forced to choose, I would prefer 50MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apologies for this open-ended question, any suggestions welcome. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;M0HXS&lt;/p&gt;&#xA;" OwnerUserId="1792" LastEditorUserId="8832" LastEditDate="2017-08-20T14:53:54.547" LastActivityDate="2017-08-20T14:53:54.547" Title="SDR with the Raspberry Pi" Tags="&lt;software-defined-radio&gt;&lt;receiver&gt;&lt;rtl-sdr&gt;&lt;modem&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6775" PostTypeId="2" ParentId="6773" CreationDate="2016-10-20T20:15:36.350" Score="-1" Body="&lt;p&gt;Wikipedia has a nice article on antenna noise temperature.  Quoting here:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In telecommunication, antenna noise temperature is the temperature of a hypothetical resistor at the input of an ideal noise-free receiver that would generate the same output noise power per unit bandwidth as that at the antenna output at a specified frequency. In other words, antenna noise temperature is a parameter that describes how much noise an antenna produces in a given environment. This temperature is not the physical temperature of the antenna. Moreover, an antenna does not have an intrinsic &quot;antenna temperature&quot; associated with it; rather the temperature depends on its gain pattern and the thermal environment that it is placed in.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Antenna noise temperature has contributions from several sources:&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;&lt;p&gt;Galactic Radiation&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Earth heating&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;The Sun&lt;/li&gt;&#xA;  &lt;li&gt;Electrical Devices&lt;/li&gt;&#xA;  &lt;li&gt;The antenna itself&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;More information can be found by consulting the actual &lt;a href=&quot;https://en.wikipedia.org/wiki/Antenna_noise_temperature&quot; rel=&quot;nofollow&quot;&gt;Site&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-10-20T20:15:36.350" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6778" PostTypeId="1" CreationDate="2016-10-22T16:12:50.970" Score="2" ViewCount="1381" Body="&lt;p&gt;I am building a 20 Mhz RF receiver out of the &lt;a href=&quot;http://radiojove.gsfc.nasa.gov/telescope/rcvr_manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;NASA radio JOVE instruction manual&lt;/a&gt; and they have recommended the use of LM387 as an audio amplifier. SA602AN as mixer IC:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/C8wjB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/C8wjB.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5420" LastEditorUserId="4076" LastEditDate="2016-10-24T16:49:12.837" LastActivityDate="2020-03-27T19:29:43.910" Title="what are the alternatives to LM387 and SA602AN?" Tags="&lt;hf&gt;&lt;receiver&gt;&lt;electronics&gt;&lt;amplifier&gt;&lt;mixer&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6779" PostTypeId="2" ParentId="6778" CreationDate="2016-10-23T00:00:11.510" Score="4" Body="&lt;p&gt;The SA602AN looks to be still available from many of the usual distributors.  (Check octopart.com or findchips.com to see which distributors have them in stock.)  The LM387 is apparently long obsolete.  A quick web search didn't reveal any pin-for-pin compatible parts still being manufactured, so if you're using the printed circuit board from the kit, then you'll need an actual LM387; they aren't hard to find on eBay.  If you're building your own circuit, either by creating your own printed circuit board or wiring the circuit by hand, then there are various alternatives.  A quick web search for &quot;lm387 equivalent&quot; suggests the NE5532 or the OPA2350 as potential substitutes, which may require minor circuit alterations.  Good luck.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-10-23T00:00:11.510" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6780" PostTypeId="2" ParentId="6778" CreationDate="2016-10-23T23:16:48.973" Score="6" Body="&lt;p&gt;LM387 is just a really old, ordinary op-amp as far as I can tell. It has a funny pin configuration, so if you have a PCB already made you need to make modifications. I suggest cutting the traces, scraping off the solder mask, and soldering wires in place with the right layout. Look for datasheets on the internet for the pin configuration. For old stuff Google, for modern stuff I prefer an online reseller like Mouser. Datasheets are free even if you don't buy the part.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any cheap opamp will work. TL072 is very common. NE5532 is also not hard to find and it can drive headphones a little louder. Either costs less than $1 USD. Or just buy whatever is available from your favorite electronics source. If you want to be safe, buy a DIP socket and then if you get the wrong op-amp you can easily swap it for another.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SA602 is still widely available so I would stick with that. It also goes by the name NE602. Don't search for the &quot;AN&quot; at the end: it will severely limit your options. Just be sure you are getting the right package (like DIP8).&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-10-24T12:05:15.597" LastActivityDate="2016-10-24T12:05:15.597" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6783" PostTypeId="2" ParentId="849" CreationDate="2016-10-25T01:19:50.180" Score="4" Body="&lt;p&gt;I live in Seoul, Korea, a city of 15 million, with lots of lights and electronics on late until 11pm.  My vertical dipoles I have created are easily 1 to 3 s-units noisier than horizontal dipoles.  Absolutely no contest.  The vertically-polarized antennas transmit DX very well, however.  I actually run two antennas -- horizontal for listening, and transmit.  The vertical for transmit (great on longpath), and less for listening, because they are so noisy here (often s5-s8 noise daytime) they are almost useless on receive.  Switching between the two is best of both worlds.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, I built a 2-el wire 15m yagi, and the noise reduction is yet another 2 to 2.5 s-units under the horizontal dipole!  Huge difference.  Even though a 2-el yagi only has just under an s-unit gain, at same height as a dipole, the noise reduction is what really takes the cake!&lt;/p&gt;&#xA;" OwnerUserId="8556" LastEditorUserId="8556" LastEditDate="2016-10-25T01:33:19.673" LastActivityDate="2016-10-25T01:33:19.673" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6784" PostTypeId="1" AcceptedAnswerId="6793" CreationDate="2016-10-25T06:14:42.377" Score="8" ViewCount="286" Body="&lt;p&gt;I have seen many discussions re: wire gauge, insulation, velocity factor and K-factor...unfortunately, statements from various sources are not always in agreement, but that is not the issue. The issue that I have never heard discussed seems like a simple matter but ??  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Here it is:&lt;/strong&gt; A wider wire, let's say &lt;em&gt;really&lt;/em&gt; wide (&lt;strong&gt;4/0&lt;/strong&gt;) is being hit with more energy than a thin wire, is it not? A square foot of anything is exposed to one half the sunlight/energy that a two square foot anything is, when both are in sunlight.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some solid copper #4 AWG (&lt;em&gt;and 6, 10, 12, and 14&lt;/em&gt;) and I have some 2/0 and some 4/0 (~1/2&quot;) stranded insulated aluminum wire. The question concerns a 14 foot, eight-element quagi that I want to build and I'm thinking that the &lt;strong&gt;4/0 for the 'quads'&lt;/strong&gt; and &lt;strong&gt;#4 for the directors&lt;/strong&gt; should pick up way more energy than all wire being #12, for instance.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't see folks writing about that anywhere which makes me wonder just how nutz is this?&lt;br&gt;&#xA;  This site is a vast repository of knowledge and I thank in advance all who want to answer/comment.&lt;/p&gt;&#xA;" OwnerUserId="8477" LastEditorUserId="8477" LastEditDate="2016-10-26T05:46:31.837" LastActivityDate="2016-10-31T13:04:37.113" Title="Wider wire = picks up more energy, yah?" Tags="&lt;antenna-construction&gt;&lt;antenna-theory&gt;&lt;wire-antenna&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6785" PostTypeId="2" ParentId="6784" CreationDate="2016-10-25T12:20:35.797" Score="8" Body="&lt;p&gt;In short, no.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In long, it's really complicated. The wider your wire, the wider the bandwidth, due to the increase in available paths. Wide multi-strand wire does better against skin effect (more conductive area).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, the &quot;more exposed area&quot; doesn't work here. You are picking up the E-field with this kind of antenna, so it's the voltages out on the tips that is important, not the cross section of current carrying in terms of the &quot;amount you pick up&quot;. Does that make sense?&lt;/p&gt;&#xA;" OwnerUserId="8034" LastActivityDate="2016-10-25T12:20:35.797" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6786" PostTypeId="1" CreationDate="2016-10-25T17:28:44.293" Score="2" ViewCount="110" Body="&lt;p&gt;Is it correct to assume that not all the key fob signals have preamble section? I am playing around with bunch of key fobs and I am trying my best to capture their OOK transmitted signals with RTL-SDR and Gnuradio companion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can not see any pattern for some of them. Does it mean that there is no preamble for some? &lt;/p&gt;&#xA;" OwnerUserId="7843" LastActivityDate="2016-10-25T17:28:44.293" Title="Capturing the key fob signal with SDR" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="0" CommentCount="4" ClosedDate="2016-11-08T17:48:19.083" ContentLicense="CC BY-SA 3.0" />
  <row Id="6787" PostTypeId="1" AcceptedAnswerId="11839" CreationDate="2016-10-25T22:15:17.887" Score="6" ViewCount="1052" Body="&lt;p&gt;While it wasn't the first to do so, the &lt;a href=&quot;https://github.com/F5OEO/rpitx&quot; rel=&quot;noreferrer&quot;&gt;rpitx software&lt;/a&gt; seems to be the most active and mature implementation of what its own comments call &quot;a code fragment by PE1NNZ&quot;. The trick is explained in Guido's original &lt;a href=&quot;http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll.html&quot; rel=&quot;noreferrer&quot;&gt;Direct SSB Generation by frequency modulating a PLL&lt;/a&gt; article — but I don't quite understand how even the original works:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The PLL oscillator can be phase modulated by short manipulations of the configured frequency. Increasing the frequency temporarily and then restoring to its original frequency, will shift the phase upwards, while decreasing the frequency temporarily will decrease the phase of the signal. In this way the phase information for generating a SSB signal can be applied to the RaspberryPi PLL by means of frequency modulation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This almost makes sense, but then he loses me a bit later:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;After some experimenting, amplitude information can be completely rejected [… talks about generating an unsuppressed carrier …]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Now I suppose that if you have complete (and drastic) control over the phase of a sine wave, you can reproduce any other continuous signal simply by &quot;walking&quot; forward and backward along half a cycle of a sine wave — basically just slewing to whichever value between -1 and +1 is needed at the moment. Is that essentially what PE1NNZ's trick reduces down too, or is that a poor way to think about it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now even if I'm on the right track above, the rpitx implementation (&lt;a href=&quot;https://github.com/F5OEO/rpitx/blob/master/ssbgen/ssb_gen.c#L169&quot; rel=&quot;noreferrer&quot;&gt;source code&lt;/a&gt;) seemingly has an additional hurdle to overcome:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rather than controlling the phase of a sine wave, my understanding is that with the Raspberry Pi &quot;hack&quot; the oscillator peripheral being used was meant to be a clock source. Wouldn't that then be a square wave generator then, i.e. generating (at least in its idealized form) only the peak -1 and +1 values and nothing in between?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Certainly I can see how discrete values could still generate an arbitrary waveform after filtering, for example pulse width or &lt;a href=&quot;https://en.wikipedia.org/wiki/Pulse-density_modulation&quot; rel=&quot;noreferrer&quot;&gt;pulse-density modulation&lt;/a&gt;. But that does not seem to be the way either PE1NNZ or the rpitx contributors seem to be thinking about this — otherwise why not simply bit-bang any GPIO pin instead of using the clock peripheral!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Somehow rpitx is converting arbitrary I/Q data to RF signals through a huge range of frequencies (130 kHz to 750 MHz) — I'd love to understand the theory behind it! Could I use the same trick to turn an FM transceiver into an &quot;All Mode&quot; radio by injecting a suitably transformed input signal?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-10-25T22:39:44.243" LastActivityDate="2018-09-11T04:02:54.157" Title="How does rpitx generate arbitrary SSB data with a clock peripheral?" Tags="&lt;software-defined-radio&gt;&lt;modes&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6788" PostTypeId="2" ParentId="6774" CreationDate="2016-10-25T22:31:55.913" Score="4" Body="&lt;p&gt;Yes, with some important qualifications, you can &quot;directly&quot; generate SSB on the Raspberry Pi. The &lt;a href=&quot;https://github.com/F5OEO/rpitx&quot; rel=&quot;nofollow noreferrer&quot;&gt;rpitx software&lt;/a&gt; you mention does that, and in combination with an RTL-SDR type dongle you would indeed have a sort of half-duplex transceiver. So in short: yes (Q1) and yes (Q2).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on that exact combination, &lt;a href=&quot;https://github.com/ha7ilm/qtcsdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;qtcsdr&lt;/a&gt; is an app that aims to make your Raspberry Pi into a amateur radio transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, all the filtering that goes into both a good receiver and — more exigently — a &lt;strong&gt;legal&lt;/strong&gt; transmitter are &quot;sold separately&quot;! This is the most important qualification.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would assume that rpitx (and qtcsdr, which uses it) generates a much, much messier signal than even the most infamous CB amplifier driven hard. (At least your signal will be much quieter :-) Check out the &lt;a href=&quot;https://www.tapr.org/kits_20M-wspr-pi.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRPi shield&lt;/a&gt; — it's not just a low-pass filter like is often needed in a typical RF chain, but rather needs to be a full band-pass filter to reign in the Pi's spurious emissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as how the SSB generation actually &lt;em&gt;works&lt;/em&gt;, that is a fascinating subject and I wish I knew too: &lt;a href=&quot;https://ham.stackexchange.com/questions/6787/how-does-rpitx-generate-arbitrary-ssb-data-with-a-clock-peripheral&quot;&gt;How does rpitx generate arbitrary SSB data with a clock peripheral?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-10-25T22:37:19.993" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6789" PostTypeId="2" ParentId="6787" CreationDate="2016-10-25T22:47:53.883" Score="5" Body="&lt;p&gt;This is an incomplete and theoretical answer as I haven't looked at rpitx in particular.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Rather than controlling the phase of a sine wave, my understanding is that with the Raspberry Pi &quot;hack&quot; the oscillator peripheral being used was meant to be a clock source. Wouldn't that then be a square wave generator then, i.e. generating (at least in its idealized form) only the peak -1 and +1 values and nothing in between?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, but a square wave is a sine wave plus harmonics, and harmonics of a square wave of fundamental frequency $f$ are all at frequencies $2f$ or higher, so a receiver tuned to $f$ will not see the difference, and if it is low-pass filtered appropriately then there is no difference in the transmitted signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this still sounds like a hack, or you wonder if modulation makes a difference, consider that it's perfectly possible to &lt;a href=&quot;https://ham.stackexchange.com/questions/1363/how-does-a-switching-mixer-multiply-the-two-signals&quot;&gt;make a RF mixer using a square wave and XOR&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;why not simply bit-bang any GPIO pin instead of using the clock peripheral!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Again, I haven't looked at the hardware capabilities involved, but most likely, the peripheral can oscillate at a much higher rate than the Pi's processor can bit-bang the output, thus allowing for a higher carrier frequency. The software control need only operate at (perhaps some small multiple of) the sample rate of the modulating signal, not the RF rate.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-10-25T22:47:53.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6790" PostTypeId="1" CreationDate="2016-10-26T09:56:23.010" Score="1" ViewCount="67" Body="&lt;p&gt;When arriving in a port, complementary to her AIS signal (encoded VHF message) it seems that the vessel also has to emit a voice message on a predifined VHF frequency to identify herself as part of the VTS process (Vessel Tracking System).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it something codified for all ports ? &#xA;Which information are given ? only name/imo/callsign ? destination berth ?cargo on board ?&#xA;Is it legal to listen to those messages ? Specifically for the US ?&lt;/p&gt;&#xA;" OwnerUserId="8560" LastEditorUserId="8560" LastEditDate="2016-10-27T10:07:23.057" LastActivityDate="2016-10-27T12:10:00.827" Title="VTS messages vs AIS" Tags="&lt;legal&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6791" PostTypeId="2" ParentId="6790" CreationDate="2016-10-26T10:53:08.863" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it something codified for all ports ? Which information are given ?&#xA;  only name/imo/callsign ? destination berth ?cargo on board ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I believe this is something which could differ from port to port. Lets take an arbitrary &lt;a href=&quot;http://www.portoflarne.co.uk/marine/vts/&quot; rel=&quot;nofollow&quot;&gt;port of Larne&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has two VTS documents available for download. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It specifies that there is a pre-arrival comms (section 3.1):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Acknowledge call&lt;/li&gt;&#xA;&lt;li&gt;Receive vessel’s information; ETA, draft, PEC, Hazardous Cargo, defects or deficiencies;&lt;/li&gt;&#xA;&lt;li&gt;Inform vessel of traffic movements, weather status, berthing or anchoring arrangements.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It also specifies that there are other responsibilities for the VTS operational staff, once the vessel has arrived in the VTS controlled area of the port:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Track and monitor vessels entering the Larne VTS area; &lt;/li&gt;&#xA;&lt;li&gt;Check vessel complies with reporting requirements; &lt;/li&gt;&#xA;&lt;li&gt;Advise vessel of Pilot boarding position, time and order of boarding - if applicable; &lt;/li&gt;&#xA;&lt;li&gt;Advise of anchorage position - if applicable; &lt;/li&gt;&#xA;&lt;li&gt;Advise vessel of relevant traffic situation; &lt;/li&gt;&#xA;&lt;li&gt;Advise vessel of any navigational/ fairway information; &lt;/li&gt;&#xA;&lt;li&gt;Advise vessel of weather and tidal information.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you take another arbitrary &lt;a href=&quot;http://www.doverport.co.uk/operations/vessel-traffic-service/&quot; rel=&quot;nofollow&quot;&gt;port of Dover&lt;/a&gt; different information is available, and the procedures are slightly different. Dover is a very busy port, so different VTS processes are required for Commercial Vessels vs small craft. You can find the procedures on the website indicated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would believe the answer to your questions is: &lt;strong&gt;no, it is not 'codified' for all ports&lt;/strong&gt;, it varies from port to port, and it is the responsibility of the master of the vessel to be familiar with the correct procedure prior to entering the port's VTS controlled area.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it legal to listen to those messages in the USA?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I will let someone more familiar with USA legislation answer that question.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2016-10-27T12:10:00.827" LastActivityDate="2016-10-27T12:10:00.827" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6792" PostTypeId="1" AcceptedAnswerId="6794" CreationDate="2016-10-26T12:02:09.153" Score="2" ViewCount="131" Body="&lt;p&gt;Just purchased a HP 8711A and have &quot;upgraded&quot; the bootrom to enable vector measurements. I am now trying to learn more about how to make better measurements and understand what's going on.&lt;br&gt;&#xA;One of the things I wanted to try is to measure the return loss of some portable antennas (for use on portable radios).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio and user are necessary parts as some kind of counterpoise for these antennas, which makes measurements rather difficult.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I:&lt;br&gt;&#xA;- Take a metal plate&lt;br&gt;&#xA;- Mount a flange mount connector on it&lt;br&gt;&#xA;- Make sure the  the plate is connected to the braid&lt;br&gt;&#xA;- Mount the antenna on this contraption&lt;br&gt;&#xA;- Use this as a substitution for the body + radio ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any other thoughts? Pitfalls I should keep in mind?&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2016-10-26T19:49:00.470" Title="Portable radio antenna measurement" Tags="&lt;antenna&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6793" PostTypeId="2" ParentId="6784" CreationDate="2016-10-26T15:10:28.340" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;A wider wire, let's say really wide (4/0) is being hit with more energy than a thin wire, is it not? A square foot of anything is exposed to one half the sunlight/energy that a two square foot anything is, when both are in sunlight.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Sunlight has &lt;strong&gt;extremely small wavelengths&lt;/strong&gt;, several orders of magnitude less than (to use the distance you mentioned) a foot. This means that the interactions of any given portion of the light with a solar panel (or even an ordinary dark object getting heated) occur in very small areas of the material, so if you analyze it as if it were an antenna, it's more like an array of tiny antennas than a bigger-in-some-dimension single antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a radio wave interacting with a dipole antenna, for example (not that far from the case of your quagi), &lt;strong&gt;the entire antenna is built around half-wavelength dimensions.&lt;/strong&gt; The area of the incoming electromagnetic wavefront that this antenna is interacting with is &lt;em&gt;not&lt;/em&gt; the length and thickness of the wire, it is more like a circle whose diameter is the antenna length. (Reality is much more complex than this; there are no simple geometric shapes, but this will do for now.) Thus, making the wire thicker does not gather significantly more energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The analogy to making your solar panel two square feet instead of one is making two identical antennas, not too close to each other and connecting them in parallel. This is not a perfect analogy, because solar cells (and heating) are treating the radiation as &lt;em&gt;non-coherent&lt;/em&gt;, meaning the phase of the signal is discarded and only the amplitude is kept. For coherent reception, as used in radio communications, the math works out that any such array of antennas or any other means of gathering more energy makes the antenna &lt;em&gt;more directional.&lt;/em&gt; That's why we measure both properties as a single value, the “gain” of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can in theory gather more energy from a radio signal without increasing directionality, by using multiple antennas and multiple &lt;em&gt;receivers&lt;/em&gt; as well — by independently demodulating from each antenna you avoid the signals cancelling each other. Imagine building lots of crystal radios and combining all their weak audio outputs into one stronger one. When the goal is actually to gather electric power from the RF field (in which case all you need is the diode rectification, no filtering or audio transducer), this is called a &lt;strong&gt;rectenna&lt;/strong&gt; and it can be built into an arbitrarily large array just like a solar panel.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-10-26T15:10:28.340" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6794" PostTypeId="2" ParentId="6792" CreationDate="2016-10-26T15:23:37.593" Score="3" Body="&lt;p&gt;You should also &lt;strong&gt;put an unun/choke on the feed line&lt;/strong&gt; at the back side of your plate to ensure that only the plate and not the plate+coax+analyzer are involved. Once you've done that, I see no reason why your proposed measurement strategy wouldn't work to give you a repeatable number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, that number won't exactly reflect the antenna's behavior in actual operation, because even if your metal plate happens to match one particular HT+arm+body configuration it won't match others. You could have several different fixtures to model different situations, but even then you have the problem of validating your model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only way I can see to do that validation is to measure the reflected power in the real configuration — i.e. either a handheld radio with a suitable meter built-in, a physically compact meter inserted in-line at the antenna port, or an analyzer in a handheld form factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't have this reference, then you can still make repeatable measurements, but you don't know what measured values correspond to the &lt;em&gt;best&lt;/em&gt; real-world performance.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For what it's worth, some rough measurements about the size of the variation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a handheld antenna analyzer which can read R, X, SWR, and return loss. The primary way in which it is different from a handheld radio is a very different case design (large and plastic rather than small and coated metal), which affects the amount of coupling to the hand.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;I attached a 1/4 wave whip (no additional ground plane) and measured return loss values between 3 and 6 dB at 146 MHz depending on how I held the unit.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A more “rubber duck” style antenna (about half length) varied between 10 and 35 dB and was much more obviously sensitive to exact positioning.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-26T19:49:00.470" LastActivityDate="2016-10-26T19:49:00.470" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6795" PostTypeId="1" AcceptedAnswerId="6796" CreationDate="2016-10-27T10:28:21.660" Score="1" ViewCount="157" Body="&lt;p&gt;I have created a TLE to represent my theoretical satellite whose orbit I wish to plot using Gpredict. I have managed to load it all up onto the program and it is looking good, but one thing remains - I want to work out an accurate-ish pass scenario, and as such want to be able to modify the satellite's footprint. Is this possible? Or does Gpredict just use a default value of 'beam angle' and scale the footprint according to altitude?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, while I am here, are there typical values for an x-band satellite's footprint? I have found that they are typically &gt;1000km diameter but not much else more than that!&lt;/p&gt;&#xA;" OwnerUserId="8572" LastEditorUserId="76" LastEditDate="2016-10-27T19:07:41.483" LastActivityDate="2016-10-27T19:07:41.483" Title="Can one modify footprints in Gpredict?" Tags="&lt;satellites&gt;&lt;software&gt;&lt;line-of-sight&gt;&lt;gpredict&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6796" PostTypeId="2" ParentId="6795" CreationDate="2016-10-27T17:37:11.163" Score="3" Body="&lt;p&gt;The footprint calculated by gpredict (and other satellite tracking software) is the area from which the satellite appears above de horizon (or, equivalently, the patch of earth seen from the satellite). This is independent of any radio link the satellite may possess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the answer is no. You cannot &lt;em&gt;modify footprints&lt;/em&gt; on gpredict.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This has nothing to do with antenna footprints for geostationary satellites, which is the area on earth covered by the satellite service. This depends strongly on the antenna design and satellite attitude.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2016-10-27T17:37:11.163" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6797" PostTypeId="1" CreationDate="2016-10-28T02:40:03.540" Score="5" ViewCount="88" Body="&lt;p&gt;My signal generator is giving DC at its RF OUT port. At 500 MHz &amp;amp; 1GHz it's giving nearly 1.5V DC when I measure the voltage between the centre pin &amp;amp; outer conductor with a multimeter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know whether this is the right way to measure or whether this output voltage is normal. The equipment is working fine and passing its self-test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be the reason for this?&lt;/p&gt;&#xA;" OwnerUserId="8575" LastEditorUserId="76" LastEditDate="2016-10-29T21:41:40.223" LastActivityDate="2016-10-29T21:41:40.223" Title="Signal generator giving DC output?" Tags="&lt;rf-power&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6798" PostTypeId="2" ParentId="6797" CreationDate="2016-10-28T18:06:06.613" Score="2" Body="&lt;p&gt;Multimeters are generally used to measure AC volts at line frequencies, i.e. 50/60 Hz, and yours is almost certainly not accurate at 1 GHz.  Similarly your multimeter's DC volts setting is designed to measure static DC volts, not the DC bias of a 1 GHz signal.  To sum up, your multimeter measurements are probably completely meaningless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to see what's really going on with your signal generator, look at the output some other way.  (Whether there is a DC bias probably isn't important, because you will almost always use a capacitor to couple the output, and the capacitor will block the DC.)  You could connect the signal generator to a radio, through a capacitor and an attenuator of course, and listen for the output.  You can make an attenuator with a few resistors.  If you hear the signal in the radio, then the signal generator probably works fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ultimate way to check what's going on with the signal generator would be to look at the output with a 1 GHz-rated oscilloscope and/or a spectrum analyzer, but those instruments probably cost a lot more than the signal generator did.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-10-28T18:06:06.613" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6799" PostTypeId="5" CreationDate="2016-10-29T18:46:14.123" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T18:46:14.123" LastActivityDate="2016-10-29T18:46:14.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6800" PostTypeId="4" CreationDate="2016-10-29T18:46:14.123" Score="0" Body="Analog audio signals and connecting or designing related equipment: transceiver mic/speaker ports, headphones, microphones, TNCs, computer sound cards. Closely related signaling such as PTT. See also: [microphone]" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T18:46:14.123" LastActivityDate="2016-10-29T18:46:14.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6801" PostTypeId="5" CreationDate="2016-10-29T18:55:52.237" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T18:55:52.237" LastActivityDate="2016-10-29T18:55:52.237" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6802" PostTypeId="4" CreationDate="2016-10-29T18:55:52.237" Score="0" Body="A function of receivers which mutes the audio when no signal is present; there are various and mode-dependent ways of making this determination. For PL/CTCSS in particular, use the [tone-squelch] tag." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T18:55:52.237" LastActivityDate="2016-10-29T18:55:52.237" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6803" PostTypeId="5" CreationDate="2016-10-29T19:00:05.043" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T19:00:05.043" LastActivityDate="2016-10-29T19:00:05.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6804" PostTypeId="4" CreationDate="2016-10-29T19:00:05.043" Score="0" Body="Loading frequency memories and other settings into radios, typically using a computer and a special programming cable." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T19:00:05.043" LastActivityDate="2016-10-29T19:00:05.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6805" PostTypeId="5" CreationDate="2016-10-29T19:05:24.027" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T19:05:24.027" LastActivityDate="2016-10-29T19:05:24.027" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6806" PostTypeId="4" CreationDate="2016-10-29T19:05:24.027" Score="0" Body="Controlling a transceiver using software running on a separate personal computer. See also: [software-defined-radio], [audio-interface]." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-10-29T19:05:24.027" LastActivityDate="2016-10-29T19:05:24.027" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6808" PostTypeId="2" ParentId="6784" CreationDate="2016-10-31T13:04:37.113" Score="3" Body="&lt;p&gt;As other answers have explained, radio waves, being of a much longer wavelength than visible light, don't &quot;hit&quot; the wire in that way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However there is a way to measure the size of the target the radio waves are hitting: &lt;em&gt;effective aperture&lt;/em&gt; ($A_{eff}$). It's just another way of specifying gain ($G$) and wavelength ($\lambda$):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ G {\lambda ^{2} \over 4\pi} = A_{eff} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you have an antenna for 10 meters with a gain of 2 (3 dBi), then the &quot;target&quot; for the radio energy is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 2 {(10\:\mathrm m)^2 \over 4\pi} = 16\:\mathrm m^2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sixteen square meters. You can use whatever wire thickness you want, but as long as the gain of the antenna is 3 dB the effective aperture does not change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case you are wondering, wire thickness in dipoles has no significant effect on gain.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-10-31T13:04:37.113" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6810" PostTypeId="1" CreationDate="2016-11-01T14:12:33.000" Score="1" ViewCount="85" Body="&lt;p&gt;I have the new UV8000E ht and I'm trying to find a magnetic antenna or at least the adapter that allows the unit to be attached  to a pl259 connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have no clue what the connector is other than the fact that it isn't SMA. &lt;/p&gt;&#xA;" OwnerUserId="8596" LastEditorUserId="4076" LastEditDate="2016-11-01T14:51:40.530" LastActivityDate="2016-12-02T03:13:33.013" Title="Magnetic antenna for the UV8000E" Tags="&lt;connectors&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6811" PostTypeId="1" AcceptedAnswerId="6911" CreationDate="2016-11-01T14:33:24.320" Score="0" ViewCount="168" Body="&lt;p&gt;I reviewed &lt;a href=&quot;https://github.com/romanz/amodem/blob/master/README.rst&quot; rel=&quot;nofollow noreferrer&quot;&gt;docs&lt;/a&gt; for amodem, and it looks like I can send files and possibly other things with this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I should only need to prep my computer as per the doc and set VOX correctly. Does anyone have experience with this software, or a recommendation for something better (linux/bsd)?&lt;/p&gt;&#xA;" OwnerUserId="7957" LastEditorUserId="4076" LastEditDate="2016-11-01T15:11:04.860" LastActivityDate="2016-12-02T14:52:12.587" Title="Using 'amodem' to transfer digitally using a UV5R" Tags="&lt;digital-modes&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;packet&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6812" PostTypeId="1" CreationDate="2016-11-01T18:46:13.260" Score="0" ViewCount="5269" Body="&lt;p&gt;I found an old Motorola Maxtrac in a parts truck I bought. I'd like to program some channels into it with a Windows 7 computer and &lt;a href=&quot;http://www.dosbox.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DOSbox&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My first issue, is I'm having trouble identifying the radio because the id tag is all worn off. Therefore I don't know which rss software to use. Does anyone have the ability to ID this radio by sight? I believe its a commercial unit, not a radius model. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, I'm unable to communicate with the radio through dos box. I have tried a ton of different cycle numbers and none seem to work with my setup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am fairly confident that I have my comm ports setup correctly. I am using a usb to serial adapter and to a ribless cable. The usb to serial adapter is comm 8 and I have edited the DOSbox config file to reflect this. Is it possible to use this setup with this type of radio? Any help or guidance at this point would be appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hhbso.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hhbso.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ITVNq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ITVNq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/STjdQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/STjdQ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ych5t.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ych5t.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8597" LastEditorUserId="76" LastEditDate="2016-11-01T20:17:06.360" LastActivityDate="2017-06-19T20:37:30.917" Title="Motorola Maxtrac Programming with windows 7 and DOSBox" Tags="&lt;mobile&gt;&lt;radio-programming&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6813" PostTypeId="2" ParentId="6810" CreationDate="2016-11-01T19:44:47.830" Score="1" Body="&lt;p&gt;According to &lt;a href=&quot;https://www.youtube.com/watch?v=JxzOt95nc4w&quot; rel=&quot;nofollow noreferrer&quot;&gt;KE0OG's video review&lt;/a&gt; (about 6:36 in), the radio has a male SMA connector, and the antenna has a female SMA connector.  That's the reverse of the Baofeng connectors, which are reverse-SMA.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-12-02T03:13:33.013" LastActivityDate="2016-12-02T03:13:33.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6815" PostTypeId="1" AcceptedAnswerId="6817" CreationDate="2016-11-03T02:02:00.317" Score="5" ViewCount="249" Body="&lt;p&gt;I'm trying to understand how the mixer in a radio actually works, at a physics level. When looking at &lt;a href=&quot;http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1993/12/page32/index.html&quot; rel=&quot;noreferrer&quot;&gt;this article&lt;/a&gt; and studying the first schematic I realized I really don't understand what balanced and unbalanced means in that context.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/b09Nx.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/b09Nx.png&quot; alt=&quot;Schematic of a double-balanced mixer&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could you explain what the difference is between the signal on either side of the transformer so I can get a better picture of what transformation is happening as the signal passes through that component? &lt;/p&gt;&#xA;" OwnerUserId="4171" LastEditorUserId="4171" LastEditDate="2016-11-03T02:31:40.900" LastActivityDate="2016-11-05T02:37:54.307" Title="In the context of the mixer in my radio, what does balanced and unbalanced mean?" Tags="&lt;electronics&gt;&lt;mixer&gt;&lt;inductor&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6816" PostTypeId="1" CreationDate="2016-11-03T02:15:02.533" Score="5" ViewCount="946" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/o1swv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/o1swv.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the output from 4NEC2 the input power is 100 W.  On the left, in blue text, is Radiat-eff. which equals 15.41%.  On the right is Radiat-power which equals 94.88 W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would expect either the first to be 94.88% or the second to be 15.41 W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why the difference?&lt;/p&gt;&#xA;" OwnerUserId="8604" LastEditorUserId="8717" LastEditDate="2019-11-05T21:34:52.793" LastActivityDate="2019-11-05T21:34:52.793" Title="4NEC2 - Radiat-eff. vs. Radiat-power" Tags="&lt;antenna-theory&gt;&lt;software&gt;&lt;jargon&gt;&lt;antenna-modeling&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6817" PostTypeId="2" ParentId="6815" CreationDate="2016-11-03T05:32:41.310" Score="2" Body="&lt;p&gt;Looking at T1, on the unbalanced side of the transformer, one leg of the input is tied to the chassis ground (the zero volt reference); the other leg is driven by a voltage source.  Because the voltages on the two legs aren't equal but opposite, the input is said to be unbalanced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The current in the primary winding of the transformer creates a magnetic flux that induces an electromotive force in the secondary winding.  Because the secondary winding includes a center tap that is tied to chassis ground, the output voltage of the two legs of the secondary winding will be equal and opposite, and therefore balanced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're still confused about the &quot;equal and opposite&quot; part, you can look at the secondary winding with a center tap as two windings in series.  Let's assume for a moment that the secondary winding is generating 10 V at this particular instant, with the top end being positive and the bottom end being negative; since we're treating the secondary winding as two windings, the top winding will generate 5 V and the bottom winding will generate 5 V.  The bottom of the top winding, also known as the center tap, will be at 0 V because it's tied to chassis ground, so the top of the top winding will be at +5 V compared to chassis ground.  The top of the bottom winding is also tied to chassis ground, 0 V, which forces the bottom of the bottom winding to be at -5 V.  The +5 V and the -5 V are equal and opposite.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-11-03T05:32:41.310" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6818" PostTypeId="1" CreationDate="2016-11-02T10:22:28.720" Score="3" ViewCount="671" Body="&lt;p&gt;I would like to build a system in which the emitter emits omnidirectional RF signals, and the receiver gets a stronger signal (it does not have to be accurate) with a) closer distance from the emitter b) better pointing with the emitter (directional receiver). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Kind of like a &quot;you're getting warm/cold&quot; game.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's the simplest technology and type of circuit that would allow me to do this? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have thought of a signal strength circuit with a directional antenna, is that the simplest way? i.e. If I wire &quot;data in&quot; of a 315MHz transmitter such as this one &lt;a href=&quot;https://www.sparkfun.com/products/10535&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.sparkfun.com/products/10535&lt;/a&gt; to Vcc, and if I build a tuned (adjustable) tank circuit + OA81 diode + ADC at the receiver, could it work?&lt;/p&gt;&#xA;" OwnerUserId="8607" OwnerDisplayName="user42875" LastEditorUserId="8832" LastEditDate="2017-02-23T20:01:52.880" LastActivityDate="2017-02-23T20:01:52.880" Title="How to make a &quot;you're getting warm/cold&quot;/&quot;fox hunting&quot; game based on RF signals" Tags="&lt;receiver&gt;&lt;antenna-construction&gt;&lt;direction-finding&gt;&lt;fox-hunt&gt;" AnswerCount="2" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6819" PostTypeId="2" ParentId="1509" CreationDate="2016-11-04T14:18:34.510" Score="1" Body="&lt;p&gt;To obtain the Doppler shift you need to know the actual emitted frequency and the &lt;em&gt;range rate&lt;/em&gt; (the first derivative of range, the distance between you and the satellite).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To compute the range rate you need two 3D vector quantities: the satellite's position &lt;strong&gt;P&lt;/strong&gt; and velocity &lt;strong&gt;V&lt;/strong&gt; relative to you. The range rate is then given by the dot product of &lt;strong&gt;P&lt;/strong&gt; and &lt;strong&gt;V&lt;/strong&gt; divided by the magnitude of &lt;strong&gt;P&lt;/strong&gt;. The vector &lt;strong&gt;P&lt;/strong&gt; divided by its magnitude is the &lt;em&gt;unit position vector&lt;/em&gt;, so what you're really computing is that component of spacecraft velocity along the direction to you; how fast it moves perpendicular to that direction doesn't really matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although most satellite programs seem to compute range rate by finite differencing range, it can be computed analytically for more precise results. Standard orbit models like SGP produce velocity as well as position as functions of time, and it is also fairly straightforward to compute the position and velocity of a ground station on the rotating earth in inertial space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: this discussion ignores relativistic effects. At relativistic speeds, there will be an additional red shift (downward Doppler shift) due to time dilation making the spacecraft oscillator appear to run more slowly. For details, see the Wikipedia article on the Relativistic Doppler Effect.&lt;/p&gt;&#xA;" OwnerUserId="8615" LastEditorUserId="8615" LastEditDate="2016-11-04T14:27:03.097" LastActivityDate="2016-11-04T14:27:03.097" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6820" PostTypeId="1" AcceptedAnswerId="6821" CreationDate="2016-11-04T19:21:01.387" Score="2" ViewCount="254" Body="&lt;p&gt;I'm currently building a rc radio system using the 433mhz RFM69W transceiver, so far everything works fine, but i am not sure about the way i laid out my antenna and how the layout cripples the efficiency of it.&#xA;(The connection is stable up to 400m to 600m with a building in between at ~13dbm output power)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pEFLf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pEFLf.png&quot; alt=&quot;this is a crude but very accurate drawing of the layout&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The wires are each around 165 mm long to form a quarter wave monopole, the layout in the re-purposed radio is exactly like in the schematic above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My main concern is the bend in the antenna and the positioning of the ground wire, would you recommend a different antenna design (helical/pre-made?), keeping in mind that the joysticks eat up most of the room except for a few shafts in the middle/sides of the housing just like here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CExeG.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CExeG.jpg&quot; alt=&quot;example&quot;&gt;&lt;/a&gt;&#xA;(not my picture, but the rc controller he built this in is laid out just like the one I am using)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And would it make a big difference at all?&lt;/p&gt;&#xA;" OwnerUserId="8616" LastEditorUserId="76" LastEditDate="2016-11-04T20:48:17.420" LastActivityDate="2016-11-04T20:57:38.877" Title="Influence of bending and asymetric ground wire on monopole antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;equipment-design&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6821" PostTypeId="2" ParentId="6820" CreationDate="2016-11-04T20:57:38.877" Score="4" Body="&lt;p&gt;I'm not experienced with RC systems, but on general antenna design principles:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The bend is fine. It's too small a feature to have much effect.&lt;/li&gt;&#xA;&lt;li&gt;The “ground” wire (really better described as a second antenna element) is fine. The antenna will radiate better in the direction that wire runs than others.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The biggest problem with this layout is that your antenna is going to be obstructed by the user's hand. You would get better results by using an antenna which extends away from the controller's casing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't want to do that, I would suggest &lt;em&gt;swapping&lt;/em&gt; the roles of the two wires. Assuming your antenna “GND” is tied to the circuit ground of the rest of the controller, that circuit ground is already somewhat capacitively coupled to the user's hands, so it's best to put the other pole of the antenna in the least-coupling position.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this theoretically gives you a horizontally polarized antenna instead of vertical-or-45°-depending polarization, which might be worse — how much polarization matters depends on how reflective the environment you're operating in is.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-11-04T20:57:38.877" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6822" PostTypeId="2" ParentId="6815" CreationDate="2016-11-05T02:37:54.307" Score="4" Body="&lt;p&gt;A balanced mixer is one that suppresses the local oscillator (LO) input in the output. A double-balanced mixer (like the one you show here) suppresses both the RF input and the LO in the output. This is often accomplished with balanced transformers, hence the name.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because T1's secondary has a grounded center tap, the voltages on its two &quot;hot&quot; output terminals are always equal and opposite in polarity with respect to ground. Assume the LO has driven T1's top output (+) and the bottom output (-). This forward biases diodes D1 and D2, and because T1's center tap is grounded, the diodes effectively clamp the lower side of T2's secondary to ground. Diodes D3 and D4 remain off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Holding that state, now consider a second signal fed to T2's primary. Because the lower line of T2's secondary is clamped to ground, the RF input will appear at the IF output &quot;right side up&quot;, i.e., in phase; if the RF input is (+), then so is the IF output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now reverse the polarity of the LO input to make the bottom output of T1 (+) and the top (-). Diodes D3 and D4 conduct while D1 and D2 remain off, clamping the &lt;em&gt;top&lt;/em&gt; of T2's secondary to ground so that the RF input to T2 appears &lt;em&gt;inverted&lt;/em&gt; at the IF output, i.e. 180 degrees out of phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if there's no signal into T2, then the LO input to T1 does not appear at the IF, and by symmetry if there's no LO input signal into T1 then the RF signal into T2 also does not appear at the IF output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mathematically, mixing is multiplication. When you multiply two numbers with the same sign (both positive or both negative), the result is a positive number. When the operands have opposite signals (one positive, one negative), the output is negative.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So this circuit multiplies the LO and RF signals and their product appears at the IF output. This is why these mixers are sometimes called &quot;product detectors&quot; when used to detect, say, SSB or CW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This circuit is a way to multiply two analog signals with simple passive components. The same operation can be done with an exclusive-OR logic gate if a positive input is mapped to a logic '1' and a negative input is mapped to a logic '0'.&lt;/p&gt;&#xA;" OwnerUserId="8615" LastActivityDate="2016-11-05T02:37:54.307" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6823" PostTypeId="2" ParentId="6513" CreationDate="2016-11-06T01:20:58.833" Score="3" Body="&lt;p&gt;The K3NG keyer probably has all the parts you need except writing out to as a keyboard emulator, but some of the Arduino hardware that the K3NG keyer software runs on has the ability to output USB HID to a computer which makes it appear to be a keyboard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The K3NG keyer might actually fill all your electronic requirements for the users input also. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Info on Arduino as a USB HID Keyboard:&#xA;&lt;a href=&quot;https://arduino.stackexchange.com/questions/484/arduino-as-usb-hid&quot;&gt;https://arduino.stackexchange.com/questions/484/arduino-as-usb-hid&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;K3NG Keyer:&#xA;&lt;a href=&quot;https://github.com/k3ng/k3ng_cw_keyer/wiki&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/k3ng/k3ng_cw_keyer/wiki&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both the Arduino and the K3NG Keyer have open source communities that would jump in to help out with any problems you run into. &lt;/p&gt;&#xA;" OwnerUserId="4171" LastEditorUserId="-1" LastEditDate="2017-04-13T12:50:10.067" LastActivityDate="2016-11-06T01:20:58.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6824" PostTypeId="2" ParentId="2034" CreationDate="2016-11-06T01:34:28.697" Score="0" Body="&lt;p&gt;Using &lt;a href=&quot;http://websdr.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;WebSDR&lt;/a&gt;, you can find people making their receivers and antennas available on the Internet. This avoids any problems your setup might have. You can find live CW QSOs, listen in and even record if you wish.&lt;/p&gt;&#xA;" OwnerUserId="4171" LastActivityDate="2016-11-06T01:34:28.697" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6825" PostTypeId="1" AcceptedAnswerId="6826" CreationDate="2016-11-06T19:58:39.307" Score="12" ViewCount="387" Body="&lt;p&gt;Yesterday I saw the following antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iBbHc.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iBbHc.jpg&quot; alt=&quot;Antenna picture&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am very puzzled, at first glance it seems a simple dish but: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The mesh is really wide (low frequency?).&lt;/li&gt;&#xA;&lt;li&gt;It is pointing to Zenith. I think that most dish antennas rest in zenith position to offer less resistance to the wind. However, in that case it seems that the antenna can be moved just in AZ, and not in EL. What do you track pointing to the zenith?&lt;/li&gt;&#xA;&lt;li&gt;It has no feeder? There is a small box that I was unable to figure out what exactly was, but definitely it was not a usual feeder.&lt;/li&gt;&#xA;&lt;li&gt;Cables obstructing the aperture? Just take a close look and you will see how there are lines between the antenna focal point and the branch ends. (Although they could be non-conductive material, I was not able to distinguish them from that distance).&lt;/li&gt;&#xA;&lt;li&gt;Last but not least, taking a closer look to the image I noticed that the antenna was not a dish! Please, see how the part pointing towards 2 o'clock is not meshed and thus, the antenna is neither a dish!&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I did an extensive Google search and asked friends but no one had seen an antenna like this before. Any of you has a clue?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="8627" LastActivityDate="2016-11-07T05:56:12.533" Title="What kind of antenna is that one?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6826" PostTypeId="2" ParentId="6825" CreationDate="2016-11-06T20:13:38.887" Score="10" Body="&lt;p&gt;&lt;strong&gt;This is a “hex beam” antenna, a multi-band HF directional antenna.&lt;/strong&gt; It is aimed in the direction you called “2 o'clock” in the photo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radial members are structural support and the wires looped around are the antenna elements; the loops of different sizes at different heights are elements for different bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feed point is on the central mast, connected to the driven elements which are on the side which is &quot;not meshed&quot; and the wires instead go from the center to the perimeter.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-11-06T20:13:38.887" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6827" PostTypeId="2" ParentId="6825" CreationDate="2016-11-07T05:56:12.533" Score="3" Body="&lt;p&gt;This is a multi-band directional antenna called a hex beam. It is not a dish, but each layer of wires is a different band directed towards the portion of the hex that is missing. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is a relatively compact antenna and considered easier to assemble compared to other options allowing it to be mounted on smaller towers and give similar performance. &lt;/p&gt;&#xA;" OwnerUserId="4171" LastActivityDate="2016-11-07T05:56:12.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6829" PostTypeId="2" ParentId="5672" CreationDate="2016-11-07T19:12:56.147" Score="5" Body="&lt;p&gt;That's for charging a 3800mAh battery using the side jack.&#xA;To charge the BL-5L 3800mAh battery you must purchase a:&#xA;- TYT TH-UVF9 battery charger for 110VAC  or&#xA;- TYT TH-UVF9D  for 12VDC.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;These are fully regulated chargers&lt;/li&gt;&#xA;&lt;li&gt;Plugs directly into side of battery, not a charger base&lt;/li&gt;&#xA;&lt;li&gt;The AC wall wart has a charging indicator.&#xA; Red while charging, Flashing Green Red when charged.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8635" LastEditorUserId="4665" LastEditDate="2016-11-08T17:10:57.563" LastActivityDate="2016-11-08T17:10:57.563" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6831" PostTypeId="1" AcceptedAnswerId="6838" CreationDate="2016-11-08T09:07:56.103" Score="5" ViewCount="129" Body="&lt;p&gt;Purchased a HP 8711A some time ago to learn how to make better measurements. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried doing an OSL calibration with a 75ohms Agilent cal kit.&#xA;When reconnecting the short after succesful calibration, I would expect to have a return loss of 0dB across the whole calibrated frequency span.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, what I consistently get is something like this:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/LlYlh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LlYlh.jpg&quot; alt=&quot;S after OSL Calibration&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know it's only .5dB, and this might be the limits of the hardware, but what I don't understand is that I can replicate this exact behaviour: after every calibration, RL of the short starts around 0dB in the beginning of the frequency span, and ends around .5dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If these are measurement errors, I'd expect the outcome to change between different calibrations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or am I wrong somewhere?&lt;/p&gt;&#xA;" OwnerUserId="8263" LastEditorUserId="8263" LastEditDate="2016-11-11T11:40:32.363" LastActivityDate="2016-11-12T14:22:27.810" Title="Measurement/calibration error after OSL calibration on VNA" Tags="&lt;measurement&gt;&lt;calibration&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6832" PostTypeId="1" AcceptedAnswerId="6833" CreationDate="2016-11-09T20:26:53.803" Score="5" ViewCount="253" Body="&lt;p&gt;I have an ICOM-7100 that I've installed in my mobile as my primary (nay, only) HAM transceiver; and I'm trying to avoid wasting a ton of space in my vehicle (not to mention money) for a proper scanner, or for a CB¹, to achieve fuller coverage of the available spectrum-space. Unfortunately, some poking around frequency-listing websites reveals that a lot of the interesting non-HAM action happens over “NFM” — which I finally ascertained² to be a 2.5kHz-deviation FM mode used by commercial / emergency-services devices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd really like to scan across such channels without installing yet-more equipment in my passenger compartment; and yet I can't find any mention whatsoever of FM deviation in my ICOM-7100 manual. Is there any way for me to intelligibly receive (or for that matter, transmit) 2.5kHz-deviation FM signals with my transceiver?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;¹ Not very related, but to my annoyance, it looks like there's no MARS/CAP modification for the 7100 that covers the CB “11-meter band”, 26.965–27.405MHz. I might &lt;em&gt;have&lt;/em&gt; to install a second damn box to talk to truckers. Bah.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;² It also looks like a huge set of the interesting frequencies are digital “Project 25,” P25, mode; I'm just assuming there's no hope of receiving those on a HAM transceiver. :P&lt;/p&gt;&#xA;" OwnerUserId="8465" LastEditorUserId="76" LastEditDate="2016-11-09T20:58:01.067" LastActivityDate="2016-11-09T20:58:01.067" Title="Receiving commercial / public-safety on a general-coverage HAM transceiver" Tags="&lt;transceiver&gt;&lt;fm&gt;&lt;equipment-operation&gt;&lt;icom&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6833" PostTypeId="2" ParentId="6832" CreationDate="2016-11-09T20:41:53.613" Score="3" Body="&lt;p&gt;Regarding your original question, according to page 5-6 of the &lt;a href=&quot;http://www.icomamerica.com/en/downloads/DownloadDocument.aspx?Document=632&quot; rel=&quot;nofollow noreferrer&quot;&gt;IC-7100 Advanced Instructions&lt;/a&gt; document, to receive &quot;narrow&quot; FM of 2.5 kHz deviation, select FILTER2 or FILTER3.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-11-09T20:41:53.613" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6834" PostTypeId="1" CreationDate="2016-11-10T06:24:20.513" Score="3" ViewCount="399" Body="&lt;p&gt;I'm trying to build a headset for my Yaesu FT-270r, which replaced a FT-250r.  I had a working setup with the FT-250r.  An electret microphone element connected to the MIC/PTT pin of the four-way connector, and a 2k2 resistor with one end connected to MIC/PTT pin, and the other end to the PTT switch and then the other side of the switch to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem I'm having with the 270 is that if I just have the mic element across the MIC/PTT pin and ground, it activates the PTT regardless of the state of the PTT switch.  If I add enough series resistance that merely connecting the mic element does not activate the PTT, then the PTT switch works correctly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, with enough series resistance that the PTT switch needs to be pressed to activate the PTT, I'm getting no (or maybe very low) audio.  If I don't use the series resistor, I get good audio, but of course that's not much use if I'm transmitting all the time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe I'm doing something wrong, but it's such a simple circuit, and I re-built it from scratch after the first version didn't work.  So I'm a bit perplexed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is anyone aware of a difference between the 250 and the 270 in this area?  Any other ideas?&lt;/p&gt;&#xA;" OwnerUserId="8648" LastEditorUserId="5222" LastEditDate="2016-11-11T18:17:29.547" LastActivityDate="2016-11-11T18:17:29.547" Title="Building a headset for a Yaesu FT-270r" Tags="&lt;diy&gt;&lt;ht&gt;&lt;yaesu&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6835" PostTypeId="2" ParentId="6816" CreationDate="2016-11-10T13:21:22.187" Score="2" Body="&lt;p&gt;I'm a NEC2 user, never used 4NEC2, but I think it's the same engine underneath.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiated efficiency is low because either:&#xA;- a lot of power is absorbed by the ground,  or&#xA;- you have a structure error, usually a violation of the guidelines near the feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two ways of calculating efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The first just considers the currents on the structure&lt;/strong&gt;. NEC doesn't use a power excitation, we specify a fixed voltage source excitation. NEC2 solves for the currents on all the segments. The input power is found by multiplying the applied voltage with the feed-segment-current found in the solution. (The 4NEC2 interface must be scaling the calculated input power to get your specified 100 W, fair enough).&#xA;NEC2 also finds all the losses in the structure, from loads if any, and from the losses in the structure, as you've specified a finite conductivity. These losses I think will account for the 5 W and the 94%. NEC2 prints out all of this - input voltage and power, losses in loads, losses in wire, etc. The remainder of the power must have been radiated.&#xA;If the structure is close to the ground, the interaction matrix is also modified to take this into account, but I'm not sure if these ground losses are included in structure loss.&#xA;A problem can arise when there is a modelling error, especially near the feedpoint, that the current found on the feed segment is not accurate. This leads to an incorrect input power, which upsets all the other power and loss calculations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Second, from the far field patterns&lt;/strong&gt;. The far fields are calculated from the currents on the structure, including the full lossy reflection from the ground if present. This is not a loss in the antenna, but a loss in the radiating EM waves. In the far field there are only TEM waves, and power density can be found from the electric field. NEC integrates the power density of the antenna pattern,  over the sphere, or in your case the half-sphere, and finds the total radiated power. This power I think is coming out to be the 15 watts that you see.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The total radiated power is a reflection of the current on &lt;em&gt;all&lt;/em&gt; segments of the model, and is usually more accurate than the calculated input power. It also includes the ground reflection losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Modelling errors&lt;/strong&gt;&#xA;If you have a modelling error, it is possible that for example the actual input power to the structure is really only 25 watts, with 5 lost in the structure resistance, and 5 lost in the ground, 15 radiated, but somehow the current on the feed segment is incorrect. This has a small impact on the patterns, as there are many segments, but a large impact on the calculated input power, as this is done with only one segment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Some modelling notes&lt;/em&gt;: I can't see much about your antenna model. If your model is simple, like a dipole with 5 to 10 fairly constant radius segments, then there will be no problem with the feedpoint impedance calculation, and the ground loss will be the cause of the power difference you see. If you have 31 segments as it seems to say, then make sure they are nice and thin, like a wire dipole. A pipe dipole shouldn't have so many segments. And the feed segment should be the same length and radius as its neighbours.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A test to try: change your sommerfeld - norton ground to a perfect ground and confirm that structure efficiency matches radiated efficiency. Or set the structure conductivity to infinite (just leave it out) and see what happens.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2016-11-11T18:37:50.837" LastActivityDate="2016-11-11T18:37:50.837" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6837" PostTypeId="2" ParentId="6834" CreationDate="2016-11-10T16:31:04.113" Score="1" Body="&lt;p&gt;This sounds very similar in interface to the FT-60, which I recently prototyped such an adapter for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try &lt;strong&gt;putting the microphone and PTT switch in series&lt;/strong&gt;. This is how the MH-37A4B earbud headset for the FT-60 seems to be wired, and ensures that the resistance is high when PTT is not engaged.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my case, I then found I had to add &lt;em&gt;parallel&lt;/em&gt; resistance (2.2 kΩ, not rigorously chosen) across the element to engage PTT, which will also of course reduce the audio level, but may be better than what you are trying.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-11-10T16:31:04.113" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6838" PostTypeId="2" ParentId="6831" CreationDate="2016-11-11T11:40:00.287" Score="2" Body="&lt;p&gt;Seems like I was indeed wrong.&#xA;The displayed trace displayed was Data/Memory (hence the /M in the top of the screenshot).&#xA;After redoing the calibration and selecting Data for display, the unit is within +/- .04dB in the whole range. My mistake...&#xA;Thanks to Default95401 on the Yahoo HP/Agilent test equipment group for pointing that out...&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2016-11-11T11:40:00.287" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6839" PostTypeId="1" AcceptedAnswerId="6840" CreationDate="2016-11-12T04:05:44.293" Score="4" ViewCount="3524" Body="&lt;p&gt;I've often heard people saying that 4G uses the 1800 MHz band but precisely what all frequencies does it work upon? Does it mean that is just uses one frequency i.e. 1800 MHz, well in that case wouldn't there be interference among signals carrying different data.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What is the difference between a frequency band and frequency channel?&lt;/li&gt;&#xA;&lt;li&gt;Why don't we directly use frequency ranges to tell what a particular technology operates upon instead of telling what band it uses. For example, why do we say that 4G uses 1800 MHz band instead of saying it uses frequencies between X MHz and Y MHz. Wouldn't it be easier to understand?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="8657" LastEditorUserId="76" LastEditDate="2016-11-12T15:56:11.273" LastActivityDate="2016-11-12T15:56:11.273" Title="How many frequency channels are there in a frequency band?" Tags="&lt;frequency&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6840" PostTypeId="2" ParentId="6839" CreationDate="2016-11-12T05:27:40.197" Score="2" Body="&lt;p&gt;A frequency band represents a range of frequencies, which are usually defined by law or regulation.  For instance, the 1800 MHz GSM band ranges from 1710.2 MHz to 1879.8 MHz, according to &lt;a href=&quot;https://en.wikipedia.org/wiki/GSM_frequency_bands&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;.  Bands are wide enough to contain many signals without interference (universally, as far as I know).  Because the frequency bands for a particular service are generally widely-spaced, it's usually quite clear what you mean by the usual shorthand definition of a band, if you're looking at a table showing the frequency ranges for the various bands for a particular service.  Yes, it would be more clear to say &quot;the 1710.2 to 1879.8 MHz band&quot;, but &quot;the 1800 MHz band&quot; rolls off the tongue much more easily.  In amateur radio practice, the shorthand name for a band usually refers to its approximate wavelength in meters rather than the frequency, for historical reasons; for instance, the &quot;20m band&quot; in the US ranges from 14 &amp;ndash; 14.350 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A channel is also a frequency range, which is usually defined by law, regulation, or general practice.  However a channel is usually much narrower than a band, because a channel is typically only wide enough for a single signal.  The intent of dividing a band into channels is to prevent interference.  Sometimes channels are given numbers, but not always.  Not all services are channelized; the amateur radio service generally uses unnumbered channels for VHF and UHF FM, according to state-wide (US) or nation-wide band plans, and the 60m band is channelized in the US because it is shared with federal government users, but other bands are usually not channelized.  In other words, operators using other ham bands can generally select any frequency inside the band, as long as the entire bandwidth of the signal is within the band allowed by law.  (Activity inside a ham band is often segregated by frequency according to voluntary &quot;gentlemen's agreements&quot; to reduce interference.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-11-12T05:27:40.197" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6842" PostTypeId="2" ParentId="6816" CreationDate="2016-11-12T18:59:04.563" Score="2" Body="&lt;p&gt;I just did a bit of tinkering with 4NEC2 and I've got an answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Input power is the power generated by the source, and ignores all losses. It might also be called &quot;Total power&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;Radiat-power&quot; calculation in 4NEC2 is the total amount of the power from the source that is &lt;em&gt;not dissipated as resistive losses in the feed system or antenna structure&lt;/em&gt;. Essentially it is the power that is not lost as heat in the antenna system itself, and it ignores external loss from the ground in the near field. It might better be described as &quot;available power&quot;, and it is the maximum power that &lt;em&gt;could&lt;/em&gt; be radiated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Radiat-Eff&quot; is the effective amount of power that makes it in to the far field, and can be thought of as &quot;useful power&quot;. It takes in to account destructive interference from interacting elements of the antenna as well as ground losses in the near field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can confirm this interpretation of the numbers by running the same basic model with a few small changes in wire characteristics in each iteration. If we build a simple resonant 1/2 wave 20 meter vertical dipole from 1mm diameter wire, oriented a 6 feet above &quot;real&quot; average ground using ideal wires (no wire load/material specified), &lt;a href=&quot;https://i.imgur.com/e9pGmOZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;we can see that &quot;radiat-eff&quot; is quite low, around 25%, but &quot;Structure Loss&quot; is 0, and &quot;Radiat-power&quot; is 100w.&lt;/a&gt; Changing the length of the wire to a non-resonant length, moving it up or down relative to ground, changing wire diameter or antenna polarization, etc has no effect on the radiated power and structural loss, but radiated efficiency does change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, &lt;a href=&quot;https://i.imgur.com/SMVK6pG.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;placing a 0.6 wavelength ideal (no load) wire in parallel to our  vertical dipole&lt;/a&gt; and spaced about 9 feet from our dipole, we've formed a vertically oriented, ideal 2 element yagi. Radiation efficiency drops by about 2% to 23%, which is not surprising. This decrease in radiated efficiency in a model with no structural losses is due to increased coupling to the very lossy ground, owing to the now larger surface area and aperture of the antenna. Our structural losses are still 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we remove the reflector and place a wire load on the original dipole and specify it as &quot;copper&quot; &lt;a href=&quot;https://i.imgur.com/yUZ5o2G.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;we can observe a small drop compared to the perfect dipole, from about 25.2% &quot;radiat-eff&quot; to around 24.9%&lt;/a&gt;. Structure loss becomes non-zero, in the case of my test model about 1 watt, and &quot;Radiat-power&quot; is now 99 watts. Changing wire diameter has the expected results of increasing or decreasing resistive losses. A small part of the input power has been lost as heat in the wire itself. Logic might suggest that a loss of 1 watt (or about 1%) in the radiated power should result in a loss of 1% in the radiation efficiency as well, but the relationship between complex impedance, power, and losses often isn't linear in antenna systems. Ground losses are so dominant in radiation efficiency that resistive losses are tiny by comparison.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we &lt;a href=&quot;https://i.imgur.com/KIYR1cY.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;put an ideal reflector back in to the model beside our now &quot;realistic&quot; vertical dipole with resistive losses&lt;/a&gt;, &quot;radiat-power&quot; changes, but not by very much, jumping from 1.08 watts to about 1.5 watts. The radiated efficiency falls considerably though, from 24.9% to about 22.75% (note that this is slightly lower than the ideal yagi), or about 3 times the increase in structural loss. We can now see the original increase in losses in the ideal yagi due to ground interaction, &lt;em&gt;plus&lt;/em&gt; a small increase due to increased structural losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We might logically expect that the &quot;ideal&quot; reflector, while decreasing radiated efficiency, wouldn't change structural losses, since that part of the structure experiences no loss. However, the model assumes that the current is distributed on our vertical dipole more or less in an ideal way when it is the only element in the model, meaning that total surface area and such are something close to maximized. When you inject another element, whether that element actually generates real losses or not, you alter the current distribution on the element that &lt;em&gt;does&lt;/em&gt; experience structural loss, resulting in an increase in current in some areas and a decrease in others. This is due to things like proximity effect, asymmetrical coupling of power between physically separated surfaces of different elements, etc. This redistribution of power is usually (but not always) to the detriment of antenna efficiency because it makes the wire effectively smaller. However, it is possible to take advantage of this effect to &quot;balance&quot; a conductor on which the current would be &quot;crowded&quot; in some areas due to geometry, but that's a lecture for a different day. I suspect the extra 0.5 watts of loss is due to proximity effect pushing some of the current off of the portion of the lossy dipole that faces the reflector, and on to the side opposite the reflector, reducing the wire's effective diameter, however this is just a theory. 4NEC2 does not have sufficiently detailed FEA to actually see cross-sectional current distribution on a single conductor, and the model that might allow us to test that theory within 4nec2 would be rather complex.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.imgur.com/wmCsKCQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;If we add a wire load to the reflector element&lt;/a&gt; we see that the radiated power drops again by about 0.6 watts, or ~0.6%, but the radiated efficiency drops by considerably less than that, just 0.1%; The same non-linearity we saw before, with changes in ground interaction dwarfing the structural losses, is responsible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In summary, Radiated Power ignores all losses not inherent to the antenna and feed line conductors themselves. If you specify wire material, it will always be less than input power, but otherwise it will always be the same as input power. Radiated efficiency is a much more complex calculation that considers ground losses and field interactions in the near field, and likely field interactions in the transition zone between near and far field. We can confirm that it is considering field interactions by running the &quot;realistic&quot; vertical yagi model with a perfect ground. Doing so reveals a small disparity between Radiated Power (97.91 watts or 97.91%) and Radiated Efficiency (97.79%). That 0.13 watts is lost due to cancellation of fields generated by the two elements.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-11-12T18:59:04.563" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6843" PostTypeId="1" AcceptedAnswerId="6844" CreationDate="2016-11-13T18:36:13.953" Score="3" ViewCount="798" Body="&lt;p&gt;I have a 5V active GPS antenna, and want to try using it on a device with a 3.3V bias provided.  Obviously, operating at an over-voltage can damage or destroy the LNA.  But what happens when the voltage is too low?  Will it work with reduced gain, or will it cause some weird state and distort the signal?  Is there a risk of damage of components?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do not know the specifications of my antenna nor my device that provides the 3.3V bias voltage.&lt;/p&gt;&#xA;" OwnerUserId="5031" LastEditorUserId="76" LastEditDate="2019-03-13T01:46:11.813" LastActivityDate="2019-03-13T01:46:11.813" Title="Generally, what happens when you power a GPS antenna or other RF amplifier with a low voltage?" Tags="&lt;lna&gt;&lt;gnss&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6844" PostTypeId="2" ParentId="6843" CreationDate="2016-11-13T22:46:54.743" Score="2" Body="&lt;p&gt;It's hard to say whether your active antenna would work properly if provided with 3.3 VDC instead of 5 VDC.  I doubt that any damage would be done, but I'm not the engineer that designed the antenna.  You might consider adding a boost regulator (and the other parts it requires) to your circuit, which could convert 3.3 VDC to 5 VDC.  Here's &lt;a href=&quot;http://www.mouser.com/ProductDetail/Torex-Semiconductor/XC9110C501MR-G/?qs=sGAEpiMZZMsGzNf1qgY4ZMpDq1nayjCKBLbGmREn0Y0%3d&quot; rel=&quot;nofollow noreferrer&quot;&gt;such a part&lt;/a&gt;, selected more-or-less at random from the astonishing variety of boost regulators on offer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your LNA may work fine with 3.3 VDC, so you might as well just try it as-is first.  A boost regulator has an inherently-noisy switching power supply inside, which might raise the noise level at the frequencies used by the GPS satellites, as @AndrejaKo points out, so there is some risk that a boost regulator would impair your circuit.  However, the switching power supply internal to the boost regulator uses many of the external parts that the boost regulator requires; this gives the engineer an opportunity to reduce the noise level on the band of interest by tweaking the component values, if the noise proves to be a problem.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-11-16T17:31:38.963" LastActivityDate="2016-11-16T17:31:38.963" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6845" PostTypeId="1" CreationDate="2016-11-14T12:30:20.473" Score="3" ViewCount="201" Body="&lt;p&gt;For a school assignment I need to calculate a link budget between two half wave dipole antennas, but I am stuck at calculating the polarisation losses in the antennas. the antennas are ideal and matched.&#xA;The antennas are 6 KM apart, the signal strengt Ps = 10 W, frequency f= 100 MHz, angle between the antennas is 50 degree and the max Gain of the antennas is 2,13dB.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/MB4gr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MB4gr.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have to calculate the link budget between S and E3.&#xA;What the teacher did the following to get the Gains with polarisation loss:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Gs3  = 10log (10^2,13 * (sin^3(90+50))^2 ) = -1,707dBi&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;G3s  = 10log(sin^2(90-50) ) = - 1,707dBi&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The problem is that I am not getting these numbers when I use these formulas and different now I am seriously confused about how I am supposed to calculate this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do know that the original formula for polarisation loss in dB is: 20 log( Cos^2(a)). But even when I use this formula I am not getting the same numbers as what the teacher gave us.&lt;/p&gt;&#xA;" OwnerUserId="8673" LastEditorUserId="8673" LastEditDate="2016-11-14T14:28:07.673" LastActivityDate="2019-01-24T01:58:36.113" Title="Polarisation loss Dipole antennas" Tags="&lt;antenna&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6847" PostTypeId="1" AcceptedAnswerId="6849" CreationDate="2016-11-15T04:36:31.543" Score="7" ViewCount="6920" Body="&lt;p&gt;I know the difference between AM and FM, but could anyone explain to me what is the differences between single side band AM and conventional FM?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far as I know the SSB modulation will reduce the transmitting power. But what is the exact function of SSB AM compared to FM ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope someone can explain to me, thank you!&lt;/p&gt;&#xA;" OwnerUserId="8677" LastActivityDate="2021-01-11T23:36:12.853" Title="Single Side Band AM vs FM" Tags="&lt;ssb&gt;&lt;fm&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6848" PostTypeId="1" AcceptedAnswerId="6855" CreationDate="2016-11-15T07:02:21.087" Score="2" ViewCount="1477" Body="&lt;p&gt;I did a (Amateur Radio) search for 'hentenna' and got not one hit. So, to boldly go where no man has gone before, I want to explore the strange new world of creating a beam antenna with &lt;strong&gt;Hentenna&lt;/strong&gt; DE, with a reflector, most likely being a non-driven version of itself, and, to save wire and space, Yagi-type directors (rods)...maybe six of them.&lt;br&gt;&#xA;  This &lt;strong&gt;Hengi&lt;/strong&gt; doesn't seem too different from a &lt;strong&gt;Quagi&lt;/strong&gt;; though, because the Hentenna is a long rectangle &lt;em&gt;perpendicular to its polarization&lt;/em&gt;, &lt;strong&gt;rod directors would be perpendicular to the Hentenna rectangles' long side&lt;/strong&gt;.&lt;br&gt;&#xA;  I would approach it like the original 14ft., 2M Quagi. There are some &quot;Hengi&quot; beam antennas but they use 1 or 2 non-driven versions of the DE as directors. Would the &lt;strong&gt;perpendicular&lt;/strong&gt; rods work like they do in Quagis and Yagis where they are more or less in the same plane as the DE? &#xA;  &lt;a href=&quot;http://n6nb.com/quagi.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://n6nb.com/quagi.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kIJOB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kIJOB.png&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also this:&lt;br&gt;&#xA;  &lt;a href=&quot;https://i.stack.imgur.com/yN0xi.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yN0xi.jpg&quot; alt=&quot;With a hentenna instead of a skeleton slot.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8477" LastEditorUserId="8477" LastEditDate="2016-11-25T21:01:20.160" LastActivityDate="2017-01-27T21:36:08.233" Title="Hentenna beam...is it possible?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6849" PostTypeId="2" ParentId="6847" CreationDate="2016-11-15T10:27:59.590" Score="12" Body="&lt;p&gt;First of all, you're not 100% right that SSB will reduce transmit power. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I often keep talking on SE about power spectral density. So let me start with that again and first assume that we have a radio that has fixed output power of 100 W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let's first take a (simplified) look at AM:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/8l0kd.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8l0kd.png&quot; alt=&quot;AM spectrum&quot;&gt;&lt;/a&gt;&#xA;We have a carrier and two sidebands. One sideband, the part in red on the picture,  actually carries useful information. The carrier is not needed, if we can precisely tune to the frequency, and the other sideband is just a copy of the red sideband. What is important is that when we sum the power over the frequency, we'd get the full power that the transmitter can provide. &#xA;So for 3 kHz of audio bandwidth, we have 6 kHz of RF bandwidth and 100 watts unevenly spread out over that range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now when we're looking into SSB, first we need to better define AM. The usual colloquial AM is actually amplitude modulation, double sideband with carrier. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;SSB is also AM, just as you mentioned, but it's amplitude modulation, single sideband with suppressed carrier.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Kqu1R.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Kqu1R.png&quot; alt=&quot;SSB spectrum&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case, for 3 kHz of audio bandwidth, we'll have our 100 W spread over not 6 kHz, but just 3 kHz. Furthermore, the carrier is eliminated as well, reducing the wasted power even more. Also, only the useful information from the red sideband is transmitted. So we can either run SSB at lower power, and get same useful density as with AM, or we can run SSB at high power and get much higher density compared to AM, resulting in better signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case of FM, we'll get a symmetrical spectrum again:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/mVomU.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mVomU.png&quot; alt=&quot;FM spectrum&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case, we'll usually get wider spectrum than usual AM which will be from around 10 kHz (European CB) to 25 kHz (older &quot;wideband&quot; FM transceivers, still used for amateur radio in some areas). The usual formula is BW=2*(Baudio+MaxDeviation). So for our 3 kHz of audio and deviation of 2 kHz, we'll need 2*(3+2)=10 kHz of bandwidth. It should also be noted that until recently, it was difficult to get low deviation values.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So again, we'll be spreading out our 100 W over wider bandwidth. On the other hand, FM does not suffer from the same issues as the AM does, so we basically get better audio quality from FM than we get from AM. The downside is that FM requires &quot;large&quot; bandwidth, resulting in lower power spectral density at the receiver. For line-of-sight communications, usually, the received power is more-or-less OK, so we can afford to waste some bandwidth for higher audio quality. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, when we need to cover grater distances, this can be an issue, and that's why SSB is often used. On shortwave, we also have the problem of bandwidth. One FM channel is around 3 SSB channels, so in cases where bandwidth is highly constrained, FM can be a problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So why aren't we just using wide SSB on VHF/UHF, where we have plenty of bandwidth?&lt;br&gt;&#xA;Well, the reasons are a bit historical. Basically, FM is much more immune to badly adjusted transmitters and receiver frequencies, compared to SSB and it's more difficult to create stable frequency reference in a mobile rig.   Furthermore, up until recently, it was a bit hard to make a small, compact, SSB transceiver. In the meantime, FM infrastructure already entrenched itself, so there's not as much demand for such devices.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2016-11-15T10:27:59.590" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6850" PostTypeId="2" ParentId="6847" CreationDate="2016-11-15T15:02:34.637" Score="9" Body="&lt;p&gt;Firstly, FM is a constant-envelope modulation, meaning the amplitude is constant. SSB, being a kind of amplitude modulation, obviously does not have a constant amplitude. Consequently, FM can employ a non-linear amplifier which is more power efficient, and thus has a longer battery life in mobile operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, SSB signals add with each other and also noise linearly. This can be good or bad, depending on what you are trying to accomplish. For example, aviation communications use AM so if two stations transmit at the same time, both can be heard. With FM, only the stronger station will be heard due to the &lt;a href=&quot;https://en.wikipedia.org/wiki/Capture_effect&quot; rel=&quot;noreferrer&quot;&gt;FM capture effect&lt;/a&gt;. Bad for air traffic control, but it also means better noise rejection in the demodulated audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, SSB channels are narrower, only as wide as the baseband passband. For voice channels this is typically 4 kHz. The width of an FM channel depends on the deviation in use, but for VHF amateur use channels are usually 15 kHz wide. As the channel gets wider, the noise power in it increases, and assuming a constant transmitter power, this means signal-to-noise ratio goes down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So as a general rule, a narrower channel means more range for every watt of transmiter power. This makes SSB a better choice for long paths on HF. On VHF and higher, range is usually limited by terrain and not power. The natural noise floor is also lower. This makes the power efficiency of SSB less important, and the increased signal quality of FM tends to win out in most applications. Long or weak path VHF applications such as moonbounce, EME, or 6M DX huntin favor SSB over FM for this reason.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-11-16T13:51:39.410" LastActivityDate="2016-11-16T13:51:39.410" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6852" PostTypeId="1" CreationDate="2016-11-17T00:29:47.307" Score="1" ViewCount="773" Body="&lt;p&gt;I have a wav file that has a selective calling tone in it. Is it possible to decode a selective call tone from a wav or mp3 file ? &lt;/p&gt;&#xA;" OwnerUserId="8687" LastActivityDate="2016-11-18T15:03:05.623" Title="Software to decode selective calling tones" Tags="&lt;tone-squelch&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6853" PostTypeId="2" ParentId="6852" CreationDate="2016-11-17T00:52:51.473" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://github.com/EliasOenal/multimon-ng&quot; rel=&quot;nofollow noreferrer&quot;&gt;multimon-ng&lt;/a&gt;, which I have used for other purposes, claims to be able to decode selective calling tones of the following protocols, among other things:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;ZVEI1 ZVEI2 ZVEI3 DZVEI PZVEI&lt;/li&gt;&#xA;  &lt;li&gt;EEA EIA CCIR&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;However, I tried it out with a couple of sample files I found on the Internet and it didn't produce any output.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-11-17T00:52:51.473" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6855" PostTypeId="2" ParentId="6848" CreationDate="2016-11-17T13:45:32.203" Score="6" Body="&lt;p&gt;Let me combine the following statements of your question&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I want to explore (the strange new world of creating a beam antenna)&lt;/p&gt;&#xA;&lt;p&gt;to boldly go where no man has gone before&lt;/p&gt;&#xA;&lt;p&gt;Would the perpendicular rods work like they do in Quagis and Yagis where they are more or less in the same plane as the DE?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I would take the following approach:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Figure out why you want to do this, e.g. extra forward-gain, extra FB-ratio and write it down, compared to a much simpler design (such as a vertical yagi with the same lenght/elements) call this your &amp;quot;success criteria&amp;quot;&lt;/li&gt;&#xA;&lt;li&gt;Get a freeware (or paid for) antenna modelling program, there are various, such as &lt;a href=&quot;http://www.qsl.net/4nec2/?&quot; rel=&quot;noreferrer&quot;&gt;4NEC2&lt;/a&gt; or &lt;a href=&quot;https://www.eznec.com/&quot; rel=&quot;noreferrer&quot;&gt;EZNEC&lt;/a&gt;, and familiar yourself with the workings. There are others as well, these are the two which simply jump to mind for me.&lt;/li&gt;&#xA;&lt;li&gt;Model your design in the program, experiment with element positions, size, height, length, until you have a good idea if you can get close to your &amp;quot;success criteria&amp;quot;&lt;/li&gt;&#xA;&lt;li&gt;Once happy with the modelling, build your design, and test.&lt;/li&gt;&#xA;&lt;li&gt;If you want you can build a reference antenna (such as a yagi) and compare the two antenna's.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Lastly I would advice: have some fun, and enjoy the modelling and building.&lt;/p&gt;&#xA;&lt;p&gt;To answer your question:&#xA;I have no idea if your perpendicular rods work in the way you propose. I could not find any reference material, nor do I have experience with such. However as your question indicates, this is more an experiment for you then a theoretical question.&lt;/p&gt;&#xA;&lt;p&gt;Saying that; there is an article describing a &amp;quot;Hentenna Beam&amp;quot; but slightly different than you propose. You can find this &lt;a href=&quot;http://www.hamuniverse.com/n5nns4elhentenna.html&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;. It is not very scientific, but it might help you with your endeavours.&lt;/p&gt;&#xA;&lt;p&gt;An interesting read is an article about an &amp;quot;Hentenna with Reflectors&amp;quot; which might help you starting while adding elements to your design. You can find that &lt;a href=&quot;http://www.qsl.net/dk7zb/Quadlong/Hentenna.htm&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Have fun exploring and experimenting !&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-11-17T13:56:51.803" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6856" PostTypeId="2" ParentId="6852" CreationDate="2016-11-17T15:51:04.080" Score="1" Body="&lt;p&gt;I would use the application Mathematica (by &lt;a href=&quot;http://www.wolfram.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wolfram&lt;/a&gt;) which has a lot of computational audio features for decoding audio streams via a given codex protocol.  Mathematica is not for everyone and as the name suggests it is a very mathematically oriented application.  Plus, it is something you have to buy yet there is a free trial period you could use to experiment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example of how Mathematica is used to perform various coding and decoding functions from an audio stream, this &lt;a href=&quot;http://www.wolfram.com/language/11/computational-audio/create-and-decode-a-morse-code-signal.html?product=mathematica&quot; rel=&quot;nofollow noreferrer&quot;&gt;page&lt;/a&gt; describes how Morse Code can be decoded from an audio stream such as wav or mp3 file (note: in this particular example, the audio stream is created as well but you can avoid those steps).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mathematica has many other audio computation features with a whole variety of graphic display methods.  I use Mathematica every single day for dabbling in computations of General Relativity and also for augmenting the computational and graphic display of antenna analysis problems in concert with NEC4 (the licensed version of NEC, similar to NEC2 but much better).&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2016-11-17T15:51:04.080" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6857" PostTypeId="2" ParentId="6852" CreationDate="2016-11-18T15:03:05.623" Score="1" Body="&lt;p&gt;So, you mean something that will give you the sequence of calling tone digits like used in ZVEI1 to ZVEI5?&lt;/p&gt;&#xA;&lt;p&gt;Yeah, those were fun 5 minutes:&lt;/p&gt;&#xA;&lt;p&gt;I got an example from &lt;a href=&quot;http://www.sigidwiki.com/wiki/ZVEI_Selcall&quot; rel=&quot;nofollow noreferrer&quot;&gt;the sigid wiki&lt;/a&gt; (specifically ZVEI1-5), converted it to mono WAV (it's stereo for some unclear reasons), and built this flow graph in GNU Radio companion from scratch:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Gbmzv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Gbmzv.png&quot; alt=&quot;Decoder Flowgraph&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;What is missing is a lookup table at the end that converts frequencies to tone digits. That's about ten lines of Python :)&lt;/p&gt;&#xA;&lt;p&gt;In action, this looks something like&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.imgur.com/jVj0kiD.gif&quot; alt=&quot;Decoder in action&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;with the plot showing the instantaneous frequency. You'd just look for the right sequence of frequencies and then you'd have your decoder. (yes, timing recovery aside)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2016-11-18T15:03:05.623" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6858" PostTypeId="2" ParentId="6753" CreationDate="2016-11-20T01:28:00.957" Score="1" Body="&lt;p&gt;There is 'amodem' for Linux;&#xA;&lt;a href=&quot;https://github.com/romanz/amodem&quot; rel=&quot;nofollow&quot;&gt;https://github.com/romanz/amodem&lt;/a&gt;&#xA;It transmits checksum (may be spoofed, use gpg keys IF IT REALLY MATTERS.&#xA;I recommend a low to medium bitrate (as per the README) unless TX/RX conditions are ideal. Observe the &lt;code&gt;--calibrate&lt;/code&gt; flag.&#xA;Tested w. Baofeng UV-5R.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-11-20T01:28:00.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6859" PostTypeId="2" ParentId="5622" CreationDate="2016-11-20T03:51:28.840" Score="0" Body="&lt;p&gt;This looks more like some kind of interface box to me... say land line to radio or something like that. I am just guessing mind you but this does not look like any radio I have ever seen and I have seen most of the equipment since the Viet Nam War.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Poe&lt;/p&gt;&#xA;" OwnerUserId="8685" LastActivityDate="2016-11-20T03:51:28.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6861" PostTypeId="2" ParentId="6812" CreationDate="2016-11-20T07:36:49.617" Score="0" Body="&lt;p&gt;I have had no luck getting any of the Motorola RSS software to run in a DOS box under windows 7 so I have an older laptop that I keep just for such occasions and it always works for me. In addition a further complication MIGHT be getting the DOS box to work with a USB style COMMPORT adapter. I would be far safer to just go back to the old style RS232 port on your old DOS computer.  I doubt this helps you out a lot because most people today junk the older laptops in favor of the newer ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Poe&lt;/p&gt;&#xA;" OwnerUserId="8685" LastActivityDate="2016-11-20T07:36:49.617" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6862" PostTypeId="2" ParentId="6731" CreationDate="2016-11-20T07:49:19.153" Score="0" Body="&lt;p&gt;It has been my experience that Pactor works best when it is in a conversation with another Pactor system, meaning it is a CONNECTED mode. It really doesn't like it when just monitoring. I believe this is especially true of the newer Pactor modes. Part of this comes from the signal margins that are present on a full circuit and the fact that Pactor can ask for a repeat of a packet if it misses a packet of data or it comes through corrupted. Keep in mind that Pactor would have to re-sync to the signal if it started losing chunks of data because of errors on the radio circuit. Without this re-syncing there could be no lock.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this helps a little&lt;/p&gt;&#xA;" OwnerUserId="8685" LastActivityDate="2016-11-20T07:49:19.153" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6863" PostTypeId="2" ParentId="6773" CreationDate="2016-11-20T12:31:31.057" Score="2" Body="&lt;p&gt;It's expected that the total noise temperature to vary with elevation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Three major effects to consider:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Sidelobe pickup of noise from the ground, this is the dominant effect&lt;/li&gt;&#xA;&lt;li&gt;Variation of atmospheric loss at different elevations, not really relevant for UHF frequencies&lt;/li&gt;&#xA;&lt;li&gt;The sky temperature itself, which varies mainly depending on whether you're on or off the galaxy. This sets a minimum for your system noise.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Here's a graph from Phil Perillat of Arecibo, about a 12 m dish.&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/lDpeg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lDpeg.png&quot; alt=&quot;12 m dish tipping curve&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;The sidelobes of a yagi will look quite different so the curve will be different, but it'll probably have a minimum when you're pointing straight up, and be nearly 300K when you're pointing at the horizon. When taking these curves, you need to be careful you don't cross the plane of the galaxy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a [map of the sky temperature at &lt;a href=&quot;https://lambda.gsfc.nasa.gov/product/foreground/f_images.cfm&quot; rel=&quot;nofollow noreferrer&quot;&gt;UHF&lt;/a&gt;  from Lambda/gsfc:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wu59R.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wu59R.png&quot; alt=&quot;408 MHz sky map&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They say &quot;&lt;em&gt;Log scale from 10 to 250 K&lt;/em&gt;&quot; so it's safe to assume you could have from as little as no significant contribution from the sky, to a completely dominant contribution, depending on where you point your antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;QST has a whole long article about sky noise at 433 MHz. Read it &lt;a href=&quot;https://safe.nrao.edu/wiki/pub/Main/AmateurRadioAstronomy/TheRadioSky_paper2.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2016-11-20T12:31:31.057" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6864" PostTypeId="1" AcceptedAnswerId="7700" CreationDate="2016-11-20T19:30:58.783" Score="13" ViewCount="2832" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/b5MMp.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/b5MMp.jpg&quot; alt=&quot;Wullenweber CDAA on Galeta Island circa 1991&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Wullenweber&quot; rel=&quot;noreferrer&quot;&gt;Wullenweber circularly-disposed antenna arrays (CDAAs)&lt;/a&gt; are large HF direction-finding antennas, sometimes colloquially referred to as &quot;elephant cages&quot;, that were popular in the Cold War.  They allowed the bearing of an incoming signal to be located to perhaps 0.5° (for the US Navy's &lt;a href=&quot;https://en.wikipedia.org/wiki/AN/FRD-10&quot; rel=&quot;noreferrer&quot;&gt;AN/FRD-10&lt;/a&gt;).  I've been fascinated by them ever since I saw the one on the Silver Strand south of San Diego, California.  Dozens were built all over the world.  Now nearly all have been demolished.  The &lt;a href=&quot;https://en.wikipedia.org/wiki/AN/FLR-9&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia article for the US Air Force's AN/FLR-9&lt;/a&gt; says &quot;advances in technology have made the FLR-9 obsolete.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What advances in technology made Wullenweber CDAAs obsolete?  What technologies are used for military HF direction finding now?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I'm talking about &lt;em&gt;fundamental&lt;/em&gt; advances in technology.  I presume if the technology were still broadly useful, then the electronics would be modernized.  To rephrase the question, why do modern militaries not use giant circular antenna arrays for HF direction finding any more?  What do they use instead?&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2016-11-21T03:45:54.300" LastActivityDate="2019-05-18T01:31:22.000" Title="Why are Wullenweber CDAAs obsolete?" Tags="&lt;hf&gt;&lt;direction-finding&gt;" AnswerCount="8" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6865" PostTypeId="2" ParentId="6864" CreationDate="2016-11-20T22:56:22.360" Score="7" Body="&lt;p&gt;First, there are better DF antennas now and they take up way less real estate.  Some of them are .. the Pusher and &quot;L&quot; and &quot;T&quot; arrays. The electronics for these is more sophisticated than the conventional &quot;Elephant Cage&quot; CDAA but they are faster if the electronics is designed and implemented correctly. The FCC in Laurel Maryland took their CDAA down and installed an  &quot;L&quot; and &quot;T&quot; array (I can't remember which now) In addition, since the solution is an electronic one instead of mostly mechanical (manual goniometer run by a motor) it is far easier to remote ALL of the controls so that it can be operated from anywhere given the correct control protocols. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, the old HF BULLSEYE NET as we knew it has been disabled now with various sites being returned back to the host governments in most of the foreign countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this has helped answer your question. &lt;/p&gt;&#xA;" OwnerUserId="8685" LastActivityDate="2016-11-20T22:56:22.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6866" PostTypeId="2" ParentId="6864" CreationDate="2016-11-20T23:17:41.003" Score="6" Body="&lt;p&gt;First of all: why is it surprising that a radio device built in the 1960s has become obsolete?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know the specific reasons why this specific type of direction finder has become obsolete, but among these reasons might simply be:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;cost of renovation &gt; benefit&lt;/li&gt;&#xA;&lt;li&gt;Shift in strategic demand for localization of these boring HF signals&lt;/li&gt;&#xA;&lt;li&gt;instead of a few circular setups, a lot of smaller setups can actually do the same or a lot better. We can now phase-synchronize distributed receiver systems through e.g. GPS. That wasn't possible in the 60s!&lt;/li&gt;&#xA;&lt;li&gt;distributed smaller multi-antenna systems allow for actual localization instead of just direction finding; the localization happens inherently and with less error instantly, instead of detecting multiple directions of arrival on multiple old systems, and then crossing lines on a map, manually, after communicating these bearings.&lt;/li&gt;&#xA;&lt;li&gt;terrible, terrible receiver bandwidth, noise, power consumption, reliability, operation cost. (best case: noisy germanium transistors. More likely in the early 60s: tube amps that eat kW of power for such a big receiver array). Noise Figure 7dB for a low-bandwidth receiver? That's not even remotely good nowadays.&lt;/li&gt;&#xA;&lt;li&gt;Operation manual suggest these amplifiers are lock-in amplifiers, and thus would be unsuitable for everything but AM and low-modulation index FM, and thus especially unsuitable for digital communications, probably.&lt;/li&gt;&#xA;&lt;li&gt;terrible antenna setup for systems where computational power allows to get higher resolution with fewer antennas&lt;/li&gt;&#xA;&lt;li&gt;antennas optimized for narrowband reception. Modern RF localization systems can track and find a lot of signals at once, spread over a large bandwidth, with a single set of antennas, through DSP&lt;/li&gt;&#xA;&lt;li&gt;Have you seen how &lt;strong&gt;large&lt;/strong&gt; these are? They're positively a big waste of space.&lt;/li&gt;&#xA;&lt;li&gt;Resolution of this system is very bad (15dB directional gain of the beamforming system) compared to modern 3-antenna setups, which are smaller, cheaper. Manual says &quot;nominal resolution 4°&quot;. That is seriously sub-par for anything built since the 90s with that many antennas to increase resolution.&lt;/li&gt;&#xA;&lt;li&gt;analog beamforming depends on physical properties of a system that are hard to maintain over time, and costly to re-calibrate&lt;/li&gt;&#xA;&lt;li&gt;availability of mobile systems that are better&lt;/li&gt;&#xA;&lt;li&gt;seriously, these are from the early/mid sixties. That's 50 years in the past. Even with ever so slight improvements in technology, it's not very likely that these would still be on par with modern technology. We have better&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;cables,&lt;/li&gt;&#xA;&lt;li&gt;lacquer,&lt;/li&gt;&#xA;&lt;li&gt;power supplies,&lt;/li&gt;&#xA;&lt;li&gt;displays,&lt;/li&gt;&#xA;&lt;li&gt;operation monitoring,&lt;/li&gt;&#xA;&lt;li&gt;building materials,&lt;/li&gt;&#xA;&lt;li&gt;thermal isolation,&lt;/li&gt;&#xA;&lt;li&gt;cooling,&lt;/li&gt;&#xA;&lt;li&gt;antenna materials,&lt;/li&gt;&#xA;&lt;li&gt;antenna simulation and&lt;/li&gt;&#xA;&lt;li&gt;measurement tools,&lt;/li&gt;&#xA;&lt;li&gt;higher construction placement accuracy&lt;br&gt;&lt;br&gt;&#xA;just to name a few things where there has been gradual, but not necessarily revolutionary improvements with respect to construction of antenna array systems in the last, I repeat, &lt;strong&gt;50&lt;/strong&gt; years.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It's really no surprise that the military has adopted different systems since then.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, however, CDAAs aren't obsolete – circular antenna sets still have nice properties when paired with the appropriate DSP algorithms. Thus, they are still in active usage in SIGINT; it's really just that 1960's analog systems are really not relevant anymore.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-11-20T23:25:22.700" LastActivityDate="2016-11-20T23:25:22.700" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6867" PostTypeId="2" ParentId="6864" CreationDate="2016-11-21T00:44:31.627" Score="-2" Body="&lt;p&gt;being a circular antenna has very little to do with it.  The Pusher is a circular antenna it is however smaller in diameter. Hams still use circular antennas for the lower bands BECAUSE they have excellent properties when it comes to DFing signals.  This allows them to rotate around the globe to pick the strongest signal available. The resolution is often better in the newer antenna types however with the best DF cut being approximately +/- 2.5 degrees.  What stops better resolution is the non-homogeneous nature of the ionosphere.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One further thing that did help to bring about the demise of the CDAA in the early to mid 90s is the drop in CW and other HF signals to obtain bearings on with the bulk of the targeted traffic moving to satellites by that time. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way these CDAA's and their successors work quite well on CW, SSB, AM, FM and even some of the newer modes even though the latter replacements might have been quite a bit faster when obtaining a bearing on a particular signal. &lt;/p&gt;&#xA;" OwnerUserId="8685" LastActivityDate="2016-11-21T00:44:31.627" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6868" PostTypeId="2" ParentId="490" CreationDate="2016-11-21T02:43:20.530" Score="0" Body="&lt;p&gt;Yes it can be done though the DMR standard is not really designed to support this. &lt;a href=&quot;https://www.trellisware.com/manet-products/tsm/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.trellisware.com/manet-products/tsm/&lt;/a&gt; are radios designed for this type of application. You would need to use more rf bandwidth due to faster modulation rate and longer gaps between tx and rx.&lt;/p&gt;&#xA;" OwnerUserId="8706" LastActivityDate="2016-11-21T02:43:20.530" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6869" PostTypeId="1" CreationDate="2016-11-22T00:44:09.970" Score="1" ViewCount="49" Body="&lt;p&gt;I want to understand what factors determine acceptable turning radius of RF cable. are the losses high for low frequency or at high frequency if cable is turned or twisted ? the cable i am referring is an coaxial cable. i want to know how cable core conducting metal diameter, sheath metal, insulator characteristics etc in RF cable effect cable turning radius.&lt;/p&gt;&#xA;" OwnerUserId="5349" LastActivityDate="2016-11-22T01:20:45.040" Title="What factors determine acceptable turning radius of RF cable operating into few GHz?" Tags="&lt;impedance&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6870" PostTypeId="2" ParentId="6869" CreationDate="2016-11-22T01:20:45.040" Score="3" Body="&lt;p&gt;The problem with bending a coaxial cable too sharply is that the cross-section of the cable is crushed out of round, which would change the characteristic impedance of that section. Just as with most other defects in transmission lines, the loss will increase with frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bending radius has no direct &lt;em&gt;electrical&lt;/em&gt; significance; it just determines how much stress there is on the materials that make up the cable, and the effect on the cable will depend on exactly what those materials are. The particular materials will also affect whether the cable is permanently damaged or it will recover when unbent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I doubt you will find any general rule for calculating the bend radius; it's a fairly complex interaction between the material properties of the at least four different elements of the cable.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-11-22T01:20:45.040" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6871" PostTypeId="2" ParentId="5622" CreationDate="2016-11-22T15:28:52.050" Score="2" Body="&lt;p&gt;It's a crypto interface and crew terminal from a military radio system. It isn't useful on its own, and a lot of equipment of this nature is not legal for civilians to buy or sell. That said, this isn't the first time I've seen that exact terminal pop up in ham radio forums, so I suspect it's a model not covered by current control policies, though I can't guarantee that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's no RF deck, it's essentially a remote control panel for a radio that would just be an enormous green box with handles and connectors on it. The buttons around the edge of the screen are multi-function keys, and on most of these, new crypto can be pushed through the headset connector using one of several different kinds of loaders. Similar units are used on aircraft for both radio and intercom systems, but I suspect this one is from either a fixed station or a modular mobile unit, as it doesn't have a plate where it would seat in a console or the like.&lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="246" LastEditDate="2016-11-22T16:44:34.073" LastActivityDate="2016-11-22T16:44:34.073" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6873" PostTypeId="2" ParentId="6445" CreationDate="2016-11-23T03:28:27.763" Score="2" Body="&lt;p&gt;Twisted-pair is just a special case of a balanced (untwisted) feedline. The twisting reduces crosstalk between the multiple pairs in the cable assembly but doesn't otherwise change the fundamental operation of the transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Category 5 UTP in particular probably isn't frequently used because it can not handle much power. I suppose in a low power or receive application it could work. The most commonly available category 5 cable is not UV resistant, and so is not appropriate in an exposed outdoor installation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Disassemble a cat 5 cable carefully, and you'll notice each pair is twisted at a different rate. Twisting the pairs at different rates &quot;mixes up&quot; the interactions due to the pairs being bundled together, and over many twists these randomized interactions between pairs tend to average out and cancel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a single antenna application, this is of little relevance. Perhaps in an antenna array where minimizing crosstalk is important (a phased array, for example) some benefit from the twisted pairs in cat 5 could be realized, but coax would be even better. Ladder line is sometimes installed twisted, but this is to keep it from fluttering in the wind, not for any particular electrical benefit.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-11-23T03:28:27.763" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6874" PostTypeId="1" CreationDate="2016-11-23T07:34:34.810" Score="10" ViewCount="421" Body="&lt;p&gt;I'm a &lt;a href=&quot;https://en.wikipedia.org/wiki/Amateur_radio_licensing_in_the_United_States#Current_license_classes&quot; rel=&quot;noreferrer&quot;&gt;General Class&lt;/a&gt; Licensee, and due to pulmonary disease I cannot operate voice. I am also about 540 feet from a 24/7 1&amp;nbsp;kW AM station. The signal is so pronounced that most audio devices in the house pick up the station. Every shortwave receiver I've tried overloads (without an antenna) from 1-30 MHz. Any suggestions?&lt;/p&gt;&#xA;" OwnerUserId="8721" LastEditorUserId="366" LastEditDate="2016-11-28T18:55:25.237" LastActivityDate="2017-03-10T00:38:32.357" Title="How to operate on HF if an AM transmitter is only 540 feet away?" Tags="&lt;digital-modes&gt;&lt;rfi&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6875" PostTypeId="1" CreationDate="2016-11-24T05:16:35.917" Score="1" ViewCount="1211" Body="&lt;p&gt;A 2m &lt;em&gt;Quad&lt;/em&gt; antenna made from 1/2&quot; tubing will have a larger bandwidth than the same &lt;em&gt;Quad&lt;/em&gt; built with 14 AWG wire.&lt;br&gt;&#xA;  Would the respective bandwidths be maintained if both &lt;em&gt;Quad&lt;/em&gt; loops were made into &lt;strong&gt;Quagis&lt;/strong&gt; by adding, say, a reflector and five directors (on a boom) that were all 14 AWG wire. Or, would the 1/2&quot; tubing &lt;em&gt;Quagi&lt;/em&gt; need 1/2 tube elements, &lt;em&gt;or even just the reflector,&lt;/em&gt; to keep its larger bandwidth?&lt;/p&gt;&#xA;" OwnerUserId="8477" LastEditorUserId="8832" LastEditDate="2017-05-25T01:13:20.170" LastActivityDate="2017-06-24T02:23:53.187" Title="Do reflector and director widths (wire size) affect Quagi bandwidth?" Tags="&lt;antenna-theory&gt;&lt;wire-antenna&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6876" PostTypeId="2" ParentId="6875" CreationDate="2016-11-24T08:33:09.903" Score="3" Body="&lt;p&gt;So, yes, the Yagi-Uda part of a Quagi has a limited bandwidth, too.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;R     A    D&#xA;&#xA;|         &#xA;|     |    &#xA;|     |    |&#xA;|     |    |&#xA;|     |    |&#xA;|=====¦====|&#xA;|     |    |&#xA;|     |    |&#xA;|     |    |&#xA;|     |    &#xA;|     &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Let's start with the reflector:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's assume the reflector has exactly length $\frac12 \lambda$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea of the reflector (labeled $R$ above) in the Yagi-Uda design is that it gets excited by the actual driven element (labeled $A$). Due to the half-period delay in emission of the energy stored that way, plus the $2\cdot \frac14\lambda$ distance, the wave hits $A$ with a total delay of one full period – that way, they interfere constructively at $A$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So from this, you can already see that spacing between the driven element $A$ and the reflector $R$ is critical to operation. Things get a little more complicated, though:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, that's nice and all, and it already gives us some directional gain, because left of $R$, $A$'s emissions and $R$'s emissions are $\frac34\lambda$ &quot;out of phase&quot;, whereas at $A$, they're in-phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, making $R$ &lt;em&gt;exactly&lt;/em&gt; half a wavelength long isn't commonly done for various reasons (you &lt;em&gt;can&lt;/em&gt; build a good Yagi-Uda with that, but you need to be very careful in alignment and stuff, and your driven element's efficiency will be sub-optimal), especially when considering that we commonly see Yagi antennas where $R$ is a bit longer than $A$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Essentially, what you'd do is make the driven element a half-wavelength dipole, and make the reflector a bit longer. Thus, the reflector becomes an element that is essentially a inductive parasitic to the driven elements – and inductive reactance means that the current in the reflector lags behind the voltage the field from the driven element causes, leading to additional delay in the emitted field. Thus, you can arrange the distances and element sizings in a way so that there's constructive interference in the far field &lt;em&gt;in front&lt;/em&gt; of the antenna, and basically destructive interference behind. The sizing of directors give you enough design freedom to theoretically repeat that as often as you like to increase your gain – for a single wavelength. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the more broadband your antenna needs to be, the less exact the Yagi-Uda calculations for the nominal wavelength apply. Thus, the more you move away from your nominal frequency, the less gain your antenna has; you'll also notice that the mismatch increases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I'm not experienced with Quagis at all. But to me, the whole point of using a frame=loop=quad antenna in place of the driven dipole and the shorted reflector dipole is exactly that: to increase antenna selectivity and thus, gain, in exchange for reducing bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I'm relatively certain that the idea of increasing a Yagi-Uda design's bandwidth and using a quad in place of driven element and a rectangle/ring in place of a reflector don't work well together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All in all, the Quagi, to me, looks a bit like a Frankentenna. It probably works pretty well for a single use case, but isn't quite as versatile as a simple Yagi. The &lt;a href=&quot;http://n6nb.com/quagi.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;design history&lt;/a&gt; indicates it was more found by accident then by analysis or simulation – which is fine, many antenna designs are happy accidents – for a very specific frequency and purpose and thus, I'd say:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the year 2016, unless someone comes up with a well-done model and simulation of the Quagi, I'd say you can probably find easier ways to build a broadband directional antenna for the same frequency range then improving the bandwidth of the driven element, then the reflector, then the directors, then the spacing of the directors, then reiterate, and match the antenna impedance, ... of a Quagi. In other words, the moment your Quagi has the same bandwidth as that of a simple Yagi with the same directors, it also has lost its advantages over that Yagi – you could have built a classical Yagi-Uda design straight away. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're after bandwidth while maintaining more than 10dBi of gain: Look at the well-known and -understood logarithmic-periodic (&lt;em&gt;&quot;logper&quot;&lt;/em&gt;) antenna type. Instead of driving one dipole, you drive a set of dipoles, each &quot;optimal&quot; for a different frequency¹. That means that unlike the Yagi, every element in a Logper antenna is driven. However, you of course arrange the elements such that you get the same directivity effects as in the Yagi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd really love to see something like a Quagi (or any other combination of well-known, proven-to-work-well-for-their-purpose antenna types) as some antenna model that I could e.g. use in OpenEMS or another electromagnetic simulation tool – &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹ It actually gets a little more complicated than that – you can't just go and parallely drive a set of dipoles and hope for great bandwidth. The logper is actually more of a design derived from antennas that have the property of &lt;em&gt;self-complementarity&lt;/em&gt;, which is the reason for it being broadband. (self-complementary means that if you draw the antenna, then take the negative, then rotate/shift it, and overlay the original and the negative, you get the whole plane without overlap or &quot;holes&quot;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you look at those, they typically can't have incredible one-sided gain – so someone took a square pattern and &quot;flattened&quot; it to achieve Yagi-style directivity. If you want to get the rough idea, have a look at the &lt;a href=&quot;https://en.wikipedia.org/wiki/Self-complementary_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;wikipedia&lt;/a&gt; article.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-11-24T08:33:09.903" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="6877" PostTypeId="1" CreationDate="2016-11-24T09:25:43.103" Score="1" ViewCount="150" Body="&lt;p&gt;I am looking at antennas for a rather unusual application: mounted under a utility pit lid (manhole cover).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The goal is to receive commercial MW/LW stations. The antenna has to be attached to the underside of the lid with a magnet. To make it easy to install we want it to be as omnidirectional as possible, because the installer can't hang around aligning it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What type of antenna is best suited to this?&lt;/strong&gt; We are willing to consider things like having two switched/combined ferrite rods at right angles, if that will work.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Should have mentioned, the received signal can be very poor and still be fine for our needs. Even if it's 95% noise that's fine, as long as there is some small amount of signal. We have made successful tests with consumer MW/LW receivers with ferrite antennas. The main issue was alignment.&lt;/p&gt;&#xA;" OwnerUserId="8727" LastEditorUserId="8727" LastEditDate="2016-11-28T09:18:20.297" LastActivityDate="2016-11-28T09:18:20.297" Title="Utility pit MW/LW omnidirectional antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;mf&gt;&lt;lf&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6878" PostTypeId="2" ParentId="3505" CreationDate="2016-11-24T17:28:10.180" Score="3" Body="&lt;p&gt;Copper indeed would be better. Silver would be better yet. These materials, however, are heavier and less rigid than aluminum. So there is that. To aluminum's advantage, it can be laser cut at very high accuracy. Copper has to be water-jet cut, at lower accuracy and higher cost. Beryllium copper alloy would be stiffer, but it's a health hazard and no shop will cut it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Copper, in time, will also corrode. And as RF travels mostly on the OUTSIDE of things, that would be a big problem in time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Conductivity in a Mag-Loop antenna's capacitor IS a concern, however, despite the low currents involved. You want a very high-Q capacitor for best effect. And ANY resistance will drag down the Q. So copper, again, if it can be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One solution which I'm presently contemplating, is use of silicone transformer oil as the electrolytic (versus vacuum or air). This gives a K of 2.71 and an anti-arc insulation of &gt; 350 V per mil. Trade off would be the (still very low) loss tangent of 0.0001 up in the HF bands. That by itself would lower Q by a tad. But counter to that, you could have copper or copper-plated plates. Their being immersed in silicone oil would prevent corrosion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for the (usually Russian surplus) vacuum variable capacitors, those are truly excellent ... with one proviso. You will be constantly tuning your Mag-Loop antenna (since Q is high) and that would mean VERY frequent re-adjustment on your surplus (already used) VVC. Look at any picture of those. There is a copper (or copper plate) bellows inside. Constant adjustment would mean fatigue. Copper has LOUSY fatigue resistance. So then while it might last a good while, don't go thinking that means forever. It will wear out, mechanically, from constant adjustment. And where, down the road, will you find an exact replacement? So then, maybe buy two?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One final thing. Do NOT simply press-fit your plates together the way I've seen done on YouTube and elsewhere. All those inter-plate contact connections. What must be the ESR accumulation from that? Braze them together for electrical unity. Use AlumiWeld or something like. It's only 25% the conductivity of Cu, but better than a press-fit, for certain. Or maybe use 112 Cu (hand cut from McMaster-Carr stock) for the spacers. That 112 Cu comes in telescoping sizes, so you could have Cu spacers on Cu tube (which runs through the plate-holes, plus inside of all a length of stainless steel threaded rod to hold things together until it's all brazed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have a final answer to all these questions as yet. I'm only working out my design now. A project for next year. I'll write an article when it's done. Can't say when that will be.&lt;/p&gt;&#xA;" OwnerUserId="8728" LastEditorUserId="218" LastEditDate="2016-11-27T13:40:22.287" LastActivityDate="2016-11-27T13:40:22.287" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6879" PostTypeId="2" ParentId="6877" CreationDate="2016-11-24T23:14:40.877" Score="3" Body="&lt;p&gt;A lid where a magnet attaches is made out of iron.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Iron is a good conductor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're trying to build an antenna in a place which is especially well-shielded against radiation. That will be very very difficult. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Omnidirectional from under a manhole cover means &quot;in the earth&quot;. If that isn't dry, then there will be little signal there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, radio waves can penetrate wet soil – as an estimate, with a very sensitive receiver and a very powerful transmitter, you could do up to 10m ground penetrating radar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But this will not be possible for any receiver that is supposed to receive an AM signal and is remotely related to ham technology (making it on-topic here). For that kind of sensitivity, you'd need extremely low noise figure, and that will be extremely expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All in all, I don't know what kind of radio broadcast receiver for mole people or explosive trigger device you want to build, but I trust physics enough to believe this won't work at your level of insight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact that you're asking about commercial MW inside populated areas (i.e. where there are manhole covers) might indicate you're Britain-based. Now, that'll also mean the broadcasters won't be pushing incredibly much power, making this a bit harder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To make things more complicated, omnidirectional won't work easily. The reason is simple – the MW/LW wavelengths are far bigger than a manhole, and thus, you can only use high-Q antennas (ferrite core antennas, for example), and those tend to have a very clear preferred direction. Having arrays of these probably won't work either – they'd interact (being all within $\ll\frac12 \lambda$).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frankly, think about it:  As you know, the typical propagation mode for commercial LF and MF is surface wave – the earth's conductive surface forms kind of a waveguide together with ionospehre – and that means that wokring MW reception is based on the fact that at the point of surface, there's little power transport. You could try to make an antenna pick up the displacement currents – but that's going to be freaky business, especially anywhere there's electrical infrastructure (which happens to be the places with manholes). &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-11-24T23:46:32.927" LastActivityDate="2016-11-24T23:46:32.927" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6880" PostTypeId="1" AcceptedAnswerId="6881" CreationDate="2016-11-25T17:34:30.103" Score="2" ViewCount="450" Body="&lt;p&gt;I have seen the shape factor of a resonant circuit defined in different places as &lt;em&gt;both&lt;/em&gt; &quot;the ratio of the -&lt;strong&gt;3&lt;/strong&gt;dB point to the -60dB point&quot;, and elsewhere as &quot;the ratio of the -&lt;strong&gt;6&lt;/strong&gt;dB point to the -60dB point&quot;. Please, which of these is correct? I can see why the -3dB point is special, it's where the reactance equals the resistance, (approximately, near enough in practice for high Q) but why -6dB?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(there doesn't seem to be a tag that is closely relevant, sorry)&lt;/p&gt;&#xA;" OwnerUserId="297" LastActivityDate="2016-11-25T19:46:13.027" Title="What is shape factor of a resonant circuit?" Tags="&lt;theory&gt;&lt;filter&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6881" PostTypeId="2" ParentId="6880" CreationDate="2016-11-25T19:36:46.413" Score="3" Body="&lt;p&gt;Well, different books / schools use different definitions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some authors just copy definitions from others and make mistakes when doing that. In this case, this is pretty likely: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Possibly, someone remembered &quot;hey, shape factor is between the point where there's half the power and -60dB of the power&quot;, then when writing down accidentally converted &quot;half the power&quot; to &quot;half the amplitude&quot;, and thus used $x [\text{dB}] = 20 \log_{10}(x[\text{linear}])$, as usual for amplitudes, instead of $10\log_{10}$, or just the other way around. The &quot;original&quot; definition might be lost in the sands of time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All in all, &lt;em&gt;shape factor&lt;/em&gt; is not a measure encountered all that often in modern literature; especially since analog filters typically have to compete with digital ones nowadays, it's become far more usual since about the 80's to refer to &lt;em&gt;transition width&lt;/em&gt; or &lt;em&gt;transition band&lt;/em&gt;, ie. the bandwidth between edge of passband (i.e. -3dB point, typically), and the point where the filter response crosses it's final/design attenuation the first time:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This figure is taken from the &lt;a href=&quot;https://mathworks.com/help/signal/examples/practical-introduction-to-digital-filter-design.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;mathworks example&lt;/a&gt; on filter design:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8Ubdk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8Ubdk.png&quot; alt=&quot;filter amplitude response naming&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wonder what sense it makes to use a fixed -60dB as reference, anyway – if your filter is designed to have a -60dB attenuation everywhere in the stopband, fine, that makes sense, but you don't generally do that. What if your filter requirements are really just -50dB (and that makes a large difference, both when designing analog and &lt;a href=&quot;https://dsp.stackexchange.com/questions/31066/how-many-taps-does-an-fir-filter-need/31077&quot;&gt;digital filters&lt;/a&gt;), and you don't actually care where the attenuation becomes -60dB (or whether that happens at all). Or what if you need a great filter because you're observing something extremely weak and go through lengths and build a -90dB-stopband filter? What use is knowing the ratio of -3dB and -60dB then?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The -60dB measure does make kind of sense in a technological environment where -60dB is actually the maximum physically possible isolation (and that's the case for board-bound electronics, and &quot;free flying low frequency filters&quot;, maybe), but that doesn't really apply to all filter designers do nowadays.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know I'm kind of annoying like that, but if you're really after having good filters: don't design them in the analog domain. It's 2016. Dynamic ranges of ADCs are plenty, by far more than what you need even with strong interferers, together with the fact that Ham bandwidths are negligible small for modern ADC bandwidths. Build an easy filter that makes sure you don't get aliases in your desired bandwidth when sampling with a certain $f_\text{sample}$, then use digital filters (for example: in your PC) to extract the signals you care about – digital filters can be made virtually infinitely steep, and the noise they might contribute due to calculation accuracy is far below anything relevant for almost all use cases, if not totally overspecified.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2017-04-13T12:47:28.700" LastActivityDate="2016-11-25T19:46:13.027" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6883" PostTypeId="2" ParentId="6845" CreationDate="2016-11-26T12:13:49.747" Score="2" Body="&lt;p&gt;I think I can decide the intent of the formula. It's wrong, as you've written it.&lt;br&gt;&#xA;I assume the drawing is a flat 2D picture of three antennas in space, not a perspective view of three antennas on the earth's surface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case I can see what you're trying to do:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gain of a dipole is 2.13 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation pattern of a dipole can be approximated by &lt;span class=&quot;math-container&quot;&gt;$\sin^2(\theta)$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you could say &lt;span class=&quot;math-container&quot;&gt;$10\log_{10}(10^{2.13/10} \sin^2(90-\alpha))$&lt;/span&gt;.&lt;br&gt;&#xA;Or better, &lt;span class=&quot;math-container&quot;&gt;$2.13 + 20\log_{10}(\sin(90-\alpha))$&lt;/span&gt;.&lt;br&gt;&#xA;Equals &lt;span class=&quot;math-container&quot;&gt;$2.13 -  3.8 = - 1.73$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is simply the gain of dipoleE3 &lt;em&gt;in the direction of dipoleS&lt;/em&gt;.&lt;br&gt;&#xA;Wikipedia has a &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Dipole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;good page&lt;/a&gt; with this picture:&lt;br&gt;&#xA;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/f/f4/RadPatt-dB.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no polarisation loss as they're in the same vertical plane. Your formula for that does look correct, but for dipoles not in the same horizontal plane,  to find the angle a you might need some tricky trigonometry.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorDisplayName="user4168" LastEditDate="2019-01-24T01:58:36.113" LastActivityDate="2019-01-24T01:58:36.113" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="6884" PostTypeId="2" ParentId="6874" CreationDate="2016-11-26T13:03:53.213" Score="4" Body="&lt;p&gt;First, find a transceiver which is properly shielded. When connected directly to a dummy load, there should be no breakthrough on any frequency (except the MW transmitter itself). Portable broadcast radio receivers are completely out of the question, but fairly recent ham gear should be ok.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, try a highpass filter to reduce the impact of the MW. I'd suggest starting on one of the higher bands, 15 m or 10 m.  A simple highpass filter can be made with a quarter wavelength short circuit stub. On 15 m that's about 2.2 m of coax.  Ideally for the stub you should use double screened coax like RG223, RG400 or hardline etc. Solder the stub into the radio end of a short jumper lead. A better filter can be made with more stubs or with discrete components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, take some precautions to reduce the pickup of the RF in the shack. Keep loop areas small - run coax, 12 V and power cables close to each other. Make a filter or trap for common-mode currents on both coax and power lines that enter the rig. Ground the coax shield to shack ground as it enters the shack. (forget about ground stakes, you're trying to keep differential voltages to a minimum). Use a horizontal dipole antenna, broadside to the MW source,  as the MW fields are mostly vertical, and still somewhat &lt;em&gt;radial&lt;/em&gt; as you're so close. Use a balun with good choking well below your HF frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may still be in  trouble, if there are any non-linear effects in any gutters, downpipes, fences or electric cables outside anywhere near the transmitter. They could cause significant harmonics and intermods on your HF frequency, which cannot be filtered out.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2016-11-26T13:03:53.213" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6885" PostTypeId="2" ParentId="3653" CreationDate="2016-11-26T18:31:51.123" Score="0" Body="&lt;p&gt;Use a step-down (buck) converter like this -&gt; &lt;a href=&quot;http://m.ebay.com/itm/251066005460?_mwBanner=1&quot; rel=&quot;nofollow&quot;&gt;http://m.ebay.com/itm/251066005460?_mwBanner=1&lt;/a&gt; , &#xA;and match the output voltage of your base charger when connected to AC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: my UV-5R charger is at ~10V. I have never measured the charge rate of my radio when docked, but if it should exceed the rated max of the buck converter you end up using, you can simply heatsink the LM2596 chip itself.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastEditorUserId="7957" LastEditDate="2016-11-26T18:47:43.280" LastActivityDate="2016-11-26T18:47:43.280" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6886" PostTypeId="1" CreationDate="2016-11-26T20:43:19.787" Score="2" ViewCount="640" Body="&lt;p&gt;I am Trying to use Funcube Dongle Pro+ on Windows with Gnu radio companion with no success.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My PC is detecting The Funcube Dongle Pro+, and it works on SDR#, But It doesn't work on Gnu Radio. I have tried Installing Ubuntu with Gnu Radio on a virtual machine and when I try to run The Flow graph Nothing shoes up in the sink and the frequency control software (Qthid) crashes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I get Funcube Dongle to work with Gnu Radio, I prefer windows but If I can get it to work on Linux it will be great too.&lt;/p&gt;&#xA;" OwnerUserId="8739" LastEditorUserId="8739" LastEditDate="2016-11-26T21:08:30.243" LastActivityDate="2016-12-06T19:01:24.687" Title="Gnu Radio with Funcube Dongle SDR" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6887" PostTypeId="1" CreationDate="2016-11-27T20:00:20.743" Score="34" ViewCount="31658" Body="&lt;p&gt;My internet provider is telling me that an antenna on my neighbor's house, which he called a ham radio antenna, is interfering with my DSL internet signal.  I'm not tech savvy at all, beyond what's necessary to function in today's world, so I'm clueless as to what this is, what its used for, or if this even a legit accusation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am, however, skeptical of this claim due to an ongoing history with my provider. I experience a problem about once a month, I call, they say they'll send someone, then after the call the problem clears up a few minutes later and their &quot;tech&quot; guy never even shows.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But this time its gone on for a week. We've replaced the modem and this is the explanation they're giving me. I feel its more likely that my provider is taking advantage of me, but I can't be sure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible that this antenna could be interfering with my internet signal? And if it is the likely factor, is there some way for my neighbor and I to both have what we need? Or is someone going to have to compromise? I don't know this guy, I don't know what he used the antenna for, but it hardly seems fair for me to ask him to take it down or stop using it. He has rights just as I do. But at the same time, this problem is interfering with my livelihood. My job requires that I have internet access at home. If this problem persists, I'm super screwed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone here offer up some advice?  And please, I'm an idiot when it comes to techie stuff. Please dumb down your language enough for me to grasp what you're talking about. Ya know.. Use laymen's terms for me.&lt;/p&gt;&#xA;" OwnerUserId="8743" LastEditorUserId="6753" LastEditDate="2016-11-29T21:13:34.583" LastActivityDate="2020-12-04T13:31:07.790" Title="Can my neighbor's ham radio antenna be interfering with my internet signal or is my internet provider just throwing blame elsewhere?" Tags="&lt;rfi&gt;" AnswerCount="14" CommentCount="10" FavoriteCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6888" PostTypeId="2" ParentId="6887" CreationDate="2016-11-27T20:55:43.340" Score="37" Body="&lt;p&gt;Could be, but likely not. In particular, almost no amateur radio station would be operating &lt;em&gt;continuously&lt;/em&gt;, so if you have a problem that is not intermittent, that's unlikely to be the source of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(If you edit your question to specify what type of internet access ('cable', DSL, microwave link…) you have, and include a picture of the antenna, we can make a more informed guess about whether they might interfere. If they're on completely different frequency bands, well then.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Talk to your neighbor. Don't lead with a complaint — just tell them that this is what your ISP is claiming and you want to get more facts. Have them tell you &lt;em&gt;when&lt;/em&gt; they're operating (transmitting), or you tell them when you're experiencing connectivity problems. If the timing doesn't match, then this can't be the cause. (Also ask them what “bands” they are operating on and write down the answer.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the timing &lt;em&gt;does&lt;/em&gt; match then things are more complex, because there could be several different situations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Your in-home networking equipment (modem, router, WiFi AP) can't tolerate the nearby signal which it should be able to.&lt;/li&gt;&#xA;&lt;li&gt;The ISP's equipment not in your house can't, ditto.&lt;/li&gt;&#xA;&lt;li&gt;The electronics are fine but the &lt;em&gt;cable&lt;/em&gt; is damaged somewhere (for cable-type internet access), letting the interfering signal in.&lt;/li&gt;&#xA;&lt;li&gt;Your neighbor's equipment is transmitting excess power on frequencies which it shouldn't.&lt;/li&gt;&#xA;&lt;li&gt;Your stuff is legal and functioning correctly, their stuff is legal and functioning correctly, but they're just too close together. In this case you'll just have to see if your neighbor can agree to avoid operating when you're working.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-11-27T20:55:43.340" CommentCount="16" ContentLicense="CC BY-SA 3.0" />
  <row Id="6889" PostTypeId="2" ParentId="6887" CreationDate="2016-11-27T22:52:11.227" Score="13" Body="&lt;p&gt;A &quot;ham radio&quot; is typically a transmit/receive system that uses certain frequencies set aside for radio amateurs to communicate with other enthusiasts. If there is a big antenna on your neighbor's roof, he/she is likely enthusiastic and quite knowledgeable in the area of radio interference; I am going to guess he/she would be happy to help you troubleshoot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Interference between your neighbor's activities and your internet signal can happen if the frequencies of the transmitter and the frequencies used by the internet provider are close enough together; and if there is some way for those signals to &quot;mix&quot;.  This can be a result of poor shielding, damaged cables, or just plain bad luck in the layout. It can also happen if your internet signals are traveling &quot;over the air&quot;: this can be because you have a satellite link, or because you use WiFi inside your house to go from the modem (the device that connects your house to the internet) to your computer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my experience, WiFi interference is much more likely between WiFi routers in adjacent homes, than between a WiFi router and a ham radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Talk to your neighbor. Bring cookies.&lt;/p&gt;&#xA;" OwnerUserId="8744" LastEditorUserId="8744" LastEditDate="2016-11-29T14:53:33.513" LastActivityDate="2016-11-29T14:53:33.513" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="6891" PostTypeId="2" ParentId="6887" CreationDate="2016-11-28T00:16:44.047" Score="1" Body="&lt;p&gt;Barring what the other answers already advised, which things are giving you trouble? Wireless devices such as tablets and laptops or wired devices such as a desktop computer? If it is only the former then the ISP is blowing smoke. The modem controls the signal coming into the home and into fully wired devices. The router projects that signal into the air for wireless devices to pick up on. If the latter has trouble but not the former then it is either your router, wireless device, or the antenna causing trouble. If the former is true, then the ISP is being an idiot altogether like usual business.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A common thing with ISP's imo is that they will never say &quot;it was our fault, sorry.&quot;, because it makes them liable for you losing connection. Note: you cannot sue for damages afaik, but you can technically sue them for failing to provide service if they do it enough. So, they will do whatever it takes and jump through whatever hoops they can to deny failing to provide service. Also, ask your neighbors if their internet is down. One time we had no internet for almost two weeks because the station went out at the corner and &quot;it's working fine. It's your fault and your 20+ neighbors. I won't say names of companies, but let's just say they have a loooong history of bad customer service, bad internet service, and generally being a bad company. Next time you call them, ask for a manager. Trust me, if it's even remotely like the place we had... you'll get hung up on or put on hold indefinitely. Or they'll say all the managers are out of the office at a &quot;funeral&quot;. (Yes, the rep claimed this then 10 minutes later the manager took the phone cause he saw the rep cursing at someone). Needless to say, this is how most customer service centers can be at times. It's not one particular place really. It's just how all places get after a while or can be when you get certain people on the phone.&lt;/p&gt;&#xA;" OwnerUserId="8749" LastActivityDate="2016-11-28T00:16:44.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6893" PostTypeId="2" ParentId="6887" CreationDate="2016-11-28T05:03:18.290" Score="-2" Body="&lt;p&gt;I'm in IT and deal with ISPs regularly. If you plug a computer into the dsl modem and turn WiFi off,  and still have the problem, then it has nothing to do with anything wireless. This includes anything using an antenna like your neighbor's equipment. Ham radio is only, though unlikely, possibly going to interfere with wireless and only when transmitting which would be occasionally not constantly. &lt;/p&gt;&#xA;" OwnerUserId="4171" LastActivityDate="2016-11-28T05:03:18.290" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6894" PostTypeId="2" ParentId="6887" CreationDate="2016-11-28T12:37:17.397" Score="9" Body="&lt;p&gt;A HF transmitter can interfere with a DSL service if the conditions are right simply by inducing more RF on the drop wire then the DSL modem (Which &lt;strong&gt;always&lt;/strong&gt; cheap out on front end electronics) can cope with. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Been there with my own DSL service when running a few hundred watts on 20M, suitable ferrite rings on the power and data wiring can sometimes help, but I would expect such problems to be intermittent (Most Hams do not transmit 24/7).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Go and talk to the neighbour, most hams are well aware of the potential for this kind of thing, and while (at least in the USA) it is not really their responsibility to fix your inadequate networking gear, they will often try to help in order to keep the peace. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Testing to find out if his rig is the problem is easy with your cooperation, and you may well find that his station has nothing to do with it (Convincing the phone company 'technician' of this is left as an exercise in frustration). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This really is the ISPs problem, not the radio operators, but having dealt with ISP support departments, you are more likely to get a fix from the ham (Who, apart from anything else, can sometimes point out to the ISP where their problem is)!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a legal perspective, the modem is almost certainly a &quot;class B computing device under FCC part 15&quot;, which means that it must accept any interference from a licensed radio station. This is to say that a licensed station is allowed to cause it interference. &#xA;Good networking kit will have better protection, but the stuff most ISPs supply as freebies is 'designed to a price'. &lt;/p&gt;&#xA;" OwnerUserId="8756" LastActivityDate="2016-11-28T12:37:17.397" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6895" PostTypeId="2" ParentId="6887" CreationDate="2016-11-28T17:34:14.113" Score="7" Body="&lt;p&gt;Actually, depending on the power of the station, it could very well cause problems with any electronic equipment.  I ran into a situation once where a band I supplied the sound system for had constant interference when playing one particular club.  One night I was so bad we were actually getting the Ham's entire conversation through the PA.  We powered down to avoid any possible damage while we figured out what to do, and we could still hear noise.  His rig was so powerful, it was actually able to move the speaker coils with the stray RF the cables were picking up.  Luckily, when we found the (huge - looked like the Eiffel Tower) antenna a half block away, we talked to him and he was shocked.  He shut down (he had been talking to someone in Kowloon) and the band was able to play.  I never found out what he did to modify his gear, but we never had a problem there again.&lt;/p&gt;&#xA;" OwnerUserId="8761" LastActivityDate="2016-11-28T17:34:14.113" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6896" PostTypeId="2" ParentId="6887" CreationDate="2016-11-28T19:30:44.277" Score="0" Body="&lt;p&gt;My answer doesn't have to do with antennas but with personal experience with DSL providers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Did the &quot;tech guy&quot; check connections leading from their box in the street to your house or did they just throw their hands up and not even try?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had problems with my DSL a long time ago too.  I connected directly to the DSL modem (didn't use my wireless at all) and still had problems but my provider was giving me the run around, just like they did with you.  I kept asking for someone to come out but they resisted.  Finally, they sent someone out but kept reminding/threatening me that I'd have to pay a fee if they had to fix something inside my condo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Luckily, the tech looked outside first and found out that something was CORRODED so the problem was from their box to the condo complex.  The internal connection from the telephone room in the condo to my unit was fine.  I don't know how different it is for a house but I think this is worth a try too.&lt;/p&gt;&#xA;" OwnerUserId="8764" LastActivityDate="2016-11-28T19:30:44.277" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6897" PostTypeId="1" CreationDate="2016-11-28T21:11:28.150" Score="2" ViewCount="2499" Body="&lt;p&gt;I'm buying the following: &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B0129EBDS2&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Defined/dp/B0129EBDS2/ref=sr_1_3?ie=UTF8&amp;amp;qid=1480215974&amp;amp;sr=8-3&amp;amp;keywords=RTL-SDR&lt;/a&gt; to analyze radio waves as something new to learn. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It needs an antenna but I am new to this field. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I buy an antenna that has a SMA Male connector does the antenna need to say it operates in the frequency of 500 kHz to 1.7 GH or does any antenna matter?&lt;/p&gt;&#xA;" OwnerUserId="8771" LastActivityDate="2016-11-28T23:15:53.227" Title="Does antenna frequency matter when trying to pick up radio waves?" Tags="&lt;antenna&gt;&lt;frequency&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6898" PostTypeId="2" ParentId="6897" CreationDate="2016-11-28T21:53:20.997" Score="6" Body="&lt;p&gt;You can think of the frequency range specification as if you did have an ideal “every frequency” antenna but the signal passes through a &lt;em&gt;filter&lt;/em&gt; before reaching the receiver. That is, any signal will be attenuated by some amount, depending on the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This attenuation does not mean that the signal cannot be received; it means that it is weaker, and therefore will have a worse &lt;em&gt;signal-to-noise ratio&lt;/em&gt; (SNR) once the noise and imperfections inherent to your receiver have their effects. If the SNR is not good enough then you will hear lots of noise (for an analog modulation) or be unable to decode the signal (for a digital modulation).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the extreme case, the signal will be so weak that it is “below the noise floor”, meaning that (in most cases) you cannot even tell it is there.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The upside of the frequency selectivity of an antenna is that it helps you &lt;em&gt;not&lt;/em&gt; receive the signals you &lt;em&gt;don't&lt;/em&gt; want. Your receiver (whether RTL-SDR, traditional analog radio, or anything else) is not perfect at selecting exactly the signals in the frequency range you have tuned it to, and some amount of &lt;em&gt;out-of-band&lt;/em&gt; signals will come in anyway and interfere with the process of demodulating the signal you actually wanted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, you should not look for an antenna whose specified frequency range matches your receiver. In fact, it would be very hard to do so — a “500 kHz to 1.7 GHz” antenna would end up being an impractically large metal structure. Instead, you should use multiple antennas which are individually suitable for various frequency ranges. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you are not transmitting, you do not need to stick exactly to the specifications of an antenna (which are generally written for transmitting and not for receiving, unless otherwise specified), but you do want to be in the right order of magnitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, my home station has three antennas I use for general receiving, and they can be (roughly) described as “HF, VHF, and UHF” — that is, useful for 3-30 MHz, 30-300 MHz, and 300-3000 MHz. Each one has a dedicated RTL-SDR device (with switches to swap them over to transmitting use), but you can also just replug things as you wish. (BNC connectors are much more convenient for this purpose than SMA connectors, since they do not have to be screwed down tightly each time.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;When you're just getting interested in things and you don't know what frequency ranges you're going to be interested in, the cheapest and most flexible way to get started is to use homemade wire antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Get some wire — solid for small rigid self-supporting antennas, stranded for large ones strung between supports — and find some way to hook it up to the coaxial jack on your receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One way is a &lt;a href=&quot;https://www.google.com/search?q=binding+post+to+bnc&amp;amp;oq=binding+post+to+bnc&quot; rel=&quot;noreferrer&quot;&gt;binding post to BNC adapter&lt;/a&gt;, in your case paired with a BNC-to-SMA adapter, and you clamp the wire in the posts. Other people like to buy connectors and solder the wires to them instead, which is better if you're handy with a soldering iron and want something for eventual long-term use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two basic parts of antenna theory you'll find helpful:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Length. If you are building a monopole, dipole, or ground-plane antenna, you have one or two wires sticking out from the feed point (where the coax meets the antenna). That wire should be roughly &lt;em&gt;one-quarter wavelength&lt;/em&gt; at the frequency of interest. That is, find the frequency, convert to wavelength, then divide by four, and cut that much wire. (Remember, as I mentioned above, that it doesn't have to be at all exact for receiving.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Polarization. The polarization of the signal affects whether your antenna's wires need to be oriented horizontally or vertically, and therefore what designs of antenna are more practical for the application.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-11-28T21:53:20.997" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6899" PostTypeId="2" ParentId="6897" CreationDate="2016-11-28T23:15:53.227" Score="4" Body="&lt;p&gt;If radios were ears, then frequencies would be pitches. Human hearing goes from about 20 to 20,000 Hz, and your radio can &quot;hear&quot; from 500,000 Hz to 1,700,000,000 Hz. There are sounds and radio waves outside those frequencies, but you just can't hear them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas have a range of frequencies they can &quot;hear&quot; also. You can connect an antenna designed for any frequency you like to the radio and nothing bad will happen, but unless the antenna &lt;em&gt;and&lt;/em&gt; the radio can hear the signal, you'll just receive silence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What frequencies you need to hear depends on what you want to receive, obviously. For example, FM radio broadcast is from 88 to 108 MHz, and the 2 meter amateur band is around 144 to 148 MHz, for example. Local regulations may be different, of course.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-11-28T23:15:53.227" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6900" PostTypeId="2" ParentId="6887" CreationDate="2016-11-29T02:17:31.697" Score="7" Body="&lt;p&gt;I'm a tier 3 network support tech at a major Canadian ISP.  Ham radio interference is a disturber our systems actually specifically check for, in relation to ADSL2+ and VDSL signals, and I've seen cases where line errors appear to have been caused by the client's own antenna. It's possible that whoever you're talking to for tech support has access to similar software listing the line disturbers. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just about anything that produces a strong enough RF field can induce current in the phone lines, causing errors. For example - we used to have an issue with treadmills next to phone jacks causing similar problems.&lt;/p&gt;&#xA;" OwnerUserId="8778" LastEditorUserId="4665" LastEditDate="2016-11-29T03:33:52.670" LastActivityDate="2016-11-29T03:33:52.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6901" PostTypeId="2" ParentId="6887" CreationDate="2016-11-29T06:49:05.180" Score="5" Body="&lt;p&gt;Short answer: Based on your description of the scenario, it's possible, but seemingly unlikely, that interference received from the ham radio is causing your problems.&lt;/p&gt;&#xA;&lt;p&gt;Longer answer:&lt;/p&gt;&#xA;&lt;p&gt;Kevin's answer is good (especially his recommendation to talk to your neighbor and get his input,) but I just wanted to add a few things regarding the technical aspects involved in answering your question:&lt;/p&gt;&#xA;&lt;h3&gt;General Background on RF Communications and Hams&lt;/h3&gt;&#xA;&lt;p&gt;Most forms of home Internet connections use RF (radio-frequency) signals to transmit the data, regardless of whether that's over a wire or over the air. This is true for DSL, cable, and any currently-popular form of wireless ISP. The only major exception to this is fiber-optic ISPs, which use light signals instead of RF signals (but even those could potentially have RF equipment in the transceivers, that is, in the modem.)&lt;/p&gt;&#xA;&lt;p&gt;Additionally, home networks use RF signals to transmit information (i.e. Wi-Fi, Bluetooth, and even wired Ethernet.)&lt;/p&gt;&#xA;&lt;p&gt;All forms of RF communication, whether wired or wireless, operate in some frequency band. In most cases, only signals (whether intentional signals or unintentional ones like harmonics and spurs) in or near the operating band will cause interference with a given communication system. The frequencies of these bands are measured in Hertz (Hz.) 1 kHz = 1,000 Hz, 1 MHz = 1,000,000 Hz, and 1 GHz = 1,000,000,000 Hz.&lt;/p&gt;&#xA;&lt;p&gt;Ham radio operators broadcast signals on &lt;a href=&quot;https://en.wikipedia.org/wiki/Amateur_radio_frequency_allocations#Band_characteristics&quot; rel=&quot;nofollow noreferrer&quot;&gt;frequencies ranging from around 135 kHz up to around 30 MHz&lt;/a&gt;. This is relatively low compared to most modern RF communication.&lt;/p&gt;&#xA;&lt;h2&gt;Potential Effects on Different Types of Internet Connections&lt;/h2&gt;&#xA;&lt;p&gt;Here's a rough guide to how different networking and Internet connection technologies work, including which frequency bands they use and how they could be affected by a ham operator:&lt;/p&gt;&#xA;&lt;h3&gt;DSL&lt;/h3&gt;&#xA;&lt;p&gt;DSL ISPs typically use quite low frequencies, &lt;a href=&quot;https://en.wikipedia.org/wiki/Digital_subscriber_line#Operation&quot; rel=&quot;nofollow noreferrer&quot;&gt;in the kHz to the tens of MHz&lt;/a&gt;. Notice that this is the same general region of the spectrum used by ham operators. Furthermore, DSL operates on normal home phone cables, which are not very well shielded because they were originally only designed to carry baseband voice signals which only go up to a bit over 3 kHz. Because of this poor shielding, all of the phone cables in your home can act as a big antenna and receive any radio signals that are being transmitted over the air nearby at high enough power levels.&lt;/p&gt;&#xA;&lt;p&gt;As such, it's actually quite possible for a ham operator who is currently transmitting enough power in the direction of your home to interfere with a DSL signal enough to cause high packet drop rates or even total connection loss, especially if your phone lines and/or DSL modem aren't shielded well (which they probably aren't.)&lt;/p&gt;&#xA;&lt;h3&gt;Cable&lt;/h3&gt;&#xA;&lt;p&gt;Cable ISPs typically use much higher frequencies in the hundreds of MHz up into the GHz. These signals are then transmitted down a coaxial ('coax') cable that is usually shielded pretty well. Since the cables are shielded reasonably and the frequency bands are quite far from those used by hams, it's very unlikely that a ham's operations could interfere with a cable Internet connection unless the ham radio was sitting right beside the cable and/or modem and transmitting a high amount of power.&lt;/p&gt;&#xA;&lt;h3&gt;Wi-Fi, Cellular Data Networks, et al.&lt;/h3&gt;&#xA;&lt;p&gt;Wi-Fi, Bluetooth, and other relatively short-range data networks generally use either the 900 MHz band, the 2.4 GHz band, or the 5.8 GHz band (and some newer equipment uses 60 GHz.) Cellular data networks generally operate from around 800 MHz to around 2.2 GHz. As such, these networking technologies all operate in frequency bands quite far from where hams broadcast. That said, unlike wired technologies, these technologies are intentionally designed to receive signals that are broadcast over the air. Due to the short length of their antennas and their receiver designs, they will not pick up signals in the ham bands well, but they will pick them up somewhat if there's enough power being broadcast.&lt;/p&gt;&#xA;&lt;p&gt;As a result of these factors, these technologies will be significantly more susceptible to interference from a ham transmission than a cable connection would be, but probably not as susceptible as a DSL connection. A ham radio transmitting close to a Wi-Fi station could take it down, but probably not one at your neighbor's house unless he's really aiming a lot of power at you.&lt;/p&gt;&#xA;&lt;h2&gt;Diagnosis&lt;/h2&gt;&#xA;&lt;p&gt;As other answers have suggested, it's quite possible for ham radio transmissions to interfere with a DSL signal. If your Internet connection is cable, though, then the tech who suggested the ham might be the problem was probably smoking something. That said, the patterns you've described for the behavior of your Internet connection suggest that, even if you are using DSL, it's more likely a problem with your modem or ISP, as it's unlikely that your neighbor is transmitting all day long.&lt;/p&gt;&#xA;&lt;p&gt;If you do use DSL, there are a couple of ways to go about confirming or denying whether your neighbor's ham radio is the source of your problems:&lt;/p&gt;&#xA;&lt;h3&gt;Talk to Your Neighbor&lt;/h3&gt;&#xA;&lt;p&gt;As others have suggested, talk to him. He'll probably tell you when he's been transmitting and the patterns of his transmit times either will or won't line up with when you've been having problems.&lt;/p&gt;&#xA;&lt;h3&gt;Use a Spectrum Analyzer&lt;/h3&gt;&#xA;&lt;p&gt;Another possibility is to use a spectrum analyzer to check out the signal integrity and look for possible interfering signals. Honestly, the tech who visited your house really should have already done this in attempt to diagnose the problem. The cable techs who have been to my house in the past have indeed hooked the line up to a handheld SpecAn to check out the signal. If you have a friend who happens to be an electrical engineer (especially an RF engineer) or an RF or ISP tech, they might be willing to bring one over and hook it up to your phone lines to see what the relevant portion of the spectrum looks like. This should pretty definitively tell you whether the problem is due to an interfering signal or not. If it is due to an interfering signal, you could hook the SpecAn up to an antenna designed for the appropriate band and see if the problem signal gets stronger as you go toward your neighbor's antenna.&lt;/p&gt;&#xA;" OwnerUserId="8782" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-11-24T19:06:48.907" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6903" PostTypeId="1" CreationDate="2016-11-30T00:18:32.383" Score="3" ViewCount="633" Body="&lt;p&gt;I thought maybe this was a 4:1 balun, but a number of 4:1 single core balun diagrams that I found online had different connections. &lt;a href=&quot;http://www.rason.org/Projects/balun/balun.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;N1HFX's balun page&lt;/a&gt; and &lt;a href=&quot;http://www.qsl.net/g4wpw/balun%20page.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;the bottom of G4WPW's page&lt;/a&gt; show a connection of one wire directly from the balanced to the unbalanced side. The pictured balun does not have such a connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is only one core and the connector at the bottom is an SO-239. I may get a chance to test it later on with a 50 ohm load and an impedance tester, but at the moment this balun is not in front of me.    &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this a current balun or a voltage balun?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What should the impedance ratio be?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/idSWn.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/idSWn.jpg&quot; alt=&quot;unknown HF transmitting balun&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2016-11-30T00:57:12.713" LastActivityDate="2016-12-03T16:03:42.550" Title="Balun identification from picture" Tags="&lt;balun&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6905" PostTypeId="2" ParentId="6903" CreationDate="2016-11-30T03:02:41.180" Score="3" Body="&lt;p&gt;Looks like it might be a clever way of winding a 4:1 voltage balun to simplify the wire routing (or just straight up incorrectly wired). I'd have to see the connections at the top more clearly to be sure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regardless, seems pretty safe to assume it's a voltage balun. The quick way to tell would be to check it for a DC short between the terminals on the unbalanced (or balanced) side. If they're shorted, it's a voltage balun, and as such, not much of a balun at all. The choking impedance from these single core 4:1 voltage baluns is so low (usually &amp;lt;500 ohms) as to be nearly useless unless your antenna has low enough impedance that yo don't need the 4:1 to begin with. W8JI and K9YC have both done good tear downs showing just how awful they are for most applications. They should be considered an impedance transformer and not much else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; drawing out the windings, it appears it is an attempt to shoe-horn a 2 core Guanella 4:1 current balun on to a single core. &lt;a href=&quot;http://vk6ysf.com/balun_guanella_current_1-4.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Figure 2 here&lt;/a&gt; shows how it would be accomplished with two cores, and the builder appears to have just decided to do a split winding on a single core, perhaps in an attempt to get the best of both worlds, good common mode isolation and a 4:1 transformation on a single core. In reality, I would guess this actually causes it to exhibit less than a 4:1 transformation, in addition to having little common mode suppression. It appears it would exhibit considerable shunt capacitance between windings, and depending on the core material, potentially a low impedance shunt path through the core.&lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="246" LastEditDate="2016-12-03T16:03:42.550" LastActivityDate="2016-12-03T16:03:42.550" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6906" PostTypeId="1" AcceptedAnswerId="6907" CreationDate="2016-11-30T23:07:14.297" Score="4" ViewCount="517" Body="&lt;p&gt;I have a question about dipole construction. I am working with a turnstile, but building dipoles to validate my system with linearly polarized transmission before moving on to circular.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My design has a turnstile deploying from a cubesat, but the elements are spaced apart by the width of the cubesat face (about 4 inches). I'm referring to the center gap, between feedpoints. This is a common design, so I know it's viable. What I want to know is how spacing the elements apart physically affects feedpoint impedance and other characteristics. I haven't been able to find literature on this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A solid explanation of how this would affect my antenna and/or links to good references would be appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UHF antenna centered on 433MHz&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Copper plated Spring Steel elements&lt;/p&gt;&#xA;" OwnerUserId="8509" LastActivityDate="2016-12-01T16:39:29.197" Title="Dipole Center Spacing" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6907" PostTypeId="2" ParentId="6906" CreationDate="2016-12-01T02:13:06.540" Score="4" Body="&lt;p&gt;If you model your feed point as being the two points where your antenna meets the body of the satellite, then you have a secondary problem which you will also have to solve: how does the signal pass between your transmitter and those two points? What are the impedances there?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think you are better off &lt;em&gt;modeling the satellite's structure as part of the antenna,&lt;/em&gt; as well as whatever internal conductors bring the two antenna elements to a single point where they can be joined to a transmission line (or directly to the transmitter's output port). This is a harder problem, likely answered not generically by theory but with the use of antenna simulation software (and some empirical testing to validate your model), but it is the problem you actually need to solve.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-12-01T16:39:29.197" LastActivityDate="2016-12-01T16:39:29.197" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6908" PostTypeId="1" CreationDate="2016-12-02T03:12:10.260" Score="2" ViewCount="153" Body="&lt;p&gt;I'm very interested in replicating a design published by NASA here : &lt;a href=&quot;https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670027843.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670027843.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically the arrangement on Page 11. I have a similar design using a hybrid coupler, and this is very nearly what I want to build in terms of antenna system, but I don't understand how the coax is attached to the antenna elements as shown in this diagram.  &lt;a href=&quot;https://i.stack.imgur.com/lEMsj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lEMsj.png&quot; alt=&quot;Phasing Network&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would assume that it would simply be the center of the coax, but this doesn't really make sense with the way I understand connecting coax to an element.&#xA;If someone could explain the connection to the antenna that would be appreciated.&lt;/p&gt;&#xA;" OwnerUserId="8509" LastActivityDate="2016-12-02T15:29:58.730" Title="Interpretation of NASA design" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6909" PostTypeId="2" ParentId="6908" CreationDate="2016-12-02T05:28:03.267" Score="0" Body="&lt;p&gt;It doesn't make much sense to me either, or rather, the details are not specified adequately. What &lt;em&gt;is&lt;/em&gt; specified in the document you linked is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The near quarterwave monopole, fed as one half of an opposed pair of antennas&#xA;  has an input impedance of the order of $80 \pm45^{\circ}$. It is therefore possible&#xA;  to match the impedance to either 50 or 100 ohms depending on system requirements.&#xA;  Usually a plot of impedance vs length of the antennas in the proper&#xA;  structure is made and a convenient value of length selected to facilitate matching.&#xA;  The matching components (all reactive) are installed in a small chamber&#xA;  in the base of each antenna. This permits the rest of the feed system to operate&#xA;  in a low loss balanced condition. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The only “opposed pairs” in this system are the pairs of antennas 180° out of phase, such as the pair of #1 and #3.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since #3 is (called) a monopole, at the end of a 50 Ω feed line, it &lt;em&gt;must&lt;/em&gt; be fed in the manner of a ground-plane antenna, with the spacecraft's outer shell connected as the ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then since there is a 50 Ω line to the left and a 50 Ω line to the right of #1, we must conclude that the thing called a matching network in fact incorporates a &lt;em&gt;power divider&lt;/em&gt; to split (or combine) the signal between #1 and the line to #3.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't find this very plausible, but it's the best interpretation I find so far of what's written there.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-12-02T15:11:48.643" LastActivityDate="2016-12-02T15:11:48.643" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6910" PostTypeId="2" ParentId="5531" CreationDate="2016-12-02T06:33:15.953" Score="0" Body="&lt;p&gt;Those regular cuts along the side of the cable are typical of a mechanical device of some sort. I am thinking that it has been mowed or at the very least run over by something sharp.&lt;/p&gt;&#xA;" OwnerUserId="6084" LastActivityDate="2016-12-02T06:33:15.953" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6911" PostTypeId="2" ParentId="6811" CreationDate="2016-12-02T14:52:12.587" Score="0" Body="&lt;p&gt;Amodem works very well for my needs. This question is no longer active. I can push 3-4KB/s after adjusting mic/spkr levels with amodem {send,recv} --calibrate. Only tried peer-to-peer, not over repeaters, which is likely frowned upon for this kind of tomfoolery anyway.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2016-12-02T14:52:12.587" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6912" PostTypeId="2" ParentId="6908" CreationDate="2016-12-02T15:29:58.730" Score="1" Body="&lt;p&gt;It's not stated explicitly in the description for figure 7 (the one from your question), but in the description for a previous and similar design, on page 8:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;To get the necessary 90' phase shift, a quarter wavelength of&#xA;  50 ohm coaxial cable is used on one ouptut. Each antenna is matched to 100 ohms and the opposite pairs are connected by a half wavelength of 50 ohm coaxial cable. This provides an effective impedance of 50 ohms at the hybrid output ports.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I assume the feedpoint impedance of 100Ω and the half-wavelength 50Ω cable holds, and they are connected like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/AJPUC.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fAJPUC.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Arranged this way, the antennas are connected through a simple T-junction power divider.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each of the antennas is a 100Ω load. If you start looking into ANT4's feedpoint, you see 100Ω. As you move back over the half wavelength of coax, you see 100Ω, but reversed in phase. At this point, ANT2 (also 100Ω) is connected in parallel. 100Ω in parallel with 100Ω makes 50Ω.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-12-02T15:29:58.730" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6913" PostTypeId="1" CreationDate="2016-12-03T16:26:39.183" Score="1" ViewCount="217" Body="&lt;p&gt;I know that it is best to twist the wires that supply DC power to a device, as to decrease the &quot;loop&quot; surface area. This diminishes the amount of RF that gets coupled in the wires as well as the radiated RF. Correct me if wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I was thinking about coax. When using coax for a DC supply (limited power, small currents), the skin effect does not affect the currents on the shield, creating (I think) just a longwire antenna, where the shield doesn't do any shielding. That would make it possibly the worst kind of conductor for DC when thinking about RF susceptibility.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this correct?&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2016-12-05T21:31:19.067" Title="Using coax for DC, good idea?" Tags="&lt;coaxial-cable&gt;&lt;rfi&gt;&lt;dc-power&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6914" PostTypeId="2" ParentId="6913" CreationDate="2016-12-03T16:44:47.367" Score="2" Body="&lt;p&gt;Any type of cable will be just as good or bad at avoiding RF pickup no matter what signal it is used for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency of the &lt;em&gt;intended&lt;/em&gt; signal on a transmission line &lt;strong&gt;does not change&lt;/strong&gt; the way it interacts with outside radiation. Therefore the amount of RFI getting into your device as a result of the cable attached is the same regardless of whether the cable carries DC, AC, or RF. (That amount should also be very small, provided that your device has a shielding metal chassis and the coaxial connector is in contact with that chassis.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The interaction of electromagnetic waves with anything that is composed of just metal and dielectrics (including empty air) follows the &lt;strong&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Superposition_principle&quot; rel=&quot;nofollow noreferrer&quot;&gt;superposition principle&lt;/a&gt;&lt;/strong&gt; (to a very good approximation). According to this principle, you can calculate the effects of the external RF impinging on the cable &lt;em&gt;separately&lt;/em&gt; from the cable transporting the signal inside it, and then &lt;em&gt;add&lt;/em&gt; the results afterward. If this were not the case, then the cable would have some nonlinear element — would be functioning as a “mixer” or “detector” — which would be very bad for the integrity of any RF signal carried on the cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, incidentally, the functionality of a coaxial cable's shield is not at all dependent on the skin effect; the effect and mode of operation is the same all the way down to DC. The case where it does have trouble is at &lt;em&gt;higher&lt;/em&gt; frequencies (microwave and up).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-12-05T21:31:19.067" LastActivityDate="2016-12-05T21:31:19.067" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6915" PostTypeId="2" ParentId="6886" CreationDate="2016-12-03T17:43:48.670" Score="2" Body="&lt;p&gt;I also have had quite some problems with linux and the FCD. It appears that is is related to bandwidth reservation of the USB bus. The FCD is a USB 1.1 device which is 12Mbit/s. As you are probably running it in a USB 2.0 port so there is a USB 2.0 to USB 1.1 arbitration unit in the USB interface chip. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The linux kernel has to allocate the bandwidth to each device USB 1.1 device on the USB 1.1 arbitration hardware and as the FCD runs at 96ksampes/second consumes a significant amount of USB 1.1 bandwidth.  For memory linux requires a contiguous allocation of the USB 1.1 bandwidth for the USB device and if you a have keyboards and mice (which generally are usb 1.1) then this fragments the USB bandwidth allocation table. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is the case you can try two things: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) remove everything else from the USB bus especially keyboards and mice. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) switch to a USB 3.0 port which seems to be better specified but INTEL and the software to drive it is better/more-consistently written. It handles USB 1.1 arbitration better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I opted for #2 and FCD seems to be working fine on linux for me. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Windows seems to do a better job of USB 1.1 arbitration/USB bandwidth allocation so yes my FCD worked in windows but not in linux. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did look into the USB software on linux with a view to fixing it but ran away crying when faced with the complexity and the possibility that each USB chipset vendor can &quot;do it differently&quot;  USB 2.0 is a box of hammers!!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recall than is was also heavily dependent on the USB silicon vendor on our PC and which USB hubs/devices you have connected so what works for some, didn't for other etc etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is a shame as I really like the FCD, but the fact that it is USB 1.1 is a real bummer for plugging and playing on linux.. I found. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As always your mileage may vary and with this particular problem you are almost guaranteed it will.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a &lt;a href=&quot;https://github.com/csete/gqrx/issues/91&quot; rel=&quot;nofollow noreferrer&quot;&gt;bug report&lt;/a&gt; for GQRX that details it, although the issue is not with gqrx but linux kernels treatment of USB devices.&lt;/p&gt;&#xA;" OwnerUserId="8806" LastEditorUserId="4665" LastEditDate="2016-12-06T19:01:24.687" LastActivityDate="2016-12-06T19:01:24.687" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6916" PostTypeId="1" AcceptedAnswerId="6917" CreationDate="2016-12-04T13:25:06.567" Score="2" ViewCount="98" Body="&lt;p&gt;Bottom line is I have got a very strange (but regular) reading on a &amp;lt; $1 type of ASK 433 MHz receiver. Have a look at it - those 3 spikes are sometimes caught by my receiver, don't know their source. But I am curious as to what they might be produced by. They don't quite look as they were carrying much information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rRy2l.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rRy2l.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8811" LastActivityDate="2016-12-15T22:44:28.990" Title="different digital modulations interference. Does it happen?" Tags="&lt;receiver&gt;&lt;modes&gt;&lt;rfi&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6917" PostTypeId="2" ParentId="6916" CreationDate="2016-12-04T14:08:43.713" Score="1" Body="&lt;p&gt;That's impossible to tell. An ASK receiver will only see amplitude (or rather: envelope) – that's its job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, signals exist with modulated phase, too, not to mention that if you do a frequency modulation, the amplitude seen by an ASK detector will look strange.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you'd need to do is look at the &lt;em&gt;raw&lt;/em&gt; signal (at 433MHz +- signal bandwidth/2) or look at an equivalent intermediate frequency signal (IF +- bandwidth/2) or, most easily, at an equivalen complex baseband signal (+- bandwidth/2). Those fully capture what the signal &lt;em&gt;actually&lt;/em&gt; does (rather than just reduce the signal to its amplitude/envelope).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Essentially, if you do that with a PC, you'd have Software Defined Radio (SDR). I think the cheap less-than $30 RTL-SDR dongles will do pretty nicely for that purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt; &lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Good news, everyone!&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;So you've got an SDR device – a RTL dongle, and now would like to use it to analyze signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I must admit that I'm not that much of a guy that handles overly many computer operating systems – whenever I can, I try to take &quot;my setup&quot; with me. So that's what I'll do here: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Get the GNU Radio live &lt;a href=&quot;https://gnuradio.org/redmine/projects/gnuradio/wiki/GNURadioLiveDVD&quot; rel=&quot;nofollow noreferrer&quot;&gt;SDR environment image&lt;/a&gt;. It's a bootable DVD image – you can thus directly burn it to a DVD (don't drop it as a file onto the DVD, but burn it as image), or use tools like &lt;a href=&quot;https://www.netbsd.org/~martin/rawrite32/download.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Rawrite32&lt;/a&gt; to write it to a &gt;= 4GB USB drive.&lt;/li&gt;&#xA;&lt;li&gt;Boot from that medium&lt;/li&gt;&#xA;&lt;li&gt;Connect your RTL dongle :)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h2&gt;GQRX-based recording&lt;/h2&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Run GQRX; it should start with something like: &lt;a href=&quot;https://i.stack.imgur.com/WbcvC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WbcvC.png&quot; alt=&quot;Device selection Dialog&quot;&gt;&lt;/a&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Under &quot;Device&quot; look for &quot;Realtek RTL…&quot; and select that&lt;/li&gt;&#xA;&lt;li&gt;&quot;OK&quot; this dialog away&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;You'll be greeted by a window looking like this:&lt;a href=&quot;https://i.stack.imgur.com/bnXmi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bnXmi.png&quot; alt=&quot;GQRX main window&quot;&gt;&lt;/a&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;you can now start the reception by clicking on the highlighted button &lt;a href=&quot;https://i.stack.imgur.com/bEI3i.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bEI3i.png&quot; alt=&quot;start button&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;you'll now see a waterfall scroll by, and the momentary spectrum in the top of the window. Adjust your frequency till you can see your signal of interest in the waterfall. I jumped to 666 MHz just to have something to show: &lt;a href=&quot;https://i.stack.imgur.com/7mD5x.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7mD5x.png&quot; alt=&quot;waterfall running&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;click on the recording button: &lt;a href=&quot;https://i.stack.imgur.com/QMabh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QMabh.png&quot; alt=&quot;recording button&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;you're greeted by a window: &lt;a href=&quot;https://i.stack.imgur.com/Npwxd.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Npwxd.png&quot; alt=&quot;recording management window&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;here you can click on the &lt;code&gt;rec&lt;/code&gt; button to make a recording in the specified folder.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;With the recording from GQRX, you can then feed offline analysis tools like audacity (File-&gt;Import-&gt;Raw Data-&gt;pick your recording-&gt;32bit float, little-endian,2 channels)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h2&gt;live analysi&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Alternatively, you can also directly do this analysis from within the GNU Radio companion. On the desktop, click the &lt;em&gt;GNU Radio Companion&lt;/em&gt; logo.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You're greeted by a window looking somewhat like this:&lt;br&gt; &lt;a href=&quot;https://i.stack.imgur.com/6LC6R.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6LC6R.png&quot; alt=&quot;Empty GNU Radio Companion&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;click the magnifying glass to activate the search function.&lt;/li&gt;&#xA;&lt;li&gt;Look for the &quot;osmocom source&quot;. Drag that onto the canvas: &lt;a href=&quot;https://i.stack.imgur.com/NM3Wl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NM3Wl.png&quot; alt=&quot;GRC w/ osmocom source&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Now, obviously, our sampling rate is not what we want. Double click on the &lt;em&gt;&quot;samp_rate&quot; Variable&lt;/em&gt;: &lt;a href=&quot;https://i.stack.imgur.com/mo8Np.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mo8Np.png&quot; alt=&quot;variable properties&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Change &quot;32000&quot; to &quot;2e6&quot;. 2MHz seems like a nice sampling rate. Close the variable property window.&lt;/li&gt;&#xA;&lt;li&gt;Now, add a slider that allows us to change the center frequency on the run: search for &quot;range&quot; in the block list again. Add at &quot;QT GUI Range&quot; to the canvas. Double click it to change its properties:&lt;br&gt; &lt;a href=&quot;https://i.stack.imgur.com/8nrib.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8nrib.png&quot; alt=&quot;Slider properties&quot;&gt;&lt;/a&gt; &lt;br&gt;should be modified to read&lt;br&gt; &lt;a href=&quot;https://i.stack.imgur.com/PBtZR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PBtZR.png&quot; alt=&quot;Center Frequency slider&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Click ok, double click on the osmocom source. For now, just use &lt;code&gt;center_freq&lt;/code&gt; (the ID of our slider!) in the &quot;Ch0: Frequency (Hz)&quot; field:&lt;br&gt;&lt;a href=&quot;https://i.stack.imgur.com/eJSrn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eJSrn.png&quot; alt=&quot;Entered &amp;lt;code&amp;gt;center_freq&amp;lt;/code&amp;gt;&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Now comes the fun part: search for &quot;time sink&quot; and &quot;frequency sink&quot; in the block list. Add both to your flow graph:&lt;br&gt; &lt;a href=&quot;https://i.stack.imgur.com/gzNHV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gzNHV.png&quot; alt=&quot;Canvas with sinks&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Click on the output port of the &lt;em&gt;osmocom source&lt;/em&gt; and the &lt;em&gt;QT GUI Time Sink&lt;/em&gt;. A connection between them appears. Repeat with &lt;em&gt;osmocom source&lt;/em&gt; and &lt;em&gt;QT GUI Frequency sink&lt;/em&gt;: &lt;br&gt; &lt;a href=&quot;https://i.stack.imgur.com/N1Sui.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/N1Sui.png&quot; alt=&quot;connected everything&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Double click the Frequency sink, and use &lt;code&gt;center_freq&lt;/code&gt; in the &quot;Center Frequency (Hz)&quot; field.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;We're ready to go!&lt;/strong&gt; Hit the the &quot;execute button&quot;: &lt;a href=&quot;https://i.stack.imgur.com/h8NF9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/h8NF9.png&quot; alt=&quot;menubar of GRC&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Because you haven't saved before, you'll be asked to enter a file name. Choose whatever you like. OK.&lt;/li&gt;&#xA;&lt;li&gt;TADAAA! Instant live display of your signal :)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You might want to close the display and go back and increase the BB and RF gain in the osmocom source. Adjust to your liking, or add another slider to make it run-time adjustable!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2016-12-15T22:44:28.990" LastActivityDate="2016-12-15T22:44:28.990" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6918" PostTypeId="2" ParentId="6916" CreationDate="2016-12-04T17:54:21.560" Score="1" Body="&lt;p&gt;I think you're asking if you the simple-looking spikes occurring after the ASK transmissions are a different mode being picked up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am quite confident they are not — rather, they are part of the end of the signal from the ASK transmitter. Note that they always occur with a specific time after the end of the ASK transmission — this is plenty of evidence by itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More speculatively:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They have a classic exponential-decay shape, which is likely not actually part of the transmitted signal but the result of a DC-blocking filter (coupling capacitor) somewhere in your receive path. Therefore I hypothesize that your waveform is inverted polarity (greater amplitude lower on the display) and the transmitter is remaining active for a while after the modulated data ends and the separated spike is the true end of the signal. If the spikes are sometimes absent, that might be due to the data ending with a 0 instead of a 1 or vice versa and the transmitter just happening to extend the last bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Marcus Müller mentioned, you can get a better picture by using a SDR receiver which records the entire input instead of just the amplitude. Avoiding the DC-blocking filter would also make it clearer by letting you see absolute signal magnitudes instead of just edges (but that's not useful for actually demodulating the intended signal, just for understanding).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-12-04T17:54:21.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6919" PostTypeId="1" CreationDate="2016-12-04T19:37:16.773" Score="1" ViewCount="102" Body="&lt;p&gt;If I have an end fed long wire in free space, say 100 ft,&#xA;how do I calculate its $R$ &amp;amp; $X$ at different frequencies? &lt;/p&gt;&#xA;" OwnerUserId="8814" LastEditorUserId="76" LastEditDate="2017-01-19T00:28:15.890" LastActivityDate="2017-01-19T00:28:15.890" Title="Antenna Impedance calculation for low frequency" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;impedance&gt;&lt;end-fed-antenna&gt;" AnswerCount="0" CommentCount="0" FavoriteCount="0" ClosedDate="2017-01-18T16:48:47.583" ContentLicense="CC BY-SA 3.0" />
  <row Id="6921" PostTypeId="1" AcceptedAnswerId="6922" CreationDate="2016-12-05T10:58:34.580" Score="3" ViewCount="137" Body="&lt;p&gt;I don't have a radio club near me, and as far as I'm aware I can't get an amateur radio license without being at a club to do the tests. Is there a way I can get an amateur radio license?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have done some reading and I can't find anything specific; all I get is dead end links or Find A Club. I can't really travel far either so I can't get to a club. I live in the north east of England.&lt;/p&gt;&#xA;" OwnerUserId="8641" LastEditorUserId="76" LastEditDate="2016-12-05T16:18:28.367" LastActivityDate="2016-12-05T16:18:28.367" Title="How do I get a license without being near a club?" Tags="&lt;license&gt;&lt;united-kingdom&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6922" PostTypeId="2" ParentId="6921" CreationDate="2016-12-05T11:55:02.100" Score="2" Body="&lt;p&gt;Well, you're not going to like the answer, because it does seem to boil down to: Find a club. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I can gather, the exams are done by RSGB so you'll need to schedule an examination date at one of the clubs and go there to take the exam. There's a list of examination locations here: &lt;a href=&quot;https://thersgb.org/services/coursefinder/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://thersgb.org/services/coursefinder/&lt;/a&gt;&#xA;From what I can see, you don't need to actually go to a course, if you can learn everything on your own or if you want to take an online course. You just need to appear for the exam. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The exams have two parts:&#xA;The practical part is very easy (or at least that's how it looks to me), you don't have to do it at the same time as the theoretical part and the results are valid for a year. We already have a question about that here: &lt;a href=&quot;https://ham.stackexchange.com/q/5304/77&quot;&gt;UK Foundation - initial practical assessment, what to expect?&lt;/a&gt; It appears that you don't actually have to go to a club to do it, you can do it from assessor's location. There's a practical part for the Foundation license and there's a practical part for the Intermediate license, but you can do both at the same time, if you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there's the written part as well, for which you'll need the practical assessment certificate. From what I can see, you'll need to appear for that part at an examination center. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can't move for some reason, perhaps it would be a good idea to contact RSBG and see what they can tell you about that. On &lt;a href=&quot;http://rsgb.org/main/clubs-training/for-students/foundation/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; page, there's the telephone number of their examinations department. Perhaps it's possible to come to some sort of an arrangement, if you're immobile.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-12-05T11:55:02.100" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6923" PostTypeId="1" CreationDate="2016-12-05T15:47:40.980" Score="3" ViewCount="971" Body="&lt;p&gt;I am trying to analyze the spectrum of wifi spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I getting a good OFDM spectrum with my HackRF at 2.412 GHz (from my first QTGUI Sink). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Jwzcw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Jwzcw.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I get nothing out of OFDM Receiver. I was wondering why.  Any help would be appreciated.&lt;/p&gt;&#xA;" OwnerUserId="7843" LastEditorUserId="76" LastEditDate="2016-12-05T16:19:39.077" LastActivityDate="2016-12-07T15:51:45.747" Title="OFDM spectrum, HACKRF, and GNUradio companion" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="0" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6926" PostTypeId="1" AcceptedAnswerId="6928" CreationDate="2016-12-06T11:49:43.907" Score="3" ViewCount="232" Body="&lt;p&gt;I would like to play around with openBTS/yateBTS (experimental, no 24/7 run). What I would like to do is to modify a UMTS/GSM module or mobile phone so it operates in a frequency that can be used with a HAM license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I looked around and think in my location, Austria, I can use this frequency because in my area there are no active hams that use ATV: 1272,0 – 1290,994 MHz.  Has anybody ever done this before? Does anybody know a good module or phone where this can be archived?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I first thought about just replacing the crystal and bypassing the filters, but i can't access them all, because some of them are in the chip. Another idea was to use a mixer to offset the output frequency and place filters behind this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the questions are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it okay to use an ATV frequency when I am sure no other ham gets disturbed?&lt;/li&gt;&#xA;&lt;li&gt;How should i modify an existing chip/mobile phone?&lt;/li&gt;&#xA;&lt;li&gt;Is one of the ideas above good enough for experimental usage?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6257" LastEditorUserId="4665" LastEditDate="2016-12-06T19:20:34.073" LastActivityDate="2016-12-06T20:13:45.567" Title="Build a HamRadio Friendly UMTS Module" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6927" PostTypeId="2" ParentId="5905" CreationDate="2016-12-06T19:27:51.380" Score="0" Body="&lt;p&gt;You'd have to take all three &quot;written elements.&quot; From the &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=licensing_2&amp;amp;id=amateur&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC Licensing&#xA;Examinations page&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In the amateur radio license examination system, there are three written examination elements [Elements 2, 3, and 4]. For each operator class, you must pass the elements indicated:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;Operator Class     Required Elements&#xA;&#xA;Amateur Extra      Written Elements 2, 3, 4&#xA;General            Written Elements 2, 3&#xA;Technician         Written Element 2&lt;/pre&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The written elements are:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;&lt;pre&gt;Element   Operation Privileges    Questions   Minimum Passing Score&#xA;&#xA;2         Technician Class        35          26&#xA;3         General Class           35          26&#xA;4         Amateur Extra Class     50          37&lt;/pre&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8805" LastActivityDate="2016-12-06T19:27:51.380" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6928" PostTypeId="2" ParentId="6926" CreationDate="2016-12-06T20:13:45.567" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;… to modify a UMTS/GSM module or mobile phone so it operates in a frequency that can be used with a HAM license.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That means you'll need external mixers – mobile chipsets are very well designed to filter exactly the frequencies relevant to exactly one standard, and you won't be able to change that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With LTE, there's support for ISM-band operation in some newer chipsets (I'm not 100% about the specifics), and that also means that the Ham/ISM overlap might be usable here; also, there's LTE allocations in what's called &lt;em&gt;digitale dividende&lt;/em&gt; in the German-speaking regions – the spectrum that was freed by shutting down the analog commercial TV stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But for GSM (where that filtering is even much more fine-granular) and UMTS, I'm afraid your only option is to use external down/upconverters to transform the downlink and uplink band of the chipset to whatever you want to use.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;How should i modify an existing chip/mobile phone?&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not at all, add external uplink/downlink frequency transverters.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Is it okay to use an ATV frequency when I am sure no other ham gets disturbed?&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Probably not; I'm not an expert for legal details, but I think that usually these bands are meant for video communication, and doing something else on there isn't OK for the others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that GSM hops (or at least, the base station can configure itself and the mobiles to do so) over a large bandwidth – potentially much wider than a TV channel. UMTS channel widths are also configurable to exceed TV channel widths. I'd strongly recommend you do your first experiments within the confines of cabling!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Is one of the ideas above good enough for experimental usage?&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Experimentation is always fun!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know how much use it'll be, however. If you need to run around with a handset that is twice as large because you had to remove its original antenna, add two mixers and a diplexer and another antenna, and uses additional battery, you might really be better off with looking into getting an SDR-based LTE basestation running in the ISM bands to work with your handset. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that cell phone and cellular infrastructure manufacturers have implemented standards that are &lt;em&gt;meant&lt;/em&gt; to push the edge of &quot;state of the art&quot;. That means that these devices' receivers are heavily optimized for a specific channel model – and channel models are frequency-dependent! You get very different problems when you do something e.g. on 1.8 GHz vs doing the same transmission on 146 MHz; however, 1272 MHz is probably a channel that &quot;might be similar enough&quot; and just work (make sure the analog parts of your cellular hardware aren't hit by TV broadcast powers – cell phones are easily a couple billion times more sensitive than TV sets).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Timing in cellular networks is also optimized so that a lot of people can participate in one cell. Thus, building e.g. a GSM network where maximum distances aren't really what you'd expect (a couple of kilometers), but signals are &quot;in flight&quot; for a lot longer, then you'd need to tweak parameters of that network – and it might happen that at some point, the hardware involved simply won't be able to accomodate a setting, or that the way the network operates makes no sense anymore.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UMTS might be an especially bad choice – it depends on code orthogonality, and that actually isn't the nicest assumption for wide-spanning networks or fast-moving communication partners, or reflectors (and that's one of the technical reasons it got superseeded by LTE). Also, I think there's more mature LTE than UMTS SDR implementations out there – have a look at &lt;a href=&quot;https://github.com/srsLTE/srsLTE&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/srsLTE/srsLTE&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-12-06T20:13:45.567" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6929" PostTypeId="2" ParentId="7081" CreationDate="2016-12-07T00:46:50.117" Score="2" Body="&lt;p&gt;Any &quot;realistic&quot; end fed wire antenna has a counterpoise which may merely be the ground or actual wire conductors on the ground or some variation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to determine R,X of the feed point (assuming that is what you want) is to compute them using NEC2.  NEC2 is very easy to use and computing the R,X input is also very easy to do as it is one of the regular (always printed) outputs for the execution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are lots of resources in the Internet available via Google search to learn how to set up the geometry input specification for your antenna and running a solution given a specified frequency.  If you want runs at multiple frequencies you can do a frequency sweep execution (starting frequency plus delta increment add-on frequency).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NEC4 is the licensed version which is newer and more accurate.  And, I mention in this particular case in that it is more accurate for ground models and ground level wire conductors for the counterpoise.  Depending on your antenna geometry and the design of the counterpose, the difference between NEC2 and NEC4 can be significant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S.  I use end fed antennas quite a bit for my portable ops which are always QRP which means that to make contacts, the antenna needs to work, and they do work.  Typically, I throw a wire up over a branch of a tree (with the help of a sling shot to throw fishing line over the branch first).  This wire is hooked directly to the enter conductor of the PL-259 I use to hook up to my rig (KX3).  The ground wire counterpoise is just a conductor laying on the ground and tied to shield conductor of the PL-259.  I actually made a PL-259 with ready to connect wires that make this task easy.  The wires are about 60 feet or so long but I have operated with shorter wires too.  The auto-tuner on the Elecraft KX3 has a wide mismatch tuning range.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2016-12-07T00:53:20.157" LastActivityDate="2016-12-07T00:53:20.157" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6931" PostTypeId="1" AcceptedAnswerId="6933" CreationDate="2016-12-07T17:17:43.397" Score="2" ViewCount="2339" Body="&lt;p&gt;I am a new General and don't quite understand how Antenna Tuners work other than changing the impedance ratio between the radio and the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is - &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I need to buy a new tuner if I buy an HF amp ? I have a Elecract HF rig that has a built in tuner (rated at 20W). I want to purchase the Hardrock-50 HF amp. I don't think the Elecraft's tuner will tune through the 50 watt amp to the antenna ? Need some advice. Thanks. 73&lt;/p&gt;&#xA;" OwnerUserId="8790" LastActivityDate="2016-12-08T13:33:02.240" Title="Will an Internal Antenna Tuner work with an external HF amplifier?" Tags="&lt;amplifier&gt;&lt;antenna-tuner&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6932" PostTypeId="2" ParentId="6931" CreationDate="2016-12-07T18:14:32.037" Score="-1" Body="&lt;p&gt;You'll want to keep the SWR of the feed line to the antenna below the limits that the amplifier can handle (typically 2:1 or so), so whether you'll need an antenna tuner or not depends on the antenna and the feed line.  Some antennas, like a dipole at its design frequency or a store-bought yagi or vertical, have SWRs below those limits, in which case you wouldn't need an antenna tuner.  Many multi-band wire antennas require a tuner.  In any event, an antenna tuner and an SWR indicator (if the tuner or amplifier doesn't include one) give the operator more versatility.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-12-07T18:14:32.037" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6933" PostTypeId="2" ParentId="6931" CreationDate="2016-12-07T19:04:16.243" Score="4" Body="&lt;p&gt;Yes, you'll need an external tuner, unless your antenna is already matched sufficiently well to 50 ohms. The objective of the tuner is to transform the impedance seen by some signal source, like your radio, or the amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The amplifier will already be designed to have a 50 ohm input. Your radio, transmitting into that, is designed for a 50 ohm output, so there's no need for a tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The amplifier will see your antenna impedance though the feedline, whatever that is. The amplifier is also designed for a 50 ohm load. If your antenna is sufficiently close to 50 ohms, then no tuner is necessary. Otherwise, you'll need a tuner somewhere between the antenna and the amplifier, since the radio's tuner will have no effect on the impedance seen by the amplifier.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2016-12-07T19:04:16.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6934" PostTypeId="1" CreationDate="2016-12-08T02:19:31.193" Score="5" ViewCount="432" Body="&lt;p&gt;When a station is repeatedly violating FCC rules, transmitting out of band etc, equipment may be confiscated in addition to the fine. I am sure they have collected a large chunk of inventory from violating hams, pirate radio stations, kilowatt CB etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does the FCC do with this equipment after confiscated? Is it for sale?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2016-12-08T07:54:09.123" LastActivityDate="2017-02-08T10:36:34.977" Title="What does the FCC do with confiscated equipment?" Tags="&lt;fcc&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6935" PostTypeId="2" ParentId="6934" CreationDate="2016-12-08T13:29:44.660" Score="0" Body="&lt;p&gt;Generally, if there is an administrative action pending against an amateur from whom equipment has been seized, that equipment is held in escrow until the case is resolved (resolved meaning a final determination is ordered and the amateur has exhausted all available appeals). Once the case is resolved in favor of the government and the equipment is formally seized, it is liquidated at auction through the GSA. &lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2016-12-08T13:29:44.660" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6936" PostTypeId="2" ParentId="6931" CreationDate="2016-12-08T13:33:02.240" Score="0" Body="&lt;p&gt;Your antenna tuner should live between whatever final amplifier you are using and the antenna. The internal ATU in your radio becomes moot when you add an external amplifier, and should not be used. Whatever amplifier you are using will have a 50-ohm input that matches the output of your transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The tuning network of your amplifier is already capable of matching a slight mismatch. It is after all a matching network. An external ATU is needed though if you wish to operate a single antenna on multiple bands where the SWR of the antenna will be higher than the amplifier network's capability to match it. &lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2016-12-08T13:33:02.240" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6938" PostTypeId="2" ParentId="6732" CreationDate="2016-12-08T19:23:30.527" Score="1" Body="&lt;p&gt;You should be able to find the answer in their service manual. &lt;a href=&quot;http://www.repeater-builder.com/yvs/pdfs/yaesu-vx-2100-2200v-service-manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.repeater-builder.com/yvs/pdfs/yaesu-vx-2100-2200v-service-manual.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8840" LastActivityDate="2016-12-08T19:23:30.527" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6941" PostTypeId="1" AcceptedAnswerId="6942" CreationDate="2016-12-10T13:31:44.883" Score="4" ViewCount="256" Body="&lt;p&gt;I'm curious how AM and FM repeaters work. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the received signal demodulated and then remodulated at the new frequency or do they use some other technique?&lt;/p&gt;&#xA;" OwnerUserId="6732" LastEditorUserId="6446" LastEditDate="2016-12-11T02:06:25.450" LastActivityDate="2016-12-11T02:06:25.450" Title="How do repeaters work? (The technical side)" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6942" PostTypeId="2" ParentId="6941" CreationDate="2016-12-10T14:57:32.347" Score="6" Body="&lt;p&gt;It is &lt;em&gt;possible&lt;/em&gt; to repeat a signal without demodulating it. This is done on some amateur satellites where it is called a &lt;em&gt;linear transponder&lt;/em&gt;. The advantage of this method is that it can carry multiple signals, and any mode, including SSB and CW. The disadvantage is that it retransmits all the noise it hears and cannot clean up the modulation along the way — very much like how putting an amplifier before your receiver can't improve the signal-to-noise ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A typical FM repeater consists of a fairly ordinary receiver and transmitter, with the audio output of the receiver connected to the (microphone) audio input of the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second most critical element is a &lt;em&gt;duplexer&lt;/em&gt;, which is a pair of very narrow filters which ensure that the receiver is not overloaded by the transmitted signal on the same antenna. (The less-usual case of a &lt;em&gt;cross-band&lt;/em&gt; repeater, which has far more frequency separation between transmit and receive frequencies, does not need a duplexer.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, you usually have a repeater controller, which can be connected to the audio, PTT, etc. signals from/to the radios in order to implement additional features (repeater ID, time-out timer, repeater linking/phone patch, etc.).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-12-10T14:57:32.347" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6944" PostTypeId="1" CreationDate="2016-12-13T14:51:21.037" Score="6" ViewCount="214" Body="&lt;p&gt;Every time I click on a PSK macro, before transmitting the message, fldigi outputs a burst of something for about a second.  This is visible but not readable on my waterfall display. It wastes time and I want to get rid of it.&lt;/p&gt;&#xA;" OwnerUserId="8859" LastEditorUserId="9450" LastEditDate="2019-07-04T16:59:46.720" LastActivityDate="2019-07-04T16:59:46.720" Title="Pre-transmission burst sent by fldigi" Tags="&lt;digital-modes&gt;&lt;fldigi&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6946" PostTypeId="1" AcceptedAnswerId="6948" CreationDate="2016-12-13T21:12:49.437" Score="7" ViewCount="817" Body="&lt;p&gt;I'm researching options for getting an &quot;I'm alive&quot; message during a disaster response out to family in another state that aren't HAMs.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are likely to be a lot of possible answers that are art and style rather than one &quot;right&quot; answer, so some possible parameters.  Let me know if this still ends up too vague.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Technician or General class.&lt;/li&gt;&#xA;&lt;li&gt;Voice (aka phone), rather than CW highly preferred.&lt;/li&gt;&#xA;&lt;li&gt;Without a repeater, or at least not one for at least several hundred miles. e.g. Western Washington to California (800+) or Idaho. (500-600)&lt;/li&gt;&#xA;&lt;li&gt;Any suggested bands/frequencies where I might find someone willing to call a landline on my behalf?  I'm familiar with UHF and VHF calling frequencies - I can look up calling equivalent freqs once I settle on a band.&lt;/li&gt;&#xA;&lt;li&gt;Portable.  Something I can pack up and take, rather than needing a permanent or very bulky antenna installation or base station. I'm wondering if, matching the other constraints, there's an option for a coiled wire antenna that I can effectively throw up a tree.  Ultra portable station - car mobile size would be ideal. I'd likely have a lot of other stuff with me.&lt;/li&gt;&#xA;&lt;li&gt;Common battery types - ideally 12v off the car.  I'm unclear on the wattage I'd need for, say 500-600 miles simplex.  100-150w seems like starting to stretch the limits on a car inverter, so I may have to look for a generator based solution.&lt;/li&gt;&#xA;&lt;li&gt;Economical.  I may be just into the realm of pipe-dreams here, but at some point the cost would make satellite phone solutions more practical. I'm okay with low-end solutions (aka 'junk brands') - a disposable solution means I'm more likely to have it with me when I need it, rather than sitting at home in a padded case.&lt;/li&gt;&#xA;&lt;li&gt;My focus is mainly on CERT short-term solutions during an event like the Cascadia subduction fault, rather than &quot;end of the world&quot; long term &quot;find the survivors.&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This is a bit of a companion question to the &lt;a href=&quot;https://ham.stackexchange.com/questions/1672/options-for-family-short-range-communication-in-an-emergency&quot;&gt;short-range family communication question&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've talked with some locals with base stations and fixed antennas - but they're mostly focused on contesting at significantly further distances.  The local ARES team does have satellite phone and bulkier base-station setups - but that's focused on more continuous and varied operation.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Satellite phones are certainly the most purpose built option here, but pricey. Ideally I'd like a solution that I might use for other things - possibly as an excuse to start getting into HF...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks in advance - WE7MOR.&lt;/p&gt;&#xA;" OwnerUserId="8863" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-06-15T15:05:32.130" Title="How would you get an &quot;I'm alive&quot; message to family in another state using amateur radio?" Tags="&lt;mobile&gt;&lt;wire-antenna&gt;&lt;emergency&gt;" AnswerCount="4" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6947" PostTypeId="2" ParentId="6946" CreationDate="2016-12-13T22:15:11.173" Score="9" Body="&lt;p&gt;The ARRL NTS (National Traffic System) is the method you would use to send messages to anyone anywhere in North America and in concert with other traffic systems to many parts of the world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NTS has many message passing scheduled times on multiple bands.  In the night time hours, 80 meters is so popular that sometimes message trafficking networks are most of the stations you can hear from 5 PM to 8 PM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find any scheduled traffic group in your area.  This &lt;a href=&quot;http://www.arrl.org/nts&quot; rel=&quot;nofollow noreferrer&quot;&gt;link&lt;/a&gt; will help you get started.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NTS works by dividing North America (USA &amp;amp; Canada) into various levels of traffic handling and areas.  The way this works is that you can contact a local (in your area) net on HF or VHF/UHF and then they take the message and relay it up to the next level that routes the message to the local traffic net in the area of the party to receive the message.  In almost all cases that I have personally handled traffic for areas in and around the Seattle area I have been given a local phone number to contact the party to pass the message.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see that you are located in Redmond (via QRZ), I am located in Kirkland, Totem Lake area.  I participate in three NTS traffic handling nets each night.  They are all on 80 meters and if you are on HF with capabilities on 80 meters you are free to join up.  Note that these are not the only ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Seattle (Western Washington and greater Northwest) Traffic Nets (a few of them):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;WARTS (Washington Amateur Radio Traffic System), meets at 5:45 PM PDT on 3975 KHz using mode SSB (LSB).  Note that these are summer hours a little later than their winter hour at 5:30 PM when the band going long as the evening draws upon us.&lt;/li&gt;&#xA;&lt;li&gt;WSN (Washington Section Net), meets at 6:45 PM PDT, on 3563 KHz using CW.  Winter hours time is 6:15 PM.&lt;/li&gt;&#xA;&lt;li&gt;OSN/1 (Oregon Section Net), meets at 6:30 PM PST, on 3569 KHz using CW.  This is the regular scheduled time, OSN/1 does not change for seasonal hours.&lt;/li&gt;&#xA;&lt;li&gt;Beaver State Net (Oregon), meets at 5:30 PM PST, on 3920 KHz using SSB.&lt;/li&gt;&#xA;&lt;li&gt;Columbia Basin Net (Oregon/Washington), meets on 3960 KHz using SSB, at 6:00 PM PST.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I could list more but will hold off for now.  Note that there is also RN7 CW net and PAN (Pacific Area Net) CW which meat also on 80 meters a little later in the evenings.  They are the next level up of traffic handling and usually handle cross country messaging.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Give some of these a try.  Just dial into the frequency of any of the nets I mention above and listen in.  Unfortunately due to the cold dark nights of winter, the short skip almost doesn't exist so sometimes hard to hear net control.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2017-06-15T15:05:32.130" LastActivityDate="2017-06-15T15:05:32.130" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="6948" PostTypeId="2" ParentId="6946" CreationDate="2016-12-13T23:20:53.500" Score="9" Body="&lt;p&gt;When establishing emergency communications in a disaster, the natural choice of band is one that will allow you to communicate out of the disaster zone.  Given the scenario you describe, a massive earthquake affecting the West Coast of North America from Northern California to British Columbia, that probably means HF.  HF privileges with a US Technician license are limited, so Technician-class licensees preparing for this scenario would do well to upgrade.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many fine HF radios that are very portable.  Almost all of the more-portable HF rigs are powered by 12 VDC, so no need for an inverter (unless you need one for a computer).  The smallest and most portable HF radios are meant for QRP operation, 5 &amp;ndash; 10 W, but for emergency communications 100 W would be better.  There are several radios that are sized to be installed in a vehicle that cover HF to UHF; one of those radios would be excellent for your purpose.  There are also many fine HF radios, some of which include VHF and UHF, that are a little larger but still quite portable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is more problematic; generally speaking, your goals of being very portable and easy to set up conflict with the goal of being an efficient radiator.  I assume that you also want a multi-band antenna, because you would probably prefer 20m &amp;ndash; 10m in the daytime, and 40m &amp;ndash; 80m at night.  (Many of the regional HF nets are on 80m.)  Here are some antennas to consider:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Long wire: a long wire, typically at least 40 m / 130 ft, up high in the trees, connected to an antenna tuner.  Advantages: inexpensive; easy to build from whatever wire is on hand; multi-band.  Disadvantages: needs lots of wire, must be up high, RF in the shack problems, external antenna tuner required, may not tune on all bands.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;G5RV / ZS6BKW: a popular but often-misunderstood wire antenna that includes a section of ladder-line feed.  Can be homebrewed or purchased.  Advantages: inexpensive; multi-band.  Disadvantages: works very poorly on some bands; needs to be up high for best performance; requires a balun and an antenna tuner.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Off-center-fed &quot;Windom&quot;: another popular but misunderstood wire antenna.  Advantages: inexpensive; multi-band.  Disadvantages: performance varies, quality of the balun is crucial; requires a balun and an antenna tuner; needs to be up high for best performance.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Loop: a wire antenna that makes a big horizontal loop, supported by trees.  Advantages: inexpensive; multi-band.  Disadvantages: requires an antenna tuner; needs to be up high for best performance; may not tune up on all bands.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Commercially-made vertical: I'm speaking of commercially-made multi-band vertical antennas that when assembled are 8 &amp;ndash; 12 m / 26 &amp;ndash; 40 ft long. Generally comes in a box that's about 1.5 m / 5 ft long.  Advantages: no need for trees; multi-band; often doesn't require a tuner.  Disadvantages: not as portable; more expensive; requires wire radials laid on the ground; low angle of radiation, which is generally better for long-range communications than intermediate-range.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Car-mounted vertical.  Advantages: if your solution is a mobile radio, than a car-mounted antenna is probably already connected.  Disadvantages: efficiency ranges from bad to terrible, depending on the band, how large the antenna is, and how much you're willing to spend; some models are quite expensive.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Backpacker vertical (my term): a vertical antenna that is meant to be as portable as possible.  Homebrew designs and commercial varieties exist.  Advantages: no trees required; very portable; antenna tuner generally not needed.  Disadvantages: flimsy; radials required; may not be able to handle 100 W; efficiency is generally low; some of the commercial models are surprisingly expensive.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;To summarize the antennas, if the antenna is to be efficient, multi-band, and portable, then we're probably talking about a wire antenna &lt;em&gt;up high&lt;/em&gt; (generally at least 1/4 &amp;lambda;).  Unfortunately, I've found that most hams just can't throw a rock attached to a cord very high, so you may wish to consider a tool to help you get the wire over the tree limb.  I use an arborist throw bag and a water-balloon slingshot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many of the wire antennas require an antenna tuner.  Many radios include antenna tuners, but many built-in antenna tuners have limited range.  An external antenna tuner generally has a better tuning range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your question is rather open-ended, so I'll stop now, rather than talking about modes, power sources, and other considerations.  I will say that if you want to use ham radio in an emergency, you should get your equipment ready and practice the techniques beforehand.  Also keep in mind that in a wide-ranging disaster, there will be a very large need for emergency communications; you might want to think about joining your local ARES group so that you can help other people too.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2016-12-13T23:20:53.500" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="6949" PostTypeId="2" ParentId="6944" CreationDate="2016-12-15T22:13:31.397" Score="5" Body="&lt;p&gt;That's a &lt;a href=&quot;http://www.w1hkj.com/RSID_description.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Reed-Solomon identification&lt;/a&gt; (RSID). It's purpose is to tell other stations what mode you are using. For PSK it's usually pretty obvious.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To disable it, look for the &quot;TxID&quot; button in the upper-right of the window, and click it to toggle it on and off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(As you might imagine, the RxID button toggles the receiving of RSIDs. When it is enabled, Fldigi will tune the receiver and switch to the correct mode automatically when it hears one.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Osb9j.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Osb9j.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2016-12-19T13:33:58.810" LastActivityDate="2016-12-19T13:33:58.810" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6950" PostTypeId="1" CreationDate="2016-12-15T22:37:01.267" Score="5" ViewCount="403" Body="&lt;p&gt;Obviously, I would expect the amount of power at a receiver would vary greatly based on distance from, and the power/efficiency of, the transmitter. But I don't really have a good sense for what &quot;ballpark&quot; the power would even be in for a &quot;good quality&quot; signal. Is it — milliwatts? picowatts?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2017-03-21T20:15:37.633" Title="What would be the typical received power of an &quot;S9&quot; signal?" Tags="&lt;receiver&gt;&lt;rf-power&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6951" PostTypeId="2" ParentId="6950" CreationDate="2016-12-15T22:37:01.267" Score="3" Body="&lt;p&gt;The answer for a literal &quot;S9&quot; value is actually pretty simple! According to the table in &lt;a href=&quot;http://www.giangrandi.ch/electronics/radio/smeter.shtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;this helpful article on S-meters&lt;/a&gt;, S9 corresponds to &lt;strong&gt;50 picowatts&lt;/strong&gt; of input power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is actually &lt;em&gt;by definition&lt;/em&gt;: a standard S9 value was defined as 50 μV in the HF range (but 5 μV for frequencies above 30 MHz) — and at 50 ohms impedance, such voltage is developed by that approximately 50 pW of power. To avoid a dependency on impedance, the standard has apparently been updated directly in terms of power. The &lt;a href=&quot;https://en.wikipedia.org/wiki/S_meter&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia S Meter article&lt;/a&gt; cites:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;IARU Region 1 Technical Recommendation R.1 defines S9 for the HF bands to be a receiver input power of -73 dBm. This is a level of 50 microvolts at the receiver's antenna input assuming the input impedance of the receiver is 50 ohms.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;All other &lt;em&gt;standard&lt;/em&gt; S-values are relative to this S9 definition [which I ended up finding in the &lt;a href=&quot;https://www.iaru-r1.org/index.php/downloads/func-startdown/776/&quot; rel=&quot;nofollow noreferrer&quot;&gt;IARU Region 1 HF Manager Handbook&lt;/a&gt;, chapter 8.2.1 rather than Wikipedia's citation]. Granted, the signal meter on any given receiver may or may not actually give readings according to this full standard, but contrary to rumors, at least there &lt;em&gt;is&lt;/em&gt; a standard.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Since I had started to work out my own estimate via &lt;a href=&quot;https://en.wikipedia.org/wiki/Free-space_path_loss&quot; rel=&quot;nofollow noreferrer&quot;&gt;Free-space path loss equations&lt;/a&gt; before I thought to simply search for the S-value definitions, I thought it'd be interesting to see what sort of &lt;strong&gt;distance&lt;/strong&gt; S9 would then correspond to given a 100W transmission between two dipoles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Re-arranging the &lt;a href=&quot;https://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Friis transmission equation&lt;/a&gt;, and neglecting all other factors, this works out to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$   R = \lambda / 4 \pi&#xA;\cdot 10^{\large (G_r + G_t + P_t - P_r)/20} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the following values:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Pr = -73 dBm (S9 power at receiver relative to millwatts)&#xA;Pt = 50 dBm (100W output power from transmitter)&#xA;Gt = Gr = 2.15 dBi (half-wave dipole gain over isotropic)&#xA;λ = 40 meters (is a fun band)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Works out to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$  40/(4\cdot\pi) \cdot 10^{\large (2.15+2.15+50+73) / 20} = 7,376,496.273 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So given an otherwise lossless system, but tempered by fairly low-gain antennas, you would, &lt;strong&gt;on the 40m band, receive an S9 signal from a 100W transmitter when it was 7375 kilometers away&lt;/strong&gt;. A longer distance than I imagined! But I guess that's reasonable given complete transmitter system efficiency and no atmospheric attenuation — if calling mere picowatts of energy a &quot;strong signal&quot; is &quot;reasonable&quot; in the first place!&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-03-21T20:15:37.633" LastActivityDate="2017-03-21T20:15:37.633" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="6952" PostTypeId="1" CreationDate="2016-12-15T23:31:32.417" Score="5" ViewCount="700" Body="&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;noreferrer&quot;&gt;Friis transmission equation&lt;/a&gt; can be given as:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Pr = Pt + Gt + Gr + 20 log10 (λ / 4πR)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Where the variables represent:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Pr: Power at the receiver&#xA;Pt: Power at the transmitter (in e.g. dBm)&#xA;Gt: gain of the transmission system (in decibels)&#xA;Gr: gain of the receiver&#xA;R: &quot;radius&quot; of signal, i.e. simply the distance between transmitter and receiver&#xA;λ: the wavelength of the signal&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The λ term is very surprising, isn't it? It very conveniently makes the units work out, but why should the frequency of a signal affect how &quot;rapidly&quot; it dissipates?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that ionspheric and other terrestrial effects tend to make HF signals propagate farther than VHF and higher, but what accounts for this &quot;increased range&quot; of low frequency signals even in theoretical free space?!&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-12-15T23:56:50.973" LastActivityDate="2016-12-15T23:56:50.973" Title="Why does path loss decrease as frequency decreases?" Tags="&lt;antenna-theory&gt;&lt;rf-power&gt;" AnswerCount="1" CommentCount="4" ClosedDate="2016-12-16T03:43:04.070" ContentLicense="CC BY-SA 3.0" />
  <row Id="6953" PostTypeId="2" ParentId="6952" CreationDate="2016-12-15T23:31:32.417" Score="3" Body="&lt;p&gt;This is actually a side effect from the receiver/transmitter gain terms in the overall equation! In short, as communication frequency gets lower, the antennas must grow bigger to keep the same gain. A bigger antenna can capture more energy overall. Therefore, lower frequency signals will be &quot;louder&quot; at the receiver — &lt;strong&gt;iff&lt;/strong&gt; its antenna is adjusted to compensate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Wikipedia article on &lt;a href=&quot;https://en.wikipedia.org/wiki/Free-space_path_loss&quot; rel=&quot;nofollow noreferrer&quot;&gt;Free-space path loss&lt;/a&gt; explains this &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Free-space_path_loss&amp;amp;oldid=732147683#Frequency_dependency&quot; rel=&quot;nofollow noreferrer&quot;&gt;frequency dependency&lt;/a&gt;) in more detail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in a sense, the equation has been simplified in a misleading way. More intuitively, instead of &lt;code&gt;λ&lt;/code&gt; ending up part of the &lt;code&gt;R&lt;/code&gt; term, the &lt;code&gt;Gr&lt;/code&gt; term would be replaced with variables corresponding to the antenna aperture and that signal wavelength &lt;code&gt;λ&lt;/code&gt;. In fact, &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Antenna_aperture&amp;amp;oldid=746408663#Friis_transmission_equation&quot; rel=&quot;nofollow noreferrer&quot;&gt;one form of the Friis equation&lt;/a&gt; makes this clearer:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Pr = Pt * (At * Ar) / (r^2 * λ^2)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The &quot;adding up gains&quot; equation in the question basically re-groups this ratio (which is much more intuitively understood) into terms of decibels (which are much more practical to use).&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2016-12-15T23:50:49.010" LastActivityDate="2016-12-15T23:50:49.010" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6954" PostTypeId="1" CreationDate="2016-12-16T04:26:08.950" Score="4" ViewCount="249" Body="&lt;p&gt;I understand that in the United States, amateur operators and even non-licensed persons may participate in domestic (and approved international) communications on bands they wouldn't normally be allowed to transmit on, using the privileges of another licensed ham who serves as control operator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a concrete example, I hold an Extra Class license and my 7 year old son has a Technician class license. He wants to help me solder up the new Omnia SDR Proficio HF transceiver kit that should be arriving tomorrow. Once it's assembled, I'd love to let him try it out too — but his privileges don't cover digital work on any of its bands except 10m. I'd like to help him try some bands with better propagation, but am not sure the etiquette for properly identifying between our two call signs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be the proper way for him to identify himself, and me as the control operator, during a digital QSO? To use an extreme example, could he call CQ with his own callsign during a JT65 exchange and mention mine only at the sign-off? In a slightly less constrained mode like RTTY/PSK, is there a standard format of identifying both the privileged licensee/operator, but also any &quot;third party traffic&quot; participant who may or may not have their own callsign?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, if he were to make a successful contact, would it be appropriate for him to log these QSOs as his own? I don't mean in a &quot;station log&quot; sense, but rather the contest-oriented sites like ARRL's Logbook of the World or eQSL, where contacts can count towards various awards and such? Since technically I would have been the control operator, would that be considered poor sport for him to count it under his own callsign?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2016-12-16T07:44:46.507" Title="Expected practices for one ham operating under another's privileges?" Tags="&lt;united-states&gt;&lt;digital-modes&gt;&lt;license&gt;&lt;contest&gt;&lt;etiquette&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6955" PostTypeId="2" ParentId="6954" CreationDate="2016-12-16T07:44:46.507" Score="2" Body="&lt;p&gt;This question is correctly marked for &quot;United-States&quot; and I am not familiar with the details of license conditions for that region.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am going to answer this question for &quot;Ireland&quot;, to provide for the larger audience. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What would be the proper way for him to identify himself, and me as&#xA;  the control operator, during a digital QSO?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A supervised operator must identify him-/her-self with the full call sign of the license holder. The practice in Ireland would be to use the post-fix &lt;code&gt;/S&lt;/code&gt; or &lt;code&gt;/Supervised&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;To use an extreme example, could he call CQ with his own callsign&#xA;  during a JT65 exchange and mention mine only at the sign-off? In a&#xA;  slightly less constrained mode like RTTY/PSK, is there a standard&#xA;  format of identifying both the privileged licensee/operator, but also&#xA;  any &quot;third party traffic&quot; participant who may or may not have their&#xA;  own callsign?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I am going to give you a more extreme example. A person is not licensed on any HAM/Amateur bands, but holds a legal Marine license for a boat. Would this person be able to use his legal Marine call sign for the activity, and only mention the control-operator / amateur license holder at the end of the QSO?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For Ireland this answer is no. No for the example I give here, and no for the example you give in your question. It is very simple, if you are not licensed for the mode/frequency/equipment, then you may operate under the license provisioning of the actual license holder using the license holder call sign.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Further, if he were to make a successful contact, would it be&#xA;  appropriate for him to log these QSOs as his own?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;For the region I am answering for, the answer would be: the contacts made &quot;supervised&quot;, and therefore using the licensed holder call sign, would have to go into the license-holder station log. &lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2016-12-16T07:44:46.507" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6956" PostTypeId="1" AcceptedAnswerId="6957" CreationDate="2016-12-16T09:20:16.723" Score="2" ViewCount="159" Body="&lt;p&gt;When using ladder line to feed an antenna, I've seen it written that &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The spacing should not be over 1 percent of the highest-frequency wavelength, and that’s the only real consideration with ladder-line spacing. &lt;a href=&quot;http://kv5r.com/ham-radio/ladder-line/ladder-line-page-3/&quot; rel=&quot;nofollow noreferrer&quot;&gt;source&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Why is this the limit? Just that the impedance will be too high the spacing is too large a fraction of wavelength?  &lt;/p&gt;&#xA;" OwnerUserId="8284" LastActivityDate="2016-12-20T21:59:17.630" Title="What dictates ladder line max frequency?" Tags="&lt;feed-line&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2016-12-21T21:30:30.563" ContentLicense="CC BY-SA 3.0" />
  <row Id="6957" PostTypeId="2" ParentId="6956" CreationDate="2016-12-16T13:13:57.030" Score="6" Body="&lt;p&gt;1% here is just an overly precise way of saying &quot;really small compared to the wavelength&quot;. The problem is that when the conductors are close together, their electrical and magnetic fields cancel; as they get farther apart, there's a larger volume around the line where the fields don't cancel, and the ladder line starts looking more like an antenna than a transmission line.&lt;/p&gt;&#xA;" OwnerUserId="105" LastEditorUserId="105" LastEditDate="2016-12-20T21:59:17.630" LastActivityDate="2016-12-20T21:59:17.630" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6958" PostTypeId="1" CreationDate="2016-12-17T01:54:46.797" Score="0" ViewCount="129" Body="&lt;p&gt;I need to transmit small amounts of data (~5kb/s) in the fastest way possible over the distance around 2500 km.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What is the the best way to carry out such transmission?&lt;/li&gt;&#xA;&lt;li&gt;How could I estimate or simulate the time of signal propagation? Some program packages maybe?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPD:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Statement about 5kb\s might be confusing, I'd like to clarify:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the time the data will be contained of Zeros, and only rarely there will be Ones. In other words nothing happens most of the time, but when something's happened – I need to know as fast as possible, faster than by the Internet (which in addition won't be always available).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the question is about the complex topic of HF propagation. I need to operate mostly in the daytime.&lt;/p&gt;&#xA;" OwnerUserId="8879" LastEditorUserId="8879" LastEditDate="2016-12-17T14:48:12.813" LastActivityDate="2017-02-18T10:04:29.897" Title="How to compute/simulate signal propagation latency?" Tags="&lt;propagation&gt;&lt;equipment-design&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6959" PostTypeId="1" CreationDate="2016-12-17T07:35:58.083" Score="1" ViewCount="598" Body="&lt;p&gt;I am trying to configure AX5043 transceiver(ONSEMI) for PSK modulation and system parameters are as follows:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Modulation          :   BPSK&#xA;Carrier Frequency   :   437.025MHz&#xA;&#xA;AX5043 chip is interfaced with PIC18F4550 micro controller using SPI.&#xA;&#xA;AX5043 is connected to Crystal Oscillator of 32MHz.&#xA;&#xA;Using internal VCO.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Now when I try to do auto ranging for the desired frequency, 437.025 MHz, which is configured in FREQA register(s), I am getting an auto-ranging error, i.e. RNGERR bit is going set after auto ranging is completed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone help me with this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you.&lt;/p&gt;&#xA;" OwnerUserId="8883" LastEditorUserId="4665" LastEditDate="2016-12-17T20:07:45.243" LastActivityDate="2017-03-04T01:54:30.167" Title="Autoranging problem for AX5043 transceiver (437.025MHz)" Tags="&lt;satellites&gt;&lt;transceiver&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6960" PostTypeId="1" AcceptedAnswerId="6962" CreationDate="2016-12-17T08:03:47.977" Score="3" ViewCount="3631" Body="&lt;p&gt;GNU Radio has a Signal Source Block which considers a set of variables to produce an output, namely sample rate, frequency and amplitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In signal processing, we define a basic waveform by its frequency, number of samples within the period and its amplitude. This holds true for waveforms such as Sine, Cosine, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In GNU Radio, the sample rate doesn't really mean sample rate. And the frequency does not mean the frequency of the signal. This is really confusing to understand. I insert a screenshot of my build below&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pBc7I.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pBc7I.png&quot; alt=&quot;GNU Radio companion showing the flow graph: Signal Source -&amp;gt;  Throttle -&amp;gt; WX GUI FFT Sink&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, if sample rate is defined in the signal generator box, we do not need another throttle box. Because the Signal Generation box must know that it shouldn't generate more than the amount of samples it's advised in the configuration. However, if we remove the Throttle Box, the CPU goes to 100% and PC gets Stuck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like a bit of clarification of on this issue. I'm sure I am wrong. People who made GNU radio must have been very smart people who have had a specific reason for doing this. I would like to know that reason. &lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorDisplayName="user4168" LastEditDate="2019-01-23T00:56:05.810" LastActivityDate="2019-01-23T00:56:05.810" Title="Signal Source Block of GNU Radio" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="6962" PostTypeId="2" ParentId="6960" CreationDate="2016-12-17T10:18:43.033" Score="6" Body="&lt;p&gt;You're on to something very right! &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In signal processing, we define a basic waveform by its frequency, number of samples within the period and its amplitude. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'd go a step further: In digital signal processing, the actual frequency doesn't &quot;exist&quot; any more. It's just &quot;a periodic signal with a period of $T$ samples&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that's exactly why for example digital filters are usually denoted relative to half the sampling frequency $f_s$ or simply $\pi$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that's exactly what the signal source does: It just takes your input of sampling rate and signal frequency, calculates $\frac{f_{sig}}{f_s}$ – and gets a value for how many samples a period should have (or how much of $2\pi$ to advance phase per sample – which is really nothing but just dividing $2\pi$ by that number).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, a signal source configured with $f_{sig}=10,\, f_s = 100$ does &lt;em&gt;exactly&lt;/em&gt; the same that a signal source with $f_{sig}=0.2,\, f_s = 2$ does. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;GNU Radio doesn't even have any notion of what this sampling rate means – it just processes samples as fast as it can. That might seem strange at first, but when you think about it, every block that takes a &quot;sampling rate&quot; parameter just needs that value to &quot;interpret&quot; some other frequency (or time) with respect to that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a flowgraph where there is some SDR or other sampling device (an &lt;em&gt;osmocom source&lt;/em&gt; getting data from an RTL-SDR, or the &lt;em&gt;USRP Sink&lt;/em&gt; bringing samples to an USRP, or just an &lt;em&gt;Audio Sink&lt;/em&gt; that attaches to a speaker, to give three examples), the samples actually only start flowing at the sampling rate physically in the hardware – GNU Radio still tries to get/give the samples as fast as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For hardware sources, the mechanism is simple: GNU Radio asks the source &quot;hey, do you have $N$ samples for me&quot;, to which the source usually responds as fast as it can, i.e. it will output the sampling rate of samples per second on average (but in &quot;chunks&quot; – GNU Radio doesn't push singular samples around. That would be far too much overhead). That limits the average rate of samples flowing through a flow graph; still, the pure software blocks will take these samples and process them as fast as possible, and then wait for the next chunk. That allows for maximum throughput – everyone works as fast as possible, and if they're done early, that's good (in fact, necessary), because it frees CPU to let the other blocks do their work, the OS do its job and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, a hardware sink will simply take some time, the number of samples offered per iteration divided by the sampling rate, to consume the samples. That will simply put &quot;pressure&quot; on the buffers (GNU Radio buffers, ie. what connects blocks with each other are simply of limited size), because when a buffer gets full, the block that puts samples into that buffer simply doesn't get asked to do that until there's enough space in there again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, that's the situation with hardware blocks in your flow graph. Now, with software-only blocks, there's nothing slowing down the flow of samples – no hardware source that simply doesn't give your more than its physical  sampling rate, and no sink that doesn't consume samples any faster.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8v53w.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8v53w.png&quot; alt=&quot;Minimal flow graph&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, in your flow graph (without the &lt;em&gt;Throttle&lt;/em&gt;), GNU Radio simply asks the &lt;em&gt;Signal Source&lt;/em&gt; to produce as many samples as there's free space in its output buffer. The &lt;em&gt;Signal Source&lt;/em&gt; happily obliges and fills that buffer with a cosine of 32 samples per period – and then tells GNU Radio it's done doing that and it in fact did produce so-and-so-many samples. GNU Radio takes that info and tells the GUI Sink &quot;Hey, there's so-and-so-many samples in your input buffer, get to work!&quot;, and the sink just goes ahead and processes these as fast as it can. It signals GNU Radio when it's done how many of the samples that it was offered it actually consumed – and GNU Radio then knows that this portion of the buffer is free again&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since that happens as fast as possible, this flow graph tends to eat up two processor cores completely, because GNU Radio is clever and maximizes throughput by distributing different blocks to different concurrent threads – that way, the source can already be producing the next chunk of samples, while the sink is still consuming the first one, leading to a scenario where there's practically no waiting for new input – there's always something to be done. Again, in a scenario where you want to process millions of samples per second coming from a hardware source, or going to a hardware sink, this is &lt;strong&gt;very&lt;/strong&gt; desirable – simply because the throughput would be hard to achieve if everyone would be waiting most of the time instead of everyone trying to work as fast as possible on their own CPU core.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Throttle&lt;/em&gt; does exactly &lt;em&gt;nothing&lt;/em&gt; to the samples. It's really just a &quot;copy the bytes from the input to the output buffer&quot; operation. But it just lets that copy action sleep() for a while to achieve an &lt;em&gt;average&lt;/em&gt; throughput of the sample rate you configured. It's thus really just a tool for simulation at medium rates. Never use &lt;em&gt;Throttle&lt;/em&gt; in conjunction with a hardware block – no two clocks are exactly the same, and if your hardware samples but a little faster than your Throttle throttles (because that's done with a rather inaccurate CPU clock time), you'll end up damaging your signal somewhere, either because your hardware sink didn't get things fast enough and had nothing to convert to analog when it was time, or because your hardware source completely runs out of buffers to put received samples to, and has to drop them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Takeaway&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;It's important to know that GNU Radio, and DSP in general, don't care about real-world sampling rates at all. It's just math applied to a sequence of numbers. How fast that sequence passes through the processing doesn't matter to the results of the math – the only point when these numbers get a physical meaning, and hence, a real sampling rate, again, is when they're passed to or from some sampling hardware.&#xA;&lt;hR&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-12-17T10:18:43.033" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="6963" PostTypeId="2" ParentId="6958" CreationDate="2016-12-17T14:15:36.087" Score="1" Body="&lt;p&gt;&lt;strong&gt;This answer applies to a previous, broader version of the question and remains in case it is of more general interest.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A distance of 2500 km rules out a line-of-sight link due to the curvature of the earth; you would need a tower a hundred times taller than the tallest manmade structure. Therefore, in order to achieve radio communication, you must reflect your signal off something, or have at least one intermediate station which receives and retransmits it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, the latency is essentially the length of the path divided by the speed of light.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some options for pure radio communications, roughly in order of increasing latency but not necessarily practical, are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;HF radio. Here, your signals are reflected/refracted by the ionosphere, so that they can proceed around the curvature of the earth entirely on their own. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The catch is that the ionosphere is not always in a condition to serve this function — primarily dependent on the time of day, but in general as variable as the weather. HF propagation is  a quite complex topic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, a good HF station requires physically large antennas. They can be as &lt;em&gt;simple&lt;/em&gt; as wire strung between two trees, though.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Relay through a satellite. This increases latency because the signal is taking a longer path (two straight lines meeting at the satellite rather than a “great circle” path).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The time taken will depend on the satellite's orbit, which also determines whether and &lt;em&gt;when&lt;/em&gt; you can use it; notably, a geosynchronous satellite is apparently fixed in the sky so you can use it continuously, but is so far out that you will always have a quarter-second of latency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need a satellite to use. All (nearly all? I forget) amateur radio satellites are in low earth orbit (so moving rapidly over the ground and not covering a very large area), and generally heavily used the easier they are to contact. Commercial communications satellites are available but would require some contract to make use of.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need a ground station, that is, a radio station that is capable of making itself heard by the satellite. This means directional, steerable antennas, for low orbit satellites; geosynchronous ones still need a directional antenna but it can be installed in a fixed direction.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Relay stations on the ground along your path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here, your problem is finding land you can put up towers on, or using a network someone else has already built. Also, the relays will add latency — more or less depending on whether they are full-duplex and how efficient they are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The amateur APRS network is in theory capable of supporting this, but in practice rarely gets a packet a long distance on purely RF relays and uses the Internet as a fallback.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Reflect your signal off the Moon!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is much like using a low-orbit satellite, in that you need high-gain (large) steerable antennas, and it adds 2.5 seconds of latency because the Moon is even farther away.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There's a good chance that your best option is to take none of the above and instead use the Internet, which will do a really good job of getting your data where you need it fast — if you can find Internet access at both ends. Or you could use a radio link over a short distance at one or both ends and transfer the data over the Internet the rest of the way.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-12-17T14:53:22.420" LastActivityDate="2016-12-17T14:53:22.420" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6964" PostTypeId="1" AcceptedAnswerId="7097" CreationDate="2016-12-19T07:28:28.130" Score="1" ViewCount="94" Body="&lt;p&gt;First post here yay!  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am repairing  Shengda sdhf dual band antenna (looks similar to a Comet x50) it showed a SWR of &gt;3 on both UHF and VHF.  I opened it up and the only connection I could see from the  centre core to the antenna element is two caps. I'm pretty sure they are broken. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are not marked though and the electronic store clerk couldn't help me either. They do have colours marked on the tip but it doesn't agree with any of my textbook identification charts. Any help would be appreciated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/vkJzL.jpg&quot; alt=&quot;The two caps in question. notice the insulation on the legs&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="5593" LastActivityDate="2017-01-18T12:28:00.477" Title="Identify these components" Tags="&lt;antenna-construction&gt;&lt;capacitance&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6965" PostTypeId="2" ParentId="6964" CreationDate="2016-12-19T10:15:16.840" Score="0" Body="&lt;p&gt;Have you tested with an ohm meter to see if they charge and discharge on the scale (alternate the test leads on the ends) They appear good. Caps usually bulge or have burn holes in them. Those look like Tantalum caps. One with a Black top with gray base  and the other purple with a yellow base. Look up Google images for color codes.     If they indicate a direct short on the meter, they could be Inductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck! &lt;/p&gt;&#xA;" OwnerUserId="8887" LastActivityDate="2016-12-19T10:15:16.840" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6966" PostTypeId="2" ParentId="798" CreationDate="2016-12-19T16:52:57.640" Score="1" Body="&lt;p&gt;Narrow Band Emergency Messaging Software (&lt;a href=&quot;http://www.arrl.org/nbems&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;NBEMS&quot;&gt;NBEMS&lt;/a&gt;) uses error-correcting modes like &lt;a href=&quot;https://en.wikipedia.org/wiki/MT63&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;MT63-2000&quot;&gt;MT63-2000&lt;/a&gt; over VHF and HF. It doesn't need much hardware: it &lt;em&gt;can&lt;/em&gt; be operated successfully by holding the HT near the computer speaker and holding down PTT, though there are more reliable ways of doing it.&lt;/p&gt;&#xA;" OwnerUserId="90" LastActivityDate="2016-12-19T16:52:57.640" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6967" PostTypeId="1" CreationDate="2016-12-20T21:35:49.253" Score="6" ViewCount="904" Body="&lt;p&gt;The ARRL's &lt;a href=&quot;http://www.arrl.org/graphical-frequency-allocations&quot; rel=&quot;noreferrer&quot;&gt;band plan chart&lt;/a&gt; includes the following text in its legend:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Test transmissions are authorized above 51 MHz, except for 219-220 MHz&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What FCC regulation is this referring to?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aren't &lt;em&gt;all&lt;/em&gt; ham bands available for transmitter testing and other experimental communications? What sort of &quot;test&quot; transmissions are allowed above this frequency but not below? (And is the cutoff really at 51 MHz, not 50.1 MHz?)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="76" LastEditDate="2016-12-20T21:38:05.800" LastActivityDate="2017-01-06T20:17:42.663" Title="What &quot;test transmissions&quot; are allowed above 51MHz?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;band-plan&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6968" PostTypeId="1" CreationDate="2016-12-21T16:13:23.067" Score="10" ViewCount="277" Body="&lt;p&gt;The FCC's rules regulating amateur radio, in &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.307#f_8&quot; rel=&quot;noreferrer&quot;&gt;47 CFR 97.307(f), paragraph 8&lt;/a&gt; defines one emissions standard/limitation as follows:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A RTTY or data emission having designators with A, B, C, D, E, F, G, H, J or R as the first symbol; 1, 2, 7, 9 or X as the second symbol; and D or W as the third symbol is also authorized.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(For context, this is describing one sort of &lt;a href=&quot;https://ham.stackexchange.com/questions/6967/what-test-transmissions-are-allowed-above-51mhz/6969&quot;&gt;signal allowed at 51 MHz and above&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I was able to find definitions for most of these &quot;first symbols&quot;, representing &quot;types of modulation of the main carrier&quot;, in &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/2.201#c&quot; rel=&quot;noreferrer&quot;&gt;§2.201(c)&lt;/a&gt; of the FCC regulations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A: Double-sideband&lt;/li&gt;&#xA;&lt;li&gt;B: Independent sidebands&lt;/li&gt;&#xA;&lt;li&gt;C: Vestigial sideband&lt;/li&gt;&#xA;&lt;li&gt;D: Emission in which the main carrier is amplitude and angle-modulated either simultaneously or in a pre-established sequence&lt;/li&gt;&#xA;&lt;li&gt;F: Frequency modulation&lt;/li&gt;&#xA;&lt;li&gt;G: Phase modulation&lt;/li&gt;&#xA;&lt;li&gt;H: Single-sideband, full carrier&lt;/li&gt;&#xA;&lt;li&gt;J: Single-sideband, suppressed carrier&lt;/li&gt;&#xA;&lt;li&gt;R: Single-sideband, reduced or variable level carrier&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;All of the &quot;second symbols&quot;, representing the &quot;nature of signal(s) modulating the main carrier&quot;:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;1: A single channel containing quantized or digital information without the use of a modulating sub-carrier, excluding time-division muliplex&lt;/li&gt;&#xA;&lt;li&gt;2: A single channel containing quantized or digital information with the use of a modulating sub-carrier, excluding time-division multiplex&lt;/li&gt;&#xA;&lt;li&gt;7: Two or more channels containing quantized or digital information&lt;/li&gt;&#xA;&lt;li&gt;9: Composite system with one or more channels containing quantized or digital information, together with one or more channels containing analogue information&lt;/li&gt;&#xA;&lt;li&gt;X: Cases not otherwise covered&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And the relevant &quot;third symbols&quot;, representing the &quot;type of information to be transmitted&quot;:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;D: Data transmission, telemetry, telecommand&lt;/li&gt;&#xA;&lt;li&gt;W: Combination of the above [presumably &quot;no information&quot;, telegraphies, facsimile, data, telephony, television]&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So that explains most of the allowable test transmissions for subbands that &#xA;reference &quot;paragraph 8&quot; as an allowable emissions standard. But I can't find what &quot;E&quot; would mean as a first symbol! It's not in Part 2, it's not in the &lt;a href=&quot;http://life.itu.int/radioclub/rr/ap01.htm&quot; rel=&quot;noreferrer&quot;&gt;ITU regulations&lt;/a&gt;, it's not &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Types_of_radio_emissions&amp;amp;oldid=739347627#Type_of_modulation&quot; rel=&quot;noreferrer&quot;&gt;on Wikipedia&lt;/a&gt;…! What is §97.307(f)¶8 referring to when it allows &quot;designators with […] E […] as the first symbol&quot;?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2017-08-18T17:33:40.523" Title="What is emissions designator &quot;E&quot; when used as a type of modulation?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6969" PostTypeId="2" ParentId="6967" CreationDate="2016-12-21T17:13:54.573" Score="10" Body="&lt;p&gt;This is indeed in the FCC regulations. In Part 97, section 305 regarding &quot;Authorized Emission Types&quot; there is the following chart which lists two relevant subbands, see in the VHF group the &lt;code&gt;6m&lt;/code&gt; row and the &lt;code&gt;Do&lt;/code&gt; ditto right below it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/rv33M.png&quot; alt=&quot;FCC table showing authorized emission types by frequency range&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tracing our way outwards from there, we find:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.305&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR §97.305(c)&lt;/a&gt; is the heart of the FCC regulation on which the ARRL legend note is based.&lt;/li&gt;&#xA;&lt;li&gt;Limited testing &lt;strong&gt;is permitted&lt;/strong&gt; on all amateur-allocated frequencies, and experimental digital modes are also cautiously permitted within the HF bands (i.e. below the frequency in question). In the HF bands, there are a number of technical and discretionary restrictions that can apply to data emissions.&lt;/li&gt;&#xA;&lt;li&gt;At 51 MHz and above there is basically no &lt;strong&gt;technical&lt;/strong&gt; restriction on emission types within the amateur allocations. Advance the radio art! (You still can't &quot;obscure your meaning&quot; or avoid good amateur practice, of course.)&lt;/li&gt;&#xA;&lt;li&gt;Yes, 51.0 MHz is really the cutoff. (There's actually a specific bandwidth restriction that &quot;hangs on&quot; up through the 2m band, but the ARRL chart's summary is accurate enough.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These answers are explored in more detail below.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Let's zero in on the difference between 50.1–51.0 MHz range vs. the 51.0-54.0 MHz range.* The first frequencies allow emissions of type &quot;MCW, phone, image, RTTY, data&quot; whereas the second allow all that and &quot;…, test&quot;. This must be exactly what the ARRL chart is referring to. So &lt;strong&gt;yes, 51 MHz is the correct boundary&lt;/strong&gt; for where &quot;test&quot; emissions may occur.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What &lt;em&gt;is&lt;/em&gt; a &quot;test&quot; emission type? The &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.3#c_9&quot; rel=&quot;nofollow noreferrer&quot;&gt;definitions section of Part 97&lt;/a&gt; says this:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Test.&lt;/strong&gt; Emissions containing no information having the designators with N as the third symbol. Test does not include pulse emissions with no information or modulation unless pulse emissions are also authorized in the frequency band&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;But to expand on that a bit, the table above also has a &quot;standards&quot; column which lists only &lt;code&gt;(2), (5)&lt;/code&gt; for the 50.1–51 MHz subband, but &lt;code&gt;(2), (5), (8)&lt;/code&gt; for the 51.0–54.0 MHz portion. The definitions of these standards are given in § 97.301(f) within numbered paragraphs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first applicable standard the two subbands here have in common is a general rule regarding allowable bandwidth:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(2) No non-phone emission shall exceed the bandwidth of a communications&#xA;  quality phone emission of the same modulation type. The total bandwidth&#xA;  of an independent sideband emission (having B as the first symbol), or&#xA;  a multiplexed image and phone emission, shall not exceed that of a communications quality A3E emission. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So for 6m (and 2m and 1.25m) one needs to limit data transmissions so they fit within the same bandwidth as a phone transmission would use. (Note how this paragraph (2) is not applicable on 73cm and above.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's the next two standards that distinguish between what might be considered &quot;data&quot; and &quot;test&quot; signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Data would be:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(5) A RTTY, data or multiplexed emission using a specified digital code&#xA;  listed in §97.309(a) of this part may be transmitted. The symbol rate must not exceed 19.6 kilobauds. A RTTY, data or multiplexed emission using an unspecified digital code under the limitations listed in §97.309(b) of this part also may be transmitted. The authorized bandwidth is 20 kHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Looks like we need to unpack this further! This standard refers to §97.309(a) and §97.309(b) to define what exactly counts as &quot;data&quot; in here. I won't paste those entire sections here, but in summary they allow:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Baudot, AMTOR, ASCII, and &quot;any technique whose technical characteristics have been documented publicly&quot; (a)&lt;/li&gt;&#xA;&lt;li&gt;&quot;an unspecified digital code&quot;, provided it's exchanged with a country which has agreed to such things, and &lt;strong&gt;not&lt;/strong&gt; &quot;for the purpose of obscuring the meaning of any communication&quot;, and assuming the FCC hasn't given more specific instructions against it. (b)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;That's already pretty broad!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the standard which seems to apply to &quot;test&quot; signals, we find:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(8) A RTTY or data emission having designators with A, B, C, D, E, F, G, H, J or R as the first symbol; 1, 2, 7, 9 or X as the second symbol; and D or W as the third symbol is also authorized.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To understand this paragraph we actually have to jump out of Part 97 and in to Part 2 of the FCC's 47 CFR to learn their definitions of &quot;Emission, modulation and transmission characteristics&quot;. If you do so, you'll find that there's not much that all those letters and numbers leave out. (For the life of me &lt;a href=&quot;https://ham.stackexchange.com/questions/6968/what-is-emissions-designator-e-when-used-as-a-type-of-modulation&quot;&gt;I can't figure out what the &quot;E&quot; modulation type is&lt;/a&gt;, but the others cover AM/SSB/FM/PM for any sort of baseband signal for any sort information….)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that this paragraph (8) standard is much broader definition than the overall &quot;test&quot; definition above, in that the third symbol is pretty much a wildcard, rather than the &quot;no information&quot; N symbol that test emissions in general are restricted to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Covering that general case, &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.305#b&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.305(b)&lt;/a&gt; says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A station may transmit a test emission on any frequency authorized to the control operator for brief periods for experimental purposes, except that no pulse modulation emission may be transmitted on any frequency where&#xA;  pulse is not specifically authorized and no SS modulation emission may be&#xA;  transmitted on any frequency where SS is not specifically authorized.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To re-summarize the deep-dive above, I think the distinction is that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You can perform brief tests carrying no information, &lt;strong&gt;anywhere&lt;/strong&gt;. (I would expect that combination of &quot;good amateur practice&quot; with the &quot;no information&quot; designation means one wouldn't ever splatter a fat AM/FM &quot;test&quot; signal over a CW-only portion of a band.)&lt;/li&gt;&#xA;&lt;li&gt;You have relatively broad leeway in many &quot;data&quot; portions of authorized bands to experiment with new modes and protocols. (Some restrictions may apply, see store for details, void in Quebec, etc. etc.)&lt;/li&gt;&#xA;&lt;li&gt;At 51.0 MHz and above, you have almost /carte blanche/ as far as permitted signal types for this broader class of &quot;paragraph 8&quot; emissions within the ham allocations, subject in the VHF bands to the bandwidth limitations of &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.307#f_2&quot; rel=&quot;nofollow noreferrer&quot;&gt;97.307(f)2&lt;/a&gt;, and only to common decency in the UHF bands (by &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.307#a&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.307(a)&lt;/a&gt;) as far as I can tell.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;*You might wonder why the the 50–50.1 MHz portion of the 6m allocation is missing from the §97.305 chart. I believe this is covered instead by the &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.301#a&quot; rel=&quot;nofollow noreferrer&quot;&gt;table in §97.301&lt;/a&gt; revealing the 6m allocation as the full 50–54 MHz (in ITU regions 2 and 3 at least), coupled with §97.305(a) which states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Except as specified elsewhere in this part, an amateur station may transmit a CW emission on any frequency authorized to the control operator.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(Or, having read through this entire answer, you might have &lt;em&gt;lost&lt;/em&gt; all sense of wonder, entirely ;-)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-12-21T17:54:21.230" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6972" PostTypeId="2" ParentId="6946" CreationDate="2016-12-23T18:44:13.317" Score="3" Body="&lt;p&gt;Regarding a response to your simple question of: letting non hams know that I am alive. Have you considered APRS? Not correctly, but commonly known as Automatic Position Reporting System. You probably already have a mobile radio and antenna. With a $107 TinyTrak position encoding device transmitting your position on 144.39 Mhz your position will be displayed and tracked on the website: &quot;aprs.fi&quot;   Anyone can see your location and the last time it was updated by entering your callsign in the search block. This system does use VHF aprs repeaters, which are fairly common. This is a great and fun system for letting your kids and friends keep track of you when you are traveling. Check out: &quot;aprs.fi&quot;  and &quot;byonics.com/tinytrak&quot;. Email me if I can help. Roy, n7pux  &lt;/p&gt;&#xA;" OwnerUserId="8915" LastActivityDate="2016-12-23T18:44:13.317" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6974" PostTypeId="1" CreationDate="2016-12-24T01:19:46.250" Score="0" ViewCount="315" Body="&lt;p&gt;What app or software can I use on my windows 10 computer(desktop) or iPhone 7 latest software to scan for interference as in another device effecting my frequencie of my Bluetooth wifi  in a 2.4 and 5 hz range. &lt;/p&gt;&#xA;" OwnerUserId="8917" LastEditorUserId="8917" LastEditDate="2016-12-26T08:28:51.430" LastActivityDate="2016-12-26T16:21:01.187" Title="How can I scan for interference" Tags="&lt;rfi&gt;" AnswerCount="3" CommentCount="3" ClosedDate="2017-01-05T19:07:08.653" ContentLicense="CC BY-SA 3.0" />
  <row Id="6975" PostTypeId="2" ParentId="6974" CreationDate="2016-12-24T01:52:23.157" Score="2" Body="&lt;p&gt;You can't.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radios built into computers are very special purpose, and they generally can only report RSSI or other information about signals in the &lt;em&gt;intended&lt;/em&gt; mode (WiFi, Bluetooth, etc.) and not arbitrary RF energy.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-12-24T01:52:23.157" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="6977" PostTypeId="2" ParentId="6974" CreationDate="2016-12-24T11:57:32.977" Score="1" Body="&lt;p&gt;If by &quot;desktop&quot; you mean an ordinary PC, then you can get a (cheap) SDR dongle (see &lt;a href=&quot;http://www.rtl-sdr.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.rtl-sdr.com/&lt;/a&gt;) and then you can use any of the SDR programs, preferably with waterfall display around suspected interference frequency. There are also some Android apps, I do not know about iPhone.&lt;/p&gt;&#xA;" OwnerUserId="8922" LastActivityDate="2016-12-24T11:57:32.977" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6978" PostTypeId="2" ParentId="798" CreationDate="2016-12-24T21:25:23.910" Score="1" Body="&lt;p&gt;Anther example is sending requests for resources from a local/county EOC to a State EOC when normal methods are down.  The amount of detailed information is too much for sending effectively/efficiently by voice.  Narrow Band Emergency Messaging/FLDIGI and WINLINK RMS have templates for Resource Request messages.&lt;/p&gt;&#xA;" OwnerUserId="8924" LastActivityDate="2016-12-24T21:25:23.910" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6979" PostTypeId="2" ParentId="1463" CreationDate="2016-12-26T09:28:28.033" Score="-1" Body="&lt;p&gt;run 1/2 watt (500mw that has about a 15db gain in to get it down your line and using lmr400) with a 24dbi parabolic at 25 feet or so you can easily go 20-30 miles assuming you don't have a mountain between you or a bunch of sky scrapers and its completely legal.&#xA;i have built the configuration many many times (mind you that it will not be but probably around 2mb/s transfer but still thats not terrible for the distance you're going) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;and for reference i have on hand experience, i have been involved in about about 20 of these link builds in western colorado and in Arizona.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also mind you don't have to have the same wattage at both ends, however it will decrees your distance, but if you are not concerned with upload speed on one end you could use say for example 100mw, with a 24dbi gain parabolic with lmr400, on one end you would save some money get faster download speeds because your closer but your upload speeds would be more like 256kb/s but you could still get about 5 miles or so, because those 24dbi parabolic are awesome antennas. and non of this power levels i have mentioned require a ham license.  &lt;/p&gt;&#xA;" OwnerUserId="8928" LastEditorUserId="8928" LastEditDate="2016-12-26T09:40:13.130" LastActivityDate="2016-12-26T09:40:13.130" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6980" PostTypeId="2" ParentId="6974" CreationDate="2016-12-26T16:21:01.187" Score="0" Body="&lt;p&gt;I have used SDR# (read: Software Defined Radio Sharp) on a Windows 10 desktop to scan for signals, while doing so seeing how the noise floor changes dramatically. SDR# uses the waterfall display to help visualize noise, which would help one who isn't experienced in these sort of things be successful. In one case, I used SDR# to identify a noisy power supply that kept me from hearing a distant radio source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The effectiveness of SDR# is related to the receiver you're using. While I was using an inexpensive TV tuner receiver, the range of the very cheap receivers are not created equally, so shop around. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;While outside the scope of your question, I would like to add that the fun that can be had with SDR in general can be addictive. There are better receivers out there and an inexpensive raspberry pi project can also be built to accomplish the same thing if you need a more portable solution.&lt;/p&gt;&#xA;" OwnerUserId="8930" LastActivityDate="2016-12-26T16:21:01.187" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6981" PostTypeId="1" CreationDate="2016-12-26T19:08:10.413" Score="2" ViewCount="505" Body="&lt;p&gt;A few of us have been experimenting with SSTV using HTs and Android phones. Acoustic coupling gets us P3 or P4 at best. Is it possible to build or buy a simple cable to connect the phone to the HT (I am using a Yaesu FT60,) or do I need something to isolate/ match input/output levels?&lt;/p&gt;&#xA;" OwnerUserId="8933" LastActivityDate="2016-12-26T21:31:49.403" Title="Yaesu FT60 to Android Phone Cable" Tags="&lt;ht&gt;&lt;sstv&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6982" PostTypeId="2" ParentId="6981" CreationDate="2016-12-26T21:31:49.403" Score="1" Body="&lt;p&gt;The wiring would be identical to a cable for APRS purposes (software TNC on the phone). I haven't found anyone doing this but I don't see why it wouldn't be possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You want an interface circuit to protect both devices, but it can be entirely passive. The two relevant protections are reducing the audio output to match the microphone input (series resistors or L-pads), and preventing any DC bias voltages from passing to the other device (series capacitors or audio transformers).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have the time right now to write up a full schematic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's some official information on Android headset electrical specifications: &lt;a href=&quot;https://source.android.com/devices/accessories/headset/jack-headset-spec.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;jack&lt;/a&gt;, &lt;a href=&quot;https://source.android.com/devices/accessories/headset/plug-headset-spec.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;plug&lt;/a&gt;. These pages are mostly focused on the button functionality but they do have some useful specifications for the mic and speaker audio.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-12-26T21:31:49.403" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6983" PostTypeId="1" AcceptedAnswerId="6985" CreationDate="2016-12-27T19:59:23.423" Score="9" ViewCount="4787" Body="&lt;h1&gt;The short version&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;My understanding is that one of the main reasons to use a balun with coax is to prevent the outside of the shield from becoming part of your antenna system. If that's the case, won't a design like the one pictured below be ineffective? Can't current flow to the outside of the shield at the coax connector, before the windings?&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;The long version&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;I'm new to the HF bands. My understanding is that baluns are good practice when feeding a dipole from coax (or any balanced system from an unbalanced one)--the idea being to ensure the currents on the two conductors are equal and opposite. With coax in particular, due to skin effect, the inside and outside of the shield act as different conductors. The inside is balanced with the center conductor, but the outside of the shield is not balanced with anything, so any current there causes undesired radiation. A balun ensures all the power goes to the antenna, not to the outside of the coax (and also works the other way, preventing undesired signals from being picked up by the outer shield).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At least that's my understanding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen a few designs for baluns, and I'll describe a couple here. The first two make sense to me, but the third doesn't, and I'm wondering why (or if) it really works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Design 1: A section of coax with one or more ferrite beads&lt;/strong&gt;&lt;br&gt;&#xA;The effectiveness would obviously depend on the beads used, but this would act as an inductor and impede RF on the outer shield, while the currents inside the shield would remain unaffected and balanced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Design 2: A coil of coax&lt;/strong&gt;&lt;br&gt;&#xA;This can be air-wound or on a core. Either way, similar to #1, inductance blocks RF on the outside of the shield while currents inside the shield pass through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Design 3: Parallel wires wrapped around a core (see picture below)&lt;/strong&gt;&lt;br&gt;&#xA;This is the one that doesn't make sense to me. The windings would block common-mode currents, sure. So I suppose your antenna would be fed a balanced signal. But the coax ends before the windings. Wouldn't that mean RF can still flow to the outside of the shield?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ee8ya.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ee8ya.jpg&quot; alt=&quot;a howebrew balun&quot;&gt;&lt;/a&gt;&lt;br/&gt;&#xA;(From &lt;a href=&quot;http://www.m0pzt.com/baluns/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.m0pzt.com/baluns/&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Some sources:&lt;/h2&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.blubrry.com/arrl_the_doctor_is_in/13267824/all-about-baluns/&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL The Doctor Is In podcast - All About Baluns&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/AntComp1-Lewallen(1).pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Baluns: What They Do and How They Do It (ARRL)&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8940" LastEditorUserId="8832" LastEditDate="2017-01-09T02:41:40.203" LastActivityDate="2017-11-05T17:19:45.163" Title="Does a balun need to be made with coax?" Tags="&lt;coaxial-cable&gt;&lt;balun&gt;&lt;toroid&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="6984" PostTypeId="2" ParentId="6983" CreationDate="2016-12-28T05:28:32.297" Score="4" Body="&lt;p&gt;Short answer: No, and in fact you'll often get more bang for your buck by &lt;em&gt;avoiding&lt;/em&gt; coaxial baluns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The description of the balun's purpose in an antenna system you quote is an oft repeated bit of &quot;common wisdom&quot; in ham radio, but it is such an over-simplification that it is at best drastically misleading and at worst, just plain wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The purpose of a balun in an antenna system is to suppress common mode current. That's it. You can (and should) use them on balanced line, even when feeding it with a balanced tuner. You can (and should) use them on balanced, resonant antennas like dipoles that are fed with unbalanced feedline, even if the SWR is perfect. You can (and should) use them between an unbalanced vertical antenna and a coaxial feedline. (A side note: Virtually every ham radio antenna system &lt;em&gt;should&lt;/em&gt; have some form of common mode suppression mechanism installed, regardless of antenna or feedline type).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coax shield behaves as two (mostly) independent conductors. The center conductor of the coax is &quot;driven&quot; by the radio, while the shield is held at ground potential. Because the coax shield has a non-zero impedance (there's some amount of resistance and reactance present, because thermodynamics), and because the inner layer of the shield is strongly coupled both inductively and capacitively to the center conductor, a current is induced on the inside of the coax shield that is, in theory, equal in magnitude and opposite in phase to the current on the center conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These two fields exist in close proximity and we hope they are precise opposites of each other, so the two fields effectively cancel each other out, preventing the feedline from radiating. &lt;strong&gt;This pervasive idea that the coax shield behaves as a grounded Faraday cage is just flat out wrong&lt;/strong&gt;. Faraday cages do not work in the near field, and the shield is most DEFINITELY in the near field of the center conductor. Also, there has to be a return path, so the shield &lt;strong&gt;must&lt;/strong&gt; carry some amount of current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice that when I mentioned the cancellation of the two opposite fields, I specifically stated that the current was flowing on the &lt;em&gt;inside&lt;/em&gt; of the coax shield. This is because skin effect causes the inside and the outside surfaces of the shield to behave as two separate conductors, connected to each other through a relatively high impedance resistor. Exactly how high the impedance of said virtual resistor is depends on the electrical and physical characteristics of the feedline, such as characteristic impedance, capacitance, length relative to frequency, and many other variables.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In an ideal world, the outside of the coax shield would have a nearly infinite impedance between it and the inner coax shield. This is because any current flowing on the outside of the coax shield cannot interact very efficiently with the current flowing on the center conductor of the coax, meaning that the field generated by the current flowing on the outside of the coax shield is not cancelled out by any other fields. &lt;em&gt;Any current flowing on the outside of the shield is free to radiate&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This also means that any current induced on the outside of the coax shield from external sources, such as a noisy appliance power supply in your home, will be free to travel back to your radio, where it will induce current on the chassis of the radio. A significant fraction of complaints about RF noise received from within the ham's own home can be tracked back to common mode currents entering the receiver via the coax shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now that we know that a coax cable behaves more like 3 conductors, not 2, let's look at how that works with a coaxial balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we take a few feet of coax and wrap it around a ferrite toroid, the fields generated by the center conductor and the inside of the coax shield are still cancelling out, nothing much has changed inside the coax. They're still in very close proximity, and Ohm's Law says that if the current is going out through the center conductor, some of it has to be coming back in via the coax shield. However, we &lt;em&gt;have&lt;/em&gt; suddenly put the outside of the coax shield in very close proximity to the ferrite toroid, and there is no opposing field to cancel the field generated by the current on the outside of the coax. Any current flowing there will couple to the toroid, primarily inductively, and a magnetic field (and current) will then be induced &lt;strong&gt;on the toroid&lt;/strong&gt;. It becomes an electromagnet. If the toroid happens to be very good at turning energy at the frequency that's passing through the coax in to heat, then much of the current flowing on the outside of the coax will turn to heat rather than making it back to the radio, or out to the antenna, while anything flowing on the inside of the coax shield or the center conductor continues on mostly unaffected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are some problems with using coax for toroid baluns. The two biggest are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Coax doesn't like to make sharp bends, so larger loops have to be made, resulting in less inductive coupling. This usually means you have to use several toroids stacked together, and a significant length of coax.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Coax isn't very good at dissipating heat. This means that if the toroid is turning lots of common mode current in to heat to get rid of it, and you've covered up most of the toroid's surface area with coax, things could get quite hot, potentially hot enough to damage the coax.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Coax baluns that don't use toroids or iron cores cannot provide sufficient common mode suppression on multiple bands, particularly if the antenna has a high impedance or poor match on one or more bands. You should be aiming for a bare minimum of 1,000 ohms of common mode impedance (&gt;2,000 is best), but air core &quot;ugly baluns&quot; typically struggle to achieve more than 500 ohms even on their designed band. On other bands, it can be even lower. The characteristic capacitance of the coax causes an ugly balun to behave like a resonant band reject filter from the common mode current's perspective, not like a broadband choke.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So the problem is not that there is current on the outside of the coax shield, the problem is that the current on the outside of the coax shield is unopposed. If we were to solder two wires to a bit of coax, one to the shield and one to the center conductor, then wrap those two wires around a ferrite toroid as your image shows, the current on the two wires interact with the toroid about equally. If the two wires were carrying unequal currents, they wouldn't cancel exactly, and a magnetic field would be induced in the toroid. By selecting materials that are very lossy at the frequency of interest, the balun can be used to dissipate &lt;strong&gt;only the portion of the current that is unopposed&lt;/strong&gt;. If 10 watts were flowing on the center conductor, but only 8 watts were flowing on the shield in total, a field equivalent to 2 watts would be induced on the toroid and turned in to heat. At that point the current on the two wires is once again balanced, and no current will appear on the coax shield, because there is no unopposed component remaining.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imbalance in antenna systems is virtually universal. They are &lt;em&gt;designed&lt;/em&gt; to radiate, which means they must, by their nature, couple heavily to their nearby environment. This inevitably means that the antenna system will be prone to picking up local common mode noise, as well as generating common mode current due to asymmetry in the antenna system. A balun is a way to ensure that the current on the two conductors is equal and opposite, nothing more or less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wire baluns have their own set of challenges, mostly heat related:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Toroids are even worse than coax at dissipating heat. If you want good choking in a coaxial balun, you'll need multiple toroids, meaning more surface area and more mass to handle waste heat. With a wire balun, it is quite possible to get excellent choking impedance from a single large toroid, but the same amount of power is dissipated, meaning that the toroids can become &lt;em&gt;very&lt;/em&gt; hot. A single core, wire balun should not be used for more than 250 watts unless you can see with a fairly good degree of certainty that your system is not generating excessive common mode currents.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="246" LastActivityDate="2016-12-28T05:28:32.297" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6985" PostTypeId="2" ParentId="6983" CreationDate="2016-12-28T15:55:50.323" Score="7" Body="&lt;p&gt;I'll explain the operation of that balun very briefly: for the differential mode (which by definition has equal but opposite currents on each conductor), each conductor induces an equal but opposite magnetic flux in the core. These magnetic fluxes cancel, and so the differential mode sees no inductance: it's as if the core and the windings aren't there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meanwhile the common mode interacts with the core like an ordinary, single wire, and sees a large inductance. This high inductance makes the common mode on the coax a high impedance (hopefully) relative to a lower impedance path like radials, the other arm of a dipole, or some other deliberate counterpoise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I think your question isn't really about how it works. Rather, it's a mental hangup right here:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;With coax in particular, due to skin effect, the inside and outside of the shield act as different conductors.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, I bet you are thinking that with the balun pictured in your question, the end of the coax is &quot;exposed&quot;, and that means common mode current can &quot;get in&quot;, causing problems. You may be thinking once the common-mode current is inside it's stuck there, isolated from the outside by skin effect. With coiled coax or coax through beads the integrity of the coax is maintained, so nothing can &quot;get in&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I remember reading statements like that many times when I was trying to wrap my head around these same concepts, and I found them very misleading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a matter of fact, the shield is one conductor. So if someone says it's acting like two different conductors, what are they trying to say? Is it &lt;em&gt;really&lt;/em&gt; like two conductors? If we can make one conductor behave like two, couldn't we exploit that to reduce the number of conductors required for all kinds of cable assemblies? And having established one conductor can behave as two conductors, are those two resulting &quot;conductors&quot; subject to the same rule? By repeated division, could we make one conductor behave as any number of conductors? If the shield is already like two conductors, why do we need a third inner conductor?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems highly suspect to me. I think it's a terrible phrasing of a property that does more to cultivate incorrect ideas than anything else. Here's how I'd put it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;The current on any transmission line can be considered the superposition of a differential mode and a common mode.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The neat thing is you can analyze each separately and independently, then &lt;a href=&quot;https://en.wikipedia.org/wiki/Superposition_principle&quot; rel=&quot;nofollow noreferrer&quot;&gt;add the two together&lt;/a&gt; and get the same result. I think that's what the statement about skin effect is trying to say. And the fact that the common mode ends up on the outside of the shield, and the differential mode on the inside is just a bit of physics trivia.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It isn't that the balanced mode current is flowing on the inside that prevents it from radiating: it's that it's cancelled by an equal and opposite current (and voltage) on the inner conductor. Look to balanced twin-lead transmission lines for a counter example: the current isn't &quot;concealed from our view&quot; by any kind of shield. And yet, they don't radiate because the &lt;a href=&quot;https://ham.stackexchange.com/q/3508/218&quot;&gt;equal but opposite fields in each conductor cancel&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantage of coax over twin-lead is that outside the shield, the cancellation of balanced mode fields is complete, whereas for twin-lead we need to go away some multiple of the conductor spacing before that happens.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's consider a cross-section of coax with equal but opposite charges on the center and shield, and the associated electric fields:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wsZWb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wsZWb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added together, there's no field at points outside the shield. That the charges are on the inside of the shield is really not the primary thing to be thinking about, because if the charges on the inner conductor went away, the charges on the shield would migrate to the outside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And so getting back to your question about the balun, you don't need to be concerned so much with the distinction between the inside and the outside of the shield. Rather, think about maintaining equal and opposite currents and charges on the shield and center. If you do that, the fields will cancel like this, and the coax won't radiate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2016-12-28T18:06:07.480" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6986" PostTypeId="2" ParentId="6946" CreationDate="2016-12-28T22:57:12.343" Score="6" Body="&lt;p&gt;Send an HF-E-Mail addressed to your familymembers using a system like &lt;strong&gt;&lt;em&gt;WinLink 2000&lt;/em&gt;&lt;/strong&gt; (&lt;a href=&quot;http://www.winlink.org&quot; rel=&quot;noreferrer&quot;&gt;http://www.winlink.org&lt;/a&gt;). It uses Radio Message Servers (RMS), which provide a bridge between the Central Message Servers (CMS) connected to the Internet and radio clients. Radio modes available for WinLink:  &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;HF&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Soundcard modes (requires audio cable between your HF SSB radio and &#xA;your PC or smartphone and PTT triggering via VOX, serial cable or CAT&#xA;cable)&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;WINMOR&lt;/li&gt;&#xA;&lt;li&gt;ARDOP (beta, will substitute WINMOR soon)&lt;/li&gt;&#xA;&lt;li&gt;Automatic Link Establishment MIL-STD-188-141&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;TNC modes (requires TNC, e.g. Pactor Controller PTC)&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;PACTOR I&lt;/li&gt;&#xA;&lt;li&gt;PACTOR II&lt;/li&gt;&#xA;&lt;li&gt;PACTOR III&lt;/li&gt;&#xA;&lt;li&gt;PACTOR IV&lt;/li&gt;&#xA;&lt;li&gt;Robust Packet&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;VHF/UHF&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;AX.25&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Packet Radio (using TNC or soundcard modem)&lt;/li&gt;&#xA;&lt;li&gt;APRS using APRSLink&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;SHF&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;TCP/IP Networks on SHF, like HamNet in continental europe (Map:&#xA;&lt;a href=&quot;http://hamnetdb.net/lsp_map.cgi&quot; rel=&quot;noreferrer&quot;&gt;http://hamnetdb.net/lsp_map.cgi&lt;/a&gt;)&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;My portable setup:  &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;FT-817ND&lt;/li&gt;&#xA;&lt;li&gt;SCS PTC-II with PACTOR III licence&lt;/li&gt;&#xA;&lt;li&gt;homemade soundcard interface (PTT via VOX with minimum VOX delay)&lt;/li&gt;&#xA;&lt;li&gt;5 Ah 12 V battery&lt;/li&gt;&#xA;&lt;li&gt;10m (~33ft) glass fiber reinforced pole (1.3 kgs)&lt;/li&gt;&#xA;&lt;li&gt;random wire or dipole&lt;/li&gt;&#xA;&lt;li&gt;MFJ-16010 manual tuner&lt;/li&gt;&#xA;&lt;li&gt;Netbook running Arch Linux, Debian Linux and Windows 10&lt;/li&gt;&#xA;&lt;li&gt;12V solar panels&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;As I spent some days in the European Alps, outside of GSM coverage area, I was able to send E-Mails on HF (depending on propagation and time of day, I've used 80, 40, 30, 20, or 17m) not only via some European RMS but also via a Canadian RMS in Nova Scotia (distance was abt 6,000 km) with 5W into 10m end-fed vertical on 40m in PACTOR III and WINMOR). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I went transalpine on my ham radio bicycle, I've used  &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;FT-100&lt;/li&gt;&#xA;&lt;li&gt;3m vertical antenna mounted on my mono-wheel bicycle carrier&lt;/li&gt;&#xA;&lt;li&gt;MFJ-929 Automatic tuner&lt;/li&gt;&#xA;&lt;li&gt;SCS PTC-II with PACTOR III licence&lt;/li&gt;&#xA;&lt;li&gt;12 V 12 Ah battery&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use different client software. &lt;em&gt;WinLink Express&lt;/em&gt; (formerly known as RMS Express) and &lt;em&gt;Airmail&lt;/em&gt; on Windows machines or a multi-platform solution like &lt;em&gt;pat&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to provide more links, but I can't due to missing reputation on ham.stackexchange&lt;/p&gt;&#xA;" OwnerUserId="5269" LastEditorUserId="5269" LastEditDate="2016-12-28T23:17:30.980" LastActivityDate="2016-12-28T23:17:30.980" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6987" PostTypeId="1" CreationDate="2016-12-28T23:38:09.737" Score="1" ViewCount="163" Body="&lt;p&gt;I need to transmit digital data, from an Arduino, Raspberry or alike, but using VHF band (aprox 150 MHz), would anyone care to suggest a cost effective device to use as transceiver? 10W would be desired, but 5W will also be accepted.&lt;/p&gt;&#xA;" OwnerUserId="8947" LastActivityDate="2016-12-30T22:09:25.717" Title="Radio Modem suggestion" Tags="&lt;digital-modes&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="7" ClosedDate="2017-01-05T21:28:34.807" ContentLicense="CC BY-SA 3.0" />
  <row Id="6988" PostTypeId="2" ParentId="490" CreationDate="2016-12-29T16:37:08.217" Score="1" Body="&lt;p&gt;A better answer is as follows (apart for the spelling )&#xA;The dmr protocol is specifically designed to allow repeaters with no duplexer and in fact full duplex working&#xA;The repeater has to be specifcaly designed to do this as the repeater has to get its timing from the incoming signal as you don't want to put this functionality in every mobile &#xA;This is a very good way of working as it uses no more channel capacity than the simplex arrangement we are using at present as we cannt nip in and use the channel which is not keyed anyway&#xA;One day all radio will be dmr and all dmr will be duplex In a few years time the transmit key will be just used for convenience to start call and save battery power during calls and to shut down at the end of the call like the rest on a land line phone&#xA;Some of the comments above refer to store and forward delays. 1 time slot is not noticeable in human speech&lt;br&gt;&#xA;The first big advantage would be to allow the halving of repeater costs and in fact probably an even bigger saving than this as a having in actual costs would bring the repeater costs down to level where we all want one allowing the econonys of scale to reduce prices by another 1/2 at least &#xA;Basically there is no reason why a repeater without a duplexer is not just a mobile with different software&#xA;The take up of duplex hand portables and mobiles is a little further away as the tx/rx spacing is only 10 MHz as opposed to 50 megahertz for gsm. This makes switching a little more difficult but not much&#xA;Personally I would like to see us as amiteurs be quick to follow this route as otherwise there may never be a free of charge solution Which would allow us to enjoy the benifits of mobile phones without the monthly fees&#xA;This could be the greatest stimulates ever to our hobby &#xA;Ted slevin&#xA;Retired chef engineer of burndept electrinics&lt;/p&gt;&#xA;" OwnerUserId="8957" LastActivityDate="2016-12-29T16:37:08.217" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6989" PostTypeId="2" ParentId="501" CreationDate="2016-12-29T17:19:28.937" Score="2" Body="&lt;p&gt;The &quot;UHF&quot; connector, as stated, is a hold-over from World War II, and has become an industry standard. A lot of hams &quot;know&quot; how to put them on coax, and, since radio is, overall, forgiving, most don't notice the folly of their installation processes (melted dielectric, poor solder wetting, etc). Me? I can install them, but prefer to crimp them on. That, however isn't pertinent to your question. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your original question has been answered well enough already, but you posed a corollary question. In my opinion, it depends on the target frequency you're working with and the size of the hardware. In general terms, I use a BNC connector for most of my lower frequency work (yeah, because they're easy to crimp, too), and SMA for anything about 1.2GHz. For me, it's often about saving space and still having efficient connectors. Both the BNC and SMA (and even the N) demonstrate a smaller impedence &quot;bump&quot; than most UHF connectors I've looked at.&lt;/p&gt;&#xA;" OwnerUserId="8958" LastActivityDate="2016-12-29T17:19:28.937" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6990" PostTypeId="2" ParentId="948" CreationDate="2016-12-30T13:13:54.003" Score="0" Body="&lt;p&gt;No legal reason why not as long as your licence conditions allow it. It would be just like linking two or more repeaters together with Echolink or AllStar.&lt;/p&gt;&#xA;" OwnerUserId="4952" LastActivityDate="2016-12-30T13:13:54.003" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6991" PostTypeId="1" CreationDate="2016-12-30T21:20:25.873" Score="0" ViewCount="73" Body="&lt;p&gt;Is it possible to digitally extract received power info (like VU meter perhaps) from and PSK31 audio (or alike), actually the mode for text encoding over audio hasn't been chosen yet and the capability (or not) to extract power info from it would be a key factor, so suggestions on this topic would also be appreciated ;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PS: this is intended in the VHF 140-160 MHZ band&lt;/p&gt;&#xA;" OwnerUserId="8947" LastActivityDate="2017-01-04T19:01:36.957" Title="Extracting received power info from teletype like audio" Tags="&lt;digital-modes&gt;&lt;vhf&gt;&lt;rf-power&gt;&lt;encoding&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6992" PostTypeId="2" ParentId="6987" CreationDate="2016-12-30T22:02:35.810" Score="1" Body="&lt;p&gt;I once spent a bit of time getting packet radio going over VHF using a Raspberry Pi and Direwolf as the modem. It worked fine using a couple of cheap Wouxon handhelds. (I've heard that Baofengs don't work as well due to the time it takes to break the squelch.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The instructions I used are here:&#xA;&lt;a href=&quot;https://andrewmemory.wordpress.com/2016/03/31/turning-a-raspberry-pi-2-into-a-packet-station/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://andrewmemory.wordpress.com/2016/03/31/turning-a-raspberry-pi-2-into-a-packet-station/&lt;/a&gt;. In short, set the Pi up as a packet node, then use Direwolf and kissattach to provide TCP/IP over packet into a sound card. Too much for an Arduino, but should be fine on a Pi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They required a Signalink to do the PTT, but I think Direwolf can do the PTT itself with an appropriate cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll leave the legalities of it up to you - but packet radio is designed for multiple stations, can route traffic through nodes (and in fact is TCP/IP), and appropriate Wouxuns can transmit 1200 baud packet at 147 MHz, so should be able to handle it at 150 MHz.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2016-12-30T22:09:25.717" LastActivityDate="2016-12-30T22:09:25.717" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="6993" PostTypeId="1" AcceptedAnswerId="6994" CreationDate="2016-12-31T00:23:40.963" Score="1" ViewCount="176" Body="&lt;p&gt;I have a pic in the VLF band at 1.5 kHz. &lt;strong&gt;What would be the origin of this peak?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The graph was obtained by running &lt;code&gt;display_qt&lt;/code&gt; in Linux from a laptop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ybTk0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ybTk0.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8969" LastEditorUserId="76" LastEditDate="2016-12-31T00:40:41.000" LastActivityDate="2016-12-31T17:35:05.043" Title="How to explain a frequency pic at 1.5 kHz?" Tags="&lt;signal-identification&gt;&lt;gnuradio&gt;&lt;vlf&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6994" PostTypeId="2" ParentId="6993" CreationDate="2016-12-31T00:40:13.847" Score="3" Body="&lt;p&gt;&lt;code&gt;display_qt&lt;/code&gt; is a GNU Radio example program. It does not display any actually existing electromagnetic signal but internally generates a 1500 Hz sinusoid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://gnuradio.org/redmine/projects/gnuradio/repository/revisions/9db614d652ca5065599d4282bd43a3b3fd0e9d12/entry/gr-qtgui/examples/c++/display_qt.cc&quot; rel=&quot;nofollow noreferrer&quot;&gt;The code&lt;/a&gt; creates a sine source and a noise source,&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;// Source will be sine wave in noise&#xA;src0 = analog::sig_source_f::make(rate, analog::GR_SIN_WAVE, 1500, 1);&#xA;src1 = analog::noise_source_f::make(analog::GR_GAUSSIAN, 0.1);&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;then sums them and sends that to the displays.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2016-12-31T17:35:05.043" LastActivityDate="2016-12-31T17:35:05.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="6995" PostTypeId="1" AcceptedAnswerId="6997" CreationDate="2016-12-31T09:05:58.160" Score="1" ViewCount="24805" Body="&lt;p&gt;I have tried programming approach frequencies into my baofeng and cannot hear any transmissions.  Freq programming was done using a desktop computer connected to the radio to frequency 121.9MHZ.  Nothing was heard, just standard background static.  Here is the  radio:  &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00HX03AMA&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amazon.com/Baofeng-Warranty-Dual-Band-Radio-Improved/dp/B00HX03AMA&lt;/a&gt;  Baofeng UV5R v2&lt;/p&gt;&#xA;" OwnerUserId="8971" LastEditorUserId="4076" LastEditDate="2016-12-31T16:29:02.577" LastActivityDate="2018-10-25T15:32:41.677" Title="Can a Baofeng UV5R receive airport radio transmissions?" Tags="&lt;baofeng&gt;" AnswerCount="3" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="6996" PostTypeId="2" ParentId="6995" CreationDate="2016-12-31T16:29:54.687" Score="3" Body="&lt;p&gt;From the amazon page you've linked to:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Frequency Range: 136-174 / 400-479.995 MHz. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, no, you can't receive 121.9 MHz. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2016-12-31T16:29:54.687" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="6997" PostTypeId="2" ParentId="6995" CreationDate="2016-12-31T17:45:18.703" Score="7" Body="&lt;p&gt;As far as I've read, all Baofeng radios do FM only. The majority of aircraft communications uses AM, so whether or not it can be tuned there, you would not hear the audio, just approximate silence (quieter the stronger the signal).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is because to a FM receiver's perspective, an AM signal is unmodulated (the frequency stays constant), and vice versa (in a FM signal the amplitude stays constant).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;In some cases, the speech may be very faintly audible, due to imperfect circuits in both the transmitter (causing frequency variation in the transmitted signal) and the receiver (having unintended sensitivity to amplitude variations).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the reverse case — attempting to receive a FM signal using an AM receiver — this can actually be used practically (improvised “slope detection”, tuning with an offset and allowing the frequency modulated signal to be converted by the edge of the receiver's filter to an amplitude-and-frequency modulate signal).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2016-12-31T17:45:18.703" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="6999" PostTypeId="2" ParentId="6991" CreationDate="2017-01-01T22:31:04.057" Score="1" Body="&lt;p&gt;That doesn't depend on the text-to-audio modulator, but on the audio-to-baseband / audio-to-RF modulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With AM, audio amplitude is proportional to received signal strength, with FM, the received signal strength has absolutely no effect on audio signal (and hence, you can't recover the received power at all; that info is simply lost on the way).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, I think you're not measuring the right thing – if you're really concerned about signal &lt;em&gt;quality&lt;/em&gt;, you'd rather go for a measure of SNR in the audio prior to text de-coding. Received power is a meaningless figure without knowing how your receiver reacts to that, how much of that power is noise or interference, and how sensitive your audio demodulator is to that, and what the effects of audio distortions on your text communication are. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I personally think you might want to ask yet another question on ham.stackexchange.com: &lt;em&gt;Given that I want to achieve X, how can I choose a digital/text data codec?&lt;/em&gt; and describe what that X and its environment is.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="1362" LastEditDate="2017-01-04T19:01:36.957" LastActivityDate="2017-01-04T19:01:36.957" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7000" PostTypeId="2" ParentId="6991" CreationDate="2017-01-02T16:42:43.703" Score="2" Body="&lt;p&gt;Assuming you are doing something like recording the audio output from an SSB radio, then the audio recording is just the RF spectrum shifted down in frequency. So, you could calculate the RMS average of the audio file, square it (since power is proportional to the square of voltage), and you'd have some measurement of power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this requires that the gain between the antenna and the audio recording is some fixed, known value. If your radio has AGC, this is certainly not the case, since the AGC will adjust the gain to produce audio recordings of approximately the same amplitude, regardless of the received power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you just want some measure of signal quality, there are other methods you could use which do not have this requirement. For example, you could estimate the signal-to-noise ratio. Alternately, if you use an encoding with forward error correction (PSK31 has none, but some variants do) you may have a means to estimate the bit error rate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-01-02T16:42:43.703" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7001" PostTypeId="1" AcceptedAnswerId="7002" CreationDate="2017-01-02T17:44:07.137" Score="2" ViewCount="405" Body="&lt;p&gt;I wonder, if a broadcasting radiostation can detect, how many receivers are tuned on it, and if it possible - how exactly this detection is happening? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="8978" LastEditorUserId="8832" LastEditDate="2017-01-19T19:26:03.117" LastActivityDate="2017-01-19T19:26:03.117" Title="Detecting the listeners" Tags="&lt;receiver&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7002" PostTypeId="2" ParentId="7001" CreationDate="2017-01-02T18:23:29.743" Score="7" Body="&lt;p&gt;No, that's not possible.  There is no practical way to determine whether the transmitted power is usefully received by an antenna, or just absorbed by the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible to detect that a &lt;a href=&quot;https://en.wikipedia.org/wiki/Superheterodyne_receiver&quot;&gt;superheterodyne receiver&lt;/a&gt; with a known intermediate frequency is powered on and tuned to a particular frequency, because the receiver's local oscillator radiates a small signal.  In the UK there is a tax on televisions, and the local authority in the past used &lt;a href=&quot;https://en.wikipedia.org/wiki/Television_licensing_in_the_United_Kingdom#TV_detector_vans&quot;&gt;television detector vans&lt;/a&gt; to detect unlicensed televisions in use, by comparing addresses with televisions running to the database of homes that paid the tax.  But scanning for tiny local oscillator signals can only be done in a small local area, because the background of RF noise would swamp any attempts at large-scale detection.  Besides, radio design has evolved and receivers use many different architectures now, so superheterodyne receivers with the same IF are no longer universal.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-01-02T18:23:29.743" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7003" PostTypeId="2" ParentId="6471" CreationDate="2017-01-03T02:13:44.730" Score="3" Body="&lt;p&gt;It also depends on the legal users of that part of the spectrum who may land up monitoring violations and reporting to FCC. Eg ARRL has monitoring volunteers who monitor for amateur band violations. I would think that it will be in the commercial interest of the cellular companies to monitor any abuse of their frequency spectrum and report t violations to enforcement agencies.&lt;/p&gt;&#xA;" OwnerUserId="8982" LastActivityDate="2017-01-03T02:13:44.730" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7004" PostTypeId="1" CreationDate="2017-01-03T07:13:38.867" Score="1" ViewCount="9345" Body="&lt;p&gt;I installed the latest MD-380 software (from &lt;a href=&quot;http://www.radioddity.com/downloads&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radioddity&lt;/a&gt;) , but I cannot get the MD-380 software to work on Windows 10.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I plug the &lt;a href=&quot;http://www.buytwowayradios.com/products/tytera/tyt-prog.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;MD-380 USB programming cable&lt;/a&gt; in my Surface Book (obviously running Windows 10), Device Manager sees &quot;STM device in DFU Mode&quot;. (Which seems to be what I want, &lt;a href=&quot;http://wiki.robotz.com/index.php/Tytera_MD-380&quot; rel=&quot;nofollow noreferrer&quot;&gt;according other documentation I've seen online&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But when I start the start the MD-380 software, I can't get the software to read the unique device number of my radio. (&lt;a href=&quot;https://i.imgur.com/GKciusL.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here is a pic of where it hangs&lt;/a&gt;. On all the howto videos online, this seems to happen automagically.)  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've uninstalled the drivers, re-installed them, and nothing.  I still keep getting the same result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any suggestions on what I might be missing here?&lt;/p&gt;&#xA;" OwnerUserId="1463" LastEditorUserId="1463" LastEditDate="2017-01-04T04:29:42.583" LastActivityDate="2018-11-12T09:52:42.350" Title="Tytera MD-380 software (DMR radio software) not working on Windows 10" Tags="&lt;digital-modes&gt;&lt;software&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7005" PostTypeId="2" ParentId="7004" CreationDate="2017-01-03T12:43:09.893" Score="0" Body="&lt;p&gt;I can't really help you with fixing the installation on Windows 10. As far as I know, Tytera's DFU mode is &lt;em&gt;ahem&lt;/em&gt; nearly standards-compliant, and their drivers are unsigned. The latter might mean you have to boot windows in a special mode were signature checking for driver installation is disabled. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyways, there's good reasons to look into alternatives; I've only become aware of the MD-380 because of its free &amp;amp; open source firmwarelet / utility library that you can find at &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://github.com/travisgoodspeed/md380tools/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/travisgoodspeed/md380tools/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;maintained by Travis, KK4VCZ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What it &lt;em&gt;can&lt;/em&gt; do is automatically download the official firmware, apply some patches to it, and then, update the device (if a compatible firmware is already loaded) or just generate a firmware image that you can load through official Tytera ways on windows (which are currently failing for you) or automatically on Linux (and OS X, I presume). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, I haven't used Windows in a rather longish time – I'm not a zealot, but it just feels awkward to me to use. For me, setting up a Linux installation is trivial, but that might or might not be different for you¹. Then, following the build instructions, I can build a firmware and utils rather quickly and use the &lt;code&gt;md380-dfu&lt;/code&gt; utility to update the MD-380.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, the process that KK4VCZ used to reverse-engineer this firmware and DFU utilities is rather interesting; you can read on it in &lt;a href=&quot;https://www.alchemistowl.org/pocorgtfo/&quot; rel=&quot;nofollow noreferrer&quot;&gt;PoC||GTFO 0x10, pp. 76&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹ however, looking at the companies you work(ed) for that I can find using minimal stalking techniques, you might have dealt with more exotic environments that e.g. Fedora or Ubuntu&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-01-03T12:59:41.553" LastActivityDate="2017-01-03T12:59:41.553" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7006" PostTypeId="1" CreationDate="2017-01-04T01:39:07.560" Score="2" ViewCount="265" Body="&lt;p&gt;I'm studying the accessory connector (DB-25) from a Kenwood NX-700 radio. It seems that I might use the AFO and/or DEO signals, but I haven't been able to get proper documentation on such pins/signals. I'd like to get the audio data received and hopefully send data via other pins on this connector too, avoiding the use of the standard mic/PTT/speaker connectors. Also, is there any pin that provides a S-meter like output?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could anyone please assist me on getting more info on these?&lt;/p&gt;&#xA;" OwnerUserId="8947" LastEditorUserId="76" LastEditDate="2017-01-05T20:03:16.243" LastActivityDate="2017-05-09T20:51:56.387" Title="Looking for documentation on Kenwood NX-700 AFO and DEO Signals" Tags="&lt;vhf&gt;&lt;kenwood&gt;&lt;audio-interface&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7007" PostTypeId="2" ParentId="6968" CreationDate="2017-01-04T09:59:22.913" Score="2" Body="&lt;p&gt;I remember back in the early 70s, when I was being trained by former WW II radio guys who were all Extra-class, and they explained that this is a confusing issue, because the common usage is not always the same as the rules.  I was first licensed in 1971, when we still tuned (and were tested) in Mc (megacycles), even though MHz was the correct way to say it.  Eventually the industry caught up (as the older Elmers became SKs) and now everyone says MHz.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Answer:  There is no official E in the first position.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Here it is from the horse's mouth:&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;&lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=licensing_2&amp;amp;id=industrial_business&amp;amp;page=2&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://wireless.fcc.gov/services/index.htm?job=licensing_2&amp;amp;id=industrial_business&amp;amp;page=2&lt;/a&gt;&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;It is clear that this list is not the same as common usage.  For instance, CW was regularly taught as being A1.  That was the correct answer on all tests I took (the last Amateur test being in 1977, then on the General Radiotelephone test in 1983).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But we all know that Morse Code is not really CW.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC's list would have a true continuous wave as being as N0.&lt;br&gt;&#xA;But the keying is considered to be a form of amplitude modulation, hence A1.&#xA;So here the FCC is correct on the tests.  It is us hams who are wrong to call it CW.  :(  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have never encountered E in the first position.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The E designator in the third position simply means it is telephony - voice communications, which can be speech or music.  Think analog.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, AM is A3E.  Amplitude modulation, single channel, telephony.  But on the tests I took it was simply called A3.  Back then it was in common usage by hams.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And most multiband ham transceivers and linear amplifiers still had the 11-meter band.   Then came along CB, which required another license and more restrictions.  That all changed when CB radio became too big to be licensed.  (I had a mail-in CB license but then the FCC gave that up in favor of regulation). Hams that liked DXing on 11 simply moved to 10 on solar max years.  (we're at a solar minimum right now - so 20 is best)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then the hams almost completely dumped AM in favor of SSB to relieve band congestion.  A lot of CBers followed suit, to get more than 23 channels.  Then the FCC changed CB to include more channels - the 40 we have now, and a 12 W PEP limit for power. And they banned commercial manufacture of 11-meter switch selections for ham radio linear amplifiers, which lasted until the advent of wideband solid-state amplifiers. Then the CBers found that 12 Watts PEP on CB SSB was sufficient on solar max years to talk to the other countries (like New Zealand) who still had 11 meters for ham radio.  Then the hams switched to FM on 10 meters to avoid QRN.  And so on..  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM radio is F3E.   Frequency modulated, single channel (even if it includes stereo encoding), telephony.  If the FM station also transmits on subcarriers for SCA channels carrying entirely different programming, then that is called F8E.  Stereo encoding is really a subcarrier, too, of course, but is considered part of the single channel because it is part of the same program.  And we were taught that it is simply F3.  Confusing enough?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham radio SSBSC (Single sideband suppressed carrier) has long been commonly called (and tested) as A3J because it is amplitude modulation, single channel,  with suppressed carrier.  SSB of this type can carry other kinds of analog audio signals such as SSTV, RTTY, AFSK, etc.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So when it is used simply to talk to other hams it is called A3J in common usage and on the tests, to differentiate it from A3 (AM).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But according to that FCC chart it would be J3E.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So here we are, 40 years later, and I would echo KL7AG, KL7AM, KL7IS and the other trainers:  It is confusing, but the only time you would need to worry about this kind of thing might be for a test.  In real life, just enjoy using it.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-18T17:33:40.523" LastActivityDate="2017-08-18T17:33:40.523" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="7008" PostTypeId="1" AcceptedAnswerId="7013" CreationDate="2017-01-04T16:56:06.390" Score="9" ViewCount="3933" Body="&lt;p&gt;I can't afford a massive tower, but I can get a weather balloon. What kind of set up would work best to get the maximum efficiency out of altitude?  &lt;/p&gt;&#xA;" OwnerUserId="5840" LastEditorUserId="5840" LastEditDate="2018-09-29T16:17:24.750" LastActivityDate="2019-08-29T16:34:53.333" Title="Could a weather balloon make a good antenna?" Tags="&lt;antenna-theory&gt;&lt;legal&gt;&lt;wire-antenna&gt;&lt;efficiency&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="7010" PostTypeId="2" ParentId="6240" CreationDate="2017-01-05T03:37:41.063" Score="2" Body="&lt;p&gt;Simply put, if the current and voltage are in phase, the SWR should be relatively low. They will be in phase for a non-reactive load, i.e., a purely resistive load: a 50 ohm resistance with no capacitance (such as an antenna too short) and no inductance (antenna too long).&lt;br&gt;&#xA;The voltage from the capacitor divider is applied equally to the positive and negative current transformer outputs (that are converted to voltages by the 27 ohm load resistors).&#xA; The turns ratio of the transformer and the voltage divider ratio of the two capacitors are matched. When the negative side current output matches the voltage divider, they should null (reverse SWR).  The positive side's current output and the divider will 'add' giving a large voltage indicating the power (or forward SWR reading).  The additional components, L2, C3, R2, are tweaks to compensate the circuits to stay calibrated over the frequency range.&#xA;As the SWR increases, the phase of the current won't match the voltage and no longer null the reverse side so a voltage is detected on the reverse side indicating a higher SWR.  The positive side's current also will be affected the same way (they won't add properly).&#xA;Somewhat simplified, but may help when trying to troubleshoot small errors.&lt;/p&gt;&#xA;" OwnerUserId="8994" LastActivityDate="2017-01-05T03:37:41.063" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7011" PostTypeId="1" AcceptedAnswerId="7189" CreationDate="2017-01-05T08:13:37.717" Score="5" ViewCount="626" Body="&lt;p&gt;Does the wire diameter of the reflector and the directors of a beam antenna affect the bandwidth or is it &lt;strong&gt;only&lt;/strong&gt; the driven element diameter that has this effect?&lt;/p&gt;&#xA;" OwnerUserId="8477" LastEditorUserId="8832" LastEditDate="2017-01-07T12:00:32.190" LastActivityDate="2017-02-06T16:22:20.713" Title="Does the wire/conductor size of all the elements affect antenna bandwidth?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7012" PostTypeId="2" ParentId="6967" CreationDate="2017-01-05T08:43:24.247" Score="0" Body="&lt;p&gt;Building on that previous answer, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My answer is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All test transmissions are covered under Sec. 97.119 Station identification:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(a) Each amateur station, except a space station or telecommand station, must transmit its assigned call sign on its transmitting channel at the end of each communication, and at least every 10 minutes during a communication, for the purpose of clearly making the source of the transmissions from the station known to those receiving the transmissions. No station may transmit unidentified communications or signals, or transmit as the station call sign, any call sign not authorized to the station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Test transmissions must not cause interference, of course, and may be for purposes of tuning new equipment or verifying a propagation path.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;No matter the purpose, this section is very strictly applied to all amateur emissions.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-01-06T20:17:42.663" LastActivityDate="2017-01-06T20:17:42.663" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7013" PostTypeId="2" ParentId="7008" CreationDate="2017-01-05T18:52:49.230" Score="4" Body="&lt;p&gt;Hoisting a vertical antenna with a balloon seems to be a fairly-common trick for Field Day.  A web search for &lt;code&gt;tethered balloon antenna&lt;/code&gt; returns many interesting results.  Here are some points brought up by several of those web pages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Ordinary round weather balloons or 36&quot; (91 cm) party balloons work okay, until the wind blows, which causes the antenna to be knocked flat.&lt;/li&gt;&#xA;&lt;li&gt;One poster suggested attaching the balloon-hoisted vertical antenna to a mast of some sort, so that when the wind blows the antenna becomes an inverted-L, rather than just laying along the ground.&lt;/li&gt;&#xA;&lt;li&gt;Several posters noted that kite-shaped balloons designed for tethering work best; the kite shape makes the balloon generate lift in the wind, so that the antenna stays more vertical.  Apparently kite-shaped balloons meant for tethering are sold for advertising purposes, to host pennants over sales at car dealerships and such.  Such balloons are also known as &lt;a href=&quot;https://en.wikipedia.org/wiki/Kytoon&quot; rel=&quot;noreferrer&quot;&gt;kytoons&lt;/a&gt;.  Here's a &lt;a href=&quot;http://www.helikites.com/&quot; rel=&quot;noreferrer&quot;&gt;commercial supplier&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Governments may have something to say about your project.  One poster suggested that in the US, tethered balloons have to be reported to the Federal Aviation Administration.&lt;/li&gt;&#xA;&lt;li&gt;Any balloon will surely leak helium over time.  Several posters said that their balloons came down after a day or two.&lt;/li&gt;&#xA;&lt;li&gt;Safety concerns abound.  Nearby power lines are obviously a concern.  The balloon should probably have a tether line in addition to the antenna wire, in case the antenna wire breaks at the ground.  A loose balloon dangling a copper wire would be dangerous.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-01-05T18:52:49.230" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7014" PostTypeId="1" AcceptedAnswerId="7015" CreationDate="2017-01-05T23:27:11.857" Score="9" ViewCount="1602" Body="&lt;p&gt;I ended up with an old straight key that has a curious feature: below the main arm that you would tap on, there's an extra metal flange that can sort of loosely pinch an extra sliding lever underneath, basically like a knife switch tipped over:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/amn53.jpg&quot; alt=&quot;Extra slide switch on an old straight key&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When moved into contact, it simply shorts the two terminals of the key. So I guess I could use it when trying to heat up an SWR meter or something, but otherwise it seems sort of useless, something you'd accidentally bump on at an inconvenient time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is my key wired up right? Seems more reasonable that this would be handy to &lt;em&gt;disable&lt;/em&gt; a key that wasn't in use, but it sure doesn't seem like the electrical layout supports that. It seems intentionally designed to do the opposite, i.e. locking the key &quot;down&quot; instead of &quot;up&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would a telegraph or radio operator ever really need the ability to leave a &quot;daaaaaaaaaaaaaaaaaaah&quot; signal going indefinitely? Did this have a more useful purpose historically, like in some sort of common multiple-key configuration?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-01-05T23:34:09.177" LastActivityDate="2019-11-10T19:19:39.773" Title="Why do some straight keys have a slider that shorts the contacts continuously?" Tags="&lt;cw&gt;&lt;equipment&gt;&lt;history&gt;" AnswerCount="5" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7015" PostTypeId="2" ParentId="7014" CreationDate="2017-01-05T23:37:19.967" Score="18" Body="&lt;p&gt;My understanding is that in at least some telegraph systems, the principle of operation was as in this circuit (where the coils depicted are actually telegraph sounders):&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/K2f8z.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fK2f8z.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, your key's shorting switch is, in radio terms, your transmit/receive switch: you close it in order to listen, and the other side actually completes the circuit with their key as they are sending code. (Note that the other side can detect the state of your key while idle — by checking for voltage across their open key.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For radio CW transmissions, this part of a key is not useful for normal operation, but you could use it e.g. while adjusting a manual antenna tuner, if your radio does not have a better function for providing a tuning signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't heard of anyone specifically wanting this feature in a key, though, except for its historical value.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-01-06T01:39:05.770" LastActivityDate="2017-01-06T01:39:05.770" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="7016" PostTypeId="2" ParentId="7014" CreationDate="2017-01-06T03:43:04.253" Score="4" Body="&lt;p&gt;The switch on the side of the key is or rather was used when tuning up a transmitter.  In the old days you had to increase drive and dip the grid of the final amplifier.  So this is simply a switch so that the operator can key his transmitter and use both hands for the operation. Today you don't tune like that UNLESS you have a high power amplifier.  But this type of tuning will usually draw the criticism from others on the band and is frowned on, and the person operating in this manner is considered a LID (poor operator) and a discourteous person.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this helps&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Poe  &lt;/p&gt;&#xA;" OwnerUserId="8685" LastActivityDate="2017-01-06T03:43:04.253" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7017" PostTypeId="2" ParentId="1019" CreationDate="2017-01-06T03:58:56.960" Score="2" Body="&lt;p&gt;If you are concerned about unintentional interference, then you should use an antenna analyzer. Some of them actually have a mode for that whereby the analyzer sends a tone that beeps; and the closer to a 1:1 match, the faster it beeps until it is a solid tone. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just make darn sure you don't transmit into you analyzer, or you will damage it and I can promise you this damage will not be repaired by the mfg for free.&lt;/p&gt;&#xA;" OwnerUserId="8685" LastEditorUserId="8717" LastEditDate="2017-06-14T13:02:26.953" LastActivityDate="2017-06-14T13:02:26.953" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7018" PostTypeId="2" ParentId="6240" CreationDate="2017-01-06T16:38:13.907" Score="1" Body="&lt;p&gt;C4/C5 form a capacitive voltage divider, L2 provides a DC return path for the meter current which needs to get back to the center tap to close that loop, and I suspect R2 lowers the Q of the undesirable L2/C5 resonance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The basic idea is that the current sense transformer develops voltage across R1 which is proportional (and in phase with) to the line current, and that this is added to the sample of the line voltage for forward power or subtracted from it for reverse power. The ratios are calculated such that with 50V and 1A flowing the voltage across R1 is twice the voltage developed by the divider network, causing the reverse power meter to read zero (Note the center tap means the subtraction of from half the voltage across R1) and the forward power meter to read 50W, if you had say 50V and 2A flowing then the voltage across R1 would be four times that developed by the divider network causing the reflected power to read 50W and the forward power to read 100W, again reasonable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do note that this circuit (If built with a coax line thru the sense transformer) requires that the screen on that line section be connected ONLY at one end. There should be a path that does not pass thru the toroid for the return current as the coax line section is intended to be an electrostatic shield.&lt;/p&gt;&#xA;" OwnerUserId="8756" LastActivityDate="2017-01-06T16:38:13.907" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7020" PostTypeId="1" AcceptedAnswerId="7030" CreationDate="2017-01-07T12:46:29.890" Score="1" ViewCount="386" Body="&lt;p&gt;I have a 20m long dipole that starts at 2m above the ground and ends at perhaps 20m above the ground. It was -10 °C here tonight (that's +14 °F), currently around zero (32 °F) and my antenna is out of tune because of this (I noticed it before with slightly warmer weather). There are also small icicles everywhere on it, of perhaps 1-2mm long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/6575/885&quot;&gt;My antenna tuner&lt;/a&gt; already was close to its limits when tuning for 20m and now its completely out of range. The obvious solution is to use a smaller capacitor to shift the range. Is that the best option, or can I better do something else to deal with the cold weather?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the transceiver to the tuner is coax, from the tuner to the antenna ladder (4m inside, 5m outside). The antenna is a 20m dipole, so two sides of 10m.&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-09T18:06:14.247" Title="Tuning an antenna with cold weather" Tags="&lt;antenna&gt;&lt;antenna-tuner&gt;&lt;weather&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7022" PostTypeId="2" ParentId="6934" CreationDate="2017-01-07T18:54:42.177" Score="4" Body="&lt;p&gt;FCC Special Counsel Laura Smith had a speech at Pacificon, a ham conference in the San Francisco area, last October. She said, after the case is closed and the equipment is confiscated they demolish it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;She further stated that they will try to change procedure to actually donate or auction the equipment instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See whole speech at &lt;a href=&quot;https://www.youtube.com/watch?v=k08DClez1aQ&amp;amp;feature=youtu.be&amp;amp;t=24m38s&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=k08DClez1aQ&amp;amp;feature=youtu.be&amp;amp;t=24m38s&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="-1" LastEditDate="2017-02-08T10:36:34.977" LastActivityDate="2017-02-08T10:36:34.977" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7023" PostTypeId="2" ParentId="7020" CreationDate="2017-01-07T19:38:40.883" Score="3" Body="&lt;p&gt;The overall antenna length being very close to a perfect 1 wavelength is the linchpin of the issue, I suspect. It is not surprising that it can be easily moved outside of the tuning capability of your tuner, as the impedance peak near resonance can be quite sharp (depending on the Q of the antenna system), allowing the impedance to change by hundreds or even thousands of ohms over a bandwidth of just a few percent of the signal's frequency. It is quite possible to see a swing from 10:1 SWR at the tuner (which is well within the range of most decent tuners)  at 14.350MHz to 100:1 at 14.450MHz in a well engineered antenna with good quality feed line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would wager that if you were to do an impedance sweep of the antenna system during warm weather, you'd find that the actual impedance maximum (indicating a perfectly resonant 1 wavelength) would be just a bit above 14.350MHz, probably not by more than a few tens of kHz. Water, ice, and snow on the antenna can contribute a small amount of electrical loading, effectively decreasing the resonant frequency, in this case dragging the impedance maximum in to the ham band. This is common with insulated antenna wire and 300 or 450 ohm &quot;window&quot; type balanced feed line. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition, the larger dielectric losses contributed by the liquid around the antenna compared to air can alter the resistive component of the complex impedance, and asymmetrical dielectric losses on the two sides of the system, especially on the balanced line, can contribute to significant imbalance and common mode current, causing the feedline to act as part of the antenna, which will further alter impedance and cause unpredictable changes to SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since one end of the dipole is quite low to the ground, just 1/10 of a wavelength or so, coupling to the ground and nearby objects is probably relatively significant. If the recent cold weather also came with a new snow fall, that may further contribute to a shift in resonant frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The point being, you are likely seeing the antenna's resonant frequency shift from somewhere above 14.350MHz to somewhere very near the 20 meter band due to loading effects of water, ice, and snow. It's also possible that the cold is causing mechanical changes to the system, such as sagging that brings some part of the antenna or feedline close to an object it can couple to. You may also be experiencing an increase in common mode current on the feed line, which will result in inaccurate SWR measurements. The BLT tuner should have good common mode isolation with that isolated balun, so I wouldn't be quite as inclined to suspect the SWR meter here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Exactly how to remedy the problem depends on quite a few variables, not least of all how much flexibility you have with the antenna location and construction. If the balanced line is &quot;window&quot; type line, sheltering it to prevent any rain or ice from accumulating on it (dust can cause problems too), or moving it up away from the ground to avoid problems from snow accumulating around it may help. A better bet would be to ensure that it is kept away from any object it could couple with by a distance of at least the distance between the two conductors, but ideally 2 or 3 times that. Replacing the window line with true ladder line can minimize problems with dielectric losses when wet or covered in ice, and would probably be the optimal solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Getting the low end of the antenna another couple of meters above the ground may also significantly improve the situation. As it is currently installed, there is almost certainly some degree of imbalance on the balanced line due to the asymmetrical interaction with the ground between the two ends of the dipole, which will make the balanced line all the more likely to interact negatively with objects around it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option would be to slightly lengthen or shorten the antenna, moving the 1 wavelength impedance maximum away from the 20 meter band. A total length of around 25 meters is often a good compromise, as it will retain good characteristics on 40m, while still allowing it to tune both 20 meters and 30 meters with a reasonably good tuner.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-01-07T19:38:40.883" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7025" PostTypeId="2" ParentId="3565" CreationDate="2017-01-07T20:09:27.323" Score="1" Body="&lt;p&gt;The reflector term cannot be applied to a repeater as we refer to them. It is a digital conference room that links many repeaters together. The repeaters are independent &quot;boxes&quot; digitally connected to these conference room &quot;relfectors.&quot;&lt;/p&gt;&#xA;" OwnerUserId="9006" LastActivityDate="2017-01-07T20:09:27.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7026" PostTypeId="2" ParentId="948" CreationDate="2017-01-07T20:13:48.043" Score="0" Body="&lt;p&gt;You can do it, but a repeater that hears well but doesn't transmit well is called a rabbit. A repeater that talks well but doesn't hear well is called an alligator. Repeater owners go to great lengths to tune their repeaters to be equal to both transmitting and receiving. Repeater owners that have a rabbit should increase the transmit power. Alligators should reduce power to properly balance the repeater.&lt;/p&gt;&#xA;" OwnerUserId="9006" LastActivityDate="2017-01-07T20:13:48.043" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7027" PostTypeId="2" ParentId="1917" CreationDate="2017-01-07T20:25:12.493" Score="0" Body="&lt;p&gt;I currently transmit with an AllStar node to a repeater on 900 MHz using a 70 cm link radio with a DPL. Because I am on a link frequency, I use simplex. When the repeater is transmitting on the output frequency, it is also transmitting on the link frequency which reduces doubling. The repeater has three radios in it. One for local receive, local transmit, and simplex linking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If someone is transmitting through AllStar, then my link radio is transmitting to the repeater. The repeater controller can determine which signal is the priority...the link channel input or the repeater channel input. What will the controller do if the link is active and a local user keys up? Two inputs are coming into the repeater. Is there a priority signal or first come first served?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the remote link radio is transmitting, it won't hear someone transmitting locally through the repeater since the link radio cannot listen while it transmits. This is a good thing.&lt;/p&gt;&#xA;" OwnerUserId="9006" LastActivityDate="2017-01-07T20:25:12.493" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7028" PostTypeId="2" ParentId="5181" CreationDate="2017-01-07T20:29:04.377" Score="0" Body="&lt;p&gt;Looking at commercial frequencies near the 2-meter band, there is no specified offset. It's all over the place. Since the use of 2-meters, 70-cm and other bands have come online and their offsets have been more orderly and match better between ham and commercial.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham is actually more organized than commercial in this regard. I think we have just learned more about channel spacing since the first 2-meter repeaters were built.&lt;/p&gt;&#xA;" OwnerUserId="9006" LastActivityDate="2017-01-07T20:29:04.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7029" PostTypeId="1" CreationDate="2017-01-07T21:01:07.630" Score="1" ViewCount="574" Body="&lt;p&gt;Looking for some PHP code to convert decimal lat and long to maidenhead locator/grid square.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I saw one answer on here for the match, but I think there was an error in it so I can't trust it. I am happy to work with the math if a ready-made PHP function does not exist.&lt;/p&gt;&#xA;" OwnerUserId="9006" LastEditorUserId="4076" LastEditDate="2017-01-09T01:33:32.260" LastActivityDate="2018-09-05T01:19:27.173" Title="Lat/Long to Maidenhead Locator in PHP" Tags="&lt;maidenhead-locator&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7030" PostTypeId="2" ParentId="7020" CreationDate="2017-01-08T15:51:24.060" Score="2" Body="&lt;p&gt;You say your dipole's total length is 20 meters, and you are using it on the 20 meter band. When the dipole's length is equal to some multiple of the wavelength (1λ, 2λ, 3λ, ...) the dipole is antiresonant, and the feedpoint impedance is at a maximum. Being the worst possible match, it will require maximum range from your tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the total length of the dipole is half a wavelength, or some odd multiple thereof (0.5λ, 1.5λ, 2.5λ, ...) the antenna is resonant. Feedpoint impedance is at a minimum, around 73 ohms. This is a good match and you don't even need a tuner, although you may need to take the antenna up and down a few times to adjust the length initially.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can explain this effect by thinking of one side of the dipole as a &lt;a href=&quot;https://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer&quot; rel=&quot;nofollow noreferrer&quot;&gt;quarter-wave transformer&lt;/a&gt;. The end of the dipole must be a high impedance (where can the current go?) So consequently the feedpoint, a quarter-wavelength away, will see a low impedance. With the dipole a total wavelength long, each side is half a wavelength long. You can think of this as two quarter-wavelength transformers together, in other words, no impedance transformation at all. So the feedpoint sees the high impedance at the end of the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect if you make your dipole any other length, you'll be able to tune it. And if you operate primarily on the 20 meter band, I'd suggest making the antenna a half wavelength at that frequency. You don't gain anything by making it longer, you'll lower SWR on the feedline and associated losses, and your tuner won't need as much range.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-01-09T18:06:14.247" LastActivityDate="2017-01-09T18:06:14.247" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7032" PostTypeId="2" ParentId="1122" CreationDate="2017-01-08T20:12:23.090" Score="1" Body="&lt;p&gt;Just adding to the above answer: If you are going to transmit SSTV on a repeater that is also used for voice, you should try to be a courteous as possible:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Make yourself aware of any popular nets that might use the repeater. Avoid sending SSTV during those times.&lt;/li&gt;&#xA;&lt;li&gt;Listen for a least a minute before transmitting.&lt;/li&gt;&#xA;&lt;li&gt;Turn down the volume on your SSTV generator, so as to prevent it from being obnoxiously loud to everyone who might be listening for voice contacts.&lt;/li&gt;&#xA;&lt;li&gt;Use fast, low-resolution modes that transmit in under 30 seconds, like the old-school 8-second black and white mode or the 12 or 24 second Robot color modes.&lt;/li&gt;&#xA;&lt;li&gt;After sending but before releasing PTT, remember to state your callsign. Might be good to also say your callsign initially.&lt;/li&gt;&#xA;&lt;li&gt;Always let the repeater drop and wait a good 30-60 seconds between transmitting images. This gives other operators a chance to chime in or protest.&lt;/li&gt;&#xA;&lt;li&gt;If anyone protests, stop.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Also, if the repeater is retransmitting on SSB you really should contact the operator first before transmitting SSTV. Remember, SSTV transmitted on SSB is considered full duty-cycle. While the SSB output on a well-engineered repeater will have no problems, others might not.&lt;/p&gt;&#xA;" OwnerUserId="9009" LastEditorUserId="9009" LastEditDate="2017-05-26T19:25:05.947" LastActivityDate="2017-05-26T19:25:05.947" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7033" PostTypeId="1" AcceptedAnswerId="7039" CreationDate="2017-01-09T05:10:05.787" Score="3" ViewCount="388" Body="&lt;p&gt;This is a follow up to another recent question of mine: &lt;a href=&quot;https://ham.stackexchange.com/questions/6983/does-a-balun-need-to-be-made-with-coax&quot;&gt;Does a balun need to be made with coax?&lt;/a&gt; In that question, we establish that a choke balun doesn't actually work by protecting the &quot;third conductor&quot; on the outside of the coax shield, so there's no need for the coax itself to be part of the balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The design in question was the sort pictured below, where a pair of regular wires are wrapped around a toroid core. I've seen this kind of design in many places, including in other balun questions on this site, so the idea must be sound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that there is no sort of precise spacing between the two wires, there must not be any sort of precise characteristic impedance, either. The question is, why doesn't this cause problems? Or does it, and you're expected to be using an antenna tuner to compensate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ee8ya.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ee8ya.jpg&quot; alt=&quot;a howebrew balun&quot;&gt;&lt;/a&gt;&lt;br/&gt;&#xA;(From &lt;a href=&quot;http://www.m0pzt.com/baluns/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.m0pzt.com/baluns/&lt;/a&gt;)&lt;/p&gt;&#xA;" OwnerUserId="8940" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-09T21:39:32.167" Title="Why don't baluns require precise conductor spacing as in twin-lead?" Tags="&lt;balun&gt;&lt;toroid&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7034" PostTypeId="1" AcceptedAnswerId="7036" CreationDate="2017-01-09T08:55:21.187" Score="1" ViewCount="1471" Body="&lt;p&gt;I need some assistance in setting up a RTL-SDR with a SpyVerter upconverter, using SDRSharp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been using the RTL-SDR on its own with success. However, when I connect the SpyVerter (the side with the USB port to the RTL, other side to the antenna) I can't receive anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I understand it, I need to set the &quot;shift&quot; setting under the &quot;Radio&quot; tab in SDRSharp to -120 MHz, which is -120,000,000.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is this the only setting that I need to change in SDRSharp?&lt;/li&gt;&#xA;&lt;li&gt;Does this mean I need to disconnect the upconverter and disable the shift when listening to frequencies in the normal range of the RTL-SDR?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I've tried Googling for this but there are very few resources on this, lots of reviews, but no tutorials or setup guides for noobs like me.&lt;/p&gt;&#xA;" OwnerUserId="9012" LastEditorUserId="8832" LastEditDate="2017-08-17T22:23:19.507" LastActivityDate="2017-08-17T22:23:19.507" Title="RTL-SDR with SpyVerter - setup" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;transverter&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7035" PostTypeId="1" AcceptedAnswerId="7038" CreationDate="2017-01-09T12:27:54.060" Score="0" ViewCount="147" Body="&lt;p&gt;What's the particularities of receiving SW-broadcasting, that uses DRM standard ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every SW-receiver can directly receive this kind of signal?&lt;/p&gt;&#xA;" OwnerUserId="8978" LastEditorUserId="76" LastEditDate="2017-01-09T15:55:20.680" LastActivityDate="2017-01-09T18:18:42.723" Title="DRM standard receiving on shortwave" Tags="&lt;receiver&gt;&lt;swl&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7036" PostTypeId="2" ParentId="7034" CreationDate="2017-01-09T15:52:40.317" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;As I understand it, I need to set the &quot;shift&quot; setting under the&#xA;  &quot;Radio&quot; tab in SDRSharp to -120 MHz, which is -120,000,000.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Is this the only setting that I need to change in SDRSharp?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm not familiar with SDR# in particular, but it makes sense that that would be the only setting you need to change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't change that setting, it doesn't mean you won't see any signals — it means that (if the upconverter is functioning properly) the signals on the air will appear at frequencies 120 MHz higher than otherwise, from perspective of the RTL device and therefore your software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One check if your upconverter is functioning would be to tune to 0 MHz (with shift set) or 120 MHz (without shift set) and see if you see a big spike on the spectrum — that should be the upconverter's local oscillator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Did you plug the upconverter into USB power?)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does this mean I need to disconnect the upconverter and disable the shift when listening to frequencies in the normal range of the RTL-SDR?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. Even if powered off, the upconverter contains filters which are appropriate for upconversion and which will prevent normal reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My own solution to this problem is to buy a second RTL-SDR device.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Further troubleshooting notes:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Remember that the only thing the shift is going to do is change the &lt;em&gt;displayed&lt;/em&gt; frequencies. You can always leave it set at 0 and try tuning around 120 to 180 MHz to find the upconverted spectrum.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Have you set up an antenna suitable for HF? Even a piece of wire strung across the room haphazardly will probably do better than a stock RTL-SDR antenna for this purpose.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Remember that HF is often a noisy environment, and you may have devices producing local noise. It's possible that everything is fine but you're only seeing the noise. Unplug the antenna — if the signal level drops all across the spectrum, then you know you &lt;em&gt;are&lt;/em&gt; receiving successfully, you just are seeing the noise that's there. If nothing changes when you unplug the antenna, then you have an inadequate antenna, a nonfunctional upconverter, or you haven't managed to tune/shift to the right part of the spectrum.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-01-09T15:52:40.317" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7037" PostTypeId="2" ParentId="7033" CreationDate="2017-01-09T15:55:04.890" Score="1" Body="&lt;p&gt;&lt;strong&gt;The wire spacing can matter in a common-mode choke balun.&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A  bifilar  choke  wound  around  a  toroid  forms  a  short  transmission  line  whose  impedance  may  be  different  from  that  of  the  line  into  which  it  is  inserted. Thus,  a bifilar  choke  can  introduces  some  mismatch.  (A  tightly  spaced  enameled #14  bifilar  winding  is  very  close  to  50  ohms.  Tightly  spaced  #14  THHN  windings  are  close  to  100  ohms.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The paragraph above is an excerpt from K9YC's excellent technical publication on &lt;a href=&quot;http://audiosystemsgroup.com/publish.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page&lt;/a&gt;. See p. 35 of &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this PDF&lt;/a&gt; linked to from there. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-01-09T15:55:04.890" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7038" PostTypeId="2" ParentId="7035" CreationDate="2017-01-09T18:18:42.723" Score="2" Body="&lt;p&gt;No, not every shortwave radio can receive DRM. A basic shortwave receiver will only support AM, conventional analog shortwave broadcasting. DRM (as well as SSB, another additional mode) are additional features that you should ensure are mentioned on the receiver's feature list before buying.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-01-09T18:18:42.723" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7039" PostTypeId="2" ParentId="7033" CreationDate="2017-01-09T18:33:40.613" Score="2" Body="&lt;p&gt;It more or less doesn't matter because it's so small, relative to wavelength. As such, a &lt;a href=&quot;https://en.wikipedia.org/wiki/Lumped_element_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;lumped element model&lt;/a&gt; is valid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can make a conjecture to that effect by looking inside your antenna tuner (or really, a lot of HF equipment). Unless it's a fancy kind, there will be wires running whatever way between the components, with no attention paid to the characteristic impedance of those connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think about it this way: imagine a change in voltage propagating down the line. When it encounters the balun, it will encounter some mismatched impedance, and some amount of the energy is reflected back. A very short time later (due to the very small size, relative to the balun) the same change, but reversed, which will send another reflection except opposite in phase back down the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If these two reflected waves occurred at exactly the same time, they would entirely cancel. In practice they aren't &lt;em&gt;exactly&lt;/em&gt; at the same time, but since the change in phase between the two is so small (remember, tiny relative to wavelength), they &lt;em&gt;almost completely&lt;/em&gt; cancel, and the effect is negligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The spacing of the wires does matter in a different way: there's some capacitance between them. We can incorporate that into the lumped model like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/gIfYu.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fgIfYu.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The inductor and the capacitor each have some &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance&lt;/a&gt;, with the inductor's impedance increasing with frequency, and the capacitor's inductance decreasing with frequency. The two form a &lt;a href=&quot;https://en.wikipedia.org/wiki/LC_circuit#Parallel_LC_circuit&quot; rel=&quot;nofollow noreferrer&quot;&gt;parallel LC circuit&lt;/a&gt;, and at the frequency where the impedances are equal, the impedance of the balun as a whole is at a maximum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's easy to add more turns to a balun, so achieving a sufficiently high inductance isn't too hard. But each turn also increases the area where the wires are close together, introducing additional capacitance. At some point there's so much capacitance that the associated impedance is so low it effectively makes the balun a short, making it ineffective as a balun.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-01-09T21:39:32.167" LastActivityDate="2017-01-09T21:39:32.167" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7040" PostTypeId="1" AcceptedAnswerId="7041" CreationDate="2017-01-09T18:56:33.973" Score="2" ViewCount="566" Body="&lt;p&gt;Does the FCC restrict how much bandwidth an amateur radio operator can transmit? I've seen restrictions for transmitting data, like packet and ATV, but, for example, could I legally use a huge bandwidth like 500 kHz to transmit FM in the 2 meter band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, studying for the extra class exam, I saw this:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The maximum bandwidth for data emission on 60 meters is 2.8kHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8805" LastEditorUserId="4665" LastEditDate="2017-01-10T04:36:07.067" LastActivityDate="2017-01-10T04:36:07.067" Title="What are the FCC's bandwidth restrictions for the various amateur bands?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7041" PostTypeId="2" ParentId="7040" CreationDate="2017-01-09T19:27:07.380" Score="2" Body="&lt;p&gt;Mostly, on HF, the FCC has chosen to limit modes of transmission and symbol rates rather than bandwidth (60 Meters is the exception, where they have limited both bandwidth and mode). For instance, you are currently allowed to use FM only on 29MHz and above, regardless of the bandwidth used. But on VHF and above, there are no legal limitations of bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So technically, yes, if you had a wide deviation FM transmitter you could use it on 2 meters. Although as I'm sure you know this would be very irresponsible [but not illegal according to current FCC rules.] &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On 10GHz and similar high bands with tons of space, it is commonplace to use wideband FM (normally a bandwidth of 200-300kHz). This allows equipment to be used with less than optimal frequency stability (which is very difficult to obtain at those high frequencies). &lt;/p&gt;&#xA;" OwnerUserId="5997" LastActivityDate="2017-01-09T19:27:07.380" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7042" PostTypeId="1" AcceptedAnswerId="7043" CreationDate="2017-01-09T19:41:16.920" Score="0" ViewCount="53" Body="&lt;p&gt;What are the standard bandwidths used on the various amateur bands?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, FM on 2 meter generally uses about 3kHz, right?&lt;/p&gt;&#xA;" OwnerUserId="8805" LastActivityDate="2017-01-09T20:34:51.673" Title="What are the standard bandwidths used on the various amateur bands?" Tags="&lt;bandwidth&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7043" PostTypeId="2" ParentId="7042" CreationDate="2017-01-09T20:14:19.490" Score="2" Body="&lt;p&gt;The standard bandwidths are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;SSB: about 2.5kHz  &lt;/li&gt;&#xA;&lt;li&gt;AM: about 10kHz  &lt;/li&gt;&#xA;&lt;li&gt;FM: about 15kHz  &lt;/li&gt;&#xA;&lt;li&gt;CW: about 50Hz &lt;/li&gt;&#xA;&lt;li&gt;Data: varies greatly, from a few Hz on up...&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The deviation of narrowband 2 meter FM is about 5kHz, but the total bandwidth is around 15kHz.&lt;/p&gt;&#xA;" OwnerUserId="5997" LastEditorUserId="5997" LastEditDate="2017-01-09T20:34:51.673" LastActivityDate="2017-01-09T20:34:51.673" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7044" PostTypeId="2" ParentId="808" CreationDate="2017-01-09T20:16:52.370" Score="2" Body="&lt;p&gt;Software defined radios (SDRs) that can transmit can certainly do this. In the &lt;a href=&quot;http://gnuradio.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;GNUradio&lt;/a&gt; software, for example, there are blocks for receiving and transmitting ATSC; cf. &lt;a href=&quot;https://coolsdrstuff.blogspot.com/2015/09/watching-atsc-hdtv-on-sdrplay-rsp.html?m=1&quot; rel=&quot;nofollow noreferrer&quot;&gt;this blog post for how to receive and decode ATSC with a SDR&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8805" LastActivityDate="2017-01-09T20:16:52.370" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7045" PostTypeId="1" AcceptedAnswerId="7046" CreationDate="2017-01-09T20:25:06.453" Score="11" ViewCount="379" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/7041/8805&quot;&gt;This answer&lt;/a&gt; claims that&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Mostly, on HF, the FCC has chosen to limit modes of transmission and &lt;strong&gt;symbol rates&lt;/strong&gt; rather than bandwidth&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Why does the FCC limit symbol rates?&lt;/p&gt;&#xA;" OwnerUserId="8805" LastEditorUserId="218" LastEditDate="2017-01-09T21:01:43.637" LastActivityDate="2020-01-13T18:50:08.363" Title="Why does the FCC put restrictions on symbol rates?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;packet&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7046" PostTypeId="2" ParentId="7045" CreationDate="2017-01-09T20:32:40.980" Score="11" Body="&lt;p&gt;That's a good question---and one that is heavily under debate currently. The FCC originally limited symbol rates as a way of limiting bandwidth for data modes indirectly (it made sense at the time). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But now that there are more advanced modulations (like the various forms of phase shift keying) that can exceed the symbol rate limitations in less bandwidth than an older modulation type like say, an FSK packet transmission, many people have been trying to get the FCC to change to a bandwidth limitation for data signals, rather than symbol rate, so that higher data throughputs can be obtained. It's a very controversial subject right now... &lt;/p&gt;&#xA;" OwnerUserId="5997" LastEditorUserId="5997" LastEditDate="2019-08-15T23:35:32.150" LastActivityDate="2019-08-15T23:35:32.150" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="7047" PostTypeId="1" AcceptedAnswerId="7382" CreationDate="2017-01-09T21:32:43.347" Score="13" ViewCount="1329" Body="&lt;p&gt;How do I receive &lt;a href=&quot;https://en.wikipedia.org/wiki/Amateur_television&quot; rel=&quot;noreferrer&quot;&gt;Amateur television (ATV)&lt;/a&gt; — e.g., NTSC in the U.S. — with &lt;a href=&quot;http://gnuradio.org/&quot; rel=&quot;noreferrer&quot;&gt;GNU Radio&lt;/a&gt; so I can play the A/V in, e.g., the &lt;a href=&quot;https://videolan.org/&quot; rel=&quot;noreferrer&quot;&gt;VLC video player&lt;/a&gt;? Are there any example GNU Radio block diagrams to accomplish such a task?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;cf. this for an example on &lt;a href=&quot;https://coolsdrstuff.blogspot.com/2015/09/watching-atsc-hdtv-on-sdrplay-rsp.html?m=1&quot; rel=&quot;noreferrer&quot;&gt;how to decode ATSC with GNU Radio and play the video in VLC&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="8805" LastEditorUserId="8832" LastEditDate="2017-05-24T21:20:09.777" LastActivityDate="2018-12-08T22:01:05.217" Title="How do I receive ATV with GNU Radio?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;atv&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7048" PostTypeId="1" AcceptedAnswerId="7061" CreationDate="2017-01-10T19:09:02.860" Score="7" ViewCount="9618" Body="&lt;p&gt;A post on &lt;em&gt;&lt;a href=&quot;http://adsbexchange.com/forums/topic/beginners-2-cantenna-easy-diy-antenna-to-improve-rangeplane-count&quot; rel=&quot;noreferrer&quot;&gt;http://adsbexchange.com/forums/topic/beginners-2-cantenna-easy-diy-antenna-to-improve-rangeplane-count&lt;/a&gt;&lt;/em&gt; uses a $\frac{\lambda}{4}$ sleeve made of a pop can beneath a $\frac{\lambda}{4}$ wire protrusion made from the core of a coaxial cable (coax with shielding removed). The protrusion connects to an SMA F connector that's lodged in a hole through the base of the popcan which in turn connects to regular coax that emerges from the bottom of the pop can. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/bFCGy.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bFCGy.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;My question is&lt;/strong&gt; -- Why does the length of the sleeve (the pop can) matter considering that the coaxial cable enclosed by it is completely shielded? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt; : Considering the comments below RE: inclined ground plane. It seems to me that the desire of the author is to impedance match to 75ohm coaxial cable.  See the image below: &#xA;&lt;a href=&quot;https://i.stack.imgur.com/nYXp0.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nYXp0.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="9020" LastEditorUserId="4076" LastEditDate="2017-01-11T23:05:49.233" LastActivityDate="2017-01-24T23:56:59.737" Title="How does the length of a metal sleeve around a (shieled) coax cable affect antenna performance?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="8" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7049" PostTypeId="1" CreationDate="2017-01-10T19:46:51.093" Score="5" ViewCount="10232" Body="&lt;p&gt;I'm trying to build a 1/2 wave &quot;Coaxial J-Pole&quot; antenna, similar to what is described &lt;a href=&quot;http://members.upc.nl/a.vrijswijk/documents/42.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/D2EMX.jpg&quot; alt=&quot;Coaxial J-Pole&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such an antenna would be great for stringing up in a tree when operating remotely, no tuner needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The trick is that I'm trying to use 75Ω RG6 coax for the matching section (because it is relatively inexpensive and low-loss), but I want a 50Ω impedance at the feed point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many single-stub matching network calculators, but almost all of them assume that the impedance of the matching network is the same as the feed point impedance. I know that such a matching network is possible because that is exactly what the traditional j-pole antenna is: a single-stub impedance transformer feeding a half-wave antenna, where the matching section impedance doesn't match the feed point impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Succinctly: How can I calculate the physical parameters of a single-stub impedance transformer when the matching section impedance doesn't match either the feed point impedance or the load impedance?&lt;/p&gt;&#xA;" OwnerUserId="9009" LastEditorUserId="8713" LastEditDate="2019-01-07T18:46:02.440" LastActivityDate="2019-12-28T14:51:16.920" Title="How to calculate single-stub match (general case)?" Tags="&lt;antenna-theory&gt;&lt;impedance&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="7050" PostTypeId="2" ParentId="7048" CreationDate="2017-01-10T20:27:47.120" Score="1" Body="&lt;p&gt;This is a quarter wave monopole antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The current on the inner conductor is fed to the vertical wire, while the current on the (inside surface of the) coax shield is fed to the soda can.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The soda can, hopefully, acts as a ground plane. Normally ground planes are made with several wires, each 1/4 wavelength in size, and bent downwards near 45 degrees (this angle adjusts the antenna impedance to 50 Ohm, so it is matched to the coax and transceiver port).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is lots of introductory material on these antennas. &lt;a href=&quot;http://www.jocet.org/papers/151-L020.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt; is one showing current distributions. &lt;a href=&quot;http://www.radio-electronics.com/info/antennas/vertical-antennas/quarter-wavelength.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Another&lt;/a&gt; one.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2017-01-10T20:27:47.120" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7051" PostTypeId="1" CreationDate="2017-01-11T07:16:40.510" Score="0" ViewCount="258" Body="&lt;p&gt;Me and my family are expats currently living in Japan where earthquakes are very frequent. It is expected that a big quake is due and it may happen anytime.&#xA;Recent big occurence was in 2011 and it was followed by a tsunami. But the main impact happened to the communication during such crisis as everybody uses the network and it gets totally jammed or due to the quake the supporting equipment and network was damaged.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whatever the reason for blackout, i would like to know if there is a 'handy' communication device available in open market that can be used when the next quake strikes, for communicating with my family without any disruption due to the quake. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since Amateur/HAM people are usually deployed for linking areas which out of reach during times like mentioned above, please suggest any two way communication device pair (sort of walkie-talkie types i imagine) which can be kept with myself at all times and the other with my family.&#xA;They should be able to communicate in a metropolitan like Tokyo and should have coverage of atleast 30-50 kms radius.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks in advance!&lt;/p&gt;&#xA;" OwnerUserId="9023" LastEditorUserId="8832" LastEditDate="2017-01-19T19:25:40.760" LastActivityDate="2017-01-19T19:25:40.760" Title="Personal communication device during blackout" Tags="&lt;ht&gt;&lt;emergency&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7052" PostTypeId="2" ParentId="7051" CreationDate="2017-01-11T09:15:39.010" Score="4" Body="&lt;p&gt;Given your criteria of Handheld transmitters with a 30-50km range, it would be difficult to do so reliably in a city environment. Here's why:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Lots of buildings are going to obstruct your signal and cause multipath interference to the parts of your signal that do get out, reducing your range&lt;/li&gt;&#xA;&lt;li&gt;Rated &quot;range&quot; on things like handheld walkie talkies that you can buy at the store are best-case scenarios (think two people standing on top of mountains or in an open field) which is not the environment you'd be in&lt;/li&gt;&#xA;&lt;li&gt;You would need much more power output than a handheld would provide to be able to reliably communicate that far while being in a city environment between tall buildings&lt;/li&gt;&#xA;&lt;li&gt;Most HF (3-30MHz) amateur radios with sufficient power, which is what the people deployed for emergency communication use, are not handheld, though you might be able to communicate that distance with a smaller radio that has an internal battery like the Elecraft KX3 with 10 watts, but this gets to my next point that:&lt;/li&gt;&#xA;&lt;li&gt;HF band communications use long wavelengths due to their low frequency, and this means to have an efficient antenna to make use of what little power you have, your antenna would have to be pretty long. Think stringing a wire for 5-50+ meters depending on the frequency you use, and hence unwieldy for emergency communications if you need to be on the move.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You may be more reliably able to communicate with less power and a shorter (but still a meter or two long) antenna on HF using CW (continuous wave - morse code) but learning that is another whole topic in itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sorry to be the bringer of bad news, but I think your best bet would be a 2m VHF/70cm UHF dual mode handheld. Though this would probably only work well if you could both get to high elevation places to avoid your signal being trapped between buildings, so try to get on top of a building above average roof height. Using 70cm/UHF would also mean the antenna would only be ~18 cm long which is less awkward to carry around than a ~50cm long 2m/VHF antenna.&lt;/p&gt;&#xA;" OwnerUserId="9024" LastActivityDate="2017-01-11T09:15:39.010" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7053" PostTypeId="2" ParentId="7049" CreationDate="2017-01-11T21:01:47.130" Score="2" Body="&lt;p&gt;You can do this graphically, with a &lt;a href=&quot;http://www.fourier-series.com/rf-concepts/smithchart.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Smith chart&lt;/a&gt;. Normally when using a Smith chart we divide all the impedances by 50 to normalize them to a 50Ω system, but you can divide by 75 (or any other number) and the results are just as valid. The Smith chart has the advantage of not requiring any complicated math, and also facilitating intuition into what matching strategies are possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also do the same with any transmission line calculator. Divide all the impedances by 75 to normalize them to 1, then multiply them by 50 to convert to what the calculator expects. Then perform the same operation in reverse with the answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you'd need to know the impedance of the thing you are trying to match. More on that at the end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an interesting example, &lt;a href=&quot;http://www.vk6uu.id.au/6-metre-repeater.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;VK6UU gives an example of a 300Ω folded dipole matched to 50Ω&lt;/a&gt; by way of a quarter-wave section of 125Ω coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tIK5p.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tIK5p.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This works because relative to 125Ω, 300Ω and 50Ω are (approximately) duals, that is they have the same magnitude &lt;a href=&quot;https://en.wikipedia.org/wiki/Reflection_coefficient&quot; rel=&quot;nofollow noreferrer&quot;&gt;reflection coefficient&lt;/a&gt;, but 180 degrees apart. You'll notice:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 125 / 300 \approx 50 / 125 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A little more generally, a quarter-wave section of transmission line of impedance $Z_0$ converts between two impedances $Z_a$ and $Z_b$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_0 / Z_a = Z_b / Z_0 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which can be algebraically solved for $Z_0$ as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z_0 = \sqrt{Z_a Z_b} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for the special case of a quarter-wave section where you can pick the transmission line impedance, this is how you can match two impedances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For arbitrary lengths of transmission line it is more complex, but if you remember that the length of the line changes the angle but not the magnitude of the reflection coefficient, then with a little trigonometry, it's &quot;simple&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All that said, the design of this antenna, &lt;a href=&quot;https://www.w8ji.com/end-fed_vertical_j-pole_and_horizontal_zepp.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;if it works as intended&lt;/a&gt;, seems to be using a &lt;a href=&quot;https://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer&quot; rel=&quot;nofollow noreferrer&quot;&gt;quarter-wave&lt;/a&gt; transformer to transform the high impedance at the end of a half-wavelength radiator into a low impedance at the feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we are talking extremes and ideal components: an open circuit (infinite impedance) and a short (0 impedance), then a quarter wavelength section of transmission line of any characteristic impedance transforms between the two.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance at the end of a half-wave radiator isn't infinite, but it is &quot;pretty high&quot;, depending on things like the diameter of the wire, and in practice, trees, towers, the ground, maybe the feedline, and other surroundings. 75Ω isn't so much different from 50Ω, so if you use 75Ω coax instead of 50Ω we can still expect that pretty high impedance to be transformed to a pretty low one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd suspect the difference is negligible compared to other details, so I would say just build the thing with 75Ω ohm coax, and you won't be so far off that you can't just incrementally adjust the length until you get a good match.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-01-11T21:12:44.117" LastActivityDate="2017-01-11T21:12:44.117" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7054" PostTypeId="2" ParentId="7048" CreationDate="2017-01-11T23:27:02.270" Score="3" Body="&lt;p&gt;Bah. Humbug. For reference, the picture on which they base this design:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7iMA3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7iMA3.png&quot; alt=&quot;Coaxial antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is clearly simply a $\frac\lambda2$ dipole, meant for coaxes fed with a &lt;em&gt;symmetric&lt;/em&gt;/ &lt;em&gt;balanced&lt;/em&gt; signal, or producing one. The more alike the width of the tube and the upper copper antenna part are, the more &quot;ideal&quot; the dipole becomes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the way they use it here, the copper pipe is part of the ground part of an &lt;em&gt;unbalanced&lt;/em&gt; receiver. So, this simply is not going to be great. What you want, as discussed in the comments, is a ground plane for a $\frac\lambda4$ monopole. And 45° radials is a well-proven, well-tested, pretty-close-to-perfect, foolproof way of implementing a seemingly endless ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the length of the can in your picture to have effect, there would be the need for a current to flow in the lower parts of that. But that current can only flow if the can is not doing its job of simulating a perfect &quot;E-field mirror&quot; overly well (otherwise the energy &quot;reflected&quot; back into the upper half-space would be 100% of what incides at any point of the plane, and since the monopole is the only driven element here, it would surprise me if the currents induced at the part where the bends start actually help very much with making this a better antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, yes, they'll be getting better reception with that at 1090 MHz than with the stock TV antenna, but that's not hard. Simply replacing the $\ne\frac\lambda4$ monopole of that (e.g. by cutting it to the right length...) and placing the antenna on a conductive (magnetic, if possible, that's why it has a magnet in its pedestal) will probably do even better. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I rant about this far too often, but this is the year 2016. Antenna theory has been around for &gt;100 years. And yes, physicists and EEs in their labs played and play around with all the conductive stuff they can get easily to build their antennas. So if someone shows up with an antenna design that seems new, expect them to use &lt;em&gt;some&lt;/em&gt; sort of simulation, or an anechoic chamber with a reference antenna to measure against, before believing any advantage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Really, EM simulation is not &lt;em&gt;that&lt;/em&gt; hard these days, and with OpenEMS, it's available for free (I'm sure there's more ham-friendly software than that, though!), and I've met more than one person who claims to have designed the perfect antenna based on the Standing Wave Voltage Ratio at the desired frequency alone. Do you know what has perfect SWVR over a huge range of frequencies? A proper matched-impedance terminator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I have a friend who went to a rather well-known faculty at an US uni for a research internship, worked on and measured their newest antenna design idea, just to figure out the antenna was so inefficient, it was converting far more energy to heat than it was emitting radio waves. The prof wasn't disappointed at all – in the end, there's also needs for good absorbers and terminators, especially in isolation applications, so this was well worth keeping in the knowledge for future investigation or publication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The point is you can't know if your antenna is good or bad without measuring its emission or at least simulating it. So, if not backed by solid data including a directivity and frequency chart, I simply apply &quot;skepticism&quot; as default reaction to antenna designs. And so should you.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-01-11T23:27:02.270" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7055" PostTypeId="2" ParentId="7048" CreationDate="2017-01-12T02:38:10.720" Score="0" Body="&lt;p&gt;&lt;strong&gt;LINKS TO THESE POSTS REMOVED DUE TO ADVISE BY SOME MEMBERS&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(1) June 07, 2014 - &lt;strong&gt;Sleeve Balun Costruction Details&lt;/strong&gt; - Use of Soda can as sleeve Balun for a Coaxial Collinear Antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(2) June 08, 2014 - &lt;strong&gt;A 1/2 λ sleeve dipole&lt;/strong&gt; - Use of of same Soda Can as Sleeve Baloon for 1/4 wavelength monopole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(3) The 1/2 λ Sleeve Dipole &lt;strong&gt;Renamed to &quot;Cantenna&quot;&lt;/strong&gt;, Aug 2014.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you see my above posts in another forum, you will know that the 1/4λ x 1/4λ Soda Can was used as Sleeve Balun (Bazooka Balun).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have originally given links to these posts, so that you can see the purpose &amp;amp; function of Soda Can, and also the performance test. Since some members objected to posting the link, I have removed these links.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The analysis of &lt;strong&gt;Phil Frost - W8II&lt;/strong&gt; looks good. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apart from theory, lot of users have found this antenna to perform very good, better than stock mag mount whip, cut to 1/4 wavelength, and placed over a food can made of iron. &lt;/p&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="9029" LastEditDate="2017-01-12T20:14:16.560" LastActivityDate="2017-01-12T20:14:16.560" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7057" PostTypeId="2" ParentId="7048" CreationDate="2017-01-12T04:05:07.480" Score="1" Body="&lt;p&gt;Simulation 2 of 2: CANTENNA&#xA;Gain = 1.9 dBi&#xA;SWR (75 ohms) = 1.5&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/0kGid.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/oLmNJ.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastActivityDate="2017-01-12T04:05:07.480" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7058" PostTypeId="2" ParentId="7048" CreationDate="2017-01-12T07:41:01.950" Score="2" Body="&lt;p&gt;&lt;strong&gt;CANTENNA IS HYBRID OF 1/4 λ GROUND PLANE AND 1/2 λ COAXIAL DIPOLE.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;In Coaxial Dipole, the sleeve (copper pipe) serves following functions:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(1) Lower limb of Dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(2) Decoupling Sleeve/Sleeve Balun, but due to very narrow gap between coax  shield and pipe, mostly filled with high loss outer plastic of coax, resulting in high loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;In Cantenna the Soda Can performs following functions:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(1) Upper surface of circular bottom acts as ground plane disc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(2) Cylinderical wall + lower surface of circular bottom acts as Decoupling Sleeve/Sleeve Balun, with a very large gap between coax shield and can wall, mostly filled by air, the losses are negligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nV2FX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nV2FX.png&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/D2TSY.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/D2TSY.jpg&quot; alt=&quot;Cantenna: Whip = 1/4λ, Dia of Can = 1/4λ, Height of Can = 1/4λ &quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="9029" LastEditDate="2017-01-13T01:12:18.400" LastActivityDate="2017-01-13T01:12:18.400" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7059" PostTypeId="2" ParentId="7048" CreationDate="2017-01-12T08:59:44.367" Score="1" Body="&lt;p&gt;&lt;strong&gt;Frequency Sweep (From 100 MHz to 2500 MHz) of 1/4 Wavelength Cantenna.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MEIjm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MEIjm.png&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/HgRyj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HgRyj.png&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastActivityDate="2017-01-12T08:59:44.367" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7060" PostTypeId="2" ParentId="464" CreationDate="2017-01-12T09:11:13.717" Score="1" Body="&lt;p&gt;SSTV from the ISS (249 miles in orbit) because its fun!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF digi modes over FM may not be as efficient as hf but they are fun to play with. New hams getting their first radio can play with the modes. That should be encouraged Give them a taste of those modes and soon you may have new General class hams on your hands. You won't get weak signal performance true, but many new hams only have an FM dual band ht anyway. Get them interested. RTTY is an excellent keyboard chat for simplex. SSTV both digital and analog is fun to use. I have run a net for over a year teaching new hams and old alike to fall in love with the various modes. You probably won't work that 100 mile range, Don't get the weak signal expectation going. 5 watts of FM simplex isn't going to work that far. But you can have fun with what it will do. Why? Because you can and it is fun. APRS isn't for everyone. But a RTTY chat is easy and works well with strong signals. &#xA;(&lt;a href=&quot;https://i.stack.imgur.com/w3sfW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://i.stack.imgur.com/w3sfW.jpg&lt;/a&gt;)&lt;/p&gt;&#xA;" OwnerUserId="9030" LastActivityDate="2017-01-12T09:11:13.717" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7061" PostTypeId="2" ParentId="7048" CreationDate="2017-01-12T15:30:55.827" Score="5" Body="&lt;p&gt;Lemma: this antenna is a dipole with one leg of it acting as a balun. Specifically, a &lt;a href=&quot;http://www.antenna-theory.com/definitions/bazooka.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;bazooka balun&lt;/a&gt; (AKA sleeve balun).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whenever you want to feed a dipole with coax, you have to &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;do something about common-mode currents&lt;/a&gt;. The trick is, one way or another, to make the common-mode currents on the coax a high impedance. Hopefully there's a much lower impedance path somewhere (like, the dipole you're trying to feed) and so there won't be much common-mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does it work?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, consider that differential-mode currents on the feedline are irrelevant to anything outside the feedline's shield since their associated fields cancel. For now, let's simplify the situation by ignoring the antenna and assuming an infinitely long feedline. And let's also ignore the inside of the feedline and consider it just a fat wire. Here's a simplified view, in cross-section:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/onTdH.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fonTdH.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, the feedline shield and the can together form another coaxial transmission line, with the feedline shield as the center, and the can as the shield. We will call this the can-coax. This transmission line is shorted at one end, and open at the other. It's a quarter wavelength long, which hints this may be a &lt;a href=&quot;https://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer&quot; rel=&quot;nofollow noreferrer&quot;&gt;quarter-wave transformer&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, consider that at the open end of the can, any common-mode current on the feedline must become a differential-mode current on the can-coax. Because, only a differential-mode current can possibly flow on the center of a coaxial transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So effectively, the common mode is in series with a shorted, quarter-wave stub:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/vX4iY.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fvX4iY.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the properties of a quarter-wave stub, the short at one end is transformed into a high impedance at the other end. Thus, the common mode is in series with a high impedance. QED.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/xlJgA.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fxlJgA.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meanwhile the outside of the can is free to function as a fat, tubular leg of a dipole. Put it all together and you get:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/UEPQn.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fUEPQn.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By virtue of being resonant at your frequency of interest, this antenna (like all dipoles) also functions somewhat like a filter, which can improve performance if your receiver has poor selectivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like Marcus Müller says, this isn't a well-engineered design, and at best it's no better than a properly installed dipole or monopole. But if all you have is some coax and a pop can, it's at least easy and inexpensive to fabricate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-12T20:40:56.783" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7062" PostTypeId="2" ParentId="7051" CreationDate="2017-01-12T17:07:55.527" Score="2" Body="&lt;p&gt;I also don't feel that a V/U ht would be practical for more than a few miles on the built in antenna. Maybe much better with a 5/8 wave mobile antenna. In a densely packed area with big buildings you are not as likely to achieve the distances you desire. There is a possibility with low band hf. But with mobile units antenna effiencies may not be helpful. HF NVIS with a buddiepole antenna may achieve your goals. You would have to try it. Every location is different. Your best bet is hf. 3.5 to 7 mhz NVIS. NVIS means that you are using low (10 ft elevation) horizontal 1/2 wave dipoles. Probably SSB. But even then you would have to try it. CW sets can be very small, low power consumption, and can work better for NVIS at hf. Good luck.&lt;/p&gt;&#xA;" OwnerUserId="9032" LastActivityDate="2017-01-12T17:07:55.527" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7063" PostTypeId="2" ParentId="1122" CreationDate="2017-01-12T17:21:37.260" Score="0" Body="&lt;p&gt;This is an issue we deal with all the time here. Currently we are seeking to expand county coverage for our SSTV and Data net with a repeater. Always ask the repeater trustee first. Always. Here we got a no from all the local repeaters. Here is why the local club repeater trustee said no. Most repeaters cannot handle the constant 100% duty cycle. That means repeater finals getting hot. Our net established guidelines for using a repeater. Only transmit pictures that are less than 1 minute in duration Scottie 2 is our preferred mode for simplex. If you are going to be operating a lot at one time use Robot modes. Robot 36 gives great color images. Stay Simplex as much as possible. Set your radio to low power or 1/2 maximum power to keep it from getting hot too. Most of the time you will not need a repeater if you have good antennas at least 20 ft elevation.&lt;/p&gt;&#xA;" OwnerUserId="9032" LastActivityDate="2017-01-12T17:21:37.260" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7064" PostTypeId="2" ParentId="7051" CreationDate="2017-01-12T17:53:41.717" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Whatever the reason for blackout, i would like to know if there is a 'handy' communication device available in open market that can be used when the next quake strikes, for communicating with my family without any disruption due to the quake. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Sure, satellite phones and pagers!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the kind of things they were invented for, enabling communication without infrastructure, as long as you get a sufficient view of the skies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will certainly not work great in the cellars of buildings, though. But that can be said for pretty much everything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For costs, the best thing I could find was &lt;a href=&quot;https://en.wikipedia.org/wiki/Iridium_Communications#Post-paid_service&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Iridium_Communications#Post-paid_service&lt;/a&gt; ; You might want to check with the Iridium folks yourself.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;One could of course think of setting up an infrastructure of repeaters that get automatically activated in case of an emergency (for example, if they're not kept &quot;off&quot; by a regular &quot;alive&quot; signal) and work off batteries. However if you do that, you'd be effectively doing little else than operating a cellular network – and I really think that DoCoMo might be better than you at doing that reliably. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might argue that in case of an emergency, you (and your family and maybe a few local hams) might be the only one trying to access these ressources, but to be honest, catastrophe services do exactly that first when they enter a region: pull up a relay infrastructure so that scouts and rescuers are able to communicate with mission control; and they do have capable equipment (at least in Germany). So, better talk to the Japanese emergency services – they might actually be happy to help you with making you part of the responders. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-01-12T17:53:41.717" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7065" PostTypeId="1" CreationDate="2017-01-12T18:14:13.177" Score="2" ViewCount="140" Body="&lt;p&gt;I have a dual-dipole antenna with a subreflector slightly above it and a ground plane below it, and attached to the ground plane is a balun. While simulating in CST microwave studios, I didn't include a balun. I'm wondering how excluding the balun might affect the s-parameters, beam patterns, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any help would be appreciated! &lt;/p&gt;&#xA;" OwnerUserId="9019" LastActivityDate="2017-06-25T03:04:50.970" Title="What effect does a balun have on s-parameter, beam patterns?" Tags="&lt;coaxial-cable&gt;&lt;balun&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7069" PostTypeId="1" CreationDate="2017-01-14T15:14:22.500" Score="1" ViewCount="300" Body="&lt;p&gt;I have set ny Yaesu FT857-D to PMS scan of the 144-148MHz FM ham band, but it doesn't seem to find anything. &#xA;However, I see the green &quot;busy&quot; light come on every once in a while during the scanning, but the scan doesn't stop.&#xA;The other strange thing is that turning the squelch down to zero has no effect on the scan, either. (Although I can open the squelch when tuned into a particular frequency)&#xA;Anyone have any ideas what could be wrong? &lt;/p&gt;&#xA;" OwnerUserId="9042" LastActivityDate="2017-01-14T16:15:37.103" Title="Yaesu FT-857D VFO scan won't stop" Tags="&lt;yaesu&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7070" PostTypeId="2" ParentId="7069" CreationDate="2017-01-14T16:15:37.103" Score="2" Body="&lt;p&gt;Based on your description, I suspect the problem is that you have tone squelch (&lt;code&gt;TSQ&lt;/code&gt;) enabled. In this mode, the audio is muted unless the signal contains the proper tone, but the receive light will still light up to indicate a non-matching signal is present. (This is true outside of scanning too.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Go to Multi Function Row &lt;code&gt;MFe&lt;/code&gt; and press the &lt;kbd&gt;A&lt;/kbd&gt; &lt;code&gt;TON&lt;/code&gt; button to cycle through encode/squelch modes to the blank position. (If the button is labeled &lt;code&gt;ENC&lt;/code&gt; instead of &lt;code&gt;TON&lt;/code&gt;, then in menu mode set &lt;code&gt;079 SPLIT TONE&lt;/code&gt; to &lt;code&gt;OFF&lt;/code&gt; first.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-01-14T16:15:37.103" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7072" PostTypeId="2" ParentId="6818" CreationDate="2017-01-15T01:37:47.777" Score="0" Body="&lt;p&gt;Well, as @Wossname indicates this is a 'game' and it can be 'played' in any frequency domain and with any modulation method you have legal permission to use.  The proper name is &lt;A href=&quot;https://en.wikipedia.org/wiki/Radio_direction_finding&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio Direction Finding(RDF)&lt;/a&gt;. It could be done with IR pulses and an IR receiver since light is just a different frequency in the RF band.  The Warm/Cold feature you are looking for is a function of the Inverse Square fall off of an omni-directional signal in open space. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of these are done with a simple transmitter unit which is creating a transmission either continuously (for the very low power units), or more likely for a foxhunt, intermittently as a set time for a set time -- every 5 minutes for a minute for instance. The amount of power is a function of the frequency/wavelength and the area you need to cover. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;During the signal on time you need to spin your receiving antenna around looking for a variation in signal strength at the receiver. Then you go someplace else and make the same measurement. Amateur receivers have a signal bar or S-Meter that indicates a decibel reading of the received signal. If you have a sensitive receiver, as you approach the signal source, you may need to attenuate the received signal so that it doesn't read full scale. Even without a directional antenna, you can use this method alone to track a signal to its source. Your body mass of water and meat is a good attenuator for many frequencies and could be used to shield your antenna (lowest signal strength and the signal would be behind you)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This &lt;a href=&quot;https://ham.stackexchange.com/questions/5261/antenna-circuit-to-hear-or-show-radio-direction?noredirect=1&amp;amp;lq=1&quot;&gt;excellent answer by Kevin Reid&lt;/a&gt; provides more technical details on the receiver side of the solution.&lt;/p&gt;&#xA;" OwnerUserId="6092" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-15T01:52:32.233" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7073" PostTypeId="2" ParentId="2149" CreationDate="2017-01-15T02:11:56.957" Score="2" Body="&lt;p&gt;Prior to having your event, contact the police who cover the area where you plan to place the unit. Explain that its a Training Aid for rouge signal detection. Offer to bring the unit in to have them examine. Explain the placement and the time that it would be located there. &#xA;Its mounted the way it is to both protect and hide its location from your searchers. Suggest painting 'Training' on the exterior or providing a tag on a chain with your contact information. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also try to find a contact at the local Emergency Communications Center to be your advocate for the regular department contacts who may not be as technologically savvy.&lt;/p&gt;&#xA;" OwnerUserId="6092" LastActivityDate="2017-01-15T02:11:56.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7074" PostTypeId="1" AcceptedAnswerId="7075" CreationDate="2017-01-15T10:06:30.310" Score="0" ViewCount="122" Body="&lt;p&gt;how important and why is the audio, ptt ev. CAT interface separation from PC? I saw solutions with separating transformers and PTT, but directly connected CAT. Does it make sense? And is there any potential separated USB cable?&lt;/p&gt;&#xA;" OwnerUserId="9047" LastActivityDate="2017-01-15T16:46:57.043" Title="Separated audio and ptt" Tags="&lt;computer-control&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7075" PostTypeId="2" ParentId="7074" CreationDate="2017-01-15T16:46:57.043" Score="0" Body="&lt;p&gt;Let's wrap this up from the back:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And is there any potential separated USB cable?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. You can buy these as isolated USB interface. They make sense in applications where e.g. medical-grade isolation between user interface and device is necessary, or where the device controlled over USB is somewhere that might experience things like discharge from large motors etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A CAT (computer-aided tuning) interface, however, classically isn't even USB – it's typically a serial controller (a UART), connected either via RS-232  level signal or TTL signaling. The USB adapter typically just contains a USB-to-serial converter doing the desired signal levels. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's much easier to electrically isolate RS-232 or TTL serial lines than USB. So do that, you can buy ready-made ICs and boards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't &lt;em&gt;need&lt;/em&gt; potential separation, however. Your transceiver's case is typically on the same level as your USB shielding or serial line signal ground. You might want to avoid noisy current loops – but you'd do that using filters/clamp-on ferrites, typically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's legitimate concern about coupling noise from switching electronics (e.g. computers) into transceivers – but it all boils down to shielding. And I'd expect your transceiver to shield and filter its inputs reasonably well – after all, what are you expecting when you accept a digital signal? It's going to come from a digital device.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-01-15T16:46:57.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7076" PostTypeId="1" CreationDate="2017-01-15T20:19:04.367" Score="3" ViewCount="7419" Body="&lt;p&gt;A length of coaxial cable radiates negligible amount of RF.&lt;br&gt;&#xA;Same length, if cut into pieces of length (λ/2 * VF), and these pieces joined again cross-connected (i.e. core of a piece to shield of adjacent piece &amp;amp; vice versa), then this length of coax becomes a very good radiator of RF. Why &amp;amp; how?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT on Feb 05, 2017:&lt;br&gt;&#xA;Added sketch below to improve the question.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/MxEgq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MxEgq.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="9029" LastEditDate="2017-02-05T21:46:26.153" LastActivityDate="2017-02-21T01:15:27.247" Title="How the Coaxial Collinear Antenna Works?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;coaxial-cable&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7077" PostTypeId="2" ParentId="7076" CreationDate="2017-01-16T09:01:17.453" Score="4" Body="&lt;p&gt;If you look at this, reduced to two segments:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;==============x==============&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;you'll notice that the voltage on the outer conductor right of the crossover is exactly the opposite (assuming infinetly small crossover and perfect impedance matching) than on the left side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let's assume we simply feed the two outer conductors at that crossover point with exactly such a voltage:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;______________-(~)+______________&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Looking familiar? Yep, that is a classical dipole!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-01-16T09:01:17.453" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7078" PostTypeId="1" CreationDate="2017-01-16T12:17:48.923" Score="3" ViewCount="442" Body="&lt;p&gt;I've seen that quite often in Morse code tables (for example &lt;a href=&quot;http://www.qsl.net/w5www/morsecode.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;), under punctuation, a semicolon &quot;;&quot;character is listed.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the &lt;a href=&quot;https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.1677-1-200910-I!!PDF-E.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU-R M.1677-1&lt;/a&gt; doesn't specify that character as a part of the International Morse code. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is: Where is the semicolon character actually defined?&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2017-01-17T18:17:28.770" Title="Where exactly is the Morse code character &quot;;&quot; defined?" Tags="&lt;cw&gt;&lt;history&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7079" PostTypeId="1" AcceptedAnswerId="7080" CreationDate="2017-01-16T16:19:10.003" Score="1" ViewCount="214" Body="&lt;p&gt;I am transmitting a FSK signal on 433,941 ± 32 kHz at 19200 baud rate. From what I read I should be able to recover my signal with a a modem centered on my carrier and having a bandwidth of 32 × 2 + 19.2 kHz. So I have defined my modem carrier-centered with a 84kHz bandwidth:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/maxOW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/maxOW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;but am getting this result:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/co4IX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/co4IX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which to me looks wonky because of no frequency changing throughout the signal (I made sure I am not transmitting only &lt;code&gt;0&lt;/code&gt; or only &lt;code&gt;1&lt;/code&gt;). Was expecting to read back something like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MylqV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MylqV.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What am I missing?&lt;/p&gt;&#xA;" OwnerUserId="8811" LastEditorUserId="76" LastEditDate="2017-01-17T19:40:36.640" LastActivityDate="2017-01-17T19:40:36.640" Title="transmitted FSK, sniffed something PSK-looking" Tags="&lt;software-defined-radio&gt;&lt;modes&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7080" PostTypeId="2" ParentId="7079" CreationDate="2017-01-16T17:28:01.943" Score="2" Body="&lt;p&gt;You say you set up your frequency shift as ± 32 kHz and that your receiver is “carrier centered” (I assume you mean at the midpoint of the two frequencies).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, the shift changes the &lt;em&gt;sign&lt;/em&gt; but not the &lt;em&gt;magnitude&lt;/em&gt; of the frequency, which looks similar to a phase shift but is not the same thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You have two options from here:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If you want to get a signal like in your last diagram, you need to set your receiver LO (“carrier”) frequency so that the &lt;em&gt;magnitude&lt;/em&gt; of the two FSK frequencies is different (i.e. do not be centered between them). Then you will see the &quot;slow and fast&quot; look in the output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is what you should do if you want to do further processing as &quot;mono audio&quot;, such as you would get from a SSB receiver.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The data you are looking at in your second picture is complex-baseband in the two stereo channels. If you take the two channels as a complex number or a point in 2D space, you will find that the value is moving in a circle about the origin. When the frequency changes from +32 to -32, it will start moving in the &lt;em&gt;opposite&lt;/em&gt; direction. This is really easy to demodulate — just look at the sign of the difference in angle between successive samples.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is what you should do if you're trying to write a straightforward SDR demodulator.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-01-16T17:28:01.943" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7081" PostTypeId="1" AcceptedAnswerId="7099" CreationDate="2017-01-16T20:22:21.597" Score="10" ViewCount="9356" Body="&lt;p&gt;It is my understanding that the feed-point impedance ($Z_a$) of an end-fed half-wave antenna is dependent on at least the following factors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$L_a$: The length of the radiating element of the antenna.&lt;/li&gt;&#xA;&lt;li&gt;$D_a$: The diameter of the radiating element of the antenna.&lt;/li&gt;&#xA;&lt;li&gt;Environment surrounding the antenna.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It it also my understanding that such an antenna is not actually resonant (Meaning the impedance is purely resistive) when $L_a = 0.5\lambda$, but rather something a tad smaller. A common number I've seen thrown around is ~$0.41\lambda$, but different sources seem to have slightly different values.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My general question is, assuming the antenna is radiating in free-space, what is the theoretical mathematical relationship between $L_a$, $D_a$, and $Z_a$?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More specifically, I'd like to know how to calculate two things:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For a given $D_a$, what value of $L_a$ (when $L_a \le 0.5\lambda)$ would give me a real (purely resistive) $Z_a$ in free-space?&lt;/li&gt;&#xA;&lt;li&gt;For a given $L_a$ and $D_a$ (or when those variables are constrained so that $Z_a$ is always real), what is the exact value of $Z_a$ in free-space?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Bonus points for elaborating on how these values are related in practical, non-free-space environments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have seen many confusing estimations for $Z_a$, &lt;a href=&quot;http://www.aa5tb.com/efha.html&quot; rel=&quot;noreferrer&quot;&gt;ranging between 1800Ω and 5000Ω&lt;/a&gt;, which is a huge range. I want to better understand what factors are involved and how to mathematically calculate the value under ideal circumstances.&lt;/p&gt;&#xA;" OwnerUserId="9009" LastEditorUserId="76" LastEditDate="2017-01-18T16:52:26.130" LastActivityDate="2021-03-02T14:47:46.317" Title="What is the impedance of an end-fed half-wave antenna?" Tags="&lt;antenna-theory&gt;&lt;impedance&gt;&lt;end-fed-antenna&gt;" AnswerCount="7" CommentCount="3" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7082" PostTypeId="1" AcceptedAnswerId="7087" CreationDate="2017-01-17T14:58:37.833" Score="1" ViewCount="94" Body="&lt;p&gt;I am trying to recover my 2FSK signal using an SDR. I have centered the SDR modem on the median frequency (the virtual carrier) and captured my signal via some 90 kHz bw modem. THis is the recording of it below. You can hardly make out the sine waves from it. I have highlit one such sine wave - 56 samples @ 2.048 MHz sampling rate = about 36.6 kHz, which is close to what I am emitting. Should the necessary modem's bandwidth be in this case 2 * 36.6 + 19.2 (baudrate) = around 90 kHz ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/y4TwY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/y4TwY.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am getting pretty much the same results with a 200 kHz bw modem. However, with a 250 kHz modem the sines are much better. But not quite perfect, like in the picture below. Am I seeing this artifact because of my actual signal's BW being wider than the calculated BW and even wider than 250 kHz or is it something else that I am missing ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2PUeX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2PUeX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;edit 1&lt;/strong&gt;&#xA;Previously the RTL AGC was turned on and the Tuner AGC turned off (with RF gain set to 48 - almost to the upper limit). The following two new captures are from 250 kHz modem with Tuner AGC turned on (the only difference from second capture above). Funny what I am noticing. Here how the beginning of the message looks like&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZCPqR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZCPqR.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and here is the end of it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GgKeG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GgKeG.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;edit 2&lt;/strong&gt; MUch better looking now with AGC off. I had to turn off AGC to both RTL and tuner in order to be able to manually set it to a custom value. That custom value was the maximum: 49.6 db; my signal is pretty faint, At 16.6 db I was barely able to see it is there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/omFx4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/omFx4.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8811" LastEditorUserId="8811" LastEditDate="2017-01-17T19:36:51.010" LastActivityDate="2017-01-17T20:08:47.673" Title="overly large bandwith for a FSK signal?" Tags="&lt;modes&gt;&lt;frequency&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7083" PostTypeId="2" ParentId="6545" CreationDate="2017-01-17T15:39:28.517" Score="3" Body="&lt;p&gt;The easiest way now is to get the &lt;a href=&quot;https://baofengtech.com/aprs-k2-trrs-cable&quot; rel=&quot;nofollow noreferrer&quot;&gt;Btech APRS-K2 Cable&lt;/a&gt;: it allows you to receive and send audio to the radio with a single cable. You can use it with the aprs.fi app or with a variety of software from a computer.&lt;/p&gt;&#xA;" OwnerUserId="5960" LastEditorUserId="738" LastEditDate="2017-09-28T14:53:12.717" LastActivityDate="2017-09-28T14:53:12.717" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7084" PostTypeId="2" ParentId="7078" CreationDate="2017-01-17T15:50:44.713" Score="2" Body="&lt;p&gt;It is not a defined part of the International Morse Code, it is a procedural sign similar to AR. As such it is not necessarily the same everywhere, there are several prosigns that vary slightly between Americans and Europeans, for example. The exclamation point springs to mind as an undefined and somewhat variable example. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some websites show -.-.-. and some show -.-.- for the semicolon, which seems to indicate a similar issue to the exclamation point. &lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="246" LastEditDate="2017-01-17T18:17:28.770" LastActivityDate="2017-01-17T18:17:28.770" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7085" PostTypeId="1" CreationDate="2017-01-17T16:19:46.510" Score="0" ViewCount="177" Body="&lt;p&gt;How can I make a simple signal booster without introducing too much noise? My first thought was to just feed the signal into transistor base (capable of 4GHz) through a 1K resistor. I could get a 1.2W output from this, and add low/high-pass filters later. Is there a better method? I will probably end up transmitting on UHF, but frequency hasn't been decided yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also need to insulate the pin sending the signal. My assumptiom is that alufoil wrapped around the wire to my breadboard, and connected to common ground will prevent leakage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cluebats, please.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: Posted in EE intentionally, it would probably take longer to get a good answer in Amateur Radio.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastEditorUserId="7957" LastEditDate="2017-01-17T16:50:16.917" LastActivityDate="2017-01-17T18:29:31.657" Title="Signal booster with transistor" Tags="&lt;rf-power&gt;&lt;rtl-sdr&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7086" PostTypeId="2" ParentId="7085" CreationDate="2017-01-17T17:37:12.290" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;My first thought was to just feed the signal into transistor base (capable of 4GHz) through a 1K resistor. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Um, you should definitely impedance-match your amplifier. That might mean you essentially have something like a close-to-50 Ω terminated line from which you &quot;steal&quot; your base current through some larger base resistor, but it should definitely not simply be &quot;signal line -&gt; 1 kΩ -&gt; base&quot;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;and add low/high-pass filters later. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Since a transistor used for power amplification will not operate within a linear range: Not later, &lt;strong&gt;now&lt;/strong&gt;. A non-linear device is a mixer, and you're producing every product (and squares) of the harmonic signals within your input, which means components at DC, at twice your carrier frequency, three times... and if you got multiple tones inside your signal, the difference and sum and difference-of-sums frequencies of these.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the end, neither us nor you nor the regulatory bodies involved want that you get beef with the &lt;a href=&quot;https://ens.dk/en/our-responsibilities/spectrum&quot; rel=&quot;nofollow noreferrer&quot;&gt;ENS&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My assumptiom is that alufoil wrapped around the wire to my breadboard,&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;RF and breadboard are already a bad combination. RF, breadboard and amplification are a recipe for unexpected emissions and crosstalk. Don't use breadboard. Get a piece of copper-clad PCB material, and use a knife to &quot;cut free&quot; traces on that, and solder your components onto that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can (that's already a bit tricky), use a trace width that implies good impedance matching (assuming you have a second copper plane on the bottom side of your board).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also testboards for RF transistors which you can order, or download the manufacturing files from the producers of these transistors. Also, it's not that hard to design a small board, e.g. with eagle or kicad, that has the right trace width, a ground plane, easy-to-solder holes or contact pads and contacts for edge coaxial connectors, and then order these for &amp;lt; 5$ from places like OSHPark.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-01-17T18:29:31.657" LastActivityDate="2017-01-17T18:29:31.657" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7087" PostTypeId="2" ParentId="7082" CreationDate="2017-01-17T20:08:47.673" Score="2" Body="&lt;p&gt;So, I asked you to reduce the gain and disable AGC (auto-gain control), and you asked my to explain why :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That had the effect of the RTL chipset no longer &quot;overloading&quot; its ADC with values that lead to negative values in the DSP chain (which is integrated in the RTL chip, I presume).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally, an AGC jobs is to adjust the gain so that exactly that doesn't happen. I don't know why yours didn't do that – but it's very probable that the RTL dongle's AGC , being designed for TV, is optimized to &lt;strong&gt;ignore&lt;/strong&gt; single carriers (e.g. interference and, in analog TV, pilot tones).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that out of the way:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't you have a &lt;em&gt;pretty&lt;/em&gt; signal!&#xA;That's extrodinarily clean.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, this is the old complex signal and positive vs negative frequencies business. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because you've set your receiver to the center between the higher and lower (FSK) subcarriers, we see them at $+f_\Delta$ and $-f_\Delta$. Now, negative frequencies only exist in complex signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A complex tone of frequency $f$ is defined as &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$e^{j2\pi f t}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;with $j=\sqrt{-1}$ being the imaginary unit, and $t$ being time. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, Euler tells us:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$e^{jx} = \cos (x) + j\sin(x)\text{ ,}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or applied to our harmonic signal&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$e^{j2\pi f t} = \cos (2\pi ft) + j\sin(2\pi ft)\text{ .}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the cosine is the &lt;em&gt;Real part&lt;/em&gt;, ie. what is visualized as the &quot;upper&quot; channel in your program, and the sine is the &lt;em&gt;Imaginary part&lt;/em&gt;, what's visualized as &quot;lower&quot; channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, what's the difference between two signals at $+f_\Delta$ and $-f_\Delta$? Let's just compare:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;e^{-j2f_\Delta t} &amp;amp;= \cos(-2\pi f_\Delta ) &amp;amp;&amp;amp;+ j\sin(-2\pi f_\Delta)\\&#xA;&amp;amp;&amp;amp;&amp;amp;\text{We know that $\cos$ is symmetric, $\cos(-x)=\cos(x)$,}\\&#xA;&amp;amp;&amp;amp;&amp;amp;\text{and that $\sin$ is anti-symmetric, $\sin(-x)=-\sin(x)$.}\\&#xA; &amp;amp;= \cos(-2\pi f_\Delta ) &amp;amp;&amp;amp;+ j\sin(-2\pi f_\Delta)\\&#xA;&amp;amp;= \cos(2\pi f_\Delta ) &amp;amp;&amp;amp;- j\sin(2\pi f_\Delta)\\\\&#xA;e^{j2f_\Delta t} &amp;amp;= \cos(2\pi f_\Delta ) &amp;amp;&amp;amp;+ j\sin(2\pi f_\Delta)\\&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the difference between a positive frequency and it's negative counterpart is only that the sign of the imaginary part is flipped. Flipping a sign is nothing but a simple 180° phase shift. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's exactly what's happening here. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, because you can't know the phase of the complex tone compared to your receiver's oscillator, the real part isn't actually a sine (a sine has value $0$ for $t=0$, right) and the imaginary part not really a cosine, but both are shifted by a random phase; that means that when you jump between $+f_\Delta$ and $-f_\Delta$, both tones make a phase jump (and not just the imaginary part). To know whether the frequency is positive, or negative, is however pretty simple:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A cosine is simply a sine, but with a &quot;phase advantage&quot; of quarter a wave, or $\frac{2\pi}4 =\frac\pi2$. So, all you need to figure out at any point is &quot;is the real part $\frac\pi2$ in front of the imaginary part, or the other way around?&quot;, and BOOM, there you go, FSK demodulator :)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-01-17T20:08:47.673" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7088" PostTypeId="1" AcceptedAnswerId="7090" CreationDate="2017-01-17T22:04:44.447" Score="0" ViewCount="289" Body="&lt;p&gt;I am thinking to equip every car in my company with APRS tracking device from amazon. I would like ask if I have to have a HAM license for it. &#xA;If yes, than for which person — I am not driving those cars, and every car has automatic tracker device, so the driver do nothing with Tx. I am asking for EU (European Union), while my cars are often going from state to state, but we are officialy in the Austria.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if no, how can I get call signs for tracker devices?&lt;/p&gt;&#xA;" OwnerUserId="9053" LastEditorUserId="76" LastEditDate="2017-01-17T22:23:18.813" LastActivityDate="2017-01-17T22:23:18.813" Title="Should I have a license for APRS on my company car fleet" Tags="&lt;legal&gt;&lt;aprs&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7089" PostTypeId="1" AcceptedAnswerId="7091" CreationDate="2017-01-17T22:12:44.703" Score="6" ViewCount="9650" Body="&lt;p&gt;I've read the post here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://electronics.stackexchange.com/questions/77256/why-do-some-radio-antennas-require-a-path-to-ground-and-some-do-not&quot;&gt;https://electronics.stackexchange.com/questions/77256/why-do-some-radio-antennas-require-a-path-to-ground-and-some-do-not&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which says&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The antenna system requires a &quot;ground plane&quot; for the radio wave to form. With dipoles, one half of the antenna is your ground. In verticals, something below must provide ground to complete the RF wave. This is usually achieved with radials, either attached to the base of the vertical, or buried below a ground mounted antenna. The presence of a metal mast/tower (which is lightning grounded) may contribute/interfere with the ground plane but it is not considered the antenna ground.&lt;/blockquote&gt;&#xA;  But, for example, 2m verticals on boats don't have ground planes. Two questions. &lt;/p&gt;&#xA;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Am I right in saying that a ground plane results in optimal radiation, but that radiation will still take place without one e.g. boats antennas still reach the horizon, though likely height and more power are required.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is a ground plane necessary for receiving? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Thanks for reading&lt;/p&gt;&#xA;" OwnerUserId="6608" LastEditorUserId="-1" LastEditDate="2017-04-13T12:33:09.227" LastActivityDate="2018-01-06T17:22:51.770" Title="Is a ground plane necessary for transmitting and receiving with a vertical (monopole) antenna?" Tags="&lt;hf&gt;&lt;vhf&gt;" AnswerCount="7" CommentCount="6" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7090" PostTypeId="2" ParentId="7088" CreationDate="2017-01-17T22:22:45.333" Score="4" Body="&lt;p&gt;If the devices are fixed to transmit on amateur APRS frequencies, then you most likely &lt;strong&gt;cannot legally use them for business purposes&lt;/strong&gt;, because that type of use is not allowed on the amateur bands — regardless of the design of the transmitter, the mode, or your license status.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Individual countries have different regulations, but there is international agreement that the amateur bands are for use by persons “without pecuniary interest” in that use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other scenarios:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If you have a license for other VHF frequencies and the trackers can be retuned to such a frequency then you could use them, but you would need your own receivers, so you would not gain the benefit of the APRS network.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you had an amateur license and the purpose you intended to put the trackers to is &lt;em&gt;not&lt;/em&gt; commercial, then you might be able to do it — but the requirements on automated transmitters like trackers vary between jurisdictions a lot more. In the US, for example, once you are licensed, you would simply set up all the trackers with your call sign (and include additional information in their messages to distinguish them, traditionally the APRS SSID).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-01-17T22:22:45.333" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7091" PostTypeId="2" ParentId="7089" CreationDate="2017-01-17T22:38:39.910" Score="4" Body="&lt;p&gt;Every antenna has two halves, meeting at the feed point (where the coax or other transmission line is attached). Both halves affect the properties of the antenna (radiation pattern, efficiency, etc.).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A vertical element and a ground plane is &lt;strong&gt;just one possibility&lt;/strong&gt; for what those two halves can be. If you omit the ground plane from a ground plane antenna, then there are only two possibilities for what happens:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You have an ineffective antenna — it does not radiate/receive well.&lt;/li&gt;&#xA;&lt;li&gt;Something else is serving as the ‘second half’.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In most designs of coax-fed antennas, what ends up being that second half is the shield of the coax cable and (if applicable) the conductive metal structure the antenna is mounted to. I don't know how antennas on boats usually are, but I bet there's a metal structure there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This &lt;em&gt;can&lt;/em&gt; work fine, but there are two potential problems:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;This conductive shape wasn't particularly designed to be an antenna, so it may not have the best characteristics for that (irregular radiation pattern, lossy, wrong impedance, etc.).&lt;/li&gt;&#xA;&lt;li&gt;It may be closer to other electronic equipment, the operator, etc. and thus (for receiving) pick up extra noise or (for transmitting) deliver significant RF energy where it is not wanted.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you're interested only in receiving for now, put up whatever antenna you can and don't worry too much. If you find you need better performance from your antenna, install a proper ground plane or other design of antenna.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-01-17T22:55:37.700" LastActivityDate="2017-01-17T22:55:37.700" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7092" PostTypeId="1" AcceptedAnswerId="7128" CreationDate="2017-01-17T22:46:29.530" Score="2" ViewCount="1850" Body="&lt;p&gt;Simple question, but for me is really important.&#xA;&quot;Can I use the APRS over TCPIP without a ham license in Europe Union (especially in Austria)?&quot;&lt;br&gt;&#xA;I consider yes, because I am not transmitting with radio, but I am not sure.&#xA;And if yes, which call sign I can use?&lt;/p&gt;&#xA;" OwnerUserId="9053" LastEditorUserId="8832" LastEditDate="2017-01-21T16:17:15.420" LastActivityDate="2018-03-07T23:49:04.727" Title="Can I use APRS over TCPIP without ham license?" Tags="&lt;legal&gt;&lt;license&gt;&lt;aprs&gt;&lt;europe&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7093" PostTypeId="1" CreationDate="2017-01-17T23:29:34.613" Score="1" ViewCount="393" Body="&lt;p&gt;My FT-990 often does not receive well after it powers up.  i.e. Tuning across various bands, changing from one VFO to the other, few if any signals are heard.  Briefly tuning up (CW) with low power will cause the radio to receive normally again.  The radio sat idle for years while I was deployed.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect the antenna switching relay contacts are the culprit.  Do you concur?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Suggestions for (easily) cleaning / burnishing them?&lt;/p&gt;&#xA;" OwnerUserId="9052" LastEditorUserId="218" LastEditDate="2017-01-20T14:21:20.103" LastActivityDate="2017-04-14T00:21:13.313" Title="Intermittent receive on FT-990" Tags="&lt;receiver&gt;&lt;repair&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7094" PostTypeId="2" ParentId="7092" CreationDate="2017-01-17T23:46:49.447" Score="4" Body="&lt;p&gt;When you send something to APRS, even via Internet, it eventually may end up retransmitted on ham radio frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, you are not allowed to use the system if you do not have valid amateur radio license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;APRS network requires you to identify using ham radio call sign which you have only if you have valid license.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2017-01-17T23:46:49.447" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7095" PostTypeId="2" ParentId="7081" CreationDate="2017-01-18T07:23:32.430" Score="4" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Monopole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;Wikipedia: Monopole Antenna&lt;/strong&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The monopole always has another set of conductors to which the&#xA;second wire from source is connected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This second coundutor may be earth, or a metal object commonly known&#xA;as &quot;ground plane&quot;.  The ground plane turns the monopole into a&#xA;virtual dipole with length each limb of virtual dipole equal to&#xA;length of monopole. Thus the half wave monopole's virtual dipole is&#xA;a  full wave dipole. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance of monopole is half of its virtual dipole's impedance.&#xA;For example a quarterwave monopole with ground planehas impedance of&#xA;36 ohms, which  is half of 75 ohms, the impedance of its virtual&#xA;dipole, the halfwave dipole.  &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;Wikipedia: Dipole Antenna&lt;/strong&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance of a dipole varies very sharply when its length is&#xA;fullwave. The equivalen monopole is half of its length, so&#xA;monopole's impedance varies very sharply when its length is&#xA;halfwave. The best way is to use simulation software to determine&#xA;impedance (R and X). A plot of R &amp;amp; X vs length by sweep can give the&#xA;point where you can get desired values.  &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you want to use formula to determine impedance, please see this&#xA;book:&#xA;     &lt;strong&gt;ANTENNA THEORY - ANALYSIS AND DESIGN    By Constantine A. Balanis&lt;/strong&gt;   Chapter 8: Integral Equations, Moment Method, and Self and&#xA;Mutual Impedances&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="9029" LastEditDate="2017-01-18T22:29:42.400" LastActivityDate="2017-01-18T22:29:42.400" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7096" PostTypeId="1" CreationDate="2017-01-18T08:23:43.917" Score="2" ViewCount="169" Body="&lt;p&gt;I am interested if I can set up all my automatic APRS GPS trackers with one call sign in Austria (like in the US)? Are there any restrictions on usage?&lt;/p&gt;&#xA;" OwnerUserId="9053" LastEditorUserId="4665" LastEditDate="2017-02-18T17:17:49.207" LastActivityDate="2017-02-18T17:17:49.207" Title="It is allowed to have more APRS trackers with one callsign in Europe Union" Tags="&lt;legal&gt;&lt;aprs&gt;&lt;europe&gt;" AnswerCount="0" CommentCount="5" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7097" PostTypeId="2" ParentId="6964" CreationDate="2017-01-18T12:28:00.477" Score="1" Body="&lt;p&gt;They are almost certainly capacitors, probably a few pF each. If it were a bigger name, you could probably find a schematic, but that seems improbable here. A high SWR could be caused by a shorted capacitor, put a continuity meter across them. If it reads short, one of them is dead. If it reads open, they're probably OK. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the caps seem OK, the antenna could have also just been detuned by thermal cycles, mishandling, or possibly from the factory. Check the SWR at various points on the bands and see where it's lowest. You may then be able to tune for a better SWR by physically manipulating the spacing between the driven elements and the reflectors, or by shortening or lengthening them. &lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-01-18T12:28:00.477" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7098" PostTypeId="1" AcceptedAnswerId="7119" CreationDate="2017-01-18T14:20:43.913" Score="3" ViewCount="425" Body="&lt;p&gt;I am planning a car expedition from the EU to the China, through a lot of countries in the east. I am interested in if I can use an APRS tracker with my call sign issued in the Austria.?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the revere question, can I use an APRS tracker in Europe/Austria with the call sign issued, for example in the Cambodia ?&lt;/p&gt;&#xA;" OwnerUserId="9053" LastEditorUserId="9053" LastEditDate="2017-01-18T16:54:02.803" LastActivityDate="2017-01-21T22:04:21.843" Title="Can I use my call sign in APRS tracker abroad?" Tags="&lt;legal&gt;&lt;license&gt;&lt;aprs&gt;&lt;europe&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7099" PostTypeId="2" ParentId="7081" CreationDate="2017-01-18T14:44:36.167" Score="11" Body="&lt;p&gt;It's very difficult to predict the impedance of an end-fed wire, other than to say it's high. Usually it's determined empirically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are looking for a theoretical formulation. Consider, the feedpoint is a voltage source which makes a difference in electric potential between to things. The end of the dipole, and...what?&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/WgDbl.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fWgDbl.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe you could imagine the feedpoint connected to a theoretical shell of infinite radius, similar to how &lt;a href=&quot;https://en.wikipedia.org/wiki/Capacitance#Self-capacitance&quot; rel=&quot;noreferrer&quot;&gt;self-capacitance&lt;/a&gt; is calculated? I'd guess the result depends strongly on the geometry of the wire, but generally the thicker the wire, the lower the impedance. I don't know of what practical value this model would be since any real antenna has at least a feedline and a ground/aircraft/spacetraft nearby which would be more significant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also calculate the impedance of an &lt;a href=&quot;https://ham.stackexchange.com/q/95/218&quot;&gt;off-center fed&lt;/a&gt; dipole, very close to the end. You'll notice the limit of that function as the feedpoint approaches the end is infinity. This is of course an approximation assuming the dipole is relatively thin, and that the capacitance to the other half of the dipole is the most relevant factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if there isn't another half of the dipole, what is the relevant factor? In practice it's going to be the ground, and the feedline. Neither is amenable to a simple expression. Simulation of your particular installation is your best bet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can make some generalizations though:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An end-fed dipole is resonant (or not) just like a more ordinary center-fed dipole. The feedpoint (in the middle, near the end, or somewhere between) is transparent to the resonance of the wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An exactly half-wave dipole isn't resonant in the sense that its feedpoint impedance has a reactive component. &lt;a href=&quot;http://www.antenna-theory.com/antennas/halfwave.php&quot; rel=&quot;noreferrer&quot;&gt;Theoretically, (73 + j42.5)Ω&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the dipole is too short, its reactance will be capacitive. When it's too long, inductive. Since the exactly half-wave dipole has a slightly inductive reactance, shortening it can eliminate the reactance. The exact amount of shortening depends on the thickness of the wire. 0.41λ sounds like a reasonable estimate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feedpoint impedances repeat with every wavelength of length. That is, in terms of feedpoint impedance, 0.5λ, 1.5λ, 2.5λ, ... dipoles all look the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the dipole becomes thicker, its bandwidth increases. That means for an equal change in length, the impedance of a thicker dipole will change less than a thinner dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the impedance must repeat with every wavelength, this also means that the highest impedance (for example, at the ends of a half-wave dipole) is lower with a thicker wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, a practical point: since the impedance at the end of a dipole is very high, the common-mode impedance looks relatively low. Successfully making an end-fed dipole then depends on very effective choking (a very high common-mode impedance), which is difficult to realize in practice. If the choking isn't very effective (meaning, the common mode impedance isn't much higher than the differential mode), then making the choking more effective will increase the impedance seen by the transmitter.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-18T14:44:36.167" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7100" PostTypeId="1" AcceptedAnswerId="7126" CreationDate="2017-01-18T16:34:56.363" Score="3" ViewCount="5734" Body="&lt;p&gt;I've purchased a couple of BaoFeng BF-888S's for personal use with friends. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been told these radios can't be used legally without a licence and given the usage, I doubt I could faithfully even attempt to sort out amateur licences (My friends and I aren't exactly radio enthusiasts).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My Question being is it legal for me to use these radios without a suitable licence? and if not, would it be possible for me to obtain a Simple Business licence within the UK without being a registered company? &lt;/p&gt;&#xA;" OwnerUserId="9059" LastEditorUserId="8832" LastEditDate="2018-06-05T14:22:30.783" LastActivityDate="2019-01-13T22:23:25.220" Title="Licensing a group of BaoFeng BF-888s in the UK" Tags="&lt;legal&gt;&lt;uhf&gt;&lt;united-kingdom&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="7101" PostTypeId="1" AcceptedAnswerId="7104" CreationDate="2017-01-19T03:54:31.583" Score="2" ViewCount="179" Body="&lt;p&gt;I debated putting this question on the electrical engineering forum vs. here. I settled on here since I figured many of you amateur radio experts have probably wondered about this too. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am interested in seeing a graphical output of all of the various frequencies that are around me. Think of this as a broad spectrum analyzer that works across as much bandwidth as I am able to access. I am not interested in the content, just what frequencies are being utilized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I would love to see how the RF environment changes as I drive my car to work every day. Are there hotspots? What is the strength? Does it vary over time? A graphic interface that shows signal strength and the frequency would be interesting as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have done several Google searches on this, and also searched on these forums. I don't have the right lingo as I can't seem to come up with anything worthwhile.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Appreciate your help / advice on this. Thanks.&lt;/p&gt;&#xA;" OwnerDisplayName="user9062" LastEditorUserId="8832" LastEditDate="2017-01-23T15:49:47.237" LastActivityDate="2017-01-23T15:49:47.237" Title="RF scanner w/ graphic output" Tags="&lt;software-defined-radio&gt;&lt;rf-power&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7102" PostTypeId="1" AcceptedAnswerId="7103" CreationDate="2017-01-19T21:10:21.587" Score="1" ViewCount="710" Body="&lt;p&gt;We're trying to ease over to Baofengs where I work, go over to MURS, and I've been trying to get the BF888s to work with the GXT1000s but all I've got is the Midland RECEIVES from the Baofeng, but it cannot transmit to the Baofeng, the green light comes on, but no sound. Now when I hold the monitor buttons on the Baofeng I can hear the transmission just fine, so I'm not sure what's up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know about Baofeng and the FCC parts business, I know everything Baofeng gets this lecture reply, I'd just appreciate the help so we can move over to a better radio.&lt;/p&gt;&#xA;" OwnerUserId="9067" LastActivityDate="2017-01-19T22:26:02.527" Title="Using Baofeng BF888s with Midland GXT1000" Tags="&lt;transmission&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7103" PostTypeId="2" ParentId="7102" CreationDate="2017-01-19T21:31:28.507" Score="1" Body="&lt;p&gt;I'm almost 100% certain you have CTCSS (Continuous Tone-Coded Squelch System) enabled on the Baofeng, also known as tone squelch.  This means that the squelch circuit (which allows a received signal to be sent to the speaker) won't open up unless the transmission has a sub-audible (in the ~65-150 kHz) audio tone sent along with it.  The green receive light &lt;em&gt;does&lt;/em&gt; turn on, but since the transmission doesn't have the proper tone, you don't hear anything.  I've replicated this behavior with my Baofeng UV-82HPs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should be able to modify this setting using Baofeng or CHIRP programming software.&lt;/p&gt;&#xA;" OwnerUserId="6446" LastEditorUserId="6446" LastEditDate="2017-01-19T22:26:02.527" LastActivityDate="2017-01-19T22:26:02.527" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7104" PostTypeId="2" ParentId="7101" CreationDate="2017-01-20T00:32:09.427" Score="2" Body="&lt;p&gt;You want &lt;a href=&quot;https://en.wikipedia.org/wiki/Electromagnetic_spectrum&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;all&lt;/em&gt; the frequencies&lt;/a&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's take it from the top down. You probably want to start with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Geiger_counter&quot; rel=&quot;nofollow noreferrer&quot;&gt;Geiger counter&lt;/a&gt; for the highest frequencies. Hopefully you don't detect much with this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below that are frequencies usually called &quot;light&quot;. Your eyes have some of that covered. The infrared and ultraviolet bits will need specialized cameras.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Around 300 GHz electromagnetic radiation tends to stop being called light and start being called &quot;radio waves&quot;. What you are describing sounds exactly like a spectrum analyzer, and specifically one with a very wide bandwidth. Expect to pay a lot of money. I don't know if anyone makes a spectrum analyzer that covers the entire RF spectrum, so expect to buy several.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can expect (among other things) that your spectrum analyzer will have a &lt;a href=&quot;https://ham.stackexchange.com/q/889/218&quot;&gt;waterfall display&lt;/a&gt; so you can visualize RF radiation in time and frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can go a little cheaper with an SDR, which can also have a waterfall display if you don't need the precise calibration and whatnot that comes with a spectrum analyzer. Getting one that goes from 0 Hz to 300 GHz is still going to be expensive. For example the &lt;a href=&quot;https://www.ettus.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;USRP&lt;/a&gt; costs approximately $1000 and goes up to 6 GHz. You'll need a variety of antennas and daughterboards to make it all work. That leaves just 6 to 300 GHz for which you'll need to purchase additional radios.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-20T00:32:09.427" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7105" PostTypeId="1" AcceptedAnswerId="7106" CreationDate="2017-01-20T00:44:09.043" Score="6" ViewCount="2069" Body="&lt;p&gt;From this poster,&#xA;&lt;a href=&quot;http://info.tek.com/AM-RSA306-Spectrum-Poster.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://info.tek.com/AM-RSA306-Spectrum-Poster.html&lt;/a&gt;,&#xA;&lt;a href=&quot;https://i.stack.imgur.com/tQ7It.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tQ7It.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;it indicates that a band around 433 MHz is globally-accepted for use as an amateur band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can this same band be used for industrial-scientific-medical (ISM) purposes?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Pertaining to North America some more info can be found &lt;a href=&quot;https://electronics.stackexchange.com/questions/293639/north-american-regulations-on-433mhz-radio&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9068" LastEditorUserId="9068" LastEditDate="2018-03-07T04:51:10.390" LastActivityDate="2018-03-07T04:51:10.390" Title="Can 433 MHz amateur bands be used for ISM purposes?" Tags="&lt;uhf&gt;" AnswerCount="5" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7106" PostTypeId="2" ParentId="7105" CreationDate="2017-01-20T02:41:52.650" Score="2" Body="&lt;p&gt;ISM (&lt;a href=&quot;https://en.wikipedia.org/wiki/ISM_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;Industrial, Scientific, Medical&lt;/a&gt;) is a pretty broad umbrella.  It is possible for devices to send data automatically on the ham 70cm band that you're talking about, but transmissions have to conform to the law.  The law varies somewhat from country to country, but there are certain rules in common:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The sender must have a ham license&lt;/li&gt;&#xA;&lt;li&gt;The transmissions must be identified by call sign periodically (every 10 minutes in the US)&lt;/li&gt;&#xA;&lt;li&gt;Transmissions for pecuniary interest (for profitable or business purposes) are not allowed&lt;/li&gt;&#xA;&lt;li&gt;Encrypted transmissions aren't allowed&lt;/li&gt;&#xA;&lt;li&gt;Cursing isn't allowed&lt;/li&gt;&#xA;&lt;li&gt;International third-party traffic (messages on behalf of someone in another country) are not allowed between some countries&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;With all those rules, there isn't much legal use of ham bands as an ISM-band alternative.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: it turns out that some countries in ITU region 1 (Europe, Africa, the Middle East west of the Persian Gulf including Iraq, the former Soviet Union, and Mongolia) do have a small ISM band allocation from 433.05 MHz to 434.79 MHz, according to &lt;a href=&quot;https://en.wikipedia.org/wiki/ISM_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;, which would seem to overlap the amateur radio 70cm band.  In countries that do have that ISM band allocation, then the answer to the question is yes: that narrow part of the ham band can be used for ISM purposes according to the laws that govern ISM operation.  So those ISM band users wouldn't need to identify with a call sign, but they would need to abide by ISM power limits and other rules.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2017-01-20T19:58:02.293" LastActivityDate="2017-01-20T19:58:02.293" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7107" PostTypeId="2" ParentId="7105" CreationDate="2017-01-20T03:11:20.593" Score="4" Body="&lt;p&gt;There is a very narrow sliver of bandwidth at 433MHz that is designated as an ISM band that overlaps the ham band, however the power limitations are quite severe, as are antenna and bandwidth limitations. Nearly all off-the-shelf ham gear would be out of specs for ISM use, and as such would have to operate under Part 97. Depending on what you want to do, it may well be legal and possible to use ham equipment to perform the same tasks, but not under the same rules. &lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-01-20T03:11:20.593" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7108" PostTypeId="1" AcceptedAnswerId="7109" CreationDate="2017-01-20T13:18:31.010" Score="6" ViewCount="1195" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WaSBj.png&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WaSBj.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Above is a connection of half-wave dipole antenna. The book states that the current profile is same at any given time instant on both the radiators, each of quarter wavelength length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now my confusion is clearly the coaxial cable is connected to both radiators. Say I am sending the signal through centre wire and the braid of the coaxial cable is always at ground. Now at any given time instant, only left end of the cable is going to have non zero potential, while the right end is always at $0V$. Then how come both radiators would have same current profile at any given time when the excitation is different for left and right radiators!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be very specific, say at any given time instant the voltage at the left end is 2.3V, so standing wave is generated in the left radiator, but on the right radiator the voltage is zero (braid is at ground), so how any excitation would happen on the right radiator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Support will be greatly appreciated. I am a total newbie in antenna systems.&lt;/p&gt;&#xA;" OwnerUserId="9075" LastActivityDate="2017-01-27T00:43:15.587" Title="Dipole Antenna Current Distribution at any Time Instant" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;dipole&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7109" PostTypeId="2" ParentId="7108" CreationDate="2017-01-20T13:55:41.557" Score="10" Body="&lt;p&gt;You have aptly discovered why a &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;balun is necessary when feeding a dipole with coax&lt;/a&gt;. You are right to think the book is wrong, because it is. With a coax feed and no balun, the current distributions on the dipole are not equal because some share of the current that should be on the right half (connected to the shield) of the dipole is instead flowing on the feedline common mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The book would be accurate had it used a balanced feedline instead, or included a balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coax shield is in fact not at 0V relative to ground, because without a balun there will be common-mode currents on it. The shield being at 0V is not a law but rather an assumption. That assumption is based on an antenna design with a properly designed feed and an absence of common-mode currents, which this design has not.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-20T13:55:41.557" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7110" PostTypeId="2" ParentId="7101" CreationDate="2017-01-20T19:48:53.310" Score="2" Body="&lt;p&gt;You probably want something like a 'waterfall' display that many Software Defined Radios (SDR) give.  Search for SDR and waterfall display!  You can get set up fairly easy with a computer and dongle.&lt;/p&gt;&#xA;" OwnerUserId="9076" LastActivityDate="2017-01-20T19:48:53.310" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7111" PostTypeId="2" ParentId="7098" CreationDate="2017-01-20T19:58:51.073" Score="0" Body="&lt;p&gt;You can if it is permitted by &lt;a href=&quot;http://www.cept.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;CEPT&lt;/a&gt;.  there are requirements, based on agreements between countries, on how your call must be listed.  Also types of modes, such as voice, CW, digital may also be allowed or disallowed. &lt;/p&gt;&#xA;" OwnerUserId="9076" LastActivityDate="2017-01-20T19:58:51.073" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7112" PostTypeId="2" ParentId="7089" CreationDate="2017-01-20T20:07:48.173" Score="0" Body="&lt;p&gt;Certain types of vertical antennas require a 'ground plane' and some do not.  Most verticals are 1/4-wave (not a dipole) and require a 'ground plane' to complete the 'virtual dipole'. On the other hand a 5/8-wave vertical does not require a 'ground plane' and is usually used on boats and cars, such as Corvettes, which have fiberglass bodies.&lt;/p&gt;&#xA;" OwnerUserId="9076" LastActivityDate="2017-01-20T20:07:48.173" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7113" PostTypeId="2" ParentId="7089" CreationDate="2017-01-20T21:03:09.673" Score="3" Body="&lt;p&gt;Any vertical that you may have seen mounted on a nonmetallic surface &lt;strong&gt;should&lt;/strong&gt; have something like a metallic  sheet or λ/4 copper tape radials (of proper dimensions) underneath it (and the coax shield connected to that). Otherwise, the outside of the shield will try and act as the return and have common-mode currents on it. How well that works depends on many factors, &lt;strong&gt;but that's not the proper way to do it to maximize communication range.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of all the physical laws that there are, none are more well-established than the fact that a bottom-fed vertical (vertical monopole) or an inverted-L needs something to &quot;push against&quot; to be most effective. Call that 'something' a counterpoise, radials, or whatever you want to; but to be effective, it's got to be there. Period.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;K5UJ put it nicely when he said &quot;The reason for radials is to collect RF currents and return them to the feedpoint since you don't have the other half of the antenna to do that, the part that would make it a dipole.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we make the statement that adding a counterpoise to a λ/4 vertical (for example) is not really necessary, then we might as well say that opening the window blinds won't make the room any brighter. Sure, maybe we can see our way around, but when we let the sun in, life is so much better.  Or, someone could say that we don't really need tires on a car. Sure, with enough ground clearance we can drive around on the rims, but isn't the car much more fun to drive with the rubber attached?   &lt;em&gt;Likewise, a proper RF ground makes the radiated signal stronger while preventing unwanted common-mode currents on the outside of the coax shield.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;http://w0btu.com/Optimum_number_of_ground_radials_vs_radial_length.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this web page&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-01-20T21:03:09.673" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7114" PostTypeId="1" AcceptedAnswerId="7117" CreationDate="2017-01-20T21:12:23.867" Score="3" ViewCount="333" Body="&lt;p&gt;Are there any open source Mathematica notebooks that interface with NEC2? I am primarily interested in plotting the NEC2 results from Mathematica.&lt;/p&gt;&#xA;" OwnerUserId="9077" LastEditorUserId="8717" LastEditDate="2019-11-05T21:45:58.120" LastActivityDate="2019-11-05T21:45:58.120" Title="Mathematica notebook for NEC2 (NEC, Numerical Electromagnics Code)" Tags="&lt;antenna&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7116" PostTypeId="1" CreationDate="2017-01-21T00:57:19.893" Score="1" ViewCount="237" Body="&lt;p&gt;I registered on K0HAM many years ago as K0WKM.  It appears that it was successfully changed later to my current call K0AX.  My registration is apparently still on the us trust server but the checking services report there is some sort of error about a space.  K0HAM no longer has a dstar repeater and there is no way from their website to contact. There are apparently no dstar repeaters in the Kansas City area for me to contact.  How can I either fix my registration or cancel it to re register somewhere else?&lt;/p&gt;&#xA;" OwnerUserId="9080" LastEditorUserId="218" LastEditDate="2017-01-21T16:18:14.333" LastActivityDate="2017-01-21T16:18:14.333" Title="Reregistering for dstar" Tags="&lt;d-star&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7117" PostTypeId="2" ParentId="7114" CreationDate="2017-01-21T04:31:51.607" Score="3" Body="&lt;p&gt;I use Mathematica with NEC4 which would work essentially the same as with NEC2.  I find Mathematica to be a great front end to NEC4 for not only graphing results but also preparing functions for various mathematical operations (i.e. doing Calculus with the resulting solutions).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Originally, I created a notebook of various functions that I wrote to perform the operations I used in plotting results or doing other operations on the solution data.  This was integrated with NEC4 to the point that I even prepared the input geometry description of the antenna using Mathematica.  Also, I would execute NEC4 from Mathematica passing the names of input data files and the names of my desired output file for subsequent loading into Mathematica structures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I no longer do that because it was just too much of a hassle to maintain and it provided no real benefits.  Now, I prepare the antenna geometry data using an editor and also several Python programs I wrote to create geometry for configurations that consisted of many &quot;wires&quot; in specific geometry patterns.  For example, radials for an antenna or patch work such as when I modeled my pickup truck as a ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I execute NEC4 as an ordinary batch like program producing the output solution file.  I also have Python programs that read and scrape the desired data from the formatted print created by NEC4 and then I create individual data files for later import into Mathematica.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a variety of execution types where I know the type of data being produced which my Python scraping programs handle.  For example, scraping the antenna feed point input data which provides the data I use to compute the SWR at the feed point.  I also scrape the gain data for producing 3D plots of the radiation field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a whole list of ideas of things to do, other graphs to produce and doing a better job of modeling transmission lines of various types using the manufacturers data (R, L, and C models).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For my 80-meter dipole that is fed with 450-ohm ladder line I do a full frequency sweep from 3.0 MHz to 54 MHz for every 10 KHz.  This is a whole lot of data.  For the gain data to do the radiation patterns my resulting data file is 240 MB in size and that is filtering the data to every 100 KHz.  However, using this data I do a full 3D interpolation of the gain data to create smoothed functions I use for example for Integration or taking Derivatives.  Using some of the Mathematica built in functions, I can use the resulting SWR data from the frequency sweep to find all the resonant spots of the antenna where I define resonance as the bandwidth of an SWR that is under 2:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, in summary, my work consists of the following:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Mathematic function source of my own functions.&lt;/li&gt;&#xA;&lt;li&gt;Python programs used to aid in creation of antenna geometry input.&lt;/li&gt;&#xA;&lt;li&gt;Python programs used to scrape the formatted output of NEC4.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Right now, I think I have around 40 of my own Mathematica functions that perform various operations or plot graphs.  And, maybe a half-dozen Python programs that generate &quot;repeated&quot; structures for antenna geometry data.  And, about 4 formatted output scraper Python programs that pull the interesting data from the so-called &quot;pretty-print&quot; produced by NEC4.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Oh, I have also modified the NEC4 program to generate other data of interest as well and also to track performance since some of my executions take as long as an hour (large frequency sweeps).  Although NEC2 is coded in Fortran ala Fortran 77 or something close to that, NEC4 is coded in Fortran 90 plus some features from Fortran 95.  NEC4 is licensed from Lawrence Livermore Laboratories.  At the time I got my license about 6 years ago it was $300.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;A Simple Example -- 20 meter vertical with perfect ground&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna itself is a ground mounted vertical that is made from 1/2 copper tubing (I actually have this antenna though not set up right now, I made it myself from Home Depot materials).  For this model I chose a perfect ground (an option in NEC4/NEC2) but a more realistic ground without radials and then a model with radials can be done as well.  I use this antenna with 4 radials so I don't get as good of an SWR as this example shows but it is a working and effective antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I first set up my Mathematica notebook environment as shown below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZdzeG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZdzeG.png&quot; alt=&quot;Notebook Setup&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The statements above establish my working directory for NEC4 work and then I import my Mathematica function library supporting the NEC4 work.  By the way, this is all done with an Apple iMac-24 running OS X El Capitan.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, I read in the antenna input solution data.  This is the data that specifies the feed point voltage (R/X), feed point current (R/X), and feed point Impedance (R/X), feed point Admittance (R/X), and Power in Watts (R) for each frequency of the specified frequency sweep (given by the data file governing the solution).  The integer values 1,1,1,0 in each column are the wire tag number, segment number, and the voltage (R/X) which is reported as integers 1 and 0 for the complex value 1.0+j0.0&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are the Mathematica statements that read in the antenna input:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/J0EzF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/J0EzF.png&quot; alt=&quot;antenna input&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see, I use a function that I wrote called readAntennaInput[] which is given the file name of the file with this data that was scraped by one of my Python programs from the NEC4 output data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The array returned, given the Mathematica label of antinput is 12 rows by 71 columns.  Each column is a different frequency for the frequency sweep.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a portion of that data:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/gfTG3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gfTG3.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see the individual frequency columns as row one designates the frequency beginning with 14.0 MHz and incrementing by 0.005 MHz until the maximum frequency of the sweep 14.35 MHz (the entire 20 meter band).  The floating point numbers you see in each column are the R and X values of the parameters mentioned above.  The two rows that have whole numbers are the R and X of the antenna feed point impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next I prepare the SWR function.  This is an interpolated function that computes the SWR based on a nominal value of 50.0 ohms Real.  Thus, SWR of 1:1 would suggest 50 ohms input impedance for the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0lfzr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0lfzr.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The function that I wrote to compute this SWR Function is called prepareSWRFunction as you see above.  With this function I can do Calculus such as find minimums, do integration, do differentiation and so on.  Most importantly it creates nice smooth plots:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/i6zWm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/i6zWm.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The plot function that I wrote uses the Calculus to find the minimum which is essentially taking the derivative and setting it to zero which all Calculus students have learned to do.  The result is reported as the first line that is labeled Minimum SWR Position Vector.  The next two lines of output basically extract the individual data of SWR and Frequency of minimum SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next is the plot itself.  The vertical Axes is SWR and the horizontal Axes is frequency.  The green line is actually the SWR curve and it is nice and flat over the entire 20 meter spectrum (the perfect ground model helps that result).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The blue horizontal line is the marker for an SWR of 2:1 which I consider my maximum for desired SWR.  The yellowish line is the minimum SWR which is 1.38:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, on this particular run I did not include the gain data so a 3-dimensional radiation field plot is not available.  If anyone is interested I can add that but probably will not get to it until next week.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2017-01-21T18:59:01.507" LastActivityDate="2017-01-21T18:59:01.507" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7118" PostTypeId="2" ParentId="7116" CreationDate="2017-01-21T13:49:19.253" Score="1" Body="&lt;p&gt;This should help &lt;a href=&quot;http://dstargateway.org/D-Star_Registration.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://dstargateway.org/D-Star_Registration.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;... Should you have any problems with registration, send email to AA4RC@ARRL.NET and include your name, callsign, and problem description. &quot;&lt;/p&gt;&#xA;" OwnerUserId="9083" LastEditorUserId="218" LastEditDate="2017-01-21T16:17:53.077" LastActivityDate="2017-01-21T16:17:53.077" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7119" PostTypeId="2" ParentId="7098" CreationDate="2017-01-21T22:04:21.843" Score="3" Body="&lt;p&gt;The actual answer is a bit complicated and depends on a lot of things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, the answer is no, with exceptions, but the number of exceptions can be large, due to bilateral or multilateral agreements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In Europe, one of the most popular treaties is the &lt;a href=&quot;http://www.erodocdb.dk/docs/doc98/official/pdf/TR6101.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;CEPT recommendation T/R 61-01&lt;/a&gt;. Read the actual file for details, but in general, if you're within the CEPT area, you'll need to add the prefix for each country, but your own call-sign would remain the same and you'd just need the CEPT license, if you have the class 1 license in Austria. Don't forget that some countries still want Morse code exam for their license. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, prefixes can get a bit complicated if you're using a device which limits the number of characters in the callsign for APRS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Things get a bit more complicated once you leave the CEPT area, that is to say, when you leave Russia. In general, you'd need to check if each country (you didn't list them, so...) has some sort of bilateral agreement with Austria and see how it would go to get an amateur license in that country. In case of some countries, you might get a short-time license with prefix plus your own callsign, like DL/XX1YYY in case of Germany, while in others you might need to get a real local callsign. This can also get a bit complicated, if the foreign administration wants to go into details of your examination, has requirements on how long you need to be in the country and so on. For example, in some countries, if you're Norwegian, and have an Austrian callsign, your Austrian license won't get recognized, but a Norwegian license would have been. Don't forget about the recognition paperwork and the potential fees that could be quite high. Some countries might also charge frequency usage fees as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the opposite case, situation is a bit worse: You'd need to get your Cambodian license recognized in your European country and then hope that they will issue you a CEPT license, so you can use the CEPT license in Europe.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, don't forget that APRS only works if you have good APRS coverage, so don't forget to take that into account!&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2017-01-21T22:04:21.843" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7120" PostTypeId="1" CreationDate="2017-01-22T04:15:15.083" Score="1" ViewCount="345" Body="&lt;p&gt;I've been looking into FM transmitters, and I've found one that I think I may use. The transmitter is based off of the KT0803L integrated circuit (&lt;a href=&quot;http://radio-z.ucoz.lv/kt_0803/KT0803L_V1.3.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://radio-z.ucoz.lv/kt_0803/KT0803L_V1.3.pdf&lt;/a&gt;). The maximum dBµV, as stated in the document, is 113 dBµV, (the minimum is 96 dBµV, typical is 103 dBµV).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(From: &lt;a href=&quot;https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf02087.html#q4&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf02087.html#q4&lt;/a&gt;) In Canada, low power FM transmitters that produce a field strength of under 100μV/m @ 30 meters can be operated legally without license, as long as they comply to Broadcasting Equipment Technical Standards 1. I've read some of the specifications of the KT0803L, but I've found no specific dBµV/m listing in the document, nor a transmit power rating in watts. I'm also not quite sure how to calculate these using the information given. I could also modify the antenna, if it means it would comply with the standards. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it likely that I would be able to use this transmitter legally, and without a license in Canada? And, if possible to find, what are the field strength levels (preferably in dBµV/m, at a certain distance) that this transmitter produces?&lt;/p&gt;&#xA;" OwnerUserId="9085" LastActivityDate="2017-03-23T22:49:35.377" Title="Would I be able to legally operate this FM transmitter without a license in Canada?" Tags="&lt;legal&gt;&lt;fm&gt;&lt;transmitter&gt;&lt;math&gt;&lt;canada&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7121" PostTypeId="1" AcceptedAnswerId="7122" CreationDate="2017-01-22T11:28:49.117" Score="4" ViewCount="98" Body="&lt;p&gt;I have designed my first QSL card but I'm worried that I may have reserved too little space for the call of the remote station. I'm worried that the buro might have trouble with it. However, I see many QSL cards on &lt;a href=&quot;http://kb3ifh.homestead.com/More-QSL-Examples.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this examples page&lt;/a&gt; with a fairly small field as well. My card currently looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JVRkK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JVRkK.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I prefer to not put the picture online so that it's a surprise when you get it).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would write the remote call under 'CALL' in letters of about 3.5mm high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would the buro be happy with this?&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastActivityDate="2017-01-22T18:10:44.863" Title="How large should the call of the remote station be on the QSL card?" Tags="&lt;qsl-card&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7122" PostTypeId="2" ParentId="7121" CreationDate="2017-01-22T18:10:44.863" Score="1" Body="&lt;p&gt;These days a majority of DXpeditions and large contest stations print the QSL data on address labels to be stuck on the QSL cards.  10-point type is common, which is about 3.5 mm high, so your plan should be fine.  You might want to leave yourself more height in case you write cards by hand, unless you are accustomed to writing neat small letters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bureau should be satisfied with anything that doesn't make the sorter hunt for the call sign, and is easily legible.  It is important to make sure that your cards are exactly 3.5 in x 5.5 in (88.9 mm x 139.7 mm), the standard size for non-Japanese QSL cards.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-01-22T18:10:44.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7124" PostTypeId="1" CreationDate="2017-01-23T04:44:50.407" Score="1" ViewCount="161" Body="&lt;p&gt;If I use RG6 coaxial cable in odd multiples of 1/4 wavelength as a serial matching stub, can I also use it, without modifying the length, as a coiled RF choke balun at the antenna feed point? &lt;/p&gt;&#xA;" OwnerUserId="9090" LastEditorUserId="76" LastEditDate="2017-01-29T15:36:06.610" LastActivityDate="2017-01-29T15:36:06.610" Title="Serial matching stub combined with RF choke" Tags="&lt;antenna&gt;&lt;balun&gt;&lt;antenna-system&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7125" PostTypeId="2" ParentId="7105" CreationDate="2017-01-23T04:59:09.570" Score="2" Body="&lt;p&gt;Since I cannot post a comment - ISM and ham radio - apples and oranges. &#xA;They both have their rules and frequencies. &#xA;Just because there is ISM in 433 MHz we do not need to know that cursing is not allowed on ham bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;ISM has regulations, licensing is not one of them! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your mileage will vary , from region to region, from country to country, that about all. &lt;/p&gt;&#xA;" OwnerUserId="9090" LastActivityDate="2017-01-23T04:59:09.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7126" PostTypeId="2" ParentId="7100" CreationDate="2017-01-23T05:22:40.607" Score="1" Body="&lt;p&gt;I agree with @Muller that getting a ham license isn't that hard.  But you will need to comply with proper station identification (every 10 minutes).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those radios can operate on the FRS (US Family Radio Service) frequencies, which do not require a license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HOWEVER, they put out too much power to be legal on that band.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a company with a license for particular channels that is all well and good, but these radios are field-programmable, so you can't ensure they are always going to be used in compliance with the license.  These radios probably aren't even eligible for use in commercial settings due to spurious outputs or some such technical details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Putting those kinds of radios in the hands of people with questionable intent is dangerous.  For instance, if they jammed aircraft frequencies (intentionally or otherwise) the investigation would come back to you having provided them.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer to your question:  Ask a lawyer.  Legal questions are not typically answered directly on this stackexchange, nor would any lawyer want to be on the hook for giving out free advice that leads to you or your friends doing something illegal.    &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-06-05T14:21:16.373" LastActivityDate="2018-06-05T14:21:16.373" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="7127" PostTypeId="2" ParentId="7124" CreationDate="2017-01-23T15:41:58.793" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Can I also use it , without modifying the length, as a coiled RF choke balun at the antenna feed point?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-01-24T19:55:24.810" LastActivityDate="2017-01-24T19:55:24.810" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7128" PostTypeId="2" ParentId="7092" CreationDate="2017-01-24T02:52:07.577" Score="7" Body="&lt;p&gt;I don't know Europe's regulations, but in the US under the FCC's jurisdiction, the onus is on the station operator to prevent unauthorized transmissions. An unlicensed individual using APRS on the internet wouldn't be violating any regulation, but the station operator who allows her station to make prohibited transmissions via the internet would be.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Likewise, the FCC does not regulate Winlink, AllStar, IRLP, or any other ham-on-internet activity. They regulate what's transmitted, and hold the station operator accountable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So while using APRS on the internet without a license may not be illegal per se, it's not allowed by the amateurs who operate the APRS network.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-01-24T02:52:07.577" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7129" PostTypeId="1" CreationDate="2017-01-24T21:51:16.093" Score="2" ViewCount="71" Body="&lt;p&gt;I have my Hack RF plugged in my TV antenna to have a cheap setup and I have observed on the spectrum analyser a signal (Bandwidth: ~400Khz) that is emitted by my old analog TV from 80ies. These are my observations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;By switching the TV on and off, the signal did the same&lt;/li&gt;&#xA;&lt;li&gt;The spectrum is not at the frequency tuned to, but some Mhz above &lt;/li&gt;&#xA;&lt;li&gt;when I switch a PAL Signal source on and off, the TV emission are changing from a constellation diagram with two concentric sources (like a donut, perhaps QAM) to a filled circle (probably noise) &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;what is that signal for? What kind of information can an old analog TV emit?&lt;/p&gt;&#xA;" OwnerUserId="9102" LastActivityDate="2017-01-24T22:14:21.897" Title="crt TV emissions" Tags="&lt;software-defined-radio&gt;&lt;measurement&gt;&lt;sstv&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7130" PostTypeId="2" ParentId="7129" CreationDate="2017-01-24T22:14:21.897" Score="2" Body="&lt;p&gt;The TV is likely not emitting any information, but rather just noise. A TV from the 80s would have been a &lt;a href=&quot;https://en.wikipedia.org/wiki/Cathode_ray_tube&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRT&lt;/a&gt; set. These work by sweeping a beam of electrons through a &lt;a href=&quot;https://en.wikipedia.org/wiki/Raster_scan&quot; rel=&quot;nofollow noreferrer&quot;&gt;raster scan&lt;/a&gt;. The aiming of that electron beam is accomplished by subjecting it to a controlled electric field, and as we know, radios are machines for detecting electric fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the raster is scanned at a regular rhythm, you are most likely receiving signals at the same frequency as the horizontal scan, or some multiple thereof. It looks like &lt;a href=&quot;https://en.wikipedia.org/wiki/PAL&quot; rel=&quot;nofollow noreferrer&quot;&gt;PAL&lt;/a&gt; scans 625 lines, 50 times per second. So the horizontal sync frequency is 625*50 = 31.25 kHz. It is probably approximately a &lt;a href=&quot;https://en.wikipedia.org/wiki/Triangle_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;triangle wave&lt;/a&gt;, so you will also find harmonics at every odd multiple: 93.75 kHz, 156.25 kHz, 218.75 kHz, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The intensity of the electron beam is further modulated as it scans the display, and so multiplied by the 31.25 kHz line frequency can generate frequency components into several MHz, depending on what's being displayed on the TV.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, if your HackRF antenna is very close to the TV, you may be overloading the receiver, causing &lt;a href=&quot;https://en.wikipedia.org/wiki/Clipping_(signal_processing)&quot; rel=&quot;nofollow noreferrer&quot;&gt;clipping&lt;/a&gt; and associated &lt;a href=&quot;http://www.ni.com/tutorial/3399/en/&quot; rel=&quot;nofollow noreferrer&quot;&gt;harmonic distortion&lt;/a&gt;, which will in effect create copies of signals at regular intervals throughout the spectrum. A CRT produces a very strong electric field with very little current, which is why they don't radiate noise very well far away. But up close the electric fields can be very strong (that's why they attract your hair).&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-01-24T22:14:21.897" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7131" PostTypeId="2" ParentId="7048" CreationDate="2017-01-24T23:56:59.737" Score="0" Body="&lt;p&gt;Results of measurements done today (January 24, 2017)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These results show that this antenna performs well at its designed frequency of 1090 Mhz. However it has low gain (≈ 1.5 to 2 dBi).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Test Setup&lt;br&gt;&#xA;&lt;img src=&quot;https://c1.staticflickr.com/1/394/32455978316_13fa26d622_h.jpg&quot; alt=&quot;test setup&quot;&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frequency vs VSWR &#xA;&lt;img src=&quot;https://c1.staticflickr.com/6/5615/32455991056_43386ed6c8_c.jpg&quot; alt=&quot;VSWR vs Frequency Sweep&quot;&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;R, X, S11,VSWR&#xA;&lt;img src=&quot;https://c1.staticflickr.com/1/508/31653207584_e924a0f94f_c.jpg&quot; alt=&quot;R,X,S11, VSWR&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastActivityDate="2017-01-24T23:56:59.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7132" PostTypeId="1" CreationDate="2017-01-25T04:46:17.563" Score="7" ViewCount="2956" Body="&lt;p&gt;I've been trying to get into RF electronics, but one thing that is holding me back is lack of test equipment. I have an old analog oscilloscope, but that doesn't help much for things like verifying filter frequency or looking at harmonics. So far I have been keeping most of my experiments to lower frequencies (say less than 10 MHz). This way I can use a breadboard and not have things go way out of spec when I wave my hands nearby. As an example, I've built a 1-MHz LC oscillator and would like to determine if there are significant harmonics present.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been considering buying an RTL2832U USB SDR dongle to use as a spectrum analyzer. The basic device doesn't go below 24 MHz, but there are some that support &quot;direct sampling mode&quot; or that contain an up-converter. E.g. &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B0129EBDS2&quot;&gt;https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Defined/dp/B0129EBDS2/&lt;/a&gt; and &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B01422FJMK&quot;&gt;https://www.amazon.com/Usmile-100KHz-1-7GHz-UpConverter-Receiver-radio/dp/B01422FJMK/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I've read, the direct sampling mode is prone to noise and requires a filter to be useful. If I understand correctly this is because the tuner chip is bypassed, allowing signals above the Nyquist frequency to alias in and potentially overload the receiver. For use as a directly-connected (through an appropriate attenuator) spectrum analyzer, would this likely still be an issue?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were to choose one with an upconverter, should I worry about it creating spurious harmonics? What about the SDR chip itself? I realize that performance isn't going to be great for such a cheap module, but I'm hoping things like frequency-dependent sensitivity can be canceled out in software.&lt;/p&gt;&#xA;" OwnerUserId="9103" LastEditorUserId="76" LastEditDate="2020-02-14T01:20:41.340" LastActivityDate="2020-02-15T11:08:13.213" Title="Using an RTL-SDR as a spectrum analyzer" Tags="&lt;rtl-sdr&gt;&lt;spectrum-analyzer&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7133" PostTypeId="2" ParentId="7132" CreationDate="2017-01-25T14:37:11.140" Score="2" Body="&lt;p&gt;In principle: yes, that will work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've never used an RTL dongle without a tuner / bypassing the same; I didn't know that was an option. But yes, as every ADC, you need to sufficiently limit the bandwidth of the signals you digitize in order to avoid aliases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you'd be getting into a slight chicken/egg situation here – you need a good filter, but have very limited ways to test it. I do think it's pretty possible to build e.g. a 3-stage LC at 1.5 MHz cutoff,  and use a &gt; 2 MS/s sampling rate and come out just fine, but I've never seen the analog characteristics of such RTL dongles in tuner bypass mode, so I simply can't tell.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd have basically the same problem in upconverter and any &quot;normal&quot; tuner operation, though – you're trusting the behaviour of an unknown device, so yeah, I'd just try with the RTL-SDR dongle in direct sampling mode with a &quot;probably working well&quot; low-pass filter, and see; at &lt;a href=&quot;http://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/&quot; rel=&quot;nofollow noreferrer&quot;&gt;USD 25&lt;/a&gt; it might not break your neck, financially.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding your specific application:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;As an example, I've built a 1-MHz LC oscillator and would like to determine if there are significant harmonics present.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Ah, that's exactly the kind of application I'd be careful about before I've made some attempts at characterizing my low-pass filter – after all, it becomes very important how effective and flat that filter is if you want to assess spurs' energies.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-01-25T14:37:11.140" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7134" PostTypeId="2" ParentId="7132" CreationDate="2017-01-25T15:37:24.097" Score="2" Body="&lt;p&gt;If you have a commercial transceiver you can reasonably assume it's free enough of harmonic distortion. You can then use that as a signal generator or a narrow-band spectrum analyzer to validate your other devices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides looking at harmonic frequencies directly, you can perform &lt;a href=&quot;http://electronicdesign.com/communications/understanding-intermodulation-distortion-measurements&quot; rel=&quot;nofollow noreferrer&quot;&gt;intermodulation tests&lt;/a&gt; to get a sense of linearity without needing a huge bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't have a commercial transceiver, then maybe you can perform a measurement anyway. Plug your oscillator into the SDR, and if you see an absence of harmonics you are probably in good shape. If you do see harmonics you won't know if it's the SDR or the oscillator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might eliminate some unknowns with the SDR by using one intended for HF. For example the Softrock kits cost about $20 and work with your computer soundcard. Still many unknowns granted, but at least you are using a validated design for its intended purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Worst case, hook these devices up to an antenna and can still make it work. Broadcast stations can be your signal generators, and public WebSDR installations can be your spectrum analyzers. Other stations will complicate measurements, but using this method you can probably rule out egregious design flaws.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, none of this will get you the precision that would come with a proper spectrum analyzer, but it may be sufficient to determine if your equipment is within limits for spurious emissions, etc.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-01-25T15:37:24.097" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7135" PostTypeId="2" ParentId="7105" CreationDate="2017-01-25T22:51:48.657" Score="2" Body="&lt;p&gt;&lt;strong&gt;In simple terms, there are some devices that simply cannot help but generate RF interference when they are being used. &lt;em&gt;So, it was long ago agreed that this RFI is legal, provided that they only radiate on certain frequencies&lt;/em&gt;.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Industrial, Scientific and Medical (&quot;ISM&quot;) frequency bands are reserved for the use of such high-power radio frequency (RF) energy radiated as a consequence of  industrial, scientific and medical purposes &lt;strong&gt;other than radio communications&lt;/strong&gt; such as amateur radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;An amateur or other radio communications license is not needed by operators of ISM equipment.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of these devices include RF induction heating and welding machines,  microwave ovens, and some medical equipment. The RF emissions of these devices --which in some cases can be transmitted very long distances-- can completely disrupt legal radio communications using the same frequency. Therefore, these ISM devices were limited to certain bands of frequencies by international treaties. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of the ISM bands &lt;strong&gt;overlap&lt;/strong&gt; amateur radio frequencies and CB channels. Regardless of that, communications operating in these bands must tolerate any interference generated by ISM applications, and users have no regulatory protection from ISM device operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.techopedia.com/definition/27785/industrial-scientific-and-medical-radio-band-ism-band&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.techopedia.com/definition/27785/industrial-scientific-and-medical-radio-band-ism-band&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/ISM_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.m.wikipedia.org/wiki/ISM_band&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-01-25T23:16:21.770" LastActivityDate="2017-01-25T23:16:21.770" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7136" PostTypeId="2" ParentId="7093" CreationDate="2017-01-26T03:48:00.507" Score="0" Body="&lt;p&gt;In my opinion the best way to approach such a problem is to do so systematically.  Try to narrow down the probable causes to focus on the likely problem.  The first thing I would do is try to determine whether the problem is inside or outside the radio.  The best way to do that is to substitute a different radio; if the problem exists with a different radio in your shack, then the problem is most likely outside the radio.  (It would also be possible that the two radios have the same problem, but that's unlikely.)  The best second radio to use for troubleshooting would be an antenna analyzer, because if you were to transmit at full power with a typical 100 W HF transceiver when the SWR changed suddenly, the transceiver's finals could be damaged.  An antenna analyzer transmits a tiny signal and monitors the SWR, and wouldn't be damaged if the SWR changed suddenly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't have an antenna analyzer or a second radio, then you might consider going to a meeting of your local ham club and asking for help.  Most ham clubs have friendly folks who would be happy to assist, especially for a veteran.  Such a ham club buddy could well be an experienced troubleshooter with an antenna analyzer who could help you zero in on the problem in no time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So assuming that you have an antenna analyzer connected instead of your FT-990, try wiggling the coax and such while you monitor the SWR.  Test both antennas and all your favorite bands.  Ideally, try doing it on a windy day so the antennas get wiggled also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the problem happens when your radio is connected but not when the antenna analyzer is connected, then the fault is probably in your radio.  If the problem happens when the antenna analyzer is connected, then the fault is probably elsewhere.  In that case, see if the problem happens with just one antenna or the other.  If it happens with both antennas, then the problem is probably in the coaxial cable, or a connector, the antenna switch, etc.  Work systematically to figure out where the problem most likely is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You mentioned that your problem is intermittent.  Intermittent problems can be a real headache, because you sometimes have to wait a while for the problem to recur so you can troubleshoot.  You say that the problem seems to happen some time after you tune up, but maybe that's just a coincidence; for example, maybe the problem goes away after the radio warms up a bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think you'd be best off having someone help you locally, but you could always try asking more questions here, or in our &quot;&lt;a href=&quot;http://chat.stackexchange.com/rooms/11162/ham-shack&quot;&gt;ham shack&lt;/a&gt;&quot; chat room (might require more reputation to use, not sure), or some other internet forum.  Good luck, and let us know how you make out in the comments to your question!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-01-26T03:48:00.507" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7137" PostTypeId="2" ParentId="7093" CreationDate="2017-01-26T12:57:36.177" Score="2" Body="&lt;p&gt;I have to ask the obvious question: is the antenna tuned when you are trying to receive? Briefly transmitting may activate an automatic tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Relay contacts sound like a reasonable hypothesis, though there could be plenty of other things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might try hooking up a dummy load, turning the power to minimum, and going through many receive/transmit cycles. Just getting the relay to move may be enough to get it working reliably again. Or it may at least get it working better, at which point you can justify the effort of opening the case, testing the relay to confirm, and replacing it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might also try giving the radio a thunk with your knuckles when it gets stuck. If the thunk gets it working again, that suggests it's something mechanical: possibly the relay, but maybe also connectors, etc.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-01-26T12:57:36.177" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7138" PostTypeId="1" AcceptedAnswerId="7146" CreationDate="2017-01-26T17:04:46.977" Score="5" ViewCount="106" Body="&lt;p&gt;I was looking through the FCC part 97 rules for robotic teleoperation, and it cites a one-watt figure for &quot;model craft&quot;. However, it also allows higher power transmissions for remotely operated stations, and beacons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The robot in question is a land vehicle that traverses very hilly/mountainous terrain, and having a higher power communications link would be very handy. Additionally, it sends back video and instrument readings from it's surroundings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What rules govern such devices? I was unable to find such regulations.&lt;/p&gt;&#xA;" OwnerUserId="9094" LastEditorUserId="76" LastEditDate="2017-01-26T19:39:00.027" LastActivityDate="2017-01-27T17:04:45.013" Title="What rules govern robotic teleoperations, when the remote device also transmits back telemetric information?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;telecommand&gt;&lt;telemetry&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7139" PostTypeId="1" AcceptedAnswerId="7140" CreationDate="2017-01-26T17:54:18.283" Score="2" ViewCount="2361" Body="&lt;p&gt;How many watts would be needed to cover a 10 mile radius with good sound for music on the 88-108 MHz FM broadcast band? &#xA;I am an amateur and for fun only. &lt;/p&gt;&#xA;" OwnerUserId="5840" LastEditorUserId="5840" LastEditDate="2017-02-08T07:23:43.437" LastActivityDate="2017-02-08T18:07:44.323" Title="How far does a watt equal in range in the FM band?" Tags="&lt;antenna&gt;&lt;fm&gt;&lt;transmitter&gt;&lt;range&gt;" AnswerCount="2" CommentCount="12" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7140" PostTypeId="2" ParentId="7139" CreationDate="2017-01-26T18:12:27.027" Score="2" Body="&lt;p&gt;This depends in your intended communication. Are you trying to hit a fixed receiver, in which case you can aim an antenna to that receiver? or are you trying to communicate with a handheld or other portable system? Are you on a portable system? Is the target system on a hill? The gain on the receive antenna, as well as the radiation pattern of your antenna makes a huge difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, the actual band used may make a difference. Many different bands permit FM operation, and some have unique properties that increase propagation distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often, a 5w handheld with a rubber duck can hit a repeater ~10-20 miles away, but this is one particular example of possible communication.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Edit:&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;As you mentioned that you want good quality for music, you'll really need a more powerful transmitter. Unfortunately, FCC part 97 (Amateur) rules &lt;a href=&quot;https://nonbovine-ruminations.blogspot.com/2010/01/more-things-you-can-do-on-amateur-radio.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;disallow music&lt;/a&gt; through the amateur radio bands, so you'll likely need a commercial FM broadcast license to do that sort of thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not qualified to talk at length about the particulars of antenna design, but there are other resources online. For broadcast FM radio, you'll need an antenna (a) in a high location, so receivers can clearly receive your signal; (b) high power, usually on the order of kilowatts. (WCBN-FM, a student radio station in Ann Arbor MI, uses a 200W transmitter, but has an effective range of around 10 miles).&lt;/p&gt;&#xA;" OwnerUserId="9094" LastEditorUserId="9094" LastEditDate="2017-01-26T21:25:34.417" LastActivityDate="2017-01-26T21:25:34.417" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7141" PostTypeId="5" CreationDate="2017-01-26T19:49:56.343" Score="0" Body="&lt;p&gt;See also:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;/questions/tagged/remote-control&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;remote-control&amp;#39;&quot; rel=&quot;tag&quot;&gt;remote-control&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;/questions/tagged/telemetry&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;telemetry&amp;#39;&quot; rel=&quot;tag&quot;&gt;telemetry&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-01-26T19:49:56.343" LastActivityDate="2017-01-26T19:49:56.343" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7142" PostTypeId="4" CreationDate="2017-01-26T19:49:56.343" Score="0" Body="Radio transmissions to control some device at a distance. Use [remote-control] instead when the device is itself an amateur station." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-01-26T19:49:56.343" LastActivityDate="2017-01-26T19:49:56.343" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7143" PostTypeId="5" CreationDate="2017-01-26T19:51:05.150" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-01-26T19:51:05.150" LastActivityDate="2017-01-26T19:51:05.150" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7144" PostTypeId="4" CreationDate="2017-01-26T19:51:05.150" Score="0" Body="Transmission of measured information from an automated station." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-01-26T19:51:05.150" LastActivityDate="2017-01-26T19:51:05.150" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7145" PostTypeId="2" ParentId="7108" CreationDate="2017-01-27T00:32:13.847" Score="1" Body="&lt;p&gt;In the interconnect between a coaxial line of Zc = 75 Ω and a half-wavelength dipole of Zin = 73 Ω, the reflections are &#xA;much more severe than one would predict. This is because the field and the current distributions in the coaxial line and at the input of the wire dipole are very different (see figure below). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The unequal currents on the dipole’s arms unbalance the antenna and the coaxial feed and induce currents on the outside of the coax shield which are the reason for parasitic &#xA;radiation. To balance the currents, various devices are used, called baluns (&lt;strong&gt;bal&lt;/strong&gt;anced-to-&lt;strong&gt;un&lt;/strong&gt;balanced transformer).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/wUsEc.jpg&quot; alt=&quot;currents in dipole and coax&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="9029" LastEditDate="2017-01-27T00:43:15.587" LastActivityDate="2017-01-27T00:43:15.587" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7146" PostTypeId="2" ParentId="7138" CreationDate="2017-01-27T17:04:45.013" Score="3" Body="&lt;p&gt;&lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1215&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.215&lt;/a&gt; has rules for &quot;model craft&quot;. It says a station &lt;em&gt;may&lt;/em&gt; be operated under those rules. To me, the intent of those rules is to allow for control of RC models without a break to identify every 10 minutes. I'd guess for a rover designed for Mars, a brief identification break is not a problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the rover is a station, and there won't be anyone at it. I'd think &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1213&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.213 Telecommand of an amateur station&lt;/a&gt; would allow operation in that case:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;An amateur station on or within 50 km of the Earth's surface may be under telecommand where:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) There is a radio or wireline control link between the control point and the station sufficient for the control operator to perform his/her duties. If radio, the control link must use an auxiliary station. A control link using a fiber optic cable or another telecommunication service is considered wireline.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) Provisions are incorporated to limit transmission by the station to a period of no more than 3 minutes in the event of malfunction in the control link.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(c) The station is protected against making, willfully or negligently, unauthorized transmissions.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(d) A photocopy of the station license and a label with the name, address, and telephone number of the station licensee and at least one designated control operator is posted in a conspicuous place at the station location.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So the salient points seem to be:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Tape a license and contact information on the rover&lt;/li&gt;&#xA;&lt;li&gt;Put a 3-minute transmit timeout on the rover&lt;/li&gt;&#xA;&lt;li&gt;The controlling station must be an &lt;a href=&quot;http://www.arrl.org/auxiliary-station-faq&quot; rel=&quot;nofollow noreferrer&quot;&gt;auxiliary station&lt;/a&gt; (which, among other things, limits you to VHF and higher frequencies) &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-01-27T17:04:45.013" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7147" PostTypeId="2" ParentId="6848" CreationDate="2017-01-27T21:36:08.233" Score="1" Body="&lt;p&gt;Yes, it works. I have constructed a 2m double hentenna (REF and DE), double boom unit, with 6 director elements on each boom out front of the loops. So, it's sort of a combo of the drawing and the photo above. The directors are all bent/crooked (6AWG) and misaligned; nothing has been tested or modeled yet. From inside my cabin in a little valley...it's amazing.&lt;/p&gt;&#xA;" OwnerUserId="8477" LastActivityDate="2017-01-27T21:36:08.233" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7148" PostTypeId="2" ParentId="7139" CreationDate="2017-01-28T01:56:30.803" Score="6" Body="&lt;p&gt;This is a &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt; question. Transmit power is just one factor: others are terrain, antennas, frequency, quality, noise, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we restrict the variables to typical values for FM commercial broadcast stations, we can use the &lt;a href=&quot;https://www.fcc.gov/media/radio/fm-station-classes&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC's rules&lt;/a&gt; to make some estimations. By that reckoning, you need a transmitter of around 50kW with an antenna 150 meters high to achieve your goal of high-quality coverage over a 20 mile radius.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, that's a very expensive transmitter. And you need a commercial license.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-28T01:56:30.803" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7149" PostTypeId="1" AcceptedAnswerId="7150" CreationDate="2017-01-28T20:38:24.260" Score="1" ViewCount="77" Body="&lt;ul&gt;&#xA;&lt;li&gt;How is it that a computer receiving packets through wifi doesn't get those wifi packets distorted often?&lt;/li&gt;&#xA;&lt;li&gt;Wouldn't things like other radio waves interfere with the signal often?&lt;/li&gt;&#xA;&lt;li&gt;How does my computers NIC deal with that?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The knowledge I have regarding how wifi works is that interpretation of the data is done through looking at the amplitude in the waves and the frequency and sin etc.&lt;/p&gt;&#xA;" OwnerUserId="9121" LastEditorUserId="4076" LastEditDate="2017-01-29T10:25:37.803" LastActivityDate="2017-01-29T10:25:37.803" Title="WIFI PACKETS AMPLITUDE AND DISTORTION" Tags="&lt;electronics&gt;&lt;software&gt;&lt;wifi&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2017-01-29T15:36:50.443" ContentLicense="CC BY-SA 3.0" />
  <row Id="7150" PostTypeId="2" ParentId="7149" CreationDate="2017-01-28T23:54:40.930" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How is it that a computer receiving packets through wifi doesn't get those wifi packets distorted often?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It does.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Wouldn't things like other radio waves interfere with the signal often?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;They do.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How does my computers NIC deal with that? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Error correction, equalizing, flexible synchronization, re-requesting lost packets on different layers.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Like what if the website data being sent from my router had the signal distorted through like radioactivity if I happened to be in Chernobyl...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What?! Radioactivity falls into different categories, but none of them interfere with RF signals. If you put your router on top of something that emits a lot of ionizing radiation, then the computer chips inside will malfunction. But that has nothing to do with RF.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The knowledge I have regarding how wifi works is that interpretation of the data is done through looking at the amplitude in the waves and the frequency and sin etc.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You don't seem to posess a lot of that knowledge, to be completely honest. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-01-28T23:54:40.930" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7151" PostTypeId="1" AcceptedAnswerId="7153" CreationDate="2017-01-29T00:11:14.560" Score="2" ViewCount="174" Body="&lt;p&gt;I noticed that when I transmit from my handheld Baofeng Radio, with the standard rubber duck antenna, that my laptop screen goes blank. This only occurs if I'm within a few feet, and even on powers down to one watt. This effect occurred yesterday evening, when it was sitting on a composite table, with rubber stops. When in my lap, or on my glass table here at my apartment, it doesn't exhibit this behavior.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This laptop basically falling apart anyway, as it was constructed very poorly. The model is an Asus Q550LF, and the CD drive broke, touchscreen doesn't work, audio interface is incorrectly size/not properly attached to the motherboard, among other issues.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is if there are standard steps that can be taken to attempt to diagnose what's going on here, and if so, how can I do them without buying a bunch of extra equipment?&lt;/p&gt;&#xA;" OwnerUserId="9094" LastEditorUserId="8832" LastEditDate="2017-02-02T17:34:02.110" LastActivityDate="2017-02-02T17:34:02.110" Title="Laptop screen goes blank when transmitting from handheld within a few feet - sometimes" Tags="&lt;united-states&gt;&lt;rf-power&gt;&lt;rfi&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7152" PostTypeId="2" ParentId="7124" CreationDate="2017-01-29T05:19:40.683" Score="1" Body="&lt;p&gt;You can, however the efficacy of the balun would highly questionable. &quot;Ugly baluns&quot; have been shown conclusively to be quite poor at reducing common mode current outside of narrow frequency ranges, as they are self resonant. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The combination of the inductance and the turn to turn and inter-conductor capacitance of the coax creates an LC tank, not a primarily inductive choke. This means that, while you may get several hundred to perhaps a thousand or so ohms of common mode impedance across a narrow resonant range, across most frequencies, common mode choking is minimal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ugly baluns must be built with particular dimensions for a given type of coax, and changing from one kind of coax to another can drastically alter the design for a given frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ferrite baluns are almost always better in almost every way, and can be constructed for $20 USD or so.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-01-29T05:19:40.683" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7153" PostTypeId="2" ParentId="7151" CreationDate="2017-01-29T10:16:34.000" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I noticed that when I transmit from my handheld Baofeng Radio, with the standard rubber duck antenna, that my laptop screen goes blank.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;ouch.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;This only occurs if I'm within a few feet, and even on powers down to one watt.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As an electrical engineer: that's still a lot of power if just wanted to communicate over a couple meters, but:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your laptop has any certification (it has, unless you illegally imported it), it should be tolerant to any let's say &quot;non-malicious&quot; interference. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So although I've played around with the cheapest Baofengs you can get on amazon.de and &lt;em&gt;saw how terrible the spurs were&lt;/em&gt;, I'm pretty sure &lt;em&gt;this should not happen&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My question is if there are standard steps that can be taken to attempt to diagnose what's going on here, and if so, how can I do them without buying a bunch of extra equipment?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, you've diagnosed the problem: The laptop breaks its FCC specification by being susceptible to lawful interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, if I were in any department of ASUS, I'd be mightily relaxed. As laptop manufacturer, I'd deal with a couple hundred upset customers per day. The least of them have tried to irradiate my devices with so much RF power that things start to fail, and it's (albeit not legally sound, probably, but I'm really not a lawyer) really easy to argue that you &lt;em&gt;just shouldn't operate a strong radio&lt;/em&gt; next to electronic equipment. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, I doubt there will be an engineer sitting down with your laptop model trying to reproduce the issue and nail down the source. However, if he did, he'd probably use exactly your radio first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem here is that you forgot to mention on which frequencies you operate. Radio modelling becomes easy when you're in the &lt;em&gt;far field&lt;/em&gt;, ie. radio waves propagate more or less as plane waves, or at least as surfaces of a growing sphere around the transmitter. In the near field, i.e. for distances between transmitting and receiving device below or in the order of single wavelengths, things get a lot more complicated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, next thing that engineer would do, if this is far-field, would be record the emissions of your radio (because, reproducibility) and analyse them. He would then either use your radio or some software defined radio (signal generator) to reproduce the waves, and feed them into a highly directional antenna and try to figure out what to point at to cause the outage. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd however presume this is near-field. That would make it a lot less worse – because usually, devices don't need to be &quot;near-field secure&quot;. No-one demands it's safe to operate your laptop right next to a 1 kW HF station :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, in that case, I'd take a signal like generated from your radio, use &lt;em&gt;a lot&lt;/em&gt; less power, and feed it into a simple dipole (trying to reproduce the mismatch/matching of your rubber ducky antenna and the Baofeng, but measuring that is another task) that I attached to a plastic/wooden arm, to minimize effects of my own body. By observing the SWVR of while I hover the dipole over the device under test, I could find the regions where power couples out of my dipole into parts of the laptop most easily. Then I'd really look at these – it's not too bad if that were e.g. the metal hinges on the laptop screen, and I'd just tell the R&amp;amp;D engineers to take care about that in the ground design of the next laptop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If, however, something like the very sensitive display signal lines running through the edge of the display absorb relevant energy, and the energy doesn't seem to be absorbed by a ground plane below those, that would actually be a reason to talk to the engineer responsible for that design – for signal lines, proper ground planes are crucial for reliable operation, and the support cases where this, out of sheer bad luck, happens to someone in a situation where he's not holding the radio himself, will cost my company real money.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;this laptop basically falling apart anyway,&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;ah, so that is a good hint: Check that all the case insides are properly connected to each other. Laptop cases around critical electronic parts are often metallized on the inside and often have small copper springs or sponges with a copper mesh around to make contact when you properly close the case, thus forming an effective shielding. If your laptop lost its mechanical integrity, this effect might be compromised. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same goes for signal connectors, by the way, and in your case, especially the LVDS connector that goes between mainboard or graphics card and your screen. Digital signal receivers are pretty good these days and might actually work OK with a &quot;half-connected&quot; LVDS pair, but if significant interference happens, that might kill the decodability. So check your connections!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-01-29T10:16:34.000" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7154" PostTypeId="1" CreationDate="2017-01-29T13:11:09.013" Score="8" ViewCount="1169" Body="&lt;p&gt;Let's assume we have the following situation: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Transmitter on moon orbit (distance from earth ~400'000km), around 433Mhz.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Transmitter power 1W, antenna gain 10dB, circular polarization. Steered to point to earth. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Receiver is on Earth. Antenna is steerable 25dB, matching circular polarization.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;On-off keying modulation.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;What data transfer speed is achievable in this configuration?&lt;/p&gt;&#xA;" OwnerUserId="546" LastEditorUserId="8832" LastEditDate="2017-02-02T12:18:22.903" LastActivityDate="2017-02-02T12:18:22.903" Title="Moon-&gt;Earth 433MHz link achievable digital bandwidth" Tags="&lt;antenna&gt;&lt;digital-modes&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;bandwidth&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7155" PostTypeId="2" ParentId="7105" CreationDate="2017-01-29T18:21:54.930" Score="2" Body="&lt;p&gt;There is (In many countries) a small slice of the 70cms band that is allowed to be used for LPD use (The name varies), basically low power, low duty cycle things like door openers, car alarm keyfobs, smart meters, and other similar applications in the (usually 10mW) power class and at low duty cycle. This is NOT ISM in the 13.6MHz, or 2.4GHz sense, the devices need type approval.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These devices must accept interference from the other band users, who can be running 40+dB more power, and while nobody tries to communicate on 433.05 (The QRM makes it pretty hopeless) interference with LPD systems on that frequency is not uncommon, mostly because they tend to use rather heavily 'cost optimised' receivers that do not react well to a signal 50dB stronger only a few KHz away. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 70cm repeater next to a used car lot is a thing of beauty and joy. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically many countries allow the use of very low power things near 433MHz without a license, but the devices must have some form of type approval and must accept interference from licensed users of the band, that allocation is now so over used that where available you are smarter to use the 868MHz allocation instead. &lt;/p&gt;&#xA;" OwnerUserId="8756" LastActivityDate="2017-01-29T18:21:54.930" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7156" PostTypeId="2" ParentId="7154" CreationDate="2017-01-29T18:52:06.143" Score="13" Body="&lt;p&gt;&lt;strong&gt;Short answer:&lt;/strong&gt; Math says max link rate is 2Mb/s if you knew the perfect channel coding. Which is still an unsolved puzzle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt; &#xA;&lt;strong&gt;Long answer:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're calculating a link rate. That is fine, and can be answered using &lt;em&gt;Shannon's Channel Capacity&lt;/em&gt;, which gives us the upper limit for bits per second that we can get across a given channel:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ C= b\cdot \log_2\left(1+ \frac SN\right)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;with $b$ being the channel bandwidth, $S$ the signal energy and $N$ the noise power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;This is a upper limit. It's a mathematically proven limit. Over a bandwidth-limited channel with a given SNR, you cannot get more bits per second reliably. There's no technical way around that limit.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, you didn't mention $b$ at all. But that doesn't matter, we'll just calculate a &quot;per Hertz of bandwidth&quot; rate, and you can multiply that with the bandwidth of your transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, $S$ is only partly specified – you said what your transmit power $P$ was, and thus, we'll simply apply free space path loss to that (which simply is &quot;since the sphere on which we distribute the energy grows, by how does the field strength go down?&quot;). This incorporates the surface of a sphere, divided by the wavelength:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;A_\text{free space} &amp;amp;= \left(\frac{4\pi d}\lambda \right)^2\\&#xA;&amp;amp;=\left(\frac{4\pi dc_0}f\right)^2\\&#xA;&amp;amp;=\frac{16\pi^2 d^2 f^2}{c_0^2}\\&#xA;&amp;amp;\approx\frac{160\,\cdot \,4^2\cdot10^{16}\,\text{m}^2\,\cdot\,4.33^2\cdot10^{12} \frac1{\text{s}^2}}{9\cdot 10^{18}\frac{\text{m}^2}{\text{s}^2}}\\&#xA;&amp;amp;\approx\frac{48000\cdot10^{16}\,\cdot10^{12}}{9\cdot 10^{18}}\\&#xA;&amp;amp;=\frac{48}9 10^{13}\\&#xA;&amp;amp;\approx 5 \cdot 10^{13}\\&#xA;&amp;amp;\approx 136\,\text{dB} &#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So $S\approx \frac{1\,\text W}{5 \cdot 10^{13}} = 2 \cdot10^{-14}\,\text W$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what is your noise power? We don't know, since we don't know your receiver!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, let's assume you operate that receiver at room temperature. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means you get -174 dBm/Hz of spectral noise power density. Ok, that means your &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\frac SN = \frac{-136\,\text{dBW}}{-204\frac{\text{dBW}}{\text{Hz}}\cdot b}= \frac{\text{Hz}}b \cdot 68\,\text{dB}\approx \frac{\text{Hz}}b \cdot 6.3\,\text{MHz}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(ignoring Noise Figure For Now&lt;sup&gt;TM&lt;/sup&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When $\frac SN$ is smaller than 1, the argument of the logarithm becomes roughly 1, and $\log 1=0$, so you can basically get nothing across. So we must postulate:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;\frac{\text{Hz}}b &amp;amp;&amp;lt; (68-\text{NF}_\text{dB})\,\text{dB}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the logarithm falls slower than $b$ rises, you'll get the best result with a $b_\text{dBHz}\lim (68-\text{NF}_\text{dB})$; assuming a Noise Figure of 5 dB, a 63 dBHz = 2 MHz channel leads to maximized $C$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$C_{max} \approx 2\,\text{MHz}\log_2\left(1+3.15\right)\approx 2\log_2(4.15)\frac{\text{Mb}}{\text s} \approx 4\frac{\text{Mb}}{\text s}$$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You &lt;strong&gt;cannot&lt;/strong&gt; get that with On-Off-keying; you need at least 2 bits per Hz. So the &quot;lowest&quot; modulation that &lt;strong&gt;might&lt;/strong&gt; be able to fulfill this purpose would be QPSK, if zero-roll-off channel filters existed. So you'd probably settle for something like 8-PSK with a whole metric effton of channel coding/error correction on top, to get even close to that. You'll probably be happy if you get a single megabit per second.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-01-29T19:09:41.450" LastActivityDate="2017-01-29T19:09:41.450" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="7157" PostTypeId="2" ParentId="7154" CreationDate="2017-01-29T20:26:43.183" Score="7" Body="&lt;p&gt;&lt;em&gt;Summary&lt;/em&gt;: Theoretical maximum in the neighborhood of 10s of megabits per second. Less than that in practice, perhaps a lot less depending on budget.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's start with the &lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;Friis transmission equation&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{r(\mathrm{dB})} =&#xA; P_{t(\mathrm{dB})}&#xA; + G_{t(\mathrm{dB})}&#xA; + G_{r(\mathrm{dB})}&#xA; + 147.6&#xA; - 20 \log_{10} (rf) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Insert the values you've given for antenna gain, transmitter power, frequency and distance, to calculate the signal power at the receiver:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;P_{r(\mathrm{dB})} &amp;amp;=&#xA; 30\:\mathrm{dBm}&#xA; + 10\:\mathrm{dB}&#xA; + 25\:\mathrm{dB}&#xA; + 147.6&#xA; - 20 \log_{10} (400,000\:\mathrm{km} \cdot 433\:\mathrm{MHz})\\&#xA;&amp;amp;= -132\:\mathrm{dBm} \\&#xA;&amp;amp;= 6.31\cdot 10^{-14}\:\mathrm{W}&#xA;\tag{1}&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now knowing the signal power, we can use the &lt;a href=&quot;https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;Shannon-Hartley theorem&lt;/a&gt; to determine the maximum theoretical channel capacity $C$ in the presence of noise power $N$, signal power $S$, and channel bandwidth $\Delta f$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;C &amp;amp;= \Delta f \log_2 \left ( 1 + {S / N} \right) \\&#xA;  \tag{2}&#xA;\end{align} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We've already calculated the signal power, but what's the noise power? Let's assume there's no interference or ambient RF noise, and that your receiver introduces no noise of its own. The only noise then is &lt;a href=&quot;https://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;Johnson-Nyquist noise&lt;/a&gt;, which is a function temperature $T$ (in kelvin), and the bandwidth of the channel $\Delta f$, and &lt;a href=&quot;https://en.wikipedia.org/wiki/Boltzmann%27s_constant&quot; rel=&quot;nofollow noreferrer&quot;&gt;Boltzmann's constant&lt;/a&gt; ($k_B \approx 1.38 \cdot 10^{-23}$)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_\mathrm{noise} = k_B \: T \: \Delta f \tag{3}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also the case for OOK (with appropriate pulse shaping) that the bandwidth of the signal is equal to the bitrate. That is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \Delta f = C \tag{4} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Combining theoretical channel capacity (2), thermal noise (3), and the bandwidth efficiency of OOK (4), we get:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ C = C \: \log_2 \left(&#xA; 1 + {S \over k_B \: T \: C}&#xA;\right)&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Solving for C:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;1 &amp;amp;= \log_2 \left(&#xA; 1 + {S \over k_B \: T \: C}&#xA;\right) \\&#xA;\&#xA;2 &amp;amp;= 1 + {S \over k_B \: T \: C} \\&#xA;\&#xA;C &amp;amp;= {S \over k_B \: T} \\&#xA;\end{align}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's approximate Boltzmann's constant and add the received signal power calculated in equation 1:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA;C &amp;amp;= {6.31\cdot 10^{-14} \over 1.38 \cdot 10^{-23} \: T } \\&#xA;\\&#xA;  &amp;amp;= {4.57\cdot 10^{9} \over T }&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In sunlight, the moon can be about 400K, and you'd then need to integrate the moon's temperature (and the 4K or so for the night sky) over your antenna's pattern to get the &lt;a href=&quot;http://www.antenna-theory.com/basics/temperature.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;noise temperature&lt;/a&gt;. The comments in Marcus Müller's answer have a little discussion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That will give you an upper bound on the possible channel capacity. It's in the neighborhood of tens of megabits per second.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd also note that you should be able to do better with QPSK: it has the same bit error rate for a given energy-per-bit as BPSK, while being able to fit the same bit rate within half the bandwidth of OOK or BPSK. A narrower channel bandwidth means less noise, and thus a higher SNR and channel capacity.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-01-31T00:11:04.580" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="7158" PostTypeId="2" ParentId="7151" CreationDate="2017-01-29T20:41:18.533" Score="0" Body="&lt;p&gt;&lt;strong&gt;A simple vertical ground plane antenna fed with a length of RG-58, and hung by a string from a ceiling (etc.) several feet from your computer should solve this.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just make one of those simple ground plane antennas with 5 pieces of solid copper wire soldered to an SO-239 connector. Google &lt;em&gt;so-239 2 meter antenna&lt;/em&gt;. Lots of good ideas and pictures there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(And &lt;em&gt;forget a J-pole!&lt;/em&gt; Its feedline &lt;em&gt;might&lt;/em&gt; have too much common-mode RF on the outside of the shield for your computer to handle. And a vertical dipole &lt;em&gt;could&lt;/em&gt; have the same problem without a proper choke balun at the feedpoint. )&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-01-29T20:41:18.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7159" PostTypeId="1" AcceptedAnswerId="7160" CreationDate="2017-01-29T22:06:38.067" Score="4" ViewCount="578" Body="&lt;p&gt;I need to setup a Linux box to run unattended capture of about 10 MHz - contiguous worth of spectrum (Hardware must support between 500 kHz and 200 MHz) targeting voice (mix of AM and FM voice broadcasts), and another process to selectively demodulate certain frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So all of these operations need to be command line / scriptable, free of a GUI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions are as follows: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;What are the best hardware options for this considering the bandwidth and frequency requirements and availability of stable linux drivers? (I was thinking one of the SDRPlay family of devices but would welcome input on this.) &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The recommended utility/stack/drivers for capturing the raw samples based on the answer for #1 (or SDRPlay if no preference) (?) &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The recommended utility/stack for selectively demodulating and producing wav or .mp3 audio outs. (?)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;(For example if someone has setup something like this (again not Windows) for recording/logging spectrum for HAM contests, that would be a similiar application to what I need)&lt;/p&gt;&#xA;" OwnerUserId="9127" LastEditorUserId="4076" LastEditDate="2017-01-30T09:43:40.013" LastActivityDate="2017-03-07T23:14:14.837" Title="Linux based SDR spectrum capture via CLI" Tags="&lt;software-defined-radio&gt;&lt;contest&gt;&lt;linux&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7160" PostTypeId="2" ParentId="7159" CreationDate="2017-01-29T22:38:32.150" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What are the best hardware options for this considering the bandwidth and frequency requirements and availability of stable linux drivers. (I was thinking one of the SDRPlay family of devices but would welcome input on this) &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So quick summation of your requirements:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;at least 10 MHz analog bandwidth and 10 MS/s (complex) or 20 MS/s (real-valued) sampling rate&lt;/li&gt;&#xA;&lt;li&gt;Be able to capture signals between 0.5 and 200 MHz&lt;/li&gt;&#xA;&lt;li&gt;Stable linux drivers&lt;/li&gt;&#xA;&lt;li&gt;Proven interface to software in which to implement selective demodulation&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What are the best hardware options for this considering the bandwidth and frequency requirements and availability of stable linux drivers. (I was thinking one of the SDRPlay family of devices but would welcome input on this) &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To make this clear: I'm affiliated with Ettus. But I really think their USRP devices make a pretty good match. We offer awesome support for our customers (or so I'm told).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They all work with UHD, the Ettus driver framework, which is free&amp;amp;open source, and works beautifully with &lt;a href=&quot;http://gnuradio.org&quot; rel=&quot;noreferrer&quot;&gt;GNU Radio&lt;/a&gt;, which lends itself excellently to the task at hand, especially thanks to the flexible and immensely CPU-effective polyphase channelizers. I'd recommend you look into the &lt;a href=&quot;http://tutorials.gnuradio.org&quot; rel=&quot;noreferrer&quot;&gt;GNU Radio Guided Tutorials&lt;/a&gt;; there's also a &lt;em&gt;GNU Radio LiveSDR environment&lt;/em&gt; that you can flash onto a USB stick and boot from so you don't have to install things locally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can use an upconverter, go for a B200mini (small &amp;amp; cheap), B200 (basically same as B200mini, but with space for GPSDO and GPIO pins, might be useful) or B210 (B200 with twice as many RX and TX chains) for cost reasons. By themselves, their LOs are tunable from 70 MHz to 6 GHz, and their instantaneous bandwidth is up to 56 MHz. USB3. They have configurable analog bandwidth and if you configure that to the 56 MHz max, and tune to the 70 MHz minimum, you could still observe (70 - 56/2) MHz = 42 MHz signals, even if you don't use a high sampling rate - all USRPs have digital tuning built in, so that you can ask the DSP logic on the USRP it self to shift a signal in frequency prior to decimating the hardware sample rate to the user sample rate you requested:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sDpGv.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sDpGv.png&quot; alt=&quot;Bandwidth visualization by myself&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to avoid the separate upconverter, go for a USRP that accepts WBX or UBX daughterboards; if you're going for multiple channels and need max fidelity, the costly TwinRX daughterboards. In your case, a N200 USRP + WBX daugtherboard could cover 10 MHz upwards, with a UBX you can basically digitize DC till 6 GHz seamlessly. These use Gigabit ethernet – which is very nice, because you can shut them away somewhere and just run a network cable to your PC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SDRPlay does do the 10 MHz bandwidth, too, but that's its max; I haven't tried it myself. The driver is &lt;a href=&quot;http://lists.gnu.org/archive/html/discuss-gnuradio/2017-01/msg00109.html&quot; rel=&quot;noreferrer&quot;&gt;closed source and hence it's illegal to distribute GPL software linked to it&lt;/a&gt;; SDRPlay has made no attempts to correct that or even help the community to develop a inspectable driver themselves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd rather go for the HackRF if I wanted to save money; proven driver, nice folks developing it, truly dedicated to supporting the open source community around that. They don't compete with Ettus for RF specs, I think, but really, great product, too.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The recommended utility/stack/drivers for capturing the raw samples based on the answer for #1 (or SDRPlay if no preference) (?) &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I already mentioned GNU Radio. It comes with everything you need: A graphical designer for your signal flow graphs, if you prefer that. It generates python code that sets up the actual runtime; the signal processing is mainly done in C++ and highly &lt;a href=&quot;http://libvolk.org&quot; rel=&quot;noreferrer&quot;&gt;optimized C&lt;/a&gt;. The Mailing list is pretty active and, in my opinion, extremely helpful. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;GNU Radio is a signal processing &lt;em&gt;block&lt;/em&gt;-oriented framework. You instantiate blocks that transform their input(s) to one or several outputs, and connect them before starting the flow graph. GNU Radio then takes care to get the data from A to B, and to maximize throughput.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's, as far as I can tell, the most important FOSS SDR framework.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, not only does it come with ready-to-use easy-to-configure filter blocks, and channelizers, it also comes with ready to use FM demods, a lot of ecosystem with e.g. folks that demodulate OP25 in GNU Radio, and much more. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding hardware interfaces: as mentioned, UHD, and thus, all Ettus devices, work seamlessly with GNU Radio. Same goes for many other devices, such as the famous RTL dongles, the HackRF, bladeRF, and quite a few more, through the excellent efforts of &lt;code&gt;gr-osmosdr&lt;/code&gt;, which integrates a lot of drivers. There's also what I'd call a driver stub for the SDRPlay in there, but as said, you can never download a binary that links &lt;code&gt;gr-osmosdr&lt;/code&gt; with the SDRPlay library, because, frankly, SDRPlay's licensing is inacceptable in a free-software-dominated landscape. I wonder what the purpose of making your driver proprietary is, if it's a driver you need to offer so that people can use your hardware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding GUI: There's exactly no GUI, unless you add one of the GUI blocks, e.g. to have a spectrum visualization. You'd not necessarily do that on the computer you're using to capture the signal – you could write a capture GNU Radio application, which you control remotely or just via scripts, which sends selected, reduced data to another computer for visualization e.g. again with GNU Radio. Doing so is as simple as having one of the several network sinks in the capture flow graph.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The recommended utility/stack for selectively demodulating and producing wav or .mp3 audio outs. (?)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Same as above – your framework should get you from hardware driver to audio file (or even audio driver output); it wouldn't be much of a useful framework. GNU Radio does that.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-01-29T22:38:32.150" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7161" PostTypeId="1" CreationDate="2017-01-30T10:32:56.737" Score="2" ViewCount="320" Body="&lt;p&gt;Is it safe to use one antenna for transmitting (main antenna PL connector) and another for reception connected to ANT IN connector at the backside panel?&lt;/p&gt;&#xA;" OwnerUserId="9131" LastEditorUserId="76" LastEditDate="2017-02-02T16:57:10.050" LastActivityDate="2017-06-24T20:25:47.400" Title="Using two antennas with IC751A — one for transmitting and another for reception" Tags="&lt;antenna-system&gt;&lt;icom&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7162" PostTypeId="1" CreationDate="2017-01-30T13:14:54.463" Score="2" ViewCount="231" Body="&lt;p&gt;Let's imagine we're at ground station trying to receive UHF signal transmitted from moon at 433 / 2400 MHz. Our antenna with 25dB gain (circular polarization) points to the moon. Our LNA has 1dB NF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What realistic spectral power density of noise we should expect in this situation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am interested in &lt;em&gt;realistic&lt;/em&gt; estimation - not counting on just temperature of receiver/moon. We have cosmic radio background - solar, galactic, both directly and reflected... We have antenna's side-lobes picking signals from elsewhere... We have hot moon that is NOT covering whole main lobe of the antenna. There must be other tricks which affect the results which you are aware of and I am not.&lt;/p&gt;&#xA;" OwnerUserId="546" LastEditorUserId="8832" LastEditDate="2017-02-02T12:18:16.493" LastActivityDate="2017-02-02T12:18:16.493" Title="Realistic UHF noise floor when receiving signal from moon - 433 / 2400MHz" Tags="&lt;uhf&gt;&lt;noise&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7163" PostTypeId="2" ParentId="7161" CreationDate="2017-01-30T14:32:32.760" Score="4" Body="&lt;p&gt;According to the user manual &lt;a href=&quot;http://www.icomamerica.com/en/downloads/default.aspx?Category=46&quot;&gt;published here&lt;/a&gt;, page 11, the receiver antenna IN and antenna OUT connectors are located before the TX/RX antenna switching relay.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Transmitter -------------------- Relay ---- PL connector&#xA;                                   |&#xA;Rcv - RX-IN - Jumper - RX-OUT -----&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;So you can connect a preamplifier between RX-OUT and RX-IN, or get the RX-OUT antenna signal to an external receiver rather than the IC751.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you get another antenna into RX-IN, you will get a very strong signal directly into your receiver every time you transmit (due to both antennas being very near). I wouldn't recommend this.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2017-01-30T14:32:32.760" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7164" PostTypeId="1" CreationDate="2017-02-01T08:03:37.927" Score="1" ViewCount="100" Body="&lt;p&gt;Need some help with my Ramsey DDF1. It comes with telescopic antennas and my son has accidentally stepped on and broken one. I'm taking the opportunity to replace them  with a SMA connector and calibrated rubber ducky antennas instead. &#xA;However the telescopic antennas screwed directly to the PCB. Am I correct in assuming that the core of the SMA connector is just soldered to that?(isolating the body of the connector from it)&lt;/p&gt;&#xA;" OwnerUserId="5593" LastEditorUserId="8832" LastEditDate="2017-02-07T07:44:47.670" LastActivityDate="2017-02-07T07:44:47.670" Title="Ramsey's DDF1 with a SMA connector" Tags="&lt;antenna&gt;&lt;connectors&gt;&lt;direction-finding&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7165" PostTypeId="2" ParentId="7162" CreationDate="2017-02-01T18:18:10.187" Score="2" Body="&lt;p&gt;It's very difficult to say. Factors like ambient man-made noise around you can vary by orders of magnitude based on your location. Likewise, your radio system's internal noise and ability to reject ambient noise can vary by orders of magnitude. The difference between a \$20 RTL-SDR dongle in an urban environment and a \$2,000,000,000 array of receivers operated by a national space agency is quite large.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming you want to know this in relation to &lt;a href=&quot;https://ham.stackexchange.com/q/7154/218&quot;&gt;your previous question&lt;/a&gt;, the noise floor might be low enough that you can achieve near the theoretical maximum capacity, or you may not be able to communicate with your satellite at all. The environmental factors are just too variable to make a more precise prediction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can empirically determine the noise floor with a spectrum analyzer, and that's probably the simplest and most accurate way to answer your question.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-02-01T18:18:10.187" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7166" PostTypeId="2" ParentId="7164" CreationDate="2017-02-02T05:20:36.730" Score="2" Body="&lt;p&gt;Here is where you'll find your answer.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://assets.tequipment.net/assets/1/26/Documents/DF1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://assets.tequipment.net/assets/1/26/Documents/DF1.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna mounting begins on page 17, and on page 19 it shows how the whip antennas are connected to the circuit board.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And your answer is Yes, the nut that holds the whip is connected to the circuit board.  So the middle of the SMA connector (core, as you called it) would be soldered where the screw is.  The surrounding part would be connected to the shield of the coax.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-02-02T05:20:36.730" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7167" PostTypeId="1" CreationDate="2017-02-02T06:50:09.540" Score="2" ViewCount="463" Body="&lt;p&gt;I would like to put up a relatively large loop antenna to cover all the HF bands. I have sloping terrain and geographically in a slight &quot;bowl&quot; with hills and/or ridges in many directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I stick with the trees on the high part of my property, it looks like I could get somewhere around 400 ft. of wire up perhaps 25ft. high on average.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, I could extend the loop to the lower end of my property, where I at have some arbor vitae that I can almost see over when standing on my porch — this would allow me to get over 500ft but most of that extra would be lower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My plan is to use a tuner in the house with around 20ft. of coax running to a balun outside, so I'm wondering what sort of tradeoffs I should consider here.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it better for a large horizontal loop to be 10ft higher on average, or 100ft longer total? Ignoring other factors, how would loop diameter and height (and slant!) affect the radiation pattern?&lt;/li&gt;&#xA;&lt;li&gt;If I can't get an exact resonance on 160m, should I aim for some other particular length of wire (perhaps optimizing the higher bands, or to get some &lt;a href=&quot;https://www.w8ji.com/windom_off_center_fed.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;OCF&lt;/a&gt;-style impedance compromise), or just string from tree to tree around the lot and let the tuner deal with it?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2017-02-02T12:19:20.043" Title="Rules of thumb for large (&quot;somewhat&quot; full wavelength) loop antennas?" Tags="&lt;antenna&gt;&lt;loop-antenna&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7168" PostTypeId="2" ParentId="7167" CreationDate="2017-02-02T12:19:20.043" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Rules of Thumb&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;ah... I can answer that&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;higher is better for DX (more lower angle lobes)&lt;/li&gt;&#xA;&lt;li&gt;lower is better for NVIS (more higher angle lobes)&lt;/li&gt;&#xA;&lt;li&gt;longer is better than shorter, but much longer than a full wave on lowest desired frequency is not needed&lt;/li&gt;&#xA;&lt;li&gt;shorter feed is better than longer feed to the tuner to minimise feed-line losses&lt;/li&gt;&#xA;&lt;li&gt;resonance is not needed if you have a short feed to tuner (or tuner at feed-point)&lt;/li&gt;&#xA;&lt;li&gt;parallel to ground is better (more even lobes) regardless of ground at angle or curve, but slant when you need too.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I am sure that you will get more scientific answers, but those are the rules of thumb I have used in the past when doing (sky) loops.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;I also kept the following in mind:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;you are using lots of wire, spanning a larger area: I always make sure that I can take it down quickly in case a &quot;situation&quot; occurs. I always made sure that I could lower and &quot;unhook the wire&quot; without climbing ladders.&lt;/li&gt;&#xA;&lt;li&gt;use counter weights to tie-off / tension: you are likely to use natural objects (such as trees) to support your loop. These objects move, therefore a counter weight tie-off-tension system will ensure you minimise damage, while maintaining tension on the wire, allowing the objects to move.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Lastly:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;Experiment!&lt;/em&gt;&lt;/strong&gt; Wire antenna's are easily to take down, change, put back up, and experiment. Sky loops are fun to play with; do expect &quot;lobes&quot; at &quot;angles/azimuths&quot; and some nulls as well...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good Luck.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2017-02-02T12:19:20.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7169" PostTypeId="1" CreationDate="2017-02-02T12:19:38.577" Score="2" ViewCount="3041" Body="&lt;p&gt;I'm putting up a multiband dipole in some tall trees. (Perhaps it's more correct to call it a &quot;&lt;a href=&quot;http://www.qsl.net/v73ns/backyardwireantennaes.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;dipole-doublet&lt;/a&gt;&quot;). The situation I'm imagining looks like this: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Z1MJh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Z1MJh.png&quot; alt=&quot;diagram of antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The legs of the antenna are each 100 feet long. They are fed in the middle by ladderline. This ladderline runs 150 feet to a 1:1 current balun (e.g. the &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-918&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ-918&lt;/a&gt;). This balun is fed with 150 feet of high quality coax (LMR-400) to an antenna tuner inside the shack. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason for doing it this way is to avoid using an &lt;a href=&quot;https://www.dxengineering.com/search/part-type/antenna-tuners/weather-resistant/yes/product-line/mfj-994brt-intellituner-remote-automatic-antenna-tuners?autoview=SKU&amp;amp;N=4294953097%2B4294949532&amp;amp;sortby=Default&amp;amp;sortorder=Default&quot; rel=&quot;nofollow noreferrer&quot;&gt;expensive remote tuner&lt;/a&gt;, and instead use a cheap balun, a &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-948&quot; rel=&quot;nofollow noreferrer&quot;&gt;cheap antenna tuner&lt;/a&gt;, and I got a good deal on the coax. :) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I can't run the ladderline all the way to the shack, because the transmission line has to be buried under a lawn for about 15 feet or so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions are: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Are the losses &lt;strong&gt;inside the coax&lt;/strong&gt; between the tuner and the balun going to be ruinously high? &lt;/li&gt;&#xA;&lt;li&gt;What will the impedance of that leg of the circuit be, assuming the tuner feedpoint is 50 ohms, and the dipole and ladderline are something realistic?&lt;/li&gt;&#xA;&lt;li&gt;Is a 1:1 current balun the right choice? &lt;/li&gt;&#xA;&lt;li&gt;Is 300 ohm ladder line the right choice? Would 400 ohms or 600 ohms be better? Does it matter? &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE&lt;/strong&gt;&#xA;This design is flawed, because the tuner does nothing to tune the impedance mismatch at the balun. As Mike Waters notes below, my drawing is basically a &lt;a href=&quot;http://www.hamuniverse.com/g5rv.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;G5RV&lt;/a&gt;, with an separate wound 1:1 balun at the ladderline feedpoint. The G5RV looks like this: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yPwkD.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yPwkD.gif&quot; alt=&quot;Picture of G5RV&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I want is &lt;a href=&quot;http://www.arrl.org/random-length-multiband-dipoles&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;, the random-length multiband dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AVipV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AVipV.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it appears in conclusion that I do need a remote tuner at the base of the ladderline feed, or I need to bring the ladderline into the shack. Or, an alternative would be to go with Phil Frost's suggestion and use a folded dipole and operate it at its resonances. I think I probably want wider-frequency coverage than the resonances of the folded-dipole, so it sounds like the tuner + simpler wire setup is more optimal for my situation. &lt;/p&gt;&#xA;" OwnerUserId="8284" LastEditorUserId="8717" LastEditDate="2020-05-28T19:04:45.090" LastActivityDate="2020-12-24T19:40:03.573" Title="Balun and tuner configuration for multiband dipole" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;balun&gt;&lt;feed-line&gt;&lt;antenna-tuner&gt;" AnswerCount="5" CommentCount="13" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7170" PostTypeId="2" ParentId="7161" CreationDate="2017-02-02T13:59:17.740" Score="0" Body="&lt;h2&gt;It is safe IF you take precautions.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If too much transmitted RF gets into the Icom's RX antenna input:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;You will transmit spurious signals&lt;/strong&gt;. The 751A (like most transceivers) shares stages in the radio with receiving and transmitting. When the signal exceeds the hold-off threshold on switching diodes, the diodes leak transmitter RF picked up by the receiving antenna into the transmitter's early stages. This results in RF feedback causing the radio to oscillate on spurious frequencies. &lt;em&gt;Your signal might also sound distorted.&lt;/em&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;YOU WILL DAMAGE PARTS&lt;/strong&gt;. The most likely damage is to the attenuator pad and early filter stages including diodes. It takes about 1/2 watt or more to cause damage, but considerably less than that to create the first condition. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;There are two informative and detailed discussions &lt;a href=&quot;http://forums.qrz.com/index.php?threads/icom-ic-751a-external-rx-antenna-overload.266646/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php/topic,43503.msg298683.html#msg298683&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;, also explaining how to prevent this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are even commercial products that you can buy to prevent this. One is &lt;a href=&quot;https://www.dxengineering.com/search/product-line/kd9sv-products-sv-fesss-front-end-savers&quot; rel=&quot;nofollow noreferrer&quot;&gt;the KD9SV Front End Saver.&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-06-24T20:25:47.400" LastActivityDate="2017-06-24T20:25:47.400" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7171" PostTypeId="2" ParentId="7169" CreationDate="2017-02-02T14:37:40.210" Score="1" Body="&lt;p&gt;This is almost certainly not going to work well on more than one or two bands. &lt;em&gt;And that's if you are &quot;lucky&quot; and  just happened to hit the right combination of antenna length/height and balanced line length/impedance&lt;/em&gt; where the impedance at the 1:1 balun just happens to be close to 50 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your design is a little like the &lt;a href=&quot;https://web.archive.org/web/20190419163817/http://www.w0btu.com/g5rv_antenna.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;G5RV&lt;/a&gt;. That took a lot of trial and error to make it work on several bands. Later, ZS6BKW used computer modeling software to fine-tune the G5RV. You would save yourself a lot of time and effort if you modeled this in &lt;a href=&quot;https://www.eznec.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC&lt;/a&gt; or a similar program.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-05-28T18:58:29.003" LastActivityDate="2020-05-28T18:58:29.003" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="7172" PostTypeId="2" ParentId="7169" CreationDate="2017-02-02T17:42:32.263" Score="1" Body="&lt;p&gt;Times Microwave LMR-400 is pretty low loss stuff, about the same at 30 MHz as &lt;a href=&quot;https://static.dxengineering.com/global/images/chartsguides/d/dxe-ll300-info-rev0.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;the 300 ohm ladder line sold by DX Engineering&lt;/a&gt;. So it's roughly the same as running ladder line all the way. Certainly many people have run setups like this and it's been fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Burying the coax transmission line is a good thing. You still want a balun to avoid most of the common-mode current. Burying the coax will make things even better. Bury it the whole length if you can. It doesn't need to be deep.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would suggest one improvement: use a 4:1 balun instead, and instead of a simple dipole, use a folded dipole. This will make it possible to get a low SWR at all points for frequencies where the dipole is resonant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use 75 ohm coax (RG-11 is a good choice), a 4:1 balun, 300 ohm ladder line, and a folded dipole, everything will be matched at frequencies where the dipole is resonant. Sounds like you already bought the LMR-400: that's fine because the difference between 50 and 75 ohms is not that much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where the dipole is 0.5, 1.5, 2.5, ... wavelengths, it will be an ideal match. Where it's 1.0, 2.0, 3.0, ... wavelengths, it will be antiresonant and you will get the worst possible match. Avoid putting one of those antiresonances on a band you want to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might also try an &lt;a href=&quot;https://www.w8ji.com/windom_off_center_fed.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;off-center fed dipole&lt;/a&gt; instead of the folded dipole. It takes some fiddling to get the lengths just right, but you can get a pretty decent match to 300 ohms on most bands. I bet it's possible to get the SWR low enough to have at worst 1dB extra loss due to SWR. You will want to add another balun at the antenna feedpoint in this case, or just run the coax all the way up to the antenna and have the balun there. Coax all the way has the advantage of not having additional loss when wet.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Are the losses inside the coax between the tuner and the balun going to be ruinously high?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It will depend on the SWR, which is going to change based on frequency. In the best case you have a 1:1 SWR. Under those conditions, for 150 feet of LMR-400 at 30MHz it's about 1 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the SWR is 5:1 then the losses go up to about 2.1 dB, and at 20:1 the losses are up to 5.3 dB. It's less than ideal, but I wouldn't call that &quot;ruinously high&quot;. Multiband antennas are always some kind of compromise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's just in the coax: you have another 150 feet of ladder line which is not without loss either.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What will the impedance of that leg of the circuit be, assuming the tuner feedpoint is 50 ohms, and the dipole and ladderline are something realistic?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It will depend on the frequency and length of the transmission lines. As the length of the transmission lines, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Reflection_coefficient&quot; rel=&quot;nofollow noreferrer&quot;&gt;reflection coefficient&lt;/a&gt; magnitude will remain the same, but its phase will change. In other words, the impedance will move around a constant-SWR circle on a &lt;a href=&quot;http://www.fourier-series.com/rf-concepts/smithchart.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Smith chart&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As drawn in the question, you have two mismatches: the dipole to the ladder line, and the ladder line to the coax. As you change frequency, the feedpoint impedance of the dipole will change, and so will the electrical length of the transmission lines.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-02-02T17:47:44.380" LastActivityDate="2017-02-02T17:47:44.380" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7173" PostTypeId="2" ParentId="221" CreationDate="2017-02-02T23:00:30.377" Score="1" Body="&lt;p&gt;C# version&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;public static String LatLonToGridSquare(double lat, double lon)&#xA;{&#xA;    double adjLat, adjLon;&#xA;    char GLat, GLon;&#xA;    String nLat, nLon;&#xA;    char gLat, gLon;&#xA;    double rLat, rLon;&#xA;    String U = &quot;ABCDEFGHIJKLMNOPQRSTUVWX&quot;;&#xA;    String L = U.ToLower();&#xA;&#xA;    if (double.IsNaN(lat)) throw new Exception(&quot;lat is NaN&quot;);&#xA;    if (double.IsNaN(lon)) throw new Exception(&quot;lon is NaN&quot;);&#xA;    if (Math.Abs(lat) == 90.0) throw new Exception(&quot;grid squares invalid at N/S poles&quot;);&#xA;    if (Math.Abs(lat) &amp;gt; 90) throw new Exception(&quot;invalid latitude: &quot; + lat);&#xA;    if (Math.Abs(lon) &amp;gt; 180) throw new Exception(&quot;invalid longitude: &quot; + lon);&#xA;&#xA;    adjLat = lat + 90;&#xA;    adjLon = lon + 180;&#xA;    GLat = U[(int)(adjLat / 10)];&#xA;    GLon = U[(int)(adjLon / 20)];&#xA;    nLat = &quot;&quot; + (int)(adjLat % 10);&#xA;    nLon = &quot;&quot; + (int)((adjLon / 2) % 10);&#xA;    rLat = (adjLat - (int)(adjLat)) * 60;&#xA;    rLon = (adjLon - 2 * (int)(adjLon / 2)) * 60;&#xA;    gLat = L[(int)(rLat / 2.5)];&#xA;    gLon = L[(int)(rLon / 5)];&#xA;    String locator = &quot;&quot; + GLon + GLat + nLon + nLat + gLon + gLat;&#xA;    return locator;&#xA;}&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="8463" LastActivityDate="2017-02-02T23:00:30.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7174" PostTypeId="1" AcceptedAnswerId="7175" CreationDate="2017-02-03T14:38:59.683" Score="3" ViewCount="406" Body="&lt;p&gt;Let's say I have something like a non-resonant dipole, so that impedance changes depending on frequency and could take any number of values.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whatever that impedance is, how does adding transmission lines or baluns change the impedance seen by the transceiver?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8832" LastEditDate="2017-02-05T02:03:50.857" LastActivityDate="2017-02-05T09:38:58.607" Title="How do transmission lines affect the impedance of some arbitrary load?" Tags="&lt;transmission-line&gt;&lt;impedance&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7175" PostTypeId="2" ParentId="7174" CreationDate="2017-02-03T14:38:59.683" Score="3" Body="&lt;p&gt;You are probably familiar with &lt;a href=&quot;https://en.wikipedia.org/wiki/Standing_wave_ratio&quot; rel=&quot;nofollow noreferrer&quot;&gt;SWR&lt;/a&gt;, where 1:1 represents a perfect match. SWR quantifies the magnitude of mismatch between two impedances, such as the antenna and the transmission line. As the two impedances become more unequal, the SWR increases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SWR does not change with the length of the transmission line, as long as that transmission line is lossless. Usually transmission losses are low enough to be negligible for impedance calculations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SWR tells you the magnitude of mismatch, but nothing about the relative impedances. For example, 25Ω and 200Ω are both a 2:1 SWR to 50Ω coax. There are also any number of complex impedances that are also a 2:1 SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a more general concept to represent mismatches: &lt;a href=&quot;https://en.wikipedia.org/wiki/Reflection_coefficient&quot; rel=&quot;nofollow noreferrer&quot;&gt;reflection coefficient&lt;/a&gt; ($\Gamma$). It's a complex number that quantifies not only the magnitude of the mismatch, but also the phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find it easiest to visualize on a &lt;a href=&quot;https://en.wikipedia.org/wiki/Smith_chart&quot; rel=&quot;nofollow noreferrer&quot;&gt;Smith Chart&lt;/a&gt;. Let's say we have a 300Ω ladder line, and a load (an antenna, say) with an (arbitrarily selected) impedance of (90+150j)Ω. In the Smith Chart, the center represents our target impedance (in this case, 300Ω) and all the impedances are normalized to that value. So we divide (90+150j)Ω by 300 to get (0.3+0.5j)Ω, and plot that on the Smith Chart:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LpFQt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LpFQt.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By measuring the distance from the center, and the angle, we get the reflection coefficient in polar coordinates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's the impedance of the antenna at the feedpoint, normalized to 300Ω. Now let's add a 300Ω transmission line of increasing length, and consider the impedance at the end of it that would be seen, for example by the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mdbb1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mdbb1.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the transmission line gets longer, the equivalent impedance moves in a clockwise circle around the center of the chart. This changes the phase of the reflection coefficient, but not the magnitude. Since the magnitude is constant, so is the SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The distance moved around that circle depends on how long the transmission line is. When its a half-wavelength, it will have gone a full circle. A full circle is just a half-wavelength because the reflection must travel over that half-wavelengh twice: there and back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can stop at any time and read our new position on the Smith chart. Then, multiply the values read from the Smith chart by the normalized impedance (300Ω in our example). In this example, we end up at (0.28-0.43j)Ω. Multiplied by 300 makes (84-129j)Ω.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What if now we add a 4:1 balun? Depending on which way we orient the balun, we can step the impedance up or down by 4. Let's step down: simply divide the impedance by 4 to get (21-32.25)Ω.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, let's add some 50Ω coax. Divide by 50 to get a normalized impedance of (0.42-0.645)Ω. Plot that:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ubsy1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ubsy1.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As before, as the transmission line gets longer, the dot moves about the center in a clockwise circle. Multiply the final location by 50 to get the equivalent impedance seen by the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As luck would have it, for this 50Ω coax we've ended up a little closer to the center, so the 50Ω coax will have a lower SWR than the 300Ω ladder line. I've just been picking arbitrary impedances and lengths, but with the careful selection of transmission line impedances and lengths this can actually be &lt;a href=&quot;https://ham.stackexchange.com/a/7053/218&quot;&gt;used to match loads&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2017-02-03T14:38:59.683" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7176" PostTypeId="2" ParentId="7174" CreationDate="2017-02-04T11:58:14.843" Score="2" Body="&lt;p&gt;The answer given by Phil Frost - W8II is comprehensive. Using Smith Chart makes it graphical and very easy to understand and very easy to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am giving below the same answer, but in a mathematical form, in case some one is interested.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aDcKe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aDcKe.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastActivityDate="2017-02-04T11:58:14.843" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7177" PostTypeId="2" ParentId="7174" CreationDate="2017-02-04T13:13:38.847" Score="0" Body="&lt;p&gt;&lt;strong&gt;An example of use of phenomenon &quot;adding transmission line changes the impedance seen by the transceiver&quot; to match impedance of antenna to impedance of receiver&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Receiver and coax impedance = 75 ohms&lt;br&gt;&#xA;Antenna impedance = 126 - j38 ohms&lt;br&gt;&#xA;Antenna is designed for 1090 MHz, λ = 275 mm&lt;br&gt;&#xA;Velocity Factor of Coax = 0.83, 1/2 λ = 1/2 x 275 x 0.83 = 114 mm  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Method:&lt;/strong&gt;&lt;br&gt;&#xA;Using Smith Chart, determine the length of Coax where resistance becomes 75 ohms i.e. transmission line circle intersects Smith Chart's circle R=1.0 (normalized to 75 ohms). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this point (in this example) the reactance seen is inductive (+ve). Calculate the value of a capacitor whose capacitive reactance (-ve) is equal to inductive reactance. Placing this capacitor in series of coax core at feed point will neutralize inductive reactance and impedance seen =75+j0 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/reOPh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/reOPh.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;SMITH CHART&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XmjQf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XmjQf.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="9029" LastEditDate="2017-02-05T09:38:58.607" LastActivityDate="2017-02-05T09:38:58.607" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7178" PostTypeId="1" AcceptedAnswerId="7181" CreationDate="2017-02-04T20:33:03.560" Score="1" ViewCount="476" Body="&lt;p&gt;Is there any difference between demodulating LSB versus USB in software from IQ samples other setting the complex mixer frequency (LO) below or above the SSB signal frequency? (and excluding any filtering required)  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would swapping the I and Q channels before mixing and demodulation make any difference?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/7180/ssb-offset-determination&quot;&gt;Moved to a new question: Is there any algorithmic way to determine if the mixed frequency offset is wrong (too high or low) other than listening for funny sounding voices?  (perhaps by checking to see if voiced vowel spectral overtones fall in a harmonic series or seem inharmonic?)&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-02-04T21:07:54.833" Title="SDR demodulation of SSB" Tags="&lt;software-defined-radio&gt;&lt;ssb&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7179" PostTypeId="2" ParentId="1196" CreationDate="2017-02-04T20:42:42.707" Score="1" Body="&lt;p&gt;IQ sampling only requires an oscillator running at a frequency at, near, or in the band of interest, and the sample rate only needs to be as wide as the band of interest.  Direct sampling requires a sampling oscillator frequency and a sample rate well above (to allow a realizable anti-aliasing filter) twice the highest frequency in the band of interest.  Thus, IQ sampling can be accomplished using a much slower (cheaper) ADC, but two of them will be required instead of just one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the band of interest is much narrower than the frequency, IQ demodulation can thus be done using much less compute power (e.g. an slow audio processor can be used instead of an FPGA or faster DSP).  &lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-02-04T22:05:26.360" LastActivityDate="2017-02-04T22:05:26.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7180" PostTypeId="1" CreationDate="2017-02-04T20:50:34.800" Score="6" ViewCount="227" Body="&lt;p&gt;Is there any algorithmic way to determine if the mixed frequency offset in an SSB SDR demodulator is wrong (too high or low), other than listening for funny sounding voices? (perhaps by checking to see if voiced vowel spectral overtones fall in a harmonic series or seem inharmonic?)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2017-02-06T17:53:52.527" Title="SSB offset determination?" Tags="&lt;software-defined-radio&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7181" PostTypeId="2" ParentId="7178" CreationDate="2017-02-04T21:07:54.833" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there any difference between demodulating LSB versus USB in software from IQ samples other setting the complex mixer frequency (LO) below or above the SSB signal frequency? (and excluding any filtering required)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, there is no difference other than the relationship of the passband and the mixer/“carrier” frequency, as you have already observed.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For USB, you downconvert (mix down) to baseband, apply a band-pass filter (with complex tap values) with edges at (more or less) 0 to +3 kHz, then ignore the I or Q output and take the other as the audio signal.&lt;/li&gt;&#xA;&lt;li&gt;For LSB, you do the same thing except that the band pass filter is around &amp;minus;3 to 0 kHz instead.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'd also like to note that there really is not such a thing as “the SSB signal frequency”. Certainly you can point at the middle of the passband, more or less, but where that frequency lies depends on the filter shape used by the transmitter and would be very difficult to measure in the presence of noise. The only precise frequency value you can define for a SSB signal is the mixer/carrier frequency, and it's much more useful all around because that's the one that you have to get right to demodulate accurately.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Would swapping the I and Q channels before mixing and demodulation make any difference?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Swapping I and Q in any signal has the effect of inverting the frequency spectrum, which converts LSB into USB and vice versa, and a 90° phase shift (which is irrelevant to anything unless you are comparing it to the unswapped version in some way).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It'd be a perfectly fine way to implement a SSB receiver to define one filter and switch between LSB and USB by swapping I and Q or not. You can also negate Q instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is useful to visualize what is going on: remember that a simple unmodulated signal is a complex sinusoid, or $(\sin(\omega t), \cos(\omega t))$. Visualize that: a point moving around the unit circle, or a helix in three dimensions. If you swap I and Q then you have $(\cos(\omega t), \sin(\omega t))$ instead, which is just a point moving in the other direction (the frequency is negated) and with a different position at any given time than the other case (the phase shift).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-02-04T21:07:54.833" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7182" PostTypeId="1" AcceptedAnswerId="7185" CreationDate="2017-02-05T02:31:07.357" Score="5" ViewCount="5794" Body="&lt;p&gt;I am just beginning with amateur radio and would like to start with an entry level handheld transceiver.  I would like to consider manufacturers based in the United States, but I have not found any.  Are there any USA handheld ham radio manufacturers?&lt;/p&gt;&#xA;" OwnerUserId="9152" LastActivityDate="2021-01-28T16:16:51.750" Title="Radio manufactured in United States" Tags="&lt;ht&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7183" PostTypeId="1" CreationDate="2017-02-05T03:18:35.737" Score="8" ViewCount="4201" Body="&lt;p&gt;To what does the term &quot;panadapter&quot; refer?  (Physical hardware or software?)  How did the term &quot;panadapter&quot; originate as related to radios or electronics? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is the term &quot;panadapter&quot; different from the spectrum and/or spectrum waterfall display on an expensive receiver/transceiver or an SDR software application?  Or is the term a superset of subset of those?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2020-02-09T22:54:06.623" LastActivityDate="2020-02-10T02:06:31.163" Title="What is a panadapter?" Tags="&lt;software-defined-radio&gt;&lt;jargon&gt;&lt;history&gt;&lt;panadapter-and-waterfall&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7184" PostTypeId="2" ParentId="7183" CreationDate="2017-02-05T12:48:40.503" Score="5" Body="&lt;p&gt;A panadapter is a device that adapts the narrow (typically 4kHz) bandwidth of a traditional receiver into a much wider bandwidth, perhaps the entire band. The &lt;em&gt;pan-&lt;/em&gt; prefix means &lt;em&gt;all&lt;/em&gt;, as in &lt;em&gt;panoramic&lt;/em&gt;, &lt;em&gt;pandemic&lt;/em&gt;, or &lt;em&gt;Pangaea&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A waterfall display isn't a panadapter, though a panadapter may have a waterfall display built in. A spectrum analyzer can also make a waterfall, but the waterfall isn't the spectrum analyzer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since most SDRs have relatively wide bandwidths, they can be used as panadapters. Many panadapters today are based on the RTL SDR design, tuned to the receiver's IF and inserted just prior to the filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An SDR used as a standalone receiver would not be a panadapter: there's nothing to &lt;em&gt;adapt&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-02-05T12:48:40.503" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7185" PostTypeId="2" ParentId="7182" CreationDate="2017-02-05T19:56:00.690" Score="5" Body="&lt;p&gt;Motorola is a US-based manufacturer that makes handheld VHF/UHF transceivers, but they are intended for business and/or government use.  Many models can be programmed for amateur frequencies though; programming usually requires a special cable, a computer, and programming software.  Compared to models aimed at the ham market the Motorola models lack many features, like the ability to scan band ranges, but if you just want to talk on a few repeaters, a Motorola HT capable of &quot;wide&quot; FM on the right band(s) should work fine.  They are quite a bit more expensive than the usual popular ham models, but on the other hand they are considered very rugged.  I looked around on eBay to see what was available, and the model I found had been made in Malaysia, but I would think that older and/or more expensive models were made in the US.  The future of business and government two-way communication is digital modes and/or &quot;narrow&quot; FM, so you would probably want an older model anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are truly determined to get a US-made HT, your best option is probably to find someone in your local club who is a current or retired two-way radio dealer who knows Motorola models, can easily get the right model (which might be used), and can program it for you.  (We have such a ham in my local club.)  You might be able to do it on your own, but you'd have a steep learning curve.  Either way, be prepared to spend quite a bit more than you would for a typical Japanese-made or Chinese-made ham HT.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-02-05T19:56:00.690" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7186" PostTypeId="2" ParentId="7180" CreationDate="2017-02-06T00:59:12.883" Score="0" Body="&lt;p&gt;I remember seeing articles about it in the past, but nothing about it in years.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most promising was to insert subaudible tones on all transmitters so the receivers can get a solid lock, like the military used to do.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-02-06T00:59:12.883" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7187" PostTypeId="2" ParentId="259" CreationDate="2017-02-06T04:16:33.227" Score="0" Body="&lt;p&gt;Many years back, I  found that I could take a little Jade 10 transistor radio that ran off a 9 volt battery, and instead hook it up to a 6 volt lantern battery, the radio went from receiving AM radio broadcast (it was strictly AM back then, this was in the mid 1960's)to picking up short wave. Now most hams now use FM for local and repeater communications, the short wave bands do see some use in folks that talk HF world wide, and that is the most interesting anyhow. I guess it depends on the age of your radio, the voltage it was made to run off, and where the radio gods hold their hands on that particular day. Many AC Radios do have a battery option.  If this is not the case, you may well be able to find a second hand AM radio that you can do the conversion on if you want.&lt;/p&gt;&#xA;" OwnerUserId="9159" LastActivityDate="2017-02-06T04:16:33.227" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7188" PostTypeId="2" ParentId="7182" CreationDate="2017-02-06T07:57:22.247" Score="4" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Are there any USA handheld ham radio manufacturers?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Sure, I found the below link by simply searching using my favourite search engine.&lt;/p&gt;&#xA;&lt;p&gt;You may consider &lt;a href=&quot;https://www.relm.com/category/product/portables/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RELM Wireless&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;[Edit 15-Jan-2021]&lt;/strong&gt;&#xA;It seems that the RELM website is now redirecting to &lt;a href=&quot;https://www.bktechnologies.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.bktechnologies.com/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I am just beginning with amateur radio and would like to start&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Be prepared to fork out some serious money if you limit yourself to US based manufactures only. Compare the prices with a Chinese HT which purchase price is around $30...&lt;/p&gt;&#xA;&lt;p&gt;Example: I &lt;a href=&quot;http://www.musi-tronics.com/_bkprice/plbkradios_1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;found&lt;/a&gt; the DHP model from RELM Wireless retailing at more that 2000 dollars. This model has obviously more features than a $30 Chinese HT, but if you are starting, and want to get on the air, then specifically looking for US based manufacturers is probably going to limit your experience of the hobby.&lt;/p&gt;&#xA;&lt;p&gt;You will probably find that many experimental electronics to supplement your HT, as well as DIY projects described on websites or magazines, will be very limited for US manufactured kit. This is simply because Japanese or Chinese kit is so much more popular.&lt;/p&gt;&#xA;&lt;p&gt;Getting support/assistance/help for popular kit is relatively easy, you can always find someone who has a similar kit.&lt;/p&gt;&#xA;&lt;p&gt;Personally I do own a Motorola, but it is a nightmare to program, the programming software and cable is closely guarded and not simple to purchase. I did manage to get it from Russia.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I would like to consider manufacturers based in the United States&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;Best advice I can give you: please reconsider.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2021-01-15T11:56:11.600" LastActivityDate="2021-01-15T11:56:11.600" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="7189" PostTypeId="2" ParentId="7011" CreationDate="2017-02-06T16:22:20.713" Score="3" Body="&lt;p&gt;This is a non-mathematical answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only difference between the driven and non-driven elements is the connection of a feedline.  Each of the elements resonance and position contribute to the characteristics of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the directors and reflectors are not of similar bandwidth to the driven element then they will not have a consistent phase and amplitude relationship with the driven element over the frequency range.  The radiation pattern depends on the summation of the energy from each of the elements.  The radiation pattern will change.&lt;/p&gt;&#xA;" OwnerUserId="9109" LastActivityDate="2017-02-06T16:22:20.713" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7190" PostTypeId="2" ParentId="7180" CreationDate="2017-02-06T17:53:52.527" Score="3" Body="&lt;p&gt;&lt;strong&gt;According to &lt;a href=&quot;https://www.google.com/patents/US7826561&quot; rel=&quot;nofollow noreferrer&quot;&gt;this 2010 Icom patent&lt;/a&gt;, there may indeed already be a way to do this.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This method uses no pilot tone, carrier, etc. A brief excerpt:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In contrast with the above prior art, the invention requires no modifications to the transmitter and so a receiver equipped with this invention can be used with any SSB transmitter in use today. It can also correct for much larger tuning errors. As discussed in detail below, this invention analyzes the properties of the transmitted human voice, independent of language and retunes the receiver to the actual transmitted signal frequency with a high degree of accuracy. This can be done faster than a trained operator can retune the radio.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Apparently, this has never been put into production, which casts some doubt about the claims made there.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-02-06T17:53:52.527" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7191" PostTypeId="1" CreationDate="2017-02-08T06:10:38.283" Score="0" ViewCount="378" Body="&lt;p&gt;I want to know about the directivity of thin dipole antenna of length 1.25λ for my assignment.Is there any formula related to its length?&lt;/p&gt;&#xA;" OwnerUserId="9171" LastActivityDate="2017-04-16T01:39:14.457" Title="What is the directivity of thin dipole antenna of length 1.25λ?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7192" PostTypeId="1" AcceptedAnswerId="7198" CreationDate="2017-02-08T12:19:44.550" Score="2" ViewCount="3879" Body="&lt;p&gt;Radio is analog, and a modem converts analog signals to digital signals and vice versa. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So is P2P sharing of digital files (like .exe, .7z, .pdf or any other file) possible using radio spectrum? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If yes then which tools do I need to do this? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does WiFi work in frequency ranges other than 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz and 5.9 GHz? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;All these frequency ranges have lower range of propagation, a lower frequency would be needed for greater propagation range. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does WiFi work in MHz or in Hz range?&lt;/p&gt;&#xA;" OwnerUserId="8064" LastEditorUserId="8832" LastEditDate="2017-06-14T20:38:55.060" LastActivityDate="2020-05-12T17:54:36.123" Title="Can we transfer digital files on radio spectrum?" Tags="&lt;digital-modes&gt;&lt;transmission&gt;" AnswerCount="6" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7194" PostTypeId="2" ParentId="7192" CreationDate="2017-02-08T17:19:43.560" Score="3" Body="&lt;p&gt;WiFi has a channel width of 20 or 40 MHz, even up to 160 MHz with 802.11ac. Theoretically WiFi could operate at a lower frequency, though there would be a number of issues. For starters, a single channel would obliterate most or all of the HF spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, there are easily thousands of digital modulations that could be used to send data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure anyone is sending large computer files on HF over large distances though. With most of the HF spectrum able to fit within just one WiFi channel, there's just not much spectrum available there. The noise is higher, and the path losses are higher also, which limits the speed attainable at realistic power levels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Within the amateur radio hobby, some people operate 300 baud AX.25 packet radio on HF, though it works quite horribly since it uses ancient technology and was not designed for this purpose. &lt;a href=&quot;http://freedv.org/tiki-index.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV&lt;/a&gt; comes to mind as a digital mode which was designed for HF and works quite well. &lt;a href=&quot;https://en.wikipedia.org/wiki/Digital_Radio_Mondiale&quot; rel=&quot;nofollow noreferrer&quot;&gt;DRM&lt;/a&gt; can also be found on the ham bands, as well as commercial broadcasting. To send files with these modulations you'd need to define an appropriate protocol.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-02-08T17:19:43.560" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7195" PostTypeId="1" CreationDate="2017-02-08T17:25:33.733" Score="5" ViewCount="291" Body="&lt;p&gt;I live in Austria (OE). There we have to change our call sign if we move beyond one of the 9 Austrian federal state's border. For example I lived near Innsbruck (Tyrol) with the sign OE7TKT. I moved to Graz (Styria) for studying - new call sign OE6TKT, next I moved to the capital Vienna - new call sign OE1TKT. Now I live in Klosterneuburg (Lower Austria) and I became OE3TKT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there similar situations in other countries?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know, in the US, you'll receive a call sign once and keep it as long as you are registered; in Germany (DL) too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tom OE3TKT (former OE7TKT,OE6TKT,OE1TKT), KW4NZ&lt;/p&gt;&#xA;" OwnerUserId="6431" LastEditorUserId="6431" LastEditDate="2017-02-22T07:42:00.850" LastActivityDate="2017-02-22T09:31:16.010" Title="Which countries require you to change your call sign if you change your residence?" Tags="&lt;license&gt;&lt;callsign&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7198" PostTypeId="2" ParentId="7192" CreationDate="2017-02-08T21:21:26.810" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Radio is analog, and modem converts analog signals to digital signals and vice versa. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Everything is analog, yet you can do digital things with the physics that is given to us. As you've noticed, when transmitting something digital over an analog channel, you typically use a &lt;em&gt;modulator&lt;/em&gt;, and to receive the same you'd need a &lt;em&gt;demodulator&lt;/em&gt;, and &lt;em&gt;modem&lt;/em&gt; is just a portmanteau of these two words.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;So is P2P sharing of digital files (.exe, .7z, .pdf or any other file) possible using radio spectrum? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, and with Wifi, Cellular networks, and many other techniques, I'm sure you're already aware of the feasibility.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If yes then which tools do I need? Does WiFi work in frequency ranges other than 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz and 5.9 GHz? All these frequency ranges have lower range of propagation, a lower frequency would be needed for greater propagation range. Does WiFi work in MHz or in Hz range?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Wifi, indeed, makes a few assumptions on the channel (ie. a microwave channel with 20 or 40 MHz width will behave differently than the much narrower, much lower, much noisier) channels you can get at shortwave, medium and longwave ranges  – how could you have 20 MHz of bandwidth if your center frequency isn't even that large?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, no, Wifi itself can't work at these frequencies. Also, Wifi has to assume a bounded flight-time of signals to work efficiently. To top that up, large-area covering WiFi networks are a &lt;em&gt;bad idea&lt;/em&gt;&lt;sup&gt;TM&lt;/sup&gt;, mainly because of the &lt;em&gt;hidden station problem&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's other techniques, but as soon as you think about it: Low-frequency spectrum simply is sparse because of the low frequency. Thus, to get sufficient bandwidth, you move to higher frequencies, which is why Cellular networks operate at 800 MHz and up. There simply was no spectrum available below.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All these frequency ranges have lower range of propagation&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's an alternative fact. There's numerous long-range and space-ground links at frequencies much higher than that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, yes, while &lt;a href=&quot;https://ham.stackexchange.com/q/3692/218&quot;&gt;Free Space Path Loss might be higher for increasing frequency&lt;/a&gt;, antennas of a given size also get higher gain – and that makes all the microwave links that are the backhaul of a lot of the high-rate communication done today feasible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P2P means Peer-to-Peer – I'm going to take that literally: It's not impossible to build a mesh network out of microwave links (in fact, that's what people do that operate cell phone towers over areas, and TV, towers on remote hilltops) and route stuff through that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's WiFi-based mesh networking – you might want to talk to your friendly &lt;em&gt;Freifunk&lt;/em&gt; enthusiast about B.A.T.M.A.N.; but I still think that for long-distance mesh networks with links that are point-to-point, you'd probably want to do with a simple frequency division microwave link (ie. one center frequency for A-&gt;B and a different one for B-&gt;A) rather than a collision-avoidance based packet network (which has no advantages in a pure point-to-point, fixed terrestrial application).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can rather easily build such a single link using (proper¹) SDRs that allow you to send arbitrary waveforms by calculating these in your PC, and do the inverse for reception. Using a network interface in your SDR application would allow you to plug together an IP network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to have omnidirectional rather than point-to-point links, you must share a single piece of spectrum across all users – which inherently divides the possible channel capacity by the number of users. You'll find, with a bit of consideration, that the easiest way to make the most of the spectrum that's available, is if there's a central node that everyone agrees on as controlling access timing – that way, for example, transmissions can be scheduled without the need for any &quot;dead periods&quot; in which stations have to listen to avoid colliding with others. If you do that, you'd be building some kind of TDMA base station, much akin to GSM / GPRS / EDGE (basically, in ascending order of flexibility in which time can be allocated to the stations) base stations. If you add the ability of base stations to communicate, and for user equipment to change between these, you've built a cellular network. Congrats!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't need high rate (and, as Phil suggested) can live with half-a-century-old technology, the AX.25 packet radio technology might be an option – but certainly not for sharing any substantial files. AX.25 itself is horrible on many levels; it is especially bad-suited for networks, as there's no good network layer that is commonly used. APRS is often used atop of that to build what can best be described as a low-rate, sparse, very suboptimal, chaotic-good aligned, networking/relay system. It reduces the possible channel utilization by not having any awareness of routes, and thus would immediately break down if a couple of stations tried to continously use the channels at max rate for any substantial amount of time (or data).&#xA;So, that's definitely not a candidate for file sharing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹I say &quot;proper&quot; because &lt;em&gt;SDR&lt;/em&gt; is often (in my opinion, mis-) used for devices that have a fixed functionality, but run the signal processing in fixed software. To be honest, under that nomenclature, every cheap Baofeng handset is an SDR.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-02-09T04:58:07.073" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7199" PostTypeId="1" AcceptedAnswerId="17379" CreationDate="2017-02-09T18:59:56.580" Score="4" ViewCount="324" Body="&lt;p&gt;I am trying to use the ISS APRS digipeater which transmits at 437.55MHz.&lt;/p&gt;&#xA;&lt;p&gt;Hardware setup consists of the following&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;ICOM IC-910H.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;The transceiver has been connected to a Windows PC running a HAM deluxe software package called Satellites. Basically, satellites tracks all spacecraft of known TLEs and perform doppler prediction. The output is then fed directly into the ICOM transceiver which has been set to &amp;quot;SATELLITE MODE&amp;quot;. Analogue modulation is set to FM&lt;/p&gt;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;Kantronics KAM XL TNC&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I connected the TNC to my linux laptop via USB-to-serial adapter. I used the screen command the serial communication&lt;/p&gt;&#xA;&lt;p&gt;sudo screen /dev/ttyUSB0 19200&lt;/p&gt;&#xA;&lt;p&gt;In command mode I use the following settings&lt;/p&gt;&#xA;&lt;p&gt;mycall XXXXXX&lt;/p&gt;&#xA;&lt;p&gt;passall on, monitor on, mcon on, flow on,&lt;/p&gt;&#xA;&lt;p&gt;paclen 70&lt;/p&gt;&#xA;&lt;p&gt;axdelay plus txdelay &amp;gt;= 3&lt;/p&gt;&#xA;&lt;p&gt;After I switched to converse mode (k) then I sent these simple messages and my location (not shown)&lt;/p&gt;&#xA;&lt;p&gt;.&amp;gt;    Hello ISS&lt;/p&gt;&#xA;&lt;p&gt;:CQ       :Hello ISS&lt;/p&gt;&#xA;&lt;p&gt;Unfortunately neither my location nor my messages showed up on ariss.net . I captured the signal by using a Tektronix PC-based spectrum analyser and got the following&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ugu9s.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ugu9s.png&quot; alt=&quot;Spectrum&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Each box is 6khz wide. This means that at -10dB, the bandwidth is around 12000Hz which is more than I expected. So here are my two questions&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Question 1:&lt;/p&gt;&#xA;&lt;p&gt;I have verified that the 9600 bps mode is switched off on the ICOM. How come the signal is that wide?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Question 2&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Is the baud rate of my AFSK 1200 audio tones dictated by ICOM or by the TNC? If it is dictated by the TNC, then which command should I use to set it to 1200?&lt;/p&gt;&#xA;&lt;p&gt;Thanks in advance.&lt;/p&gt;&#xA;" OwnerUserId="6214" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2020-09-30T18:45:21.387" Title="ISS APRS Digipeater with Kam XL and ICOM IC-910H" Tags="&lt;aprs&gt;&lt;icom&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7200" PostTypeId="1" CreationDate="2017-02-09T20:23:00.547" Score="7" ViewCount="2908" Body="&lt;p&gt;Since I'm working with wireless communications, I decided it would be good to educate myself a little and at least get a basic understanding how does a Wi-Fi antenna work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My first question is about the most basic 2.4Ghz antenna that is usually attached to every cheap Wi-Fi router you can find on the market. I stumbled upon &lt;a href=&quot;http://www.allaboutcircuits.com/technical-articles/wi-fi-antennas-part-1-fundamentals/&quot; rel=&quot;noreferrer&quot;&gt;this link&lt;/a&gt;, which happily explains that the such antenna is a half wave dipole and has a picture of it removed from plastic cover, which is copied below. Everything's fine so far, except it's hard to not see that the length of one half of the dipole on the picture is ~25mm, but 1/4 wavelength of 2.4Ghz wave is ~30mm. &#xA;Does anyone know where does that difference come from?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9q1dA.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9q1dA.png&quot; alt=&quot;photo of typical WiFi dipole antenna with plastic cover removed&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next question is about high gain Wi-Fi antennas. I found a &lt;a href=&quot;http://www.instructables.com/id/Dipole-Antenna-for-2-4-ghz-Wifi/&quot; rel=&quot;noreferrer&quot;&gt;video&lt;/a&gt; showing internals of such antenna, and it turns out that the only difference is that one half of the dipole is longer and contains a coil. The author of the video says that it is a loading coil, and if I understand correctly they are used to shorten physical antenna length. But here the standard half-wave dipole was made longer. To summarize:&#xA;How does making the antenna longer increases its gain? And why in this case only one half of the dipole was made longer?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks in advance for explanation!&lt;/p&gt;&#xA;" OwnerUserId="9181" LastEditorUserId="4665" LastEditDate="2017-02-12T19:29:05.117" LastActivityDate="2017-02-13T19:54:20.690" Title="How does Wi-Fi antenna work?" Tags="&lt;antenna-theory&gt;&lt;wifi&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7202" PostTypeId="1" CreationDate="2017-02-10T07:08:17.460" Score="1" ViewCount="245" Body="&lt;p&gt;I have a designed an arrayed dipole antenna for transmitting in 200MHz frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where I am confused is, what should be my ground system for both antennas (Transmitting, and Receiving). Say I am sending 5V to my transmitting antenna, with real ground as reference to my antenna. But in the receiving antenna side, I can have, say Arduino ground as reference. Also in the receiving antenna side, I can measure the received voltage with reference to real ground as well. But in real ground case, the real ground does not guarantee that transmitting ground and receiving antenna ground is at the same potential.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am very confused on how to configure the reference points for sending and receiving voltages for both transmitting and receiving antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Help would be greatly appreciated.&lt;/p&gt;&#xA;" OwnerUserId="9075" LastActivityDate="2017-02-15T17:27:51.013" Title="Antenna Ground System" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7203" PostTypeId="2" ParentId="7202" CreationDate="2017-02-10T16:29:32.120" Score="3" Body="&lt;p&gt;Your antenna has two terminals. You will measure the received signal, or drive the transmitted signal, as a difference between these terminals. You need to be mindful of the kind of transmission line, and if this is a balanced or unbalanced system. But probably you'll couple to the antenna through a transformer so it won't matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coax is an unbalanced transmission line. The shield is held at ground potential. By that, I mean there is no voltage difference between the shield and Earth, the tower, the antenna, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neglecting biasing, impedance matching, and other details, you might drive it like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/zMKWY.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fzMKWY.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An issue is a dipole is a balanced antenna, so to feed it properly with coax &lt;a href=&quot;https://ham.stackexchange.com/q/7108/218&quot;&gt;you need a balun at the feedpoint&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately you can use &lt;a href=&quot;https://en.wikipedia.org/wiki/Twin-lead&quot; rel=&quot;nofollow noreferrer&quot;&gt;twin-lead&lt;/a&gt; and make it a balanced system all the way. That might look like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/w7Ver.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fw7Ver.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this balanced system, at every stage there is a positive polarity and a negative polarity half of the circuit, symmetrical in voltage and impedance relative to ground. There is no ground connection at the input or the output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In both cases, receiving looks the same except the receiving antenna is on the left, and the output is going to a demodulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This balanced system has a significant disadvantage: everything is twice as complicated. One way to convert between balanced and unbalanced is to feed  a balanced signal into a center-tapped transformer. The center tap, being halfway between the balanced inputs, is at ground potential.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is why a class-AB push-pull amplifier is a common final stage, looking (simplified) something like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/c4XqP.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fc4XqP.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a working example, see the &lt;a href=&quot;https://www.tapr.org/pdf/PennyWhistleManual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;HPSDR Pennywhistle schematic&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The input and output transformers do some nice things for us:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;block the DC bias&lt;/li&gt;&#xA;&lt;li&gt;allow for impedance matching by adjusting the turns ratio&lt;/li&gt;&#xA;&lt;li&gt;provide galvanic isolation&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Galvanic isolation is especially pertinent to your question. You'll notice there's no DC path from the amplifier to either the input or the output. So ground doesn't really matter: only the current through the transformer matters. So you can connect one end of either (or both) transformer to ground, or you can make a balanced connection and not connect ground at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, consider that noise on ground is still noise. With the antenna isolated with a transformer you can avoid any possibility of ground loops which will pick up noise, and it's easier to isolate the ground reference for the receiver front-end from the digital noise, etc that might be present elsewhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For receive you probably do not need a class-AB amplifier. More likely you'll stick with the class-A amplifier in the first example. It's pretty common to isolate the input from the antenna with a simple transformer even if it's not strictly necessary. This allows for a balanced or unbalanced input and isolates the DC grounds between the antenna and the receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-02-15T17:27:51.013" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7204" PostTypeId="2" ParentId="7200" CreationDate="2017-02-10T16:49:56.273" Score="4" Body="&lt;p&gt;Between lengths of infinitesimal and one wavelength, the lobes in the radiation pattern become narrower. Here's a &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;picture from antenna-theory.com&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/369dQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/369dQ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how for the 1-wavelength antenna, the lobes are skinnier than the 0.25-wavelength antenna. A 0.5-wavelength antenna is somewhere between the two. These patterns can be calculated from the current distribution on the dipole. The math isn't simple so refer to &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna-theory.com&lt;/a&gt; if you want the math.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming antennas with negligible losses (which these are), it's a fact that as the antenna pattern becomes narrower, gain in the peak direction increases. Gain can't increase in all directions because that would violate the law of conservation of energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the dipole becomes longer than 1 wavelength, the pattern starts growing extra lobes which aren't pointing in any useful direction. The maximum gain peaks around 1.25 wavelengths (see &lt;a href=&quot;https://ham.stackexchange.com/q/1142/218&quot;&gt;5/8 wavelength monopoles&lt;/a&gt;). Beyond that the lobes continue to get narrower, but also more numerous so peak gain does not increase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that explains why the higher gain antenna is longer, but why the coil? When a dipole is (approximately) a half-wavelength long, it's resonant and has a feedpoint impedance in the neighborhood of 75 ohms. This is a good match for most transceivers, so the antenna can be connected directly to the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At different lengths, the dipole itself is no longer resonant and the feedpoint impedance will be something else. As such, some additional impedance matching will be required to efficiently couple the antenna to the radio, and that's what the coil does.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-02-10T17:04:21.673" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7205" PostTypeId="1" AcceptedAnswerId="7383" CreationDate="2017-02-10T23:07:48.980" Score="2" ViewCount="615" Body="&lt;p&gt;How thick can the metal be for a common NMO antenna mount?  I know they're meant for sheet metal but can they go as thick as 1/4&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edited to add: &#xA;By &quot;common&quot;, I mean NOT the ones designed for extra think applications. If you look on Amazon, or anywhere else, you will see many NMO mounts from many vendors that all look exactly the same. They are the kind I mean. I would like to know how thick the metal can be for one of those.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Cclsx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Cclsx.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2017-02-14T15:58:32.007" LastActivityDate="2019-04-19T17:00:22.373" Title="Maximum Thickness for NMO Mounting Surface?" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7206" PostTypeId="2" ParentId="7205" CreationDate="2017-02-11T15:52:52.587" Score="1" Body="&lt;p&gt;How big can the cable be for a &quot;standard&quot; PL-259 connector? The standard specifies the mating interface, not the mounting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just as there is no &quot;standard&quot; cable size for a connector, there's no &quot;standard&quot; mounting thickness for an NMO mount. The only thing standardized is the part the antenna screws into.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to answer your question, you'll need to read the mechanical specifications for a specific mount. They come in all kinds. And yes, some can &lt;a href=&quot;http://www.americanradiosupply.com/opek-nmo-3-nmo-to-uhf-female-so-239-adapter-2-inch-long/&quot; rel=&quot;nofollow noreferrer&quot;&gt;accommodate thicknesses greater than 1/4&quot;&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-02-11T15:52:52.587" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="7207" PostTypeId="1" AcceptedAnswerId="7208" CreationDate="2017-02-11T23:36:46.453" Score="6" ViewCount="284" Body="&lt;p&gt;I recently bought a couple of 61-mix toroids, and as usual I wrote the mix number on them before they become mystery parts. However, the ink soaked right into the ferrite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've left ferrites hanging out in the weather, getting wet and frozen without issue, but never mix 61. Given their porosity, I'm concerned wet, freezing weather may fracture them. Anyone have experience to share on that point?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-02-11T23:49:04.067" Title="Are some ferrites porous enough they should be protected outside?" Tags="&lt;ferrite&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7208" PostTypeId="2" ParentId="7207" CreationDate="2017-02-11T23:49:04.067" Score="5" Body="&lt;p&gt;I've had a couple turn up cracked when left outside in an enclosure that wasn't waterproof, but I can't say if that was freezing that did it, or just thermal cycles on a compromised toroid causing stress. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These days I hit pretty much all of them with a light coat of decent spray paint, or even a light coat of flex-seal type sealant before putting them outside. I've never had a painted toroid break. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A quick test would be to weigh a dry toroid on a digital kitchen scale with 1 gram resolution or better, let it sit in a dish of water for a minute, dry it with a towel then weigh it again. If it's gained a measurable amount of weight, it probably pulled up enough water to exert some real force. &lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-02-11T23:49:04.067" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7209" PostTypeId="2" ParentId="1710" CreationDate="2017-02-12T13:09:30.460" Score="-1" Body="&lt;p&gt;First of all, I am a Ham Radio Operator of 25 years. PER THE FEDERAL LAW covering amateur radio, PART 97, (get a copy and read it) There is NO law that says You can't set up a repeater unless it is coordinated by a local council or anyone else. You look on your frequency allocation chart from the FCC and you look at the frequencies that the FCC says you can use for repeaters. Make sure you listen to that pair of frequencies for at least 30 days and make sure nobody comes along and tries to use it. You can even do this with two frequencies from a repeater that nobody has been heard using for 30 days. The law does not even have to say you have to do these last two things but it would be a good idea. But no Ham Radio Operator can ever have any kind of ownership of any frequency. As long as you are not intentionally interfering with another ham while he or she is talking, A Ham radio operator has a right to talk on any Ham radio freq anywhere with a set aside use for voice usage by the FCC.&lt;/p&gt;&#xA;" OwnerUserId="9187" LastActivityDate="2017-02-12T13:09:30.460" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7210" PostTypeId="2" ParentId="7200" CreationDate="2017-02-12T15:02:30.600" Score="4" Body="&lt;p&gt;This is the 2nd antenna of the question (screenshot from video linked in the question).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ACT1A.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ACT1A.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below are simulation results of an antenna similar to the one above. Although simulated antenna is not for WiFi 2.4 GHz (it is for ADS-B, 1.090 GHz), this simulation gives a general idea of characteristics of this type of antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simulated antenna has two vertical sections, a coil and decoupling sleeve. Upper vertical wire is slightly longer than 5/8 λ. while lower vertical is slightly longer than 1/8 λ. The coil between two vertical section is used for phase-shifting the currents, as well as impedance matching. The decoupling sleeve is 1/4 λ in length. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;i&gt;CLICK ON IMAGES BELOW TO SEE FULL SIZE&lt;/i&gt;&lt;/strong&gt;&lt;br&gt;&#xA;.&lt;br&gt;&#xA;.&lt;br&gt;&#xA;&lt;strong&gt;Image 1 of 2 - Gain, SWR, Radiation Pattern&lt;/strong&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/GsRGw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GsRGw.png&quot; alt=&quot;Wire collinear antenna with decoupling sleeve&quot;&gt;&lt;/a&gt;&#xA;.&lt;br&gt;&#xA;.&lt;br&gt;&#xA;.&lt;br&gt;&#xA;&lt;strong&gt;Image 2 of 2 - Current Distribution&lt;/strong&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/WqOds.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WqOds.png&quot; alt=&quot;Current Distribution&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="9029" LastEditDate="2017-02-12T21:36:54.490" LastActivityDate="2017-02-12T21:36:54.490" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7211" PostTypeId="1" CreationDate="2017-02-12T21:50:14.583" Score="4" ViewCount="743" Body="&lt;p&gt;There are a variety of websites that give sample SmartBeaconing™ settings – mostly for &lt;a href=&quot;http://info.aprs.net/index.php?title=SmartBeaconing&quot; rel=&quot;noreferrer&quot;&gt;automobiles&lt;/a&gt;, but some for &lt;a href=&quot;https://softsolder.com/2010/08/24/aprs-smartbeaconing-parameters-for-bicycling/&quot; rel=&quot;noreferrer&quot;&gt;bicycles&lt;/a&gt; and pedestrians.  I've tried several of these settings and had mixed results.  Can anyone share a set of experimentally-verified ideal settings for any of the following?&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Driving on-road&lt;/li&gt;&#xA;&lt;li&gt;Driving off-road&lt;/li&gt;&#xA;&lt;li&gt;Walking on streets&lt;/li&gt;&#xA;&lt;li&gt;Hiking&lt;/li&gt;&#xA;&lt;li&gt;Bicycling on streets&lt;/li&gt;&#xA;&lt;li&gt;Bicycling on trails&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Assume that we're within the coverage area of a moderate-traffic digipeater (my reference is &lt;a href=&quot;http://aprs.fi/info/?call=N7HND&quot; rel=&quot;noreferrer&quot;&gt;N7HND in Tucson&lt;/a&gt;), so we can be reasonably certain that most of our packets will get through, and we don't want to flood the frequency.  In other words, this is not a question about how to configure a mobile APRS station for best coverage, but about how best to take advantage of an effective station setup.&lt;/p&gt;&#xA;" OwnerUserId="6446" LastActivityDate="2018-05-14T18:19:40.617" Title="What are the best APRS SmartBeaconing™ settings for different modes of transit?" Tags="&lt;ht&gt;&lt;mobile&gt;&lt;aprs&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7212" PostTypeId="1" CreationDate="2017-02-13T00:28:28.097" Score="3" ViewCount="1370" Body="&lt;p&gt;I'm playing around with an &lt;a href=&quot;http://www.sdrplay.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;SDRPlay&lt;/a&gt;. I'm using the &lt;a href=&quot;http://cubicsdr.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;CubicSDR&lt;/a&gt; app, and I'm tuning around the HF bands. I get to 5.650 MHz and I see this: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qJ5Td.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qJ5Td.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This looks like a bunch of discrete RTTY signals. How would I go about identifying and decoding some of these signals? &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.dropbox.com/sh/87v1hoz0fqgws4l/AAAkr_J1nAp6AR76BmHNYPeBa?dl=0&amp;amp;preview=Unknown-RTTY-1-5600kHz-2-12-17.m4a&quot; rel=&quot;nofollow noreferrer&quot;&gt;Audio sample 1&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.dropbox.com/sh/87v1hoz0fqgws4l/AAAkr_J1nAp6AR76BmHNYPeBa?dl=0&amp;amp;preview=Unknown-RTTY-2-5600kHz-2-12-17.m4a&quot; rel=&quot;nofollow noreferrer&quot;&gt;Audio sample 2&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Things I tried:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;I looked through the &lt;a href=&quot;http://qrg.globaltuners.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Globaltuners Frequency Database&lt;/a&gt;. 5600 kHz appears to be an &lt;a href=&quot;http://qrg.globaltuners.com/?q=5.65&quot; rel=&quot;nofollow noreferrer&quot;&gt;aeronautical band&lt;/a&gt;:&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MN4cv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MN4cv.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to &lt;a href=&quot;http://wiki.radioreference.com/index.php/MWARA&quot; rel=&quot;nofollow noreferrer&quot;&gt;this site&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;MWARA is the term for Major World Air Route Areas, which support HF Radio communications to aircraft outside of VHF range.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;&lt;p&gt;I looked around for aeronautical data formats, and found &lt;a href=&quot;http://www.sigidwiki.com/wiki/High_Frequency_Data_Link_(HFDL)&quot; rel=&quot;nofollow noreferrer&quot;&gt;HFDL&lt;/a&gt;, however these signals look and sound nothing like that format. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I opened up the &lt;a href=&quot;http://www.sigidwiki.com/wiki/Category:MF&quot; rel=&quot;nofollow noreferrer&quot;&gt;Signal Identification Wiki&lt;/a&gt; and looked for signals that appeared to have the same frequency spectrum. Each of these signals seems to have a clear signal of two tones, which confirmed my suspicions that it might be &lt;a href=&quot;http://www.sigidwiki.com/wiki/Radio_Teletype_(RTTY)&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTTY&lt;/a&gt;. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I ran &lt;a href=&quot;http://www.w1hkj.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;fldigi&lt;/a&gt; in RTTY mode and tried to decode one of the signals, but it didn't produce anything intelligible. But I may be in the wrong mode, or this is a proprietary protocol, or ... ?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;How can I systematically what this signal might be? For example step 1 is it FSK? Step 2 how many tones does it use? Step 3 what is the frequency separation? Step 4 what known protocols have these parameters? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any software packages that can do this? &lt;/p&gt;&#xA;" OwnerUserId="8284" LastActivityDate="2017-02-13T13:51:11.673" Title="How do I go about identifying an unknown digital signal?" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;&lt;hf&gt;&lt;software&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7214" PostTypeId="2" ParentId="7212" CreationDate="2017-02-13T13:51:11.673" Score="1" Body="&lt;p&gt;Unfortunately, I don't know of any free and easy to use software that does all the signal identification you need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do know of some free programs that can help you with some of the steps involved. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One is &lt;a href=&quot;http://www.sillanumsoft.org/download.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Visual Analyzer&lt;/a&gt;. It can show you the spectrum of your audio over time. By looking at the spectrum of your signal, you'll be able to see the number of tones and their individual frequencies, if your settings are correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option, which I personally didn't use all that much is &lt;a href=&quot;http://www.qsl.net/dl4yhf/spectra1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Spectrum Lab&lt;/a&gt;. It provides similar environment to Visual Analyzer, but has some extra options related to very fast and very slow Morse code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the programs I mentioned, you'll have a chance of seeing what type of modulation it is. In your case, it's a 2-FSK, which is visible from two clear peaks in the spectrum. The frequency separation can be directly read from the spectrum views programs provide. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One piece you didn't ask, but is important, is the symbol rate. As of yet, I don't know a smart way to determine it. One thing that helps, when you have high signal-to-noise ratio is to use matched filters in FL-DIGI. Usually, the tone filter size on the spectrum will match the bandwidth, but this is still very rough method. Another thing I used was to load the files in &lt;a href=&quot;https://sourceforge.net/projects/audacity/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Audacity&lt;/a&gt; and try to guesstimate the symbol period by looking at the waveforms. The bad side of both is that they're very rough. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't forget that it's possible that your high and low frequencies could be inverted, compared to what the demodulator in FL-DIGI expects. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the part 4, usually you'll need to search the Internet using the shift, baud rate and frequency and hope that a protocol will come up.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2017-02-13T13:51:11.673" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7215" PostTypeId="2" ParentId="7200" CreationDate="2017-02-13T19:03:30.047" Score="4" Body="&lt;p&gt;The antenna in photo below is the 1st antenna of the question. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/s1nKB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/s1nKB.png&quot; alt=&quot;Wi-Fi 2.4GHz 0.5 Wavelength Dipole&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is supposed to be 1/2λ long (radiator+sleeve). However its length is 2x25 mm instead of 2x30 mm. The antenna will still work even if its length is different from 1/2λ. However the impedance/swr of antenna changes as the length changes. When dipole's length is exactly 1/2λ, its impedance is 75 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please see sketch below which shows Gain &amp;amp; Radiation pattern for dipoles of lengths from 0.12λ to 1.25λ (total of both limbs):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;CLICK ON IMAGES BELOW TO SEE LARGER SIZE&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/arDfP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/arDfP.png&quot; alt=&quot;Dipole length vs radiation pattern&quot;&gt;&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dipole SWR vs Length (0.1λ ~ 2.1λ)&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Eqthn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Eqthn.png&quot; alt=&quot;dipole swr vs length&quot;&gt;&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dipole Gain vs Length (0.1λ ~ 2.1λ)&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Fi5Bm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Fi5Bm.png&quot; alt=&quot;dipole gain vs length&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dipole Impedance vs Length (0.1λ ~ 2.1λ) &#xA;&lt;a href=&quot;https://i.stack.imgur.com/xioTW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xioTW.png&quot; alt=&quot;dipole impedance vs length&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="9029" LastEditDate="2017-02-13T19:54:20.690" LastActivityDate="2017-02-13T19:54:20.690" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7216" PostTypeId="1" CreationDate="2017-02-14T01:34:52.933" Score="4" ViewCount="246" Body="&lt;p&gt;A local ham friend copied this strange, wide signal on 30 meters on his Flex 5000. Anybody know what it might be?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bHu3d.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bHu3d.jpg&quot; alt=&quot;Flex spectrogram of wide, unknown signal&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="4076" LastEditDate="2017-02-14T11:33:07.153" LastActivityDate="2017-02-20T15:06:07.877" Title="Very odd and wide 30m signal. What is it?" Tags="&lt;software-defined-radio&gt;&lt;hf&gt;&lt;signal-identification&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7217" PostTypeId="2" ParentId="7195" CreationDate="2017-02-14T01:38:02.433" Score="1" Body="&lt;p&gt;I believe in Great Britain if ham moves or travel to other area he has to change prefix.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2017-02-14T01:38:02.433" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7218" PostTypeId="2" ParentId="7216" CreationDate="2017-02-14T07:59:04.750" Score="5" Body="&lt;p&gt;If I read the instrumentation correctly, this is but 20 kHz; that's pretty wide for what I'd expect for Ham operation on HF. It's not &quot;very wide&quot; per se. (I'd define &quot;wide&quot; based on the ratio of bandwidth to center frequency, and that's but 0.2% here.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This looks a bit like an OFDM signal, especially with the hints of side lobes. 20 kHz OFDM in HF sounds a lot like &lt;em&gt;Digital Radio Mondiale&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know of any specific allocation of 10 MHz spectrum to broadcast licensees. However, since there is a really good free and open source DRM transmitter, built atop of GNU Radio, named &lt;a href=&quot;https://github.com/kit-cel/gr-drm&quot; rel=&quot;nofollow noreferrer&quot;&gt;gr-drm&lt;/a&gt;, this might very well be legitimate Ham usage; admittedly, using the high-quality channel mode for DRM does use a lot of bandwidth compared to a classical AM voice channel, but at the same SNRs, DRM sounds worlds superior if using the right voice codecs. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In Germany, for example, 10.000 – 10.150 MHz is reserved to FESTER FUNKDIENST (fixed radio service) application with &quot;messages to one or multiple recipients&quot; as primary, and Amateur Radio as secondary usage. &lt;a href=&quot;https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Frequenzplan.pdf;jsessionid=3CFE9215100CB1B4BA0C2A549FD74FE8?__blob=publicationFile&amp;amp;v=9&quot; rel=&quot;nofollow noreferrer&quot;&gt;p. 94 of the Frequenzplan&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-02-14T18:09:25.823" LastActivityDate="2017-02-14T18:09:25.823" CommentCount="12" ContentLicense="CC BY-SA 3.0" />
  <row Id="7220" PostTypeId="2" ParentId="7192" CreationDate="2017-02-14T13:58:02.593" Score="2" Body="&lt;p&gt;Amodem can be used to transmit at arbitrary baudrates on any transceiver with a TRS port, 3.5mm or 2.5mm, or any other kind. Can take a while, but the data arrives. Includes a checksum (as does zip/rar/7z/etc archives). I've transmitted a few MB on UHF, wasn't a problem. You'll need a computer on either end, a lowly PI would probably suffice. It doesn't use much CPU. You can test the program with a 3.5mm TRS on your PC, output to input. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hint: Start with lowest baudrate and go up from there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://github.com/romanz/amodem&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/romanz/amodem&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: Anything above 50KB, I'd chop up using a file splitter, since otherwise you'll be retransmitting a lot if using it at high range. 1200 baud can go 20km no problem if you have decent rx/tx antennas&lt;/p&gt;&#xA;" OwnerUserId="7957" LastEditorUserId="7957" LastEditDate="2017-02-14T14:43:59.660" LastActivityDate="2017-02-14T14:43:59.660" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7221" PostTypeId="2" ParentId="7195" CreationDate="2017-02-14T14:21:33.043" Score="2" Body="&lt;p&gt;Canada (Industry Canada) also requires amateur radio certificate holders to change call signs when they move to a different call sign prefix area&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf02102.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;RIC-9 — Call Sign Policy and Special Event Prefixes&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2017-02-14T14:21:33.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7222" PostTypeId="2" ParentId="6160" CreationDate="2017-02-14T14:25:55.963" Score="4" Body="&lt;p&gt;The VSWR isn't the problem &lt;em&gt;per se&lt;/em&gt;, it's just the impedance that appears at the transmitter's terminals. Take the load at the end of the transmission line, transform it according to the electrical length of the feedline, and put that equivalent impedance right at the transmitter's terminals and you will have the same damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A particular VSWR can result in a range of impedances. For example 5:1 on a 50 ohm line can mean 10 ohms, 250 ohms, and a range of complex impedances in between. Some of those impedances may damage the transmitter, others may not. But since the length of the feedline isn't known, it's safest to keep the VSWR low.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So why can a mismatched load cause damage? In summary, the transmitter's final stage is made of reactive components, that is components that store and release energy. These reactive components are selected to have the load absorb some of that stored energy. Without that load absorbing energy, the energy instead appears as a high voltage or high current to appear somewhere which may not be equipped to handle it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's give a very simple example to illustrate: a very simplified class-C common-source amplifier. You've probably seen such amplifiers with a resistor in place of L1, but for power amplifiers it's more common to use inductors to avoid the associated resistive losses.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/YVfW7.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fYVfW7.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the transistor is on, current through L1 increases and L1 stores energy. Let's say it's on long enough for current through L1 to rise to 1A. When the transistor is off, the voltage across the load will rise to 50V, because that's what it takes for 1A to pass through 50Ω. So we need M1 to have $V_\text{ds(max)} &amp;gt; 50\:\mathrm V$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens if the load is open? Since no current can flow through the load, the voltage will rise even higher, whatever it takes to get 1A to continue flowing through L1. In this case it will be whatever voltage causes M1 to go into avalanche breakdown. RF power transistors aren't usually avalanche rated, so this means damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can imagine other situations that lead to excessive drain current in M1 as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, a real transmitter will be more complicated. It will probably have a low-pass filter on its output, multiple transistors with complex impedances at RF, and more reactive components within for impedance matching and filtering. All these values are selected with the assumption of a 50 ohm resistive load. Which load impedances will cause failure depend on the particular topology of the amplifier.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-02-14T14:25:55.963" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7223" PostTypeId="1" AcceptedAnswerId="7224" CreationDate="2017-02-14T23:10:08.150" Score="3" ViewCount="883" Body="&lt;p&gt;I tried to make a dual-band (2m/70cm) dipole this morning by following the instructions on this page: &lt;a href=&quot;http://www.amateurradio.bz/2m-70cm_vertical_dipole_antenna.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.amateurradio.bz/2m-70cm_vertical_dipole_antenna.html&lt;/a&gt;, with the rather major significant exception of placing the antenna's elements in a groove I routed out of a 2x4 and I'm using bare #10 copper wire instead of stainless steel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I plugged a VNA into it and the antenna's lowest SWR was ~1.09 at ~124MHz. I tried it in a couple different environments and orientations and made sure there wasn't anything conductive right near the antenna (other than the wood, which I'm expecting to reduce the effective velocity factor of the wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since I have no shortage of #10 wire, I started trimming the ends in 1/2&quot; increments. I got the lowest SWR to 1.04 at 148MHz... but only while horizontal! Orienting the antenna vertically causes the lowest SWR point to jump to 1.52 at 153MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's happening here? Why was the tuning so far off? Is it the wood? Is it the copper wire? Why does orientation affect the tuning so much? I know I've got a lot of variables here, but is there one that is obviously the most important difference?&lt;/p&gt;&#xA;" OwnerUserId="6295" LastActivityDate="2017-03-13T17:08:26.920" Title="Unexpected Resonance - Dual-Band Dipole" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;impedance&gt;" AnswerCount="3" CommentCount="8" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7224" PostTypeId="2" ParentId="7223" CreationDate="2017-02-15T01:48:26.487" Score="1" Body="&lt;p&gt;It was the wood!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may &lt;em&gt;also&lt;/em&gt; be the fact that I'm using copper wire instead of stainless steel rod, but I can't test that as I don't have access to any stainless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further experimentation this evening show much more predictable results. While I thought the 2x4 would be relatively transparent to RF, simply being near the 2x4 seems to cause the whole system to seem electrically much longer than it is, thus making the antenna very difficult to tune.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At first, I thought that it was conducting RF to the wood because the wire was bare, but I cut new elements just now out of my solid-core #10 THHN, this time leaving the THHN on everywhere except where the bolts contact the wire and had basically the same results. Bending the wire away from the wood such that the tips of the dipole (where voltage is highest?) caused the match to jump from 118MHz to 137MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My best guess here is that the lumber is not fully dried and whatever water left in it is causing it to be a (poor) conductor, causing some capacitative coupling. I'd still love for anybody with more experience to chime in though, as I'm just guessing and am pretty new to making antennas.&lt;/p&gt;&#xA;" OwnerUserId="6295" LastActivityDate="2017-02-15T01:48:26.487" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="7225" PostTypeId="1" AcceptedAnswerId="7226" CreationDate="2017-02-15T20:34:28.217" Score="14" ViewCount="11555" Body="&lt;p&gt;In &lt;a href=&quot;https://ham.stackexchange.com/questions/7223/unexpected-resonance-dual-band-dipole&quot;&gt;another question&lt;/a&gt;, commenters recommended that I look into adding a 1:1 balun to a dual-band dipole to eliminate the feedline as a radiator. As I understand it, a 1:1 balun also functions as a choke, but is more efficient because... reasons?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I try to find plans to build a balun, they all seem to specify a frequency range of 1.6-30MHz. Why is that and how can I make a balun that will work on VHF and UHF?&lt;/p&gt;&#xA;" OwnerUserId="6295" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2020-12-06T00:50:54.783" Title="Where are the baluns for VHF and higher? How can one be made?" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;balun&gt;&lt;filter&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7226" PostTypeId="2" ParentId="7225" CreationDate="2017-02-16T02:05:20.403" Score="4" Body="&lt;p&gt;Let's clarify some terminology: a balun is any device used to convert between a balanced system (ladder line, dipoles) and an unbalanced one (coax, vertical monopoles). There are a lot of ways to make a balun, and a common-mode choke is one of them. A choke can also be used in balanced to balanced, or unbalanced to unbalanced connections where suppression of common-mode currents is merited.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The choke approach (or &quot;current balun&quot; as you'll sometimes hear it described) is nice because it's small, easy to fabricate, broadband, and low-loss. &quot;Small&quot; is especially an advantage on HF where other balun designs would be huge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ferite-wound chokes can be done on VHF as well. Jim Brown, K9YC has some &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;measured data on ferrites&lt;/a&gt;. Look for page 49. His data show that Fair-Rite mixes 31, 43, and 61 can all be made to work. He shows for a T240 core of any of those mixes, you can get about 600Ω on 2m with 2 turns, and 300Ω with one turn on 70cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the effective permeability of ferrites drops with increasing frequency, so it becomes difficult to get a sufficiently high choking impedance for the choke to function effectively as a balun. 300Ω isn't great but might be sufficient for some applications. You can always &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measure and see&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, VHF wavelengths are small enough that other balun designs become practical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One approach is to keep the system unbalanced all the way. If you have an unbalanced coax feedline, then put an unbalanced monopole antenna on it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Antenne_gp_vhf_3.jpg#/media/File:Antenne_gp_vhf_3.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/6/6b/Antenne_gp_vhf_3.jpg&quot; alt=&quot;Antenne gp vhf 3.jpg&quot;&gt;&lt;/a&gt;&lt;br&gt;By &lt;a href=&quot;//commons.wikimedia.org/wiki/User:F1jmm&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;User:F1jmm&quot;&gt;F1jmm&lt;/a&gt; - Own work • Self-photographed, &lt;a href=&quot;http://creativecommons.org/licenses/by-sa/3.0&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Creative Commons Attribution-Share Alike 3.0&quot;&gt;CC BY-SA 3.0&lt;/a&gt;, &lt;a href=&quot;https://commons.wikimedia.org/w/index.php?curid=11943336&quot; rel=&quot;nofollow noreferrer&quot;&gt;Link&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The three drooping wires are the &quot;ground plane&quot;. Drooping them increases the feedpoint impedance from the 37Ω of a monopole on a flat ground plane to 50Ω for a better match. Since the ground plane presents a very low impedance to the ground currents, that's where most of the current will flow. The coax common-mode is a relatively high impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some antenna designs which aren't simple monopoles use a &quot;skirt&quot; which looks like radials on a monopole. As in the monopole, the skirt looks like a low impedance ground plane, and the feedline is &quot;hidden&quot; under it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other designs are the &lt;a href=&quot;https://ham.stackexchange.com/q/3591/218&quot;&gt;folded balun&lt;/a&gt;, and the &lt;a href=&quot;https://ham.stackexchange.com/a/7053/218&quot;&gt;folded dipole&lt;/a&gt;. These designs work by getting the coax to attach at a ground potential point, while creating such a point through some clever arrangement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;a href=&quot;https://ham.stackexchange.com/a/7061/218&quot;&gt;sleeve balun&lt;/a&gt; is another possibility. It uses a quarter-wave stub to insert a high impedance in the common-mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There some antenna designs out there that claim no balun is necessary. Sometimes it's true (the balun is intrinsic in the design) and sometimes it's not. Look for an antenna model that contains a feedline such as &lt;a href=&quot;https://www.w8ji.com/end-fed_vertical.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI did with the J-pole&lt;/a&gt;. Or build the antenna and &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measure the common-mode current yourself&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2017-02-16T02:05:20.403" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7227" PostTypeId="2" ParentId="259" CreationDate="2017-02-16T10:08:14.040" Score="0" Body="&lt;p&gt;when I started out listening to the short-wave, many years ago, I quickly found out that when I used a second receiver, placed next to each other, I was able to pick up the local oscillator from it, and carefully tune it on top of an SSB station, and lo and behold, it suddenly became intelligible.&#xA;I haven't tried that method for years now, but if it worked in the 1980's I believe it will still work today!&#xA;(SSB on shortwave, using 2 AM radio receivers with shortwave coverage, such as 14MHz, 7MHz)&#xA;No modifications required whatsoever!&lt;/p&gt;&#xA;" OwnerUserId="9211" LastActivityDate="2017-02-16T10:08:14.040" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7228" PostTypeId="1" CreationDate="2017-02-16T13:04:10.853" Score="2" ViewCount="245" Body="&lt;p&gt;I need a HF link that will be (mostly hah) operational 24/365. &lt;strong&gt;Edit:&lt;/strong&gt; at least at local daytime.&#xA;The link is supposed to transmit a controlling signal (just one bit) in one direction for quite a distance (appr. 2000km &lt;strong&gt;Edit:&lt;/strong&gt; appr.2500km) with the lowest latency possible.&#xA;Due to the latency constrain filtering must not take longer than 1ms, if even 1 ms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may be a mistake, but I don't want to use any kind of FM, as it will require constant transmitting, and I only need to send the signal ~100 times a day.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I can use directional antennas. &lt;/li&gt;&#xA;&lt;li&gt;I can not use more than 1kW&#xA;transceivers. &lt;/li&gt;&#xA;&lt;li&gt;I can use several trancievers on differt bands in&#xA;parallel.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What else can I do?&#xA;How should I modulate the signal?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S. I considered other options, such as GSM, sat, fiber channel, etc, but unfortunately they are not fast enough. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reliability of 0.8 would be supergeil. (If 0.4 is the very top, I'll have to take it as well)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.P.S. About the nature of the link - you can think of an experimental setup that generates data, computer processes it in no time and generates an output - 0 or 1 (mostly 0's). On the receiving end there's other setup and it takes this 0 or 1 as an input.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPD:&lt;/strong&gt; I guess, I've chosen not the best question statement. Of course, the thing I'd like keep at minimum is the overall latency. As the propagation latency is fixed, we need to sort out the transmitting and receiving latencies, which I'd &lt;em&gt;wish&lt;/em&gt; to cram into just ~1ms (however, I've mentioned only receiving part in the original question above). The question is titled as it is in order to avoid (in other cases useful) advices to extend transmitting time to the fantastic values and gain almost 100% reliability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Add:&lt;/strong&gt; Given the power, there seems to be a technical contradiction between the transmission duration (and therefore latency) and reliability. Well, I'd like to optimize them both :)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Another thing about the processing latency constraint is the test I made on a couple of Yaesu's that I told about below in comments. The test shown that it've taken about 4ms on the receiving end to process the SSB signal, which seems a lot to me.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Also,&lt;/strong&gt; I'd prefer to keep the transmitting antenna complex on the smaller side to the possible extent.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPD2:&lt;/strong&gt; Now that I've received a couple of such wonderful and clarifying answers, I'd be more than grateful to receive suggestions about specific equipment suitable for making smaller-scale prototype – SDRs and antenna setups. &lt;/p&gt;&#xA;" OwnerUserId="8879" LastEditorUserId="8832" LastEditDate="2017-08-09T16:44:33.417" LastActivityDate="2017-08-09T16:44:33.417" Title="(HF) How to maximize probability of successful transmit given constrained packet duration?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;modes&gt;&lt;equipment&gt;" AnswerCount="2" CommentCount="13" ClosedDate="2017-02-17T16:26:12.147" ContentLicense="CC BY-SA 3.0" />
  <row Id="7229" PostTypeId="2" ParentId="7228" CreationDate="2017-02-16T14:16:49.397" Score="2" Body="&lt;p&gt;You state that you need the signal to be processed as quickly as possible, but you don't state how long the signal can take to be actually transmitted. Do you need the entire TX/RX process to occur in that 1mS? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, I think it quite unlikely that you'll achieve the desired reliability on HF, regardless of your modulation method. At this point in the solar cycle, 7-10MHz is the only frequency range that is likely to support that long of a link reliably via ionospheric propagation, and even the top end of that range will likely be unusable for several hours a day (in the very early morning hours local time) as the MUF will drop well below 10MHz over night more and more frequently as the solar cycle approaches minimum in a few years. Already it is occasionally dipping down to 8MHz. The low end of that 7-10MHz range will likely struggle to maintain the link during mid-day hours due to high D layer absorption. This seems to mean that the only viable option would be to have a frequency agile system that can determine what band currently supports the link with the available hardware, and that would not be a particularly simple task.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A further (and probably more vexing) problem is going to be noise. If you need the entire TX and RX process to occur that quickly, your signal will never be heard above the ambient noise floor even in the best of circumstances. &lt;em&gt;LOTS&lt;/em&gt; of stuff causes bursts of noise across the HF spectrum, with the noise becoming worse as frequency drops. Lightning can be heard for &gt;1,000km even on 7MHz, high energy cosmic rays can cause random static crashes, ionosondes generate rapidly sweeping tones, geomagntic disturbances can wipe out the entire HF spectrum for days at a time with deafening noise and high absorption, and nearby electronics and power transmission systems can create pops, chirps, buzzing, static, and tones varying in frequency and intensity with no real predictability. Your receiving system would have to be able to tell the difference between the signal you sent, and that continuous barrage of random noise, much of which will be similarly brief in duration on any given narrow sliver of spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That doesn't even touch Sudden Ionospheric Disturbances/Solar flares, multi-path propagation, geomagnetic storms, and atypical ionospheric propagation modes like scatter and ducting that can cause sudden and spectacular variation in received signal strength (variation in received signal strength of &gt;20dB in a matter of seconds is not all that uncommon) and noise level on single frequencies or across the entire HF spectrum at once.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hams deal with this issue primarily by using extremely narrow signals with a bandwidth of just a few Hz to a few hundred Hz, at low data rates. A JT9 signal is just 9Hz wide, and takes a full minute to send a few hundred bits. It can frequently support contacts &gt;3,000km with just a few watts and a fairly poor antenna, even in marginal conditions. A QRSS30 CW transmission takes 30 seconds to send a single bit, and can support worldwide links with just a few watts on modest antennas in all but the most extreme propagation conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can transmit a much longer signal (a few tens of milliseconds at least) and average it at the receiver, a frequency agile system with good antenna diversity may be able achieve quite good reliability when averaging it over days, especially during local winter when thunderstorms tend to be less common (unless you're in the tropics, then you're probably hosed). During the summer or during periods of high solar activity, it could prove more challenging.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are constrained to a very fast transmit and receive cycle overall, even a system like WWV/WWVB, which uses tens of thousands of watts on very good antennas, could see 24 hour average reliability swinging from 0% to 50% from one day to the next, and I strongly suspect that achieving better than perhaps 60% would be next to impossible. It is not really exaggeration to say that the entire universe conspires to generate noise on HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; Thinking on this a bit more, it might &lt;em&gt;JUST&lt;/em&gt; be possible to make a 1mS frame work at least sometimes using an intelligent, frequency agile system that can evaluate band conditions on the fly to choose 3 or more frequencies to transmit on at once. By combining the signals on multiple frequencies, you could eliminate a significant portion of the random noise, however this would be a rather demanding process. Accomplishing it within the allotted window would be an impressive feat. Large scale ionospheric disruptions, which tend to occur at least once a month and last anywhere from a few hours to a few days would still render the system inoperable, however.&lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="246" LastEditDate="2017-02-16T14:33:32.447" LastActivityDate="2017-02-16T14:33:32.447" CommentCount="14" ContentLicense="CC BY-SA 3.0" />
  <row Id="7230" PostTypeId="2" ParentId="7228" CreationDate="2017-02-16T16:27:43.317" Score="2" Body="&lt;p&gt;Well the obvious: 2000 km is 6.7 ms at the speed of light, minimum. That's assuming a straight-line path through a medium with velocity factor 1. So a latency of 1 ms is impossible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides that, you can do the obvious things to maximize your chances:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;use maximum transmit power&lt;/li&gt;&#xA;&lt;li&gt;use the highest gain antennas possible&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Minimizing your latency you'll want to implement the demodulation in an FPGA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You would want to transmit all the time. It's a general rule that the more you know about what you are looking for, the easier it is to find. By transmitting all the time you can maintain synchronization between the receiver and transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Synchronization comes in many forms. The more obvious are time and frequency. Path polarization on HF is changing all the time, so you'll also want to use an &lt;a href=&quot;http://www.antenna-theory.com/arrays/weights/lms.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;adaptive array&lt;/a&gt; to mitigate this. An adaptive array will also mitigate multipath interference, which is also constantly changing on HF. Transmitting all the time allows the parameters of that array to already be synchronized when it comes time to transmit the bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use simulations like &lt;a href=&quot;http://www.voacap.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt; to predict what bands will work best at which times of day. You'll want the capability to switch bands dynamically, since conditions often deviate from the predictions. You'll also need to avoid interference from other stations. Transmitting all the time, you can negotiate the best frequencies before you need to send the bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Diversity_scheme&quot; rel=&quot;nofollow noreferrer&quot;&gt;Frequency diversity&lt;/a&gt; is a good idea. Although spreading the signal out over a wider bandwidth increases the noise power in the channel, the signal among all the possible frequencies is coherent, achieving a &lt;a href=&quot;https://en.wikipedia.org/wiki/Process_gain&quot; rel=&quot;nofollow noreferrer&quot;&gt;process gain&lt;/a&gt; that offsets the loss from increased noise power. This doesn't improve your SNR at all, but it does make your signal more robust against narrow-band interference and fading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might experiment with including multiple bands in your frequency diversity, though there's a tradeoff between diversity and wasting some of your transmit power on a band that's not the most effective. If you're using the idle time to dynamically find the best band, it might be better to concentrate all the power into the band you've determined works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as modulation, I don't think there's anything unique about your situation. Just pick some existing modulation and transmit zeros until you need to transmit a 1. To reduce the latency you would want to pick a symbol rate much faster than 1/1ms so you don't waste time waiting for the next symbol to start. But when the event happens, you can transmit consecutive 1s. The receiver would then count the number of 1s versus 0s, and make some decision based on that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You have a tradeoff to make between latency and accuracy here: some of the bits will be wrong, so if you trigger on just one 1 bit, you'll get false triggers. Waiting for a larger number of consecutive 1s will increase accuracy, but you'll have to wait longer to reach that threshold.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All these things together, you shouldn't have any difficulty achieving your goal, except when solar storms knock out the entire HF spectrum. Even then, you might overcome it with brute force. With a 1kW transmitter (60dBm) plus a 10dB gain antenna on each end, you have an &lt;a href=&quot;https://en.wikipedia.org/wiki/Equivalent_isotropically_radiated_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;EIRP&lt;/a&gt; of 80dBm, which is huge. HF path loss predictions such as VOACAP don't assume adaptive arrays, so add maybe another 2-8dB of diversity gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is just an insane amount of power, and with adaptive techniques you should be able to mitigate most of the things that could go wrong to a large extent. In fact, you probably want to use the adaptive logic to &lt;em&gt;reduce&lt;/em&gt; power under most situations, both to avoid overloading your neighbor's receivers, and also to reduce your electric bill.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-02-16T16:27:43.317" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7231" PostTypeId="1" AcceptedAnswerId="7232" CreationDate="2017-02-16T17:54:06.970" Score="4" ViewCount="914" Body="&lt;p&gt;What signal characteristics in an SDR receiver signal path should be evaluated or computed to determine whether the audio output should be squelched or not?  What sort of computed result should be compared against a scalar squelch &quot;knob&quot; setting?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume that for FM signals, the software should look at some characteristic in the demodulated audio data stream rather than in the IQ data stream for this determination.  Is this correct?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I am looking for algorithms, not any pre-coded solutions or circuits, as my goal is to write my SDR app in 100% Swift 3.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2017-02-16T18:24:46.753" LastActivityDate="2017-02-16T18:44:33.740" Title="FM squelch SDR algorithm?" Tags="&lt;software-defined-radio&gt;&lt;fm&gt;&lt;squelch&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7232" PostTypeId="2" ParentId="7231" CreationDate="2017-02-16T18:12:28.593" Score="5" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The simplest squelch, applicable to almost all modes, and the one provided by most amateur radios' “squelch knob” as far as I've experienced, is power squelch: measure the signal power (in SDR, &lt;span class=&quot;math-container&quot;&gt;$I^2 + Q^2$&lt;/span&gt;), average over some short time interval, and compare against a threshold. This is done &lt;em&gt;before&lt;/em&gt; the demodulator as the demodulator removes amplitude/power information.&lt;/p&gt;&#xA;&lt;p&gt;The disadvantage of this technique is that the needed squelch setting varies with conditions: it must be higher than the noise floor (which varies depending on frequency and local conditions, yet lower than the minimum (allowing for fading/picket-fencing) carrier power of the expected signal.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Squelch&quot; rel=&quot;noreferrer&quot;&gt;According to Wikipedia&lt;/a&gt; (and I think I've heard about this before from another source), there is a FM-specific technique for squelch:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;A typical FM two-way radio carrier squelch circuit is noise operated. It takes out the voice components of the receive audio by passing the detected audio through a high-pass filter. A typical filter might pass frequencies over 4,000 Hz (4 kHz). The squelch control adjusts the gain of an amplifier which varies the level of noise coming out of the filter. The audio output of the filter and amplifier is rectified and produces a DC voltage when noise is present. The presence of continuous noise on an idle channel creates a DC voltage which turns the receiver audio off.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;That is, this technique operates after the demodulator and simply looks for the high-audio-frequency noise which results from the absence of a consistent carrier, making the assumption that the expected FM signal will have different frequency content.&lt;/p&gt;&#xA;&lt;p&gt;In software, this would consist of a high-pass filter → an envelope detector → averaging and comparator to control squelch.&lt;/p&gt;&#xA;&lt;p&gt;This technique should operate equally well no matter what the RF environment. If it requires any “knob” at all, that would be the threshold for deciding when the noise is too much, which can probably be set generously high, but if not, it still depends only on the &lt;em&gt;audio&lt;/em&gt; characteristics of the transmitted signals and not the RF characteristics.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A transmitter may encode information in the signal to allow precise squelch. This is common on FM amateur radio repeaters. The most commonly used method is &lt;a href=&quot;https://en.wikipedia.org/wiki/Continuous_Tone-Coded_Squelch_System&quot; rel=&quot;noreferrer&quot;&gt;CTCSS&lt;/a&gt; (a.k.a. PL) in which a so-called “subaudible” audio tone is added to the signal. The receiver mutes when the tone is absent.&lt;/p&gt;&#xA;&lt;p&gt;Because different tones can be used, this allows ignoring signals from other transmitters, provided that the intended transmission is stronger than the other (e.g. two repeaters with all their users significantly nearer to one than the other).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It seems to me that there ought to be some technique which operates on the signal &lt;em&gt;before&lt;/em&gt; demodulation to detect whether it contains more or less a single dominant frequency (as expected for a FM signal) as opposed to a “flat” spectrum of white noise (as expected for no signal), without depending on an assumption about the absolute level of the noise floor. But I am not familiar with any specific designs or how to implement them.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-02-16T18:44:33.740" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7233" PostTypeId="1" AcceptedAnswerId="7239" CreationDate="2017-02-17T04:01:38.103" Score="2" ViewCount="107" Body="&lt;p&gt;Use case: I'm considering hacking into my SoftRock RXTX to bypass the filters, then add external filters. I'm wondering if I can use just the low-pass filters I've already built, or if there's a compelling reason I'd need to also build high-pass filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know a low pass filter is necessary to attenuate harmonics in multiples of the LO. But what about high-pass filtering? Is it strictly necessary or no, and why? In other words, what reason(s) are there for removing frequencies below the band of interest prior to the mixer?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-02-17T18:39:51.547" LastActivityDate="2017-02-18T00:07:56.183" Title="What function do high-pass filters in a direct conversion receiver perform?" Tags="&lt;software-defined-radio&gt;&lt;filter&gt;&lt;mixer&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7234" PostTypeId="1" CreationDate="2017-02-17T08:00:32.980" Score="0" ViewCount="63" Body="&lt;p&gt;I have got 2 questions on transmission line. In coax line, the centre wire is Copper, and the outer line is Aluminium, as far as I can see in the coax that I have. I have got couple of questions on that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;b&gt;Question 1:&lt;/b&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/H81Bx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/H81Bx.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here this model assumes uniform resistance, conductance, capacitance ... per unit length of both wires, and then went on to derive the equations and intrinsic impedance. But this is not the case for coax line, as centre wire (Copper), and the returning wire (Aluminium) both have different resistance, capacitance ... per unit length. Say top wire and bottom wire in the diagram are Copper and Aluminium respectively.So how come we are allowed to use $$Z_0 = \frac{R + j\omega L}{\gamma}$$. Where R can either be the per unit resistance of Copper wire OR Aluminium wire, same goes for the value of inductance. So what I am reading wrong here? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second question is on the application side of this question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;b&gt;Question 2:&lt;/b&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8M2XL.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8M2XL.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say I am feeding the signal through centre wire (lets assume antenna, and coax are perfectly matched). Braid is at ground. Now as antenna is a transmission line, the upper antenna gets the entire signal, but the bottom antenna is connected to ground. In this particular case the upper half radiates, but the bottom half of the antenna does not radiate as it is at ground. But this a topology which I have seen in some of the places. This does not make sense to me, as the antenna is intended to be a half wavelength dipole antenna, and same V/I characteristic should produced in both the parts of the antenna. Instead this design puts the bottom half at flat Voltage. I must be interpreting something wrong here. &lt;b&gt;Even if we add a BALUN at the connecting point to the antenna, the signal proceeds to the top half of the antenna through Copper, and the signal to the bottom half through Aluminium. This does not make sense to me as both of them have different electrical characteristic.&lt;/b&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your guidance will be greatly appreciated. &lt;/p&gt;&#xA;" OwnerUserId="9075" LastEditorUserId="9075" LastEditDate="2017-02-17T08:28:09.250" LastActivityDate="2017-02-17T12:19:11.360" Title="Transmission Line Model of Co-ax Lines" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;transmission-line&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7235" PostTypeId="2" ParentId="7234" CreationDate="2017-02-17T12:19:11.360" Score="1" Body="&lt;p&gt;The resistance in that lumped element model does not represent the physical resistance of the center conductor. Rather, it represents all losses of the coax. That is, resistive losses in the center conductor, &lt;em&gt;plus&lt;/em&gt; resistive losses in the shield, &lt;em&gt;plus&lt;/em&gt; leakage, &lt;em&gt;plus&lt;/em&gt; dielectric losses (which will dominate at high frequency).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your second question looks like a duplicate of your previous question: &lt;a href=&quot;https://ham.stackexchange.com/questions/7108/dipole-antenna-current-distribution-at-any-time-instant&quot;&gt;Dipole Antenna Current Distribution at any Time Instant&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-02-17T12:19:11.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7236" PostTypeId="2" ParentId="7233" CreationDate="2017-02-17T20:53:57.373" Score="4" Body="&lt;p&gt;They prevent (or at least reduce) front end overload due to strong and/or messy nearby signal sources at lower frequencies. Think of the 80 meter station at Field Day blanking the 40 and 20m receivers every time it's keyed up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Chances are good that you'll be ok without them if your environment is pretty RF quiet, but it may not take all that much to cause trouble. My RTL-SDR,  modified for direct sampling (which has chicken wire for filtering I think), was wiped out on big chunks of 20m when I keyed up my hf rig on 40m, even at only 10 watts. The transmitter was a squeaky clean Elecraft, the transmit antenna was a resonant, well choked dipole more than 100 feet away, and the SDR antenna seemed to have little influence, as it occurred even with no antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good set of coaxial stubs on the transmitter, and a good band pass filter on the receiver helped a lot. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I definitely wouldnt try to use it for Field Day or SO2R without the high pass filtering, at least. &lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-02-17T20:53:57.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7237" PostTypeId="1" AcceptedAnswerId="7238" CreationDate="2017-02-17T23:38:20.503" Score="1" ViewCount="114" Body="&lt;p&gt;I'm working on a program for ham radio that involves displaying satellites. I'm currently using the Space-track.org database, but the problem with it is that it will give &quot;Saudisat 1C&quot; rather than SO-50, and things like that. Is there a downloadable database that has a friendly name and its corresponding catalog ID?&lt;/p&gt;&#xA;" OwnerUserId="9218" LastActivityDate="2017-02-18T02:13:01.577" Title="Is there somewhere I can get a database of satellite catalog IDs and their friendly names?" Tags="&lt;satellites&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7238" PostTypeId="2" ParentId="7237" CreationDate="2017-02-17T23:46:36.880" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://db.satnogs.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;SatNOGS DB&lt;/a&gt; records multiple names for satellites; for example, it has &lt;a href=&quot;https://db.satnogs.org/satellite/27607/&quot; rel=&quot;nofollow noreferrer&quot;&gt;both names you mention&lt;/a&gt;. There is &lt;a href=&quot;https://db.satnogs.org/api/&quot; rel=&quot;nofollow noreferrer&quot;&gt;a simple HTTP API&lt;/a&gt; which you can use to fetch the entire database in JSON.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The database also includes downlink/uplink information (frequencies, mode, etc). It does not include orbital elements (TLEs), which you will have to obtain from another source by cross-referencing the catalog numbers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not enough of a satellite enthusiast to say how complete or accurate SatNOGS DB is; I do know it is a relatively new project and they are accepting contributions.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-02-18T02:13:01.577" LastActivityDate="2017-02-18T02:13:01.577" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7239" PostTypeId="2" ParentId="7233" CreationDate="2017-02-18T00:07:56.183" Score="4" Body="&lt;p&gt;So, I don't know the Softrock personally, but from your description, it's a &lt;em&gt;switching mixer&lt;/em&gt; architecture.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Receiver side&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;What that means is that you mix not by multiplying the input signal with a single harmonic oscillation (a tone), but by switching it on and of.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Pre-Mixer HPF&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Mathematically, this description is omitting one interesting detail: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The operation done with the input signal $r(t)$ of the downconcerter is not actually a multiplication with a perfect square wave, i.e. a wave that has the shape &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$l'(t)  =A \cdot \text{sgn}(\sin(2\pi f t))$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;but is actually just an &quot;on- and off&quot; switching; so in the half-periods where $l'$ would be negative, it's actually zero. This leads to an actual LO function&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;l(t) &amp;amp;= \max(l'(t), 0)\\&#xA;&amp;amp;=A \max( \text{sgn}(\sin(2\pi f t),0)\\&#xA;&amp;amp;=\frac12l'(t) +\frac A2&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whereas $l'$ has a time-average of zero, we can clearly see the DC offset of $\frac A2$ of $l(t)$!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, when multiplying &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$r(t) \cdot l(t) = \frac12 l'(t)r(t) + \frac A2 r(t)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;we get the sub-$f$ content of $r(t)$ directly in baseband (to worsen it, amplified by $\frac A2$)! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, with a switching down-mixer, you must have an &lt;em&gt;input&lt;/em&gt; high-pass filter to avoid getting low-frequency input signal directly in your desired output band.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Post-Mixer HPF&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;On the output of the same mixer, you'd also want a DC-cancelling high pass filter – just because there's practically zero information in an arbitrary small bandwidth, but having a DC offset on your ADC will simply reduce your usable dynamic range. Anyway, that hpf is usually just the AC coupling you'd do anyways to get your signal onto the center of the $[0;V_\text{Full Scale}]$ range of the ADC.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Transmitter side&lt;/h1&gt;&#xA;&#xA;&lt;h1&gt;Pre-Mixer&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;You don't want DC offset from your DAC to reach the switching mixer – simply because that is typically simply a transistor, and imprinting a DC current would shift its operating point and possibly be detrimental to linearity.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Post-Mixer&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;The Mixer will introduce a DC current. You typically don't want that to reach your antenna, your HPA (same effect as for the switching transistor) or your baluns (which might be a DC short, anyway).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-02-18T00:07:56.183" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7240" PostTypeId="2" ParentId="7237" CreationDate="2017-02-18T00:58:16.210" Score="0" Body="&lt;p&gt;PyEphem, a library to calculate (relative) positions of celestial bodies, has a &lt;a href=&quot;http://rhodesmill.org/pyephem/catalogs&quot; rel=&quot;nofollow noreferrer&quot;&gt;link page&lt;/a&gt; that lists digital catalogues you can, at least partially directly import.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-02-18T00:58:16.210" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7241" PostTypeId="2" ParentId="919" CreationDate="2017-02-18T03:24:50.580" Score="3" Body="&lt;p&gt;I had the same question for a while, more in reference to resonant loop antennas, but the same principle seems to apply to folded dipoles. Eventually I figured out what I think is going on, and the key is the length of the antenna vs. the wavelength of the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A folded dipole or resonant loop antenna is, electrically, a full wavelength from one side of the feed point to the other. If the loop were straightened out, you'd see a standing wave with voltage nodes at each end and the middle, and current nodes at 1/4 and 3/4 of the length. If you then fold it back up, you can see that the electrical middle of the element is exactly across from the feed point; this means that the voltage in the middle of the antenna is neutral, while each end of the loop sees the peaks and troughs of the voltage wave. In contrast, the current peaks at the voltage nodes, in the middle of the antenna, and the current nodes are at the ends. It's probably pretty reasonable to imagine it as though the electrons are sloshing back and forth across the loop, being pushed by the feed point. This is the same type of resonance seen by a half-wave dipole antenna, but there's twice as much &quot;stuff&quot; resonating.&lt;/p&gt;&#xA;" OwnerUserId="9219" LastActivityDate="2017-02-18T03:24:50.580" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7242" PostTypeId="2" ParentId="6731" CreationDate="2017-02-18T17:07:21.583" Score="1" Body="&lt;p&gt;Your &lt;a href=&quot;https://en.wikipedia.org/wiki/PACTOR&quot; rel=&quot;nofollow noreferrer&quot;&gt;PACTOR II&lt;/a&gt; signal couldn't be decoded because PACTOR II uses proprietary encoding.  There is no open-source decoder; in order for PACTOR II to be decoded, an expensive modem from Special Communications Systems GmbH (SCS) must be used.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-02-18T17:07:21.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7243" PostTypeId="1" AcceptedAnswerId="7244" CreationDate="2017-02-19T00:46:27.810" Score="1" ViewCount="513" Body="&lt;p&gt;I recently joined my university's Cube-Sat Program and was delegated the task of looking for software that modulates and demodulates signals (~437MHz, GMSK, AX.25). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem now is that I don't understand what is required. The signal comes through a Yagi antenna and a transceiver, so wouldn't the transceiver handle the modulation and demodulation and feed in bit-strings? And if so where does a Sound-card modem come into play here? Why do I see articles in which people used sound card modems to decode satellite telemetry?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Link to article:&lt;a href=&quot;http://www.pe0sat.vgnet.nl/decoding/satellite-telemetry/sound-card-modem/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.pe0sat.vgnet.nl/decoding/satellite-telemetry/sound-card-modem/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9225" LastEditorUserId="9225" LastEditDate="2017-02-19T07:36:35.427" LastActivityDate="2017-02-19T11:42:04.957" Title="How does a transceiver work?" Tags="&lt;modes&gt;&lt;transceiver&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7244" PostTypeId="2" ParentId="7243" CreationDate="2017-02-19T11:42:04.957" Score="5" Body="&lt;p&gt;The article does in illustrate things rather nicely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's look at the receive side first:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;     Signal (@437 MHz)--&amp;gt;(x)--&amp;gt; filters --&amp;gt; IF (@x)&#xA;                          ^&#xA;                          |&#xA;Oscillator (@(437 MHz-x))-/&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;What happens is that your input RF signal at $f_\text{RF}$ is multiplied in a mixer with a tone of frequency $f_\text{LO}=f_\text{RF}-x$. The output of the mixer hence, mathematically, contains the difference frequency&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;f_\text{IF} &amp;amp;= f_\text{RF}-f_\text{LO} \\&#xA;&amp;amp;= f_\text{RF}-(f_\text{RF}-x)\\&#xA;&amp;amp;= x&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;LO&quot; stands for &quot;local oscillator&quot;, by the way, and &quot;IF&quot; for &quot;intermediate frequency&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd then typically either directly demodulate the IF signal, or downconvert it even further.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, you'll need some &lt;em&gt;hardware&lt;/em&gt; to do all this, namely, something that offers the mixer, the filters (because the mixer produces a lot of other frequencies, too), amplifiers and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The article you've linked to uses the &lt;em&gt;FunCube dongle&lt;/em&gt;. Which is a bit of a dated device that &lt;em&gt;looks&lt;/em&gt; to the operating system like a sound card. In fact, it's &lt;strong&gt;not&lt;/strong&gt; a sound card, but an IQ receiver. What that means is that the IF signal is further mixed down, in fact, to a new IF of 0 Hz (we call that baseband), and in the process converted to two &quot;orthogonal&quot; signal branches (I and Q). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These two channels are what &quot;looks like&quot; left and right of a stereo signal. &lt;strong&gt;They are not audio&lt;/strong&gt;. They are just that – complex baseband signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a whole lot of software that can demodulate GMSK in baseband, and there's a whole lot of software that does AX.25. However, which software to use depends on&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;your hardware – it's no use if the software you use can't talk to your hardware&lt;/li&gt;&#xA;&lt;li&gt;your operating system and computational environment – it's no use if you find something that works great on Windows 98, but you need your decoder to run on a screen-less Raspberry Pi somewhere in a box,&lt;/li&gt;&#xA;&lt;li&gt;your data interface – it's no use if your software has a super nice GUI to show you received packets' contents, but you need the data to be streamed via network somewhere else.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;The FunCube dongle is a hybrid Superheterodyne / Quadrature receiver system that gives you raw IQ samples. It is the one used in the article. It's a receiver only, and since you said &quot;transceiver&quot;, it can't be the device you're going to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This architecture is &lt;em&gt;not&lt;/em&gt; the &lt;em&gt;only&lt;/em&gt; type of receiver you can build. In fact, there's a lot of devices that are pure Quadrature mixing systems, or pure superhets, or directly, mixer-less undersampling systems, and all imaginable combinations of those, and that is just the range of things you'd find in common, general purpose SDR devices. There's no general answer to &quot;how does a transceiver work&quot;, because non-SDR transceivers are purpose-built for exactly the signal they deal with – and an analog TV receiver is totally incomparable to an early GSM frontend (which, fun fact, used GMSK, but typically had &quot;overdriven&quot; single-transistor receivers at a low IF) or a garage door opener.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So, your design process would probably be the following:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Choose SDR hardware. Your university is launching a CubeSAT – that's not a cheap hobby, and thus, I guess you could probably do better than a FunCube Dongle with a 192 kHz bandwidth, and an E4000 tuner that tends to misbehave in terms of phase noise. Chances also are you've existing receiver analog frontends – ie. LNA's, preselection filters and so on. Talk to someone who's knowledgeable about the available hardware! In the end, you'll have to plug your thing into an antenna that possibly already exists.&lt;br&gt;The hardest part in all this is properly defining what you need. You didn't say in which orbit your CubeSat will end up in – but chances are it's going to be a rather low, i.e. fast-moving one, and then your receiver's digital bandwidth should be wide enough to let you track the changing $f_\text{RF}$¹. So, maybe you should first ask a different question, namely &quot;&lt;strong&gt;What are the characteristics of my receiver that I have to note down as requirement when doing {insert what you're doing &lt;em&gt;exactly&lt;/em&gt;}?&lt;/strong&gt;&quot;&lt;/li&gt;&#xA;&lt;li&gt;Pick, or build, a receiver software&lt;/li&gt;&#xA;&lt;li&gt;Test and refine.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹ Doppler Effect! &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-02-19T11:42:04.957" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="7245" PostTypeId="1" CreationDate="2017-02-19T17:54:01.960" Score="1" ViewCount="75" Body="&lt;p&gt;When using a 2M/70cm diplexer for low-pass filtering (or with only one antenna on one of the two &quot;outputs&quot;), should the unused connection be left open, or terminated?  (using a suitable impedance, such as a 50 Ohm resistor or dummy load?)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2017-02-19T19:51:48.770" Title="Diplexer termination?" Tags="&lt;filter&gt;&lt;dummy-load&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7246" PostTypeId="2" ParentId="7245" CreationDate="2017-02-19T19:51:48.770" Score="5" Body="&lt;p&gt;Terminated! An open end would have a reflection coefficient of |R| = 1 (because, where would the energy go).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XSTFf.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XSTFf.png&quot; alt=&quot;Terminate&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-02-19T19:51:48.770" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7247" PostTypeId="2" ParentId="6874" CreationDate="2017-02-20T02:04:15.890" Score="2" Body="&lt;p&gt;Assuming the AM station doesn't wipe out your internet connection, how about setting up a remotely operated HF rig far offsite (friend or relative's house, etc.)?], and operating it from your home computer (laptop, et.al.)?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2017-02-20T02:04:15.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7248" PostTypeId="2" ParentId="7216" CreationDate="2017-02-20T15:06:07.877" Score="2" Body="&lt;p&gt;I also didn't notice that box before, but it has the date as well, 2017-01-08 in it(YMD), a Sunday.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The center is 10.130, and at S7 that's fairly strong. Also I think the actual signal is 26khz wide with the 3khz side lobes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think its DX. At 9am the sun is well up, the ionosphere E layer has merged back into D. There would be no grey line propigation in play. I realized there is a viable alternative answer...QRM.&lt;/p&gt;&#xA;" OwnerUserId="6092" LastActivityDate="2017-02-20T15:06:07.877" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7249" PostTypeId="2" ParentId="7076" CreationDate="2017-02-20T20:28:42.327" Score="3" Body="&lt;p&gt;I am not sure, but I feel that the attached diagram explains how a Coaxial Collinear Antenna works. Suggestions/comments are welcomed.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;Click on image to see full size image&lt;/em&gt;&lt;/strong&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/zkaG4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zkaG4.png&quot; alt=&quot;how coaxial collinear antenna works&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="9029" LastEditDate="2017-02-21T01:15:27.247" LastActivityDate="2017-02-21T01:15:27.247" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7250" PostTypeId="2" ParentId="6818" CreationDate="2017-02-20T21:50:07.783" Score="2" Body="&lt;p&gt;First the answer:  When I worked for the forest service I built single-transistor transmitters where one of the leads of the transistor was the antenna. It doesn't get any more simple than that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They used hearing aid batteries. Then we could enclose them in beeswax so we could stuff them down the throats of animals, even snakes. The batteries would last about three days. EPA said we were supposed to recover the batteries, but some of them apparently got lost on the way back. The receivers were about the size of a canteen, using D cells and hung around the neck so one operator could handle it.  We used 3-element Yagi antennas to follow the animals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now a story:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We played 2-meter &quot;rabbit hunting&quot; every Saturday for years in Fairbanks.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The receiver wasn't the key to success.  It was the antenna and the skill to use it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It turned out that instead of using Yagi antennas to find the source, the best way to get a fix was to use a tuned loop antenna and utilize the nulls in the donut-shaped pattern of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nulls are much sharper than the broader beamwidth of a Yagi or a quad.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Newer DF systems, (like the 4 antennas on police cars to find transmitter packs inserted in stolen money), use time-of-arrival, and are best used when they are close to the source.  Plus they generally can only give you 8 LEDs to indicate the first antenna (and in between two) where the signal arrives.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We didn't use computers like that.  About the only portable computer we had back then was the KIM-1, anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our loops could go for miles.    &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the record, one of our rules was to never work in teams other than having two people in the vehicle.  It was up to each pair of us to establish our own bearings.   The second rule was that the rabbit couldn't move.  But there was no rule as to how often the rabbit must transmit.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then as we got closer, we would detune the loops (with a capacitor at the top of the loop) to avoid desense in the receiver.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We had very modest prizes, like first plates of food at the inevitable BBQ.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those were really fun days.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-02-20T22:09:08.643" LastActivityDate="2017-02-20T22:09:08.643" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7251" PostTypeId="2" ParentId="5786" CreationDate="2017-02-20T22:17:03.640" Score="3" Body="&lt;p&gt;The hex grids can fit more transmitter/receivers into the same space, resulting in greater power output per square meter.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But more importantly, the one you pictured also has independent transceivers so they are individually field-replaceable.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The computer that runs it all does diagnostics on startup and can flag the bad ones so they can be fixed right away without having to have access to the back of the array.  That is key.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;No disassembly required - just pull out the bad one(s) from the front and slide in a new one, right on the flightline.  No need to pull it into a shop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just one bad TRX can cause unwanted sidelobes which can defeat the LPI (low probability of intercept) property of those arrays.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Addressing what you said about passively:  All I can mention is that the old phased arrays used switched delay lines in order to generate the pattern.  But they were very limited in the switching speed, and could not transmit during the switching. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The unit you pictured can probably track more than two dozen targets &quot;at once&quot; - of course it is scanning, but it is so fast it seems to be simultaneous.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck with your project.  I am sure you are learning a lot. &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-02-20T22:22:28.460" LastActivityDate="2017-02-20T22:22:28.460" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7253" PostTypeId="2" ParentId="7225" CreationDate="2017-02-21T21:11:44.313" Score="-3" Body="&lt;p&gt;There is one easy answer, a balun is a transformer! - a choke is a choke!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Forget you ever heard the term &quot;choke balun&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm sure you know balun stands for BALanced to UNbalanced. A 1 : 1 balun can be used to match a coax to an equal value impedance, balanced line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple choke (one to eliminate common mode currents - CMCS) can be made by winding 25 feet of coax around a one gallon ice cream container. They have a slight taper, making it easy to remove the coil after winding and securing with wire ties in 4 places or so. Note the number of turns is not the critical factor here; rather the length of coax used. This should be effective from 1.8MHz and up.&lt;/p&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="218" LastEditDate="2017-02-22T17:16:51.977" LastActivityDate="2017-02-22T17:16:51.977" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7254" PostTypeId="1" AcceptedAnswerId="7256" CreationDate="2017-02-21T21:19:52.383" Score="0" ViewCount="397" Body="&lt;p&gt;My Icom IC-706mkIIg transceiver has two output ports:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;one for its VHF/UHF bands (i.e. 2m/70cm)&lt;/li&gt;&#xA;&lt;li&gt;one for the HF bands, and also 6m!&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I have a couple of broadband VHF/UHF antennas whose transmit specs include the 6m (50MHz) band, so I'd rather have the 6m band output on the VHF/UHF port. I understand for example that the Yaesu FT-817ND allows some configuration of which bands use which of &lt;em&gt;its&lt;/em&gt; two ports, but do not see anything similar in my Icom's menu settings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any modification available to move 6m handling to the IC-706mk2g's VHF port, whether a setting I've missed, a jumper inside, or even some minor circuitry rework?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Otherwise could I accomplish this without undue loss — or expense! — via some combination of diplexers and/or other filters?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2017-02-21T23:13:40.110" Title="Using the VHF port for 6m on an Icom IC-706mkIIg transceiver" Tags="&lt;antenna-system&gt;&lt;equipment&gt;&lt;icom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7256" PostTypeId="2" ParentId="7254" CreationDate="2017-02-21T22:23:33.180" Score="2" Body="&lt;p&gt;If you don't find a solution based on modifying the radio, this is a reasonable use for two diplexers. You can, in principle, hook them up two different ways:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/tp8hw.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2ftp8hw.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These two configurations have in theory the same requirements for the two diplexers — one which separates 30&amp;minus; and 50+ MHz and one which separates 54&amp;minus; and 144+ MHz. However, the second configuration has two advantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It should have less insertion loss at other than 50 MHz, since the other bands pass through only one diplexer and not two.&lt;/li&gt;&#xA;&lt;li&gt;The bottom left diplexer deals only with frequencies 54 MHz and below, — it does not need to have good performance at UHF.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A brief search (I didn't check all the specifications in detail) shows that suitable duplexers are available from several brands (Comet, Diamond and MFJ) for prices around US $60-80 each.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-02-21T23:13:40.110" LastActivityDate="2017-02-21T23:13:40.110" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7257" PostTypeId="2" ParentId="7120" CreationDate="2017-02-21T22:45:59.427" Score="1" Body="&lt;p&gt;Normally only licensed radio-amateurs holding Advanced certifications are allowed to build radio-transmitting apparatus. Please consider getting licensed: &lt;a href=&quot;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01862.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01862.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are amateur radio clubs near where you live that may help with studying for a license as well as with answering some of your questions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The IC you mentioned has output transmit voltage of about 1V (113dBuV) or 0.02W (20 mW) into a theoretic 50-ohm load. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Under ideal conditions and assuming you are using a simple dipole antenna the field strength using the formula from&#xA;&lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_field_strength_in_free_space&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Dipole_field_strength_in_free_space&lt;/a&gt; is:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;E = 7 * SQR(0.02W) / 30m = 0.033 V/m &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;or 33000 μV/m @ 30 meters which is way above stated IC limits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More good reading here: &lt;a href=&quot;https://www.semtech.com/images/promo/Semtech_ACS_Rad_Pwr_Field_Strength.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.semtech.com/images/promo/Semtech_ACS_Rad_Pwr_Field_Strength.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck!&lt;/p&gt;&#xA;" OwnerUserId="1296" LastActivityDate="2017-02-21T22:45:59.427" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7258" PostTypeId="2" ParentId="7223" CreationDate="2017-02-21T22:52:59.767" Score="1" Body="&lt;p&gt;I suppose you were standing on the ground when you tested your antenna so rotating the elements in a vertical position made them closer to the ground effectively detuning your antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To avoid that, the antenna elements must be above the ground at least 1/4 of the wavelength - in your case higher than 2m / 4 = 50cm at all times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another factor could be your feed line. Try coiling some coax near the feed point (simple RF choke) and see if your tuning changes - &lt;a href=&quot;http://www.k3dav.com/rfchokecoil.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.k3dav.com/rfchokecoil.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1296" LastActivityDate="2017-02-21T22:52:59.767" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7259" PostTypeId="2" ParentId="7195" CreationDate="2017-02-22T09:31:16.010" Score="1" Body="&lt;p&gt;To expand on the earlier answer : in the British Isles (except the Republic of Ireland - EI), the callsign prefix changes depending on which entity the operator is in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My amateur callsign in England is G0SWG. If I operate in these entities, here is how I would have to identify myself:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;England :           G0SWG&#xA;Scotland :         GM0SWG&#xA;Wales :            GW0SWG&#xA;Northern Ireland : GI0SWG&#xA;Isle of Man :      GD0SWG&#xA;Jersey :           GJ0SWG&#xA;Guernsey :         GU0SWG&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-02-22T09:31:16.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7260" PostTypeId="1" CreationDate="2017-02-22T14:02:57.047" Score="5" ViewCount="990" Body="&lt;p&gt;What is the difference between cross-polarized yagi antennas and circularly polarized antennas?&lt;/p&gt;&#xA;" OwnerUserId="9245" LastEditorUserId="8832" LastEditDate="2017-02-25T23:12:37.213" LastActivityDate="2017-02-25T23:12:37.213" Title="What is the difference between &quot;Cross Polarized&quot; vs &quot;Circularly Polarized&quot; Antennas?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;polarization&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7261" PostTypeId="2" ParentId="7260" CreationDate="2017-02-22T14:54:04.040" Score="1" Body="&lt;p&gt;&lt;a href=&quot;http://www.antenna-theory.com/definitions/crosspolarization.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Cross polarization&lt;/a&gt; usually refers to the opposite polarization. For example vertical and horizontal are opposites, as are right-hand and left-hand circular. Theoretically, a pair of cross-polarized antennas will have zero coupling, but in practice an extra 20 to 30dB of path loss is typical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually this is an undesirable thing, but it can be exploited for diversity or multiplexing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, I wouldn't be surprised to find lay usages of &quot;cross polarization&quot; meaning circular polarization. Many circular polarized antennas have elements arranged in a cross.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-02-22T14:54:04.040" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7262" PostTypeId="1" CreationDate="2017-02-22T15:32:01.250" Score="1" ViewCount="599" Body="&lt;p&gt;I got the following plans off Martin E. Meserve's website. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LvZGT.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LvZGT.png&quot; alt=&quot;Plans for Antenna Centered at 440 MHz&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I go about assembling the antenna once I have the elements and boom? What is the impedance of the driven element? Do I need baluns or a bazooka filter for impedance matching? A choke for filtering? Do I split the driven element in two, grab a small length of 50 ohm coax, solder part of the DE each end to the center and ground the shielding?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the above paragraph suggests, I am quite confused. Any help is appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Kindly,&#xA;Steve&lt;/p&gt;&#xA;" OwnerUserId="9245" LastActivityDate="2017-02-24T16:46:08.363" Title="How to assemble an antenna (impedance matching methods)" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7263" PostTypeId="2" ParentId="7262" CreationDate="2017-02-22T17:33:06.777" Score="1" Body="&lt;p&gt;Assuming you intend to feed this antenna with coax, &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;you need some kind of balun&lt;/a&gt; to prevent common-mode currents on the feedline which will degrade the directionality of the antenna. There are many kinds of balun that would work. A bazooka balun or a choke balun are two of them. The balun may or may not also have some impedance matching capability. A &lt;a href=&quot;https://ham.stackexchange.com/q/1804/218&quot;&gt;gamma match&lt;/a&gt; and &lt;a href=&quot;https://ham.stackexchange.com/q/3591/218&quot;&gt;folded balun&lt;/a&gt; are other options. There are &lt;a href=&quot;http://www.antenna-theory.com/definitions/balun.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;many more&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For an antenna with this many elements the directionality should be high, so common-mode currents must be very small to avoid significantly degrading the pattern. You might want to &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measure the common-mode current&lt;/a&gt; and add additional choking if necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feedpoint impedance is best determined empirically or by modelling. However it is generally true of Yagi antennas that the impedance is lower than 50 ohms. A gamma match is easily adjustable. If you can measure only the SWR but not directly the impedance, this gives you the option of finding a good match by trial and error. If you have an antenna analyzer or similar which can measure the impedance, a lumped element match or a stub match are other options.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see, there are many engineering decisions to be made besides the dimensions of the Yagi elements. The feed of an antenna is an important and often neglected aspect of design. Neglecting the feed you will end up with an antenna which works, and you will make contacts, but it may not work to its fullest potential. It may not even work better than a simple vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a taste for experimentation, then by all means build this antenna and experiment with feed options. If you're anything like me, the experiments are most of the fun and the antenna might not actually be done in a year. However if your intention is to get something working immediately, consider a simpler design which includes all the feedpoint details, or a commercial antenna that requires only trivial assembly. You may build the simple design, and then when attempting a more complex design such as this you will have something for comparison, and you can judge if adding 8 more elements made an improvement.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-02-24T16:46:08.363" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7264" PostTypeId="2" ParentId="7225" CreationDate="2017-02-22T17:46:00.850" Score="1" Body="&lt;p&gt;What you really want is a choke (often called current balun), as a voltage balun (i.e a transformer) will not isolate the feedline unless the antenna is in book-ideal conditions. The minimum misbalance in the dipole and the isolation is broken.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't have experience at those frequencies but I'd try a several series toroids as other have suggested to get a minimum of 2K commonn impedance at the frequencies of interest. If you can make it 5K much better.&lt;/p&gt;&#xA;" OwnerUserId="8523" LastActivityDate="2017-02-22T17:46:00.850" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7265" PostTypeId="1" AcceptedAnswerId="7308" CreationDate="2017-02-23T08:02:53.240" Score="11" ViewCount="1074" Body="&lt;p&gt;I am not asking about the fairly well-known effect of the earth &quot;appearing less curved to radio waves&quot; that are otherwise still essentially line-of-sight, but a deeper arcanum:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the ARRL Antenna Book, 17th edition (1994) there is a discussion of &quot;Reliable VHF coverage&quot; in starting on page 23-7 in the Radio Wave Propagation chapter. The claim is made,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Because of age-old ideas, misconceptions about the coverage obtainable in our VHF bands persist. This reflects the thoughts that VHF waves travel only in straight lines, […] However, let us survey the picture in the light of modern wave-propagation knowledge and see what the bands above 50 MHz are good fro on a day-to-day basis, ignoring the anomalies [presumably referring to the tropospheric ducting of previous section] that may result in extensions of normal coverage.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It goes on, after mentioning an article by D.W. Bray, K2LMG in the November 1961 QST magazine, to present two graphs that plot &quot;tropospheric path loss&quot; against distance. The curves therein rise steeply from 120 dB of loss at a distance of 0 miles [?!] to around 180 dB near 50 miles, then level off slightly so that at 500 miles there is a path loss around 240 dB. (That's reading the 50% reliability chart roughly, there's actually 4 lines plotted for 144/50, 220, 432, and 1296 MHz, as well as a second separate chart showing 99% reliability; the 99% reliability chart is very approximately 10–20 dB worse than the 50% one at any given point.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE&lt;/strong&gt;: thanks to W0BTU Mike, here's the actual charts scanned from an earlier edition:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JzMdi.png&quot; alt=&quot;Path loss vs. distance for amateur frequencies above 50 MHz&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What &quot;modern wave-propagation knowledge&quot; is this referring to? What mechanism(s) would allow VHF signals to be 99% &lt;strong&gt;reliably&lt;/strong&gt; received 500 miles away, albeit with more than 250 dB of path loss, or 50%-of-the-time reliability with a little less loss? (These path-loss charts do NOT assume any antenna-height gain.)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-03-07T20:02:16.930" LastActivityDate="2018-10-06T02:30:01.603" Title="How does VHF/UHF propagate beyond the expected (radio) horizon?" Tags="&lt;propagation&gt;&lt;vhf&gt;&lt;uhf&gt;" AnswerCount="4" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7266" PostTypeId="2" ParentId="7265" CreationDate="2017-02-23T15:24:43.977" Score="1" Body="&lt;p&gt;I really don't know – in a review, I'd have marked that sentence as far too vague – what the author means with &quot;modern wave-propagation knowledge&quot;. If I need to benchmark that knowledge against a 31 year old Ham article, well… I don't really think it's a great advocate. &quot;Modern knowledge&quot;, to me, is probably something that is what research on an academic level has yielded and is now dissipating into technological areas such as amateur radio, and thus, an article in a ham mag might by definition, not be used as describing the state of the sciences in 1961¹.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I dispute your &quot;&lt;em&gt;expected&lt;/em&gt; radio horizon&quot;; just because a ham expert in 1961 modeled something is really no great reason to expect the same to be accurate in 1994.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, having minimal knowledge of earth observation and radio propagation modelling, I'd go for:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;having the ability to actually simulate non-trivial situations, including:&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;clearer idea of atmospheric properties such as permittivity ($\epsilon_r$) and magnetic permeability ($\mu_r$) as well as charge density ($\rho$),&lt;/li&gt;&#xA;&lt;li&gt;non-linear gradients of above properties,&lt;/li&gt;&#xA;&lt;li&gt;non-perfectly-spherical atmosphere,&lt;/li&gt;&#xA;&lt;li&gt;actually looking into things that are far, far more granular than just saying &quot;ok, here's the troposphere that we model as thing with the following diffractive index and a constant attenuation $\alpha$&quot;, including effects like weather-based inversion of conductivities etc.&lt;/li&gt;&#xA;&lt;li&gt;being able to model effects of ground conductivity etc.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;actually having data on how charged, conductive, vapor-saturated and shaped strata of the atmosphere are, based on a lot of satellite and radioastronomy experiments&lt;/li&gt;&#xA;&lt;li&gt;having a far better understanding of the interaction between large antennas and their surroundings&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹I know that article is cited in many ham places. I've never read it.&lt;br&gt; However, it seems to me that modeling VHF transmission's reach in 1961 should basically be equivalent to asking a couple of WWII and cold war radio engineers; it's really not like radio reach is not a very important strategic factor, and I'm very certain that all involved parties had very accurate recordings of how far they could reach, and will have worked to improve their models to match that, long before 1961.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These models might not have been public back in the day, but really, they also shouldn't be that much of rocket science to recreate. In 1994, there should be no &quot;surprise&quot; in how VHF propagates terrestrially – I really think it's very worth writing articles that bring research-level theory, models and experimentation to the amateur masses (which, by the beard of Hertz, are pretty good at such things), but you must then compare these to state-of-back then in academics, not in ham mags. That's just unfair – many countries simply had restrictions on radio usage during WWII, so the amateur radio community just needed a decade or two to catch up. That catching-up phase was an especially fruitful one, what with all the semiconductor technology emerging at the same time. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Downside of that being a phase is that if you look online, you still find a lot of people trying to build the 1960's kits nowadays, even trying to get the same diodes and transistors of the day – there's really no good reason you'd &lt;em&gt;want&lt;/em&gt; a Germanium noise gen– err transistor amplifier if you can have a silicon one for cheap, if you just don't stick to material from the &quot;golden era of rediscovering possibilities&quot;. I attribute that to a lot of Kit manufacturers and mag publishers just copying articles from back then, until the original source and its restrictions got lost. &lt;em&gt;Enough ranting for today.&lt;/em&gt; &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-02-23T18:21:22.210" LastActivityDate="2017-02-23T18:21:22.210" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="7267" PostTypeId="1" AcceptedAnswerId="7273" CreationDate="2017-02-23T22:11:39.797" Score="3" ViewCount="1241" Body="&lt;p&gt;I saw a video lately where someone soldered an antenna to a Raspberry Pi Zero and broadcasted radio signals. &lt;a href=&quot;https://www.youtube.com/watch?v=GXedC5dQyNk&amp;amp;t=9s&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=GXedC5dQyNk&amp;amp;t=9s&lt;/a&gt; They said they were not worried to do it because they were only going to do it for a few seconds, but I'd like to know if I could do it for extended periods of time. I am in ME, US.&lt;/p&gt;&#xA;" OwnerUserId="9249" LastEditorUserId="8832" LastEditDate="2017-02-27T14:42:51.437" LastActivityDate="2017-03-18T16:02:53.640" Title="Is it legal to broadcast an FM radio signal with a Raspberry Pi Zero?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7269" PostTypeId="2" ParentId="4915" CreationDate="2017-02-24T03:47:32.877" Score="0" Body="&lt;p&gt;All circuits will have some sort of latency.  Not to mention the QRN and maybe QRM that could trigger your circuit unnecessarily.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So instead of designing the elusive &quot;zero-latency with complete noise immunity&quot; circuit here is an alternative:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do it in software.  Keep the audio path open all the time.  With the right program it would be less likely to miss any part of a real preamble.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These kinds of input circuits are rarely connected to speakers so it wouldn't bother you by the white noise in between.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doing it this way could ensure you didn't miss the preamble because of latency in an external circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, be sure to do your due diligence and post this same question directly into Google and see if/whom has done this before you.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-02-24T03:47:32.877" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7270" PostTypeId="2" ParentId="5326" CreationDate="2017-02-24T03:54:26.683" Score="0" Body="&lt;p&gt;For all intents and purposes they are the same, yes.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a good quote from W8JI that explains it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Average power is same as equivalent work power or heating power of each cycle averaged over a significant time compared to the time when power level changes. With an unchanging (during the measurement period) power level, such as a steady unmodulated carrier applied to a constant resistance load, average power and peak envelope power are the same. If we close and hold-closed a manual telegraph key on a good stable CW transmitter, we will see the average power displayed on a power meter. It will not be the &quot;RMS power&quot;.  It is also the peak envelope power, because it is the maximum stable heating power level over some period of time that we hold the key.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is from his website on AM, here:  &lt;a href=&quot;https://www.w8ji.com/amplitude_modulation.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amplitude Modulation&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-02-24T03:54:26.683" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7271" PostTypeId="1" CreationDate="2017-02-24T04:21:56.527" Score="2" ViewCount="160" Body="&lt;p&gt;Since:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\vec F = q \left(-\nabla \phi - \frac{\partial \vec A}{\partial t} + \vec v \times \left( \nabla \times \vec A \right) \right)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would seem that a receive antenna with a current density &lt;strong&gt;J&lt;/strong&gt; whose velocity field was &lt;strong&gt;v&lt;/strong&gt; would produce enhanced reception.  Is this correct?  If so, there must be a technical name for this kind of antenna.  What is that name?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note:  I chose the potentials description of the Lorentz force equation to expose all components of the EMF in a single expression. Conduction band electrons of the receive antenna are experiencing a force that changes with time resulting from the incident EM wave. I understand that $-\nabla \phi = 0$ when Tx and Rx are exactly parallel and orthogonally positioned.  &lt;/p&gt;&#xA;" OwnerUserId="9252" LastEditorUserId="9252" LastEditDate="2017-02-26T19:13:31.967" LastActivityDate="2017-02-26T19:13:31.967" Title="Term For Receive Antenna Using Lorentz Force?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="13" ContentLicense="CC BY-SA 3.0" />
  <row Id="7272" PostTypeId="2" ParentId="5326" CreationDate="2017-02-24T14:05:44.743" Score="1" Body="&lt;p&gt;There are modulations that would not be called &quot;AM&quot; which still modulate amplitude. For example, BPSK reverses phase at a zero amplitude point. BPSK could also be considered a digital amplitude modulation where the amplitude varies between 1 and -1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, you must be careful to specify what you mean by &quot;not AM&quot;. If you mean to exclude all modulations that modulate power at all, then peak and average power could be considered the same in practice. MSK is an example that would qualify.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would only apply to the extent that the transmitted waveform has an RMS average equivalent to a sine wave. For example consider that a square wave has a higher RMS average, and thus a higher power, than a sine wave of equal amplitude. In practice the difference will be small or nonexistent for most modulations.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-02-24T14:05:44.743" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7273" PostTypeId="2" ParentId="7267" CreationDate="2017-02-24T15:08:39.703" Score="2" Body="&lt;p&gt;&lt;strong&gt;Probably, as long as you don't interfere with others' FM reception.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are allowed a maximum range of 200 feet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Judging from the length of the antenna and the apparent lack of a power amplifier, it is likely legal. I doubt whether that thing has a 50 foot range, and that's why I said that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.fcc.gov/media/radio/low-power-radio-general-information&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here is the specific FCC rules page&lt;/a&gt; (which I didn't read, &lt;em&gt;but  you should!&lt;/em&gt;).&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-02-24T15:26:13.563" LastActivityDate="2017-02-24T15:26:13.563" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7274" PostTypeId="1" AcceptedAnswerId="7276" CreationDate="2017-02-25T00:56:40.907" Score="6" ViewCount="1247" Body="&lt;p&gt;A ham is initially licensed in Hawaii as KH6ABC (example only).  If he subsequently moves to the mainland, can he keep his geographically restricted &quot;KH&quot; call sign or must it be changed?&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="8832" LastEditDate="2017-02-27T14:42:41.533" LastActivityDate="2018-12-15T21:02:36.207" Title="Can I use a Hawaiian call sign on the mainland?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7275" PostTypeId="2" ParentId="5326" CreationDate="2017-02-25T01:26:53.053" Score="-1" Body="&lt;p&gt;For &lt;a href=&quot;http://www.rfwireless-world.com/Tutorials/VSAT-tutorial.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;VSAT (Very Small Aperture Terminal)&lt;/a&gt;, I can't find anything that specifically identifies the modulation used other than to say that it uses TDMA (Time Division Multiple Access). But my experience with this type of equipment suggests that it is probably a constant envelope type of waveform while transmitting. (Such as QPSK). This is because the amplifiers used for these systems are typically non-linear and are designed to run at one power output level. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So PEP would be equivalent to Average Power for a steady transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But your average power calculation might need to take into account the duty factor, since it is a TDMA signal. If that's important to you, you should say so in your question. If you do that, we can readdress your question. &lt;/p&gt;&#xA;" OwnerUserId="4294" LastActivityDate="2017-02-25T01:26:53.053" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7276" PostTypeId="2" ParentId="7274" CreationDate="2017-02-25T08:03:19.363" Score="3" Body="&lt;p&gt;He or she can certainly keep the KH callsign and use it anywhere in the US and territories.  (I wonder if he or she thought that when operating in Samoa?  There are two sides there, as you probably know.  But since the non-American side is a territory the same rules apply.)    &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common convention is to append it with the location where the station (even a HT) is operating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if in California, you might identify on SSB as &quot;KH6ABC slant 6&quot; so people won't pile up wanting Hawaii for WAS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If in Morse code, you use the slash character, as in &quot;KH6ABC/6&quot;    (-..-.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But these are conventions, not rules.  So it is perfectly all right to just use your native callsign wherever you go in the US.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Outside the US, especially for events (such as climbing Mt. Everest) the entire expedition is generally given a callsign just for that event.  This is where WARC comes in.  It is not complicated but needs to be taken into account by the expedition leader.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inside the US it is pretty simple.  Myself, I am AL7** and though am in California, ID myself as AL7**.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where it gets interesting is if you to Alaska - where it would be &quot;KH6ABC/L7&quot; or &quot;KH6ABC slant L7.&quot;   (L7 means Alaska, whether a wl7, kl7 or an al7).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC requires that you identify yourself.  That's the end of the story with them.  Their goal is to encourage the hobby, not to fine people like with broadcast stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FYI, they are serious about ID requirements.  Simply keying up a repeater to see if you can reach it does not fit the criteria for lawful identification.  Enforcement actions are rare but can happen if it is deemed to be harmful interference.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is an interesting story along those lines, in which an operator was fined for failure to identify:  &lt;a href=&quot;http://www.kg7ydj.us/2015/12/23/we-pause-for-this-station-identification-requirements-for-amateur-radio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;ID requirements&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a case like this, the operator should have said something like &quot;AL7EM Test&quot; and the fine could have been averted.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-07-02T22:21:36.947" LastActivityDate="2017-07-02T22:21:36.947" CommentCount="13" ContentLicense="CC BY-SA 3.0" />
  <row Id="7277" PostTypeId="2" ParentId="7267" CreationDate="2017-02-25T08:32:47.260" Score="0" Body="&lt;p&gt;Part 15 operation on the FM band is not limited by distance.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is judged by the FCC based on emissions.  If they get interested in your transmissions they will send out a van with calibrated receivers and take various measurements to ensure that you are not exceeding the limits.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, with a legal antenna and power output, the range is limited to a couple of hundred feet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The good news is that you are not limited by the number of transmitters.  So if you want to cover a whole city block you are free to put legal transmitters at whatever intervals will accomplish your goals.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As always, the FCC is most interested when you cause interference with a properly licensed service.  So for that reason it is wise to make sure you are in an untilized portion of the band.   As long as nobody complains you will probably have no trouble with the FCC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This applies to both intentional radiators (the Zero) and also to unintentional spurious emissions.  As an example, if you have a fully legal setup in a  briefcase and operate it from a taxi, you're fine unless you interfere with the taxi's radios.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-02-25T08:40:11.273" LastActivityDate="2017-02-25T08:40:11.273" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7278" PostTypeId="2" ParentId="7267" CreationDate="2017-02-25T20:48:24.643" Score="5" Body="&lt;p&gt;When running rpitx or pifm on a Raspbery Pi, the &quot;transmitter&quot; output uses an unfiltered digital I/O pin.  Thus you not only need to worry about FM band interference, but emission laws and interference on any of the harmonic frequencies of the Pi transmit frequency setting, especially odd harmonics, but various non-linearities can even cause radiation on the even harmonics. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you only want to worry about the Part-15 legality of low power transmission in the FM broadcast band, you will need to add a low-pass filter with a cut-off below the second harmonic (or a band-pass filter, or both) between the Pi and the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added: The concept that seems not to be known by PiFM hobbyists is that a digital output does not produce anything close to a sinewave, but that the rectangular pulses produced by any periodic digital output consists of a spectrum containing lots of different sinusoidal components (Fourier's theorem) spattered across a huge portion of the entire RF spectrum, much of it well outside the RF band of interest.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-03-18T16:02:53.640" LastActivityDate="2017-03-18T16:02:53.640" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7279" PostTypeId="1" CreationDate="2017-02-25T21:28:36.017" Score="7" ViewCount="442" Body="&lt;p&gt;Related to this question:&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/7267/is-it-legal-to-broadcast-an-fm-radio-signal-with-a-raspberry-pi-zero&quot;&gt;Is it legal to broadcast an FM radio signal with a Raspberry Pi Zero?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to build a super-low-tech low-pass filter for VHF harmonic suppression without a PCB or any other non-trivial-to-find components?  (e.g. nothing surface-mount or tiny)  Would a bunch of coax-stub (or twisted pair) reflective notch filters work?  Hookup wire wound around a pencil inductors?  etc.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-02-26T12:51:45.810" Title="Super-low-tech VHF low-pass filter construction?" Tags="&lt;rfi&gt;&lt;filter&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7280" PostTypeId="2" ParentId="7279" CreationDate="2017-02-26T12:51:45.810" Score="2" Body="&lt;p&gt;If you've got an RTL-SDR or similar broadband VHF SDR, you could construct a wideband noise generator and use it as a sort of poor man's VNA to tune the notch on a set of coaxial stubs. A dozen or so meters of high quality coax, RG-213, 9913F, or even better, hardline, could be used to build a set of stubs that would suppress harmonics fairly well. A pair of them properly connected should be able to suppress 2nd order harmonics by something close to 30dB. 3rd order is trickier, and requires carefully designed &quot;T&quot; type stubs that have reactance compensation included to avoid attenuating the primary frequency as well. It is not a trivial process, but the required materials are the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same SDR/Noise Generator combination could potentially be used to tune a typical multipole LC filter, but that will not be at all trivial. You'll need a good L/C meter, and ideally an oscilloscope and a good clean variable signal generator to get the same attenuation as the coaxial stubs, and the components cannot be scrounged typically. You'll need low loss NP0 capacitors in very precise values and inductors wound carefully to avoid stray capacitance and thermal variation as well.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-02-26T12:51:45.810" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7281" PostTypeId="2" ParentId="7271" CreationDate="2017-02-26T18:36:29.323" Score="3" Body="&lt;p&gt;I will take a stab at a guess to suggest the OP is looking for a common type of receiving antenna (Rx) known as a Traveling Wave Antenna.  As I mentioned in my comment, the popular so-called &quot;Top-Band&quot; receiving antennas are Beverage Antennas which is a kind of Traveling Wave Antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Traveling Wave Antennas are known as Broadband Antennas because their bandwidth is usually wider than a resonant antenna (e.g. Dipole).  The Bandwidth for antennas can be measured in several different ways but for Traveling Wave Antennas it is usually defined by:&#xA;$$&#xA;Bandwidth = \frac{f_U}{f_L}&#xA;$$&#xA;Where $f_U$ and $f_L$ are upper and lower frequencies of the range of acceptable performance of the antenna (you get to define what &quot;acceptable&quot; means).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A Traveling Wave Antenna is so called because the current is traveling along the conductors.  This is different from the typical Dipole resonant antenna where the current is in &quot;Standing Waves&quot; on the conductors.  Traveling Wave antennas are also known as just &quot;Wave&quot; antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have worked through solutions using both analytical and numerical methods of resonant antennas.  Actually, only the thin-wire (where cross-section is ignored) dipole have I done using purely analytical means.  For numerical solution I have used both the Method of Moments (used by popular NEC2/NEC4) and experimented with some FTDT methods.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I have never worked on solving for the currents of a Traveling Wave Antenna so I do not know much about that.  However, in scanning some of my books in my library, I have never seen the Lorentz Force being used to somehow model the current (guessing that is what the OP is referring to).  Does not mean it is not possible though.  In fact, solving physics problems from so-called &quot;First Principles&quot; is often a popular endeavor although many times includes complexities that are not worth the effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In solving for antenna solutions, you usually work to obtain a good representation or approximation of the current on the antenna conductors (I am referring to wire antennas here, whether resonant or traveling wave). This current is the unknown and once you have the current you can solve the Helmholtz Integrals for both the vector potential $\vec{A}$ and the scalar potential $\vec{\phi}$.  Using these, you can compute the fields $\vec{E}$ and $\vec{H}$ and from those compute many other antenna parameters (etc, gain, radiation field).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the key is the current $I$, or current density $\vec{J}$ and you usually need $\vec{J}$ when the geometry of the conductors are an important part of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In one of my books, &quot;Antenna Theory and Design&quot; by Stutzman and Thiele, they begin their discussion of modeling long wire (a kind of traveling wave) antennas using a constant current as:&#xA;$$&#xA;I_t(z) = I_m\,e^{- j \beta z}&#xA;$$&#xA;Where the $z$ coordinate is along the conductive wire and $I_m$ is just some maximum current value.  $\beta$ is a phase constant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The discussion continues on from that simple start to consider more complicated traveling wave antennas (e.g. Rhombic).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend the Stutzman &amp;amp; Thiele book as a starting place.  Its handling of traveling wave antennas is more extensive and detailed than in other books I have such as &quot;Antennas For All Applications&quot; by Krauss &amp;amp; Marhefka or &quot;Antenna Theory&quot; by Balanis.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2017-02-26T19:09:56.287" LastActivityDate="2017-02-26T19:09:56.287" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7284" PostTypeId="1" CreationDate="2017-02-27T22:42:10.513" Score="4" ViewCount="446" Body="&lt;p&gt;We are setting out our roof-space as an attic, and after decorating, there will be a triangular void under the house ridge, which will be about 36&quot; wide, and 18&quot; high.  I can easily fit a standard folded dipole loop antenna for VHF FM, but the DAB (&lt;a href=&quot;https://en.wikipedia.org/wiki/Digital_audio_broadcasting&quot; rel=&quot;nofollow noreferrer&quot;&gt;Digital Audio Broadcast&lt;/a&gt;) antenna is vertically polarised, and its dipole will not fit. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am toying with the idea of using a slot antenna, with a horizontal slot in this space, and am wondering how to do this.  I have seen what I think is a 'skeleton slot' which I thing is a short-circuited horizontal folded dipole, which is shorted where the normal folded dipole feed is, and is fed instead, as if it was a slot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a blessing, the roof ridge is pointed almost exactly at the transmitter, both for VHF FM, and for DAB.  The shape of the space though limits the size of the plane into which the slot is cut.  So I thought, could I put in place, a horizontal ground plane, and build half a slot antenna on top of it, with the centreline of what would be the full slot, coinciding with the surface of the ground plane.  The plane surrounding the half lot would of course be electrically continuously with the horizontal ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would this be an effective antenna, and what would be the characteristic impedance, would it be half of the impedance of the full slot, being connected between the point on the horizontal ground plane under the centre of the lot, and the midpoint of the opposite side of the half slot?  I would expect it to be half of the typical slot antenna impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the DAB antenna, I settled for the slot.  Having seen a double YAGI antenna, with a skeleton slot as its main feeder, in place of a pair of dipoles, I concluded that the plane does not need to be infinite, or even large.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I settled for the largest piece of fibreglass reinforced foam roof insulation, which was aluminium foil coated on both side.  This turned out to be, a pentagonal shape, starting with a rectangle, 37&quot; x 19.5&quot;, with the top two corners removed to fit under the roof membrane, and a notch cut into the top point, to accept the ridge beam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;About 4&quot; from the bottom of this sheet, using a Stanley knife, working from both sides, I cut out a slot 25&quot; wide by 2&quot; high, carefully saving the cut out piece.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then using self adhesive copper screening tape, I lined out all the cut edges, both of the slot, and the periphery of the board. and finished both, with more tape, to fully short-circuit the front face to the back face of the board on all the edges, giving a generous overlap on the tape.  (The tape is reputed to use a conductive adhesive.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then I carefully removed all the copper foil from the piece cut out of the slot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, I measured to find the midpoint of the inside long faces of the slot, and carefully tinned, and made a nice solder blob on both face centres.  Taking some braid off some scrap co-ax, two pieces about 6&quot; long, I dressed, and tinned one end of each, and soldered them to the blobs on the midpoints.  These I dressed to exit the slot on what was to be the access surface, and carefully refitted the the now naked piece of foam, which I had cut out for the slot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using parcel tape, I taped across the slot, with some tension, to keep the packing piece tightly in place, and to add some mechanical strength to what would otherwise be a very fragile article.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, taking a 300 ohm to 75 ohm BALUN, Trimming the braid ends to fit, I connected it in place, and bedding it in quick-setting epoxy, I fitted the BALUN onto the naked filler piece, at the midpoint of the slot.  Realising that I had got epoxy on the co-ax securing screws, before the glue had time to set, I connected a generous length of 75 ohm co-ax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the glue had had ample time to set, I carefully installed the antenna in the roof ridge, where I had prepared a place for it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This installation is not yet properly installed, and the FM antenna is not yet prepared, so my connection to the antenna lead is a very crude twisting, and taping of wires.  Nevertheless, at least on DAB, it seems to work OK, but without the proper FM antenna, FM reception is very poor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any special care required to unite the FM antenna to the DAB antenna feed to reduce any standing wave effects?&lt;/p&gt;&#xA;" OwnerUserId="9273" LastEditorUserId="76" LastEditDate="2017-03-14T16:04:24.840" LastActivityDate="2018-07-08T23:32:16.057" Title="DAB antenna in roof space" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7285" PostTypeId="1" CreationDate="2017-02-28T00:05:41.730" Score="1" ViewCount="327" Body="&lt;p&gt;I have a generic external speaker mic with the two-pin connection (1x 3.5mm, 1x 2.5mm mono jack), which doesn't work with my FT-470 (no real surprise, figured I'd just mod it.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've started the mod, using the packet interface for this rig as a starting point (2k resistor switched between mic tip and shield for PTT, 1uF cap between mic and mic plug tip for tx audio - this works fine on this specific radio)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Everything is fine on transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On receive, when a carrier is received, audio from the mic is ending up in the rig's own AF amplifier, causing audio feedback (howling) through the speaker. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I know this is feedback because the speaker mic has a headphone jack. Plug in headphones, tune into a signal, tap the speaker mic case and you can hear the sound of tapping amplified through the headphones.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But only when there is a carrier, not just when the squelch is open.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modifying the speaker mic with a DPST switch and using the second pole to only bring the mic in-circuit on PTT seems an obvious solution, but sourcing a DPST PCB mount micro switch is proving, well, impossible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a 2k resistor in series with the PTT switch, mic plug tip and shield.&#xA;I have tried a 1uF cap in series with the mic, mic tip and mic shield, like the required packet interface wiring for this rig.&#xA;I have tried a 1uF cap in parallel with the mic, as appears (sans value) for the internal mic in the rig schematic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm putting way too much effort into this, but I'm stuck. It's a shame to not use the old rig over something so small. Original accessories are long since unavailable. If I knew what was inside, e.g. MH-12A2B, I'd just mod this speaker mic to contain the exact same components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Service manual with schematics is here.&#xA;&lt;a href=&quot;http://www.radiomanual.info/schemi/FT470_serv.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.radiomanual.info/schemi/FT470_serv.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8463" LastActivityDate="2018-03-08T09:50:38.213" Title="Old Yaesu FT-470 HT audio feedback with external speaker mic" Tags="&lt;ht&gt;&lt;electronics&gt;&lt;equipment-design&gt;&lt;yaesu&gt;&lt;microphone&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7286" PostTypeId="2" ParentId="7267" CreationDate="2017-02-28T01:27:50.297" Score="3" Body="&lt;p&gt;the limit according to &lt;a href=&quot;https://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf&lt;/a&gt;  is 150uV/m measured 3m from the antenna.  however, if one of the harmonics or IMD products interferes with another service the FCC won't care about the radiation measurement anymore, and tell you to stop transmitting immediately.  since the pi uses a GPIO pin for output, and the signal is unfiltered, the 7-or-8 bit modulation is sure to generate a lot of IMD and harmonics. the IMD may splatter in the aircraft band, and the harmonics may interfere in the emergency services bands.&lt;/p&gt;&#xA;" OwnerUserId="9274" LastEditorUserId="9274" LastEditDate="2017-02-28T01:42:15.670" LastActivityDate="2017-02-28T01:42:15.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7287" PostTypeId="1" AcceptedAnswerId="7289" CreationDate="2017-02-28T18:34:48.050" Score="1" ViewCount="506" Body="&lt;p&gt;I just installed a spare-tire mount and Browning BR-180 dual band antenna on my Jeep JK. Initial SWR testing show nothing higher than 1.4:1 across both bands so I didn't try to tweak it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then I put the spare tire back on and the SWR shot way up, over 5:1 and worse in some cases. Removing the spare again confirmed the problem, as the SWR dropped back down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What can I do to resolve this? I know others with similar installations that work fine. I'm not sure exactly what's happening.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These pics are of my installation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/H9mOx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/H9mOx.jpg&quot; alt=&quot;Back view of antenna on vehicle&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4wDIL.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4wDIL.jpg&quot; alt=&quot;Side view of mount between tire and rear hatch&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="76" LastEditDate="2017-03-01T00:50:01.863" LastActivityDate="2017-03-19T00:58:43.300" Title="High SWR on a Jeep with Spare Tire Mount" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;mobile&gt;&lt;antenna-system&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7288" PostTypeId="1" AcceptedAnswerId="7290" CreationDate="2017-03-01T15:59:19.397" Score="5" ViewCount="1101" Body="&lt;p&gt;On the UK Band Plan there are frequencies stating “QRS (slow telegraphy) Centre of Activity”. For example, 14,055 kHz on 20m and 3,555 kHz on 80m.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;What is considered slow? (&amp;lt;15 wpm?)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;How close should you stay to the stated frequencies?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="1131" LastEditorUserId="76" LastEditDate="2017-03-01T16:31:35.033" LastActivityDate="2017-07-02T22:22:54.447" Title="How slow is slow telegraphy?" Tags="&lt;cw&gt;&lt;united-kingdom&gt;&lt;band-plan&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7289" PostTypeId="2" ParentId="7287" CreationDate="2017-03-01T20:17:12.863" Score="3" Body="&lt;h2&gt;The metal wheel is detuning the antenna.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;You'll either need to:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Put the spare inside the vehicle &lt;/li&gt;&#xA;&lt;li&gt;Move the antenna&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;I would move the antenna&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;And the higher the antenna the better!&lt;/strong&gt; How about on top of that gray cap? If that truck bed cap is nonmetallic, you'll need a counterpoise to maximize your communications range. That could be made with some metallic  tape radials on the inside, properly sized and connected to the antenna's ground (the coax shield through the connector).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I just noticed what seems to be a metal luggage rack or roll bar. Can you mount it to that? A better photo of that would help. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-03-01T20:24:46.423" LastActivityDate="2017-03-01T20:24:46.423" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7290" PostTypeId="2" ParentId="7288" CreationDate="2017-03-01T22:25:54.820" Score="5" Body="&lt;p&gt;QRS actually means &amp;quot;Please slow down&amp;quot; and is not really defined as a specific speed.  So basically what they are trying to do is be as inclusive as possible.&lt;/p&gt;&#xA;&lt;p&gt;When I earned my Novice license in 1971 the speed required was 5 wpm.&lt;/p&gt;&#xA;&lt;p&gt;Then when I earned Advanced in 1977 it was 13 wpm.&lt;/p&gt;&#xA;&lt;p&gt;I am studying now for the Amateur Extra, and am amazed that there is no Morse requirement.  When I get serious I am sure I'll get it.  I'll probably make a single letter change in my callsign.  I am AL7** right now, but I want KL7**.&lt;/p&gt;&#xA;&lt;p&gt;Local lore had it that most people had a &amp;quot;plateau&amp;quot; of about 10 wpm as they  progressed in speed.  It was said that was the speed where instead of writing down letters you could hear whole words like &amp;quot;the&amp;quot; and &amp;quot;ES&amp;quot; which meant &amp;quot;and&amp;quot; and so on.&lt;/p&gt;&#xA;&lt;p&gt;My experience was different.  My plateau is about 18 wpm.  At that point you don't even write it down; you just listen to the conversation.&lt;/p&gt;&#xA;&lt;p&gt;It helps that a lot of it is preformatted, like &amp;quot;QTH IS FAIRBANKS FAIRBANKS&amp;quot; and &amp;quot;RST 999&amp;quot; and all that.  But when you get on with a conversation it takes time to learn to do that reliably.&lt;/p&gt;&#xA;&lt;p&gt;So, to answer your question #1 - I would say slow is considered to be just slow enough that the other operator can copy - they'll send &amp;quot;RRR&amp;quot; or &amp;quot;QSL&amp;quot; to let you know.  If I had to put a number on it, it would be much less than 15 - more like 5 or so.&lt;/p&gt;&#xA;&lt;p&gt;Answer #2 is pretty clear.  You simply stay on your assigned frequency.  Unless the other operator (maybe has QRM or QRN) and requests a QSY (change frequency).&lt;/p&gt;&#xA;&lt;p&gt;The UK band plan assigns 14.0-14.060 for this type of operation so clearly there is some flexibility.&lt;/p&gt;&#xA;&lt;p&gt;Here is the relevant document in terms of frequencies, which I think you referenced:  &lt;a href=&quot;http://www.hflink.com/bandplans/UK_bandplan.pdf&quot; rel=&quot;noreferrer&quot;&gt;UK Band Plan&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I am not familiar with the foundation level, but here is where it talks to power level:  &lt;a href=&quot;http://www.rsgbdata.net/wp-site/clubsandtraining/docs/foundation/EX%20307%20Foundation%20Data%202603U.pdf&quot; rel=&quot;noreferrer&quot;&gt;Reference data for the Foundation Level Examination&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;In the USA we can transmit as fast or as slow as we want, and our only concern is interference with others.&lt;/p&gt;&#xA;&lt;p&gt;OK, those are the answers, now let me tell a quick story.&lt;/p&gt;&#xA;&lt;p&gt;When US Navy radio operators used to get trained in Morse, years back, they would all have typewriters.  (In all my exams we had a pencil and paper).  But the kicker is that their typewriter keys were all just flat black.&lt;/p&gt;&#xA;&lt;p&gt;The instructor would pull down a chart at the front of the room showing the layout of the keys, and they would start transcribing what they heard.  So far, so good.  They could get up into the 20s that way, with glances up at the chart.&lt;/p&gt;&#xA;&lt;p&gt;Then at some point (early on - just a couple of days) the instructor would not pull down the chart.  From then on they were expected to develop muscle memory that would cause them to hit the right keys as they heard the code.&lt;/p&gt;&#xA;&lt;p&gt;I have heard wild stories about the speeds they could achieve.&lt;/p&gt;&#xA;&lt;p&gt;Then they would start giving them high-speed code without typing.  Wearing earphones, they heard two signals - one for each ear, and different audio frequencies.  Then they would take a quiz on what they heard.&lt;/p&gt;&#xA;&lt;p&gt;Now those were the guys who could really do the job.  They could sit and monitor code and get the gist.&lt;/p&gt;&#xA;&lt;p&gt;The single most important thing I learned in my Morse training was to not fret about missing a letter - because fretting will make you miss even more.  You need to just go on.&lt;/p&gt;&#xA;&lt;p&gt;My favorite frequencies for Morse are about 14.170-14.180, plus 80 meters.  And for SSB nothing beats 14.205.  I wonder how it is over there.&lt;/p&gt;&#xA;&lt;p&gt;Anyway, I hope you have an enjoyable experience if you do this.&lt;/p&gt;&#xA;&lt;p&gt;Thank you for an interesting question.  Upvote.&lt;/p&gt;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-07-02T22:22:54.447" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7291" PostTypeId="2" ParentId="7288" CreationDate="2017-03-02T15:23:58.437" Score="5" Body="&lt;p&gt;On the west coast USA there is a slow CW traffic net that meets each night on the 80 meter band.  The rules for this net is nothing faster than 10 wpm.  It is a dual purpose net, teaching traffic handling skills and available for those who are not up to the CW speeds for a regular net. The regular CW traffic nets are about 20 wpm on average.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, that is one definition of slow CW.  I operate almost 100 percent CW and have a pretty good feel of CW ops.  Most slower CW is around 15 wpm on average.  Once and a while I will hear someone who is below 10 wpm but not often.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the previous answer stated, the formal definition of QRS is a request for someone to slow down their CW.  And, QRQ means to speed up.  But, it also is used informally by ham operators to define either slow or fast CW as the OP used the term.  I know of a QRQ operators club that operates only at 40+ wpm.  I know of a QRQ club or group that operates at 60+ wpm.  But, most people say QRQ speeds are anything above 30 wpm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, QRS in my opinion is 15 wpm or less -- QRQ is 30 wpm or more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;About band plans for CW speed -- in the US as far as I know, there is no formal band plan for CW operating speed.  However, most QRS is found around the 050 to 060 segment of the bands.  On 20m this is 14050 to 14060 KHz, on 40m it would be 7050 to 7060 KHz and so on.  But, you can hear QRS stations all over but the most are found in these segments I mentioned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I learned CW when I was 9 (and 10) years old back in the latter part of the 1950s.  I kept putting off the task of taking my Novice test so by the time I took the Novice 5 wpm test I was easily copying 18 to 20 wpm.  Today I am still comfortable at about 20 wpm but during a contest I can play at 30 to 35 wpm without too much of a problem.  Learning CW when you are really young is the best.  I am still trying to convince my grandkids to learn CW just to have a different and unique skill among their peers.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2017-03-02T15:23:58.437" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7293" PostTypeId="2" ParentId="7287" CreationDate="2017-03-02T15:45:25.780" Score="3" Body="&lt;p&gt;The metal wheel and the steel-belted tire are big chunks of metal. Those add capacitance between the antenna and ground, so they lower the resonant frequency of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A shorter whip or a variable-length whip might work. Some mobile antennas have an adjustable length portion at the tip. If the top of the coil is the common 3/8&quot; thread, you can find a telescoping whip to get the length right, then cut a solid whip to the right length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some mobile antennas have a mast section below the coil. These are usually for bumper mounts, but might help here. Search for &quot;Hustler mast&quot;.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2017-03-02T15:45:25.780" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7294" PostTypeId="2" ParentId="7288" CreationDate="2017-03-02T15:52:36.203" Score="2" Body="&lt;p&gt;This may be a hold-over from when amateur licenses required Morse code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the US, the entry level license (Novice) required 5 words per minute, and the next two levels required 13 wpm and 20 wpm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Novices were restricted to a few small sub-bands on HF, so it was common to hear and use Morse at slower speeds there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't find the details of Morse requirements in the UK, only that they were dropped in 2003. The RSGB offers Morse competency certificates starting at 5 wpm, so that might have been the lowest requirement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://rsgb.org/main/operating/morse/certificate-of-competency/the-morse-test/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://rsgb.org/main/operating/morse/certificate-of-competency/the-morse-test/&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2017-03-02T15:52:36.203" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7295" PostTypeId="1" CreationDate="2017-03-02T18:27:46.177" Score="2" ViewCount="4149" Body="&lt;p&gt;Is there a method to limit the people with access to a simplex channel?  I would like to utilize a channel that is set up for just myself and my wife.  If I gave directions to meet somewhere I would only want her to know where and when we would meet.&lt;/p&gt;&#xA;" OwnerUserId="9294" LastEditorUserId="8832" LastEditDate="2017-03-08T21:10:18.693" LastActivityDate="2017-03-09T01:42:54.237" Title="Private Channel?" Tags="&lt;legal&gt;&lt;frequency&gt;&lt;tone-squelch&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7296" PostTypeId="2" ParentId="7295" CreationDate="2017-03-02T18:43:38.597" Score="2" Body="&lt;p&gt;No. It is not legal. You may not &lt;em&gt;hide the content of your message&lt;/em&gt; when making use of amateur frequencies, no matter what means you use to do so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Technically, all you would need is radios supporting a digital voice mode that includes encryption, but I can't name one that would definitely work simplex (e.g. &lt;a href=&quot;https://en.wikipedia.org/wiki/Project_25&quot; rel=&quot;nofollow noreferrer&quot;&gt;P25&lt;/a&gt; can be encrypted but is as far as I know always “trunked”, requiring a repeater).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to pursue this then you would need to use non-amateur frequencies, e.g. by purchasing a ‘business band’ license (details vary by jurisdiction; that's the USA concept). At this point you have to compare the cost with other methods of communication.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-03-02T18:43:38.597" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7297" PostTypeId="2" ParentId="3599" CreationDate="2017-03-02T19:08:53.533" Score="0" Body="&lt;p&gt;Half-wave antennas have one major advantage:  They do not require a ground plane.  No need to mount it on a car, or put down radials in the ground, etc.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So by their definition that would be &quot;the length.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quarter-wave verticals require ground planes (which should be roughly 5% bigger around than the antenna is tall.  For AM broadcasting this means putting down 120 wires from the antenna mount point (every 3 degrees).  Then the ground plane acts as a reflector to provide the other half of the half-wave length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a practical matter, unless you are Nikola Tesla, you want the feedpoint to be at the middle of a multiple of half-waves so the voltage is at a low while current is at a high. Handheld radios do not have that luxury, hence their definition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your clock radio doesn't need a specific antenna length for each station because 1) The stations are nearby and 2) They transmit a lot of power.  Receiver sensitivity is not an issue in those situations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For DX (long distance), you will want a resonant antenna so you capture as much of a weak signal as possible, because receiver sensitivity is finite, and you want to give it as much to work with as possible.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Receiver sensitivity is only half the story; the other is the noise floor.  All circuitry produces some amount of noise that gets amplified with the signal.  This includes external sources such as power lines.  So using a resonant antenna also helps filter out undesired external noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For operation on non-resonant antennas you will want an antenna tuner.  So yes, a 160 Meter antenna can work other frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rule of thumb is that you want to try to use odd multiples of antenna length to get as close as possible to resonance.  So, for instance, a 40 Meter dipole will work OK on 15 Meters.  But since it isn't a perfect match it always helps to have a trusty antenna tuner to dial it in better.  You can tune it by ear, or, if transmitting you can use an SWR meter to find the best match.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="76" LastEditDate="2017-03-02T19:19:42.827" LastActivityDate="2017-03-02T19:19:42.827" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7298" PostTypeId="2" ParentId="7295" CreationDate="2017-03-02T20:19:26.430" Score="4" Body="&lt;p&gt;You cannot limit others from using a channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But as long as you have a license then you can operate anywhere in the band in question, and there are a lot of underutilized frequencies.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just be sure to ID at the start of your transmission and every 10 minutes if it goes on longer than that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Privacy is relative, though.  Someone with a scanner might catch your transmissions.  You can use CTCSS to open her squelch just for you, but that won't hide you from scanners.  So in that sense there is no legal way to have a truly private channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If she has a license she can answer.  But without a license she would be in violation to even just click the PTT button to acknowledge reception of your transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might want to consider the FRS (Family Radio Service) units where both of you can talk all you want.  The better ones also can use CTCSS so neither of you need to listen to whatever other chatter may be on the same channel.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-03-02T20:40:17.743" LastActivityDate="2017-03-02T20:40:17.743" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7300" PostTypeId="1" AcceptedAnswerId="7312" CreationDate="2017-03-05T04:01:22.203" Score="2" ViewCount="7140" Body="&lt;p&gt;I have been researching how to construct a 1:1 current balun. I have a few questions and am looking for feedback on what I plan to do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, I want to use the balun from 10m to 160m at 100w.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I plan to use an Amidon FT-140-61 toroid bifilar (2 wires) wrapped with #18 magnetic wire 10 to 12 turns. I do not plan to use tape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I need to use tape? How do you use tape? Why? I've seen toroids covered in tape and I've seen tape that appears randomly wrapped on the magnet wire. Do you need to prevent the magnet wire from touching a bare ferrite toroid?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When would you need a different material type for the toroid? I've read Amidon's documentation on frequencies for their toroids, but I've also seen different frequencies shown elsewhere. Is there a chart that shows which material is best with which range of frequencies?&lt;/p&gt;&#xA;" OwnerUserId="9267" LastActivityDate="2020-08-27T03:09:25.573" Title="How do you construct a 1:1 balun?" Tags="&lt;balun&gt;" AnswerCount="4" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7301" PostTypeId="2" ParentId="7300" CreationDate="2017-03-05T19:56:04.083" Score="-1" Body="&lt;p&gt;I am no expert, but this site has loads of information, &lt;a href=&quot;http://www.dj0ip.de/balun-stuff/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.dj0ip.de/balun-stuff/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9083" LastActivityDate="2017-03-05T19:56:04.083" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7302" PostTypeId="2" ParentId="7300" CreationDate="2017-03-05T22:53:32.110" Score="3" Body="&lt;p&gt;Type 61 is probably not really suitable for a choke type current balun for 160m, and definitely not in a smaller core size like a T140. The AL of the FT140-61 is about 120, about 1/10th that of the higher permeability materials like Type 43, 31, or 73/77. You'll find it difficult to achieve sufficient choking impedance to get good common mode suppression on 80 and 160m, as you're really looking for something on the order of 2,000-5,000 ohms. You just can't cram enough turns on those lower loss materials, and you don't want low loss to begin with. A 1:1 choke type current balun only works &lt;em&gt;because&lt;/em&gt; the material is lossy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A truly effective and low loss 160-10m balun is a bit of a tricky creature to construct, because in order to get good common mode impedance at one end of the range, you'll likely have to sacrifice to some degree on the other, either by injecting additional loss on 10 meters, or accepting somewhat reduced impedance on 160 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd do best for the entire range with something like an FT240-43 (which run about $4.50 from Mouser), with 14 or so bifilar turns of good quality magnet wire on the core.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the current status of the solar cycle, personally I'd probably opt for something like a T240-31 with 12-14 bifilar turns, knowing I was injecting some loss on 10m and to a lesser extent 15m, but getting better performance on 160 and 80m. Most of the action for the next few years will be on 80-15 meters, and a in a couple years that will probably drop to 160-17m before starting to rebound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;This document&lt;/a&gt; is often referred to as the &quot;RFI bible&quot; or &quot;Balun bible&quot;, and with good reason. All the knowledge you seek is contained within, and in fairly easy to understand language. It's well worth a read and, in my opinion, should live on every ham's bookshelf.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-03-05T22:53:32.110" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7303" PostTypeId="2" ParentId="874" CreationDate="2017-03-06T18:47:00.993" Score="0" Body="&lt;p&gt;You &lt;em&gt;do&lt;/em&gt; need a license, it's just easier to get, since there's no Morse Code test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first test is the Basic, and you can pass either at the 70% level or the &quot;honours&quot; 80% level. Honours lets you operate below 30 MHz. Non-honours restricts you to VHF and above. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basic holders may operate cross-band repeaters, and same-band store-and-forward repeaters. That's clarified in an FAQ on Industry Canada's website.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is an option to take a Morse test, at 5 words per minute, and if you pass (and if you've also passed the Basic), it grants you the same privileges as getting honours on the basic: i.e., operation below 30 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other license class is Advanced, which allows higher power on some bands, the right to build your own equipment, to install club equipment, and to operate same-band repeaters. It also grants the right to the whole Amateur spectrum, in case you hadn't previously gotten your Honours and/or 5 w.p.m. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In no event does your license class restrict what operating mode you use, within the bands you're entitled to. And Canadian bandplans don't reference license class, either. So you can try Morse even if you've never passed the Morse test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's been clarified that only Advanced license holders are eligible for the CEPT certificate that allows operation while visiting certain EU countries. This is not because of the Morse, since dropping the Morse requirement is ITU-wide. It's some other element of the Advanced curriculum they're after.&lt;/p&gt;&#xA;" OwnerUserId="9314" LastActivityDate="2017-03-06T18:47:00.993" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7304" PostTypeId="2" ParentId="1459" CreationDate="2017-03-06T18:51:42.713" Score="0" Body="&lt;p&gt;The study course I've been following for the Basic exam says to say (in voice modes) &quot;N1KB mobile VE3&quot;. It suggests that for shorter distance communications, you can skip the phoentics and just say vee ee, for the prefix, but should probably use phonetics for other other elements.&lt;/p&gt;&#xA;" OwnerUserId="9314" LastActivityDate="2017-03-06T18:51:42.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7305" PostTypeId="1" AcceptedAnswerId="7306" CreationDate="2017-03-06T19:53:03.447" Score="3" ViewCount="1729" Body="&lt;p&gt;Just bought this &lt;a href=&quot;https://www.amazon.ca/NooElec-NESDR-SMArt-Enclosure-R820T2-Based/dp/B01GDN1T4S/ref=cm_cr_arp_d_product_top?ie=UTF8&quot; rel=&quot;noreferrer&quot;&gt;NESDR Smart USB dongle from Amazon in Canada&lt;/a&gt;. Wrote the company asking for drivers, but they sent links which didn't help. Anybody have a better place to download drivers for Mac OS Sierra? Thanks. &lt;/p&gt;&#xA;" OwnerDisplayName="user9315" LastActivityDate="2017-03-07T21:17:47.540" Title="Where can I download NESDR Smart (NooElec) drivers for Mac OS Sierra?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7306" PostTypeId="2" ParentId="7305" CreationDate="2017-03-06T20:27:03.253" Score="2" Body="&lt;p&gt;Unlike Windows, &lt;strong&gt;RTL-SDR on macOS (or Linux) does not require any separate driver installation.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All applications bundle their own driver code (&lt;code&gt;librtlsdr&lt;/code&gt;, often by way of &lt;code&gt;gr-osmosdr&lt;/code&gt; and GNU Radio). All you need to do is install and run whichever SDR application(s) you wanted to run.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-03-07T20:32:02.583" LastActivityDate="2017-03-07T20:32:02.583" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7308" PostTypeId="2" ParentId="7265" CreationDate="2017-03-07T05:20:19.943" Score="4" Body="&lt;p&gt;Turns out that, after turning to discussion of HF propagation for a number of intervening pages, this Antenna Book ends up getting back around to its own answer for this question!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the &quot;Scatter Modes&quot; section on page 23-30 of the same 17th edition:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The wave energy of VHF stations is not gone after it reaches the radio horizon, described early in this chapter. It is scattered, but it can be heard to some degree for hundreds of miles. Everything on Earth, and in the regions of space up to at least 100 miles, is a potential scattering agent.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;em&gt;Tropospheric scatter&lt;/em&gt; is always with us […] &lt;strong&gt;this is what produces that nearly flat portion of the curves given in an earlier section&lt;/strong&gt; on reliable VHF coverage.  … As long ago as the early 1950s, VHF enthusiasts found that VHF contests could be won with high power, big antennas and a good ear for signals deep in the noise. … &lt;em&gt;Ionospheric scatter&lt;/em&gt; works much the same as the tropo version, [… and] can fill in the skip zone with marginally readable signals scattered from ionized trails of meteors, small areas of random ionization, cosmic dust, satellites and whatever may come into the antenna patterns at 50 to 150 miles or so above the Earth. […]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;[bold added for emphasis]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It goes on similarly to discuss &quot;backscatter&quot; and &quot;transequatorial scatter&quot; before going on to a different section on &quot;auroral propagation&quot; (which can also affect VHF but is probably &lt;em&gt;not&lt;/em&gt; related to the reliable propagation graphs).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in short, &quot;scatter&quot; (in many forms) is claimed as the mechanism that allows VHF signals to be heard hundreds of miles beyond the primary &quot;radio horizon&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also believe the ARRL editors consider the experimental discoveries of the various scatter modes to be the &quot;modern wave-propagation knowledge&quot; referred to earlier — in this &quot;Scatter Modes&quot; section there are a couple historical references around the same dates as the QST article, including the &quot;early 1950s&quot; one quoted above as well as Transequitorial scatter as &quot;an amateur 50-MHz discovery in the years 1946–1947&quot;.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-03-07T20:06:23.960" LastActivityDate="2017-03-07T20:06:23.960" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7309" PostTypeId="2" ParentId="7305" CreationDate="2017-03-07T20:58:38.897" Score="0" Body="&lt;p&gt;For source code, try: &lt;a href=&quot;https://github.com/librtlsdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/librtlsdr&lt;/a&gt; (there are several forks as well).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look inside the app bundles of Gqrx or CubicSDR (possibly other OSX apps as well), you will find copies of precompiled dylib's for librtlsdr and libusb.  Those linkable dynamic shared libraries are probably the closest OS X user equivalent to a &quot;driver&quot; for RTL-SDR dongles such as the NooElec ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet another possibility is the CocoaRTLServer app, which makes an RTL-SDR USB device plugged into a Mac accessible via the rtl_tcp network protocol.  That would allow you to plug your RTL USB dongle into one Mac (or Raspberry Pi, etc.), and use it from another.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-03-07T21:17:47.540" LastActivityDate="2017-03-07T21:17:47.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7310" PostTypeId="2" ParentId="7159" CreationDate="2017-03-07T22:44:01.893" Score="3" Body="&lt;p&gt;4 Raspberry Pi's each with an RTL-SDR dongle may well be cheaper than just one of the higher bandwidth SDR capture devices or a high end Linux PC.  They run Linux.  Network them together, with each one capturing a 2.5 to 3 MHz slice of the RF spectrum of interest, totalling over 10 MHz.  That will also allow offloading your main Linux box, and allow doing significant parallel signal processing on multiple of the higher-end/newer/multi-core Pi's.  You can easily run RTL-SDR IQ captures (and signal analysis) headless, via ssh and the command line, on multiple Pi's from a centralized Linux PC (or Mac).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There now seem to be Pi variants for under $10 USD.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Downside is that the cheap RTL devices only capture 8-bit samples, and are easily front-end overloaded.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-03-07T23:14:14.837" LastActivityDate="2017-03-07T23:14:14.837" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7311" PostTypeId="2" ParentId="7004" CreationDate="2017-03-07T23:29:40.203" Score="0" Body="&lt;p&gt;My suggest is to unplug program cable and remove any drivers that you installed so far.  Plug program cable in to windows 10 with out the radio connected. An see if windows 10 can fine the drivers for you. also turn off any programing software for that radio. after you fine the drivers for windows 10 start program software and plug in radio. If you connect to radio always read the radio first before you try to write to it. good luck. Make sure your radio is off when you first connect to program cable.&lt;/p&gt;&#xA;" OwnerUserId="9325" LastEditorUserId="9326" LastEditDate="2017-03-27T07:57:51.067" LastActivityDate="2017-03-27T07:57:51.067" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7312" PostTypeId="2" ParentId="7300" CreationDate="2017-03-08T04:32:21.007" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Do I need to use tape?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;With insulated magnet wire, no. Ferrites are at least somewhat conductive, so you wouldn't want bare wire touching them. I suppose tape around the core could protect the thin insulation from sharp edges on the core.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;When would you need a different material type for the toroid?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;https://ham.stackexchange.com/q/1159/218&quot;&gt;How does one read a ferrite datasheet?&lt;/a&gt; Fair-rite has very good datasheets on each of their materials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice it can be difficult to predict the choking impedance since the core and winding geometry is very significant. More turns increases the flux in the core, but it also introduces more capacitance, moving the effective choking frequency lower and narrowing the bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's easier to determine the impedance empirically. &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;G3TXQ&lt;/a&gt; has a nice page of measured data for several designs. That should give you an idea of where to start.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also build the choke and install it, then transmit a carrier and &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measure the common-mode current&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've also measured chokes with a RigExpert antenna analyzer. I imagine other analyzers work fine. If you're using bifiliar windings, connect the pair together at each end (common-mode currents are equal on each wire), attach the two ends to a connector with leads as short as possible, and then measure the impedance with the analyzer. For a coax winding connect the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wouldn't trust an antenna analyzer to be very accurate, since most are designed to be accurate only around 50 ohms. But it's accurate enough, and gives an easy way to check the choking impedance at several frequencies, and to determine if a change is making it better or worse.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-03-08T04:32:21.007" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7313" PostTypeId="2" ParentId="7295" CreationDate="2017-03-09T01:42:54.237" Score="4" Body="&lt;p&gt;There &lt;strong&gt;is&lt;/strong&gt; a way to use radio waves to hold a private conversation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's called a mobile telephone, and they are available with surprisingly good coverage around the world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We should always use a tool appropriate for the task at hand. Amateur radio is not suitable for the use case you are describing, and a mobile phone is.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-03-09T01:42:54.237" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7314" PostTypeId="2" ParentId="1776" CreationDate="2017-03-09T04:11:19.037" Score="2" Body="&lt;p&gt;The filtering for nearby frequencies in any radio is finite. According to the &lt;a href=&quot;http://www.universal-radio.com/catalog/ht/3006spec.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;UV6D Specifications&lt;/a&gt;, the 12.5 kHz selectivity is 60 dB. The 0.8uV squelch threshold specification is -109 dBm. 1 Watt is 30 dBm. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're getting less than 30 dB isolation from transmitter to receiver in those tests based on the very short separation, so you're feeding about 0 dBm into the receiver from the transmitter, and the specified 12.5kHz selectivity is about 60 dB, with a squelch threshold of -109dBm, tallying up to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;0 dBm - 60 dB = -60 dBm &gt;&gt; -109 dBm   ==&gt;  Static noise when transmitting on channels 12.5 kHz apart in the same room.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neglecting the legality issues other answers discussed, a solution is to use the most widely separated (in frequency) channels when radios not wanting to communicate to each other are in close proximity.&#xA;For example, if you have a golf course, put the caddies on channel 1 and the host staff on channel 8, and so on.&lt;/p&gt;&#xA;" OwnerUserId="9331" LastActivityDate="2017-03-09T04:11:19.037" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7315" PostTypeId="2" ParentId="6874" CreationDate="2017-03-09T04:32:11.647" Score="3" Body="&lt;p&gt;This is not necessarily an impossible problem. You might approach the problem iteratively, with a simple monoband receiver and expand from there as you see what works.&#xA;Assuming you are able to solder, you could start with a &lt;a href=&quot;http://fivedash.com/index.php?main_page=product_info&amp;amp;cPath=1&amp;amp;products_id=5&quot; rel=&quot;nofollow noreferrer&quot;&gt;40m SoftRock receiver kit for $21&lt;/a&gt;, which plugs into your computer line-in sound card input for decoding of digital modes. On 40m (7MHz) you'd receive stations hundreds to thousands of kilometers away with a simple outdoor antenna, particularly on sensitive digital modes like WSPR and JT65.&#xA;I would build that receiver inside a metal box, and start with a few meters of wire as an antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't have interference with no antenna and short antennas, but longer antennas bring interference, consider building a &lt;a href=&quot;http://www.qsl.net/kp4md/mwfilter.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;medium-wave bandstop filter, like these demonstrated to attenuate AM broadcast by over 50 dB&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, consider that after filtering the fundamental on-channel AM transmitter, the N-th harmonics of that transmitter will be present and will have N times the bandwidth of the fundamental channel.&#xA;If the AM transmitter was on 1000 kHz, it will have significant modulation energy from about 995-1005 kHz (more if using HD Radio transmission). The second harmonic will spread from 1985-2015 kHz and so on.&lt;/p&gt;&#xA;" OwnerUserId="9331" LastActivityDate="2017-03-09T04:32:11.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7316" PostTypeId="1" CreationDate="2017-03-09T20:29:30.610" Score="3" ViewCount="855" Body="&lt;p&gt;Are there any disadvantages (or advantages) to using a long-wire HF antenna for wide-band VHF reception?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or would feedline losses make that useless compared to a ground level ducky or short whip?  (for wide-band reception/scanning, e.g. well outside the 2 bands of the 2M/440 rubber duck antenna that came with the HT, or with the short whip that came with an RTL-SDR for ADS-B reception?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would using a balun or any sort of matching network between the wire HF antenna and a VHF HT or SDR make any difference?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="8832" LastEditDate="2017-03-20T00:27:59.660" LastActivityDate="2017-03-21T01:15:02.727" Title="Using an HF antenna for VHF scanning" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7317" PostTypeId="1" CreationDate="2017-03-09T22:24:51.180" Score="2" ViewCount="948" Body="&lt;p&gt;Using a dual band &quot;rubber duck&quot; like the stock Baofeng antenna and/or the physically longer NA-771, which band will give the best results between two mountain tops given the same input power?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stereotypically the 2m VHF frequencies are considered to &quot;reach&quot; a little further due to their lower frequency and increased radio horizon. But I'm wondering if a dual-band antenna would actually give higher gain on the 70cm UHF band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does a rubber duck achieve a good match on its second harmonic via a trap, i.e. using only half the antenna to radiate on 70cm? In that case maybe both bands end up with a physically short antenna and would probably have similar inefficiencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if some other technique is used perhaps the antenna ends up being less &quot;compromised&quot; on the 70cm band versus the 2m band — either more efficient radiation and/or a better takeoff pattern?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2017-03-15T05:18:06.350" Title="Dual-band rubber duck gain on 2m vs. 70cm" Tags="&lt;antenna-theory&gt;&lt;ht&gt;&lt;vertical-antenna&gt;&lt;2m-band&gt;&lt;70cm-band&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7318" PostTypeId="2" ParentId="6874" CreationDate="2017-03-10T00:25:50.310" Score="2" Body="&lt;p&gt;Why not try a good small transmitting &quot;magnetic loop&quot; (like LNR's W4OP Loop, the AlexLoop, the AlphaLoop, etc.) along with some RFI protection around your transceiver? A narrowband directional antenna like that should help with half the problem, so you can focus on cleaning up the other power/data/microphone &quot;inputs&quot; on your transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While your situation definitely sounds dire, with a careful station design it should not be insurmountable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider that a typical 2m repeater &lt;em&gt;shares one single antenna&lt;/em&gt; between its transmitter and receiver. That is, it is simultaneously pumping a 25–100W transmission into the antenna over the very same coax used to receive the teeny tiny signal from a handheld in the next town. Not to mention, those two signals (the 25W output and the picowatt-level input) are &lt;em&gt;half a percent away&lt;/em&gt; from each other, frequency-wise!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Aside: If you changed the tuning of a guitar or violin the same relative amount, you'd barely hear the difference. If we kept track of notes up that high, the difference between 146.2 and 146.8 MHz would be only 7 &lt;a href=&quot;http://hyperphysics.phy-astr.gsu.edu/hbase/Music/cents.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;musical cents&lt;/a&gt;. This is hardly past the average audible threshold of five cents. Put another way, there's about 100 cents between a piano's middle C and the black key right next to it — &lt;em&gt;the entire US 2m allocation&lt;/em&gt; could fit &lt;em&gt;twice&lt;/em&gt; within that musical &lt;a href=&quot;https://en.wikipedia.org/wiki/Semitone&quot; rel=&quot;nofollow noreferrer&quot;&gt;half-step&lt;/a&gt; and the 0.6MHz offset just a tiny offset within.]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All that to say, in many ways a repeater inherently deals with much more severe interference than what you face. It's true that expensive duplexers and often additional filters are needed there, but in your case you have the benefit of signals that should be several octaves apart! It's a whole lot easier to keep a 550m or a 175m signal apart from a 40m signal, than keeping a 2.044m signal separate from a 2.052m one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's two things you need to avoid:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;signals overloading within your receiver&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Rusty_bolt_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;passive intermodulation&lt;/a&gt; around your house&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The first is completely within your control:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You need a well-shielded receiver, which will hopefully be designed against RF signals coming in via the power supply or accessories but may need some &quot;shoring up&quot; in those regards due to your situation. Troubleshoot this via a dummy load or cap on the antenna port.&lt;/li&gt;&#xA;&lt;li&gt;Then you need to make sure interference doesn't come in via your antenna system. The most obvious way is that your antenna itself will pick up the signal. Adding a good filter (shielded and capable of handling the broadcast power levels) should help in the case of a broadband antenna. There are also some antennas that are inherently very &quot;narrow band&quot;, such as a resonant small loop.&lt;/li&gt;&#xA;&lt;li&gt;A less obvious way can enter your antenna system is if your antenna is unbalanced. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This and more is all described in a much more authoritative way in &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing&quot;&lt;/a&gt; by Jim Brown K9YC. I've been trying to learn this stuff for a couple years now, and I still find that reference somewhat intimidating — when he says &quot;You should study this tutorial thoroughly&quot; he means it! — but he ends up boiling things down to practical actions. That guide is a perfect fit for your situation, though!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other part is a bit out of your hands:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even with a good station design, you'll still need to avoid that &quot;Rusty bolt effect&quot; of passive intermodulation. This one isn't as much in your control, since you may have little &quot;transmitters&quot; on all sorts of frequencies sprinkled throughout your neighborhood. A directional antenna will help here, and/or some additional &quot;notch&quot; filters for signals that are &quot;in your way&quot; on a particular band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might also try strike up a friendship with the broadcast engineer of the station. He might be just as interested in tracking down strong sources of intermodulation around their transmitter, or at least have more advice. His radio shack is 540 feet closer to the broadcast than you are!&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-03-10T00:38:32.357" LastActivityDate="2017-03-10T00:38:32.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7319" PostTypeId="1" AcceptedAnswerId="7323" CreationDate="2017-03-10T00:54:23.250" Score="3" ViewCount="473" Body="&lt;p&gt;I understand that most single-band repeaters will use a &lt;a href=&quot;https://www.tessco.com/yts/knowledge_center/su/pdfs/understanding_your_duplexer.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;tuned cavity duplexer&lt;/a&gt; to isolate the received signal from the transmitted signal, since the frequencies are very close and extremely sharp filtering is needed to separate them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But while the frequencies are close, another difference between the incoming and outgoing signals is just that: they are traveling in opposite directions! Could a repeater use a directional coupler to separate the two signals?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="4076" LastEditDate="2017-03-10T12:38:34.827" LastActivityDate="2017-08-08T22:37:18.097" Title="Are directional couplers ever used in duplex repeater systems?" Tags="&lt;repeater&gt;&lt;filter&gt;&lt;directional-coupler&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7320" PostTypeId="2" ParentId="7316" CreationDate="2017-03-10T03:24:38.713" Score="4" Body="&lt;p&gt;There are many problems here, only one of which has to do with impedance:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Your antenna is (I assume) &lt;em&gt;horizontally polarized&lt;/em&gt; whereas most VHF signals you might scan for (particularly ones where one end of the normal link is mobile, e.g. a car) are vertically polarized.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Your antenna will have a highly irregular pattern, with many nulls (directions in which the antenna receives almost nothing).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Your antenna will have an impedance and SWR which varies widely &lt;em&gt;within the band.&lt;/em&gt; (Since it is not constant, there is no matching network which will help over the entire band.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not a problem for receiving at all if your feed line is short enough or good enough that the loss is insignificant (compared to the strength of the signals you want to find). (But it does mean that if you look at a spectrum plot and see different signal strengths it isn't necessarily an accurate comparison.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to determine the actual loss, you would need to know the ordinary (properly matched) attenuation of the cable (either empirically or per loss-per-length specification and length of your cable) and the impedance of the antenna at a given frequency.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The MF and HF signals received by your antenna (most notably AM broadcast stations), even though they are out of band, may interfere with reception of the VHF signals you want.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;All that said, there's no harm in trying. If there's particular transmissions that you want to receive and you &lt;em&gt;do&lt;/em&gt; succeed in receiving them, then you're good. But if you want to scan for things you don't already know are there, you probably want a vertically polarized, VHF antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the upside, if you &lt;em&gt;do&lt;/em&gt; use a matching network, it will help eliminate out-of-band signals. The catch is that it makes things even less wideband, and if you want to make it adjustable to move across the band, well, that's an antenna tuner and VHF antenna tuners are not very common.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-03-21T01:15:02.727" LastActivityDate="2017-03-21T01:15:02.727" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7321" PostTypeId="2" ParentId="7319" CreationDate="2017-03-10T04:06:16.857" Score="2" Body="&lt;p&gt;Among the problems is that a directional coupler &lt;em&gt;only&lt;/em&gt; discriminates based on direction, and in a real system there will be reflections from many elements of the system beyond the coupler:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Imperfect transmission line&lt;/li&gt;&#xA;&lt;li&gt;Imperfect antenna&lt;/li&gt;&#xA;&lt;li&gt;Birds sitting on the antenna, or other environmental effects detuning it&lt;/li&gt;&#xA;&lt;li&gt;Reflective objects in sight of the antenna&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Any such reflection would end up in the receiver. A duplexer will instead discriminate based on frequency, so the reflection is re-reflected back out the antenna (very similarly to the function of an antenna tuner).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Directional couplers &lt;em&gt;can&lt;/em&gt; be used when the reflections from any of these sources are actually what is of interest, usually in RF test equipment or some types of radar.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-03-11T01:23:43.503" LastActivityDate="2017-03-11T01:23:43.503" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7322" PostTypeId="2" ParentId="7319" CreationDate="2017-03-10T12:44:26.023" Score="2" Body="&lt;p&gt;In addition to what Kevin said, if you can, you'd usually use frequency duplex.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That has technological reasons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It's nearly impossible to build a broadband (i.e. $\frac{f_\text{max}}{f_\text{min}} &amp;lt; 0.75$) directional coupler – most designs depend on the wavelength being within close limits. Filter design is a lot more flexible.&lt;/li&gt;&#xA;&lt;li&gt;for isolation purposes, and within reasonable size constraints, practically only &lt;em&gt;circulator&lt;/em&gt; are viable; those are finely tuned, very expensive devices, compared to filters&lt;/li&gt;&#xA;&lt;li&gt;the isolation of directional couplers that aren't extremely narrowband is usually much worse than what's realizable with filters. For example, you can reasonably buy 20dB-isolating circulators. Good ones sometimes reach ~43 dB. Compare that to the out-of-band suppression of your cavity filter&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-03-10T12:44:26.023" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7323" PostTypeId="2" ParentId="7319" CreationDate="2017-03-10T17:13:10.020" Score="4" Body="&lt;p&gt;Are you thinking something like this?&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/bmnsx.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fbmnsx.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say you have a really good directional coupler with a directivity of 55dB. And the antenna is a good match with a VSWR of 1.1, or equivalently a return loss of 26 dB. And the transmitter power is 10 W, or 30 dBm. And we'll say we select a directional coupler with a coupling factor of 10 dB (though as you'll see, the coupling factor doesn't really matter).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;30 dBm, after the 55 dB directivity of the coupler, and the 10 dB coupling factor, means the receiver will see 30-55-10 = -35 dBm at its input from the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say we want to hear a 1 W (20 dBm) station that's 1 km from the repeater. At 144 MHz that's a free space path loss of 76 dB, so the power received at the antenna will be in the neighborhood of 20-76 = -56 dBm. Maybe a little more after adding antenna gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That -56 dBm is then subject to the 10 dB coupling factor, so at the receiver it becomes -66 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Signal power: -66 dBm&lt;br&gt;&#xA;Noise power (from the transmitter): -35 dBm&lt;br&gt;&#xA;SNR: -12 dB&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously this is not going to work. And it's actually worse than this, because any reflected power from the antenna will also show up at the receiver. The 30 dBm of transmitter power, after the 26 dB return loss, is 4 dBm. Then subject to the 10 dB coupling factor is another -6 dBm of transmitter power finding its way into the receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-03-10T17:19:36.370" LastActivityDate="2017-03-10T17:19:36.370" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7324" PostTypeId="2" ParentId="1579" CreationDate="2017-03-10T20:18:54.207" Score="0" Body="&lt;p&gt;I like a general purpose machine grease, or plain old fashion machine oil, which is easily cleaned up with used gun patches inside the -40 to +300 °F  temperature range. Grease is oil with fillers.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some good reads may be found at: www.nmbtc.com/bearings&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, metal and grease on skin is what we call 'bear s...'.&lt;/p&gt;&#xA;" OwnerUserId="9336" LastEditorUserId="218" LastEditDate="2017-03-18T14:12:10.343" LastActivityDate="2017-03-18T14:12:10.343" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7325" PostTypeId="1" CreationDate="2017-03-11T02:24:22.707" Score="0" ViewCount="334" Body="&lt;p&gt;I'm trying to establish an AX.25 connection to a nearby RMS gateway (should be within a mile) using a Baofeng BF-F8+ on 2 meters. I'm trying to establish a connection with either RMS Express and UZ7HO sound modem on Windows or with ax25-tools axcall command with soundmodem on Linux. I am using a USB sound card and VOX mode on my radio. In both cases, I see my radio transmitting SABM several times and a variety of responses coming back, but my call out never seems to advance beyond the initial state of starting a new AX.25 connection. I'm not terribly familiar with AX.25, but it looks like the receiving software never notices the appropriate reply to continue on with. The packets I am receiving are even passing checksums correctly and I can decode some of the text contents I expect the server to be providing. Under Linux, I can even monitor the traffic with Wireshark, but it seems that axcall never sees the packet. Is it possible that my VOX has a hang time that's causing me to loose the initial response to my call?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a sample capture from one attempt with Winlink on Windows:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:53:31T]&#xA;1:Fm K7CPU-10 To KG7GAN &amp;lt;I C R0 S3 Pid=F0 Len=25&amp;gt; [17:53:36R] [+++]&#xA;SanDiego CMS via K7CPU &amp;gt;&#xA;&#xA;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:53:36T]&#xA;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:53:40T]&#xA;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:53:45T]&#xA;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:53:50T]&#xA;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:54:19T]&#xA;1:Fm K7CPU-10 To KG7GAN &amp;lt;I C R0 S1 Pid=F0 Len=21&amp;gt; [17:54:22R] [+++]&#xA;[WL2K-3.2-B2FWIHJM$]&#xA;&#xA;1:Fm K7CPU-10 To KG7GAN &amp;lt;I C R0 S2 Pid=F0 Len=35&amp;gt; [17:54:22R] [+++]&#xA;;PQ: 45631005&#xA;Wien CMS via K7CPU &amp;gt;&#xA;&#xA;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:54:23T]&#xA;1:Fm K7CPU-10 To KG7GAN &amp;lt;DM R&amp;gt; [17:54:26R] [+++]&#xA;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:54:27T]&#xA;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:54:32T]&#xA;1:Fm K7CPU-10 To KG7GAN &amp;lt;I C R0 S3 Pid=F0 Len=22&amp;gt; [17:54:36R] [+++]&#xA;Perth CMS via K7CPU &amp;gt;&#xA;&#xA;1:Fm KG7GAN To K7CPU-10 &amp;lt;SABM C P&amp;gt; [17:54:37T]&#xA;1:Fm K7CPU-10 To KG7GAN &amp;lt;DM R&amp;gt; [17:54:42R] [+++]&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="1534" LastActivityDate="2019-03-24T02:05:19.013" Title="Cannot establish AX.25 connection to RMS gateway" Tags="&lt;digital-modes&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7327" PostTypeId="1" CreationDate="2017-03-11T14:50:35.397" Score="2" ViewCount="1048" Body="&lt;p&gt;Is it possible to block a specific DMR ID Rx, sort of &quot;ignore&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, is it repeater-based, or it has to be set locally, on radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Speaking of popular md380/390 radios, there is a &quot;Call Alert&quot; feature on Contact list, but didn't find any information regarding that feature, or how it's supposed to work. Any intel on that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;" OwnerUserId="1464" LastEditorUserId="4665" LastEditDate="2020-03-17T18:42:40.957" LastActivityDate="2020-03-17T18:42:40.957" Title="Blocking a specfic DMR ID" Tags="&lt;repeater&gt;&lt;callsign&gt;&lt;station-identification&gt;&lt;dmr&gt;" AnswerCount="1" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7328" PostTypeId="2" ParentId="3680" CreationDate="2017-03-11T19:07:40.073" Score="1" Body="&lt;p&gt;Look at:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.amalgamate2000.com/radio-hobbies/radio/dunedin%20linear.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.amalgamate2000.com/radio-hobbies/radio/dunedin%20linear.htm&lt;/a&gt;&#xA;and&#xA;&lt;a href=&quot;http://www.amalgamate2000.com/radio-hobbies/radio/Rotorualinear.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.amalgamate2000.com/radio-hobbies/radio/Rotorualinear.htm&lt;/a&gt;&#xA;These are the only 2 working examples of terrestrial a linear translator I know of. And I believe they are now both off the air...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have been thinking of upgrading my 6 meter repeater to a linear translator, using a low band TV transmitter amplifier for the output stage.  Believe going from FM to SSB will yield a 10 dB improvement, and perhaps a 3 times improvement in range...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And should be even better, using Digital Voice (DV) over SSB !!!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But just may not be worth the effort, based upon lack of 6 meter activity..&lt;/p&gt;&#xA;" OwnerUserId="9340" LastActivityDate="2017-03-11T19:07:40.073" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7329" PostTypeId="1" AcceptedAnswerId="7332" CreationDate="2017-03-11T19:47:59.337" Score="4" ViewCount="353" Body="&lt;p&gt;If you have a transmitter that is perfectly on your frequency but you have an antenna with some impedance what types of losses, and of what magnitude, will you expect from a tuner in between your transmitter and antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example lets say your system as a whole with no tuner has an SWR of 3 and your system with a tuner is now 1:1. Are there power losses from an LC network used to match impedances? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are these losses called? Is it easy to calculate wasted power? Is it frequency dependant? Is there a way to approximate delivered power from a given capacitance and inductance on a line with a specific SWR?&lt;/p&gt;&#xA;" OwnerUserId="9341" LastEditorUserId="76" LastEditDate="2017-04-26T17:14:45.580" LastActivityDate="2017-04-26T17:14:45.580" Title="What kind of losses do you get from an LC network matching the antenna's impedance?" Tags="&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7331" PostTypeId="2" ParentId="3711" CreationDate="2017-03-11T23:29:03.953" Score="5" Body="&lt;p&gt;If you are using (or building) a vintage radio that does not have a narrow CW audio filter, the audio bandwidth above and below a listenable CW audio side-tone frequency can be quite unsymmetric.  By flipping the side-band, one might be able to move an interfering signal down close to 0 Hz audio frequency (inaudible), even if the audio is not bandpass filtered to any &quot;reasonable&quot; degree.  (e.g. I started out in this hobby by building a tube regenerative SW receiver.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2017-03-11T23:29:03.953" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7332" PostTypeId="2" ParentId="7329" CreationDate="2017-03-12T00:09:26.083" Score="1" Body="&lt;p&gt;An ideal LC network causes no losses whatsoever, because ideal inductors and capacitors do not dissipate power — they have no resistance. The actual loss in your matching network is determined by the actual resistances of the components. It is frequency-dependent because the overall behavior of the network is, and it is also &lt;em&gt;power&lt;/em&gt;-dependent due to saturation of inductors' magnetic cores (unless your inductors are air-core).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other major source of loss in this type of configuration is &lt;a href=&quot;https://ham.stackexchange.com/questions/7333/what-is-the-actual-loss-in-a-feed-line-with-high-swr&quot;&gt;the loss due to standing waves in the feed line&lt;/a&gt; between the antenna and tuner (just as if you were not using a tuner). This is why tuners are best placed near the antenna rather than the transmitter.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-03-12T01:19:03.283" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7333" PostTypeId="1" AcceptedAnswerId="7348" CreationDate="2017-03-12T00:17:51.090" Score="8" ViewCount="1645" Body="&lt;p&gt;It is well-known that it is unwise to have standing waves on the feed line between one's antenna and one's transmitter, unless it is a very low-loss type (e.g. ladder line), because the transmitted signal is reflected multiple times through the feed line, incurring repeated losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;How can I calculate the actual loss in dB, given that I know the SWR and the normal (with a matched source and load) loss of the feed line?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I have already found &lt;a href=&quot;https://www.dk0tu.de/users/DL5BBN/Cable_Losses_at_High_SWR/cableatten.pdf&quot; rel=&quot;noreferrer&quot;&gt;an article&lt;/a&gt; which claims to derive a formula for the loss in the obvious fashion of summing the series of reflections. But I find it not all that clearly written for purposes of making use of the answer, and I also think that it would be good to have this question answered here on Amateur Radio SE.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-05-05T20:39:17.757" LastActivityDate="2019-03-15T17:53:54.803" Title="What is the actual loss in a feed line with high SWR?" Tags="&lt;rf-power&gt;&lt;impedance&gt;&lt;feed-line&gt;&lt;antenna-tuner&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7334" PostTypeId="2" ParentId="7333" CreationDate="2017-03-12T14:11:58.817" Score="0" Body="&lt;p&gt;I must admit I am probing the fringe of my understanding of transmission line theory at this point, but it is my understanding that the &quot;number of passes&quot; is one way of viewing what's going on, but it's sort of a clunky analogy for the integration of multiple reflections. Another way to think about it is that all of the reflections in the line sum together to increase the average current in the line. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's try a (probably overly) simplified thought experiment. Imagine a simple wire that is exactly one half wavelength long at an arbitrary frequency, and which is terminated via a perfectly matched resistive load to earth (essentially a short beverage antenna, for reference). If we were to send a single positive pulse (one half of one cycle) down the line, we can imagine that at some point in time, the current measured at the far end of the wire has not yet begun to rise, as the wave is still propagating toward it, but the current at the feedpoint has returned to something arbitrarily close to zero. The pulse is &quot;half way&quot; to the far end, so the current maximum is precisely in the center of the wire. A graph of the current along the length of the wire would look something like &lt;a href=&quot;http://pages.cpsc.ucalgary.ca/~hill/papers/synthesizer/images/winwt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The pulse is perfectly absorbed by the load, and there is zero reflection. At any point in time after the pulse has been absorbed, the current at any point on the wire would be zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now imagine an imperfect termination. The pulse gets to the end of the wire and some part of it is reflected toward the feed point. We could snap that picture of the wave traveling forward toward the load, and shortly after snap a second picture of the reflected pulse, now attenuated due to partial absorption by the load, also centered up on the wire, but going the opposite direction (and inverted). If the system is ideal other than our mismatched load, the pulse would be perfectly reflected when it reached the feed point, and this ping-pong routine would continue until the pulse was fully absorbed. This is the &quot;multiple passes&quot;, but I personally find it difficult to imagine this in the context of an actual antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, we can imagine that we feed a continuous series of pulses in to this line, all of them positive, with an average power equal to 1 watt, and each new pulse beginning the instant we detect (through magic) that the current at the feed point from the previously generated pulse has reached zero. The first pulse travels to the end, and is partially reflected. A second pulse begins, and the two pass each other on the wire, summing together. The first pulse reaches the feedpoint end and is again reflected, just as the second pulse starts to reflect at the load end. At that instant, we start feeding a third pulse in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As this continues, the amount of power reaching the load end at any instant rises steadily as numerous pulses with various phase angles sum together. At some point, the total power reaching the load is greater than the power being fed in. At this point the &lt;em&gt;average power&lt;/em&gt; on the wire is greater than the 1 watt we are continuously feeding in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say that our load is absorbing exactly half the power on the wire, so for the first pulse, it dissipates 0.5 watts. Each partially  reflected pulse increases the average power on the wire until, at some point, the power being absorbed by the load is equal to the power being fed in to the wire. At this point, we've reached equilibrium, but the average power (and thus average current) on the wire is &lt;strong&gt;greater than that of our input&lt;/strong&gt;. The coax loss is derived not to the power fed in, but this average &quot;circulating&quot; power on the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same principle dictates how a two wire feed line would behave, with each partially reflected cycle adding to the average circulating current. You must calculate the input power which would yield the same average power on the line with a perfectly terminated load, and then use that in the standard loss equation. If  your load (along with standard conductive and dielectric losses) is absorbing 50% of the power that reaches it, you won't reach equilibrium with a 100w input until you have 200w circulating on the feed line. In reality it is not nearly so linear, but I must admit that the exact math to demonstrate the relationship is still a bit over my head at this point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Incidentally, this is how an extremely high Q antenna like a magnetic loop can generate thousands of volts from only 100 watts input. The feed system permits very efficient coupling of power in to the antenna itself, but the resistive and radiative losses are all quite low, requiring a spectacularly high circulating power to achieve equilibrium. That's also why it is so essential that magnetic loops be as low loss as possible, to maximize the ratio of radiation resistance to all other losses.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-03-12T14:11:58.817" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7335" PostTypeId="1" AcceptedAnswerId="7338" CreationDate="2017-03-12T15:14:01.940" Score="0" ViewCount="266" Body="&lt;p&gt;I'm a sound designer and I'm interested in using/simulating that effect of DAB radio when you have a low signal/interference, where voices become garbled, bubbling, burbling, broken up, etc. I wondered if someone could explain how the specific sonic qualities of that type of noise arise from digital radio algorithms?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My knowledge base is in digital signal processing, but not in any theory of radio codecs etc., so I'd find it really useful if you could give me an explanation that references general audio operations but not the deep technicalities of radio processes. For instance, my initial hypothesis is that it somehow arises out of extreme sudden jumps in bitrate: does that come close to the truth at all?&lt;/p&gt;&#xA;" OwnerUserId="9344" LastEditorUserId="76" LastEditDate="2017-07-09T17:19:49.560" LastActivityDate="2017-07-09T17:19:49.560" Title="How does DAB radio garbled noise come about?" Tags="&lt;digital-modes&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7337" PostTypeId="2" ParentId="7223" CreationDate="2017-03-12T16:11:18.390" Score="1" Body="&lt;p&gt;This is an interesting antenna with but with no information included &#xA;about behavior of the unique part at 70cm. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For RF insight into the design, a horizontal 2 meter dipole for 144 MHz was &#xA;modeled using #8 copper wire at 2 meters elevation. The 70cm portion was formed by wires from the feedpoint connections going down then to the sides beneath &#xA;the 2 meter arms.  This is an approximation of the &quot;U&quot; shaped elements &#xA;described in the article.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning for 144 MHz was easy. It worked out to be 19.055 inches for the &#xA;long arms with a feedpoint separation = 1.05 inches. Total &#xA;Width=39.16 inches.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Horizontally: SWR=1.5, Z=69 Ohms, Efficiency=77%, Gain=7.5 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Vertically: SWR=1.4, Z=68 Ohms, Efficiency=51%, Gain=2.6 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, tuning for 446 MHz was critical and required radically different shape &#xA;and dimensions.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Spacing between arms was much wider: 3.89 inches down &#xA;and the length of the arms much shorter: 2.12 inches... with total width=5.29 inches. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Horizontally, the &quot;L&quot; shape still radiates like a dipole with a very minor vertical component.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Horizontally: SWR=1.05, Z=50 Ohms, Efficiency=73%, Gain=9.4 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Vertically: SWR=1.02, Z=51, Efficiency=60%, Gain=6.2 dBi&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: The Z impedance of a vertical is not effected by feedpoint height.  Not so horizontally. Z goes up and down around 72 Ohms (1.4 SWR) so tuning changes with height. &lt;/p&gt;&#xA;" OwnerUserId="8229" LastEditorUserId="8229" LastEditDate="2017-03-13T17:08:26.920" LastActivityDate="2017-03-13T17:08:26.920" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7338" PostTypeId="2" ParentId="7335" CreationDate="2017-03-12T16:15:19.090" Score="1" Body="&lt;p&gt;I'm not familiar with the DAB system in particular, but I can give you a conceptual answer which I think you will find useful.&lt;/p&gt;&#xA;&lt;p&gt;In analog radio, things are straightforward. The lower the signal-to-noise ratio, the more the received signal deviates from the transmitted one, and that deviation from ideality in the RF signal results in some closely related deviation in the demodulated audio — the details depending on the modulation used. But, critically, this is on an instantaneous basis; that is, you could plot the original audio, modulated RF signal, signal received with noise, and demodulated audio on a single graph with a common time axis and there would be a consistent relationship. Therefore, since RF noise (that is not deliberate interference) is generally random from instant to instant, so is the effect on the audio.&lt;/p&gt;&#xA;&lt;p&gt;In digital radio using an audio codec, this time relationship does not hold, so more complex effects are possible because the influence of noise can cause loss or modification of portions of the audio in a consistent way over a longer time interval.&lt;/p&gt;&#xA;&lt;p&gt;(It would be &lt;em&gt;possible&lt;/em&gt; to send a digital audio signal while preserving the time relationship — for example, using a &lt;a href=&quot;https://en.wikipedia.org/wiki/Direct_Stream_Digital&quot; rel=&quot;nofollow noreferrer&quot;&gt;DSD&lt;/a&gt; bitstream, or using a modulation with &lt;a href=&quot;https://en.wikipedia.org/wiki/Symbol_rate&quot; rel=&quot;nofollow noreferrer&quot;&gt;multiple bits per symbol&lt;/a&gt; to send an entire &lt;a href=&quot;https://en.wikipedia.org/wiki/Pulse-code_modulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;PCM&lt;/a&gt; sample value at once. However, since it is neither compressed nor error-corrected, it would be very inefficient.)&lt;/p&gt;&#xA;&lt;p&gt;Generally speaking, an audio codec attempts to represent digital audio using fewer bits than would be taken by the numbers that are the original sample values. This necessarily makes some assumptions about the structure of the signal — that it contains something like voice or music. Therefore, &lt;strong&gt;if you put random or corrupted data into the decoding process, it is &lt;em&gt;more likely&lt;/em&gt; to generate something that we would call “garble” rather than “noise”, just as a matter of statistics.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Also, digital radio usually makes use of error-detecting (and error-correcting) codes. This means that it is possible for the receiver to &lt;em&gt;know&lt;/em&gt; when it is receiving corrupted data, and make a decision about what to do instead. This could be as simple as playing silence instead, but a better option for short interruptions is to proceed using the previous data. Since the decoder is in some sense &lt;a href=&quot;https://en.wikipedia.org/wiki/Synthesizer&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;synthesizing&lt;/em&gt;&lt;/a&gt; its output, it can just keep doing that, generating the same waveform for longer than intended (as opposed to literally reusing old samples, which creates an obvious glitch as anyone who's listened to a CD skip knows). This is another way you get garble — you're listening to realistic voice sounds being held for longer than makes sense.&lt;/p&gt;&#xA;&lt;p&gt;Furthermore, &lt;a href=&quot;https://en.wikipedia.org/wiki/Digital_audio_broadcasting#Audio_codec&quot; rel=&quot;nofollow noreferrer&quot;&gt;according to Wikipedia&lt;/a&gt;, DAB uses an “unequal error protection (UEP)” scheme, which means that the error-correction is biased towards preserving aspects of the encoded audio considered more critical.&lt;/p&gt;&#xA;&lt;p&gt;So your idea of “jumps in bitrate” is somewhat close to the actual situation: it's a change in how many &lt;em&gt;good&lt;/em&gt; bits the decoder has available to it, and it compensating as best it can. And in particular, the use of UEP means that a weak signal is more similar to an intentionally lower bitrate than it would be without UEP.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-03-12T16:26:10.637" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7339" PostTypeId="2" ParentId="3680" CreationDate="2017-03-12T17:32:51.710" Score="0" Body="&lt;p&gt;Yes. If you truly want to allow doubling then you want SSB. You want SSB anyway for the significant SNR advantage over AM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need to consider &lt;a href=&quot;http://www.naval.com/vos/&quot; rel=&quot;nofollow noreferrer&quot;&gt;voice-activated squelch&lt;/a&gt; so that VoIP knows when to stop/start sending audio to the internet (unless continuous streaming audio is OK). This can be implemented in software, particularly for software defined radio (SDR).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Until a few years ago, one might have done this in hardware. However, it is now feasible to do this with a full-duplex SDR (or separate SDR receiver and transmitter). In fact, I believe it might be possible for about $100 using an RTL2832 USB stick receiver and &lt;a href=&quot;https://github.com/F5OEO/rpitx&quot; rel=&quot;nofollow noreferrer&quot;&gt;Raspberry Pi transmitter&lt;/a&gt; PLUS a duplexer appropriate for your transmit/receive separation assuming you wish to use a single repeater antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the duplexer would cost a couple hundred dollars used, you might just start by using two antennas on a &quot;garage repeater&quot; setup or 2m/70cm with an inexpensive diplexer and single antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might not find off-the-shelf code for this, but the appeal is you can do it for $100 of hardware and a weekend of learning instead of a bench full of hardware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would start by understanding the &lt;a href=&quot;http://gnuradio.org/redmine/projects/gnuradio/wiki/HamRadio&quot; rel=&quot;nofollow noreferrer&quot;&gt;GNU Radio examples for ham radio&lt;/a&gt;, in particular &lt;a href=&quot;https://github.com/argilo/sdr-examples&quot; rel=&quot;nofollow noreferrer&quot;&gt;this example set&lt;/a&gt; or the &lt;a href=&quot;https://github.com/scivision/gnuradio_ham&quot; rel=&quot;nofollow noreferrer&quot;&gt;simpler GNU Radio ham radio examples&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9331" LastActivityDate="2017-03-12T17:32:51.710" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7340" PostTypeId="2" ParentId="6462" CreationDate="2017-03-12T17:36:25.093" Score="1" Body="&lt;p&gt;There is a &lt;a href=&quot;https://github.com/scivision/mlocs&quot; rel=&quot;nofollow noreferrer&quot;&gt;complete working Python program converting to/from Maidenhead/WGS84 Lat/Lon&lt;/a&gt;. &lt;/p&gt;&#xA;" OwnerUserId="9331" LastActivityDate="2017-03-12T17:36:25.093" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7342" PostTypeId="1" CreationDate="2017-03-13T00:54:10.830" Score="0" ViewCount="3105" Body="&lt;p&gt;My radio won't receive. Help? It literally went dead and I still have the rubber duck antenna&lt;/p&gt;&#xA;" OwnerUserId="9347" LastEditorUserId="4665" LastEditDate="2017-03-18T01:03:55.807" LastActivityDate="2017-03-18T01:03:55.807" Title="My Baofeng radio won't recieve but transmit does not work when I hold the MONI button" Tags="&lt;antenna&gt;&lt;baofeng&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2017-03-23T18:29:55.353" ContentLicense="CC BY-SA 3.0" />
  <row Id="7343" PostTypeId="2" ParentId="6462" CreationDate="2017-03-13T02:35:36.720" Score="0" Body="&lt;p&gt;I've created many (two, PHP is going up shortly) implementations of this on my github page. Please feel free to use these: &lt;a href=&quot;https://github.com/gravypod/maidenhead/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/gravypod/maidenhead/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm also very happy to take pulls in to either add more implementations or clean up my implementations. It would be nice to get a version for every manjor language out there. I just haven't got the time to do that sadly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've also found it hard to convert from Lat Lon to maidenhead which would be very nice to have. &lt;/p&gt;&#xA;" OwnerUserId="9341" LastActivityDate="2017-03-13T02:35:36.720" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7344" PostTypeId="2" ParentId="4968" CreationDate="2017-03-13T04:44:45.510" Score="1" Body="&lt;p&gt;Kevin Reid has the most important point--   +/-9.6 kHz is beyond the +/- 7.5 kHz bandwidth of the TS-2000 receive filters. Without first modifying the hardware (replacing filter), I would expect the receive signal to be distorted, quite possibly beyond use.&lt;/p&gt;&#xA;" OwnerUserId="9331" LastEditorUserId="10495" LastEditDate="2017-10-31T01:53:57.347" LastActivityDate="2017-10-31T01:53:57.347" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7345" PostTypeId="2" ParentId="7285" CreationDate="2017-03-13T04:53:23.980" Score="1" Body="&lt;p&gt;Consider a DPDT switch, extremely common . Open the mic on receive. The radio likely mutes mic audio when squelch closed. When you get a keypress beep or open squelch, it's probably enough audio to cover up the feedback you hear with a quiet carrier.&lt;/p&gt;&#xA;" OwnerUserId="9331" LastActivityDate="2017-03-13T04:53:23.980" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7346" PostTypeId="2" ParentId="7335" CreationDate="2017-03-13T08:44:59.523" Score="0" Body="&lt;p&gt;There are many techniques under a general category called error concealment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When a segment of streamed data is lost, the idea is to synthesize something that might plausibly belong or at least seem minimally objectionable.  It might involve using repeated samples or interpolated modeling coefficients or other ad hock insertions of synthesized or made-up stuff.  Likely, a lot of psychoperceptual research was done to select the exact concealment strategy used in any specific decoder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is all done completely after the radio chain, after the error correction logic communicates that decoding the next data packet(s) failed.  It is then the audio systems responsibility to do something other than an annoying loud pop plus silence.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-03-13T08:50:12.220" LastActivityDate="2017-03-13T08:50:12.220" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7347" PostTypeId="1" AcceptedAnswerId="7349" CreationDate="2017-03-13T16:21:11.000" Score="5" ViewCount="3057" Body="&lt;p&gt;a) Given that I don't have a frequency standard or other known transmitter available, what is the easiest way to calibrate the &lt;a href=&quot;http://www.nooelec.com/store/sdr/sdr-receivers/nesdr-smart-sdr.html&quot; rel=&quot;noreferrer&quot;&gt;NooElec NESDR SMArt&lt;/a&gt; which is using a TCXO rated at 0.5 PPM.? I.e. to determine the &lt;code&gt;PPM&lt;/code&gt; calibration value? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;b) Also, is this value frequency dependent? (How so?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;c) Are there any European frequency standard transmitters I could use?&lt;/p&gt;&#xA;" OwnerUserId="6563" LastActivityDate="2017-03-14T21:55:27.043" Title="How to determine the PPM value of a NESDR SMArt?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;calibration&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7348" PostTypeId="2" ParentId="7333" CreationDate="2017-03-13T16:29:30.130" Score="3" Body="&lt;p&gt;Assuming no tuner losses, and assuming uniform loss throughout the line (which isn't true in practice, yet can be a practical simplifying assumption, more below), feedline losses in decibels are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ -10 \log \left(L {&#xA;  1 - |\Gamma|^2 \over&#xA;  1-L^2 \: |\Gamma|^2&#xA;}\right) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; is the fraction of power transmitted by the feedline into a matched load:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L := 10^{-\text{loss in decibels}/10} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt; is the reflection coefficient:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ |\Gamma| := { \text{VSWR} -1 \over \text{VSWR} +1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h1&gt;Derivation&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Let's work an example and look at how it's derived.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Begin by calculating the loss of the feedline from the datasheet and the length. Let's say it's 0.46 dB per 100 feet, and 100 feet long, so feedline loss is 0.46 dB. Let's undecibel that and make it a ratio:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L := 10^{-0.46/10} = 0.9 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meaning, 90% of the power is transmitted, and the other 10% is absorbed by the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The math is easier if we express VSWR as a reflection coefficient &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt;. It's a complex number but we don't care about the phase of the reflection (and we can't know it from just the VSWR anyway), so we'll calculate just the magnitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ |\Gamma| := { \text{VSWR} -1 \over \text{VSWR} +1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say for our example the VSWR is 2.35:1. That's a reflection coefficient of 0.4. This is a ratio of amplitude or voltage, so square it to obtain power: 16% of power is reflected, and the other 84% is accepted by the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And let's say forward power is 100 W. Furthermore, we'll assume the transmitter contains a tuner. When the tuner is adjusted so the transmitter sees a matched load, effective the tuner is inserting an impedance in the line which cancels the reflected wave, so the transmitter doesn't see any reflected power. Since the tuner (neglecting losses) has no resistive components to absorb any power and convert it to heat, this must mean all the reflected power that reaches the transmitter is reflected again back towards the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now let's visualize what happens to that power as it reflects back and forth a few times.&#xA;&lt;br&gt;&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/b7OP4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/b7OP4.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;br&gt;&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sum all the power that was accepted by the antenna (75.6W + 9.8W + 1.3W + 0.16W + ...) to explain how much of that 100W was accepted by the antenna, and the rest was lost to the feedline. Shown in the diagram, a total of 86.8W makes it to the antenna. That means losses were:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 10 \log\left(86.8 \over 100 \right) = 0.61\:\mathrm{dB} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Through more iterations we can obtain a more precise answer, but you can see that after a few reflections the powers have become small enough to be negligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Loss in decibels is calculated from the ratio of input power to output power, so let's calculate the fraction of input power that's accepted by the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whatever the incident power at the antenna, &lt;span class=&quot;math-container&quot;&gt;$|\Gamma|^2$&lt;/span&gt; of it is reflected, and &lt;span class=&quot;math-container&quot;&gt;$1-|\Gamma|^2$&lt;/span&gt; of it is accepted. If we want to calculate the power accepted on a specific reflection, we need only find the incident power, and multiply it by &lt;span class=&quot;math-container&quot;&gt;$1-|\Gamma|^2$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To calculate the incident power, we can count the number of trips though the feedline that have happened so far, and the number of times a reflection off the antenna has occurred so far. Each trip through the feedline reduces the power by a factor of &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt;, and each reflection off the antenna by a factor of &lt;span class=&quot;math-container&quot;&gt;$|\Gamma|^2$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the first reflection, it's just one trip through the feedline and zero prior reflections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L^1 \: (|\Gamma|^2)^0 \: (1 - |\Gamma|^2) \\&#xA;\tag{accepted, 1st reflection}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the second reflection, it's three trips through the feedline, and one prior reflection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L^3 \: (|\Gamma|^2)^1 \: (1 - |\Gamma|^2) \\&#xA;\tag{accepted, 2nd reflection}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the third reflection, it's five trips through the feedline, and two prior reflections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L^5 \: (|\Gamma|^2)^2 \: (1 - |\Gamma|^2) \\&#xA;\tag{accepted, 3rd reflection}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A pattern emerges: the power accepted at each reflection is the same at the previous reflection, multiplied by&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L^2 \: |\Gamma|^2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These summed together is the total power accepted:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \sum_{n=0}^{\infty} L(1 - |\Gamma|^2) (L^2 \: |\Gamma|^2)^n&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a geometric series, and can be simplified to&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \lim_{n \to \infty}&#xA;L(1 - |\Gamma|^2)&#xA;{&#xA;  1-(L^2 \: |\Gamma|^2)^n \over&#xA;  1-L^2 \: |\Gamma|^2&#xA;} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because &lt;span class=&quot;math-container&quot;&gt;$L^2 \: |\Gamma|^2$&lt;/span&gt; is less than 1, &lt;span class=&quot;math-container&quot;&gt;$(L^2 \: |\Gamma|^2)^n \to 0$&lt;/span&gt; so the equation further simplifies to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L {&#xA;  1 - |\Gamma|^2 \over&#xA;  1-L^2 \: |\Gamma|^2&#xA;} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h1&gt;Limitations&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;A shortcoming of this model is real transmission lines don't have uniform loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Loss in a transmission line can be due to resistive loss, or dielectric loss. Resistive loss is proportional to the square of current, whereas dielectric loss is proportional to the square of voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the line is terminated in a mismatched load, standing waves form regions of high voltage alternating with regions of high current. The derivation above assumes losses occur uniformly in these regions, but in practice the resistive losses are more significant than the dielectric losses. Thus, the regions with high current have higher loss than the regions with high voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, consider a short 50 ohm transmission line, say 1/10th of a wavelength long. This line could be terminated in either 5 ohms or 500 ohms, and in either case would experience an SWR of 10:1, and the method above would predict the same loss in either case. But in actuality, this line is so short the current and voltage anywhere along its length is more or less uniform.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of the 5 ohm termination, current is going to be high, and the actual losses will be more than the equation predicts. With a 500 ohm termination, current will be low and actual losses will be less, possibly even less than the matched loss of the line. The higher the SWR, the higher the deviation from the equation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the line is electrically a multiple of half wavelengths long, there will be an equal number of high voltage and high current nodes. The effects cancel out, and actual losses are exactly as the equation predicts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also if the line is a large number of wavelengths long, there will be a large number of nodes so having one extra high voltage or high current node doesn't make a big difference overall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The practical consequence is that the equation derived here is accurate, but not always precise. In a case such as a non-resonant multi-band antenna where the electrical length and load impedance are effectively random or unknown, this equation provides an accurate estimate. If the load impedance and electrical length are known, and especially if the electrical length is less than a couple wavelengths, it may be worthwhile to employ more precise methods.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-03-15T17:53:54.803" LastActivityDate="2019-03-15T17:53:54.803" CommentCount="21" ContentLicense="CC BY-SA 4.0" />
  <row Id="7349" PostTypeId="2" ParentId="7347" CreationDate="2017-03-13T17:21:42.343" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Given that I don't have a frequency standard or other known transmitter available, what is the easiest way to calibrate the NooElec NESDR SMArt which is using a TCXO rated at 0.5 PPM.? I.e. to determine the PPM calibration value?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Find &lt;em&gt;any&lt;/em&gt; continuous broadcast signal that has a carrier and you know the nominal frequency of, and adjust the PPM value until its peak in the spectrum display is centered on that frequency value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The higher the frequency of the signal you are calibrating to, the more your local oscillator's error is magnified, so the more precise this eyeball procedure can be. (If you have a large error, it may be useful to start at a low frequency before moving up, so you don't have trouble finding the expected signal in band.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, it's only as good as the transmitter, which you don't know, but you can easily get it good enough for accurate tuning (as opposed to frequency measurement).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Also, is this value frequency dependent? (How so?)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. The physical oscillator generates a signal at a fixed frequency, and the tuned frequency is derived from that in a way which more or less involves counting — there is no systematic “analog” error in it.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-03-13T17:21:42.343" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7350" PostTypeId="1" CreationDate="2017-03-13T19:36:06.677" Score="4" ViewCount="5662" Body="&lt;p&gt;I just got an RTL-SDR dongle by Nooelec and am using CubicSDR on Mac (which supports AM, FM, and SSB), and I'm in Canada. I'm able to easily find FM radio stations, but outside of that I'm not sure where to look for interesting frequencies to listen to. (total newbie)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What frequencies should I try tuning into to find various types of signals I can listen to?&lt;/p&gt;&#xA;" OwnerDisplayName="user9315" LastEditorUserId="76" LastEditDate="2017-03-13T23:47:01.617" LastActivityDate="2018-08-16T21:14:15.290" Title="Where can I find a listening guide for different frequencies and their usages to listen to on SDR?" Tags="&lt;software-defined-radio&gt;&lt;frequency&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7351" PostTypeId="2" ParentId="7342" CreationDate="2017-03-14T02:36:58.107" Score="1" Body="&lt;p&gt;If your radio can't receive unless you hold the MONI button it can mean your squelch is set too tight.  Or, it means you can't hear static unless you hold MONI.  If it is brand new out of the box I think maybe you mean the latter.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But let's take it a step at a time.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally you don't want to hear static, but you do want to hear signals when they are present.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your post is vague but I presume that if you let go of MONI then it will transmit.  That is normal behavior.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So first, check your squelch setting.  The best way to find it is to go through the menu.  On handhelds, there is a menu button and you will find it in there.  Also on handhelds it is a secondary function of the 0 (zero) button.  But my suggestion is to stick with the menu first, and get to know what all you can find in there before using the function keys (which are different by model).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you find squelch, try different settings - 0 should make it act as if you were holding the MONI key - no squelch.  2 or 3 should be enough to quiet it down yet allow signals through.  4 or 5 will only let strong signals through.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Set it one step above where you hear static all the time - that will allow it to be at its most sensitive yet still have the static squelch function.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Please allow me to suggest a couple of edits to your question:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Change your title to &quot;My Baofeng UV-5R V2+ radio can't hear anything unless I hold the MONI button&quot;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;In your text, you can describe how you can hear things with MONI pressed but can't transmit unless you let go of MONI.  Mentioning that you are using the rubber duck indicates both that you have a handheld and that you might wonder if a better antenna would fix the problem, etc., etc.  Whatever you think is relevant to your question&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Of course, use the model number of your actual radio)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then upvote my answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Accepting my answer is very helpful, too, if it turns out it is correct and helpful.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please leave a comment on my answer describing how you made it work so others might find this question and get the answer more easily.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After you do that I'll check your tags to make sure it is even easier for others to find by searching.  I'll leave you a comment so you know when that is done - so you can see how to use them in the future.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Welcome to ham.stackexchange!&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-03-14T02:42:12.233" LastActivityDate="2017-03-14T02:42:12.233" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7353" PostTypeId="1" CreationDate="2017-03-14T05:27:23.877" Score="3" ViewCount="478" Body="&lt;p&gt;With DC hookup wire, losses are directly proportional to length. If the resistance of 100m of wire is 10 ohms then the resistance of 200m of wire will be 20 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But we measure coax loss in &lt;em&gt;decibels&lt;/em&gt; per given length. For example, &lt;a href=&quot;http://www.w4rp.com/ref/coax.html&quot; rel=&quot;noreferrer&quot;&gt;this chart&lt;/a&gt; lists RG-8X at 10MHz as having a 1dB loss per 100ft. So 200ft of this coax would have only 2dB of loss. This is &lt;em&gt;not&lt;/em&gt; twice as much loss! In fact in this case it happens to be &quot;half&quot; as much (in decibels) as twice the loss [in &quot;loss&quot;ables?].&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I mean is: if we start with 1 dB of loss for the first hundred feet, twice that loss would be 4 dB (since adding approximately 3 dB is mathematically the same as multiplying by two). But instead of 4 dB of loss, we only have 2 dB of loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's even weirder about this is that coax gets &lt;em&gt;less&lt;/em&gt; lossy as the frequency decreases. Going back to the chart we see a 2.5dB/100ft loss at 50MHz, 1.0dB/100ft at 10MHz, 0.5dB at 1MHz. Surely at 50/60Hz coax must be some sort of superconductor, then?!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do we get this scenario where at UHF frequencies a transmission line is so much &lt;em&gt;worse&lt;/em&gt; than double the power loss (basically wherever the loss per 100ft exceeds 3dB…but wait, why should the unit length matter… hmmm…), but at HF frequencies it's so much &lt;em&gt;better&lt;/em&gt;, when comparing the logarithmic losses to the linear resistance of a conductor?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-03-14T05:48:03.003" LastActivityDate="2017-03-16T00:17:08.993" Title="Why is coax loss logarithmic?" Tags="&lt;rf-power&gt;&lt;coaxial-cable&gt;&lt;electronics&gt;&lt;transmission-line&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7355" PostTypeId="2" ParentId="7353" CreationDate="2017-03-14T14:36:50.477" Score="2" Body="&lt;p&gt;In a DC (or low frequency) power line, current is constant and the voltage drop is due mainly to resistive losses. So voltage drop is proportional to wire length. Constant current and voltage drop proportional to distance gives power loss proportional to distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a transmission line (assuming no standing waves), the relationship between current and voltage is given by the characteristic impedance of the line. Losses occur due to series resistance &lt;strong&gt;and&lt;/strong&gt; parallel conductance across the dielectric.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So both voltage and current are reduced along the line, and thus the non linearity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If, say, you get 3dB loss in the 1st 100m section of line (i.e. half the power), then you'll only have 1/2 the power entering the 2nd 100m section. The 2nd section will dissipate 1/2 of that (1/4 of the total power), and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As frequency increases, the losses on the dielectric increase significantly.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2017-03-14T14:36:50.477" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7356" PostTypeId="2" ParentId="7353" CreationDate="2017-03-14T14:50:12.090" Score="4" Body="&lt;p&gt;Firstly I would note that your initial statement isn't true. Indeed, the &lt;em&gt;resistance&lt;/em&gt; of a wire increases with length, but resistance isn't loss in the same sense of transmission lines where loss is measured in &lt;em&gt;power&lt;/em&gt; or a ratio of powers. Consider:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/dnRTo.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fdnRTo.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ I_\text{source} = I_{R1} = I_{R2} = \sqrt{1 \over R_1 + R_2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{R2} = I_{R2}^2 R_{R2} = {R_2 \over R_1 + R_2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Replacing the source with a constant current or a constant voltage source we can make some linear relationships to length, but under those conditions source power changes with length also. This isn't the same sense of &quot;losses&quot; used in transmission lines which compare how much &lt;em&gt;power&lt;/em&gt; from the source makes it to the load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But this doesn't answer your question: although the relationship isn't linear, neither is it what's expected of a transmission line:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_\text{out} \propto 10^{-l} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a basic property of transmission lines that if the line is infinitely long, or terminated in a matched load, then the source will see the same impedance no matter how long, lossy, or not lossy the transmission line is. This holds for all frequencies, even DC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's no way to do that with simply a series resistor. But it can be done with a T attenuator. Here's an example of a 50Ω, 1dB attenuator:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/VroWV.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fVroWV.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance seen by V1 is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ (R_2 + R_4) || R_3 + R_1 = 50\:\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since V1 sees 50Ω, input power is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ (1\:\mathrm V)^2 / 50\:\Omega = 0.02\:\mathrm W $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll not go through the math, but the power in R4 is 1dB less, or:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 0.02\:\mathrm W \cdot 10^{-1/10} = 0.0159\:\mathrm W $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This property of not changing the impedance seen by the source holds true only &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could then imagine a transmission line as any number of these T attenuators connected together. As more are connected the total conductor resistance (R1 + R2 + ...) increases linearly, but each additional attenuator adds another 1dB of attenuation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, you can take that 1dB attenuator and divide it into two 0.5dB attenuators. And then keep subdividing infinitely until each attenuator along the length of the line is an infinitesimal section of the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this point, we are getting close to a decent model of a transmission line. Missing though is any way to transfer power efficiently since the whole thing is a resistor, and there can't be a wave in it, since a wave requires a notion of time and there's no time term in the definition of resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Solve that by adding to the model the inductance of the conductor, and the capacitance between the conductors:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/LmMaw.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fLmMaw.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since these inductors and capacitors are lossless, as long as their contribution to impedance is much larger than the resistive elements the loss will be low. Furthermore, the definition of capacitance and inductance are differential equations with time, the mathematics can support a wave.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Losses increase with frequency for (at least) three reasons:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Skin effect&lt;/li&gt;&#xA;&lt;li&gt;Dielectric losses&lt;/li&gt;&#xA;&lt;li&gt;Radiation losses&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The resistive elements in the transmission line model are more accurately functions of frequency, due to these effects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As frequency increases, skin effect constrains the current to a thinner cross-section of the conductor. This means less conductivity overall, increasing resistive losses. This is why larger-diameter coax has lower loss: there's more conductor surface area, and thus less resistive loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dielectric losses occur as the voltage alternates between opposite polarizations. Reversing the polarity of some dielectric (say, PTFE) takes some fixed amount of energy. With increased frequency this reversal occurs more times per second, meaning it consumes more power. This is why air-dielectric transmission lines have lower loss: it takes much less energy to reverse the polarity of air than something like PTFE.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radiation losses occur in coax for example when the shield is not a perfect, solid conductor. Consider coax with a braided shield: it does not provide perfect coverage, but has holes in it. At low frequencies, these holes are minuscule relative to the wavelength, making them negligible. As frequency increases the holes appear increasingly large, leading to a less complete containment of the fields within the coax, and more radiation. This is why coax intended for high-frequency use tends to incorporate foil shielding, sometimes multiple layers of it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-03-16T00:17:08.993" LastActivityDate="2017-03-16T00:17:08.993" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7357" PostTypeId="2" ParentId="7350" CreationDate="2017-03-14T15:40:16.277" Score="2" Body="&lt;p&gt;I agree that what is interesting is very subjective. You can listen to anything within the frequency range of your device. If another device uses radio frequency within that range you can listen to it. You may not understand it, but that is where learning starts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, anything below 30MHZ will most likely be AM or SSB and above will be FM though there are several exceptions to that. You could start on the low side and work your way up scanning and trying different modes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you have mentioned you've already listened to to the easy services.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every nation has a frequency coordination service usually run by the government which allocates frequencies for users within that country. The US has the FCC, and Canada has Industry Canada. That service says what power and what type of range each frequency can be used with. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because of the shared border between the Canada and the US, we have rules about what Frequency and how much power we can use for Amateur Radio, but those rules extend to frequencies well beyond the Amateur Radio Bands. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the United States and Canada. Radio devices have an ID listing which allow you to look the device up in the country's database. That is one place to start searching for things to listen to. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anything that receives or communicates with a remote device uses some portion of radio spectrum all the way up through and beyond light are listed in those services. unless it uses too low a power to be regulated or uses an unregulated section of spectrum. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are also websites dedicated to SIGnal IDentification where people share and post waveforms from their SDR's and discuss the technology surrounding the different communication processes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for what you find interesting your best way to find that is to Google for&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&quot;Thing you find interesting&quot;&lt;/em&gt; radio frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That will provide you with not only the frequency but usually some information like signal power, modulation type and expected range which can be used to listen or decode it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure about Canada specifically, but the UK has laws about what you can and can't listen to legally. The US does as well, but mostly limited to voice telecommunication.&lt;/p&gt;&#xA;" OwnerUserId="6092" LastEditorUserId="6092" LastEditDate="2018-08-16T21:14:15.290" LastActivityDate="2018-08-16T21:14:15.290" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="7359" PostTypeId="2" ParentId="7284" CreationDate="2017-03-14T16:04:02.367" Score="2" Body="&lt;p&gt;&lt;em&gt;This text was posted by the author of the question but not as an answer, so I am merely copying it here.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I tried simply connecting the two antennae together, but although it worked after a fashion, many of the stations, especially on FM, were very hissy, and noisy.  So I decided to bite the bullet, and get a signal combiner.  They seem to be like rockinghorse poo!  Many are listed, but none are stocked!  I finally found this item, not the cheapest, but at least it was in stock.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.aerialsat.com/prod/triax-tfc-fm-dab-uhf-triplexer.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.aerialsat.com/prod/triax-tfc-fm-dab-uhf-triplexer.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With this installed, like magic, it all worked, at least as well as each antenna connected separately.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess that wraps it up.&#xA;You are welcome to try it yourself.  Maybe you can improve, or do it cheaper.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-03-14T16:04:02.367" CommentCount="0" CommunityOwnedDate="2017-03-14T16:04:02.367" ContentLicense="CC BY-SA 3.0" />
  <row Id="7360" PostTypeId="2" ParentId="7347" CreationDate="2017-03-14T21:55:27.043" Score="3" Body="&lt;p&gt;I want to add some solutions to Kevins answer. Apparently I'm lucky to own the SMArt device as it is really stable with a &lt;strong&gt;PPM&lt;/strong&gt; between &lt;code&gt;0.5 - 1.0&lt;/code&gt; at all bands I've looked at. (Just as advertised.) So how do you calibrate your less stable RTL-SDR? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically there are many different ways out there. The easiest is indeed what Kevin Reid posted, whose method is shown nicely in &lt;a href=&quot;https://www.youtube.com/watch?v=mJIU04PHKTo&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; and &lt;a href=&quot;https://www.youtube.com/watch?v=gFXMbr1dgng&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; videos. However, a much more accurate way, is to calibrate against a GSM station whose known ARFCN frequencies are exact. This is what the &lt;code&gt;ADS-B&lt;/code&gt; people usually do with older SDR sticks, before using &lt;em&gt;dump1090&lt;/em&gt;. The best explanations I found, are the ones provided by [1] and [2].&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The public available code to do this is called &lt;code&gt;Kalibrate&lt;/code&gt; was originally made by Joshua Lackey from &lt;a href=&quot;https://web.archive.org/web/20131226204943/http://thre.at/kalibrate&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. Since then there have been many iterations and alternatives, but at the end of the day the original is the best, as others are either device dependent, broken or dependent on libraries that are too new or outdated. There are now dozens of &lt;a href=&quot;https://github.com/search?utf8=%E2%9C%93&amp;amp;q=kalibrate&quot; rel=&quot;nofollow noreferrer&quot;&gt;variations&lt;/a&gt; of this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally I just used the &lt;a href=&quot;http://rtlsdr.org/files/kalibrate-win-release.zip&quot; rel=&quot;nofollow noreferrer&quot;&gt;old Windows version&lt;/a&gt; as the latest Linux one didn't compile. It worked great and made sense. This is a two step process.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Find the GSM channel (ARFCN) with the highest power.&lt;/li&gt;&#xA;&lt;li&gt;Use this channel to calibrate to.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&#xA;    # We use an arbitrary gain of 30 dBm and a starting PPM of ~1,&#xA;    # and throughout most of Europe we only have EGSM for 2G.&#xA;&#xA;    $ ./kal.exe -g 35 -e 1 -s EGSM -v&#xA;&#xA;    E-GSM-900:&#xA;            chan: 6 (936.2MHz + 481Hz)      power: 297161.97&#xA;            chan: 13 (937.6MHz + 427Hz)     power: 80136.18&#xA;            chan: 45 (944.0MHz + 173Hz)     power: 72538.40&#xA;            chan: 74 (949.8MHz + 264Hz)     power: 1357267.92&#xA;            chan: 81 (951.2MHz + 157Hz)     power: 91010.07&#xA;            chan: 104 (955.8MHz -  35Hz)    power: 426084.14&#xA;            chan: 108 (956.6MHz + 128Hz)    power: 61358.88&#xA;    Found 1 device(s):&#xA;      0:  ezcap USB 2.0 DVB-T/DAB/FM dongle&#xA;&#xA;    Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle&#xA;    Found Rafael Micro R820T tuner&#xA;    Exact sample rate is: 270833.002142 Hz&#xA;    Setting gain: 35.0 dB&#xA;    meh: Scanning for E-GSM-900 base stations.&#xA;    channel detect threshold: 28151.015811&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;We see that the ARFCN &lt;strong&gt;74&lt;/strong&gt; is the strongest one, so we use it for the calibration.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&#xA;    $ ./kal.exe -v -e 1 -c 74&#xA;&#xA;    average         [min, max]      (range, stddev)&#xA;    + 235Hz         [228, 243]      (15, 4.489251)&#xA;    overruns: 0&#xA;    not found: 0&#xA;    average absolute error: 0.753 ppm&#xA;    Found 1 device(s):&#xA;      0:  ezcap USB 2.0 DVB-T/DAB/FM dongle&#xA;&#xA;    Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle&#xA;    Found Rafael Micro R820T tuner&#xA;    Exact sample rate is: 270833.002142 Hz&#xA;    meh: Calculating clock frequency offset.&#xA;    Using GSM-900 channel 74 (949.8MHz)&#xA;            offset   1: 230.82&#xA;            ...&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And thus, for this test, we get a PPM of &lt;code&gt;0.753&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[&lt;a href=&quot;https://inst.eecs.berkeley.edu/~ee123/sp16/lab/lab4/lab4-Part_I_Frequency_Calibration_Using_GSM_BaseStations.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;1&lt;/a&gt;] and  [&lt;a href=&quot;https://medium.com/@rxseger/sdr-calibration-via-gsm-fcch-using-kalibrate-and-lte-cell-scanner-on-rtl-sdr-and-hackrf-193a7fb8a3eb#.s9qbas2pz&quot; rel=&quot;nofollow noreferrer&quot;&gt;2&lt;/a&gt;]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For other implementations see: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/steve-m/kalibrate-rtl&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/steve-m/kalibrate-rtl&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/viraptor/kalibrate-rtl&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/viraptor/kalibrate-rtl&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/scateu/kalibrate-hackrf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/scateu/kalibrate-hackrf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/Nuand/kalibrate-bladeRF&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/Nuand/kalibrate-bladeRF&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/ttsou/kalibrate&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/ttsou/kalibrate&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6563" LastActivityDate="2017-03-14T21:55:27.043" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7361" PostTypeId="2" ParentId="7353" CreationDate="2017-03-15T00:16:49.280" Score="3" Body="&lt;p&gt;&lt;strong&gt;You are mixing units.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of the wire, you specify resistance. But dB refers to power, not resistance.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-03-15T00:16:49.280" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7362" PostTypeId="2" ParentId="7317" CreationDate="2017-03-15T05:18:06.350" Score="2" Body="&lt;p&gt;This is so dependent on the particular antenna, and rubber ducks are such compromise antennas anyway, probably the only way to get a useful answer is to do a shootout between specific antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pretty much all of the antennas tested by Mike W9MDB &lt;a href=&quot;http://www.miklor.com/COM/pdf/AntennaTestingW9MDB.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; seemed to have higher gain on 2m than 70cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would expect, however, that between similarly sized monoband antennas, a 70cm could have better gain than a 2m, but I don't know if that would make up for 70cm's higher path losses.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-03-15T05:18:06.350" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7363" PostTypeId="2" ParentId="4915" CreationDate="2017-03-15T05:42:37.223" Score="1" Body="&lt;p&gt;I like &lt;a href=&quot;http://www.g4ilo.com/images/usblink-cct.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;G4ILO's circuit&lt;/a&gt;, based on something by Skip Teller, KH6TY and described in more detail in the VOX Circuit section &lt;a href=&quot;http://www.g4ilo.com/usblink.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-03-15T05:42:37.223" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7365" PostTypeId="1" AcceptedAnswerId="7374" CreationDate="2017-03-15T20:39:50.850" Score="1" ViewCount="2130" Body="&lt;p&gt;I'm trying to use a RaspberryPi3 as a FM transmitter, using &lt;a href=&quot;https://github.com/rm-hull/pifm&quot; rel=&quot;nofollow noreferrer&quot;&gt;pifm&lt;/a&gt; and/or &lt;a href=&quot;https://github.com/ChristopheJacquet/PiFmRds&quot; rel=&quot;nofollow noreferrer&quot;&gt;PiFmRds&lt;/a&gt; to send audio in 88-108 MHz band. The RPi can then use the GPIO-4 pin to transmit between &lt;code&gt;1-250 MHz&lt;/code&gt;. However, nobody want to ruin their HW while still optimizing the output by using a proper antenna.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What is the best antenna design to use? (A wire, dipole or something else?)&lt;/li&gt;&#xA;&lt;li&gt;How to best connect the antenna? (I.e. Do we need impedance matching?)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I would like to avoid any amplifiers or extra active hardware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT-1:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;I'm of course fully aware of the legalities of TX on FM band.&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.mosaic-industries.com/embedded-systems/microcontroller-projects/raspberry-pi/gpio-pin-electrical-specifications&quot; rel=&quot;nofollow noreferrer&quot;&gt;Apparently&lt;/a&gt; the RPi GPIO impedance is around 30-60 Ohms.&lt;/li&gt;&#xA;&lt;li&gt;This is an antenna problem, because the question is equally valid for any transmitter. &lt;/li&gt;&#xA;&lt;li&gt;The best options I have seen so far is &lt;a href=&quot;https://fmdxing.wordpress.com/2014/07/09/simple-diy-fm-antennas-build-an-fm-loop-for-about-20/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; FM loop or &lt;a href=&quot;https://www.youtube.com/watch?v=a4RM9YNIsIM&amp;amp;feature=youtu.be&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; quad loop...&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="6563" LastEditorUserId="6563" LastEditDate="2017-03-18T05:51:21.117" LastActivityDate="2019-05-06T12:43:17.233" Title="How to best connect an FM transmitting GPIO pin to an antenna?" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;&lt;antenna-construction&gt;&lt;impedance&gt;" AnswerCount="2" CommentCount="13" ContentLicense="CC BY-SA 3.0" />
  <row Id="7366" PostTypeId="2" ParentId="7365" CreationDate="2017-03-16T05:03:17.670" Score="3" Body="&lt;p&gt;To be legal, you will need a low-pass or FM band-pass filter between the Pi's digital output and any antenna.  Otherwise, the antenna will also be transmitting at a bunch of harmonic frequencies well outside your intended band (into multiple higher frequency bands at 2X, 3X, 4X, 5X, etc. your intended FM frequency.)  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added: This is because periodic digital waveforms (produced by digital IO pins) contain lots of energy at lots of harmonic frequencies (Fourier's theorem).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, see this question: &lt;a href=&quot;https://ham.stackexchange.com/questions/7279/super-low-tech-vhf-low-pass-filter-construction&quot;&gt;Super-low-tech VHF low-pass filter construction?&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added #2: Given that the current output of a Pi's 3.3V GPIO pin is recommended to be kept below somewhere between 3 mA to 16 mA (depending on how many other GPIO outputs are being used), an impedance (resistor or ?) of somewhere in the range of 220 Ohms to 1.5k Ohms might be required somewhere in the matching network between the output and a 50 Ohm antenna load.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-03-21T18:00:10.300" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7367" PostTypeId="2" ParentId="7350" CreationDate="2017-03-16T05:28:00.447" Score="3" Body="&lt;p&gt;If you are near any airports, the AM VHF airband or aviation band (roughly between 108 and 137 MHz) is standard throughout most developed countries, and within the frequency range of most generic RTL-SDR dongles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another possibility, if you are near any navigable waters, is the VHF marine band, where many countries broadcast weather and/or sea conditions constantly or often.  Often narrow-band FM.  A  web search for Canada marine radio turns up many sites, such as: &lt;a href=&quot;http://www.offshoreblue.com/communications/vhf-ca.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.offshoreblue.com/communications/vhf-ca.php&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your national government's radio licensing agency likely has a band plan for amateur radio use.  Many of those amateur bands are in the VHF and higher region, in the range of an RTL-SDR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a suitable antenna with a good clear view of the sky, your RTL-SDR can often pick up satellite signals as various orbital objects pass overhead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many countries use VHF bands for police and fire dispatch (there are probably online scanner frequency lists for your locale in various search databases); but make sure your country's laws allow reception of such.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-03-18T04:17:29.427" LastActivityDate="2017-03-18T04:17:29.427" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7368" PostTypeId="2" ParentId="1256" CreationDate="2017-03-16T23:09:41.877" Score="7" Body="&lt;p&gt;A really easy way to do this is to take an old USB mouse (or even a new cheap one) and solder the key across the left mouse button. You can then use key directly as mouse button input on most computers and Android phones (with an OTG cable) and use with Morse software or websites expecting mouse input e.g. :-&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://morsecode.me&quot; rel=&quot;noreferrer&quot;&gt;http://morsecode.me&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.web-adventures.org/MorseBlitz/&quot; rel=&quot;noreferrer&quot;&gt;http://www.web-adventures.org/MorseBlitz/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For hours of fun and practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Update: Your question inspired me to do a little better so I created this blog post in the hope that it's useful &lt;a href=&quot;http://whaley.org.uk/andrew/blog/2017/04/28/morse-code-cw-via-usb/&quot; rel=&quot;noreferrer&quot;&gt;http://whaley.org.uk/andrew/blog/2017/04/28/morse-code-cw-via-usb/&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It covers 2 methods; the quick mouse option but also something a lot more versatile which isn't that much more effort.&lt;/p&gt;&#xA;" OwnerUserId="9364" LastEditorUserId="9364" LastEditDate="2017-04-28T13:45:15.957" LastActivityDate="2017-04-28T13:45:15.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7372" PostTypeId="2" ParentId="7287" CreationDate="2017-03-19T00:58:43.300" Score="1" Body="&lt;p&gt;I resolved the SWR issue by using an &lt;strong&gt;Arizona Rocky Road Mount&lt;/strong&gt; mount, which raised the antenna above the spare tire.  This resulted in SWRs no greater than 1.5:1 across both bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mwLz0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mwLz0.png&quot; alt=&quot;Arizona Rocky Road Jeep J/K Mount&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4748" LastActivityDate="2017-03-19T00:58:43.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7374" PostTypeId="2" ParentId="7365" CreationDate="2017-03-20T11:50:12.223" Score="1" Body="&lt;p&gt;After some further research, I've decided to answer my own questions &#xA;as I find the current answers insufficient. Evidently the &quot;best&quot; antenna also seem to be the simplest. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the article: &#xA;&lt;code&gt;&quot;Antenna 101: Let’s Review the Basics&quot;&lt;/code&gt; &lt;em&gt;by Dan Farber&lt;/em&gt; (&lt;strong&gt;AC0LW&lt;/strong&gt;) in the &#xA;magazine &lt;em&gt;The Spectrum Monitor&lt;/em&gt; [July, 2016].&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Consider once again the humble dipole. In its most basic form, it is &#xA;  cut to resonance at a desired frequency in a single band, and fed with&#xA;  coaxial cable. Notice that one side of the dipole is thus connected to&#xA;  the coax’s shield. Down at the radio end, the coax shield is connected&#xA;  to RF ground, that is to say the grounded side of the coax connector. &#xA;  This works fine with no additional RF grounding.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This and the well known fact that the impedance of a: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;code&gt;1/4-wave vertical&lt;/code&gt; with good RF ground is &lt;strong&gt;~35&lt;/strong&gt; Ohms.&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;1/2-wave dipole&lt;/code&gt; is &lt;strong&gt;~70&lt;/strong&gt; Ohms.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This matches very well with the &lt;strong&gt;GPIO impedance&lt;/strong&gt; that is believed to be &#xA;somewhere between &lt;strong&gt;30-60 Ohms&lt;/strong&gt;. (&lt;a href=&quot;https://electronics.stackexchange.com/questions/127046/what-is-output-impedance-of-a-pin&quot;&gt;How to test?&lt;/a&gt;) Thus we can expect a natural impedance matching, or at least close enough, which is probably why these simple wire antennas work so well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So as noted by the commenters in &lt;a href=&quot;http://makezine.com/projects/raspberry-pirate-radio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; link, a simple 1/4-wave wire with &#xA;a 1/4-wave ground along the table, will be quite efficient. The wires also &#xA;has to be electrically isolated, to help prevent possible static damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;How to best prevent GPIO ESD damage?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several ways applicable here:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Use a ESD/TSV chip such as the &lt;a href=&quot;http://www.ti.com/lit/gpn/tpd1e01b04&quot; rel=&quot;nofollow noreferrer&quot;&gt;TPD1E01B04&lt;/a&gt; with Cio=0.2 pF.&lt;/li&gt;&#xA;&lt;li&gt;Use a simple resistor with R &gt;= 100 K Ohms.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strike&gt;Use an inductor or inductive coil with X &gt;= 100K @ 100 MHz.&lt;/strike&gt; &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;In each case you should connect the part between the antenna wire &#xA;and device GND. Please see &lt;a href=&quot;http://hpfriedrichs.com/radioroom/bleeder/rr-bleeder.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;THIS&lt;/a&gt; excellent blog about how to prevent static and lightning damage. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;WARNING&lt;/strong&gt; I now recommend against using an inductor only, as it would force ground the GPIO pin, if set to 1 at DC during any other time, before the HF has been activated. This would surely damage your RPi.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;A simple band-pass filter&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The construction of a passive Band Pass Filter can be seen &lt;a href=&quot;https://www.youtube.com/watch?v=CuxNGWcftc8&quot; rel=&quot;nofollow noreferrer&quot;&gt;HERE&lt;/a&gt; and another filter is very nicely described &lt;a href=&quot;http://www.electronics-tutorials.ws/filter/filter_4.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;HERE&lt;/a&gt;. In the video he uses the following values, but can probably be tuned even more. &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Cgnd = 10 pF&#xA;Cio  = 2.2 pF&#xA;Rgnd = 1 K &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/THk1z.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/THk1z.gif&quot; alt=&quot;passive Band Pass Filter&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Same as in video, if R1 is removed.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;To amplify the GPIO signals&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please look at &lt;a href=&quot;http://elinux.org/RPi_GPIO_Interface_Circuits&quot; rel=&quot;nofollow noreferrer&quot;&gt;THESE&lt;/a&gt; RPi GPIO driver aspects. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;NOTE-1:&lt;/strong&gt; For those concerned about the transmitted power, I've estimated it to be about &lt;code&gt;0.37 mW&lt;/code&gt; in &lt;a href=&quot;https://raspberrypi.stackexchange.com/a/63624/17798&quot;&gt;THIS&lt;/a&gt; answer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT-1:&lt;/strong&gt; I've found a few more excellent resources that explains exactly how this should be done. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first one is: &lt;a href=&quot;https://www.tapr.org/pdf/DCC2015-QRPi-HA7DCD.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRPi - A Raspberry Pi QRP TX Shield Design&lt;/a&gt;, from where:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;However there were still one thing missing: no buffer stage to protect&#xA;  the BCM2835 SoC's clock generator output stage. Hardware failure due&#xA;  to the unbuffered operation of the WsprryPi program was reported by a&#xA;  few HAM operators, possibly due to overload from nearly broadcast&#xA;  transmitter stations. If buffer amplifier was already needed it was a&#xA;  good idea to add some gain to the system. Eventually using a single&#xA;  FET amplifier stage [fig 7] 10 dB gain achieved, delivering +20 dBm&#xA;  output power at the end of the LPF [fig 4]...&#xA;  For ESD and static discharge protection an ESD suppressor diode was &#xA;  added to the antenna terminal of the circuit. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The other ones are: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://j.mp/tapr-qrpi&quot; rel=&quot;nofollow noreferrer&quot;&gt;20M WSPR-Pi (QRPi) software installation guide for different HAM TX modes&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.tapr.org/kits_20M-wspr-pi.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Raspberry Pi QRP TX Shield for WSPR on 20 Meters&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://wsprnet.org/drupal/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Weak Signal Propagation Reporter Network&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/JamesP6000/WsprryPi&quot; rel=&quot;nofollow noreferrer&quot;&gt; WSPR transmitter using NTP based frequency calibration &lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There are several great links to filter, amplifier and buffer designs there. In addition, a simple design can allow you to transmit in the 20m HAM band several thousands of kilometers. Amazing. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The GitHub README from the last link, basically concludes all my original questions: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;As the Raspberry Pi does not attenuate ripple and noise components&#xA;  from the   5V USB power supply, it is RECOMMENDED to use a regulated&#xA;  supply that has   sufficient ripple supression. Supply ripple might be&#xA;  seen as mixing products   products centered around the transmit&#xA;  carrier typically at 100/120Hz.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;DO NOT expose GPIO4 to voltages or currents that are above the&#xA;  specified   Absolute Maximum limits. GPIO4 outputs a digital clock in&#xA;  3V3 logic, with a   maximum current of 16mA. As there is no current&#xA;  protection available and a DC   component of 1.6V, DO NOT&#xA;  short-circuit or place a resistive (dummy) load   straight on the&#xA;  GPIO4 pin, as it may draw too much current. Instead, use a&lt;br&gt;&#xA;  decoupling capacitor to remove DC component when connecting the output&#xA;  dummy   loads, transformers, antennas, etc. DO NOT expose GPIO4 to&#xA;  electro- static   voltages or voltages exceeding the 0 to 3.3V logic&#xA;  range; connecting an   antenna directly to GPIO4 may damage your RPi&#xA;  due to transient voltages such   as lightning or static buildup as&#xA;  well as RF from other transmitters   operating into nearby antennas.&#xA;  Therefore it is RECOMMENDED to add some form   of isolation, e.g. by&#xA;  using a RF transformer, a simple buffer/driver/PA   stage, two&#xA;  schottky small signal diodes back to back.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="6563" LastEditorUserId="6563" LastEditDate="2019-05-06T12:43:17.233" LastActivityDate="2019-05-06T12:43:17.233" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="7375" PostTypeId="1" CreationDate="2017-03-20T14:55:00.263" Score="2" ViewCount="148" Body="&lt;p&gt;Suppose I have a 3.3 or 5V GPIO digital signal (from an Arduino or Raspberry Pi, etc.), periodically toggling at some HF or VHF frequency.  Since it has such a &quot;dirty&quot; spectrum, I don't want to hook it up to an antenna.  But I do want to examine the signal's frequency spectrum (including harmonics/spatter,etc.) and signal levels (S-meter readings, etc.), and modulation (AM, FM, if any) with one or more of my wide-band receivers (such as an analog shortwave radio, HF transceiver, VHF HT, RTL-SDR, Funcube dongle, and etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How should I connect a CMOS digital output to a 50 ohm coax antenna input on a SW/HF/VHF radio receiver? e.g. what circuitry and construction is required for safe signal levels, DC isolation, shielding, ESD protection if needed, impedance match if needed, etc.?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2017-03-22T12:47:30.347" Title="How to safely connect a digital output to a receiver's antenna input?" Tags="&lt;software-defined-radio&gt;&lt;receiver&gt;&lt;antenna-system&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7376" PostTypeId="1" CreationDate="2017-03-20T20:39:02.647" Score="5" ViewCount="2352" Body="&lt;p&gt;A number of my RF devices have a specified safe maximum input power, for example:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&quot;The maximum RX power of HackRF One is -5 dBm. Exceeding -5 dBm can result in permanent damage!&quot; &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/HackRF-One#receive-power&quot; rel=&quot;noreferrer&quot;&gt;source&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&quot;If you look at the R820T datasheet … you can see the max input power is 10dBm&quot; &lt;a href=&quot;http://www.rtl-sdr.com/forum/viewtopic.php?p=1196#p1196&quot; rel=&quot;noreferrer&quot;&gt;source&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;For the VNWA3 a &quot;Maximum permissible external RF Input Level to TX-Out and RX-In ports: 0 dBm&quot; source: &lt;a href=&quot;https://sdr-kits.net/DG8SAQ/VNWA/VNWA_HELP.pdf&quot; rel=&quot;noreferrer&quot;&gt;page 5 (pdf)&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&quot;In any configuration the maximum input power to the RSP1 must not exceed 0dBm&quot; source: &lt;a href=&quot;http://www.sdrplay.com/Panadapterintro1.pdf&quot; rel=&quot;noreferrer&quot;&gt;page 5 (pdf)&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm wondering how I could determine a similar number for a general purpose receiver or a ham transceiver?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example the &lt;a href=&quot;http://www.universal-radio.com/catalog/hamhf/3450spec.html&quot; rel=&quot;noreferrer&quot;&gt;specifications for my IC-706MKIIG&lt;/a&gt; include some &quot;receiver sensitivity&quot; and &quot;squelch sensitivity (threshold)&quot; values in microvolts, as well as some &quot;selectivity&quot; and &quot;spurious and image rejection ratio&quot; values in decibels, but it's not clear what this means as far as safely hooking it to a signal generator, or operating near other stations at field day, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I know how much input power a commercial receiver can safely handle?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2019-04-16T19:40:07.037" Title="How to find or derive the maximum safe input power to a receiver?" Tags="&lt;receiver&gt;&lt;rf-power&gt;&lt;electronics&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7377" PostTypeId="2" ParentId="7375" CreationDate="2017-03-20T21:13:03.217" Score="3" Body="&lt;p&gt;Looks like a 5V peak-to-peak &lt;strong&gt;sine wave&lt;/strong&gt; into a 50 ohm load results in about 18 dBm of power (using my own &lt;a href=&quot;http://utils.ipcalf.com/#ppwatts&quot; rel=&quot;nofollow noreferrer&quot;&gt;Voltage to power converter&lt;/a&gt; and &lt;a href=&quot;http://utils.ipcalf.com/#dbm&quot; rel=&quot;nofollow noreferrer&quot;&gt;dBm ↔︎ watts converter&lt;/a&gt; tools so you might double-check the math). An unmodulated square wave would be 3 dB more than this; an AM or FM signal is probably somewhere in between.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is probably a damaging amount of power to most receivers, where -50 dBm is a quite &quot;loud&quot; signal normally. Since it is oscillating only between 0 and 3.3/5V, there will be a DC offset so keep that in mind too.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Option 1: Attenuate (and isolate?)&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;I'm not sure &lt;a href=&quot;https://ham.stackexchange.com/questions/7376/how-to-find-or-derive-the-maximum-safe-input-power-to-a-receiver&quot;&gt;how to find the limits for an HF transceiver&lt;/a&gt; but the RF test equipment I have ranges between -5 dBm (HackRF) to &lt;em&gt;perhaps&lt;/em&gt; 10 dBm (RTL-SDR you don't mind replacing…). So &lt;strong&gt;at minimum&lt;/strong&gt; you should have a 25 dB attenuator between a 5V sine wave and an SDR. To account for math errors or other surprises — such as accidentally enabling any pre-amps within your receiver! — start with much more attenuation and remove it until your signal is in the desired range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You shouldn't need to worry too much about power ratings on the attenuator(s) since your signal is only a sixteenth of a watt — that may be a lot for the semiconducting junctions of a receiver but not the resistors in an attenuator!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your receiver can't already handle a few volts of DC offset you'll need a DC isolator (basically a capacitor) in series too; the attenuator circuits I've seen do not provide this. For both DC isolation and RF attenuation, they are fairly simple circuits to DIY and commercial versions tend to be relatively inexpensive.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Option 2: Sample into a dummy load&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Another option would be to drive the signal you're testing into dummy load and use an &lt;a href=&quot;https://www.youtube.com/watch?v=0Kk_N_TpDeo&quot; rel=&quot;nofollow noreferrer&quot;&gt;RF sampler&lt;/a&gt; to steal a small bit of the full signal for analysis. A sampler typically uses a suitable &lt;a href=&quot;https://n9sja.com/2013/10/06/rf-oscilloscope-sampler/&quot; rel=&quot;nofollow noreferrer&quot;&gt;capacitance&lt;/a&gt; or &lt;a href=&quot;http://www.collinsradio.org/wp-content/uploads/2015/05/Build-a-Quality-RF-Power-Sampler-Jackson.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;mutual inductance&lt;/a&gt; to couple an analyzer into the test circuit. With this option, you shouldn't need additional DC isolation. Commercial variable RF sampler units tend to be somewhat expensive, but you can easily make a servicable fixed sampler yourself by &lt;a href=&quot;http://urgentcomm.com/test-and-measurement/every-toolbox-needs-one-these&quot; rel=&quot;nofollow noreferrer&quot;&gt;modified coax tee and barrel&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Caveats&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;In both cases (attenuating and sampling) the goal is to dissipate most of the power through a resistance. I've been assuming a 50 ohm load, but the GPIO pins may be better served by something else. You could try figure out what the &lt;a href=&quot;https://www.tapr.org/kits_20M-wspr-pi.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSPR-Pi&lt;/a&gt; designer assumed for 20m or attempt to gain an general answer for &lt;a href=&quot;https://github.com/F5OEO/rpitx/issues/54&quot; rel=&quot;nofollow noreferrer&quot;&gt;this 2m question&lt;/a&gt; — but I'm not sure how much it really matters?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that I've also deliberately avoided the other issues (ESD protection, impedance matching) since I simply don't know enough about the risks or practical mitigations there.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.357" LastActivityDate="2017-03-20T21:27:55.033" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7380" PostTypeId="2" ParentId="7375" CreationDate="2017-03-21T16:32:02.803" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;what circuitry and construction is required for safe signal levels&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The simple solution is to transmit into a dummy load (read, a 50 ohm resistor from the parts drawer) set near the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that doesn't provide enough coupling, you can build an attenuator of any value you need with some resistors. Search for &quot;T pad attenuator&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Find the safe input power for the receiver from  the datasheet. If you don't have a datasheet, then you can also look at typical transmitter powers and path loss for your application and determine a &quot;typical&quot; value that way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind more is not better. With increasing power, receiver distortion increases, which is not good if you are trying to measure distortion. Too little power and you are below the noise floor. Somewhere in the middle is ideal.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;DC isolation&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If your transmitter is battery powered, or powered by a DC isolated power supply, then you are already set. It's possible your receiver is already DC isolated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't want to chance it, then a 1:1 transformer is simple enough, though its specific construction will depend a lot on the frequency of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A series capacitor is also an option, making a high-pass filter with the load impedance. Just make the capacitor large enough that the cutoff of this high-pass filter is well below your transmitter frequency.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;shielding&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Use coax if you want shielding.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;ESD protection if needed&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Probably not needed. Any receiver designed to be connected to an antenna will be sufficiently robust already.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;impedance match if needed&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Since you will have a lot of attenuation, the impedance of the attenuator will dominate the impedance seen by either side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may be the case that your transmitter needs to see a higher impedance than the conventional 50 ohms to remain within its current output specifications. The simplest solution is to use an attenuator of whatever impedance the transmitter needs to see. This means the receiver won't see a 50 ohm source, but all that means is you're getting less than the maximum possible power out of the source. Since you're building an attenuator that's not a problem. There is such a thing as a resistive T match which can present a difference impedance to each side, though in this application it would be of little practical benefit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Though keep in mind the load impedance can affect the transmitter's output. Unless your antenna is also a matched load &lt;em&gt;across all frequencies&lt;/em&gt;, you may not get a realistic measurement this way. This is especially true if you are spewing noise from a GPIO pin into a random wire with zero filtering whatsoever.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-03-22T12:47:30.347" LastActivityDate="2017-03-22T12:47:30.347" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7381" PostTypeId="2" ParentId="7376" CreationDate="2017-03-21T17:08:08.080" Score="3" Body="&lt;p&gt;I'm going to start with an extremely conservative approach and work upward in power from there. It is highly likely that you can apply more power than the following analysis concludes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, I assume you are considering a transmitter and a receiver tuned to the same frequency, nearby or connected by a transmission line. That is, we are concerned with how much power we can supply as a single in-band signal, rather than the total power of signals at frequencies unrelated to the receiver's tuning (where the safe limit &lt;em&gt;may&lt;/em&gt; be higher but need not be).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Let's suppose that you have a &lt;em&gt;sensitivity&lt;/em&gt; specification for the receiver — that gives us a &lt;em&gt;minimum&lt;/em&gt; input level and we can work from there. First, if we have it in (micro)volts then we want to convert to power instead. Let's suppose that our sensitivity spec is 2.0 µV for the relevant band and mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;\begin{align}&#xA;P &amp;amp;= \frac{V^2}{R}&#xA;&amp;amp;&#xA;\frac{(2.0\:\mathrm{µV})^2}{50\:\Omega} = 8\cdot10^{-14}\:\mathrm{W}&#xA;\end{align}&#xA;$$&#xA;Then convert to dBm (decibels relative to one milliwatt) for future convenience:&#xA;$$&#xA;10\log_{10}\left(\frac{8\cdot10^{-14}\:\mathrm{W}}{1\:\mathrm{mW}}\right) = -101 \:\mathrm{dBm}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So this tells us that if we put in a -101 dBm signal it'll definitely be safe, but we won't necessarily hear it very well.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The easy conservative solution at this point is to arrange exactly that much attenuation — that is, figure the output power in dBm of your transmitter at minimum setting, and the difference between that and -101 dBm is how much attenuation you need — and then gradually decrease the attenuation until you have an adequate SNR at the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(This attenuation can be obtained using a variable (or fixed) attenuator in a coax line, or by separating two antennas with enough distance, or cross polarization or aiming high-gain antennas in the wrong direction, et cetera. Though there's a point at which the dominant signal path between transmitter and receiver will be unintended leakage from the chassis, power cables, et cetera rather than whatever's hooked up to the antenna ports.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;But we'd like a more generous figure. We can obtain one by looking for any information that implies a &lt;em&gt;ratio&lt;/em&gt; between two signals the receiver is able to receive safely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An easy one to obtain that doesn't even need a spec-sheet is an S-meter. Standardized S-units are 6 dB, and a typical S-meter will read S1 through S9 and some number of dB beyond S9. Your IC-706MKIIG has an S-meter which reads from S1 to S9 + 60 dB — an overall ratio of $(8 \cdot 6\:\mathrm{dB}) + 60\:\mathrm{dB} = 108 \:\mathrm{dB}$. So we apply that to our minimum-power figure and get $-101\:\mathrm{dBm} + 108\:\mathrm{dB} = 7 \:\mathrm{dBm}$, which is nice and large.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, I've just assumed that the sensitivity figure is “below S1” which might be wrong, and it looks like it is wrong: There's also &lt;a href=&quot;https://ham.stackexchange.com/a/6951/76&quot;&gt;a standard for the reference level of an S-meter&lt;/a&gt;, S9 = -73 dBm. So we take $-73\:\mathrm{dBm} + 60\:\mathrm{dB} = -13 \:\mathrm{dBm}$, which is smaller than the previous figure. But not by much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Actually, we can even skip the part where we started from receiver sensitivity: the S-meter scale convention implies that it should be safe for any such receiver to receive a signal between S1 and S9, or -121 to -73 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But also note, as I mentioned at the start, that it is likely that a receiver is designed with a substantial margin of safety beyond the maximum on its S-meter scale.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So in a fairly pessimistic case, let's say you have a transmitter with an output power of 5 watts and no less; that's 37 dBm. Then in order to put it at our supposedly generally-safe level of -73 dBm, we need $-73\:\mathrm{dBm} - 37\:\mathrm{dBm} = -110 \:\mathrm{dBm}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That much attenuation is probably most conveniently achieved by the approach of putting a dummy load on the transmitter and letting the leakage carry your signal. But if you have enough attenuation (given the power level, more in the form of &quot;dummy load with a sampling port&quot;) then there you go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if you have a 1 mW (0 dBm) transmitter and a safe-for-10 dBm receiver, then you don't need any attenuation at all to be safe. (Though &lt;em&gt;safe&lt;/em&gt; is likely not the same thing as &lt;em&gt;undistorted signal&lt;/em&gt;.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="-1" LastEditDate="2017-04-13T12:59:21.763" LastActivityDate="2017-03-22T03:32:08.110" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="7382" PostTypeId="2" ParentId="7047" CreationDate="2017-03-22T11:30:03.780" Score="1" Body="&lt;p&gt;It depends of what signal do you want to receive: ATSC and DVB are digital standards and you have blocks and scripts to deal with as you have seen in the webpage you linked. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;DVB has a lot of different modulation and encoding possibilities and dealing with this in GNURadio is a bit of a headache if you do not know the exact parameters to begin with. You can also try &lt;a href=&quot;http://www.pabr.org/radio/leandvb/leandvb.en.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;LeanDVB&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Analog television is a totally different beast and I don't know yet how to deal with it. IIRC, the next version of GNURadio has a MJPEG sink on the wishlist to help deal with analog TV signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using RTL receivers you can try a windows only software: &lt;a href=&quot;http://www.rtl-sdr.com/analogue-tv-with-rtl-sdr/&quot; rel=&quot;nofollow noreferrer&quot;&gt;tvsharp&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="1701" LastActivityDate="2017-03-22T11:30:03.780" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7383" PostTypeId="2" ParentId="7205" CreationDate="2017-03-22T17:44:01.840" Score="2" Body="&lt;p&gt;Per the manufacturer, Larsen, who was under contract to Motorola to design and produce the original NMO mounts:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The maximum thickness is 2.5mm&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="4748" LastActivityDate="2017-03-22T17:44:01.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7384" PostTypeId="1" AcceptedAnswerId="7387" CreationDate="2017-03-22T18:19:00.590" Score="5" ViewCount="1284" Body="&lt;p&gt;According to article 25, section I, § 4 (25.7) ITU's Radio Regulations:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The maximum power of amateur stations shall be fixed by the administrations&#xA;  concerned.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In my country this is 500W for CEPT License,  100W for CEPT Novice License, 1500W with additional permission (additional call sign for whoever has CEPT License) and 50W for &amp;lt; 30MHz or 15W for &gt; 30 MHz for automated stations. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why this exact values? Why not 1 or 2 but 1,5 KW? Is there a underlying reason? Why can't i go 1 MW if i had the money? &lt;em&gt;And yes, i know that higher power not always means larger range.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="9129" LastEditorUserId="8832" LastEditDate="2017-03-23T13:28:02.627" LastActivityDate="2017-03-23T15:07:29.350" Title="What is the purpose of limiting radio output power?" Tags="&lt;legal&gt;&lt;rf-power&gt;&lt;rfi&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7385" PostTypeId="2" ParentId="7384" CreationDate="2017-03-22T20:25:48.020" Score="6" Body="&lt;p&gt;I'd speculate a large part of the justification is that amateur stations, unlike commercial broadcast stations, are not periodically certified to meet spurious emission regulations. Or any regulations at all. While the station operator is responsible for ensuring the proper operation of his or her station, realistically amateurs will not always have the resources or technical knowledge to do this well, all of the time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, the amateur radio allocations are a shared resource. 100W is more than sufficient for worldwide communication with some skill, and with 1000W it's almost too easy. Having amateurs compete for the highest power to be louder than everyone else to get the most DX contacts would ruin the band for anyone with more modest equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, a 1kW station is already a safety hazard if not properly controlled, and can cause extremely annoying RFI issues for neighbors. Think of what a 1MW station could do. Broadcast stations operating at high power must undergo certification to assure safety, and license applications are reviewed to assure a new transmitter isn't going to cause unacceptable interference. No such regulation exists for amateurs, and regulatory bodies instead rely the good judgement of amateur station operators, and when that fails, reasonable power limits to put an upper bound on the damage that can be done.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-03-22T20:25:48.020" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7387" PostTypeId="2" ParentId="7384" CreationDate="2017-03-23T14:58:22.533" Score="4" Body="&lt;p&gt;To add to Phil Frost's answer above, I suspect the 1.5kW number used in the US is a combination of practicality and convenience.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a practicality standpoint, 1.5kW can be viewed as the point in the power to signal strength curve where your return on investment begins diminishing rapidly, at least in a hobbyist/residential scenario. To achieve a 1 S-unit improvement over a 1.5kW PEP signal, you'd need a whopping &lt;strong&gt;6kW&lt;/strong&gt;. At that point you begin to tax the typical infrastructure of a residential dwelling, as a Class AB amplifier would pull a bare minimum of 12kW to develop 6kW PEP (Class AB amps are very inefficient). In the US, the average home in the 1960s had wiring that could handle 15-20 amps, but not a heck of a lot more than that, so  operating a large amplifier could pose a safety risk without special installation considerations. The grid was also not all that robust back then, so some guy constantly hammering on the grid with rapid 20kW on/off cycles is going to present technical problems for the utility company, not to mention the neighbors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The necessary hardware to develop 6kW was also uncommon and very expensive back then, and even today would be cost prohibitive with modern components (enormous surplus Russian broadcast tubes excepted).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;100-300 watts has been the &quot;barefoot&quot; standard for HF transmitters since at least the mid 1940s, primarily owing to the availability of affordable PA tubes in that range. If you're running 6kW or more, there will be such a disparity of power between you and the &quot;average&quot; ham (3+ S-units assuming identical antennas and symmetrical propagation) that you will be unable to hear many, perhaps most, of the people who can hear you. This increases the likelihood that you will unintentionally interfere with others. As your output power increases, the inevitable spurs and harmonics of your signal also increase in power, and filtering is not always a simple matter. With the current requirements for spectral purity (-50dB I believe), a 6kW amplifier could have spurs that approach 50mW PEP. On HF in good conditions, this is sufficient for reception hundreds of miles away. Achieving the -60dB or more that would be necessary to keep the HF spectrum fairly clean is not a trivial matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally I would posit that the precise number, 1,500 watts, was a bit of rounding for the sake of convenience. A 2 S-unit (12dB) increase above the typical 100w transmitter would be 1,&lt;strong&gt;600&lt;/strong&gt; watts. To make it a nice round number that is easy to remember, 1,500 was &quot;close enough&quot;.&lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="246" LastEditDate="2017-03-23T15:07:29.350" LastActivityDate="2017-03-23T15:07:29.350" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7388" PostTypeId="1" AcceptedAnswerId="7389" CreationDate="2017-03-23T16:11:26.180" Score="2" ViewCount="9306" Body="&lt;p&gt;I had originally bought a set of BaoFeng BF-888s+ radios that perform very well and perfectly suit my needs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Needing more, I bought another set, this time buying BaoFeng BF-888s radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Same model code, except the &quot;+&quot; at the end, apparently just a restyling).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The new radios don't talk to the old radios, despite being on the same channel. Both radio sets work well among themselves, but the two sets don't communicate with each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I bought both sets from Amazon, delivered to a US address. I live in a country where regulation is not an issue (not the US).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I make both sets talk to each other?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've read somewhere that these BaoFeng radios have a programming cable (that I don't have). &lt;em&gt;If&lt;/em&gt; these radios can actually talk to each other, I would very much prefer to fix them without using a cable (e.g., using keys on the units in a way that allows configuring them), as I don't have one, and getting one would be both expensive and time consuming considering where I am now.&#xA;Otherwise, if getting a cable is the only option, is this a standard cable that can be bought in computers/electronics shops? Is their software readily available?&lt;/p&gt;&#xA;" OwnerUserId="9397" LastEditorUserId="76" LastEditDate="2017-03-23T16:43:38.457" LastActivityDate="2017-04-02T07:50:41.287" Title="Baofeng BF-888s radios don't talk to Baofeng BF-888s+ radios" Tags="&lt;baofeng&gt;&lt;equipment-operation&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7389" PostTypeId="2" ParentId="7388" CreationDate="2017-03-23T17:40:39.620" Score="4" Body="&lt;p&gt;Unfortunately, you fell into one of the traps of the Chinese radios! You can't really assume what frequencies are they programmed with. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, the radios are designed to be programmed with a certain set of frequencies, just like so-called &quot;professional&quot; radios of many other manufacturers. The &quot;channel&quot; on the radio is just a memory location, into which a frequency is written. As you figured out, you can't rely on them being the same across the models, so you'll need to make sure that on both sets of radios, same channels contain same frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, just like with many other &quot;professional&quot; radios, BF-888s aren't programmable without the cable. For &quot;professional&quot; radios, this part would normally be done by your dealer, in accordance with your license, but since you're getting the radios yourself, then you also need to do the programming on your own, or find a radio dealer close to you who might do it for you. IF you can't, then you need to get the programming cable and do it yourself. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The programming software is readily available. It might come on the CD with the cable, or you might need to get it yourself. &lt;a href=&quot;http://www.miklor.com/BF888/&quot; rel=&quot;noreferrer&quot;&gt;Here&lt;/a&gt;'s a nice page with some software versions. Another option would be to use program called &lt;a href=&quot;http://chirp.danplanet.com/projects/chirp/wiki/Download&quot; rel=&quot;noreferrer&quot;&gt;CHIRP&lt;/a&gt;. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2017-03-23T17:40:39.620" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="7392" PostTypeId="1" AcceptedAnswerId="7393" CreationDate="2017-03-25T17:37:07.923" Score="6" ViewCount="423" Body="&lt;p&gt;This was found among some old ham stuff and is believed to have been used on 2 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The vertical elements are 17 1/2&quot; long and the connector on the bottom is a standard SO-239.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna (left) and Connector (right)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(See test results below pics.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DTO9l.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DTO9l.png&quot; alt=&quot;Antenna (left) and Connector (right)&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edited to add Test Results:&#xA;I mounted the antenna to a small mounting bracket; just basically something to hold it but provided no ground plane.  Then a ~20' length of RG-58 to an SWR meter and a 3' pigtail to my HT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I got an SWR of 1.5:1 on 146.52Mhz and 1.2:1 on 446.000Mhz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also got a good, clear signal report on a repeater on 443.525Mhz that's about 11 miles away.  The antenna was inside, leaning against my couch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edited again to add: There was a comment about impedance matching being done in the mount.  There is not.  Here is the mount disassembled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MWOQg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MWOQg.png&quot; alt=&quot;Mount Exploded&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the inner assembly with the outer shell removed:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/W6Sp9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W6Sp9.png&quot; alt=&quot;Outer Shell Removed&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2017-04-03T14:55:53.017" LastActivityDate="2017-04-03T14:55:53.017" Title="What kind of antenna is this?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7393" PostTypeId="2" ParentId="7392" CreationDate="2017-03-25T19:56:34.747" Score="4" Body="&lt;p&gt;I'm sure it's a simple monopole for 2 metres. Mount it through a hole in a large metal sheet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;17.5&quot; plus the distance from the bend to the groundplane, is almost exactly 1/4 wave on 2 metres.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why two whips? I've never seen this before, but it will make it slightly broader band than a single whip. The effective radius of a pair of wires is (from memory) $r_{eff}= ({r_{wire}}^2+(spacing/2)^2)^{0.5}$. The wind resistance of the two wires might be lower than that of a single thicker conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A quick note about 70 cm: often a 2 m antenna will also resonate at 70 cm. Being about three times the frequency, the monopole is 0.75 wavelengths long at 435 MHz. Unfortunately, the radiation pattern of a 0.75 wavelength monopole, or a 1.5 wavelength dipole, is far from ideal - it has a null at the horizon. So although the SWR is good, the effectiveness is poor. The longest you can make a monopole is about 5/8 wavelengths, which needs a coil at the base to add some inductance. With care you can make this coil work for both bands, but that's a new antenna design entirely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In both cases the antenna depends on a reasonable ground plane, at least 18“ square, or a vehicle roof, etc.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2017-03-27T14:16:33.393" LastActivityDate="2017-03-27T14:16:33.393" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7396" PostTypeId="2" ParentId="3680" CreationDate="2017-03-27T03:00:24.580" Score="2" Body="&lt;p&gt;Rotorua branch 33 of NZART  2m linear repeater is still operational and has been for more than 20 years. It is a solar powered repeater and situated on a high point overlooking Rotorua Town. Output is 144.350MHz with a plus 600 shift.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More details of it can be found here&lt;br&gt;&#xA;&lt;a href=&quot;http://www.amalgamate2000.com/radio-hobbies/radio/Rotorualinear.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.amalgamate2000.com/radio-hobbies/radio/Rotorualinear.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9407" LastEditorUserId="218" LastEditDate="2017-03-28T18:40:21.940" LastActivityDate="2017-03-28T18:40:21.940" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7397" PostTypeId="2" ParentId="7388" CreationDate="2017-03-27T07:51:42.150" Score="1" Body="&lt;p&gt;All good answers and comments given.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, what strikes me is that &lt;em&gt;you do not know what frequencies you are using&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore it could very well be, and very likely, that you are using frequencies which you are not licensed for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that is the case:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It is ILLEGAL to use frequencies which you are not licensed for, or which are outside the allowable license-exempt allocations in your country.&lt;/li&gt;&#xA;&lt;li&gt;It is DANGEROUS to use frequencies which you are not sure of, as they may interfere with official communications, such as aviation, maritime, emergency services, and other licensed services.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you do not know what frequencies you are using, and/or if you are not licensed for those frequencies, I would &lt;strong&gt;strongly recommend that you STOP using the radio&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;[Edit based on commments]&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That out of the way, the answers and comments already given are detailing &lt;strong&gt;how&lt;/strong&gt; to program frequencies, but do not detail &lt;strong&gt;what&lt;/strong&gt; frequencies you should program and use.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I live in a country where regulation is not an issue (not the US).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;OK, even when living in a country without strict regulation about radio-usage, you &lt;strong&gt;should&lt;/strong&gt; try to adhere to some international agreements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;you should not use any frequency which is in use by general aviation operations.&#xA;108 MHz-136 MHz&lt;/li&gt;&#xA;&lt;li&gt;you should not use any frequency which is in use by general marine operations. 153 MHz - 163 MHz &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Furthermore I would advice you to figure out your local emergency services, by either asking, searching on the internet. I would stay away from those.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, stay away from local broadcasters. This to avoid inteference either by you or to you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hard to believe that &quot;regulation is not an issue&quot;, but you have not disclosed what country it is; so other than general statements on what frequencies to use is probably as best an answer you can get.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2017-04-02T07:50:41.287" LastActivityDate="2017-04-02T07:50:41.287" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7398" PostTypeId="1" AcceptedAnswerId="7401" CreationDate="2017-03-27T23:58:03.387" Score="6" ViewCount="9505" Body="&lt;p&gt;I use the radio for paragliding and the radio is mounted on a &quot;cockpit&quot; in front of me when flying.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When in flight my hands are busy. I can hear the radio fine (don't need an earpiece) and I can transmit fine too (others can hear me, don't need a better/closer mic).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However transmitting can be problematic because I have to take one of my hands off the controls to press and hold the PTT button on the side of the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My idea was to use a &lt;a href=&quot;http://www.miklor.com/COM/UV_Technical.php&quot; rel=&quot;noreferrer&quot;&gt;kenwood type&lt;/a&gt; cable and connecting a button/switch to the correct terminals so that I can put effectively the PTT switch about 50cm away from the radio where I can push and transmit without taking my hands off the controls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is possible, which two terminals would I be shorting? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a bonus question, would the UV-5R support dual PTT (A and B) like the UV82 described in the link?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many thanks for the help&lt;/p&gt;&#xA;" OwnerUserId="9411" LastEditorUserId="9411" LastEditDate="2017-03-28T01:00:44.963" LastActivityDate="2018-12-20T20:04:21.300" Title="How to make a PTT button for Baofeng UV-5R" Tags="&lt;baofeng&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7399" PostTypeId="1" AcceptedAnswerId="7400" CreationDate="2017-03-28T03:26:41.800" Score="1" ViewCount="118" Body="&lt;p&gt;The display for the &lt;a href=&quot;http://www.icomamerica.com/en/products/landmobile/portables/f50_series/default.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;Icom F50&lt;/a&gt; has a &quot;LOW&quot; indicator. The &lt;a href=&quot;http://www.icomamerica.com/en/downloads/DownloadDocument.aspx?Document=66&quot; rel=&quot;nofollow noreferrer&quot;&gt;Instruction Manual&lt;/a&gt; says this is the &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;OUTPUT POWER INDICATOR [which] Appears when Low 2 or Low 1 is selected.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ERanV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ERanV.png&quot; alt=&quot;Icom F50 Instruction Manual&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no other explanation though on what &quot;Low 2&quot; or &quot;Low 1&quot; is or does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is &quot;Low 2&quot; and &quot;Low 1&quot;? What are they used for?&lt;/p&gt;&#xA;" OwnerUserId="9415" LastActivityDate="2017-03-28T03:36:04.583" Title="Purpose of &quot;Low 1&quot; and &quot;Low 2&quot; on Icom F50?" Tags="&lt;icom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7400" PostTypeId="2" ParentId="7399" CreationDate="2017-03-28T03:36:04.583" Score="1" Body="&lt;p&gt;I don't have one of these radios, but as a matter of interpreting the text of the manual, page 8 says that one of the “programmable function key” functions is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;&lt;em&gt;OUTPUT POWER SELECTION KEY&lt;/em&gt;&lt;/strong&gt;&lt;br&gt;&#xA;  Select the transmit output power&#xA;  temporarily or permanently, depending on the pre-setting.&lt;br&gt;&#xA;  • Ask your dealer for the output power level for each selection&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;From this, I conclude that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The radio has at least three transmit power levels, two of which are called “Low 2” and “Low 1”. Perhaps if you push that key it will cycle through those names on the alphanumeric display along with one or more “high” power settings.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Likely the reason they are not called something more descriptive is that they are arbitrarily programmable and the decision was made not to display the actual power in watts or dBm.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It might be informative to investigate the programming options for the radio — if nothing else to assign OUTPUT POWER SELECTION to one of the function keys and see how it behaves.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-03-28T03:36:04.583" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7401" PostTypeId="2" ParentId="7398" CreationDate="2017-03-28T06:51:53.653" Score="5" Body="&lt;p&gt;You want your switch to short the shield of each of the connectors to each other, strange as that sounds. These plugs are commonly known as TRS, or tip-ring-shield, so the shield is the part closest to the body of the plug. The ones you want are both marked PTT in this image (don't let the other stuff confuse you, these pins do multiple things when connected with mic or speaker to other pins, but they transmit when connected to each other):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/XZddX.jpg&quot; alt=&quot;pinout&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Miklor page you linked to, in the fine print under the dual PTT picture, does have the answer to your other question, which is unfortunately no, the UV-82 style dual PTT only works with dual-PTT radios like the UV-82. Honestly, they're cheap and dual remote PTTs might be useful enough in your circumstance to get one just for that feature. My mom has a UV-82 and likes it very much, so I can personally recommend it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case that you do have a dual PTT radio, shorting both shields as above will transmit on the lower display channel, and shorting the tip of the 3.5mm plug (marked +V above) to the shield of the 2.5mm plug gets you the upper channel.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastEditorUserId="4452" LastEditDate="2017-03-28T07:01:00.580" LastActivityDate="2017-03-28T07:01:00.580" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7402" PostTypeId="2" ParentId="5446" CreationDate="2017-03-28T07:18:04.460" Score="1" Body="&lt;p&gt;No, HDSDR is only compatible with software defined radios, not standard transceivers like a Baofeng. There are a few SDRs that are made to connect to the sound card, but most connect via USB. If you want to experiment without spending much, try one of the common RTL-SDR USB dongles, though those are receive-only. SDRs which are capable of transmitting are fairly expensive.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-03-28T07:18:04.460" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7403" PostTypeId="2" ParentId="3743" CreationDate="2017-03-28T07:38:00.707" Score="1" Body="&lt;p&gt;Perhaps &lt;a href=&quot;http://www.dk3wn.info/p/?page_id=29535&quot; rel=&quot;nofollow noreferrer&quot;&gt;this list&lt;/a&gt; of active amateur satellites, their up and downlink frequencies, and their modulations will help you. As for their protocols, you may have to google each one and find more details.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-03-28T07:38:00.707" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7405" PostTypeId="1" AcceptedAnswerId="7408" CreationDate="2017-03-28T14:49:09.680" Score="5" ViewCount="532" Body="&lt;p&gt;I'm going to be visiting the US soon (I live in the UK), and since I've heard it's very easy to get a US amateur radio licence and it's something that could be beneficial, I thought, why not?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see that it requires an address, though. What are the requirements on this address. In particular:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Do they require it to be a residential address? Do they require it to be valid for any particular period after the exam is taken (do you have to keep it up-to-date with something which can actually reach you)?&lt;/li&gt;&#xA;&lt;li&gt;What do they send to it? Anything recurring or just one-off things?&lt;/li&gt;&#xA;&lt;li&gt;For what period of time do they typically send things to it after you take the exam?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Basically, as you might have guessed, I'm wondering if it'd be feasible to use my hotel's address. I guess alternatively I could pay for a PO Box for a short while, or something similar?&lt;/p&gt;&#xA;" OwnerUserId="9420" LastActivityDate="2017-03-28T19:51:17.260" Title="What are the requirements of the address given for a US licence?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7406" PostTypeId="2" ParentId="5959" CreationDate="2017-03-28T18:37:24.130" Score="5" Body="&lt;p&gt;From &lt;a href=&quot;http://rallynotes.com/2017/03/12v-anderson-powerpoles/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://rallynotes.com/2017/03/12v-anderson-powerpoles/&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iCSAr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iCSAr.png&quot; alt=&quot;correct orientation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a good image for orientation reference.&lt;/p&gt;&#xA;" OwnerUserId="9422" LastEditorUserId="76" LastEditDate="2017-05-28T01:55:11.157" LastActivityDate="2017-05-28T01:55:11.157" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7408" PostTypeId="2" ParentId="7405" CreationDate="2017-03-28T19:01:12.700" Score="6" Body="&lt;p&gt;The requirement of the address is that it be &lt;strong&gt;a mailing address that they can use to communicate with you.&lt;/strong&gt; It does not need to be a residential address, and it does not even need to be uniquely yours, just one that you can be reached at.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=9213d4f54b6b60df2efe65bbe4d74fdc&amp;amp;mc=true&amp;amp;node=se47.5.97_123&amp;amp;rgn=div8&quot; rel=&quot;noreferrer&quot;&gt;§97.23   Mailing address.&lt;/a&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Each license grant must show the grantee's correct name and mailing address. The mailing address must be in an area where the amateur service is regulated by the FCC and where the grantee can receive mail delivery by the United States Postal Service. Revocation of the station license or suspension of the operator license may result when correspondence from the FCC is returned as undeliverable because the grantee failed to provide the correct mailing address.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What do they send to it? Anything recurring or just one-off things? For what period of time do they typically send things to it after you take the exam?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You should not expect to receive any mail, recurring or otherwise, from the FCC, but the mail you most critically need to receive is precisely the unexpected mail (notice of problems with your operation).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Licenses are now purely electronic (you go look at the ULS database; they don't send you anything), and there are no renewal notices by mail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You &lt;em&gt;may&lt;/em&gt; receive “welcome to being a ham” mail from local organizations, and who knows how promptly that will arrive.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-03-28T19:51:17.260" LastActivityDate="2017-03-28T19:51:17.260" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7409" PostTypeId="2" ParentId="7405" CreationDate="2017-03-28T19:06:17.707" Score="4" Body="&lt;p&gt;Foreign nationals may get amateur radio licenses in the USA. The residency requirement was dropped many years ago. You do need a US address where the FCC can reach you with any official letters or other documents. This can be a Post Office Box.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You would need to apply for a FRN from the FCC as you would not have a social security number. FRNs are normally issued with your first license, but you can apply for before getting licensed.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2017-03-28T19:06:17.707" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7410" PostTypeId="2" ParentId="7388" CreationDate="2017-03-28T19:25:03.130" Score="-2" Body="&lt;p&gt;Different countries have allowed different frequencies to be used. Here is a chart comparing USA and Canada. It might help you for example have one radio on channel one the other on channel 9 . &#xA;FRS is the USA      GMRS is Canada&#xA;FRS/GMRS Channels&#xA;Channel numbers commonly used on 22 channel FRS/GMRS dual service radios are shown in the leftmost column. Most radios of this type are not capable of repeater operation and do not include the repeater input frequencies.&#xA;Common Channel ↓    Frequency  ↓    FRS Chan.  ↓    FRS Max Output ↓    FRS Max Bandwidth  ↓    GMRS Chan.  ↓   GMRS Max Ouput ↓    GMRS Max Bandwidth ↓    Usage/Notes ↓&#xA;01  462.5625    FRS 1   500 mW  12.5 kHz    GMRS 9  5 W 25 kHz  Unofficial national calling channel&#xA;02  462.5875    FRS 2   500 mW  12.5 kHz    GMRS 10 5 W 25 kHz&lt;br&gt;&#xA;03  462.6125    FRS 3   500 mW  12.5 kHz    GMRS 11 5 W 25 kHz&lt;br&gt;&#xA;04  462.6375    FRS 4   500 mW  12.5 kHz    GMRS 12 5 W 25 kHz&lt;br&gt;&#xA;05  462.6625    FRS 5   500 mW  12.5 kHz    GMRS 13 5 W 25 kHz&lt;br&gt;&#xA;06  462.6875    FRS 6   500 mW  12.5 kHz    GMRS 14 5 W 25 kHz&lt;br&gt;&#xA;07  462.7125    FRS 7   500 mW  12.5 kHz    GMRS 15 5 W 25 kHz&lt;br&gt;&#xA;08  467.5625    FRS 8   500 mW  12.5 kHz&lt;br&gt;&#xA;09  467.5875    FRS 9   500 mW  12.5 kHz&lt;br&gt;&#xA;10  467.6125    FRS 10  500 mW  12.5 kHz&lt;br&gt;&#xA;11  467.6375    FRS 11  500 mW  12.5 kHz&lt;br&gt;&#xA;12  467.6625    FRS 12  500 mW  12.5 kHz&lt;br&gt;&#xA;13  467.6875    FRS 13  500 mW  12.5 kHz&lt;br&gt;&#xA;14  467.7125    FRS 14  500 mW  12.5 kHz&lt;br&gt;&#xA;15  462.5500                GMRS 1  50 W    25 kHz&lt;br&gt;&#xA;16  462.5750                GMRS 2  50 W    25 kHz&lt;br&gt;&#xA;17  462.6000                GMRS 3  50 W    25 kHz&lt;br&gt;&#xA;18  462.6250                GMRS 4  50 W    25 kHz&lt;br&gt;&#xA;19  462.6500                GMRS 5  50 W    25 kHz  Use restricted near Canadian border&#xA;20  462.6750                GMRS 6  50 W    25 kHz  Unofficial emergency/traveler assistance channel (PL 141.3)&#xA;21  462.7000                GMRS 7  50 W    25 kHz  Use restricted near Canadian border&#xA;22  462.7250                GMRS 8  50 W    25 kHz  &lt;/p&gt;&#xA;" OwnerUserId="9427" LastActivityDate="2017-03-28T19:25:03.130" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7411" PostTypeId="1" AcceptedAnswerId="7412" CreationDate="2017-03-28T19:46:17.867" Score="3" ViewCount="170" Body="&lt;p&gt;Under the &lt;a href=&quot;http://www.arrl.org/cept&quot; rel=&quot;nofollow noreferrer&quot;&gt;CEPT&lt;/a&gt; agreement, US General and Amateur Extra class licensee can operate in Europe while traveling there.  Does that privilege still apply if the person semi or permanently resides in that European country either as a legal foreigner or dual citizen?&lt;/p&gt;&#xA;" OwnerUserId="9428" LastEditorUserId="77" LastEditDate="2017-03-29T08:43:11.493" LastActivityDate="2017-03-29T09:06:33.363" Title="Are US licensee allowed to operate under CEPT agreement if they permanently reside in Europe?" Tags="&lt;legal&gt;&lt;license&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7412" PostTypeId="2" ParentId="7411" CreationDate="2017-03-29T09:06:33.363" Score="4" Body="&lt;p&gt;&lt;strong&gt;TL;DR&lt;/strong&gt; Not under CEPT rules.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First of all, it's not &lt;strong&gt;the&lt;/strong&gt; CEPT agreement that USA is part of, it's one of many CEPT agreements and recommendations, namely the &lt;a href=&quot;http://www.erodocdb.dk/docs/doc98/official/pdf/TR6101.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;CEPT T/R 61-01&lt;/a&gt;. My advice is to always actually read the agreements and not just rely on the hear-say. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you go through the agreement, you'll be able to see that the T/R 61-01 is exclusively for non-permanent residents. Don't forget that you need the &quot;CEPT radio amateur licence&quot;, which is for the US interpreted as the hard-copy of your license and the FCC public notice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, what about permanent residency? Well, that is covered by the recommendation &lt;a href=&quot;http://www.erodocdb.dk/docs/doc98/official/pdf/tr6102.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;T/R 61-02&lt;/a&gt;. The way it works is that, after passing your license exam for a class equivalent to the CEPT class, you can (or could if USA were part of T/R 61-02) receive the Harmonized Amateur Radio Examination Certificate (HAREC). The licensing authority in the country you're residing in takes the HAREC as the proof that you passed the appropriate exams and issues you with the license for the national class that's equivalent to the CEPT class. Note that some countries still require proof of Morse code exam for their highest license! It's possible to have several license classes that are equivalent to the CEPT class.&lt;br&gt;&#xA;As I've mentioned, and can be seen in the annex 4 of the T/R 61-02, USA is not part of that agreement. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What can you do? Well, go outside of the requirements of the CEPT T/R 61-02 and see what you can do. First step is to understand that Europe is not a country (yet at least) and that things in European countries can work differently. It could happen that the country that you're going to be residing in will accept your US license. It could be that there's a more complicated or more expensive procedure you need to go through to get your license accepted. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, in Germany issuing the amateur radio license costs 70€. If you don't have a HAREC, then you need to go through a recognition procedure which is another 130€ on top of the issuing fee. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2017-03-29T09:06:33.363" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7413" PostTypeId="1" AcceptedAnswerId="7414" CreationDate="2017-03-30T03:13:26.557" Score="2" ViewCount="379" Body="&lt;p&gt;I recently made a &quot;deseret j-pole&quot; dual band antenna for basic 2m and 70cm transmitting and receiving use. I have it on a large metal tube behind my house, connected through a 50 ohm pl-259 cable, and adapted to sma-female (the one required by my baofeng UV-5RA).&#xA;here's the  problem, when it is fully connected, it doesn't transmit or receive clearly (if at all). it receives best when not even connected, but when I hold the center prong right next to the center hole on the adaper, but never touch them. what's the problem? any help is appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;here's a crude depiction of how I need to hold the cables for best connection&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ttpHr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ttpHr.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;sorry if I'm unclear.&lt;/p&gt;&#xA;" OwnerUserId="9433" LastActivityDate="2017-03-30T18:32:04.987" Title="dual band j-pole creates connectivity problems when connected all the way" Tags="&lt;antenna&gt;&lt;baofeng&gt;&lt;uv-5r&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7414" PostTypeId="2" ParentId="7413" CreationDate="2017-03-30T05:19:53.757" Score="0" Body="&lt;p&gt;You mention that it's mounted to metal - is it electrically connected to that mount? A J-pole should be ungrounded and isolated from anything metal. Also helpful is a ferrite choke around the coax near where it feeds the antenna, but most important is that it be mounted with non-conductive hardware.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-03-30T05:19:53.757" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="7415" PostTypeId="2" ParentId="5779" CreationDate="2017-03-30T13:53:08.397" Score="1" Body="&lt;p&gt;I have a TS440SAT, but have not disassembled it.  I also have a TS940SAT, which is a larger, I believe slightly newer rig.  This answer applied to the TS940SAT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TS940SAT and the TS440SAT have internal speakers.  Foam is used in the speaker system in two ways.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first is as the material which holds the speaker cone into the speaker frame.  If this has degraded, as it will, the fix is to replace the speaker.  I have purchased replacement speakers (usually called drivers, to differentiate them from finished cabinets, called speakers) from an online company: &lt;a href=&quot;http://www.parts-express.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.parts-express.com&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second use of foam I've seen in the TS940SAT is as a gasket to seal a sub-compartment around the speaker.  This prevents parts of the box from touching and buzzing as the speaker vibrates and also creates a sealed chamber around the speaker to improve bass response.  If the foam gasket has degraded, I would suggest a soft foam about 1/8&quot; thick.  If you don't easily find that, you might try some soft felt, available either from a craft store, or online from &lt;a href=&quot;http://www.mcmaster.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.mcmaster.com&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There may be other uses of foam I haven't seen in the radio.  It is unlikely that foam is used as an active component (such as for RF shielding).  Foam may be used to dampen the vibration between other sheet metal parts prone to buzzing from the audio.&lt;/p&gt;&#xA;" OwnerUserId="9109" LastActivityDate="2017-03-30T13:53:08.397" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7416" PostTypeId="1" CreationDate="2017-03-30T17:41:22.777" Score="6" ViewCount="1736" Body="&lt;p&gt;Harmonic spurs (harmonics of the transmitter frequency, as seen by a wide-band receiver or SDR) in the RF spectrum might be caused by an imperfectly sinusoidal or badly filtered transmitter carrier frequency oscillator, non-linearities in the transmitter amplifier, or non-linearities somewhere in the receiver before or inside the 1st mixer.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What might be some tests or other means for helping determine where (most of) this harmonic spur problem might be located?  Are there any ways to test this without needing to acquire extremely expensive lab equipment?  Basically, are the spurs a transmitter or receiver problem?  (assuming neither comes with manufacturer specs, e.g. home-built or kit, etc.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-03-30T17:46:56.653" LastActivityDate="2017-04-01T08:48:34.567" Title="Cause of harmonic spurs?" Tags="&lt;software-defined-radio&gt;&lt;testing&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7417" PostTypeId="2" ParentId="7416" CreationDate="2017-03-30T17:52:16.597" Score="1" Body="&lt;p&gt;I believe you have described the situation very well.  It is caused by the generation of impure signals, usually in the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other causes could include using a transmitting antenna that resonates at or near a harmonic, such as using 40 meters on a dipole and finding harmonics around the 15 meter band.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is rare for harmonics to be caused by the receiver, although you might find artifacts like &quot;birdies&quot; caused by the receiver's internal oscillator.  The cheaper the receiver the more this possibility exists.  But these would not be harmonic to the receive frequency - they are generally at fixed frequencies that may be harmonic to the oscillator's frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then consider the mixer that brings the received frequency down to the IF.  It will take the input frequency and IF oscillator, and produce the sum and difference frequencies.  Bandpass filtering is supposed to remove the spurious outputs from the mixer.  But these would not be harmonic to the receive frequency in any case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for testing, I don't really understand from the OP what exactly you are trying to test for.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the rules there are specified limits to the amount of spurious signals that are allowed to be transmitted by amateur equipment, whether type-accepted or homebrew.  As long as you are below those limits (and more importantly, as long as you are not interfering with another licensed service), they don't present an immediate problem that needs to be fixed.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-03-31T03:07:41.237" LastActivityDate="2017-03-31T03:07:41.237" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7418" PostTypeId="2" ParentId="7413" CreationDate="2017-03-30T18:32:04.987" Score="2" Body="&lt;p&gt;&lt;strong&gt;In general,&lt;/strong&gt; if making an incomplete connection to your antenna works somewhat but a complete one is entirely silent, that means you have an open or short circuit somewhere in the antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason the incomplete connection works somewhat is because you have contact (or in your particular case capacitive coupling) with a large piece of metal &lt;em&gt;and no shield connection&lt;/em&gt;. Thus, you have basically a weirdly-shaped monopole antenna consisting of the feed line and everything attached to it, and the radio's chassis as the &quot;counterpoise&quot; side of things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you make both connections solidly, the coax shield starts functioning as intended and the signal cannot pass through it. So if you have a short or open circuit anywhere along the coax or at the antenna feedback, you have basically a coax stub, which is not an antenna.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-03-30T18:32:04.987" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7419" PostTypeId="1" AcceptedAnswerId="7434" CreationDate="2017-03-30T20:52:44.803" Score="3" ViewCount="415" Body="&lt;p&gt;I’m trying to identify this signal at 928.807 MHz. A sample of the raw I/Q from gqrx is &lt;a href=&quot;https://drive.google.com/uc?export=download&amp;amp;id=0Bz-zpKkDTdb5bGF6Zi1qZlExemc&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; (9.2 MB, .wav, 48000 Hz) and this is the waterfall: &lt;img src=&quot;https://drive.google.com/uc?export=download&amp;amp;id=0Bz-zpKkDTdb5Y2t0clZRWHY1WTA&quot; alt=&quot;waterfall&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’ve tried decoding some common digital modes (including CW) with fldigi but have not had success.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’m using an RTL-SDR with a telescopic antenna, and I’m in Stillwater, OK.&lt;/p&gt;&#xA;" OwnerUserId="9438" LastEditorUserId="4076" LastEditDate="2017-04-05T12:37:13.860" LastActivityDate="2017-04-05T12:37:13.860" Title="What is this Morse code-like station?" Tags="&lt;software-defined-radio&gt;&lt;uhf&gt;&lt;rtl-sdr&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7420" PostTypeId="1" AcceptedAnswerId="7480" CreationDate="2017-03-30T22:18:25.770" Score="4" ViewCount="5970" Body="&lt;p&gt;How do you properly ground a dipole (RX only for VHF scanning) to protect it against ESD/lightning?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my set up i'm putting a dipole on my roof. I've connected the two dipole elements together with a 100k resistor, and have a balun and amplifier just under the roof, then 20m of coax to my receiver. So to protect the balun and amplifier I need ESD to shunt to ground before it reaches the amp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I ground the antenna via the mast and some heavy gauge wire leading to a grounding rod? And then connect the shield/gnd element of the dipole to the grounded mast? I could then also use a gas discharge tube on the line before the balun and amp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if I do this, won't I affect the dipole by essentially lengthening the ground side element via the mast and grounding rod?&lt;/p&gt;&#xA;" OwnerUserId="9442" LastActivityDate="2020-10-18T22:28:20.167" Title="Grounding a dipole" Tags="&lt;grounding&gt;&lt;dipole&gt;&lt;lightning&gt;" AnswerCount="5" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7421" PostTypeId="2" ParentId="7416" CreationDate="2017-03-31T01:57:56.967" Score="1" Body="&lt;p&gt;Harmonic spurs as detected in a receiver could be generated in the transmitter, the receiver, or the transmission lines or antennas in between.  Usually of course the antennas and transmission lines aren't the problem, which leaves the transmitter and receiver as potential culprits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most accurate way to test a transmitter is to connect it to a calibrated spectrum analyzer, through an attenuator of course, and directly measure the power of the harmonics relative to the output at the primary frequency, and see how clean the signal is in general.  If you don't have a spectrum analyzer, you might try asking at your local ham club to see if someone there does who could help you.  (My club has someone who owns several spectrum analyzers, who is always willing to help troubleshoot a transmitter or amplifier.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Failing that, you could always ask another ham to listen to your signal at the primary frequency, and also the harmonics, to estimate whether your transmitter is up to the standards of good amateur radio practice.  Of course hardly anyone has antennas with identical gain from one band to the next, so that method is generally only good for a rough guess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem of course could be in the receiver, especially if it's being overloaded.  Some good ways to determine if the problem is overloading in the receiver are to turn down the RF gain, switch on the internal attenuator, or insert an external attenuator in the signal path.  If attenuating the signal makes harmonics or other distortion go away, then it's safe to say that the problem was in the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Naturally, if spurs are detected in one receiver, then a simple way to determine if the problems come from the receiver is to listen to the signal with a different receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, it should be mentioned that the builder of any transmitter is responsible for ensuring that the transmitter meets regulatory specifications.  Designers of reputable kit transmitters ensure that their designs meet specifications when the kits are built correctly.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-03-31T01:57:56.967" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7422" PostTypeId="2" ParentId="7420" CreationDate="2017-03-31T05:07:33.260" Score="-1" Body="&lt;p&gt;You should ground the shield of the coax before or at the connection point to the balun, not between the balun and antenna.  Remember that the balun conversion between the balanced dipole antenna and the unbalanced coax cable.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also remember that grounding does not protect you or your equipment from a direct lighting hit.&lt;/p&gt;&#xA;" OwnerUserId="9428" LastActivityDate="2017-03-31T05:07:33.260" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7423" PostTypeId="1" AcceptedAnswerId="7424" CreationDate="2017-03-31T05:14:22.390" Score="1" ViewCount="335" Body="&lt;p&gt;My household has multiple licensed amateur radio operators that share the equipment (ham radio, computer, etc).  We would like to use Log4OM to log our QSQs and to use the program to submit them to LOTW, eLog, QRZ, etc.  However, each of us has their own corresponding accounts and we would like to keep our logs separate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can this be achieved via different Log4OM profiles?  If so is there an easy way to specify what profile to use at start up (i.e. via the command line/shortcut)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We are using the same Windows user account and do not want to utilize different Windows user accounts.&lt;/p&gt;&#xA;" OwnerUserId="9428" LastActivityDate="2017-03-31T05:52:19.920" Title="How to use Log4OM with multiple users?" Tags="&lt;software&gt;&lt;logging&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7424" PostTypeId="2" ParentId="7423" CreationDate="2017-03-31T05:30:54.243" Score="1" Body="&lt;p&gt;Loading a specific profile is quite straight forward and documented in this setting screen:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/36tPX.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/36tPX.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Source: &lt;a href=&quot;http://forum.log4om.com/viewtopic.php?t=2641#p15009&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://forum.log4om.com/viewtopic.php?t=2641#p15009&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To configure TQSL to sign with the correct LOTW key, specify a station location for each key:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6BtBi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6BtBi.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And choose the appropriate location in the LOTW Settings of Log4OM:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6NB3g.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6NB3g.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9428" LastEditorUserId="9428" LastEditDate="2017-03-31T05:52:19.920" LastActivityDate="2017-03-31T05:52:19.920" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7426" PostTypeId="2" ParentId="7420" CreationDate="2017-03-31T12:50:58.957" Score="1" Body="&lt;p&gt;Simply grounding things by connecting them to some ground rod arbitrarily stuck in the ground will not protect anything from lightning: in fact it may make lightning damage more likely. The protection comes not from grounding the antenna per se, it's having a &lt;em&gt;single point of entry&lt;/em&gt; to the station. For detail on how to ground things and for lightning protection generally, see:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you aren't going to go through the trouble of having a single point of entry as detailed in that question, my recommendation would be to not ground the antenna at all, or ground it with a separate system which is disconnected when not operating. Disconnecting the antenna will provide a degree of protection, but a &lt;a href=&quot;https://www.w8ji.com/lightning_strikes.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;direct strike will have no trouble blowing past the few feet&lt;/a&gt; between your station and the disconnected feedline. You can solve that problem with insurance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are going to properly ground the antenna &lt;em&gt;to a single point ground&lt;/em&gt;, assuming you are using a coax feedline, use a balun and ground the coax shield. Otherwise you'll &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;unbalance the antenna&lt;/a&gt;. If you are using a balanced feedline it's probably still best to run coax from the transceiver to the station entrance ground, then have a balun outside. It's difficult to make a low impedance connection to ground with a balanced feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also say you've connected the dipole halves with a 100kΩ resistor. This is already an effective bleeder for static buildup, without any need for a discharge tube. Though if you want to include a discharge tube at the station entrance also it can't hurt.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-04-13T16:51:54.667" LastActivityDate="2017-04-13T16:51:54.667" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7427" PostTypeId="2" ParentId="6545" CreationDate="2017-04-01T00:53:06.090" Score="3" Body="&lt;p&gt;In the end I used 'amodem' ( see &lt;a href=&quot;https://github.com/romanz/amodem&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/romanz/amodem&lt;/a&gt; ). After a few calibration steps, I could get decent I/O rates - considering the nature of the medium. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Compression of archives is necessary, and may be considered unethical. But the compression algorithms (e.g. 7zip, xz) are public, and anyone paying attention can read the data. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rates of &gt;=19200 baud (~2.4kB/s) are easily accomplished internationally, while IIRC 57600 baud (~7.2kB/s) are realistic domestic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope others can use this as an intro to PR.&lt;/p&gt;&#xA;" OwnerUserId="7957" LastActivityDate="2017-04-01T00:53:06.090" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7428" PostTypeId="2" ParentId="7416" CreationDate="2017-04-01T08:48:34.567" Score="6" Body="&lt;p&gt;You've nailed this!&lt;/p&gt;&#xA;&lt;p&gt;So, I'm sometimes involved in these kinds of investigations. It all gets easier when you have control over the transmitter – when some spurs disappear as soon as you turn it off, but others remain, you've ruled out the transmitter as the source of these.&lt;/p&gt;&#xA;&lt;p&gt;Then, digital receivers typically, as you notice, have different sources of spurs. As I'm usually not at the receiver that is being &amp;quot;debugged&amp;quot;, the only way to work with this is really an elimination approach; in no particular order, Problems, the way I'd approach detecting them and some mitigation hints:&lt;/p&gt;&#xA;&lt;h1&gt;Problem sources&lt;/h1&gt;&#xA;&lt;h2&gt;Harmonics all over the place: clipping?&lt;/h2&gt;&#xA;&lt;p&gt;Reduce receiver gain. Add attenuator. Can usually (often, depending on the receiver DSP chain) be seen by looking at the numerical values of samples coming from device; it should be &lt;span class=&quot;math-container&quot;&gt;$|z| &amp;lt; 1$&lt;/span&gt;. If not: Looks like &lt;span class=&quot;math-container&quot;&gt;$(1)$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;h2&gt;Spurs due to intermodulation of receive signals due to receive (typically: LN) amplifier saturation&lt;/h2&gt;&#xA;&lt;p&gt;Add attenuation in-line to receive antenna. If spurs significantly reduce, we've got this.&lt;/p&gt;&#xA;&lt;h2&gt;LO leakage &amp;amp; DC offset&lt;/h2&gt;&#xA;&lt;p&gt;Typical artifact of all direct conversion receivers. Can (on some SDR peripherals) completely be mitigated by letting the built-in DSP functionality digitally shift the receive signal in frequency prior to decimation, see &lt;span class=&quot;math-container&quot;&gt;$(2)$&lt;/span&gt;. For a &amp;quot;relatively good&amp;quot; mitigation: a notch HPF directly after the ADC is often part of SDR receivers, too.&lt;/p&gt;&#xA;&lt;h2&gt;Sampling clock spurs&lt;/h2&gt;&#xA;&lt;p&gt;Mixing products of receiver LO and ADC clock. Tune the LO a few Hertz to either side. Do they move, but keep the same distance from LO leakage?&lt;/p&gt;&#xA;&lt;h2&gt;Unwanted LO synth side products&lt;/h2&gt;&#xA;&lt;p&gt;Oscillator synthesizers are impressive devices, which are able to produce a huge number of tones from a single reference oscillator (example: MAX2871). They do that by elegantly multiplying frequencies, and having non-integer multiples through cleverly &amp;quot;jumping&amp;quot; PLLs (keyword: fractional-N PLL). That inherently, however, might produce some frequencies that are not even multiples or integer divisions of the target clock. If you can, try a configuration where you use integer-N tuning only. If that helps, there's your problem. Often, when using a wideband receiver especially if it supports &lt;span class=&quot;math-container&quot;&gt;$(2)$&lt;/span&gt;, you can choose from a whole range of physical LO frequencies without affecting what part of the spectrum you see. Experiment!&lt;/p&gt;&#xA;&lt;h2&gt;Digital Operating Clocks&lt;/h2&gt;&#xA;&lt;p&gt;SDR devices are digital devices, thus have a lot of square wave clocks... If you see something that happens to be relatively strong, and research shows it's one of &lt;span class=&quot;math-container&quot;&gt;$1\cdot f_{clock},\, 3\cdot f_{clock},\, 5\cdot f_{clock},\ldots$&lt;/span&gt;, there you go. You'll have an easier time figuring out &lt;span class=&quot;math-container&quot;&gt;$f_{clock}$&lt;/span&gt;s that appear in your device if you have a schematic, and knowledge of Firmware/FPGA images used.&lt;/p&gt;&#xA;&lt;h2&gt;Supply Noise&lt;/h2&gt;&#xA;&lt;p&gt;A classic. If the SDR has an external power supply, try a different one, ask the manufacturer about known spurs, and use ferrites where applicable.&lt;/p&gt;&#xA;&lt;h2&gt;Digital Interface Noise&lt;/h2&gt;&#xA;&lt;p&gt;Your SDR device is a USB1/2 device and you see a &lt;span class=&quot;math-container&quot;&gt;$N\cdot11$&lt;/span&gt; MHz signal, spread around with some rather &amp;quot;sinc&amp;quot;-y shape: USB's to blame, typically. Applies to other buses with other baud rates, too. Hard to mitigate if hardware's fixed.&lt;/p&gt;&#xA;&lt;h2&gt;Phase noise of LO&lt;/h2&gt;&#xA;&lt;p&gt;The aforementioned synthesizers are typically pretty good; this often stems from phase noise of the reference oscillator. If possible with yout device: try a &amp;quot;less accurate&amp;quot; (read: you got lying around) one, and compare.&lt;/p&gt;&#xA;&lt;h2&gt;Reference oscillator overtones, noise through ref oscillator input&lt;/h2&gt;&#xA;&lt;p&gt;Yeah, not all things that seem to be a good idea actually are. I've seen it more than once that people, thinking their external high-accuracy, long-time stable oscillator would significantly improve operation, only to find out later, that the reference signal not only contains the wanted (e.g. 10 MHz) tone, but also other components, partly from supplies etc. Make sure your reference is clean! If in doubt, try the internal one, too!&lt;/p&gt;&#xA;&lt;h1&gt;Illustrations&lt;/h1&gt;&#xA;&lt;h2&gt;(1)&lt;/h2&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EQgza.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EQgza.jpg&quot; alt=&quot;Clipping&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;By twitter user &amp;quot;da Swede&amp;quot;, &lt;a href=&quot;https://twitter.com/uber_security/status/844116167870627841&quot; rel=&quot;noreferrer&quot;&gt;https://twitter.com/uber_security/status/844116167870627841&lt;/a&gt;&lt;/p&gt;&#xA;&lt;h2&gt;(2)&lt;/h2&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hnGLi.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hnGLi.png&quot; alt=&quot;Offset tuning in an USRP&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;*Offset tuning with the DSP chain of an Ettus USRP&amp;quot;. By myself, copyright Marcus Müller/Ettus Research.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-04-01T08:48:34.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7429" PostTypeId="2" ParentId="7420" CreationDate="2017-04-02T05:09:53.680" Score="-1" Body="&lt;p&gt;Here is what is advertised (and recommended by Elmers in my ham club) to connect your coax to a local ground.  It is called a Lightning Arrester.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has an internal spark gap that will only be jumped by a high voltage coming in from your antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no direct connection that will have any effect on the antenna, as long as this on at the near end of the coax, and not right at the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EWVVk.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EWVVk.jpg&quot; alt=&quot;Lightning Arrester&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are available from the usual sources.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend grounding this the same place your radio chassis is grounded.  That way this is nothing but a pass-through connector with an internal spark gap.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-04-02T20:44:17.950" LastActivityDate="2017-04-02T20:44:17.950" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="7431" PostTypeId="1" AcceptedAnswerId="7432" CreationDate="2017-04-02T15:43:39.543" Score="3" ViewCount="560" Body="&lt;p&gt;I want to add a V/U antenna to my truck, but my wife started asking about weather proofing and car washes and I had no answer. How do you keep your vehicle clean after installing a new antenna, and how do I keep rain and snow and road debris out of the electrical connections?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My plan was a pickup bed post hole mount on the driver's side, 40&quot; antenna so it would only be about 6 inches taller overall than it is now with the stock radio antenna. &lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2017-04-25T15:24:29.923" Title="How do you keep your vehicle clean with a mobile antenna?" Tags="&lt;antenna&gt;&lt;mobile&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7432" PostTypeId="2" ParentId="7431" CreationDate="2017-04-02T16:21:54.427" Score="3" Body="&lt;p&gt;If you are washing your vehicle by hand or at a “touchless” automatic wash then there should be no need to do anything with an antenna that does not stick out excessively; weatherproofing should be part of proper mounting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you need to take down the antenna, then how you do it will depend on the exact construction of your antenna and mount. If you're using an antenna which mounts to a 3/8&quot;-24 stud, for example, then you can just remove the antenna, wash, and reinstall (after drying the joint). Even if the antenna is a type with a coaxial mount (e.g. NMO, PL-259) then there is a good chance there is some way to unscrew the whip portion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you should be careful about leaving exposed any type of coaxial connection (as opposed to a stud or threaded hole). Unless specified otherwise, you should &lt;strong&gt;not&lt;/strong&gt; assume that the insulator between the center and shield is weatherproof, and if it gets wet it may carry water into the coaxial cable which causes permanent damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can easily remove the entire mount with all connections intact, then you could just lay it down in your truck bed.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;You will likely have an exposed coaxial connector between your mount and the feed line to your radio. This connection does need to be weatherproofed in most cases. (N connectors are designed to be weatherproof, but I would not rely solely on that.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a specific type of tape which you use for this purpose — called variously “rubber tape”, “self-fusing tape”, “amalgamating tape”, “Coax Seal” (that being a brand name). It has the property of fusing to itself when stretched and pressed together, so that after application you do not have just layers of tape stuck together with adhesive, but rather a tightly fitting custom rubber boot, and when cut off afterward it leaves no residue and a pristine unweathered surface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I personally have used &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B001CGVEXS&quot; rel=&quot;nofollow noreferrer&quot;&gt;3M Temflex 2155 Rubber Splicing Tape&lt;/a&gt; for this and many other applications, and would highly recommend it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just remember that you have to stretch the tape as you wrap it.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-04-02T16:21:54.427" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7433" PostTypeId="2" ParentId="7431" CreationDate="2017-04-02T19:29:55.130" Score="0" Body="&lt;p&gt;What a about a good magnetic mount? The top of the cab is usually the highest part of a truck and clear of other objects that could affect an antenna and reduce the range of the signals. Simply  take it off before driving it through the car wash.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some mag mounts are quite lossy. Do your homework first.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-04-02T19:29:55.130" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7434" PostTypeId="2" ParentId="7419" CreationDate="2017-04-03T11:23:22.370" Score="2" Body="&lt;p&gt;Been probing around in your signal.&lt;/p&gt;&#xA;&lt;p&gt;The longer &amp;quot;blips&amp;quot; definitely start with a tone (... with a region where phase is a linear function of time), but then it looks rather random.&lt;/p&gt;&#xA;&lt;p&gt;So, likely, a PSK system with some constant tone preamble?&lt;/p&gt;&#xA;&lt;p&gt;My quick &amp;amp; dirty analysis tool here is Miek's &lt;a href=&quot;https://dsp.stackexchange.com/questions/38908/need-help-implementing-dct-type-4-algorithm&quot;&gt;inspectrum&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fnXww.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fnXww.png&quot; alt=&quot;Inspectrum screenshot&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;You'll need to convert your wav back to 32bit float complex first (audacity can do that. I don't know whether GQRX has a direct export functionality for that).&lt;/p&gt;&#xA;&lt;p&gt;Three representations of the signal in the picture:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;topmost, a (horizontal) waterfall of your signal (I just realized I didn't properly set the sampling rate, so ignore the time axis labels). If I hadn't put the red line across it, you'd clearly see the aforementioned tone as horizontal line at the beginning of the &amp;quot;white selection&amp;quot; (and at the end, too. If I'm doing the math right, the temporal length between these two is about 60ms)&lt;/li&gt;&#xA;&lt;li&gt;below that, a derived phase plot. Note the &amp;quot;more or less clean&amp;quot; linear phase ramps. (frequency is the derivative of phase, and if phase is linear, than frequency is a constant)&lt;/li&gt;&#xA;&lt;li&gt;below that, simply the I and Q (real and imaginary) part of the signal filtered to the (vertically white limited9 bandwidth).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-04-03T11:23:22.370" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7435" PostTypeId="2" ParentId="3488" CreationDate="2017-04-04T01:13:03.310" Score="2" Body="&lt;p&gt;It should be fine as long as you don't have it plugged in. If you have it plugged in it makes a lot of noise and it is hard to listen to.&lt;/p&gt;&#xA;" OwnerUserId="9462" LastActivityDate="2017-04-04T01:13:03.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7436" PostTypeId="1" AcceptedAnswerId="7437" CreationDate="2017-04-04T01:19:30.660" Score="1" ViewCount="2745" Body="&lt;p&gt;I would like to have an antenna outside for 2 meter VHF use but I do not want it to be expensive and I won't be allowed to put it up if it stands out too much. Does anyone know a good antenna to buy or build for this purpose.&lt;/p&gt;&#xA;" OwnerUserId="9462" LastActivityDate="2017-04-18T02:18:01.870" Title="Good Hidden Antenna For 2m" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;2m-band&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7437" PostTypeId="2" ParentId="7436" CreationDate="2017-04-04T07:25:26.613" Score="1" Body="&lt;p&gt;I just put up a fairly hidden vertical dipole for NOAA Weather Radio, but the concept is the same.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used a SO-239 socket and some solid wire from household Romex.  That way the connection to the radio is by coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my case, I soldered the vertical component directly upward, then soldered two downward components to the screw holes.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To hang it, I put a loop in the top of the driven element so I can hang it on a drywall screw.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't have a SO-239 connector on hand, you can solder it directly to the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It works!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;----EDIT:  If you want more than just a &quot;wire&quot; - take a look at this cool 2D groundplane for 2M that K7PEH put in the comments:  &lt;a href=&quot;http://www.qsl.net/wrav/2mground.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;2M Ground Plane&lt;/a&gt;  TNX&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aG2br.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aG2br.png&quot; alt=&quot;2M 2D Ground Plane antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-04-05T17:20:51.220" LastActivityDate="2017-04-05T17:20:51.220" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7438" PostTypeId="2" ParentId="7436" CreationDate="2017-04-04T11:17:33.977" Score="0" Body="&lt;p&gt;Used to use a black DIAMOND NR-770HB on top of a sky blue broomstick (literally).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Barely visible from some meters away. The steel version will be more visible when new but maybe less after some time outside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With this antenna I worked once a Corsica repeater from Barcelona (580 km / 360 Miles away) with a 4W HT.&lt;/p&gt;&#xA;" OwnerUserId="8523" LastActivityDate="2017-04-04T11:17:33.977" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7439" PostTypeId="1" CreationDate="2017-04-04T15:32:33.190" Score="2" ViewCount="242" Body="&lt;p&gt;I'm building a small APRS radio for a high altitude balloon, and I'm thinking of using an Si570 (3.3 V CMOS) at 144 MHz to drive a small class E amplifier.  I'm looking for about 1W output power.  I'm having trouble finding a FET that can operate at this frequency from 3.3 V power.  Failing that, I could use two LiPoly batteries in series to power it with about 7 V.  Does anyone know of a good device that I might use?  -Rod (KD0FFJ)&lt;/p&gt;&#xA;" OwnerUserId="9464" LastEditorUserId="9464" LastEditDate="2017-04-04T17:54:03.483" LastActivityDate="2017-04-05T12:30:48.027" Title="FET for low voltage class E amplifier" Tags="&lt;aprs&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7440" PostTypeId="1" AcceptedAnswerId="7443" CreationDate="2017-04-05T01:56:11.923" Score="7" ViewCount="835" Body="&lt;p&gt;How does frequency modulation encode both amplitude and frequency of the modulating audio signal only by varying frequency? How do both components get spread across and encoded in the side bands? I generally understand that AM side bands occupy sufficiently wide band width to recreate the spectrum of the modulating audio signal (while varying amplitude at each frequency in the spectrum of the sound wave)--so the spectrum of a side band should look basically like the spectrum of the underlying modulating audio wave. Is this understanding wrong?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding is that FM modulates the instantaneous frequency of the carrier signal according to the amplitude of the modulating signal, but the modulating audio signal should be made up of a wide spectrum of frequencies at various amplitudes that make up the underlying sound. So the carrier can only be modulated with a single frequency of varying amplitude. What about the other frequencies in the audio signal spectrum? Is this information spread out across the side bands somehow? If so, how?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I am studying for my technician license; I don't know Fourier math.)&lt;/p&gt;&#xA;" OwnerUserId="9466" LastEditorUserId="76" LastEditDate="2017-04-05T02:36:44.030" LastActivityDate="2017-04-06T13:36:20.437" Title="How does FM encode BOTH amplitude and frequencies of full audio signal spectrum?" Tags="&lt;fm&gt;&lt;math&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7441" PostTypeId="2" ParentId="7440" CreationDate="2017-04-05T02:35:09.467" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I generally understand that AM side bands occupy sufficiently wide band width to recreate the spectrum of the modulating audio signal (while varying amplitude at each frequency in the spectrum of the sound wave)--so the spectrum of a side band should look basically like the spectrum of the underlying modulating audio wave. Is this understanding wrong?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is correct, but it is useful to understand that the &lt;em&gt;process&lt;/em&gt; of amplitude modulation does not treat frequencies individually. The structure of the sidebands is a &lt;em&gt;mathematical consequence of&lt;/em&gt; the modulation process, not the process itself, which doesn't involve any frequencies explicitly at all.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My understanding is that FM modulates the instantaneous frequency of the carrier signal according to the amplitude of the modulating signal&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This statement is not correct, and could be the root of your confusion. The frequency is modulated according to the instantaneous &lt;em&gt;value&lt;/em&gt; of the signal, not the amplitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To illustrate the difference between value and amplitude, in the simple sinusoidal signal&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ y = A \sin(t),$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$y$ is the value and $A$ is the amplitude. Defining amplitude gets more subtle with more complex signals, but this is sufficient to understand the distinction. Here, $A$ is (may be) constant but $y$ is not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any signal (of the kind we are concerned with when talking about AM and FM), no matter how complex, is still a single value, a single number, varying over time. If you transform that value in some way (in FM, to frequency), and then reverse the transformation correctly (a FM demodulator), then you have the original signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice there are deliberate limitations to these processes — deviations from the mathematical ideal — which mean that the higher frequencies of the modulating signal are attenuated (bandwidth is not infinite). But those can be understood independently of the modulation techniques themselves.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-04-05T02:35:09.467" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7442" PostTypeId="2" ParentId="7439" CreationDate="2017-04-05T12:30:48.027" Score="2" Body="&lt;p&gt;First of all: Considering a class-E is a rather complex (not in parts count, but in sensitivity of the design to choosing the right Ls and Cs) thing, I'd go for: It won't kill you to use a step-up converter to first get a higher DC supply. These things are really simple to build, thanks to suppliers like &lt;a href=&quot;http://ti.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;Texas Instruments&lt;/a&gt; having wizards on their homepage where you just enter in-, output voltage and max current to source, and then are greeted with different optimizations (cost, size, stability) of possible designs including BOMs and schematics and further design helps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding choice of a FET: It all depends! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know what's going to drive your FET's gate, but chances are you'd want one with a small gate charge so that you don't need insane driver strengths to switch it fast enough. Low Rdson is probably a must – you'll need a good switching behaviour to get your class-E amp running at all, and also, you're doing this because you want efficiency, I guess, instead of simply using &quot;old-fashioned&quot; amplifier architectures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When looking for FETs, I usually consult my three main distributor's tables. They all have their web site weaknesses :( so I cross-compare a lot:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;farnell/element14&lt;/li&gt;&#xA;&lt;li&gt;mouser&lt;/li&gt;&#xA;&lt;li&gt;digikey&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Now that I've told you to step up the voltage as needed, you're getting yet another design freedom – so you'd probably just want to use an already proven, evolved class-E design and use a FET fitting that (if in doubt, post that design as a new question here and ask for FET characteristics to look for, not for FET recommendations), and build an efficient supply for that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All in all, at 1W on 144 MHz I'm not 100% class-E is really the optimum architecture. Then again, I'm not a switched-amp guru, so I trust your research and choice!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-04-05T12:30:48.027" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7443" PostTypeId="2" ParentId="7440" CreationDate="2017-04-05T20:02:49.097" Score="8" Body="&lt;p&gt;Whatever modulation we use, there's a baseband signal we wish to transmit (music, voice recording, whatever), which somehow modulates a carrier to produce the output signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your question suggests you are primarily concerned about how the frequency domain representation of the baseband translates to the frequency domain of the output. This is a valid thing to wonder, and it has particular relevance to determining how much bandwidth will be occupied by the transmission for a given input, for example. But it's not always the best way to understand a modulation scheme. That's better done in the time domain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For AM, we modulate the amplitude of that signal. Let's say the baseband signal is a square wave. Here's an example of a &quot;loud&quot; square wave and AM, with the baseband in red, and the output in blue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4EDAV.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4EDAV.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a quieter baseband input, the variation in amplitude of the output is less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/b6Ewi.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/b6Ewi.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For FM, we modify the frequency instead of the amplitude. Here again is a loud square wave. Note the large variation in frequency between the periods where the square wave is a large value, versus where it's a low value:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FTXO2.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FTXO2.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a quieter baseband input, the variation in frequency is less:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QVM3V.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QVM3V.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course in practice the baseband signal will be something more interesting than a square wave. Here's an AM example with a more complex input:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Gd8cW.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Gd8cW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note the baseband waveform can be anything at all: it can have any number of frequency components, at any number of amplitudes. But that's not necessarily relevant: all we need to know at any instant is the value of the baseband signal, and that's what the amplitude of the carrier is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And now with FM:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PqYqq.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PqYqq.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does FM look like in the frequency domain? Let's generate some waterfall plots with a sine wave baseband which changes only in frequency or amplitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Altering the baseband amplitude increases the amplitude of the FM sidebands. Here's a sine wave baseband, increasing in amplitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0014M.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0014M.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Increasing the baseband amplitude is equivalent to increasing the modulation index or deviation. You can see that even with just a sine wave baseband, there are several sidebands generated. Mathematically, these repeat out to infinity, but in practice they can be ignored at some point. A typical modulation index will be such that there are at least a few sidebands, otherwise most of the power would be in the carrier, making inefficient use of transmitter power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Altering the baseband frequency changes the spacing between the sidebands. Here's a sine wave input of constant amplitude, increasing in frequency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Qe6ef.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Qe6ef.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course in practice baseband will contain many frequency components, varying in amplitude. Because even a single baseband frequency generates several sidebands, the individual frequencies in baseband create overlapping output frequencies and the result is a jumbled mess, visually.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-04-06T13:36:20.437" LastActivityDate="2017-04-06T13:36:20.437" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7444" PostTypeId="2" ParentId="7182" CreationDate="2017-04-05T22:37:09.503" Score="-3" Body="&lt;p&gt;Baofeng is not a US manufacturer but there UV-5R is a good entry level radio. That is the the only radio I have. It is not the best radio but it is cheap and easy to program. The downside is that they use different connectors than other radios which means it can be a little hard to find accessories. &lt;/p&gt;&#xA;" OwnerUserId="9462" LastActivityDate="2017-04-05T22:37:09.503" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7445" PostTypeId="1" CreationDate="2017-04-06T03:07:54.473" Score="2" ViewCount="404" Body="&lt;p&gt;I have a baofeng UV-5RA which doesn't seem to receive properly with my j-pole antenna. my dad's radio (same model, different firmware) receives without a problem, so it's a radio issue. if I go into the menu by pressing the menu button, suddenly it receives perfectly and has no issues, but the moment it leaves the menu it breaks again. sometimes some signals can make it through while not in the menu, but it seem's random. any baofeng experts know what's going on? my firmware version is &quot;HN5RV011FB297&quot; (strange, I know.) my dad's is &quot;BFB297&quot;.&#xA;also, my radio works just fine when using my basic nagoya NA-701 antenna.&lt;/p&gt;&#xA;" OwnerUserId="9433" LastActivityDate="2017-04-07T12:27:19.263" Title="baofeng UV-5RA has issues with j-pole" Tags="&lt;antenna&gt;&lt;baofeng&gt;&lt;uv-5r&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7447" PostTypeId="2" ParentId="7445" CreationDate="2017-04-07T08:17:14.990" Score="1" Body="&lt;p&gt;Answer:  contact the seller.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I doubt the J-pole is the issue; you didn't mention about how it acts with its stock antenna.  But their QC is not all that good, and anyone selling them knows it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had one where the earphone jack wouldn't work so I couldn't use CHIRP. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The seller sent me a new body with no questions asked.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-04-07T08:17:14.990" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7448" PostTypeId="2" ParentId="6887" CreationDate="2017-04-07T12:20:37.757" Score="2" Body="&lt;p&gt;I have this same problem at my house. Whenever I am using the HF bands, my DSL modem loses link, especially in the lower HF bands, and especially when I'm transmitting with more than about 300W. This is because the phone lines to my house are not well-shielded, and the energy from my transmitter couples into the DSL lines and overloads the modem.&lt;/p&gt;&#xA;&lt;p&gt;I solved this with ferrite beads. Lots of them. I put ferrites on the phone lines to the house and the cable between the wall and my modem, and in a few other places along the phone line to the house. It eliminated almost all of my problems.&lt;/p&gt;&#xA;" OwnerUserId="8837" LastEditorUserId="8837" LastEditDate="2020-12-04T13:31:07.790" LastActivityDate="2020-12-04T13:31:07.790" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="7449" PostTypeId="2" ParentId="7445" CreationDate="2017-04-07T12:27:19.263" Score="0" Body="&lt;p&gt;What kind of pigtail are you using to connect to your jpole? I would imagine your SMA connector is probably cold-soldered or broken, and is held in place by the rigid connection of the stock antenna, but is allowed to move and open the connection when you use a pigtail. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Baofengs are absolute garbage with awful build quality and almost no quality control. You get what you pay for. &lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2017-04-07T12:27:19.263" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7450" PostTypeId="2" ParentId="7436" CreationDate="2017-04-07T16:28:39.070" Score="1" Body="&lt;p&gt;&lt;strong&gt;Options:&lt;/strong&gt; Build one or Buy one&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Assumptions:&lt;/strong&gt; This is a home base station&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Buy one:&lt;/strong&gt;&#xA;Example: this J-Pole from Arrow Antennas. &lt;a href=&quot;http://www.arrowantennas.com/osj/j-pole.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrowantennas.com/osj/j-pole.html&lt;/a&gt; runs for about $50&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a gentleman here in Utah that makes them as well, and he charges $20&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Make one:&lt;/strong&gt;&#xA;There are plenty of plans out there to make them. Such as: &lt;a href=&quot;http://www.alpharubicon.com/elect/jpolejaden.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.alpharubicon.com/elect/jpolejaden.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend using RG-8X, RG-8U, RG-213 or LMR400 coax if you are doing a longer run. This will help prevent loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stick with SO-239 connectors on the antenna, so that way your PL-259 connectors will work well with the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you switch to an HT that uses an SMA or BNC connector, you can get adapters for cheap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Visual Appeal:&lt;/strong&gt;&#xA;The 2m JPole isn't large, and can be easily painted to match it's surrounding environment. Mine is painted, and it works great!&lt;/p&gt;&#xA;" OwnerUserId="9481" LastActivityDate="2017-04-07T16:28:39.070" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7451" PostTypeId="1" AcceptedAnswerId="7459" CreationDate="2017-04-07T19:02:13.260" Score="3" ViewCount="1993" Body="&lt;p&gt;I am trying to install a VHF/UHF antenna on my truck, and I have been studying everything I need to do that. I keep reading about chokes, in particular here: &lt;a href=&quot;http://www.k0bg.com/choke.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.k0bg.com/choke.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, everything I find talking about it is in reference to 10m band and lower frequencies. Is choking necessary for the 2/70 bands?&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2017-04-13T22:15:57.540" Title="Are chokes necessary for VHF and higher frequencies?" Tags="&lt;antenna-theory&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;mobile&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7453" PostTypeId="1" AcceptedAnswerId="7474" CreationDate="2017-04-08T17:14:55.780" Score="1" ViewCount="325" Body="&lt;p&gt;What are good sources for information about the propagation of RF that details the equations behind the curtain?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been able to find some simple stuff on wikipedia but nothing fancy that I'm sure exists. There's also a lack of clarity on what these formals output. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Free-space_path_loss#Free-space_path_loss_formula&quot; rel=&quot;nofollow noreferrer&quot;&gt;Free-space path loss formula&lt;/a&gt; is a good example of this in wikipedia. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does the number you get out of this mean? Is this the effective transmission power at that distance?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any introductory sources to the papers that cover how all of this works (to the best of our current knowledge)? I'm particularly interested in:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Losses&lt;/li&gt;&#xA;&lt;li&gt;Refraction and reflection&lt;/li&gt;&#xA;&lt;li&gt;Scattering&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I am not interested in approximations of the losses a link will experiance. I am interest in the way the waves will 1) move through space and get reflected off of things (the paths they take) and 2) what kind of losses these mediums and deflections introduce (the losses experianced). Equations like the Friis equation only estimate how the wave might look in total when it gets to the other station. It does not take into account many factors like solar indexes, time of day, path the radio will travel, etc.  &lt;/p&gt;&#xA;" OwnerUserId="9341" LastEditorUserId="1362" LastEditDate="2017-04-14T18:09:02.993" LastActivityDate="2017-06-14T16:40:41.750" Title="How to learn about the physics behind propagation?" Tags="&lt;propagation&gt;" AnswerCount="5" CommentCount="13" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7454" PostTypeId="2" ParentId="51" CreationDate="2017-04-08T22:23:07.813" Score="3" Body="&lt;p&gt;What you need to do is follow the requirements of the National Electrical Code (assuming USA).&lt;br&gt;&#xA;&lt;a href=&quot;http://www.reeve.com/Documents/Articles%20Papers/Reeve_AntennaSystemGroundingRequirements.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;This article covers it well&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(ps. Failure to comply with NEC 810 is the #1 reason ham radio operators in the US have fire insurance claims denied, and why they have to buy ARRL's silly little insurance policy. If you follow NEC 810 and get permits for your work, your insurance company won't try to deny your fire claim)&lt;/p&gt;&#xA;" OwnerUserId="8837" LastEditorUserId="2988" LastEditDate="2019-06-21T20:04:21.620" LastActivityDate="2019-06-21T20:04:21.620" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="7455" PostTypeId="2" ParentId="6887" CreationDate="2017-04-09T09:50:22.767" Score="1" Body="&lt;p&gt;Like the previous answer: I'm also a ham, and when I send on frequencies around 7 Mhz (power level&amp;lt;50 Watt), my ADSL connection drops. So yes: it is possible.&lt;/p&gt;&#xA;" OwnerUserId="8843" LastActivityDate="2017-04-09T09:50:22.767" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7456" PostTypeId="1" AcceptedAnswerId="7458" CreationDate="2017-04-09T13:22:06.823" Score="8" ViewCount="2012" Body="&lt;p&gt;I see &quot;impedance&quot; used everywhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equipment has an input and output impedance.&lt;br&gt;&#xA;Antennas and feedlines all have this 'impedance' thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For someone that understands DC electronics, Ohm's law and a little bit of complex numbers, what &lt;em&gt;is&lt;/em&gt; impedance?&lt;/p&gt;&#xA;" OwnerUserId="8553" LastActivityDate="2017-04-10T00:30:33.570" Title="What exactly is impedance?" Tags="&lt;impedance&gt;&lt;antenna-system&gt;" AnswerCount="4" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7457" PostTypeId="2" ParentId="7456" CreationDate="2017-04-09T14:56:07.543" Score="-1" Body="&lt;p&gt;Impedence is a combination of capacitance, inductance and resistance at a particular frequency.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At resonance, where the capacitance and inductance balance each other out, it is dominated by resistance.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are formulas for calculating the contribution of each component, all based on frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would suggest you post this exact same question on Google like this:  &lt;a href=&quot;http://www.google.com?q=what%20is%20impedence&quot; rel=&quot;nofollow noreferrer&quot;&gt;What is Impedence?&lt;/a&gt; - there is a lot of information about it.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-04-09T14:56:07.543" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7458" PostTypeId="2" ParentId="7456" CreationDate="2017-04-09T15:33:29.317" Score="9" Body="&lt;p&gt;&lt;strong&gt;As resistance is to DC circuit analysis, impedance is to AC (or RF) circuit analysis.&lt;/strong&gt; Now let's take a closer look at what that means, from several angles. I'm going to not include any of the math, and just state without proof the various concepts' relationships.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;In simple, idealized circuit analysis of DC or digital circuits, we often assume that lots of elements are ideal and &lt;em&gt;have no resistance&lt;/em&gt;, except for things we think of as &lt;em&gt;loads.&lt;/em&gt; But in reality they do — if you short-circuit a battery, then the universe does not end, both because it only contains a finite amount of energy, and because it and the wire both have some internal, usually undesired, resistance. (Whereas in simulation, if you short-circuit a voltage source the simulator will stop with an error.) Resistance is everywhere.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The big nifty idea in AC analysis is that you can, to a point, use the same formulas you do in DC analysis even though the voltages and currents are changing all the time, as long as they are all sinusoids. But, physically, there is a novel phenomenon which just happens to line up to let the math work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a true DC analysis (nothing is changing at all, there is no time), the only way — to speak loosely — the flow of electricity can be affected is to add a resistance, which &lt;em&gt;converts electrical power into heat.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In an AC system, because we have voltages and currents that are varying, we have the possibility of inductances and capacitances — collectively, &lt;em&gt;reactances&lt;/em&gt; — which are both elements which &lt;em&gt;store energy and release it later&lt;/em&gt;. It works out that this is precisely the same as having a &lt;em&gt;phase shift&lt;/em&gt; of the sinusoidal waveform. (If we didn't have any reactances in the circuit, then all of the voltages and currents in the circuit would be exactly in phase, and a DC analysis of any given instant would give you the right answer.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It happens that the math of complex numbers is exactly the right tool to understand reactances; if you generalize resistance (real) to impedance (complex) then an imaginary impedance is a reactance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This ties into the fact that reactances do not dissipate power as heat — go around in a circle on the complex plane and you have the same magnitude.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;As resistance is everywhere, so is reactance.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Deliberately: A second way in which reactance is unlike resistance is that it is &lt;em&gt;frequency-dependent:&lt;/em&gt; the reactance of a component depends on the applied frequency as well as on its inductance or capacitance. This effect is used to create filters and oscillators — circuits that treat different frequencies differently.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Accidentally: Electrical signals have a propagation time. Therefore, there are delays. Therefore, signals can meet while out of phase, and this is &lt;em&gt;exactly the same&lt;/em&gt; as if there were deliberately introduced reactances.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Any arrangement of two conductors which carries signals over a significant distance is a &lt;em&gt;transmission line.&lt;/em&gt; Because there is distance, there is delay, which is more or less the same as inductance. Because there are two conductors, there is capacitance between them. Both of these properties scale proportionally to the length of the line. The way the math works out, if you look at the input (or output) side of the line as if it were a two-terminal circuit element, it turns out to have an impedance which is a positive real number — which, yet, is not a resistance in that it is not dissipative.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;An inductor stores energy in the magnetic field and releases it later.&lt;/li&gt;&#xA;&lt;li&gt;A capacitor stores energy in the electric field and releases it later.&lt;/li&gt;&#xA;&lt;li&gt;A transmission line &lt;em&gt;transports&lt;/em&gt; energy and releases it &lt;em&gt;elsewhere&lt;/em&gt; later.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Now, since an (ideal) transmission line is not dissipating power, we can ask the question: What happens if the circuit on the far end in some way does not itself absorb/dissipate the power? For example, an open circuit, with a resistance of infinity, clearly dissipates no power, and a short circuit, with a resistance of zero, does not either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you actually get is a wave reflection — the power comes back out of the input side of the line after a delay. This is generally undesirable because it is not useful, and can also cause damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can imagine that there would also be reflections of lesser magnitude if the properties of the far end are “too much like a short” or “too much like an open”. It turns out that these properties are exactly characterized and summarized by an impedance value. The “sweet spot” of such impedance depends on the design of the transmission line, and is known as the &lt;strong&gt;characteristic impedance&lt;/strong&gt; of the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there is no reflection of the signal, then we can conclude that the near side cannot tell when the signal has reached the far side. Therefore the length of the line does not matter. Therefore, the line could be of zero length or infinite length. We conclude that a transmission line of &lt;em&gt;any length&lt;/em&gt; looks like an impedance whose value is the characteristic impedance — provided that the circuit on the other end has that impedance also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the far end is not matched, then the near end will have an impedance which is not the characteristic impedance — but it can be different in any direction on the complex plane, depending on the exact magnitude and phase of the reflection. (This is what a &lt;a href=&quot;https://en.wikipedia.org/wiki/Smith_chart&quot; rel=&quot;noreferrer&quot;&gt;Smith chart&lt;/a&gt; illustrates.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Reflections in an antenna system are undesirable, so outside of specific applications (filtering, dividing/combining, antenna tuners), every component of an antenna system is generally designed to have the same impedance at every &lt;em&gt;port&lt;/em&gt; (place where a circuit or transmission line meets another — physically, a coaxial or balanced connector).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-04-09T15:33:29.317" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7459" PostTypeId="2" ParentId="7451" CreationDate="2017-04-09T19:01:53.247" Score="1" Body="&lt;p&gt;The article you reference has to do with protecting the controller in a screwdriver antenna. Which you don't have at VHF or UHF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The purpose of a screwdriver antenna is to lengthen or shorten the element to match the wavelength of your transmission band. VHF and UHF transmission bands are each wider than a single HF band but not wider than all of the HF bands grouped together. At VHF and UHF frequencies the ideal antenna length between the ends of the band is not that great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A feedline choke can be installed on any antenna but unless you are planning on driving a wire brush you're not going to get much induced current in your feed line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't mention what type of antenna you have or where on the truck you are mounting it. However as the linked article in the comment explains you will be fully unbalanced. Mobile installation is almost always fully unbalanced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trucks have some suboptimal  mounting locations. They are not worse than motorcycles however. Accessories that you might have for your truck will change the below information. Which is for a regular  Pickup. The main things that impact the information below would be a ladder rack or a metal cover. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best: If you are planning on through hole mounting to the center of your roof deck, the ground plane will be physically established where the connector comes through the roof. If you are just planning on the one antenna you should try to get it close to the center front back left right. This would be an effort to maximize the amount of ground plane around the antenna, and to minimize the amount of directivity that the shape of your ground plane will provide your signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good: If you are using a magmount, the ground plane is parasitic back to the radio chassis mount. A similar mounting point to the one above should be chosen. Route the cable in such a way that water won't drip in and it won't get smashed by the door as often.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Okay: Stake hole mounts I don't have a great deal of experience with. If you use the holes close to the cab these run into the same issues as a trunk mount car antenna. The metal structure of the cab drastically interferes with your radiation pattern and your match.  If you have a full size pickup the rear stake holes will be more than a wavelength from the cab at 2m however you will still get Reflections from it. &lt;/p&gt;&#xA;" OwnerUserId="6092" LastEditorUserId="6092" LastEditDate="2017-04-09T19:27:34.257" LastActivityDate="2017-04-09T19:27:34.257" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7460" PostTypeId="2" ParentId="7456" CreationDate="2017-04-09T20:05:33.460" Score="0" Body="&lt;p&gt;Simply put, &lt;strong&gt;Impedance is the combination of resistance and reactance&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reactance is zero when the current and voltage are in phase with each other.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-04-09T20:05:33.460" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7461" PostTypeId="2" ParentId="7456" CreationDate="2017-04-10T00:30:33.570" Score="0" Body="&lt;p&gt;Resistance gives the ratio of voltage to current: one ohm equals one volt per ampere. This is pretty important&lt;sup&gt;[citation needed]&lt;/sup&gt; for circuit analysis and design. But if the circuit contains capacitors or inductors, Ohm's law and resistance won't work anymore because capacitors and inductors don't have resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What they have is &lt;em&gt;reactance&lt;/em&gt;. The voltage across a capacitor can't change instantly, and the current through an inductor can't change instantly either. So if connected to an AC source which is constantly trying to change current or voltage, the inductor or capacitor will limit the voltage or current to some finite amount.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider a frictionless swing: it oscillates in both speed and height. But when speed is at a maximum height is zero, and when height is at a maximum speed is zero. This means the two are 90 degrees out of phase, which is another way of saying one happens one fourth of a cycle after the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same is true of an AC source connected to a capacitor or an inductor. If the load is an inductor, then a current maximum will happen a quarter cycle after a voltage maximum, and this is called positive reactance. For a capacitor it's the opposite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The magnitude of the reactance defines the ratio of voltage to current, similar to Ohm's law in a DC circuit. A high reactance is like a high resistance: for a given voltage there will be less current if reactance is higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reactance ($X$) depends on the inductance ($L$) or the capacitance ($C$), but also the frequency ($f$). For inductors the reactance is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ X = 2 \pi f L $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And for capacitors:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ X = -\, {1 \over 2 \pi f C} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like the frictionless swing, an AC source driving a reactive load does no work: it takes a little energy to get the system going, but then it will oscillate forever.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, real swings aren't frictionless, and real electrical circuits are not without resistance&lt;sup&gt;1&lt;/sup&gt;. To to analyze real circuits we still need resistance. If the reactance is multiplied by $\sqrt{-1}$ and then added to the resistance you get a complex number called &lt;em&gt;impedance&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance in AC circuits works in many of the places resistance works in DC circuits. For example, it can be used in Ohm's law. Series impedances add (like resistors) and parallel impedances also combine like parallel resistances. Reactance changes with frequency, which makes it possible to analyze things like filters which treat some frequencies differently from others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is very useful for analyzing many kinds of circuits, which is why when reading about AC or RF circuits you will encounter impedance so frequently.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1: But what about superconductors? A real superconducting circuit must have some non-zero area, and thus will make an antenna, even if a not very good one. Subjected to an AC current or voltage, a little of that energy will be radiated away, and that lost energy is modeled as radiation resistance. Superconductors can also lose energy to magnetic hystresis and other factors. So even with superconductors, resistance can not be avoided.&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-04-10T00:30:33.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7463" PostTypeId="2" ParentId="7453" CreationDate="2017-04-10T20:50:37.667" Score="3" Body="&lt;p&gt;You're talking about &lt;a href=&quot;https://en.wikipedia.org/wiki/Maxwell%27s_equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;Maxwell's equations&lt;/a&gt; and the &lt;a href=&quot;https://en.wikipedia.org/wiki/Electromagnetic_wave_equation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Electromagnetic wave equation&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Path loss and scattering are functions of the medium through which the waves are passing, which is reflected in the variables in these equations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia is not your best source for information about this, however.  University courses are much better.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the search you want to do:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.google.com/search?q=radio+wave+propagation+maxwell%27s+equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.google.com/search?q=radio+wave+propagation+maxwell%27s+equations&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the best results is this paper:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.farmingdale.edu/faculty/peter-nolan/pdf/UPCh29.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.farmingdale.edu/faculty/peter-nolan/pdf/UPCh29.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-04-10T20:50:37.667" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7464" PostTypeId="1" AcceptedAnswerId="7475" CreationDate="2017-04-10T21:46:44.953" Score="2" ViewCount="2121" Body="&lt;p&gt;I can receive a calibrated decibel milliwatt signal level from the output of any antenna at a given frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a given antenna gain (dbi) in the direction I want to receive the signal (including a 1/4 wave vertical or a loopstick antenna etc...), how can I calculate the field strength in µV / meter? &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2019-02-27T12:54:49.823" Title="Field Strength calculations with known antennas" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7465" PostTypeId="2" ParentId="7464" CreationDate="2017-04-10T23:35:05.397" Score="0" Body="&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Antenna_factor&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna factor&lt;/a&gt; gives, for each frequency, the ratio between electric field strength and voltage at the antenna terminals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the linked article you'll find the relation between AF and antenna aperture, and antenna gain.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2017-04-10T23:35:05.397" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7466" PostTypeId="2" ParentId="7004" CreationDate="2017-04-11T12:11:59.610" Score="3" Body="&lt;p&gt;I had the exact same issue on the MD390 and it took some very frustrating attempts to make it work. Turns out its just that the software is just doesn't have an intuitive UI. Hopefully this will help you with your MD380, which I understand to be the same radio but without the waterproofing. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Make sure you have the correct options set in the very first window that pops up (the one in your pic, make sure the freq is correct &lt;strong&gt;for your radio.&lt;/strong&gt; Mine is a VHF) &lt;/li&gt;&#xA;&lt;li&gt;Click on the read radio button. Its the one with the yellow arrow pointing away from the radio.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/1igGy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1igGy.png&quot; alt=&quot;step 1 and 2&quot;&gt;&lt;/a&gt;  &lt;/li&gt;&#xA;&lt;li&gt;This step threw me off several times until I accidentally clicked it. Click ok to actually read the radio.  &lt;a href=&quot;https://i.stack.imgur.com/t6pEz.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/t6pEz.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Now you can click on General settings or any other item to start working with the radio. &lt;a href=&quot;https://i.stack.imgur.com/HtGPJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HtGPJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="4181" LastActivityDate="2017-04-11T12:11:59.610" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7467" PostTypeId="1" AcceptedAnswerId="7469" CreationDate="2017-04-11T18:25:20.853" Score="3" ViewCount="1607" Body="&lt;p&gt;I am trying to communicate between two arduino microcontrollers using radio. For this purpose I am building a whip antenna with 4 ¼ wave radials. I've done a bit of reading and have got most of it, but all guides I've found are a bit vague on the topic of radials. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is: When it says that Radials should be grounded, does that mean they have to be connected to the actual ground, or is the ground Pin on the arduino (the &quot;minus pole&quot;) ok too? As my project is mobile, actual ground is pretty tough...&lt;/p&gt;&#xA;" OwnerUserId="9494" LastEditorUserId="8832" LastEditDate="2017-04-15T01:00:55.723" LastActivityDate="2017-04-15T15:56:35.253" Title="What do you connect antenna Radials to?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;grounding&gt;&lt;radial&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7468" PostTypeId="1" CreationDate="2017-04-11T18:56:02.267" Score="0" ViewCount="282" Body="&lt;p&gt;Can an amplified antenna be connected to a typical boombox radio with a telescoping antenna without damaging the radio?&lt;/p&gt;&#xA;" OwnerUserId="9495" LastEditorUserId="8832" LastEditDate="2017-04-12T14:42:12.677" LastActivityDate="2017-08-18T04:26:56.287" Title="Amplified antenna &amp; typical boombox radio" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;fm&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7469" PostTypeId="2" ParentId="7467" CreationDate="2017-04-11T19:49:30.423" Score="2" Body="&lt;p&gt;The radials are not connected to the earth. &lt;a href=&quot;https://goo.gl/images/sxaTyr&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here's a photo of a ground plane antenna&lt;/a&gt;. They are connected together as shown to the coax shield. This shield should be connected to the common on the board that can serve as an RF ground.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-04-11T19:49:30.423" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7470" PostTypeId="2" ParentId="7467" CreationDate="2017-04-11T19:58:23.567" Score="2" Body="&lt;p&gt;Radials are grounded to the feedpoint.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, the shield of the coax feeding the quarter-wave antenna.  For AM radio broadcasting stations, there are radials every 3 degrees (120 of them) and they are generally buried (enough so you can still mow the lawn above them), so they are at ground potential their entire length.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the radials are not themselves grounded then that is called a counterpoise, like if you install a radial system on a rooftop.  In that case the true ground is at your transmitter, then the feedline shield is the connection to the counterpoise on the roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In terms of Amateur Radio usage, there are a lot of great antennas like the &lt;a href=&quot;https://www.dxengineering.com/parts/hsr-5btv&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hustler 5BTV&lt;/a&gt; that require professional-quality ground systems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another example is if you use a magnetic mount for your antenna on the car, it couples into the metal of your car as the ground plane.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the best answer to your question can be found &lt;a href=&quot;http://www.qsl.net/wrav/2mground.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;HERE&lt;/a&gt; - the basic concept is shown in this diagram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gAV2k.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gAV2k.png&quot; alt=&quot;2M Ground Plane Antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-04-11T19:58:23.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7471" PostTypeId="2" ParentId="7468" CreationDate="2017-04-11T20:30:45.813" Score="0" Body="&lt;p&gt;Not likely that it could be damaged by an amplified antenna, no.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that the boombox is designed to use that built-in antenna, so an amplified antenna would likely overdrive the receiver and the result would be a distorted signal.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unless they have  external antenna connectors your only option would be to clip it to the whip itself.  Again, the boombox isn't designed for that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you do try an amplified antenna and the results aren't great, then you might want to fall back to just clipping on some extra length of wire to the whip.  But the antenna on the boombox is designed to be the &quot;right&quot; length, so even that may not help.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-04-11T20:30:45.813" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7472" PostTypeId="1" CreationDate="2017-04-12T12:29:28.667" Score="5" ViewCount="1925" Body="&lt;p&gt;I am using an arduino micro controller with a LoRa radio module to communicate. The shield has 2 ways of connecting an antenna: either a SMA jack or a hole for soldering. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now my problem is this: I need to get the antenna away from the module itself, so that i can get the antenna out of the container of the arduino. What ways are there of doing this? Can I just use a wire? But on the other hand, would that wire not act as an antenna itself? Are there special cables or something?&lt;/p&gt;&#xA;" OwnerUserId="9494" LastActivityDate="2017-04-12T18:54:49.003" Title="What ways are there to extend an antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7473" PostTypeId="2" ParentId="7472" CreationDate="2017-04-12T13:58:01.760" Score="9" Body="&lt;p&gt;You have an SMA connector – use that! You can buy ready-made coax cables with SMA connectors on both ends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As mentioned, what you want is a coax cable. The electromagnetic wave travels &lt;em&gt;within&lt;/em&gt; the cable, so, no, if not damaged and properly attached to the radio and to an actual antenna, it won't double as antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Very much like your TV cable doesn't emit radio waves.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-04-12T13:58:01.760" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7474" PostTypeId="2" ParentId="7453" CreationDate="2017-04-12T14:37:54.513" Score="4" Body="&lt;p&gt;Propagation is a very complex subject. To predict using purely mathematical means how a transmission from point A to B is more complex than trying to predict the throw of dice. There are stochastic processes, huge complexity, and many unknowns involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simplifications must be made, and the valid simplifications depend on your objective, the frequency, and the application, among other things. If you want to understand all the physics relevant to propagation, the best I can do is refer you to many concepts to further research.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most general solution is &lt;a href=&quot;https://en.wikipedia.org/wiki/Maxwell%27s_equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;Maxwell's equations&lt;/a&gt;. All of the other concepts discussed here are solutions to these equations with certain assumptions added. If you want an &lt;em&gt;exact&lt;/em&gt; model of how propagation occurs &lt;em&gt;in all conditions&lt;/em&gt;, this is it. These equations are the foundation of classical electromagnetism, and consequently radio, optics, and electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course to understand exactly the path from A to B would require a precise understanding of the geometry of everything in the path and near it, as well as the exact electromagnetic properties of every material within. That's not not realistically possible for complicated paths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the paths are simple we have things like the Friis transmission equation. All waves will be subject to this equation, though there may be other things contributing to the path effects. For things like space communications, or microwave links with nothing in the path's &lt;a href=&quot;https://en.wikipedia.org/wiki/Fresnel_zone&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fresnel zone&lt;/a&gt;, the Friis equation is an accurate and precise calculation of path losses. There's very little to be understood about this model besides the &lt;a href=&quot;https://en.wikipedia.org/wiki/Inverse-square_law&quot; rel=&quot;nofollow noreferrer&quot;&gt;inverse square law&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding a bit of complexity, there's the &lt;a href=&quot;https://en.wikipedia.org/wiki/Two-ray_ground-reflection_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;two ray ground reflection model&lt;/a&gt;. This is relevant for many VHF and microwave links where the ground will reflect the signal and create &lt;a href=&quot;https://en.wikipedia.org/wiki/Multipath_interference&quot; rel=&quot;nofollow noreferrer&quot;&gt;multipath interference&lt;/a&gt; due to &lt;a href=&quot;https://en.wikipedia.org/wiki/Interference_(wave_propagation)&quot; rel=&quot;nofollow noreferrer&quot;&gt;interference between the waves&lt;/a&gt;, but with otherwise clear paths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course multipath interference can occur due to reflections off buildings and other things. You might try to use &lt;a href=&quot;https://en.wikipedia.org/wiki/Ray_tracing_(physics)&quot; rel=&quot;nofollow noreferrer&quot;&gt;ray tracing&lt;/a&gt; to calculate the interference, though unless the reflecting surfaces are very much larger than the wavelength, &lt;a href=&quot;https://en.wikipedia.org/wiki/Diffraction&quot; rel=&quot;nofollow noreferrer&quot;&gt;diffraction&lt;/a&gt; will make this calculation inaccurate. A better calculation uses a &lt;a href=&quot;https://en.wikipedia.org/wiki/Electromagnetic_field_solver&quot; rel=&quot;nofollow noreferrer&quot;&gt;field solver&lt;/a&gt; to approximate a solution to Maxwell's equations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Environments often contain lossy materials, resulting in &lt;a href=&quot;https://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)&quot; rel=&quot;nofollow noreferrer&quot;&gt;absorption&lt;/a&gt;. The ground is one such common lossy material. Steel structures will incur losses due to &lt;a href=&quot;https://en.wikipedia.org/wiki/Magnetic_hysteresis&quot; rel=&quot;nofollow noreferrer&quot;&gt;hysteresis&lt;/a&gt;. &lt;a href=&quot;https://en.wikipedia.org/wiki/Joule_heating&quot; rel=&quot;nofollow noreferrer&quot;&gt;Resistive losses&lt;/a&gt; also exist in metal structures, among other things. &lt;a href=&quot;https://en.wikipedia.org/wiki/Dielectric_loss&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dielectric loss&lt;/a&gt; can occur, especially at higher frequencies. Water is a common factor in dielectric loss. At high enough frequencies, &lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_propagation#Absorption&quot; rel=&quot;nofollow noreferrer&quot;&gt;gasses in the atmosphere can cause absorption&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, modeling the contour of the Earth, buildings, and trees in the path is infeasible, so some sort of &lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_propagation_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;propagation model&lt;/a&gt; will be used which approximates typical environments. Often these are a combination of educated guesses about the environment's properties and empirical data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Skywave propagation such as on HF is very complicated due to conditions which are constantly changing. Here again, Maxwell's equations describe the behavior, but the chaotic and complex nature of the ionosphere makes a simple solution impossible. Many topics in the field of &lt;a href=&quot;https://en.wikipedia.org/wiki/Optics&quot; rel=&quot;nofollow noreferrer&quot;&gt;optics&lt;/a&gt; are relevant here. In practice empirical models are used, for example &lt;a href=&quot;http://www.voacap.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this gives you some things to research.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-04-12T14:37:54.513" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7475" PostTypeId="2" ParentId="7464" CreationDate="2017-04-12T16:12:14.413" Score="1" Body="&lt;p&gt;Given:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the receiving antenna's gain in dBi, $G_\mathrm{dBi}$&lt;/li&gt;&#xA;&lt;li&gt;the power received by the antenna in dBm, $P_\mathrm{dBm}$&lt;/li&gt;&#xA;&lt;li&gt;the frequency in Hz, $f$&lt;/li&gt;&#xA;&lt;li&gt;the impedance of free space in ohms, $Z_0$&lt;/li&gt;&#xA;&lt;li&gt;the speed of light in meters per second, $c$&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;then the field strength in V/m is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align*}&#xA;V &amp;amp;=&#xA;\:\sqrt{ 0.004\, \pi\, Z_0 }&#xA;\:f/c&#xA;\:10^{(P_\mathrm{dBm}-G_\mathrm{dBi}) / 20}&#xA;\\&#xA;&amp;amp;\approx 7.258\times 10^{-9}\: f&#xA;\:10^{(P_\mathrm{dBm}-G_\mathrm{dBi}) / 20}&#xA;\end{align*}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the frequency is in MHz and the result is in µV/m then the constant becomes more manageable:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ V_\mathrm{\mu V/m}&#xA;\approx 7258&#xA;\: f_\mathrm{MHz}&#xA;\: 10^{(P_\mathrm{dBm}-G_\mathrm{dBi}) / 20}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the receiving antenna must match the polarization of the voltage field being measured. In situations where the polarization isn't known, an isotropic receiver can be used, which is usually an orthogonal arrangement of short dipoles in 3 axes. Such an antenna can measure a voltage gradient in any direction.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I find it's easier to understand why this is true by thinking about power density rather than field strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a 1 watt isotropic antenna at the center of a sphere, the entire 1 watt of that transmitted power must pass through the sphere. The power density is then the transmitted power, divided by the surface area of the sphere. The result is a number in units of watts per square meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The receiving antenna, assuming it is identically polarized, is then a &quot;net&quot; for this energy flux. The size of the net is the antenna aperture, which can be calculated from its gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A = {\lambda^2 \over 4 \pi} 10^{G_\text{dBi}/10} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more detail, see &lt;a href=&quot;https://ham.stackexchange.com/questions/1539/what-does-the-friis-transmission-equation-represent-and-how-is-it-derived&quot;&gt;What does the Friis transmission equation represent and how is it derived?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the far field, power density and the field strength are related by the &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;nofollow noreferrer&quot;&gt;free space impedance&lt;/a&gt;, which is approximately 377Ω. Converting between power density and field strength is very much like Ohm's law. This can be derived from &lt;a href=&quot;https://en.wikipedia.org/wiki/Poynting%27s_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;Poynting's theorem&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{power density} = {\text{field strength}^2 \over \text{free space impedance}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or solved for field strength:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{field strength} = \sqrt{\text{power density} \times \text{free space impedance}}  $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, if you can measure the power density at some point, say by measuring the feedpoint power from an antenna of known gain, then you can calculate the field strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, say the antenna has a gain of 3 dBi at a wavelength of 2 meters, and you measure a power at the feedpoint of 0.1μW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The aperture is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {(2\:\mathrm{m})^2 \over 4 \pi} 10^{3\:\mathrm{dBi}/10} = 0.635\:\mathrm{m}^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power density is then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {0.1\:\mathrm{\mu W} \over 0.635\:\mathrm{m}^2} = 0.157\:\mathrm{\mu W}/\mathrm{m}^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the corresponding field strength:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \sqrt{0.157\:\mathrm{\mu W/m^2} \times 377\:\Omega} = 7705\:\mathrm{\mu V/m}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Put these three equations together and simplify to get the equation at the top.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more detail, &lt;a href=&quot;https://www.semtech.com/images/promo/Semtech_ACS_Rad_Pwr_Field_Strength.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Semtech has a good paper&lt;/a&gt; on field strength and many related topics.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-04-21T11:50:01.227" LastActivityDate="2017-04-21T11:50:01.227" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7476" PostTypeId="2" ParentId="7451" CreationDate="2017-04-12T18:49:54.283" Score="1" Body="&lt;p&gt;Choking baluns are not typically used on VHF and UHF antenna systems in a vehicle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part of the reason is that the ground plane formed by the roof or trunk of the vehicle is quite effective in isolating the feedline from common mode currents (the currents that a choking balun is trying to reduce or eliminate) at VHF and UHF frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you did try to build one from coiled coax or a parallel transmission line wrapped around a torroid, you would find that the strays at those frequencies would significantly limit their effectiveness. With careful attention to details, you could probably tune one to be effective but this is beyond the resources of the typical ham.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I recommend carrying on without one just like the rest of us do.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="76" LastEditDate="2017-04-13T22:15:57.540" LastActivityDate="2017-04-13T22:15:57.540" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7477" PostTypeId="2" ParentId="7472" CreationDate="2017-04-12T18:54:49.003" Score="2" Body="&lt;p&gt;You can make a solder-able on aerial with a length of screened wire. On the board end separate the screen from the wire inside it. The centre wire is soldered onto the hole for the aerial. The screen is soldered onto the nearest earth point. (Make sure it does not short against any thing.) At the other end you remove the screen for a section of the length, thus just the inner wire is left exposed. This is then placed where you want it to be. The screen is just that - a screen. Make the length of the exposed wire [for a frequency of 868MHz ] 8.2cm in length. Reference = Page 30 of &lt;a href=&quot;https://partner.orange.com/wp-content/uploads/2016/04/LoRa-Device-Developer-Guide-Orange.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://partner.orange.com/wp-content/uploads/2016/04/LoRa-Device-Developer-Guide-Orange.pdf&lt;/a&gt;  (I am Rob Scott of scott_electronics@yahoo.co.uk )&lt;/p&gt;&#xA;" OwnerUserId="9503" LastActivityDate="2017-04-12T18:54:49.003" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7478" PostTypeId="1" AcceptedAnswerId="7483" CreationDate="2017-04-12T22:17:20.423" Score="1" ViewCount="171" Body="&lt;p&gt;I'm studying for the General exam and I've encountered some questions about maximum baud rates on various bands. They seem... extremely optimistic. Given the trouble I've had investigating 9600 baud on 2m, I had to wonder if people are actually managing anything like the limits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondarily, how would I go about setting up a 19.6k connection on 2m or a 56.6k connection on 70cm? Are there radios that offer this as a capability, or specific TNCs, or is this just a lot of legal headroom and nobody's actually doing it?&lt;/p&gt;&#xA;" OwnerUserId="6295" LastEditorUserId="76" LastEditDate="2017-04-16T14:59:03.120" LastActivityDate="2017-04-16T14:59:03.120" Title="V/U Packet Rate Limits" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;packet&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7479" PostTypeId="2" ParentId="7478" CreationDate="2017-04-13T10:24:45.553" Score="2" Body="&lt;p&gt;There are two questions in the General exam dealing with bandwidth in the VHF and UHF bands (G1C09 and G1C11). Both of these questions are dealing with the regulatory, not technical, limits of data communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a practical perspective the limiting technical factor will be the radio you use to try to obtain 19.6 or 56 kbaud on these bands. Most FM and SSB transceivers for have modulators that are restricting the output bandwidth to that required for voice communications (about 3 kHz). Any attempt to use these modulators at the higher signaling rates required for higher speed digital communications will result in significant distortion to the modulated signal rendering the received signal useless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can overcome the modulation bandwidth restrictions by using a radio purposely designed for higher speed data communications or by modifying or building a radio to suit your needs. This is one of the great joys and privileges of having an amateur radio license - you are encouraged by the FCC to experiment in this way!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck on your General exam!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: I should add that some off the shelf UHF/VHF radio's have accessory connectors that allow a wider bandwidth. Examples are the FT-7900, the TM-V71, and the IC-208H. None of these are wide enough for the data limits of UHF and they all still use FM as the modulation method.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-04-13T15:29:00.660" LastActivityDate="2017-04-13T15:29:00.660" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7480" PostTypeId="2" ParentId="7420" CreationDate="2017-04-13T10:51:30.750" Score="3" Body="&lt;p&gt;The typical amateur radio / SWL budget will rarely allow for sufficient protection from a direct lightning strike. More often than not, the measures taken help minimize damage from a direct strike but more importantly they mitigate damage from near lightning strikes and static build-up. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the goal is to bleed static and minimize damage then mast should be grounded (this is also an NEC requirement). The grounding should be carried out with a heavy gauge conductor (minimum of #6 by NEC) leading to a ground rod. The efficacy of the ground can be improved by using wide copper straps. The ground rods should be tied to the house system ground rod(s) with a minimum of #6 AWG wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cellular industry has promoted bringing the coax down to the ground level and installing a lightning arrestor bonded directly to the ground system at this point. This is considered a best practice for amateur radio installations as well. If you cannot route the coax in this manner, installing a lightning arrestor in the coax at the mast and bonding it to the mast ground may provide some level of protection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be aware that your mast mounted pre-amp is considered lightning fodder. There is little that can be done to protect it from a near lightning strike when it is located so far from an effective ground. Some people advocate the use of an RFC (radio frequency choke) inductor across the input. This will offer some degree of protection but due to the rapid current rise (di/dt) during near lightning events, it is not likely to stop all damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your resistor across the dipole legs will prove helpful to bleed of static that is generated by winds and nearby storms. You should periodically inspect this resistor as it too will be sacrificial in the event of a nearby strike.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="1362" LastEditDate="2017-04-14T18:47:01.263" LastActivityDate="2017-04-14T18:47:01.263" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7483" PostTypeId="2" ParentId="7478" CreationDate="2017-04-15T10:09:28.950" Score="1" Body="&lt;p&gt;As mentioned above, you should make a distinction between the legal limits, and the technical feasibility, and the theoretical maxima in rates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To illustrate: Shannon's channel capacity says that over a channel with bandwidth $B$ and SNR $\frac SN$, you can do at &lt;strong&gt;most&lt;/strong&gt; the bit rate $C$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$C = B\log_2\left(1+\frac SN\right)\,\text.$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What Shannon does not say is &lt;em&gt;how&lt;/em&gt; you do that, and in fact, that problem is often unsolved, so most transceiver systems stay considerably below that rate limit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let us, however, plug in some numbers here of a rather idyllic scenario:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We go for a channel width of $B= 3\,\text{kHz} \approx 35\,\text{dBHz}$, and let's assume some ~S8 scenario, so $S=-80\,\text{dBm}$, as well as letting your receiver run at room temperature and have a Noise Figure $N_F=4\,\text{dB}$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;C &amp;amp;= 3\cdot10^3\frac1{\text s} \cdot\log_2\left(1+\frac{-80\,\text{dBm}}{-174\,\text{dBm/Hz}\cdot 35\,\text{dBHz}\cdot4\,\text{dB}}\right)\\&#xA;&amp;amp;= 3\cdot10^3\frac1{\text s} \cdot\log_2\left(1+\frac{-80\,\text{dBm}}{\left(-174+35+4\right)\,\text{dBm}}\right)\\&#xA;&amp;amp;= 3\cdot10^3\frac1{\text s} \cdot\log_2\left(1+(-80-(-174+35+4)\,\text{dB})\right)\\&#xA;&amp;amp;= 3\cdot10^3\frac1{\text s} \cdot\log_2\left(1+(-80+135)\,\text{dB})\right)\\&#xA;&amp;amp;= 3\cdot10^3\frac1{\text s} \cdot\log_2\left(1+55\,\text{dB}\right)\\&#xA;&amp;amp;\approx 3\cdot10^3\frac1{\text s} \cdot\log_2\left(10^{5.5}\right)\\&#xA;&amp;amp;\approx 3\cdot10^3\frac1{\text s} \cdot18.27\\&#xA;&amp;amp;= 54.81\,\text{kb/s}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, no matter what modulation, channel code you use, there's no chance you'll get more that 54810 bits per second error-free through that channel. So, restricting you to about $\frac13$ of that still makes no sense from an RF perspective (regulator doesn't actually care how fast you transmit, but how much spectrum you occupy with that), but it's not inherently &lt;em&gt;too&lt;/em&gt; optimistic – on a short range scenario, the receive powers might be much higher (calculate Free Space Path loss for 5 km with 2 m waves, how much power do you get when someone blasts out 750 W? My rough head calculation says you get about 20 times the capacity).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-04-15T10:09:28.950" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7484" PostTypeId="2" ParentId="7467" CreationDate="2017-04-15T15:56:35.253" Score="-2" Body="&lt;p&gt;The radials scope are to emulate a &quot;ground plane&quot; in order that your antenna to have maximal radiated lobes according this design. Also will contribute to proper impedance matching your cable (and/or transmitter).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When 100% matched, all energy transmitted will be transferred to active element and radiated, other ways, some percent will be reflected back through cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From RADIATING point of view, there is no need to connect them to anything, coupling will be magnetic. For GP antenna (and most vertical ones) you can skip radials and put a solid ground plane like GND cooper of PCB. Imagine that car antennas don't use radials, just substitute them with car roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From IMPEDANCE MATCHING point of view, you will need somehow to match 50R cable to your vertical wire and for example car antennas will use a small inductor on the base to do that. GP antennas often use a stub or just live with a small mismatch, but use that &quot;virtual ground&quot; (the radials) to match.&lt;/p&gt;&#xA;" OwnerUserId="9517" LastActivityDate="2017-04-15T15:56:35.253" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7485" PostTypeId="2" ParentId="7029" CreationDate="2017-04-16T00:09:34.043" Score="2" Body="&lt;p&gt;A quick google turned up &lt;a href=&quot;https://gist.github.com/magicbug/bf27fc2c9908eb114b4a&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://gist.github.com/magicbug/bf27fc2c9908eb114b4a&lt;/a&gt;, if that's not the one you don't trust. Looks pretty straightforward to me, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also found &lt;a href=&quot;http://www.levinecentral.com/ham/grid_square.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.levinecentral.com/ham/grid_square.php&lt;/a&gt;; there's an email address at &lt;a href=&quot;http://www.levinecentral.com/ham/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.levinecentral.com/ham/&lt;/a&gt; where you could inquire about the source.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-04-16T00:09:34.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7486" PostTypeId="2" ParentId="7191" CreationDate="2017-04-16T01:39:14.457" Score="1" Body="&lt;p&gt;I would imagine that by now, you have completed your homework. But for the sake of closing the topic, the directivity of a 1.25 wavelength, center fed (a very important qualifier!) dipole is ~3.27. Therefore the maximum possible gain is 5.15 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can apply the general formulas for field at any distance from a center fed dipole and solve for the maxima. As they are rather lengthy, if you need the specific E or H field formulas, just post back as a comment and I will supply them.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-04-16T01:39:14.457" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7487" PostTypeId="1" AcceptedAnswerId="7488" CreationDate="2017-04-17T05:12:56.787" Score="4" ViewCount="1746" Body="&lt;p&gt;I'll be visiting home soon after school lets out, and I want to build an AM crystal radio with my little brother. This is the design we'll use:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/m6GF8.gif&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://crystalradio.net/beginners/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://crystalradio.net/beginners/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll be doing my best to explain to him how this works. I understand that when a radio ray passes over an antenna, it generates an alternating electrical field in the antenna wire. If the antenna wire is the correct length for the given radio ray, the electrons in the wire will bounce back and forth in sync with the alternating field, moving faster and faster with each oscillation (resonance). I also understand how audio can be embedded in an AM signal using amplitude modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I do not understand the diagram in the diy linked above.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Where do the electrons flow?&lt;/li&gt;&#xA;&lt;li&gt;Doesn't splitting the circuit in the middle of the coil create two &quot;antennas&quot;, each with a different resonant frequency?&lt;/li&gt;&#xA;&lt;li&gt;What is the purpose of the resistor? I have looked up the internal design of  piezoelectric earpieces, and it does not appear that current flows   all the way through them.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The circuit I've chosen is similar to, but different from, the circuit shown here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/1/13/CrystalRadio.jpg&quot; alt=&quot;wikipedia&quot;&gt;&#xA;&lt;a href=&quot;https://en.wikipedia.org/wiki/Crystal_radio#Design&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Crystal_radio#Design&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was able to find some helpful material on the howstuffworks pages for AM radios, but it is not a one-to-one mapping of the design proposed in the first diagram.&lt;/p&gt;&#xA;" OwnerUserId="9524" LastEditorUserId="4076" LastEditDate="2017-04-17T15:09:49.423" LastActivityDate="2019-01-14T00:36:07.250" Title="Building a crystal radio with my brother. How does this circuit work?" Tags="&lt;am&gt;&lt;crystal-radio&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7488" PostTypeId="2" ParentId="7487" CreationDate="2017-04-17T14:04:09.093" Score="5" Body="&lt;p&gt;I'll try to address your concerns a bit! I'll be simplifying here and there, but I think you'll notice where I'm doing that.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I'll be doing my best to explain to him how this works. I understand that when a radio ray passes over an antenna, it generates an alternating electrical field in the antenna wire.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Close, but not quite :) I'll correct you here, because it makes things easier to explain below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We talk of radio &lt;em&gt;waves&lt;/em&gt;, not &lt;em&gt;rays&lt;/em&gt;. The point is that the wave actually &lt;em&gt;is&lt;/em&gt; the alternating electrical field &lt;em&gt;in the air&lt;/em&gt;. It induces a &lt;em&gt;current&lt;/em&gt; in the antenna. So, any piece of metal that you have lying around is an antenna, and there's electricity flowing through it, because there's radio waves of all kinds of sources (some natural, some man-made, some intentional, some accidental) everywhere! But: these antennas don't work overly well, and also, there's not much power at most wavelengths (see below).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If the antenna wire is the correct length for the given radio ray, &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Here's why I mentioned the wave naming: If the wave's &lt;em&gt;wavelength&lt;/em&gt; happens to be such that the antenna connects a &quot;deep&quot; and a &quot;high&quot; point in the electrical field, you get an especially strong current. So, the length of your antenna has to be in a specific relation to the wavelength of the radio signal you want to capture. If it's a bit &quot;off&quot;, that's not too bad. But you can't properly receive, for example, a 3 MHz (wavelength: 100 m) signal with an antenna that's meant to receive a 2.4 GHz (wavelength: 1/8 m). &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the electrons in the wire will bounce back and forth in sync with the alternating field,&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Exactly! The electrical field that is the wave &quot;pulls&quot; and &quot;pushes&quot; the electrons in the antenna. If we make sure the antenna is sized and shaped just right to push and pull the electrons with the most force possible, we get the strongest reception!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;moving faster and faster with each oscillation (resonance). &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The speed is fixed (it's given by the frequency of the radio wave, which is just the speed of light divided by the wave length), but with resonance, we can make much stronger currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think this calls for an analogy: get a (maybe just in your head) bucket of water. Hold it between your hands. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Slightly push it back  and forth. For some amounts of times pushing the bucket back and forth per second, the ripples on the water aren't really big. But for others, the water gets really troubled and starts making extremely high peaks! You've hit the &lt;em&gt;resonant frequency&lt;/em&gt; of your water/bucket system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With electrons, antennas and a tuned receiver, the same happens: a specific wave frequency (that is, a specific wavelength) is able to rock the electrons &lt;em&gt;just&lt;/em&gt; at the right rate so that the peaks get really high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, in your bucket experiment, the bucket is fixed, and you find the frequency that resonates well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unlike you with your bucket, the frequency is fixed (because you want to receive a specific station!), so you have to vary your bucket: Essentially, tuning your receiver is the same as shrinking or growing your bucket. The bigger the bucket, the lower the resonant frequency becomes.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I also understand how audio can be embedded in an AM signal using amplitude modulation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Great! In essence, staying in the bucket picture: The audio signal would just be how high the peaks got, which is just a result of how strongly you pushed (maintaining the same frequency, of course, that's where it gets difficult with the bucket).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;However, I do not understand the diagram in the diy linked above. Where do the electrons flow? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/956lU.gif&quot; alt=&quot;diagram from DIY article&quot;&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the electrical field pushes and pulls the electrons in the antenna back and forth – that push/pull extends down the antenna wire up into the coil – which basically acts like a reservoir of water. You push in a little current, the next moment you pull it back out, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the size of that reservoir determines at which frequencies we are in resonance. Which means, the amount of windings that are effective in the coil determines how much current can flow into the coil, get its energy stored in the magnetic field of that coil, and then flow back. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;By selecting less or more windings with the alligator clip, you get less or more reservoir – thus, you change the resonant frequency of the antenna/coil system!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Doesn't splitting the circuit in the middle of the coil create two &quot;antennas&quot;, each with a different resonant frequency? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Kind of, yes! But the other half (not attached to the antenna) is attached to ground, so nothing is received there. Keen observation!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the purpose of the resistor? I have looked up the internal design of piezoelectric earpieces, and it does not appear that current flows all the way through them.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Exactly. Piezoelectrics react to &lt;em&gt;changes&lt;/em&gt; in voltage, and other than that, basically isolate. To allow net current flow from the diode to ground, you'll need something that always passes current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, using this resistor means that you won't get all energy that you've received to drive your ear piece, but that's not all that bad.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I hope that gave you a start :) Would love to hear your feedback,  and see you back around here :)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-04-17T14:04:09.093" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="7489" PostTypeId="1" CreationDate="2017-04-17T17:14:21.093" Score="2" ViewCount="692" Body="&lt;p&gt;I am wanting to assemble a Packet Radio solution that will allow for packet radio transmission with a range of about 100 miles or better.  I am not sure what band to use, what radio to use, what antenna to use, and what terminal node controller to use (I have looked at KWM-1200+ Wireless Modem but am unsure if this will meet my needs).  Can any one point me in the right direction for a solid solution that will provide my range needs?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you,&lt;/p&gt;&#xA;" OwnerUserId="9526" LastActivityDate="2017-04-20T17:52:31.567" Title="Packet Radio at 100 miles" Tags="&lt;antenna&gt;&lt;packet&gt;" AnswerCount="3" CommentCount="3" ClosedDate="2017-04-24T21:40:25.040" ContentLicense="CC BY-SA 3.0" />
  <row Id="7490" PostTypeId="2" ParentId="7489" CreationDate="2017-04-17T17:36:09.043" Score="1" Body="&lt;p&gt;That is a pretty good distance.  There are a lot of factors that need to be considered.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, do you have good tall towers on both ends?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, do you have somebody on the other end who will help you do this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Third, is this for emergency services or something like that where it needs 100% reliability?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then of course, why not use the Internet?  It sure would be less expensive.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-04-17T17:36:09.043" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="7491" PostTypeId="2" ParentId="1469" CreationDate="2017-04-17T18:00:32.547" Score="2" Body="&lt;p&gt;For base operations, I am rather partial to the &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00AR09ATA&quot; rel=&quot;nofollow noreferrer&quot;&gt;Super Discone&lt;/a&gt; for transceiving.  I paid $69.95 for it brand new.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dJi8P.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dJi8P.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is very wideband.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that it has a SO-239 connector, so you will want good coax with PL-259 connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then you need a &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00COKNKS8&quot; rel=&quot;nofollow noreferrer&quot;&gt;pigtail adapter&lt;/a&gt; to connect it to the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://cdn2.bigcommerce.com/server2900/47f02/products/1376/images/2384/ARS_CBL_839__92034.1334623048.200.200.jpg?c=2&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://cdn2.bigcommerce.com/server2900/47f02/products/1376/images/2384/ARS_CBL_839__92034.1334623048.200.200.jpg?c=2&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is obviously not as effective as a tuned yagi for point-to-point, but if you are looking for an omnidirectional, flexible base station antenna, this is the one that I chose.  And I'm glad I did.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-04-17T18:05:57.937" LastActivityDate="2017-04-17T18:05:57.937" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7492" PostTypeId="2" ParentId="7489" CreationDate="2017-04-18T01:41:18.100" Score="5" Body="&lt;p&gt;If by &quot;packet radio&quot; you mean the common AX.25 kind used by APRS for example, you can probably forget about it. Otherwise you'll need to use HF, and also find an appropriate mode since there's nothing quite like packet on HF which works reasonably well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A VHF or higher direct link will be difficult. The radio horizon in miles of an antenna at height &lt;em&gt;h&lt;/em&gt; feet is approximately:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 1.23 \cdot \sqrt{h} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You say you have a 100 ft tower on each end, so that's $2 \cdot 1.23 \cdot \sqrt{100} \approx 25 $ miles. To make that work you'll need much taller towers, or perhaps you can place one or both of them on a mountain peak.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might also see &lt;a href=&quot;https://ham.stackexchange.com/q/1921/218&quot;&gt;How do I make a RF propagation map for a repeater?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, you could have a number of intermediate stations relay the signal. For packet radio this is called a digipeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a direct link, you'll have to resort to something fancier. Troposcatter would be fun, but we can probably rule that out due to the very high transmit power that would be required. A communications satellite would be too expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that means HF. At distances of 100 miles, &lt;a href=&quot;https://en.wikipedia.org/wiki/Near_vertical_incidence_skywave&quot; rel=&quot;nofollow noreferrer&quot;&gt;NVIS&lt;/a&gt; propagation is a good bet. You can play with &lt;a href=&quot;http://www.voacap.com/p2p/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt; to get some idea, but the strategy is probably 40 or 80 meters with a low dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can pretty reliably communicate at these distances with such a setup, but getting packet radio specifically to work will be difficult. Packet isn't a good modulation to start, and on HF it's even worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are some people running packet on HF, mostly 20 meters. It runs at 300 baud, and if you ever try it you'll find somewhere between 70% and 100% of what you hear are retransmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course this isn't HF's fault: it's just that packet is horrible. The &lt;a href=&quot;http://freedv.org/tiki-index.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV&lt;/a&gt; modem is a better example. It transmits a 1400 bit per second digital voice codec (&lt;a href=&quot;http://www.rowetel.com/?page_id=452&quot; rel=&quot;nofollow noreferrer&quot;&gt;Codec 2&lt;/a&gt;) with a reliability that's around the same as SSB. That means we can use the SSB mode in VOACAP to get some reliability prediction. For me looks like with a 100W transmitter and a good dipole, about 90% is achievable at night, and 60% during the day. With better antennas, more power, or a lower bitrate, you can get those numbers higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you want to send data, not digital voice, so you'd either need to use the FreeDV modem but send something other than Codec 2 over it, or find some other mode. There are plenty of HF data modes, but none of them are quite like packet.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-04-18T13:08:09.793" LastActivityDate="2017-04-18T13:08:09.793" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7493" PostTypeId="2" ParentId="7436" CreationDate="2017-04-18T02:18:01.870" Score="0" Body="&lt;p&gt;If you have a tree or an eave where you can hang it, I highly recommend the &lt;a href=&quot;http://www.2wayelectronix.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;N9TAX slim-jim&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been using one for years in the woods; I throw a line over a branch as high as I can get it in one of the trees I hang my hammock from, and I occasionally end up in random places where I'm maybe not technically supposed to be camping (I practice leave-no-trace, of course) and my antenna 20' in a tree has never gotten me spotted that I know of.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When my mom got her license, I talked her into one, which wasn't hard as it's about the cheapest worthwhile antenna I've found at under $25, and she's had great success with it hanging under the peak of the (non-metallic) carport roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are methods to mount it to a mast or pole, but they are sub-optimal and usually not very inconspicuous. If you have a place you can hang it, though, it's very low-key, especially in a leafed out tree or against a dark wall.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-04-18T02:18:01.870" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7494" PostTypeId="1" AcceptedAnswerId="7505" CreationDate="2017-04-18T09:39:46.080" Score="5" ViewCount="670" Body="&lt;p&gt;The previous question,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/7489/packet-radio-at-100-miles&quot;&gt;Packet Radio at 100 miles&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and specifically, &lt;a href=&quot;https://ham.stackexchange.com/a/7492/4076&quot;&gt;Phil's answer&lt;/a&gt; raised an interesting question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a 50–100 km distance situation where Line-Of-Sight beams aren't an option for communicating data, can we, given the technological advances of the last decades, again consider troposcatter a sensible mode of operation for moderately high-rate bidirectional communication?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I ask because troposcatter typically has the reputation of needing pretty large TX powers, and pretty high-gain antennas. Which does sound reasonable, since, obviously, we rely on the reflection of something which isn't such a great reflector at all, plus the area we'd illuminate with an isotropic antenna would be huge (considering a sphere with r=100 km or more).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the upside, we get great ranges if we actually do blast out a lot of power and aim large antennas at the horizon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd assume you'd want to operate somewhere around 2.3 GHz. The best model description I've found (that wasn't &quot;oh, we've always used these 2 models, and it doesn't really work all that well, but we didn't check for other models&quot; &lt;a href=&quot;http://www.nitehawk.com/w3sz/W3SZ-PackRatsConference2014.pdf&quot; rel=&quot;noreferrer&quot;&gt;example&lt;/a&gt; ) is from this nearly ancient Master's thesis:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;UNDERSTANDING TROPOSCATTER PROPAGATION&lt;br&gt;&#xA;  by&lt;br&gt;&#xA;  JOSEPH HENDERSON REYNOLDS &lt;br&gt; B.S., United States Air Force Academy, 1982&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.dtic.mil/dtic/tr/fulltext/u2/a220969.pdf&quot; rel=&quot;noreferrer&quot;&gt;available online&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After inspecting the summaries on the different models, I think that for VHF, UHF frequencies, probably what the call CCIR method II (by Boithias and Battesti) is what I'd want to look at. However, best graph I could produce on short notice (p.162 from that thesis):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WLA9e.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WLA9e.png&quot; alt=&quot;att CCIR method II&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;for other frequencies, a factor of $30\log f_\text{GHz}$ is added. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;so, I'd need to add another 3 dB; OK. Now, going for a &amp;lt; 1% outage time, I'd have to read both the upper (year average) and lower (worst month) chart's lower two curves (99% and 99.5% temporal availability). That yields something between 212 dB and 216 dB (average) / 218 dB to 222 dB (worst month) attenuation for a 150 km link.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, assuming we don't want to overdo it with antennas, an antenna gain of ~ 18dB on each end sounds realistic. Swinging with -220 dB tropo path loss, we thus get an overall loss of -184 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Admittedly, not very little, still much better than GPS reception, and we legally get up to 10 MHz of bandwidth in that band! (as far as I understand)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ok, rough capacity estimate: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uOnSa.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uOnSa.png&quot; alt=&quot;channel capacity&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rolling a few numbers in my head, assume we want to get a code bit rate of let's say 200 kb/s. We'd want to stay a solid factor of 4 below the channel capacity (&lt;strong&gt;please correct me!&lt;/strong&gt;), so that requires about 46 dBm transmit power – 40 W. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think the atmosphere will allow for reliable amplitude estimation, (&lt;strong&gt;please correct me!&lt;/strong&gt;) so I'd roll with QPSK for an initial estimate. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That gives me the rough feeling that we have plenty of headroom (like, 99 times what we use) to add robustness – be it through spreading, channel codes, or stupid spectral repetition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This all breaks down on one thing, though:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could find out &lt;em&gt;nil&lt;/em&gt; about the properties of the 2.3 GHz tropo channel w.r.t.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Doppler Spread&lt;/li&gt;&#xA;&lt;li&gt;Coherency Time&lt;/li&gt;&#xA;&lt;li&gt;Deep Fade probabilities&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I might very much be coming from an indoor / close-range background, but this feels like I might be missing something important. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Does anyone have info on the above properties of the wireless troposcanner channel&lt;/strong&gt;?&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Am I looking the wrong way, using the wrong tools to understand that channel?&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;What (amateur) digital modes over tropo are &lt;em&gt;state of the art&lt;/em&gt; (rather than &lt;em&gt;used because everyone uses them since the 70s&lt;/em&gt;)?&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Is a 40W 2.3 GHz amp suitable for PSK realistic?&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="8717" LastEditDate="2020-04-04T02:45:26.627" LastActivityDate="2020-04-04T02:45:26.627" Title="Troposcatter: really all that bad?" Tags="&lt;digital-modes&gt;&lt;propagation&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;microwave&gt;" AnswerCount="2" CommentCount="13" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7495" PostTypeId="2" ParentId="6452" CreationDate="2017-04-18T12:17:16.667" Score="2" Body="&lt;p&gt;I have just joined so have to answer instead of commenting (not enough reputation yet). I have one of these receivers and know a little about them (I have to say it performs excellently and is very nice to use).&#xA;They are now fairly old so are a bit prone to dry solder joints and dry caps. There are quite a few plugs/ connectors that can occasionally give trouble too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power supply uses a linear regulator with about 8v across it at &gt;1A and runs quite hot, which commonly gives trouble and heats up the area around it, resulting in accelerated aging of some joints, caps, etc. A small well shielded and properly bypassed DC-DC buck converter cures this - they are very common and cheap now, well worth doing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's worth mentioning that there is a small 3v lithium backup battery on the RAM unit, if this goes flat the radio goes stone deaf (brain dead). I think it's supposed to last many years but there is a procedure for replacing it before this happens (maintaining the back up voltage at all times!) or replacement non-volatile &quot;RAM&quot; units are available (it is possible to reprogram it but it's a bit of a muck about).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a very useful and welcoming users group at &lt;em&gt;&lt;a href=&quot;https://groups.yahoo.com/neo/groups/ICOMR71A/info&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://groups.yahoo.com/neo/groups/ICOMR71A/info&lt;/a&gt;&lt;/em&gt; which has lots of helpful info and supportive members that you might want to join (free). It's a radio that is well worth fixing and (relatively) easy to work on if your temporary repair fails... 73&lt;/p&gt;&#xA;" OwnerUserId="9531" LastActivityDate="2017-04-18T12:17:16.667" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7496" PostTypeId="2" ParentId="7489" CreationDate="2017-04-20T17:52:31.567" Score="1" Body="&lt;p&gt;Take a look at this article. &lt;strong&gt;Radio communication via Near Vertical Incidence Skywave propagation: an overview&lt;/strong&gt;. I'm not sure from my reading of the URL that the signals would make 100 miles.  I understand the technique is being used in ARES where communications have been destroyed by a natural disaster.  Article has some data transmission rates for various protocols.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://link.springer.com/article/10.1007/s11235-017-0287-2&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://link.springer.com/article/10.1007/s11235-017-0287-2&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9544" LastActivityDate="2017-04-20T17:52:31.567" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7497" PostTypeId="1" AcceptedAnswerId="7498" CreationDate="2017-04-20T18:12:50.717" Score="0" ViewCount="223" Body="&lt;p&gt;Trying to figure an antenna for the Si4012 RF chip. Page 26 of &lt;a href=&quot;https://www.silabs.com/documents/public/application-notes/AN639.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.silabs.com/documents/public/application-notes/AN639.pdf&lt;/a&gt; talks about feeding the two sides of the loop antenna through two pull-up inductors (LP and LM) which it fails to provide any values for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also a Word document named &lt;em&gt;Panic Button Differential Loop(Printed) Along the PCBCircumference in the 434 MHz Differential Antenna Matrix&#xA;(WES0042-01)&lt;/em&gt; whose link I can not find anymore that presents a diagram figuring the same two inductors with &quot;tbd&quot; values. And they never got discussed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, I have found this document: &lt;a href=&quot;https://www.silabs.com/documents/public/application-notes/AN436.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.silabs.com/documents/public/application-notes/AN436.pdf&lt;/a&gt; that on page 3 (as well as throughout the file) gives a diagram and some values for a pull-up inductor &lt;code&gt;Lchoke&lt;/code&gt; that appears to have the same purpose as the one I am asking about. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thing is this one is for a single ended antenna while my design comprises a differential antenna. Would it be safe to take out the value from this pdf and use it on my design ? And another  detail - I suppose THT inductors (as well as caps / resistors) are out of question on this side of the PCB and 434 MHz, correct ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;edit&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I still don't get how to size the RF choke. In the &lt;a href=&quot;https://www.silabs.com/documents/public/application-notes/AN436.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.silabs.com/documents/public/application-notes/AN436.pdf&lt;/a&gt; they ate giving the example of 315 MHz. |Z_load| here is around 56 ohm and the recommended inductance for the choke is 270 - 390 nH, thus making for an impedance |Z_choke| of 534 - 771 ohm, roughly tenfold compared to Z_load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my design, however, |Z_load| is somewhere between 500 and 600 ohm (434 MHz differential antenna). Wouldn't it be required to pick an inductor having its impedance in the 5k - 6k ohm interval in order to actually be effective at blocking the fundamental + first few armonics ?&lt;/p&gt;&#xA;" OwnerUserId="8811" LastEditorUserId="8811" LastEditDate="2017-04-21T16:22:44.493" LastActivityDate="2017-04-21T16:22:44.493" Title="pull-up inductors for a differential PCB trace antenna" Tags="&lt;antenna-construction&gt;&lt;inductor&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7498" PostTypeId="2" ParentId="7497" CreationDate="2017-04-20T19:25:41.087" Score="2" Body="&lt;p&gt;The value is specified as &quot;large&quot;. The idea is to use the inductors to provide a DC bias without affecting the RF circuit. This works because an inductor has 0 impedance at DC, but increases with frequency. With a sufficiently &quot;large&quot; inductance, by the time you get to 434 MHz the impedance will be so large that it's effectively an open circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wouldn't say through-hole components are &quot;out of the question&quot;. The important thing is to keep the layout as compact as possible, which is easier with smaller components. Leads may add additional inductance compared to surface mount components, but frequently that's either insignificant, or can be compensated.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-04-20T19:25:41.087" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="7499" PostTypeId="2" ParentId="5797" CreationDate="2017-04-20T22:17:20.417" Score="1" Body="&lt;p&gt;I made my 5 element with the driven split element like a diapole. I used cu tubing flatening one end and screwing them to a wolmonized square boom about 1/4&quot; apart on boom direct feeding coax with terminal lugs. Of course you must drill hole in flattened end for wood screw hole.Cut them a little shorter than wanted length,about 1/4 inch. I used ss cotter keys at both ends of driven sliding them equal distances in or out to match. Worked great,flat match for 5 element beam.&lt;/p&gt;&#xA;" OwnerUserId="9546" LastActivityDate="2017-04-20T22:17:20.417" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7500" PostTypeId="1" AcceptedAnswerId="7504" CreationDate="2017-04-21T01:34:30.123" Score="1" ViewCount="606" Body="&lt;p&gt;I am referring to the Harris Falcon III designed for military.  It has a frequency range from 30MHz - 870MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, when I look at commercial radios, their frequency ranges are usually limited to specific bands (i.e. 137-174MHz and 400-480MHz).  This makes me wonder why commercial radios don't support nearly the same range of frequencies.  Is it more due to legal reasons (such as frequency allocation) or to technical reasons?&lt;/p&gt;&#xA;" OwnerUserId="9547" LastEditorUserId="8717" LastEditDate="2019-12-05T20:05:42.717" LastActivityDate="2019-12-05T20:05:42.717" Title="How is the PRC-152 able to achieve such a wide frequency range?" Tags="&lt;legal&gt;&lt;frequency&gt;&lt;fcc&gt;&lt;military-surplus&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7501" PostTypeId="1" AcceptedAnswerId="7503" CreationDate="2017-04-21T04:41:35.233" Score="4" ViewCount="18656" Body="&lt;p&gt;The Baofeng UV-5R style radios have a 2 line display that can display the Name, Frequency, OR Number of the selected memory location for each of 2 memory locations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to display the Name AND Frequency using both lines for just one memory location?&lt;/p&gt;&#xA;" OwnerUserId="4748" LastActivityDate="2017-09-09T02:35:10.867" Title="Can a Baofeng UV-5R Display Both Name and Frequency Simultaneously?" Tags="&lt;baofeng&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7502" PostTypeId="1" AcceptedAnswerId="7506" CreationDate="2017-04-21T06:35:00.877" Score="0" ViewCount="284" Body="&lt;p&gt;The designs I have seen all seem to have this surrounding stitched-to-the-ground copper pour surrounding them. Why put it on a differential antenna PCB like below ? And why are those thin lower left traces brought there for ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: For the thin lower left traces question - what I wanted to ask is why are they not connected to a MCU, or, in case the pictured IC chip already contains a MCU, then why are they not terminated onto some external connector so the MCU can be programmed ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MORE EDIT: The image below was taken from page 29 of &lt;a href=&quot;http://www.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=swra161b&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=swra161b&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/P8sZ7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/P8sZ7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8811" LastEditorUserId="8811" LastEditDate="2017-04-21T11:03:22.300" LastActivityDate="2018-10-24T06:19:31.580" Title="guard planes in differential antenna PCB designs" Tags="&lt;grounding&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7503" PostTypeId="2" ParentId="7501" CreationDate="2017-04-21T08:35:41.143" Score="6" Body="&lt;p&gt;No, you cannot display &quot;Name &amp;amp; Frequency&quot; if the unit is in &quot;Channel Mode&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;what you could do is program (part of) the frequency in the &quot;Name field&quot; of the channel. This way it helps you, like a hint, of what frequency the channel is set to. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously it will get more complicated if you have different RX and TX frequencies programmed in the Channel, you need to be very creative with the name you will give it. (if not using standard offsets that is, as standard offsets will display as a little &lt;code&gt;+&lt;/code&gt; or &lt;code&gt;-&lt;/code&gt; in the display)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second line of the display is really for A/B of your VFO.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2017-04-21T08:35:41.143" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7504" PostTypeId="2" ParentId="7500" CreationDate="2017-04-21T08:40:59.153" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it more due to legal reasons (such as frequency allocation) or to technical reasons?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Both. And the dominant reason is, as always, cost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll illustrate in RX first:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, radios like these work by mixing the RF signal down – in this case, usually to a fixed IF (intermediate frequency), from which the actual demodulator (AM, FM, digital...) generates the message signal (audio, data...). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, for that mixer, you need a local oscillator (LO) that usually has to be&#xA;adjustable. The frequency of that oscillator needs to be $f_\text{RF}-f_\text{IF}$ – or an integer factor of that, in fact, since mixers produce more than one intermodulation product:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your average mixer, fed with a tone of $f_\text{LO}$ on one input, and the antenna on the other, will convert (there's a bit of a mathematical derivation that I'm skipping here) signal from $f_\text{RF}$ to $f_\text{RF}-f_\text{LO}=f_\text{IF}$. There's nice filters around $f_\text{IF}$, so that signals a little below or above $f_\text{RF}$ don't interfere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, what it'll also do is convert $f_\text{other}= n\cdot f_\text{IF}\pm m\cdot f_\text{LO}$ to $f_\text{IF}$, for a lot of different values of $n,m\in \mathbb N$. Which means: Assuming you have IF at 27 MHz, and you use a 100 MHz LO, you want to receive 127 MHz (i.e. you convert 127 to 27 MHz, because that's your IF where your demodulator gets it).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, sadly, you also get (2·100+27) MHz, (2·100-27) MHz and other intermodulation mapped onto your IF. Because the signals at 227 and 173 MHz are not of interest (but interfere), you need frontend filters to cut them out before they even reach the mixer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Analog filters are, with a high probability, the most expensive part in a professional narrowband radio. The more bands you serve, the more filters you'll need – in fact, you'll find that you'll get multiple parallel receiver chains in such devices, simply because generating a range of good LO frequencies can get daunting, and also, because impedance matching of &lt;em&gt;anything&lt;/em&gt; only applies to a limited range of frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In TX, very much the same applies, but you might even have to be more careful, because if you forget to filter a strong unwanted intermodulation product, you're not hurting yourself, you're interfering with others. And, fun fact, if you have a frequency duplex device where the receiver might be active while the transmitter is, too, but on a different frequency, and you mess up the crosstalk suppression due to not having sufficient TX filters, you might simply fry your sensitive receiver frontend with the output of your transmit PA. In less than a couple microseconds, in fact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I'm coming from a SDR background, and &quot;30–870 MHz&quot; doesn't sound all that enormously much to me – we SDR folks typically trade filter quality for frequency agility during research and design, and then, as soon as we're ready to prototype things for real usage, add filters when we know where in frequency we're going to operate. So, for the simple prototyping phase, the whole LO generation, mixing and filtering chain can fit inside a single IC or on a rather compact board. Take the popular RTL-SDR dongles: They are, too, IF receivers, but their coverage is, depending on the tuner/mixer IC used, is e.g. 24–1800 MHz. And that's with a sub-$3 tuner IC! Of course, selectivity of these devices is horrible compared to a high-end commercial receiver, and the phase stability and dynamic range can be improved, but that are all cost points that the designers of these (originally TV) receivers had to avoid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can make all that a bit better – and you'd end up with devices like &lt;a href=&quot;https://www.ettus.com/product/details/USRP-B200mini&quot; rel=&quot;nofollow noreferrer&quot;&gt;USRP B200mini&lt;/a&gt;, which can tune their LO from 70 to 6000 MHz and allow ~56 MHz to be received at any instant – so your lowest frequency is (70-56/2) MHz = 32 MHz, your highest 6028 MHz.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-04-21T08:40:59.153" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7505" PostTypeId="2" ParentId="7494" CreationDate="2017-04-21T12:38:12.730" Score="2" Body="&lt;p&gt;I don't think a better answer will come along, so I'll summarize a combination of assembled anecdotes and opinion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as I can tell, your calculations are accurate. I did a little research for &lt;a href=&quot;https://ham.stackexchange.com/questions/1497/can-tropospheric-scatter-effect-be-used-by-802-11-links&quot;&gt;Can tropospheric scatter effect be used by 802.11 links?&lt;/a&gt; and determined the requirements aren't absurd, and at least within the grasp of a typical amateur.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anecdotally, I've read of hams doing troposcatter on 2 meters. Many of the troposcatter studies I've seen don't consider anything below 2.4 GHz, so I guess it's possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course a 40W amplifier for 2 meters is common ham gear. 2.4 GHz isn't nearly as popular for hams, but a quick search turned up plenty of 10W amplifiers intended for 2.4 GHz WiFi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also was not able to find any details on the channel besides loss. However, I see many examples of military systems like these:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Siqv6.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Siqv6.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some are mounted on trucks. I've read each horn has two polarities. We can infer the quad antenna diversity setup is to counter channel fading which must be significant. Although, the military certainly has higher reliability requirements than an amateur. HF channels have similar properties and that hasn't stopped anyone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anecdotally, most of the amateur troposcatter seems to be SSB or CW from VHF DX enthusiasts. I'm not active in this space personally, but I do know some weak-signal digital modes are gaining popularity there. WSJT is notable, and JT65 in particular which I have used personally on HF. It's very slow and not meant to exchange anything but a call sign and a signal report over a QSO that lasts several minutes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;D-STAR is a popular GMSK digital voice mode since Icom puts it in all their radios. It must be the most common digital mode on amateur VHF with a moderate bit rate. It has a data mode which enables a payload of arbitrary data instead of the usual proprietary AMBE codec for voice. I've no idea how suitable for troposcatter it would be.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-04-21T12:38:12.730" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7506" PostTypeId="2" ParentId="7502" CreationDate="2017-04-21T13:52:53.740" Score="4" Body="&lt;p&gt;The PCB shown here is a demo board, described in &lt;a href=&quot;http://www.ti.com/lit/an/swra118/swra118.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this TI application note&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Point is that all the components in the schematic (p.4) that are not on top of this design are on the bottom side – and that includes two sockets, one for power only, and one that seems to carry serial data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why the lines go from that bottom copper layer up to the visible side of the board and back down? Layout! Sometimes, it's impossible to connect two things without making two lines cross. So, you build a bridge by taking one trace to the other side of the board and then back after crossing the other trace.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more info, you'd have to read that IC's data sheet, and the specification of the platform – someone certainly wrote down which pins on these (hidden) connectors do what, and the PCB designer had to live with that. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Generally, having a ground plane next to an unbalanced RF-carrying trace is a common technique – a &lt;em&gt;coplanar waveguide&lt;/em&gt;. You're right, in this case, the majority of E-Field should definitely be happening between the two balanced traces, so that's not the motivation here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you, hower, look into the document linked above, you'll find this anotated photomask of the top layer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yu3Iu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yu3Iu.png&quot; alt=&quot;copper layer&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The text further up claims that the Dipole is already impedance matched, so that basically leaves geometrically practical aspects (you need have some sort of feed towards the antenna, and you don't want to start making funky non-rectangular ground pours, and if possible, the ground should be parallel to the dipole), aesthetics, and the fact, that, at least a little bit, the traces and components close to the RF pins on the IC might interact, so it's usually desirable to have them surrounded by ground.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="13435" LastEditDate="2018-10-24T06:19:31.580" LastActivityDate="2018-10-24T06:19:31.580" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="7507" PostTypeId="2" ParentId="7501" CreationDate="2017-04-21T14:28:01.037" Score="0" Body="&lt;p&gt;Not sure about that model, but the btech (appears to be another name for the same hardware) can sync the name and frequency. It was /is an option, if I had my radio I could look it up. It might be only in the newer radios/firmware. &lt;/p&gt;&#xA;" OwnerUserId="9550" LastActivityDate="2017-04-21T14:28:01.037" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7508" PostTypeId="1" CreationDate="2017-04-22T04:38:55.290" Score="1" ViewCount="152" Body="&lt;p&gt;My team and I are using a SDR, GNU Radio, and some other hardware assembled into a custom tablet and a Python program we are writing to detect &lt;a href=&quot;https://en.wikipedia.org/wiki/IMSI-catcher&quot; rel=&quot;nofollow noreferrer&quot;&gt;IMSI Catchers&lt;/a&gt;. I have some Packet Capture files with known IMSI Catcher data I am going through to implement the detection metrics but it has been very difficult to find the data I need about GSM other than very surface data about the protocols like TDMA, CDMA, etc. or completely incomprehensible terrible documentation about the packet structure drawn in ASCII.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Are there any &lt;em&gt;good&lt;/em&gt; resources about the GSM protocol and packet contents?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most importantly with descriptions of all data fields for all packet types.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Some background, one issue that I am trying to solve and can not find documentation for is what packets, and their fields, contain information to build a list of a cells neighbors location area codes (LAC). I have found packets with neighboring cell information:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Layer GSM_A.DTAP:&#xA;    Measurement Results&#xA;    Protocol Discriminator: Radio Resources Management messages (6)&#xA;    .... 0110 = Protocol discriminator: Radio Resources Management messages (0x06)&#xA;    0000 .... = Skip Indicator: No indication of selected PLMN (0)&#xA;    ..11 1111 = RXLEV-FULL-SERVING-CELL: &amp;gt;= -48 dBm (63)&#xA;    .... .111  100. .... = BSIC-NCELL: 60&#xA;    .... ...0  01.. .... = NO-NCELL-M: 1 neighbour cell measurement result (1)&#xA;    RXLEV-SUB-SERVING-CELL: &amp;gt;= -48 dBm (63)&#xA;    0001 0... = BCCH-FREQ-NCELL: 2&#xA;    0... .... = BA-USED: 0&#xA;    .0.. .... = MEAS-VALID: The measurement results are valid&#xA;    ..11 1111 = RXLEV-NCELL: 63&#xA;    .... 000. = RXQUAL-SUB-SERVING-CELL: BER &amp;lt; 0.2%, Mean value 0.14% (0)&#xA;    .000 .... = RXQUAL-FULL-SERVING-CELL: BER &amp;lt; 0.2%, Mean value 0.14% (0)&#xA;    .0.. .... = DTX-USED: DTX was not used&#xA;    0... .... = 3G-BA-USED: 0&#xA;    DTAP Radio Resources Management Message Type: Measurement Report (0x15)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;But most docs don't even have descriptions of all of the acronyms although I have found most now, and are missing packet types I am trying to examine. There are still about 15 other metrics I need to find also, if there is authoritative documentation on GSM somewhere neither I nor my team have been able to find it.&lt;/p&gt;&#xA;" OwnerUserId="8588" LastEditorUserId="4076" LastEditDate="2017-04-22T12:34:38.673" LastActivityDate="2017-04-22T12:34:38.673" Title="Information on GSM" Tags="&lt;packet&gt;&lt;gnuradio&gt;" AnswerCount="0" CommentCount="5" ClosedDate="2017-04-24T21:39:57.600" ContentLicense="CC BY-SA 3.0" />
  <row Id="7509" PostTypeId="1" AcceptedAnswerId="7689" CreationDate="2017-04-22T12:27:18.357" Score="1" ViewCount="289" Body="&lt;p&gt;I seem to have bricked my VX-8DE yesterday after cloning it from a PC (using CHIRP)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was able to copy the data from the radio without problems. I edited it in chirp, then sent it back to the radio. After cloning was finished the VX-8 restarted and started to behave in a strange manner. It was barely reacting to any input (be it keyboard or knob). The VFO A display showed something along the lines of &lt;code&gt;b1 30.303&lt;/code&gt;, which I suppose might have been an error message of some kind, but I wasn't able to find any reference to it. The VFO B was set to the frequency I set it to before cloning and I wasn't able to change it by turning the knob. After a while the radio stopped reacting to the input entirely so I removed and reconnected the battery. Since then I wasn't able to power the radio on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to enter both microprocessor reset mode (BAND+HM/RV+Internet+Power) and the set reset mode (BAND+V/M+Power) but they won't power on the radio either. When I connect the radio to the charger it doesn't show anything on the screen and the busy LED which normally indicates the charging status doesn't lit up either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, has this happened to anyone else, and if yes were they able to get the radio working on their own? Mine is still covered by the warranty, so I'll be posting it to the local distributor on Monday, but until then I could try other options, if anyone knows of any.&lt;/p&gt;&#xA;" OwnerUserId="9145" LastEditorUserId="76" LastEditDate="2017-04-22T13:42:59.790" LastActivityDate="2017-06-01T19:52:55.577" Title="Yaesu VX-8DE bricked after cloning. Any methods to revive it?" Tags="&lt;ht&gt;&lt;yaesu&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7510" PostTypeId="2" ParentId="7501" CreationDate="2017-04-22T12:42:47.590" Score="8" Body="&lt;p&gt;Yes, kind of. You can program the A and B settings separately. Set channel A to display name, and set B to display frequency. Also, set the receiver to only listen to the monitored channel to ensure you won't run into problems. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, in channel mode, use your programmed station (ex station 12) on both A and B simultaneously. A will show your channel name alias, and B will show the frequency. It is a workaround, but it will give you what you're looking for. &lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2017-04-22T12:42:47.590" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7511" PostTypeId="1" AcceptedAnswerId="7514" CreationDate="2017-04-23T13:31:35.717" Score="6" ViewCount="1528" Body="&lt;p&gt;I just got my HAM license, and I have been thinking about getting a 1×3 vanity that I can remember more easily.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This question is partially in reference to &lt;a href=&quot;http://wireless.fcc.gov/services/index.htm?job=call_signs_3&amp;amp;id=amateur&amp;amp;page=1&quot; rel=&quot;noreferrer&quot;&gt;this passage on the FCC site&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A club station trustee of a club that has been assigned a vanity call sign is not eligible to apply for any additional vanity call signs.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;At first glance, this seems to mean that you cannot have a personal vanity call sign and a club station vanity callsign, but I'm skeptical about my ability to properly interpret this language.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More broadly, my question is that if I get a vanity callsign, is there any reason I might regret it later on or be restricted from certain things (for example, getting a different vanity callsign later on)?&lt;/p&gt;&#xA;" OwnerUserId="9480" LastEditorUserId="4076" LastEditDate="2017-04-23T17:15:43.870" LastActivityDate="2017-04-26T22:08:14.853" Title="Is there any downside to getting a vanity callsign?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;callsign&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7512" PostTypeId="1" AcceptedAnswerId="7516" CreationDate="2017-04-23T17:54:09.940" Score="0" ViewCount="143" Body="&lt;p&gt;When connecting mobile to transmitter with RF cable:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does RF connector provide complete shielding for the transmitter signal ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it  prevent the mobile from receiving other signals from other sources ? Is it possible to shield transmitter while still receiving other signal sources?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you.&lt;/p&gt;&#xA;" OwnerUserId="9564" LastEditorUserId="9564" LastEditDate="2017-04-28T08:11:53.807" LastActivityDate="2017-04-28T08:11:53.807" Title="RF connector between mobile phone and transmitter = complete shielding?" Tags="&lt;mobile&gt;&lt;rf-power&gt;&lt;rtl-sdr&gt;&lt;hackrf&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7513" PostTypeId="2" ParentId="3716" CreationDate="2017-04-23T21:11:35.357" Score="4" Body="&lt;p&gt;I have an IC 207H with a HM-133. The HM-133 came in a couple of flavors starting with the 133 then 133v HM-98s etc none of which replaced the HM-98 which came with the 207H. Dispite what ICOM factory service or the makers of the knock offs will tell you it just ain't the same. So get a real HM-98.  Which will allow the 207H programming to work from the mic. The 133 and others will require programming manually as per the owners manual.&#xA;Good Luck 73s&lt;/p&gt;&#xA;" OwnerUserId="9565" LastActivityDate="2017-04-23T21:11:35.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7514" PostTypeId="2" ParentId="7511" CreationDate="2017-04-23T23:23:37.297" Score="3" Body="&lt;p&gt;I can't think of any downside, no.  And that rule does not prevent you from picking one right now, whether or not you become a club station trustee in the future.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Myself, I have had three different callsigns.  My first two were the great in Morse but this last one is horrible in it.  But it works fine for voice.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I never thought about wanting to change what they gave me, any more than I would change the name my mama gave me.  The Funny Candy Company gives, and I took.  Kinda like the Army.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you do decide to pick a callsign, do your research, and as you are looking, think about what it will &quot;mean&quot; - Like this:  My second callsign xxxIWL ended in &quot;I Want Love&quot; and my current callsign xxxEM ends in &quot;Easy Money&quot; when I was younger, and &quot;ElMer&quot; now.  Whatever you pick, be prepared to live with it for a while.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That rule you cited deals specifically with amateur radio club station trustees, as you pointed out.  But that rule is after-the-fact.  Right now you are before-the-fact as you pick your first vanity call.  Then later, while your vanity callsign is being used by a club, you could not then try to get another vanity call for yourself.  You could withdraw as the club's station trustee and force the club to use someone else's callsign, of course, but you can't have two callsigns at the same time.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will not be restricted in any other way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let me tell you a story about how I used my callsign in a couple of very public ways.  And why I am so glad it works so well in voice and visually in digital and on my car.  You might find an idea or two in this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First of all are the vanity plates for your car.  Most states will give them to you for free.  &lt;a href=&quot;https://www.google.com/search?q=fcc%20%22amateur%20radio%20is%20a%20public%20service%22&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio is a public service&lt;/a&gt;.  And by free, I mean that in Alaska they are totally free.  Not even the normal license plate fees.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had vanity plates my whole driving life.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, I also worked with the Alaska Division of Emergency Services, and the National Guard building packet BBS ID'd itself with my callsign for about a decade.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Packet radio rules are a lot like repeaters.  You don't always have to be there; you are required to have positive control at all times, and the operation can be automatic.  Also, I had to append a &quot;-1&quot; to my callsign for the PBBS; the ADES packet BBS was xxxEM-1 so I would be allowed to check into it from home or my car using my own callsign.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We actively sought out local hams when there were disasters, like the 37,000 acre Big Lake wildfire.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.fcc.gov/general/amateur-radio-services-and-public-safety-communications&quot; rel=&quot;nofollow noreferrer&quot;&gt;The FCC established amateur radio as a voluntary, non-commercial, radio communications service. It allows licensed operators to improve their communications and technical skills, while providing the nation with a pool of trained radio operators and technicians who can provide essential communications during emergencies.&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alaska has embraced that concept.  The Packet BBS was a great way to get messages out to large numbers of civilians, and to organize volunteers.  Since it was operated from the SEOCC at Ft. Richardson, adjacent to the AST dispatch center, it became a great way to send out sitreps and collect information for use in decision-making by the Incident Commanders.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back to the vanity license plates, the responders in the field are always glad to be able to quickly look at a car and see that it is a ham and not just anyone.  They have come to rely on our help.  As you get closer then they  can look at your window sticker, if you have rank, to determine whether or not to salute.  But by then they are at ease because hams are pretty much a known quantity.  People who violate the rules do not last in this hobby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you get your preferred callsign, my advice is to get those plates. You have the ticket.  So now you have the right to display it for all to see.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No matter what you choose to do let me say &lt;strong&gt;Welcome to the community.&lt;/strong&gt;  I trust you will enjoy being a ham for years to come.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-04-24T00:42:15.963" LastActivityDate="2017-04-24T00:42:15.963" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7515" PostTypeId="2" ParentId="7511" CreationDate="2017-04-24T02:31:05.630" Score="3" Body="&lt;p&gt;There's no downside. After you've obtained a vanity call, you can always request a new sequentially assigned call. And as an individual, you can apply for a new vanity call even if you already have one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The passage you cite is due to a restriction on clubs: they may have only one vanity call sign. It's from &lt;a href=&quot;https://apps.fcc.gov/edocs_public/attachmatch/FCC-09-102A1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;WT Docket No. 09-209&lt;/a&gt; which I haven't read, but I did read the &lt;a href=&quot;http://www.arrl.org/news/fcc-issues-em-report-and-order-em-on-vanity-and-club-station-call-signs&quot; rel=&quot;nofollow noreferrer&quot;&gt;summary from the ARRL&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Limits on Club Station Licenses: Club stations may hold only one vanity call sign, but may hold an unlimited number of sequential call signs. Club stations currently holding more than one vanity call sign may renew or modify their existing station license grants, but not obtain any additional vanity call signs. The prohibition on obtaining additional vanity call signs includes in memoriam call signs formerly assigned to deceased members of the club.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's not clear to me if a club can obtain a vanity call, then relinquish it to obtain another.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-04-24T02:31:05.630" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7516" PostTypeId="2" ParentId="7512" CreationDate="2017-04-24T02:45:17.210" Score="2" Body="&lt;p&gt;Do you mean removing the antennas from each device, and connecting them directly with a piece of coax? Yes, that does provide complete shielding. Though you'd want an attenuator to avoid overloading or possibly damaging the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately this will also render the phone incapable of receiving other signals. No way around that with a passive device, due to &lt;a href=&quot;https://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;reciprocity&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-04-24T12:23:44.090" LastActivityDate="2017-04-24T12:23:44.090" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7517" PostTypeId="1" AcceptedAnswerId="7519" CreationDate="2017-04-24T08:13:06.167" Score="2" ViewCount="643" Body="&lt;p&gt;Looking at the waterfall spectrum of any ordinary FM public broadcast station (88-108 MHz), during the silence, there are 3 or 5 visible peaks. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What are they?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's possible this has a trivial answer, but I have not found a very satisfying answer. So please explain in a bit more than one sentence. &#xA;Here's a picture of what I mean.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GyOr8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GyOr8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6563" LastActivityDate="2017-04-24T21:41:53.863" Title="What are the 3 or 5 peaks in an FM broadcast during silence?" Tags="&lt;software-defined-radio&gt;&lt;frequency&gt;&lt;fm&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7518" PostTypeId="2" ParentId="7517" CreationDate="2017-04-24T08:28:44.837" Score="2" Body="&lt;p&gt;There's the stereo sum channel (Left + right), a 19 kHz pilot tone, the stereo difference channel (L-R), and the RDS carrier. Depending in where you are, the station might have further digital channels for additional systems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, if your reception is very strong (which it seems to be), you might be saturating your RX amplifier and see &quot;phantom&quot; intermodulation products that aren't actually on the air. Reduce your RX gain. If some peaks go away faster then your main peak, than you've found those.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you massively overpower your RX, your ADC will clip, and things will look horrible:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://pbs.twimg.com/media/C7bnK15WkAE8iVS.jpg&quot; alt=&quot;Clipping&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://twitter.com/uber_security/status/844116167870627841&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-04-24T08:34:04.473" LastActivityDate="2017-04-24T08:34:04.473" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7519" PostTypeId="2" ParentId="7517" CreationDate="2017-04-24T08:30:40.543" Score="4" Body="&lt;p&gt;The way that stereo sound is broadcast using a single 'channel' is to broadcast the L+R (the sum of the left channel and the right channel) signal on the centre frequency, and include the L-R (difference between the left and right channels) signal modulated on a frequency at a known difference from the main carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you are seeing is the main (L+R) carrier, the two sidebands of the 'pilot' 19kHz frequencies, and the two sidebands of the 38kHz (L-R) sub-carrier, of a stereo broadcast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;https://en.wikipedia.org/wiki/FM_broadcasting#Stereo_FM&quot; rel=&quot;nofollow noreferrer&quot;&gt;this Wikipedia entry&lt;/a&gt; for more details, as well as information about the original amateur radio origin of this system.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-04-24T08:30:40.543" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7520" PostTypeId="2" ParentId="3579" CreationDate="2017-04-24T08:40:03.357" Score="1" Body="&lt;p&gt;I want to add to Phils answer. The &lt;a href=&quot;https://en.wikipedia.org/wiki/Low_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;VLF&lt;/a&gt; around 3-30 kHz are used for submarine communication. From &lt;a href=&quot;https://en.wikipedia.org/wiki/Communication_with_submarines&quot; rel=&quot;nofollow noreferrer&quot;&gt;WikiPedia&lt;/a&gt;: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;VLF radio waves (3–30 kHz) can penetrate seawater to a depth of approximately 20 meters. Hence a submarine at shallow depth can use these frequencies. A vessel more deeply submerged might use a buoy equipped with an antenna on a long cable. The buoy rises to a few meters below the surface, and may be small enough to remain undetected by enemy sonar / radar.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;...&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Because of the narrow bandwidth of this band, VLF radio signals cannot carry audio (voice), and only transmit text messages at a slow data rate. VLF data transmission rates are around 300 bits/s – or about 35 eight-bit ASCII characters per second (or the equivalent of a sentence every two seconds) – a total of 450 words per minute. Simply shifting to 7-bit ASCII increases the number of transmitted characters per time unit by 14%. An additional shift to a 6-bit or a 5-bit code (such as the baudot code) would result in speeds of more than 600 and 700 words per minute.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Other signals around 200 kHz may be differential GPS or other radio navigation functions:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In parts of the world where there is no longwave broadcasting service, &lt;em&gt;Non-directional beacons&lt;/em&gt; (NDB) used for aero-navigation operate on &lt;strong&gt;190–300&lt;/strong&gt; kHz (and beyond into the MW band). In Europe, Asia and Africa, the NDB allocation starts on &lt;strong&gt;283.5&lt;/strong&gt; kHz. The &lt;code&gt;LORAN-C&lt;/code&gt; radio navigation system operates on &lt;strong&gt;100&lt;/strong&gt; kHz... &lt;code&gt;Differential GPS telemetry&lt;/code&gt; transmitters operate between &lt;strong&gt;283.5&lt;/strong&gt; and &lt;strong&gt;325&lt;/strong&gt; kHz. The commercial &lt;code&gt;&quot;Datatrak&quot;&lt;/code&gt; radio navigation system operates on a number of frequencies, varying by country, between 120 and 148 kHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="6563" LastActivityDate="2017-04-24T08:40:03.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7521" PostTypeId="1" CreationDate="2017-04-24T14:46:27.347" Score="2" ViewCount="1075" Body="&lt;p&gt;I'm trying to comprehend what one would see if one could observe what's happening in the antenna wire.  Is the difference between a 1 watt and a 4 watt transmitter just that the amplitude/voltage on the antenna will be higher?&lt;/p&gt;&#xA;" OwnerUserId="9570" LastEditorUserId="8832" LastEditDate="2017-04-26T02:29:26.740" LastActivityDate="2017-04-26T02:29:26.740" Title="What is output power exactly?" Tags="&lt;antenna-theory&gt;&lt;rf-power&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7522" PostTypeId="2" ParentId="7517" CreationDate="2017-04-24T19:33:01.417" Score="4" Body="&lt;p&gt;This grouping is what frequency modulation looks like whenever the &lt;em&gt;input&lt;/em&gt; to the modulator is a constant single tone of a fairly high frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(If the tone were of a much lower frequency, then you would instead see a single peak moving in a sinusoidal fashion as a straightforward understanding of frequency modulation would suggest. This can be observed on repeater transmissions that use CTCSS tones, with a fast waterfall.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The single tone that is present but that you are not hearing is the 19 kHz (higher than audible, and usually filtered out by a receiver) “pilot” tone for FM stereo encoding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM broadcast stereo works by taking the two stereo audio channels and rearranging them into a single channel where everything but the combined mono signal is of a higher-than-audible frequency. &lt;a href=&quot;https://commons.wikimedia.org/wiki/File:RDS_vs_DirectBand_FM-spectrum2.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia has a nice chart&lt;/a&gt; (including some additional features beyond stereo):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/c/cd/RDS_vs_DirectBand_FM-spectrum2.svg/1000px-RDS_vs_DirectBand_FM-spectrum2.svg.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is &lt;strong&gt;not&lt;/strong&gt; a plot of RF frequencies. This is the signal which is &lt;em&gt;sent into the FM modulator&lt;/em&gt; in place of the audio signal which a mono transmitter would use — note that the 0 to 15 kHz audible range is just audio. (This is for compatibility with mono receivers.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the stereo audio is silent, the L+R and L&amp;minus;R outputs are both silent, so the only thing in the signal (assuming none of the additional digital features charted above are present) is the 19 kHz tone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The purpose of that “pilot tone” is to allow the FM stereo decoder in the receiver to precisely locate the frequency-shifted stereo difference audio (at twice the pilot tone frequency; can be seen as &lt;a href=&quot;https://en.wikipedia.org/wiki/Double-sideband_suppressed-carrier_transmission&quot; rel=&quot;nofollow noreferrer&quot;&gt;DSB-SC&lt;/a&gt; modulation) and shift it back, despite any drift in the relevant oscillators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, the pilot tone is at a &lt;em&gt;single&lt;/em&gt; frequency; it is just the case that when that single tone goes through a FM modulator, a theoretically infinite (and in practice bandlimited) collection of sidebands is produced, which is the way FM always works.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-04-24T21:41:53.863" LastActivityDate="2017-04-24T21:41:53.863" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7523" PostTypeId="2" ParentId="7521" CreationDate="2017-04-24T19:49:14.970" Score="6" Body="&lt;p&gt;Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just like any other electronic device producing a signal, the transmitter is “really” applying a voltage to the output, which causes a current, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But we talk about power more often because power is a much more useful figure to work with for RF engineering above the level of designing circuits; voltage and current can be traded off (while power stays constant) so there's an arbitrary scaling factor that can be avoided.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(And once you have a electromagnetic wave propagating through the air, the voltage depends on the distance you measure it across, so if you want volts you can only get volts-per-meter. That's a good unit for measuring &lt;em&gt;field strength&lt;/em&gt; — but field strength is not the same thing as power (they're related by the gain of your antenna).)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What voltage you find on the conductors of the antenna will depend on exactly what two points on the antenna you measure. But it is always the case that the output power is &lt;strong&gt;proportional to&lt;/strong&gt; the square of the voltage (measured in a consistent way), just as in more familiar cases where the usual formulas apply:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P = VI = V\left(\frac{V}{R}\right) = \frac{V^2}{R} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Within the antenna, $R$ is fairly impractical to calculate, but constant for any two points (if it weren't, it wouldn't be a linear system and you would get highly undesirable &lt;a href=&quot;https://en.wikipedia.org/wiki/Intermodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;intermodulation&lt;/a&gt;). But on the feed line — the (typically coaxial) cable between the transmitter and the antenna — there is in fact a value you can use for $R$, the &lt;em&gt;characteristic impedance&lt;/em&gt; of the cable (usually 50 or 75 Ω for coaxial cables).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(In RF systems we talk about &lt;em&gt;impedance&lt;/em&gt; $Z$ instead of resistance $R$, but the difference is irrelevant to this particular question, so I stuck to basic-electricity concepts.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-04-25T14:35:27.940" LastActivityDate="2017-04-25T14:35:27.940" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7524" PostTypeId="2" ParentId="7521" CreationDate="2017-04-24T21:51:54.347" Score="2" Body="&lt;p&gt;@Kevin's answer is correct.  Power is the product of voltage and current.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your question you ask if it is just higher voltage, and it may well be, but more commonly they both go up at the same time to get more power (amplitude).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you asked how you can see what is happening on the wire, I would direct you to the Wikipedia entry, which has a great animation.  (I can't copy the animation here so you will need to follow this link to see it):  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia - Dipole Antenna&lt;/a&gt; (Right-click on this and open it in a new tab)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back in the old days, we would often use small light bulbs as dummy loads on low-power transmitters to see the amount of power being put out as we made transmitter adjustments.  We would just solder them to an antenna plug (PL-259) and plug them in instead of an antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radios today do not need transmitter adjustments so that isn't really needed, but you definitely could see the difference in power output between 1 and 4 Watts with a small bulb.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For larger transmitters we would use regular 100-Watt light bulbs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas have a characteristic impedence, Z, with three components, inductance, capacitance and resistance.  When the inductance equals (and thus cancels) the capacitance, it is called being in resonance.  This means that the only component left is resistance.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The equations are complex, and for that reason it is best to talk about properly-tuned antennas.  At that point the equation P = E x I works without any further math.  Power (Watts) equals electromotive force (Volts) times current (Amps).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The light bulbs would present a purely resistive load, simulating a resonant antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those old tube-type transmitters have several adjustments that needed to be made to tune them properly for maximum power output and we could see that by the brightness of the bulb.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you can do the same with a simple Wattmeter.  But we're hams so we had to be different and innovative.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When building a dipole it is very important that the Capacitance and Inductance truly cancel each other out.  You want a resonant antenna.  The way you do that is by adjusting the length. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;While adjusting your antenna length you use a SWR (standing-Wave Ratio) meter, which shows the amount of power being reflected back to the transmitter.  When you are at the correct length for the frequency you are using the SWR will be at its lowest as the antenna accepts the power and puts it out on the wire.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At that point the antenna is seen by the transmitter as a purely resistive load.  Thus the other equation that @Kevin showed.  p = E^2 / R  - Power in Watts equals the voltage squared divided by the resistance.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Standing waves are similar to the animation in that Wikipedia entry, except they are happening in your feedline and basically turning into heat, wasting power that would go out to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But more importantly for your answer, the patterns of current and voltage are way different in non-resonant antennas, and visualizing them is difficult and unique to each configuration.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a good reference on dipole antenna theory, including visualizations of the radiation patterns:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Full-Wave Dipole&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you will notice that the current is low in the middle in that link.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, we use half-wave dipoles where the current is highest in the middle so the voltage is the lowest.  (This is where I am diverging a bit from your assumption in the question - because at the antenna feedpoint we want highest current at lowest voltage, and that creates higher amplitude.  In other words, Amplitude is measured in terms of power, not just in terms of voltage)  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a link about all that:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.antenna-theory.com/antennas/halfwave.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Half-Wave Dipole Antenna&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each kind of antenna has a characteristic resistance.  For a dipole it is roughly 72-75 Ohms.  So you use a coax like RG-59 or RG-6 (like for cable TV) to match it and connect it to your radio.  Most radios today can handle 50-75 Ohm antennas just fine without a tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can still use non-resonant antennas with a tuner but the picture is more complex in terms of visualizing what is going on.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, I believe the best answer to your question is found at that Wikipedia page.  They have done a good job of animating what is happening with a resonant antenna so you can &quot;see&quot; it.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-04-24T22:30:40.097" LastActivityDate="2017-04-24T22:30:40.097" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7525" PostTypeId="1" AcceptedAnswerId="7527" CreationDate="2017-04-25T04:30:18.240" Score="2" ViewCount="267" Body="&lt;p&gt;What is the reason a small loop-stick antenna ( typically used for AM reception) does not have reciprocal characteristics for both reception and transmission. ( AM reception works great on those little loopsticks, but you don't get desirable results, when trying to transmit back through such a device)&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2017-04-29T01:42:05.937" Title="Reciprocity for loopstick antennas?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7527" PostTypeId="2" ParentId="7525" CreationDate="2017-04-25T12:47:53.297" Score="5" Body="&lt;p&gt;At reasonable transmission powers, the ferrite core saturates. Also, it would probably overheat, and produce a horribly distorted transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ferrite core is made of movable magnetic domains. Each of these are small bits of the material that have magnetic poles like a tiny bar magnet. Normally they are all pointing in random directions, and their individual fields cancel so the ferrite bar doesn't seem to be a magnet. A lot of matter is like this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ferrite is special in that the magnetic domains are easily moved. When an external magnetic field is applied, they all move to align with that external field. Then their fields add to the external field, and you end up with a magnetic field which is stronger than the external field would have been if the ferrite were replaced with air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This property is called &lt;a href=&quot;https://en.wikipedia.org/wiki/Permeability_(electromagnetism)&quot; rel=&quot;noreferrer&quot;&gt;magnetic permeability&lt;/a&gt;. It's this magnetic &quot;amplification&quot; that makes the loopstick antenna so effective. The ferrite stick increases the antenna aperture by concentrating the magnetic flux from far away transmitter through the center of the windings where it will induce a current that is detected by the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The trouble is the magnetic domains can become only so much aligned. At some field strength they are as aligned as they can be, and the permeability drops to zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ferrite doesn't care if the external magnetic field is coming from a distant transmitter, or the coil around it. Because the field from the transmitting coil is many orders of magnitude stronger, saturation of the core is likely unless the transmit power is very small, maybe microwatts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This saturation of the core means the antenna is highly nonlinear, and would thus introduce unacceptable distortion into the transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, the magnetic domains are &quot;sticky&quot;: it takes some amount of energy that's wasted as heat to move them. This is called hysteresis loss. When receiving this loss reduces the efficiency of the antenna, but since the field is so weak there's no significant heating. When transmitting the energy lost is higher, and without adequate cooling heat may accumulate to reach the ferrite's Curie temperature, and the ferrite's magnetic properties will be lost. &lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-04-25T12:47:53.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7528" PostTypeId="2" ParentId="7431" CreationDate="2017-04-25T15:24:29.923" Score="4" Body="&lt;p&gt;They do make weatherproof caps for NMO and SO-239 antenna mounts.  I've used those for years.  I pull up to the wash, take the antennas down and stow inside, and put the caps on.  Post wash, reverse the procedure.  Takes maybe a minute for three antennas.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2017-04-25T15:24:29.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7530" PostTypeId="2" ParentId="5203" CreationDate="2017-04-25T17:35:27.327" Score="0" Body="&lt;p&gt;It depends on how you define &quot;Most effective&quot;.  Are you looking to help or hinder the hunters?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used audio tones that were very close to the commutation rate of a doppler DF unit, specifically intending to confuse it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are looking to help people identify the fox, then you could transmit morse as bursts of tone, covering the ID requirement and the ability to distinguish the fox from other transmissions.  Something like &quot;DE K9FOX&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can find it online somewhere, the instructions for the Agrelo fox hunt transmitter might give you some clues.  I wrote the firmware for that unit many years ago.  I had a lot of options for audio tones and CW messages.&#xA;If you can't find it, email me at KC6ETE at gmail, and I'll send you info.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2017-04-25T17:35:27.327" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7531" PostTypeId="1" AcceptedAnswerId="7533" CreationDate="2017-04-26T00:16:59.737" Score="2" ViewCount="2212" Body="&lt;p&gt;What would be the difference between a two-bay antenna designed like this:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/w7VTj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/w7VTj.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and a four-bay antenna designed like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xfzrW.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xfzrW.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that everything about these two antennas are identical aside from the number of bays, what exactly does &quot;adding more bays&quot; do for a bowtie antenna?&lt;/p&gt;&#xA;" OwnerUserId="9578" LastEditorUserId="8832" LastEditDate="2017-04-26T02:30:18.993" LastActivityDate="2017-04-26T17:09:00.853" Title="What is the purpose of having multiple bays for a bowtie antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;bowtie&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7532" PostTypeId="2" ParentId="7531" CreationDate="2017-04-26T01:53:26.837" Score="0" Body="&lt;p&gt;I find I learn a lot by reading catalogs, and this was no exception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Going from &lt;a href=&quot;http://www.solidsignal.com/pview.asp?p=db8&quot; rel=&quot;nofollow noreferrer&quot;&gt;THIS AD FOR BOWTIE ANTENNAS&lt;/a&gt; they claim longer range with more bays.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That would make sense because there would be more surface area with which to capture signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously, an antenna like your diagram would be bidirectional like any dipole, but the one listed in that ad has a screen reflector on one side to make it unidirectional.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-04-26T17:09:00.853" LastActivityDate="2017-04-26T17:09:00.853" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="7533" PostTypeId="2" ParentId="7531" CreationDate="2017-04-26T04:58:25.223" Score="2" Body="&lt;p&gt;It increases the directionality and gain of the antenna. This helps it reject noise coming from directions other than towards the transmitter. The higher signal to noise ratio leads to better reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this antenna as drawn, the directions of maximum gain are two: one coming out of the page, and one in the opposite direction. Sometimes these antennas will have a reflector behind them to reduce that to just one direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a wave arriving from the maximum gain direction, the wavefront hits all the bowties at the same time. The individual signals received from each bowtie then add constructively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not immediately obvious why there's the crossover in the antenna. That is, why not are all the blue halves on one side, and the reds on the other? The reason is the two outer bowties are farther away from the feedpoint than the inner bowties. If the incoming wave hits all the bowties at the same time, but then the bowties are at different lengths from the feedpoint, by the time the signals have traveled from the bowtie to the feedpoint they will no longer be in phase, and no longer add constructively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The crossover compensates for this delay. The wave is oscillating with some period; if we wait half this period the polarity at that instant will be reversed. The crossover accomplishes the same thing, not by waiting but by crossing the wires. Meanwhile, the extra distance that must be travelled from the farther bowties introduces another half-period of delay. That half-period, plus the additional half-period of the crossover, means that we are effectively delaying the signal by a full period, which is the same as not delaying it at all.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-04-26T04:58:25.223" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7534" PostTypeId="1" CreationDate="2017-04-26T13:35:30.177" Score="2" ViewCount="869" Body="&lt;p&gt;(First of all, I hope this is the right subform, please correct me if I'm wrong)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using a 433 Mhz LoRa Radio to communicate with a high altitude balloon and am using an antenna &lt;a href=&quot;https://ukhas.org.uk/guides:payload_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;like in this guide&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know many people have the antenna facing straight down (with radials attached to the bottom of the payload). However I want to use a satellite tracker as a backup, which means the tracker should always face the sky. If the antenna were at the bottom, the payload would probably fall over when landing... Would it be bad for reception, if i just put the antenna on a side of the payload instead of the bottom? (meaning the radials would be taped to one side of the payload and the antenna would be horizontal). As the HAB will be bobbing around a lot in the wind, would it even matter in which direction the antenna faces?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: Might the way of attachment shown in the picture be a solution?&#xA;&lt;a href=&quot;https://i.stack.imgur.com/JWgcN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JWgcN.png&quot; alt=&quot;Possible solution?&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9494" LastEditorUserId="9494" LastEditDate="2017-05-02T11:59:57.007" LastActivityDate="2017-05-02T11:59:57.007" Title="Optimal antenna orientation for High altitude balloon?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7535" PostTypeId="2" ParentId="7534" CreationDate="2017-04-26T13:57:24.310" Score="0" Body="&lt;p&gt;Advantages of the upside-down monopole include:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;It's omnidirectional in the azimuthal plane, so as the balloon rotates the antenna gain doesn't change much.&lt;/li&gt;&#xA;&lt;li&gt;The gain is higher in the down direction towards Earth.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The ideal radiation pattern of a monopole like this is a bagel sliced in half, with the monopole sticking through the hole in the center. With a ground plane of finite size it changes a bit but this is still the general shape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the antenna mounted on the side, half that bagel will be pointed up to the sky where you'd just be receiving noise (though not much of it since there aren't many radios up there) or wasting transmitter power. And as the balloon rotates the pattern changes: when the antenna is on the far side of the balloon relative to your base station, gain will be pretty low.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This may or may not be a problem. Ultimately it depends on the reliability you require and your &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt;. You can use antenna modeling software to estimate the antenna gain, or build a prototype and test it empirically.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-04-26T13:57:24.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7536" PostTypeId="1" AcceptedAnswerId="7727" CreationDate="2017-04-26T15:20:17.740" Score="3" ViewCount="1220" Body="&lt;p&gt;I've often heard that the output impedance is 50Ω, and the load impedance should be matched to that and also 50Ω. While the &lt;a href=&quot;https://ham.stackexchange.com/questions/6160/why-does-high-swr-damage-transmitters-instead-of-impedance-mismatch&quot;&gt;reasons for the load impedance to be 50Ω&lt;/a&gt; are clear, is the output impedance really 50Ω and if so why? If it isn't 50Ω, what is it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wouldn't this mean a large amount of power is lost in the transmitter? Wouldn't it mean &lt;a href=&quot;https://ham.stackexchange.com/questions/7333/what-is-the-actual-loss-in-a-feed-line-with-high-swr&quot;&gt;SWR losses&lt;/a&gt; would be much higher than they actually are?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-04-28T05:50:38.703" LastActivityDate="2018-02-16T18:44:33.377" Title="What is the output impedance of a typical solid state ham transmitter?" Tags="&lt;impedance&gt;&lt;transmitter&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="17" ContentLicense="CC BY-SA 3.0" />
  <row Id="7537" PostTypeId="5" CreationDate="2017-04-26T15:32:36.740" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-04-26T15:32:36.740" LastActivityDate="2017-04-26T15:32:36.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7538" PostTypeId="4" CreationDate="2017-04-26T15:32:36.740" Score="0" Body="Bowtie antennas, such as often seen used for TV reception." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-04-26T15:32:36.740" LastActivityDate="2017-04-26T15:32:36.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7539" PostTypeId="5" CreationDate="2017-04-26T17:23:26.880" Score="0" Body="&lt;p&gt;See also:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;/questions/tagged/impedance&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;impedance&amp;#39;&quot; rel=&quot;tag&quot;&gt;impedance&lt;/a&gt; for questions about the general theory of impedance.&lt;/li&gt;&#xA;&lt;li&gt;An adjustable impedance matching network is an &lt;a href=&quot;/questions/tagged/antenna-tuner&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;antenna-tuner&amp;#39;&quot; rel=&quot;tag&quot;&gt;antenna-tuner&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-04-26T17:23:26.880" LastActivityDate="2017-04-26T17:23:26.880" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7540" PostTypeId="4" CreationDate="2017-04-26T17:23:26.880" Score="0" Body="Questions about fixed impedance matching networks, the necessity of impedance matching, etc." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-04-26T17:23:26.880" LastActivityDate="2017-04-26T17:23:26.880" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7541" PostTypeId="5" CreationDate="2017-04-26T17:31:55.373" Score="0" Body="&lt;p&gt;A SWR meter is placed inline in a feed line to measure the standing wave ratio (SWR). It may be a separate unit or integrated in a transceiver. SWR meters often measure power as well; the “crossed needle” SWR meter displays forward and reflected power directly and the user reads SWR from the point of intersection of the needles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Devices which produce their own test signal, and often measure more parameters than SWR, are &lt;a href=&quot;/questions/tagged/antenna-analyzer&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;antenna-analyzer&amp;#39;&quot; rel=&quot;tag&quot;&gt;antenna-analyzer&lt;/a&gt;s.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For questions about fixing “high SWR” problems, see &lt;a href=&quot;/questions/tagged/impedance-matching&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;impedance-matching&amp;#39;&quot; rel=&quot;tag&quot;&gt;impedance-matching&lt;/a&gt; instead.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-04-26T17:31:55.373" LastActivityDate="2017-04-26T17:31:55.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7542" PostTypeId="4" CreationDate="2017-04-26T17:31:55.373" Score="0" Body="Equipment which measures standing wave ratio (SWR). See also [antenna-analyzer]. For questions about fixing “high SWR” problems, see [impedance-matching] instead." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-04-26T17:31:55.373" LastActivityDate="2017-04-26T17:31:55.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7544" PostTypeId="2" ParentId="7536" CreationDate="2017-04-27T05:39:03.043" Score="2" Body="&lt;p&gt;Strictly speaking, the output impedance of most amateur transmitters is not specified. The specifications instead state what the output power of the transmitter will be into a 50 ohm load. Often the reader will infer that this is the condition of impedance matching or a conjugate match. While a conjugate match is the condition of maximum power transfer, it is not necessarily the condition of optimum efficiency for the transmitter. It is quite common that the manufacturer of the transmitter has specified a load impedance that improves the efficiency of the transmitter in order to reduce the power supply requirements or the heat generated by the transmitter final amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With regard to the SWR question, the output impedance of the source (the transmitter in this case) does not enter into the equation for SWR which is simply based on the relationship of the load impedance (the antenna in this case) to the characteristic impedance of the transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When a source (transmitter) initially puts power into the transmission line, it is not &quot;aware&quot; of any mismatch of the load to the transmission line. If the load matches the characteristic impedance of the transmission line, no power is reflected so the transmitter simply sees the characteristic impedance of the transmission line. If the load impedance is not a match for the transmission line then some part of the power is reflected. The amount of power reflected is equal to the reflection coefficient squared. So for a 2:1 SWR for example, the reflection coefficient is 0.333. Square that and you find that 11.1% of the power arriving at the load will be reflected back toward the source (ignoring the losses in the transmission line for now). The power returning toward the source has the effect of altering the impedance that the source &quot;sees&quot; due to the forward and reflected waves combining/interacting. The exact impedance that the source sees is a function of the SWR, the frequency, and the transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, 50 feet of Times LMR-400 on 14 MHz with a 2:1 load will present an impedance to the source (transmitter) of 33.5 +j21 or a Z of 39.5 ohms due to the reflection. The source doesn't see this new impedance until the first reflected wave has returned to the transmitter. Of course this happens at 66% to 90% at the speed of light so the resulting change in impedance occurs seemingly instantaneously. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tubed transmitters, due to their tunable output circuits through front panel adjustments, have the ability to have the output impedance of the tube final transformed to the impedance seen at the output connector. Thus once the reflected wave has altered the impedance that the transmitter sees, the operator can adjust the matching circuit to compensate, within a limited range, for the altered load impedance presented by the transmission line. This capability to alter the impedance matching circuit is functionally equivalent to the role of an external antenna tuner used with solid state transmitters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 12 volt solid state transmitter with an output power of more than a few watts, will have a final transistor amplifier circuit with a very low output impedance. In order to drive a much higher impedance 50 ohm load, the final output must be transformed through the use of an RF transformer or other suitable impedance transformation method. Since there are no operator adjustments in this output circuit like there is with a tubed final, any changes to the load impedance will alter the current through or voltage across the final transistor. Thus solid state transmitters have power foldback circuits that kick in around a 2:1 SWR in order to prevent the transistor from overheating, reaching breakdown voltage, or exceeding the maximum allowable current for the device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before coming back to the question of the transmitter returning the reflected power, we first need to account for the very real effect of transmission line loss. For every trip that the power takes along the length of the transmission line, some percent is lost. It is this back and forth movement of power along the transmission line that accounts for the extra loss due to a mismatched load. In the example above, each trip reduces the power by another 5.25% (-0.234 dB). So with a 100 watt transmitter, the power that reaches the load on the first trip is 94.75 watts (100 watts * 0.9475). 11.1% of this power (10.5 watts) is reflected back toward the transmitter. But this trip also experiences loss so the power returned at the transmitter is 9.97 watts (94.75 * 0.111 * 0.9475). All of these losses result in heat (the majority of the losses on HF bands are due to copper losses). We can now see that the transmitter NEVER returns all of the power reflected by the load since some of it is burned up as heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does a transmitter return all available reflected power to the load? The answer is yes provided the changed output impedance presented to the transmitter (due to the reflected power) does not alter the output power of the transmitter. The power that the transmitter returns toward the load will, in the above example, again have about 10% (11.1% * 0.9575 * 0.9575) returned as measured at the transmitter. This ping-pong effect continues until all of the power is transferred or burned up as heat. Generally, within 4 to 10 trips, the amount of power bouncing back and forth has become vanishingly small.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can empirically prove that the re-reflections by the transmitter are taking place by calculating the infinite geometric series of the losses occurring from the theoretical bouncing back and forth of the waves due to the multiple reflections and then comparing this to the actual output power of the antenna and the output power developed by the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is a common misconception that the output impedance of a solid state transmitter is the same as the impedance &quot;looking into&quot; the transmitter. As an active RF signal generator, this is rarely the case. In the lab, this condition can be met by using an attenuator of 20 dB on the output or more of the RF source. This effectively isolates the RF source from the reflected power and establishes the condition that the RF generator outputs a nearly constant RF voltage regardless of its load conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The output power of a solid state transmitter will be reduced by an amount exactly equal to the power reflected from the load due to the change of input impedance of the transmission line. The reflected power is added to the output of the now reduced output power of the transmitter and sent toward the antenna (load). This meets the required condition that incident power is equal to the source power plus the reflected power. It is notable that the power output of the transmitter, before the reflected power has returned to the transmitter, is the same as the total power sent toward the antenna once the reflected power has reached the transmitter (thereby altering the input impedance of the transmission line and reducing the transmitter's output power).&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-04-30T21:20:26.987" LastActivityDate="2017-04-30T21:20:26.987" CommentCount="15" ContentLicense="CC BY-SA 3.0" />
  <row Id="7545" PostTypeId="1" CreationDate="2017-04-28T08:11:03.687" Score="2" ViewCount="471" Body="&lt;p&gt;There are several methods for implementing direction finder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1.&#xA;One of the method is by using directional antenna pointing to target device, and reading the received signal strength from the target device. This method also need the device to keep transmitting,&#xA;The following &quot;direction finder&quot; use such simple directional antenna and is described here:&#xA;&lt;a href=&quot;http://www.pki-electronic.com/products/interception-and-monitoring-systems/gsm-direction-finder/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.pki-electronic.com/products/interception-and-monitoring-systems/gsm-direction-finder/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet, if this is the method that is used with the pki device, I wander how it can discern the device among other devices, because as I understand, the uplink frequency is shared among several devices nearby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2.&#xA;There are other method too, using Pseudo-doppler DF method, such as done by Balint Seeber:&#xA;&lt;a href=&quot;http://wiki.spench.net/wiki/SDRDF&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://wiki.spench.net/wiki/SDRDF&lt;/a&gt;&#xA;But I see that the demonstration is done on VHF (not GSM/LTE)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to ask:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How does the first method (directional antenna) can find a device among other with same frequency ?&lt;/li&gt;&#xA;&lt;li&gt;Can the 2nd method (SDRDF) be used to locate GSM-frequency mobile device ? and discern a device among several with same frequency ?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Thanks,&lt;/p&gt;&#xA;" OwnerUserId="9564" LastEditorUserId="8832" LastEditDate="2017-05-02T14:22:20.907" LastActivityDate="2017-05-02T14:22:20.907" Title="Direction Finder using directional antenna, digital signals amid clutter" Tags="&lt;digital-modes&gt;&lt;mobile&gt;&lt;direction-finding&gt;&lt;hackrf&gt;" AnswerCount="0" CommentCount="11" ClosedDate="2017-05-01T14:53:34.380" ContentLicense="CC BY-SA 3.0" />
  <row Id="7546" PostTypeId="2" ParentId="7525" CreationDate="2017-04-29T01:42:05.937" Score="-1" Body="&lt;p&gt;The MW AM band is full of noise .Man made ,Thermal etc .The loopstick is not efficient so it picks up a small amount of signal and a small amount of noise .The incoming SNR of the MW AM antenna will have little to do with antenna type .The incoming noise at these frequencies is greater than the noise produced by electronics in the receiver .So the MW AM receiver will perform fine on any short antenna because the overall RF/IF gain is more than enough .These sweeping statements about noise are definately not true at 2GHZ .So the MW receiver works fine on a loopstick or car radio whip or any electrically short antenna .For transmit the losses in the loopstick would have to be made up in increased transmit power .This would be expensive .The ferrite would have to be big to avoid saturation that Phil Frost warned about.Using a loopstick for TX     is like reducing transmit power which will reduce range .If there was no noise of any kind then RX gain like say a preamp would be just as effective at increasing range as say a TX power increase like say a Linear.So this is why you see big towers for AMBC and not big loopsticks.&lt;/p&gt;&#xA;" OwnerUserId="6095" LastActivityDate="2017-04-29T01:42:05.937" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7547" PostTypeId="1" CreationDate="2017-04-29T20:08:18.397" Score="1" ViewCount="617" Body="&lt;p&gt;Antenna Analyzer gives a understandable results for a Quad Antenna (photos 1, 2 &amp;amp; 3), but gives strange results for Coaxial Collinear Antenna (photo 4)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Photo 1 of 4: Test setup for Quad Antenna&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/8KM4i.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8KM4i.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Photo 2 of 4: The Quad's SWR&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/rAitD.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rAitD.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Photo 3 of 4: The Quad's Frequency Sweep vs SWR&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/9aVi0.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9aVi0.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;BR&gt;&lt;BR&gt;&lt;BR&gt;&lt;BR&gt;&#xA;Photo 4 of 4: The 12 element &lt;strong&gt;Coxial Collinear Antenna&lt;/strong&gt;'s Frequency Sweep vs SWR.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/3UV65.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3UV65.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't understand the sweep graph of Coaxial Collinear Antenna. Can any one explain this strange behavior? Has anyone else done a sweep of a Coaxial Collinear Antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many thanks&lt;/p&gt;&#xA;" OwnerUserId="9029" LastEditorUserId="76" LastEditDate="2017-05-05T20:37:36.720" LastActivityDate="2017-05-05T20:37:36.720" Title="Why Coaxial Collinear Antenna Gives Strange Graph of Frequency Sweep vs SWR?" Tags="&lt;antenna&gt;&lt;measurement&gt;&lt;antenna-analyzer&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7548" PostTypeId="1" AcceptedAnswerId="7550" CreationDate="2017-04-29T20:16:21.657" Score="1" ViewCount="258" Body="&lt;p&gt;A fan dipole is a dipole with multiple active elements, either for different frequencies or different directions (see turnstile antenna) while a cage dipole emulates a larger conductive by having multiple spaced wires for a single band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the wires in a cage dipole get farther apart, effective bandwidth goes up... but at some point, you've created a turnstile antenna. What differentiates the two? Is there a transition gradient between them? Is it about the radiating elements being parallel for the majority of their length?&lt;/p&gt;&#xA;" OwnerUserId="6295" LastActivityDate="2017-04-29T22:12:13.490" Title="Transition Point Between Fan and Cage Dipoles" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wire-antenna&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7549" PostTypeId="1" CreationDate="2017-04-29T21:18:14.190" Score="1" ViewCount="240" Body="&lt;p&gt;I would appreciate any help with this.&#xA;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="9603" LastEditorUserId="8832" LastEditDate="2017-05-02T14:24:22.547" LastActivityDate="2017-05-02T14:24:22.547" Title="I have a new Kenwood TH-F6A, Mac computer and am new to our hobby. How do I program it?" Tags="&lt;kenwood&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7550" PostTypeId="2" ParentId="7548" CreationDate="2017-04-29T22:12:13.490" Score="4" Body="&lt;p&gt;A fan dipole is usually constructed of a small-ish number (3 is typical) of thin wires, each trimmed to a specific length to have three distinct resonant modes and 3 distinct frequencies. Usually they are of substantially different lengths so each resonance falls on a different band. For example a fan dipole might be designed for 20, 17, and 15 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A cage dipole is more like a single, very fat dipole with the insides of the conductors removed. All of it is about the same length, so we can expect one resonance where the dipole is 1/2 the wavelength, and at odd multiples thereof. However the resonance is wider than that of a thin dipole, since the resonant nodes aren't confined to such a thin line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are no hard and fast rules with antenna design. There are certainly possible designs which share characteristics of each of these designs. We simply give names to established categories, much like we do with art, such as &quot;cubism&quot; and &quot;impressionism&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A turnstile antenna is quite a different beast. It is really two dipoles, each fed with a 90 degree phase shift. Such a thing can't be obtained by simply taking a fan dipole and spreading the elements farther apart. Obtaining the phase shift requires a particular feed arrangement, such as a power splitter with a 90 degree delay line on one of the branches.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-04-29T22:12:13.490" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7551" PostTypeId="2" ParentId="7549" CreationDate="2017-04-29T22:43:28.277" Score="1" Body="&lt;p&gt;Use an open source software called CHIRP: &lt;a href=&quot;http://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://chirp.danplanet.com/projects/chirp/wiki/Home&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The software will work for your radio. It is fairly universally used and not that difficult to learn. &lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2017-04-29T22:43:28.277" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7552" PostTypeId="2" ParentId="345" CreationDate="2017-04-30T18:07:29.593" Score="1" Body="&lt;p&gt;See a list of jargon here:&#xA;&lt;a href=&quot;https://www.qrz.com/page/hamspeak.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.qrz.com/page/hamspeak.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 de TF8HA&lt;/p&gt;&#xA;" OwnerUserId="9606" LastActivityDate="2017-04-30T18:07:29.593" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7553" PostTypeId="2" ParentId="7534" CreationDate="2017-04-30T20:40:09.287" Score="1" Body="&lt;p&gt;It sounds like you really have TWO questions. 1) should I use the existing standard or is there a better choice. 2) will the Sat Tracker antenna receive interference from the part 1) antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm going to address these in reverse order. The satellite tracker should probably use a fairly wide patch or sector antenna mounted on the top of the cube pointing up. You could mount it inside as well since your cubesat design is essentially rf transparent. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sheets of metal are opaque to RF which is why I asked if you were using aluminumized foam. [You may need change this depending on you're local aviation regulations for untethered balloon launches.] You want to &lt;em&gt;not&lt;/em&gt; block the GPS receiver from seeing the sky. The balloon will be effectively transparent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are using the monopole with radials, then these antennas are both on different frequencies and mostly in the null of the monopole so you shouldn't expect much interference.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your ground pointing antenna. The 1/4  wave monopole is probably your best bet from a cost and weight standpoint. A package lifted by balloon has a stable up and down but rotation is impossible to predict. This is why the monopole is useful because it's radiation pattern perpendicular to the antenna element is the same in all directions. Its also a vertically polarized signal. Meaning receiving it on a normal vertically polarized antenna on a vehicle keeps the polarization the same for best reception. With this type of antenna the null or worst place to be is directly underneath the balloon.&lt;/p&gt;&#xA;" OwnerUserId="6092" LastActivityDate="2017-04-30T20:40:09.287" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7555" PostTypeId="1" CreationDate="2017-05-02T15:08:08.580" Score="2" ViewCount="112" Body="&lt;p&gt;I've noticed that when I transmit on my HT when I'm watching TV (OTA), the signal drops and the screen goes blank (or digital &quot;static&quot;) and then returns when I stop. I've replicated the issue by artificially causing a signal loss on the TV by either covering the antenna or disconnecting it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Right now it's annoying, however, my intention is to mount the antenna (it's an outdoor Omni that I've been lazy and haven't mounted and run cable for) and it will then be within 30 feet horizontally of my VHF base station antenna. My concern is that I could burn out the TV or amp (built into the antenna) when on a net. I've never tested to see if the TV is currently impacted by my base station, the TV is downstairs, Radio is upstairs, which makes observation difficult. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I imagine I need some sort of band pass filter, but I'm not having any luck with my Google-Fu. Am I overly concerned? Do you have any specific or general recommendations? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Links: &#xA;TV Antenna: &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B01N06CBFO&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amplified Outdoor Antenna with Omni-directional&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Base Station: &lt;a href=&quot;https://www.motorolasolutions.com/en_us/products/two-way-radios/mototrbo/mobile-radios/xpr-5000-series.html#tabproductinfo&quot; rel=&quot;nofollow noreferrer&quot;&gt;Moto XPR5550e VHF 50w&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Base Station Antenna: &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00AR0AFCG&quot; rel=&quot;nofollow noreferrer&quot;&gt;Diamond X50A&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HT: &lt;a href=&quot;https://www.motorolasolutions.com/en_us/products/two-way-radios/mototrbo/portable-radios/xpr-7000e-series.html#tabproductinfo&quot; rel=&quot;nofollow noreferrer&quot;&gt;Moto Moto XPR 7550e&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4181" LastActivityDate="2017-08-05T12:05:43.410" Title="Filtering VHF FM on my DTV signal" Tags="&lt;vhf&gt;&lt;rfi&gt;&lt;filter&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7556" PostTypeId="2" ParentId="1058" CreationDate="2017-05-02T15:17:11.287" Score="2" Body="&lt;p&gt;For receiving horizontal antennas pick up a lot less manmade noise than vertical ones. So if I were you I'd try to put up a horizontal one.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastEditorUserId="9532" LastEditDate="2017-05-02T19:36:15.813" LastActivityDate="2017-05-02T19:36:15.813" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7557" PostTypeId="1" AcceptedAnswerId="7577" CreationDate="2017-05-02T15:42:03.673" Score="1" ViewCount="666" Body="&lt;p&gt;I've recently learned about linear loaded dipoles as one way of building a physically shortened antenna. As I understand it, any shortened antenna will have reduced bandwidth and linear-loaded dipoles suffer from this as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was thinking to  counteract this by adding a second parallel element about a foot from the first, folded in the opposite direction created a linear-loaded cage dipole. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is this a feasible solution? Put another way, would it actually give me usefully increased bandwidth?&lt;/li&gt;&#xA;&lt;li&gt;From a terminology standpoint, does it require a third element to be a cage dipole?&lt;/li&gt;&#xA;&lt;li&gt;Is there an all-around better option for an 80m antenna in ~70ft of linear space?  &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6295" LastActivityDate="2017-05-05T12:48:34.770" Title="Linear-Loaded Cage Dipole?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;dipole&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="7558" PostTypeId="1" CreationDate="2017-05-02T17:14:29.033" Score="4" ViewCount="1021" Body="&lt;p&gt;OFCOM states that the maximum EIRP within the UK for 2.4 GHz is 100mW. Simply put, what is the point in being able to buy 2.4 GHz high gain antennas which can say do 24dBi, which already puts the output power at 256mW?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this a case of OFCOM turning a blind eye to things, considering the USA for example has limits which far exceed the UK?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Source sites:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.digitalairwireless.com/wireless-blog/t-eirp/wifi-transmit-power-calculations-made-simples.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;WiFi Transmit Power Calculations&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://community.ubnt.com/t5/airFiber/Where-is-the-max-EIRP-info-for-the-UK/td-p/328276&quot; rel=&quot;nofollow noreferrer&quot;&gt;Max EIRP (1)&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://forums.overclockers.co.uk/threads/maximum-legal-wifi-power-output.17732457/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Max EIRP (2)&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://www.ebuyer.com/268737-tp-link-tl-ant2424b-antenna-802-11-b-g-outdoor-24-dbidirectional-tl-ant2424b?mkwid=sWA3N2WiH_dc&amp;amp;pcrid=51630194939&amp;amp;pkw=&amp;amp;pmt=&amp;amp;gclid=CNuZxcba0dMCFYW4Gwodnj8EBw&quot; rel=&quot;nofollow noreferrer&quot;&gt;24 dBi antenna&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9618" LastEditorUserId="4076" LastEditDate="2017-05-03T09:21:34.630" LastActivityDate="2017-05-03T17:33:58.450" Title="What is the point of high gain antenna with respect to the maximum EIRP" Tags="&lt;antenna&gt;&lt;legal&gt;&lt;antenna-system&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7560" PostTypeId="2" ParentId="7558" CreationDate="2017-05-02T18:03:11.650" Score="4" Body="&lt;p&gt;Not everyone is subject to that EIRP limit. For example, part of the 13 centimeter amateur band overlaps the 2.4 GHz ISM band, and a licensed amateur has a very much higher power limit. Commercial licenses also exist. Regional regulations vary but it's a safe bet there are licensed services available in most jurisdictions with a higher limit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A higher gain antenna is also more directional, and thus has better receive performance by virtue of receiving less noise from other directions. Even if power is reduced to keep the EIRP at 100 mW, a more directional antenna will have better link quality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And yes, people install these illegally. I imagine enforcement is very difficult unless there's a specific complaint.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-05-03T12:39:12.327" LastActivityDate="2017-05-03T12:39:12.327" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7561" PostTypeId="2" ParentId="7558" CreationDate="2017-05-02T19:38:19.797" Score="2" Body="&lt;p&gt;A higher gain antenna means you can use lower power for the same EIRP. Or you can use a longer cable between the transmitter and the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moreover a higher gain antenna helps you to receive weaker signals.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2017-05-02T19:38:19.797" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7562" PostTypeId="2" ParentId="7558" CreationDate="2017-05-03T10:42:11.087" Score="1" Body="&lt;p&gt;Power output limits stated in terms of EIRP can be quite helpful in the case of very low frequencies, where it is difficult to build an efficient antenna and at very high frequencies where feedline and dielectric losses become significant. In these cases, a higher transmitter power than may otherwise be allowed can be deployed to make up for these systemic losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 24 dBi antenna provides a gain of &gt;251 times that of an isotropic antenna. This means that if you put in 100 mW into this antenna, your EIRP will be &gt;25 watts - well over the 100 mW EIRP legal level. To use this antenna legally, the power going into the antenna can be no more than ~0.4 mW. This is probably rarely followed in practice. Do take care as 25 watts at this frequency can be harmful to body tissues at close range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming the directivity of the antenna favors the application, a high gain antenna offers the following advantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Increases the received signal by the same gain&lt;/li&gt;&#xA;&lt;li&gt;Reduces receive interference from other (low gain) directions&lt;/li&gt;&#xA;&lt;li&gt;Makes up for feedline loss on transmit and receive&lt;/li&gt;&#xA;&lt;li&gt;Focuses the transmit power in the desired direction reducing interference to other receivers&lt;/li&gt;&#xA;&lt;li&gt;May reduce the odds of reception of transmitted signals for nefarious purposes&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The potential disadvantages are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Mechanically more complex&lt;/li&gt;&#xA;&lt;li&gt;A larger antenna profile&lt;/li&gt;&#xA;&lt;li&gt;May not be applicable for a wide area system if gain direction is not favorable to the required coverage area&lt;/li&gt;&#xA;&lt;li&gt;Potentially higher cost&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you require coverage of a larger area and you wish to use high gain antennas you could consider multiple transceivers and multiple antennas aimed in different directions.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-05-03T17:33:58.450" LastActivityDate="2017-05-03T17:33:58.450" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7563" PostTypeId="2" ParentId="7547" CreationDate="2017-05-03T11:02:53.507" Score="2" Body="&lt;p&gt;A coaxial collinear antenna will have a usable bandwidth of 1-2 MHz at most. Sweeping a +1000 MHz bandwidth and trying to interpret the result is not a meaningful exercise. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should narrow the sweep range of your analyzer to perhaps 5 Mhz centered on the design frequency of the antenna in order to get initial data. From there you can further restrict the range in order to observe more details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also take care with any coax between the analyzer and the antenna under test. While the SWR will not be significantly altered by the use of a reasonably short length of coax, the complex impedance will be transformed (changed) by even a few inches of coax at these frequencies.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-03T11:02:53.507" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7564" PostTypeId="2" ParentId="5740" CreationDate="2017-05-03T16:52:00.913" Score="8" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;I could imagine a class D pwm system doing the Envelope and the phase modulated carrier getting clipped and fed into a class E amplifier and then you could run 100Watts with no heatsinks allowing smaller cheaper equipment .ZL4TIY&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;We have demonstrated a system very much like this. See:&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;&lt;a href=&quot;https://www.arrl.org/files/file/QEX_Next_Issue/Mar-Apr2017/MBF.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Polar Explorer&lt;/a&gt;&lt;/strong&gt;: &lt;em&gt;You may never look at your “linear amplifer” the same way again.&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;In this article, we describe the motivation for and execution of a 55-W SSB transmitter that employs: DSP to generate &amp;quot;baseband&amp;quot; envelope and phase modulation signals; a class E amplifier to increase the envelope signal amplitude for application to the drain of the class E amplifier MOSFET; a quadrature digital upconverter (QDUC) chip to produce the phase modulation gate drive at the carrier frequency.&lt;/p&gt;&#xA;&lt;p&gt;Of almost equal importance, we demonstrate means of correcting the AM-AM and AM-PM conversion errors in the amplifier system to reduce third-order intermodulation products to the range of -40dBc.&lt;/p&gt;&#xA;&lt;p&gt;We have made significant advances in the eighteen months since this article was submitted for publication.&lt;/p&gt;&#xA;&lt;p&gt;Brian Machesney K1LI and&lt;br /&gt;&#xA;Tony Brock-Fisher K1KP&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-07-13T19:09:39.553" LastActivityDate="2020-07-13T19:09:39.553" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="7565" PostTypeId="2" ParentId="355" CreationDate="2017-05-03T17:06:59.340" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://electronicspost.com/explain-the-coherent-ssb-demodulation-with-block-diagram-what-is-phase-error-and-frequency-error-in-coherent-detection/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Electronics Post&lt;/a&gt; has an item on this question which says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Due to the presence of the Hilbert transform in the output, the&#xA;  detector output will suffer from the phase distortion.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Such a phase distortion does not have serious effects with the voice&#xA;  communication. But in the transmission of music and video, it will&#xA;  have untolerable effects .&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2017-05-03T17:06:59.340" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7566" PostTypeId="2" ParentId="1336" CreationDate="2017-05-03T17:10:56.817" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I think that there was also a practical reason to do so, apart from&#xA;  any ITU rules. Most, if not all amateur equipment used 9 MHz as IF.&#xA;  Mixing 80m and 40m up and the rest down towards 9 MHz in simple&#xA;  transceivers with one BFO (Beat Frequency Oscillator) was a logical&#xA;  solution. – jcoppens Nov 14 '14 at 12:56&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, this is an incorrect answer, but one which I believed as legend until I recently simulated the heterodyning of an SSB signal up and down in frequency. The &quot;sense&quot; of the sideband does not change, regardless of the &quot;direction&quot; of the frequency conversion.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2017-05-03T17:10:56.817" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7567" PostTypeId="2" ParentId="80" CreationDate="2017-05-03T20:37:59.040" Score="0" Body="&lt;p&gt;Yes, there are inserts that you slide down the RG-58/59 cable before soldering.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After you trim and insert the cable into the PL-259 you slide those sleeves up to and and screw them into the back of the PL-259.  Then you solder.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that RG58 and 59 are slightly different in size, so you need the sleeve/insert that fits the cable.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a pinch you can get 58 into an insert made for 59, but not vice-versa.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-05-03T20:37:59.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7568" PostTypeId="1" CreationDate="2017-05-03T21:28:24.663" Score="2" ViewCount="775" Body="&lt;p&gt;Are wireless transceivers affected (performance or life) by strong magnetic fields? If yes, why?&lt;/p&gt;&#xA;" OwnerUserId="9623" LastActivityDate="2017-05-06T02:14:17.990" Title="Are wireless transceivers affected by strong magnetic fields?" Tags="&lt;transceiver&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7569" PostTypeId="1" AcceptedAnswerId="7570" CreationDate="2017-05-03T23:09:14.780" Score="3" ViewCount="444" Body="&lt;p&gt;What is the name of this antenna connector on the Kenwood TH-F6A?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/w17eB.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/w17eB.jpg&quot; alt=&quot;antenna connector&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9152" LastActivityDate="2017-05-05T02:57:09.040" Title="Antenna connector name" Tags="&lt;connectors&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7570" PostTypeId="2" ParentId="7569" CreationDate="2017-05-03T23:16:15.947" Score="5" Body="&lt;p&gt;That is a standard female SMA connector.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-03T23:16:15.947" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7571" PostTypeId="1" AcceptedAnswerId="7572" CreationDate="2017-05-04T00:24:01.877" Score="2" ViewCount="141" Body="&lt;p&gt;I want to make a DIY antenna for my Kenwood TH-F6A.  Is there any danger of damaging the radio (i.e. by trying an antenna that is unsuitable), or is it safe to experiment?&lt;/p&gt;&#xA;" OwnerUserId="9152" LastEditorUserId="8832" LastEditDate="2017-06-01T13:23:50.587" LastActivityDate="2017-06-01T13:23:50.587" Title="Antenna experimentation" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;diy&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7572" PostTypeId="2" ParentId="7571" CreationDate="2017-05-04T03:03:09.170" Score="3" Body="&lt;p&gt;If you're making a simple, tried and true design like a dipole, quarter-wave vertical, or ground plane and you measure and build it reasonably carefully from properly calculated plans, there's absolutely nothing to worry about at the power levels an HT outputs. But that may not be what you mean by experimenting, really, so I assume you want to do more than that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is some danger of damaging any radio with an unsuitable antenna. &quot;Unsuitable&quot; can mean lots of things, but usually the damaging thing is that an impedance mismatch between the antenna and feedline or an antenna which is hopelessly far from resonant on the desired frequency causes too much of the transmitted signal to be reflected back into the radio. Again, a low power HT won't be putting out enough power to cause damage in most cases, and modern radios have some built-in protection against such damage, but to be safe with a truly experimental antenna you probably want to invest in an SWR meter, which gives an indication of the reflected power.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-05-04T03:03:09.170" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7573" PostTypeId="2" ParentId="7568" CreationDate="2017-05-04T03:27:50.177" Score="2" Body="&lt;p&gt;It depends on a few things...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the magnetic field static or changing, and if changing, how fast? A quickly changing magnetic field is pretty much a basic radio transmitter in itself, so will probably affect nearby radios in the form of interference, which is an effect on performance but not life. A static magnetic field (for instance, setting a permanent magnet on the side of the radio) will probably not do much of anything, unless the magnet is extremely strong (don't put your rig in an MRI machine or particle accelerator) or the magnet happens to be very close to an inductor or transformer, and even then it may not be strong enough to do much and the negative effects should go away when the magnet does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only risk of permanent damage I can think of is to moving parts, especially sensitive ones like meters, that might get bent by too strong of a magnet and no longer align properly. And even a weak magnet near a meter will cause it to malfunction or stop working entirely as long as the magnet is nearby.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastEditorUserId="4452" LastEditDate="2017-05-06T02:14:17.990" LastActivityDate="2017-05-06T02:14:17.990" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7574" PostTypeId="2" ParentId="6513" CreationDate="2017-05-04T12:37:28.540" Score="3" Body="&lt;p&gt;I think I have built exactly what you need for practising morse. I wrote it all up in a blog :-&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://whaley.org.uk/andrew/blog/2017/04/28/morse-code-cw-via-usb/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://whaley.org.uk/andrew/blog/2017/04/28/morse-code-cw-via-usb/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a USB adapter that takes a key at one end and spits out keyboard characters into a computer at the other. It also contains a buzzer which generates the sidetone. It's really cheap and easy to build and will literally take an hour to assemble. It'll work on all computers and even Android devices without any software being installed.&lt;/p&gt;&#xA;" OwnerUserId="9364" LastActivityDate="2017-05-04T12:37:28.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7575" PostTypeId="2" ParentId="7571" CreationDate="2017-05-04T14:25:41.897" Score="5" Body="&lt;p&gt;The main risk is &lt;a href=&quot;https://ham.stackexchange.com/q/6160/218&quot;&gt;damaging the radio with a high SWR&lt;/a&gt;. You can buy a meter that will measure the SWR, or your radio may have such a meter built-in. Or you can &lt;a href=&quot;https://ham.stackexchange.com/q/615/218&quot;&gt;take precautions&lt;/a&gt; like reducing the transmit power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, you should be relatively safe with an HT. The transmit powers involved are usually low enough that it's economical simply size the transistors in the power amplifier so they will not fail at any SWR. Moreover HTs are expected to operate with their antennas in proximity to other things (like the operator) which can cause large variations in impedance and thus SWR. As such HTs should be designed to be relatively robust against such faults.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-05-04T14:25:41.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7576" PostTypeId="2" ParentId="80" CreationDate="2017-05-04T15:07:57.623" Score="3" Body="&lt;p&gt;It's best to simply get the connector sized for the cable. PL-259 connectors are available for any cable size. To put one on RG-58, there are adapters such as &lt;a href=&quot;http://www.amphenolrf.com/182107.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amphenol 182107&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zW8kG.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zW8kG.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These slide over the cable, and the threads screw into the PL-259 connectors popular among amateurs, which are normally designed to screw on to RG-8.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, there are connectors designed for direct attachment to RG-58, such as &lt;a href=&quot;http://www.amphenolrf.com/182100.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amphenol 182100&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fAqaI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fAqaI.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These require a crimp tool to install. Personally I much prefer crimping: it's easier to get a solid termination, and quicker also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, using an adapter is hardly an issue in practice. The biggest issue I have with adapters is the additional strain on the connectors: the adapters make a longer lever, making for more strain from gravity pulling down on the cable, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An adapter may also be more expensive than replacing the connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The insertion loss from an adapter is probably not significant in practice, especially with more modern connectors like BNC or N, and especially on HF. &lt;a href=&quot;http://www.qsl.net/vk3jeg/pl259tst.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;VK3JEG has some emperical data&lt;/a&gt;: a PL-259 connector had an insertion loss of 0.2 dB at 145 MHz, and much less at HF. N connector return loss was &quot;almost immeasurable&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some amount of that insertion loss is due to the non-constant impedance in the PL-259 connector, and thus some of the &quot;lost&quot; power is actually just reflected back at the source. This is equivalent to increasing the SWR, and the &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;actual losses&lt;/a&gt; in such a situation may end up as less than the insertion loss depending on the particular situation.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-05-04T15:07:57.623" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7577" PostTypeId="2" ParentId="7557" CreationDate="2017-05-04T16:58:40.207" Score="1" Body="&lt;p&gt;An 80 meter dipole shortened to a length of 70 feet or less will require some type of additional matching circuit even with linear loading. The linear loading will help to reduce some of the reactive component but the resistive part of the impedance will also require some additional adjustment. This is typically done with an ATU (Antenna Tuning Unit).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that there is likely to be an ATU in the antenna system, there is no point in trying to increase the bandwidth of the dipole by building it in a cage configuration. The ATU will take care of any SWR bandwidth limitation by shifting the match point of the antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To maximize the performance of shortened antennas, the efficiency of the antenna system is normally of the greatest concern. This usually involves design trade-offs in impedance matching techniques. One of the most efficient methods for a shortened dipole is to use capacity hats at the end of the dipole. While this is not usable in all situations, a 40&quot; diameter hat on the each end of your shortened dipole would go a long ways to obtaining an efficient match. Also consider the placement of the ATU and the losses in the feedline(s) due to SWR as part of your efficiency calculation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Chu limit is not applicable to your situation as this is typically used to be certain that the antenna can radiate the entire bandwidth of the modulated signal. Since our HF modulation methods are generally 12 KHz bandwidth or less, the calculation is meaningless. Even a very high Q antenna such as a small loop can fully handle the modulation bandwidth of HF signals. If you were considering HDTV type transmissions on UHF with a small form factor antenna, as an example, then the Chu limit might come into scope.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-04T16:58:40.207" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7578" PostTypeId="1" CreationDate="2017-05-04T17:45:54.703" Score="2" ViewCount="785" Body="&lt;p&gt;I need to design an antenna using the tool FEKO. &#xA;The antenna is supposed to work in VHF frequency and has a gain of around 2.2 dB.&#xA;What is the best material to use and what are the specifications of the materials that I need to consider before designing the antenna?&lt;/p&gt;&#xA;" OwnerUserId="9630" LastActivityDate="2017-05-04T18:06:52.337" Title="What material is best to design a dipole antenna working at VHF frequency?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;vhf&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="0" ClosedDate="2017-05-05T17:06:53.863" ContentLicense="CC BY-SA 3.0" />
  <row Id="7579" PostTypeId="2" ParentId="7578" CreationDate="2017-05-04T18:06:52.337" Score="3" Body="&lt;p&gt;This is a very generic answer, but I would avoid metals such as steel, and go with the more popular conductors like Copper or Aluminum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have several aluminum VHF antennas and they work great.&lt;/p&gt;&#xA;" OwnerUserId="9481" LastActivityDate="2017-05-04T18:06:52.337" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7580" PostTypeId="2" ParentId="7569" CreationDate="2017-05-04T23:35:05.597" Score="6" Body="&lt;p&gt;Yes, that is a standard Female SMA connector.  Heads-up to be careful when purchasing SMA antennas as there are several combinations.  Most higher-end HTs have a standard Female SMA connector on the radio, and a standard Male SMA on the antenna.  Many of the newer Chinese-made HTs invert that, with the standard Male SMA on the radio, and a standard Female SMA connector on the antenna.  Meanwhile, most WiFi equipment uses &quot;Reverse Polarity SMA&quot; (RP-SMA), where the threads are the same as the standard male &amp;amp; female, but the pin and receptacle are swapped:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Standard SMA Female = center receptacle &amp;amp; external thread&lt;/li&gt;&#xA;&lt;li&gt;Standard SMA Male = center pin &amp;amp; internal thread&lt;/li&gt;&#xA;&lt;li&gt;RP-SMA Female = center pin &amp;amp; external thread&lt;/li&gt;&#xA;&lt;li&gt;RP-SMA Male = center receptacle &amp;amp; internal thread&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;See the wikipedia article for details and images:&#xA;&lt;a href=&quot;https://en.wikipedia.org/wiki/SMA_connector&quot; rel=&quot;noreferrer&quot;&gt;https://en.wikipedia.org/wiki/SMA_connector&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had previously written here, incorrectly, that the Chinese HTs have RP-SMA connectors, which is apparently a common mis-conception among Hams (myself included).  Thanks to MoTLD for the correction. &lt;/p&gt;&#xA;" OwnerUserId="9631" LastEditorUserId="9631" LastEditDate="2017-05-05T02:57:09.040" LastActivityDate="2017-05-05T02:57:09.040" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7581" PostTypeId="2" ParentId="7557" CreationDate="2017-05-05T12:48:34.770" Score="1" Body="&lt;p&gt;A simple solution is to allow the parts of the full-sized dipole beyond your 70-ft limit to hang down, toward the ground. I believe this will have less deleterious impact on the dipole's driving-point impedance and radiation behaviors than will folding it. Since we're discussing compromises, it's worth noting that it's not necessary for the excess to take any particular angle with respect to the horizontal portion, but symmetry will help to preserve the dipole's natural broadside radiation pattern. Interaction with ground may affect the resonant frequency, so start long and trim to length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something similar could be accomplished using an &quot;inverted V&quot; configuration and turning the &quot;excess&quot; ends of the wire back toward the center support.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that the ends of the antenna will have very high voltage, so keep them away from living and flammable objects.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2017-05-05T12:48:34.770" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7582" PostTypeId="1" AcceptedAnswerId="7583" CreationDate="2017-05-05T13:36:28.973" Score="3" ViewCount="165" Body="&lt;p&gt;I have no problem triggering GB3LW, and after I release PTT I get the strong burst from the repeater confirming that it &quot;heard me&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if I use two radios, the receive-only one will &lt;em&gt;only&lt;/em&gt; hear that burst, with default settings, not me talking. If I hold down &quot;monitor&quot; on it, or set the SQL down to lowest setting, then I hear myself loud and clear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have also made contact over this repeater, so it should not be a matter of me having misconfigured both radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The baofeng UV-5RE lights up green if receiving, and activates the speaker if the tone is present. My talking doesn't light it up on the other radio (because SQL / signal strength), but the post-talking burst does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should therefore not be &quot;trigger audio frequency not received, so not activating speaker&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is: Why is &quot;my talking&quot; not being repeated as strongly enough to activate radio, but the post-talking burst is?&lt;/p&gt;&#xA;" OwnerUserId="9636" LastActivityDate="2017-05-05T13:47:16.657" Title="Why is repeater post-xmit &quot;burst&quot; stronger than repeated signal?" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="5" ClosedDate="2018-04-27T20:37:35.360" ContentLicense="CC BY-SA 3.0" />
  <row Id="7583" PostTypeId="2" ParentId="7582" CreationDate="2017-05-05T13:47:16.657" Score="5" Body="&lt;p&gt;You are probably experiencing what is called &quot;desense&quot;. The strong signal of your transmitting radio is getting into the receiver on the receiving radio and blocking its ability to receive the repeater even though they are on different frequencies. As soon as you stop transmitting, the desense is gone so your receive radio can now hear the squelch tail of the repeater.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-05T13:47:16.657" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7584" PostTypeId="2" ParentId="7555" CreationDate="2017-05-06T00:24:04.807" Score="0" Body="&lt;p&gt;&lt;code&gt;I've never tested to see if the TV is currently impacted by my base station, the TV is downstairs, Radio is upstairs, which makes observation difficult.&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a smart phone or video camera, set it up to look at and record the TV while you go upstairs and transmit.&lt;/p&gt;&#xA;" OwnerUserId="9470" LastEditorUserId="8717" LastEditDate="2017-06-05T01:51:46.617" LastActivityDate="2017-06-05T01:51:46.617" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7585" PostTypeId="1" AcceptedAnswerId="7589" CreationDate="2017-05-06T01:57:08.730" Score="5" ViewCount="9548" Body="&lt;p&gt;How big difference will it be between UV-5R 4W &amp;amp; newer UV-5R 8W (difference between 4W &amp;amp; 8W), in real life use 1 on 1 HT.&#xA;In SAME conditions, how much different distance / range will we get? (simple example)&lt;/p&gt;&#xA;&lt;p&gt;So I want to buy two HTs and change stock antennas with Nagoya NA-701, and major things that I want to use them for are:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Rare occasions use and for about 8-10 hours top max until it will be&#xA;near charger;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;will not use 8W all the time, just in case when other HT is out of reach with 4W (between two ski resorts, one car start the trip few minutes before other one..);&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;mountain - skiing, to get friends locations, to meet up;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;while travelling by car, with friends (few km separated);&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I read A LOT of topics 4W vs 8W, and most of people say it's too small difference, few are saying with hard evidence that it's a big difference (Link added).. here are some quotes (for helping other people that read this):&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;some say that thay don't want 8W radiation around their head for too long.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;5W vs 8W won't make more than a &amp;quot;mosquito-fart&amp;quot; difference in signal.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Range depends on antenna height and terrain. Those few extra Watts won't do much, if anything, but they will drain battery faster.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Don’t forget – gaining one lousy extra s-point would require 4x the original power output, which means that the UV-5R would have to deliver 16 Watts. That’s technically not possible.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;http://forums.qrz.com/index.php?threads/new-ham-here-looking-at-a-ht-4watt-or-8-watt.462945/#post-3372225&quot; rel=&quot;nofollow noreferrer&quot;&gt;(some forum talk about UV5R &amp;amp; F8HP) With 4W and the 701 antenna, best I could do was 10 miles, but with the 8W and 701, I can stand in that same spot and reach repeaters and simplex 16 miles away. The disclaimer with my location is little elevation difference, but surrounded by thick pine tree forest.&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I hope that you will help me, and that this thread will help others while still there are not so much info &amp;amp; tests about &amp;quot;UV-5R 8W&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;To simplify&lt;/strong&gt;, here's the example situation:&lt;/p&gt;&#xA;&lt;p&gt;Talk between two same HTs (4W to 4W or 8W to 8W),&#xA;with line-of-sight (&lt;strong&gt;mountain to valley or mountain to another mountain&lt;/strong&gt;) that means no earth curving,&#xA;could we produce a situation when 4W to 4W is not enough and in same spots 8W to 8W will work?&lt;/p&gt;&#xA;&lt;p&gt;And approximately what would be a difference in KM / Mile? or would it be more likely in Meters maybe?&lt;/p&gt;&#xA;&lt;p&gt;Because I'm not interested in repeater just in one on one HT use, and use of 8W would only be when other HT is out of reach with 4W, also I would use 8W just to set meeting point... so in that kind of use, I don't need to worry about &amp;quot;Brain radiation&amp;quot; or whatever.&lt;/p&gt;&#xA;&lt;p&gt;That is what I'm looking for here, in real life, will that work or not and what would be the difference in distance for the same spots if it works.&lt;/p&gt;&#xA;&lt;p&gt;I'm new to radios / frequencies / dBs and all that comes to it, but thinking would it be good to spend little more $ for 4W more (for future needs) or it's a waste of money.&lt;/p&gt;&#xA;" OwnerUserId="9642" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-10-09T13:01:59.703" Title="UV-5R 4W BFB297 vs UV-5R 8W BFP3-23 (difference 4W vs 8W)" Tags="&lt;baofeng&gt;&lt;equipment&gt;&lt;uv-5r&gt;" AnswerCount="4" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="7586" PostTypeId="2" ParentId="7585" CreationDate="2017-05-06T02:29:46.610" Score="3" Body="&lt;p&gt;Of your quoted testimonials, the one I'd put the least credence in is the 10 miles at 4w and 16 miles at 8W, because I'm not sure what they mean by the &quot;elevation difference&quot; disclaimer; at these frequencies even a small difference in location, especially in elevation, can make much more difference than doubling wattage. The rest seem pretty much spot on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4W vs 8W is slightly more than mosquito-fart difference, but not much. Most of the time it will just be a waste of battery. If the price difference means you can get the 4W plus a better antenna instead of the 8W, that's what I'd do. If you can afford both, get the 8W radio &lt;em&gt;and&lt;/em&gt; a better antenna. Options are good to have even if you seldom use them, and those extra few dB might make the difference one day. You can always transmit at medium or low power when battery life matters.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-05-06T02:29:46.610" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7587" PostTypeId="1" CreationDate="2017-05-06T06:32:10.770" Score="3" ViewCount="636" Body="&lt;p&gt;I have MFJ225 antenna analyzer. I measure coax trap filters by connecting this analyzer to PC and using IG_miniVNA application. That works fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, sometimes I need to make such measurements in portable where I do not have PC available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A friend has MFJ259 and he uses grid dip coil adapter to successfully measure traps. I tried using his adapter but got no results - meaning no DIP at all.&lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="306" LastEditDate="2017-05-06T19:52:29.713" LastActivityDate="2017-05-31T10:30:59.210" Title="Is it possible to measure antenna trap with MFJ225 without help of PC?" Tags="&lt;measurement&gt;&lt;antenna-analyzer&gt;&lt;trap&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7588" PostTypeId="2" ParentId="7585" CreationDate="2017-05-06T11:59:45.257" Score="5" Body="&lt;p&gt;The exact answer is given by the Friis equation. If you double the power, your range will increase by 1.413 times whatever it was before doubling the power if you change nothing else. This assumes you do not violate line of sight rules and that there are no additional obstructions in the longer path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could get this same effect by doubling the gain of one of the antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if you doubled the gain of both antennas and left the power as it was (4 watts), your distance is nearly doubled and you do not have the additional battery drain. The extra distance is because you are increasing the effective transmit power and the effective receive gain. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-11-18T16:37:59.337" LastActivityDate="2017-11-18T16:37:59.337" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7589" PostTypeId="2" ParentId="7585" CreationDate="2017-05-06T12:18:21.917" Score="5" Body="&lt;p&gt;4W to 8W is a doubling of power, or a 3dB increase. That's 3dB you can add to your &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt;. Provided of course that the limiting factor is the other station hearing you, not the other way around.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say with 4W you can be heard up to 10 miles away. In idealized conditions (no terrain in the way, no interference, etc) 8W increases your range to 14.1 miles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why? According to the &lt;a href=&quot;https://en.wikipedia.org/wiki/Inverse-square_law&quot; rel=&quot;noreferrer&quot;&gt;inverse square law&lt;/a&gt;, &lt;a href=&quot;https://en.wikipedia.org/wiki/Irradiance&quot; rel=&quot;noreferrer&quot;&gt;irradiance&lt;/a&gt; is inversely proportional to the square of the distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{irradiance} \propto {1 \over \text{distance}^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means multiplying the distance by $x$ will require an increase of $x^2$ in &lt;a href=&quot;http://www.antenna-theory.com/definitions/eirp.php&quot; rel=&quot;noreferrer&quot;&gt;EIRP&lt;/a&gt; to maintain the same irradiance, which can be made by increasing transmitter power or antenna gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We must also consider the &lt;a href=&quot;https://en.wikipedia.org/wiki/Line-of-sight_propagation#Radio_horizon&quot; rel=&quot;noreferrer&quot;&gt;radio horizon&lt;/a&gt;. Even if there are no hills in the way, the curvature of the Earth will get in the way at some distance. The horizon (in miles) for a station at some height (in feet) is approximated by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{horizon} = 1.41 \sqrt{\text{height}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For height in meters and horizon distance in kilometers, change the constant to 4.12.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This approximation takes into account the shape of a perfectly round Earth, and a &quot;bonus&quot; to account for atmospheric bending of the signal. It doesn't account for trees, buildings, or hills.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say your HT is 4 feet high. Your horizon is $1.41\sqrt{4} = 2.82$ miles. And the repeater is on a 50 foot tower: $1.41\sqrt{50} = 9.97$ miles. The horizons add, so beyond about 12.8 miles you no longer have a line of sight, and adding more power won't do much to increase range.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-05-06T12:18:21.917" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7590" PostTypeId="1" AcceptedAnswerId="7591" CreationDate="2017-05-06T23:33:42.960" Score="4" ViewCount="1038" Body="&lt;p&gt;I've recently came across the terms &quot;Pirate Radio&quot; and in the URL of this page, &quot;Ham Radio&quot;. What is the difference between these terms? And what is the difference between the transmission of a Pirate Radio and a Ham Radio.&lt;/p&gt;&#xA;" OwnerUserId="9249" LastEditorUserId="76" LastEditDate="2017-05-07T02:09:32.470" LastActivityDate="2017-05-07T02:09:32.470" Title="Pirate Radio vs Ham Radio" Tags="&lt;jargon&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7591" PostTypeId="2" ParentId="7590" CreationDate="2017-05-07T01:53:29.493" Score="4" Body="&lt;p&gt;There is a very clear difference.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am a Ham Radio operator.  It is vernacular to mean an Amateur Radio licensee.  I have had to pass tests to earn the privileges to operate within parameters such as power levels in specific frequency bands.  It is a great hobby and I highly recommend it for anyone.  Entry is not too difficult.  It is designed to be that way.  And people that do not play by the rules do not last in this hobby.  Prime directive is to never cause interference to any other licensed service.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pirate radio is a whole different animal.  They are people who think the airwaves belong to everybody so they just set up things like broadcast stations.  Sometimes they cause interference to other stations.  Sometimes they pick a clear frequency so they dont.  But either way, they are illegal.  The Federal Communications Commission can levy fines on them and warn them to stop.  If they do not, then their equipment is subject to seizure and forfeiture.  Not a good way to get on radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The biggest difference in the transmission of Ham Radio vs Pirate Radio comes down to two things:  Operation within power limits that are licensed to Hams vs Pirates who exceed the Part 15 limits that govern things like garage door openers.  And the second thing is the transmission of music.   Hams are not allowed to do that.  Pirate Radio stations usually do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope that clears it up for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice:  Look into joining the thousands of us Hams who enjoy having legal communications any time we choose.  It works when the phones are out, cellphone towers are not working, etc.  I, personally, have a solar power plant so I can operate for days on batteries.  There are a lot of aspects to the hobby.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check it out.  You may like what you see.  Better yet, find a local amateur radio club in your area and attend a meeting to see what the fuss is all about.  Guaranteed you will meet some interesting people.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have a great day.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-05-07T02:08:05.157" LastActivityDate="2017-05-07T02:08:05.157" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7592" PostTypeId="2" ParentId="7587" CreationDate="2017-05-07T13:05:56.687" Score="2" Body="&lt;p&gt;You can put a one-turn loop on the analyzer and use that to couple into the trap. There will be a dip in SWR where the trap is resonant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a picture from the &lt;a href=&quot;https://www.rigexpert.com/files/manuals/aa3054/aa-30-54-manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;RigExpert manual&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vQTQD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vQTQD.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connect that single-turn loop as if it were an antenna, and do an SWR sweep. The notch is the resonant frequency.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-05-07T13:05:56.687" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7593" PostTypeId="2" ParentId="5101" CreationDate="2017-05-07T14:15:52.903" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;&quot;And how is it possible to send anything without the carrier wave!&quot;&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Excellent question. It's not possible!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The picture below shows the oscilloscope image of a &quot;carrier wave.&quot; The &quot;carrier&quot; sets the RF transmission frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cWouN.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cWouN.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The picture below shows the oscilloscope image of an SSB signal modulated with two audio tones. This is a common test signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0OxbI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0OxbI.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The original image you showed is the &quot;envelope&quot; of the modulation only; the &quot;carrier&quot; wave is not included. Note how the shape of your image is the same as the shape of the peaks and valleys in the second picture above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I created these waveforms using LTSpice, a free circuit simulation program available from Linear Technology. The beauty of this program is that it allows you to simulate &quot;behavioral&quot; voltage and current sources with purely mathematical descriptions; you don't have to implement a circuit with active and passive components. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2017-05-07T14:15:52.903" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7594" PostTypeId="1" AcceptedAnswerId="7595" CreationDate="2017-05-08T00:10:40.207" Score="1" ViewCount="97" Body="&lt;p&gt;I need a powersupply for a radio board (I will shield it), and have experienced bad interference from step-down converters. I have been told to use linear regulators (LM317 or LM350) with caps to trim the current. Am I correctly informed? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have several boards, one to receive and one to transmit. Both take 4-6V in, and consume no more than 300mA. I've also found USB supplies (both battery, charger and laptop) to be very noisy, compared to just 3 AA batteries in series. Probably because they are backed by some sort of switching power supply hooey.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cluebatter up!;)&lt;/p&gt;&#xA;" OwnerUserId="9583" LastEditorUserId="76" LastEditDate="2017-07-09T17:32:40.933" LastActivityDate="2017-07-09T17:32:40.933" Title="Power supply for small radio board" Tags="&lt;rfi&gt;&lt;dc-power&gt;&lt;power-supply&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7595" PostTypeId="2" ParentId="7594" CreationDate="2017-05-08T00:53:50.727" Score="2" Body="&lt;p&gt;I would suggest an LM7805 type regulator. It will put out 5 volts for up to one amp current draw. You will need a filtered DC power source of 7 to 12 volts and a heatsink for the regulator. The 7805 regulator is quite common and very inexpensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This type of supply is called a linear supply. It is not as efficient as a switching type supply but you avoid the hash common with most switching supplies.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-08T00:53:50.727" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="7597" PostTypeId="2" ParentId="7089" CreationDate="2017-05-08T12:15:09.810" Score="1" Body="&lt;p&gt;If a vertical antenna is on a boat then the water will reflect the other half. Even better is its salt water. As for road vehicles then the vehicle creates a capacity shield away from the earth.&lt;/p&gt;&#xA;" OwnerUserId="9650" LastActivityDate="2017-05-08T12:15:09.810" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7598" PostTypeId="2" ParentId="7089" CreationDate="2017-05-08T12:23:48.220" Score="0" Body="&lt;p&gt;A vertical on good ground in the open will do well with a small number of 1/4 wave radials. Unfortunately that's not always possible, so a large amount of radials become the norm. How many depends on the environment your pushing against. Trial and error plus London gin could be the perfect answer. &lt;/p&gt;&#xA;" OwnerUserId="9650" LastActivityDate="2017-05-08T12:23:48.220" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7599" PostTypeId="2" ParentId="7089" CreationDate="2017-05-08T12:27:05.820" Score="-2" Body="&lt;p&gt;Also a good air choke 1/4 wave from the antenna will improve things...plus a good bottle of London gin.&lt;/p&gt;&#xA;" OwnerUserId="9650" LastActivityDate="2017-05-08T12:27:05.820" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7600" PostTypeId="1" AcceptedAnswerId="7605" CreationDate="2017-05-08T15:22:52.260" Score="2" ViewCount="473" Body="&lt;p&gt;I currently do not live in the USA. I would like to find out if I still have to abide by FCC regulations.&lt;/p&gt;&#xA;" OwnerUserId="9651" LastEditorUserId="5222" LastEditDate="2017-05-15T08:37:19.557" LastActivityDate="2017-05-15T08:37:19.557" Title="legal - Do FCC regulations only apply in U.S.A?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7602" PostTypeId="1" AcceptedAnswerId="7604" CreationDate="2017-05-08T17:07:36.580" Score="1" ViewCount="222" Body="&lt;p&gt;I don't really understand how FM narrow band is created, and at the same time I can't figure out how using this simple circuit of varactors (varicap diodes) we narrow the bandwidth.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/7POtt.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f7POtt.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="9652" LastEditorUserId="9588" LastEditDate="2017-05-09T15:26:34.137" LastActivityDate="2017-05-09T15:26:34.137" Title="How to generate FM narrowband using varactors" Tags="&lt;fm&gt;&lt;bandwidth&gt;&lt;varicap&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7603" PostTypeId="2" ParentId="7600" CreationDate="2017-05-08T18:13:35.303" Score="4" Body="&lt;p&gt;You need to abide the regulations of the country you reside in.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2017-05-08T18:13:35.303" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7604" PostTypeId="2" ParentId="7602" CreationDate="2017-05-09T10:54:35.583" Score="3" Body="&lt;p&gt;Narrowband &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_modulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;FM&lt;/a&gt; transmissions have a bandwidth that is about the same as the bandwidth of the modulating signal (the so-called &lt;em&gt;modulation index&lt;/em&gt; is lower than 1). Wideband FM transmissions exceed the bandwidth of the signal (broadcast FM is 150kHz wide).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To narrow the modulation bandwidth for this circuit, you might reduce the influence of the varactor on the total capacitance of the resonant circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Add a capacitor in series between the varactors and C1&lt;/li&gt;&#xA;&lt;li&gt;Increase the varactor bias voltage (increasing the width of the depletion region, lowering the change of capacitance with voltage).&lt;/li&gt;&#xA;&lt;li&gt;Make C1 bigger&lt;/li&gt;&#xA;&lt;li&gt;Lower the modulation voltage (the AC signal superimposed on the varactor bias voltage)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The first three options require retuning of the circuit. So the simplest way to do it is to attenuate the modulation signal to bring the modulation index below 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please note: Using the given component values the sweep will not be very big anyway. The few pf's from the varactors will not substantially change the total capacitance because C1's capacitance is almost a million times larger.&lt;/p&gt;&#xA;" OwnerUserId="9588" LastActivityDate="2017-05-09T10:54:35.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7605" PostTypeId="2" ParentId="7600" CreationDate="2017-05-09T12:43:14.857" Score="3" Body="&lt;p&gt;The FCC's jurisdiction is only within the United States. You'll need to comply with the regulations in the location where you are operating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, especially in the context of amateur radio, and even more so on HF, many of the &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?tpl=/ecfrbrowse/Title47/47cfr97_main_02.tpl&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC's regulations&lt;/a&gt; mirror &lt;a href=&quot;http://www.itu.int/pub/R-REG-RR-2012&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU regulations&lt;/a&gt; which are adopted pretty much everywhere. As such it's usually a safe assumption that if something is prohibited in the US, it's prohibited most other places too. For example, a spark gap transmitter is probably not allowed anywhere. Likewise, prohibitions on commercial use, broadcast of music, and so on are almost universal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The converse is not necessarily true: something allowed in the US may not be allowed elsewhere. Band allocations in particular can vary, and local jurisdictions can and often do add regulations in addition to what's agreed by the ITU. Check local regulations.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-05-09T13:29:46.293" LastActivityDate="2017-05-09T13:29:46.293" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7606" PostTypeId="2" ParentId="7600" CreationDate="2017-05-09T20:30:22.337" Score="7" Body="&lt;p&gt;If you are operating under your US callsign, you typically need to abide by both the rules of the country you're operating in, &lt;em&gt;and&lt;/em&gt; the US rules. From &lt;a href=&quot;http://www.arrl.org/us-amateurs-operating-overseas&quot; rel=&quot;noreferrer&quot;&gt;http://www.arrl.org/us-amateurs-operating-overseas&lt;/a&gt; (about CEPT/IARU):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Class 1 licensees... may operate with the same privileges they are authorized in their home country provided that they do not exceed those privileges granted to the highest class license available in the country.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if the country you're in allows you to operate on 4m but the US does not, you're not allowed to operate on 4m - as long as you're using the US callsign. If you operate under a callsign issued by that country, you're free to do so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All of this depends on the agreement that the US has with the country you're operating in. There's no general answer.&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2017-05-09T20:30:22.337" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7607" PostTypeId="2" ParentId="7006" CreationDate="2017-05-09T20:51:56.387" Score="1" Body="&lt;ul&gt;&#xA;&lt;li&gt;AFO is filtered, squelched audio.&lt;/li&gt;&#xA;&lt;li&gt;DEO is raw discriminator audio. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Here is a PDF of the &lt;a href=&quot;https://forums.radioreference.com/attachments/kenwood-ef-johnson-forum/29815d1287024000-nx-700-800-25-pin-accessory-connector-nx700out.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;NX-700 pin documentation&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9631" LastActivityDate="2017-05-09T20:51:56.387" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7609" PostTypeId="1" AcceptedAnswerId="7702" CreationDate="2017-05-10T23:39:58.490" Score="1" ViewCount="1315" Body="&lt;p&gt;Last week I upgraded and renewed my license at the same time. I did this by returning the form through W5YI. The form was complete with authorization of the upgrade by my local VEC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that now when I pull a copy of my license from the ULS/FCC site, it still shows my license operator privileges as &quot;Technician&quot; even though the expiration date has been extended (the renewal took effect but the upgrade did not).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Under Special Conditions/Endorsements it says:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;LICENSE CLASS CONVERTED PER 97.21a3&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I do qualify for an automatic upgrade from Technician to General (and this has been confirmed and proven and certified by my VEC), I am confused as to why my license class still shows as &quot;Technician&quot; rather than &quot;General&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this a mistake, or does it just take more time for the upgrade to kick in?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My VEC said we should check again in a few weeks.&lt;/p&gt;&#xA;" OwnerUserId="9666" LastEditorUserId="76" LastEditDate="2017-05-11T00:38:58.367" LastActivityDate="2017-06-04T23:22:12.557" Title="I upgraded from Tech to General and renewed at same time but my license still says Tech" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7610" PostTypeId="2" ParentId="7609" CreationDate="2017-05-11T00:14:17.123" Score="4" Body="&lt;p&gt;Here is what the reference to part 97.21a3 means:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Application for renewal of a Technician Plus Class operator/primary station license will be processed as an application for renewal of a Technician Class operator/primary station license.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So your tech plus license has been renewed as a technician license. Your general class upgrade has not yet been processed. If you do not see your general class in the ULS within the next week, you or your VEC should contact the FCC. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meanwhile, you may operate as a general class licensee by appending /AG to your call.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-11T00:14:17.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7611" PostTypeId="1" AcceptedAnswerId="7617" CreationDate="2017-05-13T00:48:32.913" Score="1" ViewCount="2863" Body="&lt;p&gt;What is the least voltage the FT-60 can be operated at?  In other words, what is the recommended voltage to change battery or charge?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Menu item number 12 (DC VLT) shows the amount of charge left in the battery and it also displays when the radio starts up.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio is fully charged at 9 volts and I'm wondering what voltage to switch the battery at.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="9673" LastEditorUserId="9673" LastEditDate="2017-05-13T17:25:14.867" LastActivityDate="2017-05-15T08:16:04.503" Title="Yaesu FT-60 Battery Life" Tags="&lt;ht&gt;&lt;battery&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7613" PostTypeId="2" ParentId="1866" CreationDate="2017-05-13T22:32:53.040" Score="2" Body="&lt;p&gt;This looks a lot like what we had at our commercial radiotelephone stations in the days before cell towers.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We built small metal boxes for the feeds to enclose it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our feedlines were thick coax.  RG-11, I believe, connected directly to the screw terminal and the shield to the mounting bracket which was connected to the radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Weather sealing was done at the connection with that terrible tar-like black tape on the inside, then we had silicone all around the small box that fit right around the connection point.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-05-13T22:32:53.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7614" PostTypeId="2" ParentId="1866" CreationDate="2017-05-14T00:48:50.580" Score="1" Body="&lt;p&gt;After you jerry-rig your coaxial connectors in whatever way you choose you want to use a product called Coax Seal which is available from Amazon &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B0002ZPINC&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.  Even though this product presents itself like a roll of thick black electrical tape it is not necessarily used like that.  You wrap up the connection to be sealed as best you can and then using your thumbs and fingers you mold the seal into and around the unusual places and form something tight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used this product with a whole slew of different types of situations and some worse configurations (for sealing) than shown in your photo.  The key though is applying enough of the seal and then molding it to fit the piece being sealed as well as to satisfy your fitness to the purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Long lasting.  I use this seal on coaxial connectors that run to my mobile antenna and under the body of my truck and the seal was just as effective after 10 years as it was the day I applied it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One thing -- it is a bear to take off unless you use some thinners and other solvents to help dissolve it.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="218" LastEditDate="2017-05-15T15:06:57.060" LastActivityDate="2017-05-15T15:06:57.060" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7615" PostTypeId="1" AcceptedAnswerId="7616" CreationDate="2017-05-14T17:16:24.363" Score="1" ViewCount="4058" Body="&lt;ol&gt;&#xA;&lt;li&gt;Are all of these the same?  Shortwave, CB, and HAM&lt;/li&gt;&#xA;&lt;li&gt;If they are not the same, which one is better?&lt;/li&gt;&#xA;&lt;li&gt;Which one can be easily hidden (doesn't HAM need a big antenna?) for broadcasting?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="9683" LastActivityDate="2017-10-23T02:33:43.447" Title="Shortwave / CB / HAM?" Tags="&lt;citizens-band&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7616" PostTypeId="2" ParentId="7615" CreationDate="2017-05-15T01:25:49.837" Score="6" Body="&lt;p&gt;Welcome to Amateur Radio Stack Exchange.  Be sure to take the &lt;a href=&quot;https://ham.stackexchange.com/Tour&quot;&gt;Tour&lt;/a&gt;.  It shows what this community expects and how to craft a question in such a way that it will attract useful answers.  In this way the database is expanded for the benefit of everyone.&lt;/p&gt;&#xA;&lt;p&gt;Here are your answers:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;No, they are not the same.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Imho, ham radio is much better.  It is just plain fun.  It can use shortwave and talk all around the world.  It can use hand-held radios to talk around town.&lt;/p&gt;&#xA;&lt;p&gt;It works when nothing else does.  Where the rubber meets the road is in emergency situations: When the cell towers quit working there will always be ham radio.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;There are small antennas for all of these.&lt;/p&gt;&#xA;&lt;p&gt;Nitpick:  The term broadcasting is point-to-multipoint, which is only done on ham radio briefly in order to establish a point-to-point connection for actual communications.  It is not like a commercial station that continuously broadcasts to anyone who cares to tune in.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Here a Q&amp;amp;A that examines some of the issues I think you are looking for:&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/3706/should-i-use-ham-or-cb-radio?rq=1&quot;&gt;Should I use ham or cb radio?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-10-23T02:33:43.447" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7617" PostTypeId="2" ParentId="7611" CreationDate="2017-05-15T08:16:04.503" Score="4" Body="&lt;p&gt;The FT-60 manual says the battery pack is a NiMH pack (&quot;FNB-83 (7.2 V, 1400 mAh)&quot;); so, as we usually use 1.2V as the nominal voltage of a single NiMH cell, a pack of 6 cells in series.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd usually make sure not to discharge a NiMH below 1.0 – 1.1 V; going deeper can damage the cell. So, the minimal voltage for a pack of 6 in series would be 6.0 – 6.6V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd very much expect your FT-60 (or the battery pack itself) to have a protection circuit that simply doesn't allow to deep-discharge your pack, i.e. your handset will very likely simply stop working as soon as the battery pack voltage drops to 6.0 V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding your 9 V: For charging, you have to apply a voltage slightly higher than what the batteries nominally supply (charging efficiency is chemically never 100%), so, when observing the voltage across the battery pack during charging, it should be &gt; 7.2 V, and a bit lower, but still &gt; 7.2 V for a short duration thereafter, but the voltage will drop very quickly as soon as you start drawing current from the battery, and then stay relatively constant (or rather: drop relatively slowly) between 7.2 V and 6.0 V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is all a bit approximate, since it depends on the making of the individual cells and the amount of current drawn, but generally, NiMH cells have a relatively flat &quot;discharge curve&quot; (i.e. after drawing an amount of mAh, how much voltage can be measured across the battery?).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The takeaway is that you can, optimally, just use the batteries until the FT-60 reports them &quot;flat&quot;, not shorter, not longer. NiMH don't (as significantly) suffer from the &quot;memory effect&quot; that NiCd exposed, so there's nothing to be lost when you really just charge your batteries overnight, and then use them as long as they work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, with the moderate current drawn by the handset, and the voltage, I would've designed the device to work with LiIon batteries – these could pack more energy into the same size and weight than NiMH – and you'd have a longer talk time. However, LiIon is a bit harder to make safe, so that might have come out a bit more expensive. Then again, those batteries are what powers smartphones these days, so the economics of scale would probably have made them cheap.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-05-15T08:16:04.503" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7618" PostTypeId="1" CreationDate="2017-05-16T19:05:03.413" Score="1" ViewCount="140" Body="&lt;p&gt;I hope the question is not too stupid, as I am very new to Radio. According to my logic, the obvious answer is no. However I believe to have read somewhere that interference may be a problem when the second frequency is close to some multiple of the first? I do not know the exact bandwidths and have no way of testing the setup beforehand. &lt;/p&gt;&#xA;" OwnerUserId="9494" LastActivityDate="2017-05-17T01:20:50.993" Title="Is there a risk of interference between a 403 MHz and a 433 MHz Radio?" Tags="&lt;transmitter&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7619" PostTypeId="1" CreationDate="2017-05-16T23:11:55.217" Score="2" ViewCount="237" Body="&lt;p&gt;I am looking to upgrade my station soon by buying a Yaesu FTM-3200dr mobile 2m radio. I am limited on funds for radio and I don't want to get the wrong type of antenna connector and wast a bunch of money. If anyone knows what type of antenna connector to get or if anyone has an antenna recommendation for this radio.&lt;/p&gt;&#xA;" OwnerUserId="9462" LastActivityDate="2017-05-22T04:27:41.897" Title="Yaesu FTM-3200dr Antenna" Tags="&lt;antenna&gt;&lt;2m-band&gt;&lt;yaesu&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7620" PostTypeId="2" ParentId="345" CreationDate="2017-05-16T23:24:58.757" Score="1" Body="&lt;p&gt;On morse code you want your transmissions to be as short as possible and so they have developed codes for frequent words or phrases. 73 is the code for best wishes, sincerely, etc.&lt;/p&gt;&#xA;" OwnerUserId="9462" LastActivityDate="2017-05-16T23:24:58.757" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7621" PostTypeId="2" ParentId="7618" CreationDate="2017-05-16T23:26:01.743" Score="2" Body="&lt;p&gt;There is the possibility that one transmitter could de-sense the other's receiver. But it is difficult to predict - you simply need to try it.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-16T23:26:01.743" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7622" PostTypeId="2" ParentId="1196" CreationDate="2017-05-17T00:11:30.333" Score="0" Body="&lt;p&gt;There are some disadvantages to using only one ADC to do direct sampling:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The phase of the RF signal is not preserved &lt;/li&gt;&#xA;&lt;li&gt;Things like envelope detection are impossible (see &lt;a href=&quot;https://en.wikipedia.org/wiki/Direct-conversion_receiver#Technical_issues&quot; rel=&quot;nofollow noreferrer&quot;&gt;Direct-conversion receiver&lt;/a&gt;)&lt;/li&gt;&#xA;&lt;li&gt;DSP libraries for SDR typically work on complex numbers, so in order to use them one needs to set the imaginary part to zero, therefore wasting half of the computation cycles&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;There is a design though that allows direct quadrature sampling: the Tayloe Detector. See&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://techham.altervista.org/SDR/An%20Introduction%20To%20HF%20Software%20Defined%20Radio.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;An Introduction to HS Software Design Radio&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://essay.utwente.nl/58276/1/scriptie_Soer.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Analysis and comparison ofswitch-based frequency converters &lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9580" LastActivityDate="2017-05-17T00:11:30.333" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7623" PostTypeId="2" ParentId="7618" CreationDate="2017-05-17T00:51:16.197" Score="1" Body="&lt;p&gt;You seem to be thinking of harmonic distortion. A signal passed through an amplifier with harmonic distortion will add new signals at multiples of the original signal. For example, if the input is at 100 MHz, then there may be new signals at 200, 300, 400, ... MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any real amplifier will produce some degree of harmonic distortion, though in any properly working station it will be negligible. Usually the odd harmonics (in the example, 300, 500, 700 MHz, ...) are stronger when an amplifier has a &lt;a href=&quot;https://en.wikipedia.org/wiki/Push%E2%80%93pull_output&quot; rel=&quot;nofollow noreferrer&quot;&gt;push-pull output stage&lt;/a&gt;, which is very common.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, harmonic distortion can not interference between 403 MHz and 433 MHz, since these numbers are not related by any integer factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Harmonic distortion is not the only mechanism that can cause interference, but it does seem to be the one you are thinking of. &lt;a href=&quot;https://en.wikipedia.org/wiki/Intermodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Intermodulation&lt;/a&gt; can also cause interference, though the frequencies where that interference appears is somewhat more complicated to predict since there are more unknowns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And of course there are many other ways interference can happen. You ask if it's &quot;possible&quot;, and strictly speaking the answer is yes. But it would be very unusual, and would require extremely cheap, poorly designed, or broken equipment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-05-17T00:51:16.197" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7624" PostTypeId="2" ParentId="7618" CreationDate="2017-05-17T01:20:50.993" Score="2" Body="&lt;p&gt;To add to what Glenn W9IQ says, it depends on how sensitive the front-end of the receiving radio is. If it is not designed to be near strong out-of-band signals, then a strong out-of-band signal could 'swamp' the receiver's front-end, meaning that it can't process signals in its intended band properly because it is effectively overloaded.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Glenn stated, it's not easy to predict. The best way to see how badly the receiver is affected by a nearby transmitter, is to try it. If transmitting causes intended signals to be wiped out, then that means that the receiver is affected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The good news is that this is not too difficult to overcome - especially since the two frequencies are not harmonically related. You can put a good band-pass filter in line with the receiving antenna and that would cut out all frequencies outside the intended band. A properly-designed high-pass filter could cut out anything below 433MHz, and would be a simpler design. If the receiver is never used to transmit, then a filter would be relatively simple to make. If the receiver also transmits, then the filter would need to handle the power of the transmitted signal as well.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-05-17T01:20:50.993" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7625" PostTypeId="2" ParentId="32" CreationDate="2017-05-17T01:43:25.593" Score="2" Body="&lt;p&gt;For a new look at this subject, see the article WORDSWORTH in the May,2017 issue of QST page 74. The thesis is to learn whole words at a time by listening at speeds at least 5 wpm beyond your capability and having long spacing between words. The tool to use is the software Data Mode program FLDIGI. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been using a word-list '100 Most Common Words' extracted from G4FON's tutorial program and an inter-word spacing of 8 characters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no one method that works for everyone but this could the method that is YOUR Silver Bullet. Give it a try.&lt;/p&gt;&#xA;" OwnerUserId="9693" LastActivityDate="2017-05-17T01:43:25.593" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7626" PostTypeId="2" ParentId="32" CreationDate="2017-05-17T02:42:17.660" Score="2" Body="&lt;p&gt;Anyone wanting to either learn CW --or improve their skills-- would do well to download &lt;em&gt;The Art &amp;amp; Skill of Radio Telegraphy&lt;/em&gt;. It contains powerful incentives and methods to learning it. &lt;strong&gt;It's a masterpiece!&lt;/strong&gt;. I printed and bound all 60+ pages; however, you don't really need to read all of it to benefit and be highly motivated and excited about it!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After the original page disappeared, I made it available at &lt;a href=&quot;http://www.w0btu.com/links.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w0btu.com/links.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whatever you do, DON'T learn the code by memorizing the printed dots and dashes, or you'll have to re-learn it all over again in order to actually use and enjoy it!  &lt;strong&gt;Learn the SOUNDS.&lt;/strong&gt; &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-05-17T02:47:17.903" LastActivityDate="2017-05-17T02:47:17.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7627" PostTypeId="2" ParentId="516" CreationDate="2017-05-17T05:31:47.653" Score="1" Body="&lt;p&gt;Any amateurs working all the way up at 440 to 475 THz ? &#xA;aka your typical red LED&#xA;aka 650nm, red laser&lt;/p&gt;&#xA;&#xA;&lt;p&gt;20W sector transmitters are pretty cheep and readily available on Amazon. &lt;a href=&quot;http://a.co/bMHXMgJ&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://a.co/bMHXMgJ&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;100mW high gain transmitters are also pretty cheep and readily available on Amazon.&#xA;&lt;a href=&quot;http://a.co/2r47axc&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://a.co/2r47axc&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9694" LastActivityDate="2017-05-17T05:31:47.653" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7628" PostTypeId="2" ParentId="6346" CreationDate="2017-05-17T12:02:42.527" Score="2" Body="&lt;p&gt;One way to estimate line-of-sight before you even step outside is to calculate the radio horizon. For the horizon distance in miles and antenna height in feet, the formula is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{horizon} = 1.23 \sqrt{\text{height}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For kilometers and meters, it is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{horizon} = 3.57 \sqrt{\text{height}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The horizons of each station add. If you need a link distance of 25km, then you might aim for a horizon of 12.5km on each side. That would require an antenna at height:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \left(12.5 \over 3.57\right)^2 = 12.26\:\mathrm m $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an approximation based on a smooth Earth with no terrain. If a station is on a hill, add that to the height. If there's a hill between the two stations, that may be a problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a quick and easy real-world check, a signal mirror and binoculars work well. A true optical line of sight isn't strictly necessary for a working RF link, but it's nice to have if the objective is a high quality, reliable path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are other complicating factors which must ultimately be considered, such as &lt;a href=&quot;http://www.mike-willis.com/Tutorial/PF6.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;atmospheric effects&lt;/a&gt;, &lt;a href=&quot;http://radiomobile.pe1mew.nl/?Calculations:Propagation_calculation:Fresnel_zones&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fresnel zones&lt;/a&gt;, interference, and other practical issues other answers have mentioned. However, if this estimation shows the radio horizon is grossly insufficient, there's little reason to continue your endeavor unless you can secure taller towers or better sites.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-05-20T16:33:03.700" LastActivityDate="2017-05-20T16:33:03.700" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7629" PostTypeId="2" ParentId="1695" CreationDate="2017-05-17T23:32:25.083" Score="0" Body="&lt;p&gt;You definitely will be better of with the Nagoya. I don't have the NA-701 but I have the NA-771. The difference is night and day.&lt;/p&gt;&#xA;" OwnerUserId="9462" LastActivityDate="2017-05-17T23:32:25.083" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7630" PostTypeId="1" CreationDate="2017-05-18T16:35:37.660" Score="3" ViewCount="1014" Body="&lt;p&gt;I have had a license since I was a kid, but have not touched anything ham radio related in years. I have been thinking about diving back in and combining it with my sailing. I'm looking for thoughts on an HF antenna that I can easily deploy when needed, which will mean at the dock or anchor and not while underway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My sailboat is a 30 feet long and has a mast that stands 38 feet above the deck. The distance from the mast step to the aft most point is 18 feet, so if this is a right triangle, the length of the hypotenuse is 42 feet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am thinking that a half wave, end fed antenna that could be made to work on 20, 15 and 10 meters would be easy to hoist between the stern and the mast head when needed and would appreciate your thoughts. Also, are there end fed quarter wave antennas?  If so I could have one for 40 meters as well. I would prefer to avoid a tuner just because it's one more thing on a small boat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One other consideration is that, being a sail boat there are 1/4 inch stainless steel cables which hold the mast up. I'm really not interested in putting insulators in these cables or trying to load them as antennas, but I am wondering what interference or impact they might create.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPDATE: The boat is used primarily for racing so this is the cause of my hesitance to modify the rig. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the mast is &quot;deck stepped&quot; which means that it's bottom sits on the deck. On most sailboats, the mast actually does down through the deck and sits just above the keel. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the top of the mast is an existing small VHF antenna for the marine VHF radio with a feedline inside the mast.&lt;/p&gt;&#xA;" OwnerUserId="9699" LastEditorUserId="9699" LastEditDate="2017-05-21T04:34:03.397" LastActivityDate="2017-05-22T14:02:42.740" Title="Suggestions for HF antenna for occasional use on my sailboat" Tags="&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7631" PostTypeId="2" ParentId="6346" CreationDate="2017-05-19T00:18:14.540" Score="1" Body="&lt;p&gt;&lt;strong&gt;&lt;em&gt;25KM is a really long distance.&lt;/em&gt;&lt;/strong&gt; You need to be up fairly high to beat the curve of the earth. If you are at sea level on a beach, and your eyes are 1.7m above the ground, the horizon would be at 4.7km. &lt;a href=&quot;https://en.wikipedia.org/wiki/Horizon#Objects_above_the_horizon&quot; rel=&quot;nofollow noreferrer&quot;&gt;Source wikipedia:Horizon&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In actuality both ends would need to be elevated so that the beam path passes high enough over terrain between the 2 points. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A cheap way to test line of sight is binoculars and a really large white or Black sheet depending on the color of the surrounding terrain. &#xA;A signal mirror would need to be aimed and it would need to be huge to be really visible. If you want to use a light, do it at night, and get one of the aircraft approved Xenon strobes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You wouldn't want to use a laser with binoculars for 2 reasons. 1) coliniated light can damage your retina when intensified by a lens. 2) the divergence of a non-commercial laser point over 25 Km probably wont be visible anyway. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A bunch of things which other answers have hit on are various type approval issues with using this for WIFI. If anyone had looked at the link, they would see that the PowerBeamAC is &lt;strong&gt;not&lt;/strong&gt; working under the 802.11ac specification. &#xA;It has a separate 802.11 antenna for configuration, but the 25km, link is advertised using a supposedly proprietary TDMA signalling for point to point. and is advertising 450Mbit/s bandwidth. It is separately type approved by the CE, FCC and IC. All of this is in the &lt;a href=&quot;https://dl.ubnt.com/datasheets/PowerBeam_ac/PowerBeam_AC_Gen2_DS.pdf&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Datasheet&quot;&gt;DATASHEET&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6092" LastActivityDate="2017-05-19T00:18:14.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7633" PostTypeId="2" ParentId="7630" CreationDate="2017-05-20T05:04:51.603" Score="0" Body="&lt;p&gt;Welcome back to the hobby.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can run a wire up to the top of the mast, insulated from it, that is great.  Then just run it to the furthest point on the boat.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From your post I presume you have an antenna tuner.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your instincts are good about not wanting to use load-bearing cabling as part of the antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The water will make a great ground.  Saltwater is slightly better, but any water is better than any earth ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Enjoy!&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-05-20T05:04:51.603" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7634" PostTypeId="2" ParentId="7630" CreationDate="2017-05-20T16:18:17.570" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm really not interested in putting insulators in these cables or trying to load them as antennas&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's a shame, because the mast and the cables probably make an excellent antenna. In fact unless you go through some trouble to get the antenna far away from the mast, or oriented orthogonally, the mast and cables are going to end up being a significant part of the antenna whether you like it or not. Remember you don't need a DC connection: mutual inductance and capacitance will couple things together at RF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't need to put insulators on the cables. Finding a good feed arrangement will take some experimentation, but there are plenty of ways to couple into the mast which don't involve any structural modifications, which I guess is your fear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the mast, cables, and hull make a closed loop anywhere, you can put a smaller loop within that and feed the small loop. The two loops effectively make a transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another method is to clamp a ferrite around one of the cables or the mast, and also run several turns of wire through the ferrite, and feed that. Again, a transformer feed. This works even if there's not a loop to feed. That is, you could clamp such a ferrite around a metal pole stuck in the ground (or the water) and make a fine antenna. A mast on a sailboat is not far from this. Might get tricky to find an appropriate ferrite at higher frequencies or higher power levels though, but might be great for QRP operation on 40 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;a href=&quot;https://ham.stackexchange.com/q/1804/218&quot;&gt;gamma match&lt;/a&gt; is another option which not only solves the problem of coupling into the mast without structural modifications, but also gives a couple variables to provide a decent match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you run a wire up the top of the mast like SDsolar suggests, you've effectively made a crude gamma match. The mast and the wire together make a transmission line. By varying the length of that wire you change the length of that transmission line. You can also decide to connect the wire at the top to the mast or not, which will give you an open or shorted transmission line stub which functions as a kind of &lt;a href=&quot;https://www.youtube.com/watch?v=GdSV2-6sYqk&quot; rel=&quot;nofollow noreferrer&quot;&gt;stub match&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are just a few options. For further ideas you can research existing methods of coupling into loop antennas or shunt feeding towers, which are similar problems.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-05-20T16:27:09.280" LastActivityDate="2017-05-20T16:27:09.280" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7635" PostTypeId="1" AcceptedAnswerId="7638" CreationDate="2017-05-20T20:50:26.680" Score="4" ViewCount="1801" Body="&lt;p&gt;I plan to build trapped multiband dipole so I read lots of documentation I found.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is one thing that confuses me: various authors recommend setting resonant trap frequency differently: some say trap should be resonant just below wanted band, some says it should be resonant in middle of the band, and some say trap should resonate just above the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is correct approach?&lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="4665" LastEditDate="2021-05-10T15:46:32.763" LastActivityDate="2021-05-10T15:46:32.763" Title="What frequency to set trap on?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;trap&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7636" PostTypeId="2" ParentId="7587" CreationDate="2017-05-20T22:13:07.357" Score="1" Body="&lt;p&gt;Well, since I resolved mystery, here is short explanation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I built my own dip adapter exactly as explained by Phil - single loop of wire connected to output of MFJ-225. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, putting loop at the side of trap (as presented in RigExpert picture) did not work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Dip measurement is quite insensitive&lt;/strong&gt;, so I had to make sure loop is set at the center of trap length. If not set that way dip may be shallow or not to show at all. I had to make loop with diameter of about 8 cm to be able to measure the biggest trap I have. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Dip is very sharp&lt;/strong&gt;. MFJ-225 must be set to narrow bandwidth or dip simply would not be visible on graph. It seems even when I got dip I could not notice it as I used wider bandwidth for graph. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found most practical to set bandwidth to 1.18 MHz and step to 1 MHz and scan until dip is noticed. Then switch to narrow bandwidth and fine step to pinpoint exact resonant frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although graph (ANT-S) looks nicer, it seems to me it is faster to find resonant frequency using plan SWR mode (ANT-G).&lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="306" LastEditDate="2017-05-31T10:30:59.210" LastActivityDate="2017-05-31T10:30:59.210" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7638" PostTypeId="2" ParentId="7635" CreationDate="2017-05-21T12:44:05.793" Score="6" Body="&lt;p&gt;In tuning a trap there are two concerns which are somewhat contradictory:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;You want the trap to have a high impedance on the target band.&lt;/li&gt;&#xA;&lt;li&gt;You want losses to be low.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The objective of a trap is to reduce the currents on the inactive portion of the antenna to a negligible amount. This doesn't require an impedance that's as high as possible: it requires only an impedance that's high enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any LC circuit such as a trap, the current or voltage circulating between the inductor and capacitor is at a maximum at resonance. The trap is a parallel LC circuit and a high impedance (high ratio of voltage to current) at resonance. Because the capacitor and inductor are in a loop, current can flow around that loop without adding to the current through the trap. That circulating current serves to charge the capacitor to a high voltage in cooperation with the voltage applied to the trap, allowing a higher voltage to be attained with less current (the definition of high impedance). But this high circulating current means high resistive losses, and the high voltage means high dielectric losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Logically then, we want to tune the trap such that the impedance in the operating band is high enough, but no higher. In practice putting the the trap resonance just outside the band is effective: for any reasonable trap design this will provide an impedance that is high enough, while keeping the resonance and associated high losses where they will not be encountered in operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning resonance to be above or below the band does not matter much. It will affect the phase shift between the active and inactive sections of the antenna, but since the inactive section of the antenna has not much current on it, this isn't very important. It will have some effect on the tuning of the antenna, and the electrical length of the antenna on bands where the trap is bypassed. But these are all things easily compensated when tuning the antenna by adjusting length, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For further reading, &lt;a href=&quot;https://www.w8ji.com/traps.htm&quot; rel=&quot;noreferrer&quot;&gt;W8JI has a good article on traps&lt;/a&gt; which includes some measured data for traps of several types.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-05-21T12:44:05.793" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7639" PostTypeId="1" AcceptedAnswerId="7641" CreationDate="2017-05-21T14:41:17.997" Score="3" ViewCount="1429" Body="&lt;p&gt;I am  very new to radio and am using two 433MHz 1/4 wavelength monopole antennas to send and receive data. On the transmitting antenna I'm going to add radials (as it is the standard in my application). However I wonder, would it help adding radials to the receiver too? On the one hand it makes sense, but on the other I wonder, why would a receiver need a ground plane? I hope you can help me and that my question is not too dumb.&lt;/p&gt;&#xA;" OwnerUserId="9494" LastActivityDate="2019-06-02T22:04:48.203" Title="Does a receiving antenna need radials?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7640" PostTypeId="1" CreationDate="2017-05-21T15:32:15.597" Score="1" ViewCount="498" Body="&lt;p&gt;So I've been following this guide on how to build an antenna for a High altitude balloon: &lt;a href=&quot;https://ukhas.org.uk/guides:payload_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;link&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the guide they say to use RG174 wire, which is why I bough some cheap RG174 wire off Ebay. I guessed that not even the Chinese could mess something as simple as wire up. However the wire I got looks a bit different to what I expected. I suspect it might not be RG174 wire but some other Coax wire. The inner wire is very thin (with a diameter of maybe 0.4 mm or so). Is that ok? Does the thickness of the wire used affect the antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suppose it isn't &lt;em&gt;that&lt;/em&gt; important that the wire is RG174 as long as it is something similar? So what do you think? Is this wire ok to use?&lt;/p&gt;&#xA;" OwnerUserId="9494" LastActivityDate="2017-05-22T23:23:49.043" Title="Is cheap Chinese coax wire ok to use as an antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wire-antenna&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7641" PostTypeId="2" ParentId="7639" CreationDate="2017-05-21T16:02:02.230" Score="12" Body="&lt;p&gt;Most antennas are reciprocal — they have the same properties when receiving as when transmitting. This means that in many ways, a good antenna design makes both a good receiving antenna and a good transmitting antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The biggest exception to this is active antennas which have an internal amplifier that only works for receiving.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the properties that you &lt;em&gt;want&lt;/em&gt; for a receiving antenna are not necessarily the same as a transmit antenna. For example, when transmitting, you care about how efficiently the antenna radiates, so that you're getting the best output for power input, and whether it can handle the power without failing (e.g. arcing, heating). Receiving does not care about this a bit, because the power is miniscule.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if you are receiving, it is often the case that you care more about the &lt;em&gt;signal-to-noise ratio&lt;/em&gt;, not the absolute amount of signal you receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now let's talk about radials (or a ground plane) in particular. Every antenna &lt;em&gt;always&lt;/em&gt; has two halves, no matter what; if you try to leave one out then either something else will replace it or your antenna won't work at all. If you leave off the radials in an antenna designed to have them, then what happens is the shield of your coax will start acting as the other half — you have instead a vertical dipole with a lower element of no particularly well-designed length or positioning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that your antenna's radiation pattern will not be what you expect — it will receive less well in some directions than it was designed to. Being a too-long antenna, it will have an extra-spiky pattern, so if the other station is moving you'll see lots of nulls (directions with very low signal strength) which is bad for reliable communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, since the coax shield is acting as an antenna element, any noise from your equipment will come into the receiver, more than it would otherwise (that is, a decreased signal-to-noise ratio).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, to summarize: put on the radials. You will get more predictable performance.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-05-21T16:27:45.583" LastActivityDate="2017-05-21T16:27:45.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7642" PostTypeId="1" AcceptedAnswerId="7645" CreationDate="2017-05-21T18:04:36.240" Score="8" ViewCount="12843" Body="&lt;p&gt;Consider these three cases:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;My understanding is that when building or installing an antenna designed to operate over a ground plane (e.g. a quarter-wave vertical), the size of the ground plane does not matter (e.g. the earth, possibly coupled using additional radial wires, or a car roof of unspecified size), provided that it is sufficiently large compared to the wavelength. This is commonly described as the ground plane acting as a reflector, so that there is effectively a second quarter-wave element “below the ground plane”. If this analogy is accurate, then obviously the larger the better.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Designs involving self-supporting radials, flat or downward-sloping, may use a specific length of radials.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A vertical resonant center-fed dipole must have a quarter-wave lower element — having the same symmetry as case 1 but physically instantiated.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;On the continuum of antenna designs between a ground plane antenna and a coaxial vertical dipole, why is it that sometimes there is a well-defined optimum size of the ground plane, or rather the antenna element which is not pointing upward, whereas sometimes it doesn't seem to matter much?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;This question is not about the size of ground-level radial networks&lt;/em&gt;, but about comparing designs which have “at least this big” ground planes such as a car roof or the Earth augmented with wires, with free-standing designs which have specific lengths of conductors.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="8717" LastEditDate="2020-11-26T19:29:35.360" LastActivityDate="2020-11-26T20:13:13.943" Title="When and why does the size of a ground plane or radials matter?" Tags="&lt;antenna-theory&gt;&lt;mobile&gt;&lt;vertical-antenna&gt;&lt;radial&gt;&lt;counterpoise&gt;" AnswerCount="7" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="7643" PostTypeId="2" ParentId="7642" CreationDate="2017-05-21T20:32:37.887" Score="2" Body="&lt;p&gt;In broadcast AM radio it is standard practice to use quarter-wave towers (because half-wave towers are expensive and more of a maintenance headache). These towers require a ground plane to reflect the signal in such a way that it virtually provides an image of the rest of the half-wave that allows for lowest voltage and highest current at the feedpoint.  (That's the how and why)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radials are set 3 degrees apart, so there are 120 of them.  Ideally it will be on nice conductive soil, and they are buried just deep enough for good coupling and also so lawn mowers can pass over without causing damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radials are cut to a quarter wavelength plus 5%.  It turns out that having the highest conductivity (the wires) provides the best match when it is at resonance.  (Every station has a matching network, also).  This is in order to provide the image necessary for lowest voltage and highest current at the feedpoint that you would find in a center-fed half-wave antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As they couple more loosely into the ground the actual effective ground plane is much larger than the wires, which helps for ground-wave propagation.  Soils vary in their conductivity, so the predictability of providing the resonant wires is the most important factor in impedance matching.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ground planes are a maintenance issue, and the way they are soldered really matters.  Corrosion gets to them and in order to pass my inspections (I did the VIP - the voluntary inspection program that prevents FCC surprise inspections - my reports went into the files at the stations and not to the FCC, and they liked me because I came with a toolbox to fix any deficiencies right then and there).  I always wanted to see good solid ground connections at the antenna base, in particular.  I always liked it when stations had a good wide low-resistance copper strap at the tower base, so even if some wires get damaged the rest would carry the freight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hustler has some excellent references for what they sggest for their 5BTV antennas, and they are similar except that no amateur is going to put out 120 wires.  In fact, you can get quite a good ground plane with many fewer wires than that.  My personal recommendation is for about 20-40 wires, and of course there are a lot of obstacles in the way of a typical ham vertical antenna installation.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Installation on a rooftop requires the creation of an artificial ground - a counterpoise.  It should be tied to earth ground at the transmitter.  I have designs for Part 15 LPAM stations that can reach out over a mile with a decent counterpoise of 20 wires.  Those must by physical necessity be less than a quarter wavelength; the vertical element is limited by regulation to 10 feet from the ground.  (I recommend the Procaster transmitter for this, which is FCC Type-accepted and includes an internal tuner, a bolted-on 9 foot antenna and a 1-foot grounding cable so it can be mounted above the counterpoise.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Downsloped grounds for vertical antennas can work at about the same length as flat ones, a quarter wavelength plus 5%.  Bandwidth is an issue for verticals that must cover an entire band like from 144-148 MHz, so you want the parts to be cut for the middle of the band range you intend to use it for in order to achieve the flattest SWR over the entire range of frequencies.  NOAA weather radio antennas should be cut for 162.5 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So is bigger always better?  It depends on your wavelength.  VHF signals have little to no ground-wave propagation mode, and the sloped radials help launch the signals skyward.  The vertical component holds the launch angle down, of course.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Performance varies slightly between coaxial dipoles and sloped-radial antennas, but not as much as you might think.  Similar at UHF.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beyond that (or even starting at 70CM) you will want to leave omni antennas behind as much as possible.  Just ask any police department what their experience was when they shifted from VHF to UHF and they'll tell you it was better before.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Portable radios work best when they have 5/8 wave antennas so they have no need for a ground plane.  Quarter-wave antennas in HTs operate under the assumption that the radio body will capacitatively couple to your body to provide a (lossy, loosely-coupled, irregularly-shaped) ground that can reflect the other quarter-wave that is missing from them (the so-called reflected image).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance is a whole different topic, and involves more than just the feedpoint of the antenna, and it runs the gamut, including matching networks in the transmitter or radio shack, feedlines, etc.  Magnetrons in microwave ovens come with an integral radiating element which matches the insides of the tube to the waveguide directly.  Only the guys in the lab coats would be able to explain impedance in that situation.  I will have to defer to others to give the math for all that.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To summarize the question about when ground plane size starts to matter:  It always does.  Even in a waveguide at 10.5 GHz.  Resonance is always best.  Compromises are made in the real world, and they all can be made to work to varying degrees.  Bigger is not always better.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance matching and resonance is king.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Matching impedance at the antenna is definitely better than matching it at the transmitter unless you want to cut your feed lines to be an odd multiple of a half wave.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-05-21T21:07:42.693" LastActivityDate="2017-05-21T21:07:42.693" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7644" PostTypeId="2" ParentId="7640" CreationDate="2017-05-21T21:13:32.923" Score="2" Body="&lt;p&gt;In antenna build part it does not matter, as it is not used as coax cable but as wire material for radiating and ground elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For cable part, as long as you keep it short (few meters) it also does not matter.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2017-05-21T21:13:32.923" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7645" PostTypeId="2" ParentId="7642" CreationDate="2017-05-22T02:20:17.760" Score="6" Body="&lt;p&gt;Perhaps consider that the objective of the ground plane is to present a low impedance. At the feedpoint, the hope is to have all the current go into the antenna, and none of it on the coax common-mode. The lower the impedance of the ground plane, the less current will be on the coax common-mode due to its relatively high impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the ground plane impedance is not very much lower than the coax common-mode, then there will be significant common-mode current, and what you have built is not the dipole or the vertical or whatever you were trying to build, but something else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An infinite ground plane would be nice, but &quot;as big as possible&quot; will do. Current decreases with distance from the feedpoint, so at far distances the current is negligible, so it doesn't matter much what the situation with the ground plane (or lack thereof) is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A car roof and a UHF antenna fit this model well. A roof 1.6 meters square is sufficient for a 440 MHz antenna to have about 1.14 wavelengths in any direction. At this size, the impact of the car geometry on the antenna may be detectable if carefully measured, but unlikely to be of any practical significance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the idea is to make the ground plane as small as possible, an electrical quarter wavelength radius is a good length. Consider a &lt;a href=&quot;https://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer&quot; rel=&quot;nofollow noreferrer&quot;&gt;quarter-wave transformer&lt;/a&gt;: looking at an open through a 1/4 wave transmission line, the open is transformed into a short. The same concept applies to radials: imagine a radial and the monopole as a piece of twin-lead that have been pulled apart at one end to make an L.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This quarter-wavelength size is especially critical in elevated monopoles, that is those without radials buried in soil. Consider, soil can be used as an OK ground plane, although resistive losses make it inefficient. If the radials have minor deficiencies the soil can make up for them without much negative impact. However, air doesn't work as a ground plane at all. If the radials are deficient, then where will that current go? The feedline common-mode? The tower? Either may end up radiating fine, but such an arrangement strictly speaking isn't a monopole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Very long elevated radials would work as well, though would not be very practical.)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A vertical resonant center-fed dipole must have a quarter-wave lower element — having the same symmetry as case 1 but physically instantiated.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If the lower element isn't symmetrical, then it isn't a center-fed dipole anymore, by definition. But &lt;a href=&quot;https://ham.stackexchange.com/questions/95/how-does-moving-a-feedpoint-off-center-in-a-dipole-affect-the-resonant-frequency&quot;&gt;off-center fed dipoles&lt;/a&gt; can work just fine. A center-fed dipole is balanced, and can be ideally fed with a balanced feedline with no need for a choke or balun. Feeding the dipole off center unbalances it, which would require a feedline unbalanced by the same ratio, or a choke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, in many vertical dipole designs, the feedline is concentric with the antenna, and half of the dipole is a radiating sleeve balun. The sleeve balun works by presenting a low impedance from the perspective of the feedpoint, and a high impedance from the perspective to the feedline. It must be an electrical quarter-wave to work, so again the length is critical. At a different length it may still make a fine radiating structure, but it would no longer intrinsically be a balun so the issue of isolating the feedline would need to be solved some other way.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-05-23T11:41:08.027" LastActivityDate="2017-05-23T11:41:08.027" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="7646" PostTypeId="2" ParentId="7619" CreationDate="2017-05-22T04:27:41.897" Score="2" Body="&lt;p&gt;Page 13 of the &lt;a href=&quot;https://www.yaesu.com/downloadFile.cfm?FileID=9266&amp;amp;FileCatID=263&amp;amp;FileName=FTM%2D3200DR%5FOM%5FENG%5FEH052N100.pdf&amp;amp;FileContentType=application%2Fpdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Operating Manual&lt;/a&gt; says that radio has a fairly standard SO-239 jack and you need a 50 ohm antenna cable with the matching PL-259 plug. This is also commonly (and confusingly) known as a &lt;a href=&quot;https://en.wikipedia.org/wiki/UHF_connector&quot; rel=&quot;nofollow noreferrer&quot;&gt;UHF connector&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as a specific antenna recommendation, my favorite is the $25 &lt;a href=&quot;http://www.2wayelectronix.com/Vhf-Slim-Jim-Antenna-with-16-or-10-rg-58-VHF-16.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;N9TAX Slim-Jim&lt;/a&gt;; just make sure you select &quot;UHF Male pl-259&quot; for the connector. If you decide to go with a dual-band 2m/440 radio or think you might upgrade to one in the future, it's worth the extra couple bucks to get &lt;a href=&quot;http://www.2wayelectronix.com/Dual-band-2m-70cm-Slim-Jim-Antenna-with-16-or-10-rg-58-DUAL-16.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;the dual band version&lt;/a&gt; of that antenna.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-05-22T04:27:41.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7647" PostTypeId="2" ParentId="7640" CreationDate="2017-05-22T07:16:55.197" Score="3" Body="&lt;p&gt;They are probably suggesting the use of RG-174 because it is very thin, and for its size it is fairly strong and relatively inexpensive. If you can imagine doing the same kind of antenna using RG-8 or RG-58 you would not get much of it up in the air, even though it would be lower loss than RG-174.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For short runs at HF, it's fine - sure it's not the highest-performance coax money can buy, but it is light and relatively inexpensive.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-05-22T07:16:55.197" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7648" PostTypeId="2" ParentId="5257" CreationDate="2017-05-22T10:25:37.737" Score="0" Body="&lt;p&gt;Have you tried adjusting VR2? That looks to control the bias for Q3 and Q5 which are both common before the VHF and UHF final transmit section splits off to each respective final amplifier circuit. VR2 looks to be an adjustment setting for the APC line. Top right corner of schematic, sorta.&lt;/p&gt;&#xA;" OwnerUserId="9717" LastActivityDate="2017-05-22T10:25:37.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7649" PostTypeId="2" ParentId="7630" CreationDate="2017-05-22T11:13:26.703" Score="3" Body="&lt;p&gt;I own an O-Day 272LE sloop and have been operating HF on it for the past several years, including serious Field Day operation from along Delaware Bay and Rehoboth Bay in Delaware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The stainless-steel cockpit railing makes a good mount for vertical antennas on the stern and bow. This allows for maximum separation from the boat's rigging. For serious FD operation, I use a telescoping MFJ 33-foot mast for 40 meters and a 1/4-wave aluminum tubing 20-meter vertical. Also have used 1/4-wave verticals for 10 and 15 meters though found there wasn't enough activity there to warrant the trouble.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also have used a gamma match on one of the shrouds to get on 80 meters and made a few QSOs with that. This could also be done for 40 meters. For casual operation I just mount a single-band mobile whip on the stern rail, such as the Hamstick or &lt;a href=&quot;http://www.randl.com/shop/catalog/product_info.php?cPath=1110&amp;amp;products_id=24013&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ-1620T&lt;/a&gt; using a mount designed for putting an antenna on a truck mirror.&lt;/p&gt;&#xA;" OwnerUserId="9719" LastEditorUserId="76" LastEditDate="2017-05-22T14:02:42.740" LastActivityDate="2017-05-22T14:02:42.740" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7651" PostTypeId="2" ParentId="7640" CreationDate="2017-05-22T23:23:49.043" Score="0" Body="&lt;p&gt;So, two conflicting aspects to this:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;yeah, as said in the other answers, the choice of coax here has probably been made more for mechanical than for RF reasons,&lt;/li&gt;&#xA;&lt;li&gt;No, that won't work as nicely. Antennas can be understood as matching circuits between transmission line impedance (typically either 50 Ω or 75 Ω) and free space impedance (120π Ω).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Thus, when dimensioning an antenna, you'll make sure that the wave impedance of whatever is used to feed the antenna (and that is, in the case of this particular antenna, exactly the coax you've bought) is actually the same impedance as the rest of your system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, if someone sells you &lt;em&gt;some&lt;/em&gt; cable that's &lt;em&gt;even cheaper&lt;/em&gt; than RG-174, chances are it's &lt;strong&gt;not&lt;/strong&gt; 50 Ω. So, you get a mismatch at where you connect the antenna to your system. Yay. So, you build a nice antenna, and then throw away power for reflections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, make sure you actually didn't get what you paid for, and if you didn't, get your money back, and get the right cable. You're the weaker part in this business; don't make yourself more of a victim as necessary. Someone else will see &quot;oh, this guy sold this 10000 times, must be good&quot;, and so you accepting non-conforming goods doesn't only hurt you – but also the ham community overall.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-05-22T23:23:49.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7653" PostTypeId="2" ParentId="3575" CreationDate="2017-05-24T03:09:30.297" Score="4" Body="&lt;pre&gt;&lt;code&gt;&quot;I'm noticing that using this formula for many bands&#xA;the resulting frequency doesn't fall within the&#xA;suggested frequency range for that plan and where&#xA;they do, many don't fall within any discernible&#xA;tolerance of the middle.&quot;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Here's why this is the case today.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the early days of radio (that is, the late 19th and early 20th centuries) &lt;strong&gt;everyone referred to the approximate wavelength in meters, rather than the actual frequency in MHz.&lt;/strong&gt; &lt;em&gt;That's simply the way it was!&lt;/em&gt; Other than Lecher wires (mostly for VHF), there was almost no way of accurately measuring the actual transmit or receive frequency with any degree of accuracy. Back in those days, there were no frequency counters or accurately calibrated VFOs. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In those days --before the days of vacuum tubes, which were a HUGE technical advancement-- all that anyone had were noisy, raucous spark transmitters, which occupied a ridiculously wide bandwidth above and below the center frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Better yet were crystal-controlled triode oscillators, even if they did have key clicks and chirps.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Later, when broadband spark transmitters gave way to narrower and much cleaner tube oscillators like this, tuning became more accurate, and it was more prudent to refer to the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And that's why we still have the word &quot;wavelength&quot; in our list of amateur radio terms. Like it or not, we're just stuck with the term, and all the confusion that came with it.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-05-24T03:16:15.300" LastActivityDate="2017-05-24T03:16:15.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7654" PostTypeId="5" CreationDate="2017-05-24T23:24:35.440" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2017-05-24T23:24:35.440" LastActivityDate="2017-05-24T23:24:35.440" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7655" PostTypeId="4" CreationDate="2017-05-24T23:24:35.440" Score="0" Body="Amateur radio television transmission and reception" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-05-25T01:13:26.857" LastActivityDate="2017-05-25T01:13:26.857" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7656" PostTypeId="1" CreationDate="2017-05-25T05:56:56.553" Score="1" ViewCount="4078" Body="&lt;p&gt;I just bought a pair of BaoFeng 888s radios and they don't work out of the box. I know they are on the illegal freqs, but I expected them to work. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I got the cable, reprogrammed them to the recommended freqs (does any one has a good *.dat file for USA?) and they still don't work with each other. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What could I possibly do wrong? I select the same channel (1-1 or 2-2) and press button to talk, but I don't hear anything coming from the other radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The speaker is working, because I can hear it saying &quot;power on&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPD: here are the frequencies I'm trying to use by following the Amazon review comment:&#xA;Out/Simplex Repeater input (use only first column if you don't have a repeater)&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;462.550 ---- 467.550&lt;/li&gt;&#xA;&lt;li&gt;462.575 ---- 467.575&lt;/li&gt;&#xA;&lt;li&gt;462.600 ---- 467.600&lt;/li&gt;&#xA;&lt;li&gt;462.625 ---- 467.625&lt;/li&gt;&#xA;&lt;li&gt;462.650 ---- 467.650&lt;/li&gt;&#xA;&lt;li&gt;462.675* --- 467.675*&lt;/li&gt;&#xA;&lt;li&gt;462.700 ---- 467.700&lt;/li&gt;&#xA;&lt;li&gt;462.725 ---- 467.725&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9733" LastEditorUserId="9733" LastEditDate="2017-05-26T04:58:38.523" LastActivityDate="2017-12-19T21:40:13.547" Title="Can't get two same BaoFeng radios to work with each other" Tags="&lt;baofeng&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7657" PostTypeId="5" CreationDate="2017-05-25T06:18:54.257" Score="0" Body="&lt;p&gt;This tag is used in relation to how relative motion can affect the perceived frequency at the receiver.  This can affect communications with satellites as they pass over, for instance.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-05-25T07:08:20.203" LastActivityDate="2017-05-25T07:08:20.203" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7658" PostTypeId="4" CreationDate="2017-05-25T06:18:54.257" Score="0" Body="For questions pertaining to the Doppler effect and how it affects radio signals" OwnerUserId="-1" LastEditorUserId="873" LastEditDate="2017-05-25T07:11:58.013" LastActivityDate="2017-05-25T07:11:58.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7659" PostTypeId="2" ParentId="7656" CreationDate="2017-05-25T11:00:43.887" Score="4" Body="&lt;p&gt;A channel can transmit on one frequency and receive on another. When you push the PTT button, watch the display to see if the frequency changes. If so, pick a channel for testing where this does not happen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radios can also encode tones in the audio path that must match on the transmitter and receiver or the receiver must be programmed to ignore these tones. The tones go by a variety of names such as PL, CTCSS, DCS, or tone. Pick a channel for testing that does not use tones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are testing on frequencies for which you are not licensed, you should transmit into a dummy load instead of an antenna to prevent violating the regulations or law.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-25T11:00:43.887" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7660" PostTypeId="5" CreationDate="2017-05-25T21:19:55.857" Score="0" Body="&lt;p&gt;For questions related to charging batteries.  Please specify the battery type in the text.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="873" LastEditDate="2017-05-29T00:54:26.550" LastActivityDate="2017-05-29T00:54:26.550" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7661" PostTypeId="4" CreationDate="2017-05-25T21:19:55.857" Score="0" Body="For questions related to charging batteries.  Please specify the battery type in the text." OwnerUserId="8832" LastEditorUserId="873" LastEditDate="2017-05-28T14:42:11.880" LastActivityDate="2017-05-28T14:42:11.880" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7662" PostTypeId="2" ParentId="7656" CreationDate="2017-05-26T00:30:52.150" Score="1" Body="&lt;p&gt;&lt;code&gt;Does any one have a good *.dat file for USA?&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try CHIRP (chirp.danplanet.com). CHIRP goes out and downloads the &quot;recommended&quot; frequencies, offsets and all, for your area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's the best software I've seen for programming my wife's Baofeng UV-5R, MUCH better than the software that Baofeng supplies on that CD.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; A Google search reveals that this is a common problem with the 888s. Here is a link to a thread about this (way too long to post here). Basically, common fixes are changing the device driver and/or the cable. &#xA;&lt;a href=&quot;http://chirp.danplanet.com/issues/4249&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://chirp.danplanet.com/issues/4249&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-05-26T12:21:06.123" LastActivityDate="2017-05-26T12:21:06.123" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7663" PostTypeId="1" CreationDate="2017-05-26T02:55:45.360" Score="2" ViewCount="75" Body="&lt;p&gt;I came across a weird case, I have a low power 440MHz repeater transmitter, which I thought to set at about 10 watts. I made this measurement using an accurate offset attenuator and service monitor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like usual, adding more lossy coax, more connectors, and greater lengths dropped the power as usual. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, when I was trying to measure loss through one of the transmit cavities of a duplexer, I was surprised to see an increase in the output power, up to 10.9 watts!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I then connected directly to the little stub of coax which I was connecting between the cavity and measurement system, and the power went up to 12 watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this mean there is an impedance mismatch somewhere down the line? I understand I am not running the best coax (only LMR240), but I thought it would still all be 50Ω.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://youtu.be/REtErgvdIPU&quot; rel=&quot;nofollow noreferrer&quot;&gt;VIDEO HERE&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2017-06-28T16:07:51.273" Title="TX output power increase when fed through filter" Tags="&lt;impedance&gt;&lt;rf-power&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7664" PostTypeId="1" CreationDate="2017-05-26T04:56:32.193" Score="10" ViewCount="809" Body="&lt;p&gt;I need some advice on setting up my first HF station in a somewhat restricted townhouse community. If I had a detached house with a backyard I’d probably already have everything setup. But with this townhouse I keep second guessing what to do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Townhouse Specs:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Freehold (I can attach things to the outside. But wish to remain discreet.)&lt;/li&gt;&#xA;&lt;li&gt;4 story&lt;/li&gt;&#xA;&lt;li&gt;No back yard&lt;/li&gt;&#xA;&lt;li&gt;Deck is located above the car garage&lt;/li&gt;&#xA;&lt;li&gt;There is a small balcony outside the 4th floor master bedroom&lt;/li&gt;&#xA;&lt;li&gt;No attic&lt;/li&gt;&#xA;&lt;li&gt;No basement&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Known:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Radio: ICOM IC-7300&lt;/li&gt;&#xA;&lt;li&gt;Power Supply: Astron RS-35M&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Need help:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Antenna&lt;/li&gt;&#xA;&lt;li&gt;Grounding (no place to install ground rod(s))&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The magnetic loop keeps coming up in my research for situations like this. And I have also read some of the SGC documentation for their Smart Tuners. If I understand correctly I could using a SG-237 and do the following without the need for a earth or counterpoise. Based on any of these I should be able to do some variation with my outdoor space (deck and balcony),&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.sgcworld.com/Publications/Books/stealthbook.pdf&quot; rel=&quot;noreferrer&quot;&gt;Center Feed (page 12)&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.sgcworld.com/Publications/Books/stealthbook.pdf&quot; rel=&quot;noreferrer&quot;&gt;Loop (page 13)&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;Apartment Loop (page 22)&lt;/li&gt;&#xA;&lt;li&gt;Portable Loaded Loop (page 23)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Do you think going with a magnetic loop like those from MFJ is a better option that doing one of the many wire antenna options with a SG-237? People seem to like MFJ magnetic loops other than some quality control issues and learning to turn it. The reviews of the SG-237 are also positive. &lt;/p&gt;&#xA;" OwnerUserId="1427" LastEditorUserId="76" LastEditDate="2017-05-26T14:04:15.653" LastActivityDate="2019-06-12T02:07:19.553" Title="Stealth HF station setup advice" Tags="&lt;hf&gt;&lt;antenna-system&gt;&lt;magnetic-loop&gt;" AnswerCount="3" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7665" PostTypeId="2" ParentId="7664" CreationDate="2017-05-26T14:03:35.917" Score="3" Body="&lt;p&gt;The design of antenna called a magnetic loop has the disadvantage that it has a very narrow bandwidth, and the frequency is set by a variable capacitor mounted on the antenna. This means that changing frequencies requires you to go to the antenna and turn a knob. If your operating position is not next to the loop, this is very inconvenient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The loops in the Smartuner document you link are not that antenna design (there is no inner loop). But they do have a similar property of placing a tuning element at the feed point of the loop — just this one is automatically controlled, which will be much more convenient, but more expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, as non-resonant antenna systems go, a tuner at the feed point is the best possible configuration for minimizing loss. If you think you can fit it in your space, that would be an excellent choice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, you do &lt;strong&gt;not&lt;/strong&gt; need a RF ground for any kind of loop antenna to function properly. If you look at &lt;a href=&quot;http://www.sgcworld.com/Publications/Manuals/230man.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;the instructions&lt;/a&gt;, the “ground” terminal of the tuner is in fact to be connected to the other half of the antenna — it's just that in vertical/“end-fed” designs the ground is the other half, but in any loop it's the other end of the loop wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on whether the tuner incorporates a proper balun (I can't tell) you may want to add a choke at the input to the tuner. This prevents the feed line from becoming unintentionally part of the antenna and radiating your transmit power (all the way back to your operating position and causing interference, computer crashes, or shocks in the worst case).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-05-26T14:03:35.917" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7666" PostTypeId="2" ParentId="1530" CreationDate="2017-05-26T14:37:48.440" Score="0" Body="&lt;p&gt;In aperture antennas, like dishes, the effective aperture is not frequency dependant. It depends on the physical dimensions and the efficiency.&lt;/p&gt;&#xA;" OwnerUserId="9740" LastActivityDate="2017-05-26T14:37:48.440" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7667" PostTypeId="1" AcceptedAnswerId="7668" CreationDate="2017-05-26T15:11:25.930" Score="2" ViewCount="409" Body="&lt;p&gt;Can I use amateur radio frequency for commercial purpose (after acquiring ham license), expecting that it would be congestion free band and give me good broadcasting performance compared to other congested ISM bands?   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Being very specific, I am now broadcasting over WiFi 2.4 GHz band. its a broadcast and thus no ACK (acknowledge) return signal is used. Due to congested band its quality is sometimes poor. Can I switch this broadcast to armature radio frequencies e.g. 2300-2310 MHz or 2390-2450 MHz wherever available]&lt;/p&gt;&#xA;" OwnerUserId="9739" LastEditorUserId="9739" LastEditDate="2017-05-26T15:22:46.150" LastActivityDate="2017-05-26T17:38:00.647" Title="Use amateur radio frequencies for commercial purpose" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;aprs&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7668" PostTypeId="2" ParentId="7667" CreationDate="2017-05-26T17:38:00.647" Score="9" Body="&lt;p&gt;This is answered somewhat in &lt;a href=&quot;https://ham.stackexchange.com/questions/2318/when-is-aprs-use-considered-commercial&quot;&gt;this question&lt;/a&gt; already, and the answer is no.&#xA;And I will add some passages about the broadcasting part.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To quote the relevant rule &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=9c74c897993f8e8f42eaa5f1fbbaf5a2&amp;amp;node=se47.5.97_1113&amp;amp;rgn=div8&quot; rel=&quot;noreferrer&quot;&gt;§97.113&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;§97.113   Prohibited transmissions. (a) No amateur station shall&#xA;  transmit:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(1) Communications specifically prohibited elsewhere in this part;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(2) &lt;strong&gt;Communications for hire or for material compensation&lt;/strong&gt;, direct or&#xA;  indirect, paid or promised, except as otherwise provided in these&#xA;  rules;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(3) &lt;strong&gt;Communications in which the station licensee or control operator&#xA;  has a pecuniary interest&lt;/strong&gt;, including communications on behalf of an&#xA;  employer, with the following exceptions:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;[...]&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(5) Communications, on a regular basis, which &lt;strong&gt;could reasonably be&#xA;  furnished alternatively through other radio services&lt;/strong&gt;.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) An amateur station shall &lt;strong&gt;not engage in any form of broadcasting&lt;/strong&gt;,&#xA;  nor may an amateur station transmit one-way communications except as&#xA;  specifically provided in these rules;&#xA;  [...]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There are commercial bands specifically for this purpose. You can apply for a license to use some frequeny exclusively, and you won't have to deal with interference. But of course you have to pay to play.&lt;/p&gt;&#xA;" OwnerUserId="6742" LastActivityDate="2017-05-26T17:38:00.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7669" PostTypeId="2" ParentId="1530" CreationDate="2017-05-26T18:17:08.507" Score="0" Body="&lt;p&gt;&lt;strong&gt;Effective aperture (Ae) is a direct function of antenna gain and operating wavelength.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From W8JI and Jasik's book, at &#xA;www.w8ji.com/capture_area_ae_effective_aperture.htm.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Ae (sometimes referred to as &lt;em&gt;capture area&lt;/em&gt;) is determined by the voltage available across a load matching the antenna feed impedance for a given electromagnetic field strength density. In simple terms if the antenna is placed in a electromagnetic field of a certain intensity, a certain amount of power will appear in the load at the antenna terminals. The area of space &lt;em&gt;around&lt;/em&gt; the antenna that provided this amount of power is the effective aperture.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Many people confuse physical area, or Ap, with effective aperture. They are not the same. Physical size only determines effective aperture as physical size might affect gain of an antenna. Gain and wavelength determines capture area, but capture area itself has nothing to do with actual physical size or physical area of the antenna.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;For example, a λ/2 wave long dipole in freespace has a capture area of about 0.13λ². This means a lossless freespace dipole has an Ae of approximately 0.13 square wavelengths. This effective aperture is about 100 times larger than the actual physical area of a thin wire dipole antenna. Energy is extracted from an elliptically shaped area slightly longer than the dipole and about λ/4 diameter at the center. This is why increasing conductor diameter or using a cage of wires will not increase electrical aperture or capture area.  As a matter of fact if we built a lossless or very low loss small dipole, perhaps λ/20 long, capture area or Ae would be within a few percent of a full size dipole!&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Length itself has very little effect unless the change in length significantly affects antenna gain. We must have a change in gain to change Ae (effective electrical aperture). &lt;strong&gt;Physical aperture (Ap) changes do not affect Ae unless the gain changes.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="218" LastEditDate="2017-05-26T18:26:47.400" LastActivityDate="2017-05-26T18:26:47.400" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7670" PostTypeId="1" CreationDate="2017-05-27T15:07:53.410" Score="1" ViewCount="3348" Body="&lt;p&gt;Radars operating in the X-band have a narrow beamwidth. Radars operating in the S and C bands have a bit more beamwidth than X band radars.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that antenna size also plays a major role. My doubt is:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Whether the beamwidth is determined only by the operating frequency? &lt;/li&gt;&#xA;&lt;li&gt;Whether it is theoretically possible to have a narrow beam width for S band radar, like X band radar? &lt;/li&gt;&#xA;&lt;li&gt;Similarly, can I have a narrow beamwidth for operating at HF frequencies?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="5349" LastEditorUserId="8717" LastEditDate="2017-05-28T21:45:57.750" LastActivityDate="2017-05-28T21:45:57.750" Title="Relation between beamwidth and operating frequency" Tags="&lt;antenna-theory&gt;&lt;shf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7671" PostTypeId="2" ParentId="7670" CreationDate="2017-05-27T16:15:55.370" Score="4" Body="&lt;p&gt;It's theoretically possible to have a narrow beam width at any frequency, but it's the ratio of size of the antenna to wavelength that determines the narrowest possible beam width. So you need either very large antennas, or very small wavelengths. Or both.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many relationships like this in physics and engineering.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Lasers&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Lasers have very narrow beam widths, so let's talk about those. Light is just a much higher frequency electromagnetic radiation, so the same physics applies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might have heard lasers produce a perfect beam of light, that is one with parallel sides which does not diverge at all. However, this is not possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the objective is to have the smallest beam width, the best kind of physically possible beam is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Gaussian_beam&quot; rel=&quot;noreferrer&quot;&gt;Gaussian beam&lt;/a&gt;. Somewhere along this beam is a &lt;em&gt;waist&lt;/em&gt;, the point at which it is narrowest. Usually the waist is the aperture from which light is emitted from the laser.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Away from the aperture, the beam diverges at some angle $\theta$ (in radians). If the wavelength is $\lambda$ and the waist diameter is $w_0$, then that angle is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \theta \simeq \frac{\lambda}{\pi w_0} $$  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From this equation you can see to decrease the beam width (decrease $\theta$), one can either decrease the wavelength, or make the aperture bigger. It's because the wavelength of light is so small that a common laser pointer, which might have an aperture of only 1mm, can create a beam which appears &quot;perfect&quot; by casual observation.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Diffraction Limit&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Diffraction-limited_system&quot; rel=&quot;noreferrer&quot;&gt;diffraction limit&lt;/a&gt; in optical imaging has a similar relationship between sharpness and wavelength. The smallest resolvable feature size $d$ again depends on wavelength, as well as the index of refraction $n$, and the half-angle subtended by the optical objective lens $\theta$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ d \simeq \frac {\lambda }{2n\sin {\theta }} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, making the lens bigger or decreasing the wavelength will allow smaller features to be resolved.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Antenna Gain and Aperture&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Some kinds of antennas have a physical aperture. For example, dish antennas. If we assumed 100% of the energy hitting that aperture was collected by the antenna, then the relationship between aperture area $A$ and gain $G$ is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A = {\lambda^2 \over 4 \pi} G $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And of course, a higher gain means a higher directivity and a narrower beam width. Real antennas don't capture energy 100% efficiently due to resistive losses, diffraction, shadowing of the dish, and so on, so there's an &quot;aperture efficiency&quot; factor that's added, which is typically around 40% to 80%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there's still the general relationship: increasing gain requires increasing aperture area or decreasing wavelength.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-05-27T16:15:55.370" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7672" PostTypeId="2" ParentId="707" CreationDate="2017-05-28T05:04:50.327" Score="1" Body="&lt;p&gt;The negative answer still applies in 2017.  Store &amp;amp; forward satellites are expensive to develop and maintain, and with the decline in terrestrial packet radio, fewer supporters are willing to kick up the dough.  It's a shame.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Jim  KV2Z&lt;/p&gt;&#xA;" OwnerUserId="9746" LastActivityDate="2017-05-28T05:04:50.327" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7673" PostTypeId="2" ParentId="3771" CreationDate="2017-05-29T05:33:24.490" Score="0" Body="&lt;p&gt;Most squelch tails you have heard are actually caused at the repeater as it tries just for a second to hold onto what might be a marginal signal.  When it decides it is lost it cuts off the transmitter.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is more and more common as agencies like the police move to UHF. I have had more than one officer tell me VHF worked better.  (He explained that the repeater was across some water and the tides would affect it, for instance.  Not to mention the buildings)&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-05-29T05:33:24.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7674" PostTypeId="2" ParentId="3606" CreationDate="2017-05-29T12:26:19.023" Score="3" Body="&lt;p&gt;The impedance along the length of the antenna is a function of the standing wave developed on the antenna. If we assume no ground losses and ignore the self capacitance at the tip of the antenna, then the following description can be applied to a monopole antenna &amp;lt;=1/4λ long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transmitter induces a voltage at the feed point of the antenna that causes current, as a function of the surge impedance of the antenna feed point, to flow. The current and voltage travel along the length of the antenna until reaching its tip. The tip of the antenna represents an impedance discontinuity near zero ohms that causes a reflected wave. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Following the notion of an open-ended transmission line, the current changes phase by 180 degrees as it is reflected while the voltage is reflected in phase. As the reflected waves meet the incident waves, the vector sum of each is produced along the length of the antenna giving rise the standing wave pattern. Once the reflected waves have reached the feed point, the conditions of varying impedance along the entire length of the antenna are now established as well as the input impedance at the feed point of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Upon steady state conditions, the input impedance of the antenna establishes the RMS input current (I) at the feed point. The power applied to the antenna is calculated as I&lt;sup&gt;2&lt;/sup&gt;|Z|. It is also known that the pattern of the current on the vertical element of a monopole antenna with an electrical length &amp;lt;= 1/4λ can be modeled as sinusoidal with near zero current at the tip and reaching maximum current at the feed point. The impedance magnitude at any point along the antenna can therefore be approximated as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;|Z| = P&lt;sub&gt;FP&lt;/sub&gt;/(I&lt;sub&gt;FP&lt;/sub&gt;sin θ)&lt;sup&gt;2&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where θ is the electrical degrees from the tip, P&lt;sub&gt;FP&lt;/sub&gt; is the transmitter power at the feed point, and I&lt;sub&gt;FP&lt;/sub&gt; is the RMS current at the feed point. Due to real world effects excluded in the opening paragraph, this can only serve as a first approximation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The insertion of any inductance or capacitance represents another impedance discontinuity along the length of the antenna. As such, it too will generate reflections and attendant phase shifts that alter the impedance of the feed point. The relative phase of the insertion point (for a given component) is the cause of the variation of input impedance as the position is changed. Careful modeling of all of the complex reflection coefficients and positions along the length of the antenna will allow the development of a nearly complete formula of the input impedance of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-29T12:26:19.023" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7675" PostTypeId="2" ParentId="7663" CreationDate="2017-05-29T15:52:07.777" Score="2" Body="&lt;p&gt;It has all of the hallmarks of a defective cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the duplexer cavity alone caused the problem, I would attribute it to load impedance. But when you removed the cavity and daisy chained the two coax cables, the result suggests a different problem. Check for bad connections in the cables, mismatched impedances, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You stated your service instruments are solid but if you find nothing else, I would also check the sampling load and its cable to the test set.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BTW - at 70 cm I recommend nothing but low loss, double (or more) shielded cable to improve rejection and lessen desense.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-29T15:52:07.777" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7676" PostTypeId="2" ParentId="7509" CreationDate="2017-05-29T16:02:44.997" Score="0" Body="&lt;p&gt;The correct sequence is&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Turn the radio off&lt;/li&gt;&#xA;&lt;li&gt;Hold down the Band, HM/RV, and TX PO buttons (3 buttons)&lt;/li&gt;&#xA;&lt;li&gt;Turn the power on&lt;/li&gt;&#xA;&lt;li&gt;Release the three buttons&lt;/li&gt;&#xA;&lt;li&gt;Press the FW key briefly&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;If this doesn't work, it is typically due to not holding down all three buttons at once. Try a different finger pattern.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-05-29T16:02:44.997" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7677" PostTypeId="1" CreationDate="2017-05-29T19:37:43.340" Score="3" ViewCount="861" Body="&lt;p&gt;I'm having a problem getting a good signal up to a repeater site on UHF. I'm running 20W in a neighborhood with lots of trees, and the signal is fading in and out due to trees and the wind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't run any more power.  Would 2 UHF Yagis mounted side-by-side, spaced 1 wavelength apart, using the same length coax (50 ohm each; this will make 25 ohms which can be made back to 50 ohms w/ a piece of RG62 35 ohm cable).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would this give a diversity effect,  say when one is noisy and the other may have a good signal getting to the repeater?    &lt;/p&gt;&#xA;" OwnerUserId="9744" LastEditorUserId="873" LastEditDate="2017-05-30T07:39:16.880" LastActivityDate="2017-05-30T19:21:48.850" Title="Can 2 uhf beam yagi antennas be used on a transmitter to get a diversity effect?" Tags="&lt;antenna-theory&gt;&lt;uhf&gt;&lt;frequency&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="7678" PostTypeId="2" ParentId="7677" CreationDate="2017-05-29T20:30:50.103" Score="3" Body="&lt;p&gt;For diversity gain, you'd need to have two receivers (or you just switch to the currently &quot;better&quot; antenna; that's called &lt;em&gt;selection combining&lt;/em&gt; in MIMO technology and kind of is the worst possible diversity mechanism).&lt;br&gt;So, no, with two antennas and only a single receive chain, there's no diversity gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can, of course, build an &lt;em&gt;antenna array&lt;/em&gt;. That would actually work by using a impedance-matching combiner to make the reception of both antennas combine constructively. You'd basically achieve a higher directivity by adding &lt;em&gt;array gain&lt;/em&gt; to your &lt;em&gt;antenna gain&lt;/em&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, I wonder how you can put two antennas at &quot;1 wavelength&quot; distance for the whole UHF band – that covers wavelengths from 10 cm to 1m. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure it would help &lt;em&gt;much&lt;/em&gt; with the fading problems – these might be happening at larger scales.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a more general comment: &lt;em&gt;Diversity&lt;/em&gt; happens when you have two different signal paths transporting the same signal; &lt;em&gt;different&lt;/em&gt; in the sense that the random effects on the signal are independent. That will almost certainly not happen for large-range communication with transmit antennas that are a mere single wavelength apart – I'd not expect any significant gain due to independent signal paths (&quot;multipath&quot;) in an outside scenario with two close antennas pointing in the same direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In indoor scenarios (e.g. your usual cheap Wifi router with more than one antenna is a diversity/MIMO transceiver!), there's way more diverse multipath, and hence, antennas placed a mere more than half a wavelength apart have a serious chance of picking up a combination of at least two independent paths. Mathematically, the system is modelled such that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;We assume one channel response from each transmit to each receive antenna&lt;/li&gt;&#xA;&lt;li&gt;We then put these into a table (and for reasons of simplicity, let's assume these channel impulse responses are completely characterized by a single complex number)&lt;/li&gt;&#xA;&lt;li&gt;We then consider that each receive antenna sees the sum of all the channels that &quot;go to it&quot;, applied to the transmit signal&lt;/li&gt;&#xA;&lt;li&gt;And then we consider that the table from above is simply a matrix, and we can multiply that matrix with the transmit signal vector (ie. a vector with the entries of what each transmit antenna sent) to get the output at each receive antenna&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;With that model in mind, we can let the transmitter choose a transmit vector, so that the process of&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;taking a vector of the signal to be transmitted&lt;/li&gt;&#xA;&lt;li&gt;an arbitrary mapping to a transmit vector&lt;/li&gt;&#xA;&lt;li&gt;applying the channel matrix&lt;/li&gt;&#xA;&lt;li&gt;and then applying a matrix that we can also arbitrarily choose&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;gives us multiple, independent channels, over the air, mathematically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is of interest to you: that usually happens by applying a singular value decomposition to the (estimated) channel matrix, so that this matrix gets split into unitary (hence, nicely invertable) matrices and a diagonal matrix (which means that whatever you put into that diagonal matrix in one element has no effect on the other elements).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-05-30T09:34:42.053" LastActivityDate="2017-05-30T09:34:42.053" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7679" PostTypeId="2" ParentId="7677" CreationDate="2017-05-30T00:39:01.307" Score="3" Body="&lt;p&gt;In your post the thing that leaps out is about using a horizontally polarized Yagi to contact a repeater which is commonly a vertical antenna.  The signal loss in this situation is large.  Try your Yagi antenna with the elements pointing up and down and see which orientation better, horizontal or vertical. Does this make a big enough difference?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for diversity reception your idea of combining horizontal and vertical signals is one approach.  The most simple is switching between two antennas.  The ARRL Antenna Handbook goes a step farther suggesting a separate radio for each antenna and listening to both radios.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simpler approach is have one arm of a UHF/VHF dipole in a vertical position to provide both polarizations in one antenna. &lt;em&gt;(This not a ground plane antenna which is vertically polarized).&lt;/em&gt;  &lt;a href=&quot;http://www.qsl.net/kk4obi/Center-fed%20L-dipoles%20Vertical.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here is the antenna model information and 4NEC2 model if you want to tailor it to your situation.&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A host of more sophisticated diversity methods exist — as you have found. Because phased vertical and horizontal Yagi antennas were not found you have a research project.  &lt;/p&gt;&#xA;" OwnerUserId="8229" LastEditorUserId="76" LastEditDate="2017-05-30T01:20:22.623" LastActivityDate="2017-05-30T01:20:22.623" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7680" PostTypeId="1" AcceptedAnswerId="7681" CreationDate="2017-05-30T11:50:02.113" Score="1" ViewCount="513" Body="&lt;p&gt;I have bought an 820T2 USB dongle, but &lt;code&gt;$ rtl_test&lt;/code&gt; detects it as Raphael Micro  820T chip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can rtl_test distinguish the two? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, how can I see, if the chip is the right one?&lt;/p&gt;&#xA;" OwnerUserId="3010" LastEditorUserId="3010" LastEditDate="2017-05-30T11:58:18.367" LastActivityDate="2017-05-30T19:05:37.847" Title="How to distinguish SDR 820T and 820T2 dongles on Linux?" Tags="&lt;rtl-sdr&gt;&lt;linux&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7681" PostTypeId="2" ParentId="7680" CreationDate="2017-05-30T12:06:10.317" Score="3" Body="&lt;p&gt;As far as I read the &lt;code&gt;rtl_sdr&lt;/code&gt; &lt;a href=&quot;http://git.osmocom.org/rtl-sdr/&quot; rel=&quot;nofollow noreferrer&quot;&gt;source code&lt;/a&gt;, no, there's no special case for anything called &quot;820T2&quot;; the relevant file is rtl_sdr.h:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;enum rtlsdr_tuner {&#xA;        RTLSDR_TUNER_UNKNOWN = 0,&#xA;        RTLSDR_TUNER_E4000,&#xA;        RTLSDR_TUNER_FC0012,&#xA;        RTLSDR_TUNER_FC0013,&#xA;        RTLSDR_TUNER_FC2580,&#xA;        RTLSDR_TUNER_R820T,&#xA;        RTLSDR_TUNER_R828D&#xA;};&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The detection in librtlsdr.c looks like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;    reg = rtlsdr_i2c_read_reg(dev, R820T_I2C_ADDR, R82XX_CHECK_ADDR);&#xA;    if (reg == R82XX_CHECK_VAL) {&#xA;            fprintf(stderr, &quot;Found Rafael Micro R820T tuner\n&quot;);&#xA;            dev-&amp;gt;tuner_type = RTLSDR_TUNER_R820T;&#xA;            goto found;&#xA;    }&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;In other words, the I²C interface of the R820 seems to be compatible to what your tuner does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm personally not even aware of a R820T2 tuner IC. If it has capabilities that the R820T doesn't have, or if your tuner doesn't work, it might be worth your time to help extend rtl_sdr by contributing to the osmocom project by writing code, mails, or doing something otherwise helpful :)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-05-30T12:06:10.317" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7682" PostTypeId="2" ParentId="7680" CreationDate="2017-05-30T19:05:37.847" Score="5" Body="&lt;p&gt;The R820T and the R820T2 differ. The R820T can set a narrow IF filter (300 kHz) - but not if the gain is set at maximum. The R820T2 can not set a narrow filter - minimum bandwidth is about 800 kHz. This is easy to see when one runs the dongles with a spectrum display software having nothing connected to the antenna input. I use Linrad, set the IF filter to 300 kHz and gain to maximum.&#xA;I see no simple way to implement a test to distinguish between the two chips in the drive routine.&#xA;/Leif&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-05-30T19:05:37.847" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7683" PostTypeId="2" ParentId="7677" CreationDate="2017-05-30T19:21:48.850" Score="1" Body="&lt;p&gt;First of all, transmit and receive should behave the same. It will be a good idea to listen to the repeater while moving the antenna (assuming a single one.) Maybe you will find that twisting it for the opposite polarization solves the problem as hinted in a previous answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If polarization is correct and moving the antenna several wavelengths from the original position does not help, you should check the difference between&#xA;horizontal and vertical polarization. In case that difference is small it is&#xA;possible that you could benefit from using circular polarization. Means stack&#xA;a H and a V antenna with a 90 degree phase shift. Elements on the same boom&#xA;or on two separated boom tubes would not matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stacking two antennas side by side is likely to not help at all. A sharper lobe is not what you need. Maybe a very different antenna with a narrow vertical lobe and a wide horizontal lobe could be better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;/Leif&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-05-30T19:21:48.850" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7684" PostTypeId="2" ParentId="1530" CreationDate="2017-05-30T21:53:51.840" Score="1" Body="&lt;p&gt;&quot;For example, a λ/2 wave long dipole in free space has a capture area of about 0.13λ².&quot; What matters is the radiation pattern, not the physical size. A very short loss-less dipole (supra-conducting coils) will have a dipole pattern&#xA;and therefore the same capture area 0.13λ². It would however have a VERY small bandwidth. The bandwidth is closely related to the Q value, the ratio between&#xA;stored energy and flowing energy. With Q=100 and a bandwidth of about 1%, the matched load at the feed-point absorbs energy from about 100 subsequent oscillations of the field and they extend over a 100 times larger volume of space than a single oscillation. Not much of a proof, but perhaps some food for thought.&#xA;/Leif&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-05-30T21:53:51.840" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7686" PostTypeId="2" ParentId="3782" CreationDate="2017-06-01T08:02:21.307" Score="0" Body="&lt;p&gt;The capture effect of receivers can cause quite a complex mess if mixing the same signal with multipath time-shifted TOAs.  Usually it will lock onto the strongest, but you might hear it switching back and forth if the signals are close enough to being equal strength.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-06-01T08:02:21.307" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7687" PostTypeId="1" AcceptedAnswerId="16918" CreationDate="2017-06-01T17:13:10.357" Score="8" ViewCount="640" Body="&lt;p&gt;There are some contests such as ARRL's Field Day that provide special categories or points for contestants who operate using emergency or battery power.  The &lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2016/2016%20Rules.pdf&quot; rel=&quot;noreferrer&quot;&gt;2016 FD rules&lt;/a&gt; for &quot;Class A - Battery&quot; stations include this text:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All contacts must be made using an output power of 5 Watts or less and&#xA;  the power source must be something other than commercial power mains&#xA;  or motor-driven generator (e.g.: batteries, solar cells, water-driven&#xA;  generator).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The same text is included for &quot;Class B - Battery&quot; stations.  The text for &quot;Class E&quot; stations is different:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Same as Class D, but using emergency power for transmitters and&#xA;  receivers.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;On first glance, this would imply that &quot;Class E&quot; stations -- but not &quot;Class A - Battery&quot; or &quot;Class B - Battery&quot; -- can use commercially-powered equipment such as computers for logging or digital modes such as PSK31, as long as all transmitters and receivers are using emergency power.  Is this an appropriate interpretation of the rules?&lt;/p&gt;&#xA;" OwnerUserId="111" LastActivityDate="2020-06-28T04:14:53.993" Title="Emergency/battery power rules for Field Day: do they include computer equipment?" Tags="&lt;contest&gt;&lt;field-day&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7688" PostTypeId="2" ParentId="1530" CreationDate="2017-06-01T17:56:57.487" Score="3" Body="&lt;p&gt;This is a topic that troubles most students and even finds it way into many technical papers and textbooks in the form of incorrect assertions and conclusions. While you will find some reasonable references to thermodynamic equivalencies in some texts, it seems the genesis of the isotropic effective aperture equation has been rarely published.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer to the question lies buried in the mechanisms of Fresnel (near field) and Fraunhoffer (far field) zones of antennas. The Fresnel zone is the specific area of interest. The non-radiating, non-dissipating (thus reactive) part of the Fresnel zone is generally considered to extend 1∕(2π) times the wavelength from the surface of the antenna. In a more general sense, this is considered the maximum distance from which EM (electromagnetic) waves can couple to a nearby object. This coupling is why the energy is not radiated or dissipated by a transmitting antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now we turn our attention to the elusive isotropic antenna. It is considered a point source - small enough in dimension compared to any other incorporated dimensions that it is dimensionless and infinitesimally small. By definition, the isotropic antenna radiates equally in all directions. By the theory of reciprocity, the isotropic antenna must then receive equally in all directions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider an EM plane wave approaching the isotropic antenna. The isotropic antenna cannot &quot;look ahead&quot; and see the plane coming when the plane wave is in its far field because the EM plane wave is not yet having any effect on the isotropic antenna. But as the EM plane wave gets very close to the isotropic antenna, it begins to cause current to flow in the isotropic antenna. How close does the EM plane need to be? The distance of the non-radiating Fresnel zone which, as stated previously, is considered to be 1∕(2π) times the wavelength of the frequency in question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the plane wave intersects the isotropic antenna (that is, the isotropic point is on the plane), the spherical receiving pattern of the isotropic antenna has the maximum possible coupling with the EM plane wave. Since the isotropic antenna is a point lying on the intersecting plane with its receive sphere bisected by the plane, the resulting pattern is a circle defined by a radius that originates at the isotropic antenna and extends for a radius of 1∕(2π) times the wavelength. This circle is the A&lt;sub&gt;e&lt;/sub&gt; (effective aperture) of the isotropic antenna. That is, it is generating current from EM waves within that radius.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But with any receiving antenna, we are more interested in determining the total power the receive antenna is able to make available to the receiver. This is a function of the radiative flux which is given in SI units of W/m&lt;sup&gt;2&lt;/sup&gt;. While we do not know the radiative flux in this case, we can compute the normalize power received (the amount of power received if radiative flux = 1 watt/m&lt;sup&gt;2&lt;/sup&gt;) by simply computing the area of the the A&lt;sub&gt;e&lt;/sub&gt;. Since the aperture is a circle and the area of a circle is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A_\text{circle} = \pi r^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;we can substitute the radius of the isotropic $A_e$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A_e = \pi \left({ \lambda \over 2 \pi}\right)^2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and simplify:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A_e = {\lambda^2 \over 4\pi} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus emerges the standard definition of the A&lt;sub&gt;e&lt;/sub&gt; of an isotropic antenna, always with a gain of one. The dependency on λ&lt;sup&gt;2&lt;/sup&gt; is simply due to the minimum radius at which the isotropic antenna (or any antenna for that matter) can begin to receive or emit EM waves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you now consider the effect of gain by any other type of antenna, you can see that it is simply increasing the area of the A&lt;sub&gt;e&lt;/sub&gt; of the isotropic antenna by the magnitude of the gain. Since the A&lt;sub&gt;e&lt;/sub&gt; is multiplied by the radiative flux and now the gain of the antenna, the received or transmitted power is scaled proportionally. It should be noted however, that the gain of an antenna does not physically extend the radius at which an EM wave can generate current in the antenna as this boundary condition is immutable. The gain and pattern of most amateur radio antennas is determined by the current vector patterns of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you find this explanation to be helpful and wish to requote it, I ask that you kindly give attribution to me, Glenn Schulz W9IQ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Footnote: The Hairy Ball Theorem has been mentioned in this thread. The Theorem states that given a ball completely covered in hair, you cannot comb the hair in such a way as to have no partline. I can prove the theorem wrong: take a comb and do a 'fro on the ball. Hair is combed - no partline. Quod erat demonstrandum.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="218" LastEditDate="2017-06-07T00:15:30.567" LastActivityDate="2017-06-07T00:15:30.567" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7689" PostTypeId="2" ParentId="7509" CreationDate="2017-06-01T19:52:55.577" Score="1" Body="&lt;p&gt;The radio came back from the Yaesu's dealer today. My warranty card now has an entry stating 'hardware processor reset'. It seems they had to open the radio to do whatever had to be done. In other words: it seems that in case like this there is nothing you can do on your own, and you're better off giving your HT to professionals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An interesting tidbit here is that according to the technician handling the radio the battery was completely drained out, despite it being freshly charged when this issue happened. So apparently it was still drawing current even though it appeared to be dead. If anything like this happens to you, you might want to disconnect the battery before shipping your radio for repairs.&lt;/p&gt;&#xA;" OwnerUserId="9145" LastActivityDate="2017-06-01T19:52:55.577" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7690" PostTypeId="2" ParentId="7687" CreationDate="2017-06-02T00:23:39.097" Score="1" Body="&lt;p&gt;Where I see the word commercial is in relation to electrical power only.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, when you are not on commercial power you can be on batteries, solar, whatever, but clearly off-grid.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is called emergency power to imply that it is the setup you would use if the whole power grid went down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It includes all devices from computers to radios, officialy.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unofficially, it also includes the TV you might set up for the kids.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a cord running to your table it is very good to have it visibly disconnected.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is a lot of fun!  When so many people are on the air you can work an amazing number with a QRP rig and a good dipole.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-06-02T06:48:20.090" LastActivityDate="2017-06-02T06:48:20.090" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7691" PostTypeId="1" AcceptedAnswerId="7693" CreationDate="2017-06-02T01:18:31.217" Score="4" ViewCount="391" Body="&lt;p&gt;I heard the SDRPlay RSP2 has an AM notch filter, but I don't want to spend that much money.  How is the RSP1 for broadcast band interference?  Will I need a preselector? I already have an MFJ-1020c but am hoping to sell it to offset some of the cost of the SDRPlay.&lt;/p&gt;&#xA;" OwnerUserId="9772" LastEditorUserId="873" LastEditDate="2017-06-02T02:41:37.987" LastActivityDate="2017-12-16T04:33:19.100" Title="SDRPlay RSP1 and broadcast band (AM) interference" Tags="&lt;software-defined-radio&gt;&lt;filter&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7692" PostTypeId="2" ParentId="7687" CreationDate="2017-06-02T20:42:33.177" Score="1" Body="&lt;p&gt;For class A battery stations the following rule applies:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All &lt;strong&gt;contacts&lt;/strong&gt; must be made using an output power of 5 Watts or less and the power source must be something other than commercial power mains or motor-driven generator (e.g.: batteries, solar cells, water-driven generator).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The key here is if a computer is in any way &lt;strong&gt;used to make the contact&lt;/strong&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Logging software is not required to make contacts. Therefore, the way the rule is worded, a computer used only for logging ought to be allowed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if a digital mode is being used, or SDR software that controls the radio, that would be a no-no because the computer would be involved in making the contact.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-06-03T14:31:44.947" LastActivityDate="2017-06-03T14:31:44.947" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7693" PostTypeId="2" ParentId="7691" CreationDate="2017-06-03T04:00:21.617" Score="2" Body="&lt;p&gt;It's not great, especially if you're in a densely populated area, but frankly neither is the RSP2. The RSP2's most compelling feature is arguably the High Z input, which does not include the AM BCB filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll see images throughout the LF and MF frequency range if you have strong AM stations in the local area. An additional preselector (it has a set of preselectors already built in) will help a bit, but a proper AM BCB band stop filter, a grounded metal enclosure, and particular attention to preventing common mode current on the feedline will get you a long way toward entirely eliminating overload.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The High Z input significantly improved performance on HF and LF, with better sensitivity particularly below 3MHz, and a bit better SNR as well, perhaps because of changes in how the signal is routed through/around the preamp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're going to use it primarily for VHF and up, the RSP1 will do just fine. If you're going to use it for 80-10m, with a bandstop filter, I think you'll find it quite usable. If you want good low band performance, the 2 is worth the extra money, to be sure.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2017-06-03T04:00:21.617" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7695" PostTypeId="2" ParentId="6864" CreationDate="2017-06-04T05:07:02.083" Score="2" Body="&lt;p&gt;Having worked as an intercept operator at these sites in the 70's I can say that there just isn't anything to intercept on the HF bands anymore.&lt;/p&gt;&#xA;" OwnerUserId="9779" LastActivityDate="2017-06-04T05:07:02.083" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7696" PostTypeId="2" ParentId="119" CreationDate="2017-06-04T14:15:27.277" Score="3" Body="&lt;p&gt;The short answer is YES you can operate in the UK if,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) you hold an U.S. FCC ADVANCED or EXTRA class license.  These two FCC license classes are recognized as a national (US) license that is equivalent to the European Conference of Postal and Telecommunications Administrations (CEPT) Radio Amateur Radio license and can operate on all frequencies allocated to this license class.  However, this equivalence and operating privilege is only valid for temporary visits.  If you intend to stay longer than the typical &quot;visitor or tourist&quot; visa allows then you have to apply for a CEPT license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The UK is a signatory to the CEPT agreement.   If operating from UK England then you need to preface your call sign with the letter M.  Isle of Man uses the MD call sign prefix.  No Ireland uses MI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;T/he U.S. FCC general class license is only recognized as the equivalent of the C/EPT Novice Radio License and can only operate in the frequency bands allocated to the CEPT Novice class.  It is also subject to the &quot;temporary&quot; Visa restriction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus if you are not going to stay longer than a tourist / visitor Visa allows then you do not need to apply for a CEPT Amateur Radio License.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When operating temporarily in a CEPT country with a US FCC license you need to have in your possession, 1) a copy of the FCC public notice DA 16-1048 09/16/2016, 2) proof of U.S. citizenship (passport), and 3) evidence of your FCC license grant.  It is good to also have a copy of the CERT agreement referenced below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why?  Many authorities are not familiar with FCC &amp;amp; CERT regulations. Imagine getting stopped by UK Customs and Border Patrol (CBP) at the London Heathrow airport with hand held radios and other radio gear in your possession!   It might raise some concern given security and safety concerns. Why do you have this equipment in your possession?  Having your FCC license, passport, FCC notice and the CEPT agreement documents will go a long way to explaining why you are in possession of this radio equipment, especially with an administrative or law officer who is not familiar with Amateur radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More information can be found in ......&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FCC Public Notice DA 16-1048  Sept. 16, 2016&#xA;AMATEUR SERVICE OPERATION IN CEPT COUNTRIES&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;...When the privileges authorized by the FCC license grant are Advanced or Amateur Extra Class operator privileges, the U.S. citizen is granted CEPT Radio Amateur License privileges, in accordance with CEPT Recommendation T/R 61-01 (as amended). When the privileges authorized by the FCC license grant are General Class operator privileges, the U.S. citizen is granted CEPT Novice Radio Amateur License privileges, in accordance with ECC Recommendation (05)06 (as amended). Both recommendations are available on the internet at &lt;a href=&quot;http://www.ero.dk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ero.dk/&lt;/a&gt;. &quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;REFER Also to document, CEPT Radio Amateur License, recommendation T/R 61-01&#xA;Approved NICE 1985: amended May 2016&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Table 1 lists the countries that  recognize a US (national) license as being CEPT license equivalent valid for &quot;temporary&quot; stays in the foreign country. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My comment: The amateur radio license requirement for Morse code proficiency was eliminated by the US FCC.  Hence, the General class license only qualifies for novice privileges since some countries only allow CEPT Radio Amateur License privileges to licensees who have demonstrated the Morse code proficiency 13 WPM in an FCC exam, or hold the EXTRA class license.   Many countries are reviewing this requirement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The FCC Advanced class license is no longer offered by the FCC but has been grandfathered.  Holders of an advanced class license had to pass the 13 WPM Morse code proficiency test thus it is also granted full CEPT Radio Amateur License privileges.  I have held the Advanced Class license since 1974. At the time, the Extra Class licensee was required to pass a 25 WPM Morse code proficiency exam.   This requirement has been eliminated.  As we all know, Morse code proficiency tests are no longer required by the FCC.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;W0JMO - Joe&lt;/p&gt;&#xA;" OwnerUserId="9781" LastEditorUserId="9781" LastEditDate="2017-06-04T20:33:14.223" LastActivityDate="2017-06-04T20:33:14.223" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7697" PostTypeId="1" CreationDate="2017-06-04T17:24:59.473" Score="0" ViewCount="593" Body="&lt;p&gt;My son was recently gifted a vintage DRAKE TR7 ham radio.  It's been &quot;in the attic&quot; for 20+ years.  When we try to power it up, the (separate) power supply turns on and we have checked with a multi-meter that the radio itself is getting power.  But nothing on the face of the receiver comes on.  Looking for suggestions on what to test next (and how).  Thanks in advance.&lt;/p&gt;&#xA;" OwnerUserId="9782" LastEditorUserId="8717" LastEditDate="2017-06-04T18:39:42.640" LastActivityDate="2017-06-04T19:17:19.347" Title="How to diagnose DRAKE TR7 power problem" Tags="&lt;power-supply&gt;&lt;repair&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7699" PostTypeId="2" ParentId="7697" CreationDate="2017-06-04T19:02:03.000" Score="1" Body="&lt;p&gt;Take a look at the Owner's manual. You might try connecting an antenna to it, and see if you can hear sounds coming out the speaker with the volume and RF gain turned up. But if the digital readout is dark, something else may be wrong&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the &lt;a href=&quot;http://www.qsl.net/4/4x6on/RADIO%20MANUALS/MISCELLANEOUS/DRAKE--TR-7-Service-Manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Drake TR7 service manual&lt;/a&gt;, as well as the &lt;a href=&quot;http://www.wb4hfn.com/DRAKE/DrakeManuals/TR7/Manual_TR7.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Owner's manual&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-06-04T19:17:19.347" LastActivityDate="2017-06-04T19:17:19.347" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7700" PostTypeId="2" ParentId="6864" CreationDate="2017-06-04T20:36:35.657" Score="7" Body="&lt;p&gt;Two major reasons HF direction finding arrays like that aren't particularly useful any more (you won't find many fixed HF DF stations at all, even more modern ones):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;As William said, HF is not used very frequently for military communications these days, it is primarily a backup to satellite systems for long distance communication, and what communications occur tend to be more mundane and of less tactical and strategic interest. You aren't likely to hear a carrier group in theater chatting on HF these days, they know that's easily intercepted and will use systems that require geographic proximity to detect (like satellites). You're much more likely to hear encrypted links between fixed stations (bases) or inconsequential communications between assets not of much interest. Some asset phoning home because of a maintenance issue, or a routine training net, etc, and you already know where those sorts of assets are: &quot;At home&quot;.&lt;/li&gt;&#xA;&lt;li&gt;Why use a massive, fixed array such as this, when an aircraft (there are several in the US inventory) can use synthetic aperture to do direction finding of similar or better accuracy, from a position much closer to the transmission in the first place, perhaps eliminating the uncertainty injected by the ionosphere, and making the intelligence far more actionable?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These days, direction finding work is of the most acute utility on the tactical level, not strategic. You've got satellite imagery and various long distance surveillance platforms for finding carrier groups in the middle of the ocean. Those assets &lt;em&gt;can't&lt;/em&gt; help you find smaller elements such as a platoon or even just a lone operative, so you employ an asset that is operating on the level where the things they're going to look for are of most interest, primarily the local/regional scale, and a single aircraft may be able to cover an area the size of a small country for such work.&lt;/p&gt;&#xA;" OwnerUserId="246" LastEditorUserId="246" LastEditDate="2017-06-05T12:44:26.957" LastActivityDate="2017-06-05T12:44:26.957" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7701" PostTypeId="2" ParentId="6864" CreationDate="2017-06-04T21:33:01.180" Score="2" Body="&lt;p&gt;Wullenwebers have been replaced by the &lt;a href=&quot;https://www.google.com/search?q=FCC%20HFDF&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC HFDF&lt;/a&gt; (&quot;huff-duff&quot;) system. Several HFDF installations are located in the USA along both the north and south borders and the east and west coasts, plus Alaska, Hawaii, and other locations such as some US possessions. Most of them are unmanned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.google.com/mymaps/viewer?mid=1HO8mc7b4WF9PAGHPrkf-cPVElU0&amp;amp;hl=en_US&quot; rel=&quot;nofollow noreferrer&quot;&gt;Google Maps has a listing of their locations&lt;/a&gt;. You can zoom into each location and view the antenna supports, but it's tough to make out all the wires so as to determine exactly what the antennas are. In spite of that, it appears most of those sites use a single V-beam, judging from the support structures (which is all I could make out from the satellite images at maximum zoom a few years back). A few apparently used the older Wullenweber arrays. You can certainly see enough to realize how simple these small HFDF antennas are compared to a Wullenweber!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC HFDF installations all tie in to a manned but automated central control headquarters. When someone transmits, their precise location is quickly recorded &lt;em&gt;and with far greater accuracy than expensive Wullenweber arrays could.&lt;/em&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the FCC uses it, according to &lt;a href=&quot;http://www.arrl.org/news/fcc-releases-warning-notices-to-several-radio-amateurs&quot; rel=&quot;nofollow noreferrer&quot;&gt;this ARRL page about it&lt;/a&gt;. For example, the FCC wrote a letter to a wayward ham that &quot;...you were heard by staff at the Commission's High Frequency Direction Finding (HFDF) Center communicating repeatedly on 14.313 MHz ...&quot;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-06-04T21:42:49.997" LastActivityDate="2017-06-04T21:42:49.997" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7702" PostTypeId="2" ParentId="7609" CreationDate="2017-06-04T23:22:12.557" Score="2" Body="&lt;p&gt;Most likely, your upgrade is still pending processing at the FCC.   I recently moved from the Midwest (region 0) to South Florida (region 4).  I requested two modifications to my Advanced Class license (yes, I have a &quot;grandfathered&quot; Advanced license grant).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modification 1) Address change to my new address in FL.&lt;br&gt;&#xA;Modification 2) Call sign change from W0JMO to W4JMO region 4 (Florida). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I requested both changes on May 17, 2017.   My call sign has still not been changed but my license address was changed within 2 days.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I spoke to an FCC representative and was informed that license class changes and call sign changes can take up to 6-8 weeks to process.   I am still waiting for the FCC to modify my call sign.  The FCC CORES database shows the call sign modification request as PENDING, and the address change as completed.  You can also download a copy of your current FCC license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Register for access to FCC CORES licensing database.&#xA;&lt;a href=&quot;https://apps.fcc.gov/cores/userLogin.do&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://apps.fcc.gov/cores/userLogin.do&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can view the status of your license modification.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W0JMO - Joe&lt;/p&gt;&#xA;" OwnerUserId="9781" LastActivityDate="2017-06-04T23:22:12.557" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7703" PostTypeId="1" AcceptedAnswerId="7704" CreationDate="2017-06-05T14:05:27.433" Score="6" ViewCount="635" Body="&lt;p&gt;What's the ideal filter for PSK31 demodulation? That is, something that minimizes ISI, while having a narrow bandwidth to reject adjacent channels, while being reasonably matched?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most PSK modes use a &lt;a href=&quot;https://en.wikipedia.org/wiki/Root-raised-cosine_filter&quot; rel=&quot;noreferrer&quot;&gt;root raised cosine&lt;/a&gt; pulse shape, thus the receiver can convolve the received signal with an identical filter which is then both perfectly matched and zero-ISI. However, PSK31 simply uses a raised-cosine envelope, which I guess means there's a second order discontinuity at each transition between 0's and 1's which increases the occupied bandwidth, and also the appropriate receive filter is not so obvious. &lt;a href=&quot;http://bipt106.bi.ehu.es/psk31theory.html&quot; rel=&quot;noreferrer&quot;&gt;G3PLX describes&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Note that the transmitter and receiver filters have to be &quot;matched&quot; to each other for the ISI performance to be right. Some systems like this use a pair of identical receive and transmit filters which are matched. If I did this and someone else came along wanting to improve the performance, they would have to get everyone else to change their transmit filters. I have therefore chosen to use the simple cosine shape for the transmitter and match that in the receiver. This leaves the way open for others to develope better receivers without new transmitters being incompatible with old. This is slightly different from the SP9VRC approach.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The few implementations I've been able to examine use a set of filter taps copied from some other implementation, or don't specifically say what the filtering is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any detailed information on these filters? Or equivalently, how would one go about designing such a filter?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-06-05T15:10:23.140" LastActivityDate="2017-07-16T11:25:15.793" Title="Filtering for PSK31 demodulation" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;&lt;filter&gt;&lt;psk31&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7704" PostTypeId="2" ParentId="7703" CreationDate="2017-06-05T15:01:16.257" Score="4" Body="&lt;p&gt;So, to maximize SNR you'd use a matched filter (which is the conjugate complex of the time-reversed TX pulse shaping filter), and assuming the pulse shaper has been reasonably chosen, that'd also a ISI-minimizing filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, psk31.txt from the &lt;a href=&quot;http://bipt106.bi.ehu.es/psk31.html&quot; rel=&quot;noreferrer&quot;&gt;original DOS program&lt;/a&gt; says&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The solution is to filter the output, or to shape the envelope amplitude of&#xA;  each bit which amounts to the same thing. In PSK31, a cosine shape is used.&#xA;  To see what this does to the waveform and the spectrum, consider transmitting&#xA;  a sequence of continuous polarity-reversals at 31 baud. With cosine shaping,&#xA;  the envelope ends up looking like full-wave rectified 31Hz AC. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, the transmit filter is half a cosine. (Not RRC. I've just corrected the wikipedia page – it said RRC.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same document doesn't state what exactly the RX filter is – only that it is supposed to be &quot;matched&quot; (which doesn't seem to mean the &quot;canonical&quot; matched filter above). The author's reasoning goes like this:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Note that the transmitter and receiver filters have to be &quot;matched&quot; to&#xA;  each other for the ISI performance to be right. Some systems like this use&#xA;  a pair of identical receive and transmit filters which are matched. If I&#xA;  did this and someone else came along wanting to improve the performance,&#xA;  they would have to get everyone else to change their transmit filters. I&#xA;  have therefore chosen to use the simple cosine shape for the transmitter&#xA;  and match that in the receiver.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I cannot help but feel this is bogus reasoning. Mathematically, it's clear that maximum SNR without ISI can &lt;a href=&quot;https://en.wikipedia.org/wiki/Matched_filter#Derivation_of_the_matched_filter&quot; rel=&quot;noreferrer&quot;&gt;&lt;em&gt;only&lt;/em&gt;&lt;/a&gt; be obtained by correlating with the conjugate reversed TX filter – and that being time-symmetric and real in the case of a cosine filter implies you get the same TX as RX filter. Stat – there's no design freedom anymore once you've chosen the TX filter, no matter how you chose that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you can correlate multiple periods (let's say 4) of RX signal with all hypothetical  permutations and get better SNR – but that's a lot more channel (de)coding than modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, best you can do is a cosine RX; everything else is higher-level error-correction. You should do that error correction – a trellis is your friend!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-06-05T15:01:16.257" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7705" PostTypeId="1" CreationDate="2017-06-06T01:02:25.023" Score="1" ViewCount="526" Body="&lt;p&gt;I want to make a software defined radio, based on the hardware device shown in the schematic diagram below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/obWXu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/obWXu.png&quot; alt=&quot;This device is CALLISTO. It can graph solar radio wave activity.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have a strong background in telecommunication engineering (I'm an electrical engineering student); but right now I have to solve this problem as a part of a project in my internship program.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a USRP B200 and I want to use a GNU Radio Companion to process the signal. At first, I just tried to recreate each block into GRC. But apparently, that's not the way it works. So, I hope someone can give me a reference on how to manipulate this schematic diagram using a software defined radio to produce exactly the same result. I know it's a lot to ask, but please help me. I'm willing to learn this.&lt;/p&gt;&#xA;" OwnerUserId="9789" LastEditorUserId="4076" LastEditDate="2020-04-26T13:37:08.133" LastActivityDate="2020-04-29T16:18:36.860" Title="How to make a software defined radio using USRP and GRC" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7706" PostTypeId="2" ParentId="7705" CreationDate="2017-06-06T02:26:19.313" Score="4" Body="&lt;p&gt;In general, a software-defined radio and one implemented in hardware will have much the same &lt;em&gt;signal paths,&lt;/em&gt; but how they are broken down into individual “blocks” will vary. In your case, following the main signal path from left to right:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;It looks like everything on the main path to the left of “Log Detect” is a conventional superheterodyne receiver. These are mostly parts that your USRP SDR hardware will replace. Everything after it would be be implemented in software. The I²C bus is presumably used for tuning and instead you will just use the methods of the USRP source block to change frequency. (Internally, this corresponds to communicating with the USRP over USB, but that is not something your code interacts with directly.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The next step will be to apply the appropriate frequency shift and low-pass filter (corresponding to the BPF in the diagram) to extract the actual desired signal. The USRP has its own filtering but it will not be optimized for your particular signal. You can read about these steps in any tutorial for building receivers in GNU Radio.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;At this point you will also want to &lt;em&gt;downsample&lt;/em&gt; (a.k.a. &lt;em&gt;decimate&lt;/em&gt;) the signal down to the lowest sample rate that still preserves the signal features you care about without consuming too much CPU power. Again, this should be covered in any good SDR tutorial. You should look at how the existing microcontroller code referenced in that diagram operates — in particular, how often the ADC is sampled.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Now we get to things specific to your application. The GNU Radio software analogue of a log detector is the &lt;em&gt;Complex to Mag^2&lt;/em&gt; (&lt;code&gt;gnuradio.blocks.complex_to_mag_squared&lt;/code&gt;) block followed by the &lt;em&gt;Log10&lt;/em&gt; (&lt;code&gt;gnuradio.blocks.nlog10_ff&lt;/code&gt;) block.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The next block in your diagram is an ADC (which function has already been handled by the USRP, of course) inside a microcontroller. The diagram doesn't tell us what the program does, so you'll have to look into that yourself. If it's standard straightforward DSP operations, then you can likely use existing GNU Radio blocks, but you may have to write a custom block. Or, you can have the signal exit GNU Radio (via some sink block) to another program or non-GR code that implements the same algorithm the microcontroller does to produce the output to the &quot;Focal Plane Unit&quot;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Everything else on the diagram — the “Clock Buffer”, the low pass filters, and voltage regulators — is just supporting hardware that is entirely irrelevant to the actual signal processing task.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So, that's everything that we can conclude just from the diagram you provided.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I strongly recommend that you find a couple tutorials on building basic software-defined receivers with GNU Radio. Even though they won't be dealing with your particular radio protocol, they will introduce the fundamental concepts of A/D conversion, quadrature, filtering, and downsampling. They're not very complex at all and once you understand those things, your problem and solution will make much more sense to you.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-06-06T02:26:19.313" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7707" PostTypeId="2" ParentId="490" CreationDate="2017-06-06T04:02:16.073" Score="1" Body="&lt;p&gt;Unication U4 and U3 radios do exactly that.&#xA;&lt;a href=&quot;http://www.comart.com.cn/show_pro_en.asp?classid=152&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.comart.com.cn/show_pro_en.asp?classid=152&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9790" LastEditorUserId="8717" LastEditDate="2017-06-06T21:32:24.277" LastActivityDate="2017-06-06T21:32:24.277" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7708" PostTypeId="1" CreationDate="2017-06-06T07:22:27.340" Score="1" ViewCount="2639" Body="&lt;p&gt;I have beacon receiver program the flowgraph is shown here&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ji8Jh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ji8Jh.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have to make the flowgraph run and stop automatically during a preset period, because I have to make the flowgraph only work when the beacon satellite passes the ground station. I am using USRP1.&lt;/p&gt;&#xA;" OwnerUserId="9791" LastEditorUserId="873" LastEditDate="2017-06-06T08:31:44.230" LastActivityDate="2017-06-06T11:44:24.973" Title="How to make GRC flowgraph run and stop automatically during some period" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;&lt;gnuradio&gt;&lt;beacon&gt;&lt;automation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7709" PostTypeId="1" CreationDate="2017-06-06T07:35:47.927" Score="1" ViewCount="1228" Body="&lt;p&gt;I'm on reasearch using USRP and GNU radio for solar flare observation. The research is making digital radio receiver in GNU radio companion and using USRP B200. Basically the purpose of system is to receive multi-frequency which in range frequency 45-870 MHz. The problem is i can't receive signal execpt of center frequency. I want the system could be able to scan signal in those range frequency above. I want to change center frequency automatically in periodically but i don't know how the way. I'm an amateur and i haven't basic using GRC. I hope someone can help me and give me reference to solve the problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regards,&#xA;Sinta.&lt;/p&gt;&#xA;" OwnerUserId="9792" LastActivityDate="2017-07-20T16:53:57.733" Title="How to change center frequency automatically in GRC?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7710" PostTypeId="2" ParentId="7709" CreationDate="2017-06-06T08:27:57.300" Score="2" Body="&lt;p&gt;That's something that is inherently hard to implement in a graphical tool. It's a very sequential program flow, and thus, the GRC approach might be the wrong one – while relatively easy to write in python, it'd be hard to do this graphically. The graphical approach to software design isn't always the easiest one (sorry, LabVIEW).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I'd recommend going through the Guided Tutorials on &lt;a href=&quot;http://tutorials.gnuradio.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://tutorials.gnuradio.org&lt;/a&gt; . Afterwards, take the python code that GRC generates out of your graphical flow graph, and amend it such that it simply is restarted with different frequencies. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-06-06T08:27:57.300" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7711" PostTypeId="1" CreationDate="2017-06-06T09:56:41.393" Score="5" ViewCount="533" Body="&lt;p&gt;following on from an earlier question about &lt;a href=&quot;https://ham.stackexchange.com/q/425/9793&quot;&gt;Iron Ore&lt;/a&gt; affecting radio waves... are there any other geological properties that can affect radio waves?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are certain frequencies more susceptible to geology than others?&lt;/p&gt;&#xA;" OwnerUserId="9793" LastEditorUserId="76" LastEditDate="2019-04-13T20:32:19.837" LastActivityDate="2019-04-13T20:32:19.837" Title="Does geology affect radio signals?" Tags="&lt;propagation&gt;&lt;earth&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7712" PostTypeId="2" ParentId="7711" CreationDate="2017-06-06T11:34:05.693" Score="9" Body="&lt;h1&gt;Other Effects&lt;/h1&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;are there any other geological properties that can affect radio waves?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes, there are other effects.&lt;/p&gt;&#xA;&lt;p&gt;Basically, &lt;strong&gt;every&lt;/strong&gt; material affects the propagation of radio waves.&lt;/p&gt;&#xA;&lt;h2&gt;Absorption&lt;/h2&gt;&#xA;&lt;p&gt;That one's kind of obvious: radio wave hits medium (e.g. soil), gets absorbed.&lt;/p&gt;&#xA;&lt;p&gt;That's the reason you can't look through a piece of coal – light is just a wave at a high frequency, and coal absorbs light very well.&lt;/p&gt;&#xA;&lt;p&gt;On the radio frequency scale, that happens with all kinds of geological materials, if they don't reflect. Since you seem to be studying something geology-related: this is commonly used for radio earth exploration. Dry sand, for example, doesn't absorb all too well, but denser/moister clay does. Thus, you can build a radar that can look through sand (using the right wavelength/frequency), and &amp;quot;see&amp;quot; the clay, the salt or the aquifer below. Keyword: &lt;em&gt;ground-penetrating radar&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;h2&gt;Reflection&lt;/h2&gt;&#xA;&lt;p&gt;Keywords: &lt;em&gt;Radar, Synthetic Aperture Radar, Remote Sensing&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;A very common thing to observe is that metal surfaces reflect radio waves – simply because metals are excellent conductors of electricity. That leads to the fact that there can't be an electrical field &lt;em&gt;inside&lt;/em&gt; the metal, and together with the physical equations describing waves, that leads to the wave having to bounce off the surface.&lt;/p&gt;&#xA;&lt;p&gt;Now, on a geological scale, that means that reflection on the ground will work better the better the ground conducts (and it will be &amp;quot;straighter&amp;quot; and less scatter-y the flatter the ground is). Thus, saltwater bodies without waves reflect waves very well.&lt;/p&gt;&#xA;&lt;h3&gt;Corner Reflectors&lt;/h3&gt;&#xA;&lt;p&gt;Also, for example, if you have a wave hitting a 90° corner of reflective material (e.g. the side of ship and its deck, a sharp cliff and the sea beneath), you get nearly all of the transmitted energy back in the direction the wave came from. That's the same principle why &lt;a href=&quot;https://en.wikipedia.org/wiki/Safety_reflector&quot; rel=&quot;noreferrer&quot;&gt;bike reflectors&lt;/a&gt; have these pyramidal structures:&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/0/0c/Corner-reflector.svg/815px-Corner-reflector.svg.png&quot; alt=&quot;corner reflection&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;You'll see that being used for radio purposes, e.g. to make vessels more visible to ship radars by maximizing the amount of radio energy getting reflected back at the emitter. Can you spot the corner reflector in this &lt;strike&gt;seal relaxation pod&lt;/strike&gt; buoy?&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/e/e5/Buoy_seal.jpg&quot; alt=&quot;Buoy with corner reflector&quot; /&gt;&lt;/p&gt;&#xA;&lt;h3&gt;Scattering&lt;/h3&gt;&#xA;&lt;p&gt;On a smaller scale, flat (&amp;quot;flat&amp;quot; in the scale of a wavelength – ie. what's flat for a 200m wavelength isn't necessarily flat for a 3cm wavelength, or for light, which has some 600 nm wavelength) surface produce a &amp;quot;sharp&amp;quot; reflection, whereas rough surfaces scatter the power in all directions, randomly.&lt;/p&gt;&#xA;&lt;p&gt;That is very commonly used in radar-based earth exploration: A satellite illuminates the earth with radio waves of horizontal polarization, and registers how much is reflected back with the same polarization, and with vertical polarization. If one polarization dominates, you have flat surfaces that you illuminate, if both polarizations are equally common, the things you illuminate randomly rotate the polarization by reflection on rough/randomly oriented smaller surfaces. You can often see SAR imagery with false colors, where one color means &amp;quot;transmitted horizontal, received vertical&amp;quot;, another means &amp;quot;transmitted horizontal, got horizontal&amp;quot;, another means &amp;quot;transmitted vertical, got vertical&amp;quot;, and you mix these together to get an overall image. Here's an example of &lt;a href=&quot;https://www.nasa.gov/topics/earth/features/haiti20100201.html&quot; rel=&quot;noreferrer&quot;&gt;NASA's SAR imagery of Haiti after the disaster there&lt;/a&gt; (that link is good – read it!).&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://www.nasa.gov/images/content/421508main_haiti20100201-full.jpg&quot; alt=&quot;SAR image with false colors&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;Vegetation with leaves and tree trunks has a high degree of random scattering, leading to much cross-polarization, which is green in the picture. Buildings have a lot of right angles, so they contain a lot of corner reflectors (see above), and thus  dominant polarizations, as well as being bright due to the high amount of reflected energy at corner reflectors.&lt;/p&gt;&#xA;&lt;h2&gt;Diffraction&lt;/h2&gt;&#xA;&lt;p&gt;Then, we have effects like diffraction – the fact that when a wave hits some kind of obstacle with an edge, it extends behind that edge. Here's an example from the wikipedia page on Diffraction. The plane wave enters from left, and then hits the yellow obstacle with a small slit in the middle.&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/4/46/Wavelength%3Dslitwidthspectrum.gif&quot; alt=&quot;Diffraction&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;The very same happens at the tops of mountains – at the crest, the waves &amp;quot;break&amp;quot; and diffract behind, reaching valleys that definitely don't have a line of sight to the transmitter.&lt;/p&gt;&#xA;&lt;p&gt;In low-incident-angle spaceborne synthetic aperture radar earth imaging, that can lead to artifacts in areas that should be in the radio shadow.&lt;/p&gt;&#xA;&lt;h2&gt;Refraction&lt;/h2&gt;&#xA;&lt;p&gt;This is usually less commonly seen with respect to geological properties, but at the same scale: if you have a material where specific electromagnetical properties change, you can &amp;quot;bend&amp;quot; waves. This is usually observed in the atmosphere, not the earth itself, so it's less of a geological than a meteorological phenomenon.&lt;/p&gt;&#xA;&lt;h2&gt;Waveguides&lt;/h2&gt;&#xA;&lt;p&gt;You might know that the wave inside coax cables is not actually transported as electrical current in the metal conductors, but as wave in the isolator between – and the same effect can be seen with the earth and well-conducting parts of the atmosphere, especially when these are being ionized by solar radiation. So, that's at least half a geological phenomenon.&lt;/p&gt;&#xA;&lt;h1&gt;Frequency Dependency&lt;/h1&gt;&#xA;&lt;p&gt;Keywords: &lt;em&gt;Electromagnetic Theory basics, Wavelength, Dipole&lt;/em&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Are certain frequencies more susceptible to geology than others?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes. But it's basically all a question of the relation of the size of the  geological feature and the wavelength. Just like a large flat piece of copper is a very good reflector for waves of let's say 2 m wavelength, but needs to be very very polished to work well as reflector for light waves (a mirror), these effects simply scale. &amp;quot;Polishing to a mirror finish&amp;quot; simply means nothing but &amp;quot;making flat at the scale of light wavelengths&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Of course, given that certain things have certain sizes, yes, things are dependent on frequency (since that is proportional to the inverse of wavelength).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-06-06T12:11:06.550" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7713" PostTypeId="2" ParentId="7708" CreationDate="2017-06-06T11:44:24.973" Score="2" Body="&lt;p&gt;This is the sort of task for which it is at least easiest to do outside of the model of GNU Radio Companion. That is, you would take the generated code and instead of executing it directly, modify it — or, perhaps, load it as a module.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First of all, I recommend changing from WX GUI to QT GUI. WX support in GNU Radio Companion is deprecated, and the generated code isn't quite the same as what I'm going to talk about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look at the generated code, you will see this structure (I've removed the irrelevant parts).&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;class GRBR(gr.top_block, Qt.QWidget):&#xA;    ...&#xA;&#xA;def main(top_block_cls=GRBR, options=None):&#xA;    ...&#xA;&#xA;    tb = top_block_cls()&#xA;    tb.start()&#xA;    tb.show()&#xA;&#xA;    def quitting():&#xA;        tb.stop()&#xA;        tb.wait()&#xA;    qapp.connect(qapp, Qt.SIGNAL(&quot;aboutToQuit()&quot;), quitting)&#xA;    qapp.exec_()&#xA;&#xA;&#xA;if __name__ == '__main__':&#xA;    main()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;As you can see, there are start and stop methods on &lt;code&gt;tb&lt;/code&gt;. All you need to do is call them (well, and also &lt;code&gt;.wait()&lt;/code&gt; immediately after every &lt;code&gt;.stop()&lt;/code&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, &lt;code&gt;main()&lt;/code&gt; will be sitting inside &lt;code&gt;qapp.exec_()&lt;/code&gt; for the lifetime of the program. You could use a separate thread, or probably better, use something within QT's event loop, which I hear would be &lt;a href=&quot;http://pyqt.sourceforge.net/Docs/PyQt4/qtimer.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;QTimer&lt;/a&gt; (I haven't programmed with Qt myself).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I mentioned above using the GRC generated code without modifying it. That would look like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;import GRBR  # GRC-generated python, loaded as a module&#xA;&#xA;def main(...):&#xA;    # exact same code as before&#xA;&#xA;if __name__ == '__main__':&#xA;    main() &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This has the advantage that you can keep developing your flow graph in GRC.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;You may also wish to consider &lt;em&gt;not&lt;/em&gt; actually stopping your flow graph. This is because stopping and restarting can have some negative effects (it does unnecessary work and some source or sink blocks have had or still have bugs related to stop/start). Instead, &lt;em&gt;gate&lt;/em&gt; the signal — that is, drop samples until you need them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way to do this on external control would be to use the &lt;code&gt;copy&lt;/code&gt; block, which has a boolean parameter called &lt;code&gt;enabled&lt;/code&gt;. As long as it is not enabled, then it discards samples rather than passing them along.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also write a bit of Python code that is a &lt;code&gt;gr.hier_block2&lt;/code&gt;, and an accompanying GRC &lt;code&gt;.xml&lt;/code&gt; file telling GRC how to use it, which bundles up the copy block and the timer control in a unit you can actually use within GRC, and not give up the use of GRC's “run” button.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(In principle, this same approach could be used to do &lt;code&gt;stop&lt;/code&gt;/&lt;code&gt;start&lt;/code&gt; control, but that seems unwise to me from a code structure perspective.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-06-06T11:44:24.973" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7714" PostTypeId="2" ParentId="7585" CreationDate="2017-06-06T19:30:06.780" Score="3" Body="&lt;p&gt;The correct answer to your question is, I believe, that you should expect an increase of between 20-40% in range, depending on the height of the repeater(s) you are trying to hit as well as your local propagation environment (e.g. urban, suburban, free space, etc.).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think it is a trickier question than it seems because it depends on how marginal you are with 4W to begin with.  Your question can't really be answered without taking the sensitivity of the receivers of the repeaters (or other stations) you want to hit into account.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Receiver sensitivity is usually expressed in terms of some &lt;em&gt;Minimum Discernible Signal&lt;/em&gt; (MDS) level for a given level of noise at the receiver.  For FM receivers, this level is usually expressed in terms of some acceptable &lt;a href=&quot;https://en.wikipedia.org/wiki/SINAD&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;SINAD&lt;/em&gt;&lt;/a&gt; - SIgnal[-to-]Noise-And-Distortion ratio.  A typical SINAD benchmark for a VHF FM receiver is 12 dB.  One example of a typical VHF MDS can be found in this &lt;a href=&quot;http://www.ab4oj.com/test/docs/r8500notes.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;IC-R8500 Test Report from AB4OJ&lt;/a&gt;, which shows a 12 dB SINAD FM MDS of -121 dBm at 147 MHz (VHF).  The same report shows an MDS of -114 dBm at 446 MHz (UHF).  It turns out, though, that we don't need the absolute sensitivity to determine how much our range might increase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On a log scale, the equation that gives us the link range is, in general:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$MDS = P_{T,dBm} + G_{T,dB} - L_{dB}(f,h_B,h_M,d_{max}) + G_{R,dB}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $G_T$ is the antenna gain at the transmitter (e.g the UV-5), $G_R$ is the antenna gain at the receiver (i.e. repeater), $P_T$ is the transmitter power, and $L$ is the propagation loss factor.  The latter depends, in general, on the frequency of operation, the antenna heights, and the distance between the two stations.  The &lt;em&gt;M&lt;/em&gt; subscript stands for our portable (&quot;mobile&quot;) and the &lt;em&gt;B&lt;/em&gt; subscript stands for our target repeater (&quot;base&quot;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If frequency and antenna heights are held constant, then, for a given MDS, we would have a low power case of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$MDS = P_{T,dBm} + G_{T,dB} - L_{dB}(f,h_B,h_M,d) + G_{R,dB}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and a high power case:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$MDS = P_{T,dBm} + 3 dB + G_{T,dB} - L_{dB}(f,h_B,h_M,d') + G_{R,dB}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To calculate the increase in range, we subtract the first equation from the second to obtain:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 3 dB - L_{dB}(f,h_B,h_M,d') + L_{dB}(f,h_B,h_M,d) = 0 $$&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;&quot;Real World&quot; propagation&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Others have suggested that $L$ is proportional to $1/d^2$.  This is certainly true for free space (&lt;em&gt;viz.&lt;/em&gt; the &lt;a href=&quot;https://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Friis equation&lt;/a&gt;), but in general the dependency on distance can vary widely depending on the propagation environment.  The &lt;a href=&quot;https://en.wikipedia.org/wiki/Hata_Model&quot; rel=&quot;nofollow noreferrer&quot;&gt;Okumura-Hata model&lt;/a&gt; includes a comprehensive set of &lt;em&gt;empirical&lt;/em&gt; equations based on field measurements under various conditions.  According to the Okumura-Hata model:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$L_{dB}(f,h_B,h_M,d) = K_0(f,h_B,h_m) + K_1(h_B)\log_{10}d$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where, with $h_B$ in meters:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ K_1(h_B) = 44.9 - 6.55\log_{10}h_B $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the $K_0$ term cancels, we need to solve:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 3 - K_1(h_B)\log_{10}d' + K_1(h_B)\log_{10}d = 0 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \log_{10}d' - \log_{10}d = \log_{10}\left(\frac{d'}{d}\right) = \frac{3}{ K_1(h_B)} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we raise both sides to the power of 10 we get:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{d'}{d} = 10^{3/K_1(h_B)} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can substitute your own local values, but assuming if the repeater tower is 20 m tall, then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$K_1(h_B) = 44.9 - 6.55*\log_{10}(20) = 36.4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;so that:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{d'}{d} = 10^{3/36.4} = 1.21$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, in this particular scenario, doubling your power from 4 W to 8 W would result in your increasing your range - in the sense of reaching new repeaters - by about 20%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that all of the above analysis presumes (1) that the Okumura-Hata model is accurate and (2) that the propagation characteristics are uniform in all directions.  Neither of these, of course, will be strictly true, but at least the model provides a non-arbitrary means with some grounding in field truth of answering your question.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Comparison to free space (&quot;line-of-sight&quot;)&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;If we are in free space, then, as others have suggested, the Friis equation applies and we have:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$L_{dB} = 10\log_{10}4\pi + 20\log_{10}d$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$K_1(h_B) = K_1 = 20$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \frac{d'}{d} = 10^{3/20} = 1.41$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which implies that our reach would increase by about 40%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, overall we can say that doubling your power should increase your range (again - meaning the range within which you are able to &quot;hit&quot; repeaters) by between 20% and 40%, depending on the extent to which you have &quot;line-of-sight&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I am assuming I didn't screw up the math along the way.  If I did, hopefully someone will correct me).&lt;/p&gt;&#xA;" OwnerUserId="9796" LastEditorUserId="9796" LastEditDate="2017-06-06T20:13:06.213" LastActivityDate="2017-06-06T20:13:06.213" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7715" PostTypeId="1" AcceptedAnswerId="7716" CreationDate="2017-06-07T19:30:19.727" Score="1" ViewCount="808" Body="&lt;p&gt;My Android phone (as many others) have FM radio receiver on-board. But apparently, it has no internal VHF antenna at all, since there is no signal at all w/o headphones plugged in and sound quality varies drastically depending on the headphone cable currently in place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I'm curious how to build dedicated antenna, particularly, which pin(s) of 3.5mm connector FM receiver uses to get a signal from. Thanks!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Finally, found my worst headphones, less strong station and the longer conductor and did the clever experiment suggested by @Kevin again. However, I'm not exactly sure how to interpret the results:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With headphones connected reception improves when an additional conductor attached to all three pins (can't really hear the difference if any)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Without headphones&lt;/em&gt; (open circuit) I've got the definite results, reception have most clear treble frequencies at Tip pin (Left), noisy treble the Ring pin (Right) and the worst at Sleeve pin (Ground).&lt;/p&gt;&#xA;" OwnerUserId="9801" LastEditorUserId="9801" LastEditDate="2017-06-07T23:09:44.400" LastActivityDate="2017-06-07T23:09:44.400" Title="What is pinout for headphone FM radio antenna?" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7716" PostTypeId="2" ParentId="7715" CreationDate="2017-06-07T19:47:21.980" Score="3" Body="&lt;p&gt;The “pinout” for this purpose could be anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Considering the perspective of the equipment designer: If you have a multi-conductor cable of any sort and you want to use it as an antenna element, it doesn't matter at all which conductor you use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(You might think that if the headphone cable is shielded then the shield would prevent it from functioning as an antenna, but that is only true if the shield is also connected through to the radio receiver. Any &lt;em&gt;single&lt;/em&gt; wire is as good as any other.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a procedure to find out what the actual implementation is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Get a headphone splitter (Y cable), and plug in headphones to one side. Coil up the cord so it doesn't work very well as an antenna.&lt;/li&gt;&#xA;&lt;li&gt;On the other side, plug in an unwired 3.5 mm plug with the shell off, or whatever else you have handy as a breakout.&lt;/li&gt;&#xA;&lt;li&gt;Touch a piece of wire or a clip lead to each of the three contacts, and see which one makes the most difference to radio reception. (Since re-radiation and crosstalk are possible, the results can be fuzzy.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It's even possible that the circuit is designed to pick up RF from &lt;em&gt;any&lt;/em&gt; of the three wires. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, you might like to read &lt;a href=&quot;https://ham.stackexchange.com/questions/5359/how-to-improve-reception-with-a-headphone-cord-antenna&quot;&gt;this existing question about improving reception in this type of receiver&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-06-07T21:32:01.937" LastActivityDate="2017-06-07T21:32:01.937" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7717" PostTypeId="2" ParentId="7453" CreationDate="2017-06-07T22:39:55.800" Score="0" Body="&lt;p&gt;In addition to what has already been recommended, I would recommend:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;W.C.Y. Lee, &lt;a href=&quot;http://amzn.to/2sEVnii&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Mobile Cellular Telecommunications&lt;/em&gt;&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Ramo, Whinnery, and Van Duzer, &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/0471585513&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Fields and Waves in Communication Electronics&lt;/em&gt;&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;J.D. Kraus, &lt;a href=&quot;http://amzn.to/2rWIi6c&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Antennas&lt;/em&gt;&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you are interested in empirical methods for estimating propagation loss in various environments, you might take a look at the &lt;a href=&quot;https://en.wikipedia.org/wiki/Hata_Model&quot; rel=&quot;nofollow noreferrer&quot;&gt;Okumura-Hata model&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also take the &lt;a href=&quot;https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-013-electromagnetics-and-applications-spring-2009/index.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;MIT undergraduate course in Electromagnetics and Applications online&lt;/a&gt; for free at MIT OpenCourseware.  You can browse the graduate courses there as well.  I think you will find the material you are looking for covered in 6.641 and elsewhere. &lt;/p&gt;&#xA;" OwnerUserId="9796" LastActivityDate="2017-06-07T22:39:55.800" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7718" PostTypeId="2" ParentId="607" CreationDate="2017-06-07T23:20:52.190" Score="3" Body="&lt;p&gt;For HF usage with 200 Msps converters and above, an 8 bit ADC will provide very good performance. You write: &quot;the sampling frequency has to be several times the target frequency&quot; but that is not true at all. It is possible to do under-sampling, listen on e.g. 144 MHz with an ADC running at 10 MHz. If you sample at 20 MHz and have an analog bandwidth of 200 MHz and set your SDR to receive 4 MHz you will find that signals at 4, 16, 24, 36, 44, 56, 64,... up to 200 MHz will provide the same output, appearently 4 MHz in the SDR. They are all aliases of different order. If you insert a filter that picks the range 144-146 MHz and rejects everything else you have a 144 MHz receiver. You would need more than 8 bits however because of the low sampling rate.&#xA;Note that the digital side will have the noise from all the alias frequencies. Do not insert a wideband amplifier after the filter!&#xA;When you sample at 200 MHz or above to receive HF signals you are under-sampling. With an interest in the range DC to 30 MHz you need a very simple filter to suppress everything above 170 MHz. Certainly you would make cut-off lower to avoid FM BC and other stuff, but the filter is extremely uncritical. On the digital side the bandwidth would be 100 MHz, but you would apply a filter to reduce the bandwidth to 2.4 kHz (SSB.) The bandwidth reduction is a factor of about 41000 (56 dB) which means that you gain 9 bit so the SSB S/N comes from a 9+8=17 bit (narrowband) ADC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case you would use the undersampling strategy at 20 MHz, S/N would be 10 dB smaller because the bandwidth ratio would be 10 times smaller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Conventional direct conversion receivers (Softrock and similar) typically use &quot;16 bit&quot; soundcards which have a noise floor of about 2 bit and a real range of 14 bit. They sample at 96 kHz so the bandwidth ratio to SSB bandwidth is 40 (16 dB) which means they give an S/N of about 14+3 bit = 17 bit. Similar to what you would get with an 8 bit ADC at 200 MHz. (An 8 bit ADC typically has a noise floor well below 1 bit.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that any ADC needs a RF voltage on the input that sweeps several ADC levels. Severe artifacts appear if the ADC gives the same value almost always. There has to be significant signals that sweep across several ADC levels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Today, with advanced graphical processors it might be interesting to use few bits at very high rates. Already the 8 bit RTL-SDR.com at 2.4 MHz can produce reasonable results:&#xA;&lt;a href=&quot;https://www.youtube.com/watch?v=NYhVvtbqaD0&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=NYhVvtbqaD0&lt;/a&gt;&#xA;With 8 bit at 240 MHz you would do 20 dB better! More cost effective would probably be 10 bit at 100 MHz (9 dB better ideally, but more like 6 dB better in real life since the noise floor vs a single bit is likely higher in a 10 bit ADC than in a 8 bit ADC.)&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-06-07T23:20:52.190" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7719" PostTypeId="1" CreationDate="2017-06-08T19:26:45.470" Score="9" ViewCount="2106" Body="&lt;p&gt;So when I try to work the ISS digipeater, what should I set the digi path to be? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My setup is a 5 W HT with a 2 m yagi connected to my phone with APRSDroid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried the past few nights with &lt;code&gt;ARISS&lt;/code&gt; &lt;code&gt;R0ISS&lt;/code&gt; and &lt;code&gt;WIDE2-2&lt;/code&gt; and none seem to get picked up (granted some passes I've tried haven't been very high, ~25°).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I can hear and decode MANY packets (more than I can generally hear while on 144.390 APRS in my area). I'm also adjusting for doppler shift. I've not heard of adjusting for polarization, what would that entail? I'm using a 3 beam yagi that I made and generally try and track it while holding it generally horizontally. I apologize, I'm fairly new to this; I've had my Tech for a few years but haven't done much with it until recently.&lt;/p&gt;&#xA;" OwnerUserId="9809" LastEditorUserId="9809" LastEditDate="2017-06-10T01:17:45.740" LastActivityDate="2018-07-19T16:01:59.933" Title="APRS digi path for ISS digipeater?" Tags="&lt;vhf&gt;&lt;satellites&gt;&lt;aprs&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7720" PostTypeId="2" ParentId="7453" CreationDate="2017-06-08T21:04:43.247" Score="0" Body="&lt;p&gt;I am converting my comments into an answer with two publications that I believe are very worthy in answering the OPs questions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Introduction to RF Propagation&quot; by John S. Seybold, Wiley Press, 2005.  A good introductory book but the focus is in commercial applications (Radar, microwave, etc.) other than HF.  Contents of book:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Electromagnetics and RF Propagation&lt;/li&gt;&#xA;&lt;li&gt;Antenna Fundamentals&lt;/li&gt;&#xA;&lt;li&gt;Communications Systems and the Link Budget&lt;/li&gt;&#xA;&lt;li&gt;Radar Systems&lt;/li&gt;&#xA;&lt;li&gt;Atmospheric Effects&lt;/li&gt;&#xA;&lt;li&gt;Near Earth Propagation Models&lt;/li&gt;&#xA;&lt;li&gt;Fading and Multipath Characterization&lt;/li&gt;&#xA;&lt;li&gt;Indoor Propagation Modeling&lt;/li&gt;&#xA;&lt;li&gt;Rain Attenuation of Microwave and Millimeter Wave Signals&lt;/li&gt;&#xA;&lt;li&gt;Satellite Communications&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And, the second book is: &quot;Ionospheric Radio Propagation&quot; published by the National Bureau of Standards, U.S. Department of Commerce, editor/author: Kenneth Davies.  1965.  This is like the encyclopedia of Ionospheric HF models for a variety of conditions.  Key topics covered (not all) include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Earth's Atmosphere, Geomagnetism, and the Sun&lt;/li&gt;&#xA;&lt;li&gt;Theory of Wave Propagation&lt;/li&gt;&#xA;&lt;li&gt;Synoptic Studies of the Ionosphere&lt;/li&gt;&#xA;&lt;li&gt;Oblique Propagation (mainly HF propagation)&lt;/li&gt;&#xA;&lt;li&gt;Signal Strength&lt;/li&gt;&#xA;&lt;li&gt;Ionospheric Disturbances&lt;/li&gt;&#xA;&lt;li&gt;Ionospheric Propagation Predictions&lt;/li&gt;&#xA;&lt;li&gt;Scatter Propagation with VHF&lt;/li&gt;&#xA;&lt;li&gt;Propagation of Low and Very Low Frequency Waves&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2017-06-08T21:04:43.247" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7721" PostTypeId="2" ParentId="6184" CreationDate="2017-06-08T21:59:01.270" Score="0" Body="&lt;p&gt;I don't think there is a clean answer to your question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cable plant designers wrestled with cascaded distortion for decades before fiber dramatically reduced the number of RF actives between the headend and the set-top box.  Generally the rule - with some physical basis - was that second order distortion (&quot;composite second order&quot;, or CSO) generally combined non-coherently, whereas third-order distortion (&quot;composite triple beat&quot;, or CTB) combined coherently.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only thing I can think of in your case would be to assume the worst case and assume that the amplified distortion products from each stage combine coherently at the end of the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think this is a very good answer, but no one has taken a stab at your question for over a year - so I felt it couldn't hurt.&lt;/p&gt;&#xA;" OwnerUserId="9796" LastActivityDate="2017-06-08T21:59:01.270" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7722" PostTypeId="2" ParentId="1196" CreationDate="2017-06-08T23:09:34.687" Score="2" Body="&lt;p&gt;It does not matter if you sample DC to 100 MHz with one 200 MHz ADC or two 100 MHz ADCs preceeded by the appropriate I/Q mixer. There are efficient algorithms to use the real-valued input from a single 200 MHz ADC to produce&#xA;an output of 100 MHz complex FFT. Have a look here:&#xA;&lt;a href=&quot;https://www.youtube.com/watch?v=kxkd8e_ijw8&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=kxkd8e_ijw8&lt;/a&gt;&#xA;I do not think suitable routines are included in standard libraries,&#xA;but it is not difficult, one feeds two subsequent time functions into I and&#xA;Q, makes the transformation and finally takes the sum and difference of&#xA;the signal and its mirror image.&#xA;Direct sampling or down conversion both allow extremely good performance. In real life, today, direct sampling is better, many radios provide a dynamic range around 150 dBc/Hz (typical ham transceivers are around 125 dBc/Hz.)&#xA;HB9DRI is developing a dual ADC unit that is soundcard compatible and that provides something like 163 dBc/Hz. As far as I can understand he will be able to supply a 144 to IQ mixer that will provide a dynamic range of about 160 dBc/Hz - but with X-tal oscillators to keep LO sideband noise really low.&#xA;Today, direct sampling uses an FPGA to do digital down conversion. That means a rather complicated hardware and a high cost. Sampling perhaps 80 MHz with a single ADC directly into the computer would allow all the processing to be done in the computer where a GPU (Graphics adapter) could do all the filtering and bandwidth reduction that is needed. The video I linked to above shows operation on a very powerful computer, but rather than using 8 i7 cores I think I could use the K600 Nvidia board. OpenCL reports that the Nvidia GPU and the Intel GPU provide similar performance.&#xA;Sampling 14 bit at 80 MHz provides an extremely good performance provided one has some kind of filtering on the input. A long-wire antenna might produce +25 dBm from the local MW station. One can not look for -130 dBm signals on 28 MHz having them present. Fairly simple filters are needed though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be careful when reading specifications. The music industry is horrible. They may specify 24 bit resolution on soundcards that have their noise floor 14 bit below saturation. Truncate at 16 bits would make no difference at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On your question: IQ is so widely used because the output fits to standard stereo soundcards and the data rate is so low that one does not have to care about algorithm efficiency.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-06-08T23:09:34.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7723" PostTypeId="2" ParentId="6184" CreationDate="2017-06-09T01:47:41.190" Score="2" Body="&lt;p&gt;There are a couple reasons to filter between each stage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly, if you don't want to transmit those harmonics, then there's not much point in amplifying them. If you have an amplifier capable of a 10W output, but half the power is in undesired harmonics, then you are only getting a useful 5W out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, you may want your amplifiers to be linear, but they never are exactly linear. In practice you'll get some degree of &lt;a href=&quot;https://en.wikipedia.org/wiki/Intermodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;intermodulation distortion&lt;/a&gt; due to the different frequency components in the signal mixing with others. These intermodulation products have the potential to become spurious emissions if they aren't somehow removed before the final output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't filter between stages, then the distortion (both harmonic and intermodulation flavors) from one stage goes into the next. This increases the power at the input, and distortion gets worse with increasing power. It also means more frequency components to mix with others, compounding the issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How much filtering is enough? Well that just depends. By examining the signal at each stage with a spectrum analyzer (or my cheap substitute: another radio) you can see how much distortion is added by each stage and add the appropriate filtering.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-06-09T01:47:41.190" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7724" PostTypeId="1" CreationDate="2017-06-09T17:06:39.450" Score="3" ViewCount="739" Body="&lt;p&gt;I've designed an pulsed RF generator (50-100 MHz) and am using a directional coupler to measure power into a 50 ohm dummy load.  The forward power from the coupler is plugged into a o-scope (hi Z input).  The issue is that I calculate what seems to be too much power (more than expected) that, while possible, I doubt.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My calculation is as follows: on scope I see 100 mV RMS, so this calculates as (0.1 V)(0.1 V)/(50 ohms) = 0.2 mW.  Since the coupler constant is 60 dB, this means the mainline power is (0.2)(1e6) = 200 W.  This seems high as the cw power during design was 100 W, although the 10% duty cycle certainly could enable 200 W during the pulses.  Does this seem correct?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also of note: the coupler (an older Werlatone, no longer manufactured) is rated for 5 kW.  Could my measurements be caused by not reaching some threshold (using too little of coupler's range)?  Also I checked the forward-power port resistance using a DVM and got 19 ohms, which I cannot make any sense of- expected short, open, or 50 ohms for this DC measurement.  Any thoughts/comments appreciated!&lt;/p&gt;&#xA;" OwnerUserId="9815" LastEditorUserId="9815" LastEditDate="2017-06-09T17:44:14.993" LastActivityDate="2017-10-27T14:50:53.527" Title="calculating power from directional coupler" Tags="&lt;rf-power&gt;&lt;directional-coupler&gt;" AnswerCount="2" CommentCount="7" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7725" PostTypeId="2" ParentId="6281" CreationDate="2017-06-10T14:19:58.067" Score="3" Body="&lt;p&gt;Some time as passed since the original posting and I suppose the student has lost interest in this problem. But for the sake of completeness, I offer the following.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It must be said (as other commentators mentioned) that the problem as stated lacks sufficient information to give an exact result. Given more scattering parameters of each system, a conversion to T parameters to facilitate multiplying and then converting back to S parameters could be utilized. When only the combined S11 result is desired, this conversion process can deploy shortcuts to save on conversions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the lack of required information , a statistical approach to the problem will yield the best available estimate. If we assume that the two stated Return Losses are unrelated, then applying RSS (Root of Sum of Squares) will yield a reasonable estimate (this is sometimes called &quot;addition in quadrature&quot;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First convert the RL figures to their respective reflection coefficient (Γ) or S11 scattering parameter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \Gamma_1 = 10^{10/-20} = 0.3162 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \Gamma_2 = 10^{20/-20} = 0.1 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then compute the RSS:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{RSS} = \sqrt{\Gamma_1^2 + \Gamma_2^2} = 0.3316 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And finally, convert the RSS back to a combined RL:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{RL} = -20 \log(0.3316) = 9.6 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It must again be stated that this results in a statistical estimate. If in fact there is significant gain, attenuation, or impedance transformation in these systems, this result could be substantially in error. In such a case, the order of the cascading could also have an effect on the results. But given the lack of information, it serves as a reasonable first order estimate. Meanwhile, I hope the good professor has removed or appropriately amended the question for future test pools.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should be noted that this method can be used successfully when attempting to account for distributed reflections from connectors, etc. subject to the limitations noted above.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-06-11T04:39:12.310" LastActivityDate="2017-06-11T04:39:12.310" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7727" PostTypeId="2" ParentId="7536" CreationDate="2017-06-12T06:26:02.443" Score="1" Body="&lt;p&gt;Inside the output of a transmitter is often a PA, consisting of a transistor and a matching network. The output impedance of the transistor is easy to define during small-signal operation. From the datasheet of an MRF1535N, s22 translates to roughly 2.5-j2ohms at 100MHz. For simplicity, I'm assuming the device is unilateral, which it is not. For max gain, 50ohm would be matched to the conjugate, or 2.5+j2. The result is a transmitter with a 50ohm output impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The output power and efficiency of a transistor can be optimized by maximizing the current and voltage swing at it's output. The limiting factors would be Imax and Vmax (Vbreakdown or 2*Vsupply). Loading the transistor with a resistance equal to Vmax/Imax results in a loadline capable of producing high power and efficiency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The MRF1535N datasheet suggests a load of 1.7-j0.2, for good PA operation. 50ohm could be matched to 1.7ohm using a quarterwave line with Zo of roughly 9ohms. The result would be a transmitter with good power and efficiency into a 50ohm load. The small-signal output impedance would be 32ohm. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the difference between a gain (conjugate) match and a power (loadline, load-pull) match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;None of this directly answers the question, &quot;what is the output impedance of a transmitter&quot;, because there's no simple answer. The transistor is typically operating nonlinearly, which can be modeled as a current source with a shunt RC that changes with voltage. This leads to the output impedance depending on the exact state of the PA and the exact state of the PA depending on the load. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Experts don't even agree regarding output impedance. Here's one view...&#xA;&quot;once a device starts to operate in any significantly nonlinear fashion,..., the whole concept of output impedance starts to breakdown, due to the fact the waveforms are no longer sinusoidal&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cripps, RF Power Amplifiers For Wireless Communications, 2006.&lt;/p&gt;&#xA;" OwnerUserId="4609" LastActivityDate="2017-06-12T06:26:02.443" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7728" PostTypeId="1" AcceptedAnswerId="7827" CreationDate="2017-06-12T11:21:33.333" Score="0" ViewCount="134" Body="&lt;p&gt;Any ideas as to what I might be picking up on SDR? They make for some strange patterns. Picked them up at the following coordinates: (31.514596, 74.345092) using GQRX, tuned to 217.25 MHz. As for the second snapshot, I'm not sure what the exact frequency was but it was close to 217.25 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dQXak.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dQXak.png&quot; alt=&quot;A strange pattern&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bYpk8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bYpk8.png&quot; alt=&quot;Another one on a similar frequency&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9827" LastEditorUserId="873" LastEditDate="2017-06-13T02:55:27.197" LastActivityDate="2017-06-26T20:25:28.017" Title="Any ideas as to what I might be picking up on SDR?" Tags="&lt;software-defined-radio&gt;&lt;vhf&gt;&lt;signal-identification&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7729" PostTypeId="2" ParentId="7728" CreationDate="2017-06-12T12:32:00.283" Score="0" Body="&lt;p&gt;According to &lt;a href=&quot;https://fccid.io/frequency-explorer.php?lower=217.2&amp;amp;upper=&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://fccid.io/frequency-explorer.php?lower=217.2&amp;amp;upper=&lt;/a&gt; it might be European television broadcasting. What is your location?&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-06-12T12:32:00.283" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7730" PostTypeId="1" AcceptedAnswerId="7731" CreationDate="2017-06-12T15:42:22.727" Score="0" ViewCount="161" Body="&lt;p&gt;How would I find a repeater in my area (Pakistan)? Are there any web resources? Can I use repeaters to listen only (using an SDR)? &lt;/p&gt;&#xA;" OwnerUserId="9827" LastEditorUserId="873" LastEditDate="2017-06-13T02:53:14.063" LastActivityDate="2017-06-13T02:53:14.063" Title="How to find repeaters in Pakistan?" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2017-06-12T21:31:15.430" ContentLicense="CC BY-SA 3.0" />
  <row Id="7731" PostTypeId="2" ParentId="7730" CreationDate="2017-06-12T16:16:13.963" Score="1" Body="&lt;p&gt;In some countries (like the US), there are numerous publications, websites and apps which list repeaters, but I don't know of such a resource for Pakistan. A good place to ask is probably the Pakistan Amateur Radio Society (PARS). Their website is: &lt;a href=&quot;http://pakhams.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://pakhams.com/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And yes, you can simply listen to a repeater with an SDR or any other radio capable of receiving the repeater's output frequency.  In fact, if you do not have an amateur radio license then you are only allowed to listen, not transmit.  &lt;/p&gt;&#xA;" OwnerUserId="9631" LastActivityDate="2017-06-12T16:16:13.963" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7732" PostTypeId="1" CreationDate="2017-06-12T21:43:36.653" Score="1" ViewCount="169" Body="&lt;p&gt;I am using a FT-65R radio and loving it much. However I have a problem with assigning&#xA;menu items to P1-P4 buttons. If I assign CTCSS menu item to, let's say P2, then after pressing P2 the menu item is correctly recalled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I can't figure out how to change individual items (TX/RX tone in this case). Usually it is done by the Fn key, but in this case Fn exits the menu item. What should I do instead?&lt;/p&gt;&#xA;" OwnerUserId="9831" LastEditorUserId="76" LastEditDate="2017-06-12T21:50:50.320" LastActivityDate="2017-06-12T21:50:50.320" Title="Yaesu FT-65R quick function keys: changing values" Tags="&lt;yaesu&gt;&lt;equipment-operation&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7733" PostTypeId="1" CreationDate="2017-06-12T22:09:40.287" Score="5" ViewCount="1188" Body="&lt;p&gt;I'd like to send raw AX.25 packets from a macOS PC using a KISS TNC (&lt;a href=&quot;http://www.mobilinkd.com/tnc2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;mobilinkd TNC2&lt;/a&gt;). I've sent APRS packets with this set up using Xastir, but I'd like to send other information besides just APRS (i.e. put my own information into the AX.25 packet).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several AX.25 terminal programs for Linux, but they all seem to rely on the AX.25 features built into the Linux kernel (which macOS doesn't have). How do I send AX.25 packets from a macOS PC?&lt;/p&gt;&#xA;" OwnerUserId="5820" LastEditorUserId="7804" LastEditDate="2019-11-04T17:37:00.363" LastActivityDate="2019-11-04T17:37:00.363" Title="AX.25 on macOS (aside from APRS)" Tags="&lt;aprs&gt;&lt;software&gt;&lt;packet&gt;&lt;macos&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7734" PostTypeId="1" AcceptedAnswerId="7735" CreationDate="2017-06-13T03:08:50.150" Score="3" ViewCount="2685" Body="&lt;p&gt;The very first New York Times article announcing the invention of the solar cell by Bell Labs in 1954 shows a man holding a brick-shaped device in the sun in one hand and a microphone in the other hand, while standing far away from any other sources of power.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The combination of wireless energy and wireless communication is very compelling.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.nytimes.com/packages/pdf/science/TOPICS_SOLAR_TIMELINE/solar1954.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Bell Labs announcement about a new solar battery&lt;/a&gt; (New York Times, 1954)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TCIgc.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TCIgc.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly they thought the most obvious first use case for solar energy would be for communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the question is in the title:  Is it possible to power your ham radio station by solar power? If so, how?&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="76" LastEditDate="2017-10-13T21:28:42.960" LastActivityDate="2017-10-29T05:16:30.780" Title="Is it possible to power your ham radio station by solar power? If so, how?" Tags="&lt;dc-power&gt;&lt;solar&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7735" PostTypeId="2" ParentId="7734" CreationDate="2017-06-13T03:08:50.150" Score="7" Body="&lt;p&gt;The answer is a resounding yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How you do it depends on whether you are mobile (like in an RV) or stationary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://youtu.be/g-hqt6pvGxo&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here is a video answer from David Casler, KE0OG&lt;/a&gt;, the &lt;code&gt;Original Genius&lt;/code&gt;, who both answers the first question and also the second. This video is a good introduction. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Key fact that must be stressed:  &lt;strong&gt;A solar charge controller is required to properly maintain the battery bank.  The batteries are the key component to the system.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Here is a plot of my first-generation single Marine battery system with a 50 Watt PV panel and a PWM (Pulse-Width Modulation) charge controller, which is still in use outside to power the electronics and the motors that sense the position of the sun and position the panels. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JUuPv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JUuPv.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This shows a healthy system for the purpose for which it is being used.  But it would not be adequate for powering ham radios while charging. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;On the other hand, MPPT controllers (explained in the video), provide a much cleaner charging waveform:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jaqpi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jaqpi.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the waveforms at the battery bank do not contain much radio hash.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This plot was taken on a day when the inverter was not turned on, for the purpose of showing the charging modes:  boost then float.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It also includes the yellow marker where the time of day would have shut the inverter off, causing the automatic relay to switch the AC portion of the system back to house power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Note also that with the MPPT controller all the panels are wired in series to provide high voltage which is converted to charging current at the Maximum Power Point.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the Renogy Commander MPPT charge controller:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xd0Pm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xd0Pm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The battery bank is built as a set of 4 deep-cycle Marine 12V 122 Ah batteries in series/parallel, resulting in a 24 Volt battery bank of 244 Ah.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fully charged to 25.2 Volts, there is 6.15 kWh stored in the battery bank.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is a LOT of power so they are protected in battery boxes and with circuit breakers (one for each output pole).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DWnzx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DWnzx.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BBUaR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BBUaR.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;It is very important that the breakers be mounted directly at the batteries.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They also serve as cutoff switches.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Handling of conductive tools is a critical issue when the boxes are open, as this kind of power can melt steel in an instant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Safety first.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The breakers are inside two of the battery boxes to provide positive and negative terminals.  Cutouts in the box lids provide physical access to the switches and reset levers.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Dave goes on at length in the video about how shading can affect solar panels - but the panels used here contain bypass diodes at each cell so they exhibit graceful degradation in a partial shading scenario.  The rest of the panel with direct exposure will still pump out the electrons.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are relatively new panels (priced at just over a dollar per watt) which contain reverse-voltage blocking diodes to prevent any possibility of them becoming a power sink.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This location has a lot of trees on the west side, so when the shading starts it is fairly decisive, as can be seen in the lower chart.  But it is clear that they continue to collect useful sunlight from the atmosphere past the times of direct exposure.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These panels are mounted on open frames for maximum cooling airflow - heat adversely affects output.  Rooftop mounts must allow for some airflow under the panels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After the 4pm cutoff there is enough sun to top off the battery bank for the night.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Generally the Inverter is on from 9am to 4pm (7 hours) with a 300 Watt load which is used for my little home and for charging the batteries.  It tallies up nicely:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 0.300 \mathrm{\,kW} \times 7 \mathrm{\,h} = 2.1 \mathrm{\,kWh} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Carrying this further to 30 days, monthly AC power production is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 2.1 \mathrm{\,kWh} \times 30 = 63 \mathrm{\,kWh} $$&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;There are 3 pairs of 100 Watt PV panels all wired in series, providing up to about 120 Volts.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power is brought in from the panels with 8 Gauge cables which present very little resistance over the 10 meter run, at this amperage.  Generally the current is in the 4 Amp range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This particular Charge Controller includes a remote meter that constantly shows the input and battery voltages.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Notice that with PWM it is not possible to run voltages this high.  The way they work you are limited to an input voltage just slightly higher than the maximum charging voltage.  So the panels are run in parallel, which means the current is higher for the same amount of power.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This has a major impact on the cable size as you might try to pull the same amount of power due to resistance at the required amperage.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{\text{loss}} = I^2\times R $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cable is expensive, so this needs to be considered in comparing the price of PWM vs MPPT especially for long cable runs.  With cable runs of any length the savings in cable cost can pay for the difference in price between PWM and MPPT&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Inside, where the PV power lands there is another of the same kind of Marine-grade circuit breaker/cutoff switch for the panel input.  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;These voltages can be quite uncomfortable if not lethal.  It is always good to use the left-hand-rule when working on this kind of circuitry:  Keep your left hand behind your back so any discharge will not go through your heart.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The MPPT controller operates on an entirely different principle.  Nothing like the switching action of PWM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This chart shows the difference:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/I5PKn.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/I5PKn.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This Renogy Commander MPPT controller is well worth the price. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For 12V radios there is a 24V to 12V converter unit like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pD92s.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pD92s.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the converter is also a regulator, so the resultant 12 Volt power is nice and clean.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Finally, here is a picture of what I have named the Sunflower power station:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cebvh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cebvh.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(In this photo they are pointing west, following the sun until it goes behind the trees)  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At night they all lay flat to protect them against any possible wind.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I've just begun &lt;a href=&quot;http://www.sdsolarblog.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;SDsolarBlog&lt;/a&gt; - the first article is worth reading because it discusses the realities of trying to use the 1 KW per square meter of sunlight that strikes the earth.  It is like trying to drink from a fire hose.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use actual math to trace the losses through the system to give a good reality check.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Here is an Imagemagick &lt;code&gt;montage&lt;/code&gt; showing the results of 6 Rpi/Nano sensors combined and uploaded to my ISP via scp. All done in &lt;code&gt;cron&lt;/code&gt; with rsa authentication.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a montage of 6 plots for the same day, showing voltages, light intensity and temperature:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SFfYw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SFfYw.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(&lt;a href=&quot;https://www.sdsolarblog.com/montage/showplot.htm?dt=2017-10-15&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.sdsolarblog.com/montage/showplot.htm?dt=2017-10-15&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The current montage can be seen at &lt;a href=&quot;https://www.SDsolarBlog.com/montage/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.SDsolarBlog.com/montage/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-10-29T05:16:30.780" LastActivityDate="2017-10-29T05:16:30.780" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7736" PostTypeId="5" CreationDate="2017-06-13T03:11:47.060" Score="0" Body="&lt;p&gt;Use this tag for any discussion that involves the sun.  Specifically, with how to capture the 1 KW per Square Meter of light energy it deposits on earth in order to convert it to electricity.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-06-13T20:41:58.357" LastActivityDate="2017-06-13T20:41:58.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7737" PostTypeId="4" CreationDate="2017-06-13T03:11:47.060" Score="0" Body="Use this tag for any discussion that involves the sun.  Specifically, with how to capture the 1 KW per Square Meter of light energy it deposits on earth in order to convert it to electricity." OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-06-13T20:42:32.553" LastActivityDate="2017-06-13T20:42:32.553" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7738" PostTypeId="5" CreationDate="2017-06-13T03:16:10.530" Score="0" Body="&lt;p&gt;Questions about AC power supplied to equipment, power distribution, wiring, connectors.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-06-13T20:42:13.953" LastActivityDate="2017-06-13T20:42:13.953" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7739" PostTypeId="4" CreationDate="2017-06-13T03:16:10.530" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2017-06-13T03:16:10.530" LastActivityDate="2017-06-13T03:16:10.530" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7740" PostTypeId="2" ParentId="7734" CreationDate="2017-06-13T14:54:03.360" Score="3" Body="&lt;p&gt;Yes, it's possible. Photovoltaic panels convert solar radiation to electrical power. Why wouldn't it be possible to run a station, or any other electrical device, on solar power?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most amateur radio equipment can run on a 12V battery, usually lead-acid. Conveniently, charging 12V lead-acid batteries is a very common application for solar panels. So the usual solution is to run the radios from the battery, while simultaneously charging the batteries with a photovoltaic panel. It can be a simple as this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NV6ZJ.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fNV6ZJ.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the simple case, it's necessary to select a panel with an open circuit voltage that matches the battery's maximum charge voltage. If the open circuit voltage is too low, the battery will never charge. And if it's too high, you won't get an overvoltage condition as you might expect, but the panel will be inefficiently loaded and there's a risk of &lt;a href=&quot;https://electronics.stackexchange.com/q/129603/17608&quot;&gt;overcharging the battery&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More sophisticated designs incorporate a charge controller. The charge controller &lt;a href=&quot;https://en.wikipedia.org/wiki/Maximum_power_point_tracking&quot; rel=&quot;nofollow noreferrer&quot;&gt;adjusts the load seen by the panel for maximum efficiency&lt;/a&gt; and has circuitry to prevent overcharging.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-06-14T09:45:11.740" LastActivityDate="2017-06-14T09:45:11.740" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7741" PostTypeId="1" AcceptedAnswerId="7743" CreationDate="2017-06-13T16:07:02.250" Score="1" ViewCount="530" Body="&lt;p&gt;I am going to mention a radio frequency of an emergency broadcast radio station in a post apocalyptic video game (I'm part of the dev team), and I would like to make a reference to real world radio. Are there any historically (or currently) famous radio frequencies?&lt;/p&gt;&#xA;" OwnerUserId="9838" LastActivityDate="2017-06-13T19:11:54.353" Title="Are there famous radio frequencies?" Tags="&lt;history&gt;" AnswerCount="1" CommentCount="4" ClosedDate="2017-06-13T20:47:09.113" ContentLicense="CC BY-SA 3.0" />
  <row Id="7742" PostTypeId="1" AcceptedAnswerId="7747" CreationDate="2017-06-13T17:38:29.117" Score="2" ViewCount="1488" Body="&lt;p&gt;I recently acquired an &lt;strong&gt;MFJ Versa Tuner II&lt;/strong&gt; model &lt;strong&gt;MFJ-949D&lt;/strong&gt; as well as a &lt;strong&gt;Kenwood TS-430S&lt;/strong&gt; radio.  The &lt;a href=&quot;http://www.mfjenterprises.com/support/MFJ-949D/MFJ-949D.pdf&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;instructions for the tuner&quot;&gt;instructions for the tuner&lt;/a&gt; state (in part):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For optimum operation of the MFJ-949D, the transmitter must&#xA;  be tuned to a 50 ohm output impedance at the frequency of&#xA;  operation. Set the ANTENNA SELECTOR switch to DUMMY LOAD&#xA;  for tuning up the transmitter.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Does this mean there is something to tune &lt;em&gt;on the radio&lt;/em&gt; before using the tuner to tune the antenna?  And if so, how is that done on the &lt;strong&gt;TS-430S&lt;/strong&gt;?&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="76" LastEditDate="2017-06-13T22:17:10.223" LastActivityDate="2018-01-12T14:39:47.603" Title="How do I set up my radio for an antenna tuner?" Tags="&lt;antenna-tuner&gt;&lt;equipment-operation&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7743" PostTypeId="2" ParentId="7741" CreationDate="2017-06-13T19:11:54.353" Score="1" Body="&lt;p&gt;The International Amateur Radio Union (IARU) has established a small set of emergency frequencies. Some of these are global and some are for one of the three IARU regions. The IARU calls these frequencies &quot;emergency centres of activity&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The full list is here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.iaru-r1.org/index.php/emergency-communications/emergency-communications-frequencies&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.iaru-r1.org/index.php/emergency-communications/emergency-communications-frequencies&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By far the most common one is 14.300 MHz. That is monitored in the US by the Maritime Mobile Service Network (&lt;a href=&quot;http://mmsn.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://mmsn.org/&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your game, if you need global broadcast, I'd use one of the global frequencies. If it is more local, use one of the regional frequencies that are around 3xxx kHz (80 m band) or 7xxx kHz (40 m band). 80m is good at nightime, 40m at daytime. Either one is regional, covering something like most of California.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The regions (&lt;a href=&quot;http://www.iaru.org/regions.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.iaru.org/regions.html&lt;/a&gt;) are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IARU Region 1: Europe, Africa, Middle East and Northern Asia&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IARU Region 2: The Americas&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IARU Region 3: Asia-Pacific&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are other frequencies for non-amateur use, mostly marine and aircraft. The primary marine distress frequency was 2182 kHz, but the US Coast Guard stopped monitoring that in 2013. Marine distress traffic now digital to satellites with GPS data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a good list of those frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/International_distress_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/International_distress_frequency&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a US-oriented throwback flavor, I'd go with the CONELRAD frequencies from the Cold War era. In case of a major attack, AM broadcast stations would shut down, with only specific stations on either 640 or 1240 kHz continuing to broadcast. Those frequencies were marked with a triangle-in-circle icon on radio dials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/CONELRAD&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/CONELRAD&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2017-06-13T19:11:54.353" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7744" PostTypeId="2" ParentId="7703" CreationDate="2017-06-13T22:08:18.110" Score="2" Body="&lt;p&gt;I was not able to find very much history on these filters, but I did track down two sets of coefficients from popular implementations, and for your pleasure, I'll present them here.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Transmit Filtering&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;The pulse shape transmitted by a PSK31 transmitter is effectively a raised cosine, twice the symbol duration. That is, we can imagine a PSK31 transmitter as sending a series of impulses of either +1 or -1, then filtered by a FIR filter with coefficients that are a raised cosine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are four such pulses:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/viXih.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/viXih.png&quot; alt=&quot;transmit pulse shape&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transmitted signal is then the sum of all these pulses. We can see there's no ISI in the transmitted signal since at the peak of one pulse (the ideal sampling point), the amplitude of the adjacent pulses is zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency response of the transmit pulse shaping filter determines the bandwidth occupied by the signal. Here it is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GGtwT.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GGtwT.png&quot; alt=&quot;PSK31 frequency response&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By modern standards, this isn't very good. Note the numerous, slowly decaying side-lobes, with the first of them only about 32dB down. As we will see, this doesn't necessarily detract from performance, provided everything within that frequency band is only white Gaussian noise. However, it does present a problem when trying to pack many signals close together, which unfortunately is frequently the case with PSK31.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Matched Filter&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;In an AWGN channel the receive filter that maximizes the signal to noise ratio is the same filter as the transmit filter&lt;sup&gt;1&lt;/sup&gt;: a &lt;em&gt;matched filter&lt;/em&gt;. So let's suppose the transmitted pulses are passed through a matched filter in the receiver. They would then become:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0SDEq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0SDEq.png&quot; alt=&quot;matched pulse shape&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice now the amplitude of the adjacent pulses is not zero at the peak of each pulse. This is inter-symbol interference (ISI). Since the signal is the sum of each pulse, when a symbol is sampled to determine if it's a 0 or a 1 we're sampling not only the current symbol but also the ones next to it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found two filter implementations that attempt to address this by not using a matched filter in the receiver. Instead, they aim to make the pulse shape such that there is zero amplitude from adjacent pulses at each sample point, while remaining as close as possible to the matched filter in frequency response.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;G3PLX Filter from fldigi&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;The first I got from fldigi, but based on the attribution in the source it appears to originate from the original PSK31 implementation by G3PLX. Again, the four pulses after passing through this filter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OcZpD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OcZpD.png&quot; alt=&quot;G3PLX pulse shape&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice the ISI is mostly eliminated: the amplitude of adjacent pulses is almost zero at the peak of the pulse being sampled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frequency response of G3PLX filter (orange), with the matched case (blue) for comparison:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IcJGy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IcJGy.png&quot; alt=&quot;matched vs G3PLX&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The somewhat faster roll-off doesn't necessarily make it better. While it could mean an adjacent signal is better rejected, it also means some fraction of the transmitted signal energy is not captured..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also a significantly different shape at the top, where it matters most (since this is where most of the power is). Any difference in shape means a reduction in signal to noise ratio.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;PSKCore DLL&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Now the second filter, which is from the PSKCore DLL. Again, pulse shapes and frequency response:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/u9tyV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/u9tyV.png&quot; alt=&quot;pskcore pulse shape&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NTJf8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NTJf8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;em&gt;Blue: matched. Orange: PSKCore.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;ISI: maybe there's another solution?&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;These two implementations sacrifice signal to noise ratio in order to use a filter with less ISI than a matched filter. We can quantify that loss by normalizing all the filters to have the same energy, with energy being the sum of the squares of their coefficients. If the coefficients are $x_1, x_2, \dots, x_n$, then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ E = \sum_{i=1}^n x_i $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By dividing each coefficient by $\sqrt E$ we get a normalized filter with $E=1$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {x_1 \over \sqrt E}, {x_2 \over \sqrt E}, \dots, {x_n \over \sqrt E} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For such a filter, if the samples represent voltage, then power in = power out. If the input pulse has E=1, then the peak of the filtered pulses output pulses are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;matched filter: 1&lt;/li&gt;&#xA;&lt;li&gt;G3PLX: 0.9538&lt;/li&gt;&#xA;&lt;li&gt;PSKCore: 0.9711&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Converting these to power in dB is for example $20 \log_{10}(0.9711) = -0.2547\:\mathrm{dB}$ so the change to SNR for each filter is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;matched: 0 dB&lt;/li&gt;&#xA;&lt;li&gt;G3PLX: -0.4109 dB&lt;/li&gt;&#xA;&lt;li&gt;PSKCore: -0.2547 dB&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Furthermore, The G3PLX and PSKCore filters still have non-zero ISI. The penalty calculation above accounts only for noise due to white Gaussian noise in the received signal; ISI remaining after filtering is additional noise that degrades decode accuracy. To give an idea of what this looks like, here is a bit stream decoded with the PSKCore filter with no noise and perfect timing:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WNEmZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WNEmZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without ISI, there would be only two lines here, with each dot being exactly a 0 or a 1. However, depending on the value of the previous and next bit being a 0 or a 1, the decoded value is shifted from this ideal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I'll offer an observation: if we know the transmit filter (we do) and the receive filter (we can pick that), we know the pulse shape, and thus the ISI. So if the pulses have a non-zero amplitude at the sampling points of other pulses, we'd know what that amplitude is. If we know what the adjacent symbols are, then we can subtract their known contributions to the ISI and eliminate it entirely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trouble is of course we don't know the adjacent symbols, not only because noise introduces uncertainty, but those adjacent symbols in turn depend on the next adjacent symbols.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Viterbi algorithm can be used to solve this problem in a computationally feasible way. It's more complex than a linear filter, but given the slow symbol rate of PSK31, the computational complexity is still trivial. The combination of a matched filter and a Viterbi detector is optimal in the case of an AWGN channel. I'm not aware of any existing decoders for PSK31 which use this technique, and I suspect it may be an improvement over current practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having prototyped a simulation in as AWGN channel, Viterbi decoding and a matched filter show a performance gain over the PSKCore approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gBOIU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gBOIU.png&quot; alt=&quot;pskcore and viterbi BER comparison&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It remains to be seen if this amounts to an improvement in a real environment with timing errors, multipath, interfering stations and so on.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Appendix: filter coefficients&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Filter coefficients from fldigi:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;// 4-bit receive filter for 31.25 baud BPSK&#xA;// Designed by G3PLX&#xA;//&#xA;&#xA;double gmfir2c[64] = {&#xA;        0.000625000,&#xA;        0.000820912,&#xA;        0.001374651,&#xA;        0.002188141,&#xA;        0.003110600,&#xA;        0.003956273,&#xA;        0.004526787,&#xA;        0.004635947,&#xA;        0.004134515,&#xA;        0.002932456,&#xA;        0.001016352,&#xA;        -0.001539947,&#xA;        -0.004572751,&#xA;        -0.007834665,&#xA;        -0.011009254,&#xA;        -0.013733305,&#xA;        -0.015625000,&#xA;        -0.016315775,&#xA;        -0.015483216,&#xA;        -0.012882186,&#xA;        -0.008371423,&#xA;        -0.001933193,&#xA;        0.006315933,&#xA;        0.016124399,&#xA;        0.027115485,&#xA;        0.038807198,&#xA;        0.050640928,&#xA;        0.062016866,&#xA;        0.072333574,&#xA;        0.081028710,&#xA;        0.087617820,&#xA;        0.091728168,&#xA;        0.093125000,&#xA;        0.091728168,&#xA;        0.087617820,&#xA;        0.081028710,&#xA;        0.072333574,&#xA;        0.062016866,&#xA;        0.050640928,&#xA;        0.038807198,&#xA;        0.027115485,&#xA;        0.016124399,&#xA;        0.006315933,&#xA;        -0.001933193,&#xA;        -0.008371423,&#xA;        -0.012882186,&#xA;        -0.015483216,&#xA;        -0.016315775,&#xA;        -0.015625000,&#xA;        -0.013733305,&#xA;        -0.011009254,&#xA;        -0.007834665,&#xA;        -0.004572751,&#xA;        -0.001539947,&#xA;        0.001016352,&#xA;        0.002932456,&#xA;        0.004134515,&#xA;        0.004635947,&#xA;        0.004526787,&#xA;        0.003956273,&#xA;        0.003110600,&#xA;        0.002188141,&#xA;        0.001374651,&#xA;        0.000820912&#xA;};&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And PSKCore DLL:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;//  Filter type:   Multiband filter&#xA;//  Design method: Parks-McClellan method&#xA;//  Number of taps  =  65&#xA;//  Number of bands =  2 &#xA;//  Band   Lower       Upper       Value      Weight&#xA;//         edge        edge&#xA;//&#xA;//  1       0.0        .03125         1.         1.&#xA;//  2        .0625     .5          .0000       286.&#xA;#define BITFIR_LENGTH 65&#xA;const double BitFirCoef[BITFIR_LENGTH*2] = { // 16 Hz bw LP filter for data recovery&#xA; 4.3453566e-005,&#xA; -0.00049122414,&#xA; -0.00078771292,&#xA;  -0.0013507826,&#xA;  -0.0021287814,&#xA;   -0.003133466,&#xA;   -0.004366817,&#xA;  -0.0058112187,&#xA;  -0.0074249976,&#xA;  -0.0091398882,&#xA;   -0.010860157,&#xA;   -0.012464086,&#xA;   -0.013807772,&#xA;   -0.014731191,&#xA;   -0.015067057,&#xA;   -0.014650894,&#xA;   -0.013333425,&#xA;    -0.01099166,&#xA;  -0.0075431246,&#xA;  -0.0029527849,&#xA;   0.0027546292,&#xA;   0.0094932775,&#xA;    0.017113308,&#xA;    0.025403511,&#xA;    0.034099681,&#xA;    0.042895839,&#xA;    0.051458575,&#xA;    0.059444853,&#xA;    0.066521003,&#xA;    0.072381617,&#xA;    0.076767694,&#xA;    0.079481619,&#xA;    0.080420311,&#xA;    0.079481619,&#xA;    0.076767694,&#xA;    0.072381617,&#xA;    0.066521003,&#xA;    0.059444853,&#xA;    0.051458575,&#xA;    0.042895839,&#xA;    0.034099681,&#xA;    0.025403511,&#xA;    0.017113308,&#xA;   0.0094932775,&#xA;   0.0027546292,&#xA;  -0.0029527849,&#xA;  -0.0075431246,&#xA;    -0.01099166,&#xA;   -0.013333425,&#xA;   -0.014650894,&#xA;   -0.015067057,&#xA;   -0.014731191,&#xA;   -0.013807772,&#xA;   -0.012464086,&#xA;   -0.010860157,&#xA;  -0.0091398882,&#xA;  -0.0074249976,&#xA;  -0.0058112187,&#xA;   -0.004366817,&#xA;   -0.003133466,&#xA;  -0.0021287814,&#xA;  -0.0013507826,&#xA; -0.00078771292,&#xA; -0.00049122414,&#xA; 4.3453566e-005,&#xA;//&#xA; 4.3453566e-005,&#xA; -0.00049122414,&#xA; -0.00078771292,&#xA;  -0.0013507826,&#xA;  -0.0021287814,&#xA;   -0.003133466,&#xA;   -0.004366817,&#xA;  -0.0058112187,&#xA;  -0.0074249976,&#xA;  -0.0091398882,&#xA;   -0.010860157,&#xA;   -0.012464086,&#xA;   -0.013807772,&#xA;   -0.014731191,&#xA;   -0.015067057,&#xA;   -0.014650894,&#xA;   -0.013333425,&#xA;    -0.01099166,&#xA;  -0.0075431246,&#xA;  -0.0029527849,&#xA;   0.0027546292,&#xA;   0.0094932775,&#xA;    0.017113308,&#xA;    0.025403511,&#xA;    0.034099681,&#xA;    0.042895839,&#xA;    0.051458575,&#xA;    0.059444853,&#xA;    0.066521003,&#xA;    0.072381617,&#xA;    0.076767694,&#xA;    0.079481619,&#xA;    0.080420311,&#xA;    0.079481619,&#xA;    0.076767694,&#xA;    0.072381617,&#xA;    0.066521003,&#xA;    0.059444853,&#xA;    0.051458575,&#xA;    0.042895839,&#xA;    0.034099681,&#xA;    0.025403511,&#xA;    0.017113308,&#xA;   0.0094932775,&#xA;   0.0027546292,&#xA;  -0.0029527849,&#xA;  -0.0075431246,&#xA;    -0.01099166,&#xA;   -0.013333425,&#xA;   -0.014650894,&#xA;   -0.015067057,&#xA;   -0.014731191,&#xA;   -0.013807772,&#xA;   -0.012464086,&#xA;   -0.010860157,&#xA;  -0.0091398882,&#xA;  -0.0074249976,&#xA;  -0.0058112187,&#xA;   -0.004366817,&#xA;   -0.003133466,&#xA;  -0.0021287814,&#xA;  -0.0013507826,&#xA; -0.00078771292,&#xA; -0.00049122414,&#xA; 4.3453566e-005&#xA;};&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt;Or more accurately, the time-reversed complex conjugate filter. But since this filter (like most pulse shaping filters) is both real and symmetrical, it works out to the same thing.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-07-16T11:25:15.793" LastActivityDate="2017-07-16T11:25:15.793" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7745" PostTypeId="2" ParentId="1019" CreationDate="2017-06-13T22:42:59.657" Score="0" Body="&lt;p&gt;Other than interference issues, the key to doing this is to follow the rules about station identification.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every transmission should be something like &quot;VK2VXK test&quot;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Really, the rules say you have to do this for the first one then every 10 minutes, but I do it with every test transmission that might radiate)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you are finished say something like &quot;VK2VXK out&quot;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-06-13T22:42:59.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7746" PostTypeId="2" ParentId="1025" CreationDate="2017-06-13T22:47:20.237" Score="1" Body="&lt;p&gt;Certainly unattended packet radio stations can operate without a control operator present.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not just digipeaters, but store-and-forward messaging systems and also the Packet BBS systems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, the station needs to be sure to identify every 10 minutes.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will notice that on voice repeaters the ID is allowed to be done in Morse code AFSK.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-06-13T22:47:20.237" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7747" PostTypeId="2" ParentId="7742" CreationDate="2017-06-13T23:05:41.090" Score="7" Body="&lt;p&gt;Your TS430S has a solid state final and no internal antenna tuner. As such it is designed to work into a 50 ohm load at all times. This means you can disregard this note in your antenna tuner manual.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the tuner was used with a radio with tube finals then you would need to heed this cautionary note. If the tuner is used with a radio that has a built in antenna tuner, the internal ATU should be placed in bypass mode.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-06-13T23:05:41.090" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7748" PostTypeId="2" ParentId="7192" CreationDate="2017-06-14T06:08:50.587" Score="1" Body="&lt;p&gt;We certainly did with the PBBS system we used at the Alaska National Guard building with the Alaska Division of Emergency Services.  That station used my callsign with a &quot;-1&quot; appended to differentiate it from my personal systems I ran at home and in my truck. That station existed throughout the 90s.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It worked great and was quite busy at times.  Basically it was a store-and-forward message system along with categorized forums like any common dial-up BBS system.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We also had a software library stored in .ZIP format but very clearly named to identify the programs as being very common to the time.  We also offered the PBBS software itself so others could set up their own nodes if they wanted.  Software downloads were done during off-peak hours by gentlemen's agreement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is worth mentioning that we never had any inappropriate communications there during the entirety of its existence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We experimented with FIDOnet but never went operational with it.  Had we done so we would have had a network of stations for message delivery similar to the way mail servers work on the Internet now.  In the end, our PBBS had the coverage we needed without the need for additional software on the ham's end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only equipment required for hams was a radio with a cable interface to the TNC and an RS-232 port to any kind of computer.  The TRS-80 Model 100 was very popular then.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Everything was plain text except the ZIPped software.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The PBBS was used heavily during disasters to distribute official daily sitreps and to provide a centralized way for participating hams that were only licensed for amateur frequencies.  We wanted all the help we could get so we purposely kept it in-band instead of using MARS frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equipment included a TAPR-2 TNC which I believe ran AX.25 protocol at 1200 bps on 145.010 simplex.  Coverage was great based on location and the 1/2 wave antenna mounted at the same location as the State Troopers dispatch center.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now that I am retired I find that I miss the good old days of radio BBS.  ;-)&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-06-17T15:35:07.897" LastActivityDate="2017-06-17T15:35:07.897" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7749" PostTypeId="2" ParentId="774" CreationDate="2017-06-14T09:06:45.700" Score="1" Body="&lt;p&gt;I believe that the use of MIMO can bring significant SNR gains for the same amount of data transmitted. Even the much simpler diversity reception could already improve the minimum discernable signal a lot (comparable to a mdeium size power amplifier). &#xA;Also on HF, MIMO and diversity can bring a lot of link improvement. See my scientific publications (search for 'ResearchGate' and 'Ben Witvliet'), and publications of Erhel and others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are not many dual channel transmitters, unless you start building something yourself or use experimental equipment such as the USRP1. But for reception there are already a few dual channel receivers, e.g. the high-end FlexRadio, the HPSDR and its commercial version Apache Labs ANAN-200D. The latter is expensive, but with some $4500 much cheaper than the professional lab equipment mentioned above. I use that one for my research.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73, Ben Witvliet, PE5B&lt;/p&gt;&#xA;" OwnerUserId="9841" LastActivityDate="2017-06-14T09:06:45.700" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7750" PostTypeId="2" ParentId="7639" CreationDate="2017-06-14T14:30:51.843" Score="0" Body="&lt;p&gt;Don't forget, the ground is the other half of your antenna with a monopole. Adding radials replaces that effect to a great degree (they are a compromise - still not as effective).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But as pointed out, the XMIT/RCV aspect is a &quot;two way street&quot;. So, in almost every case, this old axiom applies: &quot;If you can't hear 'em, you can't work 'em&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would use radials. Try it with and without and see with a small ground plane. I think that will be your answer. Best of luck and 73, Rich KF9F&lt;/p&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="9450" LastEditDate="2019-06-02T22:04:48.203" LastActivityDate="2019-06-02T22:04:48.203" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="7751" PostTypeId="2" ParentId="7192" CreationDate="2017-06-14T16:31:22.773" Score="3" Body="&lt;p&gt;There's a book that's available for free, which is very well-suited to answering your questions.  It's called &quot;Wireless Networking in the Developing World&quot;, and it's all about setting up wireless data networks across long distances inexpensively.  Look for it at wndw.net.&lt;/p&gt;&#xA;" OwnerUserId="9837" LastActivityDate="2017-06-14T16:31:22.773" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7752" PostTypeId="2" ParentId="7453" CreationDate="2017-06-14T16:40:41.750" Score="0" Body="&lt;p&gt;&quot;A Guide to the Wireless Engineering Body of Knowledge, 2nd ed.&quot; (IEEE Press, Wiley) is a reference that I use.  Chapter 4, &quot;Radio Engineering &amp;amp; Antennas&quot;, covers what you're looking for.  Also, there are a number of lectures available on online if you search for them.    &lt;/p&gt;&#xA;" OwnerUserId="9837" LastActivityDate="2017-06-14T16:40:41.750" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7753" PostTypeId="2" ParentId="1025" CreationDate="2017-06-14T22:32:58.300" Score="0" Body="&lt;p&gt;You haven't identified in which country you'll be operating - the rules vary by country.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In many countries, what you are describing would be legal (e.g. in Canada, assuming you had privileges for the frequency you wished to use).  In some it might depend on license class.  In some it might not be permissible at all.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2017-06-14T22:32:58.300" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7755" PostTypeId="2" ParentId="7014" CreationDate="2017-06-15T01:20:20.370" Score="2" Body="&lt;p&gt;I still use an antique J-38 telegraph key with my newish solid-state rigs, but I still remember my Hot Water 60 and HW-100 where it was handy for tuning. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zwRFR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zwRFR.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When tuning up tube rigs there was sometimes a two-handed job of finding the dip in the final.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the keys could hold it on in N0 format - true CW.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The origination of the shorting bar was from the old railroad telegraph stations - when they were unoccupied it would allow the signal to go through, preserving continuity of the circuit.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;btw, long ago  when I used the venerable Heathkit HD-1410 squeeze keyer, you would pull out the speed control to switch it on continuously to peak your finals.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And now, using MFJ-9420 and MFJ-9475 QRP rigs, they have a &lt;code&gt;Tune&lt;/code&gt; button on the front panel, for setting up the MFJ-971 antenna tuner, as @Kevin mentioned.  I know the basic settings that work with my antennas on each band, peak them for max QRN (or signals) then just briefly use the shorting bar to tune for min SWR.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-19T22:53:34.407" LastActivityDate="2017-08-19T22:53:34.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7756" PostTypeId="1" CreationDate="2017-06-15T02:02:45.600" Score="2" ViewCount="256" Body="&lt;p&gt;All the 6-meter repeaters in my area use a 500kHz offset, but the Kenwood TM-742A defaults to 1MHz offsets. Is there any way to make it easier to program the local repeaters into this radio?&lt;/p&gt;&#xA;" OwnerUserId="9846" LastEditorUserId="873" LastEditDate="2017-06-15T03:51:06.950" LastActivityDate="2018-05-26T08:17:52.490" Title="How to program Kenwood TM-742A 6-meter repeater offsets for 500kHz" Tags="&lt;repeater&gt;&lt;kenwood&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7758" PostTypeId="2" ParentId="7719" CreationDate="2017-06-15T19:05:36.803" Score="0" Body="&lt;p&gt;According to &lt;a href=&quot;http://www.ariss.org/uploads/1/9/6/8/19681527/k9jkm_2012_symposium_ver2.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this PDF&lt;/a&gt;, if you want to send APRS data via the ISS, you format your UNPROTO packet with the data you want to send.  The digipath is irrelevant because you're going directly to ISS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used a plain old vertical antenna with not a lot of power and got packets through.&lt;/p&gt;&#xA;" OwnerUserId="5045" LastEditorUserId="76" LastEditDate="2017-06-16T17:43:49.310" LastActivityDate="2017-06-16T17:43:49.310" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7761" PostTypeId="2" ParentId="5349" CreationDate="2017-06-16T00:19:06.173" Score="2" Body="&lt;p&gt;Well, I'm a little out of my depth, but this does seem to have all the usual parts of a gamma match: the matching section hanging off the main loop is a balanced transmission line, and the part connected to the BNC center is spaced off it, so the coax is coupled capacitively into that transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two transmission lines, and two gamma matches, one to the left and one to the right, I'm guessing one for each band. Getting a match on both bands will probably require adjustment in little steps with frequent checks on each band since the tuning for one band will have some effect on the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's some information on how gamma matches work generally: &lt;a href=&quot;https://ham.stackexchange.com/q/1804/218&quot;&gt;What is a Gamma match in the context of the driven element of a Yagi antenna?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It appears the only adjustable thing here is the spacing of the capacitor. Most pictures of gamma matches use some arrangement with tubing to make a coaxial capacitor which slides for adjustment, but I don't see why this design wouldn't work the same way. Turning the screws to bring the pieces closer together increases the capacitance. That will move the feedpoint impedance along the path of the final arrow on this Smith chart: closer spacing -&gt; higher capacitance -&gt; longer arrow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/KCq2f.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the idea would be if the feedpoint impedance is inductive, then turn the screws to bring the plates closer together. If it's capacitive, move them apart. You should be able to cancel out any reactance in the impedance. And if everything is right, you'll end up around 50Ω.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If all you have is an SWR meter, you are effectively measuring the distance from the center of that chart. In that case you don't have any information about which way you need to go, so you can just make small adjustments and see if it's getting better or worse. If the match is just terrible no matter what, it will be pretty hard to fix it except by trial and error. Might be a good excuse to build an impedance bridge :)&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-06-16T00:25:17.410" LastActivityDate="2017-06-16T00:25:17.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7763" PostTypeId="1" CreationDate="2017-06-16T09:41:00.867" Score="6" ViewCount="1722" Body="&lt;p&gt;I am trying to model Doppler shift of LEO satellite,&#xA;From my research so far I have come across the following formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{equation}&#xA;\frac{f_r}{f_s}=\frac{1-\frac{u}{c}cos\theta}{\sqrt{1-\frac{u^2}{c^2}}}&#xA;\end{equation}&lt;/p&gt;&#xA;&#xA;&lt;p&gt;that in my understanding would model the doppler shift.However the doppler curve (&lt;a href=&quot;https://georgeri.smugmug.com/My-First-Gallery/i-m8tmT5V/A&quot; rel=&quot;noreferrer&quot;&gt;https://georgeri.smugmug.com/My-First-Gallery/i-m8tmT5V/A&lt;/a&gt;) can not be extrapolated by it,since they follow a sinwave shape (as seen in the picture) not a cosine that the formula would plot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I heading in the right direction?Can someone please provide some references on how to replicate the doppler curve?&#xA;Shall I dig in more to special relativity or is a simpler way to model doppler shift?&lt;/p&gt;&#xA;" OwnerUserId="9853" LastEditorUserId="873" LastEditDate="2017-06-16T14:09:10.687" LastActivityDate="2017-06-20T17:26:02.200" Title="doppler LEO satellite" Tags="&lt;satellites&gt;&lt;doppler&gt;" AnswerCount="2" CommentCount="9" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7764" PostTypeId="1" CreationDate="2017-06-17T22:04:54.180" Score="2" ViewCount="1777" Body="&lt;p&gt;I've been told that I have &quot;RF in my signal&quot;. What does this mean? What are some potential causes of having RF in the signal?&lt;/p&gt;&#xA;" OwnerUserId="9661" LastEditorUserId="76" LastEditDate="2017-07-09T17:32:33.243" LastActivityDate="2017-07-09T17:32:33.243" Title="What does it mean to have &quot;RF in your signal&quot;?" Tags="&lt;rfi&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7765" PostTypeId="2" ParentId="3692" CreationDate="2017-06-17T22:14:22.503" Score="5" Body="&lt;p&gt;I'd like to offer a parallel and simplified explanation to W8II's correct answer above, for the mathematically-challenged VHF+ enthusiasts among us. :-)&#xA;&lt;hr&gt;&#xA;As was mentioned in recent threads here, &lt;em&gt;effective aperture&lt;/em&gt; is a measure of the power captured by an antenna. Effective aperture can be expressed as a function of the antenna gain and the wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, how does this affect real-world communications on VHF, UHF, and microwave amateur bands? Here is a &lt;s&gt;simplified&lt;/s&gt; alternative answer based on information from the book &lt;em&gt;VHF-UHF Manual&lt;/em&gt; (3rd edition, published by the RSGB). On pages 7.2 and 7.3 (photo attached) they state:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;It is the capture area of the [antenna] that determines its effectiveness in absorbing the incoming radiation: it means that as the wavelength is reduced it becomes increasingly important to design the [antenna] to have a higher gain.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yE6LH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yE6LH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In simpler terms:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;We make contact with a distant station on 144 MHz, who has an identical phased array and height as our antenna. The gains and patterns are identical. Signals are just readable.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;We then attempt to make contact with this station on 432 MHz with a scaled-down version of the 144 MHz array &lt;strong&gt;with the same gain and pattern&lt;/strong&gt;. The statement above from that book implies that we will not succeed!&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Part of the reason is that the received power at the receiver input will be significantly less on the higher band, &lt;em&gt;even though the gain of both antennas is the same&lt;/em&gt;! If we want to communicate with that distant station on the higher band, then &lt;strong&gt;we need to increase the gain of the 432 MHz array so that its aperture is the same as the 144 MHz antenna&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It goes without saying the band conditions will vary; but we are assuming that the conditions are the same for both tests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some related material:&#xA;&lt;a href=&quot;https://books.google.com/books?id=QtJ5tNdlyYAC&amp;amp;lpg=PA304&amp;amp;ots=Vd0TqH016t&amp;amp;dq=antenna%20capture%20area%20OR%20aperture%20vs%20gain&amp;amp;pg=PA303#v=onepage&amp;amp;q=antenna%20capture%20area%20OR%20aperture%20vs%20gain&amp;amp;f=false&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://books.google.com/books?id=QtJ5tNdlyYAC&amp;amp;lpg=PA304&amp;amp;ots=Vd0TqH016t&amp;amp;dq=antenna%20capture%20area%20OR%20aperture%20vs%20gain&amp;amp;pg=PA303#v=onepage&amp;amp;q=antenna%20capture%20area%20OR%20aperture%20vs%20gain&amp;amp;f=false&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.google.com/search?newwindow=1&amp;amp;safe=active&amp;amp;q=aperture+antenna+lecture+notes&amp;amp;sa=X&amp;amp;ved=0ahUKEwjrgcC417PUAhVE6YMKHR8xD1cQ1QIIkwEoBw&amp;amp;biw=1105&amp;amp;bih=863&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.google.com/search?newwindow=1&amp;amp;safe=active&amp;amp;q=aperture+antenna+lecture+notes&amp;amp;sa=X&amp;amp;ved=0ahUKEwjrgcC417PUAhVE6YMKHR8xD1cQ1QIIkwEoBw&amp;amp;biw=1105&amp;amp;bih=863&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-661-receivers-antennas-and-signals-spring-2003/readings/ch3new.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-661-receivers-antennas-and-signals-spring-2003/readings/ch3new.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.rfcafe.com/references/electrical/ew-radar-handbook/one-way-radar-equation.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.rfcafe.com/references/electrical/ew-radar-handbook/one-way-radar-equation.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Antenna_aperture&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Antenna_aperture&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-12-04T00:22:35.283" LastActivityDate="2019-12-04T00:22:35.283" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="7766" PostTypeId="2" ParentId="7764" CreationDate="2017-06-17T22:23:27.487" Score="2" Body="&lt;p&gt;It most likely means that unwanted RF from your antenna system is getting into your transceiver's audio input (microphone), distorting your audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some solutions are reducing any common-mode RF on your feedline, moving the radio and antenna further apart, or using ferrite and/or capacitors on the audio line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A power supply that cannot supply enough peak current can cause a similar effect. On voice peaks, the voltage drops.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; As &lt;a href=&quot;https://ham.stackexchange.com/a/7769/8717&quot;&gt;Scott nicely pointed out&lt;/a&gt;, the proper balun at the feedpoint can reduce common-mode RF (on the outside of the shield). What band(s) were you on when this happened? That makes a difference in which ferrite mix to use for the balun. My all-time favorite reference for common-mode chokes is &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;K9YC's PDF&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Ugly Baluns&quot; (made from coax) are often recommended, &lt;em&gt;but they are ineffective unless care is taken to use the correct number of turns wound on the proper diameter&lt;/em&gt;. &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;G3TXQ explains this beautifully on his site&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-06-18T23:25:15.547" LastActivityDate="2017-06-18T23:25:15.547" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7767" PostTypeId="1" CreationDate="2017-06-17T22:32:40.933" Score="1" ViewCount="93" Body="&lt;p&gt;I'm studying FM radio transmissions at the moment. I'm using an NTX2B transmitter to experiment naturally assumed I'd use 0V for False/No signal and 3V for True.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, a lot of articles that I came across suggested using a DC bias, so that for a 3V supply, you get 0V for False, 3V for True, and ~1.5V for no signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a particular advantage to using a DC bias like this?&lt;/p&gt;&#xA;" OwnerUserId="9856" LastEditorUserId="4076" LastEditDate="2017-06-18T05:03:51.707" LastActivityDate="2017-07-19T15:23:36.320" Title="Is there an advantage with having a DC bias for a FM radio transmission?" Tags="&lt;fm&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7768" PostTypeId="1" CreationDate="2017-06-18T02:39:39.547" Score="0" ViewCount="2884" Body="&lt;p&gt;I am looking at a base station and want to test it before purchasing can I use a magnetic mobile antenna to see if it transmits and receives without damaging it?&lt;/p&gt;&#xA;" OwnerUserId="9858" LastEditorUserId="873" LastEditDate="2017-06-19T13:51:15.087" LastActivityDate="2021-01-30T06:47:14.837" Title="Can I test a base station CB radio with a magnetic mobile antenna?" Tags="&lt;antenna&gt;&lt;transceiver&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7769" PostTypeId="2" ParentId="7764" CreationDate="2017-06-18T05:53:53.373" Score="1" Body="&lt;p&gt;One symptom of having 'RF in the shack' is that metal parts of the radio (or morse key, or microphone) will feel &quot;hot&quot; to the touch, and can give a nasty burn - or at least a bit of a surprise! Mike has already suggested several ways of reducing this, and I would add that when he talks about reducing common-mode RF on the feedline, this can sometimes be achieved inexpensively by the use of a balun. A good article explaining this can be found &lt;a href=&quot;https://www.w8ji.com/common_mode_current.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-06-18T05:53:53.373" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7770" PostTypeId="2" ParentId="7767" CreationDate="2017-06-18T10:25:58.733" Score="0" Body="&lt;p&gt;Be aware that this is an amateur (ham) radio site and your question does not pertain to ham radio. But perhaps your project is a stepping stone to an interest in communicating further  including around the world, with satellites, and the International Space Station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The NTX2B transmitter module is for the transmission of data on 433 MHz. The data input to the module should be 0 volts or 3 volts to represent 0 and 1 respectively. No other voltage or bias should be used as it may result in erratic operation.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-06-18T10:25:58.733" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7771" PostTypeId="1" AcceptedAnswerId="7776" CreationDate="2017-06-18T14:35:31.713" Score="8" ViewCount="831" Body="&lt;p&gt;I've been living as an &lt;a href=&quot;https://en.wikipedia.org/wiki/Expatriate&quot; rel=&quot;noreferrer&quot;&gt;expat&lt;/a&gt; for a decade, and my extra class license expired a little more than a year ago. I'm currently in Taiwan.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to renew my license while staying here? Can I do it completely electronically? Or do the exams still need to be issued by an examiner or some proxy? &lt;a href=&quot;https://ham.stackexchange.com/a/7408/8643&quot;&gt;This answer&lt;/a&gt; suggests &lt;em&gt;everything&lt;/em&gt; is now electronic, but is that really true for the exam?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think there is a code test any more, right? It was still required when I took the test but I think it was about to disappear. I do have a mailing address in the US with people who can open and/or forward things for me.&lt;/p&gt;&#xA;" OwnerUserId="8643" LastEditorUserId="8643" LastEditDate="2017-06-18T14:59:42.500" LastActivityDate="2021-04-30T20:53:26.897" Title="How to renew an expired US license as an expat?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7772" PostTypeId="2" ParentId="7771" CreationDate="2017-06-18T15:22:40.480" Score="1" Body="&lt;p&gt;Ordinarily, you do need to take a test in person.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you need to do is contact &lt;a href=&quot;https://www.fcc.gov/volunteer-examiner-coordinators-vecs&quot; rel=&quot;nofollow noreferrer&quot;&gt;a Volunteer Examiner Coordinator (VEC) organization&lt;/a&gt; to ask if they have or can arrange a testing session you could attend, or do a test over a video conference, or some such arrangement. It's up to the particular VEC to decide what they can do for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The VEC is also responsible for informing the FCC that they should grant you a license, so you don't need to do anything else, electronically or otherwise, than arrange for the test. (If you haven't already, you may wish to obtain a FRN beforehand to avoid disclosing your Social Security number to the examiner, but you can do that using the FCC's web site.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no code test for any license level.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-06-18T16:55:28.297" LastActivityDate="2017-06-18T16:55:28.297" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7773" PostTypeId="2" ParentId="7768" CreationDate="2017-06-18T16:35:55.000" Score="0" Body="&lt;p&gt;In general, as long as the antenna is reasonably sized for the transmitting frequency it should be fine. In other words, if you are transmitting on 30 MHZ (10 meter band) and you try to use a 12&quot; mag mount, you can either damage the radio at worst, or best case the radio clamps down the output and you won't get any signal out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that you will probably not get great performance out of it, but it should at least be good enough to test with another close by radio to make sure that the base station is actually working.&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2017-06-18T16:35:55.000" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7774" PostTypeId="2" ParentId="7763" CreationDate="2017-06-18T16:58:37.510" Score="2" Body="&lt;p&gt;The Doppler curve IS the Doppler shift. That graph you have is exactly what you will see at your receiver station. Especially for LEO satellites, you don't need to extrapolate further because the satellite is obscured by the Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You mention you are concerned about the cosine function in the equation... remember that cosine is the same thing as sine but shifted 90 degrees. You don't need to worry about that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This formula is easier to think about if you take the curvature of the Earth out of the equation. If you imagine for a moment that you are on a flat surface and you have an object coming towards you (but slightly offset from you), the frequency you receive is higher than the source it is transmitting. As it gets closer, there will be less and less velocity in your line of sight. Then, when it reaches the closest point of approach to you, your received frequency will be exactly equal to the transmitted frequency because the velocity in your line of sight to the object is exactly zero. As it continues away, your received frequency will decrease until it is far enough away that the velocity component in your line of sight is essentially equal to the object's total velocity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, the picture in the link is showing you a lot of information. If you know the transmitted frequency, then when you measure the difference between max or min frequency and that reference, you are able to determine how fast the object is traveling. If you don't know the base frequency, then you can take the average of the max and min to calculate it. Finally, you know that when the satellite crossed zero in that graph it was at it's closest point of approach to you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To summize, you are on the right track. You just have to remember that u in that equation is a relative speed in receiver's line of sight, not the speed of the satellite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the exact same principle used in sonar tracking and signal processing as well. If you can't find more on satellites, you can look there too.&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2017-06-18T16:58:37.510" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7776" PostTypeId="2" ParentId="7771" CreationDate="2017-06-18T22:24:48.833" Score="6" Body="&lt;h2&gt;You CAN renew online, and you have a two-year grace period.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;http://www.arrl.org/renewals&quot; rel=&quot;noreferrer&quot;&gt;http://www.arrl.org/renewals&lt;/a&gt;: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Amateur applications can be filed manually using paper forms or&#xA;  electronically via the web. &lt;strong&gt;Amateurs may electronically renew their&#xA;  FCC-issued licenses online&lt;/strong&gt; using &lt;a href=&quot;http://wireless.fcc.gov/uls/&quot; rel=&quot;noreferrer&quot;&gt;the FCC ULS&lt;/a&gt; . FCC permits online&#xA;  renewals at 90 days or less before a license will expire, &lt;strong&gt;and when the&#xA;  license has expired but is still within the two-year grace period for&#xA;  renewal.&lt;/strong&gt; Licenses that have been expired for more than two years are&#xA;  not eligible for renewal or reinstatement. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Amateurs may renew their licenses within 90 days before the license&#xA;  expiration date, &lt;strong&gt;or within the two-year license grace period after&#xA;  expiration&lt;/strong&gt;, by using FCC Form 605 by mail to: FCC, 1270 Fairfield&#xA;  Rd, Gettysburg PA 17325-7245.  Licenses that have been expired for&#xA;  more than two years are not eligible for renewal or reinstatement.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;For a complete list of FCC filing instructions and filing fees go to&#xA;  &lt;a href=&quot;http://www.arrl.org/call-sign-renewals-or-changes&quot; rel=&quot;noreferrer&quot;&gt;http://www.arrl.org/call-sign-renewals-or-changes&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-06-18T22:30:12.267" LastActivityDate="2017-06-18T22:30:12.267" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7778" PostTypeId="2" ParentId="7768" CreationDate="2017-06-18T22:58:10.950" Score="2" Body="&lt;p&gt;Magnetic mobile antenna is supposed to be mounted on the roof of vehicle, thus metallic roof serves as ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to use it as base station antenna, off the vehicle you have to provide similar ground plane. As it is magnetic antenna it probably does not have option to attach radials so you have to set it up on large enough sheet of metal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For VHF and UHF, side of PC case is good enough. For CB I guess it should be larger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyways, you should test transmitting on low power first (less than 5 watts) and with SWR meter. If everything is OK then you may switch to higher power (but not higher than what is antenna rated for)&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2017-06-18T22:58:10.950" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7779" PostTypeId="2" ParentId="7768" CreationDate="2017-06-19T14:01:19.120" Score="2" Body="&lt;p&gt;If you are using a magnetically-mounted antenna that is designed for mobile use, then ideally you need to put it on as large a sheet of metal as you can find. This is because a mobile antenna of this type is (as mentioned in another answer) designed to use the roof of a vehicle as a groundplane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The President Washington should only transmit about 4 watts of power (Google is your friend), so any small antenna should do for testing purposes. Do be aware that some people do like to increase the power out to 15-20W, which puts the radio out of spec. If this is the case, you would be well advised to have the radio realigned - which won't hurt anyway, as these sets are getting long in the tooth now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally though, you would want to take a power meter (a regular power/SWR meter would do just fine) and a small dummy load. Plug the dummy load into the antenna socket of the power meter, and plug the power meter into the transmitter. That will tell you how much power you are transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For testing how well it receives, any antenna will do really. A mag-mount on a balcony railing will be fine to see if the radio's receiver is working at all.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-06-19T14:01:19.120" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7780" PostTypeId="2" ParentId="7763" CreationDate="2017-06-19T17:13:10.397" Score="3" Body="&lt;p&gt;The general equation for the change in frequency due to Doppler shift is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y9F1M.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y9F1M.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where c is the speed of light, f&lt;sub&gt;O&lt;/sub&gt; is the frequency of operation, and Δv is the relative velocity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When applying this formula to the ground observation of a satellite, Δv is better described as range velocity (rate of change of distance from the satellite to observer). Because many LEO satellites are in an elliptical orbit, the math to obtain Δv as a function of time or position is not solved through simple angular calculations and therefore becomes very tedious to execute even when applying matrix math for some of the calculations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to suggest, however, that there is little value in recreating all of the calculations except for academic interest. Instead, I prefer to use a well engineered software library called PyEphem that does nearly every type of ephemeral calculation one could need (I even use this library in my home automation system to calculate the on/off times of my exterior lights to obtain automatic seasonal adjustment). This is a completely free Python library that is easily run on nearly any operating system and platform including the ubiquitous Raspberry Pi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Applying the library for amateur radio satellites is quite simple. First, acquire the TLE (two line elements) for the desired satellite. These are available from &lt;a href=&quot;http://www.tle.info/data/amateur.txt&quot; rel=&quot;nofollow noreferrer&quot;&gt;the TLE Info site&lt;/a&gt;. A typical set of TLE data contains all the necessary ephemeral variables and looks like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;OSCAR 7&#xA;1  7530U 74089B   17170.24378275 -.00000031 +00000-0 +84707-4 0  9992&#xA;2  7530 101.6303 138.8875 0011838 320.4872 153.4129 12.53627377948883&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This information is used with the PyEmphem library in the following fashion. First establish the observer location on earth (I will use Chicago, IL, USA as an example):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;my_loc = ephem.Observer()&#xA;my_loc.lon = '87.6298'&#xA;my_loc.lat = '41.8781'&#xA;my_loc.elevation = 181&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Then apply the TLE data to create a my_sat body object:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;my_sat = ephem.readtle(name, line1, line2);&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The library can now calculate a variety of data related to the next pass of my_sat at my_loc:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;info=my_loc.next_pass(my_sat)&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for example, we can print the rise and set times, maximum altitude, and the time of the maximum altitude for the next pass:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;print(&quot;AOS: %s LOS: %s Maximum Altitude: %s Maximum Altitude Time: %s&quot; % (info[0], info[4], info[3], info[2]))&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the maximum Doppler shift will occur at AOS and LOS and that the maximum altitude time is when the Doppler shift will be at zero because the range velocity (Δv) will drop to zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can also inquire as to the range velocity at any time during the pass. For example, at the start of the pass:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;my_sat.compute(info[0])&#xA;print(&quot;Range velocity: %s &quot; % (my_sat.range_velocity))&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;By applying this technique to obtain the range velocity throughout the pass, we can easily calculate the Δf of a specific pass as viewed from a specific location on earth. And all of that for only a few dozen lines of code!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can learn more about the expansive PyEphem library &lt;a href=&quot;http://rhodesmill.org/pyephem/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to explore more of the raw math behind LEO satellite calculations, the following links may be helpful:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1659&amp;amp;context=smallsat&quot; rel=&quot;nofollow noreferrer&quot;&gt;Orbit Calculation and Doppler Correction&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://etrij.etri.re.kr/etrij/journal/article/article.do?volume=22&amp;amp;issue=4&amp;amp;page=32&quot; rel=&quot;nofollow noreferrer&quot;&gt;Adaptive Doppler Correction&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.atmosp.physics.utoronto.ca/people/strong/phy499/section2_05.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Satellite Orbit Basics&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-06-20T17:26:02.200" LastActivityDate="2017-06-20T17:26:02.200" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7781" PostTypeId="1" AcceptedAnswerId="7783" CreationDate="2017-06-19T19:22:13.583" Score="3" ViewCount="726" Body="&lt;p&gt;I want to start experimenting and tinkering with antennas, starting with ½ wave dipoles. I will be measuring the AC voltages on both the transmitter and the reciever antennas simultaneously. And by changing the distance between them, I will observe the phase angle and delay time (of the EM waves) between them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I started planning with no practical experience, I stumbled at each step. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found this calibrated signal generator (&lt;a href=&quot;https://www.rf-consultant.com/calibrated-signal-generator/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.rf-consultant.com/calibrated-signal-generator/&lt;/a&gt;) and Rigol DS1102E so that I will be able to work with 100 MHz. I know the scope is rated for 100 MHz but after reading this thread (&lt;a href=&quot;https://hackaday.io/project/4327-stretching-the-limits-of-a-rigol-ds-1102e-scope&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hackaday.io/project/4327-stretching-the-limits-of-a-rigol-ds-1102e-scope&lt;/a&gt;), I was convinced that it could work well even at higher frequencies (only if we are measuring with one channel).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First problem is how to connect the transmitter antenna to the signal generator. I will use a 50 ohm coax cable of small length. Since the waveform and directivity is not critical, could I get away without adding a balun? Or would there be a risk of damaging the signal generator with signal reflections  (it has  50 ohms and +10 dBm (0.01 Watts) output) ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If no baluns is ok, I will simply split the coax inner wire and braid apart into a dipole antenna. Soldering would maybe introduce abrupt impedance changes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second and biggest problem is how to probe the antennas to see the voltage waveforms? Could I attach the probe directly on the transmitting antenna center? While measuring on the reciever antenna, could I attach the probe on the other end of the coax cable (because the probe cables could fall short of the distance between the antennas while making simultaneous measurements) ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I attach the probe to the inner wire of the coax, should I attach the ground clip to the braid? Or at 100MHz should I completely remove the ground clip to eliminate the inductive coupling of the “ground clip-antenna-probe” loop (see under the title “Beware using ground clips...” in &lt;a href=&quot;http://www.radio-electronics.com/info/t_and_m/oscilloscope/using-oscilloscope-scope.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.radio-electronics.com/info/t_and_m/oscilloscope/using-oscilloscope-scope.php&lt;/a&gt;)? Or should I probe like this (&lt;a href=&quot;http://www.gorferay.com/pic/Mifare_4k_1_49.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.gorferay.com/pic/Mifare_4k_1_49.jpg&lt;/a&gt;)?&lt;/p&gt;&#xA;" OwnerUserId="9868" LastEditorUserId="9868" LastEditDate="2017-06-20T12:31:39.580" LastActivityDate="2017-06-24T21:31:10.600" Title="How to probe a dipole antenna?" Tags="&lt;wire-antenna&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7782" PostTypeId="2" ParentId="6812" CreationDate="2017-06-19T20:37:30.917" Score="1" Body="&lt;p&gt;It has been my experience that using true DOS (not DOS box under Windows) seems to work the best for older Motorola radios. I use a Windows XP era laptop with a built in serial port (&lt;em&gt;which is important, DOS cannot recognize a USB serial port&lt;/em&gt;) and boot DOS off a thumb drive. I realize this flies in the face of all the recommendations out there to use a slow PC, but I have had no problems programming my Maxtrac or any of my other assorted old Motorola radios. This is the setup I used when I worked for a Motorola shop and we had customers with older radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To set this up yourself:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Laptop/Desktop with built in serial port (&lt;strong&gt;not&lt;/strong&gt; USB)&lt;/li&gt;&#xA;&lt;li&gt;To avoid dedicating said PC strictly to DOS, format a FAT partition on a thumb drive and install DOS on it&lt;/li&gt;&#xA;&lt;li&gt;Copy the Maxtrac software to the thumb drive&lt;/li&gt;&#xA;&lt;li&gt;Boot the drive from the programming PC&lt;/li&gt;&#xA;&lt;li&gt;Run the Maxtrac RSS&lt;/li&gt;&#xA;&lt;li&gt;Check the configuration, make sure the correct serial port is selected&lt;/li&gt;&#xA;&lt;li&gt;Attempt to read the radio&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;With my setup I did not need Mo'Slo or any other CPU speed-reducing program. The laptop in question was a Dell Latitude D630, with a Core 2 Duo processor and more RAM than DOS can access. This setup works on my two Maxtracs, and has worked for 99% of the radios I've wanted to program.&lt;/p&gt;&#xA;" OwnerUserId="9875" LastActivityDate="2017-06-19T20:37:30.917" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="7783" PostTypeId="2" ParentId="7781" CreationDate="2017-06-19T20:54:05.647" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;First problem is how to connect the transmitter antenna to the signal generator. I will use a 50 ohm coax cable of small length. Since the waveform and directivity is not critical, could I get away without adding a balun? Or would there be a risk of damaging the signal generator with signal reflections (it has 50 ohms and +10 dBm (0.01 Watts) output) ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A good signal generator should tolerate any impedance at all at its output (including a short circuit).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you should still use a balun in your antenna design, because if you construct a dipole without a balun, then the feed line will act as an antenna element (along with all of the grounded chassis metal of your signal generator, and so on). This means that you will not be measuring the antenna design you think you are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A balun for a dipole prevents this unwanted RF current, so that the antenna's behavior is independent of how it is connected (though the path of the part of the feed line near to the antenna still matters — just as does any nearby object). The same thing applies in reverse to a receiving antenna; both need baluns to be predictable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that the feed point impedance of a dipole is not (usually) 50 Ω, so you will have some reflections from the transmit antenna no matter what unless you use a suitable matching network at the feed point (which would usually be combined with the balun).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Second and biggest problem is how to probe the antennas to see the voltage waveforms? Could I attach the probe directly on the transmitting antenna center?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you do this you must do it on the unbalanced (coax, not antenna) side of the balun, otherwise the probe cable ground will upset the balance and radiate as I mentioned above.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;While measuring on the reciever antenna, could I attach the probe on the other end of the coax cable (because the probe cables could fall short of the distance between the antennas while making simultaneous measurements) ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, you can. The normal sort of operation would be to connect the feed line coax to the oscilloscope input, without using an oscilloscope probe. You must include a 50 Ω load (‘terminator’) &lt;em&gt;at the oscilloscope's end of the cable,&lt;/em&gt; either:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;a BNC tee and a terminator (which looks like a BNC male connector with a metal cap instead of a cable attached),&lt;/li&gt;&#xA;&lt;li&gt;a feed-through terminator (typically more expensive; has a BNC male and female connector), or&lt;/li&gt;&#xA;&lt;li&gt;an internal 50 Ω load provided by your oscilloscope (not a feature of your Rigol DS1102E).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This will ensure there are no reflections, and you are making a realistic measurement. (Remember that ideally the antenna should also be matched to the cable's 50 Ω. If it is not, there will still not be reflections, but the received signal will not be as strong as in the matched condition — in exactly the same way as any receiver's antenna input of the same impedance.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, you could use the probe and a regular resistor as the load at the antenna's feed point; that would be awkward in general compared to using proper coax parts but might be easier to get started with the components you have on hand to set up an experiment.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If I attach the probe to the inner wire of the coax, should I attach the ground clip to the braid? Or at 100MHz should I completely remove the ground clip to eliminate the inductive coupling of the “ground clip-antenna-probe” loop?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you are using an oscilloscope probe for RF, you &lt;em&gt;must&lt;/em&gt; have a ground connection (removing it is the worst case), and the connection should be as &lt;em&gt;short and parallel&lt;/em&gt; as you can manage (least loop area).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I mentioned above, the best option is to skip the probe and use a matched load. This is what you should do for your receiving antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your transmit antenna, if your balun has conveniently exposed wires you can hook onto them, but consider using a shorter ground lead to minimize the loop area — a custom bent piece of solid wire, coiled to fit snugly onto the shield around the &lt;em&gt;tip&lt;/em&gt; of the probe rather than the ring farther back up the shaft where a regular ground lead attaches.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option is to obtain an oscilloscope-probe-to-BNC adapter (note that there are several sizes depending on your probe tip diameter) and use it together with a tee connector to tap off the signal.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Also, since you want to compare phase, don't forget to consider the length of the cables to your oscilloscope. If you use cables of the same length and the same type of coax, then you know they have the same delay; in any other case you must account for the difference.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-06-22T20:44:22.207" LastActivityDate="2017-06-22T20:44:22.207" CommentCount="14" ContentLicense="CC BY-SA 3.0" />
  <row Id="7784" PostTypeId="1" CreationDate="2017-06-20T02:24:51.970" Score="0" ViewCount="1185" Body="&lt;p&gt;I have a pair of HopeRF LoRa RFM98 Radio Modems(based on Semtech SX1278) and I want to configure them for the longest range possible, without taking care about any second factor like transmission time and power consumption.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I made already some research until I found Semtech's official tool 'LoRa Modem Calculator Tool'. The problem is I am a beginner in the hobby of radios and the tool is just confusing for me with all the various settings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Does the tool show me all relevant configurations to achieve the longest range with my RFM? How I have to choose the settings to achieve the longest range.&lt;/strong&gt; Any other factor is not important.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tools default settings:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/1VwIA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1VwIA.png&quot; alt=&quot;LoRa Medom Calculator Tool default settings&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8230" LastActivityDate="2017-06-23T15:39:46.077" Title="LoRa Radio RFM96/98 SX1276/8 configuration settings for Longest Range" Tags="&lt;modes&gt;&lt;transceiver&gt;&lt;jargon&gt;&lt;range&gt;" AnswerCount="1" CommentCount="9" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7785" PostTypeId="1" AcceptedAnswerId="7790" CreationDate="2017-06-20T05:02:24.920" Score="2" ViewCount="899" Body="&lt;p&gt;I imagine this changes depending on what HT you are using. In my case, it is a Yaesu FT-1XDR, charging in the Yaesu CD-41 charging cradle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio itself doesn't stop me from monitoring a channel when it is in the dock, but I am wondering if it is bad practice to do so.&lt;/p&gt;&#xA;" OwnerUserId="9865" LastActivityDate="2019-10-30T18:35:07.973" Title="Is it safe to monitor a channel while charging my handheld?" Tags="&lt;yaesu&gt;&lt;battery-charging&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7786" PostTypeId="2" ParentId="7785" CreationDate="2017-06-20T05:18:18.997" Score="1" Body="&lt;p&gt;It should be perfectly safe. I have done it for ages with my Yaesu FT60R handheld so yours shouldn't be any different.&#xA;Moreover, some people use their handheld as a (semi-) fixed station using a power supply and an external antenna.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2017-06-20T05:18:18.997" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7787" PostTypeId="2" ParentId="7785" CreationDate="2017-06-20T07:35:31.853" Score="2" Body="&lt;p&gt;Well, it's a commercial product, and I'd be very surprised would Yaesu be willing to deal with the anger if it wasn't safe to do something as obvious as that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, from an engineering point of view, it would be trivial to shut off functionality not safe for use during charging – that literally takes but one transistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm also not sure what you mean with &quot;not safe&quot;; generally, if you mean &quot;not safe for a human to do&quot;, then rest assured that usually, RX operation involves little power and you don't have to worry. What I'd worry about is being close to a transmit antenna's beam when TX'ing at hundreds of Watt.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-06-20T07:35:31.853" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7789" PostTypeId="2" ParentId="7785" CreationDate="2017-06-20T14:58:17.803" Score="1" Body="&lt;p&gt;The charging cradle is an external power supply that can power the radio and charge the battery at the same time. Yes, that is safe.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2017-06-20T14:58:17.803" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7790" PostTypeId="2" ParentId="7785" CreationDate="2017-06-20T15:00:34.810" Score="2" Body="&lt;p&gt;It's perfectly safe.  Note that you will slow charging down, since you are using some of the battery's stored energy to monitor the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A better solution might be to get a second battery for your radio, along with a charging dock if you don't already have one.  With many modern hand-held radios, charging docks increase the charging rate compared to using the charger alone (they must include better charging electronics to permit this).  You can put a naked battery into most such chargers, letting you use your other battery on your handheld without being tethered to the charger.  As a bonus, having two fully-charged batteries will allow you to go into the field with significantly more runtime capacity with your radio.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2017-06-20T15:00:34.810" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7792" PostTypeId="2" ParentId="6381" CreationDate="2017-06-21T01:39:38.283" Score="2" Body="&lt;p&gt;I found a lot of MP3 files at the ARRL:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/code-practice-files&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/code-practice-files&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are pages from QST magazine, so the text is also available. There are multiple files for each text sent at various rates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have an HF receiver they also transmit code practice sessions. The schedule and frequencies are at: &#xA;&lt;a href=&quot;http://www.arrl.org/w1aw-operating-schedule&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/w1aw-operating-schedule&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Glenn&lt;/p&gt;&#xA;" OwnerUserId="9882" LastActivityDate="2017-06-21T01:39:38.283" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7794" PostTypeId="7" CreationDate="2017-06-21T03:20:21.257" Score="0" Body="&lt;ul&gt;&#xA;    &lt;li&gt;Anything not directly related to amateur radio or the science and technology of radio&lt;/li&gt;&#xA;    &lt;li&gt;Questions that are primarily opinion-based&lt;/li&gt;&#xA;    &lt;li&gt;Questions with too many possible answers or that would require an extremely long answer&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="-1" LastEditorUserId="76" LastEditDate="2017-06-21T03:20:21.257" LastActivityDate="2017-06-21T03:20:21.257" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7795" PostTypeId="7" CreationDate="2017-06-21T03:20:37.740" Score="0" Body="&lt;ul&gt;&#xA;    &lt;li&gt;The theory and practice of amateur radio&lt;/li&gt;&#xA;    &lt;li&gt;Real problems or questions that you’ve encountered&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="-1" LastEditorUserId="76" LastEditDate="2017-06-21T03:20:37.740" LastActivityDate="2017-06-21T03:20:37.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7796" PostTypeId="1" CreationDate="2017-06-21T04:41:23.450" Score="-1" ViewCount="3954" Body="&lt;p&gt;If not, what can be used as mode of communication for group trekking.&#xA;It is very urgent and important&#xA;Please suggest some better options for walkie talkies&lt;/p&gt;&#xA;" OwnerUserId="9883" LastEditorUserId="873" LastEditDate="2017-06-21T09:54:33.417" LastActivityDate="2020-01-21T07:47:36.220" Title="Is it legal to use BAOFENG BF-888S 16-CH 400~470MHz 5W Walkie Talkie in India?" Tags="&lt;legal&gt;&lt;ht&gt;&lt;india&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7797" PostTypeId="2" ParentId="7796" CreationDate="2017-06-21T07:35:20.607" Score="2" Body="&lt;p&gt;As you say in your post, that this is &lt;strong&gt;urgent&lt;/strong&gt;, there are plenty of options for you to find out information quickly:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Contact the &lt;a href=&quot;http://www.arsi.info/contact-us&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio Society India&lt;/a&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Contact the &lt;a href=&quot;http://www.wpc.gov.in/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wireless Planning &amp;amp; Coordination Wing of the Ministry of Communications and Information Technology, Department of Telecommunications&lt;/a&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Other than that, you can obviously download the &lt;a href=&quot;http://www.wpc.gov.in/WriteReadData/userfiles/file/National_Frequency_Allocation_Plan-2011.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;National Frequency Allocation Plan&lt;/a&gt;. You probably want some accompanying documentation to fully understand this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not an expert in the legalities in your country, so you will have to do some digging yourself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly you can see if there is a local ham radio club. There might be someone near you, who is able to answer your questions quickly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a good chance of the following:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;There are license-free allocations, but the Baofeng radios are not type approved for such.&lt;/li&gt;&#xA;&lt;li&gt;You may use the Baofeng, but only with appropriate license, which may require you to go through an application process.&lt;/li&gt;&#xA;&lt;li&gt;You may use the Baofeng, but only on Amateur allocations, with an amateur license, which you do not state in your post that you have one.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Based on how you asked the question, I guess you probably want to stick to the &quot;license-free type-approved&quot; use, which means &quot;general walkie-talkie&quot; equipment.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="218" LastEditDate="2017-06-21T13:16:38.563" LastActivityDate="2017-06-21T13:16:38.563" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7799" PostTypeId="2" ParentId="7764" CreationDate="2017-06-21T14:03:38.683" Score="0" Body="&lt;p&gt;I've never heard of &quot;RF in your signal&quot;. The signal &lt;em&gt;is&lt;/em&gt; RF. It doesn't make any sense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wouldn't jump to the conclusion that &quot;RF in the shack&quot; is the problem. While &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;common-mode current&lt;/a&gt; may be a &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;consequence of your antenna design&lt;/a&gt;, a distorted signal is not the first symptom I associate with those problems. Many a ham has transmitted into a coax fed dipole with no balun, and it works well enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or consider the case of a handheld radio, where &lt;a href=&quot;https://ham.stackexchange.com/q/495/218&quot;&gt;all the antenna current must flow around the radio&lt;/a&gt;. If common-mode current near the transceiver caused notable distortion, how could these work at all?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More likely, &quot;RF in your signal&quot; just means your signal is distorted, somehow. Consider the qualifications of the person who gave you this report and treat it with the appropriate degree of skepticism.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before making any conclusions, I'd try to corroborate that report, and get a more objective assessment of the distortion. Perhaps you can &lt;a href=&quot;https://ham.stackexchange.com/q/332/218&quot;&gt;listen to yourself on the internet&lt;/a&gt;, or get a report from an experienced operator (that is, not most hams). The cause of the distortion could be something pedestrian, like the mic gain is too high.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-06-21T14:03:38.683" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7800" PostTypeId="1" AcceptedAnswerId="7805" CreationDate="2017-06-21T16:50:17.627" Score="2" ViewCount="279" Body="&lt;p&gt;I have recently acquired a nice looking dummy load on military surplus sale. Being relatively new to the hobby, I assumed the connector on it was something common. Turns out it is not. So far nobody has been able to tell what it is. The most specific answer I got is that it is a 'large TNC', except I haven't been able to find anything like it. Looking for the model number on the manufacturer’s site also didn't bring up anything useful. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I thought also of replacing the connector entirely, but it turns out that the center pin and dielectric are integral parts of the resistor inside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are a couple of pictures of the load and the connector up close.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0EwGU.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0EwGU.jpg&quot; alt=&quot;The connector&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vKRxB.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vKRxB.jpg&quot; alt=&quot;The connector head on&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6XB43.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6XB43.jpg&quot; alt=&quot;The connector diameter&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tmxCz.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tmxCz.jpg&quot; alt=&quot;The load from the side&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zVQpj.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zVQpj.jpg&quot; alt=&quot;The load&amp;#39;s model number&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9145" LastEditorUserId="8717" LastEditDate="2019-12-05T20:04:36.910" LastActivityDate="2019-12-05T20:04:36.910" Title="Identify this “large TNC” coax connector" Tags="&lt;connectors&gt;&lt;equipment&gt;&lt;dummy-load&gt;&lt;military-surplus&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7801" PostTypeId="2" ParentId="7800" CreationDate="2017-06-21T17:58:13.020" Score="1" Body="&lt;p&gt;Looks like a male SC connector and the dimensions seem in the ballpark too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found this via a &lt;a href=&quot;http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/coax_con.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;Microwave Coaxial Connectors&quot; PDF&lt;/a&gt; which describes it as:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;SC&lt;/strong&gt; (OSSC) - The SC coaxial connector is a medium size, older type constant 50 Ω impedance. It is larger than the BNC, but about the same as Type N. It has a frequency range of 0-11 GHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This matches what Amphenol says about &lt;a href=&quot;https://www.amphenolrf.com/connectors/sc-type.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;their SC-Type Connector Series&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The SC-Type connector series is a medium size, 50 Ω series, with performance up to 11 GHz.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The SC-Type connectors are manufactured to meet MIL-C-39012 category D, specification sheets 35 through 43. The series meets all of the mechanical and electrical requirements of the Limited Co-ordination Specification (LC Spec.) as generated by the U.S. Air Force.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Connector mating is a .687-24 UNEF screw thread.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Tom Williams (WA1MBA) does not show this connector on his &lt;a href=&quot;http://www.wa1mba.org/rfconn.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;RF Connectors for Upper Frequencies&lt;/a&gt; page yet considers it &quot;common&quot;: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;There are many other common RF interconnects, but are not described in this treatment because their performance in the microwave region is very limited. Examples are C, HN, &lt;strong&gt;SC&lt;/strong&gt;, LC, various EIA, UHF, mini-UHF, Motorola, HV, SHV, and RCA Phono. [emphasis mine]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(Clearly that's a bit at odds with the &quot;up to 11 GHz&quot; frequency range I see cited everywhere else.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maury's &lt;a href=&quot;https://www.maurymw.com/pdf/datasheets/5A-021.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;Microwave Coaxial Connector Technology: A Continuing Evolution&quot; PDF&lt;/a&gt; also lists it amongst &quot;General purpose coaxial connectors in wide use for systems application&quot; and summarizes it as a &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Threaded version of type C for aircraft and EW applications.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-06-21T18:05:55.153" LastActivityDate="2017-06-21T18:05:55.153" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7803" PostTypeId="1" CreationDate="2017-06-22T15:50:00.583" Score="2" ViewCount="2251" Body="&lt;p&gt;I am using a bit of coax cable as an antenna (with the shielding off at the last 17.3 cm). However it is cheap Chinese cables and the shielding does not contain that many copper wires (the &quot;web&quot; isn't very thick, you can see through it).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How much would this matter? Is that sort of cable completely useless and unshielded or does it basically not matter how much wire you've got around the center, as long as its grounded and goes all the way round?&lt;/p&gt;&#xA;" OwnerUserId="9494" LastActivityDate="2017-06-22T19:39:57.960" Title="How much does the quality of coax cable matter?" Tags="&lt;antenna-theory&gt;&lt;coaxial-cable&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7804" PostTypeId="2" ParentId="7803" CreationDate="2017-06-22T16:23:07.633" Score="2" Body="&lt;p&gt;The &quot;density&quot; of the shield is called shield coverage. Copper is expensive, and in a coaxial transmission line, the shield is most of the copper. So if you want to reduce cost, reducing shield coverage is a good way to do it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most significant impacts may be&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;increased resistive losses, and&lt;/li&gt;&#xA;&lt;li&gt;increased &lt;a href=&quot;https://www.w8ji.com/coaxial_cable_leakage.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;common-mode ingress&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The degree of the impact will vary significantly by frequency. As frequency increases and wavelength decreases, the &quot;holes&quot; in the shield appear increasingly large. This is why high frequency cables often include foil shields, or even better, solid copper.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The total loss should be specified in the datasheet, usually in decibels per unit length, at several frequencies. Though for cheap Chineese cable there may be no datasheet, and even if there is one it may not be trustworthy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this coax is bundled near other cables or sources of noise, more of that outside noise will couple into the signal. More of the signal within the coax will get out, which you may regard as loss; or from the perspective of other signals, noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether this matters to you or not depends on your application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a receive application, loss is not much of a concern since both signal and noise received by the antenna are attenuated equally, and thus the signal to noise ratio remains unchanged. Unless of course the loss is so much that the signal is attenuated below the receiver's sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a transmit application loss can matter quite a lot. It is in many circumstances more economical to install a higher quality feedline with less loss than it is to install a higher power transmitter to overcome feedline loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The significance of common-mode ingress depends very much on your situation. The received signal from the antenna will already contain noise. Are there sources of common-mode noise that are significant in comparison? Is minimizing radiation from the cable a requirement? There is no general answer to these questions.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-06-22T16:23:07.633" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7805" PostTypeId="2" ParentId="7800" CreationDate="2017-06-22T16:39:36.727" Score="3" Body="&lt;p&gt;The connector is called an &quot;HN&quot; type connector. It has a 3/4-20 thread and it is usable up to 4 GHz. The Amphenol data on it is available &lt;a href=&quot;https://www.amphenolrf.com/connectors/hn-type.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IryBE.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IryBE.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-06-22T16:39:36.727" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7806" PostTypeId="2" ParentId="7803" CreationDate="2017-06-22T19:18:59.017" Score="2" Body="&lt;p&gt;There is much more to the &quot;quality&quot; of coax cable than just the shielding. Some examples:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The center conductor contributes the greatest losses at HF frequencies. The gauge, the quality of the copper, and the thickness of the copper if plated all contribute.&lt;/li&gt;&#xA;&lt;li&gt;The dielectric material contributes directly to losses at VHF and higher frequencies and indirectly at lower frequencies since its characteristics, along with the gauge of the center conductor, determines the inner diameter of the shield.&lt;/li&gt;&#xA;&lt;li&gt;The dielectric material plays a role in the voltage and power rating of the cable.&lt;/li&gt;&#xA;&lt;li&gt;Soft dielectric material can cause the center conductor to migrate from its central position which alters the impedance of the coax and reduces the power rating.&lt;/li&gt;&#xA;&lt;li&gt;The RF resistance of the shield is the second highest contributor to RF losses on HF. The smaller the inner diameter, the higher the losses. The less copper in the jacket, the higher the losses. Aluminum and tin plated shields have higher losses than pure copper shields.&lt;/li&gt;&#xA;&lt;li&gt;The quality of the outer insulating jacket partly determines the pliability of the cable and plays a direct role on the usable lifetime of the cable due to UV aging and moisture ingress.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-06-22T19:39:57.960" LastActivityDate="2017-06-22T19:39:57.960" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7807" PostTypeId="1" CreationDate="2017-06-22T22:35:31.580" Score="3" ViewCount="1104" Body="&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/applying-for-a-vanity-call&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL indicates&lt;/a&gt; that you can apply for vanity callsigns online by &quot;by connecting to the &lt;a href=&quot;http://wireless.fcc.gov/uls/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC's web site&lt;/a&gt;[ and clicking] on the icon entitled “Online Filing LOG IN”&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't seem to see any mention of vanity callsigns on the website indicated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to file vanity callsign applications online, and if so, how?&lt;/p&gt;&#xA;" OwnerUserId="9799" LastActivityDate="2020-05-04T12:37:04.827" Title="How do I apply for a vanity callsign online?" Tags="&lt;united-states&gt;&lt;fcc&gt;&lt;callsign&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7808" PostTypeId="2" ParentId="7807" CreationDate="2017-06-22T22:59:25.750" Score="5" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://wireless2.fcc.gov/UlsEntry/licManager/login.jsp&quot; rel=&quot;nofollow noreferrer&quot;&gt;Go to the FCC login page.&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Enter FRN and password and click submit.&lt;/li&gt;&#xA;&lt;li&gt;Click &quot;My Licenses&quot; on the left.&lt;/li&gt;&#xA;&lt;li&gt;Click on your callsign in the list of licenses.&lt;/li&gt;&#xA;&lt;li&gt;Click &quot;Request Vanity Call Sign&quot; on the right.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Note: Steps 3 to 5 may not work unless you already have a callsign.&lt;/p&gt;&#xA;" OwnerUserId="9799" LastEditorUserId="10859" LastEditDate="2020-05-04T12:37:04.827" LastActivityDate="2020-05-04T12:37:04.827" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="7809" PostTypeId="1" AcceptedAnswerId="7811" CreationDate="2017-06-22T23:42:36.313" Score="4" ViewCount="236" Body="&lt;p&gt;I'm thinking of building an HF transmitter for data (AX.25 or PSK31). Rather than using an IF stage, I'm thinking of generating the RF frequencies (or phases) directly with a Direct Digital Synthesis chip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The chip I'm thinking of is the &lt;a href=&quot;http://www.analog.com/media/en/technical-documentation/data-sheets/AD9834.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Analog Devices AD9834&lt;/a&gt;. It can output a 0 - 37.5MHz sine wave (that covers most of the HF bands). It picks one of two programmed frequencies based on a digital input (high--one frequency, low--the other frequency). Thus, I can get 2FSK out of it. I can do the same thing with another digital input and two programmed phases for PSK. The output power is 20 mW, so I'll need to hook it up to a power amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've never heard of anyone building a digital transmitter this way. Usually an intermediate stage is involved. Is there something I'm missing?&lt;/p&gt;&#xA;" OwnerUserId="5820" LastEditorUserId="76" LastEditDate="2017-06-23T00:04:26.407" LastActivityDate="2017-06-23T14:35:13.603" Title="Is using a DDS chip directly a viable way to transmit 2FSK and PSK on HF?" Tags="&lt;digital-modes&gt;&lt;hf&gt;&lt;electronics&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7810" PostTypeId="2" ParentId="7809" CreationDate="2017-06-23T00:17:53.727" Score="3" Body="&lt;p&gt;You could probably build a DDS exciter from this chip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be aware though that output power is closer to 1.8 mW. You were quoting the total chip power consumption. To get to any reasonable power level, it will require cascaded amplifiers. You will most likely want to think about an filtering as part of the amplification chain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally, an LO (local oscillator) is used when the DDS cannot make the frequency range necessary for the output signal. In this case, mixing the DDS output frequency with another frequency preserves the modulation scheme while allowing a higher frequency of operation. This is in contrast to using a harmonic of the DDS where the modulation scheme can be affected by the frequency multiplication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case, the DDS has sufficient range over the HF band that you should not require an LO or multiplier module in your architecture. Have fun with the project!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-06-23T14:35:13.603" LastActivityDate="2017-06-23T14:35:13.603" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7811" PostTypeId="2" ParentId="7809" CreationDate="2017-06-23T01:07:04.037" Score="2" Body="&lt;p&gt;Your question is directly answered on page 23:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;One of the areas where the AD9834 is suitable is in modulation&#xA;  applications. The part can be used to perform simple modulation&#xA;  such as FSK. More complex modulation schemes such as GMSK&#xA;  and QPSK can also be implemented using the AD9834.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There's no need for an LO and a mixer if the AD9834 can generate a sufficiently high frequency on its own. Many HF SDRs have a similar architecture, with a high-speed DAC directly generating the RF. You may need some filtering before amplification.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-06-23T10:56:00.517" LastActivityDate="2017-06-23T10:56:00.517" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7815" PostTypeId="2" ParentId="7784" CreationDate="2017-06-23T15:39:46.077" Score="2" Body="&lt;p&gt;If your interest is simply to increase range, the metrics to watch on the tool are the &quot;Link Budget&quot; and the &quot;Receiver Sensitivity&quot; (lower right screen). These two numbers will change in concert. You want to look at any settings that increase the link budget. These will create a corresponding increase (more negative) in Receiver Sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if you change the bandwidth from 500 kHz to 250 kHz you will see a corresponding increase in link budget and receiver sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not all settings will affect the link budget but those that do, you should examine to see if they will fit your application requirements.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-06-23T15:39:46.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7816" PostTypeId="2" ParentId="5679" CreationDate="2017-06-24T02:45:15.847" Score="1" Body="&lt;p&gt;An old question but for the sake of a viable answer, the PyEphem library contains all the needed functionality to perform this calculation on a realtime basis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See my description &lt;a href=&quot;https://ham.stackexchange.com/q/7763/9493&quot;&gt;here&lt;/a&gt; on StackExchange.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-06-24T02:45:15.847" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7817" PostTypeId="1" AcceptedAnswerId="7818" CreationDate="2017-06-24T02:54:43.683" Score="4" ViewCount="730" Body="&lt;p&gt;I am doing a project where I will be re-purposing an old TV satellite dish as a directional Wi-Fi antenna. The dish is circular in shape, not oval.  The dish has an arm coming from the bottom that makes a 90 degree angle with the dish. I will be adding a second arm to the end of the dish's arm that will allow me to mount an SMA antenna connected with RG-59 cable precisely where it will utilize the dish's geometry. &lt;strong&gt;I need to figure out the proper position of the antenna on the dish.&lt;/strong&gt; I want the dish to receive signal directionally where there is a zero signal elevation angle.  From my previous understanding, dishes receive their signal from space where there is an angle of elevation from the transmitter and the receiver part of the dish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I created a diagram that illustrates my plan with dimensions and calculations.&#xA;&lt;strong&gt;I need some verification with my diagram and suggestions on how to maximize the reception strength.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think that the antennae should be placed somewhere along line C in the diagram but I want to be sure before I start modifying the dish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xcDea.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xcDea.png&quot; alt=&quot;Diagram&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I've calculated the focal point on the dish to be approximately 320 mm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PS:I just realized that the 75 ohm impedance of the RG-59 cable is not optimal for the Wi-Fi adapter.  I only need about 6 inches of cable so I will try it with and without the jumper cable and compare signal levels.&lt;/p&gt;&#xA;" OwnerUserId="9896" LastEditorUserId="9896" LastEditDate="2017-06-24T05:48:11.697" LastActivityDate="2020-02-01T03:43:16.160" Title="Satelite dish modified for Wi-Fi (Signal Elevation Question)" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7818" PostTypeId="2" ParentId="7817" CreationDate="2017-06-24T03:14:24.883" Score="2" Body="&lt;p&gt;Unfortunately, your drawing is not correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To find the focal point of a symmetric parabola, measure the diameter of the open rim of the dish, call this D. Measure the depth of the dish at its center, call this c.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Calculate the focal point distance from the bottom of the dish as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ f = \frac{D^2}{16c} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the focal point is in the center of the dish, it is not offset as in your drawing. So your receive antenna will slightly shadow aperture of the dish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the physical aperture of your receive antenna, you may need to adjust it in or out from the focal point in order to fully illuminate the dipole or other element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the dish is an asymmetric parabola, the focal point will be offset from the center in order to avoid blocking the aperture. This is the type of parabola that nearly all modern home satellite dishes use. They are identified by an LNA support arm that extends from the bottom of the dish and the dish apparent elevation angle appears to be lower than the satellite capture elevation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of an asymmetric dish, the existing LNA arm should be used as a starting point to find the appropriate focal point for the dipole or other antenna element since the focal point is largely frequency independent.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-06-24T11:30:42.567" LastActivityDate="2017-06-24T11:30:42.567" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7819" PostTypeId="2" ParentId="7817" CreationDate="2017-06-24T07:50:32.110" Score="1" Body="&lt;p&gt;Please post a photo of the dish. Ku band satellite TV dishes are always offset feed, whatever their shape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The direction of firing is roughly along the feed arm. The dish is &quot;minimally offset&quot; (my term) to avoid feed blockage but not much more. So if you draw a line from the bottom edge of the dish, over the feed, that's about the direction. When aimed at the horizon, the dish will look like it's pointing about 30 degrees down towards the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've made many feeds for 2.4 and 5.8 GHz, using a three element Yagi. They work very well, you get about 50% efficiency from the dish. A patch antenna might also work, or a short CanTenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unless you have some fancy test gear, the absolute best plan is to use the original feed arm and LNB holder. Then you only have one axis to optimise, the in-out position of the feed.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2017-06-24T07:55:42.620" LastActivityDate="2017-06-24T07:55:42.620" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7821" PostTypeId="2" ParentId="7065" CreationDate="2017-06-25T03:04:50.970" Score="2" Body="&lt;p&gt;The question has not been answered and although somewhat dated, I thought I would provide some feedback.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A balun can affect all four scattering parameters. The transformation ratio, the feed characteristic impedance, and the complex load impedance all play a role. It must also be acknowledged that most real world baluns do not perform a linear translation for all complex impedances. This non linearity is difficult to effectively model. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding the &quot;beam pattern&quot;, perhaps better described as directivity, can be affected by the balun if the balun effectively prevents common mode currents on the feedline. But to see this effect, the model would need to anticipate radiation (or pickup) by the feedline. This is rarely the case unless the engineer has taken care to build this possibility into the model.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-06-25T03:04:50.970" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7822" PostTypeId="2" ParentId="428" CreationDate="2017-06-25T19:55:34.003" Score="2" Body="&lt;p&gt;Re: &quot;Finally, many transceivers will cause distortions in the JT-65 waveform when run at above a quarter to a half of their maximum power. Transceivers are meant to work with analog data, not the sharp frequency transitions of the digital signal.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;K1JT has purposefully tailored the audio output of his software so it has none of the effects mentioned above. The &quot;data&quot; signal is an analogue signal with no such &quot;sharp transitions&quot;. As only one tone is present at any time, there can be no intermodulation. In addition, since there is no AM component to the JT65 signal, the linearity of subsequent RF amplifiers is not critical. It is not necessary to de-rate output powers for the sake of linearity as is needed in PSK modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Re:&quot;As you stated, JT-65 is a weak signal mode. This should not be confused with a low power mode.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Absolutely agreed!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are no &quot;low power&quot; modes. Even WSPR will allow me to enter a power of 1kW. Not that I would ever do that but in this &quot;low power mode&quot;, its not the low power that is important. It is the fact that the power level is known and can be taken into account when assessing results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frank, g0gsr&lt;/p&gt;&#xA;" OwnerUserId="9901" LastEditorUserId="9901" LastEditDate="2017-06-25T20:12:38.523" LastActivityDate="2017-06-25T20:12:38.523" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7823" PostTypeId="1" CreationDate="2017-06-25T23:35:14.333" Score="3" ViewCount="806" Body="&lt;p&gt;My house has a corrugated metallic roof. 2500 sq. ft. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The roof is grounded via couple cables. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's your comment on using the roof as the ground for a short center-loaded vertical 80M antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks&#xA;David Hart&#xA;VE6AQF, V21C&lt;/p&gt;&#xA;" OwnerUserId="9902" LastEditorUserId="8832" LastEditDate="2017-06-26T03:17:54.843" LastActivityDate="2017-06-26T03:17:54.843" Title="Corrugated Metallic Roof used as a ground-plane for short loaded vertical?" Tags="&lt;vertical-antenna&gt;&lt;short-antenna&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7824" PostTypeId="2" ParentId="7823" CreationDate="2017-06-26T00:27:36.410" Score="3" Body="&lt;p&gt;basically: large metal plates work great as ground plane, even if not connected to earth (if large enough).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now &quot;large&quot; in &quot;large metal plate&quot; depends on the wavelength – and from the geometry of the problem stems the fact that a ground plane should be at least about one quarter of the wavelength in radius. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case, that's 80/4 m = 20m radius, or 40m across. 2500 ft² is, best case, 50 ft × 50 ft, and that's smaller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, not all is lost, because of course you still have the actual ground as ground plane, but modeling that gets much harder. For example, you'll often find that in Northern Germany, radio broadcast antennas are preferrably placed on slightly moist ground – because that increases the conductivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Luckily, field density is highest close to the antenna, so your roof will have a strong positive effect. I'm afraid that's all I can say, lacking explicit experience with such antenna systems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding corrugation: Shouldn't matter, structure size is much much smaller than wavelength, but the altered path the currents in the metal take might make for an interesting delay – might electrically look a bit as if the roof was curved downwards orthogonal to the corrugation, but ever so slightly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's probably much more interesting how well the connections/overlap between the sheet metal elements of your roof are electrically connected.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-06-26T00:27:36.410" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7825" PostTypeId="1" CreationDate="2017-06-26T08:32:28.410" Score="1" ViewCount="180" Body="&lt;p&gt;I'm planning to use a ESP8266 WiFi module with inbuilt antenna to test a concept. I plan to put it inside a wall mounted switch board/power outlet board.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Will the electrical wires seriously affect wireless signal performance?&lt;/li&gt;&#xA;&lt;li&gt;Will the signal transmit properly from inside the wall board?&lt;/li&gt;&#xA;&lt;li&gt;Is it true that the inner case of the wall enclosure being of metal&#xA;(most cases), it will reflect the radio waves? (act like a radio&#xA;speaker enclosure)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Any solutions?&lt;/p&gt;&#xA;" OwnerUserId="9906" LastEditorUserId="4076" LastEditDate="2017-06-26T08:45:51.417" LastActivityDate="2017-06-26T08:52:56.877" Title="Will very close proximity to electrical wires affect radio signals?" Tags="&lt;rfi&gt;&lt;wifi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7826" PostTypeId="2" ParentId="7825" CreationDate="2017-06-26T08:52:56.877" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Will the electrical wires seriously affect wireless signal performance?&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, electrical conductors within the near field of an antenna will actually become part of the antenna and change its properties, and here, for the worse (since the small on-PCB antenna is designed for ISM band operation, whereas the combined antenna is not).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 2.4 GHz, wavelength is $\frac cf = \frac{3\cdot10^8\,\frac{\text m}{\text s}}{2.4\cdot10^9\,\text s^{⁻1}} = 12.5\,\text{cm}$, so make sure that in the main lobe of the (intentional) antenna, there's no conductors within a couple of times that distance.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Will the signal transmit properly from inside the wall board?&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Impossible to tell without knowing the geometry. Note that the developers of such small integrated transceiver systems go through great lengths to design their systems so that they do not interfere with the integrated antennas – you'll find smartphone antennas as very peculiar elements at special places in a phone's encasing, for example, and that's a significant cost driver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you get these things wrong: Remember the ridicule Apple got when they brought out an iPhone generation that you needed to hold at a very strange angle from your head to get reception when having a phone call?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Is it true that the inner case of the wall enclosure being of metal&#xA;  (most cases), it will reflect the radio waves? (act like a radio&#xA;  speaker enclosure)&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A proper metal cage won't let much RF energy through. So, a metal enclosing is definitely nothing you want to put your antenna in.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-06-26T08:52:56.877" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7827" PostTypeId="2" ParentId="7728" CreationDate="2017-06-26T20:25:28.017" Score="2" Body="&lt;p&gt;&quot;it might be European television broadcasting. What is your location?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the spectrum, it's neither video or DAB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looks like a spurious or other radiation from a nearby source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frank&lt;/p&gt;&#xA;" OwnerUserId="9901" LastActivityDate="2017-06-26T20:25:28.017" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7828" PostTypeId="1" AcceptedAnswerId="7829" CreationDate="2017-06-27T10:22:37.877" Score="11" ViewCount="666" Body="&lt;p&gt;Last weekend we tuned a quad loop for 80 m and 40 m. Instead of cropping, we folded the isolated wire using cable ties as shown in the picture below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/shxd7.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/shxd7.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After folding several quite large sections of the wire, we got the SWR under 1.2, so this approach seems to work. However, I do not understand the theoretical background, because the wire itself has still the same length and because it is isolated there is no electrical contact and the current has to flow over the same distance. Of course, this approach has an influence on the radiation pattern, but I do not see the direct influence on the resonance.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Why does this have an influence on the standing wave?&lt;/li&gt;&#xA;&lt;li&gt;Is the result equivalent to cropping a section of the same length? Can we now just remove the excessive part and solder the wire directly and get the same result?&lt;/li&gt;&#xA;&lt;li&gt;Are there any disadvantages of folding instead of cropping, e.g. a lower radiation efficiency?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5573" LastActivityDate="2017-06-27T14:08:27.237" Title="Tuning a wire antenna by folding" Tags="&lt;wire-antenna&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7829" PostTypeId="2" ParentId="7828" CreationDate="2017-06-27T14:08:27.237" Score="10" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Why does this have an influence on the standing wave?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Although there is no electrical connection between the folded sections at DC, that analysis neglects effects that are relevant at RF. Imagine a voltage step initiated at the feedpoint. It's important to consider not just the voltage at some point on the wire, but the fields &lt;em&gt;around&lt;/em&gt; the wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's assume this is a dipole: as a positive voltage step is propagating down one half, a negative voltage step is propagating down the other half. &lt;em&gt;Between&lt;/em&gt; these halves is a changing electrical field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, this voltage step will be accompanied with some change to current as well, and associated with this current is a magnetic field around the wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the wavefront in the field reaches the folded section, the folded back section of the antenna isn't really &quot;isolated&quot; from the rest of the antenna. Indeed, the insulation provides no DC connectivity between the sections, but each wire in the folded section is within these electric and magnetic fields. Through laws like &lt;a href=&quot;https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction&quot; rel=&quot;noreferrer&quot;&gt;Faraday's law of induction&lt;/a&gt;, and more generally &lt;a href=&quot;https://en.wikipedia.org/wiki/Maxwell%27s_equations&quot; rel=&quot;noreferrer&quot;&gt;Maxwell's equations&lt;/a&gt;, these fields mean the components of the folded section interact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a simpler case, consider a capacitor. A capacitor is two plates, separated by an insulator. At DC they are isolated, but in any circuit where current or voltage is changing, the interaction of the plates through the electric field becomes relevant.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is the result equivalent to cropping a section of the same length? Can we now just remove the excessive part and solder the wire directly and get the same result?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not exactly. Because the wires in the folded section are near each other and thus tightly coupled through their mutual electric and magnetic fields, the wavefront can just propagate over the folded section at the speed of light.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, that folded section has a different impedance than a plain wire. You might consider each pair of wires a &lt;a href=&quot;https://en.wikipedia.org/wiki/Transmission_line&quot; rel=&quot;noreferrer&quot;&gt;transmission line&lt;/a&gt;, which might be open on one end, or shorted. In other words, a &lt;a href=&quot;https://en.wikipedia.org/wiki/Stub_(electronics)&quot; rel=&quot;noreferrer&quot;&gt;stub&lt;/a&gt;. The impedance of these stubs might be negligible, depending on the particular folding. But in no case is it strictly correct to say simply cropping the antenna is equivalent.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Are there any disadvantages of folding instead of cropping, e.g. a lower radiation efficiency?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's very difficult to say. You might look at loading coils and electrically shortened antennas for a more common case where this is a concern. As a very blunt guess, I'd say if the amount of folding is small relative to the overall size of the antenna, losses will be negligible.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-06-27T14:08:27.237" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7831" PostTypeId="1" CreationDate="2017-06-28T11:12:35.290" Score="3" ViewCount="1113" Body="&lt;p&gt;The ending song of an anime television series called &lt;em&gt;Le Eden de la Grisaia&lt;/em&gt; &lt;a href=&quot;https://www.youtube.com/watch?v=VgJwDeYnPYs&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; has a light flashing. I suspect it may be Morse Code. By watching the video a little more slowly than usual (frame by frame), it's easy to see that&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;dit is 2 frames&lt;/li&gt;&#xA;&lt;li&gt;dah is 6 frames&lt;/li&gt;&#xA;&lt;li&gt;intra-character gap is 2 frames&lt;/li&gt;&#xA;&lt;li&gt;gap between characters is 6 frames&lt;/li&gt;&#xA;&lt;li&gt;gap between words is 14 frames&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So it probably is Morse Code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've managed to translate it into letters. Here's my recording of the transmission. &lt;code&gt;-&lt;/code&gt; means the light is on. &lt;code&gt;&lt;/code&gt; means the light is off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the beginning:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;&lt;pre&gt;&lt;code&gt;--- - --- - --- --- - ---       --- - --- - --- --- - ---       --- --- -   -       -   --- - -   -   --- -&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Which is &quot;CQ CQ GE EDEN&quot;. Notice there is only 1 dit's time between &quot;C&quot; and &quot;Q&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And at around 1:25:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;&lt;pre&gt;&lt;code&gt;--- - -       --- - -&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Which is &quot;DD&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't used Morse Code before, so I don't know what these letters mean. What do they mean?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks to to a comment by Phil Frost. The TV show is Japanese. I looked up the Japanese equivalent of Morse Code, &lt;a href=&quot;https://en.wikipedia.org/wiki/Wabun_code&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wabun Code&lt;/a&gt;. If it's in Wabun Code, the transmission would be&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;リヘ&#xA;  ヘホヘタ&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;ホホ&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I don't know Japanese. So if anyone who sees this happens to know Japanese, please tell me whether the above makes any sense. Googling yielded no results.&lt;/p&gt;&#xA;" OwnerUserId="9915" LastEditorUserId="9915" LastEditDate="2017-06-29T02:39:43.487" LastActivityDate="2017-10-12T08:14:21.070" Title="What's this maybe-morse-code &quot;CQ CQ GE EDEN&quot; and &quot;DD&quot; in Le Eden de la Grisaia?" Tags="&lt;cw&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7832" PostTypeId="2" ParentId="7831" CreationDate="2017-06-28T11:20:47.897" Score="2" Body="&lt;p&gt;&lt;code&gt;CQ&lt;/code&gt; is common in amateur radio (not just morse) as a way to initiate communications. It basically means &quot;anyone who can hear this, please respond if you want to talk&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;GE&lt;/code&gt; could maybe be a typo of &lt;code&gt;DE&lt;/code&gt; (&lt;code&gt;-..&lt;/code&gt;), which is used in morse and text-based communications to mean &quot;this is&quot; or &quot;from&quot; and usually precedes the callsign of the person sending.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not sure about &lt;code&gt;DD&lt;/code&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9420" LastActivityDate="2017-06-28T11:20:47.897" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7834" PostTypeId="2" ParentId="7831" CreationDate="2017-06-28T21:26:27.583" Score="1" Body="&lt;p&gt;Perhaps &quot;GE&quot; means &quot;good evening&quot;!&lt;/p&gt;&#xA;" OwnerUserId="5252" LastActivityDate="2017-06-28T21:26:27.583" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7835" PostTypeId="2" ParentId="2459" CreationDate="2017-06-29T04:36:53.787" Score="3" Body="&lt;p&gt;As for regulations no changes are forthcoming, the new access to the upcoming new band privileges will bring rules related to them. However, I doubt they will be included in the newest study material since, as of yet, they do not yet have effective dates assigned. Awaiting US Government bureaucracy to complete its requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are the highlights of the newest changes:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The FCC on March 28 adopted rules that will allow secondary Amateur Radio access to 472-479 kHz (630 meters) and to 135.7-137.8 kHz (2,200 meters), with minor conditions.&lt;/li&gt;&#xA;&lt;li&gt;Amateurs operating on 472-479 kHz will be permitted a maximum equivalent isotropically radiated power (EIRP) of 5 W, except in parts of Alaska within 800 kilometers (approximately 496 miles) of Russia, where the maximum would be 1 W EIRP. [EIRP is the product of the power supplied to the antenna and the antenna gain in a given direction, relative to an isotropic antenna (absolute or isotropic gain). EIRP is equal to ERP multiplied by 1.64.]&lt;/li&gt;&#xA;&lt;li&gt;Amateurs operating in the 135.7-137.8 kHz band will be permitted to run up to 1 W EIRP.&lt;/li&gt;&#xA;&lt;li&gt;The FCC is requiring a 1-kilometer separation distance between radio amateurs using the two new bands and electric power transmission lines with PLC systems on those bands. Amateur Radio operators will have to notify the UTC of station location prior to commencing operations.The FCC Wireless Telecommunications Bureau will provide details on the notification process later, but ARRL is urging radio amateurs interested in operating on either band to register at the earliest opportunity, to avoid having to protect any “post-notification” PLCs.&lt;/li&gt;&#xA;&lt;li&gt;The FCC placed a 60-meter (approximately 197 feet) above-ground-level (AGL) height limit on transmitting antennas used on 630 meters and 2,200 meters.&lt;/li&gt;&#xA;&lt;li&gt;The bands would be available to General class and higher licensees, and permissible modes would include CW, RTTY, data, phone, and image. Automatically controlled stations would be permitted to operate in the bands.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8606" LastActivityDate="2017-06-29T04:36:53.787" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7836" PostTypeId="1" AcceptedAnswerId="7838" CreationDate="2017-06-29T11:16:11.423" Score="1" ViewCount="633" Body="&lt;p&gt;I want to build (not purchase) a wide bandwidth power combiner.&lt;br&gt;&#xA;It should combine signals from 2 TFD antennas cut for 15 MHz lower frequency and &lt;strong&gt;used for receive only&lt;/strong&gt;. Upper frequency is 30 MHz so desired bandwidth is 15 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each antenna has its own balun and the output coax cables are 50 ohm. Output from the combiner must be 50 ohm as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I remember a design based on a toroid transformer and I would like to:&lt;br&gt;&#xA;- get the circuit schematic of this design&lt;br&gt;&#xA;- get the formula to calculate the inductance and turns to wind on a T 50-6 toroid that I already have  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mario&lt;/p&gt;&#xA;" OwnerUserId="6019" LastActivityDate="2017-06-29T15:59:58.287" Title="Wide bandwidth HF power combiner schematic and formula" Tags="&lt;wire-antenna&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="7837" PostTypeId="2" ParentId="7831" CreationDate="2017-06-29T13:48:26.933" Score="1" Body="&lt;p&gt;&quot;CQ CQ &lt;em&gt;D&lt;/em&gt;E EDEN&quot; would make perfect sense, meaning &quot;This is Eden calling anyone.&quot; Though I'm not sure why a submarine would flash that on a signal lamp while submerged. &quot;&lt;em&gt;G&lt;/em&gt;E EDEN&quot; must be a mistake.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've no idea what &quot;DD&quot; at the end means. It could be Wabun code. Or it could be someone's initials or similar of significance to the show's creators. Or perhaps an obscure reference to something in the show. Or, another mistake.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-06-29T13:48:26.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7838" PostTypeId="2" ParentId="7836" CreationDate="2017-06-29T15:59:58.287" Score="1" Body="&lt;p&gt;You're probably thinking of a &lt;a href=&quot;https://en.wikipedia.org/wiki/Hybrid_coil#Single_transformer_hybrid&quot; rel=&quot;nofollow noreferrer&quot;&gt;single transformer hybrid&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/EyxYT.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fEyxYT.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resistor should be half the system impedance, so 25Ω for a 50Ω system. I'll assume a 50Ω system for the rest of the description.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P1 sees the loads on P2 and P3 in series. If we assume all loads are 50Ω, P2 and P3 in series are 100Ω. Setting the turns ratio with 10 on the P1 side and 14 with a center tap on the other side (with a center tap) makes makes a 1:2 step-down transformer (because $10^2 / 14^2 \approx 1/2$). Thus, P1 sees a matched 50Ω.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P2 sees the matched load at P1 but through a 1:2 step-down transformer (25Ω) in series with another (25Ω) to see a net 50Ω matched load. Thus, signal from P2 is equally divided between being across P1 and the resistor. P3 sees this voltage across the resistor, but it also sees the voltage across P1 in antiphase. These two cancel such that a signal applied at P2 does not appear at P3.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cost of this isolation is a loss of half the signal power from P2 or P3. For a receive application this may be negligible provided the receiver noise floor is significantly below the (additionally attenuated) received RF noise floor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Absent a datasheet, I usually look at &lt;a href=&quot;http://toroids.info/T50-6.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;torroids.info&lt;/a&gt; for data, or find a solution empirically.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-06-29T15:59:58.287" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7841" PostTypeId="2" ParentId="7807" CreationDate="2017-06-30T03:27:09.827" Score="2" Body="&lt;p&gt;Optionally there are other ways to apply for a vanity call. You could use one of the licensing services like W5YI, ARRL etc. for a fee though I would not recommend that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obtain a copy of the FCC 605 form from any VEC or even grab it online, fill it in and snail mail it. There no longer is a fee to obtain a vanity call.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Word of note: Might want to verify the call you are looking to grab is available. Check QRZ.com first (although not always 100% accurate as they can be a few days behind the updating from the FCC) to see if it is available. 1x2 and 2x1 calls are near impossible to get due to the long waiting list (only available to Extra Class license holders). 1x1 calls are strictly for Special Event stations with short term authorization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would strongly recommend you have at least 2-3 vanity calls you would consider in case the most preferred one is not available and place them on the 605 form in the order of preference. If you only place one call request on the form and it is not available or gets assigned prior to your application, then no new call will be issued.&lt;/p&gt;&#xA;" OwnerUserId="8606" LastActivityDate="2017-06-30T03:27:09.827" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7842" PostTypeId="2" ParentId="7756" CreationDate="2017-06-30T03:34:40.520" Score="1" Body="&lt;p&gt;To disable Repeater AutoShift turn the power off. Press and hold both the VFO and REV keys while turning power on. Do this again to turn Autoshift back on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manual makes mention of using the SHIFT key to override the autoshift but I am not sure how this works. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have multiples of this radio and have never had the occasion to need to use a non-standard repeater shift on 6m. No 6m repeaters near me so cannot test. This does however work on the VHF/UHF. In my experience California seems to be the most likely place where repeater shifts are non-standard but having said that, anyone can change repeater shifts.&lt;/p&gt;&#xA;" OwnerUserId="8606" LastEditorUserId="8606" LastEditDate="2017-06-30T03:54:28.463" LastActivityDate="2017-06-30T03:54:28.463" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7845" PostTypeId="2" ParentId="1859" CreationDate="2017-06-30T19:51:38.707" Score="0" Body="&lt;p&gt;&quot;...I want to use an end-fed wire antenna, but what would be the best length of wire for the 20m and 40m bands? Is there a way to work this out? This is assuming a tuner will be used...&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using a tuner, the best length NOT to use is a quarter wavelength, or odd multiples (3/4, 5/4, etc.)  The best length is a half wavelength, or even multiples (1/2, 1, 3/2 etc.).  Of course, that may be hard to get the best wavelength on one band and not the worst length on another band.  My advice is to use a wire that is between 1/2 and 3/4 wavelength on the lowest band (40 meters here).  Say, 12 meters long. &#xA;To Mike and SDSolar - the point is that quarter wavelength wires may exhibit just what you mentioned - an impedance that is out of the range of your tuner. &lt;/p&gt;&#xA;" OwnerUserId="8647" LastEditorUserId="8647" LastEditDate="2017-07-10T17:10:56.003" LastActivityDate="2017-07-10T17:10:56.003" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7846" PostTypeId="1" CreationDate="2017-07-01T17:57:33.633" Score="2" ViewCount="118" Body="&lt;p&gt;There are a number of frequencies, where a certain type of signal can be heard. The characteristics is, that every occurrence takes about 2.5k bandwidth, and it is transmitted in a continuous way. Specific is as well, that it looks like a rather broad carrier, and sounds the same in AM or L/USB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See the following screenshot of a SDR, where you can observer them three times around 8300 khz:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/YyYXC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YyYXC.png&quot; alt=&quot;SDR Screenshot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An audio example of it is at the following link (WAV, ca. 150k, ca. 5 sec): &lt;a href=&quot;https://drive.google.com/file/d/0B4ecO4IudzvrOVRUX242MkQtbFU/view?usp=sharing&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://drive.google.com/file/d/0B4ecO4IudzvrOVRUX242MkQtbFU/view?usp=sharing&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question: What is it? As it is constantly transmitted I suspect it could be a weather radar. Can anyone state what it actually is?&lt;/p&gt;&#xA;" OwnerUserId="9932" LastEditorUserId="76" LastEditDate="2017-07-31T19:42:15.147" LastActivityDate="2017-08-01T01:32:37.280" Title="Signal on various frequencies, about 2.5k bandwidth, sounds like a broken motor turning: What is it?" Tags="&lt;hf&gt;&lt;signal-identification&gt;&lt;swl&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7847" PostTypeId="1" AcceptedAnswerId="7871" CreationDate="2017-07-01T19:03:34.593" Score="2" ViewCount="1713" Body="&lt;p&gt;At first glance this appears to be a simple ground plane but there is far more going on.  The ham who built this back in the '80s is now SK and I can't find anything else like this anywhere.  The radials are 19&quot; in length, as is the vertical radiator.  The copper vertical element is 60&quot; tall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The shield of the coax is wrapped around and soldered to the copper element and the center conductor is soldered to the 19&quot; element that is suspended in the PVC insulators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ideas on what exactly is going on here?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edited to add:&#xA;I've tested this on both 2 meter and 440 and get SWRs no higher than 1.5:1 on either band with 440 being slightly better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the antenna mounted at 15' high, I am full-quieting into 2 meter and 440 repeaters 12 miles distant on 5 watts.  I did not test for directionality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When originally in use, it was mounted in an attic.  It was never meant to be in the weather for any length of time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CMtuA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CMtuA.jpg&quot; alt=&quot;The antenna&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/9R1aR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9R1aR.jpg&quot; alt=&quot;Bottom&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/rcDbK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rcDbK.jpg&quot; alt=&quot;Bottom&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/O3qjb.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O3qjb.jpg&quot; alt=&quot;Underside&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/HGfRo.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HGfRo.jpg&quot; alt=&quot;Radiator&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/D5znI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/D5znI.jpg&quot; alt=&quot;Connection&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2017-07-01T21:56:58.337" LastActivityDate="2021-01-15T00:27:38.207" Title="What kind of 2 meter antenna is this?" Tags="&lt;antenna&gt;" AnswerCount="8" CommentCount="15" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7848" PostTypeId="2" ParentId="7846" CreationDate="2017-07-01T19:08:21.900" Score="5" Body="&lt;p&gt;These are data transmissions using &lt;a href=&quot;https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing&quot; rel=&quot;nofollow noreferrer&quot;&gt;OFDM&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are government or military point to point data links. I would expect that the data would be encrypted.&lt;/p&gt;&#xA;" OwnerUserId="9901" LastEditorUserId="218" LastEditDate="2017-08-01T01:32:37.280" LastActivityDate="2017-08-01T01:32:37.280" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7849" PostTypeId="1" AcceptedAnswerId="7852" CreationDate="2017-07-02T14:41:02.897" Score="4" ViewCount="1331" Body="&lt;p&gt;I'm considering building multi-turn wire loop receive antennas for a &lt;a href=&quot;http://blitzortung.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;blitzortung.org&lt;/a&gt; lightning detection receiver. It has three separate channels for H-field antennas, operating simultaneously. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically, only two orthogonal loops in vertical planes are made and co-located, e.g like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dI5MY.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dI5MY.jpg&quot; alt=&quot;two orthogonal multi-turn wire loops in vertical planes, from skywarn-slm.at&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having enough real estate available this time, I wonder if there could be any advantage in placing loops several meters apart. Aren't directional nulls suffering from the close neighbour - other loop? (&lt;em&gt;possibly&lt;/em&gt; resulting in a poorer SNR for the given loop, if a near noise source would be otherwise in a deeper directional null)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Same question applies for adding a &lt;a href=&quot;https://i.stack.imgur.com/tz20I.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;third, horizontal loop&lt;/a&gt;. Are there any advantages in not using the same mechanical frame? When co-locating, is there anything about the feeder routing to consider? (extremely: one could route the feeder of horizontal loop in question right along the side of a vertical loop).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/tz20I.png&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I saw &lt;a href=&quot;https://i.stack.imgur.com/qHyjE.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;three colocated orthogonal loops elsewhere&lt;/a&gt;, but that was quite a different application. There, only one of loops is connected to the receiver, others are open-circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/qHyjE.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And lastly, would same considerations (from the answers to come) apply if &lt;a href=&quot;https://ham.stackexchange.com/questions/899/what-does-the-addition-of-a-shield-to-a-small-loop-accomplish&quot;&gt;shielded loops&lt;/a&gt; are used?&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Mobius loop:&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0T2tW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0T2tW.jpg&quot; alt=&quot;Mobius loop&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9934" LastEditorUserId="8717" LastEditDate="2017-08-30T23:34:33.100" LastActivityDate="2020-07-07T22:55:45.303" Title="Colocated three orthogonal wire loops for lightning detection network" Tags="&lt;antenna-theory&gt;&lt;lightning&gt;&lt;small-loop&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7850" PostTypeId="2" ParentId="7849" CreationDate="2017-07-02T18:26:10.343" Score="1" Body="&lt;p&gt;A third, horizontal loop, will give you an antenna which is horizontally polarized and omnidirectional in azmith, with nulls in the up and down directions. Would this benefit a direction finder?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I wonder if there could be any advantage in placing loops several meters apart. Aren't directional nulls suffering from the close neighbour - other loop? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I wouldn't think so. Since the fields of each are orthogonal they have no effect on each other. Adding a third loop is just as orthogonal as the other two. Just rotate it 90 degrees and it's essentially the same thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind also that if the antennas are a significant fraction of wavelength apart, the phase difference between them will make a directional antenna array. If the objective is detecting lightning strikes in any direction, this would not be productive.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;When co-locating, is there anything about the feeder routing to consider?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I think antenna modeling or empirical testing is the best way to answer this. I'd guess putting chokes on all the feeders would be good practice to minimize their influence.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And lastly, would same considerations (from the answers to come) apply if shielded loops are used?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&quot;Shielded loop&quot; is a horrible name. It's really just a loop antenna made from a tube, with the feeder inside it. The hollow antenna means the feedline is invisible to the external fields, and thus it provides a solution to the problem of feeding a balanced loop with an unbalanced feedline. In effect, it's a balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, a shielded loop might give a solution to the problem you'd otherwise have in feeding three orthogonal loops in a way that's radially symmetrical in azimuth. The feeder for the horizontal loop could run inside one of the vertical loops and thus be invisible as far as the operation of the antenna is concerned.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-07-02T18:26:10.343" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7851" PostTypeId="2" ParentId="7847" CreationDate="2017-07-02T18:48:26.650" Score="2" Body="&lt;p&gt;It looks like a homebrew job, so it's possible it's just some random design thrown together without much validation. Modelling or measuring the antenna in operation would provide definitive answers, but I'll make some guesses at what's going on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a vertical with a stub. The stub off the side is to give it a resonance on two bands. I bet it's connected at one end, but not the other? It's effectively a transmission line in series with the vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on the wavelength the stub will transform the open at one end to some other impedance. With the proper selection of length and placement, it can make the upper section of the antenna a relatively high impedance only at some frequencies while having negligible impact at others, similar to how L-C traps work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See the &lt;a href=&quot;http://www.hy-gain.com/Product.php?productid=AV-18HT&quot; rel=&quot;nofollow noreferrer&quot;&gt;AV18-HT&lt;/a&gt; for a multi-band HF vertical using a similar technique.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's interesting that the feed is not at the end of the antenna. I've never seen that done just like this, but I would think it has the same effect as &lt;a href=&quot;https://ham.stackexchange.com/q/95/218&quot;&gt;feeding a dipole off-center&lt;/a&gt;: it simply raises the feedpoint impedance. I'd bet between the intrinsically lower impedance of a monopole (35 ohms in free space) and the stub, the impedance at the base is too low, so moving the feedpoint up obtains a better match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radials serve the same function as on any other monopole: to make a virtual ground plane and provide a low impedance to common-mode currents.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-07-02T23:40:24.910" LastActivityDate="2017-07-02T23:40:24.910" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7852" PostTypeId="2" ParentId="7849" CreationDate="2017-07-03T12:34:18.523" Score="2" Body="&lt;p&gt;The lightning detection antennas are not used in any sense to triangulate or to direction find through any other method such as phasing. The three antennas are there simply to provide quasi 360° detection of lightning events. The actual direction finding is accomplished by analyzing the timing of detected lightning events from multiple sites using GPS time stamping and calculating time of fight by comparing data from multiple stations. In other words, if there was only one receive site in North America, no direction finding could be done for that region. In fact, it is acceptable to have a station with just one antenna - it simply may not be as sensitive to lightning events from certain directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With this as the background, feel free to spread out your loops if that works for you. Many people don't have that luxury which is why they have the creative colocated loops.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;Blue&quot; receiver version, the latest, has differential preamps so do not use any type of balun between the antenna and the preamp. You could place a wound coax/toroid type balun on the feedline to the receiver but keep in mind that you are dealing with very low frequencies so the typical amateur radio designs will not work well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The shielded loop antenna is not the type that hides the feedline. They are using the split shield design to form a so called H field antenna (which has nothing to do with receiving only the H field!). If you decide to use such an antenna, follow their construction notes. They are sloppy on the description of where the break in the shield should be. I would recommend it be placed exactly in the center of the circumference in order to provide an optimum differential feed.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-07-03T14:48:20.297" LastActivityDate="2017-07-03T14:48:20.297" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="7853" PostTypeId="1" CreationDate="2017-07-03T15:53:52.873" Score="1" ViewCount="141" Body="&lt;p&gt;For the past few months, I've been experiencing an odd random sound on my new computer (as well as 2 other PCs I've tested). It seems to occur only when the internet is connected. I have changed ISPs, bought a new router, and changed service from DSL to cable - but the exact sound continues. I've painstakingly ruled out all hardware or Windows causes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've recorded the sound. Here's the link: &lt;a href=&quot;https://soundcloud.com/finvarra/nuc-sound-2&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://soundcloud.com/finvarra/nuc-sound-2&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realize I'm grasping at straws, but... does anyone recognize this sound - and could it possibly be caused by a ham radio in the neighborhood? Thanks...&lt;/p&gt;&#xA;" OwnerUserId="9939" LastEditorUserId="76" LastEditDate="2017-07-03T22:38:56.543" LastActivityDate="2017-07-06T12:58:29.643" Title="Random Phantom Sound On Computer - Could it be from ham radio?" Tags="&lt;rfi&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="7854" PostTypeId="2" ParentId="7853" CreationDate="2017-07-03T16:17:21.353" Score="0" Body="&lt;p&gt;&lt;strong&gt;It is almost certainly not caused by amateur radio or CB.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I've seen cell phones sitting next to computer speakers that caused odd noises to come from the speakers. It took us a long time to figure that one out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any CB, amateur, or other antennas nearby? The only thing that I can think of that would be related to radio is a sound effect device that some CBers put on their radio. It makes a brief sound at the beginning of every transmission. And there's also &lt;em&gt;roger beep&lt;/em&gt; that occurs at the end. Both are usually far louder than the voice, and can drive the radio into saturation and generate harmonics.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-07-03T22:41:12.380" LastActivityDate="2017-07-03T22:41:12.380" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7855" PostTypeId="1" AcceptedAnswerId="7859" CreationDate="2017-07-03T17:56:40.547" Score="1" ViewCount="191" Body="&lt;p&gt;I was wondering if it is possible to control an RC car using my phone to emit the signals to control it without any external device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After a quick google search it seems like it is not possible. So if it is not possible, could someone explain to me why that is not possible?&lt;/p&gt;&#xA;" OwnerUserId="9940" LastEditorUserId="76" LastEditDate="2017-07-03T22:23:44.887" LastActivityDate="2017-07-03T22:38:36.287" Title="Connect RC car to Phone" Tags="&lt;radio-control&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7856" PostTypeId="2" ParentId="7855" CreationDate="2017-07-03T18:09:37.163" Score="1" Body="&lt;p&gt;An RC car likely operates on different frequencies than a phone. &#xA;Having said that, &lt;a href=&quot;https://www.google.com/search?newwindow=1&amp;amp;safe=active&amp;amp;site=&amp;amp;source=hp&amp;amp;q=rc+car+app&quot; rel=&quot;nofollow noreferrer&quot;&gt;Google RC car app&lt;/a&gt;. It appears there are a few.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-07-03T18:09:37.163" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7858" PostTypeId="2" ParentId="7853" CreationDate="2017-07-03T22:18:49.957" Score="0" Body="&lt;p&gt;I can't think of any feasible way that sound would be due to a radio transmission of any kind. Although &lt;em&gt;strong&lt;/em&gt; RF fields can interfere with audio electronics, they would not sound like that. Try setting a cell phone on some cheap computer speakers, for example. Anything digital (most things in modern times) would sound like noise. For AM stations you might hear the music, voice, or whatever's being transmitted, but it's usually garbled. I doubt any station is transmitting the &quot;beep-boop&quot; you are hearing and nothing else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more likely explanation is some software or some feature on your computer you don't realize you have.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-07-04T02:03:52.250" LastActivityDate="2017-07-04T02:03:52.250" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7859" PostTypeId="2" ParentId="7855" CreationDate="2017-07-03T22:38:36.287" Score="3" Body="&lt;p&gt;If your RC car used a Bluetooth radio to control it (I'm sure there are some out there), then obviously it &lt;em&gt;is&lt;/em&gt; possible and does not require any modification, just the right app on your Bluetooth-supporting phone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I'm assuming your question is about the traditional sort of RC car with a dedicated transmitter/controller, and about the &lt;em&gt;general&lt;/em&gt; reasons it &lt;em&gt;probably won't work&lt;/em&gt;. There are several problems at different levels, but it all comes down to &lt;em&gt;the two ends are too different&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Frequency.&lt;/strong&gt; Radio transmissions are at different frequencies both as a fundamental fact of physics (you have to pick one) and to avoid interfering with each other (pick one that someone else isn't using).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many physical/electronic factors making any radio more or less specifically built for a given range of frequencies &amp;mdash; the antenna, local oscillator, and filters (if any) are all built for that range and will operate poorly or not at all outside of it. Some radios are designed to work across a very wide frequency range (&quot;general coverage&quot; receivers, research/hobby SDRs, etc.) but as a result of this they have worse performance at any given narrower range. And for cell phones, the radio performance &amp;mdash; whether you have usable service or not in a given location &amp;mdash; is a key selling point.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Firmware and modulation.&lt;/strong&gt; The radio chips in your phone are not completely general-purpose SDR radios &amp;mdash; they are designed to &quot;speak&quot; a particular radio protocol (GSM, CDMA, Bluetooth, WiFi, etc.). The specific design allows them to be much more energy-efficient (longer battery life for your phone), but means that they (most likely) cannot be told to switch to the frequency your RC car expects to receive, or to send the format (modulation, protocol) of control signal it expects.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Software.&lt;/strong&gt; This is the least fundamental of the issues, but still one of them. Even if your phone's radio hardware could be &quot;convinced&quot; to do what you're looking for, you would have to have some way for your application to take control of the radio hardware. Generally, a phone operating system does not have a provision for this, and if it did there would need to be a feature for it also in the driver provided by the radio chipset's maker.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;There are also legal/regulatory issues with being able to program a radio to do something different. In most countries, devices containing radio transmitters which are sold to the general public are required to operate in specific expected ways (specific frequencies, maximum power limits, obeying various more specific rules) and be &lt;em&gt;unable&lt;/em&gt; to be reconfigured readily to send arbitrary radio signals.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-07-03T22:38:36.287" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7860" PostTypeId="1" AcceptedAnswerId="7865" CreationDate="2017-07-04T02:03:47.800" Score="1" ViewCount="309" Body="&lt;p&gt;I am wondering whether shortwave can be used as an effective distress call for a hiker who is a non-ham operator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More specifically,&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Are non-certified operators permitted to broadcast distress calls on particular parts of the spectrum?&lt;/li&gt;&#xA;&lt;li&gt;Are there user-friendly transmitters available in the US retail market that could be used for this purpose, ideally weighing &amp;lt;3kg?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Please let me know if this is a duplicate question or a bad idea.&lt;/p&gt;&#xA;" OwnerUserId="9946" LastEditorUserId="4076" LastEditDate="2017-07-04T10:54:48.120" LastActivityDate="2017-07-04T19:51:14.473" Title="Easy way for an uncertified hiker to broadcast a distress signal" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;electronics&gt;&lt;emergency&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="7861" PostTypeId="2" ParentId="7860" CreationDate="2017-07-04T02:28:04.437" Score="2" Body="&lt;p&gt;I think the term you are looking for is unlicensed rather than uncertified/non-certified.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are no provisions to use ham radio frequencies if you are not a licensee. You could use CB frequencies although this is not a guaranteed method of communications when in remote areas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps a satellite based device like &lt;a href=&quot;https://www.findmespot.com/en/?cid=100&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Spot Gen3&lt;/a&gt; would meet your requirements. No license required and ensured communications.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-07-04T02:28:04.437" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7862" PostTypeId="2" ParentId="7860" CreationDate="2017-07-04T02:51:34.023" Score="2" Body="&lt;p&gt;In case of an actual emergency, you can of course do anything you want. If it's truly a matter of communicating with somebody or else dying of exposure or being eaten by bears, then you can use absolutely any means necessary to make yourself heard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course if you are intending to carry amateur radio equipment with you when you go hiking in the wild, that equipment would be a lot more useful to you if you &lt;em&gt;did&lt;/em&gt; have an amateur radio licence. For a start you would have a good idea of standard operating procedures, but additionally you might have the ability to send an SOS in Morse code, and to pass your coordinates on to anyone who might answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have no interest in the technology of radio, or in the amateur radio community, then I would advise that your best bet would be to carry a satellite phone with you, as it will also work anywhere in the world. And can be used to call the emergency services directly. Chances are the equipment would be lighter than a short-wave transceiver plus antennas, it would be easier to set up and would work just like a regular phone.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-07-04T02:51:34.023" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7863" PostTypeId="1" AcceptedAnswerId="7864" CreationDate="2017-07-04T19:30:04.310" Score="2" ViewCount="298" Body="&lt;p&gt;I was recently given an older, but really nice broadcast FM receiver (88-108Mhz) by neighbor, but I am confused by the antenna connector and labeling.  for the FM antenna connection, there are two spring lock jacks, and it is clearly labeled 75Ω, but every other reference I can find out on the interwebs refers to 75Ω being a coax antenna, and being sub-optimal for FM.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can get a 300Ω dipole, and a 75Ω/300Ω balun adaptor, but all the adapters go to coax.  Can I cut a chunk of Coax, plug one end into the balun, and on the other  end stirp the insulation, plug the shield in one clip, and the conductor in the other on the receiver?  Is there a better option (DIY or commercial)?  Range is not a huge issue, I have plenty of FM options close to home.&lt;/p&gt;&#xA;" OwnerUserId="9952" LastActivityDate="2017-07-04T20:37:54.170" Title="75Ω Wire FM antenna" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7864" PostTypeId="2" ParentId="7863" CreationDate="2017-07-04T19:46:24.827" Score="5" Body="&lt;p&gt;In general, impedance mismatches are not very important for receiving. Unlike a transmitter, you cannot damage a receiver with a mismatch. You miss some of the signal power that you could have gotten, but this is likely to be completely insignificant compared to e.g. the positioning and design of the antenna itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Get the 300 &amp;Omega; specified antenna and just wire it in. It'll be fine. Or you can try using an impedance transformer as you proposed and see if it makes a difference, if you don't mind the price of the parts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best explanation I can think of for them specifying 75 &amp;Omega; for a wire-terminal antenna input is that they used a receiver module designed for a 75 &amp;Omega; input but didn't bother with the expense of a coaxial connector on the back. In which case, they're expecting you to just string a piece of wire from the antenna terminal, which will make a perfectly fine receiving antenna (just like one of those telescoping rod antennas) while having a fairly unpredictable impedance.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-07-04T20:37:54.170" LastActivityDate="2017-07-04T20:37:54.170" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7865" PostTypeId="2" ParentId="7860" CreationDate="2017-07-04T19:51:14.473" Score="6" Body="&lt;p&gt;If you are in mortal peril, use any means necessary to make your situation known and get help. It doesn't matter if you are licensed or not. Consider the alternative.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But a shortwave transmitter is not especially effective. Among the many issues:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A relatively high transmit power is required, meaning heavy batteries.&lt;/li&gt;&#xA;&lt;li&gt;Effective antennas are large.&lt;/li&gt;&#xA;&lt;li&gt;Propagation is unreliable.&lt;/li&gt;&#xA;&lt;li&gt;Requires some degree of training to operate.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you are looking for a radio to buy, you want a &lt;a href=&quot;http://www.sarsat.noaa.gov/emerbcns.html&quot; rel=&quot;noreferrer&quot;&gt;personal locator beacon&lt;/a&gt; (PLB). These communicate on a designated distress frequency via satellite. Compared to a shortwave radio, these have advantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Pre-programmed to do exactly one thing. Consider your mental faculties may not be at their sharpest when you are a few hours from death. Or you may be incapacitated and relying on someone else to use it.&lt;/li&gt;&#xA;&lt;li&gt;Keeps working if you lose consciousness.&lt;/li&gt;&#xA;&lt;li&gt;No ambiguity in what the transmission means.&lt;/li&gt;&#xA;&lt;li&gt;Nearly global coverage, provided you have a view of the sky.&lt;/li&gt;&#xA;&lt;li&gt;Transmits your precise location. Locating a shortwave transmitter is also possible, but more difficult and less precise.&lt;/li&gt;&#xA;&lt;li&gt;More rugged. Especially important considering half the circumstances where you might need rescue involve physical trauma, extreme temperatures, or submersion in water.&lt;/li&gt;&#xA;&lt;li&gt;Smaller.&lt;/li&gt;&#xA;&lt;li&gt;Lighter.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-07-04T19:51:14.473" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7866" PostTypeId="1" AcceptedAnswerId="7870" CreationDate="2017-07-04T20:19:16.463" Score="8" ViewCount="1083" Body="&lt;p&gt;My radio has an internal antenna tuner that can be activated to rapidly tune for the frequency in use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My antenna has a disgusting SWR for the band I want to use (as measured with an AA-54 antenna analyzer). When activating the internal antenna tuner, it reports multiple occurrences of &quot;Bad SWR&quot; (or something like that). I don't know what the radio does with that information i.e. maybe it refuses to transmit?!? (I'd have to look that up in the manual).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because of this &quot;Bad SWR&quot; report from the radio, I am fearful of burning out my radio by attempting to transmit on this problem band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I connected an external antenna tuner between the antenna feed and my radio, would/could the external tuner get the signal into &quot;the ballpark&quot; for a more tolerable SWR and then let the internal antenna tuner fine tune that ballpark SWR for a final SWR that would be acceptable to the radio? Or would it not be of any help?&lt;/p&gt;&#xA;" OwnerUserId="9953" LastEditorUserId="76" LastEditDate="2017-07-04T20:43:07.113" LastActivityDate="2019-04-09T21:48:49.620" Title="Two Antenna Tuners in Series" Tags="&lt;antenna-tuner&gt;" AnswerCount="4" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7867" PostTypeId="2" ParentId="7866" CreationDate="2017-07-04T21:27:24.523" Score="1" Body="&lt;p&gt;That won't hurt anything. Just watch your SWR. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I usually run an external tuner, and leave the one inside my transceiver off.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-07-04T23:39:18.863" LastActivityDate="2017-07-04T23:39:18.863" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7868" PostTypeId="2" ParentId="7866" CreationDate="2017-07-04T23:17:34.597" Score="2" Body="&lt;p&gt;Often internal tuners are automatic -- that is, they initiate a retune sequence when the SWR drifts too high, usually above some settable threshold or something like above 2:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are using an internal tuner with an external tuner (which is OK if done right) then you could have problems if the internal tuner is enabled for automatic mode.  What may happen is that as you adjust the external manual tuner, you may affect the SWR that the internal tuner sees and it will change automatically as a result.  This change though on the internal tuner can affect the external tuner as well.  It is even worse if the external tuner is also an automatic tuner.  Thus, internal tuners can battle with external tuners in an never ending war of attempting to get a good match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually, a tuner expects input side to be 50 ohms and therefore you should present a 50-ohm impedance to the external tuner by disabling your internal tuner.  This is the smart thing to do.  Life is simpler with only one tuner being active.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2017-07-04T23:36:02.403" LastActivityDate="2017-07-04T23:36:02.403" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7869" PostTypeId="2" ParentId="7847" CreationDate="2017-07-04T23:41:58.463" Score="2" Body="&lt;p&gt;Interesting. The ground plane and its quarter-wave up to the point where the center conductor is connected provides a high impedance point on the copper tube for currents downwards. The center conductor connects to a quarter-wave transmission line upwards. That part would not radiate, by causing the current on the copper tube and the quarter-wave element to become approximately equal and in anti-phase. The top section and the bottom section would radiate.&#xA;By proper selection of dimensions it might be possible to get the radiation from top and bottom in phase in which case one would have two stacked 0.25 wl&#xA;antennas with some gain above a simple GP antenna. I would be interested to know what simulations will show:-)&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-07-04T23:41:58.463" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7870" PostTypeId="2" ParentId="7866" CreationDate="2017-07-05T02:55:00.873" Score="5" Body="&lt;p&gt;A simple tuner might be just a capacitor and an inductor:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/eYtFl.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2feYtFl.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more flexibility, many tuners add a 2nd capacitor to make a pi network:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/74RcI.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f74RcI.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to have two such tuners:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/K1GIh.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fK1GIh.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, now you just have more elements which can be adjusted. There's nothing inherently wrong here. In fact it gives you additional tuning range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Internal tuners usually do not have much range, and it's likely with an external tuner you won't even need the internal tuner. You might consider simply disabling the internal tuner. Or if your external tuner is manual, you could adjust it for a good match at the middle of the band, then enable the internal tuner to compensate for the slight mismatch as you move within the band. If the external tuner is automatic, I can't really think of a reason you'd need both.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another possibility given your situation: skip the external tuner, and instead just pick some fixed component(s) to make a matching network. It's cheaper than buying an adjustable tuner if you don't already have one, in fact you can probably build it from scrap you already have. And you can then mount it outside at the antenna feedpoint to reduce feedline losses.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-07-05T03:01:50.147" LastActivityDate="2017-07-05T03:01:50.147" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7871" PostTypeId="2" ParentId="7847" CreationDate="2017-07-06T00:58:41.990" Score="4" Body="&lt;p&gt;I spent some more time modeling this antenna in &lt;a href=&quot;http://www.eznec.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC+ 5.0.67&lt;/a&gt;. The latest results are interesting. Below the text here are 5 images showing:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The current lobes on all the elements at 146 MHz&lt;/li&gt;&#xA;&lt;li&gt;The elevation pattern and gain for 146 MHz&lt;/li&gt;&#xA;&lt;li&gt;The current lobes on all the elements at 440 MHz&lt;/li&gt;&#xA;&lt;li&gt;The elevation pattern and gain for 440 MHz&lt;/li&gt;&#xA;&lt;li&gt;A screenshot showing the parameters that I entered into EZNEC, so you can use other antenna modeling software.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Although I don't have the feedline and source placed where they really ought to be, I believe that the patterns, current distributions along the various elements, and gains (dBi) shown for each band are close enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Note the low gain at low angles when the antenna is operated on 440 MHz&lt;/strong&gt;. The maximum gain occurs at 43 degrees! That's just too high if you're trying to access a distant station or repeater under minimal path conditions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The pattern and gain on 2 meters is pretty good; however, a much smaller 2m antenna would do about as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you'll notice, the distribution of the current lobes (shown in purple) along the elements do not seem quite right on either band. This is probably due to either:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;This model does not have the coax running from the feedpoint down through the middle of the lower section or&lt;/li&gt;&#xA;&lt;li&gt;The dimensions of the antenna are not quite optimized.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Also, if you run an auto SWR sweep in EZNEC, you'll find that the VSWR is rather high. Change the source and transmission line parameters, route the coax through a 'wire frame' representation of the lower pipe, and that ought to change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.eznec.com/autoezlink.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;AC6LA's AutoEZ plugin&lt;/a&gt; can --among other things-- optimize element lengths. However, whether it will work on this particular antenna design, I do not know &lt;em&gt;nor do I have the time to go much further than I have here&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If someone wants to continue where I left off, the EZNEC files I've been playing with are now uploaded to &lt;a href=&quot;http://www.w0btu.com/files/antenna/EZNEC/LanceSE-GP-vhf_uhf-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this directory on w0btu.com&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Having said all of this, I doubt if this is the best choice for a dual-band 2m/70cm antenna.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CqETc.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CqETc.gif&quot; alt=&quot;146 MHz azimuth plot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/HPWx6.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HPWx6.gif&quot; alt=&quot;146 MHz current distribution&quot;&gt;&lt;/a&gt;&#xA;&lt;hr&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/YPkGN.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YPkGN.gif&quot; alt=&quot;440 MHz azimuth plot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/o4vST.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/o4vST.gif&quot; alt=&quot;440 MHz current distribution&quot;&gt;&lt;/a&gt;&#xA;&lt;hr&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/icTJj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/icTJj.png&quot; alt=&quot;EZNEC parameters&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-07-06T00:58:41.990" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7873" PostTypeId="2" ParentId="7853" CreationDate="2017-07-06T12:58:29.643" Score="1" Body="&lt;p&gt;It sounds like a noise that would be made from a program running in the background. My first thought was Discord.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Diagnosing external sounds is easily done by muting the computer at the OS level, if the sound still continues, it is external to the PC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See what programs are running on both of the affected PC's, chances are they are running in the background and creating the noise.&lt;/p&gt;&#xA;" OwnerUserId="8716" LastActivityDate="2017-07-06T12:58:29.643" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7874" PostTypeId="1" CreationDate="2017-07-06T13:03:12.003" Score="3" ViewCount="180" Body="&lt;p&gt;I know the difference between AM and FM, but how does a receiver determine the carrier wave frequency, as the frequency edited during the modulating process?&lt;/p&gt;&#xA;" OwnerUserId="9961" LastActivityDate="2017-07-06T19:53:24.473" Title="FM carrier wave frequency determination" Tags="&lt;fm&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7875" PostTypeId="2" ParentId="7874" CreationDate="2017-07-06T19:53:24.473" Score="2" Body="&lt;p&gt;There are several ways.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One is &lt;em&gt;slope detection&lt;/em&gt;. By placing the carrier on the transition band of a filter, the filter's output amplitude is proportional to the frequency:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A higher frequency input moves closer to the passband, thus a higher amplitude output&lt;/li&gt;&#xA;&lt;li&gt;A lower frequency input moves closer to the stopband, thus a lower amplitude output&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Thus, a slope detector is effectively an FM to AM converter. The demodulator is completed by following the output of the filter with an AM detector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In digital implementations where the input samples are complex, the phase angle of each sample can be calculated. Then, the derivative of phase is frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;em&gt;phase-locked loop&lt;/em&gt; (PLL) is another implementation. The idea is to keep a variable-frequency oscillator synchronized in phase to the received signal. The phase of the signal and oscillator are compared, and this error signal adjusts the oscillator frequency to minimize the error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is just a small sampling: there are many other designs in use, especially in analog implementations which have a different set of rules for cost and complexity.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-07-06T19:53:24.473" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7876" PostTypeId="1" CreationDate="2017-07-07T17:15:52.383" Score="5" ViewCount="1031" Body="&lt;p&gt;I've been working on a 2m setup for hiking. My goal is to have the best possible antenna that can be used while walking, and that won't get damaged if I walk under a low branch or some other forest obstacle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The setup so far: Off the top of a backpack with a steel frame I mounted a Diamond SRH77CA whip. It is connected by a very short length of coax to the HT in a side pocket of the pack, and then I have a speaker/mic clipped to a shoulder strap:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/56iF5.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/56iF5.jpg&quot; alt=&quot;backpack with Diamond whip antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far, so good, and the whip has proved to be both rugged and stable in its mounting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to further improve the antenna's performance, I added a &quot;Tiger Tail&quot; counterpoise, following &lt;a href=&quot;http://www.hamuniverse.com/n6jsxEasy-HT_1.pdf&quot; rel=&quot;noreferrer&quot;&gt;the directions here&lt;/a&gt;. (There's more about the &lt;a href=&quot;https://wd8rif.com/pdf/ht_antennas.pdf&quot; rel=&quot;noreferrer&quot;&gt;theory behind that here&lt;/a&gt;.) It's a roughly 19&quot; wire, 14ga, hanging from the base of the antenna down the side of the frame pack. According to the theory, this &quot;transforms the 1⁄4-λ whip into a full-size center-fed 1⁄2-λ dipole&quot;. Yay for theory.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The PDF with the directions notes, &quot;The hardest part of using this Tail is getting the wire to hang straight,&quot; but with the backback frame right there, I anchored it down the side using small zip ties in a few spots, and it's running straight up and down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the question: is the steel frame of the pack possibly messing with the performance of the Tiger Tail? Does a counterpoise need to hang in free space to work properly? Or by providing a solid, well-defined counterpoise path with that wire, have I prevented the antenna from capacitively coupling to the steel in the frame?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you for your help, antenna wizards...&lt;/p&gt;&#xA;" OwnerUserId="5139" LastActivityDate="2019-06-14T18:19:06.197" Title="Tiger Tail + capacitive coupling... what's the interaction?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;mobile&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7877" PostTypeId="2" ParentId="7876" CreationDate="2017-07-07T17:26:47.683" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is the steel frame of the pack possibly messing with the performance of the Tiger Tail?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The frame is definitely interacting strongly with the antenna. With the tiger tail zip-tied to the frame you have something like a twin-lead transmission line made from the tiger tail and the frame tube, so you'll be exciting the backpack frame just as much as the tiger tail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether or not that's detrimental to performance is difficult to say. I'd say if you really want the best possible, set up a field strength meter and measure the radiated power from the antenna empirically. You might find the tiger tail doesn't improve performance significantly, since the frame is already a pretty good counterpoise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's not really a reasonable way to add a counterpoise to that setup that doesn't interact strongly with the backpack frame besides possibly mounting the whip over a ground plane such that the backpack is &quot;behind&quot; the ground plane. However, such a ground plane would be pretty cumbersome, and I'd estimate the performance improvement is negligible.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-07-07T17:26:47.683" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="7878" PostTypeId="2" ParentId="1836" CreationDate="2017-07-07T20:05:22.973" Score="1" Body="&lt;p&gt;&quot;...If I make a half wave dipole larger, its resonant frequency decreases...&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you can operate on odd multiples of half wave just like a half wave.  That is 3/2, 5/2, etc wave lengths, which will harmonically be resonant on the original frequency.  Or, in other words, an 80 meter antenna will be resonant also on 20 meters, and 5 meters.  3.5 Mhz, 14 Mhz, 56 Mhz, and so on.  Thus, the longer antenna will have a wider aperture.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will notice some directivity with the longer wire.    &lt;/p&gt;&#xA;" OwnerUserId="8647" LastActivityDate="2017-07-07T20:05:22.973" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7879" PostTypeId="2" ParentId="7847" CreationDate="2017-07-07T20:27:38.650" Score="0" Body="&lt;p&gt;It looks like a J-Pole to me, just with an added ground plane which may have been added to reduce coupling with the coax.&lt;/p&gt;&#xA;" OwnerUserId="9973" LastActivityDate="2017-07-07T20:27:38.650" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7880" PostTypeId="2" ParentId="7876" CreationDate="2017-07-07T22:17:29.867" Score="3" Body="&lt;p&gt;There is a good chance that in your original configuration, the coaxial shield acted as a sufficient counterpoise. This is essentially beneficial common mode current on the outside of the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Phil correctly points out, the coupling to the backpack frame throws doubt on any theoretical analysis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may in fact be more effective by deliberately using the frame as the counterpoise instead of an added counterpoise. Sorry, but &quot;tiger tail&quot; sounds so CBish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To do relative field strength measurements, simply involve a friend and a receiver with an S meter or other RSSI indicator. You cannot make applicable measurements by yourself without more complex remote monitoring capabilities as the presence of your body in the backpack will also influence the performance of your antenna system.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-07-07T22:17:29.867" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="7881" PostTypeId="1" AcceptedAnswerId="7885" CreationDate="2017-07-07T22:20:12.317" Score="0" ViewCount="240" Body="&lt;p&gt;How do cell phone filters filter out all the extraneous EM waves and noise (especially noise) when you get a call? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would expect a phone to have a bandpass filter to get rid of most noise but even then there is noise at still in the resulting signal.&lt;/p&gt;&#xA;" OwnerUserId="9975" LastEditorUserId="8832" LastEditDate="2017-07-08T20:14:50.670" LastActivityDate="2017-07-10T02:12:58.017" Title="Cell Phone Filter / Interference?" Tags="&lt;filter&gt;&lt;noise&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="7883" PostTypeId="5" CreationDate="2017-07-08T07:52:32.043" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2017-07-08T07:52:32.043" LastActivityDate="2017-07-08T07:52:32.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7884" PostTypeId="4" CreationDate="2017-07-08T07:52:32.043" Score="0" Body="Questions about noise in the sense of that inevitable component of any real signal. For questions about avoiding or eliminating interference from manmade sources, use [rfi] instead." OwnerUserId="-1" LastEditorUserId="76" LastEditDate="2017-07-09T17:31:36.277" LastActivityDate="2017-07-09T17:31:36.277" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="7885" PostTypeId="2" ParentId="7881" CreationDate="2017-07-08T14:16:43.397" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How do cell phone filters filter out all the extraneous EM waves and noise (especially noise) when you get a call?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Short answer: they don't. Of course, they use a bandpass filter to reject EM radiation outside the designated channel. But every radio does that. Modern cell phones also dynamically adjust their antennas so they are more sensitive in the direction of the cell tower, and less sensitive to other directions where there's only noise. But after that, there's still plenty of noise mixed with the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're wondering why you don't &lt;em&gt;hear&lt;/em&gt; the noise in the call, why it doesn't sound like a distant AM radio station in a thunderstorm, it's because the transmissions are digital. It's the same reason when you download an MP3 over WiFi it doesn't sound noisy. It's the same reason I can show you a number:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VmBQi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VmBQi.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And you see forty-two, not fcrtv-lwo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a point at which there's enough noise that the numbers can't be reliably decoded, and you do hear noise in the call. But it doesn't sound like static, because a wrong number in a digital audio doesn't sound like static. Because cell phones are used for voice, the digital coding is based on what voices sound like. The digital signal contains instructions for &lt;a href=&quot;https://en.wikipedia.org/wiki/Vocoder&quot; rel=&quot;nofollow noreferrer&quot;&gt;reproducing a human voice not unlike a human would do it&lt;/a&gt;. So when the bits are wrong, it doesn't sound like static: it sounds like a voice making nonsense sounds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the signal isn't great, a few of these errors slip in, but you don't notice them because you're paying attention to what's being said, not the audio quality. And, the codec is designed to make such things difficult to notice. For example, when a few bits of data are missing, the codec may continue making the same sound that it was making before the error to fill in the gap. Such things are difficult to notice unless you listen carefully.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When a lot of errors slip in, the phone just drops the call so you hear nothing at all.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-07-10T02:12:58.017" LastActivityDate="2017-07-10T02:12:58.017" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8885" PostTypeId="1" CreationDate="2017-07-08T18:50:10.023" Score="1" ViewCount="1080" Body="&lt;p&gt;The CB ground plane on my 43' fiberglass motorhome stinks. Has never worked correctly. If I install a piece of sheetmetal around the antenna on the roof would that help the ground plane at all? A flat piece maybe 3' x 3'?? I could screw it down but I think I would have to run a ground wire to a piece of metal near the awnings. Also the piece of sheet metal won't be under the antennae but even with it would that a make a difference?? I was going to drill a hole in the sheetmetal then lay it over and have antenna come through hole. Am I wasting my time??&lt;/p&gt;&#xA;" OwnerUserId="9978" LastActivityDate="2017-07-26T18:07:47.777" Title="CB Ground Plane on fiberglass RV" Tags="&lt;antenna&gt;&lt;citizens-band&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8886" PostTypeId="2" ParentId="8885" CreationDate="2017-07-08T22:19:09.783" Score="1" Body="&lt;p&gt;You can either install a solid ground plane or you can run 6 or more wires, 16 gauge or larger, like spokes away from the antenna. If you make the ground plane radius the same as the height of your antenna or a little longer, that should suffice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connect the ground plane in the center to the outer metal conductor of your vertical antenna. There is no need to attempt to connect the ground plane to any other metallic structure or to a real ground rod. It will work best with the one connection in the center, at the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you are all done, check the antenna with an SWR meter or an antenna analyzer. Anything less than 2:1 is fine.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-07-08T22:19:09.783" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8887" PostTypeId="1" CreationDate="2017-07-09T18:04:07.100" Score="2" ViewCount="1132" Body="&lt;p&gt;This is a sort of follow-on question from my &lt;a href=&quot;https://ham.stackexchange.com/questions/7866/two-antenna-tuners-in-series&quot;&gt;tuners in series&lt;/a&gt; question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem I am ultimately trying to solve is this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using a manufactured end-fed, half-wave 40m antenna. The manufacturer claims a certain SWR at several frequencies and I am trying to get my &lt;strong&gt;actual&lt;/strong&gt; SWR &lt;strong&gt;closer&lt;/strong&gt; to what the manufacturer claims is possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realize that my conditions won't match the manufacturer's conditions but if I can receive some overall, general guidance on what I can/should do, it would be very much appreciated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is horizontal, approximately 19 feet above ground, fed by a 100 foot RG-58X feedline. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see from this spreadsheet, my SWR is consistently higher &lt;em&gt;(with one very odd exception in the 12m band!)&lt;/em&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manufacturer used a RigExpert AA-30 for SWR readings, I used a RigExpert AA-54.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;(The 2.85 SWR I measured was drifting between 2.8 and 2.9 so I used the average value).&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W3ztA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W3ztA.png&quot; alt=&quot;Chart of my SWR vs. the manufacturer&amp;#39;s SWR&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9953" LastActivityDate="2018-08-14T18:56:24.917" Title="SWR, overall, is too high" Tags="&lt;antenna&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8888" PostTypeId="2" ParentId="8887" CreationDate="2017-07-09T23:36:58.133" Score="3" Body="&lt;p&gt;End feed antennas present a very unique challenge when it comes to comparing results and metrics. Despite a lot of erroneous information on the web, an end feed antenna requires a counterpoise of some type.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do not provide a very purposeful counterpoise of sufficient length, the antenna will use the shield of your coax as the counterpoise regardless of any unun, balun, or choke that has been installed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider how many different ways one can place the coax in an antenna installation. Some hang it in the air, some run it partially on the ground, some bury it, some run it next to gutters, some coil it up, some use long lengths of  coax, some use short lengths of coax, etc. But in all of these cases, the coax is part of the radiating and receiving antenna. It should come as no surprise then when one installation cannot duplicate that of another!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And then even if you provide a purposeful counterpoise, how many of these are of unspecified length and run out onto the ground from varying heights? Again, no basis for comparison.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should work on optimizing your installation. In general, more height is better. Experiment with a good choking balun on your coax and a purposeful counterpoise of various lengths in various orientations. With end feds, it is primarily a cut and try process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And one final thought. If your coax is part of the radiating antenna, inserting an SWR bridge or antennalyzer will actually change the tuning of the antenna slightly. It can be a very frustrating cat and mouse game.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-07-10T00:09:11.483" LastActivityDate="2017-07-10T00:09:11.483" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8889" PostTypeId="2" ParentId="1034" CreationDate="2017-07-10T01:15:19.797" Score="3" Body="&lt;p&gt;I disagree with part of the answer given by VU2NHW:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In your case, the issue &amp;amp; onus lies upon the manufacturer of the equipment experiencing interference.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is not what the FCC regulations say (assuming we are talking about US jurisdiction). Part 15 clearly puts the issue in the hands of the consumer. The only recourse the consumer has with the manufacturer is through tort law, not federal regulations. However, the consumer can use part 15 to help qualify them as an aggrieved party to allow tort proceedings if the consumer chooses to pursue this course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also case law that reasonably blocks a neighbor ftom attempting tort actions against the ham. This may not stop a filing necessarily, but it should normally bring the matter to a swift and favorable conclusion for the ham.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In these situations of neighbor complaints, the ham is advised to make sure their signal is clean (spectrum analyzer screen shots) and that they have conducted and logged any necessary RF exposure assessments. Keeping a basic log showing the time going on and off the air, the band, mode, and output power is also helpful. If the FCC then makes an inquiry, the ham can show sound due diligence and will be exonerated by the FCC. The FCC will then send a brochure and letter to the consumer advising them that the ham is operating legally and the problem is with the consumer's electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We all want to be good neighbors and help them with their interference problems. But before getting out your toroids and tools, carefully consider the litigious conditions that surround us and weigh this in your decision as to what course of action you will take.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Computer speakers are notorious for being affected by nearby EM energy. The most effective remediation is the application of toroid cores on the speaker and power leads to the speaker boxes. Depending on the length of the wires, a toroid on each end of the wire may be warranted. Toroid cores of type 31 material are generally the most effective. Get large enough cores to allow connectors to pass through the hole in the center. Make multiple turns of cable on each core as the EM choking goes up as the number of turns squared.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-07-10T14:57:26.570" LastActivityDate="2017-07-10T14:57:26.570" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8890" PostTypeId="2" ParentId="8887" CreationDate="2017-07-11T19:58:02.480" Score="2" Body="&lt;p&gt;As Glenn says, common-mode current may be an issue. So, a first step would be seeing where the currents are going: &lt;a href=&quot;https://ham.stackexchange.com/questions/1271/how-to-detect-common-mode-currents-or-rf-in-the-shack&quot;&gt;How to detect common-mode currents or “RF in the shack”?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more mundane explanation: the antenna is simply out of tune. Plotting SWR over frequency you should be able to determine if the antenna is simply too long or too short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd also note that 19 feet up for a 40 meter antenna is not very high. See how &lt;a href=&quot;https://ham.stackexchange.com/q/5470/218&quot;&gt;antenna height determines the radiation pattern&lt;/a&gt;. Besides the negative impact to antenna efficiency, that proximity to the ground will perturb the fields around the antenna, which could explain the discrepancy with the manufacturer's numbers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, it's entirely possible the antenna is just bad. Plenty of bad designs out there, and plenty of people selling them. Don't be so quick to assume the manufacturer is infallible.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-07-11T19:58:02.480" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8891" PostTypeId="2" ParentId="5498" CreationDate="2017-07-14T01:40:11.220" Score="2" Body="&lt;p&gt;General walkie-talkie radios are illegal in Japan. Even so in my military days there we used to use the ones on base in our cars when we traveled. They were not visible and we used head sets while driving. That being said we never got caught. At that time I did not even know they were not legal. Amateur is huge in Japan. I talk to people via echolink often. One fellow lives in Okinawa but was born and raised not far from where I was stationed. I catch him on a Hiroshima repeater just west of the city. He often talks to truck drivers who are licensed in Japan and they use mobiles in their rigs. But then they are doing it all legal. So without an amateur license, you run the risk of being busted. My recommendation is that  you stick to cell phones. If you happen to get out of cell range for some reason, a radio back up would be nice but if you get caught, you pay the price. In Japan that could be very costly. Play by the rules and be safe.&lt;/p&gt;&#xA;" OwnerUserId="9999" LastActivityDate="2017-07-14T01:40:11.220" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8892" PostTypeId="2" ParentId="6041" CreationDate="2017-07-14T17:14:18.207" Score="0" Body="&lt;p&gt;Whether or not you should loop up the excess or not depends on both the type of coax &lt;strong&gt;and the band&lt;/strong&gt;, &lt;em&gt;neither of which we know (yet)&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's VHF or above, then looping up the extra 40' of coax &lt;em&gt;vs. cutting off the excess&lt;/em&gt; might cause enough extra loss to deteriorate the signal to the point where you have trouble hearing and/or being heard.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-17T18:32:41.420" LastActivityDate="2019-04-17T18:32:41.420" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="8894" PostTypeId="2" ParentId="146" CreationDate="2017-07-16T01:58:48.003" Score="2" Body="&lt;p&gt;There are useful tidbits in all the answers so far.  Here are a couple more.  Not every ham has the good fortune to have conveniently spaced tall trees to hang horizontal antennas from.  On 80 meters to function well, a dipole antenna would be about 130 feet long (a half wave). Distance above ground for optimal performance would be the same distance.  Probably not practical for most hams.  The situation improves the higher in frequency you go--i.e 40 meters where the half wave length is about 66 feet with the corresponding reduction in optimal height.  I guess what I'm saying is that, on 80 put up a dipole and get it as high as you can.  It will still work at lower heights--just not as well.  A vertical on 80 is also probably also impractical (unless you use &quot;tricks&quot; which will limit it's performance) since the vertical radiator would need to be a quarter wavelength long (66 feet) and many, many ground radials which would also be about that long.  Commercially produced multi-band verticals make rather fantastic claims as to their performance. They tend to be poor performers when compared to a full sized horizontal antenna.  They're also outrageously expensive.  You can homebrew a dipole for far less than $50.00.  &lt;/p&gt;&#xA;" OwnerUserId="10006" LastActivityDate="2017-07-16T01:58:48.003" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8895" PostTypeId="2" ParentId="146" CreationDate="2017-07-16T02:24:35.203" Score="-1" Body="&lt;h2&gt;Horizontal.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;However, one of the exceptions is 160 meters.&lt;/strong&gt; If you are mostly interested on making longer distance QSOs (especially DX) contacts on 160, vertical polarization is best on that band. &lt;em&gt;Period&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w0btu.com/160_meters.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Check out this page&lt;/a&gt;. In a nutshell: What is effective on 160m are vertically-polarized antennas for transmitting, using separate antennas for receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Per W8JI on qrz.com:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Nearly all especially successful stations on 160 use a vertically polarized antenna of some type for transmitting. That's just a fact.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;The fact is....... an Inverted L with 20 or more radials at least 50 feet and hopefully 100 feet long will absolutely smoke any normal height loop antenna or dipole antenna at nearly any distance on 160 meters. The possible exception is between 20 and 200 miles.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;I have a full size 160 dipole at 300 feet, and it is never really much better than a 1/4 wave vertical at any distance in any direction. As a matter of fact, the dipole is 10-20 dB weaker than the vertical off the dipole ends. The dipole only beats the vertical broadside to the dipole, and then only rarely!! And this is with the dipole 300 feet above ground.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;As a matter of fact a low full wave loop has no gain, any horizontal wire has increased earth induced loss as it is made longer when close to earth.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://forums.qrz.com/showthread.php?t=260716&amp;amp;highlight=beverage&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://forums.qrz.com/showthread.php?t=260716&amp;amp;highlight=beverage&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nRjE2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nRjE2.png&quot; alt=&quot;Chart from ON4UN&amp;#39;s Low Band Dxing,published by the ARRL&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Having said that about 160 meters...&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;On 80 through 10, both vertical &lt;strong&gt;and horizontal&lt;/strong&gt; antennas can be good choices. You should pick whichever is convenient to erect and/or will accomplish your objective.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-08-04T18:42:15.993" LastActivityDate="2017-08-04T18:42:15.993" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8896" PostTypeId="1" CreationDate="2017-07-16T13:03:28.097" Score="1" ViewCount="72" Body="&lt;p&gt;I'm trying to listen to the CPU freq's my PC produces (kinda similar to what was done here: &lt;a href=&quot;https://github.com/fulldecent/system-bus-radio&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/fulldecent/system-bus-radio&lt;/a&gt;) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do see a clear signal that comes from the CPU (I know that because I can control it by reading memory blocks), however the distance it transmits to is very short (~20 cm).&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is there anything I can do to see the signal from a greater distance?&lt;/li&gt;&#xA;&lt;li&gt;Does it depend on the antenna ? (will a longer antenna produce better results)&lt;/li&gt;&#xA;&lt;li&gt;Does the shape of the antenna makes a difference ? (should the wire be folded into a circle or is it better as a long straight wire)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm using a random wire antenna (~60 cm long made into a circle)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dominant signal is  at ~300KHz - 450Khz and I'm using SDRPlay2&lt;/p&gt;&#xA;" OwnerUserId="10007" LastActivityDate="2017-07-17T02:55:57.713" Title="Receiving medium - low frequency CPU signal" Tags="&lt;antenna&gt;&lt;mf&gt;&lt;lf&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8897" PostTypeId="1" CreationDate="2017-07-16T17:25:24.037" Score="4" ViewCount="239" Body="&lt;p&gt;The July 14, 2017 NASA Spaceflight article &lt;a href=&quot;https://www.nasaspaceflight.com/2017/07/soyuz-2-1a-launches-kanopus-v-ik-70-satellites/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Soyuz 2-1A launches with Kanopus-V-IK and over 70 satellites&lt;/a&gt; says:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Mayak is a three-unit CubeSat which was built by Tvoii Sektor Kosmosa – or “Your Sector of Space” – an independent, crowd-funded team of engineers in conjunction with the Moscow State University of Mechanical Engineering. Mayak – meaning Lighthouse – will deploy a highly reflective tetrahedral structure.&lt;/p&gt;&#xA;&lt;p&gt;Each side of this structure has an area of four square meters, or 43 square feet. To ground observers, the satellite is expected to have an apparent magnitude of up to -10, making it one of the brightest objects in the night sky. The structure will double as a deorbit mechanism, hastening the decay of the satellite’s orbit.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;While the satellite itself is a &lt;a href=&quot;https://en.wikipedia.org/wiki/CubeSat&quot; rel=&quot;nofollow noreferrer&quot;&gt;3U cubesat&lt;/a&gt; with nominal dimensions of 10x10x30 centimeters, once the reflector is deployed the relatively flat reflecting surfaces are sizeable - each face is 4 square meters.&lt;/p&gt;&#xA;&lt;p&gt;The reflector material seems to be a &lt;a href=&quot;http://space.skyrocket.de/doc_sdat/mayak.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;metallized polymer film&lt;/a&gt;, so it may have some significant UHF reflectivity. The metal could be &lt;em&gt;extremely thin&lt;/em&gt; meaning less than 1 micron (1E-06 meters) and so the &lt;a href=&quot;https://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin depth&lt;/a&gt; may be an issue. So far I have not found many helpful sources of technical information on the project in English - the cubesat project has been carried out in Russia. &lt;a href=&quot;http://cosmomayak.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;This web site&lt;/a&gt; can switch between English and Russian but so far I can't get to many details there.&lt;/p&gt;&#xA;&lt;p&gt;There are several issues that might make this difficult. If the satellite does not have any extraordinary orientation control, it may end up random, and possibly rotating at some unknown speed. The sides will certainly not be perfectly flat. The rotation and uneven surface could be beneficial as it is more likely to &lt;em&gt;occasionally&lt;/em&gt; reflect at least &lt;em&gt;some radiation&lt;/em&gt; from a given pair of transmit and receive sites.&lt;/p&gt;&#xA;&lt;p&gt;The orbit would not be as stable or regular as other amateur satellites, and in LEO (low Earth orbit) it will be moving fairly fast.&lt;/p&gt;&#xA;&lt;p&gt;So I'm wondering if an Earth-Satellite-Earth bounce of an amateur signal of any kind might be possible and worth an attempt, and how problematic the issues I've mentioned or probably several I haven't thought of yet might be.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PJEf7.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PJEf7.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;above:&lt;/strong&gt; Mayak Reflector – Photo: CosmoMayak, From &lt;a href=&quot;http://spaceflight101.com/soyuz-kanopus-v-ik/mayak/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Spaceflight 101&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WkIbo.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WkIbo.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;above:&lt;/strong&gt; Mayak Artists conception, From &lt;a href=&quot;https://www.nasaspaceflight.com/2017/07/soyuz-2-1a-launches-kanopus-v-ik-70-satellites/&quot; rel=&quot;nofollow noreferrer&quot;&gt;NASA Spaceflight&lt;/a&gt;&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;As a historic reference, I am reminded a bit of the first ever Earth-Satellite-Earth bounce research with &lt;a href=&quot;https://en.wikipedia.org/wiki/Project_Echo&quot; rel=&quot;nofollow noreferrer&quot;&gt;Project Echo&lt;/a&gt; in the 1960's.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/van78.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/van78.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;above:&lt;/strong&gt; Echo-1 Satellite, test inflation before launch; &lt;code&gt;NSSDCA/COSPAR ID: 1960-009A, satnum 00049&lt;/code&gt;, for scale, those are people at the bottom. From &lt;a href=&quot;https://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1960-009A&quot; rel=&quot;nofollow noreferrer&quot;&gt;NASA&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8643" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-07-17T13:15:26.580" Title="Could UHF Earth-Satellite-Earth bouncing of signals off of this large metallized foil satellite be feasible?" Tags="&lt;uhf&gt;&lt;satellites&gt;&lt;reflector&gt;" AnswerCount="1" CommentCount="11" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8898" PostTypeId="2" ParentId="8885" CreationDate="2017-07-16T21:05:38.357" Score="1" Body="&lt;p&gt;Same problem with my coach.  Tried a lot of things with no good SWR results until I tried an approach like described above.  The first thing discovered is that there is some length of a wire (away from the air conditioner) that produces the best match. Once that length was found, I just taped it down to the fiberglass roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Soon it became clear that the signal was stronger in that direction (in my case, forward)and about half as loud in the opposite direction (rear).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I now know that two wires in opposite directions makes the signal about the same in all directions. More wires make no detectable difference. The only trick for tuning is that the wires need to be the same length and bit shorter than one wire to get that perfect SWR.&lt;/p&gt;&#xA;" OwnerUserId="8229" LastActivityDate="2017-07-16T21:05:38.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8899" PostTypeId="1" CreationDate="2017-07-16T22:25:32.340" Score="1" ViewCount="8326" Body="&lt;p&gt;I recently went on a ride with my local police department. I heard two beeps at the start of their transmission, and a static-ey sound at the end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use the BaoFeng UV-5R+, and was wondering if there was a way to turn on those sounds when I transmit?&lt;/p&gt;&#xA;" OwnerUserId="10013" LastEditorUserId="8717" LastEditDate="2017-07-17T00:33:59.993" LastActivityDate="2019-01-16T17:48:43.650" Title="How to make a BaoFeng start/end transmission with sound" Tags="&lt;baofeng&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8901" PostTypeId="2" ParentId="8885" CreationDate="2017-07-17T01:16:27.290" Score="1" Body="&lt;p&gt;Buy another RV! No kidding - I have a 23-ft mobile traveler that has aluminum 'shell' that is fantastic for a ground plane (the antenna does better here than in the yard with ground radials!!!). Picked up Australian station at 3AM from Kennesaw, GA one night/morning on my Yaesu 100D and a 75-ft butternut 40/75-meter vertical. The shell is a natural ground plane, no radials needed. The aluminum shell also protects operator inside from radiation....&lt;/p&gt;&#xA;" OwnerUserId="10015" LastEditorUserId="10015" LastEditDate="2017-07-17T19:15:50.137" LastActivityDate="2017-07-17T19:15:50.137" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8902" PostTypeId="2" ParentId="8896" CreationDate="2017-07-17T02:55:57.713" Score="2" Body="&lt;p&gt;In general, the length and shape of an antenna has a profound effect on the amount of power the antenna makes available to the receiver. Matching the impedance of the antenna system to that of the receiver ensures that the receiver can take advantage of the power that the antenna system delivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the low frequencies in which you are interested, I would consider a multi turn antenna on a ferrite rod core. You may have some success by extracting one from a discarded AM broadcast receiver. The impedance of this antenna will likely not match that of your SDR receiver but it may prove adequate for your needs. You could also purchase a ferrite rod and wind your own.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could measure the antenna impedance with an antenna analyzer and construct a simple matching circuit if needed. Your local ham radio club would likely make an antenna analyzer available to you. If you then need help with the matching circuit, just post back a new question on this site.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-07-17T02:55:57.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8903" PostTypeId="2" ParentId="8899" CreationDate="2017-07-17T03:01:14.770" Score="2" Body="&lt;p&gt;The double beep that you heard is probably from a trunking radio system or a repeater. As such, you cannot emulate this sound with your radio.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-07-17T03:01:14.770" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8904" PostTypeId="2" ParentId="8897" CreationDate="2017-07-17T03:36:39.683" Score="4" Body="&lt;p&gt;Given the large physical aperture of the passive reflector, I would say this presents an excellent opportunity for ESE bounces at VHF and UHF frequencies provided they maintain proper orientation of the reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the reflecting material is very thin aluminum as you suggest, there will be some loss within the reflector but not significant enough to usurp the communications potential.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can apply the Friis equation to work out some rough link budgets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tracking of the passive reflector in the sky is the same as any LEO satellite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit regarding Doppler shift:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Doppler shift will depend upon the location of the two earth stations relative to the satellite's path. This will most likely require the receiving operator to adjust the receive frequency  on a manual basis as calculating it would require prior knowledge of the other station's location. Using a mode like SSB or CW may make it easier to follow the Doppler shift due to its natural change in pitch of the received signal.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-07-17T13:15:26.580" LastActivityDate="2017-07-17T13:15:26.580" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="8905" PostTypeId="2" ParentId="2215" CreationDate="2017-07-17T11:20:37.360" Score="3" Body="&lt;p&gt;Alternator whine is caused by a small amount of AC signal component on your DC power supply to the radio. The alternator generates this AC signal as a by-product of how it works. A diode pack on the alternator converts AC current from it's windings into DC to charge the battery. The battery &quot;smooths&quot; out the pulses of energy from the alternator. For more information on this bit, see here: &lt;a href=&quot;http://auto.howstuffworks.com/alternator3.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://auto.howstuffworks.com/alternator3.htm&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To eliminate the alternator whine, you need to remove this AC signal from your DC supply. You mention that the whine has gotten worse, which probably corresponds to the deterioration of your vehicle battery — i.e. it is not smoothing the pulses out quite as well. This is a side issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The approach I would use to eliminate the whine noise, and that has worked for me before, is to run wires from the radio directly to the battery, where the smoothing should occur. Adding a filter in the supply cable, specifically the positive cured the issue for me. I used a large DC choke from an old power inverter (used for a similar job inside that) — essentially a large inductor capable of handing the current your transceiver needs — in series with the supply, followed by a large-ish capacitor (25&amp;nbsp;V, 10&amp;nbsp;000&amp;nbsp;µF) on the radio side to dissipate any noise passing through the inductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This worked pretty well for me. YMMV.&lt;/p&gt;&#xA;" OwnerUserId="8520" LastEditorUserId="250" LastEditDate="2017-07-17T14:01:25.170" LastActivityDate="2017-07-17T14:01:25.170" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8906" PostTypeId="1" CreationDate="2017-07-17T14:30:33.290" Score="2" ViewCount="124" Body="&lt;p&gt;The &lt;a href=&quot;https://metrics.wavefront.com/u/jhjFw5jNSf&quot; rel=&quot;nofollow noreferrer&quot;&gt;PSK31 specification by ARRL&lt;/a&gt; specifies:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;There is a preamble at the start of each transmission and a postamble at the end. The preamble is an idle signal of continuous zeroes, corresponding to continuous phase reversals at the symbol rate of 31.25 reversals/second. The postamble is just continuous unmodulated carrier, representing a series of logical ones. This makes it possible to use the presence or absence of the reversals to squelch the decoder so that the screen doesnt fill with noise when there is no signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;How long are the preamble and postamble? If there's no specification of length, what's common practice?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8832" LastEditDate="2017-07-18T04:12:33.023" LastActivityDate="2018-10-06T18:31:09.237" Title="How long are the PSK31 preamble and postamble?" Tags="&lt;psk31&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8907" PostTypeId="2" ParentId="8906" CreationDate="2017-07-17T16:14:12.263" Score="1" Body="&lt;p&gt;I am sorry that I cannot provide a concrete reference but I seem to recall that it is around 80 based on some receiving software requirements.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-07-17T16:14:12.263" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="8908" PostTypeId="1" CreationDate="2017-07-18T02:55:20.183" Score="2" ViewCount="1274" Body="&lt;p&gt;I live in an apartment with a metal rail patio very similar to the attached photo. I want to put a Diamond X30A on the patio but the radials will be about a foot below the top rail. Will this work, or an I better of with a simple 1/4 wave? &lt;a href=&quot;https://i.stack.imgur.com/3BIK7.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3BIK7.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10020" LastActivityDate="2018-02-26T18:58:19.217" Title="Can I install a Diamond X30A Antenna on a Balcony with a Metal Rail?" Tags="&lt;antenna&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8909" PostTypeId="2" ParentId="8908" CreationDate="2017-07-18T04:28:37.867" Score="2" Body="&lt;p&gt;Definitely better than a 1/4 wave vertical if only because of the radial requirements, but also because of increased gain.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I read the specs on the Diamond, as posted &lt;a href=&quot;http://Diamond%20Antenna%20X30A%20Dual-Band%20Base/Repeater%20Antennas%20X30A&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;https://www.amateurradiosupplies.com/product-p/ars-diamond-x30a.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AyL2B.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AyL2B.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It needs very little groundplane. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 1/4 wave antenna would require much more, and would intrude into and extrude outside the railing. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the Diamond would be the better choice, except maybe for its 4 and a half foot height.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would not suggest mounting in any way that hides part of it behind the railing.  You sat the radials would be below the top of the railing so I presume you mean outside. That could work well.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the top is touching anything I wouldn't suggest running the full rated 150 Watts through it.  It may experience some detuning, at the least.  This antenna is meant to be mounted in free space.  For that matter, so is a 1/4 wave groundplane.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reviews I find on it are all excellent.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has more gain so should outperform a 1/4 wave vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it were me I might be tempted to paint it black if there is the possibility of neighbor complaints.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-07-18T04:35:19.757" LastActivityDate="2017-07-18T04:35:19.757" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8910" PostTypeId="1" CreationDate="2017-07-18T13:27:42.530" Score="0" ViewCount="718" Body="&lt;p&gt;I have BPSK flowgraphs that work fine in simulation as well as between two USRP boards at 1200 bps and sample rate of 48000 baud. In the transmitter flowgraph, the transmitter reads HDLC bits from a file, NRZI-encode them and sends them via the USRP. The vice-versa is repeated by the receiver flowgraph which is connected to another USRP. The task at hand is to modify the receiver to work with the ICOM 910H transceiver instead of the USRP. Below is the new setup. Transmission frequency on both the USRP and the ICOM transceiver is 436Mhz.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/LgSnt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LgSnt.png&quot; alt=&quot;Experiment setup&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The modified transmitter is shown below. Since the ICOM radio has been set to USB, I have translated the signal by multiplying it with a complex sine wave with frequency 1500Hz. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/i1Qnv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/i1Qnv.png&quot; alt=&quot;Transmitter flowgraph&quot;&gt;&lt;/a&gt;&#xA;The receiver is modified as shown below. The signal is now received from the audio jack at 48000 baud. The FIR xlating filter shifts the signal down by 1500 and low-pass filter it (firdes.low_pass(1, samp_rate, 1300, 500)&#xA;&lt;a href=&quot;https://i.stack.imgur.com/x9kjT.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/x9kjT.jpg&quot; alt=&quot;Receiver flowgraph&quot;&gt;&lt;/a&gt;&#xA;Unfortunately, this time, the receiver won't decode any HDLC packets. Actually, it seems like the Costas loop is not locking as shown by the constellation diagram below. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/WzG37.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WzG37.jpg&quot; alt=&quot;Constellation diagrams&quot;&gt;&lt;/a&gt;&#xA;Any ideas, suggestions or links to resolve this issue will be highly appreciated. &lt;/p&gt;&#xA;" OwnerUserId="6214" LastActivityDate="2017-09-16T16:51:40.887" Title="GNU Radio BPSK reception from ICOM SSB audio" Tags="&lt;digital-modes&gt;&lt;gnuradio&gt;&lt;icom&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8912" PostTypeId="2" ParentId="8910" CreationDate="2017-07-18T15:57:35.447" Score="2" Body="&lt;p&gt;A good approach to troubleshooting problems is to simplify them until there's a minimal broken case. The program you have here is complex and there are many things that could be wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the radios are connected just by a cable, the constellation in your screenshot is far too noisy. That suggests there's a problem prior to the equalizer. The periodic spikes in the frequency plot are also suspect. Compare them to the spectrum of the USRP output. Is there an attenuator between the USRP and Icom?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind, the CMA equalizer can force a lot of things to look like a circle. Just because the output looks like it could be a constellation doesn't mean the input to the equalizer isn't total garbage. There will be no multipath distortion on a cable if the cable is short relative to the symbol length, so you don't need the equalizer. Try removing it to simplify the program until it's working.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Likewise you can bypass the FLL and replace it with manual tuning, and the AGC with manual gain control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The conversion from real to complex values with the Frequency Xlating FIR Filter block may not be what you expect. It converts to complex values by setting the imaginary part to zero, which has the effect of mirroring the spectrum. In other words, if the real input is a sine wave at 100 Hz, the complex output will have components at +100 and -100 Hz. Try replacing the audio source with a signal source with a frequency controlled by a GUI Range block to observe how real input frequencies map to complex output frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get from real to complex without that aliasing, you can either use a band-pass filter to remove all the negative frequencies, or use the Hilbert block to generate the imaginary component with a 90 degree phase shift from the real, eliminating the negative frequencies.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-07-18T15:57:35.447" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8913" PostTypeId="1" AcceptedAnswerId="8914" CreationDate="2017-07-18T17:01:55.080" Score="6" ViewCount="786" Body="&lt;p&gt;I just upgraded my license to Extra about a week and a half ago, so perhaps I'm supposed to know this.  The FCC database shows my upgrade to Extra, but the expiration date and callsign haven't changed.  I thought that my license would be renewed, at the very least.  Can someone shed some light on this?&lt;/p&gt;&#xA;" OwnerUserId="9464" LastEditorUserId="76" LastEditDate="2017-07-18T17:34:43.317" LastActivityDate="2018-09-25T14:36:13.487" Title="License upgrade doesn't extend term of license?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;callsign&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8914" PostTypeId="2" ParentId="8913" CreationDate="2017-07-18T17:52:31.410" Score="6" Body="&lt;p&gt;Renewal, upgrade, and change of call sign &lt;strong&gt;are three separate things,&lt;/strong&gt; except that renewal and change of call sign &lt;em&gt;may&lt;/em&gt; be requested together.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&amp;amp;SID=3dd3396683a845c655582e6b3f878a23&amp;amp;mc=true&amp;amp;n=pt47.5.97&amp;amp;r=PART&amp;amp;ty=HTML#se47.5.97_121&quot; rel=&quot;noreferrer&quot;&gt;§97.21&lt;/a&gt;   Application for a modified or renewed license grant.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) A person holding a valid amateur station license grant:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;…&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(2) May apply to the FCC for a modification of the operator/primary&#xA;  station license grant to show a higher operator class. …&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(3) May apply to the FCC for renewal of the license grant for another&#xA;  term in accordance with §§1.913 and 1.949 of this chapter. …&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As to your callsign, &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(c) Except as provided in paragraph (a)(3) of this section, a call sign obtained under the sequential or vanity call sign system &lt;strong&gt;will be reassigned to the station&lt;/strong&gt; upon renewal or modification of a station license.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I vaguely recall that you can ask the VEs to get you assigned a new sequential call sign when they submit the upgrade on your behalf, but I'm not sure about that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you can do now: you can apply for modification of your license, or if within 90 days of expiration, a combined renewal and modification, which may either:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Request that you be assigned a new sequential call sign, which will be from the series for Extra class operators, or&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Request a vanity call sign chosen by you (subject to the restrictions on vanity call signs).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For details on this process, see &lt;a href=&quot;https://transition.fcc.gov/Forms/Form605/605.pdf&quot; rel=&quot;noreferrer&quot;&gt;Form 605 (PDF)&lt;/a&gt;, which is the form for all license renewals and modifications, and Schedule D in the same document, which is abut amateur radio call signs in particular. (When you actually go to make the request, you would usually do it through the FCC ULS, not by filling out this form on paper.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-07-18T18:55:50.867" LastActivityDate="2017-07-18T18:55:50.867" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8915" PostTypeId="1" AcceptedAnswerId="8927" CreationDate="2017-07-19T05:15:29.640" Score="2" ViewCount="1182" Body="&lt;p&gt;I've been trying to get acquainted with the 4NEC2 antenna modeling program.  Perhaps this is obvious, but it's not clear to me that wires with one end in the same place are connected.  I'm attempting to model a simple quarter-wave antenna with four radials, but I'm getting results that seem suspect.  I shouldn't be seeing this symmetric pattern (picture below) along the $z$ direction.  It makes no sense.  It's as if the radials weren't even there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've compared my results to those of a vertical with four radials from Dick Reid, KK4OBI (NEC file &lt;a href=&quot;http://www.qsl.net/kk4obi/Models/KK4OBI%20model%20-%20OCF%20Vertical%204-Radials.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;).  Those show a strong asymmetry, as I would expect.  There seems to be some deep magic going on here in the NEC file that I don't understand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;-Rod AD0YX (call sign updated too!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the NEC file I'm using (updated)&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;CM High-altitude balloon 70cm antenna&#xA;CM Rodney Price AD0YX July 2017&#xA;CE&#xA;SY freq=434.65             'In wideband simplex band&#xA;SY len=71/freq             'meters/sec over MHz&#xA;SY rlen=len                'length of radials&#xA;SY angle=30                'angle at which radials droop&#xA;SY rdroop=rlen*cos(angle)  'droop along x or y axis&#xA;SY zdroop=-rlen*sin(angle) 'droop along z axis&#xA;SY height=0                'height of bottom of vertical element above radials&#xA;GW  1   11  0   0   height  0       0       height+len    #8&#xA;GW  2   11  0   0   0       rdroop  0       zdroop        #8&#xA;GW  3   11  0   0   0       0       rdroop  zdroop        #8&#xA;GW  4   11  0   0   0      -rdroop  0       zdroop        #8&#xA;GW  5   11  0   0   0       0      -rdroop  zdroop        #8&#xA;GE  0&#xA;GN  -1&#xA;EK&#xA;EX  0   1   1   0   1      0   0&#xA;FR  0   0   0   0   freq   0 &#xA;EN&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Here's the radiation pattern from 4NEC2:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cMtQf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cMtQf.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's what I get when I run the KK4OBI model:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/up14d.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/up14d.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9464" LastEditorUserId="8717" LastEditDate="2019-11-05T19:38:33.343" LastActivityDate="2019-11-05T19:38:33.343" Title="How do I specify that wires are connected in 4NEC2?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vertical-antenna&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="8917" PostTypeId="1" CreationDate="2017-07-19T12:25:27.917" Score="4" ViewCount="140" Body="&lt;p&gt;I've read in a couple sources that in a channel consisting of only additive white Gaussian noise (AWGN), at low SNR, QPSK31 is actually &lt;em&gt;worse&lt;/em&gt; than BPSK31.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/psk31-spec&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/psk31-spec&lt;/a&gt;, probably copied verbatim from &lt;a href=&quot;http://aintel.bi.ehu.es/psk31theory.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://aintel.bi.ehu.es/psk31theory.html&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;By doing simulations in a computer, and tests on the bench with a noise generator, it has been found that when the bit error-rate is less than 1% with BPSK, it is much better than 1% with QPSK and error-reduction, but when the BER is worse than 1% on BPSK, the QPSK mode is actually worse than BPSK. Therefore, if we are dealing with radio paths where the signal is just simply very noisy, there is actually no advantage to QPSK at all!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://det.bi.ehu.es/~jtpjatae/pdf/p31g3plx.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://det.bi.ehu.es/~jtpjatae/pdf/p31g3plx.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Computer simulation with BPSK&#xA;  in white noise shows that when the SNR is good, the error-correction system does win, reducing&#xA;  the low error rate to very low levels, but at the SNR levels that are acceptable in live amateur&#xA;  contacts, it's better to transmit the raw data slowly in the narrowest bandwidth. It also takes up&#xA;  less band space of course!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The reasoning seems to be that the switch from BPSK to QPSK degrades the SNR:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Suppose I devise an error-correcting system that doubles the number of transmitted bits. If I&#xA;  wanted to keep the traffic throughput the same, I would need to double the bit rate. But with&#xA;  BPSK that means doubling the bandwidth, so I lose 3dB of signal-to-noise ratio and get more&#xA;  errors. The error-correction system will have to work twice as hard just to break even! It is no&#xA;  longer obvious that error-correction wins. It is interesting to note that with FSK, where the&#xA;  bandwidth is already much wider than the information content, you can double the bit-rate&#xA;  without doubling the bandwidth, and error-correction does work.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm skeptical. Doubling the symbol rate in FSK halves the duration of the symbols, and thus halves E&lt;sub&gt;b&lt;/sub&gt;/N&lt;sub&gt;0&lt;/sub&gt;. Switching from BPSK to QPSK while holding the symbol rate the same splits the transmitter between two orthogonal systems, so again halving E&lt;sub&gt;b&lt;/sub&gt;/N&lt;sub&gt;0&lt;/sub&gt;. I don't see any reason error correction would work for FSK but not QPSK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But then, the channel decoding in QPSK31 combines two bits on the air into one bit received. So this is a doubling of energy per bit, for a net effect of no change in E&lt;sub&gt;b&lt;/sub&gt;/N&lt;sub&gt;0&lt;/sub&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's the basis for this claim that BPSK31 is worse than QPSK31 in an AWGN channel? Is there any formal proof or published empirical results to back it up?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-07-28T18:47:03.880" LastActivityDate="2017-07-28T18:47:03.880" Title="Is the error rate for QPSK31 in a white noise channel worse than BPSK31?" Tags="&lt;snr&gt;&lt;psk31&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8919" PostTypeId="1" AcceptedAnswerId="9243" CreationDate="2017-07-19T14:06:32.487" Score="5" ViewCount="268" Body="&lt;p&gt;I have sampled a section of spectrum every few Hz.  I have mean, standard deviation, and range data for every frequency sampled (and I can gather more statistics if necessary).  I've sampled for several seconds before storing the spectrum statistics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to be able to guess where man-made signals (i.e. channels) exist in this spectrum (as opposed to noise floor).  This is proving to be a difficult task, especially since the noise-floor power sometimes changes (different antenna inputs for different bands, for example.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I doubt anyone has a ready solution for this, but what are some starting points, or tips, to help me begin to identify channels?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the below image 'normal' is really autocorrelation from Pandas&#xA;&lt;a href=&quot;https://i.stack.imgur.com/CDA2s.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CDA2s.jpg&quot; alt=&quot;&amp;#39;normal&amp;#39; is really autocorr from Pandas&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="850" LastEditorUserId="76" LastEditDate="2020-02-15T16:55:33.800" LastActivityDate="2020-02-15T16:55:33.800" Title="Detecting signals using statistics" Tags="&lt;signal-identification&gt;&lt;dsp&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8920" PostTypeId="2" ParentId="8919" CreationDate="2017-07-19T15:03:44.913" Score="3" Body="&lt;p&gt;Well, this is a well-studied field (Radio Frequency Interference detection and mitigation). There are tons of literature about it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The noise you receive is theoretically Additive White Gaussian Noise (AWGN). That means that its Probability Density Function (PDF) is Gaussian, and the pdf of its samples' power is exponential. By setting a false alarm probability according to the power of the signal, you can easily detect samples that potentially are not noise. Check the point 2.2 of &lt;a href=&quot;http://ieeexplore.ieee.org/document/7326890/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; paper, for example. This threshold method is applied in the frequency domain in Frequency Blanking and Spectrogram Blanking techniques.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Normality_test&quot; rel=&quot;nofollow noreferrer&quot;&gt;Normality Test&lt;/a&gt; are used as well to evaluate if a signal is AWGN. I have read a lot of mentions to Anderson-Darling test, but I never worked with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use &lt;a href=&quot;http://ktb.engin.umich.edu/RSG/pubs_files/TGRS-2007-45-7_DeRoo-etal_Kurtosis.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kurtosis&lt;/a&gt; to see if a signal is Gaussian or not (but be careful because Kurtosis is weak against certain sinusoidal signals). If it is not Gaussian, it is likely to be man-made (however, some frequency Jammers could emit Gaussian signals). Kurtosis has been also used to detect RFI in the frequency domain, not only in the time domain (look for spectral kurtosis).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.mdpi.com/2072-4292/2/1/191&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt; you have an other interesting (and open!) paper about RFI detection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not sure if there are AWGN-like signals made by humans different that noise for jamming. &lt;a href=&quot;http://www.navipedia.net/index.php/File:Chapter_2_Spectra_GPS_Signals_L1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;The spectrum of signals encrypted with codes&lt;/a&gt; (such as GPS signals, which use Pseudo-Random-Noise codes) are sincs, and they are only flat in a small fraction of its bandwidth. Even if you are sampling this small fraction, I am not sure if the signal in time will seem Gaussian.&lt;/p&gt;&#xA;" OwnerUserId="9800" LastEditorUserId="9800" LastEditDate="2017-07-20T13:55:45.210" LastActivityDate="2017-07-20T13:55:45.210" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="8921" PostTypeId="2" ParentId="7767" CreationDate="2017-07-19T15:23:36.320" Score="1" Body="&lt;p&gt;I have never heard about it, but my hypothesis is that it could be useful if there are multiple users trying to access the media and they listen before transmitting to avoid collision (something like &lt;a href=&quot;https://en.wikipedia.org/wiki/Carrier-sense_multiple_access_with_collision_detection&quot; rel=&quot;nofollow noreferrer&quot;&gt;CSMA/CD&lt;/a&gt;). If you don't have the &quot;no signal&quot; state, you can not differentiate between transmitting one of the symbols and not transmitting.&lt;/p&gt;&#xA;" OwnerUserId="9800" LastActivityDate="2017-07-19T15:23:36.320" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8922" PostTypeId="1" CreationDate="2017-07-19T15:54:23.140" Score="1" ViewCount="1261" Body="&lt;p&gt;How do we  reconcile the ground connection between audio eqp (TNCs, soundcards etc) and transceiver? Most of the audio eqp for digimodes has only one ground. I've seen that the common practice is to use only the PTT ground, either forgetting abt the MIC ground or soldering the MIC and PTT ground together. Obviously this would break the MIC ground isolation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Related Q/A, &lt;a href=&quot;https://ham.stackexchange.com/questions/5023/mic-ground-vs-ground/8916?noredirect=1#comment13261_8916&quot;&gt;Mic ground vs ground&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10028" LastEditorUserId="218" LastEditDate="2017-07-20T02:27:10.830" LastActivityDate="2017-07-27T13:53:20.573" Title="MIC microphone ground vs common (PTT, chassis etc) ground" Tags="&lt;grounding&gt;&lt;microphone&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8923" PostTypeId="2" ParentId="8922" CreationDate="2017-07-19T17:08:03.787" Score="1" Body="&lt;p&gt;An audio interface is a very different situation than a microphone, even though they both produce the same sort of signal at the same voltage.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The microphone, specifically, must be protected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming the microphone is of the &lt;em&gt;electret&lt;/em&gt; type as is typical, the microphone has an internal amplifier circuit. This amplifier has to pick up the very weak signals from the electret microphone element itself and amplify them. Any interference that gets into this circuit could be amplified as well. The audio interface, on the other hand, probably has either a digital input or a line-level audio input. Both of these are much stronger signals which do not need amplifiers.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Source impedance differs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now considering the possibility of interference to the audio signal &lt;em&gt;from&lt;/em&gt; the microphone or audio interface to the radio: the microphone will likely have a higher output impedance than the audio interface. Therefore, the effect of any other signal coupled in will be higher with the microphone than with the audio interface.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Miscellaneous:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The microphone is connected only to the radio and is used in close proximity to it. The audio interface, on the other hand, is connected to a computer, and the interface and computer are fully shielded boxes. There's more opportunity for any noise on shields to flow &lt;em&gt;elsewhere.&lt;/em&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The stock microphone and connector may be designed to handle worse RF-in-the-shack conditions than the audio interface will. People who are using computer interfaces are likely optimizing their setups more, and fixing RF-in-the-shack to avoid crashing their computer, and using lower power levels than the maximum the radio supports.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Finally, there's plenty of circuit designs out there that simply aren't as good as they could be — they work well enough for the designer.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-07-19T17:08:03.787" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8924" PostTypeId="2" ParentId="8919" CreationDate="2017-07-20T04:56:14.737" Score="7" Body="&lt;p&gt;There is a range of possibilities, depending on what kind of signal you want to find.  I'll start from easy and move up to hard.  I'm assuming that you are using an &lt;a href=&quot;https://en.wikipedia.org/wiki/Fast_Fourier_transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;FFT&lt;/a&gt; to get your spectra.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;RFI.  An earlier poster referenced some papers on finding RFI.  I don't know precisely how that is defined, but lets assume that it is unintentional RF from things like switching power supplies (line spectra) and poorly wired auto engines (impulsive noise).  Impulsive noise is narrow in time and wide in frequency, which suggests that you simply have a look at your receiver output.  There is probably some statistical test you could apply (say, the null hypothesis is white Gaussian noise).  For line spectra, do the same in the frequency domain.  Perhaps those who know more about RFI than I do would say otherwise.  I would suggest, however, that rather than process your signal as you're doing, that you use the initial processing that I discuss next.&lt;/li&gt;&#xA;&lt;li&gt;Conventional analog signals.  By this I mean the AM, FM, SSB, etc. transmissions that you run across all the time.  These live in an intermediate region between impulses and line spectra, which makes things a bit harder.  I would suggest that you compute a power spectrum, and from that, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Autocorrelation&quot; rel=&quot;nofollow noreferrer&quot;&gt;autocorrelation&lt;/a&gt;.  This is easy if you are already using an FFT: compute the FFT, then multiply each element by its complex conjugate.  Now you have the power spectrum.  Next do the inverse FFT to get the autocorrelation.  If there's a signal there, you'll see a smeared out peak near $\tau=0$, where $\tau$ is the delay.  If it's relatively wideband, the peak will be narrower; if it's narrowband (compared to your FFT) the peak will be wider.  Look for peaks in both the power spectrum and the autocorrelation.  This works better than statistics-gathering the way you describe because it takes advantage of the coherence of the signal.  If you use a large FFT, you'll be averaging over a lot of signal, which will suppress the noise and better show you what's there.  If it's just noise, you'll see a very narrow peak right at $\tau=0$ and a flat power spectrum.&lt;/li&gt;&#xA;&lt;li&gt;Conventional digital signals.  I mean conventional from a ham radio perspective; modes like PSK31, etc.  An autocorrelation/power spectrum approach can work well here, too.  The same physical principles apply: noise averages incoherently, while signal averages coherently.  There is a caveat, however.  As signals get more bandwidth-efficient, they start to look more like white noise.  An AFSK signal like those often used in packet radio, for example, is terribly (forgive me, packet radio enthusiasts) inefficient.  It takes a lot of bandwidth to get a few bits through.  PSK31 is much better.  Some of the more modern modes, such as WSPR and relatives, are really good.  You'll see a flat spectrum across the entire signal bandwidth.  They're not trying to be sneaky.  That's just the physics of the situation.&lt;/li&gt;&#xA;&lt;li&gt;Wideband digital signals.  This is a broad category, but includes spread-spectrum signals as well as very highly optimized signals like the ones your cell phone uses.  There has been a remarkable amount of R&amp;amp;D put into these signals to make them efficient, and because they have to push a lot of bits across, they are wideband, and so the signal-to-noise ratio in any given frequency bin a few Hz across is going to be poor.  They're just plain hard to see, and there are a surprising number of them out there. This is where &lt;a href=&quot;https://en.wikipedia.org/wiki/Cyclostationary_process&quot; rel=&quot;nofollow noreferrer&quot;&gt;cyclostationary&lt;/a&gt; processing, a form of &lt;a href=&quot;https://en.wikipedia.org/wiki/Higher-order_statistics&quot; rel=&quot;nofollow noreferrer&quot;&gt;higher-order statistics&lt;/a&gt;, comes into its own.  Cyclostationary processing is used to extract the bit rate from an unknown signal.  Even if you can't see the signal through second-order statistics (like the autocorrelation) the bit rate of the signal will often pop right out of a cyclostationary approach.  The math can be intimidating, but if you're really interested, stick with it and you'll find that it's really not that hard.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Here are a few examples to illustrate the autocorrelation/power spectrum approach.  In the images, I plot the signal first, then the power spectrum, then the autocorrelation.  These are simulated signals with sampling interval $\Delta t = 1$.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;White Gaussian noise&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Flat power spectrum, autocorrelation has a peak at zero lag, flat everywhere else.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/W1VM7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W1VM7.png&quot; alt=&quot;white Gaussian noise&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Barker-coded pulse&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Radars use these to reduce their peak power requirements while maintaining range resolution.  $\sin^2 \omega/\omega^2$ structure due to the pulse shape.  Autocorrelation shows a narrow peak at zero lag.  In the wild, these pulses are much shorter than I show here, leading to flatter, wider spectra.  They can be difficult to distinguish from noise unless you have some independent way to calculate the SNR in the channel (which is difficult if you don't actually know that there &lt;em&gt;is&lt;/em&gt; a signal in the channel).  Best to just look directly in the time domain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Zs8fR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Zs8fR.png&quot; alt=&quot;Barker-coded pulse&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;FM with sinusoidal modulation&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Easy to see in both the power spectrum and autocorrelation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/79pd0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/79pd0.png&quot; alt=&quot;FM with sinusoidal modulation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Sum of all three&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Here I've set the noise $\sigma = 1/4$, the peak amplitude of the pulse to $2$, and the peak amplitude of the FM signal to $1/4$.  The fourth plot is a close-up of the autocorrelation near zero lag.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cqN0t.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cqN0t.png&quot; alt=&quot;Sum of noise, pulse, and FM signal&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9464" LastEditorUserId="9464" LastEditDate="2017-07-21T21:12:43.207" LastActivityDate="2017-07-21T21:12:43.207" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="8927" PostTypeId="2" ParentId="8915" CreationDate="2017-07-20T18:35:19.857" Score="3" Body="&lt;p&gt;Rod,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ends of wires are connected if they are at the same location. Your model is correct in this regard.  However, the wires need to be about one-quarter wavelength long rather than the full wavelength shown.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 4NEC2 software provides the Automatic Gain Test (AGT) check box when you Generate (&lt;kbd&gt;F7&lt;/kbd&gt;) the results of your model.  Use this in the early stages of modeling.  If the Gain correction is too large the results will be in red indicating the model needs to be corrected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Height for a model over ground needs to be one-half wavelength for optimum conditions.  After your model is satisfactory, adjust height according to your real conditions and see what changes. Your model at one-tenth wavelength will show most of the radiation being reflected upward.  Use the free space option if you wish to eliminate ground interactions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radial angle downward will need to be 40-45 degrees to get a minimum SWR around 50 Ohms. The 30 degree setting you show will be an impedance under 50 Ohms.  Since you use Symbols, you can use the Optimizer function to find the best (L)lengths.  Similarly, you can optimize for best angle if you use Sin()*L and Cos()*L of the element Length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the 4NEC2 model information about elevated radials.&lt;br&gt;&#xA;&lt;a href=&quot;http://www.qsl.net/kk4obi/Elevated%20Radials.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.qsl.net/kk4obi/Elevated%20Radials.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your model should be able to reproduce the results of the 4-radial model included in the study. (That model coding is not directly comparable because it uses spherical geometry and adjustable center-fed/off-center feed at any angle for all elements).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Load card (LD) is an unnecessary complication at this stage of development.&lt;/p&gt;&#xA;" OwnerUserId="8229" LastEditorUserId="5222" LastEditDate="2017-07-21T18:31:18.320" LastActivityDate="2017-07-21T18:31:18.320" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="8929" PostTypeId="1" CreationDate="2017-07-21T06:49:31.710" Score="1" ViewCount="211" Body="&lt;p&gt;I am studying on making automatic transmitter and receiver with usrp on gnuradio. Firstly, I should transmit any signal with center frequency 400,410,420,430 Mhz with 2 seconds waiting time for each frequency and it should repeat itself. Then, at the receiver side I should find the frequency changing loop and the waiting time to get the signal coming from transmitter. I am working on python code that gnuradio generates and I added for and while loop. Yet, there is nothing worthy. I'm an amateur and  working just for 2 weeks.I hope someone can help me to solve the problem.&#xA;By the way, I check the Guided Tutorials on &lt;a href=&quot;http://tutorials.gnuradio.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://tutorials.gnuradio.org&lt;/a&gt; and could not find something useful about outomatic change. &#xA;Thanks, Furkan. &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;                                ***EDITED PART***&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;what I exactly want to do is making transmitter which transmits 400,410,420,430 Mhz signals repetetive with 1 second  waiting time for each signal. For receiver part, it will know frequency range and how many second each frequency will transmitted, but it will not start at the same time with the transmitter. So, it should find the center frequency of transmitter first,then continue synchronized to the transmitter. the added code for transmitter is below but it does repeat from 400 to 430,it goes up.                                                                                                  &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;tb.show()&#xA;&#xA;def tick():&#xA;    for i in range(0,4):   &#xA;        tb.set_center_freq(tb.get_center_freq()+10e6)&#xA;        print(tb.get_center_freq())&#xA;timer = QTimer()&#xA;timer.timeout.connect(tick)&#xA;timer.start(1000)&#xA;def quitting():&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I hope it is clear now. &#xA;Thanks for all comments and helps.   &lt;/p&gt;&#xA;" OwnerUserId="10035" LastEditorUserId="10035" LastEditDate="2017-07-23T21:03:39.977" LastActivityDate="2017-07-24T15:46:07.923" Title="Automatic transmitter-receiver" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8930" PostTypeId="1" CreationDate="2017-07-21T14:02:48.520" Score="2" ViewCount="423" Body="&lt;p&gt;I've found an old antenna that once came with an HP laptop with a TV (DVB-T?) card. I decided to see if I can use that antenna for something else, so I opened it up and found the following antenna design. However, I have not seen this before, so I'm curious to know: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What is this antenna design?&lt;/li&gt;&#xA;&lt;li&gt;Is it possible to determine an approximate usable frequency range?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The element measurements are as follows:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The ground &quot;clip&quot; length is 5 cm.&lt;/li&gt;&#xA;&lt;li&gt;The ground clip width is 2 mm.&lt;/li&gt;&#xA;&lt;li&gt;The driven thin spacers leads are 2 mm in length.&lt;/li&gt;&#xA;&lt;li&gt;The wide elements are all 8.3 mm in length&lt;/li&gt;&#xA;&lt;li&gt;The wide elements are of the following widths (mm): &lt;code&gt;1.6, 7.2, 8.3, 10.1, 11.1, 12.5, 13.1, 14.0, 15.2&lt;/code&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZUYT4.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZUYT4.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The HP part numbers for this is:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;HP P/N:     411352-003&#xA;HP Spare:   412176-003&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And it look like this in its original state:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/j2lBC.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/j2lBC.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;: &#xA;This seem a bit similar to the antenna designs of &lt;a href=&quot;http://www.antennamagus.com/database/antennas/antenna_page.php?id=152&quot; rel=&quot;nofollow noreferrer&quot;&gt;Resonant Rectangular Series-Fed Patch Array&lt;/a&gt; and the &lt;a href=&quot;http://www.antennamagus.com/database/antennas/antenna_page.php?id=145&quot; rel=&quot;nofollow noreferrer&quot;&gt;Traveling Series-Fed Patch Array&lt;/a&gt;, also described a bit in this &lt;a href=&quot;https://www.researchgate.net/publication/224320554_A_Novel_Series-Fed_Taper_Antenna_Array_Design&quot; rel=&quot;nofollow noreferrer&quot;&gt;paper&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iK9ta.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iK9ta.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/mHNHS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mHNHS.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6563" LastEditorUserId="6563" LastEditDate="2017-07-24T21:51:18.013" LastActivityDate="2017-07-24T21:51:18.013" Title="What kind of antenna design is this?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8931" PostTypeId="2" ParentId="8930" CreationDate="2017-07-21T14:45:43.920" Score="1" Body="&lt;p&gt;It is an antenna made of different microstrip patches at different frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They might use this antenna to receive signals from different bands. An other option is that since the fractional bandwidth of a patch antenna is narrow ($ Bw/f_o$ is low), to achieve a large bandwidth they &quot;concatenate&quot; several patches at different but close central frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The width of each patch is calculated as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$W = \frac{c}{2f_0 \sqrt{\frac{\epsilon_r+1}{2}}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(&lt;a href=&quot;https://www.pasternack.com/t-calculator-microstrip-ant.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;source&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;so you can easily isolate the frequency at which they are tunned:&#xA;$$f_0 = \frac{c}{2W \sqrt{\frac{\epsilon_r+1}{2}}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\epsilon_r$ is the relative dielectric constant of the substrate where the antenna is located. In this case, it seems fiberglass (FR-4), which has a $\epsilon_r$ between 4.35 and 4.8 (&lt;a href=&quot;https://en.wikipedia.org/wiki/FR-4&quot; rel=&quot;nofollow noreferrer&quot;&gt;source&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 1.6 mm I think is the microstrip transmission line to feed the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to the formulas, 7.2, 8.3, 10.1, 11.1, 12.5, 13.1, 14.0, 15.2 would correspond to: 12.7 GHz, 11.05 GHz, 9.08 GHz, 8.26 GHz, 7.33 GHz, 7 GHz, 6.55 GHz, 6 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do these numbers make any sense to you?&lt;/p&gt;&#xA;" OwnerUserId="9800" LastActivityDate="2017-07-21T14:45:43.920" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="8933" PostTypeId="1" AcceptedAnswerId="8934" CreationDate="2017-07-22T11:24:16.140" Score="5" ViewCount="607" Body="&lt;p&gt;I confirm all QSOs via LOTW and eQSL but some people also request QSL cards via bureau or direct. Of course I don't want to disappoint them and I reply 100%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I find it such a burden to print sheets of labels and stick them on the cards. So I wonder: is there an efficient way to print the QSO data directly on the otherwise preprinted QSL cards?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What (not to expensive) printer can be used?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My cards are pretty heavy cardboard so a regular inkjet or laser printer does not work.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2017-07-23T09:01:34.370" Title="What is the easiest way to print data on qsl cards?" Tags="&lt;qsl-card&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8934" PostTypeId="2" ParentId="8933" CreationDate="2017-07-22T11:55:05.937" Score="4" Body="&lt;p&gt;So, the fact that laser printers work so well is that you can directly roll-on the toner – that either requires a very finely tuned linear transport of the paper to be printed on (which is mechanically complex and thus expensive), or, and that's what you find in any paper printer – keeping the paper under the right tension and having another roller opposite to the toner transfering roller to which you feed the paper under an angle (so that you can keep it flat and tensioned). Another aspect of bending the paper around rollers is that it makes it possible to put relatively long processing chains within a compact case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Same goes for inkjets – you need to make sure your piece of paper is 100% flat where you run the ink nozzles. That, together with the need to grab a single sheet of paper, make linear transport expensive to build.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, there's speciality printers, eg. for surface printing on metal or plastic signs, or of course, cardboard postcards, packaging etc. But these are large (thus making the bending radii large) or expensive, so that even there, the &quot;stick-on&quot;/label approach is often preferred.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you really can't stand the labels (which don't sound &lt;em&gt;too&lt;/em&gt; bad, to me), I'd look into getting a cheap laser cutter/engraver and running it with as little power you need to burn in the info you need :) You'll need to write a few scripts to put the text where you want it, convert it to something your cutter speaks, send that job out to the cutter etc, but bonus is you get a laser cutter for other purposes :)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-07-22T11:55:05.937" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8935" PostTypeId="2" ParentId="8933" CreationDate="2017-07-23T01:25:38.397" Score="4" Body="&lt;p&gt;I have had good success with a &quot;photo&quot; printer. I made my Word template so that it prints the data at the same time as the background image. The only downside is single sided printing. But the card stock is nice because it easily trims down to size in the paper cutter without much waste.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I print an envelope with my normal laser printer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I activated Tortola,  I got a lot of nice compliments on the card. My wife took the picture on the beach that made up the card background. I sent out a little over 100 cards printed that way.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-07-23T01:25:38.397" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8936" PostTypeId="2" ParentId="1488" CreationDate="2017-07-23T05:59:31.950" Score="0" Body="&lt;p&gt;Clubs can have station licenses on a case-by-case basis.  They are getting a lot more rare.  Any correspondence about them usually would go directly to the trustee.  These days, most club stations are the same as a ham's callsign.  But there are others, like KL7KC in Fairbanks which are grandfathered in order to keep the callsign.  In any case, it is up to the trustee to keep things in order.  So this kind of letter wouldn't usually be addressed to the station location.  KL7KC is in a CAP hanger which is rarely manned.  There would be no expectation of a quick response if a letter was to be sent there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Station licenses are definitely used for broadcast stations, and are tied to a specific location.  The FCC maintains a separate tower database the correlates stations with tower locations, too.  You need a station license and construction permit before you even begin to build a broadcast tower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham licenses go with the person, not the location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This question is a tad misleading, but it is the correct answer the way the question is asked.  The second part, suspension of the operator license, is possible.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reality is, the only reason this would apply to a ham is if they have been accused of a violation of some sort.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been a ham since 1971 and have never received anything like this from the FCC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been a broadcast engineer since 1979 and have seen many kinds of letters from the FCC show up that required my attention.  The station managers involved are always in a hurry to respond asap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I earned my General Radiotelephone Operator License back in 1983 it was required that I post it at stations where I was the engineer of record.  (Back then the announcers all needed Third Class Radiotelephone Operator Licenses, too).  But things are a lot different now.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-07-23T06:17:58.487" LastActivityDate="2017-07-23T06:17:58.487" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8937" PostTypeId="2" ParentId="8933" CreationDate="2017-07-23T09:01:34.370" Score="3" Body="&lt;p&gt;Forgive me if this isn't the case, but isn't just taking a pen and writing the few things that need to be filled out much quicker than printing out labels? Unless you really make lots of qso 's and have a large percentage requesting cards, I would imagine having the cards next to you while doing the qso, and filling them out straight away, would be the least time consuming.... And honestly, I'd prefer even an illegible handwritten card over one with a printed label, to me it has a more personal feeling.&#xA;I don't operate except on field day and such though, so sorry if it really isn't a practically reasonable idea.&#xA;Anyway you do it, it's really nice you take the time to send the cards...&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2017-07-23T09:01:34.370" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="8938" PostTypeId="1" CreationDate="2017-07-23T11:06:12.150" Score="2" ViewCount="501" Body="&lt;p&gt;I'm working on a project to transmit and receive data by radio. For the transmission, I'm using a &lt;a href=&quot;https://www.raspberrypi.org/products/raspberry-pi-3-model-b/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Raspberry Pi 3&lt;/a&gt; and the &lt;a href=&quot;http://www.radiometrix.com/content/ntx2b&quot; rel=&quot;nofollow noreferrer&quot;&gt;NTX2B&lt;/a&gt; transmitter for the transmission. For the receiving end, I am using &lt;a href=&quot;http://www.nooelec.com/store/sdr/sdr-receivers/nesdr-mini2-rtl2832u-r820t2.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;NooElec Mini 2 SDR&lt;/a&gt; as the receiver and the &lt;a href=&quot;http://cubicsdr.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;CubicSDR program&lt;/a&gt; to see a waterfall diagram of the received signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've used instructions from &lt;a href=&quot;http://hab.uggy.org/index.php?page2&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yannick&lt;/a&gt;, &lt;a href=&quot;https://ukhas.org.uk/_detail/guides:ntx2_1_47k.png?id=guides%3Alinkingarduinotontx2&quot; rel=&quot;nofollow noreferrer&quot;&gt;Linking an Arduino to a Radiometrix NTX2B Transmitter&lt;/a&gt; and &lt;a href=&quot;http://www.daveakerman.com/wp-content/uploads/2013/01/Raspberry-Jam-Pi-In-The-Sky.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dave Akerman&lt;/a&gt; to get as far as I have.  The image below shows the circuit diagram (from Dave Akerman).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zAHZw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zAHZw.png&quot; alt=&quot;Layout (from Dave Akerman)&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Sending 1s and 0s using a GPIO port&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Initially, rather than connecting the transmitter input to the TX port on the pi, I connected it to one of the GPIO ports, number 18. I instructed port 18 to switch on and off every five seconds, and was able to see the frequency shift on the waterfall diagram on my laptop. :) Success!&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;from time import sleep&#xA;import RPi.GPIO as GPIO&#xA;GPIO.setmode(GPIO.BCM) &#xA;GPIO.setup(18, GPIO.OUT)&#xA;&#xA;GPIO.setmode(GPIO.BCM) &#xA;GPIO.setup(26, GPIO.OUT)&#xA;GPIO.output(26, True)&#xA;&#xA;while 1:&#xA;     GPIO.output(18, False)&#xA;     sleep(5)&#xA;     GPIO.output(18, True)&#xA;     sleep(5)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VpaA9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VpaA9.png&quot; alt=&quot;Output for 0s and 1s&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Serialising data using the TXD port&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next step was to send data by connecting the NTX2B to the TXD port on the Pi. I was expecting to see a double peak, one for 0, and another for 1 at a higher frequency, on the waterfall diagram. However, I get just a single peak, and so I'm not sure if I'm actually transmitting the data. I tried using &lt;code&gt;setRTS&lt;/code&gt; to digitise my signal (similar to the previous experiment), however the waterfall diagram didn't show any change. Can anyone help me with this? :(&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;import serial&#xA;import time&#xA;from time import sleep&#xA;import RPi.GPIO as GPIO&#xA;&#xA;GPIO.setmode(GPIO.BCM) &#xA;GPIO.setup(26, GPIO.OUT)&#xA;GPIO.output(26, True)&#xA;&#xA;ser = serial.Serial(&quot;/dev/serial0&quot;,&#xA;                    baudrate = 115200,&#xA;                    parity=serial.PARITY_NONE,&#xA;                    stopbits=serial.STOPBITS_ONE,&#xA;                    bytesize=serial.EIGHTBITS,&#xA;                    timeout=1)&#xA;ser.setRTS(False)&#xA;time.sleep(5)&#xA;ser.setRTS(True)&#xA;time.sleep(5)&#xA;ser.setRTS(False)&#xA;time.sleep(5)&#xA;while True:&#xA;    ser.write(b'hello!')&#xA;# ser.close()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/r6QKN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/r6QKN.png&quot; alt=&quot;Output for serialised data&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9856" LastActivityDate="2017-07-23T11:29:03.453" Title="Serialising a data signal with a Raspberry Pi" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8939" PostTypeId="2" ParentId="8938" CreationDate="2017-07-23T11:29:03.453" Score="3" Body="&lt;p&gt;Your frequency deviation in the plot is somewhere in the range of 1 or 2 kHz – so, you really can't modulate it with 115.200 kHz of symbol rate!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try 9600 bd on the interface instead. It looks like the TXD input &lt;strong&gt;directly&lt;/strong&gt; modulates the output – and that means that the data clock is identical to the on-air data clock.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, to me, this sounds like you shouldn't be using an UART to talk to the device. Instead, use the SPI interface, in hopes you can make constant-rate, seemless, multi-byte transmissions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Package your data in packets (for example: take 8 byte of data at once).&#xA;Each time before you start sending, send a preamble byte (e.g. &lt;code&gt;10101010b==0xAA==170&lt;/code&gt;) so that your receiver can find your transmission, and achieve clock synchronization (yep! that's necessary!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, to improve the likelihood of successful transmissions (reduce the bit and packet error rates):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Add channel coding in your software – a 3/4-rate simple block code might do. That adds redundant info to your transmit data – but that info can be used by the channel decoder in the receiver to recognize and often even reverse bit errors&lt;/li&gt;&#xA;&lt;li&gt;Interleave the bits throughout the 8 byte packet. That means that if two consecutive transmit bits are disturbed (e.g. by a short interference), these two &quot;damaged&quot; bits end up at very far-away places in the bit stream after deinterleaving, and that means it's easier for the channel decoder to correct them&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-07-23T11:29:03.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8940" PostTypeId="1" CreationDate="2017-07-23T22:58:18.550" Score="16" ViewCount="11385" Body="&lt;p&gt;I've been a ham for over 40 years, but &lt;em&gt;never&lt;/em&gt; has there been such a prolonged period of such poor propagation. This has been especially the case over the past six months or so, &lt;em&gt;and they continue to deteriorate&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;What could possibly be the cause?&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;This is taking into account information from sites such as &lt;a href=&quot;http://www.spaceweather.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Spaceweather&lt;/a&gt; and the sites linked to from &lt;a href=&quot;http://www.w0btu.com/propagation.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page on my site&lt;/a&gt;. Even when solar conditions seem to be favorable for good band conditions, the bands are terrible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sure, there's solar flares, &lt;a href=&quot;https://www.spaceweatherlive.com/en/help/what-is-a-coronal-mass-ejection-cme&quot; rel=&quot;nofollow noreferrer&quot;&gt;CMEs&lt;/a&gt;, and other events that typically make the bands go &quot;dead&quot;. But &lt;em&gt;those effects have been taken into account&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;NOT caused by increased man-made noise&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;In many locations, man-made noise is a factor. But I asked this question from the viewpoint of hams living in quiet areas; my location is almost noise-free, and there are times when my s-meter is zero even with the preamp on.  &lt;strong&gt;This is about the signal levels dropping&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This image below is from &lt;a href=&quot;http://www.bandconditions.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;K5BIZ's website&lt;/a&gt; (which has been offline for several months now). The network of receivers feeding data to it from K5BIZ's beacons is the most reliable indicator of real-time HF band conditions we've found. The majority of the time, the arrows on each band graph there have mostly been in the red areas of the the graphs for most of these bands like below, and they closely indicate what we hear on the bands. &lt;em&gt;It wasn't always like this.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know we are near the solar minimum, but it certainly seems that something else is at play. Many other hams concur.&#xA;&lt;strong&gt;&lt;em&gt;What could it be?&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/P8zV8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/P8zV8.png&quot; alt=&quot;Typical poor band conditions&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Historically, near solar minimums the upper bands deteriorate while conditions improve on 80 and 160. My point -at the time that I originally asked this- was that &lt;strong&gt;all&lt;/strong&gt; those bands remained poor and the signal levels are much lower than in years past.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is indeed an overall increase in RFI from such devices as switching power supplies. However, in many locations (mine included) we hear little of that. Something else is definitely at play here. &#xA;&lt;hr&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/uxezb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uxezb.png&quot; alt=&quot;Dirty ice in the arctic and comment&quot;&gt;&lt;/a&gt;&#xA;&lt;hr&gt;&#xA;&lt;strong&gt;Bandconditions.com has been down. A good alternative is &lt;a href=&quot;http://www.sws.bom.gov.au/Images/HF%20Systems/Global%20HF/Ionospheric%20Map/WorldIMap0.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;this site&lt;/a&gt;&lt;/strong&gt;.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Pokfk.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Pokfk.gif&quot; alt=&quot;Refresh to see current global ionospheric propagation conditions&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-06-19T22:01:13.120" LastActivityDate="2019-06-19T22:01:13.120" Title="What is the cause of this unusually long period of terrible HF band conditions?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;space-weather&gt;&lt;ionosphere&gt;&lt;sunspots&gt;" AnswerCount="7" CommentCount="1" FavoriteCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="8942" PostTypeId="1" CreationDate="2017-07-24T14:20:10.210" Score="0" ViewCount="57" Body="&lt;p&gt;My question is that is there any method to send data from a gnuradio file (or in the generated python code) to another one? There is a transmitter file and it transmits signals with different frequencies automatically. I know the transmitted frequency range and waiting time for each frequency. In another file I should make a receiver which should work synchronized with the transmitter while it does not know when the transmitter started. So , I thought if I can take data from other file, then it will be easy to make them syncronized by knowing the frequency range and waiting time. I will appreciate any comments and advices for different ways to communicate the files.&#xA;Thanks    &lt;/p&gt;&#xA;" OwnerUserId="10035" LastActivityDate="2017-07-24T14:25:48.130" Title="communicate two different gnu radio files" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8943" PostTypeId="2" ParentId="8942" CreationDate="2017-07-24T14:25:48.130" Score="1" Body="&lt;p&gt;Well, considering transferring data between two devices is the very purpose of digital communications: yes, there are such GNU Radio programs/flow graphs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you need, however, is totally use-case specific. You'll have to implement that yourself.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-07-24T14:25:48.130" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8944" PostTypeId="1" CreationDate="2017-07-24T15:39:26.510" Score="1" ViewCount="948" Body="&lt;p&gt;I've got a GNU Radio flowgraph intended to take a signal from a USRP X310 at a 25MS/s sample rate and downsample it to 2.4576MS/s for demodulation as 9600 baud GMSK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I run the USRP straight into a FFT GUI sink, I get a nice, constantly moving graph, with the spike of the signal appearing every five seconds, as expected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As soon as I introduce either the FIR filter or the automatic gain control, I start getting overflows (error message O) and dropped packets (error message D) in the output text. After two or three signalling periods, I'm getting maybe 20 dropped packets at a time and sometimes all the output charts freeze for several seconds at a time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please, can anyone explain this behaviour to me?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DLQmr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DLQmr.png&quot; alt=&quot;USRP flowgraph dropping packets&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10056" LastActivityDate="2017-07-24T17:59:11.890" Title="Why is GNU Radio dropping packets when I introduce a Frequency Xlating FIR filter?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8945" PostTypeId="2" ParentId="8929" CreationDate="2017-07-24T15:46:07.923" Score="1" Body="&lt;p&gt;There is a problem with your code in tick. Since it is getting the current frequency and adding 10 MHz each time, there is no way of resetting it back to the starting frequency the next time tick is called. Here is a version that ensures it restarts at 400 MHz each time it is called:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt; def tick():&#xA; for i in range(0,4):   &#xA;    tb.set_center_freq(400e6+i*10e6)&#xA;    print(tb.get_center_freq())&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-07-24T15:46:07.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8946" PostTypeId="2" ParentId="8944" CreationDate="2017-07-24T17:59:11.890" Score="2" Body="&lt;p&gt;GNU Radio doesn't drop packets – it's probably the UHD source that does that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's only one reason for that happening: Due to the additional CPU workload your filter introduces, your computer becomes too slow to process the samples that come in at 25 MHz in real time – buffers fill up, and at some point, they're full, so the new samples coming from the USRP can't be put anywhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know your filter specifications – but if they're anything like your grayed out low pass, that filter is &lt;strong&gt;massive&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To use the numbers I can guess from the screenshot:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;transition width $\Delta f=5\text{ kHz}$&lt;/li&gt;&#xA;&lt;li&gt;sampling rate $f_2=2457.6\text{ kHz}$&lt;/li&gt;&#xA;&lt;li&gt;attenuation $\delta_1=60\text{ dB}=10^{-6}$ (default in most GNU Radio filter design routines)&lt;/li&gt;&#xA;&lt;li&gt;passband ripple $\delta_1=1\text{ dB}=10^{0.1}$ (wild guess, might be to benevolent, this could be much better, and hence, computationally intense)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;and put these into this formula for the number of taps (&lt;a href=&quot;https://dsp.stackexchange.com/questions/31066/how-many-taps-does-an-fir-filter-need/31077#31077&quot;&gt;further notes&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\begin{align}&#xA;N&amp;amp;\approx \frac 23 \log_{10} \left[\frac1{10 \delta_1\delta_2}\right]\,\frac{f_s}{\Delta f}\\&#xA;&amp;amp;= \frac23\log_{10}\left[\frac1{10\cdot10^{0.1}\cdot10^{-6}}\right]\,\frac{2457.6}{5}\\&#xA;&amp;amp;\approx \frac23\log_{10}\left[10^{4.9}\right]490\\&#xA;&amp;amp;\approx 800&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you've got an 800 complex taps filter running at 2.4576 MHz on a complex data stream. That's nearly 8 billion floating point multiply-accumulate operations per second. Not a good situation! No wonder your computer is overtasked with that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you need only a few kHz of bandwidth on the output, shift (using the &quot;Rotator&quot; block) in frequency first, then resample to a much lower sampling rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few issues with your flow graph:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It's absolutely not clear what you'd need more than 2 MHz for if you're demodulating something with only 9600 bd – unless your modulation is an extreme spread spectrum modulation (and it's not, it's GMSK, which has a relatively compact spectrum). &lt;/li&gt;&#xA;&lt;li&gt;The parametrizations (bandwidth) of your graphical sinks make no sense at all – you might be misunderstanding things! The Nyquist bandwidth of a graphical sink is the sampling rate going into that sink – 25 MHz for the top Qt GUI Frequency sink, 2.4576 MHz for the lower two. So, please, clean that up! It doesn't have any effect on the signal you see, it's only used for labeling the frequency axis.&lt;/li&gt;&#xA;&lt;li&gt;There's no daughterboards for the X310 that have adjustable bandwidth – the 120 kHz setting in the USRP Source has no effect at all. If you just want 120 kHz of spectrum, by all means, use a sampling rate close to that. Now, 120 kHz is so extremely low that the USRP X310 can't decimate from its internal ADC rate to that, but if you really just want 120 kHz, well, use a sampling rate of maybe 1 MHz, not 25 MHz. The USRP will internally bandlimit the signal so that it fits into that 1 MHz without aliasing.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So, start with a much, much lower USRP sampling rate. The USRP internally filters in digital domain and decimates, too, so you get the oversampling SNR gain, no matter whether you resample in software or on the USRP. Only that the USRP has an FPGA dedicated to that job, and thus your CPU is free to process the much lower load that a lower rate sample stream means to your application.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-07-24T17:59:11.890" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="8948" PostTypeId="1" AcceptedAnswerId="8952" CreationDate="2017-07-26T16:30:21.937" Score="3" ViewCount="2312" Body="&lt;p&gt;I recently bought a very wideband SDR receiver (DX-Patrol MK4, declared covered frequencies are 100kHz-2GHz). I'm experimenting with antenna designs because unfortunately I live in an apartment building in the middle of the city and is not exactly an optimal spot for radio reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far I got decent results on the VHF side with a small loop (around 1m diameter), a simple 1:1 balun (wire wrapped around a ferrite ring) and about 2m coax feedline. &lt;strong&gt;Since somebody asked: I have a feedline because I have access to a balcony. I thought having the loop outside and having some feedline is better than inside with no feedline.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, assuming that:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;There is no way I can get the whole bandwidth with the same antenna, so I can set for two separate antennas if the need arises&lt;/li&gt;&#xA;&lt;li&gt;Because of 1. I want to keep the antenna as broadband as possible&lt;/li&gt;&#xA;&lt;li&gt;Optional: the antenna can be somewhat portable&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;My questions are:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is the loop (active or not) a good solution also for the 100kHz-20MHz range or should I set for another design?&lt;/li&gt;&#xA;&lt;li&gt;How can I improve the signal/noise ratio of my current loop (I already shielded the DX-Patrol with aluminium and I suppose ferrite beads along the feedline and USB cable would also help)? Would an additional amplifier help (the SDR has already an internal LNA)?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT: thanks everybody for the answers!&lt;/strong&gt; Lots to digest but I will try to keep up.&lt;/p&gt;&#xA;" OwnerUserId="9926" LastEditorUserId="9926" LastEditDate="2017-07-27T19:49:13.280" LastActivityDate="2017-07-27T19:49:13.280" Title="Broadband antenna for SDR radio" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8949" PostTypeId="2" ParentId="8948" CreationDate="2017-07-26T17:15:27.720" Score="1" Body="&lt;p&gt;I'm assuming that you're space-constrained and entirely indoors — if that's not correct, please update your question with more details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, the simplest thing: you talk about feed line, ferrite beads, LNAs. The simplest effective thing to do is skip the feed line and connect your receiver directly to the antenna feed point, or with as short a piece of coax as you can acquire (and use an active USB extension cable if you need one to make it reach). This minimizes loss and prevents feedline radiation/reception because there isn't any.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also don't need an amplifier that way &lt;em&gt;unless&lt;/em&gt; the signals you're looking for are weak compared to the inherent noise floor of your receiver. Amplifiers are always a last resort because they add noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ferrites &lt;strong&gt;on the USB cable&lt;/strong&gt; may be useful to prevent noise from the computer from reaching the receiver, but:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Try different computers (or e.g. an Android phone if you have one) to check if your chosen computer is particularly noisy, and use a different one for the purpose if so.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you do use ferrites, it is a much more efficient use of ferrite material if the hole is large enough to pass the cable through multiple times; the suppression increases with turns squared (to a point), whereas multiple beads strung on the cable are merely linear in dB.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;As to designing suitable antennas: having an antenna of the proper configuration makes a big difference. Trying to make a broadband LF-HF antenna that's also very small just doesn't work very well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I recommend you do is acquire a generous supply of insulated stranded wire and mess around with antenna configurations — see what works for you in your environment. Watch the SDR waterfall as you experiment. and remember that &lt;em&gt;more signal is better&lt;/em&gt; whether it's a wanted signal or if it's atmospheric noise. (On the other hand, for specific interference sources that you can identify, it's reasonable to try to fiddle your antenna to null them out.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One design I'd suggest you try is to string a wire in a loop around your apartment's ceiling — as much open area as you can find, even if it ends up with all sorts of bends around corners.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, buy or build a simple cheap manual antenna tuner (I got the &lt;a href=&quot;https://www.mfjenterprises.com/Product.php?productid=MFJ-902B&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ-902B&lt;/a&gt;) and use it to play with matching at the feed point. This is something you have to adjust for different frequencies, but a tuner &lt;em&gt;can&lt;/em&gt; make a significant difference for receiving when you're using a badly-chosen-for-the-band antenna.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-07-27T17:30:42.790" LastActivityDate="2017-07-27T17:30:42.790" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="8950" PostTypeId="2" ParentId="8948" CreationDate="2017-07-26T17:31:13.990" Score="3" Body="&lt;p&gt;When I was investigating antenna geometries for 2.4 GHz, looking for extremely wideband antennas that wouldn't need tuning, I came across (&lt;a href=&quot;https://turbofuture.com/misc/How-to-Build-Your-Own-Planar-Disk-Antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;article&lt;/a&gt;) a very simple wideband antenna.  Picture two discs (pizza pans?) as elements of a dipole. One connected to the coax shield and the other connected to the center conductor; this is NOT the antenna I was simulating, but it is a similar one:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WeBZk.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WeBZk.jpg&quot; alt=&quot;PCB antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In simulation using XfDTD it worked out quite well, and was very resistant to detuning by nearby metal surfaces.  &quot;nearby&quot; of course being relative to wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 2.4 GHz I was only looking for a fraction of the bandwidth you are, but I suspect you could experiment with this and have some fun.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastEditorUserId="4076" LastEditDate="2017-07-26T21:46:02.040" LastActivityDate="2017-07-26T21:46:02.040" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="8951" PostTypeId="2" ParentId="8885" CreationDate="2017-07-26T18:07:47.777" Score="0" Body="&lt;p&gt;Ground radials can be made from wire, or from copper tape, or other similar materials.  a quarter wavelength would be best, but that's about nine feet on that band, measuring from the base of the antenna to the end of the radials.  18 feet across which I'm sure is not going to fly for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, adding even less than optimum ground radials will help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A suggestion:  Tune for resonance, match for impedance if needed.  The losses even at a 2/1 impedance mismatch are pretty trivial, and contrary to popular belief, 50 ohms isn't magically the impedance of a properly tuned antenna.  A quarter wave monopole actually comes in around 37 ohms.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Monopole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Monopole_antenna&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mobile installs are ALWAYS a compromise, even up at VHF where the vehicle is much larger in terms of wavelength.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2017-07-26T18:07:47.777" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8952" PostTypeId="2" ParentId="8948" CreationDate="2017-07-26T19:22:46.257" Score="3" Body="&lt;p&gt;Adressing your two questions first:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is the loop (active or not) a good solution also for the 100kHz-20MHz range or should I set for another design?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;fractional bandwidth of antennas&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Woah! 20 MHz is 200 times the frequency of 100 kHz. No, a loop antenna won't have that amount of bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For antennas, we measure the bandwidth in &lt;em&gt;multiples of the center frequency&lt;/em&gt;. For example, an antenna working well from 2.3 GHz to 2.5 GHz has a bandwidth of 200 MHz, with a center frequency of 2.4 GHz – that's a fractional bandwidth of $\frac{200\,\text{MHz}}{2400\,\text{MHz}} = \frac1{12}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;wideband antennas&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We tend to call antennas &quot;wideband&quot; as soon as their fractional bandwidth reaches $\frac15$. Really impressive wideband antennas reach fractional bandwidths of $\frac{11}{10}$ (UWB antennas) – and those really don't have the efficiency of an antenna you'd want to work with (aside from being very very costly to make).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, what you demand of your antenna if it has to cover 100 kHz to 20 MHz is that it has a fractional bandwidth of $\frac{19900\,\text{kHz}}{10050\,\text{kHz}}\approx 1.98$. Such antennas have not yet been invented, to my knowledge!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;loop antennas&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, a loop antenna especially has what we call high Q – it is narrowband, rather than wideband. That has a lot of advantages; for example, it can be relatively small compared¹ to the wavelength $\lambda$, and it doesn't pick up noise or interference from frequencies that you don't care about – that's primarily important to keep your first amplifier stage from becoming non-linear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quite luckily, you don't have to buy an infinite number of antennas – many antenna types can be &lt;em&gt;tuned&lt;/em&gt; to a specific frequency. Downside of tuning is that it happens mechanically – e.g. by adjusting a variable capacitor – but it works. Still, this means that the 1 MHz from 100 kHz to 1100 kHz is much harder than the 100 MHz between 1 GHz and 1.1 GHz!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;practice&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, most often, you'd encounter a set of antennas, working on different, usually separated, bands, instead of one antenna that tries to receive all these bands and the spectrum in between.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How can I improve the signal/noise ratio of my current loop (I already shielded the DX-Patrol with aluminium and I suppose ferrite beads along the feedline and USB cable would also help)? Would an additional amplifier help (the SDR has already an internal LNA)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;to amplify or not to amplify, that is the question&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gut feeling: If your receiver already has an LNA, you'd need to invest relatively much money to get an LNA with a better noise figure, so, no, that's usually not the way to go, unless your signal is below the sensitivity of your receiver, even without its input amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;sensitivity, or: the magic of oversampling&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, with SDR, defining &lt;em&gt;sensitivity&lt;/em&gt; is a bit challenging – after all, the &lt;em&gt;receiver&lt;/em&gt; is not only the thing doing the RF reception, the mixing, and the analog to digital conversion, the actual extraction of the signal of interest from the received signal (for example, the FM-modulated voice, or the PSK31 data) happens &lt;em&gt;in software&lt;/em&gt;. The trick usually employed by SDR receivers is &lt;em&gt;oversampling&lt;/em&gt;, which means that you have a signal of a given bandwidth $b$, but you sample it with a multiple of that, let's say $f_s = n\cdot b$. Then, through digital signal processing, namely filtering and decimation by $n$, you can get an SNR increase by $n$ (only applies to white noise)².&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Example&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know the MK4, but I think it's based on an RTL2832. That chip will happily give you (I think) up to 3.2 million samples per second, $f_s=3.2\,\frac{\text{MS}}{\text s}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, let's say you want to hear a CW/morse station whose bandwidth you can limit to let's say $b=1\,\text{kHz}$; therefore, our $n= \frac{f_s}{b}= 3200$; assuming perfect filtering (we can't, really, make that assumption without a bit of mathematical justification, but bear with me for the time being), that's an SNR win of $3200\approx 35\,\text{dB}$. Now, assume your actual morse decoder (might be your ear) needs an SNR of $6\,\text{dB}$ – then you can still work with an input SNR of $-29\,\text{dB}$ That's nearly thousand times the signal energy in noise!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can see that in action every time we activate our GPS receivers: The GPS signal reaching earth is really weak – in fact, it's weaker than the thermal noise in any non-cryogenically-cooled receiver. But: due to the high processing gain (correlation) of GPS receivers, that's no problem. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;advantages of SDR and their limits&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that it's digitally trivial to select &lt;em&gt;any 1 kHz&lt;/em&gt; from your sampled bandwidth – building an analog filter that could do the same would be terribly complicated, and that filter would be much worse in all relevant aspects (suppression, steepness, loss)!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, that's why we rather do high-sampling-rate SDR than analog narrowband receivers these days. As hinted at above, this hits limits when the RX chains becomes nonlinear (meaning that the amplified signal amplitude at every time instant isn't really the same factor times the input signal amplitude), because then you get intermodulation. This can happen, for example, if you put your receiver to maximum gain (to receive a weak signal), but your antenna also picks up a strong signal, which isn't filtered out before it reaches the amplifiers. The amplifier does its best, but it can only scream so loud, and suddenly, things that aren't actually there &quot;on the air&quot; get mixed into the signal of interest. But: that can often be countered with relatively relaxed analog bandpass filters (or bandstop filters, to suppress known narrowband interferers) and gain limitation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since frequency-selective antennas basically &lt;em&gt;are&lt;/em&gt; bandpass filters, that explains SDSolar's &lt;a href=&quot;https://ham.stackexchange.com/questions/8948/broadband-antenna-for-sdr-radio/8952#comment13336_8948&quot;&gt;comment&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;With the wideband capability of those receivers you will want specific antennas to focus on specific frequency ranges, even if the signal is very close to you. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Since your SDR receiver can receive such a huge swath of spectrum (100 kHz to 2 GHz), it's impossible it has a narrow bandselection filter in front of the LNA³, thus it's likely that an interferer much stronger than your signal of interest will get picked up by your receiver. If that interferer is sufficiently strong to bring your receiver into nonlinearity, you get problems. Notice that the spurious free range of LNAs is often not that small – but I haven't tested the MK4 myself, and I generally have learned not to trust marketing brochures and manuals, so I can't say at which interferer power that will happen. But: the LNA will definitely be much nicer to your signal than the RTL2832-integrated amplifiers, so do try to keep the LNA active (and if it has adjustable gain, as close as possible to maximum), and use the gain of the RTL only to make the signal &quot;fit&quot; the whole ADC range. You'll probably notice when you're overdriving any amplifier in the chain – you'll see &quot;ghost&quot; frequencies becoming stronger faster than the real-world signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹: $\lambda(f) = \frac{c_0}{f}\implies \lambda(100\,\text{kHz}) \approx \frac{3\cdot10^8\,\frac{\text m}{\text s}}{10^5\,\text{s}^{-1}}= 3\cdot10^{3}\,\text m=3\,\text{km}$, by all means, that's HUGE!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;²: Beinaymé formula&lt;/p&gt;&#xA;&#xA;&lt;p&gt;³: In fact Dynamic Range-optimized special-purpose SDRs (e.g. for localization) do have exactly that, a bank of band-selection filters, but that's &lt;em&gt;really&lt;/em&gt; expensive; good filters are actually what makes things like professional wideband measurement equipment so freaking expensive.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-07-26T19:43:56.727" LastActivityDate="2017-07-26T19:43:56.727" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8953" PostTypeId="2" ParentId="8917" CreationDate="2017-07-27T01:38:37.507" Score="1" Body="&lt;p&gt;Your reasoning is correct: in principle, given identical bit rate and signal power, the BER for BPSK and QPSK are identical. The Wikipedia &lt;a href=&quot;https://en.wikipedia.org/wiki/Phase-shift_keying#Quadrature_phase-shift_keying_.28QPSK.29&quot; rel=&quot;nofollow noreferrer&quot;&gt;article on PSK&lt;/a&gt; puts it nicely. The author there points out that you can think of a QPSK signal as two BPSK signals in the same channel, since they are orthogonal (one is built from sines, the other from cosines). You double the bit rate and double the power, and as you point out, it comes out the same in the end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there are some assumptions made in this calculation that don't necessarily hold in the real world. In order to make the calculation tractable, you have to assume (1) at the receiver you know the frequency and phase of the carrier precisely, and (2) you know precisely where the boundaries between bits occur.  Neither assumption is true in the real world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps bit synchronization in noisy conditions is harder for QPSK than for BPSK. Maybe since BPSK's phase changes at the boundaries are on average bigger than QPSK's,  you get better boundary estimates for BPSK. I'm sure there are other effects as well. The only way to be really sure is to run a simulation of a realistic demodulator, as the PSK31 author did.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would think that the effects of FEC would be a separate issue.  I didn't see an apples-to-apples comparison in the PSK31 paper you linked to, and I don't know enough about the performance of FEC as a function of SNR to comment anyway. The comparison that I saw was between QPSK with error correction and BPSK without. Assuming for the sake of argument that FEC improves BER up to a certain point, then collapses (seems reasonable), you might see the behavior described in the PSK31 paper.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is all a bit speculative, but I hope I've made clear that the devil is in the details. Theory makes use of assumptions that sometimes are violated in the real world - otherwise you can't do the calculations - but in this case, I think that a thorough simulation is really the gold standard.&lt;/p&gt;&#xA;" OwnerUserId="9464" LastEditorUserId="9464" LastEditDate="2017-07-27T02:49:27.730" LastActivityDate="2017-07-27T02:49:27.730" CommentCount="13" ContentLicense="CC BY-SA 3.0" />
  <row Id="8954" PostTypeId="2" ParentId="156" CreationDate="2017-07-27T02:15:36.740" Score="2" Body="&lt;p&gt;A Technician license is absolutely useful in emergency communications.  What you are really asking is &quot;Is tech good enough if I need to talk long distance?&quot;  The reality is local communications are just as critical (if not more critical) in times of emergency.  Simplex VHF/UHF, or access to local repeaters to get local aid is more likely what you are going to actually need in most situations.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having expanded HF privileges from General or Extra are a nice bonus, but hardly a requirement for being effective at the local level.&lt;/p&gt;&#xA;" OwnerUserId="10074" LastActivityDate="2017-07-27T02:15:36.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8955" PostTypeId="1" CreationDate="2017-07-27T02:18:47.653" Score="5" ViewCount="703" Body="&lt;p&gt;I'd like to put a WSPR or JT65-like transmitter on a high-altitude balloon, but lacking much experience with HF antennas, I don't quite know where to start. I'm thinking it will operate on 20 meters, at (obviously) low power, say 100 mW or less. Building a lightweight little transmitter with an Arduino seems do-able, and I can hang a wire from it as long as I like, within reason, but I'm not sure how to match to it, what to use for a counterpoise, and so on. Radials longer than about a foot are out, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've googled a bit, and found all kinds of stuff about HF antennas lofted by balloon, but all those are tethered to the Earth. This will be free-floating. No ground plane to be found anywhere, no transmission line (if I can help it), no big structure holding wires apart.  Weight is a big issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: another concern. The problem with a dipole occurs on the way down, after the balloon bursts at altitude.  Things go thrashing around pretty badly at that point, until the atmosphere gets thicker and the parachute can take hold. I have read at least one claim that the whole package can almost go supersonic!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I worry about what a weight at the end of a 5 meter wire might do. Especially since this won't be the only payload on this balloon. I can just imagine what a 5 meter wire weighted at both ends could do, which is what I'd be looking at if I hung the electronics package in the middle of a dipole. Far better to put the weight as close as possible to the parachute, in one place if I can do it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe I worry too much. I thought about a simple quarter-wave wire, but then what's the counterpoise?  There has to be something.&lt;/p&gt;&#xA;" OwnerUserId="9464" LastEditorUserId="9464" LastEditDate="2017-07-27T06:16:28.100" LastActivityDate="2017-08-09T17:29:03.210" Title="HF antenna design for high-altitude balloon" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="3" CommentCount="9" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8956" PostTypeId="2" ParentId="8955" CreationDate="2017-07-27T05:38:28.270" Score="3" Body="&lt;p&gt;The most sensible antenna is a wire dipole extending above and below the electronics package.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems to be how all the QRP Labs transmitters work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Self-supporting radials, or a coax cable feed to the centre of the antenna, will be much heavier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could optimise the weight by trading some length for some inductance at the transmitter, without reducing the efficiency much.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2017-07-27T05:38:28.270" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8957" PostTypeId="1" CreationDate="2017-07-27T05:57:03.143" Score="2" ViewCount="1025" Body="&lt;p&gt;I'm confused by the difference between the phase velocity and transmission line propagation velocity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://en.wikipedia.org/wiki/Speed_of_electricity&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Speed_of_electricity&lt;/a&gt;, in a good conductor, phase velocity (speed of an electromagnetic wave) is  given by&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\sqrt{2 \times \text{angular frequency} \over \text{permeability} \times \text{conductivity}}.$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From this we can calculated that 60Hz wave travels along a wire at about 3.2m/s (and group velocity is about twice this speed).  This does not gel with my experience of turning on a light switch!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Telegrapher%27s_equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;Telegraphers equations&lt;/a&gt; say that the speed of propagation in a lossless transmission line is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 1\over\sqrt{\text{inductance} \times \text{capacitance}}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which tends to give velocities up around the speed of light.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is disconnect here that I can't quite put into words.  Best I can do is - what does the phase velocity of 3.2m/sec mean and how does it relate to the result derived from the telegraphers equation (if it relates at all)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cheers&lt;/p&gt;&#xA;" OwnerUserId="10075" LastEditorUserId="218" LastEditDate="2019-12-11T17:06:10.100" LastActivityDate="2019-12-11T17:06:10.100" Title="Difference between Phase Velocity and Velocity of propagation in a transmission line" Tags="&lt;propagation&gt;&lt;transmission-line&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="8958" PostTypeId="2" ParentId="8887" CreationDate="2017-07-27T09:54:20.413" Score="1" Body="&lt;p&gt;Endfeds ( some, maybe all) depend on the coax (shield) to provide the &quot;un-needed&quot; counterpoise.&#xA;One endfed in particular strongly suggests a 16ft. long coax. When using a shorter piece, they suggest a 16ft. counterpoise wire.&#xA;I suggest you try a shorter .... as short as possible .... run of coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Matt - KF4ZGZ&lt;/p&gt;&#xA;" OwnerUserId="10078" LastActivityDate="2017-07-27T09:54:20.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8959" PostTypeId="2" ParentId="8955" CreationDate="2017-07-27T13:29:19.377" Score="4" Body="&lt;p&gt;May I suggest coaxial sleeve antennas and variants, see links below:-&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.eham.net/ehamforum/smf/index.php?topic=46338.0;wap2&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.eham.net/ehamforum/smf/index.php?topic=46338.0;wap2&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=w8hQRjI3BPk&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=w8hQRjI3BPk&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This last is a smaller 6m version, the choke balun is not needed if your Transmitter is directly&#xA;connected at this point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bazooka variant could also be of use. Do a search for 2m Bazooka and hamuniverse for more details.&#xA;Also on hamuniverse is the 20 Meter &quot;Vertical Zepp Dipole&quot; Antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This hanging upside down from the balloon should radiate as a vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;None of these require grounds, radials or counterpoises.&#xA;Hope this is useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit&lt;/strong&gt;&#xA;I have just seen the comment about weight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For RG-174 the spec is here &lt;a href=&quot;http://www.belden.com/techdatas/metric/8216.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.belden.com/techdatas/metric/8216.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a 20m dipole, we have the following calculations:-&lt;/p&gt;&#xA;&#xA;&lt;p&gt;WSPR Freq = 14.097MHz &amp;amp; JT-65 Freq = 14.076MHz, so wanted average = 14.0865MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore Lambda = 3E8/14.0865E6 = 21.297m&#xA;A half-wave coaxial dipole = 10.648m if we ignore velocity factor (worst case) we see from the specs above that the feeder weight is&#xA;11.906 Kg/Km so 11.906 g/m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore the weight would be 11.906*10.648 = 126.78g or approx. 127g.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am from the UK so here we switch to Imperial measurements:&#xA;127g = 4.48 ounces or approx. 4.5 ounces.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using RG-58 from the specs &lt;a href=&quot;https://www.pasternack.com/images/ProductPDF/RG58C-U.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.pasternack.com/images/ProductPDF/RG58C-U.pdf&lt;/a&gt;&#xA;we see 40g/m so the weight would be 40*10.648 = 425.92g or approx. 426g.&#xA;or 15 ounces, just under an imperial pound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being unfamiliar with high-altitude ballooning I am unsure if this exceeds and safe/maximum loads. Also, it seems that most people are using 434MHz licence exempt kit requiring much smaller and lighter antennas.&lt;/p&gt;&#xA;" OwnerUserId="8976" LastEditorUserId="8976" LastEditDate="2017-08-07T19:18:11.100" LastActivityDate="2017-08-07T19:18:11.100" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8960" PostTypeId="2" ParentId="8922" CreationDate="2017-07-27T13:53:20.573" Score="0" Body="&lt;p&gt;From a practical standpoint, it seems to me that any variation on the classic fully isolated sound card interface should work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.qsl.net/sra/sound_card.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.qsl.net/sra/sound_card.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look at slide 9 or 12 and simply connect the computers sound card ports or a TNC to the sound card mic &amp;amp; speaker lines.&#xA;The radios mic ground will then remain isolated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this is the correct interpretation of what the OP was asking.&lt;/p&gt;&#xA;" OwnerUserId="8976" LastActivityDate="2017-07-27T13:53:20.573" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8961" PostTypeId="2" ParentId="156" CreationDate="2017-07-27T15:14:17.787" Score="0" Body="&lt;p&gt;I used a lot of tech class licensees with Skywarn.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As others said, the tech license won't really get you into the HF area, unless you are operating as many do at Field day, under the authority of someone with a higher class license. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2017/19-2017%20FD%20-%20Control%20Operator%20Info%20-%20Who%20is%20in%20control.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/files/file/Field-Day/2017/19-2017%20FD%20-%20Control%20Operator%20Info%20-%20Who%20is%20in%20control.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See the fourth and fifth questions.  It would be better if you didn't need a control operator, but as long as the legal requirements are met you're in the clear.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2017-07-27T15:14:17.787" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8962" PostTypeId="2" ParentId="8957" CreationDate="2017-07-27T15:43:36.010" Score="4" Body="&lt;p&gt;The first equation describes a wave propagating in a &lt;em&gt;conductor&lt;/em&gt;. The second equation describes a wave propagating in a &lt;em&gt;dielectric&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Electromagnetic waves don't propagate well in good conductors. If the conductor is good, that means a small electric field in the conductor can result in a large current. With the large current comes large ohmic losses, and thus the energy is rapidly dissipated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the conductor is ideal, with infinite conductivity, an electric field can't exist in it at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, a conductor can exist at a different electric potential than the things around it, provided it's separated some kind of thing that can support an electric field. Like air, PTFE, or indeed most everyday materials that aren't conductors. These things are all &lt;em&gt;dielectrics&lt;/em&gt;. An electric field can exist in this dielectric, and it's this field which is responsible for energy transfer in everyday experience.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-07-27T15:43:36.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8963" PostTypeId="1" CreationDate="2017-07-27T17:05:06.197" Score="4" ViewCount="4932" Body="&lt;p&gt;In a &lt;a href=&quot;https://ham.stackexchange.com/questions/8948/broadband-antenna-for-sdr-radio&quot;&gt;related question&lt;/a&gt; about a broadband antenna for SDR it was suggested me to build or buy an antenna tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Since maybe it was not clear to everybody, I'm designing an antenna tuner for reception, not transmission.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Searching around I concluded that most designs are variations on two main ideas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VgDOD.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VgDOD.jpg&quot; alt=&quot;first&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first is presented, among others, &lt;a href=&quot;https://www.youtube.com/watch?v=6QwBiz_LB9M&quot; rel=&quot;nofollow noreferrer&quot;&gt;in a nice video by Stan Gibilisco&lt;/a&gt; but applies to wire antennas, whereas I would like to have a loop or dipole antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hLZbZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hLZbZ.jpg&quot; alt=&quot;second&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second is &lt;a href=&quot;http://vk5ajl.com/projects/tuner.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;presented here&lt;/a&gt; although is designed for transmission and not reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as my understanding goes, the one from Gibilisco is essentially a tank circuit defined by L and C that can be tuned to a specific resonant frequency and the inductor is used for impedance matching with the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;The other is a series LC circuit (T-network) but I don't understand why a second capacitor is needed. There is a sort of explanation on the link but I can't wrap my head around it.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore I would like feedback on what I'm thinking of building:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W6nTg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W6nTg.jpg&quot; alt=&quot;antenna tuner&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The loop (about 1m diameter) is placed outside and is directly connected to a 1:1 current balun (ferrite ring) that feeds to a coax cable going inside. The variable capacitor (50-1000pF, two gang connected together) is in parallel with a rotary switch that can insert different inductors to have different tank circuits for different bands. A variable inductor is in parallel with the tank circuit and gives the impedance matching for the radio (since I don't have one or I will need to buy one this will be inserted later in the circuit).&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is it a sensible design?&lt;/li&gt;&#xA;&lt;li&gt;If 1., is the value of the last inductor (the &quot;matching&quot; inductor) relevant?&lt;/li&gt;&#xA;&lt;li&gt;Is the balun going to change its transformer ratio (that right now is 1:1) when different inductors are switched in the circuit?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;4. Related to the second design (the VK5AJL design), why there are two capacitors? Wouldn't a L or tank circuit also work?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="9926" LastEditorUserId="9926" LastEditDate="2017-07-28T09:10:07.927" LastActivityDate="2020-01-23T00:09:25.963" Title="Antenna tuner design" Tags="&lt;diy&gt;&lt;antenna-tuner&gt;&lt;loop-antenna&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8964" PostTypeId="2" ParentId="8957" CreationDate="2017-07-27T19:43:20.690" Score="1" Body="&lt;p&gt;The speed of light (or any EM wave) slows in a material because the EM wave makes charges, such as electrons, move.  The movement of the charges then re-radiates the EM wave.  The net effect is that the EM wave slows down.  In an insulator (which is what we hams might call a dielectric) the electrons don't like to move, and therefore the EM wave doesn't slow down very much.  In a conductor, the electrons are easy to move, and therefore the EM wave slows down a lot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think your confusion is really about energy flow.  When you flip on the light switch, the light comes on pretty much instantaneously.  That's because the wire delivers energy to the light bulb right away.  But... the energy does not flow through the conductor!  Instead, it flows through the space around the conductor.  Mathematically, the energy flow is given by the Poynting vector $S = E \times H$, where $E$ is the time-varying electric field and $H$ is the magnetic field.  Here (from &lt;a href=&quot;https://en.wikipedia.org/wiki/Poynting_vector#Coaxial_cable&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;) is what happens inside a coaxial cable:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/klV1I.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/klV1I.png&quot; alt=&quot;Poynting vector in a coaxial cable&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Small circles with an &quot;x&quot; in the middle are vectors pointing into the page, and those with a dot in the middle are vectors pointing out of the page.  You can see that the energy flow takes place within the dielectric, not the conductor.  As you point out, the speed of an EM wave in a dielectric is close to that in a vacuum, so the energy moves quickly &lt;em&gt;around&lt;/em&gt; the wire to the light bulb.&lt;/p&gt;&#xA;" OwnerUserId="9464" LastActivityDate="2017-07-27T19:43:20.690" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8965" PostTypeId="1" AcceptedAnswerId="8968" CreationDate="2017-07-27T19:48:46.863" Score="3" ViewCount="3341" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/8948/broadband-antenna-for-sdr-radio&quot;&gt;On a previous question&lt;/a&gt; I asked about proper antenna design for wideband SDR receiver and ways to improve signal/noise ratio. Ideally the reciever has a range of 100kHz-2GHz. Keeping in mind is impossible to cover the whole spectrum with one antenna, I'm trying to settle with as few antennas as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Searching for wideband antenna designs I stumbled upon this examples. I would like to know which of these designs to choose, or any other you can recommend:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;The PA0RDT mini-whip&lt;/a&gt; design. Allegedly 10kHz-20MHz, used also by the famous WebSDR of the Uni Twente. Uses JFETs and I don't have a cheap source for them. I would settle for an equivalent.&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://apollo.open-resource.org/mission:log:2012:08:02:active-wideband-receiver-antenna-for-sdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Dressler&lt;/a&gt;-type antenna for 50MHz-2GHz&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.ltpaobserverproject.com/uploads/3/0/2/0/3020041/wideband_loop_antenna.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;This&lt;/a&gt; or variations thereof, loop-amplifier-balun. &lt;a href=&quot;http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt; a more complicated one that claims LW reception and up until 50MHz (just found &lt;a href=&quot;http://www.ik4hdq.net/doc/testi/loop_lb.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; also).&lt;/li&gt;&#xA;&lt;li&gt;Bonus: just found &lt;a href=&quot;http://ieeexplore.ieee.org/document/7801313/?section=abstract&amp;amp;part=1&quot; rel=&quot;nofollow noreferrer&quot;&gt;this antenna&lt;/a&gt; for 3.1-10.6GHz, can it be scaled down (or up? Down with the frequency up with the size)?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="9926" LastEditorUserId="76" LastEditDate="2017-07-27T21:09:27.390" LastActivityDate="2017-07-29T13:31:31.017" Title="Choosing a wideband antenna design" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;&lt;equipment-design&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8966" PostTypeId="2" ParentId="8963" CreationDate="2017-07-27T22:55:08.953" Score="1" Body="&lt;p&gt;For your loop antenna concept - no, it is not a sensible design but some slight tweaks will bring substantial improvement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A balun is not a universal impedance transformation or choking device. When it is presented with largely reactive loads, its characteristics differ from ideal. This often results in core losses and in worst cases, destruction of the balun in a transmitting configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A small loop antenna exhibits very high inductive reactance and very low radiation resistance. The variable capacitor is normally placed on the loop side of the diagram in order to be most effective in countering the inductive reactance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The tuning will be quite sharp so you may wish to design a remote tuning feature for the variable cap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several loop modeling tools on the Internet. Once you have modeled the antenna to determine its complex impedance, then the balun and antenna tuner can be configured to match. Doing it prior to modeling is just taking a shot in the dark.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-07-29T12:46:19.050" LastActivityDate="2017-07-29T12:46:19.050" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8967" PostTypeId="1" CreationDate="2017-07-28T15:23:51.850" Score="2" ViewCount="655" Body="&lt;p&gt;I've got a USRP X310, currently with just one daughterboard, a WBX-120. I'm writing some C which needs to operate the radio full duplex - I receive on RF A RX2 and transmit on RF A TX/RX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I'm confused as to how I identify which number channels I use, because I was under the impression that the function &lt;code&gt;uhd_usrp_set_tx_subdev_spec&lt;/code&gt; essentially attached my TX path to a particular channel. So if I call &lt;code&gt;uhd_usrp_set_rx_subdev_spec&lt;/code&gt; and then &lt;code&gt;uhd_usrp_set_tx_subdev_spec&lt;/code&gt; with &lt;code&gt;A:0&lt;/code&gt; as the subdevice, am I getting RX on channel 0 and TX on channel 1, or am I getting both on channel 0?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens when I add the second daughterboard, to be an SBX-120? In pseudocode I will be calling:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;uhd_usrp_set_rx_subdev_spec(&quot;A:0&quot;)&#xA;uhd_usrp_set_tx_subdev_spec(&quot;A:0&quot;)&#xA;uhd_usrp_set_rx_subdev_spec(&quot;B:0&quot;)&#xA;uhd_usrp_set_tx_subdev_spec(&quot;B:0&quot;)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Will these then be channels 0, 1, 2, 3? What happens if I change the order of calling &lt;code&gt;uhd_usrp_set_xx_subdev_spec&lt;/code&gt;?&lt;/p&gt;&#xA;" OwnerUserId="10056" LastEditorUserId="76" LastEditDate="2017-07-29T00:14:53.443" LastActivityDate="2017-08-29T18:05:31.643" Title="USRP: Are RX and TX on the same or different channel for single daughterboard?" Tags="&lt;software-defined-radio&gt;&lt;software-development&gt;&lt;usrp&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8968" PostTypeId="2" ParentId="8965" CreationDate="2017-07-28T15:38:05.963" Score="3" Body="&lt;p&gt;This is definitely not a definite answer, but let's start an answer to gather insights:&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;The PA0RDT mini-whip design. Allegedly 10kHz-20MHz […] Uses JFETs and I don't have a cheap source for them. I would settle for an equivalent.&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;That's just an active antenna. The antenna part is a really small rectangle, and thus, the reception efficiency is extremely small. The power levels coming out of the device are only high because noise and signal have both been amplified.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;An &quot;active antenna&quot; such as the mini-whip is really just an antenna with an integrated amplifier, nothing more or less. &lt;/li&gt;&#xA;&lt;li&gt;The mini-whip isn't a wideband antenna at all –&#xA;the antenna part is just consistently bad across all frequencies of&#xA;interest.&lt;/li&gt;&#xA;&lt;li&gt;I don't know whether we've talked about this – but usually&#xA;&quot;I can't source JFETs&quot; is more of a misunderstanding, and not a fact,&#xA;lest you're living in a really remote region of this world. Also, you can usually   replace old JFETs (depends on the type, of course) with modern&#xA;MOSFETs and get even higher input impedance with same gain &amp;amp; noise&#xA;specs.&lt;/li&gt;&#xA;&lt;li&gt;Being kilometers in wavelength, the 10 kHz – 20 MHz range will definitely require you to use an electrically short antenna, so might as well just use this&lt;/li&gt;&#xA;&lt;li&gt;Beware that the high gain of this amplifier, plus the fact that the rectangular aperture antenna actually used by the mini-whip means that it's extremely susceptible to noise pickup from nearby electronics – there's nothing &quot;preferring&quot; your signals of interest over noise of anything close to the amplifier. I'd argue you'd want to mount this antenna far away from your electronics.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h1&gt;The Dressler-type antenna for 50MHz-2GHz&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;That's a very, very interesting antenna design, from an antenna theory point of view. It's a true wideband antenna, and that's by the fact that it's basically made of a gap between two conductors that increases over its length – think of an array of dipoles, each one with a different length.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Larger, hard to build, probably not really all that efficient at the lowest frequencies, but pretty!&lt;/li&gt;&#xA;&lt;li&gt;I'd argue that it might pay most to restrict it to 200 MHz – 2 GHz; that makes building easier&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h1&gt;Loop-amplifier-balun&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Loop antennas is actually what I'd go for in the lower frequency regime. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But: Loop antennas inherently have very bandwidth. They're never wideband. You'll need to &lt;em&gt;tune&lt;/em&gt; them to achieve more frequency coverage (the bandwidth of an antenna is what it can receive at any &lt;em&gt;single&lt;/em&gt; point in time, without detuning it). The article claims its antenna is &quot;wideband&quot;, but that's not true – it's just &quot;consistently good enough with amplification&quot;, see the mini-whip (of course, a large loop diameter makes for a much more efficient receive antenna than a small patch of metal, but still, not an efficient antenna at a wavelength that is 3 orders of magnitude larger than the antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And: Amplifier circuits based on the transistor BF494... sigh. These transistors have become &lt;a href=&quot;http://www.mouser.de/ProductDetail/Fairchild-Semiconductor/BF494/?qs=UMEuL5FsraBRaTSIb6opfA==&quot; rel=&quot;nofollow noreferrer&quot;&gt;obsolete&lt;/a&gt; a long time ago – there's simply cheap replacements that are superior in every technical aspect, especially temperature behaviour, noise and inter-device variations, that engineers designing a circuit post-1990 wouldn't even consider these devices. But, that's the beef I have with ham magazines, schematics are covered by the editors for decades (not only years, decades), without critical inspection. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And that's the primary reason why there's a huge disconnect between what is technically possible and cheap these days and what's used by amateurs all over the world. Whilst the physics governing how antennas must be shaped haven't changed over the last 90 years, semiconductor device state of the art has. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's beyond me how that happens – Circuits with transistors you can't even buy (aside from the astronomic prices of people who've bought up devices as soon as they went out of production) can't really be a selling point for magazines.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;just found this antenna for 3.1-10.6GHz, can it be scaled down (or up? Down with the frequency up with the size)?&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Exactly, down with the frequency, up with the size, inversely proportionally. So, to get this from 3.1 GHz – 10.6 GHz down to 3.1 MHz – 10.6 MHz, the thing needs to be increased in size by a factor of 1000.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd argue that this is a relatively hard design to scale up. Stick with the common wideband antenna types that can be implemented &quot;flatly&quot;, being:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;logarithmic-periodic antennas (logper)&lt;/li&gt;&#xA;&lt;li&gt;Vivaldi Antennas&lt;/li&gt;&#xA;&lt;li&gt;Other tapered slot helicals (like the &quot;Dressler&quot;-type you mentioned)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h1&gt;Other, commonly encountered things&lt;/h1&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For the 50 – 250 MHz range, I'd really just go with a telescope monopole antenna – exactly the thing your old portable stereo has  (had?). I'm advising someone who's been designing, testing and verifying a DAB+ receiver with nothing more than that. It works well, and is easily tuned to any specific frequency by extending/pushing it back together to be ¼ wavelength&lt;/li&gt;&#xA;&lt;li&gt;For the impressively low frequency ranges below 30 MHz, you'll probably want a resonant antenna (I think SDSolar would agree :) ), and that means you'll need a tunably capacitor or inductor. You noticed that, and asked a question pertaining to the design of tuners. It's easier than it looks (again... ham articles being 40 to 50 years stuck in the past).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-07-28T15:38:05.963" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="8969" PostTypeId="2" ParentId="8963" CreationDate="2017-07-28T16:13:52.423" Score="4" Body="&lt;p&gt;So, yes, to tune a resonant antenna, you'll need an adjustable capacitor or inductor. You'd usually go the capacitor route, since adjustable caps are smaller, cheaper, and more exact, usually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bonus: There's &lt;em&gt;electronically&lt;/em&gt; variable capacitors! They're called &lt;em&gt;varactors&lt;/em&gt; or &lt;em&gt;varicaps&lt;/em&gt; (or just &lt;em&gt;variable capacitance diode&lt;/em&gt;), and they're a very mature (read: old &amp;amp; well-tested and used everywhere) and thus, cheap, method of tuning receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You probably have heard of what a diode does in reverse bias: it doesn't conduct. Of course, that means that there's then two conductive pieces isolated from each other. Since the blocking layer is relatively thin in a diode, these work as a capacitor. By changing the voltage bias, you can make that layer thinner or thicker, and thus, you can change the capacity of that &quot;accidental&quot; capacitor with a DC voltage. Awesome!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you design a diode for exactly that purpose, you can make sure that this effect is very well-controlled. These diodes then are sold as varicaps/varactors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.radio-electronics.com/info/data/semicond/varactor-varicap-diodes/circuits.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.radio-electronics.com/info/data/semicond/varactor-varicap-diodes/circuits.php&lt;/a&gt; has a few very minimal circuits illustrating the usage of varicaps. The back-to-back configuration is what you usually encounter:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/VAYrw.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fVAYrw.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, when you look at a typical &lt;em&gt;small loop&lt;/em&gt; (that's actually a specific term for an antenna that is &lt;em&gt;small in comparison to the wavelength&lt;/em&gt;, not generally for &lt;em&gt;small&lt;/em&gt; antennas) antenna, you'll notice it's usually simply a loop, in parallel with a capacitor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, a loop is a coil is an inductor. Inductor in parallel with capacitor makes resonant circuit. The frequency of resonance is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ f = \frac1{2\pi\sqrt{CL}}$$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;L scales with size and length of the coil, and C is usually made adjustable. Thus, in the place where in the classical small-loop antenna you'd find the manually adjustable capacitor, you could place the adjustable capacity circuit I mentioned above. Battery operation is a good idea here, for both noise and potential separation reasons; that doesn't mean you couldn't also use a bog-normal 230 V -&gt; 12 V transformer, rectify the resulting voltage, smoothen the hell out of that voltage and then add a simple voltage divider or adjustable voltage regulator to drive the varicaps, &lt;em&gt;as long as everything float&lt;/em&gt; relative to your receiver – you'll be the ground of your voltage source to one end of your receiver coil, and you don't want that to be &quot;accidentally&quot; connected to real ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding practical varicaps that you can buy: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;well, look in the places where you'd buy electronic components. I've got good experiences with Mouser, shipping was 5–6€, I think. The BB 640 series (&lt;a href=&quot;http://www.mouser.com/ds/2/196/bb640series-13352.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;datasheet&lt;/a&gt;) looks like a good match for you – nearly 20 times the maximum capacity than minimum capacity means that you can change the resonant frequency over a range of &lt;span class=&quot;math-container&quot;&gt;$\sqrt{20}$&lt;/span&gt; (see above formula for resonant frequency). If the maximum achievable capacity is too low for you, just put multiple in parallel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just throwing together a few numbers: I looked for an online one-turn loop inductance calculator. Found it, and put in a radius 0.5m loop made of 0.5mm diameter copper wire. Got a 2 µH inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then I said, ok, let's do hundred turns of that. We'll end up with 200 µH inductance. I'm neglecting nonidealities a bit, so we'll throw in a security margin of 50% afterwards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, according to &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ f = \frac1{2\pi\sqrt{LC}}\implies C = \frac1{(2\pi)^2 f^2 L}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and plugging in our L = 200 µH and f = 150 kHz, we get a maximum needed C of –including some margin– 6 nF. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For f=1 MHz, we'd need 0.13 nF = 130 pF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's bad news since 6 nF is 85 times the maximum capacity of the BB 640. That means you'd either need&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;85 parallel pairs of BB 640, so 170 BB 640 in total,&lt;/li&gt;&#xA;&lt;li&gt;a lot more turns on our coil (which isn't the worst solution, by any means!), or&lt;/li&gt;&#xA;&lt;li&gt;go up in frequency.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;We see that f contributes &lt;em&gt;square-inversely&lt;/em&gt; to the needed capacity. So, if we double the frequency we want to reach, we need to take one fourth of the capacity. Since our reliable capacity range is 19x, we can only accomodate frequencies of ca 4.2x the minimum frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can, however, switch capacitors in and out of our system – and that allows for higher frequencies, should we need them! Lower frequencies need linearly more turns of coil or linearly more varicaps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You bring up the adjustable air capacitor – of course, that's the easiest solution here, but judging from the mini-whip, I was assuming you'd be looking for a non-mechanical, remotely operatable system.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="6080" LastEditDate="2020-01-23T00:09:25.963" LastActivityDate="2020-01-23T00:09:25.963" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="8970" PostTypeId="1" AcceptedAnswerId="8972" CreationDate="2017-07-29T01:08:23.263" Score="5" ViewCount="410" Body="&lt;p&gt;I'm looking for antennas to attach to my CB radio. This one is a &quot;rubber ducky&quot; antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/xzi4h.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure what the connector is, can anyone identify it for me?&#xA;[edit] Here are some other pictures&#xA;&lt;img src=&quot;https://i.stack.imgur.com/kOtI5.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/DbmGR.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ovCLg.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="10089" LastEditorUserId="10089" LastEditDate="2017-07-29T16:15:51.787" LastActivityDate="2017-07-30T17:07:33.737" Title="What kind of antenna connector is this?" Tags="&lt;antenna&gt;&lt;connectors&gt;&lt;citizens-band&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8972" PostTypeId="2" ParentId="8970" CreationDate="2017-07-29T02:49:58.927" Score="9" Body="&lt;p&gt;I can't tell for sure without better pictures, but that looks like, not an RF connector per se, but a 3/8&quot;-24 stud. This is very common for CB antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason I say it is not an RF connector is because it only makes one electrical contact. This means it can only be used for “monopole” antennas, not for feed lines or other types of antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To confirm, first check that the end of the antenna is solid metal and not anything more complex than that. Then take the antenna down to your local hardware/home improvement store — or your garage, if you're well equipped — and try it against a 3/8&quot;-24 nut.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(3/8&quot; refers to the outside diameter, and 24 refers to the &lt;em&gt;thread pitch&lt;/em&gt; in threads per inch. The other common size is 3/8&quot;-16.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should not have any trouble finding CB antennas with a 3/8&quot;-24 thread at the base, now that you know what it is called.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-07-29T02:49:58.927" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8973" PostTypeId="2" ParentId="8970" CreationDate="2017-07-29T03:07:50.310" Score="-2" Body="&lt;p&gt;I am guessing an N-type female connector.  Already commented to that but I am using an answer to include a photo image:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NydSy.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NydSy.jpg&quot; alt=&quot;N-connector&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2017-07-29T03:07:50.310" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8974" PostTypeId="2" ParentId="8908" CreationDate="2017-07-29T04:31:55.227" Score="2" Body="&lt;p&gt;I agree that the Diamond X-30A would be the better choice. I think it should be mounted outside the metal rail using something like this off-set or cranked mast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ebay.co.uk/p/TV-Aerial-Wall-Mounting-Kit-Cranked-Offset-Pole-Mast-Outdoor-Bracket-REDUCED/1590011342?iid=141757988472&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ebay.co.uk/p/TV-Aerial-Wall-Mounting-Kit-Cranked-Offset-Pole-Mast-Outdoor-Bracket-REDUCED/1590011342?iid=141757988472&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The lower half of the mast would be strapped to the balcony's uprights, preferably in a corner, and the antenna would then be mounted such that the ground radials would be level with the top of the rail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest the use of metal clips such as circlips to attach to the rail, cable-ties are prone to damage by UV and you do not want the antenna and mast to fall from the building dragging your radio with it :-)&#xA;&lt;a href=&quot;https://www.ebay.co.uk/sch/i.html?_odkw=circlipd&amp;amp;_osacat=0&amp;amp;_from=R40&amp;amp;_trksid=m570.l1313&amp;amp;_nkw=ubilee+clipsd&amp;amp;_sacat=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ebay.co.uk/sch/i.html?_odkw=circlipd&amp;amp;_osacat=0&amp;amp;_from=R40&amp;amp;_trksid=m570.l1313&amp;amp;_nkw=ubilee+clipsd&amp;amp;_sacat=0&lt;/a&gt;&#xA;Another possibility is to use U-Bolts around the upright and into the wall bracket provided with the crank-mast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This may take the top of the antenna into view if there is a flat above, the dimensions are not that clear.&lt;/p&gt;&#xA;" OwnerUserId="8976" LastActivityDate="2017-07-29T04:31:55.227" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8975" PostTypeId="2" ParentId="8965" CreationDate="2017-07-29T13:31:31.017" Score="3" Body="&lt;p&gt;Broadly speaking, there are two ways to make a broadband antenna:&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;1: self-similar designs&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;If an antenna looks the same at any scale, then it will work the same at any frequency. Examples of such antennas are the Dressler you link, but also the &lt;a href=&quot;http://www.antenna-theory.com/antennas/wideband/bowtie.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;bowtie&lt;/a&gt;, &lt;a href=&quot;http://www.antenna-theory.com/antennas/travelling/spiral.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;spiral&lt;/a&gt;, &lt;a href=&quot;http://www.antenna-theory.com/antennas/fractal.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;fractal&lt;/a&gt;, and &lt;a href=&quot;http://www.antenna-theory.com/antennas/wideband/log-periodic-dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;log-periodic dipole&lt;/a&gt; antenna designs. Practical considerations always dictate the self-similarity can't extend to infinity, but realistic designs can cover several octaves of frequency with a match good enough for reception purposes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These designs will be best suited to the upper ranges of your 100kHz-2GHz objective, as they typically require that the lowest frequency has a wavelength on the order of the size of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;2: equally bad everywhere designs&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;If an antenna is small (say, less than 1/10th wavelength), it can be a bad antenna for a very wide bandwidth. The trouble is the impedance of this antenna will be very far from the typical 50 ohms, and so power transfer from from the antenna to the receiver may be so poor that it's unable to overcome the receiver noise floor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consequently, designs of this sort will almost always be &quot;active&quot;, meaning there's an amplifier involved. A challenge with a wideband amplifier is overload. If you live near any commercial broadcast station it may drive the amplifier into saturation, causing harmonic distortion everywhere, rendering the antenna unusable. Some designs include filters to reject broadcast bands for this reason.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since these antennas are electrically small, they will work best at the lower range of your 100kHz-2GHz objective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Broadband active whips and dipoles are relatively common. A similar design can be achieved with a loop, although it's not common.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most &quot;small&quot; or &quot;magnetic&quot; loop designs involve some capacitance at the feedpoint to make the antenna resonant at a particular frequency. Tuning the antenna this way is equivalent to putting inductance at the base of a dipole. This can very much improve the impedance match at a narrow range of frequencies, but it totally destroys the wideband characteristic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus to get a truly wideband design, it's necessary to design an amplifier to work with the antenna that does not require reactive components to tune the antenna. For dipoles, this means an amplifier with a very high input impedance. For loops, a very low input impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;High impedance JFET amplifiers as you've found are a common design. Often, these designs will specify some JFET that's inexplicably difficult to source, and expensive if you can find it. More often than not, it's because the part is decades old. You will find designs with germanium diodes for the same reason.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually, these parts can be replaced with a more modern JFET. Or with some adjustment to the biasing, a MOSFET. Given that you'll likely be designing this antenna for relatively low frequencies, transistor selection is really not that critical, and just about anything can be made to work with a little engineering. Unfortunately that's a broad topic, but maybe it gives you some ideas for further questions :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend taking a look at &lt;a href=&quot;http://www.lz1aq.signacor.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;LZ1AQ's homepage&lt;/a&gt;. In the articles along the left there's some great information on wideband active antennas, including some designs which look very reasonable.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-07-29T13:31:31.017" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8976" PostTypeId="2" ParentId="8913" CreationDate="2017-07-29T21:07:47.503" Score="2" Body="&lt;p&gt;Unless your license was set to expire within the next 90 days, it won't be renewed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the back of NCVEC 605 or numerous times on FCC 605:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;License renewals (with associated fee for vanity renewals) may only be&#xA;  completed during the final 90 days prior to license expiration, or up&#xA;  to two years after expiration.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As for your callsign, if the box labeled &quot;CHANGE my station call sign systematically&quot; was left blank, your callsign would remain the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;N2KIQ&lt;/p&gt;&#xA;" OwnerUserId="437" LastActivityDate="2017-07-29T21:07:47.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8978" PostTypeId="2" ParentId="8970" CreationDate="2017-07-30T17:07:33.737" Score="0" Body="&lt;p&gt;It is definitely not a 3/8&quot; connector. 3/8&quot; in in metric units is 9.525 mm. The image at the bottom seems to indicate that is about 6.25 mm which is 1/4&quot;. I believe this to be a mobile TV antenna element used by truckers. They usually come in pairs and mounted on the mirrors. The threading is 1/4-20. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 9.5&quot;  in length definitely not CB probably used to receive in the VHF/UHF range.&lt;/p&gt;&#xA;" OwnerUserId="6604" LastActivityDate="2017-07-30T17:07:33.737" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="8979" PostTypeId="2" ParentId="8967" CreationDate="2017-07-30T18:04:34.533" Score="1" Body="&lt;p&gt;The TX channels are separate from the RX channels. Hence, there will be a singkle, dual-stream RX streamer, and a single, dual-stream TX streamer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The subdev strings in your pseudocode aren't doing what you want; &lt;a href=&quot;http://files.ettus.com/manual/page_configuration.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;docs&lt;/a&gt;. You also don't need them – if you request a dual-stream streamer, the default behaviour is to count them ascendingly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you just get two dual-channel RX streams with &lt;code&gt;uhd_usrp_get_rx_stream&lt;/code&gt;, you just use a &lt;code&gt;uhd_stream_args_t&lt;/code&gt; that has its &lt;code&gt;n_channels&lt;/code&gt; field set to &lt;code&gt;2&lt;/code&gt;. Same for &lt;code&gt;uhd_usrp_get_tx_stream&lt;/code&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-07-30T18:04:34.533" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8980" PostTypeId="1" AcceptedAnswerId="8982" CreationDate="2017-07-30T18:27:22.760" Score="0" ViewCount="69" Body="&lt;p&gt;Speaking of the antenna in this question: &lt;a href=&quot;https://ham.stackexchange.com/questions/7847/what-kind-of-2-meter-antenna-is-this&quot;&gt;What kind of 2 meter antenna is this?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The connections are rusted and corroded so I'd like to rewire it.  If I move the shield from where it is currently attached, down to the base, will it change the characteristics appreciably?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My hope is to be able to replace the coax and install an SO-239 at the bottom, then just wire up the center conductor back where is was originally attached.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(There are a few more pictures with the original question.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0Ocru.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0Ocru.jpg&quot; alt=&quot;The antenna&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/OJxdG.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OJxdG.jpg&quot; alt=&quot;Connections&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Yh6Ga.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Yh6Ga.jpg&quot; alt=&quot;Base&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2017-07-30T18:47:54.040" LastActivityDate="2017-07-31T13:46:35.807" Title="Will rewiring this antenna change the characteristics?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8981" PostTypeId="1" CreationDate="2017-07-31T10:41:54.087" Score="3" ViewCount="162" Body="&lt;p&gt;Now that the once-extensive network of AX.25 BBSs is all but gone, I'm wondering whether there exists any archive of the many public discussions that took place there.  It seems sad to think that the years of human conversation once held on these servers is gone forever.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does such an archive exist and, if so, how does one access it?&lt;/p&gt;&#xA;" OwnerUserId="6138" LastActivityDate="2017-08-01T03:22:08.027" Title="Are packet BBS discussions archived anywhere?" Tags="&lt;packet&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8982" PostTypeId="2" ParentId="8980" CreationDate="2017-07-31T13:46:35.807" Score="2" Body="&lt;p&gt;Currently, there's a section of coax transmission line that runs from the base to the feedpoint where the center conductor exits the vertical tube.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I'm understanding correctly, you propose to replace that section of coax with a single conductor. In that case, you'll still have a coaxial transmission line in effect, with the vertical tube acting as the &quot;shield&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fields within this transmission line do not radiate, so the radiation pattern would remain unchanged. However, since this transmission line isn't designed to be any particular impedance, the feedpoint impedance will not be what it was before modification.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-07-31T13:46:35.807" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8983" PostTypeId="2" ParentId="8981" CreationDate="2017-08-01T03:22:08.027" Score="1" Body="&lt;p&gt;Not unless individual operators did so.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When we ran the PBBS at the National Guard building at Fort Richardson we would often print out relevant messages during disaster situations.  Sometimes these messages would contribute to the daily sitrep.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;More often we would retransmit them to specific users so they could be alerted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We had a couple of funny situations where the relevant users were on the internal email system but not on the PBBS, so sometimes we would retype the messages for them.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the idea of logging, or &quot;monitoring&quot; like in broadcast radio is a fairly recent development, and is used mostly to assure advertisers that the spots they pay for are actually aired.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-08-01T03:22:08.027" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8984" PostTypeId="1" AcceptedAnswerId="8987" CreationDate="2017-08-01T09:59:47.867" Score="6" ViewCount="648" Body="&lt;p&gt;Is there a simple empiric way of determining the permeability (mhu) of a ferrite object (be it a ring, rod or any form)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been thinking this for a rod: if I wind coils with different number of turns (same wire, just wind or unwind it) and measure the inductance, then given the number of turns, diameter of the rod and &quot;height&quot; of the coil I would be able to determine the permeability. I tried a couple of times but I'm getting inconsistent results. My LCR meter can measure only upwards of 0,01mH (or 10uH). Is the meter the culprit or is my method flawed?&lt;/p&gt;&#xA;" OwnerUserId="9926" LastEditorUserId="8717" LastEditDate="2021-05-10T21:52:52.743" LastActivityDate="2021-05-10T21:52:52.743" Title="Ferrite rod or core permeability determination" Tags="&lt;measurement&gt;&lt;ferrite&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="8985" PostTypeId="2" ParentId="3685" CreationDate="2017-08-01T11:10:24.333" Score="1" Body="&lt;p&gt;It's really a trade-off between transfer speeds and available transmit power. Higher your transmit power, the higher you can set your downlink carrier. You also get better transfer speeds because you can encode more information in a higher carrier frequency, using FSK or whatever. Some applications employ a sub-GHz downlink using LoRa modulation, not compromising on data rates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most amateur satellites and CubeSats are constrained by a lack of power to them, unlike traditional satellites that have some sort of solar array or power generation to power high frequency downlinks. Assuming you device a way to power it, you'd still have to clear through legals to use these GHz bands like X. Forcing most amateur radio (HAM) into the sub-GHz band as a result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;LoRa however, though my decent understanding of the concept, operates over a similar spectrum of FSK but employs chrip spread spectrum or CSS for short, using a chirp signal to encode information. The parameters of this chirp dictate the spectrum (through spread factor) and data rate. The people who make LoRa applications market it as the low-power counterpart to DSSS and other spread spectrum modulation techniques. It's got an advantage over traditional FSK in the fact that it's frequency and bandwidth can be scaled, allowing a significant increase in data rate - more spread spectrum = more data per unit time, with the same sub-GHz frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my applications, I usually settle for something like 433 MHz, FSK/LoRa. Transceivers are readily available at this bandwidth and so are amplifiers and matched antennas. I personally feel like this gives me the perfect benefit of a decent data rate with conservative power requirements, and acceptable attenuation unlike the K bands that can't stand a rainy day &lt;/p&gt;&#xA;" OwnerUserId="10105" LastEditorUserId="10105" LastEditDate="2017-08-02T18:43:27.470" LastActivityDate="2017-08-02T18:43:27.470" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8987" PostTypeId="2" ParentId="8984" CreationDate="2017-08-01T20:41:41.307" Score="5" Body="&lt;p&gt;you're on the right track to measure/calculate effective permeability.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you need to use an inductance meter that can measure up to 1 nH accurately or so.  If you're trying to use one of those $25 LCR meters , it won't have the accuracy or precision you require, plus you won't be able to zero it.   Another issue is that you'll have a wide variance in results due to the wire, winding, lengths, etc - see Silvio's comments at &lt;a href=&quot;http://www.sklaic.info/forum/index.php?topic=175.0&quot; rel=&quot;noreferrer&quot;&gt;http://www.sklaic.info/forum/index.php?topic=175.0&lt;/a&gt; . &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other method is to measure frequency resonance, by using the loop as the inductor in an LC circuit.  Put a known capacitor in series with the loop, and then use a frequency generator and frequency counter to measure the resonance (peak) frequency of the LC circuit. &lt;/p&gt;&#xA;" OwnerUserId="4295" LastActivityDate="2017-08-01T20:41:41.307" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8988" PostTypeId="2" ParentId="8984" CreationDate="2017-08-01T20:53:44.563" Score="6" Body="&lt;p&gt;Following up on @dfannin's excellent answer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most intuitive way of dealing with this would be:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;wrap your ferrite rod in halfway stable paper or so, something that certainly doesn't have high $\mu_r$ (gut feeling: baking paper is nice as it is very &quot;slippery&quot; on flat surfaces)&lt;/li&gt;&#xA;&lt;li&gt;make as many turns as you want around that; you're building a coil now, with the ferrite core.&lt;/li&gt;&#xA;&lt;li&gt;Measure ferrite core coil's inductance by one way or another&lt;/li&gt;&#xA;&lt;li&gt;carefully slip the core out of the paper. Now you have exactly the same coil, but with an air core&lt;/li&gt;&#xA;&lt;li&gt;repeat measurement&lt;/li&gt;&#xA;&lt;li&gt;since air has $\mu_r\approx1$, the ratio between the ferrite core inductivity value and the air core inductivity value is the $\mu_r$ of the core.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Downsides:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Since ferrite's $\mu_r$ is going to be &lt;em&gt;impressively high&lt;/em&gt;, you'll need a measurement method that can span easily 3 orders of magnitude&lt;/li&gt;&#xA;&lt;li&gt;high-inductivity coil (which would allow measurements with your &gt;1 mH LCR meter) might mean that even at relatively benign currents, you might be saturating the core and get it to nonlinearity (that's not all that likely, but don't rule it out before knowing how much power your meter uses)&lt;/li&gt;&#xA;&lt;li&gt;might waste a lot of copper :)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Things that can generally go wrong:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;core saturates&lt;/li&gt;&#xA;&lt;li&gt;core too small for coil, not (nearly enough) all field gets concentrated into core, so that measurement isn't proportional to core's $\mu$&lt;/li&gt;&#xA;&lt;li&gt;ohmic losses make measurement hard&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-08-01T21:43:14.527" LastActivityDate="2017-08-01T21:43:14.527" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8989" PostTypeId="2" ParentId="3685" CreationDate="2017-08-02T04:41:03.427" Score="0" Body="&lt;p&gt;Back in the day (long ago) we used to regularly tune in a weather satellite at 136 MHz.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it is certainly possible.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no technological barrier other than size and power requirements.  Not to mention that stringing a wire (tether) behind a satellite is nowhere near as simple as unwinding wires behind aircraft.  There is a lot of physics involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is an interesting story of when they tried out the concept:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.nytimes.com/1992/07/28/science/nasa-unveils-a-satellite-on-a-tether-12-miles-long.html?pagewanted=all&quot; rel=&quot;nofollow noreferrer&quot;&gt;NASA Unveils A Satellite On a Tether 12 Miles Long&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the engineers thought it might serve as an ELF antenna to communicate with submarines.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-02T04:47:27.993" LastActivityDate="2017-08-02T04:47:27.993" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8990" PostTypeId="1" CreationDate="2017-08-02T12:47:27.127" Score="3" ViewCount="868" Body="&lt;p&gt;I have to replace a faulty BFY51 Transistor. I could not find one in the market since they have been discontinued. What is a suitable replacement?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OszMt.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OszMt.jpg&quot; alt=&quot;BFY51 NPN Transistor&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10116" LastEditorUserId="4748" LastEditDate="2017-08-03T16:20:38.103" LastActivityDate="2019-04-16T04:48:45.680" Title="Can anyone please suggest a substitute for the BFY51 transistor?" Tags="&lt;electronics&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8991" PostTypeId="2" ParentId="8990" CreationDate="2017-08-02T16:10:06.723" Score="3" Body="&lt;p&gt;&lt;a href=&quot;http://www.mouser.com/Semiconductors/Discrete-Semiconductors/Transistors/Bipolar-Transistors-BJT/_/N-ax1sh?P=1z0jg5hZ1z0y4diZ1z0w6ylZ1z0w5kaZ1z0wa61Z1yzu3zjZ1z0w6i4Z1z0w6iwZ1z0stlhZ1z0w7gaZ1yyziizZ1yyzhtpZ1yyzhtlZ1yyzik6Z1yyzhudZ1yyziiq&amp;amp;Rl=ax1shZer4hZ1z0w693Z1z0w6lrSGT&quot; rel=&quot;nofollow noreferrer&quot;&gt;Searching Mouser&lt;/a&gt; for:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;NPN, BJT discrete transistors&lt;/li&gt;&#xA;&lt;li&gt;max collector-base voltage &gt;= 60 V&lt;/li&gt;&#xA;&lt;li&gt;max collector current &gt;= 1 A&lt;/li&gt;&#xA;&lt;li&gt;gain-bandwidth product &gt;= 50 MHz&lt;/li&gt;&#xA;&lt;li&gt;TO-39 package&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;yields 13 results. &lt;a href=&quot;http://www.mouser.com/ProductDetail/Central-Semiconductor/2N3019/?qs=sGAEpiMZZMshyDBzk1%2FWixvMFai5%2FBmAq2fyEdMzUxI%3D&quot; rel=&quot;nofollow noreferrer&quot;&gt;2N3019&lt;/a&gt;, the cheapest and most available result, seems like a reasonable replacement. Of course without knowing the precise details of the circuit it's impossible to say for sure if it will work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is in any sort of push-pull amplifier, you should probably replace all the transistors and not just the faulty one to maintain symmetry in the circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There seems to be nothing special about BFY51 besides the TO-39 package which isn't very common. Using a similar search at your favorite parts source I bet you can find some other replacements which are cheap and available in your area.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-02T16:10:06.723" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8992" PostTypeId="2" ParentId="1256" CreationDate="2017-08-02T19:00:57.927" Score="0" Body="&lt;p&gt;UPDATE   the site      &lt;strong&gt;www.mrx.com.au      is not workin&lt;/strong&gt;g... the owner no longer services it.... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;**to download CWCOM please visit my blogsite &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://morsepower.blogspot.co.uk/p/blog-page.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://morsepower.blogspot.co.uk/p/blog-page.html&lt;/a&gt;**&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where there are pages of info and help,.  including how to get cwcom ( written for windows ) working on LINUX and MAC machines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Also detailed instructions on how to connect external morse key to your computer.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="10120" LastActivityDate="2017-08-02T19:00:57.927" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="8994" PostTypeId="1" CreationDate="2017-08-03T14:34:28.097" Score="1" ViewCount="65" Body="&lt;ul&gt;&#xA;&lt;li&gt;smartphone: Samsung Galaxy S4 mini&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;coating is probably crome, a few microns thick&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;could it be that removing the coating will have the opposite effect, as in lowering the signal strength instead of increasing it? Because the coating is designed to reflect/focus/whatever the radiation in a purposeful way?&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;or is all of this irrelevant because the antenna emits/receives radiation only in certain directions anyway?&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10122" LastActivityDate="2017-08-09T14:21:12.450" Title="Will removing the metal coating smartphone shell (made of plastic) improve reception/signal strength?" Tags="&lt;physics&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8995" PostTypeId="2" ParentId="8994" CreationDate="2017-08-03T14:43:37.830" Score="4" Body="&lt;p&gt;Telephones are designed as a &lt;em&gt;system&lt;/em&gt;. So, yes, the plastic case, including a potential coating, have been incorporated in tests, and in consequent optimization (at least for large-scale mid- to high-end phones). Chances are you will not be improving anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The metalized surface will be thinner than the skin depth at relevant frequencies, and quite possible not as conductive as you think (I'd be happy if proven otherwise).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;or is all of this irrelevant because the antenna emits/receives radiation only in certain directions anyway?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;While technically, all the antennas in the phone do have a certain direction in which they radiate most of the energy, it's not like a phone's antenna system is designed to be highly directive – that would be counter-productive for reliable reception.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-08-03T14:43:37.830" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8996" PostTypeId="1" CreationDate="2017-08-04T03:15:29.517" Score="0" ViewCount="1176" Body="&lt;p&gt;a semi-old, mildly grumpy, damn lazy new General Class Op, back after nearly 40 years since last license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Live in an old 2 story Mediterranean Sunset District Avenues home with a flat, beam-bitumen-tar-gravel roof with a rectangular 50x24' dimension, no or very little metallic obstructions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could place a G5RV Jr at opposite long corners, ladder line feed lying horizontally perpendicular to the &quot;dipole&quot;, with a 45-50 run of coax to my second story window.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could raise it up a smudge if it would make a significant positive impact. I work mainly PSK on 20/40 20-25W and 20/40 SSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I run a 756PRO and have a nice tuner they have been workhorses during the last two years of remote deployments. I'd like to get back to CW ops as well. I'm looking for the most bands and bandwidth I can get, with as little noise as possible(like everyone else). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am also likely the most technically ignorant modern Ham around. Hence, this will be purchased, not constructed and I like the build of the ARS G5RV Jr with terminal 1:1 Balun, for our salt air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm retired/disabled ex-military, sharing a house, on a fixed limited income. &#xA;I'm going to get one day worth of roof access with help, so &quot;optimal placement&quot; first time is hoped for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect almost anything will do better than my current poorly placed Euro-Comm Vertical mounted on my window ledge on a cable dish j-pole mount (seriously), only 12' of which is truly above roof level and the coax run to my rig is about 8', air choke hanging off the ledge.&lt;/p&gt;&#xA;" OwnerUserId="10129" LastEditorUserId="76" LastEditDate="2017-08-04T15:14:19.780" LastActivityDate="2017-08-04T18:49:45.197" Title="G5RV Jr and Ladder Line feed Lying Flat on the Roof?f" Tags="&lt;wire-antenna&gt;&lt;antenna-system&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="8997" PostTypeId="2" ParentId="8996" CreationDate="2017-08-04T16:17:44.237" Score="2" Body="&lt;p&gt;Rich:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like most things with antennas, there's never a definite answer. In most cases you just have to try it. I can give you some information from my experience.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My first antenna was a G5RV hanging between two trees on the side of a hill barely 10' off the ground. The ladder line was on the ground for most of it's length, which is suppose to be bad since the line works best when away from obstructures (especially metal). Despite this, the antenna worked well, and my very first contact on PSK31 was over 7,000 miles using just 30 watts. I had many other good QSOs with that antenna before I upgraded to a full size multiband vertical on top of the hill. An antenna tuner can compensate for imperfect placement to some degree.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just an idea....what if you hung the antenna diagonally from the corners of your roof as high as you could get it (even if that was only a foot or two so it wouldn't be sitting in a puddle during rain), then stretched the ladder line out diagonally as far as possible to one of the other corners? That should reduce interactions with the roof so more of the signal would radiate out where it could do some good. Just a thought. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck, and 73,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Jon, K0ARG&lt;/p&gt;&#xA;" OwnerUserId="10131" LastActivityDate="2017-08-04T16:17:44.237" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="8998" PostTypeId="2" ParentId="8996" CreationDate="2017-08-04T18:49:45.197" Score="2" Body="&lt;p&gt;A G5RV antenna is a dipole with an impedance-matching ladder-line feed stub, with the dimensions of the wire and the ladder line carefully chosen to provide a low SWR on many bands.  (Please note that there are bands where G5RVs and variants perform terribly.  A G5RV is not an all-band antenna, it's a many-band antenna.)  A transmatch, aka antenna tuner, is usually necessary to get the SWR below 2:1.  A 1:1 current balun should be used between coax and ladder line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The design assumes that the ladder-line feed stub is perpendicular to the dipole wires, and in free space not near any conductors.  So what happens when the ladder line is lying along a roof?  In the best-case scenario, there won't be anything metal near the ladder line.  In that case, I would think that the antenna would be detuned somewhat, because the dialectric constant of the roof is different than that of air, which will make the SWR of the antenna somewhat higher.  Higher SWR would result in less power out because the efficiency of the coaxial cable and the transmatch will go down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there is a significant amount of metal nearby, then that metal will effectively become part of the antenna.  That could have lots of effects; I would think that the antenna would be more severely detuned and the efficiency of the antenna would go down because metal plumbing or wiring in your house was not designed to be a ham antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like Jon said, the usual ham approach to the problem is to try the antenna and see how it works.  Even if it's not as efficient as a G5RV up high with the ladder line in the clear, you could still make lots of contacts with such an antenna.  Be warned though that having the antenna close to the house could result in other problems, like RFI or RF in the shack.  My advice is to raise the antenna up as much as you can; if you could raise the ends of the wire even just a few feet above the roof, then the antenna would probably perform better than one laying on the roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck, and have fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-08-04T18:49:45.197" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="8999" PostTypeId="1" AcceptedAnswerId="9004" CreationDate="2017-08-04T19:00:08.233" Score="3" ViewCount="464" Body="&lt;p&gt;I was asked by a friend to take a look at an old 70-80s Iskra sst 2030 (ex Jugoslavian-slovenian company) radio. The radio seems to work fine but I can't understand which plug it uses for speakers. Any ideas?&lt;a href=&quot;https://i.stack.imgur.com/F1lCE.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/F1lCE.jpg&quot; alt=&quot;plug&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Levi is left in slovenian. The rest, no clue. Here's a foto of both channels&lt;a href=&quot;https://i.stack.imgur.com/Vy5ni.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Vy5ni.jpg&quot; alt=&quot;plug2&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9926" LastEditorUserId="8717" LastEditDate="2019-09-27T21:20:55.657" LastActivityDate="2019-09-27T21:20:55.657" Title="Iskra sst 2030 radio speaker plug" Tags="&lt;receiver&gt;&lt;audio-interface&gt;&lt;repair&gt;&lt;speaker&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9000" PostTypeId="2" ParentId="8999" CreationDate="2017-08-04T19:05:40.140" Score="0" Body="&lt;p&gt;&lt;strong&gt;Both of them&lt;/strong&gt; . Two wires each for both the left and right stereo speakers. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Desni&quot; translates to &lt;em&gt;right&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-08-04T19:05:40.140" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9001" PostTypeId="1" CreationDate="2017-08-04T19:51:44.597" Score="2" ViewCount="169" Body="&lt;p&gt;In my house, I’ve got a mag mount antenna mounted on a piece of sheet metal on top of rubber and the tip of the antenna goes into my ceiling and possibly contacts or is near to home insulation. I was just wondering if this was a hazard for fire in any way or if I’m OK. The antenna's max is 75 W, but my radio generally never puts that out. &lt;/p&gt;&#xA;" OwnerUserId="10132" LastEditorUserId="76" LastEditDate="2017-08-04T21:54:28.193" LastActivityDate="2017-08-05T14:43:32.550" Title="Can the tip of an antenna burn insulation/drywall?" Tags="&lt;antenna&gt;&lt;safety&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9002" PostTypeId="2" ParentId="9001" CreationDate="2017-08-04T20:58:22.163" Score="0" Body="&lt;p&gt;I think you will be safe as long as there is no metal behind the ceiling.  Ideally I would try to have a gap.&lt;/p&gt;&#xA;" OwnerUserId="390" LastActivityDate="2017-08-04T20:58:22.163" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9004" PostTypeId="2" ParentId="8999" CreationDate="2017-08-05T08:11:32.610" Score="5" Body="&lt;p&gt;To me, this looks very much like a &lt;a href=&quot;https://de.wikipedia.org/wiki/Lautsprecherstecker&quot; rel=&quot;noreferrer&quot;&gt;&quot;DIN Lautsprecherstecker&quot;&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Speaker_din_male_and_female.jpg/220px-Speaker_din_male_and_female.jpg&quot; alt=&quot;DIN LS&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Positive is the small hole, negative the wide slot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Loudspeaker, if I ask google, is &lt;em&gt;zvočnik&lt;/em&gt; in Slovenian – so the &quot;ZV&quot; label makes sense; you can switch between speaker pair 1 and 2.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-08-05T08:11:32.610" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9005" PostTypeId="2" ParentId="9001" CreationDate="2017-08-05T11:57:06.307" Score="-2" Body="&lt;p&gt;If your antenna is a 1/4 wave vertical, the peak voltage on it will be at the very end of the antenna. So, please don't touch it while you are transmitting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna that is well-matched has an input impedance of 50 ohms (for most radios) and an output impedance of 377 ohms (this is the impedance of free space, and all an antenna really is, is a matching device from your radio's transmitter to free space). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are transmitting 50 watts into a perfectly efficient, perfectly matched antenna, the voltage at the tip is the sqrt(50*377) = 137 volts. You &lt;em&gt;might&lt;/em&gt; arc this to a piece of metal if it were within a few thousandths of an inch, and it &lt;em&gt;might&lt;/em&gt; conduct a tiny bit of current into high impedance materials. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One concern is the effect on the impedance of the antenna having dielectric materials in the near field. Having things like drywall and fiberglass right around part of the antenna might change its impedance enough to harm the radiation pattern and efficiency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would try to remove any materials that are near the antenna. &lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2017-08-05T11:57:06.307" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="9006" PostTypeId="2" ParentId="146" CreationDate="2017-08-05T12:02:25.820" Score="0" Body="&lt;p&gt;Well, speaking from a budget point of view, you can cover 80-6 for $100 with a multiband OCF dipole, but any HF vertical is going to require a lot more budget than that - probably at least 5 times that much, and more if you need to bury radials. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most everything posted here is not relevant in light of the enormous cost difference between a well-performing dipole and a well-performing vertical for HF.&lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2017-08-05T12:02:25.820" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9007" PostTypeId="2" ParentId="7555" CreationDate="2017-08-05T12:05:43.410" Score="1" Body="&lt;p&gt;You are probably just desensitizing the receiver in the TV or the amplifier. What you need is a band-stop filter that covers the band you're transmitting on with your HT (144-148 I assume?). Place it between the antenna and amplifier or amplifier and TV to see which is being desensitized. &lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2017-08-05T12:05:43.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9008" PostTypeId="2" ParentId="9001" CreationDate="2017-08-05T14:43:32.550" Score="6" Body="&lt;p&gt;The &lt;a href=&quot;https://ham.stackexchange.com/q/1410/218&quot;&gt;peak voltage at the tip of the antenna&lt;/a&gt; is a function of the input power and the field impedance at that tip. The impedance varies based on the geometry of the antenna, but for a typical mag-mount whip it's probably not more than 5000Ω. Voltage $E$, power $P$, and resistance $R$ are related by&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P = {E^2 \over R} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ E = \sqrt{PR} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the worst-case estimate of 5000Ω and 75W, that makes the RMS voltage at the tip of the antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \sqrt{75\:\mathrm W \cdot 5000\:\Omega} = 612\:\mathrm{V_{rms}}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are concerned about arcing, the peak voltage is probably more relevant:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \sqrt 2 \cdot 612 \:\mathrm{V_{rms}} = 866 \:\mathrm{V_{peak}}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the question is then if 866 V is a hazard. That's high enough that I personally wouldn't take any chances putting it in direct contact with anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if you never start a fire, the antenna is really designed to have air around it for proper operation, not a ceiling. I'd suggest a different antenna setup.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-05T14:43:32.550" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9009" PostTypeId="1" AcceptedAnswerId="9012" CreationDate="2017-08-06T12:39:59.137" Score="3" ViewCount="1667" Body="&lt;p&gt;I'd like to implement a digital demodulator for Digital Mobile Radio (DMR). Note I'm not concerned about decoding of the audio: I realize that requires a proprietary codec.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the details of the DMR modem? I've found statements that it's 4-FSK, but few details beyond that.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-06T16:47:38.960" Title="Modulation details of Digital Mobile Radio (DMR)" Tags="&lt;dmr&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9010" PostTypeId="5" CreationDate="2017-08-06T12:46:54.027" Score="0" Body="" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-08-06T12:46:54.027" LastActivityDate="2017-08-06T12:46:54.027" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9011" PostTypeId="4" CreationDate="2017-08-06T12:46:54.027" Score="0" Body="Digital mobile radio, a digital voice mode found on VHF and UHF bands." OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-08-06T12:46:54.027" LastActivityDate="2017-08-06T12:46:54.027" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9012" PostTypeId="2" ParentId="9009" CreationDate="2017-08-06T14:24:23.620" Score="3" Body="&lt;p&gt;&lt;a href=&quot;http://www.etsi.org/deliver/etsi_ts/102300_102399/10236101/01.02.01_60/ts_10236101v010201p.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;ETSI TS 102 361-1&lt;/a&gt; Clause 10 is pretty explicit on that:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;h1&gt;10.1.2 RF carrier bandwidth&lt;/h1&gt;&#xA;&lt;p&gt;The radio system operates within a 12,5 kHz RF carrier bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;…&lt;/p&gt;&#xA;&lt;h1&gt;10.2.1 Symbols&lt;/h1&gt;&#xA;&lt;p&gt;The modulation sends 4 800 symbols/s with each symbol conveying 2 bits of information. The maximum deviation, &lt;span class=&quot;math-container&quot;&gt;$D$&lt;/span&gt;&#xA;of the symbol is defined as:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$D = 3 h / 2 T$$&lt;/span&gt;&#xA;where:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$h$&lt;/span&gt; is the deviation index defined for the particular modulation, and&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$T$&lt;/span&gt; is the symbol time (1 / 4 800) in s.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h1&gt;10.2.2 4FSK generation&lt;/h1&gt;&#xA;&lt;p&gt;This clause describes the characteristics of the constant-envelope modulation, entitled 4FSK.&lt;/p&gt;&#xA;&lt;h1&gt;10.2.2.1 Deviation index&lt;/h1&gt;&#xA;&lt;p&gt;The deviation index, h , for 4FSK is defined to be 0,27. This yields a symbol deviation of 1,944 kHz at the symbol&#xA;centre. The mapping between symbols and bits is given in table 10.3.&#xA;&lt;br&gt; [Table 10.3]&lt;/p&gt;&#xA;&lt;h1&gt;10.2.2.2 Square root raised cosine filter&lt;/h1&gt;&#xA;&lt;p&gt;Square Root Raised Cosine Filter is implemented for 4FSK so that part of a Nyquist Raised Cosine is used for the&#xA;transmit splatter filter and part is used by the receiver to reject noise. The input to the transmit splatter filter consists of a&#xA;series of impulses, scaled according to clause 10.2.3.1, and separated in time by 208,33 microseconds (1 / 4 800 s). The&#xA;method of splitting the Nyquist Raised Cosine Filter is to define the splatter filter frequency response of the Square&#xA;Root Raised Cosine Filter as the square root of the Nyquist Raised Cosine Filter. The group delay of the filter is flat&#xA;over the pass band for |f| &amp;lt; 2 880 Hz. The magnitude response of the filter is given approximately by the following&#xA;formula:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Sooooo 4FSK, 1944 Hz max deviation, shaping the data with a RRC &lt;em&gt;before&lt;/em&gt; hitting the frequency modulator.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Note I'm not concerned about decoding of the audio: I realize that requires a proprietary codec.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;He, theoretically that's true. But I know people who have &lt;a href=&quot;https://media.ccc.de/v/31c3_-_6267_-_en_-_saal_g_-_201412271600_-_osmo-gmr_what_s_up_with_sat-phones_-_sylvain_munaut&quot; rel=&quot;nofollow noreferrer&quot;&gt;shown past tendencies to reverse engineer AMBE codecs&lt;/a&gt; running integrated in handsets on dedicated DSP chips. One of the takeaways was that you've got to be relatively smart to do so properly, but on the other hand, also, that parametrizations of AMBE codecs are different, but you can often at least rudimentarily use one for a different standard and still get an understandable starting point.&lt;/p&gt;&#xA;&lt;p&gt;Ah, and in fact, Travis Goodspeed KK4VCZ, with support from DD4CR, DF8AV, and AB3TL, has simply made the DMR-specific AMBE codec from a Hytera handset run under Linux. So, yay! You &lt;em&gt;can&lt;/em&gt; decode AMBE in software on a PC (or PC-style computer), if it is an ARM (and not an x86). Even better: QEMU (a popular computer emulator) can both emulate an ARM processor (so that the firmware of the Hytera handset can be run on something that is not an ARM itself), as well as act as a &amp;quot;proxy&amp;quot; for the native host OS – so, you can run a slightly modified Hytera (STM32 microcontroller-)firmware on any of your Linux PCs. Cooool: &lt;a href=&quot;https://www.alchemistowl.org/pocorgtfo/pocorgtfo13.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;PoC||GTFO 0x13, p. 38ff&lt;/a&gt; (get all PoC||GTFO volumes from Pastor Manul Laphroig's tombs of enshrined wisdom, eg. &lt;a href=&quot;https://www.alchemistowl.org/pocorgtfo/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.alchemistowl.org/pocorgtfo/&lt;/a&gt;).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-08-06T16:47:38.960" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9013" PostTypeId="1" AcceptedAnswerId="9014" CreationDate="2017-08-07T01:22:17.750" Score="2" ViewCount="596" Body="&lt;p&gt;Due to space limitations, I'm looking at loop antenna designs. I'm starting with receive only, but hope to eventually transmit.&lt;/p&gt;&#xA;&lt;p&gt;I've seen &lt;a href=&quot;https://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;magnetic loops&lt;/a&gt; (single turn with a coupled loop) and I'm wondering: how would a second turn impact performance?&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;&lt;em&gt;Coupled loops are typically 1/5 to 1/3 of main loop in size&lt;/em&gt;&amp;quot; I'm talking about a second loop, about 1/3 the size of the main loop. Not central, but arranged like the circles on a Smith chart. Would the increased coupling help performance?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Note:&lt;/strong&gt; I'm aware just about any wire can act as a receive antenna. I could probably build this and receive quite happily on it. My concern is more for performance when I eventually trey to transmit.&lt;/p&gt;&#xA;" OwnerUserId="1610" LastEditorUserId="8717" LastEditDate="2020-09-19T18:51:29.343" LastActivityDate="2020-09-19T18:51:29.343" Title="Loop Antenna - configuration?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;magnetic-loop&gt;&lt;small-loop&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9014" PostTypeId="2" ParentId="9013" CreationDate="2017-08-07T11:54:56.867" Score="3" Body="&lt;p&gt;Adding a smaller coupled loop will have a marginal result. The smaller, coupled loop seen on some small loop designs is there to provide impedance matching. If you wish to improve the gain of your loop antenna, consider adding a second turn to the main loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding an additional turn to a small loop antenna will improve its gain. But the increase in gain to due to increased radiation efficiency, not increased directivity. Recall that gain is directivity times radiation efficiency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation resistance of a small loop antenna is normally very low and is the largest factor in its inefficiency. The radiation resistance of a small loop goes up by the number of turns squared. So by going from one turn to two turns, you have multiplied the radiation resistance by four. That is very helpful in improving its efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But there is a downside as well. Each turn has a loss based on its RF resistance. But this loss goes up linearly with the number of turns. So doubling the number of turns doubles the resistive, dissipative loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since in a typical small loop antenna the  loss resistance is much greater than the radiation resistance then the radiation efficiency (power radiated vs power applied) improvement approaches the number of turns. So a second, properly spaced turn has the potential to double the radiation efficiency and thus the gain of a small loop. As the number of turns are increased, the succesive gain in radiation efficiency starts to decline so this approximation should not be extended for additional turns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind, however, that the maximum directivity of a small loop is ~1.5. So if the loop has an ideal radiation efficiency of 1 (zero losses), the maximum possible gain is 1.76 dBi regardless of the number of turns.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-08-07T20:35:29.337" LastActivityDate="2017-08-07T20:35:29.337" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9015" PostTypeId="2" ParentId="9013" CreationDate="2017-08-07T16:09:53.367" Score="2" Body="&lt;p&gt;Larger multi-turn loops with the turns too close together can be degraded by the &quot;proximity effect&quot;: the turn in the front (or in the case of a spiral, the outermost turn) may have a certain current value at a given point on that turn; but the turn adjacent to it &lt;em&gt;next to that point&lt;/em&gt; may have a current that is quite different. This can cause (among other things) increased current in a given area. You can spread the turns out to reduce this effect, but the bottom line is that losses can be much higher than in single-turn loops.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://owenduffy.net/blog/?p=1594#more-1594&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here's what Owen Duffy states&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Small Transmitting Loops (STL) are loops of less than about 0.1λ in diameter or about 0.3λ in circumference. Below these limits, the current around the loop is almost uniform and this permits a simplified analysis.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;According to this, the total length of the conductor in a multiturn loop should be less than about 0.3λ depending on how close the turns are to each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IIRC, the two-turn loop in the 11/11 &lt;em&gt;QST&lt;/em&gt; actually had significantly more loss than the single-turn one. Here are &lt;a href=&quot;http://www.arrl.org/files/file/QST%20Binaries/Nov2011/QS1111Paun.zip&quot; rel=&quot;nofollow noreferrer&quot;&gt;the files&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-08-10T22:56:43.803" LastActivityDate="2017-08-10T22:56:43.803" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9016" PostTypeId="2" ParentId="7319" CreationDate="2017-08-07T21:54:01.460" Score="0" Body="&lt;p&gt;One small possible quibble to W8II's answer; both transmit and receive should be affected by feedline losses; because returned signal has to go both ways down the feedline whereas the received signal only has to go one way, I think you'd need to subtract &quot;x&quot; from both sides as well as an extra x from the returned transmit power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;His basic point still stands -- you can't do duplex because the local signal will overwhelm the remote signal at the receive, even under near-perfect SWR conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However I am looking into using a directional coupler with a QRPp SDR transceiver which has both TX and RX ports, so that it can use a single antenna in simplex mode (the alternative would be a coax switch or relay). Because the power is pretty low to begin with and I am not planning on using a big amplifier (will probably not amplify more than 2 watts), I think/hope that the attenuation from directivity, coupling, and feedline losses ought to be sufficient to keep the receiver from getting fried by the returned power on the transmit signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I originally said that the amount to subtract is 3db for double-feedline-loss, but after a good night's rest realized how stupid that was. Yes double is 3dB but that is relative to x, not relative to our starting transmit power.&lt;/p&gt;&#xA;" OwnerUserId="10150" LastEditorUserId="10150" LastEditDate="2017-08-08T22:37:18.097" LastActivityDate="2017-08-08T22:37:18.097" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9017" PostTypeId="1" AcceptedAnswerId="9022" CreationDate="2017-08-08T05:49:19.017" Score="1" ViewCount="7935" Body="&lt;p&gt;I want to buy a &lt;a href=&quot;http://rads.stackoverflow.com/amzn/click/B00DHHOZBI&quot; rel=&quot;nofollow noreferrer&quot;&gt;radio antenna&lt;/a&gt; for my stereo in order to pick up a few farther-away stations clearly. The outputs from the antennae that I'm seeing are to coax cables, and the input to my stereo has 75 ohm and 300 ohm connectors. What sort of adapter do I need to get in order to connect the antenna to my stereo?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://imgur.com/a/KwuFc&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt; is a picture of the back of my stereo. I believe the connection to the antenna is a coax cable with F-male connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.imgur.com/EK9z33e.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.imgur.com/EK9z33e.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10152" LastEditorUserId="218" LastEditDate="2017-08-08T18:24:49.170" LastActivityDate="2017-08-09T14:29:19.453" Title="How do I connect an antenna with coax output to my stereo?" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9018" PostTypeId="2" ParentId="9017" CreationDate="2017-08-08T07:18:54.303" Score="1" Body="&lt;p&gt;The 75 ohm connector on your receiver is designed for coaxial connections. The 300 ohm connector is for an antenna that uses a flat, two wire cable called twin lead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may need an adapter of some type to convert the connector that is on the end of the coaxial cable coming from the antenna to the type of connector on the back of your receiver if the two are not a match. These are commonly available. Post pictures of the two ends of the connection if you need assistance with the terminology to find an appropriate adapter.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-08-08T07:18:54.303" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9019" PostTypeId="2" ParentId="8994" CreationDate="2017-08-08T08:51:51.923" Score="2" Body="&lt;p&gt;I once removed the cover of an HTC One X for cleaning purposes. As curious as I am, I switched it on and noticed really poor reception. Upon further investigation, I concluded that some metal parts remaining on the cover are actually the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Googling your phone, I found &lt;a href=&quot;https://wiredornot.files.wordpress.com/2013/08/img_20130807_132347.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wiredornot.files.wordpress.com/2013/08/img_20130807_132347.jpg&lt;/a&gt; which shows several put on contacts on the covering plate. If you remove it, you will certainly disable your loudspeaker und I think the audio jack. Unfortunately, I couldn't locate the antenna. It could be on the other side of the board or one of the remaining put on contacts.&lt;/p&gt;&#xA;" OwnerUserId="10155" LastActivityDate="2017-08-08T08:51:51.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9020" PostTypeId="1" CreationDate="2017-08-08T15:31:44.613" Score="2" ViewCount="97" Body="&lt;p&gt;I have an oblong dish network antenna that I want to convert to 2m/440 usage. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have seen the one for the 14 foot dish but I do not have one.  Not sure if I should wind a coil and mount it in the center as the transmitting antenna or make some cuts in the dish itself.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any help would be appreciated.  &lt;/p&gt;&#xA;" OwnerUserId="10157" LastEditorUserId="218" LastEditDate="2017-08-09T01:55:18.727" LastActivityDate="2017-08-09T01:55:18.727" Title="Help with small dish antenna on 2m/440" Tags="&lt;vhf&gt;&lt;uhf&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9021" PostTypeId="1" CreationDate="2017-08-08T17:46:05.100" Score="2" ViewCount="919" Body="&lt;p&gt;Does a longer dipole (than half wavelength), for example twice as long, tuned to 50 Ω using an antenna tuner perform better than a half wavelength dipole for the same frequency?&lt;/p&gt;&#xA;" OwnerUserId="10159" LastEditorUserId="9493" LastEditDate="2017-08-09T02:20:46.013" LastActivityDate="2017-09-10T11:49:11.473" Title="What happens if an HF dipole is made longer?" Tags="&lt;antenna-theory&gt;&lt;hf&gt;&lt;dipole&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9022" PostTypeId="2" ParentId="9017" CreationDate="2017-08-08T18:46:18.177" Score="1" Body="&lt;p&gt;So what you have is binding posts (I assume) with a specified 75 Ω input. That's unusual, but let's run with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First of all, you &lt;em&gt;can&lt;/em&gt; use a 75-300 Ω “matching transformer” that has the right ends, and it will probably work just fine (reception does not care very much about impedance mismatches), but it's not the way to get the absolute best performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, what you want to do is to connect the 75 Ω cable &lt;em&gt;directly&lt;/em&gt; with no transformer. You can make an adapter without needing to buy any specialized parts or solder anything:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Find a friend who's throwing out some coax, or ask a cable TV installer for scraps, or worst case go buy from the hardware store:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;a standard 75 Ω &quot;F&quot; connector coaxial cable, as short as you can find.&lt;/li&gt;&#xA;&lt;li&gt;a &quot;F&quot; coupler (as you would use to connect two cables).&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Cut the cable, so you have a short piece with a connector on one end.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;Using a knife, wire stripper, or a coax stripping tool if you have one, carefully strip off the outermost insulation for an inch or so, revealing the braid (outer conductor).&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Unbraid the braid, then bundle the fine wires off to one side (so that they are not surrounding the center conductor any more) and lightly twist them together like they were a piece of stranded wire, for later convenience.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Strip off the dielectric (insulation) around the center conductor, but not so far back it'll short against the shield.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;Use the coupler to attach this to the end of your antenna cable.&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Connect the shield wire to the &quot;GND&quot; binding post and the center wire to the &quot;FM ANT&quot; binding post. Make sure no stray wires from the shield are shorting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Make sure they're not pulled down to short against each other by the weight of the coax — perhaps an adhesive cable clamp stuck onto the case over in the free space to the right would help as strain relief.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-08-08T18:46:18.177" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9023" PostTypeId="2" ParentId="9021" CreationDate="2017-08-08T19:06:25.483" Score="5" Body="&lt;p&gt;An antenna of a different length, relative to the wavelength of the signal, will have a different radiation pattern — it will transmit or receive most effectively in a different direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xBexv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xBexv.png&quot; alt=&quot;Antenna patterns for various lengths&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Strahlungscharp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;image by user Dantor from Wikimedia Commons&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(In the diagram, “L” is the length of the antenna and “l” is the wavelength.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A regular dipole has a pattern like the yellow line in this diagram — it radiates most strongly perpendicular to the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dipole twice as long (one wavelength) has the pattern shown in green — notice how it splits into two lobes and has a &lt;em&gt;null&lt;/em&gt; (approaching zero) at the perpendicular direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem with such a pattern is that — even though it seems more evenly distributed than the dipole pattern — it is harder to aim in the direction you want, because there are more nulls (four instead of two, in the two-dimensional perspective suitable for a horizontal antenna) and harder to aim away from a noise source because there are more lobes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the antenna gets even longer, there are even more lobes and nulls (as you start to see in the four-times-longer blue line).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're erecting your antenna in an arbitrary orientation and don't care about the pattern, then you &lt;em&gt;could&lt;/em&gt; use a longer antenna, but there's no reason &lt;em&gt;to&lt;/em&gt; do so.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-08-09T03:01:56.293" LastActivityDate="2017-08-09T03:01:56.293" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9024" PostTypeId="2" ParentId="8955" CreationDate="2017-08-08T19:14:03.737" Score="2" Body="&lt;p&gt;I'd seriously consider the 1909 predecessor of the J antenna by Hans Beggerow. It is, indeed, an antenna designed to hang below a balloon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4t755.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4t755.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like the modern J antenna (aka J-pole) it is a half-wave single linear conductor fed with a quarter-wave parallel wire transformer, fed in turn near or at the closed end of the transformer. With your payload/electronics package as small as it is likely to be, you can probably get by without the spiffy link coupling and figure out a simpler solution. I'd start by breaking the shorted end of the transformer, flay the feedline and just feed it there. If the impedance is too low, re-short the transformer, run some RG-174 down the transformer line a bit and find the sweet spot... just like a J antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All together this will be about 15 meters in length for the 20m band, but that half-wave wire can be very thin. This will whip around a bit, but I suspect the mass of the wire will tend to keep things reasonably plumb at most times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can find it, super thin 300 ohm twin lead parallel transmission line will serve as the 5 meter quarter-wave transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best of all this needs no additional counterpoise (or equiv.) to operate as an efficient half-wave radiator. Plus there are no concerns of coupling from the high voltage end of the sleeve to the feedline in a coaxial sleeve style antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With some planning and design you might be able to position your payload/transmitter directly at the feedpoint sweet spot by attaching it to the quarter-wave transformer at that spot. In this way the entire payload (antenna plus electronics) attaches to the balloon at the shorted end of the transformer. The potential problem is the higher voltage portion of the quarter-wave transformer wants to be well away from other conductive or dielectric materials.  Still the &quot;50 ohm&quot; feedpoint isn't too far down the transformer so this might be viable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A link to the patent (in German) along with other references is available on the J-pole antenna Wikipedia page.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/J-pole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/J-pole_antenna&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it was good enough for 1909, it's well worth a good long look now.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastEditorUserId="4306" LastEditDate="2017-08-09T17:29:03.210" LastActivityDate="2017-08-09T17:29:03.210" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9025" PostTypeId="2" ParentId="1859" CreationDate="2017-08-08T21:10:53.333" Score="4" Body="&lt;p&gt;I have used an End-Fed Long-Wire antenna for many years. &#xA;I have used it on 80M, 40M, 20M with 1:1 SWR... &#xA;I did NOT try for the shortest long-wire possible.&#xA;I did use a Long length which is several Odd Quarter-Wave-Lengths &#xA;of my target bands 40M and 20M. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is 186 feet long, up 17 ft, in the shape of a letter &quot;Z&quot; &#xA;and controlled by a Antenna Tuner and fed via 52 Ohm Coax, 32 ft long. &#xA;It is a copy of the BASIC SIMPLE LONG WIRE ANTENNA &#xA;found at w8ji website for antennas&lt;br&gt;&#xA;and &lt;a href=&quot;http://www.w8ji.com/long_wire_antenna.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w8ji.com/long_wire_antenna.htm&lt;/a&gt; &#xA;&lt;a href=&quot;https://i.stack.imgur.com/dz6SY.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dz6SY.jpg&quot; alt=&quot;W8JI Basic Simple Long Wire Antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My Long Wire has aprox. 11.5 quarter wave lengths on 20M.&#xA;My Long Wire has aprox. 5.5 quarter wave lengths on 40M. &#xA;Being aprox. odd quarter wave-lengths of the target band is important. &#xA;The Antenna Tuner will load an End Fed Long Wire effectively, &#xA;especially if it is cut to aprox. an Odd Quarter Wave-Length &#xA;of your target band... 186 ft / 16.5 ft   and 186 ft / 33 ft... &#xA;The entire antenna is #12 stranded insulated copper. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Antenna Tuner is a 1977 HeathKit HFT-9, a small QRP size tuner &#xA;of the Cap-Coil-Cap double&quot;L&quot; design. Super simple. &#xA;I use an MFJ-813, QRP-SWR-WattMeter calibrated model, &#xA;and run 1W commonly.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for effectiveness, &#xA;I have worked most Europe, All States, and Hawaii &#xA;at QRP/p 1 W  with this antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For Tuning to get more bands, as an experiment, &#xA;I simply wrapped up 5 or 10 or 15 feet of the end &#xA;in a tight loop, wrapped tape around it, and let it dangle. &#xA;The Tuner brought in 80M, 40M, 30M, 20M, 21M, at SWR 1:2 and less. &#xA;When adjusted slightly for 40M and 20M, the SWR can be 1:1 always, &#xA;as the tuner is adjusted slightly to get the entire band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;other half of the Long-Wire&quot; is called a &quot;Counter-Poise&quot; &#xA;which can be aprox. 10% to 15% of the long-wire length. &#xA;My Counter-Poise is aprox. 23 feet long, and dangles &#xA;away from my Long-Wire Antenna. &#xA;...&#xA;Counter-Poise is NOT grounded to anything. Nada, Zilch, No Ground. &#xA;W8JI writes &quot;adding ground rods can decrease RF efficiency when an insulated counterpoise is used.&quot;  I have verified this by experiment.&#xA;Inside the Shack, at the Antenna Tuner, there is a solid earth ground &#xA;for the all the equipment, including the ground of the Antenna Tuner. &#xA;...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is similar to the standard Antenna we use at all our Field Day &#xA;Installations with great success.  We toss our Long-Wires over Tree tops &#xA;and dangle the counter-poise away from the Long-Wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;...&#xA;Read the easy text written by W8JI .  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;...&#xA;Hope that helps.  Glen Ellis, K4KKQ, CW/QRP 59 years.  &lt;/p&gt;&#xA;" OwnerUserId="8402" LastEditorUserId="8402" LastEditDate="2017-08-08T21:22:04.847" LastActivityDate="2017-08-08T21:22:04.847" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9026" PostTypeId="2" ParentId="9021" CreationDate="2017-08-08T21:27:42.597" Score="1" Body="&lt;p&gt;I will try to keep this simple. If you have a dipole and its longer than a half wave you can get lobes which can give you a certain advantage and gain in certain directions. This usually only happens when it is lengthened by multiples of a wave length &lt;/p&gt;&#xA;" OwnerUserId="10160" LastActivityDate="2017-08-08T21:27:42.597" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9027" PostTypeId="2" ParentId="9021" CreationDate="2017-08-08T22:34:32.343" Score="1" Body="&lt;p&gt;The maximum gain you can obtain from a dipole is when it is 10/8 of a wavelength long (5/8 per side). It has a 4.97 dBi gain compared to a half wave dipole with 2.15 dBi gain (both are free space gains). It has a sharper, perpendicular lobe compared to a half wave dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We tend to use center fed, 1/2 wave dipoles because of the convenient feed point impedance for 50 ohm coax. The impedance of a typical center fed, 1/2 wave dipole will vary between 45 ohms and 100 ohms depending upon its wavelength height above ground. This impedance range minimises the losses in 50 ohm coax due to SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 10/8 wave dipole (aka extended double zepp) requires a tuner or matching network when used with coax since it is not even a resonant antenna much less 50 ohms impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, as a center fed dipole is lengthened well beyond 1/2 wavelength, the primary lobes point more toward the ends of the antenna instead of perpendicular to the antenna. This change in pattern is often overlooked by hams with multiband dipole installations.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-10T11:49:11.473" LastActivityDate="2017-09-10T11:49:11.473" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9028" PostTypeId="2" ParentId="9020" CreationDate="2017-08-08T22:39:33.567" Score="3" Body="&lt;p&gt;I suspect that the physical aperture size of your dish will make it a poor 2 meter antenna and a marginal 440 antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of treating it like a dish antenna, you may wish to consider making it a slotted aperture antenna. This makes a reasonable stealth antenna if that is your goal. QST had an article within the last six months, detailing such a design.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-08-08T22:39:33.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9029" PostTypeId="2" ParentId="9021" CreationDate="2017-08-08T23:19:01.423" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Does a longer dipole (than half wavelength), for example twice as long, tuned to 50 Ω using an antenna tuner perform better than a half wavelength dipole for the same frequency?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A one wavelength dipole has a very high feedpoint impedance, &lt;strong&gt;much&lt;/strong&gt; higher than 50 Ω. If you decide to feed a one-wavelength center-fed dipole with a tuner with sufficient impedance range, either of these two conditions must be met to avoid severe feedline losses:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;If you're using coax feedline, &lt;em&gt;the tuner must be at the feedpoint&lt;/em&gt;. If  the tuner is in your shack, then only a small fraction of your TX power will reach the antenna.&lt;/li&gt;&#xA;&lt;li&gt;If mounting a tuner at the feedpoint is not practical (it usually isn't!), then &lt;em&gt;you must feed it with the proper open-wire (&quot;ladder&quot;) line and a suitable balanced antenna tuner&lt;/em&gt;. It will have far less losses than coax.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Case in point: I have a 75m dipole fed with 60 to 100 feet of RG-6 coax. Although my tuner will perfectly match the shack end of the coax on 40m, my signal is very weak on 40; I have to run 600 watts to make myself heard at all in a group of friends.  I finally gave up because only one or two in the group could hear me, and then only barely when the noise on 40m was low.&#xA;Unless your coax is very short, you'll have similar experiences. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The SWR on 40m at the feedpoint is about &lt;strong&gt;93&lt;/strong&gt;; the calculated line loss with 100&#xA;  feet of:&lt;/p&gt;&#xA;  &#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;RG-6 = 6.4 dB&lt;/li&gt;&#xA;  &lt;li&gt;RG-213 = 6.3 dB &lt;/li&gt;&#xA;  &lt;li&gt;LMR-400 = 5.54 dB &lt;/li&gt;&#xA;  &lt;li&gt;14 AWG  spaced 5&quot; = 2.39 dB &lt;/li&gt;&#xA;  &lt;li&gt;Wireman 553 = 2.1 dB &lt;/li&gt;&#xA;  &lt;li&gt;12 AWG spaced 5&quot; = 1.99 dB&lt;/li&gt;&#xA;  &lt;li&gt;Wireman 551 = 1.8 dB &lt;/li&gt;&#xA;  &lt;li&gt;Wireman 552 = 1.8 dB &lt;/li&gt;&#xA;  &lt;li&gt;Wireman 554 = 1.6 dB &lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Source: &lt;a href=&quot;http://owenduffy.net/calc/tl/cllc.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;,  &lt;a href=&quot;http://owenduffy.net/calc/tl/twllc.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;, and TLDetails.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Last I looked, there were a number of online stores selling suitable spacers and the assembled line itself. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-08-09T22:15:54.397" LastActivityDate="2017-08-09T22:15:54.397" CommentCount="13" ContentLicense="CC BY-SA 3.0" />
  <row Id="9030" PostTypeId="1" CreationDate="2017-08-09T13:40:45.600" Score="2" ViewCount="1114" Body="&lt;p&gt;Here is my situation.  My antenna mast is on the opposite side of the house from my ham shack, same with the power service entrance.  I have installed ground rods roughly every 16 feet with #6 wire bonding everything starting at my power service entrance, continuing to the mast, polyphasers on an SPGP of sorts, around to the ham shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My coax is buried from the mast to where the polyphasers are going in.  My plan is to run the coax from the protected side of the polyphasers up through the soffit and through my attic over to the HAM shack.  The shack ground will enter from the side wall.  The reason I am planning on doing it this way is my walls are brick and concrete, and it is a lot easier to drill a small hole for the ground wire than to core out a hole big enough for the ground and coax.  Is there anything wrong with this approach?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Pz3Td.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Pz3Td.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10163" LastEditorUserId="76" LastEditDate="2017-08-09T14:15:24.983" LastActivityDate="2017-08-11T20:08:40.220" Title="Grounding Help - Where To Route My Wires" Tags="&lt;grounding&gt;&lt;antenna-system&gt;&lt;lightning&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9031" PostTypeId="2" ParentId="8990" CreationDate="2017-08-09T13:44:26.910" Score="0" Body="&lt;p&gt;It's also worth trying to see if you can dig up the datasheet on the BFY 51 and compare it's applicable characteristics to the replacement you are considering.&lt;/p&gt;&#xA;" OwnerUserId="10163" LastActivityDate="2017-08-09T13:44:26.910" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9032" PostTypeId="1" AcceptedAnswerId="9036" CreationDate="2017-08-09T14:19:58.837" Score="2" ViewCount="184" Body="&lt;p&gt;I'm a newbie in such domain and I was reading some articles around the internet and what attracted me most is using the GnuRadio to see NOAA images using some cheap hardware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I looked further it turned out that this cheap hardware is only for receiving and not transmitting and other hardware with Rx/Tx capabilities are expensive (&lt;a href=&quot;https://www.ettus.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;USRP&lt;/a&gt; or &lt;a href=&quot;https://greatscottgadgets.com/hackrf/&quot; rel=&quot;nofollow noreferrer&quot;&gt;HackRF One&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I am aiming to visualize some images from NOAA using the &lt;strong&gt;GnuRadio&lt;/strong&gt; but I'm confused about which dongle to buy ( Preferably with Rx/Tx capabilities). and For Rx only I found a couple of options on Amazon, so which one is more suitable for such kind of applications (Provide a link if possible). &lt;/p&gt;&#xA;" OwnerUserId="9942" LastEditorUserId="8832" LastEditDate="2017-08-20T21:47:09.783" LastActivityDate="2017-08-20T21:47:09.783" Title="Choose the right dongle for NOAA images visualization with GnuRadio" Tags="&lt;antenna&gt;&lt;rtl-sdr&gt;&lt;gnuradio&gt;&lt;hackrf&gt;&lt;usrp&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ClosedDate="2017-08-11T01:08:46.723" ContentLicense="CC BY-SA 3.0" />
  <row Id="9033" PostTypeId="2" ParentId="8994" CreationDate="2017-08-09T14:21:12.450" Score="0" Body="&lt;p&gt;The coating could be there to prevent micro-oscillations in the circuit itself.  It was definitely factored in to the design of the phone.  &lt;/p&gt;&#xA;" OwnerUserId="10163" LastActivityDate="2017-08-09T14:21:12.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9034" PostTypeId="2" ParentId="9017" CreationDate="2017-08-09T14:29:19.453" Score="0" Body="&lt;p&gt;Just make sure if you use a 300 ohm adapter you strap it across the correct terminals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;if your not worried about poking your finger save your $5 and strip the coax, twist up the shield and lace it under the ground post then bend the center conductor like a J and hook it under the post directly to the right of &quot;FM ANT.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used to have a similar receiver many years ago where they were too cheap to put an F jack on but they did have a small little piece of metal to hold the coax down.  Yours probably fell off...&lt;/p&gt;&#xA;" OwnerUserId="10163" LastActivityDate="2017-08-09T14:29:19.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9035" PostTypeId="2" ParentId="9021" CreationDate="2017-08-09T16:26:59.777" Score="0" Body="&lt;p&gt;One consequence is the radion pattern changes. Here's an animation from 0.1 wavelengths to five wavelengths for a dipole in free space, running horizontally on the page:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/T0LEv.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/T0LEv.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation pattern is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {e^{-i2\pi} \over 2\pi} {\cos({\pi L} \cos \theta) - \cos(\pi L) \over \sin \theta} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $L$ is the length of the dipole in wavelengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This should probably be normalized such that the radiation intensity integrated over all angles equals a constant, which would make a fair comparison in directivity among all lengths. I haven't worked out the math to do that yet.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-09T16:26:59.777" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9036" PostTypeId="2" ParentId="9032" CreationDate="2017-08-09T18:12:02.697" Score="2" Body="&lt;p&gt;Picking up NOAA imagery is mostly a feat of constructing a good antenna than having a high bandwidth, or great clock. Thus, for reception only, build a nice helical antenna, and any cheap RTL Dongle, as long as it works at 1.698 GHz – if you don't want to waste the signal quality you've earned through the antenna, a cheap LNA (Lna4all seems to be nice) will help. That'll cost you very little.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding working at 1.698 GHz: The Osmocom RTL-SDR &lt;a href=&quot;http://osmocom.org/projects/sdr/wiki/rtl-sdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;wiki page&lt;/a&gt; has a list of RTL dongle integrated tuners and the frequencies they reach. If in doupt, the &lt;a href=&quot;http://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/&quot; rel=&quot;nofollow noreferrer&quot;&gt;rtl-sdr.com store&lt;/a&gt; dongle comes in a nice metal case and has the R820 tuner that works up to those frequencies&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, for NOAA you need no TX; so, we can't tell any TX spec requirements from your question. All answers to your question would thus be based on guesses, and personal preferences! So, write down proper specs, and ask a new question about TX-capable SDRs. You'll want to specify:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The range of center frequencies you want to cover&lt;/li&gt;&#xA;&lt;li&gt;The instantaneous bandwidth you'd like&lt;/li&gt;&#xA;&lt;li&gt;Ideally, a Noise Figure requirement; but that's hard for a beginner to guess, so instead, &#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Describe what you want to &lt;em&gt;do&lt;/em&gt; with that SDR, in more detail than &quot;transmit&quot;:&lt;/li&gt;&#xA;&lt;li&gt;Transmit and Receive what kind of signals&lt;/li&gt;&#xA;&lt;li&gt;How weak are these signals, or from how far do they come, or what is your plan to do with these signals?&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Point is that an SDR is really just an universal device: It lets you capture the radio signals &quot;as they are on the air&quot;, and calculate the signal to be put on the air in your computer. So, an SDR doesn't serve a single purpose that we can guess from the start – you'll need to find out what you want to do, and then we'll be able to help you :)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-08-09T18:18:05.430" LastActivityDate="2017-08-09T18:18:05.430" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9037" PostTypeId="1" CreationDate="2017-08-09T20:06:18.500" Score="3" ViewCount="1197" Body="&lt;p&gt;I've heard if I have a dipole of some arbitrary length, or a random wire, the SWR can be very bad. An antenna tuner can present a decent match to the transmitter, but the SWR on the feedline will be very high, and thus ladder line is required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is ladder line really required, as opposed to coax? What are the essential properties of a feedline in this application?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-09-09T16:33:08.560" Title="Is ladder line necessary when using a non-resonant dipole through a tuner?" Tags="&lt;wire-antenna&gt;&lt;antenna-tuner&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9038" PostTypeId="2" ParentId="9037" CreationDate="2017-08-09T21:21:54.913" Score="4" Body="&lt;p&gt;This can indeed be a fine setup. With a suitably low-loss feedline, and a good tuner, just about anything can be made to function as an effective antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two factors that determine the losses in this situation:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the matched loss of the feedline, a function of length and the attenuation specified in the datasheet, and&lt;/li&gt;&#xA;&lt;li&gt;the operating SWR on the feedline, which depends on the ratio of the feedline and load impedances.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;When the SWR is greater than 1:1, some fraction of the power is reflected from the antenna, back towards the transmitter. The antenna tuner then re-reflects this reflected power back at the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Eventually, all the energy is either radiated by the antenna, absorbed by the feedline, or absorbed by the tuner. Since each parcel of energy is making multiple &quot;bounces&quot; between the tuner and the antenna, it's subject to the feedline loss multiple times. Obviously, lower feedline loss means less loss. A lower SWR means fewer bounces back and forth, so again less loss. See &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;What is the actual loss in a feed line with high SWR?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ladder-line does not intrinsically have lower loss than coax. For example, this &lt;a href=&quot;https://www.dxengineering.com/parts/dxe-ll300-5c/documentation&quot; rel=&quot;nofollow noreferrer&quot;&gt;300 ohm ladder line sold by DX Engineering&lt;/a&gt; has a loss of 0.668 dB per 100 feet at 30 MHz. Compare to &lt;a href=&quot;https://www.timesmicrowave.com/documents/resources/LMR-400.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Times Microwave LMR-400&lt;/a&gt; at 0.7 dB for the same. There's better coax, and there's better ladder-line, but generally the performance of a transmission line is a function of the dielectric and conductor resistance (mostly the latter at HF), not whether it's coax or ladder-line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QxIRH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QxIRH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;br/&gt;&#xA;&lt;em&gt;specified attenuation for DX Engineering ladder-line per 100 feet&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6fRiU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6fRiU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;br/&gt;&#xA;&lt;em&gt;specified attenuation for LMR-400&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note the significantly higher loss when the ladder-line is damp. Coax maintains its performance when wet, covered in snow, ice, or dirt, when buried, run through conduit, attached directly to a tower, etc. This is why commercial installations overwhelmingly prefer coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ladder-line does tend to have a higher characteristic impedance, somewhere between 300 and 600 ohms for common designs. This is important.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A resonant dipole is at an impedance minimum, around 72 ohms. So when the dipole isn't resonant, the impedance will be higher, with a typical maximum around 5000 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modelling software and antenna analyzers will give an SWR, but this is not the SWR on the feedline unless the feedline has a characteristic impedance of 50 ohms. Given our dipole which may be between 72 and 5000 ohms, this gives a possible SWR from 1.44:1 to 100:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With 300 ohm ladder-line, the antenna analyzer will still say the SWR is 100:1 in the worst case. But actually the SWR is only:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ { 5000\:\Omega \over 300\:\Omega } = 16.7:1 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why ladder-line tends to have a lower loss in this antenna system. Not because it is an inherently lower-loss feedline, but because the SWR is reduced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you wish to use coax, it's an easy problem to solve. A 4:1 balun on 75 ohm coax divides the load impedance by 4. So again calculating the SWR at the worst case 5000 ohm load:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ { 5000\:\Omega\:/\:4 \over 75\:\Omega } = 16.7:1 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's the same SWR as the 300 ohm ladder-line. If the coax and ladder-line have equal matched loss, their total losses will be the same also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A balun with a higher transformation ratio will reduce the SWR further, and losses with it. If the antenna impedance could be anywhere between 72 and 5000 ohms depending on operating frequency, then the best &quot;compromise&quot; feedline impedance is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \sqrt{5000\:\Omega \cdot 72\:\Omega} = 600\:\Omega $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This gives a worst-case SWR at the extremes of high and low antenna impedance of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ {600\:\Omega \over 72\:\Omega}&#xA;= {5000\:\Omega \over 600\:\Omega}&#xA;= 8.3:1 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not such a horrible SWR. This could be realized with:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;600 ohm ladder-line, or&lt;/li&gt;&#xA;&lt;li&gt;300 ohm ladder-line and a 2:1 balun, or&lt;/li&gt;&#xA;&lt;li&gt;75 ohm coax and an 8:1 balun, or&lt;/li&gt;&#xA;&lt;li&gt;50 ohm coax and a 12:1 balun.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So, in summary:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Ladder line is not necessarily lower loss, but it does have a higher characteristic impedance.&lt;/li&gt;&#xA;&lt;li&gt;Non-resonant antennas tend to have higher feedpoint impedances.&lt;/li&gt;&#xA;&lt;li&gt;With an impedance transforming balun, coax can have the same SWR as ladder-line. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-08-10T16:26:30.890" LastActivityDate="2017-08-10T16:26:30.890" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9039" PostTypeId="1" AcceptedAnswerId="9041" CreationDate="2017-08-09T23:42:39.047" Score="1" ViewCount="62" Body="&lt;p&gt;I have two 1:4 voltage baluns. If I connect them together so that I have 1:4-4:1, is that the equivalent of putting a 1:1 common mode choke on my feed line?&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2017-08-10T01:24:58.250" Title="Can I use two voltage baluns to make a common mode choke?" Tags="&lt;balun&gt;&lt;transmission-line&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9040" PostTypeId="2" ParentId="8999" CreationDate="2017-08-09T23:59:39.900" Score="3" Body="&lt;p&gt;LEVI means LEFT&lt;/p&gt;&#xA;&#xA;&lt;p&gt;DESNI means RIGHT&lt;/p&gt;&#xA;&#xA;&lt;p&gt;ZV1 is speaker one&#xA;ZV2 is speaker two&lt;/p&gt;&#xA;&#xA;&lt;p&gt;S this radio has connections for two pairs of 4 ohm speakers. I guess LEFT ZV1 and RIGHT ZV1 are main speakers and ZV2 are additional (as option).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each speaker connector is DIN speaker connector with two contacts. Wide contact is speaker minus, circular contact is speaker plus pole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/U5xEF.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/U5xEF.jpg&quot; alt=&quot;DIN speaker connector male&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do not have male connectors check this: &lt;a href=&quot;http://www.ebay.co.uk/itm/2-Pin-DIN-Hi-Fi-Speaker-Plug-Cable-Audio-Connector-PACK-of-2-Screw-Connections-/331395432695&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ebay.co.uk/itm/2-Pin-DIN-Hi-Fi-Speaker-Plug-Cable-Audio-Connector-PACK-of-2-Screw-Connections-/331395432695&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can easily stick speaker wires directly into female connectors as temporary solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Schematics&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DVhMh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DVhMh.jpg&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/I9ebK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/I9ebK.jpg&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EueDf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EueDf.jpg&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dQm7c.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dQm7c.jpg&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1iJm2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1iJm2.jpg&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2017-08-09T23:59:39.900" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9041" PostTypeId="2" ParentId="9039" CreationDate="2017-08-10T01:24:58.250" Score="2" Body="&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say you take just one of the 1:4 baluns, and connect it like so:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/lbQGs.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2flbQGs.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the winding ratios are not equal, then equal and opposite currents will not cancel each other's magnetic flux, so there will be a net non-zero flux in the core. Thus, it presents an inductance to common-mode currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if you add another in series:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/OTv9p.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fOTv9p.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;there's still non-zero flux in the core. It simply doubles the common-mode impedance.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-10T01:24:58.250" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9042" PostTypeId="1" AcceptedAnswerId="9043" CreationDate="2017-08-10T13:08:57.993" Score="3" ViewCount="571" Body="&lt;p&gt;I'm looking at buying a used &lt;a href=&quot;http://www.polyphaser.com/products/rf-surge-protection/is-50nx-c0&quot; rel=&quot;nofollow noreferrer&quot;&gt;IS-50NX-C0&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wyXzs.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wyXzs.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The listings usually say something like &quot;Used, pulled from working equipment.&quot; While I'd believe they still work as far as normal operation is concerned, I doubt the sellers have tested their surge suppression capabilities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't find much information on what's inside these things. Does it wear out over time? Can it withstand multiple strikes? Or is it likely what I'd be buying is a unit that's already toasted?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-11T15:09:08.810" Title="Are used PolyPhaser IS-50 RF surge protectors likely to work?" Tags="&lt;lightning&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9043" PostTypeId="2" ParentId="9042" CreationDate="2017-08-10T20:43:03.840" Score="4" Body="&lt;p&gt;The Polyphaser consists of a DC blocking capacitor in series with the radio and a gas discharge element in parallel with the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yCkv8.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yCkv8.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Polyphaser can normally withstand multiple &amp;lt;20 kA strikes without failing. Unfortunately, in the far majority of the cases, the gas discharge element fails in an open state. There is therefore no practical, absolute test of the the functionality of the device. Polyphaser advises that a change in SWR would be an indicator of failure.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-08-10T20:43:03.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9044" PostTypeId="1" AcceptedAnswerId="9049" CreationDate="2017-08-10T21:14:06.563" Score="11" ViewCount="2965" Body="&lt;p&gt;There are a lot of antenna tuners on the market that have various capabilities in terms of how they can allow random radiators to work with our transceivers.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What exactly do they do?  My understanding is that they can neutralize the imbalance between inductive and capacitive reactance so the transceiver can couple the most power out (or in) even though an antenna might not be resonant on a particular operating frequency, since overall impedance (Z) consists of three parts, two of which are reactance dependent on frequency:  X(sub)L and X(sub)C, and R, the radiation resistance of the whole system.  And the transmitters do not work as well into a non-resistive load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a resonant antenna these are in balance such that the characteristic radiation resistance of the antenna is presented to the transmitter.  For a plain dipole that tends to be roughly 72 ohms.  And there are many antenna analyzers out there that can assist in the physical pruning of antennas in order to reduce the SWR on the feedlines.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I remember using light bulbs to tune up old tube-type transmitters because they were mostly resistive and non-reactive at HF)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;300-ohm ladder line to a dipole requires a 4:1 balun to bring the impedance down to a range the transmitter can handle, which is typically 50-75 ohms, resistive, to keep the transmitters within their limits.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what does an antenna tuner do?  Does it reduce the SWR (loss) on the feedlines?  Or does it simply ensure a match for the transmitter so it can operate at maximum efficiency regardless of whether a signal is coupled from the antenna to the outside world?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To further complicate the question, there is the matter of Q - the measure of the bandwidth for which the antenna will most efficiently accept transmitter power and radiate it.  My understanding is that the best resonant antennas have a high Q which means a very narrow bandwidth for which they are most effective. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've often used tuners when using 80-meter dipoles on the 75-meter phone section of the band, in order to reduce indicated SWR.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similar to using 40-meter antennas on 15 meters, though that is more problematic since the harmonics don't line up as closely and it takes a better tuner than my current travel model.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the question is in two parts:  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is an antenna tuner?  If it is mounted at the transmitter is it actually tuning the antenna itself?  Does it reduce the SWR in the feedline to a non-resonant antenna, for instance?  Should the tuner be placed at the antenna instead of at the transmitter in order to reduce SWR loss (heating) in the feedline?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if it is possible to use a tuner to make a transmitter feed power into a coat hanger then why do we worry about making resonant antennas in the first place?&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="9493" LastEditDate="2017-08-11T10:03:59.563" LastActivityDate="2019-06-15T12:38:03.813" Title="What is an antenna tuner? Why bother with resonant antennas in the first place?" Tags="&lt;antenna-system&gt;&lt;antenna-tuner&gt;" AnswerCount="5" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9045" PostTypeId="2" ParentId="9044" CreationDate="2017-08-10T22:29:41.873" Score="2" Body="&lt;p&gt;Simply put:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If it is mounted at the transmitter is it actually tuning the antenna itself?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, it is &lt;em&gt;not&lt;/em&gt; tuning the antenna. It just matches the resistance and reactance at the tuner end of the feedline to your transmitter.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does it reduce the SWR in the feedline to a non-resonant antenna?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, it does &lt;em&gt;not&lt;/em&gt; change the VSWR on the feedline.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Should the tuner be placed at the antenna instead of at the transmitter in order to reduce SWR loss (heating) in the feedline?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Ideally, yes. However, that is usually not practical. It's often better to use a low-loss feedline. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;300-ohm ladder line to a dipole requires a 4:1 balun to bring the impedance down&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That &lt;strong&gt;sometimes&lt;/strong&gt; works for one (maybe two) bands, but not if you want to cover 80-10.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My understanding is that the best resonant antennas have a high Q which means a very narrow bandwidth for which they are most effective. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Not necessarily so.&lt;/em&gt; A dipole with less Q and a wider bandwidth can be very effective indeed! One way of doing this is to replace a single wire with a &quot;cage&quot;, greatly increasing the effective diameter of the element(s).&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-08-10T22:47:43.227" LastActivityDate="2017-08-10T22:47:43.227" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9046" PostTypeId="2" ParentId="7014" CreationDate="2017-08-11T04:15:22.950" Score="0" Body="&lt;p&gt;The shorting arm/bar serves the purpose exemplified by the schematic: It closes one of the two sets of parallelled switches (each of which sets consists of the key-lever-closable contacts in parallel with the shorting-arm contacts) that are connected in series with the system's sounders, thus allowing the distant station to send. (Sounders were not buzzers, BTW; they were, in effect, very sensitive relays that made metallic clicks on MAKE and BREAK.) Use of the shorting arm for radio-transmitter tuning may be more user-friendly that leaning a book or other heavy object on a straight key, but presence of the shorting bar on keys predates the existence of radiocommunication in any form.&lt;/p&gt;&#xA;" OwnerUserId="10170" LastActivityDate="2017-08-11T04:15:22.950" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9047" PostTypeId="2" ParentId="9044" CreationDate="2017-08-11T10:43:11.920" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;My understanding is that they can neutralize the imbalance between inductive and capacitive reactance so the transceiver can couple the most power out (or in) even though an antenna might not be resonant on a particular operating frequency, since overall impedance (Z) consists of three parts, two of which are reactance dependent on frequency: X(sub)L and X(sub)C, and R, the radiation resistance of the whole system. And the transmitters do not work as well into a non-resistive load.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It some cases, it's not a question of coupling power into the load. For some impedances, a mismatched load may enable &lt;em&gt;more&lt;/em&gt; power to be coupled into the load, however this would destroy the transmitter! Thus, the purpose of the tuner is also to present an impedance to the transmitter that allows it to work within the limits of its maximum current and voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radiation resistance also depends on frequency, and the tuner doesn't necessarily just cancel reactance. Consider an extreme example: a 1-wavelength long wire dipole has a radiation resistance around 4500 ohms and no reactance. That doesn't mean there's nothing for the tuner to do: the tuner needs to step down that impedance to 50 ohms.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;300-ohm ladder line to a dipole requires a 4:1 balun to bring the impedance down to a range the transmitter can handle, which is typically 50-75 ohms, resistive, to keep the transmitters within their limits.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's not the only way to use 300-ohm ladder line. If it's used in 1/2 wavelength multiples of length, then the ladder line will have no effect on the load impedance seen by the transmitter. The impedance step-down can also be accomplished with a network of inductors or capacitors, either fixed, or variable as in a tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or if the antenna wasn't matched to start, the right length of 300-ohm ladder line might result in a matched impedance at the transmitter. Using controlled lengths of feedline to match loads is called stub matching. Given the ability to pick the transmission line length and impedance, any load can be matched. If the transmission line impedance can't be picked, then any load can be matched with no more than two lengths of transmission line.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;there is the matter of Q - the measure of the bandwidth for which the antenna will most efficiently accept transmitter power and radiate it. My understanding is that the best resonant antennas have a high Q which means a very narrow bandwidth for which they are most effective.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Antenna losses reduce Q, so for example a vertical with a poor ground plane will have a lower Q and wider bandwidth. A dummy load has a Q of zero and infinite bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But losses are not the only factor. A vertical shortened by loading coil has a higher Q than one a full 1/4 wavelength long, yet the shortened vertical is generally a poorer antenna. A 1/2 wave dipole made of thicker wires, or made of a cage of wires, or thickened as in a folded dipole, has a lower Q than one made of thin wire, and yet is just as effective.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I've often used tuners when using 80-meter dipoles on the 75-meter phone section of the band, in order to reduce indicated SWR.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Tuners are often required on 80/75-meters due to two factors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;electrically shortened antennas (loading coils, for example) are frequently used to make the otherwise very large antennas manageable, and&lt;/li&gt;&#xA;&lt;li&gt;the &lt;a href=&quot;http://www.antenna-theory.com/definitions/fractionalBW.php&quot; rel=&quot;noreferrer&quot;&gt;fractional bandwidth&lt;/a&gt; of that band is very large.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is an antenna tuner?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's any network of components designed to match one impedance to another, with variable components to accommodate use at a number of frequencies or with a variety of antennas. Frequently, it's a PI network:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/8TMkg.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f8TMkg.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If it is mounted at the transmitter is it actually tuning the antenna itself?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. Arguably, if it's mounted at the antenna it's not actually tuning the antenna either, although such an arrangement can avoid additional losses in the feedline due to increased SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It just depends on how you define &quot;the antenna&quot;. As far as the transmitter is concerned, all that matters is the impedance appearing at its terminals. Some antennas could be said to contain feedlines, such as those with stub matches, or phased arrays using transmission lines for phasing delay. Are those transmission lines part of &quot;the antenna&quot;? What if a transmission line is an integral part of the antenna, such as in a zepp, or a gamma match, or a folded dipole?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does it reduce the SWR in the feedline to a non-resonant antenna, for instance?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not if it's mounted at the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Should the tuner be placed at the antenna instead of at the transmitter in order to reduce SWR loss (heating) in the feedline?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Should the tuner be placed in the shack so the knobs can be adjusted without going outside? The answer will depend on individual circumstances. Automatic tuners are significantly more expensive. While placing the tuner at the antenna does reduce mismatch losses in the feedline, those losses may not be high enough to justify the cost of a remote tuner. See &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;What is the actual loss in a feed line with high SWR?&lt;/a&gt; Reducing the SWR on the feedline also reduces the peak voltage and current on the line and any components along it such as surge supressors, which may become a limiting factor when operating at high power.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And if it is possible to use a tuner to make a transmitter feed power into a coat hanger then why do we worry about making resonant antennas in the first place?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A coat hanger at HF would be a challenging antenna to match, since its extremely small length relative to wavelength would present such an extreme mismatch that most tuners would not be able to match it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Resonant antennas are just one of many possible antenna designs. Not requiring a tuner reduces costs.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-11T10:43:11.920" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9048" PostTypeId="2" ParentId="9042" CreationDate="2017-08-11T15:09:08.810" Score="2" Body="&lt;p&gt;Polyphaser sent me a document on request. Salient points:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The only way to test the IS-50 or IS-B50 without expensive test equipment is by seeing if the VSWR&#xA;  (return loss) has increased or remove it from the line and see if the radio performance is better. Because&#xA;  the product is a DC block device, there is no way to test adequately with a multi-meter. A properly running&#xA;  product will test the same as a bad one. Normal operation, with an ohm meter you will get a short&#xA;  between pins and short between any pin and the housing (ground). The same results if the gas tube has&#xA;  failed. 95% of the time a gas tube will fail open which is also its normal state.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;[...]&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Since lightning is a natural event with varying current waveforms and return strokes there is no way to&#xA;  predict the gas tube lifetime. The current IS-50 series has been in production since 1993. It is a very&#xA;  reliable product. The first indication of impending failure will be increased insertion loss and SWR. The&#xA;  protector should be replaced immediately if insertion loss and SWR are greater than a straight through&#xA;  coax barrel connector (female to female) as full failure may or may not pass RF.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;[...]&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The MTBF (Mean Time Between Failures) is also effected by where and how the protector is installed and&#xA;  the natural variation in the intensity and number of return strokes per lightning event. The tower size,&#xA;  placement, ground conductivity, and number of storms per year can also affect MTBF. The gas tube&#xA;  manufacturer can provide raw data on gas tube failures, but in the real world, it’s relatively meaningless.&#xA;  The good news is the gas tubes will probably withstand 5 hits of 20KA each, but the N connector center&#xA;  pin will be damaged with the first 20KA hit. Good news? Yes, since it is obvious that the protector has&#xA;  done its job and should be replaced. How often could this happen? Probably never. That much current&#xA;  could only ride on the shield, and indicates a failure to properly ground the coax cable shield or a poor&#xA;  tower ground connection.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-11T15:09:08.810" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9049" PostTypeId="2" ParentId="9044" CreationDate="2017-08-11T17:08:31.467" Score="10" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;And if it is possible to use a tuner to make a transmitter feed power into a coat hanger then why do we worry about making resonant antennas in the first place?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;In a word - efficiency.&lt;/p&gt;&#xA;&lt;p&gt;Consider that a full size 40 meter, 1/2 wavelength dipole is approximately 65 feet (19.8 meters) long. A dipole that is only 2 feet (0.6 meters) long, would have a gain of  only 0.5 dB less than the 65 foot dipole. This would hardly be a noticeable difference on the air. But the problem is we cannot make the &lt;em&gt;antenna system&lt;/em&gt; efficient enough to realize that minor 0.5 dB loss. The system inefficiencies often result in substantial losses compared to a full size dipole.&lt;/p&gt;&#xA;&lt;p&gt;But we also should not be obsessed with resonant antennas - it makes little difference with practical antennas if we properly deal with their non-resonant effects. A 10/8 wave dipole has nearly double the gain of a 1/2 wave dipole. It is not resonant but can easily be matched to a transmission line with a simple matching network. A Yagi antenna is not resonant without the addition of a matching network. Also consider that many resonant antennas are not resonant at the impedance of the feedline anyway - for example, an ideal 1/4 wave ground plane vertical is resonant at approximately 34 ohms.&lt;/p&gt;&#xA;&lt;p&gt;Here are some typical sources of &lt;em&gt;antenna system&lt;/em&gt; inefficiencies:&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Radiation Resistance vs Resistive Losses&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Radiation resistance is an often misunderstood and misapplied term. The radiation resistance &lt;em&gt;of an antenna&lt;/em&gt; is caused by the radiation of electromagnetic waves. For a free space, 1/2 wave, center fed dipole of reasonable construction, the radiation resistance is ~73 ohms. Any resistive losses (power that is not radiated) in the antenna add to this radiation resistance to contribute to the feed point impedance. In the case of this dipole, there will be a very small amount of RF resistance due to the wires that make up the dipole. If we use 14 gauge (1.45 mm) wire to construct the antenna, the RF resistance will be ~2.7 ohms. The total feed point impedance would then be 75.7 ohms in this example.&lt;/p&gt;&#xA;&lt;p&gt;The efficiency of an antenna is given by the formula:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Efficiency = \left( \frac{R_r}{R_r+R_l} \right)$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;where R&lt;sub&gt;r&lt;/sub&gt; is the radiation resistance and R&lt;sub&gt;l&lt;/sub&gt; is the resistive losses.&lt;/p&gt;&#xA;&lt;p&gt;So if we apply this to our dipole example above, the efficiency would be 96.4%. By contrast, the two foot dipole will have an R&lt;sub&gt;r&lt;/sub&gt; of approximately 0.04 ohms and a comparative R&lt;sub&gt;l&lt;/sub&gt; of 0.08 ohms resulting in an efficiency of 33%.&lt;/p&gt;&#xA;&lt;p&gt;To complete this part of the efficiency picture, consider that:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Gain = Directivity \times Efficiency $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;A full size dipole has a directivity of 1.65. Multiply this times the 96.4% efficiency of the above example and the gain becomes 1.59 (2.02 dBi). For the short dipole, the directivity is 1.5. Multiply this times the 33% efficiency of the above example and the gain becomes 0.5 (-3.01 dBi). So we already have a 5 dB difference between the two antennas and there still are other &lt;em&gt;system&lt;/em&gt; losses that must be taken into account.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Matching Networks / Tuners&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;In the example of our 1/2 wave dipole, the feed point impedance of the antenna is ~ 75 ohms. If we are attempting to drive this with a 50 ohm source, we may wish to have a tuner or matching network that does the transformation between the two largely resistive impedances. In this case, a well built tuner or matching network will have an efficiency in the 80-95% range (less than 1 dB of loss).&lt;/p&gt;&#xA;&lt;p&gt;In the case of our short dipole example, the situation is a bit more complex. We need to both cancel the capacitive reactance of the dipole and match the very low feed point impedance. Without going through laborious calculations of matching network efficiencies, it would not be unreasonable to expect less than 10% efficiency (&amp;gt;10 dB loss) from the matching network. This means that at least 90% of the applied power or signal will be lost to heat in the matching network alone. Our short dipole &lt;em&gt;system&lt;/em&gt; now has a gain of -13 dBi which is more than 15 dB down from our full size dipole example. This is the equivalent to comparing the signal strength of a 100 watt transmitter to a 3 watt transmitter.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Transmission Line Loss&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;All real world transmission lines exhibit loss. This in itself is a reduction in efficiency. The specification for the transmission line lists the loss for the transmission line at a given frequency assuming that the transmission line is terminated in its characteristic impedance. When the transmission line is not terminated in its characteristic impedance, the loss of the transmission line increases (the efficiency further decreases).&lt;/p&gt;&#xA;&lt;p&gt;By placing a tuner or matching network close to the antenna to provide a match to the characteristic impedance of the transmission line, the additional losses due to a transmission line mismatch can be avoided. This maximizes the efficiency of a given transmission line.&lt;/p&gt;&#xA;&lt;p&gt;There is a secondary effect when the transmission line is not connected to a load that matches its characteristic impedance - the transmission line will no longer exhibit its characteristic impedance. Another way of saying this is it becomes an impedance transformer. For example, our 75 ohm dipole impedance in the early example when connected to 23 feet of RG213 will be transformed to 34 ohms at the transmitter end of the transmission line. The total losses in the transmission line will be 0.119 dB, of which only 0.009 dB is due to the mismatched load. A free program such as &lt;a href=&quot;http://www.ac6la.com/TLDetails.zip&quot; rel=&quot;noreferrer&quot;&gt;TLDetails&lt;/a&gt; makes quick work of these calculations:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fiLqQ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fiLqQ.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;In some cases, this transformation can be used to our advantage by transforming the antenna impedance to something that is more usable from a system efficiency perspective. In other cases, it can worsen the system efficiency. But do consider this transforming effect in light of transmitter output efficiency.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Transmitter Output Efficiency&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;The final efficiency factor to be considered is the output power of the transmitter. Most amateur transmitters are designed to deliver their rated output power when connected to a 50 ohm resistive load. Any deviation from this load will typically result in lower output power from the transmitter. This loss of transmitter output power effectively reduces the efficiency of the system.&lt;/p&gt;&#xA;&lt;p&gt;For example, a 100 watt, 50 ohm source impedance transmitter that is connected to the 23 feet of RG213 that is terminated with our 75 ohm dipole, will output 96 watts (if no protection circuits kick in). This is an output efficiency of 96% (a 0.17 dB loss). Note that this is most likely more efficient, in this example, than using an antenna tuner at the transmitter to match the transmitter impedance to the feedline impedance (even though this is a 1.5:1 SWR).&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;SWR&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;SWR is based on the relationship of the transmission line characteristic impedance to the impedance of the load on the transmission line. In the case of a transmitting system, the load is typically the antenna. In the case of a receiving system, the load is typically the receiver input impedance.&lt;/p&gt;&#xA;&lt;p&gt;Since we have already dealt with the relationship of the transmission line characteristic impedance to the load impedance in the earlier transmission line section, we need not consider SWR as another source of inefficiency.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-08-11T17:15:11.757" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9050" PostTypeId="2" ParentId="9030" CreationDate="2017-08-11T17:54:23.753" Score="1" Body="&lt;p&gt;I compliment you on the multiple ground rods, the wide spacing, and having them all bonded to the service entrance ground. This meets NEC requirements while providing an improved lightning ground system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think your system is quite good as described. My suggestions for possible improvements are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Use exothermic bonding (e.g. Cadweld) for your ground wire to ground rod connections. This results in lower maintenance and lower resistance per connection.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Increase the gauge of the wire or use copper straps between the added ground rods.  This lowers resistance and inductance between the rods.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Put another Polyphaser in your shack by your radio. This improves the lightning protection and provides redundancy in the event of a Polyphaser failure.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There is a new ARRL book by Ward Silver on grounding. I have not read it yet but it might give you some other pointers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xKGQV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xKGQV.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-08-11T17:54:23.753" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9051" PostTypeId="1" CreationDate="2017-08-11T19:09:19.977" Score="5" ViewCount="3626" Body="&lt;p&gt;I am installing a ham radio and want to properly ground it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will be including a lightning arrester that will also go the the ground. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will have a 20' mast with a long wire antenna running 130+ feet out to the south. The far end will be about 45 feet above ground level. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a ground connection on my mounting plate and also on the plate in my window that feeds the transmission lines in and out of the house. Inside I will have a 3 to 4 foot piece of copper pipe which will be common to all the cases of my system. It will be tied to the window ground feed through and from there to the ground rod.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in the North Western Arizona Desert and the ground is very dry. I am installing an 8 foot ground rod and because of the caliche I'm having to actually drill thru the dirt to put the rod in. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Would I benefit from multiple rods along the side of my house? Would copper pipe work as well, or better than, the steel rod which is copper clad? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Would it benefit my ground to run a slow drip maybe a gallon a day into the copper pipe so that the dirt at the bottom remains wet? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The pipe sections are 10' long vice the 8' of the rods. Will that help a lot or a little? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What else should I do? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What gauge wire should I use and should it be stranded, like the ground straps in a car, or solid or both?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerDisplayName="Chris Baker" LastEditorUserId="76" LastEditDate="2017-12-30T16:45:26.647" LastActivityDate="2020-09-15T13:19:58.370" Title="I am installing a ham radio and want to properly ground it" Tags="&lt;grounding&gt;&lt;lightning&gt;" AnswerCount="4" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9052" PostTypeId="2" ParentId="9030" CreationDate="2017-08-11T20:08:40.220" Score="1" Body="&lt;p&gt;Your setup looks pretty good. Bonding the grounds together is a step often overlooked, and substantially reduces the risk of lightning damage. There are still improvements that could be made however, and you'll have to decide if they are worth the effort and cost, according to the value of your radios and probability of lightning strikes in your area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The good news is I believe your installation satisfies most of the common building and fire codes, and your homeowner's insurance may cover damage if there is a strike. However I'm not a certified electrician, so having a professional check your work is not a bad idea. And some insurance policies may require a rider to cover lightning damage.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Consider that all your connections are made by wire which has a non-zero resistance, and which encircle a large area and thus have a non-zero inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vquG5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vquG5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Schematically, and simplified, you have this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/gv9ne.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fgv9ne.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;R1 represents the non-zero resistance of the Earth. I1 is the strike current passing through it. It could be due to a strike on the power lines, the tower, or even a nearby strike on the ground or a tree.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;L1 represents your connection between the grounds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's the voltage across the radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can't move the ground rods closer, so you can't reduce L1. You could use wide copper strap to reduce the inductance to a point, although that can get quite expensive. You can't change the Earth, and you can't stop lightning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Really the only solution here is to have only one connection to the radio. Then there can't be any voltage across it. So, one improvement to this scheme is to run all the cables to a single point ground. &lt;em&gt;All&lt;/em&gt; the cables, including those not on your diagram, such as power cables. If your radios are connected to a computer, all the cables connected to that, also. And if you want to follow the highest standards of lightning protection, anything conductive within four feet, even if not directly connected. With the cables traversing the attic where there are likely other electrical wiring, and possibly HVAC ducting, this may be difficult.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Route all those cables together so the loop area between them is minimized: that will help keep their potentials the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it makes things easier, you can probably do without the ground wire to the radio unless you are operating some antenna with strong common-mode currents, like a single long wire. If you can eliminate the common-mode currents (for example, &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;put a balun on a dipole&lt;/a&gt;) then a separate ground beyond what's already provided by the coax shield and the power cable adds no particular value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the power cables need to be part of this single point ground, perhaps you can move the feedline to enter where the power service does. If not, you can add a branch circuit which has a surge protective device at the same ground where your feedline enters. &lt;a href=&quot;https://diy.stackexchange.com/questions/1706/is-it-ok-to-have-mixed-grounds-and-neutrals-on-bars-in-a-breaker-box&quot;&gt;Don't ground the neutral at this point&lt;/a&gt;: that would create a serious safety hazard. Instead, &lt;a href=&quot;https://diy.stackexchange.com/q/120894/23521&quot;&gt;install a surge protective device with ground-neutral protection&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Either way, ideally the feedline and the power line from that grounding point follow the same path to minimize loop inductance, so that probably involves running a new branch circuit that follows the feedline path.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-11T20:08:40.220" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9053" PostTypeId="1" CreationDate="2017-08-11T23:02:24.600" Score="3" ViewCount="185" Body="&lt;p&gt;I am attempting to implement a PCB trace antenna; namely the sample in &lt;a href=&quot;https://www.silabs.com/documents/public/application-notes/AN639.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this document&lt;/a&gt;. Thing is the 1.17 pF for Cp1 is quite hard to achieve in a cost efficient manner with 0603 caps (I loath those smaller beasts that not many hands can solder), and, from the graph in &quot;Figure 13. Loop Antenna Simulated Mag(Zin) vs. CP1&quot; it seems that even a 2% variance in the capacitance would have a great impact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For these matters I was thinking of extending the proposed solution of adding a printed finger cap on the other side of the main antenna loop, just underneath it (page 27)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SjpZH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SjpZH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;with adding more of those finger caps. So that my design would look something like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NryqX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NryqX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;i.e. have a bank of 4 such printed finger capacitors of values .01, .02, .04 and .08 pF. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best deal I could find for the ceramic part of Cp1 was a 1.1 pF with .05 pF tolerance. That means that I would need to cover the range between 0.02 and 0.12 pF with those printed caps in the bank, so with the four values above I shall theoretically match the ceramic's value to the required 1.17 pF to a tolerance of .005 pF by cutting the traces of those finger caps not needed for the compensation. I am assuming here that I will be able to precisely measure the 1.1 pF ceramic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So this is how I would fix the problem but I don't know whether or not the introduced problems are even bigger. Thinking about more inductance getting introduced maybe ? Any other thoughts on why this may not be a very good idea ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;edit for @tomnexus answer&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I still have two problems with the stubs. You see, before the finger-caps bank idea I have also thought about making a big cap and cutting it in marked places - the first problem is the &gt; 10 cm size I would need for it. It is the same problem with the stubs - I have done the maths for Z_0 of 100 Ohms and a velocity factor of 0.82 taken from that same document mentioned above and I got some 16.9 cm for the whole 0.12 pF value. Now I don't have anything close to such dimensions on my PCB. Could I spiral those two lines on the opposite side of the side with the antenna trace (making sure to keep reasonable distances to the antenna traces and in between the stub's curls0) ? &#xA;And a second problem - I was unable to get any calculators do the Z_0 for these side by side PCB traces. Closest I could find was a copled microstrip line- but that one also has a ground plane on the other side...&lt;/p&gt;&#xA;" OwnerUserId="8811" LastEditorUserId="8811" LastEditDate="2017-08-12T14:50:16.283" LastActivityDate="2017-08-12T14:50:16.283" Title="interdigital (finger) capacitor bank for fine tuning of differential loop antenna" Tags="&lt;impedance&gt;&lt;loop-antenna&gt;&lt;capacitance&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9054" PostTypeId="2" ParentId="9053" CreationDate="2017-08-12T08:38:25.210" Score="3" Body="&lt;p&gt;Great idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why not just make a single two-wire transmission line, called an &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Stub_(electronics)&quot; rel=&quot;nofollow noreferrer&quot;&gt;open circuit stub&lt;/a&gt;, and cut it to length with a knife.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$Z=-jZ_0Cot(\beta l)$  or&lt;br&gt;&#xA;$C=1/{\omega Z_0 Cot(\beta l)}$ &lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\beta=2 \pi/\lambda$ and $\omega = 2 \pi f$&lt;br&gt;&#xA;and&#xA;$Z_0 ≈ 100 \Omega$ for a pair of 1 mm lines 1 mm apart, but use an online calculator to find a more accurate paired strip impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Put little distance marks and numbers down in the soldermask to guide you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may have reproducibility problems unless you control the PCB dielectric constant, etching, plating and masking/coating very carefully. A plain process on FR4 will vary a lot. Keeping a wider gap, one PCB thickness or more, will make it less sensitive to the dielectric constant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;0.005 pF is an impossible tolerance IMHO. Just calculate the drift in capacitance caused by a few degrees temperature change, affecting the dielectric or even the mechanical spacing. Besides, it implies you are aiming for a tuning accuracy of one part in 300, which is almost unheard of in antennas.&lt;br&gt;&#xA;As an example, a very high Q &quot;small&quot; loop for 3 MHz might have a bandwidth of 10 kHz, which is a Q of 300. But it will be made of thick copper, and will require constant re-tuning as its dimensions shift around. Good enough for a live operator to use, but it wouldn't work for unattended use without an automatic tuner.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2017-08-12T08:46:42.773" LastActivityDate="2017-08-12T08:46:42.773" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9056" PostTypeId="1" CreationDate="2017-08-13T18:29:13.743" Score="2" ViewCount="336" Body="&lt;p&gt;Polyphaser sells a &lt;a href=&quot;https://www.tessco.com/products/displayProductInfo.do?sku=24981&amp;amp;eventGroup=4&amp;amp;eventPage=1&quot; rel=&quot;nofollow noreferrer&quot;&gt;WK-1 weatherproofing kit&lt;/a&gt; for their devices that are not weatherized such as the &lt;a href=&quot;http://www.polyphaser.com/products/rf-surge-protection/is-50nx-c0&quot; rel=&quot;nofollow noreferrer&quot;&gt;IS-50 series&lt;/a&gt;. It looks like a plain sheet of weatherproofing tape like any other, such as might be used to seal coax connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm hoping to install the protector on a heavy copper bulkhead I got for a steal at a hamfest. Installed in such a way, I don't see how the assembly could be wrapped. The kit comes with instructions, which ostensibly include some clever way around this problem. However, I refuse to pay $17 for a piece of tape. What's a good way to weatherize these surge protectors?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-08-13T18:35:21.503" LastActivityDate="2018-03-12T14:08:41.853" Title="How to weatherize a Polyphaser surge protector?" Tags="&lt;lightning&gt;&lt;installation&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9057" PostTypeId="2" ParentId="9056" CreationDate="2017-08-13T19:19:31.810" Score="0" Body="&lt;p&gt;If you can disassemble the unit, apply clear RTV sealant between the two halves of the body and between the N connectors and the body. You may also need to use the sealant on the screws. Get the kind that does not emit acetic acid fumes, which could corrode internal parts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;N connectors have red silicone gaskets and don't really need sealing. &lt;em&gt;However&lt;/em&gt;, I always stretch-wrapped electrical tape tightly over the connector &lt;strong&gt;and past both ends, onto the coax and the receptacle&lt;/strong&gt;. Worked for me many times, even for UHF connectors outdoors. Many years later I unwrapped the tape and disassembled the connectors, and there was not a trace of corrosion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't forget to apply a dab of silicone dielectric grease on the center pin. That will prevent corrosion due to any moisture in the air entrapped inside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I doubt if you to have to cover everything if you do the above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some N tees that I made &lt;em&gt;many&lt;/em&gt; years ago. They were at the top of a 70' tower for several years, sealed with RTV and electrical tape just as I described above. Most of the silver oxidation occurred in the years since.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IQYqH.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IQYqH.jpg&quot; alt=&quot;W0BTU N phasing tees&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vkgoL.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vkgoL.jpg&quot; alt=&quot;W0BTU N phasing tee&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-08-13T22:16:41.113" LastActivityDate="2017-08-13T22:16:41.113" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9058" PostTypeId="2" ParentId="9056" CreationDate="2017-08-14T10:25:04.160" Score="1" Body="&lt;p&gt;I have gone the simple route for most of my outdoor connectors in recent years. I use an inverted container over the connections and leave the bottom open. This fully waterproofs the connections without any concern of diurnal condensation build up. Inspections and alterations are very easily done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I am concerned about connector corrosion, such as on a rotor lightning protector block, I apply an anti corrosion  compound such as Deoxit. Because the connections are shielded from rain and snow, the compound will not be washed  out over time.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-08-14T10:25:04.160" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9059" PostTypeId="2" ParentId="5973" CreationDate="2017-08-14T23:12:12.160" Score="0" Body="&lt;p&gt;If that is the same as the Baofeng GT-3TP, the lowest power setting on that is 1.5 Watts, so officially not legal.&lt;/p&gt;&#xA;" OwnerUserId="10185" LastEditorUserId="8717" LastEditDate="2017-08-27T01:15:43.593" LastActivityDate="2017-08-27T01:15:43.593" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9063" PostTypeId="2" ParentId="8940" CreationDate="2017-08-15T22:59:07.807" Score="0" Body="&lt;p&gt;There's no real magic, it's just the signal to noise ratio. If you're certain that the noise floor hasn't changed then the signal propagation has, and vice-versa. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any number of upper atmosphere hypotheses can lead to a lower charge density which means a lower reflection coefficient resulting in a weak bounce and lousy HF propagation. As you've pointed out at sunspot minimum the density of charged particles passing the earth is lower and that means less charge separation and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think either halogenated hydrocarbons or rising CO2 levels or global warming make a viable whipping boy for this one. They don't have enough effect in the right layers AKAIK. If you want to blame one of those anyway then it looks to be a long wait for better conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think we can blame this on North Korea's rocket testing, IIRC the ionosphere hole from the launch vehicle motor's exhaust fill back up in around 15 minutes. Aw, heck, sure we can... just hypothesize something bizarre in their fuel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, that leaves volcanism, meteor showers, and Santa Claus to consider... moving right along...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that's not it then ... the noise floor. A few billion poorly sheilded digital noise sources and the noise pedestal from cell phone LO's and IFs can't be helping. The rising average utility transmission and distribution voltage coupled with diminishing insulator maintainance may be another source of broadband noise. Someone's bound to have some noise data somewhere...&lt;/p&gt;&#xA;" OwnerUserId="10191" LastActivityDate="2017-08-15T22:59:07.807" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9064" PostTypeId="2" ParentId="9051" CreationDate="2017-08-16T12:11:14.123" Score="3" Body="&lt;p&gt;The W8JI information is pretty good, there are a few points he doesn't touch on though.&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;EARTHING&amp;quot; or Grounding is a hot subject in many areas and there are many theories related to it.&lt;/p&gt;&#xA;&lt;p&gt;The NEC and NFPA recommend that ALL &amp;quot;Extra&amp;quot; grounds attach back to the electrical service ground ( I suggest you read up on this).&lt;/p&gt;&#xA;&lt;p&gt;Arizona presents its own problems to the grounding question. I suggest you contact your county surveyor, he may be able to tell you how deep the water table is in your area or put you in contact with the state or Federal &amp;quot;Hydrologist&amp;quot; who should be able to provide the information (get a rod down into the water table if possible).&lt;/p&gt;&#xA;&lt;p&gt;Any connections you make should be made with an Anti-oxidant Grease (such as &amp;quot;No-LOX&amp;quot;) especially if connecting dissimilar metals and use as large a wire as possible.&lt;/p&gt;&#xA;&lt;p&gt;If you live in a lightning-prone area, make provision for &amp;quot;QUICKLY&amp;quot; disconnecting your station equipment from the antennas and if you're going to be absent from the station for some time DISCONNECT !&lt;/p&gt;&#xA;&lt;p&gt;This subject can get pretty involved - Google can be your friend here.&lt;/p&gt;&#xA;" OwnerUserId="438" LastEditorUserId="8573" LastEditDate="2020-09-15T13:19:58.370" LastActivityDate="2020-09-15T13:19:58.370" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="9065" PostTypeId="2" ParentId="9051" CreationDate="2017-08-16T12:48:39.773" Score="1" Body="&lt;p&gt;Where I live in Michigan, the soil is always moist a few feet down. Also, the ground system must be below the frost line, which is 46&quot; here. Thus, pounding a long rod into the soil is a natural solution, and it's easy enough with nothing more than a 5 lb engineer's hammer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm hardly an expert in grounding in dry areas, but certainly your situation is much different. Eight feet may not be deep enough to get into moist soil. And frost is hardly a concern. And digging that deep is not easy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A water drip on the grounding rod may help, if you can maintain it. Ideally you want enough to maintain moist soil, but not so much that all the salts in the soil are washed away. Even wet, your soil may not have great conductivity, so you'll still need to do more if you require a very good ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An effective ground doesn't necessarily need to go deep: it can also go out. Several ground rods, about as far apart as they are deep, connected with 6 AWG solid wire or even better 0.022&quot; solid copper strap will lower the ground impedance by spreading over a larger area. I suspect in Arizona you'd need quite a lot of ground rods to get a good ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd bet most buildings in Arizona use an &lt;a href=&quot;https://en.wikipedia.org/wiki/Ufer_ground&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ufer ground&lt;/a&gt;, which basically just means grounding to the rebar in the foundation. Since the Ufer ground likely extends through the entire foundation, its possible there's a place the rebar has been exposed and you can connect to that. It's almost certainly exposed at your electrical service entrance, but if that's not also where the feedline enters the house you have a bit of a problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other solutions are variations on the Ufer ground, which involve digging a trench or a grid of many trenches about 30&quot; deep, then laying an electrode in them surrounded by some kind of ground enhancement material. Bentonite clay is cheap, though there are engineered solutions which work better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I couldn't tell you how big this ground system needs to be. Do you need to withstand multiple direct, large strikes? Or can you settle for a lesser degree of protection? One thing you can do is see what builders are doing, since the national electric code specifies a minimum performance for grounding, then use that as a baseline.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-08-16T12:48:39.773" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9066" PostTypeId="2" ParentId="9044" CreationDate="2017-08-16T15:22:03.567" Score="1" Body="&lt;p&gt;Although the difference is buried in the answers so far, it is worth pointing out that tuning and matching are two entirely different things. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To state the obvious, tuning is ensures that the antenna is resonant at the desired frequency, matching is to achieve the desired impedance which the transmitter and/or receiver sees.&lt;/p&gt;&#xA;" OwnerUserId="10193" LastActivityDate="2017-08-16T15:22:03.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9067" PostTypeId="1" AcceptedAnswerId="9069" CreationDate="2017-08-16T17:18:33.760" Score="6" ViewCount="3152" Body="&lt;p&gt;I have a 40' section of RG-8 that is about 35 years old.  One end was terminated with a standard PL-259 and the other was soldered directly to &lt;a href=&quot;https://ham.stackexchange.com/questions/7847/what-kind-of-2-meter-antenna-is-this&quot; title=&quot;an antenna&quot;&gt;an antenna&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I removed the connector from the one end, the cable itself appeared pristine.  The other end needed a few inches removed but also appeared pristine when the obviously weathered part was removed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any reason not to reuse this cable?  I'll be using it on a dual band, 2m/440 ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edited to add: This cable has been indoors for most of its life.&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2017-08-16T22:12:02.023" LastActivityDate="2017-08-22T23:10:55.570" Title="Will coaxial cable degrade over time?" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9068" PostTypeId="1" AcceptedAnswerId="9077" CreationDate="2017-08-16T20:59:21.273" Score="8" ViewCount="1454" Body="&lt;p&gt;Can I use TV coax and a cheap TV balun to build a poor-man's OCFD? Marginal performance is acceptable if it saves money. If I could listen to 10% of transmitters within a 100 mile radius that would be acceptable. And as for the coax length, probably no more than 20 feet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just getting started and not a lot of cash. Want to do lots of listening on both my RTL-SDR and Pixie 2 40M QRP kit. (Probably would build two antennas, one for each radio.) I already have a 75-300 ohm TV balun and lots of CATV coax. &lt;a href=&quot;http://www.packetradio.com/windom.htm&quot; rel=&quot;noreferrer&quot;&gt;Per this page&lt;/a&gt; when an OCFD is 20-25 feet above ground I should use a 4:1 balun, which matches the 75-300 ratio, if I am not mistaken. And 25 feet is about the max height I can get by slinging up in the trees around my house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am aware that &lt;a href=&quot;http://www.jpole-antenna.com/2015/01/28/using-rg-59-or-rg-6-catv-cable-with-an-amateur-radio-antenna/&quot; rel=&quot;noreferrer&quot;&gt;using 75 ohm line on a 50 ohm Pixie will result in at least a 1.5:1 SWR&lt;/a&gt;, if not higher. And the RTL-SDR already has a 75 ohm input, so there's that. But I'm not going for excellent performance, just want to be able to listen to some of the transmissions in my region. Would be cool to pick up overseas as well, but that may be wishful thinking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I may transmit, but that would not be a priority.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Oh and it wouldn't be strung up 24x7, just when I wanted to go listen then taken down the rest of the time. So I'm not concerned about lightning/rain/snow/wind.&lt;/p&gt;&#xA;" OwnerUserId="10194" LastEditorUserId="10194" LastEditDate="2017-08-16T22:07:11.557" LastActivityDate="2017-10-25T20:28:15.707" Title="Use a TV coax and balun for a poor-man's OCFD?" Tags="&lt;antenna-theory&gt;&lt;coaxial-cable&gt;&lt;antenna-system&gt;&lt;balun&gt;&lt;feed-line&gt;" AnswerCount="6" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9069" PostTypeId="2" ParentId="9067" CreationDate="2017-08-16T21:42:34.163" Score="3" Body="&lt;p&gt;Yes.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Left alone in a warehouse, undisturbed, it probably degrades in some fashion, though any time I have ever seen a find like that there is usually a feeding frenzy as people take it in part or in whole for use.  So I don't have any personal knowledge about that kind of degredation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your Q, you hit the nail on the head.  Often the coax will be fine and the connectors are of the most concern, usually due to water intrusion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But consider the effects of the elements to the coax, particularly sun exposure. Any coax exposed to the elements will definitely degrade over time due to heat cycling and perhaps mechanical wear. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically the outer cladding is likely to become brittle and thus be more likely to crack if you bend it.  Then water intrusion will cause eventual degradation of the shield.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To the point of your question, RG-8 is pretty rugged, and if it is still working after 35 years I can't think of any reason not to repurpose it.  I would definitely suggest cutting the ends and installing new connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Particularly with &lt;a href=&quot;https://ham.stackexchange.com/questions/7847/what-kind-of-2-meter-antenna-is-this&quot;&gt;THAT Antenna&lt;/a&gt;.  When I saw the first pictures of it, the end that was soldered to the antenna was definitely weathered.    My very first thought was that the antenna end needed to be reterminated.  And weather sealed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I didn't notice any problems with the cable away from that end.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-16T21:49:31.137" LastActivityDate="2017-08-16T21:49:31.137" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9070" PostTypeId="2" ParentId="9068" CreationDate="2017-08-16T22:52:13.000" Score="3" Body="&lt;p&gt;Just Do It! :-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should build it with those materials you have. What have you got to lose? I believe it will exceed your expectations. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-08-16T22:52:13.000" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="9072" PostTypeId="2" ParentId="72" CreationDate="2017-08-17T06:56:34.057" Score="-1" Body="&lt;p&gt;I am going to repeat the answer I just put on a similar question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/172/secure-communication-over-amateur-band-hsmm-802-11-in-the-united-states/9071#9071&quot;&gt;Secure communication over Amateur-band HSMM / 802.11 in the United States&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;QUOTE:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If you want to do this kind of stuff in the USA, hiding and such, please stay off our ham bands.  These bands are reserved for those of us who have been properly licensed and follow the rules.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;h2&gt;We don't need any headlines like &quot;HAM RADIO OPERATOR ARRESTED FOR PASSING SECRET MESSAGES&quot;&lt;/h2&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-17T20:28:33.940" LastActivityDate="2017-08-17T20:28:33.940" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9074" PostTypeId="1" AcceptedAnswerId="9086" CreationDate="2017-08-17T10:46:58.860" Score="3" ViewCount="2641" Body="&lt;p&gt;Currently I am evaluating options for my antenna's in regards to lightning protection. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My setup is a physical disconnect of all my antennas using an outside &quot;patch panel&quot;. So every time I power up my station, I have to go outside and physically connect the antenna feeds to a patch panel which brings the feed inside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Theoretically this is probably the best protection&lt;/strong&gt;, however &lt;strong&gt;it is getting a bit of a nuisance&lt;/strong&gt;. So I am looking at alternatives.&#xA;[emphasis added, due to comments]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the obvious choices would be a lightning protector, there are various models and types, and there is plenty of information available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However I have found an &lt;a href=&quot;https://paradanradio.com/products/antenna-disconnect&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna Disconnect&lt;/a&gt; product which seems to be a good fit as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The link provided is only an example, there are others. Or even &quot;home brew&quot; circuitry which can be found by searching using a search engine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question: what would be the theoretical disadvantages of such a disconnect system ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[edit 1]&#xA;I am not in a high-risk strike area, however we do have 2-3 lightning storms annually. Direct strikes have not occurred in a 10-km radius for the last 10-years (which is obviously not a guarantee that they can not occur)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[edit 2] &#xA;I am aware of electrical code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any comments welcome.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2017-08-17T13:10:28.657" LastActivityDate="2020-08-24T17:04:00.657" Title="Lightning protection by disconnect" Tags="&lt;grounding&gt;&lt;lightning&gt;" AnswerCount="4" CommentCount="7" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9075" PostTypeId="2" ParentId="9074" CreationDate="2017-08-17T11:47:01.193" Score="1" Body="&lt;p&gt;There is not much that is better than &quot;PHYSICAL SEPARATION&quot; of feed-line from the station.&#xA;What you're already doing is the best bang for the buck, ANY kind of a switch CAN &quot;ARC OVER&quot; with a very close or direct strike (I would trust &quot;POLYPHASER&quot; devices before I would trust the switch you linked to).&#xA;If you are in a lightning prone or &quot;HIGH STRIKE&quot; area, I would not change what you're doing now nor would I trust any kind of switch or PolyPhaser alone to protect your station (I can do a lot of walking for $100).&#xA;73&lt;/p&gt;&#xA;" OwnerUserId="438" LastEditorUserId="8573" LastEditDate="2019-04-11T14:46:55.820" LastActivityDate="2019-04-11T14:46:55.820" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="9076" PostTypeId="2" ParentId="9074" CreationDate="2017-08-17T11:59:12.317" Score="1" Body="&lt;p&gt;NEC Article 810 has all the answers you need. Here is a great overview from Mike Holt:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.mikeholt.com/download.php?file=PDF/Radio_and_Television_2014NEC.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.mikeholt.com/download.php?file=PDF/Radio_and_Television_2014NEC.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Article 810 covers outdoor TV, Satellite, and Amateur Radio antennas.&lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2017-08-17T11:59:12.317" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9077" PostTypeId="2" ParentId="9068" CreationDate="2017-08-17T13:34:13.287" Score="5" Body="&lt;p&gt;OK, let me try to answer this, but this answer may also be qualified as unqualified.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a 50 Ohm receiver, and connect a perfectly (Z=R) 75 ohm antenna system, then your VSWR would be 1.5, and the &quot;load mismatch attenuation&quot; will be about 0.177dB. (with antenna &lt;strong&gt;system&lt;/strong&gt; I include feedline)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I doubt that you would actually notice this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you are using an RTL-SDR dongle with a source impedance of 75 ohm, and your feedline is 75 ohm, you use a proper 4:1 balun for a 300 ohm antenna, then you should be good to go. Even when you change over to a 50-Ohm receiver the loss due to mismatch is negligible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The unknowns here is the suggested balun, and its behaviour when used with the OCFD. Unknown is also the quality and specifications of the &quot;TV coax&quot; you are planning of using.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you are starting, and as you are only listening (no TX), I would actually fully agree with the answer given by &lt;a href=&quot;https://ham.stackexchange.com/users/8717/mike-waters&quot;&gt;Mike Waters&lt;/a&gt; unqualified or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without knowing the very specifics of the TV-balun, and TV-coax, it would be hard for anyone to come up with a qualified or quantified answer for your particular question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I did started off in this hobby as a SWL. And I have used unspecified components and material to build a range of antenna's.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;rule 1: any antenna is better than no antenna &lt;/li&gt;&#xA;&lt;li&gt;rule 2: any feedline is better than no feedline &lt;/li&gt;&#xA;&lt;li&gt;rule 3: it is a hobby in which you can go mad... watch your wallet &lt;/li&gt;&#xA;&lt;li&gt;rule 4: it is fun to experiment&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For antennas I have used from rain gutters to water pipes, as feedline I have used from TV-coax to speaker-wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used a step-ladder as antenna... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have I used TV-baluns ? -- yes I have, with various succes, pulled it down, swap in/out, try again&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have I used &quot;some coax&quot; ? -- yes I have, with various succes, sometimes it was just deaf... which means: replace.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have I used a TV-balun with TV-coax and a OCFD ? -- no, I have no practical or qualified response to that...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an SWL, work with the materials you have, work with what can be got cheaply, experiment, direct feed your OCFD, use the TV-balun... the succes rate is determined on what you hear, not what is calculated upfront. Then if you want to squeeze every single micro-dB out of your antenna system, then you can look at different materials/components, and budget for such.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And even when you calculate all this upfront, the moment you hang it outside in a tree or near a building, over real ground, the calculations may be off. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You do mention &quot;may transmit&quot;, and just a word of caution here. If you really want to TX, then I would suggest to design/build an antenna for this with known components in order to avoid damage to your transmitter. This answer was written for RX not TX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have fun! It is a great hobby, and you will be surprised what you can receive with very little.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2017-08-17T14:26:05.270" LastActivityDate="2017-08-17T14:26:05.270" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9078" PostTypeId="2" ParentId="9068" CreationDate="2017-08-17T14:13:11.633" Score="1" Body="&lt;p&gt;A direct answer to your question: Absolutely!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is nothing wrong with hobbling together an antenna out of the materials you have on hand. And, I think you will find that your proposed approach performs well for SWL with an RTL-SDR. &lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2017-08-17T14:13:11.633" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9079" PostTypeId="2" ParentId="7733" CreationDate="2017-08-17T20:41:25.400" Score="5" Body="&lt;p&gt;Xastir isn't bad at all but I recently encountered something called YAAC (Yet Another APRS Client). On it's &lt;a href=&quot;http://www.ka2ddo.org/ka2ddo/YAAC.html&quot; rel=&quot;noreferrer&quot;&gt;site&lt;/a&gt; it states the following:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;YAAC can be used as a stand-alone APRS client, an APRS RF-Internet&#xA;  gateway (I-Gate), or as a AX.25 digipeater. It supports 16 different&#xA;  data reporting views as delivered, and can be extended with&#xA;  user-written &quot;plugins&quot; to add more functionality.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm sure there's already plugins available and with the AX.25 &quot;digipeater&quot; you should be able to also send packets. Keeping in mind it should automate much of what Scott Earle pointed out earlier: &quot;crafting AX.25 packets&quot; would really be a pain. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you'd like to download it for OS X, it's available on &lt;a href=&quot;https://sourceforge.net/projects/yetanotheraprsc/&quot; rel=&quot;noreferrer&quot;&gt;Source Forge&lt;/a&gt; and the original website has source code available if you'd like to manually compile the software. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that &quot;MacAPRS&quot; has been discontinued although that too was an AX.25 iGate packet manager. Hope I've helped!&lt;/p&gt;&#xA;" OwnerUserId="10202" LastActivityDate="2017-08-17T20:41:25.400" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9083" PostTypeId="2" ParentId="7468" CreationDate="2017-08-17T21:31:45.487" Score="1" Body="&lt;p&gt;You're incredibly unlikely to damage a robust boombox receiver by upgrading the antenna. Yes it will be &quot;out of spec&quot; for the Boombox and with enough gain you'll over power the circuit in the boombox but you're very unlikely to damage the circuit. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cheapest way to boost that signal? take an alligator clip with a lot of wire and clip that baby to the end of the boombox antenna. If you're trying to tune into FM radio (85Mhz - 99.5Mhz) you're looking at about 10 total feet of antenna length for the best signal. Many antenna's are 1/4 Wavelength or similar fraction (1/6th, 1/8th etc) because it makes the product cheaper while keep adequate performance. You can improve by increasing the length and if you aren't satisfied you can also add a passive LNA (Low Noise Amplifier) which will generally form a regenerative circuit and increase the gain while automatically limiting noise. If you're hearing too much static you can also implement a filter to narrow what your Boombox is receiving. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that your boombox likely already has a proprietary LNA and filter, best to look for a schematic online of your device to develop a better plan. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're feeling ambitious or bored you're welcome to learn and experience some circuit prototyping. This &lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/95hb1768.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;link&lt;/a&gt; provides schematics for a regenerative radio circuit and as my friend once told me: &quot;it's a VERY worthwhile project&quot;. Thanks, hope I've helped!&lt;/p&gt;&#xA;" OwnerUserId="10202" LastEditorUserId="10202" LastEditDate="2017-08-18T04:26:56.287" LastActivityDate="2017-08-18T04:26:56.287" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9084" PostTypeId="5" CreationDate="2017-08-17T23:20:16.420" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-08-17T23:20:16.420" LastActivityDate="2017-08-17T23:20:16.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9085" PostTypeId="4" CreationDate="2017-08-17T23:20:16.420" Score="0" Body="Transverters, upconverters, and downconverters." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-08-17T23:20:16.420" LastActivityDate="2017-08-17T23:20:16.420" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9086" PostTypeId="2" ParentId="9074" CreationDate="2017-08-18T01:15:10.020" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;what would be the theoretical disadvantages of such a disconnect system?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Firstly, keep in mind that antennas don't cause lightning damage: grounds do. It's not clear from your description if your patch panel is grounded at the same point as your electrical service or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's not, you have two separate grounds. This doesn't comply with the NEC, and it increases the risk of lightning damage since lowest impedance path from one ground (electrical service entry) to the other (patch panel) involves going through your equipment. See &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt; and an excellent &lt;a href=&quot;https://www.w8ji.com/lightning_strikes.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;example from W8JI&lt;/a&gt; where a strike on a tree 20 feet away arced back out of the ground to travel down a beverage antenna which was grounded on the far end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming you have a good single point ground, the purpose of the disconnect, surge protector, or any other device you might put at that point is not to handle the surge current, but rather to keep all the conductors at about the same voltage. Lightning is common-mode, so fortunately most of that energy will be flowing on the shield, leaving whatever protection device you choose with a relatively small amount of energy to deal with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just any method of disconnecting may not be effective: the voltages involved may still be high enough to arc across gaps. They are certainly high enough to blow past any solid state devices. &lt;a href=&quot;https://www.w8ji.com/ground_systems.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI recommends a double-make double-break relay&lt;/a&gt;, with the reasoning being that any arcs will most likely go to ground. He does not use coaxial surge protectors, and has never had a radio damaged.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Commercial installations operate continuously and don't disconnect the antennas. Most use a DC block surge protector like the Polyphaser IS-50 series. I don't have any relay control system so I use this approach. My first one I bought new, but I recently decided &lt;a href=&quot;https://ham.stackexchange.com/q/9042/218&quot;&gt;used units are probably fine too&lt;/a&gt;. Used they go for about $25 USD, which is about as much as I'd expect to pay for a disconnect device or the parts to build one. I like that there's no chance of forgetting to disconnect something.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both these systems work, which I think shows that it's not the protectors or the disconnects, but rather the ground system that makes it work.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-08-18T12:47:23.313" LastActivityDate="2017-08-18T12:47:23.313" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9087" PostTypeId="2" ParentId="9067" CreationDate="2017-08-18T13:27:10.240" Score="1" Body="&lt;p&gt;With old coax the things you're most likely to see are UV degradation of the insulation and water ingress.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Visually inspect the insulation, looking for cracks when bent. If this cable was not exposed to the sun, it's probably fine in this regard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Water ingress will show as corrosion on the conductors, an increase in loss, or a change in characteristic impedance. The ends are most susceptible, so remove them if the shield appears corroded. For the outdoor end you might consider removing a couple feet more to be safe. There may also be nicks or fine cracks in the insulation that allowed water to enter which you may not be able to see.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Put a dummy load on the far end of the cable, and check with an antenna analyzer. The SWR should be flat over the entire range of the analyzer. If you don't have an analyzer, a directional coupler in conjunction with a signal generator or low power transmitter works also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To check for loss, you can make a simple RF detector to measure the peak voltage:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/QV7ja.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fQV7ja.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use a Schottky diode for best sensitivity, though an ordinary silicon diode like 1N4148 may work well enough. Keep the leads between the resistors, diode, and capacitor as short as possible. The voltmeter can have long leads since it's measuring DC. Ordinary 1/4W resistors are fine as long as testing is limited to low-ish powers (&amp;lt;10W) and brief (a couple seconds) periods.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I build it into a BNC connector. This one worked fine at 440 MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LhI1K.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LhI1K.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Measure the power directly from your antenna analyzer / signal generator / low power transmitter. Then put it on the end of the coax, and measure that. Power is proportional to the square of voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{loss (dB)} = 20 \log_{10} \left(V_\text{in} \over V_\text{out}\right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the cable passes visual inspection, SWR test, and loss test, it's fine to be reused. And you'll also know the loss, so you can decide if it's worth getting some better coax.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-08-18T13:45:23.953" LastActivityDate="2017-08-18T13:45:23.953" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9090" PostTypeId="2" ParentId="7664" CreationDate="2017-08-19T00:05:35.630" Score="1" Body="&lt;p&gt;If you are close to the down spout or rain gutter why don't you try loading that up but you will almost certainly need an tuner in the transmission line.  You would just feed like a single wire feet line.  Other things you may need to do is  use an UNUN at the transmitter antenna in put and the ground may need to be tuned with a series resonant circuit sometimes called an &quot;Artificial Ground&quot;. I lived in an apartment before I got married some 40+ years ago and worked an awful lot of stations and today you have all kinds of sound card digital modes are available to you making the task much easier and more reliable.  Hope this helps you in some small way.  &lt;/p&gt;&#xA;" OwnerUserId="8685" LastActivityDate="2017-08-19T00:05:35.630" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9091" PostTypeId="2" ParentId="514" CreationDate="2017-08-19T06:57:47.553" Score="0" Body="&lt;p&gt;Here's a DIY option:  I used 3 LiPo 14500 batteries and a charge controller / battery protection module to replace the NiCds in my IC2AT's original battery pack.  It's a tight fit.  The PCB holding the LED and charger jack is intact.  I now have more voltage (higher transmit power) and more capacity.  Note: perform a capacity test on your batteries when they arrive and claim a refund from seller if they don't meet the claim.  A claim exceeding 800 mAh on a 14500 is unlikely to be true.  &lt;/p&gt;&#xA;" OwnerUserId="10207" LastActivityDate="2017-08-19T06:57:47.553" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9092" PostTypeId="1" AcceptedAnswerId="9093" CreationDate="2017-08-19T23:10:46.350" Score="5" ViewCount="4842" Body="&lt;p&gt;Amateurs on the radio and online tell us we &lt;strong&gt;MUST&lt;/strong&gt; ID at the start of our transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A couple of hams on 75m sometimes take me to task for not saying my callsign right away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;'The FCC says so'.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is that true or not?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="218" LastEditDate="2017-08-20T11:51:48.013" LastActivityDate="2017-08-30T06:37:10.160" Title="How often are we required to send our callsign?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;callsign&gt;&lt;station-identification&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9093" PostTypeId="2" ParentId="9092" CreationDate="2017-08-19T23:10:46.350" Score="5" Body="&lt;h2&gt;That hasn't been the law for many years.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=ba1686bc816dd0e6aff4c393b63395aa&amp;amp;mc=true&amp;amp;node=se47.5.97_1119&amp;amp;rgn=div8&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.119&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(a) Each amateur station, except a space station or telecommand station,&#xA;  must transmit its assigned call sign on its transmitting channel at&#xA;  the end of each communication, and at least every 10 minutes during a&#xA;  communication ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Therefore, it is perfectly legal to wait until we have talked for ten minutes before we ID.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Of course, nothing says that we can't ID at the start of our transmission.)&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="76" LastEditDate="2017-08-30T01:44:30.907" LastActivityDate="2017-08-30T01:44:30.907" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9094" PostTypeId="1" CreationDate="2017-08-20T00:11:45.417" Score="1" ViewCount="671" Body="&lt;p&gt;I’m currently attempting to set up my first 440 MHz machine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From all the research I’ve done I need two radios, a controller and a duplexer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was going to go with a DR-1x. Is this correct? Would I need any other type of RF filters or will a duplexer work?&lt;/p&gt;&#xA;" OwnerUserId="10205" LastEditorUserId="4076" LastEditDate="2017-08-20T11:15:34.517" LastActivityDate="2017-08-20T11:15:34.517" Title="440 MHz repeater, how would I set one up?" Tags="&lt;repeater&gt;&lt;70cm-band&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9095" PostTypeId="2" ParentId="9094" CreationDate="2017-08-20T10:45:29.573" Score="2" Body="&lt;h1&gt;So, what &lt;em&gt;is&lt;/em&gt; a repeater?&lt;/h1&gt;&#xA;&lt;p&gt;A repeater receives the signals (messages) sent from someone, and sends them again. That increases the reach of the original sender.&lt;/p&gt;&#xA;&lt;h1&gt;So, why a duplexer?&lt;/h1&gt;&#xA;&lt;p&gt;Strictly speaking, you don't &lt;em&gt;need&lt;/em&gt; a duplexer for repeating signals, but it's damn near impossible to work without one.&lt;/p&gt;&#xA;&lt;p&gt;First of all, if your repeater's receiver part listens on the same frequencies that its transmitter is working on, you'll get into a lot of trouble – because they typically share an antenna (or closely adjacent antennas), the transmit power could easily fry a receiver. Even if it doesn't, you'd have to tell your own transmitted signals from the ones you want to receive apart. That's technically very expensive (you'd need a &lt;em&gt;huge&lt;/em&gt; dynamic range or a &lt;em&gt;circulator&lt;/em&gt;. I won't go into either.).&lt;/p&gt;&#xA;&lt;p&gt;Also, the original sender might already be reaching stations with their own signal – and those stations would suddenly see the original transmission and your repeater's copy of that. That's a very strange multipath channel, in other words, highly undesirable.&lt;/p&gt;&#xA;&lt;p&gt;So, you make sure that you take the signal, and transmit it on another frequency, not to interfere with&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the original transmission and&lt;/li&gt;&#xA;&lt;li&gt;your own receiver.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;So, to keep your receiver protected from your very high power PA output, you add a diplexer, which really is just two filters, which separate the &amp;quot;incoming&amp;quot; from the &amp;quot;outgoing&amp;quot; channel.&lt;/p&gt;&#xA;&lt;p&gt;The suppression of that diplexer filter usually is sufficient, so you don't need more filters. If you do: add them, SAW filters for the 70 cm band aren't expensive and can be bought in SMD shape.&lt;/p&gt;&#xA;&lt;h1&gt;What equipment / design procedure&lt;/h1&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;strong&gt;Antenna:&lt;/strong&gt; now, 70cm isn't really huge. If you have a roof or something of the like, it's thoroughly possible you can get multiple antennas running; even having things like a directive RX (e.g. a Yagi-Uda or a biquad) antenna and an omnidirectional or only slightly directive TX might be an option. This depends on your motivation to have that repeater! Cheapest, and simplest, will be to have a single antenna that does both RX and TX. We'll focus on that.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Diplexer:&lt;/strong&gt; to split the RX from the TX, which are already separate in frequency domain, into different signal paths. This is the only hardware in your repeater that you have to buy/build exactly for the frequencies you'll need to work with! &lt;br&gt; Decide upon which frequencies you want to listen, and on which your repeater will transmit. Ideally, you want all the receiving frequencies to be in a continuous frequency range, and the transmitting ones in a separate one.&lt;br&gt; I &lt;em&gt;think&lt;/em&gt; it's convention in the 70cm to have the matching frequency-transposed outgoing channel 5 MHz from the receive channel, but I'd be very happy if someone could verify/comment on that. &lt;br&gt; The frequencies around 440 MHz are relatively benign: They are low enough that you don't have to be afraid that even well-designed circuits simply act like capacitors and let through the signal, and they are high enough that frequency-selective components are small and cheap.&lt;br&gt;The &amp;quot;gold standard&amp;quot; for such frequencies are SAW filters (surface acoustic wave, basically, you excite a piezo crystal to mechanically oscillate, and by its geometrical properties, only certain wavelengths can travel). They are very steep, have low insertion losses, can be made very accurately and don't suffer very much from temperature/air moisture/moon phase &amp;amp; black cats-induced drifting. Also, they are produced in the billions for commercial devices, so they are cheap as hay. &lt;br&gt;I've taken the liberty too look up a few potential filters on &lt;a href=&quot;http://eu.mouser.com/Passive-Components/Signal-Conditioning/_/N-8bzuiZ1yzvvqx?P=1yx68baZ1z0vlpaZ1z0rw4nZ1yzrqsyZ1yzuwxp&amp;amp;Rl=8bzuiZer79Z1z0wn5oZ1z0wn56SGT&amp;amp;Ns=Pricing%7C0&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mouser&lt;/a&gt;.&lt;br&gt;You'll need one for the signal going into your transmit amplifier, and one for the signal going into your receiver, on different frequencies. The transmitter's one isn't as important - it's just to stop crosstalk from your receiver getting into your transmit amplifier.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Splitter/Coupler&lt;/strong&gt;: The antenna needs to be connected to &lt;em&gt;both&lt;/em&gt; the output of your TX amplifier, and the input of the filter that goes into your receiver. A &lt;em&gt;circulator&lt;/em&gt; would be perfect, but meh, they don't sell these for prices that I'd be willing to pay :) so, something like a 3dB splitter must do.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Transmitter&lt;/strong&gt;: TBD. Really, needs to output the power you want. The signal going into the transmitter comes from the receiver, and that's where the interesting action happens.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Receiver&lt;/strong&gt;: There's two ways of forwarding messages. These are &lt;strong&gt;amplify and forward&lt;/strong&gt; (where your receive signal just gets... amplified and given to a mixer that puts it onto the transmit frequency; in that case, your transmitter+receiver is just the RX filter, an LNA, a 5 MHz oscillator, a mixer, the TX filter, and a power amplifier) and &lt;strong&gt;decode and forward&lt;/strong&gt;.&lt;br&gt;The second means that your receiver takes the signal it gets and &lt;em&gt;interprets&lt;/em&gt; (or tries to) it as a message. That improves SNR. For example, if you're expecting FM voice transmissions, it would frequency demodulate it, squelch away noise, clean up the resulting audio, and then re-modulate it as FM. With digital modes, this becomes even easier to motivate: Assume your repeater &amp;quot;sees&amp;quot; a packet that, due to noise at the receiver, has a single bit error. Now, it decodes that package, and that includes forward error correction, so that the packet has 0 bit errors after FEC, and re-modulates and transmits it again.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Personally, I'm a software defined radio guy. Which means there's no question for me – the perfect repeater would observe all the incoming channels at once by digitizing the incoming RF at a sufficient rate, detects active transmitters, automatically classifies the transmissions (e.g. APRS, FM voice, SSB AM voice, D-Star, low-bandwidth DVB-T), applies the correct decoder for the individual transmission, regenerates the original signal digitally, and combines the regenerated transmissions digitally, before giving it to the digital-to-analog converter. In this scenario, the receiving hardware needs a good filter, LNA, a relatively boring SDR receiver (and an RTL dongle might do, for a start), and a PC running appropriately designed software. The transmitter is that software + TX SDR hardware, e.g. the HackRF (add a good filter between HackRF and the PA, the HackRF's spectral cleanliness is... insufficient for repeater usage), or a USRP (which can receive while it transmits, so you could use it simultaneously as receive SDR and transmit SDR), or or or.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-08-20T10:45:29.573" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9096" PostTypeId="1" CreationDate="2017-08-20T15:35:36.297" Score="11" ViewCount="1343" Body="&lt;p&gt;FM modulated radio is much more resistant to noise and can deliver better sound quality than AM radio. But FM signals also use more bandwidth than AM signals. In general a wider bandwidth signal is more resistant to noise / can send more data than a narrower bandwidth signal. The bandwidth of an FM signal can in fact be chosen, and one can create wideband or narrowband FM signals, with the wideband ones giving better sound quality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is FM's better noise resistance only a function of its larger bandwidth, or is this noise resistance also an inherent property of FM? In other words, does a narrowband FM signal that uses the same bandwidth as an AM signal still produce better sound quality?&lt;/p&gt;&#xA;" OwnerUserId="10210" LastActivityDate="2017-08-20T16:45:45.413" Title="Is FM modulation still more resistant to noise when given the same bandwidth as an AM signal?" Tags="&lt;modes&gt;&lt;fm&gt;&lt;noise&gt;&lt;am&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9097" PostTypeId="2" ParentId="9096" CreationDate="2017-08-20T16:36:20.840" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;FM modulated radio is much more resistant to noise and can deliver better sound quality than AM radio. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Under certain conditions, that is! Namely, additive noise, and a fading channel.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;or is this noise resistance also an inherent property of FM?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Huh, that surprisingly can be a pretty philosophical question about what bandwidth actually is, but let's break it down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's first assume our noise is white. That means, we have a constant noise power spectral density. That's very handy arithmetically, because that means that the noise power is simply proportional to the observed bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With AM, this simply means that audio SNR == RF SNR, if you use a filter that is as wide as the audio you want to hear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With FM, ok, we first need to figure out what you mean with &quot;the same bandwidth&quot;. Because that's pretty hard – the bandwidth occupied by an FM signal is actually hard to define, as its spectrum has a specific Bessel shape. Don't get me started.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Luckily, we have the Carson Bandwidth Rule, which gives us the amount of bandwidth needed to transport an FM signal to include at least 98% of energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That rule is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$CBW = 2(\Delta f + f_m) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With $f_m$ being the highest audio frequency we need to transport, and $\Delta f$ being the frequency deviation, ie. the largest deviation from the nominal center frequency that the carrier will be moved to. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, yes, the difference between AM and FM is that FM can actually make use of the higher bandwidth it uses to transport information. AM is damned to transport all info within the audio bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, that means that purely from a bandwidth in, bandwidth out perspective, you can never build an FM system that is more efficient than an AM system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then: let's look at the information side of things.  What you want to do when communicating is getting info from A to B. Noise might be in the way, but really, what we care about is how much of the info from A reaches B.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, let's say we pick an FM modulation that has a bandwidth $b$, and we define $\alpha$ as the ratio between the occupied bandwidth and the audio bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$b=2(\Delta f + f_m)=\alpha f_m$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;so, compared to the same audio signal transmitted using AM, we need to first reduce the bandwidth by a factor of $\frac 1{\alpha}$. Which means that only $\frac 1{\alpha}$ of the original info² reaches the FM receiver, &lt;em&gt;at all&lt;/em&gt;¹.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantage of FM really is that it only is sensitive to apparent changes in frequency, not in amplitude. That brings us to the channel model:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most channels exhibit fading of some sorts. That not only changes the amplitude of your receive signal over time (slowly, typically), but also over frequency. Which means that with AM, you might have bad luck, and just the let's say frequency 400 Hz of the carrier frequency is dampened very much, and you can't understand what the other end is saying.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With FM, certainly, you'll &quot;hit&quot; that frequency, too, but only for a short duration, and also, it doesn't really matter – as long as the noise power on other frequencies isn't higher, that does not impede the audio quality!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, there's your inherent advantage of FM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Technically, this is especially nice and easy to motivate: you're using an PLL to receive, that is, you don't look for phase changes that are faster than your audio signal's change rate (and that is, basically, the audio bandwidth) allows them to be. So, whilst your noise is certainly present on the whole CBW, what matters happens only within $2f_m$ around the current carrier position. Thus, FM makes use of the autocorrelation of the signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Takeaway:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;FM is &lt;em&gt;always&lt;/em&gt; broader than AM for the same audio bandwidth&lt;/li&gt;&#xA;&lt;li&gt;FM isn't sensitive to noise in its whole bandwidth, but only to a specific part of it&lt;/li&gt;&#xA;&lt;li&gt;The channel is nicer to FM than it is to AM&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹: This presumes that the information is spread evenly through the audio bandwidth. It's not, but taking that into consideration quickly brings us to speech modelling, and discretized speech, and voice codecs. And why analog is a dead-end, and why we know that since the 80s. But that's simply out of scope.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;²: I realize this is really hand-waving. We need to define &lt;em&gt;information&lt;/em&gt; in the context of a continuous signal — that would lead us to differential entropy and whatnot. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, we can take a shortcut, by knowing the sampling theorem (which actually is more of a result of that consideration than something that leads to it, but nevertheless): Any analog signal of finite bandwidth $f_m$ can be digitized with a sampling rate of $2f_m$. Conversely, an analog signal of bandwidth $f_m$ can carry as much info as twice that bandwidth in digital numbers, given a fixed SNR (which defines how many bits can be in each digital number). Corollary, the discrete info transportable is proportional to the bandwidth, and that directly translates to an analog info content, with finite-resolution observers. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-08-20T16:45:45.413" LastActivityDate="2017-08-20T16:45:45.413" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9098" PostTypeId="1" AcceptedAnswerId="9099" CreationDate="2017-08-20T19:03:47.540" Score="4" ViewCount="632" Body="&lt;p&gt;Why are there no frequency modulated broadcasts on the long/medium/short wave, but only on VHF? I'm sure there are many historical and political reasons (long/medium/short wave were already in use for AM when FM radio was developed, VHF still had lots of free bandwidth), but are there also technical reasons?&lt;/p&gt;&#xA;&lt;p&gt;FM radio gives a better sound quality than AM. Common FM on VHF also uses a much broader bandwidth and interchannel spacing than MW AM, so using the same bandwidth per channel much fewer FM channels would fit in the MW band than AM channels. But narrowband FM &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_deviation&quot; rel=&quot;nofollow noreferrer&quot;&gt;can be used with similar interchannel spacing as is typical for AM&lt;/a&gt;, so this is no reason not to use frequency modulation.&lt;/p&gt;&#xA;&lt;p&gt;So are there any technical reasons why narrowband FM broadcasting is not used on long/medium/short wave, and if so what are they? I'm assuming that even narrowband FM would give better audio quality than AM, am I wrong about that?&lt;/p&gt;&#xA;&lt;p&gt;(disclaimer: maybe there have been some FM transmissions on MW that I'm not aware of, in that case please read this question as &amp;quot;why are there &lt;em&gt;nearly&lt;/em&gt; no FM broadcasts on the L/M/SW ...&amp;quot;)&lt;/p&gt;&#xA;&lt;p&gt;(I'm asking out of historical interest. I'm not planning on setting up any FM on MW or something)&lt;/p&gt;&#xA;" OwnerUserId="10210" LastEditorUserId="15589" LastEditDate="2020-09-25T15:15:50.317" LastActivityDate="2020-09-25T15:15:50.317" Title="What are the technical reasons that there are no FM transmissions on the long, medium, or shortwave?" Tags="&lt;hf&gt;&lt;modes&gt;&lt;fm&gt;&lt;mf&gt;&lt;lf&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="9099" PostTypeId="2" ParentId="9098" CreationDate="2017-08-20T19:23:03.793" Score="7" Body="&lt;p&gt;So, the bandwidth argument is the dominant one. You need to incorporate the full Carson Bandwidth in your channel spacing, not only the frequency deviation! As explained in my answer to &lt;a href=&quot;https://ham.stackexchange.com/questions/9096/is-fm-modulation-still-more-resistant-to-noise-when-given-the-same-bandwidth-as&quot;&gt;your previous question&lt;/a&gt;, that &lt;em&gt;must&lt;/em&gt; be significantly larger than the bandwidth of the same audio signal in AM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aside from that, as always in Ham usage: historical reasons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you'd ask me, no sense in doing FM, either. There's digital voice modes that have a far superior &lt;em&gt;spectral efficiency&lt;/em&gt; (that's a measure for how much  info you can get across per second per bandwidth).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd recommend looking at DRM (Digital Radio Mondiale), a broadly adapted narrowband broadcast mode than can give you very clear voice over noisy 3 kHz channels. That's what India and Brazil are doing to replace their AM MW broadcast stations. Not &quot;small scale bleeding edge&quot;. This is literally &quot;state of the art for billions of people&quot; tech; using FM to make more of the MW spectrum is half a step back, not a step forward.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you need really narrow band communications (and that's what you'd want if you're working MW with a lot of people), then the digital voice modes of &lt;a href=&quot;http://freedv.org/tiki-index.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV&lt;/a&gt; are what I'd look into. 1.25 kHz channels with good voice communication, in any situation superior to AM, and not comparable to FM at all, because FM wouldn't even remotely allow voice communication at 1.25 kHz CBW. You don't need fancy hardware to use it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, FM was never an option on low frequencies simply due to bandwidth constraints, and digital modes are the logical step from AM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can only recommend to head over to the &lt;a href=&quot;http://www.rowetel.com/?page_id=452&quot; rel=&quot;nofollow noreferrer&quot;&gt;Codec2&lt;/a&gt; site, and listen in – Codec2 is the audio codec used within FreeDV. Listen to the 1300 bps sample and ask yourself whether a 1.25 kHz AM channel would have offered a comparable quality (and before the &quot;digital modes don't degrade gracefully&quot; people show up: at SNRs where this works, you won't be hearing &lt;em&gt;anything&lt;/em&gt; but static over AM. Also, FreeDV by default uses FEC, so yeah, it degrades graceful – by not degrading at all at first, and after that, the codec is still pretty robust against bit errors and &lt;em&gt;does&lt;/em&gt; indeed degrade rather graceful, compared to AM, especially in the presence of burst interferers). &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="1362" LastEditDate="2017-09-09T00:38:00.420" LastActivityDate="2017-09-09T00:38:00.420" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9100" PostTypeId="1" CreationDate="2017-08-20T19:32:15.187" Score="1" ViewCount="552" Body="&lt;p&gt;&lt;strong&gt;Setup&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We just finished an addition on our house, and I have (on the diagonal) ~65 feet of space to work with. The pitch of the roof raises ~5-6 feet from the gutters to the apex of the roof. Roof access is relatively easy, feed line is already run and I have plenty to reach most anywhere I need to go (except the extreme edges and corners, which with a Windom is irrelevant).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What I had&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before the addition, I had a 40-6m Windom up and mounted via ad-hoc &quot;satellite dish mounts&quot;, made of PVC, around 2 feet long, and drilled into the fascia of the house. &lt;em&gt;On average&lt;/em&gt;, the wire was ~6 inches off the shingles. I was &amp;lt; 2.0 VSWR on all bands the Windom covered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What I'm looking to accomplish&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to get back at least what I had, if not improve the performance. My biggest issue is the additional raise I'm going to have to deal with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Question(s)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Has anyone mounted a Windom (or similar wire antenna) on their house in a similar manner to what I'm describing above.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If &quot;Yes&quot; to #1, what did you use to &quot;defeat&quot; the pitch of the roof to get the entire Windom off the shingles?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If &quot;No&quot;, any suggestion for what to use to accomplish this? Is longer PVC (perhaps thicker) sufficient?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;(General Windom question) Is the wire of the Windom (if attached in a taut manner, using rope attached to insulators at the end of the wires sufficient to support the balun with feed line attached? Or should I consider a &quot;balun mounting&quot; solution and drill into my nice, new roof to help support it. I'm hoping the former will work.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="1556" LastActivityDate="2018-05-19T16:26:27.303" Title="Suggestions for above-roof mounting Windom" Tags="&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9101" PostTypeId="5" CreationDate="2017-08-20T20:35:18.807" Score="0" Body="&lt;p&gt;Use this tag whenever the subject includes Modulation and Demodulation of digital signals.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This may include AFSK like in RTTY, or more exotic methods like AX.25 packet radio.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-25T07:54:38.763" LastActivityDate="2017-08-25T07:54:38.763" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9102" PostTypeId="4" CreationDate="2017-08-20T20:35:18.807" Score="0" Body="Use this tag whenever the subject includes Modulation and Demodulation of in-channel digital signals.  " OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-25T07:54:52.323" LastActivityDate="2017-08-25T07:54:52.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9103" PostTypeId="2" ParentId="2074" CreationDate="2017-08-21T05:05:34.047" Score="1" Body="&lt;p&gt;To interface the radio to a computer you will have to&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Purchase a microphone for the radio and disassemble it, &#xA;noting which wire do what: Mic/PTT/Speaker&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Next you'll need&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Two female stereo jacks&#xA;Two 600 ohm audio transformers&#xA;Two male to male stereo cords&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Finally: Wire the microphone cord the transformers and the transformers to the jacks, plug the cables into your computer sound card. Enable VOX on the radio and have fun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FYI: I am a HAM, 20 years.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I purchased a GT3-TP, Baofeng UV-5 by a different name, with charging stand, DC cord, programming cable, and hand microphone, for 35 dollars. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Didn't expect much but when it arrived I assembled it, programmed in the local repeater and walked outside then hit the PTT: 94 miles, that is where my local repeater is and it works fine! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My 420 dollar Yaesu handheld sometimes works, this 35 dollars always works with good reports.     &lt;/p&gt;&#xA;" OwnerUserId="10215" LastEditorUserId="8832" LastEditDate="2017-08-22T00:12:35.027" LastActivityDate="2017-08-22T00:12:35.027" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9104" PostTypeId="2" ParentId="1279" CreationDate="2017-08-21T07:50:39.837" Score="3" Body="&lt;p&gt;There exist &lt;a href=&quot;https://en.wikipedia.org/wiki/Tunable_laser&quot; rel=&quot;nofollow noreferrer&quot;&gt;tunable lasers&lt;/a&gt;, where the output frequency can be modulated. And there exists such a thing as an &lt;a href=&quot;https://en.wikipedia.org/wiki/Acousto-optic_modulator&quot; rel=&quot;nofollow noreferrer&quot;&gt;acousto-optic modulator&lt;/a&gt; though I'm not sure if those are used to actually modulate the frequency of light.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or a more D.I.Y. method could be: shine a narrow beam of continuous spectrum light (e.g. incandescent light) through a prism. Then capture a small part of the diffracted beam, e.g. by having it shine into an optical fiber, or using a small slit. When you rotate the prism a few degrees, the frequency of the captured light varies accordingly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And accordingly to demodulate the signal: have an array of photoelectric cells and a prism in front of it. Which cell is hit by the light depends on the wavelength. Though you will then need more electronics to combine the outputs of all the cells into a single signal.&lt;/p&gt;&#xA;" OwnerUserId="10210" LastActivityDate="2017-08-21T07:50:39.837" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9105" PostTypeId="2" ParentId="5742" CreationDate="2017-08-21T22:53:53.443" Score="0" Body="&lt;p&gt;According to this:&lt;br&gt;&#xA;&lt;a href=&quot;https://sites.google.com/site/g0ftdradio/tecsun-pl660&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://sites.google.com/site/g0ftdradio/tecsun-pl660&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/l5QZw.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/l5QZw.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's about 35 Ohm.&lt;/p&gt;&#xA;" OwnerUserId="10219" LastEditorUserId="8832" LastEditDate="2017-08-22T00:14:35.433" LastActivityDate="2017-08-22T00:14:35.433" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9106" PostTypeId="2" ParentId="2285" CreationDate="2017-08-22T02:04:14.707" Score="2" Body="&lt;p&gt;145.010 was the &quot;primary&quot; packet frequency in the 90's&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lee  N4TCW&lt;/p&gt;&#xA;" OwnerUserId="10220" LastActivityDate="2017-08-22T02:04:14.707" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9107" PostTypeId="2" ParentId="9100" CreationDate="2017-08-22T20:09:56.797" Score="0" Body="&lt;p&gt;The antenna column in &lt;em&gt;The Spectrum Monitor&lt;/em&gt; magazine recently described a loop antenna on a roof shaped very similar to yours. The author just laid the loop directly on the asphalt shingles and fed it with window line. He says it performs very well. Of course this is very subjective and I realize a loop is not the same antenna as your Windom but this experience might serve as one data point that suggests you can avoid the hassle of raising the wire at all.&lt;/p&gt;&#xA;" OwnerUserId="1157" LastEditorUserId="1157" LastEditDate="2017-08-22T20:19:45.153" LastActivityDate="2017-08-22T20:19:45.153" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9108" PostTypeId="1" AcceptedAnswerId="9109" CreationDate="2017-08-22T22:13:26.777" Score="3" ViewCount="511" Body="&lt;p&gt;I own an Ed Fong TBJ-1 antenna, which is like a twin-lead J-Pole with a coax stub and some inductors added. It's enclosed in an unfinished PVC pipe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm tempted to paint the PVC with non-conductive UV inhibitors, but don't know if that will de-tune the antenna. What effect does something like Krylon paint / UV resistant clear coat have on a tuned antenna that's enclosed by PVC pipe?&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2021-01-01T16:23:29.330" Title="Effect of paint / uv coating on velocity factor of PVC" Tags="&lt;antenna-construction&gt;&lt;diy&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9109" PostTypeId="2" ParentId="9108" CreationDate="2017-08-22T22:53:39.963" Score="6" Body="&lt;p&gt;No. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if the electromagnetic material properties of the paint were drastically different than that of air, the few microns of coating won't be even measurable. (Unless that coating really is conductive paint)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another thing: You've bought an antenna. Building exact antennas is hard. If you worry about the effect of 30 µm of paint coat, then you'd also have to worry about the effect of temperature, shrinking and expanding the PVC pipe. Or the fact that no one cuts conductors for antennas with a 30 µm accuracy. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why are you worrying? It's not like your antenna was exact to a high degree anyway. In fact, measurement antennas whose directivity is known to less than a percent are &lt;em&gt;expensive&lt;/em&gt;. Price of a small car for antenna expensive. With a dipole variant antenna like yours, you'd be happy if the actual center frequency (ie. the point of highest matching to the nominal impedance) everything is let's say with +- 10% of what you expect. It won't work worse if a slight wind blows, but that would flex the PVC much more than a coating would add.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-08-23T08:04:09.963" LastActivityDate="2017-08-23T08:04:09.963" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9110" PostTypeId="2" ParentId="9067" CreationDate="2017-08-22T23:10:55.570" Score="1" Body="&lt;p&gt;Cables come in different classes. I do not remember the details, but there is for example RG8/U, RG8A/U, RG8B/U, RG223 and probably more. All those are pretty equivalent, but some have a short life time because the cheap PVC outside the screen will migrate into the polyethylene dielectric and cause&#xA;(severely) increased losses.&#xA;Read here:&#xA;&lt;a href=&quot;http://www.smeter.net/daily-facts/4/fact29.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.smeter.net/daily-facts/4/fact29.php&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A cable with a polyethylene jacket is safe for ageing, but less so&#xA;for fire. I think you can find specifications for the lifetime of different cable types if you look carefully at manufacturer data.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-08-22T23:10:55.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9111" PostTypeId="2" ParentId="9068" CreationDate="2017-08-22T23:25:42.647" Score="4" Body="&lt;p&gt;TV coax typically has foam dielectric and very low loss. On receive it&#xA;does not matter if you use 50, 60 72 or 75 ohm cable. With short cables,&#xA;losses are also not important. The cheap TV balun could be problematic, particularly if you want to transmit. It is trivial to make a 1:2 transformer to get the 4:1 impedance transformation you need, but it is hard to get bandwidth larger than 10:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest you go ahead without worrying so much about what is theoretically optimum. Start activity - then find what are the annoying limitations of your set-up. Once you know, (if you find any) you can put more interesting questions to the forum:-)&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-08-22T23:25:42.647" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9112" PostTypeId="2" ParentId="9068" CreationDate="2017-08-23T20:28:38.460" Score="1" Body="&lt;p&gt;I agree with the previous answers for your SDR receiver.&#xA;But for the Pixie, I would do this (and you said that you wanted a separate antenna for the Pixie)&lt;br&gt;&#xA;1. Simple end-fed wire 66 feet long for the Pixie antenna. This is a half wavelength at 7 MHz.  Attach the wire to the antenna terminal of the Pixie.  String it as high as possible.&lt;br&gt;&#xA;2. counterpoise of 33 feet. Attach to the ground of the Pixie.  this can lay on the floor or ground. &#xA;&lt;br&gt;&#xA;With a similar setup, I &quot;worked&quot; (contacted) a station 40 miles away - antenna and Pixie.  They really work.  Have fun!&lt;br&gt;&#xA;W3TTT&lt;/p&gt;&#xA;" OwnerUserId="8647" LastActivityDate="2017-08-23T20:28:38.460" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9113" PostTypeId="2" ParentId="9098" CreationDate="2017-08-24T05:12:50.140" Score="0" Body="&lt;p&gt;Technically from a technological point of view any  mode of transmission could be used on any frequency assuming that signal propagation is stable enough to insure reliable communication and bandwidth used was not an issue. Signal propagation on HF,MW and Lw is dependent on time of day with regard to atmospheric absorption and signal path whether skywave or groundwave .&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Skywave means propagating upwards and being reflected down towards the Earth one or more times whereas groundwave propagation is line of sight. AM and SSB are less affected by skywave propagation but FM would be unreadable. If strictly using groundwave propagation then all modes would work. On shortwave  FM is used on the 10 meter band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM is used on the VHF and UHF bands (the other modes are used as well) because propagation is pretty much line of sight which makes for a very stable signal which is required for FM to be readable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the reasons why AM is noisier than FM is that impulse noise is generally amplitude modulated ( although some noise is also frequency modulated as well) and FM receivers are designed to detect frequency variations and reject or limit amplitude variations.   &lt;/p&gt;&#xA;" OwnerUserId="6604" LastActivityDate="2017-08-24T05:12:50.140" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9114" PostTypeId="1" AcceptedAnswerId="9115" CreationDate="2017-08-24T15:00:47.607" Score="1" ViewCount="571" Body="&lt;p&gt;I've held an Advanced Class license for almost 20 years now. I've recently been kicking around the idea of biting the bullet and upgrading to Extra. I know they lifted the code requirement. Part of me wants to stay Advanced because I have the pride and knowledge that, even though I've never made a CW contact ever, I studied hard and passed my code requirement to earn my license. There is a small nagging part of me that feels like I would be cheating not passing the 20wpm test to move up to Extra. Other than the nominal additional bandwidth, is there any real advantage to upgrading my license?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73's&#xA;Jim&lt;/p&gt;&#xA;" OwnerUserId="10234" LastEditorUserId="873" LastEditDate="2017-08-25T02:10:19.003" LastActivityDate="2017-08-25T02:10:19.003" Title="Should I upgrade to Extra Class" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="1" CommentCount="6" FavoriteCount="0" ClosedDate="2017-08-24T16:55:29.967" ContentLicense="CC BY-SA 3.0" />
  <row Id="9115" PostTypeId="2" ParentId="9114" CreationDate="2017-08-24T15:42:13.347" Score="1" Body="&lt;p&gt;I recently went through exactly the same thing.  I take a lot of pride in having that 13wpm code reflected in my license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think there is a real answer to your question because it is subjective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I decided to upgrade to Extra a few months ago.  There is also a lot of pride in reaching the pinnacle, going as far as you can.  And since your license records reflect your &quot;Prev. Op. Class&quot;, having &quot;Advanced&quot; there will always show anyone who looks that you have the 13wpm accomplishment.&lt;/p&gt;&#xA;" OwnerUserId="4748" LastActivityDate="2017-08-24T15:42:13.347" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9118" PostTypeId="1" CreationDate="2017-08-25T22:28:55.387" Score="1" ViewCount="473" Body="&lt;p&gt;I was recently given a Motorola XTS 5000 (Model 1) P25 radio to play around with.  It has several local repeaters already programmed into it.  It is set for &quot;Mixed Mode&quot;, which will receive either a P25 digital signal or analog.  All the local repeaters are also set for Mixed Mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that I can receive digital or analog, via a repeater that will pass digital or analog, from a transmitting station that can transmit digital or analog, and vice versa, what is the benefit to P25?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does P25 give me that my normal analog HT won't besides the ability to transmit digitally?  Why would I want to?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edited to add:&#xA;I understand that the P25 standard offers a substantial feature set that is very powerful.  My question is more geared to the scenario where several hams are hanging out on the local repeater rag chewing.  In that case, is there any benefit to using P25 over analog?  In my limited experience, the voice quality seemed slightly inferior so I don't think there is anything to be gained there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there something else that I am missing?&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2017-08-27T00:45:45.297" LastActivityDate="2017-08-27T00:45:45.297" Title="P25 Digital vs. Analog" Tags="&lt;digital-voice&gt;&lt;p25&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9119" PostTypeId="1" AcceptedAnswerId="9120" CreationDate="2017-08-26T02:17:11.243" Score="3" ViewCount="119" Body="&lt;p&gt;As far as I can tell, currently a 20m dipole has to be within a few inches to have a reasonable SWR without a tuner. How does this change with one? Does it depend on what tuner I have?&lt;/p&gt;&#xA;" OwnerUserId="9218" LastActivityDate="2017-08-26T11:36:36.910" Title="How much leeway does an antenna tuner give me?" Tags="&lt;hf&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9120" PostTypeId="2" ParentId="9119" CreationDate="2017-08-26T09:45:59.373" Score="1" Body="&lt;p&gt;Generally, the accuracy you need is directly proportional to the wave length. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, for 20m band (==20m wavelength), let's say 3% percent of that wavelength would be in the region of &quot;less than half a meter error, and you're fine&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But: which accuracy you'll need depends on which mismatch you can tolerate. &quot;A few inches&quot; however sounds wrong – you're not using this antenna for a single fixed frequency, where there would be a theoretical &quot;optimum&quot; length, but for the whole band, so there's a range of frequencies you'll want to work with, and for all but a single one of these, your antenna will inherently be non-optimal, but it doesn't matter, because the slight mismatch (the slightly increased SWR) doesn't really hurt you all that much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet another warning: SWR isn't really number you're aiming for. It &lt;strong&gt;is&lt;/strong&gt; a useful measure for testing how well something is matched, but in the end, if I attach a 50Ω terminator to my receiver, I get a (damn near) perfect SWR. And receive exactly (damn near) nothing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your antenna has a resistive (non-radiating) component, too, and by matching to that, you improve your SNR, but you decrease your radiation efficiency. Luckily, that component should be small for metal conductors at these frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you need, in the end, is an antenna system, and that incorporates doability, the mechanical aspects of temperature and wind tolerance, the feedline, eventually baluns and stuff, and you need that antenna system to work relatively well for all that you want to do. Good SWR is just one of the aspects of that; appropriate position to actually pick up EM energy, durability and cost of the build as well as boring aspects such as it being somewhat hard to actually cut down 10m of cable to a high degree of length accuracy and spanning it in a straight-as-possible line do play a larger role, in many installations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, to your actual question:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How does this change with one (an antenna tuner)? Does it depend on what tuner I have?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's look at RX only, TX is analogous, just the other way around: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what an antenna tuner is, is really a matching circuit between the impedance of your antenna at the frequency you want to operate at, and the receiver you're using (typically, 50Ω). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the impedance is (at least for a dipole) always depending on the frequency, you adjust the tuner to convert exactly the impedance of your antenna at the frequency you want to 50Ω. That makes energy at that frequency come through without losses from antenna to receiver. Other frequencies are mismatched, so they inherently experience reflection at the tuner, and don't end up in your receiver. That's a filtering effect you get for free!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice that for resonant antennas, this usually means that if you consider your antenna to be an inductivity, you adjust a capacitor until the antenna-tuner LC circuit is in resonance at exactly the frequency of interest. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the amount of frequency &quot;variability&quot; a tuner gives you actually depends on the amount of reactive/capacitive loading it can provide &lt;em&gt;compared to the antenna&lt;/em&gt;; also note that typically, antennas work reasonably well for frequencies that are exact integer multiples (with the integers that work depending on the antenna type) of their fundamental frequency (but they do have a different directive pattern there). &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-08-26T11:36:36.910" LastActivityDate="2017-08-26T11:36:36.910" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9121" PostTypeId="1" CreationDate="2017-08-26T17:28:55.573" Score="2" ViewCount="1426" Body="&lt;p&gt;I'm working on learning Morse code, and I'm looking for a way to use my computer as a practice oscillator with a double paddle key.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm using a Linux PC, but a Raspberry Pi solution would be cool to. I do have a USB Serial adapter.&lt;/p&gt;&#xA;" OwnerUserId="1285" LastEditorUserId="76" LastEditDate="2017-08-31T17:05:36.157" LastActivityDate="2019-07-18T10:19:06.550" Title="How to use a Linux computer as a paddle key code practice oscillator" Tags="&lt;cw&gt;&lt;software&gt;&lt;linux&gt;&lt;paddles&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9122" PostTypeId="2" ParentId="9118" CreationDate="2017-08-26T22:28:44.670" Score="1" Body="&lt;p&gt;I would like to give comparison between your color tv and smart tv when try to relates analog /digital legacy radio communications and introduction of  P25 standards. Like any  smart TV P25 gives lots of advantage over legacy system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Among all other benefits of P25 standards adoption specifically on public safety communication, interoperability and efficiency of spectrum usability stand on top and visible to any party. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;P25 is adaptation of standardization of radio communications among various types of users for their communication needs. Before P25 era every other organizations have their own way of planing and implementation of  radio communications practice which is troublesome for quick interoperability needs. Also other features like user control, authorization, encryption makes robust communication experience both for admission and general user. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can get a real picture by visiting this wiki pages on P25 &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Project_25&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.m.wikipedia.org/wiki/Project_25&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="9704" LastEditorUserId="9704" LastEditDate="2017-08-26T22:37:41.183" LastActivityDate="2017-08-26T22:37:41.183" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9124" PostTypeId="5" CreationDate="2017-08-27T01:56:43.123" Score="0" Body="&lt;p&gt;Use this tag whenever the topic includes Morse code paddles.  This can include interfacing them to a keyer or a computer or explanations of how to use them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This also can be used when the subject is VibroPlex-style mechanical semi-automatic keyers operation and hookups.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-28T15:17:42.360" LastActivityDate="2017-08-28T15:17:42.360" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9125" PostTypeId="4" CreationDate="2017-08-27T01:56:43.123" Score="0" Body="Use this tag whenever the topic includes Morse code paddles.  This can include interfacing them to a keyer or a computer or explanations of how to use them." OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-28T15:18:10.783" LastActivityDate="2017-08-28T15:18:10.783" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9127" PostTypeId="2" ParentId="9121" CreationDate="2017-08-28T19:33:01.547" Score="1" Body="&lt;p&gt;Here is a solution that has been tested and works on Ubuntu 14.04 LTS.&lt;/p&gt;&#xA;&lt;p&gt;The software used is called &lt;a href=&quot;http://qsonet.com/setup_ddd.exe&quot; rel=&quot;nofollow noreferrer&quot;&gt;Didadah&lt;/a&gt;.  &lt;a href=&quot;http://qsonet.com/dahdidah.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;[PDF info]&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The paddles connect via a &lt;a href=&quot;http://www.ebay.com/itm/Sabrent-USB-to-RS-232-DB9-Serial-9-pin-Adapter-Prolific-PL2303-SBT-USC1M-/252367546441&quot; rel=&quot;nofollow noreferrer&quot;&gt;standard FTDI-based USB-A Male to DB9-Male Adapter cable&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7IKUR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7IKUR.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/abP23.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/abP23.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;(Note that this shows how the Paddles are wired to a DB9-F which plugs into the DB9-M on the Serial-to-USB Adapter cable)&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;For reference, the traditional pin assignments for DB-9 serial is shown &lt;a href=&quot;http://www.db9-pinout.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;h2&gt;This article explains the setup procedure:&lt;/h2&gt;&#xA;&lt;h2&gt;&lt;a href=&quot;http://qrqcwnet.ning.com/profiles/blogs/hook-up-your-cw-paddles-key-and-bug-to-your-linux-computer-ubuntu&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hook up your cw paddles, key and bug to your Linux computer (Ubuntu 14.04)&lt;/a&gt;&lt;/h2&gt;&#xA;&lt;p&gt;&lt;strong&gt;Excerpt:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;This video demonstrates a method to hook up your cw paddles, key and bug to your Linux computer.&lt;/p&gt;&#xA;&lt;p&gt;Dahdidah is the application chosen to perform the software cw keyer functions.&lt;/p&gt;&#xA;&lt;p&gt;A USB TO SERIAL PORT ADAPTER is used to interface the morse code instruments directly to the serial port pins to &amp;quot;key&amp;quot; Dahdidah.&lt;/p&gt;&#xA;&lt;p&gt;Jack Audio is the Linux sound engine used, with KXSTUDIO's CARLA and CADENCE.&lt;/p&gt;&#xA;&lt;p&gt;Dahdidah uses the serial port to &amp;quot;key&amp;quot; its CODE PRACTICE OSCILLATOR sound system.&lt;/p&gt;&#xA;&lt;p&gt;Dahdidah will use the WINEASIO - ASIO DRIVER - for the best audio production with near zero latency.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;hr /&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;HERE IS A LIST OF THE BASIC STEPS.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;http://qsonet.com/setup_ddd.exe&quot; rel=&quot;nofollow noreferrer&quot;&gt;DOWNLOAD Dahdidah&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;DOWNLOAD the DEB FILE to get the KXSTUDIO REPOS&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;DOWNLOAD KXstudio's CADENCE&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;DOWNLOAD KXstudio's CARLA-GIT et al,&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;DOWNLOAD KXstudio's META-WINE package&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;DOWNLOAD KXsutdio's WINEASIO&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;important: REGISTER WINEASIO&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;get your USB TO SERIAL PORT adapter working and ready to go on boot up&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;link your new ttyUSB0 SERIAL PORT ADAPTER to WINE&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;DAHDIDAH PDF MANUAL:  &lt;a href=&quot;http://qsonet.com/doc/dahdidah.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://qsonet.com/doc/dahdidah.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;AUDIO DERIVED CW KEYING CIRCUIT to key your rig&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-08-30T00:43:50.670" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9129" PostTypeId="5" CreationDate="2017-08-29T03:23:44.600" Score="0" Body="&lt;p&gt;Use this tag when the topic is about the P25 set of standards that allow a channel to be shared between both voice and data separately or together, via simplex or repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This tag should also be used when the topic includes the P25NX standards for worldwide network exchange.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-31T05:35:52.840" LastActivityDate="2017-08-31T05:35:52.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9130" PostTypeId="4" CreationDate="2017-08-29T03:23:44.600" Score="0" Body="Use this tag when the topic is about the P25 set of standards that allow a channel to be shared between both voice and data separately or together, via simplex or repeater." OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-08-31T05:34:38.880" LastActivityDate="2017-08-31T05:34:38.880" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9131" PostTypeId="1" CreationDate="2017-08-29T04:43:55.163" Score="1" ViewCount="319" Body="&lt;p&gt;Please identify the type and name of this antenna? It's a iPhone 6s cellular antenna. What material it's made of? Any reason for it's '&lt;em&gt;painted black&lt;/em&gt;'? &lt;a href=&quot;https://i.stack.imgur.com/5swsT.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5swsT.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10267" LastActivityDate="2017-09-05T15:15:54.980" Title="Type and name of this smartphone cellular antenna" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9132" PostTypeId="1" AcceptedAnswerId="9134" CreationDate="2017-08-29T07:56:36.110" Score="3" ViewCount="2364" Body="&lt;p&gt;I'm trying to build a small magnetic loop for 5W on at least 40m - 20m following ideas of &lt;a href=&quot;http://www.g4ilo.com/wonder-loop.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;G4ILO's wonder loop&lt;/a&gt;. For this, I'm using coax with a ~2mm copper core and ~1mm spacing to the braid (see 1st image below), with braid and core connected on the ends. I use 50cm of this cable for the coupling loop and 2.90m for the outer loop (which is not based on any calculation but on the length I had available). I use a 350pF variable capacitor with ~540° rotation. The antenna is placed ~12m above the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I first placed both loops as circles (see 2nd image below), pretty much as the image on G4ILO's page. I could peak the noise level on 40m and dip it but not with a satisfying SWR at all. I couldn't peak the noise level on 20m and didn't try to dip it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With some experimenting, I found out that RX improved significantly when the loops touched each other as much as possible, so I experimented with an egg-shape coupling loop inside a circular outer loop. This gave somewhat better results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I then kept the coupling loop somewhat circular and made the outer loop pear-shape so that it fits around the coupling loop (see 3rd picture). This allows me to peak noise level on 40m and dip it with near-1:1 SWR. The dip is rather sharp and I need to retune every ~10kHz. I can hear a fair number of stations but don't get any results on the reverse beacon network / webSDRs when I CQ myself. Normally, I get several spots on the RBN (with a 20m dipole, up ~5m).&lt;br&gt;&#xA;On 20m, I cannot peak noise level but I can dip to 1:1 SWR (perhaps there is so much noise on that band that the radio's AGC levels it, making it impossible to peak noise level?). The dip is much wider, I don't need to retune on 14.000 - 14.060 at all. However, also on this band no results from the RBN yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is twofold:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;I know that a 1:1 SWR does not have to be ideal (a dummy load also has 1:1 SWR). Is there a fundamental problem with my latest construction that allows me to get a 1:1 SWR but little radiation?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What can I try to improve the current construction?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/exHXp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/exHXp.jpg&quot; alt=&quot;coax used&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/cGSYU.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cGSYU.jpg&quot; alt=&quot;construction with circular loops&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/dmP1G.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dmP1G.jpg&quot; alt=&quot;construction with pear-shape outer loop&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/BchrA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BchrA.jpg&quot; alt=&quot;capacitor&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorDisplayName="user885" LastEditDate="2017-09-03T21:50:09.650" LastActivityDate="2020-12-13T02:06:04.147" Title="Optimising a small magnetic loop with 1:1 SWR but little radiation" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;magnetic-loop&gt;&lt;small-loop&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9133" PostTypeId="1" AcceptedAnswerId="9135" CreationDate="2017-08-29T13:35:45.837" Score="10" ViewCount="858" Body="&lt;p&gt;It's somewhat common to find a schematic that calls for a germanium diode in amateur radio contexts. For example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PxPLM.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PxPLM.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a QSK circuit from the &lt;a href=&quot;http://www.w1hkj.com/FldigiHelp-3.21/html/cw_keying_page.html&quot; rel=&quot;noreferrer&quot;&gt;Fldigi manual&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And yet, purchasing a germanium diode is a relatively difficult task. For example, Mouser's offerings from 600 manufacturers doesn't seem to include a germanium diode:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SjmvM.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SjmvM.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Although, they do have a few &lt;a href=&quot;http://www.mouser.com/All-Manufacturers/Semiconductors/Discrete-Semiconductors/_/N-awhngZ0?Keyword=germanium&quot; rel=&quot;noreferrer&quot;&gt;germanium BJTs&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Germanium diodes can be found elsewhere, mostly from surplus or specialty stores, for a cost orders of magnitude higher than most other discrete semiconductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is it so common for amateur designs which do not appear to have any particularly stringent performance requirements to call for a relatively expensive diode not available through commodity channels?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-09-11T20:02:02.407" Title="Why are germanium diodes specified in amateur radio designs?" Tags="&lt;electronics&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9134" PostTypeId="2" ParentId="9132" CreationDate="2017-08-29T14:03:39.127" Score="3" Body="&lt;p&gt;Getting this antenna to perform, as with any electrically small antenna, is a question of minimizing losses. Without being able to test your particular design it's difficult to say exactly what the losses may be, but here are some possible culprits:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Dielectric and conductive losses due to coupling into the wall and things inside it. Try moving it away from the wall a bit.&lt;/li&gt;&#xA;&lt;li&gt;Resistive losses in contacts. The sliding contacts in the variable capacitor are often not great. Other connections through binding posts, etc are ideally silver or gold plated, and be sure they are clean and snug.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It also appears for the coupling loop you are using the center conductor of a piece of coax, whereas G4ILO uses a plain insulated wire. It should still be possible to make it work, though if your objective is to replicate a working design you should probably start by replicating it exactly before experimenting with modifications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Losses can be further reduced by using large tubing, wide solid strap, soldered connections throughout, vacuum variable capacitors, etc. However, that would detract from the qualities of being small, cheap, easy to build, and portable. Any such antenna is necessarily going to compromise efficiency, but that doesn't mean it can't be efficient enough.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-08-30T14:34:50.080" LastActivityDate="2017-08-30T14:34:50.080" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9135" PostTypeId="2" ParentId="9133" CreationDate="2017-08-29T14:09:35.203" Score="6" Body="&lt;p&gt;The lower forward voltage drop (0.3 volts or even less), compared to silicon diodes (0.7 volts or more). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, there are some schottky diodes with a low forward voltage drop, too.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-08-29T14:09:35.203" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9136" PostTypeId="2" ParentId="9121" CreationDate="2017-08-29T15:20:16.970" Score="1" Body="&lt;p&gt;&lt;a href=&quot;http://qrqcwnet.ning.com/profiles/blogs/using-the-linux-lv2-plugin-trigger-midi-mono-as-a-morse-code-prac&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;This page&lt;/strong&gt;&lt;/a&gt; appears to be what you're looking for. This technique uses the Linux LV2 plugin. You'll have to build an interface with a 555 timer chip.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;SETUP: an UltraPico Keyer, keys a 555 TIMER CHIP..from the audio output of the 555, an audio cable is attached and goes to the input of a laptop's mic jack input...the 555 time chip sidetone is very rough sounding with lots of high pitched harmonics and key clicks...INSTEAD of trying to filter the 555's raspy tone, this video demo's using TRIGGER MIDI MONO to recreate the original 555 sidetone cw element and then a LINUX LV2 PLUGIN called TRIGGER MIDI MONO keys another CPO, a software code practice oscillator synthesizer called SIMPLE SINE GENERATOR(lv2 plugin)...this SIMPLE SINE GENERATOR has zero rise or fall time and therefore has loud key clicks...so those need to be filtered out....by another LINUX LV2 PLUGIN called CALF FILTER...calf filter does a great job of taking out all the harmonics and key clicks and produces a nicely shaped cw element audio waveform output&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;a href=&quot;http://calf-studio-gear.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://calf-studio-gear.org/&lt;/a&gt;&#xA;  &lt;a href=&quot;https://web.archive.org/web/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://web.archive.org/web/&lt;/a&gt;&lt;em&gt;/&lt;a href=&quot;http://nedko.arnaudov.name/soft/ssg/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://nedko.arnaudov.name/soft/ssg/&lt;/a&gt;&lt;/em&gt;&#xA;  &lt;a href=&quot;http://lsp-plug.in/?page=manuals&amp;amp;section=trigger_midi_mono&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://lsp-plug.in/?page=manuals&amp;amp;section=trigger_midi_mono&lt;/a&gt;&#xA;  &lt;a href=&quot;http://kxstudio.linuxaudio.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://kxstudio.linuxaudio.org/&lt;/a&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Previously, this CW REGENERATION technique was accomplished using WINDOWS VST PLUGINS, or a non free app called LINUX NATIVE REAPER. After discovering this TRIGGER MIDI MONO plugin for LINUX, this CW REGENERATION technique can now be utilized with ALL FREE LINUX APPS ...&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;NOTE: familiarity with KXstudio, and his LINUX JACK AUDIO APPS for Linux is necessary in order to understand fully, the method that is being demo'd...there are more videos in this QRQcw youtube channel to learn more about JACK AUDIO for LINUX/windows/mac and the Raspberry Pi....&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;NOTE: MIDI DATA MESSAGES, of NOTE ON and NOTE OFF are used to instruct (key) the software code practice sine wave oscillator APP called SIMPLE SINE GENERATOR. (there are other LINUX audio plugins that would also work like AMsynth) -&lt;a href=&quot;https://github.com/amsynth/amsynth&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/amsynth/amsynth&lt;/a&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;MIDI DATA MESSAGES - WHAT IS MIDI ?&#xA;  &lt;a href=&quot;http://www.instructables.com/id/What-is-MIDI/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.instructables.com/id/What-is-MIDI/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;h2&gt;&lt;a href=&quot;https://youtu.be/pgHibGT2l7M&quot; rel=&quot;nofollow noreferrer&quot;&gt;The YouTube video is here&lt;/a&gt;.&lt;/h2&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-08-29T23:42:13.847" LastActivityDate="2017-08-29T23:42:13.847" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9137" PostTypeId="5" CreationDate="2017-08-29T15:22:48.737" Score="0" Body="&lt;p&gt;Use this tag when the topic includes Digital Signal Processing.  This can be either RF signals or audio signals, or perhaps post-processing like decoding of protocols.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;/questions/tagged/software-defined-radio&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;software-defined-radio&amp;#39;&quot; rel=&quot;tag&quot;&gt;software-defined-radio&lt;/a&gt; is a perfect example of DSP-based radio.  Similarly, recording of signals for later processing (like manipulating satellite imagery to assign false colors and the like) could be considered to fall under this category.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="76" LastEditDate="2019-01-24T01:30:17.600" LastActivityDate="2019-01-24T01:30:17.600" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="9138" PostTypeId="4" CreationDate="2017-08-29T15:22:48.737" Score="0" Body="Questions about digital signal processing, whether of RF, audio, or digital signals. For RF, consider [software-defined-radio]." OwnerUserId="8832" LastEditorUserId="76" LastEditDate="2019-01-24T01:30:17.600" LastActivityDate="2019-01-24T01:30:17.600" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="9139" PostTypeId="1" AcceptedAnswerId="9162" CreationDate="2017-08-29T16:03:46.610" Score="0" ViewCount="211" Body="&lt;p&gt;Some friends and I recently placed a Kenwood TH-D72 on the summit of Saddle Mountain in Oregon, USA, and set it up as a temporary digipeater for use with APRS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4renK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4renK.jpg&quot; alt=&quot;Digipeater on Mountain&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TH-D72 successfully digipeated packets, but when our hiker summited the mountain again the next day, he found that TH-D72 was stuck on the startup splash screen and was unresponsive to any button presses (other than powering off).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven’t been able to find any reports of a TH-D72 freezing on the startup splash screen. Does anyone have experience with this? What is a likely cause of this behavior? We haven't seen the TH-D72 freeze on the splash screen before or since.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The sequence of events is roughly as follows:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;2017-08-25 15:10:33   -   Hiker sets up TH-D72 and manually sends first APRS beacon.&#xA;2017-08-25 16:30:00   -   Hiker descends mountain and leaves TH-72 on summit.&#xA;2017-08-25 19:15:44   -   First vehicle comes in range and TH-D72 digipeats an APRS position packet.&#xA;2017-08-26 05:09:17   -   Final digipeated APRS packet (all vehicles may have gone out of range at this point).&#xA;2017-08-26 06:54:40   -   Final automatic APRS beacon sent from TH-D72 (it seems to have sent beacons up to 00:30:00 apart).&#xA;2017-08-26 07:45:40   -   Hiker summits mountain again and finds TH-D72 stuck on the startup splash screen.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The radio was powered by YUASA NP7-12 12V,7.0h battery and 12V to 7.5V switching regulator. The battery manufacturer recommends keeping the battery between –15°C and +50°C for charging and discharging. The temperature on the summit was likely between 4°C and 32°C. The enclosure was vented with a fan.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two days after the hiker retrieved the enclosure with the radio and battery, we started up the TH-D72 and it successfully sent several APRS beacons. It did not freeze up. The voltage droop during packet transmission was minimal:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/pKXXa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pKXXa.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5820" LastEditorUserId="76" LastEditDate="2017-08-29T16:46:09.030" LastActivityDate="2017-09-02T09:46:21.453" Title="Kenwood TH-D72 Freeze on Splash Screen" Tags="&lt;aprs&gt;&lt;kenwood&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9140" PostTypeId="2" ParentId="9133" CreationDate="2017-08-29T20:46:15.693" Score="8" Body="&lt;p&gt;A lot of designs that include germanium diodes are older, or based on older designs, when germanium diodes were commonly available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the page for Germanium, &lt;a href=&quot;https://en.wikipedia.org/wiki/Germanium#History&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia&lt;/a&gt; says, &quot;From 1950 through the early 1970s, this area provided an increasing market for germanium, but then high-purity silicon began replacing germanium in transistors, diodes, and rectifiers&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When germanium diodes started getting replaced with silicon diodes, there was lot of old stock that could be had relatively cheaply. Hams took advantage of that in their designs.&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2017-08-29T20:46:15.693" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9141" PostTypeId="2" ParentId="9092" CreationDate="2017-08-30T06:37:10.160" Score="2" Body="&lt;p&gt;The rules are very clear on this point.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Sec. 97.119 Station identification&lt;/p&gt;&#xA;&lt;p&gt;(a) Each amateur station, except a space station or telecommand station, must transmit its assigned call sign on its transmitting channel at the end of each communication, and at least every 10 minutes during a communication, for the purpose of clearly making the source of the transmissions from the station known to those receiving the transmissions. No station may transmit unidentified communications or signals, or transmit as the station call sign, any call sign not authorized to the station.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This wording was reviewed as a formal petition in 2006-7.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.fcc.gov/document/changes-part-97-regard-amateur-radio-service-rules-97119a&quot; rel=&quot;nofollow noreferrer&quot;&gt;Changes in Part 97 With Regard to Amateur Radio Service Rules, 97.119(a) Station Identification and Proposed Changes in 47 CFR Part 97 Section 97.119, Amendment of Part 97 of the Commission's Rules, et al&lt;/a&gt;&lt;/p&gt;&#xA;&lt;h2&gt;HERE IS THE TEXT OF THE LATEST RULEMAKING ACTION ON THIS SUBJECT, POSTED JULY 9, 2007:&lt;/h2&gt;&#xA;&lt;p&gt;DISCUSSION&lt;/p&gt;&#xA;&lt;p&gt;Station identification interval&lt;/p&gt;&#xA;&lt;p&gt;Background.&lt;/p&gt;&#xA;&lt;p&gt;Section 97.119(a) of the Commission’s Rules provides that an amateur station “must transmit its assigned call sign on its transmitting channel at the end of each communication, and at least every 10 minutes during a communication, for the purpose of clearly making the source of the transmissions from the station known to those receiving the transmissions.”&lt;/p&gt;&#xA;&lt;p&gt;We have received two proposals to amend this provision.  On December 9, 2005, Murray Green filed a petition for rulemaking, RM-11346, requesting that the Commission amend Section 97.119(a) to reduce the required frequency of station identification to every thirty minutes during a communication, rather than once every ten minutes.  On May 19, 2006, Glen E. Zook filed a petition for rulemaking, RM-11347, requesting that the Commission amend Section 97.119(a) to require that the call sign be transmitted at the beginning and end of each single transmission, and at the beginning and end of a series of transmissions between stations having established communications when each transmission is less than three minutes in duration.&lt;/p&gt;&#xA;&lt;p&gt;Green argues that the station identification requirement should be relaxed because the current requirement “appears, perhaps out of an abundance of caution, to have resulted in more frequent or over-identification by Amateur Radio operators,” and requiring identification less frequently &amp;quot;would harmonize the Amateur Radio Service station identification requirement with that of other radio services and should not hinder the Commission’s enforcement of Amateur Radio regulations.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;Zook, on the other hand, argues that the station identification requirement should be tightened because “too many amateur radio operators . . . do not identify during their first transmission.  In fact, a considerable number of these operators never seem to get around to identifying even after 10 minutes of operation and a ‘fair’ number never seem to get around to giving their call sign at all.”&lt;/p&gt;&#xA;&lt;p&gt;Each petition received approximately one hundred comments. The commenters generally oppose both petitions.&lt;/p&gt;&#xA;&lt;p&gt;Decision.&lt;/p&gt;&#xA;&lt;p&gt;Based on our review of the record, we are not persuaded that the requested rule changes are necessary or supported by the amateur radio community.  The purpose of the station identification rule is &amp;quot;to clearly make the identity of the station transmitting known to those receiving the transmission.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;To achieve this purpose, the rule requires that an amateur station transmit its call sign at the end of each communication and at least every ten minutes during a communication that lasts longer than ten minutes.  The overwhelming majority of commenters believe that the current rule properly balances the burden of requiring the station to transmit its call sign with the convenience of those receiving the transmissions to determine the identity of the station making the transmissions.&lt;/p&gt;&#xA;&lt;p&gt;The commenters argue that the current requirement is not burdensome, but rather &amp;quot;is a good balance between operational flexibility and ease of identification,&amp;quot; and that the maximum ten minutes between station identification (which has been in effect for over fifty years) is short enough that those listening can discover the source of a transmission in a reasonable time.&lt;/p&gt;&#xA;&lt;p&gt;We concur.&lt;/p&gt;&#xA;&lt;p&gt;We also agree that a thirty-minute interval would be too long, because interference and variations in propagation may not permit continuous reception of a specific station for thirty minutes.&lt;/p&gt;&#xA;&lt;p&gt;In addition, we share the commenters’ concern that requiring a station receiving another station's transmission to listen for up to thirty minutes to determine the call sign of the transmitting station would compromise the ability of the amateur service to self-police, especially in light of the fact that other methods of identifying the station, such as looking up the station call sign based on the operating frequency, are not available because amateur stations do not operate on specifically assigned frequencies.  It therefore is reasonable to require amateur station identification more frequently than is required of stations in other services.&lt;/p&gt;&#xA;&lt;p&gt;We conclude, therefore, that proposing to increase the time between required station identification transmissions would not improve or enhance the operation of amateur service stations or otherwise be in the public interest.&lt;/p&gt;&#xA;&lt;p&gt;Accordingly, we dismiss the Green Petition.&lt;/p&gt;&#xA;&lt;p&gt;We also agree with the commenters that increasing the frequency of station identification as proposed in the Zook Petition is unnecessary and would be burdensome.&lt;/p&gt;&#xA;&lt;p&gt;It also could lead to congestion, such as during a contest when many amateur operators are trying to contact a distant station.&lt;/p&gt;&#xA;&lt;p&gt;Moreover, the petition does not demonstrate that so revising the station identification requirement would address the primary concern expressed by the petitioner – that many amateur radio operators do not identify their station timely or at all.  Therefore, we agree with the comments that say, in various ways, that the problem of station operators not complying with the present rule is better addressed by enforcement of the present rule, rather than a rule change.&lt;/p&gt;&#xA;&lt;p&gt;Finally, we note that while the current rule does not require identification at the beginning of a communication, many amateur stations already routinely begin a transmission with their call sign.  Accordingly, we dismiss the Zook Petition.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-08-30T06:37:10.160" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9143" PostTypeId="2" ParentId="9132" CreationDate="2017-08-30T11:14:43.897" Score="4" Body="&lt;p&gt;Small loop antennas require great attention to construction details. This is due to the (in)efficiency of a small loop antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By comparison, when constructing a simple half wave dipole, a few ohms of RF resistance has very little effect on its performance. This is because the radiation resistance of a dipole is around 73 ohms. So an additional few ohms of resistance due to construction techniques only reduces the efficiency to 95%. This would hardly be noticed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By comparison, your small loop antenna has a radiation resistance of 0.005 ohms on 40 meters and 0.087 ohms on 20 meters. With just 1/2 ohm of RF resistance, the efficiency of your small loop antenna will be 1% on 40 meters and 15% on 20 meters. And it is difficult to hold the RF (not DC) resistance to only 1/2 ohm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the 1/2 ohm numbers from above, the gain of your small loop antenna will be -18 dBi on 40 meters and -6.5 dBi on 20 meters. This means that a 5 watt transmitter will sound like a 0.025 watt and a 0.35 watt transmitter respectively compared to the same transmitter connected to a typical backyard 1/2 wave dipole. Said another way, you would be 4 and 2  S-units lower respectively. And remember, your actual efficiency is probably much worse than this example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So construction details are very important. Some thoughts:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Use copper tubing for the loops. The larger the diameter of the tubing, the better. It is the exterior surface area that matters. No current exists inside the tube.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Solder all joints.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Use wide copper straps in favor of wires.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Increase the diameter of the main loop to improve the efficiency of the antenna. The RF resistance goes up proportionally to the circumference but the radiation resistance goes up by the power of 4 so any increase in circumference is significantly beneficial. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;As Mike Waters pointed out in comments, the use of a butterfly or&#xA;vacuum style capacitor will further reduce RF resistance by&#xA;eliminating the mechanical wiper mechanism found on standard variable&#xA;capacitors.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Edit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would also like to expand a bit on the point Phil made regarding the proximity of other objects to the antenna. A small loop antenna has very strongly concentrated near field energy. This means that anything close to the loop will likely absorb, reflect, or re-radiate RF energy. This will not only affect the tuning and efficiency of the loop but it can also be quite dangerous - particularly to biological entities like pets, plants, and humans. Keep all objects as far away from the loop as possible.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-01T11:05:18.290" LastActivityDate="2017-09-01T11:05:18.290" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9144" PostTypeId="1" CreationDate="2017-08-30T19:00:30.650" Score="1" ViewCount="124" Body="&lt;p&gt;The ARRL welcome pamphlet contains instructions on building a simple ground plane antenna and specifically comments on its use by handy-talkies. However, I wonder what the actual capability of this antenna would be.  Could it handle 25 watts?  100 watts?  Does anyone know?&lt;/p&gt;&#xA;" OwnerUserId="10271" LastEditorUserId="9493" LastEditDate="2017-09-01T22:29:57.520" LastActivityDate="2017-09-01T22:29:57.520" Title="Power handling of a simple VHF ground plane" Tags="&lt;antenna&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9145" PostTypeId="1" AcceptedAnswerId="9172" CreationDate="2017-08-31T01:19:27.483" Score="2" ViewCount="1451" Body="&lt;p&gt;Using Raspbian (Debian) Linux on a Raspberry Pi 2, how can I view data from my software-defined radio via the command line over SSH? Is there an RTL-SDR client with terminal emulation?&lt;/p&gt;&#xA;" OwnerUserId="10273" LastEditorUserId="8832" LastEditDate="2017-09-01T03:08:01.560" LastActivityDate="2017-09-06T06:05:21.503" Title="Linux RTL-SDR waterfall via the command line" Tags="&lt;rtl-sdr&gt;&lt;linux&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9146" PostTypeId="1" AcceptedAnswerId="9148" CreationDate="2017-08-31T01:24:36.583" Score="1" ViewCount="126" Body="&lt;p&gt;Theoretical assumption:  I have multiple CDMA transmitters operating at same frequency and code placed 5 metres apart. My questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Does the chances of my receiver receiving the data improve? That is to say does the snr of signal improve at receiver placed 40km away ?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What is the signal strength at any point in space?  is it vector sum of strength of both signals received from both transmitters?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Can destructive interference happen at that point in space due to signal strength from multiple sources being out of phase at that point?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Does the receiver frequency tracking loop need to shift from one transmitters signal to other , if at all any changeover between two signals from different sources does happen ?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="5349" LastEditorUserId="76" LastEditDate="2020-02-15T16:56:21.417" LastActivityDate="2020-02-15T16:56:21.417" Title="Multiple CDMA transmitters with same frequency and code" Tags="&lt;digital-modes&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9147" PostTypeId="1" AcceptedAnswerId="9149" CreationDate="2017-08-31T13:49:51.900" Score="2" ViewCount="757" Body="&lt;p&gt;I'm a new ham and would like to start working HF with my mobile (my only) rig, an FT-857d. I have a handful of antennas, all of the variety that has a fiberglass base, extended by a stainless steel whip.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;IHF Iron Horse 75, 40&lt;/li&gt;&#xA;&lt;li&gt;Pro-Am mobile antenna 75&lt;/li&gt;&#xA;&lt;li&gt;Antron Hamwhips 20&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;My question is, how do I determine the correct length to set the whip extension for a given frequency? Is it a simple calculation of the total physical length of the antenna as some fraction of a wavelength? Or is the fiberglass base electrically lengthened by the wire coil evident beneath the black covering? Note: I have little other equipment besides the FT-857d; no SWR meter besides the qualitative one built in to the transceiver. While I do have an LDG YT 100 auto tuner, I don't yet have the cables necessary to connect it and I still want to set the antenna's physical length as close to optimal as possible for the SSB portion of the band.&lt;/p&gt;&#xA;" OwnerUserId="4927" LastActivityDate="2017-09-02T09:36:52.347" Title="How to tune a hamwhip-type mobile HF antenna?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9148" PostTypeId="2" ParentId="9146" CreationDate="2017-08-31T15:42:30.187" Score="3" Body="&lt;p&gt;The CDMA transmitters will have independent frequency synthesizers/oscillators that will not be phase locked with one another. The receiver is therefore subjected to pseudo random phase angles from the various transmitters. The result will be largely destructive interference. The net result is receive performance under nearly all conditions will be substantially less compared to the deployment of a single CDMA transmitter.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-08-31T15:42:30.187" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9149" PostTypeId="2" ParentId="9147" CreationDate="2017-08-31T16:03:20.890" Score="3" Body="&lt;p&gt;Congratulations on getting your ham license!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mobile antenna installations are much less predictable than installations made for fixed locations. The mobile antenna installation is affected by the poor ground that the vehicle presents and the (typically) offset location of the antenna on the vehicle. As a result, most mobile antenna installations are compromises that require more trial and adjustment than a typical home antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good SWR meter or, even better, an antenna analyzer would be a good addition to your toolkit. It will receive a lot of use throughout your ham &quot;career&quot;. If you cannot invest in one now, you probably could borrow one from a nearby ham or ham radio club. Sometimes an elmer (mentor) comes along free for the ride!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Start by adjusting your antennas per the manufacturer's instructions. This gets it into the ballpark. For most mobile antennas, you cannot directly calculate the length of the antenna as a function of wavelength because the manufacturer has added inductors or capacitors to the antenna that will throw off normal antenna calculations. Instead the manufacturer will include a chart or graph to help range in the adjustment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From there you will need to use the SWR meter or antenna analyzer to adjust the antenna to the optimum setting. The advantage of using an antenna analyzer over an SWR meter is that it gives you much more information to help optimize your antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you get your antenna adjusted and you are ready to begin mobile operations, be prepared for the unexpected. Generally a mobile antenna is much less efficient than a home antenna. So at times you will be frustrated that you can hear stations that you cannot work. When I add the &quot;mobile&quot; suffix to my call, I have found that other stations are more likely to look past the more challenging conditions in order to make the QSO. On the other hand, I am often surprised to have a European station answer my mobile CQ - that's the magic of amateur radio. Enjoy!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-02T09:36:52.347" LastActivityDate="2017-09-02T09:36:52.347" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9150" PostTypeId="2" ParentId="9145" CreationDate="2017-08-31T16:22:03.527" Score="1" Body="&lt;p&gt;You didn't specify the OS of the client from which you would like to view the remote session.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the Pi side, use the built in RealVNC to allow remote access.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your remote client is Linux based, take a look at Remmina. It is a free, open source project with support for several Linux variants.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your remote client is Windows based, evaluate TightVNC. It is free download if you don't need any extensions.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-08-31T16:22:03.527" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9151" PostTypeId="2" ParentId="9144" CreationDate="2017-08-31T16:39:05.630" Score="3" Body="&lt;p&gt;Without seeing the design you are referencing it is difficult to provide specific answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general however, the most basic VHF antenna designs will work with a 100 watt transmitter. There are some considerations as the power level rises:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Higher power transmitters are generally more sensitive to SWR&#xA;problems. This may cause them to cut back power, overheat, or in a&#xA;worst case, fail. You may need to tweak the SWR more carefully for&#xA;these power levels.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;As the power increases, the voltage along the antenna increases. This&#xA;could result in RF burns or arcing. Care should be taken to avoid&#xA;injury or damage.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Higher power transmitters pass more current through the antenna. This&#xA;can result in inefficiencies from, and heating of, small gauge wires&#xA;and similar connections.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;As power is increased, your RF exposure increases. You should&#xA;perform an RF exposure assessment for the location and power level of&#xA;the antenna involved to ensure that you are within safe limits of &#xA;exposure.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-08-31T16:39:05.630" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9152" PostTypeId="2" ParentId="9146" CreationDate="2017-09-01T03:06:30.683" Score="0" Body="&lt;p&gt;Cellphones that use this method are assigned a unique pseudo-random CDMA code to prevent just this sort of interference.  Even when they share the same frequency they can communicate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are using the same code and same frequency then they will definitely interfere with each other.  Cellphone CDMA is designed to prevent this from being a problem, by specifically not having any two phones with the same code.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any two transmitters on a single frequency will interfere in ways that are both constructive and destructive, so might find an arrangement that favors one transmitter over another.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, to ensure the best possible data transfer you will get the best results if you deviate from the specifications in your question - eliminate one transmitter or make their codes different.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-09-01T03:06:30.683" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9153" PostTypeId="2" ParentId="9145" CreationDate="2017-09-01T03:15:33.613" Score="0" Body="&lt;p&gt;This is two questions.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will presume the answer to the first is to simply start your &lt;code&gt;sdrsharp&lt;/code&gt; software&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;sdrsharp&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Then, to see it remotely, you need an xterm-compatible connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest that your best option is to install a graphical remote-viewing setup.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Three ways to do this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, enable X11 over ssh&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Procedure is to &lt;code&gt;sudo vi /etc/ssh/ssh_config&lt;/code&gt; and change it to allow X11 connections.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, you can use&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;ssh -Y hostname&#xA;echo $TERM&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The response should be &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;xterm&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Then you can issue the command to start the software&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;sdrsharp&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Second, install &lt;code&gt;tightvnc&lt;/code&gt; so you can control the console of the system.  Once that works you can open a terminal window and do the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Third, install Remote Desktop Protocol, which allows you to make virtual connections to the system which are compatible with Windows Remote Desktop client, or remmina.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;sudo apt-get install xrdp&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Then do the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are on Windows, you should be able to install OpenSSH, then use&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;SSH -X clientname&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;to get it to pull up an xterm.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-09-06T06:05:21.503" LastActivityDate="2017-09-06T06:05:21.503" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9154" PostTypeId="5" CreationDate="2017-09-01T03:36:13.870" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2017-09-01T03:36:13.870" LastActivityDate="2017-09-01T03:36:13.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9155" PostTypeId="4" CreationDate="2017-09-01T03:36:13.870" Score="0" Body="Ground-fault circuit interrupters, also known as residual current devices, as they relate to the operation of nearby or attached radio equipment." OwnerUserId="8832" LastEditorUserId="76" LastEditDate="2017-09-04T03:57:16.043" LastActivityDate="2017-09-04T03:57:16.043" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9156" PostTypeId="2" ParentId="9147" CreationDate="2017-09-01T03:45:21.533" Score="0" Body="&lt;p&gt;Congratulations both for earning your ticket and for obtaining one of the most versatile radios available these days.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend you go back to that local ham who gave you those gift antennas (if they are available) and ask them for advice.  Anybody willing to gift equipment is very likely to want to offer advice also.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Plus cabling, etc.  Maybe even loan you an SWR meter.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't discount the value of personal networking in amateur radio.  You may find your best resource is you local ham club.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2017-09-01T03:45:21.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9157" PostTypeId="1" CreationDate="2017-09-01T15:40:07.927" Score="1" ViewCount="610" Body="&lt;p&gt;I would like to construct a 2m Loop with a sense antenna. I have built just a loop antenna with great success that is resonant at 2m finding null's works quite well on local repeater outputs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to further my project and create one with a sense antenna, similar to what 80m DF units have installed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone done this or know the location to plans for building one?&lt;/p&gt;&#xA;" OwnerUserId="10280" LastActivityDate="2017-09-01T20:26:52.907" Title="2m loop with sense antenna for DF" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;direction-finding&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9158" PostTypeId="2" ParentId="8940" CreationDate="2017-09-01T20:13:38.013" Score="0" Body="&lt;p&gt;After listening to the increased noise level on 20M, and its direction, I observe that the noise has a man-made character, varies greatly over short periods, and always peaks with the peak direction of propagation, mostly NE to Europe. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's what got me googling and to this page with the same suspicion as Noah's - that man-made RFI is artificially raising the propagated noise level. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is something fundamentally different than what we used to consider a local problem, and seems like a plausible explanation for the really awful state of 14 MHz.&lt;/p&gt;&#xA;" OwnerUserId="10282" LastEditorUserId="8832" LastEditDate="2017-09-02T00:15:04.360" LastActivityDate="2017-09-02T00:15:04.360" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9159" PostTypeId="2" ParentId="9157" CreationDate="2017-09-01T20:26:52.907" Score="2" Body="&lt;p&gt;A small loop antenna is bidirectional in the direction of the plane of the antenna and has nulls that are perpendicular to the plane of the antenna. Due to its bidirectional nature, there is ambiguity as to the bearing of transmitted signal when only one receive location is in use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Through the addition of a so called sense antenna, the bidirectional pattern of the loop antenna can be transformed to a more unidirectional, cardioid pattern. The omnidirectional sense antenna is typically a simple vertical antenna. For a 2 meter sense antenna, this can conveniently be made as a quarter wave antenna although it can be, and often is, shorter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To generate the optimum cardioid pattern, the signal from the vertical antenna and the small loop antenna should of equal amplitude and combined with a 90° phase shift. This will result in the null of the cardioid pattern that is 90° from the null in the small loop pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 90° phase shift is easily accomplished with a short length of coax cable that is electrically 90° long (or an odd multiple thereof). If you use Belden 9258 (their RG8X), this would be a cable length of 1 foot, 4.5 inches at 146 MHz. Add to this, the length of the coax coming from the loop antenna. So if you have 1 foot of RG8X coming from the loop, for example, you can combine the sense antenna with a 2 foot, 4.5 inch length of coax with a tee connector and then continue with any length of coax to your receiver. You could also create the 90° phase shift through a lumped circuit. The lumped circuit has the advantage of field adjustability although once set, it should not require further adjustment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally the sense antenna will be more sensitive than the small loop antenna. Its sensitivity can be varied with a simple non-inductive variable resistor in series with the whip. This allows the antenna to be easily field adjusted. Others have had success with pruning the length of the sense antenna until the two match in signal strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the cardiod null is not as sharp as the loop null, the common practice is to allow the sense whip to be switched in and out of the circuit. This allows the initial bearing to be taken with the loop alone by finding the null of the signal and then with the whip switched into the circuit to confirm the direction. Alternating back and forth can fine tune the direction. The same procedure can be used to find the peak of the signal when the signal is too weak to discern the optimum null position. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-01T20:26:52.907" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9160" PostTypeId="1" AcceptedAnswerId="9161" CreationDate="2017-09-01T21:35:52.090" Score="5" ViewCount="4003" Body="&lt;p&gt;Since I got my HF radio a year and change ago, I've been able to hear very little except noise and the WWV time station on 10MHz. Noise seems to vary by band, but not how I'd expect:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;80m: S7-S9&lt;/li&gt;&#xA;&lt;li&gt;40m: S9+10-20&lt;/li&gt;&#xA;&lt;li&gt;20m: S2&lt;/li&gt;&#xA;&lt;li&gt;15m: S3&lt;/li&gt;&#xA;&lt;li&gt;10m: S9&lt;/li&gt;&#xA;&lt;li&gt;6m: S5&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;My setup currently looks like this:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/73Ra2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/73Ra2.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My antenna is fairly low above my house, but even killing mains power didn't reduce my noise level by any noticeable amount. I tried plugging in my 2m J-pole and it - being basically deaf on all of these frequencies - had predictable low noise on all bands, with none above S3. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The feedline for my 2m antenna has a similar-but-physically-separate path to my transceiver than the HF dipole does.&lt;/li&gt;&#xA;&lt;li&gt;The dipole is only about 15 feet in the air on the low side and 25 on the high side.&lt;/li&gt;&#xA;&lt;li&gt;The dipole, transceiver, and tuner aren't grounded, but any ground nearby would be ~20' from short 5kV power lines that run along one edge of my property. The power lines are parallel to the dipole and the dipole is currently in the only place that I can put it on my property. I've heard that putting ground rods in our soil is miserable and haven't done it yet.&lt;/li&gt;&#xA;&lt;li&gt;I live in a suburban environment.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Does my conclusion that the noise is likely to be coming in through the antenna make sense? Should grounding make a difference? What steps can I take to try to mitigate the noise?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Suggestions so far are basically:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Classic foxhunt with a small AM radio&lt;/li&gt;&#xA;&lt;li&gt;Hitting powerpoles with a stick/mallet/sledgehammer (seriously) and seeing if this affects the received noise.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6295" LastEditorUserId="6295" LastEditDate="2017-09-02T20:13:00.110" LastActivityDate="2017-11-02T17:49:11.127" Title="HF Noise Level S5 to S9+18" Tags="&lt;rfi&gt;&lt;noise&gt;&lt;parallel-dipole&gt;" AnswerCount="5" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="9161" PostTypeId="2" ParentId="9160" CreationDate="2017-09-01T22:07:38.280" Score="6" Body="&lt;p&gt;Some troubleshooting ideas:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Check your radio's power supply for noise by substituting a battery and disconnecting the PS from the wall.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Run your receiver on a battery and turn off your main breaker. Make sure any battery powered computers/tablets are fully powered off. If the noise reduces, turn off all branch breakers, turn the main breaker back on, and one by one turn on the branch breakers noting any change in noise.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Install an additional 1:1 balun close to your radio. This sometimes helps prevent local noise pickup on the coax outer shield.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Check your coax for any open or marginal connections - especially&#xA;the shield connections. Try substituting other coax.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Eliminate the tuner and short patch coax and note any change in noise levels.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Take your transceiver to a location in the country with a portable antenna and running off batteries to eliminate receiver problems. Alternatively take it to another ham's QTH that isn't suffering from noise to check it.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Borrow or rent a battery powered spectrum analyzer and walk your&#xA;QTH and the neighborhood sniffing for RFI with a small dipole or loop.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;After eliminating all other possibilities, call the power company and let them know you suspect a cracked insulator or bad transformer is causing RFI. They have techs that specialize in these sorts of problems.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-01T22:18:42.147" LastActivityDate="2017-09-01T22:18:42.147" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9162" PostTypeId="2" ParentId="9139" CreationDate="2017-09-02T09:32:39.507" Score="2" Body="&lt;p&gt;I assume you have extensively bench tested the kit and have not found any problems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having several years of experience with high altitude radios in the Alps, I would suspect that you are getting static build-up on the antenna that is glitching the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A Polyphasor, or equivalent, to ground can mitigate static build up. Failing that, a couple of megohms of non-inductive resistance across the antenna terminals may help. I have had success with the resistors in an N connector, plugged into a Tee connector at the radio.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-02T09:46:21.453" LastActivityDate="2017-09-02T09:46:21.453" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9163" PostTypeId="1" CreationDate="2017-09-02T14:11:22.213" Score="1" ViewCount="895" Body="&lt;p&gt;I am researching a way to build a pre-emphasis circuit, so I looked up the specs for different pre-emphasis standards. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example is the standard for FM broadcast, in the USA it's 75 µs. I am confused on how a filter is measured using time. What does 75 microseconds mean when referring to the pre-emphasis intensity?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="76" LastEditDate="2017-09-02T15:05:40.690" LastActivityDate="2017-09-03T10:31:02.773" Title="Pre-emphasis measurement" Tags="&lt;fm&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9164" PostTypeId="2" ParentId="9163" CreationDate="2017-09-02T15:04:11.297" Score="4" Body="&lt;p&gt;Pre-emphasis is used in FM transmissions to boost the higher frequency spectrum of the audio modulating signal. This is reversed through de-emphasis in the FM receiver. This is done to reduce noise level that would otherwise be present in the audio signal due to the triangular spectral distribution of noise in FM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 75 µs figure simply refers to the RC time constant (tau) used in the high pass filter to boost the high frequency content of the audio modulation in the transmitter. In US broadcast transmissions, tau is equal to 75 µs but it is 50 µs in most other regions of the world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \tau = R \times C $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, here is an RC circuit that provides 75 µs of pre-emphasis in the transmitter:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/3RYzN.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f3RYzN.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The actual RC values would be chosen to match the impedance of the audio amplifier chain. An RC filter with a tau of 75 µs has a cut-off or breakpoint of ~2.1 kHz. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-03T10:31:02.773" LastActivityDate="2017-09-03T10:31:02.773" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9165" PostTypeId="2" ParentId="9163" CreationDate="2017-09-02T15:05:10.420" Score="1" Body="&lt;p&gt;Wow, that was harder to find confirmation of than I thought and I still don't have any good clear citations (bad ones: &lt;a href=&quot;http://www.edaboard.com/thread33793.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;1&lt;/a&gt; &lt;a href=&quot;https://books.google.com/books?id=1FWWfcwzc5oC&amp;amp;lpg=PT220&amp;amp;ots=mSW9dsaQqi&amp;amp;dq=pre-emphasis%20filter%20time%20constant&amp;amp;pg=PT220#v=onepage&amp;amp;q=pre-emphasis%20filter%20time%20constant&amp;amp;f=false&quot; rel=&quot;nofollow noreferrer&quot;&gt;2&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The time value is the &lt;a href=&quot;https://en.wikipedia.org/wiki/RC_time_constant&quot; rel=&quot;nofollow noreferrer&quot;&gt;RC time constant&lt;/a&gt; of the resistor and capacitor in a single-pole high-pass RC filter which implements the preemphasis by attenuating lower frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The general way time relates to a filter is via the &lt;em&gt;period&lt;/em&gt; of the wave, i.e. the reciprocal of frequency. Thus a longer time is a lower frequency.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-09-02T15:12:28.557" LastActivityDate="2017-09-02T15:12:28.557" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9166" PostTypeId="2" ParentId="9160" CreationDate="2017-09-02T20:22:37.790" Score="3" Body="&lt;p&gt;Just went through the same thing last year. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One hint - does the static level lower when it rains? if the answer is yes, very likely a bad insulator or distribution transformer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Took my electric company almost 90 days to fix it, but went from +20 static down to S-2 or 3. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also using a 160-10 fan dipole here. The problem insulator was at least 100 yards from my antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other advice is all sound as well!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 es GL&#xA;Dave - KB3MOW&lt;/p&gt;&#xA;" OwnerUserId="10286" LastEditorUserId="8832" LastEditDate="2017-09-03T01:36:12.257" LastActivityDate="2017-09-03T01:36:12.257" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9167" PostTypeId="1" AcceptedAnswerId="9168" CreationDate="2017-09-03T19:41:55.797" Score="4" ViewCount="183" Body="&lt;p&gt;I am building an antenna that specifies the use of Dacron rope to help support the spreaders, but that is not readily available in Trinidad and Tobago.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What will be a good replacement with regards to UV resistance?&lt;/p&gt;&#xA;" OwnerUserId="10292" LastEditorUserId="76" LastEditDate="2017-09-03T21:19:38.913" LastActivityDate="2017-09-05T22:39:22.727" Title="Substitute for Dacron rope in antennas" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9168" PostTypeId="2" ParentId="9167" CreationDate="2017-09-03T20:06:05.500" Score="3" Body="&lt;p&gt;While UV resistance is one quality, you should also be concerned with the other qualities such as yield strength, weight, moisture absorption, and stretch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nylon and polyester ropes can often be found in a UV resistant form. In general, ropes that are used for maritime purposes, other than pure hemp, have the qualities simular to those required for antenna applications.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-03T20:06:05.500" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9169" PostTypeId="2" ParentId="9167" CreationDate="2017-09-03T20:35:52.643" Score="2" Body="&lt;p&gt;I have always used 3/16&quot; or 1/4&quot; white nylon rope. It gets stiff after awhile, but doesn't lose its strength even after 5 to 10 years outdoors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stay away from yellow polypropylene rope. It is not UV resistant and starts deteriorating in just a few months.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-09-03T21:30:43.430" LastActivityDate="2017-09-03T21:30:43.430" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9171" PostTypeId="1" CreationDate="2017-09-04T04:05:56.567" Score="3" ViewCount="1383" Body="&lt;p&gt;What is the difference between Iambic Keyer mode A and mode B?  Are there any other popular keyer modes?  Why would one choose one mode over the other?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If only one Iambic keyer mode is to be implemented, which mode should a keyer that supports only one mode support (in the U.S.)?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2017-09-04T05:54:37.640" Title="Difference between Iambic keyer modes?" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9172" PostTypeId="2" ParentId="9145" CreationDate="2017-09-04T04:35:15.833" Score="1" Body="&lt;p&gt;This is actually implementable, as specified, but you may have to code your own app.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wanted to measure whether 2 signals were present.  So I ran rtl_tcp on my Pi 3 to serve RTL-SDR IQ samples over a socket.  I then wrote 2 DSP filters (in C) that connected to rtl_tcp and measured the magnitudes of the two signals, ran the filters on the Pi 3, and printed the results to stdout over ssh.  I suppose I could have presented the 2 magnitudes as ASCII art of a 2 bar waterfall spectrograph.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My benchmarks show that a Pi 3 could also easily run an FFT on the IQ data as well as 2 simpler filters for a wider waterfall.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-09-04T05:59:44.763" LastActivityDate="2017-09-04T05:59:44.763" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9173" PostTypeId="2" ParentId="9171" CreationDate="2017-09-04T05:54:37.640" Score="5" Body="&lt;p&gt;An iambic keyer is used with two paddles. The concept is that you can hold down one paddle, say the dah paddle, to send out a string of dahs. While doing this, if you tap the dit paddle, it will insert a dit between the dahs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you hold both paddles at the same time, the iambic keyer will send alternate dits and dahs. The difference between mode A and mode B iambic keying is what happens when you release both paddles. In mode A, the keyer will finish with the last dit or dah that it was sending at the time of release. In mode B, if it was sending a dah when you release the paddles, it will add one more dit. If it was sending a dit, it will add one more dah.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is widely held (no pun intended) that mode B came about because of a logic error on an early iambic keyer. Operators got used to the effect and then found it difficult to use a corrected (mode A) keyer. As a result, most keyers offer the option to switch between mode A and mode B.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first keyer I used was a Heathkit unit that was mode A. When I try a mode B keyer, I am often making sending errors. There is no right or wrong mode - both are well established.  The receiving station cannot tell the difference. It is down to a matter of operator training and preference.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-04T05:54:37.640" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9175" PostTypeId="1" CreationDate="2017-09-04T15:44:25.320" Score="2" ViewCount="177" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rJoMF.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rJoMF.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the function of the configuration of R1, C3,C10 and R3? How does the LC tank in this circuit work?&lt;/p&gt;&#xA;" OwnerUserId="10296" LastEditorUserId="8717" LastEditDate="2019-08-01T23:05:54.733" LastActivityDate="2019-08-01T23:05:54.733" Title="How does this circuit work? Why is the antenna connected to the output of the amplification stage?" Tags="&lt;receiver&gt;&lt;cw&gt;&lt;ssb&gt;&lt;am&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9176" PostTypeId="2" ParentId="9175" CreationDate="2017-09-04T19:26:48.157" Score="4" Body="&lt;p&gt;EDIT to be more specific about the input circuit per Phil's comment:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna (aerial) is connected to the the oscillator of the first transistor stage formed by VC, L and the self capacitance of T1. This forms a classic regenerative circuit where the oscillator essentially samples a portion of the signal from the antenna as the oscillator builds up its amplitude. T2 is the quenching feature of the regenerative circuit that stops the oscillations when they have reached an amplitude sufficient to turn on T2. At this time T2 shorts out the power supply to the T1 oscillator circuit, causing it to restart its oscillating cycle. R1 prevents the power supply from being directly shorted out and forms part of the detection circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the length of the antenna will play a critical role in the correct operation of the regenerative cycle since it is directly tied to the LC circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;R1, C3,C10 and R3 form a decoupling network from the battery. This is to ensure that the comparatively high load of the LM386 audio amplifier does not affect the RF detection circuits. Without this, the audio output of the circuit will couple back through the RF circuit via the DC bus causing distortion or feedback. The decoupling network also ensures that RF is not coupled back to the LM386 due to the quenching action of T2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The detection of the FM signal is done by R2 and C2 as a low pass filter that form a basic discriminator. If the FM carrier falls on a relatively linear portion of the low pass curve, it performs an FM to AM conversion through slope conversion.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-06T08:33:32.593" LastActivityDate="2017-09-06T08:33:32.593" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9177" PostTypeId="1" CreationDate="2017-09-04T22:22:19.010" Score="4" ViewCount="1512" Body="&lt;p&gt;I bought my self a Baofeng UV-5RV2+ as an inexpensive way to introduce myself to the world of ham radio. With all of the stock components everything has been working fine. I wanted to try to increase the radios performance so I purchased a Nagoya NA-320A antenna. When this antenna is attached I have to turn the squelch to 0 or hold the moni button to receive any sort of  transmission. When the  transmission comes in (squelch-0 or moni pressed) it is very clear with little static. my question(s) is; Did I get the wrong antenna, Did I get a bad antenna, is my radio broken, or is it something else entirely? &lt;/p&gt;&#xA;" OwnerUserId="10302" LastActivityDate="2019-05-09T22:38:48.847" Title="My Baofeng UV-5RV2+ will receive a signal with rubber duck antenna but not with a new Nagoya" Tags="&lt;antenna&gt;&lt;baofeng&gt;&lt;squelch&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9178" PostTypeId="2" ParentId="9177" CreationDate="2017-09-05T02:10:37.923" Score="2" Body="&lt;p&gt;According to the web, your Nagoya NA-320A works on both the 2m and 70cm bands, matches the reverse-SMA antenna connector on your Baofeng, and works reasonably well.  So you probably chose a reasonably-good model of antenna.  Your new antenna might be broken, or there could be something wrong with your radio, or your radio might be set up incorrectly.  (Do you have it programmed for the local repeaters?  Does a repeater reply when you key it up with either antenna?  Don't expect to hear much on the factory default frequencies.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good strategy might be to find someone else with a similar Baofeng HT, and have him or her test the antenna for you, and also look at your Baofeng.  A knowledgeable operator could probably sort out your problem quickly.  A good place to meet such people would be at the meeting of your local radio club.  (Personally, I often bring my laptop and a programming cable to club meetings so I can help newbies program their HTs on the spot.)  If you're in the US, you can use the ARRL's &lt;a href=&quot;http://www.arrl.org/find-a-club&quot; rel=&quot;nofollow noreferrer&quot;&gt;club search tool&lt;/a&gt; to find a nearby ARRL-affiliated club.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-09-05T02:10:37.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9179" PostTypeId="5" CreationDate="2017-09-05T05:52:32.597" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2017-09-05T05:52:32.597" LastActivityDate="2017-09-05T05:52:32.597" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9180" PostTypeId="4" CreationDate="2017-09-05T05:52:32.597" Score="0" Body="Antennas composed of more than one dipole antenna with one feed point." OwnerUserId="8832" LastEditorUserId="76" LastEditDate="2017-09-06T20:14:52.450" LastActivityDate="2017-09-06T20:14:52.450" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9181" PostTypeId="2" ParentId="9131" CreationDate="2017-09-05T10:40:15.030" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://www.ifixit.com/Answers/View/223445/iPhone+6+cellular+antenna+location-replacement#answer223453&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ifixit.com/Answers/View/223445/iPhone+6+cellular+antenna+location-replacement#answer223453&lt;/a&gt; claims this is only the “antenna upper bus bar assembly” which connects the case (acting as the actual antenna) to the circuit. Which would also explain the six connectors.&lt;/p&gt;&#xA;" OwnerUserId="772" LastActivityDate="2017-09-05T10:40:15.030" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9183" PostTypeId="2" ParentId="9131" CreationDate="2017-09-05T15:15:54.980" Score="4" Body="&lt;p&gt;That piece is not the antenna per se. The actual antenna is formed by two pieces of the case, isolated from the rest by some plastic strips:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/v0wuu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/v0wuu.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;http://bgr.com/2015/06/21/iphone-6-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Future iPhones May Do Away With Plastic Antenna Lines (bgr.com)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the piece installed in a phone, image from &lt;a href=&quot;https://www.ifixit.com/Store/iPhone/iPhone-6s-Cellular-Antenna/IF314-014-1&quot; rel=&quot;nofollow noreferrer&quot;&gt;ifixit.com&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lMA59.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lMA59.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see two of these screws attach to the section on the top of the phone, while others attach to the section surrounding the camera.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inside the part itself is likely a matching network. Similar parts contain a chip capacitor under the black covering, and the two arms bent at 90 degrees may be a transmission line. The black covering is likely to avoid shorts to the case and other components.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-09-05T15:15:54.980" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9184" PostTypeId="1" AcceptedAnswerId="9188" CreationDate="2017-09-05T21:11:02.237" Score="12" ViewCount="553" Body="&lt;p&gt;I stayed at a resort in the U.S. recently that is located in an unpopulated area with virtually no radio reception.  To fill the gap, the resort has its own FM station that can be heard only within the resort (about a minute after you drive off the resort, it fades away completely). When you tune to the station, all you hear is one pop song after another, with fade/overlap between the songs. There is no station identification, commercials, or any other content.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only resort employee I could find that knew any details about it said that he was the one who selects the playlist, using a desktop computer application but he didn't know anything about the radio transmission technology.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone have any information about this type of station?  How does the transmitter connect to the software?  What kind of equipment (antenna, etc) would it use? What is the software he's using?  Where does it fit legally (FCC, etc)?  How the heck are they able to keep the coverage area so tightly defined?&lt;/p&gt;&#xA;" OwnerUserId="10308" LastEditorUserId="8832" LastEditDate="2017-09-06T03:53:34.037" LastActivityDate="2018-05-13T05:29:21.277" Title="Resort FM radio station" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fm&gt;&lt;software&gt;&lt;station-identification&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9185" PostTypeId="2" ParentId="283" CreationDate="2017-09-05T21:17:14.243" Score="3" Body="&lt;p&gt;Thanks for the posting everyone! &#xA;For licence test I took this approach after reading everyone's post &amp;amp; searching though all the technical details you posted.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Convert Frequency to wavelength in meters. 300 ÷ frequency. &lt;/li&gt;&#xA;&lt;li&gt;Multiplying 39 × wavelength in meters = inches of full Antenna length. &lt;/li&gt;&#xA;&lt;li&gt;Divide inches by 2 for 1/2 wave.&lt;/li&gt;&#xA;&lt;li&gt;Divide 1/2 wave by 2 for 1/4 wave.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Example. 146Mhz    300÷146=2.05 meters&lt;br&gt;&#xA;2.05×39= 79.95 inches full length in inches.&lt;br&gt;&#xA;79.95÷2= 39.95 inches 1/2 wave length in inches.&lt;br&gt;&#xA;39.95÷2= 19.985 inches 1/4 wave length in inches.&lt;br&gt;&#xA;Answer on test is 19.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example 6m.   Meters already given.&lt;br&gt;&#xA;6×39= 234 inches full wave length in inches.&lt;br&gt;&#xA;234÷2= 117 inches 1/2 wave length in inches.&lt;br&gt;&#xA;Answer on test is 112. Which is rounded answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You only have to remember find wavelength in meters &amp;amp; multiply 39 then find antenna wavelength in inches.&#xA;Please advise me if these calculation are in error or any other errors.&#xA;73's&lt;/p&gt;&#xA;" OwnerUserId="10311" LastEditorUserId="966" LastEditDate="2017-09-07T08:19:23.047" LastActivityDate="2017-09-07T08:19:23.047" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9186" PostTypeId="2" ParentId="9167" CreationDate="2017-09-05T22:39:22.727" Score="0" Body="&lt;p&gt;At low frequencies, below 50 MHz or so, you can use steel wire with porcelain isolators every 0.35 wl or so (at the highest frequency of interest.) You could use many other kinds of isolators, cheap things you could make yourself. Steel is strong and stiff....&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-09-05T22:39:22.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9187" PostTypeId="2" ParentId="9160" CreationDate="2017-09-06T02:32:53.430" Score="1" Body="&lt;p&gt;You wrote &quot;The power lines are parallel to the dipole &quot;&#xA;and &lt;strong&gt;you allow that to pass &quot;OK&quot; because&lt;/strong&gt; &#xA;&quot; the dipole is currently in the only place that I can put it...&quot;.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In theory , you are inviting inductive linking &#xA;between your dipole and the power lines. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To wit: &#xA;I have used a End-Fed Long-Wire of 188 ft , at a height of 17 ft &#xA;with power lines on three sides, all within 30 ft of antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna design here at K4KKQ :&#xA;Long-Wire is 188 ft, odd quarters for 40M and 20M.&lt;br&gt;&#xA;Long-Wire is up 17 ft, odd quarter for 20M. &#xA;&lt;strong&gt;Long-Wire is angled like letter &quot;Z&quot; &#xA;and all sides are angled aprox. 45 degrees from power lines.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connections : &#xA;Use a 1:1 current balun.&#xA;Use 50 Ohm coax directly to balun.&#xA;Use QRP antenna tuner to coax , from the QRP transmitter.&#xA;Band Noise is measurable at all times, in low &quot;S&quot; units. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Results:&#xA;Worked all Europe and all states on ONE Watt CW, 20 Meters. &#xA;Work 1000 miles to New England each weekend, on 20 Meters. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Conclusion:&#xA;&quot;power lines are parallel to the dipole&quot;  and &quot;Linking&quot; and that is why you are getting into such high Band-Noise.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Glen Ellis, &lt;a href=&quot;http://www.geocities.ws/glene77is/&quot; rel=&quot;nofollow noreferrer&quot;&gt;K4KKQ&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8402" LastEditorUserId="8402" LastEditDate="2017-09-07T13:57:59.223" LastActivityDate="2017-09-07T13:57:59.223" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9188" PostTypeId="2" ParentId="9184" CreationDate="2017-09-06T03:44:21.210" Score="13" Body="&lt;p&gt;I believe you have encountered a Part 15 radio station.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.fcc.gov/general/rules-regulations-title-47&quot; rel=&quot;nofollow noreferrer&quot;&gt;United States Code of Federal Regulations, Title 47, Part 15 (47 CFR 15)&lt;/a&gt; covers such things as garage door openers and the like.  As such, and due to the fact that they are unlicensed by definition, there is no station-identification requirement.  Note that this section covers both intentional and unintentional radiators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to the FCC, in &lt;a href=&quot;https://www.fcc.gov/general/oet-bulletins-line#63&quot; rel=&quot;nofollow noreferrer&quot;&gt;OET Bulletin 63: (October 1993)&lt;/a&gt;, page 15, operation on the FM broadcast band is limited to an effective radiated output of &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;250 uV/M as measured at 3 Meters distance&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This was originally intended to provide roughly a 200-foot transmission range.  And you can have as many transmitter as needed to cover a larger area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A typical Part 15 FM radio transmitter is the Ramsey FM100B.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PE7W2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PE7W2.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that there is no limit to the number of transmitters that can be operated, so it is possible to cover an entire city block or more if you have enough transmitters.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;(The Ramsey FM100B was also offered for overseas buyers as a 1 Watt transmitter through the addition of a secondary power amplifier board)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For longer distances, Part 15 AM is often a better choice because of the availability of radios like the &lt;a href=&quot;https://www.chezradio.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Chezradio Procaster&lt;/a&gt;, which is FCC type-certified when operated with the integrated antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/B1jHJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/B1jHJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part 15 AM is limited to 100mW power output and a 10-foot antenna-to-ground length.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This opens many possibilities especially in terms of range.  For instance, a Procaster on a rooftop with a 20-wire radial system (a counterpoise, or artificial ground) can often reach more than a half mile in radius.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Software:  For low-budget radio stations, one of the best automation systems available for free is &lt;a href=&quot;https://www.zarastudio.es/&quot; rel=&quot;nofollow noreferrer&quot;&gt;ZaraStudio&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RO2bn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RO2bn.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The particular FM transmitter shown above has 2 RCA input jacks for each Line, and a 1/8&quot; (3.5mm) jack for Mic Input.  In other words, it has an internal mixer.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only cable required to connect to a Line input from a PC is a generic one like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ebay.com/itm/New-3-5mm-1-8-Stereo-Male-to-2-RCA-Male-AUX-Audio-Stereo-Adapter-Y-Cable-Cord-/111986944968&quot; rel=&quot;nofollow noreferrer&quot;&gt;New 3.5mm 1/8&quot; Stereo Male to 2 RCA Male AUX Audio Stereo Adapter Y Cable Cord&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/epRyZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/epRyZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;As with all things FCC, the cardinal rule is that the station operator bears full responsibility to avoid interfering with any other licensed service.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;There is an active Part 15 community presence on the WWW.  There are many types of antennas in use, including carrier-current where powerlines are the primary radiators.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are interested in setting something up yourself it is worth the time to search around and learn from the experience of others.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-05-13T05:29:21.277" LastActivityDate="2018-05-13T05:29:21.277" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="9189" PostTypeId="2" ParentId="9177" CreationDate="2017-09-06T06:38:34.030" Score="5" Body="&lt;p&gt;The fact that you have a static free signal when you press the monitor button or open the squelch sounds like you may have CTCSS or DCS decode (receive squelch) turned on. This feature is normally used to ensure that the squelch does not open on your radio unless the repeater or station you are monitoring transmits its sub audible tone or digitally coded squelch code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Boefang brand refers to this feature as Select Calling and more specifically Group Calling. You can turn it on for CTCSS or DCS. Consult your manual or programming software. If you are setting this from the radio keypad, you need to enter a CTCSS or DCS code of 0 for the R-CTCSS and R-DCS values when prompted on the screen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following is excerpted from the manual and applies if you are not using memories:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;CTCSS&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Press the [MENU] button to enter the menu.&lt;/li&gt;&#xA;&lt;li&gt;Enter [1] [1] on the numeric keypad to get to Receiver CTCSS (R-CTCS).&lt;/li&gt;&#xA;&lt;li&gt;Press the [MENU] button to select.&lt;/li&gt;&#xA;&lt;li&gt;Enter the desired CTCSS sub-tone frequency in hertz on the numeric keypad.&lt;/li&gt;&#xA;&lt;li&gt;Press the [MENU] button to confirm and save.&lt;/li&gt;&#xA;&lt;li&gt;Enter [1] [3] on the numeric keypad to get to Transmitter CTCSS (T-CTCS).&lt;/li&gt;&#xA;&lt;li&gt;Press the [MENU] button to select.&lt;/li&gt;&#xA;&lt;li&gt;Enter the desired CTCSS sub-tone frequency in hertz on the numeric keypad.&lt;/li&gt;&#xA;&lt;li&gt;Press the [MENU] button to confirm and save.&lt;/li&gt;&#xA;&lt;li&gt;Press the [EXIT] button to exit the menu.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;DCS&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Press the [MENU] button to enter the menu.&lt;/li&gt;&#xA;&lt;li&gt;Enter [1] [0] on the numeric keypad to get to Receiver DCS (R-DCS).&lt;/li&gt;&#xA;&lt;li&gt;Press the [MENU] button to select.&lt;/li&gt;&#xA;&lt;li&gt;Enter the desired DCS sub-tone frequency in hertz on the numeric keypad.&lt;/li&gt;&#xA;&lt;li&gt;Press the [MENU] button to confirm and save.&lt;/li&gt;&#xA;&lt;li&gt;Enter [1] [2] on the numeric keypad to get to Transmitter DCS (T-DCS).&lt;/li&gt;&#xA;&lt;li&gt;Press the [MENU] button to select.&lt;/li&gt;&#xA;&lt;li&gt;Enter the desired DCS sub-tone frequency in hertz on the numeric keypad.&lt;/li&gt;&#xA;&lt;li&gt;Press the [MENU] button to confirm and save.&lt;/li&gt;&#xA;&lt;li&gt;Press the [EXIT] button to exit the menu.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Note that you may need the transmit T-CTCSS or T-DCS to be enabled in order to talk through repeaters in your area. Check your repeater guide.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each memory can have its own CTCSS and DCS settings. If you are using memories, consult your manual or software to disable R-CTCSS and R-DCS for the appropriate memory channels.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-06T06:45:26.830" LastActivityDate="2017-09-06T06:45:26.830" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9192" PostTypeId="1" AcceptedAnswerId="9197" CreationDate="2017-09-06T23:17:03.263" Score="4" ViewCount="500" Body="&lt;p&gt;I'm thinking about putting together an Echolink link node on my local repeater frequency so I can participate in the weekly net when out of town. This seems straightforward as it's simply:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being in an HOA, I have to try and keep my house from looking like an antenna farm / porcupine, so I thought &quot;why not a panel antenna?&quot; I figure I can build the elements out of 10AWG solid wire and place it on a vertical surface outside my house, paint it with leftover house paint, and it should be nicely unobtrusive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a reason not to build a biquad for such a purpose? Is there a better (less observable, easier to build, ...?) antenna for connecting from one known point to another?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I considered a simple dipole, but there's no good way to mount it and I have rain gutters on the side of the house that faces the repeater. A biquad, being relatively flat &lt;em&gt;and&lt;/em&gt; vaguely directional, seems like an ideal solution to this particular task.&lt;/p&gt;&#xA;" OwnerUserId="6295" LastActivityDate="2017-11-13T05:59:50.547" Title="2m Biquad - Why not?" Tags="&lt;antenna&gt;&lt;echolink&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9193" PostTypeId="1" AcceptedAnswerId="9194" CreationDate="2017-09-07T02:32:39.503" Score="1" ViewCount="186" Body="&lt;p&gt;I don't yet have any radio equipment but I find this hobby interesting and would like to learn more. I'm looking for something that isn't too basic and will keep my interest without spending too much. I saw the Baofeng uv-5r which looked cool. What sort of license would I need to get in order to use that radio? I'm just looking at occasional use for now. Would it be possible for me to use that radio to talk to my friend's walkie talkie or is that not possible with these radios? I'd definitely look at other equipment if it has that feature but I could live without it.&lt;/p&gt;&#xA;" OwnerUserId="10320" LastActivityDate="2017-09-07T03:05:55.337" Title="Recommendation for noob" Tags="&lt;united-states&gt;&lt;receiver&gt;&lt;baofeng&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9194" PostTypeId="2" ParentId="9193" CreationDate="2017-09-07T03:05:55.337" Score="3" Body="&lt;p&gt;The Technician license is the usual starting license for this hobby (Amateur &quot;Ham&quot; Radio) in the US.  You would use the radio on the VHF/UHF US licensed amateur bands to talk with other licensed ham radio operators.  You cannot talk to an unlicensed friend if it is on a license sanctioned band (unless that friend is using equipment owned and station operated by another licensed ham operator).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend looking into taking the Technician license and talking your friends into taking the license so that you would all be legal on the amateur radio bands.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2017-09-07T03:05:55.337" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9195" PostTypeId="2" ParentId="5683" CreationDate="2017-09-07T15:32:34.260" Score="0" Body="&lt;p&gt;Yes. K5URU has written &lt;a href=&quot;http://forums.qrz.com/index.php?threads/kenwood-tm-d710g-fldigi-rigcat-rig-control.508802/&quot; rel=&quot;nofollow noreferrer&quot;&gt;a QRZ forum post&lt;/a&gt; about using &lt;a href=&quot;https://sourceforge.net/projects/fldigi/&quot; rel=&quot;nofollow noreferrer&quot;&gt;fldigi&lt;/a&gt; (RigCAT, specifically) to do this. He provided a &lt;a href=&quot;http://forums.qrz.com/index.php?attachments/tm-d710g-txt.292173/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RigCAT XML file&lt;/a&gt; (change the &lt;code&gt;.txt&lt;/code&gt; extension to &lt;code&gt;.xml&lt;/code&gt;) with comments explaining his process. He gives the impression in the comments that his XML file can be improved upon--you may be able to gain more control over the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He based his work on &lt;a href=&quot;https://github.com/LA3QMA/TM-V71_TM-D710-Kenwood&quot; rel=&quot;nofollow noreferrer&quot;&gt;LA3QMA's documentation of Kenwood's rig control commands for the TM-D710&lt;/a&gt;. Note that LA3QMA lists a separate set of commands for the display unit and the main unit (both have a PC port). K5URU used only the main unit. If you wanted to extend the XML file to include commands for the display unit as well, you could:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Connect a computer (PC or microcontroller) with three RS232 ports (two for the radio units and one for the PC running fldigi). This additional computer would need to split the commands coming from fldigi and route them to either the display unit or the main unit.&lt;/li&gt;&#xA;&lt;li&gt;Write a user-space serial port device driver on the PC running fldigi to do the task above (the driver would then use two additional serial ports on the PC to connect to the radio units).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="5820" LastActivityDate="2017-09-07T15:32:34.260" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9196" PostTypeId="2" ParentId="6439" CreationDate="2017-09-08T17:02:08.487" Score="1" Body="&lt;p&gt;Sorry for the long overdue reply but you didn't tag your response with my ID so I didn't get notification of your response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The control box azimuth reading and the computer azimuth reading share a common 6 volt feed from the rotor potentiometer circuit but each has their own calibration pot. If the control box meter reading is drifting from the computer reading after warm up, I would suspect that one or the other of the calibration pots is the problem. Try rotating both VR1 and VR3 back and forth several times through their complete range immediately after spraying with a contact cleaner. Then recalibrate both after they dry out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After calibrating, leave the rotor azimuth in a fixed position. With a DVM, note the output voltage of the azimuth reading on the DIN connector of the rotor controller after you have successfully calibrated both pots. If the control box meter reading changes, you know that the problem is in that circuit. If the computer reading drifts after some time, re-check the DIN voltage reading. If that has not changed, then the problem is in your computer controller board, not in the rotor controller box. If it has changed, the problem is in the control box circuit that drives the external DIN connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feel free to post your results after going through this troubleshooting exercise if you still haven't found the problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/k0Is8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/k0Is8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-08T17:02:08.487" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9197" PostTypeId="2" ParentId="9192" CreationDate="2017-09-08T17:54:40.810" Score="2" Body="&lt;p&gt;Why not indeed. A biquad sounds like a fine solution, with the only caveat that on 2 meters (145 MHz) it will be significantly larger than the 2.4 GHz constructions typically seen. The size of the panel is on the order of one wavelength, so you're looking at something approximately 2 meters square. At that size you may want to construct the panel from a cage of wires, as a 4 square meter sheet of copper will be a little expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other difficulty is mounting the antenna high. Due to line-of-sight propagation on VHF, once the antenna is beyond the radio horizon, path losses increase sharply. This is because you must now rely on scattering off other objects to get your signal across.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, given the option of mounting a panel antenna down low on the side of the house, and mounting a smaller antenna up high, I'd opt for the latter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, HTs often come with compact antennas which are smaller than the 1/4 wavelength that would be required of a resonant monopole. Such an antenna, say mounted on your gutters for a ground plane, and painted to match your roof, may be sufficiently small that it will go unnoticed.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-09-08T17:54:40.810" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9198" PostTypeId="2" ParentId="9192" CreationDate="2017-09-08T20:25:50.227" Score="1" Body="&lt;p&gt;How about a 2- or 3-element Yagi or cubical quad? A 2-element quad would be only 1 meter (or less) square on the ends, and likely even shorter on the sides between the driven element and reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could even make the enclosure look like (or be!) a birdhouse.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-09-08T20:55:00.627" LastActivityDate="2017-09-08T20:55:00.627" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9199" PostTypeId="2" ParentId="7501" CreationDate="2017-09-09T02:35:10.867" Score="1" Body="&lt;p&gt;A new Menu 24 on the BTECH UV5X3 Triband radio is &quot;SYNC&quot; and is ON or OFF.  This is a great addition. You can program a Marine channel 16 and see &quot;CH 16&quot; in one display and &quot;156.80&quot; in the other display. For Amateur repeaters, it's nice to know the repeater callsign in one display and the actual Frequency in the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only downside is dual monitoring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If ON, and you have FREQ in the A display, and CHAN in the B display, changing either channel, either UP DOWN or by typing in a channel number, you will see the NAME in one VFO and the Frequency in the other display.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the UV5 models, there is no such capability.&lt;/p&gt;&#xA;" OwnerUserId="10336" LastActivityDate="2017-09-09T02:35:10.867" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9200" PostTypeId="1" AcceptedAnswerId="9201" CreationDate="2017-09-10T11:04:57.043" Score="5" ViewCount="1399" Body="&lt;h3&gt;Background&lt;/h3&gt;&#xA;&lt;p&gt;You're in the path of a hurricane, and the eye just passed over your head. There is no electricity (apart from your own generator or battery), there is no mobile network and there is obviously no internet availability. But you do have a working computer with an SDR (20 MHz - 3 GHz) transmitter, Ham-it-up, a Wifi router, a mobile phone and an RPi3, and a few soldering skills.&lt;/p&gt;&#xA;&lt;h3&gt;Questions:&lt;/h3&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;How can I transmit text, audio, images or videos to the outside world?&lt;/li&gt;&#xA;&lt;li&gt;What are the options available for this?&lt;/li&gt;&#xA;&lt;li&gt;What else is required to construct (or have) to do this? (In terms of antennas and hardware etc.)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;First thought is that one should try to use an amateur satellite transmission, since that signal propagation would pass through least possible weather, i.e. straight up.&lt;/p&gt;&#xA;&lt;p&gt;Second, that one should use some long wave TX that is less affected by local atmospheric conditions.&lt;/p&gt;&#xA;&lt;p&gt;I was looking at &lt;a href=&quot;https://www.researchgate.net/publication/224407584_The_Effects_of_Tropical_Weather_on_Radio-Wave_Propagation_Over_Foliage_Channel&quot; rel=&quot;noreferrer&quot;&gt;this paper&lt;/a&gt; but it only cover VHF (240 MHz) and UHF (700 MHz), so I would imagine HF or LF would be a better choice.&lt;/p&gt;&#xA;&lt;p&gt;I these days of hurricane season, I'd appreciate any practical or useful answers.&lt;/p&gt;&#xA;" OwnerUserId="6563" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-09-10T14:57:58.340" Title="How to transmit images and video through a hurricane?" Tags="&lt;software-defined-radio&gt;&lt;hf&gt;&lt;satellites&gt;&lt;transmitter&gt;&lt;emergency&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9201" PostTypeId="2" ParentId="9200" CreationDate="2017-09-10T12:21:49.427" Score="6" Body="&lt;p&gt;In general, the HF bands (1.8 MHz through 30 MHz) do not have sufficient bandwidth to support live transmission of a video signal. In the US, the FCC does not authorize an emission mode for live video on HF. The lowest available band in the US that supports live video is 70 cm (~440 MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are, however, options for transmitting pictures on HF. One of the oldest modes is SSTV (slow scan television). Despite the &quot;TV&quot; designation, it is used for sending relatively low resolution, still images. While SSTV used to require significant hardware to implement a station, this has all been replaced by free software that uses a sound card interface. As a result, there still is significant SSTV activity on HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more contemporary method of sending and receiving pictures on HF is with the FLdigi program. It offers user selectable resolution and it has 24 bit color. The integrity of the received image is based on the signal conditions. FLdigi is popular due to its free software and simple radio interface using a sound card.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PACTOR offers error correction capabilities that can improve digital file reception under varying link conditions. The cost to implement PACTOR is generally higher due to the HF modem that is required and the software licensing schemes of the various versions.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-10T12:29:58.983" LastActivityDate="2017-09-10T12:29:58.983" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9202" PostTypeId="2" ParentId="9200" CreationDate="2017-09-10T14:57:58.340" Score="2" Body="&lt;p&gt;You're asking for quite a lot: high-speed semi-reliable communication over a long range, with little to no infrastructure.  In general that's not possible; if it were, we wouldn't need the internet so much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Glenn's answer covers the HF options.  Satellite is an option if you have a high-gain VHF/UHF antenna, which can be hand-held, but passes for low-Earth-orbiting ham satellites last a few minutes at best and in that time people try to make dozens of contacts, so if you're lucky, you have the equipment and the software to predict passes, and you've practiced beforehand, then you could make a voice contact full of static lasting a few seconds.  That's probably not what you had in mind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's only one high-bandwidth mode that I can think of that might get video out of the hurricane area, and that's Broadband-Hamnet™, formerly called HSMM-Mesh™.  (No, I don't know why someone felt it necessary to trademark the name of a mode.)  The idea is that you take a wireless router such as a Linksys WRT54G, load it with custom firmware, and put a high-gain antenna on it.  The router uses channels 1-6 of the 2.4GHz ISM band, which overlaps with the upper portion of the 13cm amateur radio band.  Your new firmware drives the router to higher power, and range of up to 16 km (10 miles) is allegedly possible with a higher-gain antenna.  The router automatically finds other such routers in range, becoming a node in a mesh of nodes.  Assuming that a reasonably-dense mesh of nodes exists in range, then you have a connection broad enough to support video.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem there of course is that you would need many closely-spaced stations all keeping their equipment dry, their antennas up, and their nodes operational on battery power in a hurricane area.  That's a very demanding requirement that is unlikely to be met.  Given the current state of the art, I'm not surprised that we don't see video clips on the news of hurricanes in action provided by hams.  Sorry!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More information about Broadband-Hamnet™, formerly called HSMM-Mesh™, is available &lt;a href=&quot;http://www.broadband-hamnet.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-09-10T14:57:58.340" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9205" PostTypeId="1" CreationDate="2017-09-11T17:23:36.933" Score="2" ViewCount="272" Body="&lt;p&gt;&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=7e6f5fd156bc0d6dbadff664ff20bb6c&amp;amp;mc=true&amp;amp;node=se47.1.15_123&amp;amp;rgn=div8&quot; rel=&quot;nofollow noreferrer&quot;&gt;Title 47 › Chapter I › Subchapter A › Part 15 › Subpart A › Section 15.23 Home-built devices&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§15.23   Home-built devices.&lt;/p&gt;&#xA;&lt;p&gt;(a) Equipment authorization is not required for devices that are not marketed, are not constructed from a kit, and are built in quantities of five or less for personal use.&lt;/p&gt;&#xA;&lt;p&gt;(b) It is recognized that the individual builder of home-built equipment may not possess the means to perform the measurements for determining compliance with the regulations. In this case, the builder is expected to employ good engineering practices to meet the specified technical standards to the greatest extent practicable. The provisions of §15.5 apply to this equipment.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;You could take a device, that was not marketed as a MURS device and modify it to comply with MURS rules.&lt;/p&gt;&#xA;&lt;p&gt;Making a device does not require a licence, from what I've read or I couldn't find it. If the device is a DIY device it's a Home-built Device. It depends on the interpretation of &amp;quot;marketed device&amp;quot;. Not sure if this has ever been challenged.&lt;/p&gt;&#xA;&lt;p&gt;So technically. Depending on how the FCC interprets &amp;quot;marketed device&amp;quot; as per section 15.23.&lt;/p&gt;&#xA;&lt;p&gt;Even if that is not true, you could technically build a radio transceiver from scratch under those pretences and have it comply with MURS and transmit without a license.&lt;/p&gt;&#xA;&lt;p&gt;I think? I'd rather have someone more knowledgeable chime in. Please? Strictly on FCC rules.&lt;/p&gt;&#xA;&lt;p&gt;Loophole? Or did I miss a FCC section somewhere?&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;This isn't a question about having a license or not to broadcast/transmit.&amp;quot; It's a question on whether a build at home is a work around for a device that is normally required by manufactures the be qualified to sell as a qualified MURS device being used as MURS device for personal use as in Section 15.23.&lt;/p&gt;&#xA;" OwnerUserId="10316" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-09-12T16:53:20.333" Title="Section 15.23 &quot;Home-built devices&quot; No license required... to build? Just to Transmit. But.....?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;diy&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9206" PostTypeId="2" ParentId="9205" CreationDate="2017-09-11T18:24:49.187" Score="1" Body="&lt;p&gt;You can make one. However, as noted by others here, &lt;strong&gt;its power output must be FAR weaker than a legal MURS transceiver that you can buy&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, it'll be almost useless for ordinary purposes, unless you live right next to a MURS repeater (do they exist?).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are FCC laws about &lt;em&gt;type acceptance&lt;/em&gt;. Once you exceed a certain power level, those laws override your reference about low power home-made or modified transmitters for MURS.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-09-12T16:53:20.333" LastActivityDate="2017-09-12T16:53:20.333" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9207" PostTypeId="2" ParentId="9133" CreationDate="2017-09-11T20:02:02.407" Score="1" Body="&lt;p&gt;In this particular application, silicon diodes will almost certainly work just fine. Maybe you will have to increase the output level of the sond card to compensate for the higher forward voltage. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Germanium diodes are often found in older schematics of RF measurement instruments. These designs rely on the characteristics of germanium diodes and you have to consider the specific application to decide if and how you can substitute a different diode. &lt;/p&gt;&#xA;" OwnerUserId="5105" LastActivityDate="2017-09-11T20:02:02.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9208" PostTypeId="2" ParentId="9205" CreationDate="2017-09-11T20:55:05.437" Score="3" Body="&lt;p&gt;Part 15 is a very convoluted document. Reading only one section and trying to apply it to a specific case is not a good practice. One section may seemingly grant broad authority but another section will squash the potential application. You will find sections on home brewing, power limits, authorized frequencies, authorized emission types, and authorized applications. To properly interpret a specific possibility, you must examine all sections of part 15. Often you will find that all other sections seemingly allow your desired outcome but one section will specifically prohibit it. This is the case with your MURS homebrew application.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part 15 does not authorize any MURS type transmissions as made clear by the following that specifically disallows voice transmissions on MURS frequencies. A MURS receiver would be permitted, however. This is the only reference in part 15 that covers the MURS band with regard to allowed uses and emission types:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;§15.231   Periodic operation in the band 40.66-40.70 MHz and above 70 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(a) The provisions of this section are restricted to periodic operation within the band 40.66-40.70 MHz and above 70 MHz. &lt;strong&gt;Except as shown in paragraph (e) of this section, the intentional radiator is restricted to the transmission of a control signal such as those used with alarm systems, door openers, remote switches, etc.&lt;/strong&gt; Continuous transmissions, &lt;strong&gt;voice&lt;/strong&gt;, video and the radio control of toys are &lt;strong&gt;not permitted&lt;/strong&gt;. Data is permitted to be sent with a control signal. The following conditions shall be met to comply with the provisions for this periodic operation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(1) A manually operated transmitter shall employ a switch that will automatically deactivate the transmitter within not more than 5 seconds of being released.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(2) A transmitter activated automatically shall cease transmission within 5 seconds after activation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(3) Periodic transmissions at regular predetermined intervals are not permitted. However, polling or supervision transmissions, including data, to determine system integrity of transmitters used in security or safety applications are allowed if the total duration of transmissions does not exceed more than two seconds per hour for each transmitter. There is no limit on the number of individual transmissions, provided the total transmission time does not exceed two seconds per hour.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(4) Intentional radiators which are employed for radio control purposes during emergencies involving fire, security, and safety of life, when activated to signal an alarm, may operate during the pendency of the alarm condition&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(5) Transmission of set-up information for security systems may exceed the transmission duration limits in paragraphs (a)(1) and (a)(2) of this section, provided such transmissions are under the control of a professional installer and do not exceed ten seconds after a manually operated switch is released or a transmitter is activated automatically. Such set-up information may include data.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-12T02:42:40.423" LastActivityDate="2017-09-12T02:42:40.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9210" PostTypeId="2" ParentId="8899" CreationDate="2017-09-12T18:58:38.040" Score="4" Body="&lt;p&gt;Some of my local public service agencies (fire/police) use sound at the beginning of the transmission (BOT) as a PTT ID (a.k.a. ANI-ID or &quot;signal ID&quot;) giving dispatch the ability to see which unit number is transmitting.  The PTT id is programmed into the radio by our local Kenwood radio re-seller upon request, matching the individual's or vehicle's assigned unit number.  A brief search for ANI-ID and the UV5R yielded references to menu 15.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The BOT tone is quite useful for the following: Someone accidentally keys the mic and you know who it is. A weak signal is heard, dispatch is unable to copy the unit number, but they can see it on the radio console. You forgot who the last person to transmit was but you can see their unit number on the radio display and call back to them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A particular fire agency in the area uses an end of transmission (EOT) tone which in their case appears to be a glorified roger beep. Searches lead me to menu 39, &quot;ROGER&quot; on the UV5R menu.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The EOT tone is controversial as some people believe &quot;roger beeps&quot; are annoying while others argue that it helps prevent units from transmitting before the other is finished as they get used to waiting for the EOT tone.&lt;/p&gt;&#xA;" OwnerUserId="10358" LastEditorUserId="9493" LastEditDate="2017-09-13T12:42:44.390" LastActivityDate="2017-09-13T12:42:44.390" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9211" PostTypeId="2" ParentId="949" CreationDate="2017-09-12T19:08:56.990" Score="1" Body="&lt;p&gt;&lt;strong&gt;It appears that the simple legal answer is YES, BUT.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Transmitting on multiple frequencies is not illegal.&lt;/p&gt;&#xA;&lt;p&gt;You mentioned both 146.340 and 146.940, and those require some care:  If you are on 146.94 that is often a repeater output which would have an input on 146.34 - so even if you can hear people there, it is less likely that they would hear you on that frequency.  To work people on .94 if there is a repeater you will have much greater success transmitting on .34&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;This also means that you would be interfering with the repeater and your own input signal if you transmitted on both .34 and .94 - so that isn't a good idea at all.&lt;/p&gt;&#xA;&lt;p&gt;Plus, when working through repeaters keep in mind that many will want a CTCSS subaudible tone to unlock their squelch.  This often indicates a closed repeater, say for specific club use as opposed to being open to passing tourists.&lt;/p&gt;&#xA;&lt;p&gt;If you transmit without the tone you will likely interfere with an authorized user.  That is a definite NO.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Also, you would transmit a QRZ (pronounced cue-are-zed) instead of a CQ on an FM frequency&lt;/p&gt;&#xA;&lt;p&gt;If you do transmit on more than one frequency at a time, hopefully it is because you have the capability of answering any callbacks on any one of them.  Otherwise it would only add to congestion without any benefit to you.&lt;/p&gt;&#xA;&lt;p&gt;So that part is technically legal.&lt;/p&gt;&#xA;&lt;h2&gt;Always remember:  As with all things FCC, the paramount rule is that we never interfere with any licensed service, and that includes other hams.&lt;/h2&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-09-12T19:25:31.067" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9212" PostTypeId="1" CreationDate="2017-09-12T22:24:26.610" Score="1" ViewCount="38" Body="&lt;p&gt;I have the spectrum binned into 5kHz bins.  For each bin, I'd like to determine (via software) whether what's in that bin is primarily signal (an FM broadcast station; a ham repeater) or noise (just noise floor - no users).  Is there a standard measurement / algorithm / time-series approach for such a thing?&lt;/p&gt;&#xA;" OwnerUserId="850" LastActivityDate="2017-09-12T22:24:26.610" Title="Determining if what's on a frequency is signal, or noise" Tags="&lt;signal-identification&gt;&lt;noise&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2017-09-13T07:49:28.623" ContentLicense="CC BY-SA 3.0" />
  <row Id="9213" PostTypeId="1" CreationDate="2017-09-13T10:12:24.683" Score="0" ViewCount="60" Body="&lt;p&gt;I have a G5RV antenna.  It used to work fine.  I had it disconnected for several months.  Now I can't get it to load. I think there may be a short or open in the coax. Is there a way to determine how far out on the coax the problem might be?  Much of it is under the house and I am disabled.&lt;/p&gt;&#xA;" OwnerUserId="10361" LastActivityDate="2017-09-14T23:24:53.903" Title="Determing short or open location in antenna system" Tags="&lt;antenna-system&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9214" PostTypeId="2" ParentId="9213" CreationDate="2017-09-13T11:24:22.307" Score="4" Body="&lt;p&gt;Many of the newer antenna analyzers have the ability to locate the distance to fault on a coax transmission line. If you do not have one, usually someone in your local ham club is willing to loan one or even come out to assist with the troubleshooting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a G5RV antenna, often the problem can be in the window line connections either at the center of the antenna or where it transitions to coax cable. Corrosion from the elements is a typical problem. Unfortunately, this is difficult to determine remotely - you generally need to lower the antenna and do a hands on inspection.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-13T11:24:22.307" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9215" PostTypeId="1" AcceptedAnswerId="9634" CreationDate="2017-09-13T11:39:21.390" Score="3" ViewCount="451" Body="&lt;p&gt;I'm thinking of making my own band decoder (arduino or raspberry pi) for my Yaesu and my SunSDR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Online there are multiple sources with the BCD codes Yaesu uses but nowhere do I see a specific code for the 60m band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a code for this band? If there is, what is it?&lt;/p&gt;&#xA;" OwnerUserId="9532" LastEditorUserId="9493" LastEditDate="2017-09-13T12:44:16.817" LastActivityDate="2018-01-16T23:50:13.123" Title="Is there a Yaesu BCD code for the 60m band?" Tags="&lt;yaesu&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9216" PostTypeId="2" ParentId="32" CreationDate="2017-09-13T12:30:06.490" Score="2" Body="&lt;p&gt;Use it everyday. The secret is to forget the magic. Practice or use will always make you better. However, I would not concern myself too much with speed . Readability always wins out. Speed is incidental. The two guys who won't work you because you are too slow will never be missed in the log anyway. &lt;/p&gt;&#xA;" OwnerUserId="10356" LastEditorUserId="9493" LastEditDate="2017-09-13T12:40:12.567" LastActivityDate="2017-09-13T12:40:12.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9217" PostTypeId="2" ParentId="9215" CreationDate="2017-09-13T13:02:33.153" Score="2" Body="&lt;p&gt;Hex 0A is used for 60 meters on Yaesu radios that natively operate on 60 meters.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-13T13:02:33.153" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9218" PostTypeId="1" AcceptedAnswerId="9219" CreationDate="2017-09-13T14:31:10.430" Score="0" ViewCount="321" Body="&lt;p&gt;I´m using the Yaesu FT-8800 with the Byonics TinyTrak4 as APRS tracker in my car. There is a menu setting to bind the data jack to a VFO, but transmission is always done using main VFO. So if I talk to someone using the second VFO, the modem will send its beacon to the voice QRG.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since a few days I´m working on a modification to the rig, but I want to be sure this is really needed. My modification will intercept the communication between the main CPU and the panel CPU and supress the data transmission while in QSO...&#xA;Its open source - if you are interested have a look at &lt;a href=&quot;http://github.com/thosch1800/FT8800mod&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://github.com/thosch1800/FT8800mod&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question: Does someone know a way around (without any modification)?&#xA;I wonder if I´m the only one who owns this setup and is not comfortable with it...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: I want to be able to use my radio like a normal radio - grab the mic and start talking - plus the APRS via TT4. In my opinion it has many benefits: You need only one antenna, only one device, your able to use it like a 'normal' radio. &lt;/p&gt;&#xA;" OwnerUserId="10331" LastEditorUserId="10331" LastEditDate="2017-09-14T07:38:52.473" LastActivityDate="2017-09-14T07:55:03.107" Title="Yaesu FT-8800 + TinyTrak4" Tags="&lt;aprs&gt;&lt;yaesu&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9219" PostTypeId="2" ParentId="9218" CreationDate="2017-09-13T18:54:05.383" Score="0" Body="&lt;p&gt;I believe you may have misinterpreted the menu setting. You can select the packet   &lt;strong&gt;&lt;em&gt;receiving&lt;/em&gt;&lt;/strong&gt; band (main, right, left)  but the packet &lt;strong&gt;&lt;em&gt;transmitting&lt;/em&gt;&lt;/strong&gt; band is fixed on the main band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TinyTrak4 has a PTT input connection for the purpose of suppressing data transmissions when the transmitter is in use for other purposes. This would seem to be a good fit for your use case. To take advantage of this feature, simply route your microphone PTT line to this input. When the TT4 sees this input is grounded (via the microphone PTT), it will suppress transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are concerned about the TT4 interrupting a QSO when you are not transmitting but listening to the other station, you could add a delay timer (e.g. 555) to the PTT input to the TT4. Setting the timer for 4 or 5 minutes would hold of any TT4 transmissions during the course of most QSOs.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-14T07:55:03.107" LastActivityDate="2017-09-14T07:55:03.107" CommentCount="11" ContentLicense="CC BY-SA 3.0" />
  <row Id="9220" PostTypeId="1" AcceptedAnswerId="9221" CreationDate="2017-09-13T19:07:12.737" Score="6" ViewCount="1496" Body="&lt;p&gt;I mounted a small RX antenna (mini whip, bought from eBay) (on 10-th floor) and I want to try to listen to something. I bought a RTL-SDR with Upconverter which supports HF. RX antenna's operating range is 100kHz - 30Mhz. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;If I want to listen something. I need to set some frequency with SDR&#xA;app? And wait all the time.  At now I'm using CubicSDR and sometimes Gqrx. Frequency spectrum is so big 100kHz - 30 Mhz. Is it possible use auto search?&lt;/li&gt;&#xA;&lt;li&gt;Which frequencies to try ? I'm live in eastern Europe, Lithuania. Near Baltic sea.&lt;/li&gt;&#xA;&lt;li&gt;Is it possible to make SDR app to disable big loud noise. I want to&#xA;set trigger. If threshold exceeded I want to hear something. Are&#xA;current SDR apps capable of doing this ?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I am willing to try SDR Sharp or HD SDR. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I successfully hear AM radio stations. But I want to hear something from ham radio operators (even though I can't transmit).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9iMKg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9iMKg.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10364" LastEditorUserId="8832" LastEditDate="2017-09-15T06:10:58.510" LastActivityDate="2017-09-15T20:56:04.177" Title="RX antenna and RTL SDR with upconverter ..How to hear something?" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;transverter&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9221" PostTypeId="2" ParentId="9220" CreationDate="2017-09-14T01:04:50.013" Score="7" Body="&lt;p&gt;Fun setup! I have many of the same components and need to try them out myself, but here's a general outline. (Plenty of this may be review for you, but I'm including it for others who may not be as familiar with your equipment.)&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;The antenna&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/D4Fwo.jpg&quot; alt=&quot;Another picture of the antenna, from somewhere&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;a href=&quot;http://dl1dbc.net/SAQ/miniwhip.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;miniwhip&lt;/a&gt; (see also &lt;a href=&quot;http://owenduffy.net/antenna/PA0RDT-MiniWhip/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this article&lt;/a&gt; and &lt;a href=&quot;http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this PDF&lt;/a&gt;) is an active antenna taken to the extreme: it uses a tiny conductor to intercept a tiny bit of broadband electromagnetic field, and then amplifies it by a huge amount — perhaps on the order of +35dB gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being an active antenna it will either need to be plugged in to a DC power source, or (as is more typical) you can &quot;phantom power&quot; it via a &lt;a href=&quot;http://www.kb6nu.com/power-remote-devices-via-yourfeedline/&quot; rel=&quot;nofollow noreferrer&quot;&gt;bias tee&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the antenna is &lt;a href=&quot;http://www.pa3fwm.nl/technotes/tn07.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;amplifying the difference&lt;/a&gt; between its whip/plate and its ground:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;without any conductive connection to the outside, the entire circuit will be at the same potential&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The typical installation recommendation has you attach the ground (or the shielded outside of its coax connection) of the miniwhip to a conductive and grounded mast. For example, &lt;a href=&quot;http://www.ebay.com/itm/MiniWhip-Active-Antenna-Assembled-in-Box-HF-LF-VLF-mini-whip-sdr-RX-portable-swl-/222469570201&quot; rel=&quot;nofollow noreferrer&quot;&gt;this eBay listing&lt;/a&gt; mentions:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For max. sensitivity:&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;this antenna should be positioned as high and free from metal conductors as possible.&lt;/li&gt;&#xA;  &lt;li&gt;the ground plane of the PCB must NOT be lower than the top of the mast. (the connection to and the antenna surface itself must be ABOVE&#xA;  the top of the mast).&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;  &#xA;  &lt;p&gt;For best signal-to-noise ratio:&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;install the Miniwhip onto a well grounded mast.&lt;/li&gt;&#xA;  &lt;li&gt;connect &quot;GND&quot; of the Miniwhip PCB to that mast.&lt;/li&gt;&#xA;  &lt;li&gt;place HI-Ui ferrite cores […] on the beginning and end of all cables to block cable noise currents.&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Generally with this antenna you are encouraged to avoid electrical noise on the whip and/or its grounding as much as possible. However, that may be something to go back and optimize &lt;em&gt;after&lt;/em&gt; you've addressed the next topic…&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Avoiding overload&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Feeding a broadband active antenna into an 8-bit SDR without filtering will almost certainly cause all sorts of distortion/intermodulation/overload issues in the presence of strong signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You mentioned that you &lt;em&gt;could&lt;/em&gt; hear &quot;radio stations&quot; which I assume are high-power broadcast transmissions. These loud signals might be preventing you from receiving anything else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the &quot;AM broadcast&quot; band in the USA, I found this &lt;a href=&quot;http://www.ok1rr.com/index.php/technical-topics/40-an-efficient-mw-band-stop-filter&quot; rel=&quot;nofollow noreferrer&quot;&gt;AM band-stop filter&lt;/a&gt;. These MW broadcasts do vary from region to region, for example I also found a design apparently for &lt;a href=&quot;http://vk3il.net/projects/broadcast-band-filter/&quot; rel=&quot;nofollow noreferrer&quot;&gt;blocking similar in Australia&lt;/a&gt;. In Europe you may need a couple bandstop filters for various local AM and shortwave bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(As mentioned above, nearby electrical noise from computers and power supplies can also make strong interference.)&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Upconverted frequencies&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Since the RTL-SDR only tunes down to about 27MHz or so, you will need either a &lt;a href=&quot;https://www.rtl-sdr.com/direct-sampling-mode-hardware-modifcations/&quot; rel=&quot;nofollow noreferrer&quot;&gt;direct sampling modification&lt;/a&gt; or an upconverter to tune in to most of the HF and lower frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounds like you have an &lt;a href=&quot;https://en.wikipedia.org/wiki/Heterodyne#Up_and_down_converters&quot; rel=&quot;nofollow noreferrer&quot;&gt;upconverter&lt;/a&gt;, so you need to find the &quot;local oscillator&quot; frequency, it may be written on the device or should be listed amongst its specifications. My &quot;full band&quot; RTL-SDR unit has an integrated upconverter using 100MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The external &lt;a href=&quot;http://www.nooelec.com/store/ham-it-up.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ham It Up v1.3&lt;/a&gt; uses 125MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically what an upconverter ends up doing is &quot;adding&quot; its local oscillator frequency to every signal. So if you wanted to listen to 1040 kHz using a 125MHz upconverter, you would need to tune your SDR app to 126.04MHz at first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this is a common technique and so most apps let you enter in this frequency offset so that the display becomes more natural. For example, Gqrx calls this the &quot;LNB LO&quot; input control. CubicSDR has something similar, iirc. Note that in some apps you have to enter &quot;-125 MHz&quot; (negative) and in others you just use &quot;+125&quot;. Once you configure this, to tune e.g. 1040kHz you type in 1.040MHz directly in the display and the SDR app calculates the proper actual frequency for you.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Which frequencies to try?&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;If you're looking to hear Amateur Radio activity, you can start by consulting a &lt;a href=&quot;http://www.arrl.org/graphical-frequency-allocations&quot; rel=&quot;nofollow noreferrer&quot;&gt;band chart&lt;/a&gt; for the overall ranges where hams are allowed to operate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Within each of these allocations, there is typically a &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow noreferrer&quot;&gt;band plan&lt;/a&gt; that divides the available spectrum into particular frequencies recommended for particular activities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The band chart/plans linked above are published by ARRL, the big ham lobbyist organization in the USA. Note that amateur allocations vary slightly between nations and regions. But since it's all ultimately coordinated via the ITU, there's typically a lot of overlap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I am looking for amateur signals, I often start with the &lt;a href=&quot;http://hflink.com/jt65/&quot; rel=&quot;nofollow noreferrer&quot;&gt;JT65&lt;/a&gt; frequencies since those &quot;channels&quot; tend to provide a good density of long transmissions despite the low power typically used. E.g. if you listen at 7.039 or 7.076 MHz using an upper sideband decoder, you might hear a few 40m transmissions piled close together, sounding &lt;a href=&quot;https://youtu.be/fLI61ymgpjw?t=230&quot; rel=&quot;nofollow noreferrer&quot;&gt;almost like bad music&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Squelch the static&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;You are looking to &quot;disable big loud noise&quot;, which made me first think of a &lt;a href=&quot;https://ham.stackexchange.com/questions/1124/what-does-a-noise-blanker-really-do-and-what-are-the-side-effects&quot;&gt;noise blanker&lt;/a&gt; but your description about setting a trigger level sounds more like &lt;a href=&quot;https://en.wikipedia.org/wiki/Squelch#Carrier_squelch&quot; rel=&quot;nofollow noreferrer&quot;&gt;squelch&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most full-featured SDR apps have both noise blanking (NB) and squelch too. Sometimes there are even separate RF (radio frequency, meaning the input signal) and AF (audio frequency, meaning the decoded/demodulated signal) squelch options. They vary from app to app and sometimes I've found using them to be confusing, but most SDR apps should have them if you know where to look.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-09-15T20:56:04.177" LastActivityDate="2017-09-15T20:56:04.177" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9222" PostTypeId="1" AcceptedAnswerId="9223" CreationDate="2017-09-14T14:09:12.583" Score="2" ViewCount="395" Body="&lt;p&gt;For the purposes of this question, I am considering purchasing a Kenwood TM-D710GA (or a RC-D710). The control panel has a mounting bracket for mobile use which is intended to be attached to a flat surface, but I haven't found any description of how large the bracket is so I can tell whether it will fit where I have in mind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the dimensions of this bracket?&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-09-14T14:09:12.583" Title="What size is the Kenwood TM-D710 panel mounting bracket?" Tags="&lt;mobile&gt;&lt;kenwood&gt;&lt;installation&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9223" PostTypeId="2" ParentId="9222" CreationDate="2017-09-14T14:09:12.583" Score="6" Body="&lt;p&gt;This image of the bottom side of the bracket was taken with a flatbed scanner. The depicted dimensions were taken separately using a caliper, not by measuring on the image. The white inner area is the paper over an as-yet-unused adhesive pad; the material of the bracket is black-painted metal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2sjBd.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2sjBd.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1S1J3.jpg&quot; rel=&quot;noreferrer&quot;&gt;Unprocessed image&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-09-14T14:09:12.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9224" PostTypeId="2" ParentId="9213" CreationDate="2017-09-14T23:24:53.903" Score="1" Body="&lt;p&gt;What you are looking for is a Time Domain Reflectometer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sends signals down the line, reads the reflections and determines the distance to any impedance changes. See if one of your more well equipped Elmer's has an antenna analyzer with this feature and it will tell you a lot about your setup, including how bad your connections are.&lt;/p&gt;&#xA;" OwnerUserId="4207" LastActivityDate="2017-09-14T23:24:53.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9226" PostTypeId="5" CreationDate="2017-09-15T17:25:27.040" Score="0" Body="&lt;p&gt;In the US, there are special rules that may be applicable:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=1&amp;amp;SID=e6c60d4d2c66825fc345c0c99db26a99&amp;amp;ty=HTML&amp;amp;h=L&amp;amp;n=47y5.0.1.1.6&amp;amp;r=PART&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.215&lt;/a&gt;   Telecommand of model craft.&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;An amateur station transmitting&#xA;  signals to control a model craft may be operated as follows:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) The station identification procedure is not required for&#xA;  transmissions directed only to the model craft, provided that a label&#xA;  indicating the station call sign and the station licensee's name and&#xA;  address is affixed to the station transmitter.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) The control signals are not considered codes or ciphers intended&#xA;  to obscure the meaning of the communication.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(c) The transmitter power must not exceed 1 W.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;[54 FR 25857, June 20, 1989, as amended at 56 FR 56171, Nov. 1, 1991]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-09-15T17:25:27.040" LastActivityDate="2017-09-15T17:25:27.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9227" PostTypeId="4" CreationDate="2017-09-15T17:25:27.040" Score="0" Body="Control via radio of model/unmanned vehicles (most commonly model airplanes, quadcopters, etc.) and similar applications." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-09-15T17:25:27.040" LastActivityDate="2017-09-15T17:25:27.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9228" PostTypeId="5" CreationDate="2017-09-16T01:06:47.397" Score="0" Body="&lt;p&gt;Use this tag when the topic is related to true noise blankers that remove short impulses from the input signal, as opposed to noise limiters which are more like AGCs&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most famous noise blankers were very popular in the 80s and designed to blank out the impulses generated by Duga-3, AKA The Woodpecker.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-09-21T19:06:59.990" LastActivityDate="2017-09-21T19:06:59.990" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9229" PostTypeId="4" CreationDate="2017-09-16T01:06:47.397" Score="0" Body="Use this tag when the topic is related to true noise blankers that remove short impulses from the input signal, as opposed to noise limiters which are more like AGCs" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-09-21T19:06:54.633" LastActivityDate="2017-09-21T19:06:54.633" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9231" PostTypeId="2" ParentId="3680" CreationDate="2017-09-17T18:22:58.760" Score="-1" Body="&lt;p&gt;Tone decoding is a bit more problematic on SSB. So PL tones may not be detected if the SSB receiver's BFO is off. AM would be better at tone detection. FM is superior due to the FM capture effect for multiple keying transmitters. AM tends to allow noisy hetrodyning with multiple transmitters at the same time (i.e. double-keying). I personally suggest FreeDV over SSB with tone decoding. &lt;a href=&quot;http://www.freedv.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.freedv.org/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10379" LastActivityDate="2017-09-17T18:22:58.760" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="9232" PostTypeId="2" ParentId="1507" CreationDate="2017-09-20T06:43:53.313" Score="0" Body="&lt;p&gt;&lt;strong&gt;I do believe that it is indeed good amateur practice to do what is prudent to keep your equipment from being misused, yes.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;But let's examine the legal aspects of the rules:&lt;/p&gt;&#xA;&lt;p&gt;To quote the section in question:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§97.103   Station licensee responsibilities.&lt;/p&gt;&#xA;&lt;p&gt;(a) The station licensee is responsible for the proper operation of the station in accordance with the FCC Rules. When the control operator is a different amateur operator than the station licensee, both persons are equally responsible for proper operation of the station.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The only issue mentioned is &amp;quot;operation&amp;quot; of the station.&lt;/p&gt;&#xA;&lt;p&gt;Back up a but and you find this:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Subpart B—Station Operation Standards&lt;/p&gt;&#xA;&lt;p&gt;§97.101   General standards.&lt;/p&gt;&#xA;&lt;p&gt;(a) In all respects not specifically covered by FCC Rules each amateur station must be operated in accordance with good engineering and good amateur practice.&lt;/p&gt;&#xA;&lt;p&gt;(b) Each station licensee and each control operator must cooperate in selecting transmitting channels and in making the most effective use of the amateur service frequencies. No frequency will be assigned for the exclusive use of any station.&lt;/p&gt;&#xA;&lt;p&gt;(c) At all times and on all frequencies, each control operator must give priority to stations providing emergency communications, except to stations transmitting communications for training drills and tests in RACES.&lt;/p&gt;&#xA;&lt;p&gt;(d) No amateur operator shall willfully or maliciously interfere with or cause interference to any radio communication or signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It is very clear that the rules are very specifically addressing the operation of stations.&lt;/p&gt;&#xA;&lt;p&gt;There is no rule guidance regarding idle equipment since it cannot violate these guidelines.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;It is very clear that operation of equipment requires certain conditions be met, as per:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§97.7   Control operator required.&lt;/p&gt;&#xA;&lt;p&gt;When transmitting, each amateur station must have a control operator. The control operator must be a person:&lt;/p&gt;&#xA;&lt;p&gt;(a) For whom an amateur operator/primary station license grant appears on the ULS consolidated licensee database, or&lt;/p&gt;&#xA;&lt;p&gt;(b) Who is authorized for alien reciprocal operation by §97.107 of this part.&lt;/p&gt;&#xA;&lt;p&gt;[63 FR 68978, Dec. 14, 1998]&lt;/p&gt;&#xA;&lt;p&gt;§97.9   Operator license grant.&lt;/p&gt;&#xA;&lt;p&gt;(a) The classes of amateur operator license grants are: Novice, Technician, General, Advanced, and Amateur Extra. The person named in the operator license grant is authorized to be the control operator of an amateur station with the privileges authorized to the operator class specified on the license grant.&lt;/p&gt;&#xA;&lt;p&gt;(b) The person named in an operator license grant of Novice, Technician, General or Advanced Class, who has properly submitted to the administering VEs a FCC Form 605 document requesting examination for an operator license grant of a higher class, and who holds a CSCE indicating that the person has completed the necessary examinations within the previous 365 days, is authorized to exercise the rights and privileges of the higher operator class until final disposition of the application or until 365 days following the passing of the examination, whichever comes first.&lt;/p&gt;&#xA;&lt;p&gt;[75 FR 78169, Dec. 15, 2010]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Therefore, any uauthorized operation violates the rules, and the violator is the person who initiates such unauthorized emissions.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&lt;strong&gt;So, to answer your question:  &amp;quot;Do I actually need to lock up my station?&amp;quot; - the answer is based on your opinion of whether you feel a responsibility to prevent others from utilizing your equipment to break the law, and whether or not it requires that specific action.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-09-20T06:43:53.313" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9236" PostTypeId="2" ParentId="6404" CreationDate="2017-09-21T18:19:42.060" Score="4" Body="&lt;p&gt;A Technician Class license or better is required.  What equipment you need very much depends on the solution or solutions you pursue.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There exist well-baked schemes for creating relatively long distance vhf/uhf ham-radio-exclusive networks where radios are used to tie stations together over short range, and then many hops are used to pass traffic across longer distances.  These schemes include using off-the-shelf commercial WI-FI type gear with and without ham-radio-specific firmware.  See Broadband Hamnet/HSMM or &lt;a href=&quot;http://www.aredn.org/&quot; rel=&quot;noreferrer&quot;&gt;ARDEN&lt;/a&gt;.  Other methods use regular voice FM transceivers, off-the-shelf hardware modems (TNC-PI) or software emulated modems (DireWolf) and a Raspberry PI or other inexpensive computer, to do the links between stations.  See &lt;a href=&quot;http://tarpn.net/t/packet_radio_networking.html&quot; rel=&quot;noreferrer&quot;&gt;TARPN&lt;/a&gt;.&lt;br&gt;&#xA;&lt;p&gt;&#xA;One thing many ham radio operators don't consider as a solution, and your question kind of speaks to this, is that an individual can locate equipment in other locations or sites to boost your ability to 'get out'.   A person living in a condo in a valley can take advantage of a hilltop location.  Sometimes hams buy hilltop houses and sometimes those hams actually like participating in big projects.  Considering how inexpensive, small, and reproducible,  packet radio solutions can be, owning and operating two stations is well within the realm of possibility.  Having built two stations, you have now developed the expertise to construct a network.  Now all you need is participants.&lt;br&gt;&#xA;&lt;p&gt;&lt;/p&gt;&#xA;" OwnerUserId="10394" LastActivityDate="2017-09-21T18:19:42.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9237" PostTypeId="2" ParentId="6545" CreationDate="2017-09-21T19:01:05.903" Score="2" Body="&lt;p&gt;I recommend against using the modern inexpensive HT radios for packet, especially if you are buying the equipment on purpose for that application. You'd be much better off with 30 year old used ham radio mobile gear, with more power, more selective receiver, more predictable operation, easier UI, and less RF into your digital equipment, easier connections, easier power hookup, and nearly the same cost.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A serious consideration with modern HTs is that the designers are interesting in optimizing voice quality and battery life with no consideration for how this impacts packet radio use.  Sacrifices can easily be made which increase usability for voice, but which make packet radio work worse and be more difficult to align.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Audio level consistency.  A packet radio receiver modem wants to see an audio level that is both consistent across a packet, but also nearly the same for multiple tone frequencies on a packet.  FM voice radios don't need to behave in this way.  Indeed, voice compression, bad for packet, actually sounds great on voice. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;DC signals (BIAS) on the receive audio are also OK for FM voice, especially with built in speaker equipment, but this also is of questionable value for a packet radio modem.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;POP and CLICK removal: It is easy to remove pops and clicks from the audio by replacing annoying wave forms with duplicates of preceding or following wave forms, or by shifting the time of the wave forms.  This is a well documented (and no longer patented) scheme used originally in broadcast radio transmission.  This makes the receiver sound much better, at low cost, but makes packets less reliable, and this effect is nearly undetectable without an analog equipped logic analyzer.  It's very confusing.  I have on low authority that this is done in modern 2-way FM radio-on-a-chip devices.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Battery saving by disabling the radio: By having the control processor leave elements of the radio disabled for periods of time the radio can use less battery power while quiescent, but it would also not be awake to notice the start of a packet message.  Baofeng radios are replete with this technology.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Chinese brand-name radios have been known to emit energy at frequencies outside the ham band at levels beyond those permitted by the various government radio authorities (D.O.C. in Canada, F.C.C. in the USA).  They have also been known to emit radio waves at near transmission levels through the chassis which can impact the stability of DC wiring in the vicinity of the radio.  This is also confusing to somebody new to integrating digital, audio and RF equipment. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Used 2-way or ham radio equipment is particularly applicable to packet radio.  A used ham radio which is missing the critical CTCSS PL TONE generator is nearly useless for repeater operation but is very usable for packet radio.  Kenwood TM2550, TM7950, TM7800, are perfectly fine packet radios and are 25 watts output or better.  Yeasu and Icom have offerings in the same age-class.  Because they are not useful to non-packet hams, they show up for low prices, even competitive with brand new Baofeng UV5R radios.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the commercial 2-way market, the Kenwood TK705d or TK805d is a fine radio for packet.  Those are on ebay at under $50 delivered, even as I type.  While some commercial 2-way radios need PCs and software to program, the TK705d and TK805d are front panel programmable, or can be made that way by moving or adding a 2-pin jumper.  &lt;/p&gt;&#xA;" OwnerUserId="10394" LastActivityDate="2017-09-21T19:01:05.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9238" PostTypeId="1" AcceptedAnswerId="9294" CreationDate="2017-09-21T21:20:42.943" Score="0" ViewCount="947" Body="&lt;p&gt;The &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B01BSL58Z6&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Baofeng GT-3WP&quot;&gt;Baofeng GT-3WP&lt;/a&gt; has a feature labeled &quot;Cross band reception / transmission&quot;.  Does that mean it will function as a Cross-Band Repeater?&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="8832" LastEditDate="2017-10-02T03:55:41.383" LastActivityDate="2017-10-02T03:55:41.383" Title="Baofeng GT-3WP Cross Band Operation?" Tags="&lt;baofeng&gt;&lt;crossband-repeat&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9239" PostTypeId="5" CreationDate="2017-09-21T21:24:11.463" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2017-09-21T21:24:11.463" LastActivityDate="2017-09-21T21:24:11.463" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9240" PostTypeId="4" CreationDate="2017-09-21T21:24:11.463" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2017-09-21T21:24:11.463" LastActivityDate="2017-09-21T21:24:11.463" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9241" PostTypeId="2" ParentId="9238" CreationDate="2017-09-21T22:18:34.567" Score="1" Body="&lt;p&gt;The manual for that radio doesn't seem to specify, so I would guess that it is capable of communicating with a cross-band repeater, but probably not capable of acting as one. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Found the manual here:&#xA;&lt;a href=&quot;http://s3.image.ro.s3.amazonaws.com/download/GT-3WP-manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://s3.image.ro.s3.amazonaws.com/download/GT-3WP-manual.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9631" LastActivityDate="2017-09-21T22:18:34.567" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9243" PostTypeId="2" ParentId="8919" CreationDate="2017-09-22T16:16:22.673" Score="1" Body="&lt;p&gt;You might try taking a image capture of the spectrum waterfall for some duration, and feeding that image to a machine learning inference engine, perhaps a DNN.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The inference engine could be trained on a large image database with lots of waterfalls of lots of known or suspected signal types, similar to these signal ID databases: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.sigidwiki.com/wiki/Signal_Identification_Guide&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.sigidwiki.com/wiki/Signal_Identification_Guide&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://qrznow.com/signal-identification-guide/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://qrznow.com/signal-identification-guide/&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2017-09-22T16:16:22.673" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9244" PostTypeId="1" AcceptedAnswerId="9245" CreationDate="2017-09-22T16:36:32.290" Score="1" ViewCount="305" Body="&lt;p&gt;What I have:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;GSM 900 repeater&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;900 - 2400 MHz MIMO antenna 2xSMA&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;MIMO 4G Router works with 1800 MHz LTE&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Is it a good idea to connect GSM repeater via SMA splitter to one of the antenna cables? Will the devices interfere with each other?&lt;/p&gt;&#xA;" OwnerUserId="10399" LastEditorUserId="76" LastEditDate="2017-09-22T18:29:58.337" LastActivityDate="2017-09-22T21:09:47.437" Title="Two devices + one antenna" Tags="&lt;repeater&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9245" PostTypeId="2" ParentId="9244" CreationDate="2017-09-22T18:29:21.950" Score="2" Body="&lt;p&gt;There are different ways to “split” a coaxial connection, and some of them are wrong.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The simplest, cheapest thing you would find in SMA form factor is a &lt;em&gt;tee,&lt;/em&gt; a small device with 3 SMA (or other coaxial) connectors. &lt;strong&gt;You should not use this&lt;/strong&gt; because it will allow the transmission of one device into the receiver of the other, possibly damaging it with the high power. Also a tee used without care creates an impedance mismatch. Correct uses of a tee are either carefully-measured cases like matching stubs, connecting high-input-impedance test gear such as an oscilloscope, or very low-frequency applications where transmission line length is unimportant.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You could use a &lt;em&gt;power divider&lt;/em&gt; (or combiner, it's the same thing) — this is the same type of device as used to connect multiple TVs to one cable-TV or antenna cable. This will work in principle but the devices may interfere with each other, and the incoming signal will be reduced by 3 dB.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The best solution in this case, where the two devices are widely separated in frequency, is known as a &lt;strong&gt;diplexer&lt;/strong&gt; or &lt;strong&gt;duplexer&lt;/strong&gt;. It has three ports, one which you would connect to the antenna and two more which are frequency-specific. You would choose a diplexer whose lower-frequency range includes 900 MHz and whose higher-frequency range includes 1800 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the diplexer contains filters, it will reduce interference between the two devices (if any). In fact, it &lt;em&gt;might&lt;/em&gt; be even better than using separate antennas — but it depends a lot on the characteristics and quality of the devices' receivers and transmitters whether there will be a problem at all in either case.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-09-22T21:09:47.437" LastActivityDate="2017-09-22T21:09:47.437" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9246" PostTypeId="1" AcceptedAnswerId="9248" CreationDate="2017-09-22T23:06:18.323" Score="1" ViewCount="1371" Body="&lt;p&gt;So, I'm currently tinkering with a RTL SDR dongle and want to put an external antenna in the proper way (i.e. not by soldering a random wire on the included mcx terminated coax) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was about to buy a proper MCX-SMA pigtail and some soldering connectors, but I keep reading in descriptions things like &quot;sma male connector (... random chinglish... ) RG XXX&quot; where xxx designates a rg standard. It is my understanding that connectors have a specific width to put the coax core in. I had no idea about this. Is this critical in mounting the connector? Is it ok to get a bunch of RG-58 sized connectors so that thinner types of coax will fit as well?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you and sorry for my English &lt;/p&gt;&#xA;" OwnerUserId="10400" LastActivityDate="2017-09-23T05:58:46.133" Title="SMA connector sizes" Tags="&lt;coaxial-cable&gt;&lt;connectors&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9247" PostTypeId="2" ParentId="9246" CreationDate="2017-09-23T00:28:23.097" Score="2" Body="&lt;p&gt;Soldering coax to connectors is tricky because it is easy to melt the dielectric. I would not recommend attempting it as a beginner, especially for small coax as typically used for SMA connectors. Crimped connectors are easier and give more reliable results, but require the correct crimp tool and matching all dimensions of the coax to the connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are constructing an antenna, unless the antenna contains coax as part of its design, I would recommend avoiding working with coax at all and instead getting a connector intended for panel or PCB mounting, then soldering the antenna elements to that, then using a separate cable/pigtail to connect the dongle to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if you are specifically looking to work with random wire antennas, I would suggest not soldering anything at all and instead getting a MCX-BNC pigtail and a BNC to binding post adapter. These are both common items and will allow you to simply clamp in any wire with the binding post, or attach an alligator clip, etc. BNC connectors are also much more convenient for experimenting because you can quickly swap between two antennas, and connect a variety of other equipment and adapters.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-09-23T00:28:23.097" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9248" PostTypeId="2" ParentId="9246" CreationDate="2017-09-23T00:35:47.503" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it ok to get a bunch of RG-58 sized connectors so that thinner types of coax will fit as well?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not if you want to do it right. Proper termination of coax requires a smooth transition from the coax shield to the connector. Mechanical compatibility is an issue as well if you don't want your cables constantly breaking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've never seen a solder-on SMA connector except for semi-rigid coax. Usually they come in two kinds: clamp and crimp.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Clamp&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;An example of the clamp type is &lt;a href=&quot;https://www.amphenolrf.com/downloads/dl/file/id/35/product/3098/assembly_instructions_c44.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amphenol 901-128-11&lt;/a&gt;. This has a clamp nut assembly which the cable passes through, then the shield is folded back upon it. The plug then threads onto the clamp nut, with the folded back shield clamped between the two pieces. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JbmCx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JbmCx.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the coax is too large, it will not pass through the clamp nut. If the coax is too small, it might work well enough. The coax will flop around, which will eventually fatigue the metal in the shield. And the geometry of the connector will be out of specification, compromising high frequency performance. Below 1 GHz you may not notice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clamp connectors don't require any special tool to install. That's about the only advantage they have. In an application where the cables are frequently handled, expect them to fail either due to working themselves loose, or from the shield breaking where all the strain is focused at the clamp point.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Crimp&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;An example of a crimp connector is &lt;a href=&quot;https://www.amphenolrf.com/downloads/dl/file/id/6423/product/3034/assembly_instructions_c53.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amphenol 901-9511&lt;/a&gt;. These connector have an inner ferrule which slips between the connector shield and dielectric. An outer ferrule is then crimped over it, making both a solid mechanical and electrical connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ta9e4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ta9e4.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the coax is the wrong size in either direction then the ferrule won't fit at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Crimp connectors are the way to go. You'll have to buy a crimp tool, but they're less clunky, and the crimp provides a more solid mechanical connection which takes the strain off the cable braid. They will never come loose. They never fail.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-09-23T00:35:47.503" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9249" PostTypeId="2" ParentId="9246" CreationDate="2017-09-23T05:58:46.133" Score="1" Body="&lt;p&gt;There are so many, well made adapters and adapter cables available, it hardly pays to try to put one together. Most are available for &amp;lt; $10 USD.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/N6Xjj.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/N6Xjj.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Zp7Lf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Zp7Lf.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-23T05:58:46.133" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9250" PostTypeId="2" ParentId="1007" CreationDate="2017-09-24T07:55:03.287" Score="3" Body="&lt;p&gt;You don't exceed your own license limitations no matter what equipment is available.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there is an Extra-class licensee there then they can operate wherever they are authorized, also.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to your question, they can delegate you to do the contacts as long as they are present and you ID as them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To use their Extra bands they must maintain positive control of the station.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-09-24T22:15:47.373" LastActivityDate="2017-09-24T22:15:47.373" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9251" PostTypeId="2" ParentId="1007" CreationDate="2017-09-24T12:21:39.280" Score="3" Body="&lt;p&gt;The operating frequencies of a station under FCC jurisdiction are determined by the licensing level of the control operator of the station.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;97.105(b) A station may only be operated in the manner and to the extent permitted by the privileges authorized for the class of operator license held by the control operator.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;For you as a general class licensee to have the frequency privileges of an extra class licensee, the extra class control operator must grant you authority to use the station but the extra class licensee must remain the control operator during that time. The extra class control operator is responsible for the proper operation of the station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The station identification consists of the call sign of the station. In the case of a general using an extra class station, this requires that the call sign be that of the extra class station. You are permitted to add your call to the identification, provided it does not conflict with, or cause confusion regarding, the actual station identification.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;97.119(c) One or more indicators may be included with the call sign. Each indicator must be separated from the call sign by the slant mark (/) or by any suitable word that denotes the slant mark. If an indicator is self-assigned, it must be included before, after, or both before and after, the call sign. No self assigned indicator may conflict with any other indicator specified by the FCC Rules or with any prefix assigned to another country.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-24T12:21:39.280" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9252" PostTypeId="2" ParentId="133" CreationDate="2017-09-25T00:19:10.360" Score="3" Body="&lt;p&gt;The type and thickness (up to a point) of the metal plays a key role in the efficiency of the antenna. Efficiency is important because it is efficiency times directivity that determines the gain of the antenna. Thus the greater the efficiency, the greater the gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Efficiency is the ratio of radiation resistance divided by radiation resistance plus resistive losses. The RF resistance of the metals of the antenna are one of the causes of resistive losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the radiation resistance becomes lower, the resistive losses become more critical. So for a 70 ohm, 1/2 wavelength dipole, reasonable resistive losses do not change much. A vertical, 1/4 wave antenna has about 22 ohms of radiation resistance so resistive losses become more significant. For a small diameter, 40 meter loop antenna with a radiation resistance less than 1/10 ohm, the resistive losses become critical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resistive losses of the metal are determined by the type of metal, the surface area and thickness of the metal, and the frequencies involved. The two most common metals for antennas are copper and aluminum. While copper has lower resistive losses, aluminum is lighter and less expensive. However, since copper is more conductive, less material is required to achieve the same RF resistance as aluminum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By way of comparison, 100 feet of  common 14 gauge, copper wire has a resistive loss of ~7.1 ohms on 15 meters while the same wire in aluminum has a resistive loss of ~8.9 ohms. For a 1/2 wave dipole, this difference ratio would be negligible in terms of comparative gains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;5 feet of 1/2 inch copper has a radiation resistance of ~0.02 ohms compared to aluminum with ~0.03 ohms. This difference in a small loop antenna has a substantial influence on the gain of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For standard antenna work, five times the skin depth is the maximum thickness of the conducting material that is required. Beyond this maximum, the material is essentially unused from an RF perspective although it may contribute to other physical properties such as strength. This is why a properly copper coated steel wire can be used to make a wire antenna. As long as the copper has sufficient thickness, the RF current will never reach the much higher loss inner core of steel. On 160 meters, a 5 times skin depth in copper is ~240 micrometers. As the frequency rises, the skin depth decreases. At 10 meters, the 5 times copper skin depth is only ~ 60 micrometers. This also highlights why hollow copper or aluminum tubing can be used to save costs and weight in many cases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RF resistance and skin depth calculators abound on the Internet, making quick comparative analyses possible.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-25T00:19:10.360" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9253" PostTypeId="1" AcceptedAnswerId="9254" CreationDate="2017-09-25T07:09:49.987" Score="1" ViewCount="455" Body="&lt;p&gt;I used an RF generator transmitting FSK packets with a datarate of 50 kbps. The deviation was 12.5 kHz. With this combination of datarate and deviation the modulation index is 0.5. I found that my device undertest had an Rx sensitivity of ~102 dBm. The IF BW is approximately 100 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I left DUT settings untouched. I changed the deviation of the signal sent by the generator from 12.5 kHz to 25 kHz. Datarate remained 50 kbps. This equals to modulation index = 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found out that the sensitivity was a few dB's better. Someone told me that it is because the symbols are further apart from each other in the freq plane, and thus it is easier for the radio to demodulate it. My question is, why the wider deviation is easier for the radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio uses low IF receiver. RF is fed to an I/Q- down conversion mixer. The I/Q signals are sampled by IF ADC.&lt;/p&gt;&#xA;" OwnerUserId="5817" LastEditorUserId="9493" LastEditDate="2017-09-25T07:23:51.303" LastActivityDate="2017-09-26T16:54:57.433" Title="FSK Rx sensitivity with different deviations" Tags="&lt;modem&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9254" PostTypeId="2" ParentId="9253" CreationDate="2017-09-25T07:55:25.287" Score="0" Body="&lt;p&gt;Your receiver has very wide, excessive bandwidth. The amount of noise power reaching the demodulator is a function of receiver bandwidth. With a narrow band transmitted signal, the noise power dominates the demodulated signal. As your transmitted signal becomes wider in bandwidth, it occupies more of the demodulated bandwidth so the signal to noise ratio is improved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may be helpful to think about this in the frequency domain and dividing the received bandwidth spectrum into FFT buckets. Each bucket can be described as having a signal to noise ratio. In those buckets with no signal, the SNR is 0. In the other buckets where there is a signal, the SNR is &gt;0. If we now average the SNR of all of the buckets, we have the SNR of the entire received bandwidth. This analogy shows that for a given receiver and received bandwidth, the more buckets that contain the signal, the better the SNR as viewed over the entire received bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is  worth noting that your two examples transition between narrow band FM and wide band FM. When the DFSK modulation index, &lt;em&gt;h&lt;/em&gt;, is &gt;=1 the signal transitions from having two sidebands to a larger, potentially infinite, number of sidebands. It is also worth noting that the actual bandwidth of your DFSK signal will depend heavily on the keying shape or algorithm of your signal generator. An FM transmitter keyed directly with high dV/dt modulating signals will have a wide transmitted spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The so called Carson rule states that 98% of the signal power of an FM transmitter is contained within a bandwidth equal two times the sum of the deviation frequency and the modulation frequency, This is considered the minimum bandwidth to prevent excess distortion:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ BW_{98\%} = 2 \times  \left( \Delta F + FM \right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you would like to see an improvement in received signal sensitivity, use the minimum necessary transmit bandwidth and narrow your receiver IF bandwidth accordingly. This will minimize the noise power entering your demodulator and thus raise the SNR (Signal to Noise Ratio) of the receiver. &#xA;As an example, going from a 100 kHz receive bandwidth to a 15 kHz bandwidth will improve the SNR by over 8 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 10 \times log \left( \frac{BW_A}{BW_B} \right) = \Delta SNR $$&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-26T16:54:57.433" LastActivityDate="2017-09-26T16:54:57.433" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9255" PostTypeId="1" AcceptedAnswerId="9264" CreationDate="2017-09-25T15:58:45.623" Score="3" ViewCount="426" Body="&lt;p&gt;My club has a well used Motorola branded StationMaster UHF repeater antenna that needs to be sanded and recoated.  Besides the surface, the antenna is in very good working order so we're not interested in recommendations to replace it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen many recommendations to use products like U/V resistant polyurethane or any non-metallic U/V resistant paint. What I'd like to know is if any of you have actually had good results refinishing an antenna and what specific products you used.&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2017-09-28T01:29:27.080" LastActivityDate="2017-09-28T01:29:27.080" Title="Good Coating for a Radome" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9256" PostTypeId="1" CreationDate="2017-08-01T00:55:48.337" Score="3" ViewCount="140" Body="&lt;p&gt;I know for part 15 licensed devices, there's special FCC certification, and something similar on the Canadian side. What about for amateur radio transmitters? They follow part 97 laws, and it's the responsibility of the operator to ensure no interference. Do they still need to be FCC certified? How about on the Canadian side?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I'm a Canadian selling across the border to the US, do I need Industry Canada + FCC certification? If I only have IC, for instance, do I have to make sure nobody from the US buys my product?&lt;/p&gt;&#xA;" OwnerUserId="9218" OwnerDisplayName="Stephen" LastEditorUserId="76" LastEditDate="2017-09-25T18:52:17.960" LastActivityDate="2017-09-27T16:09:00.010" Title="What are FCC/Industry Canada certification requirements for amateur radio related products?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;&lt;canada&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9257" PostTypeId="1" AcceptedAnswerId="9268" CreationDate="2017-09-25T18:50:08.730" Score="4" ViewCount="292" Body="&lt;p&gt;I have a friend of mine that is from Puerto Rico, and hasn't heard from her family in some time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am aware of the NTS, and have considered sending a message into the area to see if any word of her family could be determined.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure what the protocol is, in a time that might be very difficult and high priority communication is required. Is there anything I should know about making an attempt to send a NTS message to check on the welfare of her family? &lt;/p&gt;&#xA;" OwnerUserId="13" LastEditorUserId="76" LastEditDate="2017-09-26T15:48:52.950" LastActivityDate="2017-09-29T09:42:34.493" Title="What is the process of sending an NTS message in to a disaster area?" Tags="&lt;procedure&gt;&lt;emergency&gt;&lt;nts&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9258" PostTypeId="2" ParentId="9257" CreationDate="2017-09-25T23:04:07.470" Score="3" Body="&lt;p&gt;You will need to originate a radiogram and pass it onto an NTS net. That either means you'll need to find someone who is active with NTS in your area, or you'll need to find a net and do it yourself (typically by searching the web for “NTS net in {your area}”). &lt;a href=&quot;http://www.texastrafficnet.org/training.asp&quot; rel=&quot;nofollow noreferrer&quot;&gt;Instructions for doing it yourself can be found here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In quick summary form: to originate a radiogram, you'll need to:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Find a radiogram form (search for ARRL Radiogram and you'll find something like &lt;a href=&quot;http://www.arrl.org/files/file/Public%20Service/RADIOGRAM-2011.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;).&lt;/li&gt;&#xA;&lt;li&gt;Fill it out appropriately: identify the status of the message, identify the sender location, identify the recipient (including phone number and/or email), send a message of up to 25 words, count those words and put them on the form as &quot;check&quot;, and add a couple of words as signature. You would use &quot;welfare&quot; priority - note that welfare traffic is handled only after all emergency and priority traffic is cleared (but before routine traffic).&lt;/li&gt;&#xA;&lt;li&gt;Pass the radiogram yourself or find a ham to do it, via NTS net (voice, digital or CW). If you can't find a net on the web, try asking the ARRL section manager for your section.&lt;/li&gt;&#xA;&lt;li&gt;Wait for an answer.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Most NTS nets are interested in picking up traffic. However, not all traffic gets delivered. In particular, the end result of an NTS message is usually a ham making a phone call or sending an email to the recipient. In an area where communications infrastructure is down, that can be a challenge. In those cases it is a lot easier for someone to send an NTS message out of a disaster area (&quot;I'm OK&quot;) rather than for a ham on the ground (who may be busy with other communications) to get in contact with a stranger inside the disaster area.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="76" LastEditDate="2017-09-26T01:10:01.550" LastActivityDate="2017-09-26T01:10:01.550" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9259" PostTypeId="2" ParentId="9257" CreationDate="2017-09-26T04:25:25.047" Score="0" Body="&lt;p&gt;Here is a relevant article:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;a href=&quot;http://www.miamiherald.com/news/weather/hurricane/article174907471.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Trying to contact family in Puerto Rico? Here’s who to call&lt;/a&gt; (Miami Herald)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excerpt:  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;As food and water have become more scarce, panicked family and friends&#xA;  in the mainland U.S. and beyond are being advised by the territory’s&#xA;  Federal Affairs Administration to do the following:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;▪  Check the map below. Puerto Rico is divided into 12 zones. Each&#xA;  zone is comprised of various municipalities. Phone numbers are listed&#xA;  for all municipalities and for each region. These phone numbers will&#xA;  connect you with the nearest Puerto Rico State Agency for Emergency&#xA;  and Disaster Management office.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;They can give you a better idea of what the conditions are like in&#xA;  specific areas.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GvlIm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GvlIm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;It’s likely that you won’t reach someone immediately, so be patient,&#xA;  officials warn.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;If you don’t know what municipality or zone your loved one is in, you&#xA;  have a few options:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;▪ Call the the Puerto Rico Federal Affairs Administration’s Washington&#xA;  D.C. office at 202-800-3133 or 202-778-0710&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Volunteers and staff are taking names and numbers and developing&#xA;  databases to check the welfare of people who remain unreachable or&#xA;  missing as the island begins to recover.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Officials say that agency is prioritizing emergency situations, like&#xA;  people who are in [dire] need of medical attention. Staffers will reach&#xA;  out to first responders on the ground and dispatch help. In the last&#xA;  48 hours, the office has received more than 10,000 calls.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;LINK TO MAP:&#xA;  &lt;a href=&quot;http://prfaa.pr.gov/wp-content/uploads/2017/09/Oficinas-Regionales.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://prfaa.pr.gov/wp-content/uploads/2017/09/Oficinas-Regionales.pdf&lt;/a&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;▪  Call the island’s government radio station WIPR at 787-777-0940 or&#xA;  787-766-0505, which is helping people figure out what zones their&#xA;  family members are in.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;▪  Contact the island’s disaster relief team by e-mailing maria1@prfaa.pr.gov&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Because of high volume, leaders are asking that you only send one&#xA;  email — no follow-ups — unless the status of your loved one has&#xA;  changed.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Include your contact information and as many details about your family&#xA;  member or friend as possible.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;▪  The American Red Cross is also helping via an online database,&#xA;  where people can mark themselves safe.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;To begin a search, contact your local Red Cross chapter. You can also&#xA;  call our free national helpline at 844-782-9441 or use the&#xA;  International Reconnecting Families Inquiry Form.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;▪  Radio station WKAQ, which lost it’s roof during the storm,&#xA;  continues to broadcast news and can be listened to online.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;HOW TO HELP&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;▪  Email maria2@prfaa.pr.gov&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;▪  Call: 202-800-3134&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Follow Monique O. Madan on Twitter: @MoniqueOMadan&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;h2&gt;------------------------------------------------------------&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Really, it is much more likely that the survivors will reach out to loved ones as they are able.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here you can see one way they are communicating back to the rest of the world:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Aq8la.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Aq8la.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And other ways:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.latimes.com/nation/la-na-puerto-rico-families-20170925-story.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hurricane Maria victims in Puerto Rico struggle to connect with their families on U.S. mainland&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SZKGV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SZKGV.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The American Red Cross just put out a request for hams for Puerto Rico.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/news/american-red-cross-asks-arrl-s-assistance-with-puerto-rico-relief-effort&quot; rel=&quot;nofollow noreferrer&quot;&gt;American Red Cross Asks ARRL’s Assistance with Puerto Rico Relief Effort&lt;/a&gt; (ARRL.org)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excerpt:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;09/24/2017&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The American Red Cross (ARC) has asked the ARRL for assistance with&#xA;  relief efforts in Puerto Rico. ARC needs up to 50 radio amateurs who&#xA;  can help record, enter, and submit disaster-survivor information into&#xA;  the ARC Safe and Well system. In the nearly 75-year relationship&#xA;  between ARRL and ARC, this is the first time such a request for&#xA;  assistance on this scale has been made. ARRL now is looking for radio&#xA;  amateurs who can step up and volunteer to help our friends in Puerto&#xA;  Rico.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The article continues on with the requirements for this service.  It is all hands on deck there.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;a href=&quot;https://www.vox.com/science-and-health/2017/9/26/16365994/hurricane-maria-2017-puerto-rico-san-juan-humanitarian-disaster-electricty-fuel-flights-facts&quot; rel=&quot;nofollow noreferrer&quot;&gt;What every American needs to know about Puerto Rico’s hurricane disaster&lt;/a&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excerpt:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The storm knocked out 1,360 out of 1,600 cellphone towers on the&#xA;  island. Many communities have been isolated from the outside world for&#xA;  days, relying only on radios for news. National Guard members told the&#xA;  Daily Beast they were struggling to communicate on the ground, making&#xA;  their ability to respond to the disaster exceptionally hard. “There’s&#xA;  no communication, that’s the problem,” said Capt. Jeff Rutkowski.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/n7X6E.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/n7X6E.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://time.com/4955279/puerto-rico-hurricane-maria-communication/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Puerto Ricans Are Hunting for Wi-Fi and Cell Signal to Contact Loved Ones&lt;/a&gt; (Time)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excerpt:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(SAN JUAN, Puerto Rico) — Margarita Aponte and her relatives cleared&#xA;  the road in front of her house with two oxen Sunday, then drove an&#xA;  hour from her devastated hometown in central Puerto Rico to the old&#xA;  telegraph building in the capital of San Juan.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;There, thousands of Puerto Ricans gathered for a chance at a resource&#xA;  nearly as precious as power and water in the wake of Hurricane Maria —&#xA;  communication. &quot;It's ringing, it's ringing, it's ringing!&quot; Aponte, a&#xA;  janitor, screamed as her phone connected to free Wi-Fi and her&#xA;  Facetime call went through to the mainland.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Her eyes filled with tears as she talked with nephews, uncles,&#xA;  brothers and sisters in Florida and Massachusetts for the first time&#xA;  since Maria destroyed nearly every cellphone and fiber optic&#xA;  connection on this U.S. territory of 3.4 million people.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The low murmur at one of two free Wi-Fi hotspots is occasionally&#xA;  interrupted by the cheering of someone getting through the largely&#xA;  jammed network. Most spend hours frowning at their phones, unable to&#xA;  connect.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&quot;There's no communication. We're in God's hands,&quot; Yesenia Gomez, a&#xA;  kitchen worker, said as she left a message for her mother in the&#xA;  neighboring Dominican Republic.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Dozens of other Puerto Ricans opted to pull over to the side of the&#xA;  road along various highways where cellphone signals were strongest.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Carlos Ocasio, a maintenance worker, picked his way through tree&#xA;  branches and broken glass bottles as he found a spot with a good&#xA;  signal. Soon, he was able to reach his brother in New Jersey.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&quot;My throat got a little choked up and I couldn't talk for a minute,&quot;&#xA;  he said. &quot;They're calling me from everywhere, asking when I'm going to&#xA;  arrive.&quot; Others in Puerto Rico and abroad called a local radio station&#xA;  to provide names, numbers, exact addresses and pictures of their loved&#xA;  ones in hopes of reconnecting.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;But for hundreds of thousands of Puerto Ricans living on the U.S.&#xA;  mainland, there has been only silence from the island.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Shirley Rodriguez, a resident of New York's Brooklyn borough, said she&#xA;  has more than 30 relatives in Puerto Rico but she is especially&#xA;  concerned about her 66-year-old mother, Mildred Rodriguez, who has&#xA;  diabetes and pulmonary hypertension and lives in Hormigueros on the&#xA;  island's west coast.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Rodriguez last spoke to her family before the storm and her relatives&#xA;  were planning on being together for it. Since then, calls to their&#xA;  cellphones have gone to voicemail.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&quot;I'm absolutely numb at this point. It's a rollercoaster of emotion,&quot;&#xA;  she said. &quot;Not knowing is extremely agonizing.&quot;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Her mother-in-law is in the San Juan area and somehow managed to&#xA;  connect with someone who works for the mayor of Hormigueros, who was&#xA;  able to tell Rodriguez that the area where her parents live escaped&#xA;  flooding. But she still doesn't know what the actual conditions are&#xA;  like.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Some in Puerto Rico expressed anger over what they said was a lack of&#xA;  communication from cellphone providers about which towers were working&#xA;  so they could drive in that direction.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&quot;They're not giving us any information,&quot; said Ricardo Castellanos, a&#xA;  business consultant. &quot;We're in a state of emergency.&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-09-29T09:42:34.493" LastActivityDate="2017-09-29T09:42:34.493" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9260" PostTypeId="1" AcceptedAnswerId="9261" CreationDate="2017-09-26T04:32:52.380" Score="3" ViewCount="1620" Body="&lt;p&gt;I used the &quot;QT GUI frequency sink&quot; and &quot;WX GUI FFT sink&quot; to measure the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I got different value. I would like to know what dB stands for in them. Whether it is dBm or just a ratio.&lt;/p&gt;&#xA;" OwnerUserId="10410" LastEditorUserId="4076" LastEditDate="2017-09-26T05:14:39.360" LastActivityDate="2017-09-26T05:17:34.583" Title="How to measure signal power in GNU Radio.(I wondered how much dBm is specific.)" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9261" PostTypeId="2" ParentId="9260" CreationDate="2017-09-26T05:17:34.583" Score="5" Body="&lt;p&gt;They don't &quot;measure&quot;, they just &lt;em&gt;display&lt;/em&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And yes, as you noticed, this is digital signal processing, so there's no physical units involved – the display axes are correctly labeled with &quot;dB&quot;, as in &quot;dB relative to an arbitrary reference vector&quot;, typically a energy=1 time signal (e.g. $(0,\ldots,0,1,0,\ldots,0)$), or a power=1 signal (e.g. $(1,\ldots,1)$).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the value displayed by WX and QT only differs by a fixed dB offset; the difference, if I remember correctly, is only the length of the DFT being used as normalizing factor for one, but not the other sink. (By the way, there's historically been a long discussion about what's &quot;right&quot; to use as references. Turns out that's hard to say.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, all is relative. If you need physical units, you'll need to calibrate your SDR device with a measurement device that gives you &quot;real world powers&quot; in Watt, dBm, eV/s or whatever.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-09-26T05:17:34.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9262" PostTypeId="2" ParentId="9255" CreationDate="2017-09-26T14:36:04.780" Score="2" Body="&lt;p&gt;We painted our antenna radomes with Aerodur, but it's a $200/litre fast curing two part paint that is quite dangerous to breathe. It wasn't chosen for its electromagnetic properties, just its toughness, but gave no trouble, two or three coats, up to 6 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd recommend any auto body paint, like a 2K two part paint.  With the right primer and surface preparation it will stick well and last a long time in the sun. We also used these for less military applications, and when we needed a gloss white finish which we couldn't get in Aerodur.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We used a lot of black paint for antennas, but perhaps it's safer to avoid it, it is possible they contain (macroscopic) carbon which could affect the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You definitely don't want to load the antenna with any substantial thickness of plastic, like putting it in a new pipe. A layer of good paint is fine, any thickness, but a plastic pipe is not ok, might upset the tuning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, you don't want to seal it airtight - make sure you don't paint over the drain hole in the bottom of the original radome. A large volume needs to breathe and drain condensation, attempting to make it airtight will just cause it to suck in moisture from somewhere unexpected.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2017-09-26T14:36:04.780" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9263" PostTypeId="2" ParentId="133" CreationDate="2017-09-26T18:29:09.477" Score="0" Body="&lt;p&gt;Another important factor is degradation due to weather and atmospheric pollutants. For VHF and UHF antennas, I have found galvanized steel wire to be durable, corrosion-free and its electrical inter-metallic contact potential is about midway between copper and aluminium = long life under exposed conditions &lt;/p&gt;&#xA;" OwnerUserId="10416" LastActivityDate="2017-09-26T18:29:09.477" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9264" PostTypeId="2" ParentId="9255" CreationDate="2017-09-26T22:36:57.020" Score="4" Body="&lt;p&gt;I have had good success with Rust-Oleum 206999 Marine Topside Paint. I prefer the white gloss version to minimize mold growth and to promote ice slippage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Proper surface preparation is important. Most weathered fiberglass will develop a mold growth in the &quot;pores&quot; of the fiberglass. In addition, the original finish may contain a wax substance. So start with cleaning the surface with a fiberglass cleaner. Then sand the surface smooth, finishing with a 120 grit paper. Remove all sanding dust using a tack rag. Then apply a thin layer of Rust-Oleum Marine Coatings Primer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once the primer has dried, apply the Topside paint in a thin coat. Apply a second coat 24 hours later if needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have found this paint to have enough elasticity to survive the constant flexing that the radome experiences on the tower and I have yet to repaint a radome after 10 years of exterior exposure.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-26T22:36:57.020" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9266" PostTypeId="2" ParentId="9256" CreationDate="2017-09-27T15:30:42.693" Score="1" Body="&lt;p&gt;Communications law is a complex subject. In your case, you have the added issue of import/export regulations. I suggest you engage a competent attorney to guide you through these matters. Here are my answers based on my understanding of the questions you have raised. Please accept that I am not acting as your attorney.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A transmitter that is capable of being operated only on the frequencies authorized to amateur radio operators under FCC jurisdiction, does not require any approval by the FCC prior to being sold by the manufacturer. However, from a commercial liability perspective, the manufacturer should ensure that the transmitter allows the amateur radio operator to be in compliance with the part 97 bandwidth, spectral purity, and power output requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A transceiver, on the other hand, will be subject to type 15 compliance requirements but typically only due to the receiver portion of the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An external RF power amplifier that will be marketed for amateur radio use is required to be certified by the FCC as described in part 97 (which further references part 2).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Industry Canada has no jurisdiction in those geographies governed by FCC regulations so any IC approval is meaningless and therefore not required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on the construction of the intended transmitter, some state or local jurisdictions may require additional electrical safety compliance through UL or ETL testing and certification, for example.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;...part 15 licensed devices, there's special FCC certification...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is not technically accurate. Part 15 covers unlicensed devices. There are three levels of required compliance, the correct one of which depends on the applicable section of the code:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Certification&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manufacturer uses a test lab accepted by the FCC to measure and document that the requirements have been met.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Declaration of Conformity&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manufacturer issues a formal statement to the FCC that the device has been tested in an accepted lab and that it is in compliance with the regulations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Verification&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manufacturer performs the necessary tests and confirms that the device conforms to the regulations. No notification is given to the FCC.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-27T16:09:00.010" LastActivityDate="2017-09-27T16:09:00.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9267" PostTypeId="2" ParentId="8908" CreationDate="2017-09-27T16:33:29.247" Score="3" Body="&lt;p&gt;Placing the antenna on a tripod on your balcony should not be a problem. It is always a good idea to perform an RF exposure assessment when locating a VHF antenna close to people.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How well the antenna will work is another matter. At VHF frequencies, most of the reliable communications comes from direct, line of site paths. When station antennas are in line of site, even very modest power levels and antenna gains will typically facilitate communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some situations, reflections, refractions, and scattering may enhance or reduce the reliability of communications. Often these tend to be unreliable due to changing foliage conditions, weather effects, and changing landscapes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Walls in buildings tend to reduce VHF communication ranges. While your balcony will provide a clear shot in one direction, the balance of your directions are to some degree attenuated by your building.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may find it advantageous to use an HT from various locations in your apartment and on your porch to determine your effective repeater and simplex coverage - both transmitting and receiving. If you find that you have some degree of omni-directional coverage from your porch, your chosen antenna should be adequate. If on the other hand, you find that the only practical coverage is in the direction of the porch opening, you may wish to consider a small Yagi antenna in order to maximize your gain in that direction. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-27T16:33:29.247" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9268" PostTypeId="2" ParentId="9257" CreationDate="2017-09-27T21:17:34.113" Score="2" Body="&lt;p&gt;As a member of the ARRL field organization, I just received this advisory based on the fact that the ARRL volunteers in PR will only be handling outbound traffic:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;...members of the public should access the American Red Cross Safe and Well System online at &lt;a href=&quot;https://safeandwell.communityos.org/cms/index.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://safeandwell.communityos.org/cms/index.php&lt;/a&gt;. Status information from friends and relatives in Puerto Rico will be entered into the system as it arrives from amateurs stationed there.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-27T21:17:34.113" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9269" PostTypeId="2" ParentId="1695" CreationDate="2017-09-27T22:26:59.453" Score="1" Body="&lt;p&gt;My solution is a collapsible telescopic quarter-wave antenna.  Collapsed, it's not much longer than the stock antenna.  Fully extended, it has significantly better gain.  Diamond makes a very good one that seems quite durable, although I'm not sure if they make it with Baofeng's strange reverse SMA connection, but other companies do. Yes, they can break, but if you are reasonably careful that won't happen.  You can always pack your stock Baofeng antenna as an emergency spare, since it's somewhat flexible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A roll-up slim jim (ideally dual band; some are monoband) is great for camping, hotel room windows, and the like.  You can throw it in a window or tree and really extend your range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider, too, adding a counterpoise, which can be home built and will help with range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also get a collapsible yagi antenna if you want maximum range, but these are fairly large when fully assembled.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2017-09-27T22:26:59.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9270" PostTypeId="2" ParentId="1695" CreationDate="2017-09-28T00:54:45.453" Score="0" Body="&lt;p&gt;I have the UV-5R and BF-F8HP.  I have the 771, 701, and 810 that I use depending on situation.  I find that even the 810 works better than the antenna that came on both radios stock and I use it in situations where even the 8&quot; 701 is inconvenient, but the 701 is my &quot;go to&quot; antenna.  If I am somewhere that I am going to be relatively stationary, then I will use the 771.  The price of these antenna makes it practical to have all three and go with what the situation dictates.&lt;/p&gt;&#xA;" OwnerUserId="10357" LastActivityDate="2017-09-28T00:54:45.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9271" PostTypeId="2" ParentId="1007" CreationDate="2017-09-28T00:57:37.207" Score="1" Body="&lt;p&gt;If the Extra is sitting where the controls can be readily accessed, they can still be considered the &quot;control operator&quot; and you a &quot;participant&quot;.  The &quot;control operator&quot; remains responsible for the transmissions in this scenario.&lt;/p&gt;&#xA;" OwnerUserId="10357" LastActivityDate="2017-09-28T00:57:37.207" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9272" PostTypeId="1" AcceptedAnswerId="9288" CreationDate="2017-09-28T01:52:39.633" Score="5" ViewCount="6974" Body="&lt;p&gt;I just passed General and purchased a FT-450D with an internal antenna tuner. While my ultimate plan is to use a G5RV, it will be a while before I can get it up. What modifications would I need to make to use a mag mount CB antenna. Would it work for 10m? Others?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like it may work simply by grounding the base. Not sure if I would have to trim it a bit. &lt;/p&gt;&#xA;" OwnerUserId="10424" LastEditorUserId="5222" LastEditDate="2017-09-29T18:13:40.027" LastActivityDate="2018-07-30T23:41:13.550" Title="Can I use a CB antenna with a ham radio?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;impedance&gt;&lt;citizens-band&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9273" PostTypeId="2" ParentId="9272" CreationDate="2017-09-28T10:23:30.323" Score="6" Body="&lt;p&gt;Congratulations on earning your General license!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may get the antenna to work using the internal antenna tuner. Make sure the antenna is on a large groundplane. Try tuning it up with low power (&amp;lt; 10 watts) at first to see if the ATU can handle the impedance matching. If it doesn't tune up, reducing the length of the vertical element may help. Try chopping off an inch or so off of the bottom at a time. Of course this will render the antenna useless for any future CB activity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do get the antenna working on 10 meters, don't expect much in the way of contacts. The higher frequency band conditions are very poor right now due to the sunspot cycle. You will find most stations have gravitated to lower frequencies or switched to low power digital modes like FT8 in order to make contacts.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-28T10:23:30.323" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9274" PostTypeId="7" CreationDate="2017-09-28T18:42:54.570" Score="0" Body="&lt;blockquote&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/help/privileges/comment&quot;&gt;&lt;strong&gt;Commenting Rules&lt;/strong&gt; and Details&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.meta.stackexchange.com/questions/423/how-do-i-write-fancy-equations-in-a-question-answer-or-comment&quot;&gt;&lt;strong&gt;How do I enter fancy math equations&lt;/strong&gt;&lt;/a&gt;?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="-1" LastEditorUserId="8717" LastEditDate="2020-11-02T01:41:43.367" LastActivityDate="2020-11-02T01:41:43.367" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="9275" PostTypeId="1" AcceptedAnswerId="9278" CreationDate="2017-09-29T11:16:44.367" Score="0" ViewCount="786" Body="&lt;p&gt;Does the Kenwood TH-D74 support Access Point and Terminal mode for D-Star like the Icom ID-51 PLUS2?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-04T18:38:28.173" LastActivityDate="2017-10-04T18:38:28.173" Title="Does the Kenwood TH-D74 support Access Point and Terminal mode for D-Star?" Tags="&lt;kenwood&gt;&lt;icom&gt;&lt;d-star&gt;&lt;kenwood-th-d74&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9276" PostTypeId="1" AcceptedAnswerId="9277" CreationDate="2017-09-29T13:25:53.743" Score="3" ViewCount="145" Body="&lt;p&gt;An &lt;a href=&quot;http://nts.ema.arrl.org/node/32&quot; rel=&quot;nofollow noreferrer&quot;&gt;HXE&lt;/a&gt; NTS message means &quot;Delivering station get reply from addressee, originate message back&quot;. On an NTS form, the origination station and location are indicated, but no other information about the originator is included. How are you supposed to address a message back to the originator? Usually sending a message includes an email, phone, address, etc, but the receiver won't necessarily have that information. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best that I can imagine is to simply listen to the traffic net that you sent it from and hope the same message comes back, but I want to see if that is really the case.&lt;/p&gt;&#xA;" OwnerUserId="13" LastActivityDate="2017-12-28T20:50:07.337" Title="How do you indicate how to contact you for an HXE message?" Tags="&lt;nts&gt;&lt;message&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9277" PostTypeId="2" ParentId="9276" CreationDate="2017-09-29T15:19:06.780" Score="1" Body="&lt;p&gt;In my experience with HXE, I end up looking up the ham's call (e.g.on eHam) and emailing the message asking for confirmation of receipt if I cannot find a phone number on-line and they are not a regular on the net. I tend to look at the significance of the message to determine how much effort I should invest in tracking down a way to contact the originator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In listening on traffic nets, it seems that once the message gets close to the originators QTH, that person is known to the local traffic net so they find a way of delivering it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If all else fails, looking up the originating call in the FCC database and mailing a copy of the message to the address on record is acceptable. This probably is probably less than desirable service time, however - especially with H&amp;amp;W messages.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-29T15:19:06.780" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9278" PostTypeId="2" ParentId="9275" CreationDate="2017-09-29T16:30:05.727" Score="2" Body="&lt;p&gt;The ICOM gateway terminal mode is a unique mode. It allows you to configure the radio to use the radio, tethered to a computer through a USB cable, to route the communications through the computer, out to the Internet, to access a remote gateway. In this mode, the RF signal of the radio is not a factor since all communications are actually going through the tethered computer and the Internet. The intended use of this mode is when you cannot access a local repeater with an appropriate gateway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fX4GV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fX4GV.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ICOM Gateway Access Point mode allows you to use another D-Star transceiver, connected to the Internet, to access a remote gateway. In this case, the RF connection is used:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/H2vjW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/H2vjW.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TH-D74 supports traditional gateway settings but in its case, the gateway must be attached to the repeater that you are communicating with through the local RF connection. There is no native option to make a gateway connection through the Internet without the use of a local repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may, however, be able to closely emulate the Icom Gateway Access Point function through the use of a local gateway device such as this OpenSpot device:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/srlWK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/srlWK.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can then use your radio without tethering to access a remote Gateway/repeater without going through a local repeater:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jI1pW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jI1pW.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-29T16:30:05.727" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9279" PostTypeId="1" AcceptedAnswerId="9280" CreationDate="2017-09-29T17:20:49.513" Score="1" ViewCount="2710" Body="&lt;p&gt;The Icom IC-51E PLUS2 but not the American version will emit a 1750Hz tone burst when you push the PTT briefly and then hold it down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is this for?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2017-09-29T17:35:02.460" Title="What is the 1750Hz tone burst for?" Tags="&lt;icom&gt;&lt;europe&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9280" PostTypeId="2" ParentId="9279" CreationDate="2017-09-29T17:35:02.460" Score="4" Body="&lt;p&gt;The 1750 tone burst is widely used in European the same way that CTCSS/PL and DCS is used for repeater access in the US. I used tone burst exclusively when living in Germany. Tone burst never caught on in the US.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-29T17:35:02.460" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9281" PostTypeId="1" AcceptedAnswerId="9283" CreationDate="2017-09-29T18:13:38.597" Score="3" ViewCount="595" Body="&lt;p&gt;Between trunk-mounting and roof-mounting a 2m/70cm antenna, both as through-hole NMO mounts, is there really that big a difference performance-wise? I mean, I know roof mounting is better, but let's face it: looks &lt;em&gt;are&lt;/em&gt; a factor for some of us (and especially our significant others), and a trunk mount is much more understated than dead center of the roof. Plus, from a convenience standpoint, if you live in a city, it's nice to be able to park in a garage without removing the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've seen the &lt;a href=&quot;http://kv5r.com/wp-content/img/ham/tig/mobileant.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;diagram&lt;/a&gt; from Larsen's catalog, but numbers don't tell the whole story. Especially not to a new ham like me. -3dB is half the signal strength gone, or put another way, just half an S-unit. I'm more curious about practical experiences (especially from people who have tried both). Plenty of people act like you're asking for trouble if you don't roof-mount, but truthfully, would I really notice those missing 3dB, and if so, would I mind it? Or will there be other effects that I'll mind?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If necessary, to give the question a little more scope, this is my first mobile installation (if it wasn't obvious). The antenna is a Larsen NMO-2/70B. I drive a 2014 Camry and live in the middle of Philly (think multistory buildings), but take that with a grain of salt. If I'm getting in my car at all, I'm pretty likely going out of town.&lt;/p&gt;&#xA;" OwnerUserId="8940" LastEditorUserId="8573" LastEditDate="2019-07-31T18:43:53.513" LastActivityDate="2019-07-31T18:43:53.513" Title="Noticeable difference between trunk and roof mount?" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;mobile&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="9282" PostTypeId="1" AcceptedAnswerId="9284" CreationDate="2017-09-29T18:23:45.717" Score="1" ViewCount="1420" Body="&lt;p&gt;I'm reading the Icom IC-51E PLUS2 manual and it says it supports the following modes:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;AM&lt;/li&gt;&#xA;&lt;li&gt;FM&lt;/li&gt;&#xA;&lt;li&gt;FM-N&lt;/li&gt;&#xA;&lt;li&gt;DV&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;What is FM-N? I'm new to amateur radio and never heard of it before. It's not listed &lt;a href=&quot;https://en.wikipedia.org/wiki/List_of_amateur_radio_modes&quot; rel=&quot;nofollow noreferrer&quot;&gt;on Wikipedia&lt;/a&gt; either.&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="76" LastEditDate="2017-09-30T14:22:57.127" LastActivityDate="2017-09-30T14:22:57.127" Title="What is the FM-N mode?" Tags="&lt;modes&gt;&lt;fm&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9283" PostTypeId="2" ParentId="9281" CreationDate="2017-09-29T18:32:04.947" Score="3" Body="&lt;p&gt;Yes there is a difference but it tends to have more to do with the pattern and efficiency of the antenna than anything else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When an antenna is mounted on the trunk, the roof line and the occupants of the vehicle tend to block RF energy in the forward direction. The rearward direction is minimally affected. So in this case, depending on the direction you are driving this may or may not make a difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Placing the antenna on the roof of the car not only gives it an unobstructed view, but it also slightly increases the size of the ground plane under the antenna. This may help to increase the efficiency (and thus gain) of the antenna somewhat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When communicating on VHF and UHF, the most reliable communications come when the stations are in line of sight to one another. The roof does give a couple of feet of added height to the antenna possibly improving the chance for line of sight communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The net of all of this is that it is difficult to come up with a hard and fast rule if one antenna location will allow communications when the other antenna will not but in general, the roof mounted antenna will be superior.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice is to do the best installation that satisfies your and your family's criterion for what is acceptable for your circumstances. You will communicate effectively in most practical situations.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-29T18:32:04.947" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9284" PostTypeId="2" ParentId="9282" CreationDate="2017-09-29T18:47:13.883" Score="4" Body="&lt;p&gt;FM-N stands for FM narrow band.This corresponds to a 2.5 kHz deviation. FM corresponds to a 5 kHz deviation. Most repeaters are still 5 kHz although with spectrum crowding, we will see more 2.5 kHz repeaters to allow more repeaters to be located in the same frequency allocation. This mirrors what is happening in the commercial 2 way market.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-09-29T18:47:13.883" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9285" PostTypeId="1" AcceptedAnswerId="9290" CreationDate="2017-09-29T22:26:55.900" Score="1" ViewCount="114" Body="&lt;p&gt;I recently got an Icom ID-51E PLUS2 and its smallest tuning step is 5kHz. I looked at &lt;a href=&quot;https://www.ukrepeater.net/repeaterlist1.htm?filter1=2M&quot; rel=&quot;nofollow noreferrer&quot;&gt;the list of repeaters in the UK&lt;/a&gt; and many are between 5kHz stops, such as 145.6125MHz. Is this expected? Do you just tune as close as possible to it or am I missing something regarding repeater operations?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="4665" LastEditDate="2017-09-30T16:02:39.127" LastActivityDate="2017-09-30T16:02:39.127" Title="Tune step not being small enough?" Tags="&lt;repeater&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9286" PostTypeId="2" ParentId="9285" CreationDate="2017-09-29T22:54:44.773" Score="1" Body="&lt;p&gt;If that radio model is actually as you describe (I'm not familiar), then you cannot use it with that repeater. A 2.5 kHz frequency error is sufficient to make (5 kHz deviation) FM unusable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can &lt;em&gt;program&lt;/em&gt; the radio with the specified frequency, as opposed to using VFO controls, that may work. Even if it only accepts 3 digits after the MHz decimal point (so that you must enter 145.612 or 145.613) then that will be a 0.5 kHz error which I would expect to be workable if not great.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-09-29T23:16:08.490" LastActivityDate="2017-09-29T23:16:08.490" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9287" PostTypeId="1" AcceptedAnswerId="9289" CreationDate="2017-09-29T23:47:50.897" Score="2" ViewCount="1104" Body="&lt;p&gt;The band plan says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Location Restriction: In addition it is very important to note that the band between 431-432MHz is not available for use if you are located anywhere within a 100km radius of Charing Cross, London.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Why is that? What is it used for? &lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2020-07-25T10:59:23.157" Title="Why is 431-432MHz forbidden for use in London?" Tags="&lt;uhf&gt;&lt;united-kingdom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9288" PostTypeId="2" ParentId="9272" CreationDate="2017-09-30T00:13:17.323" Score="2" Body="&lt;p&gt;The CB mag mount can be used on 10 meters by attaching a wire to the the shielding at the base then extending the wire to the side.  There is always some length that is resonant on whatever frequency desired.  On my particulat CB antenna the side wire was about twice the length of the vertical. Total length will be a bit longer than 8 feet (half-wave). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My very first contact as a ham was the Virgin Islands with this lashup taped on the roof of my motorhome.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beside adjusting length I later found the up or down angle of the side wire can fine tune the SWR.  The signal pattern will be stronger in the semi-circle toward the side wire... Perhaps half as loud as away from the side wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you try to extend the side wire to tune 12 or 15 meters the feedpoint will be considerably off-center. The impedance will likley be over 150 Ohms, too high for your internal tuner to handle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The down side is that 10 meters is so quiet now that few hams are trying to work that band.  I now use a 20 meter version of that side-arm antenna and a 40-20-15-10 meter end-fed antenna for multi-band work.&lt;/p&gt;&#xA;" OwnerUserId="8229" LastActivityDate="2017-09-30T00:13:17.323" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9289" PostTypeId="2" ParentId="9287" CreationDate="2017-09-30T00:26:04.270" Score="3" Body="&lt;p&gt;The restrictions are due to MOD (Ministry of Defense, military) use. There are also some secondary business users in the spectrum. If you would look at the primary allocations in the UK, you might be surprised by the amount of spectrum allocated to the MOD. Ofcom maintains spectrum allocation data on this topic:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;UK65 - By special arrangement civil Land Mobile services may operate&#xA;  within sub-bands 425.0-429.0 MHz, 431.0-432.0 MHz, 440.0-443.5 MHz,&#xA;  and 445.5-449.5 MHz in agreed areas and on a non-interference basis to&#xA;  military services. Further information can be found in the document&#xA;  &quot;Frequency sharing arrangements between civil and military services&quot;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(I also used to live in the UK)&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-03T12:50:25.357" LastActivityDate="2017-10-03T12:50:25.357" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9290" PostTypeId="2" ParentId="9285" CreationDate="2017-09-30T00:43:45.067" Score="4" Body="&lt;p&gt;While it is true that you have a 5 kHz tuning step, you do also have a 6.25 kHz and a 12.5 kHz tuning step. These should enable you to tune to the desired frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Open the quick menu screen. Push D-Pad up/down to select the tuning step. Then press D-Pad Enter to lock in that tuning step.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-09-30T01:01:44.460" LastActivityDate="2017-09-30T01:01:44.460" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9291" PostTypeId="1" CreationDate="2017-09-30T08:36:05.740" Score="1" ViewCount="163" Body="&lt;p&gt;When downloading a repeater list from &lt;a href=&quot;http://www.dstarinfo.com/RepeaterDownloads.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;dstarinfo.com&lt;/a&gt; as shown in &lt;a href=&quot;https://www.youtube.com/watch?v=BJCvLsK1cKc&quot; rel=&quot;nofollow noreferrer&quot;&gt;this video:&#xA; https://www.youtube.com/watch?v=BJCvLsK1cKc&lt;/a&gt;, there are two numeric fields:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Empty Repeater Slots&lt;/li&gt;&#xA;&lt;li&gt;Percent FM&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;What are they? What do they mean?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/f4uSf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/f4uSf.png&quot; alt=&quot;Screenshot of form&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-01T17:14:53.153" LastActivityDate="2018-03-02T05:17:51.337" Title="Empty Repeater Slots and Percent FM when downloading D-STAR repeater list" Tags="&lt;repeater&gt;&lt;d-star&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9293" PostTypeId="1" CreationDate="2017-09-30T13:02:58.840" Score="1" ViewCount="125" Body="&lt;p&gt;I have the cable connected from my phone, a Samsung Galaxy S6, to my brand new Icom ID-51E PLUS2 and when I run the app I get this error:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2j1Uq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2j1Uq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I correctly set up my radio for this, as you can see in this video:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://youtu.be/m1llAnDgYcg&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://youtu.be/m1llAnDgYcg&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ideas what else could be a problem?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-04T18:38:50.720" LastActivityDate="2018-04-03T09:58:37.437" Title="Any ideas why my phone is not connecting to my Icom ID-51E PLUS2?" Tags="&lt;icom&gt;&lt;icom-id-51-plus2&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9294" PostTypeId="2" ParentId="9238" CreationDate="2017-09-30T14:05:59.627" Score="5" Body="&lt;p&gt;I have a Baofeng handheld with similar specifications, and the short answer is no, it does not function as a repeater in any way - cross band or otherwise. I would imagine that would be a feature they would be quite specific about.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The long answer is that you can operate between both bands to use a cross-band repeater or satellite. Using software like Chirp, you can program duplex operation with the regular +/- offsets as in columns 3 &amp;amp; 6 of this screen shot using 2M repeaters as an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gkBiE.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gkBiE.png&quot; alt=&quot;2 Meter Repeaters&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or you can enter your receive frequency and select &quot;split&quot; instead of the +/- offset. You would then enter the frequency of the transmit band in the column usually used for the offset as in this image:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1Vg3m.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1Vg3m.png&quot; alt=&quot;Satellite Settings&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the capability they are stating.&lt;/p&gt;&#xA;" OwnerUserId="10085" LastActivityDate="2017-09-30T14:05:59.627" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9295" PostTypeId="1" AcceptedAnswerId="9301" CreationDate="2017-09-30T21:41:26.703" Score="2" ViewCount="934" Body="&lt;p&gt;On the &lt;a href=&quot;http://rsgb.org/main/operating/band-plans/vhf-uhf/144mhz-band/&quot; rel=&quot;nofollow noreferrer&quot;&gt;band plan for VHF for the UK&lt;/a&gt;, I can see 145.500MHz being the FM calling frequency but I cannot find any for DV. Is there one?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In contrast, &lt;a href=&quot;http://rsgb.org/main/operating/band-plans/vhf-uhf/432mhz-band/&quot; rel=&quot;nofollow noreferrer&quot;&gt;for UHF&lt;/a&gt;, I can see a calling frequency for FM at 433.500MHz and one for DV at 438.6125MHz.&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-02T16:24:39.450" LastActivityDate="2019-05-18T09:24:47.817" Title="Is there a DV VHF calling frequency in the UK?" Tags="&lt;vhf&gt;&lt;united-kingdom&gt;&lt;band-plan&gt;&lt;d-star&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9296" PostTypeId="1" AcceptedAnswerId="9300" CreationDate="2017-10-01T15:24:45.240" Score="0" ViewCount="162" Body="&lt;p&gt;On the scanning options for the Icom ID-51 PLUS2, there's one called Temporary Skip Timer that can be any of:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;5 minutes&lt;/li&gt;&#xA;&lt;li&gt;10 minutes&lt;/li&gt;&#xA;&lt;li&gt;15 minutes&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The manual says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Temporary Skip Timer&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Selects the Temporary Skip Time. When the time is set, specified frequencies are skipped for this period during a scan.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, it sounds like you can temporary skip a frequency while scanning, to not be bothered by persistent interference in a single frequency. Is that correct? If so, how do you do it? How do you actually skip a frequency? I can't find it on the manual.&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-04T18:38:38.573" LastActivityDate="2017-10-04T18:38:38.573" Title="Temporary Skip frequency on an Icom ID-51 PLUS2" Tags="&lt;icom&gt;&lt;equipment-operation&gt;&lt;icom-id-51-plus2&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9297" PostTypeId="1" AcceptedAnswerId="9298" CreationDate="2017-10-01T21:38:23.750" Score="11" ViewCount="174" Body="&lt;p&gt;I have some radios that have a special antenna connector. It looks like an SMA connector, but the dielectric is flush with the end of the connector:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/f3Mcm.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/f3Mcm.jpg&quot; alt=&quot;SMA-like connector where dielectric is flush with end of connector&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;rather than recessed the way &quot;normal&quot; SMA connectors are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qMcvi.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qMcvi.jpg&quot; alt=&quot;Normal SMA connector with recessed dielectric&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The consequence of this is that the recessed connector and the flush connector are incompatible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone know what to call the flush-style connector?&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="5222" LastEditDate="2017-10-06T22:38:55.947" LastActivityDate="2017-10-06T22:38:55.947" Title="Is there a special name (and if so what is it) for this flush-style SMA variant?" Tags="&lt;jargon&gt;&lt;connectors&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9298" PostTypeId="2" ParentId="9297" CreationDate="2017-10-01T22:58:51.987" Score="7" Body="&lt;p&gt;It is known as an SF style SMA connector. It is also commonly known as a Motorola SMA connector since they seem to be one of the few large scale users of this style connector&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find some adapters for this style of connector such as this RFB-1142-4 BNC adapter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SPPve.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SPPve.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.hitechwireless.com/rf-industries-rfb-1142-4-bnc-f-sma-f-adapter/&quot; rel=&quot;noreferrer&quot;&gt;&lt;code&gt;http://www.hitechwireless.com/rf-industries-rfb-1142-4-bnc-f-sma-f-adapter/&lt;/code&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-02T01:35:31.700" LastActivityDate="2017-10-02T01:35:31.700" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9299" PostTypeId="1" CreationDate="2017-10-02T02:56:10.953" Score="2" ViewCount="515" Body="&lt;p&gt;A local ham that I have an evening sked with on 75m (Paul, W0EBV) sent his Flex 5000 SDR transceiver to  &lt;a href=&quot;http://www.flexradio.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Flex Radio Systems&lt;/a&gt; to get it repaired a few months ago. However, it seems that &lt;strong&gt;Flex is either unable or disinclined to repair it&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Paul keeps getting the run-around and evasive answers from their official repair center. And the last time Paul called Flex, the repair technician asked him &quot;What happened, did this radio get struck by lightning?!&quot; &lt;em&gt;But nothing of the sort happened.&lt;/em&gt; Paul unplugs the antenna, etc. whenever he leaves the house. And what is more, he was in QSO with me and the local SW MO group here on 3813 when it quit. The sky was clear, no lighting. His audio became distorted and then it ceased to function at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He bought it from another ham, and it worked great up to that time. Perhaps they have a backlog of radios to repair; but if that's the case, they have not told him that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is what I believe that Paul told me, on more than one occasion. &lt;strong&gt;&lt;em&gt;And I believe what Paul told me&lt;/em&gt;&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A Google search for 'flex repair service' shows up &lt;em&gt;nothing&lt;/em&gt; (other than the Flex radio repair centers).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Paul has a dead radio and is at a loss as to what to do. How else can he get his dead Flex 5000 repaired?&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-10-02T19:09:33.757" LastActivityDate="2021-03-25T11:11:55.663" Title="Does anyone repair Flex radios other than Flex Radio?" Tags="&lt;software-defined-radio&gt;&lt;equipment-troubleshooting&gt;&lt;repair&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9300" PostTypeId="2" ParentId="9296" CreationDate="2017-10-02T13:03:08.810" Score="1" Body="&lt;p&gt;Your presumption about how it functions is correct. The skip time is a global setting for all timed skip operations. It is set from the main Menu.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to skip a channel for the timed period set from the main menu, when the scan stops on the desired frequency, press the Quick key. Then use the up/down arrows to select Temporary Skip. Finally press the Enter key. That channel will then be skipped for the programmed time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that there are two user manuals for this radio. In the US English version of the &lt;strong&gt;advanced&lt;/strong&gt; manual (A-7331-3EX), see pages 13-13 and 16-18 for the details.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-02T13:09:28.457" LastActivityDate="2017-10-02T13:09:28.457" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9301" PostTypeId="2" ParentId="9295" CreationDate="2017-10-02T15:27:22.690" Score="2" Body="&lt;p&gt;The D-Star simplex frequencies in the UK are 144.6125 MHz, 438.6125 MHz and 1298.6125 MHz.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-10-02T15:27:22.690" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9302" PostTypeId="2" ParentId="9291" CreationDate="2017-10-02T15:36:56.287" Score="1" Body="&lt;p&gt;The empty repeater slots are the remaining memories in available in your radio. The Percent FM are the number of repeaters in the list that are standard FM (i.e. not DV).&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-10-02T15:36:56.287" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9303" PostTypeId="1" CreationDate="2017-10-02T20:12:04.210" Score="1" ViewCount="862" Body="&lt;p&gt;What do I need to plug a regular set of headphones to an Icom ID-51 PLUS2? Would the &lt;a href=&quot;http://www.icomuk.co.uk/categoryRender.asp?categoryID=3766&amp;amp;productID=1166&amp;amp;tID=938&quot; rel=&quot;nofollow noreferrer&quot;&gt;Icom OPC-2144&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nlHgd.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nlHgd.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or the &lt;a href=&quot;http://www.icomuk.co.uk/categoryRender.asp?categoryID=3766&amp;amp;productID=1167&amp;amp;tID=938&quot; rel=&quot;nofollow noreferrer&quot;&gt;Icom OPC-2006LS&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AOXql.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AOXql.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;allow me to connect a regular set of headphones?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-04T18:36:11.253" LastActivityDate="2018-04-06T22:11:13.863" Title="What do I need to plug a regular set of headphones to an Icom ID-51 PLUS2?" Tags="&lt;icom&gt;&lt;icom-id-51-plus2&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9304" PostTypeId="1" CreationDate="2017-10-02T21:28:02.527" Score="5" ViewCount="747" Body="&lt;p&gt;This tower is located on the campus of my wife's employer.  She's asked around but no one seems to know the purpose of it.  Does anyone have any idea what this may be used for?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edited to add Additional Information:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This tower is located on a corporate campus in Naperville, IL, USA.  The entire complex is fenced and secure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zhHyg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zhHyg.jpg&quot; alt=&quot;Tower&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edited to add additional information:&#xA;All the cell towers we have around here look similar to these, with these types of antenna arrays.  There are no others that just have 3 verticals, so I hesitate to accept &quot;cell tower&quot; as the correct answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ssx4O.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ssx4O.png&quot; alt=&quot;Cell Tower&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/NAM3r.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NAM3r.jpg&quot; alt=&quot;Multi-Cell Tower&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2017-10-12T04:07:29.840" LastActivityDate="2017-10-12T04:07:29.840" Title="What might this tower be used for?" Tags="&lt;antenna&gt;&lt;tower&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9305" PostTypeId="2" ParentId="9304" CreationDate="2017-10-02T22:10:43.490" Score="5" Body="&lt;p&gt;That's a typical cell phone tower. The 3 antennas are phased so that they can change direction when receiving. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-10-02T22:10:43.490" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9306" PostTypeId="2" ParentId="9304" CreationDate="2017-10-02T22:11:42.123" Score="1" Body="&lt;p&gt;It's kind of hard to make out on the picture, but it looks like there's something dish-y on the right: So that's very likely a microwave point-to-point link. That might be used as some cellular network's backhaul, for some intra-company communication, video stream, basically anything that has reasonably high rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I favor the cellular backhaul theory, since a) that is very common, and b) the box at the bottom of the tower looks reasonably much like a enodeB box I know from LTE installations. Con is the lack of good fence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The three poles are probably multi-antenna elements that actually do the up- and downlink between user equipment and base station.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-10-02T22:11:42.123" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9307" PostTypeId="1" CreationDate="2017-10-03T12:16:00.410" Score="2" ViewCount="3177" Body="&lt;p&gt;My wife is a teacher at a school about 15 miles from our home.  My growing concern about a possible EMP event (natural or man-made) led me to buy a pair of Baofeng UV-5RV2+ radios in the hopes of allowing us to communicate after such an event (I intend to form a Faraday cage by wrapping them in foil in order to survive the EMP).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a 35 foot high rotating TV antenna mast at my home.  My question is what would be the best directional antenna to mount on this mast to maximize my range for transmission and receiving?  Also, what would be the best portable antenna for my wife's radio in order to maximize her range (it could be a collapsible unit that could be stored in her car).&lt;/p&gt;&#xA;" OwnerUserId="10448" LastEditorUserId="9493" LastEditDate="2017-10-03T12:55:01.147" LastActivityDate="2017-10-03T19:17:54.207" Title="best antenna for Baofeng" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9308" PostTypeId="1" CreationDate="2017-10-03T12:36:17.950" Score="1" ViewCount="103" Body="&lt;p&gt;A quick question: Is it a disaster if the two legs of a v-dipole antenna are different resistances? Thanks.&lt;/p&gt;&#xA;" OwnerUserId="10449" LastEditorUserId="9493" LastEditDate="2017-10-03T12:44:16.980" LastActivityDate="2017-10-03T17:04:41.563" Title="Resistance of antenna dipoles" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9309" PostTypeId="2" ParentId="9308" CreationDate="2017-10-03T12:48:35.353" Score="2" Body="&lt;p&gt;If you are speaking of a different DC resistance in each leg, such as would be the case when different gauges of wire are used in each leg, this normally should not be a significant problem. If you are dealing with a very extreme case, you may wish to post more details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What this would impact is the efficiency of the antenna. Efficiency is one of the factors that determine gain. But the radiation resistance of an inverted V is quite high, so any small increase in loss due to a different gauge of wire will have a minimal impact on efficiency or gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feeding the antenna with a proper 1:1 balun will also help to minimize any side effects from minor loss differences in the legs.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-03T17:04:41.563" LastActivityDate="2017-10-03T17:04:41.563" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9310" PostTypeId="2" ParentId="9307" CreationDate="2017-10-03T13:28:39.450" Score="2" Body="&lt;p&gt;Nuclear initiated EMP events are by nature, low in frequency (below 100 MHz). The estimated energy of such an EMP event is less than 1 J/m&lt;sup&gt;2&lt;/sup&gt; at the ground level. Antennas and power lines are the major collectors of this energy. Due to the low frequency nature of the EMP spectrum, an 80 meter dipole could deliver a 1 MV pulse to the feedline. The best protection for your VHF radios is to simply remove the antenna and any other cables since these act as collectors of EMP energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The aluminum foil may actually increase the susceptibility of the radio to EMP damage if not made and maintained correctly. Here are a few of the basics: The skin depth in aluminum at 1 MHz is 82 &lt;em&gt;u&lt;/em&gt;m. It is considered best practice to use a material with at least five times this penetration depth or 410 &lt;em&gt;u&lt;/em&gt;m. Common household aluminum foil is 16 &lt;em&gt;u&lt;/em&gt;m thick and heavy duty household foil is 24 &lt;em&gt;u&lt;/em&gt;m thick. As a result, a generous portion of the 1 MHz energy will pass through the foil. This effect is multiplied by the fact that larger surface area of the foil allows it to more effectively couple to the 1 MHz energy. The net result is that more 1 MHz energy could be coupled to the radio with this faux Faraday cage than with simply leaving the antenna jack open circuited.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding antennas and range, keep in mind that on VHF, most of the communications takes place on a line of site basis. You may get &quot;lucky&quot; and get just the right reflection or scattering from the geography or man made objects but this should not generally be relied upon. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few watts EIRP will allow point to point communications on VHF with line of site conditions. You should first focus on height of the antennas and then secondarily on gain. The gain of the antenna may help you overcome minor fringing, foliage attenuation, and interfering signals or noise sources but it cannot typically and reliably make up for a blocked line of site. Put another way, you could invest in expensive, high gain antennas and still not be able to reliably communicate without line of site conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two approaches you can take. You can do empirical work by experimenting with various antennas and antenna heights. This could be done with some simple home built 1/4 wave ground plane antennas placed on extendable painters poles held up by hand. Once you have communications, experiment with the power level and height required to maintain the link. Keep a log book of the results of your experiment so you can translate this into the final solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The alternative approach is to study the topology between the two locations in order to reach some general conclusions. An on-line topographical map and a drive through the area can be quite instructive. Once you have a sense of what should be possible, you can then proceed to experimentation to verify your findings.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-03T16:18:14.927" LastActivityDate="2017-10-03T16:18:14.927" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9311" PostTypeId="1" CreationDate="2017-10-03T14:08:22.513" Score="5" ViewCount="1151" Body="&lt;p&gt;Any ham radio log processing app developers?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am creating web application to manage our club award and I need to programmatically distinguish European from non European stations by call sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I cannot find viable solution so any hint is valuable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use PHP but I guess any other platform experience could be helpful.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2017-10-04T17:05:14.713" Title="How to programmatically distinguish European from non European call sign?" Tags="&lt;callsign&gt;&lt;logging&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9312" PostTypeId="2" ParentId="9304" CreationDate="2017-10-03T14:25:25.383" Score="4" Body="&lt;p&gt;The picture isn't of sufficient quality to say for sure, we would need a better closeup of the cabinets and antenna elements to say with any kind of confidence. Also without knowing the country and region where it is situated, it would be hard to compare to what existing operators use for what in said region.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on the image alone however I would say it is unlikely to be a cell phone tower, especially an LTE one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna elements appear to be omni-directional pole antenna, both from the shape and the mounting structure, which are practically never used in modern cell-phone installations. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna were in fact very slim sectorized antenna, that would indicate a high frequency (1.8Ghz+) system. Given the height of the tower (&gt;=25 metres), a mast head amplifier (MHAs) or remote radio head (RRHs) would normally be used for high frequency cell sites as you would lose a third to a half of the signal in the cabling. Again this could be due to distance the photo was taken at, but there are no visible MHAs or RRUs in the image.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The microwave dish does however suggest a multi-site or cellular system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My guess would be smart metering system, emergency services radio (e.g. TETRA), or some form of private communications such as on-site walkie talkies (e.g. PBR), fire alarm systems, etc. Could also be a very old cellular paging system. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regardless, a close-up picture of the cabinets at the bottom would tell us a lot more.&lt;/p&gt;&#xA;" OwnerUserId="10450" LastActivityDate="2017-10-03T14:25:25.383" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9313" PostTypeId="2" ParentId="9311" CreationDate="2017-10-03T14:36:03.830" Score="4" Body="&lt;p&gt;The ITU is the international body responsible for the allocation of call sign prefixes to each country. You can consult this table of allocations in order to build the necessary logic in your program to determine if the call sign in question meets your award requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example of this table of ITU allocations can be found at: &lt;a href=&quot;http://www.arrl.org/international-call-sign-series&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/international-call-sign-series&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a snip of that table:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FJMQA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FJMQA.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an alternative, you could subscribe to the QRZ.COM call sign lookup service. The data is exchanged via XML so you could resolve the country from the appropriate XML tag. This may not be fool proof, however, if the call sign in question is not in their database or if the entry contains an error.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-04T17:05:14.713" LastActivityDate="2017-10-04T17:05:14.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9314" PostTypeId="2" ParentId="9311" CreationDate="2017-10-03T15:45:39.237" Score="11" Body="&lt;p&gt;Jim Reisert AD1C regularly publishes &lt;a href=&quot;http://www.country-files.com/&quot; rel=&quot;noreferrer&quot;&gt;various downloadable country files&lt;/a&gt; containing an up-to-date list of callsign prefixes with their associated countries, continents, etc. &lt;em&gt;Those files are meant to be used by ham software.&lt;/em&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's three lines from a 2016 cty.dat file. &lt;strong&gt;Notice how the fourth column indicates the continent&lt;/strong&gt; (SA, &lt;strong&gt;EU&lt;/strong&gt;, AF).&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Guyana:  09:  12:  SA:    6.02:    59.45:    4.0:  8R:&#xA;        8R;&#xA;Croatia: 15:  28:  EU:   45.18:   -15.30:    -1.0:  9A:&#xA;        9A;&#xA;Ghana:  35:   46:  AF:    7.70:     1.57:     0.0:  9G:&#xA;        9G;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;You can download the source of &lt;a href=&quot;http://www.country-files.com/contest/tlf&quot; rel=&quot;noreferrer&quot;&gt;TLF&lt;/a&gt; and see how tlf reads and processes it. I rely on Jim's cty.dat file when I use TLF, a contest logging and dupe-checking program for Linux.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.country-files.com/cty-2710-21-september-2017/&quot; rel=&quot;noreferrer&quot;&gt;Here is Jim's latest country file&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-10-03T19:58:01.740" LastActivityDate="2017-10-03T19:58:01.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9315" PostTypeId="2" ParentId="9307" CreationDate="2017-10-03T19:09:59.047" Score="1" Body="&lt;p&gt;The easiest EMP protection I know of for hand-held radios is an ammunition box (available from Army/Navy Surplus stores).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people grind the top edge of the box and remove the rubber waterproofing gasket from the top part.  This makes a Faraday cage for warm storage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then keep the radio(s) charged, and in between charging store them with any spare batteries in the ammo box.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 701-style 8-inch flex whip antenna is the best fit for such boxes.  They are available from the usual sources. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously, a handheld antenna will not give as much range as a base or mag-mount car antenna - and those antennas, when disconnected, themselves are generally not going to burn out in an EMP event, so can be kept on standby to be connected to the radios after the event.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rotating antennas are the same - as long as they are disconnected they present no path for voltage spikes to come into the radios.  However, the directional controls themselves could well end up disabled.  It may turn out that having an omnidirectional antenna is preferable.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Having said all that, I'm sure it would be obvious that any EMP event would be so devastating that having comms just for the time batteries can last will be very brief compared to the outages of methods to recharge the batteries.  Plus, any car built after about 1990 would likely be disabled due to the internal computers that control the ignition system, et al.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-10-03T19:17:54.207" LastActivityDate="2017-10-03T19:17:54.207" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9317" PostTypeId="2" ParentId="9311" CreationDate="2017-10-04T03:00:36.027" Score="0" Body="&lt;p&gt;I did this years ago and I just looked to see if I could find the code and I must have just let it rot (entropy takes over the bits and turns them into ordered chess openings).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, my method was not fool proof because there are exceptions to the basic rules that everyone knows.  For example, I ran across a special event station in Russia or Finland (can't remember which) that failed my call sign test because it was too long at about 10 characters.  I had a sanity check on the length of I think around 8 characters.  I fixed my sanity check.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My method is straight-forward:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;US calls were easy even though there are some to watch out for such as KG4 prefix is something other than a southern state (if I remember correctly, this was years ago).&lt;/li&gt;&#xA;&lt;li&gt;I downloaded the ARRL list of official country or DX-Entity call sign prefixes and turn it into a database used by my call sign lookup.&lt;/li&gt;&#xA;&lt;li&gt;My program (since I am US resident) always checked US call sign first but as a cheat I also had the US Call sign database in a fast lookup table (all memory resident).&lt;/li&gt;&#xA;&lt;li&gt;Then, I would do a RE prefix check on the ARRL DX-entity list and usually that creates a match to ID the country or entity name (not all entries are countries).&lt;/li&gt;&#xA;&lt;li&gt;If I miss on the program, I make note of it in a log and go check on it later to see why.  Usually it is a weird case that snuck thru or maybe a special event station call sign.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;To test my program when I first ran it, I downloaded the entire QRZ.com database (I was a subscriber with permission to download) and I tested my program against every single call sign in the QRZ database to validate that we had the same DX entity name.  I actually found a few that were incorrect in the QRZ database.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wrote the program in C++ and it ran on my Mac computer and I stopped using it back around 2005 when I started using the MacLoggerDX application which had its own call sign handler.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="76" LastEditDate="2017-10-04T03:12:08.743" LastActivityDate="2017-10-04T03:12:08.743" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9318" PostTypeId="1" AcceptedAnswerId="9321" CreationDate="2017-10-04T08:22:19.917" Score="2" ViewCount="1862" Body="&lt;p&gt;I'm trying to filter a noisy serial line that comes in to a radio (mostly as a thought excercise in line filtering).&#xA;The data comes in on a RS-232 line, 9600 baud, 8n1.&#xA;I've found a lot of explanations, some of them contradicting each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I correct in believing that:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;9600 baud in our case (two states, mark or space) also means 9600 bits per second&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Maximum signal frequency is 9600 Hz (if pattern would be all 010101010)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Using those 9600 baud, only 9600/10=960 characters per second can be send (each character needs 8 bits, plus one start and one stop bit)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If I want to add ferrite beads to the input to filter for EMI, I not only need to take the maximum signal frequency into account, but also x harmonics to allow the signal to rise at a decent rate. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;How do you estimate what kind of impedance at what frequency you need to still allow fast enough rise times?&lt;/p&gt;&#xA;" OwnerUserId="8263" LastEditorUserId="8263" LastEditDate="2017-10-05T07:46:59.317" LastActivityDate="2017-10-05T07:46:59.317" Title="Baud rate/frequency/bandwith/characters per second" Tags="&lt;filter&gt;&lt;noise&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9319" PostTypeId="2" ParentId="9318" CreationDate="2017-10-04T14:55:46.890" Score="4" Body="&lt;p&gt;The issue of filtering RS-232 (or any slow digital signal) is not so much the baud rate as it is the required rise and fall time of each bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two ways to quantify this rise/fall time issue: what does the RS-232 standard say or what does your RS-232 chipset and UART require? I have formulated my answer from the perspective of the former.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RS-232 control signals should maintain a rise/fall time of less than 1 ms. When operating at 19,200 baud, data signals should maintain a rise/fall time of less than 5 &lt;em&gt;u&lt;/em&gt;s. The slew rate of the rise/fall time should not exceed 30 V/&lt;em&gt;u&lt;/em&gt;S to avoid crosstalk. Your filters must be designed to ensure these rise/fall timing constraints are met.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You did not elaborate on the type of EMI/RFI you are experiencing. Filter types commonly deployed for RS-232 signals include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;RC T filters (T for infiltrate and exfiltrate protection)&lt;/li&gt;&#xA;&lt;li&gt;In connector ferrite plates&lt;/li&gt;&#xA;&lt;li&gt;Ferrite beads (material based on filtering requirements)&lt;/li&gt;&#xA;&lt;li&gt;Hybrid cable grounds (if interference is affecting RS-232 chipset)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you are able to describe the exact nature of the interference, perhaps specific guidance could be offered.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-04T15:06:09.387" LastActivityDate="2017-10-04T15:06:09.387" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9320" PostTypeId="2" ParentId="9275" CreationDate="2017-10-04T15:19:12.777" Score="1" Body="&lt;p&gt;No. The D-74 cannot act as an access point/gateway. &lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2017-10-04T15:19:12.777" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9321" PostTypeId="2" ParentId="9318" CreationDate="2017-10-04T15:51:32.387" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Maximum signal frequency is 9600 Hz (if pattern would be all 010101010)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, your 01010101… would lead to a square wave signal, and that has an infinite spectral support, with components at every odd multiple of the symbol rate, amplitude declining with the multiple. So, no, your highest frequency is &lt;em&gt;not&lt;/em&gt; 9600 Hz&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Using those 9600 baud, only 9600/9=1066 characters per second can be send (each character needs 8 bits, plus one parity bit)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Depends on your character encoding, parity bits, as you noticed, but also flow control – your RS232 might have separate CTS / RTS lines, but more often there's start and stop bits. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If I want to add ferrite beads to the input to filter for EMI, I not only need to take the maximum signal frequency into account, but also x harmonics to allow the signal to rise at a decent rate.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The harmonics &lt;em&gt;are&lt;/em&gt; part of the signal. The question is after how many harmonics you can attenuate without killing too much signal. Rule of thumb says 5. or 7. harmonic should be enough for digital lines, but if in doubt: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The series representation of the square wave is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;\frac4\pi\sum\limits_{n=1,3,5,\ldots}^{\infty}\frac{2\pi n f_{symbol}t}{n}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;so just your own discretion!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-10-04T15:51:32.387" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9322" PostTypeId="1" CreationDate="2017-10-04T18:11:01.560" Score="0" ViewCount="1035" Body="&lt;p&gt;I'm studying for my foundation license (in the UK) and I have these diagrams:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IgRwZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IgRwZ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do the radials in a quarter or 5/8 wavelength antennas connect to the braid/shield of the coaxial cable? If so, how does that compare to the ground plane in a magnetic antenna, that is, the roof of a car, that is not electrically connected to the shield of the cable?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="9493" LastEditDate="2017-10-04T22:00:48.027" LastActivityDate="2017-10-05T14:35:23.440" Title="Do the radials of a quarter or 5/8 wavelength antennas connect to the braid of the coaxial cable?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;mobile&gt;&lt;antenna-system&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9323" PostTypeId="1" AcceptedAnswerId="9326" CreationDate="2017-10-04T18:14:38.477" Score="0" ViewCount="27" Body="&lt;p&gt;I'm studying for my foundation level licence in the UK and the book has the following diagram for a receiver:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/osrvd.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/osrvd.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why are tuning &lt;em&gt;and&lt;/em&gt; amplification in the same block? Are they perform at the same time/by the same circuitry?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do remember from secondary school the experiment of having a capacitor and a coil in resonance, increasing voltage. Is this why both happen at the same time?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2017-10-04T18:33:45.753" Title="Why are tuning and amplification in the same block?" Tags="&lt;theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9324" PostTypeId="1" AcceptedAnswerId="9363" CreationDate="2017-10-04T18:23:42.537" Score="2" ViewCount="904" Body="&lt;p&gt;I was recently reading this article from the ARRL web site,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/news/morse-code-at-140-wpm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Morse Code at 140 WPM&lt;/a&gt; (ARRL)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;about Chuck Adams, K7QO, who claims to be able to handle this speed all by himself.  Very interesting article.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to be able to copy above my natural speed, in order to get more familiar with how it sounds.  My goal is to be able to get above the need to copy text but instead transition to simply listening to conversations like we do on SSB in voice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The CW decoding software I have found is not all that reliable, though, with varying levels of accuracy.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it occurred to me that I would like to find some way to have a computer help me copy CW in an &quot;assist&quot; mode - a combination of having the computer help me with text I copy on the keyboard, by maybe flagging letters and symbols where the computer and I disagree.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neither purely me, nor purely the computer, but a combination of both.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there anything like this available?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or is there any other recommended method to achieve this goal?&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-10-07T22:31:38.887" LastActivityDate="2019-01-30T14:54:44.337" Title="How to transition CW ability to listening instead of simply copying - software assist?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9325" PostTypeId="1" CreationDate="2017-10-04T18:31:13.473" Score="1" ViewCount="356" Body="&lt;p&gt;For reception of amateur radio satellites, turnstile antennas (consisting of two crossed dipoles fed out-of-phase) are often used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zerT6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zerT6.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I've recently had an idea - what if two half-wavelength dipoles are made out of coax cable (so-called &lt;a href=&quot;http://www.hamuniverse.com/bazooka.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;bazooka&lt;/a&gt; antennas), and then connected in a T-shape like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;  ' 1/4 wl center&#xA;  '&#xA;  &quot; 1/4 wl braid bent back&#xA;  &quot;&#xA;  .&quot;&quot;&quot;&quot;&quot;----&#xA;  # 1/4  1/4&#xA;  #&#xA;  #&#xA;  #&#xA;  # feed coax&#xA;  #&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;(the vertical and the horizontal antenna cables are connected together at the middle point to the feeder cable (denoted by #)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;: The elements are connected by a phasing line of 1/4 wavelength for a 90-degree shift, not 180 as I originally described.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would this antenna work like a turnstile?&lt;/p&gt;&#xA;" OwnerUserId="10145" LastEditorUserId="8832" LastEditDate="2017-10-18T08:31:19.790" LastActivityDate="2017-10-18T08:31:19.790" Title="Would the antenna described work?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;satellites&gt;&lt;circular-polarization&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9326" PostTypeId="2" ParentId="9323" CreationDate="2017-10-04T18:33:45.753" Score="3" Body="&lt;p&gt;In general, when you see a block diagram, the point of it is that the blocks contain multiple or unspecified elements, but the diagram accurately represents the boundaries of, and connections between, those elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;“Tuning” is not a single process, and in most receivers the amplification is in multiple stages interleaved with the “tuning” elements, so having a “tuning” block followed by an “amplification” block (or vice versa) would be incorrect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;“Tuning” consists of both &lt;em&gt;filtering&lt;/em&gt; and &lt;em&gt;mixing&lt;/em&gt;, and filtering and amplification are usually desired both before and after the mixer(s).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Another question we can ask is: given that the receiver is a complex system of many elements, why did the author of this diagram sum it up in these particular three blocks?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I had made it that way, it would be because these three can be characterized as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The first block deals exclusively in RF and IF signals, and does not change the form of the signal — only its amplitude and carrier frequency.&lt;/li&gt;&#xA;&lt;li&gt;The second block is responsible for converting modulated IF/baseband to audio signals.&lt;/li&gt;&#xA;&lt;li&gt;The third block deals exclusively in audio signals.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-10-04T18:33:45.753" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9327" PostTypeId="5" CreationDate="2017-10-04T18:37:42.273" Score="0" Body="&lt;p&gt;You can learn more about this transceiver at:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.icomamerica.com/en/products/amateur/dstar/id51aplus2/default.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.icomamerica.com/en/products/amateur/dstar/id51aplus2/default.aspx&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.icomuk.co.uk/ID-51E-Plus2/Handheld_Amateur_Radio_Ham&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.icomuk.co.uk/ID-51E-Plus2/Handheld_Amateur_Radio_Ham&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-04T18:54:56.670" LastActivityDate="2017-10-04T18:54:56.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9328" PostTypeId="4" CreationDate="2017-10-04T18:37:42.273" Score="0" Body="Questions regarding the Icom ID-51A/E PLUS2 transceiver." OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-04T18:54:34.657" LastActivityDate="2017-10-04T18:54:34.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9329" PostTypeId="2" ParentId="9322" CreationDate="2017-10-04T18:39:22.743" Score="0" Body="&lt;p&gt;The 1/4 radials are directly connected to the shield of the coax. That is what that diagram is illustrating.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A magnetic mount antenna is also connected, by capacitive coupling to the roof of a car through the paint to the steel. A direct connection to the metal would be superior (less losses), but the magnet has the convenience of being quickly removable. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-10-04T18:39:22.743" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9330" PostTypeId="5" CreationDate="2017-10-04T18:40:35.727" Score="0" Body="&lt;p&gt;You can learn more about this transceiver at:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.kenwood.com/usa/com/amateur/th-d74a/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.kenwood.com/usa/com/amateur/th-d74a/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://kenwoodcommunications.co.uk/amateur-radio/vhf-uhf/handhelds/TH-D74E/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://kenwoodcommunications.co.uk/amateur-radio/vhf-uhf/handhelds/TH-D74E/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-04T18:53:00.013" LastActivityDate="2017-10-04T18:53:00.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9331" PostTypeId="4" CreationDate="2017-10-04T18:40:35.727" Score="0" Body="Questions regarding the  Kenwood TH-D74A/E transceiver" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2017-10-04T18:54:50.060" LastActivityDate="2017-10-04T18:54:50.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9332" PostTypeId="2" ParentId="9322" CreationDate="2017-10-04T18:45:41.990" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Do the radials in a quarter or 5/8 wavelength antennas connect to the mesh of the coaxial cable?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Every&lt;/strong&gt; antenna, at the feed point, has two conductors entering it and connected to &lt;em&gt;something&lt;/em&gt;. When an antenna is fed by a transmission line, that line also has two conductors (shield and center conductor, in the case of coaxial cable) which are connected to the corresponding points of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a common vertical antenna, the shield is always connected to the horizontal conductive structure underneath the vertical element, regardless of the form that structure takes. (The reverse would not work as well, because there are usually incidental indirect connections between the coax shield and ground (whether earth or chassis) at the transmitter's end of the feed line — this does not totally “short out” the antenna system — it forms an unintended loop antenna instead — but it certainly means the antenna is not functioning &lt;em&gt;as designed&lt;/em&gt;. Lots of things will work as antennas by accident, including mis-installed antennas.)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If so, how does that compare to the ground plane in a magnetic antenna, that is, the roof of a car, that is not electrically connected to the mesh of the cable?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The magnetic antenna mount has a wide metal disk in its base, close against the roof. This forms a &lt;em&gt;capacitor&lt;/em&gt;, and as you should know, capacitors can pass RF. Thus, the roof &lt;em&gt;is&lt;/em&gt; electrically connected to the shield of the feed line, just not at DC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best capacitive coupling would be obtained by using a mount with a large surface area. The other factor is the thickness of the dielectric (i.e. your car's paint), but if you're willing to scrape paint off then you might as well install a permanent hole mount instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other differences are that the radials are short and sparse whereas a good roof is contiguous and thick, but they are serving the same function anyway. &lt;a href=&quot;https://ham.stackexchange.com/questions/7642/when-and-why-does-the-size-of-a-ground-plane-or-radials-matter&quot;&gt;see this question and answer for more information on how the size of a ground plane or radials affects an antenna&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-10-05T14:35:23.440" LastActivityDate="2017-10-05T14:35:23.440" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9333" PostTypeId="1" CreationDate="2017-10-04T19:10:06.617" Score="3" ViewCount="626" Body="&lt;p&gt;One of the sample questions for the British foundation level test is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;An amateur has the choice of VHF or UHF for a particular contact of some 25km. Which statement below best describes his choice?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and the correct answer is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The VHF option is most likely to give a better signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There was an equivalent answer with UHF instead of VHF and two almost non-nonsensical ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is VHF better than UHF in this situation?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2017-11-19T00:52:14.423" Title="Why is VHF better than UHF in this situation?" Tags="&lt;propagation&gt;&lt;vhf&gt;&lt;uhf&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9334" PostTypeId="2" ParentId="9325" CreationDate="2017-10-04T19:25:18.193" Score="5" Body="&lt;p&gt;The purpose of a turnstyle antenna for satellite work is to generate a circularly polarized radiation pattern off of its axis. By adjusting the phasing of the feed to the two crossed dipoles, the circular polarization can be switched between left and right hand polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your diagram of the proposed antenna, one element is shown to meet at is end with the other element. This is essentially an inverted V antenna. Changing the phasing of the two legs will simply reduce the gain of the antenna. No circular polarization will be realized in this configuration. As a result, the antenna would not be effective as a satellite antenna.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-05T10:44:25.557" LastActivityDate="2017-10-05T10:44:25.557" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9335" PostTypeId="2" ParentId="9333" CreationDate="2017-10-04T20:03:30.447" Score="1" Body="&lt;p&gt;The answer is correct - VHF will generally be more effective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For like antennas of a specified gain (typically dBi), the energy transfer will be higher as the operating frequency is decreased.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This may at first seem to be an odd condition since if the gains of the antennas are the same and all other things are equal, shouldn't the received energy be the same regardless of frequency? The answer lies in the effective size of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, a 1/4 wave vertical antenna on VHF has a length of about 50 cm. A 1/4 wave wave vertical antenna on UHF has a length of about 17 cm. Both antennas have the same gain. But placed the same distance from their respective transmitters, the longer length of the VHF  antenna will intercept and collect more energy. Said another way, the VHF antenna is exposed to more radiant flux. Since the VHF antenna is nearly 3 times longer, it is exposed to nearly 3 times the radiant flux. As a result, the VHF antenna develops more power at the receiver terminals than the UHF antenna. In fact, the VHF signal will be more than 9.5 dB stronger than the UHF signal (~$20\log(3)$).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a deeper understanding of the impact of the change in frequency, study the Friis equation below, taking note of the frequency term, or use one of the many on-line calculators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{Path Loss (dB)} = 20\log(d) + 20\log(f) +32.44 - G_{\text{TX}} - G_{\text{RX}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$d$ = distance in km&lt;br&gt;&#xA;$f$ = frequency in MHz&lt;br&gt;&#xA;$G_{\text{TX}}$ = transmitter antenna gain in dBi&lt;br&gt;&#xA;$G_{\text{RX}}$ = receiver antenna gain in dBi&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-04T21:08:27.523" LastActivityDate="2017-10-04T21:08:27.523" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9336" PostTypeId="2" ParentId="9333" CreationDate="2017-10-05T06:08:12.910" Score="9" Body="&lt;p&gt;This is an ill-posed question, since &quot;best&quot; could mean so many things. If VHF is so plainly best, why does anyone bother with UHF at all?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you mean what option has a lower path loss, then sure VHF is the better option. But then HF would be even better. And why not go with ELF? &lt;a href=&quot;https://ham.stackexchange.com/questions/3692/is-free-space-path-loss-dependent-on-frequency&quot;&gt;As the frequency decreases, so do free space path losses&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, an ELF antenna would be many kilometers long. While ELF would certainly be &quot;best&quot; in terms of free space path loss, when considering the entire proposition including constructing such an antenna, ELF isn't &quot;best&quot; by what most people would assume as the criteria.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference between UHF and VHF is of course less extreme, but you still have to wonder, what are the optimization criteria? While VHF has a lower free space path loss, it also requires a physically larger antenna to achieve a comparable gain as UHF. So if &quot;best&quot; means &quot;minimum physical size to realize a reliable link&quot;, then there's not much difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or perhaps the use case is an interference limited point-to-point link. In this case, for antennas of equal effective aperture, the UHF antenna will have higher directivity, while likely being about the same physical size of a VHF antenna of equal effective aperture. So in this scenario UHF is superior, since the necessary directionality can be achieved by a physically smaller antenna on UHF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe you desire some degree of privacy. Again, the higher directivity at higher frequencies given a limited physical size makes higher frequencies better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or perhaps &quot;best&quot; means lowest equipment cost. Technology is always advancing, but it's generally true that electronics to operate at lower frequencies are older and cheaper, so VHF has an advantage here. In modern times the difference in cost between 144 MHz and 440 MHz isn't much, but if we are pushing the 3 GHz upper limit of &quot;UHF&quot;, the opportunities to find cheap, used gear decrease. Unless you can use consumer commodity 2.4 GHz equipment, in which case economies of scale make it the cheaper option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or perhaps &quot;best&quot; means there's an available frequency to use. UHF allocations tend to be bigger and newer, and so have more unallocated channels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does &quot;best&quot; mean lowest noise floor? The natural noise floor generally decreases at higher frequencies, but man-made noise may be the bigger issue. Depending on what man-made sources you have to contend with, this could go either way. For example if UHF means specifically the 13 cm band, you may need to contend with the 2.4 GHz ISM band, including microwave ovens, cordless phones, and consumer Wi-Fi radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or perhaps you'll consider that for frequencies too high to support ionospheric propagation, the radio horizon imposed by the height of the antennas can be more a limiting factor than raw power or free space path loss. In this case perhaps you would favor UHF for its smaller &lt;a href=&quot;https://en.wikipedia.org/wiki/Fresnel_zone&quot; rel=&quot;noreferrer&quot;&gt;Fresnel zone&lt;/a&gt;, if your link is at the limits of the radio horizon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe &quot;best&quot; means the signal can penetrate buildings. In this case VHF is the winner, since lower frequencies generally penetrate better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or perhaps you need to communicate beyond the radio horizon, or you don't have a direct line of sight. In this case UHF may be better since decreased building penetration means more effective reflection, thus allowing a building to be used as a passive reflector, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or perhaps your concern is what equipment the other operator has? Or what local repeaters exist? Such simple practical considerations often outweigh more theoretical ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could go on, but the point should be clear: while the question clearly expects an answer framed by free space path loss, this is only but one consideration, and a minor one at that. In practice on VHF and higher, radio horizon and interference are the limiting factors. For digital modulations especially, multipath distortion limits range. And while not much of a problem for hams, the monetary cost of obtaining an allocation is probably the primary factor in selecting a frequency. It's a shame that an amateur radio exam reduces what's actually a multi-faceted problem to rote memorization or just free space path loss, but there you have it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-10-05T16:36:18.570" LastActivityDate="2017-10-05T16:36:18.570" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9337" PostTypeId="2" ParentId="9293" CreationDate="2017-10-05T07:36:49.883" Score="2" Body="&lt;p&gt;As your Icom is 'brand new' as you described it, I would strongly recommend to contact Icom &lt;a href=&quot;http://www.icomamerica.com/en/support/default.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;support&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Technical Support Department&lt;/p&gt;&#xA;&lt;p&gt;Dedicated number  800-253-1498&lt;/p&gt;&#xA;&lt;p&gt;Monday - Friday 4AM to 5PM PST&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;They are there to help you.&lt;/p&gt;&#xA;&lt;p&gt;Just in case you are wondering: I did not find a number for Icom support in Argentina (based on your call) nor did I find a satisfying answer from &lt;a href=&quot;http://icomuk.co.uk/Icom_Support&quot; rel=&quot;nofollow noreferrer&quot;&gt;Icom UK website&lt;/a&gt; (based on the fact that your user profile lists UK as your location).&lt;/p&gt;&#xA;&lt;p&gt;However you may just want to &lt;a href=&quot;http://icomuk.co.uk/Contact_Us&quot; rel=&quot;nofollow noreferrer&quot;&gt;contact&lt;/a&gt; Icom UK, to see if they have a support department locally to you.&lt;/p&gt;&#xA;&lt;p&gt;Failing all that, you can try to contact the Japanese headquarters &lt;a href=&quot;http://www.icom.co.jp/world/support/contact/&quot; rel=&quot;nofollow noreferrer&quot;&gt;support&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-10-05T07:36:49.883" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9338" PostTypeId="2" ParentId="1399" CreationDate="2017-10-05T14:13:39.977" Score="1" Body="&lt;p&gt;Some claim it supposedly reduces PIM (passive interference modulation) because (pure untarnished) silver has better conductivity and skin effect than gold. Additionally gold is often plated over nickel which promotes adhesion and blocks base substrate diffusion, but nickel is ferrous and undesirable for RF connectors. Gold will tarnish if plated directly over copper.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally I think it increases MIP (money in pocket) and is mainly used over gold for that reason alone. Nothing will convince me to ever use it over gold for connectors. &lt;/p&gt;&#xA;" OwnerUserId="10464" LastEditorUserId="10464" LastEditDate="2017-10-05T14:35:04.980" LastActivityDate="2017-10-05T14:35:04.980" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9339" PostTypeId="2" ParentId="6160" CreationDate="2017-10-05T22:11:00.963" Score="1" Body="&lt;p&gt;Transmitters provide different levels of power, efficiency and distortion as the load changes.  This is studied using a technique called &quot;load pull&quot; by applying different loads to the transmitter and noting the effect on the three things mentioned above.  Then output networks are designed to provide the most optimum trade off between these three things.  For a transmitter which operates over a wide frequency range such as 1.8 to 30 MHz, this optimum load will vary somewhat with frequency.  Therefore circuitry is made as broadband as possible to optimize the load over this range.  At a given frequency and power level, changing the load seen by the transmitter by using an antenna tuner, for example, could further optimize this three way tradeoff, but the operator would have to monitor power output(easy to do) efficiency (somewhat harder to do) and distortion (quite hard to do).  Therefore it is best to assume that 50 ohms resistive load is the best to use at all frequencies and power levels. Transmitters sort of force you to do this by backing off the power when the SWR is high, meaning the load is not 50 ohms. Bypassing the &quot;SWR foldback&quot; and tuning for maximum output power is likely to cause efficiency and distortion to suffer more often than not. In a similar manner, tuning for best efficiency or distortion would probably reduce the power more often than not. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Getting back to the original question, IF one could monitor efficiency, power and distortion, one could tune at a given frequency and power level to make the transmitter run cooler with acceptable power and distortion.  This would represent the case where the load resistance AT THE OUTPUT DEVICES was somewhat higher than normal, just like the case of the audio amplifier. In practice this is quite impossible for normal wide band transceivers, which are always operating in somewhat of a compromised condition.  &lt;/p&gt;&#xA;" OwnerUserId="10466" LastActivityDate="2017-10-05T22:11:00.963" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9340" PostTypeId="2" ParentId="5133" CreationDate="2017-10-06T06:02:26.650" Score="-1" Body="&lt;p&gt;It might have to do with the actual construction of the bridge itself.The spacing of the rebar in the concrete if is less than a wavelength it could very efficiently kill signal. The weird thing with VHF/UHF signal reception is sometimes if you are X distance away from a metal object zero signal and then if you move  6&quot; inches left or right of X distance the result is great signal.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A similar effect is noticed in bridges with metal superstructures, FM broadcasts are passed no problem but AM broadcast transmission are blocked. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM broadcast band wavelength is about 3 meters in length whereas AM broadcast band the wavelengths range from 175 meters to 560 meters in length. I suspect this the cause of your reception issue.&lt;/p&gt;&#xA;" OwnerUserId="6604" LastActivityDate="2017-10-06T06:02:26.650" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9341" PostTypeId="2" ParentId="9325" CreationDate="2017-10-06T13:58:07.997" Score="0" Body="&lt;p&gt;You specify that&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the vertical and the horizontal antenna cables are connected together at the middle point (in parallel, center-braid braid-center and to the feeder cable)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Swapping the two conductors of a transmission line (in the cases where it makes sense at all) produces a &lt;strong&gt;180°&lt;/strong&gt; phase shift, not a 90° one. Therefore, this antenna design will not produce circular polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your antenna design is based on identical perpendicular elements, one of those elements &lt;em&gt;must&lt;/em&gt; have a 90° phase shift applied such as by a delay line (1/4 wave extra length of coax).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you did add a 90° phase shift to one element it seems like it could work but I'm not sure what the effect of having the two ends of differing voltage meet at a corner would be. I think at that point you would be better off using antenna modeling software to get a simulated answer.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-10-06T14:57:15.690" LastActivityDate="2017-10-06T14:57:15.690" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9342" PostTypeId="1" AcceptedAnswerId="9348" CreationDate="2017-10-06T16:11:33.683" Score="6" ViewCount="3764" Body="&lt;p&gt;I'm making my first ventures into HF with a Yaesu FT-450D and a homebrew 20 Meter inverted-V antenna a local ham helped me set up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've noticed that the 20 Meterm band seems to have lots of background noise (QRN) everywhere in the band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The S-meter is sitting at 7 constantly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;By comparison, 30m is at 5, 40m is 1, and 10m is at 1. Of course, this is connected to the same 20M antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this amount of noise normal, or am I more likely picking up something nearby that means I should change my antenna setup?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Additional notes answering comments&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I'm near Saint Louis, MO. &lt;/li&gt;&#xA;&lt;li&gt;Noise has been steady at this level as long as I have it connected to the antenna. No change between daytime and evening.&lt;/li&gt;&#xA;&lt;li&gt;It sounds somewhat similar to static you might hear on old analog TV stations, or AM radio sets. It does &lt;em&gt;not&lt;/em&gt; sound like a 60hz hum.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Resolution(ish)&lt;/strong&gt;&#xA;- Confirmed with a local ham that when 20m is dead, he reads background noise less than S1.5 at the most with his setup.&#xA;- Powering down the entire house (all breakers off) and running the radio off the car brought noise down to S3 or so.&#xA;- Investigation into individual breakers eventually led to my Uninterruptible Power Supply units. I have 5 in the house on 4 different circuits. Powering each one on individually incrementally increased the base noise level from S3 (all off) to S7 (all on).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I will research eliminating noise from UPSs separately (and probably asking a separate question). I will also be adding a 1:1 choke as soon as I can build one.&lt;/p&gt;&#xA;" OwnerUserId="10424" LastEditorUserId="8832" LastEditDate="2018-04-18T05:19:29.933" LastActivityDate="2019-01-15T01:58:00.480" Title="Is 20m noisy, or do I have a lot of local interference?" Tags="&lt;hf&gt;&lt;rfi&gt;&lt;noise&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9343" PostTypeId="1" CreationDate="2017-10-06T16:51:05.607" Score="1" ViewCount="513" Body="&lt;p&gt;I'm trying to build an array of patch antennas in order to receive a GPS signal. The idea is to build 4 patches and connect them with a corporate feed network. An example of corporate feed is this one. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/p6oVw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/p6oVw.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my design the 4 patches are oriented in 4 different direction (eg. the first one looking at EAST, the second WEST, the third NORTH and the last one looking at SOUTH).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I have two question about this design:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The output are not matched (since I'm using T-junctions) so some of the power received will come back at the antenna and will be re-radiated. Is this a problem?&lt;/li&gt;&#xA;&lt;li&gt;Can I have total cancellation if, for example, two patched receive two identical signal with 180 degree of phase shift between them?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Unfortunately I can't use other antenna design such as dipole antennas or helix. The problem is that this antenna will fly on a home-made rocket: the rocket will spin fast after lift off so I decided to design this array in order to achieve the best omnidirectional antenna possible while preserving the aerodynamics of the rocket itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rocket is fully metallic, so, no antennas inside.&lt;/p&gt;&#xA;" OwnerUserId="10469" LastEditorUserId="76" LastEditDate="2019-03-13T01:49:21.810" LastActivityDate="2019-03-13T01:49:21.810" Title="Total cancellation in corporate feed network for patch antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;feed-line&gt;&lt;phased-array&gt;&lt;gnss&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9344" PostTypeId="2" ParentId="5106" CreationDate="2017-10-06T17:07:41.273" Score="2" Body="&lt;p&gt;Google &quot;load pull&quot; and you will find that with real world solid state amplifiers, it is useful for the designer to try many different loads on an amplifier,(at its output, typically), and see what combination of real and reactive load produces the best combination of power, efficiency and distortion. The output networks of the single frequency/single power level amplifier would then be designed so that that optimum operating point corresponds with the specified design load (typically 50 ohms).  While one or more parameters might be better operating away from a 50 ohms resistive load, that would violate the designers choice of overall optimum operation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have to use a length of transmission line as a matching device, you are not operating with a flat line and loss will increase.  Not a recommended technique in most cases. You could however use a 75 ohm line to connect between a 50 ohm transmitter and a 50 ohm antenna by cutting the line to an electrical half wave.  This causes the transmitter to see the antenna impedance since to a good approximation (neglecting losses), the impedance on a line repeats each half wave. Using 75 ohm line in this way operates the line with 1.5 SWR, but this would not be a serious problem in most cases.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I see your question as asking if in the general case there is any advantage when operating into a high SWR to have a particular line length,for example a pure resistance not a mixed real and reactive one. While you will be operating away from the design load it could improve efficiency or power or distortion but probably at the expense of the other two.  Not recommended, but in some cases you might find that one line length would burn up your amplifier and another wouldn't.  In that case I suppose the one that didn't would be more optimum. The transistors would likely run cooler when the load at the transistors real and higher than the normal load.  Because of the effect of the output networks, this point would be very difficult to find.  &lt;/p&gt;&#xA;" OwnerUserId="10466" LastActivityDate="2017-10-06T17:07:41.273" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9345" PostTypeId="2" ParentId="6545" CreationDate="2017-10-06T17:16:46.527" Score="2" Body="&lt;p&gt;I built a homebrew interface that uses a small USB soundcard with mic and ear 1/8&quot; jacks. Each of those drives a 600:600 ohm transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the radio side, the transformers drive the mic and ear connections via the 2.5 and 3.5mm jacks. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also used a cheap USB to serial board to run an optoisolator to trigger the radio PTT. The reason for this is that if you use the radio VOX to initiate transmit, the radio will stay in transmit for some time after the data have been sent, and it misses the return data from the packet server. This took me some time to discover!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All that being said, I have found that it is hard to set levels properly, and my connection reliability has been spotty. I have been able to send/receive email using Winlink Express along with soundmodem software, but quite often, the system just keeps trying to connect without success, so I'm not sure that using the Baofeng radios is the best solution.&lt;/p&gt;&#xA;" OwnerUserId="10470" LastEditorUserId="8832" LastEditDate="2017-10-08T00:25:25.713" LastActivityDate="2017-10-08T00:25:25.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9346" PostTypeId="2" ParentId="9343" CreationDate="2017-10-06T17:50:19.290" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The output are not matched (since I'm using T-junctions) so some of the power received will come back at the antenna and will be re-radiated. Is this a problem?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A problem for you? It will reduce your received power, of course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A problem for anyone else? It is no more problematic than any random bit of RF-reflective metal in the environment — better, in fact, since your receiver and line loss will attenuate the signal.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Can I have total cancellation if, for example, two patches receive two identical signal with 180 degree of phase shift between them?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. &lt;em&gt;Every&lt;/em&gt; antenna design has nulls somewhere, for some combinations of transmitter direction and polarization; this is a fundamental property of receiving coherent radiation. The only complete solution is to use two or three antennas (possibly built into a single system that has multiple feed points) each with independent receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna design for a single antenna is a matter of arranging so that the nulls land in a place you don't care about as much.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-10-06T17:50:19.290" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9347" PostTypeId="2" ParentId="9342" CreationDate="2017-10-06T17:54:40.717" Score="4" Body="&lt;p&gt;At my home, background noise is typically S6-S9 pretty much all the time on anything lower than 20 meters. 17 and up is generally less noisy, although I occasionally will have some really strong noise on 10m.&#xA;In investigating this, I tried running my radio (IC-718 with a 40m cut OCF dipole, mildly sloping wires, peak at about 25 feet, directly over the house) on a battery and shutting off the entire house electrical system. This dropped the noise level to about S3-S5. However - as I switched on breakers one-by-one, I found one breaker seemed to raise the noise level more than the others, but I could not figure out where the noise was being generated, as I disconnected all the loads I could find on that circuit, and still had the noise. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One local ham suggested that it could be my doorbell transformer, as apparently they have some kind of thermal device on the transformer that can get noisy, but I cannot find my doorbell transformer! Your situation sounds similar to mine, except that 40 is very noisy for me, also. It could also be that using the 20m antenna on 40, the mismatch might be causing a loss of sensitivity. If it is any way possible to change the antenna location, see if the noise seems to lessen as you move it away from the house.&lt;/p&gt;&#xA;" OwnerUserId="10471" LastEditorUserId="9493" LastEditDate="2017-10-07T10:58:47.993" LastActivityDate="2017-10-07T10:58:47.993" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9348" PostTypeId="2" ParentId="9342" CreationDate="2017-10-06T18:57:06.783" Score="4" Body="&lt;p&gt;Make certain you have a 1:1 choking balun at the apex of your antenna. This will reduce or eliminate the possibilty of common mode currents on your feedline causing it to pickup local interference on receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some other troubleshooting ideas:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check your radio's power supply for noise by substituting a battery and disconnecting the PS from the wall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Run your receiver on a battery and turn off your main breaker. Make sure any battery powered computers/tablets are fully powered off. If the noise reduces, turn off all branch breakers, turn the main breaker back on, and one by one turn on the branch breakers noting any change in noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Install an additional 1:1 balun close to your radio. This sometimes helps prevent local noise pickup on the coax outer shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check your coax for any open or marginal connections - especially the shield connections. Try substituting other coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Eliminate any tuner, linear, SWR meters, and patch coax cables and note any change in noise levels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a lightning arrestor on your coax, try temporarily bypassing it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try temporarily removing any station grounds leaving the AC safety ground in place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take your transceiver to a location in the country with a portable antenna and running off batteries to eliminate receiver problems. Alternatively take it to another ham's QTH that isn't suffering from noise to check it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Borrow or rent a battery powered spectrum analyzer and walk your QTH and the neighborhood sniffing for RFI with a small dipole or loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After eliminating all other possibilities, call the power company and let them know you suspect a cracked insulator or bad transformer is causing RFI. They have techs that specialize in these sorts of problems.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-10-06T18:57:06.783" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9349" PostTypeId="2" ParentId="9343" CreationDate="2017-10-06T19:14:43.943" Score="3" Body="&lt;p&gt;I recommend eliminating the array altogether and instead put a single patch antenna inside the rocket body facing upward. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequencies of GPS signals will freely penetrate a non-metalic body, nose cone, and parachute. Place any other electronics below the patch antenna so as to not obscure its view of the satellite constellation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A patch antenna in this orientation will be largely insensitive to rotation of the rocket body and the patch will be positioned with its maximum gain facing the constellation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mission weight savings will be an added benefit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The OP added the condition that the entire rocket is of metal construction. The Haigh-Farr WrapAround Antenna is specifically designed for sounding rocket purposes. It is generally machined into the metal body of the rocket. In addition to GPS reception, the device can incorporate telemetry antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tMede.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tMede.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other sounding rocket designs have encapsulated a helix antenna in a synthetic tip of the metal nose cone. This has proved suitable for the trajectory through apogee. Switchable patch antennas are then used to track the decent trajectory.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-07T14:21:02.733" LastActivityDate="2017-10-07T14:21:02.733" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9351" PostTypeId="1" CreationDate="2017-10-06T21:06:09.597" Score="4" ViewCount="572" Body="&lt;p&gt;I've tried several cordless phones (most recently KX-TG570), and all seem to frequently pick up terrible RF interference. I have a neighbor that is a ham enthusiast, with large antenna masts on the first rooftop, and it does seem to coincide with his use periods. I'd prefer not to bother him about it, but if I could solve it another way, that would be great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried wrapping the phone cord in a loop to act as a filter. I also asked IP about it, and they said I never upgraded to VOIP yet. Would that really help this case? I would think the cordless hand units themselves may pick up the RF interfernce and maybe not just the physical rj11 line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I read a few other threads about internet interference, but in my case I'm more concerned about phone line RFI here.&lt;/p&gt;&#xA;" OwnerUserId="10474" LastEditorUserId="9493" LastEditDate="2017-10-14T03:58:53.977" LastActivityDate="2021-02-24T20:15:45.340" Title="Cordless phone consistently experiencing RFI" Tags="&lt;rfi&gt;" AnswerCount="6" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9352" PostTypeId="2" ParentId="9343" CreationDate="2017-10-06T21:08:38.413" Score="1" Body="&lt;p&gt;On 1) let me take you through a though experiment I created, struggling with the same problem with a ring of antennas fed to make an Omni. You can back it up by calculation later.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas are reciprocal devices. Gain in transmit is the same as gain in receive. If you transmit into the bottom port, the corporate feed / matching network works perfectly, power splits evenly and each patch radiates the same power, in phase (assuming no coupling between antennas). No need for proper isolated Wilkinson splitters with resistors; the resistors would not dissipate any power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So why worry about power reflection in receive? Just take it on trust that when receiving, the gain will be patch gain - 6 dB (assuming the patterns don't overlap, etc)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The picture when receiving is more complicated - what happens to a signal arriving on only one patch, as the network is far from matched this way around. You can work out the impedances if you're careful. The answer is that some of the power is reflected back to the receiving antenna, some is re-radiated from the other antennas in the array, and only 1/4 of the power comes out of the feed at height bottom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you do better? No, not without a switch.&#xA;Using isolated Wilkinson splitters, you know you'll suffer 3 dB each time, the power being lost in the resistors.&#xA;There's also no matching network that can efficiently combine power from any of four patches, to a single output, without loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you trust the reciprocity, you don't have to do the analysis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In summary, some power will be reflected, but it's not a problem, and there's no way to reduce the reflection/absorption losses in the network.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2017-10-06T21:08:38.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9353" PostTypeId="1" CreationDate="2017-10-06T22:40:08.460" Score="3" ViewCount="2718" Body="&lt;p&gt;Is there a way to use a Bluetooth headset with my transceiver to eliminate all the wires, like a Bluetooth adapter? It seems like all the Bluetooth applications require a smartphone in the loop somewhere, and I don't have one.&lt;/p&gt;&#xA;" OwnerUserId="10475" LastEditorUserId="8717" LastEditDate="2017-10-06T22:50:18.230" LastActivityDate="2017-10-08T16:15:43.477" Title="Bluetooth headset for transceiver?" Tags="&lt;transceiver&gt;&lt;equipment-design&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9354" PostTypeId="1" AcceptedAnswerId="9372" CreationDate="2017-10-05T16:06:44.817" Score="2" ViewCount="2728" Body="&lt;p&gt;I just built a UHF Yagi antenna for my HT, and I was thinking about adding VHF elements. If I do, could I just connect the coax directly to both sets of elements without a diplexer?&lt;/p&gt;&#xA;" OwnerUserId="10491" OwnerDisplayName="MrSchmuck" LastEditorUserId="76" LastEditDate="2017-10-06T23:44:39.427" LastActivityDate="2017-10-10T03:44:02.273" Title="Feeding a dual-band UHF and VHF Yagi antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vhf&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9356" PostTypeId="2" ParentId="9351" CreationDate="2017-10-07T00:14:01.737" Score="5" Body="&lt;p&gt;First, let me say that most hams would be delighted to have such a polite neighbor!  I would encourage you to contact your ham neighbor.  Most hams are more than pleased to help neighbors with interference problems, rather than give the hobby a bad name.  Also many hams that are active in HF (the ones with large antennas) are good at hunting down interference problems.  If you would keep a record of the times that you have interference, your ham neighbor could compare those times to his log book, which would be a help for troubleshooting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The interference is likely in the telephone line, or the power cable to the cordless phone base.  The first thing that I would try is to get two snap-on ferrite beads (which can easily be found for sale with an internet search), one for the phone cable and one for the power cable, and then wrap each cable around a ferrite bead several times.  Good luck!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3sZjq.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3sZjq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-10-07T00:14:01.737" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9357" PostTypeId="2" ParentId="9342" CreationDate="2017-10-07T00:29:36.203" Score="2" Body="&lt;p&gt;House alarm systems turn the wiring into an antenna generating RF.  The usual process of switching off the power and adding back breaker by breaker can be confusing.  The battery backup will kick in and make it seem like the circuit is NOT off when it actually is off.&lt;/p&gt;&#xA;" OwnerUserId="8229" LastActivityDate="2017-10-07T00:29:36.203" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9358" PostTypeId="2" ParentId="9351" CreationDate="2017-10-07T00:51:10.713" Score="4" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/9356/8717&quot;&gt;Good answer&lt;/a&gt;, but it should be noted that ferrite mixes are &lt;strong&gt;not&lt;/strong&gt; created equal. The choice of the mix depends on the frequency of the interference. What works on the 80 meter ham band (3.8 MHz) might not work if the interference is on CB (27 MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A great resource is &lt;a href=&quot;http://audiosystemsgroup.com/publish.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;K9YC's site&lt;/a&gt; and specifically, &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this PDF there&lt;/a&gt;. &lt;em&gt;There is no better information on common-mode RF choke design anywhere, either online or in print.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ferrite-core chokes almost always trump air-core chokes. See G3TXQ's excellent information &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;here&lt;/strong&gt;&lt;/a&gt; as to why this is true, and note how air-wound chokes have a much narrower effective bandwidth than ferrite chokes.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-10-07T01:00:35.773" LastActivityDate="2017-10-07T01:00:35.773" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9359" PostTypeId="2" ParentId="9353" CreationDate="2017-10-07T10:44:26.037" Score="1" Body="&lt;p&gt;I'm pretty certain you can find wireless headphones in the market that have &quot;standard&quot; analog plugs (like 3.5mm&quot; headphone or RCA plugs). This feels like there's a huge market for callcenters and generally, people that regularly have to make phone calls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether or not these headphones use Bluetooth or something else for wireless communication between headset and plug is a different question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, what these devices (probably) all do is the following:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Take the analog signal from the audio output of the device you want to use with your headset, digitize it&lt;/li&gt;&#xA;&lt;li&gt;Send it to the headset part using a digital modulation in some ISM band&lt;/li&gt;&#xA;&lt;li&gt;In the headset part, convert the digital signal received to an analog signal for the actual headphones&lt;/li&gt;&#xA;&lt;li&gt;Take the analog signal from the mic, digitize them&lt;/li&gt;&#xA;&lt;li&gt;send them, digitally, to the device-side part, using the same ISM band&lt;/li&gt;&#xA;&lt;li&gt;convert them to analog for the line input of the device&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Bluetooth specifies how to do the digital link part of a headset connection using its &quot;Headset Profile&quot; &lt;a href=&quot;https://en.wikipedia.org/wiki/List_of_Bluetooth_profiles#Headset_Profile_.28HSP.29&quot; rel=&quot;nofollow noreferrer&quot;&gt;HSP&lt;/a&gt;. That way, any bluetooth headset will be able to talk to any Bluetooth master (e.g. a smart phone) that speaks the same profile. (And, since that's only a software thing, many devices can).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, you can build something like that yourself rather easily! You just need a PC, a laptop, or a single-board computer with a bluetooth adapter. Adapters cost lest than ten bucks. What ever computer you use needs to have an analog line out and an analog line in. If it doesn't, you'd need to spend another hand full of dollars on a USB sound card. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you'd then do is connect the computer to your headset via bluetooth (that's usually a five to ten click procedure), then tell the audio system to monitor the analog line in on the audio output on the headset, and vice versa, monitor the audio input from the headset on the analog output of the computer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cable your computer to your rig; how to do that exactly depends on the analog line in and out interface your rig has.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-10-07T10:44:26.037" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9360" PostTypeId="2" ParentId="9353" CreationDate="2017-10-07T11:46:37.720" Score="3" Body="&lt;p&gt;Cobra makes a very adaptable Bluetooth headset/microphone that has a 10 hour talk time. The radio side of the device has a four pin connector that is easily adapted for most amateur radios. It comes with a remote PTT switch but if your radio supports VOX operation, it will typically work with that also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A real bonus with this device is that it can simultaneously mate with your phone via BT and you can switch between the phone and the radio from the headset. This is completely optional as the headset can be used directly with the radio without requiring the use of a BT phone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are widely used in the trucking industry and have a very good track record. It is regularly available on the Internet for $70.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6R8Mg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6R8Mg.jpg&quot; alt=&quot;Cobra CA BTCB4&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-07T11:52:10.910" LastActivityDate="2017-10-07T11:52:10.910" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9361" PostTypeId="2" ParentId="9354" CreationDate="2017-10-07T12:24:33.810" Score="1" Body="&lt;p&gt;It is possible to design a dual band antenna using a single driven element in order to avoid the use of a diplexer (note the correct term for this device). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On 2 meters, the driven element is ~1/2 $\lambda$ long and on 70 cm it is ~3/2 $\lambda$ long. Each band has its own reflector and director elements. An example of a commercial antenna built on this concept is the Hy-Gain DB-2345. You can download the manual &lt;a href=&quot;http://www.hy-gain.com/Downloads/index.php?productid=DB-2345&amp;amp;filename=DB-2345.pdf&amp;amp;company=hygain&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; for this antenna to get a good idea how it is constructed &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5fivH.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5fivH.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A home-brewed version of this type of dual band antenna can be found on DK7ZB's web site &lt;a href=&quot;http://www.qsl.net/dk7zb/start1.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.qsl.net/dk7zb/start1.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y5S8S.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y5S8S.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course if your interest is FM communications, you can orientate these antennas vertically, preferably using a non-metallic mast.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-10-07T12:24:33.810" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9362" PostTypeId="2" ParentId="9351" CreationDate="2017-10-07T13:07:04.437" Score="5" Body="&lt;p&gt;If the interference is coming into your telephone via the RJ-11 cable, then the type of ferrite material you use to suppress the interference will matter. Engineers refer to the type of ferrite as the &amp;quot;mix&amp;quot;, meaning what type of ferrite material is mixed to make up the device. These mixes are simply given numbers that are common place in the industry.&lt;/p&gt;&#xA;&lt;p&gt;There are two mixes that will help knock down interference from ham radio and CB transmissions: type 75 and type 31. The type 75 material is excellent at suppressing frequencies in the 150 kHz to 10 MHz range. In ham speak, this would cover the 160 meter through 30 meter bands. The type 31 material provides broad coverage from 1 MHz to 300 MHz. This would include CB and the 160 meter to 1.4 meter ham bands.&lt;/p&gt;&#xA;&lt;p&gt;Ferrite materials comes in a variety of physical shapes but the two that are most usable for your application are the toroid (doughnut looking) and the split sleeve type. Either type will work.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wteJm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wteJm.jpg&quot; alt=&quot;from palomar-engineers.com&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/HMlAW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HMlAW.jpg&quot; alt=&quot;from DXEngineering.com&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;When installing the ferrite, plan on several turns through the core so select a core with a large enough hole for this purpose. The reason is that, in general, the effectivity of the choking action goes up as the number of turns squared. So for example, 4 turns is 16 times more effective than 1 turn. Space out the turns evenly on the core, wrap them tightly around the core, and do not overlap turns.&lt;/p&gt;&#xA;&lt;p&gt;If you are not certain which core material to use, both can be applied to the same cord. Just place one after the other, winding each one individually. Alternatively, talk with your ham neighbor. Most hams are more than willing to help a friendly neighbor with any interference problems. At the very least, your ham neighbor can let you know what bands he or she is operating on so that you can select the best ferrite mix for the situation.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-10-08T06:21:36.023" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9363" PostTypeId="2" ParentId="9324" CreationDate="2017-10-07T19:03:22.757" Score="1" Body="&lt;p&gt;(Shameless plug:) I have an app called Morse Decoder in Apple's iOS App store that a few customers have told me helped them learn QRQ (high speed copy).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As with most computer software decoders, especially in QRN, QRM, and channel fading, sometimes a human can copy more accurately than the software (and sometimes vice versa).  But around or above the WPM limit at which the receiving operator can barely copy, the app might do better, and provide some decoded reference text against which one can compare their attempts at copying QRQ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Over 50 WPM, it may be easier to learn to hear whole words rather than individual letters.  I also have another free Morse Code training app in the iOS App store, titled &quot;Morse Words&quot;, that will allow one to hear what common words sound like in CW QRQ at up to 100 WPM.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-10-07T23:32:09.373" LastActivityDate="2017-10-07T23:32:09.373" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9365" PostTypeId="2" ParentId="1057" CreationDate="2017-10-08T06:28:04.640" Score="1" Body="&lt;p&gt;Here is one answer on the topic:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.eham.net/reviews/detail/11020&quot; rel=&quot;nofollow noreferrer&quot;&gt;Reviews Summary for Softrock Ensemble II Built Radio&lt;/a&gt;   (eHam review)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excerpt:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I only have a short, modest, &quot;long wire&quot; (maybe 30 feet) connected to a 9-1 balun (for 50 ohms input to radio), and getting excellent reception in Thunder Bay, Canada. I am really enjoying 20 meter SSB, as well as lots of shortwave broadcast stations!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Here is the most convenient method I have found for twinlead.  These are very inexpensive.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;No soldering required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/adKmb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/adKmb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(For a long wire, connect the antenna to the right-hand spring connector as shown in this orientation, then a shorter stub to ground to the left-hand spring connector)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To connect to BNC there are adapters such as this available for a reasonable price:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eBESN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eBESN.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The antenna itself (size, placement, etc) will determine what it brings in best.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-10-09T17:59:53.643" LastActivityDate="2017-10-09T17:59:53.643" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9366" PostTypeId="1" AcceptedAnswerId="9371" CreationDate="2017-10-08T08:39:37.060" Score="1" ViewCount="108" Body="&lt;p&gt;Newbie ham radio guy here. I just got my hands on an Icom R8500, and I'd like to record some signals on my pc. What's the proper way to do this, to minimize the added noise? Should I just use a 3.5mm cable to connect the REC out of the receiver to the Line In of my sound card, and then just use some recording software?&lt;/p&gt;&#xA;" OwnerUserId="10483" LastActivityDate="2017-10-08T16:23:53.907" Title="Recording from ICOM R8500 to pc" Tags="&lt;icom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9367" PostTypeId="2" ParentId="9304" CreationDate="2017-10-08T11:54:29.657" Score="0" Body="&lt;p&gt;The three antennas at the top are definitely a phased array.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Likely this is a cell tower, but I've seen airport radar towers that are similar as well.&lt;/p&gt;&#xA;" OwnerUserId="10485" LastActivityDate="2017-10-08T11:54:29.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9368" PostTypeId="2" ParentId="2080" CreationDate="2017-10-08T14:54:49.287" Score="3" Body="&lt;p&gt;If you are a citizen of the US or Canada, you should get a callsign in that country because you must have a callsign in that country in order to be able to transmit there as a citizen.  Also, that will allow you to use any reciprocal authority that country has to operate in other countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish, you may also get a callsign in the other country, but if you do you may only use it in that country.  It can be convenient to do so if you will operate there regularly, because your identifying will be shorter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am a Canadian citizen and at this time only have a Canadian callsign, but I am in the US frequently.  However, I only need to identify using /W0, /W7, /W6, etc. depending on where I am in the US.  If I were to do contest operation in the US I might prefer a US callsign to keep my ID string shorter.  For the VHF/UHF operation I tend to do down there, the extra ID length is of minimal consequence.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2017-10-08T14:54:49.287" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9369" PostTypeId="2" ParentId="9353" CreationDate="2017-10-08T15:00:13.570" Score="1" Body="&lt;p&gt;Some rigs (e.g. Yaesu's FTM-100 and FTM-400 VHF/UHF radios) will accept an optional Bluetooth module that will allow you to connect any Bluetooth headset.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice I'm not sure I'm happy with how Bluetooth headsets work with ham radios.  With HF rigs I tend to prefer to wear a wired headset and use a foot pedal for push-to-talk.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2017-10-08T15:00:13.570" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9370" PostTypeId="2" ParentId="9353" CreationDate="2017-10-08T16:08:56.597" Score="1" Body="&lt;p&gt;I am not sure if this should be a comment or an answer because I only cover part of the question.  First, as others have said, it is possible to use Bluetooth and trivial for listening as there are all sorts of audio adapters that plug into headphones jack and create a Bluetooth signal carrying the audio (just search on Amazon, that is where I bought mine).&lt;/p&gt;&#xA;&lt;p&gt;I was not interested in voice because I am virtually all CW (aka Morse Code), so the voice mic input part of the problem was not something I was concerned about.  So this comment is about BT and CW.&lt;/p&gt;&#xA;&lt;p&gt;It does not work.  Well, it works but the delay that Bluetooth causes creates havoc with sending CW and especially at faster speeds and in particular with fast-break-in operation.  I tried for about an hour to train my head to copy while sending and not make mistakes.  I had to slow down to about 5 wpm on a straight key before I could do this and that was with slow-break-in only.  At 20 wpm and greater, no way could I send.  I hear the dit for a letter for the first time by the time I finish the letter such as I, S, or H.&lt;/p&gt;&#xA;&lt;p&gt;Although I never tried BT with voice but if you do try with voice, make sure you are not listening to yourself by any monitor feedback system.  That will probably even mess you up with voice -- like an echo chamber.&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;Update&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;There is an active discussion about CW copy and Bluetooth headsets right now on the Elecraft forum.  The big issue of course is the delay caused by the BT latency.  But, there may be improvements.  I quote the following from a post on Elecraft forum:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;OK, I did some digging and found marketing info from Avantree.  When they say “no” latency, they mean “some” - on the order of 40 msec when used with a transmitter that supports low-latency aptx codec mode.  This sounds reminiscent of a Monty Python sketch.&lt;/p&gt;&#xA;&lt;p&gt;40 msec is about one dit at 30 wpm, which would probably throw me off. I’ve tried to listen to my own sending via various SDRs, and it’s agonizing.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I never did make actual measurements with my setup but I would guess it was probably at least one full dit and a half delay at 10 wpm.  Close to 2 dits at 20 wpm.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-10-08T16:15:43.477" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9371" PostTypeId="2" ParentId="9366" CreationDate="2017-10-08T16:23:53.907" Score="4" Body="&lt;p&gt;As long as you have in fact a line input and not a microphone input on your sound card, that is an appropriate connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If&lt;/strong&gt; you notice hum or distortion in the recorded audio, you may need to use an audio isolation transformer. (There is no need for one unless you find it necessary.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-10-08T16:23:53.907" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9372" PostTypeId="2" ParentId="9354" CreationDate="2017-10-08T18:52:53.003" Score="1" Body="&lt;p&gt;The diplexer allows you to separate the UHF and VHF signals coming from the radio.  This is useful if, for example, you wanted the uhf antenna and vhf antennas in different places or pointing different directions.   Or, if you had both antennas connected together on the same coax, but you wanted to feed them from different radios on the other end of the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If both antennas are in the same place, a diplexer on the antenna end doesn't make much sense.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Putting them on the same coax should work fine.  Generally, if the one antenna has high SWR at the other antenna's frequency, then this will act as a selector of which antenna gets most of the power from the coax at that frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If one antenna is a harmonic of the other, the power could be divided between the antennas (like a voltage divider made of resistors), which could change the impedance significantly, and you might need to adjust the matching network, and the radiation pattern would be from both antennas.  Also, if the antennas are close, they might interact distort their mutual radiation patterns even if they are not sharing the power.  These two factors can be designed for, or you can just try it and see how it works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the 440mhz band is very close to being a third harmonic of 146mhz, so a 2m antenna with sufficient bandwidth might also have low SWR on 70cm.  If this is an omnidirectional antenna, you might not even need the 70cm antenna.   If this is a directional antenna, you might want the diplexer to separate the antennas to get the best radiation pattern for each band.   Note that the arrow satellite yagi has the two antennas on the same boom, but mutually perpendicular -- this minimizes interaction between them.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2017-10-09T05:41:39.390" LastActivityDate="2017-10-09T05:41:39.390" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9373" PostTypeId="2" ParentId="9303" CreationDate="2017-10-08T19:38:51.127" Score="1" Body="&lt;p&gt;The manual for this radio is particularly unhelpful on this point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, at a guess...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For most radios with this style jack, one hole is for the microphone and the other is for the speaker.  The speaker jack could be either stereo or mono, but adapters you listed both use three ring plugs, so it isn't mono.   If it is stereo, you could plug in a regular headphones directly to the speaker jack without an adapter.  The other possibility is that it uses a stereo jack but one channel is speaker and the other is a control channel, but more typically the control channel is in the microphone jack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, there is a note in the manual that you should only plug things into this jack when the radio is off.  This is probably because you will briefly short out the jack as you put the plug in.  This could damage the radio if it is on, and could cause popping noises in the headset/speaker.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2017-10-08T19:38:51.127" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9374" PostTypeId="2" ParentId="9354" CreationDate="2017-10-09T02:15:20.303" Score="1" Body="&lt;p&gt;That is completely your choice.  It depends on whether you will use one radio or two.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since certain VHF/UHF radios are so inexpensive I can use two at a time by connecting to each yagi separately to yield full duplex - so I can hear the satellite or Space Station as I transmit.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I believe what you are asking about is similar to the antenna I use - UHF and VHF on the same boom and used with a single radio.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is mine:  &lt;a href=&quot;http://www.arrowantennas.com/arrowii/alaskanarrow.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Alaska Arrow antenna&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rN7J0.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rN7J0.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(This picture shows it without the extended boom and elements attached)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;This one uses a duplexer for use with a single radio - it is located in the handle.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4Mu9t.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4Mu9t.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zzeQ1.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zzeQ1.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrowantennas.com/inst/146440-14_All%20Suffixes_Instruction_Sheet.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Documentation&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;This antenna can theoretically handle 150 Watts without the duplexer - but I find 5 is sufficient, especially when using the full-length version with all the extra elements.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Mine is mounted on a microphone stand that allows me to rotate it for polarization as well as adjust the position to track satellites and the Space Station while adjusting for their orientation as necessary.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meanwhile I am also busy during the pass as I adjust for doppler on the transceiver.  I used 3 channels.  One for AOS, the next for the middle, then the third as it nears LOS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also have a low-power red cross-beam laser on the front of mine to help keep the direction steady along the track.  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Word to the wise:  Never use a green laser if you are pointing it upwards.  Green is where the eye is most sensitive and it could distract someone.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-10-10T03:44:02.273" LastActivityDate="2017-10-10T03:44:02.273" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9375" PostTypeId="2" ParentId="9351" CreationDate="2017-10-09T04:31:00.747" Score="1" Body="&lt;p&gt;In my experience, the RFI in a telephone system almost always comes thru the RJ-11 cable which is acting as an antenna for the RF generated by ham operators or CB operators (or, anyone else doing similar things).  Thus, filtering that interference using an RF Ferrite Core Chokes is the method to try.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Too bad Radio Shack no longer exists (or, at least all the stores in our area are long gone closing up last year sometime).  Many years ago, when such things were actually cheap, I bought about a half-dozen RFI Filters sold at Radio Shack Stores.  They have RJ-11 adapters on each end so you do not thread or wrap your cable around a ferrite.  You merely plug your RJ-11 cable into one end and the short end cable on the other side (about 3 inches long) you plug into the base of your phone or base station.  Radio Shack gave these a simple name, the only identifiable marks are the Radio Shack trade mark and then the name &quot;Telephone Interference Filter&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I still have one left.  I used them on my own phones that suffered from my own RFI and it stopped the interference cold without any problems even when I operated at about 1200 watts RF.  My neighbors on each side of my house let me know I was getting into their phones so I went over and installed a filter for each of their phone base stations -- stopped the interference, no more problems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These things work great by my experience.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have searched on-line but could not find the exact product even though I did find a radio shack on-line catalog.  I do know this.  They are designed for filtering 3 to 30 MHz RFI (says so right on the filter) and they use a number 43 ferrite mix which I know to be common for the HF frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Judging by the dimensions of this Radio Shack filter, I am betting it contains one type 43 ferrite mix of the clamp around style (that RJ-11 cable passes thru) of about 1 inch long.  I could open it up to confirm this but that would require destroying this rather well sealed container.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2017-10-09T04:31:00.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9376" PostTypeId="1" AcceptedAnswerId="9377" CreationDate="2017-10-09T18:48:27.170" Score="9" ViewCount="311" Body="&lt;p&gt;According to the FCC, if you are using an antenna other than a dipole, in 60 meters, you must keep a record of the transmission and gain of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't remember seeing any other requirement of log keeping. Why does this one exist? What's the story behind it?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2017-10-10T23:55:45.540" Title="Why is this requirement in 60m in the US?" Tags="&lt;united-states&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9377" PostTypeId="2" ParentId="9376" CreationDate="2017-10-09T18:56:12.850" Score="6" Body="&lt;p&gt;Some decades ago, the FCC used to require that US amateurs log &lt;em&gt;every single QSO.&lt;/em&gt; And those logging requirements could be somewhat complex, especially for third-party traffic with other countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's the law because&#xA;&lt;strong&gt;those 5 channels are shared with other licensed commercial services&lt;/strong&gt;. If we interfere with those, then the FCC might pay us a personal visit and see what our ERP is &lt;em&gt;and what it might have been with our 'previous' 60m antenna&lt;/em&gt; (indicated, of course, by our log).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/60m-channel-allocation&quot; rel=&quot;noreferrer&quot;&gt;Here are the 60m rules&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Amateurs may transmit with an effective radiated power of 100 W or&#xA;  less, relative to a half-wave dipole. If you’re using a commercial&#xA;  directional antenna, FCC Rules require you to keep a copy of the&#xA;  manufacturer’s gain specifications in your station records. If you&#xA;  built the directional antenna yourself, you must calculate the gain&#xA;  and keep the results in your station records.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;When using a directional antenna, you must take your antenna gain into&#xA;  account when setting your RF output power. For example, if your&#xA;  antenna offers 3 dB gain, your maximum legal output power on 60 meters&#xA;  should be no more than 50 W (50 W plus 3 dB gain equals 100 W&#xA;  Effective Radiated Power).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's intended to make sure that the ERP does not exceed those limits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;http://www.arrl.org/60-meter-faq#&quot; rel=&quot;noreferrer&quot;&gt;http://www.arrl.org/60-meter-faq#&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;How can I be sure I don't exceed the power limit?&lt;/strong&gt; &#xA;  The FCC said hams&#xA;  may run 100 W effective radiated power (ERP) on the five 60-meter&#xA;  channels. The new rules say, &quot;For the purpose of computing ERP, the&#xA;  transmitter PEP (peak envelope power) will be multiplied by the&#xA;  antenna gain relative to a dipole or the equivalent calculation in&#xA;  decibels. A half-wave dipole antenna will be presumed to have a gain&#xA;  of 0 dBd.&quot; This means if you use a half-wave dipole (about 87 feet 3&#xA;  inches for the &quot;middle&quot; channel according to the formula), set your&#xA;  transmitter's output power for 100 W PEP (many transceivers' meters&#xA;  can be set to indicate peaks), and you should be in compliance. The&#xA;  FCC asks licensees using antennas other than half-wave dipoles to&#xA;  &quot;maintain in their station records either manufacturer data on the&#xA;  antenna gain or calculations of the antenna gain.&quot; This is a new&#xA;  record-keeping requirement for amateurs. The &quot;best&quot; antenna&#xA;  configurations are those with a proven track record on the lower&#xA;  bands, keeping in mind that using a loop or an array of some kind will&#xA;  require you to &quot;do the math&quot; to ensure you are not radiating more than&#xA;  100 W ERP in any direction. For the math you must reduce your power by&#xA;  the number of decibels your antenna gain exceeds 0 dBd (0 dB relative&#xA;  to a half-wave dipole). Conversely, you can increase your transmitter&#xA;  power if your antenna exhibits loss compared to a dipole. Be prepared&#xA;  to document these situations in your station records.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.federalregister.gov/documents/2012/02/03/2012-2477/amateur-radio-use-of-the-allocation-at-5-mhz&quot; rel=&quot;noreferrer&quot;&gt;&lt;em&gt;More information from the Federal Register&lt;/em&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="76" LastEditDate="2017-10-10T02:48:18.790" LastActivityDate="2017-10-10T02:48:18.790" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9378" PostTypeId="2" ParentId="993" CreationDate="2017-10-09T21:02:44.720" Score="4" Body="&lt;p&gt;As mentioned, the law is not to cause harmful interference.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can be any frequency spacing from, or no spacing from another station if you don't cause interference.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if two stations some distance from you are hearing each other, you could use a very close frequency or even the same frequency to talk to another station close to you and as long as the other stations didn't hear it, no problem.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;They might be interfering with you, but that is also no problem if you are willing to accept it.  In the afternoon on 75 meters and in a large country such as the U.S., for example there could be multiple groups of stations on each frequency with minimal or no interference.  Even if they occasionally hear each other, no one is illegal, provided they do not prevent other users from carrying on desired communication. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the &quot;skip&quot; lengthens out, harmful interference may occur and it can lead to arguments as to who was on the channel first and thus should be protected from the newer station's use of the frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only answer to such a situation is mutual respect and courtesy leading to cooperation in frequency selection, scheduling, power levels, etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hams are generally left to work this out among themselves and it works pretty well.&lt;/p&gt;&#xA;" OwnerUserId="10466" LastEditorUserId="8832" LastEditDate="2017-10-10T00:23:54.623" LastActivityDate="2017-10-10T00:23:54.623" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9379" PostTypeId="2" ParentId="9376" CreationDate="2017-10-10T03:52:15.273" Score="3" Body="&lt;p&gt;On most bands, US Amateur Extra-class hams are allowed to transmit 1.5 kW because hams are the primary users of the band.  On 60m, US hams are secondary users of the band, and government agencies are the primary users.  The idea for the 60m band came from negotiations between governments at the 2012 and 2015 ITU World Radiocommunication Conferences, according to &lt;a href=&quot;https://en.wikipedia.org/wiki/60-meter_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;.  The US government presumably wanted to keep hams from interfering with existing users of the band, so we hams were allowed only low power, channelized operation on five frequencies only, and upper sideband as the only phone mode.  (For single-sideband operation, hams &lt;a href=&quot;https://ham.stackexchange.com/questions/1336/why-do-we-use-lsb-below-10mhz-and-usb-above-10mhz-when-operating-ssb-hf&quot;&gt;traditionally use lower sideband on frequencies lower than 10 MHz&lt;/a&gt;, but government users use upper sideband exclusively.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/60m-channel-allocation&quot; rel=&quot;nofollow noreferrer&quot;&gt;According to the ARRL&lt;/a&gt;, &quot;Our expanded privileges on 60 meters were the result of collaboration between the FCC and the NTIA – the National Telecommunications and Information Administration, the agency that manages and coordinates telecommunications activities among US government departments, the primary users of the band.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL page goes on to mention that the NTIA expressed concern about possible interference from digital modes, and requested that US amateurs limit digital operating to PSK31 and PACTOR III only.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;@MikeWaters answer explains the reasons behind the logging requirement quite well: so that the FCC will be able to estimate a station's Effective Radiated Power when investigating possible ham interference with other (government) users of the 60m band.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2017-10-10T23:55:45.540" LastActivityDate="2017-10-10T23:55:45.540" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9380" PostTypeId="2" ParentId="9051" CreationDate="2017-10-10T14:16:20.323" Score="1" Body="&lt;p&gt;The information I have recently read indicates a very complex solution, perhaps because it is not always easy to get a good/proper solution, especially in your situation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am originally from Arizona too, so I am aware of the unique problems there. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This solution worked for DC ground, AC safety, lightning protection, and RF: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The general idea is that for maximum effect you will need multiple ground rods spaced 8-10 feet apart and all connected by a large diameter wire (#6 or larger). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do not use stranded wire or braid if possible due to the fact that at RF the wires work individually instead as a single conductor and they can also be broken easier. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The illustration I saw had 8 or more rods going around the house from the main electrical box connected to more rods at the tower, and close to the operating position. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The article also stated that it was important to tie the main electrical box ground to the tower and the equipment location (often not very near each other) in this manner. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There were more excellent ideas and explanations in the article. I will try to find it on my computer and link to it later.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also the problem of the poor connection of each rod to the earth. This can be helped considerably with any of the following:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;bentonite surrounding the rods (not the lowest resistance, but much better than what you have, also needs to be kept moist to be effective, is the main ingredient in most pet litters).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;rods with chemical salts that leach into the soil but may not be effective in your soil that is dry and hard (can be expensive, dissipates into the soil, so you need to buy more salts every so often and may also be a pollutant in the soil, especially if you have a well for drinking water).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;carbon based material (somewhat effective but also dissipates into the soil, but may not be effective in your soil that is dry and hard).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;proprietary material (can be expensive and is usually something like an enhanced clay similar to bentonite mixed with other things like carbon, but often no need to keep it moist)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;conductive cement (excellent with the lowest resistance of all these solutions, but the cost will be a little expensive)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I recommend conductive cement if possible. It is a little more expensive, but it is a permanent solution and not difficult to use and does not pollute anything. You can find it if you search for it on the internet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I checked my files and the information I read was indeed at the W8JI website and I found even more information than what I read.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastEditorUserId="8832" LastEditDate="2018-04-18T05:31:01.913" LastActivityDate="2018-04-18T05:31:01.913" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9381" PostTypeId="2" ParentId="5409" CreationDate="2017-10-10T14:49:11.253" Score="1" Body="&lt;p&gt;I believe that what you want is the effect of mutual coupling of the antennas. That, I believe, can be done in EZNEC by modeling both antennas at the same time (for example the transmitting antenna in the normal way and the receive antenna as a parasitic element not connected to anything).&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-10T14:49:11.253" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9382" PostTypeId="2" ParentId="5377" CreationDate="2017-10-10T14:53:27.180" Score="0" Body="&lt;p&gt;It seems that what you need to do is to model each separately then together. Do NOT model the receive antenna with any feed when modeling them together. You can compare the single antennas to the pair to see the coupling effects on the transmitting antenna. You can then do them together with the receive antenna fed and compare that to the single receive antenna again to see the effects.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-10T14:53:27.180" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9383" PostTypeId="1" AcceptedAnswerId="9387" CreationDate="2017-10-10T14:56:49.170" Score="2" ViewCount="223" Body="&lt;p&gt;I've seen many plans for 50 Ohm dummy loads in paint cans, such as the one here: &lt;a href=&quot;https://www.nonstopsystems.com/radio/frank_radio_antenna_dummy.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.nonstopsystems.com/radio/frank_radio_antenna_dummy.htm&lt;/a&gt;. I've already assembled a functional dummy load, but have avoided using it at full power because it's currently resistors attached to copper plates in open air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to move the entire thing in to a paint can (as in the link), but have a concern. It appears to me that the can itself becomes connected to one side of the dummy load. Couldn't this allow high voltage (relative to the radio) to appear on the can itself? Is there some insulating factor I'm missing? Would another material (such as a plastic project box) be a better choice?&lt;/p&gt;&#xA;" OwnerUserId="10424" LastEditorUserId="966" LastEditDate="2017-10-11T03:12:27.677" LastActivityDate="2017-10-11T03:12:27.677" Title="Does a paint-can dummy load have high voltage on the metal can? Would an insulated container be better?" Tags="&lt;diy&gt;&lt;dummy-load&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9384" PostTypeId="2" ParentId="9383" CreationDate="2017-10-10T15:36:10.023" Score="1" Body="&lt;p&gt;Usually it is the shield side (assuming coax, but similar for other types of transmission cables) that is connected to the can via the connector. That is how they are usually made. This is necessary to provide a &quot;return&quot; path for the circuit. The shield is usually at &quot;ground&quot; potential (similar to the negative side of a battery, like in your car). This poses no safety hazard to you.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-10T15:36:10.023" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9385" PostTypeId="2" ParentId="9383" CreationDate="2017-10-10T16:23:14.030" Score="6" Body="&lt;p&gt;The metal exterior enclosure is an important component for a dummy load. The metal acts as a shield, containing any electromagnetic energy inside the can. Getting a shock is not an issue since the metal shield is at ground potential, the same as the chassis of your radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I had my Novice license, I used to use a lightbulb as a dummy load. It worked for my purposes until one day, a station in Germany answered me on my lightbulb. A great contact but after that, I bought a proper dummy load in a metal paint can - the venerable Heathkit Cantenna. I also learned about common mode current...&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-10T20:14:13.417" LastActivityDate="2017-10-10T20:14:13.417" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9386" PostTypeId="2" ParentId="5464" CreationDate="2017-10-10T17:13:30.100" Score="1" Body="&lt;p&gt;There are a lot of unknowns here. Most PSK decoders work virtually the same way. One thing to check is to make sure that your radio is set for Upper Side Band and not any other receive mode.  Other than that we will need more details.&lt;/p&gt;&#xA;" OwnerUserId="8840" LastActivityDate="2017-10-10T17:13:30.100" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9387" PostTypeId="2" ParentId="9383" CreationDate="2017-10-10T17:54:51.903" Score="7" Body="&lt;p&gt;Assuming you are using &lt;strong&gt;coaxial&lt;/strong&gt; cable and connectors, the case of the dummy load is contiguous with the shield of the cable and the usually-metal case of your radio. So touching the dummy load is not any more dangerous (i.e. not at all if everything is working normally) than touching your radio. The shields everywhere in the system remain at the same potential as your power supply ground, and the RF voltage appears only inside the coax and across the load resistor (which is isolated inside the can, of course).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to feed a canned dummy load of the same construction with &lt;strong&gt;balanced&lt;/strong&gt; feed line (window line, ladder line, etc.) then connecting one side of the line to the metal can &lt;em&gt;would&lt;/em&gt; cause the can to be energized. I think — I'm not entirely certain I'm thinking about it properly — this would also cause the antenna system to radiate, because it is no longer completely balanced. In this case, you would still want a metal can for shielding (because the interior wiring is not a properly designed transmission line), but &lt;strong&gt;both&lt;/strong&gt; conductors of the feed line would be insulated from the can.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-10-10T17:54:51.903" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9388" PostTypeId="2" ParentId="993" CreationDate="2017-10-10T21:00:29.650" Score="3" Body="&lt;p&gt;Already good answers but there is one more thing.  Once you have chosen a frequency, you should ask if it is busy.  If using voice mode, it is OK to say something like &quot;Is this frequency busy?&quot; and then pause for some time to listen for any answers.  Other modes justify other codes.  For example, CW usage would be to send QRL? which is taken to mean (in our current interpretations) &quot;is this frequency busy?&quot;.  And, then of course listen for an answer.  In CW, a common answer is just the letter C if someone is already using that frequency.  Sort of meaning &quot;Yes, the frequency is busy&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, good practice is:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;First listen and maybe more than a few seconds because you may not hear both sides of the QSO.  You could think it is unused when it isn't.  So,&lt;/li&gt;&#xA;&lt;li&gt;Ask if frequency is busy or send QRL?  Then, wait and listen for a response.&lt;/li&gt;&#xA;&lt;li&gt;If the above two steps indicate the frequency is clear then take it for your own.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2017-10-10T21:00:29.650" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9389" PostTypeId="2" ParentId="9325" CreationDate="2017-10-11T00:44:18.387" Score="-1" Body="&lt;p&gt;There are 2 main ways to create the 180 degree phase shift required for circular polarization. A delay in the feed lint (1/4 wavelength longer to one than the other) or physical (antennas at right angles). It does not matter how the phase shift is achieved, the results are the same. So if the antenna matches one of these methods, circular polarization will be achieved. Even when minor errors are present the result is still &quot;mostly&quot; circular (think oval) polarization. If these conditions are not met you will get a different result.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastEditorUserId="10495" LastEditDate="2017-10-17T00:08:38.310" LastActivityDate="2017-10-17T00:08:38.310" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9391" PostTypeId="1" AcceptedAnswerId="9399" CreationDate="2017-10-12T03:20:36.200" Score="2" ViewCount="384" Body="&lt;p&gt;I live in the middle of the Philippines. As soon as possible, financially, I want to put up the best antennas I can build. This includes, mostly, beams for all amateur bands, including, at least, antennas from 70cm to 160m, although for 80m and 160 meters a compromise such as a full sized vertical might be the best solution. It would still require a tower (preferably nonconductive) to support a full sized vertical on these bands. I would, of course, need towers to get the antennas up high enough to be more effective, especially for the lower bands. In accordance with local rules, the towers can only be a maximum of 50 meters high, due to the airport we have here. I have thought that I will probably lose little if I self-impose a limit of 40 meters +/-. Most bands require less than 40 meters for a dipole and even at 160m, a 1/4 wave vertical is only 40 meters long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also want to avoid, if possible, rotators. They are expensive and I think I can build an extra tower (or 2, or 3) cheaper than buying the rotator. I also wouldn't need wires that flex and break with age/use. I would rather have several fixed antennas that cover all directions than needing to rotate antennas. I also would consider it a benefit to just switch antennas, without a need to rotate, and virtually no delay to chose any direction, on any band, that I want&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are plenty of sugarcane fields that I rent, or could get access to, where I can put the antennas. There is also a mountain nearby and some these fields have significant slopes to take advantage of, so maybe the towers for most bands can be lower and still very effective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The biggest question in my mind is WHAT materials I can use to make the tower, and how to preserve them in this harsh environment, all while making it as affordable as possible?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Special materials that need to be ordered and shipped from another country will probably be too expensive. I know that smaller cross-sections will make the load, and required strength lower, and I might get away with cheaper materials if they can be strong enough for the load required and still be small. I also know that smaller cross-sections will probably require materials with greater strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am NOT rich and on a smaller budget, but sometimes can get a temporary increase in income (and I HOPE I can increase my usual income in the future), so it is not unreasonable to believe that if I wait patiently I will have enough money to build towers at some point. I have software to help design the towers safely. I want to use my time, which I have plenty of right now, to be prepared for this so that when the time comes I am ready and can proceed immediately.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bamboo is plentiful and cheap, but harder to preserve (it is the prefered material if I can overcome the preservation doubts I now have). I also prefer bamboo so that the antennas will perform without any nearby conductive materials if possible, especially if I build fullsize verticals for 80m and 160m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Steel (unless I use the more expensive and rust resistant varieties) will rust easily here and is expensive, and would need a lot of maintenance. Aluminum is also expensive here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have also thought about cement, plastic pipe (large diameter, filled with cement, etc.), pultrusions, using a mix of different kinds materials, etc. Using SOME steel would be acceptable, if it is limited (for cost reasons and also due to detuning the antennas and distorting patterns).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the higher frequencies it would not need great strength due to the slopes I can take advantage of. I believe that there is little need for towers higher than about .5 to .6 wavelengths for any band except VHF/UHF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What solutions (especially correct or cheaper materials and/or preservation techniques) does anyone have for this situation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sorry for the long post, but I wanted to give all the relevant information that I could.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastEditorUserId="10495" LastEditDate="2017-10-12T03:46:50.357" LastActivityDate="2018-02-10T13:14:14.167" Title="What to use to build a tower here in the Philippines?" Tags="&lt;tower&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9392" PostTypeId="2" ParentId="9391" CreationDate="2017-10-12T03:38:39.540" Score="0" Body="&lt;p&gt;I have modeled steel, as a standard for comparison, and a couple of bamboo configurations. I also wrote some simple spreadsheet tools to help me know how strong/ thick any material needs to be if I know, or can easily get, the correct yield strength information. I also considered using steel, in a limited way, to stiffen the legs of the towers. Leg stiffness and strength is the key to making it work in this application. I think almost anything is possible if I spend a lot of money, OR if I am smart enough (or someone here helps) to figure out how to do it with less money. It boils down to cost versus life of materials and degradation of signals. It would be great if I can do it with nonconductive and inexpensive materials, since in the fields there is little to nothing to foul up a good antenna design. Even the soil &quot;wants&quot; to help. It is probably very good to excellent, even when dry, although it is often wet.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-12T03:38:39.540" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9393" PostTypeId="2" ParentId="7831" CreationDate="2017-10-12T08:14:21.070" Score="0" Body="&lt;p&gt;A long time ago I lived in Japan for 2 years. I still can speak enough Japanese to hold a conversation. This seems to be just gibberish. It actually sound more like something real in English than Japanese, at least to me. Using online translators also yielded no results.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-12T08:14:21.070" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9394" PostTypeId="1" AcceptedAnswerId="9396" CreationDate="2017-10-12T08:19:26.610" Score="1" ViewCount="713" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CQkBr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CQkBr.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RH2C0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RH2C0.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As shown in two pictures，setting a different bandwidth-value in the module, the value of the coordinate axis change accordingly. How did it happen? And I want to know if gnuradio can tell us the bandwidth of signal.&lt;/p&gt;&#xA;" OwnerUserId="10410" LastEditorUserId="76" LastEditDate="2017-10-13T21:31:27.867" LastActivityDate="2017-10-13T21:31:27.867" Title="I want to know the bandwidth of this signal; problems using &quot;QT GUI Frequency sink&quot; to show it" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9395" PostTypeId="2" ParentId="7642" CreationDate="2017-10-12T12:50:03.023" Score="1" Body="&lt;p&gt;As mentioned before, the real answer is that it always matters. But in different situations it matters for different reasons. Your #1 is actually 2 different cases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First if you actually use the earth, you can't change the size. You have no choice in the matter. A better earth with low resistance and less RF power absorption is better. Therefore using radials helps reduce &quot;ground losses&quot; by lowering overall resistance and better coupling the actual earth. More are better and can balance the antenna more effectively. Making them approximately the correct 1/4 length also helps with balance. Using raised radials helps by relying less on the actual earth (less loss) while still being close to it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use a car roof (or similar object) the main purpose is to capacitively couple to the real earth. Bigger works better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your second example the radials give a path for the RF to go that is NOT the coax and to give balance to the antenna. This makes for a good radiation pattern. The fact that you can use the angle and length (and to an extent the number of radials) to tune the antenna to a better resistance match is also a plus. Walt, W5ALT did an interesting study about varying radial lengths and angles and the effects it caused. &lt;a href=&quot;http://www.hamuniverse.com/w5altradialnotes.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hamuniverse.com/w5altradialnotes.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your third example it is essentially the same as the second. The only difference is there is only one path for the RF current to flow in that half of the antenna. It still provides an RF path, balance to the antenna, and helps create a good radiation pattern.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-12T12:50:03.023" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9396" PostTypeId="2" ParentId="9394" CreationDate="2017-10-12T14:59:41.530" Score="7" Body="&lt;p&gt;GNU Radio, like any DSP system, works primarily in terms of &lt;em&gt;sample counts&lt;/em&gt;, not &lt;em&gt;time&lt;/em&gt;. Therefore, you have to add on time information — a sample rate — to get correct frequency-domain information. GNU Radio does not automatically figure out what the matching sample rates between parts of your flow graph are, so you have to set them up correctly yourself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The QT GUI Frequency Sink always starts out &lt;em&gt;displaying&lt;/em&gt; the entire range of frequencies in the digital signal — that is, between -1 and 1 cycles/sample, or $-π$ and $π$ radians/sample, or $-\frac{f_s}2$ to $+\frac{f_s}2$ where $f_s$ is the sample rate. But the sink does not &lt;em&gt;know&lt;/em&gt; what the sample rate of your signal is, so you have to tell it that in order to get a correctly &lt;em&gt;labeled&lt;/em&gt; frequency axis. That is what the (unfortunately named) “Bandwidth” parameter of the QT GUI Frequency Sink block does — it sets the scale for the frequency axis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should always set that parameter to the &lt;em&gt;sample rate&lt;/em&gt; of the signal you are providing to it.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;In order to actually measure the bandwidth:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Once you have set the sample rate properly, &lt;/li&gt;&#xA;&lt;li&gt;mouse over the left and right edges of your signal, note down the Hz values that are displayed,&lt;/li&gt;&#xA;&lt;li&gt;and subtract the larger from the smaller.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I do not know of any GR blocks that automatically measure bandwidth, but you could certainly arrange to capture FFT data and calculate it on your own outside of GR (using whatever definition of bandwidth suits your application).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="4076" LastEditDate="2017-10-13T21:29:20.307" LastActivityDate="2017-10-13T21:29:20.307" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9397" PostTypeId="1" AcceptedAnswerId="9398" CreationDate="2017-10-12T18:23:48.053" Score="3" ViewCount="795" Body="&lt;p&gt;When speaking to a portable radio transmitter the sounds usually gets distorted. However in radio stations that are dedicated to play music the sound is significantly better.&#xA;First of all, why? And second how can I make it better?&#xA;The system I use can transmit from 30Mhz to 87.975Mhz with 30Khz bandwidth (military system) and I want to play music over it (I connected the audio input to my phone).&#xA;I know it's a radio problem because when I use wire the sound is better.&lt;/p&gt;&#xA;" OwnerUserId="10499" LastActivityDate="2017-10-17T18:31:43.887" Title="Sound quality in portable FM radio devices vs dedicated stations" Tags="&lt;fm&gt;&lt;bandwidth&gt;&lt;music&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9398" PostTypeId="2" ParentId="9397" CreationDate="2017-10-12T23:59:56.253" Score="6" Body="&lt;p&gt;Bandwidth:  Broadcast FM stations are spaced 200 KHz apart, with the intention of allowing this kind of signal structure without interference:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Djn44.gif&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Djn44.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FM broadcast bandwidth of just more than 50 KHz is quite sufficient for near-CD quality stereo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normal broadcast FM uses multiplexing so the main channel includes L+R - both channels - what we call Mono. Then there is a subcarrier that sends L-R. The receiver detects the pilot signal (subcarrier) and lights up the &quot;stereo&quot; light, so the receiver knows to use a demultiplexer to separate the L and R signals which it then sends to your amplifier and speakers.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Sound quality:  FM broadcast stations always use audio processors that are specifically tuned to make it sound better than any handheld radio's microphone circuitry will be able to duplicate.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fzdsQ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fzdsQ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(This one is roughly $10,000)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They also incorporate pre-emphasis so the roll-off of higher frequencies in the receiver IF bandpass filters are not as audible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dolby sound operates on a similar principle - to counteract artifacts introduced by the entire receiving chain including the speakers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It takes a lot of work to properly tune the audio processor at a broadcast station.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Thus there is no comparison to a ham signal with 5 KHz deviation and no audio processing, with a small microphone.  It can be easily heard.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The military system you describe operates with 30 KHz deviation.  The receivers probably also have a 30 KHz bandpass filter, which means theoretically it should be able to reproduce up to 15 KHz audio frequencies.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But no filter is has perfect &quot;cliff&quot; edges, so there will be some kind of gradual roll-off at the higher audio frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One thing you can do with it for music, short of adding an audio processor, is to provide some sort of pre-emphasis.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can be done with a regular equalizer on the input.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;In broadcasting, to really tune it up well you would want to put a pink noise source (maybe an app) into the transmitter, then watch on a receiver with an audio spectrum analyzer.  Adjust the transmitter's audio-input equalizer until you get a flat response end-to-end.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-10-15T19:51:56.890" LastActivityDate="2017-10-15T19:51:56.890" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9399" PostTypeId="2" ParentId="9391" CreationDate="2017-10-13T07:32:55.133" Score="1" Body="&lt;p&gt;Have you thought about how you would get the signal from the towers (that seem to be placed rather at a large distance) to your shack? How will you compensate for the transmission losses? As for your idea of building strong, lasting, 40m high towers with bamboo, I'd think the only people that can advise you on that matter are around you, rather than the average radio amateur.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been in the Philippines a couple of times and seem to remember quite some construction being done with bamboo, and bamboo most often used to build temporary working constructions during building. Maybe ask the people who build these for their input? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or wait, and shop around for used, steel, towers?&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2017-10-13T07:32:55.133" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9400" PostTypeId="1" CreationDate="2017-10-13T16:03:46.660" Score="2" ViewCount="233" Body="&lt;p&gt;The web pages related to the unlaunched satellite were last updated in 2007, so I wonder - where is it now? Is it going to be launched someday?&lt;/p&gt;&#xA;" OwnerUserId="10145" LastActivityDate="2017-10-13T22:32:14.413" Title="What happened to AMSAT-Phase 3E?" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9401" PostTypeId="2" ParentId="9400" CreationDate="2017-10-13T22:32:14.413" Score="4" Body="&lt;p&gt;P3E (Phase 3E) was conceived and partially built by AMSAT Germany in the early 2000's. In 2015, Virginia Tech thought they would be able to secure a launch and AMSAT DE was prepared to transfer the space frame to them. This launch never materialized either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The space launch industry has changed a great deal in the last 5 to 10 years. Finding an HEO (High Earth Orbit) ride for this large of a satellite may never happen short of fully funding the launch. Such a fund raising effort has never been successfully attempted. The P3E concept was great in its time but I doubt that it will ever see space.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-10-13T22:32:14.413" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9402" PostTypeId="1" CreationDate="2017-10-14T14:22:49.567" Score="3" ViewCount="1041" Body="&lt;p&gt;In the US, just after passing your exam for Technician, General and/or Extra if you didn't have a call sign to begin with, can you request a vanity one right away or do you have to wait until one is assigned and then change it? &lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="8717" LastEditDate="2017-10-14T17:00:24.707" LastActivityDate="2018-09-10T04:14:08.937" Title="Can you request a vanity call sign when passing the exam?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9403" PostTypeId="2" ParentId="9402" CreationDate="2017-10-14T15:26:32.047" Score="8" Body="&lt;p&gt;You will have to be assigned a call sign first. To apply for a vanity, you will need an FCC Registration Number (FRN). The rule is that you cannot receive a vanity call sign from a call sign group for which your operator class is not eligible. For example, if you are operator class T (technician), you can only receive call signs from groups C &amp;amp; D. If you request a call sign from groups A or B, your application will be dismissed by the Commission. So, technically you must be licensed with a call sign first. The process is not instantaneous. It takes 18 days.&lt;/p&gt;&#xA;" OwnerUserId="997" LastActivityDate="2017-10-14T15:26:32.047" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9404" PostTypeId="2" ParentId="9402" CreationDate="2017-10-14T18:37:08.700" Score="3" Body="&lt;p&gt;There is no requirement that you have a call sign to apply for a new one.  The requirement is that you are of sufficient class to hold the call sign you apply for when the vanity application is processed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It takes 18 days to process a vanity application and around 10 days to process a new license after you pass your test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So yes, you can apply for your vanity call sign as soon as you know what license class you qualified for.  As long as your license is processed in a timely fashion, you will have your license and original call sign by the time your vanity application is processed.&lt;/p&gt;&#xA;" OwnerUserId="4748" LastActivityDate="2017-10-14T18:37:08.700" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9405" PostTypeId="2" ParentId="9184" CreationDate="2017-10-16T01:14:00.780" Score="1" Body="&lt;p&gt;Licensing does NOT only apply to commercial use.  Generally, any copyrighted material that is intended for the general public needs to be licensed (i.e., played in bars, restaurants, even Part 15 stations).  However, BMI is currently the only licensing agency that requires a license for Part 15 broadcasters.  Both SESAC and ASCAP have stated in writing that they do not require licensing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that radio broadcasters only have to worry about the copyright of the song (composer, lyricist, etc.).  Performances, at least right now, do not require licensing for over-the-air broadcasting.  That is something that the music industry is fighting to change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are streaming over the Internet, however, you require a license from Sound Exchange (which covers the song and the performance).&lt;/p&gt;&#xA;" OwnerUserId="10511" LastActivityDate="2017-10-16T01:14:00.780" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9406" PostTypeId="2" ParentId="5010" CreationDate="2017-10-16T18:24:39.940" Score="2" Body="&lt;p&gt;HF from space is nothing new.  In fact, the very first artificial satellite, Sputnik-1 (&lt;a href=&quot;https://en.wikipedia.org/wiki/Sputnik_1&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;) was heard by many hams as it transmitted on both HF (20 Mc) and VHF (40 Mc).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Now the military is going a step further with what they call next-gen HF from space.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.c4isrnet.com/c2-comms/satellites/2017/10/10/rockwell-collins-demonstrates-next-gen-hf-satellite-signals/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Rockwell Collins demonstrates next-gen HF satellite signals&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1sH7i.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1sH7i.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excerpt:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Rockwell Collins has demonstrated a next-generation high-frequency&#xA;  satellite communications system.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Rockwell used a wideband high-frequency (WBHF) system over a&#xA;  5,000-mile distance, according to a company news release. The&#xA;  demonstration was part of an Air Force Research Laboratory project to&#xA;  maintain satellite communications when communications have been&#xA;  disrupted.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;“Over the course of 30 days, Rockwell Collins’ next-generation HF&#xA;  [high-frequency] network reliably and rapidly passed data files of&#xA;  various sizes up to 1 megabyte,” the company said.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;“The demonstration, which showed significant improvement over standard&#xA;  satellite and legacy HF systems, also tested ‘store and forward’ split&#xA;  site capabilities, which is a foundational element of next-generation&#xA;  HF networks.”&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The project will continue exploring the optimum network configuration&#xA;  and waveform technologies for the new HF communications system.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-10-21T17:27:26.327" LastActivityDate="2017-10-21T17:27:26.327" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9407" PostTypeId="1" AcceptedAnswerId="9420" CreationDate="2017-10-16T20:53:28.350" Score="4" ViewCount="572" Body="&lt;p&gt;To have a groundmounted quarter wave vertical with a decent efficiency you need at least 16 radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So normally you would spread them out on the ground evenly around the base. This would give an angle of 360/16 = 22,5 degrees between two radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it make a great difference in efficiency to use the same amount of radials of the same length but to spread them out like this:&#xA;4 radials 5 degrees apart, then 75 degrees then again 4 radials 5 degrees apart and so on? Or would this only be as efficient as 4 radials?&lt;/p&gt;&#xA;" OwnerUserId="9532" LastEditorUserId="76" LastEditDate="2017-10-16T21:02:19.090" LastActivityDate="2019-09-03T09:54:44.487" Title="Radials on a vertical, spread out evenly or not?" Tags="&lt;antenna-theory&gt;&lt;vertical-antenna&gt;&lt;efficiency&gt;&lt;radial&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9408" PostTypeId="2" ParentId="9407" CreationDate="2017-10-17T00:39:18.707" Score="3" Body="&lt;p&gt;As long as the radials are symetrical it will make no noticable difference. A single radial opposite the other half of a dipole or 2 radials opposite each other will yield a reasonable pattern. The key is symetry so that the radiation pattern is not distorted. Any number of radials will do, even odd numbers, if kept symetrical. Most people agree that more radials are much better, but some argue that, especially at lower frequencies, too much time and money is spent for too little of an improvement. Note also that elevated radials need only 2 - 4 to be effective according to most people.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-17T00:39:18.707" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9409" PostTypeId="1" AcceptedAnswerId="9435" CreationDate="2017-10-17T08:02:26.377" Score="1" ViewCount="423" Body="&lt;p&gt;I am a GNU Radio beginner, and I use the following code to make the block's output-port output a &lt;code&gt;pmt&lt;/code&gt; data: &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;message_port_register_out(pmt::mp(&quot;fer&quot;));&#xA;...   &#xA;int d_pdu=cnt_int;&#xA;pmt::pmt_t pdu = pmt::mp(d_pdu);&#xA;message_port_pub(pmt::mp(&quot;fer&quot;),pdu);&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And the &quot;QT GUI Message Edit Box&quot; only can show me that date in type '&lt;code&gt;int&lt;/code&gt;'. But I can't use it as an integer data. How to change its data type? Is there a block that can make &lt;code&gt;pmt&lt;/code&gt; into &lt;code&gt;int&lt;/code&gt;?&lt;/p&gt;&#xA;" OwnerUserId="10410" LastEditorUserId="4076" LastEditDate="2017-10-18T10:32:45.220" LastActivityDate="2017-10-25T02:10:08.867" Title="GNU Radio code and data type conversion" Tags="&lt;gnuradio&gt;&lt;software-development&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9410" PostTypeId="2" ParentId="9397" CreationDate="2017-10-17T18:31:43.887" Score="0" Body="&lt;p&gt;The two audio channels have been designed for two different purposes and thus the added distortions are very likely not the same.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Music channels are designed to make mediocre music sound good and captivating to radio advertisement consumers.  Those audio channels commonly use boosting of some frequencies via sound processors to maximize that effect, and thus produce the illusion that the sound is &quot;better&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Military/aviation comm channels are designed so that the voice commands can be understood with minimal error under typical noisy conditions, thus other audio frequencies are boosted or filtered in order to render a lower error rate in receiving the voice messages (which isn't necessarily produced by flat/low-distortion/hi-fi audio quality).&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2017-10-17T18:31:43.887" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9413" PostTypeId="1" AcceptedAnswerId="9415" CreationDate="2017-10-18T20:09:35.403" Score="2" ViewCount="123" Body="&lt;p&gt;I have backgrounds on electrical communications, but know little about EM/RF. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to install outdoor antennas for experiments (receive only; I do not hold licenses, although I do intend to get one in the near future), and I want to use 4' - 8' marine antennas for this purpose. This is mainly because I want to place multiple antennas close together (so I can play with the phase differences of the signals), and yet have them tall enough so I can get line-of-sight to transmitters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that I am trying to operate these narrowband antennas on frequencies that they are not designed to operate on. (Mutual coupling is an another problem, but I can forget about that for now.) I am not sure how well these antennas will perform if I operate them on higher frequencies, say, in the 900MHz range. What could I expect if I do this? Are there any alternatives, if I want to place multiple antennas close together?&lt;/p&gt;&#xA;" OwnerUserId="10523" LastEditorUserId="8717" LastEditDate="2017-10-18T20:20:45.510" LastActivityDate="2017-10-24T12:53:17.010" Title="Could 8' Marine whip antennas operate on much higher frequencies?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9414" PostTypeId="1" CreationDate="2017-10-18T21:11:04.590" Score="2" ViewCount="88" Body="&lt;p&gt;Is there any reason to think that changing the Q of an antenna would affect the directional pattern, assuming that is the only variable that changes?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Restricting to values of Q say less than 1000.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assume this is an HF loop antenna which could reach Q values of &amp;lt;1000 somehow, and assume it is made of magic metal so that I can vary the conductivity and therefore the Q as desired without changing anything mechanically.  The capacitor is of course perfect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So as I increase resistance of the metal, does the pattern change?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I miss having access to XFDTD, I could have just simmed it.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastEditorUserId="9575" LastEditDate="2017-10-19T13:39:30.000" LastActivityDate="2017-10-20T12:40:18.933" Title="Antenna Q vs pattern shape" Tags="&lt;antenna&gt;&lt;frequency&gt;&lt;radiation-pattern&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9415" PostTypeId="2" ParentId="9413" CreationDate="2017-10-18T21:30:20.460" Score="5" Body="&lt;p&gt;If your goal is simply to gain height, why not mount multiple properly-sized antennas on a single mast? At 900 MHz, the antennas and a structure to hold them sufficiently far apart from each other would be quite small and light, so you don't need anything structurally complex. A prototype could be built out of wood, wire, cable-ties/screws/tape/glue, and whatever sort of 8' long object you can scrounge up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And it will be unnecessarily hard to rig 8' long antennas to maintain specific phase (hence distance) relationships on the scale of inches!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The primary hazards of using the wrong size of receiving antenna, for casual listening, are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It will be less efficient — this only matters if you are trying to receive weak signals, which I imagine you might care about if you're trying to locate transmitters at UHF frequencies.&lt;/li&gt;&#xA;&lt;li&gt;You will pick up more low-frequency signals which could overload the input filtering of your receiver and appear as aliases or noise — the antenna's frequency selectivity is working against you.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In most cases of wrong-sized antennas for receiving, I would tell people that it's worth trying. In yours, it seems more potentially problematic and wasteful because of the large wavelength ratio and the specific application.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-10-19T14:20:10.300" LastActivityDate="2017-10-19T14:20:10.300" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9416" PostTypeId="2" ParentId="9413" CreationDate="2017-10-18T22:16:04.573" Score="4" Body="&lt;p&gt;The problem with too-long UHF and microwave verticals is that they have an undesirable pattern. A vertical needs a very clean, low pattern with as few high-angle lobes as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We want an antenna with a low-angle lobe that's directed as close as possible to the horizon (where signals come from!). &lt;em&gt;1/4 and &lt;strong&gt;up to&lt;/strong&gt; 5/8 wavelength verticals will do that.&lt;/em&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Much longer than 5/8, and you're mostly listening towards the sky, rather that near the horizon. And that's what you'll get at 900 MHz with those too-long vertical antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should also consider whether a good beam antenna with a rotor will fit your requirements. But with phased verticals, you can instantly change what direction you want to listen towards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounds like you already have some marine antennas on hand. As Kevin pointed out, you'll likely have problems. Forget about using them for anything except the marine frequencies that they were deigned for.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-10-18T22:16:04.573" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9417" PostTypeId="2" ParentId="5068" CreationDate="2017-10-19T13:46:33.713" Score="1" Body="&lt;p&gt;Much depends on the relative sizes.  A metal flag on an HF vertical antenna is not likely to change the pattern in any way you'd notice.  A gum wrapper near a 2.4GHz antenna definitely will change the pattern. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I once did a design for a 2.4Ghz consumer product and ended up sculpting the antenna pattern with a block of nylon adjacent to the antenna, acting as a lens by diffracting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might gain some insight by looking at Remcom's web site and some of their demos for XFDTD. &lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2017-10-19T13:46:33.713" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9418" PostTypeId="2" ParentId="9414" CreationDate="2017-10-20T01:31:02.013" Score="0" Body="&lt;p&gt;Honestly, I can't give a definite answer to this question with the given information. But the general answer is that the Q alone probably will have little or no noticeable effect in the pattern. Only the bandwidth and efficiency are likely to be altered in any significant way, since you are talking about &quot;magically&quot; changing the material used. However, other related things (almost ALL parameters are interrelated SOMEHOW) MAY be affected and thus cause a change. The amount of change is still likely to be minimal, if even noticed. You could simulate the effects using a good antenna simulator program. Simply change the material used in the simulation and rerun it. In my experience this rarely has any profound effect. And many others that have posted their experiences online report little to no difference, no matter what material they use for the conductor.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-20T01:31:02.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9419" PostTypeId="2" ParentId="9414" CreationDate="2017-10-20T12:12:20.710" Score="5" Body="&lt;p&gt;In general for a given antenna evaluated on a given frequency, if whatever is changing the Q occurs uniformly or universally and does not result in a change to the effective aperture, phasing, or geometry of the antenna then the pattern will not be altered in a meaningful way. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example of a uniform change would be changing the wire gauge of a wire antenna. An example of a universal change would be changes to a matching network that do not affect element phasing. Another example of a universal change is adding resistance to the antenna feedpoint. Any of these examples could alter the Q without changing the pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Changes that affect the Q may change the gain of the antenna without any changes to its pattern. In antenna engineering, the pattern of the antenna is called &lt;em&gt;Directivity&lt;/em&gt;. It is the &lt;em&gt;Efficiency&lt;/em&gt; of the antenna times its &lt;em&gt;Directivity&lt;/em&gt; that yields its &lt;em&gt;Gain&lt;/em&gt;: $$ Gain=Efficiency \times Directivity $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the Q of the antenna relates to its efficiency , it is clear that the gain can be altered through changes in Q.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-20T12:40:18.933" LastActivityDate="2017-10-20T12:40:18.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9420" PostTypeId="2" ParentId="9407" CreationDate="2017-10-20T16:53:15.587" Score="7" Body="&lt;p&gt;The purpose of the radials is to increase the effective ground conductivity, thus reducing losses. As you propose to have 16 radials but in four groups, I'd expect the efficiency to be somewhere between 4 radials and 16 radials evenly spaced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, if you need to do this to work around some obstacle, then by all means do it. You can also make the radials shorter or slightly bent if it gets around your obstacle. Putting more copper in the ground can only make things better, regardless of how its done.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-10-20T16:53:15.587" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9421" PostTypeId="1" CreationDate="2017-10-20T20:56:12.423" Score="-2" ViewCount="289" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;strong&gt;Is it right for us hams to hide our antennas?&lt;/strong&gt; &lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;And should we tell our neighbors that we are a ham?&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-10-20T21:00:42.523" LastActivityDate="2017-10-20T21:28:33.750" Title="Is it right for Amateur Radio operators to hide their antennas?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="3" ClosedDate="2017-10-21T14:54:06.447" ContentLicense="CC BY-SA 3.0" />
  <row Id="9422" PostTypeId="2" ParentId="9421" CreationDate="2017-10-20T20:59:49.507" Score="3" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Yes it is.&lt;/strong&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;No, it's usually a bad idea.&lt;/strong&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rPRrZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rPRrZ.jpg&quot; alt=&quot;Any questions?&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Any Questions?&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;This was prompted by &lt;a href=&quot;https://ham.stackexchange.com/questions/7615/shortwave-cb-ham&quot;&gt;this question&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lots of law-abiding hams need to hide their antennas. HOA rules, objections from spouse and neighbors. Ask most any city ham: they will tell you that the mere presence of their antenna even if not connected is the &quot;cause&quot; of their neighbor's problems with their TV, radio, garbage disposal, sickness ... the list is infinite.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-10-20T21:04:53.690" LastActivityDate="2017-10-20T21:04:53.690" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9423" PostTypeId="2" ParentId="2318" CreationDate="2017-10-21T11:40:42.250" Score="0" Body="&lt;p&gt;I was browsing and saw this and I couldn't help but put my &quot;2 cents&quot; in. I think it would truly take a lawyer to properly and completely answer this question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I note the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) It may or may not be illegal. It seems to me that it depends on WHY the person did this. To get money? Simply as a method of providing a service/information? To me it seems that the transmission itself is NOT illegal, it is ONLY the other circumstances associated with it that are in question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) It would, IMHO, be very difficult to prosecute this situation. A lot of the crux of the situation has to do with intent. Intent can be hard to prove. The government may be reluctant to prosecute, whether it is or is not illegal. They may not be able to PROVE the intent, and thus whether it is actually illegal or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) You can't make it illegal for one person to do a thing and illegal for another to do essentially the same thing under approximately the same circumstances (with some obvious exceptions). In this case it seems perfectly legal for one person to transmit and that transmission be used on the internet, even though the person controlling the internet gets money. The person transmitting did nothing illegal (got no money) and the person controlling the web site did nothing illegal (didn't transmit anything). Then how can the same type of transmission or its use on a website suddenly become illegal, when it is used in exactly the same way and for the exact same purpose just because it is on another website (regardless of who is doing it)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4) That is not to say that the person doing this is completely in the clear, legally. He DID get money, but was it really his INTENT to do anything but provide information, just like others? Or was he trying to generate money by including it on his website? Does the money relate to the transmission or not? Or does the money relate to the website only? Does the money somehow not count in this situation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is an interesting and thought provoking situation in any case. I am no lawyer but I would think that this is a reasonable, even useful and helpful, use of the transmissions. The money seem unrelated to the transmitting although I admit if it suddenly increased the revenue of an existing it would not look so innocent. But I still believe it should be an allowed activity, since others can do it without being illegal, even if it needs a change to the rules to accomplish this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a side note, I believe that being sure that the rules are followed and legal issues avoided with some good pre-planning. Let different people take charge (at least legally, if not actually) of the website and the transmitter. Thus the money is separated from the transmissions, but the goal is still accomplished.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-21T11:40:42.250" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9424" PostTypeId="2" ParentId="9100" CreationDate="2017-10-21T12:45:22.493" Score="1" Body="&lt;p&gt;From your information it seems obvious that raising the antenna is a necessity in order to restore, or improve on, the former situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be helpful to know the weight of the balun and feedline, but 65 feet (only a few inches off the roof, and therefore not much feedline weight) does not sound too long if the weight of the balun is not ridiculous. I think the most difficult part is making sure the PVC pipes are sufficiently rigid, or at least strong enough to not break when tensioned enough to keep the antenna off the roof. You said the PVC was 2 feet long, but you didn't say the diameter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect it would be easier to get the antenna higher off the roof if a center support is used. Maybe it could be as simple as 2 small pieces of plywood (maybe 2 feet by 2 feet each?) joined at a 90 degree angle (with a 2x2 at the joint for strength and to make joining easier) placed with the joint up and at a 90 degree angle to the ridge. Matching &quot;v&quot; notches cut in each side of the bottom will make it fit the ridge and give it stability.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-21T12:45:22.493" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9425" PostTypeId="1" AcceptedAnswerId="9429" CreationDate="2017-10-22T19:14:53.413" Score="5" ViewCount="1263" Body="&lt;p&gt;I'm looking into ways to match a 137MHz RX dipole antenna to an unbalanced coax + amplifier. I know there are several types of baluns which can be categorized under magnetic baluns (where there are separate primary and secondary windings) and current baluns which are essentially chokes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was hoping I could build a transformer type balun, since this would allow me to choose almost any impedance matching ratio I want. I have FT50-61 and FT50-63 toroid cores, which are advertised to work as wideband transformers from 10 MHz - 200 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried winding a few 1:1 transformers for measuring purposes and the results were pretty bad, I got at least -3.5 dB insertion loss. I tried using between 2 and 8 windings of different diameters of copper and silver for both primary and secondary. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a typical response (depending on how close the windings are and how many I put on it, I can move the peak left and right by a few ten MHz only):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oV3pJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oV3pJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I'm wondering if there is a systematic approach to getting good insertion loss, maybe by moving the peak of the curve to 137 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any tips are appreciated.&lt;/p&gt;&#xA;" OwnerUserId="10536" LastEditorUserId="8573" LastEditDate="2019-11-30T02:34:26.213" LastActivityDate="2019-11-30T02:34:26.213" Title="How to build a balun transformer for 2m RX with low insertion loss" Tags="&lt;balun&gt;&lt;toroid&gt;&lt;transformer&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="9426" PostTypeId="2" ParentId="1859" CreationDate="2017-10-22T20:03:53.567" Score="2" Body="&lt;p&gt;I have used both 107 and 71 ft lengths, but didn't see much difference as my old KW At-230 tuner tuned both just fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I fed them through a 9:1 balun and 50 Ω coax with 25 ft of coax back under wire, possibly acting as counterpoise, but I'm not sure about that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Everything is well grounded in my shack. It worked pretty good on 40 &amp;amp; 20m.&lt;/p&gt;&#xA;" OwnerUserId="10537" LastEditorUserId="4076" LastEditDate="2017-10-23T19:33:51.257" LastActivityDate="2017-10-23T19:33:51.257" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9427" PostTypeId="2" ParentId="7615" CreationDate="2017-10-22T21:41:27.203" Score="2" Body="&lt;p&gt;Shortwave or HF is a broad term that describes any radio use roughly in the 1mhz-30mhz range, and includes shortwave listening, CB, and Ham Radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shortwave listening includes listening to anything in this range, including broadcast shortwave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CB and Ham Radio in the US allow receiving and transmitting on specific ranges of frequencies based on laws and rules formulated and enforced by the FCC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CB is channelized AM that anyone can use (free open license) but is limited to 5w and all of its frequencies are in the 11m wavelength band.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham Radio or Amateur Radio requires a license to transmit.   To get a license (in the US) you must pass a basic knowledge test that includes questions about the technical, legal, and safe use of Amateur Radio.  Multiple ranges of frequencies have been allocated to amateur radio with a much higher power limit, which is at least in part why there are saftey questions on the exam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CB is better if you want unrestricted communication with cheap equipment and no exam.   Amateur radio is better if you want to use more power and use more frequencies, including ones beyond shortwave.  Amateur radio equipment can be cheap or very expensive, depending on what you want it to do and how much quality you want.  There's practically no upper or lower limit on cost.  (The lower limit would be kit radios built from scraps -- almost free!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use amateur radio knowledge to build better antennas and hidden antennas, and this applies well to shortwave listening and CB as well as amateur radio.  (An antenna is an antenna, the theories work for any radio.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio (in the US) has some very minor restrictions on what you can transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Broadcasting is one person talking to many people with no expectation of a response; this is prohibited in amateur radio, as amateur radio is two way communication -- which means you have to at least occasionally stop transmitting so you can listen.   Broadcasting is prohibited.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transmitting for profit is banned in amateur radio.  It is intended to be a hobby for people to enjoy, not something you get paid for.  (If you want to transmit for profit, get a commercial license on commercial frequencies.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And lastly, amateur radio prohibits communications that are not family friendly, as it it is intended that even children might be in the hobby.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2017-10-22T21:41:27.203" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9428" PostTypeId="2" ParentId="7615" CreationDate="2017-10-22T22:46:39.150" Score="3" Body="&lt;p&gt;Ham radio is the most flexible and most capable, and I should say in my opinion, the most fun of the two Ham versus CB radio.  I am not answering for Shortwave Listener type radio hobby because that is quite a bit different in some respects and I know quite a few Ham radio operators who are also avid shortwave listeners (to non ham band broadcasts).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham radio on HF bands is world wide communication.  You can't do that usually with CB.  It is theoretically possible for a 5 watt CB signal to get good skip in the peak sunspot cycle but often there are not any other parties on varieties of countries that are replying to CB transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another difference between Ham and CB is that Ham radio offers plethora of different communications modes.  The conventional AM, SSB, CW, and FM then the various Data modes like RTTY, PSK, and a seeming myriad of others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham radio offers such esoteric activities as Moon bounce or EME (Earth-Moon-Earth communications) and also a variety of satellite capabilities for extending the reach of your signal (in particular, your VHF/UHF signal).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My favorite mode is CW and that represents close to 95 to 98 percent of all my activity.  The value of CW is that is really can cut thru the noise without using a lot of power.  Most of my CW contacts are 100 watts and less for both ends of the QSO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham radio is also a fraternity of like-minded people who join together in local amateur radio clubs, in contests, and other group activities including emergency traffic handling and offering communications in disaster areas hit by hurricanes or other calamities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To many ham radio operators, part of the enjoyment is building something -- that is, home brewing your own equipment, radios, amplifiers, antennas, and even computer assisted operations with home grown software.  Therefore, I think more than CB or other SW listening activities, Ham Radio is very much into education, training, and helping others in times of need.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2017-10-22T22:46:39.150" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9429" PostTypeId="2" ParentId="9425" CreationDate="2017-10-23T10:59:36.693" Score="3" Body="&lt;p&gt;VHF transmission line baluns are very difficult to construct due to interwinding capacitance. As a result, the balun will have an undesirable self resonant point and will not typically reach the desired transformation ratio. Note that a balun does not consist of simple primary and secondary turns but rather primary and secondary transmission lines (2 parallel wires of a specific characteristic  impedance). If a balun is made simply with conventional primary and secondary windings then the core flux plays an active role. Such a design will also have a limited number of practical impedance ratios due to the requirement of a low number of turns to minimize capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transformer capacitance consists of capacitance between turns, capacitance between windings, capacitance between layers, and stray capacitance. These can generally be modeled as a capacitor in parallel with each winding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A better approach is to use a choking balun for common mode suppression and a lumped L, T, or Pi network to achieve the desired impedance transformation ratio. In some cases, a transmission line transformer may also be suitable for impedance transformation. In order to minimize losses, the matching network should be placed directly at the antenna feedpoint, followed by the choking balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At VHF frequencies, a choking balun consisting of #31 or #43 ferrite mix beads slipped over the outer coax jacket will be the most effective since any attempt to wind the coax through a toroid form will suffer from interwinding capacitance effects. Consider using 20 or more beads on the coax.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-23T15:48:34.293" LastActivityDate="2017-10-23T15:48:34.293" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9430" PostTypeId="2" ParentId="7081" CreationDate="2017-10-23T16:36:24.437" Score="3" Body="&lt;p&gt;Model the 1/2 wave center fed antenna using the wire size, altitude, and all location attributes to determine the center fed impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;divide 600 by the 73 ohms or whatever you calculate the center fed impedance to be then multiply the answer by 600 --- you're home.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example:  $600/73 = 8.22 \times 600 = 4900$ ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the original and correct quarter wave transform using 600 ohms to represent the surge impedance of a single wire.  Earlier I edited the 600 ohm value to 380 ohms in error because some of the CAD antenna design tools apparently used approximately 380 ohms.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using repeatable measurements, the Surge impedance of a single wire verifies that the impedance of a wire unmolested by external sources will be approximately 600 ohms and will vary less with wire diameter than previously thought.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The measurement can be done at the feed point of an open wire and verified with termination value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The equation used to determine the surge impedance of a single wire is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Z = 138 \log\left(\frac{4L}{d}\right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $L$ is the length of the wire and $d$ is the diameter of the wire — same units; In space.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;INFORMATION ADDED FOR CLARITY:  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following url represents a circuit that can be used to measure the surge impedance and velocity factor of a single wire or transmission line. It is a variable voltage divider, adjustable from 50 to 1050 ohms.     &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.k9axn.com/attachments/Finished_3_jpg_final.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.k9axn.com/attachments/Finished_3_jpg_final.jpg&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following url represents the measurement of the surge impedance and velocity factor of a 54 foot length of #14 wire.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://k9axn.com/attachments/Single_wire_4.AVI&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://k9axn.com/attachments/Single_wire_4.AVI&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Important to note:  The two timing lines from the rise to 115ns represent an approximately 4 volt @ .007A wave entering the wire.  The wave will have reached the end of the wire at mid point, then return during the second half where you see the voltage rise to 8 volts and current cease.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rise and fall times are a result of instrument limitations.  Surge current behaves as purely resistive, much like the impedance of space.  It is used to calculate the radiation resistance of an antenna and is largely unaffected by proximity to the ground.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;END OF INFORMATION ADDED FOR CLARITY&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/x6W9j.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/x6W9j.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above Image represents the measurement of the Surge impedance and velocity factor of a single wire.  It can be used to measure the Surge impedance and velocity factor in coax, twin lead or any antenna wire.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The surge impedance of a single conductor or transmission line is essentially composed of two primary notions, the impedance of space 377 ohms and the energy used to accelerate electrons.  Be mindful that the electrons in a 1 KW 14MHz transmission line or antenna will remain within approximately 1/10,000 of an inch from where they started.  This can be visualized using a Newton's cradle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that information it becomes clear that the opinions regarding end fed antennas are wanting:  The impedance at the feed point is not infinite and is easily calculated.  The reflected waves/current that flow within an antenna when reaching an end are wholly reflected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next edit will consist of a cycle by cycle narrative of the measurements and events as the antenna is spooled up. &lt;/p&gt;&#xA;" OwnerUserId="10540" LastEditorUserId="10540" LastEditDate="2018-09-05T17:06:59.180" LastActivityDate="2018-09-05T17:06:59.180" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="9431" PostTypeId="2" ParentId="9413" CreationDate="2017-10-24T12:53:17.010" Score="0" Body="&lt;p&gt;An 8 foot marine antenna is not a &quot;whip&quot; but rather it is a collinear array in a fiberglass radome. As such, it consists of 1/2 wavelength elements that are phased to provide approximately 6 dBi gain for the marine band (~156 MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Operating any collinear antenna at a frequency other than what it has been designed for will likely produce very poor results. The individual elements will not be the correct electrical wavelength and the phasing of the elements will be wrong.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-10-24T12:53:17.010" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9432" PostTypeId="1" CreationDate="2017-10-24T21:34:29.780" Score="3" ViewCount="126" Body="&lt;p&gt;Really bizarre issue here. Here is an image of a signal taken from SDR Sharp: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0csa7.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0csa7.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Freq: 926.365M&#xA;Bandwidth: 30k&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, using the above measurements, here is this same signal observed in GNU Radio with the QT Waterfall Sink at 5M sample rate: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ibPvo.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ibPvo.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the same signal at 2M sample rate: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/B5ZUp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/B5ZUp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the same signal at 10K sample rate: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8Ggwc.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8Ggwc.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And at 1K: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/KPf1K.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KPf1K.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This cannot be possible?!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My GNU Radio flow is as simple as possible, but here's what it looks like: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7y7l5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7y7l5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone explain this? Surely as I close in on the signal, it should be filling up the Waterfall much more.&lt;/p&gt;&#xA;" OwnerUserId="10547" LastEditorUserId="76" LastEditDate="2017-10-25T03:36:54.967" LastActivityDate="2017-10-25T03:36:54.967" Title="GNU Radio - Signal Keeps Getting Smaller?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9433" PostTypeId="2" ParentId="9432" CreationDate="2017-10-24T22:46:34.190" Score="0" Body="&lt;p&gt;Answered my own question. It appears the SDR I am using (RTL2832U) has a minimum sample rate of 900k, which is why I was only able to observe the signal at that sample rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution was to record the signal at 900K, and then pass it through a Freq Xlating FIR Filter, with a decimation value set above 1.&lt;/p&gt;&#xA;" OwnerUserId="10547" LastActivityDate="2017-10-24T22:46:34.190" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9434" PostTypeId="2" ParentId="9432" CreationDate="2017-10-24T22:48:16.037" Score="3" Body="&lt;p&gt;Most likely, the sample rates you are asking for are unsupported by the hardware. The &lt;code&gt;osmocom&lt;/code&gt; source is just a wrapper around a bunch of specialized device drivers, and generally you're not going to notice if you don't get the sample rate you asked for unless you're also e.g. using an audio sink so you hear the audio skipping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're programmatically interacting with the source you can get a list of supported sample rates, but this isn't easy within GNU Radio Companion; the usually convenient thing to do is look at the source code within gr-osmosdr for the interface for the particular hardware you're using.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to actually get a lower sample rate, you must start with a supported sample rate and then use a decimating filter block (there are many) to convert to the one you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that having a high sample rate is not necessarily completely wasted; the information in the extra samples, as processed by the filter, allows you to get more dynamic range as if your ADC had more bits per sample.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-10-24T22:48:16.037" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9435" PostTypeId="2" ParentId="9409" CreationDate="2017-10-25T02:10:08.867" Score="0" Body="&lt;p&gt;Well!I've made song changes on the Edit Box module. Let the Edit Box output pdu-type data.&#xA;Code:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;      float d_pda = pmt::to_float(d_msg);     &#xA;      pmt::pmt_t pda = pmt::cons(pmt::PMT_NIL, pmt::make_f32vector(8, &#xA;      d_pda));&#xA;      message_port_pub(pmt::mp(&quot;msg&quot;),pda);&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Now I can use pdu_to_tagged_stream module to convert msg to float.And the float data can be shown in Number sink module.&lt;/p&gt;&#xA;" OwnerUserId="10410" LastActivityDate="2017-10-25T02:10:08.867" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9436" PostTypeId="1" AcceptedAnswerId="9438" CreationDate="2017-10-25T05:56:32.783" Score="11" ViewCount="580" Body="&lt;p&gt;I remember being surprised to learn that a CW signal has a bandwidth (albeit small), but when I thought it over, it made sense. Essentially, we are modulating the carrier with a low frequency square wave. This would explain key clicks: a perfect square wave has infinite bandwidth, but if you smooth the rising and falling edges, the bandwidth goes down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This got me thinking. If, theoretically, we could key up and key down precisely on the zero-crossings of the carrier, it seems to me that there would not be any distinct rising or falling edge. Then, would the signal have zero bandwidth?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I haven't the slightest idea whether this would be practical in practice. I have to assume either a) it's not or b) I'm wrong about this theory, because otherwise I'm sure transmitters would already do this.)&lt;/p&gt;&#xA;" OwnerUserId="8940" LastActivityDate="2018-02-28T14:09:55.590" Title="Key CW on zero crossings - zero bandwidth?" Tags="&lt;cw&gt;&lt;theory&gt;&lt;bandwidth&gt;" AnswerCount="6" CommentCount="4" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9438" PostTypeId="2" ParentId="9436" CreationDate="2017-10-25T08:22:26.620" Score="6" Body="&lt;p&gt;You raise an excellent question and your thought processes are indeed on the right track.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First some background. An ideal, uninterrupted sinusoidal carrier has zero bandwidth. Real world factors such as phase noise, amplifier distortion, etc. produce a measurable bandwidth of the carrier. When the carrier is keyed on and off as it is with Morse code, this is a special form of ASK (Amplitude Shift Keying) called OOK (On Off Keying) as it is discussed in professional literature. Normally, the bandwidth of the modulated OOK signal is minimized when the keying waveform rise and fall times take on a Gaussian or raised cosine form. Most amateur radio transceivers are using simpler RC filtering to shape the keying waveform, resulting in less than ideal bandwidth but at least avoiding the key clicks from the otherwise sharp raise and fall time of the modulating signal. In any case, it is the rise and fall shape of the keying waveform that determines the bandwidth of the modulated signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the transition of the modulating signal is synchronized with the zero crossing of the carrier signal, this is known as &lt;em&gt;coherent OOK modulation&lt;/em&gt;. This is, of course, much more difficult to implement than a simple, non-coherent RC filtering scheme so it is not commonly seen in amateur radio applications. However, when implemented properly coherent OOK does reduce, but does not eliminate, the signal bandwidth. The &quot;residual&quot; bandwidth is largely due to a variety of real world factors including non-instantaneous keying time which introduces a distortion of the carrier waveform. Any distortion, no matter how small, of the sinusoidal carrier will result in a non-zero bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[EDIT] Even with ideal zero crossing switching and ideal amplification, there will be minor sidebands but these will roll off as a function of frequency at a significantly greater rate than switching at non-zero points. With zero crossing switching, however, non-linear amplification present in most CW transmitters will likely introduce greater side band components than those caused by zero crossing switching. [/EDIT]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you could win over some of the CW aficionados with a coherent OOK transmitter but in a hobby market the commercial viability of such a transmitter would be a question of price elasticity. Perhaps in this new era of DSP based radios, the lowered cost of implementation will make this commercially viable. But given that few, such as the Elecraft K3, amateur radio transceivers implement Gaussian keying, we still have a ways to go to optimize the bandwidth of our CW signals.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-26T09:47:13.590" LastActivityDate="2017-10-26T09:47:13.590" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9439" PostTypeId="1" AcceptedAnswerId="9442" CreationDate="2017-10-25T15:10:49.327" Score="5" ViewCount="806" Body="&lt;p&gt;I recently acquired a Decibel 3-element VHF Yagi that was formerly in commercial service. I connected my MFJ-259B antenna analyzer to the antenna and found its minimum SWR at 155 MHz. I have not measured the boom length or the element lengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm told this antenna has a &quot;stub match&quot;, but that's not a matching system I'm familiar with. There is a small (apparently aluminum) tube a couple of inches above the driven element - on one side is the feed line, and on the other is a small piece of coax that is physically connected to both the driven element and the tube above, but only appears to be shorted to the short tube.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have measured the impedance of the antenna at 146 MHz to be R = 36 Ohms and X = 40 Ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I best adapt this antenna for 2 meter use? I don't think I have the proper tools to trim the element lengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Picture of the matching section:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/N4Uid.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/N4Uid.jpg&quot; alt=&quot;the matching section&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Picture of the whole antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ya9t3.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ya9t3.jpg&quot; alt=&quot;the whole antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="41" LastEditorUserId="41" LastEditDate="2017-10-31T03:15:42.560" LastActivityDate="2017-10-31T15:55:20.940" Title="How to adapt commercial VHF yagi for 2 meter amateur use?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;2m-band&gt;&lt;yagi&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9440" PostTypeId="2" ParentId="7325" CreationDate="2017-10-25T17:32:20.220" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it possible that my VOX has a hang time that's causing me to loose the initial response to my call?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, that is definitely possible. You want the lowest possible VOX threshold and, if possible, just turn it off completely and use another mechanism to trigger the PTT.&lt;/p&gt;&#xA;" OwnerUserId="738" LastActivityDate="2017-10-25T17:32:20.220" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9441" PostTypeId="2" ParentId="9068" CreationDate="2017-10-25T20:22:47.300" Score="1" Body="&lt;p&gt;FIRST; THE CHEAP T.V. BALUN I PRESUME 300 / 75 OHM &#xA;SECOND, IF U WANT TO USE T.V. COAX AND ARE RUNNING QRP IT SHOULD WORK. BUILD A BALUN. LOOK 'EM UP ONLINE. THIRD; I BUILT AN OCFD FROM LEW MCCOY'S &quot;LEW MCCOY ON ANTENNAS&quot; IT IS FED W/ DUAL 75 OHM COAX. YOU CAN SEE THAT ANTENNA HERE [&lt;a href=&quot;http://www.hamuniverse.com/kf9focfdipole.html]&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hamuniverse.com/kf9focfdipole.html]&lt;/a&gt;.&#xA;I USED RG-6 BECAUSE I GOT 200' OF IT - FREE -  QUAD SHIELD CABLE T.V. STUFF. YOU CAN USE '59, '58, '8X AT DIFFERENT V.F. THE FEEDLINE IS 130% OF A QUARTER WAVE AT THE LOWEST DESIRED QRG.&#xA;I USED 3.9 MHZ AS A DESIGN QRG. THAT GIVES [234 / 3.9 = 60 X 1.3 = 78'. I HAVE HEARD FROM GUYS IN BRAZIL, INDONESIA, AND MANY OTHER LOCALES ON HOW HAPPY THEY WERE W/ THE LOW NOISE&#xA;ON THIS ANTENNA. FED  OFF CENTER 57.5' IN, USING DUAL SHIELD  [IN THE FORM LIKE TWINAX], HAS HAD EXCELLENT RESULTS. '73 RICH - KF9F&lt;/p&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="8492" LastEditDate="2017-10-25T20:28:15.707" LastActivityDate="2017-10-25T20:28:15.707" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9442" PostTypeId="2" ParentId="9439" CreationDate="2017-10-26T06:52:52.693" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm told this antenna has a &quot;stub match&quot;, but that's not a matching system I'm familiar with.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The matching system is a delta match with a stub. A delta match cannot cancel out the reactance of the driven element so a stub is added to cancel the reactance. The spread connections of the coax on the tube form the delta match and the vertical bars form the stub.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How can I best adapt this antenna for 2 meter use? I don't think I have the proper tools to trim the element lengths.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As you noted, the antenna is setup for 155 MHz. To &quot;trim&quot; the antenna for 146 MHz, you would need to &lt;em&gt;add&lt;/em&gt; length to all of the elements since a lower frequency requires longer elements. To optimize the antenna, you would also need to re-space the elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest approach to using this antenna on 2 meters is to note the complex impedance (the R and the X) directly at the antenna at your desired two meter frequency. From this a simple matching network can be constructed to provide a 1:1 SWR on the feedline. The pattern and gain of the antenna will not be optimized but it may prove sufficient for your use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are not familiar with designing a matching network, you may wish to measure and report the R and X values at your chosen two meter frequency (directly connected to the antenna without coax) within your question so that I or others may be prescriptive regarding the matching network you will need. It will likely involve only a single inductor and a single capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[edit]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The OP has an updated post that states the impedance at the feed point of the antenna is 36+j40 at 146 MHz. A matching network consisting of a 26 pF capacitor placed across the antenna connection and a 43 nH inductor placed in series with the center coax connection will change this impedance to 50 ohms and result in a near 1:1 SWR on the coax. Such an inductor can be fashioned as 4 turns of 16 or 18 gauge bare wire spaced out 0.5 inches wound on a 0.25 inch form which is then removed. The final SWR can be adjusted by very slightly expanding or compressing the coil.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/q1OuW.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fq1OuW.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since some antenna analyzers do not properly indicate the sign of the reactive part of the impedance, it could be that the impedance is 36-j40. In this case the capacitor should be 14 pF and the inductor 68 nH. But the capacitor now goes across the coax connections and the inductor in series with the center lead of the antenna. The inductor can be fashioned as above but with 5 turns. You may also choose to use a high quality variable capacitor which can add to the adjustability of the matching network. &lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/O1Udx.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fO1Udx.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These matching networks used to take laborious calculations to derive the correct values. But now there are many programs (e.g. Elsie) and on-line calculators that take the drudgery out of the exercise. My favorite on-line calculator is &lt;a href=&quot;http://leleivre.com/rf_lcmatch.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://leleivre.com/rf_lcmatch.html&lt;/a&gt;. I used this site to calculate the values shown. Here is a screenshot of the result of the first matching network:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qmtYO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qmtYO.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I note that other LC configurations are often possible. I chose to illustrate the versions where the DC properties of the antenna were maintained.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whatever version of the matching circuit that is used, your antenna analyzer can be used to fine tune the circuit. Simply connect the matching circuit directly to the antenna (without coax) and place the analyzer on the coax side (without coax) of the matching network. Adjust until you show R = 49 to 52 ohms and X as close to zero as possible. Remove the analyzer and connect your coax cable. Double check your measurements at the far end of the coax cable. You should see an SWR close to 1:1. If not, your body and antenna analyzer capacitance may have been interacting with the antenna while you were making your adjustments. The matching circuit can be enclosed in a small plastic or metal container to protect it from the elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[/edit]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An alternative approach is to carefully adjust the spacing of the coax connections on the delta match. You may be fortunate to find a spacing that brings it into a reasonable SWR range. This should be done with the antenna supported by a non-conducting pole at least 6 feet away from ground and all other objects. This technique still will not optimize the antenna but as noted above, it may prove usable for your needs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could just as well re-optimize the entire antenna by modeling it and adjusting spacing, element length, and the matching network. But given your opening comment stating that you lack the tools to &quot;trim&quot; the antenna, I suspect this option is out of the realm of immediate possibilities. In looking at the antenna construction, it also appears that there will not be sufficient boom length to allow the optimization of the spacing.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-31T15:55:20.940" LastActivityDate="2017-10-31T15:55:20.940" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9443" PostTypeId="2" ParentId="9439" CreationDate="2017-10-26T07:15:49.260" Score="1" Body="&lt;p&gt;I agree with Glenn, but also another way to do it is to rebuild the antenna with the right lengths (expect to add 1 or 2 longer elements for the lower frequency you intend to use) and spacing (may need to lengthen the boom too, depending on the number of elements you want to use). It is a lot more work but will probably perform better and likely won't need a matching network (or at most a very simple one), maybe just a balun. You could choose a design already tested and proven from the myriad available online. You could also check the design with antenna modeling software BEFORE building. You are much more likely to get what you want (there are always tradeoffs and compromises to consider).&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-10-26T07:15:49.260" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9444" PostTypeId="2" ParentId="9436" CreationDate="2017-10-26T07:34:34.067" Score="1" Body="&lt;p&gt;Rob Sherwood &lt;a href=&quot;http://www.sherweng.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;NC0B of Sherwood Engineering Inc.&lt;/a&gt; did a study and produced a video showing that the rise time (and presumable the fall time too) is the key to reducing bandwidth. He compared rise times of 1 ms to 10 ms. Too fast of a rise time significantly increases bandwidth. To answer Dominick's question, I looked at the CTU (Contest University) files. Rob has mentioned this in nearly every one of his presentations every year he has spoken. THey can be found in the videos &lt;a href=&quot;https://www.contestuniversity.com/videos/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; or the files &lt;a href=&quot;https://www.contestuniversity.com/files/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastEditorUserId="10495" LastEditDate="2017-10-27T00:43:11.707" LastActivityDate="2017-10-27T00:43:11.707" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9445" PostTypeId="2" ParentId="9436" CreationDate="2017-10-26T17:02:30.170" Score="0" Body="&lt;p&gt;First off, there is no such thing as a signal with zero bandwidth.  That is like the imaginary line between two imaginary points - the line with no width between points of no size.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is like saying isotropic antenna.  (An FCC favorite)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There simply are no such things except as theoretical constructs - end even then, to prevent dividing by zero, they always must be expressed as limits of variables as they approach zero.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;CW transmitters always begin at zero output (what you are calling a zero-crossing, but at the boundary condition) until they are commanded to produce a signal by the closure of a contact on a key or by other means. Then they return to zero when that output command is removed.   &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;CW transmitters do not come up to full power instantaneously, and produce waveforms like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OPpr2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OPpr2.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that as this is displayed in the time domain relative to the keying frequency, the actual carrier is not visible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So even if the modulation itself (the key, acting as a switch) is a square wave, the resulting output is not truly square due to the physical constraints of the components of the transmitter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is true for both the rise and fall of the envelope.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is another example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YpuWi.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YpuWi.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this plot, relative to the carrier frequency, it is clearly seen that in a practical sense the transmitted wave envelope does indeed begin and end at the boundary conditions of zero.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, philosophers have been known to argue that it never actually reaches zero - just gets closer and closer to it.  Then the quantum physicists bring up the Planck limits, and so on, ad nauseaum.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;In the frequency domain it will look like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Biu6K.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Biu6K.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that this is a plot of a signal modulated by 1 KHz square-waves, which is why the bandwidth is spread so widely.  At 1 KHz keying, the ratio of signal to modulation frequencies are getting to the point where it is producing sidebands.  The amplitudes of the sidebands fall off in the normal way.  This plot does not show the effects of input filtering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider a generic mixer circuit - the output should always be filtered in such a way that only the desired modulated carrier is the resultant output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The risetime portion is as if it has been modulated at some very high rate.  That produces spurious emissions in the driver circuit which are then filtered out.  They should not be within the bandpass of the final power amplifier.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But since no filter is perfect some of those spurs will end up on the output.  Hence the need for guidelines regarding limitation of spurious emissions.  These are specifically regulated for FCC Type-Accepted commercial transmitters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ultimately, you want a transmitter that exhibits higher Q as a measure of how well it applies available power to the desired output frequency for higher efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is an interesting article on the subject (slightly TL;DR):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.w8ji.com/cw%20bandwidth%20analysis.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Effect of Keying Waveform on CW Bandwidth&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EXCERPT:  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the transfer function of a real transmitter is NOT linear.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;i.e., a square-wave input (where the rise and fall time is as if the frequency of modulation is at the boundary condition of the limit of it being at infinity, where the limit of the period of modulation approaches zero.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Bottom line is that since there is no carrier between the Morse elements, the output always begins at zero and ends at zero.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hand keying is at such a slow rate as compared to the carrier frequency that it is not very relevant.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The O-scope trace at the top is taken from a 630 Meter transmitter, and even then the modulation rate is still so slow compared to even that low of carrier frequency that there are no clear artifacts introduced by keying at random time relative to the carrier oscillations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;It is the modulation frequency that is the dominant factor in producing the final signal bandwidth.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;As an aside, back in the day when the FCC had monitoring stations all over, I would visit sometimes and watch as they used what they called &quot;TXID&quot; - Transmitter identification - the way a signal from a CW or FM transmitter wanders in frequency and amplitude as they were keyed up.  They were very good at this, and often could tell who was transmitting before any identifying modulation was applied.  i.e, saying or keying a callsign.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;They told me that even with the same models of transmitters made on the same production line on the same day there would be measurable differences due to the tolerances of the various components that went into the final product.  They considered this to be closely-held information at the time.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-10-27T02:14:56.987" LastActivityDate="2017-10-27T02:14:56.987" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9446" PostTypeId="2" ParentId="9436" CreationDate="2017-10-26T18:23:48.997" Score="4" Body="&lt;p&gt;There is no way to transmit information in a signal with zero bandwidth. Switching the carrier at the zero crossings would reduce bandwidth but not take it to zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a mathematical explanation on DSP StackExchange: &lt;a href=&quot;https://dsp.stackexchange.com/q/31044/4030&quot;&gt;Does “keying on” a sine wave at a zero-crossing reduce its bandwidth?&lt;/a&gt; Summary: in the worst case of switching on/off at the peak instantaneous amplitude, the sidebands fall off in proportion to 1/f. In the best case of switching at zero crossings, the proportion is 1/f&lt;sup&gt;2&lt;/sup&gt;. A significant improvement, but still far from zero bandwidth!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without delving into math, the simple explanation is that a band-limited signal must not only be continuous itself, but so too must be its derivatives. A hard switch at a zero crossing has a discontinuity in the first derivative at the switching point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For having smooth derivatives, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Gaussian_function&quot; rel=&quot;nofollow noreferrer&quot;&gt;Gaussian function&lt;/a&gt; is a limiting case because the derivative of a Gaussian function is another Gaussian. The Gaussian function comes up in the &lt;a href=&quot;https://math.stackexchange.com/q/2379271/139015&quot;&gt;central limit theorem&lt;/a&gt; for similar reasons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's generally true that &lt;a href=&quot;http://sepwww.stanford.edu/sep/prof/fgdp/c4/paper_html/node2.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;resolving something precisely in the time domain requires a wide bandwidth&lt;/a&gt; and vice-versa, and the Gaussian function is a &quot;middle ground&quot; which maximizes the rise and fall times while minimizing sidebands to the extent mathematically possible. This is because the Fourier transform of a Gaussian is a Gaussian. So in this sense, the minimal bandwidth keying envelope for CW would be a Gaussian function.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-10-26T18:23:48.997" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9448" PostTypeId="2" ParentId="7724" CreationDate="2017-10-26T20:12:16.593" Score="1" Body="&lt;p&gt;The -60 dB sampling port must be terminated with a 50 ohm resistor to match the impedance of the sampling device. You then connect your high impedance scope across this 50 ohm resistor to measure the voltage. Then simply apply Ohm's law to compute the power dissipated by the 50 ohm resistor on the sampling port. This will be 1/1,000,000 of your input power to the sampler or 1/999,999 of the power reaching the output port of the sampler.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-10-27T04:43:34.687" LastActivityDate="2017-10-27T04:43:34.687" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9449" PostTypeId="2" ParentId="5233" CreationDate="2017-10-26T20:56:32.253" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I have managed to match for 20-180MHz band&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You will not be able to match a 1.8 meter long antenna to such a wide bandwidth. Since your note says that you are doing this with Feko, I would suggest you are not applying the correct parameters or you are not correctly interpreting the results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You did not mention the feedpoint impedance to which you are trying to match but this is typically in the 50 to 75 ohm range. Just to get you in the ballpark, a vertical antenna with a height of 1.8 meters with a proper counterpoise to facilitate feeding the antenna, will have a 2:1 SWR bandwidth of &amp;lt;3 MHz and will be resonant at ~40 MHz. You are claiming a 160 MHz bandwidth so clearly something is wrong in your analysis or description.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-10-26T20:56:32.253" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9451" PostTypeId="1" AcceptedAnswerId="9455" CreationDate="2017-10-27T03:22:09.833" Score="9" ViewCount="11179" Body="&lt;p&gt;Does the particular metal used in antenna elements make any difference in element length or spacing, i.e. 1/2&quot; aluminum tube vs 1/2&quot; copper tube? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that length and diameter have an effect on resonance and impedance, but does the particular metal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is specifically about element length vs type of metal element.&lt;/p&gt;&#xA;" OwnerUserId="10560" LastEditorUserId="8832" LastEditDate="2018-04-11T02:58:42.287" LastActivityDate="2021-03-20T03:12:36.257" Title="Aluminum vs copper antenna element lengths" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="6" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9452" PostTypeId="2" ParentId="9451" CreationDate="2017-10-27T05:34:11.640" Score="7" Body="&lt;p&gt;Besides mechanical differences, the primary difference between aluminum and copper in antenna construction is RF resistance. Copper will have slightly less RF resistance for the same surface area. Increasing the surface area slightly allows aluminum to exhibit the same RF resistance as copper.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RF resistance is unique due to the tendency of the RF current to crowd around the surface of the conductor. As the frequency is increased, the RF current crowds even more toward the surface, occupying an increasingly thinner layer of the metal. Because of this effect the surface area of the conductor becomes a dominant factor in determining the RF resistance and conductors can be hollow tubes since no appreciable current would flow in the core.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But specifically to your question, RF resistance has no appreciable effect on resonance or element spacing. It will potentially impact antenna efficiency and gain. This is critical in certain classes of antennas such as small loop antennas where the radiation resistance is quite low.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With typical antennas such as a yagi, the difference in efficiency and gain due to RF resistance differences between aluminum and copper will most likely be neglible. If you are concerned about your specific case, provide more details regarding the type of antenna and the intended frequency range of operation.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-10-27T05:34:11.640" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9453" PostTypeId="2" ParentId="7724" CreationDate="2017-10-27T14:42:24.503" Score="3" Body="&lt;p&gt;A directional coupler only works if the coupled port or ports are terminated in the characteristic impedance, usually 50 ohms. Otherwise it's not able to accurately distinguish between forward and reflected power. This is apparent from &lt;a href=&quot;https://youtu.be/byF1FLdbUiA?t=4m38s&quot; rel=&quot;nofollow noreferrer&quot;&gt;the math governing its operation&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your scope has a 50 ohm termination option, use that and run coax directly into the scope. Don't use a probe at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your scope has no such feature, put a T and a 50 ohm terminator at the scope, like so:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FJsao.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FJsao.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This works well until you get into high UHF, where the physical size of the T becomes an appreciable fraction of wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note my directional coupler is bidirectional, so I've taken care to terminate the unused reflected port as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just be sure the power isn't too high to damage the scope. With a 60 dB coupling factor this is unlikely.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-10-27T14:50:53.527" LastActivityDate="2017-10-27T14:50:53.527" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9455" PostTypeId="2" ParentId="9451" CreationDate="2017-10-28T05:01:53.697" Score="4" Body="&lt;p&gt;Changing the metal in an antenna is equivalent to changing the diameter of the elements, but most metals used for antennas are so close in conductivity that the equivalent diameter change is negligible for most antenna models.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2017-11-05T03:52:58.020" LastActivityDate="2017-11-05T03:52:58.020" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9456" PostTypeId="2" ParentId="9436" CreationDate="2017-10-28T06:03:32.327" Score="2" Body="&lt;p&gt;The &quot;Coherent CW&quot; folks use something similar. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Very slow CW is keyed at zero crossings with Raised Cosine envelope to give minimal bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But yeah, it's the rise and fall times which gives key-clicks, not whether it's keyed at zero crossings or not&lt;/p&gt;&#xA;" OwnerUserId="10563" LastActivityDate="2017-10-28T06:03:32.327" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9457" PostTypeId="2" ParentId="7642" CreationDate="2017-10-28T12:05:26.687" Score="1" Body="&lt;p&gt;The length and number of buried radials desirable for a given vertical monopole depend significantly on the operating frequency and the conductivity of the earth in which they are buried. The graphic below shows an example of this for the conditions shown there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A set of 120 horizontal radial wires each λ/4 of a free-space wavelength typically have an r-f loss of 2Ω or less even when buried in earth of very poor conductivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fewer/shorter radials can produce acceptable r-f loss and antenna system radiation efficiency when buried in earth of high conductivity, say 10 mS/m or more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6hTdP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6hTdP.jpg&quot; alt=&quot;Earth Conductivity vs Loss in Buried Radials&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In followup to some &lt;em&gt;other comments&lt;/em&gt; in this thread:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&quot;In broadcast AM radio it is standard practice to use quarter-wave towers (because half-wave towers are expensive and more of a maintenance headache).&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just to note that 1/4-wave towers cannot be used by 50 kW, 24/7, non-directional &quot;Class A&quot; AM broadcast stations such as WLW, WJR, WGN etc because they do not produce at least the minimum groundwave fields required by the FCC for that class of station.  Most of those stations use towers ranging from 180 to 195 degrees in electrical height.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&quot;These towers require a ground plane to reflect the signal in such a way that it virtually provides an image of the rest of the half-wave that allows for lowest voltage and highest current at the feedpoint.&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The purpose of the buried radial wires used with such monopoles is to provide a low-resistance path for the r-f currents induced in the earth within 1/2-wavelength of the base of the monopole, as a result of its radiation.  For best system radiation efficiency they must be collected and delivered back to the r-f ground terminal of the transmit system.  The sum of those collected earth currents equals the current that flows along the monopole, itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&quot;The radials are cut to a quarter wavelength plus 5%.&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Buried radials function much differently than radials above the surface of the earth.  The r-f current existing on buried radials originates from the radiated fields of the monopole they are used with.  The source of the r-f current on elevated radials is a direct, metallic connection to the r-f generator, itself (the transmitter).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some Class A AM broadcast stations use buried radial wires longer than ~1/4 wavelength to reduce the loss of their r-f ground connection.  For example, WLS, Chicago uses 240 buried radials of 1/2 of a free-space wavelength  = ~550 feet, each.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;[Edit of Richard Fry on 29 May 2019]:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For additional insight, below is a clip describing the system electrical characteristics of monopole radiators of &lt;strong&gt;any&lt;/strong&gt; electrical height, when using buried radial wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The authors show why the lengths of such buried radial wires need &lt;em&gt;_not_&lt;/em&gt; be longer than one-half of a free-space wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mFSNA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mFSNA.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-05-29T17:02:58.253" LastActivityDate="2019-05-29T17:02:58.253" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="9458" PostTypeId="2" ParentId="9184" CreationDate="2017-10-28T17:45:57.143" Score="2" Body="&lt;p&gt;Of interest here:  in the areas under the jurisdiction of the U.S. FCC, legal unlicensed operation in the FM broadcast band is limited to systems producing a maximum field intensity of 250 µV/m at a distance 3 meters in every direction from the transmit antenna.  The applicable Rule is found in 47 CFR §15.239.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That maximum &lt;strong&gt;free-space&lt;/strong&gt; field of 250 µV/m @ 3 meters will be produced by a simple, linear, 1/2-wave, center-fed dipole radiating an r-f power of 11.43 &lt;strong&gt;nano&lt;/strong&gt;watts (0.000 000 011 43 watts).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However most of the &quot;Part 15 FM&quot; transmitters commercially available are rated for output powers of 10 &lt;strong&gt;milli&lt;/strong&gt;watts or more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is up to the transmit equipment user to comply with the law, but probably few users of Part 15 FM systems know what that requires, or how to achieve it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC is active in finding and citing unlicensed operators who do not comply with §15.239.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2017-10-28T17:45:57.143" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9459" PostTypeId="1" CreationDate="2017-10-29T21:21:15.723" Score="3" ViewCount="1896" Body="&lt;p&gt;Two years ago, my father and I both received a Tecsun PL-660 radio as a Christmas gift.  We both have had good experiences with our radios and generally enjoyed them until they recently both stopped working.  I should mention my radio has been at my house in Arizona for the last 2 years, while my Dad's radio has been in Pennsylvania.  So they have been in completely different/isolated environments.&lt;/p&gt;&#xA;&lt;p&gt;My Dad's radio died first and seemed to be completely bricked.  There was no on-screen display at all, and no combination of batteries or wall warts was going to get that radio to do &lt;em&gt;anything&lt;/em&gt;.  It was a doorstop.&lt;/p&gt;&#xA;&lt;p&gt;About a month later, my radio starting flashing the display and blinking a &amp;quot;Lo battery&amp;quot; message.  Changing the batteries and/or using the wall adapter did not improve the situation at all.  The radio simply will not turn on.&lt;/p&gt;&#xA;&lt;p&gt;Now, some cursory googling has shown a lot of people have had problems with this model of radio, and for the price they generally give up and get a new one.  However, we generally take good care of our gear and the radios were gifts so we decided to see if we could do anything...&lt;/p&gt;&#xA;&lt;p&gt;After taking apart my Dad's radio, I noticed there is a small button battery  welded to the main board.  Reading the battery in place showed it to be completely flat.  So we did some surgery and 'popped' the battery off the board.  We did some guessing as to the correct voltage, but putting 4.5v from an external set of AA's was enough to bring my Dad's previously dead radio back to life.  Almost.&lt;/p&gt;&#xA;&lt;p&gt;The display (computer?) has come back to life, we can turn on the radio and selecting different bands works.  The radio will tune and looks like it should be working.  However, we still have NO audio at the speaker or the headphone jack.  The on-screen signal strength meter is completely flat, and the internal display 'backlight' will not illuminate.&lt;/p&gt;&#xA;&lt;p&gt;I could theorize we had two separate issues, and we only fixed one of them by repairing the flat battery - or maybe we flexed/broke something when removing the original button battery from the board.&lt;/p&gt;&#xA;&lt;p&gt;So the crux of my question is for some input of what else we might check?  I don't have access to the second radio at the moment, so there is no way to find out if the battery repair is enough to bring the second radio back to life.  Until I can do that test, I figure we can continue to tinker with the radio we do have.  But what should we chase?  Obviously we aren't going to get into replacing surface mount IC's etc.  So I'm fishing.  Any ideas?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Update&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I have not pursued trying to fix this radio any further than I described in my original post.  However, I did do some research on the net and found some additional resources I thought might aid anyone else trying to repair their radio.&lt;/p&gt;&#xA;&lt;p&gt;First, I found this blog post regarding ESD repair to a Tecsun 600, which might be similar in design to the 660:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://swling.com/blog/2013/12/repairing-the-tecsun-pl-600-after-electrostatic-discharge-esd/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Repairing the Tecsun PL-600 after electrostatic discharge (ESD)&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I was also able to locate schematics for the PL-600 and PL-660 radios -  both printed in (what I am guessing is) Chinese.  I no longer can locate the URLs for those, but they can hopefully be found with some Googling...&lt;/p&gt;&#xA;&lt;p&gt;Finally, I remember reading &lt;em&gt;someplace&lt;/em&gt; that there is a 3.5v (I think?) voltage regulator on the radio mainboard, that frequently goes bad.  I think it was a surface mount component, and that is beyond my skill level to replace - so I never pursued it further.  I've never even looked for the component to see if I could locate it.  I'm mainly mentioning it because there was renewed interest in my original question, and if someone does manage to repair their radio, it would be interesting to know if that is indeed the culprit or if it's something completely different going on.&lt;/p&gt;&#xA;&lt;p&gt;I still have hope of eventually fixing these radios, but it is far down on my list of projects.&lt;/p&gt;&#xA;" OwnerUserId="10571" LastEditorUserId="10571" LastEditDate="2021-03-31T15:09:54.917" LastActivityDate="2021-04-03T16:15:45.370" Title="Repairing a Tecsun PL-660" Tags="&lt;receiver&gt;&lt;equipment-troubleshooting&gt;&lt;repair&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="9460" PostTypeId="2" ParentId="9459" CreationDate="2017-10-30T00:43:38.603" Score="5" Body="&lt;p&gt;Tecsun is very similar to Baofeng in that anybody selling them expects a certain number of DOAs and other failures.  They already know that QA on those rigs is directly reflected in the price.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the past I have had good success with getting vendors of like this to replace the radio body (no battery or antenna) simply by writing to them.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have gotten two Baofeng radio bodies shipped to me (no return necessary) and returned a Tecsun entirely this way.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On eBay they always appreciate it if you do not use the return option - instead just send them a message.   That way they will hope you can still give them positive feedback and their selling reputation doesn't take a hit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your question is about how to repair it:  My answer is that the best repair is replacement.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Give it a try.  Send them a message.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-10-31T01:01:07.437" LastActivityDate="2017-10-31T01:01:07.437" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9461" PostTypeId="1" AcceptedAnswerId="9462" CreationDate="2017-10-30T11:19:12.207" Score="2" ViewCount="85" Body="&lt;p&gt;Is it possible to make the Alinco DX70 TH operate at 10W PEP? The radio seems to be 100W and I read somewhere that you could switch it to 50W, but since my licence currently limits me to 10W, I'd like to see if that's possible.&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2017-10-30T12:24:25.713" Title="Alinco DX70 TH at 10W" Tags="&lt;hf&gt;&lt;alinco&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9462" PostTypeId="2" ParentId="9461" CreationDate="2017-10-30T12:24:25.713" Score="5" Body="&lt;p&gt;Yes you can, page 2-9 of the manual shows:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UzeNS.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UzeNS.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.alinco.com/pdffiles/&quot; rel=&quot;noreferrer&quot;&gt;source&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2017-10-30T12:24:25.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9464" PostTypeId="1" AcceptedAnswerId="9465" CreationDate="2017-10-31T16:51:51.537" Score="6" ViewCount="504" Body="&lt;p&gt;When I bought a secondhand FT-7800R at Field Day 2017, I received an MLS-100 external speaker with it. I installed it recently and having the speaker more than an inch away from the radio's mounting surface is great. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to buy more external speakers, but the MLS-100 seems absurdly expensive (about \$45) for what it is: a 12W 4-ohm, unpowered mono speaker. I expected to be able to find a bulk pack of similar speakers for $10 on Amazon or ebay, but this is proving not to be the case.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is there something that makes amateur radio speakers better or different than any other kind of unpowered speaker of equivalent wattage and impedance?&lt;/li&gt;&#xA;&lt;li&gt;Is there a common term for such speakers? I've tried searching for &quot;4-ohm mono speaker&quot;, but all I've been able to find are guides on how to get pick or install stereo speakers.&lt;/li&gt;&#xA;&lt;li&gt;Is there a good reason I couldn't purchase &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B00LSF603M&quot; rel=&quot;nofollow noreferrer&quot;&gt;something like this&lt;/a&gt; and expect it to work if I attach a mono audio cable to it?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6295" LastEditorUserId="6295" LastEditDate="2017-11-01T04:30:20.267" LastActivityDate="2017-11-01T15:20:09.250" Title="Is there a special term for amateur transceiver speakers or anything that makes them different from any other kind of speaker?" Tags="&lt;mobile&gt;&lt;audio&gt;&lt;speaker&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9465" PostTypeId="2" ParentId="9464" CreationDate="2017-10-31T17:28:58.027" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there something that makes amateur radio speakers better or different than any other kind of unpowered speaker of equivalent wattage and impedance?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Some may have audio filters, headphone jacks, or other such application-specific features.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They &lt;em&gt;could&lt;/em&gt; be somehow designed to be best at reproducing the frequencies important to intelligible speech, as opposed to a broader but overall lower frequency response or dynamic range for music, and you will see such claims but I don't know how true they are.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there a common term for such speakers? I've tried searching for &quot;4-ohm mono speaker&quot;, but all I've been able to find are guides on how to get pick or install stereo speakers.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&quot;Communications speaker&quot;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there a good reason I couldn't purchase &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B00LSF603M&quot; rel=&quot;nofollow noreferrer&quot;&gt;something like this&lt;/a&gt; and expect it to work if I attach a mono audio cable to it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, you should feel free to use any speaker of suitable impedance. Of course, that is just a driver without an enclosure, so technically it is not a complete speaker.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Note that in a mobile installation an important characteristic is whether you can get it loud enough to be heard over road noise without causing distortion. This will be affected by the impedance and efficiency of the speakers. A speaker that is poorly designed may not get loud enough without distorting (or rattling!)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-10-31T17:28:58.027" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9466" PostTypeId="2" ParentId="9160" CreationDate="2017-10-31T22:31:12.097" Score="0" Body="&lt;p&gt;I have an OCF dipole fed with dual coax. This method of feeding will drop the noise --in some cases-- by 5 S-units. I used RG-6 for the parallel conductors, 78 feet long. This antenna is 140 feet long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a common-mode choke made from 25' of RG-e coiled, wound onto a one gallon paint can, for a CMC on other antennas.&lt;/p&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="8717" LastEditDate="2017-10-31T23:18:26.383" LastActivityDate="2017-10-31T23:18:26.383" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9467" PostTypeId="2" ParentId="9464" CreationDate="2017-11-01T01:40:52.500" Score="1" Body="&lt;h2&gt;Our choice of speakers are important.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;They can make the difference between either hearing the other station clearly or straining to hear and missing part of the conversation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;But we don't need &quot;special&quot; speakers&lt;/strong&gt;, that may be expensive and not even be very good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The sound from the small tinny-sounding speaker in the top cover of that IC-765 under the monitor kept me from hearing the people that I was ragchewing with on HF SSB. So, I added those speakers, &lt;strong&gt;1&lt;/strong&gt;, &lt;strong&gt;2&lt;/strong&gt;, and &lt;strong&gt;3&lt;/strong&gt;. They are all connected to my transceiver. Tuning to any SSB signal on the HF bands, the sound from them is very clear and easy to understand. The same would be true for narrow-band FM signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lUSHg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lUSHg.png&quot; alt=&quot;W0BTU speakers&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Speakers &lt;strong&gt;1&lt;/strong&gt; and &lt;strong&gt;2&lt;/strong&gt; are older Altec Lansing &lt;strong&gt;computer speakers&lt;/strong&gt;. Even though they were not intended for amateur radio, they sound great and I highly recommend them! &lt;em&gt;Get some computer speakers and try them.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Speaker &lt;strong&gt;3&lt;/strong&gt; is an older Am-Comm Inc. digital ClearSpeech™ speaker. Most of the time, the digital noise filter is off, but it still adds a few highs that the computer speakers lack. Am-Com has since been acquired  by another company which added several adjustable levels of digital noise filtering that made it an even better speaker (so others have told me).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w0btu.com/ssb_audio-weak_signal.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;This page&lt;/a&gt; on one of my websites explains the frequency ranges that are important for us to hear weak voice signals that are almost buried in the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But good communications-style headphones are better than any speakers for hearing the weak ones! &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-11-01T02:01:24.670" LastActivityDate="2017-11-01T02:01:24.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9468" PostTypeId="2" ParentId="9464" CreationDate="2017-11-01T15:05:17.160" Score="1" Body="&lt;p&gt;There are already two answers posted with good information but here is a little bit more information to help with your selection process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Impedance&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Matching the impedance of the speaker to the speaker impedance range specified for the audio amplifier (the transceiver in your case) is important in order to ensure a maximum power transfer from your radio to your ear. An improper impedance can also introduce distortion and potentially instability in a marginally designed amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;SPL&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most speakers have a Sound Pressure Level (SPL) rating. This is an indication of how efficiently the speaker converts electrical power to acoustic power. It specifically is the sound pressure level measured at 1 meter from the speaker with 1 watt of excitation applied. The result is generally expressed in dB form. In general for a common speaker design, the larger the speaker, the greater the SPL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A higher SPL indicates a more efficient speaker. This can be important for hearing the subtleties within the sound source as a lower SPL can render low level sounds as imperceptible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Frequency Range&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency range of the speaker indicates what frequencies the speaker will reasonably reproduce. This area of characterization lacks standardization so often a close inspection of data sheets are in order to make comparisons. The general bass, mid range, and tweeter components used in audiophile systems are examples of speakers that are optimized for specific frequency ranges. The frequency range required for a specific amateur radio application depends upon the modulation mode. An standard SSB voice will be faithfully reproduced in a 200 to 2500 Hertz range. A CW signal can be used with a much narrower frequency range signal based on the preferred side tone frequency of the operator. An FM signal often has a wider response than standard SSB. Some deficiencies in frequency response can be overcome with a parametric equalizer added to the amplifier chain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should also be noted that a speaker with too large of a frequency range may prove annoying as it will be more prone to reproduce noise that is accompanying the desired signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Enclosure Design&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The speaker enclosure can have a dramatic effect on the frequency response and in some cases, the effective SPL of the speaker. A common example of this is acoustic dampening within the enclosure. Wool will generally modify the mid range frequencies while felt will modify the low end frequencies. Other methods effectively alter the geometry of the enclosure for certain frequencies. Examples of this includes porting and acoustic foam. You will find a great deal of subjective and objective information on this topic on various audiophile sites.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From an amateur radio perspective, the enclosure may also play a role in keeping RFI out of the amplifier chain.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-11-01T15:20:09.250" LastActivityDate="2017-11-01T15:20:09.250" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9470" PostTypeId="2" ParentId="9160" CreationDate="2017-11-02T17:49:11.127" Score="1" Body="&lt;p&gt;Can you&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Turn off all the power in your house&lt;/li&gt;&#xA;&lt;li&gt;Plug the radio into a battery source (i.e Car 12V) You only need to Rx so no massive power requirement.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Now listen... is this better or the same. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As there (should) be no noice coming from a 12V DC source, if you have noise there are 2 possibilities&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Your Transceiver is broken&lt;/li&gt;&#xA;&lt;li&gt;Your Ant/Env is faulty&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Following the House 12V ... can you move the radio to some place like a park/countryside and listen again only connected to 12V (if in a car - this means turning off the Engine). You will need a simple antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there is still S9+18 it is time to visit the radio repair shop.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2017-11-02T17:49:11.127" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9471" PostTypeId="1" AcceptedAnswerId="9472" CreationDate="2017-11-03T06:08:12.540" Score="6" ViewCount="275" Body="&lt;p&gt;I am starting off with the &lt;a href=&quot;https://files.ettus.com/tutorials/labs/Lab_1-5.pdf&quot; rel=&quot;noreferrer&quot;&gt;Ettus Research lab-1 - lab-5 tutorial&lt;/a&gt; to learn GNU Radio. I have set up the following super simple flow graph. I am using WX GUI as it is what used in the tutorial. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9P0C3.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9P0C3.png&quot; alt=&quot;lab-1&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This flow-graph works well for low frequencies. As indicated in the output. However my problem starts when I increase the frequency. As per my knowledge, a sampling rate of 32k is sufficient to sample a signal of maximum frequency of 16k. Hence, I am confused as to why my output is distorted. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/t44L2.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/t44L2.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1694" LastActivityDate="2017-11-03T21:22:35.550" Title="Sine signal distorted in GNU Radio" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9472" PostTypeId="2" ParentId="9471" CreationDate="2017-11-03T09:32:30.580" Score="10" Body="&lt;p&gt;Your confusion stems from the fact that your mind (and the WX GUI scope sink) uses linear interpolation between the samples. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's not right – in your case, where the signal period isn't an integer number of samples, this becomes obvious by the fact that things don't look very sinusoidal. They still are (I promise ;) ).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think about it like this: at exactly 16 kHz sampled with 32 kHz, you'd get 2 samples per period, right? So, if these samples happen to lie on the extrema of the cosine, you'd get $[+1\, -1\, +1\, -1\, \ldots]$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With 13.7 kHz not that far away from that, you &quot;mostly&quot; get alternating signs, too, but every so and so many samples, you still &quot;hit&quot; the same upper or lower half of a cosine twice. That's why things &lt;strong&gt;look&lt;/strong&gt; irregular. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Things are in perfect, nice shape! I've made a &lt;a href=&quot;https://gist.github.com/marcusmueller/f51f17a34883b5d6c07f21bac63d705e&quot; rel=&quot;nofollow noreferrer&quot;&gt;quick Jupyter Notebook&lt;/a&gt; to illustrate. If you don't have the time to read it, here's the takeaway:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/HXMtn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HXMtn.png&quot; alt=&quot;original, continuous&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TQtjP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TQtjP.png&quot; alt=&quot;sampling&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wyhwA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wyhwA.png&quot; alt=&quot;wrong interpolation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you need to do, mentally, is interpolate using a $\mathrm{sinc}$ function as interpolator. (I did that in the &lt;a href=&quot;https://gist.github.com/marcusmueller/f51f17a34883b5d6c07f21bac63d705e#file-demo_sampling_interpolating-ipynb&quot; rel=&quot;nofollow noreferrer&quot;&gt;improved version&lt;/a&gt; of the notebook with the bigger pictures in the last part.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The whole point is that although it might not look like it, these &quot;jagged&quot; samples of a 13.7 kHz oscillation still &lt;strong&gt;are&lt;/strong&gt; 100% that oscillation, and contain all the info the continuous signal had. Neat!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-11-03T21:22:35.550" LastActivityDate="2017-11-03T21:22:35.550" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9473" PostTypeId="1" AcceptedAnswerId="9479" CreationDate="2017-11-03T10:50:04.563" Score="1" ViewCount="364" Body="&lt;p&gt;My issue is regards to viewing the FM spectrum using USRP N210 &amp;amp; GNU Radio. I did try to use several blocks of GNU Radio to view an FFT plot of the FM band using the USRP N210 device. My blocks and results are as below,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZezCp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZezCp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used my mobile phone to listen to 90.5MHz FM channel and confirm that there was indeed a working FM channel at that. Actually, there has to be multiple channels in this band.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In many FM radio examples, it is possible to observe multiple bands of FM channels. Unfortunately for me, I cannot see a single one. I feel that there is something wrong with my setting in GNU radio. I post the settings I have applied to each box below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pQ1W6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pQ1W6.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nkY8z.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nkY8z.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JTDqf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JTDqf.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Marcus Müller has requested I ran the command to  find the daughter board I am using. My output is stated below. &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;user@userpc:~$ uhd_usrp_probe&#xA;linux; GNU C++ version 5.3.1 20151219; Boost_105800; UHD_003.009.002-0-unknown&#xA;&#xA;-- Opening a USRP2/N-Series device...&#xA;-- Current recv frame size: 1472 bytes&#xA;-- Current send frame size: 1472 bytes&#xA;&#xA;UHD Warning:&#xA;    Unable to set the thread priority. Performance may be negatively affected.&#xA;    Please see the general application notes in the manual for instructions.&#xA;    EnvironmentError: OSError: error in pthread_setschedparam&#xA;  _____________________________________________________&#xA; /&#xA;|       Device: USRP2 / N-Series Device&#xA;|     _____________________________________________________&#xA;|    /&#xA;|   |       Mboard: N210r4&#xA;|   |   hardware: 2577&#xA;|   |   mac-addr: 00:80:2f:0a:d5:64&#xA;|   |   ip-addr: 192.168.10.2&#xA;|   |   subnet: 255.255.255.255&#xA;|   |   gateway: 255.255.255.255&#xA;|   |   gpsdo: none&#xA;|   |   serial: F384DA&#xA;|   |   FW Version: 12.4&#xA;|   |   FPGA Version: 11.1&#xA;|   |   &#xA;|   |   Time sources: none, external, _external_, mimo&#xA;|   |   Clock sources: internal, external, mimo&#xA;|   |   Sensors: mimo_locked, ref_locked&#xA;|   |     _____________________________________________________&#xA;|   |    /&#xA;|   |   |       RX DSP: 0&#xA;|   |   |   Freq range: -50.000 to 50.000 MHz&#xA;|   |     _____________________________________________________&#xA;|   |    /&#xA;|   |   |       RX DSP: 1&#xA;|   |   |   Freq range: -50.000 to 50.000 MHz&#xA;|   |     _____________________________________________________&#xA;|   |    /&#xA;|   |   |       RX Dboard: A&#xA;|   |   |     _____________________________________________________&#xA;|   |   |    /&#xA;|   |   |   |       RX Frontend: 0&#xA;|   |   |   |   Name: Unknown (0xffff) - 0&#xA;|   |   |   |   Antennas: &#xA;|   |   |   |   Sensors: &#xA;|   |   |   |   Freq range: 0.000 to 0.000 MHz&#xA;|   |   |   |   Gain Elements: None&#xA;|   |   |   |   Bandwidth range: 0.0 to 0.0 step 0.0 Hz&#xA;|   |   |   |   Connection Type: IQ&#xA;|   |   |   |   Uses LO offset: No&#xA;|   |   |     _____________________________________________________&#xA;|   |   |    /&#xA;|   |   |   |       RX Codec: A&#xA;|   |   |   |   Name: ads62p44&#xA;|   |   |   |   Gain range digital: 0.0 to 6.0 step 0.5 dB&#xA;|   |   |   |   Gain range fine: 0.0 to 0.5 step 0.1 dB&#xA;|   |     _____________________________________________________&#xA;|   |    /&#xA;|   |   |       TX DSP: 0&#xA;|   |   |   Freq range: -50.000 to 50.000 MHz&#xA;|   |     _____________________________________________________&#xA;|   |    /&#xA;|   |   |       TX Dboard: A&#xA;|   |   |     _____________________________________________________&#xA;|   |   |    /&#xA;|   |   |   |       TX Frontend: 0&#xA;|   |   |   |   Name: Unknown (0xffff) - 0&#xA;|   |   |   |   Antennas: &#xA;|   |   |   |   Sensors: &#xA;|   |   |   |   Freq range: 0.000 to 0.000 MHz&#xA;|   |   |   |   Gain Elements: None&#xA;|   |   |   |   Bandwidth range: 0.0 to 0.0 step 0.0 Hz&#xA;|   |   |   |   Connection Type: IQ&#xA;|   |   |   |   Uses LO offset: No&#xA;|   |   |     _____________________________________________________&#xA;|   |   |    /&#xA;|   |   |   |       TX Codec: A&#xA;|   |   |   |   Name: ad9777&#xA;|   |   |   |   Gain Elements: None&#xA;&#xA;user@userpc:~$ &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;To support Marcus's second answer, I post an image of the inside of my USRP N210 below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uGPoM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uGPoM.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be really great if my mistake can be spotted.&lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorUserId="1694" LastEditDate="2017-11-04T10:58:44.917" LastActivityDate="2017-11-04T10:58:44.917" Title="Viewing the broadcast FM spectrum using a USRP N210" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;usrp&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9474" PostTypeId="1" CreationDate="2017-11-03T17:37:39.410" Score="1" ViewCount="879" Body="&lt;p&gt;I have a Baofeng UV-5R with an extended 3800 battery. The usb cable I bought only works for the dock that comes with the baofeng but I would like to only carry a cable and charge the baofeng via anker solar or usb 20K battery. I want to run everything off 5v and to be able to keep it running while i go camping. Everything else i have has been converted to usb power (flashlights and headlamps, cellphones obviously, usb to charge AA and AAA amazon batteries, and thats all I really need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried looking into 2x 18560 batteries used in powering rc cars and other small toys because the can add up to 7.4v. Worst case scenario, I can use a separate charger to charge the 18560 from the usb battery, but I'm not sure if it's the correct voltage needed to charge the baofeng (7.4v to 8.?v range), or if there is something that can do directly from my anker usb setup to the 3800 extended battery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have also seen a tyt charging cable that everyone recommends but I'm not sure if there is smarts in the device and if I can get from 12v back down to 5v (usb). It seems like a lot just to charge a 7.4-8v battery. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can the radio accept 9v? I've seen usb to 9v or 12v (switching) charging cables , but is that too high. I know enough about electricity and electronics to be dangerous, hence asking rather than blowing up a perfectly good radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any help would be appreciated.&lt;/p&gt;&#xA;" OwnerUserId="10596" LastEditorUserId="10424" LastEditDate="2017-11-09T19:39:33.077" LastActivityDate="2019-04-24T15:57:30.223" Title="UV-5R with 3800 battery... usb 5v to 7.4-8v charger" Tags="&lt;uv-5r&gt;&lt;battery-charging&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9475" PostTypeId="2" ParentId="9473" CreationDate="2017-11-03T17:50:57.260" Score="2" Body="&lt;p&gt;I don't see anything wrong with your basic GNU Radio flow graph, so it is likely a hardware configuration issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not familiar with the USRP N210 in particular, so this is a bit generic:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;In my experience, the most common software reason for getting no visible signal is incorrect gain settings. Is 15 dB an appropriate middle-of-the-road setting or is it too low or too high? I don't know what the minimum and maximum supported by the hardware are, but the FFT plot looks more like an overload than below-the-noise-floor, so try reducing it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In extreme cases, such as if you live near a broadcast station, you might even need an external &lt;em&gt;attenuator.&lt;/em&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You have selected antenna port RX2. Is your antenna actually plugged into that port, or a different one?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-11-03T21:39:17.060" LastActivityDate="2017-11-03T21:39:17.060" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9476" PostTypeId="2" ParentId="9473" CreationDate="2017-11-03T22:07:28.813" Score="1" Body="&lt;p&gt;Other common sources of problems:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;This happens more often than one would think: Are you sure your antenna is suited for the band? I've talked to way too many people that complained about bad reception, then to proceed to show they were using a 2.4 GHz antenna for 433 MHz.&lt;/li&gt;&#xA;&lt;li&gt;Many broadcast antennas you can buy have a 75Ω impedance, whereas all USRP daughterboard have 50Ω. That mismatch shouldn't pose a significant problem, though (you lose a few dB, but broadcast is usually &quot;screamingly loud&quot; compared to a USRP's sensitivity)&lt;/li&gt;&#xA;&lt;li&gt;If you really see nothing but this ca 0.005 amplitude peak in the middle, I'd argue you've got LO leakage. However, you have a very wide &quot;hill&quot; around that, as if lots of interference gets mixed down there. That is strange.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-11-03T22:07:28.813" CommentCount="5" CommunityOwnedDate="2017-11-03T22:07:28.813" ContentLicense="CC BY-SA 3.0" />
  <row Id="9477" PostTypeId="1" CreationDate="2017-11-04T06:48:53.263" Score="3" ViewCount="1366" Body="&lt;p&gt;I am a new ham and wish to mount a center-fed G5RV dipole antenna under the eaves of my house, where I have a 78' clear run available two stories above ground. The problem is a metal rain gutter which runs parallel to the antenna, about 3 feet to the side of it. My concern is that the gutter would essentially represent a short-circuit to the dipole as it is just a fraction of a wavelength away, making the antenna ineffective as a radiator. Is this true?&lt;/p&gt;&#xA;" OwnerUserId="10598" LastEditorUserId="9493" LastEditDate="2017-11-05T12:01:47.477" LastActivityDate="2017-11-09T13:42:45.810" Title="proximity of rain gutter to dipole antenna" Tags="&lt;antenna&gt;&lt;dipole&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9478" PostTypeId="1" AcceptedAnswerId="9487" CreationDate="2017-11-04T08:21:19.300" Score="2" ViewCount="966" Body="&lt;p&gt;I use a Raspberry Pi for transmitting FM on 107.9 Mhz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It uses square waves and has a power of approx 0.085 Watts, but just to be safe:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I have a 1 watt transmitter approximately 1 metre away from me whilst I'm sleeping, does this pose ANY risks?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know there's a lot of confusion about electromagnetic waves and dangers. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as I'm aware, I do not have electromagnetic hypersensitivity (I think I would know if I did).&lt;/p&gt;&#xA;" OwnerDisplayName="user10599" LastEditorUserId="8717" LastEditDate="2017-11-16T17:39:58.640" LastActivityDate="2017-11-16T17:39:58.640" Title="Is my low-power VHF transmitter dangerous?" Tags="&lt;vhf&gt;&lt;rf-power&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9479" PostTypeId="2" ParentId="9473" CreationDate="2017-11-04T09:51:01.643" Score="1" Body="&lt;p&gt;Your &lt;code&gt;uhd_usrp_probe&lt;/code&gt; output shows:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;|   |   |   |       RX Frontend: 0&#xA;|   |   |   |   Name: Unknown (0xffff) - 0&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;and&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;|   |   |   |       TX Frontend: 0&#xA;|   |   |   |   Name: Unknown (0xffff) - 0&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;this is typically the symptom of a not properly connected daughterboard, or one with broken power rails; less often, sign of a corrupted daughterboard eeprom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please try to take out and plug back in your daughterboard (you still haven't told us which daughterboard model you're using!), and try again.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The antenna I tried earlier was a 868MHz antenna. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, no chance you get good reception at 90 MHz, then, right?&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-11-04T09:51:01.643" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9480" PostTypeId="2" ParentId="9451" CreationDate="2017-11-04T16:21:08.663" Score="3" Body="&lt;p&gt;Leif SM5BSZ has made investigations on the matter by measuring Q of antenna elements in an enclosed box. Look at the fastening methods to the boom that change Q drastically, especially with iron involved. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The influence of resistivity to an actual antenna depends on grade of directivity optimization, the theoretical Q = bandwith / center frequency of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For normal low Q antennas, like a dipole or ground plane antenna, the influence have negligble effect of performance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;See it from the source here:&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://sm5bsz.com/antennas/sa/losses413.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Losses in yagi antenna elements at 413 MHz&lt;/a&gt;  (sm5bsz.com)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excerpt:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;There are several mechanisms by which element losses may increase&#xA;  above the values computed by the modelling software.&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Reduced surface conductivity due to corrosion. &lt;/li&gt;&#xA;  &lt;li&gt;Ohmic losses due to Eddy currents in the boom tube or other conducting materials near the element center. &lt;/li&gt;&#xA;  &lt;li&gt;Magnetic losses in washers, screws and other magnetic materials near the element center. &lt;/li&gt;&#xA;  &lt;li&gt;Dielectric losses in surface coatings used to prevent corrosion. &lt;/li&gt;&#xA;  &lt;li&gt;Dielectric losses in plastic plugs at the element tips.&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://sm5bsz.com/antennas/sa/losses144.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Losses in yagi antenna elements at 144 MHz&lt;/a&gt; (sm5bsz.com)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excerpt:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;At VHF frequencies element losses are much less important than they&#xA;  are at UHF frequencies because system noise temperatures are not much&#xA;  lower than the environmental temperature and therefore element losses&#xA;  only affect antenna gain, not the system noise temperature for the&#xA;  receiver even when the antenna points into cold sky.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="10601" LastEditorUserId="8832" LastEditDate="2018-04-11T03:07:52.747" LastActivityDate="2018-04-11T03:07:52.747" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9481" PostTypeId="2" ParentId="9477" CreationDate="2017-11-05T11:57:06.903" Score="6" Body="&lt;p&gt;The gutter will be in the near field of the dipole. It may affect the tuning of the dipole or its radiation pattern, but it will not &quot;short out&quot; the dipole as long as the dipole wires are not in direct contact with the gutter or downspouts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may have other conducting materials in the near field such as siding, sofette trim and conduit. Any of these may also affect the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna very close to a house may pick up more electrical interference  that is being created within the house from things like switching power supplies, television sets and LED lamps. The opposite can also be true when transmitting. The close proximity of the antenna to the house may cause interference with speakers, telephones, smoke alarms, arc fault breakers, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your G5RV design uses window line as part of its feedline. Make sure to keep this at least six inches from any metal surfaces such as siding. If you have an antenna tuner and don't require a long feedline, you will be better off feeding the dipole directly with coax connected to a choking balun. This will reduce noise pickup and allow the coax to be freely run where it is convenient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This may all sound like doom and gloom but take heart because many hams successfully use antennas in similar situations and have great success. The best advice is to give it a try to see how it works for you. Start with 10 watts or so of transmit power and see how it behaves before increasing your power. You may need to take some remedial actions but most importantly, you will be on the air!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-11-09T13:42:45.810" LastActivityDate="2017-11-09T13:42:45.810" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9482" PostTypeId="1" AcceptedAnswerId="9483" CreationDate="2017-11-05T13:21:40.183" Score="4" ViewCount="271" Body="&lt;p&gt;I have an American Amateur Extra Class licence (AC1DM) and I'm going to Portugal for a few days. Can I operate there with my licence? I'm not an American citizen.&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2019-10-04T06:55:57.937" LastActivityDate="2019-10-04T06:55:57.937" Title="Can an American licensee operate in Portugal during a visit?" Tags="&lt;united-states&gt;&lt;europe&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="9483" PostTypeId="2" ParentId="9482" CreationDate="2017-11-05T15:03:17.133" Score="4" Body="&lt;p&gt;After reading the various online sources, it looks like the answer to your question is &lt;strong&gt;no&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;US amateurs can operate in &lt;a href=&quot;https://en.wikipedia.org/wiki/Amateur_radio_international_operation#CEPT_License&quot; rel=&quot;nofollow noreferrer&quot;&gt;CEPT countries&lt;/a&gt;, but a requirement is that they be US citizens.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your user name suggests that you hold a licence in Argentina, but sadly Argentina is not a party to the CEPT agreements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your visit is only for a few days, it might not be worth it to try other options. It might be possible to get a reciprocal licence, and if you were resident in Portugal or travelling there often it would be worth considering. But if it’s just for a single trip it might not be feasible.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-11-05T15:03:17.133" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9487" PostTypeId="2" ParentId="9478" CreationDate="2017-11-06T02:02:06.087" Score="11" Body="&lt;p&gt;Electromagnetic hypersensitivity does not exist. There is no confusion. It has been rigorously refuted by science.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One watt is orders of magnitude below safe exposure limits, and indeed probably less than exposure you are likely to get from cell phones, commercial broadcast stations, WiFi, and unintentional radiation from all kinds of electronics.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-11-06T02:02:06.087" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9488" PostTypeId="2" ParentId="9477" CreationDate="2017-11-06T04:12:03.707" Score="2" Body="&lt;p&gt;I agree with Glen, but if you wanted to be more sure that the gutter is not affecting the antenna very much you could try cutting a short section (even 1 inch or less) of it every so often (say 10 feet or less) and filling it with plastic gutter (use silicone to seal it, of course). That would make the gutter too short in each section to be a serious problem.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-11-06T04:12:03.707" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9489" PostTypeId="1" CreationDate="2017-11-06T05:52:54.313" Score="5" ViewCount="6569" Body="&lt;p&gt;I just acquired a Yaesu FT-450 and am interested in what it can do when connected to my PC. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see that there is programming software available with which one can load information into the 450's memory from a spreadsheet-like file, which would be much easier than keying the data in via the buttons on the 450 front panel. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But does anybody know if there is a program available which essentially emulates a software-defined radio for the 450- that is, something that maps all the control functionality of the 450 onto the screen of the 450, so it can be operated in real-time through the keyboard and mouse?&lt;/p&gt;&#xA;" OwnerUserId="10598" LastEditorUserId="76" LastEditDate="2018-05-28T03:58:47.843" LastActivityDate="2018-05-28T03:58:47.843" Title="computer control for Yaesu FT-450" Tags="&lt;yaesu&gt;&lt;remote-control&gt;&lt;computer-control&gt;&lt;ft-450d&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="9490" PostTypeId="1" AcceptedAnswerId="9494" CreationDate="2017-11-06T12:58:07.263" Score="0" ViewCount="934" Body="&lt;p&gt;I am trying to capture a 868MHz transmission using an USRPN210 and a RF900 Daughterboard. My GNU Radio flowgraph with all settings is stated below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/s8nxt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/s8nxt.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[&lt;img src=&quot;https://i.stack.imgur.com/WEnQa.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hu6GW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hu6GW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mQsxm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mQsxm.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qdkOE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qdkOE.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is, when I try to reduce the time scale in the output GUI, the WX waterfall window gets completely stuck (freezes to black). I paste my output below. However, if I not tamper with time scale, the GUI, along with the waterfall and the FFT, continues to run.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8mS1c.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8mS1c.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorUserId="1694" LastEditDate="2017-11-08T10:34:39.653" LastActivityDate="2017-11-08T10:34:39.653" Title="GNU Radio &quot;WX GUI Waterfall Sink&quot; Freezes as Timescale is Reduced" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9491" PostTypeId="5" CreationDate="2017-11-06T15:34:24.680" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2017-11-06T15:34:24.680" LastActivityDate="2017-11-06T15:34:24.680" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9492" PostTypeId="4" CreationDate="2017-11-06T15:34:24.680" Score="0" Body="This is a special tag that is designed to be used only by the system for questions that have had all of their other tags removed. Do not add this tag to existing questions; it is reserved for use by the system to identify posts with no valid tags." OwnerUserId="8713" LastEditorUserId="76" LastEditDate="2017-11-09T19:40:16.547" LastActivityDate="2017-11-09T19:40:16.547" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9493" PostTypeId="2" ParentId="9478" CreationDate="2017-11-06T16:05:10.213" Score="3" Body="&lt;p&gt;The website &lt;a href=&quot;http://hintlink.com/power_density.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio RF Safety Calculator&lt;/a&gt; can help calculate safe RF levels for various frequencies. The website uses formulas based on FCC guidelines. It requires knowing a bit more about the setup than you have provided in your question, but some reasonable assumptions can be made.&#xA;Assuming:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;1 watt RMS power&lt;/li&gt;&#xA;&lt;li&gt;100% duty cycle (meaning % time the radio is actually transmitting)&lt;/li&gt;&#xA;&lt;li&gt;Antenna gain no better than a common dipole&lt;/li&gt;&#xA;&lt;li&gt;A distance of 3 feet&lt;/li&gt;&#xA;&lt;li&gt;Frequency of 107.9 MHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The setup is in compliance with FCC guidelines. In fact, for an &quot;uncontrolled&quot; environment (where no special consideration is made) you can get as close as roughly 1.4 feet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on the frequency, I'm going to guess you are transmitting an FM signal. The FM mode has a 100% duty cycle when you are transmitting. If you were using another mode you would adjust the average power input by the duty cycle. The link above has details on this process at the bottom of the page. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC guidelines (and as a result, the calculations on this website) are rather conservative. I probably wouldn't strap it to my head, but I wouldn't worry about it being on my night-stand.&lt;/p&gt;&#xA;" OwnerUserId="10424" LastEditorUserId="10424" LastEditDate="2017-11-06T19:47:56.307" LastActivityDate="2017-11-06T19:47:56.307" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9494" PostTypeId="2" ParentId="9490" CreationDate="2017-11-06T20:23:03.097" Score="2" Body="&lt;p&gt;The WX GUI components in GNU Radio are deprecated. Can you try using QT GUI components instead (the top block GUI option must be changed to match) and report back? If you have similar issues, update your question with the new results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both GUIs support zooming in on the spectrum by, if I remember correctly, dragging a box around the area you wish to zoom into. If there is then not enough resolution due to the FFT bin size, you will need to increase the FFT Size, or add a preceding decimating filter block, to get more resolution.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-11-06T20:23:03.097" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9495" PostTypeId="2" ParentId="9489" CreationDate="2017-11-06T20:44:31.267" Score="4" Body="&lt;p&gt;I'm not aware of an application that has full control of every feature. However, there are a variety of applications available that work for basic functions. &lt;a href=&quot;http://www.w1hkj.com/flrig-help/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FLRIG&lt;/a&gt; will give you many of the most common features. I use the related program, FLDigi, for operating digital modes with my FT-450D. Its rig control is sufficient that I don't generally have to turn back to my radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BTW, be careful about using the term software-defined radio. I understand you to mean you want software that lets you control the radio. The term software-defined radio more commonly refers to a radio that performs filtering and shaping functions in software rather than hardware. The FT-450D (and I believe the FT-450) is actually such a radio. The radio control you are asking for is commonly called &quot;rig control&quot; or some-times &quot;rig-cat&quot;.&lt;/p&gt;&#xA;" OwnerUserId="10424" LastActivityDate="2017-11-06T20:44:31.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9496" PostTypeId="1" CreationDate="2017-11-07T12:43:35.403" Score="2" ViewCount="106" Body="&lt;p&gt;I have started working on TDMA algorithms for SDR utilizing narrow band waveforms, and I have started reading about narrowband waveforms.&#xA;But I am confused about the concepts of channel bandwidth and occupying frequencies of narrow band signals. Narrow band channel bandwidth is 25 kHz and occupying frequency range is 30 - 512 MHz. But I have read so far that the bandwidth is the difference between maximum frequency, and minimum frequency and 25 kHz is not the difference of 512 MHz - 30 MHz = 482 MHz.&#xA;Please elaborate the whole concept and difference?&lt;/p&gt;&#xA;" OwnerUserId="10611" LastEditorUserId="4665" LastEditDate="2017-11-07T14:18:50.727" LastActivityDate="2017-11-07T19:47:55.773" Title="Channel Bandwidth &amp; Occupying Frequencies" Tags="&lt;bandwidth&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9497" PostTypeId="2" ParentId="9496" CreationDate="2017-11-07T19:47:55.773" Score="3" Body="&lt;p&gt;What that marketing brochure (a terrible way to start learning about a technical concept, by the way) means is that it uses narrowband channels from &lt;em&gt;somewhere within&lt;/em&gt; that 30 to 512 MHz range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That just means it allows you to pick one (or a few) of 25kHz pieces of spectrum to operate on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Narrowband&quot; is &lt;strong&gt;not&lt;/strong&gt; defined to be 25 kHz, by the way. The definition of narrowband depends on who you ask: For someone normally dealing with e.g. DVB-T signals, a 2 MHz channel might be considered narrow. For someone dealing with morse operation in HF, 150 Hz might be narrow. For someone doing modeling of channels, you'd typically expect them to say that a channel is narrow if it occupies significantly less than the coherency bandwidth – and that is something that will wildly vary between 30 MHz and 500 MHz. So, anyway you put it, calling 25 kHz &quot;narrowband&quot; is really just a marketing term here.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-11-07T19:47:55.773" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="9500" PostTypeId="1" AcceptedAnswerId="9501" CreationDate="2017-11-09T21:08:49.397" Score="5" ViewCount="127" Body="&lt;p&gt;Looking for advice to semi-soundproof my extremely noisy gas generator, which kept everybody edgy on Field Day. It's a real powerhouse, but the cost of that power is my hearing. I'm looking to buy or homebrew something lightweight that I can use to enclose the generator, but leave easy access to refilling the tank, exhaust, etc. Thoughts? Links?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a Champion 100155 : &lt;a href=&quot;https://www.championpowerequipment.com/product/100155-7000-watt-dual-fuel-generator/&quot; rel=&quot;noreferrer&quot;&gt;https://www.championpowerequipment.com/product/100155-7000-watt-dual-fuel-generator/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9166" LastActivityDate="2017-11-13T07:23:50.733" Title="How can I sound-proof my generator?" Tags="&lt;power-supply&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9501" PostTypeId="2" ParentId="9500" CreationDate="2017-11-09T22:21:48.620" Score="4" Body="&lt;p&gt;I'd argue that power law is your friend: It's probably cheapest and most reliable and least of a hazard to get a long cable and place the generator as far away as feasible, possibly behind a car, rock, very large dog, small elephant, large elephant…&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Downside of long cables of course is voltage drop due to resistance in the cable. Rule of thumb: The longer the cable, the more copper crosssection would be sensible. Before you spend lots of money on oversized cables: You can find the AWG table on every corner on the internet, and they list resistance per length for any common conductor diameter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Calculate your maximum current drawn (if using many inductive / bad-PFC devices, 1.4× that number), approach with &quot;I can live with a voltage drop of $x\in[2\ldots20]\,\text V$ for that current&quot;, calculate maximum resistance that would allow that ($U=R\cdot I$), and then just pick a cable diameter that doesn't have more over the length of cable you want to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other than that, speaking from experience with a small car with a holey muffler: Probably, the exhaust end of the engine is where most noise happens. If you have a garage of your trust, maybe ask them whether it's realistic to add a muffler without losing too much power?&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-11-10T07:31:09.633" LastActivityDate="2017-11-10T07:31:09.633" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9502" PostTypeId="1" CreationDate="2017-11-09T23:45:27.953" Score="1" ViewCount="119" Body="&lt;p&gt;&lt;a href=&quot;http://memorex-ce.com/product/amfm-pocket-radio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://memorex-ce.com/product/amfm-pocket-radio/&lt;/a&gt;&#xA;Yeah, I guess it's cheap and probably won't pick it up but...&lt;/p&gt;&#xA;" OwnerUserId="10624" LastEditorUserId="8717" LastEditDate="2017-11-10T02:53:48.860" LastActivityDate="2017-11-10T02:53:48.860" Title="Can my portable radio receive amateur radio?" Tags="&lt;receiver&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9503" PostTypeId="2" ParentId="9502" CreationDate="2017-11-10T00:07:58.493" Score="3" Body="&lt;p&gt;It looks as though your pocket radio can pick up the FM broadcast band at 88-108 MHz and the AM broadcast band from 530-1700 kHz.  There aren't any ham bands in those ranges, so sorry, but your radio shouldn't be able to pick up amateur radio transmissions.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-11-10T00:07:58.493" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9504" PostTypeId="2" ParentId="9489" CreationDate="2017-11-10T05:05:32.147" Score="3" Body="&lt;p&gt;Yaesu makes software like what you're looking for:&#xA;Go the yaesu.com and find the FT-450D page, click on the Files tab, and look for:&#xA;PCC-450 Software V1.13 and Reference Manual (07/18/14) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The PCC-450 software runs on Windows and connects to the radio over a serial port. You can drive nearly every feature of the radio. I find it easier to use this software than to go through the radio menus.&lt;/p&gt;&#xA;" OwnerUserId="10626" LastActivityDate="2017-11-10T05:05:32.147" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9505" PostTypeId="1" CreationDate="2017-11-10T14:51:43.977" Score="0" ViewCount="528" Body="&lt;p&gt;This question is &lt;strong&gt;not&lt;/strong&gt; about Frequency Hopping Spread Spectrum!  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In SDRs, say USRP, if we are transmitting in a particular frequency band, can we dynamically hop from that band and transmit from another band?&lt;br&gt;&#xA;If so, what's the range to which it can hop? If not, why can't it?&lt;/p&gt;&#xA;" OwnerUserId="10216" LastEditorUserId="8717" LastEditDate="2017-11-10T15:22:23.907" LastActivityDate="2018-06-08T21:20:20.123" Title="Hopping from one frequency band to another in SDR (ex: USRP)" Tags="&lt;software-defined-radio&gt;&lt;legal&gt;&lt;usrp&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9506" PostTypeId="2" ParentId="9505" CreationDate="2017-11-10T16:55:48.393" Score="0" Body="&lt;p&gt;I don't know for sure for USRP, but the driver's API of RtlSdr and HackRF allows to change the frequency while running. Very probably USRP allows it as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So yes it is possible if the application used supports it. The range is only limited by the allowed transmit range or your hardware.&lt;/p&gt;&#xA;" OwnerUserId="5586" LastActivityDate="2017-11-10T16:55:48.393" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9507" PostTypeId="1" AcceptedAnswerId="9508" CreationDate="2017-11-11T10:21:17.360" Score="3" ViewCount="177" Body="&lt;p&gt;Imagine we have an isotropic antenna at the origin emitting a steady sine wave at frequency $f$. Encompassing the antenna is a sphere of radius $r$ made of a fine copper mesh (with holes $\ll\frac\lambda{10}$, making it a Faraday cage). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From this sphere we remove a patch of material of size $n^{\circ}\times n^{\circ}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would the far-field pattern look like? Is there any combination of the variables ($f$, $r$, $n$) that would create a tight beam from the removed patch of material? What if instead of removing a patch of material we removed a slit from pole to pole with width $n^{\circ}$?&lt;/p&gt;&#xA;" OwnerUserId="10630" LastEditorUserId="4076" LastEditDate="2017-11-11T10:41:14.990" LastActivityDate="2017-11-15T01:34:54.770" Title="Can you create a radio beam with a Faraday cage?" Tags="&lt;antenna-theory&gt;&lt;propagation&gt;&lt;theory&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9508" PostTypeId="2" ParentId="9507" CreationDate="2017-11-11T10:46:45.283" Score="3" Body="&lt;p&gt;No, there would not be a narrow beam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's multiple ways you can show that, but most intuitively, I think is the follow:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;consider every point on that patch to be a source of an elemental wave&lt;/li&gt;&#xA;&lt;li&gt;in the center of that patch, these will interfere in a manner so that only the &quot;straight&quot; radial path has a propagating wave front. (think about it: if it wasn't straight, then it would destructively interfere with the neighboring wave sources, which excludes anything but straight)&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;even this alone would not lead to a narrow beam, but simply to a beam with your $n^\circ$ opening angle&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Close to the edges of that patch, however, there's no neighboring sources. So, the propagation happens &quot;bent away&quot; from the core of the patch. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;That phenomenon is called diffraction, and when you think about it, your experiment is just what people usually do to demonstrate diffraction:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have an experiment with a planar wave front approaching a slotted obstacle. In your case, &quot;planar&quot; is to be interpreted with respect to a polar coordinate system with the origin in the center of your sphere, but other than that: classical slit experiment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, this is basically a patch aperture, and there's nothing about single patch antennas that gives you a narrow beam. To make things worse, the smaller you choose $n$, the wider that beam becomes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd pretty much do the &lt;em&gt;opposite&lt;/em&gt; when trying to create a narrow beam (to build an antenna with high directional gain): Finding a surface where the phase difference for plane waves is constant, and other directions quickly experience destructive interference. Take that patch you removed from your mesh sphere, throw away the rest of the sphere, flip the patch inside out, pushing it a bit so that it's parabolic and use it as a reflector. That shape should remind you of an emitter type you might already know:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/Category:Parabolic_antennas#/media/File:Antena_parabolica.JPG&quot; rel=&quot;nofollow noreferrer&quot;&gt;mesh parabolic antenna, Wikimedia Commons, photograph oescalona&lt;/a&gt; &#xA;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Antena_parabolica.JPG/1024px-Antena_parabolica.JPG&quot; alt=&quot;mesh parabolic antenna, Wikimedia Commons, photograph oescalona&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-11-11T10:57:34.137" LastActivityDate="2017-11-11T10:57:34.137" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9509" PostTypeId="2" ParentId="6631" CreationDate="2017-11-12T04:46:22.237" Score="2" Body="&lt;p&gt;It looks as if the Eton Mini needs a 3 volt center-positive power supply. It's probably 3.8 mm OD, 1.4 mm ID barrel connector, but that's just a guess based on the half-inch depth specification of the radio:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Hx8hf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Hx8hf.jpg&quot; alt=&quot;Picture of jack side of radio&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since it lasts you two days on two AAA batteries (probably 1000 mAh) you can probably get by with a minimum 0.1 A (100 mA) power supply. A little more would put you on the safe side, and 1000 mAh / 1 Ah would be overkill but sure to work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any generic power supply with the right connector, voltage, polarity and amperage will work. (Power supplies with higher amp ratings will also work, but beware of power supplies with higher volt ratings.) The adapter plug's connector outer shield will need to touch the metal on the inside edge of the socket connector on the radio, and the adapter's inner connector will need to make contact with the pin inside the socket's connector on the radio. Barrel connector sockets can accommodate plugs of slightly different/incorrect sizes in a pinch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anything that advertises itself as compatible should work fine - there's nothing fancy about the power supply.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2017-11-12T04:55:48.680" LastActivityDate="2017-11-12T04:55:48.680" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9510" PostTypeId="1" AcceptedAnswerId="9511" CreationDate="2017-11-12T13:52:33.553" Score="10" ViewCount="1235" Body="&lt;p&gt;I just found out about &lt;a href=&quot;http://www.websdr.org/&quot; rel=&quot;noreferrer&quot;&gt;WebSDR&lt;/a&gt;, and I was wondering how is it possible that many listeners listen and tune to different stations simultaneously. Which components/technologies allow this, and how does this roughly work?&lt;/p&gt;&#xA;" OwnerUserId="10483" LastEditorUserId="4665" LastEditDate="2017-11-12T16:17:53.020" LastActivityDate="2017-11-13T14:38:20.283" Title="Multiple simultaneous tunings with SDR" Tags="&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9511" PostTypeId="2" ParentId="9510" CreationDate="2017-11-12T15:32:30.030" Score="8" Body="&lt;p&gt;Software-defined radio is radio where the signals are sampled and converted to digital data early in the process. This means that like any digital data, they can be copied without loss of quality. Computers can execute the same calculation many times. Thus, a SDR program can take one input and process it &lt;em&gt;differently&lt;/em&gt;, as if it were many different radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's the fundamental concept. However, making this work still requires you to have the digital signal you need — all of the hardware which works in the analog domain, gathering the radio waves and converting them into a digital signal, must be able to &lt;em&gt;simultaneously&lt;/em&gt; receive everything everyone wants.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This turns out to not be hard at all with modern electronics. Every radio signal has some &lt;a href=&quot;https://en.wikipedia.org/wiki/Bandwidth_(signal_processing)&quot; rel=&quot;noreferrer&quot;&gt;bandwidth&lt;/a&gt; — some &lt;em&gt;range&lt;/em&gt; of frequencies which it occupies. (A signal at exactly one frequency conveys no information.) SDR receiver hardware takes the signal and converts it to digital samples using &lt;a href=&quot;https://en.wikipedia.org/wiki/Nyquist_rate&quot; rel=&quot;noreferrer&quot;&gt;a sampling rate that is high enough to preserve the entire bandwidth&lt;/a&gt;. If you take a receiver capable of receiving a wide-bandwidth signal and tune it to where several narrower (and closer spaced) signals are present, the digital signal resulting contains &lt;em&gt;all&lt;/em&gt; of those signals, at different frequencies within itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such a &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency-division_multiplexing&quot; rel=&quot;noreferrer&quot;&gt;multiplexed&lt;/a&gt; signal is then processed in software using digital versions of the same components that an analog radio would — mixers, filters, and demodulators — to extract individual signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A multi-user software-defined radio simply has to run a differently-configured copy of those components for each user.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then the only remaining matter is that the receiver hardware is capable of bringing in a signal of enough bandwidth and sample rate to contain all the users' desired tunings. This is &lt;em&gt;exactly the same technology&lt;/em&gt; as enables high data rate digital wireless communications — &lt;strong&gt;high sampling rate ADCs&lt;/strong&gt; to convert those digital signals.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The other element of such an SDR is a antenna suitable for receiving the entire bandwidth. Generally, &lt;em&gt;any&lt;/em&gt; antenna &lt;em&gt;can&lt;/em&gt; be used for receiving across a wide bandwidth, but the signal level will be much weaker away from the optimal frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For “higher” bands (VHF and up), a single antenna of ordinary design can do the job, just as antennas for scanners do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Receivers for all of HF, like &lt;a href=&quot;http://websdr.ewi.utwente.nl:8901/&quot; rel=&quot;noreferrer&quot;&gt;the University of Twente WebSDR&lt;/a&gt;, take the approach of using a physical antenna that is, loosely speaking, equally bad at all frequencies of interest, followed by a built-in amplifier (LNA) to increase the signal level for the receiver — most famously in this context, the PA0RDT “Mini-Whip” design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that “all of HF” is just 30 MHz, which is not that much these days. A single Wi-Fi signal can occupy 40 MHz.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-11-12T19:26:28.550" LastActivityDate="2017-11-12T19:26:28.550" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9513" PostTypeId="1" AcceptedAnswerId="9517" CreationDate="2017-11-13T01:35:50.123" Score="2" ViewCount="152" Body="&lt;p&gt;I'm starting to study RF propagation at college, and I'm thinking about what antenna I should choose for this scenario:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dQHBP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dQHBP.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The distance between the transmitter and receiver is just 700 meters, and the link is not line-of-sight because there are 2 buildings in the way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency is 408.00625 Mhz and the bandwidth will be 12.5 Khz FM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you think a 1/2 wavelength dipole (omnidirectional) will work for this? Or would a Yagi (directional) be better? I think that a Yagi would oversize the link[?].&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which one of these antennas would be the best choice?&lt;/p&gt;&#xA;" OwnerDisplayName="user10639" LastEditorDisplayName="user10639" LastEditDate="2017-11-13T02:36:28.697" LastActivityDate="2017-11-13T13:55:31.267" Title="Which antenna would you use?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9514" PostTypeId="2" ParentId="9513" CreationDate="2017-11-13T02:11:22.323" Score="0" Body="&lt;p&gt;Taking this as a theoretical question, and not knowing anything else such as how the buildings are oriented, what they are made of, or how much power you are using, I will step out and say that in general you will get maximum signal from A to B by using a pair of Yagi-Uda antennas.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The trick, due to scattering, or knife-edge effects, plus the fact that building faces tend to change the polarity of reflections, will be the orientation of the respective antennas.  &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That answers your question as asked.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get a more precise answer would require more information.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-11-13T06:14:53.947" LastActivityDate="2017-11-13T06:14:53.947" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9515" PostTypeId="2" ParentId="9192" CreationDate="2017-11-13T05:59:50.547" Score="1" Body="&lt;p&gt;There are literally hundreds of antenna designs you could use. There are many variables to think about. The &quot;best&quot; answer probably depends heavily on what you (and the HOA) will tolerate. The Moxon you mentioned would be great, if allowed. If you need a smaller, less visible antenna then placing it as high as possible would help. You may be able to make a simple vertical dipole slightly below the top of the chimney with a reflector attached directly to the chimney and the driven element in front of it. This would be 2 elements and much less visible. Some designs need only .15 wave spacing between the 2 elements. This would give some gain and directivity to it. If made of thin wire it might be hard to see. You might even get away with calling it a &quot;TV&quot; antenna. If a TV antenna is acceptable then a Moxon, Hybrid Moxon, Yagi, or Quagi would probably be excellent.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-11-13T05:59:50.547" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9516" PostTypeId="2" ParentId="9500" CreationDate="2017-11-13T07:23:50.733" Score="0" Body="&lt;p&gt;Distance is great (except the line loss). Mufflers COULD be good if designed and installed correctly. You can even go so far as to install more than one muffler in parallel. Making the other (not the exhaust) noise quieter will take an enclosure. You could make an enclosure with a lid or extend the fuel fill opening above the enclosure. A simple box with sound dampening material (lots of things will do) on the inside will probably help. It would be nice if there is a window so that you can see the meters and controls. Be sure to check the oil level too!&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2017-11-13T07:23:50.733" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9517" PostTypeId="2" ParentId="9513" CreationDate="2017-11-13T13:09:45.977" Score="3" Body="&lt;p&gt;A complete analysis of this situation first must consider the propagation path performance, and then the types(s) of antennas to use w.r.t. the losses on that path.  This short propagation path has nearly a fixed propagation loss regardless of the antennas/patterns in use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna characteristics depend on path losses, the Z-matched power at the tx antenna input, tx antenna gain toward the rx antenna, rx antenna gain toward the tx antenna, the r-f signal needed at the receiver input connector for acceptable performance of the overall link system (including fade margin), and signal reflections from other structures and surfaces in the propagation environment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a graphic showing general considerations for point-point link paths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ahobz.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ahobz.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2017-11-13T13:09:45.977" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9518" PostTypeId="2" ParentId="9513" CreationDate="2017-11-13T13:55:31.267" Score="3" Body="&lt;p&gt;What you need is a &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt;. A higher gain antenna (such as a Yagi) adds gain to your budget and makes the link more likely to work, or allows for less transmit power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure what you mean by &quot;oversizing&quot; a link. Using an antenna with more gain than necessary has no particular disadvantage other than the antenna might be larger or more expensive than necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With buildings blocking line of sight like that, you might be better off looking for a repeater or passive reflector.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-11-13T13:55:31.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9519" PostTypeId="2" ParentId="9510" CreationDate="2017-11-13T14:38:20.283" Score="4" Body="&lt;p&gt;Tuning in an analog radio is accomplished by adjusting oscillators or filters so the desired station falls within the radio's passband. For a SSB receiver, this passband is somewhere between 3 and 6 kHz wide. The output of the demodulator then goes to a speaker. The filters can't be wider than that, otherwise you'd hear nearby stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the output is fed into an analog to digital converter such as a computer sound card, you now have an SDR. With an analog solution, tuning two stations would require a physical set of filters, oscillators, and mixers. But in a computer it's just another instance of a program running, so it's easy to have any number of concurrent listeners. The analog passband can be wider since digital filtering can further narrow the passband as necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With most of the processing done in the computer, the analog radio can become simpler. For example see the &lt;a href=&quot;http://www.wb5rvz.org/softrock_lite_ii/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Softrock Lite II&lt;/a&gt;, which is an analog radio for about $20 USD. You provide a computer and a sound card to make it an SDR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Softrock is a cheap solution, and the low sample rate of the sound card &lt;a href=&quot;https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;limits the bandwidth&lt;/a&gt; that can be processed. But with a little money it's possible to upgrade the analog to digital converter to one operating at a sample rate of tens or hundreds of MHz, and add an &lt;a href=&quot;https://en.wikipedia.org/wiki/Field-programmable_gate_array&quot; rel=&quot;nofollow noreferrer&quot;&gt;FPGA&lt;/a&gt; to handle the increased computational demand. Since the radio isn't transmitting the antenna doesn't need to be especially efficient, so a small whip into a high-impedance &lt;a href=&quot;https://en.wikipedia.org/wiki/Buffer_amplifier&quot; rel=&quot;nofollow noreferrer&quot;&gt;buffer&lt;/a&gt; makes a good wide-bandwidth antenna. With a sample rate of 30 MHz it's possible to tune the analog radio to 0-30 MHz and have the entire HF band (and everything below it) available to users over WebSDR.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-11-13T14:38:20.283" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9520" PostTypeId="1" CreationDate="2017-11-13T21:03:47.677" Score="2" ViewCount="1393" Body="&lt;p&gt;I have a &lt;a href=&quot;https://www.akg.com/perceptionwireless-system.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;low power wireless microphone&lt;/a&gt; (10 - 50 mW) with a large receiver designed to connect to a mixer/sound system.  The mic transmits in the UHF band between 530 and 860 depending on the band (see &lt;a href=&quot;http://demandware.edgesuite.net/aauj_prd/on/demandware.static/-/Sites-masterCatalog_Harman/default/dwda627f56/pdfs/Frequency%20chart%20Perception%20Wireless%20WMS45.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;frequency chart&lt;/a&gt;).  I want to build a battery powered receiver that would pick up the mic and output the audio to a standard pair of headphones.  What parts do I need?  How do I &quot;build&quot; it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have no experience in building electronics, but I would still like an answer even if I won't have the technical skill to follow it.&lt;/p&gt;&#xA;" OwnerUserId="10644" LastActivityDate="2017-11-14T18:21:19.590" Title="What parts / procedure do I need to build a UHF receiver that can connect to a standard pair of headphones" Tags="&lt;receiver&gt;&lt;diy&gt;&lt;uhf&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9522" PostTypeId="1" AcceptedAnswerId="9523" CreationDate="2017-11-13T23:52:28.830" Score="3" ViewCount="76" Body="&lt;p&gt;I've read that radio range is influenced by a lot more than the power output of the transmitter.  From what I've seen, line of sight and interference can be much more significant factors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is that also true for really low power transmissions, or is there a way to estimate the range based on power?  I'm talking about cases like the transmitters they used to make to &quot;connect&quot; your MP3 player to your normal car radio (pre bluetooth and &quot;aux&quot; inputs), or walki talkie's in the same room?&lt;/p&gt;&#xA;" OwnerUserId="10644" LastActivityDate="2017-11-15T06:16:10.617" Title="Can I estimate range of a low power transmission based on power (in mW)?" Tags="&lt;range&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9523" PostTypeId="2" ParentId="9522" CreationDate="2017-11-14T09:00:04.840" Score="5" Body="&lt;p&gt;When a transmitter and receiver antenna are in line of sight with one another, we can calculate the effective loss of the path based on the distance between the transmitter and receiver antenna, the gain of those antennas, and the frequency involved:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \text{Path Loss (dB)} = 20\log(d) + 20\log(f) +32.44 - G_{\text{TX}} - G_{\text{RX}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$d$ = distance in km&lt;br&gt;&#xA;$f$ = frequency in MHz&lt;br&gt;&#xA;$G_{\text{TX}}$ = transmitter antenna gain in dBi&lt;br&gt;&#xA;$G_{\text{RX}}$ = receiver antenna gain in dBi&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for example, a 1 km path at 400 MHz with 0 dBi antennas on the transmitter and receiver would have a free path loss of approximately 84.5 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We now need to know the minimum receive power level that the receiver requires to properly decode or playback the information or signal from the transmitter. Let's use an example of a moderate receiver with a minimum signal requirement of -113 dBm. This would correspond to a 0.5 uV signal into a 50 ohm input impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the receiver requires at least -113 dBm and we will lose 84.5 dB just due to the path losses, the transmitter must supply at least a -28.5 dBm signal (-113 dBm - 84.5 dB) or approximately 1.4 milliwatts of power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there are objects in the path that may absorb or reflect RF power, then these effects must be added to the above analysis. An example of this based on your question would be to model the effect of a human body between the transmitter and receiver. Depending on the frequencies involved, this may have no effect at all or it may increase the path loss and therefore require a higher power transmitter, a more sensitive receiver, or better (higher gain) antennas or some combination of these.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-11-15T06:16:10.617" LastActivityDate="2017-11-15T06:16:10.617" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9524" PostTypeId="2" ParentId="9520" CreationDate="2017-11-14T17:53:26.123" Score="4" Body="&lt;p&gt;Sounds like you are wanting to build a DIY FM receiver that can be tuned over a broad portion of the UHF band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[I'll leave aside any legal implications — but make sure that your goal is permitted in the jurisdiction you wish to accomplish it! Some countries are fairly lax, others are much more strict, regarding who may listen in on radio signals.]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a small taste of what an analog UHF receiver for FM signals might involve, you could start by looking at this &lt;a href=&quot;http://electronics-diy.com/simple-fm-radio-receiver.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Simple FM radio receiver&lt;/a&gt; circuit, or browse through  &lt;a href=&quot;http://circuit-zone.com/?cat=fm_radio_receivers&quot; rel=&quot;nofollow noreferrer&quot;&gt;other FM radio receiver designs&lt;/a&gt;. Note however, that these designs are for typical (usually ITU region 2) FM broadcast bands, i.e. VHF frequencies in the range of 88–108 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So at minimum you will need to adjust the tuning portions of the circuit for your desired bands. You may find some of the components used for those broadcast-band circuits do not perform well at 860 MHz, and need to be replaced with something better. You will also have to worry more about your PCB layout to avoid stray capacitance and unwanted inductance from interfering with its operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This may/may not be for the faint of heart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, I have a couple yellowed and fading amateur radio books that include DIY circuits — even &lt;a href=&quot;https://en.wikipedia.org/wiki/Vacuum_tube&quot; rel=&quot;nofollow noreferrer&quot;&gt;tube&lt;/a&gt; circuits! — for the even higher frequency 23cm band. So I don't want to discourage you, even if there's no go-to &quot;Instructable&quot; for your band of interest.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Now, if you &lt;em&gt;are&lt;/em&gt; looking for something a bit more plug-and-play, and have an Android phone/tablet, then why not pick up an RTL-SDR device and a USB OTG cable?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.rtl-sdr.com/about-rtl-sdr/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTL-SDR dongles&lt;/a&gt; were originally meant as DVB-T tuners, and can usually be found for between $10–30 USD. They can be used more generically with a wider variety of software that has sprang up, and can usually tune over the full VHF and well into the UHF range, e.g. 25–1750MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I personally like NooElec's&lt;a href=&quot;http://www.nooelec.com/store/nesdr-smart-sdr.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;NESDR SMArt&lt;/a&gt; unit, which is also available in a kit with some starter antennas. (They graciously loaned me a bunch for an SDR talk I gave, so I do have a conflict of interest.) The &lt;a href=&quot;https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTL-SDR blog's kits&lt;/a&gt; are also an easy recommend too. You can find even cheaper devices on eBay or AliExpress (try searching for RTL2832U) if you want to try one on an even smaller investment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have the cheap tuner dongle (and a small antenna), plug it into your phone with the OTG adapter, and use an app like &lt;a href=&quot;http://sdrtouch.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;SDR Touch&lt;/a&gt; or &lt;a href=&quot;https://play.google.com/store/apps/details?id=com.mantz_it.rfanalyzer&amp;amp;hl=en&quot; rel=&quot;nofollow noreferrer&quot;&gt;RF Analyzer&lt;/a&gt; to locate the signal and demodulate the audio into your headphones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's even more desktop software options available if you get hooked on SDR (like most do :-) but it sounds like your initial goal is something portable.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-11-14T18:21:19.590" LastActivityDate="2017-11-14T18:21:19.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9525" PostTypeId="2" ParentId="9507" CreationDate="2017-11-15T01:34:54.770" Score="3" Body="&lt;p&gt;I think that if the sphere is very large in wavelengths. Maybe 1000 wl and if the opening is small, maybe 10x10 wl, you would create a fairly narrow beam.&#xA;Such a small opening in such a big sphere would be close to a hole in a flat surface. The phase would be the same over the entire 10x10 wl area. It would&#xA;however be better to make a 10x10 wl equiphase wavefront by shaping a 10x10&#xA;area as a parabolic surface and irradiate it properly (not so easy) but&#xA;a 20x20 surface would easily produce a similar beam as the big sphere.&#xA;The big sphere would have an extremely ugly frequency response. It would&#xA;be a resonator with a very small leakage through the hole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand the question as purely accademic....&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-11-15T01:34:54.770" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9526" PostTypeId="1" CreationDate="2017-11-15T10:08:27.893" Score="4" ViewCount="1109" Body="&lt;p&gt;I'm new to this and am in need of guidance.  I am mounting a multi-band antenna on a 50 foot tall 1 1/4&quot; galvanized mast.  I plan to drive a ground rod at the base of the antenna and bond the mast to it.  I also plan to ground the RG-8/U at the top of the mast and at the bottom of the mast.  The mast/ground rod is on the opposite end of the house (probably 50' of wire needed) from the electric service entrance and ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions are:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;What size wire is recommended to bond the antenna ground to the electric service ground?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;When I ground the RG-8/U nearest the entrance to the house, can I ground it to ground wire running in item #1, or do I run the ground to one of the ground rods?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The ground bus that I install in the shack should be bonded to which ground rod, and should use what size wire?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Any help would be very much appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ray KK4WPB&lt;/p&gt;&#xA;" OwnerDisplayName="user10650" LastEditorUserId="8832" LastEditDate="2017-11-15T17:39:16.367" LastActivityDate="2017-11-15T17:39:16.367" Title="Antenna, input and ground bonding" Tags="&lt;antenna&gt;&lt;grounding&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9528" PostTypeId="2" ParentId="9526" CreationDate="2017-11-15T15:38:30.617" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What size wire is recommended to bond the antenna ground to the electric service ground?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'd recommend (and electrical code may require) 6 AWG solid wire, both for electrical and mechanical reasons. If the cost is acceptable, flat copper strap is even better since it has lower inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Make the connections with brazing or welding if possible. Every milliohm matters when lightning currents are involved. And mechanical connections have a way of failing. I use &lt;a href=&quot;http://www.harrisproductsgroup.com/en/Products/Alloys/Brazing/Phos-Copper/Stay-Silv-15.aspx&quot; rel=&quot;noreferrer&quot;&gt;Harris Stay-Silv 15&lt;/a&gt; with a MAPP gas torch. &lt;a href=&quot;https://www.erico.com/category.asp?category=R2162&quot; rel=&quot;noreferrer&quot;&gt;Cadweld&lt;/a&gt; is another option.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;When I ground the RG-8/U nearest the entrance to the house, can I ground it to ground wire running in item #1, or do I run the ground to one of the ground rods?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To get &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;proper surge protection for your equipment&lt;/a&gt;, everything must be grounded at a single point. Typically this is achieved by mounting a copper or aluminium sheet or bulkhead where the feedlines enter the building. Attached to this sheet are the lightning protection devices (gas discharge tubes, MOVs, etc), and then strap runs straight down from this panel into the ground system below.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The ground bus that I install in the shack should be bonded to which ground rod, and should use what size wire?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I wouldn't bother with RF grounding at the desk unless you have a single-wire feeder or &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;poorly designed antenna system&lt;/a&gt;. Without common-mode currents at the desk there's no reason for the ground. And the coax shields connecting all the equipment are already grounding the chassis. And unless your operating desk is very close to the entrance panel you can't make a low impedance RF ground anyway.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Here's my station ground almost completed as an example. This is where the feedlines enter the house: the desk is 15 feet away on the other side of the room. All the cables from the desk run to this bulkhead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the bulkhead are two gas tube surge arresters for feedlines (from Polyphaser), at electrical outlet with integrated MOV (Lutron), and a TVS diode protection device for the ethernet cable (Ubiquiti).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The braid will go to the ground rod just outside. That ground rod is connected with buried solid uninsulated 6 AWG wire to the electrical service entrance 40 feet away, with another rod every 10 feet along the way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not pictured is a larger 30 kA MOV in the main breaker panel on the other side of the house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6TOQ5.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6TOQ5.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-11-15T15:38:30.617" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9530" PostTypeId="1" AcceptedAnswerId="9532" CreationDate="2017-11-16T00:04:40.710" Score="3" ViewCount="284" Body="&lt;p&gt;As I understand it, dynamic range is the difference in dB between the strongest and weakest signal discernible by your receiver. So, the larger the dynamic range, the better, which seems intuitive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, calculating reciprocal mixing dynamic range (RMDR - dynamic range determined by the calculation of reciprocal mixing, distance in dB where the two lines cross the noise floor) shows that the closer the slope of the third-order intercept (IP3) line is to that of the ideal line for receiver amplifier compression, the smaller the dynamic range, and you want the IP3 line slope to be as close to the ideal as possible, which seems to minimize the dynamic range, which in turn seems to conflict with the original definition for dynamic range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4BkxL.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4BkxL.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What am I missing, since there seems to be a conflict here?&lt;/p&gt;&#xA;" OwnerUserId="9166" LastEditorUserId="218" LastEditDate="2017-11-17T21:08:20.747" LastActivityDate="2017-11-17T21:08:20.747" Title="Seeming conflict in the definitions of dynamic range" Tags="&lt;receiver&gt;&lt;measurement&gt;&lt;superheterodyne&gt;&lt;dynamic-range&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9532" PostTypeId="2" ParentId="9530" CreationDate="2017-11-16T20:39:55.447" Score="2" Body="&lt;p&gt;While the two terms in question share the phrase &quot;dynamic range&quot;, they are in fact, quite different metrics from one another. Therefore there is no reason to assume any type of conflict or contradiction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The basic receiver dynamic range is a measure of a receiver's ability to handle a wide range of signal strengths - from the very weakest (typically at the receiver's MDS - Minimum Discernible Signal) to the strongest. Several factors come into play that determine the receiver's dynamic range such as phase noise, noise figure, 2nd and 3rd order intercepts, 1 dB compression point, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The receiver RMDR - Reciprocal Mixing Dynamic Range became significant with the application of frequency synthesizers as the LO (local oscillator) in the superhetrodyne receiver. These synthesizers tend to have phase noise on the skirts of their envelope. Under the right conditions, a signal that is otherwise out of the passband of the IF chain can mix with this undesired LO phase noise to generate interference within the IF passband and thus interfere with desired signals in the passband. Lowering the LO skirt phase noise will improve the RMDR.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-11-16T20:45:40.867" LastActivityDate="2017-11-16T20:45:40.867" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9533" PostTypeId="1" CreationDate="2017-11-17T11:03:47.540" Score="6" ViewCount="3832" Body="&lt;p&gt;I have a couple of end-fed wire antennas I bought that came with matching baluns. One has a 9:1 unun, and I'm not sure about the other one. In addition to those, should I also put a choke balun on the coax before the matching one?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="8717" LastEditDate="2017-11-17T19:40:56.747" LastActivityDate="2019-07-08T11:29:34.600" Title="Do end-fed dipole antennas need choke baluns?" Tags="&lt;balun&gt;&lt;end-fed-antenna&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9534" PostTypeId="2" ParentId="9533" CreationDate="2017-11-17T13:22:51.120" Score="4" Body="&lt;p&gt;End fed antennas have become quite popular in recent years, primarily due to their convenient installation conditions. Many people subjectively report good results from the antenna. But how the antenna works is not often well understood.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The end fed antenna often utilizes an unun at the feedpoint of the antenna. This is done because the feedpoint impedance of an end fed half wave wire is in the 5,000 ohm range. The unun, which is typically nothing more than an autotransformer, attempts to convert the relatively high impedance of the antenna to the lower impedance of the coax. In reality, the unun does a far from ideal conversion of a simple transformer but rather contributes to a non-linear complex impedance transformation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other anomaly of an end fed antenna is that there is only one apparent connection to the antenna. The coax and transmitter, on the other hand, require that current flows in equal and opposite directions. While the unun contributes somewhat to this requirement, in most installations the balancing current actually flows on the outside of the coax shield. Due to the skin effect of RF, this is a completely distinct current from what is flowing on the inside of the shield of the coax. This is sometimes called the third wire of the coax. Thus the coax often forms part of the radiating antenna. Normally we try to avoid this condition but without any other form of counterpoise, it is nearly a requirement to make this type of antenna work reasonably well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Placing a choking balun at the feedpoint of the antenna may be counterproductive for many end fed antenna arrangements. On the other hand, it is not desirable to allow the current that is flowing on the outside of the coax to enter the shack since this can lead to RFI while transmitting. Often a good compromise is to place a choking balun on the coax just before it enters the shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have your antenna in place and have experimented with the choking balun near the shack, you could try an additional choking balun at the antenna feedpoint between the coax and the unun. Be prepared though to see a rise in SWR but potentially a helpful noise level reduction. You will need to judge based on your circumstances if this additional choking balun is helpful or not. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-11-18T03:12:49.850" LastActivityDate="2017-11-18T03:12:49.850" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9537" PostTypeId="1" CreationDate="2017-11-18T21:10:18.260" Score="0" ViewCount="68" Body="&lt;p&gt;I am looking to increase the 3G GSM reception of my mobile hotspot device by adding an antenna adapter I can attach to RS-9 port in the device. It's a simple pigtail adapter, the other end of which is supposed to be plugged into an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the hotspot lives in an arm rest compartment in a car, I’d like to keep it there without getting the antenna wires out of the car (to a shark fin or wherever).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the fact that the device and the pigtail are locked in a plastic box, would adding just a pigtail benefit reception for the device? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S. It has a reception quality of 30-60% usually, but I am still looking for an easy way to increase it for better speed and connection stability.&lt;/p&gt;&#xA;" OwnerUserId="10670" LastEditorUserId="966" LastEditDate="2017-11-28T12:09:14.613" LastActivityDate="2017-11-28T12:09:14.613" Title="Does adding just an antenna adapter to a 3G modem add to it reception power?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9538" PostTypeId="2" ParentId="5133" CreationDate="2017-11-19T00:41:08.820" Score="2" Body="&lt;p&gt;You said that you just hear white noise and not man-made interference, so I think the most likely explanation for what you are seeing is that you are in a multipath null.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These occur when a signal arrives at your receiver via a direct path and a dominant reflected path of almost the same amplitude.  When the total distance travelled by the reflected wave is a multiple of one-half wavelength different from the distance travelled by the direct path, the reflected wave will be 180 degrees out of phase and will cancel the direct path.  It is possible that the reflection is coming from a body of water, which would explain why this is occurring only on a bridge.  &lt;/p&gt;&#xA;" OwnerUserId="9796" LastEditorUserId="9796" LastEditDate="2017-11-20T02:10:15.237" LastActivityDate="2017-11-20T02:10:15.237" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9539" PostTypeId="2" ParentId="9333" CreationDate="2017-11-19T00:52:14.423" Score="0" Body="&lt;p&gt;The VHF option is best because path loss generally increases with frequency in real outdoor environments.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example where UHF might be the better option would be for an indoor link of tens of meters.   UHF is more prone to multipath scattering than VHF, which actually would provide more signal paths for the indoor UHF link over a VHF link.  The positive effects of multipath scattering (usually seen as a bad thing) over a short range would outweigh any path loss advantage at VHF. &lt;/p&gt;&#xA;" OwnerUserId="9796" LastActivityDate="2017-11-19T00:52:14.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9541" PostTypeId="2" ParentId="9537" CreationDate="2017-11-19T08:06:15.613" Score="0" Body="&lt;p&gt;Maybe a cellular phone booster might help. Just need a little creative engineering to adapt it run off the voltage in a car and mount it near the rear window to improve reception and transmission.&lt;/p&gt;&#xA;" OwnerUserId="6604" LastActivityDate="2017-11-19T08:06:15.613" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9542" PostTypeId="2" ParentId="9537" CreationDate="2017-11-19T13:02:55.967" Score="2" Body="&lt;p&gt;If your modem only has an internal antenna, then I would expect that adding an antenna that is external to the modem will improve reception. But adding a random pigtail length will not yield predictable results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The proper approach is to run coaxial cable from the modem to an antenna. The antenna could be a simple, small, vertical wire antenna that you would place on your dash or on the ledge/deck by the back window. The size of the antenna depends upon the carrier and country you are in. A 700 MHz antenna would be approximately 10 cm tall while a 2100 MHz antenna would be approximately 3.4 cm tall. If you could add details of your carrier name and country, a specific antenna design can be given.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A slightly better approach would be an external antenna. Getting the antenna outside of the metallic body of the car often greatly improves reception. Recognizing you don't want a shark fin or similar, a reasonable compromise antenna is one that simply sticks to the glass on the outside and there is a small box that sticks to the glass on the inside - no holes to drill. This type of antenna does not work well, however, near in-window defrosters or with metalized glass. But it is removable if you change your mind or you sell the car.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One other option is to simply relocate the modem to a location that is more favorable for reception. Placing the modem on the back window deck of the car may sufficiently improve reception. This may be worth testing with some temporary wiring before going the route of the external antenna.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-11-19T13:02:55.967" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9543" PostTypeId="1" CreationDate="2017-11-20T13:20:30.743" Score="6" ViewCount="1254" Body="&lt;p&gt;People &lt;a href=&quot;https://ham.stackexchange.com/search?q=outside%20of%20the%20shield&quot;&gt;often say&lt;/a&gt; common-mode current flows on the outside of the shield, while the current on the inside of the shield is always opposed by an equal but opposite current on the center conductor. This is because skin effect separates the inside and outside of the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if skin effect is isolating the inside and the outside of the shield, why would the inside-shield and center-conductor currents &lt;em&gt;always&lt;/em&gt; be equal but opposite? If skin effect makes the inside and outside of the shield distinct, why can't there be a common-mode current on the inside?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2017-11-20T18:47:34.217" LastActivityDate="2017-12-03T16:14:47.357" Title="Can a common-mode current exist on the inside of a coax shield?" Tags="&lt;coaxial-cable&gt;&lt;theory&gt;&lt;transmission-line&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9544" PostTypeId="1" CreationDate="2017-11-20T16:13:27.743" Score="1" ViewCount="254" Body="&lt;p&gt;I want to build a passive (rx-only) scanner to listen to GSM and UMTS traffic. I am not interested in breaking encryption or anything like that - but more interested in collecting statistics and such.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Things like numbers of RACH bursts. Number of active calls on a cell/frequency/channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found some things online - like OpenBTS and OpenBTS-UMTS. There are great, but the appear to be only intended to emulate and Basestation/ENodeB. I am looking for somthing a bit more generic - which can just analyse channels (e.g. in GSM scan all the common control channels and look for RACH bursts and assignment commands).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there anything like this out there? - Or can OpenBTS/OpenBTS-UMTS be made to do this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an Ettus USRP to get started with.... not really sure I want to write a stack my-self!&lt;/p&gt;&#xA;" OwnerUserId="5427" LastActivityDate="2017-11-20T16:13:27.743" Title="Is there any open-source solution to scanning / decoding GSM/UMTS traffic?" Tags="&lt;software-defined-radio&gt;" AnswerCount="0" CommentCount="5" ClosedDate="2017-11-20T18:45:00.193" ContentLicense="CC BY-SA 3.0" />
  <row Id="9545" PostTypeId="1" CreationDate="2017-11-21T14:39:45.570" Score="2" ViewCount="330" Body="&lt;p&gt;I find it on the website. Only the following passage:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;QTGUI Widgets&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The QTGUI component also includes a number of widgets that can be used to perform live updates of variables through standard QT input widgets. Most of the widgets are implemented directly in Python through PyQT. However, GNU Radio is introducing more widgets, written and therefore available in C++ that also produce messsages. The Python-based widgets only act as variables and so as they are changed, any block using those widgets to set paramters has the callback (i.e., set_value()) function's called.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Entry: An edit box that allows a user to directly set a new value for the parameter.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;And I only found a related file &quot;qtgui_entry.xml&quot; in the program.&lt;/p&gt;&#xA;" OwnerUserId="10410" LastEditorUserId="76" LastEditDate="2017-11-22T01:42:39.427" LastActivityDate="2017-11-22T01:42:39.427" Title="I want to know how QT GUI Entry is implemented in gnuradio. I am puzzled how the code is like?" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9546" PostTypeId="2" ParentId="9545" CreationDate="2017-11-21T15:31:39.353" Score="1" Body="&lt;p&gt;&lt;code&gt;qtgui_entry.xml&lt;/code&gt; in fact contains the entire implementation (not counting code already in Qt, GR, and GRC). There are no other files.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look in it you will see code creating standard Qt widgets and setting them up.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-11-21T15:31:39.353" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9547" PostTypeId="1" CreationDate="2017-11-21T19:59:34.377" Score="3" ViewCount="333" Body="&lt;h3&gt;AIS&lt;/h3&gt;&#xA;&lt;p&gt;I am receiving ship &lt;a href=&quot;https://en.wikipedia.org/wiki/Automatic_identification_system#Detailed_description:_Class_A_units&quot; rel=&quot;nofollow noreferrer&quot;&gt;AIS messages&lt;/a&gt;. These are low power, digital messages periodically sent on two marine channels close to 162mhz. This frequency is surrounded by FM broadcast, weather radio, and TV channels.&lt;/p&gt;&#xA;&lt;p&gt;I am trying to receive data packets, so I can't &amp;quot;listen with my ears&amp;quot; for the source of any interference. I am using an RTL-SDR connected to the antenna, so I can see the frequency spectrum and waterfall plot on my computer. I am trying to reduce general noise so that I can receive the low powered AIS signals more effectively.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/2214/4647&quot;&gt;This answer&lt;/a&gt; implies that interfering stations can add to the RF noise that is received, but it doesn't go into the specifics of how to determine if it is a specific cause.&lt;/p&gt;&#xA;&lt;p&gt;I have read that some possible issues caused by high power stations may be saturating a preamp, overloading the receiver front end, or frequency harmonics.  I don't know how to tell if any of these are affecting me.&lt;/p&gt;&#xA;&lt;h3&gt;Equipment&lt;/h3&gt;&#xA;&lt;p&gt;Antenna - Folded Dipole with tv baulun&lt;br /&gt;&#xA;Preamp -  TV VHF/UHF preamp (&lt;a href=&quot;http://www.avsforum.com/forum/25-hdtv-technical/1794290-rca-tvpramp1r-preamp-technical-review.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;RCA TVPRAMP1R&lt;/a&gt;)&lt;br /&gt;&#xA;Receiver - &lt;a href=&quot;https://osmocom.org/projects/sdr/wiki/rtl-sdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTL-SDR (R820T)&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Both the preamp and SDR have very wide effective frequency ranges.&lt;/p&gt;&#xA;&lt;h3&gt;Question&lt;/h3&gt;&#xA;&lt;p&gt;My assumption is that filtering out these powerful out of band stations would help reduce my received noise if they are indeed adding to the noise. I also don't want to add an FM trap or bandpass filter if it won't do anything.&lt;/p&gt;&#xA;&lt;p&gt;How can I use the SDR's frequency display (SDR#) to determine if high power signals are causing noise/interference on my reception?&lt;/p&gt;&#xA;" OwnerUserId="4647" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-12-05T08:22:40.420" Title="How can I determine if out of band interference is affecting my AIS reception?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;filter&gt;&lt;noise&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9548" PostTypeId="2" ParentId="9543" CreationDate="2017-11-21T21:46:16.157" Score="0" Body="&lt;p&gt;The statement &quot;common-mode current flows on the outside of the shield&quot; is true for a perfect shield. A low cost 60 ohm TV cable might have some common-mode current on the inside. Look at it the other way, Inject a common-mode current on the coax by use of a toroid transformer and measure the voltage between screen and inner conductor at the cable end. A perfect cable (Flexwell with 0.5 mm wall thickness copper tube for the screen) would not show any signal at all, but a low cost TV coax might show something like 60 dB below the coupling to an un-screened wire.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;leif -&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-11-21T21:46:16.157" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9550" PostTypeId="1" CreationDate="2017-11-22T06:00:30.267" Score="0" ViewCount="59" Body="&lt;p&gt;I have designed a TDMA protocol to reduce the voice spurts between voice calls in SDRs. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The protocol runs in this manner: control cycles proceeded with data cycles and again control cycles. Control cycles - data cycles - control cycles - data cycles ----&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If each control cycle is consist of 12 slots and slot size is 2.24ms then 5 control cycles takes 134.4 ms before the data cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;134.4 ms - data cycle - 134.4 ms - data cycle - 134.4 ms - data cycle&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am confused about the term i am using for this time duration of 134.4 ms. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it jitter or buffering delay? &lt;/li&gt;&#xA;&lt;li&gt;or What is more appropriate term for it?&lt;/li&gt;&#xA;&lt;li&gt;and should i need to consider the delay the source node takes in finding the destination node? &lt;/li&gt;&#xA;&lt;li&gt;and what does this delay call? &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Because control slots depend on the node id.&lt;/p&gt;&#xA;" OwnerUserId="10611" LastEditorUserId="6079" LastEditDate="2017-11-22T13:52:08.170" LastActivityDate="2017-11-22T20:38:06.160" Title="Buffering Delay/ Jitter between voice calls" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9552" PostTypeId="2" ParentId="9550" CreationDate="2017-11-22T20:31:11.313" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it jitter or buffering delay? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Neither. It's a control cycle duration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Jitter is a random variation in the period of a nominally perfectly periodic system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Buffering delay is the delay due to buffering. There's no buffering of data in your case, i.e. your data isn't delayed by buffering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't just use terms you come across! These two would've been easy to google!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;and should i need to consider the delay the source node takes in finding the destination node? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You use the word &quot;node&quot;, which strongly implies we're talking about a network that is not a trivial graph (i.e. not just a chain, a single cycle or an isolated single device).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This question makes no sense at this layer. You're on the Physical medium access layer. The question is a routing question. I don't think there's a term for what you need aside from &quot;time it takes to find a route&quot;, it won't be constant, it depends on the size of your net and the algorithm with which you search.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, it's extremely uncommon ina real-world netowrks for a source node to &quot;know&quot; the full route to its target nodes. Instead, it typically figures out the next hop (for example, such nodes can be called &quot;gateway&quot;, if they lead to access to a group of non-directly connected nodes), and just sends the frame on its way, and the nodes on the way figure out individual next hops themselves. &lt;br&gt;&#xA;This is necessary because in most cases, you're either in a scenario where a) routes aren't static (typical example: the internet), or b) routes shouldn't be transparent to the node, as the overhead of communicating the whole route info would put a great overhead on the system without any benefits (e.g. non-IP-based telephony backhaul systems).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-11-22T20:38:06.160" LastActivityDate="2017-11-22T20:38:06.160" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9553" PostTypeId="2" ParentId="6887" CreationDate="2017-11-23T13:43:36.647" Score="2" Body="&lt;p&gt;This may already have been suggested to you, but if you log the dates, times &amp;amp; duration when the problems occur &amp;amp; politely ask your neighbour to do the same when he/she is transmitting (this will normally be required by a ham anyway if such issues are observed), I feel certain that he/she will be happy to do so &amp;amp; compare both your &amp;amp; his/her data after suitable period. It highly unlikely that if the ham is not transmitting, then no interference should be found and only at those times when he/she is transmitting would issues happen. Best of luck with your attempts to stop this and as a ham operator myself, I (in line line with my conditions of license) would be happy to help out &amp;amp; resolve any potential problem that I may (or may not) have with my neighbours. &lt;/p&gt;&#xA;" OwnerUserId="10699" LastEditorUserId="76" LastEditDate="2017-12-11T19:10:18.933" LastActivityDate="2017-12-11T19:10:18.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9554" PostTypeId="2" ParentId="9543" CreationDate="2017-11-24T15:41:54.217" Score="0" Body="&lt;p&gt;The name &quot;common mode&quot; means that the current on the shield and the center conductor is traveling in a common direction.  This condition is a violation of the assumptions required to make a transmission line work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the transmission line to work correctly, the current must be in opposite directions on the shield and center conductor; in this case, the current will be on the inside of the shield and the outside of the center conductor, the induced magnetic fields will oppose and cancel, and there will be no leakage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there is common mode current, then these conditions are violated, and there will be RF leakage both into and out of the transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The world generally not being perfect, it is possible for both conditions to exist simultaneously.  In other words, you can have both common mode current and opposing current on the shield at the same time.   When this occurs, then presumably the common mode current will be on the outside of the shield and the opposing current on the inside of the shield and the portion of the current that is common mode will cause leakage.  However, it would also be possible (but unlikely--so maybe only a small fraction of the current) for the common mode current to travel in other parts of the shield and cause eddy currents, which would heat the shield rather than leak.  Poor quality coax might have a thin shield, which be less than the skin depth, allowing the two currents to mix and allowing eddy currents to be worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically, common mode current in transmission line is caused by the shield of the coax coupling with the antenna, so that matched opposing currents flow in the antenna and the outside of the shield in addition to the matching currents on the inside of the shield and the outside of the center conductor.  This coupling essentially makes the shield part of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2017-11-24T15:47:03.230" LastActivityDate="2017-11-24T15:47:03.230" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9555" PostTypeId="1" CreationDate="2017-11-24T18:44:55.400" Score="9" ViewCount="268" Body="&lt;p&gt;I want to do direct digital synthesis of a 630m band WSPR signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically I'd like to use an Atmega 328 chip running at 20 MHz to produce such a signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will use standard phase accumulator algorithm which I believe I can get to run in less than 12 cycles. This gives a frequency of 1.66 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a target frequency of 472 kHz operation, this is 3.53 times the operating frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not concerned with power efficiency in this design, any antenna I can use on 630m will have an radiation efficiency of less than 1%. As long as the transmitter can put out ~10 watts of power or so I should be fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll use a 24 bit phase accumulator that is truncated to access a wavetable with a length of 128. This corresponds to 7 bits, read on to figure this out. A phase accumulator of 24 bits gives me a frequency resolution of &lt;code&gt;1.6 MHz / 2^24 = 0.0993 Hz&lt;/code&gt; or almost 15 times the needed 1.4648 Hz precision for WSPR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to generate the signal I'll need a DAC. I am choosing to use an R2R ladder made of a precision 220 ohm resistors. I will assemble a 5-bit DAC using these resistors. Given a 5 volt operating voltage, this gives me a peak output voltage of &lt;code&gt;5.0 * 31/32 = 4.84&lt;/code&gt;. I'm not trying to synthesize a voice signal, so &quot;only&quot; 32 steps of output should be acceptable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally people use a DDS to generate a sine wave signal with a peak of +5 VDC from a microcontroller and a minimum of 0 volts. In my case I am going to generate a sine wave only in the region between 0 and pi. In other words, just the positive half. The wavetable will cover from 0 to 2 pi. In the wavetable of my DDS, I will include two other bits. Each bit will be driven high during half of the wavetable. So my DDS will actually generate 3 signals&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A sine wave that only goes between 0 and pi, basically just the positive part.&lt;/li&gt;&#xA;&lt;li&gt;A square wave with the same period as the sine wave&lt;/li&gt;&#xA;&lt;li&gt;A square wave 180 degrees out of phase of the other square wave.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This may seem pretty wacky, but the square waves allow me to select where my DAC's output is being sent. The goal here is to driven a two transistor pull push arrangement on a center tapped transformer. The output of the DAC is connected to two standard PNP (2N3906) transistors. When one of the square waves is high, the other is low. The one that is low turns on the corresponding PNP transistor. Each PNP transistor controls the drive circuit for the power transistor that is running half of the transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This allows me to use a single DAC to control two power transistors. I was a little skeptical if this would work, but the idea seems reasonable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power transistor arrangement is a BC337-40 and MJE13007 in a darlington arrangement. The MJE13007 is a common power transistor from cheap ATX power supplies. 472 kHz is definitely on the upper side of what is possible with this transistor. The gain is pretty low, something like 10 in a practical circuit. The BC337-40 was the cheapest small signal transistor I could find with a large gain and large current capacity. This transistor can easily drive ~400 mA into the MJE13007. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The MJE13007 is biased using a resistive voltage divider driven by 5 volts into a 100 ohm (upper half) resistor and 12 ohm (lower half) resistor. This gives a voltage of &lt;code&gt;5.0 * 12.0/(12.0+100.0) = 0.535 V&lt;/code&gt; bias voltage on the transistors. I have more questions about this below. It seems to work but would be extremely sensitive to the tolerances of the resistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm going to use a crummy random iron powder toroid as the output transformer. The target values I settled on is 1400 nH for the center tapped primary and 16 microhenries for the output. The output is of course going to be 50 ohm impedance such that a standard bandpass filter for 630m can be fitted. I'm not actually building that as part of this project. If the iron powder toroid becomes an issue or a bottleneck I can always buy a decent piece of material. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The actual software that runs on the microcontroller I do not anticipate being an issue. I've reviewed some other people's work and the concepts are simple enough. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly I am not going to drop an entire Atmega328 into a SPICE simulation, so in LTSpice I used a bunch of independent voltage sources to recreate what I expect out of my DAC. The definition of the MJE13007 comes directly from on-semi's website.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/irdJo.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/irdJo.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;V1 and V5 form the expected 0 to pi sinewave output from my DAC. The negative portion is irrelevant&lt;/li&gt;&#xA;&lt;li&gt;V3 and V6 form the two square waves from my DAC&lt;/li&gt;&#xA;&lt;li&gt;Q3 and Q6 are the &quot;enable&quot; PNP transistors for the darlington circuits&lt;/li&gt;&#xA;&lt;li&gt;Q1, Q2, Q4, and Q5 are the two darlingtons arrangements&lt;/li&gt;&#xA;&lt;li&gt;R2 and R8 are current limiting resistors for the base.&lt;/li&gt;&#xA;&lt;li&gt;L1, L2, L3 is the toroid&lt;/li&gt;&#xA;&lt;li&gt;R1 is my load, modeled as a 50 ohm resistor. In real life this will be an antenna&lt;/li&gt;&#xA;&lt;li&gt;R3, R4, R6, &amp;amp; R7 bias the MJE13007 transistors. V4 provides the voltage source for this. Presently 5 volts.&lt;/li&gt;&#xA;&lt;li&gt;V2 is the current source for the transformer. Presently 5 volts.&lt;/li&gt;&#xA;&lt;li&gt;R5 and R9 limit current to the &quot;enable&quot; transistors. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In real L2 would be a balanced output, it will not be tied back to earth at the transmitter. I just had to throw a ground on it so that LTSpice would run.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oELsr.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oELsr.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the output current in the load. It actually seems very reasonable. The current in R1 goes from &lt;code&gt;+200 mA&lt;/code&gt; to &lt;code&gt;-300 mA&lt;/code&gt;. I am a little confused as to why it doesn't show as symmetric. But since this is supposed to be a balanced output I do not suppose it would matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MCGIc.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MCGIc.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This an FFT of the current in R1. There are clear peaks at the first and second harmonic which a bandpass filter will need to remove. The third harmonic is down at &lt;code&gt;-55 dB&lt;/code&gt; so I am not very concerned because this is smack in the middle of 160 meters. With poor antenna efficiency taken into account this would only bother other ham operators who were in my driveway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am confused because I expected the peak I was predicting to be at 472 kHz is instead at 450 kHz. At first I thought I had some sort of distortion going on. But I ran an FFT on the voltage of V1 (the sine wave). Instead of a 236 kHz peak I see 250 kHz peak in the FFT. Given that a voltage source is a pure sine wave in LTSpice I do not understand this. Is the problem with my circuit or is the FFT in LTSpice just buggy?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is still more work to be done to make this a real thing, such as designing a circuit board. I am at this point trying to make sure I haven't made any large errors in this circuit or just plain made things more complex than needed. I've never build any transmitter before and I am mostly working from what parts are available to me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Questions&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Should I replace V4 with an LM317 ? This way I could tune the bias voltage on Q2 and Q4 with some degree of precision. Or should I just try and bias Q1 and Q5 instead?&lt;/li&gt;&#xA;&lt;li&gt;R2 and R8 I think must have to be constructed from a 1000 ohm resistor in series with a 10K pot. Otherwise the variations in the BC337-40 would make the output lopsided I think. How do I determine if a potentiometer can pass a medium frequency signal?&lt;/li&gt;&#xA;&lt;li&gt;My DAC will need to drive an op amp to create the signal used to modulate Q1 or Q5. What op-amp is appropriate for use at 472 kHz? Rail-to-rail design is preferred.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10703" LastEditorUserId="8832" LastEditDate="2018-04-13T00:57:53.613" LastActivityDate="2019-06-14T21:53:28.837" Title="How can I do direct digital synthesis of a 630m WSPR signal?" Tags="&lt;digital-modes&gt;&lt;amplifier&gt;&lt;mf&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9556" PostTypeId="1" CreationDate="2017-11-25T03:50:54.727" Score="2" ViewCount="550" Body="&lt;p&gt;I have:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A Kenwood TS-590SG.&lt;/li&gt;&#xA;&lt;li&gt;2 antennas up, a tri-band beam and a fan dipole.&lt;/li&gt;&#xA;&lt;li&gt;I run both antennas to a MFJ-998 auto tuner.&lt;/li&gt;&#xA;&lt;li&gt;I also have a MFJ versa tuner IV.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The auto tuner works good for 80-10 meters but will not tune the dipole for 160 and will not even try on 6 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was thinking about coming out of the radio to the amp then to the auto tuner using antenna 1 as an output. Take the output of that tuner to the input of the versa tuner IV and connect both antennas to the versa tuner IV. So for 80-10 I could put the versa tuner in bypass and use the auto tuner. When I wanted to try 160 or 6 meters I would turn off the auto tuner and select the antenna on the Versa tuner. When the auto tuner is off it is supposed to bypass that tuner and be on antenna 1. I had thought about using 2 antenna switches for this but thought about the bypass feature of the versa tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anybody see why this would not work?&lt;/p&gt;&#xA;" OwnerUserId="10705" LastEditorUserId="76" LastEditDate="2017-11-25T04:30:52.657" LastActivityDate="2017-11-25T22:15:59.703" Title="Using one of two antenna tuners connected in series" Tags="&lt;antenna-system&gt;&lt;antenna-tuner&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9557" PostTypeId="2" ParentId="9556" CreationDate="2017-11-25T04:28:56.107" Score="1" Body="&lt;p&gt;In principle, this will work fine. The &lt;em&gt;possible&lt;/em&gt; non-idealities are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Insertion_loss&quot; rel=&quot;nofollow noreferrer&quot;&gt;Insertion loss&lt;/a&gt; from the unused tuner (the extra cabling has some loss; the connectors and bypass switches all have impedance “bumps”).&lt;/li&gt;&#xA;&lt;li&gt;The tuner closer to the antenna will see a high SWR and therefore high voltages on its &lt;em&gt;input&lt;/em&gt; when the other one is in use, which is an unusual situation that it may not be designed to tolerate, as Glenn W9IQ's answer points out.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;(You could even &lt;a href=&quot;https://ham.stackexchange.com/a/7870/76&quot;&gt;use both tuners at once&lt;/a&gt; to get a match that would be out of range for either one by itself, but of course just like any large mismatch it is subject to feed line loss.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="8717" LastEditDate="2017-11-25T22:15:59.703" LastActivityDate="2017-11-25T22:15:59.703" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9558" PostTypeId="2" ParentId="9556" CreationDate="2017-11-25T12:01:53.310" Score="3" Body="&lt;p&gt;Two tuners in series might &quot;work&quot; but you should consider all of the factors at play.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you cannot match the antenna with a single tuner, this indicates a fairly high SWR on the line. This will cause not only higher feedline losses but could lead to the development of sufficient voltage or current on the feedline to cause its failure. This is particularly true when an amp is involved as you indicated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then consider the tuners. With a high SWR and an amplifier, at least one of the tuners could flash over (arc) due to high voltage or it could smoke due to high current. There is also the general consideration of tuner efficiency. If the two tuners combined yielded a 2 dB loss, for example, and you run a 1 kW signal through them, they will dissipate 370 watts of heat. That is a lot of heat for a tuner to safely dissipate (and generally one tuner will bear the brunt of the matching and thus heat dissipation).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you experiment with this setup, I would recommend starting at QRP power levels and then slowly raise power while monitoring the operating conditions. You may find that the combined losses and risk of damage don't make it a viable solution. Then its time to put up reasonable antennas for 160 and 6 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are planning on putting the two tuners in series but having one in bypass, all of the above still applies. An additional consideration would be if the bypass circuit on the tuner can adequately handle the associated voltage/current that will exist with the higher SWR. When operating on 6 meters, the additional tuner, even in bypass, may alter the impedance seen by the functioning tuner.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-11-25T16:01:34.277" LastActivityDate="2017-11-25T16:01:34.277" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9560" PostTypeId="1" CreationDate="2017-11-25T22:08:04.090" Score="9" ViewCount="114" Body="&lt;p&gt;I remember from my amateur radio course, and old versions of our local national regulation documents, that anyone is allowed to receive amateur radio transmissions. It's been claimed that international radio regulations (&lt;a href=&quot;http://www.itu.int/pub/R-REG-RR/&quot; rel=&quot;noreferrer&quot;&gt;ITU RR&lt;/a&gt; probably) defines amateur radio transmissions to be public. It was also said that you can record and archive amateur radio transmissions. But where exactly is this defined, and what is the wording? Does it say somewhere that you are allowed to republish the recordings?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Recently it has become a popular sport to archive amateur radio communications, for long periods of time, and republish them on the Internet. I find it a logical extension of the &quot;amateur radio transmissions are public&quot; rule, and often useful. I do it myself for APRS data, even. Data storage is cheap and becoming cheaper, so it's probably a matter of time until someone archives the whole HF amateur spectrum for a year and makes it available on a nice web SDR service.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been browsing the &lt;a href=&quot;http://life.itu.int/radioclub/ars.htm&quot; rel=&quot;noreferrer&quot;&gt;ITU RR amateur service documents&lt;/a&gt; but can't find the section. I'm particularly interested in the international rules, or common variations of it in local regulations – not just FCC's view of it.&lt;/p&gt;&#xA;" OwnerUserId="129" LastActivityDate="2017-12-27T05:22:22.140" Title="Which international regulation allows reception, archiving or republishing of amateur transmissions?" Tags="&lt;legal&gt;&lt;international-operating&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9561" PostTypeId="1" AcceptedAnswerId="9562" CreationDate="2017-11-26T04:26:33.000" Score="1" ViewCount="1117" Body="&lt;p&gt;The &lt;a href=&quot;http://wirelesshold.com/manuals.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;documentation&lt;/a&gt; says the following:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The program requires the complete installation of Mono. You install for example with apt-get the packet mono-complete.&lt;/p&gt;&#xA;&lt;p&gt;Until an installation packet is available at a later time the installation has to be done manually. Download the proper zip file to your PC. (&lt;a href=&quot;http://dv4m.ham-dmr.ch&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://dv4m.ham-dmr.ch&lt;/a&gt;) and unpack it into a directory of your choice below the home directory.&lt;/p&gt;&#xA;&lt;p&gt;In order to gain access to the USB/serial interface the user account must become a member of the group “dialout”. Open the Console and enter &lt;code&gt;sudo gpasswd —add myusername dialout&lt;/code&gt;&lt;/p&gt;&#xA;&lt;p&gt;The DV4mini program gets started by entering &lt;code&gt;mono dv4mini.exe&lt;/code&gt; in the console or you can create a desktop icon.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The link from the manual seems dead; it redirects to &lt;a href=&quot;http://www.dv4mini.de/edownload.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;a German website&lt;/a&gt; for the DV4 mini; it has no &lt;code&gt;.zip&lt;/code&gt;s containing the necessary files (&lt;code&gt;dv4mini.exe&lt;/code&gt;, &lt;code&gt;dmr&lt;/code&gt;, &lt;code&gt;dstar&lt;/code&gt;, and &lt;code&gt;dv_serial&lt;/code&gt;) to download, only &lt;code&gt;setup.exe&lt;/code&gt; installer-files that Mono won't run:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;elliottcable@ham-vm ~/Downloads $ mono ./2017_12_10_setup.exe &#xA;Cannot open assembly './2017_12_10_setup.exe': File does not contain a valid CIL image.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;Frankly, I'm a little stuck. I'm a pretty-experienced developer and *nix user, but I've never used any Windows / Mono stuff before.&lt;/p&gt;&#xA;&lt;p&gt;How the hell do I get my DV4mini software running on “PC-Linux?”&lt;/p&gt;&#xA;" OwnerUserId="8465" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-11-27T23:42:49.387" Title="How do I install the DV4mini software on Ubuntu?" Tags="&lt;digital-modes&gt;&lt;software&gt;&lt;linux&gt;&lt;d-star&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9562" PostTypeId="2" ParentId="9561" CreationDate="2017-11-26T13:09:41.903" Score="0" Body="&lt;p&gt;The very first link on the German website leads to a .zip file: &lt;a href=&quot;http://www.dv4mini.de/EU_2017_06_03_2_setup.zip&quot; rel=&quot;nofollow noreferrer&quot;&gt;link&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That zip file only contains the installer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll have to run the installer using &lt;code&gt;wine&lt;/code&gt; (Wine is easy to install under Ubuntu), and then you can run the program itself from the installation directory using &lt;code&gt;mono&lt;/code&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-11-26T13:09:41.903" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9563" PostTypeId="2" ParentId="9543" CreationDate="2017-11-26T14:50:55.387" Score="1" Body="&lt;p&gt;First, does it matter where the common-mode currents flow? Coax works as a transmission line because the (ideally) equal but opposite currents on the center and shield create opposite fields which exactly cancel for points outside the cable. Thus, it does not radiate. And by reciprocity, external interference is rejected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same concept is in play with &lt;a href=&quot;https://ham.stackexchange.com/q/3508/218&quot;&gt;twin-lead transmission lines&lt;/a&gt;: the equal and opposite current cancel. No skin effect required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Skin effect does not make the inside and the outside of the shield function as distinct conductors&lt;/em&gt;. Think about the contradictions this would make: how does current &quot;know&quot; if it should flow on the inside or the outside? How would open transmission line stubs work if the shield current on the inside &quot;wrapped around&quot; and traveled back on the outside upon reaching the end of the coax? &lt;a href=&quot;https://ham.stackexchange.com/q/6983/218&quot;&gt;How could twin-lead choke baluns work?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;There's a phenomenon similar to skin effect called &lt;a href=&quot;https://en.wikipedia.org/wiki/Proximity_effect_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;proximity effect&lt;/a&gt;. It's relevant to transformers and twin-lead, or any application where two or more conductors in proximity are carrying RF current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When two conductors are carrying currents in opposite directions (differential-mode), the current density is highest in the regions closest to the other conductor. When the current is in the same direction (common-mode), current density is highest in the regions farthest apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rJl65.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rJl65.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both skin and proximity effects arise due to &lt;a href=&quot;https://en.wikipedia.org/wiki/Eddy_current&quot; rel=&quot;nofollow noreferrer&quot;&gt;eddy currents&lt;/a&gt;. Skin effect is a special case when there's just one conductor, with the current density trying to get as far away as possible from all the other parts of the conductor trying to carry current in the same direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in the case of coax, for a common-mode current the current density will be highest on the outside of the shield since that's the farthest point away from all the other points in the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a differential-mode current the current density is highest on the inner surface of the shield and the outer surface of the center since that's the closest points between the two.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NYj6b.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NYj6b.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This isn't skin effect creating a magic barrier between the inside and outside of the shield. It's eddy currents reinforcing some currents while cancelling others. It's the same underlying physics as skin effect, but there's no magic barrier. The inside and outside of the shield are not &quot;distinct conductors&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And that the current density is highest on the outside of the shield isn't relevant for most purposes. It's cancellation of fields, not magic skin effect barriers that are responsible for making our coax not radiate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-11-26T14:50:55.387" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9564" PostTypeId="2" ParentId="9560" CreationDate="2017-11-27T05:01:15.010" Score="1" Body="&lt;p&gt;I don't think anything specifically says that amateur radio transmissions are public and can be archived, and certainly nothing prohibits it, but if you read between the lines in the rules, this is implicit.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You are not allowed to make a profit from amateur radio transmissions, so copyright enforcement would not make sense.&lt;/li&gt;&#xA;&lt;li&gt;You are not allowed to obscure the meaning of amateur radio transmissions,  so preventing someone else from listening with encryption or scrambling is not legal and there is no expectation of privacy.&lt;/li&gt;&#xA;&lt;li&gt;If you witness a usage violation of amateur radio, a suggested method of complaining about it is to turn in a recording to the FCC, so this implicitly indicates that recording and archiving would be allowed if not encouraged.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2017-11-27T05:01:15.010" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9565" PostTypeId="1" CreationDate="2017-11-27T09:52:55.123" Score="1" ViewCount="94" Body="&lt;p&gt;What is the correct sign for &quot;;&quot; in morse?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FLdigi converts &quot;-.-.-.&quot; to &quot;;&quot; whereas in various code lookup tables I see &quot;-.-.-&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can both be used or is one of the morse codes valid?&lt;/p&gt;&#xA;" OwnerUserId="4555" LastActivityDate="2017-11-27T12:59:37.730" Title="&quot;;&quot; in morse &quot;-.-.-&quot; or &quot;-.-.-.&quot;?" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="0" ClosedDate="2017-11-27T16:16:38.080" ContentLicense="CC BY-SA 3.0" />
  <row Id="9566" PostTypeId="2" ParentId="9565" CreationDate="2017-11-27T12:39:44.703" Score="0" Body="&lt;p&gt;As far as I understand in &quot;International Morse Code&quot; the '&lt;code&gt;-.-.-&lt;/code&gt;' is used as &quot;Attention&quot; or &quot;start of message&quot;. Reference &lt;a href=&quot;https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.1677-1-200910-I!!PDF-E.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on a short search, it seems that '&lt;code&gt;-.-.-.&lt;/code&gt;' is commonly accepted as semicolon in &quot;International Morse Code&quot;, and is &lt;em&gt;likely&lt;/em&gt; correct. The Wiki &lt;a href=&quot;https://en.wikipedia.org/wiki/Morse_code#International_Morse_Code&quot; rel=&quot;nofollow noreferrer&quot;&gt;article&lt;/a&gt; seems to suggest the same, but is hardly authoritative without further reference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have not found an official publication for this, as the ITU-R document referenced does not mention this character. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even section 3 &quot;&lt;em&gt;Transmission of signs for which there is no corresponding signal in the Morse code&lt;/em&gt;&quot; does not suggest an alternative code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might have stumbled on a &quot;&lt;em&gt;not formally defined, but has a common practice&lt;/em&gt;&quot;, in which case I would choose '&lt;code&gt;-.-.-.&lt;/code&gt;' as your most likely candidate, as '&lt;code&gt;-.-.-&lt;/code&gt;' has an ITU-R definition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[EDIT]&#xA;I just found a duplicate question on this site, &lt;a href=&quot;https://ham.stackexchange.com/questions/7078/where-exactly-is-the-morse-code-character-defined&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2017-11-27T12:59:37.730" LastActivityDate="2017-11-27T12:59:37.730" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9567" PostTypeId="1" AcceptedAnswerId="9568" CreationDate="2017-11-27T17:51:11.690" Score="7" ViewCount="2110" Body="&lt;p&gt;APRS uses the AX.25 protocol which assumes the Bell 202 AFSK modulation scheme to generate the actual radio signal.  Is there any reason the same signal can't be generated directly with FSK without going through the audio frequencies?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My reading suggests that the advantage of AFSK is that the audio signal can be fed to any radio mike input.  But if we ignore that, and assume a transmitter where the frequency can be controlled directly, can this be done?  Would the signal be understandable to other APRS stations?&lt;/p&gt;&#xA;" OwnerUserId="10715" LastActivityDate="2017-11-29T00:14:57.987" Title="Is there a difference between AFSK and FSK for AX.25/APRS USE?" Tags="&lt;aprs&gt;&lt;modem&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9568" PostTypeId="2" ParentId="9567" CreationDate="2017-11-27T18:53:58.610" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;My reading suggests that the advantage of AFSK is that the audio signal can be fed to any radio mike input. But if we ignore that, and assume a transmitter where the frequency can be controlled directly, can this be done?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, and it is sometimes done for APRS on HF. (This is still &quot;to the mike input&quot;, but the radio is doing SSB instead of FM.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the perspective of theory of communications, this is not much different than RTTY. (However, it would be better to use a more efficient digital modulation and error-correction coding.)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Would the signal be understandable to other APRS stations?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It would not be understandable to AFSK-on-FM APRS stations, because it is a different modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider just one of the two tones — an unchanging tone going into a FM transmitter produces a varying frequency output. On the other end, If you attempt to receive a FSK signal with a FM receiver, you will get theoretically a square wave and likely in practice alternating polarity pulses (a high-pass-filtered square wave).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you decode that? Yes, but a standard TNC can't because it expects to do its own demodulation. (Insofar as FM and FSK are the same thing, a conventional APRS transmission is &lt;strong&gt;modulated twice&lt;/strong&gt; between the bit-stream and the radio wave.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-11-27T18:53:58.610" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9569" PostTypeId="2" ParentId="9567" CreationDate="2017-11-27T19:04:32.897" Score="5" Body="&lt;p&gt;AFSK sent over a FM radio is very different to FSK, as explained in my blog post &lt;a href=&quot;http://www.rowetel.com/?p=3799&quot; rel=&quot;nofollow noreferrer&quot;&gt;FM over FSK&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;FSK over FM is not FSK when you look at the over the air waveform. The spectrum is no longer two tones bouncing back and forth.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Assuming you have a FSK modulator that takes 0's and 1's as input, then you will not be able to generate the same signal as AFSK over FM. If you have a FM transmitter that modulates the RF frequency based on the input signal level, then you could drive that from you software FSK modulator and generate AFSK over FM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a generalised SSB style up-converter with enough bandwidth (like a HackRF), you could generate the AFSK signal in software, and use that to modulate a software based FM modulator, and up-convert that entire signal to RF.&lt;/p&gt;&#xA;" OwnerUserId="10716" LastEditorUserId="1362" LastEditDate="2017-11-27T21:29:06.333" LastActivityDate="2017-11-27T21:29:06.333" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9570" PostTypeId="2" ParentId="5009" CreationDate="2017-11-28T12:38:46.943" Score="-2" Body="&lt;p&gt;This is due to plasma frequency on the ionosphere. if the frequency of the signal is greater than Wpe it can not be bounce to the ground simply goes to space, if it is less than wpe the ionosphere reflect the signal.&lt;/p&gt;&#xA;" OwnerUserId="10726" LastActivityDate="2017-11-28T12:38:46.943" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9571" PostTypeId="2" ParentId="8908" CreationDate="2017-11-28T16:53:11.070" Score="-3" Body="&lt;p&gt;If the radials are a concern, consider using a J-pole so there won't be a need for radials. However, I think the bigger problem is the operating location. That balcony will pose a problem for any 2m/70cm antenna due to the close proximity of the safety rail and rebar in the concrete construction which is in the antenna's near-field. The antenna will of course radiate, but will not be as advertised from the vendor or in reference literature. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is difficult to say with any certainty what the pattern or gain will be without modeling the setup or taking measurements. Modeling the antenna in the operating environment will be somewhat complicated and requires specialized software/tools and a knowledge of the building and materials near the antenna. Taking field measurements is simpler, but will require help from a couple of friends in different locations with an S-meter.&lt;/p&gt;&#xA;" OwnerUserId="9162" LastActivityDate="2017-11-28T16:53:11.070" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9572" PostTypeId="2" ParentId="9567" CreationDate="2017-11-29T00:14:57.987" Score="2" Body="&lt;p&gt;FSK is a modulation where the instantaneous frequency corresponds to a binary baseband signal. Given:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$x_m(t)$ is the baseband signal, perhaps a binary square wave taking values of -1 and 1,&lt;/li&gt;&#xA;&lt;li&gt;$f_c$ is the carrier frequency&lt;/li&gt;&#xA;&lt;li&gt;$f_\Delta$ is the deviation, roughly speaking the spacing between tones&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;then the modulated signal $y(t)$ as a function of time is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;y(t)=\cos \left(&#xA;2\pi f_{c}t&#xA;+ 2\pi f_{\Delta }\int _{0}^{t}x_{m}(\tau )d\tau\right&#xA;) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not by accident, this is exactly the same definition for analog FM. The only difference being the baseband signal $x_m(t)$ is analog, instead of digital. That is, FM and FSK are the same modulation, just with different baseband signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For AFSK, the same equation applies, only the carrier frequency is something in the audio range. Then, it's fed into an FM modulator, which applies the modulation a second time. Even without doing the math you can imagine applying this modulation function a second time results in a very different transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, a USB transmitter does nothing to the modulation besides shift it up in frequency. Or in terms of the equation above, it effectively changes $f_c$. Thus, AFSK over USB is actually just FSK. This is what makes USB transceivers useful for implementing novel modulations like PSK31, JT65, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible to generate FSK with an FM transmitter by feeding the binary baseband signal into the audio input of an FM transmitter. It requires calibrating the audio gain, because &quot;too loud&quot; would mean too much deviation, or too wide a tone spacing. As an example, some of the MMDVM setups use this to modulate and demodulate DMR with an analog FM transceiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-11-29T00:14:57.987" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9574" PostTypeId="1" AcceptedAnswerId="9576" CreationDate="2017-11-29T10:09:32.360" Score="0" ViewCount="1263" Body="&lt;p&gt;Just getting up to speed on the ettus B210 - basically the same as the B200 but with two Rf boards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am testing using gnuradio-companion. I have setup a very simple transmitter consisting of:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Random Src --&amp;gt; PSK Mod --&amp;gt; UHD USRP Sink (port A:A)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This worked fine (I had some frequency / gain sliders). Then I wanted to try to transmit out of both Tx ports, so I tried the following:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Random Src --&amp;gt; PSK Mod --&amp;gt; UHD USRP Sink (port A:A, freq - 1MHz)&#xA;                   |&#xA;                   +-----&amp;gt; UHD USRP Sink (port A:B, freq + 1MHz)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;It runs, but only port A:A is transmitting and I see loads of &quot;SSSSSSSS&quot;'s in the debug. If I disable either UHD USRP Sink then the other port transmits fine (i.e. I can transmit out of each one individually perfectly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So how can I send two signals (or the same signal) over both tx port?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly - I want to run two different applications one controlling each port (lets say I run two different gnuradio-companion generated python files each set to different ports)... is this possible? All I got was an error saying that no device was available when I tried to run the second instance, so I guess this may not be possible...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;&#xA;New simpler setup:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;sig-src1(samp: 1M) --&amp;gt; USRP Sink (port A:A, freq 1.85G)&#xA;sig-src2(samp: 1M) --&amp;gt; USRP Sink (port A:A, freq 1.9G)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This is connected directly to a spectrum analyser.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the output I see:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Generating: '/home/user/src/gnu-radio/SimpleDualTx.py'&#xA;&#xA;Executing: /usr/bin/python -u /home/user/src/gnu-radio/SimpleDualTx.py&#xA;&#xA;linux; GNU C++ version 5.3.1 20151219; Boost_105800; UHD_003.009.002-0-unknown&#xA;&#xA;-- Detected Device: B210&#xA;-- Operating over USB 3.&#xA;-- Initialize CODEC control...&#xA;-- Initialize Radio control...&#xA;-- Performing register loopback test... pass&#xA;-- Performing register loopback test... pass&#xA;-- Performing CODEC loopback test... pass&#xA;-- Performing CODEC loopback test... pass&#xA;-- Asking for clock rate 16.000000 MHz... &#xA;-- Actually got clock rate 16.000000 MHz.&#xA;-- Performing timer loopback test... pass&#xA;-- Performing timer loopback test... pass&#xA;-- Setting master clock rate selection to 'automatic'.&#xA;-- Asking for clock rate 32.000000 MHz... &#xA;-- Actually got clock rate 32.000000 MHz.&#xA;-- Performing timer loopback test... pass&#xA;-- Performing timer loopback test... pass&#xA;Press Enter to quit: SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS&#xA;&amp;gt;&amp;gt;&amp;gt; Done (return code -9)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This runs, but only port A:B goes into transmit. If I disable either pair of sig-src and USRP Sink the it works fine.&lt;/p&gt;&#xA;" OwnerUserId="5427" LastEditorUserId="5427" LastEditDate="2017-11-30T08:45:21.700" LastActivityDate="2021-04-17T08:44:13.680" Title="Ettus B210 USRP Is it possible to transmit on both Tx Ports either with same or different application?" Tags="&lt;gnuradio&gt;&lt;transmitter&gt;&lt;usrp&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9575" PostTypeId="2" ParentId="4961" CreationDate="2017-11-29T16:55:59.267" Score="1" Body="&lt;p&gt;Let's say you pass your ham test on a Monday Morning,&#xA;The VE who handles submitting info to the FCC submits it the same day online.&#xA;If it's 12:40 P.M and the VE files it online. It is processed by the FCC's &quot;Automotive&quot; Grant system. There is no one who approves it; It's automatically approved by the system. The License Grants the moment it's filed. The FCC's website Refreshes every hour, and posts your call sign to your FRN accordingly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not a matter of FCC Holidays delays to weekend delays. The speed of your Grant depends on the Speed of the VE to file yours and everyone else's info, if they have passed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the time, the Trustee will be lazy and just have the paperwork with them in their vehicle to take home to file later on. Normally, You can expect them to file your and everyone else's info online in 1-3 business days, When one finds time to do it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FCC Statement: It's not a Matter of National Holidays or Weekends that delay the Grant speed. Its the VE who has control!&#xA;Once Your info is filed online, the Automotive FCC system automatically Grants and posts to your FRN. The FCC data base refreshes every hour, as previously mentioned.&#xA;If anyone told you it refreshed daily at midnight or 2 A.M or 6 P.M, like i've read online.... that's 100 percent incorrect!&#xA;The system refreshes every hour!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's what you can expect!&#xA;Ninety percent of the time you will get your license granted 1-4 days after testing depending on the VE's filing speed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's &quot;almost&quot; unlikely that the trustee will file your info online by the 5th, 6th, or 7th day, Yet there are some lazy people who think they can do it whenever because they know they have 20 days before people can call the FCC asking questions or complaining.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ten percent of those who don't get their license by the 7th day or later will most likely receive it by the 14th-20th day after testing &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because.....  Let's say you live in California:&#xA;to Mail a letter to Washington DC would take a couple more days than a letter being sent from, let's say, Texas or Florida.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, take note that, If your forms were mailed out by paper... Then the FCC has to Manually Process your info, and this takes a bit more time when they receive stacks of letters to sort threw. If your mail arrives at FCC headquarters, it can be there for days before someone gets to it and processes and posts it on the ULS.&#xA;There is a big reason why E-Filing Saves the FCC time and money, and for the convenience of the person who passed the exam to get on the air faster.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're still waiting and its the 9th-12th day....Expect it no faster than the 14th day, &#xA;and don't expect it no longer than the 20th day to be posted!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't see your license posted on the FCC's website with your FRN number, Contact them for help as there may be an issue. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, i know this may not be helpful but, if you know the VE and they do not like you from past GMRS experience, they will diffidently hold your file or send it by mail to give you a hard time. This happened to a friend of mine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are on the 10th day, i would just go ahead and stop checking online because it's most likely not going to post until the 14th Business day, not including weekends because it's most likely sent by mail, and they can't process on weekends manually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, I would go ahead and use the time your waiting to just start studying for your General License, So you're able to use your Technician license till the General -- it just updates your FRN and license info. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this helps, I have a friend who works the DEPT inside Filing and Amature HM DPT&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Till Then.... 73'z&lt;/p&gt;&#xA;" OwnerUserId="10740" LastEditorUserId="13927" LastEditDate="2019-03-28T05:32:20.847" LastActivityDate="2019-03-28T05:32:20.847" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="9576" PostTypeId="2" ParentId="9574" CreationDate="2017-11-29T21:19:20.030" Score="4" Body="&lt;p&gt;UHD requires a USRP to be owned by &lt;em&gt;one&lt;/em&gt; process only, so no, you can't share the same USRP across two flow graphs, but you could use for example the ZeroMQ PUB/SUB sink/source pair to stream data in from a second application to your first flow graph. But then again, there's nothing wrong with putting a whole flow graph into a hier block¹ and using that in another flow graph.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also: Throttle is &lt;strong&gt;never&lt;/strong&gt; right in a flow graph with hardware. You've got a device with a physical sampling rate to limit how much your computer produces. If you now add a software throttle, either that throttle is useless, or it does harm. That's why we (as in: I personally) added a very prominent warning to GRC that you shouldn't be having a hardware sink and a Throttle block in the same flow graph. Read the console output in the lower half of your GRC window!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;¹ hier block: hierarchical block. See the tutorials (in order!) on &lt;a href=&quot;http://tutorials.gnuradio.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://tutorials.gnuradio.org&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-11-29T21:19:20.030" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9577" PostTypeId="2" ParentId="3679" CreationDate="2017-11-30T09:14:50.167" Score="3" Body="&lt;h2&gt;Legality is a big issue.  Not to be ignored.&lt;/h2&gt;&#xA;&lt;p&gt;&lt;strong&gt;There is no legal way for you to do as you suggest in the USA.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;This radio is too powerful to be legal on FRS.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;You need a license for GMRS.  Applications are in the $90 range.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&lt;strong&gt;MURS provides exactly the kind of service you are asking about.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;MURS is license-free&lt;/li&gt;&#xA;&lt;li&gt;All MURS radios must be FCC Type-Certified for legal use in the USA&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Thus, the Chinese radios do not qualify as being legal for this service.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Here is more info on MURS:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.itstactical.com/digicom/comms/the-best-kept-secret-in-radio-communication/&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Best Kept Secret in Radio Communication&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Excerpt:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;License free, low cost, two-way communication. What’s not to love about MURS? MURS stands for Multi User Radio Service, and is one of the best kept secrets in personal and family radio communications.&lt;/p&gt;&#xA;&lt;p&gt;Formerly available only for business communications, the FCC has kept five MURS frequencies license-free and open for public use since 2000. Handheld radios broadcasting on MURS frequencies can experience a range of two miles to eight miles depending on terrain and obstructions, while MURS Base Stations can reach up to 20 miles.&lt;/p&gt;&#xA;&lt;p&gt;The stipulations for MURS use provided by the FCC restrict any transmitter in excess of two watts, but any type of antenna is allowed as long as the tower height (with antenna) is no greater than 60 feet high. All communications must also yield to any emergency communication on the same channel.&lt;/p&gt;&#xA;&lt;p&gt;The five MURS frequencies are listed below, The 154 MHz channels can be operated on the standard 25 kHz wide band or narrow band mode. The 151 MHz channels can only be operated in narrow band mode.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;code&gt;151.820 MHz&lt;/code&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;151.880 MHz&lt;/code&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;151.940 MHz&lt;/code&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;154.570 MHz&lt;/code&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;154.600 MHz&lt;/code&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Each of the five frequencies can not only transmit voice, but also data.&lt;/p&gt;&#xA;&lt;p&gt;Another hidden benefit of MURS frequencies are the PL codes (Private Line codes) or CTCSS (Continuous Tone Coded Squelch System) which are sub-audible tones that allow users to operate on the same channel without hearing chatter directed to other users.&lt;/p&gt;&#xA;&lt;p&gt;There are 38 PL codes available to each of the five MURS frequencies, which makes for a combination of 190 different MURS channels. While this is not encryption, anyone not operating with the same PL code won’t hear your conversation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&lt;strong&gt;Various legal radios can be obtained from &lt;a href=&quot;https://www.walmart.com/search/?query=murs%20radio&amp;amp;cat_id=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;the&lt;/a&gt; &lt;a href=&quot;https://smile.amazon.com/s/ref=sr_st_price-asc-rank?keywords=murs%20radio&amp;amp;rh=i%3Aaps%2Ck%3Amurs%20radio&amp;amp;qid=1512032746&amp;amp;sort=price-asc-rank&quot; rel=&quot;nofollow noreferrer&quot;&gt;usual&lt;/a&gt; &lt;a href=&quot;https://www.ebay.com/sch/i.html?_from=R40&amp;amp;_nkw=murs%20radio&amp;amp;_in_kw=1&amp;amp;_ex_kw=&amp;amp;_sacat=0&amp;amp;_udlo=&amp;amp;_udhi=&amp;amp;LH_BIN=1&amp;amp;LH_ItemCondition=3&amp;amp;_ftrt=901&amp;amp;_ftrv=1&amp;amp;_sabdlo=&amp;amp;_sabdhi=&amp;amp;_samilow=&amp;amp;_samihi=&amp;amp;LH_FS=1&amp;amp;_sadis=15&amp;amp;_stpos=92071&amp;amp;_sargn=-1%26saslc%3D1&amp;amp;_salic=1&amp;amp;_sop=15&amp;amp;_dmd=1&amp;amp;_ipg=50&quot; rel=&quot;nofollow noreferrer&quot;&gt;sources&lt;/a&gt;.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2017-11-30T18:41:31.903" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9578" PostTypeId="5" CreationDate="2017-11-30T09:24:17.170" Score="0" Body="&lt;p&gt;MURS is the Multi-Use Radio Service.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radios must be type-certified by the FCC for legal use in the USA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power not to exceed 2 Watts&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any kind of antenna system is permitted&lt;/p&gt;&#xA;&#xA;&lt;p&gt;5 Channels are allocated for this service:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 154 MHz channels can be operated on the standard 25 kHz wide band or narrow band mode. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 151 MHz channels can only be operated in narrow band mode.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;151.820 MHz&lt;/li&gt;&#xA;&lt;li&gt;151.880 MHz&lt;/li&gt;&#xA;&lt;li&gt;151.940 MHz&lt;/li&gt;&#xA;&lt;li&gt;154.570 MHz&lt;/li&gt;&#xA;&lt;li&gt;154.600 MHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Each of the five frequencies can not only transmit voice, but also data. &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2017-12-10T17:23:19.457" LastActivityDate="2017-12-10T17:23:19.457" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9579" PostTypeId="4" CreationDate="2017-11-30T09:24:17.170" Score="0" Body="MURS is the Multi-Use Radio Service in the United States.  It is license-free.  FCC Type-certified equipment is required for the use of this service.  5 VHF channels are allocated, with a multitude of subaudible tones to control squelch." OwnerUserId="8832" LastEditorUserId="76" LastEditDate="2017-12-11T19:08:12.910" LastActivityDate="2017-12-11T19:08:12.910" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9580" PostTypeId="2" ParentId="5009" CreationDate="2017-11-30T20:34:04.557" Score="2" Body="&lt;h3&gt; Physics of Ionospheric Reflection &lt;/h3&gt;&#xA;&#xA;&lt;p&gt;As you are probably aware, solar radiation ionizes atoms and molecules in the atmosphere at altitudes of about 50 km or so and above.  The densities of free electrons produced vary from between a billion and a trillion electrons per cubic meter, depending on altitude and time of day (see below).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/HoOAe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HoOAe.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Different regions of ion density are identified with letters (D, E, F), but the boundaries between regions are not that clearly defined.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To a first approximation, the different ion &quot;layers&quot; can be thought of as kinds of reflecting mirrors for RF, but this really isn't an adequate model to describe why different RF wavelengths are reflected differently.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, the reflection of an electromagnetic (i.e. RF) wave at any boundary depends on:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Permittivity&quot; rel=&quot;nofollow noreferrer&quot;&gt;permittivities&lt;/a&gt; of on either side of the boundary&lt;/li&gt;&#xA;&lt;li&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Permeability&quot; rel=&quot;nofollow noreferrer&quot;&gt;permeabilities&lt;/a&gt; on either side of the boundary&lt;/li&gt;&#xA;&lt;li&gt;The angle at which the incident wave approaches the boundary&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A complete description of how the wave gets reflected is provided by the &lt;a href=&quot;https://en.wikipedia.org/wiki/Fresnel_equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fresnel equations&lt;/a&gt;, which include expressions for the amount of energy reflected by waves that are polarized perpendicular and parallel with respect to the reflecting medium.  An example of the Fresnel reflectance (and transmittance) is shown below for a wave traveling in free space and impinging on glass, with a permittivity 1.5 times that of free space:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/R0z2Q.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/R0z2Q.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reflection by the ionosphere is more complex because, unlike glass, the reflecting medium has free electrons that are moving and colliding with each other.  This causes the permittivity of the ionosphere to vary with frequency.  A detailed derivation of why this is so can be found &lt;a href=&quot;https://www.google.com/url?sa=t&amp;amp;rct=j&amp;amp;q=&amp;amp;esrc=s&amp;amp;source=web&amp;amp;cd=1&amp;amp;ved=0ahUKEwiGlbuxhOfXAhUk0IMKHVyuDhEQFggpMAA&amp;amp;url=http%3A%2F%2Fwww.waves.utoronto.ca%2Fprof%2Fsvhum%2Fece422%2Fnotes%2F20c-ionosphere.pdf&amp;amp;usg=AOvVaw35joRiw4o2KGUkwFyoYw4F&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;, but suffice it to say that rather than being constant, the permittivity ($\epsilon$) at any point in the ionosphere is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\epsilon = \epsilon_0\left(1 - \frac{f_p^2}{f^2}\right)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $f_p$ is known as the &lt;em&gt;plasma frequency&lt;/em&gt; and $\epsilon_0$ is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Vacuum_permittivity&quot; rel=&quot;nofollow noreferrer&quot;&gt;permittivity of free space&lt;/a&gt;. The plasma frequency in turn depends on the local ion densities described above:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$f_p = \frac{1}{2\pi}\sqrt{\frac{Ne^2}{m_e\epsilon_0}} \approx 9\sqrt{N}$$ &lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $N$ is the electron density discussed above, $e$ is the electron charge (in Coulombs), and $m_e$ is the electron mass (in kg).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With these models, we can observe a few things:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;When $f$ (our operating frequency) is much higher than the plasma frequency at any given layer in the ionosphere, that layer &quot;looks like&quot; free space.  Therefore, the wave continues in the direction that it was traveling.  At the F layer - the densest layer in terms of electron density - the plasma frequency is around 2 MHz, which would yield an effective permittivity only a small fraction lower than that of free space at 2 meters, but something much different at 80 meters.  Recall that it is discontinuity of permittivity or permeability that generally drives reflection of an electromagnetic wave.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;When the plasma frequency is &lt;em&gt;greater&lt;/em&gt; than the operating frequency, the effective dielectric constant becomes negative.  A detailed description of what this implies can be found in the reference linked above, but suffice it to say that this leads to the wave decaying exponentially with distance and never really reaching anywhere.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In between the two extremes meaningful reflection occurs, and is described by the Fresnel equations.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h3&gt;Practical Communications Engineering&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;In RF communications engineering, the plasma frequency is referred to as the &lt;a href=&quot;https://en.wikipedia.org/wiki/Critical_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;critical frequency&lt;/em&gt;&lt;/a&gt;.  There are a number of other benchmark frequencies that are referred to by the ITU:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Maximum Useable Frequency (MUF)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two different types of MUF's that are discussed:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;An &quot;operational&quot; MUF&lt;/li&gt;&#xA;&lt;li&gt;A &quot;basic&quot; MUF&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The operational MUF that can provide acceptable service given specifics of the RF link (antenna gains, transmit power, receiver sensitivity, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The basic MUF is the highest frequency by which a radio wave can travel via ionospheric propagation alone, independent of power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some definitions of MUF are in terms of the the channel being available over some percentage of the month at a specific time (e.g. 90%).  A common rule of thumb is to estimate the MUF at about 3 times the critical frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The map below (from spacew.com) shows a contour of F2-layer MUF's (in MHz) by location for the time and date indicated (302015 UTC Nov 2017):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/M918f.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/M918f.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Lowest Useable Frequency (LUF)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Lowest Useable Frequency for a specified time period is the lowest frequency that can be used for communication on 90% of the days of the month.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Frequency of Optimum Transmission (FOT)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FOT relates to the availability of a particular geographic path.  It is the best working frequency expected to be useable for a specific time (e.g. 2000UTC) for a specified percentage (e.g. 50%) of the days of the month.&lt;/p&gt;&#xA;" OwnerUserId="9796" LastEditorUserId="9796" LastEditDate="2017-12-01T04:01:56.577" LastActivityDate="2017-12-01T04:01:56.577" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9581" PostTypeId="2" ParentId="5288" CreationDate="2017-11-30T21:20:04.527" Score="0" Body="&lt;p&gt;Multipath propagation will probably be the biggest impairment to the link.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You did not mention how far apart the transmitter and receiver will be nor whether you expect to be in dense or sparse traffic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In dense traffic with some separation between you and the other vehicle, you can assume that the signal you receive will consist of one direct path plus some number of multipath reflections:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$s(t) = a_0s_0(t-\tau_0) + \sum_{i=1}^{N}a_is_0(t-\tau_i)$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you will be dealing with something called &lt;a href=&quot;https://en.wikipedia.org/wiki/Delay_spread&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;delay spread&lt;/em&gt;&lt;/a&gt;. In an urban environment, you should expect a mean delay spread of around 1 $\mu$s and a total spread of up to 3 $\mu$s.&lt;sup&gt;1&lt;/sup&gt;  In a suburban environment, you can expect lower values:  around 0.5 $\mu$s and 2 $\mu$s, respectively.&lt;sup&gt;2&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Delay spread can cause inter-symbol interference (ISI).  I would guess at a 4800 baud rate you would be safe, but I think in the end it will depend on your channel bandwidth, modulation, and error control (if any).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1.&lt;/sup&gt; &lt;sup&gt;W.C.Y. Lee, &lt;em&gt;Mobile Communications Engineering&lt;/em&gt; (2nd ed.; McGraw-Hill, 1982), p.49&lt;/sup&gt;&lt;br/&gt;&#xA;&lt;sup&gt;2.&lt;/sup&gt; &lt;sup&gt;&lt;em&gt;Ibid.&lt;/em&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="9796" LastActivityDate="2017-11-30T21:20:04.527" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9584" PostTypeId="1" CreationDate="2017-12-02T16:17:19.220" Score="3" ViewCount="120" Body="&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/P8bnJ.png&quot; alt=&quot;APRS snap&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just recently started using APRSdroid, and I've been just looking at maps, and I've noticed that in my area there are spots with just a cluster of stations on top of each other (in this specific case, in the middle of a lake??).  I'm the car icon SW of the cluster.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is going on?  I've noticed a similar behavior another town over, but on land.  Are people all just saying that's their location for personal reasons or is there another reason?&lt;/p&gt;&#xA;" OwnerUserId="410" LastActivityDate="2017-12-03T16:09:12.030" Title="APRS: what is with stations clustered in the middle of a lake?" Tags="&lt;aprs&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9585" PostTypeId="2" ParentId="9543" CreationDate="2017-12-03T11:47:52.007" Score="4" Body="&lt;p&gt;It is helpful to understand the basic functioning of a coaxial cable. But first there are two important phenomenons that must be understood in order to proceed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Skin Effect&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When direct current (time invariant current) passes through a conductor it tends to uniformly use the entire cross sectional area of the conductor. When alternating current (time variant current) passes through a conducting material, it has a tendency to concentrate the current near the surfaces of the conductor. The occurs due to the changing direction of the magnetic field associated with the alternating current resulting in a back electromotive force that tends to push the conducting electrons towards the surface of the conducting material. As the frequency of the alternating current is increased, the crowding toward the surface becomes more pronounced. Since there is less conducting area, the resistance rises with frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a common conductor such as copper, the skin effect can be quite pronounced at typical amateur radio frequencies. For example, at 1 MHz, 63% of the current flows in the outer ~0.067 mm of a round copper wire. The current decreases exponentially and this 63% level is considered one skin depth. 98% of the current is contained in four skin depths (0.298 mm) from the surface of the wire. Past five skin depths, there is for all practical purposes no current flowing in the wire. Thus the center of the wire with a radius greater than five skin depths is essentially wasted material and can be removed (making a tubular shape) or replaced with other structural materials. We see the latter in amateur radio circles in the CopperWeld® brand of wire where the inner material is steel (for strength purposes) but with an outer copper coating (for RF purposes). If the thickness of the copper coating is at least 5 skin depths for the frequency in use, the RF current will never &quot;see&quot; the higher resistance steel core due to the skin effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Proximity Effect&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When alternating current flows through a conductor and this conductor is in close proximity to another conductor carrying alternating current, the current in the conductors will tend to be crowded into smaller regions of the conductor resulting in increased resistance. It is important to note that this is in &lt;em&gt;addition&lt;/em&gt; to the skin effect. Thus the proximity effect tends to further increase the effective resistance of the conductor beyond that of the skin effect alone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the two wires are carrying current in opposite directions, the crowding tends to occur on the surfaces of the wire that are closer together. If the current is flowing in the same direction, the crowding tends to occur on the surfaces that are further apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Coax Cable&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider a coax cable with an outer shield that is several skin depths thick and with an alternating current flowing only on the inner (center) conductor. The shield is completely disconnected for this description. The alternating current flowing in the center conductor develops a magnetic field around it. Since the outer shield conductor is several skin depths thick, there is practically no magnetic field developed within the outer conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can apply Ampere's Law to determine that the magnetic field of the inner conductor will induce an equal and &lt;em&gt;opposite&lt;/em&gt; current on the inside of the outer shield (this is a working example the proximity effect). The current on the inside of the outer conductor must close on itself so that the current flowing on the outside of the shield is the same as the current flowing on the inside of the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if we connect the shield as it would be used in the usual condition for an amateur radio application, we have current flowing on the outside of the shield (due to skin effect) that is fully cancelled out due to the opposite induced current from the inner conductor described earlier. This leaves us with only the current on the inside of the outer conductor. It should be clear from this description that the result of the current flowing only on the inside of the outer conductor is therefore a result of &lt;em&gt;both&lt;/em&gt; the skin effect and the proximity effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The net result is that the shield of the coax cable acts as an electrostatic shield that, for all practical purposes, does not allow the electromagnetic energy to radiate from the coax cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Common Mode Current on Coaxial Cable&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we now bring another conductor carrying an alternating current (such as an antenna element) in close proximity to the coax, it will induce a current in the shield. If the shield is several skin depths thick, none of this induced current will appear on the inside of the shield conductor (or anywhere else inside the coaxial cable) but rather it will flow on the outside of the shield due to skin effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this condition, we have two unique currents flowing on the shield of the coax – the current flowing on the inside of the shield that is generated by the transmitter connected to the coax as well as the current that is flowing on the outside of the shield due to magnetic coupling from the antenna. With sufficient thickness of the shield, these two currents do not “see” each other since neither will (effectively) pass through the center of the shield to interact with the other. This is quite different from say the reflected current that occurs due to a mismatched load where the forward and reflected currents do “see” each other and interact to create a standing current wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the two currents have no interaction along the length of the coax it is, for all practical purposes, as if they are traveling on separate wires. Thus when describing coaxial common mode current, the exterior of the shield is often described as the “third wire” of the coaxial cable. Of course this is simply a simile but it closely fits the observable characteristics.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-12-03T16:14:47.357" LastActivityDate="2017-12-03T16:14:47.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9586" PostTypeId="1" CreationDate="2017-12-03T15:31:19.993" Score="3" ViewCount="1820" Body="&lt;p&gt;I'm checking out cheap (~$100) mobile radios on Amazon, and often times there's a question asking about FFC Part 90 certification.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an amateur radio operator looking to use a radio for amateur/emergency uses, would I benefit from procuring a radio with Part 90 certifications, be hampered by it, or would it not apply?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect that Part 90 would hamper amateur use because of the mandatory lockout feature.  For example, the &lt;a href=&quot;https://powerwerx.com/db750x-dual-band-commercial-mobile-radio&quot; rel=&quot;nofollow noreferrer&quot;&gt;Powerwerx DB-750X&lt;/a&gt; requires an &lt;a href=&quot;https://powerwerx.com/db750x-programming-software-usb-cable-kit&quot; rel=&quot;nofollow noreferrer&quot;&gt;extra kit&lt;/a&gt; to fully unlock the radios capabilities ($40 at this time).&lt;/p&gt;&#xA;" OwnerUserId="4476" LastEditorUserId="4476" LastEditDate="2017-12-03T16:33:51.687" LastActivityDate="2017-12-19T05:45:45.573" Title="Is Part 90 certification something an amateur radio operator should look for in a radio meant for amateur use?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9587" PostTypeId="2" ParentId="9584" CreationDate="2017-12-03T16:09:12.030" Score="5" Body="&lt;p&gt;Two relevant facts about APRS:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;APRS stations are not obligated to get their location from GPS. And in practice, many fixed stations have manually entered locations.&lt;/li&gt;&#xA;&lt;li&gt;It is possible to transmit an explicitly coarse location (removing digits from the right).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I do not think that this can be a coarse location because I cannot reproduce that center of lake point by dropping digits (from a latitude and longitude expressed as degrees and decimal minutes, as APRS does). Nor is it the center (or corner) of a Maidenhead grid square.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, my best hypothesis so far is that it is FOR SOME REASON a deliberately entered location for those stations. Perhaps there is a local group which did not want to reveal their home addresses and they agreed they'd all use the lake as their location, as an obviously-not-real location.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-12-03T16:09:12.030" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9588" PostTypeId="2" ParentId="9586" CreationDate="2017-12-03T16:35:19.427" Score="7" Body="&lt;p&gt;Part 90 certification is required for radios used in the USA in the land mobile services - often called commercial radio. No such certification is required for the amateur radio service. The closest we come to certification is Part 15 for our receivers and Part 97 for our linear amplifiers - but only if in either case they are commercially produced and sold as a finished product.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You &lt;em&gt;may&lt;/em&gt;, however, benefit from Part 90 certification as it relates to frequency stability and the purity of the transmitter output. But as you already stated, you often lose out as it relates to ease of programming and other features desirable to amateurs. More often than not, a Part 90 radio is more expensive than a comparable amateur radio transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are in a situation where you need access to commercial radio communications, then a Part 90 radio is handy as you can use it for land mobile and amateur radio through proper programming. You cannot, however, legally use a non Part 90 amateur radio transceiver for land mobile services.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-12-19T05:45:45.573" LastActivityDate="2017-12-19T05:45:45.573" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9589" PostTypeId="1" CreationDate="2017-12-04T01:54:23.877" Score="1" ViewCount="221" Body="&lt;p&gt;I've been looking at getting a mobile radio recently, and the &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B06XCDWT6V&quot; rel=&quot;nofollow noreferrer&quot;&gt;BTech 25x4&lt;/a&gt; seems interesting.  it's at the high end of what I want to pay, and requires a separate purchase of a &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B017MT7IFG&quot; rel=&quot;nofollow noreferrer&quot;&gt;20 dollar programming cable&lt;/a&gt;.  Since I usually buy more than 1 of this type of thing (the cable), that seems to be quite expensive.  For comparison, the UV5R cable was $7 incl shipping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a number of USB-232 cables, some of which have custom ends on them for various devices, some just a DB9.  If I'm going to need a smattering of them, I'd rather the expensive/smart part be the same, and then just make physical adapters for the dumb part.  Makes logistics and troubleshooting easier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I recalled that there was some history regarding FTDI and drivers a few years back.  Looking that up, I see that there &lt;a href=&quot;https://hackaday.com/2014/10/22/watch-that-windows-update-ftdi-drivers-are-killing-fake-chips/&quot; rel=&quot;nofollow noreferrer&quot;&gt;have been&lt;/a&gt; quite &lt;a href=&quot;https://it.slashdot.org/story/16/01/31/1720259/ftdi-driver-breaks-hardware-again&quot; rel=&quot;nofollow noreferrer&quot;&gt;the shenanigans&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why would I want an authentic FTDI chip for &lt;strong&gt;&lt;em&gt;technical reasons&lt;/em&gt;&lt;/strong&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why would I ever want to send money to a company who pulled these kind of shenanigans?&lt;/p&gt;&#xA;" OwnerUserId="4476" LastActivityDate="2017-12-04T12:34:56.960" Title="Why do I want an authentic FTDI USB-232 chip? (Shenanigans)" Tags="&lt;radio-programming&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9590" PostTypeId="2" ParentId="9589" CreationDate="2017-12-04T02:29:11.777" Score="1" Body="&lt;p&gt;In short, the official driver for Windows has been rewritten to block illegitimate copies of the chipset from working.  (There are workarounds, which generally involve using older versions of the driver.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Under Linux, since the driver is open source, it has not been rewritten to block unofficial versions.  I can't comment about Mac OS X, since I don't use it regularly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use Linux, it doesn't matter if you use the official chipset (unless you feel an ethical reason), but with Windows, it is a lot simpler if you use the official chipset cables.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2017-12-04T02:29:11.777" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9591" PostTypeId="2" ParentId="9589" CreationDate="2017-12-04T10:47:31.723" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Why would I want an authentic FTDI chip for technical reasons?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;With the FTDI-supplied silicon containing several bugs already, my wild guess is that cheap knockoffs are really bug-ridden.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The likelihood that you encounter such a bug when really just using the thing to run a relatively low-speed UART is pretty much 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, as said, FTDI's products' popularity among users of USB-to-serial adapters is probably mostly due to the fact that they write &lt;em&gt;usable&lt;/em&gt; drivers. You want these drivers, you need to buy the original device (Plagiarism aside).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's a pretty good reason, actually. If your software depends on the particular driver, you depend on the particular device. I don't know if that's the case here, or whether the BTECH software simply uses the Windows COM: port emulation that FTDI's own driver, but every other (legitimate) USB-to-serial bridge manufacturer's driver offer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact that there are knock-offs that work with the same driver puts &lt;em&gt;someone&lt;/em&gt; in a position of breaking a driver license – don't know if that's you, the knock-off cable manufacturer or the software supplier. Not a lawyer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The point that FTDI (catastrophically) tried to make is that, you know, they developed something and now there's freeloader silicon manufacturers that just live off that, and that is bad for the original developer, and it's potentially bad for reliability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can't say I agree the slightest with how they went about telling the world, but I can understand that there's a slight chance that if you're using someone else's driver for your device, it's likely that &lt;em&gt;something&lt;/em&gt; might go wrong with your device at some point, because the people designing the driver aren't the ones who designed the silicon.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;By the way, if I had to find a source of a fake FTDI chip, it'd probably be proprietary programming cables from Chinese direct-import companies on amazon marketplace. So, don't think that just because it's 20 bucks and says FTDI, there's FTDI inside.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Other than that, &lt;a href=&quot;http://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP&lt;/a&gt; can directly support your device, and really just relies on a serial port. So, you can totally circumvent the ethical issue (of either supporting counterfeiters or supporting a company that bricks other people's devices) by buying a dedicatedly &lt;em&gt;non-FTDI&lt;/em&gt; and &lt;em&gt;non-FTDI-compatible&lt;/em&gt; USB-to-Serial adapter (there's plenty!), and just use that (needs to have a linux driver. Haven't seen that being a problem.).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2017-12-04T10:55:33.460" LastActivityDate="2017-12-04T10:55:33.460" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9592" PostTypeId="2" ParentId="9589" CreationDate="2017-12-04T12:34:56.960" Score="0" Body="&lt;p&gt;The original claim of FTDI is that the fraudulent chips did not implement the usb or serial protocols correctly, and did it in an extremely inefficient way, so that they had slow data transfers and dropped characters as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They wanted to block the fraudulent chips because they did not want to support the bugs in the bad chips and did not want their reputation smeared by another manufacturer's bad clone.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2017-12-04T12:34:56.960" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9593" PostTypeId="1" AcceptedAnswerId="9602" CreationDate="2017-12-05T02:16:38.093" Score="2" ViewCount="407" Body="&lt;p&gt;I'm just starter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I bought &lt;a href=&quot;https://www.radioworld.co.uk/mfj-1622_40-2m_apartment_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ-1622 40-2M APARTMENT ANTENNA&lt;/a&gt;&#xA;(I don't have access to the roof)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I only have RTL-SDR with Upconverter (I'm on budget). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I living on 10th floor and I will use it from my balcony.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Can I listen something with dongle without tuning this antenna ? &lt;/li&gt;&#xA;&lt;li&gt;Maybe RTL-SDR run from battery. Because of computer PSU ? Any suggestion for battery ? I need 5 V ? Any suggestion for accumulator (I will buy it later)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="10364" LastActivityDate="2017-12-06T03:11:10.297" Title="Apartment antenna and rtl-sdr with upconverter" Tags="&lt;hf&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9594" PostTypeId="1" CreationDate="2017-12-05T07:11:45.687" Score="5" ViewCount="155" Body="&lt;p&gt;&lt;strong&gt;I'm specifically focusing this question on methods to get official clarification where one doesn't currently exist. I am &lt;em&gt;not&lt;/em&gt; asking this audience for interpretations.&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As part of my volunteer work with &lt;a href=&quot;https://www.ready.gov/community-emergency-response-team&quot; rel=&quot;nofollow noreferrer&quot;&gt;CERT&lt;/a&gt;, we're exploring a number of communication scenarios in training, exercises, and responses in conjunction with the city government apart from when we have &lt;a href=&quot;http://www.arrl.org/ares-races-faq&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARES/RACES&lt;/a&gt; available. As you might guess from the above, our situation is touched on by several &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=a2368b7758ba56bae054db055f46dc7d&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5&quot; rel=&quot;nofollow noreferrer&quot;&gt;Part 97 rules&lt;/a&gt;, but not exactly on-point at least as far as we're able to interpret.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've exhausted, to the best of my ability, web searches including documents at the &lt;a href=&quot;https://www.fcc.gov/help/public-safety-tech-topic-13-amateur-radio-service-support-public-safety-communications&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC.gov&lt;/a&gt; and &lt;a href=&quot;http://arrl.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL&lt;/a&gt;, and documents like the &lt;a href=&quot;http://npstc.org/documents/NIFOG%20v1.2%204-14-2008.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;National Interoperability Field Operation Guide (NIFOG)&lt;/a&gt; and the &lt;a href=&quot;https://www.ntia.doc.gov/page/2011/manual-regulations-and-procedures-federal-radio-frequency-management-redbook&quot; rel=&quot;nofollow noreferrer&quot;&gt;National Telecommunications and Information Administration (NTIA) Red Book&lt;/a&gt;. &#xA;Posting our specifics may get a variety of armchair interpretations (with all due respect, we have plenty), but we're looking for authoritative sources.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where would I go next? Examples of someone's experience doing this and tips would be great.  &lt;em&gt;Even this may be overly opinion based, but here goes.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Directly to FCC? &lt;em&gt;Start with 888-CALL-FCC&lt;/em&gt;?&lt;/li&gt;&#xA;&lt;li&gt;ARRL, then possibly FCC?  &lt;em&gt;I don't see ARRL as authoritative, but may be a resource for helping obtain an authoritative answer that would benefit other groups across the nation.&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;A lawyer who would then assist in one of the above?&lt;/li&gt;&#xA;&lt;li&gt;Make a good faith attempt to document how we non-lawyerly types have interpreted the rules, and then engage in the conversation if someone comes knocking if we put it into practice?  &lt;em&gt;(I've got a long list of &quot;not quite the answer&quot; links so far on for our situation, but this doesn't seem like a long-term solution.)&lt;/em&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;To give a flavor of some of the complication of our situation, without asking for your help interpreting the rules:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;CERT is primarily volunteer, but we operate under mission numbers from the state. There's a big intersection here between government and amateur, and there may be specific rules that apply. &lt;/li&gt;&#xA;&lt;li&gt;FCC &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.403&quot; rel=&quot;nofollow noreferrer&quot;&gt;97.403&lt;/a&gt; is the most directly on point for our main mission, but it does not directly address training and exercises.&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/90.407&quot; rel=&quot;nofollow noreferrer&quot;&gt;90.407&lt;/a&gt; is even more specific, but for a different radio service.&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/90.411&quot; rel=&quot;nofollow noreferrer&quot;&gt;90.411&lt;/a&gt; mentions civil defense activities, including simulated emergency, including drills and tests.  However, this is a different radio service.&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=9c871c7bfeef2ab34651e859c5ace865&amp;amp;mc=true&amp;amp;node=se47.5.97_1111&amp;amp;rgn=div8&quot; rel=&quot;nofollow noreferrer&quot;&gt;97.111&lt;/a&gt; touches on aspects of us, given this is about relief actions (2), emergency communications (3), and our missions would be on behalf of local government - though section (4) mentions RACES.&lt;/li&gt;&#xA;&lt;li&gt;And then we stray into limited use of amateur radio stations in emergency situations, exercises/drills, or training by non-HAMs. Typically these are HTs in a defined and controlled location, with licensed Hams on-channel and in charge as part of incident command. This is open to interpretation whether in the specific circumstances they can be considered control operators, very broadly covered in (&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=98b1c9c78968a6359d9bb71194533774&amp;amp;mc=true&amp;amp;node=se47.5.97_17&amp;amp;rgn=div8&quot; rel=&quot;nofollow noreferrer&quot;&gt;97.7&lt;/a&gt; and &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.105&quot; rel=&quot;nofollow noreferrer&quot;&gt;97.105&lt;/a&gt;) and station control (&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=98b1c9c78968a6359d9bb71194533774&amp;amp;mc=true&amp;amp;node=se47.5.97_1109&amp;amp;rgn=div8&quot; rel=&quot;nofollow noreferrer&quot;&gt;97.109&lt;/a&gt;).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8863" LastEditorUserId="8863" LastEditDate="2017-12-05T18:41:45.943" LastActivityDate="2017-12-06T09:29:13.923" Title="How to get professional or official clarification of FCC Part 97 rules for specific complicated situations?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9595" PostTypeId="2" ParentId="9547" CreationDate="2017-12-05T08:16:51.920" Score="2" Body="&lt;p&gt;I applaud you for wanting to learn how to potentially improve your AIS station. As others have commented, your questions can yield a response the size of a textbook but here are a few pointers to get you started. Perhaps some experimenting will lead you to post further questions for this forum which will help others with their understanding as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You didn't give a detailed description of your station configuration so for the purposes of this answer, I will assume that you have your SDR connected to a 50 ohm coax cable that heads towards your antenna where it is plugged into the output of the preamp. On the input side of your preamp you have a 75 ohm to 300 ohm balun connected to your horizontally strung folded dipole antenna. If this in inaccurate, correct me with a comment in response to this answer and I will adjust my answer as appropriate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Receiver Noise Level&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your SDR generates some noise within its own electronics. While the designers take care to reduce the power and spectrum of this noise, it cannot be entirely eliminated. In fact, even a simple resistor will generate a small level of noise (called Johnson-Nyquist noise) that varies with its temperature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The noise generated by the SDR is often called the noise floor of the receiver. You can roughly measure this noise by removing the coax cable from your SDR and substituting a 50 ohm, non-inductive resistor (any wattage will do) across the input of your receiver. Then observe that there are no signals on your SDR display but only noise &quot;bubbling&quot; on the bottom of the spectrum. Take note of where the peaks of this noise land on the spectrum display. Your display will typically show dBm as the vertical scale. This is a relative indication of the noise power. Record this reading for future reference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is really only an approximation because your computer is connected to the SDR and it is probably contributing some level of noise itself. But since they are both required to make a functioning receiver, you can practically view this as the noise floor of your receiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Your Coax Cable&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally your terminated coax cable (or any transmission line) should not, on its own, pick up any signals. But life is not perfect so it is always good to check out if your coax cable is doing its job. To do this, reconnect the coax cable to your SDR and disconnect the far end of the cable from the preamp and substitute your 50 ohm resistor for the preamp. Power down the preamp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Recheck your waterfall display to make certain there are no discernible signals present and that your noise floor is about the same as what you previously measured. If you spot any significant changes, start checking your coax for bad connections or for a break somewhere in the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Your Preamp&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A preamp will generate some of its own noise. This is unavoidable although the higher the quality of the preamp, generally the lower the contributed noise. You can test the amount of noise your preamp contributes by reconnecting the preamp to the coax cable,powering it up, and placing your resistor on the input of the preamp where the antenna would normally connect. The unused UHF input of your preamp should &lt;em&gt;always&lt;/em&gt; be terminated with a resistor (300 or 75 ohm as appropriate) to limit additional noise contribution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the inputs of the preamp terminated with resistors, remeasure the noise floor of your receiver. Any increase in noise is attributable to the preamp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Your Antenna&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You stated that you are using a folded dipole for reception. Normally these are used in a horizontal configuration. The ships that are transmitting their AIS signals have vertically polarized antennas. This &lt;em&gt;cross polarization&lt;/em&gt; of antennas can easily result in a 10-20 dB loss in received signal strength. While you could restring your dipole in a vertical fashion and carefully route the feedline away in a perpendicular direction, you would probably have much better success with a simple vertical antenna. At 162 MHz, a quarter wave, ground plane, vertical antenna is only ~1.5 feet (44 cm) tall. A quarter wave sleeve antenna would also make a very good choice. You could also construct a slightly more sophisticated vertical antenna that gives additional gain. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the loss of this cross polarization could be greater than the gain of your preamp, it would be worth experimenting with a different antenna. You may find that you can eliminate the preamp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Filters and Noise&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many sources of &quot;noise&quot;. Our atmosphere and the galaxies around us contribute noise of their own. Most of this noise stays well below 100 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most troubling noise to those of us using receivers is man-made noise. This constantly increasing noise floor comes from LED power supplies, computers, washers, dryers, furnaces, routers, wall warts, etc. In general though, most of this noise drops off below 100 MHz or so. There can certainly be man made noise above 100 MHz but it is not common nor generally dominant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there are interfering signals. These generally originate from intentionally generated RF signals. It could be the signal itself that interferes or it can be a mixing of these signals (&quot;intermod&quot;, short for inter-modulation) that cause the interference. These types of signals are generally not considered &quot;noise&quot; since they result in a very narrow band signal. These would generally appear as narrow spikes on your SDR display.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Intentionally generated signals can also create noise that can interfere with your desired signals. But the services that are operating around your intended received frequency are fairly tightly regulated by the FCC and are likely not to exhibit these characteristics. With that being said, I have been called into situations where the regulated transmitter was indeed &quot;dirty&quot;. There are also less common effects where a tower or other structure generates the offending signal - often called a &quot;rusty nail&quot; problem. But this is a digression from your question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Interfering signals can also be generated by your preamp when it is overloaded with a strong signal even if it is not on the same frequency. The preamp will internally create other signals that would otherwise not be present. You can detect this by bypassing and powering down the preamp and checking the waterfall display again. If the undesired spikes are still present but of lower signal strength, it is not your preamp that is causing it - it is simply amplifying an existing signal. If the offending spike is completely gone, then you may begin to suspect your preamp.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding a filter in advance of your preamp will reduce the bandwidth that your preamp will amplify and this can reduce interfering signals. But a filter will not reduce noise or interfering signals that are already present on the frequency in which you are interested. A filter will always introduce some additional loss of a few dBs but if the filter is warranted, this is usually a reasonable trade-off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After experimenting with the other factors described, if you feel a filter is warranted, you will find several on-line filter engineering programs or you can download free programs like Elsie to help you design a filter. There are many experienced engineers and practitioners on this site that can help with pointers if you get stuck.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-12-05T08:22:40.420" LastActivityDate="2017-12-05T08:22:40.420" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9596" PostTypeId="2" ParentId="9593" CreationDate="2017-12-05T13:22:37.423" Score="1" Body="&lt;p&gt;You can power your Rtl-Sdr from a battery in addition to the power supplied by the computer. In some case it is even necessary:&#xA;I have a Rtl-Sdr with an E4000 tuner that doesn't work when only powered by my Raspberry Pi 1. It needs more power than what the raspberry can supply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this, I use a Y-USB-cable, like the one you find on some external hard drives. On one side you put your Rtl-Sdr, on the other side there are 2 USB connectors, one for the data that you connect to the PC and an additional power-only connector you can connect to a USB power source. In my case a 12V lead battery with a 5V linear regulator when I power my raspberry from a battery, a simple phone charger otherwise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this setup, it will still take some power from the computer. I don't know if you can remove the +5V line from the data connector to only power from the other source. For the regulator, a dc-dc regulator might give longer battery life (nice for solar powered stuff like my Rtl-Sdr project), but a linear one will be less noisy as this is your main concern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe just use a good quality USB cable with good shielding and a ferrite core. I effectively get USB noise on my Rtl-Sdr, but it seems to come mainly from the data transfer, not the power supply.&lt;/p&gt;&#xA;" OwnerUserId="5586" LastActivityDate="2017-12-05T13:22:37.423" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9597" PostTypeId="2" ParentId="9594" CreationDate="2017-12-05T21:19:44.487" Score="5" Body="&lt;p&gt;The ARRL itself is not a law firm, but might be able to refer you to an attorney or lawyer with experience in federal communications law and FCC regulations who can appropriately advise you, and even legally represent you if needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Interpretation of random posts, web pages, or even published federal bulletins as legally authoritative by people without appropriate legal training and experience is fraught with possible dangers/risks.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2017-12-05T21:30:02.440" LastActivityDate="2017-12-05T21:30:02.440" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9598" PostTypeId="1" AcceptedAnswerId="9603" CreationDate="2017-12-05T22:13:23.657" Score="9" ViewCount="1641" Body="&lt;p&gt;In Morse code, hams use &quot;hi&quot; to indicate a laugh, and &quot;es&quot; to mean &quot;and&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where did these abbreviations come from? Both being all dots, they are short and easy to send and easy to recognize, but why these particular abbreviations?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, we use &quot;de&quot; instead of &quot;this is&quot; for similar reasons of brevity, but it's easy to see where this one comes from: &quot;de&quot; means &quot;from&quot; in Spanish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My personal guess for &quot;hi&quot; is that it just &lt;em&gt;sounds&lt;/em&gt; funny when you hear it, and almost brings to mind the rhythm of the old phrase &quot;shave and a haircut, two bits. But I could be quite mistaken; there must be more to it than that. And I have no clue where &quot;es&quot; came from.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would anyone know?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;hi hi tks es 73 de WJ6V dit dit&lt;/p&gt;&#xA;" OwnerUserId="4808" LastEditorUserId="4808" LastEditDate="2017-12-07T21:02:19.843" LastActivityDate="2019-04-03T11:44:03.327" Title="What was the origin of the Morse code abbreviations &quot;hi&quot; and &quot;es&quot;?" Tags="&lt;cw&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9600" PostTypeId="1" AcceptedAnswerId="9601" CreationDate="2017-12-05T22:59:01.593" Score="7" ViewCount="380" Body="&lt;p&gt;Sometimes when operating CW I want to send numbers that are negative.  In particular when operating outdoors during the winter and someone asks the temperature, I would like to come back in CW with -5C.  For some events like Freeze Your Butt Off, the temperature is a required part of the exchange.  I realize that almost always the temperature in Fahrenheit will be above zero, but as a Canadian Ham I would prefer to use Celsius.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best I have come up with so far is to send &lt;em&gt;M5C&lt;/em&gt;, but I am not sure that this will be well understood.&lt;/p&gt;&#xA;" OwnerUserId="355" LastActivityDate="2018-01-14T19:16:05.163" Title="How do I send negative numbers or below zero in CW?" Tags="&lt;cw&gt;" AnswerCount="3" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9601" PostTypeId="2" ParentId="9600" CreationDate="2017-12-05T23:24:26.597" Score="6" Body="&lt;p&gt;According to &lt;a href=&quot;https://en.wikipedia.org/wiki/Morse_code&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia&lt;/a&gt; there is a code for the hyphen or the minus symbol, &lt;code&gt;− · · · · −&lt;/code&gt;.  However very few hams are likely to recognize it.  In the meantime I would suggest sending &quot;MINUS&quot; or &quot;NEG&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If &quot;Freeze Your Butt Off&quot; ever grows to become a big-time contest, then contesters will work out some efficient way of communicating negative numbers.  (Or maybe most everyone will just send &quot;dah&quot; as the &quot;cut number&quot; for zero, similar to the way most signal reports in Morse code contests are &quot;5NN&quot;.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-12-05T23:24:26.597" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9602" PostTypeId="2" ParentId="9593" CreationDate="2017-12-06T00:07:10.683" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Can I listen something with dongle without tuning this antenna?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. Tuners &lt;em&gt;can&lt;/em&gt; help with receiving with an antenna of an otherwise unsuitable length, but it is absolutely worth trying without them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a useful rule: Watch the spectrum and unplug the antenna. If this causes the visible signal level all across the spectrum to go down, then you had plenty of signal from the antenna and there is no need to improve it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it did &lt;em&gt;not&lt;/em&gt; go down very much, then you'll get better reception by improving your antenna system — whether by an antenna of a different length, a tuner, a LNA, or another means.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Maybe RTL-SDR run from battery. Because of computer PSU ? Any suggestion for battery ? I need 5 V ? Any suggestion for accumulator (I will buy it later)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;DO NOT&lt;/strong&gt; wire a separate 5 V supply, whether battery or otherwise, into your USB connection unless you are willing to risk damaging the USB port/motherboard you plug it into by back-feeding power to it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The minimum safe way to do this is to use a &lt;strong&gt;USB hub&lt;/strong&gt; which accepts external power. The more-isolating way is to use a &lt;strong&gt;USB isolator&lt;/strong&gt; to separate the power connections completely. USB isolators are unusual and therefore expensive equipment, however.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option is to get a computer that does not produce significant noise. Different models can vary widely.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2017-12-06T03:11:10.297" LastActivityDate="2017-12-06T03:11:10.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9603" PostTypeId="2" ParentId="9598" CreationDate="2017-12-06T02:22:04.877" Score="12" Body="&lt;p&gt;Many Morse abbreviations and conventions come from before the days of radio, and we are relative latecomers to the game compared to the telegraphy guys. For this question, I found &lt;a href=&quot;http://ethw.org/w/images/b/bf/Morse_Telegraphy_1920.pdf&quot; rel=&quot;noreferrer&quot;&gt;an old reference here&lt;/a&gt; from a 1920 Morse Telegraphy manual where the ES abbreviation is shown in the old American code as being the code for the ampersand character &amp;amp;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is quite likely that this is the source for the ES = AND abbreviation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, the HI abbreviation seems to have originated from the telegraph abbreviation HEE (usually repeated as HEE HEE) for laughter. I have heard HEE used more than HI on air, but that was largely due to listening to old G3s and G2s back in the day. I found &lt;a href=&quot;https://ipfs.io/ipfs/QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco/wiki/Morse_code_abbreviations.html&quot; rel=&quot;noreferrer&quot;&gt;one reference that mentions it here&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2017-12-06T12:37:19.530" LastActivityDate="2017-12-06T12:37:19.530" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9604" PostTypeId="2" ParentId="9594" CreationDate="2017-12-06T09:20:46.880" Score="0" Body="&lt;p&gt;So, it boils down to what you are planning of using in regards to radio communications.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;&lt;p&gt;Either you are licensed to use certain equipment on certain&#xA;  frequencies.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Or you are not licensed.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you are not licensed, your choices will be:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;CB&lt;/li&gt;&#xA;&lt;li&gt;FRS&lt;/li&gt;&#xA;&lt;li&gt;MURS&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you are licensed you can use equipment/frequencies as your license stipulates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact that you are training or executing an exercise will not change your situation, the licensed/unlicensed still applies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have two or more licensed Radio Amateurs in your group, then these licensed Amateurs can use equipment and frequencies as stipulated by their license. But not just everyone, only those who are licensed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have two or more people with a GMRS license, then they can use GMRS. but not others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best way to go forward is to figure out what exactly is needed, then see if you have people with the appropriate licenses or not. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that this is a broad answer, but it is a broad question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are stuck, here is what you can do:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;find a lawyer with experience in this field (&lt;em&gt;this has now been mentioned multiple times in comments and answers, hopefully you get the idea that interpretation of law is done by a lawyer, and it seems that you are stuck on determination which articles are applicable for you, and how to interpret those articles. Really you need someone who has the appropriate legal education and qualification to help you&lt;/em&gt;)&lt;/li&gt;&#xA;&lt;li&gt;pick up the phone and call the FCC, but likely they will quote the regulations you already found.&lt;/li&gt;&#xA;&lt;li&gt;find your local ARES/RACES group, and hand off all communication to the licensed ops. (&lt;em&gt;In my part of the world this is actually done regulary, we get involved, and we put our training to good use&lt;/em&gt;)&lt;/li&gt;&#xA;&lt;li&gt;as this is CERT, and therefore on behalf of a government function, push the problem to the government representative, they should provide adequate comms including licenses if this is needed&lt;/li&gt;&#xA;&lt;li&gt;hire a commercial outfit who handle comms&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2017-12-06T09:29:13.923" LastActivityDate="2017-12-06T09:29:13.923" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9607" PostTypeId="1" CreationDate="2017-12-07T15:53:01.780" Score="5" ViewCount="399" Body="&lt;p&gt;I believe most of us know about the ionosphere, and skywave propagation, but I'm kind of tripping up on the D-layer. If the ionospheric D-layer absorbs HF signals (40 meters, for example) during the day, how does my signal at night reach another station in, say, Australia, who's in daylight? Shouldn't the signal be absorbed by the D-layer before it reaches him? And if it is, how is it that HF signals can go long-path or reach the other side of the globe?&lt;/p&gt;&#xA;" OwnerUserId="9166" LastEditorUserId="76" LastEditDate="2017-12-07T16:14:26.243" LastActivityDate="2017-12-23T01:49:57.890" Title="How is it possible for an HF signal to go around the world when part of it must be in sunlight?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;ionosphere&gt;&lt;long-path&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9608" PostTypeId="2" ParentId="9607" CreationDate="2017-12-07T16:36:51.663" Score="6" Body="&lt;p&gt;The D region does not affect all HF (3 MHz to 30 MHz) in the same way.  For low frequencies, 2 to 4 MHz, the D region absorbs most signals during the sunlight times of the day.  However, somewhere around the 3.5 to 4.5 MHz zone, the absorption starts to fall off as frequency is increased and these signals will penetrate the D region and reach the E region where they are reflected back to Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the frequency of signals increases more, reaching 10 MHz and beyond, the attenuation caused by the D region falls significantly and signal strengths improve.  Also, signals will penetrate further into and thru the E region reaching the F1 region as frequency increases more and again such signals are reflected back to Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, attenuation of signals (absorption by D-region) affects those signals of the 160 and 80 meter band mostly with some lesser attenuation taking place at 40 meter band at some times but usually this is not nearly as strong as the lower frequencies.  Above the 40 meter band, essentially no attenuation by the D-layer.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2017-12-07T16:36:51.663" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9609" PostTypeId="2" ParentId="9607" CreationDate="2017-12-07T18:06:03.790" Score="3" Body="&lt;p&gt;There is also &lt;em&gt;gray-line propagation&lt;/em&gt;, where signals can travel around the world &lt;em&gt;at the circular dusk/dawn annulus&lt;/em&gt;. In that region, it is neither totally dark nor totally light. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Long-Path&lt;/strong&gt; QSOs are usually made following the path of this grayline (shown below). However, QSOs via the shortest path is more common than long-path (which has greater attenuation). Hams have worked DX for over 100 years using this...&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;In the period before, during, and after &lt;strong&gt;Sunset&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;In the period before, during, and after &lt;strong&gt;Sunrise&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It is not unusual to hear the same station with an echo on it. That's usually caused by receiving the short path signal first, followed by the delayed long-path signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/O5Cug.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O5Cug.png&quot; alt=&quot;Grayline region&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-12-07T20:06:47.383" LastActivityDate="2017-12-07T20:06:47.383" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9610" PostTypeId="2" ParentId="7081" CreationDate="2017-12-08T12:34:42.733" Score="1" Body="&lt;p&gt;Below is a graphic showing the free space radiation pattern envelope and input Z of an end-fed, 1/2-wave (EFHW) antenna, for the other conditions shown there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation pattern maximum field is centered on the physical center of the antenna, but the pattern in this graphic was shifted to the left so as better to show the nulls off the ends of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;NOTE:  Antennas and transmitters both are two-terminal devices, and will supply/radiate almost no energy if only one of their terminals is connected. The short, so-called counterpoise conductor of an &quot;end-fed&quot; antenna in reality means that this configuration is an off-center-fed dipole, as stated in the graphic.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mprSM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mprSM.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2017-12-08T17:25:50.410" LastActivityDate="2017-12-08T17:25:50.410" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9611" PostTypeId="1" AcceptedAnswerId="9624" CreationDate="2017-12-08T16:23:59.283" Score="5" ViewCount="568" Body="&lt;p&gt;Right, not directly ham radio related, but this puzzles my ham brain.  I have several TVs connected to a distribution amp connected to an outside antenna.  All but one work fine, and the one won't pull in the strong stations, but does fine with the weaker ones.  If I unscrew the F so that only the center conductor touches, it gets the strong stations as well.  I've been trying to come up with an explanation, but have failed so far.  I tried disconnecting all the other TVs (thinking it's a ground loop or something) with no success.  What would cause that and how would I fix it?&lt;/p&gt;&#xA;" OwnerUserId="9974" LastEditorUserId="76" LastEditDate="2017-12-08T16:52:09.190" LastActivityDate="2017-12-11T17:31:03.950" Title="TV strong station has no signal when coax is connected" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;antenna-system&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9612" PostTypeId="2" ParentId="9611" CreationDate="2017-12-08T17:09:08.163" Score="5" Body="&lt;p&gt;I'm not at all sure about the exact situation, but I predict that you will find that the cable between the distribution amplifier and this particular TV set is damaged.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, when you omit the shield connection to a coaxial cable, it starts operating more like an unshielded single wire — a monopole antenna, if the other end is disconnected. For example, if you have a piece of coaxial cable that is not connected on either end, and connect it to a receiver (using a F, RCA, or &quot;UHF&quot; connector, or other type with a protruding center pin), it will function as an antenna until the shield makes contact and then it will be silent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your cable works better without the shield connection, that strongly suggests that there is damage which means that it cannot function as a proper coaxial cable but can function as &quot;a piece of wire&quot;, and the TV signal works in that case because of some combination of direct capacitive coupling and antenna behavior.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-12-08T17:09:08.163" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9613" PostTypeId="2" ParentId="9611" CreationDate="2017-12-08T18:28:03.817" Score="5" Body="&lt;p&gt;You may be overloading the front end of the &quot;faulty&quot; TV, creating adjacent channel interference or some other kind of distortion.  The loss you introduce by only loosely coupling the receiver may be bringing down the signal level to a point where it is no longer impairing the receiver.  The fact that a distribution amp is inline with your television probably plays a role in your problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used to work for a company that supplied tuners for digital televisions and I have worked personally with TV manufacturers in Japan, Korea, China, and the U.S. I can tell you that there is huge variation in the quality of DTV front ends.  The performance standards that TV sets need to meet in the U.S. are minimal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a standard for receiver performance called &lt;a href=&quot;https://www.atsc.org/recommended-practice/a74-receiver-performance-guidelines/&quot; rel=&quot;nofollow noreferrer&quot;&gt;A/74&lt;/a&gt;, but compliance is not mandatory for TV sets.  Compliance was mandatory for the so-called &quot;coupon&quot; converter boxes, but testing at my company's lab identified major manufacturers who weren't complying, including LG and a company that manufactures for Walmart.  We met with the FCC, several Congressmen, and a Senator to raise the issue.  Everyone was polite, but no one did anything - even though tax-payer dollars were subsidizing non-compliant boxes.  So if that was the industry response to a standard that &lt;em&gt;was&lt;/em&gt; mandatory, you can imagine the response to one that isn't.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if the set meets or exceeds all ATSC performance standards, it still is no guarantee that there wouldn't be a problem.  It's possible that all of the sets meet A/74, but the problem set doesn't have as much margin. &#xA; There is a really good overview of interference mechanisms at work for ATSC &lt;a href=&quot;https://ham.stackexchange.com/questions/9611/tv-strong-station-has-no-signal-when-coax-is-connected&quot;&gt;here&lt;/a&gt;.  The author (Charlie Rhodes), who is very well respected in the industry, makes the case that even if standards are adhered to, they may not be adequate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some distribution amps have a variable gain setting.  If you have it set to the max (or even if not), you might try backing the gain down a little and seeing if that improves the situation without losing the signal on your other sets.&lt;/p&gt;&#xA;" OwnerUserId="9796" LastEditorUserId="9796" LastEditDate="2017-12-11T17:31:03.950" LastActivityDate="2017-12-11T17:31:03.950" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9614" PostTypeId="2" ParentId="9611" CreationDate="2017-12-09T13:56:24.060" Score="2" Body="&lt;p&gt;Looks like a massive overdrive of the receiver's input (frontend).&#xA;To validate I'd suggest to (experimentally) attach some potentiometer (wiper shorted to one end) parallel to the receiver's input. Thus you would be able to variably load the incoming signal - bringing the level down.&#xA;Looks a bit as if the frontend were stuck at it@ highest gain - any means of attenuation (some AGC) being inoperational.&lt;/p&gt;&#xA;" OwnerUserId="10852" LastActivityDate="2017-12-09T13:56:24.060" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9615" PostTypeId="2" ParentId="9600" CreationDate="2017-12-09T14:22:28.490" Score="1" Body="&lt;p&gt;The dash (-....-) would be the usual way to denote negative numbers.&#xA;If some HAM does not easily decode this: well, it's time to improve your capabilities :)&lt;/p&gt;&#xA;" OwnerUserId="10852" LastActivityDate="2017-12-09T14:22:28.490" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9616" PostTypeId="2" ParentId="9598" CreationDate="2017-12-09T14:27:34.803" Score="1" Body="&lt;p&gt;In German, &quot;hihihi&quot; is the transcript of the sound of giggling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Which could be transcribed as heeheehee in the English language.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus the theory of &quot;hee&quot; 'mutating' to &quot;hi&quot; might hold. &lt;/p&gt;&#xA;" OwnerUserId="10852" LastActivityDate="2017-12-09T14:27:34.803" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9617" PostTypeId="1" CreationDate="2017-12-09T20:56:40.923" Score="1" ViewCount="321" Body="&lt;p&gt;I was thinking of creating a 2.4 GHz WiFi wireless link with a directional, circular polarized antenna but I am not sure if that would work for such a long distance. The antenna cant weigh more than 1 pound which is a major limitation.&#xA;I appreciate any suggestions&lt;/p&gt;&#xA;" OwnerUserId="10856" LastActivityDate="2017-12-14T14:27:11.360" Title="What is the optimal antenna for a high altitude weather balloon?" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;wifi&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9618" PostTypeId="1" CreationDate="2017-12-09T21:46:55.890" Score="0" ViewCount="92" Body="&lt;p&gt;What kind of hardware/circuitry would be needed for a device to be able to transmit and receive over a range of frequencies at once?&lt;/p&gt;&#xA;" OwnerUserId="10855" LastActivityDate="2017-12-09T23:37:30.200" Title="Are there receivers and transmitters that can be tuned to multiple frequencies at once?" Tags="&lt;receiver&gt;&lt;frequency&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2017-12-10T18:59:41.003" ContentLicense="CC BY-SA 3.0" />
  <row Id="9619" PostTypeId="1" CreationDate="2017-12-09T23:20:51.917" Score="7" ViewCount="2138" Body="&lt;p&gt;Can I talk on 2 meters from the east coast to the west coast without using repeaters?&lt;/p&gt;&#xA;" OwnerUserId="10857" LastEditorUserId="76" LastEditDate="2017-12-11T19:11:06.473" LastActivityDate="2017-12-13T03:15:38.093" Title="Can I talk 2 Meter VHF across the United States" Tags="&lt;antenna&gt;&lt;united-states&gt;&lt;propagation&gt;" AnswerCount="6" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9620" PostTypeId="2" ParentId="9618" CreationDate="2017-12-09T23:37:30.200" Score="1" Body="&lt;p&gt;A software-defined radio (SDR) with appropriate programming can transmit and receive multiple signals inside a given band.&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2017-12-09T23:37:30.200" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9621" PostTypeId="2" ParentId="9619" CreationDate="2017-12-09T23:49:56.200" Score="6" Body="&lt;p&gt;There is a list of &lt;a href=&quot;http://www.arrl.org/distance-records&quot; rel=&quot;noreferrer&quot;&gt;distance records&lt;/a&gt; on the ARRL website. Looking at these, I would say that it might be technically possible to hold the absolute minimum of what could be called a ‘contact’ (e.g. callsign and signal report exchange) across such a distance perhaps once every ten or twenty years when exceptional conditions are all in alignment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer the second part of the question, all very long distance contacts on VHF are made using highly directional antennas, or an array of such antennas (such as a &lt;a href=&quot;http://qrznow.com/2m-yagi-beam-antenna-144-mhz-10-element-super-light-high-gain-owl-gt/&quot; rel=&quot;noreferrer&quot;&gt;multi-element Yagi&lt;/a&gt;, and usually take place in CW (Morse code) or possibly SSB (single sideband, voice).&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-12-09T23:49:56.200" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9622" PostTypeId="2" ParentId="9617" CreationDate="2017-12-10T00:07:11.403" Score="4" Body="&lt;p&gt;2.4 GHz is most definitely not the way to go, unless you very much know what you're doing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The free-space path loss over a fixed distance increases with the square of your frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whilst one could argue that an antenna with fixed area would at the same time increase its directivity with the square of frequency, this doesn't help you very much, because it'll be very hard to steer an antenna on a floating balloon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, go for lower frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that I'm really not saying that you can't use the 2.4 GHz band at all - one could very easily implement a transponder that uses dsss with a massive spreading factor, and just work at an extremely low rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Paired with a high tower and thus, line-of-sight channels and little interference, this could work well (I'm not making this up. I know 2.4GHz systems that operate nlos over multiple km with maybe 20dBm). But your wording, your use of the tag &quot;wifi&quot; and the overall tone suggested you expect existing consumer standards to work - bad news, they won't.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-12-10T00:07:11.403" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9623" PostTypeId="2" ParentId="9617" CreationDate="2017-12-10T15:16:52.917" Score="4" Body="&lt;p&gt;I've never launched a balloon, but I'd guess gravity would keep the antenna oriented vertically so circular polarization is unnecessary weight. If you did want circular polarization, put it on the ground station. It will mean a 3 dB penalty to your link budget.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;Free space path loss&lt;/a&gt;, with $r$ being the distance in meters, and $f$ the frequency in Hz, is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{r(\mathrm{dB})} =&#xA; P_{t(\mathrm{dB})}&#xA; + G_{t(\mathrm{dB})}&#xA; + G_{r(\mathrm{dB})}&#xA; + 147.6&#xA; - 20 \log_{10} (rf) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$P$ is the transmit power and $G$ the receiver and transmitter gains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;WiFi transmit power might be 1 watt, or 30 dBm at most (local regulations and equipment capabilities vary). A monopole antenna on the balloon may have a gain of 5 dBi, at the optimal orientation. The distance to the balloon is at a minimum 20,000 meters, if it's not very high, and directly overhead. And a reasonable directional WiFi antenna at the ground station might be 20 dBi. So:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \begin{align}&#xA; &amp;amp;30\:\mathrm{dBm}&#xA; + 5\:\mathrm{dBi}&#xA; + 20\:\mathrm{dBi}&#xA; + 147.6\\&#xA; &amp;amp;- 20 \log_{10} (20,000 \cdot 2,400,000,000)\\&#xA;&amp;amp;= -71\:\mathrm{dBm}&#xA;\end{align}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would work, assuming an otherwise quiet environment, and you can reasonably point the ground antenna in the right direction. As a rule of thumb, WiFi requires a received signal strength of:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;-60 dBm: excellent signal (typical design goal for commercial installations)&lt;/li&gt;&#xA;&lt;li&gt;-70 dBm: good signal&lt;/li&gt;&#xA;&lt;li&gt;-80 dBm: marginally working, at reduced data rates and with some packet loss (probably sufficient for basic telemetry)&lt;/li&gt;&#xA;&lt;li&gt;-90 dBm: buried in the noise floor, will not work at all&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Keep in mind, this is a &lt;em&gt;best case&lt;/em&gt; estimation. In reality:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the balloon will probably be farther away (if it's &lt;a href=&quot;https://ham.stackexchange.com/a/7628/218&quot;&gt;below the horizon&lt;/a&gt;, losses are very much higher and I doubt it will work at all)&lt;/li&gt;&#xA;&lt;li&gt;there will be some noise (microwaves, neighbor's WiFi equipment, etc)&lt;/li&gt;&#xA;&lt;li&gt;the antennas may not be aligned optimally&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Improving the antenna gain with a larger dish on the ground or a collinear array would provide additional margin. If you have an amateur radio license and the right equipment, you may be able to operate at higher powers and on a &lt;a href=&quot;https://en.wikipedia.org/wiki/13-centimeter_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;frequency not available for public use&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll have to run these numbers for the maximum distance you expect, and add some &quot;fade margin&quot; to account for noise, misalligned antennas, etc. Before launching the balloon you should get some attenuators and test the equipment at the expected signal levels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're unable to make it work, and assuming you need just basic one-way telemetry, WiFi is not really the best way to go. The slower the data rate, the less power is required, and WiFi is probably far faster than you need. WiFi also requires bidirectional communication to send acknowledgements, which means added complexity and weight on the balloon. Using a lower frequency will make aiming the antenna less critical.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-12-14T14:27:11.360" LastActivityDate="2017-12-14T14:27:11.360" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9624" PostTypeId="2" ParentId="9611" CreationDate="2017-12-10T15:20:06.783" Score="3" Body="&lt;p&gt;Problem resolved.  I put a splitter in before the amp and put the problem TV on one output and the input of the amp on the other.  Now all TVs have all the appropriate channels.  I could probably have accomplished the same with an attenuator on the TV itself, but I don't have one so I went with the no-cost solution.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2017-12-10T15:20:06.783" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9625" PostTypeId="2" ParentId="9619" CreationDate="2017-12-10T17:22:51.470" Score="4" Body="&lt;p&gt;I believe that you could do so via EME - &lt;a href=&quot;https://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Earth_communication&quot; rel=&quot;nofollow noreferrer&quot;&gt;Earth-Moon-Earth&lt;/a&gt; - communication, or &quot;moonbounce&quot;.  There are tons of resources dealing with moonbounce &lt;a href=&quot;https://www.dxmaps.com/eme.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding is that it has been done before (and is maybe done regularly) on 2 meters via EME while operating within FCC limitations. &lt;/p&gt;&#xA;" OwnerUserId="9796" LastEditorUserId="9796" LastEditDate="2017-12-10T22:11:05.827" LastActivityDate="2017-12-10T22:11:05.827" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9626" PostTypeId="2" ParentId="9619" CreationDate="2017-12-10T19:22:11.910" Score="2" Body="&lt;p&gt;For all practical purposes, &lt;/p&gt;&#xA;&#xA;&lt;h2&gt;NO.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;It would take a gigantic antenna array, a lot of power, and very exceptional conditions indeed! As Scott nicely explained, &lt;a href=&quot;https://ham.stackexchange.com/a/9621/8717&quot;&gt;&quot;Once every ten or twenty years&quot;&lt;/a&gt; is exactly right, and is almost the equivalent of a &lt;strong&gt;NO&lt;/strong&gt; answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would almost never happen on FM, and &lt;em&gt;definitely&lt;/em&gt; not from a mobile!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This 2 meter antenna array was built by Dave Olean K1WHS, in Maine (&lt;a href=&quot;http://directivesystems.com/144-mhz/&quot; rel=&quot;nofollow noreferrer&quot;&gt;owner of Directive Systems and Engineering&lt;/a&gt;), a long-time 2m DXer and EME op. He had that stacked and phased very-low-angle array pointed down the east coast during a 2m contest a few years ago. IIRC, even with two different kinds of exceptional propagation enhancements taking place simultaneously, &lt;strong&gt;and&lt;/strong&gt; the fact that some of the farthest stations that he worked was because some of the signals were over water, he never even made it all the way down the east coast*. &lt;em&gt;And most of the 2m stations he was working had towers, high-gain arrays, and linear amplifiers as well!&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*(Having said that, with that nice array Dave heard so many stations that it sounded like a contest on 20 meters! :-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you see what kind of challenge you face if you want to work from coast-to-coast on 2 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TBLnZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TBLnZ.jpg&quot; alt=&quot;K1WHS stacked 2m array1&quot;&gt;&lt;/a&gt;  &lt;a href=&quot;https://i.stack.imgur.com/wq00V.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wq00V.jpg&quot; alt=&quot;K1WHS stacked 2m array2&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-12-13T03:15:38.093" LastActivityDate="2017-12-13T03:15:38.093" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9627" PostTypeId="2" ParentId="7849" CreationDate="2017-12-10T21:32:16.647" Score="2" Body="&lt;p&gt;FORGET the third &lt;strong&gt;horizontal&lt;/strong&gt; (yellow) loop antenna!&lt;/p&gt;&#xA;&lt;p&gt;I finally disabled mine because it caused me no end of trouble with noise pickup and thousands of spurious signals sent to the BT (Blitzortung) servers in Europe. Although it appears in the official documentation, I have not been able to find &lt;em&gt;anyone&lt;/em&gt; who is using one. Most are using just two vertically-polarized loops 90 degrees apart. That's all that are needed.&lt;/p&gt;&#xA;&lt;p&gt;A better way is to have three H-field (magnetic) loops, all vertical, 60 degrees apart. (That's what I intend to do.) Several BT stations are using ferrite rods purchased from the BT people in a delta configuration.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;In the forum, the developers have since retracted any recommendations for a horizontal loop. It was one of those &quot;Well, it seemed like a good idea at the time&quot; things.&#xA;&lt;p&gt;I now have two Blitzortung lightning receiver stations, 1977 and 2294. If you are a participant you can see the antenna on &lt;a href=&quot;https://forum.blitzortung.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://forum.blitzortung.org&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-07-07T22:55:45.303" LastActivityDate="2020-07-07T22:55:45.303" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="9628" PostTypeId="2" ParentId="9619" CreationDate="2017-12-10T22:03:17.410" Score="0" Body="&lt;p&gt;Aside from the very rare cross-continent band openings mentioned elsewhere in answers here, you can do precisely what you say using intermediary services such as IRLP (the Internet Radio Linking Project), Allstar, or Echolink (these need not necessarily be used via repeaters), but the Internet is being used as a transport between the two ends.  Even HF communications aren't consistently reliable coast to coast in North America; the continent is just too wide once you get north of the Gulf of Mexico.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2017-12-10T22:03:17.410" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9629" PostTypeId="2" ParentId="9619" CreationDate="2017-12-11T18:35:30.503" Score="5" Body="&lt;p&gt;Sometimes a VHF signal &lt;strong&gt;can&lt;/strong&gt; be heard clearly, thousands and thousands of miles away! The usual mechanism is &lt;a href=&quot;http://www.engineeringradio.us/blog/2010/05/e-skip-tropospheric-ducting-and-other-vhf-propagation-phenomena/&quot; rel=&quot;noreferrer&quot;&gt;tropospheric ducting&lt;/a&gt;. It's an essentially &lt;strong&gt;random, temporary occurrence&lt;/strong&gt;, not something you can rely on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a &lt;strong&gt;reliable&lt;/strong&gt; means of direct communication, you can &lt;strong&gt;not&lt;/strong&gt; expect to talk from east coast to west coast on the 2m band without using repeaters. VHF is not practical for use at distances like that, which would be in the range of 2000–3000 miles beyond the horizon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF &lt;em&gt;can&lt;/em&gt; propagate &lt;a href=&quot;https://ham.stackexchange.com/questions/7265/how-does-vhf-uhf-propagate-beyond-the-expected-radio-horizon&quot;&gt;beyond its basic &quot;radio horizon&quot;&lt;/a&gt;, primarily due to scattering. However, if you look at the charts in that link, you'll see that at a distance of &lt;strong&gt;only 500 miles&lt;/strong&gt; there is already &lt;strong&gt;about 240 dB of path loss&lt;/strong&gt; you'd need to overcome.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the legal limit of 1500W, you could transmit a 60 dBm signal. Let's say you need a -130 dBm signal for successful receipt. (This would be an &quot;S3 signal&quot;. For VHF, S9 is defined as -93 dBm and each S-unit is 6dB.) Since 60  dBm [the transmitted power] minus 240 dBm [the path loss] is -180 dBm, you need 50 dBm of additional gain to meet that -130 dBm goal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To put this in perspective, consider this &lt;a href=&quot;http://www.antennas-amplifiers.com/2m-High-gain-Yagi-144-MHz/144MHz-XPOL-Antenna-PA144-XPOL-28-9&quot; rel=&quot;noreferrer&quot;&gt;10 meter long, 14 element Yagi&lt;/a&gt; — it's advertised to have 16.63 dBi of gain. Put one of those at each end and you're still almost 18 dB short. You might be able to add a pre-amp at the receiver, but only if the signal is still above the noise at that location. (Since we were aiming for only an S3 signal, I'm not sure how good the chances of that would be!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suppose you might use two parabolic dishes each in the realm of 14–16 meters in diameter to get 50 dBm of gain but remember we started with the situation at only 500 miles. The United States is &lt;strong&gt;about 7 dB wider&lt;/strong&gt; than that — probably even more so as far as path loss goes. So now we're talking dishes in excess of 20m diameter, at minimum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short, trying to use &lt;strong&gt;reliable&lt;/strong&gt; atmospheric scattering of 2m signals across the United States is probably harder than bouncing your signal off the moon, i.e. sending your signal out a distance of 1.2 light-seconds and then receiving, after it has travelled that distance &lt;em&gt;back&lt;/em&gt; again, whatever manages to reflect off the lunar surface! (&lt;a href=&quot;https://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Earth_communication&quot; rel=&quot;noreferrer&quot;&gt;Earth-Moon-Earth communication&lt;/a&gt; has between 251 and 253 dB of path loss.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Unless, as another commenter points out, your antennas are reeeeeeeeally high. Plugging two 500,000 ft high antennas into &lt;a href=&quot;http://www.qsl.net/kd4sai/distance.html&quot; rel=&quot;noreferrer&quot;&gt;KD4SAI's VHF/UHF Line of Sight Calculator&#xA;&lt;/a&gt; gives you a nice 2000 mile line-of-site distance. The &lt;a href=&quot;https://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;noreferrer&quot;&gt;Friis path loss&lt;/a&gt; is only about 146 dBm at that range. So, raising the stations to about 95 miles high at each end &lt;em&gt;does&lt;/em&gt; give you a much more auspicious start, link-budget-wise — if you spend enough on the mast, you could use fairly cheap antennas ;-)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2017-12-11T19:49:27.653" LastActivityDate="2017-12-11T19:49:27.653" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9630" PostTypeId="1" CreationDate="2017-12-12T03:50:27.427" Score="4" ViewCount="320" Body="&lt;p&gt;When listening to our local repeater, which is now a combined P25/analog machine, every once in a while my squelch opens to a blast of digital noise. I've noticed this problem with at least two different Baofeng radios (a UV-3R+ and a UV-82). I have a receive tone set (146.2) so during a digital QSO I should hear nothing, just see a receive light, which is mostly what happens. But when it breaks through it's not just a momentary annoyance, the squelch stays open for the duration of that transmission - and a QSO which breaks squelch once often does it more than once - so the radio just ends up turned off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Essentially, we can no longer monitor our local repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are others having the same problem, and if so, is it with P25 specifically or do other digital modes sometimes break tone squelch on analog radios? Is it related to the tone in use, perhaps a harmonic of the audio frequencies P25 modulates, and if so what tones are safe to use with P25? Is it sloppy tone filtering on the part of our ultra-cheapie analog radios or does it affect &quot;quality&quot; analog radios as well? Is it an odd interaction with the Baofeng squelch tail elimination or some other &quot;feature&quot; of the radio that's on by default, or even just a firmware bug affecting just a few radios? Or is it on the transmit side with somebody's P25 radio transmitting out of spec or somehow configured to send an analog tone on a digital transmission (is that even possible?) and the repeater is passing it through?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, am I the only one experiencing this (as indicated by the dearth of results in my googling) and I just need to replace these old non-firmware-upgradeable clunkers?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks, and 73&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2017-12-12T13:28:50.443" Title="Why does P25 occasionally break through tone squelch on my analog HTs?" Tags="&lt;digital-modes&gt;&lt;baofeng&gt;&lt;squelch&gt;&lt;p25&gt;&lt;tone-squelch&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9632" PostTypeId="2" ParentId="9630" CreationDate="2017-12-12T13:28:50.443" Score="1" Body="&lt;p&gt;It could be a bug in the repeater controller (it's perfectly possible to transmit digital data with a PL tone), but I'd suspect the Baofengs as your problem.  They're not the best radios, and they're priced accordingly.  Borrow a better HT (ideally Icom, Yaesu or Kenwood, but Alinco makes pretty good handhelds too although they're harder to find) and see if it does the same thing for you.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2017-12-12T13:28:50.443" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9633" PostTypeId="2" ParentId="9619" CreationDate="2017-12-12T14:56:05.230" Score="2" Body="&lt;p&gt;While this answer is not about crossing the USA/continent, there has been long distance attempts cross-Atlantic on the 2 meter band, the following will give you some info on what was attempted:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last serious attempt was in 2014, this &lt;a href=&quot;http://www.brendanquest.org/home.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;crowd&lt;/a&gt; used an &lt;a href=&quot;http://www.brendanquest.org/antenna.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;43-element yagi&lt;/a&gt; to cross the Atlantic in order to qualify for the &lt;a href=&quot;http://www.irts.ie/cgi/st.cgi?brendan&quot; rel=&quot;nofollow noreferrer&quot;&gt;Brendan Award&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: the Brendan award has never been awarded, so it will be pretty amazing if a group actually manages to do a 2-way QSO crossing the Atlantic, within the rules of the award.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is amazing, that this crowd actually managed a one-way signal at their last attempt, 3840 KM. Unfortunately this was not qualified under the Brendan rules, as you can read in the &lt;a href=&quot;http://www.brendanquest.org/epilogue.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;epilogue&lt;/a&gt;. Basically the signal was bounced off the ISS passing at the exact same moment of the (one-way) signal. As the ISS is a man-made object in space, this was excluded from the application for a Brendan Plate (the &quot;plate&quot; would have been awarded for the one-way contact if not for the ISS bounce.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this will give you some information in regards long-distance QSO's on the 2-meter band. It is all about amps, antenna, and mode, and a good bit of luck.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2017-12-12T15:06:53.533" LastActivityDate="2017-12-12T15:06:53.533" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9634" PostTypeId="2" ParentId="9215" CreationDate="2017-12-13T12:14:39.093" Score="2" Body="&lt;p&gt;The bcd code for 60 metres is the same as 40 metres. (03 Hex) 0A is the code for 6 metres.&#xA;I used a Arduino and monitored the output (HEX on LCD) while winding the radio tuning knob through the whole of the radios frequency range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a table showing the decoded output for an Australian Model FT-857D&#xA;If you look at the Begin / End Frequency you can find the Binary / Hex output for the bands. (ie: 60 metres and 40 metres is Bin 0011 or 03 Hex)&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;General Coverage  &#xA;&#xA;   BeginMhz  EndMhz  BINARY HEX  &#xA;      0.100   0.499   1101  0D  &#xA;      0.500   1.499   1110  0E  &#xA;      1.500   2.499   0001  01  &#xA;      2.500   4.449   0010  02  &#xA;      4.500   7.449   0011  03  &#xA;      7.500  10.449   0100  04  &#xA;     10.500  14.449   0101  05  &#xA;     14.500  18.449   0110  06  &#xA;     18.500  21.499   0111  07  &#xA;     21.500  25.499   1000  08  &#xA;     25.500  32.999   1001  09  &#xA;     33.000  56.000   1010  0A  &#xA;     76.000 108.000   1011  0B  &#xA;    118.000 137.000   1011  0B  &#xA;    137.000 164.000   1011  0B  &#xA;    420.000 470.000   1100  0C  &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="10867" LastEditorUserId="10867" LastEditDate="2018-01-16T23:50:13.123" LastActivityDate="2018-01-16T23:50:13.123" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9635" PostTypeId="2" ParentId="7719" CreationDate="2017-12-14T15:53:17.780" Score="1" Body="&lt;p&gt;According to the &lt;a href=&quot;http://www.ariss.org/uploads/1/9/6/8/19681527/k9jkm_2012_symposium_ver2.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;PDF that Duston mentioned&lt;/a&gt;, your UNPROTO path should be &lt;code&gt;CQ VIA ARISS&lt;/code&gt;.  &lt;code&gt;WIDE2-2&lt;/code&gt; would cause your packets to be repeated twice if terrestrial digipeaters should hear them.  Presumably you're using the ISS VHF APRS frequency 145.825 MHz rather than the North American terrestrial APRS frequency 144.39 MHz, so &lt;code&gt;WIDE2-2&lt;/code&gt; packets shouldn't be unnecessarily digipeated, but &lt;code&gt;WIDE2-2&lt;/code&gt; would be incorrect.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-12-14T15:53:17.780" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9636" PostTypeId="1" CreationDate="2017-12-14T20:07:31.717" Score="2" ViewCount="136" Body="&lt;p&gt;&lt;strong&gt;Background info:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I own an SDR (model &quot;SDRPlay RSP1&quot;) and I have a fully working HDSDR software system installed on my PC.  I can successfully use this to tune-in to my local airport's radio traffic and identify individual transmissions from specific aircraft that I can follow on the FlightRadar website (although the audio quality is fuzzy and indistinct for all but very close aircraft).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using a fairly cheap, portable discone antenna, which sits inside the front window of my house (I cannot put it on the roof for about 47 reasons I won't go into).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ETsc2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ETsc2.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am currently studying for my Ham licence in the UK and I'd like to get some experience listening to some &quot;normal&quot; Ham traffic (voice and CW would be of main interest).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;My problem:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am having a great deal of difficulty actually finding &lt;em&gt;anything&lt;/em&gt; to listen to on the air.  I have used the RSGB band plan (2017) to attempt to find radio users communicating on a lot of different frequencies, but I'm rapidly realising that I must doing it all wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Things that I think might be wrong with my setup:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Poor location for the antenna (upstairs bay window, no good solid ground plane near it).  It's sitting on a wooden windowsill in a brick building.&lt;/li&gt;&#xA;&lt;li&gt;User error in operating the system.  I'm a newbie, but I can understand that I need to set my RX bandwidth to match the modulation and band type that I'm interested in.  I understand the waterfall graph and how to size the bandwidth to  encompass the full extent of the transmission.&lt;/li&gt;&#xA;&lt;li&gt;Is the UK simply not very active in Ham bands? (doubtful)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Finally, the questions:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like there's nothing to listen to, apart from FM national radio (obnoxiously loud and clear), Airband (sporadic, weak, garbled and frankly a bit boring) and the occasional walkie talkie on the building site over the street (highly entertaining but not likely to improve my Ham skills).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the problem likely to be the lack of a real physical ground-plane for my antenna?  Is it an unsuitable antenna?  Or is it my lack of skill in driving the HDSDR software?  Or something else?  Perhaps my house is a pretty decent Faraday cage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;&#xA;After a few days of nothingness, I finally managed to find a rag-chew on 432,121 kHz FM.  I was hearing both sides of the conversation (a fascinating discussion on the relative merits of Japanese vs Norwegian winter driving regulations).  The accents were familiar to me as locals.  The audio was pretty dire quality, a lot of hiss which I was able to mitigate somewhat by messing with the bandwidths and applying NR filters.  Managed to get the names of both people and one of the callsigns.  Looked up the callsign and he's based about 10-15 miles from me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I thought that was pretty awesome, even though it's not exactly a DX :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the band has gone quiet again.  I'm starting to think that my antenna placement is no good.&lt;/p&gt;&#xA;" OwnerUserId="6744" LastEditorUserId="6744" LastEditDate="2017-12-20T19:21:35.603" LastActivityDate="2017-12-20T19:21:35.603" Title="How to find transmitting (voice and CW) Amateur stations in UK?" Tags="&lt;software-defined-radio&gt;&lt;dipole&gt;&lt;united-kingdom&gt;" AnswerCount="1" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="9637" PostTypeId="2" ParentId="9636" CreationDate="2017-12-15T01:50:53.380" Score="5" Body="&lt;p&gt;The UK band plan for the 2m (VHF) band can be found &lt;a href=&quot;http://rsgb.org/main/operating/band-plans/vhf-uhf/144mhz-band/&quot; rel=&quot;noreferrer&quot;&gt;here on the RSGB website&lt;/a&gt;. In the UK, the 2m band is between 144.000MHz and 146.000MHZ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of note is the section 145.5935 - 145.7935MHz, which are the repeater outputs. Depending on where you are in the UK, there should be at least one repeater that you can here there. Whether or not there is any activity is another matter! If you listen on every channel between those frequencies for more than 15 minutes, you should hear &lt;em&gt;something&lt;/em&gt;. If only because all repeaters send their ident in morse code every 15 minutes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, the 70cm UHF band also has repeaters, with outputs in the section 432.994 – 433.381MHz (this is from the &lt;a href=&quot;http://rsgb.org/main/operating/band-plans/vhf-uhf/432mhz-band/&quot; rel=&quot;noreferrer&quot;&gt;RSGB band plan for the 70cm band&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would recommend that you also try listening on the HF bands, as these can be very busy, and tend to be longer range than VHF and UHF. For local stations (i.e. within your region of the UK), try the 40m and 80m bands. For international traffic, day and night, try the 20m band. The frequencies for these bands can be found on &lt;a href=&quot;http://rsgb.org/main/operating/band-plans/hf/&quot; rel=&quot;noreferrer&quot;&gt;the RSGB's band plan for HF bands&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck with your listening! We all started like this, and it's a fun part of the hobby.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-12-15T01:50:53.380" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9638" PostTypeId="2" ParentId="7691" CreationDate="2017-12-16T04:33:19.100" Score="2" Body="&lt;p&gt;I bought the RSP2, and it suffers from AM broadcast band interference on HF bands, even with the AM/FM filter on. I have a 1Kw transmitter at 1350KHz about 4 Km from my house, and it bleeds thru on all HF, however when you select a ham band it seems better ??? Anyway, I am building a high pass filter to cut out anything below 2 MHz, there is no other option. Or you can buy one. I love the receiver, no regrets, if I lived further from the transmitter I wouldn't have any issues.&lt;/p&gt;&#xA;" OwnerUserId="10879" LastActivityDate="2017-12-16T04:33:19.100" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9641" PostTypeId="2" ParentId="1695" CreationDate="2017-12-19T05:55:40.020" Score="1" Body="&lt;p&gt;I found that the stock Baofeng antenna with counterpoise actually performs slightly better than the Nagoya 771. The Nagoya with a counterpoise is slightly better still and is the configuration I use most of the time. The Baofeng seems to benefit more from a counterpoise than does my TYT UV8000H. So, at least with Baofeng HT's, a counterpoise seems to be the best way to immediately improve TX performance.&lt;/p&gt;&#xA;" OwnerUserId="10884" LastActivityDate="2017-12-19T05:55:40.020" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9642" PostTypeId="1" CreationDate="2017-12-19T12:22:50.443" Score="1" ViewCount="282" Body="&lt;p&gt;What I'm really curious about is if anyone can provide a high level overview of the two technologies. I know that they are both utilizing the DMR standard, but from what I have read is that the way which the repeaters signal radios is slightly different. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I have read that Motorola requires each talkgroup to be given a specific time-slot whereas Hytera does not do this and intelligently assigns time-slot allocation based on availability. Is there any truth to this? &lt;/p&gt;&#xA;" OwnerUserId="10887" LastActivityDate="2017-12-19T12:22:50.443" Title="What are the key differences between Hytera DMR and MotoTRBO?" Tags="&lt;dmr&gt;" AnswerCount="0" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9643" PostTypeId="1" CreationDate="2017-12-19T14:43:47.103" Score="1" ViewCount="125" Body="&lt;p&gt;I have been performing several weak signal tests using the DMR mode. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of three things seems to happen when a signal gets weak.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Audio is completely dropped for duration of weak signal. &lt;/li&gt;&#xA;&lt;li&gt;Audio becomes distorted and garbled giving the &quot;R2D2&quot; sound due to high bit rate error.&lt;/li&gt;&#xA;&lt;li&gt;Audio frame snippets are repeated several times like a broken record. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I understand why case 1 and 2 happens, but I am confused on the repeated audio packets. Could this have to do with the receiver &quot;waiting&quot; for the signal to come back as an attempt to make up for what is lost? If so, Why does it only occur occasionally on weak signal dropouts and not every time?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this example, the audio is completely lost before the repeating occurs: &#xA;&lt;a href=&quot;http://kd0whb.duckdns.org/dmr_repeated.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;Audio Snippet Link&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The hardware on both ends is the TYT MD380&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2017-12-19T22:04:48.620" LastActivityDate="2017-12-19T23:09:39.230" Title="DMR Repeated Audio Packets" Tags="&lt;digital-modes&gt;&lt;digital-voice&gt;&lt;dmr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9644" PostTypeId="2" ParentId="7656" CreationDate="2017-12-19T21:40:13.547" Score="1" Body="&lt;p&gt;You have to program the ctcss codes or the dcs codes. Like say your on channel 8 on both radios but one is on channel 8 127 and the other radio is on channel 8 134, they have a certain amount of privacy codes per channel and if the codes aren't the same on both radio they will not work properly. &lt;/p&gt;&#xA;" OwnerUserId="10888" LastActivityDate="2017-12-19T21:40:13.547" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9645" PostTypeId="2" ParentId="9643" CreationDate="2017-12-19T23:09:39.230" Score="2" Body="&lt;p&gt;Repeating the last frame to fill in holes from missing frames is a common digital voice technique. For small rates of frame loss, repeating a frame now and then is less noticeable than silence.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-12-19T23:09:39.230" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9647" PostTypeId="1" AcceptedAnswerId="9648" CreationDate="2017-12-20T02:27:10.430" Score="3" ViewCount="89" Body="&lt;p&gt;I’m reading a radio theory book, Radio Theory Handbook by Ron Bertrand VK2DQ, which suggests that electron flow (ie current flowing from negative to positive) is used in radio theory and design.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In the electrical trades it is common to hear of current flow from positive to negative. This is called the conventional direction of current flow. This is just what it says, a convention. Current flow is electron flow and it is from negative to positive. Conventional current flow is mostly used in Electrical Engineering. In Radio there is a greater tendency to do what I have done in this book and that is to use electron flow; current flows from negative to positive.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The author then says that one should think of current travelling the opposite way to the arrow in a diode or transistor, which seems like a bad idea to me. I know conventional current flow from positive to negative is technically ‘wrong’, but it’s the convention that is used pretty much everywhere. Is this author right, in saying that electron flow is used in radio theory, rather than conventional current flow?&lt;/p&gt;&#xA;" OwnerUserId="582" LastEditorUserId="76" LastEditDate="2017-12-20T14:24:35.197" LastActivityDate="2017-12-21T03:55:12.060" Title="Conventional or electron current" Tags="&lt;electronics&gt;&lt;theory&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9648" PostTypeId="2" ParentId="9647" CreationDate="2017-12-20T07:26:44.130" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Current flow is electron flow and it is from negative to positive.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is what we call class A hogwash.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Current notation is just a convention. Going by electron flow is not righter than going the other way around.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Conventional current flow is mostly used in Electrical Engineering.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As an EE, can confirm.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In Radio there is a greater tendency to do what I have done in this book and that is to use electron flow; current flows from negative to positive&quot;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As an EE with a bit of focus on communications I can say:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is simply not true. The standard literature on radio theory, wave propagation and the like all use currents and current densities that are coherent with the electrical field. And that goes from positive to negative potential. That implies that current should flow in the same direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of you don't do that, you end up with a set of Maxwell's equations that might still work, but have different signs as the ones you meet everywhere. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, get another book. This one doesn't stick to nearly 150 years of conventions, and there's really no good reason for making the things you learn harder to compare to what basically everyone else does.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-12-20T07:26:44.130" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9649" PostTypeId="2" ParentId="9647" CreationDate="2017-12-20T07:33:26.230" Score="2" Body="&lt;p&gt;In general, you will find that the electrical engineering field uses conventional current flow (current flows from positive to negative connections). This is re-enforced by some of the symbology used in electrical engineering - a notable example of this being a solid state diode with the arrow showing the direction of conventional current flow. With that being said, you will find some electrical engineering professors and engineering texts that prefer to discuss current flow in the sense of electron travel - even though they don't really &quot;travel&quot; very far. But this approach is clearly in the far minority within the electrical engineering community.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, the physics majors will more often prefer to discuss current flow in the &quot;electron flow&quot; manner since this allows a more convenient description of some of the underlying mechanisms of physics. So if you are in a broader research organization or in an academic setting, you will find it necessary to be able to freely switch between the two concepts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the suggestion that describing radio wave mechanics on the basis of electron flow is more likely symptomatic of someone who's background or training comes from the physics side rather than the electrical engineering side. Radio wave theory is easily explained using either approach. Most electrical engineers will stick with conventional flow even when describing radio wave theory.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To underscore the somewhat debatable nature of this topic, consider that even the notion of electrons being negative is agreed upon only by a matter of convention as well.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-12-20T07:33:26.230" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9650" PostTypeId="1" CreationDate="2017-12-20T08:25:06.420" Score="2" ViewCount="151" Body="&lt;p&gt;I am just about to make my inland waterways’ marine VHF radio license in Germany. In Germany, all inland marine VHF radios must be equipped with an &lt;a href=&quot;https://en.wikipedia.org/wiki/Automatic_Transmitter_Identification_System_(marine)&quot; rel=&quot;nofollow noreferrer&quot;&gt;ATIS&lt;/a&gt; transmitter, which basically sends the stations’ call sign digitally by frequency shift keying when releasing the PTT, on the same channel as the voice transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unlike DSC used in international shipping, the ATIS codes are not decoded on the receiving units and can neither be used by other ships to identify the sender, nor there is a way to call a ship or land station, if its ATIS number would be known. I have no idea if anybody can or does decode these digital transmissions, and with which benefit. To my eyes, the system only has drawbacks, mainly you need additional circuits inside your maritime radio, and the “noise” it causes, or even more circuits, called “ATIS killer”, to suppress that noise on the receiving side. (I searched for, but I didn’t either find a smart phone app that uses its microphone to decode the ATIS signal, if the onboard units can’t. &lt;a href=&quot;https://youtu.be/hTgo9KXnQqY&quot; rel=&quot;nofollow noreferrer&quot;&gt;There is such for weather fax&lt;/a&gt;, that was why I started digging for it.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was searching for the reasons why ATIS was introduced for inland waterways’ marine VHF, but I was not able to find anything informative. What were the reasons why those countries introduced the ATIS system for inland waterways’ marine VHF radio? What problem should it solve, and did it actually solve it?&lt;/p&gt;&#xA;" OwnerUserId="10892" LastEditorUserId="8717" LastEditDate="2017-12-21T04:00:50.607" LastActivityDate="2017-12-21T04:00:50.607" Title="What were the reasons why ATIS identification was introduced?" Tags="&lt;vhf&gt;&lt;history&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9651" PostTypeId="1" AcceptedAnswerId="9653" CreationDate="2017-12-20T10:42:44.353" Score="4" ViewCount="679" Body="&lt;p&gt;I would like to use SDR to receive &lt;strong&gt;and&lt;/strong&gt; transmit on CB, UHF and VHF. Is this possible and if so what type of equipment will I need (antennae, dongle etc)? I currently have both UHF/VHF and CB but atm have separate antennae for each rig. Reading about SDR I think I can have one single antenna and use the computer magic to allow me to work with all frequencies that antennae receives, am I mistaken?&lt;/p&gt;&#xA;" OwnerUserId="10894" LastEditorUserId="8717" LastEditDate="2021-02-06T02:10:14.603" LastActivityDate="2021-02-06T02:10:14.603" Title="SDR set up that will TX &amp; RX on CB, UHF and VHF" Tags="&lt;software-defined-radio&gt;&lt;equipment&gt;&lt;united-kingdom&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9652" PostTypeId="2" ParentId="9651" CreationDate="2017-12-20T12:43:43.117" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Reading about SDR I think I can have one single antenna and use the computer magic to allow me to work with all frequencies that antennae receives, am I mistaken?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, I always explain it that way: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An SDR is like a soundcard on speed. Usually, with a mixer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what the SDR does (in Receive direction) is take a spectrum of bandwidth $B$ (for example, 10 MHz) around a center frequency $f_c$. So, all signals between $f_c - \frac B2$ and $f_c + \frac B2$. It then mixes them down, usually to baseband, which means that these frequencies all get shifted by $f_c$, so that the same $B$ wide swath of spectrum ends up around 0 Hz, that means in $-\frac B2$ to $+\frac B2$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, it uses, just like a sound card, a fast (dual) ADC to digitize the full $B$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, flexibility comes from two things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;You now got a digital signal. FM? AM? SSB? PSK? APRS? Doesn't matter, it's in your computer, you just pick the right software to demodulate that. Also, you can have a digital filter in software that is much sharper than any physical filter and select exactly one channel.&lt;/li&gt;&#xA;&lt;li&gt;The $f_c$ is usually pretty freely choosable. So, you can tune your SDR to receive e.g. 20 MHz to 30 MHz, or you can tune it to 140 to 150 MHz. In the end, the original center frequency doesn't matter for the processing of the signal.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So much for theory. In practice, of course, a couple of things must still work out:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;your SDR must actually be able to tune to all frequencies you want. If it doesn't, this can often be compensated with an external up- or downconverter, but that'd basically not achieve your single device goal&lt;/li&gt;&#xA;&lt;li&gt;As you might know, mixers aren't inherently perfect. They tend to not only mix down the intended frequency, but also harmonics of that (amongst doing other interesting things). Hence, an SDR must include some sort of selection filter that avoids unwanted intermodulation products. Now, the more flexible a device is, the less fixed and the less great these filters can be. Not a problem if your antenna only works well for the frequency band you're interested in. Not as cool if your antenna actually works for multiple bands. So, you &lt;strong&gt;might&lt;/strong&gt; need preselection filters. Details can really only be discussed if we know what SDR you're considering. &#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A commonly overrated problem is deafening by stronger transmitters in the same band. Whilst this might be a problem in extreme situations (and you can only remedy that with analog filtering), it's astonishingly easy to avoid (offset tuning, oversampling, predistortion). &lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2017-12-20T12:43:43.117" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9653" PostTypeId="2" ParentId="9651" CreationDate="2017-12-20T14:41:36.507" Score="5" Body="&lt;p&gt;You didn't mention which country you're in, but in the US, it is only legal to transmit on CB with a &quot;type-accepted&quot; radio.  In other words, the manufacturer of the radio must apply to the FCC for permission to sell the model.  It's not legal to build your own CB transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding using a single antenna for multiple bands, a transmitter typically expects the antenna to have a certain impedance.  It is possible to use a single antenna for multiple bands, but in that case a simple antenna will have quite a wide variety of impedances across the multiple bands.  For a very low-powered transmitter this may not pose a problem.  For higher-powered transmitters, a mismatched load can cause very high voltages that can easily damage the transmitter.  (Modern high-powered transmitters often include a circuit to automatically reduce power when a mismatch is detected, to protect the electronics.)  Another problem is that the efficiency of the transmitter and the feedline can vary considerably if the frequency strays far from the optimal range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How to design an antenna and feedline system for a wide range of frequencies deserves to be a separate question here, but let me say that the most economical solution to the problem is often to have separate antennas and a coaxial switch to choose between them.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-12-20T14:41:36.507" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9654" PostTypeId="2" ParentId="9650" CreationDate="2017-12-20T18:07:54.700" Score="2" Body="&lt;p&gt;ATIS simply provides automatic identification of the vessel transmission. This is helpful in eliminating the requirement for the typically non professional ship radio operator to manually identify. It also effectively shortens transmission time allowing better utilization of crowded channels while ensuring easy identification of the ship and transmitter. This is particularly helpful with authenticating distress,  interfering, or unlawful calls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;ATIS is a subset of DSC (Digital Select Calling) with a format specifier of 121. Thus any standard DSC decoder on the receive channel can read the ship identification information. ATIS data is only sent on the transmitting channel (unlike full DSC on channel 70) and only upon key release with an ~285 ms data burst. Because the data sent is only an index to the ship identification, the 'Belgisch Instituut voor Postdiensten en Telecommunicatie' database must be accessed to resolve the actual vessel name.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The data packet is sent with 1200 baud FSK using 1.3 kHz and 2.1 kHz tones. Because the tones are in the normal audio passband and because the data transmission is quite short, fully blocking of the data audio is difficult without applying a digital delay to the audio channel. If you wish to homebrew a decoder instead of simply blocking the packet, the DSC message format is well documented.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-12-20T18:58:10.840" LastActivityDate="2017-12-20T18:58:10.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9655" PostTypeId="2" ParentId="9647" CreationDate="2017-12-21T03:55:12.060" Score="0" Body="&lt;p&gt;Here is a simple way of understanding this. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;In vacuum tubes, we have a heated cathode (filament) which emits negatively-charged electrons. And those electrons are attracted to the positively-charged anode (plate).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The cathode is always connected to the negative side of the power supply. And the anode is always connected to the positive terminal of the same power supply.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The negative-charged electrons &lt;em&gt;always&lt;/em&gt; flow &lt;strong&gt;from negative to positive&lt;/strong&gt;,  and &lt;em&gt;never&lt;/em&gt; from anode to cathode. &lt;em&gt;It's that simple.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people think that positively-charged protons are involved here, but &lt;em&gt;nothing could be further from the truth&lt;/em&gt;. Protons and neutrons are bound to the nucleus, and &lt;strong&gt;only&lt;/strong&gt; a particle accelerator (&quot;atom smasher&quot;) can break them loose from their bonds. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2017-12-21T03:55:12.060" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9656" PostTypeId="2" ParentId="1394" CreationDate="2017-12-21T04:44:00.367" Score="-4" Body="&lt;p&gt;Gold coating used is so this that once plugged it couple of times, the useful gold film gets worn of, exposing usually just very cheap metal. You can't see it, the scratches are microscopic but contact is no longer made with gold.&#xA;Gold plated connectors are nothing but a gimmick and in fact gold plated connectors are usually made of much less conductive metals than ordinary type.&lt;/p&gt;&#xA;" OwnerUserId="10901" LastActivityDate="2017-12-21T04:44:00.367" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9657" PostTypeId="1" CreationDate="2017-12-21T18:14:41.920" Score="1" ViewCount="77" Body="&lt;p&gt;I am currently attending a radio technology course. We continuously work on radio sets that are sometimes used as manpacks by the Army. In order to learn how to operate them we work in close proximity to the sets and their antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antennas are generally whip type or long rods. Such as these :&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6UMNw.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6UMNw.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/37YL4.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/37YL4.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio sets generally output around 25-50W in the 30-90MHz frequency range. Can that possibly cause damage to my iPhone?&lt;/p&gt;&#xA;" OwnerUserId="10905" LastActivityDate="2017-12-21T18:14:41.920" Title="Can a radio antenna damage a phone?" Tags="&lt;antenna&gt;" AnswerCount="0" CommentCount="3" ClosedDate="2017-12-21T21:40:49.250" ContentLicense="CC BY-SA 3.0" />
  <row Id="9658" PostTypeId="1" AcceptedAnswerId="9662" CreationDate="2017-12-22T03:33:54.380" Score="5" ViewCount="2461" Body="&lt;p&gt;Many radio coverage tools yield results in dB(μV/m). For example, &lt;a href=&quot;http://lrcov.crc.ca/main/&quot; rel=&quot;noreferrer&quot;&gt;CRC-COVWEB&lt;/a&gt; or nearly any tool based on the &lt;a href=&quot;https://en.wikipedia.org/wiki/Longley%E2%80%93Rice_model&quot; rel=&quot;noreferrer&quot;&gt;Longly-Rice model&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The unit occurs in regulations sometimes as well. For example, &lt;a href=&quot;http://www.arrl.org/the-fcc-s-new-rf-exposure-regulations#table1&quot; rel=&quot;noreferrer&quot;&gt;maximum permissible exposure&lt;/a&gt; limits may be given in V/m, which seems like a similar unit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's a dB(μV/m)? How is it defined? I'd like to see some math.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And why use it, instead of some other more familiar unit?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2017-12-22T03:39:03.400" LastActivityDate="2017-12-25T12:32:41.607" Title="What is dB(μV/m), and what are its applications?" Tags="&lt;math&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9659" PostTypeId="2" ParentId="1584" CreationDate="2017-12-22T08:02:08.847" Score="9" Body="&lt;p&gt;I am a UK licensed Radio Amateur with some 39 years experience.  I also design and build LTE cellular systems for a living.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best suited Amateur Radio spectrum for LTE operation is the 2.3 GHz band - this can easily accommodate a LTE-TDD (single frequency) system operating in LTE Band 40.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that both FCC (and European) regulations for Amateur Radio do not allow the transmission of ENCRYPTED communications - and that LTE is designed with encryption integrated into the system; however, this can be got around by using PUBLICALLY KNOWN keys, i.e. use keys consisting of all'0's.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can see Amateur LTE being particularly useful in emergency/disaster situations  as a means of communicating with members of the public in distress - although there are more regulatory issues involved with licensed amateurs communicating with unlicensed operators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, as a previous poster has indicated - it is possible to obtain an experimental license from the FCC for LTE operation. Note - it is &lt;em&gt;not&lt;/em&gt; possible to run a commercial service on experimental spectrum.&lt;/p&gt;&#xA;" OwnerUserId="10911" LastEditorUserId="5025" LastEditDate="2019-03-05T15:23:58.350" LastActivityDate="2019-03-05T15:23:58.350" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="9660" PostTypeId="1" CreationDate="2017-12-22T10:20:27.990" Score="0" ViewCount="116" Body="&lt;p&gt;So I am part of an SDR project using GNU Radio and USRPs, where we are trying to set up a link between USRPs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ideal is similar to the DARPA spectrum challenge (&lt;a href=&quot;https://spectrumcollaborationchallenge.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://spectrumcollaborationchallenge.com/&lt;/a&gt;). We are trying to change the tx_frequency in order to avoid interference or signal jamming. I am looking for a method or a protocol to implement to synchronise rx with tx's frequency changes.&lt;/p&gt;&#xA;" OwnerUserId="10910" LastEditorUserId="4076" LastEditDate="2018-01-02T14:57:33.500" LastActivityDate="2018-01-02T14:57:33.500" Title="Tx-Rx synchronisation to frequency changes" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9661" PostTypeId="2" ParentId="9658" CreationDate="2017-12-22T13:02:48.703" Score="2" Body="&lt;p&gt;A dB(&lt;strong&gt;µV/m&lt;/strong&gt;) is a decibel relation for a sub-unit of &lt;strong&gt;V/m&lt;/strong&gt;, which is appropriate for units of the e-field intensity of a radiated e-m wave existing between two physical points in space separated by a linear distance of one meter. These units are used commonly by the FCC, and other regulators of the use of the e-m spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Examples:  0 dB(µV/m) = 1 microvolt/meter; 60 dB(µV/m) = 1,000 microvolts/meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often the unit dB(µV/m) is written as simply &quot;dBu.&quot; However that term is meaningless as an SI definition* because the basic unit of measure (volts) is not included, and must be inferred by the reader.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;see &lt;a href=&quot;https://en.wikipedia.org/wiki/SI_derived_unit&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/SI_derived_unit&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2017-12-22T13:15:15.263" LastActivityDate="2017-12-22T13:15:15.263" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9662" PostTypeId="2" ParentId="9658" CreationDate="2017-12-22T13:09:12.013" Score="6" Body="&lt;p&gt;&lt;strong&gt;TL;DR:&lt;/strong&gt; $\frac{V}{m}$ and $\text{dB}(\mu V/m)$ are units for the &lt;a href=&quot;https://en.wikipedia.org/wiki/Field_strength&quot; rel=&quot;noreferrer&quot;&gt;field strength of an electric field&lt;/a&gt;. For a practical application skip to the end!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Derivation of the field strength&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A point charge $q_1$ generates a field strength* of $E = \frac{1}{4\pi\varepsilon_0}{q_1\over r^2}$ at a distance of $r$. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is derived from &lt;a href=&quot;https://en.wikipedia.org/wiki/Coulomb&amp;#39;s_law&quot; rel=&quot;noreferrer&quot;&gt;Coulomb's law&lt;/a&gt; that is $F=\frac{1}{4\pi\varepsilon_0}{q_1q_2\over r^2}$ giving the force acting on two charges $q_1$ and $q_2$ at a distance of $r$. It can be rewritten as&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$F=q_2 \cdot \frac{1}{4\pi\varepsilon_0}{q_1\over r^2}=q_2\cdot E$ or the other way around $E = \frac{F}{q_2}$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So from the field strength $E$ we can calculate the force on a &lt;a href=&quot;https://en.wikipedia.org/wiki/Test_particle#Test_particles_in_plasma_physics_or_electrodynamics&quot; rel=&quot;noreferrer&quot;&gt;test charge&lt;/a&gt; of $q_2$ by multiplication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now for the units. If we have a test charge of $q_2 = 1\,C$ that experiences a force of $F = 1\,N$, we get a field strength of $E = \frac{F}{q_2} = \frac{1\,N}{1\,C} = 1\,\frac{N}{A\cdot s} = 1\,\frac{N\cdot m}{A\cdot s\cdot m} = 1 \frac{V}{m}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;* I use the scalar form and assume all amounts have the same sign and direction for simplicity.&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Decibel&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But your actual question was about $\text{dB}(\mu V/m)$, but that is just a numerical transformation to get values that are easier to calculate with in real world applications, because the values are usually very small. $0\,\text{dB}(\mu V/m)$ corresponds to $1 \frac{\mu V}{m}$ and that is $10^{-6} \frac{\mu V}{m}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So this is a usual &lt;a href=&quot;https://en.wikipedia.org/wiki/Decibel&quot; rel=&quot;noreferrer&quot;&gt;decibel conversion&lt;/a&gt;. For example to get the field strength in $\frac{V}{m}$ for $45\,\text{dB}(\mu V/m)$ we calculate&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$E = 10^{-6} \frac{V}{m} \cdot 10^\frac{45}{20} = 178 \cdot 10^{-6} \frac{V}{m}$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 20, because $E$ is a field quantitiy and not a power quantity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;From field strength to reception power&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now we know what $\text{dB}(\mu V/m)$ is. Its main advantage is that it specifies the properties of the electic field without the need to take the reception antenna or the receiver into account!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, it does not help a lot for radio transmission, because we usually do not receive with force meters attached to probe charges, but antennas and receivers ;-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This transformation to get the reception power is not straightforward, because it highly depends on the antenna and other parameters, but I can give an approximative calculation. For this we need the &lt;a href=&quot;https://en.wikipedia.org/wiki/Wave_impedance#Wave_impedance_in_free_space&quot; rel=&quot;noreferrer&quot;&gt;wave impedance in free space&lt;/a&gt; $Z_0 = \sqrt{\frac{\mu_0} {\varepsilon_0}}$. With this we get the &lt;a href=&quot;https://en.wikipedia.org/wiki/Surface_power_density#Far_field&quot; rel=&quot;noreferrer&quot;&gt;surface power density&lt;/a&gt; in the far field of $S = \frac{E^2}{Z_0}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And with the &lt;a href=&quot;https://en.wikipedia.org/wiki/Antenna_aperture&quot; rel=&quot;noreferrer&quot;&gt;antenna aperture or effective area&lt;/a&gt; $A_w$ that is for example $\frac{\lambda^2}{4\pi}$ for an &lt;a href=&quot;https://en.wikipedia.org/wiki/Isotropic_radiator&quot; rel=&quot;noreferrer&quot;&gt;isotropic radiator&lt;/a&gt; or $0.1305\, \lambda^2$ for a half wave dipole, where $\lambda$ is the wave length, we can then calculate the reception power&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$P = S \cdot A_w = \frac{E^2}{Z_0} \cdot A_w$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Complete example&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lets say we want to estimate the reception quality of the &lt;a href=&quot;http://www.db0zu.org/&quot; rel=&quot;noreferrer&quot;&gt;DB0ZU&lt;/a&gt; repeater on the &lt;a href=&quot;http://m.osmtools.de/0gPSc2rITxB0fvuv2qvCi5&quot; rel=&quot;noreferrer&quot;&gt;Zugspitze&lt;/a&gt; at &lt;a href=&quot;http://m.osmtools.de/0gddC2rCTsB0goRC2rjZI5&quot; rel=&quot;noreferrer&quot;&gt;Ohlstadt&lt;/a&gt; in a distance of $30\,\text{km}$ with &lt;a href=&quot;https://www.outdooractive.com/de/wanderung/zugspitz-region/wanderung--zum-ohlstaedter-wasserfall/23107787/&quot; rel=&quot;noreferrer&quot;&gt;a nice unobstructed view to the Zugspitze&lt;/a&gt; (except for the cow). We assume a radiation power of $1\,W$ and a frequency of $145\,\text{MHz}$ ($\lambda = 2.07\,\text{m}$).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to &lt;a href=&quot;http://lrcov.crc.ca/main/&quot; rel=&quot;noreferrer&quot;&gt;CRC-COVWEB&lt;/a&gt; we get $45\,\text{dB}(\mu V/m)$ in Ohlstadt. Look above for the calculation to get $178 \cdot 10^{-6} \frac{V}{m}$ from this. We can then calculate a surface power density of&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$S = \frac{E^2}{Z_0} = \frac{\left(178 \cdot 10^{-6} \frac{V}{m}\right)^2}{377\,\Omega}$ &lt;a href=&quot;http://www.wolframalpha.com/input/?i=(10%5E(45%2F20)*10%5E(-6)%20(V%2Fm))%5E2%2F(377%20Ohm)&quot; rel=&quot;noreferrer&quot;&gt;$= 84\,\frac{pW}{m^2}$&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming we receive with a half wave dipole without further losses, we get a reception power of&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$P = S \cdot A_w =  84 \frac{pW}{m^2} \cdot 0.1305\, \lambda^2 = 84 \frac{pW}{m^2} \cdot 0.1305\, (2.07\,\text{m})^2 $ &lt;a href=&quot;http://www.wolframalpha.com/input/?i=(10%5E(45%2F20)*10%5E(-6)%20(V%2Fm))%5E2%2F(377%20Ohm)%20*%200.1305%20*%20%20(2.07%20meter)%5E2&quot; rel=&quot;noreferrer&quot;&gt;$= 4.6 \cdot 10^{-11} W$&lt;/a&gt; $=&#xA;-73\,\text{dBm}$. That is a nice S9+20 dB signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For an isotropic radiator we have to replace the 0.1305 with $\frac{1}{4\pi}$ and get $-75\,\text{dBm}$. This result is in line with &lt;a href=&quot;http://www.giangrandi.ch/electronics/anttool/rx-field.shtml&quot; rel=&quot;noreferrer&quot;&gt;the calculator found here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Shortcut calculation&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All the calculations above can be combined resulting in a single formula.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$P_r \,(\text{dBm}) = E \,(\text{dB}\mu V/m) - 20 \cdot \log_{10}\,\, f \,(\text{MHz}) - 77.2$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for our example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$P_r = 45 - 20 \cdot \log_{10}(145) - 77.2 = -75\,\text{dBm}$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This approach is taken from Christopher Haslett, &quot;Essentials of Radio Wave Propagation&quot;, Cambridge University Press, 2008. Chapter 2 also provides some more explanation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Comparison with free space path loss&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of using the CRC-COVWEB tool, we can also estimate this reception power of an isotropic radiator by using the &lt;a href=&quot;https://en.wikipedia.org/wiki/Free-space_path_loss#Free-space_path_loss_in_decibels&quot; rel=&quot;noreferrer&quot;&gt;free space path loss model&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\mbox{FSPL(dB)} = 20\log_{10}(d) + 20\log_{10}(f) + 20\log_{10}\left(\frac{4\pi}{c}\right)$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since there are no obstacles between the Zugspitze and Ohlstadt the result should be quite similar. And in fact,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\mbox{FSPL(dB)} = 20\log_{10}(30\,\text{km}) + 20\log_{10}(145\,\text{MHz}) + 20\log_{10}\left(\frac{4\pi}{c}\right) = 105\,\text{dB}$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$1 W = 30\,\text{dBm}$, so the reception power is $-75\,\text{dBm}$.&lt;/p&gt;&#xA;" OwnerUserId="5573" LastEditorUserId="5573" LastEditDate="2017-12-22T16:49:17.010" LastActivityDate="2017-12-22T16:49:17.010" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9664" PostTypeId="2" ParentId="9660" CreationDate="2017-12-23T01:13:06.850" Score="2" Body="&lt;p&gt;that looks like it's a Cognitive Radio challenge.  so, if a frequency is already in use, you want to find an idle frequency to use instead.  you could use something similar to ALE (Automated Link Establishment)  where all radios in a network keep track of what frequencies are usable, what frequencies are in use, and choose a frequency to communicate with another specific station, or to send allcall/anycall requests.  look on github for examples of cognitive radio&lt;/p&gt;&#xA;" OwnerUserId="10914" LastActivityDate="2017-12-23T01:13:06.850" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9666" PostTypeId="2" ParentId="9658" CreationDate="2017-12-23T12:26:29.007" Score="3" Body="&lt;p&gt;&lt;strong&gt;Introduction&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In amateur radio, we are used to giving signal reports in the form of &quot;S-units&quot;. The S-unit is based on the amount of power at the receiver's input terminals. Thus we can see that the gain of the receive antenna plays a role in the level of the S-unit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In professional circles, it is more common to be concerned with the &quot;field strength&quot; of the signal in the area in which the receive antenna is located. This measurement must then specifically eliminate the effect of the receive antenna. Field strength is typically expressed as volts per meter or V/m. Often the field strength is quite small so it may be shown as mV/m (millivolts per meter) or μV/m (microvolts per meter). It is also common to do a logarithmic comparison to 1 μV/m in dB form. This can be shown as dB(μV/m) or often simply dBμ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The Math&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Start with the notion of an isotropic antenna centered in a sphere of radius $r$. The antenna is illuminating the sphere uniformly with RF energy. We can then imagine that there are a certain number of watts per square meter on the surface of the sphere at some point called $O$. This is an expression of RF power density.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we express the radius of the sphere in meters, we can then directly calculate the power density as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$P_d=\frac{P_t}{4\pi r^2} \tag 1 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $P_d$ is the resulting power density in watts/meter&lt;sup&gt;2&lt;/sup&gt;, $P_t$ is the input power to the isotropic antenna in watts, and $r$ is the radius of the sphere in meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By definition, the isotropic antenna has a linear gain of 1. We can expand equation 1 to work for any gain of transmitting antenna, provided the point of maximum gain is at the observation point $O$ on the sphere:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$P_d=\frac{P_t G_t}{4\pi r^2} \tag 2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $G_t$ is the linear gain of the transmitting antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can now convert the power density to field strength (intensity) in $\mathrm{V/m}$ by applying Ohms law using the impedance of free space which is $120\pi$ ohms:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$E=\sqrt{P_d120\pi} \tag 3 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the field strength in volts/meter at the observation point $O$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But now we must detect this signal using a receive antenna. The antenna will not necessarily intercept exactly one square meter of power from the transmitter. The effective intercept area or capture area of an antenna is known as the Effective Aperture:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$A_e=\frac{G_r\lambda^2}{4\pi} \tag 4 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $A_e$ is the effective aperture in meters&lt;sup&gt;2&lt;/sup&gt;, $G_r$ is the linear gain of the receive antenna and $\lambda$ is the wavelength of the received signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power received by the antenna is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$P_r=P_dA_e \tag 5 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The receive antenna will convert the received power to voltage according the impedance of the antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$E_r=\sqrt{P_rZ_{ant}} \tag 6 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $E_r$ is the voltage at the receive antenna terminals and $Z_{ant}$ is the impedance of the receive antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Combining equations 5 and 6 and solving for $P_d$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$P_d=\frac{E_r^2}{A_eZ_{ant}} \tag 7 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And finally combining equations 3 and 7:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$E=\sqrt{\frac{E_r^2 120\pi}{A_eZ_{ant}}} \tag 8 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This gives us the field strength in $\mathrm{V/m}$ after &quot;backing out&quot; the effect of the receive antenna. We can now convert the linear numerical $E$ from equation 8 in $\mathrm{V/m}$ referenced to $1\:\mathrm{\mu V/m}$ in decibel form:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\mathrm{dB(\mu V/m)}&#xA;=20 \cdot \log\left( E \over 10^{-6}\:\mathrm{V/m} \right) \tag 9$$&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="218" LastEditDate="2017-12-25T12:32:41.607" LastActivityDate="2017-12-25T12:32:41.607" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9667" PostTypeId="2" ParentId="1394" CreationDate="2017-12-25T13:51:33.693" Score="1" Body="&lt;p&gt;GOLD is an excellent conductor, plating of contacts with Gold is mostly found in low current and low voltage (less than 100 Ma &amp;amp; less than 50 Volt) circuits where there is little chance of arcing (which would burn/melt the plating off the contact).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a product on the market called &quot;COOL-AMP&quot;, which allows you to effectively SILVER PLATE contacts and most any other metal surfaces when properly applied (expensive stuff but works very well).&lt;/p&gt;&#xA;" OwnerUserId="438" LastEditorUserId="8717" LastEditDate="2017-12-25T20:53:56.040" LastActivityDate="2017-12-25T20:53:56.040" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9668" PostTypeId="1" AcceptedAnswerId="9669" CreationDate="2017-12-25T15:02:25.467" Score="2" ViewCount="167" Body="&lt;p&gt;I am following &lt;a href=&quot;http://www.ukaranet.org.uk/uk_amateurs/bobgreef/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this design for a simple decametric radio telescope&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bJ7q4.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bJ7q4.jpg&quot; alt=&quot;diagram of telescope&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand the principle that a radio wave hits the metal inducing an electric current that can be measured, but I do not understand the meaning behind the structure.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Why does there need to be a copper circle and a wire mesh to detect the waves?&lt;/li&gt;&#xA;&lt;li&gt;Why does the copper need to be a circle with a gap?&lt;/li&gt;&#xA;&lt;li&gt;How would one determine the sizes of the loop and mesh required to measure radio waves with wavelengths that are tens of meters?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10922" LastEditorUserId="76" LastEditDate="2017-12-25T15:05:00.397" LastActivityDate="2017-12-27T00:34:14.640" Title="Physics behind this decametric radio telescope" Tags="&lt;antenna-theory&gt;&lt;loop-antenna&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9669" PostTypeId="2" ParentId="9668" CreationDate="2017-12-25T15:47:27.387" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Why does there need to be a copper circle and a wire mesh to detect the waves?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The electromagnetic radio field exerts a force on the charges in the antenna, creating a very small voltage and current measured by the radio. The parts must be good conductors for the charges to be easily moved without much loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The copper circle is the basic antenna, and the mesh is a reflector, making the antenna more directional. Were it not directional it would still work, but it would be even more difficult to separate astronomical sources from terrestrial ones.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why does the copper need to be a circle with a gap?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The gap is the feedpoint, where the radio attaches to measure the charge movement in the antenna. Without a gap, how would the radio attach? There are other possible ways, but a gap works fine and is easy to build.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How would one determine the sizes of the loop and mesh required to measure radio waves with wavelengths that are tens of meters?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;With antennas, all dimensions are relative to wavelength. So if you wanted to build a similar antenna for half the frequency or twice the wavelength, double the dimensions. The spacers would become 60cm long, and the loop diameter 106cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, 21 MHz is a wavelength of approximately 1.4 meters. All the dimensions in this antenna are significantly smaller than that, making it an &lt;em&gt;electrically small&lt;/em&gt; antenna, and it may work just as well for a wide range of frequencies with no modification.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2017-12-25T15:47:27.387" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9670" PostTypeId="2" ParentId="1037" CreationDate="2017-12-25T21:46:38.060" Score="1" Body="&lt;p&gt;&lt;em&gt;From &lt;a href=&quot;http://www.w0btu.com/ssb_audio-weak_signal.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this webpage&lt;/a&gt;:&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;&lt;strong&gt;TL;DR:&lt;/strong&gt;&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Get rid of the audio below 300-500 Hz*, and then use audio processing (compression) to raise the average power.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*This is accomplished by:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Choosing a suitable microphone, and&lt;/li&gt;&#xA;&lt;li&gt;Equalizing the audio (if possible)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Details:&lt;/h2&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Audio which is primarily the mid-range portion of the human voice&#xA;  (i.e. 300 to 2400 Hz.) carries better over long distances. (It is also&#xA;  frequency-efficient on crowded bands). The downside is that this type&#xA;  of narrow audio is not as enjoyable to listen to in a ragchew where&#xA;  signals are S9+. &lt;em&gt;The wider audio is more pleasant to listen to for&#xA;  extended periods, but is not good for contesting, DX chasing, or use&#xA;  on crowded bands&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rWjZv.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rWjZv.gif&quot; alt=&quot;Optimum audio for high intelligibility&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;It is therefore good practice to eliminate the low frequencies below&#xA;  about 300 Hz, because intelligible speech does not require the&#xA;  transmission of frequencies lower than 300 Hz. To do so adds&#xA;  practically nothing to intelligibility. Elimination of the frequencies&#xA;  below 200 or 300 Hz removes a large percentage of the high energy&#xA;  speech components that do not contribute to intelligibility. (see Fig.&#xA;  2-9 below). Such elimination permits the transmitter to concentrate&#xA;  its efforts on only the essential portions of speech power. In&#xA;  practice, this means something like a 3 to 6 dB improvement in system&#xA;  effectiveness, equivalent to doubling or quadrupling its output power&#xA;  even before any speech processing.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;To increase the average power of the voice signal without increasing&#xA;  the peak power, … by emphasizing the low-power, high-frequency&#xA;  components of the speech signal, and attenuating the high-power,&#xA;  low-frequency components of the speech signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Speech processing (compression) is most useful when we do this!&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Figure 2-9 shows power-vs.-frequency distribution in the average human&#xA;  voice over a range of approximately 200 Hz to 3000 Hz. This curve&#xA;  indicates that the greatest concentration of speech power is at low&#xA;  frequencies. Fortunately, &lt;em&gt;it is the low-frequency components of speech&#xA;  which contribute the least to intelligibility&lt;/em&gt; since these frequencies&#xA;  generally occur in the vowel sounds. As a result, the low frequencies&#xA;  may be attenuated without undue loss of speech intelligibility. The&#xA;  low-power, high-frequency components present in a voice signal can be&#xA;  pre-emphasized to provide some increase in the average power level of&#xA;  the signal. &lt;strong&gt;Since it is the high-frequency components which&#xA;  predominate in the consonant sounds, some emphasis of the high&#xA;  frequencies improves intelligibility. In other words, it's far more&#xA;  important for us to hear the S's, C's and high-frequency sounds like&#xA;  those.&lt;/strong&gt; If we don't, we may not understand what the guy at the other&#xA;  end is saying!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;h2&gt;Wattmeter needle swing:&lt;/h2&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Our power output meter and/or plate current&#xA;  meter is &lt;strong&gt;NOT&lt;/strong&gt; a reliable indicator of how well the other station hears&#xA;  us! Fig. 2.9 below clearly shows why.&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;There is more power in lower-frequency (bass) frequencies, so we observe more meter swing&lt;/li&gt;&#xA;  &lt;li&gt;There is less power in higher-frequency (treble) frequencies, so we observe less meter swing (unless compressed or processed).&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/O177m.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O177m.gif&quot; alt=&quot;Wasted power in lower frequencies&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;This is only a portion of &lt;a href=&quot;http://www.w0btu.com/ssb_audio-weak_signal.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;the article&lt;/a&gt;.&lt;/strong&gt; Much more information --with references-- can be found &lt;a href=&quot;http://www.w0btu.com/ssb_audio-weak_signal.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;there&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2017-12-26T00:18:08.857" LastActivityDate="2017-12-26T00:18:08.857" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9671" PostTypeId="1" AcceptedAnswerId="9675" CreationDate="2017-12-26T23:53:00.007" Score="3" ViewCount="236" Body="&lt;p&gt;I have doubts regarding the control authority of the amateur radio satellites, because recently we have drastic changes to Internet control by FCC as the next major decentralized communication system that can affect the way we communicate in future is the Amateur radio in the free world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, can any one country make a decision based on those satellites? I ask this because recently Israel capital decision is also headed by the US, and it is accepted by the UN. So, can it be controlled or not?&lt;/p&gt;&#xA;" OwnerUserId="10928" LastEditorUserId="873" LastEditDate="2017-12-27T02:54:49.560" LastActivityDate="2018-01-02T07:52:10.280" Title="Who regulates ham radio satellites?" Tags="&lt;legal&gt;&lt;satellites&gt;" AnswerCount="4" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="9672" PostTypeId="2" ParentId="9668" CreationDate="2017-12-27T00:34:14.640" Score="1" Body="&lt;p&gt;This is a complicated way of making a short dipole antenna - an E-field sensor. There should be an isolator, an unun on the coax near the mesh otherwise the coax would be the dominating place where currents go. There is also a risk for conducted interference on the cable. The antenna is simply two modest capacitors to infinity separated by 30 cm. It might resonate near 21 MHz The capacitance between the two parts plus the capacitance to infinity form C. The wire to the copper part forms L. &#xA;For a better E-field sensor look here &lt;a href=&quot;https://www.youtube.com/embed/ItLkn8r4s3E&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/embed/ItLkn8r4s3E&lt;/a&gt; Change the toroid and remove the tuning cap to move the resonance from MW to 21 MHz.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2017-12-27T00:34:14.640" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9674" PostTypeId="2" ParentId="9671" CreationDate="2017-12-27T03:00:21.457" Score="0" Body="&lt;p&gt;All satellites, commercial and amateur (and possibly even military) are regulated by the ITU, an agency of the U.N.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Source: &lt;a href=&quot;https://en.wikipedia.org/wiki/Space_law&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2017-12-27T03:00:21.457" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9675" PostTypeId="2" ParentId="9671" CreationDate="2017-12-27T16:45:41.310" Score="6" Body="&lt;p&gt;When all the communications of a satellite qualify as amateur radio satellite communications, then the frequency coordination is carried out by &lt;a href=&quot;http://www.iaru.org/satellite.html&quot; rel=&quot;noreferrer&quot;&gt;IARU&lt;/a&gt;. ITU delegates this function to IARU.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The link provides instructions and information for filing a coordination request.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Background: &lt;a href=&quot;http://www.amsatuk.me.uk/iaru/finished_detail.php?serialnum=311&quot; rel=&quot;noreferrer&quot;&gt;I filed a satellite coordination&lt;/a&gt; in 2013, launch was in june 2014.)&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2017-12-27T16:45:41.310" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9676" PostTypeId="1" AcceptedAnswerId="9678" CreationDate="2017-12-27T21:37:39.470" Score="4" ViewCount="697" Body="&lt;p&gt;I've ordered two mini whip antennas from Ebay (Russia) for HF and MW.  As power lines cross my city property in a L shape - the only way to get away from them is to go up.  So I'm hoping that going 5-20 feet above my roof line will reduce the extreme RFI that is on the power lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the best option for mounting a mini whip high above the roof?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm considering using 10 ft emt.  Is it safe to go any higher (say 20 feet) or do I need cables or a tower to do so?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to mount two of them so I can phase them.  I'm considering using the sewer pipe (which already has a diamond discone), chimney, or gutter/side of the roof.&lt;/p&gt;&#xA;" OwnerUserId="8521" LastEditorUserId="8717" LastEditDate="2017-12-30T22:59:29.613" LastActivityDate="2018-01-02T19:03:13.090" Title="Suggestions for mounting a mini-whip as high as possible" Tags="&lt;hf&gt;&lt;antenna-construction&gt;&lt;rfi&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9677" PostTypeId="2" ParentId="221" CreationDate="2017-12-28T02:12:38.850" Score="0" Body="&lt;p&gt;Just an improvement for one of the answers above from Ossi Väänänen &#xA;starting with this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt; void calcLocator(char *dst, double lat, double lon) {&#xA;    [...]   &#xA;&#xA;      dst[0] = (char)o1 + 'A';&#xA;      dst[1] = (char)a1 + 'A';&#xA;      dst[2] = (char)o2 + '0';&#xA;      dst[3] = (char)a2 + '0';&#xA;      dst[4] = (char)o3 + 'A';&#xA;      dst[5] = (char)a3 + 'A';&#xA;      dst[6] = (char)0;&#xA;    }&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Consider converting the dst values to ascii characters.&#xA;Replace the dst array entries above with the following:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;  dst[0] = char(o1+65) ;&#xA;  dst[1] = char(a1+65) ;&#xA;  dst[2] = char(o2+48) ;&#xA;  dst[3] = char(a2+48) ;&#xA;  dst[4] = char(o3+97);&#xA;  dst[5] = char(a3+97) ;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Plus 65 gives you the ascii letter values for upper case, +48 for numbers, and +97 for lower case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example results as follows:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;char grid[4];&#xA;calcLocator(grid,gps.location.lat(),gps.location.lng());&#xA;&#xA;Serial.print(grid);&#xA;&#xA;// results will be in the following format:&#xA;AB01ab&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;73's all&lt;/p&gt;&#xA;" OwnerUserId="10935" LastActivityDate="2017-12-28T02:12:38.850" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9678" PostTypeId="2" ParentId="9676" CreationDate="2017-12-28T14:52:31.443" Score="2" Body="&lt;p&gt;First and foremost consider the safety aspects of your intended installation. You should ensure that if the antenna and its supports were to fall, it should not contact the power lines. The same consideration should be given for the installation process to ensure that under no circumstances should the antenna, mast, or cabling nor any equipment used for the installation be able come into accidental contact with the power lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, elevating the antenna by 10 to 20 feet may have a minimal effect on the amount of RFI received from local sources. If the noise source is in the near field of the antenna, then the results can be unpredictable. If the noise source is in the far field of the antenna, then it will basically follow the inverse square law. For example, if the far field noise source is 100 feet away when the antenna is on the ground and you now elevate the antenna by 10 feet, the noise will decrease by less than 1% - an imperceptible amount. Elevating the antenna may help with increasing the amount of desired signal, however, and this would have a positive effect on the Signal to Noise Ratio (SNR).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question of the mast construction depends on several factors - the yield strength of the mast, the inner and outer diameters of the mast, the height of the mast, and the wind load of the load at the top of the mast (your active antenna system). These factors can be used to calculate if the mast will bend under specified wind conditions and the amount of stress the mounting system for the mast (bending moment at the base of the mast) needs to endure to support the mast under the calculated conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The calculations are rather laborious. I have an Excel spreadsheet that I use in an attempt to reduce the number of errors. For example, I show that with a 1 inch OD mast, 0.1 inch wall thickness, 35 kpsi yield strength, with a 1 square foot of cylindrical wind load at the 8 foot position, the maximum wind speed it can survive is 67 mph (108 km/h). This will have a total moment of &gt; 3,620 in-pounds (&gt; 410 nm). This is the equivalent moment of an average adult pushing as hard as they can on a pipe 1 meter from the mounting point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are interested in the detailed formulas, post back in the comments and I will add them to this answer. Alternatively, you can find the formulas and a spreadsheet here:&#xA;&lt;a href=&quot;http://thebont.com/spreadsheets/AnalysisOfAntennaMastStrength.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://thebont.com/spreadsheets/AnalysisOfAntennaMastStrength.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-12-28T16:24:05.970" LastActivityDate="2017-12-28T16:24:05.970" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9679" PostTypeId="2" ParentId="9671" CreationDate="2017-12-28T17:16:05.380" Score="3" Body="&lt;p&gt;While @Juancho correctly addressed the practical frequency coordination aspects, the OP's question seems to indicate concern regarding the regulation of what is and is not communicated using the satellites. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the USA, the permissible communications on, and the remote control of, amateur radio satellites is regulated by the FCC as defined in Part 97. A licensee wishing to use a satellite for communications should consult the jurisdictional regulatory authority for their operations.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-12-28T17:16:05.380" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9680" PostTypeId="2" ParentId="9676" CreationDate="2017-12-28T18:26:41.190" Score="1" Body="&lt;p&gt;Vertical antennas depend upon a ground plane to work properly.  You could elevate the vertical if you use tuned 1/4 λ horizontal elements (often called a counterpoise) to replace the more traditional ground plane made of radial wires running along the ground.  Elevated verticals are often more efficient, but the disadvantage is that you're then confined to a single band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think that if you were to elevate a vertical with no ground plane using a conductive mast, then your results would probably be terrible.  Your reception of far-field signals, the signals that you want to receive, would probably be terrible, but the near-field signal, that is noise from the power lines, could well be full-strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice would be to start simply, by trying a single ground-mounted vertical with a proper ground plane.  When you know how that works then you can try elevating it, and if you like the results of that experiment, then try phasing the vertical with another vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trying to receive HF and MW signals from a small city lot with power lines overhead can be challenging.  A cheap mini-whip antenna in those circumstances is unlikely to be satisfactory in any configuration, in my opinion.  Assuming that you're only trying to receive, in your shoes I think I might try attaching a wire to a guyed fiberglass pole with some sort of air-wound inductor at the bottom, with several long radials running along the ground.  (If you'd also like to transmit, then try a commercially-made multiband vertical instead.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd also like to echo Glenn's safety concerns: whatever you do, make sure that your antenna can't accidentally touch the power line under any circumstances.  Hams have been killed erecting antennas that accidentally touched power lines.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2017-12-28T18:26:41.190" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9681" PostTypeId="1" CreationDate="2017-12-28T19:47:39.323" Score="4" ViewCount="214" Body="&lt;p&gt;I received this signal around 7 MHz. I've checked all over the &quot;Signal Identification Wiki&quot;, but cannot find anything similar to this. I'm pretty sure this is some simple FSK, but that is the exact type?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal is at around 2200Hz (in audio file). Partial spectrogram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wAuFN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wAuFN.png&quot; alt=&quot;partial signal spectrogram&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The WAV can be downloaded here: &lt;a href=&quot;https://nofile.io/f/CjEk6A513W8/radiodata.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://nofile.io/f/CjEk6A513W8/radiodata.wav&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10937" LastEditorUserId="8717" LastEditDate="2017-12-28T20:36:57.520" LastActivityDate="2018-01-05T21:39:21.260" Title="What type of signal is this?" Tags="&lt;signal-identification&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9682" PostTypeId="2" ParentId="9276" CreationDate="2017-12-28T20:50:07.337" Score="1" Body="&lt;p&gt;Usually with NTS the originating station, which is always a ham radio station, receives the acknowledgement of delivery which is usually returned via NTS message using ARL numbered phrases like ARL 47 means delivery was successful and ARL 67 is not delivered for a stated reason.  An example of non-delivery reason would be bad phone number as many times a phone number of recipient is included in the message delivery instructions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NTS has a network of layered message handling sections that include local nets, section nets, and regional nets.  A regional net might be something like RN6 or RN7 and a section net is something like OSN (Oregon Section Net) and WSN Washington State Net.  I only mention OSN and WSN because I am a member of those nets but there are others in North America.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If for some reason you can not deliver back thru the NTS messaging system then another form of acknowledgement can be done and you are open to take your pick of phone call, e-mail, or routing back to who you actually received the message.  This last method is often the most common but not the most formal which is to use the NTS messaging system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In answering this question, I am answering from my own experience in NTS message traffic handling and not because I just read it in the ARRL documentation.  I say this because it has been years since I read the ARRL NTS documentation and there could be more detail and even changes from the methods I and others I know employ.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2017-12-28T20:50:07.337" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9683" PostTypeId="1" CreationDate="2017-12-29T05:40:07.457" Score="3" ViewCount="670" Body="&lt;p&gt;So I am working on a low cost ham radio beacon using my Baofeng UV-5R radio because it is easy to use and portable. I built a simple PTT interface for a Raspberry Pi and wrote some python to transmit the information I want. However, there is one problem. I want the option to have to radio plugged in to its charger to be able to transmit for long periods of time without dying but when I plug the radio into the wall and use Raspberry Pi to transmit audio it produces a very loud hum over the radio signal and it is completely unusable. This does not happen when I plug a battery operated audio source (such as a phone) into the radio, only when I use a wall powered source such as the Pi or a computer. it also does no occur when the radio is using battery power and the Pi is plugged into the wall. It does happen when using a simple male to male aux cable and VOX PTT. I can't seem to find the problem however I suspect it to be an issue with common grounds or something of the like but I have no idea how to solve it if that is the case. Please help!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mr. Schmuck&lt;/p&gt;&#xA;" OwnerUserId="10491" LastEditorUserId="10491" LastEditDate="2017-12-29T07:05:16.517" LastActivityDate="2019-09-30T00:42:13.130" Title="Baofeng radio produces hum when plugged into charger" Tags="&lt;mobile&gt;&lt;baofeng&gt;&lt;grounding&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9684" PostTypeId="2" ParentId="9683" CreationDate="2017-12-29T10:25:28.053" Score="3" Body="&lt;p&gt;Probably the charger you're using. I ran into a similar issue with a QRP receiver I was running off a wall wart. Try with a different wall wart, or maybe a few windings through a toroid.&lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2017-12-29T10:25:28.053" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9685" PostTypeId="2" ParentId="9683" CreationDate="2017-12-29T13:46:10.103" Score="2" Body="&lt;p&gt;The symptoms you related sound like a classic ground loop problem. One solution is to galvanically isolate the PI circuit from the radio. This technique allows the signals to pass but not stray currents. Here is a simple circuit containing only three parts that can be built for under $10 with new parts.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/i84pP.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fi84pP.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The audio transformer isolates the audio signal while the optoisolator isolates the push to talk (PTT) signal. There should be no other direct connections between the PI and the radio (or its power supply).&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2017-12-29T14:15:20.203" LastActivityDate="2017-12-29T14:15:20.203" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9686" PostTypeId="1" CreationDate="2017-12-29T20:00:39.507" Score="2" ViewCount="475" Body="&lt;p&gt;I got a brand new Kenwood D-710G under the Christmas tree and have been exploring many of its functions. This one has me stumped:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I set, let's say, Band A to a frequency of 131.550 (AM) to monitor aircraft digital transmissions (ACARS)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I cannot get either Band down into the aviation area. Please consider step by step directions as I am deep into the confusion area!&lt;/p&gt;&#xA;" OwnerUserId="10942" LastEditorUserId="76" LastEditDate="2017-12-29T20:44:50.893" LastActivityDate="2018-12-25T22:24:04.630" Title="Programming Aviation Band on Kenwood D-710G?" Tags="&lt;kenwood&gt;&lt;equipment-operation&gt;&lt;airband&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9687" PostTypeId="2" ParentId="9686" CreationDate="2017-12-29T20:43:35.193" Score="3" Body="&lt;p&gt;First of all, &lt;strong&gt;only Band A&lt;/strong&gt; (left side) can be tuned to the aviation band; if you try to use Band B it will not work. Press the left &quot;BAND SEL&quot; button (volume knob). Then you should be able to use the tuning knob to tune to the frequency you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it skips over the aviation band, then the first thing to check is that the aviation band is not masked. This is covered in the secondary &quot;CD-ROM&quot; manual, page &quot;OTHER OP-1&quot;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;Turn the transceiver power OFF.&lt;/li&gt;&#xA;  &lt;li&gt;Press the left or right [BAND SEL] + Power ON.&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;The band mask display appears.&lt;/li&gt;&#xA;  &lt;/ul&gt;&lt;/li&gt;&#xA;  &lt;li&gt;Rotate the Tuning control to select the band you want to hide (or return to normal).&lt;/li&gt;&#xA;  &lt;li&gt;Press the Tuning control to set the selected band.&lt;/li&gt;&#xA;  &lt;li&gt;Rotate the Tuning control to set the band to select USE or MASK.&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;USE allows you to see and use the band as normal. MASK hides the band on the display.&lt;/li&gt;&#xA;  &lt;/ul&gt;&lt;/li&gt;&#xA;  &lt;li&gt;Press the Tuning control to set the selection.&lt;/li&gt;&#xA;  &lt;li&gt;Press the [ESC] to exit.&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(Caution: the paragraph at the beginning of the section about &quot;hide the frequency display&quot; has nothing whatsoever to do with the actual function being described. Evidently even Kenwood's technical writers were confused by the choice of &quot;band&quot; to refer both to frequency bands and what another radio might call VFOs.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I checked that my own TM-D710G can receive 131.550 MHz as you mentioned (with the band not masked).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2017-12-29T20:43:35.193" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9688" PostTypeId="1" CreationDate="2017-12-30T09:18:07.780" Score="0" ViewCount="79" Body="&lt;p&gt;I bought two RF modules that were made by different manufacturers. They were both labeled 315MHz on the manufacturers' websites. However, when I tested their frequencies with SDR#, I saw that even though they both fell into the 315MHz range, their frequencies aren't exactly the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will the two RF modules be able to communicate with each other?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please kindly refer to the screenshot below for the tested frequencies:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6ltXQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6ltXQ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10946" LastActivityDate="2017-12-30T23:30:20.900" Title="Can two 315MHz RF modules communicate with each other if none of their frequencies are exactly 315MHz?" Tags="&lt;transceiver&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9689" PostTypeId="2" ParentId="9051" CreationDate="2017-12-30T12:23:45.633" Score="-1" Body="&lt;p&gt;This Might be Helpful !&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://sites.auburn.edu/admin/facilities/spw-bid-calendar/11-150%20AU%20Regional%20Airport-Construct%20a%20Self-Supporting%20Radio%20Tower/Project%20Documents/1/Motorola_R56_2005_manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://sites.auburn.edu/admin/facilities/spw-bid-calendar/11-150%20AU%20Regional%20Airport-Construct%20a%20Self-Supporting%20Radio%20Tower/Project%20Documents/1/Motorola_R56_2005_manual.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Motorola has done quite a bit of research on this subject.&#xA;Good luck.&lt;/p&gt;&#xA;" OwnerUserId="438" LastActivityDate="2017-12-30T12:23:45.633" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9690" PostTypeId="1" AcceptedAnswerId="9692" CreationDate="2017-12-30T22:26:58.790" Score="0" ViewCount="422" Body="&lt;p&gt;I got a brand new &lt;a href=&quot;http://www.hytera.com/navigation.htm?newsId=256&amp;amp;columnType=product&amp;amp;pageType=newDetail&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hytera PD785G&lt;/a&gt;. When I turn it on, it says that it needs to be programmed. I've got a USB programmer cable and I know that there are official &lt;a href=&quot;http://www.hytera.com/productResources.htm?columnId=416&amp;amp;proId=256&quot; rel=&quot;nofollow noreferrer&quot;&gt;drivers and software&lt;/a&gt; for download.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I get most out of my radio using those drivers or is there some open source project which offers additional features?&lt;/p&gt;&#xA;" OwnerUserId="890" LastEditorUserId="76" LastEditDate="2017-12-31T01:44:31.413" LastActivityDate="2017-12-31T05:42:04.903" Title="Alternative software for Hytera PD785G" Tags="&lt;software&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9691" PostTypeId="2" ParentId="9688" CreationDate="2017-12-30T23:30:20.900" Score="3" Body="&lt;p&gt;It is difficult to give a specific answer based on the limited information supplied. Here are some general considerations:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Most receivers will have a tolerance for locking onto a transmitter's frequency. The specific tolerance is fully dependent on the design that has been implemented by the manufacturer. But consider that even with modules supplied by the same manufacturer, there will be a tolerance associated with the transmit frequency for which the receiver must adjust accordingly.&lt;/li&gt;&#xA;&lt;li&gt;There is more to consider than simply frequency tolerance when mixing modules from different manufacturers. The modulation mode, the modulation index, the encoding methods, etc. must be matched between the receiver and the transmitter. For example, if the transmitter is sending with amplitude modulation (AM) and the receiver is decoding signals using frequency modulation (FM), even if they are on the same frequency, the two will not be compatible.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2017-12-30T23:30:20.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9692" PostTypeId="2" ParentId="9690" CreationDate="2017-12-31T05:36:00.690" Score="1" Body="&lt;p&gt;Go with the official drivers and software. (I'd recommend that for any radio: that will let you know things are running.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some radios (Tytera MD-380, MD-390 and the clone Retevis R3, R8 and Zastone D900) have unlockable boot loaders and reverse-engineered firmware, but the Hytera PD785G is not in that group.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2017-12-31T05:42:04.903" LastActivityDate="2017-12-31T05:42:04.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9693" PostTypeId="1" AcceptedAnswerId="9694" CreationDate="2018-01-01T04:04:02.707" Score="1" ViewCount="1557" Body="&lt;p&gt;I was doing some research about the relation between wavelength and antenna size and shape. I was mostly interested in 15KHz rf range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on my research I found the following:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A squarish shape antenna is the best sender/receiver&lt;/li&gt;&#xA;&lt;li&gt;Wavelength of the 15Khz frequency is around 14990 meter&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A simple antenna with half the wavelength of signal can send/receive this frequency but it can be altered to smaller size by using thin wire wrapped around a ferrite object. (Same method used in AM antenna design).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, let say if I use the wire gauge 26 ( with 0.4mm / 0.0159 inch diameter), how many wire turns (loops) is required for a 50mm (~ 20 inch) square shape antenna to send/receive this 15Khz signal?&lt;/p&gt;&#xA;" OwnerUserId="10952" LastEditorUserId="76" LastEditDate="2018-01-01T04:25:13.567" LastActivityDate="2018-01-02T13:55:00.233" Title="Designing VLF antenna" Tags="&lt;antenna-theory&gt;&lt;vlf&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9694" PostTypeId="2" ParentId="9693" CreationDate="2018-01-01T19:08:00.523" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;A squarish shape antenna is the best sender/receiver&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There is no practical basis for this assertion.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Wavelength of the 15Khz [SIC] frequency is around 14990 meter [SIC]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The formula for the reasonable approximation of wavelength is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\lambda (in\space meters) = \frac{300}{Frequency\space in\space MHz} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since 15 kHz is 0.015 MHz, it has a wavelength of ~20,000 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When a loop antenna is constructed with a loop circumference that is less than 1/10 wavelength, it is classified as a small loop antenna. When designing these types of antennas, one of the most important factors to which the engineer must pay attention is the &lt;em&gt;efficiency&lt;/em&gt;. Small loop antennas have very low radiation resistance which gives rise to an inefficient antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna efficiency is defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$efficiency = \frac{R_r}{R_r+R_l} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where R&lt;sub&gt;r&lt;/sub&gt; is the radiation resistance and R&lt;sub&gt;l&lt;/sub&gt; is the RF resistive losses of the antenna and any losses in the core material.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see from equation 2 that as the radiation resistance is reduced, for a given resistive loss, the efficiency drops precipitously.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation resistance of a multi-turn loop antenna that is wound around a high permeability material, such as ferrite or iron powder, is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_r=197n^2\mu_{er}^2\left(\frac{C}{\lambda}\right)^4 \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where C is the circumference of the loops in meters, n is the number of turns of wire and $\mu_{er}$ is the effective relative permeability of the material around which the loops are wound. If the loops are air wound, simply set $\mu$&lt;sub&gt;er&lt;/sub&gt; to 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see from equation 3 that for a given core material, as the number of turns are increased, the radiation resistance goes up according to the number of turns squared.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The approximate RF resistance of the loop antenna is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_l=n*C*R_{wire} \tag 4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where R&lt;sub&gt;wire&lt;/sub&gt; is the RF resistance of the wire in ohms/meter. The RF resistance of 26 gauge (AWG) copper wire at 15 kHz is 1.265 ohms/meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The gain of the small loop antenna is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$G=1.5*n*efficiency \tag 5$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Armed with these formulas, you can calculate all of the parameters for any proposed 15 kHz small loop antenna. What you will find is that very small antennas such as you suggest will be very low gain antennas due to low efficiency. Whether or not such an antenna is adequate for your application depends on many other factors such as receiver sensitivity, transmitter power, distance, etc.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-02T13:55:00.233" LastActivityDate="2018-01-02T13:55:00.233" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9695" PostTypeId="2" ParentId="9671" CreationDate="2018-01-02T07:23:34.737" Score="0" Body="&lt;p&gt;For the United States of America:&#xA;&lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/amateur-radio-service&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/amateur-radio-service&lt;/a&gt;&#xA; For the rest of the world, I have done little to no research but believe the overall governing body would be the International Telecommunication Union, or ITU, a body of the U.N.&#xA;Here would be the wiki site which was referred to as not being available&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/International_Telecommunication_Union&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/International_Telecommunication_Union&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10954" LastEditorUserId="873" LastEditDate="2018-01-02T07:52:10.280" LastActivityDate="2018-01-02T07:52:10.280" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9696" PostTypeId="1" AcceptedAnswerId="9697" CreationDate="2018-01-02T10:43:46.327" Score="1" ViewCount="819" Body="&lt;p&gt;Here's a picture of my SDR receiver setup...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cc3cg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cc3cg.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;This entire setup lives indoors as I'm not able to put anything up on the roof right now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding of a discone antenna is that the downward diagonal elements are supposed to act as an arbitrary, floating ground plane against which the vertical elements resonate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This setup works as it is but I'm getting problems with pickup on the metal case of the SDR.  If I put my hand on the metal case (anodised Aluminium enclosure well connected to the ground plane of the receiver PCB) then the noise floor on my HDSDR software jumps up massively.  What was a relatively quiet waterfall becomes a bright red mess as soon as I lay my hand on the case.  That said, I cannot hear any difference in the demodulated signal (2 Meter band, AM for instance).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems in my mind like this pickup should be prevented because of the connection to a real earth ground (via the PC's mains power supply).  There is good connductivity between the diagonal elements of the Discone and earth ground (less than 2 Ohms at DC, according to my multimeter).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The USB is about 2 metres long, the Coax is about 3 metres.  All connectors are soundly fastened and have good conductivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: The SDR device is entirely USB powered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Questions&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is clear that the PC's USB connection is pulling the metal case down to &quot;Earth ground&quot;.  Is this detrimental to the use of a discone antenna?  Is it bad to have a metal case on an SDR?  Is there anything I can do to improve this setup?&lt;/p&gt;&#xA;" OwnerUserId="6744" LastEditorUserId="6744" LastEditDate="2018-01-02T15:27:01.963" LastActivityDate="2018-01-02T15:27:01.963" Title="SDR - discone antenna setup" Tags="&lt;software-defined-radio&gt;&lt;antenna-theory&gt;&lt;receiver&gt;&lt;grounding&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9697" PostTypeId="2" ParentId="9696" CreationDate="2018-01-02T12:11:07.460" Score="4" Body="&lt;p&gt;The symptoms described are consistent with common mode currents. These are undesired currents flowing on the outside of the shield of the coax (desired currents flow on the inside of the shield and the center conductor). The result is that the exterior shield of the coax acts as part of the antenna. By touching the coax or the electrically connected SDR enclosure, your body becomes part of the antenna system altering its performance for better or worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common mode currents can be suppressed by installing a choking balun on the coax as it exits the discone. Ferrite type baluns are usually the best but you can experiment with simply winding 6 to 8 turns of coax in a 6 to 8 inch diameter bundle. This is a compromise balun that works best over the range of a few ham bands. Experiment with the number of turns and the diameter to optimize your results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These types of baluns can be effective up to 30 MHz or so. With higher frequencies, other methods must be deployed. Unfortunately, the higher frequency solutions are usually effective for a single band and its odd multiples. An example of this is to use a coax connection that is electrically an odd 1/2 wavelength long for the frequency that is being received. This tends to present a high impedance to the common mode currents. But because the length of the coax must be adjusted according to the frequency, it is only practical for a small range of frequencies. Another example of this type of frequency dependent solution is a sleeve balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One side effect of reducing common mode currents is that your antenna may not perform as well as it had. Sometimes the coax shield acting as part of the antenna is helpful to the overall antenna performance, despite the negative effects. Experimentation will determine what is best for your situation.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-02T12:50:31.743" LastActivityDate="2018-01-02T12:50:31.743" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9698" PostTypeId="2" ParentId="9681" CreationDate="2018-01-02T18:45:30.057" Score="1" Body="&lt;p&gt;I copied a test transmission from H.A.A.R.P. on this frequency in the 1990s. It was on 6.99 MHz @ 0430 - 0435 UTC. I have a card from them 3/8/97 confirming my reception. Perhaps that's what it is.&lt;/p&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="966" LastEditDate="2018-01-05T21:39:21.260" LastActivityDate="2018-01-05T21:39:21.260" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9699" PostTypeId="2" ParentId="9676" CreationDate="2018-01-02T19:03:13.090" Score="0" Body="&lt;p&gt;USE SKED 80 PVC UR WINDLOAD IS MINIMAL, BUT I WOULD PARACORD GUY IT JUST TO BE SAFE.&#xA;IF UR NOISE LEVEL IS HIGH, U MIGHT CONSIDER A PARALLEL COAX FEED [SORT OF LIKE BALANCED LINE, ONLY SHIELDED.] 2 - 50 OHM COAX IN PARALLEL WILL GIVE U 100 OHMS, BUT THAT SHOULD WORK O.K.&#xA;I USE AN OCFD FED THAT WAY [USING RG-6 75 OHM] AND HAVE MADE ANTENNAS LIKE IT FOR OTHERS.&#xA;NOTHING BUT GOOD COMMENTS - SOME CLAIM A 5 S-UNIT REDUCTION IN NOISE LEVEL. U CAN SEE IT HERE &lt;a href=&quot;http://www.hamuniverse.com/kf9focfdipole.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hamuniverse.com/kf9focfdipole.html&lt;/a&gt;TO GET AN IDEA OF THE FEEDLINE. '73 AND GL RICH, KF9F&lt;/p&gt;&#xA;" OwnerUserId="8492" LastActivityDate="2018-01-02T19:03:13.090" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9700" PostTypeId="2" ParentId="9681" CreationDate="2018-01-02T23:42:13.510" Score="-2" Body="&lt;p&gt;First Guess is PSK-31 loaded as a CW signal, offset to 2200. &lt;/p&gt;&#xA;" OwnerUserId="8402" LastActivityDate="2018-01-02T23:42:13.510" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9701" PostTypeId="1" CreationDate="2018-01-03T01:50:58.363" Score="0" ViewCount="593" Body="&lt;p&gt;DARA (you know, Hamvention) TNG is looking for projects. Thursday, I will be proposing building and characterizing a vertically-polarized 1 wavelength on a side reentrant rhombic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since in doing the presentation I want to show how a Rhombic gets its fabulous gain, I need to find out gains of various long wires, especially integer wave length wires, 1, 2, and four wavelengths long.&lt;/p&gt;&#xA;" OwnerUserId="10960" LastEditorUserId="76" LastEditDate="2018-01-03T02:32:02.287" LastActivityDate="2018-03-04T04:32:29.547" Title="Gain in long wire antennas" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vhf&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9702" PostTypeId="2" ParentId="9701" CreationDate="2018-01-03T02:48:47.803" Score="1" Body="&lt;p&gt;A 1 wavelength long wire has a 2.75 dBi free space gain, 2 wavelengths is 4.75 dBi and 4 wavelengths is 6.75 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have the formulas at the top of my head to support this data. I am referencing Figure 1 in Chapter 13 of the 20th edition of the ARRL Antenna Book.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a paper I have from Cebik in antenneX Online Magazine, he shows  2.99, 4.81 and 6.98 dBi respectively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These two sources show reasonable agreement. I would anticipate higher gain when the antenna is close to ground. If you need the formulas, indicate so in the comments and I will look them up for you.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-03T03:25:40.157" LastActivityDate="2018-01-03T03:25:40.157" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9703" PostTypeId="1" AcceptedAnswerId="9704" CreationDate="2018-01-03T19:07:20.630" Score="8" ViewCount="328" Body="&lt;p&gt;If an unlicensed operator is operating phone on an amateur frequency under the direct supervision of a licensed operator for, say, longer than ten minutes, should the unlicensed operator say the call sign of the licensed operator, or should the licensed operator take the mic and say it? This is not like in Field Day or a special event station, which are covered under a different rule [97.119(d)].&lt;/p&gt;&#xA;" OwnerUserId="9166" LastEditorUserId="8717" LastEditDate="2018-01-28T03:02:10.853" LastActivityDate="2018-01-28T03:02:10.853" Title="Who should announce the call sign when an unlicensed operator is transmitting?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;&lt;station-identification&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9704" PostTypeId="2" ParentId="9703" CreationDate="2018-01-03T20:53:41.707" Score="5" Body="&lt;p&gt;Yes - they can ID your station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part 97 does not specify who must identify your station, rather, that it must be done in 10 minute intervals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a licensee, you are ultimately responsible for all transmissions that come from your station. If there is third party traffic (your friend talking), this means you must be present at the control point to disable the transmitter should any violation of part 97 occur. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You must be in control of the equipment at all times, and are still responsible to make sure that your station identification is given per part 97.&lt;/p&gt;&#xA;" OwnerUserId="9236" LastActivityDate="2018-01-03T20:53:41.707" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9705" PostTypeId="1" AcceptedAnswerId="9707" CreationDate="2018-01-03T23:37:45.887" Score="5" ViewCount="159" Body="&lt;p&gt;I often hear people say brief statements or sentences after giving their callsign for the final time. Examples that I have heard on the air are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&quot;[callsign] clear&quot;&lt;/li&gt;&#xA;&lt;li&gt;&quot;[callsign] listening&quot;&lt;/li&gt;&#xA;&lt;li&gt;&quot;[callsign] testing&quot;&lt;/li&gt;&#xA;&lt;li&gt;&quot;[callsign] back to the net&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I've also heard people identify and then give a one or two sentence goodbye. This seems to be common practice, at least on my local repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this sort of thing widely considered acceptable? If so, how long can I go on transmitting after identifying for the final time? Has the FCC issued any opinion or taken any enforcement actions that might shed light on their interpretation of this phrase?&lt;/p&gt;&#xA;" OwnerUserId="10859" LastActivityDate="2018-01-04T05:49:33.890" Title="How strictly is &quot;the end of each communication&quot; defined for the purpose of station identification?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9706" PostTypeId="1" AcceptedAnswerId="9710" CreationDate="2018-01-04T00:46:45.760" Score="5" ViewCount="246" Body="&lt;p&gt;I was reading about &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Ground-penetrating_radar&quot; rel=&quot;noreferrer&quot;&gt;GPR devices&lt;/a&gt; recently.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Considering the operation frequency of these devices, how they can go that deep (up to 50 feet)?  Normally you would only expect a Hz to KHz range signal to go that deep into the ground.&lt;/p&gt;&#xA;" OwnerUserId="10952" LastEditorUserId="76" LastEditDate="2019-04-13T20:32:09.603" LastActivityDate="2019-04-14T08:18:51.123" Title="How can Ground Penetrating Radar work?" Tags="&lt;propagation&gt;&lt;equipment-design&gt;&lt;earth&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9707" PostTypeId="2" ParentId="9705" CreationDate="2018-01-04T05:49:33.890" Score="7" Body="&lt;p&gt;I'm not aware of any FCC opinions, but I can give my own interpretation, which is: a sentence is fine, as long as it keeps to a single thought and doesn't go to Faulknerian or Hawthornean lengths. If it serves the purposes of &lt;em&gt;identifying&lt;/em&gt; and &lt;em&gt;ending the transmssion&lt;/em&gt; at pretty much the same time, there isn't much room for complaint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The intent of the reg is that if anyone hears you doing something problematic, they should be able to find out who you are by listening from that point onward to catch your callsign. So be courteous and don't cause problems. Keep your signoff brief, and, if in doubt, keep it pro forma. The cases of &quot;[call] testing&quot; and &quot;[call] monitoring&quot; are standard practice, and certainly no one objects to a CW operator sending &quot;pse k&quot; at the end of a CQ. Something like &quot;[call], wishing everyone a happy new year, clear&quot; is arguably bad form, but unlikely (in my opinion) to draw you a fine or a letter. Maybe a postcard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did some searching of violation notices on fcc.gov containing &quot;97.119&quot; or &quot;end of each communication&quot;. Many of them, and the majority of the fines, involved operators who deliberately didn't ID at all, usually in together with jamming, playing music, or non-amateur activity. One amateur who accidentally left the radio on and a CW keyer sending an endless string of dits was asked to send an affidavit basically convincing the FCC it wouldn't happen again. A few were dinged for chatting 20 minutes or more without IDing, and one for making &quot;several short transmissions&quot; without ID. I didn't come across any complaints against operators who had too much to say after their final ID.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2018-01-04T05:49:33.890" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9708" PostTypeId="2" ParentId="9706" CreationDate="2018-01-04T12:31:25.567" Score="0" Body="&lt;p&gt;Although I admit more ignorance than knowledge in this area, I remember reading many places (don't remember where) about how deep radio waves penetrate the earth with regards to transmitting and earth losses (and how to avoid the losses). I remember that even at HF the penetration can easily be be several feet, and if memory serves correctly, it gets deeper with lower frequencies. Although it may not be related (again I plead ignorance) it reminds me of the skin effect, which causes the signal to be closer to the surface of the conductor as the frequency rises (less &quot;deep&quot; in the conductor). It is therefore not unreasonable to believe that at these ELF and VLF frequencies the signals can penetrate the ground to a very deep level. Hope this helps.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastActivityDate="2018-01-04T12:31:25.567" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9710" PostTypeId="2" ParentId="9706" CreationDate="2018-01-04T15:44:39.980" Score="9" Body="&lt;p&gt;There is a special adaptation of the Friis equation, called the Radar Equation, that describes the range of a radar system. Here is a &lt;em&gt;basic&lt;/em&gt; version that calculates the maximum range of a radar system:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_{max}=\sqrt[4] {\frac {P_tG^2\lambda^2\sigma}{P{_{r(min)}}*(4\pi)^3*L}} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $R_{max}$ is the maximum range in meters, $P_t$ is the transmit power in watts, $G$ is the linear gain the combined transmit and receive antenna, $\lambda$ is the wavelength in meters of the frequency, $\sigma$ is the effective radar target cross section in square meters, $P_{r(min)}$ is the minimum receiver power required in watts, and $L$ is a linear loss factor to consolidate all losses other than free space effects encountered in the radar path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if we take a 2 GHz radar (0.15 meters) with 10 watts of transmit power, a receiver with 0.25 $\mu$V of sensitivity (1.25e&lt;sup&gt;-15&lt;/sup&gt; watts for a 50 ohm system), an antenna with a linear gain of 31.6 (15 dBi), a 1 square meter metal target and no other path losses, we calculate a maximum effective distance of 3,085 meters (10,121 feet).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We would now need to account for the losses of earth (rock, soils, sands and water) to apply this to a ground penetrating radar. This can be factored into $L$ in equation 1. I do not have data at hand to suggest what the possible attenuation factors would be for various forms of earth so instead, it may be instructive to rework equation 1 to solve for the maximum attenuation that can be accommodated over a specified distance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$L={\frac {P_tG^2\lambda^2\sigma}{P{_{r(min)}}*(4\pi)^3*R_{max}^4}} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we set $R_{max}$ to 15.24 meters (50 feet) as questioned by the OP and leave all other parameters the same, we find that an additional path loss ($L$) of ~92 dB (~1.68e&lt;sup&gt;9&lt;/sup&gt; linear attenuation) could be accommodated before the radar would not be able to detect a signal from a 1 meter square metal target 15.24 meters below the surface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So armed with these basic formulas, one can run various &quot;what if&quot; scenarios to get a sense of what is possible. Do keep in mind that this is a very simplified form of the radar equation that does not 'reflect' (pun intended) all of the factors involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did find some very basic soil attenuation data at &lt;a href=&quot;https://archive.epa.gov/esd/archive-geophysics/web/html/ground-penetrating_radar.html&quot; rel=&quot;noreferrer&quot;&gt;https://archive.epa.gov/esd/archive-geophysics/web/html/ground-penetrating_radar.html&lt;/a&gt;. Here is an extract of attenuation in the 40 to 1,500 MHz range:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4kcW8.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4kcW8.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-04T16:32:39.360" LastActivityDate="2018-01-04T16:32:39.360" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9712" PostTypeId="1" AcceptedAnswerId="9720" CreationDate="2018-01-05T14:20:22.433" Score="3" ViewCount="566" Body="&lt;p&gt;Ok, I get that &quot;RF hash&quot; is some sort of slang for &quot;RF interference&quot; (think CB), but does it refer to a particular type or source of interference? Do tell.&lt;/p&gt;&#xA;" OwnerUserId="9166" LastEditorUserId="76" LastEditDate="2019-04-13T20:23:06.707" LastActivityDate="2019-04-13T20:23:06.707" Title="What is RF hash?" Tags="&lt;rfi&gt;&lt;jargon&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9713" PostTypeId="2" ParentId="9712" CreationDate="2018-01-05T15:48:33.353" Score="1" Body="&lt;p&gt;When I think of &quot;RF Hash&quot; I think of a constant &quot;sparky&quot; sort of interference, like an insulator arcing, or RF noise from an electric motor or some gas discharge lamps or lamp dimmers.   Compared to, say, lightning (non-repetitive) or white noise (not &quot;sparky&quot;.)  Whether that's the CBers definition or not, I don't know.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-01-05T15:48:33.353" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9714" PostTypeId="1" CreationDate="2018-01-05T19:47:22.247" Score="3" ViewCount="1540" Body="&lt;p&gt;Instead of using a metal vehicle roof or multiple radials as the counterpose to a shortened vertical antenna, can one use two of them, one pointed downward to construct a balanced vertical dipole, and mounting the pair up higher?  Are there any advantages or disadvantages to doing this over using a bunch of random length radials around the base of a lower vertical?  (other than needing to string the feed-line out roughly horizontally for some lambda distance...)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-01-09T17:26:37.843" Title="Using two short mobile HF antennas to make a vertical dipole" Tags="&lt;dipole&gt;&lt;vertical-antenna&gt;&lt;radial&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9715" PostTypeId="1" CreationDate="2018-01-06T07:36:47.003" Score="0" ViewCount="814" Body="&lt;p&gt;Prior to transmission, almost all wireless systems perform encoding on data to improve the packet reception rate. These may include, Forward Error Correction, Interleaving, Whitening, Gray Coding etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I'm finding it difficult to understand the purpose of &quot;Data Whitening&quot;. From my understanding, Whitening makes sure that there are no continuous &quot;1&quot;'s or &quot;0&quot;'s in the transmitted packet. Common literature say that this &quot;diversity&quot; improves the performance of the &quot;physical Channel&quot; I.e. the wireless channel in this case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to know how exactly does introducing &quot;data whitening&quot; improves the physical layer performance of a wireless channel. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any other advantages to Data Whitening?&lt;/p&gt;&#xA;" OwnerUserId="1694" LastActivityDate="2018-01-06T16:20:20.900" Title="How exactly does Data Whitening improve performance?" Tags="&lt;usrp&gt;&lt;encoding&gt;&lt;whitening&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9716" PostTypeId="1" AcceptedAnswerId="9717" CreationDate="2018-01-06T07:49:42.167" Score="5" ViewCount="360" Body="&lt;p&gt;Is it safe to define that Data Whitening is always X-ORing a payload with a pheudorandom sequence known to both receiver and transmitter? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In more detail, lets assume the following case. I have the exact pseudorandom string that is used for Data Whitening of a SX-1234 transceiver (a random transceiver). Lets also assume that I have captured the &lt;strong&gt;already whitened payload&lt;/strong&gt; received by another SX-1234 transceiver. Provided SX-1234 does not perform any other encoding steps other than data whitening, if I simply X-OR my received payload with the pseudorandom string, will I get back the originally transmitted data? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, what other methods are there for data whitening other than simple X-ORing. &lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorUserId="1694" LastEditDate="2018-01-06T08:01:45.140" LastActivityDate="2018-01-06T16:14:20.267" Title="How is Data Whitening done?" Tags="&lt;encoding&gt;&lt;whitening&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9717" PostTypeId="2" ParentId="9716" CreationDate="2018-01-06T16:14:20.267" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it safe to define that Data Whitening is always X-ORing a payload with a pheudorandom sequence known to both receiver and transmitter?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, but that's a very common way of doing it. However, you can scramble and whiten a sequence by pushing it through an appropriate Linear Feedback Shift Register, and I'd assume that this is even more commonly applied in practice.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I have the exact pseudorandom string that is used for Data Whitening of a SX-1234 transceiver (a random transceiver)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That is a rather uncommon case. As said above, I'd assume most systems do NOT just XOR with a fixed sequence, but scramble the data itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And even for systems where the data is XOR'ed with a pseudorandom sequence, I'd assume that for whitening reasons, you'd want that sequence to be long. Such sequences aren't stored, but again, generated using things like linear feedback shift registers, or other algebraic approaches. Such a sequence can easily become &lt;em&gt;very&lt;/em&gt; long. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, unless SX-1234 is a very old standard, it's questionable that you &quot;captured&quot; the whole sequence. Maybe you mean you've got the generator for the same sequence? Then you &quot;only&quot; have to sync up to your data stream. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's very hard to estimate the current state in that sequence from a short observation (that's a requirement for good pseudorandom generators, and it's often very desirable, again, for autocorrelation/whitening reasons). So your syncing can, often, only be approached by a brute force trial of all possible shift – a usually impractical approach.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Provided SX-1234 does not perform any other encoding steps other than data whitening, if I simply X-OR my received payload with the pseudorandom string, will I get back the originally transmitted data? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. If SX-1234 is prudent enough to whiten the data, then it'll certainly also employ channel coding (and that can be, if you don't know anything about the channel code, pretty much encryption). Oh, and let's not forget interleaving, which, especially for systems that transmit long streams of data, is employed to convert burst errors into sporadic errors (which the channel code can much easier correct).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-01-06T16:14:20.267" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9718" PostTypeId="2" ParentId="9715" CreationDate="2018-01-06T16:20:20.900" Score="3" Body="&lt;p&gt;Imagine your data is &lt;strong&gt;not&lt;/strong&gt; white. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means that at certain periods, it contains more variance, and hence information, than on others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's bad, because now certain frequencies become more sensitive to noise than others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other than that: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many things that a receiver needs to do (AGC, equalization, synchronization) depend on the temporal stochastic properties of your signal. For example, if you have a blind equalizer, it has to assume it knows the spectrum of your transmit signal without having already successfully received it. The only way of ensuring (in the stochastic sense, &quot;almost sure&quot;) that it has this knowledge without reducing the transinformation is to make sure the transmit signal is whitened.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-01-06T16:20:20.900" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9719" PostTypeId="2" ParentId="7089" CreationDate="2018-01-06T17:22:51.770" Score="1" Body="&lt;p&gt;Note that some writers believe that a primary function/purpose of elevated radials is to shield an elevated vertical monopole such as a vertical ground plane antenna from the earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This does seem intuitive, but in reality the free space radiation patterns of a λ/4 ground plane driven against pairs of elevated, λ/4, horizontal radials at its base and a center-fed, λ/2 vertical dipole are very similar (see the NEC4.2 analysis below). Other things equal, any effects/changes due to reflections from the earth or another surface will be very nearly the same for the radiation patterns of &lt;strong&gt;both&lt;/strong&gt; of these configurations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When pairs of horizontal elevated radials are separated by horizontal spans of 180° then the net far-field radiation from them essentially is zero. This is the result of the radiation from one side of the pair arriving 180° out of phase with the other side of the pair, as r-f currents are flowing in opposite physical directions on each side of that pair. All of the useful radiation from a vertical ground plane antenna originates from the r-f current flowing along the vertical conductor located physically above the horizontal radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As shown in the graphic below, the elevated, co-linear pairs of horizontal radials of a ground plane antenna do not shield a likewise-elevated vertical conductor above them from interaction with, or radiation toward the earth. They serve as part of the current path connecting the antenna system to the r-f &quot;ground&quot; return of the source (the transmitter). &lt;em&gt;Without such a path, no antenna system will produce useful radiation.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The source for the r-f current flowing on the buried radials used&#xA;with a monopole antenna is the r-f current flowing in the earth&#xA;within λ/2 of the base of the monopole, as a result of radiation from&#xA;that monopole. The sum of that current at the common point of the&#xA;buried radials exactly equals the r-f current that can/will flow on&#xA;the monopole, itself.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The source for the r-f current flowing on the elevated radials used&#xA;with an elevated monopole antenna is a direct, wire connection to the&#xA;r-f source (transmitter), using an all-physical conducting path such&#xA;as the outer conductor of a coaxial transmission line between the&#xA;antenna system input terminals and the transmitter.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Elevated radials function much differently than buried radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bLU43.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bLU43.jpg&quot; alt=&quot;NEC4.2 Analysis:&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-01-06T17:22:51.770" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9720" PostTypeId="2" ParentId="9712" CreationDate="2018-01-06T18:58:14.677" Score="4" Body="&lt;p&gt;Discovered on another thread (eham) that &quot;RF hash&quot; is slang for broadband noise, meaning a) RF interference that has an unusually large bandwidth (continuously spread) or b) covers multiple frequency ranges over an unusually large spectrum (non-continuous spread).&lt;/p&gt;&#xA;" OwnerUserId="9166" LastActivityDate="2018-01-06T18:58:14.677" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9721" PostTypeId="2" ParentId="6300" CreationDate="2018-01-07T15:05:41.363" Score="1" Body="&lt;p&gt;I have used a variety of vertical wires (usually NOT quarter wave length for any given band) with auto-couplers at their feed points as described above and agree totally with the author about their HF utility. Tall tree halyards and extended fiberglass poles have been my favorite ways to suspend wires.  Hard to understand why so many folks don't like putting down the radial wires though. I almost never use less than 40 radial wires of 30-50 foot lengths on top of the dirt.  That's true even when I operate portable in the woods of western Wisconsin every summer. The putting down and taking up of the radial wires in that portable setting are just part of daily exercise for the low back, essential for old codgers like me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In sum, these are in my view great antenna systems if you put in a little upfront work.  My favorite couplers have included the Icom AH-4, the SGC-230, and the MFJ-998RT (for legal limit power).  I have ALWAYS used chokes on the coax lines running to those couplers, one at the input to the coupler and another one right outside the shack. The &quot;DC voltage injector&quot; used with the MFG unit works great--I have used it flawlessly with a 200-foot run of RG-213 in Vermont during winter ops. &lt;/p&gt;&#xA;" OwnerUserId="10983" LastActivityDate="2018-01-07T15:05:41.363" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9722" PostTypeId="1" AcceptedAnswerId="9723" CreationDate="2018-01-07T21:28:24.940" Score="10" ViewCount="245" Body="&lt;p&gt;A recent discussion about SWR led to the assertion that a length of coax cable will ultimately limit the SWR to which the transmitter will be exposed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By experimenting with an SWR calculation tool like &lt;a href=&quot;http://www.ac6la.com/tldetails1.html&quot; rel=&quot;noreferrer&quot;&gt;&lt;em&gt;TLDetails&lt;/em&gt;&lt;/a&gt;, there appears to be a basis for this assertion. For example, with a 100 foot length of RG-8X coax on 15 meters, the SWR at the transmitter end never goes above 5.8:1. Even an open or shorted cable at the far end does not raise the SWR above this limit. Experimenting with different lengths and types of coax changes the limit but there always seems to be a limit of some kind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is causing this and what it the math behind it? Can this be used to 'fix' a high SWR at the antenna?&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="76" LastEditDate="2018-01-12T16:39:58.670" LastActivityDate="2018-01-12T16:39:58.670" Title="Does Coax Limit the Maximum SWR a Transmitter 'Sees'?" Tags="&lt;coaxial-cable&gt;&lt;antenna-system&gt;&lt;transmission-line&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9723" PostTypeId="2" ParentId="9722" CreationDate="2018-01-07T21:28:24.940" Score="6" Body="&lt;p&gt;The source of the SWR limit on the transmitter end is the losses in the feedline. In general, the higher the matched line loss, the lower the maximum SWR that will be present at the transmitter end. Since the SWR limit is the result of losses in the feedline, the efficacy of the 'high SWR fix' must be considered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mechanism has to do with the trips that the transmitter power must make along the length of the feedline. A simple example will help to describe the effect:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First consider a feedline that has a 3 dB matched loss connected to a 100 watt transmitter. We can convert dB loss to a percent loss:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\text{Percent Loss} = \frac {1} {10^{(L_{dB}/10)}}*100 \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where L&lt;sub&gt;dB&lt;/sub&gt; is the loss in dB form.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that when the 3 dB matched line is terminated in its characteristic impedance, only 50% of the transmitted power (50 watts) will arrive at the antenna end of the line and be aborbed/radiated by the load. The other 50% has gone up as heat in the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hyz0R.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hyz0R.jpg&quot; alt=&quot;Figure 1&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now instead of a matched load, let's consider a most extreme case of leaving the far end of the coax cable open. In this condition, 100% of the power arriving at the open end is reflected back towards the transmitter. As before, only 50% of the transmitted power (50 watts) arrives at this open connection. This is now fully reflected back toward the transmitter. But just as the forward power was attenuated, so is the reflected power by the same percent. So only 25 watts arrives back at the transmitter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/12xbH.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/12xbH.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can now calculate the SWR at the transmitter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\text{SWR}=\frac{1+\sqrt {P_r/P_f}}{1-\sqrt {P_r/P_f}} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where P&lt;sub&gt;r&lt;/sub&gt; is the reflected power, P&lt;sub&gt;f&lt;/sub&gt; is the forward power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SWR at the transmitter is 3:1 in this example. Quite an amazing transformation of an infinite SWR at the far end of the feedline but it comes about as power dissipated in the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now let's generalize the example by creating an equation that allows us to calculate the maximum SWR at the transmitter end based on the matched line loss. Note that in the open end example, the power arriving back at the transmitter was attenuated twice. We can represent this as the square of the loss (i.e. loss times loss). Then if we use equation 2 but normalize the transmit power at 1 watt, the lower P&lt;sub&gt;f&lt;/sub&gt; factor goes away. This leaves us with the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\text{SWR}_\text{max}=\frac {1+\sqrt{\text{Percent Loss}^2}} {1-\sqrt{\text{Percent Loss}^2}}=\frac {1+\text{Percent Loss}}{1-\text{Percent Loss}} \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we now make a plot of formula 3, we get the following view of matched loss vs. maximum SWR:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lMJ4x.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lMJ4x.jpg&quot; alt=&quot;Figure 3&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formula 3 can be converted to a version that directly uses dB matched loss:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\text{SWR}_\text{max}=\frac {1}{\tanh \left({\frac{L_{dB}}{8.686}}\right)} \tag 4$$&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-12T13:26:55.970" LastActivityDate="2018-01-12T13:26:55.970" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9724" PostTypeId="2" ParentId="9714" CreationDate="2018-01-07T23:56:10.020" Score="5" Body="&lt;p&gt;To begin the discussion, it is helpful to understand the effects of shortening any antenna to a length below resonance. In all cases, the directivity of the antenna is reduced but this tends to be a fairly uniform reduction regardless of how much shortening occurs. The reduction in length also reduces the radiation resistance of the antenna. This is significant in that as radiation resistance is reduced, the effect of losses in the antenna is amplified. Efficiency of an antenna is defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Efficiency=\frac {R_r}{R_r+R_l} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where R&lt;sub&gt;r&lt;/sub&gt; is the radiation resistance of the entire antenna (not simply the resistive component of the feedpoint impedance&lt;sup&gt;1&lt;/sup&gt;) and R&lt;sub&gt;l&lt;/sub&gt; are the resistive losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The gain of the antenna is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Gain=Directivity*Efficiency \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it becomes clear that as an antenna is shortened, the directivity is reduced and efficiency tend to go down the further the antenna is shortened, having a compound effect in reducing the gain of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 1/4 wave vertical antenna with a substantial ground plane over real ground and a vertical, 1/2 wave dipole over real ground will have approximately the same gain of ~ 0 dBi. This includes all of the effects listed above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now to the question of which is better, the answer comes down to which is the more efficient component - the vertical's ground plane or the second shortened element that makes up the dipole? This of course depends on the specific comparison and the construction elements involved. But we can generalize an answer by saying if the ground plane is highly efficient and the dipole is made up of two of the comparatively inefficient elements as used for the vertical component of the vertical antenna, the dipole will have twice the inefficiency and therefore have a gain of -3 dB compared to the vertical antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note 1: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a common error made in many antenna texts and on Internet postings that equate radiation resistance of a lossless antenna to the resistive component of the feedpoint impedance. While this is often the case with common amateur radio antennas, there are many exceptions. For example, as amateurs we are well versed in the lossless, center fed, 72 ohm feedpoint impedance of a 1/2 wave dipole in free space. But if we take the same antenna and feed it 1/3 from the end instead of the center, we will observe a much higher resistive component of the feedpoint impedance. But the radiation resistance of the antenna is still 72 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not a trivial exercise to correctly determine the radiation resistance of an antenna. Fortunately, many antenna designs have already been characterized. We are also fortunate that in the amateur radio community, most of our linear antennas are 1/2 wavelength or shorter and we tend to feed them at the current maxima point. When these conditions are met, then the resistive component of the feedpoint impedance of the antenna &lt;em&gt;generally&lt;/em&gt; consists of the radiation resistance of the entire antenna plus the resistive losses of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example of where this knowledge can be very helpful is determining how many radials to add to a 1/4 wavelength vertical antenna in order to maximize its efficiency. If the antenna meets the earlier stated requirements, then monitoring the resistive component of the feedpoint impedance will show the increase in efficiency (reduced resistive losses) as each radial is added. When the efficiency improvement becomes asymptotic, it is no longer productive to add additional radials.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-09T16:47:49.143" LastActivityDate="2018-01-09T16:47:49.143" CommentCount="9" ContentLicense="CC BY-SA 3.0" />
  <row Id="9725" PostTypeId="2" ParentId="5902" CreationDate="2018-01-08T00:07:04.213" Score="2" Body="&lt;p&gt;It all depends on what your expectations are. At the beginning of 2018 We are at or near the solar minimum. Still, you can routinely work lots of stateside stations on 80, 40, and 20 meters with a simple entry level station --say 100 watts and a dipole. Tune across those bands and you will hear lots of signals most days. Nets are active and people are communicating. There are lots of 59+ signals to be heard. But they are mostly stateside. Upgrade to a beam or Hex Beam and of course you will make more contacts with better signal strength.  15 and 10 meters are pretty dead most of the time these days.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm hearing Europeans several times per week on 20 m. And can often work them on SSB or CW from my mobile system consisting of 90 watts and an inexpensive 20 m HamStick magnetically mounted on the center of the roof of my mini-van. The rig is nothing special, a 20 year old Kenwood TS-570 with the stock mobile hand-mike...just an old reliable utility rig. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally I'm having a lot of casual fun on HF, rag-chewing and working a little dx.  But its a very different world than a &quot;hot solar cycle&quot; at its peak. I was first licensed in 1958 at the peak of cycle 19. So I have also experienced the-best-of-times.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you have to ask yourself, What are my expectations? Do I like the challenge? What do I need for it to be enjoyable and worth while.    &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope to see you on the bands. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;K0SDZ/Bill&lt;/p&gt;&#xA;" OwnerUserId="10988" LastActivityDate="2018-01-08T00:07:04.213" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9726" PostTypeId="2" ParentId="538" CreationDate="2018-01-08T04:09:19.903" Score="0" Body="&lt;p&gt;For SWL reception, I have never used a balun. It could in fact reduce unwanted RF, but even random turns of coax can produce enough positive results on receive-only usage. For transmitting, it is obviously a completely different scenario, and I always use 1:1 baluns on half-wave dipoles and Yagis.&lt;/p&gt;&#xA;" OwnerUserId="10991" LastActivityDate="2018-01-08T04:09:19.903" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9727" PostTypeId="2" ParentId="6300" CreationDate="2018-01-08T06:42:59.100" Score="0" Body="&lt;p&gt;What's the attraction of a vertical?   Pick one or more of these:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I already tried a horizontal dipole for 5 years.   I no space to rotate the horizontal, and I wanted to try hitting the states in the nulls.   I decided the tips of the horizontal were too close to the shack and I was getting direct radiation in the shack.  The horizontal coupled with my phone line where the vertical doesn't.  I've got space for a vertical but not for a horizontal -- and the ground wires are buried so nobody notices.   I've only got one support, and a horizontal needs three.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the best answer for a ham is &quot;already tried something else, time to try a vertical&quot;.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-01-08T06:42:59.100" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9729" PostTypeId="2" ParentId="8940" CreationDate="2018-01-08T14:42:09.023" Score="-2" Body="&lt;p&gt;Bands were down, for the first several months figured it was temporary, even though repeatedly Space Weather had no proton showers or other anomalies to explain it.  Been a ham for over 50 years, never remember anything like it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've begun to suspect some sort of human activity is poisoning the ionosphere.  Perhaps a state actor is doing it deliberately for some nefarious purpose, or&#xA;the proliferation of metallic space junk is knocking out the charged particles up there by some as yet unknown mechanism, or perhaps the fluorocarbon induced ionospheric holes have hit a critical size.   &lt;/p&gt;&#xA;" OwnerUserId="10995" LastActivityDate="2018-01-08T14:42:09.023" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9730" PostTypeId="1" AcceptedAnswerId="9734" CreationDate="2018-01-08T17:53:00.147" Score="9" ViewCount="1004" Body="&lt;p&gt;I've been thinking about putting 20m and 10m dipoles up in my attic (HOA), but I also intend to soon put some Ethernet cable to a WAP (with PoE) through the attic. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was intending to feed this with CAT5e cable because I have lots of it and it's cheap, but I recently started thinking about the problems that the two might cause for each other in a proximity of 4-6 feet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I worry about the data on the CAT5 being affected by CW/Data/SSB at 100 W on a resonant dipole whose elements are only a few feet away? Will activity on the CAT5 be noticeable on my dipoles? Does using shielded cable make a significant difference here?&lt;/p&gt;&#xA;" OwnerUserId="6295" LastEditorUserId="76" LastEditDate="2018-01-08T18:24:08.070" LastActivityDate="2018-01-12T07:43:17.013" Title="Attic Dipole - Impact of Ethernet over CAT5/6" Tags="&lt;rfi&gt;&lt;antenna-system&gt;&lt;transmission-line&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9731" PostTypeId="1" AcceptedAnswerId="9733" CreationDate="2018-01-08T18:47:43.810" Score="5" ViewCount="1270" Body="&lt;p&gt;I know that verticals are normally chosen for their low angles of radiation without obscene heights, but I'm not especially interested in DX and am primarily looking for local coverage via NVIS. I've not had great luck with dipoles at my home (parallel 5kV power lines under a wavelength away for 20m and below, I think, are the reason here). I was reading an old question and saw &lt;a href=&quot;https://ham.stackexchange.com/a/6302/6295&quot;&gt;an answer&lt;/a&gt; that talked about using a vertical for NVIS, which I've never heard of.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Knowing that 1/4λ verticals are known in VHF/UHF applications to have nearly isotropic patterns, I'm not sure how to reconcile that with the &quot;verticals are great for DX&quot; thing for HF. What gives and how can I do 160/80/40m NVIS with a vertical?&lt;/p&gt;&#xA;" OwnerUserId="6295" LastActivityDate="2018-01-09T14:51:00.730" Title="Can a vertical antenna be used for NVIS?" Tags="&lt;vertical-antenna&gt;&lt;nvis&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9732" PostTypeId="2" ParentId="9731" CreationDate="2018-01-09T00:29:19.817" Score="3" Body="&lt;p&gt;If you want NVIS (predominately high-angle radiation, for closer-in stations rather than DX), &lt;strong&gt;then you don't want a vertical.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, you want something like a &lt;strong&gt;horizontal&lt;/strong&gt; dipole (or inverted-vee), or a horizontal loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna that that post described was a top-loaded vertical. Its top was connected to the mid-point of the horizontal wire. In that configuration, the horizontal wire will radiate very little.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used inverted-L antennas with great success. The majority of the radiation is vertically-polarized at low angles (great for DX). However, there is enough high-angle radiation from the horizontal, sloping section to work closer-in stations. See this page about &lt;a href=&quot;http://www.w0btu.com/160_meters.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;my 160m inverted-L&lt;/a&gt;. It was built for 160m, but I was amazed at the performance on 75, 40, and 20 meters.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-01-09T04:47:21.713" LastActivityDate="2018-01-09T04:47:21.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9733" PostTypeId="2" ParentId="9731" CreationDate="2018-01-09T00:49:48.137" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Knowing that 1/4λ verticals are known in VHF/UHF applications to have nearly isotropic patterns&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is not a valid assertion. A UHF/VHF vertical antenna has &gt; 0 dBi gain (more succinctly a directivity &gt;1) so by definition it cannot have nearly an isotropic pattern. Its primary directivity is toward the horizon at about a 22 degree elevation (although highly dependent on the the ground plane and the elevation of the antenna).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm not sure how to reconcile that with the &quot;verticals are great for DX&quot; thing for HF&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You cannot reconcile it because the two conditions are not both true. A well constructed vertical antenna will have its primary gain toward the horizon which is what gives it its desired DX characteristics. A 1/2 wave dipole antenna needs to be mounted about 1/2 wavelength above ground to achieve a similar effect.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What gives and how can I do 160/80/40m NVIS with a vertical?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;NVIS with a vertical antenna is not a practical application as @mikewaters points out. The general concept for NVIS is to erect an antenna that directs most of its energy &quot;straight up&quot; so that the atmospheric reflections come back to earth in close proximity to your station. The vertical antenna actually has a hole (negative gain) in its pattern in the vertical direction.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I've not had great luck with dipoles at my home&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It would be helpful if you could give a more complete description as to what this means. That could be a starting point for getting your NVIS station working properly.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-01-09T00:49:48.137" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9734" PostTypeId="2" ParentId="9730" CreationDate="2018-01-09T01:08:30.947" Score="11" Body="&lt;p&gt;Having Ethernet and your antenna co-located is not an ideal situation. But then most amateur antenna situations involve compromises. The general idea of the following recommendations is to take as many precautions as practical to minimize the interference possibilities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend that your Ethernet cable to your WAP be a CAT6 &lt;em&gt;shielded&lt;/em&gt; cable (STP). While obviously not needed for your Ethernet environment, the improved twists of the CAT6 cable along with the foil shield will improve the immunity of the Ethernet cable to ingress from your antenna while transmitting as well as increase the attenuation of leakage from the Ethernet cable to your antenna while receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your Ethernet cable should also have a few toroid cores of type 43 material spaced along its length to further improve the performance of the shield. Wrap 4 to 6 turns of the cable around each toroid. This attenuates common mode currents that may be flowing along the exterior of the Ethernet shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your transmission line to the antenna should be a double shielded type coax (braid plus foil). This helps to minimize ingress / egress from your transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use a high quality, ferrite 1:1 balun at the feedpoint of the antenna. This helps to reduce common mode currents on the cable that can cause interference to your Ethernet from your transmitter or cause interference from the Ethernet to your receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ensure that your coax length is not close to an odd multiple of 1/4 wavelength (electrical length) for the bands on which you wish to operate. An ideal length is an odd multiple of 1/2 electrical wavelength as this presents the highest impedance for common mode currents. Note that this electrical wavelength relates to the outside of the shield and is influenced by the type of jacket that is on the exterior of the coax cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pay attention to the layout of the cables and antenna. To the greatest extent possible, have cables cross in a perpendicular fashion instead of running or meeting in a parallel fashion. Similarly have the antenna in a perpendicular orientation to the Ethernet cable. This helps to minimize the coupling between the two systems.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-11T12:14:09.813" LastActivityDate="2018-01-11T12:14:09.813" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9735" PostTypeId="2" ParentId="9731" CreationDate="2018-01-09T12:06:06.970" Score="0" Body="&lt;p&gt;As &lt;a href=&quot;https://ham.stackexchange.com/questions/6300/what-is-the-attraction-of-vertical-antennas-for-hf/6302#6302&quot;&gt;my answer&lt;/a&gt; is quoted in the OP's question, let me elaborate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically on my T-antenna with auto tuner at feed point/base, as the OP left a recent comment asking about this antenna, hence the focus of this antenna in this answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is a T-antenna, which means a vertical radiator 10m high, and a top-spanning 30m horizontal at each end, originally built for 160m and 80m. It resembles a T, hence I call it my T-antenna, I do believe this is an accepted term though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using it over the last 3 years, I get reasonable DX performance for 160m and 80m. Due to the vertical aspect of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However the auto tuner is capable of matching this antenna for 40m, and I discovered that it has &lt;strong&gt;&lt;em&gt;some&lt;/em&gt;&lt;/strong&gt; NVIS properties for 40m, this is probably due to the 2x 30m horizontal legs of the T-top.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Discovered by accident, but it did allow me to use this antenna for NVIS 40m to the extend that I do not use my horizontal dipole all that much anymore. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it still spans 60m horizontally, which is actually more than a 40m dipole. So if you are space restricted, this would not be an ideal antenna for NVIS purposes. Its main purpose is still 160/80m DX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just to be clear, I built this antenna as an experiment, and decided to keep it. There were no scientific designs involved, nor modelling. I could go up 10m, so I did, I could go wide 30m at each side, so I did. I put an auto tuner at feed point, and I played radio. That is all, so if looking for a scientific answer for T-antenna's which are designed for band X, but have properties on band Y, then this is not your answer. For more scientific calculations of a T-antenna, you can see &lt;a href=&quot;http://www.strobbe.eu/on7yd/136ant/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page&lt;/a&gt; although originally written for the 136kHz band.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2018-01-09T14:51:00.730" LastActivityDate="2018-01-09T14:51:00.730" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9736" PostTypeId="2" ParentId="9730" CreationDate="2018-01-09T12:11:15.543" Score="2" Body="&lt;p&gt;I have multiple antenna's, feedlines and Ethernet cables in close proximity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To add to the great answer already given:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have used STP in stead of UTP for all my Ethernet connections. This reduced cross interference greatly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did not have an affect on RX by activity of the Ethernet connections, but I certainly had &quot;unexpected network behaviour&quot; when TX-ing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can get STP in Cat5e and Cat6. I would recommend Cat6-STP, but it is more expensive than Cat5e and/or UTP variants.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that you have Cat5e already at hand, so maybe this is not an option for you.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2018-01-09T12:11:15.543" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9737" PostTypeId="2" ParentId="9714" CreationDate="2018-01-09T14:36:41.320" Score="3" Body="&lt;p&gt;People can and do use a pair of mobile antennas to make shortened dipoles. A &quot;&lt;a href=&quot;https://www.flickr.com/photos/opalmirror/2922368213&quot; rel=&quot;nofollow noreferrer&quot;&gt;hamstick dipole&lt;/a&gt;&quot; is one example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One application for such an antenna is in a mobile station which for whatever reason requires a horizontal polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also a quick way to make a small antenna where space would not allow for a full-sized dipole, such as an attic antenna, or a station in an apartment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, a station that needs to be portable, where radials are not easily installed and hanging a wire dipole is not feasible, perhaps for field day.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantages are much the same a dipoles generally, most usually that no radials need be installed. For installation on a vehicle with a metal body, the vehicle body makes a sufficient ground plane. But I can think of a few reasons a dipole may still be desirable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For line-of-sight propagation the &lt;a href=&quot;https://ham.stackexchange.com/a/7628/218&quot;&gt;radio horizon&lt;/a&gt; is increased. For higher frequencies there's likely no need to use a shortened antenna, but perhaps on 6 and 10 meters this may be of some value for local communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Getting the antenna higher also reduces ground losses, by reducing ground current density. Although the metal body provides some counterpoise, the Earth ground is still significant. Since losses are proportional to the square of current (P = I&lt;sup&gt;2&lt;/sup&gt;R), moving the antenna away from the ground reduces ground losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna can be raised to at least a half wavelength, reflection from the ground will create an image antenna that is effectively a phased array which increases gain at low radiation angles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or if the antenna is raised to a lesser height and turned horizontal, that image antenna increases upwards radiation which may be useful for &lt;a href=&quot;https://ham.stackexchange.com/q/9731/218&quot;&gt;NVIS propagation&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-01-09T17:26:37.843" LastActivityDate="2018-01-09T17:26:37.843" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9738" PostTypeId="2" ParentId="9731" CreationDate="2018-01-09T14:48:38.493" Score="1" Body="&lt;p&gt;If the installation site permits, a dipole antenna in a vertical &quot;Vee&quot; configuration has radiation patterns suitable for NVIS applications -- and can have useful low-angle radiation, as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The graphic below shows its performance on the 40/80/160m bands for the conditions shown there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Directivity (&quot;gain&quot;) is highest in the 40m band, and feedpoint Z is more difficult to match to 50 ±j0 Ω on the lower bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YlHFw.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YlHFw.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-01-09T14:48:38.493" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9740" PostTypeId="2" ParentId="7742" CreationDate="2018-01-09T19:40:22.557" Score="-3" Body="&lt;p&gt;First of all there is no such thing as an antenna &quot;tuner&quot;. The closest to that is the guy who trims a driven element to the resonance. You can &quot;couple&quot;, you can &quot;match&quot;, but not tune unless you change the physical dimensions of the radiating element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna is part of a system made along with the feedlines, coax, traps, etc. These are what must be dealt with by your transmitter. The mislabeled tuner is a box on the desk that deals with the reflected RF by &quot;matching&quot; energy from the transmitter to the mismatched load feedline and antenna. A &quot;coupler” does the same. None of these devices &quot;tune&quot; the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that being said, you are the one supplying the RF that RF goes from your final output stage to the coupling device, and on to the feedline then the antenna. An auto-tuner does not tune the antenna either, it cuts back the output power to a level that the final stage can safely tolerate. If you bypass the internal tuner and use your manual tuner, don’t use both.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Worried about the SWR? 1.5:1 = 4 w. Reflected; 2.0:1 = 11w. Reflected even a 3:1 SWR only returns 25 out of 100 watts. That 25 is, just like the others, burned up in the mismatched portion of the system. To grasp it - think of the power used by a train going along a straight track now think of the train going to the same point but around a hill to get there. The power delivered between the engine and the tracks requires more going around the curved route but the distance between the two points remains the same. Was the power lost? No, it was the same from the engine but the curve took that amount of power from the engine for a longer time.&lt;/p&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="9493" LastEditDate="2018-01-12T14:39:47.603" LastActivityDate="2018-01-12T14:39:47.603" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9741" PostTypeId="1" AcceptedAnswerId="9742" CreationDate="2018-01-09T20:45:08.827" Score="2" ViewCount="61" Body="&lt;p&gt;With reference to an RLC Club Deluxe 2 repeater controller:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What is the maximum size of a command?&lt;/li&gt;&#xA;&lt;li&gt;What is the maximum size of a macro?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The manual does mention &quot;Limits on Macros&quot; but all it says is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Since one macro can call another, you may wonder if macro 500 could&#xA;  call 501, which could call 502, which could call 503, etc., until you&#xA;  recalled 100 macros or so. The answer is not quite. There are other&#xA;  limits. One is that if the total time it takes the processor to decode&#xA;  and execute the whole chained macro sequence is more than one half&#xA;  second or so, the controller may reset itself. It is unlikely that you&#xA;  will ever reach this limit (it would probably take more than 20 macros&#xA;  are hooked together even come close to this limit). The other limit&#xA;  restricts how deeply the macros can be nested (called from another&#xA;  macro). This is not a limit on how many commands can be called inside&#xA;  of a macro. It is not a limit on how many macros can be executed from&#xA;  one Mac. It is a limit on one macro calling another macro that calls&#xA;  another macro that calls another macro.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="313" LastActivityDate="2018-01-23T16:01:33.367" Title="Maximum size of a command on an RLC Club Deluxe 2" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9742" PostTypeId="2" ParentId="9741" CreationDate="2018-01-09T21:16:02.870" Score="1" Body="&lt;p&gt;Each macro can hold 100 bytes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are 200 standard commands, another 300 that are for internal macros and another 500 for user macros.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;OP Edit: I was able to find a &lt;a href=&quot;http://s230753592.onlinehome.us/ftp/rlc-club/manuals/dlx2_215_searchable.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;searchable version of the manual&lt;/a&gt;. There I found only one reference to a maximum command length, and it also happens to mention a macro maximum length.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The message length is limited to the maximum command length (about 200&#xA;  characters) or if used in a macro, by the space left in a macro (less&#xA;  than 100 characters).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;For the macro size limit, we refer to a URL in a comment by &lt;a href=&quot;https://ham.stackexchange.com/users/9493/glenn-w9iq&quot;&gt;glenn-w9iq&lt;/a&gt;, which takes us to the &lt;a href=&quot;http://s230753592.onlinehome.us/wiki/index.php?title=RLC-Club_FAQs#Q:_What_are_the_macro_size_limits_on_the_RLC-Club.3F&quot; rel=&quot;nofollow noreferrer&quot;&gt;RLC-Club FAQs&lt;/a&gt; page on the RLC wiki.  It says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Q: What are the macro size limits on the RLC-Club?   &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A: All RLC-Club macros can hold up to 100 bytes. A byte of macro&#xA;  storage roughly corresponds with a digit stored in it, but that&#xA;  relationship isn't exact. The easiest way to find out how much space a&#xA;  macro takes is to program it, then ask the controller how full the&#xA;  macro is with command 054. If you want to figure it out manually, use&#xA;  the equation 1 + (3 * NumCommands) + TotalDataDigits =&#xA;  MacroSizeInBytes. For example:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt; 055 500                 ; erase macro - doesn't use any space&#xA; 056 500 036 001 002 003 ; speak &quot;one two three&quot; - one command, 9 data digits&#xA; 056 500 038             ; be quiet - one command, no data digits&#xA; 056 500 000 12          ; connect ports 1 and 2 - one command, 2 data digits&#xA; ;&#xA; Total space used = 1 + ( 3 * 3 ) + 11 = 21 bytes.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So for lack of anything more specific, it appears these are the answers: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The maximum size of a command is &quot;about 200 characters&quot;.&lt;/li&gt;&#xA;&lt;li&gt;The maximum size of a macro is 100 bytes which is &quot;less than 100 characters&quot;.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="313" LastEditDate="2018-01-23T16:01:33.367" LastActivityDate="2018-01-23T16:01:33.367" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9744" PostTypeId="2" ParentId="615" CreationDate="2018-01-10T11:49:32.290" Score="0" Body="&lt;p&gt;I do not think that most modern Antenna Tuners are all that great at reducing TVI, as most of them are NOT PI- Networks.  Most of the newer tuners are T- Networks, which tune just fine, but are inherantly Hi Pass filters!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if your transmitter doesn't contain some good low pass filters, the radio will put out a lot of energy outside the intended frequency range&lt;/p&gt;&#xA;" OwnerUserId="11000" LastActivityDate="2018-01-10T11:49:32.290" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9745" PostTypeId="2" ParentId="615" CreationDate="2018-01-10T15:47:48.480" Score="0" Body="&lt;p&gt;1) How can I transmit without an antenna tuner? &#xA;-As mentioned by several answers, you can transmit without a tuner if the SWR isn't too high (I do it all the time.)  I'd also add that even a resonant antenna can still have an SWR because the impedance doesn't match the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) Are there any rule-of-thumb tests/calculations I may do to determine whether an antenna is a decent fit for a given band?&#xA;-For a simple mono band center-fed dipole, the rough formula is &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;l=433/f&#xA;where:&#xA;l is in feet and;&#xA;f is in MHz.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;If the antenna is not simple then I don't even bother with calculations and go with trial-and-error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) How did they tune antennas back when the hobby was still new? &#xA;-Other pieces of test equipment no one has mentioned are a noise bridge and a grid dip meter.  (IIRC, an antenna analyzer is essentially a combination of the two with some other stuff thrown in, but I may be wrong.)  You can tune antennas with those as well.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-01-10T15:47:48.480" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9746" PostTypeId="2" ParentId="7742" CreationDate="2018-01-10T17:43:10.337" Score="0" Body="&lt;p&gt;Good answers so far (two of them) but there is one more important item that is not actually a direct answer to you specific question.  However, I have run across a number of new ham operators over the decades that did not know this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna tuner must be the last item in your RF chain between radio (e.g. transceiver) and antenna system.  Thus, after the antenna tuner is transmission line (baluns or loading coils too) and the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A typical station with transceiver, amplifier, SWR meters, antenna tuner should be in this order:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Transceiver &amp;lt;--&amp;gt; Amplifier &amp;lt;--&amp;gt; SWR Meter &amp;lt;--&amp;gt; Tuner &amp;lt;--&amp;gt; Antenna System&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The impedance between the Antenna Tuner and the Antenna System itself is likely not to be 50 ohms; that is, the SWR is NOT 1:1.    Usually most of the equipment in that station expects to see a 50-ohm matching impedance (exceptions for tube based TX or Amps).  In particular, the SWR meter expects to see 50 ohms both on its input and output and without this 50 ohm match the SWR meter does not give accurate results.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastEditorUserId="1563" LastEditDate="2018-01-10T21:34:28.483" LastActivityDate="2018-01-10T21:34:28.483" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9747" PostTypeId="1" AcceptedAnswerId="9748" CreationDate="2018-01-11T21:05:50.360" Score="3" ViewCount="856" Body="&lt;p&gt;I am using &quot;HDSDR&quot; software to demodulate a WFM broadcast (&quot;Classic FM&quot; in the UK, on 100.1 MHz, 192 KHz bandwidth).  I'm using an &quot;SDRPlay RSP1&quot; software defined radio and a cheap indoor discone antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm trying to understand more about the audio demodulation and I'm puzzled by the spectrum display.  Here's a screengrab...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lwmfc.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lwmfc.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Annotation &quot;A&quot; is (according to wiki) the &quot;Pilot Frequency&quot; at 19 Khz.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Annotation &quot;B&quot; is a rather fascinating pattern that is clearly part of the stereo audio modulation.  But it is centred at 38 KHz, which is far above human hearing capability.  Although I notice that it's also twice the pilot freq.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Annotation &quot;C&quot; is RBDS.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h2&gt;Question(s)&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;What is the nature of the pattern in annotation &quot;B&quot;?  When music is playing this area is rich with visible modulation.  But when it's just a simple human voice (the radio show presenter) speaking this area goes totally invisible and blends into the background without a trace.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I vaguely suspect that a human voice (0 Hz to 4 Khz or thereabouts) lacks the dynamic range to show up on the AF waterfall.  In contrast, a human voice speaking with some very quiet backing music (e.g. an advertisement track playing) does show up on the AF waterfall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the station doing something special to the broadcast AF modulation during a musical segment, which is absent when the presenter is speaking?  Or is it literally that the presenter's voice isn't rich enough in dynamic range to even show up at all?&lt;/p&gt;&#xA;" OwnerUserId="6744" LastEditorUserId="6744" LastEditDate="2018-01-11T21:20:45.163" LastActivityDate="2018-01-20T14:49:51.077" Title="Understanding WFM modulation" Tags="&lt;software-defined-radio&gt;&lt;receiver&gt;&lt;modes&gt;&lt;fm&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9748" PostTypeId="2" ParentId="9747" CreationDate="2018-01-11T22:26:22.237" Score="12" Body="&lt;p&gt;Your “B” is the stereo difference signal of broadcast FM stereo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is placed at twice the pilot frequency so that it can be recovered by having the receiver lock onto the pilot signal and frequency-double it to obtain the &lt;em&gt;subcarrier&lt;/em&gt; signal marking the position of the difference signal. The receiver uses this subcarrier to shift it in frequency down to the audible range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference signal is the right audio channel subtracted from the left audio channel. The receiver adds the difference signal to the basic mono audio to obtain the left channel, and subtracts to obtain the right channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, &lt;strong&gt;if the audio being played by the station is mono or mostly centered, the difference signal is zero or almost zero&lt;/strong&gt; and disappears from the waterfall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The primary advantage of this modulation scheme is that it is compatible with mono receivers (and a stereo receiver can fall back to mono for better sound quality if the signal is weak).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-01-11T22:26:22.237" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9749" PostTypeId="2" ParentId="9730" CreationDate="2018-01-12T07:43:17.013" Score="4" Body="&lt;p&gt;Ethernet cable has a minimum bending radius (check the specs of your cable).   When feeding it through toroids, don't wind it tighter than that.   Exceeding the bending radius causes the twists in the twisted pair to come undone somewhat, and will make the cable leak.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-01-12T07:43:17.013" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9750" PostTypeId="2" ParentId="6611" CreationDate="2018-01-12T15:38:07.700" Score="2" Body="&lt;p&gt;I'm using a 5/8 wave 2m mag mount on a 2'x 2' piece of sheet metal in the attic. I live in NW New Jersey on a small hill and reliably hit repeaters 50-60 miles from me.&lt;/p&gt;&#xA;" OwnerUserId="11012" LastActivityDate="2018-01-12T15:38:07.700" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9751" PostTypeId="1" AcceptedAnswerId="9752" CreationDate="2018-01-13T14:09:07.007" Score="3" ViewCount="323" Body="&lt;p&gt;Newly licensed HAM here. Are QSL cards only exchanged during DX, or could they be exchanged with local contacts as well? How does one request a card? I’ve heard there are bureaus that route cards; is this the most appropriate way to send a card?&lt;/p&gt;&#xA;" OwnerUserId="11016" LastActivityDate="2018-01-26T14:04:26.713" Title="QSL cards and distance minimums" Tags="&lt;qsl-card&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9752" PostTypeId="2" ParentId="9751" CreationDate="2018-01-13T15:06:45.183" Score="6" Body="&lt;p&gt;They can be sent to anyone you've had a QSO with, whether it's that DX contact or the person next door. You can send them directly through the mail, or through the outgoing QSL bureau. Generally, you'd want to use the QSL bureau if you are sending out a large batch of cards, to save on postage. You can request a card just by asking when you make the conact, or send out a card and wait for one to come back (usually you have something like &quot;QSL PSE&quot; (QSL please) on your card that you mark or circle indicating that you'd like a QSL card in response) &lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2018-01-13T15:06:45.183" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9753" PostTypeId="2" ParentId="9751" CreationDate="2018-01-14T10:58:50.570" Score="6" Body="&lt;p&gt;You may also wish to consider electronic QSL sites like &lt;a href=&quot;http://www.eqsl.cc/qslcard/Index.cfm&quot; rel=&quot;noreferrer&quot;&gt;eQSL&lt;/a&gt; and &lt;a href=&quot;http://www.arrl.org/logbook-of-the-world&quot; rel=&quot;noreferrer&quot;&gt;Logbook of the World&lt;/a&gt;. These types of sites allow QSL information to be automatically exchanged between stations. In many cases, they are directly integrated into the ham's logging program.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While not as visually appealing as a printed QSL card, these nearly instantaneous electronic QSLs are virtually free and they can be used for many of the popular awards if you get into &quot;paper (award) chasing&quot;. You can still send paper QSL cards through the mail but due to ever increasing postal costs, many hams have gone fully electronic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another service you may wish to consider is &lt;a href=&quot;http://globalqsl.com&quot; rel=&quot;noreferrer&quot;&gt;Global QSL&lt;/a&gt;. They print on demand a double sided, color card filled out with the QSO details and then mail it for you. You can manage 10 different profiles through their site and change card graphics at will.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-15T12:25:52.933" LastActivityDate="2018-01-15T12:25:52.933" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9754" PostTypeId="2" ParentId="4938" CreationDate="2018-01-14T13:07:41.543" Score="5" Body="&lt;p&gt;While in Chirp go to Duplex and set it to &quot;OFF&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the duplex is set to off then transmission on this channel will be disabled (if the radio supports this capability).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thomas&lt;/p&gt;&#xA;" OwnerUserId="11021" LastActivityDate="2018-01-14T13:07:41.543" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9755" PostTypeId="2" ParentId="9600" CreationDate="2018-01-14T19:16:05.163" Score="1" Body="&lt;p&gt;You can use Kelvin as temperature scale.&#xA;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/Kelvin&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.m.wikipedia.org/wiki/Kelvin&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11023" LastActivityDate="2018-01-14T19:16:05.163" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9756" PostTypeId="2" ParentId="3718" CreationDate="2018-01-14T21:35:42.943" Score="1" Body="&lt;p&gt;There certainly have been satellites using 435 MHz uplink: for example, &lt;a href=&quot;https://amsat-uk.org/satellites/telemetry/strand-1/&quot; rel=&quot;nofollow noreferrer&quot;&gt;STRaND-1&lt;/a&gt;, in which I had some minor involvement, used 435 MHz LSB. I don't believe we had an unencrypted uplink capability, though - however, you may well find hamsats that have. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The satellite went quiet fairly quickly, but if you do manage to receive any telemetry from it - it did wake up again for a while, so this is not impossible - the team and I would be delighted to hear!&lt;/p&gt;&#xA;" OwnerUserId="11024" LastActivityDate="2018-01-14T21:35:42.943" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9757" PostTypeId="1" AcceptedAnswerId="9758" CreationDate="2018-01-15T16:44:51.503" Score="8" ViewCount="342" Body="&lt;p&gt;It is fairly well understood that due to transmission line losses, the SWR as measured at the transmitter will be less than the SWR at the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of the new antenna analyzers and some vector network analyzers can 'zero out' or compensate for the losses in the transmission line. This allows them to display the SWR at the antenna while taking the SWR measurement at the transmitter end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can something similar be done using a much less expensive, conventional SWR meter or dual needle SWR meter?&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-16T01:08:15.520" LastActivityDate="2018-01-16T01:08:15.520" Title="SWR Measured at the Transmitter versus SWR at the Antenna" Tags="&lt;antenna&gt;&lt;transmission-line&gt;&lt;impedance-matching&gt;&lt;math&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9758" PostTypeId="2" ParentId="9757" CreationDate="2018-01-15T16:44:51.503" Score="5" Body="&lt;p&gt;Given the matched loss of the feedline and the SWR at the transmitter, we can calculate the SWR at the antenna in three simple steps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First convert the SWR at the transmitter to the corresponding magnitude of the reflection coefficient (Gamma), or MRC for short within the context of this answer. The MRC is the magnitude of the complex ratio of the reflected voltage wave to that of the incident voltage wave. We can calculate the MRC using this formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$|\Gamma|=\frac {\text{SWR}-1}{\text{SWR}+1} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where SWR is the SWR (without the :1 notation) at the point of measurement. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if the SWR at the transmitter is 3:1, the corresponding MRC ($|\Gamma|$) at the transmitter is 0.5.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now we convert this MRC at the transmitter to its corresponding MRC at the antenna by reversing the effect of the losses in the feedline:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$|\Gamma_{\text{ant}}|=\frac{|\Gamma_{\text{xmtr}}|}{e^{(-2*L_{\text{dB}}/8.6858)}} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where L&lt;sub&gt;dB&lt;/sub&gt; is the matched loss of the feedline in dB. Note that the division by 8.6858 converts dB loss to Nepers - a more convenient unit for transmission line calculations. The effect of this loss on SWR has been described in &lt;a href=&quot;https://ham.stackexchange.com/questions/9722/does-coax-limit-the-maximum-swr-a-transmitter-sees&quot;&gt;Does Coax Limit the Maximum SWR a Transmitter Sees&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using formula 2 with a feedline that has a matched loss of 1.0 dB along with the previously calculated 0.5 MRC at the transmitter, we find that we have an MRC of 0.63 at the antenna. We can now convert this to the SWR at the antenna using the formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\text{SWR}=\frac{1+|\Gamma|}{1-|\Gamma|} \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So we find using formula 3, that the SWR that measured 3:1 at the transmitter &#xA;is 4.4:1 at the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These formulas are not too difficult to do on a hand calculator, but by placing them into a spreadsheet, it is possible to construct a nice chart depicting the transmitter SWR versus antenna SWR for a given amateur band:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lXAdv.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lXAdv.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This idea could be extended to show a differently colored series plot on the chart for each band of interest using the respective matched feedline loss for the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: It should be pointed out that the antenna SWR as calculated here is technically the &lt;em&gt;minimum&lt;/em&gt; antenna SWR. This is due to the coax limiting the maximum possible SWR at the transmitter as presented in &lt;a href=&quot;https://ham.stackexchange.com/questions/9722/does-coax-limit-the-maximum-swr-a-transmitter-sees&quot;&gt;Does Coax Limit the Maximum SWR a Transmitter Sees&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-15T21:44:58.757" LastActivityDate="2018-01-15T21:44:58.757" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9759" PostTypeId="1" AcceptedAnswerId="9760" CreationDate="2018-01-15T17:15:06.170" Score="6" ViewCount="279" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/9758/218&quot;&gt;SWR Measured at the Transmitter versus SWR at the Antenna&lt;/a&gt; says the neper is &quot;a more convenient unit for transmission line calculations&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why exactly? What is a neper, and what about it makes it more convenient than the more common decibel? Are there some examples of equations which are more complicated in decibels?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-01-16T15:46:22.863" Title="Why is the neper a useful unit for transmission line calculations?" Tags="&lt;math&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9760" PostTypeId="2" ParentId="9759" CreationDate="2018-01-15T20:11:53.077" Score="7" Body="&lt;p&gt;A neper, just like a decibel, is a logarithmic expression of ratios. The decibel uses the base-10, or decadic, logarithm while the neper uses the natural, or Euler constant, logarithm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The decibel is strictly defined as the ratio of two powers. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$dB=10\log_{10}\left(\frac{P_1}{P_2}\right) \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While it is common to see a decibel formula based on voltage or current, such a ratio is only valid if the impedance of the two terms is the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The neper is simply defined as the ratio of voltage or current (or more generally, 'field' values):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Np=\ln\left(\frac{V_1}{V_2}\right) \text{ or } \ln\left(\frac{I_1}{I_2}\right) \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It can be shown that 1 neper is equal to $20\log_{10}(e)$ or about 8.6858 decibels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One way to think about a natural logarithm is that it can be used to calculate how much time it takes to get a certain growth. The inverse function, e&lt;sup&gt;x&lt;/sup&gt;, can be used to calculate growth given a certain amount of time. In fact e is sometimes referred to as the universal rate of growth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This has many applications in the area of electronics. As an example, the formula for voltage across a capacitor as a function of time (growth/decay) as it discharges through a resistor makes use of this relationship:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_C{(t)}=V_0*e^\left({\frac{-t}{RC}}\right) \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where R is the discharge resistance in ohms, C is the capacitance in Farads, t is the time in seconds, and V&lt;sub&gt;0&lt;/sub&gt; is the initial voltage across the capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly transmission line equations have the notion of growth or decay of voltage and current as a function of time or length. Transmission line attenuation is such as example. The attenuation of a transmission line ($\alpha$) is generally given as nepers/meter or nepers/kilometer. Thus for a given length of transmission line, the attenuated voltage at any point along the line is simply given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_{(l)}=\frac{V_0}{e^{\alpha l}} \tag 4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where V&lt;sub&gt;0&lt;/sub&gt; is the original voltage, $\alpha$ is the attenuation in nepers/meter, and l is the point in the transmission line in meters from the initial voltage V&lt;sub&gt;0&lt;/sub&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same form of the calculation using attenuation expressed in dB/meter results in:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_{(l)}=\frac{V_0}{e^{\left(\frac{\alpha l}{8.6858}\right)}} \tag 5$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\alpha$ is expressed in dBs/meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An alternative form to equation 5 would be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_{(l)}=\frac{V_0}{10^{\left(\frac{\alpha l}{20}\right)}} \tag 6$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where again $\alpha$ is expressed in dBs/meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus it can be seen that equation 4 is slightly simpler in form compared to equation 5 or 6. The simplicity of equation 4 also makes the derivation of the &quot;rate of growth&quot; clearer. There is no need to ask, for example, what is the 8.6858 factor doing there?&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="218" LastEditDate="2018-01-16T15:46:22.863" LastActivityDate="2018-01-16T15:46:22.863" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9761" PostTypeId="1" AcceptedAnswerId="9762" CreationDate="2018-01-16T04:19:55.173" Score="4" ViewCount="632" Body="&lt;p&gt;I am studying for the technician exam and I have come across the section on carrier waves, basebands, and various kinds of modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It makes sense to me that you create a signal by combining the baseband, which carries data, with the carrier signal (a sine wave of some kind) before transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is - why? What would stop us from just transmitting the raw data (voice or whatever) as it is? My guess is that &quot;voice&quot; frequencies for example are in the range of 300hz - 3000hz and we need to &quot;boost&quot; them up to the frequency we are on (for example 167.000 MHz). However this is just a guess.&lt;/p&gt;&#xA;" OwnerDisplayName="user11031" LastActivityDate="2018-01-17T13:57:06.413" Title="Why are carrier waves necessary?" Tags="&lt;modes&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9762" PostTypeId="2" ParentId="9761" CreationDate="2018-01-16T10:27:25.453" Score="5" Body="&lt;p&gt;The simplest answer is that the modulating signal, while it could be electromagnetic, will not have the desired propagation characteristics to carry out effective communications. By mixing the modulating signal with the carrier, the resulting signal has a much higher frequency that results in the desired propagation effects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hams often find that they cannot make their desired contacts on a given band (short frequency range) so they switch bands in the hope of making a contact. The modulating signal stays the same but the carrier frequency is dramatically changed as they switch bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having the ability to change the carrier frequency also helps to avoid interfering signals or talk with another ham by tuning to their transmitting frequency.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-16T11:12:52.927" LastActivityDate="2018-01-16T11:12:52.927" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9763" PostTypeId="2" ParentId="9761" CreationDate="2018-01-16T15:37:32.130" Score="-2" Body="&lt;p&gt;Let's start with sound.  Sound itself is a series of positive and negative waves meaning&#xA;the sound pressure becomes higher and lower than the surrounding air.  That's how the &#xA;sound propagates.  AM transmissions are similar in that the signal starts as the carrier&#xA;and then the modulation makes the signal strength more or less.  What eventually comes out&#xA;of the transmitter (we're still talking AM here) is the carrier wave plus the heterodyne&#xA;products [q.v.], the carrier wave frequencies plus (and minus) the audio frequencies.  So &#xA;that's why we need a carrier wave.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what happens if you made a fancy filter and removed the carrier (and what the heck, how &#xA;about the &quot;Minus&quot; heterodyne product while we're at it since it's just a mirror image of the &#xA;&quot;Plus&quot; heterodyne), what do you have?  Effectively, you have your audio frequencies shifted &#xA;up to RF and nothing else.  That's called Single Side-Band (SSB.)  And just to complete the &#xA;thought, in order to receive SSB so that you can understand it, you need to reintroduce the &#xA;carrier wave in the receiver itself or else all you'll hear is something like a duck quacking.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And one more thing, FM is completely different, this analogy doesn't work.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-01-16T15:37:32.130" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9764" PostTypeId="2" ParentId="9761" CreationDate="2018-01-17T13:57:06.413" Score="3" Body="&lt;p&gt;This really depends on what you consider to be a &quot;carrier wave&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you consider it a sine wave at RF, then it may or may not be present. For example, an analog AM or FM station transmitting silence is just a pure tone: the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But silence in single-sideband (SSB) doesn't have a transmitted carrier: in fact if there's no audio doing into the microphone, the transmitter doesn't transmit anything. This is because is simply the baseband signal (voice into the microphone, for example) shifted up in frequency. If the transmitter is tuned to 10,000,000 Hz, and you whistle in the microphone a 500 Hz tone, the transmitter shifts that up by 10,000,000 Hz and transmits a tone at 10,000,500 Hz. In a sense, this is &quot;transmitting the raw data&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, 10,000,000 Hz is still the &lt;em&gt;carrier frequency&lt;/em&gt;. Although it's not part of the transmission, the transmitter somehow needs to convert the baseband frequencies (your voice) up to RF. It does this by multiplying the baseband signal with a 10,000,000 Hz oscillator in a &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_mixer&quot; rel=&quot;nofollow noreferrer&quot;&gt;mixer&lt;/a&gt;. This alone is effectively an AM transmitter, so to make an SSB transmitter requires additional complexity to remove the second sideband from the transmission.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-01-17T13:57:06.413" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9765" PostTypeId="1" AcceptedAnswerId="9766" CreationDate="2018-01-18T19:03:08.200" Score="5" ViewCount="1809" Body="&lt;p&gt;I'd like to add a band-pass filter to my Baofeng UV-82 to make it comply with the spurious emissions requirements.  Ideally it would be a rigid device with SMA or BNC connectors that would fit between the radio and the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm open to building my own, but it would have to be a foolproof design because I don't have the test equipment to verify it.  Buying one is also an option as long as the price is reasonable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see how bad the emissions are in this video that I found: &lt;a href=&quot;https://youtu.be/mLjc3-gSU-M?t=6m14s&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://youtu.be/mLjc3-gSU-M?t=6m14s&lt;/a&gt;  When transmitting on 145 MHz, there are strong signals from 35 MHz up to 1.025 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What can you recommend?  (Besides the obvious &quot;buy a better radio&quot; suggestion.  I don't have the budget for that.)&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2018-01-21T07:03:00.320" LastActivityDate="2018-01-30T23:31:17.660" Title="Small band-pass filter for HT?" Tags="&lt;baofeng&gt;&lt;filter&gt;" AnswerCount="2" CommentCount="10" ContentLicense="CC BY-SA 3.0" />
  <row Id="9766" PostTypeId="2" ParentId="9765" CreationDate="2018-01-18T22:26:34.493" Score="4" Body="&lt;p&gt;If you want cheap, building your own is not difficult. Here's a simple low pass pi filter:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/bHasE.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fbHasE.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The values of the components should be such that they have a reactance of 50 ohms at the cutoff frequency, which should be just a little above the top of the 2-meter band, if that's your objective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For better attenuation you can cascade two of these together. Since you'll end up in one section with two capacitors in parallel, you can replace this with a single capacitor of half the capacitance for an equivalent circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the output power of the HT probably isn't more than 5W, you won't need unusually high-voltage capacitors. You want to keep the leads as short as possible to minimize stray inductance. I'd use large chip capacitors. At 2 meters you can probably get sufficient inductance out of air-cored coils you wind yourself from enameled wire over a pen or something for a form. Align them with their axes at right angles to minimize coupling between them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps build it in a small cast-aluminium box or copper pipe (suggestion from comments), put a couple SMA connectors on it, and you should be golden.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2018-01-19T15:35:48.240" LastActivityDate="2018-01-19T15:35:48.240" CommentCount="17" ContentLicense="CC BY-SA 3.0" />
  <row Id="9767" PostTypeId="2" ParentId="9751" CreationDate="2018-01-19T12:32:10.550" Score="1" Body="&lt;p&gt;I had someone hand me an eyeball QSO card.   I think that would be the minimum distance.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-01-19T12:32:10.550" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9769" PostTypeId="2" ParentId="9747" CreationDate="2018-01-20T14:49:51.077" Score="0" Body="&lt;p&gt;The graphic below might help explain what was shown in the OP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This graphic shows the baseband spectrum at the output of the r-f channel demodulator of an FM stereo receiver, before the spectrum above ~18 kHz is sent to, and processed by its stereo decoder to recover the discrete L and R stereo audio signals of the original program.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GL24T.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GL24T.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-01-20T14:49:51.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9770" PostTypeId="2" ParentId="9765" CreationDate="2018-01-20T22:09:26.840" Score="3" Body="&lt;p&gt;[This was from comments by @MarcusMüller and myself. I've moved them to this answer.]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't underestimate the filtering effects of an antenna. It's most important how the spurs &quot;close&quot; to your intended frequency are – the rest will be attenuated by the antenna (do try to at least theoretically estimate the attenuation, though!). Antennas can actually be made resonant for only a small bandwidth – maybe that's actually key to a solution here, because it's anyway likely that you'd want to use an antenna that's not a full-sized monopole :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A recent ARRL review of a Baofeng handheld did it the way the it was done in the video the OP found --with similar results-- which was a bad example that perhaps the video's creator copied. The way to do this test would be to transmit with the stock antenna, and pick up the signal using a broadband antenna (such as a Discone) out in the open and at least a a couple of wavelengths away, and feed the received signal into his spectrum analyzer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not to say that the Baofeng is a marvel of technical engineering excellence. ;-) &lt;em&gt;Any transmitter should be able to use a broadband antenna --like a discone-- without transmitting those spurs, and it appears that this one cannot do that.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="6080" LastEditDate="2018-01-30T23:31:17.660" LastActivityDate="2018-01-30T23:31:17.660" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9771" PostTypeId="1" AcceptedAnswerId="9772" CreationDate="2018-01-22T00:23:50.287" Score="5" ViewCount="429" Body="&lt;p&gt;I'm messing around on WebSDR and by just scanning through I sometimes come across these continuous tones in USB. One in particular was 28.800 MHz USB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've picked them up on nearly every WebSDR unit I've used. &lt;a href=&quot;http://waku.no-ip.org:8901/&quot; rel=&quot;noreferrer&quot;&gt;This&lt;/a&gt; one in particular was the most recent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems weird that an entire frequency would be occupied by a single tone. Is this a coded tone of some kind? It doesn't sound like it modulates at all. Maybe its for testing the tuning of your gear? &lt;/p&gt;&#xA;" OwnerDisplayName="user11031" LastActivityDate="2018-01-22T00:54:21.707" Title="What are these continuous sine wave tones I keep hearing?" Tags="&lt;hf&gt;&lt;frequency&gt;&lt;noise&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9772" PostTypeId="2" ParentId="9771" CreationDate="2018-01-22T00:54:21.707" Score="9" Body="&lt;p&gt;A pure tone is an unmodulated signal — it carries no data. Almost nobody intentionally transmits a pure tone — it would be wasteful. The exceptions are the time-and-frequency reference signals like &lt;a href=&quot;https://en.wikipedia.org/wiki/WWV_(radio_station)&quot; rel=&quot;noreferrer&quot;&gt;WWV&lt;/a&gt;, but they have modulated time information in addition to the carrier which serves as a frequency reference signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you are receiving is almost certainly &lt;em&gt;unintentional&lt;/em&gt; transmission. Any oscillator, or clock in the digital-electronics sense, usually ends up radiating some of its output through the attached circuitry. Particularly when the oscillator is inside the receiving equipment, it is known as a “spur” or “birdie”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The popular RTL-SDR has a 28.8 MHz oscillator inside, so you will see a signal there if the WebSDR you were using is based on that hardware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other unintentional transmissions may be more complex than pure tones, either because they are intentionally modulated signals intended to pass through cables (e.g. USB) or because they are controlled or perturbed in some fashion (e.g. switching power supplies under varying load).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-01-22T00:54:21.707" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9773" PostTypeId="1" CreationDate="2018-01-22T04:46:57.280" Score="6" ViewCount="324" Body="&lt;p&gt;When I got my license about 50 years ago, I believe the only punctuation marks on the test were the period, comma, question mark, and slash mark.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once on the air, I heard and used the usual prosigns, [AR], [BT], [SK], [KN]. I also frequently heard and used [HH] to indicate an error, and dit-dididit (the American Morse ampersand). There were a few others less commonly used but generally understood when I started out: [AS] (wait), [VE] (acknowlegement), didit-dit (American Morse C, used to ask if frequency in use). Also [AA], used only in formal message handling as a separator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's it. Nothing else. But the internet today has tables of Morse code characters for all sorts of other punctuation marks and accented characters. (See &lt;a href=&quot;https://en.wikipedia.org/wiki/Morse_code&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia&lt;/a&gt; or &lt;a href=&quot;http://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.1677-1-200910-I!!PDF-E.pdf&quot; rel=&quot;noreferrer&quot;&gt;ITU Recommendation&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wonder if anyone has actually used any of these other characters, or heard them being used. Do hams who converse on CW in languages other than English ever use the accented characters? Is anyone using the new at sign (@) character  that was added relatively recently? Who ever used those additional punctuation marks?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not an question about opinion as to whether or not the use of these characters is a good thing. It is also not a question about whether these other characters have been documented on paper or on the internet. This is a question about under what circumstances and at what times these seemingly-rare characters have been used on the air as a regular practice, rather than a theoretical possibility.&lt;/p&gt;&#xA;" OwnerUserId="11059" LastEditorUserId="11059" LastEditDate="2018-01-22T16:21:40.600" LastActivityDate="2019-02-16T20:39:29.870" Title="Has anyone actually heard or used rare Morse code characters on the air?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9774" PostTypeId="1" CreationDate="2018-01-22T15:01:23.587" Score="2" ViewCount="50" Body="&lt;p&gt;When tuned around 87.5-88 FM, a strange repetitive sound can be heard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The title &lt;a href=&quot;https://www.youtube.com/watch?v=MofYHilG2ec&amp;amp;t=10&quot; rel=&quot;nofollow noreferrer&quot;&gt;'Les Professionnels' from 'Air'&lt;/a&gt; start with this sound.&lt;/p&gt;&#xA;" OwnerUserId="11063" LastEditorUserId="8717" LastEditDate="2018-01-22T15:11:26.150" LastActivityDate="2018-01-22T15:11:26.150" Title="What is this sound on FM radio?" Tags="&lt;receiver&gt;" AnswerCount="0" CommentCount="0" ClosedDate="2018-01-22T15:09:21.440" ContentLicense="CC BY-SA 3.0" />
  <row Id="9775" PostTypeId="2" ParentId="9773" CreationDate="2018-01-22T16:29:45.057" Score="3" Body="&lt;p&gt;A few years ago, I used the @ symbol when transmitting my email address. The other ham did not know the symbol, so I re-transmitted the word &quot;at&quot; instead. After that exchange, I realized that the time to send the @ symbol (.––.–.) takes longer than simply sending &quot;at&quot;. That was the last time I used the @ symbol.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-01-22T16:29:45.057" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9776" PostTypeId="2" ParentId="9773" CreationDate="2018-01-22T18:29:37.457" Score="0" Body="&lt;p&gt;About 20 years ago I had a experience similar to Glenn's, only reversed. I was the one who had to look up the unfamiliar (to me) @ character that the other ham sent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A ham proficient with and active on CW should be able to answer this. Have you been active on CW lately?&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-01-22T18:35:52.480" LastActivityDate="2018-01-22T18:35:52.480" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9777" PostTypeId="1" CreationDate="2018-01-23T22:21:50.543" Score="0" ViewCount="238" Body="&lt;p&gt;Can we expect a Loop Antenna such as a Chameleon F-Loop Antenna transmit and receive from the USA's midwest to Australia on HF using an average 100 watt SSB transmitter and an average receiver?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, on what bands might this be possible?&lt;/p&gt;&#xA;" OwnerUserId="11068" LastEditorUserId="8717" LastEditDate="2018-01-24T17:35:00.090" LastActivityDate="2020-06-25T13:36:38.477" Title="Can a Loop Antenna send and receive 10,000 miles away" Tags="&lt;propagation&gt;&lt;rf-power&gt;&lt;loop-antenna&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9778" PostTypeId="1" AcceptedAnswerId="9779" CreationDate="2018-01-24T00:24:17.303" Score="17" ViewCount="3673" Body="&lt;p&gt;For ham radio operators, the SWR meter is a ubiquitous piece of equipment. There are dozens of standalone models on the market and most modern transceivers and antenna tuners have this functionality built in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ham with an interest in antennas has probably had their hands on SWR meter. Operating them is relatively straight forward but understanding how they work seems to be another matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is an abundance of descriptions in texts, magazines, and on the Internet that attempt to describe how an SWR meter (or its close cousin a directional watt-meter) works. Some of these even state that the meter is able to actually separate the forward and reverse power, voltage, or current. &#xA;After looking at the schematics for many of these devices, this seems dubious. Others attempts at describing its underlying mechanisms, such as &lt;a href=&quot;https://ham.stackexchange.com/questions/6240/how-should-this-swr-meters-directional-coupler-work&quot;&gt;How Should this SWR Meter's Directional Coupler Work&lt;/a&gt; don't seem to come to a consensus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do these instruments really work? What is the basic math behind it?&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-10-09T21:43:18.440" Title="How does an SWR meter really work?" Tags="&lt;impedance&gt;&lt;rf-power&gt;&lt;coaxial-cable&gt;&lt;transmission-line&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="8" FavoriteCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9779" PostTypeId="2" ParentId="9778" CreationDate="2018-01-24T00:24:17.303" Score="21" Body="&lt;p&gt;&lt;strong&gt;Dispelling the Myth&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To begin with, the typical HF SWR meter does not have the ability to separately sample the forward and reverse power, voltage, or current. Any description of the device or its circuitry that suggests this capability is flawed. We can show this empirically with two different experiments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Experiment 1&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connect a 100 ohm resistor directly to the output of a 50 ohm SWR meter (no coax cable) and directly connect the input of the SWR meter to the transmitter (no coax cable). The resistor will dissipate all the power that the transmitter can put out into the 100 ohm load - no reflections of voltage, current or power since there is no transmission line. Yet the meter will show a 2:1 SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Experiment 2&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connect the transmitter directly to the input of the 50 ohm SWR meter. On the output of the SWR meter connect a 75 ohm coaxial cable and attach a 75 ohm load to its end. Since the load matches the Z&lt;sub&gt;o&lt;/sub&gt; (characteristic impedance) of the coax cable, there are no reflections of voltage, current or power on the coax cable. Yet the meter will show an SWR of 1.5:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;How Does it Work?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The typical HF SWR meter works by sampling the complex voltage and current at the point of insertion from which it calculates the effective SWR at the point of insertion on a transmission line with a characteristic impedance of 50 ohms (or whatever impedance for which the SWR meter is designed). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The term &quot;effective&quot; is used here because the calculation is performed regardless of whether a transmission line is present or not and regardless of the actual characteristic impedance of any transmission line that is present.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Sampling the Voltage&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SWR meters use one of three different methods to sample the complex voltage at the point of insertion.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ADQya.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fADQya.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In each case, the voltage sampling circuit steps down the higher voltage that is present on the transmission line at the point of insertion to a more manageable lower voltage for the SWR meter circuit. In the case of the resistive and capacitive divider circuits, the upper element is typically adjustable to allow the SWR meter to be calibrated (more about this later).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The voltage present on the transmission line at the point of sampling is the complex sum of all of the forward voltages plus the sum of any reflected voltages resulting from a mismatched load and source. This can be expressed as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_\text{line}=V_f+V_r \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where V&lt;sub&gt;f&lt;/sub&gt; is the complex forward voltage and V&lt;sub&gt;r&lt;/sub&gt; is the complex reflected voltage at the point of sampling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The sampled voltage from any of the above circuits can then be expressed as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_1=(V_f+V_r)*k_1 \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where k&lt;sub&gt;1&lt;/sub&gt; is the scaling constant as determined by the voltage sampling circuit design. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Sampling the Current&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nearly every SWR meter uses the same technique to sample the complex current that is present on the transmission line at the point of insertion. The technique involves a circuit that at first glance looks like a step-up voltage transformer with a load resistor on the secondary, but it is actually a special configuration known as a wide band current transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A wide band current transformer converts the RF current that is passing through its primary side, to a proportional RF voltage on the secondary side. The conversion takes place by placing a load resistor (sometimes called the burden) on the secondary side. The load resistor must be much smaller than the characteristic impedance of the secondary side of the transformer for this current to voltage conversion to be proportional.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/3U3NC.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f3U3NC.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transformer is typically a toroid device with the center conductor of the transmission line passing through the hole of the toroid to form a 1 turn primary winding with the secondary winding wrapped multiple times through the toroid form.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tP0Wq.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tP0Wq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The complex current that is present on the transmission line at the point of sampling is the difference between the forward current and the reflected current:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$I_\text{line}=I_f-I_r \tag 3$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where I&lt;sub&gt;f&lt;/sub&gt; is the complex forward current and I&lt;sub&gt;r&lt;/sub&gt; is the complex reflected current. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The complex voltage resulting from the sampled current using a wide band current transformer can then be expressed as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_2=(I_f-I_r)*k_2 \tag 4$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where k&lt;sub&gt;2&lt;/sub&gt; is the transformation factor, in volts/amp, as determined by the wide band current transformer circuit design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Calculating SWR and Power&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We now need a way to use the sampled voltage and current to calculate the SWR as well as the forward and reflected power. Most equations for calculating these values involve knowing the forward voltage and the reflected voltage. But so far we only have V&lt;sub&gt;1&lt;/sub&gt; which is proportional to the sum of these complex voltages as shown in equation 2. There is, however, another way of expressing the complex current that is present at the sampling point that can help us:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$I_\text{line}=\frac{V_f-V_r}{Z_o} \tag 5$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where Z&lt;sub&gt;o&lt;/sub&gt; is the characteristic impedance of the transmission line, typically 50 ohms in amateur radio applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can then substitute equation 5 into equation 4:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_2=(V_f-V_r)*\frac{k_2}{Z_o} \tag 6$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now we subtract V&lt;sub&gt;2&lt;/sub&gt; in equation 6 from V&lt;sub&gt;1&lt;/sub&gt; in equation 2:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_1-V_2=\Bigl((V_f+V_r)*k_1\Bigr)-\Bigl((V_f-V_r)*\frac{k_2}{Z_o}\Bigr) \tag 7$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a Z&lt;sub&gt;o&lt;/sub&gt; of 50 ohms, if we set the k&lt;sub&gt;2&lt;/sub&gt; to k&lt;sub&gt;1&lt;/sub&gt; ratio to 50, equation 7 is greatly simplified:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;&lt;sub&gt;&lt;sub&gt;[Edit: Formulas 8 and 9 have been updated]&lt;/sub&gt;&lt;/sub&gt;&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_1-V_2=((V_f+V_r)-(V_f-V_r))*k_1=V_r*2*k_1 \tag 8$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keeping the same k&lt;sub&gt;2&lt;/sub&gt; to k&lt;sub&gt;1&lt;/sub&gt; ratio but adding V&lt;sub&gt;1&lt;/sub&gt; and V&lt;sub&gt;2&lt;/sub&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_1+V_2=((V_f+V_r)+(V_f-V_r))*k_1=V_f*2*k_1 \tag 9$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the 2*k&lt;sub&gt;1&lt;/sub&gt; term is a constant known to the designer, it is easily factored out in subsequent applications of equations 8 and 9.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This adding and subtracting of V&lt;sub&gt;1&lt;/sub&gt; and V&lt;sub&gt;2&lt;/sub&gt; had in the past been accomplished with a switch on the SWR meter. Now it is more common that V&lt;sub&gt;1&lt;/sub&gt; is fed into a center tap of the secondary of the wide band current transformer. With the appropriate circuit values, one leg of the transformer is then V&lt;sub&gt;1&lt;/sub&gt;+V&lt;sub&gt;2&lt;/sub&gt; while the other leg is V&lt;sub&gt;1&lt;/sub&gt;-V&lt;sub&gt;2&lt;/sub&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since power is proportional to voltage squared, equation 8 gives us a voltage that is proportional to reflected power while equation 9 gives us a voltage that is proportional to forward power. Each of these voltages are fed to their respective meter movement where the logarithmic scale drawn on the meter face does the conversion of the linear meter deflection, that is based on voltage, to power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/X4rY3.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/X4rY3.jpg&quot; alt=&quot;Dual Needle SWR Meter&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The conversion of forward power and reflected power to SWR is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$SWR=\frac{1+\sqrt{\frac{P_r}{P_f}}}{1-\sqrt{\frac{P_r}{P_f}}} \tag {10}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or alternatively the conversion of V&lt;sub&gt;f&lt;/sub&gt; and V&lt;sub&gt;r&lt;/sub&gt; to SWR is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$SWR=\frac{1+(V_r/V_f)}{1-(V_r/V_f)} \tag {11}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The meter face pictured above shows the intersection of the two needles on the 2:1 SWR line which corresponds to equation 10 for the powers shown. The SWR meter designer simply plots a number of SWR values on the meter corresponding to the intersection of the forward and reflected powers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Calibrating the SWR Meter&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The typical calibration routine for the SWR meter is to attach a resistive load that is equal to the Z&lt;sub&gt;o&lt;/sub&gt; of the feedline directly to the output of the meter. A transmitter outputs the appropriate amount of power to the input of the SWR meter. The voltage dividing network is then adjusted such that P&lt;sub&gt;r&lt;/sub&gt; is equal to 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since P&lt;sub&gt;r&lt;/sub&gt; is proportional to (V&lt;sub&gt;r&lt;/sub&gt;)&lt;sup&gt;2&lt;/sup&gt;, we can see from equation 7 that this adjustment is simply ensuring that k&lt;sub&gt;2&lt;/sub&gt;/k&lt;sub&gt;1&lt;/sub&gt;=50 for an SWR meter that has been designed for 50 ohm feedline.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-10-09T21:43:18.440" LastActivityDate="2018-10-09T21:43:18.440" CommentCount="19" ContentLicense="CC BY-SA 4.0" />
  <row Id="9780" PostTypeId="1" AcceptedAnswerId="9782" CreationDate="2018-01-24T05:49:55.623" Score="8" ViewCount="10630" Body="&lt;p&gt;So, I've built a couple 1/4λ ground plane antennas for Airband and Marine band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't transmit, I'm just listening, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, constructing ground plane antennas with the radials and getting the impedance to be 50Ω is rather easy, not so for the 5/8λ it would seem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I couldn't find decent formulas or calculations to calculate the coil at the foot of the vertical element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radials are supposed to be 1/4λ, while the vertical active element should be 5/8λ, with a velocity factor of 0.98. However, when measuring the vertical antenna element: should the 5/8λ length be measured from the top of the coil up to the top of the element, or including the coil?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And how to determine the diameter, the number of windings, and the flare-ing (how tightly the coil should be wound) for the coil? I only found dodgy formulas and tables for 20m and other bands like that, but they never depend on the frequency or wavelength, they just use a couple constants out of nowhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to calculate the dimensions myself by using the actual formulas, that depend on the frequency or wavelength, etc. if that makes sense.&lt;/p&gt;&#xA;" OwnerUserId="11070" LastActivityDate="2021-02-08T14:29:30.797" Title="calculating all specifics for a 5/8 antenna" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9782" PostTypeId="2" ParentId="9780" CreationDate="2018-01-24T12:41:57.810" Score="7" Body="&lt;p&gt;I congratulate you on your interest in working out the design issues from the ground up. Understanding the theoretical and comparing this to the field results is the beginning of a life long enjoyment of antenna experimentation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The Antenna&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By way of background, a 5/8 wave antenna is the &lt;a href=&quot;https://ham.stackexchange.com/q/1142/218&quot;&gt;highest directivity, single element, linear antenna that you can construct&lt;/a&gt;. But the construction details are important in order to efficiently convert directivity into gain. Paying attention to the effect of the ground plane, using the right materials and matching the impedance of the antenna to the impedance of the coax and the coax impedance to the receiver impedance can all play a role in wringing out the last drop of gain from the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 5/8 wave antenna is a non-resonant antenna. This means that when perfectly constructed, it will have an impedance that is made up of a real part and an imaginary part. Generally the imaginary part will be capacitive and the real part will not match 50 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Steps&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are the steps that I would follow in planning a 5/8 wave antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1.) Model the antenna to maximize the gain and calculate the complex impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2.) Engineer a matching network to convert the complex impedance of the antenna to the characteristic impedance of the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3.) Construct and contrast field results with the models. Tweak as needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Way back when I was an engineering student, we did all of these calculations in long form (OK, not a slide rule but with a calculator and graphing paper). Today it is much more efficient to use modeling tools and then compare these results with some manual calculations if desired.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Modeling the Antenna&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a free antenna modeling program called &lt;a href=&quot;https://www.eznec.com/demoinfo.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC&lt;/a&gt; that can be used to model your antenna. Other than consulting tables in text books, this is the only practical way of estimating the gain and feedpoint impedance of your antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can adjust parameters such as element lengths, type of material, gauge of material, frequency, height above ground, etc. within the model to see how these parameters affect the results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are looking for a good reference book on antenna theory and construction, I recommend &lt;a href=&quot;https://www.arrl.org/shop/ARRL-Antenna-Book-23rd-Softcover-Edition/&quot; rel=&quot;nofollow noreferrer&quot;&gt;the ARRL Antenna Book&lt;/a&gt;. If you are more interested in the pure theory and mathematics associated with antennas, the seminal text is &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/0070354227&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antennas&lt;/a&gt; by John D Kraus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Designing a Matching Network&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several web sites and stand alone tools that can calculate the matching network. My favorite site is &lt;a href=&quot;http://leleivre.com/rf_lcmatch.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Le Leivre&lt;/a&gt;. With this tool you can enter the complex input and output impedances and it will show all possible L type matching networks that will do the job along with the correct component values.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to wind your own inductor for the matching network, the approximate formula for a single layer, air wound inductor is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$L=\frac{(n^2*d^2)}{(18*d+40*l)} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where L is the inductance in microhenries, d is the coil diameter in inches, l is the coil length in inches, and n is the number of turns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can expand or contract the length of the coil a bit to fine tune the inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This formula is the Wheeler formula for English units that was empirically derived in the early 1900's. Since it is an empirical formula, the effect of $\mu_o$ and $\mu_r$ is factored within the constants. The above version of the formula is generally valid when the diameter of the coil is much larger than the diameter of the wire and where the spacing between turns is minimal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More than 50 years later, Wheeler and others used computer modeling to derive a much more precise formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$L=0.0002\pi D_kN^2*\ln{(1+\frac{\pi}{2k})}+\left(2.3004+3437k+1.7636k^2-\frac{0.047}{(0.755+\frac{1}{k})^{1.44}}\right)^{-1} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where D&lt;sub&gt;k&lt;/sub&gt; is the coil diameter in mm, N is the number of turns and k is the ratio of the winding diameter to length. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="218" LastEditDate="2018-01-25T20:18:37.630" LastActivityDate="2018-01-25T20:18:37.630" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9785" PostTypeId="2" ParentId="9777" CreationDate="2018-01-24T17:43:58.670" Score="2" Body="&lt;p&gt;The short answer is &lt;em&gt;rarely, if at all&lt;/em&gt; on SSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w0btu.com/magnetic_loops.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;STLs are notoriously lossy&lt;/a&gt;, since their radiation resistance is in the milliohm range. The best ones are made from large copper tubing, vacuum variable capacitors, and heavy copper straps connecting the two to minimize the I²R losses. &lt;em&gt;And those losses need to be MUCH less than the radiation resistance.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This type of STL has neither. It's so lossy, that exceeding its rated power limit can heat it up to the point where it is either damaged or destroyed. I'm not saying it's worthless, but I believe that your money would be better spent on a better antenna for the purpose you mention. A tribander is your friend. :-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://owenduffy.net/blog/?p=10707#more-10707&quot; rel=&quot;nofollow noreferrer&quot;&gt;Owen Duffy&lt;/a&gt; has some information on that antenna:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;... Chameleon’s published VSWR curve reconciles reasonably with the&#xA;  realistic NEC-4.2 model and analysis of it suggests &lt;strong&gt;radiation&#xA;  efficiency on 20m is around 4%. ...&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(He has much more information on his site about how lossy &lt;a href=&quot;http://owenduffy.net/blog/?s=stl&quot; rel=&quot;nofollow noreferrer&quot;&gt;STLs&lt;/a&gt; are.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You would have a far better chance using a dipole or vertical than &lt;em&gt;any STL&lt;/em&gt;. Even then, it would have to be 20 meters or above. And during this low part of the sunspot cycle, those bands are rarely open.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-01-24T20:23:20.427" LastActivityDate="2018-01-24T20:23:20.427" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9786" PostTypeId="1" AcceptedAnswerId="9788" CreationDate="2018-01-24T19:45:30.890" Score="6" ViewCount="7781" Body="&lt;ol&gt;&#xA;&lt;li&gt;If i have equations for subtraction of 27dBm-3dBm=27dBm how can this be written as 24 dB.&#xA;I convert the 27dBm and 3dBm -&gt; &lt;code&gt;10^2.7-10^0.3&lt;/code&gt;.But how can we simply subtract the two dBm &lt;/li&gt;&#xA;&lt;li&gt;Whereas if we have a calculation of 8dBm - (-90dBm)= 98dB this is represented as 98dB and not 8dBm?&#xA;Shouldn't we convert both the dBm like &lt;code&gt;(10^0.8-10^(-9))&lt;/code&gt; and then convert into dBm.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Could someone hep me explain why we represent the first equations result in dBm whereas the second equations result in dB?&lt;/p&gt;&#xA;" OwnerUserId="11071" LastEditorUserId="76" LastEditDate="2018-01-24T20:16:49.310" LastActivityDate="2018-01-25T18:49:30.363" Title="Decibel subtraction in dBm and dB" Tags="&lt;rf-power&gt;&lt;math&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9787" PostTypeId="2" ParentId="9777" CreationDate="2018-01-24T20:02:58.807" Score="3" Body="&lt;p&gt;Very unlikely. 100W SSB over 9,000 miles is already a challenging path, but these antennas are very inefficient which will make it nearly impossible. Let's simulate with &lt;a href=&quot;http://www.voacap.com/p2p/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kUeq2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kUeq2.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is 100 W SSB, with 0 dBi antennas at each end, and a quiet noise floor. If the receiver is near a city, man-made noise will make the situation much worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your best chance is on 20 meters, at 2100 UTC, where the circuit reliability is 23%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;0dBi is a &lt;em&gt;very&lt;/em&gt; generous estimate of that antenna's gain. Unfortunately VOACAP doesn't offer a worse antenna to simulate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, turning the power down to 10 W is a 10 dB reduction. If we are considering each end of the link to have one of these loop antennas, that makes this case equivalent to a -5 dBi antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hjuDj.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hjuDj.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now at best, circuit reliability is 8%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think -5 dBi is too optimistic for this antenna. Turning down the power to 1 W is equivalent to a -10 dBi antenna on each end:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wM4Cp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wM4Cp.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now your best shot is down to 2%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, these are simulations for today. We're currently at a low spot in the solar cycle, but in a few years conditions will be better. Not better enough to enable reliable communication over this path all the time, but perhaps enough to make it worthwhile to try. You can play with the simulator parameters for all kinds of scenarios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you did want to communicate over this path, with these antennas, a more sensitive mode will make it feasible. CW or PSK31 would be better, JT9 would be better still. With JT9 and a little luck, you could probably make a contact.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-01-24T20:02:58.807" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9788" PostTypeId="2" ParentId="9786" CreationDate="2018-01-24T20:16:11.017" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I convert the 27dBm and 3dBm -&gt; &lt;code&gt;10^2.7-10^0.3&lt;/code&gt;. But how can we simply subtract the two dBm&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you convert to exponential form then you must simultaneously replace subtraction with division (or addition with multiplication), so you have $10^{2.7} / 10^{0.3}$ instead of $10^{2.7} - 10^{0.3}$. Then you will see that you get the same result:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$2.7 - 0.3 = 2.4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\frac{10^{2.7}}{10^{0.3}} = 10^{2.4}$$&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;why we represent the first equations result in dBm whereas the second equations result in dB?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The first one is incorrect and the second one is correct. (There must be something else wrong with what you wrote down, because it is not the case that $27 - 3 = 27$, of course.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any time you subtract two dB values with a reference level specified (dBm, dBW, dBFS, etc.) you get a ratio expressed as decibels, which is independent of the reference level and therefore should not be written with one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$  27\,\mathrm{dBm} - 3\,\mathrm{dBm}=24 \,\mathrm{dB} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$  27\,\mathrm{dBm} - 3\,\mathrm{dBm} \neq 24 \,\mathrm{dBm} \tag{dimensionally incorrect} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To understand &lt;em&gt;why&lt;/em&gt; these are the rules, consider this exercise:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we have 1000 mW (or 30 dBm), that is the same as 1 W (or 0 dBW).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now suppose we compare that to 100 mW, 20 dBm; 0.1 W, -10 dBW. Again, all of these are the same power expressed differently. If we subtract decibels, or divide the regular values, then we get the same number out:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$&#xA;\begin{align*}&#xA;1000\,\mathrm{mW} / 100\,\mathrm{mW} &amp;amp;= 10&#xA;&amp;amp;&#xA;30\,\mathrm{dBm} - 20\,\mathrm{dBm} &amp;amp;= 10 \,\mathrm{dB}&#xA;\\&#xA;1\,\mathrm{W} / 0.1\,\mathrm{W} &amp;amp;= 10&#xA;&amp;amp;&#xA;0\,\mathrm{dBW} - (-10\,\mathrm{dBW}) &amp;amp;= 10 \,\mathrm{dB}&#xA;\end{align*}&#xA;$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you &lt;strong&gt;divide&lt;/strong&gt; two figures with equal units, you get a unitless (dimensionless) number. When you &lt;strong&gt;subtract&lt;/strong&gt; two dB values with the same reference level, the reference level goes away. These are exactly the same mathematical phenomenon.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-01-24T22:05:33.500" LastActivityDate="2018-01-24T22:05:33.500" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9789" PostTypeId="1" AcceptedAnswerId="9792" CreationDate="2018-01-25T10:58:25.513" Score="2" ViewCount="1254" Body="&lt;p&gt;I am creating a radio receiver to pick up &quot;walkie talkie&quot; chatter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;success it works fine! I can hear people when they speak on the radio, the only problem i am having is that when no one is speaking the static is insane! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is very little to no static when someone is talking but there is more than my ears can bear. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question: How can I filter out the interference when the radio is &quot;idle&quot; from the image its clear to see I have a very high center frequency  (which is just silence and constant)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and then I have some &quot;static&quot; between -70 and -80 db, when there is radio chatter the db jump above -60, so I am guessing I need to filter out everything lower? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am very new to this any guidance on how and what to do would be appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3gDJG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3gDJG.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11074" LastActivityDate="2018-01-25T14:40:19.340" Title="How to trim out background noise GRC" Tags="&lt;gnuradio&gt;&lt;software-development&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9790" PostTypeId="2" ParentId="9751" CreationDate="2018-01-25T13:00:16.607" Score="0" Body="&lt;p&gt;I've always known QSL cards to be sent for only HF contacts. But if you are using a non-repeater simplex contact I guess it would be accepted. As an example, a long distance simplex contact from mountaintop.&lt;/p&gt;&#xA;" OwnerUserId="11037" LastEditorUserId="9493" LastEditDate="2018-01-26T14:04:26.713" LastActivityDate="2018-01-26T14:04:26.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9791" PostTypeId="1" CreationDate="2018-01-25T13:36:09.683" Score="2" ViewCount="66" Body="&lt;p&gt;Is it possible to configure a external mic, specifically, a Icom HM-75LS, to switch between the two VFOs when pressing a button on an Icon ID-51 Plus2?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2018-03-01T17:12:49.887" Title="Change VFOs with external mic button in Icon ID-51?" Tags="&lt;icom-id-51-plus2&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9792" PostTypeId="2" ParentId="9789" CreationDate="2018-01-25T14:40:19.340" Score="3" Body="&lt;p&gt;Since you tagged your question with GNU Radio, I am assuming that is your SDR software package.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look under level controllers, you will find a function block called &quot;Power Squelch&quot;. This function:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Sets the threshold (in dB) where the squelch control switches between MUTED and UNMUTED states. If Ramp is enabled, there in an ATTACK state between MUTED and UNMUTED and a DECAY state between UNMUTED and MUTED.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the functional equivalent of the squelch control on an FM communications receiver although in GNU Radio, it is not restricted to FM. It will act as an audio gate or switch that mutes the audio until a signal above the threshold is received.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-01-25T14:40:19.340" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9793" PostTypeId="2" ParentId="9786" CreationDate="2018-01-25T18:49:30.363" Score="1" Body="&lt;p&gt;You wrote:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If i have equations for subtraction of 27dBm-3dBm=27dBm how can this&#xA;  be written as 24 dB&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm not sure you wrote that correctly. In fact I'm certain of it. I just can't tell what part is wrong.  You appear to be jumbling the dB and dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My guess is you wanted to ask&#xA;27dBm - 3dB = ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that's true (it's a common enough type of calculation), then the answer is 24dBm (not 24dB as you wrote)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you meant:&#xA;27dBm - 3dBm = ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;then you need to understand that this kind of calculation is not common.  You are asking&#xA;500mW - 2mW = ? which is 498mW (or 26.97dBm)&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-01-25T18:49:30.363" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9794" PostTypeId="2" ParentId="9780" CreationDate="2018-01-25T20:45:49.500" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/3783/218&quot;&gt;The impedance of a 5/8 monopole is around (75−425j)Ω&lt;/a&gt;, although it's sensitive to the diameter of the element(s), size of the ground plane, etc. You won't find formulas because it's the sort of thing that's easier to get approximately correct and then adjust empirically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modelling your antenna first will yield a better approximation of the impedance, and allow optimization of other parameters. You'll still need to tweak it at the end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(75−425j)Ω isn't a great match to a 50Ω system, so you will need some kind of matching network. Generally, the solution is to add a series inductance of 425jΩ which cancels the reactance, leaving a 75Ω feed impedance which is close enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reactance and inductance are related by frequency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ X_{L}=2\pi fL$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having determined the necessary inductance, the inductor can be designed with any number of online calculators, or this formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ L= {n^2 d^2 \over 18d+40l} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Glenn W9IQ explains, this is an empirical formula so the constants don't have any deeper meaning. $d$ and $l$ are the diameter and length in inches, and $n$ is the number of turns. Generally aiming for the diameter and length to be approximately equal is a good starting point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also strive to use a sufficiently thick conductor that losses are low, otherwise the inductor losses will more than offset the improvement in directivity.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;However, when measuring the vertical antenna element: should the 5/8λ length be measured from the top of the coil up to the top of the element, or including the coil?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;For a theoretical construction, the matching inductor has zero size and so it doesn't matter. In practice the inductor should still be small so it should not matter much. Consider it just one of many variables that will require empirical adjustment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="9493" LastEditDate="2018-01-27T00:49:34.270" LastActivityDate="2018-01-27T00:49:34.270" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9795" PostTypeId="2" ParentId="6015" CreationDate="2018-01-25T21:17:05.257" Score="1" Body="&lt;p&gt;To reverse engineer anything, you need a sample to look at. Can you generate valid 13FSK signals?  If so, then you need to capture it.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, you'll need manipulate the transmitted payload so you can compare &quot;before and after&quot; to see what changed.&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-01-25T21:17:05.257" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9796" PostTypeId="1" AcceptedAnswerId="9797" CreationDate="2018-01-26T09:18:44.143" Score="3" ViewCount="66" Body="&lt;p&gt;I'm not really too technical when it comes to radio, but I understand that in AM, a shortwave radio generates the carrier frequency so that it can mixed with the received station and then removed, leaving the signal which was modulated with the carrier wave during broadcast.  What's keeping the two carrier waves (broadcaster and receiver) in sync?   Won't there be phase problems if they are not in sync?&lt;/p&gt;&#xA;" OwnerDisplayName="user9468" LastActivityDate="2018-01-26T11:19:12.737" Title="Carrier wave timing" Tags="&lt;receiver&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9797" PostTypeId="2" ParentId="9796" CreationDate="2018-01-26T11:19:12.737" Score="1" Body="&lt;p&gt;The simplest of AM receivers is called a crystal detector. Here there is no mixing of frequencies at all. The received RF energy is directly converted back to an audio frequency by a simple diode. It is such a simple design, that many of as children received a crystal radio kit to put together. It generally had less that six parts to assemble and it didn't even require a battery. But the shortcoming of this type of receiver is that it is not very sensitive. So while it could receive local AM stations, there was no chance of it receiving foreign AM stations, for instance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to improve the sensitivity of receivers, the heterodyne receiver was developed. Here it takes in the AM station's carrier frequency and mixes it with another frequency. This mixing action produces a new (third) intermediate frequency which is then amplified inside the receiver and finally converted to audio again through something as simple as a diode or other more efficient means. The advantage of this design is that a very high gain, efficient amplifying chain can be designed for the intermediate frequency. In fact, this amplifying stage is called the IF stage (for Intermediate Frequency).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a typical AM receiver, the IF works at a frequency of 455 kHz (455,000 Hertz). So the AM station carrier frequency is mixed with another frequency whose difference is 455 kHz. This results in the conversion of the carrier frequency to 455 kHz. As an example, if we are trying to receive an AM station that is broadcasting at 620 kHz, we can mix that with a frequency of 1,075 kHz to convert the 620 kHz to 455 kHz (1075-620=455). If we then wish to tune in an 800 kHz station, the mixing frequency would be 1255 kHz so that the resulting frequency would again be the 455 kHz IF frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With regard to phasing problems, there is no worry. We really don't care at all about the phase of the carrier frequency or the phase of the IF chain relative to the carrier frequency since our goal is only to recover the audio that is contained in the amplitude (the envelope) of the carrier wave.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-01-26T11:19:12.737" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9799" PostTypeId="1" AcceptedAnswerId="9800" CreationDate="2018-01-26T17:32:17.403" Score="5" ViewCount="439" Body="&lt;p&gt;I'm working on the design of a dual band transmitter for use on a high altitude balloon.  I'll be transmitting on 2 meters and 20 meters (APRS and WSPR) with about 50 mW.  To keep the weight to an absolute minimum, I'm designing it to use a single antenna for both bands.  Using 4nec2 modeling I came up with an off center fed (20M 1/2 wave) dipole having a feedpoint positioned where the impedance is about 200 ohms on both bands (using 38 AWG wire.)  A diplexer circuit will merge the outputs of the 2M and 20M RF paths and match the impedance to the antenna.  I estimate this antenna configuration should weigh less than 1 gram.&#xA;Any advice from experienced wire antenna/ high altitude balloon experimenters before I commit too much to hardware? &lt;/p&gt;&#xA;" OwnerUserId="11077" LastActivityDate="2018-01-27T11:44:51.187" Title="HF/VHF antenna for high altitude balloon" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;2m-band&gt;&lt;wspr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9800" PostTypeId="2" ParentId="9799" CreationDate="2018-01-27T02:35:15.347" Score="4" Body="&lt;p&gt;It is equally important to consider the pattern of the antenna. If you hang a 1/2 wave antenna vertically, there will be minimal radiation in the earth facing direction. This will be most problematic for HF NVIS contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also wish to check the RF resistance of 38 AWG wire on 2 meters. I roughly calculate it to be &gt; 100 ohms at 146 MHz for 10 meters in length. This will have significant effect on the efficiency, and thus the gain, of the antenna on 2 meters. At 20 meters, it is &gt; 40 ohms, which can also be a significant factor in the performance of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have you modeled the directivity and efficiency of the antenna to ensure it meets your path budget?&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-27T11:44:51.187" LastActivityDate="2018-01-27T11:44:51.187" CommentCount="12" ContentLicense="CC BY-SA 3.0" />
  <row Id="9801" PostTypeId="1" AcceptedAnswerId="9803" CreationDate="2018-01-27T13:43:52.533" Score="8" ViewCount="368" Body="&lt;p&gt;I am wondering how hams transmit coordinates in Morse code. Considering that coordinates can be represented in many different formats (such as DD, DDM, DMS, WGS84, etc.) and that an error in the decoding of the coordinates can mean a lot, it seems reasonable to think that there are some rules in this regard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any rules/conventions for transmitting coordinates in Morse code?&lt;/p&gt;&#xA;" OwnerUserId="7832" LastEditorUserId="9493" LastEditDate="2018-01-28T13:05:35.320" LastActivityDate="2018-01-29T01:19:42.370" Title="Are there any rules/conventions for transmitting coordinates in CW?" Tags="&lt;cw&gt;&lt;procedure&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9802" PostTypeId="2" ParentId="9801" CreationDate="2018-01-27T17:13:35.723" Score="-3" Body="&lt;p&gt;In Morse Code you would give your longitude and latitude. If you have a ham license the number denotes your location while the prefix of the ham’s call sign (call sign = license) denotes the country code. This means that when you start or find a cw conversation in which you wish to participate, the first thing you do is send your call sign.&lt;/p&gt;&#xA;" OwnerUserId="11085" LastEditorUserId="9493" LastEditDate="2018-01-29T01:19:42.370" LastActivityDate="2018-01-29T01:19:42.370" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9803" PostTypeId="2" ParentId="9801" CreationDate="2018-01-27T17:30:42.140" Score="4" Body="&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/grid-squares&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;Send your Grid Square&lt;/strong&gt;&lt;/a&gt;. It's short, includes your latitude and longitude, and is in common use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, mine is EM37. For greater location accuracy, I would send EM37CG.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A grid square measures 1° latitude by 2° longitude and measures&#xA;  approximately 70 × 100 miles in the continental US. A grid square is&#xA;  indicated by two letters (the field) and two numbers (the square).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Each subsquare is designated by the addition of two letters after the&#xA;  grid square, as FN44ig. These more precise locators measure 2.5&#xA;  minutes latitude by 5 minutes longitude, roughly corresponding to 3 ×&#xA;  4 miles in the continental US.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-01-28T00:03:55.767" LastActivityDate="2018-01-28T00:03:55.767" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9805" PostTypeId="2" ParentId="9703" CreationDate="2018-01-28T02:53:29.810" Score="0" Body="&lt;p&gt;Short answer -- anyone can give your call sign, as long as it is done, and a licensed ham is the control operator and you authorize the use of your call sign.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-01-28T02:53:29.810" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9806" PostTypeId="1" CreationDate="2018-01-28T14:30:37.047" Score="4" ViewCount="171" Body="&lt;p&gt;NEC4.2 gives some insight into this ...&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2018-01-28T22:39:02.013" LastActivityDate="2018-01-28T22:39:02.013" Title="How Does Earth Conductivity Affect the &quot;Takeoff Angle&quot; of a Vertical Monopole?" Tags="&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9807" PostTypeId="1" CreationDate="2018-01-28T16:31:34.430" Score="1" ViewCount="313" Body="&lt;p&gt;Using a Cushcraft MA5B beam, when I apply high power from an amplifier, the SWR will go up and down intermittently. Something is breaking down at high power  (200-500 W).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a new coax feedline, RG213 and checked grounds. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could it be the matching box on the antenna?&lt;/p&gt;&#xA;" OwnerUserId="11091" LastEditorUserId="9493" LastEditDate="2018-01-29T01:08:26.540" LastActivityDate="2018-01-29T03:25:40.163" Title="Intermittent High SWR" Tags="&lt;antenna&gt;&lt;rf-power&gt;&lt;yagi&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9808" PostTypeId="2" ParentId="9806" CreationDate="2018-01-28T20:45:15.840" Score="5" Body="&lt;p&gt;A common belief is that Earth conductivity mostly affects the &quot;takeoff angle&quot; of a vertical monopole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However the NEC4.2 study below shows that the shape of the radiation patterns is quite similar when the same monopole system is installed at sites where Earth conductivity differs through the range from poor to excellent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The biggest effect when going from poor to excellent Earth conductivity (other things equal) is due to the reduced loss of the antenna system path to r-f ground (Earth), when the radial wires are buried in Earth having greater conductivities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is mostly this reduced loss that is responsible for those greater low-angle fields — not to a lower takeoff angle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this study there is approximately 1.8dB more power radiated in the elevation angle of maximum directivity for 30 mS/m Earth than for 0.5 mS/m Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jOjZZ.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jOjZZ.jpg&quot; alt=&quot;*enter image description here*&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-01-28T20:45:15.840" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9809" PostTypeId="2" ParentId="9807" CreationDate="2018-01-29T00:44:11.483" Score="5" Body="&lt;p&gt;The MA5B is rated for 1,200 watts PEP. 200 watts is certainly well below that threshold. Things to check:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Arcing, corrosion or moisture inside the match box&lt;/li&gt;&#xA;&lt;li&gt;A loose or corroded connection from the matchbox to the driven element&lt;/li&gt;&#xA;&lt;li&gt;Loose or corroded connections in the &quot;X hats&quot;&lt;/li&gt;&#xA;&lt;li&gt;A waterlogged, corroded or otherwise failed trap&lt;/li&gt;&#xA;&lt;li&gt;Loose or corroded connections in the telescoping joints in the elements&lt;/li&gt;&#xA;&lt;li&gt;Loose joints between the elements and boom&lt;/li&gt;&#xA;&lt;li&gt;Loose or corroded coax connections&lt;/li&gt;&#xA;&lt;li&gt;Overheating or voltage breakdown of a balun&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I would also recommend substituting a dummy load in place of the antenna to eliminate problems with coax, tuners, SWR meter, amplifier, switches, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the problem is on a particular band, pay close attention to the applicable traps per point 4 above. The traps have a coil on each end. Water and bug ingresses is a common problem.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-29T03:25:40.163" LastActivityDate="2018-01-29T03:25:40.163" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9810" PostTypeId="2" ParentId="1394" CreationDate="2018-01-29T04:09:28.710" Score="5" Body="&lt;p&gt;Gold plated contacts provide reliable switching when the wetting current is low, because there is no oxide to breach for electrical contact to occur.  Ex: a pushbutton switch used to signal a microcontroller digital input has a pullup resistor sized to flow 50 uA when the switch is closed.  A switch without gold plating might not be reliable. &lt;/p&gt;&#xA;" OwnerUserId="11094" LastActivityDate="2018-01-29T04:09:28.710" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9811" PostTypeId="2" ParentId="5405" CreationDate="2018-01-29T12:43:58.470" Score="1" Body="&lt;p&gt;4nec2 software does include a means of generating .NEC input data files. The path to do that is shown in the clip below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/g11Lm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/g11Lm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-01-29T12:43:58.470" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9812" PostTypeId="2" ParentId="3675" CreationDate="2018-01-29T13:31:54.387" Score="3" Body="&lt;p&gt;Below are NEC4.2 analyses showing the intrinsic, free space radiation patterns of (1) a ground plane antenna having two pairs of co-linear, λ/4, horizontal radials spaced at ±90°, and (2) a comparison of the free space elevation pattern of the ground plane antenna to that of a λ/2, center-fed dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The λ/2 dipole has about  0.7dB more gain than the λ/4 ground plane, but otherwise their radiation patterns are very similar, and would be similarly affected by the propagation environment (e.g., reflections from the earth and/or other surfaces).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;Graphic 1&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MmJf0.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MmJf0.jpg&quot; alt=&quot;Graphic 1&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;Graphic 2&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hWOI1.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hWOI1.jpg&quot; alt=&quot;Graphic 2&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-01-29T13:31:54.387" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9813" PostTypeId="1" AcceptedAnswerId="9834" CreationDate="2018-01-29T16:55:54.933" Score="4" ViewCount="170" Body="&lt;p&gt;An FM radio receiver, using a 1 kHz tone at 3 kHz deviation has a 12 dB SINAD (Signal To Noise and Distortion) of -116 dBm. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to increase the 12 dB SINAD sensitivity of the receiver to at least -121 dBm to increase the weak signal performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say I have an RF preamp, which, at the frequency of my receiver has 10 dB of gain with a 1 dB noise figure. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What process should I follow to calculate the new 12 dB SINAD sensitivity of the receiver with the preamp installed and whether it will provide sufficient amplification to increase my 12 dB SINAD sensitivity to -121 dBm?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="9493" LastEditDate="2018-01-30T13:22:42.027" LastActivityDate="2018-01-31T17:12:30.507" Title="Use noise figure and gain to calculate weakest signal radio can receive?" Tags="&lt;receiver&gt;&lt;noise&gt;&lt;snr&gt;&lt;lna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9815" PostTypeId="2" ParentId="9791" CreationDate="2018-01-30T04:54:32.453" Score="1" Body="&lt;p&gt;From &lt;a href=&quot;https://www.manualslib.com/manual/628105/Icom-Id-31a.html?page=65&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.manualslib.com/manual/628105/Icom-Id-31a.html?page=65&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;■ Optional HM-75LS&lt;/p&gt;&#xA;&lt;p&gt;The optional HM-75LS allows you to remotely select operating frequencies, memory channels, etc.&lt;/p&gt;&#xA;&lt;p&gt;Remote control functions can be selected from three settings. These can be selected with &amp;quot;MIC Simple Mode&amp;quot; in the FUNCTION menu.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;MENU ➪ FUNCTION ➪ MIC Simple Mode (p. 44)&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;The HM-75LS has a lock switch on the backside to prevent accidental frequency changes, and so on.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Be sure to turn power OFF when plugging or unplugging the HM-75LS to and from the [SP/MIC] jack.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;SIMPLE:&lt;br /&gt;&#xA;[A]Toggles the Monitor function&lt;br /&gt;&#xA;[B]Turns the Call channel mode&lt;br /&gt;&#xA;[p] Select memory channel 0&lt;br /&gt;&#xA;[q] Select memory channel 1&lt;/li&gt;&#xA;&lt;li&gt;NORM-1: (default)&lt;br /&gt;&#xA;[A]Selects the Call channel mode&lt;br /&gt;&#xA;[B]Toggles the VFO mode and Memory mode&lt;br /&gt;&#xA;[p] Frequency or memory channel 'UP'&lt;br /&gt;&#xA;[q] Frequency or memory channel 'DOWN'&lt;/li&gt;&#xA;&lt;li&gt;NORM-2:&lt;br /&gt;&#xA;[A]Turns the Monitor function&lt;br /&gt;&#xA;[B]Toggles the VFO mode and Memory mode&lt;br /&gt;&#xA;[p] Frequency or memory channel 'UP'&lt;br /&gt;&#xA;[q] Frequency or memory channel 'DOWN'&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;The SIMPLE mode can select only three channels, and is useful for group operations during touring, and so on.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;The VFO mode cannot be selected from the microphone when Simple mode is selected.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It appears that it can change the VFO mode in the normal-2 mike mode but I did not see that it can change to the other VFO. I did not see any way to program it differently. There may be a method that I am not aware of but I doubt it.&lt;/p&gt;&#xA;" OwnerUserId="10495" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-01-30T16:13:35.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9816" PostTypeId="2" ParentId="9813" CreationDate="2018-01-30T11:49:16.313" Score="1" Body="&lt;p&gt;Phil's answer is sound from a technical perspective since there is not sufficient data to fully answer the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a more pragmatic perspective, if you wish to increase the 12 dB SINAD sensitivity of your receiving &lt;em&gt;system&lt;/em&gt;, you should:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Minimize feedline losses&lt;/li&gt;&#xA;&lt;li&gt;Increase the gain of your antenna&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Your required 5 dB improvement in sensitivity is usually well within reach by optimizing these two factors. Any improvement in gain or reduction of losses in these these two areas directly contribute to an increase in sensitivity with no degradation of your 12 dB SINAD.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-01-30T11:49:16.313" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9817" PostTypeId="1" CreationDate="2018-01-30T13:46:48.863" Score="3" ViewCount="468" Body="&lt;p&gt;&lt;strong&gt;I tried a metallic reflector which works well in terms of radiation, but considerably degrades the return loss and adds more complexity to the design.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mx4lg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mx4lg.png&quot; alt=&quot;3D radiation pattern&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CWJFw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CWJFw.png&quot; alt=&quot;planar radiation pattern&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11103" LastEditorUserId="8717" LastEditDate="2018-01-30T21:25:53.627" LastActivityDate="2018-01-30T21:25:53.627" Title="What is the easiest way to eliminate a beam antenna's backward radiation (rear lobe)?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;yagi&gt;&lt;radiation-pattern&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9818" PostTypeId="1" AcceptedAnswerId="9819" CreationDate="2018-01-30T14:41:27.560" Score="3" ViewCount="148" Body="&lt;p&gt;In writing an &lt;a href=&quot;https://ham.stackexchange.com/a/9814/218&quot;&gt;answer to &quot;Use noise figure and gain to calculate weakest signal radio can receive?&quot;&lt;/a&gt; I've managed to confuse myself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe this much is true:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ T_\text{eq}&#xA;=T_1&#xA;+{T_2 \over G_1}&#xA;+{T_3 \over G_1 G_2}&#xA;+\cdots \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let's say the 2nd component is a 3 dB resistive attenuator at room temperature. Then:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ T_\text{eq}&#xA;=T_1&#xA;+{290\:\mathrm K \over G_1}&#xA;+{T_3 \over G_1\cdot 0.5}&#xA;+{T_4 \over G_1 \cdot 0.5 \cdot G_3}&#xA;+\cdots \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;OK maybe it wasn't a resistive attenuator exactly, but a feedline with 3 dB loss. So let's make that feedline shorter, so much so that it's lossless:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ T_\text{eq}&#xA;=T_1&#xA;+{290\:\mathrm K \over G_1}&#xA;+{T_3 \over G_1 1}&#xA;+{T_4 \over G_1\: 1\: G_3}&#xA;+\cdots \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Couldn't we consider a section of lossless feedline as three cascaded shorter sections of lossless feedline?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ T_\text{eq}&#xA;=T_1&#xA;+{290\:\mathrm K \over G_1}&#xA;+{290\:\mathrm K \over G_1\cdot 1}&#xA;+{290\:\mathrm K \over G_1\cdot 1 \cdot 1}&#xA;+{T_5 \over G_1\cdot 1 \cdot 1 \cdot 1}&#xA;+\cdots \tag 4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wait a minute, as we further divide the feedline, noise approaches infinity!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can't be right. Where's the error in my reasoning?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="9493" LastEditDate="2018-01-30T15:55:17.360" LastActivityDate="2018-01-30T18:14:12.517" Title="Accounting for feedlines in noise temperature calculations" Tags="&lt;noise&gt;&lt;math&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9819" PostTypeId="2" ParentId="9818" CreationDate="2018-01-30T17:43:13.953" Score="2" Body="&lt;p&gt;The equivalent noise temperature of a passive device, is approximately given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$T_\text{e}=(A-1)T \tag 5$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where A is the linear attenuation (1/Linear Gain) and T is the physical temperature of the device in Kelvin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus the equivalent noise temperature of a passive device with 3 dB of attenuation at room temperature is: G=0.5, A=2, T&lt;sub&gt;e&lt;/sub&gt;=290 K. This is correctly reflected as the T&lt;sub&gt;2&lt;/sub&gt; term in equation 2 of the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The equivalent noise temperature of a lossless device (G=1, A=1) at any ambient temperature, using equation 5, is 0 K (noiseless). So for the examples in formula 3 of the question, the T&lt;sub&gt;3&lt;/sub&gt; value should be 0 K, not 290 K  as shown. Similarly in formula 4 of the question, T&lt;sub&gt;3&lt;/sub&gt;, T&lt;sub&gt;4&lt;/sub&gt; and T&lt;sub&gt;5&lt;/sub&gt; should all be 0 K. The associated terms then drop away.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-30T18:01:51.850" LastActivityDate="2018-01-30T18:01:51.850" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9820" PostTypeId="2" ParentId="9818" CreationDate="2018-01-30T18:04:27.707" Score="2" Body="&lt;p&gt;The noise temperature for a feedline should be:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ T = 290\:\mathrm K\: (A-1) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $A$ is the ratio of input power to output and will be greater than 1 for any real feedline. For example, a feedline with 2 dB loss has:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ A = 10^{2/10} = 1.585 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 290 K term can be replaced with the physical temperature of the line if it is not at room temperature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is because only the loss part of the transmission line contributes its thermal noise. Think of it this way:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Tp4dL.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fTp4dL.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An attenuator is not typically built as a single series resistor, but from a noise equivalence perspective we can consider it so, with R&lt;sub&gt;attenuator&lt;/sub&gt; being some value required to achieve the necessary attenuation, which will also depend on the source and load impedances. As the transmission line becomes lossless, R&lt;sub&gt;attenuator&lt;/sub&gt; approaches zero, and thus so too does the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rigorous mathematical proofs are given elsewhere (maybe I'll include one here when I get my head around them):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.reeve.com/Documents/Noise/Reeve_Noise_3_AttenAmpNoise.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.reeve.com/Documents/Noise/Reeve_Noise_3_AttenAmpNoise.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.dtic.mil/dtic/tr/fulltext/u2/265414.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.dtic.mil/dtic/tr/fulltext/u2/265414.pdf&lt;/a&gt; (page 33)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arcetri.astro.it/~mosca/radioastronomy/corso/node28.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arcetri.astro.it/~mosca/radioastronomy/corso/node28.html&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;As an example, consider a transmission line (or any attenuator) at room temperature (290 k) with a loss of 10 dB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ T = 290\:\mathrm K (10^{10/10} - 1) = 2610 \:\mathrm K $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems odd for a passive device to have a noise temperature greater than it's physical temperature, as if it had infinite loss it would be simply a resistor and we'd expect thermal noise to be the only contribution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But consider, if the receiver sees a noise power equivalent to a resistor at some temperature, but it's actually seeing that through an attenuator, then the original source must have been even noiser. As the attenuation approaches infinity the effective noise temperature must also approach infinity to account for the fact that the source has been attenuated.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-01-30T18:14:12.517" LastActivityDate="2018-01-30T18:14:12.517" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9821" PostTypeId="2" ParentId="9817" CreationDate="2018-01-30T18:57:41.177" Score="2" Body="&lt;p&gt;From the picture, it looks like you have a log-periodic antenna rather than a Yagi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In either case, optimizing some parameter like front-to-back ratio involves optimizing the spacing and length of the elements. In the case of the log-periodic antenna this is more difficult given the broad-band nature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such optimization can be done by trial and error, either in modeling or empirically. Some antenna design software can automate the process.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-01-30T18:57:41.177" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9822" PostTypeId="2" ParentId="9817" CreationDate="2018-01-30T19:18:23.903" Score="3" Body="&lt;p&gt;No real world antenna exhibits &quot;zero&quot; power in any particular direction. Careful design can minimize the power in the unwanted direction but not eliminate it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a yagi antenna, the front to back ratio is the difference of the decibel gain of the forward, major lobe less the decibel gain of the lobe 180 degrees from the forward lobe. Thus a yagi antenna with a 20 dB front to back ratio would have 100 times less power transmitted or received in the rearward facing direction compared to the forward direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When designing a yagi antenna there is an unavoidable interaction between the gain of the forward lobe and the front to back ratio. If you optimize the front to back ratio, the rearward lobe is reduced but the main lobe becomes wider and has reduced gain. If you optimize the gain, you tend to reduce the front to back ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the average ham, optimizing the forward gain tends to be the desirable outcome. However, if you suffer from interference from directions other than your desired signal direction, optimizing the front to back ratio could improve your signal to noise ratio while receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In reviewing the azimuth plot in the question, it appears that the design is significantly sub-optimized. The major lobe is not in the forward direction and the front to back ratio appears to be ~0.5 dB. You may find it advantageous to start with a well designed model and then experiment with single changes in order to observe the results of the change. As @MikeWaters pointed out, some modeling packages can optimize a design based on your stated preferences.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-30T19:27:18.773" LastActivityDate="2018-01-30T19:27:18.773" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9823" PostTypeId="1" CreationDate="2018-01-30T20:34:44.620" Score="4" ViewCount="493" Body="&lt;p&gt;NEC4.2 provides some information about this topic that may be of interest to some readers.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="76" LastEditDate="2019-04-13T20:36:56.937" LastActivityDate="2020-03-04T13:08:02.147" Title="How Does the Performance of Elevated Radials Differ from That of Buried Radials?" Tags="&lt;vertical-antenna&gt;&lt;earth&gt;&lt;counterpoise&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9824" PostTypeId="2" ParentId="9823" CreationDate="2018-01-30T20:34:44.620" Score="6" Body="&lt;p&gt;The number of horizontal radial wires used in an elevated &quot;counterpoise&quot; can be &lt;strong&gt;far&lt;/strong&gt; fewer than the 120 buried wires used by most AM broadcasters, and the even fewer numbers of buried wires often used with vertical monopoles, inverted Ls etc by amateur radio operators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Several AM broadcast stations use 3 or 4 pairs of λ/4, co-linear, horizontal radial wires installed 10-15 feet above the earth, spaced equally from each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Monopoles using such elevated radials can have elevation pattern peak directivity and &lt;strong&gt;measured&lt;/strong&gt; radiation efficiency about equal to that when using 120 x λ/4 buried radials (other things equal). Wire conductors connecting the antenna system to the earth are neither needed nor used to achieve this performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is true because the source of the r-f current flowing on elevated radials is a direct, wire path through the 2nd conductor of the transmission line to/from the transmitter. The source of r-f current flowing on buried radials is the r-f current flowing in the surface of the earth within λ/2 of the base of the monopole, as the result of its radiation -- which necessarily must travel through a lossy conductor (Earth) to reach those radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason such broadcast stations installed elevated radials is almost always related to the nature of the earth at the transmit site -- typically too rocky to permit using buried radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a NEC4.2 comparison of the patterns/directivities of a λ/4 monopole for the configurations and conditions shown there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/COZLh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/COZLh.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added March 4, 2020:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another analysis of this is shown in the more recently done study/graphic below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the performance of these antenna systems when installed at sites with relatively poor Earth conductivity is fairly similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aw8Nv.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aw8Nv.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-03-04T13:08:02.147" LastActivityDate="2020-03-04T13:08:02.147" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="9826" PostTypeId="1" AcceptedAnswerId="9828" CreationDate="2018-01-31T00:18:50.710" Score="3" ViewCount="1350" Body="&lt;p&gt;An answer to &lt;a href=&quot;https://ham.stackexchange.com/questions/9714/using-two-short-mobile-hf-antennas-to-make-a-vertical-dipole&quot;&gt;this question&lt;/a&gt; suggests that raising a vertical dipole sufficiently can create the effect of a phased array.  How about the opposite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How low can a vertical dipole be mounted?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can a vertical dipole be mounted with the bottom tip at or nearly at ground level?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can one partially or fully bury the bottom half of the dipole (in a deep enough vertical hole), instead of using a bunch of ground radials as the counterpose for the top half of the vertical dipole?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="9493" LastEditDate="2018-01-31T11:16:22.970" LastActivityDate="2018-01-31T14:43:43.720" Title="How low can a vertical dipole be mounted?" Tags="&lt;antenna-theory&gt;&lt;dipole&gt;&lt;vertical-antenna&gt;&lt;radial&gt;&lt;counterpoise&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9827" PostTypeId="2" ParentId="9826" CreationDate="2018-01-31T01:34:08.340" Score="3" Body="&lt;p&gt;The voltage is high near the end of any dipole. If you locate the bottom end of a vertical dipole at --and especially below!-- the ground, you are greatly increasing the losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is really no specific distance from the earth to the bottom end of the dipole to the earth, above which is good and below which is bad. It just needs to be up and away from the the earth as far as is practical, unless you like heating the planet rather that having the other station hear you. :-)&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-01-31T02:10:06.203" LastActivityDate="2018-01-31T02:10:06.203" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9828" PostTypeId="2" ParentId="9826" CreationDate="2018-01-31T02:39:50.257" Score="5" Body="&lt;p&gt;Here is an analysis of a vertical, 1/2 wavelength, 2 meter dipole suspended at various heights above ground:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UxU0j.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UxU0j.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see, as you raise the bottom end of the antenna from near ground level up to about 7 wavelengths, the gain increases. At the same time, the elevation angle of the maximum gain decreases (becomes closer to the horizon). As you continue to raise the height of the antenna, the gain becomes somewhat cyclic but the elevation angle remains low.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you put the bottom end of the antenna directly in contact with the ground, or buried in the ground, the gain will further decrease and the resonance of the antenna will shift. Ultimately, it would be preferable to have a 1/4 wave monopole with an appropriate number of ground or elevated radials in order to realize the maximum gain of this configuration. See &lt;a href=&quot;https://ham.stackexchange.com/questions/9806/how-does-earth-conductivity-affect-the-takeoff-angle-of-a-vertical-monopole&quot;&gt;How Does Earth Conductivity Affect the “Takeoff Angle” of a Vertical Monopole?&lt;/a&gt; and &lt;a href=&quot;https://ham.stackexchange.com/questions/9823/how-does-the-performance-of-elevated-radials-differ-from-that-of-buried-radials&quot;&gt;How Does the Performance of Elevated Radials Differ from That of Buried Radials?&lt;/a&gt; for more information regarding the ground wire construction implications of 1/4 wave vertical ground plane antennas near the earth.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-01-31T14:43:43.720" LastActivityDate="2018-01-31T14:43:43.720" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9829" PostTypeId="1" AcceptedAnswerId="9830" CreationDate="2018-01-31T15:01:19.300" Score="2" ViewCount="1126" Body="&lt;p&gt;I'm trying to make a WBFM receiver without using WBFM Receive block. So I've tried this way&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vVsCt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vVsCt.png&quot; alt=&quot;FM receiver flowgraph&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it won't work. The problem is &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;RuntimeError: flow graph has loops!&lt;/strong&gt; &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and I need to use loop feedback for implement FM demodulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Very pleasure for any suggestions and advises.&lt;/p&gt;&#xA;" OwnerUserId="11108" LastEditorUserId="11108" LastEditDate="2018-02-01T16:59:44.350" LastActivityDate="2018-02-01T16:59:44.350" Title="How can I make WBFM receiver without using WBFM Receive block?" Tags="&lt;fm&gt;&lt;gnuradio&gt;&lt;usrp&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9830" PostTypeId="2" ParentId="9829" CreationDate="2018-01-31T15:13:19.017" Score="5" Body="&lt;p&gt;&lt;strong&gt;General principle:&lt;/strong&gt; In GNU Radio you cannot ever have a flow graph with a loop in it. If you wish to have feedback of some kind, it must be implemented in a single block.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(There are many existing blocks that do this, such as AGC blocks and IIR filter blocks, and classes to help create them, though they still require writing C++ code.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you do &lt;strong&gt;not&lt;/strong&gt; need feedback to implement a FM demodulator. The key block to FM demodulation in GNU Radio is the &lt;strong&gt;Quadrature Demod&lt;/strong&gt; (&lt;code&gt;gnuradio.analog.quadrature_demod_cf&lt;/code&gt;) block. This block takes in a complex signal and outputs the phase difference — or instantaneous frequency — of every successive pair of samples, which is exactly the core of FM demodulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides the Quadrature Demod block, you will want&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A low-pass filter on the input, as with any demodulator.&lt;/li&gt;&#xA;&lt;li&gt;A suitable FM de-emphasis filter (provided in the &lt;strong&gt;FM Deemphasis&lt;/strong&gt; block).&lt;/li&gt;&#xA;&lt;li&gt;Optionally a DC blocking filter, because if the input signal is not centered at 0 there will be a corresponding DC offset in the output audio, which will create clicks at start/stop if minor or clipping of the audio if severe.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-01-31T15:13:19.017" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9831" PostTypeId="1" CreationDate="2018-01-31T16:03:38.310" Score="1" ViewCount="144" Body="&lt;p&gt;I just got a Kenwood TM-V71A, and I really want to use it for Echolink operation as a simplex node. I got it mostly working, but there's one huge problem - it's constantly transmitting over the Internet when there's no signal. I was testing on ECHOTEST. Basically it goes: RX -&gt; Idle 1 sec -&gt; TX until it gets a signal over RF and that signal goes away -&gt; Idle 1 sec -&gt; RX. TX/RX are based on Echolink (i.e. RX means the radio is transmitting what Echolink receives). Does anybody have any ideas what's causing this or how to fix it?&lt;/p&gt;&#xA;" OwnerUserId="1285" LastActivityDate="2019-05-16T20:02:53.593" Title="TM-V71A Echolink - Constantly Transmitting" Tags="&lt;kenwood&gt;&lt;echolink&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9832" PostTypeId="1" AcceptedAnswerId="9833" CreationDate="2018-01-31T17:01:19.627" Score="11" ViewCount="809" Body="&lt;p&gt;There are many things I might do enable my station to hear weaker signals that would otherwise be buried in noise. Just a few possibilities:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Install a nice LNA&lt;/li&gt;&#xA;&lt;li&gt;Increase antenna gain&lt;/li&gt;&#xA;&lt;li&gt;Reduce feedline losses&lt;/li&gt;&#xA;&lt;li&gt;Buy a better receiver&lt;/li&gt;&#xA;&lt;li&gt;Move to a quieter location&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Is there a way I can quantitatively calculate the effect these changes on my station's weak-signal receive performance?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-05-20T11:55:50.453" Title="How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?" Tags="&lt;noise&gt;&lt;math&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9833" PostTypeId="2" ParentId="9832" CreationDate="2018-01-31T17:01:19.627" Score="11" Body="&lt;p&gt;Try the &lt;a href=&quot;https://en.wikipedia.org/wiki/Friis_formulas_for_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;Friis noise formula&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ F_{eq} = F_1 + {F_2-1 \over G_1} + {F_3-1 \over G_1 G_2} + \cdots \tag 1 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$F_n$&lt;/span&gt; is the noise factor of the n-th component, and likewise &lt;span class=&quot;math-container&quot;&gt;$G_n$&lt;/span&gt; is the gain. The noise factor &lt;span class=&quot;math-container&quot;&gt;$F$&lt;/span&gt; is the linear ratio form of the noise figure which is given in decibels.&lt;/p&gt;&#xA;&lt;p&gt;For example, the first component may be an LNA, the second component a transmission line from the LNA to the receiver, and the third component the receiver itself.&lt;/p&gt;&#xA;&lt;h2&gt;Example 1: a good LNA on a crappy receiver&lt;/h2&gt;&#xA;&lt;p&gt;I read somewhere an RTL-SDR has a noise figure of 6 dB, or a noise factor of 4. Let's say we have an LNA with a noise figure of 1 dB (1.26) and a gain of 20 dB (100). By equation 1:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 1.26 + {4-1 \over 100} = 1.29 = 1.11\:\mathrm{dB} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Thus, the addition of the LNA has brought the noise factor from 6 dB down to 1.11 dB by dividing the RTL-SDR's noise by the LNA's gain.&lt;/p&gt;&#xA;&lt;p&gt;The additional power into the receiver increases distortion and reduces dynamic range, but that's a different can of worms.&lt;/p&gt;&#xA;&lt;h2&gt;Noise factor of passive components&lt;/h2&gt;&#xA;&lt;p&gt;This is easy: the &lt;a href=&quot;https://ham.stackexchange.com/q/9818/218&quot;&gt;noise factor is equal to the attenuation&lt;/a&gt;, assuming the thermodynamic temperature (as measured by a thermometer) of the component is &amp;quot;room temperature&amp;quot;, conventionally 290 K (17 °C or 62 °F). And logically, the noise figure is equal to the loss in decibels.&lt;/p&gt;&#xA;&lt;p&gt;So, a piece of coax with 4 dB of loss has a noise figure of 4 dB. The noise factor and attenuation are &lt;span class=&quot;math-container&quot;&gt;$ 10^{4/10} = 2.51 $&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;This is true for any passive component, like a filter, or even antenna inefficiencies.&lt;/p&gt;&#xA;&lt;h2&gt;Example 2: not putting the LNA at the antenna&lt;/h2&gt;&#xA;&lt;p&gt;Same as before, but with a 4 dB loss feedline between the LNA and antenna.&lt;/p&gt;&#xA;&lt;p&gt;Antenna -&amp;gt; 4 dB loss -&amp;gt; LNA -&amp;gt; receiver&lt;/p&gt;&#xA;&lt;p&gt;We'll need to know the gain of the coax for the &lt;span class=&quot;math-container&quot;&gt;$G_1$&lt;/span&gt; term, which will be less than one. It's the reciprocal of the attenuation: 1/2.51 = 0.398&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 2.51&#xA; + {1.26 - 1\over 0.398}&#xA; + {4 - 1\over 0.398 \cdot 100}&#xA; = 3.24 = 5.10\:\mathrm{dB}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The feedline noise dominates, negatively impacting the system in two ways:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It adds &lt;a href=&quot;https://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;Johnson-Nyquist&lt;/a&gt; noise generated by the resistive losses of the cable, represented by the &lt;span class=&quot;math-container&quot;&gt;$F_1$&lt;/span&gt; term, and&lt;/li&gt;&#xA;&lt;li&gt;it reduces the power passed to the next stage, making the noise power added by that next stage more significant, represented by the &lt;span class=&quot;math-container&quot;&gt;$G_1$&lt;/span&gt; term.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h2&gt;Example 3: put the LNA at the antenna&lt;/h2&gt;&#xA;&lt;p&gt;Same as before, but now with the LNA at the antenna:&lt;/p&gt;&#xA;&lt;p&gt;Antenna -&amp;gt; LNA -&amp;gt; 4 dB loss -&amp;gt; RTL-SDR&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 1.26&#xA; + {2.51-1 \over 100}&#xA; + {4-1 \over 100 \cdot 0.398}&#xA; = 1.35 = 1.30\:\mathrm{dB}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Almost as good as example 1 where there was no feedline.&lt;/p&gt;&#xA;&lt;h2&gt;How does noise figure relate to SNR in practice?&lt;/h2&gt;&#xA;&lt;p&gt;Noise figure is the reduction in signal to noise ratio (SNR) under an assumption: the input noise is equivalent to the Johnson-Nyquist noise of a resistor at 290 K. 290 K is very quiet: it's the same noise power you'd get from a dummy load at room temperature. Often input noise is more.&lt;/p&gt;&#xA;&lt;p&gt;The relationship of input SNR to output SNR is related not only to the receiving system's noise, but the input noise:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ { \text{SNR}_\text{in} \over \text{SNR}_\text{out} }&#xA;= 1 + {T_\text{sys} \over T_\text{in}} \tag 2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;When &lt;span class=&quot;math-container&quot;&gt;$T_\text{sys} \ll T_\text{in}$&lt;/span&gt; the right hand side of the equation approaches 1, thus &lt;span class=&quot;math-container&quot;&gt;$ \text{SNR}_\text{in} \approx \text{SNR}_\text{out} $&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;To make sense of that brings us to...&lt;/p&gt;&#xA;&lt;h2&gt;Introducing noise temperature&lt;/h2&gt;&#xA;&lt;p&gt;A resistor produces &lt;a href=&quot;https://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;Johnson-Nyquist noise&lt;/a&gt; due to thermal motion of the charge carriers within it. The noise power is related to the temperature by:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {P \over B} = kT \tag 3 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$P$&lt;/span&gt; is the power in watts&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$B$&lt;/span&gt; is the bandwidth in Hz over which that power is measured&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$k$&lt;/span&gt; is the Boltzmann constant, approximately 1.381e&lt;sup&gt;-23&lt;/sup&gt; joules per kelvin&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$T$&lt;/span&gt; is the temperature of the resistor, in kelvin&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;It's useful to pretend all noise is generated by a resistor at some temperature, which makes noise temperature a useful unit for &amp;quot;noisiness&amp;quot; that may or may not be directly related to thermodynamic temperature as measured by a thermometer.&lt;/p&gt;&#xA;&lt;p&gt;Noise factor and noise temperature are related by:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ T = 290\,(F-1) \tag 4 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ F = {T \over 290} + 1 \tag 5 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This leads to an alternate version of the Friis noise formula expressed in noise temperature rather than noise factor:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ T_{eq} = T_1 + {T_2 \over G_1} + {T_3 \over G_1 G_2} + \cdots \tag 6 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;h2&gt;What's the input noise temperature?&lt;/h2&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.itu.int/rec/R-REC-P.372-14-201908-I/en&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU-R P.372-14&lt;/a&gt; provides some excellent data on environmental noise temperatures. The document is worth a read, but here are a few relevant figures from it:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ziOdf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ziOdf.png&quot; alt=&quot;figure 1&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VyKTH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VyKTH.png&quot; alt=&quot;figure 2&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TTgwi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TTgwi.png&quot; alt=&quot;figure 3&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Each figure covers a different frequency range, noise temperature on the right axes, and equivalent noise figure on the left. The noise temperature doesn't come anywhere near 290 K within HF. At microwave frequencies 290 K might be realistic, provided no man-made noise and an antenna directional enough to avoid the sun.&lt;/p&gt;&#xA;&lt;h2&gt;Example 4: huge loss and a cheap receiver at different frequencies&lt;/h2&gt;&#xA;&lt;p&gt;We'll use an RTL-SDR with 12 dB of loss due to feedline and antenna inefficiencies:&lt;/p&gt;&#xA;&lt;p&gt;Antenna -&amp;gt; 12 dB loss -&amp;gt; RTL-SDR&lt;/p&gt;&#xA;&lt;p&gt;The 12 dB noise figure of the feedline is equivalent to a noise temperature of 4306 K. And the 6 dB NF of the RTL-SDR is 865 K.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ T_{eq}&#xA; = 4306\:\mathrm K&#xA; + {875 \over 10^{-12/10}}&#xA; = 18174\:\mathrm K&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;By equation 5 that's a noise figure of 18 dB.&lt;/p&gt;&#xA;&lt;p&gt;Let's say we're using this at 400 MHz in a city. Line A (man-made noise) in figure 3 puts external noise temperature around 3000 K. So by equation 3:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ { \text{SNR}_\text{in} \over \text{SNR}_\text{out} }&#xA;= 1 + {18174\:\mathrm K \over 3000\:\mathrm K}&#xA;= 7&#xA;= 8.49\:\mathrm{dB} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Under these conditions, this terrible station will make the SNR 8.49 dB worse. Bad, but not as bad as the 18 dB noise figure would suggest.&lt;/p&gt;&#xA;&lt;p&gt;Now what if this is a 7 MHz station is a very quiet location? Figure 2 is hard to read precisely since it spans 18 orders of magnitude, but line D (galactic noise) at 7 MHz is at least 300,000 K.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ { \text{SNR}_\text{in} \over \text{SNR}_\text{out} }&#xA;= 1 + {18174\:\mathrm K \over 300000\:\mathrm K}&#xA;= 1.06&#xA;= 0.256\:\mathrm{dB} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Attempts to reduce noise with an LNA, better receiver, etc. are futile. The SNR must be improved at the source, for example by increasing antenna directivity.&lt;/p&gt;&#xA;&lt;h2&gt;Summary:&lt;/h2&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Improving system noise performance only matters if the external noise isn't already dominating.&lt;/li&gt;&#xA;&lt;li&gt;Increasing antenna directivity improves SNR even if external noise dominates.&lt;/li&gt;&#xA;&lt;li&gt;On HF, external noise is probably dominating.&lt;/li&gt;&#xA;&lt;li&gt;Noise figures assume an external noise of 290 K, which is really quiet: about as quiet as things can get for a terrestrial antenna. Noiser environments make the noise figure matter less.&lt;/li&gt;&#xA;&lt;li&gt;Feedlines, filters, antenna inefficiency, or any other passive component that has loss also introduces noise.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Finally a caveat: distortion is a detriment to receive performance also. The gain of an LNA may reduce the significance of the receiver's noise, but it will also increase distortion. Always consider the whole picture.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-05-20T11:55:50.453" LastActivityDate="2021-05-20T11:55:50.453" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="9834" PostTypeId="2" ParentId="9813" CreationDate="2018-01-31T17:12:30.507" Score="0" Body="&lt;p&gt;It's difficult to quantify the relationship between SINAD and noise figure. SINAD measures the signal quality at the output of the radio, so effects of the demodulator and sometimes even speaker are included.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Noise figure quantifies the internal noise generated by a component. This will degrade SNR, but the amount by which SNR is degraded depends on the input noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's an apples to oranges comparison, with some additional unknowns thrown in. We'd need to know:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How the demodulated signal quality (SINAD) relates to the RF input SNR.&lt;/li&gt;&#xA;&lt;li&gt;What the external noise (man-made and natural RF interference) is.&lt;/li&gt;&#xA;&lt;li&gt;The receiver's noise figure.&lt;/li&gt;&#xA;&lt;li&gt;Other details of your station, such as feedline losses and antenna gain.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;But if you want to know generally how noise performance can be quantified and what your 1 dB NF LNA might be able to do about it, check out, see:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/9832/how-can-i-calculate-the-effects-of-an-lna-antenna-gain-etc-on-noise-performan/9833#9833&quot;&gt;How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-01-31T17:12:30.507" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9835" PostTypeId="1" AcceptedAnswerId="9840" CreationDate="2018-01-31T18:10:11.153" Score="2" ViewCount="1602" Body="&lt;p&gt;I am new to HF. I'd like to put up an 80m delta loop. Due to aesthetic considerations I need to use coax to the shack. If tuned for 3.55MHz, I anticipate having a good SWR on 80m, 40m, and 20m. The transceiver is an Icom 7300 which tunes SWR 3:1 or less. Trying to avoid buying a tuner. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question, essentially, is whether the feedline and balun choice can be optimized for not just one, but two bands — 80m and 40m. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;— Bring down a length of 450 ohm line, then a balun, then coax? (What length, what balun?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;— Balun in the air at feedpoint (4:1?), then coax all the way? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;— Something else?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have read much about impedance, SWR, quarter wavelengths, and I simply do not have the background to make sense of it. Maybe one of you will make it click. Thanks.&lt;/p&gt;&#xA;" OwnerUserId="11100" LastEditorUserId="9493" LastEditDate="2018-02-01T00:46:56.300" LastActivityDate="2018-02-02T13:04:30.923" Title="Feedline and balun for 80m horizontal delta loop" Tags="&lt;antenna-theory&gt;&lt;coaxial-cable&gt;&lt;balun&gt;&lt;feed-line&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9836" PostTypeId="1" CreationDate="2018-02-01T16:08:15.857" Score="2" ViewCount="67" Body="&lt;p&gt;Here is one example of such, based on a NEC study...&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-02-02T13:10:09.317" Title="How Might Nearby Re-Radiators Affect the Radiation Patterns of a Transmit Antenna?" Tags="&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9837" PostTypeId="2" ParentId="9836" CreationDate="2018-02-01T16:08:15.857" Score="2" Body="&lt;p&gt;The NEC4.2 study/graphic first below shows how a structure comprised of conductors to (roughly) emulate the a-c power lines in a wood-frame house might affect the radiation patterns of a 40m-band vertical monopole located six feet away from one side of that house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The effects of this may be different than those expected. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/8wdQg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8wdQg.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Below are the patterns for that monopole and its buried ground rod, by themselves (other things equal).&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1XcJ3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1XcJ3.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Added on 2 Feb 2018:  This may be drifting too far off the original topic, but  the affect of even relatively tall structures with steel frames on the FAR FIELDS of a transmit antenna can be negligible, as long as the dimensions of the structure are small enough in terms of wavelength.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Below is a graphic showing the measured relative fields of an AM broadcast station on both sides of a path from a distant transmit antenna toward, and past such a structure.&lt;/strong&gt; &lt;em&gt;RJF&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/77lHr.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/77lHr.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2018-02-02T13:10:09.317" LastActivityDate="2018-02-02T13:10:09.317" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9839" PostTypeId="1" AcceptedAnswerId="9846" CreationDate="2018-02-01T21:51:20.020" Score="2" ViewCount="1333" Body="&lt;p&gt;I'm planning on putting a quarter wave ground plane antenna in my attic for use with 2m/70cm.  In order to keep the feed line short, it needs to be near my TV antenna.  Is there a rule of thumb for the minimum distance between the two antennas?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Accessing the attic is a real pain, so I'd like to put the new antenna in a good spot on the first try.  The TV antenna is a yagi which is pointed away from area where I want to put the ham antenna.  The ham antenna will be connected to a 5 watt transmitter initially, but I'd like to eventually upgrade to 50 watts.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Update&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;It's been a while and I'm not experiencing any interference issues.  I went with the quarter wave ground plane antenna, even though it's omnidirectional.  My radio transmits 5 watts.  I installed the ham antenna about five feet behind the TV antenna, with the lower end of the radiating element about two feet higher than the TV antenna.  The things that seem to be helping are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The TV antenna is highly directional and points away from the ham antenna.&lt;/li&gt;&#xA;&lt;li&gt;The antennas have different polarizations (horizontal for TV and vertical for ham).  I suspect this is helping more than anything else.&lt;/li&gt;&#xA;&lt;li&gt;The ham antenna doesn't radiate much power downward, so the vertical separation should be helping at least a bit.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2019-03-06T20:06:58.943" LastActivityDate="2019-03-06T20:06:58.943" Title="How to determine the minimum distance between ham and TV antennas" Tags="&lt;antenna&gt;&lt;rfi&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="9840" PostTypeId="2" ParentId="9835" CreationDate="2018-02-02T02:14:14.143" Score="2" Body="&lt;p&gt;Edited to reflect a horizontal loop:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The delta loop should be at least 1$\lambda$ in circumference for the lowest band. The following analysis is for a horizontal, equilateral triangle loop with all three corners at 60 feet. Each leg is 94.37 feet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is fed in the center of the any legs with a 4:1 balun with the 4x side connected to the base and the 1x side connected to 50 ohm coax to your IC-7300. The center feed optimizes the results compared to a corner feed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The performance by CW/digital band segment of this antenna is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;80 meters, SWR 1.7:1, 6.7 dBi gain at 87°, 0 dBi gain at 22° &lt;/li&gt;&#xA;&lt;li&gt;40 meters, SWR 1.7:1, 7.1 dBi gain at 32°, 0 dBi gain at 9°&lt;/li&gt;&#xA;&lt;li&gt;20 meters, SWR 1.6:1, 9.6 dBi gain at 16°, 0 dBi gain at 4°&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These results were obtained over real, average ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 4:1 balun was chosen because the impedance of the feedpoint of the antenna for each band is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;80 meters 133-j50&lt;/li&gt;&#xA;&lt;li&gt;40 meters 272-j105&lt;/li&gt;&#xA;&lt;li&gt;20 meters 279-j80&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Since you specified that you need to run coax into your shack, it is best to transform the impedance at the antenna in this case and run coax all the way into the shack. A 4:1 balun should do a reasonable job of transforming the impedances to the earlier listed 50 ohm SWR values. Other combinations of ladder lines and baluns are possible but with no practical advantage.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-02-02T13:04:30.923" LastActivityDate="2018-02-02T13:04:30.923" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9841" PostTypeId="2" ParentId="9839" CreationDate="2018-02-02T15:02:40.733" Score="0" Body="&lt;p&gt;You may need to do some experiments.  It will also depend on what band your TV channels are.  You don't state where in the world you live.  (TV channels can also be on multiple bands, e.g. in North America where VHF-HI and UHF are both still used in some areas).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My instinct is that greater separation will be your friend, especially when transmitting at higher power.  This will also reduce the effects of your TV antenna on your signal pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, consider putting the TV antenna or the ham radio antenna outside, if your living arrangements permit it.  Since you seem to be getting adequate service with an attic-mounted TV antenna, having the ham antenna outside would be ideal in terms of getting superior range.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-02-02T15:02:40.733" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9842" PostTypeId="1" CreationDate="2018-02-03T02:49:37.017" Score="3" ViewCount="671" Body="&lt;p&gt;I just got my technician license, and I'm just fooling around a bit on the Grundig.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm trying to pull in WWV from NJ,&#xA;so 1st, is that possible with the radio whip?  I've tried the built-in whip on 5, 15 &amp;amp; 20 Mhz at 4 PM and at 9 PM.  nothing&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next question: I have a spool of galv fence wire, bent it into a very tight loop, at the spool and pushed it into Female - female SO239.  Screwed that into 100 Ft brand new RG8X cable.  Pulled out 40 feet and taped it 7 feet high in the house. Nothing on 5,15 or 20 Mhz .&#xA;More details.  I probably have 30 feet of coax coiled at the radio. ( vs coiling it near the wire antenna.&#xA;IMPORTANT : I have NOT cut 40 feet off the spool.  I have the coax attached to the pigtail ON THE SPOOL and ran 40 feet out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;do I need to cut the wire off the spool?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What am I doing wrong?  It was my understanding that even 15 feet of wire upstairs, with the radio and myself down in the basement, would be good enough?&lt;/p&gt;&#xA;" OwnerUserId="11123" LastEditorUserId="8717" LastEditDate="2018-02-03T03:22:51.327" LastActivityDate="2018-09-12T22:01:22.763" Title="Simple antenna for an old Grundig Satellit 800" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9843" PostTypeId="1" CreationDate="2018-02-03T15:09:10.450" Score="4" ViewCount="580" Body="&lt;p&gt;Prompted by a previous question found at &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt; -- an answer there included the following text:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&quot;For transmission lines (twin-lead or coax) to not radiate, each conductor must carry equal and opposite currents. It's these equal and opposite currents canceling each other that results in zero net field away from the transmission line. If the currents are not equal and opposite, then they don't cancel, and the difference results in an external electromagnetic field, and your transmission line radiates like an antenna.&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A sketch included in that link (repeated below), and the comments about it there are unclear as to how the common-mode r-f current flowing on a &lt;strong&gt;braided&lt;/strong&gt; outer conductor of a perfectly terminated coaxial cable always is confined to the inner surface of that braid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Skin effect&quot; keeps most of the r-f current flow very close to the surface of a conductor.  But in a braided conductor, what prevents that current from being distributed ~ equally around the circumference of each unit conductor of that braid?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it was/is, then wouldn't the outer surface of that outer conductor always be &quot;hot&quot; for r-f energy, just as are both conductors of twin-lead transmission line?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is understandable that r-f current flowing on the inner surface of the outer conductor of &lt;strong&gt;rigid&lt;/strong&gt; coaxial transmission line could not cross to its outer surface until functional paths existed for that purpose, usually at the load end of the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Isn't that also true when the outer conductor is braided, if that braid provides paths for r-f current to flow from the ID to the OD of the outer conductor along its entire length?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sQq1P.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sQq1P.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-02-14T12:36:18.873" Title="Is RF current always confined to the inner diameter of a braided outer conductor of coaxial cable?" Tags="&lt;coaxial-cable&gt;&lt;balun&gt;&lt;theory&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9845" PostTypeId="2" ParentId="9843" CreationDate="2018-02-04T02:32:16.617" Score="0" Body="&lt;p&gt;Assuming decent coax that is properly terminated, and where the braid is not corroded and the strands are in good contact with each other, any small holes in the braid act like a waveguide below cutoff. Therefore, any radiation from the braid is &lt;em&gt;usually&lt;/em&gt; inconsequential in amateur practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, in some cases there can be &lt;em&gt;some&lt;/em&gt; radiation and/or &lt;em&gt;some&lt;/em&gt; unwanted signal ingress. That's one of the reasons for double- and quad-shielded flexible coax (or solid shield coax).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, if the unbalanced coax is connected directly to a dipole without a suitable balun, we will then have common-mode currents flowing on the outside of the shield. The shield will then radiate (as shown in the graphic) a significant signal, as well as pick up unwanted RFI, etc. whether the shield is braided or solid.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-02-04T02:32:16.617" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9846" PostTypeId="2" ParentId="9839" CreationDate="2018-02-04T02:39:28.047" Score="2" Body="&lt;p&gt;As other have commented, there is no sure way of avoiding damage or interference when the antennas are in close proximity. But there are a few things you can do to minimize the chance of interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Place the Ground Plane 180° From the Front of the TV Antenna&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By placing the ground plane antenna in the opposite direction of the primary gain lobe of the TV antenna, the amount of signal from your VHF/UHF transmitter that is coupled into your TV antenna system will be minimized. The Friis equation helps to estimate the effect:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$P_\text{rx}=P_\text{tx}G_\text{tx}G_\text{rx} \left(\frac{\lambda}{4\pi D}\right)^2 \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where P&lt;sub&gt;rx&lt;/sub&gt; is the power in watts received by the receiver, P&lt;sub&gt;tx&lt;/sub&gt; is the power of the transmitter in watts, G&lt;sub&gt;tx&lt;/sub&gt; is the linear gain of the transmitting antenna, G&lt;sub&gt;rx&lt;/sub&gt; is the linear gain of the receive antenna, $\lambda$ is the wavelength in meters, and D is the distance between antennas in meters. Note that the antennas cannot be in each other's near fields. This can be largely avoided by separating the antennas by at least 1 wavelength (2 meters).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To convert dB gain or loss to linear gain or loss:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$G_\text{linear}=10^\frac{G_\text{dBi}}{10} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we assume that your ground plane antenna has a 2 dBi gain, the back end of the TV antenna has a -10 dBi gain, 5 watts of transmit power on two meters, and the distance between the antennas is 6 feet, formula 1 tells us that the power in the receive antenna will be 6.32 milliwatts. That is the equivalent of being within 1470 feet from a 15,000 watt ERP VHF television station with a 5 dBi gain TV antenna pointing directly at the TV station. That is a lot of power!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see from equation 1 that doubling the distance between the antennas, the received power is cut by 75%. Thus placing your antenna 12 feet from the TV antenna would result in 1.58 milliwatts at the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Avoid Using TV Antenna Amplifiers&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;TV antenna amplifiers are, by necessity, very wide bandwidth amplifiers. The power received from your ground plane antenna could cause IMD (intermodulation distortion) within the amplifier which could affect the desired TV signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Use Less Transmit Power&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF and UHF stations primarily rely on line of site for communications. You may find that you can easily talk into a nearby repeater with a few 100 milliwatts. This will greatly reduce the possibility of interference with the TV system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Use a Directional Transmit Antenna&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A small VHF/UHF Yagi pointed away from the TV antenna could add 10 dB or more of path loss to the signal that gets coupled into the TV antenna. The practicality of this solution depends on the direction of the repeaters or other hams with which you wish to communicate.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-02-04T02:39:28.047" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9847" PostTypeId="1" AcceptedAnswerId="9849" CreationDate="2018-02-04T08:26:16.753" Score="1" ViewCount="146" Body="&lt;p&gt;I have two Chinese Pixie kits that I've assembled.  I think they are pretty interesting, from a QRP / tinkering stand-point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Looking at the schematic below, where is the beat frequency coming from?&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know Q1 is part of the crystal oscillator and Q2 is essentially the power-amp during transmit, but what is mixing with the incoming signal to create the CW tone instead of the simple hissing you'd hear?  I simply cannot see where this is happening.  I &lt;em&gt;do&lt;/em&gt; understand all of the other areas of the circuit (power supply area, keying, audio amp and low-pass filter on the antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pixie schematic&#xA;&lt;img src=&quot;https://www.pismotek.com/media/pixie-schematic.jpg&quot; alt=&quot;Pixie schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to do more tinkering with this, but before I do, I really would like a firm knowledge of what is acting as the BFO here.&lt;/p&gt;&#xA;" OwnerUserId="1738" LastEditorUserId="76" LastEditDate="2018-02-05T03:02:53.857" LastActivityDate="2018-02-05T03:02:53.857" Title="How does this Pixie circuit produce a beat frequency?" Tags="&lt;electronics&gt;&lt;oscillator&gt;&lt;qrp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9849" PostTypeId="2" ParentId="9847" CreationDate="2018-02-04T13:30:20.000" Score="4" Body="&lt;p&gt;Q1 forms a &lt;a href=&quot;https://en.wikipedia.org/wiki/Colpitts_oscillator&quot; rel=&quot;nofollow noreferrer&quot;&gt;Colpitts crystal oscillator&lt;/a&gt;. It uses the reverse biased D2 as a varicap (variable capacitor) to pull the crystal frequency by 700 to 800 Hz, This frequency beats with the received frequency to produce the audible CW tone. The adjustability of the pull through W1 also allows a simple, limited range RIT function during receive.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="873" LastEditDate="2018-02-05T02:58:14.553" LastActivityDate="2018-02-05T02:58:14.553" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9850" PostTypeId="1" CreationDate="2018-02-04T18:35:52.167" Score="2" ViewCount="2652" Body="&lt;p&gt;Please don't laugh.  I am totally ignorant about amateur radio.  When I tried to use the internet to answer questions, all I have found are formulas and charts I don't understand.  For example; I looked for instructions for erecting an inverted L antenna.  I really needed to know how mush of the wire is used for the horizontal portion and how much for the vertical portion.  I was hoping for percentages (60/40 or 70/30 etc.), instead all I have found is a formula.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have purchased a Palstar R30A receiver and want the best possible reception.  I was advised to use a 160/6 inverted L antenna with balum, so I purchased one.  Now that I have it, the wire is much too long for my location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Did I receive bad advice?  I didn't know what questions to ask.  What are my options?  By the way, what does 160/6 represent?&lt;/p&gt;&#xA;" OwnerUserId="11136" LastActivityDate="2018-03-11T22:09:29.970" Title="Long Wire Antenna for SWL" Tags="&lt;wire-antenna&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9851" PostTypeId="2" ParentId="9850" CreationDate="2018-02-04T21:51:48.750" Score="6" Body="&lt;p&gt;First, I believe the 160/6 might refer to the antenna's coverage of the 160 meter band through the 6 meter band, with all other ham bands between included.  Only important if you plan to transmit.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're only interested in short wave listening, it simplifies the antenna requirement.  My suggestion is to string up whatever length of wire you have.  More is better but don't stress over a premade antenna not fitting your lot.  Simply cut to size.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The balun can be optional for simply receiving.  In fact, I would connect with the balun and then later bypass the balun just to compare.  Part of the fun of experimenting!  Have fun and discover what works.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this helps.  &lt;/p&gt;&#xA;" OwnerUserId="11094" LastActivityDate="2018-02-04T21:51:48.750" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9852" PostTypeId="1" CreationDate="2018-02-05T08:44:10.997" Score="0" ViewCount="187" Body="&lt;p&gt;A little background - I own a 2012 Dodge Charger Pursuit that I am turning into my mobile ham station. It already has most of what I need, but I ran into something I want to ask a question about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has wiring provided to the center console area for accessories. This includes 3 20a always-on and 3 20a accessory circuits. It also has a dedicated ground wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it make more sense to do my own power distribution to the trunk and mount the transceiver there? I don't mind running extensions for mic and control unit (I'm thinking of the icom id-4100a), or does it make more sense to run the antenna cable from the trunk to the center console and wire the radio in there? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm on the fence, so I want to see what you all think :-)&lt;/p&gt;&#xA;" OwnerUserId="11140" LastActivityDate="2018-02-16T01:11:13.487" Title="Console vs Trunk mount" Tags="&lt;mobile&gt;&lt;transceiver&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9853" PostTypeId="2" ParentId="9852" CreationDate="2018-02-05T13:54:42.397" Score="2" Body="&lt;p&gt;The &lt;a href=&quot;http://www.icomamerica.com/en/products/amateur/mobile/id4100a/specifications.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;ID-4100A draws 13 amps&lt;/a&gt; on high power (50W). The voltage rating specified in the &lt;a href=&quot;http://www.icomamerica.com/en/downloads/DownloadDocument.aspx?Document=856&quot; rel=&quot;nofollow noreferrer&quot;&gt;manual&lt;/a&gt; is 13.8 V DC ±15%; therefore, the minimum voltage &lt;em&gt;at the transceiver&lt;/em&gt; is 11.73 volts. Many transceivers will not transmit if the voltage drops to that level. Therefore, if you run DC all the way to the trunk, you'll need to use fairly large conductors to minimize the voltage drop. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.icomamerica.com/en/downloads/DownloadDocument.aspx?Document=856&quot; rel=&quot;nofollow noreferrer&quot;&gt;instruction manual&lt;/a&gt; suggests mounting it under the passenger seat, and the detachable console below the dash. The power leads could be smaller located there. Ohm's Law and a chart showing resistance per foot are your friends. You have to calculate the drop in &lt;strong&gt;both&lt;/strong&gt; the + and - leads, and don't forget that there is additional voltage drop across fuses, connectors, and the console wiring.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-02-05T14:14:16.377" LastActivityDate="2018-02-05T14:14:16.377" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9854" PostTypeId="1" CreationDate="2018-02-06T16:55:57.530" Score="8" ViewCount="254" Body="&lt;p&gt;I was studying ground wave propagation, my book writes the lines about it without explaining it. I really do not know any explanation for these queries coming in my mind. I've Googled it, and you will get nothing so good for these queries on Ground wave propagation.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;When the radio signal travels along the earth's surface, how it&#xA;induces current in it? (I read somewhere that the electric field&#xA;part of the wave will make electrons go out of association with the&#xA;nucleus, all this happening in earth, hence currents)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;How will the wave tilt towards the earth after the induction of&#xA;current in the earth?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The attenuation of the surface increases very rapidly with increase&#xA;in frequency of the signal. How?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Note: Answer only for the level of Class 12 students required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I seriously do not know anything about the last two questions. Any help would be praised for the one who will solve all these three questions.&lt;/p&gt;&#xA;" OwnerUserId="11144" LastEditorUserId="8717" LastEditDate="2018-02-06T17:34:27.863" LastActivityDate="2018-10-13T11:34:36.460" Title="Communications : Ground wave propagation" Tags="&lt;antenna&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9855" PostTypeId="1" AcceptedAnswerId="9858" CreationDate="2018-02-07T14:00:27.687" Score="4" ViewCount="442" Body="&lt;p&gt;I am currently thinking about joining the shortwave radio community, and know that if I was going to operate one in the U.S., I would need a license to operate in a certain range. But I am not living in the United States, I am living in the island nation of Haiti (located in the Caribbean, I hope this picture is not copyrighted):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zHhHA.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zHhHA.gif&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have tried to find any laws, but can't find anything on it. But all in all, I don't want the authorities showing up at my door, asking for a license.&lt;/p&gt;&#xA;" OwnerUserId="11146" LastEditorUserId="218" LastEditDate="2018-02-08T20:47:29.627" LastActivityDate="2021-05-02T04:04:01.640" Title="Do I need a license to operate as a ham in Haiti?" Tags="&lt;legal&gt;&lt;license&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9856" PostTypeId="2" ParentId="9854" CreationDate="2018-02-07T14:09:50.420" Score="9" Body="&lt;p&gt;So, I'll take this very smoothly. The idea is to take you from ray optics gradually to an understanding of radiomagnetic waves as actual waves, and show that it all makes sense.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;1&lt;sup&gt;st&lt;/sup&gt; idea: Refraction on a material interface (high-&gt;low density)&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;We remember what happens when we have ray of light, leaving a optically denser medium (e.g., water) into a less dense one (e.g. air):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8aXZI.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8aXZI.png&quot; alt=&quot;Refraction on water-air interface&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ray is &lt;em&gt;refracted&lt;/em&gt; away from the normal of the interface (image taken from &lt;a href=&quot;https://en.wikipedia.org/wiki/Refraction&quot; rel=&quot;noreferrer&quot;&gt;wikipedia's refraction article&lt;/a&gt; &amp;amp; cropped).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can actually calculate how $\theta_1$ and $\theta_2$ are related; it's &lt;em&gt;Snell's law&lt;/em&gt; that you might already know:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\frac{\sin(\theta_1)}{\sin(\theta_2)}= \frac{n_2}{n_1}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;with $n_i$  being the &lt;em&gt;refractive index&lt;/em&gt; of the medium (air or water).&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;2&lt;sup&gt;nd&lt;/sup&gt; idea: Water on a sphere&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Now, imagine you're standing on sphere (like, a planet). Your planet is completely covered in very very salty water, and above that, is air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're of the water-dwelling kind, and you hold an orange laser pointer nicely horizontally:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JGUsg.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JGUsg.png&quot; alt=&quot;Geometric drawing&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, in this drawing, you stand at point $B$, and hold your laser pointer straight vertically (that is, perpendicularly to the planet radius $\bar{BA}$. At point $C$, the ray hits the saltwater-air interface in the angle $\delta$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our job is now to find $\delta$, because we know the refractive indices of air and saltwater, and we can then calculate under which angle the ray will leave the saltwater¹.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We know that on the saltwater-air-interface, the ray will be refracted &lt;em&gt;away&lt;/em&gt; from the normal, that is, closer to the ocean surface. So, the ray will already have one &quot;bend&quot;, that looks like it &quot;hugs&quot; the ocean surface curvature a bit. &lt;/p&gt;&#xA;&#xA;&lt;h1&gt;3&lt;sup&gt;rd&lt;/sup&gt; idea: Water in layers.&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Now we realize that this ocean is pretty deep, and that the water isn't constantly salty – the deeper waters are way more salty than the waters close to the surface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's even think these different degrees of saltiness come in layers. Then, we can imagine there being a lot of interfaces like the water-air interface from the second idea :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since salty water is at the bottom and has a higher refractive index than less salty water, we get such a bend at every interface. The ray is getting bend more and more to &quot;hug&quot; the spheres, until, at the end, it practically &quot;rides&quot; on a circle-like shape that it really can't leave (because it's always refracted back a little bit more).&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;4&lt;sup&gt;th&lt;/sup&gt; idea: From rays to waves&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Now, the first big thing to simply swallow is: Laser light and, let's say, mediumwave radio broadcast, are really just the same thing: electromagnetic waves. There's zero difference between them, other than that an orange laser has maybe a wavelength of 600 nm, whereas your medium wave broadcast might have a wavelength of 600 m, that is, one billion of the wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, whereas the saltwater layers seem &quot;huge&quot; to a ray of light, which you might have already learned to model as &quot;plane wave front&quot;, these layers might be &quot;small&quot; compared to the wavelength of a medium wave transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, imagine that instead of a small, cute laser pointer, you used a giant lamp consisting of thousands of laser pointers, mounted atop of each other: A large &quot;tower&quot; that shines kind of a beam (consisting of many laser rays). Now, the lower laser pointers are in deeper, saltier waters, and get bent more within shorter distance than the upper ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's an old analogy that physics teachers often employ: imagine this group of rays being a marching band, nicely arranged to  all start marching at the exact same instant. While the upper-water band members move relatively straight and only rarely meet a water-water level interface, the band members close to the ground are often making a bend in their path. The overall front of the marching band seems to &quot;slouch&quot; around the curvature of the earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This analogy isn't as bad as it sounds at first: The refractive index $n$ is actually just a measure for how much slower than in vacuum the light is in that medium. So, the &quot;deepwater rays&quot; simply &lt;em&gt;are&lt;/em&gt; slower than the &quot;not as saltywater rays&quot;. That means that the whole wavefront (marching band front) does follow a curve.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;5&lt;sup&gt;th&lt;/sup&gt; idea: we don't have salty water, but earth will do.&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Obviously, you're not a water-dwelling alien controlling a giant marching band consisting of laser beams. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, you have an antenna. But that antenna very much sends out an electromagnetic wavefront. As electromagnetic waves permeate air, trees, hills, dry earth, not-so-dry-earth, small animals, large animals, buildings, tapestries and people, they are, just like the special case of visible light, slowed down in media. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of ground waves, the lower parts of the wave front permeates earth. Earth has a higher conductivity as air – and that means it slows down the electromagnetic wave. How that slowing down happens isn't actually very easy to explain - in the end, earth has physical properties that increase its $n$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹ I haven't had the time to properly test my calculations, but if they are correct, that angle is, if we set the earth radius to 1, $\delta=90° - 2\arcsin\left(\pm \sqrt{\frac l{2+2l}}\right)$, but that's actually not that important here. If you want to have some geometry in your presentation, deriving that angle from the ratio of earth radius (set arbitrarily to 1) and water height would definitely be a cool thing.&lt;br&gt;&#xA;For the things I want to explain, it's not important what this angle is, exactly.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-02-07T14:09:50.420" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9857" PostTypeId="1" CreationDate="2018-02-07T16:34:46.467" Score="5" ViewCount="189" Body="&lt;p&gt;I have been listening for signals (any) of the Space-X Falcon Heavy. Just out of curiosity. And I am wondering if anyone has received any.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to the &lt;a href=&quot;http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Falcon-9 User Guide&lt;/a&gt; table 4.6 looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aXCN7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aXCN7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although it mentions &quot;Falcon launch vehicles&quot; without further model specification, I am not 100% sure if the Falcon-Heavy frequencies are the same as the Falcon-9&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are my questions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Has anyone found a frequency table/chart for the Falcon-Heavy? or confirmation that the Falcon-9 frequencies are applicable for the Falcon-Heavy?&lt;/li&gt;&#xA;&lt;li&gt;Has anyone received a signal which potentially is from the Falcon-Heavy? If you have, please describe your setup.&lt;/li&gt;&#xA;&lt;li&gt;What software (other than GNU radio) is capable of decoding the telemetry with PCM/FM encoding/modulation?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Meanwhile I will continue my quest using various search engines, and offcourse listening in...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My setup for this cheap-ish attempt is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Airspy SDR&lt;/li&gt;&#xA;&lt;li&gt;&quot;Direct TV&quot; down converter for 2.4GHz &lt;/li&gt;&#xA;&lt;li&gt;Wifi yagi 13dBi (I had nothing else in the 2.2GHz range)&lt;/li&gt;&#xA;&lt;li&gt;&quot;tested&quot; with a signal generator (from friend), this setup can receive 2.2GHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="873" LastEditDate="2018-02-10T13:58:44.973" LastActivityDate="2018-02-10T13:58:44.973" Title="I would like to listen to a red roadster in space" Tags="&lt;satellites&gt;&lt;swl&gt;&lt;telemetry&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9858" PostTypeId="2" ParentId="9855" CreationDate="2018-02-07T16:40:03.037" Score="4" Body="&lt;p&gt;There is precious little information available online, but it seems highly probable that amateur radio is regulated in Haiti.  The regulator is called CONATEL and has a website (&lt;a href=&quot;http://www.conatel.gouv.ht&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.conatel.gouv.ht&lt;/a&gt;) but I was unable to find any information on its website about amateur radio (&quot;radio amateur&quot; in French).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are hams in Haiti with callsigns, though, which is strong evidence that there is some regulation.  Some websites allege that there may only be a few licensed hams in Haiti, perhaps in the single digits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would suggest contacting CONATEL and asking them.  Haiti could sure use some more radio amateurs, since it's so prone to natural disasters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:  Here is a blog post that has some postal contact information for an amateur radio club in Port-au-Prince:  &lt;a href=&quot;http://f4czv-richard.blogspot.ca/2017/12/haiti-le-radio-club-dhaiti-fetera-ses.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://f4czv-richard.blogspot.ca/2017/12/haiti-le-radio-club-dhaiti-fetera-ses.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9844" LastEditorUserId="9844" LastEditDate="2018-02-08T03:37:42.880" LastActivityDate="2018-02-08T03:37:42.880" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9859" PostTypeId="2" ParentId="9857" CreationDate="2018-02-07T18:55:55.263" Score="5" Body="&lt;p&gt;Good find of all the frequencies and powers, it sounds like you have all the right basic equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But sadly for the roadster, you're too late, it's out of range. The video link is designed for a few hundred km, and it's probably half a million km away already.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming the batteries on the spacecraft are still OK. It's transmitting 44 dBm.&#xA;The path loss at 2221 MHz, 500,000 km (at time of writing, 10 km/s for 14 hours) will be something like 210 dB.&#xA;A receiver with a 100 Kelvin system temperature and 3 MHz bandwidth has a background noise power of -114 dBm, and needs -100 dBm to achieve modest SNR.&#xA;So you need a 66 dBi antenna, which is 100 m diameter.&#xA;At 500 km the same equation yields 6 dBi, which you get from a little patch antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's nothing (technical) to stop you trying on the next launch.  Legal... it depends where you live.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2018-02-07T20:37:16.617" LastActivityDate="2018-02-07T20:37:16.617" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9860" PostTypeId="2" ParentId="9850" CreationDate="2018-02-08T05:52:18.260" Score="2" Body="&lt;p&gt;Where are you using the radio ? In the City... In the countryside ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The City will be much noiser (from an RF standpoint).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are heaving &quot;solid noise&quot; everywhere that you tune too - you may have some local RFI (Radio Frequency Interference) due to your computers, Tv, Strip Tube lights, A/C etc.... The easiest way to fund this out is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;a) Get your radio running on a car battery (12V)&#xA;   b) Turn all the electricity off in your house/flat !!!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If things improve drastically you are causing the issue. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If things stay the same ... it is something outside your house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the issue is outside your house - disconnect your very large antenna, and replace with a simple vertical - as in a piece of wire (obviously take care due to power lines etc) plugged into to your receive socket.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2018-02-08T05:52:18.260" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9861" PostTypeId="2" ParentId="9843" CreationDate="2018-02-08T13:54:27.317" Score="1" Body="&lt;p&gt;A differential-mode current on the shield is always found exclusively on the inside surface of the shield, even if there are holes. It's not due to the current being trapped inside, but rather that it wants to be that way due to eddy currents, the same mechanism behind skin effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine a primary current flowing through a solid, cylindrical conductor. Let's pretend it's a uniform current through the entire cylinder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fBh8T.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fBh8T.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The primary current (straight red line) has an associated magnetic field (green circle). The &lt;a href=&quot;https://physics.stackexchange.com/q/343192/24140&quot;&gt;right-hand rule&lt;/a&gt; determines the direction the magnetic field curls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because this is an AC current, that magnetic field is constantly changing. This in turn induces eddy currents (red circles) by &lt;a href=&quot;https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction&quot; rel=&quot;nofollow noreferrer&quot;&gt;Faraday's law of induction&lt;/a&gt;. The &lt;em&gt;left&lt;/em&gt;-hand rule determines &lt;a href=&quot;https://en.wikipedia.org/wiki/Lenz%27s_law&quot; rel=&quot;nofollow noreferrer&quot;&gt;which way they go&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can consider the net current we observe as the superposition of the primary and eddy currents. In the center of the conductor the eddy currents oppose and cancel the primary current, meaning very little net current in the center of the conductor. On the outside of the conductor the eddy and primary currents point in the same direction, so this is where most of the current is found.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Within the conductor, the eddy currents cancel the magnetic field. But the conductor is still surrounded by a magnetic field in space around it. And surrounding the space around the center conductor is the shield, which will intercept that magnetic field and thus have eddy currents induced within it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TGgIq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TGgIq.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because we're talking about a piece of coax with only differential-mode current, we know there's an equal but opposite current in the shield, going down. Look now at the orientation of the eddy currents and the effect they would have on a downward current in the shield: current on the inside of the shield is reinforced, whereas current on the outside of the shield is cancelled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why differential mode current is on the inside of the shield. It's not because it's &quot;trapped inside&quot; by skin effect. Rather, it doesn't want to get out. Eddy currents give rise to skin effect which describes a single conductor. When there are two conductors the interaction between them must be considered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The tendency for currents in two nearby conductors in opposite directions to have the highest current density in the regions nearest each other is called proximity effect. We see this not only in coax, but also in balanced transmission lines and transformer windings:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rJl65.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rJl65.png&quot; alt=&quot;cross section of a twin-lead transmission line&quot;&gt;&lt;/a&gt;&lt;br/&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the currents are in the same direction, the opposite occurs: the current density is highest in the regions furthest apart. This is why skin effect can't be circumvented simply by making a thicker wire from thinner, individually insulated strands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's because of issues like this I find the &quot;skin effect&quot; or &quot;three conductor&quot; explanation of coax unsatisfying. It leads to a mental model of demons trying to get out and wreak havoc, contained by a magic skin effect barrier. What if there are holes in the barrier, as in the braid? &lt;a href=&quot;https://ham.stackexchange.com/q/6983/218&quot;&gt;Do the ends need to be sealed?&lt;/a&gt;  Instead I find it more intuitive to think of the &lt;a href=&quot;https://ham.stackexchange.com/a/3509/218&quot;&gt;equal but opposite fields&lt;/a&gt; of the shield and center currents cancelling each other. This leads to a better intuition about what's required to prevent coax from radiating, and it works with balanced transmission lines also.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-02-08T14:17:18.457" LastActivityDate="2018-02-08T14:17:18.457" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9862" PostTypeId="2" ParentId="9505" CreationDate="2018-02-08T19:22:33.083" Score="1" Body="&lt;p&gt;There is nothing which fundamentally prevents any radio, software defined or otherwise, from changing bands dynamically. Next to me I have a Yaesu FT-897 which is quite old and not an SDR, but it can change bands in the time it takes to switch a relay, commanded to do so either by a button press or a command from the serial port on the back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact software has little to do with it: while the software defines the modulation, the transmit frequencies are limited by hardware, such as filters, oscillators, and amplifiers.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-08T19:22:33.083" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9863" PostTypeId="2" ParentId="9857" CreationDate="2018-02-09T17:08:36.177" Score="2" Body="&lt;p&gt;The batteries are now dead and there is no onboard power source, so we cannot listen to it. See the comments at &lt;a href=&quot;https://space.stackexchange.com/questions/25010/current-position-of-starman&quot;&gt;https://space.stackexchange.com/questions/25010/current-position-of-starman&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-02-09T17:08:36.177" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9864" PostTypeId="2" ParentId="9391" CreationDate="2018-02-10T13:14:14.167" Score="0" Body="&lt;p&gt;Keith,&#xA;       I am all planning my relocation back to the PI - we will be in Central Luzon, So I also have been thinking of which tower to build.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe that the best tower for the PI would be a crank up tower. For the following reasons&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;U-Beams are readily available&lt;/li&gt;&#xA;&lt;li&gt;Local workforce is good in steel work&lt;/li&gt;&#xA;&lt;li&gt;It would be relatively cheap.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;However it will require&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Solid foundation (rebar &amp;amp; concrete)&lt;/li&gt;&#xA;&lt;li&gt;A &quot;tilt-plate&quot; assuming you are going to fit a Yagi/Steppir etc&lt;/li&gt;&#xA;&lt;li&gt;A Maximum mast height of 12-15m &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I do not mind using a rotator - as the directivity (in my opinion) is a necessity (especially in contests). There are some OLX shops selling some ham gear, mainly based in Cebu rather than Manila it seems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would be most interested on hearing your thoughts/development on this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73s de Tim. A45WG&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2018-02-10T13:14:14.167" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9865" PostTypeId="1" AcceptedAnswerId="9872" CreationDate="2018-02-10T23:14:58.877" Score="1" ViewCount="266" Body="&lt;p&gt;On a repeater I frequently listen to there are a handful of expected automated messages. Namely, at the top of the hour it tells the time and the callsign, and every 10 minutes it sends out it's callsign in morse code. The voice for the top-of-the-hour call is typically an automated female voice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Recently, at seemingly random times a male automated voice comes in and says something along the lines of&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;O-N-I-X HOLT(?) ANALOG XX.XX - WELCOME TO THE (CALLSIGN) REPEATER&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I've been googling and I can't seem to find what this means. In particular the &lt;code&gt;XX.XX&lt;/code&gt; that is listed off changes each time. 2 minutes ago it was &lt;code&gt;13.8&lt;/code&gt;, a few hours ago it was &lt;code&gt;12.8&lt;/code&gt;. There were a few numbers last night too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm guessing this is just another part of the technology stack this particular ham's repeater is running. I'm intrigued by the numbers though and what this actually is. Is it sending a message about signal strength or something?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hopefully this isn't too obscure. Thank you!&lt;/p&gt;&#xA;" OwnerDisplayName="user11031" LastActivityDate="2018-12-28T22:43:41.703" Title="Trouble figuring out what is meant by this repeater callout?" Tags="&lt;repeater&gt;&lt;message&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9866" PostTypeId="2" ParentId="9865" CreationDate="2018-02-11T00:15:33.910" Score="5" Body="&lt;p&gt;13.8 and 12.8 are plausible as battery voltages. It is possible that this repeater is solar-powered; to test this theory, notice if the number varies consistently with the time of day (and weather).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do not know what “O-N-I-X HOLT(?)” might mean. “ANALOG” could mean that this is associated with (or is also) a digital-voice repeater in some way.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-02-11T00:15:33.910" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9867" PostTypeId="1" AcceptedAnswerId="9868" CreationDate="2018-02-11T12:25:05.493" Score="3" ViewCount="443" Body="&lt;h2&gt;Problem&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;I'm planning on mounting a vertical HF multiband antenna on the edge of my roof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the presence of a paved walkway and some other similar property constraints, I have no room for radials anywhere near the mounting area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I do have a saltwater canal behind my yard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ks8bI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ks8bI.png&quot; alt=&quot;Antenna/House/Canal Drawing&quot;&gt;&lt;/a&gt; This is a rough and not-to-scale rendering of the situation. The red tapered cylinder represents the vertical antenna. The green part is the yard. Then there is the seawall and the canal itself. The yellow cylinder would be a floating foil-lined tube to maximize surface area and maintain water surface contact as the tides rise and fall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The base of the antenna will be about 10ft above the surrounding grade and the canal is about 60ft away from the antenna mounting point.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Questions:&lt;/h2&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Can this idea work to provide a good ground for transmission?&lt;/li&gt;&#xA;&lt;li&gt;How should I connect the antenna to this somewhat distant ground?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;h2&gt;Thoughts:&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;If I were just to try this without seeking advice, I'd run coax with the center conductor attached to the antenna base ground out to the floating tube, probably in some PVC pipe to protect the cable itself from the soil. Is that a reasonable plan?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried modeling this in CocoaNEC, but the transmission line interface is broken and the project hasn't seen active development for a while.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've considered mounting the antenna on the sea wall itself, but the surrounding area makes that tricky.&lt;/p&gt;&#xA;" OwnerUserId="11166" LastEditorUserId="76" LastEditDate="2019-04-13T20:26:44.680" LastActivityDate="2019-04-13T20:26:44.680" Title="Not-too-distant saltwater ground" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;grounding&gt;&lt;earth&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9868" PostTypeId="2" ParentId="9867" CreationDate="2018-02-11T13:54:52.023" Score="7" Body="&lt;p&gt;With the canal 60 feet away it's not of much help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The objective with a monopole antenna is not just to have any ground connection, but to have a low-loss ground &lt;em&gt;plane&lt;/em&gt; under the base of the antenna. The ground plane provides the return current and creates an &lt;a href=&quot;https://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;noreferrer&quot;&gt;image antenna&lt;/a&gt;. The return current density is highest where it converges at the base of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a rule of thumb, a radius of a quarter-wavelength around the base is where the ground is most important. Small improvements can be realized by extending the ground out as far as two wavelengths. Beyond that, the ground is insignificant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The canal is so far away, and only on one side of the antenna, so it will have negligible effect on the antenna. The antenna's operation will be dominated by things closer to the base, like the feedline, or the wire you run from the antenna to the canal. You'll essentially have a vertical with one radial.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If at all possible, I'd suggest considering alternate antenna designs. Verticals can be made to work well with as few as two radials, but this involves tuning them to be resonant, and raising them several feet off the ground. This minimizes the current in the soil, thus minimizing losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without deliberately installing radials you will make some contacts, and if that's all you're able to install then by all means go for it. But it's far from ideal.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-11T13:54:52.023" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9869" PostTypeId="2" ParentId="7047" CreationDate="2018-02-11T18:07:16.980" Score="-2" Body="&lt;p&gt;You can break this into 2 parts....&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;GNU Radio for USB receive &#xA;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;Freq 14.225-14.230&lt;/li&gt;&#xA;&lt;/ol&gt;&lt;/li&gt;&#xA;&lt;li&gt;Output Sink as a WAV File&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Then With the Wave file - try and understand the Decoding Process. I would try with.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Matlab&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;When you have got this working then - maybe you can put this process into GNU Radio as a custom Python Module.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2018-02-11T18:07:16.980" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9870" PostTypeId="2" ParentId="6015" CreationDate="2018-02-11T18:10:38.390" Score="0" Body="&lt;p&gt;If you mean you are looking at something like Pactor 3 or 4 ... then good luck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did have a look at this a few years ago after buying a very expensive (but functional) Pactor 3 Modem....&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I apologize that this is not a more constructive comment. However such Digital transmissions are usually compressed (possibly using commercial&#xA;algorithms) and may additionally use proprietary codecs.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2018-02-11T18:10:38.390" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9871" PostTypeId="2" ParentId="9867" CreationDate="2018-02-12T04:58:45.160" Score="-2" Body="&lt;p&gt;After many years of quite different antennas, I tried the Cush-Craft R5 vertical, since it's designed to compensate for all the variables. My situation is on Mustang Island, on the Texas Gulf Coast, thus I'm quite well acquainted with salt water and salt air. Salt water grounds need attention regularly to check on efficiency, as well as salt air degradation of antennas. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gil Gibbs WA5YKK&lt;/p&gt;&#xA;" OwnerUserId="11173" LastActivityDate="2018-02-12T04:58:45.160" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9872" PostTypeId="2" ParentId="9865" CreationDate="2018-02-12T20:35:47.263" Score="4" Body="&lt;p&gt;I agree with Kevin Reid that this is probably a telemetry readout for a battery, but here's a little bit more guesswork:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Another repeater in the same linked repeater system is installed at Onyx Peak in California. Perhaps the readout is O-N-Y-X (probably the text-to-speech system doesn't have the word Onyx in its dictionary).&lt;/li&gt;&#xA;&lt;li&gt;It's not &quot;Holt&quot;, it's &quot;volts&quot;.&lt;/li&gt;&#xA;&lt;li&gt;My guess is that &quot;analog&quot; doesn't relate to the fact that it's an analog repeater, but instead is the readout for what type of telemetry it is -- probably the package has several digital inputs (which are either not used in this case, or only read out if they're in an unexpected state) and one or two ADCs for monitoring batteries or temperatures.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;In this scenario, &quot;Onyx volts&quot; is the name of the measurement, &quot;analog&quot; is the type, and 12.8 is the value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a more definitive answer, then you might consider contacting someone associated with the N6LXX repeater system and asking them.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2018-02-12T20:35:47.263" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9873" PostTypeId="1" CreationDate="2018-02-13T01:50:05.877" Score="2" ViewCount="173" Body="&lt;p&gt;If the &quot;floor&quot; of the graph in my SDR is at -110dB, and when I key up, it goes to -70dB, and the wattage is 5W....is there a direct correlation between dBs and wattage?&lt;/p&gt;&#xA;" OwnerUserId="11176" LastEditorUserId="8717" LastEditDate="2018-02-14T00:30:40.083" LastActivityDate="2018-02-14T09:37:14.530" Title="Measuring dBs with software defined radio" Tags="&lt;software-defined-radio&gt;&lt;measurement&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9874" PostTypeId="2" ParentId="9873" CreationDate="2018-02-13T03:21:00.253" Score="4" Body="&lt;p&gt;Decibels express ratios. SDRs are often not calibrated to any reference, so when it says &quot;-110 dB&quot;, that's relative to some arbitrary reference power. Often the reference is &quot;full scale&quot;, meaning the full range of the ADC. Still, that doesn't directly relate to power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the measurement goes from -110 dB to -70 dB, that's a difference of 40 dB. That's a ratio of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 10^{40/10} = 10000 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So whatever you were measuring, the power is now 10,000 times greater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a signal source of some known power, you can calibrate the SDR. Say you have a signal generator that you know outputs 1 mW, and the SDR reads this as -10 dB. Now adding 10 dB to any measurement from the SDR yields decibels relative to 1 mW, or dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind when measuring powers on a waterfall display the total power must be integrated over the bandwidth it occupies. For an unmodulated carrier with very narrow bandwidth this may not matter, but if the signal is modulated to have 4 kHz bandwidth, the transmitter power is now spread across multiple bins in the waterfall. The power represented in each bin must be summed to calculate the total transmitter power.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-13T03:21:00.253" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9875" PostTypeId="2" ParentId="9873" CreationDate="2018-02-13T10:42:43.920" Score="1" Body="&lt;p&gt;I use this as a very practical A/B comparison &quot;measurement&quot;. Not very scientific, but to give me an indication on antenna performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have two 2m dipoles, which I call my &quot;reference antennas&quot;. They are as identical as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I place them 2m appart, with an SDR on one end, and a HT 2m TX on the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will key up the HT, and I get a X dB rise in the spectrum. This is my reference 0 point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will then replace the TX antenna with another home brew antenna. Key up again, and this will result in Y dB rise in the spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Suppose that Y is better than X, then I can conclude that the Y antenna is Y-X dB better &lt;em&gt;in this particular setup&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This itself does not give me any dBi or dBd or any other scientific measurement other than one is better than the other.... I can use this to further improve the antenna's.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple, and very rough, &quot;comparison tool&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[EDIT based on comment]&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;So lets same my reference is 40 db....i test somewhere else and its&#xA;  45db....somewhere else is 5db better&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The trick to doing an A/B comparison is to only change 1 element of your reference setup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to answer your comment question: if you change location, then ensure that only the location changes, and the rest of the setup remains the same. The &quot;measurement&quot; is now a comparison in relation to the &quot;location change&quot;, not a change of equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example: If I am using my own reference antenna's which I normally place at a specific point in a field behind my property, about 20 meters away from any building, I will get a particular spectrum response. If I move this whole setup to another location, about 1 meter away from a big steel garage door, I get another measurement. Either better or worse, but the location and the surroundings have changed the properties of the setup and is influencing the &quot;measurement&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would be a test to see how the big steel garage door (and other environmental differences) is influencing the received RF in that particual setup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So yes; if by moving your test to &quot;somewhere else&quot; gets you a +5dB difference, then the new location is +5dB &quot;better&quot; on RX. You just need to figure out why that is. It might not be actually &quot;better&quot; at all, just an influence of environment. And the &quot;5 dB&quot; would be questionable as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would not use such a setup to test &quot;locations&quot; I would more be inclined to use it as comparison of equipment such as: transmitters, receivers, antenna's, coax... Furthermore I would use it as far away from property, buildings, trees and the like to minimize influence from that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As already given in a very good answer, there is a relation between dB's &quot;measured&quot; and &quot;Watts&quot;, but to actually derive one from another using a simple SDR would be very rough and open to influence of other environmental factors. Unless you have calibrated equipment, and a very (RF) clean room.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this answer I have used the word &quot;measured&quot; as quoted &lt;code&gt;&quot;measured&quot;&lt;/code&gt;, as I would not consider this a true scientific measurement. It really is a comparison using a particular type of equipment, which is far from calibrated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Who says that if the spectrum has a 40 dB response on your computer screen, that it is a real 40 dB... what is the influence of the LNA in the SDR ? Is the software the A/D converters, the LNA, the tuner, filters, all calibrated ? --&gt; no, they are not. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;My advice; don't try to use this [setup] to try to calculate &quot;Watts&quot; based on &quot;dB's&quot;.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2018-02-14T09:37:14.530" LastActivityDate="2018-02-14T09:37:14.530" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9876" PostTypeId="2" ParentId="9843" CreationDate="2018-02-14T12:36:18.873" Score="1" Body="&lt;p&gt;Is RF current always confined to the inner diameter of a braided outer conductor of coaxial cable?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quick answer: No.  And when it isn't, it's called common mode current.   Common mode current is typically induced by external fields between the coax shield and other objects (like the antenna), rather than the RF current injected into the end of the cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common mode current can be blocked by chokes/baluns, or discouraged by careful symmetrical arrangement of the coax and antenna.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-02-14T12:36:18.873" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9877" PostTypeId="2" ParentId="7847" CreationDate="2018-02-14T15:49:32.847" Score="-1" Body="&lt;p&gt;*&#xA;I'll agree with the idea of the homebrew vertical being a J-pole, with a nice SWR. Since it was in an attic, it might have been intended for local repeaters.&#xA; 1. emphasized text&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*&lt;/p&gt;&#xA;" OwnerUserId="11173" LastActivityDate="2018-02-14T15:49:32.847" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9878" PostTypeId="2" ParentId="9598" CreationDate="2018-02-14T18:08:45.717" Score="5" Body="&lt;p&gt;I've heard that is short for hee hee hee.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also heard it was a prosign meaning &quot;HUMOR INTENDED&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All of these are wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Actually, laughter in Morse code, if pronounced &quot;HO HO&quot;, like Santa's laugh. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It comes from the old American Morse code where the letter &quot;O&quot; was sent as a dit-short pause and another dit. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;SO, instead of sounding like HI or HEE, it should be sent like H E E.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should sound like di-di-di-dit  dit dit, or H E E.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look up the old American Morse code and the letters CORYZ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When radio came around and where most OPs started as landline telegraphers, they brought HO HO with them.&lt;/p&gt;&#xA;" OwnerUserId="11182" LastEditorUserId="218" LastEditDate="2018-02-17T19:13:11.077" LastActivityDate="2018-02-17T19:13:11.077" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9880" PostTypeId="1" CreationDate="2018-02-15T18:19:56.937" Score="1" ViewCount="652" Body="&lt;p&gt;I have been researching and trying to plan out how to run the grounding/cables for a new ham radio room that will be in a new cabin being built. Since I am starting with dirt, I should have flexibility (in theory). I will have 3 PL-259 cables run into my ham radio room from outside the cabin. I am planning on having two ground rods installed 8' beneath the cement foundation of the house, bonded together, with 4 AWG copper wire feeding from each ground rod through two flexible receptacles to two separate wall mounted ground plates. There are two plates to allow for two separate stations. (Grounding loop problems?) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Do I cause problems putting the grounding rods beneath the cement foundation of the cabin? The advantage is that I am not punching a hole through my wall which could lead to water issues down the road. As a note, the rods proximity to equipment will be about 7 ft.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Should I bond the two grounding rods to the cabin ground system as well?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Does it matter that I will need to have the antennas grounded separately from my radio? The antennas will be at least 50 feet from my radio.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;My AC/DC radio power supply connects to the AC ground. My radio's ground is connected to the power supply. Should I doubly ground the radio to the grounding plane and to the power supply? I guess technically I would be bonding to the power supply, but I am really trying to avoid RF issues.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Thanks for any help you can offer.&lt;/p&gt;&#xA;" OwnerUserId="11190" LastEditorUserId="9493" LastEditDate="2018-02-15T19:49:42.507" LastActivityDate="2018-02-18T17:35:39.487" Title="Grounding plan for new ham shack - good/bad idea?" Tags="&lt;grounding&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9882" PostTypeId="1" CreationDate="2018-02-15T21:33:50.087" Score="3" ViewCount="2953" Body="&lt;p&gt;My primary vehicle is a Smart car, with a roof that's a piece of plastic(100% moon roof). Not the most awesome of cars to use for grounds. I'm building a bumper mounted antenna tower, EMT with some square tube. Earlier today I stumbled across an article on 2 meter slot antennas cut in to satellite dishes. Literature is repetitive either directed towards that subject or TV and UHF broadcasting. I like the idea of a Dipole analogue that doesn't look like an antenna... Currently the 1/2 wave whip makes it look MORE like a cheap RC toy...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This isn't a basic theory question, more of a practical application...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the questions are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would a Slot antenna cut into a piece of 1.5 inch wide, 1/8 inch thick bar stock work? Minimal expense and I can get it almost anywhere. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would that be better than just cutting the slot into the bars? I can't find out if that's very directional, I assume I'd cut it in the top and use weep holes, cheapest option. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any better Ideas?&lt;/p&gt;&#xA;" OwnerUserId="10709" LastActivityDate="2020-08-20T16:37:28.040" Title="Slot antenna for 2 meter mobile" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;mobile&gt;&lt;2m-band&gt;" AnswerCount="5" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9883" PostTypeId="2" ParentId="9882" CreationDate="2018-02-16T00:27:58.673" Score="2" Body="&lt;p&gt;This was published in the March 2018 QST. Maybe this or a variant would work for you&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w6nbc.com/articles/2018-03QSTdesigncompetition.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w6nbc.com/articles/2018-03QSTdesigncompetition.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2018-02-16T00:27:58.673" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9884" PostTypeId="2" ParentId="9852" CreationDate="2018-02-16T01:11:13.487" Score="1" Body="&lt;p&gt;You're better off spending time routing power for the radio and future accessories. Spending time now adding in relays and fuse blocks will make adding things easier. Later on you might want to add in a second radio, 6m or HF. Go bigger on the wire, it's cheaper to plan ahead then redo it later. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd recommend running new wire from the battery instead of tapping off of the 6Ga wire. Blowing a fuse for your radio's isn't a big deal, losing half the car if the main blew isn't near as fun. Size your fuse's rationally. Keep it looking clean and you'll thank your self later. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore those signal wires have more issues with voltage drop, smaller wire has way more resistance. It's generally more advisable to extend power vs signals. &lt;/p&gt;&#xA;" OwnerUserId="10709" LastActivityDate="2018-02-16T01:11:13.487" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9885" PostTypeId="2" ParentId="9882" CreationDate="2018-02-16T12:57:08.120" Score="2" Body="&lt;p&gt;So you don't want a whip, as it makes the Smart Car look like a &quot;RC Toy&quot; (although some in the hobby, me at least, will disagree, afterall antennas on cars are fantastic)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And you don't want to hinder and doors/trunk/whatever opening, as you use the vehicle for certain purposes... (fair enough)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And you cannot use any mag-mount, as the vehicle is largely plastic, which also means you don't have a &quot;ground plane&quot; or whatever name you want to give it. (Technically the metal horizontal parts of a vehicle will act as a capacitor to earth when properly bonded. But some think the car itself is the ground plane)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are thinking of a &quot;slot antenna&quot; but just to realize that a &quot;slot&quot; in the &quot;slot antenna&quot; is the same size as a 1/2 wave dipole, the &quot;slot antenna&quot;, besides that it will be directional (not good for mobile use) will be quite large... which you do not want (the &quot;RC toy&quot; effect again)... as well as difficult to mount. If you have already a problem with 1/2 wave whip, then the slot will be even bigger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, it will be doubtful if you can actually use a slot antenna for VHF, as these are mostly designed for much higher frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't mind doing a bit of DIY: you can get antenna's for the 87-108 MHz which you can stick to a windscreen (front or back), example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4vu1b.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4vu1b.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will have take out any active/passive components, and tune it for 2m. But it will not obstruct doors, it will not have a visual impact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Efficiency and how this works is hard to say. I have not done this (yet).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer your specific questions:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Would a Slot antenna cut into a piece of 1.5 inch wide, 1/8 inch thick&#xA;  bar stock work? Minimal expense and I can get it almost anywhere.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That is not how a slot antenna works, please look up some designs online. Examples:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.eetrend.com/files-eetrend/antena-part8.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.eetrend.com/files-eetrend/antena-part8.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.qsl.net/n1bwt/ch7_part1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.qsl.net/n1bwt/ch7_part1.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;em&gt;there are many more&lt;/em&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You will quickly find that your approach is too simplistic to produce a working model.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Would that be better than just cutting the slot into the bars? I can't&#xA;  find out if that's very directional, I assume I'd cut it in the top&#xA;  and use weep holes, cheapest option.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As per previous answer, the design is much more complex. (and) Yes, a slot antenna is a directional antenna which is not suitable for mobile use.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2018-02-16T13:10:59.740" LastActivityDate="2018-02-16T13:10:59.740" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9887" PostTypeId="2" ParentId="9880" CreationDate="2018-02-16T16:58:55.280" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Do I cause problems putting the grounding rods beneath the cement foundation of the cabin? The advantage is that I am not punching a hole through my wall which could lead to water issues down the road.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;They might be difficult to inspect, but if the attachment to them is done with something that won't corrode or fall off, that shouldn't be an issue. So don't use a mechanical clamp, but instead braze or weld.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it seems like a silly thing to do. OK, maybe you've avoided a hole in the wall, but what are you doing to do about all the other holes for feedlines, electrical service, water and waste lines, natural gas, AC compressor, etc?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is a new building, I'd build an Ufer ground. Most likely there will be rebar in the foundation: just take some care to make it all electrically interconnected, and leave some exposed at a few points for attachment. In some jurisdictions building codes require an Ufer ground as it's a reasonable way to get a ground with sufficiently low impedance in dry climates where a ground rod would be insufficient.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Should I bond the two grounding rods to the cabin ground system as well?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Most building codes require it. Not connecting the grounds can encourage static discharges which provide an ignition source. If the static doesn't ignite something, then lightning will when it arcs across the HVAC ducting, electrical wiring, and water piping since it provides &lt;a href=&quot;https://www.w8ji.com/lightning_strikes.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;a lower impedance path between the grounds&lt;/a&gt; than the soil between them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the fire hazard doesn't scare you, consider where you'd prefer lightning current to go: through a copper wire buried in the ground, or through your station equipment?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does it matter that I will need to have the antennas grounded separately from my radio? The antennas will be at least 50 feet from my radio.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;From an antenna performance perspective, no. From a safety perspective, no, as long as the grounds are bonded together as required by building codes. For lightning protection, you must have a single point ground, though if the antennas are &lt;em&gt;also&lt;/em&gt; grounded in additional places on the unprotected side of the single-point ground (for example, at the tower base) that's fine, and often desirable to reduce the surge current. See &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My AC/DC radio power supply connects to the AC ground. My radio's ground is connected to the power supply. Should I doubly ground the radio to the grounding plane and to the power supply? I guess technically I would be bonding to the power supply, but I am really trying to avoid RF issues.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If your &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;feedlines are properly isolated from the antennas&lt;/a&gt; and free of common-mode currents, you don't need to worry much about your grounding situation (or lack thereof) causing RF issues. Best I can tell, the amateur radio grounding mythos is a holdover from the days when single-wire feeders were common. With a well designed antenna feed and proper application of baluns, grounding becomes irrelevant for RF performance since there's no RF current to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lightning protection is where it matters. Again see &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt; for more detail.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-02-18T17:35:39.487" LastActivityDate="2018-02-18T17:35:39.487" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9889" PostTypeId="2" ParentId="7536" CreationDate="2018-02-16T18:44:33.377" Score="0" Body="&lt;p&gt;If in the transmitter there is an impedance matching circuit and likewise a matching circuit external to the transmitter the reflected power from the load will see some kind of an impedance match not necessarily perfect such that some portion of the reflected power is consumed by the dynamic impedance of the output device such as the plate circuit of a vacuum tube or the collector of a transistor and the power going back to the antenna from the transmitter reflection will be reduced.  &lt;/p&gt;&#xA;" OwnerUserId="11196" LastActivityDate="2018-02-16T18:44:33.377" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9890" PostTypeId="1" CreationDate="2018-02-16T21:32:35.947" Score="1" ViewCount="64" Body="&lt;p&gt;I apologize in advance if this isn’t the right place to post this, but I though some of you might know the answer to my question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many people say that having your phone in your pocket (while not in flight mode) is a bad idea, due to the radio frequency that is being transmitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don’t disagree with RF transmissions being able to cause various types of cancer to various parts of the body, but what I don’t understand, is &lt;em&gt;how&lt;/em&gt; one’s phone can transmit RF signals while &lt;strong&gt;not in flight mode, but not in ringing/call mode either.&lt;/strong&gt; What does the phone transmit to the cell tower when it’s not receiving/is in a call?&lt;/p&gt;&#xA;" OwnerUserId="11197" LastEditorUserId="76" LastEditDate="2018-02-16T22:20:33.227" LastActivityDate="2018-02-16T22:33:17.993" Title="Do phones transmit RF when they’re not in a call?" Tags="&lt;transmission&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9891" PostTypeId="2" ParentId="9890" CreationDate="2018-02-16T22:20:09.770" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I apologize in advance if this isn’t the right place to post this, but I though some of you might know the answer to my question.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Welcome. This question is arguably off-topic because it is about the cell network which is &lt;strong&gt;not amateur&lt;/strong&gt; radio, but it can be answered on general principles of radio communications, so I'll do that.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;what I don’t understand, is how one’s phone can transmit RF signals while not in flight mode, but not in ringing/call mode either. What does the phone transmit to the cell tower when it’s not receiving/is in a call?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The cell network needs to know &lt;strong&gt;where the phone is&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Suppose that there were no such transmissions and you hadn't used your phone for a few days. Then when someone called you, &lt;em&gt;every cell tower in your provider's coverage area&lt;/em&gt; would have to transmit that message and listen for your phone's response, because you could be anywhere as far as the network knows. This is a scaling problem: every call started would be occupying some of the network capacity &lt;strong&gt;everywhere.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, your phone regularly transmits short messages, and whichever cell towers receive that message well are the ones that will transmit when an incoming call or other data needs to get to your phone. The same thing happens continuously while you are in a call to ensure that audio always gets through even if you move (unless you move to an area not covered by &lt;strong&gt;any&lt;/strong&gt; cell).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Another factor is of course that phones today have many “apps” and other features which are not just making calls but transferring data for other reasons — these are other reasons to transmit that are not making a call. But those are really just the same as calling from a high-level perspective of how the network and protocol works.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-02-16T22:33:17.993" LastActivityDate="2018-02-16T22:33:17.993" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9892" PostTypeId="1" AcceptedAnswerId="9901" CreationDate="2018-02-17T09:05:15.660" Score="0" ViewCount="111" Body="&lt;p&gt;I would like to know if it's ok to transmit amateur radio frequencies via my HT through a Bearcat police scanner to someone that has an FRS radio, and in turn they respond on their FRS radio which my HT can receive via dual band receive. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I, being a licensed a ham operator, can transmit on an amateur frequency which goes through the scanner to my friend, who hears it like a relay then transmits back to me on FRS frequency. We both use separate frequencies that only get connected through the scanner.  Is that illegal?&lt;/p&gt;&#xA;" OwnerUserId="11198" LastEditorUserId="218" LastEditDate="2018-02-24T03:27:25.840" LastActivityDate="2018-02-24T03:27:25.840" Title="Legality of relay through a scanner in the US" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9893" PostTypeId="1" CreationDate="2018-02-17T16:33:34.563" Score="5" ViewCount="2327" Body="&lt;p&gt;I'm installing an antenna which will require a matching network. (A fixed network: the load will not change.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm also building some low-pass filters to reduce transmitted harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be a simple exercise to design an ordinary 50Ω filter through normalized tables (which assume equal input and output impedances), and follow that with a matching network. Maybe a pair of inductors or capacitors can be combined, but not much is saved. Furthermore the characteristic of the filter is perturbed, as the reactance of the matching network will change over frequency in a way which was not considered in the filter design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I wonder: is there a more intelligent way to design a filter for unequal input and output impedances? Perhaps a way which involves fewer components, or affords additional design flexibility, for example to steer component values to standard values, or minimize loss? How?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-02-19T02:10:25.547" LastActivityDate="2018-02-19T02:10:25.547" Title="How can the design of an RF filter also encompass impedance matching?" Tags="&lt;equipment-design&gt;&lt;filter&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9894" PostTypeId="2" ParentId="9893" CreationDate="2018-02-17T17:49:46.850" Score="1" Body="&lt;p&gt;So, to answer your: &quot;Is it possible?&quot; question: yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, and in fact, it's more inevitable than possible!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you know, one of the major challenges in RF design is that not only do you need to match components and transmission lines at a single frequency (or wavelength, depending on how you look at it), but usually across a whole bandwidth! Generally, the larger that bandwidth becomes, the harder it is to sustain a good match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, what happens outside that bandwidth where you've successfully matched? Right, signal energy gets reflected at the impedance discontinuity, and hence, doesn't &quot;move forward&quot; through the signal chain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's &lt;em&gt;exactly&lt;/em&gt; what a filter is!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, any passive filter can be understood as frequency-selective matching network. Consider the simple RC low-pass: at low frequencies, its complex impedance is very much dominated by the real-valued resistance, but as soon as you get close to the  the cutoff frequency, you see the phase of transmission increase – which reflects the fact that the imaginary part of the impedance now reaches the magnitude of the real part. From the (hopefully) purely real-valued wave impedance of the transmission line, you now see a complex impedance, not even with the same absolute value. You get reflections (which basically means you get higher SWR).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what one can do here: Read about the problems of making high-bandwidth matching circuits, and just do &lt;em&gt;the opposite&lt;/em&gt; to get a filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or really, just design a filter whose impedance at passband works to match in- to output :) The RC example actually works pretty nicely here: you actually have two degrees of freedom when designing an RC filter, one is the resistance, and the second the capacitance; as the we assume that $f_c = \frac1{2\pi RC}$ is fixed, you'll find that actually, you can't just pick any capacitance – the ratio of $R$ to $C$ is fixed by that requirement!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, pick your $R$ so that at the frequencies you want to pass, your complex impedance is usable as matcher.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-02-17T17:49:46.850" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9895" PostTypeId="1" AcceptedAnswerId="9902" CreationDate="2018-02-17T18:31:21.037" Score="0" ViewCount="95" Body="&lt;p&gt;I'm reading through a &lt;a href=&quot;http://www.ivarc.org.uk/uploads/1/2/3/8/12380834/5._bartletts.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;tutorial on filter design and Bartlett's bisection theorem&lt;/a&gt;. It gives an example of a filter with 2.909k terminations:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GJRam.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GJRam.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, the right side of the filter is scaled by a factor of 2.2:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PWA8p.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PWA8p.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I understand the significance of R2: this may represent the antenna impedance for example. The calculated filter response is only valid for the given load impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what of R1? I've not seen filters with actual resistors in them: this seems like a waste of perfectly good transmitter power. And I may not know the output impedance of the transmitter either, though I do know it's important that looking into the filter, the transmitter sees 50 ohms. It's unclear to me how this requirement is satisfied when performing the filter design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And for that matter, is characterizing the load impedance as a resistor really accurate? For example, a half-wave dipole may have a known resistive impedance at resonance, but if the filter is intended to suppress spurious emissions then it must work at other frequencies where the dipole will present a potentially very different impedance. What can be said about the performance of the filter under these conditions? Will it still effectively suppress harmonics?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-23T21:44:59.330" Title="What's the practical significance of the source impedance in an RF filter?" Tags="&lt;theory&gt;&lt;filter&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9896" PostTypeId="2" ParentId="9895" CreationDate="2018-02-17T18:46:39.670" Score="0" Body="&lt;p&gt;This seems slightly implausible due to the particularly high value of 2.909 kΩ, but taking the circuit diagram literally, I would expect V1 to be an ideal voltage source and R1 to be the modeled source impedance, not part of the filter.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-02-17T18:46:39.670" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9897" PostTypeId="1" AcceptedAnswerId="9919" CreationDate="2018-02-17T21:55:32.230" Score="1" ViewCount="2718" Body="&lt;p&gt;I got myself a TV &quot;Rabbit Ears&quot; module originally for a TV. It came with a small length of coax, permanently attached to the antenna foot, and a Belling-Lee connector on the other end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My idea was to use an RG-58 coax with an SMA plug with this antenna, because it is easy to make a handle for it, and it's easy to store.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inside the mounting point for the two telescopic antennas, there is a ferrite core, with a couple loops around it, going off to the two telescopic antennas:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/esgAY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/esgAY.png&quot; alt=&quot;Balun schematic&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the schematic, (a) is four turns, (c) and (d) are two turns, each. As I said it's a dual-ferrite core, so two holes in one block of ferrite &lt;em&gt;(ignore the center tap on the (a) side, I couldn't find a transformer symbol with one inductor on one side, and two disjunct inductors on the other, with a core)&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also made a couple of pictures:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eAIaZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eAIaZ.jpg&quot; alt=&quot;Balun&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They &lt;em&gt;are&lt;/em&gt; rather shoddily soldered together, and while handling the center core wire broke off from the solder point:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZBkQM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZBkQM.jpg&quot; alt=&quot;Balun, other side (ignore the broken connection between core and balun)&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see in the pictures above, then it's one ferrite block with two holes in it. A wire running from core to shield of the coax goes through both holes, looping four times. Then, each from the core and the shield a wire loops through either hole, twice and then connects to either of the two telescopic antennas, which I have removed, so handling is a bit easier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since this is a TV UHF antenna, this has to be 75 Ω, but I'm wondering how I should now modify the balun, such that the impedance is 50&amp;nbsp;Ω.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My first approach was to remove the balun altogether, and directly solder a length of 50&amp;nbsp;Ω RG-58 to either of the antenna solder points and that'll be it. But I'm not entirely sure that would be a good approach, since I believe the balun is here for a reason...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of coming up with just a number of turns, it would be nice, if someone could provide a formula how to calculate these, or a place where I can find further information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE:&lt;/strong&gt;&#xA;I think I've found the device that was wired up in my antenna in blog post &lt;em&gt;&lt;a href=&quot;https://onetransistor.blogspot.de/2015/10/wideband-antenna-matching-transformer.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Make a wideband antenna matching transformer&lt;/a&gt;&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, it's a 4:1 balun, with 75 Ω on the coax-side. This means the antenna has an impedance of 300&amp;nbsp;Ω. 300&amp;nbsp;Ω for a dipole? It sounds strange to me, but I don't know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming this &lt;em&gt;is&lt;/em&gt; a 300 Ω antenna, I'd need a 6:1 transformer / balun to match it up with 50&amp;nbsp;Ω. The closest I can practically wire up is a 2 and 5 turns transformer, resulting in a 6.25:1 transformer. I'm not sure that would be even usable. The closest match without going into crazy figures is 49 and 20 turns, resulting in 6.0025:1, which I think would be close enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think I have a way of finding out the exact impedance of my rabbit ears antenna, so I guess I just have to assume it's 300Ω going by the fact how the balun / transformer was wired up, etc.&lt;/p&gt;&#xA;" OwnerUserId="11070" LastEditorUserId="366" LastEditDate="2018-04-23T16:15:13.690" LastActivityDate="2018-04-23T16:15:13.690" Title="Turn 75 Ω TV &quot;Rabbit Ears&quot; with a balun into a 50 Ω dipole antenna" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;dipole&gt;&lt;balun&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9898" PostTypeId="2" ParentId="9897" CreationDate="2018-02-17T22:51:52.720" Score="1" Body="&lt;p&gt;The impedance ratio is the square of the turns ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That multi-aperture core is known as a binocular core. There's some info about it &lt;a href=&quot;http://www.w0btu.com/Beverage_antennas.html#Beverage_Antenna_Transformers&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-02-17T22:51:52.720" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9899" PostTypeId="1" CreationDate="2018-02-18T02:35:40.937" Score="0" ViewCount="144" Body="&lt;p&gt;One of my neighbors is an emergency personal and has a police radio at home so he knows when to respond. Anyways, the other day, I saw an article on MAKE on how to make a radio station with a Raspberry PI. This uses GPIO pin 4 to generate a FM frequency and broadcast. I was wondering how legal this is and if it would interfere with my neighbors emergency radio. Thanks for any help&lt;/p&gt;&#xA;" OwnerUserId="11206" LastActivityDate="2018-02-18T15:09:06.763" Title="Can a Harmonics from an Raspberry PI FM Transmitter Interfere with Emergency Bands?" Tags="&lt;fm&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9900" PostTypeId="2" ParentId="9893" CreationDate="2018-02-18T06:32:07.087" Score="0" Body="&lt;p&gt;It is quite possible to combine filtering and impedance matching. In fact, this essentially a design requirement for any type of filter where the input and output impedances are not equal. Practicality and balance enter into the equation, however, when it comes to complexity, efficiency, practical circuit values, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the amateur radio world we see this balance play out. Our transmitter contains the necessary harmonic filtering to meet industry practices/expectations. The filtering effectiveness is only for a specified load (typically 50 ohms resistive). If our antenna is not a 50 ohm resistive load, we might use an antenna tuner to convert the antenna impedance (or more precisely to convert the impedance of the  feed line at the transmitter end) to 50 ohms. We do this to maximize radiated power without any consideration of filtering effectiveness.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna tuner is typically an L network consisting of a capacitor and inductor that the operator adjusts until the desired match is made. It is interesting to note that the adjustments made by the operator also affect the high or low pass characteristics of the LC filter that the tuner forms but the operator doesn't care because the necessary filtering has been dealt with in the transmitter. The operator is only concerned with its impedance matching function.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the design engineer of the transmitter and the tuner, I could reason that I will save costs and component count by combining the LC values in the tuner with the LC values in my output filter of the transmitter. But the challenge is now that as the operator adjusts component values to match the load, he or she is also adjusting the harmonic suppression characteristics of the transmitter. I must therefore provide additional indicators or methods to the operator  to ensure the effectiveness of the filter for any particular load setting. So the design complexity has actually increased and the operator has a presumably more difficult procedure that must be followed compared to isolated filter and impedance matching circuits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We even see this balance issue in modern transmitters that contain an internal, automatic antenna tuner - all under a common control circuit. Typically there are still separate harmonic filters for each band in addition to the LC antenna tuner function. The seemingly obvious approach of combining these circuit values and functions does not always lower the cost or complexity of the design.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-02-18T06:32:07.087" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9901" PostTypeId="2" ParentId="9892" CreationDate="2018-02-18T07:42:22.077" Score="7" Body="&lt;p&gt;In the US, at least, you'd fall afoul of the rules in a few places in 97.113, &quot;Prohibited transmissions.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;97.113(a)(5)(b) says &quot;An amateur station shall not engage in any form of broadcasting, nor may an amateur station transmit one-way communications except as specifically provided in these rules...except that communications directly related to the immediate safety of human life or the protection of property may be provided by amateur stations to broadcasters for dissemination to the public where no other means of communication is reasonably available before or at the time of the event.&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there's 97.113(a)(5) &quot;No amateur station shall transmit: Communications, on a regular basis, which could reasonably be furnished alternatively through other radio services.&quot; It would certainly not be hard to argue that GMRS or MURS might better suit your communications needs.&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2018-02-18T07:42:22.077" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9902" PostTypeId="2" ParentId="9895" CreationDate="2018-02-18T08:08:48.883" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;And I may not know the output impedance of the transmitter either, though I do know it's important that looking into the filter, the transmitter sees 50 ohms. It's unclear to me how this requirement is satisfied when performing the filter design.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The input impedance of the filter is typically specified so as to match the output impedance of the signal source. This allows maximum power transfer from the source generator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The input impedance of the filter circuit can be validated by doing series/parallel circuit analysis starting from the load resistor and working backward toward the source. The voltage of the source should be shorted out for this analysis leaving the source resistance as the last circuit element to be factored into the series/parallel analysis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As mentioned by Kevin Ried AG6YO, R1 and V1 in your schematic represent the signal source with R1 as the output impedance of the source. R1 does not waste output power of the signal source, but only represents the source impedance. In amateur radio, the transmitter output power is specified into a specific load impedance, typically 50 ohms. This is not necessarily the output impedance of the transmitter as the transmitter's output impedance is time variant. But it is the impedance at which the amplifier will develop its specified output so this is an acceptable proxy for output impedance of the signal source and the desired input impedance of the filter in this case.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And for that matter, is characterizing the load impedance as a resistor really accurate? For example, a half-wave dipole may have a known resistive impedance at resonance, but if the filter is intended to suppress spurious emissions then it must work at other frequencies where the dipole will present a potentially very different impedance. What can be said about the performance of the filter under these conditions? Will it still effectively suppress harmonics?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You are correct to question the validity of the filter characteristics when connected to a load impedance that varies with frequency, such as a typical antenna where reactance is added in series with the feedpoint resistance as the frequency moves away from resonance. The frequency response of the filter must be analyzed at each frequency in question with the appropriate complex load at that frequency. This will typically result in a different characteristic curve than found with a simple resistive load. The affect of this change can generally be minimized adding an additional filter pole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A load that changes its complex impedance with frequency also presents the conundrum that the signal source (a transmitter, for example), does not see the desired impedance looking into the filter. That is to say that the input impedance of the filter is dependent on the impedance at the output of the filter. So the changing impedance of the antenna with a change in frequency changes the load impedance of the filter which changes the input impedance of the filter which is the load the transmitter sees. This results in a reduction in power of the transmitter which is typically accompanied by a change in harmonic content. So to avoid this multi-variable situation in lab tests or simulation, it is best to analyze each in isolation and mathematically combine the results.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-02-23T21:44:59.330" LastActivityDate="2018-02-23T21:44:59.330" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9903" PostTypeId="2" ParentId="9899" CreationDate="2018-02-18T15:09:06.763" Score="2" Body="&lt;p&gt;So, this is a rather well-researched thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The theory behind using a raspberry pi to transmit FM is the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many microcontrollers, and that in this case includes the Pi's processor, have the ability to generate what we call &lt;em&gt;PWM&lt;/em&gt; signals, &lt;em&gt;Pulse Width Modulation&lt;/em&gt;. I'll scratch an example from this class of signals to give you a feeling:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think of signal that is either high or low, and has a fixed period. Within that period, the first part is high, the second part low. The percentage of high is what we call &quot;duty cycle&quot;, and if you smooth that signal enough, varying that percentage would allow you to generate an adjustable voltage; that's what PWM is most often used for&lt;sup&gt;[citation needed]&lt;/sup&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, as said, the Pi has such a PWM unit, and that works simply the following way:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You have a counter that you load with an initial value &lt;code&gt;start&lt;/code&gt;. Then it simply counts down by one every clock cycle of your CPU, until it reaches &lt;code&gt;0&lt;/code&gt;, and then resets to &lt;code&gt;start&lt;/code&gt; – without you (as a programmer) having to do anything about it. It's just a hardware counter. &lt;br&gt;&#xA;Now, the interesting aspect about that counter is that it is combined with a thresholder: As long as the counter value is over &lt;code&gt;threshold&lt;/code&gt;, the hardware sets an output pin high, afterwards low.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt; start=5    \     \     \     \     &#xA;             \     \     \     \    &#xA;              \     \     \     \   …………&#xA; threshold_____\_____\_____\_____\__&#xA;                \     \     \     \ &#xA;          0      \     \     \     \&#xA;&#xA;clock cycle 1234567890123456789&#xA;&#xA;output      HHHHLLHHHHLLHHHHLL…&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;That way, by setting &lt;code&gt;start&lt;/code&gt; with your software, you can set the period of your PWM ($\frac{\text{start}}{f_\text{CPU}}$) and by setting &lt;code&gt;threshold&lt;/code&gt; the percentage of time it's on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, assume that &lt;code&gt;threshold&lt;/code&gt; is always programmed to be half &lt;code&gt;start&lt;/code&gt;. That way, you always get a 50% duty cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you draw that, you'll notice it looks like &lt;a href=&quot;https://commons.wikimedia.org/wiki/Category:Square_waves#/media/File:Wave_square_labels.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;¹:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Wave_square_labels.svg/1000px-Wave_square_labels.svg.png&quot; alt=&quot;Square wave&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;a href=&quot;https://en.wikipedia.org/wiki/Square_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;square wave&lt;/a&gt;, with its period being adjustable by changing &lt;code&gt;start&lt;/code&gt;! That's exactly what happens on the Pi for FM: by changing start the frequency of a square wave is modified.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, we're talking about keeping the spectrum clean. Luckily for us, the spectrum of a square wave is known; remember (or hear for the first time) that the spectrum of anything that is truly periodic consists only of a sum of complex weighted sines and cosines; we call that the &lt;em&gt;Fourier Series&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of the (odd symmetric) square wave, that series reduces to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\begin{align}&#xA;x(t) &amp;amp;= \frac{4}{\pi} \sum_{k=1}^\infty \frac{\sin\left(2\pi(2k - 1)ft\right)}{2k - 1} \\ &#xA; &amp;amp;= \frac{4}{\pi} \left(\sin(2\pi ft) + \frac{1}{3} \sin(6\pi ft) + \frac{1}{5} \sin(10\pi ft) + \cdots\right)\text,&#xA;\end{align}&#xA;with $f=\frac1T= \frac1{\frac{\text{start}}{f_\text{CPU}}}=\frac{f_\text{CPU}}{\text{start}}$ being the fundamental frequency of your square wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what's interesting here is &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the frequencies of those sine components and&lt;/li&gt;&#xA;&lt;li&gt;their amplitude, as the square of these are the &lt;em&gt;power&lt;/em&gt; that's on that frequency.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Let's start with the frequencies: you can read those from the argument of the $\sin()$: You get $1\times$, $3\times$, $5\times$, … every odd number the fundamental frequency (the sine makes a full period in $2\pi$, divide its argument by that).&lt;br&gt;&#xA;That is used by the intentional FM transmission: That way, your PWM doesn't have to have a frequency of let's say 100 MHz itself; it's enough if it runs at $\frac13$ of that, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you're right, the other harmonics are all going to be there, too! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But notice how they're all space $2f$ apart? That means if our PWM frequency is 33.33 MHz (to produce 100 MHz using the harmonic at $3f$), then the first unintentional sine tone is at 166.67 MHz. That's pretty far away, and one can relatively easily suppress that with a simple LC filter, or simply by using an appropriately narrowband antenna!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What also helps is that this 166.67 MHz tone has only $\frac15$ of the amplitude of the square wave; power goes with amplitude squared, so that's only $\frac1{25}=4%$ of the square wave's power. For higher harmonics, the attenuation is stronger!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let's assume there's actually police radio around 166.67 MHz (I don't think so, but it's the worst case scenario): 4% of &lt;em&gt;what&lt;/em&gt; power?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's pretty hard to say without extensive measurements and hand-matching the antenna to your Pi's output impedance, but let's say the Pi actually is able to deliver full power during the High State, and exactly zero in the Low state, and would actually produce a perfect square wave. In that case, average power is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\frac 12\cdot I_\text{out,max}\cdot V_\text{high} = \frac 12 \cdot 16\,\text{mA}\cdot 3.3\,\text{V} = 26.4\,\text{mW}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll see less than 10% of that in real life, because matching is hard and no way in this world can the Pi ramp up the current to full 16 mA in that time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, that would imply about 0.1 mW at 166.67 MHz. Luckily, an electrically short antenna with a bit of curl and capacitive ballast (which I'd guess is what most people would use for this&lt;sup&gt;[citation needed]&lt;/sup&gt;) would not have that amount of bandwidth, and dampen that by another 5 dB or so; that would drop that power to -15 dBm. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;¹ figure by MrLejinad on Wikimedia Commons&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-02-18T15:09:06.763" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9904" PostTypeId="1" CreationDate="2018-02-19T01:49:01.083" Score="5" ViewCount="448" Body="&lt;p&gt;&lt;a href=&quot;http://www.ivarc.org.uk/uploads/1/2/3/8/12380834/3._nortonstheorem.pdf&quot; rel=&quot;noreferrer&quot;&gt;This article from Itchen Valley Amateur Radio Club&lt;/a&gt; describes an interesting technique called &quot;Norton's transform&quot;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6HbuS.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6HbuS.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This results in a negative capacitor, but in a circuit where there are other parallel capacitors which can be combined, the result can be positive and thus realizable. My particular interest is in filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately I can't find any other information on &quot;Norton's transform&quot;. Of course there's &lt;a href=&quot;https://en.wikipedia.org/wiki/Norton%27s_theorem&quot; rel=&quot;noreferrer&quot;&gt;Norton's theorem&lt;/a&gt; of which I have a simple understanding, and while I wouldn't be surprised if the two are related, it's not immediately obvious to me how.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a simple explanation of how this works? And can it be generalized to provide a similar impedance transformation in other circumstances, such as with inductors, or shunt components?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="76" LastEditDate="2018-02-19T02:46:50.923" LastActivityDate="2018-08-02T15:17:24.497" Title="What is Norton's transform?" Tags="&lt;electronics&gt;&lt;theory&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9905" PostTypeId="1" CreationDate="2018-02-19T02:59:47.470" Score="0" ViewCount="2694" Body="&lt;p&gt;My brother just bought me and himself a set of bf-f8hp radios for setting up two way communication while we are on long motorcycle trips. Now, this radio seems like overkill and I don't want to meet with anything illegal. How can I set this up?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondary question, what other cool stuff can I do with it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Completely oblivious when it comes to this stuff, but I'm eager to learn.&lt;/p&gt;&#xA;" OwnerUserId="11212" LastEditorUserId="8717" LastEditDate="2018-02-19T14:10:01.417" LastActivityDate="2018-02-23T18:51:37.170" Title="Bf-f8hp radios and no idea what I'm doing" Tags="&lt;legal&gt;&lt;ht&gt;&lt;baofeng&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9906" PostTypeId="2" ParentId="9905" CreationDate="2018-02-19T04:37:41.277" Score="4" Body="&lt;p&gt;From what I can tell, the BF-F8HP is very similar to the UV-5R. These links may help answer your question.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/7100/licensing-a-group-of-baofeng-bf-888s&quot;&gt;licensing a group of BaoFeng BF-888S&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/3679/can-a-baofeng-uv-5r-be-used-on-frs-gmrs-and-murs&quot;&gt;Can a Baofeng UV-5R+ be used on FRS, GMRS, and MURS?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/6382/on-which-of-these-frequencies-can-i-transmit-without-a-license&quot;&gt;On which of these frequencies can I transmit without a license?&lt;/a&gt;    &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/623/using-my-baofeng-uv-5r-to-talk-to-walkie-talkies&quot;&gt;Using my Baofeng UV-5R to talk to walkie talkies&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-02-19T04:37:41.277" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9907" PostTypeId="1" CreationDate="2018-02-19T06:17:40.527" Score="4" ViewCount="498" Body="&lt;p&gt;For a normal 5 watt handy working in VHF or UHF freq with 50 ohm antenna  , is it possible to use a same length coax cable instead of a stub antenna, so as to work like a crude antenna. Will this only result in extra capacitance/ VSWR damaging the system ?  &lt;/p&gt;&#xA;" OwnerUserId="11174" LastActivityDate="2018-05-26T13:04:58.360" Title="Coax cable as antenna for 5 watt handy" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;&lt;impedance-matching&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9908" PostTypeId="2" ParentId="9907" CreationDate="2018-02-19T13:52:40.527" Score="7" Body="&lt;p&gt;The electrically shortened antennas often found on HTs are not simple pieces of wire, but coils:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Uhf_cb_wit_rubber_ducky_exposed.jpg#/media/File:Uhf_cb_wit_rubber_ducky_exposed.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/b1blz.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;em&gt;By Shootthedevgru at English Wikipedia, &lt;a href=&quot;https://creativecommons.org/licenses/by-sa/3.0&quot; rel=&quot;noreferrer&quot; title=&quot;Creative Commons Attribution-Share Alike 3.0&quot;&gt;CC BY-SA 3.0&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coil adds inductance over the length of the antenna, making it appear electrically longer than it is physically. Without the inductance, the antenna would need to be approximately a quarter-wavelength long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A length of coax of the same physical length would not have this inductance, so would not be a good replacement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides the issue of length, using a length of coax, with the coax connector attached the usual way, screwed into the antenna connector on the HT isn't an antenna at all since the shield would surround the center conductor which would otherwise be the antenna. It's just a feedline, with no antenna on the end.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-19T13:52:40.527" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9909" PostTypeId="2" ParentId="9907" CreationDate="2018-02-19T17:35:20.877" Score="1" Body="&lt;p&gt;You can remove the shielding of the coax leaving only the center conductor, but as mentioned in the comments the length will be off since this is way less then 1/4 wavelength and there is nothing added to increase the inductance.  if the coax is 1/4 wavelength then it will work great.  &lt;/p&gt;&#xA;" OwnerUserId="11122" LastActivityDate="2018-02-19T17:35:20.877" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9910" PostTypeId="2" ParentId="1399" CreationDate="2018-02-19T22:09:26.683" Score="4" Body="&lt;p&gt;(I'm a retired USN Electronics Tech.) This is what they taught us about why the Navy chooses silver over other options.&lt;/p&gt;&#xA;&lt;p&gt;The oxides (aka tarnish) that forms on silver in air is nearly as conductive as the unoxidized silver. That is not the case with gold, nickel, tin, and so on. Thus when silver in a connection oxidizes you lose little conductivity and there is little increased resistance. That makes it ideal for corrosion friendly environments such as high humidity and/or salty sea air.&lt;/p&gt;&#xA;" OwnerUserId="11215" LastEditorUserId="8573" LastEditDate="2020-08-16T14:59:35.630" LastActivityDate="2020-08-16T14:59:35.630" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="9911" PostTypeId="1" CreationDate="2018-02-20T00:35:57.073" Score="3" ViewCount="533" Body="&lt;p&gt;I just started using a couple of low power radio modules in my project (&lt;a href=&quot;http://www.hoperf.com/rf_transceiver/modules/RFM69HCW.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;HopeRF RFM69HCW&lt;/a&gt;).&#xA;I made them work; they successfully transmit messages in a limited range (5-10 meters). Now I would like to improve that range (with a minimal message loss).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My problem is choosing the Bit rate, the frequency deviation, and the Rx Bandwidth for the channel filter (the settings I'm currently using are quite random: Br=19600, Fdev=2*Br, RxBw=Br). So I went on the web looking for a good-looking function describing the relationship between these three parameters and the transmission range, looking forward to writing a function like &lt;code&gt;setBitRate(unsigned int x) {Br = x; Fdev = func1(x); RxBw = func2(x);}&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of that, documents explaining the meaning of those parameters aside (very interesting but often too complex for me, specially those concerning the channel filter), I found some (not many) configuration tables, like this one in the source of the &lt;a href=&quot;https://github.com/PaulStoffregen/RadioHead&quot; rel=&quot;nofollow noreferrer&quot;&gt;RadioHead RFM69 library&lt;/a&gt; (I'll only reproduce a fragment of it here; in this case RxBw is set implicitly and therefore not showed in this list):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;FSK_Rb2Fd5 = 0,    ///&amp;lt; FSK, Whitening, Rb = 2kbs,    Fd = 5kHz&#xA;FSK_Rb2_4Fd4_8,    ///&amp;lt; FSK, Whitening, Rb = 2.4kbs,  Fd = 4.8kHz &#xA;FSK_Rb4_8Fd9_6,    ///&amp;lt; FSK, Whitening, Rb = 4.8kbs,  Fd = 9.6kHz &#xA;FSK_Rb9_6Fd19_2,   ///&amp;lt; FSK, Whitening, Rb = 9.6kbs,  Fd = 19.2kHz&#xA;FSK_Rb19_2Fd38_4,  ///&amp;lt; FSK, Whitening, Rb = 19.2kbs, Fd = 38.4kHz&#xA;FSK_Rb38_4Fd76_8,  ///&amp;lt; FSK, Whitening, Rb = 38.4kbs, Fd = 76.8kHz&#xA;FSK_Rb57_6Fd120,   ///&amp;lt; FSK, Whitening, Rb = 57.6kbs, Fd = 120kHz&#xA;FSK_Rb125Fd125,    ///&amp;lt; FSK, Whitening, Rb = 125kbs,  Fd = 125kHz&#xA;FSK_Rb250Fd250,    ///&amp;lt; FSK, Whitening, Rb = 250kbs,  Fd = 250kHz&#xA;FSK_Rb55555Fd50,   ///&amp;lt; FSK, Whitening, Rb = 55555kbs,Fd = 50kHz for RFM69 lib compatibility&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I did try to understand it's logic, but I couldn't. For instance, why does this list suddenly change from &lt;code&gt;Fd = 2*Rb&lt;/code&gt; (until line 7) to &lt;code&gt;Fd = Rb&lt;/code&gt; (from line 8)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found different lists, whit different parameters, but I never found a logic behind them.&#xA;Does a (even complex) function which relates bit rate, frequency deviation and channel filter bandwidth exist? Or where all these settings likely found experimentally? Am I trying to relate unrelated settings (I admit that I have a poor understanding of them, especially of the third), or am I forgetting some strongly related ones?&lt;/p&gt;&#xA;" OwnerUserId="8880" LastEditorUserId="8880" LastEditDate="2018-02-23T10:37:42.317" LastActivityDate="2018-02-24T14:01:27.997" Title="Relations between bit rate, frequency deviation and channel filter bandwidth" Tags="&lt;uhf&gt;&lt;transceiver&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9912" PostTypeId="2" ParentId="9907" CreationDate="2018-02-20T04:27:50.743" Score="2" Body="&lt;p&gt;If you want an antenna at the end of a length of coax, in my experience, simply stripping the last 1/4 wave of coax and leaving the inner exposed, does not work. The VSWR is high and unstable, as the other half of the dipole is completely undefined.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What works a lot better is to carefully extract the inner from the braid, or re-attach the braid, and fold it back down against the coax. So now you have a 1/2 wave dipole, with the coax running down against the lower, grounded half. You could even put some heat shrink over it, but it's better to keep the braid slightly away from the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have access to a VSWR meter, try building these and running your hand down the coax. In the first case the VSWR changes dramatically as your hand moves, in the second it will be more stable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want an antenna directly on the HT without any coax, then stripping off the sheath is fine, and a quick and easy way to get a 1/4 wave monopole without soldering. Your tuning will almost certainly be wrong on your first try - either cut it while attached to an MFJ style antenna tester, or try a range of lengths and see which ones work best for getting in to distant repeaters. &lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2018-02-20T04:33:22.090" LastActivityDate="2018-02-20T04:33:22.090" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9913" PostTypeId="2" ParentId="9897" CreationDate="2018-02-20T16:55:11.403" Score="4" Body="&lt;p&gt;A little impedance mismatch on the receiver is not a big deal. 75 to 50 ohms is an SWR of 1.5:1. For most applications, anything under 1.6:1 is considered a &quot;good match&quot;. For a receive-only application, &lt;a href=&quot;https://ham.stackexchange.com/q/382/218&quot;&gt;the match is even less critical&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides, the impedance of the antenna is going to vary with its surroundings and how the ears are oriented.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, you've said you don't have an antenna analyzer to accurately measure the impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given all this, little is to be gained by improving the match, and between environmental variation and the lack of equipment to measure it, any attempt you would make at improving the match would lack sufficient precision to make the difference between 50 and 75 ohms relevant in comparison.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were in your situation, I'd just repair the solder joint and perhaps put a different connector on it. It will work fine.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-20T16:55:11.403" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9914" PostTypeId="1" AcceptedAnswerId="9915" CreationDate="2018-02-21T06:52:26.257" Score="2" ViewCount="138" Body="&lt;p&gt;I'm running &lt;a href=&quot;http://gqrx.dk&quot; rel=&quot;nofollow noreferrer&quot;&gt;GQRX&lt;/a&gt; on Mac OS X 10.11.6 hooked up to an &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B0129EBDS2&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTL-SDR dongle&lt;/a&gt;.  I noticed when I'm tuned anywhere between ~56 MHz on down to 25.680 MHz I see evenly spaced signals on the FFT.  But when I tune to 25.679, they disappear completely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the higher end, the signals are faint (here I am tuned to 56 MHz):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dwVfA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dwVfA.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They become more pronounced as I work my way down (here I am tuned to 43 MHz):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ldakj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ldakj.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are most pronounced when I'm tuned to 25.680 MHz.  But when I tune to 25.679 MHz they disappear entirely.  Here I am switching back and forth between 25.679 and 25.680 MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zcQoU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zcQoU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's causing this?  Since I see signals below 25.3 MHz when I'm tuned to 25.680 but they disappear when 25.679 I tend to think this is a bug.  If so, is it hardware or software related?&lt;/p&gt;&#xA;" OwnerUserId="11221" LastEditorUserId="6079" LastEditDate="2018-02-21T09:34:42.597" LastActivityDate="2018-02-21T14:38:06.267" Title="FFT showing evenly spaced signals when tuned to ~56 MHz down to 25.680" Tags="&lt;software-defined-radio&gt;&lt;rfi&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9915" PostTypeId="2" ParentId="9914" CreationDate="2018-02-21T09:29:03.970" Score="3" Body="&lt;p&gt;It is very hard to say definitely what this is, however it looks like the pattern from a switching powersupply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Switching powersupplies are very common now-a-days, they are everywhere, from your laptop supply, your phone charger, LED lights, and many other devices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First thing I would do (if you are running this on a laptop) to run the laptop on batteries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then it is a &quot;trial and error&quot; method.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Go to your switch/fuse board, and turn of the zone's one by one, to see if this improves/changes the patterns. Make sure you notify other people in the house that you are about to do so, ensure that washing machines and the like are finished their cycles.. and so on so forth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have found the offending zone or zones, then investigate what is powered through those circuits, and work on from there. Please note that there could be hardwired devices, such as security camera's, which you cannot individually switch off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are in close proximity to your neighbours, the inteference may come from a next door propery. In which case a bit of friendly-neighbour politics comes into play. Proof that it is not your own devices, just switch off the main-breaker, and see what happens.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once found the offending device or devices, then you need to apply various methods of getting rid of the interference, apply some filters... it is very hard to answer this in a general way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most radio clubs would have experts in EMI/RFI and related subjects, they may have tips/tricks as well.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2018-02-21T09:35:51.623" LastActivityDate="2018-02-21T09:35:51.623" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9916" PostTypeId="2" ParentId="9914" CreationDate="2018-02-21T14:38:06.267" Score="2" Body="&lt;p&gt;The fact that the evenly-spaced signals are quite strong at 25.680 MHz and gone completely at 25.679 MHz strongly suggests that the signals are internally-generated.  Spurious signals generated inside the receiver are often called &quot;birdies&quot;, as described in &lt;a href=&quot;https://ham.stackexchange.com/questions/9771/what-are-these-continuous-sine-wave-tones-i-keep-hearing&quot;&gt;this similar question&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An excellent way to test whether or not birdies are the problem would be to connect another receiver of a different design to your antenna, and see if the other receiver picks up the evenly-spaced signals.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-02-21T14:38:06.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9917" PostTypeId="2" ParentId="9905" CreationDate="2018-02-21T14:46:43.487" Score="1" Body="&lt;p&gt;You didn't specify in which country you will be using the radios, and that affects the answer greatly.  The world is a big place, and the Internet gets to most of it!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In most countries, however, the only way to use such a radio legally will be to get a commercial VHF or UHF license, or an amateur radio (ham radio) license.  A ham radio license that lets you use such radios is pretty easy to get in quite a lot of countries, and often inexpensive.  (In Canada, for example, it's possible to get a callsign for free or low cost, not counting whatever study materials you choose to get.)&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-02-21T14:46:43.487" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9918" PostTypeId="2" ParentId="3770" CreationDate="2018-02-22T03:18:53.483" Score="0" Body="&lt;p&gt;If you use DCS instead of CTCSS then it adds an extra layer of image and interference rejection&#xA;But either way should be good for your situation&lt;/p&gt;&#xA;" OwnerUserId="11225" LastEditorUserId="9844" LastEditDate="2018-02-23T18:46:00.343" LastActivityDate="2018-02-23T18:46:00.343" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9919" PostTypeId="2" ParentId="9897" CreationDate="2018-02-22T06:18:41.997" Score="3" Body="&lt;p&gt;The feedpoint impedance of the rabbit ears antenna will be 72 ohms or less. It is basically a dipole antenna with shortened legs and potentially orientated in a Vee configuration. So with 50 ohm coax, attempting to exactly match impedance is a frivolous exercise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any notion of the balun correcting SWR is ill conceived. In a receive configuration, the SWR is established by the relationship of the receiver input impedance and the Z&lt;sub&gt;o&lt;/sub&gt; of the feedline. The antenna is the signal source. Any mismatch between the receiver and the feedline will cause the impedance of the transmission line at the antenna end to be transformed. If this transformed impedance is not a match for the feedpoint impedance of the antenna, the antenna will not transfer its maximum received power to the feedline causing it to re-radiate some of the power. Given the potentially wide variation of the antenna impedance, matching the two impedances through a matching device is not warranted. A more practical approach is realized by simply adjusting the antenna length and configuration for the best received signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A properly constructed balun will minimize common mode currents on the coax but with a compromise antenna such as rabbit ears, concern about common mode currents is not warranted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice would be to simply connect the 50 ohm coax directly to the rabbit ears and make the best of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The balun as pictured appears to be a transmission line transformer, probably a 4:1 configuration. Such devices do not work on the basis of turns ratios like more typical transformers. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-02-22T06:24:33.453" LastActivityDate="2018-02-22T06:24:33.453" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9920" PostTypeId="1" CreationDate="2018-02-22T07:22:30.933" Score="1" ViewCount="53" Body="&lt;p&gt;I'm new to the forum, and I've been advised that this is a good place to get experienced opinion. I lived in a three storey terraced house in Mid Wales. It is terraced on three sides with the house on one side being taller than mine. There are also two very tall solid chapels  on each side of the road  a few metres away. I have access to a small area at the rear which is about two and a half metres by 2 and a half metres.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a vertical sandpiper on the roof but this has limited success because of the taller buildings around my house., I also have a 69ft zeppelin aerial which runs from the guttering at one corner of the roof, (about 30 ft high) passing above  my neighbours smaller Cottage and garden to a plastic downpipe on one of the chapels at the bottom of my neighbour's garden (about 20ft up).. Unfortunately because of the proximity of the very old sound system the HF can interfere with the sound system in the chapel even on qrp&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a telegraph pole about 10 ft away from the chapel and the same distance from my house which is accessible. I could move the end of the Zeppelin to the telegraph pole. This would mean that it would be 3 or 4 ft down from a mains distribution cable that comes to my house. The Zeppelin and the mains cable would not be exactly parallel and over the length of the Zeppelin they would end up about 6 feet apart at the building..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would only have to move the farthest end of the Zeppelin. At the moment the cables are about 10 feet apart at the far end and about 6 feet apart at the house end and I don't experience any interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would moving the Zepp to the pole present any interference problems for either my reception or the local dwellings via the electricity network please &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The attached pic is not too clear, but you can get an idea of the layout. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keith. &lt;/p&gt;&#xA;" OwnerUserId="11227" LastActivityDate="2018-02-22T13:03:53.357" Title="Could I run a Zepp antenna from a telegraph pole underneath a mains cable?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9921" PostTypeId="2" ParentId="9920" CreationDate="2018-02-22T13:03:53.357" Score="6" Body="&lt;p&gt;I wouldn't do it. Power lines carry noise from all the houses attached to them, and with your antenna in such close proximity you'll probably hear all of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Likewise, when transmitting you'll likely couple a fair bit of RF into the power line. That could cause even more interference with your neighbors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also a safety hazard. If that power line should fall and come into contact with the antenna you may be in for a surprise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's probably also illegal.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-22T13:03:53.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9922" PostTypeId="1" CreationDate="2018-02-23T01:43:10.977" Score="1" ViewCount="2376" Body="&lt;p&gt;I have been given several hundred feet of very high quality 75 ohm coax. I need a run of about 36' from my QRP transmitter (FT-817 with elecraft T1 tuner) to an EFHW antenna (about 75' long). Running the coax will be a difficult task so I am curious about the effect of using this 75 ohm coax instead of 50 ohm.  Frequencies will be 3-54mhz. I have been using this antenna but with a temporary piece of 50 ohm coax and need to relocate the feed end of the antenna which results in a much longer run (was about 10').&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a limited understanding of the issues involved but I think the 25 ohm difference would not cause much of a problem. However I request advice and guidance before I install the coax because of the difficulty of the install. &lt;/p&gt;&#xA;" OwnerUserId="11202" LastEditorUserId="9493" LastEditDate="2018-02-24T03:16:28.443" LastActivityDate="2018-02-24T03:16:28.443" Title="Impedance effect of using 75 ohm coax between transmitter and an EFHW antenna" Tags="&lt;wire-antenna&gt;&lt;impedance&gt;&lt;coaxial-cable&gt;&lt;qrp&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9923" PostTypeId="2" ParentId="3770" CreationDate="2018-02-23T02:49:05.120" Score="1" Body="&lt;p&gt;DCS uses a rotating series of codes like 257257257257 which in this case is 257 repeated continually. CTCSS uses a sub audible single tone like say 100 hz. Once a CTCSS squelch is open, wide band noise like intermod or computer hash can keep the squelch open after the transmitted carrier when its sub audible tone stops, resulting in unwanted noise at the receiver. Sometimes the noise can have enough of the required sub audible tone to open the squelch and keep it open, resulting in jammed repeaters etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However with DCS when the rotating code stops, the squelch can not be kept open by outside interference. Also at the end of the transmission the transmitting radio sends a &quot;close squelch&quot; command which causes the receiving radio to close its squelch before the transmitting radio ceases its transmission. This eliminates the common squelch tail resulting in a much cleaner end of transmission.  The voice just stops without any noise or tail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;DCS works much better in urban high noise environments and in my opinion produces a much nicer &quot;sound environment&quot;. There is voice, then no voice, without the CTCSS hiss and crash at the end. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 3 digit rotating code like 257 means that code 572 and 725 will give the same 57257257257 sequence so only some of the codes are listed. If 257 is the code, then although 725 and 572 will generate the same sequence the listed 257 should be used so as not to confuse the user into thinking they are distinct codes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try it on simplex. Set up two memories on the same frequency. One with CTCSS and one with DCS. Then have both operators change together between the memories and do a &quot;side by side&quot; comparison. I have been using DCS on repeaters and simplex for years and really like it. &lt;/p&gt;&#xA;" OwnerUserId="11202" LastActivityDate="2018-02-23T02:49:05.120" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9924" PostTypeId="1" CreationDate="2018-02-23T05:31:50.677" Score="2" ViewCount="111" Body="&lt;p&gt;I need to impedance match an IF mixer circuit to a 10.7MHz crystal filter. One of the inductors was calculated to be 44 $\mu$H. So I need a relatively large value inductance in a small package to fit a small printed circuit board. Is it ok to use a molded choke for this purpose or will the earth stop turning?&lt;/p&gt;&#xA;" OwnerUserId="11230" LastEditorUserId="9493" LastEditDate="2018-02-24T18:24:08.053" LastActivityDate="2018-02-24T18:24:08.053" Title="Inductors for Impedance Matching" Tags="&lt;electronics&gt;&lt;impedance-matching&gt;&lt;inductor&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9925" PostTypeId="1" CreationDate="2018-02-23T12:52:44.133" Score="1" ViewCount="350" Body="&lt;p&gt;How should I start if I want to design a compact antenna for 2 meter band using the principle of meander antenna? I noticed meander antennas are frequently used in mobile devices and notebooks for 2.4 and 5.5 GHz devices (Bluetooth, Wifi) as well as various kinds of mobile phones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to get to something, preferably flat or pen-shaped, and I wanted to try meander antenna because they are reportedly the most efficient radiators with regard to their small physical dimensions.&lt;/p&gt;&#xA;" OwnerUserId="11232" LastEditorUserId="76" LastEditDate="2018-02-24T23:00:04.120" LastActivityDate="2018-02-24T23:00:04.120" Title="How to design a meander antenna for 2 meter band?" Tags="&lt;antenna&gt;&lt;2m-band&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9926" PostTypeId="2" ParentId="9922" CreationDate="2018-02-23T13:18:39.857" Score="1" Body="&lt;p&gt;It won't make much of a difference. In fact, if the feedpoint impedance of the antenna is closer to 75 ohms than 50 ohms, it may be better. And if this is much higher quality coax (thus, lower loss) than the alternative, it will certainly be better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the coax impedance does not match the load (antenna) impedance, two things happen, which may or may not be a significant problem:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The VSWR is higher than 1:1, and thus there will be &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;additional losses&lt;/a&gt;, and&lt;/li&gt;&#xA;&lt;li&gt;the impedance seen by the transmitter will be the load impedance, centered around a constant-VSWR circle centered on 75 ohms.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;It's easy to see what this &quot;constant-VSWR circle&quot; on a &lt;a href=&quot;https://en.wikipedia.org/wiki/Smith_chart&quot; rel=&quot;nofollow noreferrer&quot;&gt;Smith chart&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or to put it mathematically, VSWR is defined by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \left(\text{load impedance} \over \text{coax impedance}\right)^{\pm 1} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;±1 is selected to give whichever provides a value greater than 1. So let's say the load impedance is 50 ohms, and you are using 75 ohm coax. That's an SWR of 1.5, because $75/50 = 1.5$. Then depending on the feedline length, the transmitter might see any impedance that satisfies:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \left(\text{impedance seen by transmitter} \over 75\right)^{\pm 1} = 1.5 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it might be 50 ohms, or 112.5 ohms, or any number of complex impedances in between.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this a problem? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, was your load matched to 50 ohms in the first place? End-fed antennas are notoriously difficult to predict, so probably not. So the impedance gets rotated about whether you use 50 ohm or 75 ohm coax, but you probably have a tuner which will be adjusted so the transmitter sees 50 ohms regardless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if you don't have a tuner, a 112.5 ohm load isn't that bad for most transmitters. You'd have to consult the transmitter specifications to see the range of permissible impedances for it to deliver its rated power, but in many cases you'll be fine.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-23T13:18:39.857" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9927" PostTypeId="2" ParentId="9925" CreationDate="2018-02-23T14:59:35.383" Score="1" Body="&lt;p&gt;I think the easiest way is to start with a working design (Google is full of it) for an other band and upscale (or downscale) it for the 2m band.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2018-02-23T14:59:35.383" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9928" PostTypeId="2" ParentId="9925" CreationDate="2018-02-23T16:34:45.227" Score="2" Body="&lt;ol&gt;&#xA;&lt;li&gt;Start with a straight dipole or monopole&lt;/li&gt;&#xA;&lt;li&gt;Put kinks in it&lt;/li&gt;&#xA;&lt;li&gt;Add or subtract length as necessary&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;It usually ends up somewhere between 50% to 60% of the straight-wire length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could find the appropriate length by modelling or trial and error. KK4OBI has &lt;a href=&quot;http://www.qsl.net/kk4obi/Meander%20Dipole.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;a chart which will get you close&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although if you want something pen-shaped, the typical &quot;rubber-ducky&quot; antenna that comes with most mobile radios is a wire wound in a helix, which could be described as a &quot;helical meander antenna&quot;, or an antenna that meanders in three dimensions instead of two. The reason they aren't used more frequently in consumer electronics is they can't be printed on a PCB. I doubt you will find much difference in performance between a meander antenna and a helical antenna of similar size.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-23T16:34:45.227" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9929" PostTypeId="2" ParentId="9905" CreationDate="2018-02-23T18:51:37.170" Score="1" Body="&lt;p&gt;These are great little radios. I really do like them. However, in the U.S., there seems to be no way to legally transmit with these radios without a license. Not even on the unlicensed bands since these radios are not certified for FRS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My suggestion is to get a Ham Radio license. You only need a technician license for VHF and UHF and wouldn't require more than a day or two to study and pass the test. Good luck.&lt;/p&gt;&#xA;" OwnerUserId="1715" LastActivityDate="2018-02-23T18:51:37.170" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9930" PostTypeId="1" CreationDate="2018-02-23T19:51:30.393" Score="3" ViewCount="422" Body="&lt;p&gt;My 8 year old and I are trying to figure out how to get this crystal radio we made working. It's based off this &lt;a href=&quot;https://www.youtube.com/watch?v=8XR9Uzy2RPM&quot; rel=&quot;nofollow noreferrer&quot;&gt;youtube video&lt;/a&gt;. We get clicks when we put the crystal ear piece either side of the resistor but nothing more yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My son tried a really long aerial, wire winding all around the house, and for ground he had a wire hooked to a bolt pushed into a pot with dirt. (However I'm not sure whether we actually tried both these at the same time!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why does it need a ground, and will it work without one?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How long does the aerial need to be?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does the covered copper coil need to be thinner wire? Whats the relationship between the wire size and amount of turnings, and the length of arial needed? We have about 200 windings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would be great to understand this a little bit more and actually get it working.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's some photos:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pja4a.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pja4a.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/nqrpw.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nqrpw.jpg&quot; alt=&quot;Where ground connects and the lever&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/bXstC.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bXstC.jpg&quot; alt=&quot;   &quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/AMwBH.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AMwBH.jpg&quot; alt=&quot;crystal ear piece either side of the resistor&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/UVxfN.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UVxfN.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/g6gpa.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/g6gpa.jpg&quot; alt=&quot;Windings&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11093" LastEditorUserId="966" LastEditDate="2018-02-28T01:26:59.383" LastActivityDate="2018-03-01T19:35:50.193" Title="How do I get my crystal radio to receive?" Tags="&lt;antenna-construction&gt;&lt;grounding&gt;&lt;crystal-radio&gt;" AnswerCount="3" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="9931" PostTypeId="2" ParentId="9930" CreationDate="2018-02-23T20:07:47.077" Score="3" Body="&lt;p&gt;A bolt pushed into a pot full of dirt will never work! &lt;em&gt;You need a ground return to planet earth itself&lt;/em&gt; for your crystal radio. :-) This could be as simple as the screw on a plastic cover that holds an electrical outlet in place. That's what I did when I was a kid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, some of those connections look &quot;iffy&quot;. Make sure they are all making contact with an ohmmeter set at the lowest resistance scale (unless you have one with an auto-ranging feature).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also use a copper-clad steel rod --available from hardware stores, home improvement stores, or electrical supply houses-- driven into the earth. Use an ordinary stainless steel hose clamp or (more expensive) a bronze clamp made for the purpose.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-03-01T19:35:50.193" LastActivityDate="2018-03-01T19:35:50.193" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="9932" PostTypeId="2" ParentId="9922" CreationDate="2018-02-23T20:11:18.237" Score="1" Body="&lt;p&gt;When considering atypical coax cable for ham applications, there are a few  things that can come into play.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Shielding Material&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check that the shielding material is capable of being properly terminated in a PL-259 style connector. If the shield consists of braid plus foil, a crimped style connector may be the best choice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Suitable Connector&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dimensions of 75 coaxial cable are different than those of 50 ohm cable. The result is that a standard 50 ohm coax cable connector may not properly fit over the dielectric and the braid of the 75 ohm cable. Check in advance to make sure you have a good fit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Jack Material&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not all jackets are suitable for outdoor use. For example, the PVC jacket on Belden 9116 75 ohm cable is not rated for outdoor use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Voltage Rating&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most coax cables carry a maximum RMS voltage rating. This will either be influenced by safety agency ratings or the maximum voltage that will not perforate the dielectric material of the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The maximum RMS voltage on the coax is calculated as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_\text{RMS}=\sqrt{P_\text{xmtr}*Z_o*SWR} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So with a 75 ohm coax, a transmitter power of 100 watts, and a 1:1 SWR the maximum RMS voltage on the line will be ~87 volts. But when the SWR is 25:1 as it could be on a wide coverage antenna, the maximum RMS voltage rises to ~433 volts. This would be well above the 300 volt RMS maximum voltage rating of Belden 9116 75 ohm cable, for example but well below the 2700 RMS voltage rating of Belden 8215 75 ohm cable. Check the manufacturer's datasheet for the specifications of the cable you will be using.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Tuner Connections&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use a 50 ohm patch cord between your transmitter and the tuner, the transmitter will be able to develop its maximum rated output. The tuner will convert the 50 ohm impedance to match the impedance seen at the tuner end of the coax cable going to the antenna. This is the optimum configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Coax Loss&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The wide frequency range implies a potentially large SWR range. This can cause significant losses in the coax as the SWR increases. The tuner may match the transmitter to the coax but the SWR is still present. Depending on the coax, the majority of your transmit power could go up as heat in the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using low loss coax and placing the tuner closer to the antenna will help to minimize these losses.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-02-23T20:49:54.120" LastActivityDate="2018-02-23T20:49:54.120" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9933" PostTypeId="2" ParentId="9930" CreationDate="2018-02-24T02:16:34.807" Score="5" Body="&lt;p&gt;This design of a crystal radio relies on the capacitance of the antenna and the inter-winding capacitance of the inductor as well as the inductance of the inductor to form the tuned circuit. The length of the antenna can therefore play a role in the ability to tune in AM stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I agree with Mike regarding the soldered connections. Go through them all again and reheat and apply solder. Your annealed wire must be scraped or sanded down to bright, bare copper wherever there is a connection unless your annealing is the self melting type.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It appears from your picture that your slider bar on the inductor is not making electrical contact with the coil. That area on the top of the coil must also be sanded to expose the bare copper. The slider bar itself does not appear to be a good conductor - a brass rod would be a better choice. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For longer term reliability, you may wish to use brass screws and washers throughout. You can also solder to these if you wish to make it bullet proof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The selection of the diode can make a big difference in performance. A 1N34 or a Schottky diode are good choices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You mentioned that you have connected a ground wire but this is not visible in your pictures. It should be attached to the coil on the end opposite from the antenna.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-02-28T10:11:15.917" LastActivityDate="2018-02-28T10:11:15.917" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9934" PostTypeId="2" ParentId="9907" CreationDate="2018-02-24T10:34:43.477" Score="-1" Body="&lt;p&gt;Grid dip the coax to quarter wave, then put half wave wire on the center conductor end. Should work fine but clunky. Why not buy one of the longer antennas made for walkies?&lt;/p&gt;&#xA;" OwnerUserId="11236" LastActivityDate="2018-02-24T10:34:43.477" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9935" PostTypeId="1" CreationDate="2018-02-24T10:51:31.577" Score="0" ViewCount="109" Body="&lt;p&gt;Why does USB have so much less audio output than LSB? I've checked all settings and they are correctly set or not used, like AGC etc. Using same band pass on both modes. &lt;/p&gt;&#xA;" OwnerUserId="11236" LastEditorUserId="9493" LastEditDate="2018-02-24T12:27:42.273" LastActivityDate="2018-02-25T19:26:08.070" Title="SDR (RTL-SDR v3) USB audio much less than LSB" Tags="&lt;software-defined-radio&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9936" PostTypeId="2" ParentId="9924" CreationDate="2018-02-24T11:56:24.683" Score="1" Body="&lt;p&gt;In general, a choke would not be a good choice for this type of circuit as explained below. Given the relatively high frequency of your application, I would expect that you could find more suitable values or topologies for your impedance transformation requirement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Technically, the difference between a choke and an inductor is only a matter of application. A choke is an inductor that is designed to pass DC while blocking RF current. However, from a practical perspective there can be significant differences.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since a choke is designed to block RF, generally the choke will have a relatively low Q (quality factor). It may consist of many, multi-layer windings using a relatively small gauge wire. With a small diameter wire, the DC is free to use the complete cross section of the wire while the RF cannot due to skin effect. Thus as the frequency increases, the RF sees more series resistance in the inductor which lowers its Q, thus increasing its losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the intended application of RF chokes, they are not always temperature stable either. In a critical matching circuit, this could result in  a temperature based variation in the transform.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, RF chokes have distributed capacitance that results in a self resonant frequency of the choke. In a critical application such as a tuned circuit, this parasitic capacitance can have a detrimental effect if it is not included in the design model.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-02-24T11:56:24.683" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9937" PostTypeId="2" ParentId="9935" CreationDate="2018-02-24T12:18:32.317" Score="1" Body="&lt;p&gt;Not knowing your level of experience with the various amateur radio modes, be aware that for a given SSB (single side band) signal, only one of the side bands (upper or lower) is transmitted. The carrier and the other side band are significantly suppressed in the transmitted signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since USB (upper side band) tends to be used on the higher frequency bands, you may simply be experiencing the difference in gain of your DSP or your antenna system on these higher frequencies. Normally, a properly configured AGC block will minimize this variation but it cannot completely eliminate it.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-02-24T12:18:32.317" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9938" PostTypeId="1" CreationDate="2018-02-24T13:09:29.143" Score="1" ViewCount="502" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZdKLX.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZdKLX.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Location: Michigan, USA&lt;/li&gt;&#xA;&lt;li&gt;Frequency: 7.074 MHz&lt;/li&gt;&#xA;&lt;li&gt;Time: 1300 UTC&lt;/li&gt;&#xA;&lt;li&gt;Vertical axis: 15 seconds per division&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Most of this is FT8, and some JT65 can be seen as well. But buried in here is something else, labeled &quot;A&quot;. It appears to be some kind of 8-FSK, possibly with the same 15 second interval as FT8.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Labeled &quot;B&quot; is a similar signal, though it appears to have a wider tone spacing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are these &quot;A&quot; and &quot;B&quot;?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-03-26T20:20:59.137" Title="What's this digital mode on 40 meters?" Tags="&lt;signal-identification&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9939" PostTypeId="2" ParentId="9911" CreationDate="2018-02-24T13:54:26.727" Score="1" Body="&lt;p&gt;There are two primary theorems that come into play to address your question - the Nyquist theorem and the Shannon-Hartley theorem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Nyquist&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Nyquist theorem defines the maximum channel capacity for a &lt;em&gt;noiseless&lt;/em&gt; channel. His formula to express this is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$C=2B\log_2{M} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where C is the channel capacity in bits per seconds, B is the maximum bandwidth of the channel in Hertz and M is the number of signaling values (2 for binary, 4 for QPSK, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This formula suggests that we could simply keep increasing the number of signal values and the channel capacity would increase &lt;em&gt;ad infinitum&lt;/em&gt;. But no real world channel is noiseless so ultimately noise becomes the limiting factor. This is where the Shannon-Hartley equation becomes important.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Shannon-Hartley&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Shannon-Hartley theorem describes the maximum channel capacity based on the signal to noise ratio of the channel:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$C=B\log_2{(1+S/N)} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where C is the maximum channel capacity in bits per second, S is the signal power, N is the noise power, and B is the channel bandwidth in Hertz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can see that the Shannon theorem therefore places an &quot;upper bound&quot; on maximum channel capacity based on the signal to noise ratio of the system and the bandwidth of the channel. For example, with a 30 dB signal to noise ratio (a linear power ratio of 1000) and a 3 kHz bandwidth, the maximum channel capacity is ~30,000 bits per second. If we can improve the signal to noise ratio to 40 dB (a linear power ratio of 10000), the maximum channel capacity rises to ~40,000 bits per second.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Application in RF Systems&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the distance between the transmitter and receiver is doubled, the received signal strength is quartered while the noise power remains the same (provided there are no noise sources that come into closer proximity as a result). Thus the signal to noise ratio has been quartered. We can therefore apply the Shannon theorem to determine the effect of doubling the distance between the transmitter and receiver:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$C_\Delta=\frac{B\log_2{(1+(S/N)*0.25)}}{B\log_2{(1+S/N)}}=\frac{\log_2(1.25)}{\log_2(2)}=0.322 \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So we can see that with each doubling of distance between the antennas, the maximum channel capacity is reduced by approximately 68%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can overcome this loss in maximum channel capacity by increasing the gain of the transmit or receive antennas or increasing the power of the transmitter. But it is clear that if no other steps are taken, doubling the distance means we must reduce the bit rate by about 68% to maintain communications.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-02-24T14:01:27.997" LastActivityDate="2018-02-24T14:01:27.997" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9940" PostTypeId="1" AcceptedAnswerId="9941" CreationDate="2018-02-24T17:28:19.380" Score="1" ViewCount="454" Body="&lt;p&gt;I found a listing for a repeater with 0MHz offset and I don't know what to expect from a repeater like this that is different from a traditionally offset repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://repeaterbook.com/repeaters/details.php?state_id=53&amp;amp;ID=7958&quot; rel=&quot;nofollow noreferrer&quot;&gt;repeaterbook.com/repeaters/details.php?state_id=53&amp;amp;ID=7958&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="11235" LastActivityDate="2018-02-25T10:10:46.640" Title="How do 0 offset repeaters differ from offset repeaters?" Tags="&lt;repeater&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9941" PostTypeId="2" ParentId="9940" CreationDate="2018-02-24T18:04:31.773" Score="2" Body="&lt;p&gt;It is most likely an erroneous listing. W7BMW does not appear as a coordinated repeater in the Seattle area, according to WWARA - the local repeater coordinating body. See &lt;a href=&quot;https://www.wwara.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.wwara.org&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While the W7BMW entry might be an EchoLink or IRLP reference as noted by rclocher3, a quick check on the repeaterbook.com site of a few other repeaters shows the data is not very reliable. For example, there is an AA7SS repeater listed as 445.925 with a +5 MHZ offset. That would put the input frequency outside of the amateur radio band. According to WWARA, this repeater is in fact on 441.175 with a +5 MHz offset.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You would be well served to use a more reliable data source than repeaterbook.com.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-02-25T10:10:46.640" LastActivityDate="2018-02-25T10:10:46.640" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9942" PostTypeId="2" ParentId="9938" CreationDate="2018-02-24T19:29:57.117" Score="1" Body="&lt;p&gt;&quot;A&quot; appears to be T10, a mode available on the JTDX app.&#xA;I believe &quot;B&quot; is simply an artifact from one of the over-driven FT8 signals on the band.&#xA;No doubt I'll be corrected if I'm wrong :)&#xA;73&#xA;Dave - KB3MOW&lt;/p&gt;&#xA;" OwnerUserId="10286" LastActivityDate="2018-02-24T19:29:57.117" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9943" PostTypeId="1" CreationDate="2018-02-24T20:23:23.730" Score="1" ViewCount="6504" Body="&lt;p&gt;I'm looking at a getting a Yaesu FT-60 but have found that the FT-70 is priced similarly (add \$30-\$50).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm having a hard time determining the key differences between the two. Reading up online, it sounds like the FT-70 is an upgraded FT-60 but I can't figure out what's better about the FT-70.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only notable differences I can see are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;FT-70&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Lighter, shorter&lt;/li&gt;&#xA;&lt;li&gt;Louder internal speaker&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;FT-60&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Thinner&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;What other differences justify the price of the FT-70 over the FT-60?&lt;/p&gt;&#xA;" OwnerUserId="11235" LastEditorUserId="76" LastEditDate="2018-02-24T22:59:07.310" LastActivityDate="2018-03-03T21:59:22.543" Title="Yaesu FT-60 vs. FT-70" Tags="&lt;ht&gt;&lt;yaesu&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9944" PostTypeId="2" ParentId="9940" CreationDate="2018-02-25T00:19:10.247" Score="2" Body="&lt;p&gt;The repeater in question is an &lt;a href=&quot;http://www.echolink.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Echolink&lt;/a&gt; and &lt;a href=&quot;http://www.irlp.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;IRLP&lt;/a&gt; node, not a traditional repeater.  A traditional repeater is on a mountaintop or on a tall building or tower; it simultaneously retransmits whatever it hears, so that the station calling into the repeater has the increased range resulting from the repeater's high location, expensive antenna, and high-powered transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An Echolink or IRLP node is somewhat different.  It's a transceiver connected to a computer with an internet connection.  Whatever the node hears over the air is sent via the internet to other users and/or nodes, and whatever the computer picks up from the internet is retransmitted over the air.  Because the communication is half-duplex, meaning only one operator can talk at a time, the node only occupies one frequency, rather than the pair of frequencies that a traditional repeater uses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's possible to combine a traditional repeater with an Echolink or IRLP node, so that when it receives RF it retransmits the signal locally and also sends the audio over the internet, and whatever is received from the internet is broadcast over the repeater just like a locally-received signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Echolink and IRLP are generally used to link nodes and repeaters over the internet.  (Echolink can also be used as software on a computer, with no radio involved, by users who have proved they have current amateur radio licenses.)  The owner of the node in question listed his node in the repeater directory because the node is a resource to VHF/UHF operators in the area, similar to a repeater.  Because the node uses only a single frequency, it's in the directory as a &quot;0 MHz offset repeater&quot;.  For North American hams, the ARRL Repeater Directory is pickier: it lists repeaters only, and not Echolink and IRLP nodes that aren't part of a repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, Echolink and IRLP are similar, and a node can participate in both systems, but not simultaneously.  At any given time the node can participate in one system or the other, but not both.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-02-25T00:19:10.247" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9945" PostTypeId="2" ParentId="9943" CreationDate="2018-02-25T14:06:50.940" Score="2" Body="&lt;p&gt;Frankly, the biggest difference I immediately see is the difference in batteries: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whereas the FT-60 uses NiMH batteries, the FT-70 is lithium-based.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's significantly higher &lt;em&gt;energy&lt;/em&gt; density in LiIon, which explains the weight difference, and: a charged LiIon battery will hold load without noticeable charge loss for weeks to month (depending on design, even years, but that won't be the case here), even after intense use¹, while NiMH does suffer under high self-discharge right from the start.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other than that: the generation change implies better DSP, leading to &lt;em&gt;probably&lt;/em&gt; better speech understandability, lower power usage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The firmware on the FT-70 is updatable; this might or might not turn out to be an advantage in the future.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹ battery design is an involved topic; of course, there's limiting factors here: discharging at high rates under very cold conditions might lead to increased self-discharge etc, but it's pretty unlikely your LiIon battery will ever see the same self-discharge rates as brand new NiMH (wikipedia says 0.5% to 4% per &lt;em&gt;day&lt;/em&gt; for NiMH at room temperature, and medium-sized lithium polymer batteries typically do something like 4% in a &lt;em&gt;month&lt;/em&gt;)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-02-25T14:06:50.940" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9946" PostTypeId="2" ParentId="9935" CreationDate="2018-02-25T19:26:08.070" Score="0" Body="&lt;p&gt;Figured out the audio level difference between USB and LSB. With USB the AGC selection became active then using LSB it turned off. Settings are not permanent but need checking for each frequency selected! 73, Jim K5BTV   &lt;/p&gt;&#xA;" OwnerUserId="11236" LastActivityDate="2018-02-25T19:26:08.070" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9947" PostTypeId="2" ParentId="6471" CreationDate="2018-02-25T22:18:11.913" Score="-1" Body="&lt;p&gt;Because of how spread out they are today, the FCC has become more of a complaint-driven organization. In short, if people don't complain about your illegal activity, you might probably never get turned in. If people do complain, the FCC typically forwards the complaints to the Amateur Auxiliary, who's in charge of locating the offending parties.&lt;/p&gt;&#xA;" OwnerUserId="9166" LastEditorUserId="8717" LastEditDate="2018-02-25T23:00:55.930" LastActivityDate="2018-02-25T23:00:55.930" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9948" PostTypeId="1" CreationDate="2018-02-25T23:32:15.983" Score="3" ViewCount="11519" Body="&lt;p&gt;Will the propagation on the High Frequency bands come back up soon?? I am referring to the 3 to 30 MHz range.&lt;/p&gt;&#xA;" OwnerUserId="11114" LastEditorUserId="8717" LastEditDate="2018-02-25T23:46:32.007" LastActivityDate="2019-04-21T04:38:59.217" Title="When will propagation on HF improve?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9949" PostTypeId="2" ParentId="9948" CreationDate="2018-02-25T23:43:46.650" Score="0" Body="&lt;p&gt;The short answer is &lt;em&gt;nobody knows&lt;/em&gt;. Many of us want to know the same thing! :-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I asked &lt;a href=&quot;https://ham.stackexchange.com/questions/8940/what-is-the-cause-of-this-unusually-long-period-of-terrible-hf-band-conditions&quot;&gt;a similar question here&lt;/a&gt;. One of these days I'll update it with some information I found, which seems to indicate &lt;em&gt;never&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-02-25T23:43:46.650" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9951" PostTypeId="1" CreationDate="2018-02-26T14:57:54.053" Score="0" ViewCount="152" Body="&lt;p&gt;Is SDR technology a way for me to listen to a large group of stations or even the entire FM band at once?&lt;/p&gt;&#xA;" OwnerUserId="11242" LastEditorUserId="218" LastEditDate="2018-02-26T15:46:13.503" LastActivityDate="2018-02-26T17:13:36.863" Title="Playback entire FM Band" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9952" PostTypeId="2" ParentId="9948" CreationDate="2018-02-26T17:04:36.320" Score="4" Body="&lt;p&gt;We are approaching a sunspot minimum, so higher frequency HF bands will not work well. I assume you know this, and your QRZ page says you are mostly active on 40 meters which wouldn't be affected as much by sunspot activity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I challenge the premise of the question, that conditions are especially bad, even accounting for sunspot activity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anecdotally, I don't find this true at all. Two days ago I got up at dawn and made FT8 contacts from my midwest USA location to Figi (12,000 km) and Australia (15,500 km) on 40 meters. Japan (10,000 km) is a bit of a challenge, but mostly because I'm not awake at the right time of day. Europe isn't even a challenge. None of this is atypical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have anything special for a station: just a 100W transmitter and a dipole. Nor am I in an especially quiet location: my neighbors are about 50 meters away. In fact, the main difficulty I have in making contacts isn't propagation: it's trying to find a free frequency. FT8 is completely packed on 40 and 20 meters. The WARC bands are only mostly packed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I won't provide sources (mostly because I don't want to do the research right now), but I'd bet these factors can contribute to the perception of decreased HF activity:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The &lt;a href=&quot;https://ham.stackexchange.com/q/1282/218&quot;&gt;number of CW operators&lt;/a&gt; is on the decline due to rising popularity of digital modes and elimination of the licensing requirement in most (all?) countries.&lt;/li&gt;&#xA;&lt;li&gt;HF proficiency among hams is also declining since VHF and UHF radios are cheaper, easier, and available at the lowest levels of licensing. Internet linking provides long-distance communication previously possible only on HF. That the internet isn't radio doesn't seem to bother many people. Some are content to forgo even a repeater, instead communicating over a &lt;a href=&quot;http://arrl-ohio.org/digital/Amateur%20Radio%20Digital%20Hotspot%20Comparison.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;digital voice hotspot&lt;/a&gt; connected directly to the internet.&lt;/li&gt;&#xA;&lt;li&gt;Fewer people are interested in rag-chewing since today this social function is serviced by the internet and cell phones.&lt;/li&gt;&#xA;&lt;li&gt;The number of licensed hams overall is declining.&lt;/li&gt;&#xA;&lt;li&gt;Operators believe conditions are poor, so don't bother getting on the air.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;FT8 is by far where I see most HF activity. I can turn on the radio any time a day, and every 15 seconds monitor at least a dozen (frequently more) QSOs going on. Usually about 5 of them are calling CQ, and if I'm on at an appropriate time of day for the band, many of them are intercontinental.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And things are changing very fast: maybe A year ago it was all about JT65, which is nearly dead now. PSK31, also extremely popular a year ago, is about as dead as JT65. I'd estimate there's enough CW activity to be comparable to FT8, but it's spread out more so a little harder to find without a skimmer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By one account the &lt;a href=&quot;http://forums.qrz.com/index.php?threads/average-age-of-cw-operators-from-my-log.493654/&quot; rel=&quot;nofollow noreferrer&quot;&gt;average age of a CW operator is 68&lt;/a&gt;, and I would not be surprised if once these people are gone, CW will fade away from common usage.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-02-26T17:04:36.320" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9953" PostTypeId="2" ParentId="9951" CreationDate="2018-02-26T17:13:36.863" Score="6" Body="&lt;p&gt;Yes. To actually do it, you need:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;SDR receiver hardware with (slightly more than) 20 MHz bandwidth to capture the entire FM broadcast band.&lt;/li&gt;&#xA;&lt;li&gt;A computer, fairly powerful (definitely not a Raspberry Pi or such).&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;SDR software which can be configured to actually do this. Many receiver programs are focused on receiving a single signal; my own ShinySDR can do multiple but not as efficiently as a purpose-built program.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The likely place to start to make this actually happen would be to use GNU Radio, a framework for making SDR applications. GNU Radio's polyphase channelizer can efficiently separate all the FM channels since they are conveniently equally spaced. You will also need something to &lt;em&gt;do&lt;/em&gt; with the hundred separate channels other than playing them all at once (unless that mess is what you wanted).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-02-26T17:13:36.863" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9955" PostTypeId="1" CreationDate="2018-02-27T04:04:32.843" Score="1" ViewCount="453" Body="&lt;p&gt;So I talked to my neighbor about my Raspberry PI, harmonics and his emergency radio. He told me to fire it up, as we saw the FCC sticker on it, meaning it is in compliance with Part 15. I started my broadcast on 91.60 MHz. He didn't notice anything, but when he checked his phone, no service. He told me to turn off the transmitter, and like that, his 4 bars of LTE came back. &#xA;He decided to use a SDR radio and we found that there is a harmonic of my radio transmission around 75.60 MHz? How is this possible and is there a way to fix this as I don't want to anger the cell phone company.&lt;/p&gt;&#xA;" OwnerUserId="11206" LastEditorUserId="9493" LastEditDate="2018-02-28T01:09:21.560" LastActivityDate="2018-02-28T14:35:38.817" Title="Weird Harmonic Issue on Raspberry PI FM Transmitter" Tags="&lt;united-states&gt;&lt;vhf&gt;&lt;rfi&gt;&lt;equipment-design&gt;&lt;transmitter&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9957" PostTypeId="2" ParentId="9955" CreationDate="2018-02-27T09:56:44.487" Score="5" Body="&lt;p&gt;There are many articles which describe how to use a R-Pi to emit (=transmit) a signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However what most, if not all, articles fail to describe is that this signal is a very rough signal, usually not even a sinus, and has harmonics. It is these harmonics (=spurious emissions) which can cause interference to a whole range of services and devices when not properly filtered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even when you manage to filter out these spurious emissions with a lot of filters, it would be questionable if it is legal to transmit for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transmitting usually involves having a license for specific frequencies or bands. For those bands which are &quot;free to use&quot; usually are restricted by &quot;type approved equipment&quot; which I am sure a R-Pi without filters is not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the frequencies you are mentioning in your post, are likely in the FM-broadcast band, and are likely to cause interference to services. The second harmonics, and third harmonics are likely to cause interference in frequencies which are used by official services (aviation, police, ambulances, fire departments) depending on your location. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Higher harmonics could cause interference to other services, as yourself has noticed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;&lt;em&gt;STOP&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Dont do this unless you:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Know how to control/filter harmonics&lt;/li&gt;&#xA;&lt;li&gt;Know how to handle suppress spurious emissions, phase noise, and others&lt;/li&gt;&#xA;&lt;li&gt;Know how to measure/adjust and test your transmitter and emitted signal&lt;/li&gt;&#xA;&lt;li&gt;Know the law in regards transmitting on your chosen frequency&lt;/li&gt;&#xA;&lt;li&gt;Have a license.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I am all for experimentation, but this is just something you shouldn't do without proper knowledge, to ensure that you do not interfere with official services.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2018-02-27T09:56:44.487" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9958" PostTypeId="2" ParentId="9955" CreationDate="2018-02-27T12:42:18.690" Score="5" Body="&lt;p&gt;You are observing a practical example of harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Harmonics of a Square Wave&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You do not mention how you are generating the signal with your Pi but it probably uses a simple square wave generator. Square waves have the characteristic that in addition to the fundamental frequency (the frequency that is being directly generated by the program in your Pi) there are also all of the odd harmonics present. This means it will generate the fundamental frequency, and that frequency times 3, times 5, times 7, etc. All of these frequencies are present simultaneously but as the harmonic is increased, the power decreases until eventually it is very difficult to detect very high order harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9pu14.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9pu14.jpg&quot; alt=&quot;from http://www.informit.com/articles/article.aspx?p=1374896&amp;amp;seqNum=7&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in your case, it is unlikely the Pi is generating a fundamental frequency 91.6 MHz. You can work backwards by dividing 91.6 by odd numbers to see what possible fundamental frequency is being used. The frequency your neighbor observed at 75.6 MHz is also an odd harmonic. The cell phone observation means that there are likely odd harmonics present at 700 MHz or greater. If you spend a little more time with your Pi and an SDR, you will likely see many of the harmonic signals gradually decreasing in amplitude for higher order harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many transmitters take advantage of harmonics to generate transmitted signals that are multiples of its fundamental oscillator. But good design practices (and a plethora of regulations) dictate that bandpass filters be used so that the transmitted signal consists primarily of the desired harmonic. The fundamental frequency and all other undesired harmonics are greatly reduced in amplitude to the point of being negligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Experimenting&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I applaud experimenting as a learning vehicle. Be aware of the regulations that govern your experiments so you don't run afoul of them. Experimenting with very low power and no antenna in a basement helps to keep your experimentation contained. Consider building a bandpass filter and then compare your Pi output to your original findings using the SDR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;FCC Regulations&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Part 15 designation that your Pi carries refers to its classification as a &quot;non-intentional radiator&quot;. When you turn your Pi into a transmitter, it is then an &quot;intentional radiator&quot; under part 15. The regulations allow you to transmit a signal with a field strength of 150 μvolts/meter measured at a 3 meter distance throughout the 88-216 MHz range (ref CFR 47.15.209). So you are not prohibited from transmitting in this range but you must restrict your signal to these relatively low power levels (expressed as a field strength). The nice part is that as you go higher in frequency, you are actually allowed a stronger field strength. But your harmonic frequency field strength will go down as frequency goes up. So if you are in compliance on the 88-216 MHz range, you should automatically be on all higher frequencies provided that you do not have any amplification or filtering stages that would alter the naturally decaying amplitude of the higher order harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Part 15 regulations can be very confusing when trying to interpret them for a particular circumstance. The ARRL (American Radio Relay League) has a nice layman's overview of Part 15 &lt;a href=&quot;http://www.arrl.org/part-15-radio-frequency-devices&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-02-28T01:01:39.657" LastActivityDate="2018-02-28T01:01:39.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9959" PostTypeId="1" CreationDate="2018-02-27T17:58:18.417" Score="1" ViewCount="103" Body="&lt;p&gt;I want to experiment with different mechanical designs for some Yagi antennas for 440 MHz through perhaps 2.3 GHz. I am looking for some adhesives and/or potting-like materials that would be relatively RF-inert at those frequencies. Can anyone make a suggestion for a material?&lt;/p&gt;&#xA;" OwnerUserId="8573" LastEditorUserId="76" LastEditDate="2018-02-27T18:57:45.263" LastActivityDate="2018-02-28T17:41:57.463" Title="RF inert adhesive for building antennas in the UHF to low GHz region" Tags="&lt;antenna-construction&gt;&lt;uhf&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9961" PostTypeId="2" ParentId="9959" CreationDate="2018-02-27T22:18:52.600" Score="2" Body="&lt;p&gt;Take a look at &lt;a href=&quot;http://www.epicresins.com/ElectronicsPotting/RFdevices&quot; rel=&quot;nofollow noreferrer&quot;&gt;Epic Resins&lt;/a&gt;. They have epoxies and potting compounds that are characterized into the GHz range. &lt;a href=&quot;https://www.masterbond.com/industries/adhesives-microwave-and-rf-applications&quot; rel=&quot;nofollow noreferrer&quot;&gt;Master Bond&lt;/a&gt; is another possible source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do be aware that when assembling antennas using epoxy, that it can act as a dielectric material. This can affect the primary design parameters of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-02-28T17:41:57.463" LastActivityDate="2018-02-28T17:41:57.463" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9962" PostTypeId="1" AcceptedAnswerId="16875" CreationDate="2018-02-28T13:39:49.817" Score="3" ViewCount="532" Body="&lt;p&gt;Is there a complete and programming language independent specification available for the &lt;a href=&quot;http://qrznow.com/new-digital-mode-from-k1jt-ft8/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FT8&lt;/a&gt; digital mode?  Detailed enough to implement both transmit and receive SDR software from scratch in two different programming languages?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, for what popular digital modes are full (programming language and computer independent) specifications available?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The goal is to have a target for an advanced SDR programming exercise in an any arbitrary (Turing and computationally complete) programming language (such as Perl or Swift or Basic or ARM m0 assembly, etc.). This would be for the software equivalent of building ones own radio from basic components (L, C, R, FETs, tubes, wires, etc. -&gt; lines-of-code of elementary ops)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added: A specification for reliable very-weak-signal (below the noise floor) protocol that is legal to use in within the U.S. amateur bands is preferred.  A specification that requires advanced programming and DSP knowledge is not a problem.  I do not consider code (other than platform-agnostic algorithmic pseudo-code) or precompiled binaries to be a proper specification.  It would be desirable to have the specification complete enough that two independent teams using two different programming languages and platforms could interoperate (communicate) using their implementations of the specified protocol.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-03-02T02:24:33.443" LastActivityDate="2020-07-10T03:11:22.930" Title="Is there an FT8 or other weak-signal digital mode specification available?" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;&lt;software-development&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9963" PostTypeId="2" ParentId="9436" CreationDate="2018-02-28T14:09:55.590" Score="0" Body="&lt;p&gt;From a mathematical point of view, any finite length (e.g. keyed) signal has infinite bandwidth.  You can reduce the side-bands by choosing a keying envelope whose FT has low sidebands, which implies slowed rise/fall times of the envelope and to a diminishing degree all its derivatives.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-02-28T14:09:55.590" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9964" PostTypeId="2" ParentId="9962" CreationDate="2018-02-28T14:25:10.670" Score="1" Body="&lt;p&gt;I don't believe FT8 has a complete specification besides the source code, which is openly available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RTTY is an option. It doesn't need much of a specification since it's so damn simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PSK-31 is marginally less simple. &lt;a href=&quot;http://www.arrl.org/psk31-spec&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL hosts a specification&lt;/a&gt;, among others. The QPSK variant has very basic FEC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On HF, I don't know what more exists which may qualify as &quot;popular&quot;. If &quot;you can find it on the air sometimes&quot; is popular enough, then you have some more options:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's &lt;a href=&quot;https://freedv.org/freedv-specification/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV&lt;/a&gt;, though the modulation isn't really much more interesting than PSK-31 and there's no FEC. All the complexity here is in &lt;a href=&quot;http://www.rowetel.com/?page_id=452&quot; rel=&quot;nofollow noreferrer&quot;&gt;the codec&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a little &lt;a href=&quot;http://www.drm.org/specification/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Digital Radio Mondiale&lt;/a&gt; activity on HF, from WinDRM and EasyPAL. Ostensibly. I'm not sure if these programs really follow the DRM specification. You could always tune in to DRM broadcasters outside the amateur bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF has a few more options, kinda. &lt;a href=&quot;http://www.etsi.org/deliver/etsi_ts/102300_102399/10236101/02.02.01_60/ts_10236101v020201p.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;DMR&lt;/a&gt; is well-specified, but uses AMBE, a proprietary codec. I can't find an official looking specification for D-STAR, but if you don't mind piecing some things together it's out there. It also uses AMBE. Finally there's &lt;a href=&quot;http://www.project25.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;P25&lt;/a&gt;: its &lt;a href=&quot;http://www.project25.org/images/stories/ptig/20160128_Approved_P25_TIA_Standards_Q1-2016.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;standards&lt;/a&gt; seem to be downloadable if you search around. Again, proprietary codec.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know about DMR and P25, but D-STAR has a bit in the header which indicates a raw data rather than voice payload. I don't know if you'll find any of this on the air, though I've heard of hams deploying it in special situations. Might be a possibility if you want something you can implement fully without proprietary components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, you can offload the AMBE coding to a &lt;a href=&quot;http://nwdigitalradio.com/thumbdv-ordering-now-open/&quot; rel=&quot;nofollow noreferrer&quot;&gt;ThumbDV&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-03-01T02:02:15.407" LastActivityDate="2018-03-01T02:02:15.407" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9965" PostTypeId="2" ParentId="9955" CreationDate="2018-02-28T14:28:00.850" Score="0" Body="&lt;p&gt;Connecting an antenna to a Raspberry Pi GPIO (usually 4 or 18) clocked at HF/VHF rates without a low-pass filter (and band-pass filter for higher frequencies) is a bad idea.  This filtering is required to remove digital waveform harmonics before they get to any sufficiently radiating antenna.  The Part 15 certification is only for the Pi board/module with no added antennas.  Even long proto-board wires can cause local interference when connected to clock signals toggling at high enough rates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It might be possible to meet legal transmission requirements in the broadcast FM band in certain jurisdictions by sufficiently (low pass) filtering the GPIO output signal before it reaches a small enough (gain limited) antenna.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-02-28T14:35:38.817" LastActivityDate="2018-02-28T14:35:38.817" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9966" PostTypeId="1" AcceptedAnswerId="9968" CreationDate="2018-02-28T18:03:22.440" Score="2" ViewCount="78" Body="&lt;p&gt;The small antenna itself has an &lt;span class=&quot;math-container&quot;&gt;$S_{11}$&lt;/span&gt; of -3 dB around MICS band (verified with simulation and network analyzer). In application, the antenna is mounted on a transceiver PCB of 30*15*0.8 mm which has 2 metal layers. From simulation, including the PCB into the antenna model (by modeling it as a thin cubic with 2 metal faces) made the &lt;span class=&quot;math-container&quot;&gt;$S_{11}$&lt;/span&gt; reach to -15 dB, with an increase of 50 MHz in resonant frequency and the &lt;span class=&quot;math-container&quot;&gt;$S_{11}$&lt;/span&gt; curve gets a lot sharper. The small antenna is quite poor as a radiator because there is a dimension restrict for the device. I guess adding the PCB just improves impedance matching with no contribution to radiation. My question is how should I conclude the influence from the PCB. Is it a grounding effect, or coupling, or extra impedance?&lt;/p&gt;&#xA;" OwnerUserId="11250" LastEditorUserId="8717" LastEditDate="2019-11-05T19:36:45.420" LastActivityDate="2019-11-05T19:36:45.420" Title="How to consider the influence from the PCB that a small antenna is mounted on?" Tags="&lt;antenna-theory&gt;&lt;impedance-matching&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="9967" PostTypeId="1" AcceptedAnswerId="9969" CreationDate="2018-03-01T08:05:42.820" Score="1" ViewCount="599" Body="&lt;p&gt;What type is the DC jack on the Baofeng UV5R base charger? I want to buy a splitter so that I can charge multiple radios with the same car/wall charger.&lt;/p&gt;&#xA;" OwnerUserId="11251" LastEditorUserId="76" LastEditDate="2018-03-01T14:50:16.710" LastActivityDate="2019-07-15T23:28:13.573" Title="DC connector type for Baofeng UV5R base charger" Tags="&lt;baofeng&gt;&lt;uv-5r&gt;&lt;dc-power&gt;&lt;battery-charging&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9968" PostTypeId="2" ParentId="9966" CreationDate="2018-03-01T12:31:58.883" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The small antenna is quite poor as a radiator because there is a dimension restrict for the device.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It is important to separate cause and effect when designing antenna systems. Recall that the directivity of an infinitesimally small dipole has a directivity of 1.5 compared to a full size 1/2 wavelength dipole with a directivity of 1.64. That is less than a 0.5 dB difference in gain if the antenna systems have the same efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The key issue to focus on with small antenna systems is efficiency (R&lt;sub&gt;r&lt;/sub&gt; and R&lt;sub&gt;l&lt;/sub&gt;). This puts the antenna, its matching circuits, transmission lines, and the PA design under scrutiny to wring out every bit of possible efficiency improvement. For example, I often see students and experienced engineers struggling to match a 50 ohm PA output to a low impedance, compromise antenna. What they fail to consider is that the naturally low output impedance of the PA is undergoing an unnecessary and lossy double impedance transformation. So look at the problem from a systems approach and not just as an antenna design exercise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the end, you are trying to optimize a compromise based on cost, performance, reliability, and time to market.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My question is how should I conclude the influence from the PCB. Is it a grounding effect, or coupling, or extra impedance?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You haven't given adequate geometric details to fully consider this question. But in general, the PCB material will act as a dielectric that is in the near field of the antenna. As such it will exhibit resistive losses (think efficiency!), it can alter the distributed inductance or capacitance of the antenna thereby shifting the optimal operating frequency (from a matching perspective), and it can introduce phase delay in the near fields.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;...made the &lt;span class=&quot;math-container&quot;&gt;$S_{11}$&lt;/span&gt; reach to -15 dB, with an increase of 50 MHz in resonant frequency and the &lt;span class=&quot;math-container&quot;&gt;$S_{11}$&lt;/span&gt; curve gets a lot sharper. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The &lt;span class=&quot;math-container&quot;&gt;$S_{11}$&lt;/span&gt; parameter is only an issue when considering the matching circuit. As a secondary indicator, however, when &lt;span class=&quot;math-container&quot;&gt;$S_{11}$&lt;/span&gt; remains low over a broader frequency range, the Q of the antenna has been reduced. If all other factors are equal, this is a strong indicator of increased losses in the antenna (system). Recall that the &quot;best&quot; and broadest &lt;span class=&quot;math-container&quot;&gt;$S_{11}$&lt;/span&gt; parameter is realized with a fully resistive, non-radiating load.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="13435" LastEditDate="2018-10-24T02:34:55.073" LastActivityDate="2018-10-24T02:34:55.073" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="9969" PostTypeId="2" ParentId="9967" CreationDate="2018-03-01T14:56:55.627" Score="6" Body="&lt;p&gt;The plug used in the Baofeng base is a 5.5 mm/2.1 mm barrel connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you cannot simply parallel a bunch of base charger units and power them off of a single AC or DC adapter without properly considering the total current required. The stock AC wall wart for the charger puts out 10 volts at 0.5 amps. Each charging base will require 0.5 amps. So, for example, if you wish to wire three charging bases in parallel (it won't work in series), you will require a power supply that puts out 10 volts at 1.5 amps (0.5 amps times 3). &lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-03-01T14:56:55.627" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9970" PostTypeId="1" AcceptedAnswerId="9974" CreationDate="2018-03-01T16:00:18.350" Score="1" ViewCount="51" Body="&lt;p&gt;The application is an implanted sensor and I am asked to characterize the transmission channel. I did measurements with bio-equivalent liquid and got a plot of the path loss over distance. The professor asked me to apply the log-distance path loss model to my result and I got a nice figure by fitting the measured results in a semi-log graph. However, I highly doubt if it makes sense as I do not think the wave in the bio-equivalent liquid is the same as that in the air (even with obstacles).&lt;/p&gt;&#xA;" OwnerUserId="11250" LastActivityDate="2018-03-02T12:12:13.180" Title="Is it correct to apply the log-distance path loss model for an in-body radio propagation?" Tags="&lt;propagation&gt;&lt;path-loss&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9971" PostTypeId="2" ParentId="9962" CreationDate="2018-03-01T17:15:18.333" Score="4" Body="&lt;p&gt;The closest I could find to a specification for FT-8 was on the Wikipedia page for WSJT. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In answer to your second question. I lead an open source project that is designing an implementation of the DVB-S2 and DVB-S2X protocols for amateur terrestrial and space use. The uplink is frequency-division-multiple-access. The downlink is the time-division-multiplexed DVB signal. Advanced SDRs are pretty much a requirement here for both development and deployment. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transport layer is not MPEG, but is another standard from DVB called GSE, for generic stream encapsulation. This allows IP data to be shipped over the DVB-S2/X link at much lower overhead, and allows for the operator to use voice, voice memo, text, image, video, or any other data that the application layer prepares. We will not be building in a low-rate codec. We have not been happy with codec performance in any amateur digital product. We recommend high rate CODEC2 or Opus, decided at the application layer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We have really liked working with and learning about DVB-S2/X. You can find our project website at &lt;a href=&quot;https://phase4ground.github.io/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://phase4ground.github.io/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many amateur television enthusiasts have switched to DVB-T, so that's another substantial and completely specified open standard available to amateur radio experimenters. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;All of these specifications (and many more) are open and available at &lt;a href=&quot;https://www.dvb.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.dvb.org/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our uplink is ~75kHz channels of M-ary minimum shift keying. The channels are received by a polyphase filter bank, which in and of itself is a wonderful area to work on. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are channel assignments and we use Adaptive Coding and Modulation (this is included in the specification along with Constant Coding and Modulation and Variable Coding and Modulation modes). Your station will get as much throughput as possible depending on reported signal-to-noise ratios. Adjustments to coding and modulation will be autonomous. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It isn't necessary to limit research consideration to narrowband weak signal modes that I believe would require some reverse engineering to fully specify. &lt;/p&gt;&#xA;" OwnerUserId="8462" LastActivityDate="2018-03-01T17:15:18.333" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9972" PostTypeId="2" ParentId="9930" CreationDate="2018-03-01T18:54:22.517" Score="3" Body="&lt;p&gt;I am no expert on House Wiring, but when mine was done, all the pipes in the house (central heating and water) were all grounded for safety reasons. I believe these were all connected to the main ground in the electrical cupboard where the meter is and the electrician checked to make sure it was a &quot;good earth&quot;. So if you see the Green/Yellow wires attached to your water pipes (copper ones), then attaching an earth to one of those may suffice. I have know amateurs to place a metal spike in the ground and keep it watered in the dry months.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I agree with the others that the winding does need to have the insulation removed to make a good contact with the slider. There has to be a circuit here, not an open circuit.&lt;/p&gt;&#xA;" OwnerUserId="11254" LastActivityDate="2018-03-01T18:54:22.517" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9974" PostTypeId="2" ParentId="9970" CreationDate="2018-03-01T21:50:44.007" Score="3" Body="&lt;p&gt;First consider what the Free Space Path Loss (FSPL) equation is modeling. As power propagates from the transmitting antenna &lt;em&gt;in free space&lt;/em&gt;, it continues to spread out, lowering the power density (watts per square meter) at the receive antenna locus. On the receive side, the effective aperture (square meters) of the receive antenna is fixed for a given frequency. So as the distance is increased, the received power is decreased according to the inverse square law. The balance of the formula adjusts for the gain of the receive and transmit antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider what &lt;em&gt;is not&lt;/em&gt; included in the FSPL equation: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The human body acts as a dielectric. This dielectric will likely introduce additional path loss. The  permittivity ε, permeability μ, and conductivity σ of the human dielectric would have to be included in the model. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FSPL equation requires that the receive and transmit antennas be oriented such that the direction of their stated gains are pointed toward each other. This may not consistently be the case in your application so you may need to include some factor to adjust for potential misalignment of the antennas. In the simple case of polarity misalignment, this could introduce a significant loss factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FSPL equation does not include any effects from absorption, scattering, reflection or refraction of signals. Depending on the frequencies involved, any bones, cartilage, denser tissues, urolithiasis, nephrolithiasis, etc. may cause such effects that would then need to be included in the model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are probably a few additional considerations that are not coming to mind at the moment but the above exemplify the need for a more rigorous model beyond simple FSPL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Testing Methodolgy&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In response to questions by the OP in the comments:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using an SA is an excellent choice provided that the target receiver has been well characterized and documented so as to be able to translate SA observations to the expected receiver performance. The receive antenna, feedline, and feedline length should be identical to the target configuration to avoid errors in projected performance. If the complex input impedance of the SA does not match that of the target receiver, construct and characterize an appropriate impedance transformation network if you are not comfortable with mathematically netting out the effects of the mismatch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding the challenges of modelling or testing a heterogeneous medium, I must say I am not a biomed engineer. But I would consider volunteer, cadaver or animal testing in order to validate my models. The biomed engineering field is well established and may have suitable, qualified models for your application that could raise the confidence level of the prediction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you have completed and have validated your heterogeneous model(s), describe the results in the form of a link budget. You can add a further burden to the budget to ensure an appropriate safety factor. Depending on the application, there may be safety or regulatory requirements that must also be addressed.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-02T12:12:13.180" LastActivityDate="2018-03-02T12:12:13.180" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="9978" PostTypeId="1" CreationDate="2018-03-02T15:00:30.573" Score="1" ViewCount="171" Body="&lt;p&gt;I have &quot;inherited&quot; what I believe to be a G5RV antenna with two 51 foot wire centerfed radiators. If I remember correctly from measuring 2 months ago, there is about 31 feet of 450 ohm ladderline  which then interfaces with the 52 ohm coax through a sealed choke of some sort.  I do not know if it is current balun or voltage balun or whatever. At the far end of the feedline where the coax connects to the transceiver through an antenna tuner, an ohm meter across the coax center conductor and its outter shield shows a virtual short. Am I correct in assuming that that is ok because the choke is essentially one side of a transforrmer coil and I won't hurt the old Yaesu FT901 boat anchor w/ 6146 tube finals upon tune-up? &lt;/p&gt;&#xA;" OwnerUserId="11253" LastActivityDate="2018-03-02T16:09:38.520" Title="Is a &quot;shorted&quot; coax feedline ok for a G5RV type antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;coaxial-cable&gt;&lt;feed-line&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9979" PostTypeId="2" ParentId="9978" CreationDate="2018-03-02T15:19:42.153" Score="2" Body="&lt;p&gt;Yes, it is okay that a DC measurement shows a short.  An antenna analyzer would probably be a better test for you.&lt;/p&gt;&#xA;" OwnerUserId="4748" LastActivityDate="2018-03-02T15:19:42.153" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9980" PostTypeId="2" ParentId="9978" CreationDate="2018-03-02T16:09:38.520" Score="2" Body="&lt;p&gt;It's very difficult to say. The DC short or not isn't relevant: it's the impedance at the transmit frequency that's important, which you'd measure with an antenna analyzer or similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A DC short may or may not be indicative of a problem. There are some balun designs that look like shorts. There are some that do not. Some matching networks include a shunt inductor which makes a DC short. But there may be no such matching network installed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it were my station, I wouldn't make any assumptions. I'd start isolating components until I determined precisely where the short is, and only then make a determination if it's a problem or not.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-03-02T16:09:38.520" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9981" PostTypeId="2" ParentId="1273" CreationDate="2018-03-02T17:17:16.580" Score="1" Body="&lt;p&gt;To me it is kind of like the word &quot;up&quot;.  My dipole is up means something totally different than my computer being up.  It depends on the context.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When hams talk about a DX station, they are normally talking about a DX entity for DXCC award.  As such a DX station could be next door if you haven't worked a station within your own DX entity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other meaning is a &quot;Distance Transmission&quot;.  I general consider any contact that isn't line of sight as DX.&lt;/p&gt;&#xA;" OwnerUserId="4083" LastActivityDate="2018-03-02T17:17:16.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9982" PostTypeId="2" ParentId="9855" CreationDate="2018-03-02T18:58:51.883" Score="0" Body="&lt;p&gt;Because of ITU treaty, all amateurs that transmits on HF must have a license.&lt;/p&gt;&#xA;" OwnerUserId="4083" LastActivityDate="2018-03-02T18:58:51.883" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9983" PostTypeId="1" AcceptedAnswerId="9986" CreationDate="2018-03-02T23:22:05.057" Score="2" ViewCount="902" Body="&lt;p&gt;I've been experimenting with APRS for the last year or so.  There are a lot of areas that I go that don't have digipeaters or iGates.  (Luckily, I live about three blocks from one, so around home I'm good!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm debating building a portable iGate/digipeater... something I can deploy wherever I stay for a few days that can get packets online and repeated, if there isn't good APRS infrastructure nearby.  I'd prefer that this would run under Linux, as that is my preferred operating system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What suggestions can you make for hardware and software?  Something Raspberry Pi-based might be pretty inexpensive to build, and portable, but I'm open-minded.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastEditorUserId="13615" LastEditDate="2018-11-17T16:22:11.447" LastActivityDate="2018-11-17T16:22:11.447" Title="Building a portable APRS iGate/digipeater" Tags="&lt;aprs&gt;&lt;equipment&gt;&lt;portable&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9984" PostTypeId="1" CreationDate="2018-03-03T02:00:18.963" Score="2" ViewCount="907" Body="&lt;p&gt;I want to build a 1:1 unun for a 6M dipole.  Power level 100W.  What core material should I use?&lt;/p&gt;&#xA;" OwnerUserId="11265" LastEditorUserId="8717" LastEditDate="2018-03-03T02:46:25.903" LastActivityDate="2018-04-16T23:34:36.487" Title="What core material do I need to construct a 1:1 unun for 6M?" Tags="&lt;vhf&gt;&lt;balun&gt;&lt;ferrite&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9985" PostTypeId="2" ParentId="9984" CreationDate="2018-03-03T12:55:08.497" Score="1" Body="&lt;p&gt;As Mike Waters points out, your application requires a balun since a 1/2 wave dipole is balanced and the coax is unbalanced. The purpose of the balun is to enforce equal current in both dipole legs. It performs this function by preventing current from flowing on the outside of the coax shield by presenting a high impedance path to exterior shield currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use a toroid form comprised of mix 31 or mix 43 material to construct a 6 meter balun. A 240 size toroid with three or four turns of coax wound uniformly through the toroid will prove effective. Wide, evenly spaced turns are important  to minimize the interwinding capacitance.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-03-03T12:55:08.497" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="9986" PostTypeId="2" ParentId="9983" CreationDate="2018-03-03T15:37:57.343" Score="2" Body="&lt;p&gt;A Raspberry Pi running Direwolf is definitely a reasonable option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a receive-only iGate, a number of people have had success with a Pi and an RTL-SDR dongle, running rtl_fm and direwolf. Nice and easy, no fuss, but of course it won't digipeat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recently built myself a setup using a Pi and the DRA-818V chip (specifically, SV1AFN's DRA-818V board), with a USB soundcard to go between them, and that's worked pretty well too. I use it as a mobile node, not a digipeater, and with only 1W of transmit power, it arguably wouldn't make a very good digipeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could of course try adding an amplifier to that setup, but it's probably a better idea to hook up to a proper radio (perhaps an HT, or a little mobile rig). As long as the radio has some external way to operate the PTT, the same setup of Pi + direwolf + USB sound card will work fine. Direwolf will drive a rasPi GPIO for PTT, so you can generally rig something up using no more than a transistor or two. Or you could use something like a SignaLink in place of the USB soundcard, at the cost of a bit more bulk.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2018-03-03T15:37:57.343" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9987" PostTypeId="2" ParentId="9983" CreationDate="2018-03-03T18:28:06.190" Score="1" Body="&lt;p&gt;The RX iGate with a RTL-SDR dongle is pretty easy to setup. The hard part of a  TX digipeater is keying the radio,like hobbs mentioned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I bought a Argent data systems t3-micro in hopes of making a fill-in digipeater or using a spare mobile radio for TX while driving; depending on that I needed.  I should get back to that project... &lt;/p&gt;&#xA;" OwnerUserId="9083" LastActivityDate="2018-03-03T18:28:06.190" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9988" PostTypeId="2" ParentId="9943" CreationDate="2018-03-03T21:59:22.543" Score="0" Body="&lt;p&gt;I own an FT-60, and I've also been looking to add another Yaesu HT to my collection. An additional &quot;feature&quot; Yaesu is touting with their FT-70s is digital capability, as Digital radio (DMR specifically) is increasing in popularity and use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But there's a catch...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What Yaesu is offering as &quot;digital&quot; is their own proprietary &quot;System Fusion&quot; digital, otherwise known as c4fm, if memory serves. C4fm is not interoperable with DMR, or D-STAR. You -may- be able to get it to hear DMR/DSTAR if you have something like a Shark OpenSpot or some other way to translate between formats. But my Elmers say that won't be easy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73s, WE0IRD&lt;/p&gt;&#xA;" OwnerUserId="11267" LastActivityDate="2018-03-03T21:59:22.543" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="9989" PostTypeId="1" AcceptedAnswerId="9991" CreationDate="2018-03-04T07:39:04.873" Score="1" ViewCount="125" Body="&lt;p&gt;I'm interested in doing some experimentation with custom modulation in the 915 ISM band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Off-the-shelf radio modules use specific known modulations (FSK, QAM, etc.) so those won't work for my purposes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've never built my own transmitter before and wanted to know what parts are recommended to do this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the moment I am thinking of using an AD9850 for the IF of a superhet design, but I don't know what I should use for the up converter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any suggestions or warnings are appreciated.&lt;/p&gt;&#xA;" OwnerUserId="11268" LastEditorUserId="8832" LastEditDate="2018-04-12T16:46:55.023" LastActivityDate="2018-04-12T16:46:55.023" Title="Parts for a 915 MHz low power transmitter" Tags="&lt;diy&gt;&lt;modes&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9990" PostTypeId="2" ParentId="9962" CreationDate="2018-03-04T08:17:53.977" Score="2" Body="&lt;p&gt;I do have the specification for JT9 if that is of interest to you.&#xA;It is currently in the form of a pdf.  Would you like it emailed to you?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or would you prefer I paste it on this forum as ASCII text (where the&#xA;formatting is a bit strange, but...&lt;/p&gt;&#xA;" OwnerUserId="11269" LastActivityDate="2018-03-04T08:17:53.977" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="9991" PostTypeId="2" ParentId="9989" CreationDate="2018-03-04T09:53:31.873" Score="3" Body="&lt;p&gt;What you're describing sounds a lot like a software-defined radio :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, first of all, you can buy these in various degrees of impressiveness.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, you could also consider getting an Quadrature modulator, i.e. a mixer that takes IQ baseband signals on one side and spits out RF signal on the other. Connect that to the cheap DAC you have lying around - your soundcard, and, if it doesn't come with an integrated LO, to an oscillator. Component-wise, analog devices is probably the go-to supplier of such mixers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding warnings: well, whatever you do, a mixer doesn't only produce the intermodulations you want, so be sure to check the spectrum and add band pass filters as appropriate. For quick checking, having a RX-only SDR, even if its only a dozen-of-bucks RTL-SDR, is a helpful tool :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding suggestions on how to generate the signals: no matter whether you use a commercial off-the-shelf SDR or a selfbuilt one, you now can generate your signal in software! That's way more flexible than always having to fiddle with hardware to generate a slightly different waveform. If you're in for a bit of fun on signal generation and analysis: maybe start with the &lt;a href=&quot;https://tutorials.gnuradio.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;GNU Radio Guided Tutorials&lt;/a&gt;; it's how I generate my custom modulations, it comes with an extensive toolbox of existing math and modulation building blocks, and there's plenty of applications out there that use GNU Radio to implement different transmission modes – be it something mundane as simple PSK31 transceivers, or something cool as a full DAB+ implementation. In fact, GNU Radio itself comes with an implementation of many DVB standards, and that's maybe something you'd want to have a look at.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-03-04T11:31:56.583" LastActivityDate="2018-03-04T11:31:56.583" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9992" PostTypeId="1" CreationDate="2018-03-04T16:34:42.127" Score="2" ViewCount="341" Body="&lt;p&gt;Popular amateur radio &quot;below-the-noise-floor&quot; communication modes (such as JT65, et.al.) seem to mostly use FSK, whereas NASA's deep space network appears to use M-PSK for (extremely) weak signal telemetry.  Why would one choose one modulation scheme over the other when designing a (new *) protocol for extremely weak signal QSOs?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(assuming the next layer uses typical interleaving/FEC/ECC/convolutional coding for multi-bit and burst error tolerance, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(* as full specs do not appear to be available for many of these existing amateur radio modes)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-03-06T13:48:11.887" Title="FSK or M-PSK for weak signal communications?" Tags="&lt;modes&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9993" PostTypeId="1" CreationDate="2018-03-04T18:21:42.700" Score="2" ViewCount="7454" Body="&lt;p&gt;&lt;strong&gt;If I connect two antennas to one radio using a t connector will it work?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a connect 2 antennas (a mag mount + a dipole?) to the same radio with an adapter will it work normally on 2M band and will it cause extra interference?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, if it works would this give me an added range/better signal over using just one of the antennas?&lt;/p&gt;&#xA;" OwnerUserId="11270" LastEditorUserId="8832" LastEditDate="2018-04-12T16:45:14.167" LastActivityDate="2019-04-04T13:55:24.130" Title="If i connect two antennas to one radio using a t connector will it work?" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;wire-antenna&gt;&lt;2m-band&gt;" AnswerCount="4" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="9994" PostTypeId="2" ParentId="9993" CreationDate="2018-03-04T19:50:29.463" Score="6" Body="&lt;p&gt;For receiving it should work up to a certain level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the impedance will be completely different from that of a single antenna. So the SWR will be too high for transmitting and reception will normally be less efficient than with a single antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to use two different antennas is to use a coax switch.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastEditorUserId="8573" LastEditDate="2018-04-30T12:51:52.467" LastActivityDate="2018-04-30T12:51:52.467" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9995" PostTypeId="2" ParentId="9992" CreationDate="2018-03-04T21:17:36.530" Score="4" Body="&lt;p&gt;First, we should be clear that neither of these modulation methods allow signals below the noise floor to be decoded. The oft quoted -dB figures for FT-8 et al are really quoting the signal strength below the noise floor of an audio bandwidth  of ~ 2.5 kHz. But through digital signal processing of the audio channel, these modes are actually using an occupied bandwidth of 50 Hz or less. So if the reported SNR ratio was based on the actual data bandwidth, the reported signal strength would be well above the noise floor. The noise floor in dB (watts) of a receiver is determined by the bandwidth of the receiver:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$${Noise Floor} = 10\log_{10}(kTB) \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where k is the Botlzmann's constant (1.38064852×10&lt;sup&gt;−23&lt;/sup&gt; J/K), T is the temperature in Kelvins, and B is the bandwidth in Hertz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So using equation 1, we can see that a 50 Hz receiver bandwidth has ~17 dB noise floor advantage over a 2.5 kHz receiver bandwidth. Since the noise floor of a 50 Hz bandwidth is ~17 dB lower, the signal to noise ratio  (SNR) expressed in dB improves by the same ~17 dB. This is the same effect we see when comparing the ability to copy an SSB signal compared to a CW signal using a narrower receive bandwidth. But reducing the bandwidth comes at the price of a reduced data rate reaching the limit expressed by the Shannon-Hartley formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$C=B\log_2(1+\frac{S}{N}) \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where C is the maximum channel capacity, B is the channel bandwidth in Hertz, S is the signal strength in Watts, and N is the noise power in Watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding the modulation modes, PSK has an approximately 3 dB SNR advantage over other modes. The reason we do not see it commonly deployed on HF is that the standard amateur radio transceiver does not support carrier phase modulation so AFSK or APSK are the only viable means of modulation. If we were to develop special purpose HF transceiver capable of supporting carrier PSK modulation, we could capture an additional 3 dB of SNR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MPSK reduces the complexity of the receiver since there is no requirement to acquire/track the carrier as there would be with PSK. Here is a synopsis of a decoding technique described in IEEE Transactions on Communications (ISSN 0090-6778); 38; 300-308:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A differential detection technique for MPSK (multiple-phase shift keying), which uses a multiple-symbol observation interval, is presented, and its performance is analyzed and simulated. The technique makes use of maximum-likelihood sequence estimation of the transmitted phases rather than symbol-by-symbol detection as in conventional differential detection. Thus, the performance of this multiple-symbol detection scheme fills the gap between conventional (two-symbol observation) differentially coherent detection of MPSK and ideal coherent of MPSK with differential encoding. The amount of improvement gained over conventional differential detection depends on the number of phases M and the number of additional symbol intervals added to the observation. What is particularly interesting is that substantial performance improvement can be obtained for only one or two additional symbol intervals of observation. The analysis and simulation results presented are for uncoded MPSK. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-06T10:25:29.877" LastActivityDate="2018-03-06T10:25:29.877" CommentCount="14" ContentLicense="CC BY-SA 3.0" />
  <row Id="9996" PostTypeId="2" ParentId="9993" CreationDate="2018-03-05T00:32:18.793" Score="8" Body="&lt;p&gt;Assuming that both antennas are 50 Ω resistive, they will combine in parallel for a 25 Ω load impedance when transmitting. This will cause the transmitter to see a 2:1 SWR. This is a 0.333 voltage reflection coefficient so ~11% of the transmitter power will be returned to the transmitter from the tee junction. The remaining 89% of the power will be split between the two antennas resulting in approximately 44% of power to each antenna. The net effect is an ~ 3.5 dB loss to each antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above scenario assumes that the transmitter does not further fold back the output power as part of an SWR protection mechanism nor does the transmitter final burn out due to elevated SWR. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to deploy an antenna with additional gain, you will be far more successful with a purpose built antenna for that purpose.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="4076" LastEditDate="2018-03-05T17:36:45.150" LastActivityDate="2018-03-05T17:36:45.150" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="9997" PostTypeId="1" AcceptedAnswerId="9998" CreationDate="2018-03-05T09:49:46.583" Score="0" ViewCount="1217" Body="&lt;p&gt;I am a big fan of the Yaesu FT-450D but there is one really frustrating quirk that took some time to figure out.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FT-450 has a keyer jack on the front panel.  It is the lower of two 1/8 inch jacks at the upper left.  The labeling is not highlighted very well, but can be seen with enough light.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.radiomanual.info/schemi/YAESU_HF/FT-450_user.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yaesu FT-450D User Manual [PDF]&lt;/a&gt; describes how to use this jack on manual pages 46-48 in the PDF version, which correspond to pages numbered 44-46 in the printed version.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To enable keyer mode you must first be set to USB and CW modes.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To begin, press the &lt;kbd&gt;KEYER&lt;/kbd&gt; button.  The KEYER indicator lights up on the screen to confirm it.  This enables the sidetone but does not activate the transmitter.  This is handy in order to confirm your wiring and for practice with the paddles..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to use it on the air you press the &lt;kbd&gt;F&lt;/kbd&gt; button then the &lt;kbd&gt;VOX/STO&lt;/kbd&gt; button.  The BK-IN indicator will light up to indicate that it will activate the transmitter in QSK mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When a straight key is plugged with a mono 1/8 inch plug, it generates a side tone for practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The jack is touchy, so the plug might need to be jiggled in order for it to work correctly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To use paddles requires the use of a stereo plug, where the tip is for dit and the middle is for dah, as switched to ground by the paddles.  (This can be swapped in software as described in the manual)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my problem was when I plugged in my paddles.  They would not activate the keyer at all.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This particular set of paddles:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/stiaP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/stiaP.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which provide a 1/8 inch stereo jack output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connected to the rig by an audio-quality male-to-male 1/8 inch stereo pigtail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are no menu changes necessary to switch between straight keys and paddles.  The radio is smart enough to know the difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My problem is that the straight key works fine but the paddles are not responding at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question:  How to make it work?  I know I have all the correct components.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-03-05T09:57:58.370" LastActivityDate="2018-04-01T04:06:43.203" Title="Yaesu FT-450D How to troubleshoot problems with the Keyer jack" Tags="&lt;yaesu&gt;&lt;connectors&gt;&lt;paddles&gt;&lt;ft-450d&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="9998" PostTypeId="2" ParentId="9997" CreationDate="2018-03-05T09:49:46.583" Score="0" Body="&lt;p&gt;Turns out that the stereo jack on the FT-450 is very picky about the connectors.  Not to say it is a bad design but when it doesn't work it can be frustrating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The solution was to simply turn the cable around.  The radio is not happy with one of the connectors but is very happy with the other end.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moral of the story:  The jack on the radio is not very tolerant of connectors that are not exactly perfect.  Jiggling can sometimes help but not always.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the paddles are working great with the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Go figure.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;This setup works great now.  The paddles have non-stick rubber feet and is just heavy enough that it can be used without having to fasten it down.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It helps to use a padded mouse pad for wrist support.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-04-01T04:06:43.203" LastActivityDate="2018-04-01T04:06:43.203" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10000" PostTypeId="1" CreationDate="2018-03-05T15:58:26.493" Score="1" ViewCount="287" Body="&lt;p&gt;What HF transceivers will support remote operation without requiring a computer at the remote station?&lt;/p&gt;&#xA;&lt;p&gt;Here's a start:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;ICOM 7610&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Flex Radios (not sure which)&lt;/p&gt;&#xA;&lt;p&gt;Any others?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="5516" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-03-06T21:58:03.217" Title="Which HF transceivers can be operated remotely via Ethernet port without a host computer?" Tags="&lt;remote-control&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10001" PostTypeId="2" ParentId="9993" CreationDate="2018-03-05T17:19:31.623" Score="7" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I connect two antennas to one radio using a t connector will it work? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That depends on your t-connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your tee really is just a branch in the inner conductor and connected outer conducters, than the other two answers are correct: your input impedance will be different than your output impedance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If, however, the tee is meant to be used in a system with constant impedance, and most are, then it's going to be built in a way that matches all inputs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your specific case, there's good reason to simply implement such a splitter yourself, as you want to have control over the splitting/combination. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The typical way to do that here is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers#Wilkinson_power_divider&quot; rel=&quot;noreferrer&quot;&gt;&lt;em&gt;Wilkinson Power Divider&lt;/em&gt;&lt;/a&gt; in coaxial implementation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/en/4/48/Wilkinson_divider.png&quot; alt=&quot;Wilkinson Divider in coax impl&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that, not only do you split the power half and half (if you transmit into P1), or combine with equal gain (if you receive on P2 and P3), but you also &lt;em&gt;isolate&lt;/em&gt; P2 and P3, meaning that no power from P2 ends up on P3 and vice versa.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was just assuming you're using 50Ω line; if you're not, that $\frac\lambda4$ piece needs to be $\sqrt2$ of your system's impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;71Ω might be hard to get, 75 Ω usually easy; the mismatch should be minimal.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If a connect 2 antennas (a mag mount + a dipole?) to the same radio with an adapter will it work normally on 2M band &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What's &quot;normally&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess no, this is not going to work like you expect: you combine/split equally. That means you've just built an antenna array out of two completely different antennas. That array will have a directive gain depending on the phase, efficiency and relative position of the two antennas that will be practically impossible to predict without extensive simulation.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;and will it cause extra interference?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Interference will be picked up as before, but you have a directional antenna now. So, you might be getting more or less interference, depending on where your sources of interference are relative to the antenna system pattern described above.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Also, if it works would this give me an added range&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Only if the above directional gain points in the direction you want to work&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;/better signal&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;same&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;over using just one of the antennas?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What you want to have seems to be &lt;em&gt;diversity gain&lt;/em&gt;. ON5MF's answer actually already describes one diversity reception method: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Selection combining, where you simply switch to the one antenna that has better SNR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming you place the two antennas far enough so that their reception paths are uncorrelated, you'd get a diversity gain of 50% (assuming independent, Rayleigh-distributed paths). That means, having the second antenna to select from gives you, on average, an SNR that you work with that's 50% better than if you had nothing to choose from.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you'd want to have real combining gain, you'd need two independent receivers. Ideally, you'd do &lt;em&gt;optimum combining&lt;/em&gt; (since you mention the presence of interference), but to limit complexity here, you'd normally just start with two synchronous receivers, and add up their signals, weighted with a factor that has an amplitude that reflects the SNR of that single receiver, and a phase correcting the receive phase. That would give you an SNR that is the sum of the two received SNRs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This second solution, however, would require a dual-channel synchronous SDR solution, and I'd guess you don't have that lying around, so:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As ON5MF suggested, get a switch. A good idea would be to monitor the &quot;unused&quot; channel with a cheap RTL-SDR to notice if the signal strength or interference level suddenly changes and switching might make sense again.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-03-05T17:19:31.623" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10002" PostTypeId="2" ParentId="9992" CreationDate="2018-03-05T17:34:52.127" Score="4" Body="&lt;p&gt;We'll have to lay down some rules for the comparison:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For a fair comparison, the energy per bit in each scheme under consideration is constant. So, a &quot;fair&quot; alternative would be switching from 4-PSK to 8-PSK while maintaining the same transmitter power and halving the symbol rate.&lt;/li&gt;&#xA;&lt;li&gt;Likewise, the noise spectral density is constant.&lt;/li&gt;&#xA;&lt;li&gt;Forward error correction, interleaving, etc. are not considered, as it's assumed these methods would be applied with equal efficacy regardless of the underlying modulation.&lt;/li&gt;&#xA;&lt;li&gt;&quot;Weak signal&quot; means we wish to maximize the probability of correctly decoding a bit under noise-limited conditions.&lt;/li&gt;&#xA;&lt;li&gt;The comparison is in an additive white Gaussian noise (AWGN) channel, that is one where there's only white noise, and no multipath, etc.&lt;/li&gt;&#xA;&lt;li&gt;Frequency shift keying and phase shift keying are the only options.&lt;/li&gt;&#xA;&lt;li&gt;Implementation details (complexity, non-ideal properties of the receiver, etc) are irrelevant.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If we consider just &lt;em&gt;binary&lt;/em&gt; phase shift keying or frequency shift keying, PSK wins handily. You can even halve the symbol rate and use 4-PSK, and get the same performance as 2-PSK in half the bandwidth. The bit error rates for binary PSK and coherently detected&lt;sup&gt;1&lt;/sup&gt; binary FSK are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{b(BPSK)} = Q \left( \sqrt{2E_b \over N_0} \right) \tag 1 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ P_{b(BFSK)} = Q \left( \sqrt{E_b \over N_0} \right) \tag 2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $N_0$ is the noise spectral density, $E_b$ the energy per bit, and Q a scaled version of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Error_function&quot; rel=&quot;nofollow noreferrer&quot;&gt;error function&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ Q(x)=\operatorname {erfc} \left({\frac {x}{\sqrt {2}}}\right),\ x\geq 0 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note the $2$ in the $2E_b$ factor of equation 1 means transmitter power goes twice as far for BPSK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4-PSK has the same BER as 2-PSK: it is effectively 2 orthogonal 2-PSK signals. It's easy enough to understand intuitively, examining the constellation diagram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VEPLa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VEPLa.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each symbol contains two bits. If we're left of the vertical axis, the first bit is a 0. Otherwise it's a 1. Since the first bit is determined only by the position left or right, the position up or down is irrelevant, or orthogonal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Orthogonality is key. Taking this idea further to 8-PSK results in an increase in BER since the symbols are no longer orthogonal.²&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:PSK_BER_curves.svg#/media/File:PSK_BER_curves.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/7/77/PSK_BER_curves.svg/1200px-PSK_BER_curves.svg.png&quot; alt=&quot;PSK BER curves.svg&quot;&gt;&lt;/a&gt;&lt;br&gt;&lt;i&gt;By &lt;a href=&quot;//commons.wikimedia.org/wiki/User:Splash&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;User:Splash&quot;&gt;Splash&lt;/a&gt; - Own work, &lt;a href=&quot;http://creativecommons.org/licenses/by-sa/3.0/&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Creative Commons Attribution-Share Alike 3.0&quot;&gt;CC BY-SA 3.0&lt;/a&gt;, &lt;a href=&quot;https://commons.wikimedia.org/w/index.php?curid=2196675&quot; rel=&quot;nofollow noreferrer&quot;&gt;Link&lt;/a&gt;&lt;/i&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now back to FSK. With binary FSK there are two tones, each conveying a 1 or a 0. But as with PSK the order can be increased: if we have 4 tones, each maps to two bits. With eight possible tones, a single tone conveys 3 bits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With PSK, as the order was increased the bandwidth went down and the error rate went up. With FSK the opposite happens. This is because unlike PSK, with FSK we can add more tones while retaining orthogonality, provided there's sufficient bandwidth to space them apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why does this work? Imagine a receiver that looks at a single frequency and has to decide if a tone is present there or not. At some transmitter power and tone period this will work reliability, and each period communicates one bit. Say tone present = 1, and absent = 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if there are 16 such receivers, the detection of a tone present communicates not one bit but four (there are sixteen possible combinations of four bits). The more possible tones, the more bits are communicated per tone, with no additional transmitter power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or equivalently, we could slow the symbol rate but hold the bit rate constant, putting more time and thus energy into each tone and making it easier to detect. Conveniently, decreasing the symbol rate also decreases the minimum spacing between the tones to maintain orthogonality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.atlantarf.com/FSK_Modulation.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Atlanta RF provides a nice graph&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/a9g1Y.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/a9g1Y.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The weak-signal performance-enhancing properties of wide bandwidths are reflected in the (modified here to assume white Gaussian noise) Shannon-Hartley theorem:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ C =  B \log_2 \left( 1+\frac{S}{N_0 B} \right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$C$ is the channel capacity, in bits per second&lt;/li&gt;&#xA;&lt;li&gt;$B$ is the bandwidth, in hertz&lt;/li&gt;&#xA;&lt;li&gt;$S$ is the signal power, in watts&lt;/li&gt;&#xA;&lt;li&gt;$N_0$ is the noise power spectral density, in watts per hertz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So while increasing the bandwidth does decrease the SNR term, it increases the $B$ term faster.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;1: Coherent FSK detection is the most complex, and most accurate method of detection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2: However, it does improve spectral efficiency. Many applications are bandwidth limited, so higher-order constellations are popular. For example, Wi-Fi uses at the higher data rates 64-QAM to cram the highest bit rate possible in the limited bandwidth available.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-03-06T13:48:11.887" LastActivityDate="2018-03-06T13:48:11.887" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10003" PostTypeId="1" AcceptedAnswerId="10004" CreationDate="2018-03-05T19:32:32.663" Score="1" ViewCount="192" Body="&lt;p&gt;Electric fence RFI is ruining reception on our &lt;a href=&quot;http://en.blitzortung.org/forum.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;VLF lightning receivers&lt;/a&gt;, and we need a material to place around neighbors' fence wires to suppress the noise being radiated. Preferably, a &lt;strong&gt;split&lt;/strong&gt; bead, because the fence charger is not readily accessible and everything belongs to someone else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.fair-rite.com/product-category/suppression-components/round-cable-emi-suppression-cores/low-frequency-200-khz-30-mhz-75-material/&quot; rel=&quot;nofollow noreferrer&quot;&gt;This is the lowest freq stuff that I've found&lt;/a&gt;. It's range is 200 kHz to 30 MHz.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-05-04T20:16:41.363" LastActivityDate="2020-05-04T20:16:41.363" Title="Need a ferrite suppression material for choking 15 kHz to 60 kHz" Tags="&lt;rfi&gt;&lt;ferrite&gt;&lt;vlf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10004" PostTypeId="2" ParentId="10003" CreationDate="2018-03-05T19:49:14.733" Score="5" Body="&lt;p&gt;I don't think it will work to add suppression to the fence. The fence charger is designed to support heavily reactive loads by generating pulses every second or two. The pulses are formed by dumping the charge of a capacitor bank through a step up transformer. Any additional reactance will be a very minor load delta.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My experience (several miles of e fence here) shows that interference is usually the result of a poor grounding field for the charger or arcing along the circuit e.g. insulators, buried wire, gates, or lightning arrestors. If it is an old &quot;weed burning&quot; charger, it should be replaced for safety and interference sake.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, though, ferrite materials are not suitable for low frequency applications. Look at powdered iron materials like #26 instead.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-05T23:33:16.863" LastActivityDate="2018-03-05T23:33:16.863" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10005" PostTypeId="2" ParentId="10000" CreationDate="2018-03-05T21:41:24.337" Score="-3" Body="&lt;p&gt;As to the second part of your question I would add the IC-7200, which I studied recently.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Yaesu FT-450D has a serial port which I use with a USB converter to send commands like channel programming, and in fact has a program which duplicates the front panel on-screen.  So Ethernet is not required for control of the FT-450D.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;As to the primary question, the short answer is that there isn't any such thing, as worded in the OP.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Here is why:  Ethernet itself is simply a cable with specific wiring.  In order to use it effectively you need devices that can send the proper voltages and data pulses to communicate data.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, in order to actually do anything with it there must be a device on the other end of the cable sending commands to the radio.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now we get down to the definition of a &quot;host computer&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, an Arduino with an Ethernet shield could be used to send commands to such a radio.  (Not saying this would be easy).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Arduinos are classified as &quot;microcontrollers&quot; - yet by my definition I would call them little computers since they are programmable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Raspberry Pi is a small inexpensive Linux computer with a built-in Ethernet port and could potentially be used to send commands to such radios.  (Again, not saying it would be easy - Linux software for these radios is not well-developed)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short, my opinion (and practice) is that to get the most out of any kind of data connection with such radios, what you will find most useful is a Windows computer.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It can be a small laptop (like I use with my FT-450D).  I run Windows 7 and the software works great.  The computer came from Walmart for $88 on rollback - an HP 3115m.  But then I added a Solid-State Drive and topped off the memory, plus bought the ADMS-450 programming software, bringing the cost up to a couple of hundred in total.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am very glad to be able to program my radio this way.  it is well worth it just to be able to program the channels.  I very rarely use the full front-panel program.  The radio is right next to me so I do not need any kind of remote control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't quite understand the motivation for asking this question, but it probably isn't money since these are expensive radios to start with.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my case I saved a couple of hundred by buying the FT-450D instead of the IC-7200, then used that savings to pay for the laptop.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are on the right track investigating these issues.  But it would make the most sense to use the full potential of what you pay for, IMHO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this answer helps.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;ADDITIONAL INFORMATION IN IN COMMENTS THAT ARE NOT IN THE OP:  The control point is 4200 km from the transceiver.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Answer:  There are many examples of doing this such as Echolink.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rest of my answer stands, as it would definitely require a computer at the control point, even if all it runs is Echolink software or a browser.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no such radio that can do this without a computer at the control point(s) and to provide the Internet tunnel(s).&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-03-06T21:58:03.217" LastActivityDate="2018-03-06T21:58:03.217" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10006" PostTypeId="1" CreationDate="2018-03-05T23:30:28.003" Score="3" ViewCount="319" Body="&lt;p&gt;If somebody were to setup a pirate radio signal that was broadcasting static would the people tuned in to that frequency be able to tell?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that there was nothing already on that frequency what kind of equipment would one need to be able to tell that this static was being broadcast and was distinct from the static that occurs in absence of any signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’m assuming that if people tried to use that frequency and found that their signal was being jammed they would know and could triangulate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there some measure of power that would come through or would the broadcast static be indistinguishable from no signal?&lt;/p&gt;&#xA;" OwnerUserId="11278" LastEditorUserId="76" LastEditDate="2018-03-06T17:39:18.497" LastActivityDate="2018-03-08T00:57:53.960" Title="Can jamming a channel with white noise be detected?" Tags="&lt;rfi&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="10007" PostTypeId="1" CreationDate="2018-03-06T03:45:56.777" Score="3" ViewCount="1042" Body="&lt;p&gt;I have a detached garage that is approximately 15 feet high.  The garage is approximately 20 feet from my home  I will be using a Kenwood D-710GA radio, a Grandmaster SWR Meter and a 6 foot comet GP-3 antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’m thinking of using a 2” pipe as a mast.  The pipe will be driven 4 feet into the ground and mounted to the concrete side of the garage.  I’d appreciate your thoughts on the following:  I’ve read an antenna mast should extend 3 foot above the antenna.  Is this necessary?  I was thinking of terminating the pipe 3 foot higher than the garage and attaching the antenna to this part.  The antenna would be 6 foot above the roof of the garage (a three foot overlap of the pipe/antenna). Will this work and be safe?  Or, do I have to extend the pipe 9 foot above the roof (6 foot for the antenna and 3 additional feet).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition to the pipe being driven into the ground and attaching it to grounding rods is there anything else I can do to make sure the antenna is properly grounded?   One last question.  For safety reasons I plan to disconnect the coax from the radio when there is a chance of rain.  Is there anything else I can do to reduce the possibility of my equipment being damaged or someone being hurt if the antenna is hit by lightning?  Thank you for your help    Jeff&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Can you use 1 antenna mast (pole) for 2 different radio antennas?  I understand there should be a 3-foot separation between antennas.   However, I am limited to the amount of space I can use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's what I'm thinking.  Attaching 2 antennae to opposite sides of the 2&quot; pipe I will be using as an antenna mast.  The pole/mast will be anchored to the concrete wall on my garage.  Once they antenna are mounted I thought of using multiple tennis balls on each antenna to prevent one from touching the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you for your thought on this&lt;/p&gt;&#xA;" OwnerUserId="11279" LastEditorUserId="8717" LastEditDate="2018-03-09T16:49:36.683" LastActivityDate="2018-03-09T16:49:36.683" Title="Antenna installation for a base station" Tags="&lt;antenna&gt;&lt;grounding&gt;&lt;safety&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10008" PostTypeId="2" ParentId="10007" CreationDate="2018-03-06T10:12:33.920" Score="4" Body="&lt;p&gt;Regarding the overlap of the mast to the antenna, there should be about 1 foot of overlap as shown in this picture:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MRFUM.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MRFUM.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The top of the pipe must stay below the decoupling radials in order for the antenna to function properly. This puts the top clamp within an inch or so of the top of the pipe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that on VHF and UHF FM, line of site is key to reliable communications. The higher you can place your antenna, the better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding other things to think about, here are a few ideas:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Use high quality coax like RG-213 or LMR-400 to reduce losses&lt;/li&gt;&#xA;&lt;li&gt;Use a VHF/UHF lighting arrestor on the coax at the base of your mast&lt;/li&gt;&#xA;&lt;li&gt;Bond your ground rods to your house electric service ground&lt;/li&gt;&#xA;&lt;li&gt;Seal the top of the pipe to reduce water ingress that promotes rusting/freezing&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-06T11:07:49.357" LastActivityDate="2018-03-06T11:07:49.357" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10009" PostTypeId="2" ParentId="10006" CreationDate="2018-03-06T11:20:40.753" Score="8" Body="&lt;p&gt;The station would not really transmit static but rather white (or perhaps pink) noise. This would sound like static but as the observer tunes across the transmitter's frequency, the static would increase notably in volume (assuming amplitude modulation) and decrease again as the transmitting bandwidth is passed. Any signal strength indicator on the receiver, such as an S meter, would also indicate the received signal. These would be clear indicators to the observer that this is not simply atmospheric static or internally generated thermal noise. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The source of the signal is easily found using standard direction finding techniques since there is still an observable signal from the transmitter.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-06T19:26:26.150" LastActivityDate="2018-03-06T19:26:26.150" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10010" PostTypeId="2" ParentId="10007" CreationDate="2018-03-06T16:04:44.387" Score="2" Body="&lt;p&gt;I would say the mast must extend only high enough to provide appropriate mechanical support. Glenn W9IQ provides a great illustration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having the mast extend above the antenna might provide some degree of lightning protection since the mast, rather than the antenna will take most of the strike current. But I'd regard this as a &quot;nice to have&quot; rather than a requirement. In the case of installing a vertical on the mast you'd need to get the antenna horizontally away from the mast. Sometimes you see this on towers, like this one &lt;a href=&quot;http://www.ka1rci.net/ka1rci_repeater/rpt_tower_repairs_office_main.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;on the KA1RCI repeater network&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4Xyjw.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4Xyjw.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, given you have just a small mast rather than a huge tower, I'd say this is just unnecessary complexity and cost with very little benefit. Instead, I'd recommend following &lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike&quot;&gt;good lightning protection practices&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-03-06T16:04:44.387" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10011" PostTypeId="2" ParentId="5355" CreationDate="2018-03-06T18:03:26.673" Score="1" Body="&lt;p&gt;We definitely need more information to answer appropriately, but I'm willing to answer as best I can with the information given. The receiver you have chosen is referred to as an Ultralight and is generally regarded as a decent performer. I am not aware of any significant issues although there are always possibilities of &quot;duds&quot; in any receiver line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You say &quot;virtually nothing&quot;; So that means you receive something. Good. What was it? When were you listening? How was the sound quality/signal quality? What other times have you tried and what were you expecting?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are currently at least 50 to 75 countries left broadcasting on shortwave these days. There may have been more in the past, but there still are quite a few. It's true that many of the major European broadcasts to North America in our evening hours have ceased, but shortwave is still alive and well in much of the developing world. One simply has to look at the last few issues of Glenn Hauser's excellent &lt;a href=&quot;http://worldofradio.com/dxldmid.html&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;DX Listening Digest&quot;&gt;&quot;DX Listening Digest&quot;&lt;/a&gt; to see that there is quite a bit on the air to hear, especially in part of the world such as New England.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A casual tune across the 49 m band in your local afternoon or early evening should produce at least a dozen countries spread across North America, Europe, Africa, and South America broadcasting in various languages.If this is not happening, I would first suspect a local noise source is blocking the signals, especially if you are indoors. As an amateur radio operator you are no doubt familiar with how much RFI has increased in a typical household in the last 20 or 30 years. So, with that in mind, look to options such as listening outdoors to see if the problem goes away, connecting to an outdoor antenna or even a random piece of wire put out the window, etc. You can also use the Tecsun on batteries that mouse grid to try to hunt down the source of the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please let us know what you find.&lt;/p&gt;&#xA;" OwnerUserId="11281" LastActivityDate="2018-03-06T18:03:26.673" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10012" PostTypeId="1" CreationDate="2018-03-06T20:22:35.687" Score="3" ViewCount="1067" Body="&lt;p&gt;I didn't fully understand all the finer details of AM, so I'd like an explanation for the following behavior: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have 3 radios. In AM mode, one of the radios, when modulated, increases output power on my PEP-reading meter. On the two other radios, the output power decreases, as I provide modulating signal. Same also happens in the average mode as well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is happening here?&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2018-03-06T22:36:29.603" Title="Why does the output power of some AM transmitters increase when modulated and of others decrease?" Tags="&lt;rf-power&gt;&lt;am&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10013" PostTypeId="2" ParentId="10012" CreationDate="2018-03-06T22:30:41.723" Score="3" Body="&lt;p&gt;First a bit of background on AM modulation and power levels. If we start with a 100 watt carrier and no modulation, we would measure 100 watts peak and average power. They are the same due to lack of modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When 100% amplitude modulating a 100 watt carrier, the PEP (Peak Envelope Power) is 400 watts. The carrier average power will be 2/3 of the 100% of the modulated average power. The other 1/3 of the modulated average power goes into the upper and lower sidebands so each sideband has 1/6 of the modulated average power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most modern solid state transceivers have a 100 watt maximum output. Their output is controlled through an ALC (Automatic Level Control) circuit that monitors the &lt;em&gt;peak&lt;/em&gt; power of the output and adjusts the drive levels accordingly so at to not exceed this peak.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now when we use one of these solid state rigs to generate AM, we set the carrier output to 25 watts knowing that the peak power will then be 100 watts at 100% modulation. But the ALC is watching the output and during 100% modulation, it cuts the &lt;em&gt;peak&lt;/em&gt; power back to 25 watts. This puts the carrier output in the 7.5 watt range. When no modulation is present, the carrier output goes back up to 25 watts! Not all radios have this odd ALC characteristic. If I recall correctly, the Yaesu FT-1000D is an example of one that properly handled the ALC action during AM. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution for the radios that cut back carrier power at 100% modulation is to inject an adjustable negative voltage into the ALC control circuit connection on the back of the radio. A 9 volt block battery with its positive lead connected to the radio's ground and a 100k $\Omega$ potentiometer will do the trick:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/tgCmi.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2ftgCmi.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the radio's power control wide open, slowly adjust the negative ALC voltage using the pot until the carrier output power is 25 or so watts. Then adjust the mike level control to achieve 100 watts PEP at 100% amplitude modulation. Don't forget to disconnect this ALC injection circuit when operating in other modes if you wish to have full power output.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-06T22:36:29.603" LastActivityDate="2018-03-06T22:36:29.603" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10014" PostTypeId="2" ParentId="10006" CreationDate="2018-03-06T23:33:26.530" Score="3" Body="&lt;p&gt;It really depends. In wireless communications, it's often the case¹ that the majority noise is actually happening &lt;strong&gt;in&lt;/strong&gt; the receiver – which is why you'd want a low noise figure on your receiver. So, there's usually no &quot;broadcast static&quot; – the majority of that noise power happens &lt;em&gt;in&lt;/em&gt; your receiver, not &lt;em&gt;on the air&lt;/em&gt;. Many receiver architectures will increase the sensitivity if there's no strong (intended) signal in the air, leading to amplified noise, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In these bands, the pure presence of an increased noise floor would give away the presence of a broadband interferer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, things aren't quite that easy in general: Whilst a single &quot;non-jammer&quot; interferer usually isn't white in spectrum as what you describe as &quot;static&quot; would usually be, a sufficient number of summing interferers with random properties would both be white in spectrum and gaussian in amplitude distribution, making the detection of your jammer harder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, receivers with multiple receive paths cannot be deceived: Your transmitter would be detectable to transmit from a single direction, and thus, if you, for example, add up the signal from two antennas with just the right phase, you could isolate your transmitter well, because they constructively add with that phase, but cancel out with other phases. That technology, both in receive and transmit direction, is called &lt;em&gt;Beamforming&lt;/em&gt;, and it works with any signal (note that the receiver noises in both receive paths are independent and never add up constructively, whereas the artificial jamming signal is correlated on both antennas). It's basically a form of triangulation. You can also do the same with distributed antenna systems that coordinate their observations in a central point, so that you can do &lt;em&gt;trilateration&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On large scale, that belongs in the category of things that you'd typically do to do radio surveillance for signal intelligence, airspace security, or cellular infrastructure coordination. So, that's broadly employed wherever there's industrialized areas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you try that, especially with high TX power, prepare for a visit from your local regulating body, asking you &lt;em&gt;very&lt;/em&gt; nasty questions. It might be a criminal offense, depending on which bands you interfered with and where you are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹ HF, if I remember correctly, being the most prominent exception&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-03-06T23:33:26.530" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10015" PostTypeId="1" AcceptedAnswerId="10020" CreationDate="2018-03-07T03:29:23.330" Score="4" ViewCount="3543" Body="&lt;p&gt;I'm planning to build an FM radio receiver using the instructions on&#xA;&lt;a href=&quot;http://www.instructables.com/id/Build-your-own-Crude-FM-Radio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.instructables.com/id/Build-your-own-Crude-FM-Radio/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The schematic uses a BF199 transistor which is marked &quot;obsolete&quot; by some component suppliers. What would be a current and widely available equivalent?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to search at my preferred shop, &lt;a href=&quot;https://www.rs-online.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.rs-online.com&lt;/a&gt; using the following properties:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Si NPN RF Transistor&lt;/li&gt;&#xA;&lt;li&gt;Vcb max 40V&lt;/li&gt;&#xA;&lt;li&gt;hFE min 38&lt;/li&gt;&#xA;&lt;li&gt;ft 1100 MHz&lt;/li&gt;&#xA;&lt;li&gt;Pc 350 mW&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And did not find anything suitable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The original data sheet is here: &lt;a href=&quot;https://www.mouser.com/ds/2/308/BF199-1118776.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.mouser.com/ds/2/308/BF199-1118776.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11283" LastEditorUserId="8717" LastEditDate="2019-11-22T22:34:24.267" LastActivityDate="2019-11-22T22:34:24.267" Title="What are some equivalents of a BF199 transistor?" Tags="&lt;receiver&gt;&lt;electronics&gt;&lt;fm&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10016" PostTypeId="2" ParentId="10015" CreationDate="2018-03-07T04:06:47.883" Score="2" Body="&lt;p&gt;&lt;strong&gt;A 2N5109 will work just fine&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.mouser.com/ds/2/68/2n5109-16404.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Datasheet here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-11-15T18:41:12.267" LastActivityDate="2019-11-15T18:41:12.267" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10017" PostTypeId="1" AcceptedAnswerId="10019" CreationDate="2018-03-07T04:51:55.323" Score="8" ViewCount="1957" Body="&lt;p&gt;I am planning to organise a simple fox hunt, a family event. This includes building a transmitter. I am currently considering the following schematics:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://maker.pro/education/diy-fm-transmitter&quot; rel=&quot;noreferrer&quot;&gt;https://maker.pro/education/diy-fm-transmitter&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.buildcircuit.com/simple-steps-for-making-fm-transmitter/&quot; rel=&quot;noreferrer&quot;&gt;http://www.buildcircuit.com/simple-steps-for-making-fm-transmitter/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Both target the 88-110 MHZ band, but that range of frequencies requires licensing. I live in Ireland and according to the local rules the following bands seem to be available:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;26.957 – 27.283 MHz (no further requirements)&lt;/li&gt;&#xA;&lt;li&gt;40.660 – 40.700 MHz (no further requirements)&lt;/li&gt;&#xA;&lt;li&gt;49.82 – 49.98 MHz, 10 mW ERP, no other requirements&lt;/li&gt;&#xA;&lt;li&gt;169.4 - 169.475 MHz, 500 mW ERP, Duty cycle &amp;lt; 10% Max 50 kHz channel spacing&lt;/li&gt;&#xA;&lt;li&gt;433.050 – 434.790 MHz, 10 mW ERP, Duty Cycle ≤ 10 %&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This is how I understand the document &lt;a href=&quot;https://www.comreg.ie/media/dlm_uploads/2015/12/ComReg0271R9.pdf&quot; rel=&quot;noreferrer&quot;&gt;https://www.comreg.ie/media/dlm_uploads/2015/12/ComReg0271R9.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, from the list above 169 MHz range seems to be the closest to 110 MHz. My plan is to first build the transmitter within the 88-110 MHz range, verify using common radio receiver that it works and then tune up to 169 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume that if I play with the coil inductor (add or remove turns) and/or capacitor the shift from 110 to 169 MHZ will be possible. I found a surprisingly affordable frequency counter on Amazon and hope it will help me to validate the frequency (so that I do not skip to 200 MHz).&#xA;&lt;a href=&quot;https://www.amazon.co.uk/gp/product/B01B3ZCP3U/&quot; rel=&quot;noreferrer&quot;&gt;https://www.amazon.co.uk/gp/product/B01B3ZCP3U/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would that work? Is this how tuning is normally done?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: The desired communication distance is up to 100-200 meters from the fox box in a park (within line of sight).&lt;/p&gt;&#xA;" OwnerUserId="11283" LastEditorUserId="9493" LastEditDate="2018-03-07T13:27:01.373" LastActivityDate="2018-03-09T16:49:02.377" Title="How to tune an FM transmitter to a specific frequency?" Tags="&lt;legal&gt;&lt;frequency&gt;&lt;fm&gt;&lt;transmitter&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10018" PostTypeId="2" ParentId="10017" CreationDate="2018-03-07T10:07:31.680" Score="1" Body="&lt;p&gt;not quite sure what to say about &quot;how is it normally done&quot;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;how it can be done&quot; depends on the transmitter architecture you're using, and any non-my-first-diy-fm-transmitter will be a bit more complex in the way they generate the RF oscillation :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the principle for many of these will be the same: you change an energy-storing element (either a capacitor or an inductor (coil)); you measure what that does to your operating frequency, and with that info calibrate the frequency scale on your device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding legality:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can't really comment qualifiedly, have measured none of these circuits, but &quot;1 General Information&quot; demands&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All radio and telecommunications terminal equipment must comply with the essential requirements and other relevant provisions of the R&amp;amp;TTE Directive before being placed on the market or put into service in Ireland.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That requires suppression of out-of-band spurs as well as sufficient stability to be sure that your transmitter doesn't drift away from the frequencies it's allowed on. The latter might be a real problem: Your circuit is pretty temperature-dependent and will generally tend to drift (which is why real-world transmitters typically a bit more complex). However, nothing says it's &lt;em&gt;impossible&lt;/em&gt; to make, by carefully trimming, and pampering your circuit, to make it stable enough. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether your location application or your transmit power is legal in your band: I honestly have no idea, and would have to read that document in full. You also have zero means to measure emitted power, raising completely different questions regarding legality than frequency!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding band selection:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think table 1 is pretty clear here, the band between 169 and 173 MHz can only be used with very low duty cycles, your transmitter must be off for 99% of time. I doubt this is optimal for fox hunting, unless you have extensively clever receiver design (as in, a computer-aided TDMA system. Not happening.). So, 169 MHz is right out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your best bet is the 173.2375 – 173.275 MHz band, where no duty cycle restrictions apply. However, that band is only 37.5 kHz wide. This means your transmitter needs to be &lt;em&gt;pretty&lt;/em&gt; frequency-exact. I predict that this will be a major obstacle when employing such simple, uncompensated circuits – any temperature, supply voltage, antenna condition change (rain, potentially wind, close large objects moving) will influence the operation frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you really want to build a transmitter yourself instead of eg. buying a cheap SRD handset that you can program to that frequency you should probably stay away from instructables.com, and the other websites you're using, and would need to aim for more advanced circuits. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, I'm a computer person (in fact, I'm a Software Defined Radio person, where we control such parameters in software). I'd frankly directly go for something that a manufacturer has calibrated and with which I can talk to digitally and simply tell it what frequency to synthesize. Now, that would require a relatively large engineering effort for you to build – cannot recommend. Annoyingly, most cheaply available programmable oscillators end at 150, 165 or 170 MHz. Just below what you need...&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-03-07T11:05:15.153" LastActivityDate="2018-03-07T11:05:15.153" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10019" PostTypeId="2" ParentId="10017" CreationDate="2018-03-07T12:53:45.623" Score="4" Body="&lt;p&gt;I will assume you will get the legal issues sorted so I will address the circuit itself. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look at the second circuit you referenced, you will find L1 and VC1 in parallel. These form a tuned circuit that sets the output frequency of the transmitter (ignore the polarity symbol on VC1, it is a remnant of the circuit editor on this site):&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/34lnk.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f34lnk.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula for the resonant frequency of this circuit is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Frequency=\frac{1}{2\pi\sqrt{LC}} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where Frequency is in Hertz, L is the inductance in Henries and C is the capacitance in Farads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case you may find it helpful to solve equation 1 for LC:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$LC=\left(\frac{1}{Frequency*2\pi}\right)^2 \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where resonance is achieved by any combination of inductance and capacitance where their product equals the right side of equation 2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So with L1 = 0.1 $\mu$H, VC1 would need to be set to about 26 pF to hit the middle of the FM band (98 MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to adjust the output frequency to ~170 MHz, VC1 would need to be set to approximately 9 pF according to equation 1. But the recommended capacitor for VC1 probably will not go that low so select a different variable capacitor that can be adjusted to this value; or place a 10 pF capacitor in series with VC1; or use a 10 pF fixed capacitor instead of VC1 and simply stretch or compress the windings of L1 a bit to adjust the frequency. Your frequency counter will make this a straight forward process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the capacitor value gets quite small, the circuit may not behave as expected due to stray capacitance. You can overcome this by reducing the inductance value. For example, 4 turns of wire wound on a 0.25 inch form and spaced out to make a coil that is about 0.5 inches long will form an inductance of ~0.04 $\mu$H. A 22 pF capacitor in parallel with this will get you into the 170 MHz range. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The circuit will be sensitive to the presence of your hand or any metal tools. You can make the inductor adjustment with a small wooden stick to avoid this problem. A stiff piece of plastic (e.g from a plastic milk jug) can serve as a poor man's adjustment tool for the variable capacitor.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-09T16:49:02.377" LastActivityDate="2018-03-09T16:49:02.377" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10020" PostTypeId="2" ParentId="10015" CreationDate="2018-03-07T13:03:57.840" Score="3" Body="&lt;p&gt;This is not a terribly critical application, and there are many transistors that would work. If you have some NPN transistors on hand, try those. It may work anyway, with some reduction in gain. If you'd like to buy new transistors, I'd look for something with a high gain bandwidth product.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-03-07T13:03:57.840" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="10022" PostTypeId="2" ParentId="9303" CreationDate="2018-03-07T22:02:53.370" Score="0" Body="&lt;p&gt;I am not sure, but have these suggestions to offer.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The Icom HM-75LS speaker-mic has a headphone jack on it.  At a minimum, you could plug one of these into your ID-51, and then plug your headphones into the speaker-mic.  As a bonus, you could clip the speaker-mic onto your shirt or jacket so that you wouldn't need to raise the radio to your mouth for transmitting.  (Headphones would only be for listening.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You should be able to craft an audio cable that does what you suggest.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Bear in mind the the task is different if you only intend to listen versus have the microphone component of a computer or phone headset work with the radio.  (To me, a &quot;regular set of headphones&quot; is listen only, but many headphones these days have built-in microphones for use with mobile phones.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The OPC-244 adapter posted at the top of your post converts the narrowly-spaced terminals to a more normal spacing, compatible with the typical speaker-mics and headsets for Kenwood &lt;em&gt;et al&lt;/em&gt;.  If you're familiar with this configuration, you might have some knowledge about what your options are.  As far as I know, the pinout is the same as the radio provides, but with different physical spacing.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-03-07T22:02:53.370" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10023" PostTypeId="1" AcceptedAnswerId="10024" CreationDate="2018-03-07T22:30:08.767" Score="3" ViewCount="156" Body="&lt;p&gt;I'm looking for any timecode station (like WWV/B, CHU, etc.) with an SNR &gt; 0 dB that I should be able to receive in Boston Mass. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;WWVB at 60 kHz has a phase modulation that one can apparently receive on the east coast, but the signal is borderline to begin with and I'd like something I can see or hear without code gain. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;CHU in Ottawa, Canada transmits on 3 frequencies, including 3.33 MHz at 3kW but I don't know if I should be able to receive it. I haven't managed to yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course I can receive GPS but that's not the point.&lt;/p&gt;&#xA;" OwnerUserId="11288" LastEditorUserId="8832" LastEditDate="2018-03-08T00:59:54.253" LastActivityDate="2018-03-08T10:06:07.947" Title="Are there any terrestrial timecode signals receivable in Boston Massachusetts?" Tags="&lt;snr&gt;&lt;wwv&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10024" PostTypeId="2" ParentId="10023" CreationDate="2018-03-07T23:29:48.803" Score="4" Body="&lt;p&gt;WWVB propagation does vary in amplitude. And its BPSK phase modulation makes it a bit tricky to lock to. But if you narrow the bandwidth enough, signal is most always above the noise.&lt;br&gt;&#xA;Here's an example plot of WWVB amplitude in a fringe area similar to Boston...left half is night-time while right half is day-time. Each sample is exactly one second long. Bandwidth of this receiver is about one hertz.&lt;br&gt;&#xA;You see three different amplitude samples, because the integrated amplitude each second can take on three different digital codes (low, high, or sync).&lt;br&gt;&#xA;The vertical amplitude scale is arbitrary, proportional to volts, not watts.&#xA;Antenna was a 0.7 m loop at ground level resonated to 60 kHz. A ferrite rod antenna produces similar results.&lt;a href=&quot;https://i.stack.imgur.com/Z5oc7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Z5oc7.png&quot; alt=&quot;wwvb carrier amplitude&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11132" LastActivityDate="2018-03-07T23:29:48.803" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10025" PostTypeId="2" ParentId="5378" CreationDate="2018-03-07T23:38:25.730" Score="1" Body="&lt;ol&gt;&#xA;&lt;li&gt;Forget Baofeng.&lt;/li&gt;&#xA;&lt;li&gt;Buy an old &lt;code&gt;Kenwood THD7&lt;/code&gt; for little more. I have one for 18 years and is rock solid still. It has APRS built-in and many other useful things. You can easily connect it to your PC.&lt;/li&gt;&#xA;&lt;li&gt;take a look at my website: &lt;a href=&quot;http://www.so6agj.pl/project-gps.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.so6agj.pl/project-gps.php&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;If you need code or hardware instructions please write me a message.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;" OwnerUserId="11289" LastActivityDate="2018-03-07T23:38:25.730" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10026" PostTypeId="2" ParentId="10023" CreationDate="2018-03-07T23:40:54.200" Score="1" Body="&lt;p&gt;You should be able to pick up WWVB at 60 kHz, or WWV at 2.5, 5, 10, 15, and 20 MHz.  Propagation should allow you to routinely receive at 60 kHz, 2.5 MHz, and 5 MHz most nights unless the ionosphere has been disturbed by an event such as a solar flare.  That would likely be your most reliable propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During the day time you should be able to receive 15 MHz on most days.  10 MHz should come through best in the mornings and evenings.  20 MHz should come through during the day time when the sunspot number is reasonably high, or when propagation is otherwise favorable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This assumes that you have a reasonably effective antenna.  A typical inexpensive WWVB-synchronized clock uses a fine coil of wire around a ferrite rod.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-03-07T23:40:54.200" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10027" PostTypeId="2" ParentId="7092" CreationDate="2018-03-07T23:46:12.590" Score="2" Body="&lt;p&gt;Contrary to other answers, there are ARPS networks out there that can be used without a Ham license. The key, as @PhilFrost points out, is that your original packet must not make it out to RF. The APRS-IS network is specifically focused on supporting an Internet backbone for APRS that might originate or be destined for RF and so requires a Ham license before sending any packets to it, but there are two other, compatible networks that specifically disallow RF transmission of their data, &lt;a href=&quot;http://wxqa.com/servers2use.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;CWOP&lt;/a&gt; and &lt;a href=&quot;http://info.aprs.net/index.php?title=FireNet&quot; rel=&quot;nofollow noreferrer&quot;&gt;FireNet&lt;/a&gt;. Both of them tend to be focused around collecting weather data, but will pass any APRS packets receive to other TCP/IP clients attached to the network. All traffic on APRS-IS is replicated on FireNet which also includes a lot of higher volume NWS messages/alerts.&lt;/p&gt;&#xA;" OwnerUserId="1534" LastEditorUserId="4665" LastEditDate="2018-03-07T23:49:04.727" LastActivityDate="2018-03-07T23:49:04.727" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10030" PostTypeId="2" ParentId="10017" CreationDate="2018-03-08T07:30:57.713" Score="0" Body="&lt;p&gt;As buying everything pre-made would take away the fun of building something yourself, I'd propose to look into kits which you can at least assemble yourself. The transmitter is the one on which legal restrictions apply, so that one might be a good candidate for getting it pre-made, or in kit form.&#xA;If you want help, get in touch with a local ham radio club. Your mileage may vary, but quite certainly there's someone very eager to help you out if you want to make frequency and/or power measurements. Just sent them an email and ask, you might be surprised. Helping others (or elmering) is supposed to be highly valued among hams (as is building things yourself). &#xA;Or maybe someone has an ardf transmitter that you can lend, and build your own receiver for.&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2018-03-08T07:30:57.713" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10031" PostTypeId="2" ParentId="10017" CreationDate="2018-03-08T08:38:01.367" Score="1" Body="&lt;p&gt;Let me chime in, as I am in Ireland, and have at least some knowledge of the regulations. However I can see at other answers have already addressed this, so I am not going to repeat this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Let me give you a solution for your family-day-fox-hunt&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;100 mW EIRP TX&lt;/li&gt;&#xA;&lt;li&gt;legal&lt;/li&gt;&#xA;&lt;li&gt;cheap&lt;/li&gt;&#xA;&lt;li&gt;unlimited FREE RX devices for your family memembers&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If it is just for the family fun day (and lets forget about the fun building electronic circuits) you can do the following:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;get a cheap/old Wifi router&lt;/li&gt;&#xA;&lt;li&gt;most of them run on 9V or 12V, so you can run it on a battery of some sort&lt;/li&gt;&#xA;&lt;li&gt;some you can turn down the power output if you want to make it challenging&lt;/li&gt;&#xA;&lt;li&gt;get mobile phones and install a &quot;Wifi tracking or finder app&quot;&lt;/li&gt;&#xA;&lt;li&gt;configure the Wifi router with a recognizable SSID&lt;/li&gt;&#xA;&lt;li&gt;hide the Wifi router where you have your family day.&lt;/li&gt;&#xA;&lt;li&gt;try to find it with phones....&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Lots of fun, everyone has a phone, so you have not only solved the TX problem, you have given everyone a method of RX, for all ages !&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Building transmitters if fun, and this is probably something where you could say: &quot;we have all done it&quot;. The frequency which is most versatile to experiment with is 87-108 MHz, which is the FM broadcast band. You will need to experiment with filtering and the like. And with a max ERP of 50 nW there is not much of a range. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You do have to start somewhere when you want to do this, but it will be a while before you can build a transmitter with larger power output, which can be used for your intended family day. (as other answers have already covered this)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;[EDIT after reading some more documents about the legality]&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was surprised about the frequency ranges mentioned, hence my edit here.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;ref: &lt;a href=&quot;https://www.comreg.ie/industry/radio-spectrum/licence-exemptions/list-of-licence-exemptions/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Comreg 06/47R&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;ref: &lt;a href=&quot;https://www.comreg.ie/industry/radio-spectrum/radio-frequency-plan-for-ireland/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Comreg 13/118R&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;ref: &lt;a href=&quot;https://www.comreg.ie/publication/permitted-short-range-devices-ireland/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Comreg 02/71R11&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It seems to me that most of the frequencies you are listing have a very specific license exemption, e.g. cordless phones, baby monitors, radar-to-wall, and other applications. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would strongly advice to stay away from those &quot;seems to be good to use&quot; frequencies. These frequencies are NOT for &quot;Private Mobile Radio&quot; (PMR for short). The license exempt allocations for PMR are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;434.04 – 434.79 MHz (10 mW)&lt;/li&gt;&#xA;&lt;li&gt;446.00 - 446.10 MHz (500 mW) channelized&lt;/li&gt;&#xA;&lt;li&gt;446.10 - 446.20 MHz (500 mW) channelized digital only&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;However for those license exempt frequencies there are actually type-approval requirements in the appropriate legistlation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The relevant documents can be found on &lt;a href=&quot;http://www.irishstatutebook.ie/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Electronic Irish Statute Book&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;S.I. 93 of 1998&lt;/li&gt;&#xA;&lt;li&gt;S.I. 405 of 2005&lt;/li&gt;&#xA;&lt;li&gt;S.I. 160 of 2006&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Clearly stipulating that the equipment used for those need to be &quot;type approved&quot;, and will bring a extensive list of requirements for such approval.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, Document 06/47R stipulates the following:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All radio and telecommunications terminal equipment must comply with&#xA;  the essential requirements and other relevant provisions of the R&amp;amp;TTE&#xA;  Directive before being placed on the market or put into service in&#xA;  Ireland.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Which was already mentioned in another answer, this will bring requirements in regards to spurious emissions and harmonics.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Under Irish legislation (The Wireless Telegraphy Acts 1926 - 1988),&#xA;  all apparatus for Wireless Telegraphy requires a licence unless that&#xA;  apparatus has been specifically exempted from licensing under Irish&#xA;  legislation by means of an Exemption Order.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Which comes down to &lt;em&gt;&quot;you may not own a tranmitter, unless licensed, or unless license exempt&quot;&lt;/em&gt; And we already know that the license exempt equipment need to be type approved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So your options are getting narrower once you start reading the detail of the legislation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The PMR devices (properly type approved and license exempt) are widely available in many stores around Ireland. They are called PMR446 devices, and sold as &quot;walkie-talkie&quot;. These will have a 500 mW output and can be loads of fun. Some of them have microphone inputs where you can feed it with a signal of some sort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Conclusion&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a &quot;family day of fun in the park&quot; and therefore in a public place, I would higly recommend you stick to type-approved equipment, or the Wifi I mentioned before. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Personal Opinion&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't let this stop you from experimenting, there are some good answers here which can get you going in building simple transmitting circuits. Just don't expect to build anything with large power output and be sure you are able to measure and adjust/filter spurious emissions and harmonics... this will be a learning journey.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe that many experimenters do so in the 87-108 MHz FM broadcast band, and keep the power output under 50 nW. This I mention above as well. Technically speaking this license exemption for Short Range Devices, also need type approval, and also a CE mark certification. But I could not find any other frequency allocation for such experimentation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not even sure if there is an allocation you could &quot;officially&quot; use for experimentation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Did I built transmitters in that frequency range?&lt;/em&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Yes I did, learned a lot, had some fun. But never with large power, and never used them for &quot;public&quot; functions/family-days-in-the-park.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2018-03-08T10:54:16.407" LastActivityDate="2018-03-08T10:54:16.407" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10032" PostTypeId="2" ParentId="10023" CreationDate="2018-03-08T10:06:07.947" Score="1" Body="&lt;p&gt;Apart from the American time signal stations on shortwave. There is also CHU the Canadian time signal from Ottawa on 3.330 MHz, 7.850 MHz, and 14.670 MHz using USB mode. &lt;/p&gt;&#xA;" OwnerUserId="6604" LastActivityDate="2018-03-08T10:06:07.947" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10034" PostTypeId="2" ParentId="9948" CreationDate="2018-03-09T18:42:14.620" Score="0" Body="&lt;p&gt;At times like this, when the sunspot activity is low, you're going to find a lot better luck running FT8, JT65, or JT9, rather than SSB or PSK31. Sunspots are areas on the sun that give off huge amounts of UV radiation, some of which make their way to Earth. More than the usual amount of UV radiation that the sun shines on us, this extra burst of UV interacts with atomic Oxygen in the upper ionosphere, producing a refractive effect on all HF radio waves, but especially on upper HF frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, when the sunspots return in force, probably around 2024, you're going to hear a lot of talk about SSB on 10 meters again. Until then, the propagation you're currently experiencing is fairly &quot;normal&quot; without sunspots, and your best bet might be to check out the digital modes.&lt;/p&gt;&#xA;" OwnerUserId="9166" LastActivityDate="2018-03-09T18:42:14.620" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10035" PostTypeId="2" ParentId="9850" CreationDate="2018-03-10T01:05:30.087" Score="1" Body="&lt;p&gt;It is first important to know what frequency you will be using. The higher the frequency, the shorter the antenna and vice versa. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A basic formula for a dipole antenna (not an L antenna) would be to divide your operating frequency in MHz (e.g. 15 Mhz) into 468. That will give you the length of your antenna in feet (e.g. 31.2 feet). From this, you can make a dipole antenna = ----------x----------- or an inverted vee antenna (Google 'dipole antenna','inverted vee antenna' or 'how to construct a half wave HF dipole antenna').&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be advised that the dipole and inverted vee antennas are directional. So depending on where you live and with whom you wish to communicate, you will ideally want to align your antenna broadside to that direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A vertical or discone antenna will allow you to transmit and receive in a 360 degree pattern.&lt;/p&gt;&#xA;" OwnerUserId="11302" LastEditorUserId="9493" LastEditDate="2018-03-11T22:09:29.970" LastActivityDate="2018-03-11T22:09:29.970" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10036" PostTypeId="2" ParentId="32" CreationDate="2018-03-10T05:14:30.997" Score="3" Body="&lt;p&gt;I have a couple of CW Morse code trainer Android apps that are perfect for a beginner. One is a CW Koch Morse code trainer that includes CW abbreviations and prosigns and includes interfaces for both RX and TX, the other is a Morse code practice oscillator with straight and iambic keys that translates into English and CW prosigns as you practice. Both apps are available on Google Play and the Amazon Appstore. You may find more information on these webpages:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.kg9e.net/apps/AmateurHamRadioMorseCodeTrainer/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.kg9e.net/apps/AmateurHamRadioMorseCodeTrainer/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.kg9e.net/apps/AmateurHamRadioPracticeKeys/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.kg9e.net/apps/AmateurHamRadioPracticeKeys/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the interest of full disclosure, I have a pecuniary interest in the above referenced apps. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8gcb0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8gcb0.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zZv7B.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zZv7B.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Bwdx9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Bwdx9.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/55uUe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/55uUe.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11303" LastEditorUserId="8713" LastEditDate="2019-04-19T14:32:46.517" LastActivityDate="2019-04-19T14:32:46.517" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10037" PostTypeId="1" CreationDate="2018-03-10T07:18:00.430" Score="4" ViewCount="242" Body="&lt;p&gt;I'm a newly licensed ham tech. I am trying to figure out if I am doing everything correctly to setup a wireless temperature monitoring station that uses the 70cm band (specifically 433.4MHz) in the USA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This setup will involve a station that is positioned on a lake about 300-400 feet from a receiving station in my house. The station located on the lake will transmit water temperature data once per hour with transmission durations of 1 second or less (more likely milliseconds). The receiving station will receive this data and upload it to the internet. This is for environmental non-commercial purposes. The data will not be encrypted but will be in some form of a binary protocol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm planning to tune the transceivers to use the least amount of power required for successful communication. I read somewhere that I should include my callsign on the outside of the device that is transmitting as well as in the actual data being transmitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The station on the water will be in a locked box preventing anyone from manually interfering with the equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some SDR equipment that I have been using to listen on 433.4MHz to make sure that I'm not going to interfere with anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I have any bad assumptions or am I overlooking anything? Some feedback would be really appreciated. I haven't had much luck finding resources that spell this stuff out. I have looked at some references for APRS, but all that I have found seems pretty specific -- it seems like what I want to do is in the same spirit of APRS, but may use a different protocol etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any links to solid references would be appreciated as well.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Update:&#xA;I currently have some 433MHz transceivers that are very affordable, extremely easy to interface with (serial), and can be operated at both 5v and 3.3v: elecrow.com/download/HC-12.pdf My weather station is going to be powered by arduino and my receiving station will be powered by a raspberry pi. Now that I am a licensed ham, can I use these transceivers in the US? &lt;/p&gt;&#xA;" OwnerUserId="11304" LastEditorUserId="11304" LastEditDate="2018-03-10T16:07:32.510" LastActivityDate="2018-03-10T18:22:43.507" Title="Wireless temperature data logger in the USA on 433MHz" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;aprs&gt;&lt;weather&gt;&lt;automation&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10038" PostTypeId="2" ParentId="10037" CreationDate="2018-03-10T08:58:48.130" Score="1" Body="&lt;h1&gt;Legal discussion&lt;/h1&gt;&#xA;&#xA;&lt;h2&gt;To ISM or not to ISM, that is the question&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;So, in Europe, 433 MHz is an ISM band – you could even operate a device there if you weren't a licensed Ham! That also includes the fact that if you choose to go for unlicensed operation rather than amateur licensed operation, the no-encryption rule, and the callsign rule (both of which frankly don't make overly much sense in this day and age, in my humble opinion) don't apply to your use case. Now, in the US, it's not an ISM band, but if I read your question correctly, it wouldn't hurt you if you had to switch to the 900 MHz ISM band. (whether you do that or not doesn't really matter for the technical discussion below)&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;ISM band situation&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Now, that's about how much legal advice about the situation in the USA I can give; I'm not a lawyer, and a European on top of that. Generally, even ISM-band devices must adhere to regulations. It really depends on the legislation, but for example, in Europe, there's what we call &quot;Short Range Devices&quot;, and the rules these must fulfill are rather lax – depending on the band, low duty cycle, low transmit power and negligible out-of-band emissions ensured by &quot;appropriate&quot; engineering. Nothing about spending a few grand on lab testing and certification as necessary for other operational classes.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Technical discussion&lt;/h1&gt;&#xA;&#xA;&lt;h2&gt;Tickling you with a bit of background&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Now, your weather station needs pretty much next to no data rate at all – you can happily spread out energy as much in time and/or frequency as you want to, given you then &quot;collect&quot; it at the receiver again. That's what for example GPS does – the satellites' signals at the receiver are usually all below thermal noise floor, but due to integrating over enough time, your GPS still works reliably.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We typically call these technologies &lt;em&gt;spread spectrum&lt;/em&gt;. There's quite a few different implementations. For example, if you want to work with readily engineered long-range modules that you can just wire up to a microcontroller and easily talk to, LoRa is a manufacturer-proprietary technology for machine-to-machine communication (M2M, exactly what you're doing!) in ISM bands. It should work reliably over the comparatively short distance you're trying to cover, even if it uses higher frequencies. It uses what they call &lt;em&gt;Chirp Spread-Spectrum&lt;/em&gt;, which is an interesting thing to do, though not inherently extremely intuitive from a theoretical point of view.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you instead want to build this yourself, you could very easily build your own spread-spectrum transmitter. It's not hard at all – in fact, if you have a transmitter that uses a linear modulation, and can feed it with any data stream you want, it's pretty easy. Think about &lt;em&gt;Direct-Sequence Spread Spectrum&lt;/em&gt;, DSSS: Typically, you just go and multiply a symbol by a symbol sequence and transmit that. Imagine, you want to transmit the &lt;em&gt;bits&lt;/em&gt; &lt;code&gt;110011&lt;/code&gt;. Now, you say that a 0-bit is -1, and 1-bit is +1. Instead of just transmitting &lt;code&gt;+1 +1 -1 -1 +1 +1&lt;/code&gt;, you pick a sequence, let's say &lt;code&gt;+1 +1 -1 -1&lt;/code&gt; as spreading code. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, you take each of your transmit symbols, and multiply it by the sequence (so you replace &lt;code&gt;+1&lt;/code&gt; by &lt;code&gt;+1 +1 -1 -1&lt;/code&gt; and &lt;code&gt;-1&lt;/code&gt; by &lt;code&gt;-1 -1 +1 +1&lt;/code&gt;), and just transmit the result (after concatenating what you've got):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;+1 +1 -1 -1 +1 +1 -1 -1 -1 -1 +1 +1 -1 -1 +1 +1 +1 +1 -1 -1 +1 +1 -1 -1&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the receiver, you just correlate with the same spreading sequence. That basically means you're taking the received signal, four values of that, and multiply it point-by-point with &lt;code&gt;+1 +1 -1 -1&lt;/code&gt;, then sum up the four values you've gotten, and get an amplitude. Then, you shift your input signal by one, and do the same. Whenever you get nice and high values, you've &quot;hit&quot; a transmit signal (instead of just noise).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a bit of a trick to picking these spreading sequences. You want them to have a well-shaped autocorrelation function, meaning that when you multiply them with themselves, shifted by any amount of time but 0, they will have low values, but high values when multiplied-summed without any time offset. That way, you can actually successfully synchronize your receiver to your transmitter and eliminate as much of the channel influence as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From this requirement comes that you get better performance for longer sequences (that's kinda logical – the more values you add up, the higher your value gets if you're actually multiplying with the right sequence instead of noise), and that you'll pick sequences that aren't periodical in themselves – because if they were, they'd be similar to a shifted version of themselves, and thus would not fulfill the autocorrelation criteria. If in doubt, &lt;em&gt;Gold codes&lt;/em&gt; are a good source of such sequences, and don't be shy about length – modern wide area network standards allow for sequences up in the dozens of thousands of symbols in length¹.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, if you have a transmitter that can either send &lt;code&gt;+1&lt;/code&gt; or &lt;code&gt;-1&lt;/code&gt; (or QPSK, or anything that is a linear modulation, which pretty much is everything but plain FSK, really), then you can also make it send &lt;code&gt;+sequence&lt;/code&gt; and &lt;code&gt;-sequence&lt;/code&gt; just by replacing the raw data with the coded data. To let your receiver know that you're about to start sending data, you could also prepend your callsign to the weather station data, and encode that along with it. That would a) give you a preamble and b) fulfill the ham callsign requirement. &lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Implementation approaches&lt;/h2&gt;&#xA;&#xA;&lt;h2&gt;Buying dedicated RF transceiver chips / boards&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;You could implement that transmitter with a cheap microcontroler that integrates a radio frontend; for example, TI sells the &lt;a href=&quot;http://www.ti.com/lit/ds/symlink/cc1310.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;CC1310&lt;/a&gt;, and an &lt;a href=&quot;http://www.ti.com/tool/launchxl-cc1310#buy&quot; rel=&quot;nofollow noreferrer&quot;&gt;eval kit board&lt;/a&gt; costs 30$ (also comes in a &lt;a href=&quot;http://www.ti.com/tool/LAUNCHXL-CC1350-4&quot; rel=&quot;nofollow noreferrer&quot;&gt;433 MHz version&lt;/a&gt;. Haven't worked with that, but the chip does come with built-in support for spreading sequences, so that sounds nice for your application, and you could have one on both ends of your link, and probably TI will give you some example code to make them talk to each other.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;A quick word about why these devices exist&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Notice: exactly what you're building is something that is of large commercial interest, so it's no big surprise TI and other companies try to make it easy to use their products to implement what you want! Integrating that with a microcontroller makes a lot of sense – people that build devices like weather stations don't want to have yet another chip on their board that only does the RF, and then a microcontroller to control that RF chip, and then hope that they can avoid having yet another microcontroller just to control the weather sensing devices, they want one controller to at least do the job of the RF interface reliably, and they want someone who had the time to test all this to have implemented the radio control layer. Makes much more sense that way.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;A self-built receiver&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;If you want to implement the receiver yourself, you'll need the correlator, and something to sync. You said you had an SDR – I simply postulate that as you're building something cool, another 10$ RTL dongle won't hurt you much, so you can just receive that signal, and do the above correlation (which, really, is just a FIR filter with the reversed sequence as taps) in software – for example, on a cheap small computer like the raspberry pi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd go into detail here – but &quot;how do I build a DSSS receiver with a Raspberry Pi, an RTL dongle and minimal effort, matching my transmitter&quot; would be worth opening a new question, if this is the way to you choose to go, and I don't want to overburden you with details at this point. But really, other people have built SDR receivers (and transmitters) for such systems. For example, see this &lt;a href=&quot;https://github.com/kit-cel/gr-lpwan&quot; rel=&quot;nofollow noreferrer&quot;&gt;gr-lpwan&lt;/a&gt; presentation that, with less than 5 mW transmit power worked on 2.4 GHz (which has more than 10dB more path loss for the same distance than 433 MHz, if I'm not mistaken!), &lt;a href=&quot;https://youtu.be/FU0fXjH1ufA?t=9m40s&quot; rel=&quot;nofollow noreferrer&quot;&gt;worked over a couple of kilometers, even in the shadow of large buildings&lt;/a&gt;; don't let yourself be scared by the math and complexity. This is a full implementation of a complex standard, not a &quot;works for my weather station (and that's enough for now)&quot; approach.&#xA;&lt;hr&gt;&#xA;¹ Talking about IEEE802.15.4-LECIM in case anyone wonders.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-03-10T10:05:47.120" LastActivityDate="2018-03-10T10:05:47.120" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10039" PostTypeId="1" CreationDate="2018-03-10T10:01:55.260" Score="1" ViewCount="67" Body="&lt;p&gt;I cannot understand while the AM modulations have sidebands which are of a frequency higher than the carrier.  If for example we are modulating a 4kHz signal to a carrier of 1MHz how we end up with a 1.004MHz if the 4kHz is in the amplitude not in the frequency.  In the signal we still have the 1MHz which is the highest frequency.  &lt;/p&gt;&#xA;" OwnerUserId="11305" LastActivityDate="2018-03-11T11:27:28.920" Title="Why AM modulation side bands have higher frequencies than the carrier?" Tags="&lt;modes&gt;&lt;am&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10040" PostTypeId="1" AcceptedAnswerId="10052" CreationDate="2018-03-10T10:14:28.420" Score="5" ViewCount="1859" Body="&lt;p&gt;I watched &lt;a href=&quot;https://www.youtube.com/watch?v=oiBi9RbNBUY&quot; rel=&quot;noreferrer&quot;&gt;this video&lt;/a&gt; of a very nice explanation of a &lt;em&gt;simple dipole&lt;/em&gt; and &lt;em&gt;1/4-wave monopole&lt;/em&gt;. In that video they show how you can impedance match the &lt;em&gt;1/4-wave monopole&lt;/em&gt; by bending the 4 (&lt;em&gt;virtual ground plane&lt;/em&gt;) pins downwards at an angle, $\theta$, from the horizontal plane. Doing this we can get any impedance ($Z$) between 25 and 70 $\Omega$. This is also very well explained &lt;a href=&quot;http://www.comportco.com/~w5alt/antennas/notes/ant-notes.php?pg=21&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;. However, on the previous page of that last explanation, the impedance also varies somewhat (between 20 to 40 $\Omega$), with the height, $h$, above true ground of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to see a &lt;em&gt;accurate&lt;/em&gt; equation, perhaps in the functional form of:  $Z = f(h, \theta)$. Or maybe even more applicable, as $\theta = g(h, Z)$. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Is there such an equation available?&lt;/strong&gt; &lt;/li&gt;&#xA;&lt;li&gt;(&lt;em&gt;If not, how would I go about finding one?&lt;/em&gt;)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Cck89.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Cck89.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Picture from &lt;a href=&quot;https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;: &#xA;I found &lt;a href=&quot;http://jocet.org/papers/151-L020.pdf&quot; rel=&quot;noreferrer&quot;&gt;this&lt;/a&gt; paper, but the derivation doesn't &lt;em&gt;properly&lt;/em&gt; include the angle dependence. Also, I don't trust the derivation, as they say the currents are cancelling in the radials, but if they are not at right angles to the radiator, I guess they can't cancel in that direction perpendicular to the horizontal plane?&lt;/p&gt;&#xA;" OwnerUserId="6563" LastEditorUserId="6563" LastEditDate="2018-03-11T11:19:41.320" LastActivityDate="2018-03-15T20:50:01.613" Title="How can I calculate the 1/4-wave monopole impedance dependence on groundplane angle?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;impedance&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10041" PostTypeId="2" ParentId="10037" CreationDate="2018-03-10T18:22:43.507" Score="1" Body="&lt;p&gt;In the US, if you don't want to reinvent the wheel then your easiest solution would probably be &lt;a href=&quot;http://www.aprs.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;APRS&lt;/a&gt;, more specifically the &lt;a href=&quot;http://www.wxqa.com/cwop_info.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Citizen Weather Observer Program&lt;/a&gt;, which is a standardized system to send weather station data to the National Oceanic and Atmospheric Administration via APRS and/or the internet.  Thousands of weather stations in North America already participate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the weather station end, you would need:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A power source, possibly solar.&lt;/li&gt;&#xA;&lt;li&gt;A weather station that sends its data through a serial connection in a format recognized by the software or the controller.&lt;/li&gt;&#xA;&lt;li&gt;A computer running software, or a &quot;weather station controller&quot;, that receives the serial weather data and outputs APRS-formatted packets.  See the CWOP page I linked to for a comprehensive list of software and hardware solutions; a Raspberry Pi could serve as an inexpensive computer that doesn't draw much power.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If the weather station is only 300 &amp;ndash; 400 feet from the house, then the easiest way to do the wireless link might be Wi-Fi to a computer in the house, which could send the weather data via the internet.  But if you want to use APRS, then you would also need:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A hardware TNC such as the &lt;a href=&quot;https://www.byonics.com/tinytrak4&quot; rel=&quot;nofollow noreferrer&quot;&gt;TinyTrak4&lt;/a&gt;, or a &quot;software TNC&quot;, which is software that would output tones through a sound card that can be coupled directly to a radio&lt;/li&gt;&#xA;&lt;li&gt;A VHF and/or UHF radio tuned to the APRS frequency&lt;/li&gt;&#xA;&lt;li&gt;A suitable antenna&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So far I have assumed that you live close enough to an existing digipeater that can conveniently receive the APRS packets and put them on the internet for you.  If you can hear packets on 144.39 MHz, then you probably are in range of such a digipeater (or a digipeater that could relay packets to an internet-connected digipeater).  You can also look at &lt;a href=&quot;https://aprs.fi&quot; rel=&quot;nofollow noreferrer&quot;&gt;aprs.fi&lt;/a&gt; to see a map showing digipeaters and other packet stations near you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are within reach of such a digipeater, then sending the weather data as packets over the North American packet frequency of 144.39 MHz would probably be your simplest solution.  At the house, you could see the data moments later that had been relayed via the internet by the digipeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if there is no nearby digipeater, or if you are bound and determined to use the 70cm band (APRS on the 70cm band is much more uncommon, but can and has been done) then you could construct your own digipeater at the house to relay the packets to the internet.  That could be an asset to other APRS users in the area, as well as to your weather station.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-03-10T18:22:43.507" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10042" PostTypeId="2" ParentId="9850" CreationDate="2018-03-10T18:45:17.347" Score="1" Body="&lt;p&gt;I'm sorry that I didn't see your question earlier.  As @AlmostDone says, &quot;160/6&quot; means that the antenna is designed to work from the 160m band to the 6m band, in other words 1.8 MHz to 54 Mhz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How much of your antenna should be horizontal and how much should be vertical is not very important, but you'll want the antenna to be as high as you can practically accomplish, because the higher it is the better you will receive far-away shortwave stations.  If the wire is too long for your property, then a good solution could be to weave it back and forth a bit, or bend it so that it wraps around your property.  (Gentle bends, such as 60° or less, would be better than sharper bends.)  The horizontal part of the antenna won't do much for receiving shortwave broadcasts, but do help make the impedance of the antenna more convenient for the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have to cut the wire, it will change the impedance of the antenna and make it difficult to sell as @EdwinvanMierlo says.  For receiving, the impedance of the antenna often doesn't matter very much, but for transmitting it does matter; so I'd recommend not cutting the wire if you might try to resell the antenna later, or if you are thinking about getting an amateur radio license and transmitting with the antenna later.  If you have to cut it, try to cut off as little as possible; if you have to lop off more than about a third, then the impedance of the antenna might become a problem for the receiver at the lower frequencies.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2018-03-10T19:21:37.973" LastActivityDate="2018-03-10T19:21:37.973" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10043" PostTypeId="1" AcceptedAnswerId="10051" CreationDate="2018-03-10T19:02:34.267" Score="0" ViewCount="1556" Body="&lt;p&gt;TX works at 433 MHz and sends a burst of 64 bytes every second. The burst itself lasts for 102.4 ms. The width of TX signal is 400 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RX is an Spectrum Analyzer (R&amp;amp;S FSL6) with a receiving antenna. RBW is 100 kHz, VBW is 300 kHz, span is 6 MHz, sweep time is 2.5 ms. &quot;Max hold&quot; is used to obtain the peak value of the received signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is observed that (1) background noise level would rise ~10 dB once &quot;Max hold&quot; is selected: normal -70 dBm, max hold -60 dBm (no additional changes to SA settings) (2) If not read immediately after &quot;Max hold&quot; is selected, peak value would keep increasing gradually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;What is the &quot;valid period&quot; for readings in &quot;Max hold&quot; regarding the burst signal? [From the comment, &quot;Max hold&quot; is regarded as valid eternally.]&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Based on the settings, did the SA sweep too fast or too slow? Could this be the reason for non-eternal &quot;Max hold&quot; reading?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is it normal to have the spectrum/noise level risen upon selecting &quot;Max hold&quot;?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="11250" LastEditorUserId="76" LastEditDate="2020-02-14T01:09:10.513" LastActivityDate="2020-02-14T01:09:10.513" Title="Spectrum Analyzer: using &quot;Max hold&quot; for peak detection of a burst signal" Tags="&lt;equipment-operation&gt;&lt;spectrum-analyzer&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10045" PostTypeId="1" AcceptedAnswerId="10047" CreationDate="2018-03-10T20:39:33.417" Score="3" ViewCount="299" Body="&lt;p&gt;Cheap &amp;amp; simple transceivers are readily available online that allow you to transmit serial data over UHF/VHF frequencies such as 433MHz (approximate range of 1000m). It seems that these are popular in places like Europe where these devices operate in the EU ISM bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the legality of using these devices in the US if you are a licensed ham operator?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the specific device in question:&#xA;&lt;a href=&quot;https://www.elecrow.com/download/HC-12.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.elecrow.com/download/HC-12.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On ebay:&#xA;&lt;a href=&quot;https://www.ebay.com/itm/433Mhz-HC-12-SI4463-Wireless-Serial-Port-Module-1000m-Replace-Bluetooth-TOP/401051275954?epid=26007567495&amp;amp;hash=item5d6084d2b2:g:JawAAOSwMHdXS9OD&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ebay.com/itm/433Mhz-HC-12-SI4463-Wireless-Serial-Port-Module-1000m-Replace-Bluetooth-TOP/401051275954?epid=26007567495&amp;amp;hash=item5d6084d2b2:g:JawAAOSwMHdXS9OD&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm interested in using these to transmit temperature data from a body of water to my house for non-commercial purposes. I can include my callsign in the data transmission and make it visible on the outside of the transmitting device. I would only be transmitting once per hour for no more than 1 second (probably milliseconds) unencrypted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that there are existing solutions on different frequencies and using different protocols (APRS etc). Just curious if I wanted to use these little 433MHz transceivers if it will be more trouble than it is worth due to legal reasons or people getting upset with me doing non-standard stuff.&lt;/p&gt;&#xA;" OwnerUserId="11304" LastActivityDate="2018-03-11T20:59:34.913" Title="What is the legality of data modes over UHF/VHF in the US?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;aprs&gt;&lt;weather&gt;&lt;automation&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10046" PostTypeId="2" ParentId="10040" CreationDate="2018-03-10T21:58:25.620" Score="1" Body="&lt;p&gt;&lt;a href=&quot;http://www.qsl.net/kk4obi/Elevated%20Radials.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt; is the antenna modeling information for 1,2,4,6 and 8 ground plane radials at various angles of slope.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And &lt;a href=&quot;http://www.qsl.net/kk4obi/Center-fed%20L-dipoles%20Vertical.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; for impedance of a vertical dipole relative to angle on bend of the lower half.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And &lt;a href=&quot;http://www.qsl.net/kk4obi/Standard%20vertical.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; for relative impedance as the wavelength fraction elevation of the feedpoint above ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With this insight into the fundamental behavior of RF on wire you will better understand what is behind the observed behavior of the antenna once it is in the operating position when the influences of things nearby are constant. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you would want to make an antenna model where you set your wire size, radial angle, feedpoint elevation, etc., the appropriate 4NEC2 models are provided with each of the above studies.  These will give a better approximation.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Precise modeling requires velocity factors, transmission line details and inclusion of interactive things such as exact ground characteristics, pipes, wiring, walls, roofing, gutters, reflective surfaces and vegetation.&lt;/p&gt;&#xA;" OwnerUserId="8229" LastEditorUserId="6563" LastEditDate="2018-03-15T20:50:01.613" LastActivityDate="2018-03-15T20:50:01.613" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10047" PostTypeId="2" ParentId="10045" CreationDate="2018-03-11T04:15:24.417" Score="2" Body="&lt;p&gt;Telemetry is explicitly allowed in §97.111.&lt;/p&gt;&#xA;&lt;p&gt;You must use an authorized &amp;quot;digital code&amp;quot;, which probably means ASCII. And you must use a publicly documented technique. I don't see any specification in the manual of how this device works, but it's probably something simple like FSK, so no difficulty there.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§97.309   RTTY and data emission codes.&lt;/p&gt;&#xA;&lt;p&gt;(a) Where authorized by §§97.305(c) and 97.307(f) of the part, an amateur station may transmit a RTTY or data emission using the following specified digital codes:&lt;/p&gt;&#xA;&lt;p&gt;(1) The 5-unit, start-stop, International Telegraph Alphabet No. 2, code defined in ITU-T Recommendation F.1, Division C (commonly known as “Baudot”).&lt;/p&gt;&#xA;&lt;p&gt;(2) The 7-unit code specified in ITU-R Recommendations M.476-5 and M.625-3 (commonly known as “AMTOR”).&lt;/p&gt;&#xA;&lt;p&gt;(3) The 7-unit, International Alphabet No. 5, code defined in IT--T Recommendation T.50 (commonly known as “ASCII”).&lt;/p&gt;&#xA;&lt;p&gt;(4) An amateur station transmitting a RTTY or data emission using a digital code specified in this paragraph may use any technique whose technical characteristics have been documented publicly, such as CLOVER, G-TOR, or PacTOR, for the purpose of facilitating communications.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;§97.307 is where data transmissions are authorized. For the 70 cm band these two paragraphs apply, permitting just about any reasonable digital transmission. I don't see any specification of the bandwidth used by the module, so be sure it's under 100 kHz.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(6) A RTTY, data or multiplexed emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must not exceed 56 kilobauds. A RTTY, data or multiplexed emission using an unspecified digital code under the limitations listed in §97.309(b) of this part also may be transmitted. The authorized bandwidth is 100 kHz.&lt;/p&gt;&#xA;&lt;p&gt;(8) A RTTY or data emission having &lt;a href=&quot;https://en.wikipedia.org/wiki/Types_of_radio_emissions&quot; rel=&quot;nofollow noreferrer&quot;&gt;designators&lt;/a&gt; with A, B, C, D, E, F, G, H, J or R as the first symbol; 1, 2, 7, 9 or X as the second symbol; and D or W as the third symbol is also authorized.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I would not assume a $3.55 radio from China does not spew spurious emissions. With an amateur license you can operate uncertified equipment, but still the lack of a regulatory certification should raise suspicion.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§97.307 (c) All spurious emissions from a station transmitter must be reduced to the greatest extent practicable. If any spurious emission, including chassis or power line radiation, causes harmful interference to the reception of another radio station, the licensee of the interfering amateur station is required to take steps to eliminate the interference, in accordance with good engineering practice.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Somewhat surprisingly, it seems numbers are put to spurious emission requirements for HF equipment, and 30-225 MHz, but not above. So:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§97.101 (a) In all respects not specifically covered by FCC Rules each amateur station must be operated in accordance with good engineering and good amateur practice.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;With such a low transmit power (100 mW max), there's really no excuse for spurious emissions strong enough to be detectable by your neighbors.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-03-11T04:15:24.417" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="10048" PostTypeId="1" CreationDate="2018-03-11T08:46:02.493" Score="1" ViewCount="113" Body="&lt;p&gt;I’m looking to build a vacuum-tube based linear amplifier.  I’d like to do it all tube based, including the power supply. The original ARRL design I’m looking at (from the 60s) has two paralleled 807s delivering 150w, with 700v on the plates at 200ma. I was thinking perhaps I could double the output power to 300w by paralleling up four 807s. I guess that would draw twice the current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The original power supply has a pair of 6DE4s for rectification, feeding a 5U4G. Assuming the transformer can handle the current draw, could I beef up the power supply to handle the four 807s by having 2 paralleled pairs of 6ED4s feeding a paralleled pair of 5U4Gs?&lt;/p&gt;&#xA;" OwnerUserId="11258" LastEditorUserId="8717" LastEditDate="2018-03-11T19:42:01.997" LastActivityDate="2018-03-12T01:24:32.593" Title="Parallel tube amplifier power supply using 6DE4 tubes" Tags="&lt;amplifier&gt;&lt;power-supply&gt;" AnswerCount="1" CommentCount="9" ClosedDate="2018-03-26T03:37:56.133" ContentLicense="CC BY-SA 3.0" />
  <row Id="10049" PostTypeId="2" ParentId="10045" CreationDate="2018-03-11T11:05:29.570" Score="4" Body="&lt;p&gt;You may be able to operate the device without consideration of your amateur radio status. &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/15.231&quot; rel=&quot;nofollow noreferrer&quot;&gt;CFR 47 Part 15.231&lt;/a&gt; permits the low power use of 433 MHz without a license provided certain transmission repetition rates and maximum field strength rates are met. 433 MHz is commonly used by non-licensed home weather stations under part 15 provisions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you need to increase the range under part 15 use, consider increasing the  receive antenna gain as this is not restricted under part 15.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to use a part 15 device in Amateur radio service that does not use one of the specified encoding methods enumerated in part 97, you can do so on any amateur band 33 cm and up. See the table in 97.305(c) and note where the right column references 97.307(f)(7). This is the reference that additionally allows &quot;any&quot; code (encoding technique) that is not called out specifically in 97.309. This would include the allowed use of undocumented codes.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-11T20:59:34.913" LastActivityDate="2018-03-11T20:59:34.913" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10050" PostTypeId="2" ParentId="10039" CreationDate="2018-03-11T11:27:28.920" Score="1" Body="&lt;p&gt;The answer is that the two frequencies are mixing to produce the sum and difference of the two.  Note that this is simply the &lt;em&gt;frequency&lt;/em&gt; component. So in your example, not only is 1.004 MHz produced but so is 0.996 MHz. Collectively these are called the sidebands. Depending on the desired transmission mode, one of these resulting frequencies may be filtered out. For example, if the desired transmission mode was LSB (lower side band), the original 1.0 MHz carrier and the 1.004 MHz signal would be filtered out leaving only the 0.996 MHz signal - the lower sideband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In AM (and SSB and DSB), the &lt;em&gt;amplitude&lt;/em&gt; of the frequencies resulting from the mixing is controlled by the amplitude of the audio modulating signal. So in the LSB example above, the amplitude of the 0.996 frequency is following the amplitude of the 4 kHz audio modulating signal.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-03-11T11:27:28.920" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10051" PostTypeId="2" ParentId="10043" CreationDate="2018-03-11T18:22:00.193" Score="3" Body="&lt;p&gt;It is important to understand that the SA takes some finite time to sweep (calculate the FFT buckets) for the frequency range in question. It is quite possible with a short duration signal that the sweep will catch none or only a small portion of a narrow band signal on a single sweep. On another pass it will potentially catch the peak of the narrow band signal spectrum. Depending on how often and at what value the sweep catches the signal will determine if it is visible and to what amplitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Placing the SA in a max hold mode will cause the display to persist all maximum values from each FFT (fast Fourier transform) bucket. So now instead of a bucket briefly rising in value and then falling back to potentially noise level, it remains at its highest peak as long as the max hold mode is engaged. Eventually the entire spectrum and amplitude of the periodic signal will be persisted on the display as long as the max hold mode is engaged. The effect can be that the amplitude and bandwidth of the signal appears to grow over time. It will eventually stabilize in shape and amplitude. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Noise is detected in the same manner using max hold since noise is just another signal. Noise is generally random in nature so a simple single sweep may not catch it. When the SA is in max hold mode, it eventually finds a random noise event in each FFT bucket. This raises the apparent overall noise floor. In the UHF spectrum this noise is generally the result of thermal component noise and external RFI (radio frequency interference). RFI, in contrast to thermal noise, is often repeatable and identifiable.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-12T15:57:52.397" LastActivityDate="2018-03-12T15:57:52.397" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10052" PostTypeId="2" ParentId="10040" CreationDate="2018-03-11T20:25:38.263" Score="7" Body="&lt;p&gt;Once a ground plane antenna is 0.5 wavelengths or so above ground, there is no significant effect from the ground on the impedance of the antenna so it can be ignored.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A close approximation of the real part of the feedpoint impedance in ohms of a 1/4 wave ground plane antenna in free space is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Z_{real}=20+\frac{2}{3}\theta \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\theta$ is the degrees of radial drop (0=horizontal) and 0$\le\theta\le$60.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The imaginary impedance in ohms can also be closely approximated by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Z_{imag}=-29+0.7\theta \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a simulation of the complex impedance of such an antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Hmrk5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Hmrk5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see that at ~45 degrees of droop, the real part of the impedance is ~52 ohms. It can also be observed that at other angles there can be an appreciable imaginary impedance for which compensation could be added to negate its effect on SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Recall, however, that impedance or SWR is not a figure of merit for an antenna. The highest gain of this type of antenna in free space occurs when the radials droop 90°. In this configuration, the antenna can be viewed as a vertical, 1/2 wave dipole or a 1/4 wave sleeve antenna if the feedline enters from within the bounds of the extremities of the radial field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;A Deeper Examination&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In comments now moved by the moderator, the OP bemoaned the notion that amateur radio operators have lost their technical edge as no one was able to give fundamental equations to support the observable effect of impedance change due to ground plane droop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I participate on this board to help mentor hams as well as to learn from the many other willing regulars and even the visitors on this site. Since this is obviously a volunteer effort, I differentiate the level of effort I put into my responses from the type of response I would give in a professional setting. However in the spirit of helping the OP to gain a broader understanding, I offer the following.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The graph that I presented above is done with a technique called moment method. In the distant past as a student, I was required to demonstrate that I could calculate this long hand. But just as I no longer calculate a square root by hand, I used a computer tool to quickly get to the answer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another technique that can be used to derive the complex radiation resistance is to integrate the Poynting vector over a large sphere and then equate this power to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$(I_o/\sqrt{2})^2R_o \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $R_o$ is the radiation resistance at the current maximum point and $I_o$ is the peak time value of current at that point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet another approach is to use the induced EMF method&lt;sup&gt;1&lt;/sup&gt; but this can only determine the self impedance and it will be limited to length to diameter ratio &gt; ~100. It is, however, a closed form calculation. To fully calculate the self impedance with this method requires a 40 step or so derivation which I will not execute here. But the interesting result is that for a 1/2 wave dipole (recall that this is the realized configuration of a 90 degree drop of the radials) the real part of the self impedance is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_{11}=30Cin(2\pi) \tag 4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the function $Cin(2\pi)$ evaluates to 2.44.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same method applied to a quarter wave radiator over a large ground plane results in:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_{11}=15Cin(2\pi) \tag 5$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take note that this lengthy computation results only in a simple change of the constant. This method closely agrees with the moment method presented above. It should also be recognized that this is another demonstration of the well known feedpoint impedance comparison of a 1/4 wave antenna over a large ground plane and 1/2 wavelength, center fed antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The imaginary part of the self impedance can be similarly calculated with the induced EMF method if this information is required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;sup&gt;&lt;sup&gt;&lt;sup&gt;1&lt;/sup&gt;P.S. Carter, “Circuit relations in radiating systems and applications to antenna problems,” Proc. IRE, 20, pp.1004-1041, June 1932&lt;/sup&gt;&lt;/sup&gt;&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-14T17:18:03.850" LastActivityDate="2018-03-14T17:18:03.850" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="10053" PostTypeId="2" ParentId="10048" CreationDate="2018-03-11T23:20:26.080" Score="3" Body="&lt;p&gt;I would encourage you to reconsider this project as it not simply a matter of paralleling all of the tubes to double the output power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you parallel more finals (807's in this case) the input and output impedance of the stage will decrease. This will require a redesign of the output circuit of the final stage at a minimum. If it has input filtering/matching circuit, which many old designs did not, this will require redesign as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You mention:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The original power supply has a pair of 6DE4s for rectification, feeding a 5U4G&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This seems quite unlikely as the 6DE4 'TV damper' tubes are normally used for rectification in this application. I would infer that two of them indicate a full wave rectifier with a center tapped transformer. A 5U4G is a single tube, full wave rectifier. Why would one tube be cascaded into the other except in the case of a voltage doubler circuit?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You must also consider the filter inductors and capacitors must be increased in order to maintain the original ripple current. The filament transformers will also need to be doubled or have increased current ratings in order to support the additional tube filaments.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-12T01:24:32.593" LastActivityDate="2018-03-12T01:24:32.593" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10054" PostTypeId="1" AcceptedAnswerId="10056" CreationDate="2018-03-12T03:23:54.677" Score="6" ViewCount="844" Body="&lt;p&gt;I'm brand new to shortwave radio and have been researching what kind of a receiver to get. I'll use it on the antenna I'll build (longwire, 50-100 feet) for shortwave listening; no transmitting. Right now I have my sights on a Tecsun PL-360 as it's affordable and has an external antenna port. My question is: Would the portable ~$40 Tecsun get damaged somehow by a 100-foot antenna because it's designed to work with shorter, portable antennas? I really don't know if that's something I need to worry about when only receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason I want such a cheap receiver and not something better but more expensive is because I just want to make sure the antenna's working properly. Once I'm happy with it I'll hook it up to an RTL-SDR device and plug that into a computer. I just don't want to spend hundreds on a receiver I'll only use a few times.&lt;/p&gt;&#xA;" OwnerUserId="11310" LastEditorUserId="9493" LastEditDate="2018-03-12T12:42:52.110" LastActivityDate="2018-03-24T16:29:43.353" Title="Can an antenna be too powerful for certain receivers?" Tags="&lt;antenna-theory&gt;&lt;receiver&gt;&lt;wire-antenna&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10055" PostTypeId="2" ParentId="10054" CreationDate="2018-03-12T09:49:54.410" Score="1" Body="&lt;p&gt;So, the magical relationship between antenna size and your receiver is that a larger antenna tends very much to have a larger &lt;em&gt;effective area&lt;/em&gt;, which simply means it extracts field energy from a larger area that the radio wave you want to receive penetrates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words: you get more &lt;em&gt;power&lt;/em&gt; at your receiver. That's cool, because more power means &quot;more power relatively to the noise inherent to your receiver's electronics&quot;, which means it's possible to receive weaker signals without them being &quot;drowned&quot; in noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thing is that, in fact, receivers in effect are sensitive measurement equipment, and you don't want to overload them. Technologically, it's (almost) always preferably to have a &lt;em&gt;low noise amplifier&lt;/em&gt; (LNA) as the very first element in your receiver's signal chain, and these are often constructed with very fine structures of a semiconductor process that is less prone to noise, but more sensitive to being damaged by too much power than your average silicon semiconductor. But I digress, as for the shortwave band, &quot;normal&quot; amplifiers are totally fine, and the chances that a cheap AM broadcast handset comes with an impressive LNA are rather slim, seeing that you typically just buy an IC that does the AM and FM reception integrated in one small package for you, and that those ICs have been around for four decades now, allowing for a huge range of cost/quality tradeoffs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, usually, you rely on your receive signal still being weak, even with a larger antenna, and that it won't fry your receiver, lest you put your long wire receive antenna next to your neighbor's transmit antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, your device of choice doesn't come with any rating for maximum input power – which isn't surprising, since its been designed with the antenna you see on the pictures in mind, and it probably works unless you directly couple that antenna into a transmitting circuit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/N4guJ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/N4guJ.jpg&quot; alt=&quot;Tecsun&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;AM Antenna&quot; is of course a mislabeling. Antennas generally don't care about the modulation used, what is meant is &quot;long-, medium- and shortwave antenna&quot;; the shape suggests (as does its purpose) it's a ferrite core antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You won't get happy when you attach your long wire antenna the same way you attach this ferrite core antenna: These antennas are high-impedance and very selective. Hence, the port where it's plugged in will also be very high impedance, and that will make it practically impossible for the receiver to get significant amounts of power from your long wire antenna, which has low impedance, which needs to be &quot;sunk&quot; into a matching-impedance receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, don't do this to you – if you want to observe the power coming from your antenna, either borrow, buy or build a power meter (I've learned not so long ago that there's logarithmic power meter ICs, these would be fun to try out), or: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Really, an SDR dongle comes for 6 to 29$. It won't be perfectly matched to your long-wire antenna, either, but much, much better than the port on the Tecsun thingie. You get signal samples instead of some arbitrary FM &amp;amp; AM demod combo IC that will do &lt;em&gt;anything&lt;/em&gt; to the received signal. These samples would not only make it very simple to decode the audio of AM broadcasts, but also allow you to get a quantitative comparison of different antenna behaviours, over MHz'es of bandwidth, instantly. Oh, and thanks to the fact that there's free &amp;amp; open source software, you can not only receive &quot;boring&quot; AM broadcast, but also things like FreeDV, or, depending where you live, broadcast standards like DRM (shortwave AM replacement in India, and Australia; India just build a small 1MW transmitter, so, I don't know, but I think it's possible that one could receive it from rather far away if conditions are good).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, not only would an SDR dongle be cheaper, it would also be more versatile and better suited for the job.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-03-12T09:55:15.360" LastActivityDate="2018-03-12T09:55:15.360" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="10056" PostTypeId="2" ParentId="10054" CreationDate="2018-03-12T10:27:16.193" Score="7" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Would the portable ~$40 Tecsun get damaged somehow by a 100-foot antenna because it's designed to work with shorter, portable antennas? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Unless you are within a kilometer or two of a very high power transmitter, there is no chance of your antenna collecting enough power damage your receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are more likely to cause damage to your receiver from static build up on the antenna or nearby lightning strikes inducing too much power into your receiver's front end. Disconnecting the antenna and shorting it to ground when not in use and adding a basic lightning protection circuit will mitigate this potential. On a receive only antenna, another technique to bleed off potentially damaging static build up is to connect a 5-10 meg ohm, non-inductive resistor between the receiver end of the antenna and ground.  &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-12T13:13:56.097" LastActivityDate="2018-03-12T13:13:56.097" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10057" PostTypeId="1" CreationDate="2018-03-12T19:46:01.993" Score="1" ViewCount="269" Body="&lt;p&gt;I thought it was time to build a balanced-balanced antenna tuner so I mechanically ganged two B&amp;amp;W 3852 rotary inductors to make a balanced L network. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It appears that the 16 uH inductors I used are not sufficient for the job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you have any ideas how I could increase the variable inductance in this design or how to make it work with the inductors I have?&lt;/p&gt;&#xA;" OwnerUserId="11315" LastEditorUserId="8832" LastEditDate="2018-04-12T16:40:37.787" LastActivityDate="2018-04-12T16:40:37.787" Title="Rotary Inductor Replacement" Tags="&lt;antenna-tuner&gt;&lt;transmission-line&gt;&lt;inductor&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10058" PostTypeId="2" ParentId="3770" CreationDate="2018-03-12T21:37:59.583" Score="1" Body="&lt;p&gt;Digital Coded Squelch will not cut any noise out of analog FM transmissions, and it will NOT &quot;add an extra layer of image and interference rejection&quot;,  DCS is not some kind of RF magic - it is simply a 'digital number sequence' imposed on the audio and it itself is a form of audio which is filtered out of the speech part of the audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, DCS is potentially harder to be tripped accidentally but if there is so much noise and interference that an analog CTCSS fails to work properly, you have other seriously severe problems that should be addressed first and not merely covered up with DCS. Attempting to use DCS to cut/fight interference is exactly like putting lipstick on a pig - i.e. under the lipstick it's still the same pig and same smell.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fortunately, digital does always mean better, it is all about the proper implementation. Furthermore using DCS will exclude a whole bunch of equipment from pre-DCS years - equipment often with superior RF performance and real serviceability. Unless of course that is exactly what you want to do: exclude more stations and prevent communications by further separating yourself from the ultimate spirit and purpose of Ham Radio.&lt;/p&gt;&#xA;" OwnerUserId="11317" LastEditorUserId="9493" LastEditDate="2018-03-13T01:38:28.567" LastActivityDate="2018-03-13T01:38:28.567" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10059" PostTypeId="2" ParentId="10057" CreationDate="2018-03-13T04:32:23.577" Score="2" Body="&lt;p&gt;One thing you might try is to add a fixed inductor in series with your rotary inductors to reach the overall required inductance.  To maintain balance, I would wind two identical inductors, each on a toroid core with the same wire spacing.  By using toroids, the magnetic fields are contained so that they don't couple to each other or to the rotary inductors.  I would mount them up off the chassis to minimize winding-to-chassis capacitance, but with identical mounting orientation and distances to minimize imbalance.  To operate higher band(s), the fixed inductors might have to be switched out, but again implement any switching arrangement with symmetry to optimize balance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you didn't indicate the power level and band(s) of interest, the exercise of core selection is left to you; you should be able to find this in various ARRL and core manufacturers' publications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However you solve it, please comment back with your final solution so others can benefit.&lt;/p&gt;&#xA;" OwnerUserId="11094" LastActivityDate="2018-03-13T04:32:23.577" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10061" PostTypeId="2" ParentId="10057" CreationDate="2018-03-13T10:20:24.410" Score="1" Body="&lt;p&gt;Here is a schematic for a simple, wide range balanced to balanced tuner:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/TzQBo.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fTzQBo.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It consists of a 32 $\mu$H variable inductor (which you already have) and two double gang 470 pF capacitors. The voltage and current ratings will depend on the power levels you wish to run and the range of impedances the tuner will experience. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to feed this with a coaxial connection, you can simply put a good current balun with the appropriate transformation ratio on the input of the tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are missing any of the parts to build a tuner, swapfests still are a good source. You may also have some success buying parts as replacement parts from some of the commercial tuner manufacturers. &lt;a href=&quot;http://www.mfjenterprises.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ&lt;/a&gt;, for example, has their variable capacitors and rotary inductors available for purchase. They published them on their website and in their catalog. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-13T16:13:20.717" LastActivityDate="2018-03-13T16:13:20.717" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10062" PostTypeId="1" CreationDate="2018-03-13T17:56:23.937" Score="2" ViewCount="186" Body="&lt;p&gt;I received two UV5R plus radios a couple of years ago as a gift to use for hunting. I've never used them, but I now have time on my hands due to some medical issues so figured I'd play around with them. I'm using them as scanners for police, fire and road crews.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is fun to listen, but one radio gets the signals I'd expect - mainly local stuff, maybe everything in a 20 mile radius. They other one is getting signals from  50-60 miles away. Is that normal? They have the same antennas. So is one radio sub par or do I have one that's above average?&lt;/p&gt;&#xA;" OwnerUserId="11323" LastEditorUserId="9493" LastEditDate="2018-03-13T18:48:41.647" LastActivityDate="2018-03-16T20:22:33.510" Title="Distance of Received Signals" Tags="&lt;antenna&gt;&lt;ht&gt;&lt;range&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10063" PostTypeId="2" ParentId="10062" CreationDate="2018-03-13T19:02:47.773" Score="4" Body="&lt;p&gt;The earlier iterations of the Chinese radios had their issues. This has gotten notably better in the last year or two but people largely dismiss minor issues since they are so inexpensive. So it could be a quality problem with one of the radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It could also be a difference in the performance of the antennas. Try swapping the antennas as an experiment. If the receiving distance follows the antenna then you know you have your culprit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At VHF and UHF frequencies, communications are largely limited to line of sight. But signals can bounce off of certain objects. So if the radios are not side by side and on the same frequency for your comparisons, you could be experiencing issues with the path of the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When receiving an FM signal, the audio is unmuted through the squelch control circuit. If one radio has a &quot;tighter&quot; squelch than the other, it may be receiving the signal but it simply isn't unmuting so that you can hear it. Try using the monitor function, which forces open the squelch, to compare the two radios while receiving a signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If all other things are equal, a VHF frequency will be usable over a longer distance than a UHF frequency. So make your comparisons on the same frequency at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, the only way to tell definitively is to use a calibrated RF signal generator to measure the MDS (minimum discernable signal) of each radio and compare that to the manufacturer's specifications.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-16T20:22:33.510" LastActivityDate="2018-03-16T20:22:33.510" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10064" PostTypeId="2" ParentId="10062" CreationDate="2018-03-13T19:08:14.820" Score="3" Body="&lt;p&gt;The manufacturing processes used for this brand of radio aren't very consistent.  So, it wouldn't surprise me at all if one worked better than the other.  You might also notice differences in how well the batteries fit, how sensitive the microphones are, etc.  It's hard to say if one is subpar or the other is above average.  That's because par for this brand is all over the place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll find similar issues with all of the budget-friendly radio brands.  This has earned them a poor reputation in the ham radio community.  But if you have one that works well enough, there's no reason why you can't keep using it.  I only own one radio, and it's a Baofeng.  It's not a great radio, but it works well enough for my current needs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you seem to have some time on your hands, you should consider studying for the entry-level (technician class in the US) license exam.  It likely won't take long, and it will open up a lot of options for using your radios.  I think you'll find that being able to transmit is a lot more enjoyable than just listening.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2018-03-13T21:54:41.013" LastActivityDate="2018-03-13T21:54:41.013" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10065" PostTypeId="2" ParentId="6014" CreationDate="2018-03-14T11:24:55.447" Score="3" Body="&lt;p&gt;Without all the technical banter take a look at &lt;a href=&quot;http://www.g0ksc.co.uk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;G0KSC site on Yagi design&lt;/a&gt;. Justin explains it quite well... The bottom line is when using a non conductive boom or simply isolating the element's from a conductive boom the Yagi becomes much much quieter as far as the signal to noise floor goes. A matter of hearing the someone or not?? My conclusion from building many different Yagi's for vhf/uhf/hf.... is I agree.. &lt;/p&gt;&#xA;" OwnerUserId="11327" LastEditorUserId="4665" LastEditDate="2018-03-14T20:48:26.400" LastActivityDate="2018-03-14T20:48:26.400" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10067" PostTypeId="1" CreationDate="2018-03-14T16:01:36.113" Score="1" ViewCount="74" Body="&lt;p&gt;TH-74D Why doesn't regular Vox work on D-Star?  It only works if &quot;Transmit when Busy&quot; is turned on. Bad for interruptions.  &lt;/p&gt;&#xA;" OwnerUserId="11331" LastEditorUserId="76" LastEditDate="2018-03-15T03:17:52.393" LastActivityDate="2018-03-15T03:17:52.393" Title="Kenwood TH-D74 VOX on D-Star" Tags="&lt;ht&gt;&lt;kenwood&gt;&lt;d-star&gt;&lt;kenwood-th-d74&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10068" PostTypeId="1" CreationDate="2018-03-14T18:19:46.950" Score="2" ViewCount="250" Body="&lt;p&gt;My D-star registration is not with a gateway with a call sign, but (REGIST). This is the way my registration reads: D-star Gateway Registration (REGIST). I can log in, but it is not recognized on any D-star repeaters. I get (RPT?). Any advice would be helpful.&lt;/p&gt;&#xA;" OwnerUserId="11335" LastEditorUserId="11335" LastEditDate="2018-03-15T18:08:36.060" LastActivityDate="2018-05-16T18:15:01.837" Title="My D-star registration is not with a gateway with a call sign, but (REGIST)" Tags="&lt;d-star&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10069" PostTypeId="2" ParentId="10067" CreationDate="2018-03-14T20:46:39.267" Score="1" Body="&lt;p&gt;OK after a couple of weeks I just stumbled onto the answer!  Basic Vox only works if you have squelch turned on to at least a minimum setting. &lt;/p&gt;&#xA;" OwnerUserId="11332" LastActivityDate="2018-03-14T20:46:39.267" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10070" PostTypeId="1" AcceptedAnswerId="10071" CreationDate="2018-03-15T18:16:04.597" Score="1" ViewCount="142" Body="&lt;p&gt;I've been trying to build a ham related website. I'm looking for a list of call signs. Here's the trick: I need the URL to change based on the zip code. I want to be able to put the link on a page, have someone click on it and not have to do anything else. I have checked three resources: The ULS database, QRZ, and Radio QTH. The lists are there, but the URL does not change based on individual searches.&lt;/p&gt;&#xA;" OwnerUserId="1861" LastEditorUserId="76" LastEditDate="2018-03-15T18:33:30.060" LastActivityDate="2018-03-16T10:27:35.297" Title="Linkable lists of call signs in a specific zip code" Tags="&lt;united-states&gt;&lt;software&gt;&lt;callsign&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10071" PostTypeId="2" ParentId="10070" CreationDate="2018-03-15T19:58:23.887" Score="2" Body="&lt;p&gt;You can use radioreference.com, as in this example:  &lt;a href=&quot;https://www.radioreference.com/apps/ham/?action=search&amp;amp;zipcode=12345&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.radioreference.com/apps/ham/?action=search&amp;amp;zipcode=12345&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="6080" LastActivityDate="2018-03-15T19:58:23.887" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10072" PostTypeId="2" ParentId="10070" CreationDate="2018-03-16T10:27:35.297" Score="1" Body="&lt;p&gt;If you are building a site that allows someone to put in a zip code to see the hams around them, it may prove more beneficial to allow them to see the hams that are within a certain mile radius of the zip code. I did this for a club that was offering licensing classes and wanted to send postcards to all of the hams of a particular license class within a specified radius.&lt;/p&gt;&#xA;&lt;p&gt;If this interests you, take a look at a site like &lt;a href=&quot;http://zipcodestogo.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;zipcodestogo&lt;/a&gt;. I programmatically entered the zip code and radius and then stripped out the zip code information from the returned page. I then used this to filter a SQL database of the ULS data that was downloaded weekly from the FCC site. The ULS download is well documented by the FCC. This is what &lt;a href=&quot;http://qrz.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRZ&lt;/a&gt; uses for their U.S. call sign lookups.&lt;/p&gt;&#xA;&lt;p&gt;You can also drive the addresses of your filtered results to place pins on Google Maps to get a nice view of the ham population in the selected area.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-03-16T10:27:35.297" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10073" PostTypeId="2" ParentId="10068" CreationDate="2018-03-17T17:22:14.670" Score="1" Body="&lt;p&gt;I'm not sure what &quot;(REGIST)&quot; means, but preferably you should contact the repeater administrator or equipment dealer person who registered you to fix the problem.  If you do a web search for &quot;D-STAR registration check&quot; you'll find several web pages that can look up your registration status, and which repeater you were registered on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If for some reason the original administrator is unable to help, then get to know a local repeater administrator and ask him or her for help.  (I'm under the impression that it's a lot more difficult for a different administrator to fix a registration problem.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-03-17T17:22:14.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10074" PostTypeId="1" AcceptedAnswerId="10075" CreationDate="2018-03-17T18:20:59.770" Score="6" ViewCount="268" Body="&lt;p&gt;There is an iron chimney near my house that is not used anymore. It is ~15 meters in length and ~0.5 meter in diameter. How good will it be as an antenna for rtl-sdr?&lt;/p&gt;&#xA;" OwnerUserId="1128" LastEditorUserId="8717" LastEditDate="2018-03-17T19:28:59.147" LastActivityDate="2018-09-03T19:11:17.620" Title="Will an iron chimney work well as an antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10075" PostTypeId="2" ParentId="10074" CreationDate="2018-03-17T23:51:53.287" Score="5" Body="&lt;p&gt;Assuming that your RTL-SDR covers VHF and up, 15 meters is too tall. You would be better off using it as a support for a suitable antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Iron has &lt;em&gt;far&lt;/em&gt; more losses than copper, aluminum, or other non-magnetic materials. Having said that, on HF a 15 x .5 meter pipe should have considerably less loss than a thin 15 meter iron wire and could be used for receiving with just a ground rod at the base. However, for transmitting you will need to minimize the losses with a good RF ground at the base, the feedpoint (and not just a ground rod!) consisting of suitable radial wires, either elevated or laid on the surface of the ground.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-03-18T21:22:07.553" LastActivityDate="2018-03-18T21:22:07.553" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10076" PostTypeId="1" AcceptedAnswerId="10078" CreationDate="2018-03-18T15:39:40.807" Score="2" ViewCount="2750" Body="&lt;p&gt;Given this question from the full license exam in the UK:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the field strength at a distance of 7m from an antenna with an effective radiated power of 100W?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;in which the answer is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;10 V/m&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;How do you calculate it?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="9493" LastEditDate="2018-03-18T20:05:20.063" LastActivityDate="2018-03-19T20:15:58.210" Title="How do you calculate the field strength at a given distance?" Tags="&lt;antenna-theory&gt;&lt;united-kingdom&gt;&lt;physics&gt;" AnswerCount="2" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10077" PostTypeId="2" ParentId="3663" CreationDate="2018-03-18T16:11:19.767" Score="1" Body="&lt;p&gt;While I'm not very experienced with packet radio (it's on my list of projects), I can comment in general on using IMAP on low-bandwidth connections.  I have extensive experience using it on dial-up TCP/IP connections (PPP), which are much slower than modern broadband connections and have much higher latency.  These are aspects it has in common with packet radio connections, although packet radio is much slower still (I was getting about 40kbps down and 28kbps up on dialup, and packet is either 1200 or 9600 bps bidirectionally and single duplex).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IMAP is ... well ... nearly unbearable on low bandwidth and high latency connections.  It takes very long periods of time to negotiate connections and download messages.  Watching the traffic using a packet analyzer (tcpdump), the protocol is very chatty.  With packet radio being single duplex, I think using IMAP over packet radio would verge on being unbearable unless the amount of email in the IMAP account is very small, indeed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That having been said, by all means, experiment with it and post your findings.  I may just try the same to satisfy my instincts about it.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-03-18T16:11:19.767" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10078" PostTypeId="2" ParentId="10076" CreationDate="2018-03-18T19:07:36.980" Score="5" Body="&lt;p&gt;The field strength in volts/meter as a function of effective radiated power and distance is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$E=\frac{7.01\sqrt{P_{ERP}}}{d} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where d is the distance from the radiating antenna in meters and P&lt;sub&gt;ERP&lt;/sub&gt; is the effective radiated power in watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you can see your sample problem was chosen such that the 7 meter distance cancels out the upper 7.01 term so you are simply left with the square root of 100 which results in 10 volts/m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formula 1 is derived from the long form of first calculating the power density on the imaginary sphere that has the transmitting antenna as its center and the point of observation on the surface of the sphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The area of the sphere is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$A=4\pi r^2 \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where r is the radius of the sphere (or in this case the distance from the transmitting antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power density is then calculated as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$S=\frac{P_TG_T}{4\pi r^2} \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where P&lt;sub&gt;T&lt;/sub&gt; is the transmitter power and G&lt;sub&gt;T&lt;/sub&gt; is the linear gain of the transmitting antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the problem states &quot;effective radiated power&quot;, this means that gain of the transmitting antenna in this case is ~1.64 for a 1/2 wavelength dipole. Thus we find that the power density is ~0.266 watts/m&lt;sup&gt;2&lt;/sup&gt;. Had the problem stated &quot;effective isotropic radiated power&quot;, the gain would be 1 to reflect the gain of an isotropic antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the power density is assumed to be in free space with an impedance of 377 ohms, we can use a variant of Ohm's law to find the field strength:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$E=\sqrt{377S} \tag 4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This results in the same answer as equation 1 with a field strength of ~10 V/m. Equations 3 and 4 can be combined and reduced to form equation 1. I leave this as an exercise for the reader.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would also be good to take note of the comments by @RichardFry. For this analysis to be accurate, the observation distance must be in the far field of the antenna and the propagation must satisfy the &quot;free space&quot; condition.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-19T12:22:52.757" LastActivityDate="2018-03-19T12:22:52.757" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10079" PostTypeId="1" AcceptedAnswerId="10080" CreationDate="2018-03-18T19:30:52.360" Score="1" ViewCount="346" Body="&lt;p&gt;For example, A1A is &quot;morse telegraphy by on-off keying&quot;. What are the others?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="9493" LastEditDate="2018-03-19T12:49:20.010" LastActivityDate="2018-03-19T12:49:20.010" Title="What are all the three letter codes for the different emission designators?" Tags="&lt;modes&gt;&lt;encoding&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10080" PostTypeId="2" ParentId="10079" CreationDate="2018-03-18T19:41:21.330" Score="4" Body="&lt;p&gt;I found the answer in this article in the Wikipedia: &lt;a href=&quot;https://en.wikipedia.org/wiki/Types_of_radio_emissions&quot; rel=&quot;nofollow noreferrer&quot;&gt;types of radio emissions&lt;/a&gt;. From that article you can construct the different codes for different modes but there's a list of common examples:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;A3E&lt;/strong&gt;: AM speech communication – used for aeronautical communications&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;F3E&lt;/strong&gt;: FM speech communication – often used for marine radio and many other VHF communications&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;20K0 F3E&lt;/strong&gt;: Wide FM, 20.0 kHz width, ±5 kHz deviation, still widely used for Ham Radio, NOAA weather radio, marine, and aviation users and land mobile users below 50 MHz &lt;a href=&quot;https://en.wikipedia.org/wiki/Types_of_radio_emissions&quot; rel=&quot;nofollow noreferrer&quot;&gt;1&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;11K2 F3E&lt;/strong&gt;: Narrow FM, 11.25 kHz bandwidth, ±2.5 kHz deviation – All Part 90 Land Mobile Radio Service (LMRS) users operating above 50 MHz were required to upgrade to narrowband equipment by 2013-01-01. [2] [3] [4]&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;6K00 F3E&lt;/strong&gt;: Even Narrower FM, future roadmap for Land Mobile Radio Service (LMRS), already required on 700 MHz public safety band&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;J3E&lt;/strong&gt;: SSB speech communication, used on HF bands by marine, aeronautical and amateur users&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;R3E&lt;/strong&gt;: SSB with reduced carrier (AME) speech communication, primarily used on HF bands by the military (a.k.a. compatible sideband)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;N0N&lt;/strong&gt;: Continuous, unmodulated carrier, formerly common for radio direction finding (RDF) in marine and aeronautical navigation.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;A1A&lt;/strong&gt;: Signalling by keying the carrier directly, a.k.a. Continuous Wave (CW) or On-Off Keying (OOK), currently used in amateur radio. This is often but not necessarily Morse code.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;A2A&lt;/strong&gt;: Signalling by transmitting a modulated tone with a carrier, so that it can easily be heard using an ordinary AM receiver. It was formerly widely used for station identification of non-directional beacons, usually but not exclusively Morse code (an example of a modulated continuous wave, as opposed to A1A, above).&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;F1B&lt;/strong&gt;: Frequency-shift keying (FSK) telegraphy, such as RTTY.[a]&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;F1C&lt;/strong&gt;: High frequency Radiofax&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;F2D&lt;/strong&gt;: Data transmission by frequency modulation of a radio frequency carrier with an audio frequency FSK subcarrier. Often called AFSK/FM.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;J2B&lt;/strong&gt;: Phase-shift keying such as PSK31 (BPSK31)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2018-03-18T19:41:21.330" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10081" PostTypeId="2" ParentId="10076" CreationDate="2018-03-19T20:15:58.210" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How do you calculate it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In the general case, you use a numerical EM field solver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without a specification of the antenna geometry and exactly which point 7 meters away is under consideration, this is not an answerable question. Even with such specifications the answer is very complex to calculate, and not the sort of thing one would casually do with a pencil for an exam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Only if 7 meters away is in the far field, meaning several wavelengths away can we use the impedance of free space and power density to calculate the field strength as Glenn W9IQ explains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this point 7 meters away is not in the far field, the geometry of the antenna is very relevant. At very close distances, a dipole will have a stronger voltage field than a small loop antenna, for example. The near-field strength has little to do with the radiated power density.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since nothing in the question establishes that the operating wavelength is significantly less than 7 meters, and there are many amateur bands with a wavelength far in excess of 7 meters, there is insufficient information in the question to make a correct answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apparently, the UK exam has a &lt;a href=&quot;https://ham.stackexchange.com/q/9333/218&quot;&gt;pattern of asking such grossly oversimplified questions&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-03-19T20:15:58.210" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10082" PostTypeId="1" AcceptedAnswerId="10083" CreationDate="2018-03-19T23:37:57.387" Score="3" ViewCount="456" Body="&lt;p&gt;This is question a3i3-1 from the practice questions in the book &quot;amateur radio Exam Secrets&quot;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A series resonant circuit has 10V peak across it when at resonance. At that frequency the resistance of the coil is approximately 4Ω and the Q-factor is calculated as 100. The voltage across the capacitor will be about&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A 40V&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;B 100V&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;C 400V&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;D 1000V&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I don't know the answer yet, but looking it up won't help me because I'm stuck in how to calculate the answer. How do you do it?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2018-03-21T12:50:08.713" LastActivityDate="2018-03-23T16:37:24.633" Title="Series resonant circuit, how to calculate voltage across the capacitor?" Tags="&lt;electronics&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10083" PostTypeId="2" ParentId="10082" CreationDate="2018-03-20T07:49:25.923" Score="8" Body="&lt;p&gt;I encourage students to draw a simple schematic when it comes to word problems such as these. Here is an ideal series resonant circuit:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ps9qR.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fps9qR.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the problem states that the circuit is in resonance, the inductive reactance equals the capacitive reactance making this ideal circuit a dead short (0 ohms) across the signal generator. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the real world is not ideal. The inductor is made up of multiple turns of wire. This wire has an RF resistance which must be shown in the circuit for a proper analysis. So we modify the ideal circuit to a more practical circuit to reflect this resistance:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/zPiOT.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fzPiOT.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the current through the circuit is limited only by the value of R1 which we are told is 4 ohms at the frequency in question. We are also told that the voltage across the series circuit is 10 volts (peak) so the current through the circuit is given by Ohm's law:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$I=E/R \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This formula allows us to calculate that the current in the circuit, when it is at resonance, is 2.5 amps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We are not given the values of L1 or C1 but we are given the Q (quality factor) of the circuit which is 100. Recall the formula for the Q in a series resonant circuit is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Q=\frac{X_L}{R}=\frac{X_C}{R} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where X&lt;sub&gt;L&lt;/sub&gt; is the inductive reactance of the inductor, X&lt;sub&gt;C&lt;/sub&gt; is the capacitive reactance of the capacitor and R is resistance of the inductor (or more generally of the series circuit). Since the problem gives us the Q and the R, we can re-arrange formula 2 to solve for X&lt;sub&gt;C&lt;/sub&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$X_C=Q*R  \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can now compute that the capacitive reactance at the unknown frequency is 400. The voltage across the capacitive reactance is calculated using Ohm's law:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$E=I*R \tag 4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the 2.5 amps that was calculated earlier as the current in the circuit, we find that the voltage across the capacitor with its 400 ohm reactance is 1000 volts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps a good lesson in sizing caps for the application!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-03-23T16:37:24.633" LastActivityDate="2018-03-23T16:37:24.633" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10084" PostTypeId="1" CreationDate="2018-03-20T17:35:53.827" Score="1" ViewCount="97" Body="&lt;p&gt;thanks for the answer i love ham radios.&lt;/p&gt;&#xA;" OwnerUserId="11353" LastEditorUserId="76" LastEditDate="2018-03-20T17:47:02.700" LastActivityDate="2018-03-20T17:47:02.700" Title="what frequencies can i transmit on without a license in NM?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;ht&gt;" AnswerCount="0" CommentCount="0" ClosedDate="2018-03-20T17:47:09.997" ContentLicense="CC BY-SA 3.0" />
  <row Id="10085" PostTypeId="2" ParentId="10074" CreationDate="2018-03-20T20:42:46.613" Score="2" Body="&lt;p&gt;It is a quarter-wave at 60 meters, 5 MHz. With the large diameter, losses would be negligible despite the poor conductivity and magnetic losses in iron. This would be a good transmit antenna if you can find a way to feed current into it&#xA;with low losses. I think that would be possible with an appropriate set of ground plane wires and maybe a better metal (aluminium foil) on the lowest&#xA;couple of meters so you could couple by use of fairly short high Q couplers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For receive with an rtl-sdr, just use it to support something for the frequency of interest. For HF, a thin wire from the top, for vhf a 15 m high tower to mount antennas on is excellent:-)&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-03-20T20:42:46.613" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10086" PostTypeId="1" AcceptedAnswerId="10089" CreationDate="2018-03-21T12:31:38.430" Score="5" ViewCount="166" Body="&lt;p&gt;This is question a3a1-1 from the set of practice questions in the &quot;amateur radio Exam Secrets&quot; book:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;An antenna is connected by a short feeder to the input to a radio receiver. Everything is correctly matched to 50Ω and a sensitive, high impedance RF voltmeter placed across the feeder records an input to the receiver of 10μV. The receiver is disconnected and the level of the RF signal noted. The reading will be about:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and the correct answer in 20μV. Why is that?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="9493" LastEditDate="2018-03-21T14:28:10.647" LastActivityDate="2018-11-01T06:50:59.240" Title="RF signal level when the antenna is disconnected" Tags="&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10087" PostTypeId="2" ParentId="10074" CreationDate="2018-03-21T13:38:24.470" Score="-2" Body="&lt;p&gt;Not so much! Iron is a poor conductor of RF and will likely result in spurious transmissions.&lt;/p&gt;&#xA;" OwnerUserId="9449" LastEditorUserId="9449" LastEditDate="2018-09-03T19:11:17.620" LastActivityDate="2018-09-03T19:11:17.620" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10089" PostTypeId="2" ParentId="10086" CreationDate="2018-03-21T13:54:54.887" Score="10" Body="&lt;p&gt;The situations described, schematically:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/uBuQe.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fuBuQe.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the source and load are matched (R&lt;sub&gt;antenna&lt;/sub&gt; = R&lt;sub&gt;receiver&lt;/sub&gt;), you will be measuring the voltage in the first case through a voltage divider such that the measured voltage will always be half the open-circuit voltage.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-03-21T16:43:39.770" LastActivityDate="2018-03-21T16:43:39.770" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10090" PostTypeId="1" AcceptedAnswerId="10093" CreationDate="2018-03-24T03:12:49.583" Score="1" ViewCount="245" Body="&lt;p&gt;I'm interested in building a relay for analog video sent from an R/C aircaft. The idea is to get around obstacles like hills and increase distance a bit. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rather than just applying more power, I wondered if I could build something that would act as a relay station for everything from about 5700-5900Mhz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm thinking about an amp in the range of 0.5w to 1Wa with a directional antenna hookup up to each side. Several of us would be flying behind a hill or obstacle, while the relay would be in a position that is LOS to both us and the aircraft.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd have to keep the input antenna from &quot;seeing&quot; the output antenna as much as possible, how much of an issue is this? Would two patch antennas facing away from each other work? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What issues would I need to be aware of with the amp? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, if is this easier or harder at different frequencies? Maybe 2.4Ghz, or 1.3Ghz or 900Mhz? &lt;/p&gt;&#xA;" OwnerUserId="8380" LastActivityDate="2018-03-28T13:22:40.120" Title="building a relay for 5.8Ghz?" Tags="&lt;repeater&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10091" PostTypeId="2" ParentId="3840" CreationDate="2018-03-24T03:25:25.117" Score="1" Body="&lt;p&gt;If you mean 2.4Ghz for video, how are you going to control the R/C model? 2.4Ghz spread spectrum is the most common R/C control link. A 2.4Ghz video transmitter would probably swamp your R/C control RX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've done a 3.5mi flight with 2.4Ghz control and 5.8Ghz video. That was a 200mW video transmitter, and a &quot;pepperbox&quot; antenna. It's very directional. It has a 160deg beam width, but 60deg beam height. I was also out in the middle of nowhere where the noise floor was really low (and I wouldn't damage anything if I crashed and I knew I could retrieve if I crashed). The flight was pretty much straight and flat. I say all this to say that the environment and antennas matters a lot. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general you'll have better luck with video on lower frequencies. 900Mhz is about the lowest I have seen folks use for video, antennas get pretty big though. It might be hard to find ready-made gear for anything else. I have seen some compact 1.3Ghz antennas. &lt;/p&gt;&#xA;" OwnerUserId="8380" LastEditorUserId="8380" LastEditDate="2018-10-15T13:04:59.137" LastActivityDate="2018-10-15T13:04:59.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10092" PostTypeId="2" ParentId="10054" CreationDate="2018-03-24T10:35:08.510" Score="1" Body="&lt;p&gt;Your proposed big antenna could be too much for a cheap receiver. You probably will not blow any front end transistors, but MW or AM overload could give spurious responses, birdies, blocking, cross modulation etc. An experimental small series cap starting at say 10pF will improve matters by making the long antenna think that it is a short antenna. This reduces the signal input but it also reduces the noise. I found this quite workable 40 years ago. Cheap solid state SW receivers had BJT Autodyne converters. Front-end selectivity was not good, especially when there was no tuned RF stage. Modern cheap receivers can have a broadband antenna input which could even be worse. You could build a simple tuned preselector which would improve any receiving system.&lt;/p&gt;&#xA;" OwnerUserId="6095" LastEditorUserId="8717" LastEditDate="2018-03-24T16:29:43.353" LastActivityDate="2018-03-24T16:29:43.353" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10093" PostTypeId="2" ParentId="10090" CreationDate="2018-03-24T18:39:04.597" Score="5" Body="&lt;p&gt;Let's work an example. Say the aircraft transmits at 1 watt, or 30 dBm, on 2.4 GHz. The aircraft is 500 meters away, giving a &lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;free space path loss&lt;/a&gt; of 92 dB. Between transmit and receive antennas perhaps there is 10 dBi gain, so the power received at the relay is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 30\:\mathrm{dBm} - 92\:\mathrm{dB} + 10 \:\mathrm{dB} = -52\:\mathrm{dBm} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meanwhile, the relay is re-transmitting this signal at a power of 30 dBm. the isolation between the antennas really depends on the antenna design, but let's say you have a patch antenna with a null in its pattern that's 30 dB less than its peak gain. You have two of these which you position carefully so each is in the other's null, so you have a total of 60 dB isolation between them. That means the relay transmit power making it into the relay receiver is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 30\:\mathrm{dBm} - 60\:\mathrm{dB} = -30\:\mathrm{dBm} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meaning, the signal from the aircraft the relay is trying to receive is 22 dB below the &quot;noise&quot; created by the relay's own transmitter. This will not work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Somehow you need to introduce additional isolation such that the aircraft can be heard above the relay's own transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This could be done by filtering in frequency. The farther apart the receive and transmit frequencies, the less steep the filter transition must be. So a cross-band relay will be cheaper and simpler.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternating between receive and transmit in time is also possible, though perhaps not for a continuous analog video stream. With packetized digital video however, very reasonable.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-03-28T13:22:40.120" LastActivityDate="2018-03-28T13:22:40.120" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10095" PostTypeId="1" CreationDate="2018-03-27T16:12:55.463" Score="2" ViewCount="253" Body="&lt;p&gt;I just got an SDRPlay and an MFJ-1708SDR transmit switch.  I use the the PTT on my Flex to key the amp, so I am wondering if the RF sense is fast enough to protect my SDR radio?&lt;/p&gt;&#xA;" OwnerUserId="4083" LastEditorUserId="9493" LastEditDate="2018-03-27T16:57:44.040" LastActivityDate="2018-03-27T21:53:11.243" Title="Is MFJ-1708SDR safe with RF switching" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10096" PostTypeId="2" ParentId="10095" CreationDate="2018-03-27T21:53:11.243" Score="4" Body="&lt;p&gt;In your description, you state that your Flex controls the amp. Be aware that the MFJ switch is only rated to 200 watts PEP. Exceeding this limit is an invitation for failure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If wired properly and used within its specifications, the MFJ switch should protect your SDR input. I have no experience with this switch but I would recommend that you pay attention to sequencing of all devices in the RF path at the start and end of a transmission. At a minimum, the Flex should be programmed to delay its RF output on PTT assertion for a sufficient time to allow the MFJ switch to transition to transmit mode prior to the Flex emitting RF. The amp also needs time to switch so the Flex delay should be at least as long as the longest switch time of the two and then add a 20% safety margin. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally you would key the MFJ, wait a sufficient time for it to switch,  then key the amp and wait for its R to T switch delay, and then finally allow RF from the transmitter. Reverse the sequence upon release of the PTT. This scheme ensures that any transients or oscillations from the amp cannot find their way into the SDR input. There are add on sequencer circuits designed to perform these functions if your existing equipment does not directly offer sufficient sequencing features.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also add an input protection device, such as those sold by DX Engineering and others, to the SDR input as another layer of protection.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-03-27T21:53:11.243" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10097" PostTypeId="2" ParentId="3840" CreationDate="2018-03-28T10:51:21.653" Score="0" Body="&lt;p&gt;You might be looking for &lt;a href=&quot;https://befinitiv.wordpress.com/wifibroadcast-analog-like-transmission-of-live-video-data/&quot; rel=&quot;nofollow noreferrer&quot;&gt;wifibroadcast&lt;/a&gt;, a form of low latency digital video broadcasting (motivated by controls of R/C models...)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Prominent features:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;uses Raspberry pi&lt;/li&gt;&#xA;&lt;li&gt;uses raw wifi frames, thus does not need association between the receiver and the transmitter&lt;/li&gt;&#xA;&lt;li&gt;video is received as long as the receiver is in range, with increasing number of errors as the signal drops (but the connection does not drop sicne there is no connection)&lt;/li&gt;&#xA;&lt;li&gt;low latency&lt;/li&gt;&#xA;&lt;li&gt;kilometer(s) range is achievable in good conditions&lt;/li&gt;&#xA;&lt;li&gt;diversity (reception with two different antennas) can improve reception under low signal/noise/reflections conditions&lt;/li&gt;&#xA;&lt;li&gt;unfortunately, wifi hardware does not pass frames with errors, which makes the reception less ideal (lower range) than it could be&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8922" LastActivityDate="2018-03-28T10:51:21.653" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10099" PostTypeId="1" AcceptedAnswerId="10101" CreationDate="2018-03-28T21:47:50.710" Score="2" ViewCount="815" Body="&lt;p&gt;From my understanding a return loss bridge basically consists of three terminals: an RF input, a DUT output and a RF output which goes to say a spectrum analyzer; I understand that the RF input signal goes to the DUT output, and any reflected power from the DUT goes to the RF output (Spectrum analyzer).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider a 3 terminal circulator: signal connected to terminal 1 is allowed to go to terminal 2 but not terminal 3, signal from terminal 2 is allowed to go to terminal 3 but not terminal 1, and so on. So if I connect an RF input to terminal 1 of the circulator, a DUT to terminal 2 and a spectrum analyzer to terminal 3, isnt that the same as a return loss bridge?&lt;/p&gt;&#xA;" OwnerUserId="4491" LastEditorUserId="76" LastEditDate="2018-03-28T23:26:51.097" LastActivityDate="2018-03-29T02:09:46.307" Title="What's the difference between a Return Loss Bridge and a Circulator?" Tags="&lt;electronics&gt;&lt;swr-meter&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10100" PostTypeId="2" ParentId="10099" CreationDate="2018-03-28T23:25:55.827" Score="1" Body="&lt;p&gt;(Disclaimer: I only just did some research on return loss bridges, not having heard of them before. Perhaps someone else will come along with a more knowledgeable answer.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are right that the two devices are similar in the abstract description of their function. The differences are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;They are differently &lt;em&gt;implemented.&lt;/em&gt; A circulator uses a &lt;strong&gt;permanent magnetic field&lt;/strong&gt; to influence propagating waves to produce its directional behavior. A return loss bridge, at least all the designs I have reviewed, uses conventional electronic components.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;They have different &lt;em&gt;performance characteristics.&lt;/em&gt; Most notably, a circulator generally has a &lt;strong&gt;much narrower bandwidth&lt;/strong&gt;, which is undesirable in test equipment. Several sources say that return loss bridges have high insertion loss (compared to directional couplers, which are a third type of device) as a tradeoff with bandwidth, which acceptable for measurement but not for power applications.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-03-28T23:25:55.827" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10101" PostTypeId="2" ParentId="10099" CreationDate="2018-03-29T02:09:46.307" Score="5" Body="&lt;p&gt;For an ideal circulator, all the power entering one port exits the next port in the rotation and no other. So all the power in port 1 exits port 2, all into port 2 exits port 3, and all into port 3 exits port 1. This is expressed by the &lt;a href=&quot;https://en.wikipedia.org/wiki/Scattering_parameters&quot; rel=&quot;noreferrer&quot;&gt;scattering matrix&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ S={\begin{pmatrix}0&amp;amp;0&amp;amp;1\\1&amp;amp;0&amp;amp;0\\0&amp;amp;1&amp;amp;0\end{pmatrix}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or a 4 port circulator:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ S={\begin{pmatrix}0&amp;amp;0&amp;amp;0&amp;amp;1\\1&amp;amp;0&amp;amp;0&amp;amp;0\\0&amp;amp;1&amp;amp;0&amp;amp;0\\0&amp;amp;0&amp;amp;1&amp;amp;0\end{pmatrix}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A return loss bridge might be more commonly known in the amateur radio hobby as an SWR bridge. These often employ some kind of directional coupler to measure the return loss. See &lt;a href=&quot;https://ham.stackexchange.com/q/9778/218&quot;&gt;How does an SWR meter really work?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like a circulator, a directional coupler can discriminate between forward and reverse power, but not in the same way. An ideal directional coupler's scattering matrix:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ S ={\begin{pmatrix}0&amp;amp;\tau &amp;amp;\kappa &amp;amp;0\\\tau &amp;amp;0&amp;amp;0&amp;amp;\kappa \\\kappa &amp;amp;0&amp;amp;0&amp;amp;\tau \\0&amp;amp;\kappa &amp;amp;\tau &amp;amp;0\end{pmatrix}} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;$\tau$ is the transmission coefficient, the ratio of voltage entering the input port which exits the output port. Typically this is a number close to 1, because usually it's desirable for the directional coupler to be transparent with regard to the input and output ports.&lt;/li&gt;&#xA;&lt;li&gt;$\kappa$ is the coupling coefficient, the fraction of voltage entering the input port which exits the coupled port. Typically this is a small number, since the objective is to &quot;sample&quot; the main signal while minimally disturbing it.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Naturally the law of conservation of energy requires $\tau^2 + \kappa^2 \le 1$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A directional coupler is a reciprocal device, so the previous descriptions but with &quot;input port&quot; exchanged with &quot;output port&quot;, and &quot;coupled port&quot; exchanged with &quot;isolated port&quot; apply equally. Electrically these ports are interchangeable: it's only the labels on the box, and possibly the connectors that distinguish them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A circulator can be used as, or as part of a duplexer, allowing one port to be used simultaneously by a receiver and a transmitter. Or by terminating one port of the circulator in a dummy load it can function as an isolator, sending all reflected power to the dummy load. In this way the transmitter will always &quot;see&quot; a matched load, even if the antenna is not matched. Although, the dummy load may get very hot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A directional coupler can not do these things. Because the coupling coefficient is small (and must be, if we want a high transmission coefficient), it does &lt;a href=&quot;https://ham.stackexchange.com/q/7319/218&quot;&gt;not make a good duplexer&lt;/a&gt;. Nor can it be made to function as an isolator at all, because it's a reciprocal device: if it's going to pass one power in one direction, it must do so identically in the other direction.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-03-29T02:09:46.307" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10102" PostTypeId="2" ParentId="7081" CreationDate="2018-03-29T13:29:46.340" Score="2" Body="&lt;p&gt;Below is a more elaborate analysis of an EFHW, with a length of vertical coaxial cable attached at its feedpoint.  It includes the effects of radiation from the &quot;unchoked&quot; r-f current that could flow along the outer surface of the outer conductor of the coaxial cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other details are shown in the Comment block at the lower left section of the graphic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VDKtA.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VDKtA.gif&quot; alt=&quot;wit&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-03-29T13:29:46.340" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10105" PostTypeId="1" AcceptedAnswerId="10107" CreationDate="2018-04-01T04:02:54.460" Score="5" ViewCount="1379" Body="&lt;p&gt;Tower is up and pre-stretched multi-strand 14 Ga wires are cut &amp;amp; terminated for a &lt;a href=&quot;https://www.SDsolarBlog.com/fan-dipole.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;multiband fan-style dipole antenna system&lt;/a&gt;.  Location is the desert southwest of the USA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stringing up parts of it are going to be a challenge due to topography, and it will require lengthy tie-down cord on the end of the 75/80 Meter portions.  Monofilament would definitely stretch and break down in the sun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I'm intending to use paracord and have a quantity of Mil Spec 7 Stranded Type III Nylon black paracord on hand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question:  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;1)  Will paracord hold up well enough in the hot sun?  And does the color matter?  i.e., will black paracord degrade noticeably faster than white?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2)  Is there a better alternative?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;FYI, I used the same antenna wire mentioned here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/10118/hf-swl-antenna-wire-will-plain-16-gauge-copper-wire-work-well-enough&quot;&gt;HF SWL antenna wire? Will plain 16-Gauge copper wire work well enough?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-04-06T17:32:31.003" LastActivityDate="2018-05-04T22:07:07.463" Title="Dipole antennas: Will paracord hold up well enough in the sun? Is there a better alternative?" Tags="&lt;antenna-construction&gt;&lt;parallel-dipole&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10107" PostTypeId="2" ParentId="10105" CreationDate="2018-04-01T14:02:55.033" Score="6" Body="&lt;p&gt;Paracord is a usurped and abused term for a wide variety of cords. The US Military previously specified 6 different types of paracord. It is also known as parachute or 550 cord. Originally constructed of nylon to allow shock absorbance in parachutes there are now many made of polyester and other materials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When considering its use for supporting an outside dipole there are three things to keep in mind: UV resistance, stretch and working strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A UV resistant material should be used for outdoor applications or the material will turn brittle and ultimately yield. Nylon, for example, deteriorates under long term exposure to the sun (UV). Check the supplier's specification and pick a UV resistant version. Color itself will not be a factor in UV susceptibility if the cord is already UV rated although some colors may fade under long term exposure to the sun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Paracord was originally designed to stretch. This may be helpful in providing some wind survivability for the dipole if stretched between trees, for example, but too much stretch may make it difficult to properly tension the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dipole with a balun and coax cable can require considerable tension in order to attain the desired catenary droop. You can use on-line calculators to determine the minimum working load  for the paracord or simply use a pull scale (fishing, luggage, etc.) on your installation to measure the applied tension to ensure you are operating below the working load of your paracord.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your supporting cord will rub against trees or other supports, you should take measures to guard against abrasion or choose an abrasion resistant construction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are not committed to using paracord, there are several cords suitable for antenna applications. Mastrant by &lt;a href=&quot;http://www.dxengineering.com/search/product-line/mastrant-antenna-support-and-guy-line-ropes?autoview=SKU&amp;amp;sortby=Default&amp;amp;sortorder=Default&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Engineering&lt;/a&gt; or &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B079C8583F&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amazon&lt;/a&gt; is one such example.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="8832" LastEditDate="2018-04-29T20:56:42.160" LastActivityDate="2018-04-29T20:56:42.160" CommentCount="8" ContentLicense="CC BY-SA 3.0" />
  <row Id="10108" PostTypeId="1" AcceptedAnswerId="10109" CreationDate="2018-04-02T14:26:20.203" Score="3" ViewCount="649" Body="&lt;p&gt;I have an SWR-001, which seems to be released under two different brands, MyDEL and Sharman. The MyDEL SWR-001 looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3nFzg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3nFzg.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and the Sharman one looks the same except for the label on the bottom left (it looks like Sharman could afford a brand and MyDEL didn't):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2c8rz.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2c8rz.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case I'm wrong about these two devices being the same, I have the first one, the one with the label SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feeder goes from my Icom IC-7300 to the SWR-001 and the SWR-001 in turn is connected to an LDG IT-100 autotuner (which also has the data lead to the IC-7300 for auto-tuning).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After finding an clear frequency, I set my radio to FM mode and 100W. I then set the SWR-001 Range to 300W, Function to CAL, and Power to FWD. I press the PTT and adjust the CAL knob until the needle shows 100W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this procedure correct to calibrate the SWR-001 to measure the SWR?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I do it with the tuner turned on or off? The results are quite different and I don't know the theory behind the calibration procedure to be able to figure out what's going on on my own.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, it seems this calibration only works at a certain frequency or band and when I change to a different band I should re-calibrate. Is this correct?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This calibration has no effect on measuring power, does it? &lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2018-04-23T19:22:25.960" LastActivityDate="2018-04-23T19:22:25.960" Title="Am I calibrating my SWR meter, SWR-001, correctly?" Tags="&lt;equipment-operation&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="10109" PostTypeId="2" ParentId="10108" CreationDate="2018-04-02T15:11:45.710" Score="4" Body="&lt;p&gt;The calibration procedure is only used for determining the SWR - the forward and reflected power reading are not impacted. If you change power levels or frequency, you need to perform the calibration again to read the SWR. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The calibrate procedure is to set the needle to the CAL position on the meter, not to the 100 watt reading as you described. Then flip the switch to  SWR to read the SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As your LDG tuner adjusts its match point, you will probably need to do a minor tweak on the calibration of the SWR meter. But the job of the tuner is to present a 1:1 SWR to the transmitter so if the tuner is able to find a match, your SWR meter will always show a 1:1 SWR or equivalently, 0 watts reflected power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is a good practice to use only 10 watts or so when adjusting your antenna tuner. This helps to reduce stress on the transmitter and the tuner. If the tuner interfaces properly to your transmitter, it may automatically cut power when tuning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you read the SWR with the tuner in bypass mode, you are seeing the SWR of your antenna system before the tuner attempts to make this a 1:1 SWR for the transmitter. Take such readings using low power and record them in your logbook. Then later if you suspect antenna problems you compare the readings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your IC 7300 has a built in antenna tuner. If you are using your LDG tuner, it is probably best to disable the 7300 internal tuner.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-02T15:34:36.510" LastActivityDate="2018-04-02T15:34:36.510" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10112" PostTypeId="1" CreationDate="2018-04-02T19:32:31.883" Score="9" ViewCount="122" Body="&lt;p&gt;I'm crossing the English channel on a ferry soon and I'd like to do some radio while on it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to my license (full British Ofcom amateur radio license), to be able to do this, I need permission from the master of the vessel. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What should this permission look like? I take it should be written.&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="8832" LastEditDate="2018-04-02T23:25:13.897" LastActivityDate="2018-04-03T20:31:15.943" Title="Getting permission from the master of the vessel" Tags="&lt;united-kingdom&gt;&lt;etiquette&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10113" PostTypeId="2" ParentId="10112" CreationDate="2018-04-03T20:15:37.960" Score="4" Body="&lt;p&gt;Written permission or prohibition to bring ham radio gear on board is proffered by some of the large cruise lines. For example, &lt;a href=&quot;https://help.carnival.com/app/answers/detail/a_id/2261/~/carnival-cruise-line-additional-prohibited-items%2C-exemptions-and-other&quot; rel=&quot;nofollow noreferrer&quot;&gt;Carnival&lt;/a&gt; gives written permission by way of their published policy where as &lt;a href=&quot;https://www.ncl.com/prohibited-items&quot; rel=&quot;nofollow noreferrer&quot;&gt;Norwegian&lt;/a&gt; specifically denies permission to possess ham radio equipment on board (or even a satellite phone!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once on board, the captain of the ship must be approached to garner permission to operate. You can expect to be asked about the antenna, the frequencies involved, the amount of power, and how the radio will be powered. The captain will view most of this information with an eye toward the safety of fellow passengers and the potential for interference with on-board radio equipment.  If the captain is so inclined he or she will then give verbal permission but most likely with the caveat that at his or her request, you must immediately cease operations. The captain most certainly will not take the time during boarding to grant you any type of written permission - everything will be verbal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So unless your country's regulations specifically require that you obtain written permission, you should be able to operate with the captain's verbal permission. Do keep in mind that your home country's radio regulations may only be applicable when you are within your country's own territorial waters. If you are in international waters, often the flag of the ship determines the applicable regulations for the ham radio operator.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-03T20:31:15.943" LastActivityDate="2018-04-03T20:31:15.943" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10115" PostTypeId="1" AcceptedAnswerId="10116" CreationDate="2018-04-05T03:49:03.393" Score="2" ViewCount="91" Body="&lt;p&gt;It is rumoured that radio handsets are sometimes used in Canada on 2-metre amateur bands without being certified with Industry Canada. Some of those sets may be modified or reprogrammed to operate on 2m commercial bands, it is said. That would of course be against Industry Canada regulations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it theoretically possible to have a radio handset which is compliant with Industry Canada regulations for use on both 2m amateur bands and 2m commercial bands, &lt;em&gt;and&lt;/em&gt; properly certified by Industry Canada? Can anyone give examples of handsets which meet these criteria?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding of Industry Canada regs for commercial bands is that a mobile handset must not provide a way of choosing arbitrary frequencies in the field. At most they can permit switching between pre-programmed channels. The programming must be done with a gadget separate from the handset (like a special cable and computer and software).  My understanding of the Canada regs for amateur radio are that it is permitted and normal to handsets to provide a way — like a numeric keypad — of choosing arbitrary frequencies in the field. However, the keypad is not required for amateur gear, and it is compliant to use a radio with pre-programmed channels on amateur bands. And my understanding is that a handset is only regs-compliant if it is actually certified with Industry Canada, and is on IC's list of compliant radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If my understanding is correct, then it isn't clearly impossible for one handset to comply with regs for both amateur and commercial 2m bands. But I would like answers that can confirm it is theoretically possible to comply. If there are examples of real handsets that are Industry Canada certified, that's a convincing way to demonstrate that it is possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just to be clear, regs also specify operator licensing. For instance, an operator transmitting on amateur frequencies must hold (or be supervised by a holder of) an amateur radio licence. But I'm not concerned here with regs about operators, just regs about handsets.&lt;/p&gt;&#xA;" OwnerUserId="719" LastEditorUserId="719" LastEditDate="2018-04-05T23:58:56.907" LastActivityDate="2018-04-05T23:58:56.907" Title="Are any handsets compliant with Canadian regs usable on both 2M amateur and 2M commercial bands? Is this even possible?" Tags="&lt;legal&gt;&lt;transceiver&gt;&lt;2m-band&gt;&lt;canada&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 3.0" />
  <row Id="10116" PostTypeId="2" ParentId="10115" CreationDate="2018-04-05T13:19:49.157" Score="3" Body="&lt;p&gt;According to &lt;a href=&quot;http://narc.net/forums/showthread.php/96-LMR-Radios-and-operator-certification-requirements&quot; rel=&quot;nofollow noreferrer&quot;&gt;Alan McLean of Industry Canada&lt;/a&gt; if a radio approved for use in LMR service in Canada, for example, can be software reprogrammed (without hardware modifications) to be used on the amateur bands, then such reprogramming and use is permitted by any Canada amateur radio license class as it is considered an SDR under section 44:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In regard to the use of commercially manufactured &quot;Software Defined&quot; radio equipment within the Amateur Radio Service: &#xA;  Provided that the equipment has been manufactured capable of operating within a frequency range inclusive of those frequencies assigned for use by the Amateur Radio Service and can be configured &quot;Solely&quot; by means of software programming, the programming and use of these devices by an amateur radio operator holding a Basic, or Basic with Honours certificate is permissible.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It appears that Industry Canada is responsive to licensee's questions so if you have any remaining questions, you may wish to directly contact them via email.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-04-05T13:19:49.157" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10117" PostTypeId="1" AcceptedAnswerId="10164" CreationDate="2018-04-05T16:35:48.353" Score="3" ViewCount="1811" Body="&lt;p&gt;I am mounting my first antenna.&#xA;It is a TRAM 1481 (about 16' height), which will be placed on a 20' pole, on my home's flat roof (about 25' height).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To properly stabilize the pole/antenna:&#xA; - How far up the pole should I tie the cables?&#xA; - How far away from the pole should I place the cables' anchors?&#xA; - Any minimum amount of cables I should use?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was planning to tie the cables up 16' and place the anchors around 3' away.  I will then need around 16.3' of cable per anchor to tie to the pole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But is there a formula to determine all this?&lt;/p&gt;&#xA;" OwnerUserId="11385" LastActivityDate="2020-12-26T03:12:31.750" Title="Stabilization of an antenna pole with anchoring cables" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10118" PostTypeId="1" AcceptedAnswerId="10120" CreationDate="2018-04-05T16:37:08.857" Score="3" ViewCount="2092" Body="&lt;p&gt;Planning to set up a HF antenna for RX-only.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I can't decide what kind of wire to use.  I want to buy something new.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My first thought is to buy a spool of 16 Gauge copper wire, but am hoping to not destroy my wallet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will that work well, or are there other design characteristics I should consider?&lt;/p&gt;&#xA;" OwnerUserId="11352" LastEditorUserId="8832" LastEditDate="2018-04-06T20:14:35.973" LastActivityDate="2018-04-23T00:51:13.830" Title="HF SWL antenna wire? Will plain 16-Gauge copper wire work well enough?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;equipment-design&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10119" PostTypeId="1" AcceptedAnswerId="10121" CreationDate="2018-04-06T00:03:08.307" Score="5" ViewCount="204" Body="&lt;p&gt;It is the size of a BNC but has threads.  For an RF output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ehbz6.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ehbz6.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I need to adapt it to SO-239.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;----------------------------------------------&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Tip o' The Hat to Glenn and Scott.  TNC it is.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This cable works great:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ebay.com/itm/20-TNC-male-to-PL-259-SO-239-female-RG58-cable-jumper-pigtail-MADE-IN-USA/321959141223&quot; rel=&quot;nofollow noreferrer&quot;&gt;TNC Male to SO-239 pigtail&lt;/a&gt;  (eBay)&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-04-09T20:50:29.510" LastActivityDate="2018-04-09T20:50:29.510" Title="What is this connector?" Tags="&lt;connectors&gt;&lt;tnc&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10120" PostTypeId="2" ParentId="10118" CreationDate="2018-04-06T00:14:57.077" Score="3" Body="&lt;p&gt;I believe plain copper (presumably non-insulated) will be a non-optimal choice - particularly because it will stretch.  Plus, since it is coming from a spool it is very easy to kink it which can cause it to break - constant worry.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the old days we would use the Alaska Way to take care of the stretching problem by hard-drawing it:  We'd take plain copper wire and tie it off to the bumper of a truck, with an intentional kink in it right before the bumper.  Then we would slowly drive forward to stretch it until it broke at the kink.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You would be amazed how far it would stretch until it was strong enough to break at the kink.  During the process it is important to watch out for unintentional kinks, of course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But that was then and this is now. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Now I use &lt;strong&gt;Hard-drawn 7-strand 14 Gauge Copper antenna wire&lt;/strong&gt;.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.amateurradiosupplies.com/product-p/10173.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.amateurradiosupplies.com/product-p/10173.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(This is a listing for 200 feet on a spool for $32.99 + shipping.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I bought two spools recently and it is great stuff.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GgO8j.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GgO8j.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(This example photo shows 50 feet from an eBay listing)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;And of course, an antenna is not simply made of a piece of wire.  To make the total skyhook you'll want to mount it.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I also use small egg insulators at the end of the wire, with the antenna wire folded back and secured with a small hose clamp:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ebay.com/itm/152565482141&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ebay.com/itm/152565482141&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9l08h.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9l08h.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ebay.com/itm/131441937300&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ebay.com/itm/131441937300&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/URXg1.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/URXg1.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;To string it up I use 3mm Mastrant-P for a particular run where it is used for tensioning - can't have the long 80-meter wires drooping down over the yard&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ebay.com/itm/Mastrant-3mm-Diameter-Mastrant-P-Braided-Rope-w-Twisted-Core-100-Foot-Length/112827110869&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ebay.com/itm/Mastrant-3mm-Diameter-Mastrant-P-Braided-Rope-w-Twisted-Core-100-Foot-Length/112827110869&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OeAg5.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OeAg5.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm building a &lt;a href=&quot;https://www.sdsolarblog.com/fan-dipole.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;multi-band fan-shaped dipole&lt;/a&gt; that will be up for years to come, so decided the price was worth it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/10105/dipole-antennas-will-paracord-hold-up-well-enough-in-the-sun-is-there-a-better&quot;&gt;Dipole antennas: Will paracord hold up well enough in the sun? Is there a better alternative?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Paracord works but stretches more.  So it is fine for shorter runs and a lot more affordable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ebay.com/itm/Paracord-100-Feet-Mil-Spec-7-Strand-Type-III-Nylon-Parachute-Cord/262931740204&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ebay.com/itm/Paracord-100-Feet-Mil-Spec-7-Strand-Type-III-Nylon-Parachute-Cord/262931740204&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AvpIT.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AvpIT.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;This is Mil-Spec 7-strand Type III Nylon at a very affordable price&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;You can decide whether the wallet trumps quality.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-04-23T00:51:13.830" LastActivityDate="2018-04-23T00:51:13.830" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10121" PostTypeId="2" ParentId="10119" CreationDate="2018-04-06T00:18:41.673" Score="7" Body="&lt;p&gt;It looks like a female &lt;a href=&quot;https://en.wikipedia.org/wiki/TNC_connector&quot; rel=&quot;noreferrer&quot;&gt;TNC connector&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="873" LastEditDate="2018-04-06T00:27:06.470" LastActivityDate="2018-04-06T00:27:06.470" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10123" PostTypeId="1" AcceptedAnswerId="10124" CreationDate="2018-04-06T10:31:44.080" Score="1" ViewCount="226" Body="&lt;p&gt;I'm considering building this yagi for some local contests: &lt;a href=&quot;http://www.i1wqrlinkradio.com/antype/ch90/chiave3.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.i1wqrlinkradio.com/antype/ch90/chiave3.htm&lt;/a&gt;. The question is should the elements be electrically connected to the boom or not? I sort of hope that they should as it makes construction easier, and on this guy's 430MHz yagi he explicitly states that they should be, however no mention is made of that in the 2m yagi page.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks in advance!&lt;/p&gt;&#xA;" OwnerUserId="11431" LastEditorUserId="9493" LastEditDate="2018-04-06T11:29:01.490" LastActivityDate="2018-04-06T11:29:01.490" Title="Yagi elements connected to boom?" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10124" PostTypeId="2" ParentId="10123" CreationDate="2018-04-06T10:58:47.310" Score="4" Body="&lt;p&gt;Physically, it should make little difference - symmetry tells us that at the connection point, no potential can exist, and without potential, no current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's fairly common practice to build especially larger yagi-uda with the elements simply screwed into, welded onto or crimped into the boom for stability reasons.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-04-06T11:05:04.287" LastActivityDate="2018-04-06T11:05:04.287" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10126" PostTypeId="1" AcceptedAnswerId="10132" CreationDate="2018-04-06T21:26:44.657" Score="7" ViewCount="1082" Body="&lt;p&gt;Is there a way to estimate the maximum number of turns which can be used with a ferrite core used as a common mode choke?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is known that the impedance of such a choke is proportional to the square of the number of turns and so there is a strong incentive to use multiple turns.  But it is also known that there is a limit due to what looks like a sort of resonance phenomenon and, once that limit is exceeded, increasing the number of turns has either no influence or negative influence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is an excellent paper on the subject by Jim Brown (K9YC)  ( &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://audiosystemsgroup.com/RFI-Ham.pdf&lt;/a&gt; ).  &lt;s&gt;Unfortunately, his maximum frequency of interest is about 100 MHz&lt;/s&gt; and my application is VHF and UHF. [edit: this sentence is wrong]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ferrite core manufacturers provide excellent information for impedance of a single turn at different frequencies.  This can be used to estimate the impedance when using multiple turns, so long as the limit is not reached; that limit could be as low as 1 turn!  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am willing to buy bunches of cores and measure them, but it would seem to be more efficient if I could somehow estimate an ideal geometry and use that as a starting point.  For example, if the limit is due to core volume, maybe lighter cores would be the preferred starting point.  Or if it is somehow related to diameter or circumference, then perhaps a smaller, wider core would be better. &lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="8717" LastEditDate="2018-07-26T17:25:32.860" LastActivityDate="2018-07-26T17:25:32.860" Title="What is the maximum number of turns in a ferrite core used as a common mode choke?" Tags="&lt;ferrite&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10127" PostTypeId="1" AcceptedAnswerId="10128" CreationDate="2018-04-07T10:27:15.570" Score="3" ViewCount="730" Body="&lt;p&gt;I want to do some satellite communication so I thought why not build my own helix antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found this page: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://jcoppens.com/ant/helix/index.en.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Helix antenna design and construction details&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most things are clear except for the turn spacing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My guess is that it gives a divisor of the wavelength which is used for one turn of the helix. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I don't know, after some thinking, that this makes no sense because the wave length is given by the frequency and the turns are given as a separate input.&lt;/p&gt;&#xA;" OwnerUserId="6257" LastEditorUserId="8832" LastEditDate="2018-04-11T02:44:18.250" LastActivityDate="2018-04-11T02:44:18.250" Title="What is the turn spacing on a Helix Antenna?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;satellites&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10128" PostTypeId="2" ParentId="10127" CreationDate="2018-04-07T15:36:01.790" Score="6" Body="&lt;p&gt;During his long career, J.D. Kraus studied, and experimented extensively with, helix antennas. There is a large body of published work in college text books on this subject. The following summarizes some of the key construction details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ideal circumference of each turn of the helix antenna is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$C=\lambda \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\lambda$ is the free space wavelength of the frequency for which the antenna is designed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The circumference of a circle is related to diameter by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$D=C/\pi \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Substituting equation 2 into equation 1, we have the diameter of each helix turn:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$D=\lambda/\pi \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The distance between each turn of the helix is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$S=0.225\lambda \tag 4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Kraus found that an optimum reflector for a helix fed with 50 ohm coax cable is a metalic cup with a diameter of 0.75$\lambda$ and a rim around the cup with a height of 0.375$\lambda$. The helix is centered inside the cup with the center of the coax attached to the helix through a hole in the bottom of the cup and the shield of the coax connected to the cup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cup can be used to fix non-conductive supports for the helix in order to improve the mechanical rigidity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The number of turns control the half power beamwidth (HPBW) and thus the directivity and gain of the helix. The HPBW in degrees is approximated as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\text{HPBW}\cong\frac{52}{C_\lambda \sqrt{nS_\lambda}} \tag 5$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where n is the number of turns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, a 16 turn helix constructed with the above dimensions will result in a HPBW of ~26° and with efficient construction &gt;15 dBi gain. The polarization will be nearly circular.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-07T21:37:13.493" LastActivityDate="2018-04-07T21:37:13.493" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10129" PostTypeId="1" CreationDate="2018-04-08T07:50:21.233" Score="4" ViewCount="5515" Body="&lt;p&gt;I'm trying to program my Boafeng bf-f8hp with the chirp software, but as I have to do, &quot;Download From Radio&quot;, after I choose the appropriate maker, product and model, all I get is an error message which reads, &quot;An Error has occured: The Radio did not respond.&quot;&#xA;I've unplugged all, restarted computer and plugged all back in, turned on radio, same result. &#xA;Ideas?&lt;/p&gt;&#xA;" OwnerUserId="11440" LastEditorUserId="4076" LastEditDate="2018-04-10T10:58:23.477" LastActivityDate="2021-01-15T02:09:22.287" Title="BF-F8HP: &quot;Radio did not respond&quot; when trying to use CHIRP" Tags="&lt;baofeng&gt;&lt;radio-programming&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10130" PostTypeId="2" ParentId="10129" CreationDate="2018-04-08T11:33:33.567" Score="5" Body="&lt;p&gt;The most common error is not selecting the correct COM port for the virtualized USB cable.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-04-08T11:33:33.567" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10131" PostTypeId="2" ParentId="10126" CreationDate="2018-04-08T11:58:08.797" Score="5" Body="&lt;p&gt;The primary issues with coax wound common mode chokes are;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The inductive reactance of the choke can cancel out the capacitive reactance associated with the feedline shield thereby worsening the CM situation&lt;/li&gt;&#xA;&lt;li&gt;The resistive component of the choke is not sufficient such that the core undergoes an undesirable temperature rise&lt;/li&gt;&#xA;&lt;li&gt;The interwinding capacitance forms a self resonant circuit which reduces the choking action&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;At VHF and UHF frequencies these pitfalls can be even more exasperating as windings become a significant fraction of a wavelength and the selection of suitable core materials diminishes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may wish to examine other methods of common mode suppression such as 1/4 wavelength sleeve baluns or transmission line baluns before attempting the coax on a ferrite choke approach. But if you care to pursue some lab work with ferrites you may find the VNA measurement method used by  &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/#measurement&quot; rel=&quot;nofollow noreferrer&quot;&gt;Steve G3TXQ&lt;/a&gt; to be helpful. His published work is for HF baluns but the measurement technique should be extensible to the higher bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you are mostly likely to find, however, is that there is no number (minimum or maximum) of coaxial turns on a ferrite core that will make an adequate CM choke at frequencies above 100 MHz.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-08T20:27:57.260" LastActivityDate="2018-04-08T20:27:57.260" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10132" PostTypeId="2" ParentId="10126" CreationDate="2018-04-08T12:05:14.057" Score="6" Body="&lt;p&gt;The &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;noreferrer&quot;&gt;K9YC paper you mention&lt;/a&gt; gives data up to 1 GHz on page 49:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BB01h.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BB01h.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These data show for these core types the maximum number of turns is just one or two. Furthermore, it's quite difficult to achieve a choking impedance above 1 kΩ. That's not very much, and for many applications you'd want more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get a higher choking impedance will require a larger core, and so ferrite chokes can become quite expensive at higher frequencies. For this reason it's often worth considering &lt;a href=&quot;https://ham.stackexchange.com/q/7225/218&quot;&gt;other techniques&lt;/a&gt; to supplement or replace them.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-04-08T12:05:14.057" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10133" PostTypeId="1" CreationDate="2018-04-08T22:06:28.483" Score="5" ViewCount="1537" Body="&lt;p&gt;A direct hit on my home by lightning is very, very unlikely.  However, many lightning strikes that hit Earth nearby are by far the main hazard for ham radio gear (in my opinion, after 60 years in the hobby). The huge electromagnetic pulse generated by such nearby strikes spreads in all directions at the speed of light.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been taught that such EMP will induce voltage on antenna wires, power lines, guy lines, etc—anything that can serve as an &quot;antenna&quot; for the pulse will have a voltage induced, sometimes very substantial.  Here's the question: Doesn't such an EMP impose a voltage spike on both the braid of a coax feed line as well as on its center conductor?  And, if so, how does a gas-discharge tube protection gadget on the center conductor of coax provide any safety at all? I am thinking that the old-fashioned idea of just &quot;disconnect the coax and throw it out the window&quot; still has appeal.&lt;/p&gt;&#xA;" OwnerUserId="10987" LastEditorUserId="76" LastEditDate="2018-04-08T23:17:55.513" LastActivityDate="2018-04-12T00:48:42.170" Title="Lightning strikes nearby and coaxial cable" Tags="&lt;antenna-system&gt;&lt;lightning&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10136" PostTypeId="2" ParentId="10133" CreationDate="2018-04-09T11:08:32.327" Score="1" Body="&lt;p&gt;A gas discharge lightning arrestor should be installed directly on the grounding system that consists of multiple ground rods properly spaced and bonded together. The case of the lightning protector directly bonds the shield of the coax to the ground rods to dissipate (bring to near earth potential) any shield induced currents. The gas discharge tube conducts when high voltage is present to dissipate any center conductor currents to the ground system. Ideally the low impedance ground rod system takes most of the induced current thereby saving the station equipment from damage. Professional installations such as cell (mobile phone) sites are successfully protected by such well engineered systems. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna systems can also build up dangerous or damaging voltages from wind or rain in the absence of lightning. A good lightning protection system can help protect equipment in this case as well when a manual disconnect procedure might be overlooked.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Disconnecting the antenna from the station is an approach that is commonly mentioned although this requires a realtime awareness of conditions that warrant the disconnect. Keep in mind that this techique may not protect the antenna and feedline from damage. Also remember to carefully discharge any built up charge prior to reconnecting the antenna system to the station. Use low power to check the antenna system SWR upon reconnecting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The subject of lightning protection can take many pages to convey the best practices and nuances. The ARRL has recently published a &lt;a href=&quot;https://www.arrl.org/shop/Grounding-and-Bonding-for-the-Radio-Amateur/&quot; rel=&quot;nofollow noreferrer&quot;&gt;book&lt;/a&gt; by Ward Silver on the subject that I recommend as a good reference. The ARRL also has linked information on grounding available on their &lt;a href=&quot;http://www.arrl.org/grounding-and-bonding-for-the-amateur&quot; rel=&quot;nofollow noreferrer&quot;&gt;website&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-04-09T11:08:32.327" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10137" PostTypeId="1" AcceptedAnswerId="10144" CreationDate="2018-04-09T14:11:31.317" Score="5" ViewCount="1436" Body="&lt;p&gt;I'm very new to shortwave radio,  as evidenced here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/10054/can-an-antenna-be-too-powerful-for-certain-receivers&quot;&gt;Can an antenna be too powerful for certain receivers?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to build a longwire receive-only antenna for the HF frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been using the source:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://users.telenet.be/d.rijmenants/en/swl.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;SWL - Shortwave Listening&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;as a guide, but it isn't clear whether it's using 50 or 75 ohm coax cable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The source says that if you use a coax you should also use a balun, but I don't know whether it should have a 9:1 ratio like the source says or whether I should calculate the impedance of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should the antenna be a specific length to receive the HF frequencies best? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a decent amount of space to work with so an antenna 75 feet long or less will be doable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I need to worry about SWR? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm wondering whether I even need to consider all this as I'm just making a receiving longwire; I'm pretty sure I need a coax as I live nearby other houses (i.e. sources of noise), but do I need to have a transformer, antenna tuner, match impedance, etc. or am I just overthinking this? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way the antenna system will be hooked up to a RTL-SDR dongle - this might be important to some answers.&lt;/p&gt;&#xA;" OwnerUserId="11310" LastEditorUserId="8717" LastEditDate="2018-07-03T18:46:58.003" LastActivityDate="2018-07-04T12:41:36.297" Title="How important is the impedance and resonance of a receive antenna?" Tags="&lt;antenna-construction&gt;&lt;hf&gt;&lt;rtl-sdr&gt;&lt;swl&gt;" AnswerCount="5" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10138" PostTypeId="2" ParentId="10133" CreationDate="2018-04-09T15:40:04.280" Score="1" Body="&lt;p&gt;Most lightning damage does not come from EMP, that is, energy received by electromagnetic radiation. Much more significant is the electrical potential difference between two points in the soil created as 15 coulombs of charge are dumped in an extremely short span of time in a small area, with current on the order of 30 kA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this reason, an &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;effective protection system&lt;/a&gt; must ground the station at only one point. With a single point ground the protected zone may rise to a high electric potential relative to some distant point, but as any two points within the protected zone are at the same potential, the equipment just &quot;floats over&quot; the surge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where possible, the potential difference within the protected zone is minimized by maximizing the conductivity between components. For grounded components this is easy: simply connect them with a lot of copper.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For signal lines this is more difficult, because signals can't simply be shorted to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of coax, the shield already affords a high degree of protection to the center conductor within. For the same reason signals don't &quot;leak out&quot; of the coax, most of the surge energy can't get in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The gas discharge tube (GDT) is meant to deal with the residual. If the potential difference between the center and shield is sufficient to ionize the gas the tube acts effectively as a short, clamping the difference between them to some value which is hopefully below the damage threshold of the connected equipment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-04-09T15:40:04.280" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10139" PostTypeId="2" ParentId="10137" CreationDate="2018-04-09T17:11:25.407" Score="3" Body="&lt;p&gt;The simple case would be a 75 foot wire whose far end is an open-end tied to a high support, and whose near end feeds directly to your SDR-dongle. It is assumed the dongle is a single-ended input whose other termination is RF-grounded through your PC.&lt;br&gt;&#xA;It is likely that your SDR-dongle has a low-impedance antenna input, perhaps 50 ohms. At some frequencies, this will work well. At other frequencies a poor match delivers less power to your SDR-dongle. A 75 foot wire would favour the low end of the HF frequency space, where it mimics a quarter-wave vertical. As the frequency goes higher, a poorer match to a low-impedance SDR would be where your antenna mimics a half-wave end-fed wire.&lt;br&gt;&#xA;Does this poor match make the antenna useless at certain frequencies? Certainly not, if your SDR receiver noise floor is decent....(a sensitive receiver). For transmitting, a good match would be more important for the health of a transmitting power amplifier but of less importance for a receiver where signal loss creates insignificant heat (nanowatts).&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding some coax between antenna-end and SDR might change the impedance that your SDR sees, and also change the frequency spans where the antenna is decently matched (and poorly matched). Coax will likely add some small signal loss too.&lt;br&gt;&#xA;For casual listening, throw up a good long wire, whose end comes conveniently-close to your SDR, and a short length of coax to make up the difference. If a band-segment becomes particularly interesting to you, a simple L-section tuner could improve signals, if that band-segment is poorly matched. But many receivers have enough sensitivity that perceived improvements may be minor. Fussing over a &quot;proper&quot; receiving antenna, especially over a wide frequency range like the whole HF spectrum is not worth the trouble if &quot;casual&quot; listening is a goal.&lt;/p&gt;&#xA;" OwnerUserId="11132" LastActivityDate="2018-04-09T17:11:25.407" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10140" PostTypeId="2" ParentId="443" CreationDate="2018-04-10T01:40:19.837" Score="0" Body="&lt;p&gt;I had a mag mount attached to the fender of my van (fiberglass roof and hood) and only about 75% of the base was able to fit on the top of the fender. Well when I got on the highway, up to about 60 mph and hit a bump, off went the antenna, hanging about 2 feet off the van, guy next to me beeped and braked, I pulled right over and drug it back in the window.  No accident, but learned my lesson.&#xA;That being said I have the same mag mount antenna on top of my Jeep and it stays on through the bumps and craters of I-95 at 80mph. So I'd say, from experience, if 100% of the base is attached to metal, you should be good. That being said, there's an exception for every rule...&lt;/p&gt;&#xA;" OwnerUserId="11445" LastActivityDate="2018-04-10T01:40:19.837" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10141" PostTypeId="1" AcceptedAnswerId="10142" CreationDate="2018-04-10T03:22:19.520" Score="3" ViewCount="732" Body="&lt;p&gt;In this scenario, I would have a base station connected to a modem that essentially allows me to access the internet/local network via radio, irately I am not fully aware of what information I need to provide to have a proper answer, as I am new to the community, but I am more than willing to learn.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;tl;dr: how fast can one transmit and receive at half-duplex on any given amateur radio frequency?&lt;/p&gt;&#xA;" OwnerUserId="11446" LastActivityDate="2018-04-10T04:22:55.467" Title="What are the maximum possible speeds of download over Amateur Radio frequencies?" Tags="&lt;software-defined-radio&gt;&lt;mobile&gt;&lt;internet&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10142" PostTypeId="2" ParentId="10141" CreationDate="2018-04-10T03:56:10.190" Score="4" Body="&lt;h1&gt;maximum rate&lt;/h1&gt;&#xA;&lt;p&gt;There's no upper boundary really other than SNR. There's no general number.&lt;/p&gt;&#xA;&lt;p&gt;There's what information theorists call &lt;em&gt;channel capacity&lt;/em&gt;, which simply relates the amount of bits per second you can get, at most, theoretically, across a channel of given bandwidth &lt;span class=&quot;math-container&quot;&gt;$B$&lt;/span&gt; at given signal-to-noise ratio. The formula simply states&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$C=B\log_2 \left(1+\text{SNR}\right)$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The idea is simple: the better your SNR, the more different symbols you can tell apart, which means a single symbol carries more bits of information. The higher the bandwidth, the more symbols per second you can send.&lt;/p&gt;&#xA;&lt;p&gt;Note that this is a theoretical upper limit, and doesn't say how you'd go about implementing something that does that rate. In radio communications we often come pretty close to this boundary with modern systems. Just don't expect something as &amp;quot;technologically braindead&amp;quot; as ax.25 to even nearly achieve that. But, for example, there's amateur radio bands with relatively large bandwidths in the upper microwave region, and with a good (read: low-noise) link on a large bandwidth, Gbit/s are certainly feasible. It all depends on how you use your spectrum and how much spectrum you've got and how little noise there is on that!&lt;/p&gt;&#xA;&lt;p&gt;The derivation of that formula isn't that simple; the core takeaway is just that&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Transport capacity doesn't care about the carrier frequency at all. It cares about bandwidth and SNR.&lt;/li&gt;&#xA;&lt;li&gt;You can't say how much data you'll be able to transport without saying what technology you want to employ there.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;h1&gt;internet access&lt;/h1&gt;&#xA;&lt;p&gt;I'm not sure amateur radio is what you need at all. Most jurisdictions simply forbid encrypted / private communications over amateur radio frequencies, and that means that you wouldn't even be legally allowed to open a HTTPS website (which, luckily, are most important websites these days) or check your emails via IMAP over TLS (and I must happily say that only very few email providers of mostly lesser reputation still allow unencrypted access).&lt;/p&gt;&#xA;&lt;p&gt;I think you might really prefer to just get commercial ISM-band equipment to build a directive link in unlicensed spectrum (as opposed to spectrum you access under amateur license), even if that limits the available power (and thus the SNR, the thus the rate). Often, that's the cheaper choice, and sometimes even the faster: where I'm from, HAMNET, which is an internet-alike backbone access technology, is legally restricted to 5 MHz of spectrum in the 2.4GHz region, whereas plain WiFi uses 40 MHz. Sure, the Ham allocation allows higher powers, but as you can see from the formula above, you'd need 256 times the power of WiFi (at same noise level) to achieve the same as an eightfold bandwidth increase.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-04-10T04:22:55.467" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10143" PostTypeId="2" ParentId="10137" CreationDate="2018-04-10T12:58:58.350" Score="1" Body="&lt;p&gt;Yes, do experiment, and &quot;toss a length of wire in a tree&quot; is definitely how most SWL's are starting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However if you have a choice, the you should avoid 1/2 wave lengths, or multiples thereof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good source of information is here &lt;a href=&quot;http://udel.edu/~mm/ham/randomWire/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://udel.edu/~mm/ham/randomWire/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if you scroll down to the little table, you are probably interested in &lt;code&gt;row d&lt;/code&gt; or &lt;code&gt;row e&lt;/code&gt;. In the next table you will find what lengths to avoid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for 80-40-30-20-17-15-12-10 meter bands, you can get away with a length of 72 feet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For 160-80-40-30-20-17-15-12-10 meter bands, you can get away with a length of 143 feet.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2018-04-17T12:42:38.570" LastActivityDate="2018-04-17T12:42:38.570" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10144" PostTypeId="2" ParentId="10137" CreationDate="2018-04-10T23:01:37.147" Score="5" Body="&lt;p&gt;The answers given so far provide good food for thought. I would like to add a slightly different perspective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Today's home is loaded with sources of RFI (radio frequency interference). Routers, computers, wall warts, LED lamps, solar inverters, video cameras, etc. all are potential sources of RFI that interfere with the weak signals of short wave signals from distant countries. More and more, the need to keep the antenna system away from these local RFI sources is the reality of short wave listening. Not only must the antenna be distanced from the RFI but care must be taken that the feedline, typically coax, does not pickup these local RFI sources.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas such as long wires and end fed &quot;half waves&quot; suffer from common mode currents on the feedline. These common mode currents cause the coax to pickup local RFI sources and couple them into the receiver. This problem can be mitigated by using a balanced antenna, such as a dipole, and connecting the coax to the dipole using a wide band, 1:1 current balun. This will minimize the local RFI pickup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this over-thinking the issue? Some may say yes. But anything from a coat hanger to a log periodic antenna on the top of an 80 foot tower will receive signals. It is only a question of effectiveness for the effort and expense. You will need to make that determination.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-04-10T23:01:37.147" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10145" PostTypeId="2" ParentId="10129" CreationDate="2018-04-11T02:32:19.513" Score="2" Body="&lt;p&gt;Another common error is related to their quality control.  I had a unit (UV-5R+) that wouldn't work, like that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Contacted the seller and they sent me a new &quot;body&quot; - and it worked.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in a case where you are really stuck, I suggest you contact the seller.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2018-04-11T02:32:19.513" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10146" PostTypeId="2" ParentId="763" CreationDate="2018-04-11T03:26:28.923" Score="0" Body="&lt;p&gt;I agree with the other answers.  And that it comes down to the definition of propagation...  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can yell in a large empty room and be heard on the other side.  But if you fill that room with noise sources and I yell at the same volume, my voice is still propagating the same power levels across the room, but gets lost in the noise.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I suggest a brief substitution of &quot;propagation&quot; to instead be &quot;the distance to which a message can be delivered&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that substitution I would mention that CW signals can very often reach places where SSB cannot.  Narrow bandwidth filters are a great help for the receiver as it cuts out most of the noise, for instance.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;CW has proven to be very capable of getting the message through in adverse conditions.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;I believe that the answer to your post is a qualified no.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Just because I can propagate my voice all the way across the room whether I am singing (FM) or yelling (AM) does not determine whether it is able to be heard.&lt;/strong&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The qualifier is that CW is an exception to the rule because of the active filtering and tuning of the receiver to receive a narrow-band single frequency while cutting out the extraneous noise..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Add in frequency hopping at a &quot;unit&quot; rate and it gets even better.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2018-04-11T03:26:28.923" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10148" PostTypeId="2" ParentId="10133" CreationDate="2018-04-11T22:46:09.380" Score="0" Body="&lt;p&gt;Actually, the shield of the coax does not protect the center conductor at all from lightning.   Lightning can travel up the coax as common mode current on both the shield and center conductor at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the coax can act as a capacitor, storing the charge of the lightning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gas discharge tubes need to not only short the shield to ground, but also the shield to the center conductor to bleed away this stored voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typical coax is rated for 600v before it internally arcs, so you could easily have up to 600v between shield and ground.  I've seen reputable commercial RF installers recommend surge protection not only at both ends of the coax, but also in multiple places along the run for runs longer than 75ft just to bleed off this capacitive voltage.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-04-11T22:46:09.380" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10150" PostTypeId="2" ParentId="5377" CreationDate="2018-04-12T01:22:05.453" Score="1" Body="&lt;p&gt;I think you have not clearly formulated your question. You write that you are, &quot;...trying to find near field mutual coupling,&quot; but I suspect that you actually want to know the amount of current / voltage / power induced in a second antenna when you drive a first antenna with a specified amount of voltage / current / power. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is available directly from 4NEC2 by driving the first antenna as specified and observing the current in the second antenna (which does not include a source). You can simulate the load impedance attached to the second antenna by placing a load in the second antenna's appropriate segment. Naturally, the power in the load is Z*I^2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;It seems that what you need to do is to model each separately then together.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes... and... the quantity you want to measure is the mutual impedance. Mutual impedances between elements are measured by measuring the impedance of any driven element with other elements open- or short-circuited. These values are then combined to calculate the driving-point impedance of each element given its specified current and phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is clearly described in chapter 11 of the ARRL's &lt;em&gt;Low Band DXing&lt;/em&gt; by John Devoldere, ON4UN.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-04-12T01:22:05.453" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10151" PostTypeId="2" ParentId="5683" CreationDate="2018-04-12T09:26:30.193" Score="2" Body="&lt;p&gt;At this website:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://iz6rdb.trentalancia.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;Free Ham Radio Software Web Page&lt;/a&gt; (iz6rdb)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;you can find C code that I wrote to perform the following operations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;tune a specified frequency;&lt;/li&gt;&#xA;&lt;li&gt;tune a specified channel;&lt;/li&gt;&#xA;&lt;li&gt;configure the TNC (Terminal Node Controller);&lt;/li&gt;&#xA;&lt;li&gt;check that the transceiver is alive or read the firmware version.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The code can be easily compiled with gcc or with your favourite C compiler and each program can be executed from the command-line, from a script and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this helps.&lt;/p&gt;&#xA;" OwnerDisplayName="user11454" LastEditorUserId="8832" LastEditDate="2018-04-12T16:37:16.580" LastActivityDate="2018-04-12T16:37:16.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10152" PostTypeId="1" CreationDate="2018-04-15T16:21:21.283" Score="1" ViewCount="246" Body="&lt;p&gt;I'm working on a morse code geocache puzzle. Firstly I had to listen to Morse code and I got the following words from it &lt;/p&gt;&#xA;&#xA;&lt;p&gt;SYGYO UMPET KUSIK MUMWY MOPPE MACOP TUGNY WAAXT MUFAJ MIAMG TUGND&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect that these words might be morse code /telegrahic codes with numbers attached and was wondering if anyone could recommend an online source to find out what they mean?&lt;/p&gt;&#xA;" OwnerUserId="11467" LastEditorUserId="76" LastEditDate="2018-04-15T17:01:34.823" LastActivityDate="2018-04-15T17:09:09.603" Title="Morse code in a puzzle" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10153" PostTypeId="2" ParentId="10152" CreationDate="2018-04-15T17:09:09.603" Score="4" Body="&lt;p&gt;For what it's worth, these look far more like general &quot;puzzle words&quot; than Morse code abbreviations/prosigns.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Morse code abbreviations/prosigns generally are three or fewer characters long, or look like obvious abbreviations (e.g. PSE and TNX for &quot;please&quot; and &quot;thanks&quot;). &lt;a href=&quot;https://en.wikipedia.org/wiki/Morse_code_abbreviations&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here's a list from Wikipedia&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Your list is uniformly five letters per word. This looks very much like a puzzle sort of thing.&lt;/li&gt;&#xA;&lt;li&gt;I don't recognize any interesting substrings (even if the first one looks a bit like my callsign, heh).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I think you'll need to look elsewhere for the rest of the puzzle.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-04-15T17:09:09.603" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10154" PostTypeId="2" ParentId="10118" CreationDate="2018-04-15T20:23:24.197" Score="4" Body="&lt;p&gt;I'd use copper clad (30%) steel wire.  It's stronger, less stretchy, and less costly, and the current only flows on the outside of the wire so the steel is irrelevant to the resistance of the conductor.  You can also get a plastic covered version of this wire.  This wire with a dark green plastic coating is very stealthy.   &lt;/p&gt;&#xA;" OwnerUserId="11470" LastActivityDate="2018-04-15T20:23:24.197" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10156" PostTypeId="1" AcceptedAnswerId="10157" CreationDate="2018-04-16T08:33:32.110" Score="5" ViewCount="120" Body="&lt;p&gt;I'm mostly sure this will be ok, but I'd like to confirm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a switching power supply (can't remember the model right now, but it's for ham use, 13.8V/30A) and I'd like to power both the FT-857D as well as the power/SWR meter from it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any reason I shouldn't do this?&lt;/p&gt;&#xA;" OwnerUserId="11474" LastEditorUserId="9493" LastEditDate="2018-04-16T12:28:58.473" LastActivityDate="2018-04-16T12:31:17.053" Title="Powering transceiver and SWR/power meter from same supply?" Tags="&lt;transceiver&gt;&lt;swr-meter&gt;&lt;power-supply&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10157" PostTypeId="2" ParentId="10156" CreationDate="2018-04-16T10:08:51.990" Score="4" Body="&lt;p&gt;This should not be a problem at all. It is commonly done this way. Hopefully the switching supply has been designed for ham radio use. If not, you may find some &quot;birdies&quot; on your receiver which are remnants of the switching frequency of the supply getting into your receiver and potentially interfering with desired signals or simply causing annoying tones (thus &quot;birdies&quot;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good safety practice is to have a low amperage (~1 amp) fuse on the outlet of the power supply to which the SWR meter positive wire is connected. This prevents overheating the wires and risking a fire in the event of a short circuit somewhere downstream.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your transceiver power cable probably already has in-line fuses to protect it.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-16T12:31:17.053" LastActivityDate="2018-04-16T12:31:17.053" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10158" PostTypeId="1" AcceptedAnswerId="10162" CreationDate="2018-04-16T12:05:44.397" Score="5" ViewCount="857" Body="&lt;p&gt;I am developing a hobby project to detect/measure the distance between my cell phone and a cell tower (GSM tower).&lt;br&gt;&#xA;I am newbie. I don't even know whether this is possible or not.&lt;br&gt;&#xA;I have following hardware:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Raspberry Pi 3&lt;/li&gt;&#xA;&lt;li&gt;RTL2832u&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I am planning to use OpenBTS and the FreeSwitch stack in the future for advanced feature development.&lt;/p&gt;&#xA;" OwnerUserId="11475" LastEditorUserId="8713" LastEditDate="2019-04-07T14:26:57.830" LastActivityDate="2019-04-07T14:26:57.830" Title="Cell Tower distance measurement" Tags="&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10159" PostTypeId="2" ParentId="9984" CreationDate="2018-04-16T23:34:36.487" Score="1" Body="&lt;p&gt;In addition to what Glen W9IQ said, also consider using a Fair Rite #46 material mix.  This is electrically similar to #43 and in some regions is much less expensive. &lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2018-04-16T23:34:36.487" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10160" PostTypeId="2" ParentId="9897" CreationDate="2018-04-17T00:00:20.580" Score="1" Body="&lt;p&gt;I might be misinterpreting the second photograph, but that looks a lot like a 4:1 Guanella balun (see &lt;a href=&quot;http://www.hbphoto.com/Radio/Baluns_101.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hbphoto.com/Radio/Baluns_101.pdf&lt;/a&gt; , slide 18).  If you are in the United States, you can buy one of these in any hardware store for very little money.  The link you provided is also a 4:1 Guanella balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect the main purpose of this is &lt;em&gt;not&lt;/em&gt; to provide a 4:1 impedance transformation, though.  I suspect the main purpose is to reduce common mode current and, like every other contributor on this page has already said, you probably do not need it. &lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2018-04-17T00:00:20.580" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10161" PostTypeId="2" ParentId="10117" CreationDate="2018-04-17T07:50:23.367" Score="2" Body="&lt;p&gt;As general rule, anchoring point at the ground should not be closer than half of the height where guying line is attached to the pole (guying line slope would be 30 degrees). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Optimal is to have ground anchoring point at the distance which is the same as height where guying line is attached to pole (guying line slope would be 45 degrees).&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2018-04-17T07:50:23.367" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10162" PostTypeId="2" ParentId="10158" CreationDate="2018-04-17T10:22:42.290" Score="7" Body="&lt;p&gt;One approach would be to capture the &lt;a href=&quot;https://wikipedia.org/wiki/Cell_ID&quot; rel=&quot;noreferrer&quot;&gt;GSM Cell ID&lt;/a&gt;. This uniquely identifies a particular GSM site. You can then lookup this ID in a database such as one offered by &lt;a href=&quot;https://combain.com&quot; rel=&quot;noreferrer&quot;&gt;Cobain&lt;/a&gt; to determine the tower location. If your application serves a very limited geography, you could build your own database to suit your needs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to calculate distance, you will need to geo locate your receive site through a GPS signal, manual entry, or other means. You could then use Google Map services to show the two points and the distance between them.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-04-17T10:22:42.290" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10163" PostTypeId="2" ParentId="10137" CreationDate="2018-04-17T12:16:24.030" Score="0" Body="&lt;p&gt;I decided to add another answer. This because I was curious about some of the &quot;calculators&quot; which would calculate the &quot;ideal&quot; length of wire. These calculators can be found by simple searches.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of those simply take the &quot;mid&quot; of the band, and calculates lengths to avoid. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I decided to create a simple calculator in &lt;code&gt;python3&lt;/code&gt; as that is my preferred scripting language. See code below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Usage parameters:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-b:a,b,c&#xA;-b:a&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This runs the calculation just on bands a, b, c specified, comma-seperated, no-spaces&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-b:a-b&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This runs the calculation on all bands a to b (including a, including b), ensure a is lower in frequency than b, and no spaces. Example &lt;code&gt;-b:80-20&lt;/code&gt; which will run for 80,60,40,30,20 m bands.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-b:all&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This runs the calculation on all defined bands. This is the default and can be omitted&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-margin:x&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This defines the x% margin to add to the edge of the bands, to ensure that the calculation stays away from half wave on band edges. Example if x is given as 10, and band is the 40m band, and this band is defined as 7000-7200 kHz, then the band edges are + and - the 10% of the bandwidth: e.g. 6980-7220 kHz. If this x is given as -50, then it calculates only the exact middle of the band, e.g. 7100 kHz. if this is given as 50, then it will be 6900-7300 kHz. By default this is 10%, and can be ommitted.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-min:y&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This is the minimum wire length to be calculated, based on factor y of the lowest frequency wavelenght. By default this is 0.25 which is a quarterwave on the lowest frequency as a minimum for wirelength. Default is 0.25 and can be omitted.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-max:z&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This is the maximum wire length to be calculated based on factor z of the lowest frequency wavelength. By default this is 2 and can be omitted.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-res:2&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This is the (metric) resolution of the results, indicating decimal places after the decimal point for all calculations. 2 will indicate a resolution of centimeters, 1 will indicate a resolution of 10-cm, 0 will indicate a resolution of 1 meter. Default is 2 and can be omitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Example usage:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To calculate 160,80,40 meter bands, with default resolution, default minimum and default maximum, and a default margin:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;longwire.py -b:160,80,40&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Result:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-------------------------------------------------------------------&#xA;Random Longwire Antenna Calculation&#xA;Input parameters:&#xA;-------------------------------------------------------------------&#xA;Bands         : ['160', '80', '40']&#xA;Minimum factor: 0.25    (of lowest frequency)&#xA;Maximum factor: 2       (of lowest frequency)&#xA;Margin        : 10    % (band edge adjustment)&#xA;-------------------------------------------------------------------&#xA;&#xA;Avoidance for band: 160 [[74.26, 84.27], [148.52, 168.54], [222.78, 252.81], [297.04, 337.08], [371.3, 421.35]]&#xA;Avoidance for band: 80 [[39.16, 43.23], [78.32, 86.46], [117.48, 129.69], [156.64, 172.92], [195.8, 216.15], [234.96, 259.38], [274.12, 302.61], [313.28, 345.84], [352.44, 389.07]]&#xA;Avoidance for band: 40 [[20.78, 21.49], [41.56, 42.98], [62.34, 64.47], [83.12, 85.96], [103.9, 107.45], [124.68, 128.94], [145.46, 150.43], [166.24, 171.92], [187.02, 193.41], [207.8, 214.9], [228.58, 236.39], [249.36, 257.88], [270.14, 279.37], [290.92, 300.86], [311.7, 322.35], [332.48, 343.84], [353.26, 365.33]]&#xA;&#xA;Start Lengths [[42.13, 337.08]]&#xA;Take away avoids [[74.26, 84.27], [148.52, 168.54], [222.78, 252.81], [297.04, 337.08], [371.3, 421.35]]&#xA;New Lengths [[42.13, 74.25], [84.28, 148.51], [168.55, 222.77], [252.82, 297.03]]&#xA;Take away avoids [[39.16, 43.23], [78.32, 86.46], [117.48, 129.69], [156.64, 172.92], [195.8, 216.15], [234.96, 259.38], [274.12, 302.61], [313.28, 345.84], [352.44, 389.07]]&#xA;New Lengths [[43.24, 74.25], [86.47, 117.47], [129.7, 148.51], [172.93, 195.79], [216.16, 222.77], [259.39, 274.11]]&#xA;Take away avoids [[20.78, 21.49], [41.56, 42.98], [62.34, 64.47], [83.12, 85.96], [103.9, 107.45], [124.68, 128.94], [145.46, 150.43], [166.24, 171.92], [187.02, 193.41], [207.8, 214.9], [228.58, 236.39], [249.36, 257.88], [270.14, 279.37], [290.92, 300.86], [311.7, 322.35], [332.48, 343.84], [353.26, 365.33]]&#xA;New Lengths [[43.24, 62.33], [64.48, 74.25], [86.47, 103.89], [107.46, 117.47], [129.7, 145.45], [172.93, 187.01], [193.42, 195.79], [216.16, 222.77], [259.39, 270.13]]&#xA;&#xA;-------------------------------------------------------------------&#xA; Results:&#xA;-------------------------------------------------------------------&#xA; from 43.24  to 62.33  meters (mid 52.78  m)&#xA; from 64.48  to 74.25  meters (mid 69.37  m)&#xA; from 86.47  to 103.89 meters (mid 95.18  m)&#xA; from 107.46 to 117.47 meters (mid 112.47 m)&#xA; from 129.7  to 145.45 meters (mid 137.57 m)&#xA; from 172.93 to 187.01 meters (mid 179.97 m)&#xA; from 193.42 to 195.79 meters (mid 194.6  m)&#xA; from 216.16 to 222.77 meters (mid 219.47 m)&#xA; from 259.39 to 270.13 meters (mid 264.76 m)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EXTRA:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may specify a frequency range in kHz in stead of bands. Example, 15 MHz to 20 MHz, minimum 1/8 wave on lowest frequency, maximum 1 wave on lowest frequency, with a 10cm resolution, and a 20% margin for the band edges:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;longwire.py -range:15000-20000 -margin:20 -min:0.125 -max:1 -res:1&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Result:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;-------------------------------------------------------------------&#xA;Random Longwire Antenna Calculation&#xA;Input parameters:&#xA;-------------------------------------------------------------------&#xA;Bands         : ['custom']&#xA;Range         : 15000-20000 kHz&#xA;Minimum factor: 0.125   (of lowest frequency)&#xA;Maximum factor: 1.0     (of lowest frequency)&#xA;Margin        : 20.0  % (band edge adjustment)&#xA;-------------------------------------------------------------------&#xA;&#xA;Avoidance for band: custom [[7.1, 10.7], [14.2, 21.4], [21.3, 32.1], [28.4, 42.8]]&#xA;&#xA;Start Lengths [[2.7, 21.4]]&#xA;Take away avoids [[7.1, 10.7], [14.2, 21.4], [21.3, 32.1], [28.4, 42.8]]&#xA;New Lengths [[2.7, 7.0], [10.8, 14.1]]&#xA;&#xA;-------------------------------------------------------------------&#xA; Results:&#xA;-------------------------------------------------------------------&#xA; from 2.7    to 7.0    meters (mid 4.8    m)&#xA; from 10.8   to 14.1   meters (mid 12.4   m)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Comments and improvements of the code are very welcome !&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Here is the code:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;#!python3&#xA;# -*- coding: utf-8 -*-&#xA;&#xA;# Author: Edwin van Mierlo&#xA;# Call sign: EI2HEB&#xA;&#xA;# No claims of functionality are being made, no warrantees either&#xA;&#xA;# You may re-use this code anyway you see fit&#xA;# Just give me some credit&#xA;&#xA;###############################################################################&#xA;## IMPORTS                                                                   ##&#xA;###############################################################################&#xA;import sys&#xA;&#xA;###############################################################################&#xA;## GLOBAL DEFAULTS                                                           ##&#xA;###############################################################################&#xA;# Band definitions&#xA;# low is the lower band edge in kHz&#xA;# high is the upper band edge in kHz&#xA;# the key is the 'band name'&#xA;BANDS_D = {&#xA;         &quot;160&quot;:{&quot;low&quot;:1800,  &quot;high&quot;:2000},&#xA;         &quot;80&quot; :{&quot;low&quot;:3500,  &quot;high&quot;:3800},   ## upto 4000 in USA&#xA;         &quot;60&quot; :{&quot;low&quot;:5250,  &quot;high&quot;:5450},   ## varies by region&#xA;         &quot;40&quot; :{&quot;low&quot;:7000,  &quot;high&quot;:7200},   ## upto 7300 in USA&#xA;         &quot;30&quot; :{&quot;low&quot;:10100, &quot;high&quot;:10150},&#xA;         &quot;20&quot; :{&quot;low&quot;:14000, &quot;high&quot;:14350},&#xA;         &quot;17&quot; :{&quot;low&quot;:18068, &quot;high&quot;:18168},&#xA;         &quot;15&quot; :{&quot;low&quot;:21000, &quot;high&quot;:21450},&#xA;         &quot;12&quot; :{&quot;low&quot;:24890, &quot;high&quot;:24990},&#xA;         &quot;10&quot; :{&quot;low&quot;:28000, &quot;high&quot;:29700},&#xA;         &quot;6&quot;  :{&quot;low&quot;:50000, &quot;high&quot;:54000}&#xA;        }&#xA;&#xA;# for calculation purposes, you still want&#xA;# to stay away from half wave of band edges&#xA;# this margin can be expressed in a percentage &#xA;# of the span of the band. Example:&#xA;# If 10% is used as margin for the 40m band&#xA;# and 40m band is defined as &quot;low&quot;:7000,  &quot;high&quot;:7200&#xA;# then the calculation will take a lower edge of 6980&#xA;# and will take an upper edge of 7220&#xA;MARGIN = 10&#xA;&#xA;# the minimum length is at least &#xA;# MINIMUM * (lowest frequency wave length)&#xA;# By default this is set to 0.25 to ensure &#xA;# that the calculated lengths are at least&#xA;# a quarter wavelength on the lowest frequency.&#xA;MINIMUM = 0.25&#xA;&#xA;# by setting the maximum to a meaningfull value&#xA;# if forces the calculation to stop at a value of &#xA;# MAXIMUM * (lowest frequency wave length)&#xA;# this ensures the calculation actually stops&#xA;# default is set to two times the wavelength of &#xA;# the lowest frequency&#xA;MAXIMUM = 2&#xA;&#xA;# you can set the resolution of the calculation&#xA;# which by default is set to 2 digits after&#xA;# the decimal point. Which is centimeters&#xA;# by setting this to 3 it will be milimeters &#xA;METRIC_RESOLUTION = 2&#xA;&#xA;###############################################################################&#xA;## INTERNAL FUNCTIONS                                                        ##&#xA;###############################################################################&#xA;def _get_band_edges(bands_d, index, margin):&#xA;    start_freq = int(bands_d[index]['low'])&#xA;    stop_freq = int(bands_d[index]['high'])&#xA;    lower_bandedge = start_freq - ((stop_freq - start_freq) * (margin/100))&#xA;    upper_bandedge = stop_freq + ((stop_freq - start_freq) * (margin/100))&#xA;    return lower_bandedge, upper_bandedge&#xA;&#xA;def _get_wirelength_limits(frequency, minimum, maximum, metric_res):&#xA;    wavelength = 300/(frequency/1000)&#xA;    return (round(wavelength * minimum, metric_res), &#xA;            round(wavelength * maximum, metric_res))&#xA;&#xA;def _get_band_avoidance(lower_bandedge, &#xA;                        upper_band_edge, &#xA;                        min_wire_length, &#xA;                        max_wire_length, &#xA;                        metric_res):&#xA;    avoid = []&#xA;    half_wave_low = round(300/(lower_bandedge/1000)/2, metric_res)&#xA;    half_wave_high = round(300/(upper_band_edge/1000)/2, metric_res)&#xA;    avoid.append([half_wave_high, half_wave_low])&#xA;    factor = 2&#xA;    current_high = half_wave_high&#xA;    while current_high &amp;lt; max_wire_length:&#xA;        current_low = round(half_wave_low * factor, metric_res)&#xA;        current_high = round(half_wave_high * factor, metric_res)&#xA;        if current_low &amp;gt;= min_wire_length:  &#xA;            avoid.append([current_high, current_low])&#xA;        factor += 1&#xA;    return avoid&#xA;&#xA;&#xA;def _get_good_lenghts(lengths, avoid, metric_res):&#xA;    my_lengths = []&#xA;    step = 1/(10**metric_res)&#xA;    for length_range in lengths:&#xA;        my_lengths += _recursive_check(length_range, avoid, step, metric_res)&#xA;    return my_lengths&#xA;&#xA;def _recursive_check(good, bad, step, metric_res):&#xA;    # end of good is smaller than start of bad&#xA;    if good[1] &amp;lt; bad[0][0]:&#xA;        if good[0] &amp;lt; good[1]:&#xA;            return [good]&#xA;        else:&#xA;            return []&#xA;    l = []&#xA;    if (bad[0][0] &amp;gt; good[0]) and (bad[0][0] &amp;lt; good[1]):&#xA;        l.append([good[0], round(bad[0][0] - step, metric_res)])&#xA;        if bad[0][1] &amp;lt; good[1]:&#xA;            l += _recursive_check([round(bad[0][1] + step, metric_res), good[1]], &#xA;                                  bad[1:], &#xA;                                  step,&#xA;                                  metric_res)&#xA;    elif ((bad[0][0] &amp;lt; good[0]) &#xA;          and (bad[0][1] &amp;lt; good[1]) &#xA;          and (bad[0][1] &amp;gt; good[0])):&#xA;        l += _recursive_check([round(bad[0][1] + step, metric_res), good[1]],&#xA;                               bad[1:],&#xA;                               step,&#xA;                               metric_res)&#xA;    elif (bad[0][0] &amp;lt; good[0]) and (bad[0][1] &amp;gt; good[1]):&#xA;        return l&#xA;    elif (bad[0][0] &amp;gt; good[0]) and (bad[0][1] &amp;gt; good[1]):&#xA;        l.append([good[0], round(bad[0][0] - step, metric_res)])&#xA;    else:&#xA;        l += _recursive_check(good,&#xA;                              bad[1:],&#xA;                              step,&#xA;                              metric_res)&#xA;    return l&#xA;&#xA;def _get_multi_band(bands_d, bands_l, minimum, maximum, margin, metric_res):&#xA;    lower_bandedge, upper_bandedge = _get_band_edges(bands_d, &#xA;                                                     bands_l[0], &#xA;                                                     margin)&#xA;    min_wire_length, max_wire_length = _get_wirelength_limits(lower_bandedge, &#xA;                                                              minimum, &#xA;                                                              maximum, &#xA;                                                              metric_res)&#xA;    my_lengths = [[min_wire_length, max_wire_length]]&#xA;&#xA;    my_avoids = []&#xA;    for band in bands_l:&#xA;        lower_bandedge, upper_bandedge = _get_band_edges(bands_d, &#xA;                                                         band, &#xA;                                                         margin)&#xA;        avoid = _get_band_avoidance(lower_bandedge, &#xA;                                    upper_bandedge, &#xA;                                    min_wire_length, &#xA;                                    max_wire_length, &#xA;                                    metric_res)&#xA;        my_avoids.append(avoid)&#xA;        print('Avoidance for band:', band, avoid)&#xA;    print()&#xA;    print('Start Lengths', my_lengths)&#xA;    for avoid in my_avoids:&#xA;        print('Take away avoids', avoid)&#xA;        my_lengths = _get_good_lenghts(my_lengths, avoid, metric_res)&#xA;        print('New Lengths', my_lengths)&#xA;    return my_lengths&#xA;&#xA;###############################################################################&#xA;## EXTERNAL FUNCTIONS                                                        ##&#xA;###############################################################################&#xA;def main(bands_d, bands_l, minimum, maximum, margin, metric_res):&#xA;    &quot;&quot;&quot;&#xA;    bands_d = dictionary of bands, example:&#xA;&#xA;    BANDS_D = {&#xA;         &quot;160&quot;:{&quot;low&quot;:1800,  &quot;high&quot;:2000},&#xA;         &quot;80&quot; :{&quot;low&quot;:3500,  &quot;high&quot;:3800},   &#xA;         &quot;60&quot; :{&quot;low&quot;:5250,  &quot;high&quot;:5450},   &#xA;         &quot;40&quot; :{&quot;low&quot;:7000,  &quot;high&quot;:7200},   &#xA;         &quot;30&quot; :{&quot;low&quot;:10100, &quot;high&quot;:10150},&#xA;         &quot;20&quot; :{&quot;low&quot;:14000, &quot;high&quot;:14350},&#xA;         &quot;17&quot; :{&quot;low&quot;:18068, &quot;high&quot;:18168},&#xA;         &quot;15&quot; :{&quot;low&quot;:21000, &quot;high&quot;:21450},&#xA;         &quot;12&quot; :{&quot;low&quot;:24890, &quot;high&quot;:24990},&#xA;         &quot;10&quot; :{&quot;low&quot;:28000, &quot;high&quot;:29700},&#xA;         &quot;6&quot;  :{&quot;low&quot;:50000, &quot;high&quot;:54000}&#xA;        }&#xA;&#xA;    bands_l = list of the keys of the dictionary of bands to run the &#xA;              calculation on. This is either 1 of the keys, all of the keys&#xA;              or a subset of keys&#xA;&#xA;    minimum = minimum wirelength expressed as a minimum factor of the lowest&#xA;              frequency wavelength&#xA;&#xA;    maximum = maximum wirelength expressed as a maximum factor of the lowest&#xA;              frequency wavelength&#xA;&#xA;    margin  = band edge correction expressed as a percentage of band width&#xA;&#xA;    metric_res = digit precision expressed in number of digits &#xA;                 after decimal point&#xA;    &quot;&quot;&quot;&#xA;    my_lengths = []&#xA;    my_lengths = _get_multi_band(bands_d, &#xA;                                 bands_l, &#xA;                                 minimum, &#xA;                                 maximum, &#xA;                                 margin, &#xA;                                 metric_res)&#xA;    return my_lengths&#xA;&#xA;###############################################################################&#xA;## INTERACTIVE CODE                                                          ##&#xA;###############################################################################&#xA;if __name__ == '__main__':&#xA;    minimum = MINIMUM&#xA;    maximum = MAXIMUM&#xA;    margin = MARGIN&#xA;    bands_d = BANDS_D&#xA;    metric_res = METRIC_RESOLUTION&#xA;    bands_l = [key for key in bands_d]&#xA;    if len(sys.argv) &amp;gt; 1:&#xA;        # command line parameters are set&#xA;        for arg in sys.argv[1:]:&#xA;            # looping through the command line parameters&#xA;            if '-b:' in arg:&#xA;                # bands set in commandline&#xA;                my_bands = arg.split('-b:')[1]&#xA;                if my_bands.lower() == 'all':&#xA;                    # bands_l variable already defined&#xA;                    pass&#xA;                elif '-' in my_bands:&#xA;                    # range of bands in commandline&#xA;                    bands = [str(b) for b in my_bands.split('-') if str(b) in bands_l]&#xA;                    if len(bands) == 2:&#xA;                        start = bands_l.index(bands[0])&#xA;                        stop = bands_l.index(bands[1]) + 1&#xA;                        bands_l = bands_l[start:stop]&#xA;                elif ',' in my_bands:&#xA;                    # individual bands in commandline&#xA;                    if ',' in my_bands:&#xA;                        # multiple bands specified&#xA;                        bands = [ str(b) for b in my_bands.split(',') if str(b) in bands_l]&#xA;                        bands_l = bands&#xA;                else:&#xA;                    # single band specified&#xA;                    bands_l = [my_bands]&#xA;            if '-min:' in arg:&#xA;                # minimum length set in commandline&#xA;                minimum = float(arg.split('-min:')[1])&#xA;            if '-max:' in arg:&#xA;                # maximum length set in commandline&#xA;                maximum = float(arg.split('-max:')[1])&#xA;            if '-margin:' in arg:&#xA;                # margin set in commandline&#xA;                margin = float(arg.split('-margin:')[1])&#xA;            if '-res:' in arg:&#xA;                metric_res = int(arg.split('-res:')[1])&#xA;            if '-range:' in arg:&#xA;                # customer frequency range specified&#xA;                low = int(arg.split('-range:')[1].split('-')[0])&#xA;                high = int(arg.split('-range:')[1].split('-')[1])&#xA;                bands_d = {&quot;custom&quot;:{&quot;low&quot;:low, &quot;high&quot;:high}}&#xA;                bands_l = [&quot;custom&quot;]&#xA;    print()&#xA;    print()&#xA;    print('-------------------------------------------------------------------')&#xA;    print('Random Longwire Antenna Calculation')&#xA;    print('Input parameters:')&#xA;    print('-------------------------------------------------------------------')&#xA;    print('Bands         : {}'.format(str(bands_l)))&#xA;    if bands_l == ['custom']:&#xA;        print('Range         : {}-{} kHz'.format(str(bands_d['custom']['low']), &#xA;                                                 str(bands_d['custom']['high'])))&#xA;    print('Minimum factor: {}   (of lowest frequency)'.format(str(minimum).ljust(5)))&#xA;    print('Maximum factor: {}   (of lowest frequency)'.format(str(maximum).ljust(5)))&#xA;    print('Margin        : {} % (band edge adjustment)'.format(str(margin).ljust(5)))&#xA;    print('-------------------------------------------------------------------')&#xA;    print()&#xA;    my_lengths = main(bands_d, bands_l, minimum, maximum, margin, metric_res)&#xA;    print()&#xA;    print('-------------------------------------------------------------------')&#xA;    print(' Results:')&#xA;    print('-------------------------------------------------------------------')&#xA;    if len(my_lengths) == 0:&#xA;        print('No wirelengths found with current parameters')&#xA;        print('-------------------------------------------------------------------')&#xA;    else:&#xA;        for lengths in my_lengths:&#xA;            if lengths != []:&#xA;                print(' from {} to {} meters (mid {} m)'.format(str(lengths[0]).ljust(6),&#xA;                                                                str(lengths[1]).ljust(6),&#xA;                                                                str(round((lengths[0] + lengths[1])/2, metric_res)).ljust(6)))&#xA;&#xA;###############################################################################&#xA;## END                                                                       ##&#xA;###############################################################################&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2018-04-17T13:03:19.980" LastActivityDate="2018-04-17T13:03:19.980" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10164" PostTypeId="2" ParentId="10117" CreationDate="2018-04-17T15:39:35.943" Score="6" Body="&lt;p&gt;What you have is a basic civil engineering problem. You might calculate a &lt;a href=&quot;https://en.wikipedia.org/wiki/Shear_and_moment_diagram&quot; rel=&quot;noreferrer&quot;&gt;sheer and moment diagram&lt;/a&gt;, look up all the material properties, and calculate the failure points of all the components. In the case of an antenna, the most significant force is usually wind, and the objective is to make it strong enough that the structure doesn't blow over. It gets quite complex however.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead you may opt to employ &quot;That Looks About Right&quot; (TLAR) engineering principles, where you look at other things that have worked, combine some experience and intuition, and come up with something about right. You might look at the &lt;a href=&quot;https://static.dxengineering.com/global/images/chartsguides/r/roh-9h50.pdf&quot; rel=&quot;noreferrer&quot;&gt;ROHN H20 push-up mast guy plan&lt;/a&gt;. The H20 has a maximum height of 19.25 feet, so not unlike your pole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/65pcd.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/65pcd.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here you can see the top set of wires is up about 19 feet, and is 18 feet away from the base. The drawing is not to scale. ROHN also has a 2nd set of wires at the midpoint. Since this is a push-up mast it's in two sections, so this is unavoidable. If you have a single 20 foot pole you might do without, depending on the rigidity of your pole and maximum wind load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally you would not want to bring the anchor point closer to the base than this. You propose having the anchor point only 3 feet away from the base, and I think that's only marginally better than no guying at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider, the wind wants to blow the pole over (blue). That force is countered by two others: tension on the guy wire (green), and compression on the mast (red). There is potentially also a bending moment if the mast is connected rigidly to the ground, through for simplicity I've omitted it here. All the forces must be balanced if the mast is to remain stationary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MHufi.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MHufi.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see, in the left example with a steep angle there is significantly more force on the guy wire and the mast for the same wind load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a rule of thumb, anchor points about as far away from the base as the pole is high is a good compromise between strength and minimizing wire length and footprint.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-04-17T15:50:27.190" LastActivityDate="2018-04-17T15:50:27.190" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10165" PostTypeId="1" AcceptedAnswerId="10167" CreationDate="2018-04-17T16:54:24.137" Score="1" ViewCount="78" Body="&lt;p&gt;I am taking the test for my first USA Amateur Technicians license on Saturday. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been studying and give myself a good (90%) chance that I'll pass the test. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since many of you have successfully gone through this testing regime, what are some best practices based on your experience and essential knowledge to pass?&lt;/p&gt;&#xA;" OwnerUserId="11352" LastEditorUserId="11446" LastEditDate="2018-04-19T01:13:27.300" LastActivityDate="2018-04-19T01:13:27.300" Title="What knowledge is essential for USA Technician license?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="2" CommentCount="2" ClosedDate="2018-04-17T18:02:10.743" ContentLicense="CC BY-SA 3.0" />
  <row Id="10166" PostTypeId="2" ParentId="10165" CreationDate="2018-04-17T17:28:58.013" Score="1" Body="&lt;p&gt;Keep writing practice tests and reading the course material.  The more familiar you are with everything, the better your odds are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Get a good night's sleep before the exam, so that you're not tired.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Relax - if you fail, you can try again before too long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck!&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-04-17T17:28:58.013" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10167" PostTypeId="2" ParentId="10165" CreationDate="2018-04-17T17:37:39.620" Score="1" Body="&lt;p&gt;Somewhat tongue-in-cheek - Where's the 90% coming from - are you taking practice exams and, if so, answering 90% of the questions correctly, or are you answering correctly the minimum required 75% of questions only 90% of the time?  &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Of course keep studying - ID the problem questions and develop some schemes to remember the correct answers.  Note the answer choices are always in the same order (A,B,C,D) - not that I recommend rote memorization!&lt;/li&gt;&#xA;&lt;li&gt;Get there early. Bring the recommended pencils, IDs etc.  Don't start the test under time pressure.&lt;/li&gt;&#xA;&lt;li&gt;Be sure to answer all questions - realize that the &quot;all of the above&quot; and similar answers are very often NOT the right answers (unlike many typical multiple choice tests).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Good luck!&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-04-17T17:37:39.620" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10168" PostTypeId="1" AcceptedAnswerId="10170" CreationDate="2018-04-18T07:49:36.533" Score="4" ViewCount="1602" Body="&lt;p&gt;I have a basic CB SWR meter, I can’t see any reason why it can’t be used on other HF bands and be at least indicative of what the SWR is, even if the absolute power measurement is inaccurate. Is this a correct assumption? I also assume that the meter might be useable up to 10m and possible 6m but above that it would introduce problems - too much loss, for example. Is this also correct?&lt;/p&gt;&#xA;" OwnerUserId="11431" LastActivityDate="2018-12-18T12:48:57.740" Title="Can a CB SWR meter be used for HF amateur bands?" Tags="&lt;antenna&gt;&lt;swr-meter&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10169" PostTypeId="1" CreationDate="2018-04-18T09:14:27.673" Score="1" ViewCount="144" Body="&lt;p&gt;I couldn’t find a better place to ask this question, so I have asked it here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am looking to transmit and receive internet connectivity wirelessly over a distance of 6 miles (9.7 km) with a minimum 300Mb transfer rate. This is not exclusive to amateur radio frequencies but is exclusive to publicly available frequencies (to buy or access openly).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am seeking to transmit internet connectivity from an area that has DSL which I need to an area that has only satellite access available, which does not fit my needs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: I am in the US so FCC rules apply.&lt;/p&gt;&#xA;" OwnerUserId="11446" LastEditorUserId="11446" LastEditDate="2018-04-22T22:34:35.917" LastActivityDate="2018-04-22T22:34:35.917" Title="What wireless communication technologies can travel long distances with a high bandwidth?" Tags="&lt;software-defined-radio&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;mobile&gt;&lt;satellites&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10170" PostTypeId="2" ParentId="10168" CreationDate="2018-04-18T09:59:17.890" Score="5" Body="&lt;p&gt;Many hams have re-purposed CB SWR meters but there are so many variations that some caution and testing is warranted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many CB meters were not designed to handle the higher power levels of amateur transceivers. A 100 watt transmitter could cause component failures within the meter. While the most likely result is simply the failure of the meter, I wouldn't rule out the possibility of it causing a short across, or open of, the transmission line. Remember that these meters were designed for an unsophisticated, and at times cost sensitive, market. The engineering can be dubious. With that being said, many meters have been used successfully at 100 watts - perhaps due to the SWR meter manufacturer recognizing the propensity for rule breaking power levels deployed on this band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can test the SWR accuracy on various bands using lower power and a 50 ohm dummy load - it should show a 1:1 SWR. Then parallel another 50 ohm dummy load (borrow it from a friend or club if you do not have a second one) by using a coaxial tee connector and repeat the SWR test. This time it should show a 2:1 SWR. These tests will give you an indication on which bands the calibration is adequate for your purposes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the meter directly reports forward and reflected power, you can further test the meter by reversing the in and out connections and compare the readings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the meter into the VHF and UHF bands is questionable but you can repeat the above tests to qualify the meter on these bands. Make certain your dummy loads are rated for these bands as well in order to make the test results meaningful.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-18T15:43:32.203" LastActivityDate="2018-04-18T15:43:32.203" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10171" PostTypeId="2" ParentId="10169" CreationDate="2018-04-18T10:56:29.117" Score="1" Body="&lt;p&gt;To support that type of bandwidth you will generally be using microwave (&gt; 2 GHz) or higher frequencies. Reliable communications will be limited to line of sight situations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This type of application is well beyond the homebrew capabilities of most hobbyists.  The good news is commercial world has a wide range of cost effective products available for these types of applications. The frequencies, power levels, antenna gains, and licensing requirements are generally country specific. To get started, you may wish to look at a company like &lt;a href=&quot;https://www.ubnt.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ubiquity&lt;/a&gt;. There are many such companies on the market and most offer excellent guides for properly and legally deploying their products.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-18T12:52:27.273" LastActivityDate="2018-04-18T12:52:27.273" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10172" PostTypeId="2" ParentId="10169" CreationDate="2018-04-18T12:58:43.527" Score="5" Body="&lt;p&gt;All kinds of digital microwave technologies can do this, including WiFi. It takes a good antenna location high from the ground, and good antenna gain / transmit power. Commercial wireless ISPs do it regularly. With a good antenna and cooperative terrain (no hills in the way), it could be done with consumer 802.11 equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mind the link budget, and the radio horizon. For example, see &lt;a href=&quot;https://ham.stackexchange.com/q/6346/218&quot;&gt;How to test Line-of-Sight radio at 5GHz at range 25Km or less?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-04-18T13:10:28.597" LastActivityDate="2018-04-18T13:10:28.597" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="10173" PostTypeId="1" AcceptedAnswerId="10176" CreationDate="2018-04-18T15:49:20.870" Score="6" ViewCount="3534" Body="&lt;p&gt;I hear all the time, &quot;you need a balun between your balanced dipole and unbalanced coax to stop the common-mode current&quot; when it seems the proper advice is &quot;you need something to stop common-mode current (full stop).&quot; Sure, attaching a balanced system (e.g. dipole) to an unbalanced system (e.g. coax) is a frequent source of common-mode current. But, &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole/543#543&quot;&gt;this answer&lt;/a&gt; points out that even with a so called &quot;balanced&quot; antenna connected to a balanced feedline, the antenna often isn't really balanced, so some sort of common mode choke is a good idea no matter what.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if the same advice applies either way, &lt;em&gt;why do we make such a big distinction between balanced and unbalanced?&lt;/em&gt; My assumption is that it's one of a couple things:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Misconception: A lot of people may not realize a common-mode choke is recommended anyway.&lt;/li&gt;&#xA;&lt;li&gt;Old knowledge: This is sort of a special case of misconception. Maybe in the past, we didn't think of common-mode suppression as a generally recommended thing, and only later did it become common knowledge that this is a good thing even in balanced systems. Meanwhile, outdated information persists.&lt;/li&gt;&#xA;&lt;li&gt;Other reasons to differentiate: Even though common-mode suppression is a good idea regardless of balanced vs. unbalanced, there may be other ways we &lt;em&gt;do&lt;/em&gt; treat them differently, or other reasons to distinguish between them.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;My suspicion is the first one is true to some degree, but that the third case is the main reason.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To further muddy the waters, I'm seeing the word &quot;balanced&quot; used in two seemingly different ways. One is in the sense above where, for example, we have a &quot;balanced&quot; dipole that's actually unbalanced because one side is close to a hunk of metal, causing it to present an unbalanced impedance at the feed point. The other way I've seen it used is to represent a system where the two conductors have equal and opposite voltages relative to ground, versus unbalanced where one of the conductors is grounded. Are these two uses of the word actually the same thing? If so, how?&lt;/p&gt;&#xA;" OwnerUserId="8940" LastEditorUserId="9493" LastEditDate="2018-04-22T10:58:20.780" LastActivityDate="2018-05-04T20:32:52.987" Title="Why do we distinguish between balanced and unbalanced?" Tags="&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;balun&gt;&lt;choke-balun&gt;" AnswerCount="4" CommentCount="4" ContentLicense="CC BY-SA 3.0" />
  <row Id="10174" PostTypeId="1" CreationDate="2018-04-18T15:51:49.273" Score="3" ViewCount="511" Body="&lt;p&gt;I am trying to design a loop antenna for operation at 2.4 GHz, I would like for it to have above 2.5 dB gain at 2.4 GHz and have relatively good return loss (&amp;lt;-10 dB).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have started my design as shown in the pictures. I am concerned with the radiation pattern cut at phi=90 degrees:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rSFht.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rSFht.png&quot; alt=&quot;E-Cut&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I feel as though this plane cut should be circular in shape. Is there any way I can adjust the antenna to produce the desired radiation pattern?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rufVr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rufVr.png&quot; alt=&quot;Front of antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wyWdk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wyWdk.png&quot; alt=&quot;Back of Antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0rZ3K.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0rZ3K.png&quot; alt=&quot;S1,1&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vRry2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vRry2.png&quot; alt=&quot;H-Cut&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1YWdU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1YWdU.png&quot; alt=&quot;Farfield Pattern&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11484" LastEditorUserId="9493" LastEditDate="2018-04-21T09:40:45.327" LastActivityDate="2018-04-21T18:15:20.917" Title="Microstrip Loop Antenna Design" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="10175" PostTypeId="2" ParentId="10173" CreationDate="2018-04-18T17:16:47.067" Score="1" Body="&lt;p&gt;In the real world, most center-fed dipoles are balanced; and when we feed them with balanced line there is seldom a need for a balun where that feedline connects. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This post may help answer your question. Look at Phil Frost's first answer here:&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole/543#543&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-04-18T18:43:49.040" LastActivityDate="2018-04-18T18:43:49.040" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10176" PostTypeId="2" ParentId="10173" CreationDate="2018-04-18T18:42:10.817" Score="4" Body="&lt;p&gt;There are balanced feedlines (twin-lead), and balanced antennas (dipoles), and similar things all described as &quot;balanced&quot;. In this sense, balance means the two halves of the thing have equal impedance relative to &lt;em&gt;ground&lt;/em&gt;. Here, &lt;em&gt;ground&lt;/em&gt; does not mean whatever is called ground on the schematic. Rather, it means &quot;the environment&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider twin-lead for example. If the &lt;a href=&quot;https://ham.stackexchange.com/q/3508/218&quot;&gt;spacing between the conductors is small relative to wavelength&lt;/a&gt;, we can say they are effectively in the same space. And the wires have the same geometry. Since they're both the same (for frequencies low enough that this is a valid approximation), of course they are going to have the same impedance to the environment. Meaning, if an electromagnetic wave from a distant transmitter reaches the feedline, each half of the twin-lead will be affected equally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This same property means if we drive the twin-lead with each half having an equal but opposite current, each individual half will have surrounding it an equal but opposite electromagnetic field. But these equal but opposite fields cancel, and thus the feedline does not radiate. It's this property that allows a feedline to move electromagnetic energy from one end to the other without much loss, or carry a signal from an antenna to a receiver without picking up noise from everything around the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this reason, in discussion of feedlines, and the antennas and radios to which they are connected, you may encounter discussion of &lt;em&gt;current balance&lt;/em&gt;. This just means equal but opposite currents, also known as differential mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coax is not a balanced feedline, which can be seen by considering how it would pick up an electromagnetic wave from a distant transmitter, for example. The wave will interact with the shield just like a fat wire, effectively an antenna. But the center conductor, being screened from the environment by the shield, isn't affected at all. The two parts of coax do not have equal impedance to ground, thus it is not balanced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But coax does require &lt;em&gt;balanced current&lt;/em&gt;. Only if the currents on the shield and center conductor are equal but opposite will the coax act as a feedline. Otherwise, it will radiate, or pick up noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's for this reason the common-mode choke is so ubiquitous. Regardless of whether the feedline or antenna attached to it is balanced or unbalanced, differential mode current (AKA, balanced current) through it sees a low impedance, whereas common mode current (the remainder) sees a high impedance.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-04-18T18:42:10.817" CommentCount="3" ContentLicense="CC BY-SA 3.0" />
  <row Id="10177" PostTypeId="2" ParentId="10168" CreationDate="2018-04-18T21:57:03.313" Score="2" Body="&lt;p&gt;To add to Glenn's excellent advice, &lt;em&gt;some&lt;/em&gt; &quot;CB&quot; SWR meters &lt;strong&gt;will&lt;/strong&gt; handle the legal limit on HF with ease.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I have two or three old Radio Shack meters that will do that. I have compared them with other meters of high quality (such as the wattmeter in my Collins 312B-4) and they are plenty accurate enough from 1.8 to 30 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, I always tuned at low power until the line VSWR was low, and afterwards always turned the calibration pot fully CCW to ensure the meter was not destroyed at high power.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-04-18T21:57:03.313" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10179" PostTypeId="1" AcceptedAnswerId="10183" CreationDate="2018-04-19T23:47:04.737" Score="9" ViewCount="396" Body="&lt;p&gt;For example, in this screenshot:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0fjIL.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0fjIL.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;WSJT shows !Italy, !Serbia, !U.S.A. What does it mean?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="10431" LastEditDate="2018-04-20T09:17:26.357" LastActivityDate="2018-04-20T09:23:16.350" Title="What does exclamation mark mean in FT8 CQ calls in WSJT?" Tags="&lt;software&gt;&lt;ft8&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10180" PostTypeId="2" ParentId="10179" CreationDate="2018-04-20T02:14:19.670" Score="0" Body="&lt;p&gt;It looks like the FT8 client you are using is parsing the callsign of people calling CQ, and displaying their DXCC entity prefixed by a !.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-04-20T02:14:19.670" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10181" PostTypeId="5" CreationDate="2018-04-20T02:18:23.437" Score="0" Body="&lt;p&gt;For questions specifically about the FT8 mode&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2018-04-20T02:18:23.437" LastActivityDate="2018-04-20T02:18:23.437" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10182" PostTypeId="4" CreationDate="2018-04-20T02:18:23.437" Score="0" Body="For questions specific to the FT8 mode" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2018-04-20T02:18:23.437" LastActivityDate="2018-04-20T02:18:23.437" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10183" PostTypeId="2" ParentId="10179" CreationDate="2018-04-20T09:23:16.350" Score="6" Body="&lt;p&gt;That is something that is activated by &quot;Show DXCC entity and worked before status&quot; (selectable on the &quot;Settings&quot; &gt; &quot;General tab&quot;). From the manual:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;When this option is checked WSJT-X appends some additional information&#xA;  to all CQ messages displayed in the Band Activity window. The name of&#xA;  the DXCC entity is shown, abbreviated if necessary. Your “worked&#xA;  before” status for this callsign (according to log file wsjtx_log.adi)&#xA;  is flagged with a single character and a change of background color,&#xA;  as follows:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;!  Default color bright purple: New DXCC entity&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;~  Light pink: You have already worked this DXCC entity but not this&#xA;  station&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Green: You have previously worked the calling station&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2018-04-20T09:23:16.350" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10184" PostTypeId="1" AcceptedAnswerId="10186" CreationDate="2018-04-20T12:17:18.440" Score="5" ViewCount="277" Body="&lt;p&gt;Doppler shift mitigation has been studied extensively in the literature. In my implementations of satellite receivers (using GNU Radio), I use predicted Doppler shift from a software (GPredict) to compensate for Doppler shift. After that, I use a Frequency-Locked Loop (FLL) for course carrier synchronization. This approach works very well.&#xA;However, I have been trying to implement new carrier frequency synchronizers that will enable operations without the help of an external software. When I looked at the literature again (Umberto Mengali book, chapter 3), carrier frequency recovery is divided into two cases:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;When the frequency offset is much lower than the symbol rate (&amp;lt; 10%?)&lt;/li&gt;&#xA;&lt;li&gt;When the frequency offset is in the order or the symbol rate&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The two cases listed above are pretty straightforward to implement (I'm in the process of doing so). However, there are other cases, such as those at S-band which use &quot;low rate telemetry&quot; in the order of a few 10s of kilobytes. The Doppler shift is many orders of magnitude higher than the symbol rate. Can anyone suggest any algorithm that can work in this case? All I want to avoid is the use of an external software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks.   &lt;/p&gt;&#xA;" OwnerUserId="6214" LastActivityDate="2018-04-23T01:39:28.987" Title="Doppler shift compensation without using predictive modelling" Tags="&lt;software-defined-radio&gt;&lt;satellites&gt;&lt;doppler&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 3.0" />
  <row Id="10185" PostTypeId="2" ParentId="10174" CreationDate="2018-04-21T09:41:05.270" Score="3" Body="&lt;p&gt;By nature, the radiation pattern of a small loop antenna will not be uniform in the azimuth. It will typically have the classic bipolar lobe pattern with nulls in the quadrature positions as shown in your plots.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should either consider classes of antennas that are omnidirectional in the azimuth (e.g. monopoles, vertical dipoles, horizontal slot, etc.) or phase two loops that are oriented 90 degrees from one another. In the latter case, the pattern will be pseudo omni in the azimuth and the solution will likely require two PCBs and an interconnecting transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You state that you require 2.5 dB gain. Note that this is an ambiguous statement since there is no normative reference. It should likely be stated as  either dBi or dBd gain. In professional circles, dBi is used almost exclusively but it still should be explicitly stated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that you also specified an RL without stating the Z&lt;sub&gt;O &lt;/sub&gt; of the transmission line, the output impedance of the transmitter, or the input impedance of the receiver. All of which are essential facts in order to engineer a solution that fully meets the requirement.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-21T18:15:20.917" LastActivityDate="2018-04-21T18:15:20.917" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10186" PostTypeId="2" ParentId="10184" CreationDate="2018-04-21T18:50:02.287" Score="2" Body="&lt;p&gt;You can actually implement something like that as a rake-style receiver: Simply put up an array of (partially overlapping) more narrowband receivers and let them run in parallel until one &quot;locks&quot; onto a signal, and then follow that (typically: higher-order costas loop; and: I can heartily recommend fred harris' &lt;a href=&quot;https://www.gnuradio.org/wp-content/uploads/2017/12/fred-harris-Band-Edge-Filters.ppt&quot; rel=&quot;nofollow noreferrer&quot;&gt;slides&lt;/a&gt; and &lt;a href=&quot;https://www.youtube.com/watch?v=Zmjk9NE-3k0&amp;amp;list=PLbBQHMnVMR43mM18y4r8L7l8bbYMgloFx&amp;amp;index=34&quot; rel=&quot;nofollow noreferrer&quot;&gt;recording&lt;/a&gt; from GRCon'17 on &lt;em&gt;band-edge filtering&lt;/em&gt;; also, I recommend watching Andy Wall's &lt;a href=&quot;https://www.youtube.com/watch?v=uMEfx_l5Oxk&quot; rel=&quot;nofollow noreferrer&quot;&gt;Talk on &lt;em&gt;Symbol Clock Recovery and Improved Symbol Synchronization Blocks&lt;/em&gt;&lt;/a&gt;, &lt;a href=&quot;https://www.gnuradio.org/wp-content/uploads/2017/12/Andy-Walls-Samples-to-Digital-Symbols.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;slides&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, assume you get an initial lock, what to do now? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously, your control loop needs not only correct stationary phase (first-order costas loop would do that), but also frequency offset (which is nothing but a linear phase shift over time; second order costas), and, to make matters worse, possibly even a shift in frequency over time (that's why I said &quot;higher-order costas&quot; above).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can of course go ahead and just do a &quot;blind&quot; high-order phase control loop; but that would never be as good as something as something able to predict the frequency development over time. Basically, what you'd want to do is to find the signal, observe how its phase develops on short term, and infer the &quot;Doppler trajectory&quot;, which is the result of the satellite/receiver geometry. Then, you'd base your corrections on that prediction, and only use the control loops to get rid of residual error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That can get very interesting in effect – what you'll basically be doing is building kind of the frequency-over-time-equivalent to a matched filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another observation: If you've got a beamforming receiver setup, that geometrical prediction would directly allow for adjusting the relative phase shifts of the individual receive chains – which would both have an effect on the beam pattern and the described frequency / phase correction. The same idea applies if you have a directive antenna – say a dish – that mechanically follows the path of the satellite!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-04-21T18:50:02.287" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10187" PostTypeId="2" ParentId="10173" CreationDate="2018-04-22T11:03:19.163" Score="1" Body="&lt;p&gt;A current mode balun is typically used for suppressing common mode current on the transmission line. It can also be used for impedance transformation as seen in a 4:1 current balun design, for example.  A so called choking balun is the equivalent of a current mode balun without impedance transformation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider that most antennas are neither balanced nor unbalanced but rather somewhere in between. So a more constructive way of thinking about the ports of a current mode balun  is simply that the &quot;bal&quot; port should connect to the antenna and the &quot;un&quot; port to the transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A coaxial cable transmission line and a balanced transmission line are both capable of carrying common mode currents. The physics are slightly different, but the result is the same - the feedline radiates and the feedline can couple undesired signals into the antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So when using a balanced line, a current mode balun is still warranted in order to suppress common mode current. You may include impedance transformation as part of the design to facilitate matching the balanced line to the antenna feedpoint impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an incidental comment, what amateur radio operators typically overlook is that the electrical length of the transmission line plays a significant role in the susceptibility of the transmission line to common mode currents. This is true for unbalanced (coax) and balanced transmission lines with or without a current balun.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-22T14:56:54.230" LastActivityDate="2018-04-22T14:56:54.230" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10189" PostTypeId="2" ParentId="10168" CreationDate="2018-04-22T14:49:52.740" Score="2" Body="&lt;p&gt;Your assumption is correct. It would definitely be usable for 10m. The basic circuit design can range from simple to complex but for it to work at all there is a minimum design requirement that should provide you with a usable device. I don’t feel that 6m is out of the question. I’d compare  the forward power indication of your transmitter’s power meter with that shown by the SWR meter in question and note any tendency for the outboard meter to show meaningfully less forward power. If it does not, you may be safe in assuming that the diodes utilized in the design are operating within their frequency operating range. &lt;/p&gt;&#xA;" OwnerDisplayName="user11476" LastActivityDate="2018-04-22T14:49:52.740" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10190" PostTypeId="2" ParentId="10184" CreationDate="2018-04-23T01:20:53.420" Score="0" Body="&lt;p&gt;This is a great Q&amp;amp;A.  It is fun to think about all this, and I have learned a lot by reading the various ideas here.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So let me toss in my 2 cents worth, speaking as a former Commo who had to deal with Doppler on a routine basis.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of predictive modeling we simply went out and figured out what worked.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back at Fort Richardson we would track a few of the Oscars with hand-held Alaskan Arrow antennas.  (They can not only be aimed but also rotated to peak the signal based on polarization)  Whether at the Center or out in the field, the procedures were the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This was grunt-work field comms.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It all had to fit in a backpack and be ready for use in minutes.  Our &quot;2&quot; man would give us the pass predictions for the day.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our mantra was MIW - Make It Work.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So we would use CHIRP to pre-program the Yaesu VX-8DR radios with three NFM channel pairs for each bird.  The Alaskan Arrow has a diplexer (their word) so one radio can work both VHF and UHF alternately.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;AOS:  5 KHz Above Center - for when it pops up moving towards us&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;CTR:  Center Frequency   (145.800 simplex for the ISS, for instance)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;LOS:  5 KHz Below Center - for when it is moving away ready to vanish&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;It was important for the radio man to have a quick way to simply rotate the channel selector to track the Doppler shift for the very few minutes we would get at 61 Degrees latitude.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes I would do it all alone, handling the radio in one hand and the antenna in the other.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At our latitude it was important to use the full-length Alaska Arrow to get the most gain so I mounted mine to a microphone stand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our comm windows were short.  But we Made It Work.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So, even though there was not a lot of math involved at the level I see here in this Q&amp;amp;A, this was the end result - it worked reliably.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could talk to our own field units and sometime even reach California ham operators.   &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Adjusting for Doppler was not optional in the least.  Very important part of the setup.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;To get Full Duplex, it is definitely a two-man job.  Two radios and a hand-held antenna.  The Alaskan Arrow allows you to bypass the diplexer and simply connect the UHF radio to one set of elements and the VHF radio to the other.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Of course, Full-Dup has not been supported by ARISS for voice, in my experience.  It is usually just VHF-Simplex.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We always just listened for them.  Too much QRM for us to try to compete.  &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For all the birds it is not polite to try to overpower others so we stayed strictly at 5 Watts output (with high-gain antennas).  We found that in general hams are usually polite on OSCARs.  Most QRM is accidental.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Now that I live Outside, in the contiguous states, the comm windows would be longer, so perhaps I would use 5 channels with 5 KHz spacing.  &lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-04-23T01:39:28.987" LastActivityDate="2018-04-23T01:39:28.987" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10192" PostTypeId="1" CreationDate="2018-04-23T19:19:26.333" Score="4" ViewCount="127" Body="&lt;p&gt;If you have automatic prompt for logging on WSJT-X, at the end, you get this dialog:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TPE2k.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TPE2k.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does the &quot;Retain&quot; checkboxes do when you check them?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2018-04-24T00:56:23.870" Title="What does retain mean in the logging of WSJT-X 1.8.0?" Tags="&lt;ft8&gt;&lt;wsjt-x&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10193" PostTypeId="1" AcceptedAnswerId="10197" CreationDate="2018-04-23T22:51:25.667" Score="9" ViewCount="488" Body="&lt;p&gt;HAM operators who build their own HF rigs typically do so using discrete components. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, for VHF and UHF rigs, an operator can make use of monolithic transceiver ICs on the market &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, there is this one for 30MHz ~ 1200MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.akm.com/akm/en/product/datasheet1/?partno=AK2401&quot; rel=&quot;noreferrer&quot;&gt;AK2401 Direct Conversion Transceiver IC&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Why aren't there monolithic HF ICs like this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would seem that since the frequencies are lower, the circuit design would be easier. I can only think of an economic reason:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The market is small. Whereas VHF and UHF is used for commercial radios, a tunable HF rig is used mostly by hams only.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Are there technical reasons we don't see monolithic HF ICs?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="5820" LastEditorUserId="8832" LastEditDate="2018-04-26T19:44:42.913" LastActivityDate="2018-04-26T19:44:42.913" Title="Why don't monolithic HF transceiver ICs exist?" Tags="&lt;hf&gt;&lt;diy&gt;&lt;transceiver&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 3.0" />
  <row Id="10194" PostTypeId="2" ParentId="10192" CreationDate="2018-04-24T00:56:23.870" Score="5" Body="&lt;p&gt;When those boxes are checked, the values entered will be retained as the defaults for the next QSO to be logged.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unchecked, the fields will revert to blank.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-04-24T00:56:23.870" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10195" PostTypeId="2" ParentId="10193" CreationDate="2018-04-24T16:08:23.443" Score="3" Body="&lt;p&gt;At high frequencies, (3 30 MHz), the resonant component values (inductors and capacitors) would require physical sizes larger than may be  practical on current IC fabrication equipment. I’m speaking strictly about conventional superheterodyne methods.  On the other hand there are monolithic a.m. radio circuits that utilize the TRF (tuned radio frequency method)  my understanding is that TRF is not a technology applicable to the complexities of current amateur radio requirements however. &lt;/p&gt;&#xA;" OwnerDisplayName="user11476" LastActivityDate="2018-04-24T16:08:23.443" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10197" PostTypeId="2" ParentId="10193" CreationDate="2018-04-24T19:45:00.930" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Why aren't there monolithic HF ICs. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There are, in the shape of actual (broadcast) AM receiver ICs, which can most likely with minimal effort be also used to transmit.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;However, are there technical reasons we don't see monolithic HF ICs?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Your market considerations are something I'd &lt;strong&gt;very much&lt;/strong&gt; agree with. Why build a monolithic IC for something that is rarely needed, and if needed, can be done by the potential customer with low cost and effort without any dedicated ASIC? Let me elaborate:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can often simply use the IF interface of a superhet UHF FM transceiver chip as direct HF AM circuitry. The older Philips FM receiver ICs are known to be prone to &quot;accidental&quot; HF operation by interference on the IF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're only after AM modulation: What do you even need? All you'd need for transmission is a mixer – and the NE612 will happily do that. Same for superhet reception, followed by an envelope detector (a.k.a. diode).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, this is 2018 – you can actually directly synthesize all you need for HF transmission with any mid-class microcontroller (that'd be some IF at a rather low frequency, seeing that ham bandwidths in that band are very low, and something to mix that with, which can easily be generated with the chip-integrated PLLs and PWM units) plus an external filter, which might or might not be very complex – in the end, if you need little output power (e.g. to drive an amplifier), your an RC lowpass filter could easily work with large resistances and low capacitances, so it would be very compact. You typically don't need much in terms of high-pass filtering – your antenna simply won't work for lower frequencies (plus, high-pass filtering can be done with an CR high pass filter of the same order of size).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I'd argue, this is an SDR world:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;There's monolithic chips for everyone who wants them – just that they are cheap microcontrollers and need to be programmed with software to do what you want, and would, much like most monolithic UHF ICs, only need external filtering components; that includes both RX and TX capabilities.&lt;/li&gt;&#xA;&lt;li&gt;With (not that much) more expensive digital logic, you could directly sample (ADC) or directly synthesize (DAC) at HF frequencies any arbitrary waveform, which includes AM, FM, Digital Radio Mondial (DRM), Codec2, …&lt;/li&gt;&#xA;&lt;li&gt;And anything that can enough bandwidth of stereo audio (so, any midrange audio DAC with) can be abused as IQ baseband DAC, giving the same flexibility as the previous point; leaves you with the need for an external quadrature mixer (and those exist as monolithic ICs). Or you only use smaller bandwidth (a bit less than half of the Audio DAC's sampling rate or lesser), and go for low-IF and a single mixer.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Oh, by the way, the SteveM of Osmocom fame has just released his &lt;a href=&quot;https://osmocom.org/projects/osmo-fl2k/wiki&quot; rel=&quot;noreferrer&quot;&gt;fl2k project&lt;/a&gt;,  which... uses a monolithic IC that was designed to synthesize analog video (VGA to be specific) to convert things that are far higher in frequency than HF directly. So, there's literally a 5 € device on the market that can directly be used as DC..HF..UHF (and with harmonics, far above that) SDR transmitter on any PC-style hardware with USB3 for direct sampled HF with free software. USB2 would be totally sufficient for HF-typical bandwidths, too, but you'd need to exploit the third harmonic (or fifth).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-04-24T19:45:00.930" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10198" PostTypeId="1" AcceptedAnswerId="10199" CreationDate="2018-04-25T04:08:21.767" Score="6" ViewCount="601" Body="&lt;p&gt;I've been trying to &quot;hack&quot; my garage door using an SDR (LimeSDR) for a high school physics project, and I have run into a snag.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I look at the signal and demodulate it using ASK in Ultimate Radio Hacker (URH), I seem to be getting a signal that makes no sense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I get.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;10011001101110001011100010111011100110011 [Pause: 70854 samples]&#xA;  1110001000100010001001101110011001101110001 [Pause: 78094 samples]&#xA;  10011001101110001011100010111011100110011 [Pause: 74099 samples]&#xA;  1110001000100010001001101110011001101110001 [Pause: 78071 samples]&#xA;  10011001101110001011100010111011100110011 [Pause: 74078 samples]&#xA;  1110001000100010001001101110011001101110001 [Pause: 78096 samples]&#xA;  10011001101110001011100010111011100110011 [Pause: 74111 samples]&#xA;  1110001000100010001001101110011001101110001 [Pause: 66865 samples]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;...but the dip switch on my Garage door clicker is set to 010100010101.....&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Confusing, right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, so now I figure out that my garage door clicker is meant to work with many different types of garages, from rolling code to dip switch. So I look up whether my garage door opener uses a rolling code or dip switches, and I find out that since it was made in 1996 and it is a model 2000SD Chamberlain Green Button, it uses something called &quot;Billion Code&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't seem to find out any details on what this is and I desperately need your help.&lt;/p&gt;&#xA;" OwnerUserId="11224" LastEditorUserId="13000" LastEditDate="2019-07-31T18:44:17.593" LastActivityDate="2019-07-31T18:44:17.593" Title="What is &quot;Billion Code&quot; for garage door openers from around 1996?" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10199" PostTypeId="2" ParentId="10198" CreationDate="2018-04-25T05:46:39.870" Score="6" Body="&lt;p&gt;The billon code refers to a generation of transmitters that could transmit up to ~3.5 billion different codes. Although there were a large number of codes possible, the transmitter always transmitted the same code each time the button was pressed, unlike more modern versions where the code changes each time the button is pushed (a rolling code).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The DIP switch on your remote could either be that it is facilitating a dual standard remote (e.g. an earlier standard) or the DIP switch selects on of ~ 4096 different codes out of the ~3.5 billion possible. I would guess based on your decoded output stream that it is the former.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you have already decoded the fixed bit strings that your transmitter puts out. You can see that it consistently repeats. Now you simply recreate that bit stream in your SDR transmitter and you can open the door using your SDR.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-28T17:33:25.657" LastActivityDate="2018-04-28T17:33:25.657" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10201" PostTypeId="1" AcceptedAnswerId="14565" CreationDate="2018-04-26T01:28:01.310" Score="10" ViewCount="175" Body="&lt;p&gt;I would like to prepare for the Technician exam.  I think I read somewhere that the ham Technician exam has material that is revised every 4 years.  And that the new set of questions will be coming out later this year.   Is this correct?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this book the latest version of questions?....or should I wait a few months to get an updated guide about new exam questions?: &lt;a href=&quot;http://www.arrl.org/ham-radio-license-manual&quot; rel=&quot;noreferrer&quot;&gt;http://www.arrl.org/ham-radio-license-manual&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="11510" LastEditorUserId="76" LastEditDate="2018-04-27T21:04:12.260" LastActivityDate="2019-05-21T11:16:21.870" Title="Ham Technician Exam Material" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10202" PostTypeId="2" ParentId="10201" CreationDate="2018-04-26T01:48:55.273" Score="3" Body="&lt;p&gt;From &lt;a href=&quot;http://www.arrl.org/question-pools&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/question-pools&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;TECHNICIAN Class (Element 2) Pool is effective July 1, 2014 and is &#xA;  valid until June 30, 2018.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;GENERAL Class (Element 3) Pool is effective July 1, 2015 and is  valid&#xA;  until June 30, 2019.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;EXTRA Class (Element 4) Pool is effective July 1, 2016 and is valid&#xA;  until June 30, 2020.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That having been said, it typically only takes people a week or two to study and successfully pass the technician exam.  I'd suggest not waiting.&lt;/p&gt;&#xA;" OwnerUserId="313" LastActivityDate="2018-04-26T01:48:55.273" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10203" PostTypeId="2" ParentId="1488" CreationDate="2018-04-26T03:09:56.163" Score="1" Body="&lt;p&gt;You as an individual ham actually hold two licenses printed on one piece of paper, an operator license and station license (it actually shows both). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The station license permits you to build an Amateur radio station. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The operator license describes your class of privileges for actually operating it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w5yi.org/page.php?id=146&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w5yi.org/page.php?id=146&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11515" LastEditorUserId="9493" LastEditDate="2018-05-04T22:09:35.470" LastActivityDate="2018-05-04T22:09:35.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10204" PostTypeId="2" ParentId="10201" CreationDate="2018-04-26T10:50:28.840" Score="5" Body="&lt;p&gt;Looks like the answer is right on the front cover.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5tbva.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5tbva.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All the exam Questions with Answer Key, for use &lt;strong&gt;July 1, 2018 to June 30, 2022&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-04-26T10:50:28.840" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10205" PostTypeId="2" ParentId="9842" CreationDate="2018-04-26T15:16:09.323" Score="1" Body="&lt;p&gt;WWV is transmitted on 5, 10, 15, 20, 25 MHz from each of two locations.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;WWVB from Boulder, Colorado&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;WWVH from Hawaii&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So with the Grundig you should be able to receive at least WWVB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Propagation varies by time of day.  And we are at a point of very low solar activity, which limits the skip at higher frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the Desert Southwest it is pretty normal to hear it at 5 MHz during the evening/night, and 10 MHz during the day on a whip antenna using a Tecsun PL-880 - a very similar radio in terms of sensitivity.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the absence of interference or locally-produced radio noise, I would expect about the same from NJ.&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2018-04-26T15:16:09.323" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10206" PostTypeId="1" CreationDate="2018-04-26T15:35:49.383" Score="2" ViewCount="80" Body="&lt;p&gt;I'd like to build an audio interface cable from my smartphone to my Yaesu FT-60 which incorporates VOX (since the Yaesu doesn't have VOX functionality) for APRS apps on the phone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm having problems with RFI on my interface cable from the 5W 144.39 MHz signal the Yaesu is outputting. I'd like to measure just the RFI signal that's being impressed on my interface cable so I can attempt to model it in SPICE.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have several questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Both devices are battery powered and their audio grounds are tied together. However, their grounds are floating relative to my scope's earth ground. The RFI signal appears on both the audio signal lines and the audio ground line connecting both devices. It seems like earth-grounding my audio ground with my scope probe might effect my measurements. Should use two probes--one on the audio signal, the other on the audio ground and leave the probe's grounds disconnected?&lt;/li&gt;&#xA;&lt;li&gt;Even with my scope probe disconnected from my interface cable, I get a significant RFI signal on that channel. This makes me wonder if the RFI I'm measuring on my scope is being conducted by the interface cable or by the scope probe and wire itself. Is there some way I can make sure I'm measuring the RFI on the audio interface cable in isolation?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I can think of two approaches for #2:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Use two channels. Connect one to the audio interface cable and leave the other in roughly the same position as the first. Then subtract the second channel from the first to yield just the RFI that's on the interface cable. However, if there's any phase shift on one channel relative to the other, it seems like this subtraction won't work.&lt;/li&gt;&#xA;&lt;li&gt;I have a faraday box with 50 Ohm SMA pass-throughs on it. Put the FT-60 and interface cable in the faraday box. Connect the scope channel to the SMA passthrough and then put some sort of probe inside the box. I could use my scope probe again, but it seems like I would run into the same problem with RFI on the probe. Should I just use a SMA-&gt;BNC-&gt;mini-grabber inside the faraday box and connect that to the audio interface cable?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="5820" LastActivityDate="2018-04-27T07:05:48.383" Title="How should I measure RFI on the headset cable from a hand-talkie?" Tags="&lt;rfi&gt;&lt;measurement&gt;&lt;audio-interface&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10207" PostTypeId="2" ParentId="7642" CreationDate="2018-04-26T15:40:46.263" Score="-3" Body="&lt;p&gt;Most hams confuse &quot;counterpoise&quot; with &quot;groundplane&quot; and the two are totally different.&#xA;A counterpoise is what you call the other half of a 1\2 wave dipole.&#xA;A groundplane is simply the rf reflector for a radiator.&#xA;This is why most incorrectly think that 1\4 wave groundplane radials need to be the same length as the radiator when in fact they should be a minimum of 10% longer than the radiator and can be many times longer.&#xA;This is just one of many old wives tales created and perpetuated by the ham community.&lt;/p&gt;&#xA;" OwnerUserId="11519" LastActivityDate="2018-04-26T15:40:46.263" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10208" PostTypeId="2" ParentId="1437" CreationDate="2018-04-26T16:47:30.797" Score="1" Body="&lt;p&gt;Correction.  Simplex is a mode of communication regardless of frequency band or modulation being used.  Simplex in Amateur Radio is one way communication at a time between two communicating stations. When simultaneous transmission is used with capable equipment, it's called full duplex, meaning both stations can transmit and receive at the same time.  There are other modes of communication as defined by the data communications world outside of Amateur Radio. Simplex by their definition is a device transmitting in one direction only, not able to reverse direction.  Half duplex is a single transmission one way at a time, but is able to reverse direction. You could say Amateur Radio Simplex is really half duplex communication.   &lt;/p&gt;&#xA;" OwnerUserId="11520" LastActivityDate="2018-04-26T16:47:30.797" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10209" PostTypeId="2" ParentId="10206" CreationDate="2018-04-27T04:31:50.553" Score="2" Body="&lt;p&gt;I doubt that SPICE modeling will be successful. There are required criterion that you do not have available such as the impedances at frequency of each device connection, the impedance characteristics of the connecting cable, the skin depth and effectiveness of the shield, etc. As you have observed, you will also struggle measuring the common mode current at the frequencies even with a proper current probe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more pragmatic approach is to take remedial measures:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Wrap a few turns of the cable on a type 31 torroid core. Do this on both ends of the cable. This will mitigate common mode currents on the cable.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Install a 0.1 $\mu$F capacitor to ground from each signal line in the cable. This may be necessary on both ends of the cable.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Keep the cable as short as possible but avoid lengths close (+/- 10%) to odd multiples of 1/4 $\lambda$ long.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-27T07:05:48.383" LastActivityDate="2018-04-27T07:05:48.383" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10210" PostTypeId="1" CreationDate="2018-04-27T17:36:42.327" Score="2" ViewCount="248" Body="&lt;p&gt;Considering &quot;skin effect&quot;, does the surface finish of Aluminum tubing have any practical effect on antenna efficiency at HF frequencies (5-30 MHz)?&#xA;For example: Aluminum tubing as manufactured - rough surface, etc,  versus the same tubing but polished. Specifically referring to small transmitting magnetic loop antennae.&lt;/p&gt;&#xA;" OwnerUserId="11526" LastActivityDate="2018-04-27T18:59:42.203" Title="Skin effect - rough versus polished surface" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10211" PostTypeId="1" AcceptedAnswerId="10213" CreationDate="2018-04-27T18:33:05.200" Score="12" ViewCount="2287" Body="&lt;p&gt;I am a relatively new ham, and haven't joined any club yet or participated in any nets. I have, however, hit a repeater just to know I can do it. I was told my sound was scratchy (no surprise there) but I want to hear how bad it is. I tried listening to myself from a second radio, but didn't hear anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;My setup:&lt;/strong&gt; A BaoFeng UV-5R connected to the antenna through a 25 ft cable. The antenna is a Tram 1185 Amateur Dual-Band Magnet Antenna or something similar, and is mounted on my roof about 20 ft above the ground. I'm broadcasting at 5W, and I know the radio is set up correctly because I've had people respond to me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What I did:&lt;/strong&gt; In the evening when the repeater was free, I keyed up on the BaoFeng, while listening to another 5W handheld with a rubber duck antenna nearby. The second radio didn't make any sound until I stopped broadcasting, then both radios played the beeps from the repeater indicating the end of broadcast. This is on the 2m band, and the repeater has a 600kHz offset.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What I think is going on:&lt;/strong&gt; My guess is that my broadcast is so close to the second radio that it is hurting my SNR to the point where the second radio can't isolate the signal on the frequency it's listening on. Is that because my cheap BaoFeng is transmitting spurs or other out-of-band noise? Is it because the other handheld isn't filtering out noise well enough? &lt;strong&gt;Is this something common when radios are so close, or is it specific to my equipment/setup?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="11522" LastEditorUserId="76" LastEditDate="2018-04-27T20:36:42.623" LastActivityDate="2019-04-11T14:46:31.917" Title="Why can't I hear myself from a second radio when bouncing off a repeater?" Tags="&lt;repeater&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10212" PostTypeId="2" ParentId="10210" CreationDate="2018-04-27T18:41:45.623" Score="3" Body="&lt;p&gt;If the variation in the surface finish is less than 10% of the skin depth for the frequencies involved, the effect will be minimal. The skin depth will be the most shallow at your upper 30 MHz limit of your question. In aluminum this translates to a skin depth of ~15 $\mu $m. Here is a graph of the attenuation effect (from &lt;a href=&quot;http://www,microwaves101.com&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;microwaves101.com&quot;&gt;microwaves101.com&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/79AkB.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/79AkB.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An RMS or RA finish of ~64 (ISO 9) or better (smaller) would be required to stay under the 10% of skin depth rule. When the surface roughness is 1 skin depth, you can experience ~60% more loss in the conductor. For reference, sanding your aluminum with 240 grit sandpaper will leave a surface roughness of ~0.47 $\mu$m - well below the 10% of skin depth rule.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in general, the more you polish your aluminum in a low efficiency application like a loop, the better the antenna efficiency, and thus gain, will be but anything approaching a mirror like finish is overkill on HF. Do not forget to clear coat it once you are done or the formation of aluminum oxide will discount your earlier polishing efforts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also wish to consider using pure copper tubing. While the skin depth is slightly less (~12 $\mu$m), its lower resistivity brings efficiency gains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Increasing the diameter of the tubing also reduces the resistive losses. So before you attempt a mirror like finish, you may wish to consider larger diameter tubing as a more practical approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also recall that the larger in diameter that you make your loop, the more efficient it becomes. The rate of  increase in radiation resistance is faster than the rate of increase of resistive losses so it is worth considering.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-04-27T18:59:42.203" LastActivityDate="2018-04-27T18:59:42.203" CommentCount="2" ContentLicense="CC BY-SA 3.0" />
  <row Id="10213" PostTypeId="2" ParentId="10211" CreationDate="2018-04-27T19:35:50.913" Score="12" Body="&lt;p&gt;You are experiencing what is commonly called desense (short for desensitization). The strong signal of your transmitter overloads your receiver making it unable to demodulate the much weaker, on-channel signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the filters throughout the radio provided a much narrower bandwidth, this effect would be mitigated. But front end filters with less than 600 kHz bandwidth are not practical for an ordinary radio. On a 2 meter repeater, for example, such filters consist of 4 to 6 &quot;cans&quot; that are each 8-12 inches in diameter and ~24 inches tall. This allows the repeater transmitter and receiver to share an antenna while operating on 600 kHz spacing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may have some success by reducing your transmit power to the lowest level needed to hit the repeater. Separating the radios further, coax cables and antennas can also bring a measure of improvement.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="8713" LastEditDate="2019-04-11T14:46:31.917" LastActivityDate="2019-04-11T14:46:31.917" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10214" PostTypeId="2" ParentId="10211" CreationDate="2018-04-27T20:02:58.370" Score="3" Body="&lt;p&gt;Even driving too closely to another ham operating similarly to your scenario can do the same.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say you and a ham buddy are talking to one another from your cars using a repeater, and you drive to the same place to meet. As your cars approach each other, his TX will overwhelm your RX (and vice versa) and you will experience the same problem.&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-04-27T20:02:58.370" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10215" PostTypeId="1" CreationDate="2018-04-27T20:22:54.293" Score="3" ViewCount="102" Body="&lt;p&gt;Will I need to take the Technician exam again when I test for General if my Technician license is over 4 years old?&lt;/p&gt;&#xA;" OwnerDisplayName="user11527" LastEditorUserId="76" LastEditDate="2018-04-27T20:34:54.650" LastActivityDate="2018-04-30T18:02:37.560" Title="Testing requirements for 5 year old tech license to take general exam" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10216" PostTypeId="2" ParentId="10215" CreationDate="2018-04-27T20:34:32.053" Score="3" Body="&lt;p&gt;If you got your license after March 21, 1987, then when applying for General you do not need to take the Technician examination again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The relevant regulation is &lt;a href=&quot;http://www.ecfr.gov/cgi-bin/text-idx?SID=c89c6646e415ced62cde7df69e8f017a&amp;amp;mc=true&amp;amp;node=se47.5.97_1505&amp;amp;rgn=div8&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.505&lt;/a&gt;, which says&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The administering VEs must give credit as specified below to an examinee holding any of the following license grants:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;which is followed by a table specifying that if you hold “Technician Plus; or Technician granted on or after March 21, 1987”, then you get credit for Element 2, which is the formal name for the Technician exam.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-04-27T20:34:32.053" CommentCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10218" PostTypeId="5" CreationDate="2018-04-28T16:18:38.223" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-04-28T16:18:38.223" LastActivityDate="2018-04-28T16:18:38.223" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10219" PostTypeId="4" CreationDate="2018-04-28T16:18:38.223" Score="0" Body="Techniques for testing the functionality of radios and other equipment. Do not use this tag for license examinations; use [license] instead." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-04-28T16:18:38.223" LastActivityDate="2018-04-28T16:18:38.223" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10220" PostTypeId="1" CreationDate="2018-04-28T17:45:23.873" Score="10" ViewCount="446" Body="&lt;p&gt;Today I came across a problem in terminating RG8 cable using this PL259 plug.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have never had this type and it arrived in a pile of parts; I have tried to puzzle it together but without positive effect. While googling i came only across crimping and screw-in; I also checked YT but no luck with this type.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could someone who work with this type connector tell me how this should looks like and what order parts should go together in?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reference I gave them numbers (random numbers, I don't know which comes first etc).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/i5iyt.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/i5iyt.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11533" LastEditorUserId="76" LastEditDate="2018-04-29T02:39:25.457" LastActivityDate="2018-09-04T00:00:48.763" Title="How terminate RG8 coaxial cable using PL259 (UHF) - screw - gasket - solder type?" Tags="&lt;coaxial-cable&gt;&lt;connectors&gt;&lt;pl259-so239-connector&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 3.0" />
  <row Id="10222" PostTypeId="2" ParentId="10215" CreationDate="2018-04-30T18:02:37.560" Score="2" Body="&lt;p&gt;You will get credit for Element 2 as long as your license is valid. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bring a copy of your existing license that we can keep. Volunteer Examiners conducting testing sessions usually do not have access to copiers and we have to include a copy of your license in the paperwork we turn in after the exam session. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can take element 3 for General and if you pass that you can opt to take Element 4 for Extra. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might also want to let them know ahead of time you are trying to upgrade from Technician. It takes 3 VE to conduct a testing session, for General and Extra, the VEs must be Extras. For Technician they can be Generals. While most VE are Extras, there are are few General VEs who can only give Element 2 tests for Technicians. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2018-04-30T18:02:37.560" CommentCount="0" ContentLicense="CC BY-SA 3.0" />
  <row Id="10224" PostTypeId="2" ParentId="1174" CreationDate="2018-05-02T01:52:39.190" Score="0" Body="&lt;p&gt;If you want to go to the extreme have a look here:&#xA;&lt;a href=&quot;https://www.youtube.com/watch?v=-mCRLfUnXTE&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=-mCRLfUnXTE&lt;/a&gt;&#xA;At 8:40 into the video you can see a way to almost completely&#xA;eliminate the problem. Look at the entire video to get an&#xA;idea of the magnitude of the problem.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-05-02T01:52:39.190" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10225" PostTypeId="2" ParentId="1804" CreationDate="2018-05-02T02:14:41.143" Score="2" Body="&lt;p&gt;The gamma match is problematic. It surely allows a perfect impedance match having two degrees of freedom, but the balun effect is questionable. The screen of the coax is connected to the center of a half wave element. That means that it is connected to two open-ended quarter-wave conductors. In free space they would have a very high impedance at the ends and consequently the impedance at the center would be very low. That means that the voltage on the coax screen would be very low so not much signal would be sent onto the screen of the coax (or not much qrm would be picked up if the coax has interference on its outside.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A half wave dipole where two quarter wave rods are fed in anti-phase is a good radiator with Z=free space impedance (300 ohms) divided by about 6. But if one feeds them in phase, radiation from both sides will cancel and the impedance&#xA;at the center goes towards zero while the impedance at the ends becomes very high. The midpoint becomes a good groundpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In real life it is different. Practical experience: A friend of mine had an EME array with several long yagis on 144 MHz. They all had a gamma match which was isolated from the boom tube. There was however a performance problem. A simple test: Take one antenna, point it straight into the sky with the reflector well above ground. Put a field strength meter on the last director and look at the reading while moving the hand along the coax. Big variations were observed meaning that a substantial current is flowing on the coax screen. Add a sleeve balun. That makes the current on the screen negligible. That was long ago, but as I can recall performance was improved&#xA;by more than 1 dB (That is a lot on EME)&#xA;The explanation is that the physical midpoint is not the electrical midpoint. If you would make a dipole from two rods of different diameter and feed them in phase radiation would not cancel and consequently the impedance at the midpoint would not be very low. It would be necessary to make the thicker side shorter.&#xA;The gamma match destroys the symmetry of the radiator so there is a substantial RF voltage at the center. This causes some loss of power and maybe more importantly pick up of conducted interference.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastEditorUserId="9758" LastEditDate="2018-05-04T22:30:25.750" LastActivityDate="2018-05-04T22:30:25.750" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10226" PostTypeId="1" CreationDate="2018-05-02T17:34:54.827" Score="2" ViewCount="236" Body="&lt;p&gt;ID5100 mounted mobile in center console with only faceplate and mic exposed. Also have bluetooth headset. &#xA;Besides the speakers built-in and external sp1 or sp2 does a handheld mic AND speaker like on the HT's exist?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bluetooth thru car audio is cool for monitoring but not for transmit (feedback)   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Working on a external speaker system now for both output jacks. &lt;/p&gt;&#xA;" OwnerUserId="11554" LastEditorUserId="873" LastEditDate="2018-05-03T00:41:58.687" LastActivityDate="2018-05-09T17:46:50.080" Title="ID5100 is a Speaker Mic avail?" Tags="&lt;mobile&gt;&lt;speaker&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10227" PostTypeId="1" AcceptedAnswerId="10229" CreationDate="2018-05-02T22:15:43.587" Score="5" ViewCount="653" Body="&lt;p&gt;Intuitively, we all understand that an antenna at fractional wavelengths will not radiate well even with perfect impedance matching systems. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I understand the efficiency of antenna has a few factors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Conduction losses (due to finite conductivity of the metal that forms the antenna)&lt;/li&gt;&#xA;&lt;li&gt;Dielectric losses (due to conductivity of a dielectric&#xA;material near an antenna)&lt;/li&gt;&#xA;&lt;li&gt;Impedance mismatch loss&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This still does not explain why a 1-foot long dipole antenna on 160 meters does not radiate well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I have 100 Watts RF input, and a theoretical perfect matching system to transform my radios independence to the very high impedance of &amp;lt;1/10 fractional wavelength antenna such that there is no reflected power and no ohmic losses in the antenna, where does this 100 watts go, and why is it not all radiated in the form of RF energy as well as that of say a 1/4 wavelength vertical?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8717" LastEditDate="2018-05-02T23:09:02.357" LastActivityDate="2018-05-07T11:57:23.707" Title="Antenna Efficiency" Tags="&lt;antenna-theory&gt;&lt;impedance&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10228" PostTypeId="1" CreationDate="2018-05-02T22:23:43.750" Score="4" ViewCount="356" Body="&lt;p&gt;I'm not sure whether it's more appropriate to ask this question here, or in the dsp.stackexchange.  But I'll try here first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There seems to be a lot of information available on the filtering and demodulation of SSB signals in the analog or time-domain.  But my iOS RTL-SDR radio app is doing all of it's fine tuning and filtering in the frequency domain (via overlap-add FFT fast convolution).  So I'm wondering what would be the cleanest method of filtering in the frequency domain, without just emulating the chain of processes needed in the time domain or with an analog SSB demodulator.  For instance, a Hilbert transformer isn't needed, since the input to the complex FFT filter already has the imaginary component of the complex or IQ signal provided by an RTL-SDR (or other similar SDR front-end).  And asymmetric filtering can be accomplished in the complex IQ frequency domain without shifting the signal’s spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's one possible idea:  Shift my FFT lowpass filter from being magnitude symmetric around DC to either only the positive or negative frequency side of DC (equivalent to using a complex FIR filter impulse response of the same length or order).  Mirror/flip the retained side (positive or negative frequencies for USB or LSB) to the other side of DC and complex conjugate it, resulting in a strictly real time-domain signal after the fast-convolution IFFT.  Feed that result to a simple AM demodulator.  Would that work?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there another canonical and clean SSB demodulation method?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-05-03T01:50:57.683" LastActivityDate="2018-05-09T00:34:48.263" Title="SSB filtering in the frequency domain?" Tags="&lt;software-defined-radio&gt;&lt;filter&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10229" PostTypeId="2" ParentId="10227" CreationDate="2018-05-02T22:56:34.060" Score="12" Body="&lt;p&gt;In theory, if you had lossless conductors in the antenna  and a lossless matching network, your shortened, 1 foot dipole would have a gain of only ~0.7 dB less on 160 meters than the gain of a full size 1/2 wavelength dipole. But the world is far from perfect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The efficiency of an antenna is defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\text {Efficiency}=\frac {R_r}{R_r+R_l} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $R_r$ is the radiation resistance of the antenna and $R_l$ is the resistive losses of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an antenna becomes shorter, its radiation resistance drops significantly. As you can see from formula 1, this causes the otherwise negligible resistive losses to significantly impact the efficiency of the antenna. Any inefficiency is simply dissipated as heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The gain of an antenna is defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\text {Gain}=\text {Directivity}*\text {Efficiency} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the antenna is shortened, the directivity drops slightly from 1.64 for a 1/2 wavelength dipole to 1.50 for an infinitesimal dipole. This, combined with the lowered efficiency, results in an overall drop in gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now let's plug your example into the above formulas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation resistance of a free space shortened dipole is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_r=197L_\lambda^2 \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $L_\lambda$ is the length of the dipole expressed as a fraction of the wavelength (length in meters / 160 meters in this case).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your 1 foot 160 meter dipole antenna example would therefore have an $R_r $ of only ~0.7 milliohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RF resistance of 1 foot of 12 gauge wire at 1.8 MHz is ~17 milliohms (ref. &lt;a href=&quot;http://chemandy.com/calculators/round-wire-ac-resistance-calculator.htm&quot; rel=&quot;noreferrer&quot;&gt;http://chemandy.com/calculators/round-wire-ac-resistance-calculator.htm&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Note: The following paragraph and the subsequent formula results are the result of Phil's critique of my original answer regarding resistive losses.]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RMS current distribution in a very short dipole without end loading decays linearly from the maximum at the center point to zero at the ends of the antenna. As a result, the &lt;em&gt;average&lt;/em&gt; RMS current of the short dipole is 1/2 that of the feedpoint current. Since resistive heat losses are the result of current squared, we must apply a 0.25 correction factor (0.5 squared) to the calculated calculated RF resistance of the wire in order to account for this RMS current slope along the length of the short dipole. The effective resistance of the wire in this shortened dipole is therefore ~4.3 milliohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Populating formula 1 tells us that the antenna will have a 14% efficiency. This means that 86 of your 100 watts of applied power goes to waste as heat. Formula 2 tells us that the antenna will have a free space gain of 0.21 or -6.8 dBi. For comparison, an efficient, full 1/2 wave dipole in free space has 2.2 dBi of gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, a shortened antenna has a reactive component at its feedpoint that must be dealt with. This, in combination with a low resistive component, can be difficult to match to normal amateur transmission lines resulting in additional losses in the matching circuit and a corresponding reduction in antenna system gain.  Of course if the matching circuit does not provide a match to the $Z_o$ of the transmission line, there will be additional losses in the transmission line and a possible reduction in the transmitter output power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You mentioned dielectric losses. These are normally minimal at HF frequencies in a properly designed matching network.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-07T11:57:23.707" LastActivityDate="2018-05-07T11:57:23.707" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="10230" PostTypeId="2" ParentId="10228" CreationDate="2018-05-03T00:02:40.040" Score="3" Body="&lt;p&gt;For DSP with complex samples, whether you are working in the time domain or the frequency domain, you &lt;em&gt;don't need&lt;/em&gt; an AM demodulator, or complex conjugation, or a Hilbert filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You say you have available a shifted low-pass filter — in other words a band-pass filter suitable for SSB. From the output of that filter, &lt;strong&gt;discard the imaginary part.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;That's it. You're done. You have a real audio signal.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The fundamental elements of SSB demodulation are&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the downconversion (a.k.a. mixing or frequency shift) from RF to audio baseband, and&lt;/li&gt;&#xA;&lt;li&gt;the band-pass filtering to the standard 3-ish-kHz passband.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Everything else you might hear about (intermediate frequencies, BFOs, decimation, or the FFT and inverse FFT you're doing) is an implementation detail of a particular approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Possibly interesting tangent: you could even implement it with only low-pass; you would shift the input signal to put the desired SSB passband centered around 0 Hz, low-pass filter, then shift back up to only positive audio frequencies.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-05-03T03:36:48.197" LastActivityDate="2018-05-03T03:36:48.197" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10231" PostTypeId="1" AcceptedAnswerId="10236" CreationDate="2018-05-03T07:28:09.660" Score="4" ViewCount="790" Body="&lt;p&gt;During the month of May (2018) a lot of Belgian club stations can use callsigns in the format OT70xxx. (The xxx is always 3 letters, for example our club station uses OT70TRA.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In WSJT-X it seems impossible to set this call as 'mycall'; the call gets truncated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any clues how we could solve this? Except for making QSOs with all text in 'free text'?&lt;/p&gt;&#xA;" OwnerUserId="9532" LastEditorUserId="8573" LastEditDate="2018-05-03T15:23:26.050" LastActivityDate="2019-11-18T21:06:34.780" Title="Long callsigns in WSJT-X?" Tags="&lt;ft8&gt;&lt;wsjt-x&gt;&lt;jt65&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10232" PostTypeId="1" AcceptedAnswerId="10233" CreationDate="2018-05-03T08:48:09.690" Score="2" ViewCount="271" Body="&lt;p&gt;I have a YT-100 connected to my FT-857d in my remote-by-default shack in the attic (i.e. I operate it over a VNC connection from elsewhere in my house). Whenever I change band I have to go up to the attic to press the button to re-tune the ATU. It's an easy enough process as it finds the match itself, however it's a bit of a pain to do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question is, if I just start transmitting without re-tuning, will the ATU detect the mismatch and trigger a re-tune on its own?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Follow-up question (if it doesn't re-tune itself) - is anyone aware of an interface between the remote jack on the rear of the ATU and a PC to simulate pushing the tune button?&lt;/p&gt;&#xA;" OwnerUserId="11431" LastEditorUserId="76" LastEditDate="2018-05-03T15:23:02.387" LastActivityDate="2018-05-03T15:23:02.387" Title="Does an LDG YT-100 automatically trigger a tuning cycle if the SWR is high?" Tags="&lt;antenna-tuner&gt;&lt;remote-control&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10233" PostTypeId="2" ParentId="10232" CreationDate="2018-05-03T11:32:47.410" Score="2" Body="&lt;p&gt;The YT-100 will not automatically initiate a tuning cycle when there is high SWR present.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is, however, a simple solution to your problem. The YT-100 has a 1/8 inch jack that facilitates a remote tune button (see page 16 of the manual). You could run a shielded, decoupled cable to a push button at a convenient location; you could use an RF keychain remote control device to avoid the use of the cable all together; or you could connect the input to a TCP/IP switch to toggle it remotely from your PC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are comfortable with homebrewing, you could put an SWR detector circuit on the input of the tuner that automatically triggers a tune cycle if a given SWR threshhold is exceeded.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-03T13:20:55.290" LastActivityDate="2018-05-03T13:20:55.290" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10234" PostTypeId="2" ParentId="10231" CreationDate="2018-05-03T13:33:35.020" Score="2" Body="&lt;p&gt;According to K1JT himself, the callsign field is rather restricted and must meet the same parameters as the one for JT65.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://sourceforge.net/p/wsjt/mailman/message/35254350/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://sourceforge.net/p/wsjt/mailman/message/35254350/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-05-03T13:33:35.020" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10235" PostTypeId="2" ParentId="2226" CreationDate="2018-05-03T15:29:44.010" Score="1" Body="&lt;p&gt;I'm looking at the Service Manual for the TK-805D and it shows +13.8 Vdc on pin 1 and +5 Vdc on pin 6.  Mind you, these readings are hand written by whom ever posted this manual.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you have the part number off the back of the microphone?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know this is a 3 year old post and hopefully you ere able to get your answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I love this little radio, just don't like the microphone as it's the old style Kenwood mic (overly large).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rod&#xA;KC7CJO&lt;/p&gt;&#xA;" OwnerUserId="11560" LastActivityDate="2018-05-03T15:29:44.010" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10236" PostTypeId="2" ParentId="10231" CreationDate="2018-05-04T04:27:39.857" Score="4" Body="&lt;p&gt;For the current &quot;77-bit&quot; versions of FT8 and MSK144 (as supported by wsjt-x version 2.0, released in late 2018, and newer), you can use these callsigns without doing anything special. Any combination of letters, numbers, and slashes, up to 11 characters total, can be used as a callsign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your callsign is &quot;nonstandard&quot;, meaning that it doesn't follow the rules described below for pre-2.0 versions, there are some differences in behavior:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Your CQ or CQ-response messages won't include a grid square (there are no bits available for that)&lt;/li&gt;&#xA;&lt;li&gt;In other messages during a QSO with you (signal report / RRR / 73 / RR73), either your callsign or the other party's callsign will be replaced by a 12-bit &quot;hash&quot; instead of transmitting the callsign directly.&lt;/li&gt;&#xA;&lt;li&gt;When callsigns are hashed, they are displayed in angle brackets like &lt;code&gt;&amp;lt;KC2G&amp;gt;&lt;/code&gt; in the wsjt-x GUI.&lt;/li&gt;&#xA;&lt;li&gt;Hashing shouldn't make any difference to your life 99% of the time, but occasionally a &quot;hash collision&quot; will occur (two callsigns on the air at the same time share the same hash), leading to confusion about who is calling who.&lt;/li&gt;&#xA;&lt;li&gt;The protocol is designed so that each party transmits their own and the other party's complete (non-hashed) callsign at least once during each QSO, which should satisfy amateur radio operating rules.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Using versions of wsjt-x prior to 2.0 (including the version in effect when this question was asked), such callsigns were impossible; the only callsigns that could be used in a complete QSO were &quot;standard&quot; 28-bit callsigns. &quot;Standard&quot; callsigns use a complicated encoding which covers the great majority of amateur callsigns in the world, but excludes some special ones like the one in the question, and cannot support most prefixes and suffixes. The rules for standard callsigns are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;there must be a digit,&lt;/li&gt;&#xA;&lt;li&gt;there cannot be more than three letters after the last digit,&lt;/li&gt;&#xA;&lt;li&gt;there cannot be more than two characters (either letters or numbers) &lt;em&gt;before&lt;/em&gt; the last digit.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In version 2.0, callsigns that conform to these rules will use the standard encoding and not have to worry about hashing.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2019-11-18T21:06:34.780" LastActivityDate="2019-11-18T21:06:34.780" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10237" PostTypeId="2" ParentId="10105" CreationDate="2018-05-04T20:21:07.163" Score="1" Body="&lt;p&gt;It does work well although weather will eventually get to it.  I got at least 10 years out of some salvaged from an old chute probably made in the 50s. Used to support a dipole made of #3 wire (some old 100 A drop line), both for the centre uphaul (always use a loop so you can pull it down when, not if, the feedline connections break) and for the ends tied to trees.  When it broke, replaced with UV stable black rope sold for this purpose.  I got mine from Davis RF. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A related tip: soldered joints on wire that needs to flex is a bad idea. One thing that works well are Marrettes - the electrical wiring twist-on connectors.&lt;/p&gt;&#xA;" OwnerUserId="11569" LastEditorUserId="8717" LastEditDate="2018-05-04T22:07:07.463" LastActivityDate="2018-05-04T22:07:07.463" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10238" PostTypeId="2" ParentId="10173" CreationDate="2018-05-04T20:32:52.987" Score="-3" Body="&lt;p&gt;Suggest reading the following for a understandable and thorough treatment of common mode chokes including easy to build (that is, can you wrap some wire around a toroid?) ones, with better performance and much cheaper than commercial units.  K9YC is a professional engineer with decades of experience and a practical bent.&lt;br&gt;&#xA;&lt;a href=&quot;http://audiosystemsgroup.com/publish.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://audiosystemsgroup.com/publish.htm&lt;/a&gt;&#xA; and look for:&#xA;RFI, Ferrites, and Common Mode Chokes For Hams&#xA;73, George VE3YV/K8HI  &lt;/p&gt;&#xA;" OwnerUserId="11569" LastActivityDate="2018-05-04T20:32:52.987" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10239" PostTypeId="2" ParentId="10227" CreationDate="2018-05-05T03:01:09.523" Score="0" Body="&lt;p&gt;In short: &lt;em&gt;if&lt;/em&gt; you had the perfect matching system you described and a lossless antenna, there would be no losses. But those pesky laws of physics prevent us from making anything perfect, and even getting anywhere &lt;em&gt;close&lt;/em&gt; to perfect may not be so easy. Instead of the 1-foot dipole you suggested, let's try a 5-meter long dipole instead (i.e. a half-wave for 10m). Most people have room for one of those, right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case, the radiation resistance goes all the way up to 192 milliohm, which is actually of the same order of magnitude as the resistive losses, which become 282 milliohm at this length. And the reactance becomes about 240kOhm capacitive. I don't know what kind of a network it takes to match 50R to 0.474-240000j at 1.8MHz and handle 100W, but seeing as how I can't just buy one at DXE and solve all of my problems, it stands to reason that such a box is either &lt;em&gt;incredibly&lt;/em&gt; inefficient on its own, or else requires coils bigger than the 160m antenna I've avoided putting up.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2018-05-05T03:01:09.523" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10241" PostTypeId="1" CreationDate="2018-05-06T05:42:22.067" Score="3" ViewCount="89" Body="&lt;p&gt;It's said that in order to decrease multi-path effects on receiving antennas that your antenna pattern should have a sharp slope near the horizon.  Why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;for example this is article mentioned it.(Comparative Study of High-Performance&#xA;GPS Receiving Antenna Designs&#xA;Neus Padros, Juan I. Ortigosa, James Baker, Magdy F. Iskander, Fellow, IEEE, and Bryce Thornberg)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;a very sharp slope is also desirable near the horizon directions to&#xA;  minimize the effect of the multipath signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="11580" LastEditorUserId="11580" LastEditDate="2018-05-08T05:30:14.733" LastActivityDate="2018-05-08T10:34:18.180" Title="Antenna Patterns and Multipath Effect" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10242" PostTypeId="2" ParentId="10241" CreationDate="2018-05-06T10:20:30.827" Score="5" Body="&lt;p&gt;On HF (1.5 to 30 MHz) amateur radio operators use antennas with the major directive lobe close to the horizon in order to maximize the distance the signal will travel. At these frequencies the signals bounce off of the ionosphere - so by minimizing the incident angle, the distance of communications tends to be maximized. Multipath signals are rarely a problem on HF although they can happen. One of the most interesting means is &quot;long path&quot; where the signal takes the longest path around the earth. Under the right conditions this results in a strange echo effect due to the time delay of the long path compared to the short path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On higher frequencies (VHF and higher), antennas with a major lobe to the horizon are generally preferred in order to maximize the gain for the line of sight conditions. Here multipath signals can readily occur due to signal reflections off of structures, for example. If multipath is a concern then an antenna with directivity in the azimuth can be deployed and the antenna is then turned in the direction of the most favored signal path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Edit]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the citation that the OP added to the question as an example, the multipath issue is specific to receiving GPS satellite signals. In this case, it is desirable to only receive the signals directly from the overhead satellite constellation in order to achieve the desired GPS accuracy since the calculated position is based on the precise time delays between signals from multiple satellites.  GPS signals are in the microwave region so they are very conducive to reflecting off of ground based structures, for example. Any satellite signals indirectly received as reflections off of ground based objects introduces timing (delay) errors due to the longer time of flight for the reflected signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The author is therefore making the point that, in the case of GPS signals, the antenna should have a &lt;em&gt;minimum&lt;/em&gt; gain (also called a null) near the horizon so as to effectively attenuate any ground based signals due to reflections in favor of the desired signals directly from the satellites overhead. A typical antenna for GPS is a patch antenna that has a broad, major gain lobe (or multiple lobes) directly overhead but with very poor gain at the horizon. An alternative GPS antenna design is a quad helix (spiral) antenna that has similar pattern characteristics.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-08T10:34:18.180" LastActivityDate="2018-05-08T10:34:18.180" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10243" PostTypeId="2" ParentId="10220" CreationDate="2018-05-06T21:29:25.860" Score="2" Body="&lt;p&gt;Following up on Phil's comment, there is a decent cutaway view:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.mouser.com/datasheet/2/159/d73059_001-54085.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Pomona Model 73059 UHF Plug, Clamp Type, RG 8&lt;/a&gt; (mouser.com)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excerpt:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yDYV4.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yDYV4.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2018-05-06T21:29:25.860" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10244" PostTypeId="1" CreationDate="2018-05-08T03:43:28.757" Score="5" ViewCount="640" Body="&lt;p&gt;In order to route my antenna feedlines out of my house, I have to pass through a wall, into the garage and through another wall. All of this involves four 90 degree turns. I am wondering what the possible issues would be with using 2 inch electrical conduit with a couple of conduit bodies (small housing with a cover to help pull wire through an angle). My worry is that the tight turns that these would introduce are not good for coax, specifically LMR 400. Without a conduit though, I fear that the lines could be damaged being exposed in my garage. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I spoke with an elmer in my club and he recoomended I use Pl-259 90 degree elbows inside the conduit body. I had heard that these tend to attenuate signal rather greatly, but he said that was not his experience. I then saw this video &lt;a href=&quot;https://www.youtube.com/watch?v=5AgFum5K7bw&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=5AgFum5K7bw&lt;/a&gt; which also supports his claim. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is a good solution?&lt;/p&gt;&#xA;" OwnerUserId="687" LastEditorUserId="687" LastEditDate="2018-05-30T16:57:37.687" LastActivityDate="2020-09-02T20:56:38.510" Title="What are the implications of pulling LMR400 through EMT conduit with several 90 degree conduit body fittings" Tags="&lt;feed-line&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10245" PostTypeId="2" ParentId="10244" CreationDate="2018-05-08T12:42:42.620" Score="7" Body="&lt;p&gt;I am sure you will get many good suggestions for your situation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The higher quality coax cables do have a specification for their minimum bend radius during install. For LMR-400 it is 1 inch (25.4 mm) [ref. &lt;a href=&quot;https://www.timesmicrowave.com/documents/resources/LMR-400.pdf&quot; rel=&quot;noreferrer&quot;&gt;https://www.timesmicrowave.com/documents/resources/LMR-400.pdf&lt;/a&gt;].&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I talked with a Times Microwave technical sales specialist and here is his answer regarding bends:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;You can bend the cable to a 1” radius and leave it. You just do not want to continue to bend it to such a small radius since it will start to work harden the conductors. If you are planning to get down to such a tight radius, we’d recommend first pulling the cable around a mandrel of roughly 2” diameter such as a piece of pipe. There is no problem with the 1” radius as long as it’s done in a controlled manner.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Without knowing your installation limitations, instead of pull boxes try to use sweep elbows where the pipe turns. The gradual radius is much easier on the cable and your installation will be much less stressful on you as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't forget to include moisture drains in the pipe if it is has exterior exposure. The diurnal cycles will cause condensation build up in the pipe that will eventually flood the pipe if a suitable drain is not provided.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-08T15:41:25.607" LastActivityDate="2018-05-08T15:41:25.607" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="10246" PostTypeId="1" CreationDate="2018-05-08T16:09:21.957" Score="9" ViewCount="775" Body="&lt;p&gt;What is IQ imbalance in the output of complex or quadrature downconverter/demodulator/mixer? What are the causes and effects of IQ imbalance? (A spike in the spectrum display of RF noise?)  Are there any SDR algorithms for reducing the negative effects (if any) of IQ imbalance in a digitized complex or IQ signal before further signal detection or demodulation?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-05-08T17:50:01.730" LastActivityDate="2018-05-09T03:17:49.767" Title="IQ imbalance after quadrature mixing" Tags="&lt;software-defined-radio&gt;&lt;receiver&gt;&lt;transverter&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10247" PostTypeId="2" ParentId="10246" CreationDate="2018-05-08T16:31:46.700" Score="6" Body="&lt;p&gt;A quadrature mixer contains two signal paths, I and Q. For a sinusoidal input into the mixer, the outputs will be in quadrature. It's this property that allows a quadrature mixer to distinguish between frequencies above and below the LO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Discarding one of the I or Q components still works as a mixer, but input frequencies above and below the LO become indistinguishable. For example if the LO is set to 10 MHz, and the output of the mixer shows a signal at 100 kHz, it's unknown if the original signal is at 10.1 MHz or 9.9 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the isolation between negative and positive frequencies to be complete, the I and Q components must have equal gain and quadrature phase. When this is not the case, images of the input signal appear at the mixer output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imbalance between the I and Q components comes from component variation, a result of manufacturing processes, temperature, and aging. For example, variance in resistance may result in one component having higher gain than the other. Variations in capacitance or inductance may result in unequal, frequency dependent phase delay.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Correction involves finding the best phase and magnitude coefficients to minimize images. If a test input of a single tone can be applied this is pretty easy. If a test input signal is not possible, then the positive frequencies can be compared with the reversed negative frequencies and the coefficient adjusted to minimize their correlation. See &lt;a href=&quot;https://github.com/osmocom/gr-iqbal&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/osmocom/gr-iqbal&lt;/a&gt; for an example.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="9493" LastEditDate="2018-05-09T03:17:49.767" LastActivityDate="2018-05-09T03:17:49.767" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10248" PostTypeId="2" ParentId="10244" CreationDate="2018-05-08T19:33:04.757" Score="-2" Body="&lt;p&gt;A 90 DEGREE BEND IN 1/2&quot; EMT MUST HAVE AN INSIDE BEND RADIUS OF 6&quot;. &#xA;SINCE YOU HAVE SEVERAL BENDS YOU MIGHT INSERT PULL POINTS [ A I/2&quot; FITTING LIKE A HANDI-BOX OR SIMILAR] TO HELP MAKE THE PULL. A GOOD WAY TO PULL IS A PAIL OF WATER AND IVORY FLAKES. MIXED INTO A RUNNY PASTE TO BE SLOPPED ON THE CABLE AS IT IS PULLED FROM THE OTHER END. [PRESUMABLY YOU'LL BE USING A SNAKE OR TAPE.OR YOU CAN BUY WIRE - EZ. THE FLAKE MESS WILL DRY AND YOU'LL BE SET. GOING TO 3/4&quot; WOULD SIMPLIFY THINGS. WITHOUT SEEING THE INSTALLATION, IT SOUNDS LIKE YOU HAVE YOUR WORK CUT OUT FOR YOU. BEST OF LUCK &lt;/p&gt;&#xA;" OwnerUserId="8492" LastActivityDate="2018-05-08T19:33:04.757" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10249" PostTypeId="2" ParentId="10228" CreationDate="2018-05-09T00:34:48.263" Score="2" Body="&lt;p&gt;If you want to do SSB in the frequency domain:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) Compute the complex FFT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) Pick the frequency band of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) Perform a backwards FFT on the bins that contain the&#xA;   signal of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically the sampling rate would be 192kHz I and Q and&#xA;one would want 3 kHz for SSB. That means that the inverse&#xA;FFT would have to be 64 times smaller. (VERY small CPU load) The time&#xA;domain signal would be 64 times slower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many interesting complications, but the above is the method used in Linrad to do frequency shift, filtering and decimation. It is very CPU efficient. &lt;a href=&quot;http://www.sm5bsz.com/linuxdsp/linrad.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sm5bsz.com/linuxdsp/linrad.htm&lt;/a&gt; With appropriate windows and overlapping FFTs one can get extremely good dynamic range (freedom of resampling spurs.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Receiving SSB is a linear process. One has to do two things:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) Apply a filter to remove everything outside the frequency band of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) Do a frequency translation to place the frequency of the suppressed carrier at DC (zero frequency.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It does not matter in which order we do those things (it is a linear process) and it does not matter if we do it in many steps. In analog radios we use multiple conversions and in DSP we typically filter and decimate in several steps. It is just a matter of convenience. When Linrad uses the 2 MHz wide FFT from a Perseus, the hardware has applied filtering and decimation from the original raw data at 80 MHz.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-05-09T00:34:48.263" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10250" PostTypeId="2" ParentId="10246" CreationDate="2018-05-09T00:57:21.107" Score="4" Body="&lt;p&gt;IQ imbalance causes a spur at the mirror image frequency:-( If your LO is at 7.050 MHz a signal at 7.040 MHz will show up as an image spur at 7.060 MHz and a signal at 7.060 MHz will show up as a spur at 7.040 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IQ imbalance is caused by various imperfections in the hardware. I and Q are obtained from mixing the input RF signal with two versions of a LO signal that are 90 degrees out of phase. There are two problems. The mixers and subsequent amplifiers differ in gain. Typically something like 0.5%. Depending on hardware the phase might differ. For two reasons. The 90 degree phase shift between I and Q might have a (small) time shift and also there might be an anti-alias filter in the channels that could give a slightly different phase shift at the high end of the frequency range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In modern hardware, like the Airspy HF+, the main problem is the amplitude imbalance. This means that the I/Q imbalance can be eliminated just by computing the correlation between the signal at a frequency F and the signal at its mirror image. The correlation gives a complex coefficient that can be applied to the signal to eliminate the mirror image. This is implemented in the HF+ drive routine. It works well just because the I/Q imbalance is not much depending on the frequency. (In the HF+ the evaluation of correlation puts an extra weight on the frequency one is currently tuned to.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Linrad uses a very different strategy. That is because it was originally developed for the WSE converters that have VERY sharp anti-alias filters and&#xA;an IQ imbalance that changes rapidly with frequency. The user is required to run a calibration procedure.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-05-09T00:57:21.107" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10251" PostTypeId="1" AcceptedAnswerId="10256" CreationDate="2018-05-09T06:38:34.643" Score="3" ViewCount="163" Body="&lt;p&gt;I have moved to a new flat which is on the 4 floor, luckily the landlord has let me put an OCF dipole outside with coax feeding through an existing hole in the window frame. I'm looking for some earthing opinions as a dedicated grounding rod is out of the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I considered bonding the rig to its DC supply chassis-chassis however the PSU lacks an ground lug (it is earthed via the 13A plug) so should I bond the rig to the earth terminal at the outlet? A friend suggested providing an rf earth via the rig to an artificial ground unit and that to the outlet earth or a length of random wire.&lt;/p&gt;&#xA;" OwnerUserId="11594" LastEditorUserId="9493" LastEditDate="2018-05-09T15:32:04.907" LastActivityDate="2018-05-09T16:49:50.480" Title="Electrical Earth" Tags="&lt;antenna-theory&gt;&lt;grounding&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10252" PostTypeId="2" ParentId="10226" CreationDate="2018-05-09T08:13:44.510" Score="1" Body="&lt;p&gt;Pin 3 on the modular mic connector, which is AF OUT on some Icom models (e.g. the IC-706) is labeled as &quot;HM-207 detection, grounds when HM-207 is connected&quot; on the ID-5100. So it appears that the 5100 doesn't have audio out on the mic jack, and any Icom-supplied mic with a speaker in it is incompatible. Any third-party speaker mic for this radio (I don't know if such a thing exists) would have to have both the modular mic connector &lt;em&gt;and&lt;/em&gt; a 1/8&quot; audio plug for the speaker audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for feedback through the car speakers — do you have &quot;TX monitor&quot; set? If so, does turning it off improve things?&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2018-05-09T17:46:50.080" LastActivityDate="2018-05-09T17:46:50.080" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10255" PostTypeId="1" CreationDate="2018-05-09T16:20:24.123" Score="1" ViewCount="262" Body="&lt;p&gt;I'm currently working with a satellite that has AX.25 + Reed Solomon code (truncated RS(255,223)) in GNU Radio. Since there is no frame synchronization pattern, the 0x7e flags are used for frame delimiting followed by the bit de-stuffing. To make sure that the Reed-Solomon code is utilized properly, CRC is not used. So far the frames can be decoded perfectly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't performed BER tests (I will probably do this and compare results with any framing that doesn't do stuffing like CCSDS) on the implementation but I received a claim (and probably a right one) that the Reed-Solomon code can completely fail to properly correct errors in case there is error occurrence in stuffed bits. There were suggestions of putting provisions to detect any errors that may arise in bit stuffing before RS decoding. How would I accomplish this?&lt;/p&gt;&#xA;" OwnerUserId="6214" LastEditorUserId="1362" LastEditDate="2018-07-11T18:50:21.587" LastActivityDate="2018-07-11T18:50:21.587" Title="AX25 + Reed Solomon : Bit stuffing errors" Tags="&lt;gnuradio&gt;&lt;packet&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10256" PostTypeId="2" ParentId="10251" CreationDate="2018-05-09T16:36:53.467" Score="5" Body="&lt;p&gt;Congratulations on getting permission to install an antenna. There are many hams that rent that would love to be in your position.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Phil correctly asks, why do you need an earth connection? Here are some possible reasons to be thinking about earthing in your situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Common Mode Current&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An OCF antenna is an inherently imbalanced antenna. Such an antenna directly fed with coax will likely cause common mode current to flow on the shield of the coax. The effects from common mode current can include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;RF shocks or burns from the touching the transceiver, microphone, or power supply when transmitting&lt;/li&gt;&#xA;&lt;li&gt;Interference to nearby electronic devices such as headphones, speakers, stereos, smoke alarms, PCs, etc. when transmitting&lt;/li&gt;&#xA;&lt;li&gt;Problems bringing the SWR into specification&lt;/li&gt;&#xA;&lt;li&gt;Short adjustments to the length of coax cable or simply touching the coax cable causes changes in the SWR&lt;/li&gt;&#xA;&lt;li&gt;Interference from local electronics devices such as TVs, PCs, routers, etc. getting into your receiver during receive&lt;/li&gt;&#xA;&lt;li&gt;The antenna pattern does not exhibit the expected behavior&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you experience any of these issues, you may be able to reduce the common mode current by installing a high quality, 1:1, &lt;em&gt;current&lt;/em&gt; balun at the feedpoint of the antenna. There is virtually no downside to such a balun so it is often recommended as a preventative measure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Make certain that the length of your coax cable is not an odd multiple of a quarter wavelength on any bands on which you wish to operate. Incorporate a +/- 5% safety margin in your length calculations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For severe cases, placing another 1:1 current balun on the coax just before it enters the shack may prove helpful. These are sometimes called &quot;isolation baluns&quot; or similar to indicate that both sets of connections are SO-239s to facilitate easy coaxial connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Lightning Protection&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lightning protection mechanisms and its associated earthing (grounding) system are often controlled by local code or regulations. In much of the USA, for example, the NEC specifies minimum lightning protection requirements. Many hams will install a static discharge unit on the coaxial cable which is bonded to a field of specially installed ground rods. These rods must then be properly bonded to the facility's electrical safety ground system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the very high di/dt characteristics of lightning, an effective protection system utilizes very short, low resistance, low inductance connections in order to shunt as much current as possible to the ground field in order to mitigate potentially large voltage spikes. All internal shack equipment should be connected to the common lightning ground connection through an equipotential connection point. A shack located on a fourth floor makes all of this a very difficult task. In such situations, you must often make due with the best that you can. If you can run a large gauge ground wire down to a ground rod below your window, this might suffice for your lightning ground connection. Connecting to the safety ground of the apartment wiring is a last resort and will probably be minimally beneficial. But do consult your local codes and regulations to make certain you are in compliance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you simply cannot install an effective lightning protection system, then try to leave your antenna disconnected from the station when not in use and when lightning is in the vicinity. Ideally the entire coax should be moved outside of the building when not in use so as to keep any lightning or static discharge current as far away as possible from the shack equipment, occupants, and furnishings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Safety Ground&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mains circuits in most modern buildings include a safety ground as part of the wiring and this is brought out as a ground or earth pin on the respective outlets. The purpose of this ground is to provide a safe return of AC current in the event of a wiring failure elsewhere in the system or in the connected device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a ham radio perspective, most modern equipment is powered by a 12 volt AC to DC power supply so the mains circuit and its safety ground terminates in one place within this supply. The need to further bond the chassis of all other low voltage equipment to the safety ground is largely a carryover from the days of tubed equipment and may not be warranted. If the equipment chassis are already connected to an equipotential ground point for lightning protection, then further connecting to the mains ground can introduce unintended ground loops. Some of the DC power supplies no longer connect the minus 12 volt pin to the chassis of the supply for this reason (if permitted by local regulations).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some local regulations may require specific inter-equipment safety ground wiring so always make sure to consult your local regulations or a knowledgeable electrician before finalizing your installation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Further Reading&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL recently published a new book that covers all aspects of station grounding: &lt;a href=&quot;https://www.arrl.org/shop/Grounding-and-Bonding-for-the-Radio-Amateur/&quot; rel=&quot;noreferrer&quot;&gt;Grounding and Bonding for the Radio Amateur&lt;/a&gt; by Ward Silver. The book does a nice job of summarizing best practices in all aspects of safety, lightning, and RF grounds.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-09T16:49:50.480" LastActivityDate="2018-05-09T16:49:50.480" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10258" PostTypeId="2" ParentId="1480" CreationDate="2018-05-10T17:32:32.727" Score="1" Body="&lt;p&gt;For testing a radio, a dummy load is the answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For an antenna, an antenna analyzer would probably be best, but let's say  you are trying to measure the SWR of your antenna by using a radio as the source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, listen first, then transmit, measure and identify. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are no designated (legally or by agreement) frequencies for testing.&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-05-10T17:32:32.727" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10259" PostTypeId="2" ParentId="10129" CreationDate="2018-05-10T18:40:57.350" Score="3" Body="&lt;p&gt;A lot of the USB programming cables are not supported by the new Windows drivers that are installed automatically -specifically those with the Prolific PL-2303 USB chip set. You 'can' sometimes use them by downloading and installing an older driver. Better to get a proper cable though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/CableGuide&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP Cable Guide&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11604" LastEditorUserId="9493" LastEditDate="2018-05-16T02:17:28.577" LastActivityDate="2018-05-16T02:17:28.577" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10260" PostTypeId="1" CreationDate="2018-05-10T19:31:50.200" Score="6" ViewCount="5223" Body="&lt;p&gt;When using Morse Code as an accessibility/disability communication or input method, are there any non-alphanumeric dot-dash sequences that are more common or more suitable for meta-commands, such as “speak the last string”, “send command string to wheelchair”, or just to enter carriage-returns or capitalize the next letter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There does already seem to be a common control or meta-command for backspace (6 or 8 dots?)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-06-14T22:24:21.987" Title="Morse Code meta-command sequences?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10263" PostTypeId="1" AcceptedAnswerId="10264" CreationDate="2018-05-11T12:29:55.683" Score="4" ViewCount="457" Body="&lt;p&gt;I paste below a superhetorodyne based Software Defined Radio Architecture for an Rx channel below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Sfnmq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Sfnmq.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Suppose the IF signal has a max frequency of 50 MHz and 50 MHz IF BW. In that case, is it possible to just use an ADC of only 50 MSps for sampling process? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to Nyquist, an ADC should sample at 2X the max frequency of IF. But here, the DDC produces 2× samples once the IQ conversion is completed. So I feel like it fulfills Nyquist criteria before sending IQ samples to the PC/DSP. &#xA;I.e. After the IQ conversion, the number of samples produced is equal if an ADC of twice the speed were used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This concept is very clearly  proposed in this video (timed to the precise point)&#xA;&lt;a href=&quot;https://youtu.be/BK9QkHxeYQI?t=430&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://youtu.be/BK9QkHxeYQI?t=430&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see that this may not be a way of getting around Nyquist but can get away with purchasing a slower ADC by using this method for software defined radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also understand that this way of Super Heterodyne design of a Software Defined Radio hardware can be more difficult and expensive and perhaps also outdated and never used compared to Direct Sampling Method architecture. But I am merely interested in the technicality of this concept. &lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorUserId="4076" LastEditDate="2018-11-25T18:09:38.723" LastActivityDate="2018-11-25T18:09:38.723" Title="Sampling a 50 MHz Max Frequency 50 MHz BW Signal with a 50 MSps ADC" Tags="&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10264" PostTypeId="2" ParentId="10263" CreationDate="2018-05-11T17:57:42.950" Score="3" Body="&lt;p&gt;In the diagram above, the A/D converter must have a sample rate which is strictly more than twice the maximum frequency output by the RF tuner. So for a 50 MSPS A/D converter, that's a maximum analog frequency up to but not including 25 MHz. In practice it will be less, subject to the limitations of the antialiasing filter implementation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What follows is irrelevant. Once the signal has been converted to digital real signals the aliasing has already happened and nothing can undo that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the mixer was analog, it would then be possible to have two 50 MSPS A/D converters, one for the I channel and one for the Q channel. This would allow an analog input bandwidth of up to but not including 50 MHz, from -25 MHz to 25 MHz. This works because the quadrature shift was accomplished in the analog domain.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-05-11T17:57:42.950" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="10265" PostTypeId="2" ParentId="10263" CreationDate="2018-05-11T20:54:50.067" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;In that case, is it possible to just use an ADC of only 50MSPS for sampling process?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, for 50 MHz of bandwidth, you'll need 100 MS/s, if we're doing this in real-valued sampling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is (one of the, but the dominating) technical reason why for high-bandwidth applications, the superheterodyne receiver architecture like the one you show in your picture is not generally chosen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, many (not all) SDRs use &lt;em&gt;direct conversion&lt;/em&gt;, or &lt;em&gt;quadrature mixing&lt;/em&gt; to &lt;em&gt;complex baseband&lt;/em&gt;. Equivalent complex baseband is a topic covered in all digital communications textbooks, so I'm not going to elaborate on it much here, but it just shifts the signal instead of to an IF to baseband, i.e. so that it's around 0 Hz, but for that you require then mixing with one cosine and one sine, essentially, and after that, a dual-channel ADC. Advantage is now that it's sufficient to sample at 2× 50 MS/s instead of 1× 100 MS/s.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;But here, the DDC produces 2X samples once the IQ conversion is completed. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, not necessarily. You mix down to complex baseband, and on the way, you can decimate  by a factor of 2 without any loss in information.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-05-11T20:54:50.067" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="10266" PostTypeId="1" CreationDate="2018-05-11T21:01:16.933" Score="2" ViewCount="848" Body="&lt;p&gt;I have a Yaesu FTM-400XDR, but this applies equally to at least the FTM-100 series and probably other radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you program memory channels/frequencies, you can select one of three options:  Select, Skip and Off(blank).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Select is obvious - in memory scan mode, the radio scans these program settings and ignores all others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Skip vs. Off/Blank is eluding me however.  What is the functional difference between them?  Is there some mode in the radio where they act differently?&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-05-11T21:01:16.933" Title="Yaesu memory programming - skip vs. select vs. off/blank? FTM-100/400 series" Tags="&lt;yaesu&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10267" PostTypeId="2" ParentId="10266" CreationDate="2018-05-11T21:01:16.933" Score="3" Body="&lt;p&gt;It seems on at least the FTM-400 series, there is a use for this.  You can set the scan mode to &quot;all mem&quot; or &quot;select mem&quot;:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;in &quot;all mem&quot; mode, the radio will scan all of the programmed channels, &lt;em&gt;unless&lt;/em&gt; they are set to &quot;skip&quot;.  In other words, this gets &quot;select&quot; channels plus &quot;off/blank&quot; channels.&lt;/li&gt;&#xA;&lt;li&gt;in &quot;select mem&quot; mode, which seems to be the default, the radio will only scan &quot;select&quot; channels.  All others are skipped.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So in practice, this gives you three sets of programs:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&quot;Select&quot; will always be scanned, in either mode; these are frequencies you always want to scan&lt;/li&gt;&#xA;&lt;li&gt;&quot;Off/Blank&quot; will only be scanned in &quot;all mem&quot; mode; these are frequencies you sometimes want to scan, but sometimes don't&lt;/li&gt;&#xA;&lt;li&gt;&quot;Skip&quot; will never be scanned; these are frequencies you never want to scan.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I just figured this out today and thought I'd share, in case it benefits others.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-05-11T21:01:16.933" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10268" PostTypeId="1" AcceptedAnswerId="10269" CreationDate="2018-05-11T22:12:33.240" Score="0" ViewCount="100" Body="&lt;p&gt;I need some proof that the electric (E-field) and the magnetic component (H-field) of a lightning stroke both propagate at the speed of light, and that there is not a significant delay between them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please? :-)&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-05-12T14:47:51.737" Title="Does the E-field propagate faster that the H-field?" Tags="&lt;propagation&gt;&lt;theory&gt;&lt;lightning&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10269" PostTypeId="2" ParentId="10268" CreationDate="2018-05-11T23:35:29.407" Score="4" Body="&lt;p&gt;The E and H fields of all RF signals travel at exactly the same speed - the speed of light. The phase relationship between the two fields remains constant as they travel through various mediums.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lightning in itself is not an RF signal but it does emit RF (with E&amp;amp;H waves) as it propagates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[EDIT]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After reading some of the additional dialog provided by the OP in response to my answer, I believe the other party is talking about detecting the E field of a capacitor with the storm system being one &quot;plate&quot; and the earth forming the other &quot;plate&quot; of the capacitor. Note that this is quite different from the paired oscillating E and H fields of an RF signal propagating through space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inside of an ideal, charged capacitor there exists only an E field that is measured in Coulombs (shown as a unit of C). One proton has a charge of 1.6 x 10&lt;sup&gt;-19&lt;/sup&gt; C.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a capacitor where the diameter of the plates are substantially larger than the gap between the plates, there will exist an equal charge in the space between the plates. When this charge reaches 3x10&lt;sup&gt;6&lt;/sup&gt; N/C, the air inside the capacitor will break down and a spark (lightning in this case) is formed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it seems that the proposal is to measure the electric field of the capacitor formed by the storm system and the earth as a predictor of the potential of lightning. The referenced probe would form another plate in the capacitor - not to be confused with an antenna. This may work in principle although there will be a substantial difference in the E field as measured when between the plates (inside the storm system) and outside of the plates (near the edge of the storm). If prediction is not the goal, then edge detection of the collapsing E field, as a result of a dielectric breakdown of the air exhibited as lightning, may be a solution.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-12T14:47:51.737" LastActivityDate="2018-05-12T14:47:51.737" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="10270" PostTypeId="2" ParentId="526" CreationDate="2018-05-12T20:55:44.530" Score="2" Body="&lt;p&gt;You can turn a small dish antenna into a 2m, 1 1/4m, and 70cm antenna by cutting 3 slots into it. The dish really has room to cover all 3 bands with a coax attached in the appropriate locations for each band. This has nothing to do with the current feed horn. In fact you can cut a slot antenna into any piece of sheet metal that is large enough for your desired freq. FYI, a horizontal slot antenna has vertical polarization.&lt;/p&gt;&#xA;" OwnerUserId="11610" LastEditorUserId="9493" LastEditDate="2018-05-16T02:11:00.373" LastActivityDate="2018-05-16T02:11:00.373" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10271" PostTypeId="2" ParentId="6538" CreationDate="2018-05-13T11:54:22.050" Score="2" Body="&lt;p&gt;I was trying to research some info and I came across your thread.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My guess is they took the audio output from the 1520 kHz tuner and fed it in the input of a 450.040 MHz transmitter. That's why it can be heard in the UHF region. In this way, FM or AM or frequency doesn't matter, because its only an audio feed from an 1520 kHz tuner. You could have listen to a 1520 kHz tuner and a 450.040 MHz tuner at the same time. There should be a delay between the two tuners, I would guess.&lt;/p&gt;&#xA;" OwnerUserId="11617" LastEditorUserId="9493" LastEditDate="2018-05-16T02:15:43.500" LastActivityDate="2018-05-16T02:15:43.500" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10272" PostTypeId="1" AcceptedAnswerId="10274" CreationDate="2018-05-13T18:22:11.293" Score="5" ViewCount="1995" Body="&lt;p&gt;Why do most HTs have 2m and 70cm as the two bands? Is it just out of history or tradition, licensing restrictions, or is there something in the transceiver or antenna design that would make these the two obvious frequency bands of choice?&lt;/p&gt;&#xA;" OwnerUserId="11462" LastActivityDate="2018-05-16T17:42:08.943" Title="Why are 2m and 70cm the common frequencies on HTs?" Tags="&lt;ht&gt;&lt;2m-band&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10273" PostTypeId="2" ParentId="10272" CreationDate="2018-05-13T22:53:00.197" Score="4" Body="&lt;p&gt;History and tradition are good choices of words, yes. Historically, they have been the most popular bands for mobile work; the antennas are small enough for a vehicle and many repeaters have been constructed for that reason.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;6 meters used to be a  popular mobile band back in the 50s and 60s. (For that matter, so were 80 and even 160.) All those bands required a larger antenna, and back in those days many hams made their own. And since 2m and 440 were so popular, 220 never caught on except in some terrestrial and EME circles.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-05-13T22:53:00.197" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10274" PostTypeId="2" ParentId="10272" CreationDate="2018-05-14T01:10:47.887" Score="4" Body="&lt;p&gt;Worthy of mention is that 432MHz is a harmonic of 144MHz, meaning that the antenna can be much simpler; if it's (electrically) an odd number of half-waves on 2m, it's also an odd number of half-waves on 432MHz.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-05-14T01:10:47.887" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10275" PostTypeId="1" CreationDate="2018-05-14T07:17:15.410" Score="2" ViewCount="91" Body="&lt;p&gt;Sometimes on a net, net control acknowledges a check-in that I haven't heard. That is, I hear some check-ins but not others. Not poor signal, just silence. But net control hears it.&#xA;Why might that be?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Me: new ham, Yaesu HT]&lt;/p&gt;&#xA;" OwnerUserId="11145" LastActivityDate="2018-05-14T11:07:28.977" Title="why does net control hear a check-in which I do not hear?" Tags="&lt;uhf&gt;&lt;procedure&gt;&lt;audio&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10276" PostTypeId="1" AcceptedAnswerId="10281" CreationDate="2018-05-14T08:35:29.403" Score="4" ViewCount="177" Body="&lt;p&gt;A Digital Down Converter (DDC) is usually used to convert Real Digital Signals at a high frequency to baseband (centered around 0Hz). DDC does this so by producing negative and positive frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, &lt;strong&gt;at the same time&lt;/strong&gt;, perhaps using an approach as follows, is it possible to &lt;strong&gt;downconvert&lt;/strong&gt; a real digital signal present at the DDC as well as &lt;strong&gt;generate the corresponding I,Q&lt;/strong&gt; from it? How can we prove that it can be done? (mathematically or by other means)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LjD6C.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LjD6C.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorUserId="1694" LastEditDate="2018-05-14T09:06:16.010" LastActivityDate="2018-05-14T19:58:58.437" Title="Can a Digital Down Converter, at the same time, generate I,Q streams &amp; Downconvert?" Tags="&lt;software-defined-radio&gt;&lt;direct-conversion&gt;&lt;superheterodyne&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10277" PostTypeId="2" ParentId="10275" CreationDate="2018-05-14T11:07:28.977" Score="2" Body="&lt;p&gt;Congratulations on your new license! Since you referenced an HT, it would seem you are talking about VHF or UHF nets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF and UHF signals are generally line of sight communications. If your antenna is too low, a signal can be blocked by buildings, hills, etc. If the net control station (NCS) has better elevation or antenna height, the NCS will be able to hear more stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another possibilty relates to gain/sensitivity. If the NCS has a higher gain antenna system or a more sensitive receiver, the NCS will be able to receive weaker signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you are using your flexible rubber antenna on your HT and the NCS is using a collinear antenna on a 50 foot tower, the NCS will generally hear more stations than you can. Work to improve the height and gain of your antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of few other less likely possibilities are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Your squelch is set too high. Try opening the squelch to see if you can hear some of the stations that the NCS can hear.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you are using a repeater, make sure you have the correct transmit CTCSS tone programmed and don't initially use a receive tone.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If on a repeater, make sure you are not operating upside down (transmit and receive frequencies transposed).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-05-14T11:07:28.977" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10278" PostTypeId="2" ParentId="10272" CreationDate="2018-05-14T14:54:49.820" Score="1" Body="&lt;p&gt;One reason 1.25m / 220MHz is not too popular is that not many other countries than the US have allocations in it, just like we (the US) do not have the 4m band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other reasons including what was previously said, could be size/practicality of antennas and useful RF distance. 6m has better propagation and bigger antennas, 23cm smaller antenna/more manageable but quite a bit line of sight propagation. Everything is a trade off in RF. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Virtually any HF antenna on a mobile is a compromised antenna by using coils to make it electrically longer than it physically is, which reduces its effectiveness, but there are those that do it because they can.&lt;/p&gt;&#xA;" OwnerUserId="9083" LastEditorUserId="9673" LastEditDate="2018-05-16T17:42:08.943" LastActivityDate="2018-05-16T17:42:08.943" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10280" PostTypeId="2" ParentId="10211" CreationDate="2018-05-14T16:30:25.420" Score="1" Body="&lt;p&gt;Get yourself an extension cable for the earphone output of the receiving Baofeng and remote it into another location in your house. Put it about 30 to 40 feet away. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That should provide enough isolation to avoid desense. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not then place a 10 to 20 dB pad between the receiving units antenna and the radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If push comes to shove order a 25' long RG-316 cable off e-bay and insert it between the pad attached to the radio and the whip antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The combo of distance and added attenuation should knock down the local signal strength enough so as not to overload the 2nd Baofeng's input.&lt;/p&gt;&#xA;" OwnerUserId="11627" LastEditorUserId="8832" LastEditDate="2018-05-15T08:35:59.453" LastActivityDate="2018-05-15T08:35:59.453" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10281" PostTypeId="2" ParentId="10276" CreationDate="2018-05-14T17:36:12.183" Score="4" Body="&lt;p&gt;One way to convert a real-valued signal into a complex-valued one is to set the complex part to zero. This has the effect of &quot;mirroring&quot; the spectrum: all the negative frequencies are the mirror of the positive frequencies. This can be seen by the Fourier transform property for any real $f(x)$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \hat f(-\omega) = \overline{ \hat f(\omega) } \tag 1 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here the overline indicates the complex conjugate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A DDC is usually implemented by multiplying the input by a complex sinusoid to shift the desired signal to 0 Hz, which works due to this Fourier transform pair:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ f(x)e^{iax} = \hat f(\omega - a) \tag 2 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After shifting the desired signal to 0 Hz, a filter removes out-of-channel interference. Since the negative frequencies that appeared as a consequence of setting the complex part of the real input to zero are removed by a filter, a DDC implemented in this way need not do anything in particular to generate the complex-valued output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The alternative is for the DDC to operate entirely with real numbers. So rather than calculating $f(x)e^{iax}$ as in equation 2, it calculates $f(x) \cos(ax)$. As with a simple analog mixer the result is output frequencies at the sum and difference frequencies of the input and the LO. One of these image frequencies must then be removed by filtering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maintaining precise and stable phase and amplitude relationships between the real and imaginary parts in an analog circuit is difficult. However in digital implementation this is a non-issue, so it's common to see digital processing done almost entirely in the complex domain. As such, in some sense it's &lt;em&gt;more&lt;/em&gt; work to implement a DDC which does not output complex samples.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-05-14T17:36:12.183" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10282" PostTypeId="1" AcceptedAnswerId="10289" CreationDate="2018-05-14T17:56:22.393" Score="4" ViewCount="46" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aPf2f.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aPf2f.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;Referring to the above picture, can an antenna array mounted on Node A direct beams towards Node B and Node E, &lt;strong&gt;without&lt;/strong&gt; the need for an antenna rotator (or manually orienting the antenna array towards the respective nodes)? In other words, can the antenna array orient its beam along the vertical direction (along the line joining Node B and Node E)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The motive for this question is related to the upcoming IEEE 802.11ad standard. By operating at 60 GHz, users communicate with one another through directional beams pointing at each other. Without the use of mechanical rotators for the antennas, how could these users possibly orient their beams in a changing/moving environment?&lt;/p&gt;&#xA;" OwnerUserId="4639" LastEditorUserId="4639" LastEditDate="2018-05-14T18:04:42.950" LastActivityDate="2018-05-14T21:59:18.723" Title="Vertically orienting beams with antenna arrays" Tags="&lt;phased-array&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10283" PostTypeId="1" CreationDate="2018-05-14T18:08:19.373" Score="4" ViewCount="376" Body="&lt;p&gt;I have a decent-sized but not huge yard (roughly 50x100' / 15x30m) and I'd like to get on the 160-metre band.  It's hard enough to get out on this band so I'm looking to do something reasonably efficient.  Bonus if it can do well on 80m too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realize there will be some subjectivity to the results but I'd like some suggestions as to what the practical alternatives might be.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Right now I'm thinking some sort of a vertical antenna ought to do fine (adequately long radials will be a problem though), and we have an easement behind our yard where I could run a Beverage-like wire antenna quite a long distance, along the fences.  I'd have to be discreet about it but none of the fences open to the easement (it's like an alley but grassy and not used), so it might be an option if it will help me on receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I on the right track?  A simple 160m dipole would be perfect but there simply isn't space.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2020-06-10T05:49:39.937" Title="Antenna suggestions for 160m band in smallish yard?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;vertical-antenna&gt;&lt;160m-band&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10284" PostTypeId="5" CreationDate="2018-05-14T18:10:48.607" Score="0" Body="&lt;p&gt;Use this tag anytime your question relates to the 160m band:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;receivers&lt;/li&gt;&#xA;&lt;li&gt;transmitters/transceivers&lt;/li&gt;&#xA;&lt;li&gt;amplifiers&lt;/li&gt;&#xA;&lt;li&gt;antennas&lt;/li&gt;&#xA;&lt;li&gt;operation (e.g. noise considerations, privileges)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9844" LastEditorUserId="9844" LastEditDate="2018-05-14T20:47:30.170" LastActivityDate="2018-05-14T20:47:30.170" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10285" PostTypeId="4" CreationDate="2018-05-14T18:10:48.607" Score="0" Body="Questions about antennas, other equipment, and operating practices specific to the 160-metre/meter band." OwnerUserId="9844" LastEditorUserId="76" LastEditDate="2018-05-14T20:48:17.737" LastActivityDate="2018-05-14T20:48:17.737" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10286" PostTypeId="2" ParentId="7211" CreationDate="2018-05-14T18:19:40.617" Score="1" Body="&lt;p&gt;I think it's going to be difficult to find experimentally-verified values because the experiments haven't been conducted.  (Maybe you want to volunteer :).)  There is also a lot of subjectivity here because the accuracy required is going to vary greatly by application and situation, and the amount of APRS traffic in an area is going to dictate how frequently a station can send telemetry without causing congestion on the APRS frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where I live (southern Saskatchewan, Canada) there are quite few APRS users and only a couple of digipeaters and iGates covering a very large area of land.  I have the luxury of being able to send quite a lot of packets without causing flooding.  On the other hand, next week I'll be in the Dallas-Fort Worth area and I imagine such frequency of transmission won't be as welcome there because of such a large number of people in such a small area, and presumably, a commensurate number of APRS transmissions plus better infrastructure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The beaconing on my Yaesu FT-400XDR allows me to configure telemetry transmission by direction change, speed and time.  The slower you're going, the fewer packets you need to send.  The more often you're changing course, the more often you need to send.  At a point, even if you're motionless, you want to send another packet to confirm that you are still in the same location.  But what is the exact delay you should use?  It's so hard to be concrete because it depends on the purpose.  In my case, I send out the packets because I experiment with APRS, I want hams at home to be able to see where I am and I want the opportunity to chat with other hams while driving.  Packets sent every five minutes are probably adequate most of the time for what I'm doing.  As you point out on your question, though, people on foot doing emergency communications might need to send out packets quite often.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, too - the more packets you send, the more of a hit you'll provide to the APRS transmitter's battery, if its portable.  So that's yet another consideration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So - in summary - I don't think anyone can give a blanket recommendation, just some general things to think about, and then some local experimentation is going to be required.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-05-14T18:19:40.617" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10287" PostTypeId="2" ParentId="10276" CreationDate="2018-05-14T19:58:58.437" Score="1" Body="&lt;p&gt;Before any decimation, a signal needs to be sufficiently bandpass or lowpass filtered such that any image frequency spectrum, that could alias with the desired spectrum after decimation, is first removed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So with a narrow enough band-pass filter inserted ahead in the signal path, a sub-sampling decimator-complex-downconverter could be done in one step.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, a narrow enough band-pass filter likely is far more costly/difficult to implement than a low-pass filter and decimator placed after the quadrature down-converter.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-05-14T19:58:58.437" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10288" PostTypeId="2" ParentId="10283" CreationDate="2018-05-14T21:39:43.557" Score="5" Body="&lt;p&gt;Almost any 160 meter antenna is a compromise. With limited space or budget, the compromise tends to be larger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At first glance, a dipole that is shortened by loading coils might appear quite attractive. With well designed coils, the efficiency of a shortened dipole can be relatively good and the gain can be within a few dB of a full length dipole. But unless the dipole can be hung very high (&gt; 40 meters and optimally 80 meters), the directivity of the antenna will be largely vertical making it more effective for local communications (NVIS).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Vertical antennas facilitate longer paths but they require a good ground system in order to improve their efficiency, especially with a shortened vertical element (&amp;lt; 40 meters). Many hams have success with an inverted L arrangement. A starting length of 40 meters of wire is common with as much vertical as possible and the balance of the wire running horizontally from the top of the vertical piece. This horizontal component is viewed as a capacitance hat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounds like your situation will not allow elevated ground plane wires. As a result, run as many wires in all directions for as long as you possibly can and keep them very near the surface. Consider leaving them on the lawn secured with lawn staples so they sink into the thatch. The highest current in the ground wires will be near the vertical so more wires are generally better up to perhaps 60 or so wires depending upon your ground conditions. More wires has no downside other than additional cost and effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to minimize losses in the feedline, use a remote tuner at the base of the antenna. You may need to supplement the tuner with a large conductor base loading coil. Unless you are running high power, you can then run RG8X back to your shack with virtually no feedline losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ability of the antenna to work on other bands will depend upon your final chosen geometry. You can model multiband performance with a NEC based program.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="8717" LastEditDate="2018-05-15T18:30:45.980" LastActivityDate="2018-05-15T18:30:45.980" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10289" PostTypeId="2" ParentId="10282" CreationDate="2018-05-14T21:59:18.723" Score="2" Body="&lt;p&gt;A practical approach for steerable patterns at these frequecies is to use electronically steerable arrays. These can take on various forms but a simple example consists of 2 or 4 vertical elements that are phased to steer the major lobe in the desired direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, a dish or high gain yagi on 60 GHz has a very small footprint. This could be placed inside a radome and turned with a simple servo motor arrangement. Since the entire antenna is protected from the elements, no special considerations for a motor enclosure is warranted.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-05-14T21:59:18.723" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10290" PostTypeId="2" ParentId="10283" CreationDate="2018-05-15T13:58:04.140" Score="0" Body="&lt;p&gt;I've read about DDRR antennas as well.  Here's an article about a 40m version: &lt;a href=&quot;http://www.w1npp.org/events/2010/2010-F~1/ANTENNAS/LIMITED/711202~1.PDF&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w1npp.org/events/2010/2010-F~1/ANTENNAS/LIMITED/711202~1.PDF&lt;/a&gt; A quick Google search will likely return a 160m version or one that can be easily scaled.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, I remain skeptical and have never built one, and my Elmer called them his &quot;mole suppressors.&quot;  YMMV.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-05-15T13:58:04.140" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10291" PostTypeId="2" ParentId="1124" CreationDate="2018-05-15T23:15:38.130" Score="3" Body="&lt;p&gt;The traditional noise blanker that Phil, W8II describes is useless when there are strong signals within the passband of the blanker. Strong in relation to the interference pulses that is. Blanking the strong signals causes keying clicks that become stronger than the original interference...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two traditional ways, reduce the blanker bandwidth to place strong signals outside the blanker path or increase the bandwidth (very much.) At 100 times larger bandwidth the pulses contain 100 times more energy and are also 100 times shorter (if you are lucky) If the wider bandwidth does not give many more strong signals the 100 times larger bandwidth is a 40 dB advantage. In the seventies I was using a blanker on 144 MHz with a 5 MHz bandwidth with excellent results in Stockholm where many strong stations were present on the band: &lt;a href=&quot;http://www.sm5bsz.com/blanker.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sm5bsz.com/blanker.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was made aware of selective blankers a couple of years later: &lt;a href=&quot;https://ieeexplore.ieee.org/document/1447305&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ieeexplore.ieee.org/document/1447305&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My attempts to attenuate strong signals by use of NMR failed, but with the Pentium MMX enough CPU power had become available to do selective limiting in software. &lt;a href=&quot;http://www.sm5bsz.com/pcdsp/sellim.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sm5bsz.com/pcdsp/sellim.htm&lt;/a&gt; (this is part of a description of my first SDR in a PC: &lt;a href=&quot;http://www.sm5bsz.com/pcdsp/pcdroot.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sm5bsz.com/pcdsp/pcdroot.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Today anyone can use Linrad which has a feature to route strong signals outside the blanker. Here is a demo: &lt;a href=&quot;https://www.youtube.com/watch?v=qMd5y036HtA&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=qMd5y036HtA&lt;/a&gt; &#xA;&lt;a href=&quot;http://www.sm5bsz.com/linuxdsp/blanker/leon2001/leon2001.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sm5bsz.com/linuxdsp/blanker/leon2001/leon2001.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Operating the blankers in Linrad is non-trivial, but it can be very rewarding. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Perseus v5 has a &quot;vectorial blanker&quot; which sometimes can be very useful. I do not know how it works but you can see some of it here: &lt;a href=&quot;https://www.youtube.com/watch?v=sA36EzcS684&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=sA36EzcS684&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-05-15T23:15:38.130" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10293" PostTypeId="1" AcceptedAnswerId="10296" CreationDate="2018-05-16T21:30:46.350" Score="6" ViewCount="4190" Body="&lt;p&gt;Power supplies for ham radio equipment (and other equipment of course) seem to come in two flavours:  switching and linear.  The switching gear tends to be cheaper and smaller as well as more efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding is that switching supplies are more prone to creating RFI, but otherwise there is not much functional difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is that the gist of it, or is there more?  From the user's perspective, what is the advantage of one versus the other?&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2019-12-25T21:04:02.283" Title="Practical differences between switching and linear power supplies?" Tags="&lt;dc-power&gt;&lt;power-supply&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10294" PostTypeId="1" CreationDate="2018-05-16T21:36:57.413" Score="2" ViewCount="512" Body="&lt;p&gt;I've learned online some very thin information about how many hams will use 100 Hz CTCSS tones on their APRS transceivers to be able to make voice contacts with hams who are also using APRS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been experimenting with APRS for the past couple of years and have upgraded my car rig to a dual bander that supports APRS on one of the VFOs and it's been a great travel companion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We're about to engage in a long highway trip (3,000 km) and I'd like to know more.  How does this work?  I've already configured my APRS this way and the local iGate/digipeater is still digipeating my packets fine and relaying them to the Internet.  I assume the remaining stations I hear on the speaker are ones also using tone?  Presumably they are able and willing to make voice contact?  What's the proper operating procedure to do this?&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-05-17T14:11:16.493" Title="APRS - using 100 Hz CTCSS for voice contacts" Tags="&lt;aprs&gt;&lt;2m-band&gt;&lt;simplex&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10295" PostTypeId="2" ParentId="10293" CreationDate="2018-05-16T22:07:17.277" Score="3" Body="&lt;p&gt;You've pretty much hit the nail on it's proverbial head:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both are power supply &lt;em&gt;architectures&lt;/em&gt;, and as such generally fulfill the role of providing a constant-as-necessary voltage source (or current source, for some applications, but we're most likely talking about voltage sources).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, you can imagine a linear power supply simply as a self-adjusting resistor. It adjusts its resistance exactly as much as to drop enough voltage so that the voltage between its output terminal and its ground terminal is constant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, that means that $V_{drop}\cdot I_{output} = P_{wasted}$, i.e. all that voltage drop is waste heat. You hence simply can't do that for overly large voltage drops or overly large currents, because &lt;em&gt;things get hot&lt;/em&gt;. Things getting hot means you need beefier voltage regulator ICs and larger heat sinks. That's expensive. For large voltage drops, and security critical things, you simply can't do that, because no (affordable) semiconductors exist that support both the power and sufficient isolation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, a switch-mode power supply works by having an &lt;em&gt;energy storage&lt;/em&gt; from which it takes small portions of energy. In a typical topology, this means that you have your input voltage over a coil, which of course starts to build up a magnetic field. Then, you switch the in- or the output off and on again, to bring the voltage across that coil onto your target output voltage. The energy taken by the output in shape of current is taken from the coil's magnetic field, so that the amount of switching on and off needs to accomodate the target voltage and the amount of current drawn, and the fact that a higher input voltage can &quot;recharge&quot; the coil faster.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a bit of cleverness, you can, that way, even step up voltage! Something that's impossible to do with linear power supplies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look at the power wasted, there theoretically is zero: energy is just being converted from input electrical current to magnetic field and back to output current at a different voltage, and all these processes are theoretically lossless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, you of course get the resistances in your coil's wires and the losses in the coil's core as well as resistances in the switch (typically, a transistor), so things are maybe 80% to 98% efficient – but that's way, way more efficient then let's say converting 1A of current from 12 V to 5V: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a linear supply $I_{out}=I_{in}$ (plus losses), so $P_{in}=V_{in}\cdot I_{in}=V_{in}\cdot I_{out} = V_{in}\frac{P_{out}}{V_{out}}=\frac{V_{in}}{V_{out}}P_{out}$, with a switch mode supply $P_{out}=P_{in}$, only! Which means that the linear supply scheme uses $\frac{12}5=2.4$ times as much power!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding noise:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, switching necessarily means that you switch a current on and off, and you'll see that on the output side of your coil, as &lt;em&gt;ripple&lt;/em&gt;. Typically, a smoothing capacitor takes the job of reducing that ripple to a degree sufficient for the electronics supplied to work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, reducing doesn't mean getting totally rid of, and you'll need to design a smoothing stage that fits your need: if your need is just driving a microwave oven's clock display, ripple-rich (hence, noisy) output voltage doesn't matter to  you at all. If you're trying to pick up some weak transmission on a frequency close to the frequency your switch mode supply works at (or one of its harmonics), you'll have a harder time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In professional lab and SDR equipment, which still often is cost-, size- and power-restricted, you'll often actually find a cascade of power supplies; for example:&lt;br&gt;&#xA;A set of switchers to step down the 6 to 9 V (which usually comes from a switch-mode &quot;wall wart&quot;, converting grid to something safe for humans to touch) input to 5 V, 3.3 V and 1.8 V; the last voltage to be converted to 1.2 V through a low-drop linear supply for the high-speed digital logic and memories, 3.3 V for direct usage by the digital interface ICs, which don't care about noise nor very exact voltage overly much, and 5V to be regulated with another set of linear supplies for all the analog signal chain, with plenty of RC low pass filters in between the switching power supply, the linear regulator, and if small and constant current draw allows, between linear regulator and the device (amplifier, mixer, adjustable attenuators, microwave switches...).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-05-16T22:07:17.277" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10296" PostTypeId="2" ParentId="10293" CreationDate="2018-05-16T22:20:32.510" Score="6" Body="&lt;p&gt;The only reason &lt;em&gt;to&lt;/em&gt; use a linear power supply is to reduce electrical noise (or if as an exercise in electronics you want to build your own power supply without using integrated circuits, or if you need your equipment to double as doorstops).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also quite possible that if you do want to reduce noise, you will be better served by adding filters to, or upgrading, other power supplies in your house than by choosing a linear supply for your transceiver. (For example, my apartment's HF noise level went from useless to tolerable by winding the DC cables for my internet equipment (cable modem and WiFi AP) several turns around ferrite cores. The noise from the Alinco switching supply I run my transceivers from is unnoticeable compared to everything else.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Details on some of the factors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Noise.&lt;/strong&gt; A switching power supply inherently generates high-frequency signals as it, well, switches. The frequency and power of the noise that is seen at DC output — or the air — depends on the design of the supply. Many cheap switching power supplies as seen in consumer electronics will radiate significant noise compared to one recommended for amateur radio use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Naively looking at the typical noise frequencies (in the kHz) suggests that this noise may be a problem for HF operation but not typically for VHF, and this is &lt;em&gt;generally&lt;/em&gt; true, but remember to consider any intermediate frequencies used by your gear, and also the possibility of interference with AF signals (such as your microphone).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Efficiency.&lt;/strong&gt; A linear power supply inherently wastes some energy — it takes the (usually) AC line voltage, reduces it to an unregulated lower voltage (still higher than the desired output) with a transformer, rectifies it, then regulates it precisely using a &lt;strong&gt;linear regulator&lt;/strong&gt;. A linear regulator is effectively a variable resistor in series with the output that “drops” the excess voltage — generating heat. Therefore, linear supplies generate lots of heat and require large heat sinks. Switching supplies still generate heat since they are not made of nonexistent ideal components, but much less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your “ham shack” is not air-conditioned, you will directly appreciate the efficiency of a switching power supply.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A switching power supply can operate at a much larger range of input voltages. This doesn't mean just not having to pick 110V/220V; it also means that it can compensate for significantly lowered input voltage by drawing more current from the input, whereas a linear power supply will stop regulating because the fixed transformer ratio produces too low a pre-regulation voltage. This is usually not that relevant.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Size and weight, obviously enough.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-05-16T22:41:45.680" LastActivityDate="2018-05-16T22:41:45.680" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10297" PostTypeId="1" CreationDate="2018-05-17T01:46:04.367" Score="2" ViewCount="198" Body="&lt;p&gt;Every time I check into a net, there is a short &quot;tune&quot; before the net to announce the net is starting on a repeater. Here is a recording:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://kd0whb.duckdns.org/id/preamble.m4a&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://kd0whb.duckdns.org/id/preamble.m4a&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After hearing the preamble, I just made an ID using the variation of tones and occasionally air it on my repeater locally. Are there any legal issues with the following ID? I don't know if it is considered &quot;music&quot; or not, it is just a short sequence of sine wave tones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://kd0whb.duckdns.org/id/musicid.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://kd0whb.duckdns.org/id/musicid.wav&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="8717" LastEditDate="2018-05-17T13:49:49.617" LastActivityDate="2018-05-17T19:43:59.263" Title="Legality of short &quot;jingles&quot;" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="5" ClosedDate="2018-06-28T14:48:38.280" ContentLicense="CC BY-SA 4.0" />
  <row Id="10298" PostTypeId="2" ParentId="10294" CreationDate="2018-05-17T03:55:55.607" Score="2" Body="&lt;p&gt;I think it depends a little on the particular radio in question. On my Yaesu FTM-400 I will receive any APRS beacon within range of my radio that transmits a 100 Hz tone (the digi won't forward the 100 Hz tone). However when another station has a 100 Hz tone set, I will get an audible beep when the beacon comes through announcing that the other station is transmitting with a 100 Hz tone. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe the general procedure is to call CQ on the APRS frequency, make contact with the other station, then to agree on another frequency and finally QSY to that frequency for the QSO. That way you only impact the APRS channel momentarily and then are off that frequency so as to not impact other stations.&lt;/p&gt;&#xA;" OwnerUserId="11640" LastEditorUserId="9493" LastEditDate="2018-05-17T14:11:16.493" LastActivityDate="2018-05-17T14:11:16.493" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10299" PostTypeId="2" ParentId="10297" CreationDate="2018-05-17T19:15:11.280" Score="2" Body="&lt;p&gt;Here are the two search occurrences of &quot;music&quot; from the FCC amateur rules from &lt;a href=&quot;http://www.arrl.org/part-97-text&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/part-97-text&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;§97.113   Prohibited transmissions.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(4) &lt;strong&gt;Music&lt;/strong&gt; using a phone emission except as specifically provided&#xA;  elsewhere in this section; &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(c) No station shall retransmit programs or signals emanating from any&#xA;  type of radio station other than an amateur station, except&#xA;  propagation and weather forecast information intended for use by the&#xA;  general public and originated from United States Government stations,&#xA;  and communications, &lt;strong&gt;including incidental music&lt;/strong&gt;, ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;[bold text mine]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is how &lt;a href=&quot;https://www.merriam-webster.com/dictionary/music&quot; rel=&quot;nofollow noreferrer&quot;&gt;Merriam-Webster defines music&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;a : the science or art of ordering tones or sounds in succession, in&#xA;  combination, and in temporal relationships to produce a composition&#xA;  having unity and continuity&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;b : vocal, instrumental, or mechanical&#xA;  sounds having rhythm, melody, or harmony ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I think those tones fit this definition, don't you?&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-05-17T19:43:59.263" LastActivityDate="2018-05-17T19:43:59.263" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="10300" PostTypeId="1" CreationDate="2018-05-17T19:17:39.883" Score="3" ViewCount="90" Body="&lt;p&gt;Not sure if this is the right place to ask, but I'm trying to build a system of multiple WiFi access points that are spread out across a store. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since every smartphone and WiFi enabled device regularly sends out a &quot;discovery&quot;-packet to check if hotspots are around, I'm trying to keep track of that and see where people go inside that store, to have statistics on how many people that look at the display window actually go inside and to the checkout and similar things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now my problem is that the WiFi signal of my access points goes way too far and every smartphone gets detected on all hotspots.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How would one go about shortening the distance of a WiFi signal?&lt;/p&gt;&#xA;" OwnerUserId="11642" LastEditorUserId="9493" LastEditDate="2018-05-17T22:13:10.647" LastActivityDate="2018-05-18T14:04:46.213" Title="Making WiFi access point range shorter on purpose" Tags="&lt;antenna-construction&gt;&lt;wifi&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10301" PostTypeId="2" ParentId="10300" CreationDate="2018-05-17T22:30:15.420" Score="3" Body="&lt;p&gt;For a device to register with the access point, it must receive a transmit signal from the access point (AP). This largely consists of the AP transmitting its SSID so that it can be detected by the client device. If the client does not see the SSID, it often cannot detect the AP unless it is in active use by another client. The goal is therefore to effectively reduce the detectable range of the SSID.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One method of shortening the range is to reduce the transmit power of the AP. Many APs have a configuration menu setting that allows you to reduce the transmit power. You may wish to experiment with various settings to see what works for your situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option is to deliberately degrade the antenna performance by shortening it. This would largely be experimental and non-reversible but simply clipping the antenna shorter with a stout wire cutters will have this effect. If the AP has more than one antenna, they must all be clipped  or alternatively leave only one installed and clip that antenna. Continue to clip the antenna(s) shorter until the desired range is achieved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A third option is to use an attenuator. These devices reduce both the transmitted and received signal level. They are available in various levels of attenuation denoted by dB ratings - the large the number, the more the attenuation. Start with a 20 dB attenuator for each antenna and experiment from there. You will need to find an attenuator that fits the connectors of your AP antennas and the AP itself. Sometimes some connector adapters are required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A fourth option is to attempt to shape the pattern of the antenna. Consider putting the AP in a larger tin can (like a popcorn can) so that it's antennas is well contained in the depth of the can. This will largely restrict the effective range to an area that projects as a cone from the open end of the can.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that AP frequencies are in the microwave region and are very susceptible to bouncing off of objects to reach their destination. This may frustrate some of your efforts to reduce the range. You may need to combine some of the above options to reach your goal.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-05-17T22:30:15.420" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10302" PostTypeId="1" CreationDate="2018-05-17T23:47:26.020" Score="5" ViewCount="79" Body="&lt;p&gt;Why to some weak signal digital modes (jt9, jt65, etc.) require knowing a clock time?  Does knowing this clock time provide any gain in signal detection ability? (lower required S/N?)  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What clock synchronization accuracy to what master clock source is required?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-05-18T03:13:27.420" Title="Weak signal digital modes and clock synchronization" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;&lt;jt65&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10303" PostTypeId="2" ParentId="10302" CreationDate="2018-05-18T01:24:52.727" Score="3" Body="&lt;p&gt;Knowing when a signal is likely to be present helps the software to decode signals. If signals are of varying lengths, and sent at any time, then it's much harder to decode weak signals that may or not be present.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An analogy is the 'old' RS-232 serial data protocol, which could run in 'synchronous' (clocked) or 'asynchronous' modes: knowing from the clock signal when a byte is going to start and when it is going to finish, allows more data to be sent down the wire because you don't need to add 'start bits' and 'stop bits' to tell the listener when a byte starts and stops.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having everyone send their signal from hh:mm:00-hh:mm:47 means that the software KNOWS exactly when data will be present. And if it can't find any signals that start and end within that exact timeframe then it is certain that there is nothing decodable sent in that time slot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, by synchronising the times during which data can be sent, allows the software designers to make assumptions while decoding that VASTLY improve the throughput of data at extremely low signal levels.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-05-18T01:24:52.727" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10304" PostTypeId="2" ParentId="10302" CreationDate="2018-05-18T03:13:27.420" Score="1" Body="&lt;p&gt;According to the &lt;a href=&quot;http://physics.princeton.edu/pulsar/k1jt/wsjtx-doc/wsjtx-main-toc2.html#SYSREQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSJT system requirements&lt;/a&gt;, the time must be synchronized within ±1 second.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's generally the case that the more that is known about a signal, the easier it is to detect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of WSJT, the software records a 4 kHz or so wide swath, and then must find and decode all the signals in it. It must work this way because the nature of the transmission isn't really amenable to interactive tuning by a human operator like CW or SSB are. Furthermore, being able to simultaneously monitor dozens of transmissions and pick the most exciting is a big appeal of the mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;WSJT transmissions follow a limited format, and are of a fixed length. To successfully decode them requires identifying the start and the end of the message. The transmissions also occur somewhere within a range of possible frequencies within the receiver passband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the start time fixed, the search for signals involves only one dimension: frequency. If signals could start at any time there are now two dimensions, frequency &lt;em&gt;and time&lt;/em&gt;. The computational complexity is thus squared.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course the time isn't &lt;em&gt;exactly&lt;/em&gt; synchronized, so there's still a little time synchronization that needs to happen. However, knowing the start of the message within ±1 second is better than knowing nothing at all about the time.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-05-18T03:13:27.420" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10305" PostTypeId="1" AcceptedAnswerId="10319" CreationDate="2018-05-18T12:20:57.227" Score="4" ViewCount="1360" Body="&lt;p&gt;I would like to use a small trx first for listening CW on 7030 kHz and then for transmitting, locally, among friends. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My conditions are &quot;prohibitive&quot; as for antennas: a block of flats, 4th floor in 8 floor building. Among other blocks of flats. Administration will not allow antennas - i.e.I need to go 'clandestine' or operate from a bench in a park so as not to attract attention.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live in a capital city where there are plenty of CW addicts, I dream about being able to first listen to them on CW and then respond. No need to go DX; I would be happy to communicate locally. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was thinking of a random wire matched with a capacitor and a coil but I am not an engineer. What would you recommend? I need only to have it tuned around 7.030 Mhz qrp calling freq and fit my pocket for bench operation or in a window for swl.&lt;/p&gt;&#xA;" OwnerUserId="1303" LastEditorUserId="9493" LastEditDate="2018-05-19T21:52:37.703" LastActivityDate="2019-09-28T10:24:19.450" Title="Tune a very short 3-5m random wire for 40m (around 7.030 MHz) for listening or occasional QRP CW sending" Tags="&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;qrp&gt;" AnswerCount="6" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10306" PostTypeId="2" ParentId="10300" CreationDate="2018-05-18T14:04:46.213" Score="0" Body="&lt;p&gt;Shortening the range is a poor way of estimating distance. Different phones have different sensitivities on their WiFi radios so you won’t have a high degree of accuracy. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, you should measure the relative strength of the WiFi signals. There’s some code floating around that does this in reverse for blind people in shopping malls. You should also be able to do the same with your routers although you may need either custom firmware or APIs that expose the SSIDs that the routers see and their relative strength. &lt;/p&gt;&#xA;" OwnerUserId="11462" LastActivityDate="2018-05-18T14:04:46.213" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10307" PostTypeId="2" ParentId="10305" CreationDate="2018-05-18T15:18:36.507" Score="2" Body="&lt;p&gt;Clandestine can be very effective.  A thin wire hanging out of your window is hard to see, especially if you only have it outside while operating.  Commercially built tuners aren't expensive either.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option to consider is MCW (modulated CW) where you send the Morse tones over audio via VHF/UHF FM.  If you have enough CW fans there you may be able to get enough interest.  Or for that matter, VHF or UHF CW.  It's far less common, but not unheard of.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-05-18T15:18:36.507" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10308" PostTypeId="2" ParentId="10305" CreationDate="2018-05-18T16:06:23.010" Score="1" Body="&lt;p&gt;For listening, you can use any length of wire you like (longer than this will be better at that frequency, but even a short wire will pick up strong transmissions).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for transmitting, you would be far better off using a higher frequency, given your antenna limitations.  Depending on the range you require, the 10m or 6m band will work with most HF radios, and if you have a capable transmitter, line-of-sight CW on 2m or 70cm or even shorter bands might be worth considering, too.  You don't say what country you're in but this would all be dependent on having the appropriate license and the appropriate band being legal in your country for amateur radio.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-05-18T16:06:23.010" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10309" PostTypeId="1" CreationDate="2018-05-18T20:12:46.723" Score="3" ViewCount="559" Body="&lt;p&gt;I'd like to get started doing portable HF work and I'd like some information on antenna possibilities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My broad (and somewhat flexible) criteria are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;By &quot;portable&quot; I mean it can be carried in a modestly-sized vehicle such as a sedan/saloon and hauled on foot a reasonably short distance.  I don't intend to take the antenna to mountaintops (unless there's a road there :) ).&lt;/li&gt;&#xA;&lt;li&gt;Multiband is preferred, but I'm better off on a single band than on no bands.   Assume I have a tuner, although a portable antenna that can be made resonant on multiple bands would be a nice thing.&lt;/li&gt;&#xA;&lt;li&gt;I prefer something I can buy over something I can build partially because of my general building skill, and principally because of lacking time.  Recommend a type of antenna, rather than a specific commercial product.&lt;/li&gt;&#xA;&lt;li&gt;The antenna should be able to be set up by a solo operator.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm attracted to the &lt;a href=&quot;http://www.buddipole.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;Buddipole&lt;/a&gt; system for a few reasons, although I wonder sometimes if I might be better with a longer dipole and some means of putting the thing up.  The Buddipole seems usable just about anywhere, though, which is a huge plus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since specific product recommendations are off topic here, can you give me some guidance as to the types of antennas that might be suitable for this situation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to be able to use full barefoot power (i.e. 100 watts), and would work principally in SSB mode with occasional CW.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastEditorUserId="9844" LastEditDate="2018-05-19T01:38:07.950" LastActivityDate="2018-12-08T17:43:57.217" Title="How should I select an HF antenna for portable work?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;portable&gt;" AnswerCount="5" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10310" PostTypeId="1" CreationDate="2018-05-18T20:46:32.033" Score="6" ViewCount="618" Body="&lt;p&gt;Shows the word OFF on screen when PTT is pressed. In settings &quot;TX&quot; is set to on, what am I missing?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manual is no use due to poor translation and general incompleteness.&lt;/p&gt;&#xA;" OwnerUserId="11650" LastEditorUserId="15929" LastEditDate="2019-11-30T02:33:30.930" LastActivityDate="2019-11-30T02:33:30.930" Title="Alinco DJ-500T handheld radio will not transmit, why?" Tags="&lt;equipment-operation&gt;&lt;alinco&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10311" PostTypeId="2" ParentId="10309" CreationDate="2018-05-18T22:36:16.337" Score="0" Body="&lt;p&gt;There are a number of portable magnetic loop antennas available that fit your criteria.  Many are flexible enough to store in typical vehicles; the conductors are typically large diameter coaxial cable.  Most are designed to tune across a few adjacent bands.  They perform well at low height and are easy for one person to set up.  Disadvantages include narrow bandwidth and limited transmit power.&lt;/p&gt;&#xA;" OwnerUserId="11651" LastActivityDate="2018-05-18T22:36:16.337" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10312" PostTypeId="2" ParentId="10310" CreationDate="2018-05-18T22:59:38.643" Score="5" Body="&lt;p&gt;This indicates that you are attempting to transmit out of band. This is typically a symptom of having the wrong offset (+/-) programmed for that channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you visit &lt;a href=&quot;http://www.alinco.com/faq.html&quot; rel=&quot;noreferrer&quot;&gt;the Alinco FAQ page&lt;/a&gt; you will find this advice for similar models.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-19T00:24:23.367" LastActivityDate="2018-05-19T00:24:23.367" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10313" PostTypeId="1" CreationDate="2018-05-19T01:02:20.143" Score="5" ViewCount="906" Body="&lt;p&gt;While a normal voice channel is ~10kHz-15kHz in bandwidth, some digital modes can be significantly wider.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any legal restrictions on how much bandwidth I could use for amateur radio communications (e.g. video chat over ham radio)?&lt;/p&gt;&#xA;" OwnerUserId="11652" LastEditorUserId="11652" LastEditDate="2018-05-19T03:17:06.283" LastActivityDate="2018-05-21T15:43:41.157" Title="Is there a legal limit to the bandwidth of a signal used in the amateur bands?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;digital-modes&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10315" PostTypeId="2" ParentId="10313" CreationDate="2018-05-19T13:02:35.673" Score="7" Body="&lt;p&gt;Summary:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;In all cases, no more bandwidth than necessary. §97.307(a), (b)&lt;/li&gt;&#xA;&lt;li&gt;In data portions of LF, MF, and HF bands, 500 Hz. §97.3(c)(2)&lt;/li&gt;&#xA;&lt;li&gt;In the phone portions of LF, MF, and HF bands, no more than &amp;quot;the bandwidth of a communications quality phone emission of the same modulation type.&amp;quot; 4 kHz is a good number to put on it, being a typical limit of an SSB emission. §97.307(2)&lt;/li&gt;&#xA;&lt;li&gt;6 and 2 meters: 25 kHz. §97.307(5)&lt;/li&gt;&#xA;&lt;li&gt;1.25 m and 70 cm: 100 kHz. §97.307(13), (8)&lt;/li&gt;&#xA;&lt;li&gt;everything above 70 cm: no explicit limitation: follow &amp;quot;good amateur practice.&amp;quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;For reference, relevant sections of &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1307&quot; rel=&quot;noreferrer&quot;&gt;§97.307&lt;/a&gt; (emphasis added):&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(a) No amateur station transmission shall occupy &lt;strong&gt;more bandwidth than necessary&lt;/strong&gt; for the information rate and emission type being transmitted, &lt;strong&gt;in accordance with good amateur practice&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;p&gt;(b) Emissions resulting from modulation must be confined to the band or segment available to the control operator. Emissions outside the necessary bandwidth must not cause splatter or keyclick interference to operations on adjacent frequencies.&lt;/p&gt;&#xA;&lt;p&gt;[...]&lt;/p&gt;&#xA;&lt;p&gt;(f) The following standards and limitations apply to transmissions on the frequencies specified in §97.305(c) of this part.&lt;/p&gt;&#xA;&lt;p&gt;[...]&lt;/p&gt;&#xA;&lt;p&gt;(2) No non-phone emission shall exceed &lt;strong&gt;the bandwidth of a communications quality phone emission of the same modulation type.&lt;/strong&gt; The total bandwidth of an independent sideband emission (having B as the first symbol), or a multiplexed image and phone emission, shall not exceed that of a communications quality A3E emission.&lt;/p&gt;&#xA;&lt;p&gt;[...]&lt;/p&gt;&#xA;&lt;p&gt;(5) A RTTY, data or multiplexed emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must not exceed 19.6 kilobauds. A RTTY, data or multiplexed emission using an unspecified digital code under the limitations listed in §97.309(b) of this part also may be transmitted. &lt;strong&gt;The authorized bandwidth is 20 kHz.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;(6) A RTTY, data or multiplexed emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must not exceed 56 kilobauds. A RTTY, data or multiplexed emission using an unspecified digital code under the limitations listed in §97.309(b) of this part also may be transmitted. &lt;strong&gt;The authorized bandwidth is 100 kHz.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;[...]&lt;/p&gt;&#xA;&lt;p&gt;(13) A data emission using an unspecified digital code under the limitations listed in §97.309(b) also may be transmitted. &lt;strong&gt;The authorized bandwidth is 100 kHz.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The definition of &amp;quot;Data&amp;quot; in &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_13&quot; rel=&quot;noreferrer&quot;&gt;§97.3(c)&lt;/a&gt; includes a limitation on bandwidth:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(2) Data. Telemetry, telecommand and computer communications emissions having (i) designators with A, C, D, F, G, H, J or R as the first symbol, 1 as the second symbol, and D as the third symbol; (ii) emission J2D; and (iii) emissions A1C, F1C, F2C, J2C, and J3C having an occupied &lt;strong&gt;bandwidth of 500 Hz or less when transmitted on an amateur service frequency below 30 MHz&lt;/strong&gt;. Only a digital code of a type specifically authorized in this part may be transmitted.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-05-21T15:43:41.157" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10316" PostTypeId="1" AcceptedAnswerId="10317" CreationDate="2018-05-19T19:43:30.573" Score="2" ViewCount="163" Body="&lt;p&gt;While checking out the local hardware store wire section, I came across thermostat wire priced significantly lower than other types. I have been trying to determine the reason but details online are skimpy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to play with different HF style of antennas at low cost for some SOTA QRP and wondered if this might fit the bill without breaking the bank?&lt;/p&gt;&#xA;" OwnerUserId="11654" LastEditorUserId="9493" LastEditDate="2018-05-19T20:36:35.807" LastActivityDate="2018-05-20T21:21:20.297" Title="Thermostat wire for antennas?" Tags="&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10317" PostTypeId="2" ParentId="10316" CreationDate="2018-05-19T19:51:16.827" Score="1" Body="&lt;p&gt;Thermostat wire will be cheaper than the wire near it on home-improvement shelves because it is smaller — it does not carry high current or high voltage in the intended application, so it does not need to be thick or have strong insulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This, in itself, is fine for HF antennas — except in high-power applications, the current is not a problem, and the voltage is better addressed by distance than by insulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it is probably &lt;strong&gt;solid&lt;/strong&gt; wire. Solid wire is not a good choice for portable wire antennas because repeated bending will fatigue and break the copper. (It's okay to use solid wire for a self-supporting rigid antenna such as is found in VHF and higher frequencies, though copper is a bit soft for that application.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should look for &lt;em&gt;stranded&lt;/em&gt; wire for building antennas if you want them to last.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-05-20T21:21:20.297" LastActivityDate="2018-05-20T21:21:20.297" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10318" PostTypeId="2" ParentId="10316" CreationDate="2018-05-19T20:43:05.553" Score="2" Body="&lt;p&gt;I agree with @KevinReidAG6YO that it is generally better to use stranded wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But given the itinerant nature of a SOTA activation and the apparent low cost of the wire, I would say go ahead and use it! Try not to flex it in a tight bend too often or it will break. When you are done with an activation, roll it into a loop of six or so inches in diameter to minimize the work hardening of the wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When it does finally fatigue, simply pull out another length and start again.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-05-19T20:43:05.553" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10319" PostTypeId="2" ParentId="10305" CreationDate="2018-05-19T21:38:37.223" Score="1" Body="&lt;p&gt;Very short antennas have very close to the same directivity as a full size 1/2 wave antenna but their efficiency, and as a result gain, can suffer. The gain of an antenna is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Gain = Directivity * Efficiency \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The efficiency is the result of losses in the wire and, in your case, in the matching network that is needed to make the antenna work with your transmitter. So will you want to use the largest gauge wire possible for your situation and make very good solder joints at all connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using EZNEC, I modeled a 6 meter (2 pieces, 3 meters each) center fed dipole in a vertical orientation for this example. The bottom end of the antenna was 7 meters above ground. I did not adjust for building proximity. At 7.030 MHz, the antenna impedance will be 5.4 -j1826 ohms. As a shortened antenna, the 1826 ohms of capacitive reactance is not unexpected. The 5.4 ohms of resistance is low but a manageable number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A matching network such as this can be used to adjust to impedance to 50 ohms:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/kwwzf.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fkwwzf.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I designed this simple L matching network using &lt;a href=&quot;http://leleivre.com/rf_lcmatch.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://leleivre.com/rf_lcmatch.html&lt;/a&gt;. The transmitter side of the matching network is 50 ohms so a convenient length of RG8X coax could be connected to this point and run to the transmitter. The coil should be made of fairly large diameter wire or even 1/4 inch soft copper tubing from the hardware store. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the inductor shown, a construction example would be 0.25 inch soft tubing wound 10 inches in diameter, 7 inches long, and with 14 turns. The circuit can be adjusted by slightly expanding or compressing the coil. Keep in mind that this is a very big coil that must be placed at the center of dipole to optimize the efficiency but you may be able to cleverly use it to support the antenna. Many other coil geometries are possible. You can calculate alternate coil details using a site such as &lt;a href=&quot;http://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This may not be the exact antenna you envisioned but it gives you an idea how to go about designing a compromise antenna. At your building height, you should give thought to using a vertical or horizontal, shortened dipole antenna. It may serve you well if you pay attention to construction details that can affect efficiency and thus gain.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-19T22:09:16.723" LastActivityDate="2018-05-19T22:09:16.723" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10320" PostTypeId="2" ParentId="10305" CreationDate="2018-05-20T23:18:02.357" Score="1" Body="&lt;p&gt;One of my favorite things to do is QRP field operation with compromised antennas.  The easiest is just a piece of wire with one end thrown over a tree branch and a counterpoise wire laying on the ground.  I use a sling shot to launch 20 lb fishing line up and over a branch (up to about 15 to 20 feet high).  My antenna is a single wire about 40 to 65 feet long.  And, yes, an antenna tuner is required.  The antenna tuner built in to my Elecraft KX2 QRP rig handles just about any wires I have put up.  The counterpoise wire laying on the ground is absolutely required for good performance.  Adjusting its position on the ground relative to the wire on up in the air is helpful to getting a good match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My best performing antenna for field/portable work though is my Buddipole antenna.  Although I work primarily CW on 20 meters, I have had many contacts on 40 meters too.  Yes, you have to spend money but I consider that money well spent.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2018-05-20T23:18:02.357" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10321" PostTypeId="1" AcceptedAnswerId="10322" CreationDate="2018-05-21T01:59:16.730" Score="3" ViewCount="343" Body="&lt;p&gt;I have 3 Motorola CDM750s that I’m using to build a multi-purpose, portable, temporary repeater.  There are 1 VHF and 2 UHF radios.  I want to be able to use it as either an in-band UHF repeater or as a UHF/VHF cross-band repeater.  I have a duplexer tuned to the UHF frequencies I plan on using and a UHF/VHF diplexer for the cross-band configuration.  The antenna will be a Diamond X30A dual band base/repeater antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to make it fairly simple for someone to change the configuration.  I wonder if I could run the duplexer and diplexer in series so it would be unnecessary to reconfigure the antenna cabling.  Basically, the 2 UHF radios would go to the duplexer and then the antenna feed from that goes to the UHF side of the diplexer, where it combines with the VHF feed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realize I’ll have to use the same input frequency on both the in-band and cross-band repeaters, but that’s not a big deal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any reason why this wouldn’t work?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is a bad idea, I would appreciate alternate suggestions.&lt;/p&gt;&#xA;" OwnerUserId="4748" LastActivityDate="2018-05-21T11:09:30.663" Title="Using a Duplexer and Diplexer in Series" Tags="&lt;repeater&gt;&lt;crossband-repeat&gt;&lt;duplexer&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10322" PostTypeId="2" ParentId="10321" CreationDate="2018-05-21T11:09:30.663" Score="6" Body="&lt;p&gt;Yes, it will work with the proper attention to details. I have done the same in the past at two repeater sites to take advantage of the coverage of the dual band antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do take care as the third harmonic of two meter frequencies can come close to 70 cm frequencies. You will want to plan your frequencies to keep as much separation as possible. Making the 2 meter radio the receiver when cross banding largely avoids this issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Care should also be taken to use double or quad shielded coax with N connectors throughout and to carefully decouple all control lines and power cables between the radios. You may also need to incorporate additional shielding between the radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before building the repeater, it is a good idea to check the spectral purity of the transmitters with a spectrum analyzer. This can save hours of frustrating debug time later. When you have the SA setup, also check the UHF to VHF ports isolation of your diplexer. I found that performance to specs varies widely.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-05-21T11:09:30.663" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10323" PostTypeId="2" ParentId="10305" CreationDate="2018-05-21T13:16:53.800" Score="0" Body="&lt;p&gt;I am now thinking about g4fon magloop. &lt;a href=&quot;http://www.g4fon.net/MagLoopTwo.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.g4fon.net/MagLoopTwo.htm&lt;/a&gt; Contemplate using RG58 coax shield as radiator. 0.5mm dia.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Calculations &lt;a href=&quot;http://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Antenna efficiency: 30% (-5.3 dB below 100%)&#xA;Antenna bandwidth: 34.2 kHz&#xA;Tuning Capacitance: 126 pF&#xA;&#xA;Capacitor voltage: 333 volts RMS&#xA;Resonant circulating current: 1.85 A&#xA;Radiation resistance: 0.131 ohms&#xA;Loss Resistance: 0.308 ohms&#xA;Inductance: 4.08 microhenrys&#xA;Inductive Reactance: 180 ohms&#xA;Quality Factor (Q): 205&#xA;Distributed capacity: 19 pF&#xA;&#xA;Antenna &quot;circumference&quot;: 7 meters&#xA;Loop antenna    Side length: 0.875 meters&#xA;Antenna diameter: 2.1 meters&#xA;&#xA;Comments:&#xA;The specified conductor length of 7 meters is OK.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;To tune I would have to use a constant high voltage 100pF and a variable capacitor to fine tune it.  I will ask Ray Gof, g4fon, what his opinion is.&lt;/p&gt;&#xA;" OwnerUserId="1303" LastActivityDate="2018-05-21T13:16:53.800" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10324" PostTypeId="1" CreationDate="2018-05-21T21:20:33.490" Score="9" ViewCount="577" Body="&lt;p&gt;On 2018 July 1, the FCC's question pool for the Technician class license will be changing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone written up a summary of the updates or made a list of differences from the previous pool? What are the most significant changes I should be aware of when helping prospective hams study for the test?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found the new question pool at &lt;a href=&quot;http://www.ncvec.org/page.php?id=369&quot; rel=&quot;noreferrer&quot;&gt;http://www.ncvec.org/page.php?id=369&lt;/a&gt; and it includes some errata notes but as far as I can tell they are edits made from earlier drafts of the &lt;strong&gt;new&lt;/strong&gt; pool rather than differences from the old.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2019-04-07T04:25:41.320" Title="What changes are being made to the Technician question pool in 2018?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10325" PostTypeId="1" CreationDate="2018-05-21T22:36:40.957" Score="4" ViewCount="221" Body="&lt;p&gt;Is it normal for the antenna conector of the radio to have 18ohm resistence between the inner socket(signal) and the thread (ground)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I connect the antenna works fine if only the inner plug makes contact, if the outer metal part of the antenna touches the radio it stops receiving anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio is a Yaesu FT-747 and the antenna is a Sirtel Santiago 1200&lt;/p&gt;&#xA;" OwnerUserId="11665" LastEditorUserId="76" LastEditDate="2018-05-21T22:51:18.290" LastActivityDate="2018-05-28T10:13:45.030" Title="Radio stops receiving as soon as the antenna is threaded all the way" Tags="&lt;antenna-system&gt;&lt;connectors&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10326" PostTypeId="2" ParentId="10325" CreationDate="2018-05-21T22:59:57.430" Score="3" Body="&lt;p&gt;Very loosely speaking, you should expect the radio's antenna connector to measure 50 ohms. But that is only true if you are measuring it using an RF signal in the frequency band the radio is expecting, not using the DC output of an ohmmeter, so 18 ohms is entirely reasonable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact that making the shield connection causes you to stop receiving signals is a very good indication that &lt;strong&gt;either the antenna is defective or that it is completely unsuitable for the band you are trying to receive.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, you'd make exactly the same observations if you were to partially plug in a piece of coax with no antenna on the other end. This is because, without the shield connected, the coax might as well be a plain wire, and any old wire stuck in the antenna port will make a receiving antenna of some effectiveness.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-05-22T00:15:58.050" LastActivityDate="2018-05-22T00:15:58.050" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10327" PostTypeId="2" ParentId="10325" CreationDate="2018-05-22T12:17:23.767" Score="1" Body="&lt;p&gt;You may have a short in the connector on the coax such that when only the centre connector is attached the coax+antenna forms an antenna but when the shield is connected you just have a short across the antenna terminal.&lt;/p&gt;&#xA;" OwnerUserId="11431" LastActivityDate="2018-05-22T12:17:23.767" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10328" PostTypeId="2" ParentId="10309" CreationDate="2018-05-23T08:18:02.187" Score="3" Body="&lt;p&gt;I use telescopic fiberglass pole (10 to 12 meters is sufficient) and home made dipole antennas, single band and multiband (some trapped dipoles some linked dipoles). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It does the job pretty well and it can fit in my backpack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I mostly use &quot;hybrid&quot; multiband dipole which consists of 20/17 meter trapped dipole and optional attachments for 40 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;20/17 meter dipole can also be used as vertical dipole using the same fiberglass mast to get more DX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is all very easy to set up by single person. System is light enough to even do not need guying, just good fixation at the bottom of the mast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could try it. It is actually quite cheap solution and all pats are reusable for other projects if you end up not happy (which I doubt).&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2018-05-23T08:18:02.187" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10329" PostTypeId="1" CreationDate="2018-05-23T19:11:00.323" Score="6" ViewCount="16325" Body="&lt;p&gt;I have a Baofeng UV 9R Handheld that I just recently bought and received in the mail brand new, however as much as I like this handheld device I am maxed out with frustration as far as manual programming of this device is concerned. Does anyone have any answers to help guide me in manually programming my UV 9R?&lt;/p&gt;&#xA;" OwnerUserId="11672" LastEditorUserId="76" LastEditDate="2018-05-23T19:31:48.697" LastActivityDate="2018-12-31T14:29:29.787" Title="Baofeng UV 9R Handheld programming" Tags="&lt;baofeng&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10330" PostTypeId="1" CreationDate="2018-05-23T22:17:24.220" Score="2" ViewCount="32" Body="&lt;p&gt;The 'plating material' materials and constants of the &lt;a href=&quot;http://hamwaves.com/antennas/inductance.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Single-Layer Helical Round Wire Coil Inductor Calculator&lt;/a&gt; appear wired-in. &#xA;There appears no 'un-plated' option. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How to use this calculator to work with un-plated magnet wire? &lt;/p&gt;&#xA;" OwnerUserId="11673" LastEditorUserId="218" LastEditDate="2018-05-24T13:23:35.550" LastActivityDate="2018-05-24T13:23:35.550" Title="The 'plating material' materials and constants of the constants" Tags="&lt;impedance&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10331" PostTypeId="2" ParentId="10329" CreationDate="2018-05-23T22:20:15.817" Score="9" Body="&lt;p&gt;Almost nobody programs Baofeng and similar radios by hand: too difficult, as you discovered.  The thing to do is to get your hands on a programming cable and programming software.  If you go to a meeting of a ham radio club, there's a good chance that someone will have the cable and the software right there, and will be able to program your radio for you in five minutes.  If however you want to do it yourself, it's not too difficult.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inexpensive programming cables for sale abound on the internet, but there's a catch.  Most of the inexpensive cables contain a USB-to-serial chip that's a close copy of a chip made by Prolific, so much so that Windows identifies them as Prolific chips.  Windows Update will try to download the latest Prolific driver for the clone chips.  Unfortunately for unsuspecting owners, Prolific responded to the flood of cloned chips by changing their driver to only work with genuine Prolific chips, so if you have the latest driver, a programming cable based on a cloned chip won't work.  There is a work-around described &lt;a href=&quot;http://www.miklor.com/COM/UV_Drivers.php&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;, which involves disabling automatic hardware driver updates, uninstalling any driver that's already installed, and then manually installing an old driver version.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that sounds like too much hassle, you can get a programming cable based on a chip made by FTDI, or run the software on Linux rather than Windows; the Linux driver &quot;just works&quot;.  You can also buy the programming cable and software package sold by &lt;a href=&quot;https://www.rtsystemsinc.com/&quot; rel=&quot;noreferrer&quot;&gt;RT Systems&lt;/a&gt;, which also have the reputation of &quot;just working&quot;, but are expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't choose the RT Systems route, then you'll need programming software.  Baofeng has free software for their radios.  (I don't remember, but the software might be specific to particular models.)  Their software works fine, but another alternative which I prefer is the free software called &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;noreferrer&quot;&gt;CHIRP&lt;/a&gt;, which is excellent, and works for just about every ham VHF/UHF radio that can be programmed by a serial cable.  There are versions of CHIRP for most every operating system.  CHIRP is frequently updated, and there is a lively mailing list that is friendly to newbies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd also like to recommend the site &lt;a href=&quot;http://www.miklor.com/&quot; rel=&quot;noreferrer&quot;&gt;miklor.com&lt;/a&gt;, which is chock-full of good information for owners of Baofeng and similar radios.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-05-23T22:20:15.817" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10332" PostTypeId="2" ParentId="9907" CreationDate="2018-05-23T23:03:52.273" Score="0" Body="&lt;p&gt;youtube has a video of a piece of coax with the last 19&quot; being separated between the center, pulling it out of the sheath. poor mans dipole. seemed to work&#xA;&lt;a href=&quot;http://bit.ly/2scIYD7&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://bit.ly/2scIYD7&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11654" LastEditorUserId="11654" LastEditDate="2018-05-25T17:52:04.893" LastActivityDate="2018-05-25T17:52:04.893" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10333" PostTypeId="2" ParentId="10330" CreationDate="2018-05-24T10:40:12.373" Score="1" Body="&lt;p&gt;Notice that the calculator does not require an input for the material characteristics of the underlying wire but rather only the plating. This is a clear indication that the author expects the AC current to be fully contained within the skin material. This would be plausible given the &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin effect&lt;/a&gt; of AC current. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can select two forms of copper if your wire has no plating. Also note that the pull down material selector pre-populates the conductivity and permeability fields as a matter of convenience. You may manually populate these fields for other materials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are using common solid copper wire, &lt;em&gt;annealed copper&lt;/em&gt; would be a suitable choice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The website is authored by Serge Stroobandt, ON4AA as indicated on the &lt;a href=&quot;http://www.hamwaves.com/index/en/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;homepage&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-24T11:50:31.700" LastActivityDate="2018-05-24T11:50:31.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10334" PostTypeId="1" AcceptedAnswerId="10335" CreationDate="2018-05-24T22:54:00.037" Score="9" ViewCount="402" Body="&lt;p&gt;I was reading &lt;em&gt;New Ham Radio License&lt;/em&gt; by AG6IF and the author says something strange in the context of station/operator identification:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Use the standard ham phonetics, not the Air Force version, or the Fire Department's version or something you heard on TV.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As far as I know, the USAF uses the NATO phonetic alphabet. This suggests that the ham radio phonetic alphabet isn’t the same as the &lt;a href=&quot;https://en.wikipedia.org/wiki/NATO_phonetic_alphabet&quot; rel=&quot;noreferrer&quot;&gt;NATO phonetic alphabet&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the author confused? Am I confused? Are there multiple alphabets? Should I not be using military / air traffic phonetics?&lt;/p&gt;&#xA;" OwnerUserId="11462" LastEditorUserId="11462" LastEditDate="2018-05-25T01:53:26.567" LastActivityDate="2018-05-25T17:13:25.623" Title="Is there a different ham radio phonetic alphabet?" Tags="&lt;callsign&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10335" PostTypeId="2" ParentId="10334" CreationDate="2018-05-25T02:58:17.300" Score="4" Body="&lt;p&gt;Many hams use nonstandard phonetics (or alternate standard and nonstandard when repeating themselves). The author of the above quote is probably aware of this but feels it is not best practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect that the author meant to convey “don't use what you think is cool or what you may have heard on other bands, use what is standard &lt;em&gt;here&lt;/em&gt;” and went a little too far in listing not-ham things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as I know, there are no specific elements of the NATO phonetic alphabet which are &lt;strong&gt;not&lt;/strong&gt; in common use in ham radio — except perhaps that the NATO modified pronunciation of numbers (“tree”, “fower”, “fife”, “niner”) is uncommon. Also, “kilo” is often replaced with “kilowatt” even by people who do not otherwise use nonstandard phonetics.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-05-25T17:13:25.623" LastActivityDate="2018-05-25T17:13:25.623" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10336" PostTypeId="1" CreationDate="2018-05-25T15:46:57.870" Score="5" ViewCount="627" Body="&lt;p&gt;I'm looking at the raw packet data from &lt;a href=&quot;http://aprs.fi&quot; rel=&quot;noreferrer&quot;&gt;http://aprs.fi&lt;/a&gt;. I see packets such as these:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;ROSLDG&amp;gt;APN390,HEBOWX,OR2*,qAR,MKSRDG:@015805z4501.34NF12351.41W_000/000g000t053r000p000P000h92b......U2k &#xA;W7KKE-9&amp;gt;TTRSUT,NEWPRT*,OR2-1,qAR,W7GC-3:'4]. {nv/]&quot;3z}&#xA;KG7HEL-3&amp;gt;AAAPPP,WIDE1-1,WIDE2-1,qAR,BEAVRT:'vX&amp;lt;0x1c&amp;gt;&amp;lt;0x1c&amp;gt; &amp;lt;0x1c&amp;gt;#/&amp;gt;TEMP1-1 digi running on battery= [Latitude and longitude are both 0]&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Where is the specification for the information that comes after the &lt;code&gt;:&lt;/code&gt; at the end of the path information? I can find &lt;a href=&quot;http://www.aprs.org/doc/APRS101.PDF&quot; rel=&quot;noreferrer&quot;&gt;a specification&lt;/a&gt; for APRS data as it is packeted into an AX.25 packet, but not for the messages that come from an APRS-IS server. Can I assume that anything after the &lt;code&gt;:&lt;/code&gt; is in the same format as the Information Field in the APRS AX.25 specification? What happens to non-printables?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've surmised that the &lt;code&gt;'&lt;/code&gt; and &lt;code&gt;@&lt;/code&gt; after the &lt;code&gt;:&lt;/code&gt; are APRS Data Type Identifiers, but I have no idea what the &lt;code&gt;&amp;lt;0x1c&amp;gt;&lt;/code&gt; stuff is in the last packet.&lt;/p&gt;&#xA;" OwnerUserId="5820" LastActivityDate="2018-06-24T17:17:42.323" Title="Help understanding the information field in an APRS-IS message" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10337" PostTypeId="2" ParentId="10336" CreationDate="2018-05-25T16:51:55.413" Score="3" Body="&lt;p&gt;Everything after the : is the payload that the station is sending out.  While there are conventions so that the data is meaningful, I don't believe there are any standards.  For example, the first line is a weather report, Wind calm (0 mph at 0 degrees, 0 mph gust), temp 54, no rain, RH 92% etc).  The second line is probably a compressed location packet (compressed so that it takes less time to send.)  In the last line, the &amp;lt;0x1c&gt; probably represents a non-printable character (CTRL+Z or EOF).  Since non-printable characters are, well, not printable the software either on the sending or receiving end likely converted the 0x1C (binary) to the string &amp;lt;0x1C&gt; so that it would be printable (and if needed human readable.)  Beyond that, without knowing the software sending the telemetry, there's not much more you can learn from it.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-05-25T16:51:55.413" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10339" PostTypeId="1" CreationDate="2018-05-26T19:05:29.703" Score="3" ViewCount="252" Body="&lt;p&gt;Not including special event callsigns, which group (country/class/etc) of hams have and use the longest callsigns? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that theoretically the longest would be a (3x4) or 8 character callsign but are these in use? I’m interested in which countries in actual practice issue incredibly long callsigns to individuals. &lt;/p&gt;&#xA;" OwnerUserId="11462" LastEditorUserId="11462" LastEditDate="2018-05-28T03:15:39.750" LastActivityDate="2018-05-28T03:15:39.750" Title="Which country’s hams have the longest call signs?" Tags="&lt;callsign&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10340" PostTypeId="1" AcceptedAnswerId="10342" CreationDate="2018-05-28T00:04:16.300" Score="5" ViewCount="1279" Body="&lt;p&gt;Some American hams are lucky enough to have four letter call signs such as: K1JT&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are American hams the only ones with the possibility of a four letter call sign? Is there another country that grants four letter call signs to individuals on a regular basis (and not just to the royal family, special events, clubs, etc). &lt;/p&gt;&#xA;" OwnerUserId="11462" LastEditorUserId="11462" LastEditDate="2018-05-28T03:12:30.723" LastActivityDate="2018-05-28T06:56:00.080" Title="Are Americans the only hams with four-letter callsigns?" Tags="&lt;callsign&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10341" PostTypeId="2" ParentId="10339" CreationDate="2018-05-28T00:19:06.077" Score="3" Body="&lt;p&gt;A long call sign that was recently pointed out on this site is a special club call sign in Belgium. As discussed &lt;a href=&quot;https://ham.stackexchange.com/questions/10231/long-callsigns-in-wsjt-x&quot;&gt;here&lt;/a&gt;, it is too long to be encoded in FT-8 and is in the form OT70xxx.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-28T00:45:11.953" LastActivityDate="2018-05-28T00:45:11.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10342" PostTypeId="2" ParentId="10340" CreationDate="2018-05-28T02:02:25.363" Score="6" Body="&lt;p&gt;The type of call signs that you referenced are referred to as 1x2 (one by two) call signs in the USA. Due to the limited number of such call signs and their historical significance, these are the most sought after in the USA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But 1x2 call signs are not unique to the USA. Consider the well publicized (but commonly misunderstood) G5RV antenna, named after the UK 1x2 call sign holder that invented it. The call is currently held by a UK club in commemoration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An even more rare call is a 2x0 call sign. A popular example of this was King Hussein of Jordan, JY1. While he could obviously obtain any Jordanian call sign, he was known for his personable on the air conversations despite his political standing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the USA, hams may apply for a 1x1 call sign that may be used for special events for a limited time. The call is then recycled for future applicants.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the call sign prefix (the part before, or including, the number) is assigned by the ITU. A listing may be found &lt;a href=&quot;http://www.arrl.org/international-call-sign-series&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-28T02:07:40.747" LastActivityDate="2018-05-28T02:07:40.747" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10343" PostTypeId="2" ParentId="9489" CreationDate="2018-05-28T03:45:03.797" Score="1" Body="&lt;p&gt;Yes, remote control is not only possible, but it is easy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FT-450D is not like a naked SDR.  It may be one internally, but it does not need a program like SDR# to operate it.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That being said, there is a great program available that allows the front panel of the radio to appear on your screen, and you can use the keyboard and mouse to control it via the USB cable that is used for the Must-Have ADMS-450 programming software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.dxengineering.com/parts/rtp-adms-450-usb&quot; rel=&quot;nofollow noreferrer&quot;&gt;RT Systems Radio Programming Software and Cable ADMS-450-USB&lt;/a&gt; (DX Engineering)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the USB Cable installed, run this software for on-screen remote control:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.yaesu.com/downloadFile.cfm?FileID=8352&amp;amp;FileCatID=42&amp;amp;FileName=PCC%2D450D%5FV102.zip&amp;amp;FileContentType=application%2Fx%2Dzip%2Dcompressed&quot; rel=&quot;nofollow noreferrer&quot;&gt;PCC-450 Software V1.13 and Reference Manual (07/18/14)&lt;/a&gt;  (Yaesu.com)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;To see all of the Yaesu software and documentation for the FT-450D, click here and then select the Files button:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&amp;amp;ProdCatID=102&amp;amp;encProdID=870B3CA7CFCB61E6A599B0EFEA2217E4&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yaesu FT-450D&lt;/a&gt;  (Yaesu.com)&lt;/p&gt;&#xA;" OwnerUserId="8832" LastActivityDate="2018-05-28T03:45:03.797" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10344" PostTypeId="2" ParentId="10340" CreationDate="2018-05-28T06:26:11.593" Score="2" Body="&lt;p&gt;In YU ham or club may get 2x1 call too.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2018-05-28T06:26:11.593" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10345" PostTypeId="2" ParentId="10340" CreationDate="2018-05-28T06:56:00.080" Score="1" Body="&lt;p&gt;You have 4 character call signs in Ireland as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example would be &lt;a href=&quot;https://www.qrz.com/lookup/EI0Z&quot; rel=&quot;nofollow noreferrer&quot;&gt;EI0Z&lt;/a&gt; (you are likely to be prompted for login following this link)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are rare, and are either &quot;old&quot; or given only to clubs and only for a specific purpose, such as contesting.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2018-05-28T06:56:00.080" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10346" PostTypeId="2" ParentId="10325" CreationDate="2018-05-28T10:13:45.030" Score="2" Body="&lt;p&gt;I did some more testing and it turns out the fault is in the &lt;strong&gt;coax wire&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not a normal cable, it's a vertical magnetic mount and when I use this cable conecting both live and ground it kill all RF signal but it's not shorted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you for your answers.&lt;/p&gt;&#xA;" OwnerUserId="11665" LastActivityDate="2018-05-28T10:13:45.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10347" PostTypeId="1" CreationDate="2018-05-28T10:24:13.320" Score="3" ViewCount="232" Body="&lt;p&gt;In some countries, Ham licensing is still cumbersome even for citizens, and operation prohibited by foreigners.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm curious what the situation is like in Taiwan now. Years ago, there was little difference between the license and licensing process for a Ham station and that for a large commercial radio station. Also bringing equipment into the country yourself was prohibited and subject to on-the-spot confiscation. I think things have improved now, but I don't know to what extent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These days, what are the rules regarding non-citizens operating licensed stations in Taiwan, does a citizen need to be present? Is self-importing of one's personal equipment still prohibited?&lt;/p&gt;&#xA;" OwnerUserId="8643" LastEditorUserId="76" LastEditDate="2018-05-29T18:37:46.517" LastActivityDate="2019-11-05T21:37:58.270" Title="Current rules in Taiwan for operating licensed stations, bringing in personal equipment?" Tags="&lt;legal&gt;&lt;license&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10348" PostTypeId="1" AcceptedAnswerId="10372" CreationDate="2018-05-28T10:31:17.327" Score="3" ViewCount="1562" Body="&lt;p&gt;I've just get my license, and I'm reviewing some equipend my father in law had when he passed away. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have found a dipole antenna with 15m aprox in each side, so, 60m band antenna. It feels weird to have an antenna for that band and not for 20 o 40 or 80.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions is: Can I use this antenna for some other band? If it's posible. Is there some rule to use dipoles in other bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have an anntenna analyzer to watch for dips in swr.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My (naive) hypothesis is that it could be used for bands like 10m, it being 3/2λ of that band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: &#xA;I just find out that the antanna I have is this one: &lt;a href=&quot;https://en.wikipedia.org/wiki/G5RV_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/G5RV_antenna&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you &lt;/p&gt;&#xA;" OwnerUserId="11665" LastEditorUserId="11665" LastEditDate="2018-05-31T21:27:59.190" LastActivityDate="2019-06-30T23:03:46.920" Title="One dipole for multiple bands?" Tags="&lt;antenna&gt;&lt;dipole&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10349" PostTypeId="2" ParentId="10348" CreationDate="2018-05-28T12:13:22.193" Score="-3" Body="&lt;p&gt;You can use it for receiving on any band, of course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, antennas may work on third harmonics.  For example, 2m and 70cm are close third harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes they work on second harmonics (i.e., 10m and 20m), especially dipoles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So your 60m antenna may work on 30m and 15m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have an antenna tuner (or one is built into the radio), you might be able to operate it all band, but you may have high SWR and common mode current in the feedline.  High SWR without a tuner can damage the radio; high SWR with a tuner will incur large losses in the feedline, but might work anyway.  Common mode current can be partially suppressed at low power with a balun, sometimes built into the antenna.  The danger of common mode current (besides typically higher SWR) is RF radiated directly from the coax, possibly in the shack and on the chassis of the radio.  (Watch out for RF burns.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, you could create a fan dipole to get additional bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't have an antenna analyzer, you should at least have an SWR meter built into the radio.  You can operate on a mismatched antenna at low power (1w or less preferably, up to 5w maybe) without damaging the radio.  (High SWR may make the radio arc internally short term and overheat long term.)  Most radios have a TUNE button for this purpose.  Check the manual on your radio to be sure what power it uses.  If you don't have a tune button, you can use a CW key and put out a test pulse.  Start at the lowest possible power and watch the SWR meter, and raise it slowly to make sure the SWR doesn't increase when you put out more power.   Remember, the SWR the radio sees may be lower than the real SWR because of loss in the transmission line.  An SWR below 1.5 is typically considered good with negligible loss.  Most solid state radios can tolerate an swr of 2 or lower.  Most tube radios can tolerate an swr of 10 at 100W.  Tuners may also be able to take swr of 10, but may arc internally at higher swr or higher power depending on the tuner.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-05-28T12:13:22.193" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10350" PostTypeId="2" ParentId="10348" CreationDate="2018-05-28T14:40:24.330" Score="2" Body="&lt;p&gt;If this is indeed a 60m dipole, it would be resonant somewhere around 5.35 MHz. Three times that is approximately 16 MHz, which unfortunately doesn't fall on a ham band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However it might not be a 60m dipole either. A 60m dipole has a length of about 13.25 meters on each half.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or it might be that where the antenna was installed, proximity to the ground, other conductive structures, or common-mode currents on the feedline significantly altered the resonant frequency from the ideal free-space model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would suggest you acquire an antenna tuner if you don't have one. You can probably get the dipole to tune on most bands with it, and while this won't be the most efficient arrangement, with less than 100 feet of reasonable LMR-400 type coax you'll still be able to make some contacts and get your feet wet. The most important thing is to get the antenna as high as possible, at least a quarter wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The tuner will also have an SWR meter, which will allow you to adjust the length of the antenna to be a better match and thus more efficient, or build more dipoles, or multi-band designs like a fan dipole.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-05-28T14:40:24.330" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10351" PostTypeId="1" AcceptedAnswerId="10352" CreationDate="2018-05-28T14:55:22.230" Score="3" ViewCount="3881" Body="&lt;p&gt;&lt;strong&gt;Yaesu FT-450D Transceiver&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;USB-to-DB9 cable installed to the CAT interface&lt;/li&gt;&#xA;&lt;li&gt;Computer runs the ADMS-450 channel-programming program fine.&lt;/li&gt;&#xA;&lt;li&gt;Computer can run the PCC remote-control program fine.  &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;DATA connector has these pins:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UbxHR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UbxHR.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the cable looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JjTvU.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JjTvU.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;DATA connector is attached to the computer's audio in/out jacks &lt;/li&gt;&#xA;&lt;li&gt;Computer can record receive-audio fine.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The Operator's Manual shows an external TNC for RTTY and PSK, wired like this&lt;/strong&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/69Dic.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/69Dic.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So I admit to being a bit confused as I thought the data cable would be all that would be necessary to use software digital modes from the laptop.  Now I see that the PTT line is n/c.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It does function as a very good analog interface, and makes good recordings.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The goal is to use the laptop as a CW keyboard and memory keyer.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps the simplest option would be to use the &lt;strong&gt;Keyer&lt;/strong&gt; jack directly with a Python program on a RPi3B from the junk box.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it is possible to do it with the existing connections that would be best.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In searching around with Google there seems to be very little information about doing this.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;QUESTION:  How to use the FT-450D for CW from the computer?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do you key the carrier remotely?  Is it possible to use the CAT interface to send CW?&lt;/p&gt;&#xA;" OwnerUserId="8832" LastEditorUserId="8832" LastEditDate="2018-05-30T16:35:58.177" LastActivityDate="2018-09-14T19:46:36.867" Title="Yaesu FT-450D CW from computer - DATA and CAT connectors" Tags="&lt;cw&gt;&lt;yaesu&gt;&lt;remote-control&gt;&lt;ft-450d&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10352" PostTypeId="2" ParentId="10351" CreationDate="2018-05-28T16:37:50.080" Score="4" Body="&lt;p&gt;The &quot;data&quot; cable you picture provides only audio in and out. Some other device, like a TNC or a computer, must provide the modulation and demodulation to provide any data capability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, the cable picture does not expose the PTT connection on the data port, so with that cable alone there's no way for the computer to key the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you do say you have a &quot;USB-to-DB9 cable&quot; installed. Yaesu calls this the CAT port. You can use this connection to key the transmitter, as well as control most other functions of the radio such as frequency, mode, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounds like all you need to do is configure your CW keyer software to use the CAT interface to control the radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How this is done depends on the software, but any reasonably modern software like &lt;code&gt;fldigi&lt;/code&gt; or &lt;code&gt;Ham Radio Deluxe&lt;/code&gt; does have the capability. Look through the setup menus and you should be able to find it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8832" LastEditDate="2018-05-29T16:28:25.307" LastActivityDate="2018-05-29T16:28:25.307" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="10353" PostTypeId="1" AcceptedAnswerId="10360" CreationDate="2018-05-29T01:22:55.950" Score="3" ViewCount="135" Body="&lt;p&gt;Is there any point to keeping the CSCE form after the FCC registers the exam/upgrade in its database? I'm trying to go paperless in my old age and if there's no reason not to have the paper copy, into the shredder it goes.&lt;/p&gt;&#xA;" OwnerUserId="11462" LastEditorUserId="873" LastEditDate="2018-06-01T03:37:12.847" LastActivityDate="2018-06-02T10:01:01.870" Title="Is there any point to keep the CSCE after the FCC registers the upgrade?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10355" PostTypeId="1" AcceptedAnswerId="10357" CreationDate="2018-05-29T12:37:29.690" Score="3" ViewCount="211" Body="&lt;p&gt;I connected a &lt;a href=&quot;http://www.ni.com/en-in/support/model.usrp-2901.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;USRP 2901 (B210)&lt;/a&gt; to an amplifier I designed. The USRP seems to shutdown every time I try to transmit. I guess I messed up with the input impedance matching on the amplifier. Is it the impedance mismatch that is causing the USRP to shutdown? If so, how high a mismatch can it handle?&lt;/p&gt;&#xA;" OwnerUserId="11096" LastEditorUserId="76" LastEditDate="2018-05-29T18:41:24.450" LastActivityDate="2018-05-29T20:50:15.343" Title="How high an SWR can the USRP 2901 (B210) handle?" Tags="&lt;software-defined-radio&gt;&lt;antenna-system&gt;&lt;impedance-matching&gt;&lt;usrp&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10356" PostTypeId="1" AcceptedAnswerId="10359" CreationDate="2018-05-29T20:49:27.013" Score="7" ViewCount="421" Body="&lt;p&gt;I'm taking the exam to upgrade my licence to Extra soon, but I'm concerned the ULS might not update in time for Field Day, when I'm supposed to be supervising (and using my call-sign for) my club's GOTA station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I'm not operating outside the portion of the spectrum permitted to General class licencees, do I need to use the /AE suffix?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My reading of §97.119.f.3 Seems to indicate that I MUST use the suffix if I pass, even when in the general portion of the band.&lt;/p&gt;&#xA;" OwnerUserId="4646" LastEditorUserId="76" LastEditDate="2018-05-29T21:34:10.250" LastActivityDate="2018-05-29T23:17:20.167" Title="Is using /AE compulsory?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10357" PostTypeId="2" ParentId="10355" CreationDate="2018-05-29T20:50:15.343" Score="2" Body="&lt;p&gt;The B210 / NI-USRP 2901 has no problems with an open end condition or a short: You can't damage the transmitter with its own power. There's no significant PA on that board. So, it can handle any mismatch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, shutting down (whatever that means) isn't a reaction anyone included in the hard- or software in reaction to an impedance mismatch.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-05-29T20:50:15.343" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10358" PostTypeId="2" ParentId="1412" CreationDate="2018-05-29T22:19:22.187" Score="1" Body="&lt;p&gt;Have a look in some issues of QST. They provide spectra for keyed signals from tested transceivers. That is &quot;the RF bandwidth of a typical CW signal.&quot;&#xA;The minimum bandwidth is often assumed to be something like 25 Hz, but with appropriate frequency stability one would get the best copy at a bandwidth around 18 Hz for normal hand keyed CW. 20 years ago I was very active on CW EME (moonbounce) and I always optimized bandwidth for weak stations. It is enough to let through the first side-bands that would be present when transmitting a series of dots. The slowest keying station was OK1MS and his signal was best received at a bandwidth of 12 Hz. I was receiving with about 5 seconds of delay using a time span of 15 seconds (10 in the past and 5 into the future) to lock to the carrier of the CW signal by means of a power weighted least squares fitting. This way the filter was always kept symmetric around the signal. Mistuning by a single Hz would destroy performance since that would cause loss of one or the other side-band.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-05-29T22:19:22.187" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10359" PostTypeId="2" ParentId="10356" CreationDate="2018-05-29T22:53:33.557" Score="11" Body="&lt;p&gt;The key wording is in 97.9(b) as referenced in 97.119:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;...is authorized to exercise the rights and privileges of the higher operator class...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and 97.119 says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;When the control operator is a person who is exercising the rights and privileges authorized by §97.9(b)...&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So you only need to use the /AE suffix when you are using privileges only available to an extra class operator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best of luck on the exam!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-29T23:17:20.167" LastActivityDate="2018-05-29T23:17:20.167" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10360" PostTypeId="2" ParentId="10353" CreationDate="2018-05-29T23:01:18.230" Score="2" Body="&lt;p&gt;You can shred it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only time where such paperwork proved valuable was from the days of &quot;Tech Plus&quot; (passed written element 3A and 5 WPM code).  The FCC eventually reverted Tech Plus to Tech licenses. When the code requirement for General was dropped, former Tech Plus licensees could get &quot;automatic&quot; upgrades  to General if they could show paper proof of their former status. This was back in the days when paper, not bits, mattered.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-02T10:01:01.870" LastActivityDate="2018-06-02T10:01:01.870" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10361" PostTypeId="1" AcceptedAnswerId="10362" CreationDate="2018-05-30T09:13:23.277" Score="2" ViewCount="74" Body="&lt;p&gt;It is claimed in blogs and other unverified internet sources that circular polarized RF signals are better for penetrating structures, such as walls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example &lt;a href=&quot;https://www.mobilemark.com/download/engineering-white-papers/white-papers/CP-White-Paper.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;, there are many others when you search. All of them unverified, or not clearly explained.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More scientific information and papers tend to be about optics and polarization of light. While comparable to a certain extent, it does not explain the claims in regards to RF, both Amateur bands, such as 70/23cm nor consumer WiFi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few years ago, I took those claims and built myself some RHCP &quot;clover&quot; antennas and helix antennas for home WiFi distribution. Living in a period house, with 3 ft thick walls, my signal attenuation declined from room to room, and therefore WiFi reception improved throughout the property. Practically confirming the claims made.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Over the years I have built various circular polarized antennas and experimented on many different frequencies (70cm, 23cm, as well as consumer WiFi)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Throughout time, I have shared my practical solution with many, and others have reported back similar results. Again practically confirming the claims.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;None of this without any real explanation why this is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However a few days ago someone asked me... why ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And other than explaining E-planes, random reflection of building materials with &quot;unknown properties&quot;, and the &quot;chance&quot; that &quot;some&quot; signal is not reflected, I could not explain this phenomenon clearly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Do circular polarized signals have better penetration properties compared to linear polarized signals?&lt;/strong&gt; &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;and if so: why?&lt;/strong&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2018-05-30T15:35:52.750" LastActivityDate="2018-05-30T15:35:52.750" Title="Why is it claimed that circular polarized RF has better penetration properties compared to linear polarized RF?" Tags="&lt;circular-polarization&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10362" PostTypeId="2" ParentId="10361" CreationDate="2018-05-30T09:50:30.923" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Does circular polarized signals have better penetration properties compared to linear polarized signals?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In general, no. Maxwell's equations don't give us any indication why that should be the case. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At least, that is, for homogeneous media:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;and if so: why?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If this is an observed phenomenon, then it might have to do with the structure of obstacles being penetrated: a vertical steel rebar might interact with vertically polarized waves stronger than with circularly polarized ones, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd be a bit careful about comparing your home-made clover with the linear antennas that came with your WiFi-equipment:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Might simply be luck; the indoor WiFi scenario is one based on multipath propagation including reflections, and it's impossible to predict performance of two antennas in the same (linear) polarization plane. I could imagine that making a difference for wavelengths larger than the distance of steel armaments in concrete. I doubt it makes a lot of difference in WiFi – you don't need a lot of concrete to attenuate that by 60 dB, and whether there's appropriately polarized conductors inside that won't do much.&lt;/li&gt;&#xA;&lt;li&gt;If we're talking about rooms with specular reflectors (e.g. sheet metal etc), we might get periodic deep fades in places where the reflected wave &quot;meets&quot; the original wave for linear polarization; not sure it happens in the same manner for circular; not an attenuation, but a resonator phenomenon if that's the case!&lt;/li&gt;&#xA;&lt;li&gt;Might simply be that your antenna is &lt;em&gt;better&lt;/em&gt; in the sense that it focuses more energy in the right direction, or is more efficient (I doubt efficiency makes a huge difference here). There's a lot of indications the directivity is the real difference here: the amount of angular range covered by a Wifi stick or patch antenna is definitely larger than that of any significantly helical helix antenna, and probably still larger than that of a clover antenna, so you might simply be covering less space with the same amount of energy. (potentially breaking EIRP regulations underway)&lt;/li&gt;&#xA;&lt;li&gt;WiFi performance is often dominated by interference; since your interferers would be linearly polarized, they'd lose a couple dB. (but that usually won't make a huge difference). That effect would diminish if all WiFi devices were to use the same circular polarization&lt;/li&gt;&#xA;&lt;li&gt;You're comparing SISO systems. Modern WiFi systems are often MISO or MIMO, and for these, diversity vs uniformity considerations might lead to a preference of linear antennas in orthogonal planes.&lt;/li&gt;&#xA;&lt;li&gt;confirmation bias of people who've rebuilt your antennas and spent much work on that&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;That is not to say that your observation isn't right – I thoroughly believe it could be – but I could imagine that what you're observing for WiFi is more of a multipath/interferer environment and directivity effect than an absorption phenomenon.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-05-30T09:50:30.923" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10363" PostTypeId="1" AcceptedAnswerId="10364" CreationDate="2018-05-30T18:21:47.893" Score="4" ViewCount="46" Body="&lt;p&gt;I would like to ask how can I connect device, which have female reversed TNC connector with antenna which have female normal TNC. Could somebody help me?&lt;/p&gt;&#xA;" OwnerUserId="11690" LastActivityDate="2018-05-31T14:05:43.840" Title="How to connect female reversed with female normal TNC" Tags="&lt;tnc&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10364" PostTypeId="2" ParentId="10363" CreationDate="2018-05-30T19:34:15.533" Score="1" Body="&lt;p&gt;You need the applicable reverse-polarized TNC adapter.  Sounds like you have a standard TNC Female on your antenna &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DkUUV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DkUUV.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and a RP-TNC Female on your device.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/biHDy.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/biHDy.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you confirm? &lt;/p&gt;&#xA;&#xA;&lt;h2&gt;----------&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Added 31-May-2018&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on your comments I'm concerned that you are not certain of your determination of the existing connectors.  (It's easy to confuse standard TNCs with RP-TNCs and males with females etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If those pictured above are truly what you have then the following pair of adapters would work:&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;This TNC-Male to N-Female adapts the antenna connector to N-female&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.l-com.com/coaxial-coaxial-adapter-n-female-tnc-male&quot; rel=&quot;nofollow noreferrer&quot;&gt;L-com Item # AXA-NFTM&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rCCuw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rCCuw.png&quot; alt=&quot;L-com Item # AXA-NFTM&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;This N-Male to RP-TNC-Male adapts the first adapter to the device connector:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.l-com.com/coaxial-coaxial-adapter-n-male-rp-tnc-plug&quot; rel=&quot;nofollow noreferrer&quot;&gt;L-com Item # AXA-NMRTP&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/BcMkj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BcMkj.png&quot; alt=&quot;L-com Item # AXA-NMRTP&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8573" LastEditorUserId="8573" LastEditDate="2018-05-31T14:05:43.840" LastActivityDate="2018-05-31T14:05:43.840" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="10365" PostTypeId="1" CreationDate="2018-05-30T20:00:12.887" Score="5" ViewCount="185" Body="&lt;p&gt;My antenna is copper, elements and the beam. I would like to bolt them together where they cross. Would stainless bolts work? Just sweating them together lets them twist and move some in high winds. &lt;/p&gt;&#xA;" OwnerUserId="11681" LastEditorUserId="8717" LastEditDate="2018-05-30T20:03:27.083" LastActivityDate="2018-05-31T11:45:38.877" Title="Will stainless steel bolts work with my copper antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10366" PostTypeId="1" AcceptedAnswerId="10368" CreationDate="2018-05-31T08:44:07.907" Score="2" ViewCount="32" Body="&lt;p&gt;I am answering some questions about my course of radio links and I came across with the question about explaining interference in fixed and mobile wireless systems. As far as I know ALL wireless system are susceptible to radio frequency interference (RFI), electrical interference and intermodulation (independently of the wireless system we are talking about). Thus my questions is what are the interferences you can encounter on the basis of fixed and mobile systems? Are they different?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would appreciate if a book is also recommended to dive into details&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="11695" LastActivityDate="2018-05-31T16:32:58.683" Title="Interference difference: fixed and mobile wireless systems" Tags="&lt;rfi&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10367" PostTypeId="2" ParentId="10365" CreationDate="2018-05-31T10:04:51.183" Score="7" Body="&lt;p&gt;Stainless steel fasteners, lead and tin are compatible with copper. Lead tin solder, however, has poor mechanical strength as you have apparently discovered. Solder can be used to improve conductivity and moisture ingress and is best when used with other mechanical strengthening measures. So the use of stainless fasteners to improve the mechanical strength of your antenna is practical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Avoid the use of aluminum or zinc fasteners with copper as these will cause the fastener to deteriorate through the mechanism of galvanic corrosion. If a copper wire must be directly attached to a galvanized metal such as tower leg, a stainless steel shim can be placed between them to avoid the galvanic corrosion since stainless steel is compatible with both materials. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-31T11:45:38.877" LastActivityDate="2018-05-31T11:45:38.877" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10368" PostTypeId="2" ParentId="10366" CreationDate="2018-05-31T10:41:42.110" Score="1" Body="&lt;p&gt;The question is quite broad - it could be improved through some context.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, consider that fixed antenna installations can be highly optimized. Distance and height can be used to minimize locally generated interference. Antenna directivity can be used to separate interfering signals from the desired signals. In a fixed application, long term interference can be located and often mitigated. Fixed antenna installations can generally take advantage of more space to install larger and more efficient antennas that result in more gain which may be used to improve the desired signal while minimizing interfering signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a mobile application, the space and topology of the antenna installation is limited which often results in compromises. Directivity to avoid interference is often not practical while the antenna is moving so most mobile antenna installations are largely omnidirectional in the azimuth (horizontal compass) plane. Interfering sources come and go according to the location of the mobile antenna and the location of the interfering signal. It is not practical to mitigate these itinerant noise or interfering signal sources.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-05-31T10:41:42.110" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10369" PostTypeId="1" AcceptedAnswerId="10370" CreationDate="2018-05-31T12:52:24.460" Score="0" ViewCount="72" Body="&lt;p&gt;I built an RF power amplifier with about 10 to 13 dB gain operating at about 100 MHz. It amplifies signal from about 50 to 100mW to about 1W. Inspite of the amplification, I don't see a real improvement in the range of coverage. I just observe a range of about 20 to 40m. There are a lot of buildings and walls here. Is it because of the walls that the range is not improving? I am just transmitting Frequency modulated analog audio.&lt;/p&gt;&#xA;" OwnerUserId="11096" LastActivityDate="2018-05-31T22:02:12.503" Title="RF Coverage range doesn't improve inspite of increased Tx power" Tags="&lt;amplifier&gt;&lt;range&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10370" PostTypeId="2" ParentId="10369" CreationDate="2018-05-31T16:23:53.650" Score="3" Body="&lt;p&gt;Transmit range involves a number of factors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Propagation&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 100 MHz your signal range will be largely limited by line of site (LOS) although you may experience some fringing and reflections. This means that no matter how much you increase the transmit power, you cannot predictably increase your range beyond LOS. Increasing the altitude of the transmit or receive antenna to achieve LOS is the only way to correct this condition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obstructions often attenuate RF signals. At 100 MHz manmade wood structures are largely RF transparent. Concrete and other materials have a higher loss factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Antenna System&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your antenna system is not a good impedance match for your amplifier's output impedance or your antenna system is quite lossy, your transmitted power will be substantially less than you might expect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the polarization of the transmit and receive antennas are not matched, you can experience substantial losses. Losses in the order of 20 dB or more have been reported. Either match the polarization or make one of the antennas circularly polarized as a compromise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Design Error&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have not verified the increased output power with a reasonably calibrated watt meter, you may not have achieved the 10 dB gain you are anticipating&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Minimum Discernable Signal (MDS)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every receiver has an MDS power level that must be met before a received signal can be detected. If your system does not deliver sufficient power to the receiver's antenna to meet or exceed this threshhold, your 10 dB increase is not sufficient. You could improve upon this by further increasing the transmitted power or increasing the efficiency or directivity of your antenna system. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-05-31T22:02:12.503" LastActivityDate="2018-05-31T22:02:12.503" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10371" PostTypeId="2" ParentId="10366" CreationDate="2018-05-31T16:32:58.683" Score="0" Body="&lt;p&gt;For fixed, licensed stations, such as commercial broadcast stations, part of obtaining that license requires establishing the coverage area of the transmitter, and determining that there will be no conflicts with other stations. Since the transmitter is fixed, it's feasible for some combination of geography and frequency to be exclusively reserved for that station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But with mobile stations, some other transmitter on the same frequency can move into the same area. In some allocations, like the ISM bands in which WiFi operates, it's a free-for-all where everyone just has to deal with it. Other allocations are made to specific companies (cell phone networks) or government organizations (military, police) or purposes (aviation and maritime communication). Each allocation has specific rules for how to handle interference.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-05-31T16:32:58.683" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10372" PostTypeId="2" ParentId="10348" CreationDate="2018-06-01T04:11:14.427" Score="2" Body="&lt;p&gt;I wrote an article about the G5RV --and variants thereof-- at &lt;a href=&quot;http://www.w0btu.com/g5rv_antenna.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w0btu.com/g5rv_antenna.html&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A popular variant is the ZS6BKW.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Neither the G5RV nor the ZS6BKW antenna works on 30 or 60 meters.&lt;/li&gt;&#xA;&lt;li&gt;The G5RV does NOT work well on 17 or 10 meters. The SWR is a little&#xA;better on 80 than the ZS6BKW.&lt;/li&gt;&#xA;&lt;li&gt;The ZS6BKW does NOT work well on 15&#xA;meters, and needs a tuner to work well on 80.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I improved on the general design, but it requires:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;75 ohm feedline, which many hams are somehow reluctant to use&lt;/li&gt;&#xA;&lt;li&gt;A switchable (in and out) section of ladder line.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Our modification to the G5RV and ZS6BKW antennas, while also somewhat of a compromise of frequency ranges and VSWR, lets us use all HF bands between 80 and 10 except 30 and 60* meters. (Details on the website above.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It depends on what bands you want to work. Choose your poison. ;-)&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-06-01T04:16:58.310" LastActivityDate="2018-06-01T04:16:58.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10373" PostTypeId="1" CreationDate="2018-06-01T12:48:18.420" Score="2" ViewCount="793" Body="&lt;p&gt;I am looking into connecting a TNC-Pi to a Kenwood TM-241A for AMPRNet operation. I thought it was going to be fairly straightforward as each pin on the TNC-Pi seemed to have its own analogue on the transceiver's end, until I came across this diagram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FGlri.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FGlri.jpg&quot; alt=&quot;TNC to TM-241A connection diagram&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a few questions about this. For one, why does it use the external speaker output instead of the Rx output pin on the transceiver? Second, why does the TNC connect to the transceiver's ground instead of the microphone input ground? Third, what are those little circles that seem to loop around another wire?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did notice that this diagram isn't specific to the TNC-Pi, so I might not have to worry about any of this.&lt;/p&gt;&#xA;" OwnerUserId="11701" LastActivityDate="2018-06-02T12:22:35.250" Title="Connecting TNC-Pi to Kenwood TM-241A" Tags="&lt;aprs&gt;&lt;kenwood&gt;&lt;connectors&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10374" PostTypeId="2" ParentId="10373" CreationDate="2018-06-01T14:48:29.953" Score="-1" Body="&lt;p&gt;Those circles represent the shield. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-06-01T14:48:29.953" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10375" PostTypeId="2" ParentId="10373" CreationDate="2018-06-01T15:16:06.407" Score="2" Body="&lt;p&gt;It likely uses the external speaker output because not all rigs (especially older ones) have an RX audio output pin.  And even if a rig does, it's possible that the audio output is before de-emphasis is applied so the TNC wouldn't be able to decode reliably.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As Mike said, the circles represent the cable shield.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as the microphone ground, read here: &lt;a href=&quot;https://ham.stackexchange.com/questions/8922/mic-microphone-ground-vs-common-ptt-chassis-etc-ground&quot;&gt;MIC microphone ground vs common (PTT, chassis etc) ground&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-06-01T15:16:06.407" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10376" PostTypeId="1" CreationDate="2018-06-01T18:15:49.987" Score="9" ViewCount="264" Body="&lt;p&gt;&lt;a href=&quot;https://youtu.be/Y5SGkI7NUg8&quot; rel=&quot;noreferrer&quot;&gt;Video&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was lucky to catch the QRM start this morning @ approximately 10 AM Pacific Standard time. It was wide, starting around 3000 kHz up to 10000 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It starts fast then slows to a crawl. The noise has pronounced high/low bumps as you'll see in the video. Almost like a train with high/low boxcars rolling through ...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rolling was faster before I started recording.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once it stops, it is very still with minor drift +/- and is present until approximately 10 PM Pacific Standard time. When it stops rolling, it does not start up again. It present periodically throughout the bands from 80 -&gt; 30 meters. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before and after 10 AM/PM, it is not present anywhere that I can see.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would cause rolling QRM like this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I caught it yesterday and powered-down my house at the breaker only leaving one circuit up for the radio and switching circuits to validate whether or not it was the house. To the best of my knowledge, it is not my house but something in the environment radiating RFI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Living in Las Vegas, NV, we have a lot of solar rooftops that could perhaps contribute to this in some way. However, it lasts until 10 PM which is far past sunset.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Radio FT-950&lt;/li&gt;&#xA;&lt;li&gt;Astron RS-35M power supply&lt;/li&gt;&#xA;&lt;li&gt;Active Mini-Whip antenna&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="11702" LastEditorUserId="4076" LastEditDate="2018-06-04T13:54:56.880" LastActivityDate="2018-08-27T22:35:45.500" Title="Rolling QRM from 3000-10000 kHz - What Is It?" Tags="&lt;noise&gt;" AnswerCount="1" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="10377" PostTypeId="2" ParentId="10373" CreationDate="2018-06-02T11:51:37.373" Score="1" Body="&lt;p&gt;As you have speculated, the wiring diagram you show is not correct for the TNCPi. Consult page 10 of your TM-241A user manual for the pin-out of your front panel connector and page 10 of the TNCPi manual for the DB9 pinout.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TNCPi does not have a Thevenin mike ground like the TM-241 does, so you can experiment with connecting the shield for the transmit audio to the mike ground (pin 7) or the chassis ground (pin 8) on the transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you connect the audio output from your tranceiver's mike jack (pin 6) to the RXinput of the TNCPi (pin 5), you have the advantage that the audio level into the TNC is independent of the radio's front panel volume control. The radio's speaker will still be active so you can monitor for traffic and you can still turn the speaker volume down when desired. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't obtain enough audio level from pin 6 of your transceiver to drive the TNC, you may have to resort to using the speaker output jack or consider changing R4 (1k) on the TNC to 4.7k to reduce the loading on the signal from pin 6 of the TM-241.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As noted by @mikewaters, the circles in the diagram indicate the use of a shielded cable. The connection to the circle represents the connection of the cable shield.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-02T12:22:35.250" LastActivityDate="2018-06-02T12:22:35.250" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10379" PostTypeId="1" AcceptedAnswerId="10382" CreationDate="2018-06-03T03:11:56.043" Score="11" ViewCount="2039" Body="&lt;p&gt;I read the Wikipedia article about &lt;a href=&quot;https://en.wikipedia.org/wiki/Spark-gap_transmitter?wprov=sfti1&quot; rel=&quot;noreferrer&quot;&gt;spark-gap transmitters &lt;/a&gt; and I have to admit that I’m even more confused as to what the spark-gap actually did. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The article references this simplified circuit diagram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5hDDk.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5hDDk.jpg&quot; alt=&quot;spark gap&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it seems to me (and correct me where I’m confused):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the power source is a battery so the spark itself is a DC spark and not AC of any frequency&lt;/li&gt;&#xA;&lt;li&gt;there’s an antenna so the spark-gap isn’t the EMF radiator &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So what is the spark gap exactly doing? I had originally thought it was acting as an oscillator / signal generator but if it’s a DC spark that doesn’t seem to be the case. And if it’s the EMF generator then what’s the antenna doing? And why is here an inductor and capacitor on the right side in an LC configuration?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some light would be appreciated.&lt;/p&gt;&#xA;" OwnerUserId="11462" LastEditorUserId="11462" LastEditDate="2018-06-04T17:24:36.813" LastActivityDate="2018-06-04T17:24:36.813" Title="What does the spark-gap do in a spark-gap transmitter?" Tags="&lt;transmitter&gt;&lt;history&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10381" PostTypeId="2" ParentId="10379" CreationDate="2018-06-03T04:42:25.643" Score="4" Body="&lt;p&gt;the spark gap's purpose is to very suddenly change the current in the LC circuit to which the antenna is, in fact, directly connected. the sudden change produces a very strong inductive kick in that circuit, producing a suddenly-rising voltage in it. that sudden rise gets filtered by the capacitor and inductor, causing them to resonate at the transmitting frequency with an amplitude that exponentially decays as RF energy gets radiated out of the circuit and into space via the antenna.  Careful choice of the circuit components and spark gap length then cause the spark breakdown to occur at a repetition rate in the audio frequency range, thus producing a wave train consisting of successive mHz oscillations that decay and get replaced by fresh oscillations at a rate of hundreds of Hz. the waveform is heard at the receiver as an amplitude-modulated carrier with significant sideband widths. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dozens of refinements to this basic idea were made over the years before vacuum tubes were eventually invented, to stabilize the spark, quench it purposefully, allow it to be easily keyed to produce morse code, and couple the oscillations to the antenna so as to maximize the efficiency of the process. &lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2018-06-03T04:42:25.643" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10382" PostTypeId="2" ParentId="10379" CreationDate="2018-06-03T07:25:36.120" Score="10" Body="&lt;p&gt;The spark gap is a simple, low-tech way of generating high frequencies. It was the only way of generating them before valves and transistors were invented.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As C1 charges up through R1, eventually the air in the spark gap breaks down, becoming a short circuit.&#xA;The breakdown of a spark gap happens over just a few nanoseconds. (It turns off much more slowly when voltages on C1 and C2 become equal).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The current through the spark gap is a sort of square up, exponential down. The leading edge contains frequency components up to at least 100 MHz. The bandwidth of a step change is roughly 0.35 / the rise time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These high frequency components are what excite the tuned circuit, or if you like, are filtered by the tuned circuit, so that only the kHz or MHz component passes through the circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency might have been 500 kHz (Titanic) or later a few MHz. If the loaded Q of the LC circuit is 50, at the frequency of interest, the resonant circuit will &quot;Ring&quot; for 50 cycles, decaying to about half its initial amplitude. This is called a damped wave. At each spark the transmitter sends one of these short, wide, damped RF pulses. (I think as they often had resonant antennas, the loaded Q would have been much lower). The decay process takes about 100 microseconds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note also that a Q of 50 will lead to a transmitted signal bandwidth of perhaps 10 kHz, much more depending on what threshold you use for bandwidth, which is quite wide by today's standards and much more than required for morse code. This is why Damped Wave emissions are not allowed by modern radio amateur laws.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Spark gaps up to 1910 simply triggered themselves again and again as C1 charged up enough to cause breakdown. This lead to a random pattern of the bursts of RF, which made a hissing sound in the headphones when detected by a simple AM receiver like a crystal set. You probably know the hissing sound of a randomly triggered spark.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Titanic was one of the first ships to have a new rotary spark gap, triggered by a rotating disc with metal studs, between the terminals of the spark gap. This made the breakdown happen at regular intervals, a few hundred times per second. These make a new buzzing sound in the receiving headphones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lots more about the radios on Titanic, &lt;a href=&quot;http://marconigraph.com/titanic/wireless/mgy_wireless.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2018-06-04T05:19:30.000" LastActivityDate="2018-06-04T05:19:30.000" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10383" PostTypeId="2" ParentId="10379" CreationDate="2018-06-03T16:12:32.263" Score="2" Body="&lt;p&gt;Step 1, short out the spark gap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Step 2, lots of current flows through the inductor L, building up magnetic lines of flux (magnetic field) around the inductor L.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Step 3, remove the short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Step 4, the current stops flowing through L, causing the magnetic field to collapse, causing a massive reverse voltage across the coil (Back EMF), charging the capacitor C2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Step 5, the field around L has collapsed to 0V, the capacitor C2 now discharges into L the inductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Step 6, this oscillation, L -&gt; cap -&gt; L -&gt; Cap -&gt; L carries on slowly reducing in size as power is lost due to the resistance of L the inductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Step 7, This is 'kicking' a tuned circuit (L and C2) causing it to oscillate. As others have mentioned the frequency of oscillation depends upon the value of L and C2. How long the oscillation lasts for before it decays to zero volts, depends mainly upon the value of the resistance of L the inductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Step 8, Once amplifiers became available, it could be arranged for a small pulse to be sent to the L and the C, to keep it oscillating.&lt;/p&gt;&#xA;" OwnerUserId="11708" LastActivityDate="2018-06-03T16:12:32.263" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10386" PostTypeId="1" AcceptedAnswerId="10390" CreationDate="2018-06-04T17:22:55.030" Score="6" ViewCount="275" Body="&lt;p&gt;I don't quite understand the regional callsign system for the USA. At first it seems to make sense with CT, MA, ME, NH, RI, and VT being region 1 and then going west NJ and NY are region 2, and then DC, DE, MD, PA for region 3.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But why does it end with California Region 6? And why are IL, IN, and WI    region 9? They're in the mid-west!!!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A rational system would have California / Hawaii being region 9 or region 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What was the historical reason for regions 6 and 7-9 being so oddball?&lt;/p&gt;&#xA;" OwnerUserId="11462" LastEditorUserId="11462" LastEditDate="2018-06-06T02:42:22.810" LastActivityDate="2018-06-06T02:42:22.810" Title="USA/callsigns: Why is California region 6? And the midwest in regions 7-9?" Tags="&lt;united-states&gt;&lt;callsign&gt;&lt;history&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10388" PostTypeId="2" ParentId="10324" CreationDate="2018-06-04T19:01:23.897" Score="2" Body="&lt;p&gt;There's a decent summary &lt;a href=&quot;https://blog.hamstudy.org/2018/01/first-look-at-the-2018-element-2-technician-class-question-pool/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-06-04T19:01:23.897" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10389" PostTypeId="2" ParentId="7100" CreationDate="2018-06-05T07:46:03.817" Score="1" Body="&lt;p&gt;&lt;strong&gt;TL&amp;amp;DR&lt;/strong&gt; It seems that your only option is to obtain an Amateur Radio license for all those who need to use the Baoffeng hand sets. The sets do not qualify, or is unlikely to qualify, for any license exempts nor for business radio use.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;Disclaimer&lt;/strong&gt;: I am not a lawyer, and although I am quoting legislation, for legal advice please seek advice from a lawyer in your country.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My Question being is it legal for me to use these radios without a&#xA;  suitable licence?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, is the answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sorry to &quot;bust the bubble&quot; but unless you get an Amateur Radio license you may not use these sets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may NOT use them on PMR/446-MHz, as they are not typed approved. &lt;a href=&quot;http://www.legislation.gov.uk/uksi/2003/74/contents/made&quot; rel=&quot;nofollow noreferrer&quot;&gt;Legislation here&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;SCHEDULE 7&#xA;    PART II&#xA;        2.  Prescribed apparatus taken into service before 1st May 2000 must also—&#xA;&#xA;            (a)be approved by the Secretary of State under section 84 of the 1984 Act for the purposes of these Regulations; or&#xA;            (b)be approved to the standard referred to in Part IV of this Schedule by a national administration following type testing at a test laboratory&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The correct answer (already given, and I can only repeat this) is to get an Amateur Radio license for all those who want to participate.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;would it be possible for me to obtain a Simple Business licence within&#xA;  the UK without being a registered company?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I believe you can get a Simple Business license, you just need to apply. If you can use the Baoffengs?... that need to be seen, but my best guess here is: No, as &lt;a href=&quot;http://www.legislation.gov.uk/uksi/2010/1823/made/data.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;the legislation&lt;/a&gt; is hinting to being licensed to particular equipment, or equipment with specific specifications (which I am doubtful the Baoffeng would be classified):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Requirements that must be met for the grant of a licence&#xA;5.—(1) Licences shall be granted by OFCOM, either—&#xA;    (a) in relation to particular equipment; or&#xA;    (b) in relation to any equipment falling within the description specified in the licence and expressed by reference to such factors (including factors confined to the manner in which it is established, installed or used), as are described in the licence.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2018-06-05T07:46:03.817" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10390" PostTypeId="2" ParentId="10386" CreationDate="2018-06-05T10:04:13.170" Score="9" Body="&lt;p&gt;The origins of the amateur radio call sign districts can be traced to 1912 when the Department of Commerce, Bureau of Navigation created nine radio inspection districts to enforce the 1912 &lt;em&gt;Act to Regulate Radio Commerce&lt;/em&gt;. Primary foci of the act were to regulate ship to ship and ship to shore radios including those used on the Great Lakes. As a result, all nine offices where located at port cities where the inspections would be concentrated. They were:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Boston, MA&lt;/li&gt;&#xA;&lt;li&gt;New York, NY&lt;/li&gt;&#xA;&lt;li&gt;Baltimore, MD&lt;/li&gt;&#xA;&lt;li&gt;Savannah, GA&lt;/li&gt;&#xA;&lt;li&gt;New Orleans, LA&lt;/li&gt;&#xA;&lt;li&gt;San Fransisco, CA&lt;/li&gt;&#xA;&lt;li&gt;Seattle, WA&lt;/li&gt;&#xA;&lt;li&gt;Cleveland, OH and then later Detroit, MI&lt;/li&gt;&#xA;&lt;li&gt;Chicago, IL&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Take note that there were only nine districts defined at that time. It is also noteworthy that the first seven numbered offices were located at ocean port cities while Cleveland/Detroit and Chicago are Great Lake ports. If you look at the numbering, you can see the ocean port districts were numbered starting in the east with Boston as 1 and moving around the map in a clockwise fashion to the west ending with Seattle as 7. Then the two non-ocean, Great Lake port locations were assigned the remaining two numbers in an east to west fashion as well. This is not a documented methodology but it is my analysis as to the apparent logic of the numbering scheme.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On July 1, 1928 Alabama was transferred from the 5th district to the 4th district. Over time, other states were moved between districts and some that were originally split between districts were resolved to their present day districts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The current form of the Amateur Radio call signs came to be in 1928 as a result of the International Radio Convention of 1927. While the provisions of the convention did not come into force until January 1, 1929, the Radio Division of the Department of Commerce announced that it wished to publish the &quot;new&quot; style of amateur radio call signs in June of 1928. The 1927 convention assigned the W and K prefixes to the US for use for amateur radio call signs (N was also available but the Navy used this at the time). The June 1927 edict was that all amateur radio stations in the continental United States add a W prefix to their call while those in Alaska, Hawaii, Porto Rico, and the US Virgin Islands should add a K prefix to their call. Thus a station with a call of 4ABC would immediately become W4ABC if it was on the continental United States.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In 1945-46, it was determined that the 9th District served too large of an area so Missouri, Kansas, Colorado, Iowa,  Nebraska, South Dakota, and North Dakota would be grouped under a new tenth district. For purposes of call signs, this district was designated as 0.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-05T15:20:33.837" LastActivityDate="2018-06-05T15:20:33.837" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="10391" PostTypeId="1" CreationDate="2018-06-05T15:09:37.700" Score="5" ViewCount="478" Body="&lt;p&gt;The Secretary of our club passed away unexpectedly last week.  With Field Day rapidly approaching in the U.S., the board is wondering if there is any legitimate way for the club to use the deceased member's call sign for Field Day operations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can get permission from his only surviving relative but I don't know if that is satisfactory.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can a club use the call sign of a very recently deceased member for Field Day operations?&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="8832" LastEditDate="2018-06-21T16:46:40.420" LastActivityDate="2018-06-21T16:46:40.420" Title="Using a Deceased Club Member's Call Sign for Field Day" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;callsign&gt;" AnswerCount="2" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="10392" PostTypeId="2" ParentId="10391" CreationDate="2018-06-05T15:35:37.820" Score="4" Body="&lt;p&gt;I am sorry for your loss and I can appreciate your desire to honor him or her in such a way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, such designated control operator use of a call is not permitted. 97.103 (b) states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The station licensee must designate the station control operator...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is not possible posthumously and probably wouldn't be allowed even if granted &lt;em&gt;ante mortem&lt;/em&gt; in written form.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your club could go through the process of obtaining the call for your club station or a licensed relative could obtain the call and allow you to use it but I doubt either could happen in time for this year's Field Day. The FCC process involves manual inspection of documents which will likely sideline the application for too long of a period for you to obtain a grant by June 23rd.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are an ARRL member or your club is an ARRL affiliate, you may want to call the ARRL VEC desk and ask what their recent experience is with the processing time for club or near relative honorarium call requests. This will help you judge if it is even a possibility.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-05T16:16:33.470" LastActivityDate="2018-06-05T16:16:33.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10394" PostTypeId="2" ParentId="10391" CreationDate="2018-06-05T17:27:34.580" Score="4" Body="&lt;p&gt;I too am sorry for your loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I presume that your club would like to obtain your deceased member's call sign as a &quot;vanity&quot; (not sequentially issued) call sign for the club.  The procedure is to first notify the FCC that your member has passed away, and request that the license be canceled.  The ARRL has a &lt;a href=&quot;http://www.arrl.org/cancelling-a-license&quot; rel=&quot;nofollow noreferrer&quot;&gt;web page&lt;/a&gt; that summarizes how to do so; you'll need some sort of proof, such as a copy of an obituary printed in the newspaper, or a copy of the death certificate.  The request can be submitted online, by fax, or by mail.  That web page says that the FCC typically take one to two weeks to cancel the license.  You can discover whether the license has been canceled by checking the FCC ULS database online.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once the license has been canceled, your club may submit a &quot;vanity&quot; call sign application request to the FCC.  A club call signs is assigned to a trustee, that is a person who is responsible for the club's use of that call sign.  A club can have any number of call signs, but for new applications, a person is only allowed to be a trustee for a single club call sign.  In other words, the person listed on the application as the potential trustee must not already be the trustee of a club call sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The vanity call sign request can be submitted online.  The FCC's web site has &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/amateur-radio-service&quot; rel=&quot;nofollow noreferrer&quot;&gt;instructions&lt;/a&gt;.  The proposed trustee will need to have a high-enough license class for the call sign; in other words, if the call sign is a 1x2, then the proposed trustee will need an Amateur-Extra-class license.  The license application can be submitted online; the proposed trustee will need an FRN (FCC registration number).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The license application should specify the &quot;in memoriam&quot; provision, which indicates that the request is for the club to assume the call sign of the former member.  If the application doesn't include that provision, then the request will be rejected.  It would be a good idea for the club to get written permission from the surviving relative.  The proof doesn't need to be submitted with the application, but it should be kept on file in case the application is disputed.  (People have tried to abuse the vanity call sign system, skipping the usual two-year wait, by fraudulently obtaining call signs with the &quot;in memoriam&quot; provision before.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To process vanity call sign applications, the FCC first wait 17 calendar days.  Then, on the morning after the first federal work day thereafter, the FCC process the applications received on that day.  (&lt;a href=&quot;http://www.ae7q.com/query/text/Vanity.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Source&lt;/a&gt;)  Once the FCC's online database shows that the club call has been transferred, then you may use it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Field Day this year is on the 23rd and 24th of June, 18 days from now.  Unfortunately there won't be enough time for your club to get the call sign canceled and the vanity application processed before Field Day.  You might as well get the ball rolling though, so that you can use the call sign for next year's Field Day!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-06-05T17:27:34.580" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10397" PostTypeId="1" CreationDate="2018-06-06T18:21:18.107" Score="3" ViewCount="667" Body="&lt;p&gt;Last year, a group of us placed a battery-powered 2m digipeater using a J-pole antenna on a mountaintop. We're planning on doing the same this year except we plan to &lt;a href=&quot;https://ham.stackexchange.com/questions/9139/kenwood-th-d72-freeze-on-splash-screen&quot;&gt;use a surge arrestor from the feed line ground to the metal railing&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iOTum.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iOTum.jpg&quot; alt=&quot;Rig and railing&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is a J-pole an appropriate antenna for this situation? Would you recommend a different type of antenna considering we have a ground available to us in the form of the metal railing?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna assembly in the picture is two fiberglass pull-rods screwed together with a short feed line and a 2m roll-up J-pole antenna. The performance of the setup pictured was fine--other digipeaters, up to 193 miles away, heard this station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some requirements are:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Collapsable for carrying in a backpack&lt;/li&gt;&#xA;&lt;li&gt;Omnidirectional&lt;/li&gt;&#xA;&lt;li&gt;No horizontal elements that other visitors can trip over or poke themselves on&lt;/li&gt;&#xA;&lt;li&gt;Somewhat visually unobtrusive. The antenna above has fishing line guy-wires&lt;/li&gt;&#xA;&lt;li&gt;Taller than the railing&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Here's a &lt;a href=&quot;http://360panos.com/panos/SummitSaddleMountain.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;panorama&lt;/a&gt; taken by someone else of the summit. The railing is over 50ft long in roughly a U shape. The top is rocky dirt. The posts are set in cement forms and are immovable.&lt;/p&gt;&#xA;" OwnerUserId="5820" LastEditorUserId="5820" LastEditDate="2018-06-06T22:03:21.927" LastActivityDate="2018-06-06T22:03:21.927" Title="Is a J-pole an appropriate antenna for mounting to a steel handrail?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;vhf&gt;&lt;grounding&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="10398" PostTypeId="2" ParentId="10397" CreationDate="2018-06-06T20:05:35.090" Score="4" Body="&lt;p&gt;I have several years of experience operating in the high Alps in Switzerland as well as the lower range mountains in der Pfalzer Wald and der Schwartzwald (the Black Forest) in Germany on UHF, VHF, and HF. For omni UHF and VHF, I would highly recommend a simple quarter wave groundplane that is easily broken down into a backpack. I could find no signal advantage to various forms of J pole antennas. I believe common mode current issues offset any potential marginal gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My best quarter wave, omni antenna included four ground plane (counterpoise) rods that screwed into an SO-239 like base that was threaded to receive the four elements. A downward pitch of 30 to 45 degrees achieved a nearly perfect 50 ohm resonant (non reactive) match. The pitch of the elements also made the antenna self supporting on stumps and even large rocks worked well. The antenna assembled and disassembled in less than a minute and easily fit in my backpack. If the hike was shorter, I would include a 3.5 meter collapsible painter's pole that I could post into the ground or lash to railings or benches at outlooks, towers, castles, etc. I even set one up inside the glass visitor center at the Jungfraujoch. I have lashed it to railings several times at the famous location for the filming of the James Bond episode &lt;em&gt;On Her Majesty's Secret Service&lt;/em&gt; on Piz Gloria at the spot where the female sleeper agents were curling and where the helicopters hovered to defeat Ernst Stavro Blofeld aka Comte Balthazar de Bleuchamp (Telly Savalas). For some reason, despite my best efforts, I could  get no better than '007' signal reports from there...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are up to carrying a small, easily broken down yagi, this is the best solution as often you can predict the favorable direction for signals making the 6 to 9 dBi gain worth the extra effort.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are into satellite contacts, high mountain ranges can greatly extend the AOS  (acquisition of signal) to LOS (loss of signal) time if you are on the peak or the right face. This also often allows better contacts with a well constructed quarter wave due to the lower percent of ground clutter in the overall path or, alternatively, the reduced path loss. Know your grid location as these are often sought after areas for chasers. It seems that you can gain a couple of S units of quieting simply based on your grid square regardless of your antenna prowess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And don't overlook self spotting when mountain topping. Most hams are happy for the heads up in order to log a rare one.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-06-06T20:05:35.090" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10401" PostTypeId="1" CreationDate="2018-06-08T00:26:26.800" Score="7" ViewCount="989" Body="&lt;p&gt;I am very new to general RF/radio in general other than basic WiFi, but I'm looking at the feasibility and cost of a long range (&gt;200M between nodes, sometimes probably 500+M) in flat terrain, relatively low power (solar + 12V SLA, short term usage) and &lt;em&gt;probably&lt;/em&gt; fairly low bandwidth needs (couple of hundred Kbps?), but bi-directional/fully shared. So in starting doing some searches/research, I came across this SX1276 based module (&lt;a href=&quot;https://www.adafruit.com/product/3072&quot; rel=&quot;noreferrer&quot;&gt;https://www.adafruit.com/product/3072&lt;/a&gt;) that's relatively cheap, even if I need it for a few dozen or more nodes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My concept is to use a fixed mesh, or star mesh topology as the distance between a centrally located node and the furthest away may be as much as 2+ km, possibly 3+. That's long term planning, my first attempt would likely be a handful of nodes perhaps 400-600m from a central point. The advantage of this area is flat as a pancake, although lots of varying height temporary structures, although the antennas would not be placed very high, 6-10 feet off the ground so they may or may not have perfectly clear line of sight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on my reading of LoRaWan, it's really designed to be a central star network topology without much bi-directional communication, in general. And LoRa could, in theory, perhaps, do a mesh network but it'd need a non-trivial amount of software layered on top of the transceiver access code. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did come across &lt;a href=&quot;https://ieeexplore.ieee.org/document/8048465/&quot; rel=&quot;noreferrer&quot;&gt;https://ieeexplore.ieee.org/document/8048465/&lt;/a&gt; which is very interesting. In my naive reading of it, it implies that if you simply immediately re-transmit each packet once received (and ignore it once you've re-transmitted it) you essentially can flood a mesh network of LoRa devices reasonably efficiently despite collisions and such. I did see there's more to it than that with seeing to do offset concurrent transmission and other bits that I didn't get to. If that concept actually works reasonably well, it shouldn't be too difficult, in theory, to put a basic layer on top of a LoRa transceiver to spread data through a mesh (that doesn't actually know about each other really) in an easy to implement fashion which spans several square kilometers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So...disabuse me of this and show me how naive and unknowing I am and I should tuck my tail between my legs and run away :)&lt;/p&gt;&#xA;" OwnerUserId="11729" LastEditorUserId="9493" LastEditDate="2018-06-15T07:10:07.637" LastActivityDate="2019-12-26T14:01:06.903" Title="LoRa radio transceiver for PtP mesh?" Tags="&lt;diy&gt;&lt;packet&gt;&lt;mesh-network&gt;" AnswerCount="4" CommentCount="6" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10402" PostTypeId="1" CreationDate="2018-06-08T06:34:26.590" Score="2" ViewCount="1005" Body="&lt;p&gt;I'm interested if it is possible to have a data radio modem that works on the UHF band 400MHz for TCP/IP communication. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I have in mind is something similar to a router, but using UHF band for more range. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem that I come across is that there are so many serial RS232 based data radio modems, but they don't have Ethernet and they operate very slowly. These are common. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it that hams are just not keeping up with the technology or is it not possible to modulate a UHF signal to get a few hundred Kbps? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why not take the technology and modulation schemes used in 3G or 4G cellular networks and apply the same compression/modulation and whatever else into a radio modem that will operate much faster at 400MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;3G and 4G networks are extremely fast and 400MHz is only about half the frequency of them, so I'm thinking in theory, you could probably still get some pretty reasonable speed at these frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any devices out there like this that are not thousands of dollars? Could one be built by an amateur using say a raspberry PI and some type of RF module? Maybe a software defined radio like hack RF?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any legal regulations that talk specifically to this?&lt;/p&gt;&#xA;" OwnerUserId="1817" LastEditorUserId="8832" LastEditDate="2018-06-21T02:43:09.217" LastActivityDate="2018-06-21T02:43:09.217" Title="Fast TCP/IP radio modem on UHF band" Tags="&lt;software-defined-radio&gt;&lt;legal&gt;&lt;digital-modes&gt;&lt;hackrf&gt;&lt;modem&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10403" PostTypeId="2" ParentId="10402" CreationDate="2018-06-08T08:04:02.670" Score="1" Body="&lt;p&gt;I know there's actually people working on a system for that band. It'll be SDR-based.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's no technical restriction that says you can't have a couple hundred kilobits per second in a couple hundred kilohertz. It might just be the case that for commercial bands, the available bandwidth isn't attractive and regulatory restrictions make it unfeasible to implement a high-rate system. Since different regulations apply to Ham radio, this is solvable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Glenn, however, raises an important point: In some regions, you simply cannot legally transport high data rates. That's kind of a stupid legislation, but it's how it is. In Europe, as far as I know, usage of this band is subject to bandwidth, but not data rate restrictions.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-06-08T08:48:06.753" LastActivityDate="2018-06-08T08:48:06.753" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10404" PostTypeId="2" ParentId="10402" CreationDate="2018-06-08T08:28:27.310" Score="7" Body="&lt;p&gt;As you might suspect, the data rate impacts the required RF bandwidth. Besides the data rate, the modulation method, encoding, packet overhead, duplexing, and other factors ultimately determine the required RF bandwidth. As an example, the 4G network has a data speed of ~20 Mbps and consumes a bandwidth from to 5 to 20 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the United States, the 70 cm allocation extends from 420 MHz to 450 MHz in ITU region 2 for a total of 30 MHz of bandwidth. For US regions in ITU 1 or 3, this drops to 430 MHz to 440 MHz. In the US, hams on this band may not cause interference to radiolocation services (e.g. PAVE PAWS) that overlap this allocation. This would suggest that the technique would require a guard receiver and be adaptive to lock out bandwidth segments. The 420-430 MHz segment is also allocated on a primary basis to other services and not even available to hams north of &quot;Line A&quot;. But the most significant limitation for data in this band is spelled out in 97.307(f)6:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A RTTY, data or multiplexed emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must not exceed 56 kilobauds. A RTTY, data or multiplexed emission using an unspecified digital code under the limitations listed in §97.309(b) of this part also may be transmitted. The authorized bandwidth is 100 kHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, at least in the US, there is insufficient permitted data rate to support your request. Since the US is the largest ham radio market, manufacturers may not have a large enough remaining market to support the development of such equipment even if other regions of the world have sufficient bandwidth allocated to the ham community.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the US, the the data rate and bandwidth limits are lifted beginning with the 33 cm band (902-928 MHz in ITU 2 only). This band is granted as a secondary allocation and hams must also accept interference from industrial, scientific, and medical (ISM) equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the 13 cm and 9 cm bands, US hams have been very successful re-purposing equipment designed for consumer WiFi applications to the frequencies allocated to hams in the US on a primary basis where more power and higher gain antennas are permitted. See &lt;a href=&quot;http://www.broadband-hamnet.org/&quot; rel=&quot;noreferrer&quot;&gt;Hamnet&lt;/a&gt; as an example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, consider that for hams in the US, the TCP/IP traffic cannot contain encrypted or obscured information. This includes all encryption uses of TLS such as HTTPS and WSS type protocols. There is a limited encryption exemption for space telecommand purposes.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-06-08T08:28:27.310" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10405" PostTypeId="1" CreationDate="2018-06-08T19:10:21.253" Score="1" ViewCount="123" Body="&lt;p&gt;I got some RF equipment for free (it was going to the trash and I 'rescued' it). It's almost new, and seems expensive, but i don't know it's purpose. Googling the model numbers yields very little information :(&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The equipment in question:&#xA;&lt;a href=&quot;https://imgur.com/a/AEIoKwz&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://imgur.com/a/AEIoKwz&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;img src=&quot;https://i.imgur.com/iEqkice.jpg&quot; &gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;img src=&quot;https://i.imgur.com/hdBb7RL.jpg&quot; &gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;img src=&quot;https://i.imgur.com/27iN40h.jpg&quot; &gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;img src=&quot;https://i.imgur.com/KijHqFS.jpg&quot; &gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;img src=&quot;https://i.imgur.com/ufNIRJm.jpg&quot; &gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="11736" LastEditorUserId="4076" LastEditDate="2018-06-09T12:13:34.590" LastActivityDate="2018-06-09T13:07:46.500" Title="I just got this RF equipment but i don't know what's for" Tags="&lt;electronics&gt;&lt;amplifier&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10407" PostTypeId="2" ParentId="10405" CreationDate="2018-06-09T01:01:42.170" Score="0" Body="&lt;p&gt;This is a guess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looks like satellite reception stuff.  Hook a few dishes on one side and then hook a few different receivers on the other side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looks like some of the outputs for the receivers are bandpass filtered.  Looks like some of the outputs have different line levels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could imagine one or more satellite dishes could feed several receivers, each receiver listening to multiple channels.&lt;/p&gt;&#xA;" OwnerUserId="11739" LastActivityDate="2018-06-09T01:01:42.170" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10408" PostTypeId="2" ParentId="10260" CreationDate="2018-06-09T01:14:08.673" Score="3" Body="&lt;p&gt;Perhaps try local resources and active websites.  Sometimes a large, vibrant community is better than mediocre standards.&lt;/p&gt;&#xA;&lt;h1&gt;Morse Codes for Computer Access&lt;/h1&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.makoa.org/jlubin/morsecode.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.makoa.org/jlubin/morsecode.htm&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;...&lt;/p&gt;&#xA;&lt;p&gt;I have codes defined in two &amp;quot;groups&amp;quot; and use a code to switch between them. This enables me to reuse the same codes for different functions in different groups. A third code group contains codes that are always active, such as commands to switch between the other code groups.&lt;/p&gt;&#xA;&lt;p&gt;Modifier keys (Shift, Control &amp;amp; Alt) release after the next code for a non-modifier key is sent. If a modifier key is needed to remain active for multiple keys then the hold/release code can be used to keep it active until the hold/release code is sent again.&lt;/p&gt;&#xA;&lt;p&gt;To move the mouse pointer, send the code once for the direction (up/down/right/left) then the repeat code (a single sip). The mouse continues to move in that direction until either a single sip or puff will stop it. The standard mouse move is set to move 4 mickeys. When I need to be more precise I send the &amp;quot;mouse zoom&amp;quot; code which changes the mouse moves to 1 mickey.&lt;/p&gt;&#xA;&lt;p&gt;A &amp;quot; &lt;strong&gt;·&lt;/strong&gt; &amp;quot; is a sip and a &amp;quot; &lt;strong&gt;-&lt;/strong&gt; &amp;quot; is a puff.&lt;/p&gt;&#xA;&lt;h1&gt;Alpha-Numeric Code Group&lt;/h1&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WD0eK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WD0eK.png&quot; alt=&quot;Alphabet, numbers, and control keys assigned dots and dashes&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;h1&gt;Mouse/Windows Code Group&lt;/h1&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TJ8O2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TJ8O2.png&quot; alt=&quot;Keyboard combinations, cursor movement keys, and mouse movements assigned dots and dashes&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The above website had links to other resources as well.  The above seems to be an article &lt;a href=&quot;https://at-eadl.blogspot.com/2018/04/morse-codes-for-computer-access.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;&amp;quot;Morse Codes for Computer Access&amp;quot; in &lt;em&gt;Assistive Technology and Electronic Aids for Daily Living&lt;/em&gt;&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="11739" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-06-14T10:50:13.720" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10409" PostTypeId="2" ParentId="10405" CreationDate="2018-06-09T02:24:23.277" Score="0" Body="&lt;p&gt;It looks like gear for distributing TV signals (satellite and otherwise, so it ranges from VHF up to microwave) around a building. Maybe some of it could be useful as coax switches or duplexers for amateur use, perhaps in a repeater site. Or put it all up for auction online and see what it fetches and what cool gear you can get with the result.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2018-06-09T02:24:23.277" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10410" PostTypeId="1" AcceptedAnswerId="10412" CreationDate="2018-06-09T04:48:58.297" Score="1" ViewCount="995" Body="&lt;p&gt;I'm trying to do impedance matching between my PCB antenna and my circuit. My PCB antenna has a measured impedance of 49.4 - j8.1 ohms. The operating frequency is 915 MHz. The goal of matching is to move the circuit impedance as close to 50 ohm as possible.&lt;/p&gt;&#xA;&lt;p&gt;The designed matching network is Pi-type as attached &lt;a href=&quot;https://i.stack.imgur.com/FasWH.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FasWH.jpg&quot; alt=&quot;here&quot; /&gt;&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;My process is as follows and it follows the instruction here: (&lt;a href=&quot;http://wisp.wikispaces.com/WISP+Measurement+Procedures?responseToken=016c891618c82df3ef37a9c2b69cf236&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://wisp.wikispaces.com/WISP+Measurement+Procedures?responseToken=016c891618c82df3ef37a9c2b69cf236&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Step 1:&lt;/strong&gt; Shorten Lm1 by a small wire (perhaps it's inductance is 2 nH?). Leave other components blank.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Step 2:&lt;/strong&gt; Measure the input impedance of the circuit afterwards by a Network Analyzer. It gave 0.355 + j42 Ohm.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Step 3:&lt;/strong&gt; Use that value as the load impedance to find an appropriate network topology by using Smith V4.0, a free software. I've tried this topology&#xA;&lt;a href=&quot;https://i.stack.imgur.com/IhOvj.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IhOvj.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;So Lm1 was replaced by a resistor of 50 Ohm, while Cm2 was replaced by an inductor of 23.5 pH. No Cm1.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Step 4:&lt;/strong&gt; Start to replace the components as designed in Step 3. Firstly add Cm2, then add Lm1. Do Step 2 after replacing any component (for example, measure the input impedance again after replacing Lm1).&lt;/p&gt;&#xA;&lt;p&gt;All measurements were performed as 1-port measurement on VNA (Vector Network Analyzer).&lt;/p&gt;&#xA;&lt;p&gt;There are two problems:&lt;/p&gt;&#xA;&lt;p&gt;1/ Step 4 problem: Anytime I replaced any component, the measured input impedance was totally different than it should be by being simulated in Smith V4.0. For example, if I add a shunt capacitor of 2 pF, the measured Zin was not be 1.3 + j81.2 Ohm as found by using Smith V4.0 software. I did not record the result so I do not remember the exact result, but I can say that it was totally different both in values and the direction that the impedance should move. I'll get back this situation with numerical values.&lt;/p&gt;&#xA;&lt;p&gt;2/ Matching performance: Even I finally got the measured Zin ~ 50 Ohm, not by designing in software but by replacing and guessing and replacing again the components, the delivered power after matching was lower than before matching! In theory, the power must be higher because less power mismatch!&lt;/p&gt;&#xA;&lt;p&gt;My friend got the same 2nd problem when he tried to match his transducer. The signal he got after matching was more noisy than before.&lt;/p&gt;&#xA;&lt;p&gt;Could anyone help me explain these things? Any suggestion/comment is highly appreciated. Thank you for your time.&lt;/p&gt;&#xA;&lt;p&gt;------- Updated for response for Mr. Glenn W9IQ-------------------------------&lt;/p&gt;&#xA;&lt;p&gt;Thank you so much for your comments and your kind explanation @Glenn W91Q. I'll keep in my mind the correct terms. Let me explain more about my measurement set up.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;1/ Calibration of the test cable&lt;/strong&gt;:&#xA;I used a SHORT-OPEN-LOAD adapter and a coaxial cable (Pic 1). The cable is terminated by a kind of SMA adapter (I don't know how to name it). I need that adapter to connect my antenna/circuit to the cable. So, I attached the SHORT-OPEN-LOAD adapter to the cable through that adapter for calibration. So, it means I calibrate both the cable and that adapter. Am I correct?&#xA;I followed the calibration procedure of this video &lt;a href=&quot;https://www.youtube.com/watch?v=GKHHy61qRak&amp;amp;t=18s&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=GKHHy61qRak&amp;amp;t=18s&lt;/a&gt;. But I chose 1 port calibration instead. I used Agilent E5062A VNA model.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GAWyb.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GAWyb.jpg&quot; alt=&quot;Píc&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;2/Set up for antenna input impedance measurement&lt;/strong&gt;:&#xA;I connected my dipole antenna to the cable as follows. The SMA connector attached to the antenna is used to connect the antenna to the circuit. The antenna will be a receiving one, not a transmitting one. It was designed using HFSS tool kit. The simulated reflection coefficient is -22 dBm @912 MHz.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xtlag.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xtlag.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;By using S11 measurement mode, Smith Chart display tool of the VNA, I found the impedance of (antenna + SMA connector). It must be INPUT impedance, right?&lt;/p&gt;&#xA;&lt;p&gt;To get the impedance of as close to 50 ohms as possible, the antenna was tuned by cutting its length. I also added a matching circuit (plz see below). The final impedance I got, using this set up, was 49.4-j8.1 ohms.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vcZ2m.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vcZ2m.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;3/Set up for receiver input impedance measurement&lt;/strong&gt;:&#xA;The same set up as above was applied for this.&lt;/p&gt;&#xA;&lt;p&gt;Can I ask you for more clarifications?&lt;/p&gt;&#xA;&lt;p&gt;1/ I thought my measurement set up as illustrated above was wrong, because I did not connect the antenna/receiver ground to the shield of the VNA cable as you mentioned earlier. And I still cannot imagine how to do this. If you've got some images for this, I'd highly appreciated it if you can share some.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The VNA must &lt;strong&gt;have two connections&lt;/strong&gt; to the antenna under test. This perhaps is basic but I have seen students completely ignore the ground (shield) connection to the VNA cable or they simply connect it to any convenient ground point on the circuit, treating it like a basic DC ground.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;2/ The impedance I got from the set up of measuring input impedance of the receiver was far from 50 ohms. So, I need another matching circuit to move it close to 50 ohms, right?&lt;/p&gt;&#xA;&lt;p&gt;Thank you again for your time.&lt;/p&gt;&#xA;" OwnerUserId="11740" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2020-04-18T00:08:35.630" Title="Impedance matching between antenna and load - Theory and Practice?" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10411" PostTypeId="1" AcceptedAnswerId="10414" CreationDate="2018-06-09T06:38:37.190" Score="0" ViewCount="1992" Body="&lt;p&gt;As illustrated in my previous post, I got stuck with the matching circuit between an receiving antenna and my circuit, including a rectifier and sensory circuits. I got confused with input and output impedance of antenna and of the circuit. Please correct me if I'm wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1/ The goal of matching is to match antenna INPUT impedance to INPUT impedance of the circuit?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2/ Receiving antenna INPUT impedance: &#xA;- The impedance seen from the circuit? &#xA;- In practice it is captured by measuring S11, Smith Chart at 1 port by Vector Network Analyzer? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;3/ Circuit INPUT impedance:&#xA;- The impedance seen from the antenna?&#xA;- In practice it is captured by measuring S11, Smith Chart at 1 port by Vector Network Analyzer?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm sorry if my questions look so silly. But I think maybe somebody get confused like me. So, if you have any idea, please comment. Thank you very much.&lt;/p&gt;&#xA;" OwnerUserId="11740" LastEditorUserId="11740" LastEditDate="2018-06-09T06:51:24.660" LastActivityDate="2020-07-26T21:18:58.150" Title="Input and output impedance of antenna/circuit: theory and measurement methods?" Tags="&lt;antenna&gt;&lt;measurement&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10412" PostTypeId="2" ParentId="10410" CreationDate="2018-06-09T10:10:18.960" Score="2" Body="&lt;p&gt;Please take the following commentary not as a hollow or haughty criticism but rather to help your technical learning and to help you to communicate more effectively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When communicating in a technical field, it is important to be as concise and as accurate as possible. While corrections can be inferred in some cases, this is not optimal. In a half duplex forum such as this, it also helps you to get the answer you desire in the most expedient fashion. There are a few things in your question, in addition to my comment to your question, that don't seem to be correct:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;perhaps it's impedance is 2 nH&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;An impedance is given in ohms. 2 nH is short for 2 nanohenries, a unit of inductance. You probably mean to say &quot;perhaps it is an inductance of 2 nH&quot;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Lm1 = 50 Ohm&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The schematic designation of Lm1 indicates that this component is an inductor. The 50 ohms indicates an impedance. Normally this equality should be set to a component value (e.g. Lm1 = 2 nH) unless it is a statement or equation giving the impedance of Lm1 (e.g. the impedance of Lm1 at 915 MHz is 11.5 ohms). This is a case where your statement is ambiguous.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;if I add a shunt capacitor of 2pH&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The Farad (F) is the base unit of measure for a capacitor. The base unit of measure for an inductor is Henry (H). This is again an ambiguous statement.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For example, if I add a shunt capacitor of 2pH, the measured Zin will not be (1.3 + j*81.2) Ohm. The result I got is totally different. I don't know why.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There is no analysis of this possible without you giving the measurement you observed. &quot;Totally different&quot; is not a quantification.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the measured Zin will not be (1.3 + j*81.2) Ohm&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This one is minor but the complex impedance you referenced (and all other such impedance references) should be written in the form of 1.3+j81.2. Notice there are no parenthesis or asterisk (*) in the nomenclature. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Measurement Technique&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When working at these high frequencies, correct measurement technique is essential.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The VNA must be correctly calibrated at the frequency of measurement and using the test cables and connectors that will be used for the measurements. This typically consists of an iterative technique of sequentially placing shorted, open, and resistive loads at the end of the measurement cable following the prompts of the VNA calibration procedure. This has the effect of removing the transmission line effects of the test cable and its connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna under test must be oriented as it would be used in the application. All test equipment, test benches, fixtures, cables, connectors, etc. must not be placed in close proximity to the antenna as these will couple to the antenna and affect the results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The length and orientation of traces on the PCB that connect the VNA cable to the antenna can alter the measured antenna impedance. For example, at 915 MHz, a wire or PCB trace length length of more than 20 mm can have significant implications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The VNA must have two connections to the antenna under test. This perhaps is basic but I have seen students completely ignore the ground (shield) connection to the VNA cable or they simply connect it to any convenient ground point on the circuit, treating it like a basic DC ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Interpreting the Measurements&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My PCB antenna has a measured impedance of (49.4 - j*8.1) ohm&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you have an antenna with an impedance of 49.4-j8.1 ohms and your transmitter has an output impedance of 50 ohms, there is no point in attempting to get a better match. Any losses that may occur as a result of this slight mismatch are decimal dust. A matching circuit would likely introduce more losses than it would remove.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Measure the input impedance of the circuit afterwards by a Network Analyzer. It gave (0.355 + j*42) Ohm&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you have an antenna system with an impedance of 0.355+j42 ohms and the goal is a 50 ohm antenna system, you have a serious problem that needs correcting. Either the measurement is wrong or your antenna system is improperly designed/constructed. If the antenna (without the matching network) has this impedance, then the realized antenna design is incorrect. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Except in the most dire of circumstances, the antenna impedance should have a resistive component (the part before the +/- j) of at least a few ohms. Anything less than this tends to make the matching circuit have more loss and it makes the antenna itself less efficient. In general, transmit power is turned to heat instead of radiated as intended in this case.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Even I finally got the measured Zin ~ 50 Ohm, not by designing in software but by replacing and guessing and replacing again the components, the delivered power after matching was lower than before matching!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This conclusion is difficult to resolve given all of the above mentioned issues. It would be helpful if you stated what components you finally selected and in what configuration you placed them. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your measurement technique is not correct, you may not have a 50 ohm input impedance to your antenna system. Alternatively, you may not be correctly measuring the transmit power in both cases. Some explanation of the equipment and technique used for this measurement would be helpful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Better Answer&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Edit: This section has been revised based on the additional information provided by the OP]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you for posting the pictures and additional commentary. Your situation is now much clearer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The calibration fixture that you used for the VNA is fine. Well done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The connection to the antenna is fine. The connector will take care of completing the shield (ground) connection to one side of your dipole and the center connection to the other side of the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Make certain that when you are testing the dipole, that it is away from other objects and that the test cable is routed at a right angle to the antenna for at least two antenna lengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trimming the dipole as you described is a good way to tune it. Well done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding the measurement of the input impedance of your receiver. The design is unique in that the diode circuits will make the input impedance non-linear when compared to input power. Most calculations for matching networks assume a linear response for a given frequency. Thus your approach to try different values until the input impedance matches ~50 ohms may be valid but as the input power level varies, the results may vary as well. You may find better results if you reduce the power level of the VNA to more closely match that which is expected from the actual WISP signal. From this, you can either better calculate the matching values or better validate your 'cut and try' values.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xnCIE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xnCIE.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should also check that you have correctly installed the Q1 and Q4 circuitry. Any errors in this section will effectively short out the antenna input rendering your VNA measurements and impedance matching efforts invalid. By the same token, make sure that 'Transmit_RFID' is near ground when making your measurements. If this is not connected, I recommend grounding it during your testing to ensure that the transistors are biased to an off state.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-09T18:09:18.260" LastActivityDate="2018-06-09T18:09:18.260" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10413" PostTypeId="1" CreationDate="2018-06-09T11:38:01.587" Score="3" ViewCount="361" Body="&lt;p&gt;Where can I find information about the digital modes and how to get started on them? I would like a concise yet easy to understand tutorial.&lt;/p&gt;&#xA;" OwnerUserId="11742" LastActivityDate="2018-06-14T21:00:24.587" Title="How/where can I learn about ft8?" Tags="&lt;digital-modes&gt;&lt;modes&gt;&lt;ft8&gt;" AnswerCount="1" CommentCount="3" ClosedDate="2018-06-25T13:49:43.743" ContentLicense="CC BY-SA 4.0" />
  <row Id="10414" PostTypeId="2" ParentId="10411" CreationDate="2018-06-09T11:41:56.523" Score="1" Body="&lt;p&gt;It is common convention to represent input and output as dictated by the signal flow (or more strictly current flow). A transmitter emits a signal from its output. Its output has an associated impedance. A receiver processes a signal from its antenna connection. This is therefore an input with an associated impedance. A circuit that connects to an output generally does so through its input and visa versa.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna is capable of receiving RF signals and transmitting RF signals. In the case where it is receiving signals, the antenna is considered the signal source (an output) to the remainder of the circuit such as a receiver or measurement instrument which is the load (an input). In the case where the antenna is transmitting signals, it is regarded as the load (an input) for the transmitter or measurement instrument (an output).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna has a measurable impedance at its feedpoint. The impedance is the same for transmitting (input impedance) and receiving (output impedance). It is generally easier to measure the input impedance of the feed point while injecting a signal into the antenna's feedpoint and measuring (or calculating from other measurement points) the resulting complex current and voltage at the antenna feedpoint. This is what is happening when you measure the impedance of the antenna with a one port VNA configuration. While this technique measures the feedpoint (input) impedance of the antenna while transmitting, the feedpoint (output) impedance during receive can be inferred due to reciprocity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RGpqR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RGpqR.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is generally desirable that we match the impedance of the load connected to a signal source to the impedance of the signal source in order to achieve the rated or desired power transfer. In RF work, the impedance that is commonly used by convention is 50 ohms but this is by no means a requirement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a transmitter which has a 50 ohm load specified, the rated power of the transmitter will be realized when the load is also 50 ohms. This wording is specifically chosen - you should not infer &quot;maximum power is transferred&quot; since often the output power of a transmitter is rated for a specific load impedance but the output impedance of the transmitter may be something other than 50 ohms (for example, to improve the efficiency of the transmitter).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When an antenna is the load for the transmitter, it is then desirable to have an antenna with a 50 ohm impedance. Fortuitously, if the transmitter is part of  a transceiver, the transceiver's receive antenna impedance is also typically specified as 50 ohms. Once again, do not infer that &quot;the input impedance of the receiver is 50 ohms&quot; but only that it is specified to connect to a 50 ohm antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This notion of the specified impedance verses the &quot;actual&quot; input or output impedance becomes burdensome to articulate, so often the shortened term &quot;impedance&quot; is used in favor of the more accurate, albeit verbose, form of &quot;the specified antenna impedance&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When an antenna feedpoint impedance is not the desired impedance, such as 50 ohms, then a matching network can be used to transform the feedpoint impedance of the antenna to the desired impedance. The matching network is a two port device. One port is connected to the antenna. This port is designed to be a conjugate match to the impedance of the antenna. The other port of the matching network connects to the transmitter/receiver. This port is typically designed to be 50 ohms or whatever is called for in the transmitter/receiver specification. In combination, these two ports &lt;em&gt;transform&lt;/em&gt; or &lt;em&gt;match&lt;/em&gt; the impedance of the antenna to the impedance of the transmitter/receiver specification.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the antenna feedpoint impedance is the same under transmit and receive conditions, the two port matching network performs the matching function in both use cases. But these matching networks are not lossless. The losses can be asymmetric. The capacitors, inductors, and transformers used in such networks waste power in the form of heat. The design topology and components are generally optimized to minimze these losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically a fixed value antenna matching network is designed by measuring or calculating the feedpoint impedance of the antenna (without any matching network) and calculating the requisite values. This calculation used to be a laborious hand calculation but there are now many on-line tools that remove the burden. For example, for designing L type matching networks, I prefer the &lt;a href=&quot;http://leleivre.com/rf_lcmatch.htmlp&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://leleivre.com/rf_lcmatch.html&lt;/a&gt; site.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once the values of the matching network have been calculated and a prototype built, it would be possible to place this circuit on a VNA and measure the transformation characteristics using a two port technique. But it is often easier to attach the matching circuit to the antenna and measure the input impedance of the remaining open port using a one port measurement and make appropriate adjustments from that point. The one port VNA measurement technique is such an example. Since the goal is to have the input of the network match the specified transmit/receive impedance, a one port measurement directly provides the necessary information.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-09T17:45:34.140" LastActivityDate="2018-06-09T17:45:34.140" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10415" PostTypeId="2" ParentId="10405" CreationDate="2018-06-09T12:36:50.283" Score="3" Body="&lt;p&gt;&lt;strong&gt;TL;DR&lt;/strong&gt;: Sat TV equipment, 75Ω, probably analog. Obsolete. If anything, keep smallest switch matrix.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's commodity satellite TV equipment. &#xA;Let's go through this:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;a Bias injector (hence the different voltages next to each port) and satellite dish control signal multiplexer (DiSEqC uses control signals at 22 kHz, for example) for satellite dish motors and LNBs; probably of not much use unless you want to control a satellite dish motor whilst receiving commercial satellite TV – there's very likely some filters in there that restrict the usefulness for other bands. But you can't know without testing.&lt;/li&gt;&#xA;&lt;li&gt;More interestingly, this is an antenna switch. Sat dish feeds often have two polarizations, and this seems to have been used for a system with linear (H=horizontal, V=vertical) polarization. But you can use that to switch anything – the polarization of the antenna doesn't change anything about the wave on the cable. Anyway, it won't be of help unless your signal happens to be in the upper or lower band (H=high, L=low), because the fact that this is printed on the device almost certainly means there's filtering to these bands inside. But again, you can't be sure, and would have to measure. Maybe it's really just a set of four switches with four positions each, and then this would be rather cool. Control of these probably happen through digital signals sent by the consumer set-top box (DiSEqC). &lt;br&gt; The splitter is just a four-way splitter of unspecified power characteristics. &lt;/li&gt;&#xA;&lt;li&gt;see switch from 2. But larger.&lt;/li&gt;&#xA;&lt;li&gt;see 2.&lt;/li&gt;&#xA;&lt;li&gt;see 2.&lt;/li&gt;&#xA;&lt;li&gt;a set of amplifiers; the trimmers probably just set two different bias voltages of a RF transistor and a matching PIN diode or something. Doubtful it's very useful for anything but analog satellite TV. It's not going to be extremely Low-Noise (the LNA usually being part of the LNB right at the feed), nor high-output power (just being used to amplify enough to serve the longest cable in a residential complex). &lt;/li&gt;&#xA;&lt;li&gt;That's an obsolete 24-port &lt;em&gt;100 Mbit/s&lt;/em&gt; switch. The gigabit rating only applies to the two uplink ports. Dump it. A 20€ electronics store gigabit switch has more bandwidth, plus you pay for electricity.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Generally, sat TV equipment tends to use 75Ω impedance rather than 50Ω (which is what most signal processing equipment tends to use). So, at least at one point, you might have to match your system's impedance to these.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding selling these off: If my suspicion is right, then everything about these, if it cares about frequencies and bandwidths at all, is optimized for analog Sat TV reception. That's obsolete, and I guess that's the reason these were tossed in the trash. Blind guess: You'll be able to sell these to someone who knows what they do, and needs specific parts from them. However, these people also have access to the internet, and can just order new components (and these UHF/VHF things at these powers and noise figures really only cost cents to dollars each, you pay for the integration in a good box and measurement/calibration); the prices you'll fetch will be modest. The highest potential profit I'd attest the switch matrices – the likelihood of these being useful for modern sat installations is highest, but then again, I haven't seen someone put up a set of dishes with multiple LNBs each in years. The age of large Sat TV installations might simply be over, with those wanting a large selection of high-def video opting for online services in middle Europe (which is where the power plugs suggest this equipment is from).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I'd inspect the switches to figure out whether I can control them without a sat-TV receiver (or by using a sat TV set top box, coupled only through a let's say 50 kHz RC low pass?), and whether they work well enough at the frequencies &lt;em&gt;you&lt;/em&gt; want to operate. If that's the case, you have a set of 75Ω low-power switches, which is nice if you want to switch multiple antennas between multiple receivers. I wouldn't trust these to be bidirectional (measure!) nor to carry more than 1 W RF per port.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-06-09T13:07:46.500" LastActivityDate="2018-06-09T13:07:46.500" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10416" PostTypeId="1" AcceptedAnswerId="10417" CreationDate="2018-06-09T14:52:05.490" Score="1" ViewCount="687" Body="&lt;p&gt;I have been doing some research online and I found that some sources say if you have a full wave dipole antenna, there would be no transmission on the other hand some sources say that this is not true.  I would like to know which one is true.  Also I would like to know why the lengths of lambda/4 are used the most.  Can a different length be used to achieve the same or better performance?  I presume that it may be the smallest multiple length hence that's why it is used.  Can someone please explain this in terms of electric and magnetic fields and how the antenna is resonating.&lt;br&gt;&#xA;At what other lengths would the antenna resonate?&lt;/p&gt;&#xA;" OwnerUserId="11305" LastActivityDate="2018-06-13T04:14:11.603" Title="How the performance of the half wave dipole antenna changes as the length changes?" Tags="&lt;antenna&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10417" PostTypeId="2" ParentId="10416" CreationDate="2018-06-09T22:41:31.563" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;...if you have a full wave dipole antenna, there would be no transmission...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Here begins the misunderstanding of antenna directivity, antenna efficiency, and antenna impedance. Let's analyze each one independently and then bring it all together using the above example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Directivity&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Directivity of an antenna can be defined as the power density the antenna radiates in the direction of its strongest emission versus the average power density radiated in all directions, assuming 100% antenna efficiency. Since an isotropic antenna has a perfectly uniform power density in all directions and by definition 100% efficiency, the directivity of any antenna can also be defined as the power density the antenna radiates in the direction of its strongest emission versus the maximum (or minimum or average) power density of an isotropic antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So directivity is a special case of gain:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Gain=\text{Directivity}*\text{Efficiency} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;when efficiency = 1 (100%).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can plot the directivity of a dipole in free space:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/h4v6C.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/h4v6C.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From this plot we can make several observations:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 1/2 wave dipole has a linear directivity of 1.64 or ~2.15 dBi gain using the formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$dBi=10*\log_{10} \left(\frac {\text{Directivity}}{\text{Isotropic Directivity}}\right) \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where Isotropic Directivity = 1 by definition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we continue along the chart, we find the next highest directivity dipole is a 1.25 (10/8) wave dipole with a directivity of 3.18 or approximately 5 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Continuing further to the right along the chart, we can make the general observation that the maximum directivity after the 10/8 wave dipole occurs at 3 wavelengths and the next highest peak occurs every wavelength thereafter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before leaving the directivity analysis, it should be noted that for directivity to be effective for communications, the directivity in the direction of the communications must adequate to support the communications given the other factors involved. One should not infer that maximum directivity must be in the direction of the other station but rather that the minimum required directivity in the direction of the other station must be met by the antenna under evaluation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Antenna Impedance&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to transfer the rated power of the transmitter to the antenna, the input impedance of the antenna must match the specified load impedance of the transmitter, which is typically 50 ohms (50+j0 ohms). It is therefore instructive to plot the complex impedance of various lengths of a dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tNrNQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tNrNQ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here we can see that the free space dipole comes the closest to the specified 50+j0 impedance when the length is 1/2 wavelength. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next highest directivity dipole, the 10/8 wave dipole, has a free space impedance of ~185-j890 ohms. Such a dipole would require a matching network (antenna tuner) to transform this impedance to 50 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next highest directivity dipole, the 3 wavelengths dipole, has a free space impedance of ~1070+320j ohms. An antenna tuner would be required here as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Efficiency&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The efficiency of an antenna system consists of the resistive losses of the antenna conductor, the losses of the feedline, and the losses of the matching circuit (antenna tuner). If the antenna tuner or matching network is located between the antenna and the feedline, the feedline losses are minimized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The matching network should be carefully selected for the required matching conditions so as to minimize loss. When using an L type matching network with the inductor in series, the inductor generally contributes the highest loss in the matching circuit. Using a conductor constructed with a large diameter conductor will minimize the resistive losses in this configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the antenna conductor can reasonably be selected to minimize resistive RF losses due to skin effect, it is the efficiency of the matching network and the feedline that typically determines the gain of the antenna system for a given length of dipole. Consider that at 100% efficiency, the gain of a 2 inch dipole on 160 meters is only ~0.4 dB less than that of a 1/2 wavelength dipole. The problem is that we cannot obtain 100% efficiency in the matching network or the radiating element due to the extremely low complex impedance of the 2 inch dipole. As a result, the realized gain is much worse than directivity alone would indicate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The One Wavelength Dipole&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is instructive to examine the case of the 1 wavelength dipole. It has an impedance of ~3430-j760 in free space. Its directivity is ~2.36 or ~3.7 dBi. This is ~1.5 dB better than a 1/2 wavelength dipole. If this antenna where operated on 20 meters, it would require an ~26 pF capacitor across the antenna and an ~4.7 uH inductor in series with the antenna to bring it to a 50 ohm impedance (see &lt;a href=&quot;http://leleivre.com/rf_lcmatch.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://leleivre.com/rf_lcmatch.html&lt;/a&gt;). With a careful design, the loss of this L network could be kept to less than 1 dB. Add to this the loss of the double length of wire and the gain over a 1/2 wavelength dipole is marginal at best.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The pattern of the free space 1 wavelength dipole is roughly broadside:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YY4Ke.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YY4Ke.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So we may roughly conclude that the effort, space, and componentry of a 1 wavelength dipole in free space results in marginal, if any, gain compared to its much simpler and smaller, 1/2 wavelength counterpart.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-13T04:14:11.603" LastActivityDate="2018-06-13T04:14:11.603" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10419" PostTypeId="1" AcceptedAnswerId="10420" CreationDate="2018-06-10T11:22:46.267" Score="6" ViewCount="792" Body="&lt;p&gt;I created a simple sketch in GNU Radio that multiples two signals. One is a sine and the other is cosine. I paste a screenshot of it and its results below. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/O4LF2.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O4LF2.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have heard that in DSP, we can do almost perfect signal processing. Hence, I assume phenomena such as LO leakage and doubly balanced mixers are not applicable when already digitized signals are multiplied such as in the presented case. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, after multiplying the following two consine signals in GNU Radio, I expect to see the sum &amp;amp; difference frequencies; nothing else. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To my surprise, I am seeing a big peak at the sum frequency followed by a series of multiple peaks on the FFT.  I'm curious to know what I am missing here.&lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorUserId="76" LastEditDate="2018-06-10T14:13:25.867" LastActivityDate="2018-06-10T14:13:25.867" Title="GNU Radio sinusoid multiplication does not produce perfect results" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10420" PostTypeId="2" ParentId="10419" CreationDate="2018-06-10T11:52:16.710" Score="11" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I expect to see the sum &amp;amp; difference frequencies.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You're multiplying two &lt;em&gt;complex sinusoids&lt;/em&gt;, not a $\sin$ and a $\cos$, but&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$e^{j2\pi f_1t}\cdot e^{j\left(2\pi f_2t-\frac\pi2\right)}= e^{j2\pi(f_1+f_2)-j\frac\pi2}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, only the sum frequency, as it should.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I am seeing a big peak at sum frequency followed by a series of multiple peaks on the FFT. I'm curious to know what I am missing here.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;First of all, don't forget that unless your signal's period perfectly fits in the FFT length, you'll see &lt;em&gt;leakage&lt;/em&gt;, i.e. the effect of convolution with a sinc. Your signal has a period of $\frac4{15}$. You'll find that you can't divide 1024 by that and get an integer. So, from a pure mathematical point of view, you &lt;em&gt;must&lt;/em&gt; see leakage here. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, look at the scale of things: your theoretic peak is more than 120 dB above all your other side peaks. That's OK. That's a factor of $10^{12}$, and around the numerical accuracy of the floating point numbers used in this software. I can't think of a case where that becomes a problem&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-06-10T11:52:16.710" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10421" PostTypeId="1" CreationDate="2018-06-10T18:31:35.353" Score="2" ViewCount="139" Body="&lt;p&gt;Could a aluminum irrigation system over about two acres work as a ground plane? Pros and cons? Shaped like an F but with 4 horizontals rather than 2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/OafJn.jpg&quot; alt=&quot;irrigation system 2” pipe above ground&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes it has water in it. The two top horizontals are 60 feet long, the bottom two are about 150 feet long. The feeder line on the left is also about 150 feet. Would it work and where would I connect the vertical Hustler  antenna?&lt;/p&gt;&#xA;" OwnerUserId="11745" LastEditorUserId="8573" LastEditDate="2018-06-12T00:30:22.623" LastActivityDate="2018-12-05T08:02:32.920" Title="Irrigation system for ground plane" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="10422" PostTypeId="1" AcceptedAnswerId="10423" CreationDate="2018-06-10T22:13:59.420" Score="1" ViewCount="116" Body="&lt;p&gt;Today I was trying to measure the SWR of a new aerial on my car which has 3 loading coils. Whilst doing this I took the whip out on the top to see how drastically I might have needed to cut the antenna and for reasons I can’t explain the SWR reading stayed the exact same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was using an analyzer going through the different bands just in case you were wondering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any idea on why this would occur? I’ve been licensed for 10 years and I just don’t know where to start.&lt;/p&gt;&#xA;" OwnerUserId="11747" LastEditorUserId="9493" LastEditDate="2018-06-15T07:07:02.860" LastActivityDate="2018-06-15T07:07:02.860" Title="Removing the whip on a 2m/70cm antenna makes no difference" Tags="&lt;antenna&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10423" PostTypeId="2" ParentId="10422" CreationDate="2018-06-11T15:08:01.797" Score="5" Body="&lt;p&gt;If the SWR was very poor with the whip installed, you could simply be hitting the limits of your analyzer. Inexpensive analyzers are not very precise when the load is very poorly matched.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, something may be broken. Perhaps the analyzer, or the feedline you are using to connect it, the antenna mount, or the antenna itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest testing each component individually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Test the antenna analyzer with a dummy load. A dummy load should be a 1:1 SWR on every frequency. You can also try 25 ohms or 100 ohms and you should see a 2:1 SWR at every frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coax can be tested by putting a dummy load on one end, and the analyzer at the other: you should measure 1:1 at all frequencies. If jiggling the cable yields spikes in the reading, you have a poor connection somewhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check for shorts with an ohmmeter in all your cables and the antenna mount.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-06-11T15:08:01.797" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10424" PostTypeId="2" ParentId="10422" CreationDate="2018-06-11T19:18:24.887" Score="2" Body="&lt;p&gt;In addition to what Phil said, don't forget that a long (or just very lossy) feedline can mask problems by showing you a lower swr than if you would measure at the antenna directly. If the cable losses are high enough, your measurements at the end of the cable when you change things on the antenna side might not show you as much difference in swr as you would expect to see. &#xA;If the cable isn't molded to the antenna, try to measure at the antenna directly. If it is, you might be able to short the antenna to ground and check if that has the expected measurement result. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some (colinear) antennas might be shorted at the end by design, so if you would find it shorted at DC, don't jump to conclusions too quickly. &lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2018-06-11T19:18:24.887" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10425" PostTypeId="1" CreationDate="2018-06-12T02:50:26.073" Score="1" ViewCount="157" Body="&lt;p&gt;Ware can I find the programming software for this radio It's cold awr advantage programming software for the 4000 4002 anyone know or has a copy of it to send on email to Mr ouly of you can email me at jlucas6671@yahoo.com thanks &lt;/p&gt;&#xA;" OwnerUserId="11751" LastActivityDate="2018-06-12T02:50:26.073" Title="AWR_4000 by awc programming software" Tags="&lt;software&gt;" AnswerCount="0" CommentCount="0" ClosedDate="2018-06-12T04:23:19.530" ContentLicense="CC BY-SA 4.0" />
  <row Id="10428" PostTypeId="2" ParentId="10421" CreationDate="2018-06-12T06:48:25.223" Score="3" Body="&lt;p&gt;Provided that the system is continuous metal pipe with no galvanic isolators, plastic couplings, plastic valves or other electrical discontinuities, the pipe should make a very good ground system for most HF antennas. The fact that the pipe is above ground is a real plus as this helps to minimize earth losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that if you plan a vertical HF antenna, the highest current density is in the area near the base of the antenna. Try to place the antenna near one of the tee pipe junctions so as to provide the best possible return path for the evanescent currents in the near field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can electrically couple to the aluminum pipe with a stainless steel strap. Make certain that no copper comes into direct contact with the aluminum - use stainless steel shims between the two. Some promote the use of copper to aluminum compounds such as DeOxIt that is used in electrical panels. This is not suitable for long term exposure to weather so it should not be relied upon in the long term. If you do use it, open the joint every year or so to inspect and reapply the grease based compound as needed.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-05T08:02:32.920" LastActivityDate="2018-12-05T08:02:32.920" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10429" PostTypeId="1" CreationDate="2018-06-13T10:42:40.330" Score="2" ViewCount="1279" Body="&lt;p&gt;I have as assignment to make a half wave dipole antenna, that radiates at 433 MHz. I am trying to figure out how to use a coaxial cable as transmission line. I know that the coaxial cable is unbalanced and an ideal half wave dipole is balanced. To properly connect these two is a balun required. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The main question I have about the coaxial cable is how do I connect the coaxial cable to the dipole when only the inner conductor transfers the signal? What is the best way to connect it together, taking in consideration that I also need a 180 degrees shifted signal connected to one of the arms of the dipole? &lt;/p&gt;&#xA;" OwnerUserId="11756" LastEditorUserId="9493" LastEditDate="2018-06-15T07:11:33.947" LastActivityDate="2018-06-15T07:11:33.947" Title="Connecting a coaxial cable as feed to a halfwave dipole" Tags="&lt;dipole&gt;&lt;balun&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10430" PostTypeId="2" ParentId="10429" CreationDate="2018-06-13T15:31:20.850" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How do I connect the coaxial cable to the dipole&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Using a balun. That's its job.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;when only the inner conductor transfers the signal&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is an incorrect assumption. Current always flows in loops, so there is always an equal and opposite current &lt;em&gt;somewhere.&lt;/em&gt; In a coaxial cable, the signal is carried by both the inner conductor and the outer conductor (or, in some perspectives, “in the space between them”).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you connect the inner and outer conductor of a coaxial cable to the two arms of a dipole then the dipole will in fact work as an antenna — but the outer conductor of the cable will &lt;em&gt;also&lt;/em&gt; radiate/receive. &lt;em&gt;This&lt;/em&gt; is the problem a balun solves. If you ignore it, you will still have an antenna, but possibly not the antenna you intended to design.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-06-13T17:26:33.750" LastActivityDate="2018-06-13T17:26:33.750" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10431" PostTypeId="1" CreationDate="2018-06-13T15:55:58.393" Score="7" ViewCount="1291" Body="&lt;p&gt;I'm new to ham and quickly finding that the new and old equipment I'm accumulating at an alarming rate has an equally alarming array of connectors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;UHF PL-259&lt;/li&gt;&#xA;&lt;li&gt;BNC&lt;/li&gt;&#xA;&lt;li&gt;SMA&lt;/li&gt;&#xA;&lt;li&gt;Type N&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Is there any downside to consolidating on BNC as my main connector and getting adapters to go from the other 3 types to BNC? My main use purposes are: SDR, QRP on HF (including SOTA), UHF/VHF FM and DMR. I doubt I'll ever set up a full power HF base station.&lt;/p&gt;&#xA;" OwnerUserId="11462" LastActivityDate="2018-06-19T21:21:35.497" Title="Is there any downside to consolidating on BNC connectors for HF?" Tags="&lt;antenna&gt;&lt;connectors&gt;" AnswerCount="4" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10432" PostTypeId="1" CreationDate="2018-06-13T17:20:26.033" Score="2" ViewCount="44" Body="&lt;p&gt;My car stereo has terrible reception on a single AM station.  Other cars get the signal fine and other channels on radio are received fine.  I have contemplated some sort of booster for the antenna or replacing the antenna entirely but not pursued either option as other stations are coming in fine.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reception on this single station gets significantly worse when I use the USB ports to charge a device. I can not detect, however, any change as the engine revs/speeds change.  None of the other stations degrade when the USB is in use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am obviously not a radio enthusiast/expert and apologize if this is not the proper forum for this type of question.  Thanks in advance, though, for any guidance/feedback anyone might be able to provide.&lt;/p&gt;&#xA;" OwnerUserId="11757" LastActivityDate="2018-06-13T18:28:18.507" Title="Poor reception on single AM channel" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;am&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10433" PostTypeId="2" ParentId="10432" CreationDate="2018-06-13T18:21:32.967" Score="2" Body="&lt;p&gt;I'm going to answer this in general terms first, then address your specific case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two things make your reception bad:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;too little power that makes it from the sender to your radio receiver&lt;/li&gt;&#xA;&lt;li&gt;too much power of noise that reaches your radio receiver, compared to the power from the sender.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Your problem seems to be of the second category. Specifically, the noise we're talking about seems to be electromagnetic interference from a bad USB charger. (and not, for example, of thermal noise that happens to different degrees in any non-superconductive amplifier in this universe)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That interference seems to contain a lot of energy at a specific frequency – the channel you'd like to receive. That's nothing unusual. Chargers typically contain a so-called &lt;em&gt;switch-mode power supply&lt;/em&gt;, which basically switches of an energy-storing and -releasing element to step down the car's 12 V to something that is USB-compatible (5 V). That comes inevitably with some noise. And if the amount of times said switch is toggled per second happens to be the frequency of your station, or an (odd) integer factor of that, then you'll have something that makes receiving AM impossible on that particular (set of) frequency (ies). And: that switching has, albeit only with little power, to happen even if nothing is plugged in, so that the USB voltage is there the moment you plug something in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The noise is inevitable, but it can be well contained. And in fact, devices &lt;em&gt;must&lt;/em&gt; be designed that they don't interfere with radio. But that's a question of design quality and cost, and I'd guess that car USB chargers aren't exactly stellar in that category.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Get rid of that USB charger; that might imply you need to unplug it internally (somewhere under the plastics in your dashboard, for example), maybe it even has its own fuse. Adding an antenna booster is not really likely to help – it would possibly amplify the noise just as well as your current radio does. (The fact that it might be mounted far away from said USB charger might help, though – but the fact that you're adding more connectors and cables to your receiver might at the same time hurt.) &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-06-13T18:28:18.507" LastActivityDate="2018-06-13T18:28:18.507" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10434" PostTypeId="2" ParentId="10431" CreationDate="2018-06-13T18:35:43.393" Score="5" Body="&lt;h1&gt;PL-259&lt;/h1&gt;&#xA;&lt;p&gt;I'd really stay the hell away from PL-259. Undefined wave impedance, different manufacturer conventions, adapter stock of either decades of unknown storage (potentially in some moldy military box) or cheapest-supplier production are the main sources… It's a good thing that connector is becoming less common. It's something that you really don't want to deal with above ca 30 MHz.&lt;/p&gt;&#xA;&lt;h1&gt;connector comparison&lt;/h1&gt;&#xA;&lt;p&gt;As long as all your cabling/connector systems use the same impedance, why not. BNC is a cheap and robust connector.&lt;/p&gt;&#xA;&lt;p&gt;It certainly isn't known to make the highest-quality connections when compared to SMA or Type-N; however, as said, it's mechanically usually less flimsy then SMA connectors, and you need none of the higher frequency range you can reach with SMA.&lt;/p&gt;&#xA;&lt;p&gt;There's good things to be said about Type-N: It's what's typical for measurement equipment, and many low- to medium-power mobile basestation systems use it. It's a very reliable connector, it makes connections that are typically more resilient to humidity and vibration, it's mechanically more exact and thus lower in reflections.&lt;/p&gt;&#xA;&lt;p&gt;You buy these advantages with increased cost and complicated unscrewing and screwing.&lt;/p&gt;&#xA;&lt;p&gt;Clearly, I'd prefer Type-N at the output of a 100W amplifier. For my receiver, I frankly wouldn't care if we're actually talking about HF.&lt;/p&gt;&#xA;&lt;p&gt;Of all the acceptable connectors, BNC is definitely the one having the lowest frequency range. So, if you later decide you're into UHF/microwave, bad news, you need to switch back to SMA or Type-N.&lt;/p&gt;&#xA;&lt;p&gt;That being said, this is all about &lt;em&gt;what you'd typically expect&lt;/em&gt; when buying connectors of these types.  Amphenol RF sells BNC connectors that are specified to work with 0.2 dB insertion loss and -55 dB leakage at up to 3 GHz. But you'd pay more for one of these than for your average Type-N. At the same time, there's cheap crummy Type-N connectors that simply don't mate well and have loose mechanical dimensioning, so that their property is well below what you'd see in medium quality BNC installations.&lt;/p&gt;&#xA;&lt;p&gt;After all, this boils down to: Get the datasheet or a feeling for the quality/precision for what you're buying. Compare your most likely solutions for insertion loss and leakage – and compare that to what your application needs. Got a 2 W PA? Well, nevermind those 0.7 dB insertion loss – they won't hurt anyone, but you lose a few milliwatt in power. Got 2 kW? Maybe you want to know how much energy is converted to heat or reflected back at your ampl.&lt;/p&gt;&#xA;&lt;h1&gt;conclusion&lt;/h1&gt;&#xA;&lt;p&gt;If you want to keep the option for higher frequencies,  don't need much power / voltage capability, go for SMA. It's medium-priced.&lt;/p&gt;&#xA;&lt;p&gt;If you want the most reliable connections or need to handle much power, go for Type-N. (attention: 50 Ω and 75 Ω variants exist!)&lt;/p&gt;&#xA;&lt;p&gt;As a compromise up to 4 GHz, BNC is nice and cheap. Watch out – BNC exists in 75 Ω and 50 Ω versions. Don't buy anything where you don't know which one of these you get. Note that the 50Ω cabling ones go higher in frequency, and as a rule of thumb, price, quality and whether you want to do UHF/VHF with them are correlated.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-06-13T21:00:23.820" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10437" PostTypeId="1" AcceptedAnswerId="10438" CreationDate="2018-06-14T12:53:03.007" Score="5" ViewCount="49" Body="&lt;p&gt;I am interested in creating a square outer-conductor with round inner-conductor air coax post for a hex beam antenna. I found the extremely useful information at:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/1304/how-do-i-design-a-round-or-square-coaxial-transmission-line-to-have-a-specific-i&quot;&gt;How do I design a round or square coaxial transmission line to have a specific impedance?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://fermi.la.asu.edu/w9cf/articles/square/square.html&quot; rel=&quot;noreferrer&quot;&gt;http://fermi.la.asu.edu/w9cf/articles/square/square.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, from a practical standpoint, in these explanations it is not clear to me what is the most appropriate measurement to use for the square outer conductor's single-side diameter. For example, if I use 2&quot; x 2&quot; x 0.125&quot; square tube for construction of the air-coax, for the calculations should I use the outer 2&quot; diameter, the inner 1.85&quot; diameter, or the 1.925&quot; average diameter?&lt;/p&gt;&#xA;" OwnerUserId="11762" LastActivityDate="2018-06-15T17:11:25.347" Title="For air coax calculation, what is correct diameter metric vis-à-vis tube stock thickness?" Tags="&lt;diy&gt;&lt;impedance&gt;&lt;coaxial-cable&gt;&lt;transmission-line&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10438" PostTypeId="2" ParentId="10437" CreationDate="2018-06-14T13:37:44.787" Score="4" Body="&lt;p&gt;Coaxial cable impedance is determined by the dialectric between the two conductors and the distance between the faces of the conductors. So normally it is the outer diameter of the inner conductor and the inner diameter of the outer conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The facing surfaces being a controlling factor is due to the skin and proximity effects that tend to keep the current on the skin of the conductor and on the surfaces (skins) that are closest to each other. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thickness of the tubes will probably not be a factor other than for mechanical and geometry factors. Normally though, you should have 4 to 5 skin depths for the lowest frequency in the application. This is in addition to the inner conductor having a sufficiently large enough diameter so as to minimize RF resistance at the highest frequency of application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Kevin Schmidt's formula for the characteristic impedance of coax made with a square outer conductor and a round inner conductor is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Z_o=138\log_{10}(1.08D/a) \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $D$ is the inside dimension of one side of the square tube and $a$ is the outside diameter of the inner round conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the square tube dimension, $D$, is the inside of one side of the tube or equivalently, the outside dimension of one side of the tube minus the wall thickness times two.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-15T17:11:25.347" LastActivityDate="2018-06-15T17:11:25.347" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10439" PostTypeId="2" ParentId="10413" CreationDate="2018-06-14T21:00:24.587" Score="1" Body="&lt;p&gt;With a quick search I found several documents where you can get information about using FT8:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Get%20on%20the%20Air%20with%20HF%20Digital/Getting%20Started%20on%20FT8.pptx&quot; rel=&quot;nofollow noreferrer&quot;&gt;Getting Started on FT8&lt;/a&gt; — ARRL-hosted powerpoint&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.physics.princeton.edu/pulsar/K1JT/FT8_Operating_Tips.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;FT8 operating guide&lt;/a&gt; — PDF with setup and tips, hosted by the inventor of the mode&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.jimcarson.com/2017/setting-up-ft8/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Setting up FT8&lt;/a&gt; — a blog post that looks helpful&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For a bit more background:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FT8 is a &quot;digital mode&quot;, so any general setup and basic techniques you'll find for using apps like &lt;a href=&quot;https://en.wikipedia.org/wiki/Fldigi&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fldigi&lt;/a&gt;, or &lt;a href=&quot;https://www.packetradio.com/pdfzips/jt65-hf-setup.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;JT-65&lt;/a&gt; — or &lt;a href=&quot;https://en.wikipedia.org/wiki/WSJT_(amateur_radio_software)&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSJT&lt;/a&gt; for any of its older modes — will apply.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Typical equipment usage&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;In recent history, hams generally use one or two additional pieces of equipment between their personal computer and transceiver:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;something to get audio data in/out of the radio. The &lt;a href=&quot;http://www.tigertronics.com/slusbmain.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;SignalLink&lt;/a&gt; and &lt;a href=&quot;http://www.westmountainradio.com/rigblaster.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;RigBlaster&lt;/a&gt; products are two commercial offerings, or its possible with a little care to simply wire the up the audio input/output from a cheap USB sound card dongle to a traditional transceiver.&lt;/li&gt;&#xA;&lt;li&gt;[optional] a &quot;CAT&quot; (computer aided tuning) interface, which will be some sort of rig-specific cable and serial interface that can typically read and change the VFO settings, and trigger the PTT circuitry under the control of software running on the personal computer. This is not strictly necessary, as one could tune by hand and use either VOX or manual intervention, but recommended if you intend to do more than dabble.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;These work together as follows: the radio is set to Upper Side Band mode and tuned below the frequency where digital QSO's are happening. By ear you would typically hear fast little &quot;tunes&quot; which vary depending on the digital mode, but now these are being fed into the sound card input of the PC instead. You run an application that &quot;records&quot; [or listens to…] these sounds and processes them. This application also can generate the same sort of signals and &quot;play&quot; them back to the radio in place of the normal microphone input.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;SDR radios&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;An SDR like the &lt;a href=&quot;https://www.multus-sdr.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Multus kit&lt;/a&gt; or the &lt;a href=&quot;http://www.flexradio.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FlexRadio gear&lt;/a&gt; really just takes the above combination further — instead of dealing with a 3-kHz band of audio-frequency data, they let you process a whole 96kHz or wider swatch of baseband signal around their built-in digitally-controlled VFO. This usually means a single USB cable can do all the work, without the SignalLink and CAT adapters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Unfortunately, most digital mode ham apps were built in the PC era and before the rise of SDR. In practice, using an SDR with ham software ends up being an exercise in &lt;em&gt;simulating a vintage rig&lt;/em&gt; with &quot;virtual serial cables&quot; and &quot;virtual audio cables&quot; to emulate the rig control and 3kHz filtering and such … hopefully I don't sound too bitter ;-)&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;FT8 specifically&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;FT8 is just one &quot;digital mode&quot; option among many. AFAICT, the main [and perhaps only?] implementation right now is found in the &lt;a href=&quot;https://physics.princeton.edu/pulsar/k1jt/wsjtx.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSJT-X&lt;/a&gt; application for Windows/Linux/macOS.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2018-06-14T21:00:24.587" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10440" PostTypeId="2" ParentId="10260" CreationDate="2018-06-14T21:31:01.610" Score="0" Body="&lt;p&gt;The &quot;GBoard&quot; software keyboard built into Android since 5.0 offers a &lt;a href=&quot;https://support.google.com/accessibility/android/answer/9011881&quot; rel=&quot;nofollow noreferrer&quot;&gt;Morse code mode&lt;/a&gt;, but I have not found thorough documentation. Their &lt;a href=&quot;http://morse.withgoogle.com/learn&quot; rel=&quot;nofollow noreferrer&quot;&gt;training webapp&lt;/a&gt; only includes &lt;a href=&quot;https://github.com/googlecreativelab/morse-learn/blob/master/scripts/morse-dictionary.js#L15&quot; rel=&quot;nofollow noreferrer&quot;&gt;letters A–Z&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few command sequences are, however, readily apparent via the UI:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/gK89a.jpg&quot; alt=&quot;Google&amp;#39;s marketing image for Morse keyboard&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;code&gt;..--&lt;/code&gt; — space&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;----&lt;/code&gt; — backspace&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;.-.-&lt;/code&gt; — return&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;....-.&lt;/code&gt; — shift [uppercase]&lt;/li&gt;&#xA;&lt;li&gt;&lt;code&gt;.-----&lt;/code&gt; etc. (like numbers with an extra dah) — pick autocomplete suggestion&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The author of &lt;a href=&quot;http://www.tandemmaster.org/morse_code.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page&lt;/a&gt; seems to have been involved with the development of the GBoard interface, but not very many of her punctuation sequences worked for me when I tried it today.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE&lt;/strong&gt;: I may or may not have disassembled a GBoard APK and tracked down its character mapping: &lt;a href=&quot;https://gist.github.com/natevw/0fce6b56c606632f8ee780b5d493f94e&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://gist.github.com/natevw/0fce6b56c606632f8ee780b5d493f94e&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Main observations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the control characters already visible in the UI (and listed above) appear to be the only ones supported internally.&lt;/li&gt;&#xA;&lt;li&gt;there are a few special &quot;extended&quot; characters, such as &lt;code&gt;.--.--&lt;/code&gt; for &lt;code&gt;}&lt;/code&gt; and &lt;code&gt;......&lt;/code&gt; for &lt;code&gt;^&lt;/code&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2018-06-14T22:24:21.987" LastActivityDate="2018-06-14T22:24:21.987" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10441" PostTypeId="1" AcceptedAnswerId="10467" CreationDate="2018-06-14T23:06:03.387" Score="8" ViewCount="377" Body="&lt;p&gt;I was reading &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/0872590011&quot; rel=&quot;noreferrer&quot;&gt;200 Meters and Down&lt;/a&gt;  but one thing that was unclear to me was that hams in the 1920s were operating on the 200 meter frequency, which is around 1.5 Mhz .... or 1500 kilocycles to use the old phrasing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's unclear to me is &lt;em&gt;how&lt;/em&gt; they were able to measure frequencies that high. Up to around 20 kHz you could use audio frequencies, but how do you measure Hertz above 20 kilocycles -- especially just using vacuum tubes? &lt;/p&gt;&#xA;" OwnerUserId="11462" LastEditorUserId="76" LastEditDate="2018-06-15T01:08:04.613" LastActivityDate="2018-06-19T00:47:13.050" Title="How were 1920s hams able to measure megahertz frequency?" Tags="&lt;equipment-operation&gt;&lt;measurement&gt;&lt;history&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10442" PostTypeId="2" ParentId="10441" CreationDate="2018-06-15T04:09:15.627" Score="5" Body="&lt;p&gt;The US National Bureau of Standards (NBS) had a system for basic measurement of frequencies as early as 1911. They used very basic calculations to determine the resonance of an LC circuit. The math was greatly advanced in 1923 in an article in &lt;em&gt;Radio Broadcast&lt;/em&gt; magazine entitled &quot;&quot;Reducing the Guesswork in Tuning&quot;. The method involved careful measurements of the physical dimensions of the capacitors and inductors that were applied to the equations. There is little doubt that the hams of that period closely followed and took advantage of this development.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During this same early 1920 period, the NBS was already experimenting with quartz oscillators as a frequency standard. They collaborated with other labs to continue their research. By 1929, Bell Labs had delivered four 100 kHz (kc at the time), temperature controlled crystal oscillators (TCXO). The uncertainty of these oscillators were estimated to be 10 ppm. These became the NBS primary frequency standards in this period.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-06-15T04:09:15.627" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10443" PostTypeId="1" CreationDate="2018-06-15T08:47:02.330" Score="2" ViewCount="1177" Body="&lt;p&gt;I was wondering how the current flows in a coaxial cable. Say for instance that the inner conductor transfers the signal, so there flows a current. How will in the outer conductor(shield), flow a current with a 180degrees phase shift compared to the inner conductor.&lt;/p&gt;&#xA;" OwnerUserId="11756" LastActivityDate="2018-06-15T11:31:26.067" Title="Current flow in a coaxial cable" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10444" PostTypeId="2" ParentId="10443" CreationDate="2018-06-15T11:31:26.067" Score="1" Body="&lt;p&gt;The RF current in a coaxial cable flows from the signal source (e.g. a transmitter), through the center conductor to the load and then back through the outer conductor of the coax, to the signal source. This is the conventional current flow description since the outer conductor is generally grounded at the signal source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 180° phase shift of the current on the outer conductor exists simply because the current is flowing in the opposite direction compared to the center conductor. For a coaxial cable to function as a transmission line and not an antenna, not only must the shield current phase be 180° from the center conductor current but the current in both must be of equal amplitude. If either of these conditions are not met, the coax will radiate.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-06-15T11:31:26.067" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10445" PostTypeId="2" ParentId="6538" CreationDate="2018-06-15T14:00:56.280" Score="1" Body="&lt;p&gt;The 450-451 MHz band is often used by news media, broadcast TV and AM radio. They use it for communications between the station and the news vans, or between the station and the traffic helicopters. In addition, they use it for something called &lt;a href=&quot;https://en.wikipedia.org/wiki/Interruptible_foldback&quot; rel=&quot;nofollow noreferrer&quot;&gt;Interruptible foldback&lt;/a&gt; which is a stream containing the programming and occasionally commands from the studio to the &quot;reporter on the scene&quot;. I hear these often, and it's just minutes and minutes of broadcast programming that suddenly stops.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I Googled and found some exact listings for the Boston media market - your area will have different frequencies but used for a similar purpose. &lt;a href=&quot;http://scan-ne.net/wiki/index.php?title=Media_and_Fire_Buff&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://scan-ne.net/wiki/index.php?title=Media_and_Fire_Buff&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can be handy to listen to, if you get traffic reports direct from the helicopter during rush hour!&lt;/p&gt;&#xA;" OwnerUserId="11765" LastEditorUserId="9493" LastEditDate="2018-06-16T22:55:56.380" LastActivityDate="2018-06-16T22:55:56.380" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10447" PostTypeId="1" CreationDate="2018-06-15T23:02:07.190" Score="2" ViewCount="212" Body="&lt;p&gt;Can a generic/typical analog SSB transmitter be used to send PSK modulated digital signals?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, how does that work?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is a computer or DSP interfaced with an SSB transmitter?  Line level audio to microphone input?  Or some other form of injection to the IF or RF stages.  If audio, and since a microphone input is designed for voice, what kinds of issues (AGC? Compression? Audio filtering? etc.) can occur when trying to inject audio to create a clean PSK RF output.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-06-17T16:13:32.690" LastActivityDate="2018-06-17T16:13:32.690" Title="Can an SSB transmitter be used to transmit PSK?" Tags="&lt;digital-modes&gt;&lt;ssb&gt;&lt;psk31&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10448" PostTypeId="1" AcceptedAnswerId="10450" CreationDate="2018-06-16T02:35:42.400" Score="1" ViewCount="174" Body="&lt;p&gt;I was using FT8 through a remote in RCForb. Reception in FT8 is spotty through the remote. I do not have an HF rig to test if the remote is the problem. So far, I think it is the delay through the internet that is causing the spotty reception, just as receiving would be difficult if your computer clock was off by 0.6 seconds. Is there a way to also delay the decoding in WSJT-X?&lt;/p&gt;&#xA;" OwnerUserId="11769" LastActivityDate="2018-06-16T08:35:20.893" Title="Can WSJT-X's timing account for delay from RCForb?" Tags="&lt;remote-control&gt;&lt;ft8&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10449" PostTypeId="2" ParentId="10447" CreationDate="2018-06-16T03:03:58.703" Score="8" Body="&lt;p&gt;The short answer is &quot;absolutely!&quot;. :-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I started out using Digipan on Windows, but other software such as Fldigi has been released since then.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Audio from the sound card to the mic input --and from the transceiver's audio out to the sound card's input-- is usually used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To prevent hum from a ground loop, it is recommended to use 600:600 ohm isolation transformers between both audio lines. They are available from Mouser Electronics, but I have always used ones removed from old 56K dial-up modems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The main problem heard on the bands is when the audio input to the mic is so high that clipping occurs. That makes the signal much wider than necessary, and you'll make many enemies as a result (trust me).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some relevant information &lt;a href=&quot;http://www.w0btu.com/digital_modes.html&quot; rel=&quot;noreferrer&quot;&gt;on my website here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-06-16T03:11:57.927" LastActivityDate="2018-06-16T03:11:57.927" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10450" PostTypeId="2" ParentId="10448" CreationDate="2018-06-16T08:04:59.637" Score="2" Body="&lt;p&gt;When you suspect timing problems with FT8 decodes, simply manually adjust your computer clock to see if the situation improves. This is also the standard recommendation when you suspect the transmitting station's clock is off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is quite possible that you are having timing issues since the Internet is nondeterministic. It is not uncommon that in a multipacket transmission that a packet that was sent earlier will arrive after a packet that was sent later. Requests for resends of bad or missing packets contributes to nondeterminism. If the packet is sent via a connectionless protocol, such as simple UDP messaging, packet loss is also common.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The audio CODEC used in RCForb will also play a role in the success rate of FT8 decodes. It certainly introduces latency on both ends of the connection that may affect FT8 timing. It may also alter the effective audio bandwidth and bandwidth shape which can raise havoc with FT8 decodes.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-16T08:35:20.893" LastActivityDate="2018-06-16T08:35:20.893" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10451" PostTypeId="1" CreationDate="2018-06-16T10:20:17.227" Score="0" ViewCount="250" Body="&lt;p&gt;I have been trying to match my NFC reader coil of size 20*20 cm with a three element circuit - one capacitor in series, another in parallel and one resistor in parallel. I have been using Texas Instruments' method to match the coil. The procedure I'm using is described in this &lt;a href=&quot;http://www.ti.com/lit/an/sloa135a/sloa135a.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;link&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm getting a reasonable Q of 25, but the coil is not exactly matched to 13.56 MHz. I'm able to match it to 1 MHz give or take from 13.56 MHz. I think I might not have accounted for parasitic elements in the circuit. While following the procedure mentioned above, the calculated impedances and the ones mentioned in the VNA differ by a lot. I have tried to populate the PCB with through hole and SMD components with the latter giving slightly better Q. Can someone help me understand how to get close to the calculated results and how to set up the coil without too much effect of loose contacts or parasitics? Thank you!&lt;/p&gt;&#xA;" OwnerUserId="11770" LastActivityDate="2018-06-17T00:12:45.420" Title="NFC coil matching - Q factor improvement" Tags="&lt;antenna-construction&gt;&lt;hf&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10453" PostTypeId="2" ParentId="10451" CreationDate="2018-06-16T10:36:07.760" Score="1" Body="&lt;p&gt;To begin with, your Q is too high. Your passband shape will cause too much sideband attenuation. NFC requires a 2 MHz passband so your Q should be &lt;em&gt;no larger than&lt;/em&gt; 7. That is to say that your should not &lt;em&gt;improve&lt;/em&gt; the Q as your title suggests but rather that you should make it &quot;worse&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without knowing the specific circuit values ($C_s$, $C_p$, and $R_p$), it is difficult to further analyze your circuit. I recommend that you edit your question to reflect the aforementioned values if you would like further guidance. Also report the measured complex impedance of your antenna without the matching network installed. A picture of your assembly (with a scale in view) along with pictures of your PCB layers would also be helpful.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-17T00:12:45.420" LastActivityDate="2018-06-17T00:12:45.420" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10454" PostTypeId="1" AcceptedAnswerId="10457" CreationDate="2018-06-16T12:37:34.143" Score="6" ViewCount="376" Body="&lt;p&gt;I draw two possible architectures for Software Defined Radios below. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the first architecture, I,Q signals are generated at the mixer stage and two ADCs are required. The FPGA down-samples the samples from ADCs and forwards them the USB PHY. Digital Down Conversion is not mandatory in this design (pls correct me if I am wrong).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/c3Uke.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/c3Uke.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In contrast to the first design, the second architecture has only 1 ADC. &#xA;It only creates the I,Q signals inside the FPGA with the help of DSP. The ADC samples at 2x the max frequency present at the input of the Mixer to avoid aliasing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nwBGM.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nwBGM.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am curious to know why an engineer should opt to go ahead with the 1st design over the 2nd design. It seems USRP N210 is having a very similar architecture to the first. So what disadvantages does the second design (I already know ADC needs to be 2X speed, so neglecting that fact) bring to the designer? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, what are some reasons to chose the second design?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks for answering my questioning mind!&lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorUserId="1694" LastEditDate="2018-06-16T15:28:49.030" LastActivityDate="2018-06-19T08:26:05.653" Title="Advantages of IQ generation at Mixer Stage or within FPGA for SDRs" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;usrp&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10455" PostTypeId="1" CreationDate="2018-06-16T17:07:45.150" Score="3" ViewCount="89" Body="&lt;p&gt;So my shortwave radio has adjustable AGC constant with settings between 0.1 s to 8 s. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I always find myself using the fastest AGC settings. Often, I experience 20-30 dB fades and if I use the slower AGC settings, what happens is that the station is too weak to be received until the AGC compensates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, I can't seem to figure out why or when would I want to use the slower AGC constant. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2018-06-16T20:14:30.707" Title="What's the use case behind long AGC constants?" Tags="&lt;receiver&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10456" PostTypeId="2" ParentId="10455" CreationDate="2018-06-16T20:14:30.707" Score="6" Body="&lt;p&gt;CW is one reason. CW is on-off keying, so if the AGC reacts at a timescale similar to or shorter than the transitions of the signal, it will partially cancel the signal, making it &quot;muddy&quot; and more difficult to copy. 15wpm morse has a dit length of 0.08 seconds, making a dah or an inter-letter space around 0.24 seconds, so a fast 0.1s AGC will do it quite a bit of harm. This doesn't really explain the &lt;em&gt;very&lt;/em&gt; long settings, but it does explain why an AGC constant of 1 second or so is useful.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2018-06-16T20:14:30.707" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10457" PostTypeId="2" ParentId="10454" CreationDate="2018-06-17T11:22:20.740" Score="5" Body="&lt;p&gt;Well, the need for one ADC that's twice as fast is definitely a very important factor!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same &quot;it gets harder with rising frequency&quot; argument applies to the anti-aliasing filter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Building a low-pass filter of pass band edge frequency $f_{cutoff}$ and stopband start frequency $f_{stop}$ depends in complexity on how narrow the transition between pass- and stopband is, &lt;em&gt;in terms of passband width&lt;/em&gt;. In other words, if you want your stopband to start 1 MHz after your passband ends, it's easier if your passband ends at 10 MHz than if it ends at 20 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, remember that SDR architectures are also born out of demand to fit a specific use case, which often entails specific communication standards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is kind of a recursive argument, but: Standards like LTE, WiFi, or DVB-T were invented with the quadrature mixer in mind. That means that they can work around the technological problems of the quadrature mixer (mostly, LO leakage leading to a DC spur, meaning that in all these OFDM systems, the DC carriers are left unused, as that's where you'd see your LO)!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-06-17T11:22:20.740" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10458" PostTypeId="2" ParentId="10447" CreationDate="2018-06-17T11:28:05.117" Score="2" Body="&lt;p&gt;Yes, that's mathematically and technologically possible. Because Mike already said the latter, let me elaborate on the math side:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that SSB is really just AM, with one half of the transmit spectrum suppressed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, do the following thought experiment: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You want to transmit a single RF tone at frequency 100.5 kHz. All you have is a SSB transmitter that can tune in 1 kHz steps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you can do is simply tune to 100 kHz, use the upper side band, and send a 500 Hz tone. Simply because AM does nothing but mixing up your baseband signal by a carrier frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you think about that, you could also PSK-modulate your 500 Hz tone. You will have a PSK transmission at 100.5 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, regarding what things to worry about:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;filtering: the bandwidth of the sideband you're using must fit the bandwidth of PSK you're transmitting. &lt;/li&gt;&#xA;&lt;li&gt;That bandwidth in turn is defined by your PSK modulator's &lt;em&gt;pulse shape&lt;/em&gt;. A common pulse shaping filter is the root raised cosine, but that's just a popular choice that allows for easy matched filtering in the receiver. If you want to use a digital mode, you'd want to stick with the pulse shape they define¹.&lt;/li&gt;&#xA;&lt;li&gt;AGC: TX Side: won't do anything, since PSK is inherently constant-envelope, if you look at it from the perspective of the control loop in charge of keeping voice amplitude about constant: the symbols themselves have constant power, and the transitions between them happen much faster than a control loop that mustn't destroy voice would be allowed to correct; in control theory speech: the bandwidth of amplitude variations of any reasonable PSK transmission is much higher than the AGC loop filter's bandwidth.&lt;/li&gt;&#xA;&lt;li&gt;AGC: RX Side: adjusting the gain of an amplifier does have an effect on phase, which is ummm not optimal if your information is &lt;em&gt;in&lt;/em&gt; that phase. So, in a proper PSK receiver system, you'd start with high gain, and wait to see the start of a transmission by its preamble. You'd use that preamble, which usually is long and robust enough, to &quot;train&quot; the AGC and then &quot;lock&quot; it to the resulting gain setting. Nice thing about PSK is that it's relatively robust against driving receiver amplifiers slightly nonlinearly, so in doubt, the algorithm that does the &quot;what's the proper AGC setting&quot; is allowed to risk slight overdrive in case the transmission strength increases during one packet. Now, you'd typically design your packets to have a length that is no longer than what you'd assume your channel to &quot;hold&quot; a gain value, but that's &lt;em&gt;system&lt;/em&gt; design, and might be leading too far.&lt;/li&gt;&#xA;&lt;li&gt;Now, you mentioned that the SSB input might very well be fitted for voice comms, and that's a real problem: No way on earth that thing is going to have a flat passband – it might emphasize voice frequency components that are expecially relevant for understandability, and cut off very early. Also, might intentionally not be a linear system.  Your only way around that is actually compensating that on TX side. If you want more bandwidth than your voice input is reasonably flat about, you'll need to pre-equalize your signal so that it comes out of that voice filter &quot;flat&quot;. Finding the equalizer that does that is usually a non-trivial task. It'd be enough to find the perfect equalizer once, and use it to counter the emphasis of the voice filter, but from a practical point of view: Have you considered sniffing your own signal with e.g. an RTL dongle and using your &lt;em&gt;known&lt;/em&gt; own &quot;perfect&quot; transmit signal to find an equalizer that reverts the filter effect? Do that in a loop, and iteratively convolve the equalizer coefficients that get automatically estimated with your momentary TX equalizer taps to pre-equalize your transmissions. If my thinking is right, your estimator will in the end converge to a &quot;need no more equalization&quot; state, which means that your pre-equalizer does what it should.&lt;/li&gt;&#xA;&lt;li&gt;Since equalizers are hard, start with low baud rates = low bandwidth first. Maybe a 100 Hz tone with 50 bd – that'd be trivial to come up with: &lt;img src=&quot;https://gist.githubusercontent.com/marcusmueller/ef3afb4936a3cfaedf222e08827a7e7f/raw/7a2b0677a356b2765446c43581fb3814702904f6/audio-PSK.grc.png&quot;&gt; &lt;a href=&quot;https://gist.githubusercontent.com/marcusmueller/ef3afb4936a3cfaedf222e08827a7e7f/raw/7a2b0677a356b2765446c43581fb3814702904f6/audio-PSK.grc&quot; rel=&quot;nofollow noreferrer&quot;&gt; GRC File - open in GNU Radio companion&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-06-17T13:25:05.960" LastActivityDate="2018-06-17T13:25:05.960" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="10459" PostTypeId="1" CreationDate="2018-06-17T14:08:44.807" Score="3" ViewCount="517" Body="&lt;p&gt;I have been designing a 20 x 20 cm square NFC reader antenna which looks like this:&lt;a href=&quot;https://i.stack.imgur.com/ZNsNz.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZNsNz.jpg&quot; alt=&quot;NFC Reader antenna front&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/5zmOd.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5zmOd.jpg&quot; alt=&quot;NFC Reader antenna back&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to make it work and detect NFC tags at certain distance, it needs to be matched. To do that I was trying to implement a really easy three component matching procedure described in here &lt;a href=&quot;http://www.ti.com/lit/an/sloa135a/sloa135a.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ti.com/lit/an/sloa135a/sloa135a.pdf&lt;/a&gt;. Unfortunately it did not work for me. The first step in this procedure is to measure the impedance of the unmatched coil. What would you ideally expect is to have a neglectably low resistance (like 1-2 Ohm) and some positive reactance (like 450-500 Ohm). At this step I'm having a surprisingly high resistance - up to 200 Ohm. This ruins the whole matching procedure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I was still able to make this antenna work trying various capacitors and resistors with different values. You can see the resulting equivalent circuit that I have drawn on the second picture of the antenna. I have a 27 pF capacitor in series with the coil and a 51 kOhm resistor in parallel with it. I have measured the inductance of the coil - it is approximately 3.5 uH. Measured S11 curve for this antenna can be seen here: &lt;a href=&quot;https://i.stack.imgur.com/ezL5i.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ezL5i.jpg&quot; alt=&quot;NFC Reader - S11&quot;&gt;&lt;/a&gt; It has a quality factor of approximately 15.5. Antenna is working and it works pretty good, detecting the tags up to 12 cm distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that I completely don't understand how this antenna works and I'm puzzled with the fact that it is resonating at 13.4 MHz. With 27 pF capacitor and 3.5 uH coil in series it should have been resonating around 16.37 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anybody have any idea about why this is happening and how the antenna works? I would really appreciate any considerations or ideas about my design. Probably I'm doing something wrong or matching procedure is wrong or layout is incorrect.&lt;/p&gt;&#xA;" OwnerUserId="11776" LastEditorUserId="76" LastEditDate="2018-06-17T14:43:37.253" LastActivityDate="2018-06-17T20:47:48.377" Title="Understanding of NFC Reader Antenna matching" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;hf&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10460" PostTypeId="2" ParentId="4938" CreationDate="2018-06-17T14:44:21.163" Score="3" Body="&lt;p&gt;I did apparently succeed in inhibiting transmit on a UV-5RA memory(reports Firmware version BFB297 but above BFB296 may not be updated with each revision) without using a computer.   The method used was to set the offset and direction such that you were instructing the radio to transmit on 0Hz.   The behavior while programming isn't quite what you would expect, and I initially thought I was unsuccessful, but it still appears to disable transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When actually transmitting, the display should change color to yellowish (depends on menu settings) and the signal strength icon should appear.  It will also display the transmit frequency instead of the receive frequency if they are different but won't change if the transmit frequency is invalid.  If you have inhibited transmit, display should not change in any way (unless you receive a transmission) other than the backlight may come on afterwards if it was off.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have included very detailed instructions below.   In many cases, those who need to inhibit transmit the most (non-licensed operators) may be those least skilled in operating the radio.   Also, even many licensed operators have difficulty programming these model radios even when trying to do something normal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the example below, I put 146.850 in memory 126; replace those values wherever they appear with the desired ones. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some notes on operation:&#xA;In these instructions, [MENU] is preceded by [EXIT] to make sure you are starting from the correct state (not in menu).  When entering one or two digits after menu as a shortcut to a specific menu item, type those digits quickly or radio will time out.  If an instruction says &quot;Repeat&quot; something &quot;until&quot; something, repeat the operation as many times as necessary until you see the correct state on display; as a bonus, the available settings will repeat in a loop so you don't have to catch the correct setting the first time and can see exactly what is changing on the display and which most closely resembles the desired setting (in case you are uncertain about which part of the display to look at).   Target value could be in top line, bottom line, mode indicators (mostly above top line), channel numbers (to right of top/bottom lines), carets (to left of top/bottom line).  The carets show you whether top or bottom line is active.  In menus, the top line shows the menu item name and the bottom shows the value and you hit [MENU] to bounce back and forth between them and repeat [UP ARROW] and/or [DOWN ARROW] to select the desired menu item (if on top line) or value (if on bottom line).   Returning to the top line using [MENU] enters a value, pressing [EXIT] before doing so will abort the change.   Instead of using arrows to select menu item you can enter a one or two digit (quickly) value while on top line and for some values you can enter digits on bottom line.  When entering a sequence of digits, do so quickly as the radio will time out if you take too long; in most cases you can simply repeat the digit sequence from the start as you will be in the same state you were in before you started entering digits though the menu item or value may have changed.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Consider perform a PARTIAL (VFO) reset to disable any weird or leftover settings that might be written to memory.  [EXIT] [MENU] [4] [0] (show &quot;RESET&quot;) [MENU] Repeat [up arrow] until bottom line says &quot;VFO&quot; [MENU] (show &quot;SOURCE?&quot;) [MENU] (briefly show &quot;WAIT...&quot;).    Warning.  If you don't select VFO, you will erase all your memories. Hit [EXIT] to abort.&lt;/li&gt;&#xA;&lt;li&gt;Turn of dual watch as it is reported to interfere with programming.  [EXIT] [MENU] [0] [7] [MENU] Repeat [up arrow] until second line says &quot;OFF&quot;, [MENU] [EXIT]&lt;/li&gt;&#xA;&lt;li&gt;Switch to top line: Repeat press [A/B] until caret points upward&lt;/li&gt;&#xA;&lt;li&gt;Switch to VFO mode.  Repeat press [VFO/MR] until channel numbers disappear.&lt;/li&gt;&#xA;&lt;li&gt;Repeat press [BAND] (if present) until top line shows a frequency in the desired band&lt;/li&gt;&#xA;&lt;li&gt;Erase channel 126: [EXIT] [MENU] [2] [8] (Show &quot;DEL-CH&quot;) [MENU] [1] [2] [6] [MENU] [EXIT].   Subsitute desired channel number for 126 in this and subsequent instructions.  If channel is not blank, radio may not save to it and/or will save the second half (TX frequency) instead.&lt;/li&gt;&#xA;&lt;li&gt;Set frequency to desired value (example 146.850 = [1] [4] [6] [8] [5] [0])&lt;/li&gt;&#xA;&lt;li&gt;Set OFFSET to same value [EXIT] [MENU] [2] [6] (show &quot;OFFSET&quot;) [MENU] [1] [4] [6] [8] [5] [0] [MENU] [EXIT]&lt;/li&gt;&#xA;&lt;li&gt;Set duplex direction (SFT-D) to minus [EXIT] [MENU] [2] [5] (show &quot;SFT-D&quot;)[MENU] Repeat [up arrow] until display shows minus (&quot;-&quot;) [MENU] [EXIT]&lt;/li&gt;&#xA;&lt;li&gt;setting T-CTCSS is probably unnecessary since you are trying not to transmit (but don't rely on repeater not keying up as proof of non-transmission).  You could set R-CTCSS if desired and appropriate.&lt;/li&gt;&#xA;&lt;li&gt;At this point, you should be able to test before saving.  Press [PTT] and make sure the signal strength indicator in the upper left hand corner is not displayed and the backlight color doesn't change to yellowish (depends on menu settings).   &lt;/li&gt;&#xA;&lt;li&gt;Save first half of settings to channel 126: [EXIT] [MENU] [2] [7] (Show MEM [MENU] [1] [2] [6] [MENU] [EXIT] (You can also type in the memory channel number instead of using up arrow).   If voice is on, radio will say &quot;receive memory&quot;.&lt;/li&gt;&#xA;&lt;li&gt;Press [*] to enter reverse mode.  Display will not show 000.000 or &quot;R&quot; as you would expect but apparently we are still good.&lt;/li&gt;&#xA;&lt;li&gt;Save the second half of settings (transmit) to channel 126: [EXIT] [MENU] [2] [7] [MENU] [1] [2] [6] [MENU] [EXIT].  If voice is on, radio will say &quot;transmit memory&quot;&lt;/li&gt;&#xA;&lt;li&gt;Press [*] to exit reverse mode&lt;/li&gt;&#xA;&lt;li&gt;Repeat Press [VFO/MR] until channel numbers appear on right side of the display (once should be sufficient in this case).&lt;/li&gt;&#xA;&lt;li&gt;Select channel 126: [1] [2] [6]&lt;/li&gt;&#xA;&lt;li&gt;Press the [PTT] button and observe the display to see if the signal strength icon shows up; if you have inhibited transmit, it should not.  It could also show up (accompanied by sound) if an incoming signal is received at same time.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The insane method of writing to memory twice is a perversion of a procedure required in some other non-chinese radios if, and only if, you need to program an &quot;odd split&quot;.   Those radios would save the transmit and receive settings when you saved a memory but let you overwrite the transmit setting using a separate write instruction if you needed to program an &quot;odd split&quot;.   Odd splits were a way of programming transmit and receive frequencies that were not related to one another by a standard offset value or were separated by a very large offset that might be hard to enter into offset setting or that you wouldn't want to reuse for any other channel.   Odd splits might even cross band boundaries such as using a cross band repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I went to save the results in a memory channel, however, I thought it wasn't working.   Normally, you have to save, hit REVerse ([&lt;em&gt;]), save again, and hit REVerse ([&lt;/em&gt;]) again to exit reverse; this proceedure is necessary to save both the RX and TX frequencies.  But when I hit reverse, the display showed 146.850 and not 000.000.   So I thought I had failed.    But when I tried to check in on the net, the radio did not transmit (nor complain).  And closer inspection appears to indicate it is not transmitting.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had also tried the split to zero method using SAVE, enter 000.000 as frequency, and SAVE again method (alternative to doing OFFSET, SFT-D, REVerse that you can't test before saving) but it wouldn't accept 000.000 as a frequency.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After you are done, clean up your mess.  Set offset back to an appropriate value for the band (000.600 VHF, 005.000 UHF).  Set SFT-D back to OFF.     Make sure radio isn't left in reverse mode.   Performing another partial reset is one way to accomplish this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this method fails, you will actually transmit so use a dummy load, a frequency you are licensed to transmit on (or a control operator who is) and state your call sign, or at the very least an unused frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an old question but this page is still the top search response.&lt;/p&gt;&#xA;" OwnerUserId="8882" LastActivityDate="2018-06-17T14:44:21.163" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10461" PostTypeId="2" ParentId="10459" CreationDate="2018-06-17T19:31:44.613" Score="4" Body="&lt;p&gt;It is very difficult to help you with analyzing a circuit when clearly, and as you stated, your measurements were in error. The electrically fractional wavelength loop will have a very low feedpoint resistance of less than 1 ohm - not the ~200 ohms you incorrectly measured. Until you correct your measurement error, any further analysis will be conjecture.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You mentioned that you measured the inductance of the loop antenna. This is not a helpful metric. The complex impedance of the antenna at the design frequency, prior to adding any matching network components, is the critical metric for calculating the matching circuit components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also take note that your measured Q is a little too high. It should be no more than 7 in order to properly pass the sidebands associated with NFC. Reducing the Q will likely increase your effective NFC distance provided the reduced Q is not obtained through additional resistive swamping.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-17T20:47:48.377" LastActivityDate="2018-06-17T20:47:48.377" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10462" PostTypeId="1" AcceptedAnswerId="10463" CreationDate="2018-06-18T08:37:49.053" Score="4" ViewCount="209" Body="&lt;p&gt;Apologies if this not the right place for this question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm into electronics and now endeavouring into radios and communications.&#xA;Unfortunately I'm not sure what terms to use to find what I'm looking for so I will describe it here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have my home and a rural property around 100km from home.&#xA;I'd like to setup a radio system that I can communicate between both properties. In addition I'd like (if possible) to extend this to a unit in my truck as a third point of contact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What system should I look for? FM, AM, VHF?&#xA;In case of a disaster, which of the above would be more ideal to have?&lt;/p&gt;&#xA;" OwnerUserId="11779" LastEditorUserId="9493" LastEditDate="2018-06-18T13:45:00.493" LastActivityDate="2018-06-19T02:28:36.677" Title="Two way ham radio to communicate between two stations" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;equipment&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10463" PostTypeId="2" ParentId="10462" CreationDate="2018-06-18T11:59:04.137" Score="6" Body="&lt;p&gt;The answer to your question involves both technical and regulatory issues.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Technical Considerations&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio signals can travel between two locations on earth either by line of sight or by propagation which involves bouncing signals off of the atmosphere or other objects. In general, line of sight is a reliable means of communications whereas the use of propagation can yield variable results due to atmospheric conditions, weather, etc. The frequency of the signal determines if it can travel via the propagation of the atmosphere. As the frequency is increased, more of the signal tends to pass through the atmosphere out to space instead of being reflected back to earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For line of sight communications, the two antennas must be able to &quot;see&quot; each other. This means there can be no substantial RF barrier in the line drawn between the two antennas. This includes the earth. If we consider the earth to be a perfect sphere, the height of the antenna can be used to determine the distance a signal can travel until it meets the horizon. Radio waves can go slightly further than the horizon in practice. The following formula approximates necessary elevation to be able to reach a specified &lt;em&gt;radio horizon&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\text{Antenna Height (meters)}\approx(D/4.12)^2 \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where D is the distance to the radio horizon in kilometers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So your 100 km distance would require a tower of approximately 590 meters to support your antenna. If you place a tower at both locations, then they would need to be &lt;em&gt;only&lt;/em&gt; a quarter of this height or approximately 147 meters each. Obviously, this is not a practical solution. If, however, your locations in New Zealand are strategically located on tall hills, you may get most of the needed elevation from the local geography.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formula 1 is only a rough approximation. There are software packages and sites such as &lt;a href=&quot;http://www.va3xpr.net/three-easy-steps-to-creating-rf-coverage-maps-like-a-pro/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt; available that take into account the specific geography of the planned radio locations to reliably predict the suitability of particular frequencies, antenna heights, antenna gain, power, etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Certain radio frequencies regularly &lt;em&gt;bend the rules&lt;/em&gt; and accomplish fairly reliable communications beyond the apparent radio horizon. In the US amateur radio frequency allocations, our 6 meters band (50 MHz) can often support 100 km range distances with modest antenna heights.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For frequencies below 50 MHz, the signals tend to travel longer distances than line of sight due to propagation. The most common form of propagation involves the signal bouncing off of the ionosphere and back down to earth at some distant location. It is even possible to obtain multiple bounces allowing the signal to circle the earth. Unfortunately, propagation conditions vary widely due to weather, conditions on the sun, and the time of day making it difficult to secure reliable communications between two locations. There are however fairly good tools to predict the distance a signal can travel via the current or forecasted propagation conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One technique involving propagation that is frequently used by the military and by hams to obtain short range communications is to deploy simple antennas that essentially aim the RF signal straight up to the atmosphere. By choosing the right frequencies for the atmospheric conditions, the signal tends to be reflected nearly directly downward from the atmosphere effectively spreading the signal over a circle near area the station. Communications in the 800 km range and greater are regularly attainable. The frequencies involved are usually in the 3 MHz to 8 MHz range. The amateur radio 80 and 40 meter bands are often used for this mode of communications dubbed &lt;em&gt;near vertical incident skywave&lt;/em&gt; or NVIS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Particularly when relying on propagation to carry out communications, the amount of transmit power, the type of antenna, and the mode of communications play a substantial role in the effective distance of communications. Voice communication modes tend to be the least range efficient while specialty data communication modes (including Morse code) tend to be the most range efficient. Recent advances in modulation techniques and digital signal processing are blurring this distinction to some degree, however.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio operators also make use of repeaters and satellites that pick up signals and retransmit them in order to increase the effective range of the station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, consider that emergency communications brings in other dimensions such as backup power for the radios, the ability to deploy temporary antennas to replace ones that are damaged, etc. The technical knowledge and experience of an amateur radio operator can prove valuable in emergency circumstances but it does not displace preparedness.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Regulatory Considerations&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most countries tightly regulate the use of the frequency spectrum within their territorial control. In most countries, amateur radio operators obtain a license by passing a technical written test. Once you have obtained an amateur radio license, you are typically restricted in the type of communications you can carry out with your license. In the US, for example, an amateur radio station may not be used for &quot;pecuniary interests&quot;. This rules out most types of business communications. Also be aware that generally all parties wishing to use the radios without supervision must obtain an amateur radio license - but check your local regulations in this regard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another viable option available in many countries is to obtain a business license for your radio system. Regulations vary widely but you generally receive a fixed frequency allocation for your use and communications can be of a business or personal nature. Again, check your local regulations.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-19T02:28:36.677" LastActivityDate="2018-06-19T02:28:36.677" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="10464" PostTypeId="1" AcceptedAnswerId="10465" CreationDate="2018-06-18T13:51:44.117" Score="4" ViewCount="139" Body="&lt;p&gt;I am testing a long cable run (about 90m). This cable has been used outside and inside, for temporary setups.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've set up my VNA with the correct values (velocity factor,...) and the distance to fault is correct when I just connect one side to the RF out connector (S11). I don't see any obvious impedance bumps when looking at the DTF measurement.&#xA;DC resistance of the center conductor and shield is according to the manufacturer specifications for that length. There is no (measurable) DC loss between shield and center. Capacitance is defined at 56pF/m, I measured 5.82nF which seems to correct. So all seems allright.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the datasheet specifies 25.8dB loss per 100m at 1Ghz, but I am measuring 43dB loss (S21).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am wondering if this could be caused by:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;possible moisture in the foam PE dielectric &lt;/li&gt;&#xA;&lt;li&gt;other reasons?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Anything I might be missing? Any other tests I could perform?&lt;/p&gt;&#xA;" OwnerUserId="8263" LastEditorUserId="1362" LastEditDate="2018-06-19T00:26:52.710" LastActivityDate="2018-06-19T00:26:52.710" Title="Why is the insertion loss of my coax cable higher than expected?" Tags="&lt;coaxial-cable&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10465" PostTypeId="2" ParentId="10464" CreationDate="2018-06-18T14:19:46.773" Score="5" Body="&lt;p&gt;Based on your description, I would suspect moisture damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moisture ingress in coax cables typically results in the corrosion of the copper braided wires in the shield. The oxide that forms increases the RF losses of the shield. A simple resistive test of the shield is not usually sufficient to detect this condition. If the center conductor is multi-stranded, a similar oxide problem can result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moisture ingress in coaxial cable left exposed to weather often occurs at the ends the cable but micro cracking in the outer jacket, animal damage, an abraded jacket, etc. are also common causes of ingress. Cable that is partially subterranean and not fully sealed can pull in moisture due to differential diurnal heating and cooling. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-06-18T14:19:46.773" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10466" PostTypeId="2" ParentId="10431" CreationDate="2018-06-18T18:22:28.020" Score="4" Body="&lt;p&gt;I avoid UHF connectors as much as possible. My shack is all Type N outdoors (weatherproof) and all BNC indoors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UHF connectors work fine for HF and even above that. But I hate connectors where you have to wiggle and retighten, then they still leak. Just a poor design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've never seen UHF connectors on current professional broadcast gear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UHF connectors don't have a &quot;real spec&quot; because the military and commercial gear doesn't use them. The best we have is the Amphenol spec, but that only covers Amphenol connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check the specs for each type. You'll notice that the specs for Type N and BNC are much longer, because they have specs for things like contact resistance. Also, note the peak voltage ratings. UHF is 500 V, BNC is 500 V, Type N is 1500 V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UHF: &lt;a href=&quot;https://www.amphenolrf.com/connectors/uhf.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amphenolrf.com/connectors/uhf.html&lt;/a&gt;&lt;br&gt;&#xA;BNC: &lt;a href=&quot;https://www.amphenolrf.com/connectors/bnc.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amphenolrf.com/connectors/bnc.html&lt;/a&gt;&lt;br&gt;&#xA;Type N: &lt;a href=&quot;https://www.amphenolrf.com/connectors/n-type.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amphenolrf.com/connectors/n-type.html&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, Oak Hills Research makes a BNC panel socket that fits in a UHF panel hole. Very handy. I used that to build the Oak Hills dummy load kit with a BNC connector. The connector is on their parts page: &lt;a href=&quot;http://www.ohr.com/parts.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ohr.com/parts.htm&lt;/a&gt;  &lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2018-06-18T18:22:28.020" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10467" PostTypeId="2" ParentId="10441" CreationDate="2018-06-19T00:17:04.853" Score="5" Body="&lt;p&gt;[Discovered this via &lt;a href=&quot;https://ham.stackexchange.com/questions/10441/how-were-1920s-hams-able-to-measure-megahertz-frequency#comment16524_10442&quot;&gt;a comment on another answer&lt;/a&gt;.]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to &lt;a href=&quot;https://en.wikipedia.org/wiki/Lecher_lines&quot; rel=&quot;noreferrer&quot;&gt;their Wikipedia article&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Lecher lines&lt;/strong&gt; were used as frequency measuring devices until frequency counters became available after World War 2.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The idea is to short a transmission line after some distance, forming what we now would call a &lt;a href=&quot;https://en.wikipedia.org/wiki/Stub_(electronics)&quot; rel=&quot;noreferrer&quot;&gt;resonant stub&lt;/a&gt;. The resonant reflections set up standing waves; the nodes of &lt;em&gt;those&lt;/em&gt; waves could then be detected with an RF probe:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The voltage goes to zero at nodes located at multiples of half a wavelength from the end, with maxima called antinodes located midway between the nodes. Therefore, the wavelength λ can be determined by finding the location of two successive nodes (or antinodes) and measuring the distance between them, and multiplying by two.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;But in practice, rather than having a fixed distance-to-short and moving an RF current probe, it sounds like usually there was a movable &quot;shorting bar&quot; under which was marked an appropriate scale:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In operation, the U end acts as a coupling link and is held near the transmitter's tank coil, and the shorting bar is slid out along the arms until the transmitter's plate current dips, indicating the first node has been reached. Then the distance from the end of the link to the shorting bar is a half-wavelength.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Apparently Lecher lines were even used to calculate the speed of light (working from known frequencies back…) before the turn of the century, &quot;an important confirmation of James Clerk Maxwell's theory that light was an electromagnetic wave like radio waves&quot;!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;By September 1946, a &quot;Frequency measurement at UHF&quot; article in Radio News still listed this technique, as well as others which have already been mentioned in other answers/comments here:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;[…] in general practice such great accuracy is not necessary, and frequency measurements at u.h.f. are generally performed by the following methods:&lt;/p&gt;&#xA;  &#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;Wavemeters.&lt;/li&gt;&#xA;  &lt;li&gt;Lecher wires.&lt;/li&gt;&#xA;  &lt;li&gt;Heterodyne frequency meters. &lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;IIUC, what the article describes as a wavemeter is essentially a resonant circuit with a conveniently-labelled variable capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(A PDF of the full issue is currently linked as the &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Lecher_lines&amp;amp;oldid=833633332#cite_note-Endall-1&quot; rel=&quot;noreferrer&quot;&gt;first citation&lt;/a&gt; on the Lecher lines article, which starts on page 50.)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2018-06-19T00:47:13.050" LastActivityDate="2018-06-19T00:47:13.050" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10468" PostTypeId="2" ParentId="10454" CreationDate="2018-06-19T08:15:42.517" Score="3" Body="&lt;p&gt;I would like to add a bit of my intelligence to this topic as I did some extra reading. This answer isn't a stand alone answer but merely a minute extension to the answer posted by Marcus Muller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I feel like one strong reason to generate/extract I,Q waveforms at an earlier stage in architecture-1 is to stop the interference by negative frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More specifically, at the mixer stage, LO multiplies with the RF signal from the antenna. In that case, if  the down converted band comes about/near 0Hz, then parts of the down converted band band may fall to the negative frequency side which will in turn fall back on top of the positive band. This will contaminate the whole intelligence. This process is elaborated below.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/CPafS.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CPafS.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In contrast, if we extract IQ at at the earliest state, we eliminate this problem. This is because I,Q can represent negative frequencies. Hence, at times our LO goes near RF frequency, we can still sustain the intelligence of the message that was transmitted without corrupting it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope I made some sense. &lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorUserId="1694" LastEditDate="2018-06-19T08:26:05.653" LastActivityDate="2018-06-19T08:26:05.653" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10469" PostTypeId="2" ParentId="10431" CreationDate="2018-06-19T20:50:18.057" Score="1" Body="&lt;p&gt;I agree with the sentiment to avoid UHF connectors if at all possible, and in your case, BNC is a better choice if you were to consolidate down to one connector, as long as you're not running crazy high power. For me, they've handled 500 watts without batting an eye, but they're not incredibly durable and very not weather proof. They're cheap enough to replace all the UHFs in the world, however. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Big caveat: BNC connectors for thick cable, like RG-8 or greater, are rare, expensive, and not very durable at the connector interface. That's the only good argument for UHF IMO - they're cheap and natively works with cheap, abundant, low loss RG-8 cable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd also give thought to TNC connectors - it's a threaded BNC that works up to 11GHz, and several types are weatherproof. They're a lot easier to attach/remove than an SMA while still providing good microwave coverage. They're a standard on aircraft for their vibration durability, so they'd also work well on mobile radios...I do wish that was the standard in ham radio instead of UHF!&lt;/p&gt;&#xA;" OwnerUserId="392" LastActivityDate="2018-06-19T20:50:18.057" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10470" PostTypeId="2" ParentId="10431" CreationDate="2018-06-19T21:21:35.497" Score="1" Body="&lt;p&gt;Connectors do cause a lot of problems. Avoid them as much as you can outdoors. Use a soldering iron to make permanent connections where you do not need to connect and disconnect. (Antenna stacking cables for example.) Outdoors waterproofing is essential. When I do T connections or connect a 70 ohm cable to a 50 ohm one for impedance transformation after a T I first solder thin copper foil to make a continous screen. I keep a reasonable distance with teflon insulators to keep the impedance right. (trivial up to about 500 MHz.)&#xA;Then, with epoxy and wowen glassfibre I make the connection mechanically strong and to some extent water tight. Then, very important, I use self vulcanizing tape to cover the joint as well as a couple of cm of the outer jacket of the cables. This provides perfect water proofing. Finally it is necessary to protect the self vulcanizing tape with PVC tape. Make it at least 3 layers if you want more than 10 years lifetime.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For indoor usage, BNC is excellent. You have to be aware of two problems however. Firstly there are computer grade BNC connectors.. They are TOTALLY USELESS for radio. The screen does not connect properly. You would get intermodulation and poor isolation from local noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The standard BNC connectors for radio as well as the N connectors have a too low contact pressure for the screen. This results in pick-up of local interference (computer switch power etc.) as well as in intermodulation. I have shown this in a couple of videos and Internet pages:&#xA;&lt;a href=&quot;http://sm5bsz.com/lir/nfprec/nfprec.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://sm5bsz.com/lir/nfprec/nfprec.htm&lt;/a&gt; Look under the header &quot;connectors.&quot;&#xA;In this video you can see something about IM3 produced in connectors: &lt;a href=&quot;https://www.youtube.com/watch?v=Cy7mbpvBwsg&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=Cy7mbpvBwsg&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can mate a N male with a BNC female, BUT DO NEVER DO THAT!! The diameter of the N center pin is larger and you might bent the center connector of the BNC for a too low contact pressure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SMA connectors are critical. Must be mounted correctly and cleaned properly &lt;a href=&quot;http://www.sm5bsz.com/lir/loss/1296/cleaning/propanol.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sm5bsz.com/lir/loss/1296/cleaning/propanol.htm&lt;/a&gt; &#xA;Just using them without cleaning can cause all sorts of problems. I do not remember where, but i think problems have occured in one of my videos.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Conclusion:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BNC is fine.&#xA;N-connectors behave exactly like BNC with respect to&#xA;contact pressure.&#xA;UHF connectors are excellent on frequencies below 200 MHz. Beware that some of them come with poor dielectric. You need teflon or the most common brown material which I do not know exactly what it is. There are UHF connectors with&lt;br&gt;&#xA;plexiglass (acryl) dielectric and also PVC. They are VERY lossy. The UHF connectors provide a better connection than BNC or N because of the much larger contact area. Use adjustable pliers to tighten firmly. Make sure that the UHF connector is rotated into the correct position.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-06-19T21:21:35.497" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10472" PostTypeId="1" AcceptedAnswerId="10475" CreationDate="2018-06-20T05:55:12.387" Score="9" ViewCount="315" Body="&lt;p&gt;I am surprised how the Superheterodyne Receiver still works and is still in use after coming to realise the impact of Image Frequencies on its performance. Basically, I'm curious how engineers make such an architecture work despite the affect made by Image Frequencies at multiplication stage of Super Heterodyne Architecture. I illustrate the affect of Image Frequencies using the following diagram.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rxyQw.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rxyQw.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As seen, It seems our intelligence on right hand side can be destroyed by the Image Frequencies (whole band of it) standing to the left side to the LO once both signals go through the mixer. I think this is an unavoidable scenario because making Band Pass Filters to eliminate signals close to the left hand side of LO is not practical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine a busy band such as 868MHz. The complete spectrum is busy and filled with &lt;strong&gt;very closely spaced out&lt;/strong&gt; &lt;strong&gt;powerful transmissions&lt;/strong&gt;. In such cases, I can be certain that there will definitely be powerful signals to the left of my LO. Hence, the resulting down converted difference frequency band will always represent both bands to surrounding the LO. This can be more clearly seen by the figure below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2y2Pz.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2y2Pz.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am very interested to know how engineers despite this phenomena still make excellent use of this architecture. What am I missing?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please note that I am fully aware that this problem is eliminated in the later Homodyne architecture. But I would like to make my question very specific to this architecture. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks for your answer/s. &lt;/p&gt;&#xA;" OwnerUserId="1694" LastEditorUserId="1694" LastEditDate="2018-06-20T11:27:37.620" LastActivityDate="2018-06-20T16:49:15.453" Title="How Could Superheterodyne Receiver Ever Work?" Tags="&lt;receiver&gt;&lt;equipment-design&gt;&lt;mixer&gt;&lt;superheterodyne&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10473" PostTypeId="1" CreationDate="2018-06-20T10:13:06.683" Score="1" ViewCount="378" Body="&lt;p&gt;I am planning on building a half-wave dipole that is fed by a coaxial cable. I found a way to do this on antenna-theory (&lt;a href=&quot;http://www.antenna-theory.com/definitions/foldedbalun.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.antenna-theory.com/definitions/foldedbalun.php&lt;/a&gt;).  The article talks about shorting the current that exists due to inductance in the antenna element, by using a folded balun. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know if by using this method it also matches the real parts, if not, is there some way to do this, when I also use the folded balun? The coaxial cable is going to be 50 ohms. &lt;/p&gt;&#xA;" OwnerUserId="11756" LastEditorUserId="4665" LastEditDate="2018-06-20T13:17:09.487" LastActivityDate="2018-06-20T15:00:32.547" Title="Folded balun, impedance matching" Tags="&lt;dipole&gt;&lt;balun&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10474" PostTypeId="2" ParentId="10473" CreationDate="2018-06-20T15:00:32.547" Score="1" Body="&lt;p&gt;A folded balun is effectively a shorted transmission line stub in parallel with the antenna.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ayGlI.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fayGlI.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A quarter-wave transmission line transforms a load impedance to its dual. In this case the load is the short at the end, and the dual of a short is an open. So from the perspective of the feedpoint (represented by V1), the balun looks like an open circuit. An open circuit in parallel with the dipole looks like just the dipole. In other words, the balun has no effect on the feedpoint impedance. It serves only to provide a ground point where the coax shield can be connected, and it can do that because at the middle of the short everything is symmetrical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Making the balun shorter or longer would have the effect of putting some reactance in parallel with the dipole. If the balun is shorter than a quarter wavelength, it will appear as an inductor. If it's longer, a capacitor. At any length it continues to function as a balun since the ground point is still symmetrical with respect to the rest of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I can't say this is a very common thing to do. A half-wave dipole is already a good match to coax, so typically no additional matching is required.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-06-20T15:00:32.547" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10475" PostTypeId="2" ParentId="10472" CreationDate="2018-06-20T16:49:15.453" Score="14" Body="&lt;p&gt;The answer is simple: filtering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, let's say the desired signal is at 800 MHz, and the intermediate frequency (IF) is chosen to be 100 MHz. Mixing the 800 MHz signal with a 900 MHz local oscillator (LO) would get the signal into the desired 100 MHz IF, because 900 - 800 = 100.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But also the image frequency of 1000 MHz would end up at the IF, because 1000 - 900 = 100.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution is simple: add a filter between the antenna and the mixer such that there are no signals at 1000 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The designer can select the IF to make this easier. A higher frequency IF moves the image frequency farther away, making the image frequency easier to reject. However this also makes it more difficult to obtain a sharp band-pass filter at the IF, since the fractional bandwidth will be smaller. This is one of the reasons for the superheterodyne design: a high first IF makes image rejection easier, while a lower frequency second IF makes a sharp channel filter easier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The designer can also put the LO above or below the target frequency, which may place the image frequency such that it avoids broadcast bands which are likely to contain strong interference, etc.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-06-20T16:49:15.453" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10476" PostTypeId="1" AcceptedAnswerId="10478" CreationDate="2018-06-22T05:34:40.220" Score="1" ViewCount="129" Body="&lt;p&gt;Can the Q of a loop antenna be changed?&lt;br&gt;&#xA;If so what are some common techniques?  (Formulae appreciated).&lt;/p&gt;&#xA;" OwnerUserId="11793" LastActivityDate="2018-12-05T08:04:40.867" Title="Can the Q of a loop antenna be changed?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="10477" PostTypeId="2" ParentId="10309" CreationDate="2018-06-22T12:55:36.213" Score="5" Body="&lt;p&gt;Portable antennas are always a compromise. The best antenna in terms of radiation efficiency will be the one that compromises the least. That means basically two things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;make it big&lt;/li&gt;&#xA;&lt;li&gt;get it high (or install many radials to reduce ground losses)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The best antenna in terms of portability will be:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;easy to move (small)&lt;/li&gt;&#xA;&lt;li&gt;easy to set up (not high)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;My advice would be to choose the largest antenna you can which is portable enough. Maybe a Buddipole is what you need, but don't forget you can also throw a half-wave wire dipole over a tree.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-06-22T12:55:36.213" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10478" PostTypeId="2" ParentId="10476" CreationDate="2018-06-23T12:31:35.507" Score="1" Body="&lt;p&gt;An RF tag system is designed to function in the near field of the antennas. The frequencies involved are in the 13 MHz range and the antennas used in these applications are defined as electrically short antennas (&amp;lt;0.1 &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The near field region of the reader antenna has reactive, evanescent currents that easily couple to nearby conducting materials. It is this phenomenon that the passive tag uses to easily harvest energy via its antenna in order to send its response. Any reduction of near field currents or near field distance will result in a shortened read range due to insufficient coupling in order to power the tag.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The OP specifically asked about altering the Q of the antenna system. This can be done by altering the physical aperture of the antenna or by the matching network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is important to understand that the Q of the antenna system determines its bandwidth. If the Q become too high, the narrower bandwidth may not allow proper reading of the tag. As the Q is lower through its matching network, the read range will be reduced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can alter the Q in an existing configuration by changing the value of the resistor in the matching network of the reader. This will also require adjustment of the other matching elements. As the resistance increases, the Q of the antenna system increases and vice versa. Removing the resistor entirely will maximize the Q for a given antenna. Since the resistor effectively dissipates power in order to lower the Q, the higher the value of the resistor, the greater the currents in the near field of the antenna and vice versa.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mathematical approach to analyzing the matching network is an exercise in simple parallel/series reduction to determine the effect of the dissipative effect of the resistor. A blanket formula is not possible due to the various topologies of matching networks.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-05T08:04:40.867" LastActivityDate="2018-12-05T08:04:40.867" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10480" PostTypeId="1" CreationDate="2018-06-23T18:33:36.150" Score="2" ViewCount="667" Body="&lt;p&gt;I have recently bought a 4g Sim Card Router (TP-Link mr6400) and a 4g exterior LTE Antenna. With testing I have now doubled my connection speed. To go one step further, I am looking at the possibility of getting the aerial even higher up my house to chimney level (I'm going to test beforehand). Is there a specific cable other than LTE /4G Antennen-extension cable (i.e. what I'm Googling). What do I need to be looking out for exactly? Also, will there be a loss in signal through a cable of roughly 10 meters, and would it be even noticeable if I were to possibly double my speed again?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I take the aerial up higher I should get a stronger signal? I may also look into a Yagi antenna in the future with more research.&lt;/p&gt;&#xA;" OwnerUserId="11797" LastEditorUserId="8717" LastEditDate="2018-06-24T19:11:17.407" LastActivityDate="2018-06-25T20:56:51.743" Title="4G extension cable and antenna height?" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;wifi&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10481" PostTypeId="2" ParentId="10480" CreationDate="2018-06-23T19:38:11.637" Score="4" Body="&lt;p&gt;If you elevate the antenna, you will absolutely increase your range, &lt;em&gt;provided that the feedline loss is low enough&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coax should be mostly vertical, or the coax loss could offset the height gain. To minimize loss, it should be as short as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That 30m cable is 3mm diameter, according to that Amazon listing; it is likely RG-174. RG-58 coax would have lower losses.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-06-25T20:56:51.743" LastActivityDate="2018-06-25T20:56:51.743" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10482" PostTypeId="1" CreationDate="2018-06-24T05:02:00.107" Score="-2" ViewCount="194" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/P041j.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/P041j.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why the back lobes have such a large area??? I think it may be like &lt;a href=&quot;https://www.cisco.com/c/dam/en/us/products/collateral/wireless/aironet-antennas-accessories/prod_white_paper0900aecd806a1a3e.doc/_jcr_content/renditions/0900aecd806a1a3e_null_null_null_08_07_07-03.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.cisco.com/c/dam/en/us/products/collateral/wireless/aironet-antennas-accessories/prod_white_paper0900aecd806a1a3e.doc/_jcr_content/renditions/0900aecd806a1a3e_null_null_null_08_07_07-03.jpg&lt;/a&gt; &#xA;this image on the right side figure. That may look normal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the data from pattern file excel:&lt;strong&gt;2 0 0 360&lt;/strong&gt; 0 -13.31 1 -13.21 2 -12.93 3 -12.46 4 -11.85 5 -11.17 6 -10.50 7 -9.86 8 -9.28 9 -8.75 10 -8.24 11 -7.75 12 -7.26 13 -6.78 14 -6.32 15 -5.90 16 -5.53 17 -5.23 18 -4.99 19 -4.80 20 -4.67 21 -4.57 22 -4.52 23 -4.51 24 -4.53 25 -4.61 26 -4.73 27 -4.90 28 -5.08 29 -5.25 30 -5.34 31 -5.30 32 -5.10 33 -4.78 34 -4.36 35 -3.92 36 -3.50 37 -3.13 38 -2.84 39 -2.61 40 -2.44 41 -2.32 42 -2.24 43 -2.19 44 -2.17 45 -2.17 46 -2.22 47 -2.30 48 -2.43 49 -2.60 50 -2.80 51 -3.04 52 -3.29 53 -3.56 54 -3.85 55 -4.12 56 -4.32 57 -4.36 58 -4.12 59 -3.52 60 -2.58 61 -1.42 62 -0.18 63 1.06 64 2.21 65 3.27 66 4.22 67 5.09 68 5.87 69 6.60 70 7.29 71 7.94 72 8.59 73 9.22 74 9.84 75 10.43 76 11.01 77 11.55 78 12.04 79 12.50 80 12.90 81 13.26 82 13.58 83 13.85 84 14.10 85 14.32 86 14.52 87 14.71 88 14.87 89 15.02 90 15.14 91 15.23 92 15.28 93 15.29 94 15.26 95 15.17 96 15.04 97 14.86 98 14.63 99 14.37 100 14.07 101 13.74 102 13.37 103 12.98 104 12.56 105 12.09 106 11.58 107 11.01 &lt;/p&gt;&#xA;" OwnerUserId="11738" LastEditorUserId="11738" LastEditDate="2018-06-29T02:05:22.357" LastActivityDate="2018-06-29T02:05:22.357" Title="How do I understand this figure about antenna pattern?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="6" ClosedDate="2018-06-29T06:11:55.813" ContentLicense="CC BY-SA 4.0" />
  <row Id="10484" PostTypeId="1" AcceptedAnswerId="10487" CreationDate="2018-06-24T19:01:37.637" Score="5" ViewCount="390" Body="&lt;p&gt;I am trying to figure out if it is possible to replace inductors like this&#xA;&lt;a href=&quot;https://i.stack.imgur.com/3oJUU.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3oJUU.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; wound by 0.1mm (diameter) copper wire&#xA;with multilayer 0805 SMD inductors. &#xA;Those are supposed to be used inside band-pass filters. Right now &lt;a href=&quot;https://www.linuxquestions.ru/files/f/332/Screen%20Shot%202017-11-17%20at%2020.31.31.png&quot; rel=&quot;noreferrer&quot;&gt;there are&lt;/a&gt; 2 coils but I am thinking if it is worth using SMD inductors + trimmer capacitors there. The main goal is to reduce footprint on the board. &#xA;I want to make cheap mobile rig so am looking for ways to make it lightweight and compact.&lt;/p&gt;&#xA;" OwnerUserId="11243" LastActivityDate="2018-06-27T20:49:17.070" Title="How different is Q-factor of SMD inductor from regular one?" Tags="&lt;equipment-design&gt;&lt;inductor&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="10485" PostTypeId="1" AcceptedAnswerId="10489" CreationDate="2018-06-25T02:50:56.437" Score="2" ViewCount="423" Body="&lt;p&gt;I’m considering buying a Midland GXT1000VP4 radio set from amazon here: &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B001WMFYH4&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amazon.com/dp/B001WMFYH4/ref=cm_sw_r_cp_api_6BfmBbBQZ5VBY&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In Suburban Pennsylvania how much range could I expect from these walkie-talkies? Could I possibly open one/both up and attach an external antenna to extend the range?&lt;/p&gt;&#xA;" OwnerUserId="11806" LastEditorUserId="105" LastEditDate="2018-06-25T13:55:04.637" LastActivityDate="2018-06-25T16:48:46.807" Title="Could I expect 12 mile range with the GXT1000VP4 radios?" Tags="&lt;antenna&gt;&lt;range&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10486" PostTypeId="2" ParentId="10480" CreationDate="2018-06-25T04:44:31.020" Score="1" Body="&lt;p&gt;If your antenna is already outside on a pole, adding coax to lift it up will probably not help your Internet connection speed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The small gain in signal strength from being higher up will be offset by the loss in the longer cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say you use a length of LMR195, which is about 0.5 dB/m at 1800 MHz. By extending the cable 10 m, you'll cause a 5 dB additional loss. You may not get that much additional signal from the increase in height.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you should do is add a &lt;em&gt;second external antenna&lt;/em&gt;. The router has two antenna connectors and LTE uses both in a full MIMO fashion. Adding a second antenna on the mast will allow it to work as designed. It is best to mount the second antenna with the opposite polarisation to the first, but a reasonable vertical separation of 0.5 m will also work. There are also dual-pol antennas in one housing, with two connectors, which will also help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See some test videos showing the doubling &lt;a href=&quot;https://youtu.be/BAaAWdwUjJo&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; , and an explanation &lt;a href=&quot;https://m.youtube.com/watch?v=WB1VMMeTJq0&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2018-06-25T04:44:31.020" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10487" PostTypeId="2" ParentId="10484" CreationDate="2018-06-25T04:49:49.820" Score="8" Body="&lt;p&gt;SMD chip inductors, compared to larger ones, will generally have:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;lower Q&lt;/li&gt;&#xA;&lt;li&gt;higher DC resistance&lt;/li&gt;&#xA;&lt;li&gt;higher SRF&lt;/li&gt;&#xA;&lt;li&gt;lower DC saturation current, if they're ferrite cored&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;But read the datasheet and see if they'll work for your application. Often the higher SRF, smaller size and lower cost are the most important factors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For filter design trade-off, I'd suggest:&lt;br&gt;&#xA;First design the filter with ideal components.&lt;br&gt;&#xA;Then simulate it again with real inductor resistance and Q. (Choose inductors that have SRF several times your operating frequency). &#xA;Adjust inductance to bring the filter back into tune.&lt;br&gt;&#xA;Compare performance to the ideal filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This will give you an idea of the additional losses in the filter due to the small components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For simulations, if you don't already have a tool, I recommend QUCS. It's old and slightly cranky, but it's free and can do almost anything. Others might know better free software.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2018-06-27T20:49:17.070" LastActivityDate="2018-06-27T20:49:17.070" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10488" PostTypeId="1" CreationDate="2018-06-25T06:12:51.470" Score="6" ViewCount="215" Body="&lt;p&gt;I live in the 4th floor of a building with one side facing south and the other north. I am able to use my 2M mobile base transceiver with a mobile magnet mount antenna placed just outside the window. I get fairly decent coverage of areas on one side of the building with this setup. My question: Is there a simple way to couple two mobile antennas (one on each side of the building) so I have good coverage of both (north and south) sides at the same time?&lt;/p&gt;&#xA;" OwnerUserId="11807" LastEditorUserId="76" LastEditDate="2018-06-25T13:36:26.320" LastActivityDate="2018-06-25T13:36:26.320" Title="Two antennas on different sides of a building" Tags="&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;2m-band&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10489" PostTypeId="2" ParentId="10485" CreationDate="2018-06-25T10:54:56.523" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;In Suburban Pennsylvania how much range could I expect from these&#xA;  wallow talkies?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, this if very hard to answer, other than &quot;it depends&quot;.&#xA;If you have an absolute clear day, high pressure, no obstruction (what so ever, not even a bird flying), you may get 12 miles or even more, hilltop to hilltop. However this would be rare and an exception to the normal performance. As terrain and environment changes, you would expect 1-2 mile radius, and even that cannot be guaranteed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be a hit and miss at a distance of 12 miles.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Could I possibly open one/both up and attach an external antenna to&#xA;  extend the range?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You could, but you will be breaking the law. Under FCC rules for FRS the unit need to be type approved, and with that comes the stock antenna. The moment you open it up and tamper with the antenna (read: connect your own antenna) you will break this type-approval.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although the following picture is technically breaking the rules (as you increase EIRP) you will get a more directional performance out of your handset without opening and tampering:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VpVUF.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VpVUF.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;(source: &lt;a href=&quot;http://on3jt.byze.be/build-a-lowcost-yagi-antenna-for-pmr446&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://on3jt.byze.be/build-a-lowcost-yagi-antenna-for-pmr446&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a GMRS license, you will be able to use higher power outputs, and your chances will be improved. See &lt;a href=&quot;https://en.wikipedia.org/wiki/Family_Radio_Service#List_of_FRS_channels_compared_to_GMRS&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;code&gt;here&lt;/code&gt;&lt;/a&gt; for a table with allowed power outputs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately the radio you mention does not lists its power outputs in the &lt;a href=&quot;https://midlandusa.com/wp-content/uploads/2012/02/GXT1000-Owners-Manual1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;code&gt;manual&lt;/code&gt;&lt;/a&gt;, I suggest that you contact technical support to get more information&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2018-06-25T10:54:56.523" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10490" PostTypeId="2" ParentId="10485" CreationDate="2018-06-25T11:16:34.433" Score="3" Body="&lt;p&gt;These radios will operate largely on a line of sight basis with a slight boost from refraction. This is known as the radio line of sight. It is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$D\approx1.41\sqrt{H} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where D is the distance in miles and H is the antenna height in feet. Any difference in elevation should be included in H. Note that D is only an approximation since the earth is not perfectly round and the atmospheric conditions affect the refraction. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you are holding the radio at a height of 5 feet and there are no obstructions (trees, buildings, hills, etc.) between you and the other radio that is at ground level, the range would be ~3.2 miles assuming both radios locations are at the same earth elevation. If the other radio is also held at 5 feet, the range would nearly double.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get to your desired 12 mile range, each radio would need to be at a height of a little over 18 feet, for example - provided that there are no obstructions between the radios at this height.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Changing the antenna would not substantially increase the range since the limiting factor is the line of sight. You should also note that FCC regulations prohibit changing the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formula 1 also points out the marketing centric nature of the 36 mile distance claim. While this figure is likely based on a &lt;a href=&quot;https://en.wikipedia.org/wiki/Link_budget&quot; rel=&quot;nofollow noreferrer&quot;&gt;link budget&lt;/a&gt;, it is not easily attained unless you have the fortuitous situation of having the equivalent of each radio at ~165 feet with no obstructions in-between.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In Amateur Radio and GMRS services, repeaters are used to boost range. The repeater antenna is usually at a significant elevation giving the repeater a large radio horizon. The repeater picks up the signal and retransmits it on another frequency thereby greatly increasing the effective range of individual radios. You can read more about GMRS repeaters at &lt;a href=&quot;https://www.mygmrs.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.mygmrs.com&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-25T16:48:46.807" LastActivityDate="2018-06-25T16:48:46.807" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10492" PostTypeId="2" ParentId="10488" CreationDate="2018-06-25T13:31:04.380" Score="9" Body="&lt;p&gt;As one solution, you can combine the antennas with a power divider. See &lt;a href=&quot;https://ham.stackexchange.com/q/1764/218&quot;&gt;How to combine two 50 Ω antennas such that they appear as one 50 Ω load?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This makes your pair of antennas into a phased array. If there's no overlap between their coverage, you effectively lose half your antenna gain, or 3 dB. This is because on transmit, half your power goes into the other antenna which sends that power in the &quot;wrong&quot; direction. And by &lt;a href=&quot;https://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot; rel=&quot;noreferrer&quot;&gt;reciprocity&lt;/a&gt; the same happens on receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice there will be some overlap in their coverage, you will get areas of constructive and destructive interference between the two antennas depending on their relative phase. The effect will be &lt;a href=&quot;https://ham.stackexchange.com/a/3801/218&quot;&gt;grating lobes&lt;/a&gt;. I'd guess however it's no worse than all the reflections already present in an urban environment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, you could install a switch, and select the antenna which works best for a particular situation. This avoids the 3 dB loss and grating lobes, but of course you have to operate the switch.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-06-25T13:31:04.380" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10493" PostTypeId="1" AcceptedAnswerId="10497" CreationDate="2018-06-25T17:43:15.793" Score="2" ViewCount="96" Body="&lt;p&gt;I don’t have much experience with radios, but I was wondering if it would possible to have two CB or GMRS radios that will connect to each other over 8-12 Miles og distance? My budget is about $175. If it helps I would know what direction the other radio would be, it’s in Lancaster PA so not a bunch of interference, and it could be outside on a deck. What would y’all recommend, and is this even a reasonable request for my budget? Thanks a ton.&lt;/p&gt;&#xA;" OwnerUserId="11806" LastActivityDate="2018-06-29T20:17:15.630" Title="Is it possible to get a set of radios that will work 10 Miles in suburbs?" Tags="&lt;antenna&gt;&lt;united-states&gt;" AnswerCount="1" CommentCount="0" ClosedDate="2018-06-26T11:38:33.120" ContentLicense="CC BY-SA 4.0" />
  <row Id="10494" PostTypeId="1" AcceptedAnswerId="10496" CreationDate="2018-06-25T18:48:09.730" Score="1" ViewCount="94" Body="&lt;p&gt;When I hear that a base camp antenna has a range of 15-50 Miles does that mean it could reach a radio with a small antenna within that range, or that it would need to reach a radio with the same antenna?&lt;/p&gt;&#xA;" OwnerUserId="11806" LastActivityDate="2018-06-25T19:43:23.277" Title="What does an antenna range really mean?" Tags="&lt;antenna&gt;&lt;range&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10496" PostTypeId="2" ParentId="10494" CreationDate="2018-06-25T19:43:23.277" Score="7" Body="&lt;p&gt;With so many variables (antenna height, terrain, power, receiver sensitivity, frequency band, modulation mode, line loss, interference, time of day, other obstacles, (just to name a few)) such &quot;ratings&quot; are generally meaningless.  About all you can glean is that the manufacture claims that such an antenna might have more gain than one that claims a range of, say, 5-10 miles.  And even then, Your Mileage May Vary.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-06-25T19:43:23.277" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10497" PostTypeId="2" ParentId="10493" CreationDate="2018-06-25T21:58:45.770" Score="1" Body="&lt;p&gt;This depends largely on the elevation and clear line-of-sight conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will find your answer under this question&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/10485/9493&quot;&gt;Could I expect 12 mile range with the GXT1000VP4 radios?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;included a simple formula so that you may arrive at a concise conclusion.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-29T20:17:15.630" LastActivityDate="2018-06-29T20:17:15.630" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10498" PostTypeId="1" CreationDate="2018-06-26T00:51:58.507" Score="5" ViewCount="745" Body="&lt;p&gt;If I wanted to build a mostly-portable-but-still-comprehensive kit to use in emergencies, either my own, or simulated ones through ARES or RACES, what should I put in the kit?  I'd prefer responses to be generic (see below), though I won't complain about specific gear lists.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm thinking no larger than a set of these Rigid boxes from Home Depot: &lt;a href=&quot;https://www.homedepot.com/p/RIDGID-22-in-Pro-Organizer-Black-222571/205440492&quot; rel=&quot;noreferrer&quot;&gt;top&lt;/a&gt;, &lt;a href=&quot;https://www.homedepot.com/p/RIDGID-22-in-Pro-Tool-Box-Black-222570/205440481&quot; rel=&quot;noreferrer&quot;&gt;middle&lt;/a&gt;, &lt;a href=&quot;https://www.homedepot.com/p/RIDGID-22-in-Pro-Gear-Cart-Black-222573/205441921&quot; rel=&quot;noreferrer&quot;&gt;base&lt;/a&gt;.  As far as antenna, no more poles and antennas than a single person can carry in a large/XXL duffle bag.  I'm thinking tripod mount, &lt;a href=&quot;http://wb3gck.craiglabarge.com/drive-on-portable-antenna-support/&quot; rel=&quot;noreferrer&quot;&gt;vehicle tire mount&lt;/a&gt;, or rope-in-a-tree mount.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;1 - 3 mobile radios&lt;/li&gt;&#xA;&lt;li&gt;Emergency scanner&lt;/li&gt;&#xA;&lt;li&gt;Power supplies for above&lt;/li&gt;&#xA;&lt;li&gt;Enough battery capacity to run them for xx hours&lt;/li&gt;&#xA;&lt;li&gt;SWR meters for the bands in use by the radios above&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://learn.adafruit.com/freq-show-raspberry-pi-rtl-sdr-scanner/usage&quot; rel=&quot;noreferrer&quot;&gt;One of these widgets&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;Book with local repeaters&lt;/li&gt;&#xA;&lt;li&gt;Laptop with programming cables for radios&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4476" LastEditorUserId="4476" LastEditDate="2018-06-26T23:25:03.737" LastActivityDate="2018-06-28T21:10:47.363" Title="What should I put in a &quot;Go box&quot;, &quot;Go bag&quot;, or &quot;go kit&quot; for emergency communications?" Tags="&lt;diy&gt;" AnswerCount="2" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="10499" PostTypeId="2" ParentId="10309" CreationDate="2018-06-26T02:25:30.910" Score="4" Body="&lt;p&gt;End-fed half-waves (EFHW) are popular with &lt;a href=&quot;http://sotadata.org.uk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;SOTA&lt;/a&gt; operators, and they understand portable. If you'll be operating where there are trees, you can tie a rock to some cord, throw it over a tree, and hoist up a 10 meter piece of wire.  If no trees, you'll have to carry a 30 ft fishing pole, but they can be found and the collapse to fit into a trunk.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a suitable impedance matching unit, 10 meters of wire will operate well on 20 meters as an EFHW.  Replace the matching unit with a binding-post-to-BNC adapter, add a 20 meter counterpoise, and the hoisted wire acts as a 1/4 wave on 40 meters.  If you have an ATU, it will also suffice on 17m and 30m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've personally used this on hundreds of outings.  You can't get much more portable than a coil of 24 AWG wire.  While RF in the shack can be a problem for an EFHW, you aren't in a shack when you're portable.  It may be sensitive to noise, but if you're portable, you're probably not near RFI sources.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Building an EFHW - You can certainly build the impedance matcher, but there are many available commercially.  You'll generally have to cut a length of wire.  Borrow an antenna analyzer to trim it to length.  That's a level of &quot;construction&quot; which someone who is all thumbs can handle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Loops can be fiddly for HF.  Dipoles require supporting center and ends which can be a chore for a rapid portable setup.  EFHW goes up quick, is easy to carry, and is reasonably effective.&lt;/p&gt;&#xA;" OwnerUserId="11810" LastActivityDate="2018-06-26T02:25:30.910" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10501" PostTypeId="2" ParentId="10482" CreationDate="2018-06-26T18:16:30.967" Score="2" Body="&lt;p&gt;Yes, you might find this article on &lt;a href=&quot;https://www.cisco.com/c/en/us/products/collateral/wireless/aironet-antennas-accessories/prod_white_paper0900aecd806a1a3e.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna Patterns and their meaning&lt;/a&gt; helpful. In it they provide a diagram showing the typical plot as you would see it drawn; you have already linked to substantially the same image in your question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/K7UOP.jpg&quot; alt=&quot;Cisco antenna pattern example&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see that &lt;em&gt;in this case&lt;/em&gt;, 0º is the &quot;front&quot; of the antenna, +90º is the left side, -90º/270º is the right side, and ±180º is the back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think your question is, &quot;why does my data show a 'main lobe' off to the left side; why is the maximum gain centered around 90º instead of at 0º?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We cannot answer this question, because you have not told us:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;how the data was obtained&lt;/li&gt;&#xA;&lt;li&gt;what the data is supposed to represent&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You have shown a chart that looks odd if interpreted as a &quot;final&quot; azimuth plan pattern. But:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;perhaps the data is from a raw collection and has not been centered to the physical antenna?&lt;/li&gt;&#xA;&lt;li&gt;perhaps it is an elevation plane pattern instead? (this seems plausible given the lack of symmetry even if re-centered!)&lt;/li&gt;&#xA;&lt;li&gt;what others are teasing about: perhaps the data isn't from any antenna measurement at all but something else?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;We cannot tell since you have not given us any context of where this data came from and what it is documented to represent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note also in that article:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The orientation of the actual plot is largely dependent on the orientation of the antenna in the measurement system and that's all there is to it.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You can see this at play if you look at their Yagi example diagrams, where the main lobe is recorded at 90º rather than 0º.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Interpreting any plot data depends on &lt;a href=&quot;https://en.wikipedia.org/wiki/Metadata&quot; rel=&quot;nofollow noreferrer&quot;&gt;metadata&lt;/a&gt;, i.e. some sort of annotation/documentation with details about how it was gathered and its relative reference. Without that it's not much more than random numbers.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;By the way, here's an example of an elevation pattern from the same article. Because of ground plane effects, the pattern is not so symmetrical:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/hMUZ4.jpg&quot; alt=&quot;Cisco elevation diagram example&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2018-06-27T17:36:05.590" LastActivityDate="2018-06-27T17:36:05.590" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10503" PostTypeId="2" ParentId="10498" CreationDate="2018-06-27T13:36:00.383" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I wanted to build a mostly-portable-but-still-comprehensive kit to use in emergencies, either my own, or simulated ones through ARES or RACES, what should I put in the kit?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you are active in ARES or RACES, they will support served agencies. The potential needs of these agencies and your role within the organization will determine the contents of your go-kit. My local ARES has a field operations manual that includes two levels of go-kits for the average member. The go-kit and your skills get tested and refined through regular drills, simulations, and desk-top exercises. We also update our field manuals based on the lessons learned from these drills.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Your Role&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can imagine that if your role is to staff an EOC (Emergency Operations Center) or a Comms Trailer, your go-kit might be rather sparse - probably an HT and your personal effects. On the other hand, if your role is to provide comms support for your local SAR (Search and Rescue) team, your go-kit might be rather extensive including the ability to deploy cross band, hill top radios, for example. In my case, my go-kit is actually a go-truck as I have state wide responsibility to provide technical assistance in the event an emergency. I have spare repeaters, antennas, RFI kits, AC and DC distribution systems, a spectrum analyzer, technical reference manuals, etc. that get loaded into the truck based upon the needs. Clearly this go-kit is different from most people's idea of a go-kit. The point is knowing your role is the key to stocking your go-kit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Deployment Location and Duration&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The location and duration of your deployment has a profound impact on the contents of your go-kit. Most of us could comfortably operate for 8 hours or so with just our technical gear. Beyond that, issues such as personal hygiene, F&amp;amp;H (Food and Hydration), sleeping gear, etc. start to come into focus and must be addressed in the go-kit plan or in the site logistics plan.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The duration and location can also impact the power requirements of your portable/mobile operations. If your assignment is to do police or fire ride-alongs for support comms, do you have the right gear to plug into the vehicle power and to deploy an antenna on the vehicle? Your stack of batteries may only last for a few hours and then you may find that your cigarette adapter cord isn't usable because all sockets are already taken or at capacity. On the other hand, if you are providing comm relays for a wild fire team, your nifty solar panel may not be at all practical since the sun is too obscured by smoke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Practice&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hopefully your ARES/RACES team conducts a couple of drills a year to test the environment, your skills, and your gear. This also helps to understand the served agency's command structure, their terminology, their temperament, and the type of comms they really need (perhaps contrasted to what they asked for). It also gives them a chance to experience your capabilities and expertise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Practicing with the served agencies may also highlight unanticipated issues. For example, many are surprised when their trusty $40 Chinese HT is rendered completely useless in an RF dense environment like an EOC. The lesson learned may be that a different radio is needed for the go-kit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the absence of organized practice drills you should, at the very least, setup your gear in the envisioned field conditions and try operating it for the duration you anticipate being deployed. This not only enhances your skills, but it will test the readiness and completeness of your gear. It is usually the basic things that get overlooked - things such as flashlights, pens, communication forms, frequency charts, a comfortable chair, headphones, medications, contact supplies, etc. that are not thought of in advance but become painfully obvious with realistic practice and drills.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Laptop with programming cables for radios&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;While at first glance, this would could fall under the category of &quot;be prepared&quot;, I would cynically view this as a red flag indicating lack of preparation. Today's radios typically have a hundred or more memories in them. With proper planning, the radio can be programmed in advance for most scenarios. For example, our ARES field manual has all of the frequencies listed for all repeaters in our county and all adjoining counties. The list includes simplex, reverse repeater pairs, and predetermined cross banding frequencies. We regularly offer programming of radios with this list at our meetings. Our field manual also includes all FRS, GMRS, MURS, NWS, and served agency frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;While the laptop could prove helpful, is there other gear that could take its place that would be more effective in helping you to carry out your role?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Identification&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Emergency situations generally involve restricted access to certain locations. You must have the right identification with you to gain access. Your served agencies will facilitate gaining the proper credentials including recognized photo ID cards. For unanticipated issues, having your passport, drivers license, and a copy of your FCC license(s) may be helpful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Grab Lists and Refresh Lists&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While a basic go-kit can be prepared in advance, many times there are things that need to be grabbed at the last minute. Examples include medications, snacks, identification, or a generator and gas can. A list that is prominently attached to your go-kit can help you to avoid forgetting these items &quot;in the heat of the battle&quot;. Force yourself to check-off items on the list as they are packed if your list includes more than a few items.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also use a grab list to enhance your go-kit for longer or different deployments. The grab list could include the items needed to expand your day go-kit to a three day go-kit, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Several items in your go-kit may have expiration dates and should be replaced or refreshed on a periodic basis. Examples include alkaline batteries, bottled water, snack bars, hand warmers, and gasoline. Keep a &quot;refresh&quot; list of these items along with a &quot;replace by&quot; or &quot;do by&quot; date. Take this list in hand once a month and check for anything in need of attention. Don't forget to include charging rechargeable batteries on this list as well as periodic maintenance items such as generator start-up and test, oil changes, updating programmed frequencies, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The Family&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Emergency deployments usually involve leaving the family behind while you go on your assignment. Don't overlook their own safety/security and their concerns about your safety while you are deployed. Your go-kit should include plans and capability to communicate with your family. They should have a complementary plan accessible to them at home so they know how they can get in touch with you. Don't forget to practice this plan with them as well.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-27T13:54:42.387" LastActivityDate="2018-06-27T13:54:42.387" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10504" PostTypeId="1" CreationDate="2018-06-27T23:41:27.667" Score="6" ViewCount="278" Body="&lt;p&gt;A comment on &lt;a href=&quot;https://ham.stackexchange.com/questions/10498/what-should-i-put-in-a-go-box-go-bag-or-go-kit&quot;&gt;this question&lt;/a&gt; says to &quot;check the cluster&quot;. What does it mean to &quot;check the cluster&quot;? I'm guessing it's a website. I did an internet search and &lt;a href=&quot;http://www.hamcluster.net/Map.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hamcluster.net/Map.aspx&lt;/a&gt; seems to be limited to DX.&lt;/p&gt;&#xA;" OwnerUserId="4476" LastEditorUserId="76" LastEditDate="2018-06-29T14:10:17.043" LastActivityDate="2018-12-02T19:01:37.713" Title="I was told to check the cluster. What does that mean and how do I do that?" Tags="&lt;jargon&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10505" PostTypeId="2" ParentId="10504" CreationDate="2018-06-28T00:01:16.767" Score="3" Body="&lt;p&gt;Typically,  &quot;the cluster&quot; &lt;em&gt;is&lt;/em&gt; the DX Cluster. The terminology goes back to the 80s.  There are a few ways to get to it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.dxsummit.fi&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.dxsummit.fi&lt;/a&gt;.  is one.&#xA;&lt;a href=&quot;http://www.eham.net&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.eham.net&lt;/a&gt; has a version as well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What were you asking about that generated the &quot;check the cluster&quot; response? &lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-06-28T00:01:16.767" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10506" PostTypeId="1" AcceptedAnswerId="10508" CreationDate="2018-06-28T03:52:45.277" Score="9" ViewCount="718" Body="&lt;p&gt;Many, if not most, ham radio kits (transceivers, tuners, ununs, baluns) require the builder to hand wind and tap their own toroids. (&lt;a href=&quot;https://qrpguys.com/wp-content/uploads/2018/05/tri-band_vertical_assy_042918.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;example&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a considerable area of stress for newbie builders and a failure point for their builds. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can’t think of another component that builders have to essentially make themselves. We don’t wind our own (non-RF) transformers and inductors, for example. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even the bitX folks have a small army of Indian women who are handwinding their toroids for their kits. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why do we have to hand wind our own toroids? Is there something specific to ham toroids that makes them unamenable to mass production? Did they used to be mass produced? Is the market too small because we’re the only folks still using tapped toroids?&lt;/p&gt;&#xA;" OwnerUserId="11462" LastEditorUserId="9493" LastEditDate="2018-06-28T14:51:17.360" LastActivityDate="2018-11-26T19:00:08.250" Title="Why do we have to hand wind toroids?" Tags="&lt;diy&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10508" PostTypeId="2" ParentId="10506" CreationDate="2018-06-28T10:00:34.763" Score="8" Body="&lt;p&gt;Some things are best answered in Song. I don't want to encourage you, but you might hum along to the tune of &lt;em&gt;Eye Of The Tiger&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;It's the wind of the donut&lt;br&gt;&#xA;  It's the thrill of the built&lt;br&gt;&#xA;  Rising up to the challenge of our fingers&lt;br&gt;&#xA;  And the last known capac'tor puffs its smoke in the night&lt;br&gt;&#xA;  and he's watching us all with the eeeeeye of the winder&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, seriously, kits are generally bought because you &lt;em&gt;want&lt;/em&gt; to build something. And self-wound coils are actually possible – how cool is being the manufacturer of your own discrete components?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On a less enthusiastic note, no, there's no reason to wind your own low-power 3.3 µH  inductors as done in the kit you linked to. (You can &lt;a href=&quot;https://www.mouser.de/Passive-Components/Inductors-Chokes-Coils/Fixed-Inductors/_/N-wpczZ1yzvvqx?P=1z0wrgx&amp;amp;Ns=Pricing|0&quot; rel=&quot;nofollow noreferrer&quot;&gt;buy&lt;/a&gt; these, for like, cheap, even for significant currents).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, only problem being that your component reality is that aside from your inductance, you get capacitive effects between windings – so, you either get RF inductors that are wound with that in mind, or you get power inductors that can handle high currents at lower frequencies (where these parasitic effects play little role, and other, higher-µ, core materials still work well).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;High inductance needs either a lot of core material, or higher-µ material, but higher-µ material usually is pretty lossy (and hence leads to lower inductivity and lower Q for the resulting inductor) at high frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's really all not impossible to buy, but bear in mind that you're right, low-volume components are more expensive – buying a bunch of toroid cores, on the other hand, is cheap, since they are used for all kind of inductivities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, discrete coils are, technically, typically the passive component type with the &lt;em&gt;worst&lt;/em&gt; tolerance ranges. So, any circuit that involves an inductivity is thus designed to deal with a large range of values that are &quot;around the nominal value, but not quite the nominal value&quot;; tolerances of 10 or even 20% aren't unusual for power inductors, for example. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if anything, that's the component you want to let people build themselves, and then work around its inaccuracies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let us take a look at the larger 8 µH self-wound inductor in that kit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;QRPGuys Website says it's rated for 10W. It's pretty certain that the largest wave impedance in this system is 50Ω and the lowest around let's say 20Ω, so let's consider the current flowing through a 20Ω system as the worst-case sustained current:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\begin{align}&#xA; P &amp;amp;= U\cdot I\\&#xA;   &amp;amp;= (I\cdot R) \cdot I\\&#xA;   &amp;amp;= I^2 \cdot R\\&#xA;\implies I &amp;amp;= \sqrt{\frac PR}\\&#xA;&amp;amp;=\sqrt{\frac{10\,\text{W}}{20\,\text{Ω}}}\\&#xA;&amp;amp;=\sqrt{\frac12}\sqrt{\frac{\text{VA}}{\frac{\text{V}}{\text{A}} }}\\&#xA;&amp;amp;=\frac1{\sqrt2}\sqrt{\text{A}^2}\\&#xA;&amp;amp;\approx 0.7A&#xA;\end{align}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, let's be careful engineers and overdimension by a factor of 2, so look for 8 µH that guarantees a current of 1.4 A. That inductor's only used for matching at 40 m, i.e. needs to work at 7.5 MHz. Mouser gives me &lt;a href=&quot;https://www.mouser.de/Passive-Components/Inductors-Chokes-Coils/Fixed-Inductors/_/N-wpczZ1yzvvqx?P=1yzdotaZ1yzdosgZ1yzdot5Z1yzdot1&amp;amp;Rl=wpczZer9dZ1z0wp1oZ1z0wq5iSGTwpczZer7uZ1z0wkkfZ1z0wpatSGT&amp;amp;Ns=Pricing%7c0&quot; rel=&quot;nofollow noreferrer&quot;&gt;20 results&lt;/a&gt; and the cheapest is around 55¢ + VAT.  Note that I didn't search for exactly 8 µH, but for +- 10% of that, because, oh well, nothing is ever perfect in this system, and using 7.5 µH certainly hurts less than not accounting for inductivity loss of a TR68-2 toroid at frequencies above 10 MHz...&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4665" LastEditDate="2018-11-26T19:00:08.250" LastActivityDate="2018-11-26T19:00:08.250" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10509" PostTypeId="2" ParentId="10506" CreationDate="2018-06-28T11:15:23.273" Score="12" Body="&lt;p&gt;I suspect the primary reason that the kit supplier does not ship the kit with prewound toroids is that there is insufficient volume to make it economical to have them commercially wound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A second possibility is that the kit supplier views winding toroids as a desirable part of the kit building experience.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A third possibility is that the kit supplier is simply trying to keep the cost of the kit as low as possible since prewound toroids would be more expensive. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A fourth possibility is that the kit supplier is a small, home based business that is not sophisticated enough, or has no desire, to develop a supply chain that can provide prewound toroids.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are machines that wind toroids but their cost is generally out of reach for the hobbyist.  Here is an example from &lt;a href=&quot;http://spwindustrial.com/toroid-coil-winding-machine&quot; rel=&quot;noreferrer&quot;&gt;http://spwindustrial.com/toroid-coil-winding-machine&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bpEWa.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bpEWa.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few years ago I built a solid state, 7 band, linear amplifier. Halfway through winding all the toroids for the bandpass filters, I nearly bought such a machine!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also a maker movement to create homemade toroid winding machines such as this one from &lt;a href=&quot;http://www.instructables.com/id/Simple-Toroidal-Coil-Winder/&quot; rel=&quot;noreferrer&quot;&gt;http://www.instructables.com/id/Simple-Toroidal-Coil-Winder/&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4rLMp.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4rLMp.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-06-29T10:27:36.030" LastActivityDate="2018-06-29T10:27:36.030" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10511" PostTypeId="2" ParentId="10498" CreationDate="2018-06-28T21:10:47.363" Score="2" Body="&lt;p&gt;The Amateur Radio Emergency Service (ARES) for example uses the following checklist (source is &lt;a href=&quot;http://www.arrl.org/files/file/ARES_FR_Manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/files/file/ARES_FR_Manual.pdf&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Basic Deployment Equipment Checklist:&#xA;    When responding to an emergency event, or even a training exercise,&#xA;    there is a minimum set of equipment and personal gear you should bring&#xA;    with you to get the job done. Basic items include:&#xA;        • 2-meter hand-held&#xA;        • 2-meter mag-mount antenna and coax&#xA;        • Earphone&#xA;        • Paper and pencil&#xA;        • ARES ID card&#xA;        • Extra batteries&#xA;        • Appropriate clothing&#xA;        • Food and water&#xA;        The majority of these items should be kept in a “Ready Kit.” Just pick &#xA;    it up on your way out the door for deployment. You might also consider the &#xA;    items on the following list for inclusion in this ready kit, designed to &#xA;    allow you to stay in the field for up to 72 hours.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The same document has a &quot;72 hour&quot; checklist, as well as some interesting info about the operations of ARES. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this is a helpful starting point!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2018-06-28T21:10:47.363" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10512" PostTypeId="1" CreationDate="2018-06-30T09:01:16.573" Score="0" ViewCount="68" Body="&lt;p&gt;I'm not a radio expert and I've never posted on this forum before.  My request might also seem odd but hopefully someone can help me.  I am pretty much a total layman on this subject so will probably be using terms that sound common to people here and I've little understanding of.  Not even sure what tags to use (and as someone with a decent rep elsewhere on Stack Exchange I know this can be a problem to some)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm involved with the hobby of Geocaching, incase you've not heard of it its a global treasure hunting game using GPS coordinates to find hidden containers. In some cases the hiders construct elaborate puzzles for the solver to crack to reveal where a container is hidden. The puzzle I'm trying to crack has been unsolved for almost 7 years with no one finding it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The puzzle has a theme of Cold War espionage, I've found various recordings on line of Morse code that I've translated. There are also several recordings which simulate Soviet radio stations and numbers stations. The morse code I've deciphered also refers to broadcasts happening at specific times on specific days. I've also got various frequencies in Kilocycles per second and metre band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if possible could you let me know the following?   ( I know stack overflow people like separate questions on separate threads but as it's all related closely seems better than explaining myself multiple times)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) Is it actually possible for an amateur to set up some kind of radio broadcast to run at specific times which would then run indefinitely for the past 7 years like a Numbers Station?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) The messages I've decoded include the following &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Broadcasts in English this Saturday and Sunday at 10.30 pm 0.30am GMT on 665 1106 1554 7190 9530 9665 9735 and 9745 kilocycles per second. At 8.30 am GMT the broadcast is also transmitted on 7320 and 9520 kilocycles per second. ' &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I've tried listening using the GlobalTuners website listening from a radio in Teeside.  I'm convinced i can faintly here morse code being broadcast for two minutes at those times.  My friends think I'm imagining it (possibly because I want it to be true)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) Other information I've got refers to&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;You can hear our transmission everyday at at 13 hours GMT and the 13, 16, 19 and 25 meter band.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I've also got coordinates for specific locations in Scarborough, UK in another clue. (these are not where I'm trying to find the geocache) Is it possible that I need to pick up some kind of amateur radio enthusiast signal at those locations at that time?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anyone can give me any advise and say &quot;yes, this sounds like its possible and an amazing puzzle, let us help get a recording of the message&quot; or &quot;No what your suggesting is impossible&quot; that would be great!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ultimately is it possible for someone close to Scarborough to get a recording during this time?    I'm this close to buying a radio that can record and getting train there one weekend and hoping I'm right but want to check with people who know the subject first.&lt;/p&gt;&#xA;" OwnerUserId="11798" LastActivityDate="2018-06-30T10:47:53.600" Title="Can someone help record a specific radio signal at a specific time to help solve a radio based puzzle?" Tags="&lt;jargon&gt;" AnswerCount="1" CommentCount="0" ClosedDate="2018-06-30T11:06:14.420" ContentLicense="CC BY-SA 4.0" />
  <row Id="10513" PostTypeId="2" ParentId="10512" CreationDate="2018-06-30T10:47:53.600" Score="4" Body="&lt;p&gt;The transmissions quoted most likely are not occurring. The quantity of frequencies is suspicious for any broadcasting service and some of the frequencies themselves are not suitable for broadcasting purposes. Also consider that the significant financial commitment needed to maintain such a broadcast regime for all these years, even on one frequency, makes such a scheme dubious.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, all western countries heavily regulate frequency usage with an expensive and difficult licensing process. This further precludes the possibility of any GC enthusiast supporting such a broadcast scheme. Licensed amateur radio operators cannot legally use most of the quoted frequencies and we are generally not allowed to make third party &quot;broadcasts&quot; of this type.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My GC senses say that given the string of numbers in your decoded messages, perhaps what you are looking for is already in your hand...&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-06-30T10:47:53.600" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10514" PostTypeId="2" ParentId="10504" CreationDate="2018-06-30T11:43:06.303" Score="5" Body="&lt;h2&gt;Definition&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;A DX cluster is a venue (a website or &lt;a href=&quot;https://en.wikipedia.org/wiki/Telnet&quot; rel=&quot;nofollow noreferrer&quot;&gt;Telnet&lt;/a&gt; session) where amateurs may post information about the callsign and frequency of a desirable DX station, so that others may see the posts and then work them if desired.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Per &lt;a href=&quot;https://en.m.wikipedia.org/wiki/DX_cluster&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.m.wikipedia.org/wiki/DX_cluster&lt;/a&gt; :&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A DX cluster is a network [or &quot;cluster&quot;] of computers, each running a software package dedicated to gathering, and disseminating, information on amateur radio DX (long-distance contact) activities.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The first DX cluster software, PacketCluster&lt;a href=&quot;https://www.google.com/search?newwindow=1&amp;amp;safe=active&amp;amp;source=hp&amp;amp;ei=bro-W97jBqq_jwSI1KmQBQ&amp;amp;q=list%20of%20dx%20clusters&quot; rel=&quot;nofollow noreferrer&quot;&gt;2&lt;/a&gt; was realized by US radio amateur Dick Newell, AK1A in the late 1980s, and quickly became popular as a means of exchanging DX-related information. Before the Internet became widely available, the nodes running the cluster software would connect via radio links at certain frequencies allocated within the amateur radio bands. Users of the system would then connect to a node using frequencies different to those used by the nodes.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;When the Internet became widely available, the system was expanded to make use of telnet connections to Internet nodes, in addition to the already established packet radio nodes. Users of internet nodes connect to a particular node using telnet client software.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&quot;DX&quot; (long distance) can have different meanings, &lt;em&gt;depending on what band you are using and where you are located&lt;/em&gt;. &lt;a href=&quot;http://on4kst.com/chat/start.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://on4kst.com/chat/start.php&lt;/a&gt; is the one I use during 160m CW contests. It lists all the bands EXCEPT for the &quot;DX bands&quot; 10, 12, 15, and 20.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;History&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;They started using radio, well before the Internet. Most of those were &lt;em&gt;local&lt;/em&gt; DX &quot;clusters&quot; (though they were not called that back then) on VHF and UHF repeaters. Then Packet Radio came along, followed by PacketCluster software which came into wide use.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Types of DX clusters&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;There are different types of clusters. Some clusters are not necessarily about a foreign country (DX). Assuming you are in the USA, a post may be about a station in a rare US state or grid square, for example. &quot;The&quot; cluster implies that there is only one. Thus when you were told that, you may have been given incomplete information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Telnet&lt;/strong&gt; clusters are accessed from a terminal window (or command prompt), and are text-based rather than graphical.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Other uses&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;A DX Cluster can also be used to announce upcoming contests and DXpeditions, as well as enable users to chat amongst themselves.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Lists of DX Clusters&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;There are too many DX clusters to list here. Google &lt;em&gt;&lt;a href=&quot;https://www.google.com/search?newwindow=1&amp;amp;safe=active&amp;amp;source=hp&amp;amp;ei=bro-W97jBqq_jwSI1KmQBQ&amp;amp;q=list%20of%20dx%20clusters&quot; rel=&quot;nofollow noreferrer&quot;&gt;list of dx clusters&lt;/a&gt;&lt;/em&gt;. As &lt;a href=&quot;https://ham.stackexchange.com/a/10505/8717&quot;&gt;Mike said&lt;/a&gt;,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;http://www.dxsummit.fi&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.dxsummit.fi&lt;/a&gt;. is one. &lt;a href=&quot;http://www.eham.net&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.eham.net&lt;/a&gt; has a version as well. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-12-02T19:01:37.713" LastActivityDate="2018-12-02T19:01:37.713" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="10518" PostTypeId="1" CreationDate="2018-07-01T16:01:35.100" Score="0" ViewCount="117" Body="&lt;p&gt;Some months back I bought a pair of XT180s and they've worked great. The problem is that it seems one of them was not charging all this time (I was wondering why the charging station only lit the light for one of the radios but not the other but I did nothing about it). Today finally the battery ran out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I have two questions:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;How do I access the battery pack in them?&lt;/strong&gt; I can't seem to figure it out, and manual is not very helpful:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;To remove the battery compartment door, press the tab at&#xA;  the bottom of the compartment door.&lt;/li&gt;&#xA;  &lt;li&gt;Install the NiMH batteries into the battery compartment.&lt;/li&gt;&#xA;  &lt;li&gt;Replace the battery compartment door.&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;And there is not even a diagram as to where the compartment door may be, ugh!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;How do I fix the problem?&lt;/strong&gt; I can likely replace the battery; I should have a suitable replacement somewhere assuming that I can open it up somehow, but that's hardly a fix. Should I return them to the store?&lt;/p&gt;&#xA;" OwnerUserId="11835" LastEditorUserId="9493" LastEditDate="2018-07-02T15:39:41.343" LastActivityDate="2018-07-04T02:50:34.367" Title="Motorola XT180 not charging" Tags="&lt;ht&gt;&lt;repair&gt;&lt;battery-charging&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10519" PostTypeId="1" AcceptedAnswerId="10520" CreationDate="2018-07-01T21:46:09.520" Score="10" ViewCount="328" Body="&lt;p&gt;E.g.:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;7.2-7.3MHz are Region 2 but not Region 1. My license is &quot;from&quot; Region 1.&lt;/li&gt;&#xA;&lt;li&gt;1.25 meter band is not available in the UK&lt;/li&gt;&#xA;&lt;li&gt;Operating from aircraft is not permitted in the UK. Would it be if I visited the US?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I realise that any frequencies not allowed in Region 2 would of course be a no-no when transmitting inside Region 2.&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="9636" LastEditDate="2018-07-01T22:24:10.317" LastActivityDate="2018-07-05T08:44:36.897" Title="Full UK license visiting US: Can I use frequencies in US but not UK license?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;united-kingdom&gt;&lt;international-operating&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10520" PostTypeId="2" ParentId="10519" CreationDate="2018-07-01T22:39:40.800" Score="10" Body="&lt;p&gt;You're correct in your understanding about region: given that you're operating in a part of the US that is in Region 2 (there are a few US overseas territories in Region 3), you need to conform to the Region 2 band plan, and not any other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FCC regulation 97.301(b), concerning authorized frequencies, grants the same privileges to a CEPT (non-novice) license-holder as to the holder of an Amateur Extra license (the highest class of license in the US). Since you will be in the United States, this is the only thing that governs what you are and aren't allowed to do, not your privileges in your home country. Your UK full license meets the criteria, so you have all of the privileges of an Extra while operating in the US, in terms of frequencies, aerial operation, and whatever else.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2018-07-01T23:03:44.167" LastActivityDate="2018-07-01T23:03:44.167" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10521" PostTypeId="2" ParentId="10518" CreationDate="2018-07-02T00:47:13.787" Score="1" Body="&lt;p&gt;I will answer the final question: &quot;Should I return them to the store?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If they are still under warranty, return them and get a replacement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the battery is a sealed unit inside, then opening them might void the warranty - and if it's not, then chances are it's the charging circuitry that has failed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Return them and get a replacement - I don't know why you even have to ask. Faulty goods == return.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-07-02T00:47:13.787" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10522" PostTypeId="2" ParentId="4951" CreationDate="2018-07-02T23:40:10.760" Score="-2" Body="&lt;p&gt;Never ever connect your radio or amp directly to the vehicle battery. You always ground to body of the vehicle. Positive can go to battery but best to follow manufacturer on location. If your new radio comes with a fuse on the ground, cut it off so as to only fuse the positive lead. &lt;/p&gt;&#xA;" OwnerUserId="11838" LastEditorUserId="9493" LastEditDate="2018-07-03T16:11:42.270" LastActivityDate="2018-07-03T16:11:42.270" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="10523" PostTypeId="2" ParentId="9651" CreationDate="2018-07-03T02:03:19.353" Score="0" Body="&lt;p&gt;Para experimentacion y usando cargas ficticias, sin antena, puedes hacer un transceptor usando por ejemplo limesdr (transceptor fullduplex) o tambien hackrf one (halfduplex)&#xA;El hackrf one se adapta muy bien a la ideologia de transceptor de radio aficionado y puede funcionar desde 1mhz a 6ghz aunque es de 8bit y eso lo hace mas vulnerable al ruido.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A efectos de experimentacion y poniendo en lugar de antena una carga de 50 ohmios, no tienes ningun problema.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Seria interesante hacer una comunidad de radioaficionados programadores y hacerle una gui web en java script.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Per Google translate:&lt;/strong&gt;&#xA;For experimentation and using dummy loads, without an antenna, you can make a transceiver using for example limesdr (fullduplex transceiver) or hackrf one (halfduplex). The hackrf one adapts very well to the ideology of amateur radio transceiver and can operate from 1mhz to 6ghz although it is 8bit and that makes it more vulnerable to noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For experimentation purposes and putting a 50 ohm load in place of antenna, you have no problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be interesting to make a community of amateur radio programmers and make a web guide in java script.&lt;/p&gt;&#xA;" OwnerUserId="11839" LastEditorUserId="8717" LastEditDate="2018-07-03T14:49:41.687" LastActivityDate="2018-07-03T14:49:41.687" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10525" PostTypeId="1" AcceptedAnswerId="10527" CreationDate="2018-07-03T12:24:13.700" Score="3" ViewCount="278" Body="&lt;p&gt;For monopole antennas, the ground plane acts as another arm of an equivalent dipole antenna. I'm wondering how we can expect the behavior of that antenna in practice, because the ground plane is usually used for components soldered on it. For instanse, please have a look at the following photo (Source: &lt;a href=&quot;http://hig.diva-portal.org/smash/get/diva2:299692/FULLTEXT01&quot; rel=&quot;nofollow noreferrer&quot;&gt;THE STUDY AND&#xA;IMPLEMENTATION OF MEANDER-LINE ANTENNA FOR AN INTEGRATED TRASNSCEIVER DESIGN&lt;/a&gt;). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XWPG2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XWPG2.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have 2 questions:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1/ The antenna is matched to be 50 ohm at &lt;strong&gt;A&lt;/strong&gt; (Fig. a). So, to measure it in practice, the author designed a 50-ohm transmission line which connects &lt;strong&gt;A&lt;/strong&gt; to &lt;strong&gt;B&lt;/strong&gt;. Am I right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2/ With some components soldered on the ground plane in Fig. d, I think the input impedance and the performance of that antenna, if measured again at &lt;strong&gt;A&lt;/strong&gt;, must be changed compared to those of the antenna only in Fig. b and c. That kind of antenna is significantly dependent on the ground plane. So, how can we know, when designing an antenna, an antenna will perform better or worse with integrated components like Fig. d?&#xA;I understand that we just can design and measure the antenna performance without these components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any suggestions would be highly appreciated.&lt;/p&gt;&#xA;" OwnerUserId="11740" LastActivityDate="2018-07-04T13:44:08.583" Title="Antenna design - Ground plane in simulation and in practice" Tags="&lt;antenna-construction&gt;&lt;measurement&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10526" PostTypeId="2" ParentId="10525" CreationDate="2018-07-03T15:43:06.697" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The antenna is matched to be 50 ohm at A (Fig. a). So, to measure it in practice, the author designed a 50-ohm transmission line which connects A to B. Am I right?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. This choice means that the difference in overall physical structure versus Fig. d is smaller than if the design used a smaller PCB.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For monopole antennas, the ground plane acts as another arm of an equivalent dipole antenna.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Remember that in the situation usually described this way, the monopole is &lt;em&gt;perpendicular&lt;/em&gt; to the ground plane. On the other hand, when we speak of ground planes of PCBs we mean circuitry being laid &lt;em&gt;parallel&lt;/em&gt; to the plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this picture, the closest analogue of the monopole's ground plane is the &lt;em&gt;edge&lt;/em&gt; of the PCB ground plane that is adjacent to the antenna. The portion that is further away from the antenna can be thought of as being “buried underground” or “in the shadow”; will still have some effect on the antenna, because the radiation and currents do propagate in that direction, but it will be much smaller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note also that the added components in Fig. d are placed as far away from the antenna as possible. Thus, the influence of the added components on the antenna structure is minimized. If we consider how big to make this separation — well, we're outside of my expertise, but &lt;a href=&quot;https://ham.stackexchange.com/a/7645/76&quot;&gt;I've heard that&lt;/a&gt; it's good for antenna ground planes/radials to be at least a quarter-wavelength in radius, which is not exactly satisfied here but is close.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And remember, any physical implementation of an antenna will have many other flaws compared to a simple model of the antenna type (e.g. the feedpoint being of a significant size rather than being a point) — one's goal should not be to make things exactly fit the ideal but to tweak the antenna so that it functions well when used in a real environment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally: This is all sloppy intuitive reasoning. True answers come from antenna simulations.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-07-04T13:44:08.583" LastActivityDate="2018-07-04T13:44:08.583" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10527" PostTypeId="2" ParentId="10525" CreationDate="2018-07-03T16:06:38.953" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The antenna is matched to be 50 ohm at A (Fig. a). So, to measure it in practice, the author designed a 50-ohm transmission line which connects A to B. Am I right?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The antenna by itself is not a 50 ohm, resonant antenna. It will likely have a complex impedance that needs to be transformed to a 50 ohm purely resistive impedance (typically). That is the job of the matching network. I believe you can see the matching network in picture B just above the highlight box you added.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the matching network, the designer has used a transmission line known as a GCPW (Grounded Coplanar Waveguide). Like any transmission line, the goal is to conduct RF current from point A to point B without radiating any RF energy while minimizing losses (attenuation). In this case, the GCPW has likely been designed to have a Z&lt;sub&gt;O&lt;/sub&gt; of 50 ohms. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the ideal case, the output impedance of the transmitter or receiver is specified as 50 ohms impedance and the antenna impedance has been transformed to a 50 ohm impedance. This minimizes the losses along the 50 ohm transmission line and allows the specified power to be conducted between the two points with minuscule radiation from the GCPW.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I think the input impedance and the performance of that antenna, if measured again at A, must be changed compared to those of the antenna only in Fig. b and c. That kind of antenna is significantly dependent on the ground plane. So, how can we know, when designing an antenna, an antenna will perform better or worse with integrated components like Fig. d?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The primary difference between picture B and D is that the transmitter/receiver components have been added to the board. These components are independent of the monopole portion of the antenna. The transmitter/receiver could also have been placed on another PCB (printed circuit board) but then some interconnect scheme would need to be used. This likely would reduce the reliability and increase the cost of the assembly but it may be necessary in some situations in order to meet form factor requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding the ground plane on the circuit board, this will inevitably form part of the antenna. A monopole antenna needs a return path for current. If a return path is not specifically provided, such as the second element in a dipole for example, the RF will find a return path through other means. In the case of this meander antenna, the ground plane on the circuit board becomes part of the antenna and thus radiates. This can be a design challenge because RF current is now flowing through the copper ground plane on the board and this can easily couple to other circuit elements. The designer needs to take care that this effect is understood through simulation and controlled in the implementation through careful attention to current path details. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-07-03T16:06:38.953" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10528" PostTypeId="2" ParentId="10518" CreationDate="2018-07-03T19:31:24.193" Score="0" Body="&lt;p&gt;Is this clip that you need to access the battery?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wopcp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wopcp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8573" LastEditorUserId="8573" LastEditDate="2018-07-04T02:50:34.367" LastActivityDate="2018-07-04T02:50:34.367" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10529" PostTypeId="2" ParentId="10137" CreationDate="2018-07-03T23:11:00.350" Score="1" Body="&lt;p&gt;I have an MFJ 9200 CW rig that only transmits in CW on ham freqs, but I can listen on SW broadcast freqs. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I &lt;strong&gt;always&lt;/strong&gt; carry it on bikepacking and backpacking trips.  I spend over 6 months a year in the outdoors.  I rarely actively operate, but &lt;strong&gt;I use it every night to listen on SW broadcast bands and just monitoring the convos on the ham bands.&lt;/strong&gt; I use a 21 foot piece of # 24 wire with a piece of 550 cord tied on the end. Then I throw it over a tree limb and string it in a vertical fashion.  Sometimes (rarely) I’ll ground my rig case with a short non-resonant wire and tent stake if there’s any need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;21 feet does great for listening on all freqs!!!!  My point is that 21 feet of wire should do just fine if you want to cover all bands...  I’d put it vertical for listening&lt;/strong&gt;.  No worries about SWR unless you’re going to transmit.  I use a small Z match when transmitting.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can get as complicated or as simple as you’d like when it comes to antenna’s!!  I like simple...  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the RTL-SDR, you could run a piece of RG-175 that isn’t resonant on any freqs you monitor to a bnc/banana plug at ground level with the 21 foot wire going straight up (vertical) and you could just connect the “ground” side of the banana/bnc to a copper rod directly in the ground with a few inches of wire.  That’ll do pretty darn good I’d bet!!!!!  I also use a 71 foot wire on occasion.  Adding the coax will cause more RFI pick up as said before but if it’s total length isn’t resonant on any freqs you monitor then it’ll help.  &lt;/p&gt;&#xA;" OwnerUserId="10992" LastEditorUserId="9493" LastEditDate="2018-07-04T12:41:36.297" LastActivityDate="2018-07-04T12:41:36.297" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10530" PostTypeId="1" AcceptedAnswerId="10531" CreationDate="2018-07-04T04:44:18.430" Score="1" ViewCount="5947" Body="&lt;p&gt;Do you think it would work to combine a HackRF One and an amp like the following to create a QRP SDR?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ebay.de/itm/2-700MHz-RF-Broadband-Power-Amplifier-Modul-fur-Radio-Transmission-FM-VHF-UHF-HF/323302195262?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D52979%26meid%3D2961120e3ec142838a66192021a112e6%26pid%3D100675%26rk%3D1%26rkt%3D15%26sd%3D232489001964%26itm%3D323302195262&amp;amp;_trksid=p2481888.c100675.m4236&amp;amp;_trkparms=pageci%3A32b44a89-7f44-11e8-ae46-74dbd1802faa%7Cparentrq%3A63964d3e1640aad75da04c2efff3d392%7Ciid%3A1&quot; rel=&quot;nofollow noreferrer&quot;&gt;Link to eBay&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Output of HackRF is approximately 10dBm, which fit's this amp nicely...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the disadvantage of a wide frequency range amp? Or in other words, why is not everybody doing it that sells HF, VHF and UHF amps separately? Are there any frequency specific components in it? Or is it just the case that the higher the frequency gets, the higher the requirements for hardware components gets? &lt;/p&gt;&#xA;" OwnerUserId="11842" LastEditorUserId="9493" LastEditDate="2018-07-04T12:36:36.330" LastActivityDate="2018-07-04T12:36:36.330" Title="HackRF + Amplifier = HF/VHF QRP Radio?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;amplifier&gt;&lt;hackrf&gt;&lt;dynamic-range&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10531" PostTypeId="2" ParentId="10530" CreationDate="2018-07-04T05:23:26.177" Score="5" Body="&lt;p&gt;Just to answer the second part of the question, you do not want an amplifier that has too wide a bandwidth, mainly to lower the complexity (and hence also the cost) of the amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All users of radio spectrum (including radio amateurs) must not cause any interference to other users of the radio spectrum, and that means that out-of-band transmissions must be kept to an absolute minimum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since all radios generate &lt;em&gt;some&lt;/em&gt; out-of-band signals, there is usually some degree of filtering to make sure that those signals are kept to a minimum. More expensive radios usually have much more filtering than cheaper models.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An amplifier will amplify all signals within its passband, and so if you had a wideband amplifier that amplifies all signals from Top Band (around 1.8MHz) to the 70cm band (around 430MHz), it would also amplify any spurious signals coming out of the transmitter. (And this is before we talk about parasitic oscillations within such a wideband amplifier.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this reason, all good amplifiers that support multiple frequencies have a switched passband, where each band is selected individually (usually manually, but solid-state amplifiers have started to include automatic band switching) and there are good filters on the input and output to keep out-of-band signals to a minimum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This obviously adds to the cost and complexity of an amplifier, and to cover a very large number of bands would at some point become prohibitively complicated or expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A better alternative is to use less expensive components, and design an amplifier for a specific band or set of bands (e.g. HF, VHF or UHF, or perhaps a VHF/UHF amplifier that does not cover HF).&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-07-04T05:23:26.177" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="10532" PostTypeId="2" ParentId="10530" CreationDate="2018-07-04T05:26:51.853" Score="0" Body="&lt;p&gt;If you are in the US, there is a limit on the number of dB increase a RF amplifier can have, and I'm certain that one is way past it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It also says it is a FM amplifier, which limits it pretty good to a few bands. &lt;/p&gt;&#xA;" OwnerUserId="9083" LastActivityDate="2018-07-04T05:26:51.853" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10533" PostTypeId="1" AcceptedAnswerId="10534" CreationDate="2018-07-04T14:14:28.087" Score="2" ViewCount="122" Body="&lt;p&gt;Could you please tell me which kind of this antenna is? I supposed it is a modified dipole, but not quite sure. Is there any available equation for calculating the original dimensions of this type of antenna? Thank you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Wy6ja.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Wy6ja.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11740" LastActivityDate="2018-07-05T00:02:16.730" Title="What type of this antenna is it?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10534" PostTypeId="2" ParentId="10533" CreationDate="2018-07-05T00:02:16.730" Score="3" Body="&lt;p&gt;As mentioned in the comment (why not make that an answer? I would have upvoted it), this looks like an RFID tag antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These antennas usually provide three functions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;to receive RF at a specific frequency and allow it to be decoded&lt;/li&gt;&#xA;&lt;li&gt;to receive RF energy and convert to DC, to power the IC in the middle&lt;/li&gt;&#xA;&lt;li&gt;to allow the IC to transmit back a signal that can be picked up by the tag reader&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;To satisfy these purposes, it has to operate on at least two frequencies. Possibly three frequencies, if the power to drive it is separated from the frequency it receives on - and possibly one, if it listens then transmits on the same frequency, although that would require the IC to be more complicated, and the antenna would not need to be as complicated as it is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As also mentioned in the comment (that should have been an answer), these antennas are usually created by experimentation, tweaking the shapes and sizes of the different parts of the antenna to get the best overall performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Honestly, it looks like some kind of folded dipole with an additional dipole attached to the sides. This would give it fairly good characteristics on several different frequencies, and it has probably been optimized through experimentation for the frequencies it is intended to operate on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have an antenna analyser (or a dip-meter) you can work out what those frequencies are by using a coil of wire and putting it around the antenna, and seeing where the impedance changes.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-07-05T00:02:16.730" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10535" PostTypeId="2" ParentId="10255" CreationDate="2018-07-05T00:08:37.570" Score="1" Body="&lt;p&gt;I'm quite confused by your question. I suspect you are talking about a satellite which is using the &lt;a href=&quot;http://www.stensat.org/docs/FX-25_01_06.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;FX.25 protocol&lt;/a&gt; (on &lt;a href=&quot;https://en.wikipedia.org/wiki/FX.25_Forward_Error_Correction&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;), which is an extension of the original AX.25 protocol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FX.25 is a compatible extension, as such the AX.25 packet is encapsulated inside the extra information of FX.25. The AX.25 is still decodable by a normal TNC, so it's format is still complete, with CRC and all (note that they are called Frame Check Sequence - FCS).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frame synchronization pattern you mention is probably the 'correlation tag', which is a pattern with implicit redundancy (called a Gold code).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Wikipedia article mentions a very basic on-the-air test, which shows an approx 30% improvement (the article doesn't mention which RS code was used).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can imagine that erronous bit stuff-decoding could wreak havoc on reception. On 'talk' links (mainly ASCII), bit stuffing rarely happens. But transferring binary data would probably suffer a lot more. This probably accounts for the relatively high number of remaining errors in the test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't confuse me for an expert. I only recently learned about FX.25 myself, but was reading up.&lt;/p&gt;&#xA;" OwnerUserId="1290" LastActivityDate="2018-07-05T00:08:37.570" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10536" PostTypeId="1" AcceptedAnswerId="10539" CreationDate="2018-07-05T08:16:44.723" Score="-4" ViewCount="103" Body="&lt;p&gt;I am wondering if there's any chance to get a short fragment of ATC/pilot radio exchange of any flight to/from small airport of Talkeetna (Alaska). This airport seems to be not present on &lt;a href=&quot;http://liveatc.net&quot; rel=&quot;nofollow noreferrer&quot;&gt;liveatc.net&lt;/a&gt;, and I just don't know any other web resources of that kind. I imagine that there might be some local amateurs streaming (I do know the frequency: 123.6 MHz) but I don't even know where to search for that kind of things - some local forums, etc? I googled and found some websites, for example &lt;a href=&quot;https://www.globaltuners.com/receiver/list.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;GlobalTuners&lt;/a&gt; (doesn't have what I need), &lt;a href=&quot;http://www.remotehams.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RemoteHams&lt;/a&gt; (requires callsign which I don't have) - any other suggestions?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S. why I need this: I'm making a small video (non-commercial of course, only for friends) about our recent Denali expedition, including the footage of our flights from Talkeetna to the basecamp and back. Intensive radio exchange during the whole flight made an authentic background but unfortunately I could not record it as it was only audible in the headphones. So it would be cool to find a sound track replacement.&lt;/p&gt;&#xA;" OwnerUserId="11846" LastActivityDate="2018-07-05T11:18:10.600" Title="where to look for (live or recorded) air traffic conversations for a specific area?" Tags="&lt;united-states&gt;&lt;software-defined-radio&gt;&lt;airband&gt;" AnswerCount="1" CommentCount="5" ClosedDate="2018-07-05T14:03:45.720" ContentLicense="CC BY-SA 4.0" />
  <row Id="10537" PostTypeId="2" ParentId="10519" CreationDate="2018-07-05T08:44:36.897" Score="6" Body="&lt;p&gt;As a UK license holder operating in the United States, you will be operating under CEPT Recommendation T/R 61-01.&lt;/p&gt;&#xA;&lt;p&gt;According to the &lt;a href=&quot;https://www.ecodocdb.dk/download/2ae38a89-e58a/TR6101.pdf&quot; rel=&quot;noreferrer&quot;&gt;CEPT regulations&lt;/a&gt;(PDF), it explicitly states that:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The CEPT Licence permits utilisation of all frequency bands allocated to the Amateur Service and Amateur Satellite Service and authorised in the country where the amateur station is to be operated.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;With a note that:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Special attention should be paid to the difference in frequency allocations to the radio amateur services in the three ITU Regions&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;According to their &lt;a href=&quot;https://www.cept.org/files/12338/FAQ%20Radio%20Amateur%20Updated%208%20February%202017.docx&quot; rel=&quot;noreferrer&quot;&gt;FAQ document&lt;/a&gt;(MS Word document), this is also the case:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;Whose operating privileges should the visitor use?&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;The operating privileges for the visitor operating under the CEPT Licence are defined by the COUNTRY BEING VISITED, NOT THE PRIVILEGES IN HIS &lt;em&gt;[sic]&lt;/em&gt; OWN COUNTRY.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;So you have full access to all the US bands, regardless of where you are from. Just make sure to operate according to the US regulations at all times.&lt;/p&gt;&#xA;&lt;p&gt;(Source for this information: the &lt;a href=&quot;http://rsgb.org/main/operating/licensing-novs-visitors/operating-abroad/&quot; rel=&quot;noreferrer&quot;&gt;Operating Abroad&lt;/a&gt; page on the RSGB website.)&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-07-05T08:44:36.897" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10539" PostTypeId="2" ParentId="10536" CreationDate="2018-07-05T11:00:03.247" Score="1" Body="&lt;p&gt;126.3 MHz is the Talkeetna CTAF (Common Traffic Advisory Frequency). You may have heard some traffic on this frequency while in-flight. Pilots use this to advise other pilots that they are in the area of Talkeetna  since their is no ATC (Air Traffic Control) facility at the airport. You will likely not find a monitoring site for this frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may find some suitable recordings  or an Internet listening station of the Anchorage ARTCC (Air Route Traffic Control Center) as they handle all   APCH/DEP (Approach and Departure) for Talkeetna on 125.55/254.3.  It may take some listening before hearing a Talkeetna related exchange, however.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-07-05T11:18:10.600" LastActivityDate="2018-07-05T11:18:10.600" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10544" PostTypeId="1" AcceptedAnswerId="10546" CreationDate="2018-07-09T00:12:36.240" Score="1" ViewCount="1167" Body="&lt;p&gt;So my idea is I might use a keyboard to enter text.  I would use an Arduino to control the ham radio.  The problem is that I have no idea on how to use the Arduino to control the radio.  Also, what speed would I expect and what software would I use?  Is there Arduino code for this purpose?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;-KM6MCM&lt;/p&gt;&#xA;" OwnerUserId="11861" LastEditorUserId="9493" LastEditDate="2018-07-09T13:08:53.833" LastActivityDate="2018-07-09T17:52:37.080" Title="Using a Baofeng UV-5R V2+ as a Portable Packet Radio" Tags="&lt;baofeng&gt;&lt;2m-band&gt;&lt;packet&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10546" PostTypeId="2" ParentId="10544" CreationDate="2018-07-09T17:52:37.080" Score="4" Body="&lt;p&gt;As far as I know, none of that series &quot;speaks&quot; APRS by itself, so you'd need your external controller to generated the AFSK tones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whilst it's possible to generate AFSK at such low rates with an arduino or the like – wouldn't a simple &quot;proper&quot; computer like a raspberry pi or so not be the better choice here?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could basically run any ham software for linux on that, and there's certainly plenty of choices for APRS then.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Raspberry Pi Zero would absolutely suffice in terms of compute power, you just add your keyboard, and USB sound card that you connect to the baofeng, and would be done (likely, you could also hook up the headset's PTT contact to a GPIO to). With a fully blown raspberry pi, you could even get models that include the audio interface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both the Pi Zero as well as the larger Pi 3 and Pi 2 come in variants with integrated bluetooth connectivity - a good idea if you want to connect say a wireless keyboard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally: AFSK 1200bd is so simple, you could absolutely implement that simply setting the PWM units of the pi to different frequencies (or worse, just bitbang GPIO). That way you could basically implement APRS on a 5$ - 10$ Pi Zero without additional 5$ on a USB sound card, but then you'd have to come up with your own software that implements the APRS stack. In case you'd always wanted to work with the linux kernel, you could certainly add that as a physical network interface for AX.25 packets. If I'm correctly educated, then G4KLX implemented AX.25 as part of the network stack in the Linux kernel decades ago, and &lt;a href=&quot;http://tldp.org/HOWTO/AX25-HOWTO/x61.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;it's been there ever since&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You see, using a full linux computer like a Raspberry Pi (Zero) or one of its many, many competitors solves many problems at once: No need to write your own keyboard driver (that's actually hard to do on a microcontroller like the arduino), no big hassle implementing the physical (so, AFSK) side of things, and as a big bonus, AX.25 integrates as protocol, just like IP,  into the operating system and you can thus leverage a truckload of existing software to get your packets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another approach would be using you smart phone's headset port to talk to the Baofeng's headset port – I bet &quot;there's an app for that&quot; and all you need to do is find a way to do some audio level shifting, maybe, and some way to activate transmission. Your baofeng can probably do that already, if it has voice activity detection. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-07-09T17:52:37.080" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="10549" PostTypeId="1" CreationDate="2018-07-10T18:19:47.560" Score="5" ViewCount="294" Body="&lt;p&gt;Recently, &lt;a href=&quot;https://ham.stackexchange.com/questions/10544/using-a-baofeng-uv-5r-v2-as-a-portable-packet-radio&quot;&gt;I asked a question&lt;/a&gt; about using an Arduino to send packet radio. I noticed that the top record speed for packet radio is 1 megabit/second, on a modified radio.  Someone mention on stack overflow that the normal speed is around 120 kilobits/second!  So is there an alternative to packet radio for sending digital bits over ham?&lt;/p&gt;&#xA;" OwnerUserId="11861" LastEditorUserId="9844" LastEditDate="2018-07-12T12:07:06.397" LastActivityDate="2018-07-12T12:07:06.397" Title="Are there any Alternatives to Packet Radio for sending digital data?" Tags="&lt;packet&gt;&lt;linux&gt;" AnswerCount="1" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="10552" PostTypeId="2" ParentId="10549" CreationDate="2018-07-11T10:39:11.390" Score="4" Body="&lt;p&gt;In absence of a clear indication of what Amateur Radio band is being targeted here, an answer for the 13 cm band:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use 802.11g/OFDM with a 20MHz bandwidth on 2400-2450 MHz Amateur band. You could even modify existing/consumer Wifi equipment to do so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;This would give you a (theoretical) 54 Mbits/sec throughput.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously you need to check that you are licensed to do so, and I would advise you to check the bandplans as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are 3 regions with different bandplans, &lt;a href=&quot;https://www.iaru-r2.org/band-plan/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the 3 regions only Region-2 details the following footnote:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Broadband applications can be used in 2410 – 2450 MHz with the maximum&#xA;  CW of 22 MHz. The broadband applications should not cause interference&#xA;  on satellites communications&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;*) &lt;em&gt;I believe the bandplan contains a typo. I seriously believe that where &quot;CW&quot; is mentioned in this footnote, it should read &quot;BW&quot; indicating Bandwidth.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Region-1 bandplan does not list such footnote, and Region-3 does not list anything above 1300 MHz. If you are located in those regions I would advise to consult with your regulatory body.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2018-07-11T10:39:11.390" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10553" PostTypeId="2" ParentId="1820" CreationDate="2018-07-11T11:29:19.393" Score="0" Body="&lt;p&gt;&lt;em&gt;I have built a simple ground plane antenna for 70cm with a connector, 4 radials, and one vertical element. The RF ground is connected to the radials, and the RF is connected to the vertical. ... IF I went outside, connected one end to a deep ground rod, and the other end to the vertical element, would the radiation be the same?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Both&lt;/strong&gt; conductors of a transmission line convey equal amounts of r-f energy, just 180° out of phase with each other.  One conductor of the transmission line may have a conducting path to Earth ground at/near a transmitter, but that does not negate its ability to pass r-f energy between that transmitter and its load (antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;» An &quot;r-f ground&quot; does not exist at the distant end of a conductor having its near end connected to a buried, vertical ground rod. «&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Probably the antenna system described in the OP already has a physical path connecting one conductor of its 2-conductor transmission line to some form of a nearby &quot;ground&quot; reference, such as the buried ground rod of the a-c service lines entering the building, and powering the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other things equal, there would be relatively little electrical difference in the performance of this antenna system if the transmission line conductor now connected to the common point of the radials of the ground plane antenna was disconnected at the antenna feedpoint, and reconnected there to a different conductor providing essentially the same function.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-07-11T11:29:19.393" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10554" PostTypeId="1" AcceptedAnswerId="10555" CreationDate="2018-07-11T18:18:27.683" Score="7" ViewCount="155" Body="&lt;p&gt;My understanding is that there used to be more timely overlap between commercial and amateur radio technology — e.g. helping study ionospheric propagation, relatively early adoption of &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation#History&quot; rel=&quot;noreferrer&quot;&gt;SSB technology&lt;/a&gt;, up through re-purposing business equipment for voice and packet use on 2m/70cm bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But now as a ham I feel like knowing about Baudot and &quot;varicode&quot;, setting up an APRS bridge, WinLink and EchoLink…? These might be interesting from a historical/cultural perspective, but hardly overlaps what I might learn from a wireless engineering curriculum nowadays. I guess I could buy a shiny D-STAR/WIRES-X setup and send lo-res pictures of the sunset through a local repeater — but given that the underlying AMBE patent &lt;em&gt;expired&lt;/em&gt; last year, I'm not sure how much that does to &quot;advance the state of the radio art&quot;!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My impression is that the ham world lost its connection with the commercial wireless &quot;side&quot; when that market largely shifted from business bands over to cellular service providers and standards. I know hams are able to re-purpose Wi-Fi equipment and some ham groups have worked on interesting projects like &lt;a href=&quot;http://www.broadband-hamnet.org/&quot; rel=&quot;noreferrer&quot;&gt;HSMM-Mesh&lt;/a&gt; — is there any similar effort using cellular specifications and equipment?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess this would entail things like:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Are there any cellular bands that are close enough to amateur allocation for off-the-shelf cellular modems/filters/antennas to work?&lt;/li&gt;&#xA;&lt;li&gt;Does any relatively modern generation of cell technology have enough public datasheets for home/hobby use?&lt;/li&gt;&#xA;&lt;li&gt;Can baseband chips be configured sufficiently to e.g. disable encryption and enable identification as usually required by amateur licensing?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For example, I have an old Firefox phone where most of the OS is open source, and I know the SDR/security/open-source crowds have been playing with base station deployments for a while (e.g. &lt;a href=&quot;http://openbts.org/&quot; rel=&quot;noreferrer&quot;&gt;OpenBTS&lt;/a&gt;) but I am unsure what licensing regime if any they are working under. Is the underlying phone hardware flexible enough that hams could convert it for use under amateur radio guidelines?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2018-07-11T18:51:56.757" LastActivityDate="2018-07-12T08:59:01.757" Title="Is there a practical way for hams to participate in cellular-related technology advances?" Tags="&lt;legal&gt;&lt;wifi&gt;&lt;history&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10555" PostTypeId="2" ParentId="10554" CreationDate="2018-07-12T08:59:01.757" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Are there any cellular bands that are close enough to amateur allocation for off-the-shelf cellular modems/filters/antennas to work?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yep, thanks to the fact that what is a GSM band in Europe is the American 33cm band.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does any relatively modern generation of cell technology have enough public datasheets for home/hobby use?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, 2G and later standards are all accessible, and far as I can tell, at least from a physical layer perspective for free.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Can baseband chips be configured sufficiently to e.g. disable encryption and enable identification as usually required by amateur licensing?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes! Or, well, all these features are defined  and/or negiotiated by/with the mobile network operator. So, you might need a custom SIM card to work with your modified/custom GSM base station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can heartily recommend visiting the &lt;a href=&quot;http://osmocom.org/projects/cellular-infrastructure/wiki&quot; rel=&quot;nofollow noreferrer&quot;&gt;osmocom project&lt;/a&gt;, which is a forerunner in FOSS cellular infrastructure – not only with respect to developing SDR-based and building commercial hardware-based base stations, but also with respect to building a whole backend network, so that one can make and route actual phone calls, data, messages …&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To little surprise, cellular networks are complex beasts, and there's a lot of network components that have to play along with each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, as said, you can use an SDR as your cellular base station, or integrate commercially available base station hardware into an infrastructure of your own. Frankly, from a development point of view, going the SDR route might be more sensible. (Of course, this is all a bit of a point of view: 4G base stations are 100% SDR, but with very application specific design (filters, rates, accelerators for certain operations…))&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Emphasis mine:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For example, I have an old Firefox phone where &lt;strong&gt;most of the OS&lt;/strong&gt; is open source, &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;most&lt;/strong&gt; of it, aside from the firmware running on the baseband chip e.g. from qualcomm. You won't get to meddle with that. Anyway, you don't need to, usually, as these things are really flexible and are typically controlled in a lot of parameters via negotiation and setup by software.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;and I know the SDR/security/open-source crowds have been playing with base station deployments for a while (e.g. OpenBTS) but I am unsure what licensing regime if any they are working under.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'll venture to say that most &quot;playing around&quot; doesn't happen with ham licenses (impossible in commercial settings completely, not very useful elsewhere) but by requesting temporary/experimental/… licenses from the respective authority. Terms of that really depend.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is the underlying phone hardware flexible enough that hams could convert it for use under amateur radio guidelines?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;these being? I mean, we're getting &lt;em&gt;very&lt;/em&gt; country-specific here. But, for example, there's the requirement to not use encryption. Check – that's just something that the handset chooses itself based on what the basestation and communication with the SIM module tell it. Identification with Call Sign? You're running with custom SIM cards, anyway, so there's a direct mapping between any IMSI or IMEI and call sign, if you want so, but if you actually want to transmit the call sign: you're sending unencrypted data, so just stuff it in some regularly sent data frames going nowhere. I've seen people actually pulse their GSM base station's output power, so that to an AM receiver, it sounded like Morse. worst case resort, but works; these technologies can deal with fading, and turning your power down looks just like that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other requirements might be bandwidth; and here, again, it really depends on jurisdiction. Some countries allow maximum data rates, other don't restrict that (much better idea, obviously); that precludes a few cellular standards, but not others (you can have very narrowband LTE, for example).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-07-12T08:59:01.757" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10556" PostTypeId="1" AcceptedAnswerId="10557" CreationDate="2018-07-12T12:59:40.793" Score="8" ViewCount="1859" Body="&lt;p&gt;Are there FCC regulations that specifically limit digital data rate on the amateur bands? Are there any recent or proposed changes? If so, what are they specifically?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8717" LastEditDate="2020-03-15T18:34:35.867" LastActivityDate="2020-05-02T18:29:42.917" Title="Do FCC regulations limit digital data rate?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;digital-modes&gt;&lt;bandwidth&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10557" PostTypeId="2" ParentId="10556" CreationDate="2018-07-12T14:04:05.287" Score="11" Body="&lt;h3&gt;The Current FCC Regulations (as of July 2018)&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Parts 97.305(c) and 97.307(f) regulate digital modes primarily by symbol rate. The table in 97.305(c) maps bands/frequencies to specific symbol rate limitations in 97.307(f) as follows:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(2) No non-phone emission shall exceed the bandwidth of a communications quality phone emission of the same modulation type. The total&#xA;  bandwidth of an independent sideband emission (having B as the first symbol), or a multiplexed image and phone emission, shall not exceed that of a&#xA;  communications quality A3E emission.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(3) Only a RTTY or data emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must not&#xA;  exceed 300 bauds, or for frequency-shift keying, the frequency shift between mark and space must not exceed 1 kHz.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(4) Only a RTTY or data emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must not&#xA;  exceed 1200 bauds, or for frequency-shift keying, the frequency shift between mark and space must not exceed 1 kHz.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(5) A RTTY, data or multiplexed emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must&#xA;  not exceed 19.6 kilobauds. A RTTY, data or multiplexed emission using an unspecified digital code under the limitations listed in §97.309(b) of this part also may be transmitted. The authorized bandwidth is 20 kHz.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(6) A RTTY, data or multiplexed emission using a specified digital code listed in §97.309(a) of this part may be transmitted. The symbol rate must&#xA;  not exceed 56 kilobauds. A RTTY, data or multiplexed emission using an unspecified digital code under the limitations listed in §97.309(b) of this part also may be transmitted. The authorized bandwidth is 100 kHz.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(7) A RTTY, data or multiplexed emission using a specified digital code listed in §97.309(a) of this part or an unspecified digital code under the&#xA;  limitations listed in §97.309(b) of this part may be transmitted.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(13) A data emission using an unspecified digital code under the limitations listed in §97.309(b) also may be transmitted. The authorized&#xA;  bandwidth is 100 kHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In general, the HF bands impose symbol restriction number (3) above limiting data to a symbol rate of 300 baud. A notable HF exception is 28.0 to 28.3 MHz where restriction number (4) above applies, raising the symbol rate to 1200 baud.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the 6 and 2 meter bands, restriction number (5) above applies, limiting the data to a symbol rate of 19.6 kbaud.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From 219 to 220 MHz, restriction number (13) above applies, limiting the data transmission to a bandwidth of 100 kHz - a notable regulatory exception. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From 222 to 225 MHz and the entire 70 cm band, restriction number (6) above applies, limiting the data to a symbol rate of 56 kbaud.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For all frequencies higher than the 70 cm band, restriction number (7) above applies, effectively removing any symbol rate restriction.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;The ARRL Petition&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;On November 15, 2013 the ARRL filed a &lt;a href=&quot;http://www.arrl.org/attachments/view/News/72517&quot; rel=&quot;noreferrer&quot;&gt;petition&lt;/a&gt;, now designated &lt;a href=&quot;https://www.fcc.gov/ecfs/search/filings?proceedings_name=RM-11708&amp;amp;q=RM%5C-11708&amp;amp;sort=date_disseminated,DESC&quot; rel=&quot;noreferrer&quot;&gt;RM-11708&lt;/a&gt;, with the FCC to eliminate the HF symbol rate restriction in favor a data regulation built upon a 2.8 kHz occupied bandwidth:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Specifically, ARRL proposes to delete all references to symbol rate from 97.307(f) of the Commission's rules; to create a conforming amendment to part 97.305(c) of the rules; and to establish a bandwidth limit of 2.8 kilohertz for Amateur data emissions below 29.7 MHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;When asked why the ARRL felt this petition was needed, it responded in a &lt;a href=&quot;http://www.arrl.org/files/file/FCC%20Documents/RM-11708_FAQ.pdf&quot; rel=&quot;noreferrer&quot;&gt;Q&amp;amp;A document&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;HF data emissions are now limited to symbol rates that are based on the long-obsolete technology of the early telephone modems. Regulation by symbol rate is not appropriate for present and future generations of digital data modes because it prohibits the use of some new, efficient modes but does not prevent the introduction of digital data modes that have much wider bandwidths than are now in use.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This proposal has languished in the FCC's hands for a number of years. I would encourage any interested US Amateur Radio operator to &lt;a href=&quot;https://www.fcc.gov/ecfs/filings/express&quot; rel=&quot;noreferrer&quot;&gt;file comments&lt;/a&gt; with the FCC.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-07-13T11:46:01.667" LastActivityDate="2018-07-13T11:46:01.667" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10558" PostTypeId="1" CreationDate="2018-07-12T15:01:00.580" Score="5" ViewCount="226" Body="&lt;p&gt;I've been reading the impedance matching chapter of Bowick's excellent RF Circuit Design book and I have a question.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For those who haven't read this book (or have but can't remember!), the chapter discusses L and 3 element matching networks (very intuitively, I might add) with some helpful examples before moving to an introduction to the Smith Chart.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;He uses some of the earlier matching examples (solved using equations) and shows how the same result can be obtained using the Smith Chart.&#xA;The text points out that adding reactive elements in series with a resistor is a simple matter of adding the appropriate imaginary quantity, thus moving you along the constant resistance circle. Likewise, adding reactive elements in shunt can be achieved with the conductance form of the Smith Chart again using a simple addition or subtraction.  If you use a combined impedance and conductance chart you can easily model ladder networks, which of course is exactly what you need for an L, Pi or T matching network.  If you need to match one impedance to another (one would be a conjugate), you simply identify the two impedances on the chart (normalized if necessary) and track a path between the two using the rules above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What I don't understand is, where is the reflection coefficient in any of this?&lt;/strong&gt;  If I understand the chart correctly, it basically maps the reflection coefficient for a normalized characteristic impedance to every possible (within reason) impedance (or conductance).  In other words, the charts &quot;meaning&quot; is related to reflection.  But, it seems to me that the kind of impedance matching operation described above is simply using the impedance(conductance) map and its ability to express complex addition and subtraction to move from one point to another and each points relationship to reflection isn't really relevant.  I worry I've missed an important point here.  I hope this question isn't too confusing.&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="873" LastEditDate="2018-07-15T00:40:46.143" LastActivityDate="2018-07-15T00:40:46.143" Title="Impedance matching using Smith Chart and relationship to reflection" Tags="&lt;impedance-matching&gt;&lt;smith-chart&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10559" PostTypeId="2" ParentId="10558" CreationDate="2018-07-12T16:05:16.390" Score="4" Body="&lt;p&gt;You are correct that there is a clear correlation. Perhaps your Smith chart does not have the following scales along the bottom?:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oXv1a.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oXv1a.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The technique is to use your compass to measure from the center of the chart to the normalized load impedance (z&lt;sub&gt;L&lt;/sub&gt;). Then relocated the compass pin to the point marked &quot;CENTER&quot; in the above scales and read the reflection coefficient from the scale at the mark of the compass.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-07-12T16:05:16.390" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="10560" PostTypeId="1" CreationDate="2018-07-12T18:55:47.710" Score="2" ViewCount="170" Body="&lt;p&gt;Can I use an amateur radio for a science fair? If so, do I need to prove that I have an active license?&lt;/p&gt;&#xA;" OwnerUserId="11861" LastEditorUserId="873" LastEditDate="2018-07-15T00:54:55.730" LastActivityDate="2018-08-30T23:13:26.450" Title="Amateur Radio for Science Fair" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;2m-band&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="10561" PostTypeId="2" ParentId="10560" CreationDate="2018-07-12T19:56:20.147" Score="1" Body="&lt;p&gt;The short answer is &lt;em&gt;probably&lt;/em&gt;. Since amateur radio is a scientific hobby, that would be a great science fair project.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should check with the science fair administrators before you do a lot of preparation, but I cannot fathom why any science fair would reject an amateur radio exhibit. I suggest you make certain that you present your exhibit as &lt;em&gt;scientific&lt;/em&gt; somehow, and not just present it as (for example) &quot;Hey, I can talk to the local net, and that's fun&quot;, or present it only from the aspect that hams sometimes use it to provide a public service (like storm spotters, or disaster communications when no telephones are working).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, &lt;em&gt;bring a copy of your license&lt;/em&gt;. You can print it from the ULS page, I believe. My wife and I keep a copy of our FCC licenses with us at all times.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-07-12T20:20:17.303" LastActivityDate="2018-07-12T20:20:17.303" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10562" PostTypeId="1" AcceptedAnswerId="10566" CreationDate="2018-07-13T00:02:10.010" Score="3" ViewCount="1025" Body="&lt;p&gt;As a urban ham (Harvard Square, Cambridge MA), I'm on the hunt for RFI rejecting antenna configurations. After hours of research, I've come across many strong recommendations for loop antennas, since they supposedly respond less to electric fields. In reviewing my options, I see there are several different classes of these antennas such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Passive loop antenna such as the well loved W4OP (&lt;a href=&quot;https://www.lnrprecision.com/store/W4OP-Loop-Antenna-Manual-Tuning-p69633466&quot; rel=&quot;nofollow noreferrer&quot;&gt;store link&lt;/a&gt;, &lt;a href=&quot;https://www.eham.net/reviews/review/147555&quot; rel=&quot;nofollow noreferrer&quot;&gt;eham review&lt;/a&gt;) - these often have a variable capacitor tuner with an apparently high Q which supposedly helps with noise rejection. (I suppose this avoids RFI on adjacent bands that would somehow swamp or add noise to the region you're interested in? But why would that be the case at all?)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Active loop antennas &lt;a href=&quot;https://www.dxengineering.com/parts/dxe-rf-pro-1b&quot; rel=&quot;nofollow noreferrer&quot;&gt;the much loved Clifton antenna&lt;/a&gt;, the &lt;a href=&quot;https://www.dxengineering.com/parts/cha-floop-plus20&quot; rel=&quot;nofollow noreferrer&quot;&gt;Chameleon&lt;/a&gt;, etc - seems to have what looks like a pre-amp but no tuning or variable cap&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;On further digging, the major advantage of an active antenna would seem to be amplification that pushes signals over the line loss of the cabling. That hardly seems to account for the field reports that active antennas are somehow better at noise rejection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question - what is really the best approach for noise rejection in an RFI-washed space (easily 100 families within a 2 minute walk)? Which approach actually provides the best SNR? Does the pre-amp perform some other function that makes up for the apparent lack of tuner? Why don't we see active loop models that also tune? And why does the tuning on the passive loop help reduce noise? &lt;/p&gt;&#xA;" OwnerUserId="11878" LastActivityDate="2018-07-14T22:26:02.040" Title="How do active loop vs. passive loop differ in terms of noise rejection?" Tags="&lt;rfi&gt;&lt;loop-antenna&gt;&lt;magnetic-loop&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10563" PostTypeId="2" ParentId="10562" CreationDate="2018-07-13T01:53:09.053" Score="4" Body="&lt;p&gt;&lt;strong&gt;Poor Loop Gain&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The small (&amp;lt;0.1 wavelength in circumference) loop antenna has very low gain. While the size somewhat lowers the directivity, the primary reduction in gain is due to inefficiency as a result the very low feedpoint resistance. When an antenna has reduced gain, not only are the desired signals reduced, so is any noise (QRN) since noise is another RF signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Directionality&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The loop has a directional characteristic so if it happens to be oriented towards the desired signal (in the plane of the loop) and away from (perpendicular to the plane of the loop) the source of the noise, the noise will be suppressed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Loop Q&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding the tuning of the loop as a source of noise reduction, this will not typically be the case. While a loop antenna with its tuning circuit has a relatively narrow bandwidth, it is at least an order of magnitude wider than the receiver's audio bandwidth. As a result, the Q of the loop antenna system has no appreciable affect with regard to noise. It may, however, prevent receiver overload from near frequency QRN.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Loop Inductive Characteristics&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Concerning the effect of the inductive characteristics of a small loop on locally generated noise, keep in mind that noise is another RF signal. As a result, noise has both an electric field and a magnetic field. Therefore the loop cannot somehow ignore noise to any greater or lessor degree than any other RF signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;An Amplified Loop&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An amplified loop simply makes up some of the gain lost in a passive loop. If there is noise present, it will amplify it along with the signal. Arguably the amp actually generates some noise itself but on the lower HF bands, this will not be a factor. The relatively low feedline losses, assuming a matched load, are not a justification for an amplifier on the HF bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Basis for Local Noise Reduction&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most likely source of observed local noise reduction when using small receiving loops is that they typically do not suffer from common mode currents (CMC) on the feedline. When CMC is present, it will alter the pattern of the antenna and couple noise near the feedline into the received signal. By contrast, most other classic antennas, such as a dipole or monopole, require special attention to minimize CMC. If A/B comparison tests do not factor CMC, the test is likely invalid.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-07-13T01:53:09.053" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10566" PostTypeId="2" ParentId="10562" CreationDate="2018-07-13T13:26:21.770" Score="6" Body="&lt;p&gt;Loops (active or passive) don't have the RFI rejection capabilities they are often claimed to have. RFI is electromagnetic radiation just like the signal, and it's not possible to design an antenna which accepts one but not the other. See &lt;a href=&quot;https://ham.stackexchange.com/q/606/218&quot;&gt;Can I reduce RFI/noise at the antenna?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Loops have the same directionality as a dipole, however their polarization is complementary. That can be useful when the polarization of the signal is fixed, such as AM broadcast radio which is always vertically polarized. A vertical monopole or dipole provides no azimuthal nulls, however a loop oriented in a vertical plane can be rotated to position the two nulls towards a source of interference. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Passive loops tune the highly inductive intrinsic impedance of the loop with a variable capacitor. The Q of this resonant circuit is extremely high, giving it a very narrow bandwidth. I'd consider this far more of an annoyance than any kind of advantage: any change in frequency requires re-tuning. However, perhaps if you are using an extremely poor receiver you may notice some improvement by eliminating sources of spurious signals from deficient filtering or nonlinearities. Then again, building a band-pass filter would give a similar advantage and be more convenient to use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When constructed with special attention to minimizing resistive losses, and with a high-voltage capacitor, passive loops can be used for transmitting. However they are still very inefficient, and I would not recommend a loop for transmitting unless extreme portability was the primary requirement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Active loops don't try to tune the impedance, but instead have a preamplifier designed to function well with the loop's highly reactive impedance. This has an advantage of very wideband operation. However that can also be a disadvantage: for example if you are near a broadcast station the preamplifier may be overloaded and rendered unusable on all frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's unlikely the preamplifier provides any benefit regarding noise. Remember the preamplifier amplifies noise and signal, plus adds some noise of its own. See &lt;a href=&quot;https://ham.stackexchange.com/q/9832/218&quot;&gt;How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?&lt;/a&gt; for more details.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-07-13T13:26:21.770" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10567" PostTypeId="1" CreationDate="2018-07-13T14:25:54.723" Score="3" ViewCount="750" Body="&lt;p&gt;Does addition of a remote feed-point antenna tuner affect the use of the coax braid as a radiator? If it no longer &quot;radiates&quot; in such a setup, what does? Is a shack or remote tuner better for surpression of common mode currents and RFI noise reduction?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many &lt;a href=&quot;https://www.eham.net/ehamforum/smf/index.php?topic=80316.0&quot; rel=&quot;nofollow noreferrer&quot;&gt;references&lt;/a&gt; suggest use of an external tuner rather than a shack tuner: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;With a tuner at the antenna there is no mismatched tranmission line&#xA;  to exhibit increased loss due to a high VSWR. The coaxial transmission&#xA;  line between the tuner and the transmitter is operated at a low VSWR&#xA;  (near 1:1) and exhibits no extra loss.&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;At the same time, my understanding from &lt;a href=&quot;http://palomar-engineers.com/wp-content/uploads/End-Fed-Antenna-Secrets-Hamcomm-2017.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;other sources&lt;/a&gt; is that in a non-resonant antenna setup, the coax itself acts as a radiator.&lt;/p&gt;&#xA;" OwnerUserId="11878" LastActivityDate="2018-09-26T13:51:34.833" Title="Benefit to remote antenna tuner for end-fed non-resonant antenna?" Tags="&lt;antenna&gt;&lt;rfi&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10568" PostTypeId="2" ParentId="10567" CreationDate="2018-07-13T15:11:46.743" Score="5" Body="&lt;p&gt;The benefit of placing a tuner at the antenna (rather than at the transmitter) in any circumstance is a reduction in the SWR on the coax. This results in a &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;reduction of losses&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a bit of myth that a bad SWR causes common mode current (radiating coax), but this isn't the whole picture. At the feedpoint, current is divided between the common and differential modes according to their relative impedances, just like current divides between parallel resistors. Common-mode current isn't the result of a bad SWR &lt;em&gt;per se&lt;/em&gt;, but rather a differential mode impedance which fails to be significantly higher than the alternative (usually, the common-mode of the antenna, assuming there's a properly designed antenna such that it's possible).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, assume a &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;resonant dipole with a balun&lt;/a&gt; which results in a common-mode impedance of 5000 ohms. The differential-mode impedance of a half-wave dipole is somewhere around 72 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the half-wave dipole the SWR meter might indicate 75/50 = 1.44:1, not bad. Because 72 is much less than 5000, almost all the current will be differential mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now imagine the dipole is a full wavelength long, where its impedance might be 5000 ohms. The SWR meter in this case will indicate something very high. Because the differential and common modes have equal impedances, half the current will be differential mode. One might conjecture a bad SWR leads to common-mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what if the end of the coax has not an antenna, but a short? In this case the differential-mode current is 0 ohms, and there will be no common-mode current. But there will be a horrible SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or consider a half-wave dipole as before, but with no balun and a feedline that is a quarter wavelength long. This will result in a very low common mode impedance: the coax in this case is effectively just as good as another dipole leg. There will be horrible common mode current problems, despite what's likely a good indicated SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All current must be balanced by an opposite current somewhere, because &lt;a href=&quot;https://en.wikipedia.org/wiki/Charge_conservation&quot; rel=&quot;nofollow noreferrer&quot;&gt;charge is never created nor destroyed&lt;/a&gt;. An end-fed antenna is very much like a vertical without any radials. The balancing current comes from &quot;ground&quot;, whatever that might be. It might the ground, as in Earth's surface. But usually the coax shield is closer and more conductive, and it functions as a single radial.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you aim to reduce common-mode current in an end-fed antenna, you can do two things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Add chokes to increase the common-mode impedance.&lt;/li&gt;&#xA;&lt;li&gt;Add radials or some other kind of counterpoise to provide a lower impedance path for that balancing current. (In doing so you might also avoid Earth currents, increasing the efficiency of the antenna.)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Remember that the current will favor the lowest impedance path available, so adding chokes when there's not a lower-impedance alternative is futile.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-09-26T13:51:34.833" LastActivityDate="2018-09-26T13:51:34.833" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="10569" PostTypeId="1" CreationDate="2018-07-13T18:20:30.603" Score="5" ViewCount="651" Body="&lt;p&gt;Urban ham here (Cambridge, MA - FN42ki - KC1JZE) looking for tips to make this hobby possible in the city. I rarely can hear both sides of HF phone transmissions, and have yet to make contacts despite dozens of attempts on 80/40/20m using commonly described &lt;a href=&quot;https://www.youtube.com/watch?v=bXHWhfgGZps&quot; rel=&quot;noreferrer&quot;&gt;CQ etiquette&lt;/a&gt; over a full week. I do occasionally pick up what I assume are LatAm Spanish ham contacts. I've shut down breakers to whole house and run on 12V battery and saw some improvement but still not able to make contacts. Most webSDRs I connect to see to have much clearer signals and far less noise than my rig. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been soaking up resources like &lt;a href=&quot;https://ham.stackexchange.com/questions/606/can-i-reduce-rfi-noise-at-the-antenna&quot;&gt;RFI Noise at Antenna&lt;/a&gt;, and &lt;a href=&quot;http://palomar-engineers.com/rfiemi-solutions/common-mode-noise-coax-filter/&quot; rel=&quot;noreferrer&quot;&gt;Common Mode Noise Filter - Coax - Palomar Engineers®&lt;/a&gt;, and &lt;a href=&quot;http://palomar-engineers.com/wp-content/uploads/End-Fed-Antenna-Secrets-Hamcomm-2017.pdf&quot; rel=&quot;noreferrer&quot;&gt;this PDF&lt;/a&gt;. Also have read the AARL book &lt;a href=&quot;http://www.arrl.org/arrl-s-small-antennas-for-small-spaces&quot; rel=&quot;noreferrer&quot;&gt;Small Antennas for Small Spaces&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What reasonable investments can I make in my signal path that will reject noise on a tiny plot of land (a tiny backyard with a tree)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Right now my signal path is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Antenna: 50' medium gauge wire from fence to ~50' tree, dropping vertically down&lt;/li&gt;&#xA;&lt;li&gt;4:1 LDG unun, ground connected to a pre-existing natural gas feed grounding wire - appears to be tied to copper/metal headed into the street&lt;/li&gt;&#xA;&lt;li&gt;50' LMR-400 stiff cabling snaked into a basement office/ee lab&lt;/li&gt;&#xA;&lt;li&gt;LDG AT-200 ProII tuner (not grounded, but grounding has not made much apparent difference), tunes most bands around 1:1.5 - 1:2.6 SWR&lt;/li&gt;&#xA;&lt;li&gt;3' RG8X coax&lt;/li&gt;&#xA;&lt;li&gt;ICOM-7300 grounded with a 20' run back to the same ground point (doesn't make much difference if disconnected.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I've tried a few different end-fed long wire non-resonant antenna configurations but not seeing different results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the right order of things to change? On the table:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Remote tuner with grounding wire&lt;/li&gt;&#xA;&lt;li&gt;Counterpoise in addition or in replacement to ground connection&lt;/li&gt;&#xA;&lt;li&gt;Addition of common mode choke at tuner and/or receiever&lt;/li&gt;&#xA;&lt;li&gt;Addition of feedline chokes at unun or near entrance to house&lt;/li&gt;&#xA;&lt;li&gt;Swapping to a loop antenna&lt;/li&gt;&#xA;&lt;li&gt;Trying one of these DX canceling phasers with active antennas&lt;/li&gt;&#xA;&lt;li&gt;Roof mounted antenna&lt;/li&gt;&#xA;&lt;li&gt;Learn CQ&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Much appreciated for the collective wisdom here.&lt;/p&gt;&#xA;" OwnerUserId="11878" LastActivityDate="2018-07-19T17:18:07.380" Title="Signal path to maximize RFI rejection in an urban environment" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;rfi&gt;&lt;antenna-system&gt;&lt;noise&gt;" AnswerCount="5" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10570" PostTypeId="1" CreationDate="2018-07-13T19:32:07.027" Score="0" ViewCount="94" Body="&lt;p&gt;I have a question about FSK modulation I'm going to frame in terms of a hypothetical:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine that you are transmitting a message to an ET in another solar system. The message is encoded in binary and embedded in the radio signal using FSK modulation. Lets say the signal is broadcast at 5 GHz and FSK +50kHz (i.e. 0 = 5,000,000 kHz and 1 = 5,000,050 kHz). Finally let's say you want to broadcast @ 1 bit per second.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now lets say the message you send is &quot;1111111111&quot; (10 ones).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would the ET recipient of this message be able to decode it without knowing the bit rate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My argument would be no, since to the ET it would just look like an unmodulated signal at 5000050 kHz that lasts for 10 seconds. If the ET didn't know the bit rate, it would be impossible for it to determine whether there was 100 ones or 10 ones encoded in the signal unless some zeroes were present as well. Is this correct? Would the presence of zeroes in the message even help determine the bit rate?&lt;/p&gt;&#xA;" OwnerUserId="11886" LastEditorUserId="873" LastEditDate="2018-07-15T00:35:18.413" LastActivityDate="2018-07-15T00:35:18.413" Title="How to decode a message with unknown bit rate in interstellar signal" Tags="&lt;digital-modes&gt;&lt;modes&gt;&lt;math&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="10571" PostTypeId="2" ParentId="10570" CreationDate="2018-07-13T19:52:24.250" Score="2" Body="&lt;p&gt;You are correct that you need to solve this problem somehow. Here are two ways to do it for normal practice:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Put a known symbol sequence at the beginning of your transmissions, which allows the receiver to detect the rate of symbol transitions and synchronize to it. This is called a &lt;a href=&quot;https://en.wikipedia.org/wiki/Syncword&quot; rel=&quot;nofollow noreferrer&quot;&gt;preamble or syncword, among other names&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A long message can be broken up into packets, repeating the preamble for each.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Arrange so that you are never sending a long sequence of only one symbol, but always have some transitions. This can be &lt;a href=&quot;https://en.wikipedia.org/wiki/Bit_stuffing&quot; rel=&quot;nofollow noreferrer&quot;&gt;bit stuffing&lt;/a&gt; or other schemes.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;(Explaining &lt;em&gt;symbols&lt;/em&gt;: if you are sending one bit at a time you have two symbols; if you send two bits at once by sending one of four different frequencies, that's four symbols, and so on.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a receiver who &lt;strong&gt;doesn't&lt;/strong&gt; know the parameters of the transmission or how it is encoded, there is no way they can tell &quot;symbol rate is 1 symbol per second&quot; from &quot;symbol rate is 2 symbols per second, but all the symbols we've seen so far happen to be paired up (like &lt;code&gt;0011000011001111&lt;/code&gt;)&quot;. They can only presume that you're not using a wasteful encoding, and decode using the shortest symbol time they've seen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example in the specific ET communication problem, you could send the integers in unary (or the Fibonacci sequence or your choice of Obvious Simple Mathematical Thing) and use that as your preamble and also &quot;there is intelligence here&quot; signal.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;010110111011110111110111111011111110...&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;In this case, every &lt;code&gt;0&lt;/code&gt; symbol demonstrates the shortest symbol time, and it's easy to note that the &lt;code&gt;111...&lt;/code&gt; increases by the length of a &lt;code&gt;0&lt;/code&gt; each time. If you recorded that as an unknown signal, you would quite readily notice the timing, yes? And algorithms can do even better.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-07-14T13:33:33.917" LastActivityDate="2018-07-14T13:33:33.917" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10572" PostTypeId="2" ParentId="10570" CreationDate="2018-07-14T11:44:03.740" Score="4" Body="&lt;p&gt;An FSK signal which is the same symbol repeated is an unmodulated carrier, and like an unmodulated carrier, it contains no information. Making some assumptions about the bit shaping filter it might be possible to make a reasonable estimate of the symbol rate judging by the growth and decay of the envelope at the start and end of the transmission, but it's an exercise of little practical value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A real &lt;a href=&quot;https://youtu.be/sMb00lz-IfE&quot; rel=&quot;nofollow noreferrer&quot;&gt;signal with information in it will have bits that are unpredictable&lt;/a&gt;. Consider: when we want to make information as compact as possible, we compress it. And a compressed file is nearly random bits. For related reasons, random bits can't be compressed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means in a transmission with information in it, it's extremely unlikely to have a repetition pattern which makes the symbol rate ambiguous. As such, the symbol rate will not be difficult to estimate for example by Fourier analysis: the highest frequency in the baseband signal is likely the symbol rate. Once the symbol rate is approximately known, a clock recovery algorithm can be applied to synchronize to the clock more precisely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Real-world applications use techniques such as &lt;a href=&quot;https://en.wikipedia.org/wiki/Bit_stuffing&quot; rel=&quot;nofollow noreferrer&quot;&gt;bit stuffing&lt;/a&gt; to ensure there are some transitions to facilitate clock recovery even when the data to encode is a long repetition. However in the realm of interstellar communication it's likely your objective is exchange of information, not sending a copy of the empty space of an unused hard drive. As such you're not likely to require bit stuffing: it would only make decoding more difficult.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-07-14T11:44:03.740" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="10573" PostTypeId="1" CreationDate="2018-07-14T12:59:22.433" Score="0" ViewCount="205" Body="&lt;p&gt;Comments posted on various websites relating to amateur radio posit that the groundwave is unimportant for skywave paths.  Is this concept correct?&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2018-07-15T08:58:27.653" LastActivityDate="2018-07-24T12:06:37.350" Title="Should Hams Using Skywaves Be Concerned About Their Groundwave Radiation?" Tags="&lt;propagation&gt;&lt;vertical-antenna&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="10574" PostTypeId="2" ParentId="10573" CreationDate="2018-07-14T12:59:22.433" Score="0" Body="&lt;p&gt;While the groundwave may not be present at a given receive location, this does not mean its existence and value are unimportant. They ARE important especially for vertical monopoles, as, for horizontal plane distances near the radiator they are an indication of the overall performance of the transmit antenna system — including its production of the radiation useful for skywave service.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a graphic illustrating the reality that (other things equal), as the groundwave is improved by reducing the ohmic loss in the path to r-f ground for that antenna system, so also is the skywave improved.  &lt;strong&gt;&lt;em&gt;The greater the groundwave radiated/launched by a vertical monopole, the greater the skywave.&lt;/em&gt;&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Discussion of the graphic presentation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Z = Elevation in meters above Earth, and E = Field Intensity in millivolts/meter existing at elevation Z at a horizontal distance of 1,000 meters from the base of the radiator (level Earth).   The notation at the upper right corner of the graph shows that it lies on the 45° departure angle from the base of the monopole (1000 feet vertical height AGL @ 1000 feet horizontal distance from the monopole base).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the radiation at/above/below that departure angle reaches the ionosphere, decaying at a 1/r rate — which rate applies to sky waves, not ground waves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is necessary to include the surface (ground) wave in a &quot;Method of Moments&quot; antenna system analysis such as possible using NEC4x in order for &lt;strong&gt;all&lt;/strong&gt; of the fields launched by a vertical monopole in the elevation sector of interest to appear correctly, leading to an accurate understanding of these principles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;R. Fry, CPBE&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5OnwC.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5OnwC.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2018-07-20T09:19:53.087" LastActivityDate="2018-07-20T09:19:53.087" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11573" PostTypeId="2" ParentId="10569" CreationDate="2018-07-14T13:16:03.203" Score="3" Body="&lt;p&gt;&lt;strong&gt;Definitely do:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Counterpoise in addition or in replacement to ground connection&lt;/li&gt;&#xA;  &lt;li&gt;Roof mounted antenna&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Or generally, some improvement to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your existing antenna sounds like effectively a vertical with no radials. This means much of the ground current is in the soil. The soil is a resistor. Resistors convert electrical energy into heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ICOM-7300 is capable of 100W which should be sufficient for SSB when conditions are good, but not if 90% of that power is just making warm dirt.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would see if your signal is even heard on some WebSDRs, in conjunction with &lt;a href=&quot;http://www.voacap.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt; to see what combination of bands, times, and locations are likely to work. You won't make many contacts if no one can hear you!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, my first recommendation is to focus on the antenna. A good antenna will help you on receive and transmit, and costs very little.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One way to go is a dipole. A dipole requires no radials, is cheap, easy to install, and works &lt;em&gt;great&lt;/em&gt;. It needs to be at least a quarter wavelength high (but even higher is better) and a half-wavelength long. Depending on the space you have this might limit operation to higher frequencies. I'd suggest 20m to start, simply because there's a lot of activity there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another way is to install radials, at least 16 of them. But it's a lot of work, and in the city there's often not enough space on the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A roof mounted vertical is a way around this. My first station was in a suburban 1/4 acre lot with a 1000 square foot ranch. I had a &lt;a href=&quot;https://www.dxengineering.com/parts/hsr-4btv&quot; rel=&quot;nofollow noreferrer&quot;&gt;4BTV&lt;/a&gt; in the center of the roof, with 16 radials which ran to the edge of the roof. This worked well because the roof was the largest flat space where I could lay radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately this roof antenna was also pretty noisy since the house wiring was only a few feet below. If you can do it, I'd recommend the dipole first: if you can string it up in 50' trees to get it farther from the house that will reduce the RFI. But either will be a big improvement over your current antenna, I bet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Highly recommended:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Addition of feedline chokes at unun or near entrance to house&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In the city there's really not much you can do about the ambient RFI, but you can get the antenna as far away as possible from nearby sources. But without a common-mode choke, the feedline &lt;em&gt;is&lt;/em&gt; the antenna, and it comes in the house and connects to the radio, which is connected to the house wiring, which is connected to computers, switch-mode power supplies, etc. Without a choke, all these RFI spewing devices are literally &lt;em&gt;directly attached&lt;/em&gt; to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At a minimum, a &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;choke at the feedpoint&lt;/a&gt; is a good idea. Another one at the entrance to the house can't hurt. If you like, &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measure the common-mode current&lt;/a&gt; to quantify the improvement you get from a particular configuration. Remember that by &lt;a href=&quot;https://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;reciprocity&lt;/a&gt;, if you measure a common-mode current on something when transmitting, that thing is also part of the receiving antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your &quot;turn the house breaker off&quot; test is also a good one. Ideally you're receiving RFI only from your neighbors. After getting the common-mode current under control, you might work to identify noisemakers in your own home and put chokes on them, making them less efficient radiators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If you want:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Learn CQ [assuming you mean CW]&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It takes much less power to get an intelligible CW signal, so if you want to invest the time to learn Morse code, this certainly will extend your range. Many digital modes have sensitivity similar to or better than CW, so that's another route which doesn't involve learning Morse code. The FT8 and JT65 modes provided by &lt;a href=&quot;https://physics.princeton.edu/pulsar/k1jt/&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSJT&lt;/a&gt; software are a good example, though don't allow for free-form &quot;rag-chewing&quot;. If that's your preference, you might look at PSK31 or even old-school RTTY.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;I wouldn't bother:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Swapping to a loop antenna&lt;/li&gt;&#xA;  &lt;li&gt;Trying one of these DX canceling phasers with active antennas&lt;/li&gt;&#xA;  &lt;li&gt;Remote tuner with grounding wire&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/10562/218&quot;&gt;As discussed previously&lt;/a&gt;, loop antennas aren't really all that great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Phasers could work theoretically: with a phased antenna array you have a more directional antenna system and can null out noise sources. But most of them are cheaply made, and I think you'll be disappointed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A remote tuner might reduce feedline losses, but if you &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;do the math&lt;/a&gt; on the actual losses on 50' of LMR-400, you'll probably find they aren't more than a few dB. &lt;a href=&quot;https://ham.stackexchange.com/q/382/218&quot;&gt;A tuner won't provide any significant improvement to receive performance&lt;/a&gt;. A grounding wire is irrelevant because there should be no common-mode current to ground in a proper antenna system.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-07-14T13:27:34.280" LastActivityDate="2018-07-14T13:27:34.280" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11575" PostTypeId="2" ParentId="10562" CreationDate="2018-07-14T22:26:02.040" Score="1" Body="&lt;p&gt;I beg to differ.  Been fighting noise for 25 years in the Boston burbs. Verticals and end fed wires are worst, dipoles better, wire loops better still. Magloops are best, been using for 20 years, check &quot;K1QAR&quot; on AM Fone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Had so much noise in my Newton Ma QTH last year that I could barely hear the monster bible thumper at 15610 on a quickie wire loop, but the magnetic loop picked up the hams with a reasonable (S3-4) noise level.   My guess is that the magnetic near field doesn't hear the primarily electric near fields of the nearby (strongest) noisemakers. The low SWR on the coax (no antenna tuner needed) cuts common mode.  I got the best performance on 40 meters, since an 80 meter loop would be too big (13'), and doing 20 without a beam did not appeal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BUT, there is no free lunch -- For 40 meters 20' of 3/4 inch copper tubing  and a 15kV vacuum variable aren't cheap, and you have to make a voltage proof motor mount and drive shaft and find space for a 7' diameter hula hoop. It handles a 500W amp so I can rag chew.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Get a stepper motor tuning drive (DC motors in commercial loops are uselessly imprecise).  Tuning is the big bugbear -- 1 degree of capacitor shaft rotation will typically take it off frequency, since to be efficient (I shoot for 50%) the Q has to be that high. Steppers are much simpler now (check Pololu.com) that robotics hobbyists have emerged as a market. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Details google my call K1QAR, come by the Aesop shop at minuteman Airfield in Stow, or track me down at the Flea at MIT (tomorrow)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;" OwnerUserId="15054" LastActivityDate="2018-07-14T22:26:02.040" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11578" PostTypeId="5" CreationDate="2018-07-15T00:44:01.767" Score="0" Body="&lt;p&gt;For more information about Smith charts, see here: &lt;a href=&quot;https://en.wikipedia.org/wiki/Smith_chart&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Smith_chart&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2018-07-15T00:44:01.767" LastActivityDate="2018-07-15T00:44:01.767" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11579" PostTypeId="4" CreationDate="2018-07-15T00:44:01.767" Score="0" Body="For questions related to Smith charts" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2018-07-15T00:44:01.767" LastActivityDate="2018-07-15T00:44:01.767" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11582" PostTypeId="2" ParentId="10573" CreationDate="2018-07-15T15:00:22.983" Score="3" Body="&lt;p&gt;Typically groundwave and skywave paths cover completely different distances and will not interfere, so coupling there is not likely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, an antenna with good skywave propagation may have a higher gain at elevation angles appropriate for skywave than its gain at angles appropriate for groundwave propagation, or both angles could have similar gains, so the relationship between skywave and groundwave strength is unclear and may or may not be related.  With the right antenna, the groundwave elevation angle might even be a null with no radiation at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modeling of the specific antenna involved would be necessary to determine if there is any relationship between groundwave and skywave propagation for that antenna.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2018-07-22T13:00:34.553" LastActivityDate="2018-07-22T13:00:34.553" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11583" PostTypeId="1" AcceptedAnswerId="11585" CreationDate="2018-07-15T19:29:51.527" Score="3" ViewCount="1726" Body="&lt;p&gt;I would like to be able to connect my radio to my computer in order to record audio. It seems like this would just be a matter of getting the right cable, but after trying a few cables (listed below), I'm realizing it's not that simple. I would like to be able to record audio so that I could save morse to practice decoding, record call signs so I can update a log book later on, and - somewhere down the line - be able to do something like record connections with satellites / ISS).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;My Setup&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Baofeng UV-5x3 &lt;/li&gt;&#xA;&lt;li&gt;MacBook Pro running High Sierra (10.13.5)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What I've tried&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have naively attempted to use these cables to connect to my Mac:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B078KJKK2C&quot; rel=&quot;nofollow noreferrer&quot;&gt;Retevis 2 Pin to 3.5mm Adapter&lt;/a&gt; (with a male-to-male audio cable)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B01LMIBAZW&quot; rel=&quot;nofollow noreferrer&quot;&gt;BTECH APRS-K1 Cable&lt;/a&gt; (tried this both with and without a APRS-K1 Cable, Reverse Connector Adaptor, which was shipped along with the first cable)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In both cases, the Mac doesn't receive any audio. Thinking that the issue might be with configuring the Mac's audio, I tried connecting each cable to my car's auxiliary input (which I can use to play audio from my iPhone). There again, I didn't hear anything from the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After searching online, I've seen a lot of people just use their computer's external microphone to record audio. It seems like there should be an easy way to send radio output directly to a computer, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Related&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found that these existing questions provided interesting information, but didn't quite answer my question:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/2093/how-to-hook-up-my-computers-audio-output-to-my-cb-radio/2094#2094&quot;&gt;How to hook up my computer&amp;#39;s audio output to my CB Radio?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/6766/confusion-about-radio-computer-interfaces-tnc-cat-trrs-wolphi-link&quot;&gt;Confusion about radio-computer interfaces: TNC, CAT, TRRS, Wolphi Link, ...?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="12900" LastActivityDate="2018-07-16T02:03:23.680" Title="What cable is needed in order to record audio from a Baofeng UV-5x3 on a computer?" Tags="&lt;baofeng&gt;&lt;connectors&gt;&lt;audio-interface&gt;&lt;audio&gt;" AnswerCount="1" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11585" PostTypeId="2" ParentId="11583" CreationDate="2018-07-16T02:03:23.680" Score="2" Body="&lt;p&gt;I built an audio interface that connected from an HF radio to my Mac, a few years ago. Obviously, I was concerned with ground loops and hum and suchlike, because I intended to use the interface to transmit too, so I used audio transformers as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the one thing I found that surprised me was that (as mentioned in comments by Kevin) the Mac has a slightly odd audio connection system. As Kevin says, it’s a TRRS arrangement, but in order to make the Mac ‘see’ that there is a microphone connected, you need to put a diode between one of the Rings and ground. This is to allow the macOS to detect whether a microphone is present or not, and thus enable incoming audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just used a regular small-signal silicon diode (1N4148 I think), and suddenly the Mac could ‘see’ that there was an audio input and allowed incoming audio through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use a continuity tester on a pair of Apple-compatible headphones with a microphone to determine which Ring should have the diode, and which way round it should be.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, to be ultra-paranoid about the safety of your expensive computer when connected to a famously ‘cheap’ radio, you might want to consider an audio transformer too :)&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-07-16T02:03:23.680" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11588" PostTypeId="1" AcceptedAnswerId="11593" CreationDate="2018-07-16T11:37:20.010" Score="1" ViewCount="683" Body="&lt;p&gt;Can someone please give me a clue here? I'm having problems receiving data from the IC 9100 radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to receive ax25 packets using FSK G3RUH modulation with an IC-9100 radio. It is configured to work on D-USB mode (on the settings menu the radio data mode is on USB). The radio is connected to PC using an A to B USB cable. As for the modem, I'm using a Soundmodem of George Smart M1GEO under Debian 9 Stretch. The radio is also connected to an SSB7000 preamplifier and crossed yagi antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When sending periodic AX25 beacon from a secondary transceiver, I can see received signal on the ICOM LCD but I can't see any traffic on the Ax25 port. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To clear any doubts about the cp210x drivers (whether they re configured or not the right way) I consulted silicon labs site and they confirm that all new linux system have pre-built cp210x module. the only difference that exists between the latter and the one they have in their site is the GPIO driver support. Also from what i have seen in forums one can use the driver already supported  and don t have to install new ones. To confirm that my system really support them, I used the following commands (alongs with screanshots of the output i got):&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;lsusub&#xA;&lt;a href=&quot;https://i.stack.imgur.com/QZR62.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QZR62.png&quot; alt=&quot;lsusb command&quot;&gt;&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;cat /proc/asound/cards&#xA;&lt;a href=&quot;https://i.stack.imgur.com/hXn1S.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hXn1S.png&quot; alt=&quot;asound cards&quot;&gt;&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;dmesg | grep cp210x&#xA;&lt;a href=&quot;https://i.stack.imgur.com/YLAc5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YLAc5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Finally, here are the specs of the ttyUSB0 (same for ttyUSB4):&#xA;&lt;a href=&quot;https://i.stack.imgur.com/GNVQ7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GNVQ7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;..ctd...&#xA;&lt;a href=&quot;https://i.stack.imgur.com/WIf3h.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WIf3h.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think that the installed cp210x driver works just fine... unless there is somthing else i m not aware of... PLease would you help me on this.. I m just lost. Thank you so much for taking the time to read my post. Best&lt;/p&gt;&#xA;" OwnerUserId="12902" LastEditorUserId="12902" LastEditDate="2018-07-24T13:56:29.760" LastActivityDate="2020-09-15T09:38:43.820" Title="Receiving audio output from IC-9100 through USB port" Tags="&lt;digital-modes&gt;&lt;equipment&gt;&lt;audio-interface&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11589" PostTypeId="2" ParentId="10569" CreationDate="2018-07-16T11:46:57.627" Score="3" Body="&lt;p&gt;As a new ham, you may have more success answering a CQ since you will then know that you can at least hear the other station over your local noise. Answering a CQ also requires less finesse so you are less likely to be identified as a newbie. But we have all gone through this phase so I can assure you that once you get a few QSOs under your belt, you will be more comfortable and successful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would also encourage you to get active in a local ham radio club as you will find many mentors (also known as Elmers) that can look at your antenna situation and listen to your on the air practices. Club members may also have handy tools such as an antenna analyzer that they can bring with them to accelerate antenna troubleshooting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With regard to your antenna, here are a few thoughts.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Radials&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;You describe your antenna as nearly vertical, coming down to a fence in your back yard. It appears that your backyard fence is typical metal chain link type fence. You may be able to use this as the other half of your antenna by connecting outer coax connection to the metal fence where the vertical wire meets it. A coax grounding block makes this an easy connection:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aKAbM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aKAbM.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also use a lightning arrestor type device and connect the ground tab to the fence:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1UlJd.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1UlJd.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Make sure to waterproof this connection. At the same time, I would eliminate the connection to your gas pipe ground wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doing this will change your antenna from an end fed, vertical wire to something closer to a vertical antenna with a ground plane (with the fence as the ground plane). This should give you a more favorable directional pattern.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Common Mode Current&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Common mode current (CMC) is often not well understood by hams. When common mode current exists on a coax, or more generally the feed line, the coax becomes part of the antenna instead of simply being the feed line. This is usually undesirable as then your antenna comes directly into your shack picking up any noise close to the coax. CMC also alters the directional properties of the antenna. CMC can also alter the expected SWR of an antenna (but higher SWR does not cause CMC).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best defense in your case against CMC is to use a high quality 1:1 choking balun (not unun) installed at the feedpoint of your antenna. The job of the choking balun is to &quot;choke off&quot; CMC so your coax does not become part of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Try Eliminating the Unun&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;The 9:1 unun you have installed is likely not necessary and may even be detrimental once you install radials (e.g. your fence) as part of the vertical antenna. On 40 and 80 meters, your 50 foot vertical is already shorter than a 1/4 wave which means that it will have a low feedpoint impedance. The 9:1 unun will attempt to further reduce this feedpoint impedance making the SWR even worse. On 20 meters, the unun is of marginal benefit.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-07-16T12:44:28.397" LastActivityDate="2018-07-16T12:44:28.397" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11591" PostTypeId="1" AcceptedAnswerId="11592" CreationDate="2018-07-17T00:50:42.197" Score="1" ViewCount="111" Body="&lt;p&gt;I'm having an issue with some handheld transmitters, and not sure if they're bad, or the newly-installed antenna is bad, or if this even makes sense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been using a handheld Icom aviation radio (model A23) within a hangar (ie, a metal-skeleton building) without any specific issues. We installed a base station antenna (B-ANT) with the hopes of being able to get better range from the handheld. The handheld was plugged in via an adapter cable and suddenly started transmitting intermittently. By that, I mean that when depressing the PTT the received audio sounded as if the PTT was being rapidly pressed and let go, at a rate of about 5hz. Additionally the red LED &quot;RX/TX indicator&quot; flashed at the same rate. In fact, I thought that it might be a bad PTT switch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's weird is that this continued even when the external antenna was removed and the stubby antenna was replaced when the handheld was in proximity to the antenna cable. It happened consistently when within a foot of the antenna cable, but only began consistently working properly when &gt; 20 feet from the antenna cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This happened from a second Icom handheld radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It did not happen with a Yaesu handheld aviation radio, even when that radio was connected directly to the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's happening here?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additional Info:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't find an impedance rating for the antenna, but it's specifically recommended for some of their base stations (e.g., &lt;a href=&quot;http://www.icomamerica.com/en/products/avionics/groundcom/a110/specifications.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;the A110&lt;/a&gt;), which have 50ohm impedance. Their handhelds (e.g., &lt;a href=&quot;http://www.icomamerica.com/en/products/avionics/handheld/a24/specifications.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;the A24&lt;/a&gt;) also have a 50ohm impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did find a &lt;a href=&quot;https://www.ameradio.com/doc/Icom_B-ANT_spec_sheet.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;spec sheet for the antenna&lt;/a&gt; if that's relevant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While this antenna is sold with the base station radios, I haven't seen it recommended for handhelds; I assumed that's mostly just a function of not a lot of demand for external antennas with handheld tranceivers.&lt;/p&gt;&#xA;" OwnerUserId="12907" LastEditorUserId="12907" LastEditDate="2018-07-17T06:22:31.707" LastActivityDate="2018-07-17T13:55:00.383" Title="Why would a nearby antenna cause intermittent transmission?" Tags="&lt;antenna&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11592" PostTypeId="2" ParentId="11591" CreationDate="2018-07-17T02:29:46.397" Score="2" Body="&lt;p&gt;A nice theory that unfortunately does not explain everything is that the antenna is mismatched. If the impedance of the antenna, as installed, at the transmission frequency, is not near the value the transmitter expects, then some or all of the transmitted power is reflected and the transmitter may be damaged, or shut itself down or reduce power to avoid overheating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cycling behavior you observed is plausibly the result of a protection circuit being tripped, or of damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this does not explain why it would now happen when only &lt;em&gt;near&lt;/em&gt; the now disconnected antenna. The only thing I can think of is that the radio is now damaged in a way which makes it especially sensitive to reflected signals, and in this case the reflection is coming from the base antenna. But it's fairly implausible that the disconnected antenna would cause this and that just, say, carrying the radio around in general would not.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The antenna may have other than the presumed 50 ohm impedance if&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;it is damaged or defective, or&lt;/li&gt;&#xA;&lt;li&gt;it was installed close to metal objects in an inappropriate way.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;To check this theory, find a radio technician or a ham friend with an antenna analyzer that goes up to the relevant frequency, and have them check the antenna as installed.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-07-17T13:55:00.383" LastActivityDate="2018-07-17T13:55:00.383" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11593" PostTypeId="2" ParentId="11588" CreationDate="2018-07-17T10:33:59.003" Score="1" Body="&lt;p&gt;You need to install the Icom USB drivers on your PC. You mentioned that your PC is running Linux but I am not aware of any Linux drivers from Icom - I only see Windows support on &lt;a href=&quot;https://www.icom.co.jp/world/support/download/firm/IC-7600/usb1_20/&quot; rel=&quot;nofollow noreferrer&quot;&gt;their website&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have successfully installed the Icom drivers and connected the radio via the USB cable, you will see two new USB devices. You must select the USB2 option for receiving data. The Icom radio must also be configured to route the data to USB2 using menu option 63.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-07-17T10:33:59.003" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11594" PostTypeId="1" AcceptedAnswerId="11595" CreationDate="2018-07-17T18:31:03.737" Score="2" ViewCount="1573" Body="&lt;p&gt;I am working with USRP N210 and USRP B200 radios with GNURadio. I have connected the TX/RX port of one radio to the RX2 port of the other with an RF cable as a simulated radio link. In GNURadio, I have been setting my transmitter gain and receiver gain to 10 dB in the UHD: USRP Source and Sink blocks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recently heard that when connecting my radios to a signal generator, I should set the output power to -10 dB to protect the radios' RF front end components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have I been setting my gain too high / frying my radios? How high is too high? What gain settings should I use in my link mockup? If I connect to a signal generator or antenna link, what power attenuator should I use?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks for any and all help!&lt;/p&gt;&#xA;" OwnerUserId="12908" LastActivityDate="2018-07-17T18:43:18.280" Title="USRP Safe Gain Values" Tags="&lt;rf-power&gt;&lt;gnuradio&gt;&lt;usrp&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11595" PostTypeId="2" ParentId="11594" CreationDate="2018-07-17T18:42:04.947" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I have connected the TX/RX port of one radio to the RX2 port of the other with an RF cable as a simulated radio link.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;DO NOT DO THAT.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Always, always, always, in any case, under all circumstances, use an attenuator when directly connecting the output of one radio to the input of the other.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Have I been setting my gain too high / frying my radios?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Ettus specifies -15 dBm as the maximum damage-free input power for nearly all of their radio frontends, with the B200 being a bit of an exception and taking a couple dB more. Depending on the daughterboard in your N210, your frequency, sampling rates and of course the signal you're sending, the other radio might be producing up to 20 dBm. That's more than &lt;strong&gt;2000 times&lt;/strong&gt; the damage-free maximum input power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is &lt;em&gt;damage-free&lt;/em&gt;. Not &lt;em&gt;sensible input&lt;/em&gt;; &lt;strong&gt;stop what you're doing now, use an attenuator, there's no excuse&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How high is too high? What gain settings should I use in my link mockup?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Depends on your N210 daughterboard, and the signal you're transmitting. On &lt;a href=&quot;https://files.ettus.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://files.ettus.com/&lt;/a&gt; you'll find  &lt;em&gt;performance charts&lt;/em&gt;, which give &lt;em&gt;very rough&lt;/em&gt; output powers for a single tone signal at full amplitude given frequency and gain for the common daughterboards.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If I connect to a signal generator or antenna link, what power attenuator should I use?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There can't be no general answer to that, but the obvious one: enough attenuation to guarantee your input power stays solidly below -15 dBm.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-07-17T18:42:04.947" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11596" PostTypeId="2" ParentId="11594" CreationDate="2018-07-17T18:43:18.280" Score="2" Body="&lt;p&gt;According to &lt;a href=&quot;https://kb.ettus.com/B200/B210/B200mini/B205mini#Input_Power_Levels&quot; rel=&quot;nofollow noreferrer&quot;&gt;the Ettus Research Knowledge Base&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The maximum input power for the B200/B210/B200mini/B205mini is 0 dBm.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Power Output &gt;10dBm&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;10 dBm to 0 dBm is a difference of 10 dB, so an attenuator of &lt;em&gt;at least&lt;/em&gt; 10 dB would be advisable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More would probably be a good idea, since the specifications specify a minimum performance: transmitter output may be more than 10 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, even 0 dBm is an extremely high power to receive in practice from an antenna. A lower input power is more realistic, and will likely result in better performance due to decreased nonlinear distortions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you like, you could &lt;a href=&quot;https://ham.stackexchange.com/questions/352/what-is-a-link-budget-and-how-do-i-make-one&quot;&gt;calculate path loss&lt;/a&gt; for some situation of antennas, transmit power, and frequency, and introduce an attenuator of a similar value to what would be encountered in practice.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-07-17T18:43:18.280" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11597" PostTypeId="2" ParentId="10569" CreationDate="2018-07-17T23:45:29.027" Score="2" Body="&lt;p&gt;I suggest you investigate your local E-fields and H-fields. Then decide whether you want an E-field sensor (whip antenna) or an H-field sensor (a loop) for receiving. There are good reasons for using different antennas for receive and transmit. The receive antenna may have less than 1% efficiency - you just want it to not pick up local fields. The transmit antenna should have high efficiency but it does not matter if it picks up interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest you look through all of these videos:&#xA;&lt;a href=&quot;http://www.youtube.com/watch?v=ItLkn8r4s3E&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.youtube.com/watch?v=ItLkn8r4s3E&lt;/a&gt;  (24 minutes)&#xA;&lt;a href=&quot;http://www.youtube.com/watch?v=zsZTX7MQSGQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.youtube.com/watch?v=zsZTX7MQSGQ&lt;/a&gt;  (48 minutes)&#xA;&lt;a href=&quot;http://www.youtube.com/watch?v=kgMbaJDFu9M&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.youtube.com/watch?v=kgMbaJDFu9M&lt;/a&gt;  (55 minutes)&#xA;&lt;a href=&quot;http://www.youtube.com/watch?v=C65u7Pmz7a0&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.youtube.com/watch?v=C65u7Pmz7a0&lt;/a&gt;  (21 minutes)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is two and a half hours. You might find parts of it&#xA;irrelevant to your problem (and boring) but it is all there for&#xA;a reason, something that comes later may require an understanding&#xA;of previous parts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For interference fighting:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) Eliminate problems at source as well as you can. Bad switch&#xA;power in your own home can be replaced or provided with adequate filters.&#xA;Some of your neighbours might be friendly and accept that you offer&#xA;them another led light (or whatever) or place a ferrite core on some of their wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) Investigate your local fields and select the optimum location for an E-sensor, an H-sensor or possibly several of them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) With more than one field sensor for receive you can use a phasing system to cancel one particular noise source. That can be done automatically with a two channel radio as you can see in the videos, but it can also be done manually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With many sensors, many analog balancing units you could eliminate several of the local interference sources. Combine two sensors to eliminate a particular QRM. Then combine two other sensors to eliminate the same QRM. Finally combine the outputs of both combiners to eliminate a different QRM. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course digital technology could do this MUCH better, but to my knowledge there is no hardware available today.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-07-17T23:45:29.027" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11599" PostTypeId="2" ParentId="6378" CreationDate="2018-07-18T14:57:36.670" Score="3" Body="&lt;p&gt;According to this chart, 2016 was not the solar minimum. We appear to be at or very near the minimum right now. However, we won't know for sure until some more time passes.&lt;/p&gt;&#xA;&lt;p&gt;Yesterday on &lt;a href=&quot;http://www.spaceweather.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;spaceweather.com&lt;/a&gt;, the following information appeared:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;THREE WEEKS WITHOUT SUNSPOTS: The sun has been blank for 21 days--3&#xA;whole weeks without sunspots. To find an equal number of consecutive&#xA;spotless days in the historical record, you have to go back to&#xA;July-August 2009 when the sun was emerging from an unusually deep&#xA;solar minimum. &lt;strong&gt;Solar minimum, welcome back&lt;/strong&gt;!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Uq9xE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Uq9xE.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Space weather forecasters have long wondered, will the next solar&#xA;minimum (2018-2020) be as deep as the previous one (2008-2009)?&#xA;Twenty-one days without sunspots is not enough to answer that&#xA;question. During the solar minimum of 2008-2009, the longest unbroken&#xA;interval of spotlessness was ~52 days, adding to a total of 813&#xA;intermittent spotless days observed throughout the multi-year minimum.&#xA;The corresponding totals now are only 21 days and 244 days,&#xA;respectively. &lt;em&gt;If&lt;/em&gt; this solar minimum is like the last one, we still&#xA;have a long way to go.&lt;/p&gt;&#xA;&lt;p&gt;At the moment there are no nascent sunspots on the solar disk, so the&#xA;spotless days counter is likely to keep ticking. Stay tuned for more&#xA;blank suns.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-07-18T14:57:36.670" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11601" PostTypeId="1" AcceptedAnswerId="11602" CreationDate="2018-07-19T05:34:07.613" Score="4" ViewCount="171" Body="&lt;p&gt;I suspect that the &quot;white residue&quot; between the coax cable jacket and connector is the result of environmental damage but I could not confirm it yet. Did anyone have a similar issue and if so what was the cause? Thanks, AL6B.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/r0Epb.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/r0Epb.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bSRoP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bSRoP.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5114" LastEditorUserId="5114" LastEditDate="2018-07-20T03:05:12.227" LastActivityDate="2018-07-20T03:05:12.227" Title="Suspected Damage in Coax Cable" Tags="&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11602" PostTypeId="2" ParentId="11601" CreationDate="2018-07-19T11:12:03.313" Score="6" Body="&lt;p&gt;It appears to be typical moisture ingress. The joint between the coax and the connector is not inherently waterproof. A damaged jacket can also be the source of moisture ingress. Normally the connector to coax joint must be covered with a self sealing adhesive tape or heat shrink tubing with an interior thermal adhesive in order to protect it from the elements. If the connector is a PL259 the entire connector should be dressed similarly since it also is not waterproof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, the jacket corrosion also impedes the proper flow of RF current. You may be able to cut off a foot or two and if there is no further corrosion, you can then install a new connector and waterproof the assembly.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-07-19T11:12:03.313" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11603" PostTypeId="2" ParentId="10569" CreationDate="2018-07-19T16:28:53.690" Score="1" Body="&lt;p&gt;Consider using WSPR to measure your antenna propagation.  It is a free download and will give strong clues as to where your signals are going.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2018-07-19T16:28:53.690" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11604" PostTypeId="2" ParentId="10569" CreationDate="2018-07-19T17:18:07.380" Score="1" Body="&lt;p&gt;It may be a worthwhile exercise to install a simple dipole antenna to see how you do.  20m is a pretty easy band to work, with reasonable antenna lengths, and a dipole antenna will remove the requirement for an antenna tuner in most cases.  Almost all of your transmitted signal will actually leave the antenna, instead of being lost in the tuning.  This is what I did.  If you can make contacts on 20m, then you'll be in a better position to try other antennas to see what they will do for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The big issue with a random wire antenna is that it isn't matched well to many ham frequencies.  The tuner will make the radio happy, but it doesn't help with transmission efficiency.  That having been said, I actually used a random wire antenna at my cottage for my first few HF contacts (including Slovenia from VE5-land) and did really well, but I was in an S1 noise environment, which helped immensely, and the ionosphere was much more cooperative in 2013 than it is today.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One other advantage of dipoles - no ground plane is necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Give one a try and see how you do.  If buying one is out of your budget (they're easy to find online), they're reasonably easy to build.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-07-19T17:18:07.380" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11605" PostTypeId="1" AcceptedAnswerId="11607" CreationDate="2018-07-20T00:12:42.023" Score="0" ViewCount="212" Body="&lt;p&gt;I've always been reading my AM modulated signal on a Bird wattmeter and trying to set the carrier to 1/4 of the peak envelope power (PEP).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Recently, I was told by a CBer that you only can see it that way on a scope, and that with a PEP meter, you should be setting the carrier to 1/2 the PEP. Is this correct? Have I been doing it wrong?&lt;/p&gt;&#xA;" OwnerUserId="1817" LastEditorUserId="76" LastEditDate="2018-07-20T01:02:58.590" LastActivityDate="2018-07-22T11:22:51.517" Title="Peak envelope power should be 2:1 or 4:1 on meter?" Tags="&lt;modes&gt;&lt;rf-power&gt;&lt;measurement&gt;&lt;am&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11606" PostTypeId="2" ParentId="11605" CreationDate="2018-07-20T00:57:01.977" Score="3" Body="&lt;p&gt;It depends...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a 100% steady modulated carrier, the PEP will be 4 times the unmodulated carrier power. The average power under this condition will be 1.5 times the unmodulated carrier power with 2/3 of this contained in the carrier and 1/3 in the sidebands (1/6 each in the USB and LSB sidebands).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The real issue is - are you obtaining 100% modulation? For example, a plate modulated 6146 final (or nearly any pentode or tetrode final) will only reach a PEP that is 2 times the unmodulated carrier because the positive peaks are about 50% of the negative peaks. In this case your friend would be correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, keep in mind that if you use a scope instead of a PEP meter, you will likely be viewing the amplitude of the voltage - not power - at the point of insertion of the scope. This will work for comparing relative voltages of the carrier to the modulated signal since both are sampled at the same impedance. However, recall that the voltages observed will be relative to the square root of the powers present.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-07-22T11:22:51.517" LastActivityDate="2018-07-22T11:22:51.517" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11607" PostTypeId="2" ParentId="11605" CreationDate="2018-07-20T00:57:06.487" Score="4" Body="&lt;p&gt;Say the unmodulated carrier amplitude (voltage) is 1. At 100% modulation, the envelope will vary between amplitude 0 and 2. So at peak, the &lt;em&gt;amplitude&lt;/em&gt; is twice an unmodulated carrier, but because power is proportional to the square of amplitude, &lt;em&gt;power&lt;/em&gt; is $2^2=4$ times the carrier power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I think your CBer friend has it backwards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are looking at the signal on a scope, you are likely looking at amplitude, and peak amplitude should be twice that of an unmodulated carrier, assuming 100% modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are monitoring the signal with a peak power meter, peak power should be four times that of an unmodulated carrier.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-07-20T13:31:11.370" LastActivityDate="2018-07-20T13:31:11.370" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11608" PostTypeId="2" ParentId="5211" CreationDate="2018-07-20T23:40:34.770" Score="2" Body="&lt;p&gt;From the intended operating or design frequency point that you made the 3:1 swr reading go down 1 mhz and measure the swr. Did the swr go up or down? If the swr reading went down then the radials are too long and can be clipped 1/8&quot; ata a time until &amp;lt;1.5:1 swr is accomplished.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If on the other hand when you change frequency down by 1 mhz the swr goes up, then go up 1 mhz from the intended operating or design frequency. If the swr goes down then the antenna is too short and you must add length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;K2PHD&lt;/p&gt;&#xA;" OwnerUserId="12923" LastActivityDate="2018-07-20T23:40:34.770" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11615" PostTypeId="1" CreationDate="2018-07-23T16:49:25.310" Score="0" ViewCount="118" Body="&lt;p&gt;I need a FM receiver that is capable of receiving ultrasonic audio frequencies above the standard wide band FM range of 15 KHz. I'd like something that can receive signals up to 60 kHz if possible: I'm using JQAM software to generate QAM with a soundcard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any options for this that are relatively inexpensive? Could I build one? I am not a master at electronics, but if there were not too complicated schematics I could follow, that would be good.&lt;/p&gt;&#xA;" OwnerUserId="1817" LastEditorUserId="218" LastEditDate="2018-07-24T03:24:15.387" LastActivityDate="2018-07-24T03:24:15.387" Title="Ultrasonic FM receiver" Tags="&lt;receiver&gt;&lt;diy&gt;&lt;fm&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11616" PostTypeId="2" ParentId="11615" CreationDate="2018-07-23T16:57:14.800" Score="3" Body="&lt;p&gt;Well, it'd be trivial to modify an existing &lt;em&gt;software&lt;/em&gt; FM receiver to have a larger audio bandwidth (typically that means a larger control loop bandwidth). The hardware cost would actually be below 10€ with a china-imported RTL-SDR dongle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, GNU Radio comes with a simple, parameterized FM receiver and you can set that to basically any bandwidth you'd like. In fact, it comes with three from which you can choose:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W5BGa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W5BGa.png&quot; alt=&quot;FM demodulator chains&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've quickly built this for you, in hopes it'll be helpful at understanding the ideas. You shouldn't be expecting the same output from the three, but I hope the whets your interest in SDR; yes, that's three different FM receivers; and yes, that's Not Much Work&lt;sup&gt;TM&lt;/sup&gt; to have something to play with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the question really is where you'd get the FM signal, and what that signal actually should contain – from the top of my head, very wide FM doesn't make much sense in many potential radio channels, signal model-wise, so I'm a bit curious what your application is. Please don't build yet another PSK-in-Audio-over-FM transceiver. These things were spectrum-wise a bad idea from the start, and given the existence of SDRs there's no excuse to build one in 2018 (as you don't need to pack your data into audio for FM transmission to use affordable hardware anymore).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-07-23T17:42:16.547" LastActivityDate="2018-07-23T17:42:16.547" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11617" PostTypeId="1" AcceptedAnswerId="11618" CreationDate="2018-07-23T18:45:49.303" Score="9" ViewCount="1793" Body="&lt;p&gt;I've been dealing with S7 static on 40 meters ever since I got started a few weeks ago.  It's so bad that I have to use my RF ATT so that the static is not deafening.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did some research about finding noise sources (mostly wall warts) and common mode noise as well as the benefits of ferrite chokes.  I have tried choking the antenna feedpoint as well as the point before entering the house- to no avail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My current setup is a TS-830S with coax going out the window to a dipole up in some trees.  At the dipole feed point is 8 loops of RG-8x clamped by a 1&quot; ID mix 31 ferrite bead.  That coax runs to a T connector right next to my house.  The T connector is clamped onto a ground rod.  The bottom of the T has a Palomar Engineering bleeder resistor.  The other end of the T has 8 loops of LMR-240 in another clamp on 1&quot; ID 31 bead before entering the house.  Just at the feed point on my rig, I have another 8 turns into a toroid (#31).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before the chokes and grounding- it was just a run of coax straight to the radio from the dipole.  It made no difference either way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then one day I decided to try 40 meters at 2 o'clock in the afternoon.  It was quite dead.  In addition to that, there was no noise at all.  We're talking less than S1.  I turned off the radio and went about the rest of my day.  I cam back at 8pm and turn the radio on.  This time there was tons of activity and S7 noise.  The noise is just static.  No hum or buzz.  Just snow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact that I had near zero noise in the afternoon leads me to believe my house does not contain the source of this noise.  My computer and TV were on at the time and it was still rather quiet.  Only once the band opened up did the noise come in.  What else can I try?  Can I rule out my house or neighbors as the source of noise?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: Link to sound of the noise &lt;a href=&quot;https://streamable.com/uiyd4&quot; rel=&quot;noreferrer&quot;&gt;https://streamable.com/uiyd4&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="12939" LastEditDate="2018-07-25T20:30:41.680" LastActivityDate="2018-07-25T20:30:41.680" Title="High 40m noise floor during the evening but quiet in the afternoon" Tags="&lt;noise&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11618" PostTypeId="2" ParentId="11617" CreationDate="2018-07-23T19:03:36.733" Score="2" Body="&lt;p&gt;Night-time propagation on the low bands is significantly better than that during the day.  Static crashes from lightning can be heard from hundreds of miles away on 160m-40m and more so at night.  Summer-time noise can be much worse generally than winter-time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is NOT to say that you don't have a local radiator from people being home from work - say a plasma TV or other such nonsense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does it sound like? Can you record it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.arrl.org/sounds-of-rfi&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL&lt;/a&gt; website has several noise examples to listen to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;edit&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on your recording I'd say that was normal atmospheric noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;/edit&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="8573" LastEditorUserId="8573" LastEditDate="2018-07-25T18:54:36.647" LastActivityDate="2018-07-25T18:54:36.647" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11619" PostTypeId="2" ParentId="11617" CreationDate="2018-07-23T20:54:42.610" Score="2" Body="&lt;p&gt;Firstly, you can &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measure common-mode current&lt;/a&gt;. That will give you some idea of how effective your choke is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, I suggest getting a battery to power a receiver, and flipping off the main breaker in your house. Does the noise floor go down? If so, turn things back on one circuit at a time, identify the culprits, and replace / relocate / shield / choke them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're friendly with your neighbors, try the same there. Or wait for a power outage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If testing indicates the antenna choke is effective and there are no obvious noise sources in your house, congratulations: this is about as good as it gets! &lt;a href=&quot;https://ham.stackexchange.com/a/9833/218&quot;&gt;Noise is naturally stronger with decreasing frequency&lt;/a&gt;, and S-meters are rarely calibrated to any standard, so a S7 noise floor on 40 meters may just be ordinary. The noise floor will naturally go up as the band opens at night as you are able to hear more distant natural and man-made noise sources.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-07-23T20:54:42.610" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11620" PostTypeId="2" ParentId="10573" CreationDate="2018-07-24T12:06:37.350" Score="0" Body="&lt;p&gt;An interesting conclusion is possible with reference to the NEC4.2 study posted in this thread.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Maximum field intensity from both of the monopoles compared shows that their greatest relative fields (E/Emax) exist in the horizontal plane.  Certainly these fields must be included in the ground- (or surface-) waves radiated by these systems.&lt;/li&gt;&#xA;&lt;li&gt;The ratio of the field intensities radiated in the horizontal plane at a horizontal distance of 1 km from these two systems is 50.2/14.6 = 3.44 (approx).&lt;/li&gt;&#xA;&lt;li&gt;Radiated field intensity varies as the square root of radiated power.&lt;/li&gt;&#xA;&lt;li&gt;Therefore the antenna system using 16 buried radials each 50' in length is radiating 3.44², or about &lt;strong&gt;11.8X the power&lt;/strong&gt; radiated by the system using only a single 8' buried ground rod (with other things equal).&lt;/li&gt;&#xA;&lt;li&gt;Following the process of items 1-4 above for the fields in the NEC4.2 graphic at a height of 300 meters AGL and a horizontal distance of 1000 meters (a &quot;takeoff angle&quot; of ~16.7°), the field ratio is about 45/12 = 3.75X.&lt;/li&gt;&#xA;&lt;li&gt;The E-field ratio for these conditions is somewhat greater at 16.7° than at 0° because the surface wave field is attenuated at a rate greater than 1/r, while the fields radiated toward elevation angles producing skywaves always decay at a 1/r rate.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;A conclusion from this: &lt;em&gt;The greater the radiated groundwave fields for these conditions, the greater the radiated skywave fields.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-07-24T12:06:37.350" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11621" PostTypeId="1" CreationDate="2018-07-25T00:24:58.893" Score="2" ViewCount="322" Body="&lt;p&gt;I am considering the ramifications of monitoring my refrigerator conditions using ham radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can the radio on the refrigerator be under automatic control using my call sign so that I do not need to be at a control point?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is including technical monitored data in the transmission permitted?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thoughts on this and maybe advice on better approaches would be appreciated.   But please channel your inner Mr Rogers when responding.&lt;/p&gt;&#xA;" OwnerUserId="4820" LastEditorUserId="8717" LastEditDate="2018-07-25T14:50:31.440" LastActivityDate="2018-07-25T15:04:12.093" Title="Can I monitor a refrigerator using ham radio?" Tags="&lt;legal&gt;&lt;transceiver&gt;&lt;telemetry&gt;" AnswerCount="1" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="11622" PostTypeId="1" CreationDate="2018-07-25T09:29:39.193" Score="1" ViewCount="32" Body="&lt;p&gt;This question was asked in Electrical Engineering 2 days ago but hasn't received very informative responses.&#xA;&lt;a href=&quot;https://electronics.stackexchange.com/questions/387255/decide-coherent-time-and-fade-duration-through-empirical-studies-on-the-channel&quot;&gt;https://electronics.stackexchange.com/questions/387255/decide-coherent-time-and-fade-duration-through-empirical-studies-on-the-channel&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I. Scenario: &#xA; - TX floating in the lossy heterogeneous medium (a mud-like fluid mixed with leaves and small rocks) with undetermined positions within a limited region;&#xA; - RX fixed in the air and closed to the boundary of air-lossy medium;&#xA; - Frequency 500 MHz&lt;/p&gt;&#xA;&#xA;&lt;p&gt;II. The study: &#xA; - The received signal level was recorded every 30 seconds for 30 minutes and sometimes no signal could be detected for a while. The measurement was repeated several times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;III. Results: &#xA;An example of the received signal spectrum is as below.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/zt1gR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zt1gR.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Questions: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Can I assume 3 minutes to be the coherent time of the channel?&lt;/li&gt;&#xA;&lt;li&gt;Can I assume the no-signal period to be fade duration? &lt;/li&gt;&#xA;&lt;li&gt;How to model the channel when the TX-RX distance was not stable? Can I develop a model for the changes of received signal against time?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="11250" LastActivityDate="2018-07-25T09:29:39.193" Title="To decide coherent time and fade duration from measured received signal spectrum and relate them to channel modeling" Tags="&lt;propagation&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11623" PostTypeId="2" ParentId="11621" CreationDate="2018-07-25T15:04:12.093" Score="3" Body="&lt;p&gt;If you wish to transmit a measured parameter under US FCC Part 97 regulations, you would be operating under the telemetry rules. This is defined as &quot;A one-way transmission of measurements at a distance from the measuring instrument.&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Telemetry transmissions are generally permitted under the same conditions that &quot;Data&quot; transmissions are permitted. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The issue of automatic control is a distinct topic. Automatic control means there is no control operator at a local or remote control point. For 6 meters and shorter wavelengths (e.g.VHF and UHF transmitters) automatic control of data (and thus telemetry) transmitters is permitted:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;97.221 Automatically controlled digital station.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) This rule section does not apply to an auxiliary station, a beacon station, a repeater station, an earth station, a space station, or a space telecommand station.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) &lt;strong&gt;A station may be automatically controlled while transmitting a RTTY or data emission on the 6 m or shorter wavelength bands&lt;/strong&gt;, and on the 28.120-28.189 MHz, 24.925-24.930 MHz, 21.090-21.100 MHz, 18.105-18.110 MHz, 14.0950-14.0995 MHz, 14.1005-14.112 MHz, 10.140-10.150 MHz, 7.100-7.105 MHz, or 3.585-3.600 MHz segments.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Depending upon your specific implementation choices, other rules and limitations may apply.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-07-25T15:04:12.093" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11624" PostTypeId="1" CreationDate="2018-07-25T15:27:38.790" Score="3" ViewCount="144" Body="&lt;p&gt;I have a TS-830S that was initially doing about 60W in CW at 10m and 70W at 40m.  I've heard these things are capable of at least 100W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Determined, I started doing research on what components to look at in addition to the tubes.  I'm able to get ALC with CAR at 5 on 40 and 8 on 10 meters- so I think the drive is sufficient.  This lead me to suspect the final tubes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before getting a pricey set of tubes- I tried some of the cheaper avenues.  I have replace the C7 C8 and L1 components of the final cage with a kit from hybridrestore.com.  Next- I replaced the cathode and screen resistors with another kit from the same vendor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I didn't get much power out of that- but I did notice the tubes we easier to neutralize.  I use an SDR running SDR# as my second receive and tune to a dip in signal strength with SG.SW OFF.  The dip was much sharper and more pronounced- but it could have been placebo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally I decided to try new tubes.  I got a pair of NOS tubes from an ebay vendor with lots of good rep.  I put them in the radio and &quot;cooked&quot; the getters a bit- maybe 5 minutes- with the SG switch off.  Clearly that wasn't long enough, because a tube arched and the resistors went out of spec.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found some 1/2W metal film resistors on ebay in 100ohm and 20ohm for replacement.  And this time cooked the getters for a good hour.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Things appear to be working.  And I'm getting about 90W on 40m and 80W on 20m.  But I want to get more out of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that the power differences here are negligible.  This is more for my satisfaction of getting and old rig running at peak performance again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is- what would you suspect next?  Maybe the tubes are not quite &quot;NOS&quot; as claimed?  Should I try newly manufactured Chinese tubes that haven't been sitting on the shelf for 30 years?  Should I replace the HV caps?  I'm getting an 800V reading on the HV meter.  Anything else to look at next?&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="4665" LastEditDate="2018-07-25T18:57:20.380" LastActivityDate="2019-06-11T12:01:56.780" Title="Restoring full output power to rig with tube finals" Tags="&lt;rf-power&gt;" AnswerCount="1" CommentCount="15" ContentLicense="CC BY-SA 4.0" />
  <row Id="11625" PostTypeId="1" CreationDate="2018-07-25T20:10:55.543" Score="2" ViewCount="619" Body="&lt;p&gt;Notice the vertical antenna on the truck. &lt;s&gt;I believe this first antenna is referred to as a &quot;dipole&quot;&lt;/s&gt;, mounted vertically. CB to coax, coax to antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The shell of the truck is fiberglass. Even the front bumper is plastic. Of course there is metal; door frames and the frame itself. The shell is also dipped in a rust proofing solution and I had to clean out threads in the truck that the screws go in. So the screws tap into metal instead of the coating from the rust proofing. I also grounded the mounts that I installed on the truck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZFtSG.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below, you'll notice the second  antenna I mounted horizontally making what looks like a very skinny and upside down capital &quot;T&quot;. It's only mounted there, the second antenna isn't wired to the radio or the first antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Will this setup work? Will this create the needed reflective element?&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Nsy2Z.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user12947" LastEditorUserId="76" LastEditDate="2018-08-13T16:10:11.617" LastActivityDate="2021-01-10T14:40:58.620" Title="CB Radio Ground Plane (or lack thereof)" Tags="&lt;antenna-theory&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="11629" PostTypeId="1" CreationDate="2018-07-26T17:20:03.873" Score="6" ViewCount="557" Body="&lt;p&gt;My old man worked in avionics for 30+ years and taught me nearly everything I know about radios, like how a superheterodyne receiver works, how the ionosphere refracts signals, etc. He grew up only a half hour away from the ARRL headquarters, and I'm very curious if he ever had a license.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;How far back does the online FCC license database go?&lt;/li&gt;&#xA;&lt;li&gt;If I'd like to go further back than that, how would I do that research? Would that be an FOIA request?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="12954" LastEditorUserId="9844" LastEditDate="2018-08-01T16:35:27.417" LastActivityDate="2018-08-04T03:27:56.150" Title="Are old USA amateur radio licenses in the public FCC database?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11630" PostTypeId="2" ParentId="11629" CreationDate="2018-07-26T20:05:26.637" Score="4" Body="&lt;p&gt;The FCC online database doesn't offer old callsigns like that.  Searching online might yield some hits&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://archive.org/search.php?query=callbook&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://archive.org/search.php?query=callbook&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They're graphics and not easily searched.&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-07-26T20:05:26.637" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11631" PostTypeId="1" CreationDate="2018-07-27T14:49:23.580" Score="1" ViewCount="1699" Body="&lt;p&gt;I'm planning to make a magnetic loop antenna mainly for receiving LW, MW, and SW radio broadcasting bands, as well as perhaps the 2.2km band and 630m band.&#xA;(Not all of them with the same antenna, I'mm gone start with LW probably, so I can listen to foreign radio stations).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I want to attach that antenna to the input of an RTL SDR, which has a 50Ω coax input. I can use the RTL SDR in direct sampling mode going from basically 1kHz to around 25MHz, so that's technically no problem, but I'm unsure how to attach the magnetic loop antenna (my first one is just gonna be something similar to &lt;a href=&quot;https://swling.com/blog/2018/05/bill-scores-a-homebrew-lw-mw-magnetic-loop-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm also planning to make a ferrite core antenna, and see how that works out. But that's for a later question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I can use online calculators to get things down like the diameter, the number of turns, and the values for the tuning cap. But I'm unsure about how to attach it to the SDR. I have trouble figuring out the coupling loop which then goes to the 50Ω RG58 coax. So, I'd need a little help and/or ideas with that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;OK, now to clarify further, I'd like to build a loop antenna as described here:&#xA;&lt;a href=&quot;http://www.angelfire.com/mb/amandx/loop.html]&quot; rel=&quot;nofollow noreferrer&quot;&gt;AM Loop Antenna Calculator - UMR EMC Lab Formula&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So according to that and the build instructions I can make a box AM loop antenna for the sort of frequency range I'd like.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The pic up loop in those designes goes once around the entire loop of the antenna, and has nearly the same diameter. But how do I actually &lt;em&gt;design&lt;/em&gt; the pick up loop? I.e. I have to match it to the 50Ω impedance of the coax cable.&#xA;The build instructions just tell me to get a length of wire, and do a single turn around the perimeter of that antenna, but I don't see how that just matches the 50Ω impedance of my coax.&lt;/p&gt;&#xA;" OwnerUserId="11070" LastEditorUserId="11070" LastEditDate="2018-07-30T15:43:58.000" LastActivityDate="2019-01-24T17:59:49.923" Title="How to attach a magnetic loop antenna to the 50Ω coax of an RTL SDR?" Tags="&lt;rtl-sdr&gt;&lt;magnetic-loop&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11632" PostTypeId="1" AcceptedAnswerId="11634" CreationDate="2018-07-28T06:03:18.470" Score="0" ViewCount="78" Body="&lt;p&gt;I was thinking, since visible light has a much higher EM frequency than radio wave light, its bandwidth also has a far higher max data transmission rate, so people have been researching how to use this &quot;Li-Fi&quot; for close-range data transfer. &lt;strong&gt;What is the equation for a maximum data transfer rate for a given bandwidth&lt;/strong&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been referred to &lt;em&gt;two&lt;/em&gt; Wikipedia &#xA;pages &lt;a href=&quot;https://en.wikipedia.org/wiki/Nyquist_rate&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Nyquist Rate&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;https://en.wikipedia.org/wiki/Symbol_rate&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Symbol Rate&quot;&gt;here&lt;/a&gt;. Both I've tried extremely hard to understand, but they did not answer my initial question. I would &lt;strong&gt;SINCERELY&lt;/strong&gt; appreciate if you could answer my question. Thanks in advance.&lt;/p&gt;&#xA;" OwnerUserId="12958" LastActivityDate="2018-07-28T11:16:47.593" Title="What is the equation relating maximum data transfer rates for a given EM bandwidth" Tags="&lt;bandwidth&gt;&lt;math&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11634" PostTypeId="2" ParentId="11632" CreationDate="2018-07-28T10:51:20.167" Score="2" Body="&lt;p&gt;The formula you are seeking comes from the &lt;a href=&quot;https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;Shannon-Hartley theorem&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$C=B\log_2\left(1+\frac{S}{N}\right)\tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where C is the channel capacity in bits per second, B is the bandwidth in hertz, S is the signal power and N is the noise power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula specifies the theoretical upper bound on the information rate for an arbitrarily low data error rate. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see from the formula that it is not simply a matter of the channel bandwidth but also the signal to noise ratio of the channel. Ham radio operators are enjoying digital exchanges where the noise power is &lt;em&gt;greater&lt;/em&gt; than the signal power but this results in a very low channel capacity. It is still fascinating to make contact with a ham half way around the world with a signal than cannot even be heard above the static. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also need to consider that a LiFi channel could have substantial overhead in the packets to accommodate routing, error checking, handshaking, etc. So the data portion of the transmission will be at a lower rate than the formula might first suggest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider an LED light bulb where you can vary the color of the bulb from the color red (~450 THz) through to the color green (~550 THz) in order to transmit data. This provides an available bandwidth of 100 THz. That is 1 x 10&lt;sup&gt;14&lt;/sup&gt; hertz - a lot of bandwidth. The limitation in this case will not be the bandwidth of the channel but rather the capability of the transmit and receive electronics which will probably be limited to around 1 GHz of bandwidth or so with today's technologies. Whether or not this is a cost effective bandwidth for the consumer market is another matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a LiFi application you must also consider that there is substantial interference from other light sources. Since these are not Gaussian noise sources, they cannot be plugged in the &quot;N&quot; part of equation 1. Instead, the system will likely need to include a robust CRC (Cyclic Redundancy Check) or equivalent in order to detect and correct for this interference. This feature will further reduce the bandwidth available for the actual data.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-07-28T11:16:47.593" LastActivityDate="2018-07-28T11:16:47.593" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11635" PostTypeId="2" ParentId="11625" CreationDate="2018-07-29T01:53:08.680" Score="2" Body="&lt;p&gt;as you might guess from it’s name, a dipole consists of two parts, in opposition to each other. A vertical antenna like yours needs an opposing component to act against (usually the earth, or a large plane of metal called a groundplane), and for mobile antennas the ground is usually provided by the metal body of the vehicle. You will notice that the outer part of the coax is connected to the bracket - that would usually connect to the metal body of the vehicle, except that you say your truck is largely fibreglass. This presents us with a few problems, but it’s nothing insurmountable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can get to the inside of the bodywork where the bracket is bolted on the inside, connect some medium-heavy wires to the bolts (they are also connected to the outer of the coax), and run them in a straight line sideways and down in as many directions as you can, for as far as you can. I’d say three wires would be good, four or five better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These wires will be invisible from the outside, and should help balance the antenna to good effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have some eyelet connectors &lt;img src=&quot;https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcRrKiNJ2mFkQInWwKk90VZYTG1OMLvQCyAt4JijE9NQ3OXVlF6ASA&quot; alt=&quot;like these&quot;&gt; then these would be ideal, to allow for a good connection to the antenna.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-07-29T01:53:08.680" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="11638" PostTypeId="1" AcceptedAnswerId="15185" CreationDate="2018-07-30T07:15:42.693" Score="4" ViewCount="203" Body="&lt;p&gt;The terms of the foundation licence allow for use of Commercial radios and kits that conform to IR2028. IR2028 basically says that the kits must operate within amateur bands .&#xA;I cannot find any kit that conforms to IR2028.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could an Intermediate Licence holder build a kit and have it tested by a full licence holder and then use it?&lt;/p&gt;&#xA;" OwnerUserId="11749" LastEditorUserId="14873" LastEditDate="2019-09-02T08:05:53.707" LastActivityDate="2019-09-02T08:05:53.707" Title="UK Foundation Licence holder use of kits" Tags="&lt;legal&gt;&lt;united-kingdom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11641" PostTypeId="2" ParentId="11631" CreationDate="2018-07-31T05:07:45.300" Score="5" Body="&lt;p&gt;You may be overthinking this.  To make a long story short, just connect it and tune the capacitor to resonance and don't worry about the impedance of your pickup loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When tuning the radio to antenna system for a transmitter, you have to impedance match the load to minimize reflections because power loss is typically a big deal.  Reflections lead to high SWR, and high SWR leads to higher power losses in the coax and heating in both the coax and the radio and all these problems lead to lower transmission efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a receiver, the power levels are lower, and the losses are much lower, so this is not a big concern.  Typically your amplifier makes up for any weakness in the signal, and you are more concerned about noise from both the amplifier itself and surrounding signals.  (re: amplifier, see noise figure.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the radio antenna system, you need to match the load to 50 ohms.  In a transmitter, the load is the antenna.  In a receiver, the load is the radio.  Usually the feed line between the antenna and the radio is 50 ohms.  So you match the 50 ohm radio to the 50 ohm coax to the (maybe) 50 ohm antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a receiver, the radio is already 50 ohms, so the matching there is already done.  Making the antenna 50 ohms helps a bit, but it helps a lot more if the antenna is resonant on the target frequency to maximize the weak signal it gets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, in the end, you connect the coax to the radio, and how you connect the antenna to the coax is not that big a deal for a receiver, especially since you won't be pumping watts of power through that connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a small loop antenna (circumference typically less than 1/10 wavelength) used for either receiving or transmitting, the easiest way to tune it is to listen to your receiver and adjust your tuning capacitor for maximum signal strength.  The small loop's bandwidth is so narrow that you don't even have to tune in a signal to check for resonance -- when it is off frequency, you won't even get static; so just tune for maximum static at the desired frequency, and when there is a signal there, you'll get that as well.  The reason you don't see a lot of discussion about how to tune your pickup coil is because the coil becomes part of what affects the antenna's impedance; so however you connect it, if you tune for maximum signal, you'll already have the best balance between resonance and impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my suggestion is to connect the loop any way you can to the coax, and then test it.  If you are unsure you selected the best way, try other methods and see if the signal is stronger.  More than likely, all methods that work at all will work well enough.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2018-07-31T05:21:12.523" LastActivityDate="2018-07-31T05:21:12.523" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11643" PostTypeId="2" ParentId="11631" CreationDate="2018-07-31T12:42:38.610" Score="4" Body="&lt;p&gt;You don't necessarily need a coupling loop. Nor do you need to worry too much about matching the antenna to 50 ohms. Firstly, because &lt;a href=&quot;https://ham.stackexchange.com/q/382/218&quot;&gt;SWR is not very important for receive performance&lt;/a&gt;, and secondly because on a cursory search it seems the RTL-SDR at least when modified for direct sampling doesn't have a 50 ohm input impedance anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest connection method is simply to connect the shield to one end of the loop, and the center conductor to the other end. While this works OK, it will suffer from common-mode current on the feedline. If you are planning to put the antenna outside away from noise sources, or utilize the azimuthal nulls in the loop pattern, the common-mode current may be a problem worth solving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One solution is a &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;ferrite balun, just the same as would be used for a dipole&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another solution is a &lt;a href=&quot;https://ham.stackexchange.com/a/2423/218&quot;&gt;&quot;shielded&quot; loop&lt;/a&gt;. The shield isn't so much about shielding anything as it is making a balun. However it's not very feasible to make a shielded loop with more than one turn. You could use a smaller shielded loop as a coupling loop within a larger, multi-turn loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some designs employ a small preamplifier installed directly at the antenna feedpoint. This preamplifier usually has a balanced input so no balun is necessary. These are called &quot;active&quot; antennas. &lt;a href=&quot;http://www.lz1aq.signacor.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;LZ1AQ has some nice designs with schematics and kits available&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wouldn't overthink the problem. I'd recommend building a prototype and iterating on the design, ideally with two prototypes so you can do A/B comparisons. Especially with electrically small antennas like magnetic loops, you want to optimize for signal to noise ratio, not absolute power.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-07-31T12:42:38.610" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11645" PostTypeId="1" AcceptedAnswerId="11720" CreationDate="2018-08-01T19:29:40.223" Score="3" ViewCount="390" Body="&lt;p&gt;I was listening to a commercial FM radio station on 100.9 MHz, and this intermittent weird sound kept coming through it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.negativeiongenerators.com/images/share/temp/S%231.m4a&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;Here is a recording of it&lt;/strong&gt;&lt;/a&gt;. The audio starts at about 15 seconds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounded like some data signal or screeching and beeping interrupted my listening experience, it did so periodically. It sounds like if you accidentally call a fax machine and you get that buzzing and screeching sound.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It was powerful enough to take out the station; I don't know if it was coming from the station itself, or if it was interference from another source. I had problems before with Internet signals getting through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No other stations that I get have this problem.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a single-wire loop antenna that I have to twist to get clearer reception, and a Kenwood digital tuner. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another observation is that the day was cloudy. I had no problem with reception other than static. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there anything I can do to prevent this?&lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="8717" LastEditDate="2018-08-06T16:30:26.940" LastActivityDate="2018-08-17T15:11:42.693" Title="What is this odd data/screeching/fuzzy signal?" Tags="&lt;receiver&gt;&lt;rfi&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11646" PostTypeId="2" ParentId="9904" CreationDate="2018-08-02T00:02:57.110" Score="1" Body="&lt;p&gt;An excellent description is here:  &lt;a href=&quot;https://en.wikipedia.org/wiki/Equivalent_impedance_transforms&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Equivalent_impedance_transforms&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sorry, I do not have sufficient brainpower to summarize :-)&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2018-08-02T00:02:57.110" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11648" PostTypeId="2" ParentId="9904" CreationDate="2018-08-02T14:03:04.573" Score="0" Body="&lt;p&gt;Negative capacitance can be substituted with inductance at a single AC frequency. Since impedance wise they are opposites. That goes with replacing the transformer if it has more impedance then the caps. I'm fussy on the transformation, the math for all that eludes me most days. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm actually seeing this transformation attributed to Darlington, not Norton.&lt;br&gt;&#xA;&lt;a href=&quot;https://en.wikipedia.org/wiki/Equivalent_impedance_transforms&quot; rel=&quot;nofollow noreferrer&quot;&gt;Christopher Morgan K8NVH's wikipedia article on Equivalent impedance transforms&lt;/a&gt;&#xA;&lt;a href=&quot;https://pdfs.semanticscholar.org/deda/d6cf542143e5dd8d935bd67936b622bae792.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;A History of Network Synthesis and&#xA;Filter Theory for Circuits Composed of&#xA;Resistors, Inductors, and Capacitors&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10709" LastEditorUserId="9493" LastEditDate="2018-08-02T15:17:24.497" LastActivityDate="2018-08-02T15:17:24.497" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11650" PostTypeId="2" ParentId="11629" CreationDate="2018-08-03T13:45:27.757" Score="4" Body="&lt;p&gt;To answer the second question:  I looked up &lt;a href=&quot;https://archive.org/search.php?query=callbook&quot; rel=&quot;nofollow noreferrer&quot;&gt;the reference&lt;/a&gt; I've copied from @mike65535, and it is as useful as a Callbook itself.  I looked up my parents in the 1966 Callbook (k1uzg and k1uzk) and found their listing.  I also looked up my original call (wa1jms) and found that I wasn't yet licensed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The archive includes several years of the Callbook.  Each contains scans of the original Callbook pages, organized like the Callbook: 0-land, 1-land, 2-land, etc, and then alphabetically by suffix.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The scan is at the lowest possible resolution and the scan is functional, although finding a call can be like pulling it out of a pileup.  I accessed the archive with my cell phone and was helped by having a magnifier and squinting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In an earlier comment I noted when I was retesting for my long-lapsed license, I needed to prove my previous license to avoid the code test.  For the particular VE, a Callbook showing my call would have been sufficient proof.  If I had this archive, I might have avoided taking a 5 wpm code test after 25 years of inactivity.  Fortunately, the code was burned into my brain deeper than I thought, and 5 wpm is very slow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have just re-read my answer, and it isn't very helpful for your problem.  You need to search by name, since you don't have your father's call.  I focused on the wrong aspect of the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would forget about the FCC database and concentrate on general &quot;old-fashoned&quot; Googling.  Search for his name.  If there are too many hits, add &quot;radio&quot;, &quot;amateur radio&quot;, or &quot;ham radio&quot;.  If you know his company, Google with that company name.  Check if there is a radio club at the company -- many larger companies have clubs.  Look for other hams in the area where he lived.  The &lt;a href=&quot;http://hams.mapmash.com/hammap.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;site&lt;/a&gt; shows all the currently licensed hams by area or zip code.  Contact them and see if they know your old man.  Maybe first contact the ones with old calls.  You can use &lt;a href=&quot;https://www.qrz.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;qrz.com&lt;/a&gt; to look up the local calls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wish you all the best finding information about him.  Hams are a friendly lot with long memories.  If he was a ham, you'll probably be able to find a thread to follow.&lt;/p&gt;&#xA;" OwnerUserId="9109" LastEditorUserId="9109" LastEditDate="2018-08-04T03:27:56.150" LastActivityDate="2018-08-04T03:27:56.150" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11651" PostTypeId="1" AcceptedAnswerId="11652" CreationDate="2018-08-04T00:52:08.143" Score="2" ViewCount="823" Body="&lt;p&gt;Has the HF spectrum become noisier over the decades due to man-made interference? Is this a reason why HF band activity appears to be declining?&lt;/p&gt;&#xA;" OwnerUserId="6095" LastEditorUserId="366" LastEditDate="2018-08-12T05:52:20.133" LastActivityDate="2019-10-05T18:36:12.827" Title="What has happened to HF?" Tags="&lt;hf&gt;&lt;rfi&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11652" PostTypeId="2" ParentId="11651" CreationDate="2018-08-04T10:51:37.443" Score="12" Body="&lt;p&gt;HF propagation is not only limited by manmade interference but also by natural phenomena like sunstorms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, I'd account that to social and technological reasons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;HF activity suffers very much from the &lt;em&gt;old men's club's image&lt;/em&gt; phenomenon (a term that I just invented!): How attractive is it to join a communication group that consists of old men? &lt;/li&gt;&#xA;&lt;li&gt;Old men get older and die. That reduces the pool of people able to use HF.&lt;/li&gt;&#xA;&lt;li&gt;Ham radio generally is losing a bit of appeal because, well, it's lost all specialness to be able to talk someone at the other end of the globe, because that's what we do all day using the internet. Thus, flaky speech or Morse communication itself has not much benefit.&lt;/li&gt;&#xA;&lt;li&gt;good HF antennas tend to be large. Compare to the overall trend of migration to metropolitan areas.&lt;/li&gt;&#xA;&lt;li&gt;Rent is pretty much going up everywhere. Having a garden with a shed increases in price!&lt;/li&gt;&#xA;&lt;li&gt;HF comms do bear attractiveness to engineer types due to the fact that there's much to be technically improved (compare: WSPR, FT8), but that's usually not what people have in mind when they say &quot;HF band activity&quot;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So, yeah, doing long-range bad-quality speech communication with old men simply isn't that attractive these days.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find you're in the wrong with your observation of declining activity, however. Last time I talked to larger groups of hams (which was in Friedrichshafen at HAMRADIO'18), they were all totally astonished by the &lt;em&gt;count of contacts&lt;/em&gt; made in the last months – all due to FT8. FT8 offers a new exciting technological aspect to ham radio, and hence is used far and wide, with hundreds of thousands of contacts¹. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you ask me, this is all a self-made problem of how ham education is done: Instead of focusing on modern technology, people are taught CW, and proper voice comms conduct, and outdated tech. That does a tremendous job at keeping the hobby's reality compatible to techniques and technology of the 1940s to 50s, but guess what, people's interests moved on with the technology that around that time left ham radio in the dust.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;¹ Technologically, FT8 is not even &lt;em&gt;that&lt;/em&gt; exciting, and it's quite obvious that it's cleverer than the classical digital modes and by far far far cleverer than trying to do analog modes² over low-SNR links. It's early 1980's state-of-the art communications, with computer frontends, at best. The only cool thing is the channel code, an LDPC, but older channel codes could have achieved similar performance, albeit at the cost of higher computational complexity (not that it matters much, at these symbol rates)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;² the discussion whether analog or digital modes offer better communication quality for speech has been pretty much scientifically answered in the mid-80s. Digital wins. There's no good reason people are still doing AM or FM communications for voice other than cost in the case of least-end handsets (albeit even the cheapest Baofeng handhelds for 20€ do DSP for audio, so even that doesn't count anymore) and backwards compatibility with the 1940s.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-10-05T18:36:12.827" LastActivityDate="2019-10-05T18:36:12.827" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11655" PostTypeId="2" ParentId="11651" CreationDate="2018-08-06T01:06:04.643" Score="5" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;It is a measurable fact that there is more electronic noise across the radio spectrum now than ever before.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;However, I doubt that it has directly had much effect on the amount of amateur radio activity on the HF bands. There are many other factors (see Marcus' answer for some of those) that contribute to the decline of activity on any given band or group of bands.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Finally, to address the question in the title: We have been at an extreme solar minimum for several years now, the likes of which has very likely never been seen since the discovery of radio. This is (in my opinion) &quot;what has happened to HF&quot; recently. There have been extended periods of no sunspot activity on the sun at all, and this all contributes to making HF conditions miserable.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-08-06T01:06:04.643" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11656" PostTypeId="2" ParentId="11651" CreationDate="2018-08-06T02:03:22.493" Score="3" Body="&lt;p&gt;Man-made noise has some detriment to HF communications. &lt;a href=&quot;https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-13-201609-I!!PDF-E.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU-R P.372-13&lt;/a&gt; illustrates:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VyKTH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VyKTH.png&quot; alt=&quot;figure 2&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note how the man-made noise at a quiet receiving site (C) is above the minimum atmospheric noise (B) from 70 kHz to 5 MHz. The full document has more figures that characterize noise specifically by time of day, season, and geography. But the gist is that at the quietest sites in this band (which includes the amateur 80 and 60 meter allocations), about half the time the noise floor is dominated by man-made noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At higher frequencies the man-made noise drops below natural sources (galactic noise, D) at quiet locations, but the man-made noise in cities (E) is on the order of 20 dB higher in cities, even worse indoors or in densely populated areas. That's well above natural sources. This graph ends at 10 MHz, but the trend continues with city man-made noise being about 20 dB higher than natural sources for the rest of the HF band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's hard to say if this is &quot;a reason why HF band activity appears to be declining&quot;. The question has been &lt;a href=&quot;https://ham.stackexchange.com/q/8940/218&quot;&gt;asked before&lt;/a&gt;, though the poster of that question asserts the problem is &lt;em&gt;not&lt;/em&gt; man-made noise. The trouble is in the word &quot;appears&quot;. A lot of things contribute to appearances, quite likely many of them social as Marcus Müller explains.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-08-09T03:08:38.267" LastActivityDate="2018-08-09T03:08:38.267" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11657" PostTypeId="1" AcceptedAnswerId="11662" CreationDate="2018-08-06T07:41:50.420" Score="5" ViewCount="718" Body="&lt;p&gt;According to &lt;a href=&quot;http://www.antenna-theory.com/basics/aperture.php&quot; rel=&quot;noreferrer&quot;&gt;http://www.antenna-theory.com/basics/aperture.php&lt;/a&gt;, the power received by an antenna depends on the power density of the incoming wave, the wave length (which I consider to be fixed) and the antenna gain. So if I want to receive more power I need to build an antenna with higher gain, but this means that the antenna would be much more directive. Let us say that I want to stick with a non directive antenna, because I do not know in advance the direction I will be receiving from.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to the equations in the webpage, there is nothing I can do to improve the received power once I fix wave length and gain. However, this strikes me: I would expect a bigger antenna to intercept more RF power, and thus making more available at its terminals. Why does not this happen? Are there tricks (maybe using non linear components?) to actually collect more incoming RF power in all directions, without making the antenna directional?&lt;/p&gt;&#xA;" OwnerUserId="1654" LastActivityDate="2018-08-07T22:38:59.470" Title="Why does not a bigger antenna receive more power?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11659" PostTypeId="2" ParentId="11657" CreationDate="2018-08-06T11:49:29.217" Score="0" Body="&lt;p&gt;A larger antenna can give you more power and not just more gain. Some examples:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dish is not an antenna, but part of an antenna system.  The antenna in a dish system is aimed at the dish, and the surface area of the dish increases the effective aperture of that antenna.  The dish and antenna must mutually focus radiation of interest on each other for this to work.  The antenna is said to cover or illuminate the dish.  Typically you want a compromise between the antenna's beam exactly covering the dish and its highest gain covering the dish, so typically there is some overshoot with some small gain behind the dish where it falls over the edge.  Similarly, the antenna will be at or near the focus of the dish.  Note that the curvature of the dish refocuses the antenna, so this may also change gain and directionality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can take three directional antennas (for example, a moxon with a 170 degree beam angle, maybe 120 degrees of which is high gain), mount them on a single tower, and couple them together, aiming them in different directions (i.e., spaced at 120 degrees).   The result is an omnidirectional pattern of higher gain than a dipole but less directional than the single antenna.  Note that in this configuration the apertures of the moxons (mostly) add, not the gains.  (There may be some constructive and destructive interference at the edges where they overlap.  It also helps the tower isn't shadowing any of them.)   (Note that cell towers do this, except that those antennas are typically not coupled and each goes to a separate radio.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be effective at a particular wavelength, an antenna needs to have a length that is a significant fraction of that wavelength (ideally 1/2).  This is unreasonable for an AM broadcast antenna (590khz has wavelength 520m, ideal antenna would be 260m).  To make this a reasonable sized antenna, the wire can be wrapped in a coil.  Unfortunately, this severely reduces its aperture.  To increase the aperture and make the antenna effective, it is wrapped around a powdered ferrite core which concentrates the fields without making it larger.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2018-08-06T22:58:57.107" LastActivityDate="2018-08-06T22:58:57.107" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11660" PostTypeId="2" ParentId="11657" CreationDate="2018-08-06T12:26:22.247" Score="2" Body="&lt;p&gt;One way to accomplish this is by stacking multiple vertical dipoles or horizontal &quot;halo&quot; loop antennas (or a turnstile array with two straight dipoles at 90°) on a vertical mast. Such an array can have nearly 360° coverage and increased gain over a single vertical or loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such an antenna array can be said to be directional, but in a practical way: it has increased gain at lower angles --towards the horizon-- but decreased gain at the unwanted higher angles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antennas are connected using a carefully designed &quot;phasing harness&quot; made from either balanced line (for UHF and above) or coax (usually VHF). They are often used by FM broadcast or television stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;This is the pattern and gain of the antenna described above:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VcmGM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VcmGM.png&quot; alt=&quot;Array plot as described above&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;For comparison, here is the gain and pattern of a dipole:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fdT7M.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fdT7M.png&quot; alt=&quot;Vertical dipole for comparison&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It appears that the stacked array wins, even if it has those high lobes. It has quite a bit more gain at low angles than the dipole.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="10565" LastEditDate="2018-08-07T22:38:59.470" LastActivityDate="2018-08-07T22:38:59.470" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11661" PostTypeId="2" ParentId="11657" CreationDate="2018-08-06T14:00:04.973" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Let us say that I want to stick with a non directive antenna, because I do not know in advance the direction I will be receiving from.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;With this as the starting point, consider that there is no real antenna that has an omni-directional property  - so you cannot &quot;stick&quot; with this type of antenna in the real world. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We sometimes think of monopole antennas as omnidirectional but in fact they are far from it. The monopole and its derivatives such as vertical collinear antennas have a omnidirectional pattern in the azimuth but only for a specific elevation. If the elevation angles of the approaching plane waves are not equal, the monopole family will receive these signals with differing gains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The isotropic antenna is the only truly omni-directional antenna. But this is only a theoretical construct - there are none in existence.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;However, this strikes me: I would expect a bigger antenna to intercept more RF power, and thus making more available at its terminals.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In a very broad sense for a given wavelength, the larger the physical aperture of an antenna the greater possibility for it to intercept more power from the plane wave and make this available to the receiver system. But the increase in physical size also alters its radiation / reception pattern along with the feedpoint impedance. So the trade offs need to be considered.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Let us say that I want to stick with a non directive antenna, because I do not know in advance the direction I will be receiving from.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Since all real world antennas start with some directionality, some compromise in this goal is necessary. You may find electronically steerable antenna arrays to be an interesting study in this regard. They can achieve very high gain over a relatively broad pattern. While this gain in a given direction is itinerant in nature, it can be used to find and lock onto a signal source to realize its maximum gain during reception of that signal. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-07T21:21:30.283" LastActivityDate="2018-08-07T21:21:30.283" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11662" PostTypeId="2" ParentId="11657" CreationDate="2018-08-06T18:57:30.970" Score="6" Body="&lt;h2&gt;Argument A: reciprocity&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;By &lt;a href=&quot;https://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;reciprocity&lt;/a&gt;, we can flip this question around and ask it from the perspective of the transmitter. Assuming we've done the obvious like minimize feedline losses, and we're holding the geography, frequency, and so on constant, how can we get a higher fraction of the transmitter's power to appear at the receive antenna's feedpoint?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the transmitter has some omnidirectional antenna like a vertical monopole, most of the radiated energy is going in the wrong direction to ever reach the receiver, and is thus lost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Increasing the directivity of the transmitting antenna sends a higher proportion of the transmitter's power towards the receiving station, accomplishing the goal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should be intuitively obvious from the law of conservation of energy that a higher gain is the only option here, which if losses are already minimized means a higher directivity. &lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Argument B: phase coherence&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Consider you have an omnidirectional antenna like a vertical monopole, and the received power at the feedpoint is 1μW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wanting to receive more power, you install another identical antenna beside it. This 2nd antenna, having a nearly identical path to the transmitter as the 1st, receives another 1μW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In total you're receiving 2μW, but to get the full 2μW combined into a single port requires that the phases of the two antennas are adjusted so they add coherently.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, this means the array has acquired more directivity. While some phasing arrangement may work for one transmitter location, there will be other possible geometries which place the transmitter closer to one of the antennas and farther from the other, thus altering the phase at which the signals combine. Thus the antenna array is no longer omnidirectional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, while a longer wire, or a larger array of antennas will indeed intercept more power, it's not possible to &lt;em&gt;coherently&lt;/em&gt; combine those powers without increasing directivity.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;MIMO&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;An array of antennas does indeed receive more power, the difficulty is it's often unknown what phasing of the antennas will result in the signal combining coherently. One solution is to make the phasing variable, and to dynamically adjust it for maximum signal clarity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern communication systems (Wi-Fi, cell phones) can do this dynamically by separately digitizing the signal from each antenna, then dynamically adjusting the phasing in software. This is effectively an antenna array that's always &quot;pointed&quot; in the optimal direction, thus obtaining a higher link quality without the disadvantages of a directional antenna.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Collinear arrays&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;For terrestrial communications in predominately flat terrain, it's safe to assume the other station is near the horizon, that is, not flying overhead, and not underground, although the direction may be unknown. In these cases it's possible to maintain a &lt;a href=&quot;https://en.wikipedia.org/wiki/Omnidirectional_antenna#/media/File:L-over2-rad-pat-per.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;omnidirectional (meaning uniform along the azimuth) pattern&lt;/a&gt; by increasing the directivity in the elevation axis. That is, making a &quot;flatter&quot; doughnut.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often this is achieved with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Collinear_antenna_array&quot; rel=&quot;nofollow noreferrer&quot;&gt;collinear array&lt;/a&gt;. A quarter-wave monopole above a ground plane has gain of 5.2 dBi, and a dipole 2.2 dBi: when you see omnidirectional antennas with higher gains they are usually collinear arrays with a &quot;flatter&quot; pattern.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-08-07T16:07:45.497" LastActivityDate="2018-08-07T16:07:45.497" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11663" PostTypeId="2" ParentId="6887" CreationDate="2018-08-06T19:49:34.837" Score="0" Body="&lt;pre&gt;&lt;code&gt;If someone with a CB or HAM using 500 watts to over 2000 watts..&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;(Also referred to as kW for Kilowatts) the pure power being transmitted can actually interfere with nearby DSL AND CABLE lines!&lt;br&gt;&#xA;Particularly if the connections are not very solid.  If the shielding on the particular cable line form the pole to the customer is not properly grounded or there is just very high power nearby, the RF signal can introduce quite a lot of &quot;Noise&quot; into the line and interfere with the internet signal.  It does NOT have to be in the same frequency range as the power of the transmitted RF is high enough to simply interfere with the signal.&#xA;   Further evidence I had that this was the case was that my computers' wired Speaker system would pick up the neighbor's voice and he could be heard through the speakers as he keyed up high power.  It would ALSO be picked up by my WIRED headphones that use a standard Micro USB cable! (10ft cord)  It would cause havok with my computer as well.  My WiFi network would drop and I would have to at times reset the routers and modem to get it back!&#xA;    So yes, a nearby high power HAM radio transmission can disrupt MANY different electronic systems.  I will have to do research to find out if there are legal issues with it since the neighbor will not acknowledge he even uses the radio, but I recognize his voice coming over my speakers!  Kinda hard to say you are not causing the problem when your voice is heard in the interference.  Safe to say he's using very high power.  As a tech for over 40 years and an ECM tech in the USAF, I have a background in radio and in interfering with signals!  ;-)&#xA;    (However, such interference is NOT common.  I seem to be dealing with an extreme case)&lt;/p&gt;&#xA;" OwnerUserId="13010" LastActivityDate="2018-08-06T19:49:34.837" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11664" PostTypeId="1" CreationDate="2018-08-06T22:48:48.740" Score="3" ViewCount="1120" Body="&lt;p&gt;I have two 2-meter antennas, a &lt;a href=&quot;https://www.jpole-antenna.com/shop/2-meter-amateur-radio-j-pole-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;copper J-Pole&lt;/a&gt; and a &lt;a href=&quot;http://www.hy-gain.com/Product.php?productid=VB-25FM&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hy-Gain VB-25FM&lt;/a&gt;. The J-Pole is my all-around antenna, what I use for general 2 meter stuff like connecting to my local repeaters using my main 2-meter radio. The VB-25FM will be used to establish a connection to a specific ham that lives across town from me to play around with digital modes on a different radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My thinking was it would be great if I could mount the VB-25FM mid-way up the mast, and then mount the J-Pole on the very top. Would this work, or is it a bad idea?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="6657" LastEditorUserId="8717" LastEditDate="2018-08-07T14:43:04.813" LastActivityDate="2018-08-17T11:16:24.147" Title="Mounting a J-Pole and Yagi on the same mast" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;vhf&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11665" PostTypeId="2" ParentId="11664" CreationDate="2018-08-07T14:25:42.860" Score="1" Body="&lt;p&gt;I've done exactly that, except instead of a 2m yagi, I have a VHF/UHF Log-periodic antenna (a.k.a. a TV antenna) midway up the mast.  The only question is if the manufacturer of the Yagi recommends mounting it that way.  Based on a brief look at the manual, I'd say yes.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-08-07T14:25:42.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11666" PostTypeId="2" ParentId="11664" CreationDate="2018-08-07T20:01:43.317" Score="2" Body="&lt;p&gt;&lt;strong&gt;Near and Far Fields&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To mount the two antennas in close proximity to one another, you should minimally ensure that neither reactive (near) field interferes with the reactive field of the other in order to avoid disturbing the pattern or gain of either antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reactive near field is generally defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R\approx0.62\sqrt{\frac{D^3}{\lambda}} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where R is the radius (separation distance), D is the longest linear dimension of the antenna in meters and $\lambda$ is the wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of two antennas, calculate R for each one and add the results together. For example, if one D is 1 meter, the other D is 2 meters and the band is 2 meters:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_1\approx0.62\sqrt{\frac{1^3}{2}}$$&#xA;$$R_1\approx0.88 \text{ meters}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_2\approx0.62\sqrt{\frac{2^3}{2}}$$&#xA;$$R_2\approx1.24\text{ meters}$$&#xA;So the minimum separation would be ~2.1 meters. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to play it safer and have each antenna in the other's Fraunhofer zone (far field) then use the formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R=\frac{2D^2}{\lambda} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where D is the maximum linear dimension of the two antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the same example as above, the maximum linear dimension is 2 meters which would yield a distance of 4 meters. But since you are dealing with stacked vertical antennas, the radiating near field in the direction of the other antenna is greatly suppressed. Therefore this is an excessive distance in your application. A compromise between the results of the two formulas should prove sufficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Common Mode Current&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The J pole antenna is notorious for the development of common mode current on the coax. This results in the coax becoming part of the radiating / receiving antenna. Since this coax will likely pass adjacent to your yagi, the above near and far field calculation efforts will be nullified without a proper current balun on the J pole feedpoint to mitigate the common mode currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Receiver Overload&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you plan on operating both radios at the same time, take into account that while transmitting on one antenna, a good deal of this power arrives at the other antenna. This can overload the receivers front end or, in a worst case, damage the receiver even if they are not on the same frequency.You may wish to use the &lt;a href=&quot;https://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Friis equation&lt;/a&gt; to help estimate the amount of power impressed upon the receiver. Use the gain of the each antenna in the direction of the other (which will be far less than their stated maximum gain). You may find this thread on &lt;a href=&quot;https://ham.stackexchange.com/questions/7376/how-to-find-or-derive-the-maximum-safe-input-power-to-a-receiver&quot;&gt;&quot;How to find or derive the maximum safe input power to a receiver?&quot;&lt;/a&gt; to also be helpful.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-13T00:34:14.583" LastActivityDate="2018-08-13T00:34:14.583" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11667" PostTypeId="1" CreationDate="2018-08-07T20:34:33.270" Score="6" ViewCount="231" Body="&lt;p&gt;I have created a software (gnuradio) that performs modulation/demodulation and supports a number of modulation schemes and error correcting codes. I'm in the process of evaluating the BER vs SNR for this software by using a secondary industrial-grade hardware. This device can measure the BER. Unfortunately, the device does not have the capability of measuring the input signal SNR, which means I have to measure it manually. At the moment, I'm thinking of using a spectrum analyzer. Basically, I will compare the signal level relative to the noise floor and derive the SNR (simple subtraction since everything is in dBs). However, I was looking for suggestions on more elegant methods of doing this and what type of hardware would be required.&lt;/p&gt;&#xA;" OwnerUserId="6214" LastEditorUserId="4076" LastEditDate="2020-04-26T13:39:02.070" LastActivityDate="2020-04-26T13:39:02.070" Title="SNR measurement for a BPSK/QPSK signal" Tags="&lt;software-defined-radio&gt;&lt;rf-power&gt;&lt;gnuradio&gt;&lt;testing&gt;&lt;snr&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11668" PostTypeId="1" AcceptedAnswerId="11669" CreationDate="2018-08-08T09:21:00.743" Score="20" ViewCount="3030" Body="&lt;p&gt;I have the possibility to buy a very inexpensive 2.4m parabolic satellite dish and I would like to build a radio telescope from it. Originally this dish was designed to be a satellite TV antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I replace the TV LNB with radio receiver tuned for 1420MHz (hydrogen lines) and use the dish as radio telescope? Does the focal length of such an antenna depend on the frequency for which it was designed? &lt;/p&gt;&#xA;" OwnerUserId="4133" LastEditorUserId="-1" LastEditDate="2018-08-09T16:14:40.993" LastActivityDate="2019-05-29T22:45:15.000" Title="Can I build a radio telescope out of a parabolic TV satellite dish?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;satellites&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11669" PostTypeId="2" ParentId="11668" CreationDate="2018-08-08T10:10:58.233" Score="16" Body="&lt;p&gt;The primary factor to consider is the directivity of the parabolic antenna. It is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$d=\frac{(\pi D)^2}{\lambda^2} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where D is the diameter of the dish and $\lambda$ is the wavelength of operation, both in the same units.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To convert frequency to wavelength in meters, we use:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\lambda=\frac{300}{f} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where f is the frequency in megahertz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since your frequency of interest is 1420 MHz, we apply formula 2 to convert this to a wavelength of 0.211 meters. With a dish diameter of 2.5 meters, formula 1 give us a directivity of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$d=\frac{(\pi D)^2}{\lambda^2}=\frac{(\pi 2.5)^2}{0.211^2}=1386$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We now need to convert this directivity to linear gain. Here the standard antenna formula applies:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$G=d*e \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where d is the directivity from formula 1 and e is unitless efficiency with a value of 1 indicating 100% efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most parabolic antennas have efficiencies in the 60% to 70% range. For a conservative estimate, if we assume a 50% efficiency, the linear gain of your parabolic antenna is 693. We can convert this to dBi gain using:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$G_{dBi}=10\log_{10}(G) \tag 4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which nets ~28 dBi in this case. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With diligence, you may be able to obtain a 70% efficiency which will raise the gain to ~30 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The beamwidth of the parabolic antenna is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$\theta\approx\frac{70\lambda}{D} \tag 5$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 3 dB beamwidth of your parabolic antenna will therefore be ~6°.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The focal point of a parabolic antenna is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$f=\frac{D^2}{16c} \tag 6$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where c is the depth of the parabolic reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see from this formula, that it is not a function of wavelength. So the focal point of the dish remains largely the same regardless of frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You now must consider the sensitivity and noise of your receive system and the expected field strength of a 1420 MHz hydrogen marker to determine if this is sufficient gain for your radio telescope operation. There is hope for success as several university students have used a similar configuration for their projects.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-09T16:07:23.443" LastActivityDate="2018-08-09T16:07:23.443" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11670" PostTypeId="2" ParentId="11651" CreationDate="2018-08-08T17:33:42.397" Score="7" Body="&lt;p&gt;Before looking for reasons why HF activity &quot;appears to be declining&quot;, we should look for evidence that HF activity &lt;em&gt;is&lt;/em&gt; declining — so let's look at some available sources of data. While contests may not be fully representative of the broader HF community, they &lt;em&gt;do&lt;/em&gt; involve a lot of people, and they provide a ready source of reliable data that goes further back in time than things like lotw/eqsl/pskreporter. So let's see.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;CQ WW DX CW:&lt;/h2&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;1987 - 2,602 entrants, #1 had 12,387 QSOs, #100 had 2,281 QSOs&lt;/li&gt;&#xA;&lt;li&gt;1997 - 3,063 entrants, #1 had 14,770 QSOs, #100 had 3,561 QSOs&lt;/li&gt;&#xA;&lt;li&gt;2007 - 4,705 entrants, #1 had 14,642 QSOs, #100 had 4,285 QSOs&lt;/li&gt;&#xA;&lt;li&gt;2017 - 7,940 entrants, #1 had 12,892 QSOs, #100 had 4,850 QSOs&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h2&gt;CQ WW DX SSB:&lt;/h2&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;1987 - 2,615 entrants, #2 had 15,602 QSOs*, #100 had 2,882 QSOs&lt;/li&gt;&#xA;&lt;li&gt;1997 - 3,354 entrants, #1 had 14,927 QSOs, #100 had 3,514 QSOs&lt;/li&gt;&#xA;&lt;li&gt;2007 - 4,873 entrants, #1 had 12,637 QSOs, #100 had 4,280 QSOs&lt;/li&gt;&#xA;&lt;li&gt;2017 - 8,124 entrants, #1 had 13,872 QSOs, #100 had 4,344 QSOs&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;*: The #1 entrant in 1987 is listed as having 32,767 QSOs, which is a supicious number, being 2^15-1, and probably a data error.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;ARRL International DX Contest (CW):&lt;/h2&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;2007 - 2,569 entrants, winner had 5,326 QSOs&lt;/li&gt;&#xA;&lt;li&gt;2017 - 3,837 entrants, winner had 6,788 QSOs&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;What I see in this survey of HF contest results is a mix — the top performers are flat to &lt;em&gt;maybe&lt;/em&gt; slightly down, but the number of competitors submitting logs has shown a &lt;em&gt;sharp increase&lt;/em&gt;, resulting in many more operators/teams getting within striking distance of the winners (as reflected in the consistent increase in the 100th-place QSO totals for CQWW).  What I &lt;em&gt;don't&lt;/em&gt; see is any evidence that band performance is so bad as to severely hamper the chances of making a contact, or that the pool of HF operators (even code-qualified ones!) available to enter contests is shrinking.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2018-08-08T17:33:42.397" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11671" PostTypeId="2" ParentId="11668" CreationDate="2018-08-08T19:02:37.563" Score="5" Body="&lt;p&gt;It's been done before. The University of Groningen astronomy department runs (ran?) &lt;a href=&quot;https://stargazerslounge.com/topic/89455-satellite-dish-radio-astronomy/&quot; rel=&quot;noreferrer&quot;&gt;a couple of 2.5 m dishes&lt;/a&gt; for radio astronomy exercises. IIRC they mainly observe our Sun (strongest radio source).&lt;br&gt;&#xA;So I'd say yes, that dish could be a good starting point. &lt;/p&gt;&#xA;" OwnerUserId="13019" LastActivityDate="2018-08-08T19:02:37.563" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11673" PostTypeId="1" CreationDate="2018-08-09T02:26:21.490" Score="2" ViewCount="478" Body="&lt;p&gt;I am new at this. I would like to transmit an audio signal cleanly using WBFM but I see two signal peaks occur around my fundamental frequency when I start transmitting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case I am using a 1Khz tone but also when I send a song, at high frequencies the song is distorted due to the two signal peaks that appear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I fix this? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yZJkX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yZJkX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/AQSHZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AQSHZ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13023" LastEditorUserId="13023" LastEditDate="2018-08-10T05:59:23.900" LastActivityDate="2018-08-10T05:59:23.900" Title="LimeSDR Mini + Raspberry Pi 3 B+ Transmission problem" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;transmitter&gt;" AnswerCount="0" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="11674" PostTypeId="2" ParentId="11668" CreationDate="2018-08-09T12:52:15.340" Score="1" Body="&lt;p&gt;Yes, although not a very big one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The wavelength at 1420 MHz is 21.11 cm. Thus the aperture of this telescope is roughly:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ { 240\:\mathrm{cm} \over 21.11\:\mathrm{cm} } = 11.4\ \text{wavelengths} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Probably somewhat less, considering inefficiencies.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For comparison, the wavelength of green light is around 500 nm. So in terms of the ability to resolve features, this 2.4 meter radio telescope is roughly equivalent to an optical telescope with an objective of a miniscule:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 0.00005\:\mathrm{cm} \cdot 11.4 = 0.00057 \:\mathrm{cm} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, the -3 dB beamwidth of a 2.4 meter dish at 1420 MHz is approximately 6 degrees. Meaning, 3 degrees any direction away from the axis of maximum gain, the sensitivity of the antenna has diminished by half. With such a wide beam, you will be limited to observing only very large astronomical features.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-08-09T12:52:15.340" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11675" PostTypeId="1" AcceptedAnswerId="11676" CreationDate="2018-08-09T19:56:01.447" Score="2" ViewCount="210" Body="&lt;p&gt;A ham I know who is antenna-challenged logs onto an Internet site where he has QSOs with other licensed hams worldwide via his computer's microphone and speakers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He says &quot;it's just like being on HF&quot;, and he loves it! But I'll be darned if I can remember what it is. &lt;strong&gt;It's not Echolink, not digital, and no RF is used&lt;/strong&gt;. Anyone know the URL?&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-08-18T18:14:59.433" LastActivityDate="2018-08-18T18:14:59.433" Title="Internet ham QSO website?" Tags="&lt;internet&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11676" PostTypeId="2" ParentId="11675" CreationDate="2018-08-09T20:03:19.370" Score="2" Body="&lt;p&gt;The service I have heard of that simulates HF communications is &lt;a href=&quot;http://www.hamsphere.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;HamSphere&lt;/a&gt; [&lt;a href=&quot;https://en.wikipedia.org/wiki/HamSphere&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia article&lt;/a&gt;]. It is a paid service.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think there might be another similar site but that's all I remember.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-08-09T20:03:19.370" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11677" PostTypeId="2" ParentId="126" CreationDate="2018-08-10T17:41:02.073" Score="0" Body="&lt;p&gt;One advantage of a vertical antenna (not yet mentioned) is that you can hang a vertical wire over a single tree, while a horizontal antenna needs at least two trees.  I use my 50 foot high tree for my vertical 80 meter.  Yes, it needs 66 feet of wire to tune properly, but I simply bend the wire over the top and then down.  Most of the signal radiates from the lower parts of the vertical antenna, where the most current is.&lt;br&gt;&#xA;My method of building the antenna was to throw a &lt;em&gt;string&lt;/em&gt; over the tree, and tie the wire to the string and pull up the wire, up and over.    &lt;/p&gt;&#xA;" OwnerUserId="8647" LastActivityDate="2018-08-10T17:41:02.073" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11679" PostTypeId="1" AcceptedAnswerId="11681" CreationDate="2018-08-11T12:19:19.253" Score="1" ViewCount="121" Body="&lt;p&gt;I am fixing up an old classic Yaesu FRG7 general coverage AM/SSB/CW HF receiver. The BFO section is a rudimentry 455 kHz IFT configured as a carrier reinsertion oscillator that that is made to run USB or LSB by switching a small trimmer cap either in or out of the circuit.The overall stability of SSB demodulation seems to be surprisingly good on 80m.The Wadley loop system used implies that the higher bands will also be good. Hence there is no real incentive to use two crystals for USB and LSB. We keep the BFO. AM detection is done with an envelope detector. I have not heard any AM on the amateur bands. I can get lots of SW broadcast stations coming in strong at night. There is a lot of fading. Would a synchronous detector help here? Would loosely coupling some 455 kHz IF to the BFO be a simple way of achieving this?&lt;/p&gt;&#xA;" OwnerUserId="6095" LastEditorUserId="873" LastEditDate="2018-08-11T12:50:46.397" LastActivityDate="2018-08-11T13:42:18.950" Title="BFO locked synchronous AM detection" Tags="&lt;hf&gt;&lt;receiver&gt;&lt;am&gt;&lt;mixer&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11681" PostTypeId="2" ParentId="11679" CreationDate="2018-08-11T13:42:18.950" Score="2" Body="&lt;p&gt;AM synchronous detection will certainly reduce or eliminate selective fading. It generally isn't implemented simply due to the increased cost and complexity. But you will certainly be pleased with its performance if you enjoy listening to AM shortwave broadcasts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think you would find that the easiest design that you could retrofit to the receiver would be the addition of a high gain  amplifier off of the IF. This is injected into a final mixer. Since the AM signal is hard limited by this amplifier stage, its output is the AM carrier without modulation. This makes it an ideal injection component for the final mixer to recover the baseband audio.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-08-11T13:42:18.950" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11682" PostTypeId="1" CreationDate="2018-08-11T22:47:29.307" Score="0" ViewCount="106" Body="&lt;p&gt;A certain RF transistor has a source - reflection coefficient with a magnitude of .105 and a phase angle of 160°. When plotted on the Smith Chart, the normalized impedance is .825 +j .06 Ω. What is the actual or unnormalized impedance? What does it depend on? Is it 50(.825 +j .06 Ω) or 41 +j 3 Ω? Is the Smith Chart automatically normalized to 50 when dealing with RF transistor reflection coefficients that were derived from S - parameter equations and when determining the actual impedance the transistor wants to see? &lt;/p&gt;&#xA;" OwnerUserId="11230" LastEditorUserId="8717" LastEditDate="2018-08-12T00:29:44.043" LastActivityDate="2018-08-12T15:38:56.813" Title="Reflection Coefficient to Impedance transformation on the Smith Chart" Tags="&lt;impedance&gt;&lt;electronics&gt;&lt;smith-chart&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11683" PostTypeId="1" AcceptedAnswerId="11686" CreationDate="2018-08-12T02:13:21.607" Score="2" ViewCount="195" Body="&lt;p&gt;I have just set up my first AIS receiving station with compliments of Marinetraffic.com. They have supplied me with a Comar SLR350Ni receiver and a &lt;a href=&quot;http://www.sirioantenne.it/en/products/vhf/gp-3-e&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sirioantenne.it/en/products/vhf/gp-3-e&lt;/a&gt; antenna. I have already upgraded the cable to a more heavy duty type.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My station is &lt;a href=&quot;https://www.marinetraffic.com/en/ais/details/stations/4365&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.marinetraffic.com/en/ais/details/stations/4365&lt;/a&gt;. I'm actually about 30Mt ASL and have a direct line of sight to the coast about 2.2Km from shore.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is how can I improve my coverage area and distance using a different type of antenna rather than using the one supplied? I have another station slightly South of me that seems to cover a far greater distance and gets attributed with far more vessel sightings than what I'm currently able to achieve?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do realise that height is a major factor but short of mounting a longer mast on my tripod on the roof, I'm not sure of what more I can do without the neighbors complaining.&lt;/p&gt;&#xA;" OwnerUserId="13034" LastEditorUserId="76" LastEditDate="2018-08-12T03:52:51.820" LastActivityDate="2018-08-12T14:33:54.390" Title="Improving coverage of AIS receiving station" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;&lt;range&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11684" PostTypeId="1" AcceptedAnswerId="11704" CreationDate="2018-08-12T03:44:00.397" Score="3" ViewCount="224" Body="&lt;p&gt;The minivan in front of us blew a tire and pulled over, a long way away from mobile signal. We couldn't find a spare tire. I have a Technician license; if I'd had my Baofeng BF-F9 V2 with me, is there a way I could have used it to help that family out?&lt;/p&gt;&#xA;" OwnerUserId="13035" LastEditorUserId="9493" LastEditDate="2018-08-14T15:12:01.903" LastActivityDate="2018-08-14T15:46:09.617" Title="Non-life-threatening emergency in the US?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;emergency&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11685" PostTypeId="2" ParentId="11682" CreationDate="2018-08-12T12:14:57.637" Score="2" Body="&lt;p&gt;Since you know the complex reflection coefficient, you can simply use this formula to calculate the complex impedance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Z=Z_O\frac{1+\rho}{1-\rho} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming the characteristic impedance is 50+j0 ohms, your transistor has an impedance of ~40.9+j3 ohms. You will notice that this is the normalized Smith chart impedance times 50 ohms (assuming it is normalized to 50 ohms). This is true since the normalization process simply divides the actual impedance by the normalization impedance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To achieve maximum power transfer, the load on the transistor would be the complex conjugate of this or 40.9-j3 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Its S11 parameter may be computed as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$S11=20\log{(|\rho|)} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would result in an S11 value of -19.6 dB in your case.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-12T15:38:56.813" LastActivityDate="2018-08-12T15:38:56.813" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11686" PostTypeId="2" ParentId="11683" CreationDate="2018-08-12T12:48:37.353" Score="1" Body="&lt;p&gt;Your line of sight to the ship transmitting the AIS signal is one of the more limiting factors. Usable AIS VHF signals will travel just slightly further than line of sight conditions. This is known as the radio horizon. I have plotted the height in meters you will require in order to obtain a desired receive distance of AIS signals:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YTDAv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YTDAv.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This chart assumes the transmitting station on the ship or boat has an antenna height of 2.5 meters ASL (Above Sea Level). If you do not obtain sufficient height of your receive antenna for the distance you desire, no other remedy will reliably increase your range. If you have trees, buildings, poles, etc. between your receive antenna and the transmitting antenna, the range will be less than this chart predicts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming your receiver is optimized, and you have met the height requirement, there are a other few things to think about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your coax cable introduces losses into your AIS signal which effectively weakens the signal. Keeping the coax as short as possible and using higher grade coax can mitigate the effects. Hams would typically use LMR-400 or equivalent for a VHF application such as this but you may also have success with a high grade 75 ohm cable TV coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The location of the antenna will determine its susceptibility to man made interference from a variety of household and industrial electronics. Keeping the antenna as far away from these as possible will minimize the interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna design can have a profound effect on received signal strength. Your current antenna is marginal in this respect. A collinear style antenna would offer you much more gain while retaining your omnidirectional coverage. The antenna will be taller than the one you are presently using. It is generally enclosed in a thin fiberglass radome to protect the antenna itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another antenna option is a small, vertical yagi antenna. A three or four element yagi will dramatically improve your received signal strength. It is a directional antenna but when pointed toward the water, its beamwidth should offer quite good coverage for AIS signals. But it is directional so it will favor some areas over others. The yagi antenna will not be any taller than your current antenna and it resembles a typical TV antenna to the untrained eye.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-12T14:33:54.390" LastActivityDate="2018-08-12T14:33:54.390" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11688" PostTypeId="1" CreationDate="2018-08-12T16:04:25.577" Score="8" ViewCount="1419" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FqV9c.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FqV9c.jpg&quot; alt=&quot;Is this a broadcasting antenna?&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We bought an old house and found an antenna inside the attic of the house. I don't know much about antennas or radio but searching in Google I found a similarly shaped one and it describes it as a broadcasting one. Is that what this antenna is? If so, can it be used to receive my local TV signal instead? If not, does an antenna like this have any value?&lt;/p&gt;&#xA;" OwnerUserId="13039" LastEditorUserId="-1" LastEditDate="2018-08-14T15:10:15.450" LastActivityDate="2018-08-14T15:10:15.450" Title="Is this a broadcasting antenna?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11689" PostTypeId="2" ParentId="11688" CreationDate="2018-08-12T16:42:04.223" Score="9" Body="&lt;h3&gt;What you've got&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;First, a small point of terminology: the question you want to ask is whether it is a &lt;em&gt;transmitting&lt;/em&gt; antenna, not &lt;em&gt;broadcasting.&lt;/em&gt; &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_13&quot; rel=&quot;nofollow noreferrer&quot;&gt;Broadcasting has a formal definition which (in the US) is &quot;Transmissions intended for reception by the general public&quot;.&lt;/a&gt; We like to be precise about this because we are &lt;em&gt;not allowed to broadcast.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That does look like it might be a radio amateur's antenna. In fact, it looks like an antenna that was intended to be installed vertically that was hung sideways from the rafters instead (note the three-way symmetry of the metal plate but with one rod missing).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not likely to be &lt;em&gt;particularly good&lt;/em&gt; for TV reception, because it is too large. An antenna that is much larger than the wavelength of the signal it is being used to receive will&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;have a very unpredictable pattern — which directions it is good or bad at at receiving signals from, and&lt;/li&gt;&#xA;&lt;li&gt;pick up more irrelevant signals on lower frequencies (longer wavelengths). The receiver can ignore them, but there's always a limit.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There will also be an &lt;em&gt;impedance mismatch&lt;/em&gt; due to the antenna not being intended for TV bands and being designed for a different impedance. But impedance mismatches don't matter too much for receiving — at worst it doesn't work.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Course of action&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;If your primary goal is to get good TV reception, then your best course of action is to install a completely separate TV antenna in your attic — or even better, on top of your roof — and possibly reuse the &lt;em&gt;path&lt;/em&gt; of the existing coax to run a standard 75 Ω TV coax line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you think it'll be a fun project to try to use the antenna for your TV and don't mind spending a two-digit amount of money on the experiment, then it's worth hooking it up to see what happens. (Your TV, or your FM radio, or shortwave (international) radio if you are interested in that.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even a bad antenna that's on top of the house may be better than a good one installed lower down. In general cases, you're not going to hurt a receiver by trying out an antenna with it.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Hooking it up&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Broadly, all you need to do is follow the coaxial cable down to wherever it ends, and hook it up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you will most likely need an adapter, because the connector on the end of the cable will not be a TV-coax &quot;F&quot; connector. Most likely, it will be a &quot;UHF&quot;/&quot;PL-259&quot; connector, or an &quot;N&quot; connector. You can find an adapter from either of those, or any other common RF connector, to a &quot;F&quot; type connector which is the kind used for TV antennas and cable TV; it will cost a few dollars.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The reason I say that it won't be an &quot;F&quot; connector is because amateurs &lt;em&gt;most often&lt;/em&gt; don't use &quot;F&quot; connectors, and because the coax is too thick for a standard &quot;F&quot; connector — besides eyeballing the size, I also faintly see it is marked &quot;RG 8/U&quot; on the part running across the top of the photo.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3ZVLM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3ZVLM.jpg&quot; alt=&quot;N and UHF connectors&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-08-13T14:52:54.567" LastActivityDate="2018-08-13T14:52:54.567" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11691" PostTypeId="2" ParentId="11688" CreationDate="2018-08-12T16:44:56.063" Score="13" Body="&lt;p&gt;It appears to be a &quot;vertical&quot; CB ground plane antenna that had been mounted or stored in a horizontal orientation. It is not suitable for effective TV or FM reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also noteworthy that one of its three ground plane elements is missing in the picture. It likely that it had to be removed to place the antenna into that location.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-12T21:15:06.593" LastActivityDate="2018-08-12T21:15:06.593" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11692" PostTypeId="1" CreationDate="2018-08-12T21:13:09.383" Score="4" ViewCount="205" Body="&lt;p&gt;In his July 2018 article in CQ magazine entitled “Lightning (and EMP) Surge Protection for HF Radios”, Steven Karty, N5SK based much of his analysis for properly specifying a GDT (Gas Discharge Tube) on an equation used by Huber+Suhner (S+H) and further promulgated by Peter Sypher, KC4SI in a paper entitled “An Improved Formula for Peak Voltage Calculation in an RF Transmission Line” dated 17 May 2017.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula championed by the article is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_{peak}=\sqrt{2Z_OP_{out}}*(1-\rho_L) \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where Z&lt;sub&gt;O&lt;/sub&gt; is the characteristic impedance of the transmission line, P&lt;sub&gt;out&lt;/sub&gt; is the output power of the transmitter and $\rho_L$ is the reflection coefficient of the load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the N5SX article, the author took exception to a peak voltage equation referenced by K5PA in a July/August 2016 QEX article entitled “Radio Frequency (RF) Surge Suppressor Ratings for Transmissions into Reactive Loads”. The KC4SI paper also takes exception to this equation. The K5PA equation, often shown in ARRL publications and so referenced by K5PA, is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_{peak}=\sqrt{2Z_OP_{out}SWR} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The author states that formula 2 is less accurate than formula 1. Is this correct?&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="76" LastEditDate="2018-08-13T16:23:58.747" LastActivityDate="2018-08-14T13:55:24.717" Title="Is this transmission line peak voltage formula published in CQ Magazine more accurate?" Tags="&lt;impedance-matching&gt;&lt;transmission-line&gt;&lt;lightning&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11693" PostTypeId="2" ParentId="11692" CreationDate="2018-08-12T21:13:09.383" Score="2" Body="&lt;p&gt;Equation 1 as proposed in the article has two primary shortcomings:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;It does not address losses in the line. As a result, the formula may overstate the maximum peak voltage.&lt;/li&gt;&#xA;&lt;li&gt;It requires that Z&lt;sub&gt;G&lt;/sub&gt; (the output impedance of the generator) closely matches the Z&lt;sub&gt;O&lt;/sub&gt;. This is rarely the case except in a controlled lab environment. As a result, the equation generally understates the maximum peak voltage.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Since the use of equation 1 was centered upon selecting an appropriate GDT for lightning/EMP protection, shortcoming #2 is the most significant since this may cause the GDT to fire under normal operating conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a practical example which illustrates shortcoming #2: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Consider a ½ wavelength transmission line with a Z&lt;sub&gt;O&lt;/sub&gt; of 50+j0 ohms (therefore lossless). At the end of this transmission line is a 150+j0 ohm load. At the other end of the transmission line is a 100 watt output transmitter connected to a properly adjusted, lossless impedance matching circuit (the antenna tuning unit or ATU). Since the transmission line is ½ wavelength long, the input impedance of this length of transmission line is also 150+j0 ohms. A properly adjusted ATU will therefore transform the output impedance of the transmitter to 150+j0 ohms, providing a conjugate match to deliver the maximum available power to the load. Since the condition of maximum power transfer has been satisfied, 100 watts is applied across the input impedance of the transmission line.&lt;/em&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using a derivation of Ohm’s law, the peak voltage is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_{peak}=\sqrt{2Z_OP_{out}}=173.2 \text{ volts} \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whereas equation 1 would predict:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_{peak}=\sqrt{2*50*100}*(1-0.5^2)= 150 \text{ volts}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This represents a greater than 15% error in this case. Most concerning is that the error underestimates the maximum voltage, defeating the very purpose of referencing the equation - to properly size a GDT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fundamental cause of this error is due to the failure to account for the additional reflection coefficient caused by the Z&lt;sub&gt;G&lt;/sub&gt; (output impedance of the generator) not matching the Z&lt;sub&gt;O&lt;/sub&gt; of the transmission line. This additional reflection coefficient will cause a reflection from the load, arriving at the source, to be partially (in this case) reflected back toward the load. These reflections continue as an infinite series. The voltage reflections from the generator that are additive to the load voltage reflections increase the peak voltage on the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we now apply the above example to equation 2, the result is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_{peak}=\sqrt{2Z_OP_{out}SWR}=173.2 \text{ volts}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which is the correct result. However, equation 2 has the following shortcomings:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The equation is quite accurate for low loss lines when ZG=ZIn but in all other cases, it will overstate the maximum peak voltage&lt;/li&gt;&#xA;&lt;li&gt;In the case of higher loss transmission lines, the equation can overstate the peak maximum voltage even when ZG=ZIn. This is mitigated by measuring the SWR at a point near the generator.&lt;/li&gt;&#xA;&lt;li&gt;For large values of SWR, the results become dubious. As SWR approaches infinity, the term under the radical approaches infinity. Clearly this would exceed all practical limitations of the generator. The significance of this shortcoming cannot fully quantified as it largely depends upon various parameters of the generator such as open circuit voltage, output impedance, protection circuits, etc.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Conclusion&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equation 1 is accurate for a lossless transmission line when the impedance of the generator matches the characteristic impedance of the transmission line. This would be the case in a controlled lab environment. When equation 1 is used with a configuration that includes a properly adjusted ATU, it will exhibit the following error:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aP0Ng.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aP0Ng.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equation 2 is accurate for a lossless transmission line when the impedance of the generator matches the input impedance of the transmission line. This would be the case when a properly adjusted ATU at the transmitter end is used. When formula 2 is used with a configuration in which the generator impedance matches the characteristic impedance of the transmission line, it will exhibit the following error:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lAaTZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lAaTZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more general formula that lacks the simplicity of the above formulas but works in any Z&lt;sub&gt;G&lt;/sub&gt; to Z&lt;sub&gt;O&lt;/sub&gt; or Z&lt;sub&gt;in&lt;/sub&gt; relationship as well as for low loss lines is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$V_{peak}=\frac{1+\rho_Le^{-2\gamma l}}{1-\rho_Le^{-2\gamma l}\rho_G}\frac{\sqrt{2P_GZ_G}}{Z_G+Z_O}2Z_O \tag 4$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\rho_G$ is the generator reflection coefficient, $\gamma$ is the complex propagation coefficient of the transmission line and l is the length of the line as measured from the load to the generator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equation 4 assumes that the generator behaves as a Thevenin source. This may not always be the case, especially if the generator has an SWR protection (foldback) feature and more generally for higher SWRs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;&lt;sub&gt;&lt;sub&gt;This Q&amp;amp;A has been extracted from a white paper written by W9IQ as a result of communications with the author of the CQ article. This whitepaper is available from W9IQ upon email request.&lt;/sub&gt;&lt;/sub&gt;&lt;/sub&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-14T13:55:24.717" LastActivityDate="2018-08-14T13:55:24.717" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="11694" PostTypeId="2" ParentId="11684" CreationDate="2018-08-12T21:46:55.397" Score="6" Body="&lt;p&gt;Because the situation does not rise to the level of &quot;imminent threat to life or property&quot; you would not be permitted to &quot;use any means neccessary&quot; to carry out your communications. As a result, you would need to pass your traffic using simplex or an available repeater on ham radio frequency allocations if you are under US jurisdiction at the time. A simple &quot;request for assistance for a stranded motorist&quot; would be sufficient.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-08-12T21:46:55.397" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11695" PostTypeId="2" ParentId="11684" CreationDate="2018-08-12T22:15:02.197" Score="0" Body="&lt;p&gt;The Baofeng BF-F9 is an 8-watt UHF/VHF handytalky. With those frequencies you only have line of sight (a few miles) with the stock antenna, and maybe a little better (20-40 miles) if you were to string up a J-pole antenna up a tree. If you were to climb a mountain, you might be able to hit a more distant repeater. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, it’s not going to do you a whole much but it’s better than nothing. An emergency j-pole is certainly something to consider having in your go bag. &lt;/p&gt;&#xA;" OwnerUserId="11462" LastActivityDate="2018-08-12T22:15:02.197" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11696" PostTypeId="1" AcceptedAnswerId="11697" CreationDate="2018-08-12T23:07:16.740" Score="1" ViewCount="179" Body="&lt;p&gt;&lt;strong&gt;Antenna properties:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Height x Diameter = 3.3 inches x 1.4 inches  &lt;/li&gt;&#xA;&lt;li&gt;Test Frequency: 900 MHz&#xA;(Wavelength = 33 cm or 13 inches)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I see some conflicting formulas to calculate the near field distance for an antenna w.r.t. the frequency of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Method 1:&lt;/strong&gt; (multiple sources)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Reactive Field &amp;lt;= 0.63 x sqrt(Height^3/Wavelength) ===&gt; 2.6 cm or 1.02 inches&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Method 2:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Reactive Field &amp;lt;= Wavelength ===&gt; 33 cm or 13 inches&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Which one applies here accurately?&lt;/p&gt;&#xA;" OwnerUserId="6722" LastEditorUserId="8717" LastEditDate="2018-08-12T23:25:04.220" LastActivityDate="2018-08-14T12:11:08.667" Title="True near field distance for a short monopole antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;propagation&gt;&lt;antenna-system&gt;&lt;path-loss&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11697" PostTypeId="2" ParentId="11696" CreationDate="2018-08-13T00:17:42.867" Score="1" Body="&lt;p&gt;The general formula for reactive field does not incorporate height, but rather maximum dimension of the antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R\approx 0.62\sqrt{\frac{D^3}{\lambda}} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where D is the maximum dimension in meters and $\lambda$ is the wavelength in meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that this results in an approximation in meters, not an exact answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiative near field (between the reactive near field and the Fraunhofer region) ends at a distance from the antenna as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R\approx \frac{2D^2}{\lambda} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your second formula is technically correct as it uses &quot;&amp;lt;=&quot;. When you compare the more concise results of formula 1, it does not conflict with the broad prediction of your second formula.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-13T01:12:23.733" LastActivityDate="2018-08-13T01:12:23.733" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11699" PostTypeId="2" ParentId="9842" CreationDate="2018-08-13T21:26:23.120" Score="1" Body="&lt;p&gt;Answer to question 1:  Yes you should be able to pull in WWV on 5 - 10 - 15 MHz at all hours of the day, from NJ, with the higher frequency during the day, and the lower frequency at night.  Something might be wrong with your radio, make sure you have fresh batteries, and so on.  If you are hearing other stations, (try 6060 kHz for Radio Havana) then try 3330 or 7530 KHz for CHU time signals in Canada, best at night.  Another thing, you may need to go outside, if your building is blocking signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Answer to question 2:  You should not need an external antenna with your Grundig.  The whip antenna should suffice for any reception need. Your Grundig is built to add lots of gain to what the whip antenna can detect.  Again, check your radio, check for fresh batteries, go outside, and so on.  I also have a Grundig (Yacht Boy) and I find that it works horrible with an external antenna.&lt;/p&gt;&#xA;" OwnerUserId="8647" LastActivityDate="2018-08-13T21:26:23.120" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11700" PostTypeId="1" CreationDate="2018-08-14T10:50:28.340" Score="1" ViewCount="122" Body="&lt;p&gt;Is &lt;a href=&quot;https://ham.stackexchange.com/search?q=Friis%20equation&quot;&gt;the Friis equation&lt;/a&gt; sufficient to make this calculation?  Must other considerations also be evaluated?&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="218" LastEditDate="2018-08-15T14:52:09.077" LastActivityDate="2018-08-19T11:37:34.333" Title="How is RF Power at Receive Antenna Output Terminals Calculated?" Tags="&lt;propagation&gt;&lt;rf-power&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11701" PostTypeId="2" ParentId="11700" CreationDate="2018-08-14T10:50:28.340" Score="1" Body="&lt;p&gt;Below is the output screen of a spreadsheet calculator using the Friis equation, displaying received r-f power based on transmit/receive system parameters when using a free space propagation path.  Numeric values in the yellow-shaded cells may be entered by the user.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The spreadsheet also automatically calculates and displays&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the mid-path radius distance for clearance of the 0.6 Fresnel zone, as such Fresnel clearance provides the propagation loss of a free-space path&lt;/li&gt;&#xA;&lt;li&gt;the r-f voltage present across a 50 Ω output termination of a loss-free matching network at the receive antenna output terminals.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This Excel-type spreadsheet is available at &lt;a href=&quot;https://nofile.io/f/19jUxxDHCJE/Friis+Transmission+Equation+Speadsheet+(Fry).xls&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://nofile.io/f/19jUxxDHCJE/Friis+Transmission+Equation+Speadsheet+(Fry).xls&lt;/a&gt; — free to download and free to use.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IOuHW.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IOuHW.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next below is a graphic illustrating the effect on the e-field produced by insufficient clearance for the Fresnel zone with various heights above ground of the receive antenna, for the conditions shown there.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/wGN9J.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wGN9J.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next below to illustrate the significance of Fresnel zone clearance is the result of a Longley-Rice calculation for the path loss from FM broadcast station WIOG to a receive site in northern Livingston county, MI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For those coordinates and antenna heights AGL and the frequency, the terrain profile plus earth curvature along the path shows blockage of the 0.6 Fresnel zone radius starting at about the mid-point of the path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the path geometry exactly allowed clearance of the 0.6 Fresnel zone for its entire length then the received field intensity would exactly equal that of a free-space, unobstructed path, and as based on the Friis equation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this example the 0.6 Fresnel zone obstruction contributes about 8.9 dB of additional loss to that LOS path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UJ6av.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UJ6av.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2018-08-19T11:37:34.333" LastActivityDate="2018-08-19T11:37:34.333" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11702" PostTypeId="2" ParentId="11664" CreationDate="2018-08-14T11:19:15.287" Score="1" Body="&lt;p&gt;The long technical answer here leaves out several huge factors.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Polarization -- typically in this type of setup, you'd have the yagi horizontally polarized and the j-pole vertically polarized.   This significantly reduces interactions between the two.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radiation pattern -- Again, in the typical arrangement, these two antennas would mutually be in each other's null direction which would significantly reduce their interaction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the two antennas would be in each other's near field where polarization and the radiation pattern are less settled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The typical amateur radio way to find out is to set it up and test.  It sounds like you will be putting two radios on these antennas anyway -- connect them both, transmit on one, and see if that signal gives the other radio front end overload.  Start at low power first.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2018-08-17T11:16:24.147" LastActivityDate="2018-08-17T11:16:24.147" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11703" PostTypeId="2" ParentId="11696" CreationDate="2018-08-14T12:11:08.667" Score="2" Body="&lt;p&gt;Below is the output result of a NEC4.2 analysis of an electrically short monopole, showing its near-field boundary radius to be located about 30 meters from the base of that monopole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The groundwave field beyond about 30 meters decays at &lt;em&gt;nearly&lt;/em&gt; a 1/r rate, but not exactly 1/r because of the surface wave propagation losses present for these conditions — even for the short path shown.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iSJ52.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iSJ52.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-08-14T12:11:08.667" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11704" PostTypeId="2" ParentId="11684" CreationDate="2018-08-14T15:46:09.617" Score="4" Body="&lt;p&gt;If there's no mobile phone coverage, it's likely there are also no repeaters in range of the Baofeng. You could try the conventional simplex calling frequencies of 146.52 MHz (2m) and 446 MHz (70 cm) to see if someone nearby can help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A blown tire isn't an emergency, so there's no particular protocol to follow. Simply, &quot;This is [your call], I'm with a motorist in need of a spare tire at [describe location], can anyone assist?&quot; would suffice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Range with a handheld UHF/VHF radio isn't great, maybe on the order of 10 km in flat terrain. If being out of mobile phone coverage also means you're in the middle of nowhere with few people around, it's unlikely there's someone in range, that's a ham, that's monitoring the calling frequencies, and willing and able to help beyond what you could personally do for the stranded motorist. Practically speaking, offering a ride to the nearest town may be more helpful.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-08-14T15:46:09.617" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11705" PostTypeId="2" ParentId="615" CreationDate="2018-08-14T18:50:58.967" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;•How did they tune antennas back when the hobby was still new?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This part of your question has not yet been answered.  The technique used was to set up a transmission line consisting of parallel wires to an antenna.  It is possible to use a hand-held meter along the transmission line to determine the relative voltages on the line at different points of the line. The line exhibits standing waves on the line, that is, the peaks and lows are steady in place and can be found and measured.   The ratio of the high voltage to the low voltage is the standing wave ratio - S.W.R. Adjusting the antenna also affected the SWR, as we know.  When the peaks and valleys of the voltage differences evened out, and there were no more peaks or lows, then the SWR was 1:1 and the antenna was &quot;tuned&quot;.   &lt;/p&gt;&#xA;" OwnerUserId="8647" LastActivityDate="2018-08-14T18:50:58.967" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11707" PostTypeId="2" ParentId="615" CreationDate="2018-08-14T19:40:53.833" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;•How did they tune antennas back when the hobby was still new?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/11708/how-did-hams-manage-to-tune-their-antennas-before-vswr-meters&quot;&gt;Answer moved to a new question here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-08-14T23:19:49.370" LastActivityDate="2018-08-14T23:19:49.370" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11708" PostTypeId="1" AcceptedAnswerId="11709" CreationDate="2018-08-14T23:18:13.593" Score="10" ViewCount="1069" Body="&lt;p&gt;In the early 20th century --back when the hobby was still new-- before VSWR meters and antenna analyzers were invented, how did radio operators know whether they were tuned for maximum power out?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;This is not asking about antenna tuner design or operation.&lt;/em&gt; &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-08-14T23:24:23.967" LastActivityDate="2019-10-12T01:37:03.933" Title="How did hams manage to tune their antennas before VSWR meters?" Tags="&lt;antenna-system&gt;&lt;impedance-matching&gt;&lt;swr-meter&gt;&lt;testing&gt;&lt;history&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11709" PostTypeId="2" ParentId="11708" CreationDate="2018-08-14T23:18:13.593" Score="17" Body="&lt;ol&gt;&#xA;&lt;li&gt;Mostly, they used &lt;strong&gt;RF Ammeters&lt;/strong&gt; in series with the antenna. The first ones were &lt;a href=&quot;https://en.wikipedia.org/wiki/Ammeter#Hot-wire&quot; rel=&quot;noreferrer&quot;&gt;&lt;strong&gt;hot-wire ammeters&lt;/strong&gt;&lt;/a&gt; which were &lt;em&gt;completely mechanical&lt;/em&gt; devices. One end of a thin nichrome wire (or other wire of sufficiently high resistance) inside the meter was coupled directly to the pointer shaft (often wrapped around it); the other end was anchored to the meter case. As the wire got warm and expanded due to the antenna current flowing through it, the spring-loaded pointer shaft rotated clockwise. &lt;br&gt;&lt;br&gt;Later, an improved RF ammeter design --that featured slightly faster response and improved RF isolation-- used an external &lt;a href=&quot;https://en.wikipedia.org/wiki/Thermocouple&quot; rel=&quot;noreferrer&quot;&gt;&lt;strong&gt;thermocouple&lt;/strong&gt;&lt;/a&gt; which sensed the temperature of a high-resistance wire in series with the antenna. The thermocouple was connected to a millivoltmeter (or milliammeter?) with the scale calibrated in amperes. The more current, the hotter the wire and the thermocouple junction. The higher the junction voltage of the thermocouple, the higher the meter reading.&lt;/li&gt;&#xA;&lt;li&gt;Another method was a &lt;strong&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Neon_lamp&quot; rel=&quot;noreferrer&quot;&gt;neon lamp&lt;/a&gt;&lt;/strong&gt; coupled to the antenna. The brighter it glowed, the higher the voltage.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;In both cases&lt;/strong&gt; the operator tuned for maximum, either max current or max voltage, &lt;strong&gt;which indicated maximum power into the antenna&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's how I tuned my homebrew transmitters for max back in the late '60s and '70s. My RF ammeter was a WWII military surplus unit (pictured below), and measured from 0-10 amps. The meter was fed from a thermocouple unit inside the case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/X1Gzr.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/X1Gzr.png&quot; alt=&quot;WWII surplus BC-442-A RF ammeter&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Later, at VHF frequencies, &lt;a href=&quot;https://ham.stackexchange.com/questions/10441/how-were-1920s-hams-able-to-measure-megahertz-frequency/10467#10467&quot;&gt;Lecher wires&lt;/a&gt; were also used.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-01-24T23:30:31.813" LastActivityDate="2019-01-24T23:30:31.813" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="11710" PostTypeId="1" CreationDate="2018-08-15T11:40:15.653" Score="2" ViewCount="272" Body="&lt;p&gt;Let's say you have two mobile simplex transceivers running on (for example) SSB. Mobile means that the antenna height and TX power have limitations. Say if we limit the Antenna height to 2m and the TX power to 100w. In an urban environment the optimum frequency is not clear. VHF/UHF does not like obstructions, but there is less noise than say HF. Lower HF would do well getting around obstructions, but noise could be bad and poor antenna efficiency could easily waste most of the transmitter power. What frequency would be best?&lt;/p&gt;&#xA;" OwnerUserId="6095" LastEditorUserId="8717" LastEditDate="2018-08-15T16:31:52.563" LastActivityDate="2018-08-21T14:34:40.533" Title="Radio Range vs. Frequency" Tags="&lt;frequency&gt;&lt;range&gt;" AnswerCount="3" CommentCount="7" FavoriteCount="1" ClosedDate="2018-08-23T02:49:42.857" ContentLicense="CC BY-SA 4.0" />
  <row Id="11712" PostTypeId="2" ParentId="11710" CreationDate="2018-08-15T14:49:48.447" Score="-3" Body="&lt;p&gt;What's the optimum place to live?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's the optimum car to buy?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like your question, these are complicated questions without an easy answer. There are many trade-offs involved, and simultaneously optimizing all of them is usually not possible. And often, practical requirements override the myriad technical issues. For example, the best place to live is one where you have a job, family, or friends. The best frequency is one where there's a repeater in range that you're licensed to use. If you're installing the repeater, the best frequency is one that's available.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-08-15T14:49:48.447" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11713" PostTypeId="1" CreationDate="2018-08-15T18:40:04.587" Score="1" ViewCount="146" Body="&lt;p&gt;I built a 40m vertical using the W8AMZ design &lt;a href=&quot;https://www.amateurradiosupplies.com/v/vspfiles/assets/images/40m_vertical_monopole_-_manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amateurradiosupplies.com/v/vspfiles/assets/images/40m_vertical_monopole_-_manual.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Seems to be working for the most part.  But I'm not sure if it's really exhibiting a 22 degree takeoff angle.  I have it about 8 feet off the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I get really strong signals from closer QTHs.. like +20 or +40 over S9.  I'm in western NY state and i get the strongest signals from NJ, WV, MI.  TX is pretty solid, but it really starts to fade around AZ and CA as well as NV.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's hard to tell if it's just a propagation thing or a distance thing.  The fact that the closer stations are booming makes me think it's a combination of distance and high takeoff angle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you think lowering or raising the antenna would change anything?  I have the radials as close to 180 degrees and level as possible.  How critical is that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: as far as dealing with common mode current is concerned, I have 8 turns of the RG8X feedline going through one of these at both the feedpoint and shack entrance: &lt;a href=&quot;http://palomar-engineers.com/ferrite-application-experts-2#!/FSB31-1-ID=1-RFI-Range-1-300-MHz/p/74532157/category=21480229&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://palomar-engineers.com/ferrite-application-experts-2#!/FSB31-1-ID=1-RFI-Range-1-300-MHz/p/74532157/category=21480229&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After that, the feedline goes througha T connector which is attached to a round rod.  The bottom part of the &quot;T&quot; has a PL-259 connector with a bleeder resistor across it: &lt;a href=&quot;http://palomar-engineers.com/antenna-products/antenna-static-bleeders/Coax-Static-Bleeder-p74882773&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://palomar-engineers.com/antenna-products/antenna-static-bleeders/Coax-Static-Bleeder-p74882773&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="12939" LastEditDate="2018-08-16T15:33:16.020" LastActivityDate="2018-08-16T15:55:09.033" Title="vertical 40m antenna takeoff angle" Tags="&lt;antenna-theory&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11714" PostTypeId="2" ParentId="11713" CreationDate="2018-08-15T23:57:55.563" Score="3" Body="&lt;p&gt;If you model this antenna, it does predict a 22° takeoff with the radials 8 feet off the ground. Doubling the height would change the take off to perhaps 21°.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may wish to consider a good current mode balun at the feedpoint and another one prior to entering the shack in order to reduce common mode current which will alter the directional characteristics of the antenna. If you can bury the coax in a couple of feet of ground immediately below the antenna, this will also help reduce common mode currents. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have an antenna analyzer, you may also wish to experiment with adding additional radials. While this will not have any significant effect on the takeoff angle, it may improve the efficiency of the antenna. Keep adding radials until the feedpoint impedance of the antenna no longer changes to any significant degree.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-08-15T23:57:55.563" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11715" PostTypeId="2" ParentId="11713" CreationDate="2018-08-16T01:08:24.117" Score="2" Body="&lt;p&gt;Your description isn't too far off from predictive models, like &lt;a href=&quot;http://www.voacap.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vUJkZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vUJkZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;40m works very much better when the entire path is in darkness. At 8 or 9 PM in western NY, at this time of year (August), it is still light for the Western US. As such you won't have great results in that direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And in the other direction to the East, you get a whole lot of ocean, with marginal coverage of Western Europe and Northwest Africa.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's hard to definitively say without qualitative measurements with a field strength meter, but I'd guess your antenna is just fine. Radial orientation isn't critical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My suggestion: wait until later in the night (here's 0900 UTC):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NHAVf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NHAVf.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or try a different band, like 20m at 0000 UTC:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fyJJ8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fyJJ8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or 30m at 0000 UTC (SSB isn't allowed on 30m, though this model is for SSB anyway for consistency):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MF7S4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MF7S4.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-08-16T15:55:09.033" LastActivityDate="2018-08-16T15:55:09.033" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11716" PostTypeId="1" CreationDate="2018-08-16T11:23:20.117" Score="2" ViewCount="77" Body="&lt;p&gt;I've put up &lt;a href=&quot;https://physics.stackexchange.com/questions/421371/electromagnetic-transmission-in-regards-to-environment&quot;&gt;this question&lt;/a&gt; already on physics.SE but I miss an answer to the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My assumption: A 5 GHz band provides a higher bandwidth and therefore is more stable as it can support more users compared to a 2.4 GHz band. But the latter has a higher range and can be considered more stable in this aspect.&#xA;Hence, I've read that the Intel wigig is a 60 GHz band but supports only a range of 10 m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to know two things: The bandwidth is not the frequency, right? Why can the 5 GHz band support more participants than the 2.4 GHz? &#xA;Furthermore: How is the possible range connected to the frequency?&lt;/p&gt;&#xA;" OwnerUserId="13062" LastEditorUserId="4665" LastEditDate="2018-08-16T18:11:08.330" LastActivityDate="2018-08-16T18:11:08.330" Title="Range of wireless signals" Tags="&lt;transmission&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11717" PostTypeId="2" ParentId="11716" CreationDate="2018-08-16T12:15:58.467" Score="6" Body="&lt;p&gt;It is an oversimplification to say lower frequencies have longer range. See &lt;a href=&quot;https://ham.stackexchange.com/q/3692/218&quot;&gt;Is free space path loss dependent on frequency?&lt;/a&gt; It's more accurate to say the range of a half-wave dipole decreases as frequency increases. But then so too does the size: a tiny half-wave dipole simply intercept less energy. Solution: antenna arrays, which become increasingly feasible as frequency increases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bandwidth is not frequency. Bandwidth is the difference between the lowest frequency and the highest frequency used by a radio signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's another sense of &quot;bandwidth&quot; for digital communications: it's how fast bits can be sent. The two are related by the &lt;a href=&quot;https://ham.stackexchange.com/q/11632/218&quot;&gt;Shannon-Hartley theorem&lt;/a&gt;. Another variable in the Shannon-Hartley theorem is the signal-to-noise ratio. This is another thing limiting the range of WiGig: to achieve those high speeds requires a very good signal. Signal quality diminishes with distance as the radio signal spreads out due to the inverse square law.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Higher frequencies generally support higher bandwidth simply because there are more possible frequencies at high frequency. Are there more 5-digit numbers or 20-digit numbers?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a real example, the amateur &lt;a href=&quot;https://en.wikipedia.org/wiki/40-meter_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;40 meter band&lt;/a&gt; goes from 0.0070 to 0.0073 GHz in the US. Thus the bandwidth of the entire band is 0.0003 GHz. Since the entire band must support multiple users, the bandwidth of an individual signal is much less, typically 0.000004 GHz or less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By comparison, the &lt;a href=&quot;https://en.wikipedia.org/wiki/23-centimeter_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;23 centimeter band&lt;/a&gt; goes from 1.24 to 1.3 GHz, and so is 0.06 GHz wide. This makes it 200 times bigger than the 40 meter band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A WiGig channel is 2.16 GHz wide, whereas WiFi is 0.02, 0.04, or 0.08 GHz wide. That makes the WiGig channel too wide to even fit in the same 2.4 and 5 GHz allocations used by WiFi, so the only option is to go higher in frequency, where there's room.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-08-16T15:43:41.357" LastActivityDate="2018-08-16T15:43:41.357" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11719" PostTypeId="2" ParentId="11710" CreationDate="2018-08-16T14:15:08.313" Score="6" Body="&lt;p&gt;This is an interesting question and while we may not be able to get to an exact answer, we can certainly explore the issues to consider.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First we start by calculating a primitive link budget. The transmitter has an output power of 100 watts or 30 dBm. If we assume a 50 ohm input impedance receiver will have adequate reception (20 dB of quieting) with a 0.5 μV signal across its input, this is a -113 dBm signal. Both of these values may be calculated using:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$dBm=10\log{\frac{P}{.001}} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where P is the power in watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference between these two values, 163 dB, is the maximum, total attenuation that will be acceptable in the communications link to support reliable communications .&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first loss we must consider is the FSPL (free space path loss) for the various bands in question. This will account for the power density due to the gradual spreading of the signal and for the effective aperture of the reference isotropic antenna. A decibel version of FSPL is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$FSPL_{dB}=20\log(d)+20\log(f)+32.45 \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where d is the distance in kilometers and f is the frequency in megahertz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we calculate the FSPL for the 80 meter band at 25 kilometers (about 15 miles) between stations, we find it is ~72 dB. The same distance on 70 cm has an FSPL of ~113 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FSPL must be subtracted from our primitive link budget of 163 dB. So for 80 meters, we have 91 dB of remaining link budget and for 70 cm we have 50 dB of remaining link budget. This remaining budget must account for all antenna gains/losses and any additional attenuation in the path such as building, trees, terrain, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the question places a two meter limit on the height of the antenna, we can make some rough estimates with respect to antenna gain. A 2 meter vertical antenna on 80 meters will have a gain of approximately -20 dBi near the horizon. A 2 meter tall collinear vertical on 70 cm could have a gain of approximately 8 dBi near the horizon. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the same antenna on both vehicles, the total antenna gain on 80 meters is -40 dBi. We add this to the remaining link budget of 91 dB for 80 meters which leaves us with 51 dB. This is the total additional attenuation that we could tolerate and still carry out successful communications on 80 meters. Note that remaining link budget has gone down because the antennas introduce addition loss in the link. Similarly, we have 66 dB remaining on the 70 cm budget. In this case, the budget has gone up because the antennas have introduced gain in the link. In both cases, this a significant amount of additional attenuation that we could tolerate on the links.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From this point, models can be used to estimate the additional attenuation in an urban environment. This will typically include estimates for the various materials and the terrain between the stations. For the upper frequency bands in particular, re-radiation and multipath must also be considered. Man-made noise is even creeping into the UHF range. For the lower frequency bands, propagation effects, such as NVIS (near vertical incidence skywave), and atmosperic plus man-made noise could also come into play.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-16T20:34:26.057" LastActivityDate="2018-08-16T20:34:26.057" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11720" PostTypeId="2" ParentId="11645" CreationDate="2018-08-17T02:07:53.480" Score="2" Body="&lt;p&gt;Welcome the land of QRM also known as man made noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realize this came from the headphone jack, so it recorded as stereo. its really a mono signal, both channels have the same wave form. because you used a lossy compression it would be may make it harder to try and decode it. (not that I'm that good mind you)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It kind of sounds like a problem we had here with a paging company. They were putting out 50Kw and as the transmitter unkeyed, the transmitter frequency would drift down from 465mhz down to into the VHF ham band. You would only hear it if you were within about a mile of the transmission site, The repeater didn't hear it because it used a PL for interference reduction. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is how you go about tracking it down...&#xA;First confirm you can hear it on more than one receiver and in more that one place. This means that the thing you hear is real (for other people's verification).  Then you can either go the Foxhunt route yourself, or contact the Radio Station on 100.9 and hopefully they can convince someone to do so. If you can prove that the interference is over a chunk of their listening audience, and affects say, their advertising then getting them to act on it is easier. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look at the audio as a wave form, you can see that the noise starts earlier than 15 seconds and runs until about 23, starts just before 30, and runs to 38. so its 9-10 seconds with a 5-7 second gap between transmissions. The encoding is likely some sort of audio FSK.&lt;/p&gt;&#xA;" OwnerUserId="6092" LastEditorUserId="6092" LastEditDate="2018-08-17T15:11:42.693" LastActivityDate="2018-08-17T15:11:42.693" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11721" PostTypeId="1" AcceptedAnswerId="11724" CreationDate="2018-08-17T08:55:06.667" Score="2" ViewCount="932" Body="&lt;p&gt;My friends and I are going off to college ~180 miles/290 kilometres apart. As a project, we are looking into creating a data communication connection between our two schools. Our requirements would be:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;180 mile/290 km range&lt;/li&gt;&#xA;&lt;li&gt;~1 Mb/s connection speed both ways&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Becoming licensed for amateur radio would be assumed in order to take advantage of lesser regulations/more frequency options.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any technologies attainable at the enthusiast level that would offer these features?&lt;/p&gt;&#xA;" OwnerUserId="13065" LastEditorUserId="9844" LastEditDate="2018-08-19T23:57:27.983" LastActivityDate="2019-08-27T16:45:00.477" Title="Amateur Radio Long Distance Data Communication" Tags="&lt;united-states&gt;&lt;digital-modes&gt;&lt;diy&gt;&lt;wifi&gt;&lt;range&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11722" PostTypeId="2" ParentId="11675" CreationDate="2018-08-17T12:43:21.783" Score="-1" Body="&lt;p&gt;ECHOLINK may be the internet service being used.&lt;/p&gt;&#xA;" OwnerUserId="8229" LastActivityDate="2018-08-17T12:43:21.783" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11723" PostTypeId="2" ParentId="11721" CreationDate="2018-08-17T13:41:05.563" Score="2" Body="&lt;p&gt;In a word, No.  For 1Mb/s you'd need a line-of-sight connection, so over a 180-mile path, you would need multiple hops.  The alternative would be satellite communications but the ham satellites have neither that kind of throughput nor are geostationary (meaning you'd get at best a few minutes of connectivity per pass).  Voice communication would be possible, as would low speed (300bps) data communication.  And even if you did, there'd be no guarantee of privacy.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastEditorUserId="9844" LastEditDate="2018-08-19T23:57:19.833" LastActivityDate="2018-08-19T23:57:19.833" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11724" PostTypeId="2" ParentId="11721" CreationDate="2018-08-17T14:27:03.747" Score="2" Body="&lt;p&gt;The most accessible way to get digital communication at that speed is WiFi. You could use unmodified consumer equipment, or getting a ham license would allow you to use frequencies not usually available to the public, as well as much higher limits on power and antenna gain. Of course the ham route would add additional restrictions, like it must be strictly non-commercial, and can't be encrypted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Propagation at these frequencies for the most part requires line-of-sight, and 180 miles (290 kilometers) is too far on flat terrain. Even if you had a 100 meter tower at each end, you might get approximately 82 km. The general formula is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ 4.12 \sqrt{h} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where $h$ is the antenna height in meters, this gives the radio horizon in kilometers. The horizon distances from each end add together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the terrain isn't flat, and one or both ends is atop a hill or mountain, you can get more range. There are &lt;a href=&quot;http://wiki.opendigitalradio.org/Coverage_planning&quot; rel=&quot;nofollow noreferrer&quot;&gt;tools which can predict radio coverage&lt;/a&gt;. Unfortunately my favorite, &lt;a href=&quot;http://www.crc.gc.ca/covlab&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRC-COVWEB&lt;/a&gt;, seems to be defunct. You can also use &lt;a href=&quot;https://www.heywhatsthat.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;HeyWhat'sThat&lt;/a&gt; just to check line of sight. It doesn't account for towers but it will show an elevation plan between two points, and then you can see how big the towers would need to be from that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another possibility is troposcatter, see &lt;a href=&quot;https://ham.stackexchange.com/q/1497/218&quot;&gt;Can tropospheric scatter effect be used by 802.11 links?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or perhaps you can set up routers at intermediate points. This is an especially good option if there is a high vantage point visible from each of your respective schools. If so it's quite likely there's already a ham repeater(s) on it, and while they may not provide the data connectivity you seek, repeaters are often administered by a club. The club will likely be able to help you get access to the site, or at least introduce you to the right people.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can accept a much lower data rate, HF can reach 180 miles easily. However you won't be able to attain more than a few kilobits per second.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-08-17T14:27:03.747" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="11727" PostTypeId="2" ParentId="11708" CreationDate="2018-08-18T19:51:13.297" Score="-1" Body="&lt;p&gt;Just to add one more method...&#xA;I remember around 1940 Dad showing me how tuning for maximum current could be done by touching your tongue to one of the feed wires.  I had read about this but never really believed it until his demonstration.&lt;/p&gt;&#xA;" OwnerUserId="8229" LastActivityDate="2018-08-18T19:51:13.297" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11728" PostTypeId="2" ParentId="2080" CreationDate="2018-08-19T09:01:14.650" Score="1" Body="&lt;p&gt;If anyone else out there has done both the US and Canadian tests, I think they will agree that the Canadian tests are significantly harder for anyone who does not have a solid electronics background.  So, if the reader can legally test in the US and use in Canada then do so as the Technician and General are quite easy with a couple weeks of study and there are lots of choices for both paid and free study aids... not so for the Canadian certificates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are no really free study guides for the Canadian and the paid study helps are only fair at best... and because the two major sources of paid study guides for Canada know you have no choices their guides are quite steep for the quality provided....  Add to that, that the test is not at par to the American test and the test questions are designed to fail the applicant (many questions have 2 &amp;amp; 3 sometimes correct answers that you have to figure what the author wants as an answer not what is necessarily the correct answer as very few are cut and dry with  1 correct answer and 3 wrong ones)...  Had I not had an electronics background and had written all 3 American tests and passed understanding the electronics behind the questions I wouldn’t have stood a chance testing in Canada...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the good news for those testing in Canada IF you are in a major center is that there are a number of clubs that will test you the basic course (generally for a fee or upon joining) but most take about 2/12 months of weekly classes and study time between... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;BTW, I believe there is no longer any requirement to use both your call and location (eg N0OBZ/VA3) while in Canada so American’s take the US test and make life easy on yourself.&lt;/p&gt;&#xA;" OwnerUserId="13073" LastEditorUserId="11434" LastEditDate="2018-08-19T23:57:40.537" LastActivityDate="2018-08-19T23:57:40.537" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11730" PostTypeId="1" CreationDate="2018-08-19T22:01:42.450" Score="3" ViewCount="1750" Body="&lt;p&gt;I live in a fairly sheltered valley but there are several hill-top VHF repeaters that I can receive very well.  However the one repeater in particular I want to transmit to, I can't reach well.  I know my signal is reaching it, because it will auto-respond its call sign when I transmit, but I get reports that my signal is unintelligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've using a BaoFeng F9V2+ with a Nagoya NA-771 antenna and I've also tried a Slim Jim but have not been successful at getting an intelligible signal through.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, would using a copper-pipe J-Pole be any more likely to be successful than the Slim Jim or are they pretty much equivalent?&lt;/p&gt;&#xA;" OwnerUserId="13077" LastEditorUserId="76" LastEditDate="2018-08-20T00:44:30.433" LastActivityDate="2018-09-03T18:47:34.430" Title="Is a copper J-Pole antenna better than a Slim Jim for transmitting?" Tags="&lt;antenna&gt;&lt;vhf&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11731" PostTypeId="2" ParentId="11730" CreationDate="2018-08-20T00:43:23.307" Score="4" Body="&lt;p&gt;I'm not familiar with empirical results for these particular antenna designs, but in general, &lt;a href=&quot;https://ham.stackexchange.com/a/2373/76&quot;&gt;an antenna constructed out of thicker conductors will have a wider bandwidth&lt;/a&gt;. That is, its impedance will be more consistent across the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Theoretically, this is an improvement because you will get a better impedance match across the band, including the input frequency of your target repeater. However, the actual effect is likely to be small (unless you have a particularly long or lossy feed line between your radio and antenna), and it might even happen to be worse if the new antenna is not well tuned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unless it's really cheap and easy for you to build a copper J-pole, consider building or buying a Yagi type antenna — even a 3-element one — and aiming it at the repeater. This &lt;em&gt;will&lt;/em&gt; improve your signal strength.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-08-20T00:43:23.307" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11732" PostTypeId="2" ParentId="11730" CreationDate="2018-08-20T01:57:18.173" Score="5" Body="&lt;p&gt;The slim jim antenna has no more or less gain than a J pole antenna - despite many Internet claims to the contrary. Any perceived difference in gain is likely due to CMC (common mode current) since both antennas promote CMC on the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is an argument to be made that a larger conductor improves efficiency and therefore gain.  But for antennas that are at least 1/4 wavelength or longer, as in this case, the effect will typically be in the sub dB range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also find references to the TOA (take off angle) being different between the J pole and the slim jim. Antenna range measurement and simulations show this to not be the case. This apparently came about when Fred Judd, G2BCX stated that the slim jim has a better TOA than a (5/8 wave) ground plane. This comparison was later morphed on the Internet to be a comparison between the slim jim and a J pole. Any such perceived difference in TOA is most likely attributable to CMC.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-20T10:16:07.523" LastActivityDate="2018-08-20T10:16:07.523" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11733" PostTypeId="1" CreationDate="2018-08-20T08:44:38.783" Score="5" ViewCount="192" Body="&lt;h1&gt;General setting&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;I'm playing around with an RTL-SDR and recently captured some FM spectrum in Hannover, Germany. I want to undersand what's going on, so I've read a lot about FM and its spectra, but I can't completely make sense out of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZUU39.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZUU39.png&quot; alt=&quot;Level in dBFS as a function of Frequency in MHz&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Problem&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;At the moment of taking the samples, the channel at 98.7 MHz must have been silent (at least, the pattern looks like what the real-time spectrum shows me when nobody is talking). It looks like only the stereo pilot tone at 19 kHz is being transmitted at that time. This would make sense with the spacing of the lines, being approximately 20 kHz apart from each other.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Things I've tried unsuccessfully&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;However, I'm still confused. As I understand it, the amplitude of the spectral lines should be given by the Bessel function of first order with respect to the modulation index (frequency deviation is 75 kHz). Performing &lt;code&gt;abs(besselj(-4:4,75/19))&lt;/code&gt; in Matlab gives me &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;[0.2732    0.4277    0.3769    0.0458    0.4001    0.0458    0.3769    0.4277    0.2732]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;20*log10(abs(besselj(-4:4,75/19)))&lt;/code&gt; gives&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;[-11.2692   -7.3769   -8.4757  -26.7828   -7.9567  -26.7828   -8.4757   -7.3769  -11.2692]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This appears to be congruent with the Bessel diagrams I've seen. However, this is not what I see in the spectrum. I've also tried different modulating frequencies, but nothing seems to give those amplitudes. Can anyone point me to why this is?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried to simulate a frequency modulation of the pilot tone and a single tone at 57 kHz (approximating) RDS. However, this only makes things worse, and looks even more different from the recorded spectrum.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Summary of questions&lt;/h1&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What is being modulated (what does the MPX spectrum look like during silence)?&lt;/li&gt;&#xA;&lt;li&gt;How to explain those spectral amplitudes (as you can see, for other channels, the amplitude relations and line spacings look similar during silence, just not visible as nicely because of low power level)?&lt;/li&gt;&#xA;&lt;li&gt;What happened to the RDS carrier? Why does the spectrum resemble the one of a single-tone modulating signal?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="13080" LastEditorUserId="76" LastEditDate="2020-02-09T23:46:18.670" LastActivityDate="2020-02-09T23:46:18.670" Title="FM spectral amplitudes during silence" Tags="&lt;software-defined-radio&gt;&lt;fm&gt;&lt;panadapter-and-waterfall&gt;" AnswerCount="1" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11734" PostTypeId="2" ParentId="1013" CreationDate="2018-08-20T10:51:29.197" Score="0" Body="&lt;p&gt;According to the ARRL &lt;em&gt;Handbook&lt;/em&gt; section on Transmitters, &quot;indirect FM&quot; using a phase modulator used to be the most popular method to generate an FM signal. Since instantaneous frequency is the time differential of phase, the baseband audio signal was passed through an integrator (i.e., low-pass filter) and a compensating pre-emphasis amplifier before being applied to the phase modulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This method seems to have successively given way to &quot;direct FM&quot; with the advent of varactor diode, PLL and DDS technologies.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-08-20T10:51:29.197" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11735" PostTypeId="2" ParentId="11730" CreationDate="2018-08-20T11:28:34.827" Score="4" Body="&lt;p&gt;In a situation like this, gain helps a bit, but usually height helps more.  So whichever antenna you can get higher will probably work best.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also there are some odd propagation things around mountains, check out knife edge propagation and fresnel zones.  Without getting into technical details, you can take advantage of constructive and destructive interference of multipath propagation by moving a small antenna within an area very roughly less than 1/2 wavelength to find the spot where you get the maximum reception.  This spot will also give you the clearest signal when you transmit. &lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2018-08-21T11:28:51.127" LastActivityDate="2018-08-21T11:28:51.127" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11736" PostTypeId="1" CreationDate="2018-08-20T13:15:38.277" Score="0" ViewCount="529" Body="&lt;p&gt;Suppose that a ham radio setup uses several antennas with a 50 ohm coaxial switch to operate some natively unbalanced antennas and some balanced ones through baluns at the feedpoint. An RF ground for all equipments in the chain going to a copper strip and then through a single point to the ground seems a good practice when operating unbalanced antennas, if I understand &lt;a href=&quot;https://ham.stackexchange.com/questions/34/when-is-rf-grounding-necessary-and-when-is-it-not&quot;&gt;When is RF grounding necessary, and when is it not?&lt;/a&gt; well.&#xA;But then, if the active antenna is balanced, should the RF ground be severed by a switch too? Basically, what happens if an RF ground is used with a balanced antenna (when a balun IS used)?&lt;/p&gt;&#xA;" OwnerUserId="13081" LastEditorUserId="9493" LastEditDate="2018-08-20T15:01:32.167" LastActivityDate="2018-08-21T10:33:33.703" Title="RF ground and balanced antennas" Tags="&lt;grounding&gt;&lt;balun&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11737" PostTypeId="2" ParentId="11736" CreationDate="2018-08-20T14:47:26.607" Score="1" Body="&lt;pre&gt;&lt;code&gt;    _________________    _________________&#xA;                     \  /&#xA;                      ||&#xA;                      ||&#xA;                      ||&#xA;                      ||&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This is a sketch of a common sort of balanced antenna — a simple dipole. Notice that it is symmetric, electrically as well as physically. There is &lt;em&gt;no place to connect&lt;/em&gt; a ground; if you did, say, connect one side to earth, it would no longer be balanced (the impedance between that side of the line/antenna and earth would be greatly reduced while the other side would not, so it is unbalanced exactly by the definition of balance).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you also have a balun and you might ground the &lt;em&gt;unbalanced&lt;/em&gt; side of the balun (or more precisely, the shield of the feed line as soon as it comes down in reach of a suitable grounding point). Theoretically, this makes no difference if the balun does its job perfectly and other things are ideal, but if not, this will reduce the unwanted common mode, and this grounding point is much better &lt;em&gt;for this purpose&lt;/em&gt; than having additional grounding at the transceiver or other 'shack' equipment because it's right at the source.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-08-20T14:47:26.607" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11738" PostTypeId="2" ParentId="11736" CreationDate="2018-08-20T14:48:36.573" Score="1" Body="&lt;p&gt;From the perspective of the coax, a balanced and unbalanced antenna are identical provided they are properly installed. That means the dipole will need a balun, and the vertical will need radials (and still maybe a choke as well). In either case, at any instant at any point on the coax, the current on the shield is equal in magnitude but opposite in direction to the current on the center conductor. That is: all current is differential-mode; common-mode current is zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Charge_conservation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Electric charge is neither created nor destroyed&lt;/a&gt;, so if there's any current on the RF ground, there must be somewhere in the universe an opposite current to balance it. Because in the antenna setups under consideration the currents on the feedline are already balanced, and there's no &quot;remainder&quot; common-mode current, there is no such thing. So, there's no current on the RF ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, there's no reason to disconnect it. There's no reason for it to exist, either, aside from exceptional circumstances like a &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;lightning strike&lt;/a&gt; or some kind of fault, like a powerline falling on the antenna. It's entirely irrelevant to operation of the antenna under normal circumstances.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-08-20T14:48:36.573" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11739" PostTypeId="2" ParentId="1013" CreationDate="2018-08-20T16:25:30.943" Score="2" Body="&lt;p&gt;Phase-modulated voice is equivalent to FM, modulo differences in frequency response. An FM transmitter contains a pre-emphasis circuit to counteract this effect, making the two effectively equivalent on the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the US extra class question pool:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;E7E06 (A)&lt;br&gt;&#xA;  &lt;em&gt;Why is de-emphasis commonly used in FM communications receivers?&lt;/em&gt;&lt;br&gt;&#xA;  &lt;strong&gt;A.&lt;/strong&gt; For compatibility with transmitters using phase modulation&lt;br&gt;&#xA;  B. To reduce impulse noise reception&lt;br&gt;&#xA;  C. For higher efficiency&lt;br&gt;&#xA;  D. To remove third-order distortion products&lt;br&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;An unmodulated carrier of angular frequency $\omega_c$ is simply:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ y(t) = \cos(\omega_c t) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$\omega_c t$ is the phase at time $t$. For phase modulation we simply add the baseband signal $m(t)$:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ y_\mathrm{PM}(t) = \cos\left(\omega_c t + m(t) \right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that frequency is the instantaneous rate of change of phase. In other words, frequency is the derivative of phase. Likewise, phase is the integral of frequency. So to derive the expression for frequency modulation we just throw in an integral:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ y_\mathrm{FM}(t) = \cos\left(&#xA;\omega_c t&#xA;+ \int _{0}^{t}m(\tau )d\tau&#xA;\right) $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This doesn't have too much effect on the signal because:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ \int \cos x\,dx=\sin ax+C \\&#xA;\int \sin x\,dx=-\cos ax+C $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the difference between PM and FM is an integration of the baseband signal. This changes the phase of the baseband signal but that's not important for a voice transmission. The integration also effectively low-pass filters the baseband signal, since a sinusoid of equal amplitude but higher frequency has less area under each positive half-cycle, and thus the maximum of its integral is less. The pre-emphasis in the FM transmitter high-pass filters the baseband signal prior to the modulator, counteracting this effect, thus making PM and FM transmitted signals effectively equivalent.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-08-20T16:25:30.943" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11740" PostTypeId="1" CreationDate="2018-08-20T23:37:40.050" Score="1" ViewCount="190" Body="&lt;p&gt;I have a problem with strong and constant received noise, from S7 to S9+20.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've shut off the power, both in my house and two neighbors' houses. &#xA;I took my portable rig with a Hustler antenna and searched the neighborhood. The noise seems to be at my house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've turned off the solar and main power day and night. It never changes strength, rain or shine, night or day. Not a street light either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm using an MFJ 1798 vertical. I've had it for several years now. When I first installed it, the SWR was low. Now, something has changed. Now it's out of tune slightly, and I hear steady hash-like QRN. I called MFJ about the changing of the tuning, and they said the balun came partially unwound. It has not. Could my antenna system be the problem?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have exhausted all of my ideas to solve this problem. Has anyone else come across a similar problem that you were able to solve from which you could share some insight? Can you recommend anything else that I should test or try in order to reduce or eliminate the QRN?&lt;/p&gt;&#xA;" OwnerUserId="13084" LastEditorUserId="8717" LastEditDate="2018-09-08T19:18:11.537" LastActivityDate="2018-09-08T19:32:23.957" Title="What can I do about my strong RF noise?" Tags="&lt;rfi&gt;&lt;vertical-antenna&gt;&lt;noise&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11741" PostTypeId="1" AcceptedAnswerId="11742" CreationDate="2018-08-21T02:07:00.840" Score="2" ViewCount="534" Body="&lt;p&gt;I am a new ham and I was just given a G5RV Jr. I have about 20 feet of coax plus about 60 feet of 450 ohm ladder line I can feed it with.  Can I extend the G5RV Jr. feed line with the ladder line I have, and then connect it to the coax and still tune it successfully? Would I need the recommended 1:1 balun, or something else?  Thanks.&lt;/p&gt;&#xA;" OwnerUserId="9772" LastEditorUserId="8717" LastEditDate="2018-08-21T02:21:45.153" LastActivityDate="2018-08-22T22:14:17.513" Title="G5RV Jr. fed with ladder line and coax" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;feed-line&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11742" PostTypeId="2" ParentId="11741" CreationDate="2018-08-21T02:20:34.533" Score="3" Body="&lt;p&gt;That length of 450 ohm ladder line is important. In order to have a reasonable VSWR on the bands that the G5RV was designed for, you should not change it unless you want to cover different bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The G5RV and the &quot;Jr.&quot;, while good antennas on some bands, was invented before antenna modeling programs (such as EZNEC) were available. After they were, ZS6BKW modeled it and changed a few things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have my own improved variation of this antenna design. Much more information about this is &lt;strong&gt;&lt;a href=&quot;http://www.w0btu.com/g5rv_antenna.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/search?q=g5rv&quot;&gt;Many questions about the G5RV have been asked and answered here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-08-21T02:40:32.627" LastActivityDate="2018-08-21T02:40:32.627" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11743" PostTypeId="2" ParentId="8940" CreationDate="2018-08-21T05:47:20.860" Score="-3" Body="&lt;p&gt;A lot has to do with fewer hams out there and many that lack ability or motivation to setup antennas that work.&#xA;Just something I have noticed over the years...laziness?&#xA;Jim&lt;/p&gt;&#xA;" OwnerUserId="13085" LastActivityDate="2018-08-21T05:47:20.860" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11744" PostTypeId="2" ParentId="11736" CreationDate="2018-08-21T10:33:33.703" Score="1" Body="&lt;p&gt;Below is a NEC4.2 study of the effects of r-f current flow on the &lt;em&gt;outer surface&lt;/em&gt; of the &quot;grounded&quot; outer conductor of a coaxial transmission line connected to an unbalanced antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A true r-f ground does not exist at the top of an unburied conducting path whose base is connected to a true r-f ground (e.g., Earth).  Any r-f current flowing on that conducting path produces e-m radiation for the same reasons it does when flowing on the antenna conductors, themselves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/n9Znx.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/n9Znx.gif&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-08-21T10:33:33.703" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11745" PostTypeId="2" ParentId="11733" CreationDate="2018-08-21T10:57:02.800" Score="1" Body="&lt;p&gt;It may help to see the display of the demodulated, baseband output spectrum produced by an SDR (below).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/88epp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/88epp.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-08-21T10:57:02.800" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11746" PostTypeId="2" ParentId="11710" CreationDate="2018-08-21T12:17:18.783" Score="-1" Body="&lt;p&gt;Good things to recognize in understanding the performance of this system are that:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The software often used to evaluate these situations usually is set&#xA;by the operator to consider only the &quot;far field&quot; radiation, and&#xA;ignore the surface wave&lt;/li&gt;&#xA;&lt;li&gt;The far-field calculations of MoM software such as NEC assume a flat reflecting plane for systems not evaluated for their performance in free space, and show the field or gain existing for an infinite distance from the radiator&lt;/li&gt;&#xA;&lt;li&gt;The propagation environment of item 2 above does not apply to relatively short, terrestrial, point-point paths over real, curved Earth&lt;/li&gt;&#xA;&lt;li&gt;If the surface wave is not included, NEC and similar software is not appropriate to evaluate the performance of short, point-point terrestrial paths — such as used by a VHF/UHF HT to reach a repeater.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Below is a NEC4.2 study of a 6m transmit system linking to a distant repeater, &lt;em&gt;including its radiation at the lower elevation angles producing the surface wave&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It can be seen that the radiation from an elevation angle of only 0.8° is responsible for the field intensity arriving at the repeater antenna (Earth curvature has a ~negligible effect on this analysis, for this path length).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;A NEC far-field (only) analysis for this setup would show almost no radiation from this transmit antenna at an elevation angle of 0.8°.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added later:  It would be useful to me and perhaps others if the person downvoting this answer would add a comment to it offering the reason for doing so.  Nothing given in the answer is factually inapplicable as a response leading to an accurate analysis of the question asked in the OP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FWsZB.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FWsZB.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2018-08-21T14:34:40.533" LastActivityDate="2018-08-21T14:34:40.533" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11747" PostTypeId="2" ParentId="11740" CreationDate="2018-08-22T01:59:31.513" Score="2" Body="&lt;p&gt;Welcome to hamSE, Robert. Since you say that it's only slightly out of tune, I seriously doubt that this has anything at all to do with your antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You say that you shut off the power to your house, yet the noise is at your house. I suspect you have something on or near your electric pole arcing. Power lines are notorious for doing that and making our hobby less than what we should expect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have you checked the coax? A loose shield &lt;em&gt;might&lt;/em&gt; be the cause. And check the SWR right at the antenna, as what you measure at the station end might very well be incorrect depending upon the electrical length of the coax.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-09-08T19:32:23.957" LastActivityDate="2018-09-08T19:32:23.957" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11748" PostTypeId="2" ParentId="11740" CreationDate="2018-08-22T06:49:15.700" Score="3" Body="&lt;p&gt;You killed the main AC circuit breaker to your house, but still detect RF noise centered at your house?  Battery operated devices (laptop?, electric car?), systems with battery backup, and batteries with DC-DC converters can still produce, perhaps radiate, RF noise.  The solar panels might have DC-DC converters that can't be switched off.  Try throwing a pool cover over them.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-08-22T06:49:15.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11749" PostTypeId="2" ParentId="919" CreationDate="2018-08-22T13:35:33.793" Score="0" Body="&lt;p&gt;This statement &quot;I guess the real question might be what mechanism makes a folded dipole work better than a regular dipole.&quot; is misleading as I see it. A folded dipole has a 4 times higher impedance, compared to a simple dipole with the same wire diameter it has more bandwidth, but compared to a simple dipole with the much larger effective diameter you would get by use of two parallel wires on each side of an ordinary dipole I suspect there would be no bandwidth advantage. Compare a,b and c here: &lt;a href=&quot;https://www.google.com/search?q=multi-wire+dipole&amp;amp;client=firefox-b&amp;amp;tbm=isch&amp;amp;source=iu&amp;amp;ictx=1&amp;amp;fir=mKRhPlFY3mh3qM%253A%252CVjVXClZ9wzOVcM%252C_&amp;amp;usg=AFrqEzceJB6YnKbgc3ke89eLH9UlnKIr-Q&amp;amp;sa=X&amp;amp;ved=2ahUKEwjIvIfYwv_cAhXk-ioKHd7jBMEQ9QEwAHoECAUQBA#imgrc=VS3uPj4nnt8a6M&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.google.com/search?q=multi-wire+dipole&amp;amp;client=firefox-b&amp;amp;tbm=isch&amp;amp;source=iu&amp;amp;ictx=1&amp;amp;fir=mKRhPlFY3mh3qM%253A%252CVjVXClZ9wzOVcM%252C_&amp;amp;usg=AFrqEzceJB6YnKbgc3ke89eLH9UlnKIr-Q&amp;amp;sa=X&amp;amp;ved=2ahUKEwjIvIfYwv_cAhXk-ioKHd7jBMEQ9QEwAHoECAUQBA#imgrc=VS3uPj4nnt8a6M&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;B is a folded dipole. The open halfwave element does not contribute. A and C are equivalent as I can understand, but the feed impedance is different (by a factor of 9 I would guess.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Making the wire diameter different for the two half wavelength parts of a folded dipole makes the impedance transformation different. As I understand it, the impedance is given by the current ratio of the elements to which power is fed at the center and the elements that are shorted (fed by the voltage&#xA;on the tips of the fed elements.) The bandwidth, as I understand it is given by the effective area of all wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The folded dipole is also a loop antenna, but in normal configurations the electric dipole radiation is orders of magnitude larger than the magnetic dipole radiation. The electric dipole radiation pattern has a zero in the plane of the dipole while the magnetic dipole pattern (a doughnut) does radiate in the plane of the (folded) dipole. In case you make your &quot;folded dipole&quot; a circle to give it the maximum possible magnetic moment, you would find that the radiation pattern is more like a magnetic dipole than an electric dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want an electric dipole antenna (because that is the desired radiation pattern) folded or straight dipoles should be equivalent if they use the same number of wires with the same spacing. It is probably best to use a straight dipole (maybe with many parallel wires for bandwidth) because the lower feed impedance makes it easier to eliminate common mode interference on the cable with balun or common mode choke.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-08-22T13:35:33.793" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11750" PostTypeId="1" CreationDate="2018-08-22T16:21:29.340" Score="8" ViewCount="2456" Body="&lt;p&gt;Just of curiosity...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Outside of kits/ham produced prototypes, Do you know about any commercially produced 6m handhelds?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should be technically feasible despite the fact that it would be more cumbersome than VHF / UHF radios, But I recall that CB operators have 27 Mhz handhelds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you know the historical/technical/marketing other reason for them not to exist?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or maybe they do exist and I cannot find any positive info about them...&lt;/p&gt;&#xA;" OwnerUserId="13081" LastActivityDate="2021-01-29T09:47:50.037" Title="Were there any 6m handhelds produced ever?" Tags="&lt;ht&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11751" PostTypeId="2" ParentId="11750" CreationDate="2018-08-22T16:42:59.690" Score="8" Body="&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Yaesu_VX_series&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yaesu VX-5R&lt;/a&gt; had/has 50-54 MHz FM, 5 watts. Nice compact little radio!&lt;br&gt;&#xA;I think the VX-7 and VX-8 can also transmit on 6 m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It had a little extension of the rubber duck to make it work at 50 MHz, though I doubt it was very efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna calculation:&lt;br&gt;&#xA;The whip is about 25 cm long, so I'll consider a 0.5 m dipole. Radiation resistance the dipole is 1.4 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;. Reactance is about -1500 ohms, resonating this with a coil will introduce the rest of the 50 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; resistance, probably giving a reasonable match. Efficiency is thus about -15 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further thoughts:&lt;br&gt;&#xA;When talking to someone with a full-size dipole, like a repeater, the gain of the 6 m antenna will be partially compensated for by the reduced path loss. The path loss is 6 dB smaller at 6 m, compared to 2 m. Assuming the gain at 2 m is -3 dBi, and the gain at 6 m is -15 dBi, at 6 m the handheld will deliver only 6 dB less signal to the repeater.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2018-09-28T10:14:41.573" LastActivityDate="2018-09-28T10:14:41.573" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11752" PostTypeId="2" ParentId="11741" CreationDate="2018-08-22T22:14:17.513" Score="1" Body="&lt;p&gt;A G5RV antenna extended with more ladder line is just a dipole with a ladder-line feed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You certainly can do that, though to call it a G5RV isn't really accurate. Like Mike Waters explains, the length of the ladder line in the G5RV design is important, as it's part of a &lt;a href=&quot;https://en.wikipedia.org/wiki/Stub_(electronics)#Stub_matching&quot; rel=&quot;nofollow noreferrer&quot;&gt;stub match&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even though the result is no longer a G5RV, you may still get a decent antenna since even cheap ladder line has loss comparable to good coax, and thus even a moderately high SWR on the feedline may result in &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;acceptable losses&lt;/a&gt;, especially if you either get lucky or fiddle with the dipole length such that the SWR isn't astronomical on any band you intend to use.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-08-22T22:14:17.513" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11753" PostTypeId="1" AcceptedAnswerId="11755" CreationDate="2018-08-22T23:05:46.850" Score="2" ViewCount="955" Body="&lt;p&gt;What is the best way to impedance-match a simple, resonant loop antenna (intended for transmission) to a 50 ohm amplifier?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assume that the antenna is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;circular, with a circumference equal to the design frequency&lt;/li&gt;&#xA;&lt;li&gt;resonant at 2 GHz&lt;/li&gt;&#xA;&lt;li&gt;constructed from copper magnet wire, side-fed by semi-rigid coax&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I have read that when the perimeter matches the signal wavelength, the antenna impedance is entirely real. But what is it? Simply the resistance of the antenna wire? If that's the case, should I measure the resistance of the antenna wire, and then insert a series resistor to bring the total real impedance to 50 ohms?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or must I use a stub tuner and a signal analyzer? Or something else?&lt;/p&gt;&#xA;" OwnerUserId="13094" LastActivityDate="2018-08-23T00:54:47.400" Title="Design and impedance matching for simple resonant loop antenna (2 GHz)" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="11754" PostTypeId="2" ParentId="11753" CreationDate="2018-08-23T00:10:34.513" Score="1" Body="&lt;p&gt;The precise impedance depends on the particular geometry, but 100 ohms is a ballpark estimate for a full-wave loop. Antenna modelling can generate a more precise estimate. Or the design can be prototyped and the impedance determined empirically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the impedance will almost certainly be greater than 50 ohms, no amount of series resistance will match the antenna to 50 ohms. There are few applications where you'd want to do that anyhow: such a matching technique would waste a significant fraction of the transmitter power in simply making the resistor warm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, most RF impedance matching is performed with reactive components: inductors, capacitors, and transmission lines. There are infinite ways to combine such components to achieve a match, the best solution really depends on the requirements, like if it needs to be cheap to mass-manufacture or easy for a hobbyist to assemble, if it needs to be small, or wideband, etc.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-08-23T00:54:47.400" LastActivityDate="2018-08-23T00:54:47.400" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11755" PostTypeId="2" ParentId="11753" CreationDate="2018-08-23T00:12:23.160" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I have read that when the perimeter matches the signal wavelength, the antenna impedance is entirely real.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Note that that is the same as saying it is resonant.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;But what is it? Simply the resistance of the antenna wire?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. The (real) impedance of a resonant antenna consists of two components: the loss resistance you have already thought of, and the &lt;a href=&quot;https://en.wikipedia.org/wiki/Radiation_resistance&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;radiation resistance&lt;/em&gt;&lt;/a&gt;. The loss resistance accounts for the signal being turned into heat in the wire; the radiation resistance accounts for the signal actually being radiated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to find out the radiation resistance, you must calculate, simulate, or measure it. In general, the impedance of a full-wavelength loop antenna is in the vicinity of 100 ohms (citation: assorted web sites that all agreed).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The internet generally seems to recommend a &lt;a href=&quot;https://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer&quot; rel=&quot;nofollow noreferrer&quot;&gt;quarter-wave transformer&lt;/a&gt; for matching a loop — this is likely because 75 ohm coax is readily available and a fairly good approximation to the needed intermediate impedance (the geometric mean of the two other impedances).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you need a better match than those approximations, then you will want to measure the impedance of the loop, and possibly construct a matching circuit on a custom PCB (using discrete components or a PCB transmission line).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-08-23T00:27:50.387" LastActivityDate="2018-08-23T00:27:50.387" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11756" PostTypeId="1" CreationDate="2018-08-23T07:06:47.967" Score="2" ViewCount="435" Body="&lt;p&gt;Back in ye olden days before SWR meters and auto-tuners, how was a ordinary household lightbulb used to help tune an antenna system?  What did the circuit and tuning procedure look like?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="873" LastEditDate="2018-08-23T08:26:55.873" LastActivityDate="2018-08-24T11:36:02.920" Title="Lightbulb as an SWR detector?" Tags="&lt;impedance-matching&gt;&lt;swr-meter&gt;&lt;history&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11757" PostTypeId="2" ParentId="919" CreationDate="2018-08-23T15:30:03.240" Score="4" Body="&lt;p&gt;Close coupling between the folded dipole's two long, parallel wires induces a nearly identical current in the &quot;coupled&quot; wire as is impressed on the &quot;driven&quot; wire. (Electromagnetics engineers will see this result as necessary because the boundary conditions on the ends of the two wires are the same.) Thus, half of the current from the power delivered to the antenna flows in the driven wire, half flows in the coupled wire. And, while the pattern remains the same regardless of whether the ends of the two wires are connected, the impedance is strongly affected because the phases of the voltages at the wire ends change. (Different boundary conditions at the ends, since they're not connected.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the power delivered to the antenna is known, and power = current x voltage, then the voltage at the feedpoint must double to compensate for the current being cut in half.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With resistance equal to the ratio of voltage to current, doubling the voltage and halving the current at the feedpoint increases the feedpoint impedance by a factor of four over a single-wire dipole.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-08-23T15:30:03.240" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11758" PostTypeId="1" CreationDate="2018-08-23T16:13:47.760" Score="4" ViewCount="419" Body="&lt;p&gt;I'm really passionate about signals and communications ever since I was a child where we &quot;built satellites&quot; - little did I know that it would become part of my future.  So here is my first question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When was the first radio transceiver built and by whom?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.google.co.za/search?q=When+was+the+first+radio+Transceiver+(Transmitter%2FReceiver)+build+and+by+whom&amp;amp;rlz=1C1GCEB_enZA788ZA788&amp;amp;oq=When+was+the+first+radio+Transceiver+(Transmitter%2FReceiver)+build+and+by+whom&amp;amp;aqs=chrome..69i57.277j0j7&amp;amp;sourceid=chrome&amp;amp;ie=UTF-8&quot; rel=&quot;nofollow noreferrer&quot;&gt;Search&lt;/a&gt; on Google brings one to Wikipedia&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When was the first radio transceiver (transmitter/receiver) built and by whom&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Search Results&#xA;Featured snippet from the web&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nh7kO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nh7kO.jpg&quot; alt=&quot;R&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;strong&gt;first radio receiver&lt;/strong&gt;s invented by &lt;strong&gt;Marconi&lt;/strong&gt;, Oliver Lodge and Alexander Popov in 1894-5 used a primitive &lt;strong&gt;radio&lt;/strong&gt; wave detector called a coherer, invented in 1890 by Edouard Branly and improved by Lodge and &lt;strong&gt;Marconi&lt;/strong&gt;.&#xA;Radio receiver - Wikipedia&#xA;&lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_receiver&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Radio_receiver&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13099" LastEditorUserId="9493" LastEditDate="2018-08-23T17:05:48.173" LastActivityDate="2018-08-25T03:51:52.717" Title="When was the first radio transceiver (transmitter/receiver) built, and by whom?" Tags="&lt;transceiver&gt;&lt;history&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11761" PostTypeId="2" ParentId="11756" CreationDate="2018-08-24T04:14:43.000" Score="4" Body="&lt;p&gt;I don't know much about this, but for what it's worth I do have a rather distant memory of doing this long ago, before transistor RF power amps became affordable and before I had a way to measure SWR or harmonic content of the transmitter output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transmitter was a very basic VFO, buffer and a 6V6 RF final, maybe 3 or 4W RF output max. The antenna was roughly 1/4 wave of wire strung out the window to a nearby tree (with an electric fence insulator at the end), using a pi coupler for matching, all very experimental and mostly built from parts of old valve receivers that I'd been lucky enough to be given. The valve output stage was robust enough to cope with severe mismatches. I remember getting RF burns from the antenna connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My equipment was only a small multimeter, a very simple field strength meter (that used the multimeter), a borrowed portable transistor receiver that had short wave bands, and a soldering iron, so there was a lot of guesswork and experimental method involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was being mentored by a ham who was very kind and encouraging to me. He had lent me a copy of the ARRL handbook, and gave me ideas to try. He had been a Post Office/marine radio op in the war I think, and he knew a lot about getting things working with very little test equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He told me that a (15W) &lt;strong&gt;230V lightbulb in series with the antenna at the output of the pi coupler&lt;/strong&gt; could be used as an indication of how much power was getting to the antenna. &#xA;The pi coupler was adjusted until the lightbulb glowed brightest and it was then removed, and the field strength meter was used to peak the pi coupler settings. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking back on it I have little idea of how effective this method was in adjusting SWR, but I remember it made adjusting the coupler much easier than just using the field strength. The current in the bulb obviously does not actually indicate SWR, but serves as a rough initial indication of the matching of output stage to antenna I think. It was certainly quite reassuring to see direct evidence of current in the antenna circuit anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cheers.&lt;/p&gt;&#xA;" OwnerUserId="9531" LastActivityDate="2018-08-24T04:14:43.000" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11762" PostTypeId="2" ParentId="11756" CreationDate="2018-08-24T10:09:05.210" Score="4" Body="&lt;p&gt;Mainstream hams first started to appreciate SWR in the 1940's. In that era some of the first SWR meters started to come on the market. But their accuracy and frequency range was quite limited. Toward the end of the 1940's military surplus coaxial cable was hitting the ham market. Up to that point, ladder line was typically used for most ham antenna installations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In October of 1947, Charles Wright, W4HVV wrote an article in QST bemoaning the accuracy and availabilty of SWR meters for &quot;28 mc&quot; and higher. His article, entitled &lt;em&gt;The Poor Man's Standing-Wave Indicator&lt;/em&gt;, described a simple twin lamp (2 volt, 60 mA each) arrangement connected to a one turn pickup loop that when placed in parallel with the ladder line would give a relative indication of SWR. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FCpPM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FCpPM.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When SWR is low, one lamp glows. As SWR increases, the second lamp begins to glow. By visually calibrating it using various dummy loads, the author was able to estimate the SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally, the on-line QST archives are only available to members but I did find a full copy &quot;in the clear&quot; for your reading enjoyment &lt;a href=&quot;http://www.rfcafe.com/references/qst/twin-lamp-qst-october-1947.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-24T11:36:02.920" LastActivityDate="2018-08-24T11:36:02.920" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11763" PostTypeId="2" ParentId="11758" CreationDate="2018-08-24T10:42:45.457" Score="4" Body="&lt;p&gt;This is tough to nail down since even the term transceiver is subject to interpretation. It is also often the case that a given answer may only be applicable for a specific geography.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But with those caveats in mind, from a US perspective, I believe the RCA 5 meter ATR-213 introduced in the 1930's might be one of the earliest entries in the US market. It sold for $20. Here is an ad for its 1937 successor the ATR-219:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/HTbkO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HTbkO.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Hallicrafters SR-75 was introduced in 1950 and is probably the first US product that would begin to match our current concept of a transceiver but with a crystal controlled, 10 watt transmitter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2y9W3.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2y9W3.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In 1957, Collins introduced their first ham transceiver, the KWM-1 to compete with Hallicrafters. They touted theirs as the first &lt;em&gt;mobile&lt;/em&gt; transceiver. Transmit and receive frequencies were controlled with a single knob. Split operation required an optional accessory. It sold for over $8,000 in today's US dollars! It makes the new IC-7300 look even more like a bargain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/A1XVd.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/A1XVd.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I strongly suspect that there is comparable history in the German, Italian, England, and Soviet Union marketplaces based on their general technological development in that era.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-08-24T11:29:29.330" LastActivityDate="2018-08-24T11:29:29.330" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11764" PostTypeId="1" AcceptedAnswerId="11765" CreationDate="2018-08-24T15:19:23.440" Score="2" ViewCount="351" Body="&lt;p&gt;I am working on putting together a 40 meter delta loop using a 1/4 wavelength of RG-6 as the matching section.  However I'm unsure of where to create my feedpoint choke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I coil up the RG6 right at the feedpoint of the antenna itself?  Or do I coil up the 50 ohm RG8x at the point where it feeds into the 75 ohm matching section?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: My choke consists of 8 turns of coax through a mix 31 big clamp on bead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/A1AKP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/A1AKP.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="8717" LastEditDate="2018-08-25T00:53:34.873" LastActivityDate="2018-08-25T01:53:14.323" Title="Choke at feed point of delta loop with Q match" Tags="&lt;antenna&gt;&lt;loop-antenna&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11765" PostTypeId="2" ParentId="11764" CreationDate="2018-08-24T17:26:50.407" Score="5" Body="&lt;p&gt;The choke should go at the transition between unbalanced and balanced, &lt;strong&gt;which is where the RG-6 meets the ends of the loop wire.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You talk of coiling coax: I suggest you coil it around a ferrite core and not just air. The trouble with air-core &quot;chokes&quot; is they have no resistance, only reactance, in common-mode. Depending on what the common-mode impedance is in the rest of the antenna system, adding this reactance might actually tune the common-mode to resonance, making things &lt;em&gt;worse&lt;/em&gt;. A good choke has a substantially resistive impedance: this is guaranteed to raise the overall common-mode impedance in all cases. See &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/#inductive_chokes&quot; rel=&quot;nofollow noreferrer&quot;&gt;additional explanation by G3TXQ&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8717" LastEditDate="2018-08-25T01:53:14.323" LastActivityDate="2018-08-25T01:53:14.323" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11766" PostTypeId="2" ParentId="11764" CreationDate="2018-08-24T20:10:50.630" Score="4" Body="&lt;p&gt;&lt;strong&gt;Forget about air-core chokes&lt;/strong&gt;. G3TXQ's page that Phil links to in his excellent answer here shows just how much superior ferrite chokes are than air core choke baluns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please visit k9yc.com and download &lt;a href=&quot;http://k9yc.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;rfi-ham.pdf&lt;/a&gt;. Jim Brown there on page 36 recommends a choke balun made by wrapping 8 turns of the coax &lt;em&gt;at the antenna feedpoint&lt;/em&gt; through four stacked 2.4&quot; diameter #31 ferrite cores. They cost about $7 from &lt;a href=&quot;http://www.mouser.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.mouser.com&lt;/a&gt;. And don't wrap the RG-6 too tight! That PDF tells how to properly wrap it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a similar choke balun that I made, at the base of &lt;a href=&quot;http://www.w0btu.com/160_meters.html#inv-l_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;my 160m inverted-L&lt;/a&gt;. Those are the exact Fair-rite #31 cores I mentioned above, with RG-6 coax. You don't need to make the loops as big as I did.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8h8lv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8h8lv.png&quot; alt=&quot;W0BTU 160m choke balun&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(For 1.8 MHz, it really should have had more turns and cores, but it worked very well nonetheless.) I used this antenna on 160 through 20 meters, with great results.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-08-24T23:41:47.297" LastActivityDate="2018-08-24T23:41:47.297" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11767" PostTypeId="2" ParentId="11758" CreationDate="2018-08-25T03:51:52.717" Score="1" Body="&lt;p&gt;In 1898 Nikola Tesla made presentation of his remote controlled boat. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It did not only send and receive using radio waves but also used complex encoding to send commands though simple radio channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.engadget.com/2014/01/19/nikola-teslas-remote-control-boat/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.engadget.com/2014/01/19/nikola-teslas-remote-control-boat/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2018-08-25T03:51:52.717" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11771" PostTypeId="2" ParentId="11721" CreationDate="2018-08-26T13:26:35.913" Score="0" Body="&lt;p&gt;I think one thing overlooked here is the practical logistics of operating Ham radio from a University.  Having done so at U. Central Florida, I can attest that one must be part of an Amateur Radio Club on campus which has a fixed station set up with antennas suitable for your purposes.  If the equipment and logistics do not exist, they must be &quot;created&quot; and financed in some way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Student government usually holds the purse strings for major club purchases.  Thus you would have to provide a compelling reason for the university to purchase equipment necessary to create these links from school to school and also offer some public benefit for the expenditure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you and your friends are all Engineering students perhaps the College of Engineering might find Amateur Radio a good teaching tool and could supply the necessary resources as part of independent study.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Truly the most difficult part of this quest is the antenna(s).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the meantime, using radio for basic email type communications is as easy as a local WINLINK system to inject your messages into an internet backbone to get them the rest of the distance to your friends via radio on the other end.  While not strictly radio to radio, the experiences are invaluable and keep your comms away from the school's email servers.  Not a bad benefit on it's own. ;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be creative in your quest!!!&lt;/p&gt;&#xA;" OwnerUserId="6248" LastActivityDate="2018-08-26T13:26:35.913" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11772" PostTypeId="1" CreationDate="2018-08-26T15:56:10.510" Score="3" ViewCount="188" Body="&lt;p&gt;I bought a Kenwood audio breakout cable having only the kenwood connector (3.5mm and 2.5mm-in-one) on one end and up to me to add connectors on the other side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It came with a nice diagram for how to wire it up, but also said that a 1µF capacitor should be added in series with the microphone if it's a dynamic mic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which microphones are &quot;dynamic&quot;, needing this capacitor?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens with non-dynamic mics if I add the capacitor?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My plan is to add two 3.5mm connectors to connect to a computer (specifically &lt;a href=&quot;https://www.amazon.co.uk/gp/product/B00KAE2L1C&quot; rel=&quot;nofollow noreferrer&quot;&gt;this USB audio card&lt;/a&gt;) and trigger tx with VOX, so a USB sound card is what I'm most interested in how to properly set up.&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="1362" LastEditDate="2018-08-28T21:29:58.997" LastActivityDate="2018-08-28T21:29:58.997" Title="Is a connecting computer sound output equivalent to connecting a &quot;dynamic&quot; mic?" Tags="&lt;audio-interface&gt;&lt;microphone&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11773" PostTypeId="2" ParentId="11772" CreationDate="2018-08-26T16:36:00.567" Score="6" Body="&lt;p&gt;A dynamic microphone is basically a speaker in reverse. A diaphragm moves a magnet in proximity to a coil, varying the magnetic flux though the coil and inducing a current in it. You can in fact use a speaker as a dynamic microphone, though the sound quality is quite colored.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A condenser microphone is a capacitor. (In some places and times, &quot;condenser&quot; is synonymous with &quot;capacitor&quot;.) One plate is fixed, and the other is the diaphragm. The capacitor is biased with a constant charge. As the diaphragm moves the distance between the plates changes, and thus the capacitance charges. Since the charge is constant, the voltage varies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Condensers require a source of power to bias the capacitor, and in practice they must also include a buffer to convert the high condenser output impedance to something appropriately low for a long cable. It often takes the form of a simple FET integrated with the microphone capsule. Rather than running another pair of wires just to power the microphone, it's common to use the same wires to deliver power by employing a bias tee:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/VcW2G.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fVcW2G.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This circuitry would be inside the radio so a microphone can simply be plugged in without additional components. The capacitor serves to block DC while allowing AC (the audio signal) to pass. In this way the circuitry inside the radio can bias the audio signal to whatever voltage is required by the design, independently of the bias voltage to power the microphone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By adding another series capacitor to the left of V1 you're blocking the bias voltage from reaching the microphone. In the case of a dynamic microphone this is important, since the coil of a dynamic microphone looks like a short to DC. As such your microphone would become a heater, then a smoke machine, then a paperweight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this would also block the bias voltage necessary to run a condenser microphone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To determine what kind of microphone you have, it's best to just read the manual.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A USB sound card isn't a microphone at all. The sound card output may already include a series capacitor, but I wouldn't count on it. Since the sound card doesn't need a bias voltage to power it, I would include a series capacitor to be sure, similar to a dynamic microphone. You may also find the sound card output is much too loud, so adding a voltage divider to attenuate the sound card output may be necessary.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-08-26T16:36:00.567" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11775" PostTypeId="2" ParentId="10376" CreationDate="2018-08-27T22:35:45.500" Score="2" Body="&lt;p&gt;I've seen similar 'roving' signals emanating from low quality switching type power supplies, which can generate noise at multiple harmonically related frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you've mostly ruled out local sources, you might have to do a bit of sleuthing with a small directional loop antenna and a portable receiver. A cheap RTL type SDR receiver with a down-converter for HF hooked to the USB port on a laptop PC can work well for this, such as one of the AirSpy radios, as you can monitor lots of radio spectrum at once. A small wire loop antenna maybe 8-12&quot; diameter should provide enough directivity, as long as there's enough signal. The hours of operation suggest maybe a device used by a nearby neighbor who is home during the day - maybe a television or radio power supply, or a charger for a laptop or tablet.&lt;/p&gt;&#xA;" OwnerUserId="13119" LastActivityDate="2018-08-27T22:35:45.500" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11776" PostTypeId="1" CreationDate="2018-08-28T02:22:50.287" Score="3" ViewCount="1801" Body="&lt;p&gt;These newer HTs seem to have a different pinout than the older Yaesu HTs. The older HTs used a single 3.5mm TRRS plug - these use a two-plug connector, with a 2.5mm jack and a 3.5mm jack, similar to the &lt;a href=&quot;https://ham.stackexchange.com/q/1891/13122&quot;&gt;Kenwood/Baofeng style&lt;/a&gt;, but with the two plugs closer together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the the different contacts on these two plugs, and how would you trigger PTT?&lt;/p&gt;&#xA;" OwnerUserId="13122" LastActivityDate="2021-05-11T16:28:20.667" Title="What is the external mic/speaker pinout for the Yaesu FT-4XR / FT-65R / FT-25R / SSM-16B?" Tags="&lt;yaesu&gt;&lt;audio-interface&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11778" PostTypeId="1" AcceptedAnswerId="11779" CreationDate="2018-08-28T11:31:05.447" Score="2" ViewCount="522" Body="&lt;p&gt;I saw many designs for creating DIY antennas for NOAA (~137MHz) and ADS-B (~1090MHz) but never seen it in a PCB implementation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I have a rookie question: why nobody uses PCB antennas for such tasks?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe it is easy to make even with the &quot;Iron Transfer Method&quot; and get a smaller size with the same conductor length (making the conductor &quot;wavy&quot;).&#xA;What might be the catch?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S. I know nothing about antennas :)&lt;/p&gt;&#xA;" OwnerUserId="13124" LastActivityDate="2018-08-29T08:14:14.690" Title="Do PCB antennas suit for NOAA and ADS-B?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11779" PostTypeId="2" ParentId="11778" CreationDate="2018-08-28T13:43:51.990" Score="4" Body="&lt;p&gt;A simple antenna has at least one dimension that is approximately, or larger than,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$L = \frac{1}{4} \lambda = \frac{1}{4} \frac{c}{f}$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\lambda$ is the wavelength, which can be computed from the speed of light $c$ and the frequency $f$. For 137 MHz, that's 55 cm or 1.8 ft. That's a pretty big PCB! At 1090 MHz, this is less of a problem, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next question is what design you're using. The simplest antenna design is a rigid wire one quarter wavelength long (the length I mentioned above), but if that is what you want, a piece of solid-core wire is cheaper and easier to obtain than a PCB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some more complex antennas that can be readily made on PCBs are specifically wide-bandwidth, for receiving over an unusually wide frequency range, or more directional, for long-range point to point communication — both not being the problem these applications are trying to solve.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the squiggly complicated PCB antennas you may have seen are trying to solve the problem of stuffing a decent antenna, with needed electrical properties, into a tiny space, as in a cell phone. (Or just avoiding needing a separate component to solder on.) The tradeoff is that these ‘electrically small’ antennas may have different matching requirements, narrower bandwidth, and be &lt;em&gt;less efficient,&lt;/em&gt; which matters mostly for transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, overall, yes, you could make a PCB antenna for these signals, but it's not the right technology.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-08-28T19:13:54.570" LastActivityDate="2018-08-28T19:13:54.570" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11780" PostTypeId="1" CreationDate="2018-08-28T13:49:21.170" Score="4" ViewCount="2409" Body="&lt;p&gt;Do I need a separate device to use digital modes with the IC-7300 or do I just need to connect the 7300 to my computer via USB in order to use WSJT-X for FT8?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you.&lt;/p&gt;&#xA;" OwnerUserId="13125" LastActivityDate="2018-08-29T00:00:20.937" Title="Can the IC-7300 be connected straight to a computer and use WSJT-X for FT8?" Tags="&lt;icom&gt;&lt;ft8&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11781" PostTypeId="2" ParentId="11780" CreationDate="2018-08-28T17:39:32.417" Score="8" Body="&lt;p&gt;Yes, you only need a USB2 A to B cable.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The IC-7300 already has an integrated sound card, for audio signal transmission, and an integrated serial port for remote control, both of which are connected to computer using the USB2 B port at the back of the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some rare cases, you might also want a Icom CT-17 compatible interface cable. Namely, the radio also has a CT-17 compatible serial input.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to control the frequency and key the radio in RTTY mode and at the same time, switch between the mark and space using the serial port, but without using DTS/RTS pins, then you need the capability to have two serial ports on the radio, for which a CT-17 compatible cable is needed.&lt;br&gt;&#xA; Otherwise, the USB cable is enough.&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="873" LastEditDate="2018-08-29T00:00:20.937" LastActivityDate="2018-08-29T00:00:20.937" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11782" PostTypeId="2" ParentId="1415" CreationDate="2018-08-28T19:00:13.303" Score="2" Body="&lt;p&gt;You can always download the EchoLink software and see if your repeater is listed, then find someone who will listen for you while you're mobile. It's available for cellphones but I'm not sure how well it works on data rather then wifi since I don't tend to use it when I'm mobile with a HT anyway. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use the same repeater on a regular basis, it might be a good idea to drive around and build up your own radius map of where you can reach the repeater from so you'll have a good idea where you'll be able to reach the repeater in future.&lt;/p&gt;&#xA;" OwnerUserId="13126" LastActivityDate="2018-08-28T19:00:13.303" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11783" PostTypeId="2" ParentId="11778" CreationDate="2018-08-28T20:29:11.163" Score="2" Body="&lt;p&gt;I'm guessing by PCB antenna you mean specifically the kind where the trace folds back on itself, resulting in a physically smaller antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are non-PCB antennas which use similar techniques to achieve a smaller size. For example, hams will be familiar with the ubiquitous rubber ducky antenna on VHF handhelds. Here, &lt;a href=&quot;http://www.g4ilo.com/diy-ducky.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;G4ILO builds one for the 2 meter band&lt;/a&gt;, which at around 145 MHz is pretty close to your 137 MHz target.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0bx31.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0bx31.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rather than printing a trace on a PCB, a wire is coiled around a form. The coil adds inductance which makes the antenna appear longer electrically than it is physically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Printing a meandering trace on a PCB has the same effect. As you can see in the image above, this antenna is about 6.5 inches (without any shortening, it would have been 19.5 inches at 145 MHz) which is a pretty large PCB. The choice to manufacture an antenna on a PCB versus wire is usually for cost reasons, but at this size the economics might not work out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1090 MHz however is not far in frequency from GPS, where &lt;a href=&quot;https://google.com/search?q=gps+pcb+antenna&amp;amp;tbm=isch&quot; rel=&quot;nofollow noreferrer&quot;&gt;PCB antennas are very common&lt;/a&gt;. I'm sure somebody is using PCB antennas at this frequency.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-08-28T20:29:11.163" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11784" PostTypeId="2" ParentId="11778" CreationDate="2018-08-28T22:15:47.697" Score="7" Body="&lt;p&gt;PCB is an appropriate and useful way of making antennas for higher frequencies, say from 900 MHz and up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My company made thousands of GSM antennas for window mounting (in the days of car-installed cell phones). These were a fan dipole for 900 and 1800 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a PCB antenna I found on the web, for example:&#xA;&lt;img src=&quot;https://i.stack.imgur.com/9foLq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We also made all sorts of high gain Omni antennas, for 1.3 GHz video links, 2.4 GHz, 5.8 GHz, on long thin PCBs housed inside thin wall fibreglass tubes. No zigzags, these were full sized stacks of dipoles fed with transmission lines, all on the board.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would say the best way of mass-producing a modest gain 1090 MHz Omni, say 6 to 9 dBi, is with a PCB antenna. It can be done with soldered coax alternating inside and outside, or with little brass tubes soldered to coax cut just so, but the PCB is the simplest and most repeatable. It need only be 10 mm wide, so doesn't cost very much. Of course it takes some simulations and then several prototypes to get the design right, so not the best route for a one-off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://f5ann.pagesperso-orange.fr/AntenneStrip-line1090MHz/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt; is an example of an ADS-B antenna made with PCB, and a picture taken from this page.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/jtGBo.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2018-08-29T08:14:14.690" LastActivityDate="2018-08-29T08:14:14.690" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11785" PostTypeId="1" AcceptedAnswerId="11799" CreationDate="2018-08-29T02:54:18.427" Score="6" ViewCount="392" Body="&lt;p&gt;I'd like to play around with ax.25 connections.  It seems that if I have more than one radio (operating on different frequencies) that I would want to have multiple ax.25 interfaces.  Direwolf creates a &lt;code&gt;/tmp/kisstnc&lt;/code&gt; symlink to the KISS pty device, and this path is hardcoded.  This means you can only run a single instance of Direwolf providing a KISS pty interface...and since &lt;code&gt;kissattach&lt;/code&gt; seems to only work with character devices, this would seem to limit a system to a single ax.25 interface when using direwolf.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I want to run multiple direwolf-controlled ax.25 interfaces, what are my options?  Am I thinking about this the wrong way? Is there a way to attach an ax.25 interface to Direwolf's KISS network port rather than using the pty device?&lt;/p&gt;&#xA;" OwnerUserId="13127" LastEditorUserId="13127" LastEditDate="2018-09-02T12:35:53.160" LastActivityDate="2018-09-02T12:35:53.160" Title="Using Direwolf with multiple radios?" Tags="&lt;aprs&gt;&lt;packet&gt;&lt;direwolf&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11786" PostTypeId="1" AcceptedAnswerId="11788" CreationDate="2018-08-29T11:55:14.840" Score="3" ViewCount="1449" Body="&lt;p&gt;I am making DIY antenna for a home project. The antenna is going to be &quot;V-dipole&quot; with leg length about 53cm. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I didn't find a thick copper wire, but I have a lot of thin core from tv antenna cable. &#xA;&lt;br&gt;I am attending to twist a few thin wires together (without isolation, of course) in order to get a less-bendy leg. Something like this: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0oK7P.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0oK7P.jpg&quot; alt=&quot;twisted copper wires&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, does the twist make any changes in physical antenna characteristic? Skin effect? &#xA;I guess it is the same conductor, which probably will have less resistance than a single thin wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you.&lt;/p&gt;&#xA;" OwnerUserId="13124" LastActivityDate="2018-08-29T14:19:35.387" Title="Twisting copper wire for a less-flexible DIY antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11788" PostTypeId="2" ParentId="11786" CreationDate="2018-08-29T14:19:35.387" Score="4" Body="&lt;p&gt;Your thought processes are on track - the primary electrical impact is on the RF resistance of the wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Twisting the wires effectively creates a larger wire diameter with more surface area. The additional surface area reduces the RF resistance attributable to skin effect. Depending on the frequencies involved, this may be of minimal benefit. Based on the geometry of your antenna, it appears that you are in the 130 MHz range. If so, the radiation resistance of the antenna is around 70 ohms which means it would take at least of couple of ohms to have a significant effect on efficiency. The formula for antenna efficiency is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Efficiency=\frac{R_r}{R_r+R_l} \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where R&lt;sub&gt;r&lt;/sub&gt; is the radiation resistance of the antenna and R&lt;sub&gt;l&lt;/sub&gt; is the resistive losses in the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Efficiency is multiplied times directivity to specify the gain of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One thing to consider is that corrosion between the individual strands can offset the increased surface area. We often see this when a coaxial cable gets water inside the jacket. The braided outer conductor becomes corroded and it no longer makes an effective shield. But since mechanical strength is your primary reason for twisting the wires, this will probably have negligible impact on the performance of your antenna.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-08-29T14:19:35.387" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11789" PostTypeId="2" ParentId="10401" CreationDate="2018-08-29T20:39:18.153" Score="1" Body="&lt;p&gt;Ham LoRa does seem to exist, although I haven't seen any mention of it around the Boston MA area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think to make best use of LoRa on Ham frequencies, one could use the European version that works in the 70cm band.  With that, one could higher power level (limited by one's local power limits which vary by physical location) and better antennas -- Yagis for fixed, point-to-point service and verticles for multipoint repeater service.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For protocols, one could use something based on UUCICO (the basis of UUCP), the old Unix protocol behind UseNet and mail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But one ham in a region isn't enough to be interesting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73, K1UZK (once WA1JMS)&lt;/p&gt;&#xA;" OwnerUserId="9109" LastActivityDate="2018-08-29T20:39:18.153" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11790" PostTypeId="2" ParentId="10560" CreationDate="2018-08-29T21:47:21.813" Score="1" Body="&lt;p&gt;It will depend on the science fair, as well as who the fair is affiliated with (if anyone). For instance, the &lt;a href=&quot;https://student.societyforscience.org/rules-all-projects&quot; rel=&quot;nofollow noreferrer&quot;&gt;Intel International Science and Engineering Fair says&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Projects must adhere to local, state and U.S. Federal laws, regulations and permitting conditions. In addition, projects conducted outside the U.S. must also adhere to the laws of the country and jurisdiction in which the project was performed.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Adhering to laws means you'll need to have a ham license to transmit (or find a ham who will is willing to act as control operator at all times when you transmit).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next, &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;All projects must adhere to the requirements of the affiliated fair(s) in which it competes to qualify for participation in the Intel ISEF. Affiliated fairs may have additional restrictions or requirements. Knowledge of these requirements is the responsibility of the student and Adult Sponsor.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So even if you have a license or a control operator, you'll need to check with the fair itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, be aware that there may be &lt;a href=&quot;https://student.societyforscience.org/hazardous-chemicals-activities-or-devices&quot; rel=&quot;nofollow noreferrer&quot;&gt;additional requirements&lt;/a&gt; when using RF:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A risk assessment (documented on Form 3) must be conducted when a student’s project involves radiation beyond that normally encountered in everyday life. Non- ionizing radiation includes the spectrum of ultraviolet (UV), visible light, infrared (IR), microwave (NW), radiofrequency (RF) and extremely low frequency (ELF).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2018-08-30T23:13:26.450" LastActivityDate="2018-08-30T23:13:26.450" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11791" PostTypeId="1" CreationDate="2018-08-30T01:19:20.107" Score="6" ViewCount="12375" Body="&lt;p&gt;I'm new to radios. Only ever used them for squad communication in airsoft. I have two Baofeng UV-5R handhelds and would like to use them this week to communicate on a family camping trip with no cell service. I wanted to know how to do this legally in central Pennsylvania. Thank you.&lt;/p&gt;&#xA;" OwnerUserId="13132" LastEditorUserId="76" LastEditDate="2018-09-08T03:23:54.193" LastActivityDate="2018-09-08T03:23:54.193" Title="How do I legally use a Baofeng UV-5R radio for communication?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;uv-5r&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11792" PostTypeId="2" ParentId="11791" CreationDate="2018-08-30T01:46:29.320" Score="10" Body="&lt;p&gt;In the United States, for the most part, all radio transmissions fall into one of three categories:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The &lt;strong&gt;operator&lt;/strong&gt; is allowed to transmit on that frequency (amateur, &quot;business band&quot;, aviation, military, etc.)&lt;/li&gt;&#xA;&lt;li&gt;The &lt;strong&gt;radio&lt;/strong&gt; is allowed to transmit on that frequency (CB, FRS, MURS).&lt;/li&gt;&#xA;&lt;li&gt;The transmissions are very low-power (&quot;Part 15&quot;: WiFi, Bluetooth, lots of other things).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Your radio is not very low-power. Your radio does not meet the requirements of CB or similar services, most significantly that it not be able to transmit &lt;em&gt;other&lt;/em&gt; than on the relevant frequency bands. Therefore, you may not currently use it except to receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest way to be able to use it legally — or in general, to use radio transmitters for personal communication purposes (that aren't cell phones or such) — is for you and your family members to get &lt;strong&gt;amateur radio&lt;/strong&gt; licenses (and obey the relevant rules).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The process is simple: you take a test about radio theory and operating procedure, and receive a license. The test is multiple-choice and administered by individuals called Volunteer Examiners (VEs) (who are organized into groups called VECs) usually in regularly scheduled sessions. There may or may not be a fee for the test depending on the policies of the VEC in question. There are multiple levels of test and license; for your purpose you only need the first one, a “Technician” license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Many people cram for the test and pass it in the same day.&lt;/strong&gt; Or, gently paced self-study is readily possible. There are books, classes, and free online resources. If you'd like to jump in and see what the test is like, I personally recommend &lt;a href=&quot;https://hamstudy.org/&quot; rel=&quot;noreferrer&quot;&gt;HamStudy.org&lt;/a&gt;; it's free to take practice tests and read the questions and answers there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you receive your license, it will include your &lt;em&gt;call sign.&lt;/em&gt; You must include your call sign in all transmissions; there are other rules, but this is the one that most affects everyday activity. Everyone using a radio must have their own license, unless they are being directly supervised by a license holder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good resource for learning more about amateur radio in the United States is the American Radio Relay League (ARRL) — &lt;a href=&quot;http://www.arrl.org/getting-licensed&quot; rel=&quot;noreferrer&quot;&gt;here's their page on getting licensed&lt;/a&gt;. (Note that the ARRL is a VEC but not the only VEC.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you'd like to know more about amateur radio, feel free to look around here, and ask more questions if you can't find answers already — it is the focus of our site, as you can tell by the name!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;[The beginning of this answer was previously posted &lt;a href=&quot;https://ham.stackexchange.com/a/6383/76&quot;&gt;here&lt;/a&gt;.]&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-08-30T14:15:29.753" LastActivityDate="2018-08-30T14:15:29.753" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11797" PostTypeId="1" AcceptedAnswerId="11802" CreationDate="2018-08-31T08:50:05.030" Score="9" ViewCount="378" Body="&lt;p&gt;The ham radio frequency allocations tend to comprise a larger frequency range for increasing frequency (&lt;a href=&quot;https://ham.stackexchange.com/a/5085/5573&quot;&gt;also see this plot&lt;/a&gt;). For example, the 40 meters band is from 7,0 to 7,2 MHz, thus 200 kHz, while 23 centimeters is from 1240 to 1300 MHz, thus 60 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, it would not be possible to extend the 40 meters band to 60 MHz since it would cover everything from LF up to 5 meters, but on the other hand, 200 kHz in the 23 centimeters band can deliver the same amount of information (in the Shannon sense) as in the 40 meters band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this reason, we tend to use more bandwidth-hungry transmissions techniques on the higher bands, but apart from enabling new applications, such as HAMNET, where we need the higher bandwidth, would this really be necessary?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it really only that there are less potential users per bandwidth in the higher frequencies or is there something that would make applications with larger bandwidth infeasible for low frequencies or ones with smaller bandwidth infeasible for high frequencies?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S.: Of course, I am happy about every hertz of available ham radio bandwidth and I do not intend to change the allocation. This is only a question out of curiosity.&lt;/p&gt;&#xA;" OwnerUserId="5573" LastEditorUserId="5573" LastEditDate="2018-08-31T09:00:41.653" LastActivityDate="2018-08-31T15:35:35.773" Title="Why do the ham radio bands get broader with increasing frequency?" Tags="&lt;frequency&gt;&lt;bandwidth&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11798" PostTypeId="2" ParentId="10401" CreationDate="2018-08-31T11:43:37.207" Score="0" Body="&lt;p&gt;Let me stress the fact mentioned by @mike65535 again: Couple of hundred kbps is not what LoRa is designed for. It is more in the area of IEEE 802.15.4 (ZigBee etc.) even though you might have to reduce the distance between the nodes a bit depending on the environment and your ability to build good antennas or even amplifiers if you like.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The plus is that there is already well-proven hard- and software available and a lot of existing experience in the area of collision-free data transmission in mesh applications. It is even not very difficult to build your own IEEE 802.15.4 hardware from existing ICs such as the ATmega256RFR2 or the AT86RF23X series.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, since we are talking about ham applications here: It is trivial to use existing IEEE 802.15.4 hardware in the 13 cm ham radio band and I have already done that successfully.&lt;/p&gt;&#xA;" OwnerUserId="5573" LastActivityDate="2018-08-31T11:43:37.207" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11799" PostTypeId="2" ParentId="11785" CreationDate="2018-08-31T12:13:47.303" Score="5" Body="&lt;p&gt;I've put together something that is conceptually similar to @user3486184's comment, but without actually using &lt;code&gt;chroot&lt;/code&gt;. I'm taking advantage of SystemD to manage both direwolf and the subsequent kissattach command necessary to activate an ax.25 interface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I created the following &lt;a href=&quot;https://fedoramagazine.org/systemd-template-unit-files/&quot; rel=&quot;noreferrer&quot;&gt;Systemd template unit&lt;/a&gt; and installed it&#xA;into &lt;code&gt;/etc/systemd/system/direwolf@.service&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;[Unit]&#xA;Description=Direwolf %I soundcard modem&#xA;&#xA;[Service]&#xA;Type=simple&#xA;&#xA;PrivateTmp=true&#xA;ExecStart=/usr/bin/direwolf -t 0 -p -c /etc/direwolf/%i.conf -q h -q d&#xA;&#xA;# Relocate /tmp/kisstnc symlink to /run/direwolf/&amp;lt;instance name&amp;gt;.&#xA;ExecStartPost=/bin/timeout 10 /bin/sh -c 'while ! test -c /tmp/kisstnc; do sleep 1; done; cp -a /tmp/kisstnc /run/direwolf/%i'&#xA;&#xA;# Clean up symlink on exit.&#xA;ExecStopPost=/bin/rm -f /run/direwolf/%i&#xA;&#xA;[Install]&#xA;WantedBy=multi-user.target&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;A &quot;template unit&quot; allows you to start multiple distinct instances of a&#xA;service using the same unit file.  To start a template unit, you run&#xA;&lt;code&gt;systemctl unitname@instancename&lt;/code&gt;, and the value of &lt;code&gt;instancename&lt;/code&gt; is&#xA;available to you in the unit as &lt;code&gt;%i&lt;/code&gt;.  So with the example above, I&#xA;could run:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;systemctl start direwolf@uhf&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Or:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;systemctl start direwolf@vhf&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Etc.  This will start up Direwolf pointing at a configuration named&#xA;after the instance; in other words, given the latter example, this&#xA;would run:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;/usr/bin/direwolf -t 0 -p -c /etc/direwolf/vhf.conf -q h -q d&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The unit makes use of the &lt;code&gt;PrivateTmp&lt;/code&gt; directive, which when set means&#xA;that each service gets its own &lt;code&gt;/tmp&lt;/code&gt; directory that is not shared&#xA;with anything else.  This allows each Direwolf instance to create it's&#xA;own &lt;code&gt;/tmp/kisstnc&lt;/code&gt; symlink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An &lt;code&gt;ExecStartPost&lt;/code&gt; runs after Direwolf has started.  It waits for the&#xA;&lt;code&gt;/tmp/kisstnc&lt;/code&gt; link to show up, and then it copies that into&#xA;&lt;code&gt;/run/direwolf/&amp;lt;instancename&amp;gt;&lt;/code&gt;.  If I run both of the above &lt;code&gt;systemctl&#xA;start ...&lt;/code&gt; commands, I would end up with &lt;code&gt;/run/direwolf/uhf&lt;/code&gt; and&#xA;&lt;code&gt;/run/direwolf/vhf&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've created a companion &lt;code&gt;kisstnc@.service&lt;/code&gt; unit that looks like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;[Unit]&#xA;Requires=direwolf@%i.service&#xA;After=direwolf@%i.service&#xA;&#xA;[Service]&#xA;Type=simple&#xA;ExecStart=/usr/sbin/kissattach /run/direwolf/%i %i&#xA;&#xA;[Install]&#xA;WantedBy=multi-user.target&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;With this in place, I can simply run &lt;code&gt;systemctl start kisstnc@uhf&lt;/code&gt; and&#xA;then:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Systemd will start the &lt;code&gt;direwolf@uhf&lt;/code&gt; service, because the&#xA;&lt;code&gt;kisstnc@uhf&lt;/code&gt; service &lt;code&gt;Requires&lt;/code&gt; it to run first.&lt;/li&gt;&#xA;&lt;li&gt;The &lt;code&gt;direwolf@uhf&lt;/code&gt; unit creates the &lt;code&gt;/run/direwolf/uhf&lt;/code&gt; symlink&lt;/li&gt;&#xA;&lt;li&gt;The &lt;code&gt;kisstnc@uhf&lt;/code&gt; unit runs the appropriate &lt;code&gt;kissattach&lt;/code&gt; command&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For this to work, your &lt;code&gt;/etc/ax25/axports&lt;/code&gt; file must have port names&#xA;that match the instance names you're using in the above commands.  For&#xA;example, something like:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;uhf     TEST-0      0   128 2   Direwolf@radio0&#xA;vhf     TEST-1      0   128 2   Direwolf@radio1&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="13127" LastActivityDate="2018-08-31T12:13:47.303" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11801" PostTypeId="2" ParentId="11797" CreationDate="2018-08-31T13:32:29.857" Score="7" Body="&lt;p&gt;There are some straightforward reasons I can think of which apply to all spectrum allocations, not just amateur radio:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;In a lot of cases, the bandwidth of a RF device is relative; if you are using the same physical principles, but change the dimensions/values to double the operating frequencies, everything scales up equally so you have a device with twice the bandwidth. Thus, it is more technologically feasible to use more bandwidth for a single transmission as frequency increases, so there is motivation to make proportionally larger allocations to be able to employ such modes.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;From a historical perspective: at any given time after the invention of radio there has been demand for many uses of spectrum &lt;em&gt;that can be used by the technology of the day.&lt;/em&gt; And as we look back, higher frequencies were less practical, and also the bandwidths of the signals that people wanted (or considered reasonable) to transmit were lower. So, what looks like a reasonable size of pieces to delineate and hand out scales with the technological characteristics.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I don't know to what degree these factors have been &lt;em&gt;explicitly&lt;/em&gt; considered in allocations, vs. just working with the needs and desires of the time. Answering that would require looking at the history of spectrum allocation and the &lt;a href=&quot;https://en.wikipedia.org/wiki/International_Telecommunication_Union&quot; rel=&quot;noreferrer&quot;&gt;ITU&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-08-31T13:32:29.857" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11802" PostTypeId="2" ParentId="11797" CreationDate="2018-08-31T14:08:27.387" Score="8" Body="&lt;p&gt;There's more space at higher frequencies so the allocations can be bigger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider the difference between 15 MHz and 30 MHz, and the difference between 5,015 MHz and 5,030 MHz. It's a 15 MHz change either way, but in the first case involves a &lt;em&gt;halving&lt;/em&gt; of wavelength, whereas in the later case the wavelength changes only by a factor of 0.997. Since the way radio waves interact with their environment is largely dependent on their wavelength, we should expect that 15 MHz will be very different from 30 MHz, but 5,015 MHz and 5,030 MHz will be nearly identical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, frequencies below 50 kHz can penetrate seawater, with the lower frequencies penetrating more. So these low frequencies find application in submarine communication, but the entire band of usable frequencies here is less than 50 kHz wide.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF (3,000 to 30,000 kHz) doesn't penetrate seawater to a significant depth, but it does support ionospheric communication which is great for global communications. This is a band of 27,000 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Above 30,000 kHz, ionospheric propagation isn't possible, so reliable communication is generally limited to line of sight. Above 30,000,000 kHz, atmospheric attenuation starts becoming a significant problem. So that means a band of 29,970,000 kHz is usable for line of sight radio communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a very broad categorization, but you can generally see there are not many frequencies that have similar behaviors to a relatively low frequency like 15 MHz, whereas there are many frequencies similar to a high frequency like 1,500 MHz. As such, allocations at lower frequencies must be smaller if one particular user is not to monopolize all frequencies usable for a particular application.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-08-31T15:35:35.773" LastActivityDate="2018-08-31T15:35:35.773" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11803" PostTypeId="1" CreationDate="2018-08-31T16:20:51.207" Score="3" ViewCount="1592" Body="&lt;p&gt;I am considering buying the IC-7300. What kind of connector will I need to connect it to an external power supply? Or, does it come with a connector that I can splice on to a power cable coming from the DC power supply?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, will I need something like this adaptor?&#xA;&lt;a href=&quot;https://www.gigaparts.com/powerwerx-hf4-pp.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.gigaparts.com/powerwerx-hf4-pp.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you.&lt;/p&gt;&#xA;" OwnerUserId="13125" LastActivityDate="2018-08-31T17:35:10.107" Title="What kind of power plug does the ICOM IC-7300 need?" Tags="&lt;icom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11804" PostTypeId="2" ParentId="11803" CreationDate="2018-08-31T17:35:10.107" Score="4" Body="&lt;p&gt;A new IC-7300 comes with the power harness that plugs into the radio. The other end is connectorless so you can adapt it to your power supply using lugs, PowerPoles, stripped ends, etc.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-08-31T17:35:10.107" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11805" PostTypeId="1" CreationDate="2018-08-31T18:11:19.893" Score="9" ViewCount="2290" Body="&lt;p&gt;Say I have a wire antenna that is slightly (a few percent) too long for the desired frequency (of resonance or lowest SWR).  What are the options, other than cutting the wire(s) and very likely ending up with an antenna wire that is now too short (by miss-measuring, or when re-strung, moved higher, environment changes, etc.)?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I fold the tips or the wires into a small flat circle or figure 8 (similar to a perpendicular capacitive hat)?  Or loop the wire near the feed point?  Or coil wire around a dowel somewhere in the middle?  Etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added: Is the answer different if the wire is insulated?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-09-02T17:24:41.803" LastActivityDate="2018-10-23T15:08:39.540" Title="Wire antenna slightly too long" Tags="&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="5" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11806" PostTypeId="2" ParentId="11805" CreationDate="2018-08-31T18:25:37.887" Score="5" Body="&lt;p&gt;Simply fold the excessive lengths at the ends 180° back along the dipole and tape them to the antenna. It's that simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/7828/tuning-a-wire-antenna-by-folding&quot;&gt;See this post, where insulated wire was used&lt;/a&gt;&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other methods you mention may work, but the above is an easy, time-tested and effective method of raising the resonant frequency of a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest against coiling wire around a dowel somewhere in the middle.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-09-02T22:36:44.043" LastActivityDate="2018-09-02T22:36:44.043" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11807" PostTypeId="2" ParentId="11805" CreationDate="2018-08-31T18:28:11.870" Score="8" Body="&lt;p&gt;You should not make any coil in the middle of the antenna as that will greatly change its RF characteristics. Instead, bundle up the wire at the ends in some fashion:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;One practical solution is to fold the wire back on itself and fasten the free end onto the main line; then you have a loop you can also use for supporting the antenna, though you might want to use a “rope thimble” or other large diameter support to keep it from being sharply kinked, depending on the size and material of the wire and whether you expect to adjust it repeatedly. Electrically, this is mostly like using thicker wire, so it doesn't change the antenna characteristics much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is some dispute about how equivalent this is to a shorter wire if the wire is insulated. To be sure, you could remove the insulation where the end is joined on, but of course that may introduce other problems such as excess wear on stranded wire of a portable antenna. Or you could adjust the length until the antenna is a decent match regardless of whether cutting it would produce different results.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you want something more adjustable and have support solved, wind the excess wire length at the ends onto a spool; this will form an inductor, but since the far end of that inductor is open circuit it can't have significant current flowing and so has minimal effect on the antenna. &lt;a href=&quot;https://ham.stackexchange.com/a/5558/76&quot;&gt;There are existing antennas that work this way&lt;/a&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-09-02T22:50:32.590" LastActivityDate="2018-09-02T22:50:32.590" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11810" PostTypeId="2" ParentId="971" CreationDate="2018-09-01T05:15:31.720" Score="2" Body="&lt;p&gt;Very good answer @phil (Phil Frost - W8II).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;@Adam (Adam Davis) - Another reason is that repeaters are usually located on high-sites where there are a lot of repeaters installed.  On these high-sites it would also have line of site to the other high-sites in the area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are Inter-modulation involved one these sites where phantom transmissions could occur.  A lot of these sites has hi-low pass filters (ie. cavity filters) which filter out these and other frequency so that the repeater only re-transmits the communications that it should, and nothing else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope that this answers you the &quot;use-case&quot;.  P&lt;/p&gt;&#xA;" OwnerUserId="13099" LastActivityDate="2018-09-01T05:15:31.720" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11811" PostTypeId="1" CreationDate="2018-09-01T06:29:00.640" Score="8" ViewCount="201" Body="&lt;p&gt;Why are the radio bands organized by multiples of three?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example the HF band is from 3–30MHz and UHF is from 300–3000MHz. Why not multiples of 2? Or plain powers of ten?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="76" LastEditDate="2020-02-15T16:56:48.947" LastActivityDate="2020-02-15T16:56:48.947" Title="Why are radio frequency ranges aligned on multiples of 3?" Tags="&lt;frequency&gt;&lt;jargon&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11812" PostTypeId="2" ParentId="11811" CreationDate="2018-09-01T06:29:00.640" Score="14" Body="&lt;p&gt;The ITU bands &lt;strong&gt;are&lt;/strong&gt; actually delineated along plain powers of ten! They're just hiding a bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the description above a &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Radio_spectrum&amp;amp;oldid=855679116#ITU&quot; rel=&quot;noreferrer&quot;&gt;table of all the bands&lt;/a&gt; on Wikipedia:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;As a matter of convention, the ITU divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten ($10^n$) metres…&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So the HF band is from 100–10m, or the UHF band is from 1–0.1m. Neat!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;3&quot; comes up only when the bands are given in &lt;strong&gt;frequency&lt;/strong&gt; instead of &lt;strong&gt;wavelength&lt;/strong&gt;. The usual conversion between those is given &lt;a href=&quot;http://www.radiomods.co.nz/radiomath.html&quot; rel=&quot;noreferrer&quot;&gt;for example&lt;/a&gt; as:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;3&lt;/strong&gt;00 divided by wavelength in meters equals frequency in MHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;[emphasis mine]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That formula is in turn just the general &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Wavelength&amp;amp;oldid=856475338#Sinusoidal_waves&quot; rel=&quot;noreferrer&quot;&gt;frequency vs. wavelength relationship&lt;/a&gt; with the ideal 299,792,458 m/s propagation velocity (i.e. the speed of light in a vacuum) rounded to 300 Mm/s.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the &quot;3&quot; in all our bands is simply because the ITU defined them as simple magnitudes of ten along one unit (wavelength in meters), which happens to be related to another unit (frequency in hertz) by way of factors/definitions that round to three [with its own zeros after it].&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2018-09-01T06:29:00.640" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11815" PostTypeId="2" ParentId="3487" CreationDate="2018-09-01T14:48:24.903" Score="1" Body="&lt;p&gt;One of the biggest problems people have is that the inexpensive Chinese radio programming cables often use cloned or pirated Prolific USB-to-serial chipsets.  Modern Windows drivers usually don't work with these cables.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can buy a good, legitimate-chipset programming cable - Kenwood-brand ones are the safest bet but off-brand ones using the FTDI chipset tend to be more reliable.  This chipset seems to have less issues with piracy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another solution is to use the Linux operating system.  Being open-source, it's impossible for hardware developers to block off-brand versions of their hardware from working, because the developer community can remove these artificial restrictions.  I'll let you make your own moral decision about whether you want these cheap clone cables to work, but in Linux, they will work.  CHIRP is well-supported under Linux.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastActivityDate="2018-09-01T14:48:24.903" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11816" PostTypeId="1" AcceptedAnswerId="11890" CreationDate="2018-09-01T17:38:05.733" Score="14" ViewCount="1739" Body="&lt;p&gt;The US government is proposing to shut down the &lt;a href=&quot;https://en.m.wikipedia.org/wiki/National_Institute_of_Standards_and_Technology&quot; rel=&quot;nofollow noreferrer&quot;&gt;NIST&lt;/a&gt; standard time and frequency stations &lt;a href=&quot;https://en.m.wikipedia.org/wiki/WWV_(radio_station)&quot; rel=&quot;nofollow noreferrer&quot;&gt;WWV&lt;/a&gt;, &lt;a href=&quot;https://en.m.wikipedia.org/wiki/WWVH&quot; rel=&quot;nofollow noreferrer&quot;&gt;WWVH&lt;/a&gt;, and &lt;a href=&quot;https://en.m.wikipedia.org/wiki/WWVB&quot; rel=&quot;nofollow noreferrer&quot;&gt;WWVB&lt;/a&gt; in Colorado and Hawaii.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that actually happens, are there any free or inexpensive &lt;strong&gt;alternative frequency standards&lt;/strong&gt; available so that we can accurately calibrate our transceivers, frequency counters, etc. with at least 1 Hz accuracy?&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.google.com/search?q=wwv+discontinued&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.google.com/search?q=wwv+discontinued&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.eham.net/articles/41765&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.eham.net/articles/41765&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/news/concern-rising-within-amateur-radio-community-over-wwv-wwvh-shut-down-proposal&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/news/concern-rising-within-amateur-radio-community-over-wwv-wwvh-shut-down-proposal&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://forums.qrz.com/index.php?threads/wwv-discontinuing-operations.624002/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://forums.qrz.com/index.php?threads/wwv-discontinuing-operations.624002/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/WWVB&quot; rel=&quot;nofollow noreferrer&quot;&gt;WWVB&lt;/a&gt; is a time station only; without its radio transmissions, millions of &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Radio_clock&quot; rel=&quot;nofollow noreferrer&quot;&gt;consumer &quot;atomic&quot; radio clocks&lt;/a&gt; would have nothing to keep them accurate.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-12-24T17:23:19.717" LastActivityDate="2018-12-24T17:23:19.717" Title="WWV, WWVH, and WWVL may be shut down. Are there any alternatives?" Tags="&lt;transceiver&gt;&lt;equipment&gt;&lt;testing&gt;&lt;calibration&gt;&lt;wwv&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11817" PostTypeId="2" ParentId="5752" CreationDate="2018-09-01T18:06:41.347" Score="3" Body="&lt;p&gt;My Granddad was a navigator on Halifax medium bombers during WWII. As such he would use Morse code. He in turn taught my father (a small boy after the war) Morse code and they would practice by tapping on the pipework in the house, from bedroom to bedroom, in the middle of the night,  much to the annoyance of Grandma. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was enthralled at this and wanted to learn Morse code, and the first thing Grandad taught me was Best Bent Wire l. I can still remember the Morse today.&lt;/p&gt;&#xA;" OwnerUserId="13146" LastActivityDate="2018-09-01T18:06:41.347" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11818" PostTypeId="2" ParentId="11805" CreationDate="2018-09-01T19:04:06.937" Score="-2" Body="&lt;p&gt;Since you know that the antenna is a few percent long, then you know exactly how long to make it (by flat fold).  No cut and try if you do not add capacitance by making a loop or coil.&lt;/p&gt;&#xA;" OwnerUserId="8229" LastActivityDate="2018-09-01T19:04:06.937" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11819" PostTypeId="2" ParentId="11816" CreationDate="2018-09-01T19:45:12.730" Score="12" Body="&lt;p&gt;In &lt;a href=&quot;https://www.kb6nu.com/no-wwvb-no-problem/&quot; rel=&quot;noreferrer&quot;&gt;No WWVB? No problem!&lt;/a&gt;, KB6NU points at two projects that show you how to build your own low-powered WWVB-replacement to keep your clocks in sync:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://www.anishathalye.com/2016/12/26/micro-wwvb/&quot; rel=&quot;noreferrer&quot;&gt;μWWVB&lt;/a&gt;: A Tiny WWVB Station. This project uses an attiny44 microcontroller and a USGlobalSat EM-506 GPS module to simulate WWVB.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://www.instructables.com/id/WWVB-radio-time-signal-generator-for-ATTINY45-or-A/&quot; rel=&quot;noreferrer&quot;&gt;One Component Radio Clock Time Transmitter&lt;/a&gt;: This project uses an attiny45 microcontroller to simulate WWVB. As is, you set the time by changing some defines in the code. You’ll probably want to change that to get the time variables from a GPS source or an ntp source, but at least you’ll be able to generate the 60 kHz once you have that time information.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13127" LastActivityDate="2018-09-01T19:45:12.730" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11823" PostTypeId="5" CreationDate="2018-09-02T12:36:59.837" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2018-09-02T12:36:59.837" LastActivityDate="2018-09-02T12:36:59.837" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11824" PostTypeId="4" CreationDate="2018-09-02T12:36:59.837" Score="0" Body="Dire Wolf is a software &quot;soundcard&quot; AX.25 packet modem/TNC and APRS encoder/decoder. It can be used stand-alone to observe APRS traffic, as a tracker, digipeater, APRStt gateway, or Internet Gateway (IGate)." OwnerUserId="13127" LastEditorUserId="13127" LastEditDate="2018-09-05T20:12:06.353" LastActivityDate="2018-09-05T20:12:06.353" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11825" PostTypeId="2" ParentId="11805" CreationDate="2018-09-02T17:15:08.013" Score="0" Body="&lt;p&gt;Important note: the technique of folding back to shorten the antenna's electrical length relies on a short circuit being created along the entire length of the folded-back section. Folding back the ends will have no effect on the antenna's electrical length if the wire is insulated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Despite the obvious common sense of this note, I made this mistake - once!&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-09-02T17:15:08.013" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11829" PostTypeId="2" ParentId="11730" CreationDate="2018-09-03T18:47:34.430" Score="0" Body="&lt;p&gt;Line of sight is key when dealing with FM and considering you are using a HHT radio the wattage is probably 5-8watts max.  Right?  A J Pole has no real gain and I fear the loss would be worse than using a simple SMA antenna.  &lt;/p&gt;&#xA;" OwnerUserId="9449" LastActivityDate="2018-09-03T18:47:34.430" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11830" PostTypeId="1" CreationDate="2018-09-04T01:06:27.753" Score="1" ViewCount="115" Body="&lt;p&gt;I ordered a ham radio from eBay (doesn't matter which one) and I have gotten a completely different one than what I ordered. I'm quite new to amateur radio so please excuse my innocence/idiocy. I received a ZaStone D900 and while I wait for eBay to fix the order, I thought I would learn a bit more about it. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;How is this different from a normal ham radio (like a Yaesu or a Kenwood)?&lt;/li&gt;&#xA;&lt;li&gt;If it is different, is there a way to use it like a ham radio?&lt;/li&gt;&#xA;&lt;li&gt;How useful is UHF compared to VHF (the radio only came with a UHF antenna)?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Thanks in advance guys!&lt;/p&gt;&#xA;" OwnerUserId="13160" LastEditorUserId="9493" LastEditDate="2018-09-04T01:46:56.800" LastActivityDate="2019-07-07T03:04:41.547" Title="Help with ZaStone D900" Tags="&lt;uhf&gt;&lt;equipment-operation&gt;&lt;dmr&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11831" PostTypeId="2" ParentId="11830" CreationDate="2018-09-04T01:56:03.007" Score="1" Body="&lt;p&gt;The radio you received is a UHF DMR HT. If you have a DMR repeater in your area, you will be able to do some testing of the radio. You can locate a repeater by visiting &lt;a href=&quot;https://www.repeaterbook.com/repeaters/niche/index.php?mode=DMR&quot; rel=&quot;nofollow noreferrer&quot;&gt;RepeaterBook&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first step is to register with &lt;a href=&quot;https://www.radioid.net&quot; rel=&quot;nofollow noreferrer&quot;&gt;radioid.net&lt;/a&gt; to get your own Radio ID. This will then need to be programmed into the radio in order to make it usable on a repeater. If you change DMR radios later, you can use the same DMR ID with the new radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After that, you may find it helpful to review how DMR works and what are some of the best practices. There are several nice on-line guides for this purpose such as &lt;a href=&quot;http://www.dmrfordummies.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DMR for dummies&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-09-04T01:56:03.007" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11832" PostTypeId="2" ParentId="11816" CreationDate="2018-09-04T07:09:11.247" Score="12" Body="&lt;h1&gt;GPS-based frequency standards&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;@larsks &lt;a href=&quot;https://ham.stackexchange.com/a/11819/4076&quot;&gt;answer&lt;/a&gt; rightly pointed at devices that use GPS to generate the 1-second pulsing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's the correct way to go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Curiously, these modules only address the once-per-second accuracy issue, not the frequency standard issue, which GPS is indeed commonly used to solve:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll find a lot of modules on the market that will not only give you a Pulse Per Second (PPS), but also a frequency standard signal, most commonly 10 MHz, but there's other frequencies, too.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Frequency standards in cellular infrastructure&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;GPS-discplined oscillators (GPSDOs) are really common in cellular base station technology, where you must very accurately coordinate frequency (and time), to be able to use the (billions of euros) licenses for the limited spectrum you've got most efficiently – avoid the guard band between you cell's &quot;own&quot; band and the neighboring cell, as well as minimize frequency-error induced losses in transmission.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;GPS-disciplined oscillators&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Thus, in the professional world, WWVB and similar things are pretty much forgotten, since the signal simply is too narrowband to give you a good frequency and timing estimate within short time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find a lot of these modules on the surplus/used market – Trimble GPS comes to mind, for example – but you can also build such things yourself:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://opendigitalradio.org&quot; rel=&quot;noreferrer&quot;&gt;Opendigitalradio&lt;/a&gt; project (a project to establish broadcasting systems for digital audio broadcasting), or rather &lt;a href=&quot;http://mpb.li&quot; rel=&quot;noreferrer&quot;&gt;Matthias HB9EGM&lt;/a&gt; himself, has built a &lt;a href=&quot;http://www.opendigitalradio.org/lea-m8f-gpsdo&quot; rel=&quot;noreferrer&quot;&gt;GPSDO&lt;/a&gt;: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lwHcI.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lwHcI.jpg&quot; alt=&quot;ODR GPSDO&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aside from the uBlox LEA-M8F GPS receiver, reference clock + PPS generator module, there's barely anything on that board – a chip to regulate the supply voltage, and one to protect against ESD if one decides to solder on the USB debugging plug. Then, one buffer for 30.72 MHz (or configurable frequency, IIRC) and PPS each.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't know if it'll need special communication via the serial port headers soldered on below to start (don't actually think so!), but these could be trivially supplied using just any $5 USB-to-TTL adapter out there.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Why are those more expensive than the typical GPS module?&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Note that the LEA-M8F is much more expensive than your average GPS module, just because it's also supplying a reference frequency, not only location and PPS. I know that people also simply use digital PLLs (i.e. counters) and VCOs to generate reference clocks from the PPS signal – it's easy: I count the oscillations between two rising PPS edges (there's a lot of microcontrollers that can do that in hardware for you, without any need for running a counter in software). If it's higher than it should be, lower the control voltage to the VCO, and vice versa. Of course, the better your VCO gets, and the better you filter that control voltage, and the smartser you get at calculating the adjustment, the less overshoot and beat frequency you'll have.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means that if you don't need the speed at regulation and the full accuracy that a proper GPSDO can give you, a simple GPS receiver that gives you only a PPS can also be used as a frequency standard. About it's quality compared to WWVB, see the next section.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Comparison of even cheapest GPS-based solution to what you can achieve using WWVB&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;But: if you can leave your microcontroller + GPS running all day, have a good place to put your GPS antenna (i.e. any roof) and thus your oscillator can have all time in the world to reach a stable frequency, well, pretty sure that $10 in hardware will give you a better frequency standard than most WWVB receivers; leave alone the timing accuracy, which is (really) laughable in WWVB: &lt;br&gt;&#xA;GPS specifies some +- 50 ns accuracy, whereas you're free to calculate which SNR you'll need to achieve that in a receiver that has maybe 100 Hz of bandwidth. Hint: It's a lot of SNR; the diagrams you find online for WWVB act as if the edge of the PPS are &quot;straight up&quot;, of course, that's physically/mathematically impossible within limited bandwidth, so these edges are very sloped actually, and to get a reliable timing estimate, you'd have to &quot;count the second&quot; when you cross a very exact voltage threshold – but noise will make these slopes &quot;jiggly&quot;, and thus, you'll need to average enough of these crossing times to get a good estimate. GPS isn't &lt;em&gt;that&lt;/em&gt; different there, but the bandwidth is much higher, so that each PPS is already the result of quite a lot of averaging. &lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Commercially availability of GPSDOs&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;As said above, such devices are &lt;em&gt;necessary&lt;/em&gt; for cellular infrastructure – and there's a lot of demand for that, so there's company specializing in such devices, Trimble, or &lt;a href=&quot;http://www.jackson-labs.com&quot; rel=&quot;noreferrer&quot;&gt;Jackson Labs&lt;/a&gt; for example.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Observation/Correction based approach&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;also known as: give me a lousy clock, but tell me its error.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A completely different approach can be taken if you've got a device from which you can extract the mixing frequency (base): There's tools like &lt;a href=&quot;https://github.com/ttsou/kalibrate&quot; rel=&quot;noreferrer&quot;&gt;kalibrate&lt;/a&gt; (I think that's even shipped with some Linux distros!) with which you can just scan the frequencies on which GSM works, and estimate the GSM &quot;carrier frequency&quot; (it's a tiny bit more complicated, but in essence it's just estimating a carrier), &lt;em&gt;based on your device's inaccurate clock&lt;/em&gt;. &lt;br&gt;&#xA;Now, GSM is cellular, and is, you guess it, frequency-based off GPS. You use those estimates to measure the error of your receiver's frequency, and thus, you can now just incorporate that relative error (e.g. &quot;the frequency is off by -0.0008%&quot;) to just adjust the frequency you configure e.g. your classical transceiver to, if you base it off the same reference frequency.&lt;br&gt;&#xA;I've not done it, but if you have a (modified) RTL-SDR dongle with a slightly more stable oscillator (which is ... not hard to achieve), you could add a high-z-input buffer to that oscillator, modify Kalibrate to work with the RTL-SDR, and use the estimated error. You'd have a &quot;correctable&quot; 28.8 MHz oscillation – which &lt;em&gt;can&lt;/em&gt; be extremely helpful, especially when you consider that there's a lot of very flexible LO synthesizers, which you could feed with 28.8 MHz and use to generate a Phase-locked 10 MHz (or 20 MHz, or 2.4 GHz or, really, whatever rationally related frequency) directly from that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a whole bunch of so-called &lt;em&gt;clock nuts&lt;/em&gt; (I call them like that, because the only two I personally know call themselves such) that specialize in having good frequency and time standards. If that's your thing: Go for their community ;)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="8717" LastEditDate="2018-09-04T12:36:33.037" LastActivityDate="2018-09-04T12:36:33.037" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11837" PostTypeId="1" AcceptedAnswerId="12453" CreationDate="2018-09-05T14:09:54.213" Score="2" ViewCount="109" Body="&lt;p&gt;I have an [clone of] an Icom OPC-478 programming cable for my IC-208H. I thought I read that I can use that same cable to do CI-V with my IC-706 if I can find an 1/8&quot; mono (male) to 1/8&quot; stereo (female) adapter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I understood correctly, the OPC-478 has a TRS with audio on T, data on R and ground on S, whereas CI-V is just a TS with data on T and ground on S.  Do I have it right?  &lt;/p&gt;&#xA;" OwnerUserId="9974" LastEditorUserId="76" LastEditDate="2018-09-05T16:22:53.317" LastActivityDate="2018-12-21T15:06:19.983" Title="Using an OPC-478 programming cable for CI-V" Tags="&lt;connectors&gt;&lt;icom&gt;&lt;audio-interface&gt;&lt;computer-control&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11838" PostTypeId="2" ParentId="5387" CreationDate="2018-09-06T09:22:32.870" Score="2" Body="&lt;p&gt;Elmering a new ham on this subject suggests to me that you might want to tweak your description. Specifically, an SSB signal is not typically derived from an AM signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest form of amplitude modulation is &quot;on-off keying&quot; - simply turning a carrier wave on and off. The spectrum of such a signal includes the carrier plus sidebands at the keying rate. We hams refer to this as &quot;CW.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you smoothly change the amplitude of the carrier wave, rather than just switching it on and off, you get a similar but more complex result because &lt;em&gt;varying&lt;/em&gt; the carrier amplitude is more complex than simply turning it on and off. Still, the result comprises spectra at the frequency of the carrier and sidebands that correspond to the modulating signal. This is &quot;AM.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The type of SSB generation you describe is referred to as the &quot;filter&quot; method. It does not begin by generating an AM signal. Instead, it begins by &lt;em&gt;multiplying&lt;/em&gt; together the carrier wave and the modulating audio signal in a circuit called a balanced modulator. The resulting spectra comprise &lt;em&gt;only&lt;/em&gt; the sidebands - the carrier is cancelled in the multiplication. The sideband filter only has to attenuate the unwanted sideband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An SSB/CW receiver uses a &quot;product detector&quot; to recover the sideband information, whether that information is from discrete on-off keying or from continuous modulation. (Note how the word &quot;product&quot; reminds us of &quot;multiplication.&quot;) The product detector performs the same function as the balanced modulator. but instead of producing RF from a carrier and baseband inputs, it produces baseband output by multiplying RF input with a carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an aside, a &quot;balanced mixer&quot; can be used as a balanced modulator. The multiplication process is the same.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-09-06T09:22:32.870" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11839" PostTypeId="2" ParentId="6787" CreationDate="2018-09-06T09:55:38.550" Score="4" Body="&lt;p&gt;SSB comprises both amplitude and phase components. For any instant, plot the baseband signal's Q (quadrature) and I (in-phase) components on the y-axis and x-axis, respectively. The amplitude is the length of the vector from the origin to this (I,Q) point. The phase is the angle between this vector and the x-axis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PE1NNZ modulates the amplitude of the clock driver by changing its drive strength. Only eight levels are available, corresponding to just 3 bits of audio resolution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PE1NNZ is only able to modulate the frequency of the clock generator. Instantaneous frequency is the time derivative of instantaneous phase. PE1NNZ takes the time derivative of the phase by taking differences of successive phase calculations and changing the frequency of the clock generator accordingly.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2018-09-11T04:02:54.157" LastActivityDate="2018-09-11T04:02:54.157" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11840" PostTypeId="2" ParentId="5108" CreationDate="2018-09-06T10:29:48.853" Score="2" Body="&lt;p&gt;SSB is typically demodulated by a &quot;product detector&quot; which, as its name implies, &lt;em&gt;multiplies&lt;/em&gt; the incoming RF signal by a carrier signal. If the carrier signal is at the frequency which was used to create the SSB signal in a &quot;balanced modulator&quot; - a multiplying frequency mixer - the product detector output is the demodulated sideband energy.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-09-06T10:29:48.853" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11842" PostTypeId="5" CreationDate="2018-09-06T12:58:14.887" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2018-09-06T12:58:14.887" LastActivityDate="2018-09-06T12:58:14.887" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11843" PostTypeId="4" CreationDate="2018-09-06T12:58:14.887" Score="0" Body="Questions specific to rules, regulations, and practices in India." OwnerUserId="8713" LastEditorUserId="8713" LastEditDate="2018-09-06T14:58:16.057" LastActivityDate="2018-09-06T14:58:16.057" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11844" PostTypeId="5" CreationDate="2018-09-06T12:58:59.700" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2018-09-06T12:58:59.700" LastActivityDate="2018-09-06T12:58:59.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11845" PostTypeId="4" CreationDate="2018-09-06T12:58:59.700" Score="0" Body="Questions specific to rules, regulations, and practices in European countries." OwnerUserId="8713" LastEditorUserId="8713" LastEditDate="2018-09-07T12:59:39.047" LastActivityDate="2018-09-07T12:59:39.047" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11847" PostTypeId="1" CreationDate="2018-09-06T15:59:36.430" Score="4" ViewCount="1025" Body="&lt;p&gt;Will putting a ferrite bead or beads near (but not at) the end(s) of a wire antenna electrically lengthen or shorten it?  (lower or raise its resonant frequency)?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-12-19T14:48:59.080" Title="Ferrite beads on a wire antenna?" Tags="&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11848" PostTypeId="2" ParentId="11847" CreationDate="2018-09-06T16:57:51.367" Score="4" Body="&lt;p&gt;Lengthen. The bead increases the inductance, similarly to a loading coil. Near the ends the current is low, so the effect is diminished compared to the same coil near the feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wouldn't recommend it for a transmitting antenna. Ferrites have significant loss, and may saturate. Non-linear components are definitely not something you want in a transmitting antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-09-06T16:57:51.367" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11850" PostTypeId="1" AcceptedAnswerId="11861" CreationDate="2018-09-06T21:07:40.667" Score="7" ViewCount="473" Body="&lt;p&gt;I've been studying and building test circuit for actually several YEARS now, so far with no success. It sounds ridiculous but it's true.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I feel like I have a good understanding or RLC circuits, I can calculate phase shifts and impedances etc., I am good with simplifying series/parallel combination circuits, good with transistor and NFET amplifiers, and good in working out input and output impedance (in this case not a good grasp of complex impedance).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is I feel like I need a real Elmer at this stage to help me put it all together, on my own I'm getting nowhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The trouble is that the hobby has changed, courses have changed... all the courses I looked at teach legality, legislation, etc. While this may be very important for end users to follow these guidelines and be licensed to do so for me that's not where the 'passion' of the hobby is.I'm just trying to receiver but not transmit so I won't be annoying anyone (although I know some receivers leak RF from their LO).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that I'm in a remote area so it's unlikely I'll find someone locally to learn from. Is anyone aware of online resources where I can get that sort of learning? I don't need links to the legal and legislative aspect of the hobby, that there's already tons of, I'm asking people who are passionate about electronics, not law.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT undone for clarity&lt;/p&gt;&#xA;" OwnerDisplayName="user13171" LastEditorDisplayName="user13171" LastEditDate="2018-09-16T00:45:27.310" LastActivityDate="2018-09-16T00:45:27.310" Title="Learning RF electronics" Tags="&lt;receiver&gt;&lt;electronics&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11851" PostTypeId="1" AcceptedAnswerId="11854" CreationDate="2018-09-06T21:18:12.990" Score="5" ViewCount="229" Body="&lt;p&gt;I do not understand.  Is ham radio the only legal way to broadcast on shortwave radio?  I mean for a &quot;regular&quot; person, not a million dollar radio station.  I saw lots of shortwave broadcasting equipment, but it all looks like it is illegal to use because of the FCC rules.  As far as I know, LPFM isn't an option, and I am not interested in a CB.  This is for hobby interests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:  Is amateur radio the same as ham radio?  I saw a lot of references to AR on here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In USA.&lt;/p&gt;&#xA;" OwnerUserId="13182" LastEditorUserId="9493" LastEditDate="2018-09-07T07:51:38.670" LastActivityDate="2018-09-07T07:51:38.670" Title="Is HAM the only non-criminal/civil broadcasting a person can do that doesn't own a shortwave radio station?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="3" CommentCount="10" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11852" PostTypeId="2" ParentId="8940" CreationDate="2018-09-06T21:19:39.977" Score="3" Body="&lt;p&gt;In an effort to find some hard data, I wrote to Dr Carl Luetzelschwab, K9LA. Carl responds:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;The main reason is because we've basically been under solar minimum conditions for two years - and it looks like it's going to continue. We were spoiled by [&lt;em&gt;shorter - Ed.&lt;/em&gt;] solar minimum durations prior to the minimum between Cycle 23 and 24.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The graph Carl attached to his response summarizes the data:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5cLBl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5cLBl.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-04-04T01:49:24.050" LastActivityDate="2019-04-04T01:49:24.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11853" PostTypeId="1" CreationDate="2018-09-06T21:39:27.277" Score="3" ViewCount="100" Body="&lt;p&gt;Is there an established way of scanning frequencies, while avoiding listening to digital signals or static? For example, is there a scanner on the market which will allow you to blacklist a specific frequency? Or a way of blacklisting with some SDR software? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd prefer this over adding a bunch of pre-coded frequencies, as these typically are not up to date on Radioreference. It's also not as fun :). &lt;/p&gt;&#xA;" OwnerUserId="13184" LastEditorUserId="13184" LastEditDate="2018-09-06T21:45:49.973" LastActivityDate="2018-12-14T04:03:30.603" Title="How to scan while avoiding digital/noise frequencies?" Tags="&lt;digital-modes&gt;&lt;receiver&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11854" PostTypeId="2" ParentId="11851" CreationDate="2018-09-06T22:02:01.190" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;is HAM the only legal way to broadcast on shortwave radio?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. An Amateur Radio (&quot;ham&quot;) license doesn't even allow you to broadcast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In most jurisdictions, including the US-American one, amateur radio is restricted to directed communication.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I saw lots of shortwave broadcasting equipment, but it all looks like it is illegal to use because of the FCC rules.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, for broadcasting you'll need a license. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;This is for hobby interests.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The amateur radio license is meant for exactly that: Hobby &lt;em&gt;communications&lt;/em&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's generally the tendency to not allow &lt;em&gt;hobby broadcasting&lt;/em&gt;, because: broadcasting implies that a single station&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;reaches a lot of receivers at once,&lt;/li&gt;&#xA;&lt;li&gt;doesn't limit itself in occupancy and&lt;/li&gt;&#xA;&lt;li&gt;can't (on short term) share the medium.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It's logical that any part of the spectrum would be instantly &quot;full&quot; if regulatory bodies like the FCC allowed broadcasting without a license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I'm afraid, if you really want to &lt;em&gt;broadcast&lt;/em&gt; and not &lt;em&gt;directedly communicate with someone specific&lt;/em&gt;, you'll have to get a commercial license for the band you want to use, pretty much anywhere on this planet (including satellites in orbit).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-09-06T22:02:01.190" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11855" PostTypeId="2" ParentId="11851" CreationDate="2018-09-06T22:30:51.437" Score="6" Body="&lt;p&gt;For clarity, I am splitting your question &quot;Is HAM the only legal way to broadcast on shortwave radio?&quot; into two parts:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;em&gt;Is&lt;/em&gt; ham radio a legal way to broadcast on shortwave from the USA?&lt;/li&gt;&#xA;&lt;li&gt;Under what circumstances &lt;em&gt;could&lt;/em&gt; I legally do shortwave broadcasts?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Amateur (or, &quot;ham&quot;) radio is &lt;strong&gt;not&lt;/strong&gt; a legal way to broadcast on shortwave. The United States &lt;a href=&quot;https://www.gpo.gov/fdsys/pkg/CFR-2009-title47-vol5/pdf/CFR-2009-title47-vol5-part97.pdf&quot; rel=&quot;noreferrer&quot;&gt;FCC's rules for amateur radio&lt;/a&gt; (which through ITU agreements tend to be similar to other countries' rules) are very specific and clear on broadcasting:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;An amateur station shall not engage in any form of broadcasting, nor may an amateur station transmit one-way communications except as specifically provided in these rules; nor shall an amateur station engage in any activity related to program production or news gathering for broadcasting purposes, […]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So if you want to be the next &lt;a href=&quot;https://www.washingtonpost.com/local/obituaries/art-bell-mysterious-narrator-of-the-american-nightscape-is-dead-at-72/2018/04/14/b6f2b278-4015-11e8-974f-aacd97698cef_story.html&quot; rel=&quot;noreferrer&quot;&gt;Art Bell&lt;/a&gt;, an amateur radio license is not your ticket — though a ham hobby could be a great introduction to the technology.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That being said, I'm not sure what would legally prevent &lt;em&gt;two&lt;/em&gt; hams mutually arranging a frequent &quot;net&quot; and using it for talk show banter, using radio settings that &quot;happened&quot; to be compatible with shortwave receivers. There'd certainly be questions relating to &quot;minimum transmitter power necessary to carry out the desired communications&quot;, limitations on &quot;transmissions to a different country&quot;, and remaining in &quot;accordance with good amateur practice&quot;. And of course no cussing, vulgaraties, or music/jingles. But as far as I can tell, there's no &lt;em&gt;written&lt;/em&gt; requirement that would prevent &lt;a href=&quot;https://www.urbandictionary.com/define.php?term=Ragchew&quot; rel=&quot;noreferrer&quot;&gt;rag chews&lt;/a&gt; from being interesting to listen to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more proper route, however, would be to either get a &lt;a href=&quot;https://www.fcc.gov/general/high-frequency-broadcasting&quot; rel=&quot;noreferrer&quot;&gt;HF broadcasting license&lt;/a&gt; which would require a sizable commitment, or explore &lt;a href=&quot;https://www.fcc.gov/media/radio/low-power-radio-general-information&quot; rel=&quot;noreferrer&quot;&gt;low power&lt;/a&gt; options for small scale fun.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2018-09-06T22:30:51.437" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11856" PostTypeId="1" CreationDate="2018-09-06T22:58:37.223" Score="8" ViewCount="1912" Body="&lt;p&gt;While studying for his U.S. General class license, my son wondered about the &quot;balanced modulator&quot; referred to by a few questions in the FCC pool.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quoting KB6NU's &lt;a href=&quot;https://www.kb6nu.com/2015-general-class-study-guide-section-g7c-receivers-and-transmitters-filters-oscillators/&quot; rel=&quot;nofollow noreferrer&quot;&gt;General Class study guide&lt;/a&gt; to give a sense of the two questions:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Filters are also used in amateur radio transmitters. A filter is used to process signals from the balanced modulator and send them to the mixer in a single-sideband phone transmitter. (G7C01) A balanced modulator is the circuit used to combine signals from the carrier oscillator and speech amplifier and send the result to the filter in a typical single-sideband phone transmitter. (G7C02)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Coming from the SDR world, I'm much more familiar with &quot;mixers&quot; being used for frequency conversion, and I tend to think of SSB from that perspective (i.e. raw baseband that's simply been upconverted). Other test pool questions want me to conceive of SSB as generated by an AM signal that's somehow had its carrier [sharply!?] filtered out afterward. Neither of those sounds like this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short, the term &quot;balanced modulator&quot; is unknown to me (despite working through the same exam pool a few years ago ;-] ) and my initial web searches on a small screen didn't turn up very much information either. Among Google results on a bigger screen today, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Armstrong_phase_modulator&quot; rel=&quot;nofollow noreferrer&quot;&gt;Armstrong phase modulator&lt;/a&gt; does come up but that seems more for FM than SSB, and, as far as I can tell, only &lt;em&gt;uses&lt;/em&gt; a balanced modulator rather than explaining what one is….&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the core principle(s) of a balanced modulator? What is the significance of them being &quot;balanced&quot;? In broad strokes how would one design/build one in practice? Are they still used in commercial SSB transceivers and/or modern kit radio circuitry?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="9844" LastEditDate="2018-09-10T04:23:31.050" LastActivityDate="2018-09-10T04:23:31.050" Title="What exactly is a &quot;balanced modulator&quot;?" Tags="&lt;modes&gt;&lt;ssb&gt;&lt;mixer&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11857" PostTypeId="2" ParentId="11856" CreationDate="2018-09-06T23:15:57.393" Score="5" Body="&lt;p&gt;Partial answer, because I don't know the actual electronics theory, but I hope which will help make progress towards a complete answer: A balanced modulator &lt;strong&gt;is a mixer&lt;/strong&gt; with a particular feature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basic analog mixer designs tend to include the carrier in the output, whereas a balanced modulator is one which is designed to &quot;suppress&quot; the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, if you feed an audio signal and a RF carrier into a mixer that is not &quot;balanced&quot;, you will get AM output (possibly with unstable carrier power level?), whereas a balanced modulator will give you DSB-SC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're generating SSB by filtering the output of a mixer fed by the audio signal, this means that you only need to filter out the opposite sideband rather than also the carrier — twice the frequency difference and hence less demanding on the filter.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-09-06T23:25:00.777" LastActivityDate="2018-09-06T23:25:00.777" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="11858" PostTypeId="2" ParentId="11856" CreationDate="2018-09-07T02:36:31.560" Score="6" Body="&lt;p&gt;To put it simply, a balanced modulator is a mixer which has two inputs and two outputs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The outputs are (input1 + input2) and (input1 - input2). So, if the inputs are 100kHz and 1kHz, the outputs are 101kHz and 99kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For transmitting: If the inputs are 1MHz and (voice), the outputs are the lower sideband of the voice and the upper sideband of the voice, centered on 1MHz. Effectively a &quot;double sideband, suppressed carrier&quot; signal of voice modulated on a 1MHz (suppressed) carrier. One of the sidebands can be filtered out (if you want to transmit USB or LSB) when it's transmitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For receiving: Working the other way, you mix the received single sideband with a 1MHz signal, to generate enough of the original voice to be intelligible (since the lower and upper sidebands are mirrors of each other, you only need one to rebuild the original signal, it's just slightly trickier to tune by ear).&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-09-07T02:36:31.560" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11859" PostTypeId="2" ParentId="11851" CreationDate="2018-09-07T07:45:31.170" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;the only legal way to broadcast on shortwave radio? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;We need to talk about alternatives!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're looking into shortwave because he wants to cover a large geographical area, then simple things like web radio could very easily be the solution – at least if the audience has internet access.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Considering current price-per-kB in the US for prepaid cards, you'll get pretty far even with the smallest packages!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's run a few numbers, here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6Mh9I.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6Mh9I.png&quot; alt=&quot;comparison table&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First takeaway: the bitrate you'll need for pretty epic sound quality using a &quot;every mobile phone and PC has that installed already&quot; codec &lt;em&gt;easily&lt;/em&gt; fits through somewhat decent 2G cellphone data. Cell phone coverage in the US isn't all that bad – you can probably reach of your audience that way!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As soon as you go for shortwave-comparable qualities, things get &lt;em&gt;really&lt;/em&gt; easy to transport across the internet. For reference, I've added the last column, which shows you how much internet transfer volume you'd have to have to listen to eight hours of your station every day of a month. It's rather unlikely that, as a hobby, you'll even be transmitting 8 hrs/day of useful programming, but if you did, that's how much monthly volume you'd want your audience to spend on you :) Corollary: if you've got but a dozen to a hundred occasional listeners, you could even completely save on RF equipment and possibly necessary licenses, and invest that in data SIM cards that you hand out to your listeners so that they can listen to you over the internet, &lt;em&gt;for a pretty long time&lt;/em&gt;, depending on how much power you thought to push out of your antenna.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-09-07T07:45:31.170" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11861" PostTypeId="2" ParentId="11850" CreationDate="2018-09-08T10:30:53.950" Score="4" Body="&lt;p&gt;I am always happy to hear of someone that is trying to better their understanding and education. Congratulations and welcome.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I agree that it is nice to have someone to personally talk with but let's start with some basics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To do proper prototyping and to understand where you are going wrong with RF circuits, you need some basic test equipment. A DVM, a wide bandwidth oscilloscope, an RF generator, a variable power supply, and an RLC meter are the minimum. Then you need a nice assortment of components from which you can draw - resistors, capacitors, transistors, standard IC's, etc. You also need a good library of technical information - manufacturer data sheets, text books, and on-line help are rich sources of information with the catch that many Internet sources can send you down the wrong path. So without trying to sound old school, some good books are essential. Consider publications from the ARRL, such as the Handbook, or from RSGB as good sources of practical, RF information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are serious about RF design, you need to tackle complex math. It really isn't too difficult once you get a few basics down - or as I have told students - it really is not that complex once you master the basics! Excel now has fairly good complex math support so that you can play with basic concepts and formulas to confirm or re-enforce your learning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a similar vein, you need to be comfortable with logarithmic math. RF electronics easily achieves a system power gain of 1,000,000 and more. It gets tiring to keep writing all of those zeros, decimal places, and exponents. The dB should be your best RF friend.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you haven't already done so, assemble a few RF kits to deepen your understanding. A receiver, a transceiver, or even a kit for some test gear that you need are great ways to learn by hands-on observation and experimentation. Start with a few simple kits and work your way up to more complex kits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An alternative to kits is to build circuits based on the datasheet examples from IC and transistor manufacturers. Many times their sample circuits are nearly complete designs that allow you to learn from the assembly and testing process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have a few kits under your belt, come up with a usable, practical circuit that you would like to design. Having a purpose for the circuit provides more motivation and clarity than simply 'trying something'. But like the kits, be realistic with your first few ventures. Don't shoot for a DSP receiver but rather something like an RF field strength meter. Then work your way up to the big goal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't hesitate to use this forum to ask questions. There are a lot of bright and experienced people here that are more than willing to help. So do some research and if you come up dry or uncertain, come here for answers (but not opinions).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may find some local resources in the form of 'maker' events or ham radio clubs in your area. Attend ham radio/electronic 'swapfests' in your area. You can buy parts for your parts draws cheaply and often meet like minded people. Many university professors are more than willing to take a non-student under their wing when they see a truly motivated individual. I got my start in electronics in grade school thanks to a university professor who was willing to correspond with me (yes, the pre-email era) on digital circuit topics. My first question for him was to ask how a JK flip flop worked. Thanks to his generosity, I had designed and built a 50 MHz frequency counter by my freshman year in high school. It was a powerful lesson for me and I have since followed in his path. I was also blessed to have a great ham radio mentor, Walt Fitting - W9OI, who was a constant source of inspiration and motivation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, if all else fails, seeing that you are in New Zealand, I would be willing to come down for say a month or two to personally tutor you. Or so my wife tells me as she compiles her travel itinerary. Wait... I am getting an update... apparently it will take 3 months to properly tutor you.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-08T11:09:32.960" LastActivityDate="2018-09-08T11:09:32.960" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11863" PostTypeId="2" ParentId="11856" CreationDate="2018-09-08T13:34:18.867" Score="2" Body="&lt;p&gt;A balanced modulator is a kind of mixer. Specifically, it's one that works in all four &quot;quadrants&quot;, that is combinations of each of the two input voltages being positive or negative. Along with that come certain other expectations about the device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could draw a graph of the two input voltages $v_1$ and $v_2$, and it would look like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/j3gc0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/j3gc0.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any possible input to the mixer at an instant is a point somewhere on this graph. If both voltages are zero, that's the point in the middle. As $v_1$ increases, we go up. As $v_2$ increases, we go right.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's consider simple amplitude modulation where $v_1$ is the baseband signal, and $v_2$ is the carrier, at 50%, 100%, and 150% modulation. On the left for each case is the ideal mixer output, and on the right a shaded region showing the region in which the inputs will fall on the graph under these conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FLDEz.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FLDEz.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 50% modulation, the baseband signal is always significantly more than zero, so only the upper parts of the first and second quadrant are encountered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 100% modulation, the baseband signal touches zero but is never negative, so the first and second quadrant are used all the way down to the origin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 150% modulation, the baseband signal goes negative, which means an inversion of the output as operation enters the 3rd and 4th quadrants.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A mixer which can operate in all four quadrants, producing the inverted signal as would be expected of an &quot;ideal&quot; mixer where $v_\text{out} = v_1 \times v_2$, is a balanced modulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some mixers can't produce $v_\text{out} = v_1 \times v_2$ in all four quadrants. They may clip the output rather than inverting it when crossing into the 3rd and 4th quadrants:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fpX1U.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fpX1U.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such mixers are not balanced modulators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why does this matter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider: the difference between 50% and 100% modulation in AM is that the latter has a decreased carrier power in relation to the sidebands. As the modulation increases beyond 100%, the sideband power continues to increase and the carrier power decreases. When the modulating signal is &quot;balanced&quot;, meaning it spends as much time being positive as it does negative, the carrier power reaches zero and you're left with just the sidebands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For generating AM this is no good, but for SSB it's great since there's no need to somehow remove the carrier. Only the unwanted sideband needs to be removed, and that can be done with a sharp filter, or by combining with a second modulator but at a 90 degree phase shift.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-09-08T13:34:18.867" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11865" PostTypeId="1" CreationDate="2018-09-09T13:39:19.290" Score="7" ViewCount="1633" Body="&lt;p&gt;For a transmitting dipole antenna, its length is important. If it is close to half the wavelength, it will be efficient and most of the input power will be radiated. &#xA;How important is the length of dipole in case of receiving antenna? Will a dipole of given length as inefficent as receiver as a transmitter? As far as receiving is concerned, how inefficient will a $\lambda$/10, $\lambda$\100 and $\lambda$\1000 dipole antenna relative to a $\lambda$\2 dipole?&lt;/p&gt;&#xA;" OwnerUserId="13204" LastActivityDate="2020-04-02T17:06:19.970" Title="Efficiency of short dipole receiving antenna" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;dipole&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11866" PostTypeId="2" ParentId="11865" CreationDate="2018-09-09T14:52:00.910" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Will a dipole of given length as inefficent as receiver as a transmitter?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, antennas are reciprocal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's the common theme in ham radio that &quot;matching your antenna for TX is more important than for RX&quot;, which is based on the fact that 1/2 of the power put out by your transmit amplifier might be very much and damage your amplifier if reflected back, but:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a pure link perspective, it doesn't matter whether you lose x dB at the transmitter or at the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While one could reasonably give you an answer to your &quot;what's the efficiency of a $\frac\lambda{10}$ dipole&quot;, asking that question $\frac1{1000}$ of the wavelength makes no sense, since everything is an (potentially extremely ineffective) antenna for any wavelength; if you need your antenna to be $\frac1{1000}$ of the wavelength in size, you simply don't use a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, when you cross three orders of magnitude, typically, physical effects that play no role at one wavelength become dominant. So, the questions related to high wavelength-to-antenna-size questions can only actually be answered sensibly when you say which bands you actually aim for. The methods and elements from which you can build a 200m antenna simply aren't the same as for 10 GHz...&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-09-09T14:52:00.910" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11867" PostTypeId="2" ParentId="11865" CreationDate="2018-09-09T15:35:57.167" Score="3" Body="&lt;p&gt;As antenna geometry (including length) changes, so does its radiation gain pattern in 3D space. According to reciprocity, the pattern of receive efficiency has an equivalent change.  So the receive efficiency also depends on the direction of the RF source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reciprocity implies that, just as one could increase transmit power to compensate for a less efficient transmit antenna, one could increase receiver gain to compensate for a less efficient receive antenna.  However, even if both the received signal and received noise roughly scale together, and thus can be compensated for in a receiver by gain, at some point the lower signal level from a less efficient antenna will drop below the thermal noise (and other internal and nearby RF noise sources) of the receiver front-end or LNA, and gain won't help (the S/N).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-09-09T22:11:11.663" LastActivityDate="2018-09-09T22:11:11.663" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11869" PostTypeId="2" ParentId="11865" CreationDate="2018-09-09T18:22:13.460" Score="8" Body="&lt;p&gt;The efficiency of any antenna has a direct impact on the gain of the antenna. The gain of the antenna equally effects transmit and receive - a characteristic known as reciprocity. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The highest gain dipole is a 10/8 wave dipole. When you begin to shorten that dipole, its gain drops. When the dipole becomes very short (&amp;lt;&amp;lt;1/10 &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;) it is called an infinitesimal dipole. Its gain drops significantly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To see what why the gain of the dipole is dropping, we need to understand the primary factors that make up antenna gain (in linear form):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{Gain} = \text{Directivity} \times \text{Efficiency} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The directivity of the dipole antenna does not change a lot because of its size. For example, a 1/2 wavelength dipole has a directivity of 1.64 and an infinitesimal dipole has a directivity of 1.5.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The major factor impacting gain, in the case of this dipole question, is efficiency. Efficiency is defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\text{Efficiency}=\frac{R_r}{R_r+R_l}  \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where R&lt;sub&gt;r&lt;/sub&gt; is the radiation resistance and R&lt;sub&gt;l&lt;/sub&gt; is the resistive losses in the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation resistance is the dominating factor in most cases. A 1/2 wave dipole in free space has a radiation resistance of 72 ohms. A 0.05 wavelength dipole has a radiation resistance of only 0.49 ohms. To see the effect this has, let us assume that the losses in the antenna are simply related to the length of wire. If the 1/2 wavelength antenna had say 1 ohm of losses, then the 0.05 wavelength antenna would have 0.1 ohms of losses since it is 1/10 the length of the 1/2 wave dipole. According to equation 2, this makes the efficiency of the 1/2 wave dipole 98.6% and the efficiency of the 0.05 wavelength dipole 83.1%. While this is not yet the complete efficiency story, if we pause here to plug these numbers into equation 1, the gains so far are are 1.63 (2.12 dBi) and 1.25 (0.98 dBi).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To complete the efficiency picture we need to look not just at the antenna but rather at the antenna system. This includes any matching network and transmission lines. For the latter, the calculations are fairly straight forward and it is length and frequency dependent so I will not address that here. But the matching network warrants some scrutiny.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The goal of the matching network is to transform the feedpoint impedance of the antenna into an impedance that minimizes the losses in the transmission line (when viewed from a transmitting perspective). In the case of a 1/2 wavelength dipole, as it is brought close to earth, its feedpoint impedance nearly matches the impedance of common coaxial cable (50 ohms) so no matching network is needed. Thus we can assign 100% efficiency to the matching network in this case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The infinitesimal dipole is very short compared to a wavelength so its feedpoint impedance is dominated by capacitive reactance while the real part of its impedance is a fraction of an ohm (0.49 ohms in the earlier example). The matching network will therefore contain sufficient inductive reactance to neutralize the capacitive reactance and it will contain other reactive or transformative components to raise the real part of the impedance by a factor of 100 or so. Analyzing the efficiency of such a network requires a significant effort but efficiencies in the 20% range or less are not uncommon. Using this coarse estimate, this introduces another 7 dB or so of losses for the 0.05 wavelength infinitesimal dipole bringing its gain to 0.25 (-6.02 dBi).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To wrap up this analysis consider that the gain difference between the two antennas in this example is 8.17 dB. If 100 watts into the 1/2 wavelength antenna would barely allow another station to hear you, you would need to use more than 656 watts into the 0.05 wavelength dipole to achieve the same result. And to receive the other station, because of reciprocity, they would need to increase their power by nearly 7 times or you would need to find a receiver with 2.6 times more sensitivity (since sensitivity is expressed in field units such as &lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;V and therefore the square root of power).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And finally, the radiation resistance of other lengths of infinitesimal dipoles is related by approximately the square of their fractional wavelength. So a 0.005 wavelength dipole has 1/100 the radiation resistance of our 0.05 wavelength dipole. Noting that the resistive losses only went down by 1/10,  if all other things are equal, and without considering the matching network efficiency, the antenna efficiency has dropped to 33%.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="218" LastEditDate="2019-11-10T16:49:36.873" LastActivityDate="2019-11-10T16:49:36.873" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11872" PostTypeId="1" AcceptedAnswerId="11878" CreationDate="2018-09-10T11:12:30.933" Score="9" ViewCount="635" Body="&lt;p&gt;Firstly, feel free to move this to Electronics SE if it's not on-topic, but it's strongly related to ham radio and RF circuitry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reading Hayward's classic &quot;&lt;em&gt;Solid State Design for the Radio Amateur&lt;/em&gt;&quot; and looking for inspiration, I came across the following push-pull PA design that I didn't quite understand (Chapter 4, Pg 62).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cg816.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cg816.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have a problem with T1 and T2, &lt;strong&gt;it's T3 and T4 I'm struggling with&lt;/strong&gt;.  T1 is a straightforward 4:1 impedance transformer; it doubles the current at the output and so &quot;looking back into&quot; T1 the source appears to have 4 times less impedance.  No problems there.  T2 has the dotted secondary tied to ground and so the current flowing into the dot (transformer action) leaves the other end of the secondary negative. Now we have anti-phase signals of equal amplitude at the transistor bases, turning each transistor on and off alternately.  Again no problems there, it's straightforward push-pull action.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But here's where the wheels fall off for me! &lt;strong&gt;What's the purpose of T3 (and T4 which I believe has a similar purpose)?&lt;/strong&gt; Here's what the author says: &quot;&lt;em&gt;The third core [in the input section of the amplifier] ensures that the load presented to T2 is balanced. Each transistor sees a driving impedance of 6.25 ohms&lt;/em&gt;&quot;.  I've included a hand-sketched re-arrangment of the circuit to help me understand and I can sort of see how the current produced by the full potential of the balanced signal (anti-phase peak-to-peak) is driven through one or other transistor bases.  Does this account for the halving of impedance &quot;seen&quot; by each transistor as the author says? &lt;strong&gt;But then, wouldn't this happen anyway, without T3??&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UhJyS.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UhJyS.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11875" LastActivityDate="2020-08-06T23:13:53.037" Title="What is the purpose of the transformer at the input (and output) of this RF push-pull amplifier" Tags="&lt;amplifier&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11873" PostTypeId="1" CreationDate="2018-09-10T12:13:08.003" Score="10" ViewCount="1156" Body="&lt;p&gt;How to calculate internal impedance of a dipole antenna? Its resistance has two components ie wire resistance and radiation resistance, both these can be calculated using formula. Are there formula to calculate capacitance and inductance of an antenna? Or they are calculated empirically only?&lt;/p&gt;&#xA;" OwnerUserId="13212" LastEditorUserId="9493" LastEditDate="2018-09-13T09:02:48.263" LastActivityDate="2018-10-16T20:14:37.617" Title="Are there formulae to calculate capacitance and inductance of an antenna?" Tags="&lt;antenna-theory&gt;" AnswerCount="5" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11874" PostTypeId="2" ParentId="11872" CreationDate="2018-09-11T03:59:26.767" Score="3" Body="&lt;p&gt;T4 is the collector DC feed transformer. The inductance of each side of the transformer acts as an RF choke at the amplifier's operating frequency. The antiphase connection of the windings prevents DC saturation of the core material.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By coupling the currents in the bases of Q1 and Q2, T3 is a lossless means to compensate for the wide variation in transistor parameters that are to be expected. This reduces distortion and improves stability.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-09-11T03:59:26.767" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11875" PostTypeId="2" ParentId="11873" CreationDate="2018-09-11T04:55:49.743" Score="-4" Body="&lt;p&gt;There is no formula to calculate reactance, it has to be empirically determined.&lt;/p&gt;&#xA;" OwnerUserId="13215" LastActivityDate="2018-09-11T04:55:49.743" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11876" PostTypeId="2" ParentId="11873" CreationDate="2018-09-11T05:46:51.763" Score="1" Body="&lt;p&gt;I assume you are referring to the feedpoint resistance and reactance. Stearns, K6OIK, &lt;a href=&quot;https://www.fars.k6ya.org/docs/antenna-impedance-models.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna Impedance Models&lt;/a&gt;, presented at ARRL &lt;em&gt;Pacificon&lt;/em&gt; 2004 is an excellent treatment of the subject.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that a center-fed, infinitely thin, physical half-wave dipole in free space has an impedance of 73+j42.5 ohms; many of the calculations in the reference use this as the baseline for computation.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2018-09-11T15:51:41.617" LastActivityDate="2018-09-11T15:51:41.617" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11878" PostTypeId="2" ParentId="11872" CreationDate="2018-09-11T19:59:00.653" Score="6" Body="&lt;p&gt;T4 is just this idea:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/tCYDZ.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2ftCYDZ.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes it's done this way:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/E00z0.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fE00z0.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The primary of XFMR1 is equivalent to T4 from the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since T4 provides the collector load for the transistors, it's a factor in voltage gain. For a differential-mode input, the collector currents correspond to magnetic flux in the same direction in T4, thus T4 presents a high impedance and voltage gain is maximized. For undesirable common-mode input (which could come from dissimilar gain in the transistors), magnetic flux cancels and T4 looks like a short to Vcc, minimizing voltage gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're right T3 isn't ideally necessary, but it serves to keep things balanced despite variation in components. Consider a simplified case where the load is just a pair of 10 ohm resistors that might vary by +/- 10%:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/eX2GC.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2feX2GC.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;T2 (ideally) requires that the current is equal in each of the windings, but since the resistors are not equal, the voltages across the resistors are not equal. The addition of T3 remedies the situation: in the common mode it appears as a short to ground. Thus, at the right side of T2 there will always be equal but opposite currents &lt;em&gt;and&lt;/em&gt; voltages. Or as the author puts it, T3 &quot;ensures that the load presented to T2 is balanced&quot;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-09-11T19:59:00.653" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11880" PostTypeId="2" ParentId="11873" CreationDate="2018-09-11T23:28:49.613" Score="7" Body="&lt;p&gt;A couple of minor comments on terminology. It isn't so much the &quot;internal&quot; impedance of the antenna but it is typically the &quot;feed point&quot; impedance that is of concern. This is the impedance seen where the transmission line connects to the antenna. Another common impedance of interest is the radiation resistance. This is the effective resistance attributable to converting the RF signal to a radiating electromagnetic wave. This impedance is often of interest when determining the efficiency of an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, there are many such formulas just like the ones in the answer you saw linked in the comments. From an academic and research perspective, the formulas are under constant improvement and refinement. This usually translates into more complexity in the formulas in exchange for greater accuracy or detail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most professional antenna engineers and amateur radio antenna enthusiasts have transitioned to antenna modeling software. These software packages produce extensive data such as the input impedance but also go on to produce renderings of radiation patterns and other useful information. Within an hour or so, nearly any common antenna can be extensively analyzed using such software without any knowledge of calculus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Several of these packages are available for free or on a trial basis. Here is one popular example: &lt;a href=&quot;https://www.qsl.net/4nec2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;4NEC2&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-13T06:21:53.283" LastActivityDate="2018-09-13T06:21:53.283" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11881" PostTypeId="1" AcceptedAnswerId="11884" CreationDate="2018-09-11T23:59:24.897" Score="1" ViewCount="1046" Body="&lt;p&gt;I just purchased a TYT UV-390 (Non-GPS) on Amazon.  It arrived, I unboxed it and charged it and turned it on and it's asking for a password.  The same goes if I try and read or write to it using CPS MD-UV380 v1.07.  The directions specifically say to use the 380 CPS with the 390 CPS resulting in an &quot;Incorrect model number&quot; error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've hit the Interwebs with a fury and tried suggested default passwords (00000000,77777777,99999999) and found CPS versions to remove passwords from MD-2017 and MD-380 models.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any suggestions?&lt;/p&gt;&#xA;" OwnerUserId="13222" LastEditorUserId="76" LastEditDate="2019-05-28T21:09:12.417" LastActivityDate="2019-05-28T21:09:12.417" Title="How Can I Remove a Password From a TYT MD-UV390 (Non-GPS)?" Tags="&lt;ht&gt;&lt;equipment-operation&gt;&lt;tyt&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11884" PostTypeId="2" ParentId="11881" CreationDate="2018-09-12T11:53:49.973" Score="4" Body="&lt;p&gt;Contact the Seller for technical support. Explain that the unit is not working without a password and that this was not provided with the shipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If no further support is available then consider the unit dead on arrival and start a refund and return process. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this sold through Amazon, then you do need to involve Amazon customer service. Online, you can click on &lt;code&gt;HELP&lt;/code&gt; and take it from there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Making this a community wiki as this answer was already given in comments.]&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="9493" LastEditDate="2018-09-13T04:52:19.697" LastActivityDate="2018-09-13T04:52:19.697" CommentCount="0" CommunityOwnedDate="2018-09-12T11:53:49.973" ContentLicense="CC BY-SA 4.0" />
  <row Id="11886" PostTypeId="2" ParentId="5209" CreationDate="2018-09-12T15:39:48.877" Score="1" Body="&lt;p&gt;The ID-51A plus advertises that it finds FM repeaters via GPS location. I have tried everything but it does not work as advertised. It has worked in only one location where I live but I have tried it while traveling with no luck.&lt;br&gt;&#xA;I called Icom support, they gave me some info that did not work. Very disappointing! They also state that the ID-5100A mobile does find FM repeaters but I do not trust them. I am probably not going to buy Icom in the future &lt;/p&gt;&#xA;" OwnerUserId="13228" LastActivityDate="2018-09-12T15:39:48.877" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11887" PostTypeId="1" CreationDate="2018-09-12T15:49:40.550" Score="3" ViewCount="471" Body="&lt;p&gt;I'm preparing for the USA Technician exam and I was reading in the manual that the ideal size for a dipole is following this strange formula: 1/2-lambda. But based on what I read after, it seems it means 1/2*lambda. Is it right ? And does it mean that each dipole spoke is 1/4*lambda ? Then that would mean you can only emit frequencies that are harmonics to that lambda ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nicolas&lt;/p&gt;&#xA;" OwnerUserId="13164" LastEditorUserId="13164" LastEditDate="2018-09-13T13:21:05.377" LastActivityDate="2018-09-13T13:21:05.377" Title="The right antenna size" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;math&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11888" PostTypeId="2" ParentId="11887" CreationDate="2018-09-12T16:02:01.437" Score="5" Body="&lt;p&gt;The classic dipole is a half-wave antenna. This means that the total length of the antenna is lambda/2.  So writing it as 1/2-lambda is OK from an English language point of view, but not IMO as a rigorous mathematical formula.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a half-wave dipole, each side of the feedpoint is one-half of that or a quarter-wave.&lt;/p&gt;&#xA;" OwnerUserId="8573" LastEditorUserId="8573" LastEditDate="2018-09-12T18:31:19.197" LastActivityDate="2018-09-12T18:31:19.197" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11889" PostTypeId="2" ParentId="11887" CreationDate="2018-09-12T17:09:41.017" Score="4" Body="&lt;p&gt;If you make a dipole exactly a half-wavelength long, then it will be too long and out of resonance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula for determining the length of a half-wavelength dipole in feet is 468÷frequency in MHz. That's shorter than the actual wavelength in free space which is 492÷MHz.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-09-12T17:09:41.017" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="11890" PostTypeId="2" ParentId="11816" CreationDate="2018-09-12T18:12:59.403" Score="3" Body="&lt;p&gt;Don't forget about &lt;a href=&quot;https://en.wikipedia.org/wiki/CHU_(radio_station)&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHU&lt;/a&gt; (and &lt;a href=&quot;https://www.nrc-cnrc.gc.ca/eng/services/time/short_wave.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here is the official site&lt;/a&gt;) which is the Canadian equivalent to WWV.  It's at lower power and it's not as well-located geographically (it's located near Ottawa), but it's receivable in most of the eastern US and increasingly less well as you head west.  Here in VE5-land (Saskatchewan) I certainly receive it sometimes, but I also don't have an ideal HF antenna setup either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It transmits at 3 kW at 3.33 and 14.67 MHz as well as with 10 kW of power at 7.85 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One nice feature is that it frequently transmits time data in Bell 103 modem format, which is fairly easy to decode.  It of course also has spoken word time.&lt;/p&gt;&#xA;" OwnerUserId="9844" LastEditorUserId="9844" LastEditDate="2018-09-12T18:26:57.033" LastActivityDate="2018-09-12T18:26:57.033" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11891" PostTypeId="2" ParentId="11887" CreationDate="2018-09-13T07:04:37.907" Score="3" Body="&lt;p&gt;There are already a couple of nice answers to your question. I thought I would add a little more context - no need to vote for this as it is tangential to the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 1/2 wavelength (1/2 $\lambda$) long dipole is one of the most basic and easy to deploy antennas. It is popular because when it is cut and fed in the center, it very closely matches the impedance of the most popular transmission line - 50 ohm coax. This helps to minimize power lost in the coax as a result of a mismatch. Such a mismatch is also the cause of elevated SWR (standing wave ratio). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The wire on each side of the feed point of a dipole is called a &quot;leg&quot;. In the case of a 1/2 $\lambda$, center fed dipole each leg is 1/4 $\lambda$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The length of a dipole is not limited to  1/2 $\lambda$. If the dipole becomes significantly shorter than 1/2 $\lambda$, the mismatch to the transmission line becomes high and so the losses in the transmission line go up. The antenna also becomes inefficient in itself which results in more power converted to heat and less radiated as electromagnetic energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dipole longer than 1/2 $\lambda$ can also be used. In fact, a dipole that is 10/8 $\lambda$ will actually have more gain than a 1/2 $\lambda$ dipole. The disadvantage is that it takes a little more work to make it a match for 50 ohm coax. Dipoles longer than 10/8 $\lambda$ can be used as well but they will generally not offer any more gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In recent years, there has been a great deal of interest in feeding a dipole at a spot other than its center. So called OCF (off center fed) dipoles offer the possibility of a multi-band dipole with reasonable matching to 50 ohm coax. Typically it is a 1/2 $\lambda$ or slightly longer dipole for the lowest frequency of interest and then at higher frequencies, it simply acts as a &gt;1/2 $\lambda$ dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other dipoles get specific names due to their historical references such as the double Zepp (from its Zeplin origins), extended double Zepp, a doublet, the G5RV, etc. Some of these designations may also imply the use of an open wire feedline instead of coax. But in the end, they are simply another form of a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there is the so called &quot;End Fed Half Wave&quot; (EFHW) antenna. This is a piece of wire that is the length of a 1/2 $\lambda$ dipole but instead of being split somewhere to create a feed point, it is left as one solid piece of wire and the coax is attached to the end. This is a very misunderstood antenna by many hams. It takes careful construction and installation techniques to achieve performance comparable to a center fed 1/2 $\lambda$ antenna. Many of these antennas are used in a multiband configuration. Their popularity is due to the convenience of feeding it from one end.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-13T13:09:35.850" LastActivityDate="2018-09-13T13:09:35.850" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11892" PostTypeId="2" ParentId="11881" CreationDate="2018-09-13T12:45:32.380" Score="5" Body="&lt;p&gt;I contacted the seller and am still waiting on a satisfactory reply. HOWEVER, I did seem to find a workaround. Thanks for everyone's response!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remove Password MD380/90 &#xA;1. Go to folder the CPS is in (C:\TYT)&#xA;2. look for file - setting.ini&#xA;3. Right click and edit&#xA;4. password=0 change to password=password&#xA;5. Save &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connect radio to PC and turn on in normal mode. &#xA;a. Read Code plug from radio. &#xA;b. General Settings remove all 3 passwords &#xA;c. Save Code plug &#xA;d. Write back to radio &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This worked and it looks like my codeplug was corrupt&lt;/p&gt;&#xA;" OwnerUserId="13222" LastActivityDate="2018-09-13T12:45:32.380" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11893" PostTypeId="2" ParentId="11850" CreationDate="2018-09-13T19:36:23.077" Score="4" Body="&lt;p&gt;I heartily recommend the three-volume set, &quot;Hands-on Radio Experiments,&quot; by Ward Silver, N0AX. These books organize Ward's excellent &lt;em&gt;QST&lt;/em&gt; columns to develop knowledge in specific areas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ward introduces the free &lt;em&gt;LTSpice&lt;/em&gt; circuit simulator in volume 2. This is a great way to delve into virtually every aspect of electronic design without the expense of building a lab. I have used &lt;em&gt;LTSpice&lt;/em&gt; to better understand published circuits and to develop my own low-cost, high-power, SSB transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have Elmered younger and older students alike with the Snap Circuits SC-300 home electronics learning lab. It's also a good complement to &lt;em&gt;LTSpice&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/shop/ARRL-s-Hands-On-Radio-Experiments-Volume-1-and-2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hands-on Radio Experiments, volumes 1 and 2&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/shop/ARRL-s-Hands-On-Radio-Experiments-Volume-3/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hands-on Radio Experiments, volume 3&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-09-13T19:36:23.077" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11895" PostTypeId="1" CreationDate="2018-09-14T04:03:02.063" Score="2" ViewCount="2497" Body="&lt;p&gt;Effective area of a dipole is $\lambda^{2}/4*\pi$. Consider 1 GHz em waves. Consider two antenna of length 15cm ie half wave length and 1 cm. Both have same effective area. This is very non-intuitive as the area does not depend on the length of the dipole. What explains this non-intuitive formula? Why should one bother about antenna length , particularly when receiving is concerned?&lt;/p&gt;&#xA;" OwnerUserId="13235" LastActivityDate="2018-09-15T02:12:22.120" Title="Effective area of a dipole" Tags="&lt;dipole&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11896" PostTypeId="2" ParentId="11895" CreationDate="2018-09-14T04:21:42.663" Score="5" Body="&lt;p&gt;The preferred term is effective aperture. Effective aperture is defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$A_e=\frac{\lambda^2}{4\pi}G \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $\lambda$ is the wavelength of operation and G is the linear gain of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you can see from equation 1 that you need to include the gain of the antenna - this was not reflected in your formula. The gain of the antenna is defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Gain=Efficiency * Directivity \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 1/2 wave dipole has a directivity of 1.65. When you shorten the dipole, it's directivity decreases but quickly reaches a terminal value of 1.5 no matter how much more it is shortened.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What has the ultimate impact on the A&lt;sub&gt;e&lt;/sub&gt; in the case of a small dipole is its efficiency. Efficiency is defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Efficiency=\frac{R_r}{R_r+R_l} \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where R&lt;sub&gt;r&lt;/sub&gt; is the radiation resistance and R&lt;sub&gt;l&lt;/sub&gt; is the resistive losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the dipole size becomes smaller compared to a 1/2 $\lambda$ dipole, its radiation resistance drops precipitously as a function of the square of its fractional wavelength. For like construction materials and methods, R&lt;sub&gt;l&lt;/sub&gt; only drops proportionally to the fractional wavelength. Thus the efficiency rapidly drops with the shrinking size of the dipole. Since this reduces the gain of the antenna the A&lt;sub&gt;e&lt;/sub&gt; of the antenna is also reduced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a given wavelength, the A&lt;sub&gt;e&lt;/sub&gt; of the antenna is directly proportional to its gain. But A&lt;sub&gt;e&lt;/sub&gt; provides a construct that helps to visualize the collection aperture of the antenna as a plane wave intersects it. The larger the aperture, the greater the total received signal power that is made available at the feed point of the antenna. It is this power that determines the signal strength at the receiver input terminals.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-14T04:35:24.617" LastActivityDate="2018-09-14T04:35:24.617" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11897" PostTypeId="2" ParentId="10347" CreationDate="2018-09-14T07:53:13.820" Score="2" Body="&lt;p&gt;See the &lt;a href=&quot;http://www.ctarl.org.tw/bv5ya/eng-2015-16/e_main1.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Chinese Taipei Amateur Radio League&lt;/a&gt; (CTARL) web site for a link to information for &lt;a href=&quot;http://www.ctarl.org.tw/bv5ya/2009-10/VSTR-op.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Visitors and short-term residents of Taiwan wishing to operate an Amateur Radio station in Taiwan&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Visitors and short-term residents of Taiwan wishing to operate an Amateur Radio station in Taiwan may apply for a Temporary Operating Permit after being sponsored by &lt;strong&gt;a licensed Taiwan host whose station they may operate&lt;/strong&gt; during the period in which the issued permit is valid. Amateur Radio station licenses in Taiwan license the specific transmitting and radiating equipment operated, and the temporary permit is an operator permit only, so &lt;strong&gt;no transmitting equipment may be legally brought into Taiwan by visiting Amateur Radio operators&lt;/strong&gt;.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CTARL officers are identified at &lt;a href=&quot;http://www.ctarl.org.tw/bv5ya/eng-2015-16/HQ.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Headquarters and Branche Offices&lt;/a&gt;. I recommend you reach out to the entire HQ staff as well as the branch representative for the region you plan to visit.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-09-14T07:53:13.820" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11898" PostTypeId="1" CreationDate="2018-09-14T11:12:28.143" Score="2" ViewCount="61" Body="&lt;p&gt;i am considering building two movable (concrete base with wheels) non metallic poles with hooks every ten centimeters or so, in order to test wire dipoles of various sizes at various heights with an antenna analyzer, far from obstacles (let's say in a field).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you think it's better to use non conductive masts to avoid parasitic influence on the measurement or is it overkill?&#xA;Is there anything else on antenna metrology I should know for this project?&lt;/p&gt;&#xA;" OwnerUserId="13081" LastEditorUserId="76" LastEditDate="2018-09-14T14:13:58.863" LastActivityDate="2018-09-14T14:13:58.863" Title="Wire dipole antenna proving ground / test bench" Tags="&lt;antenna-construction&gt;&lt;dipole&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11899" PostTypeId="2" ParentId="11898" CreationDate="2018-09-14T12:13:39.590" Score="4" Body="&lt;p&gt;Under ideal conditions you should strive to keep all conductive materials that are not part of the antenna system out of the near field of the antenna. This generally means non-conductive supports.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a practical matter, if you are supporting horizontal dipoles, there is very little current at the open end of each leg so very little radiation occurs in this region. There is generally high voltage present, however, due to the standing waves on the antenna. If the ends of the antenna are properly insulated and spaced reasonably (e.g. &gt;1/10 $\lambda$) away from the supports, this should not cause problems - particularly if the only source of excitation is a fractional watt antenna analyzer. The spacing also serves to minimize capacitive coupling with the supports.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-09-14T12:13:39.590" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11900" PostTypeId="1" AcceptedAnswerId="11903" CreationDate="2018-09-14T15:30:00.047" Score="1" ViewCount="435" Body="&lt;p&gt;I just bought a Yaesu FTDX3000D and would like to see the SWR.  Is it possible to display the SWR on the FTDX3000D?  If so, what menu option would that be?  I'm not finding it.&#xA;I searched for this answer both here and in Google, but am not finding anything.  Thanks.   &lt;/p&gt;&#xA;" OwnerUserId="9772" LastActivityDate="2018-09-15T01:39:37.990" Title="FTDX3000D SWR Meter" Tags="&lt;yaesu&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11901" PostTypeId="2" ParentId="11895" CreationDate="2018-09-14T17:21:28.217" Score="2" Body="&lt;p&gt;The &lt;em&gt;effective area&lt;/em&gt;, also called &lt;em&gt;effective aperture&lt;/em&gt;, is the power observed at the antenna feedpoint, divided by the &lt;a href=&quot;https://en.wikipedia.org/wiki/Irradiance&quot; rel=&quot;nofollow noreferrer&quot;&gt;irradiance&lt;/a&gt; to which the antenna is exposed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Irradiance is expressed as power per area, for example &quot;1 microwatt per square meter&quot;. Effective aperture is an area. For example if the irradiance is 1μW/m&lt;sup&gt;2&lt;/sup&gt; and I observe 2μW at the antenna feedpoint, the antenna's effective aperture must be 2 square meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is simply another way of expressing gain. Gain ($G$) and effective aperture $(A_e$) are related by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ G = {4 \pi A_e \over \lambda^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So when you say a quarter wave dipole and a much smaller dipole have the same effective aperture, you are saying they have the same gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, you are saying they have a gain of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ G = {4 \pi (\lambda^2 / 4 \cdot \pi ) \over \lambda^2} $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which simplifies to&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$ G = \pi^2 \approx 9.87 $$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is incorrect. A lossless, infinitesimal dipole has a gain of 1.5. A half-wave dipole has a gain of 1.64.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That aside, it is a valid question to ask why the gain of a half-wave and a short dipole are almost the same. It seems like the short dipole, being physically much smaller, would have a smaller effective aperture and thus a smaller gain. And yet, the gain never goes below 1.5 no matter how small the dipole becomes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is that this ideal, theoretical infinitesimal dipole is lossless, so all the energy is radiated eventually. As such, there's no way to decrease the gain except to decrease the directivity of the antenna, which isn't possible as long as the geometry fits the definition of a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, as the dipole becomes shorter its impedance becomes more reactive. To transfer power to or from the antenna then requires a matching network which must handle increasing peak current and voltage. Theoretically, this reactive power can circulate between the antenna and matching network without loss, but real matching networks are not lossless. Thus in practice, efficiency (and thus gain and effective aperture) approaches zero as the dipole approaches zero length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By reciprocity the same is true when receiving: gain does not decrease below 1.5 regardless of the size of the dipole. Comparing a quarter wave dipole and an extremely small lossless dipole, each receives about the same power (a gain of 1.64 vs 1.5 respectively), but the current and voltage in the case of the small dipole will be extremely large due to the tremendous reactive power.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-09-15T02:12:22.120" LastActivityDate="2018-09-15T02:12:22.120" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11903" PostTypeId="2" ParentId="11900" CreationDate="2018-09-15T01:39:37.990" Score="1" Body="&lt;p&gt;After a little more digging I found the answer. SWR is an option on the meter display.  You can display ALC or power output or SWR or one of a few other options by pressing the &quot;Scope&quot; button a few times and changing the Meter option. &lt;/p&gt;&#xA;" OwnerUserId="9772" LastActivityDate="2018-09-15T01:39:37.990" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11905" PostTypeId="1" CreationDate="2018-09-15T12:14:08.053" Score="2" ViewCount="985" Body="&lt;p&gt;I built a CW receiver using  NE602 for the 20m band. Unfortunately, I do not receive any CW or SSB signals, only some noise and sometimes broadcast stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The schematic here shows the circuit that I built. What is wrong in the oscillator and input stages of ic that can not focused on 14 - 14.35 mhz (20m amateur band)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In oscillator section as you see i used two 220pf capacitor that are in series with each other so the total capacitance is equal to 110pf . &#xA;For resonance  at 14 mhz with present inductor (1uH) we need a capacitor value 129pf   using formulae:                    (C=1/39.5 * F^2 * L)        so if the varactor diode can induce about 19pf , the work is done (110+19=129)   the second image show the internal transistor of ne602 chip and relationship between pins 6 and 7 and the other parts of oscillator section&#xA;                                     (&lt;a href=&quot;https://i.stack.imgur.com/e1HLp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://i.stack.imgur.com/e1HLp.jpg&lt;/a&gt;)&lt;img src=&quot;https://i.stack.imgur.com/Ih38x.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8JWFy.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="13241" LastEditorUserId="8717" LastEditDate="2018-09-15T22:30:10.933" LastActivityDate="2018-09-15T22:30:10.933" Title="Receiver using a NE602 oscillator-mixer not working" Tags="&lt;receiver&gt;&lt;equipment-design&gt;&lt;20m-band&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11907" PostTypeId="2" ParentId="11905" CreationDate="2018-09-15T14:30:29.747" Score="2" Body="&lt;p&gt;In your schematic, there is no way that the IC can get any power because:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;DC cannot flow through capacitors. I suggest that you look at a &lt;a href=&quot;https://www.google.com/search?q=ne602&quot; rel=&quot;nofollow noreferrer&quot;&gt;NE602 data sheet&lt;/a&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;There is no power being applied to pin 8.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I assume that you are receiving broadcast stations, digital transmissions, etc. Without power to the IC, it's just acting as an AM detector.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-09-15T14:35:44.907" LastActivityDate="2018-09-15T14:35:44.907" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11908" PostTypeId="1" CreationDate="2018-09-15T17:00:28.507" Score="5" ViewCount="361" Body="&lt;p&gt;Consider a dipole antenna fed by a coax (say, longer than the antenna) with a signal reasonably close to the dipole's resonant frequency.  Various sources say that the feed-line should approach the antenna perpendicularly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the effects (SWR, radiation efficiency, pattern, etc.) if the feed-line incidence angle is different from 90 degrees, from a few degrees away from perpendicular, all the way to close to parallel to the dipole?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of the feed-line being very close to parallel to the dipole, it seems like this would be geometrically similar to an end-fed antenna.  If so, would a current balun placed on the coax a quarter wavelength from the dipole center help?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-09-21T11:32:18.813" Title="What are the effects of different feed-line incidence angles?" Tags="&lt;antenna-theory&gt;&lt;coaxial-cable&gt;&lt;feed-line&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11909" PostTypeId="2" ParentId="11908" CreationDate="2018-09-15T19:59:39.350" Score="3" Body="&lt;p&gt;When the coaxial cable is in the near field of a center fed, 1/2 wavelength dipole and it does not run perpendicular to the antenna, it is subjected to imbalanced near field currents. The coupling effect will be cos $\theta$. The result is that the exterior braid of the coax may carry common mode current. OCF and end fed antennas also promote common mode current due to their inherent imbalance. Running the coax parallel to the dipole should be avoided.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The significance of the common mode current is dependent upon factors such as coax length, the grounding of the coax, common mode chokes, the frequency of operation, imbalance of the antenna, etc. Antenna modeling programs can be used to estimate the subseptibility of a particular configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The effects of common mode currents can include RF shocks in the shack, interference with home electronics, coupling of nearby RFI into the antenna, alteration of antenna resonance/SWR and an alteration of the antenna pattern and gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A common mode choke at the feed point of the dipole and another one at the shack entrance or at least out of the near field of the antenna can be deployed to mitigate the effects. Ferrite based common mode chokes or 1:1 current baluns tend to be the best multiband performers. Some report success by burying the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also helpful to avoid odd multiples of 1/4 wavelength coax as this promotes the formation of common mode currents. Note that the coax velocity factor does not come into play since this current is on the exterior of the braid. Instead, use a 0.95 to 0.97 velocity factor to account for the outer coaxial jacket.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-16T18:07:36.293" LastActivityDate="2018-09-16T18:07:36.293" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11910" PostTypeId="1" CreationDate="2018-09-16T00:51:34.640" Score="3" ViewCount="335" Body="&lt;p&gt;Circuit appears to be working but very easily breaks into oscillation - sometimes just getting up from my desk triggers it, or while tuning, and sometimes after a few seconds with no disturbance that i'm aware of.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;circuit is built on a tin plate from a flattened 9V battery case... because i'm keeping leads as short as i can inductors are probably too near each other?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not confident yet with s-paramenters so i left it out of my calculations...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AJPaF.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AJPaF.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/L0haf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/L0haf.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/VeNTQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VeNTQ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/jd0JE.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jd0JE.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&#xA;as requested, image of circuit and scope traces&#xA;&lt;a href=&quot;https://i.stack.imgur.com/O0MM8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O0MM8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;when transmitter is off or when not tuned in&#xA;&lt;a href=&quot;https://i.stack.imgur.com/bJ0pU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bJ0pU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;tuned in, 400 hz mod clearly visible :) but it's hard to get this, typically it is self oscillating..&#xA;&lt;a href=&quot;https://i.stack.imgur.com/KNVZk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KNVZk.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;and suddenly.... the frequency of the oscillation is totally dependent on the tuned circuit, it is fully tunable accross the full range of the trimmer 5 - 50 pf.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/QKrjj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QKrjj.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user13171" LastEditorDisplayName="user13171" LastEditDate="2018-09-20T08:52:13.063" LastActivityDate="2019-01-10T13:45:22.357" Title="78.5MHz AM receiver self-oscillation" Tags="&lt;receiver&gt;&lt;am&gt;&lt;oscillator&gt;&lt;airband&gt;" AnswerCount="3" CommentCount="10" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11912" PostTypeId="2" ParentId="11873" CreationDate="2018-09-16T22:47:33.800" Score="0" Body="&lt;p&gt;you can calculate the impedance of your actual antenna if you setup a test jig and take a number of readings. w2aew explains this very well in a youtube video &lt;a href=&quot;https://www.youtube.com/watch?v=eYN7dhdt1Dw&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=eYN7dhdt1Dw&lt;/a&gt; this method requires a signal generator and an oscilloscope, we don't all have the luxury to own these items but you can still learn the theory of what he's doing. you either need to be confident in complex number maths, have a nice scientific calculator or use online tools to solve the maths. the equation itself is just like solving current and resistance in simple voltage divider circuits... but each element has an amplitude and phase.&lt;/p&gt;&#xA;" OwnerDisplayName="user13171" LastActivityDate="2018-09-16T22:47:33.800" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11913" PostTypeId="2" ParentId="32" CreationDate="2018-09-17T01:04:03.577" Score="1" Body="&lt;p&gt;In my experience teaching several students new to Morse Code, the fastest way to increase &lt;em&gt;receiving&lt;/em&gt; speed is by &lt;em&gt;sending&lt;/em&gt; more. This seems to build up students' sense for &lt;em&gt;words&lt;/em&gt; rather than just for &lt;em&gt;letters&lt;/em&gt; and tends to lead more naturally to a sense for phrases and sentences.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since it seems too great an additional burden for students to compose in their heads the text to be sent, I have them open a familiar book or magazine and just start sending the words as they read them. The most frequently used words soon start to flow as whole units. Once they get up to about 10WPM, I have them begin sending material out of their heads, alternating back to printed material as necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At about the 15WPM level, I have them listen to individual 35-40WPM words. It surprises them how quickly they're able to pick up words at these much higher speeds, gives them confidence and inspires them to use what they have learned on the air.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-09-17T01:04:03.577" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11914" PostTypeId="1" AcceptedAnswerId="11927" CreationDate="2018-09-17T01:42:29.893" Score="2" ViewCount="121" Body="&lt;p&gt;I just installed a brand new deep cycle marine battery. It goes thru a charger-inverter and will switch over automatically if the power goes down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is what to do with the other two (old) batteries.  Both old batteries are deep cycle marine also.  But one is 10 years old and the other is 20 years old.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does any elmer anticipate any issue with hooking up the other two batteries in parallel with the new battery?&lt;/p&gt;&#xA;" OwnerUserId="8647" LastEditorUserId="8717" LastEditDate="2018-09-19T18:42:22.807" LastActivityDate="2018-09-19T18:42:22.807" Title="Deep-cycle marine battery life question" Tags="&lt;battery&gt;&lt;battery-charging&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11915" PostTypeId="2" ParentId="1352" CreationDate="2018-09-17T09:18:15.353" Score="3" Body="&lt;p&gt;If you check out the resources provided by Alex Shovkoplyas, VE3NEA in&#xA;&lt;a href=&quot;http://www.dxatlas.com/Dev/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.dxatlas.com/Dev/&lt;/a&gt;&#xA;you will find a variety of examples of callsign parsing. His prefix list contains REGEX matches for each country, but be aware that he uses HIS OWN syntax for callsign matching:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 'Mask' field in PREFIX.LST is used for callsign resolution. &#xA;The following meta symbols are used in the mask:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;'@' - any letter&#xA;'#' - any digit&#xA;'?' - any character (letter or digit)&#xA;[AC] - A or C&#xA;[A-C] - A, B, or C.&#xA;[AC-E] - A, C, D, or E.&#xA;'.' - no characters are allowed after this simbol. &#xA;      Example: '??#@@.' matches all calls with 2-letter suffixes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;His symbols MUST be substituted for other types, to use the mask with other languages:Javascript, VB.Net, PHP, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also find REGEX strings in the AD1C Country Files.&lt;/p&gt;&#xA;" OwnerUserId="13250" LastActivityDate="2018-09-17T09:18:15.353" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11916" PostTypeId="1" CreationDate="2018-09-17T13:50:34.450" Score="2" ViewCount="510" Body="&lt;p&gt;I was working with the &lt;a href=&quot;https://en.m.wikipedia.org/wiki/3GPP&quot; rel=&quot;nofollow noreferrer&quot;&gt;3GPP&lt;/a&gt; release 14.6, and it mentioned that modern communication systems have cross polarized antennas, and in order to perform beam-forming we need to co-phase our pre-coder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pre-coding is an algorithm we use at the transmitter side in order to aid our performance at the receiver.&#xA;We model our system as $y = Hx$ where H is the channel,x is transmitted data and y is received data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of sending $x$ we send $Wx$ where W is our pre-coder, our system would then be $y = HWx$ assuming we have the channel at the transmitter side we can just make $W = H^{-1}$ that way the channel doesn't affect the data. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does co-phasing between cross-polarized antennas mean and how does it affect my precoder?&lt;/p&gt;&#xA;" OwnerUserId="13252" LastEditorUserId="13252" LastEditDate="2018-09-17T16:47:09.017" LastActivityDate="2018-09-18T02:37:08.960" Title="What does co-phasing of cross-polarized antennas mean?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11917" PostTypeId="2" ParentId="11916" CreationDate="2018-09-17T15:11:50.587" Score="1" Body="&lt;p&gt;Changing the phase angle between signals applied to transmit (or receive) antennas of differing polarizations (i.e., &lt;em&gt;cross&lt;/em&gt; polarized) can only change the angle of the polarization or its &quot;sense&quot;; it cannot be effectively used for beam forming. Beam forming results when the phase angle is changed between signals applied to two or more transmit antennas (or tranduced from two or more receive antennas) of the &lt;em&gt;same&lt;/em&gt; polarization (i.e., &lt;em&gt;co&lt;/em&gt;-polarized).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One may accomplish beam forming by co-phasing two or more cross-polarized antennas. This is most easily understood when the two cross-polarized antennas are of the same design.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2018-09-17T21:51:38.283" LastActivityDate="2018-09-17T21:51:38.283" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11918" PostTypeId="1" CreationDate="2018-09-17T20:56:43.353" Score="12" ViewCount="3097" Body="&lt;p&gt;Capacitive hats seem to be advertised as an option for mobile vertical antennas.  One mentioned advantage is the they can widen the SWR bandwidth, making the antenna easier to tune.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What might be the effect of using capacitive hats, not on a mobile vertical, but symmetrically on both ends of a wire dipole, or a shortened dipole?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since wind loading isn't as much of an issue on non-mobile wire antennas, it seems almost any size capacitive hat might be possible by using arbitrarily large sheets of conductive wire screen material (hung or inside toy hoops, etc.).  How might varying the size of the capacitive hats (from tin-can lid to patio door size) change the antenna's characteristics?  (SWR, SWR bandwidth, radiation resistance, pattern, and etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added: Other than an increase in wind loading, is there any downside?  Why shouldn't every dipole have a little conductive disk (or more) at the end?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-09-18T19:09:29.970" LastActivityDate="2019-01-24T04:10:55.763" Title="Capacitive hats on wire dipoles?" Tags="&lt;antenna-construction&gt;" AnswerCount="4" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="11919" PostTypeId="2" ParentId="11918" CreationDate="2018-09-18T01:53:08.883" Score="5" Body="&lt;p&gt;Capacitive end loading has the effect of electrically &quot;lengthening&quot; a dipole (i.e. tunes it to a lower frequency). Similar to mid-loading with an inductor but with 3 notable differences:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Capacitive loading is less lossy&lt;/li&gt;&#xA;&lt;li&gt;Capacitive loading has higher bandwidth&lt;/li&gt;&#xA;&lt;li&gt;Capacitive loading raises the radiation resistance more than an equivalent inductive loading&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Potential downsides, other than mechanical issues such as wind loading:  There are none.  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why shouldn't every dipole have a little conductive disk (or more) at the end?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;For dipoles already tuned to the proper frequency, I would answer &quot;they do not need it&quot;.  For other cases... it gets difficult to describe so please see the flow chart below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZT7oN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZT7oN.png&quot; alt=&quot;dipole decision tree&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Summary:  Best case would be a full size, half-wavelength, tuned dipole. But if there is a wire length restriction for whatever reason, adding a set of &quot;cap hats&quot; is truly a no-brainer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a normal dipole that does not &quot;need&quot; capacitive end loading, there &lt;em&gt;may&lt;/em&gt; still be a case for adding small &quot;tin can lids&quot; to the end --and, of course, shortening the wire a little to keep the tuned frequency constant.  I cannot cite the reference, but it seemed to state that adding slight capacitive end loading like this gave a slight increase in radiation resistance.  For &quot;fussy&quot; people such as me, this is enough to encourage adding cap hats to all of my otherwise-perfect dipoles.  Unfortunately, I cannot cite that reference, did not memorize the optimal cap hat size, have not verified independently, and do not know how to measure radiation resistance.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2018-09-20T21:54:36.650" LastActivityDate="2018-09-20T21:54:36.650" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11921" PostTypeId="2" ParentId="11918" CreationDate="2018-09-18T02:50:28.100" Score="5" Body="&lt;p&gt;A capacitance hat used on a shortened antenna ($\le$ 1/8 λ for verticals and $\le$ 1/4 λ for dipoles) converts a largely triangular current distribution with the maximum current at the feedpoint, to a more uniform current distribution or alternatively, it lessens the peak current in the antenna element. This has the effect of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1.) Raising the R&lt;sub&gt;r&lt;/sub&gt; (radiation resistance) of the antenna and thus improves the efficiency of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;2.) It helps to neutralize the inherent capacitive reactance of the shortened antenna and thus generally makes matching the antenna to the feedline an easier task. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like all shortened antennas, the bandwidth of the antenna is typically less than a &quot;full size&quot; version of the antenna. But the hat will generally broaden the bandwidth compared to other methods of matching the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The concept of capacity hats on dipoles is not new. Here is a picture of a commercial dipole from DX Engineering. Note the clearly visible wire hats:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9Coe7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9Coe7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a photo from &lt;a href=&quot;http://www.dj0ip.de/spiderbeam/the-spiderbeam/add-on-40m-dipole/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DJ0IP&lt;/a&gt; showing his 40 meter cap hat dipole below his spider beam:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gpxRx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gpxRx.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The classic modeling approach is to treat the antenna (or in the case of a dipole, each leg) as an open ended transmission line in order to calculate the impedance magnitude of the antenna (or the leg). The degree of wavelength of the antenna (or leg) is also computed. These values allow the reactance that is required to make up the &quot;missing degrees&quot; of the antenna element. Finally, the capacitive reactance required in the capacitance hat is computed. The following universal reactance curve for an open or shorted transmission line is used to compute the reactance required based on the missing degrees:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7oAoH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7oAoH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;&lt;sub&gt;source: QST, September 1978, Designing a Vertical Antenna by Walter Schulz K3OQF &lt;/sub&gt;&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inspection of the above diagram shows that if the element is a full 90° (1/4 wavelength) in length, then the transmission line effect will transform the infinite impedance of the open end to a near zero impedance (with near zero reactance) on the opposite end. For any electrical length in-between, the ratio of capacitive reactance to impedance is depicted.  If the antenna is of simple wire construction, an impedance calculator such as &lt;a href=&quot;https://chemandy.com/calculators/round-wire-impedance-calculator.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://chemandy.com/calculators/round-wire-impedance-calculator.htm&lt;/a&gt; may prove sufficient to determine the initial impedance magnitude of the wire. The commonly used formula for calculating impedance magnitude is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$Z_{MAG}=60(ln\left(\frac{2L}{r}\right) -1) \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where L is the length of the antenna or the leg of a dipole and r is the radius of the conductor, both in the same units.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The capacitance of the capacitive hat can be approximated from:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$C_{pF}\approx0.89D \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where D is the diameter of the capacitance hat in inches.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equation 2 is a reasonable approximation for circular capacitance hats constructed with plates, meshes or skeletal elements (e.g. spokes with a circumferential wire). It is important that the radius of the capacitance hat be &amp;lt;0.1 wavelengths so that the hat does not become a radiating element rather than strictly a capacitor at the end(s) of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The capacitive reactance of the hat in ohms is given by the standard capacitive reactance formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$X_C=\frac{1}{2\pi fC} \tag 3$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where f is the frequency in hertz and C is the capacitance in farads.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-19T13:19:26.407" LastActivityDate="2018-09-19T13:19:26.407" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11922" PostTypeId="1" AcceptedAnswerId="11923" CreationDate="2018-09-18T15:53:11.680" Score="9" ViewCount="601" Body="&lt;p&gt;I have a basic question about power supply requirements for typical transceivers.  I'm looking at the specs for a Kenwood TM-V71A, which is a 50W mobile transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I figured that a 50W transceiver running on a 12V(-ish) power supply would pull around 4A max, but the specs for this radio show a &quot;maximum current drain&quot; of around 13A. How does that work?&lt;/p&gt;&#xA;" OwnerUserId="13127" LastActivityDate="2018-09-19T03:31:33.470" Title="Understanding power supply requirements" Tags="&lt;dc-power&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11923" PostTypeId="2" ParentId="11922" CreationDate="2018-09-18T17:23:53.073" Score="9" Body="&lt;p&gt;A 50W transmitter is one that can create 50 watts of RF output. The RF amplifier is never 100% efficient, so the input power requirements will always be higher than the output power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, the maximum current drain accounts for startup transients and other peaks in excess of the average current drain.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-09-18T17:23:53.073" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11924" PostTypeId="2" ParentId="11922" CreationDate="2018-09-18T19:16:05.277" Score="3" Body="&lt;p&gt;Note that even when not transmitting, a transceiver will draw power for the receiver, audio amplifier, control panel processor and display, etc.  That idle power adds on top of the power sent thru the antenna output connector divided by the amplifier efficiency (the rest of that power/energy heating up the shack).&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-09-18T19:16:05.277" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11925" PostTypeId="2" ParentId="11922" CreationDate="2018-09-19T03:31:33.470" Score="3" Body="&lt;p&gt;The circuitry in a standard radio transceiver will probably draw around an amp while it is powered on - this includes the CPU, display and other such things that are always running. Handheld radios obviously try to keep this current as a minimum, because they run on batteries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While receiving, there is also the power used by the receiving circuitry, and the audio amplifier, while there is audio being sent to the speakers. This can use an additional amp or so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the real current draw is when transmitting, where most of the current is used by the PA (power amplifier) final stages. These usually operate in class A, AB or B, which are not very efficient - but offer good linearity, and thus low distortion. See the Wikipedia entry on &lt;a href=&quot;https://en.wikipedia.org/wiki/Power_amplifier_classes&quot; rel=&quot;nofollow noreferrer&quot;&gt;Power Amplifier Classes&lt;/a&gt;. These amplifiers require large heatsinks to dissipate the 'waste' energy as heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that mobile and handheld radios that only transmit FM can use class C amplifiers, which are non-linear, since they always transmit at a constant power. These are much more efficient than class A, AB or B amplifiers, and mean that mobile or handheld FM-only radios use less power when transmitting, and require smaller heatsinks.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-09-19T03:31:33.470" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11926" PostTypeId="2" ParentId="11918" CreationDate="2018-09-19T14:09:10.053" Score="0" Body="&lt;p&gt;To elaborate, the free-space, far-field &lt;strong&gt;&lt;em&gt;directivity&lt;/em&gt;&lt;/strong&gt; of a linear, 1/2-wavelength-long, center-fed, perfect dipole varies from that of an &quot;infinitesimal,&quot; linear, center-fed, perfect dipole only by about 0.4dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However the &lt;strong&gt;&lt;em&gt;gain&lt;/em&gt;&lt;/strong&gt; of each of those configurations depends on the ratio of  radiation resistance to the sum of radiation resistance with all other heat-dissipating, ohmic losses present in the antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those other losses typically are larger for Z-matched antenna systems using loading coils, traps, and/or &quot;capacitance hats&quot; with electrically short radiating conductors — which system gain may be reduced by many decibels from that when using a &quot;full sized,&quot; unloaded radiator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Reference: &lt;em&gt;Antennas,&lt;/em&gt; 3rd Edition, Kraus/Marhefka, pp 23-26].&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-09-19T14:09:10.053" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11927" PostTypeId="2" ParentId="11914" CreationDate="2018-09-19T14:23:08.250" Score="4" Body="&lt;p&gt;When you parallel batteries, the combined reliability generally becomes less than the least reliable battery. In reliability engineering, this follows the equation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_S=R_1*R_2*R_3 \tag 1$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $R_1, R_2,R_3$ is the reliability of the respective individual batteries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The older batteries are inherently more unreliable. Battery failure modes can cause the charging system to not properly charge the individual batteries and it can reduce the available energy when a load demand is asserted. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only failure mode that does not reduce the system reliability is a failure to an open condition. This is rarely seen on secondary batteries except when they contain integrated charge controllers, which is not the case for typical lead acid type batteries. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To exemplify the formula, imagine that the new battery is 95% reliable and that the old batteries are 50% reliable. The combined reliability is 0.95*0.5*0.5 or 23.8% compared to 95% for the new battery alone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aside from failures of the individual batteries, you may find that your charge controller is either not equipped to handle the combined charge current or it will not properly detect a charged condition of the combined batteries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to make your system redundant, at least from the battery perspective, you need to design the system to reliably charge each battery and also allow for each battery to independently supply the load regardless of the state of the other batteries. The reliabilty of a such a redundant system is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;$$R_P=1-\frac{1}{\frac{1}{U_1}+\frac{1}{U_2}+\frac{1}{U_3}} \tag 2$$&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where $U_1, U_2, U_3$ is the respective unreliability of each battery. Unreliability is defined as 1 minus reliability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the same individual reliabilities from earlier, this would result in a combined battery reliability of  ~96% - not really worth the effort given the marginal improvement over the 95% reliability of the new battery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are relying on this battery system for any critical function, I would recommend against combining the batteries.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-19T15:38:41.423" LastActivityDate="2018-09-19T15:38:41.423" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11928" PostTypeId="1" CreationDate="2018-09-19T16:06:39.990" Score="1" ViewCount="250" Body="&lt;p&gt;I am curious as to what happens to a symmetrical dipole center-fed with balanced feeder-line. Let's assume the dipole is arranged as a sloper - that means it's not parallel to ground (horizontal). Additionally there are several buildings, trees or other conductors or in short, the dipole might be mechanically symmetric but electrically it is unbalanced. The balanced feeder-line is made of 12cm spacers and travels along a path between two surrounding buildings (each 2m distance) until it reaches the symmetrical coupler (ATU). The setup is a crowded city so this scenario should show a bad condition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to theory and books there shouldn't be expected any issues related to imbalance and common-mode. But is that true in reality? Let's go further and assume our balanced feeder-line is mechanically not symmetric, for example one lead is 5 or 10cm shorter/longer than the other one. It is self-explanitory that a ham radio operator wouldn't do that intentionally. Is it earrated to use a choke as shown here? (see attachment)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.wolfgang-wippermann.de/balun1zu1undefklein.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.wolfgang-wippermann.de/balun1zu1undefklein.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a 21 winding  Reisert balun scheme (it reverses the windingopposite for lower capacitive coupling). He says that placing this choke between a symmetrical feeder line and a coupler will prevent imbalance (common mode current) through the wires. It will not prevent imbalance occured through stray emmission. Makes sense for me but I would like to hear your comments. Will this choke placed right after the output of a symmetrical coupler prevent imbalance currents, that are caused by the example mentioned?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.dg0sa.de/balunatuhl.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.dg0sa.de/balunatuhl.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 Nick!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2XG2P.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;electrical not symmetrical&lt;/a&gt;!&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Sqekh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;balun for undefined impedances&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13242" LastEditorUserId="9493" LastEditDate="2018-09-19T17:27:45.410" LastActivityDate="2018-09-21T17:42:52.650" Title="Using a common-mode choke on symmetrical antenna system" Tags="&lt;dipole&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11929" PostTypeId="1" CreationDate="2018-09-19T16:32:58.373" Score="5" ViewCount="128" Body="&lt;p&gt;References are made on this and other websites to the effect that loading coils can/will supply &quot;missing degrees&quot; to electrically short radiators.  But do they?&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-09-21T15:01:48.933" Title="Do Loading Coils Supply &quot;Missing Degrees&quot; to Electrically Short Radiators?" Tags="&lt;antenna-construction&gt;&lt;short-antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11930" PostTypeId="2" ParentId="11929" CreationDate="2018-09-19T16:32:58.373" Score="3" Body="&lt;p&gt;Antenna theory, M-o-M software, and experience all show that although a properly-sized loading coil at the feedpoint terminals of an antenna can offset the capacitive reactance of an electrically short radiator to create a terminal impedance of R &lt;strong&gt;±j 0&lt;/strong&gt; Ω (resonance), that loading coil does essentially nothing as far as increasing the &lt;em&gt;radiation resistance&lt;/em&gt; of that short antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The loaded radiator system may become ~self-resonant over some range of frequencies, but at reduced SWR bandwidth and with reduced radiation efficiency for the system, because the ESR of the loading coil must be added to the loss of the network needed to match the feedpoint terminal impedance to a transmission line connected there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However those effects may be acceptable if they enable installing an antenna suited for the physical constraints of an installation site.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;The text and graphic below were added 21 Sept 2018&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There may be some who believe that a loading coil has an electrical length and radiation resistance related to the &lt;strong&gt;linear&lt;/strong&gt; length of the conductor used to construct that coil.  However as stated by J. Kraus in &lt;em&gt;Antennas&lt;/em&gt;, 3rd Edition, p. 296 and shown by NEC4.2, such coils have very nearly the same electrical length and radiation resistance as a single, linear conductor having the same end-end, overall length (aperture) as the coil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note in the NEC study below that the coil contains a conductor of about 100 meters in length, which is greater than one-half wavelength at that operating frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that 100-meter, ~1/2-wavelength conductor was straight (linear), its radiation resistance at that frequency would be (approx) 100 Ω.   Yet as shown in the Comment block in that graphic, when that 100m conductor is wound in the form a self-resonant coil, its radiation resistance is only &lt;strong&gt;0.23 Ω&lt;/strong&gt;. (Also note that the gain of the antenna system modeled in this NEC study is at least 15 dB below what it would be if using a ~1/2-wavelength, base-driven, linear monopole.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, such loading coils are very ineffective in adding &quot;missing degrees&quot; to an electrically short, linear radiator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only practical value/purpose of a loading coil is to offset the capacitive reactance of an electrically short radiator, to provide resonance for that antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EbLLV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EbLLV.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2018-09-21T15:01:48.933" LastActivityDate="2018-09-21T15:01:48.933" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11931" PostTypeId="2" ParentId="11914" CreationDate="2018-09-19T18:41:28.187" Score="2" Body="&lt;h2&gt;I'll bet those old batteries are just plain worthless.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Based on our experience with many deep-cycle golf cart and automotive batteries, those 10- and 20-year-old batteries almost certainly are &lt;strong&gt;not&lt;/strong&gt; capable of accepting anywhere near a full charge. At best, some cells &lt;em&gt;may&lt;/em&gt; work to &lt;em&gt;some&lt;/em&gt; degree while other cells are just plain dead, Jim. ;-) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can determine that for yourself by attempting to charge them (one at a time) and then see how long the battery voltage stays above 12.6 VDC under load. I think you'll find that they are completely worthless for any purpose and should be disposed of.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had ~24 used 6 volt golf cart batteries in series to store electricity from a wind generator. Batteries constantly would fail, and so I finally gave the unfinished project to an uncle and moved on to other things.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-09-19T18:41:28.187" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11932" PostTypeId="2" ParentId="11928" CreationDate="2018-09-19T20:48:13.900" Score="3" Body="&lt;p&gt;You could look at this many ways:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Theoretical: if the system is balanced throughout, there's no need for a choke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Practical: the antenna's surroundings, slope of the antenna, and other variations will unbalance the system somewhat, so a choke may be a good idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pragmatic: a little common-mode current isn't a problem &lt;em&gt;per se&lt;/em&gt;. Especially if the antenna is strung between buildings in a crowded city, the antenna might pick up just as much noise as the feedline, so there's little to gain by reducing common-mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lazy: just install the choke: it can do no significant harm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Empirical: &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measure the common-mode current&lt;/a&gt; and find out.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-09-19T20:48:13.900" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11933" PostTypeId="2" ParentId="11908" CreationDate="2018-09-21T11:32:18.813" Score="2" Body="&lt;p&gt;Note that odd multiples of a 1/4 wave of coax are good for SWR -- in other words, that segment of coax will become part of the antenna if it is resonant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Placing a balun at the right length may help, assuming you don't care (or desire) that the resonant section of coax will radiate and alter the radiation pattern of the antenna, and don't care about all the other effects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Carolina Windom (OCF dipole) places a balun at the feedpoint and another inline balun at 1/4wl down the coax assuming a wavelength of 10m.  It does this specifically to add the 10m band to an antenna that would otherwise not work well on this band.  (Note: if you are doing this on purpose, don't forget to use the feedline's velocity factor when calculating the length.)&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-09-21T11:32:18.813" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11934" PostTypeId="2" ParentId="11928" CreationDate="2018-09-21T13:56:37.500" Score="0" Body="&lt;p&gt;Any imbalance in the source, the transmission line or the load can give rise to common mode currents. I make this point because we often see only the antenna (the load) as the culprit when in fact the &quot;balanced&quot; tuner and the routing or construction of the transmission line can be culprits as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The addition of a common mode choke, such as the one depicted in the linked pdf, will generally be helpful in reducing common mode currents. However, if the differential to common mode impedance ratios become extreme, the balun may not function as intended. High SWR and high common mode current can also lead to destructive failure modes of the balun. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Contrary to the &quot;undefinierte Impedanzen&quot; claim in the paper, poorly matched baluns can cause non zero reflection coefficients independent of its efficacy as a common mode current suppressor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A balun that is connected to an impedance that has a significant capacitive reactance may cause odd impedance transformations due to the formation of a parallel LC circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are using balanced transmission line and you wish to measure the balanced and common mode currents, you can construct a simple instrument such as this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/q8u6Z.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/q8u6Z.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The details of this instrument are discussed by the author on his &lt;a href=&quot;http://users.tpg.com.au/users/ldbutler/Line_Diff_Long_Meter.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;website&lt;/a&gt;. Do exercise caution as this author has previously published articles that are, in my opinion, grossly wrong and even his referenced web page contains errors. But the meter and his descriptions for how to apply it to measure tuner balance, etc. are correct in the context of this topic.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-21T17:42:52.650" LastActivityDate="2018-09-21T17:42:52.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11935" PostTypeId="2" ParentId="8913" CreationDate="2018-09-22T00:33:39.333" Score="-1" Body="&lt;p&gt;If I am not mistaken, I believe a license is good for 8 years.  So when a class of license is upgraded, the expiration date should remain intact.  Congratulations on your extra class license.&lt;/p&gt;&#xA;" OwnerUserId="13262" LastEditorUserId="9493" LastEditDate="2018-09-25T14:36:13.487" LastActivityDate="2018-09-25T14:36:13.487" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11936" PostTypeId="1" AcceptedAnswerId="11937" CreationDate="2018-09-22T12:28:06.870" Score="7" ViewCount="228" Body="&lt;p&gt;I just passed my technician exam and received my callsign from the FCC (KC1KHV).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was surprised by the two letter prefix, which seems to come from the class D group.  According to &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/amateur-radio-service/amateur-call-sign-systems&quot; rel=&quot;nofollow noreferrer&quot;&gt;the FCC documentation on the topic&lt;/a&gt;, a technician license should come from the class C group, which has:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A K, N, or W prefix&lt;/li&gt;&#xA;&lt;li&gt;A region number&lt;/li&gt;&#xA;&lt;li&gt;A three letter suffix&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I see that it says &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;When the call signs in any regional-group list are exhausted, the selection is made from the next lower group&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;but there are clearly still class C callsigns available (I have my eye on a vanity callsign which falls into this category).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's up here? Am I just misreading things?&lt;/p&gt;&#xA;" OwnerUserId="13127" LastEditorUserId="4076" LastEditDate="2019-11-26T16:58:40.683" LastActivityDate="2019-11-26T16:58:40.683" Title="FCC callsign with incorrect group letter" Tags="&lt;united-states&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11937" PostTypeId="2" ParentId="11936" CreationDate="2018-09-22T15:30:29.043" Score="8" Body="&lt;p&gt;When the FCC issues your first call sign to you, they do not look backwards through their list of assigned call to see if there are any unused calls that they can reassign. Instead, they use a sequential numbering system from a block of previously unissued call signs.  This is the so called sequential call sign assignment since it is simply the next sequential call in their list. Technician class licensees will currently be issued a sequential call from the class D pool.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on your sequentially issued call sign, we can see that in district 1 the FCC is currently issuing licenses from the KC1K sequence. After issuing the 626 possible calls in this group. They will probably move onto KC1L. For every prefix group, there are approximately 16,900 issuable call signs. After exhausting all of those calls, they will probably move onto the KD1A block, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But now that you have your new license, you are free to apply for any available group C or D vanity call, which includes a 1×3. Good luck!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-09-22T15:30:29.043" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11938" PostTypeId="2" ParentId="11910" CreationDate="2018-09-22T16:34:47.360" Score="2" Body="&lt;p&gt;When designing circuits for the VHF region, careful design and construction practices must be utilized in order to obtain stable and repeatable gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are a few thoughts that may improve the reliability of your circuit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1.) Increase the drain resistance. This will reduce the tendency for UHF oscillations (and reduce the gain).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2.) Use toroids for your inductors if possible. Toroid forms help to provide self shielding of the inductor. If you cannot do this, orient the axis of the inductor such that it points towards the amplification stage in order to minimize stray coupling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3.) Keep all wire lengths as short as possible but in particular, minimize the gate lead length and its associated connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4.) You may get some improvement by installing a vertical shield over the FET to isolate the input from the output. Notch the shield to allow the shield to fit tightly over the FET.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;5.) Consider using a common gate topology with sufficient drain resistance to combat UHF oscillations. This will have lower gain which can be made up with a second stage of RF amplification if needed.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-09-22T16:34:47.360" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11939" PostTypeId="1" CreationDate="2018-09-23T05:28:26.490" Score="0" ViewCount="245" Body="&lt;p&gt;I am new to amateur radio and am having trouble getting my head around antenna theory. Can anyone suggest a good 'introduction to antennas' that doesn't get too technical?  Thanks.&lt;/p&gt;&#xA;" OwnerUserId="13265" LastEditorUserId="76" LastEditDate="2018-09-23T14:10:32.487" LastActivityDate="2018-09-24T23:24:47.020" Title="antenna theory for beginners" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="2" ClosedDate="2018-09-24T23:25:09.083" ContentLicense="CC BY-SA 4.0" />
  <row Id="11940" PostTypeId="1" CreationDate="2018-09-23T10:33:26.140" Score="5" ViewCount="4017" Body="&lt;p&gt;I plan on installing a vertical antenna soon. I expect it to cover from 80 meters to 10  (or perhaps 6). I plan on putting down 32 radials. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am wondering if 16 66' and 16 33' radials will be just as efficient for the higher bands as would having fewer radials separately cut for each band of interest. (Eg. 8 radials each for 80, 40, 20 &amp;amp; 10.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same question differently: If I cut all the radials for 80 meters, would it negatively affect the signals of 40, 20, 10, etc.?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone know the answer to this or where I can find it?&lt;/p&gt;&#xA;" OwnerUserId="13125" LastEditorUserId="8717" LastEditDate="2018-09-23T17:16:52.063" LastActivityDate="2020-01-08T16:22:46.710" Title="Radial length for vertical antennas?" Tags="&lt;vertical-antenna&gt;&lt;radial&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11941" PostTypeId="2" ParentId="11939" CreationDate="2018-09-23T13:36:12.483" Score="1" Body="&lt;p&gt;Three books come to my mind:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the evergreen Karl Rothammel: Antenna Book,&lt;/li&gt;&#xA;&lt;li&gt;Joseph J. Carr: Practical Antenna Handbook, which is technical, but it starts from the very beginning, and an exciting reading as well,&lt;/li&gt;&#xA;&lt;li&gt;and the (latest edition of the) ARRL Antenna Book that I didn't read myself, but it says it's a reference book of (HAM) antennas, it&#xA;may help, too.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerDisplayName="user13267" LastEditorUserId="1362" LastEditDate="2018-09-24T19:27:49.093" LastActivityDate="2018-09-24T19:27:49.093" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11942" PostTypeId="2" ParentId="11939" CreationDate="2018-09-23T13:46:29.000" Score="0" Body="&lt;p&gt;&lt;em&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/Why%20an%20Antenna%20Radiates.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Why Antennas Radiate&lt;/a&gt;&lt;/em&gt; clearly describes how antennas produce the electromagnetic fields we use for radio communication. Replacing complex mathematics with an intuitive, visual presentation, author Ken MacLeish, W7TX, describes the electric fields produced by static charges, the magnetic fields produced by moving charges (i.e., current) and the electromagnetic fields produced by accelerating charges.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having these fundamental concepts under one's belt is essential to understanding the differences between simple antennas and the operation of complex designs.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-09-23T13:46:29.000" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11943" PostTypeId="1" CreationDate="2018-09-23T15:22:19.710" Score="3" ViewCount="141" Body="&lt;p&gt;We are building a 4 ft diameter mag loop using 1&quot; copper tube.  The coupling loop will be at the top of the loop (we are using a large vacuum cap in a weatherproof box and it is too heavy to be permanently at the top of the loop in the high winds in Colorado).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can we run the feedline within the copper tube from the top of the loop, exiting near the bottom of the loop tube?  Is this a better solution than simply having the feedline drop across the nearfield?&lt;/p&gt;&#xA;" OwnerUserId="13269" LastEditorUserId="76" LastEditDate="2018-09-23T16:01:12.910" LastActivityDate="2018-10-23T14:40:58.253" Title="Running mag loop feedline INSIDE the loop tube" Tags="&lt;antenna-construction&gt;&lt;magnetic-loop&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11944" PostTypeId="2" ParentId="11943" CreationDate="2018-09-23T20:33:46.357" Score="1" Body="&lt;p&gt;It is a tough call.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly the inside of the tube carries no RF current. This would suggest that routing the coax in the tube would be a safe approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But my concern is that where the coax exits the loop, there will be a strong tendancy for the uniform, high current on the outside of the loop to couple to the exterior of the coaxial shield giving rise to common mode currents on the coax. A secondary issue is due to the reduction of the loop surface area where the coax exits. This will raise the RF impedance in this area causing some reduction in efficiency and possibly localized heating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The alternative route of letting it drop near the loop also provides the opportunity for coupling of common mode currents but at least there is a minor separation possible in this case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In either case, a good common mode choke on the coax is warranted. You may wish to experiment with the two techniques. An RF clamp-on ammeter would help to remove ambiguity/subjectivity from the experiment..&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-09-23T20:33:46.357" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11945" PostTypeId="1" AcceptedAnswerId="11947" CreationDate="2018-09-24T15:10:01.223" Score="3" ViewCount="432" Body="&lt;p&gt;I have some historical data on radio stations, but unfortunately, the dataset only has these variables:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;the power of the transmitter, in watts&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;the coordinates of the radio tower&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Unfortunately, I don't have &lt;strong&gt;any&lt;/strong&gt; data on the characteristics of the antenna(s) or the radio towers themselves, e.g. their height. Anecdotally, the frequencies of these stations are from 500 to 1500 kilocycles, which I believe are AM frequencies.&lt;/p&gt;&#xA;&lt;p&gt;I asked a &lt;a href=&quot;https://physics.stackexchange.com/q/428589/83985&quot;&gt;similar question on the physics.SE&lt;/a&gt; and was told that, with an example of a 500 W transmitter, I can &lt;em&gt;very&lt;/em&gt; roughly estimate the strength at a distance of, say, 10 km, as&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;At a distance of &lt;span class=&quot;math-container&quot;&gt;$10km$&lt;/span&gt;, that power is uniformly distributed over a sphere of radius &lt;span class=&quot;math-container&quot;&gt;$10km$&lt;/span&gt;. In other words, the power per &lt;span class=&quot;math-container&quot;&gt;$m^2$&lt;/span&gt; will be&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\frac{500}{4 \pi r^2}$&lt;/span&gt; in units of &lt;span class=&quot;math-container&quot;&gt;$\frac{watt}{m^2}$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;In this example, this gives me approximately &lt;span class=&quot;math-container&quot;&gt;$4 \times 10^{-7} \frac{\text{watts}}{m^2}$&lt;/span&gt;, or &lt;a href=&quot;http://www.wolframalpha.com/input/?i=4*10%5E-7+watts+to+dbm&quot; rel=&quot;nofollow noreferrer&quot;&gt;-33.98 dBm&lt;/a&gt; per square meter.&lt;/p&gt;&#xA;&lt;p&gt;With that number in hand, is there anything I can say about a receiver's ability to pick up that signal? As in, a standard household radio receiver in the 1920s could, on average, audibly receive signals down to strength -25 dbm, so it probably wouldn't be able to pick up this signal?&lt;/p&gt;&#xA;&lt;p&gt;Or is the more appropriate way to &lt;a href=&quot;https://ham.stackexchange.com/q/10076/13271&quot;&gt;convert this power into &lt;span class=&quot;math-container&quot;&gt;$V/m$&lt;/span&gt;&lt;/a&gt; and use an approximation of the audible area &lt;a href=&quot;https://en.wikipedia.org/wiki/Signal_strength_in_telecommunications&quot; rel=&quot;nofollow noreferrer&quot;&gt;like in this article&lt;/a&gt;?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;(Yes, I know this is an overly simplistic approximation; I'm trying to do the best I can with the extremely limited data that I have. It was recommended that I ask here, so any information is most welcome!)&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="13271" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-07-01T10:12:23.073" Title="Using approximate signal strength at a distance to estimate reception strength of a radio station" Tags="&lt;propagation&gt;&lt;rf-power&gt;&lt;history&gt;&lt;physics&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11946" PostTypeId="2" ParentId="11940" CreationDate="2018-09-24T16:01:39.750" Score="6" Body="&lt;p&gt;Rule of thumb: if the radials are elevated, at least two resonant radials for each band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the radials are buried or lying on the surface, at least 16 radials, each at least a 1/4 wavelength at the lowest operating frequency, and don't worry about resonance: just get as much wire in the ground as you can. More and/or longer is better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The objective of any radial system is to avoid current in the soil by presenting a lower impedance alternative. Current in soil is undesirable since it dissipates power in ohmic losses, reducing antenna efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In an elevated radial system, the separation between the radials and the soil surface provides isolation, meaning the current in each is largely independent. The soil and radials could be considered two parallel current paths, as such the one with the lowest impedance will take most of the current. Thus, it's important to minimize the radial impedance by ensuring some radials are resonant on any band used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a buried radial system, soil and radials are tightly coupled due to their proximity. Low ground losses are achieved not by providing a low impedance alternative but rather by effectively increasing soil conductivity by stuffing it full of copper. Thus, attempting to reduce radial impedance by cutting some of the radials to be shorter to be resonant on higher frequencies is futile or even counterproductive.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-01-08T16:22:46.710" LastActivityDate="2020-01-08T16:22:46.710" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11947" PostTypeId="2" ParentId="11945" CreationDate="2018-09-24T17:08:46.223" Score="3" Body="&lt;p&gt;We have some clues from a historical perspective. In the January 1917 edition of &lt;em&gt;The Radio Experimentor&lt;/em&gt;, author H. Winfield Secor noted that approximately 50 kW (kilo-watts) of transmitter power was required to reach a 3,000 to 4,000 mile range with CW. He then went on to note that 10 μA (micro-amperes) is considered a weak receive signal while 20 μA is a strong signal. He also recorded an important fact that 10 μA is equivalent to 0.01 μW (micro-watts). From this we can calculate the input impedance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Z_{in}=\frac{P}{I^2} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where P is the power in watts and I is the current in amperes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So we see that the apparent input impedance that supports Secors statistics is 100 ohms. We can then re-arrange equation 1 to return watts based on amps:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$P=Z_{in}*I^2=100*I^2 \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using equation 2, we can then translate the 10 μA field signal level to 0.01 uW or -50 dBm and the 20 uA signal to 0.04 uW or -44 dBm since:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$dBm=10 \log \left(\frac{P}{0.001 watts}\right) \tag 3$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where dBm is the decibels compared to 1 mW (0.001 watts).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just as a basis for comparison, modern radios easily achieve 0.25 μV (micro-volt) MDS (minimum discernible signal) sensitivity across a 50 ohm input impedance. We compute power in this case as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$P=\frac{E^2}{R} \tag 4$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where E is the voltage in volts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is equivalent to 0.00125 pW (pico-watts or 10&lt;sup&gt;-12&lt;/sup&gt; watts) or -119 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secor does not make it clear if his references are the input currents to the receiver or if this is the field strength (the square root of irradiance) in the field of the receiver antenna. But the basis of the article was to assemble a compendium of competing methods of detection so I believe it would be safe to say that this was the required current at the input to the receiver terminals. Supporting this notion is the clarifying note from the author: '&lt;em&gt;Technically speaking, radio detectors are usually rated by the amount of electrical energy in ergs necessary to actuate them.&lt;/em&gt;' when he was referencing the earlier listed micro amperes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To compare your tabular data with this historical reference, you would need to presume that the equivalent receive and transmit antenna gains for the path in question are used in the comparison. You would also need to presume that the path loss is equal. Then, as you noted in your question, you can compare potential distances simply as a function of power and the inverse of distance squared.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do note that Secor's article is based upon CW transmissions so AM detection may have different statistics. Also note that during the 1915 to 1930 period, there were significant advances in detector technology and receiver architectures. As a result, there could be a significant error range in your estimates depending upon the exact period of comparison.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-25T01:50:07.733" LastActivityDate="2018-09-25T01:50:07.733" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="11948" PostTypeId="2" ParentId="11945" CreationDate="2018-09-25T10:17:21.030" Score="3" Body="&lt;p&gt;The methodology needed to accurately calculate the radiated r-f power needed to generate a given field intensity at some distance along a terrestrial path is highly complex — probably beyond the practical possibility of posting in an answer here, even in outline form.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the U.S. FCC has developed a set of propagation charts relating to this topic, which provide a fairly straightforward way of answering this question for frequencies in the AM broadcast band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a link to a paper based on those propagation charts.  It includes some background information along with several plots showing the distance to a groundwave field intensity of 0.5 mV/m, which is about the minimum field needed by a consumer-level AM broadcast receiver with a built-in antenna, given sufficiently low co- and adjacent-channel interference from other AM stations, and a receive site having sufficiently low ambient r-f noise levels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://rfry.org/Software%20Download/Freq%20and%20Conductivity%20as%20Factors%20in%20MW%20Field%20Intensity.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Factors in MW Signal Coverage&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-07-01T10:12:23.073" LastActivityDate="2019-07-01T10:12:23.073" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11949" PostTypeId="1" AcceptedAnswerId="11950" CreationDate="2018-09-25T14:25:14.147" Score="2" ViewCount="207" Body="&lt;p&gt;Second (and last hopefully) question on the classic &lt;em&gt;Solid State Design for the Radio Amateurs&lt;/em&gt; (SSDRA) book by Hayward et al.  Again it's a power amplifier circuit (Chapter 4, pg. 66), and again it's related to baluns.  Is it just me or are baluns complicated to understand (at times)?  Here's the circuit, with the balun in question identified as T2 at the output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6P0LG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6P0LG.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's my spice interpretation of the balun and it's no coincidence that it has a similar layout to that found in the balun analysis paper by G3TXQ (&lt;a href=&quot;http://www.karinya.net/g3txq/baluns/baluns.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.karinya.net/g3txq/baluns/baluns.pdf&lt;/a&gt;). On the right-hand side is the balanced load (pins 1 and 2 in the original SSDRA circuit) and on the left side is the unbalanced input, with pins 4 and 5 going to ground (these pins are AC grounded in the original).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sYVvY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sYVvY.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, it's very similar to the 1:1 voltage balun described in this document, except that the polarity (dot) of the tertiary winding is reversed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TtoJd.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TtoJd.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without doing any analysis on the SSDRA balun, I figured it was going to be a voltage balun and I was expecting the voltages across the balanced load to be equal, as with the conventional voltage balun given in the G3TXQ document.  I was wrong.  In fact the winding directions of the SSDRA balun seem to generate a short in the unbalanced source.  That sortof makes sense, since the voltage across L1 and L2 cancel leaving a short to ground.  See the spice current across R4 below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1kKMZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1kKMZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, my question is: what exactly is this balun doing?  &lt;/p&gt;&#xA;" OwnerUserId="11875" LastActivityDate="2018-09-26T14:23:54.707" Title="Power Amplifier Balun Question" Tags="&lt;balun&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11950" PostTypeId="2" ParentId="11949" CreationDate="2018-09-25T16:23:58.720" Score="4" Body="&lt;p&gt;I believe it's a misprint. Comparing the drawing showing the construction of the balun with its schematic representation, it does appear the dot on the lowermost winding (terminals 2 and 5) is backwards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we build it like the schematic suggests, consider the application of a differential mode input on the balanced side:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ayxDY.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fayxDY.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;V1 drives current in L3 and L1, but the polarity of these windings are opposite, resulting in zero net magnetic flux. Thus it's as if the inductors aren't even there, and V1 sees a short. Not a useful property in this application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However if we flip L3 the other way:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/LU3yx.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fLU3yx.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now L1 and L3 are working together rather than cancelling each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Vcc is attached to the center tap (with a little filtering), and half of the primary winding is the load for each of the transistors. So at a basic level, each half of the amplifier is just a common-emitter amplifier:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Z174N.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fZ174N.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-09-26T14:23:54.707" LastActivityDate="2018-09-26T14:23:54.707" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="11951" PostTypeId="1" CreationDate="2018-09-25T21:01:48.427" Score="4" ViewCount="268" Body="&lt;p&gt;I am building a ground and wall penetrating frequency modulated continuous wave radar. The only components that I have not been able to track down are the antennas. I need two antennas (one for transmit and one for receive) that cover the frequency range of 100MHz to 1GHz (or as much of that range as possible). I have searched a lot of different sites and was hoping someone here might be able to suggest something I haven't come across yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is for a university project, so I am unfortunately limited by budget and an imperfect understanding of what exactly I need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically what I am trying to do is transmit a ramped signal from the low end of my range (100MHz) up to the high end of the range (1000MHz) into the ground and then be able to receive the signals back to calculate if they are bouncing off of anything buried underground. The lower frequencies allow me to see objects at greater depths. I am hoping to find something that will cover the whole range, but so far there is a plethora of options in the 1GHz and above ranges and almost nothing ultra wideband in the lower than 1GHz range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifications I have so far: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Freq Range: 100MHz-1000Mhz&lt;/li&gt;&#xA;&lt;li&gt;Impedance: I planned on an external network to match, so whatever is available.&lt;/li&gt;&#xA;&lt;li&gt;Size: Need to fit 2 antennas in an approximate area of 2x3 ft maximum&lt;/li&gt;&#xA;&lt;li&gt;Price: Budget for 2 antennas $100 &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13278" LastEditorUserId="9493" LastEditDate="2018-09-26T11:13:16.090" LastActivityDate="2018-09-26T14:04:35.347" Title="100MHz to 1000MHz Antennas for Transmit and Receive" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="11952" PostTypeId="1" CreationDate="2018-09-26T05:30:30.830" Score="2" ViewCount="193" Body="&lt;p&gt;I'm trying to receive a UHF TV signal 86 miles away. Considering the height of the transmitting antenna and the height of the receiving antenna, I should be able to just make line-of-sight between them... but the signal will be weak and probably perturbed in a number of ways.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can now occasionally receive this signal using 1 DB8 &quot;bedspring&quot; antenna. The popular DB8 TV antenna consists of 4 vertically stacked bowties in parallel with 4 vertically stacked bowties. In the center of the lines that connect these two arrays in parallel is a matching transformer to convert the 150 ohm balanced signal from the parallel arrays to a 75 ohm unbalanced output. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to vertically stack two DB8s to try to achieve a theoretical +3db additional gain. It seems I should be able to do this by removing the matching transformer from each DB8 and connecting the two antennas in parallel by simply running two parallel lines (spaced and sized appropriately) from the center feed point of the top DB8 to the center feed point of the bottom DB8... in place of the matching transformers. This puts the 150 ohms of the top DB8 in parallel with 150 ohms of the bottom DB8 to yield 75 ohms at the center of the lines connecting the two antennas. Then, using a 1:1 current balun, I can convert the 75 ohms balanced to 75 ohm unbalanced to match my 75 ohm coax downfeed. This is the lowest possible loss method I can imagine to combine two DB8s. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sounds easy but I've been around a long time and in my experience, antennas seldom behave exactly the way theory predicts. Has anyone ever tried this? Is there a better way?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Edit: Following Glenn's excellent advice, I've disassembled the baluns on each array and hope to begin experimenting with the phasing harness this weekend. For those interested, below are pictures of the PC board inside balun enclosure.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/B5I8M.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/B5I8M.jpg&quot; alt=&quot;Balun - LC side&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/6u4kv.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6u4kv.jpg&quot; alt=&quot;Balun - Ground plane side&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13281" LastEditorUserId="13281" LastEditDate="2018-09-29T18:16:20.953" LastActivityDate="2018-09-29T18:16:20.953" Title="Stacking DB8 &quot;bedsprings&quot;" Tags="&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;bowtie&gt;" AnswerCount="1" CommentCount="6" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11953" PostTypeId="2" ParentId="11951" CreationDate="2018-09-26T11:33:05.153" Score="1" Body="&lt;p&gt;You didn't say if you need something directional, but I'll assume you do.&#xA;There are a number of trivially fractal antennas that have this bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most popular of those is the log periodic antenna; you can look at it as a series of stacked parallel mutually driven dipoles.  Each dipole will need to be roughly a half wavelength long.  at 1G, that would be about 15cm, at 100mhz 1.5m, and the boom to hold the elements might also be about that long.  (In other words, it'll be a bit bigger than your size requirements.)  However, there's ways to make log periodic antennas that fold or disassemble easily, so if this size limit is for storage, it may still work. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next antenna I'd suggest is a (log periodic?) spiral antenna.  It has a fairly wide radiation pattern if it's flat, but if you put the spiral on a cone, it becomes highly directional.  Again, the size of the spiral will approach a half wavelength in diameter, so it may be too large for the lower frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More basic antennas (which would probably need to be larger to be effective) would include a horn or a corner reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might be able to cheat a bit and use a smaller versions of the above antennas that would work on the lower frequencies, but at a reduced effectiveness and probably a worse match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IF you didn't want something directional, stacked discones might work.  Again, the lowest frequency will be large, but there are ways to fold it for storage.  A single discone would also work, but the radiation pattern is ugly for the higher frequencies (which might be ok for receive but is unlikely to be useful for transmit).  The higher frequency discones you might want to make out of solid sheet metal; the lower frequencies could be skeletonized with just stiff wires arranged in a cone and joined at the narrow end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It might also be possible to combine some of the above with &quot;loaded&quot; elements that are shortened by adding coils in the dipole element.  However I've not seen any designs that combine bandwidth with loaded elements, so you'd probably have to find someone to design it for you and you might end up with discrete frequencies in the range rather than a full spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the larger consumer grade outdoor TV antennas include both a log periodic and corner reflector antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only difference between a transmitting antenna and a receiving antenna is that matching matters more for transmitting antennas, and receiving antennas are sometimes made cheaper by using thinner wires.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2018-09-26T11:39:04.107" LastActivityDate="2018-09-26T11:39:04.107" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11954" PostTypeId="2" ParentId="11910" CreationDate="2018-09-26T13:18:36.617" Score="0" Body="&lt;p&gt;There is much about the topology of your first stage amplifier that looks like an oscillator. It's reasonable to try a design that is more likely to be stable: the common-gate amplifier. This topology sports low input impedance and high output impedance, which seem to be a good fit to the rest of your design:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is an LTSpice model of a possible circuit using the MPF102:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9IRLk.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9IRLk.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the J310 or similar is often preferred for VHF applications because the reverse-transfer capacitance is about 10X smaller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 3-dB passband of the input filter is about 68MHz to 88MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/S2gi9.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/S2gi9.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and the voltage gain is about 20dB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wtB3C.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wtB3C.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a plot of the frequency response:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jDTvM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jDTvM.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be sure to follow all of the recommendations in the earlier post, particularly shielding the input from the output as well as possible. Also, don't assume that your toroidal inductors are correct: the magnetic materials have large permeability variations, so measure them to ensure you get the expected results.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2018-09-29T10:57:30.783" LastActivityDate="2018-09-29T10:57:30.783" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11955" PostTypeId="2" ParentId="11951" CreationDate="2018-09-26T14:04:35.347" Score="1" Body="&lt;p&gt;A log-periodic dipole array on printed-circuit board from &lt;a href=&quot;https://www.wa5vjb.com/products1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;WA5VJB&lt;/a&gt; might provide an acceptable off-the-shelf solution. Note, though, that size is dictated by the low-frequency response. Dropping the 400MHz low end of his largest unit to the 100MHz you desire will drive a 4X increase in at least one dimension.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-09-26T14:04:35.347" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11956" PostTypeId="2" ParentId="4867" CreationDate="2018-09-26T20:22:56.197" Score="1" Body="&lt;p&gt;I would bring a small canister of helium, small weather balloon, light wire, tiny fishing pole and float your antenna up to increase your range. All these things would be valuable in an emergency situation in other ways.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or send the the whole hand held radio up and use a Bluetooth mic eliminating the need for a electrical or antenna running the length of the fishing line. &lt;/p&gt;&#xA;" OwnerUserId="5840" LastEditorUserId="5840" LastEditDate="2018-09-29T15:53:00.613" LastActivityDate="2018-09-29T15:53:00.613" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11957" PostTypeId="2" ParentId="4867" CreationDate="2018-09-27T11:24:45.143" Score="1" Body="&lt;p&gt;If all your radios will near the same height (plateau) with nothing between them (like mountains), then the biggest limitation will be the curvature of the earth.  With a 2m radio, this limits you to pretty close to 3-5 miles between radios where reception starts to get questionable.   If your groups are each just under 5 miles apart, pretty much only neighboring groups will be able to hear each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to increase the distance is to raise the height of one or all the antennas.  At the margins, even a foot matters.  A balloon might help, but a collapsible push up pole would help more.  (Or a J-pole hung from a tree, if you have trees.)  Another possibility is to get longer antennas suitable for the frequency you are using.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antennas are above the frame of the backpack, then the metal in the frame will not interfere.  You could ground the radio to the frame, but it would be equally effective to hang a pigtail from the radio.  (Either arrangement helps if you mount the radio to the backpack instead of holding it.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to get really crazy, you could probably hard mount the antenna on the frame with some kind of extension and run coax to the radio so the weight of the antenna doesn't stress the radio.   A simple monopole won't work in this situation -- you need a full dipole (which a pigtail provides) or a J-pole or something.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can find a repeater within range, it gives you the height necessary to cover the distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whatever you do, I suggest you try it (with some distance) before you go on the trip.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-09-27T11:24:45.143" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11958" PostTypeId="2" ParentId="4867" CreationDate="2018-09-27T21:48:28.437" Score="0" Body="&lt;p&gt;Antennas, for plain olde FM ... the higher the better, the bigger the better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer the question, take as much as is resonable to lug along. Probably some testing before hand is in order.&lt;/p&gt;&#xA;" OwnerUserId="8704" LastActivityDate="2018-09-27T21:48:28.437" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="11959" PostTypeId="2" ParentId="11952" CreationDate="2018-09-28T10:40:48.273" Score="2" Body="&lt;p&gt;The degree of additional gain from phasing two of the arrays will largely come down to the phasing harness and the balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you are focusing on a single UHF frequency, I recommend an open line phasing harness between the two arrays after removing the supplied balun on each array. Use multiples of 1/2 wavelength of open wire transmission line from each panel. This will replicate the impedance of each panel and result combined impedance of Z/2. The characteristic impedance of the phasing harness sections does not matter if you use multiples of 1/2 wavelength. Close attention to the length of each line is important in order to ensure proper phasing from each panel. Don't forget to adjust for the velocity factor of the phasing sections. If completely open lines with no insulators are possible, you could achieve a velocity factor close to 1. If you have a few spacers, the velocity factor may approach 0.98 or so. Multiply your calculated 1/2 wavelength multiple by the velocity factor to determine the physical length required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have an antenna analyzer or VNA at your disposal, it would be helpful to measure the complex impedance of each array and then confirm the resulting complex impedance of the phased arrays. This will remove a great deal of the ambiguity in the solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to transform the combined impedance to an impedance more suitable for a balun, you may have success with a shorted 1/2 wavelength (or longer) open wire transmission line of any impedance. Connect one end of the open wire transmission line to the junction of your phasing harness and temporarily short the other end. The balun is connected between these two points. By adjusting the connection point of the balun and the position of the shorting element, you can generally obtain a suitable match for the balun. Here again the use of an antenna analyzer or VNA would be helpful in reducing the iterations necessary for the best match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are up for home brewing an antenna, you may have success with a trough reflector design. With a 45° vertex, a theoretical gain of 17 dBi can be achieved with a single dipole element. At UHF frequencies, the reflector can be made of a screen mesh. The ARRL Antenna book gives the basic design parameters.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-09-28T12:12:37.377" LastActivityDate="2018-09-28T12:12:37.377" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11965" PostTypeId="1" CreationDate="2018-10-02T11:11:47.530" Score="0" ViewCount="1225" Body="&lt;p&gt;Since adding a reflector and a director horizontally to a dipole (as in a three element Yagi) causes the beam to reflect horizontally, what should happen if reflectors above and below the dipole were added?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dipole less than a half a wavelength above the ground radiates up. But, if one were to add reflectors above and below the dipole (or even a standard three element Yagi) would not that cause the beam to be horizontally directed?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am imagining this for an HF antenna, but I presume the theory would apply to any type of Yagi or dipole antenna.&lt;/p&gt;&#xA;" OwnerUserId="13125" LastEditorUserId="13125" LastEditDate="2018-10-02T13:39:54.870" LastActivityDate="2018-10-02T16:40:54.693" Title="If one were to add reflector elements above and below a dipole would it change the direction to horizontal?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11966" PostTypeId="2" ParentId="11965" CreationDate="2018-10-02T15:11:14.840" Score="3" Body="&lt;p&gt;In a Yagi, the beam direction is the result of constructive interference between all three elements. Typically the elements are spaced about a 1/4 wavelength. The reflector is ahead about 90 degrees (a 1/4 oscillation) in phase, and the director behind about 90 degrees. The phase of each element is a consequence of its spacing and length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When viewed from the front of the beam where gain is greatest, the reflector is a 1/4 wavelength farther away, and the director a 1/4 wavelength closer. This counteracts the phase shift just described, and the result is the wavefronts from each element are arriving in phase from this perspective. The constructive interference is what gives the antenna high gain in this direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Behind the beam, this is reversed: the relative distances of the elements adds another 90 degree phase shift on top of the 90 degree shift they already had, meaning each individual wavefront arrives 180 degrees out of phase. These opposite waves cancel, meaning the antenna has very low gain (ideally zero gain) in this direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kDQfe.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kDQfe.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;em&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Yagi_antenna_animation_16_frame_1.6s.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;By Chetvorno [CC0], from Wikimedia Commons&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason for the radiation pattern of a dipole over ground is similar: it's the consequence of the wavefronts from two radiating elements arriving in phase or out of phase. Only in this case the 2nd element is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;image antenna&lt;/a&gt; that exists as a consequence of the ground. As a simplification, whenever an antenna exists on one side of a conductive plane (like the ground), we can imagine that plane as a mirror, and pretend there's an identical antenna on the other side of the mirror. The only difference is the phase of this image antenna is opposite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So consider a dipole a quarter wavelength above ground. This makes the image antenna a half wavelength away from the dipole, and 180 degrees out of phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At low elevation angles, the distance to the real dipole or the image antenna is equal, so there's no phase change. So the wavefronts arrive 180 degrees out of phase, and cancel. So no radiation here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Directly overhead, the image antenna is a 1/2 wavelength away, adding 180 degrees of phase to it. Now the wavefronts from the real dipole and the image antenna arrive in phase, so there is high gain in this direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Raise the dipole to a half wavelength, and now the relative phase and distances of the image antenna result in a null directly overhead, and a maximum at 30 degrees above the horizon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now to your question: could adding more elements to a dipole that is less than a quarter wavelength high improve gain at low elevation angles?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, depending on just where they were added, and their relative phase to the main element, sure. However, since you're already starting from a situation where some of the elements aren't in the right phase, you'll never get better than a compromise solution. And at least some of these elements will need to be at least a half-wavelength high. If the support structure for holding an element that high exists, why not just put a simple dipole up there and skip the reflector business?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, proximity to the ground has another detrimental effect: restive losses. The ground isn't a perfect conductor, so whenever there's current in the ground, transmitter power is being lost. This is why we put down radials for example. Getting the antenna higher reduces the current density in the ground, and thus the loss. To have some kind of antenna close to the ground which is still efficient will require improving the ground conductivity somehow.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-10-02T16:40:54.693" LastActivityDate="2018-10-02T16:40:54.693" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11967" PostTypeId="2" ParentId="11965" CreationDate="2018-10-02T15:11:42.557" Score="2" Body="&lt;p&gt;Following the pattern of a traditional parasitic reflector element as used in a Yagi-Uda array, there is more benefit to adding elements in the horizontal plane of the driven element than there is in adding them in the vertical plane. This is even more true if, as you suggest, one contemplates adding two parasitic elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your observation that, &quot;A dipole less than a half a wavelength above the ground radiates up,&quot; is key. Were one to add two &quot;reflectors&quot; at a typical spacing of ~0.1-wavelength above and below the driven element, &lt;em&gt;all&lt;/em&gt; of the elements would still be less than a half-wavelength above ground, so the opportunity to lower the radiation angle is minimal.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-02T15:11:42.557" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11970" PostTypeId="1" AcceptedAnswerId="11972" CreationDate="2018-10-03T22:46:17.863" Score="-4" ViewCount="126" Body="&lt;p&gt;Would appreciate insight on efficiency of PSK31 on various HF band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would 300 to 1000 km generally achievable if suitable band are chosen, according to day night and sun spot cycle using low power QRP and simple 3 meters vertical antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please fill in the table like below. I only have VHF FM license. No experience on HF nor digit modes. Assume 5 watts, vertical antenna of about 3 meters, retransmission allowed. May be aiming for says 70% chance of the message transmitted success rate. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;3.5MHz,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best sun spot cycle, 300km day, 400km night&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Worst sun spot cycle, 200km day, 300km night&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Present sun spot cycle, 250km day, 350km night&lt;/p&gt;&#xA;&#xA;&lt;p&gt;..... other frequencies.....&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;&#xA;&lt;p&gt;=========== answer my own question&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.voacap.com/hf/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.voacap.com/hf/&lt;/a&gt;   I found this site which answer my question. One can enter two QTH and it predicts propagation, received signal in dBW, SNR for time and months&lt;/p&gt;&#xA;" OwnerUserId="1473" LastEditorUserId="1473" LastEditDate="2018-10-04T19:14:54.187" LastActivityDate="2018-10-04T19:14:54.187" Title="Transmission distance of PSK31 on various HF band" Tags="&lt;psk31&gt;" AnswerCount="2" CommentCount="3" ClosedDate="2018-10-04T08:24:06.057" ContentLicense="CC BY-SA 4.0" />
  <row Id="11971" PostTypeId="2" ParentId="11970" CreationDate="2018-10-04T00:23:04.597" Score="2" Body="&lt;p&gt;Transmission distance isn't limited by mode.  It is limited by frequency, and sometimes power.  Even given frequency and power, you can only give broad generalities on distance, because band conditions can make propagation vary in both directions by orders of magnitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, psk31 is a narrower bandwidth than many modes, which allows power to be concentrated, and digital modes frequently can be readable with a higher signal to noise ratio than phone modes, both of which effectively increase distance.  But neither of these is unique to psk31.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-10-04T00:23:04.597" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11972" PostTypeId="2" ParentId="11970" CreationDate="2018-10-04T01:35:36.083" Score="4" Body="&lt;p&gt;This question is far too general to merit definite answers. There are free propagation prediction tools that can help you understand the possibilities. I recommend PropView, a component of the &lt;a href=&quot;http://dxlabsuite.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Lab Suite&lt;/a&gt;. With this tool, you can evaluate propagation paths between geographic locations based on solar weather conditions, operating mode, transmitter power, etc.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-04T01:35:36.083" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11973" PostTypeId="1" CreationDate="2018-10-04T06:32:50.260" Score="1" ViewCount="126" Body="&lt;p&gt;I have recently taken on programming radios for my workplace in Chicago, IL. We have an old base station (Kenwood TK863G-1) that I wanted to know if it would be possible to use as a repeater similar to how law enforcement does. What I mean by this is use the vehicle installed transceiver to relay or repeat the traffic to and from a uhf handheld. This would help get better coverage to our main building on campus when we are on the other end of campus or making a run to the gas station down the road.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess to break down this question I want to know two things...&#xA;1. How would I go about setting up a relay/repeater in a vehicle to relay traffic from nearby handhelds on our chosen frequencies (at least one but would be nice to relay/repeat our 3 to 5 channels)?&#xA;2. Can I use our existing Kenwood TK-863G-1 to accomplish the scenario above. If not, can you suggest some cheap alternatives?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks everyone :)&lt;/p&gt;&#xA;" OwnerUserId="13323" LastActivityDate="2018-10-07T13:57:25.680" Title="Repeating UHF Handheld via UHF vehicle transceiver" Tags="&lt;uhf&gt;&lt;repeater&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="11974" PostTypeId="1" CreationDate="2018-10-04T07:19:00.720" Score="1" ViewCount="100" Body="&lt;p&gt;I am a noob to a lot of amateur radio and I am investigating and planning a repeater setup to be installed in my workplace. We are on a hospital campus in Chicago, IL and have many tall buildings around us. Thus our 30-50 Kenwood TK-3160 and TK-3360's are not powerful enough to penetrate the many concrete walls to always provide the best reception on all ends of the building and across campus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wanted to see what suggestions the community has for a cost effective repeater setup for a scenario where we would be repeating 3-5 channels of uhf traffic. There is one other repeater on campus but we do not have access or permission to mess with it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A functionality that we would like to have is to also repeat the NOAA weather channel for our area to a uhf channel for our handhelds to tune into. I believe NOAA broadcasts on vhf if I remember correctly. So some suggestions with the functionality would be nice too!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the 3 channels we are using just for our building are on the same frequency for transmitting and receiving, do we need to have a separate channel for each direction? &lt;/p&gt;&#xA;" OwnerUserId="13323" LastEditorUserId="8717" LastEditDate="2018-10-06T23:03:52.773" LastActivityDate="2018-10-07T12:41:09.050" Title="Repeater for 1/4 square mile campus" Tags="&lt;uhf&gt;&lt;repeater&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="11975" PostTypeId="1" AcceptedAnswerId="11979" CreationDate="2018-10-04T14:19:52.113" Score="2" ViewCount="174" Body="&lt;p&gt;An outside source is broadcasting an RF signal at 406 MHz. I want to know if it's possible to receive this signal with one antenna, and then simply send the signal to another antenna that sends it right back out. I want this to be a simple circuit where the receiving antenna only receives and the transmitting antenna only transmits. The transmitting antenna can have a slightly different frequency but it would need to be as close to 406 MHz as possible. The intention is to reflect a signal right back at it's source, in as simple of way as possible. Will this work?&lt;/p&gt;&#xA;" OwnerUserId="13324" LastEditorUserId="8573" LastEditDate="2020-09-15T13:20:54.947" LastActivityDate="2020-09-15T13:20:54.947" Title="Can I reflect a radio wave by receiving it with one antenna and then sending it back out with another?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11976" PostTypeId="1" AcceptedAnswerId="11980" CreationDate="2018-10-04T14:30:24.087" Score="2" ViewCount="45" Body="&lt;p&gt;I have previously implemented an APRS transmitter from scratch by manually generating the modulated sine wave. In this implementation, I did NZRI encoding over the entire packet (including postamble and preamble), though only the payload bytes were bit stuffed. This approach worked fine, but I'm wondering if this was a coincidence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm looking at making a new APRS transmitter, and now I'm having doubts about whether the flag bytes are NZRI encoded or not. I can't find any documentation that says for sure one way or the other. &lt;/p&gt;&#xA;" OwnerUserId="13325" LastActivityDate="2018-10-05T00:32:07.637" Title="In HLDC framing/Bell202 encoding, are the flag bytes NZRI encoded?" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11977" PostTypeId="1" AcceptedAnswerId="11978" CreationDate="2018-10-04T15:18:07.537" Score="5" ViewCount="150" Body="&lt;p&gt;I'm new to ham (although I've had a license for a long time) and I'm having issues with receiving on a basic handheld. I have a cheap BaoFeng UV-82HP and I keep getting full signal noise at random times. I have gotten this on different channels in different locations. When I'm not getting the noise, I get clean and clear transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Video Evidence:&lt;/strong&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://youtu.be/nupqlH3-eQ0&quot; rel=&quot;noreferrer&quot;&gt;https://youtu.be/nupqlH3-eQ0&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Power/Ground Troubleshooting:&lt;/strong&gt;&lt;br&gt;&#xA;The unit is a battery operated handheld, so I don't have to worry about power input.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Antenna Troubleshooting:&lt;/strong&gt;&lt;br&gt;&#xA;I have tried three different antennas including a rubber duck and they all have the same issue. I assume the rubber duck doesn't need grounding as it is very small and not really ground-able.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume that means that means the noise is a defect in the radio?&lt;/p&gt;&#xA;" OwnerUserId="13326" LastActivityDate="2018-10-15T13:22:38.677" Title="How do I have a full signal of noise on a handheld?" Tags="&lt;antenna&gt;&lt;ht&gt;&lt;baofeng&gt;&lt;noise&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11978" PostTypeId="2" ParentId="11977" CreationDate="2018-10-04T16:53:01.707" Score="3" Body="&lt;p&gt;That's not noise, it's digital voice. DMR, DSTAR, and P25 are digital modes that find popular use on the amateur bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some repeaters are digital-only. Others are dual-mode, so you will encounter a mix of digital and analog FM, depending on what the other station is transmitting. If you can find information on the repeater, you will probably discover what modes it supports.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On a cursory look, it does not appear the UV-82HP supports any digital modes, so unfortunately you won't be able to participate without a different radio or some software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Related: &lt;a href=&quot;https://ham.stackexchange.com/questions/11853/how-to-scan-while-avoiding-digital-noise-frequencies&quot;&gt;How to scan while avoiding digital/noise frequencies?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-10-15T13:22:38.677" LastActivityDate="2018-10-15T13:22:38.677" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="11979" PostTypeId="2" ParentId="11975" CreationDate="2018-10-04T17:06:49.973" Score="7" Body="&lt;p&gt;Yes, it's possible. Simply connecting two antennas with a feedline will do this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to reflect the signal right back at the source, you can more simply just omit the second antenna, and terminate the feedpoint of the first antenna in a short or leave it open. Since the short or open can't accept any power, any power received by the antenna must eventually be re-radiated by it, or lost in the resistance of the antenna, etc. &lt;a href=&quot;https://en.wikipedia.org/wiki/Chaff_(countermeasure)&quot; rel=&quot;nofollow noreferrer&quot;&gt;Chaff&lt;/a&gt; works on this principle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't imagine any practical application for this, however. Sometimes people construct passive reflectors this way to get a line-of-sight signal around an obstruction. But reflecting the signal directly back at the source seems rather pointless, since the field strength at the source is already strong. The minuscule power reflected back at the source is insignificant compared with the power already at the transmitter. It's like trying to burn out the sun with a mirror.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-10-05T09:06:33.150" LastActivityDate="2018-10-05T09:06:33.150" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11980" PostTypeId="2" ParentId="11976" CreationDate="2018-10-05T00:32:07.637" Score="1" Body="&lt;p&gt;The challenge with the HDLC/Bell 202 &quot;standard&quot; is that it is poorly defined and so it results in varietal implementations. One is often left to test a questionable element against a variety of implementations to find what works best. And often &quot;best&quot; is not the measure but rather &quot;what works well in this circumstance?&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ken Finnegan, W6KWF compiled perhaps one of the best examinations of the &quot;standard&quot; as a Masters degree student at California Polytech. His paper can still be found on-line &lt;a href=&quot;https://www.google.com/url?sa=t&amp;amp;source=web&amp;amp;rct=j&amp;amp;url=https://www.tapr.org/pdf/DCC2014-Amateur-Bell-202-Modem-W6KWF-and-Bridget-Benson.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;on the TAPR website&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have found that the flag byte functions without bit stuffing, then you are most likely correct. Ken points out that payload and frame checksum must be bit stuffed. From this one can infer that the flag bytes are not subjected to bit stuffing since they are not part of either. Furthermore, bit stuffing is required after every five 1's and clearly the 0x07e flag byte consists of 6 consecutive 1's so if this has worked for you in the past without bit stuffing, there exists at least some population of the implementations that agrees with your methodology. Go with that until you find a larger population of contrarians.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-10-05T00:32:07.637" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11981" PostTypeId="2" ParentId="7265" CreationDate="2018-10-05T11:30:35.747" Score="2" Body="&lt;p&gt;Terrestrial, point-point propagation paths can exist due to diffraction of the radiated e-m fields over terrain peaks and man-made structures, with each diffraction adding loss at the receive antenna to the normal inverse-distance field loss for an LOS path of that total length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The graphic below illustrates this for an FM broadcast station, where the line-of-sight path is severely obstructed, but the signal can be received well beyond those obstructions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The real propagation path would consist of several straight-line segments over terrain peaks, joined together to connect the transmit and receive antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this example, the additional loss due to diffractions compared to an LOS path of that total length is shown to be 76.59 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The received field will vary over time depending on atmospheric K-factor and other conditions.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/RjH7i.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RjH7i.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-10-05T11:30:35.747" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11982" PostTypeId="1" AcceptedAnswerId="11986" CreationDate="2018-10-05T15:12:58.610" Score="1" ViewCount="419" Body="&lt;p&gt;I am upgrading from an HT to a Kenwood TM-V71A. Yay! But this means I&#xA;need to install some antennas and run feed lines into my&#xA;shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm going to be installing antennas in my attic (the feed lines will&#xA;exit the attic, run down the side of the house, and re-enter in the&#xA;shack, for a total length of ~30ft).  I've read many articles that&#xA;suggest external cable runs like this should be grounded near the&#xA;point they re-enter the house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am planning on standardizing on BNC connectors. What are my options&#xA;for grounding these cables? I haven't been able to find a BNC&#xA;grounding block.  There are lightning arrestors, but these are pricey&#xA;and seem like overkill given that the antennas are in the attic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These feed lines are located on the opposite side of the house from&#xA;the ground spike. What is my best option for a ground connection?&#xA;Would I need to install a new ground spike?&lt;/p&gt;&#xA;" OwnerUserId="13127" LastActivityDate="2018-10-06T02:52:53.350" Title="Wiring questions: grounding, attic antennas, BNC connectors" Tags="&lt;grounding&gt;&lt;wiring&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11983" PostTypeId="2" ParentId="11982" CreationDate="2018-10-05T17:09:44.683" Score="5" Body="&lt;p&gt;If you are in a jurisdiction that requires compliance with the US NEC (National Electric Code), you will probably find that there is no requirement for grounding the cable or having a lightning arrestor on the cable. This is because the NEC grounding requirement (article 810) starts with the presence of a mast mounted or tower mounted antenna or associated equipment. This obviously does not fit your situation. You might, however, find that an electrical inspector will interpret the NEC differently and can insist that you comply with his/her interpretation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The NEC states that if you are using coaxial cable with an outdoor antenna that you only need a grounding block to ground the shield. If the grounding block connects to a ground rod other than the same ground rod that serves as the safety ground for your electrical service, you must bond the new ground rod to the electrical service ground. This bonding must be done with 6 AWG or larger wire. You can elect to use a listed lightning arrestor in place of the grounding block as this still grounds the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aside from the NEC issue, I would not install a ground connection to this cable. It introduces a failure point at the junction, it may increase RF noise on the coax, and it creates a fair bit of work and expense for no discernible return.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you later add outdoor antenna(s), then you should revisit this issue and look at the best practices for a single point ground connection for your station.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-10-05T21:44:00.990" LastActivityDate="2018-10-05T21:44:00.990" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11985" PostTypeId="2" ParentId="7265" CreationDate="2018-10-06T02:30:01.603" Score="1" Body="&lt;p&gt;Historically, this is the best time of year (Late September through early December) in the northern hemisphere to enjoy VHF and UHF propagation enhancements (&quot;band openings&quot;) caused by sharp air temperature differences between two (or more) distinct layers of air. &lt;em&gt;These occur far &lt;a href=&quot;http://www.amateur-radio-wiki.net/images/7/77/Vk4yeh_atmosphere.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;below the ionosphere&lt;/a&gt;&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, band openings can occur in any season. The two types --somewhat related-- are described below.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Temperature Inversions&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;By far, the most common type. Just &lt;strong&gt;&lt;em&gt;two&lt;/em&gt;&lt;/strong&gt; layers in the troposphere are are involved. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often incorrectly referred to as &quot;ducting&quot;, these occur where there is a sudden change in air temperature vs. height, and can even cover an area encompassing many hundreds of square miles. They usually occur along a &lt;a href=&quot;https://en.wikipedia.org/wiki/Occluded_front#Description&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;cold occlusion&lt;/em&gt; or &lt;em&gt;occluded front&lt;/em&gt;&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;While most common in the fall and spring, I know a ham in Ohio who observed a spectacular band opening years ago in January, where the temperature dropped from above freezing to -20° F in a matter of hours. (It would have been even more spectacular had other hams known about it, but there was no Internet or VHF DX clusters in those days.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Tropospheric Ducting&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;A genuine duct consists of &lt;strong&gt;&lt;em&gt;three&lt;/em&gt;&lt;/strong&gt; layers of air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They can be spectacular and extend over a greater distance, but &lt;strong&gt;are rare&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A true tropo duct almost never covers an area anywhere near as large as a temperature inversion. By *waveguiding&quot; I assume that &lt;a href=&quot;https://ham.stackexchange.com/questions/7265/how-does-vhf-uhf-propagate-beyond-the-expected-radio-horizon/11981#comment11734_7266&quot;&gt;Marcus&lt;/a&gt; means &quot;tropospheric &lt;em&gt;ducting&lt;/em&gt;&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is what a duct looks like. More details can be found &lt;a href=&quot;http://www.amateur-radio-wiki.net/index.php?title=Tropospheric_ducting&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1G1sg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1G1sg.jpg&quot; alt=&quot;Tropospheric duct&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Features common to both inversions and ducts&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Both inversions and ducts &lt;em&gt;usually&lt;/em&gt; occur when the air is relatively calm. Once it gets windy, the air masses start to mix and the band opening gradually disappears.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Experienced VHF/UHF enthusiasts understand that whenever a hot day followed by a rapid and large temperature drop in the evening occurs, there might be a good opening. &lt;em&gt;The larger the drop, the better the DX.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can tell if you have a band opening in your area by transmitting on 146.94 (or another very common FM repeater frequency) followed by receiving countless beeps, heterodynes, and distant repeater IDs when you unkey and listen. During the better band openings, all it takes is an HT to experience that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on who you ask, that can either be a blessing or a nuisance. ;-) They can and do cause interference to both local and distant repeater groups. Hams operating SSB or CW below ~144.250 or on simplex FM frequencies within that area are treated to a special delight.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-10-06T02:30:01.603" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="11986" PostTypeId="2" ParentId="11982" CreationDate="2018-10-06T02:41:23.970" Score="1" Body="&lt;p&gt;First, although it increases your cable cost slightly, I recommend using only plenum rated cable for attic installation.  It's a fire concern.  Second, as long as you have good grounding on your radio and power source and you have no exposed metal outside the house, you should be fine without grounding your cable.  References to grounding just prior or after the cable enters the shelter normally assumes exterior mounting of your antenna on a tower or mast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, depending on the size of coax you're using and the care given to installation, ground kits may do more harm than good in your application.  The LMR and RG cables with woven outer conductors are easy to damage when removing the section of jacket necessary for installing a ground kit, effectively changing the cable impedance at that point (insertion loss).  Some insertion loss is natural and unavoidable, but excessive loss is excessive.  Coax with solid outer conductors are more sturdy and thus easier to install grounding on without cutting into or deshaping the outer conductor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, I always recommend grounding your outer shield as much as you reasonably can.  Ensure your grounding is the shortest electrical path to earth ground.  Ground wires should never run up, zigzag, etc.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When planning your grounding, dont forget to consider the type and alkalinity of the ground you're sitting on.  Sand or sandy loam is excellent for frying appliances and radios.  If you have that type of soil, I strongly recommend an UPS, surge arrestor or polyphaser, in addition to a ground kit and bussbar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you described your planned install, I would suggest a small bussbar mounted in the attic just below your cable exit port.  Install a polyphaser, or at the very least a ground cable with ring connector, inline between your antenna pigtail and the coax run.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Run a length of #6 jacketed stranded ground wire from whichever you installed there directly to your bussbar.  Then, on a separate lug on the bussbar, run jacketed stranded #2 ground wire outside and straight down the side of the house to a ground rod sunk at least six feet below ground, eight feet would be better.  (I'm sure there's a video on youtube of how to drive a ground rod in the most compacted soil using a bottle of water.  It works.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because of skin effect, your #2 cable, bussbar, and ground rod can all be copper coated aluminum which will be just as effective and less expensive.  For a clean install, use crimp on lugs and heat shrink all connectors.  For the connection to your ground rod, a welded connection is best, because you avoid oxidation developing between your #2 and ground rod connection.  A mechanical ground rod clamp works well too and is less difficult to install, although I recommend applying ample No-lox and periodic inspection of the tightness of that connector.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's highly important to you to replace your radio as seldom as possible, I would also install a second bussbar and #2 run just below your shelter cable entry port.  This run of #2 can exit your cable port, run down the side of your shelter, and be buried at least a foot deep along the straightest path to your ground rod.  If the distance from your shelter to the ground rod is more than ten or twelve feet, install a second ground rod closer to your shelter and connect to that instead.  &lt;/p&gt;&#xA;" OwnerUserId="13336" LastEditorUserId="13336" LastEditDate="2018-10-06T02:52:53.350" LastActivityDate="2018-10-06T02:52:53.350" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="11988" PostTypeId="1" CreationDate="2018-10-06T05:54:39.680" Score="0" ViewCount="71" Body="&lt;p&gt;I have a course challenge. It involves calculating an FFT of an audio signal of 2 combined frequencies (up to 20KHz) then sending it over LoRa through to a fixed receiver. There will be an interferer. Spreading factor is fixed. Grading is based on power consumed by the transmitter and time between start of calculation and receiving an acknowledgement from the receiver. The exact degree of each grading is not unknown.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We may modify any parameters, such as antenna, baud / bitrate, etc, FFT calculation, compression.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a strategy for compressing the values in single bits. Is this possible:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The receiver will receive a bit to start counting, and at that point, it will start counting on its internal clock. Once the transmitters internal clock = x * 100 nanoseconds, where x refers to the value being sent and 100 nanoseconds is the likely accuracy of a GPS signal, it will send a 1 bit. The receiver, having felt x * 100 nanoseconds delay, will decode this message as having the value x.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The benefit will be sending 1 bit vs 16 bits of information will use less power on the radio module, but the waiting could be a penalty for time and static / dynamic waste due to leakage + counting nanoseconds on the accumulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recognize LoRa had a minimum required packet size, but given a required spreading factor of 7 and likely redundancy to deal with an interferer, is this a worthwhile scheme?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: The transmitter and receiver are two copies of the same hardware microcontroller.&lt;/p&gt;&#xA;" OwnerUserId="13338" LastEditorUserId="13338" LastEditDate="2018-10-06T09:38:37.517" LastActivityDate="2018-11-05T13:00:40.530" Title="Can timing information be used to compress data for LoRa transmission?" Tags="&lt;transmission&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="11989" PostTypeId="2" ParentId="11988" CreationDate="2018-10-06T12:13:06.540" Score="1" Body="&lt;p&gt;I think you are taking the wrong approach. Take some time to look at the overhead of a LoRa packet. It contains addressing, checksums, handshaking, etc. It is a large enough overhead that sending one bit vs two bytes results in almost no time or power difference. So unless you are allowed to alter the complete LoRa stack, your timing scheme will not score well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Focus on your FFT routine efficiency and give serious consideration to high gain antennas. The antennas will mitigate the interferer and allow you to reduce your transmitter power. The transmitter power will likely turn out to be the largest part of your power budget. As an example, a 10 dB improvement in system antenna gain would allow you to reduce the transmit power by a factor of 10. Many LoRa kits use negative dBi antennas so this type of gain is easily attained with modest Yagi style antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also take at look at the LoRa devices themselves for power management opportunities like turning off GPS, sleeping subsystems until needed, etc.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-10-06T12:59:57.707" LastActivityDate="2018-10-06T12:59:57.707" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11992" PostTypeId="2" ParentId="8906" CreationDate="2018-10-06T18:31:09.237" Score="0" Body="&lt;p&gt;The official page has two demo audio files, for BPSK and QPSK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Open in Audacity and one can see the preamble and postamble. There seem slight different on two files.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Preamble is about 3 seconds. Postamble is about 2 seconds. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://aintel.bi.ehu.es/psk31.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://aintel.bi.ehu.es/psk31.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1473" LastActivityDate="2018-10-06T18:31:09.237" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11996" PostTypeId="2" ParentId="11973" CreationDate="2018-10-07T11:44:46.567" Score="1" Body="&lt;p&gt;First, let's start on the legal side of the equation. If you are in the US, you are required to have a license for your business radios as well as for your planned repeater. You do not get to pick the frequencies, they are assigned to you by an FCC approved frequency coordinator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The license application is not particularly difficult or expensive but it is loaded with terminology that can be a barrier for the uninitiated. You would probably be better off to use a professional service the first time through the process to avoid having your application rejected by the FCC. You generally have one license that covers all of your radios, the repeater, and at least two assigned frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the technical side, the transmit and receive frequencies will be 5 MHz apart. This is so that the repeater can simultaneously receive and transmit with minimal interference to itself. Even then, a very high isolation filter, called a duplexer, is required so that the receiver in the repeater is not &quot;desensed&quot; by its own transmitter. Desensing refers to the repeater receiver losing sensitivity for the desired signal due to a strong interfering signal - from the transmitter in this case. The coax cable used throughout must be at least double shielded to further prevent desense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The repeater must sense a desired signal on its receiver and turn on the transmitter. It must then turn off the transmitter a short time after the receiver loses its signal. The repeater must transmit its FCC assigned license number, generally via morse code, generally during every 15 minutes of operation. All of these functions are typically performed by a piece of hardware called a repeater controller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transmitter used in a repeater must be FCC certified for the service. Generally the transmitter type is chosen to survive the tougher duty cycle of the repeater and to minimize any interference to the receiver due to phase noise and IMD.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this introduction makes you aware that a successful repeater installation can be rather expensive and it requires a fair bit of technical expertise in addition to some expensive test equipment to get it to function properly and legally. In addition, the Chicago area is very &quot;RF dense&quot; which can raise many technical challenges. You may wish to get someone with the appropriate experience involved in your project.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an alternative, see my suggestion for WiFi radios in my answer to &lt;a href=&quot;https://ham.stackexchange.com/q/11974/9493&quot;&gt;your other question&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-10-07T12:38:58.487" LastActivityDate="2018-10-07T12:38:58.487" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11997" PostTypeId="2" ParentId="11974" CreationDate="2018-10-07T11:56:27.237" Score="1" Body="&lt;p&gt;This question is largely a continuation of &lt;a href=&quot;https://ham.stackexchange.com/q/11973/9493&quot;&gt;your previous question&lt;/a&gt; so I will only address the unique aspects here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A repeater will generally only serve one pair of frequencies so it is limited to one conversation at a time. Both analog and digital repeaters have a capability to place radios into groups so that one group does not hear the conversations of another group. But only one group is allowed to talk at any one time on a single repeater. You of course can have multiple repeaters but this will require careful planning to avoid cross repeater interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You generally will not be permitted to continuously retransmit the NOAA broadcasts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding the frequencies, each repeater will require a separate transmit and receive frequency that will be assigned to you by an FCC approved frequency coordinator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your campus is blanketed with WiFi, you may wish to consider a license free radio system such as the &lt;a href=&quot;http://www.icomamerica.com/en/products/network/wlan/ip100h/default.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;Icom IP100H&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/98T2C.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/98T2C.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This removes the requirement for a repeater infrastructure and would also allow the continuous transmission of NOAA reports. Even if your IT department would need to extend your WiFi coverage to suit your needs, you may find this approach to be economically and technically advantageous.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-10-07T12:41:09.050" LastActivityDate="2018-10-07T12:41:09.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11998" PostTypeId="2" ParentId="11973" CreationDate="2018-10-07T13:57:25.680" Score="2" Body="&lt;p&gt;The first requirement for any repeater is that it be able to simultaneously receive and transmit; this capability is known as &lt;em&gt;full duplex&lt;/em&gt; operation. A &lt;em&gt;duplexer&lt;/em&gt; - a pair of sharp filters - is required to prevent the repeater's transmitted signal from overwhelming the repeater's receiver. While an external duplexer could be added, I see no evidence in the manual for the Kenwood TK863G that it can operate in full duplex mode, so I don't believe it can serve your application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some mobile amateur radios, e.g., &lt;a href=&quot;http://yaesu.com/indexVS.cfm?cmd=DisplayProducts&amp;amp;ProdCatID=106&amp;amp;encProdID=0C4855ADE6394D514EAABAE148B93F5C&amp;amp;DivisionID=65&amp;amp;isArchived=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yaesu FT-8900R&lt;/a&gt;, can operate &lt;em&gt;cross band&lt;/em&gt; full duplex. That is, the mobile transceiver receives signals from radios on one band and retransmits those signals on another band, employing a built-in duplexer. Radios of this description were used by the hams on Dominica to temporarily replace repeaters destroyed by Hurricane Maria in 2017. Such installations can be &quot;daisy chained&quot; to expand the coverage of a single, central repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the urban environment you describe, I suspect that the locations of the &quot;mobile&quot; units would have to be carefully chosen to account for building reflections. Likewise, users would be required to change their &quot;up/down&quot; band pairs depending on their proximity to the mobile unit serving their location.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-07T13:57:25.680" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="11999" PostTypeId="1" CreationDate="2018-10-08T02:06:22.470" Score="3" ViewCount="193" Body="&lt;p&gt;I got stuck with impedance matching for an antenna. Any added components in the matching network gave a result totally different from what a  Smith chart predicts. Let me explain this clearer.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;First, by shortening L2,C8,L5,C23, I measured my antenna &quot;raw&quot; impedance (without matching) at ANT1 terminal (please see attached my matching network). It gave Za_raw = 133 +j 226 (ohm). RF+ is the input feed line of my antenna. There is a SMA connector at ANT1. It connects the rest of my circuit to the antenna.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/lqQjO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lqQjO.jpg&quot; alt=&quot;matching network&quot;&gt;&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Then, if I replace C23 with an inductor L = 47nH, the measured impedance at ANT1 terminal is 60 + j160 (ohm)!!! But using Smith chart, with Zload = Za_raw, a serial added L of 47nH would give Za = 133 + j 496 (ohm). You can see this in the following figure.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/q0TmR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/q0TmR.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;All measurements were conducted using a VNA. 1-port calibration was done before measuring. Any suggestions are highly appreciated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;****Modified on 17 Oct.**&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is my construction. I shorten L2, C8, L5 &amp;amp; C23 using wires. The physical length of the feed line is about 29.5mm.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The reason for the complicated matching network is that, at first, I would like to make 2 measurement points: at ANT11 and ATN1. ANT1 should be the input impedance of my circuit, while ANT11 should be the antenna input impedance. But later, I thought I don't need to do that. I just need to tune the input impedance of the whole circuit (with all components soldered) at ANT1 to be 50 ohm!&lt;/li&gt;&#xA;&lt;li&gt;Why 50ohm? In my measurement, at the resonant frequency (around 915 MHz), the impedance at ANT1 is 50ohm!&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Am I right?&#xA;&lt;a href=&quot;https://i.stack.imgur.com/r63YI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/r63YI.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11740" LastEditorUserId="11740" LastEditDate="2018-10-17T04:57:34.573" LastActivityDate="2018-10-19T01:38:41.323" Title="Impedance matching: Why do components behave totally differently from theory?" Tags="&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12000" PostTypeId="1" AcceptedAnswerId="12009" CreationDate="2018-10-08T05:06:29.300" Score="5" ViewCount="149" Body="&lt;p&gt;I recently inherited a CelWave fiberglass antenna pictured below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is marked that it's for 959.9875 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The model number appears to be either 339 or 359.  It is 96 1/2 inches from base to tip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I checked it on my MFJ Antenna Analyzer and found it start to get a decent SWR over 460 MHz.  I expected as much since half of 960 is 480.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any way this antenna can be disassembled and retuned for use in the 70cm ham band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't mind even if there is risk involved.  It didn't cost me anything and I have no use for it as it is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/l6z4R.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/l6z4R.jpg&quot; alt=&quot;Antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VUGu7.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VUGu7.jpg&quot; alt=&quot;Catalog Number&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GMMMq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GMMMq.jpg&quot; alt=&quot;Measurement&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2018-10-10T15:19:37.373" LastActivityDate="2018-10-10T16:54:42.220" Title="Can this 960 MHz CelWave fiberglass antenna be retuned for the 70cm band?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12002" PostTypeId="2" ParentId="11999" CreationDate="2018-10-08T08:02:39.343" Score="1" Body="&lt;p&gt;According to my calculations, if you have a 1.35 pF shunt across the 133+226i antenna you get 60.7-191i. Then add 60.9nH in series (20% off from your 47nH) gives you the 60+160i that you're seeing. Is it possible this could be happening in your setup? Possibly your hookup wire had 1.35 pF capacitance and about 14nH parasitics? Actually I don't yet understand how a length of coax behaves as a function of wavelength. Would it behave this way if cut to the wrong length?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&#xA;included some calculations for an example.&#xA;I did this to the best of my knowledge and best intentions, however if inaccurate or unhelpful I'm sure someone will correct me and we both learn :P&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NLfXS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NLfXS.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6psLF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6psLF.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user13171" LastEditorDisplayName="user13171" LastEditDate="2018-10-19T01:38:41.323" LastActivityDate="2018-10-19T01:38:41.323" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12004" PostTypeId="2" ParentId="11999" CreationDate="2018-10-08T10:48:27.483" Score="6" Body="&lt;p&gt;Firstly, at 900+ MHz, shorting out components to take antenna impedance measurements is not a good practice as the lead length can be a substantial portion of a wavelength. Stray inductance and capacitance must also be avoided.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, your matching network appears horribly complicated for an impedance matching circuit. Generally, a simple &quot;L&quot; network (one inductor and one capacitor) will accomplish the match. If you are attempting to do something else with the network, such as bandpass shaping, please edit your question to explain this. You should also state the desired final impedance of your antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thirdly, without seeing your physical construction, it is likely that the wires or traces of your shorted out matching network are acting as a transmission line. Any transmission line length that is not a multiple of 1/2 wavelength will transform the antenna impedance. At 915 MHz, even a 30 mm length of transmission line has relevant transformative properties. In order to properly model this, you would need to know the electrical wavelength and the characteristic impedance of this unintended transmission line. This is yet another reason to take the impedance measurement directly at the antenna feed point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So start by taking a better impedance measurement of your antenna. Then to see how a simple L matching network functions, plug your measured impedance value into &lt;a href=&quot;https://leleivre.com/rf_lcmatch.html&quot; rel=&quot;noreferrer&quot;&gt;this on-line calculator&lt;/a&gt;. You can then take the reported L network values and put them in your Smith chart to help you visualize the effect of the two matching components. If later you then would like to see the math behind this on-line calculator, open another question to that effect.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-10-08T12:00:51.503" LastActivityDate="2018-10-08T12:00:51.503" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12005" PostTypeId="2" ParentId="4975" CreationDate="2018-10-09T00:45:30.090" Score="3" Body="&lt;p&gt;SSN is an abbreviation for &quot;Smoothed Sunspot Number&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How the sunspot number should be smoothed depends entirely on what you are doing. Every useful ionospheric model specifies the manner in which recent solar activity is to be conveyed. If wish to run HF propagation predictions using the VOACAP forecasting engine, for example, then you would generate a smoothed sunspot number in the manner it prescribes:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.voacap.com/choosingssn.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.voacap.com/choosingssn.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additional information you may find helpful is here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-indices/sunspot-numbers/documentation/readme_sunspot-numbers.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-indices/sunspot-numbers/documentation/readme_sunspot-numbers.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="88" LastActivityDate="2018-10-09T00:45:30.090" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12007" PostTypeId="1" AcceptedAnswerId="12008" CreationDate="2018-10-09T23:48:55.563" Score="8" ViewCount="232" Body="&lt;p&gt;From time to time I'm a new ham's first contact - usually on a repeater. If I want to send the new ham a QSL card, how should I distinguish a repeater contact from a non-repeater contact? Is there a standard?&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2018-10-12T12:30:46.573" Title="What should I put on a QSL card for a repeater contact?" Tags="&lt;repeater&gt;&lt;qsl-card&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12008" PostTypeId="2" ParentId="12007" CreationDate="2018-10-10T07:49:19.437" Score="12" Body="&lt;p&gt;I never saw a standard in the last 25 years. I usually put something in the comment like 'using repeater xxx'. Where the xxx is the callsign of the repeater.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2018-10-10T07:49:19.437" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12009" PostTypeId="2" ParentId="12000" CreationDate="2018-10-10T16:54:42.220" Score="4" Body="&lt;p&gt;The wavelength at 959.9875 MHz is approximately one foot. So this antenna is approximately eight wavelengths long. That means it is not a simple monopole or dipole. Based on the dimensions I would guess it is a co-linear array of dipoles with the objective of increasing gain towards the horizon by suppressing radiation at less useful high angles, while maintaining an omnidirectional pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That the antenna has a decent SWR does not necessarily mean it's any good on 480 MHz. For a co-linear array to work as intended, each element must be in phase so they interfere constructively at the horizon. The phase of each element is controlled by transmission lines or reactive elements within the antenna, all of which have frequency-dependent behavior. It is unlikely the phasing components continue to perform their function at any frequency but the one for which it was designed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consequently, the antenna elements will most likely be out of phase, resulting in a radiation pattern which is worse than something much simpler.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple A/B test using a simple 1/4 wave monopole (or whatever else you have lying around, or can quickly improvise) as a reference should be sufficient to make a determination. If the mystery antenna isn't significantly better than the reference antenna, you can reasonably infer the phasing is all messed up and this antenna isn't going to be useful, even if it is a good match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You certainly could disassemble it and modify it to work better, however that will be a more advanced effort. Even that may not work so well: halving the frequency requires doubling the size for an equivalent design. Generally it's easier to make things shorter, while making them longer is...harder.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-10T16:54:42.220" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12010" PostTypeId="2" ParentId="12007" CreationDate="2018-10-10T22:33:05.787" Score="-2" Body="&lt;p&gt;Nothing. You do not send QSL for repeater contacts, only for direct contacts.&lt;/p&gt;&#xA;" OwnerUserId="306" LastActivityDate="2018-10-10T22:33:05.787" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12012" PostTypeId="1" AcceptedAnswerId="12022" CreationDate="2018-10-11T16:43:07.563" Score="3" ViewCount="923" Body="&lt;p&gt;In discussion around another Q&amp;amp;A here, &lt;a href=&quot;https://ham.stackexchange.com/questions/12000/can-this-960-mhz-celwave-fiberglass-antenna-be-retuned-for-the-70cm-band#comment17760_12001&quot;&gt;Glenn W9IQ commented&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The directive gain difference between a half wavelength dipole and an infinitesimal dipole is only 0.39 dB&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm curious where this number comes from. I recall from e.g. the FCC amateur licensing tests the &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Decibel&amp;amp;oldid=861348405#Antenna_measurements&quot; rel=&quot;nofollow noreferrer&quot;&gt;relationship between dBi and dBd&lt;/a&gt;; to summarize that Wikipedia link:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;dB(isotropic) – the forward gain of an antenna compared with the hypothetical isotropic antenna, which uniformly distributes energy in all directions.&lt;/li&gt;&#xA;&lt;li&gt;dB(dipole) – the forward gain of an antenna compared with a half-wave dipole antenna. &lt;strong&gt;0 dBd = 2.15 dBi&lt;/strong&gt; [emphasis mine]&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Based on a naïve understanding of &quot;half wavelength dipole&quot; and &quot;infinitesimal dipole&quot; I would expect the the gain difference to be 2.15 dB, not 0.39 dB. What am I missing?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2018-10-11T23:39:20.957" Title="Gain difference between half-wave and infinitesimal dipole?" Tags="&lt;antenna-theory&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12013" PostTypeId="2" ParentId="12012" CreationDate="2018-10-11T17:04:42.050" Score="2" Body="&lt;p&gt;An infinitesimal dipole is not the same thing as an isotropic antenna.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;An &lt;a href=&quot;https://en.wikipedia.org/wiki/Isotropic_radiator&quot; rel=&quot;nofollow noreferrer&quot;&gt;isotropic antenna&lt;/a&gt; is a mathematical notion for comparing antenna patterns. &lt;strong&gt;It cannot exist&lt;/strong&gt; — not just as a matter of physical construction, but also of arrangement of electromagnetic fields — because there is no possible arrangement of &lt;em&gt;polarization&lt;/em&gt; of the wave which covers the sphere of all directions away from the antenna (mathematically, this is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Hairy_ball_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;hairy ball theorem&lt;/a&gt;).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;An infinitesimal dipole (also known as a &lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna#Hertzian_dipole&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hertzian dipole&lt;/a&gt;) has a dipole radiation pattern — for a dipole of any length whatsoever, the radiated field goes to zero along the axis of the dipole. (This pair of zero points means that a consistent polarization pattern can exist.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, more of the radiation must go out in other directions, compared to an isotropic antenna, and so the design must have gain over an isotropic antenna.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I don't know the theory to explain where the figure of 2.15 dBi comes from, but I hope this explains why there is a difference at all.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-10-11T17:09:49.533" LastActivityDate="2018-10-11T17:09:49.533" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12014" PostTypeId="1" AcceptedAnswerId="12015" CreationDate="2018-10-11T17:16:30.133" Score="1" ViewCount="781" Body="&lt;p&gt;I'm getting ready to build an &lt;a href=&quot;http://shop.qrp-labs.com/qcx&quot; rel=&quot;nofollow noreferrer&quot;&gt;HF / CW kit&lt;/a&gt; and just finished setting up a workbench in my garage. While I was wrapping up, I started wondering if the cold temperatures this winter might be harmful to any of the radio equipment. I live in Portland, OR, so I don't expect the temperatures to get too extreme, but it does seem possible for my garage to hit freezing temperatures. Are low / freezing temperatures known to be harmful to ham radio equipment?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To give a sense of what equipment I have on hand.. my shack is currently pretty simple - I have a pair of inexpensive VHF/UHF handheld HTs (&lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B01J2W4JUI&quot; rel=&quot;nofollow noreferrer&quot;&gt;BTECH UV-5X3&lt;/a&gt;), and will have the DIY HF radio on hand soon. In the coming year, I may add other equipment (e.g. power supply, tuner, an actual base station, etc). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It &lt;em&gt;seems&lt;/em&gt; like electronics in general would be okay with the cold (it hasn't really occurred to me in the past to be worried about other electronics in the cold). At this point, though, I want to be really careful before leaving expensive equipment or hard-to-build projects in conditions that may eventually prove harmful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Really appreciate any thoughts / advice!&lt;/p&gt;&#xA;" OwnerUserId="12900" LastActivityDate="2018-10-12T23:17:49.047" Title="Are cold temperatures harmful for ham radio equipment?" Tags="&lt;diy&gt;&lt;equipment-protection&gt;" AnswerCount="5" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12015" PostTypeId="2" ParentId="12014" CreationDate="2018-10-11T17:39:54.247" Score="3" Body="&lt;p&gt;Amateur radio equipment is not greatly different from electronics in general. Some items might be unusually chunky and robust (e.g. a manual HF antenna tuner is a box full of metal shapes and insulators). Some might be unusually fragile — but more likely in an electronic way (if you misuse this you destroy an input circuit; this tuned circuit changes tuning with temperature; that sort of thing) than environmentally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notable items for cold temperatures:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Batteries in general perform worse in cold conditions, and may be damaged.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Lithium-ion batteries are at risk; I have found varying statements of the exact conditions, but you should definitely not charge them below freezing (0°C? some lower freezing temperature of the battery electrolyte?) and possibly should not let them reach that temperature even when not in use.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Lead-acid batteries can be more readily damaged by freezing &lt;strong&gt;when they have low charge&lt;/strong&gt;, because the state of charge affects the electrolyte's ratio of water to sulfuric acid and thus the freezing point. However, as we can see from the fact that almost every car has a lead-acid battery in it — as long as you keep them mostly charged, you should be fine for all reasonable garage temperatures.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;LCD displays will be faint and slow to update in lower temperatures. You can partially compensate for the faintness with a &quot;contrast&quot; setting if one is available (I see that your planned kit does have one).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-10-11T17:39:54.247" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12016" PostTypeId="2" ParentId="12012" CreationDate="2018-10-11T17:57:30.850" Score="3" Body="&lt;p&gt;This is well explained on the Wikipedia entry for &lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;dipole antenna&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;infinitesimal&quot; dipole to which you refer is also called a &lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna#Hertzian_dipole&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hertzian dipole&lt;/a&gt;. As shown in the Wikipedia entry, this theoretical construct has a gain of 1.5. The gain of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna#Half-wave_dipole&quot; rel=&quot;nofollow noreferrer&quot;&gt;half-wave dipole&lt;/a&gt; is 1.64. The dB ratio of (1.64/1.5) is 0.39dB.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-11T17:57:30.850" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12017" PostTypeId="2" ParentId="12014" CreationDate="2018-10-11T18:13:30.487" Score="1" Body="&lt;p&gt;The semiconductors which comprise the bulk of components in all modern ham gear are rated to operate over at least the &quot;commercial&quot; temperature range whose low end is 0C / 32F.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since most active and passive components have a positive temperature coefficient of resistance, one would expect inrush current to be the dominant failure mode. The negative coefficient characteristic of thermistors can protect against low-temperature inrush current. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check with the factory or your favorite outlet to see if your power supply and/or rigs already have these parts installed. Otherwise, distributors like &lt;a href=&quot;https://www.digikey.com/products/en/circuit-protection/inrush-current-limiters-icl/151&quot; rel=&quot;nofollow noreferrer&quot;&gt;Digikey&lt;/a&gt; and &lt;a href=&quot;https://www.mouser.com/Circuit-Protection/Thermistors/Inrush-Current-Limiters/_/N-axfxj&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mouser&lt;/a&gt; sell inexpensive parts under the heading of &quot;inrush current limiters.&quot;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-11T18:13:30.487" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12018" PostTypeId="2" ParentId="12012" CreationDate="2018-10-11T18:33:06.423" Score="0" Body="&lt;p&gt;The gain difference is because the short dipole has a triangular current distribution, while the half wave dipole is sinusoidal.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(the triangle is actually the end bits of a sinusoidal shape, but if its very short, that's a triangle).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the same feed current, the sinusoidal distribution has slightly more moment - area under the current graph if you like - so slightly higher gain.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Wikipedia article on dipoles is really good too, just skim over the equations like I do and read the conclusion.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2018-10-11T23:39:20.957" LastActivityDate="2018-10-11T23:39:20.957" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12019" PostTypeId="2" ParentId="12014" CreationDate="2018-10-11T18:36:01.487" Score="4" Body="&lt;p&gt;The other answers do a good job of covering the theoretical risks and the manufacturers' recommendations.  I wouldn't think that you would bump into those limits in a garage in Portland, Oregon.  As a practical matter, if I were &quot;in your shoes&quot;, then the only thing that I would worry about would be condensation.  Moisture can be a problem for some electronics.  So if dew is forming on your rig, warm it up until the dew goes away before powering the equipment.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-10-11T18:36:01.487" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12020" PostTypeId="2" ParentId="12014" CreationDate="2018-10-11T18:40:11.817" Score="2" Body="&lt;p&gt;I think Kevin and Brian covered the important aspects, and these are the failure modes I'd expect to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aside from the battery damage, nothing too dramatic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's unlikely your electrolytic caps freeze, but that would be another fatal blow to your equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that there's a lot of parameters of your electronic components that change with temperature – not only do semiconductors become less conductive, and resistors become more conductive, in isolation, you have to account for the combination of all such effects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if you have a control loop that controls the output voltage in a voltage regulator, that's often done by an internal transistor used to mirror/amplify the voltage over an external resistor. Now, if both the resistance of the resistor and the amplification speed due to reduced electron mobility in low temperatures in the transistor, then your power supply suddenly has a slightly (maybe not even measurable) drop in voltage, but a very measurable drop in the ability to react to sudden load changes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That slight misbehaviour can lead to permanent damage, if for example you turn on your PA, which draws a lot of power, but that leads to a load jump, which in turn leads to a sharp voltage drop (due to the above effects), which then might lead to damage, e.g. because something becomes improperly biased.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, long story short: Devices are designed for a specific range of temperatures. That range is typically specified for every device you can buy. Operating things outside of that is a &quot;good luck!&quot; situation when the device you operate becomes a little more complex than a handful of transistors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Realistically, and from experience: Heat is way more problematic; things heat up all by themselves, but they can't cool down. Make sure your things don't get wet (be sure to ventilate and not have your device be colder than moist air).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-10-11T19:56:13.677" LastActivityDate="2018-10-11T19:56:13.677" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12021" PostTypeId="2" ParentId="12012" CreationDate="2018-10-11T20:09:46.323" Score="2" Body="&lt;p&gt;I sense that the question may be along the line of &quot;If a dipole becomes infinitely small, isn't it essentially an isotropic antenna?&quot; since this would be the only way an antenna could have 0 dBi gain at 100% efficiency. So I will construct this answer around a discussion of an isotropic antenna and the notion of antenna gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An isotropic antenna is a theoretical construct for an antenna that radiates equally in all directions. The isotropic antenna is a point source and is always considered to be 100% efficient (all power applied is radiated as electromagnetic radiation). It is helpful to picture this antenna at the center of a large sphere and the radiant flux (radiant power) from the antenna illuminating the sphere. The isotropic antenna would therefore uniformly illuminate the sphere - there would be no brighter or darker spots anywhere on the sphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna gain can be generally defined as the peak radiant flux divided by the average radiant flux of the antenna. If we go back to the illuminated sphere concept, we would find the brightest spot on the sphere, measure the radiant flux at this spot, and divide this by the average radiant flux around the entire sphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if we consider that the isotropic antenna uniformly illuminates the sphere, the peak radiant flux is the same as the average radiant flux. The linear gain of the isotropic antenna is therefore 1. Recalling that dB is a comparison of powers and that radiant flux is a power term, we can convert this linear gain of 1 compared to an isotropic antenna (itself), and the result is the familiar 0 dBi term.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider that any other antenna construct is not capable of illuminating the sphere equally. That is to say that there will always be one or more spots on the sphere that are brighter (a higher radiant flux) than other spots on the sphere. Thus if we compute the maximum radiant flux divided by the average radiant flux of such an antenna, the linear gain of this 100% efficient antenna will always be greater than 1. If the linear gain is greater than 1, then it follows that the dBi gain must be greater than 0. Thus any antenna, other than an isotropic antenna, has a gain of &gt; 0 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Up to this point, I have asserted that the referenced gains are for 100% efficient antennas. Antenna gain without consideration of efficiency (i.e. independent of efficiency) should more properly be called directivity. So in the above discussion, directivity may rightfully be substituted for gain when considering all antennas to be 100% efficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could now dive into equations to compute the specific gain for various dipole constructions but my guess is this is not at the heart of the question. If the OP would like to explore specific formulae, please comment and I will enhance my answer accordingly.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-10-11T20:09:46.323" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12022" PostTypeId="2" ParentId="12012" CreationDate="2018-10-11T22:29:27.577" Score="4" Body="&lt;p&gt;Infinitesimal and isotropic are not the same thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Infinitesimal&lt;/em&gt;: an indefinitely small quantity; a value approaching zero. In the case of an infinitesimal dipole, we're talking about the length of the dipole. Kinda. More on that below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Isotropic&lt;/em&gt;: having a physical property that has the same value when measured in different directions. In the case of antennas, we're talking about &lt;a href=&quot;https://en.wikipedia.org/wiki/Radiant_intensity&quot; rel=&quot;nofollow noreferrer&quot;&gt;radiant intensity&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An isotropic antenna, that is, one which radiates with equal intensity in any direction, is not realizable. The mathematical proof comes from the &lt;a href=&quot;https://en.wikipedia.org/wiki/Hairy_ball_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;hairy ball theorem&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Someone with a radio background will hear &quot;dipole&quot; and think &quot;two wires&quot;. But someone with a physics background thinks a different thing. An &lt;a href=&quot;https://en.wikipedia.org/wiki/Electric_dipole_moment&quot; rel=&quot;nofollow noreferrer&quot;&gt;electric dipole&lt;/a&gt; is two equal but opposite electric point charges separated by some distance. An &lt;em&gt;infinitesimal&lt;/em&gt; dipole is the limiting case when the distance between these charges approaches, but does not reach zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The electric field looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/p8f1Y.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/p8f1Y.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;By &lt;a href=&quot;https://commons.wikimedia.org/wiki/User:Geek3&quot; rel=&quot;nofollow noreferrer&quot;&gt;Geek3&lt;/a&gt; &lt;a href=&quot;https://creativecommons.org/licenses/by-sa/3.0&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Creative Commons Attribution-Share Alike 3.0&quot;&gt;CC BY-SA 3.0&lt;/a&gt;, from &lt;a href=&quot;https://commons.wikimedia.org/wiki/File:VFPt_dipole_animation_electric.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikimedia Commons&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, these separated charges come from the charge accumulation at the ends of the antenna as current takes charge away from one end while charge is being deposited in the other end. Of course in a real antenna the charge is distributed throughout the antenna: the infinitesimal dipole is a simplification with just two points, defined only by a direction and a &lt;a href=&quot;https://en.wikipedia.org/wiki/Electric_dipole_moment&quot; rel=&quot;nofollow noreferrer&quot;&gt;moment&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If an infinitesimal dipole oscillates as an antenna does, then it can be shown with a lot of math derived from &lt;a href=&quot;https://en.wikipedia.org/wiki/Maxwell%27s_equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;Maxwell's equations&lt;/a&gt; that the electric far-field is proportional to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ E(\theta, \phi) = {1 \over r} \sin(\theta) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where the antenna is along the z axis, and:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt; (theta) is the angle away from the z axis,&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\phi$&lt;/span&gt; is the angle away from the x axis (irrelevant here, since the dipole is omnidirectional),&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$r$&lt;/span&gt; is the distance away from the antenna&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So the field is strongest when &lt;span class=&quot;math-container&quot;&gt;$\theta = \pi/2$&lt;/span&gt;, corresponding to the horizon, if the antenna is vertical. The electric field decreases with &lt;span class=&quot;math-container&quot;&gt;$1/r$&lt;/span&gt;, and since power is proportional to the square of voltage this means power would decrease with &lt;span class=&quot;math-container&quot;&gt;$1/r^2$&lt;/span&gt;, the inverse square law.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The corresponding formula for a half-wave dipole is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ E(\theta, \phi) \propto {&#xA;\cos\left( \pi \cos \theta \over 2 \right)&#xA;\over&#xA;r \sin\theta&#xA;}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see graphically, the half-wave dipole is just a little more &quot;pointed&quot;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UUjdB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UUjdB.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, if the two antennas have equal efficiency, the half-wave dipole will have just a little more gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why so? No one actually builds infinitesimal dipoles: theoretically their gain is about the same but in practice their efficiency is extremely low. However, they are mathematically simple, and a very good approximation of real antennas can be made by modeling them as a collection of infinitesimal dipoles. The caveat is the infinitesimal dipole model assumes uniform current throughout, so we must divide the antenna into pieces small enough that each individual piece has mostly uniform current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thinking of a half-wave dipole in this way, you can now consider it sort of a colinear array of infinitesimal dipoles. It isn't physically large enough to yield a lot of gain, but it does yield just a little: 0.39 dB. We see that in the graph above.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-11T22:29:27.577" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12023" PostTypeId="1" AcceptedAnswerId="12025" CreationDate="2018-10-11T22:35:58.837" Score="3" ViewCount="1970" Body="&lt;p&gt;When discussing improvements to my home HDTV Antenna/distribution system a colleague brought up the need to terminate all coax, even unused splitter ports.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding of the way terminator works is that they prevent wave reflection, which can cause ghosting in analog signals and in my case - digital HDTV - noise. However for the reflection to introduce noise I assume you need some cable length, so that the reflected signal is actually offset from the main one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a splitter the length is very short - limited to the splitter's own wiring. Would that still be enough to cause noise? If not, could it even have the inverse effect of preventing an in-phase reflection from actually boosting the signal's strength to used ports?&lt;/p&gt;&#xA;" OwnerUserId="13369" LastActivityDate="2018-10-12T01:36:06.897" Title="It it really useful to terminate unused 75Ω outputs on a coax splitter?" Tags="&lt;uhf&gt;&lt;coaxial-cable&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12024" PostTypeId="2" ParentId="12023" CreationDate="2018-10-11T22:57:10.343" Score="3" Body="&lt;p&gt;Lack of termination is a particular case of impedance mismatch. An impedance mismatch on one port of a power divider (&quot;coax splitter&quot;) means that the common port of the divider itself will not present the the intended impedance to the incoming signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(From a circuit analysis perspective, this is the same thing as a lumped-component network of some sort that has the wrong impedance on its ports for the pair of transmission lines attached to it. No lengths of unterminated line are necessary.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This mismatch will cause reflections which propagate backwards along the line. What happens after that depends on the electrical characteristics of the next thing-that-is-not-a-transmission-line the reflection hits, but a simple case is if there is another similar mismatch in the line, which will produce the second (forward) reflection called ghosting, the time between reflection depending on the length of line between those two defects.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-10-11T22:57:10.343" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12025" PostTypeId="2" ParentId="12023" CreationDate="2018-10-12T01:36:06.897" Score="5" Body="&lt;p&gt;Terminating unused ports will never make things worse, and indeed is necessary to provide &quot;ideal&quot; behavior. Is ideal behavior really necessary? It depends on the application. Is your setup working now? If so, terminators aren't necessary :-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A typical splitter has these properties:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It has an input port and two output ports, which we'll call A and B.&lt;/li&gt;&#xA;&lt;li&gt;It has high &lt;em&gt;isolation&lt;/em&gt;, meaning power going into one output port doesn't show up at the other output port.&lt;/li&gt;&#xA;&lt;li&gt;It is &lt;em&gt;matched&lt;/em&gt;, meaning the impedance looking in to any port is the same (usually one of 75 or 50 ohms).&lt;/li&gt;&#xA;&lt;li&gt;It is &lt;em&gt;reciprocal&lt;/em&gt;, meaning it works in either direction: it can also be used as a &lt;em&gt;combiner&lt;/em&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This sounds like nothing could go wrong: since the outputs are isolated then leaving one of them unterminated couldn't cause problems with the other output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, when the port is left open, it reflects &lt;em&gt;all&lt;/em&gt; the power, and then you have to consider how that affects the other components. Even though the ports may be labeled &quot;output&quot;, they are still inputs because the splitter is reciprocal. Power reflected from an output port is an input that must be considered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, say 1 W enters the input port. One output is connected to a TV, which we assume is properly terminated internally. The other port is left open. (In practice the power is orders of magnitude less: I want to keep the numbers simple.)&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/GC2eu.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fGC2eu.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;1 W enters the input.&lt;/li&gt;&#xA;&lt;li&gt;The splitter divides that power evenly between the outputs. So 0.5 W comes out of each output.&lt;/li&gt;&#xA;&lt;li&gt;On port A, that power is converted to heat in the TV and we don't need to worry about it anymore.&lt;/li&gt;&#xA;&lt;li&gt;On port B, there's nowhere for the power to go so it's reflected. Now it's an input on &quot;output B&quot;. Although it's called an &quot;output&quot;, because the splitter is a &lt;em&gt;reciprocal&lt;/em&gt; device, it works an an input, too.&lt;/li&gt;&#xA;&lt;li&gt;Half of the reflected power is lost as heat in the splitter.&lt;/li&gt;&#xA;&lt;li&gt;The other half is sent out the &quot;input&quot; port.&lt;/li&gt;&#xA;&lt;li&gt;Depends on what's attached to the input port!&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;If the input port is also 75 ohms, the reflected power is absorbed there, and we don't ever see it again. This reflected power means the source does not &quot;see&quot; 75 ohms, however that's unlikely to be an issue in practice for a TV system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if the input port isn't 75 ohms, the reflected power gets re-reflected and is sent another time into the input port. Now you have the opportunity for ghosting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However in most cases, a number of factors combine to make this not that big of a deal.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The source may not be 75 ohms, but it's not usually that far off. So the source does end up absorbing a significant fraction of the reflected power.&lt;/li&gt;&#xA;&lt;li&gt;The real world is already full of reflections. If the source is an antenna, it already contains time-shifted &quot;ghosts&quot; from the signal finding its way to you by multiple paths of differing length. An HDTV receiver employs &lt;em&gt;channel equalization&lt;/em&gt; to compensate for this to some extent.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-12T01:36:06.897" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12026" PostTypeId="2" ParentId="4896" CreationDate="2018-10-12T09:02:06.637" Score="1" Body="&lt;p&gt;I'd say the average DAB+ receiver is unlikely to support AAC-LD or AAC-ELD, because AAC used in DAB+ (optionally with SBR and PS) uses a 960 granule length, unlike most AAC used elsewhere, which uses 1024. I don't know if ELD or LD exist for this granule length. The AAC codec is used in superframe-mode, with 120ms frame duration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding delay in general in a DAB transmission chain:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Some latency also comes from the time interleaver (see ETSI EN 300 401 v2.1.1 Clause 12)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In transmission mode I (the only one used since v2), one transmission frame lasts 96ms, also adding to the end-to-end latency&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;As @frank-johnson also mentioned, the distribution network sending ETI to all modulators of the transmitter network can also add several seconds of delay.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;DAB wasn't designed for low-delay applications, and the latency of the codec only makes up a small part of the overall end-to-end delay.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to experiment with generating DAB signals, have a look at &lt;a href=&quot;http://www.opendigitalradio.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.opendigitalradio.org&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13373" LastActivityDate="2018-10-12T09:02:06.637" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12027" PostTypeId="2" ParentId="12007" CreationDate="2018-10-12T12:30:46.573" Score="4" Body="&lt;p&gt;I'd just add a note indicating the repeater frequency and call sign somewhere on the QSL card you send.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My XYL and I like to give &lt;a href=&quot;http://www.arrl.org/first-contact&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL First Contact&lt;/a&gt; awards to people we've made their first contact with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many times they're local people we know, so we just have the printed certificate sent to us.  Then we give it to the person at our next encounter.&lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2018-10-12T12:30:46.573" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12028" PostTypeId="1" CreationDate="2018-10-12T12:52:39.173" Score="2" ViewCount="169" Body="&lt;p&gt;I am starting the process of installing a vertical ant (6BTV) and radial ground system. I am ready to buy the wire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to know if there is an electrical difference between 14 gauge and 18 gauge wire when used as a radial ground system?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would also like to know how long the 18g will last compared to the 14g?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, can the 18g wire be reasonable expected to last ten to fifteen, or even twenty, years while laying on the dirt with grass growing over it? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How long might 14g wire be expected to last?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you for your time.&lt;/p&gt;&#xA;" OwnerUserId="13125" LastEditorUserId="76" LastEditDate="2019-04-13T20:31:38.570" LastActivityDate="2019-04-13T20:31:38.570" Title="Ground radials: Electrical difference between 14 gauge and 18 gauge? Lifespan difference?" Tags="&lt;radial&gt;&lt;earth&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12029" PostTypeId="1" CreationDate="2018-10-12T13:34:30.573" Score="1" ViewCount="204" Body="&lt;p&gt;I don't know about you guys, but I've always been somewhat confused by fundamental mixer action.  I've always been left unsatisfied by the standard trig identity explanation as one that's a tad too abstract.  It has a kind of &quot;it just is&quot; feel about it and that always makes me want to dig deeper.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;So my question is, how does a mixer create a carrier frequency and sidebands?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've answered this question with my own intuition about how mixing works and how sidebands are formed and it would be good to get some feedback from more informed members.  I'd also love to hear other peoples intuition as I find this topic very confusing.&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="11875" LastEditDate="2018-10-14T17:47:06.230" LastActivityDate="2018-11-15T13:24:49.973" Title="Finding an Intuitive Explanation of Mixer Theory" Tags="&lt;mixer&gt;" AnswerCount="4" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12030" PostTypeId="2" ParentId="12028" CreationDate="2018-10-12T15:38:52.217" Score="5" Body="&lt;p&gt;Larger wire will have less resistance. However, the resistance of the radials in either case is negligible compared to the soil resistance, so I wouldn't worry about it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Longevity would be my concern. Commercial broadcast towers use 10 gauge bare wire. Anecdotally, there are plenty of amateurs happily using 18 gauge wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.copper.org/resources/properties/protection/underground.html&quot; rel=&quot;noreferrer&quot;&gt;Corrosion depends on many factors&lt;/a&gt;. Corrosion rates could be anywhere &lt;a href=&quot;http://www.coppertubing.co.za/copper-tubing-manufacturers-contact-3/copper-underground-galvanic-corrosion&quot; rel=&quot;noreferrer&quot;&gt;from 0.0002 to 0.15 mm/year&lt;/a&gt;, depending on soil conditions. Solid wire will last longer than stranded, due to decreased exposed surface area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;18 gauge wire has a radius of 0.51mm. Most soils won't be especially aggressive. At a rate of 0.0002 mm per year, it takes approximately 2500 years to corrode all the way through. So assuming favorable soil conditions, you'll be dead long before the wire rots away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the bigger concern is mechanical strength. Digging animals can chew through wire or push it up. Frost heave and thermal expansion/contraction can cause the wire to pop up where it's subject to snags by foot traffic or mowers. Digging to plant a tree, etc. could cut a wire with a shovel. I'd expect to lose more radials this way than by corrosion. In my freezing, mole-infested location I bury the radials to anchor them more securely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the amateur, repairs are cheap and easy. So economically it makes little sense to spend a lot of money on robust wire. If 18 gauge wire hits the price point you need to install enough radials to have an efficient antenna, I'd say go for it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-12T15:38:52.217" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12031" PostTypeId="2" ParentId="12028" CreationDate="2018-10-12T15:42:47.957" Score="0" Body="&lt;p&gt;The longevity of your radials will depend on many factors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Wire material: copper, aluminum, steel&lt;/li&gt;&#xA;&lt;li&gt;Wire coating: bare, enamel, vinyl, galvanized&lt;/li&gt;&#xA;&lt;li&gt;Environment, e.g., acidity of rainfall, soil, etc.&lt;/li&gt;&#xA;&lt;li&gt;Common connection means: bolted, twisted, soldered, etc.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The effectiveness of your radial &quot;field&quot; will depend on soil losses and coverage of the area in which your signal's electromagnetic waves are produced. The nature of your radial implementation will depend on how much time and treasure you want to invest, &quot;treasure&quot; comprising real estate as well as hardware. It's also important to separate efficiency from your need/desire to have the radials produce resonance at the antenna's feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My QTH suffers from perhaps the poorest soil conductivity in the US, according the the map in &lt;em&gt;Reference Data for Radio Engineers&lt;/em&gt;. Add to that the deleterious effects of acid rain resulting from power plants in the midwest and you have a very difficult situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W8WWV published an article in &lt;em&gt;Ham Radio&lt;/em&gt; magazine many years ago which described a very cost-effective scheme which has served me well for over a decade: lay lengths of 4-ft wide galvanized steel fence to form a screen on the ground. Greg's analysis concluded that returns diminish rapidly for more then eight (8) such &quot;radials&quot; and when the length of each &quot;radial&quot; exceeds the height of the vertical radiator. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, each &quot;radial&quot; delivers substantial screening of the lossy ground. As an added bonus, these &quot;radials&quot; are easily rolled up if necessary, but they also &quot;disappear&quot; fairly quickly into the grass if you want to mow over them.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-12T15:42:47.957" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12032" PostTypeId="2" ParentId="12014" CreationDate="2018-10-12T23:17:49.047" Score="3" Body="&lt;p&gt;I have had a Yaesu FT890 stored in an unheated shed in Saskatchewan for 15 years. Just recently dusted it off, and it fired up just fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It gets to -40C here for weeks at a time in winter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;YMMV of course, but its one datapoint :-)&lt;/p&gt;&#xA;" OwnerUserId="13377" LastActivityDate="2018-10-12T23:17:49.047" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12033" PostTypeId="2" ParentId="9854" CreationDate="2018-10-13T11:34:36.460" Score="-1" Body="&lt;p&gt;The sections on the propagation of radio waves included in the &lt;em&gt;Radio Engineers' Handbook&lt;/em&gt; 1st Ed., 10th Impression (1943) by F. E. Terman present a detailed analysis of this subject which may be useful here.  A clip from it with his opening comments about &quot;wave tilt&quot; is shown below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A Google search will identify sources for this complete textbook in printed form; possibly even as a free download in PDF format.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1SJJh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1SJJh.jpg&quot; alt=&quot;Radio Engineer&amp;#39; Handbook, page 697&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-10-13T11:34:36.460" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12034" PostTypeId="2" ParentId="12029" CreationDate="2018-10-13T16:04:52.360" Score="1" Body="&lt;p&gt;An intuitive picture of mixing can be created by understanding musical beat notes.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is a beat note?  If you play two equal amplitude sinewave-like notes slightly out of tune, instead of hearing two notes, you will usually hear something called a beat note or a periodically amplitude modulated note.  If one gets out their handy dandy audio spectrum analyzer (or strobe tuner), one will find that the pitch of this new note is no longer at either of the two original note frequencies, but halfway in between.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However if you now plot this new additive waveform on your computer, you might note the phase of the new modulated sinewave changes to the opposite phase between every &quot;hump&quot;.  But a simple way to get rid of this phase change is to add a large enough sinewave of that new halfway-between center frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now all you've done is added 3 sinewaves of slightly different frequencies (two equal sidebands and a carrier halfway between them), but a plot show you've ended up with the exact same waveform as an envelope modulated carrier that an AM modulator would create via signal multiplication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So an assumption that these two different domain representations are the same thing would be reasonable under various conditions (linearity, time-invariance, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If adding 3 sinusoids gives the same result as multiplying 2 sinusoids, then the inverse should also hold true, and a multiplying mixer should produce a signal with a carrier and two side bands (in an FFT plot of the 3 sinusoids).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-10-15T17:02:39.777" LastActivityDate="2018-10-15T17:02:39.777" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12035" PostTypeId="1" AcceptedAnswerId="12038" CreationDate="2018-10-13T22:37:47.567" Score="1" ViewCount="185" Body="&lt;p&gt;This is a followup to &lt;a href=&quot;https://ham.stackexchange.com/q/11945/13271&quot;&gt;this question&lt;/a&gt; of mine. From reading the &lt;a href=&quot;https://en.wikipedia.org/wiki/Medium_frequency#Propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;wiki article&lt;/a&gt;, I get that:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Radio waves at MF wavelengths propagate via ground waves and reflection from the ionosphere ( called skywaves).  Ground waves follow the contour of the Earth. At these wavelengths they can bend (diffract) over hills, and travel beyond the visual horizon, although they may be blocked by mountain ranges.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Apart from not locating the source of transmissions right by a mountain range, is there any way in which elevation &lt;em&gt;does&lt;/em&gt; come into consideration when placing a transmitter, radio tower, etc.?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realize this is somewhat of a vague question, but since my dataset doesn't have good data on conditions in the ionosphere, I'm left trying to consider other factors in my (extremely) rough estimates, as in my other questions.&lt;/p&gt;&#xA;" OwnerUserId="13271" LastEditorUserId="8717" LastEditDate="2018-10-13T23:00:28.903" LastActivityDate="2018-10-14T10:40:10.817" Title="Is there any way in which elevation *does* affect medium frequency (AM radio) transmissions?" Tags="&lt;propagation&gt;&lt;transmitter&gt;&lt;am&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12036" PostTypeId="1" CreationDate="2018-10-14T03:04:21.383" Score="5" ViewCount="366" Body="&lt;p&gt;I was on my laptop watching a show and I paused to look something up and since there was no sound I could hear a voice talking. It sounded distorted like it was coming over a radio and I couldn't make out what was saying. There does not appear to be any unusual process running on the laptop. As I listen more it sounds like the man is having a whole conversation with someone else. There is a truck stop right by their house. Is it possible that my laptop is picking up a CB radio frequency?&lt;/p&gt;&#xA;" OwnerUserId="13380" LastEditorUserId="5222" LastEditDate="2018-10-23T21:58:08.703" LastActivityDate="2018-10-23T21:58:08.703" Title="Can my laptop pick up CB radio frequencies?" Tags="&lt;rfi&gt;&lt;frequency&gt;&lt;citizens-band&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12038" PostTypeId="2" ParentId="12035" CreationDate="2018-10-14T10:40:10.817" Score="4" Body="&lt;p&gt;Groundwave field intensities in the MW broadcast band depend almost entirely on radiated power, frequency, and Earth conductivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a map of the 0.5 mV/m groundwave contour of radio station KOA, Denver (50 kW transmitter, 850 kHz, omnidirectional transmit antenna).  Their transmit site is close to the eastern edge of the Rocky Mountains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The average propagation path loss is higher in the directions of the mountain range, but that is due to the lower relative conductivity of Earth in the Rockies, not because they are &quot;blocking&quot; the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Granted, there can be valleys/canyons within mountainous terrain areas where MW signals are seriously reduced by blockages.  The coverage map below shows the general case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/l3maw.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/l3maw.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-10-14T10:40:10.817" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12040" PostTypeId="2" ParentId="12029" CreationDate="2018-10-14T12:00:22.460" Score="0" Body="&lt;p&gt;Understanding how mixing actually works can be hard to grasp in an intuitive way.  This explanation aims to shed some light on how mixing works in a way that doesn’t involve complicated maths.  It doesn’t trot out the usual trig identity explanation, which I find falls short of a comprehensive explanation.&#xA;Instead, the explanation rests on two major insights: an intuitive way of understanding Fourier analysis and the idea of multiplication as a scaling operator that scales the presence of the modulating signal and its effect on the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let’s get the multiplication aspect out of the way first, since it’s the easier of the two to understand.  Mixing occurs when two signals are multiplied by each other.  &lt;strong&gt;Not added or subtracted – multiplied, this is very important&lt;/strong&gt;.  Let’s assume the carrier signal in a 1kHz sine wave and the modulating signal is a 100 Hz square wave of 50% duty cycle and is either on or off.  If you “add” these two frequencies, you would get energy at the points in the cycle where the modulating signal is zero simply because &lt;em&gt;some value&lt;/em&gt; + zero = &lt;em&gt;some value&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if you &lt;em&gt;multiply&lt;/em&gt; the two frequencies, you get zero energy where the modulating signal is zero and a scaled output of the carrier signal (scaled according to the magnitude of the modulation signal) where the modulation signal is non-zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This example, where the modulating signal is either on or off, makes it easier to understand the multiplicative effect and indeed many mixers operate using this exact method.  However, you can see that the same principal applies when the modulating signal is a sine wave and you have points in the cycle where the amplitude falls to zero.  &lt;strong&gt;You could say that modulation introduces a &lt;em&gt;rate of change&lt;/em&gt; to the carrier and this idea of a changing carrier gives rise to the side bands, as explained below.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let’s have a look at the product of two sine waves, one at 1kHz and one at 100Hz produced by Maxima:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/7G9NV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7G9NV.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here you can clearly see the multiplication operation at work.  Notice how the amplitude of the carrier signal drops to zero at intervals coinciding with the drop in the amplitude of the modulating 100Hz signal.  Notice also, how the carrier is &lt;em&gt;changing&lt;/em&gt; up and down at a particular rate determined by the modulation frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next thing to understand is a beautifully intuitive way to visualize how Fourier analysis “detects” the presence of energies at specific frequencies.  Similar intuition is available at several sources.  My favorites are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.i-programmer.info/programming/theory/3758-understanding-the-fourier-transform.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Stuart Riffle's bead and stick intuition&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=spUNpyF58BY&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;3Blue1Brown&amp;#39;s Fourier Visualized&quot;&gt;3Blue1Brown's Fourier Visualized&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In either case, the essential intuition is the idea of spinning the signal at different frequencies and measuring the &quot;balance&quot; of the resulting plot.  If the signal is spun at a frequency where energy is present, the correspondence of the spin frequency and the peaks in the signal will skew the plot off-balance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's relatively easy to imagine spinning the signal at the carrier frequency and consider &#xA; the resulting plot as a series of loops off to one side.  The loop magnitudes will change according to the modulation but the average will still be an off-centre vector indicating energy at the carrier frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the sideband's are trickier to understand.  My intuition is related to the rate of change of the carrier.  If you imagine the signal is spun at the carrier frequency as before but now you want to match the rate of increase (or decrease) at every instant as the carrier ramps upwards (or downwards) according to the modulation.  &lt;strong&gt;Then you will need to spin faster (or slower) to catch that ever rising (or falling) slope&lt;/strong&gt; and you will understand that the sideband frequency is that frequency that produces a non-destructive increase (or decrease) to the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The example chosen here is the ideal scenario of multiplying two pure sine waves to simplify the explanation.  In reality, a practical mixer will exhibit an exponential or chopping type action.  In these cases, the multiplication is inherent to the process alongside many other mathematical terms (power terms) and whilst you get the “multiplying action” described above, you also get other types of signal operations that will produce additional intermodulation products.&lt;/p&gt;&#xA;" OwnerUserId="11875" LastActivityDate="2018-10-14T12:00:22.460" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12041" PostTypeId="2" ParentId="12029" CreationDate="2018-10-14T23:48:52.510" Score="0" Body="&lt;p&gt;I found the discrete case of sampling easier to initially grasp. Imagine you have a sine wave with frequency = 1, that is it completes a full cycle in each unit on the &lt;em&gt;x&lt;/em&gt; axis:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ly8ni.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ly8ni.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if you sample that with frequency = 1 (meaning, on each integer of the &lt;em&gt;x&lt;/em&gt; axis), you are sampling at the same phase each time, so you just get a straight line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/KNsb5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KNsb5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is because the sampling frequency and signal frequency are equal, so their difference is zero. A frequency of zero is a straight line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we change the sampling frequency to 1.1 (meaning, we sample at every 1/1.1 or about every 0.90909090 units along the &lt;em&gt;x&lt;/em&gt; axis), then we get something more interesting:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sBTwj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sBTwj.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A sine wave with frequency 0.1 appears because the sampling frequency (1.1) minus the signal frequency (1) is 0.1.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-14T23:48:52.510" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12042" PostTypeId="1" AcceptedAnswerId="12703" CreationDate="2018-10-14T23:49:22.797" Score="1" ViewCount="148" Body="&lt;p&gt;What I want to do is add digital voice (DMR, D-Star, Fusion) capability to an existing dual band mobile or HT. Similar to adding APRS functionality using APRSDroid and a bluetooth TNC. Reading &lt;a href=&quot;https://ham.stackexchange.com/questions/6683/dmr-dstar-p25-software-encode-decode&quot;&gt;here&lt;/a&gt;, I understand this can't be done purely in software yet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm looking for something that I think is a bit like the DV hotspot devices out there like the JumboSpot or DVMega. As I understand it, those devices let an existing DV radio get onto a network when an repeater isn't available. Their &quot;upstream&quot; to the DV network of choice is over the Internet, their local connection to the DV radio is UHF or VHF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine a DVMega-type device that is capable of encoding/decoding AMBE packets and generally running a particular DV protocol. This is using a TNC to talk to the radio and is also talking over bluetooth serial to an Android phone. The phone would have a UI for picking talk groups and other DV-specific items.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is: Can anyone point me at devices that do this, or technical reasons why what I'm looking for can't exist?&lt;/p&gt;&#xA;" OwnerUserId="8380" LastEditorUserId="8380" LastEditDate="2018-10-26T01:41:16.547" LastActivityDate="2019-01-26T05:44:56.427" Title="DVMega / DVDongle with a TNC connection to radio" Tags="&lt;modification&gt;&lt;digital-voice&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12043" PostTypeId="2" ParentId="12036" CreationDate="2018-10-15T00:14:51.700" Score="9" Body="&lt;p&gt;Yes, very strong radio signals can be picked up by just about any device with a speaker and a transistor in it. The transistor acts as a &lt;a href=&quot;https://en.wikipedia.org/wiki/Rectifier&quot; rel=&quot;noreferrer&quot;&gt;rectifier&lt;/a&gt;, forming a crude &lt;a href=&quot;https://en.wikipedia.org/wiki/Envelope_detector&quot; rel=&quot;noreferrer&quot;&gt;envelope detector&lt;/a&gt;. Amplitude modulated voice can be heard quite clearly, single-sideband modulated voice is quite garbled but often still somewhat intelligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No cause for alarm: it won't damage your laptop and it's nothing malicious going on. Probably just some trucker with an illegal CB amplifier.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-15T00:14:51.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12044" PostTypeId="2" ParentId="11853" CreationDate="2018-10-15T02:13:58.530" Score="1" Body="&lt;p&gt;You didn't specify what hardware you are using, so I'll give a generic answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to just eliminate static, that's what squelch is for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beyond that, there is no &quot;established&quot; method that is not specific to the scanner you are using.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some scanners have a lock out button that will blacklist a signal while the scanner is stopped on it, so it will be ignored in subsequent passes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would not be hard to add similar functionality to SDR software.&#xA;I've seen several SDR projects designed to recognize specific modes; this might make it possible to blacklist digital modes when they are found.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-10-15T02:13:58.530" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12046" PostTypeId="1" AcceptedAnswerId="12047" CreationDate="2018-10-15T14:14:34.953" Score="9" ViewCount="2387" Body="&lt;p&gt;Is it legal to transmit using HackRF one (in Germany), the purpose is to do some Lab research and Academic experiments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;for example i want to broadcast an FM signal using HackRF one and try to receive it using another hardware (RTL-SDR).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If no is there another legal alternative?&lt;/p&gt;&#xA;" OwnerUserId="11773" LastEditorUserId="218" LastEditDate="2018-10-15T14:20:46.660" LastActivityDate="2018-10-17T23:21:56.857" Title="Is it legal to transmit with HackRF one?" Tags="&lt;legal&gt;&lt;fm&gt;&lt;transmission&gt;&lt;hackrf&gt;&lt;germany&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12047" PostTypeId="2" ParentId="12046" CreationDate="2018-10-15T14:29:34.103" Score="8" Body="&lt;p&gt;You'll need an &lt;em&gt;experimental radio license&lt;/em&gt; (Versuchsfunk) from Bundesnetzagentur &lt;a href=&quot;https://www.bundesnetzagentur.de/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/SpezielleAnwendungen/Versuchsfunk/versuchsfunk-node.html&quot; rel=&quot;noreferrer&quot;&gt;link&lt;/a&gt; for research operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For demonstration/teaching purposes, a &lt;em&gt;demonstration radio license&lt;/em&gt; (&lt;a href=&quot;https://www.bundesnetzagentur.de/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/SpezielleAnwendungen/Demonstrationsfunk/Demonstrationsfunk-node.html&quot; rel=&quot;noreferrer&quot;&gt;Demonstrationsfunk für Bildungseinrichtungen&lt;/a&gt;) would be in order.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not a lawyer nor have I ever applied for either of these; I'd recommend contacting BNetzA on these aspects. Whenever I contacted them, they were super friendly and swift.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A loophole here &lt;strong&gt;might&lt;/strong&gt; (again, ask BNetzA if in doubt) be general low power transmitter licenses as used by e.g. the small dongles that you can plug into your iPhone to make your car stereo receive on FM what your phone is playing. I know that there's a pretty low power limit for these (nW range), but that might be perfectly suitable for your use case. What I don't know is whether the devices in question need to be type-approved (which would rule out the HackRF completely, as it can do &lt;strong&gt;anything&lt;/strong&gt;) or whether guaranteeing that your device &lt;strong&gt;won't&lt;/strong&gt; do anything bad is sufficient at these power levels.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-10-15T14:29:34.103" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12049" PostTypeId="2" ParentId="12046" CreationDate="2018-10-15T17:13:01.870" Score="7" Body="&lt;p&gt;As for other legal alternatives, one might be transmitting inside a suitably shielded Faraday cage.  I’ve seen such facilities at labs where various prototype and pre-production (and competitors?) electronics systems were being tested to measure how far out-of legal compliance they were.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-10-15T17:13:01.870" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12052" PostTypeId="2" ParentId="1282" CreationDate="2018-10-16T13:21:10.750" Score="5" Body="&lt;p&gt;From my experience, not many. Not many at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Learning CW at speeds that facilitate conversation, vs just sending callsigns and signal reports, is, frankly, daunting. I've only been a ham for a few years and I avoided it at first for that very reason. I tried learning it that first year and when I'd hear the 'old' hands banging away at 25+ wpm, I gave up thinking there's NO way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I always end up tuning over to the CW frequencies and there's ALWAYS somebody operating CW no matter the band conditions. So, I've since changed my tune, taken the CWOps course, and and am now practicing everyday so that I can join in. I'm also encouraging all the non-cw hams in my club to join me. Since we're all new to it, I've found quite a few takers. CW is fun, and it seems to embody the spirit of ham radio for me, so I try to impart that to them as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, there are not many new hams using CW, but we can change that. At the very least, lets try to! &lt;/p&gt;&#xA;" OwnerUserId="8480" LastActivityDate="2018-10-16T13:21:10.750" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12054" PostTypeId="2" ParentId="11873" CreationDate="2018-10-16T20:14:37.617" Score="3" Body="&lt;p&gt;In David Leeson's (W6NL) Nov/Dec 2018 &lt;em&gt;QEX&lt;/em&gt; article, &quot;The Story of the Broadband Dipole,&quot; he cites the work of Tang, et al, on the &quot;Equivalent Circuit of a Dipole Antenna Using Frequency-indpendent Lumped Elements.&quot; (from &lt;em&gt;IEEE Transactions on Antennas and Propagation&lt;/em&gt;, Vol 41, No. 1, Jan 1993, pp. 100-103).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Leeson recommends this schematic equivalent as an adequate representation for a center-fed dipole:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/AU9DU.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fAU9DU.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;with: &lt;span class=&quot;math-container&quot;&gt;$h$&lt;/span&gt; as the dipole &lt;strong&gt;half-length&lt;/strong&gt; and &lt;span class=&quot;math-container&quot;&gt;$a$&lt;/span&gt; as the wire radius, both in meters, &lt;span class=&quot;math-container&quot;&gt;$\omega_0$&lt;/span&gt; as the resonant frequency in Hz and &lt;span class=&quot;math-container&quot;&gt;$R_{a0}$&lt;/span&gt; the radiation resistance at resonance in ohms:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$C_{11} = \frac{27.82\mathsf x 10^{-12} h}{ln(2h/a)-1.693}$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$L_{11} = \frac{1}{\omega_0^2C_{11}}+C_{11}R_{a0}^2$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$R_{11} = \frac{L_{11}}{C_{11}R_{a0}}$$&lt;/span&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-16T20:14:37.617" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12057" PostTypeId="1" CreationDate="2018-10-17T12:12:21.713" Score="5" ViewCount="912" Body="&lt;p&gt;Currents at the base of an elevated, 5/8-wave, vertical ground-plane (GP) transmit antenna are lower than when that vertical conductor is 1/4-wavelength.  Does this mean that the performance of the elevated radials is less important in producing optimal radiation from a 5/8-wave, elevated GP antenna?&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-10-17T12:12:21.713" Title="Are Elevated Radials Necessary for Elevated, 5/8-wave &quot;Ground-Plane&quot; Antennas?" Tags="&lt;antenna-system&gt;&lt;vertical-antenna&gt;&lt;radial&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12058" PostTypeId="2" ParentId="12057" CreationDate="2018-10-17T12:12:21.713" Score="5" Body="&lt;p&gt;Elevated radials are &lt;em&gt;required&lt;/em&gt; in order to increase/optimise the radiation possible from any such elevated &quot;GP&quot; monopole or whip antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the elevated radials are symmetrically arranged and lie in the horizontal plane, then their net far-field radiation is zero. However the r-f current at the common point of those radials is &lt;strong&gt;not&lt;/strong&gt; zero — it is the same as the current that flows into the base of the vertical antenna conductor above that common point. All of the useful far-field radiation from such antennas is produced by the single vertical conductor, not by elevated horizontal radials just below it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currents at the common-point of the radials for a given, Z-matched r-f power at the feedpoint are smaller for such 1/2-wavelength and 5/8-wavelength monopole/whip antennas. But those currents cannot be zero if the antenna is to radiate anything at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Regardless of their absolute value, any percentage reduction in the sum of those radial currents due to the elevated radials being &quot;sub-optimal&quot; reduces the e-m radiation that antenna (alone) will produce, by that same percentage.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-10-17T12:12:21.713" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12060" PostTypeId="2" ParentId="12046" CreationDate="2018-10-17T23:21:56.857" Score="0" Body="&lt;p&gt;I've also seen things like this done with the two units directly connected via a section of coax instead of antennas on each.   Of course, for this to work, you need to keep power levels very low and there may still be some &quot;unintentional radiation&quot; and in some cases you may still need attenuators inline.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-10-17T23:21:56.857" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12063" PostTypeId="1" CreationDate="2018-10-18T20:15:58.927" Score="0" ViewCount="289" Body="&lt;p&gt;I have a Baofeng UV-5R, but no USB programming cable. I also have a Baofeng BF-888S with a USB cable. Is it safe to use the 888S cable on the UV5R?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was able to find a &lt;a href=&quot;https://baofengtech.com/pccable&quot; rel=&quot;nofollow noreferrer&quot;&gt;cable description on the Baofeng site&lt;/a&gt;, but it does not list the compatible models.&lt;/p&gt;&#xA;" OwnerUserId="890" LastActivityDate="2018-10-18T20:15:58.927" Title="Can I use the BF-888S programming cable on the UV-5R?" Tags="&lt;baofeng&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12064" PostTypeId="2" ParentId="12063" CreationDate="2018-10-18T20:15:58.927" Score="2" Body="&lt;p&gt;Yes, it's compatible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to &lt;a href=&quot;https://baofengradio.us/baofeng-ftdi-usb-cable.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;baofengradio.us&lt;/a&gt;, the compatible models are&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;UV-5R and UV-5R V2+&lt;/li&gt;&#xA;  &lt;li&gt;BF-F8+ and BF-F9 V2+&lt;/li&gt;&#xA;  &lt;li&gt;UV-82 and UV-82 V2+&lt;/li&gt;&#xA;  &lt;li&gt;BF-888S and the ATR-22&lt;/li&gt;&#xA;  &lt;li&gt;997-S&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;With that information, I have connected the UV-5R and I was able to use the Chirp software with it.&lt;/p&gt;&#xA;" OwnerUserId="890" LastActivityDate="2018-10-18T20:15:58.927" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12065" PostTypeId="1" AcceptedAnswerId="12066" CreationDate="2018-10-18T21:02:58.733" Score="2" ViewCount="6984" Body="&lt;p&gt;I'm using an Anroid app for learning CW. In Germany, it's common to define the speed in CPM (&quot;characters per minute&quot;, or German BPM for &quot;Buchstaben pro Minute).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the Morse trainer I use specifies WPM (&quot;words per minute&quot;). Is there a conversion between the two?&lt;/p&gt;&#xA;" OwnerUserId="890" LastActivityDate="2021-02-08T09:39:27.450" Title="Converting WPM to CPM" Tags="&lt;cw&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12066" PostTypeId="2" ParentId="12065" CreationDate="2018-10-18T21:02:58.733" Score="4" Body="&lt;p&gt;Morse characters have different lengths. A series of Es is much shorter than a series of Os. Therefore, the WPM is perhaps a better choice, because a word contains different characters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on the two standard 5 character words &quot;Paris&quot; and &quot;codex&quot; and their dot-dash-ratio, the WPM/CPM factor has been calculated as 5. So&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;6 WPM = 30 CPM&lt;/li&gt;&#xA;&lt;li&gt;10 WPM = 50 CPM&lt;/li&gt;&#xA;&lt;li&gt;12 WPM = 60 CPM&lt;/li&gt;&#xA;&lt;li&gt;20 WPM = 100 CPM&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Morse_code#Speed_in_words_per_minute&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt; has this explanation, but does not further specify who first came up with these two words:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;There are two common typical words: &quot;PARIS&quot; and &quot;CODEX&quot;. PARIS mimics a word rate that is typical of natural language words and reflects the benefits of Morse code's shorter code durations for common characters such as &quot;e&quot; and &quot;t&quot;. CODEX offers a word rate that is typical of 5-letter code groups (sequences of random letters).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and later&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The &lt;em&gt;[Federal Communications]&lt;/em&gt; Commission specifies Morse code test elements at 16 code groups per minute, 20 words per minute, 20 code groups per minute, and 25 words per minute. The word per minute rate would be close to the PARIS standard, and the code groups per minute would be close to the CODEX standard. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="890" LastEditorUserId="890" LastEditDate="2018-12-12T15:17:43.623" LastActivityDate="2018-12-12T15:17:43.623" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12067" PostTypeId="2" ParentId="1437" CreationDate="2018-10-19T02:27:42.310" Score="1" Body="&lt;p&gt;Simplex implies transmission and reception on the same frequency without using a repeater. The band plan specifies that no repeaters are ever to transmit or receive on calling frequencies, nor should other operating modes, such as cross-band communication or remote control use them. In addition, it is expected that you can make initial contact on the calling frequency, but that you subsequently agree with each other to move the conversation to an alternative frequency (if you are going to speak to each other for more than a few minutes) to keep the calling frequency free for others' use.&lt;/p&gt;&#xA;" OwnerUserId="13411" LastActivityDate="2018-10-19T02:27:42.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12068" PostTypeId="1" CreationDate="2018-10-19T07:06:39.447" Score="5" ViewCount="103" Body="&lt;p&gt;If one passed the Extra written test in the late '90s at an ARRL test center but did not get the 20wpm endorsement, yet is an Advanced operator, would they now be upgraded to Extra class or do they need to retest? As I stated, I passed the written in the '90s at an ARRL test center.&lt;/p&gt;&#xA;" OwnerUserId="13414" LastEditorUserId="9844" LastEditDate="2018-10-19T20:21:14.597" LastActivityDate="2018-10-19T20:21:14.597" Title="Is a US Extra class exam from the '90s valid to upgrade from Advanced class today?" Tags="&lt;united-states&gt;&lt;cw&gt;&lt;license&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12069" PostTypeId="1" CreationDate="2018-10-19T12:20:09.460" Score="2" ViewCount="131" Body="&lt;p&gt;Conventional wisdom based on the far-field (only) patterns calculated by M-o-M software such as NEC show that low-angle radiation from a horizontal dipole is very low, and zero in the horizontal plane.  Is this belief valid?&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-10-23T13:17:53.063" Title="How Does the Low-Angle Radiation of a Horizontal Dipole Compare to That of a Vertical Monopole?" Tags="&lt;dipole&gt;&lt;vertical-antenna&gt;&lt;radiation-pattern&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12070" PostTypeId="2" ParentId="12069" CreationDate="2018-10-19T12:20:09.460" Score="2" Body="&lt;p&gt;The very small low-angle radiation noted above is the result of excluding the surface wave from the NEC calculations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also the commonly-used &quot;far-field only&quot; patterns calculated by NEC are based on an infinite distance from the radiator, and if a ground plane is included, it is considered to be flat. Both of these elements can lead to a misunderstanding of the real-world performance of antenna systems modeled in NEC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a comparison of NEC patterns including the surface wave. It shows the radiated field intensities at one wavelength in the horizontal plane for elevation angles from zero to about 17.2 degrees, with 100W of Z-matched r-f power at the antenna feedpoints.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Conclusions are left to readers to consider.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7BgyY.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7BgyY.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-10-19T12:20:09.460" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12072" PostTypeId="2" ParentId="12068" CreationDate="2018-10-19T13:49:08.677" Score="6" Body="&lt;p&gt;&lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.505&quot; rel=&quot;nofollow noreferrer&quot;&gt;§ 97.505&lt;/a&gt; (&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1505&quot; rel=&quot;nofollow noreferrer&quot;&gt;alternate reference&lt;/a&gt;) covers the ways to get credit for an exam element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you passed the test in the 90's, you would have earned a &quot;certificate of successful completion of an examination&quot; (CSCE). According to §97.505(b), a CSCE is valid for only 365 days, so unfortunately you'll have to test again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to §97.505(a), an unexpired advanced license is valid for credit towards elements 2 and 3, so you will need to pass only element 4 to upgrade to extra. If the license is expired the credit is only for element 3, so you'll also have to pass element 2. You must bring evidence of the license to the VE. If you don't have a copy of the license, you can &lt;a href=&quot;http://wireless2.fcc.gov/UlsApp/UlsSearch/license.jsp?licKey=624518&quot; rel=&quot;nofollow noreferrer&quot;&gt;get it from ULS&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-10-19T18:15:19.167" LastActivityDate="2018-10-19T18:15:19.167" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12073" PostTypeId="1" CreationDate="2018-10-19T20:56:04.183" Score="4" ViewCount="1046" Body="&lt;p&gt;To the extent that FT8 is a way to bring people into the hobby or re-ignite passion among those who haven't been on the air in a while, what's the easiest way to get someone on the air with this new mode? Cost is a factor, but simplicity of components and ability to transceive (not simply send a signal) are relevant too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's safe to assume this is someone who has a cell phone, laptop/PC, or Raspberry Pi and can be convinced to take any of these paths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bonus points for addressing the US license requirements too.&lt;/p&gt;&#xA;" OwnerUserId="8284" LastEditorUserId="873" LastEditDate="2018-10-22T13:47:37.857" LastActivityDate="2019-11-28T18:35:27.637" Title="What is the minimum equipment necessary to get on the air with FT8?" Tags="&lt;united-states&gt;&lt;digital-modes&gt;&lt;hf&gt;&lt;ft8&gt;&lt;qrp&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12075" PostTypeId="1" CreationDate="2018-10-20T08:30:41.147" Score="6" ViewCount="824" Body="&lt;p&gt;I'm in the process of building a RF buffer-amplifier chain for a VFO and I'm experiencing a design issue trying to impedance match between the sections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The issue I'm having is that many (most) of the circuit designs documented are characterized with a source or load impedance of 50 ohms.  Lets take the following snippet as an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aJziM.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aJziM.png&quot; alt=&quot;Vackar Buffer Amp&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Taken from &lt;a href=&quot;https://nt7s.com/files/QRPHomebuilder.pdf&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt; pg. 520.  I've prototyped this buffer amp at 50 MHz and works quite nicely.  It gives a gain of just over 3 and a power output of ~12dBm.  But, the key point is that all of these characteristics are based on a reflected collector impedance of ~260 ohms and &lt;strong&gt;assume a 50 ohm load&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I'd like to follow this pre-amplifier with a power amp and many of the examples I'd like to prototype have an impedance transformer at the input.  Something like the following is very common:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7u1yg.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7u1yg.png&quot; alt=&quot;RF Power Amplifier&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And again, the amplifier is documented assuming the signal generator at the input has a 50 ohm output impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my case, I would like to combine these two amplifiers into a pre-amp and power amp chain.  The obvious solution is to combine the transformers into a single transformer that presents ~260 ohms to the collector of the pre-amp and ~6 ohms at the base of each power transistor base (in the power amplifier shown T1 is a 4:1 impedance transformer =&gt; 50 ohms becomes 12.5 and each base sees half of that).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, I've lost my fixed 50 ohm impedance.  If I combine the transformers I make the collector load of the pre-amp directly dependent on the RF input impedance of the power amp transistors (which is nearly always a complex quantity and is non-trivial to measure).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;So, I'd like to know if there are any &quot;tricks&quot; to pin the inter-stage impedance to a particular value or is there nothing for it but to characterize the input impedance of the power amp?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="9493" LastEditDate="2018-10-20T12:28:59.407" LastActivityDate="2018-10-24T19:54:13.220" Title="Impedance Matching between RF Amplifier Stages" Tags="&lt;impedance-matching&gt;&lt;amplifier&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12076" PostTypeId="2" ParentId="12075" CreationDate="2018-10-20T15:36:37.497" Score="5" Body="&lt;p&gt;There is no need to &quot;pin&quot; an interstage impedance. You may directly transform from the native output impedance of one stage to the native input impedance of the next without going through an intermediate transformation or termination.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When designing an interstage transformer, the general design rule is to ensure that the inductive reactance of each winding is at least 10 times the impedance to which it is connected. This ensures that the transformer winding impedance does not swamp out the attached impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also take care to think through the transformer topology. Take note that the first circuit uses isolated windings for the output transformer while the second circuit uses an autotransformer at its input stage. The combined impedance transformation will require isolated windings so as to restore a ground referenced output of the previous stage.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-10-20T15:36:37.497" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12077" PostTypeId="2" ParentId="12075" CreationDate="2018-10-20T18:30:00.807" Score="2" Body="&lt;p&gt;T1 in the &quot;power amp&quot; schematic you provided is a 4:1 step down transformer. Its purpose is to match - that is, maximize power transfer between - the preceding stage and the power amp transistors, whose high impedance is &quot;swamped&quot; by the 10-ohm resistors. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can match the ~260-ohm driver to the PA by replacing T1 with a 16:1 step down transformer and replacing the 10-ohm resistors with 15-ohm resistors. You might find it simplest to accomplish the higher step down ratio by adding a second &quot;copy&quot; of T1 between the input and T2. Simulation indicates that an inductance of 1-uH should suffice for each of the four windings on T1a and T1b:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oqVHa.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oqVHa.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-20T18:30:00.807" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12078" PostTypeId="2" ParentId="12073" CreationDate="2018-10-20T20:32:39.030" Score="5" Body="&lt;p&gt;Without getting into specific product recommendations, I believe the simplest way is as follows:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Obtain a license.  An amateur license is required for using amateur bands.  I am not aware of any non-amateur bands using FT8.  A technician-level license is sufficient in USA for VHF and UHF but it looks like a General level license is needed for the HF bands.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Buy a radio.  Pretty much any radio that supports SSB.  Easier if it has a phono out and a mic in; even easier yet if it has a digital audio out and digital audio in.  Of course, more power is better, but 5 Watts is plenty for talking across many hundreds of miles, especially if you have a good antenna.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Download FT8 software.  The software is freely available here: &lt;a href=&quot;https://physics.princeton.edu/pulsar/k1jt/wsjtx.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://physics.princeton.edu/pulsar/k1jt/wsjtx.html&lt;/a&gt;  This software covers many different digital modes similar to FT8.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Hook the radio up to the computer (or tablet or whatever).  You might need a special cable depending on the radio.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Synchronize your computer's clock either using a GPS or one of the network clock synchronization protocols.  FT8 requires your clock to be accurate within a second.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Start using FT8.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Once you start working with this, you will quickly see what opportunities exist to make the setup a little better.  But this is enough to get started quickly and inexpensively.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Full requirements for FT8 are listed at &lt;a href=&quot;https://physics.princeton.edu/pulsar/k1jt/wsjtx-doc/wsjtx-main-2.1.0.html#SYSREQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://physics.princeton.edu/pulsar/k1jt/wsjtx-doc/wsjtx-main-2.1.0.html#SYSREQ&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="10489" LastEditDate="2019-11-28T18:35:27.637" LastActivityDate="2019-11-28T18:35:27.637" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12082" PostTypeId="1" AcceptedAnswerId="12273" CreationDate="2018-10-21T02:22:10.930" Score="1" ViewCount="378" Body="&lt;p&gt;I have an interest in studying and researching how radio technology can be used in other fields of electronics. What kind of license should I look into so I can carry out some experiments or research? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My interest is &lt;strong&gt;&lt;em&gt;Data propagation in Radio contexts&lt;/em&gt;&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My intent is to experiment with Ham radio equipment to research viable Data networking and create equipment off of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I working at any band or VHF, UHF etc. that I fit and what I can do with once I have the documents in hand. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I intended to do was co op existing radio hardware into designs or create external addons or chips to plug into your desktop or an existing sets. The reason why I ask this question is that I am fully aware of the idea that you need paper work to fully operate the transmitter or work in the bands. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I don't intend to operate as a full blown &quot;Station&quot; but rather in a controlled environment, do I need an operational license or is there a specialty documentation that I can get to permit to me to use the equipment that I am co opting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radiation will be at times emitted but the bulk of the time the radiation will be confined. I will have to at times radiate but hopefully in low power modes. High power if permitted.&lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorDisplayName="user4168" LastEditDate="2019-01-21T02:26:32.390" LastActivityDate="2019-01-21T02:26:32.390" Title="What kind of ham radio license should I get?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;equipment-design&gt;" AnswerCount="3" CommentCount="17" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12083" PostTypeId="1" AcceptedAnswerId="12085" CreationDate="2018-10-21T13:09:06.297" Score="5" ViewCount="803" Body="&lt;p&gt;I've been receiving satellite signals in the L-band (~1.7GHz), recently.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These signals are RHCP. So far, I've been using a DIY helical antenna in axial mode, and a patch antenna with cropped or clipped corners.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My favorite tool to calculate the latter, is btw. this: &lt;a href=&quot;http://kempbros.github.io/antennas/Patch_Antenna_Generator/&quot; rel=&quot;noreferrer&quot;&gt;http://kempbros.github.io/antennas/Patch_Antenna_Generator/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, when a signal is RHCP, I need an RHCP antenna to receive it, that's quite logical, and I can visualise in my head, how the propagation works, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But now I'd like to use a dish as a reflector, but as I imagine things, the reflector works like a mirror, and will change the polarity of the circular polarized signal. So to receive a RHCP signal with a parabolic dish antenna (receiving element pointed at the dish, similar to how the LNB is mounted on a Ku-band antenna for satellite TV), I'd need a LHCP antenna in the focal point of the dish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At least that's how I understand it, but like I said, at this point I'm super confused.&lt;/p&gt;&#xA;" OwnerUserId="11070" LastActivityDate="2018-10-23T12:39:23.503" Title="Does a parabolic reflector dish change circular polarity?" Tags="&lt;antenna-theory&gt;&lt;circular-polarization&gt;&lt;reflector&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12084" PostTypeId="2" ParentId="12082" CreationDate="2018-10-21T14:15:47.937" Score="0" Body="&lt;p&gt;You may be able to conduct your research on one or more of the &quot;ISM&quot; bands, set aside for industrial, scientific and medical research without a license. Though there are some regional variations, most of the bands can be used worldwide.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-21T14:15:47.937" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12085" PostTypeId="2" ParentId="12083" CreationDate="2018-10-21T14:27:30.210" Score="9" Body="&lt;p&gt;A parabolic reflector reverses the sense of circular polarization. so your feed must have the opposite sense or &quot;handedness&quot; to the incoming signal to avoid significant polarization loss.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-21T14:27:30.210" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12086" PostTypeId="2" ParentId="8940" CreationDate="2018-10-23T12:26:17.283" Score="-2" Body="&lt;p&gt;Heard another possibility on the &quot;street&quot;.  The proliferation of 'space junk' may have something to do with the singularity of the recent HF propagation decline.  My recollection of a recent score keeper's reports is that there are 166 million pieces of man made stuff in orbit larger than 1 mm (or is it 1 cm?) weighing of the order of 8000 tons, including 4000 satellites and pieces from 500 collisions.  Could that stuff be affecting the ionosphere?&lt;/p&gt;&#xA;" OwnerUserId="13433" LastActivityDate="2018-10-23T12:26:17.283" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12087" PostTypeId="2" ParentId="12083" CreationDate="2018-10-23T12:39:23.503" Score="0" Body="&lt;p&gt;A way to avoid rebuilding an existing RHCP antenna would be to use a second, planar, reflector which would re-invert the polarization's handedness.  If the satellite is close to the horizon, for example, the reflector could be tower mounted at a near 45 degree angle to beam the signal to a ground mounted dish, which may also be more convenient than a tower mounted dish.&lt;/p&gt;&#xA;" OwnerUserId="13433" LastActivityDate="2018-10-23T12:39:23.503" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12088" PostTypeId="2" ParentId="12069" CreationDate="2018-10-23T13:17:53.063" Score="0" Body="&lt;p&gt;The reflection of an E field wave is well known to be 180 degrees out of phase with the incident wave, given a pure E field and a perfect reflector. Real world ground conditions, and the shift of the wave from pure E to a mix of E and H fields somewhat dilutes this effect, as shown by the chart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If low angle signal strength is the objective, an interesting alternative is an H, or magnetic, wave generating antenna, as classical theory shows this energy is reflected in phase by the ground.  Personal on-air 40 meter band amateur radio experience with such an antenna, a so-called magnetic loop, has borne this out.  A 7 foot diameter loop 7 feet off the ground has consistently performed as well reaching DX as others' dipoles several times higher. &lt;/p&gt;&#xA;" OwnerUserId="13433" LastActivityDate="2018-10-23T13:17:53.063" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12089" PostTypeId="2" ParentId="11943" CreationDate="2018-10-23T14:40:58.253" Score="1" Body="&lt;p&gt;My apologies for my tardiness in updating the bulldogtrust site. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am too skeptical to try coax inside one side of the loop tubing, due to high voltage and asymmetrical capacitance it would introduce at the exit point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My simple minded solution, discovered first on a Russian website, uses capacitive feed at the loop's tuning capacitor.  Each side of the tuning capacitor is coupled to each side of the coax through 10-50 pF of capacitance (depending on band and loop size) per side to match 50 ohm coax.  With a kilowatt there is 6 or 8 kV difference between loop and coax there, so high voltage high Q capacitors are necessary.  A practical solution is a series string of 3 or 4 small inexpensive USSR surplus doorknobs on each side of the tuning capacitor.  A a series string of 3-5 39, 47 or 100pF at 3 kV from Ebay will provide trial and error tapping choices for getting a match. (I use a 15 kV vacuum tuning capacitor to handle my kW amp)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hung from a tree branch, the capacitor at the bottom of the loop should have sufficient distance to ground to be both safe and efficient. (1 diameter is usually sufficient)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Incidentally, a reasonably efficient loop will be too sharp in tuning to use a DC motor.  Stepper motors (NEMA 17 is sufficient) and controllers (T-500) from pololu.com with a generic quadrature rotary encoder is one way to go.  &lt;/p&gt;&#xA;" OwnerUserId="13433" LastActivityDate="2018-10-23T14:40:58.253" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12090" PostTypeId="2" ParentId="11805" CreationDate="2018-10-23T15:08:39.540" Score="3" Body="&lt;p&gt;My technique for wire antennas is to twist an eyelet about 10-20% in from the end of each leg, and attaching the support rope there.  Letting the dipole ends dangle down allows a much more convenient way for trial and error fine tuning the end loops, since the attachment doesn't have to be re done each time.  Also, moving the highest voltage point away from the attaching rope and trees reduces rain detuning and loss from induced antiphase currents.&lt;/p&gt;&#xA;" OwnerUserId="13433" LastActivityDate="2018-10-23T15:08:39.540" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12091" PostTypeId="1" CreationDate="2018-10-23T15:42:16.957" Score="5" ViewCount="1141" Body="&lt;p&gt;I’m looking for information about the diameter of a ground plane disk that I can use with a regular car radio and car type antennas in my home. DIY would be best, or any other ideas for a antenna that will work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have tried Google, but have found nothing useful for what I’m trying to accomplish.&lt;/p&gt;&#xA;" OwnerUserId="13434" LastEditorUserId="8717" LastEditDate="2018-10-23T19:12:23.247" LastActivityDate="2018-10-23T22:15:35.793" Title="Size of ground plane disk for vertical antennas?" Tags="&lt;antenna-construction&gt;&lt;vertical-antenna&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12092" PostTypeId="2" ParentId="12091" CreationDate="2018-10-23T18:13:30.263" Score="4" Body="&lt;p&gt;Rule of thumb: the ground plane radius should be at least a quarter wavelength.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-23T18:13:30.263" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12093" PostTypeId="2" ParentId="12091" CreationDate="2018-10-23T19:16:30.827" Score="4" Body="&lt;p&gt;If I understand correctly, you have an antenna intended for a car body, but you'd like to use it loose in your house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A solid ground plane will work, and it should be a quarter wave radius. For FM Radio, wavelength is about 3 m, so the ground plane should be 1.5 metres in diameter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of a solid ground plane, you could use four radial wires, 0.75 m long, extending at right angles to the whip antenna. They should all be connected to the ground bolt or metal base of the whip. You could use coat hangers or any other stiff wire - diameter and type is not important so select something that is mechanically strong enough. This will be a lot lighter and cheaper than the solid metal ground. It is what's done when mounting a whip on a fibreglass vehicle, or through a tile roof.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2018-10-23T19:16:30.827" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12094" PostTypeId="2" ParentId="12091" CreationDate="2018-10-23T21:56:25.947" Score="0" Body="&lt;p&gt;For AM (530 to 1700 kHz) you don't want a ground plane! &#xA;A ferrite loop antenna made for the purpose would be far better, as would an outdoor wire.&#xA;The other answers for FM (88-108 MHz) are good ones.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-10-23T22:15:35.793" LastActivityDate="2018-10-23T22:15:35.793" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12095" PostTypeId="1" CreationDate="2018-10-24T08:32:30.667" Score="1" ViewCount="216" Body="&lt;p&gt;I have a GSM Modem that works on 2300MHz Frequency (LTE), but it could only receive 3 bar of signal strength.&#xA;I plan to make a DIY directional antenna that is made specifically for this Frequency spectrum.&#xA;From the online search, I found that people can make antenna either for 2.4GHz or 5GHz using the same material, same shape, but with a different measurement.&#xA;So, my understanding is that we could make an antenna to work on a specific frequency by changing the measurement of the element.&#xA;-- I am thinking about DIY bi-quad antenna --.&#xA;Will it work?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another thing that is kind of related to my question is that,&#xA;This modem not only works on 2300MHz but also work on other frequency as well.&#xA;Just like a cell phone. This modem, depending on what network carrier I use, also changed its frequency based on the frequency used by that mobile provider or carrier.&#xA;Let say that 5 mobile network operator/Carrier in my country work on 850MHz, 900 MHz, 1800MHz, 1950MHz and 2300MHz. How the internal antenna work on all of those frequencies, are they using 5 different antennae inside of the device or they can use one antenna that works on all of that frequency spectrum?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By making one specific antenna for each one of those frequencies spectra will it improve the signal quality received by the modem?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume that the manufacturer of such device makes it able to receive so much different frequency is so that the device can be compatible with every mobile carrier, not necessarily because that the internal antenna inside the device is able to work on that wide range of the spectrum. I think by making a specific antenna for one specific frequency could improve the performance of the device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please do correct me if there are a lot of mistake in my way of thinking and my understanding of the matter. I just wanted to learn. :)&lt;/p&gt;&#xA;" OwnerUserId="13437" LastActivityDate="2018-10-24T14:19:39.163" Title="Is it possible to make antenna for one specific frequency?" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;mobile&gt;&lt;net&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12096" PostTypeId="1" CreationDate="2018-10-24T11:12:36.203" Score="5" ViewCount="377" Body="&lt;p&gt;Can anybody provide me with an idealised formula that describes the radiation pattern of an omnidirectional dipole antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In particular I am interested in the formula that creates a plot similar to the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Gbvup.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Gbvup.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: I am looking for a simplified closed-form equation, not a full field simulation.&lt;/p&gt;&#xA;" OwnerUserId="13438" LastActivityDate="2018-10-24T14:47:35.860" Title="Dipole antenna radiation field equation" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12098" PostTypeId="2" ParentId="12096" CreationDate="2018-10-24T13:49:46.263" Score="7" Body="&lt;p&gt;The antenna you describe is &quot;omnidirectional&quot; only in the &lt;em&gt;xy&lt;/em&gt;-plane; it has zero radiation along the &lt;em&gt;z&lt;/em&gt;-axis. Thus, your dipole is mounted vertically; i.e., &lt;em&gt;x&lt;/em&gt;=0 and &lt;em&gt;y&lt;/em&gt;=0 for all segments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to &lt;em&gt;Antennas&lt;/em&gt; by John Kraus, the far &lt;em&gt;E&lt;/em&gt;-field for a center-fed &lt;span class=&quot;math-container&quot;&gt;$\lambda/2$&lt;/span&gt; dipole in free space is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$E = \frac{\cos\left({\pi\over 2}\cos\theta\right)}{\sin\theta}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a vertically mounted antenna, &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt;=0 at the horizon of the plot.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="218" LastEditDate="2018-10-24T14:47:35.860" LastActivityDate="2018-10-24T14:47:35.860" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12099" PostTypeId="2" ParentId="12095" CreationDate="2018-10-24T14:19:39.163" Score="2" Body="&lt;p&gt;It is possible that the antenna designed for 2.4-GHz will work well enough on 2.3-GHz because the difference in wavelength is only about 4%. But, to make it work better, increase every dimension of every antenna component by a factor of 2.4/2.3. That is, increase not only the lengths of the conductors, but also any spaces between conductors and, ideally, the thicknesses of the conductors themselves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There may, indeed, be several different antennas inside your device. Depending on the relationships between the bands served, a single antenna may work on more than one band, reducing the number of antennas required to serve all of the carriers. Passive &quot;matching&quot; circuits may be inserted between an antenna and the active circuitry to improve system performance on a given band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many antenna geometries whose performance is independent of frequency over a wide range. You can find an example that may fit your requirements at &lt;a href=&quot;http://www.wa5vjb.com/products1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kent Electronics&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-24T14:19:39.163" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12100" PostTypeId="2" ParentId="12075" CreationDate="2018-10-24T19:54:13.220" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;(most) of the circuit designs documented are characterized with a source or load impedance of 50 ohms.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;True, but not important.  In order to match impedence, the output impedance of the previous stage should match the input impedance of the next stage.  That's all you need.  Using bipolar transistors, for example, the output impedance is approximately equal to the collector resistor.  The input impedance is roughly equal to beta times the emitter resistor, if not bypassed.  &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;building a RF buffer-amplifier chain for a VFO &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Therefore, if building a buffer, you don't need to match impedances, but just to lightly load the oscillator.  Just the opposite of matching.  &lt;/p&gt;&#xA;" OwnerUserId="8647" LastActivityDate="2018-10-24T19:54:13.220" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12101" PostTypeId="1" CreationDate="2018-10-25T08:11:45.993" Score="5" ViewCount="1173" Body="&lt;p&gt;I have a Flex 3000 connected via RG-11 coax to a inverted V fan dipole tuned for 40m and 20m on my roof. I have an &quot;ugly&quot; balun up on the mast by the antenna. I further have the feed-line going into a lightning suppressor where the line enters into the house and is connected to my 8 foot ground rod. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I realize that my coax is not 50ohm (it's 75ohm) but I'm operating at 80, 40, and 20m. My SWR is 1.1 on 40m and 1.4 on 20m and my ATU takes care of the rest. My understanding is that this should not be much of a factor on HF. In fact this coax is plenum rated so it has the extra shielding as well so it's very well guarded from external interference. Unless of course that extra shielding is having the reverse effect allowing even more RFI to flow down the shielding as it's acting as a fantastic antenna. Hence why I'm trying to do what I'll explain next... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm trying to reduce various RFI on 80m and 40m (some 20m) coming into my shack (and also eliminate RFI going out to various devices by my transmissions) but have not had much success. I'm trying to use ferrite cores to help reduce some of this... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have these Fair-Rite ferrite cores from www.mouser.ca...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.mouser.ca/ProductDetail/Fair-Rite/2631803802?qs=%2Fha2pyFadui69ZHDvBYwaNp1oYkvVAjIv5TPhphggYvPCnPIGmFbbQ%3D%3D&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mouser Link&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which should be these specific cores on the Fair-Rite Site...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.fair-rite.com/product/round-cable-emi-suppression-cores-2631803802/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fair-Rite Link&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding is that these are the #31 material as mentioned in numerous documents, not the least of which is Jim Brown's (K9YC) Guide to RFI, Ferrites, Baluns, and Audio Interfacing (often times noted as the &quot;Bible&quot; of RFI finding and reduction)...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've played with these toroid cores on an off for the past 3 years. I keep coming back to them as I'm hoping to reduce the RFI in my shack. However each time I've tried to use these cores, they've made exactly zero difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example I have a known source of RFI which is a birdie caused by my main 27&quot; monitor (an Apple model). I see this birdie on 80m. I've tried wrapping the power cord multiple times and no luck. Zero effect. However this is just a birdie so I can deal with it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another example is when I'm transmitting I hear the RFI over my speakers in the shack. This is a Logitech 5500 system. It all works from a main sub woofer that all the speakers then connect too. I've disconnected all the speakers and still get the RFI through the main woofer. I've wrapped the power cord of the woofer about a dozen times through two cores each. Zero difference on the RFI leaking into the speaker. As mentioned I use a Flex 3000 so having a PC and a speaker is essential. Again I can get around this and use wireless headphones but it's not ideal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've also tried a Bifilar choke as detailed in a presentation PDF from K9YC again starting on page 45 here &lt;a href=&quot;https://www.qsl.net/w/wa3mej//Articles/K9YC/CoaxChokesPPT.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.qsl.net/w/wa3mej//Articles/K9YC/CoaxChokesPPT.pdf&lt;/a&gt; I have a picture of the one I've made... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MVgrg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MVgrg.jpg&quot; alt=&quot;My Bifilar Choke wound with #14 THHN wire&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This was done with #14 THHN wire as detailed in the presentation above on page 47. This was connected to my feed-line on one end and the other end went straight into my flex-3000.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have various other sources within my house that I'm attempting to deal with but I'm trying to mitigate a few of them with cores. But the cores just seem to make absolutely no difference. Either I've got the wrong cores or I'm missing something and am not doing it correctly? I bought these things and I would've thought I would have at least seen marginal improvements but so far they've been useless.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any suggestions on what I'm missing?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE 1&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's some pictures of my antenna setup and my ugly balun. Obviously the height of the antenna is not ideal but this is up on the second floor. I've since added a vertical dipole (Comet 250B) which is not shown. As you can see the balun has coax seal all over it so I'll have to pull all that off and switch out the balun for my ferrite choke. I notice in the pictures that the coax seems to be drooping on my balun which I didn't notice earlier. Could this also be a factor?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've also included a picture of my new ground setup...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0PmlC.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0PmlC.jpg&quot; alt=&quot;Antenna Setup&quot;&gt;&lt;/a&gt;&#xA;Antenna Setup&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/erWei.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/erWei.jpg&quot; alt=&quot;Ugly Balun&quot;&gt;&lt;/a&gt;&#xA;Ugly Balun&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/E8ae9.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/E8ae9.jpg&quot; alt=&quot;New Ground Setup&quot;&gt;&lt;/a&gt;&#xA;New Ground Setup&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Update 2&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried to make a quick and dirty version of the RFI detector that Phil Frost - W8II has pointed out. This is based not he link provided in the first answer below. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a couple of pictures of my detector. It include the snap on ferrite with 10 turns of wire through into a breadboard where I just plugged in the components for now. I'm using a 101 nf cap (I assume that it is nF as there is only the number on it) and a 47 Ω and 100 Ω resistor. You'll see a red LED. I don't have any diodes handy at the moment but have them on order. I thought I would try the LED to see if it would work. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately I don't get any reading on my multimeter. I have it set to 200mA and I put the ferrite beside my feed line. It just reads 00.0 all the time when I transmit. I'm not sure if that's good as I don't have any common mode current, or more likely I've done the detector wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a picture of my detector and my multimeter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cA7yZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cA7yZ.jpg&quot; alt=&quot;Detector&quot;&gt;&lt;/a&gt;&#xA;Detector&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GD9uZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GD9uZ.jpg&quot; alt=&quot;Multimeter&quot;&gt;&lt;/a&gt;&#xA;Multimeter&lt;/p&gt;&#xA;" OwnerUserId="13444" LastEditorUserId="13444" LastEditDate="2018-11-18T09:35:07.743" LastActivityDate="2018-11-18T09:35:07.743" Title="Is this the Correct Ferrite Core to Reduce RFI as a Common Mode Choke?" Tags="&lt;rfi&gt;&lt;ferrite&gt;&lt;choke-balun&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12102" PostTypeId="2" ParentId="6995" CreationDate="2018-10-25T09:47:45.227" Score="1" Body="&lt;p&gt;Yes, it can receive air band transmissions but upper the frequency limit is 127 MHz or 128 MHz. I can get the airport but the speech very faintly audible. This is because from an FM receiver perspective, an AM signal is unmodulated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, I can receive AM signals with a Baofeng UV5R but the sound is awful. You can watch my videos on youtube kourosh delpak or instagram radiofrequency.ep&#xA;&lt;a href=&quot;https://www.instagram.com/p/Bo9MTg1DCdT/?taken-by=radiofrequency.ep&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.instagram.com/p/Bo9MTg1DCdT/?taken-by=radiofrequency.ep&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13376" LastEditorUserId="9493" LastEditDate="2018-10-25T15:32:41.677" LastActivityDate="2018-10-25T15:32:41.677" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12103" PostTypeId="2" ParentId="12101" CreationDate="2018-10-25T12:00:49.687" Score="4" Body="&lt;p&gt;That does look like a fine core to use, and the photo of your construction looks good. Your coax isn't causing any problems with noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try putting the choke at the &lt;em&gt;feedpoint&lt;/em&gt;, not at the &lt;em&gt;radio&lt;/em&gt;, in lieu of the ugly balun you have now. A choke at the radio will do little since the coax shield, connector, and enclosure of the radio already form a continuous shield around all the receiving circuitry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The objective with the balun is to &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;eliminate common-mode current on the feedline&lt;/a&gt;. A feedline with common-mode current is part of the radiating and receiving antenna, and since it runs into the shack it's close to all kinds of noise generating electronics. A functional balun suppresses common-mode current on the feedline so only the antenna, which is farther away from noise sources, is the only part radiating or receiving. Often this reduces RFI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ugly baluns can be ineffective. Since they are a purely reactive impedance they can't dissipate noise power, only redirect it. In some cases the reactance of the ugly balun combines with the common-mode reactance of the feedline or tower to make a resonant circuit which is worse than no balun. A properly selected ferrite on the other hand has a significant resistive component to its impedance, and thus works in all cases as it can convert noise power to heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fixing RFI problems like you describe can be difficult if you don't know what's working and what isn't. If you aren't certain that feedline common-mode problems have been eliminated, trying to fix a noise source by putting ferrites around it is a futile exercise since all the wiring in your home is part of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I suggest you &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measure the common-mode current&lt;/a&gt; with the ugly balun, and then with the ferrite choke. You might try different ferrite choke designs to find one that works well. The number of turns, core material, and core geometry make a difference. The &lt;a href=&quot;https://www.qsl.net/w/wa3mej//Articles/K9YC/CoaxChokesPPT.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;K9YC presentation you referenced&lt;/a&gt; discusses it in some detail. &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;G3TXQ also has some good data&lt;/a&gt;. You can use these resources as a starting point for a design and then confirm the results with measurement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Only after confirming feedline common-mode issues are resolved, go around the house and identify noise sources. Putting ferrites on the cables leaving a noisy device eliminates the &quot;antenna&quot; they use to radiate noise.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-25T12:00:49.687" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="12105" PostTypeId="2" ParentId="12101" CreationDate="2018-10-25T14:34:33.803" Score="1" Body="&lt;p&gt;In addition to everything Phil wrote, a possible &quot;quick fix&quot; might result if you wrap several turns of every cable between the radio and the PC through a ferrite toroid. I have encountered several cases of RFI resulting from ground loops and other mismatches between pieces of connected equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may need to &quot;divide and conquer&quot; the total, complex problem of multiple conductors and their interactions into multiple, simpler problems. For example, what happens if you replace the Flex+PC with a standalone rig operating off a battery? Eliminating conductors and their interactions, one by one, may be the only way to identify the culprit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My dad and Elemer, K1DXB (SK), suffered terrific RFI until he replaced his metal desk with a wooden unit. Apparently, the conductive desk created troublesome coupling paths!&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-25T14:34:33.803" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12107" PostTypeId="2" ParentId="12101" CreationDate="2018-10-25T20:26:16.543" Score="3" Body="&lt;p&gt;The answers here are excellent and I have little to add other than to emphasise / RFI problems are hard /&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider the case of the RFI problem discussed in Electronics Stack Exchange ( &lt;a href=&quot;https://electronics.stackexchange.com/questions/402021/how-do-i-specify-a-low-rfi-led-driver/402029#402029&quot;&gt;https://electronics.stackexchange.com/questions/402021/how-do-i-specify-a-low-rfi-led-driver/402029#402029&lt;/a&gt; ).  Everything has been ferrited to death (5000 ohm common mode chokes surrounding all wires connected to the source and the receiver) and yet S9-11 noise levels appear across multiple bands when the device operates.  A tiny little transformer, being fed an unfiltered sawtooth current, is radiating enough to make it 30 feet to the properly-choked receiving antenna, ruining several bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fix is to replace the offending device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes you do everything &quot;right&quot; and it still just is not enough.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2018-10-25T20:26:16.543" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12108" PostTypeId="1" CreationDate="2018-10-25T23:25:24.287" Score="1" ViewCount="562" Body="&lt;p&gt;When do I log a callsign suffix in the logbook when I hear them say something like portable or QRP after their callsign? I'm specifically referring to cases where they don't use stroke or slash between the two. If I hear AA1AA stroke portable, I would assume I should log it as AA1AA/P, but if they just just say portable following the callsign, I just put the callsign down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a more specific case, I had this question for the ARRL September VHF contest. In that contest, I know that marking rovers is critical and I would always add /R to their callsigns, but the rules say nothing about other suffixes of that type. In general I'm curious about any sort of voice contest like this. For a digital contest like RTTY, it's clear exactly what the callsign and suffix is used and needs to be logged. It's just with voice, hearing portable, low-power, QRP, it's not clear if that's part of the call unless there's something in the rules requesting documentation for it. And then, there's satellites...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My goal is to maximize the chance I'll properly get a confirmation with the contest log upload or Logbook of the World. Do they give some leniency in matches if the suffix isn't critical to the contest rules?&lt;/p&gt;&#xA;" OwnerUserId="1534" LastActivityDate="2018-10-26T14:16:21.790" Title="When to log a callsign suffix for a QSO?" Tags="&lt;contest&gt;&lt;callsign&gt;&lt;logging&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12110" PostTypeId="1" AcceptedAnswerId="15529" CreationDate="2018-10-26T02:11:36.227" Score="4" ViewCount="570" Body="&lt;p&gt;A half wave center-fed dipole has a resonant frequency where the input impedance appears to be purely resistive. How can this be, when the voltage and current distribution along the length of a half wave dipole when fed with an AC waveform of the resonant frequency are seemingly not in phase and in fact appear to be 90 degrees out of phase?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-10-23T22:13:50.607" LastActivityDate="2019-10-23T22:13:50.607" Title="How can the impedance of a half wave dipole at its resonant frequency be purely resistive when the voltage and current are seemingly not in phase?" Tags="&lt;antenna-theory&gt;&lt;dipole&gt;&lt;impedance&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12111" PostTypeId="1" CreationDate="2018-10-26T02:48:13.773" Score="1" ViewCount="300" Body="&lt;p&gt;I read that arrl is petitioning the FCC to expand the privileges of the technician license. Can you summarize those changes with the schedule?&lt;/p&gt;&#xA;" OwnerUserId="11284" LastActivityDate="2018-11-26T18:01:55.330" Title="2018/2019 proposed expansion of technician privileges" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12112" PostTypeId="1" CreationDate="2018-10-26T02:52:24.640" Score="7" ViewCount="769" Body="&lt;p&gt;If the input impedance of a resonant half wave dipole at the feed point is 75 + j0 ohms, then if an AC sine wave voltage V is applied to the feed point, how can the voltage at the center be zero ? Ohms law always applies correct ? So for the rms value then voltage is Vrms = Irms x Z right ? so Z = Vrms / Irms = Vrms / 75 +j 0 = 0.&lt;/p&gt;&#xA;&lt;p&gt;The picture from Wikipedia below clearly shows that the voltage is always zero at the center. My understanding is that this picture shows the standing waves on a dipole. The standing waves are the result of the applied AC voltage across the feed point and vary in amplitude over time but have a fixed voltage profile in space along the length of the dipole. I thought that anywhere along the length of the dipole ohms law always applies.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8niio.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8niio.gif&quot; alt=&quot;Dipole standing waves animation&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Is the 'voltage' in the picture the voltage potential with respect to the center of the dipole ? and the one which results from that applied to the feed point ? The applied voltage potential difference results in a current which is the movement of electrons in the dipole in one direction during the positive half cycles of the ac waveform and in the opposite direction during the negative half right ?&lt;/p&gt;&#xA;&lt;p&gt;What am i missing.&lt;/p&gt;&#xA;&lt;p&gt;Is the voltage not really zero but rather I / Z = I / 75 + j 0 which is not zero ?&lt;/p&gt;&#xA;&lt;p&gt;And then, if the voltage is not really zero, how come it's ok to connect the center of the driven element in a yagi to the boom because the voltage at the center is zero ?&lt;/p&gt;&#xA;&lt;p&gt;Someone please help before my brain implodes !!!! :)&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-07-03T06:46:43.090" LastActivityDate="2020-07-03T23:25:30.463" Title="How can the voltage at the center of a resonant half wave dipole be zero if the input impedance is 75 ohms?" Tags="&lt;antenna-theory&gt;&lt;impedance&gt;&lt;dipole&gt;&lt;math&gt;" AnswerCount="3" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12113" PostTypeId="1" AcceptedAnswerId="12115" CreationDate="2018-10-26T07:33:43.617" Score="16" ViewCount="4776" Body="&lt;p&gt;Amplitude modulation uses the modulation of the amplitude of a carrier wave to transmit data while leaving the carrier frequency constant, and in the case of FM it's just the other way round.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8vxtJ.gif&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8vxtJ.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is a modulation of the frequency in an AM signal not used to transmit additional information, e.g. two audio channels or RDS information?&lt;/p&gt;&#xA;" OwnerUserId="13372" LastEditorUserId="13372" LastEditDate="2018-10-29T16:15:55.130" LastActivityDate="2018-10-29T16:15:55.130" Title="Why do we not use AM and FM at the same time to transmit more information?" Tags="&lt;fm&gt;&lt;am&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12114" PostTypeId="2" ParentId="12108" CreationDate="2018-10-26T08:21:50.947" Score="1" Body="&lt;p&gt;if they say &quot;&lt;em&gt;callsign&lt;/em&gt; portable&quot; then it's definitely &quot;&lt;em&gt;callsign&lt;/em&gt;/p&quot;. The /QRP has no 'real' value &quot;&lt;em&gt;callsign&lt;/em&gt;/QRP&quot; is the same as &quot;&lt;em&gt;callsign&lt;/em&gt;&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my country (Belgium) according to the law only these suffixes are allowed:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;/M for a mobile station&lt;/li&gt;&#xA;&lt;li&gt;/MM for a maritime mobile station&lt;/li&gt;&#xA;&lt;li&gt;/P for a portable station&lt;/li&gt;&#xA;&lt;li&gt;/A for a station operating from an other place than the address mentioned in the licence&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;/QRP etc are THEORETICALLY not allowed. But I don't think this has ever been enforced.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2018-10-26T08:21:50.947" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12115" PostTypeId="2" ParentId="12113" CreationDate="2018-10-26T08:27:36.163" Score="15" Body="&lt;p&gt;QAM modulates both the phase (= frequency) and amplitude of the signal.&lt;/p&gt;&#xA;" OwnerUserId="13390" LastActivityDate="2018-10-26T08:27:36.163" CommentCount="13" ContentLicense="CC BY-SA 4.0" />
  <row Id="12116" PostTypeId="2" ParentId="12110" CreationDate="2018-10-26T12:23:25.477" Score="1" Body="&lt;p&gt;The phase and current of the r-f energy along each half of a dipole are the result of natural laws, which show that current must be at/near zero at the far ends of the dipole while voltage there must be maximum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The practical concern to the user of that dipole is its self-impedance at its feedpoint terminals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A thin-wire, center-fed dipole that physically is 1/2-wavelength long has a feedpoint self-impedance of 73 +j43.5 Ω in free space (source: Kraus' &lt;em&gt;Antennas&lt;/em&gt;, 3rd Edition, p. 446).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To achieve resonance (where the voltage and current at its feedpoint are in phase and the &quot;j&quot; term of its impedance is zero), that dipole must be shortened a few percent, which somewhat reduces that 73 Ω radiation resistance — as a function of the O.D. of the radiating conductors of that dipole.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2018-10-26T12:38:00.800" LastActivityDate="2018-10-26T12:38:00.800" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12117" PostTypeId="2" ParentId="12113" CreationDate="2018-10-26T14:05:35.793" Score="13" Body="&lt;p&gt;It turns out that we &lt;em&gt;DO&lt;/em&gt; simultaneously use frequency and amplitude modulation: our everyday term for this is &quot;single sideband.&quot; As described on &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia&lt;/a&gt;, single-sideband is a special case of quadrature modulation in which the quadrature component (Q) is derived directly from the in-phase component (I) of the modulating signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This effect becomes evident upon examination of the waveform of an SSB signal produced by modulating tones of 700Hz and 1900Hz:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/5OSiP.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5OSiP.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the period of the envelope is 833&lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;s, a frequency of 1200Hz, which is the difference between the frequencies of the two modulating tones. At the &quot;cusp&quot; of the waveform, it experiences a 180-degree phase reversal, whose accurate reproduction is essential to a clean output. The mathematical combination of these amplitude and phase modulation components produces the two tones that are offset from the frequency of the carrier wave.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-26T14:05:35.793" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12118" PostTypeId="2" ParentId="12113" CreationDate="2018-10-26T14:13:57.890" Score="-2" Body="&lt;p&gt;The two different techniques are not just different ways of modulating the signal. As you can see from the frequency units in your examples, FM carrier frequency is about two orders of magnitude higher than AM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that FM can modulate a much higher signal frequency than AM, and this leads to greater fidelity (i.e. sound quality). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FM carrier frequency is also a lot less susceptible to interference effects (particularly atmospheric). This is because it is fairly easy for random attenuation, reflection and refraction to change the amplitude of a signal (thus interfering with AM) but more difficult for it to change the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When FM became popular in the 1970s, it was regarded as a major technology leap - similar to DAB today. So much so, that &lt;a href=&quot;https://www.youtube.com/watch?v=HV3zWSawJiw&quot; rel=&quot;nofollow noreferrer&quot;&gt;Steely Dan wrote a song about it&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13452" LastEditorUserId="13452" LastEditDate="2018-10-29T14:33:49.227" LastActivityDate="2018-10-29T14:33:49.227" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="12119" PostTypeId="2" ParentId="12108" CreationDate="2018-10-26T14:16:21.790" Score="2" Body="&lt;p&gt;The general rule of thumb is to log what you copy. When the sending station submits their log, they should enter what you copied as the &quot;sent&quot; callsign, which should cover you. If you find otherwise in the log-checking report for the contest, you can challenge it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, I &lt;em&gt;never&lt;/em&gt; enter spurious suffixes like &quot;/QRP&quot; and I have never been penalized for this practice. As an experienced contester, I always work these stations last because they insist on wasting my time with unnecessary information.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-26T14:16:21.790" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12120" PostTypeId="2" ParentId="12111" CreationDate="2018-10-26T14:20:57.390" Score="1" Body="&lt;p&gt;A standard internet search produces this item from the &lt;a href=&quot;http://www.arrl.org/news/arrl-requests-expanded-hf-privileges-for-technician-licensees&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL&lt;/a&gt; with the information you seek. The FCC has not yet sought public comment, which would be the first step toward a Notice of Proposed Rule Making (NPRM). Given the lack of FCC action to date, any forecast for implementation would be speculative.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-26T14:20:57.390" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12121" PostTypeId="1" AcceptedAnswerId="12124" CreationDate="2018-10-26T19:13:30.797" Score="5" ViewCount="62" Body="&lt;p&gt;Let's assume I have built a SMA-to-waveguide transition that flares out into a horn antenna. There's no flange between transition and horn, it's made of a single metal sheet. The antenna has tuning screws, and my goal is to find the screw position giving least reflected power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously, I don't have a suitable VNA with which I could measure the antenna S11 parameter. I do however have an uncalibrated power meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which of the following methods gives best results?&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Receiver: Connect power meter to horn antenna, aim it at another RF source, find screw position that maximises power indication.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Circulator: Connect TX to circ 1, circ 2 to horn antenna, circ 3 to power meter. Find screw position that minimises power indication.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Directional coupler: connect TX through coupler to horn antenna, s.t. part of the reflected power is coupled towards the power meter. Tune screws, find minimum power.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The underlying more general question is: given that I don't need accurate absolute S11 or VSWR values, what shortcuts can I take to get the best out of my antenna?&lt;/p&gt;&#xA;" OwnerUserId="13373" LastActivityDate="2018-10-27T00:25:21.920" Title="What is the best approach for measuring return loss of a home-made 3cm horn?" Tags="&lt;impedance-matching&gt;&lt;measurement&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12122" PostTypeId="1" CreationDate="2018-10-26T20:02:24.947" Score="1" ViewCount="3958" Body="&lt;p&gt;What is electrical length in detail? Why is it so that 1/4 wave , 1/2 wave dipole antenna works properly and not a full wave antenna? What is the role of electrical lengths in degree?&lt;/p&gt;&#xA;" OwnerUserId="13462" LastEditorUserId="8717" LastEditDate="2018-10-26T20:55:28.167" LastActivityDate="2018-11-12T22:39:20.187" Title="What is Electrical length in RF and how to electrically cut and measure the RF cable in degree?" Tags="&lt;antenna-theory&gt;&lt;coaxial-cable&gt;&lt;dipole&gt;&lt;feed-line&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12123" PostTypeId="2" ParentId="12122" CreationDate="2018-10-26T20:49:02.730" Score="3" Body="&lt;p&gt;The concept of &quot;electrical length&quot; begins with the concept of wavelength, &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; - the distance over which the value of a periodic phenomenon repeats, expressed as: &lt;span class=&quot;math-container&quot;&gt;$$\lambda=\frac{c}{f}$$&lt;/span&gt; When describing electromagnetic wave propagation in free space, &lt;em&gt;c&lt;/em&gt; is the speed of light in a vacuum - 300 million meters per second - and &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is the frequency of the signal creating the wave, in Hertz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Electromagnetic waves propagate more slowly in materials or at boundaries. The velocity factor, &lt;span class=&quot;math-container&quot;&gt;$\nu$&lt;/span&gt;, represents this slowing and is less than one (except in free space, where it is exactly one). This modifies the wavelength equation:&lt;span class=&quot;math-container&quot;&gt;$$\lambda=\frac{\nu c}{f}$$&lt;/span&gt;&#xA;For example, the wave propagating along the conductor of a dipole antenna to produce radio waves encounters the interface between the conductor and free space, slowing the wave by about 5%; i.e., &lt;span class=&quot;math-container&quot;&gt;$\nu$&lt;/span&gt;~0.95. This is why a resonant half-wave dipole is shorter than &lt;span class=&quot;math-container&quot;&gt;$c/f$&lt;/span&gt; would calculate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a transmission line, &lt;span class=&quot;math-container&quot;&gt;$\nu$&lt;/span&gt; depends on the dielectric material between the conductors. Many coaxial cables have &lt;span class=&quot;math-container&quot;&gt;$\nu$&lt;/span&gt;=0.66, so the wavelength at a given frequency is about 1/3 less than it would be in free space. The wave propagating in a line that is one wavelength long experiences one full cycle of change, equivalent to 360 degrees. A shorter line produces proportionately fewer cycles of change, longer lines proportionately more, which can be expressed as fractions or multiples of 360 degrees.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quarter-wave, half-wave and full-wave dipoles all work &quot;properly,&quot; but it can be challenging to match the feedpoint impedance of the antenna to the impedance of the transmission line, which is necessary to maximize power transfer from the transmitter to the antenna. Circuits using lumped-elements, transmission lines of various lengths and impedances, or combinations of lumped and distributed elements may be employed to optimize system performance.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2018-10-26T20:55:46.560" LastActivityDate="2018-10-26T20:55:46.560" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12124" PostTypeId="2" ParentId="12121" CreationDate="2018-10-27T00:19:07.617" Score="2" Body="&lt;p&gt;The circulator is the most sensitive method, because all of the reflected power goes to the power meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some thoughts:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Are you sure that the circulator is working correctly at your frequency? Any issues with it will come out in the results.  &lt;/li&gt;&#xA;&lt;li&gt;It is best to pad the source and the power meter, with 6 to 10 dB attenuators, to improve their own matching so that the reflections don't distort the picture.&lt;/li&gt;&#xA;&lt;li&gt;You could attempt to calibrate or just validate this method by comparing the power readings seen, with port 2 terminated, shorted and open circuit.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A transmitted power test is the least sensitive to antenna mismatch, but if all you are trying to do is optimise output power, not SWR, then it doesn't really matter if you're at 3:1 SWR or 1:1 SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are using it as a receive antenna, with an LNA, then you could tune for noise performances instead. You would point it at a cold part of the sky and tune the antenna for minimum noise power. In a transceiver it might be best to optimise for noise performances and just accept the reasonably good transmit match that you would get.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, you should worry about polarisation. You don't specify the horn type, but if it's big and square it could easily support both polarisations. Are the tuning screws in any way designed to induce circular polarisation? If they're not all in the E plane, they might be. This would be a new measurement challenge, beyond just matching.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2018-10-27T00:25:21.920" LastActivityDate="2018-10-27T00:25:21.920" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12128" PostTypeId="1" CreationDate="2018-10-27T21:06:05.020" Score="3" ViewCount="320" Body="&lt;p&gt;I paired my old Kenwood TS-50 with serial, by using FTDI TTL-232-5V-AJ USB to serial converter. &#xA;I used ideas from here:&#xA;&lt;a href=&quot;http://steeman.be:8080/posts/TS-50%20USB%20Interface/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://steeman.be:8080/posts/TS-50%20USB%20Interface/&lt;/a&gt;&#xA;and here&#xA;&lt;a href=&quot;https://i.imgur.com/BmYMq2v.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://i.imgur.com/BmYMq2v.jpg&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have Linux Ubuntu 18.04 and I can detect my serial to usb converter, by using dmesg:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;[ 1596.365806] ftdi_sio 1-5:1.0: FTDI USB Serial Device converter detected&#xA;[ 1596.365857] usb 1-5: Detected FT232RL&#xA;[ 1596.371078] usb 1-5: FTDI USB Serial Device converter now attached to ttyUSB0&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;To be sure that I can connect to serial port I first wanted to be sure by checking that connection works with minicom, but it gives me:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;minicom: cannot open /dev/ttyUSB0: Permission denied&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Despite I am in dial out group and I did all that is written here: &lt;a href=&quot;https://websistent.com/fix-serial-port-permission-denied-errors-linux/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://websistent.com/fix-serial-port-permission-denied-errors-linux/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can temporary solve that by using it with sudo. That I did, but minicom says, that ir is offline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also tried rigctl:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;ffu@ffu-desktop:~&lt;span class=&quot;math-container&quot;&gt;$ rigctl -m 201 -r /dev/ttyUSB0 -s 4800 -v&#xA;rig_open: error = IO error &#xA;ffu@ffu-desktop:~$&lt;/span&gt; sudo rigctl -m 201 -r /dev/ttyUSB0 -s 4800 -v&#xA;Opened rig model 201, 'TS-50S'&#xA;&#xA;Rig command: f&#xA;rigctl_parse: input_line: f&#xA;get_freq: error = Invalid parameter&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Its looks like from me that apparently something is wrong at OS level, but what?&lt;/p&gt;&#xA;" OwnerUserId="13476" LastEditorUserId="9844" LastEditDate="2018-11-01T13:26:21.997" LastActivityDate="2018-11-01T13:26:21.997" Title="Kenwood TS-50 and USB to Serial" Tags="&lt;kenwood&gt;&lt;linux&gt;&lt;computer-control&gt;" AnswerCount="0" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12129" PostTypeId="1" AcceptedAnswerId="12130" CreationDate="2018-10-28T01:29:21.520" Score="1" ViewCount="803" Body="&lt;p&gt;I have a resonant half wave dipole which is one continuous length and not separated in the middle, fed using a gamma match, and with the braid of the coax joined to the exact electrical center of the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does this gamma match arrangement act as a balun ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does AC current flow back down the outside of the coax if i don't use an rf choke ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2018-10-28T01:37:46.163" LastActivityDate="2018-10-28T02:30:49.103" Title="How does a gamma match on a dipole work as a balun?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12130" PostTypeId="2" ParentId="12129" CreationDate="2018-10-28T02:30:49.103" Score="4" Body="&lt;p&gt;The gamma match was discussed at length in a previous &lt;a href=&quot;https://ham.stackexchange.com/questions/1804/what-is-a-gamma-match-in-the-context-of-the-driven-element-of-a-yagi-antenna&quot;&gt;Ham Stack Exchange&lt;/a&gt; answer. Current flow on the shield is, theoretically, prevented by its connection to a point of zero potential - the center of the element - &lt;em&gt;as long as the center of the antenna is, in fact, a point of zero potential.&lt;/em&gt; Since any construction asymmetries and the antenna's environment may cause current imbalance that could produce voltage imbalance, it is possible that current will flow on the outside of the shield. Whether the current magnitude is sufficient to distort the antenna pattern or interact with other structures must be evaluated on a case-by-case basis.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-28T02:30:49.103" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12131" PostTypeId="1" AcceptedAnswerId="12206" CreationDate="2018-10-28T02:44:10.757" Score="3" ViewCount="303" Body="&lt;p&gt;As I understand, voltage is a measure of the potential difference between two points, and voltage causes current to flow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see lots of descriptions on how dipoles work with lots of references to the voltages on the dipole and to the ratio of the voltage of the standing waves on a dipole and along the transmission line etc etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone tell what these voltages are measured with respect to ...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;... because i'm all confused.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2018-11-07T15:47:18.820" Title="What is the voltage on a half wave dipole measured with respect to?" Tags="&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12132" PostTypeId="2" ParentId="12131" CreationDate="2018-10-28T03:14:35.133" Score="5" Body="&lt;p&gt;Any voltage can be measured with respect to any reference point you like, because the electric field has a value everywhere. &lt;strong&gt;Some reference points are more useful than others.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if you put your one of your DC voltmeter probes in some arbitrary point in empty air, the electric charges making up the meter probe, and the impedance of the meter, disturb the measurement so much it looks like there is no effect. But if you held up your probes some distance apart while standing inside an oversized high-voltage capacitor, you'd get a reading — if you didn't cause it to arc over by being there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Another example, less relevant but to emphasize the point: there &lt;em&gt;is&lt;/em&gt; some potential difference between two electric circuits that aren't wired together in any way. However, you can't readily measure it because as soon as you place a voltmeter between them, it discharges through the meter. We call these phenomena “electrostatic”, and in order to detect them you need special ultra-high-impedance electrostatic instruments — or for the difference to be large enough that you touch something and notice the shock of the sudden flow of current that equalizes the charge and potential.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;What reference point to use, in the specific cases you mentioned:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the voltages on the dipole &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;An ideal dipole is completely symmetric, so a good reference point, and probably the one that any analysis you've seen uses, is the center of the dipole.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the voltage … along the transmission line&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Common transmission lines have two conductors; the voltage of interest is the voltage between those two conductors at some position along the line. (Other transmission lines are &lt;a href=&quot;https://en.wikipedia.org/wiki/Waveguide_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;waveguides&lt;/em&gt;&lt;/a&gt;, which carry electromagnetic waves inside or &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-wire_transmission_line&quot; rel=&quot;nofollow noreferrer&quot;&gt;outside&lt;/a&gt; a single conductor. In this case, there is still a potential difference but it is in the propagating electric field that is guided by the waveguide.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to relate the potential at a point on an antenna to a point on its feed line, then you have to take into account how the antenna is connected to the feed line — what matching devices are used at that interconnection — and also how the feed line is physically located (it is, after all, metal in the presence of an electromagnetic wave); there is no simple single answer.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-10-28T14:09:31.137" LastActivityDate="2018-10-28T14:09:31.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12134" PostTypeId="2" ParentId="2127" CreationDate="2018-10-28T16:37:05.643" Score="-1" Body="&lt;p&gt;My radio stopped receiving anything at all one day. It turned out the rubber duck antenna had broken some how.&lt;/p&gt;&#xA;" OwnerUserId="13481" LastActivityDate="2018-10-28T16:37:05.643" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12135" PostTypeId="2" ParentId="12131" CreationDate="2018-10-28T19:48:06.127" Score="4" Body="&lt;p&gt;For ease of analysis, the voltages impressed on the feedpoint terminals of a dipole by a two-conductor transmission line are referred to a theoretical plane at the midpoint of the terminals, that plane representing a virtual ground. That is, rather than using one terminal as the &quot;common&quot; point against which the other terminal varies sinusoidally from 0 to V, the two terminals vary from +V/2 to -V/2 in opposite polarity when referred to the mid-plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This symmetry is obvious for a balanced feedline and a &quot;T&quot; match, the symmetrical version of the gamma match. The gamma match, about which you asked in an &lt;a href=&quot;https://ham.stackexchange.com/questions/12129/how-does-a-gamma-match-on-a-dipole-work-as-a-balun&quot;&gt;earlier post&lt;/a&gt;, is an asymmetric (or, in antenna parlance, &quot;unbalanced&quot;) matching technique that exploits the asymmetric nature of a coaxial feedline by connecting the shield of the coax to the midplane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solutions to Maxwell's equations for the electromagnetic fields around the dipole require that equal and opposite currents flow on both sides of the dipole, restoring the &quot;balanced&quot; behavior we observe.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2018-10-28T22:09:01.133" LastActivityDate="2018-10-28T22:09:01.133" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12136" PostTypeId="1" AcceptedAnswerId="12138" CreationDate="2018-10-29T05:56:03.643" Score="1" ViewCount="162" Body="&lt;p&gt;What's the noise floor according to this picture?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AG5Ut.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AG5Ut.jpg&quot; alt=&quot;Noise Floor on 20m&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the noise floor S5 as it shows in the Signal meter at the top right or is it S1 as it shows on the panadapter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason why I ask is I'm trying to determine if I'm chasing after general RFI that's bringing up my noise floor or if it's not actually that bad?&lt;/p&gt;&#xA;" OwnerUserId="13444" LastActivityDate="2018-10-29T08:53:01.600" Title="What's the Noise Floor?" Tags="&lt;rfi&gt;&lt;noise&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12138" PostTypeId="2" ParentId="12136" CreationDate="2018-10-29T08:53:01.600" Score="1" Body="&lt;p&gt;I always struggle a bit myself interpreting such spectral plots – the y-axis is &lt;em&gt;power&lt;/em&gt;, but to assess the noise &quot;intensity&quot;, we'd need to convert that into a &lt;em&gt;power density&lt;/em&gt;, i.e. &quot;power per bandwidth&quot;. Now, what's the bandwidth of every single x-point in that graph? Is it specified somewhere?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What we can do is take the -98dBm that's specified top right, and assume that's the power collected over the 2.9 kHz bandwidth highlighted in white in the spectrum plot (and set on the lower right in the picture.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That yields a spectral density of -98dBm/2.9 kHz ~= -98 dBm - 34 dBHz = 132 dBm/Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That would be 42 dB above thermal noise. For a microwave receiver, a noise figure of 40 dB would be catastrophic, but for low frequencies like 14 MHz, I'm not so sure. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;CCIR Report 322 claims noise floor could be 40 dB above thermal noise; but that report is over 50 years old! The sensitivity even of extremely good receivers back in the day as well as the selectivity of extremely good filters of that age would not stand well compared to modern receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The main problem is that the report is based on 1960's models of atmospheric and galactic noise, as well as on 1960's levels of man-made interference. I sincerely doubt the latter point has much to do with what we see today, and I'm not convinced our understanding of the atmosphere hasn't long progressed beyond that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, if 1963's data helps you in any way, no, that's at least not significantly above expected noise floor.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-10-29T08:53:01.600" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12139" PostTypeId="1" CreationDate="2018-10-29T08:59:04.427" Score="0" ViewCount="518" Body="&lt;p&gt;Can anyone answer this question : &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a 4 element yagi antenna which is horizontally polarized. Let's say it has a front to back ratio of 20 dB.  Does that front to back ratio apply to received signals just for horizontal polarization, or for received signals of any polarization ? For a vertically polarized received signal, would only the parts of the yagi which have a vertical component, for example the diameter of the tubing of the elements, be involved in reception ? Then when looking towards the yagi from behind, for a vertical wavefront which is really thin, the yagi would look like say 4 x 19 mm high thin slivers of antenna in a row spaced by the distance between the elements, which doesn't have any front to back ratio at all ... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My brain hurts.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2018-10-29T09:11:39.430" LastActivityDate="2018-10-30T04:47:38.827" Title="Does a horizontally polarised yagi antenna have the same front to back ratio for horizontal and vertical received signals?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12140" PostTypeId="1" CreationDate="2018-10-29T09:42:13.263" Score="0" ViewCount="136" Body="&lt;p&gt;Does a vertically or horizontally polarized electromagnetic wavefront have a thickness ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or is it really thin and just the height or width of it's wavelength ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna#/media/File:Dipole_receiving_antenna_animation_6_800x394x150ms.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yKPfe.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="218" LastEditDate="2018-10-31T00:58:56.347" LastActivityDate="2018-10-31T15:23:07.273" Title="Does a vertically or horizontally polarized electromagnetic wavefront have a thickness?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12142" PostTypeId="1" AcceptedAnswerId="12147" CreationDate="2018-10-29T16:43:16.080" Score="15" ViewCount="5872" Body="&lt;p&gt;At first glance Morse code looks like a digital mode - there are dits and dahs, two values which contain the information of the transmission. Alternatively, at any point in time there either is a signal, or there isn't.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Morse code follows the following pattern:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;dit: tone for one unit (1)&lt;/li&gt;&#xA;&lt;li&gt;dah: tone for three units (111)&lt;/li&gt;&#xA;&lt;li&gt;separation between elements: silence for one unit (0)&lt;/li&gt;&#xA;&lt;li&gt;separation between letters: silence for three units (000)&lt;/li&gt;&#xA;&lt;li&gt;separation between words: silence for seven units (0000000)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;As mentioned in a &lt;a href=&quot;https://www.youtube.com/watch?v=HY_OIwideLg&quot; rel=&quot;noreferrer&quot;&gt;Vsauce video&lt;/a&gt;, however, Morse code doesn't actually require only two different values, but actually three: dits, dahs and spaces. He goes on to explain that any Morse transmission can be broken up into three components: a dit with one unit space (10 in his notation), dah with a space (1110) and a separator character (00, two dits in length). From this he argues that it is actually a trinary, rather than a binary code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But is it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After all, any transmission can be represented as either a high or low signal voltage at the receiver, sent in a pattern of one bit per dit. The information is encoded entirely in two separate, discrete values. How this information is afterwards decoded is a matter of choice I would argue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems similar to the ASCII scheme - the information to what letter corresponds to what bit sequence is just a matter of definition, but the information is still binary. Analogous to that, Morse code is nothing more than an encoding with variable-length 'bytes'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;From a strict definition (what is it?), is Morse code (CW) a binary mode? Or is it trinary, or something else entirely?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="13372" LastEditorUserId="13372" LastEditDate="2018-10-29T17:21:04.627" LastActivityDate="2019-03-22T17:56:53.767" Title="Is Morse code a digital, binary mode?" Tags="&lt;digital-modes&gt;&lt;cw&gt;" AnswerCount="11" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12143" PostTypeId="2" ParentId="12139" CreationDate="2018-10-29T16:45:36.453" Score="1" Body="&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It can't. The cross-polarization loss of a linear antenna (such as the dipole elements in your Yagi-Uda antenna) is infinite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, you won't see really vertically polarized signals &lt;em&gt;at all&lt;/em&gt; with a horizontal antenna. So, there's &lt;em&gt;undefined&lt;/em&gt; forward/backward gain.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For a vertically polarized received signal, would only the parts of the yagi which have a vertical component, for example the diameter of the tubing of the elements, be involved in reception ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;They wouldn't, unless they are wrongly dimensioned from the start; they should be too small to &quot;rotate&quot; anything (because that would be bad for horizontal polarization), so anything that's vertically polarized stays vertically polarized, and doesn't cause any current in the antenna feed.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The yagi would look like say 4 x 19 mm high thin slivers of antenna in a row spaced by the distance between the elements, which doesn't have any front to back ratio at all&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;'xactly! :)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-10-29T16:45:36.453" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12144" PostTypeId="2" ParentId="12142" CreationDate="2018-10-29T17:05:16.223" Score="7" Body="&lt;p&gt;The mode hams call &quot;CW&quot; is also called &quot;on-off keying&quot; (OOK) - a hint to the fact that it &lt;em&gt;is&lt;/em&gt; a binary code. Dots, dashes and spaces are usually sized in multiples of the &quot;dot time&quot;: one dot time &lt;em&gt;on&lt;/em&gt; for a &quot;dot,&quot; one dot time &lt;em&gt;off&lt;/em&gt; for the &quot;space&quot; between dots and dashes within a given character, three dot times &lt;em&gt;on&lt;/em&gt; for a &quot;dash&quot;. Spaces between letters and words comprise other dot time multiples. These multiples can be adjusted for purposes of readability or &quot;personality.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An earlier &lt;a href=&quot;https://ham.stackexchange.com/questions/1542/coherent-cw-synchronization&quot;&gt;Ham Stack Exchange&lt;/a&gt; answer described how these properties are exploited to improve the signal-to-noise ratio of CW signals.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-29T17:05:16.223" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12145" PostTypeId="2" ParentId="12142" CreationDate="2018-10-29T18:14:38.227" Score="1" Body="&lt;p&gt;Fully agreeing with Brian!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just to answer your formal question:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;From a strict definition (what is it?), is Morse code (CW) a binary mode? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;and, from your title,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is Morse code a digital, binary mode?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Digital&lt;/em&gt; is easy: A digital signal is a signal&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;that only takes discrete values,&lt;/li&gt;&#xA;&lt;li&gt;is only defined at a discrete axis (e.g. time, position, angle, impulse…)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The question is: What &lt;em&gt;are&lt;/em&gt; the values of your signal, and what's the axis?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd not understand Morse as an OOK (though I'd certainly start decoding it as such), but as a &quot;long-short keying&quot;. In that understanding, we get as the axis along the signal changes not time, but just &quot;index&quot; (first symbol, second symbol, third…), and as values just &quot;short on&quot;, &quot;short off&quot;, &quot;long on&quot;, &quot;long off&quot;, and &quot;very long off&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that, the dots, dash, inter-dot/dash spacing, inter-letter and inter-word spacing are representable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, in that understanding, Morse would be a digital, quinternary code.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-10-29T18:14:38.227" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12146" PostTypeId="2" ParentId="8940" CreationDate="2018-10-29T19:09:57.390" Score="1" Body="&lt;p&gt;It's pretty clear that we've reached the ~10.7-year solar cycle minimum in the midst of a low part of the ~87-year Gleissberg Cycle. See &lt;a href=&quot;https://en.wikipedia.org/wiki/Solar_cycle&quot; rel=&quot;nofollow noreferrer&quot;&gt;this explanation from Wikipedia&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Occam's Razor points toward this relatively simple (though unfortunate for us hams) scientific explanation rather than other explanations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As usual, some hams are responding to this problem by innovating with new weak-signal methods like FT8. &lt;/p&gt;&#xA;" OwnerUserId="13485" LastActivityDate="2018-10-29T19:09:57.390" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12147" PostTypeId="2" ParentId="12142" CreationDate="2018-10-29T20:01:02.433" Score="21" Body="&lt;p&gt;According to Shannon (in  &lt;em&gt;A Mathematical Theory of Communication&lt;/em&gt; - and who's going to argue with Shannon?) there are really only four symbols in Morse, not five: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&quot;dit&quot; (defined as one unit time on followed by one unit time off)&lt;/li&gt;&#xA;&lt;li&gt;&quot;dah&quot; (three unit times on followed by one unit time off)&lt;/li&gt;&#xA;&lt;li&gt;&quot;letter space&quot; (two unit times off) (should follow a dit or dah symbol)&lt;/li&gt;&#xA;&lt;li&gt;&quot;word space&quot; (four unit times off) (should follow a dit or dah symbol)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You don't need a fifth symbol for the intra-letter space because you can't represent a &quot;dit&quot; or a &quot;dah&quot; without &lt;em&gt;some&lt;/em&gt; space following it. So by defining the dit and dah symbols as above, you get the intra-letter spaces without adding to the symbol count. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aside from that, I believe we are dancing around the distinction between &lt;em&gt;line states&lt;/em&gt; and the &lt;em&gt;channel code&lt;/em&gt;. The line state in Morse usage is binary but the channel code is not. Per Shannon, the channel code has four different symbols. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another example of a channel code is EFM, &lt;a href=&quot;https://en.wikipedia.org/wiki/Eight-to-fourteen_modulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;eight-to-fourteen modulation&lt;/a&gt;,  which encodes every eight bits of end-user data as a 14-bit word. The allowable 14-bit words are chosen so that each has zero DC offset (same number of 0's and 1's) and to limit the number of successive 1's and of successive 0's. It is used on Compact Discs and other optical digital media. &lt;/p&gt;&#xA;" OwnerUserId="5227" LastEditorUserId="5227" LastEditDate="2018-12-04T18:32:47.760" LastActivityDate="2018-12-04T18:32:47.760" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12148" PostTypeId="1" AcceptedAnswerId="12294" CreationDate="2018-10-29T21:06:13.847" Score="2" ViewCount="468" Body="&lt;p&gt;The grounded-grid amplifier that I am looking at requires 1100 volts Max.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How do I safely deliver this rated voltage without getting hurt?&lt;/li&gt;&#xA;&lt;li&gt;Should I consider a alternative amplifier?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;By request here are the specs of the amp. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It is dual tube ground grid amp. &lt;/li&gt;&#xA;&lt;li&gt;Wattage is expected up in the hundreds. &lt;/li&gt;&#xA;&lt;li&gt;Square tuned cavity. &lt;/li&gt;&#xA;&lt;li&gt;Amp will be coupled to a wave guide system. &lt;/li&gt;&#xA;&lt;li&gt;Operates in the MHZ region. &lt;/li&gt;&#xA;&lt;li&gt;Details in the 1976 amateur radio handbook pages 228 - 231. &lt;/li&gt;&#xA;&lt;li&gt;Power supply will be designed into the overall unit and will not be home brewed. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;My intent with the amp is that it plays a central part in this design that i am working on. Power will be delivered via separate power source. The applications will be bountiful, currently, I am in the design phase, I cannot yet be able to operate. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the sake of it, I want to add this. My intent with the amp was to be used as part of a unit that will be designed for Data transmission via a wave guide system. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason why I came here for help was that the amp came from an radio handbook the overall unit will be built as part of a radio unit. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is intended to be in the electrical engineering, then put it their.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anyone can propose a alternative amp I will be fine with that. The only thing that I am worried about is the amount of voltage that I have to generate is mind blowing. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is their something missing that is needed to put up that people need so this question can be answered? &lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="12988" LastEditDate="2018-11-12T17:44:14.473" LastActivityDate="2018-11-27T21:49:43.890" Title="How to supply high voltage to an amplifier in a safe way?" Tags="&lt;amplifier&gt;&lt;safety&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12149" PostTypeId="1" CreationDate="2018-10-29T22:08:51.980" Score="0" ViewCount="413" Body="&lt;p&gt;I have designed a &lt;code&gt;LoRaWAN&lt;/code&gt; gateway and it is under testing. I have been using &lt;code&gt;omnidirectional&lt;/code&gt; &lt;code&gt;3dBi&lt;/code&gt; dipole antenna FRP (Fibre-glass Epoxy Antenna) for 868 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is the picture of my antenna (please ignore the specification in the picture):&#xA;&lt;a href=&quot;https://i.stack.imgur.com/woLxA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/woLxA.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to know how to calculate height required for getting a particular range. What would be minimum and maximum height for my setup? And what factors limit the height of the LoRaWAN antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been reading about &lt;code&gt;Fresnel Zone&lt;/code&gt; and understand that any obstacle in the zone will limit the range and solution would be to increase the height of the antenna or the end node. However, since I don't have much knowledge with the antennas, I think i might be missing concepts like fresnel zone. Please help me. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I came across another interesting concept. It limits the range of the &lt;code&gt;LOS&lt;/code&gt; communication due to curvature of the earth. The link over &lt;a href=&quot;http://www.hamuniverse.com/lineofsightcalculator.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; relates range to height of the antenna. According to the calculator presented in the website, I shouldn't go below 10 meter in height, to get atleast 10 km of the range.&lt;/p&gt;&#xA;" OwnerUserId="13490" LastEditorUserId="13490" LastEditDate="2018-10-29T22:23:09.270" LastActivityDate="2018-10-30T23:23:28.680" Title="Antenna height for LoRaWAN Gateway" Tags="&lt;antenna&gt;&lt;line-of-sight&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12150" PostTypeId="2" ParentId="12142" CreationDate="2018-10-29T22:11:27.180" Score="2" Body="&lt;p&gt;I believe the question is confusing the difference between something &lt;em&gt;being&lt;/em&gt; a natural basis for a language, versus whether something could be adequately &lt;em&gt;represented&lt;/em&gt; by one in a mathematical / encoding sense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is clear that morse code can be represented adequately using a binary representation / encoding. This is not surprising, since a binary representation can be created to represent much more complex bases anyway, such as the latin alphabet (e.g. ASCII).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you would probably agree that this doesn't make the latin alphabet a binary one in nature. Rather, the alphabet's elementary particles (the letters) can be used to form more complex constructs (the words). So in this sense, the English language is most naturally regarded as a 26-base system (because there are 26 elementary letters-particles).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, while it is possible to represent morse code using binary encoding, one would be hard pressed to argue that this is the most natural representation for it, or that this makes it a binary 'alphabet'. It is rather intuitive to consider the 'dit', 'dah', and 'separator' as the elementary particles that combine to form more complex constructs ('morse code'). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could of course try to argue that the 'dah' is not a well-suited, natural atomic particle for the morse code language, hence you can accept the 'binary' representation of '10', '1110', '00' etc, but I would argue that this is not really a good interpretation of the nature of morse code words; it is far more intuitive to conceive of morse code letters as composed by elementary dits, dahs, and separators as the elementary particles. If you need three bits to express a 'dah', then you're using essentially using four 'atomic particles' in your chosen representation, to express what is essentially a single natural atomic particle in the morse language, which seems like a rather inefficient way of expressing the language. Remember that binary is the choice of digital signals because of the electrical nature of transistors which deal with such signals most efficiently. But there's no reason for morse code to abide by that requirement, so a more efficient representation which is more natural to morse code (and its transmission by telegraph) would presumably have been preferable to such a binary encoding among telegraphers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to the separate question of whether it should be possible to consider the dit and dah itself as a sufficient number of elementary particles to fully express the morse code language, the answer to this is no (and hence it is not a naturally binary 'alphabet'). You can confirm this by attempting to express morse code in the absence of spaces. The reason telegraphers could rely on only dits and dahs is because they also had the added element of time, which could simulate word separation. When these need to be written down on paper as symbols, however, the word separator needs to be made explicit, thus making morse code a ternary system. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another way to see why time in itself is not a trivial aspect, but actually adds information is to treat it as if it's a separate signal transmitted in parallel with your dits and dahs. You now have two signals to consider at each time point, one in the dit-dah dimension which tells you whether you're dealing with a dit or a dah at that timepoint, and one in the time dimension, which tells you if you're dealing with a dit-dah particle, or not (i.e. a separator). Since these are two independent binary signals, your receiver at the other end would have to process a 4-bit signal. However, this can be encoded more efficiently as a 3-bit signal, since when the time series has a separator, the ditdah series is ignored. Thus the most efficient and natural representation for morse code is a ternary one.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;PS. I forgot about the distinction between a 'letter separator' and a 'word separator', but the above arguments still apply. You could make the case for a quaternary base instead of a ternary one incorporating a bespoke 'word separator' particle, or accept the ternary one and accept the inefficiency that comes with always having to represent a 'word separator' using a slightly less efficient representation using a 'diphthong'.&lt;/p&gt;&#xA;" OwnerUserId="13489" LastActivityDate="2018-10-29T22:11:27.180" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12151" PostTypeId="2" ParentId="12142" CreationDate="2018-10-29T22:31:44.820" Score="0" Body="&lt;p&gt;It's a matter of interpretation. Consider &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;-- --- .-. ... .     -.-. --- -.. .&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As written, it's a trinary code: dash, dot, and space. We can analyze it on a higher level, though: &lt;code&gt;--&lt;/code&gt; represents 'm', &lt;code&gt;---&lt;/code&gt; is 'o', etc. On this level, we have several dozen symbols: you can't translate Morse Code into the normal English alphabet just knowing that &lt;code&gt;-&lt;/code&gt; is &quot;dah&quot; and &lt;code&gt;.&lt;/code&gt; is &quot;dit&quot;, you need to know the whole &quot;alphabet&quot;. We can also analyze at a lower level: just as &lt;code&gt;-&lt;/code&gt; and &lt;code&gt;.&lt;/code&gt; are made up of black and white pixels, dits and dahs are made up of sound and silence, and thus are binary. Certainly, it is false to say &quot;Morse Code is a binary code made up of dits and dahs&quot;, in that on that level, it's not binary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One thing that makes analysis complicated is that Morse Code is that, for many of these levels, we are far from filling the space of combinations. For instance, on the binary level, we have that a dit is 1, and a dah is 11 (or possibly 111), and then there are spaces of 0, 00, 000, or 0000. There is no 0000 or 1111. Going up a level, there are many combinations of dits and dahs that don't represent any character. This suggests that these levels are not the appropriate level to analyze Morse Code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, any actual physical implementation of Morse Code will not be truly be discrete &quot;silence&quot; versus &quot;fixed level&quot;. It's a continuous system, so volume varies continuously between silence and sound, and there's bounce, etc. So there's yet another sense in which communication through Morse Code is done through an analog channel, but interpreted as discrete. The disagreement is then over on what level of abstraction we should consider the conversion from analog to digital to occur. Do we convert each unit of time to a 0 or 1, depending on the volume during that unit of time, and &lt;em&gt;then&lt;/em&gt; convert those 0s and 1s to dits and dahs? Do we convert a period of sound surrounded by silence to a dit or dah directly? Or something else?&lt;/p&gt;&#xA;" OwnerUserId="13492" LastActivityDate="2018-10-29T22:31:44.820" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12152" PostTypeId="2" ParentId="12140" CreationDate="2018-10-30T01:36:19.947" Score="1" Body="&lt;p&gt;In antenna theory, a plane wave is the spherical propagating wave that, after a short distance, appears essentially as a flat plane wave to the observer's antenna. This is due to the rapid expansion of the spherical wave and the relatively small size of a receiving antenna compared to the sphere. This can be likened to the sensation that the earth is flat from an individual's point of observation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;thickness&quot; of the plane wave is determined by how long the originating transmitter continues to transmit. As an example, imagine sending a single dit in morse code at 13 WPM. At this speed, a dit lasts approximately 100 milliseconds. Since an RF signal travels at 300,000 kilometers/second in free space, the &quot;thickness&quot; of this plane wave is 30,000 kilometers. If nothing else is sent from the transmitter, the plane wave will have passed the receiving antenna in ~100 milliseconds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In deference to comments made to this post, a harmonic plane wave is technically a flat surface (i.e. two dimensions) of identical phase from the emitting device. A true harmonic plane wave does not exist as it would require an infinite amount of energy to generate it. So we often take the liberty of analyzing EM energy as a plane wave when in fact it is not. It is in this same context of inexactitude that I consistently referenced thickness in quotes since in truth this would comprise an infinite number of non-existent two dimensional plane waves. That would be quite pedantic but not necessarily helpful.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-10-31T15:23:07.273" LastActivityDate="2018-10-31T15:23:07.273" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12153" PostTypeId="2" ParentId="12112" CreationDate="2018-10-30T01:42:31.093" Score="3" Body="&lt;p&gt;The simple answer is that the graphic is not accurate. There is an RMS voltage present at the center feed point of the dipole that follows Ohm's law relative to the feed point impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most likely, the graphic is attempting to make the point that a center fed half wave dipole is fed at the current maxima. As such, the feed point voltage is therefore at its minima - but not zero.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-10-30T10:57:50.890" LastActivityDate="2018-10-30T10:57:50.890" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="12154" PostTypeId="2" ParentId="12149" CreationDate="2018-10-30T02:15:55.030" Score="3" Body="&lt;p&gt;At VHF and above, communication is easiest when the stations have a clear line of sight. Without line of sight, a link is achieved only by reflection and diffraction off/around other objects in the environment, and this must be offset by higher transmit powers or antenna gain if there is insufficient margin in the &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Estimating coverage in the absence of a clear line of sight requires some non-trivial modelling. I used to link to some tools using the Longley-Rice model, however I can no longer find any that are freely available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However if you do have line of sight, then there are some simple calculations that can be done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At long distances, Earth's curvature limits the line of sight distance. On flat terrain, the &lt;em&gt;radio horizon&lt;/em&gt; describes the maximum distance for line-of-sight communication. It can be estimated by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{horizon in kilometers} = 4.12 \sqrt{\text{antenna height in meters}} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, an antenna mounted 2 meters high has a horizon of about 5.8 km. At 10 meters high, 13 km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The horizons from each end add, so if one station has an antenna a 2 meters, and the other at 10, the maximum line of sight distance is approximately 18.8 km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is practically speaking no maximum height, so mount the antenna as high as you can.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio waves have a much longer wavelength than visible light and thus can't be focused to a tight beam like a laser pointer. Consequently, to minimize loss it's important not only to keep clear the direct line between the stations, but some area around that line as well. As a design rule of thumb, the area that &quot;should be kept clear&quot; is usually defined by the first &lt;a href=&quot;https://en.wikipedia.org/wiki/Fresnel_zone&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fresnel zone&lt;/a&gt;, which is the locus of points where a ray reflected off that point would arrive with a 180 degree phase delay compared to a direct ray. It's an ellipsoidal region between the antennas which is thickest in the middle, with a radius (in meters) of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 8.656 \sqrt{ \text{distance in km} \over \text{freq. in GHz}} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 868 MHz and at your maximum range of 10 km, this gives the 1st Fresnel zone at its thickest point a radius of 29.3 meters, meaning you should hope to achieve a clear line of sight between the stations, and also clear the zone up to 29.3 meters around that line, especially in the middle.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-10-30T23:23:28.680" LastActivityDate="2018-10-30T23:23:28.680" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="12155" PostTypeId="2" ParentId="12142" CreationDate="2018-10-30T03:49:35.313" Score="2" Body="&lt;p&gt;Morse code is sent over a digital link. The link might use electromagnetic waves (in various parts of the spectrum), sound waves, electrical signals in a conductor or any other binary signalling method you can come up with. (E.G. tug on a rope, tapping a pipe or whatever.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The digital link is modulated between two states, which for  CW means turning a carrier wave off and on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern day digital links use a clock signal to break down transmissions into single bit values. Synchronous transmission requires sender and receiver to use a single clock signal which they can both access. Asynchronous transmission means the receiver must reconstitute the timing signal from the received signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Samuel Morse did not have to go into these detail. Effectively he used a signal coding scheme of&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;On signals of two noticeably different lengths - short and long for dit and dah,&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Combinations of various numbers of dits and dahs to encode letters,&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Off signals of three noticeably different lengths - short to separate dits and dahs, medium to separate successive letters and long to separate words.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The human brain can decode this scheme with training and allow for differences in fists and speed. Mathematical analysis can quantify and assign a number of time units for dits,  dahs, and spaces used in standard practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While CW might be used in parlance to refer to Morse code it is not the same. CW is a type of digital transmission link. When used to transmit Morse it operates  asynchronously - a separate clock signal is not sent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At a low level, Morse uses 5 ( or 4 depending how you analyse it mathematically) signal state timings to form dits, dahs, inter letter and inter word spaces.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At a higher level Morse interprets dits, dahs and spaces as letter and words.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So Morse code combines multiple sets of coding schemes:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;transmission link: asynchonous binary&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;bit detection: binary, repeating the same bit if it lasts more than one unit of time. More related to computerized decoding rather than by wet-ware in the brain. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;low level decoding: quaternary from the POV that it recovers dits, dahs, inter letter and inter word spaces.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;high level decoding reverses the &lt;em&gt;encoding scheme&lt;/em&gt; used to assign dits and dahs to letters and combines them into words. When using &quot;Morse&quot; to refer to the encoding scheme itself, distinctions of binary, ternary, quaternary etc. are out of context.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13496" LastActivityDate="2018-10-30T03:49:35.313" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12156" PostTypeId="2" ParentId="12139" CreationDate="2018-10-30T04:47:38.827" Score="0" Body="&lt;p&gt;The pattern of any antenna can be divided into Vertical and Horizontal components (these are not the only choice sometimes we use LHCP and RHCP, etc). For V and H we're looking at the Theta (up/down) and Phi (left/right) electric fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(we analyse antennas as transmitters, its easier, and they work the same when receiving)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the yagi will create some V and some H radiation on every direction, but the radiation is mostly H and mostly in front. For a well designed yagi, if we call the front Hpol radiation intensity 0 dB, then I estimate: sidelobes of -10 dB. Exactly sideways -15. Backlobes -15. Exactly behind it there is a hole, -20 dB. This is an azimuth cut, moving around in the Theta=0 plane. So far so good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now plot the Vpol radiation. The amount of this is strongly dependent on the feed and matching, how well balanced the coax is, whether the mast resonates at that frequency. I am going to guess for a typical Hpol yagi installed on a metal mast and Gamma fed, the Vpol radiation will be -15 dB in front, compared to the Hpol in front. Going around the antenna though, I don't expect it to change much. As the mast, cable etc are radiating, it will be roughly omnidirectional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an aside, If the yagi were floating in free space with only a tiny transmitter connected to the feedpoint, the Vpol radiation would be much less, perhaps -40 dB compared to Hpol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to answer your question - well first the front to back ratio needs to be carefully defined to make sense. I would start with this: &lt;strong&gt;The ratio of total power radiated to the back, to total power radiated to the front&lt;/strong&gt;. Because when you look at F/B ratio, you're interested in the rejection of &lt;em&gt;all&lt;/em&gt; signals from the back, not just horizontal ones. Perhaps there is a more complete definition out there.&lt;br&gt;&#xA;It doesn't help the amateur to talk about the Vpol F/B ratio, but you could certainly define it and calculate it. For an Hpol antenna, Vpol F/B might be close to 0 dB.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2018-10-30T04:47:38.827" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12157" PostTypeId="1" CreationDate="2018-10-30T12:25:15.337" Score="1" ViewCount="121" Body="&lt;p&gt;The voltage at the center of a resonant half wave dipole can't be zero because the current is at a maximum in the middle. If the voltage was zero then there would be zero current right ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How then can the type of yagi antenna where the elements aren't insulated from the boom work ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because apparently it's ok to mount the elements including the driven element at the center not insulated from the boom because as everyone knows the voltage in the middle is zero and so it's ok to join the elements directly to the boom. &lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2018-11-12T01:55:32.963" Title="If the voltage at the center of a half wave dipole isn't zero, then how do Plumber's Delight yagi antennas work?" Tags="&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12158" PostTypeId="2" ParentId="12157" CreationDate="2018-10-30T13:29:49.113" Score="1" Body="&lt;p&gt;Without realizing it, you are asking the same question that was answered in this &lt;a href=&quot;https://ham.stackexchange.com/questions/12131/what-is-the-voltage-on-a-half-wave-dipole-measured-with-respect-to&quot;&gt;Ham Stack Exchange&lt;/a&gt; item. I considered referring to &quot;plumbers delight&quot; construction in my answer there, but thought it might be off-topic, so I refrained. The net is that the center of a yagi element is a &lt;em&gt;virtual&lt;/em&gt; ground to which a conductive boom, as well as the coax feedline shield, may be connected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which is not to say that a conductive boom will be electrically inert. It is likely that element lengths will need adjustment when compared to their lengths for a non-conductive boom. How much adjustment depends on the details of the array: length, element and boom diameters, etc.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2018-10-30T13:29:49.113" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12159" PostTypeId="2" ParentId="12142" CreationDate="2018-10-30T16:07:32.770" Score="0" Body="&lt;p&gt;No, it is a ternary system (or trinary system; trinary and ternary are the same).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's because you only use dots, dashes, and spaces to represent the world.  These are called &quot;trits&quot; in a ternary system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a binary system, you use only 1 or 0 to represent the world, and these are called &quot;bits&quot;.&lt;/p&gt;&#xA;" OwnerUserId="13503" LastActivityDate="2018-10-30T16:07:32.770" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12160" PostTypeId="1" CreationDate="2018-10-30T17:35:02.460" Score="0" ViewCount="104" Body="&lt;p&gt;Recently, I have received an antenna from one of the Chinese manufacturer and they haven't disclosed the detailed specification with us.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is the picture of my antenna (please ignore the specification in the picture): &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VuWcU.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VuWcU.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The specification that are provided by the vendor are over &lt;a href=&quot;https://www.scribd.com/document/391982278/YJC-60302-G01&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Frequency: 865-867 MHz&lt;/li&gt;&#xA;&lt;li&gt;Gain: 3dBi&lt;/li&gt;&#xA;&lt;li&gt;VSWR &amp;lt; 3.0 : 1&lt;/li&gt;&#xA;&lt;li&gt;Radiation Pattern: Omnidirectional&lt;/li&gt;&#xA;&lt;li&gt;Impedance: 50 ohm&lt;/li&gt;&#xA;&lt;li&gt;Length (From connector to Antenna End): 500mm&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I want to know from it's size and gain, Can we predict it's antenna type (e.g. Collinear antenna), it's design (dipole or mono-pole), internal construction, polarization and various other parameters? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These kinds of antennas look to be standard and I think others who have used them in the past can help me in identifying my own antennas. I am waiting for my manufacturer to share detailed specification but I am not sure how long will they take.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to my calculations, the wavelength for 865 MHz signal would be &lt;code&gt;0.346580 meters&lt;/code&gt;. So, for half-wave dipole, the length should be &lt;code&gt;0.17329 meter&lt;/code&gt;. However, length of my antennas is bigger than that. I think that's why it is &lt;code&gt;collinear&lt;/code&gt; dipole array antenna. Please correct me if I am wrong.&lt;/p&gt;&#xA;" OwnerUserId="13490" LastEditorUserId="13490" LastEditDate="2018-10-30T17:56:12.747" LastActivityDate="2018-10-30T18:29:32.630" Title="Antenna Type of a Chinese Antenna" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12161" PostTypeId="2" ParentId="12160" CreationDate="2018-10-30T18:29:32.630" Score="1" Body="&lt;p&gt;It's most likely some kind of co-linear array of dipoles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The lack of a ground plane means it's not a monopole. And as you've calculated, it's substantially physically longer than a half-wave dipole would be. Further supporting the notion of some kind of array, the indicated gain of 3dBi is greater than the gain of a simple half-wave dipole (2.15 dBi).&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-30T18:29:32.630" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12162" PostTypeId="2" ParentId="12142" CreationDate="2018-10-30T19:40:40.130" Score="-4" Body="&lt;p&gt;Morse code using only a given ratio of lengths is only a binary code because the intelligence is transferred by a two state (on/off) method. Now for the difference, each character is sent via combinations of these on/off signals in various combinations. The old railroad code went even further to change the pulse width, if you will, by changing the spacing distance between pulses, or the length of the dash (short dash / long dash). Normal radiotelegraph code uses a fixed set of binary digits, a dash equal to the length of 3 dots. Therein lies the binary aspect. Just because there is a difference in character spacing which correlates to a baud speed, both are considered binary in nature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, if you didn't turn either what we consider a binary signal or a radiotelegraph signal on it wouldn't be binary; if you turned it on and didn't turn it off it also wouldn't be binary.&lt;/p&gt;&#xA;" OwnerUserId="8496" LastEditorUserId="76" LastEditDate="2018-10-31T00:21:36.800" LastActivityDate="2018-10-31T00:21:36.800" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12163" PostTypeId="2" ParentId="12157" CreationDate="2018-10-30T22:59:50.073" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The voltage at the center of a resonant half wave dipole can't be zero because the current is at a maximum in the middle. If the voltage was zero then there would be zero current right?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So you're saying zero voltage implies zero current?&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JzYQa.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fJzYQa.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's the voltage at the ammeter AM1?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're asking &quot;which end&quot; does it matter? What's the impedance of an ideal ammeter and what's that imply about the difference in voltage from one end to the other?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's the current through the ammeter?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-30T22:59:50.073" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12164" PostTypeId="2" ParentId="12140" CreationDate="2018-10-31T01:19:26.740" Score="3" Body="&lt;p&gt;That image illustrates the electric field just along one line for &quot;clarity&quot;. The line is shown in dark grey, running perpendicular to the antenna, from the lower-left to upper-right of the image. I suppose the author thought trying to show an animated electric field in three dimensional space when mapped onto a two-dimensional image would just be too much information to be clear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The length of the green arrows should not be interpreted as any kind of &quot;width&quot;. Rather, the length of the arrow is proportional to the electric field intensity at the single point at the base of the arrow. This kind of visual analogy is a common way to represent a &lt;a href=&quot;https://en.wikipedia.org/wiki/Vector_field&quot; rel=&quot;nofollow noreferrer&quot;&gt;vector field&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's another visualization of an electric field around an oscillating dipole (source: &lt;a href=&quot;https://gfycat.com/MelodicThornyHairstreak&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://gfycat.com/MelodicThornyHairstreak&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MEmDS.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MEmDS.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here we can see the oscillating electric field exists all around the dipole in three dimensions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this animation it also appears that the field changes everywhere at once, which implies that the distance visible from one side of the image to the other is much less than one wavelength. If we could &quot;zoom out&quot;, we would see the field doesn't actually change everywhere at once, but that changes begin at the origin and then propagate out at the speed of light.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-10-31T01:19:26.740" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12165" PostTypeId="2" ParentId="10401" CreationDate="2018-10-31T02:53:23.577" Score="1" Body="&lt;p&gt;A few comments on amateur LoRa:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;As others have pointed out, the datarate is measured in tens of bytes per second. Not thousands... Forget about file transfer!&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;LoRa is spread-spectrum and therefore can be used on the 1.25m-band and shorter, with maximum 25W PEP.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Enhanced propagation at 1.25m (versus 33cm where LoRa is typically used) opens up exciting possibilities of range. I would expect range similar to a well-equipped 2m SSB/CW station.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;LoRa is a modulation scheme (analogous to FM), while LoRaWAN is a protocol and topology (analogous to an analog Echolink repeater system).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;There's a project called &quot;loraham&quot;, spearheaded by the hacker Travis Godspeed, which gathered quite a bit of interest. It is a PTP mesh in the spirit of APRS. &lt;a href=&quot;https://github.com/travisgoodspeed/loraham&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/travisgoodspeed/loraham&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13508" LastActivityDate="2018-10-31T02:53:23.577" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12166" PostTypeId="2" ParentId="12112" CreationDate="2018-10-31T03:05:42.977" Score="3" Body="&lt;p&gt;&amp;quot;Voltage&amp;quot; is not a very specific term: it only means &amp;quot;the value of something measured in volts&amp;quot;. You might as well ask, &amp;quot;How can a sheet of paper have a meterage of 0.1 mm when it's on Mt. Everest with a meterage of 8848 meters?&amp;quot; Of course comparing &lt;em&gt;thickness&lt;/em&gt; to &lt;em&gt;elevation&lt;/em&gt; doesn't make much sense, even though both are measured in meters. But if you'd never been introduced to the concepts of thickness and elevation because they were both commonly called &amp;quot;meterage&amp;quot;, it would be quite confusing.&lt;/p&gt;&#xA;&lt;p&gt;So maybe it will help to understand exactly what thing is being measured by &amp;quot;voltage&amp;quot;.&lt;/p&gt;&#xA;&lt;h2&gt;electric potential difference (volts)&lt;/h2&gt;&#xA;&lt;p&gt;When someone says &amp;quot;the voltage of this battery is 1.5 volts&amp;quot;, they are measuring &lt;em&gt;electric potential difference&lt;/em&gt;. This kind of voltage is always a difference between two points. An electric potential difference of 1.5 volts means for each coulomb of electric charge moved from the first point to the second point requires 1.5 joules of work. It is similar to saying &amp;quot;this hill is 10 meters tall&amp;quot;, which says something about how much work must be done to lift a rock from the base of the hill to the top.&lt;/p&gt;&#xA;&lt;p&gt;The feedpoint in an antenna isn't a &lt;em&gt;point&lt;/em&gt; in the mathematical sense. So when discussing the voltage at the feedpoint, someone &lt;em&gt;could&lt;/em&gt; mean the &lt;em&gt;electric potential difference&lt;/em&gt; between the usually two parts of the feedpoint, like the center conductor and shield of a coaxial connector.&lt;/p&gt;&#xA;&lt;h1&gt;electric potential (volts)&lt;/h1&gt;&#xA;&lt;p&gt;When someone says &amp;quot;the voltage at the center of a dipole is zero&amp;quot; they are measuring &lt;em&gt;electric potential&lt;/em&gt;. Protons and electrons (and other fundamental particles) have an electric charge. Opposite charges attract, and like charges repel through the electromagnetic force. To pull two opposite charges apart increases their electric potential, just like pulling a rock away from Earth increases its gravitational potential.&lt;/p&gt;&#xA;&lt;p&gt;Unlike electric potential difference, electric potential can be defined on just one point. You've no doubt you've seen visualizations of gravity wells where massive objects pull down a rubber sheet. We can define a similar visualization for the electromagnetic force, and since we have both positive and negative charge there can be wells and hills:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/31F2w.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/31F2w.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The height of this sheet is the electric potential. At infinity the sheet is flat, this is by definition an electric potential of zero volts. The colored lines are contours with constant potential: moving around them neither increases nor decreases electric potential. Moving up or down one volt requires 1 joule of work per coulomb of charge moved.&lt;/p&gt;&#xA;&lt;p&gt;Notice there's one contour that's hard to see: it's a straight line directly on the &lt;em&gt;y&lt;/em&gt; axis, equidistant between the two charges. Because it's equidistant from two equal but opposite charges, the potential here is zero volts. This is what &amp;quot;voltage is zero at the center of a dipole&amp;quot; means.&lt;/p&gt;&#xA;&lt;h2&gt;electric field intensity (volts per meter)&lt;/h2&gt;&#xA;&lt;p&gt;What is &lt;em&gt;not&lt;/em&gt; zero is the &lt;em&gt;electric field intensity&lt;/em&gt;. It's the gradient of electric potential, and measured in volts per meter. This value is &lt;em&gt;not&lt;/em&gt; zero at the center of a dipole: as you can see there's actually a quite steep slope at the origin of the graph.&lt;/p&gt;&#xA;&lt;p&gt;And here I believe lies the crux of your issue. If you've done any lumped circuit analysis, you've probably equated &amp;quot;voltage&amp;quot; to &amp;quot;electric potential difference&amp;quot;. That difference gives rise to an electromotive force, and if there's a conductive path across the distance, current. But when making the jump from lumped element analysis to electric field analysis, &lt;em&gt;electric field intensity&lt;/em&gt; is the thing analogous to what you've been calling &amp;quot;voltage&amp;quot; in that it relates to electromotive force, and thus current.&lt;/p&gt;&#xA;&lt;h2&gt;some facts about dipoles without the word &amp;quot;voltage&amp;quot;&lt;/h2&gt;&#xA;&lt;p&gt;The center of a dipole is a single point. At this point, the electric field potential is zero, and the electric field intensity is non-zero. The non-zero electric field intensity means the mobile electrons in the antenna are moved by the electromotive force they experience, thus current is also nonzero at the center. The feedpoint is most likely two points, as in a coax center conductor and shield. Since these two points are separated by space, there is a nonzero electric potential difference between them.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-07-03T23:25:30.463" LastActivityDate="2020-07-03T23:25:30.463" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12167" PostTypeId="1" CreationDate="2018-10-31T03:59:02.027" Score="6" ViewCount="300" Body="&lt;p&gt;I was plotting constant-gain circles on the Smith chart the other day for a potentially unstable RF transistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recently read on-line that for a potentially unstable transistor the maximum gain that can achieved is the MSG or maximum stable gain. MSG is simply the ratio of the magnitude of S21 over the magnitude of S12.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For my transistor, the MSG in absolute gain 162.5 or 22.1dB as shown on the attached Smith chart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The on-line article also said that &quot;one should never try to tease more gain from the transistor than the MSG&quot;. I have the output stability circle plotted and the unstable region marked as UR on the Smith chart. Notice that some of the 22.1dB constant-gain circle is located pretty far away and outside of the output stability circle's unstable region.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the heck of it, I plotted gain circles all the way up to the ludicrous values of 50 and 100dB to see what would happen. The 29dB gain circle is dangerously close to but still outside the output stability circle's unstable region.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Only when I jumped to 50 and 100dB did the gain circles just align with the output stability circle. Apparently, gain seems to be infinite with respect to a potentially unstable transistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is it about MSG that makes it the final word on stable gain when, I'll say, the 23 or even the 26dB gain circle, or at least part of it, seems safely out of the output stability circle's unstable region and seems like there would still be some safe terminating impedances, although not many, available, right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes Sir, here's the link. &lt;a href=&quot;https://www.microwaves101.com/encyclopedias/stability-factor&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.microwaves101.com/encyclopedias/stability-factor&lt;/a&gt;. However it doesn't say much about Maximum Stable Gain and I haven't been able to find much &lt;em&gt;more&lt;/em&gt; information about it then I already know on-line. I know that for an unconditionally stable transistor the maximum gain that can be had is the Maximum Available Gain or MAG. In my book, 'RF Circuit Design' by Chris Bowick, Bowick discusses Maximum Available Gain but not Maximum Stable Gain. When I Plot the constant-gain circles for an unconditionally stable transistor, I found that as the gain is increased, the radius of the circle decreases. When MAG is achieved, the circle becomes a single point on the Smith chart and the equation for the radius of the constant-gain circle becomes undefined. This isn't the case for a potentially unstable transistor. At MSG, the constant-gain circle seems to reach its' smallest radius at 22.1dB(MSG) then increases slightly at 26dB, a little more at 29dB, quite a bit more at 50dB and stays at that size through the ridiculous 100dB gain value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So is the maximum gain that can be had from a potentially unstable transistor simply at the point where the constant-gain circle reaches its' smallest radius, at MSG = 22.1dB for my transistor, even though the 23,26 and 29dB gain circles still have a portion of their locus outside the output stability circle?     &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EREMw.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EREMw.jpg&quot; alt=&quot;Gain Circles on Smith Chart&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11230" LastEditorUserId="11230" LastEditDate="2018-11-01T03:54:46.717" LastActivityDate="2018-11-01T03:54:46.717" Title="Beyond Maximum Stable Gain of a transistor" Tags="&lt;electronics&gt;&lt;smith-chart&gt;" AnswerCount="0" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12169" PostTypeId="1" AcceptedAnswerId="12214" CreationDate="2018-10-31T15:50:40.230" Score="7" ViewCount="570" Body="&lt;p&gt;I bought a RTL-SDR (blue one with little MCX antenna). I modified its Q branch, and can receive short wave radio with Degen 31MS antenna now.&#xA;For MW, Degen 31MS antenna has a ferrite bar antenna coupler to work with the internal antenna of the radio. I don't have a ferrite bar antenna.&#xA;How can I make a ferrite bar antenna for RTL-SDR?&lt;/p&gt;&#xA;" OwnerUserId="13512" LastEditorUserId="13615" LastEditDate="2018-11-17T16:23:37.043" LastActivityDate="2018-11-17T16:23:37.043" Title="How to make a ferrite bar antenna for RTL-SDR?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;rtl-sdr&gt;&lt;ferrite&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12172" PostTypeId="2" ParentId="10086" CreationDate="2018-11-01T06:50:59.240" Score="1" Body="&lt;p&gt;The receiver is effectively acting as a shunt across the meter. Once the receiver is removed from the circuit the &quot;shunt&quot; is removed so the meter shows the true reading. &lt;/p&gt;&#xA;" OwnerUserId="13522" LastActivityDate="2018-11-01T06:50:59.240" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12176" PostTypeId="2" ParentId="5892" CreationDate="2018-11-01T19:35:19.680" Score="1" Body="&lt;p&gt;KB9RLW Kevin Loughin has a good &lt;a href=&quot;https://www.youtube.com/watch?v=VAV9Wws-Bs0&quot; rel=&quot;nofollow noreferrer&quot;&gt;YouTube video&lt;/a&gt; on his 9:1 unun build.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He used it for his HF vertical fed like an end fed antenna. I built one of these with full success for an elderly ham who also uses a manual tuner and/or his rig tuner which will load so many HF bands 6-160 meters. Yah, hard to believe - how? There is a 3&quot; coil with about 20+ turns inline on the vertical and with 2 tuners makes it happen – hi hi. Easily works on 15-80 so he was tickled happy. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as type of core I used - 31 mix 240 size x 2 similar to KB9RLW's. We used silicone insulated wire but try any good solid copper - heavier if running power. We used 14 and 16 gauge as he only runs 100watts. I believe this one will take 500 watts though with dual cores. It pays to have books on unun/baluns like the CQ publication with Jerry Cevick - or others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider a hybrid design that has a 1:1 core wound above the 9:1 unun.&#xA;Don’t be afraid to experiment some - you will be proud like us of the results. By the way, I wound a 4:1 balun 1st and it did not work for so many bands as this one did using a couple radials and copper rod - this is worth it.&lt;/p&gt;&#xA;" OwnerUserId="13530" LastEditorUserId="9493" LastEditDate="2018-11-01T22:43:49.547" LastActivityDate="2018-11-01T22:43:49.547" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12177" PostTypeId="1" CreationDate="2018-11-02T00:35:52.617" Score="1" ViewCount="721" Body="&lt;p&gt;Following is my understanding of some theory and the questions are at the end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this right ? ... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A standing wave is an AC waveform oscillating at a particular frequency which has a varying amplitude as time progresses (only in a sinusoidal fashion if the AC source is emitting a sine wave, which in our case it hardly ever is), but has a fixed amplitude profile in space (or length) along say in this case the inside of some coax, and is the interference pattern created when two AC wave forms traveling in opposite directions cross paths (and the superposition theorem explains this). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And remembering that the AC wave forms in question are in reality just the movement of electrons (which is current which is coulombs per sec) in sympathy with the potential difference of the output of the AC source, which hardly ever is a sine wave, away from the antenna during the periods of source output which have a positive voltage with respect to the AC ground, towards the antenna during the negative periods, the whole thing moving in space away from the source at the speed of light x the velocity factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At any one particular point along a transmission line, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;VSWR is the the ratio (one divided by the other) of two things : &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The potential difference between the maximum value in volts of an existing oscillating standing wave on the outside of the inner conductor and the inside of the coax shield at that point.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The potential difference between the minimum value in volts of an existing oscillating standing wave on the outside of the inner conductor and the inside of the coax shield at that point.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I've noticed that there are a few different kinds of SWR meters, some use a Bridge and some use a Directional Coupler. The different kinds probably have advantages and disadvantages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However i want to point out that no SWR meters measure the Standing Wave Ratio directly right ? They either measure the ratio of peak voltage for two wave forms traveling in opposite directions (directional coupler) or measure the apparent change in impedance inflicted upon the source by the presence of the standing waves (bridge) ... is that right ? So they indirectly measure SWR and even more indirectly measure the impedance match of the coax to the antenna. That's like a 3rd hand me downed measurement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also it's probably worth noting here that the VSWR on a transmission line, excluding I2R losses, is the same at every point along the transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there is an error current flowing on the outside of the coax due to incorrect balancing of the coax to the antenna because the AC current flowing on the inside of the shield splits up between the antenna and the outside of the shield because the impedance that the outside of the coax presents to the AC signal is not negligible compared to the antenna impedance, then apparently according to various sources such as the ARRL Antenna Handbook this can affect a VSWR measurement because it results in a &quot;Common Mode Impedance&quot; which affects the measurement made by the SWR meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone tell me EXACTLY how the presence of current on the outside of the coax changes the VSWR reading ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, what are the other causes if any of a SWR meter changing it's reading as the length of coax is changed ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Oh and btw the answer i'm looking for is not : SWR meters are designed to work with a specific feed line impedance and if that impedance isn't the correct value the SWR meter doesn't measure correctly.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2018-11-02T04:05:42.050" LastActivityDate="2018-11-06T20:15:30.603" Title="Exactly why do some SWR meters give a changing reading depending on the length of coax used to connect to an antenna?" Tags="&lt;antenna-theory&gt;&lt;impedance-matching&gt;&lt;transmission-line&gt;&lt;math&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12178" PostTypeId="2" ParentId="12177" CreationDate="2018-11-02T00:59:22.333" Score="6" Body="&lt;p&gt;The SWR is related to the reflection coefficient &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \Gamma = {Z_L - Z_0 \over Z_L + Z_0 } $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{VSWR} = {1+|\Gamma| \over 1 - |\Gamma|} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; is the feedline impedance, usually 50 ohms, and&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_L$&lt;/span&gt; is the load (nominally, the antenna) impedance.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The reflection coefficient is a complex number and thus takes into account the phase of the reflection, but the SWR depends only on the magnitude of the reflection coefficient. &lt;em&gt;If the load impedance is held constant&lt;/em&gt;, then changing the feedline length (neglecting losses in the feedline) changes the phase but not the magnitude of the observed reflection at the source end of the feedline, due to the changing delay provided by the line. Because SWR by definition does not care about phase, SWR does not change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If adding additional length increases losses, then the SWR will improve. Consider a feedline so long its loss is nearly infinite: it's indistinguishable from a dummy load. When the line loss is not substantially less than the return loss, the length of the line can be very significant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But when there are common-mode currents, the feedline is effectively part of the antenna. So changing the feedline length is effectively changing the antenna, and thus &lt;em&gt;changing the load impedance&lt;/em&gt;. Thus SWR changes.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-11-06T02:56:11.187" LastActivityDate="2018-11-06T02:56:11.187" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="12179" PostTypeId="2" ParentId="12177" CreationDate="2018-11-02T01:29:49.373" Score="3" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Can someone tell me EXACTLY how the presence of current on the outside of the coax changes the VSWR reading ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;When RF current is flowing on the outside of a coaxial cable, the exterior shield has become part of the radiating antenna. The presence of the SWR meter disturbs this common mode current. Therefore relocating the meter changes the common mode current, thereby altering the antenna feed point impedance which alters the SWR.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Or, what are the other causes if any of a SWR meter changing it's reading as the length of coax is changed ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The losses in the coax cable changes the SWR. The power traveling towards the load is reduced by the coaxial losses and the reflected power is again reduced by the coaxial losses. The longer the coaxial cable, the greater the losses and therefore the SWR is further reduced. While these losses are usually dominated by conductive I&lt;sup&gt;2&lt;/sup&gt;R losses, dielectric and radiative losses contribute to the effect.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;VSWR is the the ratio (one divided by the other) of two things :&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The potential difference between the maximum value in volts of an existing oscillating standing wave on the outside of the inner conductor and the inside of the coax shield at that point.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The potential difference between the minimum value in volts of an existing oscillating standing wave on the outside of the inner conductor and the inside of the coax shield at that point.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Neither one of these is correct. The voltage and current between the inner braid and the center conductor at any point along the coaxial cable will be equal but opposite in phase. This is the required condition for a coaxial cable to function as a transmission line. When the load does not match the characteristic impedance of the coaxial cable, power will be reflected toward the source. If the source impedance does not match the characteristic impedance, some of the returned power will be reflected back to the load. These reflections combine to form a standing wave so named because there are observable minima and maxima voltages and currents at fixed points along the length of the coax. SWR can be defined as the ratio of an observed minima voltage or current to the nearest  voltage or current maxima.&lt;/p&gt;&#xA;&lt;p&gt;The voltage minima and maxima is measured across the two conductors at each point. The current minima and maxima can be measured in either conductor but both readings must be taken from the same conductor in order to properly cancel the sign due to the direction of the current.&lt;/p&gt;&#xA;&lt;p&gt;A modern SWR meter does not measure the minima and maxima of voltage or current but instead relies on other observable effects caused by the standing wave. If you wish to understand how an SWR meter functions, check out &lt;a href=&quot;https://ham.stackexchange.com/q/9778/9493&quot;&gt;How does an SWR Meter Really Work?&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-11-02T11:51:57.630" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12185" PostTypeId="1" AcceptedAnswerId="12192" CreationDate="2018-11-03T14:50:12.733" Score="1" ViewCount="599" Body="&lt;p&gt;Now that I have a working G5RV Jr. and have had some good luck with DX (Croatia and Venezuela on 20m, Morocco on 40m from Michigan at 100w output), of course I want to mess with the configuration.  It's sort-of an inverted vee at about a 145 degree angle, the max height is a little over 23 feet and the ends are about 16 feet above ground (antenna is 52 feet long).  The ends of the antenna are well above my house and above all the neighboring objects except for trees of course.  I'm new at antenna modeling and I tried to model an inverted vee with MMANA just to see what the improvement would be if I increased the height in the middle by about 6 feet, and the ends by maybe a little higher, giving a sharper angle as well, but I wasn't impressed with the results.  Like I said, though, I'm new at modeling antennas.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, I'm currently limited to 100w output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So basically I'm looking for advice from more experienced people. I probably shouldn't expect a significant boost in performance for a 6 foot height increase at either 20m or 40m, should I?  I mean, it's not like I'll open up Japan or Australia by raising it by 6 feet, right?&lt;/p&gt;&#xA;" OwnerUserId="9772" LastEditorUserId="8717" LastEditDate="2019-11-05T19:37:50.640" LastActivityDate="2019-11-05T19:37:50.640" Title="Raising height of inverted V by 2 meters" Tags="&lt;antenna&gt;&lt;inverted-vee&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12189" PostTypeId="1" AcceptedAnswerId="12191" CreationDate="2018-11-05T05:32:39.887" Score="5" ViewCount="1874" Body="&lt;p&gt;I see RF applications requiring 50 ohm termination to avoid any open port reflections. Curious what is actually inside a 50 ohm termination connector. Is it simply a 50 ohm resistor? But then it is rated for certain frequency range, so makes me think it is something more than a resistor.&lt;/p&gt;&#xA;" OwnerUserId="6722" LastActivityDate="2018-11-05T15:00:13.447" Title="What is inside a 50 ohm termination?" Tags="&lt;rf-power&gt;&lt;frequency&gt;&lt;connectors&gt;&lt;reflector&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12190" PostTypeId="2" ParentId="12189" CreationDate="2018-11-05T06:02:42.870" Score="0" Body="&lt;p&gt;Terminating coaxial lines such as those used for Ethernet networks is important to prevent reflections as you state.  But, these terminators can get more sophisticated than a mere passive 50 ohm resistor although that works too in many situations.  Other terminators may involve other reactive components (e.g. inductors or capacitors) depending on the environment and coaxial cable.  And, there are even active terminators that control voltage across the terminating resistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since these terminators are used in specific applications like Ethernet  or SCSI cables and other high-speed data cable connections the frequency range is usually predetermined by the design of the signaling that is used.  So, having to handle some unspecified frequency is not usually a design problem.  In this last statement I admit to not knowing the latest technology in this area as my own knowledge is a number of years old.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I am sure you can find lots of very good information on the internet.  Just search for links involving high-speed data coaxial cable termination or look into the 10Base2 Ethernet or other (e.g. SCSI) specifications that are available on-line.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2018-11-05T06:02:42.870" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12191" PostTypeId="2" ParentId="12189" CreationDate="2018-11-05T06:14:48.573" Score="9" Body="&lt;p&gt;It depends on the frequency range the termination is rated for, and the power handling required. High power and high frequency is very difficult.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At HF, any old non-inductive 50 Ω resistor will do. For higher power, we'd put many resistors in series and parallel, perhaps on a heat sink or in a can of oil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At VHF and UHF I've made very good terminations with a pair of 100 Ω chip resistors soldered flat on an SMA connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Above this, the inductance of the resistors gets too much, and they start to be made of a carbon impregnated board, with an appropriate surface resistivity to match the transmission line, and gradually absorb the power. This could be done with a gentle taper in the stripline on the lossy board, to further improve its high frequency behaviour. The very best are sold for calibration of network analysers, these are thousands of dollars each.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a high power, low PIM, well matched load, we've also used a long roll of thin .078&quot; rigid coax. The loss of 3 dB per metre, over 5 metres, both ways, adds up to a 30 dB return loss, even if the other end is an open circuit. With a mere mortal termination on the far side, this can be even better. In ohms, the impedance including all inductance of the connections is within 0.5 Ω of 50 Ω, even at many GHz, no mean feat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A termination will have a specification for return loss, which is the reflection it produces in a 50 Ω system, and the frequency range this is valid for. A cheap one will be say 20 dB return loss from DC up to 1 GHz. A better SMA one might be 30 dB up to 8 GHz. Really good ones will be over 40 dB return loss, and/or work up to 10s of GHz, depending on the connector used. &lt;a href=&quot;https://www.minicircuits.com/WebStore/terminations.html&quot; rel=&quot;noreferrer&quot;&gt;Mini-Circuits have an excellent selection of modest priced ones on their website&lt;/a&gt;, but look at Weinschel and HuberSuhner for fancier ones.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="76" LastEditDate="2018-11-05T15:00:13.447" LastActivityDate="2018-11-05T15:00:13.447" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12192" PostTypeId="2" ParentId="12185" CreationDate="2018-11-05T13:40:22.550" Score="3" Body="&lt;p&gt;When a dipole is less than a 1/4 wavelength above ground, the image antenna formed by the reflection from the ground creates destructive interference at low angles, making the antenna quite useless for DX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 40 meters, a quarter wavelength is about 35 feet, more than the current 23 feet at apex. The effect will be diminished if you are not also able to raise the ends of the antenna, but still the effect will be more than nothing. Raising the antenna will direct more power at low angles useful for DX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, getting the antenna farther from the ground reduces ground losses. If your soil conductivity is low, this can be very significant.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-11-05T13:40:22.550" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12193" PostTypeId="1" AcceptedAnswerId="12197" CreationDate="2018-11-05T21:47:12.293" Score="2" ViewCount="156" Body="&lt;p&gt;Is there any difference in the voltage (potential difference wrt center) and current (rate of flow of electrons) distribution for a half wave dipole fed in the middle (dipole cut in the middle,) or fed with a gamma match (dipole one piece) ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2018-11-14T15:09:46.930" Title="Is there any difference in the voltage and current distribution for a half wave dipole fed in the middle, or fed with a gamma match?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12197" PostTypeId="2" ParentId="12193" CreationDate="2018-11-06T19:34:30.507" Score="2" Body="&lt;p&gt;At the highest level, no. Current is still highest in the middle, and voltage highest at the ends. The radiation pattern is practically identical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking more closely, there must be differences, otherwise it would be indistinguishable from a center-fed dipole. Part of the gamma match can be viewed as a shorted transmission line in parallel with the feedpoint. The currents on this transmission line can then be considered the superposition of the common mode and the differential mode. The common mode radiates as a dipole would. The differential mode does not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See also &lt;a href=&quot;https://ham.stackexchange.com/a/1899/218&quot;&gt;What is a Gamma match in the context of the driven element of a Yagi antenna?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-11-06T19:34:30.507" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12198" PostTypeId="1" CreationDate="2018-11-06T19:38:21.613" Score="20" ViewCount="4914" Body="&lt;p&gt;I know very little about antennas. I know, that for a certain frequency the antenna needs a certain lengths for good sending/receiving conditions.&#xA;Often the antenna is at the end of a cable. Why doesn't the length of the cable count in addition to the length of the antenna?&lt;/p&gt;&#xA;" OwnerUserId="13557" LastEditorUserId="13615" LastEditDate="2018-11-17T16:22:38.880" LastActivityDate="2018-12-30T02:22:22.050" Title="How does the signal know where the cable ends and the antenna starts?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12199" PostTypeId="2" ParentId="12198" CreationDate="2018-11-06T20:14:38.853" Score="9" Body="&lt;p&gt;Antennas are often resonant. Their physical dimensions are adjusted so standing waves develop at a particular frequency, like a bell rings at a particular tone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feedlines are not usually resonant. Usually an engineer ensures the end of the feedline is terminated (by the antenna or the radio) with an impedance that matches the characteristic impedance of the feedline. This ensures that as a wavefront reaches the end of the feedline it's fully absorbed and none of it is reflected back. Since there are ideally no reflections of energy in this configuration, resonance can't happen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are of course counterexamples. Non-resonant antennas exist in some applications, especially when the antenna must be physically small, or in receive-only applications where efficiency isn't as important. And transmission lines can be used to introduce controlled phase shifts into the signal, for example to make phased arrays or matching networks, and for this they must be cut to specific lengths that depend on frequency.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8717" LastEditDate="2018-11-06T21:10:31.213" LastActivityDate="2018-11-06T21:10:31.213" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="12201" PostTypeId="2" ParentId="12198" CreationDate="2018-11-06T20:32:02.800" Score="27" Body="&lt;p&gt;An excellent question! Without diving too deep into the theory, let's start with a few basic terms. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;signal&quot; that an antenna is receiving or transmitting is called an electromagnetic wave. This is exactly the same type of wave as light. It is just that our eyes are sensitive to a narrow range of frequencies that we call light. Electromagnetic waves that are lower in frequency behave exactly the same but we cannot see them. These lower frequencies are generally called RF (radio frequencies). Antennas are used to radiate (transmit) and receive electromagnetic RF signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cable or wire that goes between the antenna and a receiver or transmitter is called a transmission line. We use this term even if the cable is simply used for receiving purposes. A transmission line is specifically designed to not radiate an electromagnetic wave but only transport it from one end of the transmission line to the other. There are several types of construction that can meet this requirement but you are probably most familiar with &lt;a href=&quot;https://en.wikipedia.org/wiki/Coaxial_cable&quot; rel=&quot;nofollow noreferrer&quot;&gt;coaxial cable&lt;/a&gt; - the same type of cable that is used for &quot;cable TV&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/H0CrK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/H0CrK.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of the coaxial cable, the outer shield keeps the electromagnetic wave contained between the outer shield and the inner conductor. And as it does so, the electromagnetic wave moves from one end of the cable to the other. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The device that generates the electromagnetic wave is called the source. This could be a transmitter or, when receiving a signal, it is the antenna. At the other end of the transmission line is the load. When transmitting, the antenna is considered the load and when receiving it is the receiver that is the load. By convention, the electromagnetic wave travels from the source end to the load end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now armed with these few terms, we can restate your question as: Why isn't the transmission line included as part of the antenna when accounting for the length of the antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simple answer is to realize that an antenna is specifically designed to receive or radiate electromagnetic waves. And you are correct that the dimensions of the antenna play a key role in its overall performance. But now contrast this to the transmission line that is specifically designed to &lt;em&gt;not&lt;/em&gt; radiate electromagnetic waves. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can draw a comparison here to a garden hose and a sprinkler. The garden hose is specifically designed to transport the water from one end to the other without leaking any of it along the way (although I have a few hoses that seem not to have gotten that memo). The sprinkler, on the other hand, is specifically designed to &quot;leak&quot; water in a very specific pattern and volume.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope that is the level of answer you were expecting. Feel free to use the comments to ask for any clarifications or additional depth.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-30T02:22:22.050" LastActivityDate="2018-12-30T02:22:22.050" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12203" PostTypeId="1" CreationDate="2018-11-07T03:29:48.043" Score="10" ViewCount="224" Body="&lt;p&gt;I'm designing a small UHF data transceiver for the 70cm band, based on a Silicon Labs EZRadioPro Si4463 IC. Modulation is FM, 12.5kHz channel step. The concept is similar to &lt;a href=&quot;https://www.silabs.com/documents/public/application-notes/AN656.pdf&quot; rel=&quot;noreferrer&quot;&gt;SiLabs' AN656 application note&lt;/a&gt; but with a different power amp BJT as the NESG270034 and NESG250134 are obsolete.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Design goal is 1W out (+30dBm) at 3V or 5V supply, from a +13dBm or +20dBm driver source. I figure that's about 17dB of gain. 500mW would also be passable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been looking at alternatives to the RF BJT, and have hit a small problem. Many RF BJT manufacturers only provide component models for expensive commercial tools like Agilent ADS or Microwave Office. For instance, Infineon provide S2P models (which I understand are usable with RFsim99) for most of their parts, but NXP only seem to offer S2P data for their high-power (25W+) amplifiers and not for their discretes (except some discontinued ones like the BFG135).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any free or low cost tools which can be used to design the matching networks for FM UHF power amplifiers using the ADS models?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd also be interested in hearing suggestions on other UHF PA transistors I should look at but I think that might be better suited to a separate question!&lt;/p&gt;&#xA;" OwnerUserId="13541" LastEditorUserId="76" LastEditDate="2018-11-07T15:17:01.407" LastActivityDate="2020-12-04T13:35:36.977" Title="UHF FM power amplifier design without expensive software" Tags="&lt;electronics&gt;&lt;impedance-matching&gt;&lt;amplifier&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12205" PostTypeId="2" ParentId="12131" CreationDate="2018-11-07T12:23:16.823" Score="0" Body="&lt;p&gt;Antennas respond to or create electro-magnetic (e-m) fields. The intensity of the electric field component of an e-m wave can be defined as the voltage difference between two points in space separated by a linear, physical distance — typically, one meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The magnitude of the radiated e-field is a function of the values it has at two different physical locations in space, independent of a separate &quot;reference&quot; potential.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-11-07T12:23:16.823" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12206" PostTypeId="2" ParentId="12131" CreationDate="2018-11-07T15:38:43.827" Score="2" Body="&lt;p&gt;&quot;Voltage&quot; is anything measured in volts. &lt;em&gt;Electric potential difference&lt;/em&gt; requires a reference voltage because it's a &lt;em&gt;difference&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, &lt;em&gt;electric potential&lt;/em&gt;, which is also measured in volts, is defined at a single point. 1 volt is one joule per coulomb. Increasing the potential of a charged object by 1 volt requires 1 joule of work per coulomb of charge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The choice of &lt;a href=&quot;http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/gravpe.html#c1&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;zero potential&quot; is arbitrary&lt;/a&gt;, but for antenna analysis it's usually assumed to be potential at infinity. Assuming the system being analyzed has zero net charge, this is equivalent to defining zero potential as the mean potential of every point in the system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When discussing antennas, it's usually assumed the quantities discussed are RMS values of a sinusoidal oscillation. So to say &quot;electric potential is zero at the center of a dipole&quot; also means &quot;electric potential at the center of a dipole is unchanging&quot;. Which makes sense, because as one side of the dipole is increasing in potential, the other side is decreasing by a similar amount. The center has a potential in the middle of these two extremes, and since each half is changing by equal in magnitude but opposite in sign amounts, the net change is zero at the middle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not electric potential, but electric potential &lt;em&gt;difference&lt;/em&gt; that relates to current. So that the potential is zero in the middle of the dipole does not mean the charges there don't want to move. At some instant in the antenna's operation, one end of the antenna will be at a positive potential, and the other at a negative potential. All the positive charges in the middle (protons) will try to move towards the negative potential side, while the electrons do the opposite. The electrons are mobile and thus &quot;fall down&quot; the difference in potential like rocks falling down a ramp, and this gives rise to the current in the antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-11-07T15:47:18.820" LastActivityDate="2018-11-07T15:47:18.820" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12207" PostTypeId="1" AcceptedAnswerId="12208" CreationDate="2018-11-08T01:50:39.880" Score="2" ViewCount="676" Body="&lt;p&gt;I sometimes run a VHF radio net for our club, on a 145.170 MHz channel served by a repeater with a -600 KHz offset.  People who program their transceiver with the proper repeater offset mode use it with no problem. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But some people fail to use repeater offset mode. They transmit simplex on the repeater's output frequency. I hear them, because they happen to be close enough to my station that their signal reaches me simplex. But they aren't using the repeater, and others further away from them don't hear them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming I have spare radios for that band, how can I set them up to detect this situation? I want to find out that it's happening and let them know to fix their transceiver mode.  I can imagine setting a spare transceiver to listen, simplex, on the repeater's &lt;em&gt;input&lt;/em&gt; frequency. If I see that spare transceiver receive at the same time as I hear the station on the repeater's output frequency, then it's likely that station is configured correctly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if I hear a station on the repeater's output frequency, but &lt;em&gt;don't&lt;/em&gt; see the spare transceiver receive, then it could be one of two situations. Either the station is configured wrong, transmitting simplex on the repeater's output frequency, or the station is configured correctly but is distant, so their transmission makes it to the repeater but not to my spare transceiver. I don't see how to tell these two cases apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be clear (because repeater offset notation always confuses me), we publish the channel as &quot;145.170 MHz -600&quot;. That means the repeater transmits on 145.170 MHz, and receives on 144.570 MHz. Our transceivers complement this: receive on 145.170 MHz, and transmit on 144.570 MHz.&lt;/p&gt;&#xA;" OwnerUserId="719" LastActivityDate="2018-11-08T20:36:21.250" Title="How can I tell if someone is mistakenly transmitting on a repeater output frequency, instead of the (offset) input frequency?" Tags="&lt;repeater&gt;&lt;radio-programming&gt;&lt;net&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12208" PostTypeId="2" ParentId="12207" CreationDate="2018-11-08T02:04:29.883" Score="5" Body="&lt;p&gt;Some ways, roughly in order of increasing difficulty but also automatability:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Most repeaters have a &quot;courtesy beep&quot; they transmit when their squelch detects the end of an incoming transmission, followed by a period of silence. A direct transmission from a different, normal, transmitter will not have the courtesy beep and silence unless it was deliberately imitated.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The repeater will have a generally consistent signal strength and the other transmissions will likely be weaker, or at least not match exactly:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;You can observe the difference on your S-meter, if your receiver has one.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You will hear more of the noise that is characteristic of a weak FM signal than from the repeater. Of course, you can also get that noise on the way to the input of the repeater, but in my experience the noise will sound different in the two cases (because of the audio-frequency characteristics of the repeater).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Have a direction finding system. Observe that the direct transmission is coming from a different direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This could be as simple as a Yagi antenna pointed at the repeater and a second &quot;omnidirectional&quot; antenna. Connect the second antenna to a second receiver on the output frequency and notice when the ratio of signal strengths does not favor the Yagi by the normally observed amount.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some work has been done on &quot;fingerprinting&quot; transmitters using, if I remember correctly, the frequency deviations at the beginning and end of transmission as the transmitter powers up and down. You could implement this on SDR receiver hardware, and look for transmissions that do not match the characteristics of the repeater's transmitter.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-11-08T15:05:56.310" LastActivityDate="2018-11-08T15:05:56.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12209" PostTypeId="2" ParentId="12207" CreationDate="2018-11-08T02:31:11.930" Score="2" Body="&lt;p&gt;It is highly unlikely that the station transmitting on the output of the repeater will have exactly the same signal strength as the repeater transmitter. Simply monitor the signal strength of the transmission and if it is not typical for the repeater output, the station is likely transmitting on the output.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-11-08T02:31:11.930" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12211" PostTypeId="1" CreationDate="2018-11-08T13:05:56.597" Score="2" ViewCount="146" Body="&lt;p&gt;In the summer of 1974 I worked as a water taxi operator in Howe Sound with the headquarters in Horseshoe Bay. One of the requirements of employment required me to get what I remember as being a &lt;strong&gt;Restricted Radio License&lt;/strong&gt; for operating the radio communication equipment between the vessels and HQ. My understanding at the time was that the license was valid for life. I have lost my records of this license and wish to inquire where and through what avenue, so I may secure a copy... and even if the license is still valid in 2018. &lt;/p&gt;&#xA;" OwnerUserId="13578" LastEditorUserId="76" LastEditDate="2018-11-08T14:03:09.230" LastActivityDate="2018-11-11T04:42:43.943" Title="I received a RESTRICTED RADIO LICENSE in 1974. Is it still valid?" Tags="&lt;license&gt;&lt;canada&gt;" AnswerCount="2" CommentCount="0" ClosedDate="2018-11-11T14:30:05.120" ContentLicense="CC BY-SA 4.0" />
  <row Id="12212" PostTypeId="2" ParentId="12211" CreationDate="2018-11-08T16:42:01.650" Score="1" Body="&lt;p&gt;According to &lt;a href=&quot;https://www.tc.gc.ca/eng/marinesafety/oep-navigation-radiocomms-faqs-1489.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this Canadian government web site&lt;/a&gt;, marine radio licenses are no longer required for vessels operating in Canadian waters only, and not the territorial waters of another country.  If you're planning to travel to another country, then the thing to do is probably to contact Industry Canada to see if your license is still valid.  (Here's a link to their &quot;&lt;a href=&quot;http://www.ic.gc.ca/eic/site/icgc.nsf/eng/h_07026.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;contact us&lt;/a&gt;&quot; page.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-11-08T16:42:01.650" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12213" PostTypeId="2" ParentId="12207" CreationDate="2018-11-08T20:36:21.250" Score="3" Body="&lt;p&gt;Some repeaters filter the CTCSS tone. If that's the case, then if you detect one, then it isn't going through the repeater. Some repeaters use a different tone on the output than on the input...also a way to tell.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-11-08T20:36:21.250" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12214" PostTypeId="2" ParentId="12169" CreationDate="2018-11-09T03:36:39.567" Score="2" Body="&lt;p&gt;Looking at an Amazon listing, it appears that the Degen 31MS active antenna has three ways to connect to a radio. The first is via a direct ANT jack, the second is via clips to existing wire (likely telescoping) antennas, and the third is some sort of ferrite bar coupler that you're mentioning. A brief search didn't bring up a user manual or anything like that (link?). My guess of what their coupler is, without anything physical in hand to examine, and without any documents to support, is that it's an external ferrite bar with a number of copper wire turns wrapped around it, to be placed over the location of the internal antenna of your radio receiver to couple signal into the receiver. A quasi-transformer, if you will. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To make something like that is fairly simple - all you need is a ferrite bar. Where would you find one? Well... many old AM/FM clock radios or the like used these bar antennas for reception. Take one apart and you'll probably find one. Simply connect up the two ends of the coil to the leads from your Degen, and off you go. Or just buy a bar and a spool of copper wire, and start winding.&lt;/p&gt;&#xA;" OwnerUserId="13420" LastActivityDate="2018-11-09T03:36:39.567" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12215" PostTypeId="2" ParentId="7333" CreationDate="2018-11-09T08:39:27.767" Score="-1" Body="&lt;p&gt;There are some useful charts on this web page which show the additional loss V SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.astrosurf.com/luxorion/qsl-transmission-line2.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.astrosurf.com/luxorion/qsl-transmission-line2.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;G4KUY&lt;/p&gt;&#xA;" OwnerUserId="13580" LastActivityDate="2018-11-09T08:39:27.767" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12217" PostTypeId="1" CreationDate="2018-11-10T11:11:38.093" Score="0" ViewCount="377" Body="&lt;p&gt;As titled, I'd like to explore the output power of a simple diode-based rectifier circuit, excited by an antenna (assumed to be 50 ohm impedance). Please give me some advice as to how to do this. It is related closely to the simulation modes, isn't it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1/ Harmonic balance mode:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;To get the numerical values of power ( Pout= Vout * Iout): Harmonic balance is the best?&lt;/li&gt;&#xA;&lt;li&gt;Is it correct to model the antenna as a P_1tone as the following screenshot? Is it correct that the input power to the rectifier can be varied by varying that power source?&lt;/li&gt;&#xA;&lt;li&gt;Same question, with multi-band antenna. How to model it in HB mode?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;2/ S parameter mode:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;To get the response in terms of S-para and Z, it is the best?&lt;/li&gt;&#xA;&lt;li&gt;Same question with the above questions, with 1-band and multi-band antennas? In my simulation, I simply used a 50-ohm terminal to model the 1-band antenna, but not quite sure it is correct. And I don't know how to deal with multi-band ones.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'd highly appreciate if someone could help me in these.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/BniVo.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BniVo.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11740" LastEditorUserId="8717" LastEditDate="2019-11-06T02:14:48.523" LastActivityDate="2019-11-06T02:14:48.523" Title="ADS Simulation: How to model an antenna in a simple rectifier circuit?" Tags="&lt;antenna&gt;&lt;electronics&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12218" PostTypeId="1" CreationDate="2018-11-10T15:14:05.230" Score="5" ViewCount="2157" Body="&lt;p&gt;I'm really new to this, and I was wondering how the whole PTT system works? I have a headset with microphone, and a Baofeng UV-82 radio. I know the radio has its own PTT button, but is there any kind of PTT button that could be attached to it via wire as simply as possible?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="13584" LastEditorUserId="76" LastEditDate="2018-11-10T16:43:20.800" LastActivityDate="2019-01-15T00:18:01.610" Title="How do PTT buttons work?" Tags="&lt;baofeng&gt;&lt;transmitter&gt;&lt;audio-interface&gt;&lt;microphone&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12219" PostTypeId="2" ParentId="12218" CreationDate="2018-11-10T15:40:56.563" Score="14" Body="&lt;p&gt;The basic PTT (push to talk) button on the HT is a simple switch that is normally open and when it is pressed, the switch is closed (conducting). Internally to the radio, this applies power to the PA (power amplifier) stage of the transmitter, it idles the receiver, it switches the frequency synthesizer to generate the correct transmit frequency and a number of other &quot;housekeeping&quot; actions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An external PTT switch is easily added. Here is a nice diagram from the &lt;a href=&quot;http://www.miklor.com/COM/UV_Technical.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;miklor.com&lt;/a&gt; site.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iXqFR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iXqFR.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see the switch to the far left of the circuit. It is wired to the outer most &quot;ring&quot; of each plug. Closing (pressing or toggling) that switch will cause the radio to transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the schematic from the same site showing the dual PTT and the optional data connection:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gxtL2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gxtL2.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-15T00:18:01.610" LastActivityDate="2019-01-15T00:18:01.610" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12220" PostTypeId="2" ParentId="12217" CreationDate="2018-11-10T16:07:49.140" Score="2" Body="&lt;p&gt;In order to properly model an antenna in your example, you need to be very specific as to the type of antenna and its installation details. Once this is specified, the antenna can be modeled as a signal generator with a source impedance equal to the characteristic impedance of the antenna. If it is a common antenna with a typical installation, you may be able to look up the impedance. If not, you will need to model the antenna with a tool such as &lt;a href=&quot;https://www.eznec.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal level available from the receive antenna will also depend upon its irradiance due to distance, applied power, directivity, efficiency, and polarity of the transmitting antenna. These values can be applied to the &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Friis&lt;/a&gt; equation in order to resolve the maximum power available from the receive antenna when the transmit and receive antennas are within line of sight with each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For multi band applications you simply iterate through the above for each band involved.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-11-11T14:45:57.870" LastActivityDate="2018-11-11T14:45:57.870" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12221" PostTypeId="2" ParentId="12211" CreationDate="2018-11-11T04:42:43.943" Score="1" Body="&lt;p&gt;I suspect that you're referring to the Canadian &quot;Restricted Radio Operator's&quot; licence. This is a certificate of proficiency for operators of licenced aeronautical radios and in the past there were versions for maritime and commercial radio operators. I suspect that you probably had the now-obsolete maritime version for your job as a water taxi operator. The RRO licence doesn't grant any frequency privileges (it's not an Amateur Radio licence), any radio you choose to operate would still be subject to licencing for whatever radio service it's classified in so I can't see the RRO licence being of any use to you now. According to the current information for the RRO licence: &quot;Contact your local district office of Industry Canada if your certificate is lost or requires replacement&quot;. The current RRO licence information is available at: &lt;a href=&quot;https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01397.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01397.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13585" LastActivityDate="2018-11-11T04:42:43.943" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12224" PostTypeId="2" ParentId="12198" CreationDate="2018-11-11T23:34:09.180" Score="4" Body="&lt;p&gt;RF signals have no consciousness so they really don't know anything. All they can do is follow the laws of physics. When a signal is traveling in a transmission line conductor there is another signal of equal amplitude and opposite direction (phase) traveling in the other conductor close by. The RF fields from those two signals (almost) cancel so no (or very little) energy is lost to radiation from a transmission line. But suddenly those two signals split up and go off at right angles to each other at the dipole feedpoint so there is no other field close by to cancel the antenna's fields. Both signals are now free to radiate their fields as RF signals propagating through the air - and they do just that. When in the transmission line, the RF signals in each wire are traveling in opposite directions, i.e. are differential. But when one wire takes a 90 degree left hand turn and the other takes a 90 degree right hand turn, it results in the two currents flowing in the same direction, i.e. changes them to radiating antenna currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So when does the feedline have an effect on the system and when does it not have an effect? If the feedline SWR is 1:1, it is called &quot;flat&quot; and the feedpoint impedance of the antenna equals the Z0 characteristic impedance of the feedline. This is called the &quot;matched line&quot; case and if there are no common mode signals present, the feedline has very little effect on the conditions surrounding the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if the SWR on the feedline is not 1:1, the feedline becomes a &quot;tuned feeder&quot; and is an active part of the antenna system the length of which determines such things as resonant frequency and the impedance seen by the source transmitter. Some of this effect is explained on my web page at:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w5dxp.com/notuner/notuner.HTM&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w5dxp.com/notuner/notuner.HTM&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2018-11-17T21:01:54.670" LastActivityDate="2018-11-17T21:01:54.670" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12225" PostTypeId="1" CreationDate="2018-11-11T23:52:02.800" Score="3" ViewCount="560" Body="&lt;p&gt;My unit is 25' by 25' each side and the front is 22' across. The overhang is about one foot with aluminum and vinyl underneath. If I wrap an OCF dipole (fed with 4:1 balun) around this overhang in close proximity to the aluminum support angle, how will all this affect the antenna? Most of my operating will be QRP - 5 watts or less. I am trying to &quot;hide&quot; most of the antenna. &lt;/p&gt;&#xA;" OwnerUserId="13592" LastEditorUserId="8717" LastEditDate="2018-11-17T21:53:10.273" LastActivityDate="2018-11-17T21:53:10.273" Title="Will wrapping an antenna around my house next to metal affect it?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12226" PostTypeId="2" ParentId="1410" CreationDate="2018-11-12T00:03:02.830" Score="2" Body="&lt;p&gt;For those of you with EZNEC or some other antenna modeling software, there is a way to answer this question using EZNEC. Model a 1/4WL stub in free space taking care not to violate any geometry checks. Put a 100w source at one end of the stub and a 10 megohm load at the other end of the stub. Adjust the stub length and user defined wire loss to obtain the resistive feedpoint impedance of a dipole looking into the stub. Then display the load data. It will tell you the voltage at the end of a dipole. I set my 4 MHz stub for 70 ohms and got 879 volts across the 10 megohm load resistor. The additional user defined wire loss is equivalent to the power lost from the dipole through radiation.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2018-11-12T00:03:02.830" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12227" PostTypeId="2" ParentId="12157" CreationDate="2018-11-12T00:15:44.000" Score="1" Body="&lt;p&gt;The voltage at the feedpoint of a 1/2WL dipole is only not zero if the dipole is fed in the center. If the dipole is not fed in the center, the voltage at the center is indeed zero volts. For a 100% plumber's delight beam, the driven element is usually fed with a gamma match or a delta match and the voltage in the center is indeed zero volts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feedpoint of an antenna is not a point. It is actually two points. Halfway between those two points, the voltage is zero.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2018-11-12T01:55:32.963" LastActivityDate="2018-11-12T01:55:32.963" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12228" PostTypeId="2" ParentId="12193" CreationDate="2018-11-12T00:39:59.427" Score="0" Body="&lt;p&gt;The voltage at the feedpoint of a center-fed 50 ohm dipole driven by 100 watts is 70.7 volts RMS. If you gamma feed that same dipole, the voltage at the center is zero. At that center point in a gamma fed dipole, all of the RF energy existing at that point is in the magnetic field and zero in the electric field. At the tips of the dipole where the current is necessarily zero, all of the RF energy existing at those points is in the electric field. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These points, above, exist on a plane that is perpendicular to the dipole. The MOM (method of moments) equations indicate that the electric field, associated with voltage, on the plane drawn between the two (perfectly balanced) feedline wires at the center point of the balanced dipole will undergo complete destructive interference and therefore be zero at all points on that plane. The conservation of energy principle tells us that if there is zero electric energy at all points on that plane, then all of the existing EM energy has to be in the magnetic field associated with the current. Of course, at the center plane of the dipole, there is a time where the electric field is zero while the instantaneous magnetic field is zero indicating that any existing EM energy is located somewhere other than on that center plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the animation in &quot;How can the voltage at the center of a resonant half wave dipole be zero if the input impedance is 75 ohms?&quot;, one can see that there are times when the voltage is zero all along the dipole and times when the current is zero all along the dipole. When the voltage is zero, the E-field is zero and all of the EM energy is in the H-field. When the current is zero, the H-field is zero and all of the EM energy is in the E-field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that, unlike voltage and current where we use the dot product for power,  when we are dealing with E and H fields, the power is proportional to the cross product, so either E or H can be zero and power (energy) still exist.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the feedpoint of a center-fed dipole is not a point - it is two points with a space (insulator) in between the two points. Ideally, at the point at the center of the insulator, the electric field is zero just as it is with a gamma feed. Since the voltage is proportional to the electric field, the voltage would also be zero as it is with a gamma feed. If the dipole is fed with coax and no balun at the feedpoint, this ideal situation probably will not exist.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer the question: There is negligible difference in the radiation patterns between a properly center-fed dipole and a properly gamma-fed dipole.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2018-11-14T15:09:46.930" LastActivityDate="2018-11-14T15:09:46.930" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12229" PostTypeId="2" ParentId="12112" CreationDate="2018-11-12T00:51:00.563" Score="4" Body="&lt;p&gt;Look closer at the diagram. At the two wires coming from the source, the voltage is NOT always zero. The only way for the voltage at the center &lt;strong&gt;point&lt;/strong&gt; to be zero is for the two source wires to occupy the same &lt;strong&gt;point&lt;/strong&gt; which is impossible. Think about the voltage as an electric field which is indeed zero at the &lt;strong&gt;point&lt;/strong&gt; halfway between the two wires.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2018-11-12T00:51:00.563" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12230" PostTypeId="2" ParentId="12110" CreationDate="2018-11-12T01:26:21.783" Score="4" Body="&lt;p&gt;Andrew, a dipole is a standing wave antenna. That means that the energy existing on the dipole that hasn't been radiated is in standing waves which do not change phase. The equation for a standing current wave is &lt;span class=&quot;math-container&quot;&gt;$I(x,t) = I_{\max} \sin(kx) \cos(\omega t)$&lt;/span&gt;. The distance &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt; determines the magnitude of the standing wave, not the phase. Only time determines the phase. At any instant in time, the phase of the standing wave is the same all up and down the length of the antenna. At resonance, the standing wave voltage and standing wave current are everywhere in phase. The forward current and reflected current are coherent phasors of close to equal magnitudes rotating in opposite directions. It's obvious that their sum would have constant phase. Same is true for the forward and reflected voltage phasors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Phase has two different meanings for this context. The amplitudes of the voltage standing wave and current standing wave are out of phase in time but the phase of the voltage standing wave and current standing wave are in phase, i.e. equal in time.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorDisplayName="user4168" LastEditDate="2019-01-24T04:20:11.810" LastActivityDate="2019-01-24T04:20:11.810" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12232" PostTypeId="2" ParentId="12122" CreationDate="2018-11-12T15:19:45.387" Score="2" Body="&lt;p&gt;The relationship between wavelength and frequency of an RF signal is the speed of light. One wavelength equals the speed of light divided by the frequency. If the medium in which the light (or radio wave) is traveling is something other than free space, the velocity factor of the medium can slow down the speed of light. Transmission lines have a velocity factor ranging from about 0.66 to about 0.95, i.e. transmission lines slow down the speed of light. One wavelength is one cycle of RF and is thus 360 degrees. We often need a certain number of degrees of transmission line at a certain frequency to accomplish a certain task, like matching an antenna to a transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An example might help. I use a Smith Chart to determine that I need a length of 146 degrees of 300 ohm twinlead to match my 39 foot dipole on 20m. The Velocity Factor (VF) of my 300 ohm twinlead is 0.83. I calculate one wavelength of that twinlead on 20m as VF*c/f = 0.83*984/14.2 = 57.5 feet. Since one wavelength equals 360 degrees, the length I need is 57.5(146/360) = 23.32 feet. This length will satisfy my goal of a 50 ohm SWR less than 2:1. I can add any reasonable Number of 1/2 wavelengths (N*57.5/2) and still have a 50 ohm SWR of less than 2:1. In the above equation, c is the speed of light in free space and f is the target frequency in MHz.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2018-11-12T22:39:20.187" LastActivityDate="2018-11-12T22:39:20.187" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12234" PostTypeId="2" ParentId="12225" CreationDate="2018-11-13T03:35:36.493" Score="2" Body="&lt;p&gt;It is nearly impossible to accurately model this configuration but some general observations can be made.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Placing any antenna, including an OCFD, in very close proximity to other metal objects will generally detune the antenna. This will typically negatively impact the expected SWR- especially in a multiband configuration such as an OCFD. While SWR is not an indication of antenna performance, an elevated SWR may lead to higher feed line loss and may necessitate the need for additional matching measures such as a tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Altering the geometry of a wire antenna, such as wrapping it around a house, will also detune the antenna but more importantly, it will alter its directivity. The impact of this changed directivity is hard to predict - it could prove beneficial in covering more directions, for example. The venerable G5RV dipole design by Louis Varney exploited this type of feature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When running a low power transmitter, these antenna compromises become more significant. But with that being said, every antenna has compromises. You may wish to simply experiment with your OCFD design to see how it works for you. Having an antenna analyzer available will provide you greater insight as you experiment.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-11-13T04:47:56.920" LastActivityDate="2018-11-13T04:47:56.920" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12235" PostTypeId="1" AcceptedAnswerId="12236" CreationDate="2018-11-13T09:18:47.257" Score="5" ViewCount="698" Body="&lt;p&gt;I live in Moscow, Russia and use DIY indoor magnetic loop antennas to listen amateur radio. Recently I received quite strong signals from Italy (20m, IV3UTV) and Slovenia (40m, S51CK), both operators are ~2000 km from me. One thing I don't quite understand is that both countries are south-west from me, and the antenna is hanging on a window that faces east.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see two possibilities. There is a tall concrete building not far away that probably could reflect those signals. Or maybe short waves can just pass through my building? What explanation is more plausible?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I tried to find the answer on my question using Google. Everyone is telling on how short waves reflect off the ionosphere, but I didn't manage to find the information on how they behave when they meet a concrete building.)&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="76" LastEditDate="2018-11-13T15:28:06.517" LastActivityDate="2018-11-13T15:28:06.517" Title="Do short waves pass through or reflect off concrete buildings?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;magnetic-loop&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12236" PostTypeId="2" ParentId="12235" CreationDate="2018-11-13T10:59:04.703" Score="8" Body="&lt;p&gt;The concrete is relatively transparent to radio waves of such large wavelengths (it attenuates, it doesn't reflect). However, &lt;strong&gt;steel&lt;/strong&gt; bars within concrete typically convert that concrete to a solid reflector from the perspective of a wave with such a large wavelength. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, that effect scales: Just as your microwave oven's front door has a metal plate with holes that are too small for microwave radiation to actually pass through, when you scale up from ca 20 cm microwave oven wavelength to 20 m shortwave wavelength, you can scale up your metal bar spacing, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, your way of thinking &quot;what specifically is it reflected off&quot; isn't 100% right. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When wavelengths are larger or in the same order of magnitude as obstacles (houses, walls, towers, trees, trucks, trains…), you start noticing that ray optics doesn't really represent the way electromagnetic waves work; you get diffuse effects such as refraction, and with a lot of obstacles, even in the optic model, you get more effects like scattering than specular reflections.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-11-13T10:59:04.703" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12237" PostTypeId="1" AcceptedAnswerId="12265" CreationDate="2018-11-13T13:05:38.640" Score="1" ViewCount="162" Body="&lt;p&gt;I'm using symbol sync block (symbol_sync_ff) on my project and i use many different sps values that i need reset on runtime.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm trying to reset sending clock_est tag. Is this the right way to reset the sps value?&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;key = pmt.intern(&quot;clock_est&quot;)&#xA;value = pmt.to_pmt((0.0, 45.0))&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="13599" LastActivityDate="2019-05-20T17:04:25.940" Title="Reset the sps on symbol sync block GNU Radio" Tags="&lt;rtl-sdr&gt;&lt;gnuradio&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12238" PostTypeId="2" ParentId="12237" CreationDate="2018-11-13T14:55:53.807" Score="1" Body="&lt;p&gt;From &lt;code&gt;gr-digital/lib/symbol_sync_ff_impl.cc&lt;/code&gt;:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;// got a clock_est tag&#xA;timing_offset = static_cast&amp;lt;float&amp;gt;(&#xA;                   pmt::to_double(pmt::tuple_ref(t-&amp;gt;value, 0)));&#xA;clock_period = static_cast&amp;lt;float&amp;gt;(&#xA;                   pmt::to_double(pmt::tuple_ref(t-&amp;gt;value, 1)));&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;So, if you want to set the timing offset to 0 and the clock period to 45, then, yep, that's the correct code. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because I think there will be future visitors to this question: Generally, the documentation can be found under &lt;a href=&quot;https://www.gnuradio.org/doc/doxygen/classgr_1_1digital_1_1symbol__sync__ff.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.gnuradio.org/doc/doxygen/classgr_1_1digital_1_1symbol__sync__ff.html&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-11-13T14:55:53.807" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12239" PostTypeId="1" AcceptedAnswerId="12241" CreationDate="2018-11-13T20:51:49.320" Score="2" ViewCount="395" Body="&lt;p&gt;I'm looking at dual band (2 m &amp;amp; 70 cm) antenna designs for my next project.  A very interesting one to me is the &lt;a href=&quot;http://wb0tge.com/?page_id=33&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mighty Woof&lt;/a&gt;, which is essentially a fan dipole made of copper pipe. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7di0a.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7di0a.jpg&quot; alt=&quot;Mighty Woof antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would the extra elements in this antenna affect the radiation pattern at all, or should it have essentially the same pattern as a regular dipole?&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="8717" LastEditDate="2018-11-13T23:25:27.497" LastActivityDate="2018-11-14T00:03:00.857" Title="Fan dipole radiation pattern" Tags="&lt;antenna-theory&gt;&lt;parallel-dipole&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12240" PostTypeId="2" ParentId="12239" CreationDate="2018-11-13T22:39:50.493" Score="3" Body="&lt;p&gt;Basically, fan dipoles &lt;em&gt;should&lt;/em&gt; have similar patterns, as only one dipole is resonant at a time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, individual dipoles in any arrangement where they all share a common feedpoint should be spaced far enough apart from each other so as to minimize the interaction between them. Whether the design that you mention has them far enough apart would have to be determined by &lt;a href=&quot;https://www.eznec.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;modeling&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that in this case, they are nearly harmonically related (3*146.6=440). &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-11-13T23:20:51.323" LastActivityDate="2018-11-13T23:20:51.323" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12241" PostTypeId="2" ParentId="12239" CreationDate="2018-11-14T00:03:00.857" Score="5" Body="&lt;p&gt;The Mighty Woof article seems to indicate that those are 1/2WL fan dipoles. Two fan dipoles will interfere if one of the dipoles is resonant on both bands. Unfortunately, 144-148 times three is 432-444 so a 1/2WL dipole on 2m will be a resonant 3/2WL &quot;dipole&quot; in parallel with a 1/2WL dipole on 70cm. It would be akin to having a fan dipole for 40m/15m on HF which I just modeled and the radiation pattern is cloverleaf. Most hams don't attempt a 40m/15m fan dipole - they just use the 40m dipole on 15m and live with the cloverleaf pattern. Seems a 1/2WL horizontal dipole used on 2m would work on 70cm the same way. If it is rotatable, you would have to remember to aim it 45 degrees from broadside on 70cm. However, if this antenna is used as a vertical, it will suffer the same fate as using a 2m 1/4WL vertical on 70cm, i.e. the take off angle will be high, something that considerably reduces the effectiveness on VHF/UHF.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2018-11-14T00:03:00.857" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12242" PostTypeId="2" ParentId="12198" CreationDate="2018-11-14T02:47:11.863" Score="1" Body="&lt;p&gt;&quot;Why doesn't the length of the cable count in addition to the length of the antenna?&quot; It is not so easy to point to the misunderstanding here. Surely the length of the feeder cable matters in some cases. In the first place, sensors for E-fields or H-fields are often described as antennas (loop antennas or whip antennas.) That is misleading because very small (in wavelength) antennas depend on using specific types of amplifiers to provide wideband coverage. For transmit they require VERY special low noise matching that makes the bandwidth VERY  limited. Many antennas used by amateurs actually use the feed line as the radiator. If there is a common mode current, (the currents on the two conductors are not exactly equal) the cable is radiating. (Or usually more important, picking up interference.)&#xA;An antenna cable that is perfectly well installed to not radiate at all might have a length that provides an impedance match to the antenna so cable length is sometimes important.&#xA;I think the &quot;simple&quot; question does not have a simple answer. With a purist attitude, the transmission cable is &quot;ideal&quot; and then its length does not matter. The &quot;ideal&quot; antenna is matched to the cable at the frequency of operation and then the cable length does not matter. There is a confusion between field sensors (active devices) and antennas. In real life nothing is ideal. As I understand it, most operators have non-ideal antennas that suffer from pick-up of local E- or H- fields because of inadequate means to force common mode currents on feed cables to be zero.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-11-14T02:47:11.863" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12244" PostTypeId="1" AcceptedAnswerId="12245" CreationDate="2018-11-14T17:20:55.693" Score="5" ViewCount="733" Body="&lt;p&gt;I'm attempting to follow this white paper in order to build an antenna. This is my first antenna and as such I have a rather simple question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.dropbox.com/s/6fpfn2p9filc9ol/DIY%20137MHz%20WX-sat%20V-dipole%20antenna.pdf?dl=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;DIY 137 MHz APT Weather satellite antenna by Adam-9A4QV&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=9WNmhfpWxdk&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=9WNmhfpWxdk&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should one of these legs go to ground and the other to signal from the coaxial cable? It's unclear to me from the diagram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SwWYe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SwWYe.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether or not the terminal block is conductive through the center horizontal plane. IE is the top and bottom legs of the antenna separated and thus one goes to signal and one to ground or are they connected in which case they both are connected to both (which I admit makes no sense)?&lt;/p&gt;&#xA;" OwnerUserId="13604" LastEditorUserId="13606" LastEditDate="2018-11-15T19:35:38.323" LastActivityDate="2018-11-15T19:35:38.323" Title="RF Antenna - V pole - Should one leg go to ground and the other to signal?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12245" PostTypeId="2" ParentId="12244" CreationDate="2018-11-14T17:43:25.407" Score="7" Body="&lt;p&gt;One leg of the antenna goes to the center conductor and the other leg of the antenna goes to the braided shield of the coaxial cable. The terminal block is just a way to make the connections, and it has two electrically separate positions. You can use any means of making the connection you have handy, as long as it is small compared to the wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Vocabulary tip: the junction between the cable (&lt;em&gt;feed line&lt;/em&gt;) and the antenna is called the &lt;em&gt;feed point&lt;/em&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;However, it's worth noting that this is a poor design. Specifically, it has no &lt;em&gt;balun&lt;/em&gt; — a device for converting between a &lt;em&gt;balanced&lt;/em&gt; device (the antenna, which as you can see is symmetric) and an &lt;em&gt;unbalanced&lt;/em&gt; one (the coaxial cable, which has an inside and outside conductor that are very different). This means that the shield of the coaxial cable will act as part of the antenna, and the performance will vary depending on how the cable is routed. It may pick up common-mode noise traveling from your receiving equipment along the cable, which can be a consideration when trying to receive weak signals from sources such as satellites.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can read more about what a balun is and how it works in this application in the question &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-11-14T17:43:25.407" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12246" PostTypeId="2" ParentId="12244" CreationDate="2018-11-14T17:44:49.697" Score="3" Body="&lt;p&gt;It doesn't matter which wire is connected to which side of the V-dipole, as they both carry the same signal information (just 180 degrees out of phase with each other).&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-11-14T17:44:49.697" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12247" PostTypeId="1" AcceptedAnswerId="12248" CreationDate="2018-11-15T04:12:19.960" Score="11" ViewCount="2054" Body="&lt;p&gt;My understanding of why movie characters say &quot;break&quot; and &quot;over&quot; during radio conversations is based on &lt;a href=&quot;https://answers.yahoo.com/question/index?qid=20090526114244AASorM7&quot; rel=&quot;noreferrer&quot;&gt;this answer&lt;/a&gt;, which says that people using half-duplex devices often will want to let others on the channel interrupt them with something more urgent rather than hogging the channel with a long transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But why say &quot;break&quot; or &quot;over&quot; rather than have the devices chirp at the end of each transmission? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My only experience with walkie talkies has been with toys like Cobra and Motorola, which chirped whenever a user let go of the transmission button.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GM85t.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GM85t.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does the protocol of saying &quot;break&quot; only exist wherever devices don't support chirping?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;I looked at &lt;a href=&quot;https://ham.stackexchange.com/help/on-topic&quot;&gt;https://ham.stackexchange.com/help/on-topic&lt;/a&gt; to see whether this question belongs on this site or elsewhere and couldn't tell.&lt;/sub&gt;&lt;/p&gt;&#xA;" OwnerUserId="13609" LastEditorUserId="13615" LastEditDate="2018-11-17T16:23:25.060" LastActivityDate="2018-12-05T14:35:04.660" Title="Why say &quot;break&quot; and &quot;over&quot; on walkie-talkies instead of an automatic chirp?" Tags="&lt;procedure&gt;&lt;etiquette&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12248" PostTypeId="2" ParentId="12247" CreationDate="2018-11-15T10:42:36.357" Score="10" Body="&lt;p&gt;&quot;Break&quot; is commonly used among amateur radio operators to mean &quot;I am not done speaking yet&quot;, such as when talking through a repeater that requires transmission breaks every minute or so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Over&quot; has a specific meaning in military communications, &quot;I expect a response from you&quot;.  Amateur operators seem to more-or-less use it in this context also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Out&quot; has a specific meaning in military communications, &quot;This conversation is finished.  Do not respond&quot;.  This is not often  used among amateur operators.  The amateur equivalent is &quot;Clear&quot; which means something along the lines of a polite &quot;I will not transmit again&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice that an auto-generated chirp cannot communicate the subtle differences between &quot;break&quot;, &quot;over&quot;, and &quot;clear/out&quot;.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2018-11-16T11:13:32.170" LastActivityDate="2018-11-16T11:13:32.170" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="12249" PostTypeId="2" ParentId="352" CreationDate="2018-11-15T12:40:27.180" Score="1" Body="&lt;p&gt;A practical solution to examine the performance of a terrestrial radio link doesn't require the consideration of very small contributors to that performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Link performance that considers the major factors such as frequency, radiated power, receive system sensitivity, free space LOS path loss, added losses due to direct path and Fresnel zone obstructions/reflections from the earth, etc can be calculated usefully by allowing  sufficient &quot;fade margin&quot; to account for temporal path loss variations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is one example of software using this approach to evaluate the expected performance of an FM broadcast station for the conditions shown there.  The analysis includes the effects of terrain elevations along the great circle path between the transmit and receive antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that despite a significant obstruction to the LOS path and Fresnel zones, the fade margin calculated for this application exceeds 20 dB — which would permit very high link reliability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hlMOX.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hlMOX.gif&quot; alt=&quot;Longley-Rice Path Analysis&quot;&gt;&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2018-11-15T12:49:16.627" LastActivityDate="2018-11-15T12:49:16.627" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12250" PostTypeId="2" ParentId="352" CreationDate="2018-11-15T13:15:11.740" Score="2" Body="&lt;p&gt;Let me take the later question out of the title.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;how do I make one?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;By using a tool, such as &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.ve2dbe.com/rmonline.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio Mobile Online&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.ve2dbe.com/rmonlineinfoeng.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Help is here, you don't need a free account to read it&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This is a free tool, and will work for Amateur Radio frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you get started, in order to display a &quot;Link&quot;, you do the following&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Use &quot;New Site&quot; from the main menu to setup both TX location and RX location&lt;/li&gt;&#xA;&lt;li&gt;Use &quot;New Link&quot; from the main menu to setup a new link.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This will get you a nice graphical representation of your link, and accompaning data which was used for its calculation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;YMMV.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2018-11-15T13:15:11.740" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12251" PostTypeId="2" ParentId="12029" CreationDate="2018-11-15T13:24:49.973" Score="0" Body="&lt;p&gt;One can look at a signal in the time domain and, if it is not a perfect sine wave, Fourier analysis tells us that more than one frequency exists. For instance, a square wave contains the fundamental frequency plus many odd harmonics which can be seen on a spectrum analyzer - a device that effects a Fast Fourier Transform (FFT) on the signal from the time domain to the frequency domain.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a plot of an AM signal in the time domain and in the frequency domain. It is obvious from the time domain graph that the carrier signal Amplitude is being Modulated (AM). The frequency domain graph makes it clear that the modulation frequency is a single sine wave that creates the two sidebands characteristic of an amplitude modulated signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ni.com/cms/images/devzone/tut/am1.JPG&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ni.com/cms/images/devzone/tut/am1.JPG&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Seems to me that mixer products are &lt;strong&gt;&lt;em&gt;intuitively obvious&lt;/em&gt;&lt;/strong&gt; when displayed in the frequency domain, i.e. seeing is believing. $25 SDR dongles plus free software running on a PC provide a great visual learning experience about carriers and sidebands from DC to 1+ GHz.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2018-11-15T13:24:49.973" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12252" PostTypeId="1" AcceptedAnswerId="12257" CreationDate="2018-11-15T15:47:48.793" Score="8" ViewCount="561" Body="&lt;p&gt;I need to calculate the antenna gain in both dimensions: azimuth and elevation.&#xA;The datasheet of the antennas I am using has two different radiation patterns, one for the elevation and one for the azimuth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the two angles I can derive 2 different values of gain, but then I don't know how to compose these values to obtain the overall gain. &#xA;Should I sum them? Should I interpolate them?&lt;/p&gt;&#xA;" OwnerUserId="13611" LastEditorUserId="9493" LastEditDate="2018-11-16T06:54:00.060" LastActivityDate="2018-11-18T00:47:13.947" Title="How to derive antenna gain from radiation pattern" Tags="&lt;antenna&gt;&lt;radiation-pattern&gt;&lt;path-loss&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12255" PostTypeId="2" ParentId="12225" CreationDate="2018-11-16T04:13:19.577" Score="2" Body="&lt;p&gt;Sounds like you face the challenges of many hams worldwide who are trying to get in on the fun while not irking the neighbors, landlords, and/or HOA rules; so firstly, relax and know that you will still have fun and make some contacts with the wire antenna you describe.  after all, it's 'amateur' radio because we don't have to have a perfect setup to enjoy our hobby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will definitely notice that even a carefully-pruned antenna will detune and behave outside the predicted patterns of that same antenna in (mostly) free space.  Anything generally within 1/4-wavelength of your antenna will usually interact with it.  Basically, the nearby aluminum support angle will absorb some of that transmitted RF energy.  It should be noted that loop designs like quad antennas or horizontal loops are less prone to interacting with nearby objects, so if I were you I would compare, in modeling software, your OCF dipole with a horizontal loop that follows the perimeter of your home.  You would still want to use the 4:1 balun at the feedpoint (and you will want to model this as well).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NePLg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NePLg.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I highly recommend learning to use antenna modeling software.  use it not just to model the antenna in free space, but you can also model other metallic objects so you can get a better sense of what you're up against.  For me, modeling antennas has helped me decide on what to build and what to retire from my antenna farms.  It has helped me avoid some major pitfalls before I even went outside to put up an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're a Linux user, there are a number of antenna modeling applications free for the download:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://radio.linux.org.au/?sectpat=antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna modeling software for Linux&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For Windows, I highly suggest 4nec2, also free:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.qsl.net/4nec2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;4NEC2 site&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Macintosh users rejoice, there is cocoaNEC:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w7ay.net/site/Applications/cocoaNEC/&quot; rel=&quot;nofollow noreferrer&quot;&gt;cocoaNEC site&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, try putting that antenna up there and see how it goes!  It might not be perfect but it will still be better than no antenna.  &lt;/p&gt;&#xA;" OwnerUserId="13615" LastEditorUserId="8717" LastEditDate="2018-11-17T21:30:10.240" LastActivityDate="2018-11-17T21:30:10.240" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12256" PostTypeId="2" ParentId="6543" CreationDate="2018-11-16T05:27:31.183" Score="1" Body="&lt;p&gt;I do a lot of off-network travel and one thing I found out is that you can &lt;a href=&quot;https://support.google.com/maps/answer/6291838?co=GENIE.Platform%3DAndroid&amp;amp;hl=en&quot; rel=&quot;nofollow noreferrer&quot;&gt;cache Google Maps as described on this link&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then your Google Maps app will keep running as long as you have GPS (and if you don't you likely have bigger problems).  &lt;/p&gt;&#xA;" OwnerUserId="13615" LastActivityDate="2018-11-16T05:27:31.183" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12257" PostTypeId="2" ParentId="12252" CreationDate="2018-11-16T06:50:29.273" Score="4" Body="&lt;p&gt;First a bit of context regarding terminology.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In antenna engineering, we use the term &quot;loss&quot; to refer to RF energy that is lost as heat. This is typically an undesirable loss that creates inefficiency in the antenna system. This is the loss that Phil addressed in his (now deleted) answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When we speak about the directionality of an antenna, we use the term &quot;gain&quot;. Gain is typically expressed in decibel form and in comparison to a reference antenna such as an isotropic antenna (dBi) or a free space dipole (dBd). Even when the gain is negative, it is still referred to as gain. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I edited your question as I believe you are actually asking about the &lt;em&gt;gain&lt;/em&gt; of the antenna, not loss, and how to interpolate between the azimuth and elevation &lt;em&gt;gain&lt;/em&gt; plots (thanks for confirming this in your later comments).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Plot Styles&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some gain plots will have 0 dB as the outer circle of the plot. This is an indication that 0 dB refers to the maximum possible gain of the antenna. The actual dBi or dBd value of this gain can be determined by looking at the antenna specification sheet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another style of plot, favored by the &lt;a href=&quot;http://www.arrl.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL&lt;/a&gt; for example, shows the actual maximum possible gain on the outer circle of the plot. In this case the outer circle units should be shown as dBi or dBd.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Interpreting Plots&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By convention, unless stated otherwise, the azimuth plot shows the maximum possible gain for each direction (regardless of elevation). The elevation plot will show the maximum possible gain for a given elevation but only in the direction of the maximum azimuthal gain. To then collectively interpret these plots, you would typically start with the azimuth plot to determine the direction with the maximum gain and then look at the elevation plot to determine at what elevation angle this maximum gain occurs. These two points from the two graphs will show the same gain. No further interpretation is needed. You may also examine the elevation gain in that direction for any other elevation angle of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Other Azimuthal Directions&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are considering an azimuthal direction that does not show the maximum possible gain, you should not refer to the elevation plot as the elevation pattern at that direction may be quite different from what is shown. You should instead obtain or generate a 3D model of the antenna pattern which you can examine or slice for the direction and elevation of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Oblique Angle Gain&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Edit: Added based on further details from the OP in comments]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The azimuth and elevation plots are of little use when the direction of interest is not within the primary lobe of the antenna. In this case, I recommend using &lt;a href=&quot;https://ac6la.com/autoez.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;AutoEZ&lt;/a&gt; along with &lt;a href=&quot;https://www.eznec.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC&lt;/a&gt; to develop a model of the antennas involved. This will be an initial investment in effort that can then be quickly re-used to calculate the gain of the antenna pair at any oblique angle. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The AutoEZ tool is Excel based. It drives the EZNEC engine and allows a wide variety of &quot;what if&quot; type calculations from which you can derive tabular gain numbers for a wide range of azimuth/elevation angle pairs. You could also build in your Friis calculations into AutoEZ to give you a direct go/no-go analysis for any subscriber situation.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-11-18T00:47:13.947" LastActivityDate="2018-11-18T00:47:13.947" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12259" PostTypeId="2" ParentId="12252" CreationDate="2018-11-16T14:03:07.483" Score="1" Body="&lt;p&gt;Define the Antenna structure into a free available NEC Software like EZnec, MMANA-GAL or others and you are able to calculate everything of the radiation patterns, gain, losses, currents, voltages, resistance, the complex and real resistance of the entire antenna Building and the rf-field (E/H) shape. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, you can see shape of the E and H field and the distribution of the rf gain related by the radiation angle of the rf-field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am a Radio Amateur and must know, how the antenna's E/H near-field shape looks like.  &lt;/p&gt;&#xA;" OwnerUserId="13618" LastActivityDate="2018-11-16T14:03:07.483" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12260" PostTypeId="1" CreationDate="2018-11-17T03:34:57.447" Score="1" ViewCount="561" Body="&lt;p&gt;I've notice a couple of times over the past couple of weeks that the noise floor, particularly on 40 and 80, is exceptionally high as the grayline passes me into night. I'm looking at the general band conditions right now from qrz/spaceweather and they are showing as good for both day and night on 40/80m. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm unsure if it's something in my area or something to do with my equipment? I have a Flex 3000 connected to a Comet 250Bx and a homemade 20/40m fan dipole I made through a fairly cheap antenna switch. I was working 20/30/40M on the comet earlier today but then I returned about 30 minutes later and the noise floor had jumped. Normally I'm down around S1 but it's up at S4 and above on the waterfall and s7 on the signal meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just want to ensure something isn't awry on my equipment. There are ice crystals in the air. Not sure if that is a factor? Also when I switch to my fan dipole the noise drops but I still see the interferance (the big bit of noise on the right.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I switch to my fan dipole that noise is significantly worse on 40m. It's better on 80m. I'm guessing this is because my dipole is tuned for 20/40m. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also in a couple of days I expect this noise to slowly fall away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a picture of my 40m signal first and then 20m and finally 160m...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9iNZ8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9iNZ8.png&quot; alt=&quot;40M&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/0oioD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0oioD.png&quot; alt=&quot;20M&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/RZPqq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RZPqq.png&quot; alt=&quot;160M&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13444" LastEditorUserId="13615" LastEditDate="2018-11-17T07:24:28.710" LastActivityDate="2021-03-06T10:18:08.007" Title="High Noise Floor on 40/80m at Night" Tags="&lt;rfi&gt;&lt;noise&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12261" PostTypeId="2" ParentId="12260" CreationDate="2018-11-18T03:49:06.183" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm unsure if it's something in my area or something to do with my equipment?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Since the effect is time dependent, it is most likely RFI caused by a timed electrical device. Based on the time of day, it could be related to a lighting device such as a mercury vapor lamp, an LED light, holiday decorations or similar. It could also be some type of industrial process that is starting up at that time of day.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the spectra of the signal, you may be able to track it down with a portable radio and a short whip or loop. Before setting out in the neighborhood, turn off your main breaker and shutdown battery operated devices in your own home to make certain it is not a locally grown noise. When you are out searching for the source keep your situational awareness elevated and be cognizant of your appearance to any observers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck with the hunt!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-11-18T03:49:06.183" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12262" PostTypeId="1" AcceptedAnswerId="12263" CreationDate="2018-11-19T21:07:40.837" Score="5" ViewCount="1625" Body="&lt;p&gt;I'm going to buy Yaesu FT-891 as my first transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that I can measure SWR with it if I use FM mode and minimum power, which is 5W for this transceiver. However, I don't know whether it's always safe. For instance, if I connect a completely untuned wideband antenna, the SWR can be large and all 5W will return to the transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I also need something like an MFJ-259C for preliminary tuning of the antenna or will I be just fine with only the FT-891?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="9493" LastEditDate="2018-11-20T11:50:19.290" LastActivityDate="2018-11-21T19:54:11.067" Title="Do I need a separate SWR meter if the transceiver has one built-in?" Tags="&lt;impedance-matching&gt;&lt;swr-meter&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12263" PostTypeId="2" ParentId="12262" CreationDate="2018-11-20T13:29:54.883" Score="8" Body="&lt;p&gt;You'll be fine to start without an additional SWR meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An SWR meter doesn't provide any protection. With or without an SWR meter, you'd want to start on a new antenna on low power, then increase power only after measuring the SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't worry too much. If transmitting at much less than maximum power you won't damage anything even with the worst possible load. The peak voltage and current at low power is still less than when transmitting full power into a matched load. If you make a mistake, the radio's protection circuitry should reduce power automatically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An external SWR meter only gets you more precise measurements. Some radios only have an unlabeled bar graph for &quot;SWR&quot; which gives only a qualitative measurement. Some may not indicate SWR directly but instead are just showing the power reduction due to the protection circuitry, and thus may not indicate any issue until the power is increased. A proper SWR meter will probably show both forward and reverse power on a meter calibrated in watts, and often there's a way to adjust the range so the meters provide a useful measurement at high and low powers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wouldn't spend money on an antenna analyzer unless you are specifically interested in antenna design.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-11-20T13:29:54.883" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12264" PostTypeId="2" ParentId="9948" CreationDate="2018-11-21T02:31:37.570" Score="1" Body="&lt;p&gt;It has been reported by &lt;a href=&quot;http://spaceweather.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;the Space Weather website&lt;/a&gt; this week (late November 2018) that the first sunspots from &lt;a href=&quot;https://en.wikipedia.org/wiki/Solar_cycle_25&quot; rel=&quot;nofollow noreferrer&quot;&gt;Solar Cycle 25&lt;/a&gt; have now been seen, with an ephemeral higher-latitude sunspot with reversed magnetic polarity briefly making an appearance on Sunday (18th November 2018). From the Space Weather site, they think that the current minimum should last less than a year more, and then conditions will improve. This is exciting news for those of us who were dreading an extended minimum period!&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-11-21T02:31:37.570" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12265" PostTypeId="2" ParentId="12237" CreationDate="2018-11-21T13:47:28.070" Score="1" Body="&lt;p&gt;I found the solution to my problem: increase the max deviation value parameter in the block, because the sps range that the block allows is the nominal value +- the user specified allowed deviation.&lt;/p&gt;&#xA;" OwnerUserId="13599" LastEditorUserId="13599" LastEditDate="2018-12-21T15:17:48.003" LastActivityDate="2018-12-21T15:17:48.003" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12266" PostTypeId="2" ParentId="12082" CreationDate="2018-11-21T16:25:26.423" Score="1" Body="&lt;p&gt;Ham Radio is not broadcasting or a &quot;cloud&quot;, and each transmission must have a Control Operator actually supervising to assure no inteference.  Ham radio is non-commercial.&lt;/p&gt;&#xA;" OwnerUserId="13641" LastEditorUserId="8717" LastEditDate="2018-11-25T02:37:59.233" LastActivityDate="2018-11-25T02:37:59.233" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12267" PostTypeId="1" CreationDate="2018-11-21T16:59:32.317" Score="1" ViewCount="81" Body="&lt;p&gt;I have been monitoring power  of a P25 control channel (at about 850MHz). For awhile, 24 hours a day.  I graphed the power over a couple of weeks and it is almost sinusoidal, decreasing significantly at night, and ramping back up in the day.  This is just power, not SNR.  This seems to be the case on other frequencies I've been monitoring as well.  What causes this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm in an urban area, south US.&lt;/p&gt;&#xA;" OwnerUserId="850" LastEditorUserId="4076" LastEditDate="2018-11-21T19:02:55.577" LastActivityDate="2018-11-21T19:02:55.577" Title="Why does signal power drop every night?" Tags="&lt;propagation&gt;&lt;uhf&gt;&lt;rf-power&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12268" PostTypeId="2" ParentId="12267" CreationDate="2018-11-21T18:45:39.373" Score="5" Body="&lt;p&gt;That's a GSM band. If there's still GSM service in that band, it's very common to see Mobile Network Operators (MNOs) turn of base stations at night, effectively enlarging the remaining cells. I've witnessed that very drastically in a German city center, where telefonica used to completely switch of one of their 3G base stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is done because power consumption is the nr. 1 cost driver in established cellular networks for MNOs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;850 MHz is by now also used as LTE/4G band by sprint. LTE is even more flexible in all aspects of power management.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, you can probably simply observe the amount of power the base station observes as uplink from the cellular phones – more phones doing data or voice means more power in the air. It's really that simple. Every bit you transport needs fractions of a Joule. Transport more bits, see more power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Downlink is just the same; when there's fewer phones that get data, you can more generously assign spectrum to each user, meaning that you need less power density to service these users with the same level of service. In a deep-night scenario, it's thoroughly possible that a vast amount of the time/frequency plane is simply unused. You have to buy your spectrum allocations for the peak volume you want to service. That means you underutilize it when there's noone to request that.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-11-21T18:45:39.373" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12269" PostTypeId="2" ParentId="12262" CreationDate="2018-11-21T19:54:11.067" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm going to buy Yaesu FT-891 as my first transceiver.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Aleksander - Good choice!  I also have the same rig.&lt;br&gt;&#xA;I don't rely on the internal SWR meter of the rig - the rig meter is really rather crude, compared to the meter on a good Antenna Tuner.  My antenna is a simple dipole fed with ladder line.  I use a Tuner and match to all bands. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now for you, you are correct when you say that you will also be using an untuned antenna and with high SWR much of the energy will be returned to your rig.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At five watts, however, you will not damage the rig.  But you will lose much of that power to heat energy at high SWR.  Not the best situation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you are using an untuned dipole (fed by ladder line hopefully) you should be using an Antenna Tuner.  A good AT will have a meter on it.  I would rely on the meter on the Tuner. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You want to operate on FM?  So, that would be on six meters band?  Because I don't know of any FM operations on any lower band, perhaps some on 10 meters.  Is this decision because of your license level?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, you obviously COULD operate with using just the rig's SWR meter.  But why?  Should be a meter on the Tuner. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When tuning, I take into account the fact that with a high SWR, the rig (most modern rigs do this) will automatically reduce power to protect the rig.  That is, if the SWR is high and I have the rig set to 100 watts, the rig will automatically reduce power output to very low.  I think around 10 watts.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, when I tune to a new band, or even a new part of a current band, I will set my power way down (10 watts) to start tuning.  Only when I have a match at 10 watts, do I up the power and retune.  BTW I find that I need to retune when I raise the power.  Don't know why this is the case.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My simple advice is that if you are using an untuned antenna, you should use an Antenna Tuner to match the antenna to the rig.  The rig expects 50 ohms resistive, and the tuner converts whatever the antenna is presenting to what the rig expects.  That is, if you have expertly used your Antenna Tuner to properly tune the antenna.  And that is a whole nother question and reply.  If you ask that, I will reply to that.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;73, and happy hamming!&#xA;Joe, W3TTT&lt;/p&gt;&#xA;" OwnerUserId="8647" LastActivityDate="2018-11-21T19:54:11.067" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12270" PostTypeId="2" ParentId="2297" CreationDate="2018-11-21T20:14:41.830" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;...will probably be out of phase with the signal sent by the transmitter.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I think this might help you visualize what is happening when you have an untuned antenna and a high SWR on the line, tuned with an Antenna Tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SWR stands for Standing Wave Ratio.  An SWR of 1:1 means that the peaks and valleys of the wave are equal, which is desired.  However, a high SWR means that the peaks and valleys (nodes) have a high ratio.  If you could go along the feed line and measure the voltage (or current) at different places on the line, you would find that the voltage varied to the ratio of the SWR.  In fact, in early radio (1920, for example) this was how they actually measured SWR.  They would have a feed line and go with their measuring equipment to sample the voltages along the line.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the fact is that the Standing Waves were just that - Standing still so they could be measured.  The peaks and valleys stayed in place and didn't move around on the line.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that the power magically is in phase with itself.  The power does not jitter around like you are thinking, instead, the power organizes itself into standing waves.  Really.  I know that this goes against your common sense.  But this is the fact. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So when we say that the radio energy is bounced back and forth between the tuner and the antenna, it is in standing waves that are organized, and reach the antenna (the original signal and the bounced signals) together.  And thus are radiated together.  The bounced signals radiate a certain percentage on each bounce, so eventually are all radiated (except for heat loss in the line).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which is a good reason for using ladder line instead of coax when using a Tuner and untuned antenna.  Because coax will exhibit greater resistance and greater heat to the bouncy signals with high SWR.  Ladder line is much better in this respect. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One more thing.  The time lag between the original signal and the bounced signals is very small.  Say you are on 7.268 MHz, and say &quot;CQ&quot;. The audio will vary maybe 2 or 3 thousand times.  But the radio will vary over 7 million times.  Each cycle of audio is changed to 2 or 3 thousand radio &quot;cycles&quot;.  So if the bouncey radio Standing Waves bounce 5 or even 10 times until completely radiated, all of the bounces will be in approximately the same phase of the audio cycle.  So it doesn't really matter the time delay of the bounces.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;vry 73, &#xA;Joe W3TTT&lt;/p&gt;&#xA;" OwnerUserId="8647" LastEditorUserId="8647" LastEditDate="2018-11-21T20:24:20.643" LastActivityDate="2018-11-21T20:24:20.643" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12271" PostTypeId="1" CreationDate="2018-11-22T01:01:36.633" Score="3" ViewCount="291" Body="&lt;p&gt;Flying around the area, I noticed this from the air - I have tried doing some searching but have been unable to find the name of the design or its specific use;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is this massive antenna, and what is it used for?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://binged.it/2S5mM8W&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/p8LXo.png&quot; alt=&quot;picture of antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also what appears to be a giant Yagi in the same field, see below StreetView image with both antennas visible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.google.com/maps/@47.4939607,-122.2544781,3a,78.4y,132.2h,106.06t/data=!3m6!1e1!3m4!1sXCQsKNovOWryBiOQxij_ag!2e0!7i13312!8i6656&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5JUnC.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically, what would these types of antennas be used for? This is somewhat near the coast, (Seattle, WA) [47.493135, -122.253059] and also somewhat near an airport.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are these somehow related to aviation? Early warning defense systems? General comms?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;click the pictures for closeups, I can take actual pictures if requested&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="5618" LastEditorUserId="5618" LastEditDate="2018-11-22T15:00:16.777" LastActivityDate="2018-11-22T16:07:58.950" Title="What are these large antenna structures (used for)?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12272" PostTypeId="2" ParentId="12271" CreationDate="2018-11-22T02:48:24.483" Score="5" Body="&lt;p&gt;From the view shown it appears to be an HF discone antenna.  Characterized by sloping elements beginning at the top of the structure spaced radially around the vertical support, and topped with a capacitance hat.  &lt;/p&gt;&#xA;" OwnerUserId="11094" LastActivityDate="2018-11-22T02:48:24.483" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12273" PostTypeId="2" ParentId="12082" CreationDate="2018-11-22T14:03:49.827" Score="3" Body="&lt;p&gt;If you're going to transmit a signal in the designated amateur bands youll need an appropriste level license.  Todays levels are Techncian, General then Amateur Extra. Get Gordon Wests study materisls, or even download a study app like ham radio test prep, and go from there.  Yiu may find you enhoy the hobby beyond your research work.&lt;/p&gt;&#xA;" OwnerUserId="13653" LastActivityDate="2018-11-22T14:03:49.827" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12274" PostTypeId="2" ParentId="2297" CreationDate="2018-11-22T15:40:40.530" Score="1" Body="&lt;p&gt;&lt;em&gt;&quot;After &quot;bouncing&quot; back and forth the part of the signal that will be transmitted will probably be out of phase with the signal sent by the transmitter.&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems to be the crux of the question. The phase shift in the RF carrier caused by the reflected wave delay(s) is irrelevant because the length of the transmission line can vary the phase shift by any amount including 360 degrees if the feedline is one wavelength long. There is no HF amateur mode that I know of that depends on the phase of the RF signal for data transmission. It would be nice to be able to send a data bit with every HF RF cycle but Mother Nature seems to have other ideas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the real question is: What effect does the round trips made by the reflected waves on the transmission line have on the (audio) frequency phase of the modulation of the radiated waves?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With each round trip to the tuner and back to the antenna feedpoint, the magnitude of the reflected wave decreases until it has negligible effect. So let's assume after being re-reflected 20 times, the re-reflected wave has no effect. Let's assume that 20 re-reflections take four microseconds at the speed of light in the medium. Does it make sense that if an individual reflected wave is damped and disappears (losses and radiation) after four microseconds that it cannot possibly have much effect on a modulating signal with a cycle time of 1000 microseconds (e.g. 1000 Hz)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since we don't depend upon HF/RF phase shifts to convey any information, worrying about HF/RF phase shifts is a waste of time. Since the delay in the re-reflected waves traveling at the speed of light in the medium is negligible compared to the cycle time of our modulating waves, worrying about audio modulation frequency phase shifts is a waste of time at HF/RF (except maybe for software designers).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, at UHF and higher frequencies, re-reflections can be a problem.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2018-11-22T15:47:58.880" LastActivityDate="2018-11-22T15:47:58.880" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12275" PostTypeId="2" ParentId="12271" CreationDate="2018-11-22T16:07:58.950" Score="1" Body="&lt;p&gt;The second photo shows a Log Periodic antenna which is large enough for wide coverage of most of the HF bands.  I know that FEMA stations have these types of antennas and are primarily used for emergency communications nation wide when there is some catastrophic event.  There is such a FEMA station in Bothell Washington which several antennas including a Log Periodic.  There is also a FEMA station similarly equipped in Salem, Oregon.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2018-11-22T16:07:58.950" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12277" PostTypeId="2" ParentId="6114" CreationDate="2018-11-23T22:10:35.313" Score="1" Body="&lt;p&gt;Function FromMaidenhead(m As String) As Variant&#xA;Dim lat As Double, lon As Double&lt;/p&gt;&#xA;&#xA;&lt;p&gt;lat = (Asc(Mid(m, 2, 1)) - 65) * 10 + Val(Mid(m, 4, 1)) + (Asc(Mid(m, 6, 1)) - 97) / 24 + 1 / 48 - 90&#xA;lon = (Asc(Mid(m, 1, 1)) - 65) * 20 + Val(Mid(m, 3, 1)) * 2 + (Asc(Mid(m, 5, 1)) - 97) / 12 + 1 / 24 - 180&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FromMaidenhead = Format(lat, &quot;00.000000&quot; &amp;amp; &quot;° &quot;) &amp;amp; Format(lon, &quot;000.000000&quot; &amp;amp; &quot;° &quot;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;End Function&lt;/p&gt;&#xA;" OwnerUserId="13657" LastActivityDate="2018-11-23T22:10:35.313" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12278" PostTypeId="1" CreationDate="2018-11-24T17:07:51.900" Score="3" ViewCount="504" Body="&lt;p&gt;I have a Yaesu FT-101EE, D-104 Mike, MFJ-929 Antenna Tuner, &lt;a href=&quot;http://www.balundesigns.com/content/OCF%20Antenna.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;80-10 OCF Dipole Antenna&lt;/a&gt; with a MFJ balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When ever I key up for more than a few seconds, the wifi network goes down for a couple of minutes disconnecting any attached devices.  A couple of minutes later after transmitting, it wifi network comes back.  The router does not turn off or reset, it just seems to shut down the wifi signal.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The NetGear N600 router is in the house, the radio is upstairs in the detached garage.  I don't believe any devices are using 5 GHz.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The balun is attached to a 6' horizontal pole attached to the back of the garage, approximately 25' high. The wires run from the balun across the property behind and parallel to the house and garage. There is approximately 8' of coax from the antenna tuner to the balun. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I have been using the 80 meter band.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Any ideas on what I can do to fix this?&lt;/p&gt;&#xA;" OwnerUserId="13658" LastEditorUserId="76" LastEditDate="2018-12-25T20:02:02.533" LastActivityDate="2018-12-26T14:45:58.003" Title="My radio in the garage is temporarily shutting down the wifi when I key up" Tags="&lt;rfi&gt;&lt;wifi&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12280" PostTypeId="2" ParentId="12278" CreationDate="2018-11-25T05:46:51.613" Score="3" Body="&lt;p&gt;Sounds like the router is getting front end overload.&#xA;Either your OCF dipole is too close to the router, or you are getting common mode current on the coax and it is radiating along the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A balun on the coax in the right place might help if it is common mode current.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-11-25T05:46:51.613" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12281" PostTypeId="2" ParentId="12278" CreationDate="2018-11-25T15:51:03.377" Score="2" Body="&lt;p&gt;I agree with user10489's answer but would like to expand a bit on what to do about it. A signal of some sort appears to be interfering with something associated with the router and there does not seem to be enough information to pinpoint an exact cause.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As stated by user10489, adding a balun or common mode choke in the appropriate place(s) on the feed line (see &lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://audiosystemsgroup.com/RFI-Ham.pdf&lt;/a&gt; for far more information than I could possibly describe) would probably help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good resource on common mode chokes is &lt;a href=&quot;http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf&lt;/a&gt; .  Far more information than could be described here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, check all of the feedline, tuner, and antenna connections.  A bad connection could be the cause of the interfering signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there an ethernet wire between the wifi router and whatever is upstream of it?  If so, place a common mode choke there as well since it could be the upstream device that is having difficulty.  In fact, if it is the upstream device, any of the wires attached to it could be acting like an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before adding hundreds of € worth of common mode chokes across every wire in your house, check the connections between your radio and antenna and then run the following test:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Log in to your N600.  Go to the &quot;Status&quot; screen; look for the device ethernet address and also the list of attached devices.&lt;/li&gt;&#xA;&lt;li&gt;Key up on 80 meters.  (You are using the full 130 watts on SSB, right?) &lt;/li&gt;&#xA;&lt;li&gt;Observe the changes on the N600.  This should give you a clue where to look.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2018-11-25T15:58:08.037" LastActivityDate="2018-11-25T15:58:08.037" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12282" PostTypeId="1" CreationDate="2018-11-25T20:24:03.120" Score="5" ViewCount="304" Body="&lt;p&gt;In most schematics of ham radio receivers and transmitters the inductor is mostly given specifically as the number of turns around some certain toroidal ferrite ring (for example). This corresponds to a certain inductance, which more often than not is just a standard value, say 220uH. These exist also as &quot;lumped element&quot; components, like the ones in the picture:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xRM05m.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xRM05m.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems a precise inductance is quite difficult to achieve (with homemade coils) and measure, whereas with store-bought inductors this problem is largely gone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why are hand-wound inductors so common?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it just a nostalgia thing? Do they tolerate more power? Why don't we need to do this with capacitors as well?&lt;/p&gt;&#xA;" OwnerUserId="13372" LastActivityDate="2018-11-26T00:32:34.850" Title="Why are hand-wound coils so common if commercial inductors are available?" Tags="&lt;inductor&gt;" AnswerCount="2" CommentCount="3" ClosedDate="2018-11-26T11:06:06.580" ContentLicense="CC BY-SA 4.0" />
  <row Id="12283" PostTypeId="2" ParentId="12282" CreationDate="2018-11-25T20:38:45.493" Score="1" Body="&lt;p&gt;Speaking only for myself... I have found air-wound coils to be relatively easy to make and tolerant of misuse.  In the several instances I would have preferred to buy an inductor, I found it difficult to find something appropriate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So --for me-- it is mostly ignorance.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2018-11-25T20:38:45.493" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12284" PostTypeId="1" AcceptedAnswerId="12288" CreationDate="2018-11-25T20:53:58.807" Score="5" ViewCount="771" Body="&lt;p&gt;When designing a resonant circuit, for example as a local oscillator, the product of &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; determine the resonant frequency according to&#xA;&lt;span class=&quot;math-container&quot;&gt;$$f_{res} = \frac{1}{2\pi \sqrt{L C}}.$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means that we can reach a frequency of &lt;span class=&quot;math-container&quot;&gt;$7030 \text{ kHz}$&lt;/span&gt; for example with &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$L = 2.33 ~\mu H$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$C = 220~pF$&lt;/span&gt;, or&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$L = 23.3 ~\mu H$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$C = 22~pF$&lt;/span&gt;, or&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$L = 513 ~nH$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$C = 1~nF$&lt;/span&gt;, etc.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If we increase the inductance, the quality factor of the circuit should increase, since &#xA;&lt;span class=&quot;math-container&quot;&gt;$$Q = \frac{X_L}{R} = \frac{1}{R}\sqrt{\frac{L}{C}}.$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does the quality of the &lt;span class=&quot;math-container&quot;&gt;$LC$&lt;/span&gt; circuit continuously increase with increasing &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt;, or is there a maximum that can be reached at some &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt;-to-&lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; ratio? How do I find this ratio and wit this pick the best combination of &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; for my circuit?&lt;/p&gt;&#xA;" OwnerUserId="13372" LastEditorUserId="9493" LastEditDate="2018-11-26T03:23:31.967" LastActivityDate="2018-12-04T11:33:18.767" Title="Is there a best ratio of L to C in a resonant circuit?" Tags="&lt;electronics&gt;&lt;oscillator&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12285" PostTypeId="1" AcceptedAnswerId="12286" CreationDate="2018-11-25T21:11:21.873" Score="5" ViewCount="781" Body="&lt;p&gt;I have a lot of 'donated' coax that has been given to me with unknown provenance. I'm wondering what things I can do that can determine whether I keep it or send to the tip? Some of the things I have thought about doing are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Physical inspection - look for oxidisation of shielding braid, damage to plastic sheath&lt;/li&gt;&#xA;&lt;li&gt;Continuity testing, short circuits between inner and outer.&lt;/li&gt;&#xA;&lt;li&gt;plug into dummy load and do an SWR sweep&lt;/li&gt;&#xA;&lt;li&gt;Measure cable loss and compare against specifications&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The big one is cable loss - Any thoughts on how I can measure that cheaply? I don't have any calibrated test equipment for that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any other tests I should think about?&lt;/p&gt;&#xA;" OwnerUserId="5501" LastActivityDate="2019-12-10T20:42:48.073" Title="Testing for 'Bad' Coax" Tags="&lt;diy&gt;&lt;coaxial-cable&gt;&lt;testing&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12286" PostTypeId="2" ParentId="12285" CreationDate="2018-11-25T22:04:38.690" Score="4" Body="&lt;p&gt;You're on the right track with the first items in your list. &#xA;Assuming that you have a wattmeter and a dummy load that both match the impedance of the coax, it's a simple matter to measure the loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Measure the power with the wattmeter at the source, and then measure it again at the load. The difference between the two wattmeter readings is your loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$N_{dB} = 10\log_{10}\left(\frac{P_2}{P_1}\right)$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that this technique depends on the calibration of the wattmeter, and does not itself detect if the coax has damage leading to reflection rather than dissipation (you would want to verify the SWR is as good as without the coax, before assuming the watt figures are good).&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="4076" LastEditDate="2018-11-26T10:58:19.470" LastActivityDate="2018-11-26T10:58:19.470" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12287" PostTypeId="2" ParentId="12282" CreationDate="2018-11-26T00:32:34.850" Score="2" Body="&lt;p&gt;There is also the matter of how much current the device needs to carry. A hand-wound coil made from a few turns of relatively heavy copper (compared to the off-the-shelf devices shown in the question) will pass a lot more current than a tiny pre-bought inductor. The ones in the picture look like 1/4W or so, but you could easily put 5W into a small hand-wound coil with the same inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A hand-wound coil would also have a known (or at least calculated) Q, for which the circuit was designed.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-11-26T00:32:34.850" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12288" PostTypeId="2" ParentId="12284" CreationDate="2018-11-26T03:22:02.450" Score="7" Body="&lt;p&gt;There is no hard and fast rule. Consider that in some LC circuit applications, a lower Q may be desirable in order to achieve a wider bandwidth. In other cases, a very high Q may be desirable for narrow selectivity, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both the inductor and the capacitor in a resonant circuit may affect the Q of the circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Q of the inductor is determined by its inductive reactance divided by its series resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Q_L=\frac{X_L}{R_L} \tag1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since inductance is generally a factor of  turns squared and since the resistance of the inductor is a factor of turns, this first order analysis indicates that the lower the inductor value for a given wire type/diameter and for a given construction method, the higher the Q of the inductor. The higher the Q of the inductor, the higher the Q of the resonant circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Q of a capacitor is determined by its capacitive reactance divided by its effective series resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Q_C=\frac{X_C}{ESR_C} \tag2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In most practical cases, the ESR of the capacitor is a factor only in series resonant circuits. In a parallel resonant circuit, generally the series resistance of the inductor will dominate the Q. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a series resonant circuit, the resistive losses of the inductor and capacitor are simply added. Since you quoted the formula for a series resonant circuit, this should be your approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Q=\frac{1}{R_L+ESR_C} \sqrt{\frac{L}{C}} \tag3$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before selecting a final inductor value, make certain that its self resonance will not negatively affect your circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The insertion loss under this scenario is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{Insertion Loss} = 20\log\left({1-\frac{Q}{Q_L}}\right) \tag 4$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where Q&lt;sub&gt;L&lt;/sub&gt; is as noted above and Q is the series circuit Q as noted in the equation in your question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other factors that may come into play, depending upon the application, are the inductance and the Q of the inductor over a wide frequency range; the stability of the capacitor over a wide temperature range; and the size, weight, tolerance, cost and availability of the components.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-04T11:33:18.767" LastActivityDate="2018-12-04T11:33:18.767" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12289" PostTypeId="2" ParentId="12285" CreationDate="2018-11-26T16:21:43.870" Score="3" Body="&lt;p&gt;A cursory physical inspection and an SWR sweep are usually sufficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Blatant physical damage, like internal shorts or breaks in continuity, will be found by the SWR sweep. So in your physical inspection you're looking for things which might not impact the SWR, like outer insulation that's cut or damaged which may eventually lead to water ingress.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could measure loss, but I can't think of any likely mechanisms of loss that wouldn't also lead to anomalies on the SWR sweep, so I wouldn't worry about it too much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my experience, the problems with salvaged coax are most usually the connectors. Hams are notorious for buying cheap connectors and then installing them incorrectly. I'll wiggle the connections while the SWR sweep is running: any mechanical issues will show up as extreme spikes in the SWR. If the connectors are at all questionable I'll install new ones, and this also affords an opportunity to inspect the conductors for oxidization, an indicator of water ingress.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-11-26T16:21:43.870" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12290" PostTypeId="1" AcceptedAnswerId="12291" CreationDate="2018-11-26T16:22:07.037" Score="3" ViewCount="1510" Body="&lt;p&gt;A great many moons ago, I spent a 24 hour period with a HAM radio connected to a PC, and listening to transmissions from a massive number of sources. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of the transmissions included Morse, RTTY, SSTV with some plain audio as well... on the PC, I could scroll through a large number of frequencies, looking for interesting signals to listen in to, and potentially 'decode' using the PC to display appropriate output. The software would decode the transmission live, if I had it set to the correct option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would I need to do this now? I'd obviously need some kind of antenna and a method of connection, but this is where my knowledge fails. I've done some googling, but not knowing much about current technology, I don't know what is relevant or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be clear, I'm looking for a receive ONLY setup, with minimal financial outlay.&lt;/p&gt;&#xA;" OwnerUserId="13666" LastEditorUserId="13666" LastEditDate="2018-11-27T07:37:37.600" LastActivityDate="2018-11-27T19:39:30.420" Title="What equipment do I need to receive radio and connect to PC for listening" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;&lt;computer-control&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12291" PostTypeId="2" ParentId="12290" CreationDate="2018-11-26T17:25:45.030" Score="4" Body="&lt;p&gt;A generic search term you might use is “Software Defined Radio” or SDR (a topic which covers much more than your specific question).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equipment possibilities for your specific question includes SDR hardware that covers the frequency bands of interest and that can be connected to your PC via USB or Ethernet, SDR software compatible with the specific SDR hardware device, plus a suitable antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many SDR hardware products and vendors that cover a wide spread of performance levels and price points, from RTL-SDR USB dongles (for on the order of a couple dozen USD), to high-end SDR boxes (that cost thousands).  Which to choose depends on more specifics about your requirements (budget, frequency bands supported, sensitivity, bandwidth, broadcast and image rejection, software options, and etc.). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using a cheap RTL-SDR USB stick on HF requires either one that supports Q mode direct sampling, or an additional upconverter box.  (Note that when paying “as little as possible”, to some degree you get what you pay for in terms of signal reception.). Other less cheap but common USB connected SDR boxes might include Airspy HF+, SDRPlay, HackRF, LimeSDR, and others.  High-end SDR units might include ones from Ettus Research. (Hopefully updates and any of my omissions will be added to the comments below).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will also need SDR software running on your PC.  Many of the SDR hardware choices support multiple software application options for the PC (or Mac, or Linux/Raspberry Pi/etc., even iPhone, iPad, and Android devices) that supports the operation you describe.  Some of the SDR software applications are freeware or open source.  Some are not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some amateur radio HF rigs also include built-in capability, or allow attaching panadapters, or allow connecting to PC software via USB or stereo sound card, which may support similar functionality.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-11-27T19:39:30.420" LastActivityDate="2018-11-27T19:39:30.420" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12292" PostTypeId="1" AcceptedAnswerId="12293" CreationDate="2018-11-26T17:59:03.830" Score="2" ViewCount="621" Body="&lt;p&gt;I need to create a setup where I have three radio transceivers (869.4MHz) setup in a straight line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I need to be able to communicate, in both directions, from the centre pole to the outside two poles, and back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had planned to use &lt;a href=&quot;https://cpc.farnell.com/rf-solutions/ant-yag23/antenna-yagi-868mhz-gsm-23db/dp/RF00411&quot; rel=&quot;nofollow noreferrer&quot;&gt;yagi aerials&lt;/a&gt; but, whilst that's fine for the two outside poles, it means my centre pole has an issue as it could only face in one direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I guess I now have 3 options:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Revert to an omni aerial in the middle &lt;/li&gt;&#xA;&lt;li&gt;Use two separate&#xA;transceivers, each with its own yagi aerial, facing one in each&#xA;direction &lt;/li&gt;&#xA;&lt;li&gt;Attaching two yagi aerials to a single transceiver&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Is 3 actually viable?&lt;/p&gt;&#xA;" OwnerUserId="13667" LastActivityDate="2018-12-02T14:02:04.167" Title="Can I use two yagi aerials back-to-back for a bi-directional system?" Tags="&lt;transceiver&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12293" PostTypeId="2" ParentId="12292" CreationDate="2018-11-26T18:51:37.600" Score="8" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Two Yagi antennas on the same antenna port could work for this application.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Join the feed lines from the two antennas with a &lt;strong&gt;power divider&lt;/strong&gt; for proper impedance matching.&lt;/li&gt;&#xA;&lt;li&gt;Make sure that they are mounted in-line with each other with the two driven elements some multiple of a whole wavelength apart. This ensures that the rearward radiation of one won't partly cancel out the other.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Alternatively, you could design a single antenna which radiates in both directions. This is an uncommon application so you might not find one off the shelf, but antenna modeling software can help you verify a design before building it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest design I can think of for the purpose is an &lt;strong&gt;array antenna&lt;/strong&gt;, which contains multiple identical elements. Depending on the phasing and spacing, a row of vertical dipoles could radiate either perpendicular to or parallel to the line; often there is a reflector but you would omit that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible that an antenna designed like a Yagi (single driven element) but with two sets of directors instead of a reflector element would work well.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You might find that a simple dipole antenna at the center and Yagis at the ends give you an adequate link.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-11-26T23:25:48.497" LastActivityDate="2018-11-26T23:25:48.497" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12294" PostTypeId="2" ParentId="12148" CreationDate="2018-11-27T01:23:18.440" Score="1" Body="&lt;p&gt;Those are good questions you asked.  I can share what I've done in the past when building amps.  But first, I'd like to caution you about your plans.  By the nature of your questions, I strongly suggest you not build equipment that utilizes this level of voltage.  Too many unforgiving mistakes lie in wait that can result in lethal shock. But if you choose to proceed, please read about electrical safety first, and have someone experienced with high voltage assist with the project.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Safety message aside, now on to suggested implementations.  I infer from your question that you are asking how to convey the voltage from an external power supply to the amplifier in a safe manner.  Very good question.  Because of the voltages involved, the component choices are few.  My first amplifier I built used a Millen high voltage connector and high voltage wire used in CRT TVs at the time.  These connectors are still available surplus at places like Fair Radio Sales.  The connector worked but I was never satisfied with the wire to connector junction because the conductor was too easily exposed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I built my second amplifier, I used RG11 coax mated with an HN coaxial connector.  This arrangement is well within the 1100V you mentioned in your question.  The RG11 is rated to 5kV I believe, and the HN connector working voltage is 1500; the connector dielectric withstand voltage is also 5kV.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although I haven't used them, another option is the Alden line from Amphenol.  I recently saw two different ones on a surplus parts web site, one rated 15kV and the other 30kV.&lt;/p&gt;&#xA;" OwnerUserId="11094" LastActivityDate="2018-11-27T01:23:18.440" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12295" PostTypeId="2" ParentId="12148" CreationDate="2018-11-27T02:36:53.343" Score="1" Body="&lt;p&gt;The only safe method of doing this is to have the power supply safely inside --or directly attached to-- the same enclosure as the amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did that here with my own homebrew legal-limit HF linear amplifier. It's in a 6' rack; the 4kV power supply is on the bottom, and the amplifier is above it. No wires exposed at all.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-11-27T21:49:43.890" LastActivityDate="2018-11-27T21:49:43.890" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12296" PostTypeId="2" ParentId="12290" CreationDate="2018-11-27T09:35:24.763" Score="2" Body="&lt;p&gt;I agree with &lt;em&gt;hotpaw2&lt;/em&gt; but there's an even cheaper solution. You can also use the many different webSDR's that are around the world.&#xA;With those you only need an internet connection.&#xA;These are some places to start:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.websdr.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.websdr.org/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://sdr.hu/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://sdr.hu/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Google will give you a ton of extra possibilities.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2018-11-27T09:35:24.763" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12298" PostTypeId="2" ParentId="12290" CreationDate="2018-11-27T12:34:25.940" Score="1" Body="&lt;p&gt;Other answers here cover SDR well, but software defined radio with dedicated SDR hardware is not the only way to do radio things with a computer.  You can also take nearly any radio with a speaker output (ham radio or not) and use an audio cable to connect the radio's speaker out to your computer's sound card line in.  Many software packages (example: FLdigi, freedv) can then view the audio and decode digital modes.  This could potentially cost no more than just the audio cable if you have an existing radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to transmit as well, it may be a bit more complicated.  If your radio has a line in, it's easy, just connect a wire from your computer's speaker out to the radio's line in, and make sure that all operating system events are set to not emit sound (which might accidentally go over the radio).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your radio only has a microphone in, you will need something (like a rigblaster) to convert the computer's speaker out into the radio's microphone in, matching impedance and voltage levels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For either receive or transmit, you you may want to also control the radio from the computer.  (Software /controlled/ radio)  Many modern ham radios have a serial port on them; higher end ham radios may actually have a USB port or ethernet port which might include both control and audio.  Older radios may have a radio specific accessory port that includes serial and audio lines that can be split out to the correct connectors for your computer.  (I've built several of these for different radios after buying the necessary plugs for the radio.)&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-11-27T12:34:25.940" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12299" PostTypeId="1" AcceptedAnswerId="12303" CreationDate="2018-11-27T13:28:23.163" Score="9" ViewCount="159" Body="&lt;p&gt;To receive the amateur radio license Klasse A (HAREC) in Germany it is &lt;a href=&quot;https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Amateurfunk/AmtsblattverfuegungenAFu/Vfg812005ge228ndertdurcId8698pdf.pdf?__blob=publicationFile&amp;amp;v=4&quot; rel=&quot;noreferrer&quot;&gt;since 2005 not required anymore&lt;/a&gt; to pass a CW exam, due to a corresponding change in the Radio Regulations. However, the exam is still available as a voluntary addition to Klasse E or A.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I can legally operate in CW without this &lt;a href=&quot;https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Amateurfunk/AntraegeundFormulare/FblZulassungTeilnhmeAmateurfunkdienst_09_11_16.pdf?__blob=publicationFile&amp;amp;v=8&quot; rel=&quot;noreferrer&quot;&gt;80€ exam&lt;/a&gt;, what exactly is the purpose of offering it, if not just as a personal 'proof of accomplishment'?&lt;/p&gt;&#xA;" OwnerUserId="13372" LastActivityDate="2018-11-29T13:49:52.057" Title="What is the purpose of the German CW exam if it is not required to use CW?" Tags="&lt;license&gt;&lt;cw&gt;&lt;germany&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12300" PostTypeId="1" CreationDate="2018-11-27T13:45:03.053" Score="6" ViewCount="972" Body="&lt;p&gt;I'm in the &quot;information gathering&quot; phase of a RF Power Meter project and the design I fancy (&lt;a href=&quot;https://www.qsl.net/sz1a/download/build%20an%20rf%20power%20meter.pdf&quot; rel=&quot;noreferrer&quot;&gt;W7ZOI Power Meter&lt;/a&gt;) calls for a feed-through capacitor at the output port.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aYWO7.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aYWO7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that a feed-through capacitor is essentially a &quot;trap&quot; or low-pass filter that is typically employed to reduce RF emissions through enclosures.  They look a little like this in chassis-mount format:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eHUF1.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eHUF1.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thing is, they're not particularly common these days and tend to be expensive in my part of the world, especially when you include shipping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I have a couple of questions:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is there a more modern approach that RF designers use to isolate RF within metal enclosures?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Has anyone tried to emulate a feed-through with basic cheaper components (I'm thinking capacitors, coils and perhaps co-ax)?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="13615" LastEditDate="2018-11-29T06:55:33.483" LastActivityDate="2018-11-29T10:40:37.710" Title="Feed-through Capacitors" Tags="&lt;rfi&gt;&lt;electronics&gt;&lt;capacitance&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12301" PostTypeId="2" ParentId="12300" CreationDate="2018-11-27T14:08:43.890" Score="5" Body="&lt;p&gt;Feed-through capacitors are still commercially available but their use in commercial applications has fallen off so prices have risen over the last few years. The concept with the feed-through capacitor was to provide an RF capacitive bypass to ground while providing a stout connection through the wall of the enclosure. When I see them at a swapfest for a reasonable price, I always pick them up for future projects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your application, the purpose of the feed-through capacitor is to keep RF that may be present on the connection to the DVM from feeding back into the signal conditioning electronics. If you do not plan on using a DVM with your version, you can eliminate this connection all together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do wish to use the DVM connection, you can readily substitute an equal value capacitor connected as closely as possible to the entrance to the enclosure and grounded to the enclosure. You can enhance the bypass effect with a few ferrite beads of type 31 or 43 material or even a small toroid of the same material with a few turns of hookup wire wrapped through the center of the toroid. Position the beads or toroid as close to the entrance to the enclosure as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could perhaps improve the RF immunity by converting this connection to a shielded cable connector but most handheld DVMs only have &quot;banana&quot; style connectors so you would still introduce the possibility of RF being conducted into the conditioning electronics. Professional bench or rack type DVMs often offer a BNC style connection. If this is your case, then a shielded connector and cable would further improve the RF immunity of the conditioning electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When it comes to keeping RF out of sensitive electronics a &quot;belt and suspenders&quot; (aka belt and braces) approach is a best practice. The more preventative measures, the better the results.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-11-27T14:16:11.110" LastActivityDate="2018-11-27T14:16:11.110" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12302" PostTypeId="2" ParentId="12300" CreationDate="2018-11-27T15:32:34.303" Score="3" Body="&lt;p&gt;The reason to use a bypass capacitor instead of a simple capacitor to ground is that you'd typically want to keep the series inductance to ground as low as possible. So take this model of a capacitor with parasitic series inductors:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/U6YZZ.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fU6YZZ.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and make it something more like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/y2Giq.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fy2Giq.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(values not representative and also not equal between forms)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Leaded capacitors really have a problem acting as pure capacitor at high frequencies, simply because the leads have a high degree of inductance themselves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, elegant engineers came up with capacitors that you simply &quot;wrap&quot; around your signal line and &quot;insert into ground&quot;; your photo shows an excellent example of that. An example data sheet of different kind of three-terminal capacitors can be found &lt;a href=&quot;https://www.murata.com/~/media/webrenewal/products/emc/emifil/knowhow/20to22.ashx&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the ubiquity of SMD components and cheaply available PCB manufacturing (e.g. oshpark.com), parasitic inductivity in shunt capacitors lost their edge – as long as your working on &quot;benign&quot; frequencies (which this sub-GHz power meter does).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, this is 2018: get yourself a download of &lt;a href=&quot;https://kicad-pcb.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;KiCad&lt;/a&gt;, and input the schematic in there. Layout the matching board, using the relatively well hand-solderable 0805 size of components. Unlike the design from the article, you'd be able to have signal lines well-surrounded by ground planes with plenty of vias.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That should eradicate the need for feed-through capacitors. If you still feel like having one: I don't deem &lt;a href=&quot;https://eu.mouser.com/Passive-Components/Capacitors/Feed-Through-Capacitors/_/N-5g96Z1yzvvqx?Ns=Pricing%7c0&amp;amp;P=1z0x7weZ1z0x7orZ1z0x7vwZ1z0x75a&quot; rel=&quot;nofollow noreferrer&quot;&gt;0.11 €&lt;/a&gt; to be especially expensive, which you'd pay for an SMD feedthrough cap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's good tutorials on working with KiCad; oshpark directly accepts kicad board files.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a bit of personal commentary on the article: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think that the calibration they did is insufficient; and the resulting dynamic range they promise hence overstated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd personally would say: Buy a used power splitter from a measurement company (seems a bit more trustworthy than their thick passives in a box approach). Then, go and design a circuit around one of the plenty &lt;a href=&quot;https://www.analog.com/en/parametricsearch/10697#/p4466=0|30000000&amp;amp;p4467=1000000000|86000000000&amp;amp;p4781=|Envelope/Peak%20Detectors|non-RMS%20Responding%20Detector|Power%20Amplifier%20Controller|RF%20Log%20Detector|RF%20RMS%20Detector|RMS%20Responding%20Detector|SDLVA%20Detector&amp;amp;ps3=1.1|8&amp;amp;d=sel|0|3979|4228|4466|4467|4781|4799|4842|s8|s5&quot; rel=&quot;nofollow noreferrer&quot;&gt;existing RF power meter IC&lt;/a&gt;s – it's going to be in the same order of complexity as the device from the article you cited, but you solve a whole lot of sources of inaccuracies right from the beginning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which one you pick would really depend on the frequency range you're considering; I don't know if the device presented in the article is exactly the span you care about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd probably tend towards using a Texas Instruments &lt;a href=&quot;http://www.ti.com/product/lmh2110?qgpn=lmh2110&quot; rel=&quot;nofollow noreferrer&quot;&gt;LMH2110&lt;/a&gt;, as that really needs minimal external circuitry to measure powers. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2018-11-29T10:40:37.710" LastActivityDate="2018-11-29T10:40:37.710" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12303" PostTypeId="2" ParentId="12299" CreationDate="2018-11-27T15:49:39.677" Score="6" Body="&lt;p&gt;There still are some countries where proof of the CW exam is necessary to be allowed to operate on HF. So when you visit those countries and you want to operate under the CEPT-system you need to prove you did the CW exam.&#xA;In Belgium we are not required to do the CW exam anymore to get our HAREC licence but we also still have the possibility to pass it.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2018-11-27T15:49:39.677" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12305" PostTypeId="2" ParentId="12284" CreationDate="2018-11-28T02:24:03.287" Score="1" Body="&lt;p&gt;There is definitely a best L to C ratio. You write:&#xA;For 7030 kHz for example&#xA;L=2.33 μH and C=220 pF, or&#xA;L=23.3 μH and C=22 pF, or&#xA;L=513 nH and C=1 nF, etc.&#xA;If we increase the inductance, we can use a thinner wire for the same unloaded quality factor in all those cases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assume the unloaded Q=300 in all the cases. If you make a parallel resonator in a 50 ohm feed line the loaded Q and therefore the bandwidth will be very different in the different cases. The impedance at resonance for Q=300 is (maybe approximately, I used a nomogram)&#xA;L=2.33 μH and C=220 pF, R=3000 ohms loaded Q=5, loss=1.6%, bw=1.4 MHz or&#xA;L=23.3 μH and C=22 pF, R=30000 ohms loaded Q=1(?) loss=0, bw=80 MHz or&#xA;L=513 nH and C=1 nF, R=660 ohms loaded Q=23 loss=8% bw=300 kHz etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An unloaded LC resonator can be regarded as a series or parallel resonator. Just two components. It is the way you connect it to something else that determines which kind it is. Unloaded Q is the same. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you connect something in series with L and C (now I am doing qualified guessing) with Q=300 you should find this in a 50 ohm system on resonance:&#xA;L=2.33 μH and C=220 pF, R=0.3 ohms or&#xA;L=23.3 μH and C=22 pF, R=3 ohms or&#xA;L=513 nH and C=1 nF, R=0.066 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A resonator that has an unloaded to loaded Q ratio above 10 will attenuate by less than 10%. (0.4 dB) If the unloaded to loaded Q=2, the loss would be 3 dB and the bandwidth given by the loaded Q. Parallel or series the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One can also use an LC resonator as series and parallel at the same time. Inject a current into the resonator and take out the voltage across it. Yoy can find one example here: &lt;a href=&quot;https://www.youtube.com/watch?v=BgZUuX0tzn8&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=BgZUuX0tzn8&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-11-28T02:24:03.287" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12307" PostTypeId="2" ParentId="2257" CreationDate="2018-11-28T02:39:13.557" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;QRZ seems to be commonly used to mean “Someone other than the station&#xA;  I just worked, please call”&#xA;  This is the way I always understood it.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;but while trying to research this answer I found one document claiming&#xA;  that it is appropriate only for “could not copy previous call” and not&#xA;  for “I want someone else from the pileup now” — but I also found a &#xA;  bunch of other mutually contradictory advice.&#xA;  To me the QRZ call after a finished QSO means &quot;Call anyone, I have noticed&#xA;  there were other stations calling me b efore my lkatest QSO.&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If I did not see any other station on my waterfall after finishing a QSO&#xA;I would call CQ and not QRZ after completion.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2018-11-28T02:39:13.557" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12309" PostTypeId="1" AcceptedAnswerId="12314" CreationDate="2018-11-28T07:49:13.613" Score="3" ViewCount="2851" Body="&lt;p&gt;I would like to use a shortened whip antenna with a coil in it's base, e.g. OPEK HVT-400B. My transceiver maximum power is 100 W (and antenna's - 120 W). To make the antenna work I need counterpoise wires. As I understand using three 1/4 wavelength wires just laying on the ground in all directions with 120° between them is considered a good practice, or a starting point at least.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I don't know is whether counterpoise can conduct a large current and thus I don't know how thick these wires should be. For instance, can I use thin wires from an Ethernet cable or a long USB cable? If not, what gauge is recommended?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="76" LastEditDate="2019-04-13T20:31:56.790" LastActivityDate="2019-04-13T20:31:56.790" Title="How thick should counterpoise wires be?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;counterpoise&gt;&lt;earth&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12310" PostTypeId="2" ParentId="11667" CreationDate="2018-11-28T11:33:23.517" Score="1" Body="&lt;p&gt;FLDigi will calculate the SNR for a PSK31 signal based on the spectrum scope.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2018-11-28T11:33:23.517" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12311" PostTypeId="2" ParentId="12309" CreationDate="2018-11-28T14:24:17.670" Score="5" Body="&lt;p&gt;The purpose of the counterpoise is to provide an efficient means of conducting the return RF current of the antenna. In the absence of an efficient counterpoise, the current will return through the lossy earth or poorly quantified paths such as coaxial cable shields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An efficient counterpoise will carry the same current as the primary radiating element. A quarter wave vertical antenna with an efficient counterpoise has a feedpoint impedance of ~34 ohms. We can use Ohm's law to calculate the current:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$I=\sqrt{\frac{P}{R}} \tag1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where I is the current in amps, P is the power in watts and R is the resistance in ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So a 100 watt transmitter fed into a 34 ohm antenna will result in ~1.4 RMS amps. When you have three counterpoise radials, the maximum current in each radial is 1/3 of the antenna current or ~0.47 RMS amps in this example. And generally this current density is dominant near the base of the antenna and becomes less as you move away from the base.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before selecting a wire gauge, the construction of the wire must be considered. A pure copper wire is easier to analyze than a copper clad wire. In recent years, doorbell type wire, for example, has largely become copper clad. Because the specifications of the copper cladding is rarely published, you should shy away from cladded wires if you have other options since the steel core of the wire is quite lossy if the copper plating cannot carry the majority of the RF current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then finally, the gauge of the wire and the frequency of operation determines its losses. As the frequency rises, the current becomes more crowded on the surface of the wire due to &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;noreferrer&quot;&gt;skin effect&lt;/a&gt;.  As an example, a 24 gauge copper wire that is 2.5 meters long (about 1/4 wavelength at 28 MHz) has a DC resistance of ~0.2 ohms but at 28 MHz it has an AC (RF) resistance of ~ 2.2 ohms. You can calculate the AC resistance for any wire size with various online calculators such as &lt;a href=&quot;https://chemandy.com/calculators/round-wire-ac-resistance-calculator.htm&quot; rel=&quot;noreferrer&quot;&gt;this one&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you are attempting to increase the efficiency of your antenna, a good goal is to keep the total AC resistance of your counterpoise to less than 1% of the ideal feed point impedance. From the earlier example, 1% of 34 ohms is 0.34 ohms. Since you are using 3 wires, each wire should be 1 ohm or less (0.34 * 3). So the 24 ga wire for 28 MHz would not meet this goal while an 18 gauge, or larger, wire would.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, more than 3 radials are desirable for a ground mounted counterpoise. You can see from the example, that as you install more radials, it is possible to also effectively reduce the gauge of the wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has also been empirically determined that ground mounted radials do not need to be tuned to a 1/4 wavelength to be effective. Generally more shorter radials are better than a few 1/4 wave radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With all of this being said, don't suffer from analysis paralysis. Any radials of any gauge wire of any construction is generally better than no radials at all.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-11-28T14:30:55.637" LastActivityDate="2018-11-28T14:30:55.637" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12312" PostTypeId="1" CreationDate="2018-11-28T14:28:24.473" Score="0" ViewCount="46" Body="&lt;p&gt;I am currently looking for a good solution to create a simple VHF dipole connected to a RF preamplifier / band pass filter. The intended use is 88-108 FM RX. I see basically two solutions for a rigid antenna design  : &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;two classic screw terminal consumer telescopic antennas for each dipole leg.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;two BNC terminated telescopic antennas for each leg.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I prefer the BNC solution because it is sturdier and easier to streamline and connect to a PCB with through hole sockets. However I wonder what to do with the BNC ground terminal. Keep it floating, connect it to the circuit common ground, or shunt it with the center pin and dipole leg ? &#xA;FIY I will use a surface mount common mode choke rated for VHF, so the dipole will balanced. The preamp case is unshielded, only the RF preamplifier circuit path will be copper clad.&lt;/p&gt;&#xA;" OwnerUserId="13081" LastEditorUserId="9493" LastEditDate="2018-11-29T00:32:33.020" LastActivityDate="2018-11-29T00:35:43.070" Title="Indoor RX VHF dipole and preamplifier box" Tags="&lt;receiver&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12313" PostTypeId="2" ParentId="2257" CreationDate="2018-11-28T21:19:22.573" Score="4" Body="&lt;p&gt;The answer is very simple: a contest station &quot;running&quot; a frequency calls &quot;QRZ?&quot; because it is faster than calling CQ and giving the call sign.  The station running the frequency isn't trying to get only people who have called before to call when he or she sends &quot;QRZ?&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The station running the frequency can't call &quot;QRZ?&quot; forever, because soon new stations on the frequency won't know what the running station's call sign is (unless they are using a spotting network).  To have stations ask what the running station's call sign is slows down the run rate, so a good contester will remember to call CQ with the call sign periodically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Search &amp;amp; pounce&quot; stations trying to work the station running the frequency can respond to either &quot;QRZ?&quot; and &quot;CQ&quot;, assuming that the running station's call sign is known.  One should pay attention to the timing so as to call at the correct moment, because a mistimed call can temporarily tie up the frequency for everyone and especially irk the running station.  Contesting is all about making simple contacts very efficiently, so it's important to understand and work with the running station's rhythm.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2018-11-28T21:19:22.573" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12314" PostTypeId="2" ParentId="12309" CreationDate="2018-11-28T23:54:27.250" Score="3" Body="&lt;p&gt;With only three radials, the wire you use is probably not very relevant. Although a smaller wire has a higher resistance and thus loss, with only three radials directly on the ground your losses will still be dominated by the resistive loss of the soil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a rule of thumb, a good ground requires at least 16 radials. It's not critical that they be exactly a 1/4 wavelength long, though as a rule of thumb they should be at least that long. Using a shortened whip makes the requirement for a good ground even more important, as the shortening increases the current and the resistive losses with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the time you have 16 radials, the wire does not need to be especially thick since the current is distributed among each of them. Losses are proportional to the square of current, so each doubling of the number of radials reduces the copper losses by a factor of 1/4. But more significantly, more radials puts more of the current in the copper and less in the soil, which is a bigger win. I'd choose 32 radials of 30 AWG over 3 radials of 8 AWG for sure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So use whatever enables you to put down a lot of radials. I would recommend nothing thinner than 14 AWG just for mechanical robustness, but if you want to keep things really cheap and salvage wires out of cat 5 or whatever, go for it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-11-28T23:54:27.250" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12315" PostTypeId="2" ParentId="12312" CreationDate="2018-11-29T00:35:43.070" Score="1" Body="&lt;p&gt;There is no problem with using the BNC version of the telescoping elements. Because the shield of the BNC is not connected to anything, there is no reason to connect it to your circuit in any fashion. So leave it floating and proceed with your project.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have fun!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-11-29T00:35:43.070" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12316" PostTypeId="2" ParentId="12309" CreationDate="2018-11-29T03:15:00.490" Score="2" Body="&lt;p&gt;&lt;strong&gt;Can you elevate the radials?&lt;/strong&gt; Two or three &lt;em&gt;properly installed&lt;/em&gt; elevated radials can be just as effective as 120 on the ground!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By &lt;em&gt;properly installed&lt;/em&gt;, I mean that they should be roughly 10 feet high &lt;strong&gt;and&lt;/strong&gt; have an effective common-mode choke on the coax right at the junction of the radials and coax shield. &lt;strong&gt;This junction MUST NOT BE GROUNDED&lt;/strong&gt;. Try and make the radials as symmetrical as you can in relation to the vertical antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;http://www.w0btu.com/Optimum_number_of_ground_radials_vs_radial_length.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page about ground radials in general&lt;/a&gt; and &lt;a href=&quot;http://www.w0btu.com/160_meters.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one with descriptions and photos of mine&lt;/a&gt; about 1/3 of the way down the first page.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, be sure and click on the relevant links on the first page.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-11-29T03:37:36.133" LastActivityDate="2018-11-29T03:37:36.133" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12317" PostTypeId="1" CreationDate="2018-11-29T09:58:04.983" Score="5" ViewCount="742" Body="&lt;p&gt;Currently my location is Nepal. We use the ICOM f-7000 radios without the antenna tuner. We use the frequencies round about 5-9 MHz, for communication over distances between 150 and 400 km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During the summer time during the day the radio works fine in all frequencies. But during the winter time there is hardly any communication possible on any frequency. The best chance is the lowest frequency within the range. What could be the problem? &lt;/p&gt;&#xA;" OwnerUserId="13683" LastEditorUserId="218" LastEditDate="2018-11-30T15:57:00.373" LastActivityDate="2018-12-01T03:19:01.990" Title="Why are the lower HF frequencies not working during winter day time?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;icom&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12319" PostTypeId="1" AcceptedAnswerId="12324" CreationDate="2018-11-29T13:24:14.010" Score="10" ViewCount="501" Body="&lt;p&gt;I got my Amateur Extra ticket some time ago. I was able to discover what my score was (the number of questions I got wrong). However, my examiner was not able to tell me specifically which questions I had answered incorrectly, and to this day it still irks me. Isn't the whole point of licensing academic, i.e., to make sure that operators are knowledgeable? I would like to have been able to go back and study on those questions where I obviously didn't have enough knowledge or might have been confused.&lt;/p&gt;&#xA;&lt;p&gt;So why can't people who pass the test but got a few wrong learn which questions they got wrong? I am not asking for the right choice on the test, only the questions and the answers on the test, so I can go back and figure it out afterwards.&lt;/p&gt;&#xA;" OwnerUserId="6274" LastEditorUserId="8573" LastEditDate="2021-01-23T03:50:17.433" LastActivityDate="2021-01-23T03:50:17.433" Title="Why does ARRL license examination procedure preclude students from discovering what questions they got wrong on licensing tests" Tags="&lt;united-states&gt;&lt;license&gt;&lt;volunteer-examiners&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12320" PostTypeId="2" ParentId="12319" CreationDate="2018-11-29T13:47:38.737" Score="6" Body="&lt;p&gt;I can see your point definitely, but I think the process attempts to remain consistent with the past and prevents the examiners from being further burdened during the testing session.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although, in the US,  the ARRL is making the rules now (apparently), historically, the FCC examiners did NOT discuss the results of the tests.  You were handed the questions and answer sheet, and after turning them in, were told if you passed or failed.  It was not considered their place to potentially get into a discussion with the candidate (pass or fail) on the various topics. Even though one might presume that the current volunteer examiners might be more amenable to discussion (than the previous FCC guys), I think it's a good idea to separate the testing from the learning.&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-11-29T13:47:38.737" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12321" PostTypeId="2" ParentId="12299" CreationDate="2018-11-29T13:49:52.057" Score="2" Body="&lt;p&gt;The original reason for the CW requirement was that there was no other mode. :) The reason that I was given in 1953 is that emergency/distress calls were often in CW. Nowadays, IMO tradition-inertia is the probable reason. It would be interesting to poll German hams to see how many have ever heard a CW distress call.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2018-11-29T13:49:52.057" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12322" PostTypeId="2" ParentId="12292" CreationDate="2018-11-29T16:42:51.413" Score="4" Body="&lt;p&gt;Merely trim the reflector element of one yagi to the length of the first director and it will become bi-directional enough to get the job done without the expense of another yagi and harness.&#xA;Some retuning of the gama match may be needed &lt;/p&gt;&#xA;" OwnerUserId="13685" LastActivityDate="2018-11-29T16:42:51.413" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12323" PostTypeId="1" AcceptedAnswerId="12327" CreationDate="2018-11-29T19:33:52.800" Score="5" ViewCount="506" Body="&lt;p&gt;I've build an air capacitor like the one described in &lt;a href=&quot;https://www.eham.net/articles/5217&quot; rel=&quot;noreferrer&quot;&gt;this article&lt;/a&gt;, although I used 1 mm thick single side copper boards (FR4) instead of solid copper sheets. I would like to use such capacitors in my next projects, e.g. an antenna tuner and a magnetic loop antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is - I have no idea what is the maximum transmit power I can use with such capacitors. How would you recommend to measure it? Or maybe there is a common knowledge that such capacitors can handle power up to X (25 W, 100 W, ...) without any problems? &lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2018-12-03T18:26:38.533" Title="How can I determine/measure power rating of a DIY air capacitor?" Tags="&lt;diy&gt;&lt;capacitance&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12324" PostTypeId="2" ParentId="12319" CreationDate="2018-11-29T20:08:48.250" Score="13" Body="&lt;p&gt;Having participated as a volunteer examiner in a few test sessions, I think there are a number of reasons this is the case:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;We tend to quietly give the pass/fail results — and should offer the number wrong with an encouraging &amp;quot;you nailed it!&amp;quot; or &amp;quot;you were so close this time!&amp;quot; — as soon as we've finished processing them. Most of the time others are still taking their own tests. Discussing the questions/answers when they might be overheard would definitely not be appropriate in this setting.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The way the ARRLs tests are generated is randomized and they are graded using a key completely separate from the particular question set itself. When we check your answers we don't even know what the topic was, without finding back the test booklet. Since everything needs to be done in triplicate, the volunteers are usually busy enough keeping accountable with scoring and paperwork already.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Also, while we try to be approachable and congenial (and I haven't witnessed a case where an examinee became combative or even particularly disgruntled) the ARRL's VEC guidelines are very careful to guard both the authority and the objectivity/professionality of the examiners. Perhaps the ARRL feels the integrity of the testing process would be more at risk if there was too much discussion of the test itself?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Finally, in my understanding, the whole point of the &amp;quot;random questions from a published test bank&amp;quot; is to encourage knowing a wide body of knowledge or at least a full set of answers. If you failed the test, knowing what you got wrong may not help you anyway since the next test you get will likely have different questions anyway. (In fact, so long as they pay the fee again, examinees are welcome to retake a failed element during the same session. When you're on the line, luck becomes an element.) If you &lt;em&gt;passed&lt;/em&gt; the test — well, now you're on your way to learning most of the material even better; &amp;quot;hands on&amp;quot; this time!&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;As to your question in the comments why it can't be an administered &lt;em&gt;computerized&lt;/em&gt; test, I don't think that it's entirely due to the ARRL's culture. &amp;quot;We drove to the big city and then didn't get our callsign from the bureau until months had passed&amp;quot; nostalgia or not, tech has been a part of of ham radio for long enough.&lt;/p&gt;&#xA;&lt;p&gt;I think it's a much more practical concern: our VE group and many others like it does &lt;strong&gt;not&lt;/strong&gt; have a dedicated facility. We hold test sessions every other month in the basement of a Boy Scout office. Dealing with enough laptops or even tablets to service the dozens of examinees who show up would be a nightmare.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2021-01-18T18:28:39.993" LastActivityDate="2021-01-18T18:28:39.993" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12326" PostTypeId="2" ParentId="12319" CreationDate="2018-11-30T01:53:14.323" Score="6" Body="&lt;p&gt;Unlike the ARRL, if you take your exam at a session given by the &lt;a href=&quot;https://www.laurelvec.com/?pg=about&quot; rel=&quot;nofollow noreferrer&quot;&gt;Laurel VEC&lt;/a&gt;, the VEs are not only allowed but encouraged to go over the missed questions with the candidates for exactly the reason you state; to help you learn the material.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is true whether you pass or fail the exam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I am both an ARRL VE Team Liaison and Laurel VEC Team Lead.)&lt;/p&gt;&#xA;" OwnerUserId="4748" LastEditorUserId="4748" LastEditDate="2018-12-22T04:47:41.740" LastActivityDate="2018-12-22T04:47:41.740" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12327" PostTypeId="2" ParentId="12323" CreationDate="2018-11-30T11:49:12.807" Score="6" Body="&lt;p&gt;Congratulations on your home brew project! It is great to see experimentation of this type.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The two primary parameters for a capacitor are working voltage and ESR (effective series resistance), with the former being of primary interest in this case. How much power can be applied to a circuit containing a capacitor is a derivative of these parameters and of other elements in the circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Working Voltage&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The working voltage of a capacitor is determined primarily by the dielectric strength of the materials making up the capacitor and the construction details. In your case, this will consist primarily of the dielectric strength of FR4 material, the dielectric strength of air, and the construction details of your capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FR4 material is typically rated at 20 kV/mm. So your 1 mm thick FR4 material will breakdown (conduct) at approximately 20 kilovolts. But there are some caveats that must be taken into consideration. If you look at the cut edge of copper clad FR4 under magnification, you would see that some of the copper has been formed so as to wrap over the edge of the FR4 material. The dielectric strength of this area is no longer based on the dielectric strength of the FR4 but rather that of air. For a variable capacitor, even if the edge copper is carefully controlled, there will still be an effective air gap as the edges of the rotor and stator meet as they start to mesh. The edges of the copper also create an enhanced &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Potential_gradient&quot; rel=&quot;nofollow noreferrer&quot;&gt;potential gradient&lt;/a&gt;. If the board is etched, instead of cut, so as to leave a perimeter of FR4 material around the rotor or stator, this condition can be better controlled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dry, room temperature air at sea level has a dielectric strength of approximately 3 kV/mm. Notice that this is about 1/7th of that of FR4. So unless your design is carefully controlled so as to ensure a pure FR4 interface at all times, it is better to use the 3 kV/mm value as a breakdown voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When calculating a working voltage for a capacitor, consider that if the breakdown voltage is met or exceeded, it results in a catastrophic event. So typically you should build in at least a 50% safety factor to allow for construction tolerances, variation in humidity and altitude, etc. Also consider that when working with AC/RF voltages, the values are typically expressed as RMS voltages. For the capacitor, you are more concerned with peak voltages. For sinusoidal voltages:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_{Peak}=V_{RMS}\sqrt{2} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Effective Series Resistance&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ESR becomes a significant factor if the capacitor is passing large amounts of current or if the ESR is large enough so as to appreciably affect the Q of the circuit. This is typically not the case for variable capacitors. If you are interested in the more complex math for calculating ESR, indicate so in your comments and I will supplement this answer with those details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Power vs Voltage&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power that can be applied to a circuit containing a capacitor is largely of matter of the other elements in the circuit. For example, a simple small loop antenna used on HF frequencies with only 100 watts of applied power can easily develop more than 5 kV across the tuning capacitor. The same type of situation can arise in an antenna tuner application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To work through the math of a particular circuit, see this &lt;a href=&quot;https://ham.stackexchange.com/questions/10082/series-resonant-circuit-how-to-calculate-voltage-across-the-capacitor&quot;&gt;StackExchange Question and Answer&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Testing Your Design&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to do some non-destructive testing of your capacitor, search out a &lt;a href=&quot;https://en.wikipedia.org/wiki/Hipot&quot; rel=&quot;nofollow noreferrer&quot;&gt;hipot&lt;/a&gt; tester. The hipot tester will limit, or terminate, the current if a voltage breakdown occurs allowing you to better quantify the voltage characteristics of the capacitor.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="1362" LastEditDate="2018-12-03T18:26:38.533" LastActivityDate="2018-12-03T18:26:38.533" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12328" PostTypeId="2" ParentId="12323" CreationDate="2018-11-30T12:26:12.423" Score="2" Body="&lt;p&gt;Maximum amperage of the capacitor may also be limited by the smallest feed wire in the path and by the thickness and width of the metal in the plates of the capacitor, and possibly the skin depth of the components as well.  (In other words, if the skin depth for the frequency you are using is too close to the thickness of the metal in your plates, the effective resistance will increase.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Making any of these too small will effectively raise the resistance and ESR of the capacitor under high amperage conditions.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-11-30T12:26:12.423" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12329" PostTypeId="2" ParentId="12323" CreationDate="2018-11-30T19:15:07.130" Score="2" Body="&lt;p&gt;To expand on Glenn's answer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ESR, i.e. the losses in your capacitor that aren't caused by ohmic heating of the copper but by conversion of change of electrical field to heat in the dielectric (i.e. the FR4 and air) can be written as&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\text{ESR} = \frac{\tan \delta_\text{FR4}}{\omega C}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;with &lt;span class=&quot;math-container&quot;&gt;$\tan \delta\approx 0.01$&lt;/span&gt; being the material loss coefficient specific to (good) FR4, &lt;span class=&quot;math-container&quot;&gt;$\omega = 2\pi f$&lt;/span&gt; being the angular frequency of operation and &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; being capacity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, what &lt;em&gt;is&lt;/em&gt; your &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt;? I can only guess that. Based on the (slightly disappointing) 220pF: if you manage to replace all air in that capacitor with FR4, you should be getting around 4.2 to 4.7 times that capacitance (that factor happens to be the relative dielectric constant &lt;span class=&quot;math-container&quot;&gt;$\varepsilon_r$&lt;/span&gt; of FR4), so about 1 nF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming you operate this thing at 100 MHz, &lt;span class=&quot;math-container&quot;&gt;$\omega = 628\cdot 10^6 \,\text{s}^{-1}$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Putting this all together:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;\begin{align}&#xA;\text{ESR} &amp;amp;= \frac{10^{-2}}{628\cdot 10^6 \,\text{s}^{-1} 10^{-9} \frac{\text{As}}{\text V}}\\&#xA;&amp;amp;= \frac{10^1}{628}\frac{\text{V}}{\text{A}}\\&#xA;&amp;amp;= 0.016 \,\text{Ω}&#xA;\end{align}&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FR-4 has a heat capacity of ca. 1300 J/°K, meaning that you can pour in about 1/4 of the energy that you'd need to put into water to heat by the same temperature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's nice, because you wouldn't want to heat your capacitor to more than 100°C, for touching as well as mechanical reasons (and things get dangerous at around 140°C), so simply don't put in more energy than you'd put into a cup of water ¼ the size to make that boiling hot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, to heat a cup of tea (that's my weight estimate for your cap, you notice how much I'm guessing here) to near-to-boiling hot, I'd put it onto a 160 W stove. So, 40 W in dielectric losses seems pretty safe for your capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's the inherent downside of using a dielectric in your variable capacitor: Hot air simply escapes; your dielectric can't.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The big advantage is that air can't store much electrical field energy; its &lt;span class=&quot;math-container&quot;&gt;$\varepsilon_r$&lt;/span&gt; is pretty much 1. The higher that, the smaller a capacitor of identical capacitance can get.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-11-30T19:15:07.130" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12330" PostTypeId="2" ParentId="12285" CreationDate="2018-11-30T19:17:54.593" Score="1" Body="&lt;p&gt;In addition to the above tests, and if:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the coax is of some reputable brand and has type markings on the jacket,&lt;/li&gt;&#xA;&lt;li&gt;you have access to a LCR meter,&lt;/li&gt;&#xA;&lt;li&gt;the cables are of sufficient length,&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;you might want to check the capacitance and compare to the capacitance in the datasheet. This is usually marked as F per meter/100 meter/feet/... Calculate the expected capacitance for the length you have, and compare to the measured capacitance between jacket and the center. &#xA;If there is a large amount of moisture ingress (for example after prolonged outdoor use), this could affect the capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is also a test that can help you get a rough estimate of the length of longer lengths of (installed) cable.&#xA;I have used this at work to check an expected 285m run of coax cable installed on the winch of a ship. Somewhere in the signal path we had a problem, but access to connections was difficult. By measuring the capacitance (in addition to a pulse reflection test), we found that the cable on the winch was the culprit.&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2018-11-30T19:17:54.593" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12331" PostTypeId="1" CreationDate="2018-11-30T19:33:39.477" Score="3" ViewCount="4073" Body="&lt;p&gt;I was reading up on a &lt;a href=&quot;https://www.eham.net/reviews/detail/11746&quot; rel=&quot;nofollow noreferrer&quot;&gt;radio review&lt;/a&gt;, and it mentioned something I was not familiar with, &quot;Busy Channel Lockout&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfamiliar with the term, I did an &lt;a href=&quot;https://duckduckgo.com/?q=BUSY%20CHANNEL%20LOCKOUT&amp;amp;t=ffsb&amp;amp;ia=web&quot; rel=&quot;nofollow noreferrer&quot;&gt;Internet Search&lt;/a&gt;, but didn't get back much, and for some reason the most promising results did not work.  &lt;a href=&quot;https://www.raveon.com/carrier-detect-and-busy-channel-lockout-a-collision-avoidance-mechanism/&quot; rel=&quot;nofollow noreferrer&quot;&gt;This page&lt;/a&gt; seems to be product specific, but it appears that it's a way to prevent radios from transmitting on top of each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is Busy Channel Lockout?  Why do I want, or not want, this feature?  Is this feature often abbreviated to BCL?&lt;/p&gt;&#xA;" OwnerUserId="4476" LastEditorUserId="8717" LastEditDate="2018-11-30T22:07:01.750" LastActivityDate="2018-12-02T13:02:41.597" Title="What is &quot;Busy Channel Lockout&quot;? Why do I want to control this feature?" Tags="&lt;jargon&gt;&lt;equipment-operation&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12332" PostTypeId="1" CreationDate="2018-11-30T21:25:11.587" Score="2" ViewCount="133" Body="&lt;p&gt;After reading the commentary in &lt;a href=&quot;https://ham.stackexchange.com/q/12247/4476&quot;&gt;this question&lt;/a&gt; and its answer, it's apparent that ham procedures/norms/protocols/etiquette are substantially different than military and public safety radio procedures.  And it turns out that I am much more familiar with the latter than the former.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Public safety radio operator norms are much more varied than military radio operator procedures, but I believe they are usually similar and based on military procedures.  If you didn't know, they vary by region, department, service (Fire, police, ambulance, EMS, etc), and many other factors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What should a ham radio operator who is more familiar with military and public radio procedures know about ham radio procedures?  Which procedures are the most different and cause the most problems when operating on the different spectrums for different purposes?&lt;/p&gt;&#xA;" OwnerUserId="4476" LastEditorUserId="9493" LastEditDate="2018-12-01T17:38:54.763" LastActivityDate="2018-12-02T13:55:27.527" Title="What are the differences of ham radio procedures compared to military or public safety procedures?" Tags="&lt;united-states&gt;&lt;procedure&gt;&lt;etiquette&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12333" PostTypeId="1" CreationDate="2018-11-30T22:12:22.253" Score="0" ViewCount="103" Body="&lt;p&gt;Q1.1: Why can a helix calculator not be used for linearly loaded antennas? Those online calculators suggested that the turn pitch/wavelength should be around 0.25. However, a typical linearly loaded ANT-433-HETH (link as below) has such rate to be 0.05. How then should a linearly loaded antenna be designed? &#xA;&lt;a href=&quot;https://linxtechnologies.com/wp/wp-content/uploads/ant-433-heth.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://linxtechnologies.com/wp/wp-content/uploads/ant-433-heth.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Q1.2: There are various dimensions of linearly loaded antennas available for the same frequency but with different lengths. How should one choose the best design for the application?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Q2.1: In real applications, the ground plane (the PCB to mount the antenna) would probably be smaller than the referenced ground plane from the antenna vendor's design. For example, the above mentioned antenna is claimed to have 50 Ohm impedance but they also claim that &quot;Electrical specifications and plots measured on a 7.62 x 19.05 cm (3.00&quot; x 7.50&quot;) ground plane&quot;. Therefore, should one infer that the return loss, VSWR, and impedance at 433 MHz would be poorer than they claim?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia has said this.&#xA;&lt;a href=&quot;https://en.wikipedia.org/wiki/Helical_antenna#Normal-mode_helical&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Helical_antenna#Normal-mode_helical&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Q2.2: Considering the above mentioned situation, the antenna would not match the transceiver modules which claim to be 50 ohms. Will the matching conditions ever be met?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Q3: In some cases, linearly loaded antenna is sold together with the radio transceiver module, such as the HC-12 (link as below). Someone said that there is a special matching network on the transceiver module so that the 1 km system range could be possible. If I change the linearly loaded antenna for another one that is designed for 433 MHz (since there are both antenna pin and ipex interface on that tcvr module), would the new combination really work?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.banggood.com/HC-12-433-SI4463-Wireless-Serial-Module-Remote-1000M-With-Antenna-p-973522.html?cur_warehouse=CN&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.banggood.com/HC-12-433-SI4463-Wireless-Serial-Module-Remote-1000M-With-Antenna-p-973522.html?cur_warehouse=CN&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11250" LastEditorUserId="9493" LastEditDate="2018-12-03T10:52:39.070" LastActivityDate="2018-12-03T10:52:39.070" Title="How to characterize and select UHF linearly loaded antennas?" Tags="&lt;antenna&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12334" PostTypeId="2" ParentId="12331" CreationDate="2018-12-01T00:47:50.170" Score="1" Body="&lt;p&gt;BCL or LO is a common term (and feature) with most - if not all, scanner receivers. Some amateur radio equipment has this feature as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically it's primary function is to 'lock-out' (exclude) that particular memory channel from the memory scanning, when you have the radio in 'scan' mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, there might be a particular channel you have programmed into memories that you don't wish to listen to at the time, therefore you can lock it out and stop the radio's scan from stopping on that memory channel each rotation.&lt;/p&gt;&#xA;" OwnerUserId="9824" LastActivityDate="2018-12-01T00:47:50.170" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12335" PostTypeId="2" ParentId="12317" CreationDate="2018-12-01T03:19:01.990" Score="4" Body="&lt;p&gt;At distances of 150 to 400 kilometers, you will largely be relying on reflection of your signal by the ionosphere. In the winter the atmosphere receives less solar radiation and the ionosphere's index of refraction is less. This increases the &lt;a href=&quot;https://en.wikipedia.org/wiki/Critical_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;critical frequency&lt;/a&gt; in the winter, putting the receiving station in the &lt;a href=&quot;https://en.wikipedia.org/wiki/Skip_zone&quot; rel=&quot;nofollow noreferrer&quot;&gt;skip zone&lt;/a&gt; unless you use a lower frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To gain an intuitive understanding of how this works, look at a glass of water. Looking through the side of the glass at a shallow angle it appears reflective like a mirror. But at a steeper angle it becomes transparent like a window:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/v6fva.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/v6fva.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ionosphere interacts with radio waves in much the same way: different layers have different indices of refraction, and at some angles this can result in the radio waves being reflected back towards earth. For the purposes of terrestrial radio communication, we need the ionosphere to be like a mirror, not a window.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is what creates the &lt;a href=&quot;https://en.wikipedia.org/wiki/Skip_zone&quot; rel=&quot;nofollow noreferrer&quot;&gt;skip zone&lt;/a&gt;. For short distances, the angle to the ionosphere is too steep, and thus the ionosphere looks like a window. In this example, communication with anything closer than 1000 km is not possible by ionospheric reflection, because the signal instead escapes to space:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7sMTH.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7sMTH.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This refractive behavior is frequency dependent. A prism works because the index of refraction of glass is different for the different frequencies of visible light. It is the same for the ionosphere. As the radio frequency decreases, the waves are bent more. At some point, even waves straight up are reflected back towards earth, and the skip zone disappears:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LwvSJ.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LwvSJ.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency at which this occurs is called the &lt;a href=&quot;https://en.wikipedia.org/wiki/Critical_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;critical frequency&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The critical frequency also changes with the seasons, time of day, and solar conditions. Generally, more solar radiation increases the critical frequency. So the critical frequency is higher during the day than the night, higher in summer than winter (because the days are longer), and higher when the &lt;a href=&quot;https://en.wikipedia.org/wiki/Solar_cycle&quot; rel=&quot;nofollow noreferrer&quot;&gt;solar cycle&lt;/a&gt; is at its maximum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what's happening to you in the winter is the critical frequency is lower due to the shorter days and less radiation of the atmosphere, and so at higher frequencies the receiving station is too close because it's in the skip zone. If you get just the right frequency you might even find you can communicate with farther stations, but not closer ones. So, you must decrease frequency to get below the critical frequency where your signal will be reflected at nearly vertical angles.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-12-01T03:19:01.990" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12338" PostTypeId="2" ParentId="12333" CreationDate="2018-12-01T11:16:49.973" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Q1.1: Why cannot use the helix calculators for rubber ducky antenna? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Because the helix calculators have different goals. A helix antenna as understood by these calculators is meant to be a directive antenna, whereas the average rubber ducky antenna is just meant to be a short monopole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short: because one is meant for designing directive antennas, the other is not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Read the wikipedia article closely! &lt;em&gt;Normal-mode&lt;/em&gt; vs &lt;em&gt;Axial-mode&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Q1.2: Even as rubber ducky antenna for a certain frequency, there are various dimensions available, with different electrical length. Then, how to choose?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Based on datasheet data matching your requirement. In antenna construction, there's more than one way to achieve something, and you always have to do trade-offs between things like bandwidth, efficiency, mechanical stability, weight, …&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Oh, and cost. If you're buying antennas, you might be interested in the cost :)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Q2.1: In real applications, the ground plane (the PCB to mount the antenna) would probably be smaller than the reference ground plane from the antenna vendor's design&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;um, depends on the vendor's reference design. There's a lot of vendors of handset-related components (for example, SiLabs sells FM modem ICs and they have plenty of appnotes). I'm pretty sure there's designs with &quot;small&quot; ground plane to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Honestly, if you sell an antenna whose prime application is handset devices, and assume your customers will be carrying around 1 m² of ground plane, you're doing something wrong in terms of RF modelling.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For example, the above mentioned antenna is claimed to have 50 Ohm impedance but they also claim that &quot;Electrical specifications and plots measured on a 7.62 x 19.05 cm (3.00&quot; x 7.50&quot;) reference ground plane&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's not a reference design, that's a measurement setup – and it makes sense to measure with a good ground. Smaller ground, as well as about anything about the placement of the antenna, will lead to mismatch. But that's how it is – if you're building integrated RF devices, antenna matching has to be part of your design process. It's important that the antenna starts out with a usable impedance somewhere close to the (typically 50Ω) impedance that you'd want to use. But matching networks or lumped elements are usually inevitable.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Therefore, does it imply that the return loss, VSWR, and impedance at 433 MHz would be poorer than they claimed?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You use a poorer ground than was used for measurement, you get poorer performance. I don't think that's overly surprising! Monopole antenna manufacturer can't do anything about &lt;em&gt;your&lt;/em&gt; ground plane, but give you a design starting point.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Q2.2: Considering the above mentioned situation, the antenna would not match the transceiver modules which claimed to have matched to 50 Ohm. Then, again, how to choose rubber ducky antenna? Will the matching ever be met?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Since rubber ducky antennas are only parts of transmitter systems, yes, &lt;strong&gt;you&lt;/strong&gt; are the one in charge of making a good match. But: you'll have to do that anyway. Not-so-dirty, not-so-secret: Your average  RFIC doesn't have perfect 50Ω source impedance, either, so matching is done on that end, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the reasonable engineering approach here is to have a matching network between the monopole and the transmission line, and one between the transmission line and the RFIC. If things are nice and you need to optimize for cost, simplify or omit one of these two networks by matching the transmission line to antenna or RFIC (instead of say 50Ω); but usually, you'd win little by that and then can't optimize the matching networks individually anymore, so you don't.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Q3: In some cases, rubber ducky antenna is sold together with the radio transceiver module, such as HC-12 (link as below).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I say this every 18.34h, so I will say this again: If you want electronic components, buy them somewhere you get a good datasheet. Banggood, aliexpress, ebay, amazon are not places to buy components. If you've never seen a good datasheet: go to any reputable electronics distributor website and get the datasheet for any name-brand inductor. A stupid, 10ct, SMD inductor. A passive device. If your complex digital transceiver IC comes with less documentation than an inductor, don't buy it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here, it would've been especially simple: the module is essentially just the &quot;Figure 1: Application Schematic&quot; from the &lt;a href=&quot;https://www.silabs.com/documents/public/data-sheets/Si4464-63-61-60.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Si4463 RFIC data sheet&lt;/a&gt;. If a supplier can't even link to the data sheet of their central component: Buy somewhere else. They don't have technical staff, and they're distributing their &quot;support load&quot; to &quot;the internet&quot; hoping that strangers will help their customers. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Someone said that there are special matching network on the transceiver module so that the 1 km system range could be possible.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Come on, you know that range isn't only a function of a matching network, but of path loss, antenna efficiency and directivity, intereference level, noise level in the receiver (which is dominated by temperature), data modulation robustness, forward error correction, multipath propagation in the channel, …&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, &quot;someone said&quot; is about as good &quot;as my imaginary friend suggested&quot;. Only that your imaginary friend probably is not interested in boasting or selling his products...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But yeah, read that datasheet that I linked to above, especially Fig.1. There's a proper matching network &lt;em&gt;right there&lt;/em&gt; in the data sheet. Of course, that point is totally moot if you bring a 433 MHz transmission line to a rectangular through-hole, which simply is not an RF-capable interface at all, and will have a random impedance, relative to the driving transmission line, and can't be matched away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the board design is of unknown quality, and we don't know what it can do due to lacking documentation, no-one can ever tell whether 1km is possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could throw around sensitivity numbers from the datasheet, calculate the free-space loss and antenna gains, but really, due to the black-box module design, we might simply see orders of magnitudes of behaviour differing from a theoretical calculation. So, with that level of documentation, I won't be wasting my time on that.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If I change the rubber ducky for another antenna that resonantes at 433 MHz (since there are both antenna pin and ipex interface on that tcvr module), would the new combination really work?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Nobody can know without trying, because that module comes without any documentation or even a specification of the impedance of the coax connector &lt;strong&gt;at all&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, honestly. I don't even know what this has to do with amateur radio, but don't buy this underspecified stuff, which probably ships with the antenna unsoldered to avoid the need for certification for US/EU imports, which it'll almost inevitably can't get.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, go to the central RFIC's &lt;a href=&quot;https://www.silabs.com/products/wireless/proprietary/ezradiopro-ism-band-transmitters-recievers-transceivers/device.si4463&quot; rel=&quot;nofollow noreferrer&quot;&gt;product page&lt;/a&gt;. You'll notice there's a lot of documentation there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're looking for &quot;AN643: Matching…&quot;. That'll tell you how to match your receiving end to the 50Ω transmission line. You'll do the same for the antenna, which has an impedance dependent on ground plane, and placement of other non-1-&lt;span class=&quot;math-container&quot;&gt;$\varepsilon_r$&lt;/span&gt; materials around the device (e.g hands and heads on a handset).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll notice that a perfect match for a single antenna impedance is nice and all, but you'll need &lt;em&gt;robustness&lt;/em&gt;, i.e. a match that is still &quot;OK&quot; when the antenna impedance isn't as expected. So, design your matching network to &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-12-01T11:16:49.973" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12340" PostTypeId="2" ParentId="12331" CreationDate="2018-12-02T11:45:17.203" Score="3" Body="&lt;p&gt;In my experience, the Busy Channel Lockout or Busy Channel is the name for a feature which is completely different from what Cranky Emu describes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Busy Channel Lockout prevents transmission on a frequency which is, or appears to be, already in use. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally, you'd be able to hear the other side which is transmitting using your receiver, and avoid transmitting until the channel is free.&lt;br&gt;&#xA;However, with more complex squelch systems, such as CTCSS and DCS, becoming more common, it can happen that your receiver is receiving another signal, but is muted due to squelch settings.&lt;br&gt;&#xA; This might lead you to believe that the channel is free and that you can transmit on it. If you do transmit on it, you could create interference to the transmission already in progress. Do note that some radios, especially those without screens, might not have any way, other than audio, to signal that there is another squelched user on the channel. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, depending on the implementation, the busy channel lockout feature might also work even if the CTCSS or DCS are not in use. It might prevent radio from transmitting as long as there's some signal on the frequency. This can cause issues which prevent the radio from transmitting in case where the radio is picking up interference which is not related to communication.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also a bit of background:&lt;br&gt;&#xA; In some jurisdictions, commercial users might receive licenses for frequencies shared with other users, but with each group having different squelch settings. With receive squelch, and busy channel lockout, it's possible to create a feeling of privacy, in sense that members of other talk groups won't be able to just listen in to the traffic which is not from their own group.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, in some parts of Europe, the 2 m amateur band, and the 70 cm amateur band are still used for analog cable television and digital to analog set top boxes. The cable TV infrastructure might radiate, creating large number of carriers which might break squelch of radios and also trigger busy channel lockout. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2018-12-02T11:45:17.203" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12341" PostTypeId="2" ParentId="12331" CreationDate="2018-12-02T13:02:41.597" Score="2" Body="&lt;p&gt;In respect to Andre's answer, it is really going to depend on the radio. Different companies use different terminology, or the same terminology differently.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, in your experience of BCL, this is also commonly referred to as TX Inhibit. Same thing, different way of saying it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of this radio, Andre is correct. It disables tx when the frequency is busy, the review says it cannot be disabled, which is not correct. When you program the radio via software, there will be a setting to disable the BCL&lt;/p&gt;&#xA;" OwnerUserId="9824" LastActivityDate="2018-12-02T13:02:41.597" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12342" PostTypeId="2" ParentId="12332" CreationDate="2018-12-02T13:55:27.527" Score="3" Body="&lt;p&gt;Ham radio procedures derive from multiple sources, including:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the laws that govern the license&lt;/li&gt;&#xA;&lt;li&gt;the NATO phonetic alphabet (which should be identical to what the military uses, but differs from what many local police uses)&lt;/li&gt;&#xA;&lt;li&gt;Q codes which originated from morse code usage; these are used heavily in digital modes, and occasionally in phone modes, and occasionally frowned on for phone modes and FM repeaters (i.e., usage varies a lot)&lt;/li&gt;&#xA;&lt;li&gt;the local customs and practices (i.e, those of the local club or repeater you are using)&lt;/li&gt;&#xA;&lt;li&gt;customs recommended by (ARES) training and courses such as FEMA IS-100 IS-200 IS-700 IS-800, ARRL EC-001 EC-016, etc.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The best way to get use to ham radio practices is to listen for a while and join a local club.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-12-02T13:55:27.527" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12343" PostTypeId="2" ParentId="12292" CreationDate="2018-12-02T14:02:04.167" Score="2" Body="&lt;p&gt;Yagi antennas typically have a large back lobe.  Their front to back ratio is always much larger than their front to side ratio.  It is not uncommon to make contacts off the back side of a yagi.  (Or start a contact that way and flip to get a better signal.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, one option would be to install a single yagi on the pole and test if you can reach both sites.  If not, flip it and test again.  If one site is closer than the other, this might work well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That failing, you could build a bidirectional three element yagi with a driven element between two directors (as suggested by Jim Navotney above), or a two element yagi with two driven elements and an antenna switch to flip between them...&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-12-02T14:02:04.167" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12344" PostTypeId="1" AcceptedAnswerId="12345" CreationDate="2018-12-02T18:39:48.803" Score="1" ViewCount="65" Body="&lt;p&gt;I have a G5RV Jr. antenna on a fiberglass mast at 10m height.  The only metal on the mast is a 1/8&quot; thick steel guy ring with stainless steel snap links, plus a few small metal screws.  Hanging freely, the twin lead on the G5RV Jr. is about six inches away from the guy ring and snap links. (The guy ring is also about three feet from the feed point for the antenna elements, which are in an inverted V configuration.) Can I expect any significant negative effects (i.e. impact on SWR or RF in the shack) from that one guy ring?  Thanks.   &lt;/p&gt;&#xA;" OwnerUserId="9772" LastEditorUserId="8717" LastEditDate="2018-12-02T23:41:57.010" LastActivityDate="2018-12-02T23:41:57.010" Title="Effect of small amount of metal on twin-lead" Tags="&lt;antenna-construction&gt;&lt;transmission-line&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12345" PostTypeId="2" ParentId="12344" CreationDate="2018-12-02T19:04:20.867" Score="2" Body="&lt;p&gt;For the wavelengths (10m upwards) that antenna operates on, small metal objects shouldn't matter significantly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anything, they just change the antenna impedance ever so slightly. But since that antenna needs to be used with a tuner anyways, that's not even a downside.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-12-02T19:04:20.867" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12346" PostTypeId="1" AcceptedAnswerId="12349" CreationDate="2018-12-02T22:40:17.517" Score="2" ViewCount="203" Body="&lt;p&gt;This task is our milestone, even the lecturer doesn't know how to do it, I will be grateful for even the smallest clue, thank you in advance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are given two, identical, parallel, short dipoles perpendicular to the OX axis connecting their centers, located at a distance of λ / 4 and supplied with a phase shift of π / 2 (figure below). How much higher is the energy flux density (in dB) sent in the direction of the positive half axis OX by the described pair of dipoles from the density of the power jet sent in the direction described by the azimuthal angle φ = 52 ° and the angle of elevation Θ = 37 °?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QirAC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QirAC.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13706" LastActivityDate="2018-12-04T17:19:45.363" Title="Yagi-Uda antenna - energy flow density calculation" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12347" PostTypeId="1" AcceptedAnswerId="12348" CreationDate="2018-12-03T00:54:44.907" Score="2" ViewCount="240" Body="&lt;p&gt;I have one straight horizontal wire antenna 35 meters (114.83 feet) long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to make it work the best on average for the 80, 40, 20 ,15 and 10 meter amateur bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone tell me the best place for the feed point to make it work the best on all the bands ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm happy to use an antenna matcher, can put the feed point anywhere and shorten the antenna but not lengthen it, and can probably remove the 10 m band.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2018-12-03T02:16:56.780" LastActivityDate="2018-12-07T14:45:27.170" Title="Can anyone tell me how to make a 35 m long wire antenna work on 80, 40, 20, 15 and 10 metres?" Tags="&lt;wire-antenna&gt;&lt;dipole&gt;&lt;antenna-tuner&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12348" PostTypeId="2" ParentId="12347" CreationDate="2018-12-03T01:37:10.133" Score="5" Body="&lt;p&gt;I suggest you feed it in the center with open-wire (ladder) line and a balanced antenna tuner. (I have done that for many years). With the right tuner, you can obtain a near-perfect match anywhere on those bands. Also, feeding it in the center eliminates the need for a good RF ground or radial system, as opposed to end-feeding it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/10061/8717&quot;&gt;Glenn, W9IQ has a schematic here&lt;/a&gt; of a balanced-to-balanced tuner that some may find useful if placed between commonly-available balanced tuners (that use ferrite baluns) and the antenna to increase the impedance range. The tuner I made was different, using link-fed, tapped coils in parallel with a variable capacitor, but Glenn's design appears to cover a much wider range of bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may find that certain lengths of feedline are difficult to match on some bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Choose (or build) &lt;a href=&quot;https://ham.stackexchange.com/questions/111/50-ohm-coaxial-cable-vs-450-ohm-or-600-ohm-ladder-or-window-line/193#193&quot;&gt;ladder line with low loss&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-12-03T02:04:15.610" LastActivityDate="2018-12-03T02:04:15.610" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12349" PostTypeId="2" ParentId="12346" CreationDate="2018-12-03T03:59:03.517" Score="3" Body="&lt;p&gt;Here are some hints :&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) two dipoles usually interact strongly, so the current on one is dependent on the current in the other. This is how a Yagi Uda antenna works - the elements are mostly parasitic, i.e. not driven by a source, but still carry current.&lt;br&gt;&#xA;In this case you don't have to worry about this at all. The two currents are given.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) the fields at some point in space are the &lt;em&gt;linear superposition&lt;/em&gt; of the time-varying fields due to the current in each element - without considering the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) you need to find an expression, in a textbook or online, for &lt;em&gt;the retarded electric potential&lt;/em&gt; of a half wave dipole. This is the electric (or magnetic) field in space due to the current on the element.&lt;br&gt;&#xA;Most importantly, it contains an &lt;span class=&quot;math-container&quot;&gt;$e^{-j \beta r}$&lt;/span&gt; term, which is a the delay in time caused by being some distance away. Hence &quot;retarded&quot;. This term is key to adding the two fields correctly. You'll need to find &lt;span class=&quot;math-container&quot;&gt;$r$&lt;/span&gt; for each dipole, for each of the positions you want to find the total field... this will be an expression in &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\phi$&lt;/span&gt;.&lt;br&gt;&#xA;It also contains a &lt;span class=&quot;math-container&quot;&gt;$1/r$&lt;/span&gt; term which you will ignore, because when you're far away, these terms are identical. &#xA;And a &lt;span class=&quot;math-container&quot;&gt;$sin^2\theta$&lt;/span&gt; term, which is the radiation pattern.&lt;br&gt;&#xA;Note there is no &lt;span class=&quot;math-container&quot;&gt;$\phi$&lt;/span&gt; term because each dipole radiates equally in all directions. The pattern of the array will come out when you find the vector sum of the fields.&lt;br&gt;&#xA;Also some constants which aren't important if you're looking for the ratio of two fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4) You only need consider Theta-directed fields - and most derivations will only consider these anyway, in the far field.  In the near field there are radial fields too, but these die off as &lt;span class=&quot;math-container&quot;&gt;$1/{r^2}$&lt;/span&gt; so don't matter in the far field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;5) finally, the power flux density is the square of the electric field (times a constant).&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2018-12-03T18:41:15.530" LastActivityDate="2018-12-03T18:41:15.530" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12352" PostTypeId="1" CreationDate="2018-12-04T03:42:50.100" Score="3" ViewCount="97" Body="&lt;p&gt;Forgive what may be a basic inquiry from a new enthusiast. I am new to amateur radio, just barely passed Technician and General tests. I am also a pilot and have an RR class licence. I believe that I have what is required to transmit on aviation frequencies from the ground according to 47 CFR Part 87 Subpart B §87.18 and §87.47. (My intent is to provide periodic back-country ground support to fellow pilots.) I have found several mobile radios that can monitor aviation frequencies but haven't found one that can transmit. Is there such a thing? There appears to be a few portable models that can, but haven't been able to find a mobile transceiver. &lt;/p&gt;&#xA;" OwnerUserId="13713" LastEditorUserId="4665" LastEditDate="2018-12-05T18:43:38.657" LastActivityDate="2018-12-05T18:43:38.657" Title="Mobile 2m / 70cm dual band with aviation frequency TX capability" Tags="&lt;united-states&gt;&lt;am&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12353" PostTypeId="2" ParentId="12352" CreationDate="2018-12-04T04:00:39.733" Score="-1" Body="&lt;p&gt;I did a quick Google search, and found this one : &lt;a href=&quot;http://www.icomamerica.com/en/products/avionics/mobile/a120/default.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.icomamerica.com/en/products/avionics/mobile/a120/default.aspx&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also there is this one : &lt;a href=&quot;http://www.icomamerica.com/en/products/avionics/panelmount/a220/default.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.icomamerica.com/en/products/avionics/panelmount/a220/default.aspx&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am sure others exist, but I found those with a quick search. I can't comment as to their suitability, however.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This one claims to cover all the frequencies you wanted : &lt;a href=&quot;http://www.icomamerica.com/en/products/avionics/mobile/xbandair/default.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.icomamerica.com/en/products/avionics/mobile/xbandair/default.aspx&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2018-12-04T04:00:39.733" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12354" PostTypeId="1" AcceptedAnswerId="12356" CreationDate="2018-12-04T05:28:42.740" Score="0" ViewCount="436" Body="&lt;p&gt;And also, can anyone tell me how? Using Arduino or any other way ...&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="9493" LastEditDate="2018-12-05T10:38:49.653" LastActivityDate="2018-12-05T10:38:49.653" Title="Is it legal to transmit scrambled or encrypted voice via SSB on ham bands?" Tags="&lt;united-states&gt;&lt;ssb&gt;&lt;encryption&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12355" PostTypeId="2" ParentId="12352" CreationDate="2018-12-04T06:57:57.657" Score="1" Body="&lt;p&gt;Congratulations on your new license!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't believe you will find this type of radio. The aviation band uses amplitude modulation and the amateur bands for conventional repeaters and local communications use frequency modulation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The aviation band radio must be FCC certified to part 87 to be legally used for transmitting. The FAA must also approve the radio prior to FCC certification commencing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Add to all of this the limited market for such a combined radio and the likelihood is quite small.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you add a requirement such as DMR or Fusion for the amateur radio portion, the likelihood is further decreased.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-04T08:45:25.460" LastActivityDate="2018-12-04T08:45:25.460" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12356" PostTypeId="2" ParentId="12354" CreationDate="2018-12-04T08:16:50.907" Score="11" Body="&lt;p&gt;In the US, the FCC prohibits this type of operation if the &lt;em&gt;purpose&lt;/em&gt; is to obscure the meaning of your transmission.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;97.113 Prohibited Transmissions&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(4) ... messages encoded for the purpose of obscuring their meaning...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In response to filings on this topic, the FCC has made it clear that this prohibition includes encryption. The FCC has also illuminated in &lt;a href=&quot;https://docs.fcc.gov/public/attachments/DA-13-1918A1.pdf&quot; rel=&quot;noreferrer&quot;&gt;its orders&lt;/a&gt;, the intent of section 97.113:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;... to help maintain the noncommercial character of the&#xA;  amateur radio service by prohibiting certain types of transmissions.&#xA;  The primary protection against exploitation of the amateur service and&#xA;  the enforcement mechanism in the amateur service is its&#xA;  self-regulating character...To ensure that the amateur service remains a non-commercial service and self-regulates, amateur stations&#xA;  must be capable of understanding the communications of other amateur  stations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There are exemptions to this for things such as space command codes, etc. but those are not applicable to your question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A respondent to FCC proceedings on this topic made an insightful observation:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For governments around the world to permit amateur radio to continue, it must be perceived as harmless. The strength of harmlessness is destroyed by encryption.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You can use digital voice modes that are well published if the purpose is not to obscure the meaning of your transmission. One that has gained some interest for use on the HF bands is &lt;a href=&quot;https://freedv.org/&quot; rel=&quot;noreferrer&quot;&gt;FreeDV&lt;/a&gt; that uses open source voice codecs and is free for use.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-04T08:37:29.227" LastActivityDate="2018-12-04T08:37:29.227" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12357" PostTypeId="2" ParentId="12247" CreationDate="2018-12-04T12:15:09.733" Score="1" Body="&lt;p&gt;Break is actually discouraged in the amateur community here.  Break indicates you want to break into the conversation, but frequently is too short for people to distinguish who you are which is a problem if multiple people try it at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, just say your call sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Over might be used in simplex, but most repeaters have courtesy tones, which fulfill the same purpose, so it is strongly discouraged in that context.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Along with &quot;clear&quot; I frequently hear &quot;clear on your final&quot;, which not only indicates that the speaker will not transmit again, but will wait for your last word.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, &quot;clear and monitoring&quot; which means the speaker has had their say and won't transmit again for a while, but is still listening.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2018-12-05T14:35:04.660" LastActivityDate="2018-12-05T14:35:04.660" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12361" PostTypeId="1" CreationDate="2018-12-05T05:49:34.260" Score="1" ViewCount="122" Body="&lt;p&gt;I'd like to estimate the power density from a 13.56 MHz power source in a near-field WPT (wireless power transfer) scenario. Using a spectrum analyzer with a receiving antenna will give the E-field measurements, while for near-field WPT the magnetic coupled resonance is the used method (non-radiation). So, I suppose I cannot use spectrum analyzers to measure what I want. I'm wondering if there is any measurement method to measure the power (in dBm) emitted from a source to be harvested by a loop antenna in near-field concept. Any advice would be highly appreciated.&lt;/p&gt;&#xA;" OwnerUserId="11740" LastEditorUserId="76" LastEditDate="2020-02-14T01:22:13.303" LastActivityDate="2020-02-14T01:22:13.303" Title="How to measure the power emitted from an HF antenna in near-field WPT?" Tags="&lt;antenna-theory&gt;&lt;rf-power&gt;&lt;measurement&gt;&lt;spectrum-analyzer&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12362" PostTypeId="2" ParentId="4980" CreationDate="2018-12-05T07:46:05.113" Score="0" Body="&lt;p&gt;The antiparallel diodes VD1,VD2 of type BAP794 form the subharmonic mixer, this type of mixer is efficient for even order harmonics of the local oscillator, here, harmonic 2 is used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This type of mixer can be traced to a 1955 patent &lt;a href=&quot;https://patents.google.com/patent/US2706775A/en&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://patents.google.com/patent/US2706775A/en&lt;/a&gt; one can see on the patent diagram the antiparallel diode valves of type 6AL5, patent text mentions &quot;The converter characteristic requires that the local oscillator employed be operated at one half of the normal oscillation frequency&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more recent text is &quot;High-Order Subharmonically Pumped Mixers&#xA;Using Phased Local Oscillators&quot; it is worth reading the Intro paragraph which gives an overview of the topic.&lt;/p&gt;&#xA;" OwnerUserId="8579" LastActivityDate="2018-12-05T07:46:05.113" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12364" PostTypeId="2" ParentId="12361" CreationDate="2018-12-05T10:34:10.717" Score="4" Body="&lt;p&gt;WPT (wireless power transfer) is typically performed using flat, multi-turn coils (inductors) as antennas. In some cases, the coils are self resonant based on their parasitic capacitance and self inductance in order to avoid the losses in a typical matching network. Due to the close proximity of the two coils, the &lt;a href=&quot;https://www.electronics-tutorials.ws/inductor/mutual-inductance.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;mutual inductance&lt;/a&gt; must also be considered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The amount of power that can be transferred is heavily influenced by ensuring that the input impedance of the transmitting coil is a conjugate match for the Z&lt;sub&gt;O&lt;/sub&gt; of the transmitter and that the load impedance, Z&lt;sub&gt;L&lt;/sub&gt; is a conjugate match for the overall system. Because the mutual impedance factors into this condition, it is typical that the system is first modeled in order to reduce the unknowns prior to commencing construction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the system is closely coupled, the load impedance of the receive antenna should also be included in the modeling exercise. Unlike a radio link with identical antennas in their far fields, the mutual inductance factor often causes the optimum load impedance of the receive antenna to be different than the transmitting coil input impedance even though the coiled antennas are identical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/coOJ2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/coOJ2.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specific to your question as to how to measure the transferred power, place a high impedance RMS RF voltmeter across the load resistor on the receiving coil and apply Ohm's law to resolve the power:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$P=\frac{E_{RMS}^2}{R} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, you may use an oscilloscope. In this case, the observed voltage will be peak to peak. To calculate power:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$P=\frac{E_{p-p}^2}{8R} \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power term can then be converted to dBm:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$dBm=10\log\left(\frac{P}{.001}\right) \tag 3$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are interested in a fairly easy read, and the basic math, regarding WPT you may enjoy the practical academic paper by Minfan Fu, Tong Zhang, Xinen Zhu and Chengbin Ma entitled &lt;a href=&quot;http://umji.sjtu.edu.cn/lab/dsc/files/Papers/Conferences/2013_Fu_WPT.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;A 13.56 MHz Wireless Power Transfer System Without Impedance Matching Networks&lt;/em&gt;&lt;/a&gt;, to which the above diagram is credited. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-05T10:45:25.273" LastActivityDate="2018-12-05T10:45:25.273" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12365" PostTypeId="1" CreationDate="2018-12-05T12:58:50.753" Score="1" ViewCount="180" Body="&lt;p&gt;I am looking for data that compares the number of transmissions per month or year among the various digital modes such as DMR, D-star and Fusion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to see how popular these technologies have been over time.&lt;/p&gt;&#xA;" OwnerUserId="13724" LastEditorUserId="4076" LastEditDate="2018-12-05T19:01:16.550" LastActivityDate="2019-12-31T21:01:15.177" Title="Digital Modes Transmission Traffic Comparisons" Tags="&lt;digital-modes&gt;&lt;d-star&gt;&lt;dmr&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12366" PostTypeId="2" ParentId="6382" CreationDate="2018-12-05T17:30:39.853" Score="-6" Body="&lt;p&gt;None of them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should reprogram on 154.570 &amp;amp; 154.600 low power (MURS Radio Service FCC part 95)&lt;/p&gt;&#xA;" OwnerUserId="13725" LastActivityDate="2018-12-05T17:30:39.853" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12367" PostTypeId="1" CreationDate="2018-12-05T22:03:13.157" Score="2" ViewCount="1170" Body="&lt;p&gt;Can someone tell me why exactly a transistor non-linear power amplifier will amplify an AM signal without noticeable distortion, but will distort an SSB signal, giving the familiar scratchy sound where low amplitude audio is broken up and choppy.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keeping in mind that a 100 % modulated AM signal has voltage levels at zero like this :&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Amplitude_modulation#/media/File:Amplitude_Modulated_Wave-hm-64.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/b/b0/Amplitude_Modulated_Wave-hm-64.svg&quot;&gt;&#xA;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2018-12-07T21:39:58.140" LastActivityDate="2018-12-16T04:02:28.980" Title="Why does a Class-C non-linear power amp distort SSB but does not distort AM?" Tags="&lt;electronics&gt;&lt;amplifier&gt;&lt;ssb&gt;&lt;am&gt;" AnswerCount="2" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="12372" PostTypeId="2" ParentId="12365" CreationDate="2018-12-06T18:48:10.470" Score="1" Body="&lt;p&gt;I think this is an interesting question, but seems hard to answer. In the USA, perhaps you could FOIA the FCC to see what their monitoring stations cover and/or if they collect any data on this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Otherwise, the digital modes you are asking about (DMR, D-star and Fusion) are typically used on the VHF/UHF bands. These transmissions do not propagate far, and so are by nature a &quot;local&quot; thing. Just sampling one local area would not necessarily be representative, either. I'm sure it varies between one group of users on one repeater vs. another repeater, and some wider regions will tend to different modes than others, and it likely varies significantly between, say, Europe vs. USA vs. South America vs. Asia…&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on the motive for your question, maybe a better approach or new followup question would be to see if radio sales numbers are available? Not that everyone uses the digital features, but it at least would reveal potential.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another alternate approach might be to look in the repeater databases (or general radio system listings) and see which protocols are represented most.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, if you primarily want to get a radio compatible with nearby contacts, see if there's an in-person general ham or repeater club or a social media group of hams in your city/district. If asked, I'm sure they'd be happy to offer some opinions of the best type to get based on what's popular locally.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2018-12-06T18:55:15.613" LastActivityDate="2018-12-06T18:55:15.613" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12373" PostTypeId="1" CreationDate="2018-12-06T22:26:15.510" Score="6" ViewCount="266" Body="&lt;p&gt;I'm building a radio communication system for an amateur rocket project. We've decided to use LoRa 868MHz system. My question is, which antenna for the ground station will be the best choice? We're aiming for both vertical and horizontal gain, as we have to receive telemetry both mid-flight and after landing, to locate the rocket. Also, if QFH, then how to maintain precision while building such a small QFH antenna?&lt;/p&gt;&#xA;" OwnerUserId="13735" LastEditorUserId="8573" LastEditDate="2018-12-09T14:35:28.800" LastActivityDate="2018-12-09T14:35:28.800" Title="Antenna for receiving 868MHz rocket telemetry: QFH(QHA), Helical, or?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;uhf&gt;" AnswerCount="1" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12374" PostTypeId="2" ParentId="12367" CreationDate="2018-12-06T22:35:01.637" Score="2" Body="&lt;p&gt;Trying to feed an SSB (or AM) signal to the gate or grid of a Class C amplifier will only produce an output on SSB peaks, which &lt;strong&gt;severely distorts the signal&lt;/strong&gt;. And at the same time, out-of-band products (&quot;splatter&quot;) is produced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A Class C amplifier should only be gate- or grid-driven by a signal whose amplitude does not vary, such as FM. In AM, it is only amplifying the carrier signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In AM, the Class C output stage is always run at a constant power level and the audio modulation is commonly applied to the anode (or drain), &lt;em&gt;never the gate or grid&lt;/em&gt;. The RF drive is constant, and the grid is biased several times the cutoff bias, which significantly increases its efficiency (over 30% as compared to a linear amplifier).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;strong&gt;modulated output signal has voltage levels at or near zero only as a result of applying the audio to the anode&lt;/strong&gt;. A Class-C amplifier &lt;em&gt;is only for amplifying the unmodulated carrier&lt;/em&gt;. &lt;strong&gt;It never should be used to amplify an AM signal&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Amplitude_modulation#Simplified_analysis_of_standard_AM&quot; rel=&quot;nofollow noreferrer&quot;&gt;the &lt;strong&gt;Wikipedia article on AM&lt;/strong&gt;&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In a class-C amplifier, less than 50% of the input signal is used (conduction angle Θ &amp;lt; 180°). &lt;strong&gt;Distortion is high&lt;/strong&gt;.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Anode (plate) modulation. A tetrode's plate and screen grid voltage is&#xA;  modulated via an audio transformer. The resistor R1 sets the grid&#xA;  bias; both the input and output are tuned circuits with inductive&#xA;  coupling.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Q5O1n.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Q5O1n.png&quot; alt=&quot;High level AM plate modulation in a Class C amplifier&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a vacuum-tube tetrode, but the very same principle applies to a triode &lt;strong&gt;or any solid-state class-C amplifier&lt;/strong&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-12-09T02:35:14.043" LastActivityDate="2018-12-09T02:35:14.043" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="12375" PostTypeId="1" AcceptedAnswerId="12376" CreationDate="2018-12-07T02:10:41.383" Score="2" ViewCount="122" Body="&lt;p&gt;This GBTimes article &lt;a href=&quot;https://gbtimes.com/a-tiny-chinese-satellite-is-orbiting-the-moon-and-allowing-radio-amateurs-download-images?feature=chinas-change-4-mission-to-the-far-side-of-the-moon&quot; rel=&quot;nofollow noreferrer&quot;&gt;A tiny Chinese satellite is orbiting the Moon and allowing radio amateurs to download images&lt;/a&gt; links to &lt;a href=&quot;https://twitter.com/w2rtv1/status/1026059755763191808&quot; rel=&quot;nofollow noreferrer&quot;&gt;this tweet&lt;/a&gt; which shows a high gain UHF? antenna pointed at the Moon, and that's about all I can understand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The spacecraft is &lt;a href=&quot;https://space.skyrocket.de/doc_sdat/dslwp-a.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Longjiang-2&lt;/a&gt; a a satellite launched together with the communications relay satellite Queqiao, (which will be the relay for the Chang'e 4 lander launching tomorrow).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The text I don't understand reads:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;2018-05-08 0730-0930 UTC 32-50 degrees EL -- all 11 decodes tonight on JT4G very strong , FT991A 17db LNA, 1/4 hardline 24ft ,Gulf Alpha 8 x 11 beam H-POLE.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Question:&lt;/strong&gt; Is it possible to translate all of that to something that someone with no VHF/UHF experience would understand?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;fyi I don't know about Longjiang-2, but Queqiao is in a halo orbit behind the Moon, so it's not exactly in a lunar orbit as much as it is in orbit around the Earth, a few thousand km behind the Moon, and in 1:1 resonance with the Moon.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oFSue.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oFSue.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="8643" LastEditorUserId="8643" LastEditDate="2018-12-07T02:20:39.820" LastActivityDate="2018-12-07T02:31:14.490" Title="Help understanding this tweet about receiving images from satellite behind the Moon" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12376" PostTypeId="2" ParentId="12375" CreationDate="2018-12-07T02:31:14.490" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;32-50 degrees EL -- all 11 decodes tonight on JT4G very strong , FT991A 17db LNA, 1/4 hardline 24ft ,Gulf Alpha 8 x 11 beam H-POLE.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;JT4G - digital signal mode, &lt;a href=&quot;http://physics.princeton.edu/pulsar/k1jt/JT2_JT4.TXT&quot; rel=&quot;noreferrer&quot;&gt;http://physics.princeton.edu/pulsar/k1jt/JT2_JT4.TXT&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FT991A - Yaesu FT991A radio &lt;/p&gt;&#xA;&#xA;&lt;p&gt;17dB LNA - low noise amplifier (with 17dB gain perhaps) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;1/4 hard-line - the coax connecting the radio to the antenna &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Gulf Alpha 8 x 11 beam H-POLE - the antenna being used &lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2018-12-07T02:31:14.490" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12377" PostTypeId="2" ParentId="12373" CreationDate="2018-12-07T11:12:08.463" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;My question is, which antenna for the ground station will be the best choice?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This answer to this question requires that some data be gathered and calculations performed in order to provide a reliable answer. The primary formula is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Friis equation&lt;/a&gt; but I will break it into its constituent parts. You have not given enough of the data required to calculate your specific situation, so I will work through some examples.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Link Budget&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The link budget is a determination of the maximum loss that the signal can endure and still allow for reliable communications. This data can normally be gathered from the manufacturer's data sheets for the receiver and transmitter. These figures are typically expressed in the units of dBm (decibels compared to 1 millwatt). Let's assume for this exercise that the receiver has a sensitivity of -130 dBm and the transmitter puts out 10 dBm. The link budget is therefore:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$dB_{Link}= dBm_t-dBm_r \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which yields 140 dB in this case. Often the manufacturer's data is a bit optimistic so we will build in a safety factor for this later.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Free Space Path Loss&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next factor that comes into play is the free space path loss (FSPL). This phenomenon occurs because the signal is spreading out as it travels so this reduces the irradiance for a given receive antenna aperture (think about how a flashlight/torch shone on an object, appears to be dimmer the further away the object becomes) . FSPL in dB is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$dB_{FSPL}=20\log\left(\frac{4\pi d}{\lambda}\right) \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is the wavelength of the frequency involved (300/Frequency in MHz) and d is the distance in meters. The dB is a unit that compares the ratio of two powers. Because it is calculated using a logarithm, very large or small ratios are expressed as a more &quot;manageable&quot; number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 868 MHz signal has a wavelength of ~0.346 meters. The distance is the line of sight distance to the maximum expected altitude of the rocket. Consider that this must also include the downrange drift of the rocket as well as the separation distance of the receive antenna sight from the launch point. To take an extreme number, let's use the ~118 km achievement of the GoFast rocket. This gives us an FSPL of ~133 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This 133 dB is subtracted from the 140 dB link budget calculated earlier leaving 7 dB. Because this number is positive, we have 7 dB of link budget &quot;left over&quot; so the antennas can offer moderate performance and still meet this requirement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But to use a more practical example for amateur rockets achieving a maximum line of sight height of say 500 meters, the FSPL is ~85 dB. Subtracting this from the 140 dB link budget leaves a very respectable 55 dB budget. This means that there is plenty of link budget left - the antennas can be quite marginal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Antenna Gain&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna gain can be loosely thought of as how well an antenna can focus its radiated power. The higher the gain of the antenna, generally the narrower (more focused) the main lobe (beam) of the antenna becomes. The same concept can be applied to an antenna that is receiving signals. The gain of the receive antenna and the gain of the transmit antenna added together is the total antenna gain. Antenna gain is typically specified as dBi (dB gain compared to an isotropic antenna)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna on the rocket will likely have minimal or negative gain due to the constraints of rocket mass and geometry as well as the orientation of the antenna relative to the ground station. For example, a small dipole installed along the length of the rocket body would normally have a gain of ~ 5 dBi. But if the ground station is directly under at the launch point, the gain could be closer to -10 dBi due to the main lobe of the antenna being perpendicular to the body of the rocket and therefore not favorable in the direction of the ground antenna. This often makes a strong case for locating the ground antenna somewhat downrange in order to have a better gain perspective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the ground antenna, one must give consideration to the fact that as the gain of the antenna increases, the main lobe typically becomes narrower. This often then necessitates that the ground antenna be steerable to follow the flight path of the rocket. For a low altitude rocket, it may be sufficient to point the ground antenna towards the expected apogee.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The referenced QFH (Quadrifilar Helix) has been optimized to allow non-geosynchronous satellite signals to be received without the need to aim the antenna towards the path of the satellite. The trade-off is that the antenna has relatively low gain due to its main lobe being nearly hemispherical. The gain depends heavily on construction details but typically ranges from 0 to 3 dBi.The QFH antenna also has circular polarization. If used with a linearly polarized antenna, there is a 3 dB gain penalty incurred.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we use these two antennas together and include the 3 dB penalty for circular to linear cross polarization, the combined worse case gain is -13 dB and the best case gain is 5 dB. It is a best practice to allow at least a 10 dB safety margin in the link budget but even with this we still have ample (positive) dB's left in the link budget so this antenna pair should function well for this sample application. It might, however, be marginal for the GoFast rocket example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the construction complexity of a QFH antenna, I would consider a simple quarter wave ground plane antenna or a vertical 1/2 wave dipole as the ground antenna for this example. Either one would be kept at least 1 meter off of the ground via a non-conducting support with the top of the antenna tilted to ~60 degrees away from the line of trajectory of the rocket. Due to the large remaining link budget, an error in the tilting of either of these antennas will not be detrimental to communications. The gain of either of these antennas will exceed 4 dBi and the 3 dB polarization penalty is not incurred. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Recovery Phase&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finding the rocket once it has returned to ground presents some unique challenges. The foliage and ground will attenuate the transmitter signal and the terrain will scatter the transmitter signal. The receive antenna needs to be directional so that you can scan for the location of the rocket by sweeping the main lobe of the antenna back and forth. The receive antenna must also be easily carried in order to &quot;go into the field&quot; to find the downed rocket. A small Yagi antenna works well for these purposes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically visual or GPS tracking of the landing trajectory gets the observer very close to the actual landing location. This helps in the recovery phase since this effectively increases the link budget. In the event of a parachute failure, the recover phase can be very frustrating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Conclusion&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Friis equation provides an analytical method to determine if line of sight communications are possible. The example worked through in this answer is purely hypothetical so the OP should collect the parameters that apply to the specific application and use the described formulas to calculate the necessary antenna gains for the specific application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the link budget cannot be met with reasonable antennas, then the receiver sensitivity, the transmitter power, and even the frequency used are candidates for improving the link budget to make it a reliable communications system.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-07T18:39:25.123" LastActivityDate="2018-12-07T18:39:25.123" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12378" PostTypeId="2" ParentId="12347" CreationDate="2018-12-07T14:45:27.170" Score="0" Body="&lt;p&gt;I have a 23 meter wire antenna strung as an inverted-L. 7m up, the rest horizontal (between 2 trees). Lowest point where the coax is connected about 1m above the ground. I have not done calculations, but have a manual tuner in the shack (with about 12m of coax). A ground pin of 1m deep directly under the inverted L and a counterpoise wire of about 10m length (more wires in many directions would be better but I have no space) looseley covered just under the ground surface. Tunes on all bands: 160m to 6M, including all WARC and 60M.&#xA;Simple to make and it works - don't expect too much DX but I have worked around the world on it (100W).&lt;/p&gt;&#xA;" OwnerUserId="13739" LastActivityDate="2018-12-07T14:45:27.170" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12379" PostTypeId="1" CreationDate="2018-12-08T12:21:38.917" Score="2" ViewCount="81" Body="&lt;p&gt;Are there combo handheld radios for CB and amateur radio? If so, is it practical?&lt;/p&gt;&#xA;" OwnerUserId="13743" LastEditorUserId="76" LastEditDate="2018-12-08T17:08:17.653" LastActivityDate="2018-12-08T17:08:17.653" Title="Are there hand held radios for both Amateur and CB?" Tags="&lt;ht&gt;&lt;citizens-band&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12380" PostTypeId="1" CreationDate="2018-12-08T12:57:58.923" Score="2" ViewCount="49" Body="&lt;p&gt;I wish to fit this on the house gable end, however the location has a metal phone line bracket that will be just bellow the antenna radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will this cause any detrimental effects?&lt;/p&gt;&#xA;" OwnerUserId="13744" LastEditorUserId="4076" LastEditDate="2018-12-09T00:48:12.903" LastActivityDate="2018-12-09T12:48:11.493" Title="Triband vertical antenna 6/2/70" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12381" PostTypeId="2" ParentId="10309" CreationDate="2018-12-08T14:11:02.047" Score="0" Body="&lt;p&gt;I use normally linked dipoles, but there is a fine design called NorCal Doublet (not commercialized, Google for it) that allows you to work from 10 to 40 m on a pole of 6 to 8 m. It is very light and I have good results while being used as inverted V. Anyway, best ones have been reached using linked inverted V center fed dipoles with light coax like RG174.&lt;/p&gt;&#xA;" OwnerUserId="13688" LastEditorUserId="9493" LastEditDate="2018-12-08T17:43:57.217" LastActivityDate="2018-12-08T17:43:57.217" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12382" PostTypeId="2" ParentId="12379" CreationDate="2018-12-08T16:03:28.577" Score="6" Body="&lt;p&gt;No, there are not, because it is not legal to have a radio that can transmit in both CB and amateur radio bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be legal, CB radios must be part 95 type accepted.  The FCC prohibits a device to be both part 95 type accepted and capable of being used in amateur radio frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, many amateur radios are also wide band receivers, and can receive CB.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-12-08T16:03:28.577" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12383" PostTypeId="1" AcceptedAnswerId="12384" CreationDate="2018-12-09T02:51:20.883" Score="1" ViewCount="202" Body="&lt;p&gt;I am putting a run together from my shack to a new 2 meter antenna I've built.  I'm blessed to have many trees on my property and I'll be placing the new antenna about 90 ft from the ground by hanging it off a pine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The plan is to use LMR400 for the run from the shack to antenna which is about 200' total.  To make antenna installation easier and friendlier for maintenance I was planning on using RG8x on the actual antenna installation and tie in the LMR400 about 15 feet away from the antenna to the RG8x at the top of the tree.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently I'm running the antenna on about 100' of RG8x but its not really positioned high enough (its about 25' off the ground).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume there will be some negligible loss when transitioning from LMR400 to RG8x but I hadn't heard of people doing this.  Perhaps its common practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm running the cable tomorrow and wanted to see if there was some insight to avoid climbing the pine more than a few times :)&lt;/p&gt;&#xA;" OwnerUserId="12971" LastActivityDate="2018-12-09T04:28:15.223" Title="Using LMR400 and RG8x in the same feedline" Tags="&lt;coaxial-cable&gt;&lt;feed-line&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12384" PostTypeId="2" ParentId="12383" CreationDate="2018-12-09T04:28:15.223" Score="3" Body="&lt;p&gt;It is perfectly fine to mix two different types of coax like this, providing that they have the same impedance (in this case 50Ω). Any loss in good splices should be negligible. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-12-09T04:28:15.223" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12385" PostTypeId="2" ParentId="12142" CreationDate="2018-12-09T08:08:02.893" Score="1" Body="&lt;p&gt;There are two layers to Morse Code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First:  Amplitude Modulation using the two symbols, &lt;em&gt;Mark&lt;/em&gt; and &lt;em&gt;Space&lt;/em&gt;. This layer is binary. Timing is quantized as the &quot;dit&quot; time. So higher level symbols can be represented as a string of Marks and Spaces aka ones and zeros.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second:  There are four symbols made from the first layer,&lt;br&gt;&#xA;  &lt;em&gt;dit&lt;/em&gt; 10&lt;br&gt;&#xA;  &lt;em&gt;dah&lt;/em&gt; 1110&lt;br&gt;&#xA;  &lt;em&gt;letter space&lt;/em&gt; 00&lt;br&gt;&#xA;  &lt;em&gt;word space&lt;/em&gt; 0000&lt;br&gt;&#xA;NOTE:  Other combinations of 1 and 0 are not allowed. Disallowed combinations means that there is less information contained in a given number of bits, or alternately, there are extra bits required for a given amount of data (redundancy).  This redundancy makes the code more suitable for human recognition. &lt;/p&gt;&#xA;" OwnerUserId="13749" LastEditorUserId="11434" LastEditDate="2018-12-09T14:36:30.330" LastActivityDate="2018-12-09T14:36:30.330" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12387" PostTypeId="2" ParentId="12380" CreationDate="2018-12-09T12:26:56.483" Score="2" Body="&lt;p&gt;For safety sake, make absolutely certain that the wire and bracket is a phone line and not a power line. Miscategorizing the line could be fatal. Also, generally an overhead phone line is in close proximity to an overhead power line. Make certain that you have ample clearance from the power line, during and after installation. Consider your reach distance, your antenna height, your ladder, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bracket, since it is below the ground plane, will probably not have any affect unless it is quite large. I would, however, be thinking about the phone line itself. There is the possibility that enough RF energy could couple to the phone line so as to create RF interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple preventative measure would be to snap on a couple of RFI suppression ferrite cores on the phone line (never the power line!). This may help to mitigate any potential RFI. Using one core of type 31 or 43 material and one core of type 61 material would cover the full frequency range of your antenna. Snap on ferrite cores are available from a wide variety of vendors such as the one from DigiKey:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3QrfB.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3QrfB.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-09T12:48:11.493" LastActivityDate="2018-12-09T12:48:11.493" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12389" PostTypeId="1" AcceptedAnswerId="12390" CreationDate="2018-12-10T14:02:13.770" Score="4" ViewCount="2158" Body="&lt;p&gt;&lt;br&gt;&#xA;I was using a 10-ish meter wire as my HF rx antenna. That's all I can install in my QTH. However I realised that my ~10 m wire can be turned into an end fed dipole for 20 meter band. &lt;br&gt;&#xA;But there is a question:&#xA;If I install my tuner close to antenna end, can i just plug it into the autotuner or should I connect a 9:1 UNUN first?&lt;/p&gt;&#xA;" OwnerUserId="13758" LastActivityDate="2020-02-21T15:43:01.650" Title="Do I need an 9:1 UNUN for a half-wave end fed?" Tags="&lt;balun&gt;&lt;antenna-tuner&gt;&lt;end-fed-antenna&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12390" PostTypeId="2" ParentId="12389" CreationDate="2018-12-10T14:34:31.480" Score="3" Body="&lt;p&gt;An end fed, 1/2 wavelength antenna will have a relatively high impedance of 5k ohms or more. So a 9:1, or greater, ratio of balun may reduce the impedance sufficiently to help your tuner get a match and help avoid a voltage flash-over in your tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there is another issue that may require some planning. When using an end fed antenna, the current on the antenna needs a return path. If you do not provide a good RF ground or counterpoise, the return current will be via your tuner and radio cabinets. This can lead to RF &quot;bites&quot;, RF in the shack causing interference, and even RF burns. If you are running QRP, this may not be an issue. But if you are running 100 watts or more, the effects can be quite pronounced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend you try to install at least a 10 meter counterpoise wire - multiple wires spread out are even better. These can be run vertically down to the ground with the other end attached to the coax braid by the antenna connection. If you lay it in grass, within one season it will disappear into the thatch and sod and will not be seen again - you can even mow over the area.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2018-12-10T14:34:31.480" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12391" PostTypeId="1" AcceptedAnswerId="12393" CreationDate="2018-12-10T14:47:27.883" Score="5" ViewCount="8004" Body="&lt;p&gt;&lt;br&gt;&#xA;I was searching for &lt;em&gt;DIY end-fed antenna.&lt;/em&gt;&lt;br&gt;&#xA;Some of the articles I found say that for a 1/2 wavelength end-fed I need a &quot;small to no counterpoise&quot; (with a lambda*0.05 m counterpoise), but some other articles say that I need &quot;a good RF ground in close proximity to the end of the antenna&quot;.&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Initially, I thought that a good RF ground is required for a random wire antenna but not for 1/2 wavelength one. But I just got an answer here saying that it is needed.&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the truth? What type of end-fed requires a &quot;small to zero counterpoise&quot;?&lt;/p&gt;&#xA;" OwnerUserId="13758" LastEditorUserId="8717" LastEditDate="2018-12-10T17:24:55.427" LastActivityDate="2021-03-28T20:05:49.813" Title="Does a 1/2 wavelength end-fed antenna need a good RF ground?" Tags="&lt;antenna-theory&gt;&lt;end-fed-antenna&gt;&lt;counterpoise&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12392" PostTypeId="2" ParentId="12391" CreationDate="2018-12-10T15:19:13.900" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I was searching for DIY end fed antenna.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;end-fed: A monopole?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;a good RF ground in close proximity to antenna end&quot;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's true for a ¼ wavelength monopole, where the ground acts as &quot;mirror&quot; and lets the antenna behave like a half-wavelength dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't want a full-wavelength dipole (unless you like grating lobes...), so, for a half-wavelength antenna, you avoid the mirror ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You wouldn't end-feed a half-wavelength antenna. You would normally divide it in its middle and make a half-wave dipole out of it, which is a good antenna.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-12-10T15:19:13.900" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="12393" PostTypeId="2" ParentId="12391" CreationDate="2018-12-10T16:10:01.063" Score="3" Body="&lt;p&gt;No, it is not needed, but it can improve the antenna system. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An EFHW is simply a half-wave length of wire and a matching device, and that's it. Counterpoises are commonly added to shunt common mode reflections when operating outside of the wire's resonant frequency to avoid RFI issues (&quot;RF in the shack&quot;). An RF ground (defined here as either very conductive ground, or a radial or grid system of wires beneath the antenna with a radius at least 1/4λ from the antenna center) isn't required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, that ground system improves the conductivity of the ground, which can have a positive effect on the radiation pattern, but little to no beneficial effect on the VSWR. It can also serve the purpose of the counterpoise if the ground side (shield) of the coax is connected to it near the antenna's feedpoint, but that's far more effort than it's worth. &lt;/p&gt;&#xA;" OwnerUserId="392" LastActivityDate="2018-12-10T16:10:01.063" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12394" PostTypeId="2" ParentId="12391" CreationDate="2018-12-10T18:54:30.340" Score="8" Body="&lt;p&gt;An end-fed half-wave operates on a principle that, for lack of a better name, I will call &quot;voodoo&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look at the standing wave on a half-wave element in isolation, you see that the center is the point of highest current and lowest voltage (therefore lowest impedance), and the ends are the points of highest voltage and zero current (therefore infinite impedance). The factors that make the impedance &lt;em&gt;less&lt;/em&gt; than infinite, and therefore make it possible to feed the antenna at all, are the same parasitic/environmental factors that we usually ignore in a quick-and-dirty analysis of an antenna because they're unpredictable and hard to quantify — things like stray capacitance with nearby objects, losses in the matching system, the fact that things we model as zero size actually have physical extent, and (especially) interaction with the feedline. A great many end-fed systems are dependent on feedline radiation to really work; since feedline radiation is generally a cause of RFI problems, operators try to use chokes to raise the common-mode impedance of their feedline, only to find that the feed impedance of their antenna has gone up as well, and they can no longer get a good match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These issues lead to all sorts of creative solutions to try to make end-feds behave, and one of the simplest ways to make an end-fed behave less like an end-fed and more like a dipole is to make it less of an end-fed and more of a dipole. By adding a &quot;counterpoise&quot; to an end-fed, you are adding some kind of an element on the &quot;other side&quot; of the feedpoint. In other words, you're moving the feedpoint away from the end. In other other words, you've turned your end-fed into something more like a (very) off-center fed dipole. The current at this new feedpoint is greater, the impedance is merely &lt;em&gt;large&lt;/em&gt;, and with proper matching, power will actually &lt;em&gt;want&lt;/em&gt; to go into the antenna. This makes the antenna's behavior more predictable based on its own characteristics, and less sensitive to where it's placed, how it's fed, and other &quot;voodoo&quot; factors.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2018-12-10T19:23:13.597" LastActivityDate="2018-12-10T19:23:13.597" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12395" PostTypeId="1" AcceptedAnswerId="12402" CreationDate="2018-12-10T19:11:24.787" Score="7" ViewCount="2718" Body="&lt;p&gt;I would like to make a 1:1 balun with &lt;a href=&quot;https://www.chipdip.ru/product0/30651&quot; rel=&quot;nofollow noreferrer&quot;&gt;М1000НМ&lt;/a&gt; ferrite core (magnetic permeability - 1000) and 1 mm thick copper wire using triple bifilar winding. Unfortunately I didn't manage to find a clear instruction on how to determine the required number of turns. Some sources say to use 3-5 turns, others suggest to use about 20.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to use the balun in 3.5-14.35 Mhz range. The target impedance is 50 ohms. I would like to use the balun as a part of a dipole, to connect a coax cable to it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a lot of copper wire. If I just wind as many turns as possible (it will be about 20 for this core) will it be OK?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPD: TWIMC I've found a great article that explains a lot about baluns and why my original idea to use a voltage balun with a dipole was not that great &lt;a href=&quot;http://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/AntComp1-Lewallen(1).pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/AntComp1-Lewallen(1).pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPD2: Here is a research done by G3TXQ on RFI chokes which you might find very useful &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.karinya.net/g3txq/chokes/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-01-15T08:27:38.507" LastActivityDate="2019-01-15T08:27:38.507" Title="How to determine number of turns for a 1:1 balun?" Tags="&lt;dipole&gt;&lt;electronics&gt;&lt;balun&gt;&lt;choke-balun&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12396" PostTypeId="1" CreationDate="2018-12-10T20:37:26.207" Score="8" ViewCount="479" Body="&lt;p&gt;I'm working out the science behind mounting an antenna on a vehicle, and I came across the concept of ground planes.  &lt;a href=&quot;https://ham.stackexchange.com/a/2022/4476&quot;&gt;This answer&lt;/a&gt; says that longer is better but don't worry about it too much, but &lt;a href=&quot;https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this article&lt;/a&gt; focuses on 1/4 wave ground planes, as do most other articles and products.  I'll be mounting a monopole whip antenna like &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B003H3DTGE&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I use a coil for a radial to get a linearly shorter wire and still make a good ground plane?  &lt;a href=&quot;https://en.wikipedia.org/wiki/Whip_antenna#Electrically_short_whips&quot; rel=&quot;nofollow noreferrer&quot;&gt;Rubber ducky&lt;/a&gt; antennas do this for the main antenna, but I'm interested in using the concept for the ground plane radials.  This antenna will primarily be for transmitting on VHF and UHF frequencies, but will receive on many others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This antenna will be mounted on a tailgate / tire rack, and while there is some room for radials or a sheet of metal for a ground plane or radial, there isn't much more than a foot or so, possibly less.  Some directions will have more room than others: the back moreso than in between the tailgates, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't want you to get distracted with my particular mounting setup, but here's where I'm planning on mounting it, which is a Smittybilt Atlas bumper and tire carrier.  Jeep images are random from a &lt;a href=&quot;https://duckduckgo.com/?q=smittybilt%20atlas%20bumper&amp;amp;t=ffsb&amp;amp;iax=images&amp;amp;ia=images&amp;amp;iai=https%3A%2F%2Fsams4x4.com%2Fimages%2FF923.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;DDG search&lt;/a&gt;.  There will be some kind of interference with the tire carrier top tube, but I was hoping to mitigate that with a good ground plane.  I will cover the tube with some kind of non-conductive material in case the antenna ever makes contact there while I am transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3PKlp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3PKlp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;NOTE:&lt;/strong&gt; The black part is a bolt.  The Antenna is mounted on a small piece of angle iron in an L shape.  My first idea was to put a piece of sheet metal as a ground plane perpendicular to the antenna, but when I started looking into ground planes, realized that often they use radials instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/avmyl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/avmyl.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4476" LastEditorUserId="4476" LastEditDate="2018-12-11T19:41:05.190" LastActivityDate="2018-12-13T23:39:36.640" Title="Can I use a helical ground plane radial in the same way that a loading coil works?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12397" PostTypeId="2" ParentId="10310" CreationDate="2018-12-11T02:15:03.570" Score="4" Body="&lt;p&gt;Glenn's answer here gave me the nudge I needed. Checking through parameters, I found #11 ... Offset ... &lt;strong&gt;5.000 seemed default setting.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With Offset at 5.000 the transmitter was stopped because that would mean operating on an Out of Band frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The anonymous OM who posted &lt;a href=&quot;https://www.youtube.com/watch?v=jPCzJV3gPYQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=jPCzJV3gPYQ&lt;/a&gt; did an admirable job of walking through initial programming, but  everything I tried threw an &quot;&lt;strong&gt;&lt;em&gt;OFF&lt;/em&gt;&lt;/strong&gt;&quot; error. Simplex gave me full power out, but neither + nor - responded properly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I painstakingly spooled down all the way from 5.000 to 0.600 and guess what.&#xA;Yup. Just broke squelch on our repeater!&lt;/p&gt;&#xA;" OwnerUserId="13761" LastEditorUserId="13761" LastEditDate="2018-12-14T04:16:48.283" LastActivityDate="2018-12-14T04:16:48.283" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12398" PostTypeId="2" ParentId="12391" CreationDate="2018-12-11T14:56:49.207" Score="4" Body="&lt;p&gt;The EFHW (end fed half wave) needs to be classified as a specific case of the class of end fed wire antennas. The name is even a bit of a misnomer since the EFHW is often operated on multiple bands and therefore is no longer a half wave antenna. And due to the implementation details, the antenna is in fact often not even a half wave at its design frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But let's start with the general situation of a half wavelength long piece of wire. As long as it remains a half wavelength long, the gain and radiation pattern of the antenna is the same even if we feed this half wave wire at various points along its length. At nearly every point that we choose to feed it, the antenna will &lt;strong&gt;&lt;em&gt;not&lt;/em&gt;&lt;/strong&gt; be resonant - that is to say at nearly every feedpoint, there will be reactance. Technically speaking, even a center fed half wave antenna is not resonant - we shorten it slightly from a true half wavelength in order to make it resonant when center fed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you feed a half wave antenna in its center, the antenna feedpoint is balanced - that is to say that each half of the antenna has the same impedance and so the same current would naturally flow into each half of the dipole. At any other feedpoint, the two parts of the antenna exhibit different impedances which results in different effective currents in the two sections. This can present challenges as it relates to the feed system. The corrective action is often a current balun that &quot;forces&quot; the same current into each part of the antenna in an effort to reduce the inevitable common mode current on the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The extreme case of imbalance when feeding a half wave antenna occurs when it is fed from the end. The impedance at the end of the antenna will be quite high - typically 5,000 ohms or more. To tame this high impedance, an impedance transformer of at least 9:1 and as high as 49:1 is often used. This transformer is a simple autotransformer so it can do nothing to reduce common mode current on the feedline. It also tends to be quite lossy when used over a wide frequency range. This helps improve the SWR due to the lower Q but this comes at the expense of reducing the efficiency, and thus gain, of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is often overlooked in an end fed antenna design is that the current that is present on the half wave element needs a method of returning to the transmitter in order to allow the antenna to efficiently radiate. There are erroneous claims on the Internet that the autotransformer somehow provides this path but that is simply not true. The autotransformer provides a return path for some of the current on the feedline (in the form of a reflection) but not for the current on the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet we know that an EFHW &quot;works&quot; to some degree as many people have success with this style of antenna - so where is the path for the return current? The answer is highly dependent on the installation. In most cases, the external braid of the coax provides the return path. When this happens, the braid is actually part of the radiating antenna. So it transpires in this case that the claimed half wave antenna is no longer a half wave at all! This also means that the antenna pattern is likely not what would be suggested by the spacial orientation of its half wavelength piece of wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other installations, if the shield connection of the autotransformer is directly grounded to an earth ground system, the return path will largely be through the lossy earth (although some shield current can still exist). Due to the lossy earth, the antenna system efficiency, and therefore gain, is reduced. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The third installation variation is to install counterpoise wires that drop from the elevated transformer down to the ground and then run along the ground. In this case, these wires will typically also form part of the radiating antenna but at least a good part of the return current comes via these wires instead of the lossy earth. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-11T16:58:38.673" LastActivityDate="2018-12-11T16:58:38.673" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12399" PostTypeId="2" ParentId="12396" CreationDate="2018-12-11T17:14:26.387" Score="2" Body="&lt;p&gt;If all you want to do is achieve a resonant feedpoint impedance, one spiral radial will come close, by acting as a counterpoise. I don't know where the radiation from a single spiral radial would go. If you want to prevent the radials from radiating, the usual method is to use N times two identical horizontal radials pointing in opposite directions. Since the identical currents in each two identical radials are flowing in opposite directions, their horizontal far fields tend to cancel. It seems logical to assume that two identical opposing horizontal spiral radials would not radiate much.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2018-12-11T17:14:26.387" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12400" PostTypeId="2" ParentId="12396" CreationDate="2018-12-11T17:37:17.807" Score="2" Body="&lt;p&gt;The so called ground plane is there primarily to help feed the antenna in a predictable, controlled manner. In the absence of the ground plane, the coax cable becomes part of the antenna which has an effect on the radiation pattern; the impedance and therefore the SWR; and the efficiency and therefore the gain. As the ground plane design is compromised from &quot;ideal&quot;, some of these factors come into play.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a simple example of the effect of the ground plane, consider that an ideal quarter wave VHF or UHF vertical antenna has an impedance of ~34 ohms. In order to better match this to 50 ohm coax, a common technique is to bend down the ground plane radials so they are 45 degrees below horizontal. While this provides a better match, it also alters the radiation pattern of the antenna - moving it closer to the pattern of a 1/2 wave vertical dipole. The result is that some of the transmitted power is wasted as it is directed below the horizon of the base of the antenna towards the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best advice for your situation is to simply try your ground plane options to see how they work for you. Try to keep the ground plane in symmetry. Ideally you should test the SWR of the antenna with a more optimum ground plane and then with your compromised ground plane in order to compare SWR and signal strength results. Keep in mind that the radiation pattern of the antenna may be altered by the location of the antenna as well as the compromised ground plane. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;[EDIT]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on the diagram that you added, a radial (wire) radial system will work for your installation. You will have some issues with directivity due to the metal in the tailgate. It would be better if you could elevate the base of the antenna so that it is even with the lower edge of the rear glass. The roll bar will still interfere with the pattern but it will be better in general.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On my Jeep (YJ Wrangler) I use a lip mount bracket on the front hood positioned on the opposite side of the AM/FM broadcast antenna. The hood and front quarter panel provide a reasonable, albeit asymmetric, ground plane.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-13T23:39:36.640" LastActivityDate="2018-12-13T23:39:36.640" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12401" PostTypeId="2" ParentId="12396" CreationDate="2018-12-11T18:16:55.440" Score="1" Body="&lt;p&gt;As Glenn and Cecil have already said, you &lt;em&gt;could&lt;/em&gt; use them. However, if your tailgate/tire rack was metal, you likely wouldn't need any radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Helical radials, having inductance, would take some trial-and-error unless they were modeled. Some better alternatives:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Two straight radials for UHF likely wouldn't take up enough room to&#xA;warrant helices.&lt;/li&gt;&#xA;&lt;li&gt;For 2m, the radials could be bent into opposing&#xA;semi-circles or zigzag in lieu of helices.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;To minimize interaction between the different radials for each band, they should be 90° apart from each other (i.e. the UHF pair would be pointed E-W, and the VHF radials would be oriented N-S).&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-12-11T18:29:56.973" LastActivityDate="2018-12-11T18:29:56.973" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12402" PostTypeId="2" ParentId="12395" CreationDate="2018-12-11T21:56:07.310" Score="6" Body="&lt;p&gt;The ideal number of turns depends on core material, geometry, and frequency. This is why you find such variance in how many turns should be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More turns increases the choking impedance up to a point, but decreases the choke's self-resonant frequency (SRF). Once the SRF goes below the operating frequency, adding more turns increases the distributed capacitance and decreases the overall choking impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could determine the optimal number of turns empirically. &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;Measure the common-mode current&lt;/a&gt; when transmitting a test signal, then add or remove turns until you find a number of turns that minimizes the common-mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With appropriate test equipment the choking impedance can be measured directly as well. See &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/#measurement&quot; rel=&quot;noreferrer&quot;&gt;G3TXQ's method&lt;/a&gt;, for example.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-12-12T02:36:15.787" LastActivityDate="2018-12-12T02:36:15.787" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12403" PostTypeId="2" ParentId="12367" CreationDate="2018-12-12T01:01:39.203" Score="3" Body="&lt;p&gt;A class C amplifier indeed distorts AM and causes widespread splatter just as it does for SSB signals. BUT if you have a class C amplifier and apply modulation to it by superimposing the modulation signal on the supply voltage you can produce excellent AM modulation. The graph &quot;150% modulation&quot; in the question is not what one normally would see. With typical AM modulators the signal would go to zero and not reverse phase when the modulating signal goes negative. By use of a schottky mixer one could do AM that reverses the phase for negative modulation voltages and that would eliminate the splatter, but for the question about class C amplifiers that is not relevant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A class C amplifier (ideally) provides no output at all below a certain threshold. Maybe 20% of the peak power. If the signal is compressed to never go below say 25% of the peak power you could use a class C amplifier. That is surely true for FM, but also for AM at 50% modulation. The class C amplifier also has a sharp limit for maximum power that has not to be exceeded. Actually that is more of a problem in class AB amplifiers that may have a grid resistor with a large time constant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is however a trick, variable class amplifiers. Easy with tubes. Use a grid resistor that would change the operation point when grid current flows. Set the amplifier to operate in class AB, or maybe class B as long as the grid current is zero. When the grid current starts, a suitable resistor would bring the tube(s) into class C. The important thing is to make the time constant for DC on the grid much smaller than the time constant of the signal. Our AM or SSB signals might contain frequencies up to maybe 5 kHz so it is necessary that the time constant on the grid corresponds to at least 500 kHz for variable class to work as intended. The amplifier should be tuned for a class C signal. The transfer function is a bit curved not only at low levels, but also at high levels, but it is possible this way to get some extra power without causing problems to neighbouring hams.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The important thing is the transfer function. Output power vs input power. A properly tuned class C amplifier has a transfer function that is zero for powers from zero to perhaps 25% of maximum power. Then the function is a reasonably straight line. In this region grid current is zero or small. At higher powers the transfer function bends which of course causes distortion.&#xA;Normal operation in class C is to drive the amplifier deeply into saturation, but if driving the amplifier mildly into saturation the distortion will be of low orders and not harmful - but peak power would be higher than from a common linear amplifier. When operating like this one needs an oscilloscope with two power detectors. One for input power and one for output power so one can see the transfer function on an oscilloscope in x vs y mode. In variable class, the amplifier would operate in class A until grid current occurs. As grid current increases the class would change into AB, B and ultimately C. The transfer function will be a little S-like. Bending softly at both ends - at the low end depending on the idle current. It is extremely important that the time constant on the grid is very much shorter than the time constant for the modulation. &#xA;As a contrast, a conventional amplifier design aims at best possible linearity. That is often associated with a very sharp corner at saturation. That would be a VERY bad source of splatter in case saturation is reached. Even worse is amplifiers that have a high impedance for the grid bias with a large time constant. It would change the grid bias and bring the amplifier into class C which would cause disastrous splatter. Not uncommon - at least not in the tube ages from where I have my practical experiences.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This URL:&lt;a href=&quot;https://www.radio-electronics.com/info/rf-technology-design/am-amplitude-modulation/modulation-index-depth.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.radio-electronics.com/info/rf-technology-design/am-amplitude-modulation/modulation-index-depth.php&lt;/a&gt; provides a picture of 100% AM modulation. The image showing &quot;Amplitude modulated index of more than 1.0&#xA;i.e. over-modulated&quot; is however false. The same error on over-modulation is displayed here: &lt;a href=&quot;https://electronics.stackexchange.com/questions/107128/what-is-overmodulation&quot;&gt;https://electronics.stackexchange.com/questions/107128/what-is-overmodulation&lt;/a&gt; it seems that this idea has become widespread, but it is not true at all. What we have in real life is demonstrated here: &lt;a href=&quot;https://www.quora.com/For-the-AM-modulation-modulation-index-not-be-greater-than-unity-is-it-true-or-false&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.quora.com/For-the-AM-modulation-modulation-index-not-be-greater-than-unity-is-it-true-or-false&lt;/a&gt; Rather than changing sign, the signal abruptly goes to zero when overmodulation occurs. That would cause wideband splatter. Must not ever occur!!!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In modern hardware one might produce AM by use of a schottky mixer. Then the signal would behave as in the links that I claim to be wrong. The resulting AM would most probably sound bad in a conventional AM detector, but I think it would sound perfectly OK in a synchronous detector. Such a signal would not cause splatter and might actually be an interesting new modulation mode, but just labelling it AM would probably lead to confusion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An AM broadcaster produces AM with a high efficiency class C amplifier that is modulated on the supply voltage. The supply voltage can not go negative. Today it would be possible to reverse the phase by 180 degrees at the point where the supply voltage reaches zero and amplify the signal 180 degrees out of phase proportional to the amplitude as long as the signal is negative. That would be a technology halfway to double sideband with suppressed (but nonzero) carrier. Easily received with modern synchronous detectors. Skipping the carrier saves 6 dB of power. In real life much more since modulation is not near 100% most of the time. I am pretty sure we will not see this kind of modulation in the broadcasting world since digital modes give significantly bigger advantages. I think conventional AM will live for still quite some more time - and that modulation index above 1 will not occur in the broadcasting world. Modulation index up to perhaps 1.8 could be something fun for radio amateurs to experiment with. Conventional AM, max 95% modulation (or so) is inefficient on a typical linear amplifier (as compared to a plate or screen+plate modulated class C amplifier. With 180% modulation one would be fairly close to DSB with a suppressed carrier - and that might be power efficient.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastEditorUserId="9758" LastEditDate="2018-12-16T04:02:28.980" LastActivityDate="2018-12-16T04:02:28.980" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12406" PostTypeId="1" AcceptedAnswerId="12427" CreationDate="2018-12-13T02:29:37.540" Score="9" ViewCount="299" Body="&lt;p&gt;I have a cheap baofeng uv-5r, and I sometimes hear an intermittent transmission which pulses past the squelch threshold with periods of dead space between, roughly 0.75 seconds or less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My job uses a repeater and radioreference.com lists the used frequency as 151.18 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have trouble hearing them on the baofeng, but not my alinco dj500t, a question I'm sure for a separate post as to why.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyways I hear this pulse on both the work frequency and MURS channel 1 (151.88 MHz). Can anyone shed light on this? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In summation of the question, is it possible someone transmitting on a nearby frequency is being picked up?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To add to the final question, it seems to me that listening on 151.00 MHz could potentially monitor the whole 151.**** MHz area, based on the way my alinco functions, of this I'm very unsure, and don't want to seem unintelligent, but I am very new, is that possible?&lt;/p&gt;&#xA;" OwnerUserId="13767" LastEditorUserId="4076" LastEditDate="2018-12-13T10:14:06.860" LastActivityDate="2018-12-29T19:33:39.420" Title="If someone transmits on 151.88 MHz and I listen on 151.18 MHz, how likely would I hear their transmission?" Tags="&lt;receiver&gt;&lt;baofeng&gt;&lt;uv-5r&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12411" PostTypeId="2" ParentId="12406" CreationDate="2018-12-13T10:14:56.103" Score="4" Body="&lt;p&gt;In theory, this is a question of the bandwidth - or better said of 2 bandwidths.&#xA;In practice it's much more complex. But let's have a look at bandwidth theory first:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the bandwidth of your transceiver&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;the bandwidth of the signal interfering you.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Let's assume you have your receiver on 151,180,000 Hz. &lt;/li&gt;&#xA;&lt;li&gt;Let's further assume your receiver has a bandwidth on FM of 15 kHz.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;This means that you will receive signals between 151,180,000 +/- 7.5 kHz which means that whenever a signal is transmitted between 151,172,500 and 151,187,500 you will receive it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other part is the transmitting signal:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also have a bandwidth there. So let's assume you have a signal on 151,880,000 with a bandwidth of 1 MHz (maybe for transmitting digital data). Thus it will interfere between 151,380,000 and 152,380,000 (+/- 500 kHz). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question is - will you be interfered by this signal on your frequency 151,180?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer is: it depends. In theory no, because the interfering bandwidth does not touch your receiver frequency (see above). In practice your receiver is not ideal - and speaking about Baofeng, it's as far from ideal as it can be - by still working more or less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many reasons why even good and expensive receivers have troubles with signals on other frequencies. In a nutshell &lt;strong&gt;it's just a question of the signal strength of the other signal and of the filter quality of the receiver&lt;/strong&gt;. Also the frequencies of both signals matter, because they might be mixed up into new frequencies in the reception path of the transceiver. I assume that the signal on 151,88 is very strong. &lt;/p&gt;&#xA;" OwnerUserId="13317" LastEditorUserId="13317" LastEditDate="2018-12-13T23:17:40.613" LastActivityDate="2018-12-13T23:17:40.613" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12413" PostTypeId="1" AcceptedAnswerId="12421" CreationDate="2018-12-13T13:51:14.190" Score="3" ViewCount="199" Body="&lt;p&gt;In the context of &lt;a href=&quot;https://ham.stackexchange.com/questions/12065/converting-wpm-to-cpm/12066?noredirect=1#comment18523_12066&quot;&gt;wondering how to convert&lt;/a&gt; characters per minute to words per minute, it was pointed out that CODEX and PARIS are used as typical words for measuring speed of CW operators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the wikipedia &lt;a href=&quot;https://en.wikipedia.org/wiki/Morse_code#Speed_in_words_per_minute&quot; rel=&quot;nofollow noreferrer&quot;&gt;states&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;There are two common typical words: &quot;PARIS&quot; and &quot;CODEX&quot;. &lt;br&gt;&#xA;  PARIS mimics a word rate that is typical of natural language words and&#xA;  reflects the benefits of Morse code's shorter code durations for&#xA;  common characters such as &quot;e&quot; and &quot;t&quot;. &lt;br/&gt;&#xA;  CODEX offers a word rate that&#xA;  is typical of 5-letter code groups (sequences of random letters).&#xA;  Using the word PARIS as a standard, the number of dot units is 50 and&#xA;  a simple calculation shows that the dot length at 20 words per minute&#xA;  is 60 milliseconds. Using the word CODEX with 60 dot units, the dot&#xA;  length at 20 words per minute is 50 milliseconds.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'll argue that neither PARIS nor CODEX are themselves typical in morse communication. The assumed typical length of five letters seems, at least for English, unfounded, too:&lt;br&gt;&#xA;Even if we assume that a keyer would omit articles like &quot;the&quot; and &quot;a&quot; regularly, prepositions (&quot;on&quot;, &quot;at&quot;, &quot;by&quot;, &quot;for&quot;…) should be rather common and are much shorter. Longer words tend to get abbreviated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, since the wikipedia doesn't actually cite its sources: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Who (and: when) decided CODEX and PARIS would be appropriate for words-per-minute estimates?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;and&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Are there statistics to back this up?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-12-14T23:24:50.340" Title="Why were &quot;PARIS&quot; and &quot;CODEX&quot; considered &quot;typical words&quot;?" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12414" PostTypeId="1" AcceptedAnswerId="12417" CreationDate="2018-12-13T15:25:42.113" Score="3" ViewCount="1827" Body="&lt;p&gt;It's easy to understand, conceptually anyway, the difference between a horizontally polarized antenna and a vertically polarized one, when referenced to ground.  However, when they are pointed nearly straight up at a satellite that reference is effectively lost. Yet communications with satellites require different polarizations.  How does that work?&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-12-15T14:40:53.417" Title="Antenna polarization when dealing with satellite communications" Tags="&lt;antenna&gt;&lt;satellites&gt;&lt;polarization&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12415" PostTypeId="2" ParentId="12414" CreationDate="2018-12-13T15:33:59.080" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;However, when they are pointed nearly straight up at a satellite that reference is effectively lost&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Satellite communications typically uses &lt;em&gt;circular&lt;/em&gt; polarizations instead of &lt;em&gt;linear&lt;/em&gt; (horizontal/vertical) for that exact reason; that's why when you open e.g. sat-TV feedhorns, you'll often find &quot;snail&quot;-shaped structures inside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With clockwise and counterclockwise, you don't need absolute orientation; what's important is the same &quot;rotational direction&quot;, if you will.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2018-12-13T15:33:59.080" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12416" PostTypeId="1" CreationDate="2018-12-13T17:49:21.010" Score="3" ViewCount="1019" Body="&lt;p&gt;Looking to build a crystal radio, need help with the coil. I'm looking to get something to work with 1/4&quot; thin wall copper tubing. Already have some nice diodes and whatever capacitors/resistors I need. I don't care if it is AM or shortwave, I can make more more than one. For shortwave I'll soon be building this  &lt;a href=&quot;https://i.stack.imgur.com/DWtns.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DWtns.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the AM radio I built, and it does really well, I have two stations nearby (within a mile or two) in the mid and high AM band. It uses taps instead of a slider. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9Lxuh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9Lxuh.jpg&quot; alt=&quot;how a crystal radio works&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that's about my comfort zone right now, I plan on going all the way though, so post them if you got them. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I already read about how to make the forms for an air coil and reinforcement if needed, so no problem there. I figure I can solder taps onto the coil as needed. &lt;strong&gt;The big problem is my intended size is way outside the norms, so is this possible?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="13773" LastEditorUserId="8717" LastEditDate="2018-12-13T17:59:16.600" LastActivityDate="2018-12-13T19:59:52.650" Title="Air Coil AM &amp; Shortwave Crystal Radio Using 1/4&quot; Copper Tubing" Tags="&lt;diy&gt;&lt;crystal-radio&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12417" PostTypeId="2" ParentId="12414" CreationDate="2018-12-13T17:52:09.710" Score="9" Body="&lt;p&gt;Satellite engineers tend to use circular polarization for two reasons:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;When a linearly polarized signal travels through the atmosphere&#xA;there are anomalies, such as &lt;a href=&quot;https://en.wikipedia.org/wiki/Faraday_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;Faraday rotation&lt;/a&gt;, that alter the&#xA;polarization of the EM wave.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The geographic reference of the satellite polarization changes for&#xA;a non-stationary satellite as it traverses its path above the earth-bound point of observation.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Either of these conditions can introduce significant antenna system losses when linear polarization is involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A circularly polarized EM (electro-magnetic) wave refers to a wave that rotates between horizontal and vertically polarization and all planes in between. The rotation cycle repeats once per wavelength. When viewing the wave in the direction of travel, a clockwise rotation is considered right hand circular (RHC) polarization while a counter (anti) clockwise rotation is considered left hand circular (LHC) polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateurs often use cross polarized linear yagi antennas for circularly polarized satellite communications. Technically these produce an elliptical polarization. With a simple control of the phasing network, a near RHC or LHC polarization can be achieved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The loss between antennas of mismatched polarization, when one involves circular polarization and the other is linear, is typically limited to 3 dB. This is contrasted to the loss between a worst case horizontal and vertical polarization that can incur a &gt;20 dB loss (in theory, an infinite loss). There is a similar high loss when a RHC polarized antenna is used with a LHC polarized signal and vice versa.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[EDIT]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are interested in this topic, there is a very nice article on antenna polarization experiments by first year MIT engineering student, 18 year old Adeline Hillier AA7HH, in the January 2019 issue of QST. It is great to see this type of interest and enthusiasm from an aspiring electrical engineer.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-15T14:40:53.417" LastActivityDate="2018-12-15T14:40:53.417" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12418" PostTypeId="2" ParentId="12416" CreationDate="2018-12-13T19:52:00.860" Score="3" Body="&lt;p&gt;Congratulations on a nice home-brew project! I started my journey into amateur radio with a crystal set such as yours.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Making the inductor (coil) out of copper tubing is overkill from an electrical standpoint since very little current is involved. But you certainly gain significant mechanical strength and perhaps more importantly, aesthetic appeal from using copper tubing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may be best to give you some of the simple math behind your crystal radio design in order to help you with your inductor construction. The inductor and the capacitor form a tuned circuit. Your circuit uses a parallel resonant construction which allows the desired signal to continue to the diode detector and the earphone while all other signals are effectively shorted out. The frequency in Hertz that the parallel resonant circuit allows to pass is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$f=\frac{1}{2\pi \sqrt{LC}} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where L is the value of the inductor in henries and C is the value of the capacitor in farads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically we deal with values of capacitors and inductors that are much smaller than a farad or henry. In the case of your first schematic, for example, the capacitor value is shown in picofarads or 10&lt;sup&gt;-12&lt;/sup&gt; farads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the specifics of winding your inductor, it is best to rearrange formula 1 to find the value of L for a given capacitor value and a given target frequency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$L=\left( \frac{1}{(2\pi f)} \right )^2 C^{-1} \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for your shortwave example, if your capacitor is set to 500 pF (500 x 10&lt;sup&gt;-12&lt;/sup&gt; farads) and you wish to receive a frequency of 5 MHz (5 x 10&lt;sup&gt;6&lt;/sup&gt; hertz), then L would be ~2 microhenries (2 x 10&lt;sup&gt;-6&lt;/sup&gt; henries).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can then use any number of on-line calculators to get the winding dimensions for your inductor. You need to pick a calculator that allows you to specify the gap between turns (or winding pitch) such as &lt;a href=&quot;http://electronbunker.ca/eb/InductanceCalc.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt;. According to this calculator, a coil 75 mm in diameter comprised of 7 turns of 6.35 mm wire (0.25 inch copper tubing) with a 12.7 mm pitch (a gap of 0.25 inches between windings) would fit the bill.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The tap for the antenna on the coil can be determined experimentally. Simply adjust for maximum signal strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With regard to receiving short wave stations using a crystal radio, unfortunately many governments are closing their shortwave broadcast facilities. Crystal radio sets are not particularly sensitive so unless you live in close proximity to operating shortwave broadcast stations, you may not be able to tune in many stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have fun with the project!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-13T19:59:52.650" LastActivityDate="2018-12-13T19:59:52.650" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12419" PostTypeId="1" CreationDate="2018-12-14T13:16:17.350" Score="2" ViewCount="489" Body="&lt;p&gt;In order to generate circular polarization in a crossed-yagi, a 90° phase delay is required between the horizontal and the vertical antenna. In practice, this is achieved either by making a mechanical shift of lambda/4 or by using phasing stubs. However, some cots antenna have a mechanical plane offset different than the lambda/4. Indeed in my case, I have a 70cm 2x19 elements antenna from Tonna that I want to set up for satellite operations. To achieve right-hand circular polarization, a phasing harness was purchased&#xA;                  &lt;a href=&quot;http://www.wimo.de/download/1808xx.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.wimo.de/download/1808xx.pdf&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the antenna datasheet, a mechanical offset of 200mm is specified. When consulting other forums and by using online phasing calculators, an extra length of -18.83 mm is needed (see screenshot). On the other hand, the phasing calculations provided in the harness datasheet are totally different. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone please give me a clue here? I would reaaaaally appreciate it. I'm really lost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/41khu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/41khu.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="12902" LastEditorUserId="9493" LastEditDate="2018-12-14T17:57:30.133" LastActivityDate="2019-01-13T19:00:50.200" Title="How to use 70 cm WiMo phasing harness for a COTS crossed yagi antenna?" Tags="&lt;uhf&gt;&lt;yagi&gt;&lt;circular-polarization&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12420" PostTypeId="2" ParentId="12419" CreationDate="2018-12-14T14:40:13.760" Score="1" Body="&lt;p&gt;The problem with the result of the online calculator you pictured is that your DE spacing is already greater than &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;/4 (~172 mm). As a result, you must &lt;em&gt;remove&lt;/em&gt; the indicated length from the coax feeding the leading DE in order to achieve an overall 90 degree phase shift . That is to say that your mechanical spacing is 105 degrees so you need to &lt;em&gt;remove&lt;/em&gt; 15 degrees from the harness in order to achieve a total phase shift of 90 degrees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The WiMo formula, on the other hand, is simply wrong - unglaublich!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The correct formula for DE spacing &amp;lt;&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;/2:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$L_{physical}=(\lambda/4-\Delta_{DE})*VF \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$\Delta_{DE}$&lt;/span&gt; is the distance between driven elements and &lt;span class=&quot;math-container&quot;&gt;$VF$&lt;/span&gt; is the velocity factor of the coax. A negative result indicates the coax must be shortened by that amount as noted above.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-14T18:01:37.897" LastActivityDate="2018-12-14T18:01:37.897" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12421" PostTypeId="2" ParentId="12413" CreationDate="2018-12-14T20:57:32.753" Score="2" Body="&lt;p&gt;Answering the 2nd part:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There seem to be many research articles and business documents reporting statistics on average word lengths, in characters, which seem to vary with language, dialect, corpus, and even over time.  The lengths reported seems to cover a range between 4 and 6 letters, which makes rounding to integer 5 (at some point in history) a reasonable compromise (for large English and German corpuses).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There also exist many tables of statistics of relative letter frequencies in various Western languages (see various cryptography books), which could be converted into an average dot length for a given length word.  A quick Monte Carlo simulation I ran seems to show that 5 letters randomly chosen using the statistical distribution from a &lt;a href=&quot;https://en.wikipedia.org/wiki/Letter_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia table of relative letter frequencies in English&lt;/a&gt;, will average somewhere around 50 to 51 dot times in duration, using International Morse Code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The word &quot;PARIS&quot; seems to fit within these statistical ranges for word lengths and letter frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A random selection of search results:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://arxiv.org/pdf/1208.6109.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://arxiv.org/pdf/1208.6109.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://diuna.biz/length-of-words-average-number-of-characters-in-a-word/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://diuna.biz/length-of-words-average-number-of-characters-in-a-word/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://practicalcryptography.com/cryptanalysis/letter-frequencies-various-languages/english-letter-frequencies/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://practicalcryptography.com/cryptanalysis/letter-frequencies-various-languages/english-letter-frequencies/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Specialized abbreviations seem to be a performance optimization  or data compression process, not included in the pre-encoded corpus.  Also, short words might seem more common; but that might be due to an &quot;availability bias&quot; error in human cognition.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a random additional factoid, according to Wikipedia: &lt;a href=&quot;https://en.wikipedia.org/wiki/Morse_code#International_Morse_Code&quot; rel=&quot;nofollow noreferrer&quot;&gt;International Morse Code&lt;/a&gt; was standardized at the International Telegraphy Congress in 1865 in &lt;strong&gt;Paris&lt;/strong&gt; and was later made the standard by the &lt;a href=&quot;https://www.itu.int/en/history/Pages/ITUBorn1865.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;International Telecommunication Union (ITU)&lt;/a&gt;.   There exists an &lt;a href=&quot;https://www.itu.int/rec/R-REC-M.1677-1-200910-I/&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU document on International Morse Code encoding&lt;/a&gt;, however it doesn't mention speed of encoding in words.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-12-14T23:24:50.340" LastActivityDate="2018-12-14T23:24:50.340" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12423" PostTypeId="1" CreationDate="2018-12-16T01:57:26.777" Score="7" ViewCount="273" Body="&lt;p&gt;Does anyone know how to --or have any experience with-- water or oil-cooling the anode? Since forced-air cooling is required, the sound from the blower and the exhaust air would be too noisy for my ears.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They look similar to an 8877, but have &lt;em&gt;removable&lt;/em&gt; finned copper anode coolers.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/lVh2P.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lVh2P.jpg&quot; alt=&quot;GS35B&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have two of &lt;a href=&quot;http://gs35b.com/&quot; rel=&quot;noreferrer&quot;&gt;those tubes&lt;/a&gt;, and I would &lt;em&gt;love&lt;/em&gt; to build a legal-limit amplifier using at least one of them. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-12-16T17:12:49.053" LastActivityDate="2018-12-19T23:03:54.233" Title="Water cooling a GS-35B in lieu of air cooling?" Tags="&lt;diy&gt;&lt;electronics&gt;&lt;amplifier&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12425" PostTypeId="2" ParentId="12423" CreationDate="2018-12-16T11:56:21.737" Score="7" Body="&lt;p&gt;The GS-35A tube is the liquid cooled version of the same tube. Some hams have fabricated their own version of a liquid cooling jacket to replace the fins on the GS-35B:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sR2Xn.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sR2Xn.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://www.realhamradio.com/liquid-cooling.htm&quot; rel=&quot;noreferrer&quot;&gt;designer&lt;/a&gt; of this jacket correctly highlights the challenges of selecting and maintaining the liquid medium since it is exposed to the full anode high voltage. Deionized water will require regular maintenance to maintain its insulating properties. Generally a liquid with lower maintenance requirements is selected with the tradeoff being lower specific heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While liquid cooling does reduce the in cabinet blower noise, the liquid medium will require cooling in the form of forced air, mechanical refrigeration, or other means. The result is that the noise can be relocated to an area away from the operator, but not entirely eliminated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will still require some forced air cooling in the cabinet in order to keep the seals of the tube intact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With all of that being said, if noise reduction in the shack is the goal, I would design the amplifier to be blower cooled and remotely controlled. A few servo motors, some bandswitch relays and some remote metering seems much more practical and hassle free.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-16T13:00:21.097" LastActivityDate="2018-12-16T13:00:21.097" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12427" PostTypeId="2" ParentId="12406" CreationDate="2018-12-17T06:22:27.110" Score="2" Body="&lt;p&gt;It's possible for a strong enough interfering RF signal to overload the front end amplifier(s) of a receiver.  Once overloaded into a non-linear range, all bets are off as to the resulting bandwidth of the interfering signal, which could then splatter into many nearby channels. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the stop-band attenuation of any of a receiver filters is poor, it's possible for a strong enough signal in a stop-band to blast right through the stop-band, above the squelch or demodulation threshold, and then possibly alias down to a different or image frequency during any heterodyning, digital sampling or processing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible for a strong enough interfering RF signal to couple into a receiver's wiring past any RF or IF filtering stages (even directly into the audio amplifier or the DC power supplies), thus potentially turning the receiver into a wide band demodulator of some sort.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2018-12-29T19:33:39.420" LastActivityDate="2018-12-29T19:33:39.420" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12430" PostTypeId="1" AcceptedAnswerId="12431" CreationDate="2018-12-17T21:53:58.987" Score="1" ViewCount="91" Body="&lt;p&gt;Will a mobile antenna --either mag mount or NMO mount-- couple to surrounding objects such as tall trees, taller trucks, buses, or even people walking by?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that is the case, would you get slightly better transmission signal if you parked in a crowded parking lot? As you get a better ground plane?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an SG7500 NMO mount on the roof of my car, a little bit to the left side. Radio is a TMV71A. Last night, after I stepped out while talking on the repeater, the NET controller then told me that my signal just degraded a lot. The signal returned to normal after I got back in. It was not noisy outside, and so I believe it is a bonding issue.&lt;/p&gt;&#xA;" OwnerUserId="13362" LastEditorUserId="8717" LastEditDate="2018-12-17T23:26:56.523" LastActivityDate="2018-12-18T01:45:29.953" Title="Mobile VHF/UHF antenna coupling to surrounding objects?" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12431" PostTypeId="2" ParentId="12430" CreationDate="2018-12-18T01:45:29.953" Score="2" Body="&lt;p&gt;You've got plenty of ground plane on your roof and there is probably nothing wrong with your antenna installation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's better thought of as a matter of propagation. Radio waves are reflected, refracted, diffracted, or absorbed, to various amounts, by &lt;strong&gt;everything&lt;/strong&gt; in the environment. Objects nearby will &lt;em&gt;change&lt;/em&gt; the radiation pattern of your antenna, but whether that change is for the better or for the worse depends on which direction the other station is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When using FM, there's a fairly sharp transition from enough signal to be clearly heard to a very noisy signal, so a small change in how well your signal reaches the repeater can make a big audible difference. You've probably heard the &quot;picket fencing&quot; effect when your radio or someone else's is in motion and quickly flutters into and out of intelligibility. This is the same thing you experienced, except from a different cause, and it didn't cycle since the object (you) didn't keep moving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't bother trying to fix your system — there will always be better and worse physical arrangements, and you'll just be changing which ones there are. Instead, be prepared to try parking differently if you need to make a contact while stationary.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-12-18T01:45:29.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12432" PostTypeId="1" CreationDate="2018-12-18T08:42:17.630" Score="4" ViewCount="136" Body="&lt;p&gt;Pex is cheap and comes pre-coiled, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;3/8&quot; pex is 0.360&quot; ID.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1/2&quot; is 0.485&quot; ID&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fill with &quot;sea water&quot; using distilled water and sea salt to proper concentration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use for AM and/or Shortwave coil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sea water is HIGHLY conductive and interacts with radio waves. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I need some suggestions for the size of the coil and how many turns, I intend to test it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm within 2 miles of a couple radio stations, @ ~1100 and ~1400 so sensitivity issues will be minimal. &lt;/p&gt;&#xA;" OwnerUserId="13774" LastEditorUserId="13774" LastEditDate="2018-12-18T22:07:02.547" LastActivityDate="2018-12-20T21:01:17.077" Title="Can I create a functional crystal radio using a plastic coil filled with seawater as the inductor?" Tags="&lt;receiver&gt;&lt;crystal-radio&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12433" PostTypeId="2" ParentId="10168" CreationDate="2018-12-18T12:48:57.740" Score="0" Body="&lt;p&gt;I ran 800 watts (out) through a Dosy meter for many years w/o issue.&#xA;Having said that, I dont know about current production, this was 20 years ago.&#xA;I cant speak for how accurate they can be on the rest of the HF spectrum.&#xA;ymmv&lt;/p&gt;&#xA;" OwnerUserId="13793" LastActivityDate="2018-12-18T12:48:57.740" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12434" PostTypeId="1" AcceptedAnswerId="12435" CreationDate="2018-12-18T13:48:32.783" Score="5" ViewCount="366" Body="&lt;p&gt;I receive OOK signals from a remote control in 433MHz. I'm using a dongle RTL-SDR on GNU Radio. &#xA;The FFT output signal from the RTL-SDR Source block is represented on the picture: &lt;a href=&quot;https://i.stack.imgur.com/s9om9.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/s9om9.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, why i have two signals with similar amplitude? Shouldn't it be only one?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal in the time domain:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/8UAzZ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8UAzZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The output in time domain after demodulate:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/J0kqY.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/J0kqY.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13599" LastEditorUserId="13599" LastEditDate="2018-12-18T15:46:57.880" LastActivityDate="2018-12-18T21:09:30.710" Title="FFT showing 2 signals - GNU Radio" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12435" PostTypeId="2" ParentId="12434" CreationDate="2018-12-18T16:07:26.003" Score="9" Body="&lt;h3&gt;What's going on&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Most software-defined radios use &lt;strong&gt;quadrature&lt;/strong&gt; in their signal processing architecture. This means there are two copies of the signal processing chain, with local oscillators that are 90° apart in phase while being otherwise identical. Once they reach software, they can be processed using complex number arithmetic (hence the &quot;real&quot; and &quot;imaginary&quot; labels on GNU Radio's time domain graph) which makes various signal processing operations much more straightforward.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if there is a problem with &lt;em&gt;one&lt;/em&gt; of the two signals paths, such that there is significantly different gain between them (there will always be &lt;em&gt;some&lt;/em&gt; mismatch since real components aren't perfect and even DSP has finite precision), then you will see what you see here — the signal appearing mirrored, having similar peaks on the positive and negative-frequency sides. (You can experiment with this in GNU Radio — take a signal, convert complex to pair of floats, multiply one by a constant, then convert back to complex, and watch the mirror image appear.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically in your images, notice that the copy is &lt;strong&gt;at the same frequency with opposite sign&lt;/strong&gt; (&amp;minus;0.23 and +0.23) and also that it is &lt;strong&gt;very strong&lt;/strong&gt; — in the time domain plot the line is nearly ±1.0, which is the absolute maximum representable value in the hardware. All RF hardware will deal worse with strong signals, but digital clipping like you seem to have here will abruptly produce spurious signals of many kinds.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;What to do&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;What you can do is turn off the AGC on your RTL-SDR — it is not good at this task because it does not leave any headroom for suddenly appearing signals — and then set the manual gain setting until the spurious peak appears less but you still have enough signal to process. If that doesn't suffice, then install an attenuator in the antenna line, or relocate the antenna farther away. (Or try unplugging the antenna entirely; strong signals may be picked up anyway.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, if you are solely trying to pick up that OOK signal and don't care about selecting it out of other nearby signals (filtering) or the cleanliness of the pre-demodulation signal, then you could just leave things the way they are and not try to tweak it. (The &lt;em&gt;general&lt;/em&gt; risk here is that the receiver might be damaged by a too-strong signal, which you can't tell from the current situation once it's gotten strong enough to clip, but that seems unlikely from a simple battery-powered remote control.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-12-18T21:09:30.710" LastActivityDate="2018-12-18T21:09:30.710" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12439" PostTypeId="2" ParentId="12432" CreationDate="2018-12-19T13:34:17.303" Score="5" Body="&lt;p&gt;Sea water is not that conductive: about 5 S/m. By comparison, the conductivity of copper is about 60000000 S/m, so seven orders of magnitude more conductive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The low conductivity of sea water will effectively appear as a resistance in series with the coil. This will increase losses in the coil, reducing sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But worse, it will decrease the &lt;a href=&quot;https://en.wikipedia.org/wiki/Q_factor&quot; rel=&quot;noreferrer&quot;&gt;Q factor&lt;/a&gt; of the LC filter, reducing selectivity. The resulting &quot;radio&quot; would be incapable of tuning to an individual station. Perhaps this isn't too much of a concern, since given the sensitivity issues you will have to be very close to a transmitter to hear anything, at which point that single transmitter is probably the strongest source of RF around.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess technically we could call this a &quot;radio&quot;, though by this definition you could attach just about anything conductive to a diode and call it a radio. For any practical application, copper (or really, most metals) is a better choice: it's smaller, cheaper, electrically superior, non-corrosive, and solid at room temperature.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-12-19T13:34:17.303" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12440" PostTypeId="1" CreationDate="2018-12-19T18:32:56.717" Score="8" ViewCount="340" Body="&lt;p&gt;We have a repeater here in Southern California (Sylmar K6GE 147.435), and no matter what time of day or night there are a great many operators spewing tremendous profanity, disrespect and meanness toward one another.  This is embarrassing and makes if very hard for parents to get their children into ham radio when the air is full of this nastiness.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Considering profanity is prohibited by FCC and there are supposed to be Auxiliary monitors helping police this type of thing, what can one do to find out if there are any actions being taken to track down and punish these nasty operators?&lt;/p&gt;&#xA;" OwnerUserId="13724" LastEditorUserId="9493" LastEditDate="2018-12-24T14:13:40.330" LastActivityDate="2021-01-27T21:50:50.020" Title="How to clean up profanity on airwaves" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;repeater&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12441" PostTypeId="2" ParentId="12440" CreationDate="2018-12-19T19:03:10.110" Score="9" Body="&lt;p&gt;I've heard --from reliable sources-- that about the only thing that can stop that is to make recordings that you can send to the FCC. Include well-thought-out documentation with callsigns, times and dates, frequencies, and any other relevant information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL &lt;a href=&quot;http://www.arrl.org/amateur-auxiliary&quot; rel=&quot;noreferrer&quot;&gt;may contact the FCC&lt;/a&gt; for you.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2018-12-19T19:03:10.110" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12443" PostTypeId="2" ParentId="12423" CreationDate="2018-12-19T23:03:54.233" Score="1" Body="&lt;p&gt;One might consider using &quot;Latent heat of vaporization&quot; to transfer many BTU's away. Liquid water turning to vapor (steam) will rise and can carry a large amount of heat to a condenser and flow back to the boiler (tube) via gravity. Keep it a closed loop system.&#xA;&lt;a href=&quot;https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1966/05/page18/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1966/05/page18/index.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="607" LastActivityDate="2018-12-19T23:03:54.233" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12447" PostTypeId="2" ParentId="12432" CreationDate="2018-12-20T21:01:17.077" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Can I create a functional crystal radio using a plastic coil filled with seawater as the inductor?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, of course.  Matter of fact, you can make a crystal radio without any inductor, too.  Connect the antenna, diode, Hi-Z earphones, and ground wire, all in series.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coil/capacitor is to tune the radio, filtering out all other stations except for the one station that is tuned in.  I would recommend a capacitor in parallel with the coil, to properly tune.  Crystal radios are very forgiving to build.  Especially with a big outdoor antenna, and a 50,000 watt blowtorch station a few miles away. You might even be able to hook up a small speaker.  Go for it.  &lt;/p&gt;&#xA;" OwnerUserId="8647" LastActivityDate="2018-12-20T21:01:17.077" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12449" PostTypeId="2" ParentId="1227" CreationDate="2018-12-20T21:19:38.003" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I want to minimize &quot;RF in the shack&quot; ... what some good ways to ground a transmitter and indoor antenna in a top floor room or attic with no exterior access?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Adding to what Phil Frost said (above), which I agree.  Also, you can use an &quot;artificial ground&quot;.  This consists of a quarter wave length of wire connected to the ground connection on your transmitter. The artificial ground absorbs RF.  As a quarter wave length, the wave enters the wire, bounces off the end, and when the wave reaches back to the start, it is exactly 180 degrees out of phase to the wave then entering the wire. The two waves cancel. So it absorbs any RF energy at the tuned frequency.  Of course, it works only at the frequency/wavelength that it is built for.  You could add artificial ground wires for each band that you operate.  &lt;/p&gt;&#xA;" OwnerUserId="8647" LastEditorUserId="76" LastEditDate="2018-12-20T22:10:31.763" LastActivityDate="2018-12-20T22:10:31.763" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12450" PostTypeId="2" ParentId="3523" CreationDate="2018-12-20T21:29:25.370" Score="1" Body="&lt;p&gt;I am copying my answer to another similar question. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If I want to minimize &quot;RF in the shack&quot; ... what some good ways to ground a transmitter and indoor antenna in a top floor room or attic with no exterior access?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Adding to what Phil Frost said (above), which I agree. Also, you can use an &quot;artificial ground&quot;. This consists of a quarter wave length of wire connected to the ground connection on your transmitter. The artificial ground absorbs RF. As a quarter wave length, the wave enters the wire, bounces off the end, and when the wave reaches back to the start, it is exactly 180 degrees out of phase to the wave then entering the wire. The two waves cancel. So it absorbs any RF energy at the tuned frequency. Of course, it works only at the frequency/wavelength that it is built for. You could add artificial ground wires for each band that you operate. &lt;/p&gt;&#xA;" OwnerUserId="8647" LastEditorUserId="76" LastEditDate="2018-12-20T22:10:51.053" LastActivityDate="2018-12-20T22:10:51.053" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12452" PostTypeId="2" ParentId="3523" CreationDate="2018-12-21T13:45:42.653" Score="2" Body="&lt;p&gt;Note that the context is an &lt;strong&gt;&lt;em&gt;RF ground&lt;/em&gt;&lt;/strong&gt; the purpose of which is to reduce or eliminate &quot;RF-in-the-shack&quot;. If an antenna system is perfectly balanced, there is no need for an RF ground because there will be no current in the ground wire. Moral: Avoid unbalanced antenna systems (OCFs and EFs) if one's shack is on the second story. (Please note that a vertical with radials has balanced voltages AND currents if the feedpoint impedance of the antenna and the feedpoint impedance of the radials are equal, i.e. &quot;balanced&quot; can have two different meanings.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;RF-in-the-shack&quot; really means &lt;strong&gt;&lt;em&gt;RF voltage&lt;/em&gt;&lt;/strong&gt; in the shack which is what bites us when the chassis is &quot;hot&quot;. We can have high RF current in the shack and not even realize it. The purpose of a 1/4WL wire connected to the transmitter chassis is to move the voltage maximum point from the transmitter chassis out to the end of the 1/4WL of wire. There is just as much RF energy in the shack as before but we have forced it into the magnetic field (current) on the transmitter chassis rather than existing in the electric field (voltage). But that 1/4WL of wire will radiate just like 1/4WL of a 1/2WL dipole antenna (and may be physically too close to the operator). The energy in the forward and reflected waves on that 1/4WL wire does NOT cancel. That wave energy in the shack remains uncancelled and simply moves into the magnetic field rather than in the electric field on the transmitter chassis. But since that 1/4WL of counterpoise wire radiates like an antenna, it is better to avoid having to install it - better to have a balanced antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An &quot;artificial ground&quot; box (MFJ-931) is somewhat like an antenna tuner for the ground wire. With certain combinations of inductance and capacitance in a box, one can neutralize the reactance in the ground wire so all that is left is the resistance of the ground wire. Note that this is the RF resistance, not the DC resistance. If one has an artificial ground box and the wire to ground is 1/4WL, neutralizing the reactance will not help as the RF resistance is sky high. If a ground wire is run from the second story to earth ground, it needs to be a multiple of 1/2WL but like the 1/4WL counterpoise, it will radiate just like an antenna element. Better to have a balanced antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: This posting does not address lightning protection or safety grounding.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2018-12-21T14:15:51.930" LastActivityDate="2018-12-21T14:15:51.930" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12453" PostTypeId="2" ParentId="11837" CreationDate="2018-12-21T15:06:19.983" Score="1" Body="&lt;p&gt;I finally obtained one of the described adapters, and I can confirm that yes, it does indeed work fine.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2018-12-21T15:06:19.983" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12454" PostTypeId="1" AcceptedAnswerId="12455" CreationDate="2018-12-21T20:26:41.810" Score="7" ViewCount="1011" Body="&lt;p&gt;I've got a 27dBm signal that I'm going to put through a 6dB attenuator. How do I work out the resultant signal in dBm?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried Googling that without any luck.&lt;/p&gt;&#xA;" OwnerUserId="13815" LastEditorUserId="8717" LastEditDate="2018-12-21T20:48:32.127" LastActivityDate="2018-12-21T23:48:11.607" Title="dBm signal minus dB" Tags="&lt;rf-power&gt;&lt;measurement&gt;&lt;math&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12455" PostTypeId="2" ParentId="12454" CreationDate="2018-12-21T21:15:48.973" Score="8" Body="&lt;p&gt;Decibels are all &quot;ratios&quot; at their core. A unitless dB is a simply a ratio of one number to another, perhaps input power relative to output power. We can also use decibels for absolute values, by fixing the denominator to a standard reference — e.g. one milliwatt in dBm. But the most convenient thing about decibels is that, although they are ratios, because they have been &quot;logarithm&quot;-ed, we can add and subtract them instead of having to multiply and divide.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you have a 27 dBm signal attenuated by 6 dB, the result will be a 21 dBm signal, since 27 minus 6 is 21.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could have looked at this by saying &quot;I've got a 500 mW signal which I'm going to put through an attenuator which divides signals by 3.98&quot; and gotten a result of 125.6 mW. That's not so bad with a calculator, but a bit harder to do precisely in our head especially after we add in more links (amplifiers, antenna gain, coax/path losses, etc.) to a communications system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found a page &lt;a href=&quot;http://www.animations.physics.unsw.edu.au/jw/dB.htm&quot; rel=&quot;noreferrer&quot;&gt;dB: What is a decibel?&lt;/a&gt; that goes more in depth if you're interested in the underlying math. That page is in the context of audio, but the concepts are generalizeable. In fact, going beyond decibels entirely, a &lt;a href=&quot;https://en.wikipedia.org/wiki/Slide_rule&quot; rel=&quot;noreferrer&quot;&gt;slide rule&lt;/a&gt; uses the same underlying principle to make general multiplication/division easier without an electronic calculator.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2018-12-21T21:36:19.860" LastActivityDate="2018-12-21T21:36:19.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12456" PostTypeId="2" ParentId="12454" CreationDate="2018-12-21T23:48:11.607" Score="7" Body="&lt;p&gt;Think about it this way. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;27 dBm means 27dB above a milliwatt.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take 6dB away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you have something that's 21 dB above a milliwatt. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, 21 dBm.&lt;/p&gt;&#xA;" OwnerUserId="8573" LastActivityDate="2018-12-21T23:48:11.607" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12459" PostTypeId="2" ParentId="3523" CreationDate="2018-12-22T11:22:52.040" Score="0" Body="&lt;p&gt;RE: &lt;strong&gt;Note: This posting does not address lightning protection or safety grounding.&lt;/strong&gt; —  Most of the a-c-powered tx/rx equipment in use includes a connecting path from the circuit &quot;common&quot; (typically, via the chassis to the &quot;ground&quot; pin of its a-c mains cord).  However, the path through the a-c mains wiring to the mains &quot;ground&quot; can have high reactance in the r-f spectrum, which won't provide a good r-f ground to the ham equipment, and reduces its effectiveness as a lightning and/or safety ground.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2018-12-22T11:22:52.040" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12463" PostTypeId="1" AcceptedAnswerId="12663" CreationDate="2018-12-23T22:32:02.647" Score="9" ViewCount="1886" Body="&lt;p&gt;The solar system on my house creates horrible rfi on all hf bands during the day when the sun is out, it goes away when it's not sunny. Any one got any ideas how to get rid of the rfi ? I already tried putting capacitors across the high voltage solar panel inputs on the inverter, made no difference.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2020-10-29T12:28:24.937" Title="How can I get rid of RFI coming from my house solar panel inverter?" Tags="&lt;rfi&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12466" PostTypeId="1" CreationDate="2018-12-24T10:57:21.427" Score="0" ViewCount="176" Body="&lt;p&gt;So I've been looking at my different options for 6 meter mobile antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question mainly pertains to grounding. I've heard hams talk about needing a ground to the frame of the vehicle when using HF. I don't know if this is also important for 6 meters or not. It would be much easier for me to get a mag mount, but I'm unsure if the grounding will be good enough at 6 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I do go the mag mount way, there are two options I'm looking at: A standard 1/4 wave NMO or a DC grounded 1/4 wave NMO. The DC grounded one has a coil. I'm assuming this coil is going to ground because there is no need to load this antenna as it is already 1/4 wave long. This leads me to think that the DC ground is serving some other purpose. Could it be to help the ground performance on a mag mount? (This is what I'm hoping.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I do manage to ground the antenna properly, my impression is that 6 meters would be the apex of mobile communication. The size of the roof is very close to the right size for a ground plane on this band. In addition, the antenna is pretty much the largest without being loaded. Being in a hilly environment, I think this should be the best band.&lt;/p&gt;&#xA;" OwnerUserId="1817" LastEditorUserId="13615" LastEditDate="2018-12-29T03:59:46.903" LastActivityDate="2018-12-29T03:59:46.903" Title="6 meter mobile antenna grounding" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12468" PostTypeId="2" ParentId="12463" CreationDate="2018-12-24T13:43:13.110" Score="6" Body="&lt;p&gt;The inverter in your solar panel system utilizes a high frequency switcher to regulate the voltage and convert it to AC for feeding back into the mains. Some solar panels also use an &amp;quot;optimizer&amp;quot; on the back of the solar panel that is a smaller switching device designed to optimize the usable energy from the individual, or small group of, panels. Both of these devices can radiate switching noise through the wires connected to them which act as antennas This switching noise is generally rich in harmonics that can easily pollute the entire HF spectrum.&lt;/p&gt;&#xA;&lt;p&gt;You may not be able to entirely eliminate the switching noise but judicious use of ferrite suppression devices may knock it down to an acceptable level. Before considering any modifications to your solar panel system, be aware that both the mains and the DC side of the system can contain voltages that are capable of producing lethal currents in the human body. You may also be subject to local regulations that limit what you or anyone else can do in the way of modifications. Don't overlook the effect of any modifications on your solar system warranty.&lt;/p&gt;&#xA;&lt;p&gt;Since you are working with existing wiring, the easiest form of ferrite suppression is the clamp on variety:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XoGrQ.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XoGrQ.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;You will need to acquire an assortment of type 31 and type 75 ferrite clamp on beads (don't use uncharacterized, junk box beads). The type 75 material is most effective at low HF frequencies while the type 31 material covers the balance of the HF and low VHF spectrum. Place at least one of each type of bead on all well insulated wires, as close as safely possible to where they enter and exit the inverter and any optimizers. Do not place beads on bare wires or in locations where they can come in contact live conductors such as screw terminals. Don't overlook control and network cables. Multiples of each bead per wire will increase the RFI suppression effectiveness. If you can wrap more than one turn of wire through the snap on core, its effectiveness is generally multiplied by the square of the turns. For example, 3 turns is the equivalent of 9 beads.&lt;/p&gt;&#xA;&lt;p&gt;Ferrite material choking performance degrades in the presence of strong DC current. For this reason, it is better to pass both DC wires from the solar panels through the same snap on ferrite as this will eliminate the DC bias in the core. This may necessitate purchasing some snap on ferrites with a larger dimension hole in order to accommodate both DC wires.&lt;/p&gt;&#xA;&lt;p&gt;If you work through a disciplined process of noting the noise level at a given frequency, adding beads to a selective location and then checking for any change in the RFI level, you may be able determine where installing more beads would be most effective.&lt;/p&gt;&#xA;&lt;p&gt;It is also a good time to review the location of your HF antenna system relative to the solar panel system. Increased distance of the antenna and feedline from the solar system will tend to reduce the RFI. Also check to make sure you don't have common mode currents on your antenna feedlines as this will couple the locally produced RFI into your receiver. Proper current baluns and balanced antennas help to mitigate these common mode currents.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-12-26T15:47:18.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12469" PostTypeId="2" ParentId="12466" CreationDate="2018-12-24T13:52:30.760" Score="1" Body="&lt;p&gt;The bonding of automotive panels and structures is generally done to reduce RFI that can affect in-vehicle electronics. On 6 meters, this may not be at all necessary but you will not know until you try it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 1/4 wavelength vertical antenna will produce an SWR of ~1.5:1 in an efficient installation. Keep in mind that the relatively high RF resistance of the steel panels of the vehicle add to the inefficiency of the ground plane. Due to the short length of coax involved, a base matching coil to reduce the SWR is generally not warranted from a feedline loss perspective as the losses in the matching circuit will nearly equal any coax losses due to the slightly elevated SWR in the no coil version. However, your 6 meter transmitter may put out slightly less power when faced with a 1.5:1 SWR. In this case you may be able to justify the use of an antenna with a base matching network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The height of a 1/4 wave antenna for 6 meters can place a fair bit of strain on an NMO mount. Regularly check your installation to make certain that everything is properly tightened and snug.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-24T19:58:35.223" LastActivityDate="2018-12-24T19:58:35.223" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12470" PostTypeId="1" CreationDate="2018-12-24T17:27:15.190" Score="4" ViewCount="559" Body="&lt;p&gt;I recently purchased a cheap RTL-SDR kit to experiment with SDRs and different frequency bands. &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B011HVUEME&quot; rel=&quot;nofollow noreferrer&quot;&gt;This kit&lt;/a&gt; came with 23cm and 100cm telescoping antennas. I now wish to use the 100cm antenna to pick up NOAA APT signals at 137 MHz. Many sites with instructions for a V-Dipole antenna for this purpose indicate that a 53cm half-wave antenna works well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there something special about telescoping antennas such that they only work when fully extended, or can I partially retract the 100cm antennas to 53cm to get the proper length?&lt;/p&gt;&#xA;" OwnerUserId="13831" LastActivityDate="2018-12-25T15:18:17.533" Title="Partially Collapse Telescoping Antenna to Change Effective Length" Tags="&lt;antenna&gt;&lt;dipole&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12471" PostTypeId="2" ParentId="12470" CreationDate="2018-12-24T18:03:53.183" Score="2" Body="&lt;p&gt;Yes, you can partially collapse a telescoping antenna. There are no special considerations versus other types of antenna elements / monopoles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a slight effect from the thickness of the antenna — thicker conductors, such as the telescoping elements closer to the base, exhibit more bandwidth (less selectivity). This is usually not very significant at all for receiving purposes, but if you're trying to pick out a single signal then you can theoretically get a &lt;strong&gt;small&lt;/strong&gt; reduction of out-of-band interference by extending the thinner sections of the antenna rather than the thicker ones, provided that you also get the length exactly right (adjusting to maximize the power of the received signal).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2018-12-24T18:03:53.183" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12472" PostTypeId="2" ParentId="12470" CreationDate="2018-12-24T18:15:41.267" Score="1" Body="&lt;p&gt;53cm is ~1/4 wavelength on 137 MHz. I can't tell if your antenna is a single vertical monopole element or a rabbit ears type dipole. Assuming it is a single vertical element, if you provide a ground plane and set the length to 53 cm, you will have a resonant ground plane vertical on ~137 MHz. The ground plane could be a pizza pan or metal filing cabinet, etc. and coupling to it can be either coax braid direct wiring or capacitive coupling through magnets (if any).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it is a rabbit ears type dipole, each element needs to be set to 53 cm and you can skip the ground plane.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2018-12-24T18:15:41.267" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12473" PostTypeId="2" ParentId="12470" CreationDate="2018-12-24T20:47:31.953" Score="2" Body="&lt;p&gt;Telescoping antennas work at any length you set them.  They are always connected internally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Speaking from experience, being able to move the antenna around to find the best signal makes a much bigger difference than fine tuning its length.&lt;/p&gt;&#xA;" OwnerUserId="1087" LastActivityDate="2018-12-24T20:47:31.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12475" PostTypeId="2" ParentId="12470" CreationDate="2018-12-25T14:26:54.633" Score="0" Body="&lt;p&gt;Radio frequency currents flow largely along the surface of a conductor due to &lt;a href=&quot;https://wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin effect&lt;/a&gt;. As a result, the center portion of a conductor typically plays no role in the conduction of RF current.  The conductor can be hollow or filled with any other material and it will have minimal effect, provided the surface conductor is sufficiently thick.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your telescoping antenna also exhibits skin effect. As a result, the part that is telescoped inside another section plays no practical role in conducting RF current to your SDR antenna input - it is as if it is not even there. Only the visible, outside surface of the telescoping element functions as the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When configuring a dipole antenna, the overall length in meters is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$l=\frac{142.5}{f} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is the frequency in MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equivalently, the length of a dipole in feet is given as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$l=\frac{468}{f} \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The length of each leg is one half of &lt;span class=&quot;math-container&quot;&gt;$l$&lt;/span&gt;. The length is typically not extremely critical for receive applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The NOAA APT transmissions are right hand circularly polarized satellite signals (RHCP). The dipole antenna is linearly polarized. As a result you will experience about 3 dB of signal loss. This is typically an acceptable loss for this application. Keep your dipole antenna horizontally orientated and at least 1 meter away from other objects including the earth.  Turn it about the vertical axis that is perpendicular to the telescoping elements for the best signal strength.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-25T15:18:17.533" LastActivityDate="2018-12-25T15:18:17.533" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12476" PostTypeId="1" AcceptedAnswerId="12495" CreationDate="2018-12-25T17:34:40.137" Score="-1" ViewCount="187" Body="&lt;p&gt;My approach is that a radio wave is made from zillion of accelerated electrons which emit zillions of photons. Since the current flows in a open circuit, the antenna generator works against something like a capacitor. So I want to know, is my imagination comparable with the radio specialists knowledge? Could it be that the power output of an antenna often looks like below?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y3ToP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y3ToP.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The red line is the ideal sine curve. The axis to the right is the time, the other axis is the power output. The blue line is the curve in reality, which one can get from an antenna generator. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From theoretical assumptions only, I suppose that the following points improve the curve closer to a sine&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;to some extend a longer antenna,&lt;/li&gt;&#xA;&lt;li&gt;a lower frequency of the antenna generator,&lt;/li&gt;&#xA;&lt;li&gt;a capacitor on the end of the antenna rod.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The background is my &lt;a href=&quot;https://physics.stackexchange.com/questions/449947/why-are-longwave-radio-towers-so-tall/449969?noredirect=1#comment1009211_449969&quot;&gt;answer&lt;/a&gt; to the question “Why are longwave radio towers so tall?”.&lt;/p&gt;&#xA;" OwnerUserId="13834" LastEditorUserId="13834" LastEditDate="2018-12-26T06:54:01.683" LastActivityDate="2018-12-29T01:51:35.923" Title="Output power curve of an antenna" Tags="&lt;antenna-system&gt;" AnswerCount="3" CommentCount="13" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12477" PostTypeId="2" ParentId="12278" CreationDate="2018-12-25T21:21:49.720" Score="1" Body="&lt;p&gt;To add to the excellent answers here, here's what I did here to solve this problem. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This common-mode LAN choke is 14 turns of CAT5e wound on a 2.4&quot; OD Fair-Rite toriod core made of type 31 ferrite. Mouser Electronics and Newark Electronics stocks them, about $7 each.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These can also be used for choking any common-mode RF on the router's power supply (&quot;wall-wart&quot;) cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/a8sd2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/a8sd2.png&quot; alt=&quot;LAN common-mode choke 1&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I already have a similar coax choke at the feedpoint of my low backyard dipole, except there are fewer turns and about four of these chokes stacked.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2018-12-25T21:46:01.697" LastActivityDate="2018-12-25T21:46:01.697" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12478" PostTypeId="2" ParentId="9686" CreationDate="2018-12-25T22:24:04.630" Score="0" Body="&lt;p&gt;I never saw a viable answer here.  Realize this post is a year old, hopefully it is answered somewhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution is to select band A, left side by pressing the left volume control on the right side of the display.  Then press F, followed by pressing the left volume control button.  I'm not sure how to do this repeatedly but what I did was press F then the volume until I hit the desired frequency band.  There are other tweaks needed like frequency spacing, etc.  The MCP-6A software tool is ideal for updating and setting the options.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Jinglish in the manual is very poor for the supurb quality of the radio!&lt;/p&gt;&#xA;" OwnerUserId="13835" LastActivityDate="2018-12-25T22:24:04.630" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12479" PostTypeId="2" ParentId="12476" CreationDate="2018-12-26T01:00:10.780" Score="2" Body="&lt;p&gt;It's important to be clear about definitions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Power&lt;/em&gt; in this context is usually defined as the product of &lt;a href=&quot;https://en.wikipedia.org/wiki/Root_mean_square&quot; rel=&quot;nofollow noreferrer&quot;&gt;root-mean-square&lt;/a&gt; (RMS) voltage and current. Assuming transmission of an unmodulated carrier, power is constant over time because RMS current and voltage are constant over time, by the definition of RMS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It makes no sense to think about power &quot;between&quot; the peaks and valleys of current or voltage. All electromagnetic radiation oscillates at some frequency, and thus must necessarily cross zero periodically. If the voltage and current didn't cross zero, there could be no oscillation, and thus no radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of power, what about just voltage? Again assuming only an unmodulated carrier, voltage is exactly a sine wave. This holds true at any antenna length, at any frequency, and even if there are &lt;a href=&quot;http://www.k0bg.com/caphats.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;capacitors&lt;/a&gt; or &lt;a href=&quot;https://en.wikipedia.org/wiki/Loading_coil&quot; rel=&quot;nofollow noreferrer&quot;&gt;inductors&lt;/a&gt; as part of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm guessing by your drawing you're thinking the antenna looks somehow like a capacitor to the transmitter. &lt;strong&gt;But it does not: typically the antenna is tuned so that it looks like a resistor, because the antenna is tuned to be resonant. Resonance is by definition a zero reactance, so the antenna impedance must be resistive.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What if the antenna isn't resonant? Well, in that case we can just forget about antennas and just ask what happens if an AC voltage source is connected to a capacitor:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Etg39.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fEtg39.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer is the voltage across the capacitor is still sinusoidal. It has to be, by definition of how voltage sources work. The voltage across C1 is equal to the voltage across V1, by &lt;a href=&quot;https://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws#Kirchhoff&amp;#39;s_voltage_law_(KVL)&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kirchoff's voltage law&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What about current? Also sinusoidal. The current through a capacitor is given by the equation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ I(t) = C {\mathrm d V(t) \over \mathrm d t} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt; is time, &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; is capacitance, and &lt;span class=&quot;math-container&quot;&gt;$V$&lt;/span&gt; is voltage. If &lt;span class=&quot;math-container&quot;&gt;$V(t)$&lt;/span&gt; is some sinusoidal function, then by basic calculus it should be clear &lt;span class=&quot;math-container&quot;&gt;$I(t)$&lt;/span&gt; is another sinusoid, shifted 90 degrees in phase and scaled in amplitude by a factor of &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only time the voltage between any two points in any antenna, or the current through any segment of an antenna is not a sinusoid is when the signal being transmitted is not a sinusoid. Even then, in practice it's usually pretty close to a sinusoid, especially if we're only looking at a few cycles since any modulation which would modify the sinusoid is usually slow compared to the period of the oscillation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By &lt;a href=&quot;https://en.wikipedia.org/wiki/Fourier_analysis&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fourier analysis&lt;/a&gt; we can see that anything which isn't pretty close to a sine wave will contain energy on many frequencies. When a transmitter is transmitting on unintended frequencies that's called &lt;em&gt;interference&lt;/em&gt;, and a good part of an RF engineer's job is avoiding precisely that, since it tends to make the legitimate users of those unintended frequencies upset.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8717" LastEditDate="2018-12-27T22:20:21.270" LastActivityDate="2018-12-27T22:20:21.270" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12482" PostTypeId="1" AcceptedAnswerId="12483" CreationDate="2018-12-26T14:27:13.930" Score="3" ViewCount="172" Body="&lt;p&gt;I'm new to RTL SDR, and I noticed there's a &quot;dark region&quot; (around 700-900MHz), and I haven't figured out why this is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My device's tuner is a Fitipower FC0012, where could I find the pinout and dataspecs for this tuner?&lt;/p&gt;&#xA;" OwnerUserId="13841" LastEditorUserId="13615" LastEditDate="2018-12-31T15:39:24.463" LastActivityDate="2018-12-31T15:39:24.463" Title="RTL SDR &quot;dark region&quot;" Tags="&lt;software-defined-radio&gt;&lt;hf&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12483" PostTypeId="2" ParentId="12482" CreationDate="2018-12-26T14:33:57.127" Score="5" Body="&lt;p&gt;700-900MHz is &quot;blocked&quot; by law in the US and a number of other countries due to a (now antiquated) law that was designed to prevent wideband communications receivers from eaves dropping on old analog cellphones, which broadcast in the clear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These days it's entirely unnecessary, but it's still on the books because regulators are lazy like that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for removing the limitation, I couldn't say, not being terribly familiar with the current SDR software offerings. In the case of these RTL-SDR dongles, it seems virtually certain the block is being applied in software, not hardware.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2018-12-26T14:33:57.127" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12484" PostTypeId="2" ParentId="12278" CreationDate="2018-12-26T14:45:58.003" Score="0" Body="&lt;p&gt;To add one more inexpensive troubleshooting suggestion: The RF may not be coming in via any typical signal path, whether wifi or CAT5. A variety of issues such as poor mains grounding, distance from the mains ground point, faulty GFCI outlets, or just a stretch of mains wiring that happens to be a resonant length on an HF band can cause a significant amount of RF to get onto the chassis of the router. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Computers in general tend to look poorly upon intruding RF (which can look like or interfere with clock signals) on their ground plane, and in technical terms, will &quot;freak the heck out&quot;. I could crash my wifi router at my last apartment by transmitting specifically on 15m, despite living in a new building that was up to code. In my current house, the same router has no issue with 15m due to a different antenna configuration and different mains wiring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding an &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B073MCGBP5&quot; rel=&quot;nofollow noreferrer&quot;&gt;AC line filter&lt;/a&gt; to the mains supply of the router will eliminate any RF that may be on the mains, and has the added bonus of cutting down on RFI to your receiver from cheap power supplies. I usually buy an inexpensive power strip and cut the cord, then install the line filter on the power strip cord for convenience. This combined with wrapping a few feet of the router's DC power cord around a type 43 toroid fixed the problem I had with the wifi router in my apartment. If you have a lot of noise on your receiver that goes away when operating your radio via battery, you may also find that a line filter on the cord of your radio PSU helps to cut down on that noise, as it can travel both directions.&lt;/p&gt;&#xA;" OwnerUserId="246" LastActivityDate="2018-12-26T14:45:58.003" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12486" PostTypeId="2" ParentId="9865" CreationDate="2018-12-27T01:54:15.520" Score="4" Body="&lt;p&gt;The message is generated by the N6LXX controller at Onyx peak. The &quot;ANALOG&quot; portion of the message is identifying which analog port is being reported on the controller and as suspected, the readout is the measured analog voltage of the solar charged battery stack. It was decided on the day we brought Onyx on line to monitor the status/condition of the battery system. &lt;/p&gt;&#xA;" OwnerUserId="13844" LastEditorUserId="9493" LastEditDate="2018-12-28T22:43:41.703" LastActivityDate="2018-12-28T22:43:41.703" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12488" PostTypeId="2" ParentId="12476" CreationDate="2018-12-27T07:26:37.273" Score="-3" Body="&lt;p&gt;After some research I’m able to answer my - honestly not well formulated - question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my question I’m using a AC-motor to push and pull electrons inside a wire. Any wire is a resistor and some amount of the kinetic energy of the moved electrons gets dissipated into heat. Having a long enough wire, all the power from the DC-generator will be used for heating the wire. The sketch of the power consumption is a sine, where the negative part is folded up (image 1):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/giNiWm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/giNiWm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The setup with only a wire is a transmitter. Because any acceleration of charges is accompanied by the emission of photons. The interaction of all these photons produces a radiation. This radiation is modulated in the sense that the number of emitted photons follows the frequency from the antenna generator. To prevent such a radiation coaxial cables were invented.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Suppose that open circuits were unknown, it would be possible to build a real working antenna from the wire. What has to be done is to shield one half of the wire. Building a tower from concrete with a lot of metal in it and providing the wire first on the outside and then inside the tower, one dissipate the radiation in the inside to heat and the outside cable is a real working radio transmitter. Adding some modulation to the frequency or changing the power, one could transmit informations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such a device loses half of the transmitted energy. Now the blue graph in the sketch shows the theoretically emitted energy and the red graph alludes to the real emitted energy (image 2).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W8k7Jm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W8k7Jm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An open circuit will don it with more efficiency. But only cutting and and reducing the length of the wire, the number of moved by the generator electrons get reduced. The generator works into void and the emitted energy is very low. The black graph represents energy dissipation into heat (image 3).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eZEeTm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eZEeTm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding a small capacitor to the end of the open wire we get a better result. For some time the electrons are able to flow into the capacitor and the current in the wire flows for a longer time. By this we reducing the heat losses and transmitting more power. Making the capacitor big enough the circuit is tuned to its resonant frequency and the heat losses are reduced to a minimum. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That’s not all. The electrons in the charged capacitor at the end of the half wave are working against the generator and this is the reason why the emitted energy is shifted to the left in the sketch (image 4).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2jnESm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2jnESm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Folding the capacitor to an antenna rod, one get a real working transmitter (touch the sketch, if it’s not animated).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TXSEb.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TXSEb.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://de.wikipedia.org/wiki/Antennentechnik&quot; rel=&quot;nofollow noreferrer&quot;&gt;Source&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What, if the length of the antenna rod does not match the needed capacity to be tuned? Like in low frequency transmissions. It’s simply looks like image 3. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I has had to asked: “Was such a dis-tuned transmitter built, was the received power measured and does the result looks like in image 3. Sorry that I was sloppy.&lt;/p&gt;&#xA;" OwnerUserId="13834" LastEditorUserId="13834" LastEditDate="2018-12-27T13:22:26.340" LastActivityDate="2018-12-27T13:22:26.340" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12489" PostTypeId="2" ParentId="5133" CreationDate="2018-12-27T08:41:00.907" Score="0" Body="&lt;p&gt;Faraday cage example.  Without an external antenna to pick up the modulation you will not have reception. &#xA;Another good example is cell phone reception in a home with a metal roof. &lt;/p&gt;&#xA;" OwnerUserId="13846" LastActivityDate="2018-12-27T08:41:00.907" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12493" PostTypeId="1" CreationDate="2018-12-27T20:49:35.760" Score="2" ViewCount="148" Body="&lt;p&gt;This antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GEWcT.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GEWcT.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;comes with an balun (or unun) that has three connectors. One for the coaxial cable to the radio, one for the antenna and one for the earth. My understanding is that the earth is an RF earth, correct? If that's the case, why isn't it just using the mesh of the coaxial cable, isn't that connected to the RF ground in the radio?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="76" LastEditDate="2019-04-13T20:36:04.303" LastActivityDate="2019-04-13T20:36:04.303" Title="What's the earth in this antenna exactly?" Tags="&lt;antenna&gt;&lt;grounding&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12494" PostTypeId="1" AcceptedAnswerId="12498" CreationDate="2018-12-27T21:42:53.073" Score="1" ViewCount="2094" Body="&lt;p&gt;On the back of the Icom IC-7300 there's a ground connector:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7t5pD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7t5pD.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manual goes on to say this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MFOhe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MFOhe.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this an electrical or RF ground?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="76" LastEditDate="2019-04-13T20:35:47.520" LastActivityDate="2019-04-14T18:53:44.220" Title="Is the ground on the back of the Icom IC-7300 an electrical or RF ground?" Tags="&lt;grounding&gt;&lt;icom&gt;&lt;icom-ic-7300&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12495" PostTypeId="2" ParentId="12476" CreationDate="2018-12-27T22:01:23.363" Score="1" Body="&lt;p&gt;Firstly, I think someone may or may not agree with the concepts proposed here, but that doesn't make it a bad question. The OP has a background in physics and is asking how comparable are his observations to that of experienced hams, this forum would seem an ideal place to ask such questions, but it also means he looks at things a little bit differently than the rest of us mere mortals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;If I understood correctly&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;the model is looking at the 'electron mass' (for lack of a better phrase) of the wire.&#xA;In a given cycle, the voltage source will try push in x electrons into the wire, and then take back the same number of electrons back in the -ve half.&#xA;Because the voltage source is a sine wave the power plot also resembles a sine wave.&#xA;But what happens if the wire is not long enough, i.e. it physically does not carry said number of electrons.&#xA;The voltage (and power) will peak too soon, much like when a capacitor is charged it will not accept anymore electrons.&#xA;The OP added a capacitor, here the capacitor is akin to increasing the length of the wire, i.e. it provides it with more &quot;electron mass&quot;, and things are back in phase again.&#xA;But too much &quot;mass&quot; and we start getting back-currents... here I would think the power peaks too late (?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What makes this analogy hard to grasp is that in practice, if the antenna is too short for the desired frequency we get a capacitive component in the impedance, and we correct it by adding inductance... in the OP model the solution is too add more &quot;mass&quot; to the wire, he does it by adding a capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would argue we could add &quot;mass&quot; by making the wire &lt;strong&gt;thicker&lt;/strong&gt;, then in practice you'd be sacrificing gain for bandwidth.. as indeed happens with real antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope I got that right... but the point is, if it's a bad model, please someone explain why?&#xA;As a noob, I am always searching for interesting analogies to help me understand complex concepts, antenna theory is a complex concept! Much like how water pipe analogies help beginners learn DC concepts.. I know the hams in this forum long ago stopped thinking in terms of water pipes..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&#xA;Many are pointing out that inductance was not mentioned in the model. At the lower frequencies, such as provided by the DC motor source, inductance would have very little effect and capacitance would dominate in his observations. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question for the OP, is this all theoretical or are you getting these values from an actual setup ?&lt;/p&gt;&#xA;" OwnerDisplayName="user13171" LastEditorUserId="9493" LastEditDate="2018-12-29T01:51:35.923" LastActivityDate="2018-12-29T01:51:35.923" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12496" PostTypeId="2" ParentId="12494" CreationDate="2018-12-28T12:08:30.917" Score="0" Body="&lt;p&gt;It's an electrical ground.  The idea is that you connect devices to a common ground point (the electrical ground of your house for example) so that the chassis of your devices are at the same electric potential to reduce/eliminate the potential for an electric shock &lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2018-12-28T12:08:30.917" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12497" PostTypeId="2" ParentId="12493" CreationDate="2018-12-28T14:10:27.590" Score="4" Body="&lt;p&gt;The ground/earth connection is for a length of wire that acts as a counterpoise.  The instructions for the antenna (if there are any) may specify how long this wire needs to be (typically 1/4 wavelength).  If you don't have one, the coax shield will end up being the counterpoise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/12391/does-a-1-2-wavelength-end-fed-antenna-need-a-good-rf-ground/12398#12398&quot;&gt;Does a 1/2 wavelength end-fed antenna need a good RF ground?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2018-12-28T14:10:27.590" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12498" PostTypeId="2" ParentId="12494" CreationDate="2018-12-28T15:55:47.077" Score="6" Body="&lt;p&gt;It's all of the above:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;an RF ground&lt;/li&gt;&#xA;&lt;li&gt;a 12 V power ground&lt;/li&gt;&#xA;&lt;li&gt;a lightning ground, for what it's worth&lt;/li&gt;&#xA;&lt;li&gt;a chassis ground to prevent &quot;buzz&quot; on the chassis if your shack 0V is not earthed&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The manual says to connect it to a ground rod, &lt;em&gt;to prevent TVI, BCI&lt;/em&gt;.  If you used an end-fed antenna without a ground or counterpoise, the mains wiring (through your power supply) would become the RF counterpoise, making the house wiring carry a lot of RF current. This might interfere with your TV and audio electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a 12 V ground, it will (likely) be connected to the 0 V terminal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a lightning ground, it may help a little with lightning current on the coax. Of course not the whole strike, but if there is a small induced current after your earthed entry plate, the current will all flow on the coax braid. Earthing the chassis with a thick, wide, short conductor will reduce the voltage drop on the coax, reducing the current transferred to the centre conductor and into the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, switch mode power supplies are often floating, with the negative or 0 V terminal not earthed. This leads to all the equipment floating at about half the supply voltage (strictly limited to &amp;lt;&amp;lt; 1 mA, so irritating and painful, not dangerous).&#xA;This current also flows in the audio or USB cable shield, if you connect the radio to your PC. A solid ground of the chassis will prevent this 50 Hz buzz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could get much of the same benefit by earthing the coax braid as it enters the shack, except that 1) the coax is sometimes disconnected, as you change antenna, it's good that the chassis is still earthed for the 50 Hz buzz, and 2) The ground strap should be thicker than the coax, for lightning purposes.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2018-12-28T15:55:47.077" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12499" PostTypeId="2" ParentId="12493" CreationDate="2018-12-28T18:03:35.370" Score="3" Body="&lt;p&gt;As imabug says, without a RF ground, the coax may become part of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't want the shield of the coax acting as a counterpoise for two reasons.  You may not have good control of its length which may detune the antenna, and using it that way puts common mode current on the coax and may bring RF into your shack, raising the risk of RFI and radiation burns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas that intentionally use the coax shield as RF ground typically interrupt the coax with an un-un at a measured distance from the antenna feed point both to control the length and to limit common mode current on the rest of the coax.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2018-12-28T18:03:35.370" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12500" PostTypeId="1" CreationDate="2018-12-28T21:39:52.173" Score="2" ViewCount="411" Body="&lt;p&gt;I'm new to radio and SDR but, as a hobby project, I'm trying to decode a 2FSK radio signal received by an RTL-SDR that I sent using an SI4463 transmitter.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qZ2fA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qZ2fA.png&quot; alt=&quot;here is the Gnu Radio Blocks I'm using&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The record file contains 3 packets, but I'm able to recover only one packet.&#xA;Is there mistakes I've made in the GNUradio blocks?&lt;/p&gt;&#xA;" OwnerUserId="13856" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2018-12-28T22:46:04.053" Title="How to decode 2FSK signal with SDR?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;gnuradio&gt;" AnswerCount="0" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12501" PostTypeId="2" ParentId="12494" CreationDate="2018-12-29T03:50:00.900" Score="2" Body="&lt;p&gt;It's merely a bolt through the case. Under normal operation it shouldn't carry any current, so insofar as grounds come in neatly categorized &quot;kinds&quot;, I'd say it's for safety.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not part of the RF system, or shouldn't be under normal circumstances. If the feedline currents aren't balanced, then this ground connection would be one possible path for those common-mode currents. But it is much better to &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;address those issues at the feedpoint&lt;/a&gt;. With a properly designed and installed antenna there should be no common-mode current, and thus no current that would use the ground lug.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It can improve safety. Anything connected to earth by a low impedance can't have a voltage much different than earth, and thus, can't present much of a shock hazard. Many electrical appliances are grounded through the 3rd pin on the wall outlet for this reason&lt;sup&gt;1&lt;/sup&gt;, but the IC-7300 may be powered by a battery or isolated 12 V power supply with no earth connection. If through some fault (frayed wiring perhaps, or a powerline that's fallen on the antenna outside) the chassis were to come in contact with a dangerous voltage, nothing bad may happen until someone touches the radio, completing the circuit with meat. If the radio is earthed, such a fault will instead blow a fuse or circuit breaker.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's often the case that for reasons of &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;lightning protection&lt;/a&gt; or antenna design the coax shield is earthed anyway, so the ground lug is redundant as long as the coax is connected. However given the above safety concern it may be prudent to connect the ground lug anyway so the chassis remains grounded even when the coax is being moved about. To avoid creating a low impedance path for surge currents, you'd want the ground lug connection to follow the same path, and terminate at the same grounding panel as the coax.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt; Appliances that don't use the earth pin are usually &lt;a href=&quot;https://en.wikipedia.org/wiki/Appliance_classes#Class_II&quot; rel=&quot;nofollow noreferrer&quot;&gt;class II&lt;/a&gt; or double insulated appliances which take extra precautions to reduce the possibility of such a fault occurring.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2018-12-29T03:50:00.900" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12503" PostTypeId="1" CreationDate="2018-12-29T16:32:41.253" Score="3" ViewCount="1905" Body="&lt;p&gt;In V1.9 of WSJT-X, there was a feature that allowed one to change the color of stations already logged. This was necessary in knowing whether or not to respond to a given CQ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In version 2, I am unable to determine whether or not I have already logged a potential contact that is calling CQ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to have WSJT-X V2 signify whether or not one has logged a given call sign?&lt;/p&gt;&#xA;" OwnerUserId="13125" LastEditorUserId="76" LastEditDate="2018-12-29T17:38:56.363" LastActivityDate="2021-05-04T02:10:02.313" Title="WSJT-X V2: How to identify stations already logged?" Tags="&lt;digital-modes&gt;&lt;software&gt;&lt;ft8&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12505" PostTypeId="1" AcceptedAnswerId="12514" CreationDate="2018-12-29T19:24:32.890" Score="2" ViewCount="93" Body="&lt;p&gt;How do antennas behave as they are moved to near-field distances? Can they still receive a radio signal over a distance closer than a wavelength?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Background:&lt;br&gt;&#xA;In &lt;a href=&quot;https://physics.stackexchange.com/questions/450431/how-rf-receivers-receive-waves-with-bigger-wavelenght-than-the-distance-between&quot;&gt;this comment&lt;/a&gt; it is said, that the device “has a probably ferrite loaded loop antenna (a coil with a core) and there is a direct magnetic coupling (just as in a magnetic transformer) between that and the transmitter”.&lt;br&gt;&#xA;I suppose, that an electric coupling between two antenna rods is also possible.&lt;/p&gt;&#xA;" OwnerUserId="13834" LastEditorUserId="9493" LastEditDate="2018-12-30T00:35:45.800" LastActivityDate="2018-12-30T11:40:37.130" Title="How do antennas behave as they are moved to near-field distances?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12506" PostTypeId="1" AcceptedAnswerId="12507" CreationDate="2018-12-29T19:55:38.390" Score="0" ViewCount="1215" Body="&lt;p&gt;In a couple of days I am going to a mountain cabin and I were thinking about making myself a semi broadband antenna for LF/HF (300KHz - 20MHz or so) for receiving only.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was thinking about creating either a simple longwire (10m) or a dipole (2x5-7m). It seems like I wont be able to get hold of any ready made baluns/chokes, or any ferrite cores/toroids to make a balun myself by that time. Seems like no one here is selling stuff like that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since I wont be able to balance the antenna, would a good option be to use two coax cables as feed lines? Using the center core of the coax for both legs of the dipole? And then connecting the shield of each coax to earth together with one of the cores?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PS: I am a total beginner with radio/HAM/Antennas, so a lot of the terms, wordings, theory behind any of this. eg. Connecting one of the dipole halfs to earth and nothing else makes no sense to me.&lt;/p&gt;&#xA;" OwnerUserId="9935" LastEditorUserId="76" LastEditDate="2018-12-29T21:40:29.730" LastActivityDate="2018-12-31T03:15:59.930" Title="Simple Longwire/Dipole Antenna design" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;coaxial-cable&gt;&lt;dipole&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12507" PostTypeId="2" ParentId="12506" CreationDate="2018-12-29T21:40:01.147" Score="1" Body="&lt;h3&gt;Dipole&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;For a &lt;strong&gt;receiving&lt;/strong&gt; antenna, you do not &lt;em&gt;need&lt;/em&gt; a balun. You will experience more noise from whatever equipment is located at the radio end of the feed line, and the antenna pattern and impedance will be less predictable because the feed like will to some degree be acting as part of the antenna, but it will still work. Even transmitting antennas &lt;em&gt;can&lt;/em&gt; be constructed without baluns and are often used this way in low-power portable operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Construct your dipole elements of wire, and at the feed point (center) connect one wire to the coax center and one wire to the coax shield.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Single element&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;If you prefer using a single wire (possibly more convenient to erect), connect the shield to the actual earth using a short wire to a metal stake. This should happen at the feed point — the point where the coax ends and the antenna wire begins — not the radio's end of the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This design does not need a balun, though it might benefit from impedance matching (again, not critical for receiving), which would be more precisely an &quot;unun&quot; (both the antenna and the coax are unbalanced devices in this case).&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Another note&lt;/h3&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Since I wont be able to balance the antenna, would a good option be to use two coax cables as feed lines? Using the center core of the coax for both legs of the dipole? And then connecting the shield of each coax to earth together with one of the cores?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This might make a balanced line; I'm not sure. But for it to do anything useful you would also need a balun at the receiver end. Otherwise, the receiver itself connects the shield side of its antenna port to (its) ground, so one of your two coax lines would be just acting as a wire tied to ground on the outside of the shield, so it has no effect, or at least the line is not balanced any more because the two sides are attached to unbalanced things.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general: the radio's antenna port is not balanced, so to properly connect it to a balanced antenna you will always need a balun &lt;em&gt;somewhere in the system.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(But, to reiterate: a receiver will still work without a balun. Possibly less well, but you'll still receive signals.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2018-12-29T23:17:01.633" LastActivityDate="2018-12-29T23:17:01.633" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12508" PostTypeId="1" AcceptedAnswerId="12510" CreationDate="2018-12-29T22:29:50.070" Score="11" ViewCount="1083" Body="&lt;p&gt;I am constructing a small loop antenna; apprx 4' diameter, will be used with an antenna tuner (mounted at the feedpoint) and 100W transmitter, and hope to use it on 20m, 40m, and maybe other bands if possible.  I can add a tuning capacitor to make it resonate on one of the bands but cannot help wondering... what does that get me?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is a resonant antenna more efficient?  I would assume so, but seem to recall that the increased efficiency is not really all that much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Question &lt;a href=&quot;https://ham.stackexchange.com/questions/9044/what-is-an-antenna-tuner-why-bother-with-resonant-antennas-in-the-first-place&quot;&gt;What is an antenna tuner? Why bother with resonant antennas in the first place?&lt;/a&gt; seems to address what I am asking, but the answer is still unclear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case it matters, it is not a continuous loop, there is a break opposite the feed point (where the tuning capacitor would be placed).  The antenna uses a gamma match to better align the feed point impedance to the line impedance.  The main purpose is to learn what to expect from these sorts of loops as I plan to build a much larger one and would prefer to make my mistakes on a small scale first. &lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2018-12-31T15:12:10.283" LastActivityDate="2020-03-03T09:05:04.527" Title="What is the advantage of making an antenna resonant?" Tags="&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12510" PostTypeId="2" ParentId="12508" CreationDate="2018-12-30T00:05:30.063" Score="8" Body="&lt;p&gt;Resonance or non-resonance does not have a direct effect on the efficiency or gain of the antenna. A resonant antenna is one that has only resistance without any reactance (capacitive or inductance) at its feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To transfer the maximum available (or rated) power from a transmitter to its load (the antenna system in this case), the impedance of the antenna system must match the specified load impedance of the transmitter. Most transmitters specify a 50 ohm load without any reactance. If the antenna system has reactance (i.e. it is not resonant) the transmitter will not be able to put out its rated power. This is the primary reason we tend to try to &quot;resonate&quot; the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine if transmitter manufacturers specified a 50 ohm resistive with 23 ohms of inductive reactance (50+j23) as the required load impedance. We would all be working to &quot;non-resonate&quot; our antenna systems to meet this specification in order to put out the rated power!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is important to note that most antennas, even when resonant, do not have a 50 ohm impedance. It is therefore often required to add some type of matching network to the antenna system to transform the impedance to 50 ohms so that the transmitter can put out its rated power. The matching circuit may be designed to cancel out any reactance in addition to transforming the resistive component of the antenna system to 50 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One more point about non-resonant antennas. We generally consider a 1/2 wavelength dipole to be essentially resonant. When we extend its length to 10/8 of a wavelength long, it is no longer a resonant antenna. Yet this length of a dipole has the highest gain of any dipole configuration. Clearly antenna resonance and gain bear no direct relationship.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The Small Loop Resonance Question&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The small loop the OP referenced, without any matching network, will have a feedpoint impedance with a very low radiation resistance (&amp;lt;&amp;lt;1 ohm on 40 meters) and a very high inductive reactance (&gt;&gt;500 ohms). To put this in perspective, this amounts to an SWR&lt;sub&gt;50&lt;/sub&gt;&gt;5,000:1 - well out of bounds for a typical antenna tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If such an impedance were connected to the end of a piece of 50 ohm coax cable that is connected to a transmitter rated for a 50 ohm load, there would be high losses in the cable due to the high SWR and the transmitter would put out a fraction of its power (if it doesn't shut down all together) due to the load being far from 50 ohms resistive. A well designed small loop antenna will have a gain of &amp;lt; -15 dBi. The coax and transmitter losses under this scenario could easily attribute another 20 dB of loss rendering the station communications ability very ineffective. So a matching network is generally required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The matching network in a typical small loop consists of the feedline connected to a smaller loop that magnetically couples to the larger loop. This portion of the matching circuit effectively acts as a transformer that raises the low radiation resistance of the larger loop to close to 50 ohms in the smaller loop. The other part of the matching network is a variable capacitor across a break in the larger loop. This capacitor is adjusted such that it largely cancels out the inductive reactance present in the large loop with an equal, but opposite, capacitive reactance. The net result is typically an SWR&lt;sub&gt;50&lt;/sub&gt; of &amp;lt;2:1. Due to the high Q of a small loop antenna, the capacitor will require adjustment for relatively small changes in the operating frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should be noted that the small loop matching network described does not appreciably change the gain of the small loop. The gain of the small loop is largely constrained by its relatively small dimension compared to the wavelength involved and due to its very low radiation resistance that lowers its efficiency. The matching circuit loss is negligible compared to the latter so there is no practical change in efficiency, and thus gain, of the antenna. As explained earlier, the real advantage of the matching circuit is to allow the transmitter to output its rated power and for the losses in the coax to be minimized. The math related to efficiency and gain are given in my answer to the SE question that the OP referenced earlier.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-31T12:57:09.733" LastActivityDate="2018-12-31T12:57:09.733" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12511" PostTypeId="2" ParentId="12508" CreationDate="2018-12-30T00:41:02.667" Score="0" Body="&lt;p&gt;As long as a near-conjugate match to the antenna feedpoint impedance is achieved, resonance and/or non-resonance doesn't matter at all. Let's assume we have antenna1 with 50 ohms of radiation resistance and no reactance at the feedpoint vs antenna2 with 100 ohms of radiation resistance and +j100 ohms of reactance at the feedpoint, (assuming negligible losses in the antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For antenna1, we adjust our transmitter output to get 1.414 amps of current flowing through the 50 ohms radiation resistance. For antenna2, we adjust our antenna tuner to get 1.0 amps of current flowing through the 100 ohms of radiation resistance. Which antenna is more efficient and which will radiate the most power?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power radiated by antenna1 is 50(1.414)^2 = 100 watts&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power radiated by antenna2 is 100(1.0)^2 = 100 watts&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power radiated by the resonant antenna1 is identical to the power radiated by the non-resonant antenna2. When are we going to lay that old XYL's tale to rest? The very basic purpose of an antenna tuner is to maximize the current flowing through the radiation resistance of the antenna. When it maximizes the current flowing through the radiation resistance of the antenna, it necessarily must accomplish a near-conjugate match not only at the antenna feedpoint but also at the transmitter output thus satisfying the maximum power transfer theorem's requirement of a conjugate match at every point in a conjugately matched system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a low-loss system, when we tune our antenna tuners for a 50 ohm Z0-match at the tuner input, we have tuned to a near conjugate match both at the tuner output AND also at the antenna feedpoint. The things that keeps those near conjugate matches from being perfect conjugate matches are the (hopefully) minor losses in the tuner and feedline.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2018-12-30T02:03:19.487" LastActivityDate="2018-12-30T02:03:19.487" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12512" PostTypeId="2" ParentId="12503" CreationDate="2018-12-30T01:10:28.137" Score="3" Body="&lt;p&gt;Set your &quot;New Call&quot; to one color and your &quot;CQ in message&quot; to a different color. My new call CQs are green and my &quot;CQ in message&quot; are light red. The light red indicates that I have worked the station before because it is not a &quot;New Call&quot;. And as Chris said, JTAlert also works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The logic is that the combination of &quot;New Call&quot; and &quot;CQ Only&quot; result in New Call CQs and anything left over from that having &quot;CQ in Message&quot; is not a New Call. I'm glad it worked for you.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2018-12-31T00:09:32.573" LastActivityDate="2018-12-31T00:09:32.573" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12513" PostTypeId="2" ParentId="12506" CreationDate="2018-12-30T01:10:38.010" Score="1" Body="&lt;p&gt;Like Kevin Reid says, you could be fine without a balun, especially at a mountain cabin where there there may be nothing to generate noise. For a receiving application, proper attention to the feed arrangement keeps the feedline from becoming part of the antenna, and since the feedline is usually near computers, switch-mode power supplies, and other sources of noise inside, this can be a huge improvement. However if there's no electricity besides a battery and your radio at the cabin, then none of these noise sources won't be around.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if you did want to make a balun, there are options that don't require any sort of ferrite core. Many depend on a quarter-wavelength transmission line, but you want a broadband antenna so let's exclude those.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One option is a folded dipole.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/u3VBq.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fu3VBq.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes folded dipoles are made from ladder line since it provides two parallel conductors. The two conductors are shorted at the ends, and one of the conductors is cut in the middle to make the feedpoint, labeled A and B. It could then feed like an ordinary dipole, either with a balanced feedline, or with coax and a balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But notice the center of the other wire is ground: the voltages on the left and right are always equal but opposite, just what you want from a coax shield. If you could somehow connect the shield there, but then also connect to the feedpoint on the other side...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Solution: build the folded dipole from metal tubing, with a tee at the ground point where the feedline can enter, then pass inside the antenna to the feedpoint on the other side. If 10 meters of tubing isn't what you had in mind, then just use coax, which is already a tube!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GzqbO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GzqbO.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The connections you need to make for such a construction are drawn in blue. Note that it's the shields of the coax that make the folded dipole, while the feedline runs inside the left half of the antenna to connect at the feedpoint at the top. The center conductor on the right half does nothing: cut it off and ensure it can't come in contact with the other parts. &lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2018-12-31T03:15:59.930" LastActivityDate="2018-12-31T03:15:59.930" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12514" PostTypeId="2" ParentId="12505" CreationDate="2018-12-30T01:37:32.047" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How do antennas behave as they are moved to near-field distances? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The near field zone of an antenna consists of highly reactive fields that can easily couple to nearby conductive objects. As a result, antennas that are in the near field of another can easily transfer power between them. Whether or not communications is possible under this closely coupled condition is a factor of transmit power, receiver sensitivity and any system related losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;System losses can arise due to the mutual impedance which is defined as the negative ratio of the voltage &#xA;induced at the open terminals of one antenna to the current in other antenna. This mutual impedance alters the self impedance of the feedpoint which typically results in mismatch losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another source of system loss relates to the dominant form of the reactive waves in the antenna near field. Close coupling of a near field inductive dominant antenna (such as a small loop) with a near field electrostatic dominant antenna (such as a short dipole) antenna can give rise to system losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is reasonable to generalize that if two antennas enable communications in their far field that bringing them within the near field of the other will still allow communications to occur.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Can they still receive a radio signal over a distance closer than a wavelength?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If the antennas permit communications at a distance of greater than one meter, then they will also permit communication at a distance of less than one wavelength. With all other things being equal, the power received by the receiving antenna in its far field is inversely related to the distance squared. So for example, moving from 2 wavelengths to 1 wavelength of separation results in a 4 times power increase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas that are spaced less than one wavelength apart may still be in their far fields.  A &lt;em&gt;rough approximation&lt;/em&gt; of the near field boundary is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$r\approx 0.62\sqrt{\frac{D^3}{\lambda}} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where D is the maximum antenna dimension in meters and &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is the wavelength in meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Applying formula 1 to a 30 cm antenna operated at 11 meters (27 MHz), the near field region would start at  approximately 30 mm from the antenna. Although this is a very rough approximation, it is clearly far less than the 11 meter wavelength involved.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2018-12-30T11:40:37.130" LastActivityDate="2018-12-30T11:40:37.130" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12518" PostTypeId="2" ParentId="12463" CreationDate="2018-12-31T03:38:01.230" Score="-1" Body="&lt;p&gt;Possibly bad DC-to-DC converters inside the solar panels. Ferrite clamps on the wiring won't help if the panels themselves are radiating broad-spectrum RF noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One solution (other than complete removal/replacement) might be closable overhead shutters, or throw an opaque tarp or curtain over your entire solar array during times you want to operate on HF.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2018-12-31T03:38:01.230" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12522" PostTypeId="1" AcceptedAnswerId="12523" CreationDate="2018-12-31T16:46:08.337" Score="8" ViewCount="502" Body="&lt;p&gt;I saw someone on 20m FT8 this morning calling &quot;CQ NM&quot;. What does NM mean in this context? The followed the NM with their call and grid as usual.&lt;/p&gt;&#xA;" OwnerUserId="13877" LastActivityDate="2018-12-31T17:39:34.050" Title="What does CQ NM mean in FT8?" Tags="&lt;ft8&gt;&lt;wsjt-x&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12523" PostTypeId="2" ParentId="12522" CreationDate="2018-12-31T17:39:34.050" Score="10" Body="&lt;p&gt;Now that I've seen a few other 2 letter abbreviations, I've figured out it means they're looking for a contact in New Mexico.&lt;/p&gt;&#xA;" OwnerUserId="13877" LastActivityDate="2018-12-31T17:39:34.050" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12527" PostTypeId="1" AcceptedAnswerId="12529" CreationDate="2019-01-02T15:48:22.457" Score="4" ViewCount="108" Body="&lt;p&gt;Many (QRP) homebuilders offer their projects as kits. A popular series nowadays is the &lt;a href=&quot;http://www.hfsignals.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;BITX&lt;/a&gt;. There are often mailing lists connected to those projects; I am a member of several.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm wondering how these communities come into being. Should I have an awesome project that I'd like to provide as a kit, where would I go? Specifically,&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Would it be considered inappropriate to advertise my own project on, say, the BITX mailing list?&lt;/li&gt;&#xA;&lt;li&gt;Or are there more general mailing lists (not tied to a particular device) that I don't know about?&lt;/li&gt;&#xA;&lt;li&gt;Do club magazines publish notifications of such projects?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Or perhaps there is some other way? Or would you typically first build it with some friends (from the local club or so) and then hope the word gets spread?&lt;/p&gt;&#xA;" OwnerDisplayName="user885" LastEditorUserId="13615" LastEditDate="2019-01-02T20:25:06.927" LastActivityDate="2019-01-02T20:25:06.927" Title="How do homebuilders find an audience to distribute kits to?" Tags="&lt;diy&gt;&lt;internet&gt;&lt;etiquette&gt;&lt;qrp&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12528" PostTypeId="1" CreationDate="2019-01-02T16:09:27.060" Score="-2" ViewCount="127" Body="&lt;p&gt;According all the answers to a question about &lt;a href=&quot;https://ham.stackexchange.com/questions/12508/what-is-the-advantage-of-making-an-antenna-resonant&quot;&gt;What is the advantage of making an antenna resonant&lt;/a&gt; different lengths of the antenna rod could be tuned to resonance with the antenna generator.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;You can introduce shift with additional components to get the antenna to look resistive again, and get the best signal power from it. But the gain will not be as in the ideal case. &lt;a href=&quot;https://ham.stackexchange.com/a/12509/13834&quot;&gt;Source&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In my understaning the tuning of antennas with different lengths to the same frequency leads to different voltages, with which the electrons in the rod get drived. Different voltages lead to different accelerations of these electrons and this leads to the emission of photons with different energy content.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’m curious about the reflection behaviour of the radiation as a function of the used voltage. The reflection could be from the ionosphere as well as from buildings or other obstacles.&lt;/p&gt;&#xA;" OwnerUserId="13834" LastActivityDate="2019-01-02T23:10:58.310" Title="Reflection behaviour of the radiation as a function of the used voltage" Tags="&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12529" PostTypeId="2" ParentId="12527" CreationDate="2019-01-02T16:52:28.287" Score="2" Body="&lt;p&gt;As the saying goes, if you build a better mousetrap, then the world will beat a path to your door; but in the modern era, you do need to get the word out first somehow.  A website with complete information about your awesome kit is essential.  That way, interested hams can find your site either directly from a URL, or from a search engine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't neglect the time-honored way of promoting a product: old-fashioned marketing.  A great way to do it is to have a booth at a convention, such as &lt;a href=&quot;http://www.qrparci.org/fdim&quot; rel=&quot;nofollow noreferrer&quot;&gt;Four Days in May&lt;/a&gt;, run by &lt;a href=&quot;http://www.qrparci.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRPCI&lt;/a&gt;, a large and well-respected QRP club.  Consider sending sample kits to clubs or hams who would write about your product.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether one can pitch one's own product on a mailing list or forum depends upon the rules of the mailing list or forum, which should be observed and respected.  By far the biggest QRP mailing list is &lt;a href=&quot;http://mailman.qth.net/mailman/listinfo/qrp-l&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRP-L&lt;/a&gt;, and their published rules seem fairly permissive, so it's probably OK there.  There is a usually-unwritten rule that should be strictly observed though, and that is that you should disclose up front that you are the one selling the kits; that way, list members know that your opinion is biased.  Posts from well-known and established participants tend to carry more weight than posts from people who just joined the list.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-01-02T16:52:28.287" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12530" PostTypeId="2" ParentId="12527" CreationDate="2019-01-02T16:55:17.777" Score="2" Body="&lt;p&gt;It happens slowly and organically. Yes, most of these folks have probably mentioned on bulletin boards, forums, or mailing lists that they have a new project they're working on. They aren't running around putting those notes in all the lists though. They're putting it on lists in which they're active members and in ways they think that community might like, accept, and be interested in. If you aren't an active contributing member in the BITX mailing list, they might frown on you throwing up an unsolicited advert. You also likely won't get much attention.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, many of these projects start as small club projects and kits and grow through several revisions as interest grows. You build a cool project and take it to a local club meeting and they think it's cool so you order a small batch of PCBs for your friends. They tell their friends and ask if you're going to do another run, etc. Maybe you make enough of these kits or they're sufficiently advanced that you get a reputation like Ashhar Farhan for making really cool stuff. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Zero to BITX popularity doesn't happen overnight, though.&lt;/p&gt;&#xA;" OwnerUserId="1309" LastActivityDate="2019-01-02T16:55:17.777" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12531" PostTypeId="2" ParentId="12528" CreationDate="2019-01-02T17:28:46.200" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I’m curious about the reflection behaviour of the radiation as a function of the used voltage. The reflection could be from the ionosphere as well as from buildings or other obstacles.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;At reasonable power levels, the way in which the environment reflects (or refracts or absorbs) radio waves is &lt;a href=&quot;https://en.wikipedia.org/wiki/Rusty_bolt_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;mostly&lt;/a&gt; linear — it obeys the &lt;a href=&quot;https://en.wikipedia.org/wiki/Superposition_principle&quot; rel=&quot;nofollow noreferrer&quot;&gt;superposition principle&lt;/a&gt;. Saying that a radio wave has a higher voltage (between specified points) than another is the same as saying it has higher amplitude (or power). If you send 10 watts in some particular direction and observe 1 watt on a nearby receiver, then you can know that sending 20 watts will give you (almost) 2 watts back. It's linear.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Different voltages lead to different accelerations of these electrons and this leads to the emission of photons with different energy content.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is not correct. I think you are thinking of optical phenomena where the photons are understood to be emitted from energy level transitions of individual atoms. Here, everything is bigger and slower. The radio-frequency photons come from the change in the overall electromagnetic field of the antenna, which is driven by the signal generated by the transmitter (also an electromagnetic wave, just one confined to a transmission line). The frequency, and therefore energy per photon, is set by the transmitter; it cannot be changed by the antenna.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-01-02T17:28:46.200" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12532" PostTypeId="2" ParentId="12528" CreationDate="2019-01-02T17:43:31.677" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Impedance_of_free_space&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once the single frequency RF signals leave the antenna, the photons all have the same energy content and the same ratio of electrical to magnetic field, approximately 377 ohms. In the far field, that ratio is unrelated to the voltage on the antenna. The energy content of all individual photons of the same frequency is identical, i.e. the individual photons from a QRP station have the same energy content as the individual photons from a QRO station on the same frequency. The total number of photons is what is different, not the individual photons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether a conjugately matched antenna element is resonant or non-resonant, the voltage will be whatever it takes to cause the current to be the magnitude necessary for (the square of that current) times (the radiation resistance) to be the maximum available radiated power. That follows from the maximum power transfer theorem applied to RF signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's get some definitions straight. Assuming that we are feeding an antenna at a current maximum point, the feedpoint impedance can be thought of in two parts: The part that radiates the power is called the radiation resistance. The part that dissipates power is called the loss resistance and is made up of ground losses, I^2*R losses, dielectric losses, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By definition, the radiation resistance radiates all of its power and dissipates zero power as heat. By definition, it is impossible for the radiation resistance to dissipate heat.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-01-02T23:10:58.310" LastActivityDate="2019-01-02T23:10:58.310" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12533" PostTypeId="2" ParentId="12528" CreationDate="2019-01-02T18:30:49.803" Score="5" Body="&lt;p&gt;The energy of a photon is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ E={\frac  {hc}{\lambda }} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$E$&lt;/span&gt; is energy, in joules (though with the proper change in &lt;span class=&quot;math-container&quot;&gt;$h$&lt;/span&gt;, electron-volts are also frequently used)&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$h$&lt;/span&gt; is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Planck_constant&quot; rel=&quot;nofollow noreferrer&quot;&gt;Planck constant&lt;/a&gt;, approximately 6.63×10&lt;sup&gt;−34&lt;/sup&gt; joule-seconds&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$c$&lt;/span&gt; is the speed of light, 299792458 meters per second&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is the wavelength, in meters&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Changing the length of the antenna, the transmitter power, feedpoint impedance or transmitter power (and consequently feed voltage) does not change the photon energy. The only way to change the photon energy is to transmit at a different frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consequently, changing the antenna length will have no effect on how signals propagate, except to the extent that the new antenna may have changed efficiency or gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radios are well described by classical electromagnetic theory, so there's not much reason to be thinking about photons or other quantum effects. In fact unless you are very familiar with quantum physics, thinking of radio operation in terms of photons is more likely to cultivate misconceptions than insight.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-01-02T20:29:41.310" LastActivityDate="2019-01-02T20:29:41.310" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12536" PostTypeId="1" CreationDate="2019-01-03T14:35:37.693" Score="5" ViewCount="903" Body="&lt;p&gt;I was checking out the &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/B004QJKO52&quot; rel=&quot;noreferrer&quot;&gt;gizmo&lt;/a&gt; mentioned in this &lt;a href=&quot;https://ham.stackexchange.com/questions/10054/can-an-antenna-be-too-powerful-for-certain-receivers&quot;&gt;question&lt;/a&gt;, and I see that it can receive &quot;shortwave&quot; in the frequency range 2300-21950 kHz.  Most times I see &quot;shortwave&quot; mentioned, it's by sales or nontechnical people to describe any number of things.  I've taken it to mean that it covers commercial AM and FM stations in the 87-108 MHz (FM) and  520-1710 kHz(AM) range, and possibly the weather band (~160 MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the Tecsun also can receive in 2300-21950 kHz.  What does this frequency range do?  What is it used for?  Why would this be useful in a presumably emergency-related receiver?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Searching for that range finds product reviews for this device and similar devices.  I was able to find &lt;a href=&quot;https://dpdproductions.com/pages/commercial-radio-broadcast-frequencies&quot; rel=&quot;noreferrer&quot;&gt;this chart&lt;/a&gt;, but it has no explanation.&lt;/p&gt;&#xA;" OwnerUserId="4476" LastEditorUserId="4076" LastEditDate="2019-01-03T16:07:43.647" LastActivityDate="2019-01-03T18:39:26.327" Title="What is the frequency range 2300-21950 kHz used for?" Tags="&lt;frequency&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12537" PostTypeId="2" ParentId="12536" CreationDate="2019-01-03T15:54:06.437" Score="4" Body="&lt;p&gt;Frequencies are allocated by governments, often in accordance with international treaties.  You didn't say what country you're in, but in the United States that broad frequency range has dozens of allocations; see &lt;a href=&quot;https://upload.wikimedia.org/wikipedia/commons/c/c7/United_States_Frequency_Allocations_Chart_2016_-_The_Radio_Spectrum.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this chart&lt;/a&gt; (PDF) published by the US Department of Commerce, and linked to from &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_allocation&quot; rel=&quot;nofollow noreferrer&quot;&gt;this Wikipedia article&lt;/a&gt;.  By the way, I'm not sure what &quot;fixed&quot; means on the chart, but I suspect that those allocations are to the US Government.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally speaking, &quot;shortwave&quot; refers to frequencies from 3 &amp;ndash; 30 MHz.  Signals at those frequencies reflect off the ionosphere, at least some of the time, so those frequencies are useful for long-range communication.  The Tecsun receiver you mentioned probably includes those frequencies so that users can tune in the shortwave broadcast and amateur bands contained in that frequency range.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-01-03T15:54:06.437" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12538" PostTypeId="2" ParentId="12536" CreationDate="2019-01-03T18:39:26.327" Score="11" Body="&lt;p&gt;&quot;Shortwave&quot; means roughly the same thing as &quot;HF&quot;: 3 to 30 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It definitely does &lt;em&gt;not&lt;/em&gt; include the FM broadcast (around 90 MHz, too high) or AM broadcast (around 1 MHz, too low) bands received by a typical car radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shortwave frequencies have the unique property of supporting ionospheric propagation, which means under the right conditions they can propagate globally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3 to 30 MHz is a large chunk of spectrum and it is not all allocated to any one use. Of particular interest may be the shortwave broadcast bands which are several allocations set aside by the ITU (and thus in turn, most national regulatory authorities) for broadcast stations intended to be received by the public.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the potential for global propagation, these broadcasts tend to offer interesting international programming not available on the ordinary AM and FM bands. International news (sometimes propaganda), language lessons, and religious broadcasts are some of the things you might find.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ITU allocated shortwave broadcast bands are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;3200-3400 kHz&lt;/li&gt;&#xA;&lt;li&gt;3900-4000 kHz&lt;/li&gt;&#xA;&lt;li&gt;4750-4995 kHz&lt;/li&gt;&#xA;&lt;li&gt;5900-6200 kHz&lt;/li&gt;&#xA;&lt;li&gt;7200-7450 kHz&lt;/li&gt;&#xA;&lt;li&gt;9400-9900 kHz&lt;/li&gt;&#xA;&lt;li&gt;11600-12100 kHz&lt;/li&gt;&#xA;&lt;li&gt;13570-13870 kHz&lt;/li&gt;&#xA;&lt;li&gt;15100-15800 kHz&lt;/li&gt;&#xA;&lt;li&gt;17480-17900 kHz&lt;/li&gt;&#xA;&lt;li&gt;18900-19020 kHz&lt;/li&gt;&#xA;&lt;li&gt;21450-21850 kHz&lt;/li&gt;&#xA;&lt;li&gt;25670-26100 kHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Not all of these allocations are permitted globally, nor are all broadcasters following the rules and staying within the allocations. It's not difficult to find stations just tuning around, or use a site like &lt;a href=&quot;https://www.short-wave.info/&quot; rel=&quot;noreferrer&quot;&gt;short-wave.info&lt;/a&gt; to find known stations.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-01-03T18:39:26.327" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12539" PostTypeId="1" AcceptedAnswerId="12540" CreationDate="2019-01-03T22:07:39.657" Score="9" ViewCount="807" Body="&lt;p&gt;The seminal work &lt;a href=&quot;http://www.hamradio-operating-ethics.org/&quot; rel=&quot;noreferrer&quot;&gt;&quot;Ethics and Operating Procedures for the Radio Amateur&quot;&lt;/a&gt; suggests in subsection II.8.1 to perform tuning only on a dummy load.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Sometimes before transmitting it is necessary to tune (adjust) the transmitter (or&#xA;  antenna tuner). Tuning should in the first instance be done on a dummy load. If&#xA;  necessary, fine tuning can be done on a clear frequency with reduced power, after&#xA;  having asked if the frequency is in use.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;My understanding is that a dummy load matches the transceiver impedance so tuning is probably a) not necessary and b) without any predictive value for how the actual antenna will work with the tuning parameters.&#xA;What am I missing?&lt;/p&gt;&#xA;" OwnerUserId="13899" LastEditorUserId="218" LastEditDate="2019-01-04T16:07:37.853" LastActivityDate="2019-01-04T16:51:54.603" Title="Why does &quot;Ethics and Operating Procedures&quot; suggest tuning on a dummy load?" Tags="&lt;antenna&gt;&lt;procedure&gt;&lt;equipment-operation&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12540" PostTypeId="2" ParentId="12539" CreationDate="2019-01-03T22:23:25.610" Score="11" Body="&lt;p&gt;The text you refer to seems to be (emphasis mine):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Sometimes before transmitting it is necessary to tune (adjust) the transmitter (or antenna tuner). Tuning should &lt;strong&gt;in the first instance&lt;/strong&gt; be done on a dummy load.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is not referring to the use of an antenna tuner, whether integral or external. Rather, it is referring to tuning the final output stage (&quot;finals&quot;) of a vacuum-tube-based transmitter (or external power amplifier). These are also impedance-matching adjustments, but involve elements internal to the transmitter/amplifier rather than exclusively the transmitter to the antenna. (The antenna impedance is also involved, so in some cases there could be some amount of antenna matching, if not as much as a dedicated antenna tuner. Or so I understand — I'm not an expert on this part of the technology.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Solid-state radios operate differently and do not require these adjustments, so the recommendation you read does not apply. However, there are other uses for transmitting into a dummy load — for example, checking if your microphone is working, you're not over-modulating, or even that a computer-controlled transmission is correctly controlling your radio's frequency and PTT.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-01-04T03:42:38.813" LastActivityDate="2019-01-04T03:42:38.813" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12541" PostTypeId="2" ParentId="12539" CreationDate="2019-01-04T04:00:28.937" Score="2" Body="&lt;p&gt;There are two ways the text could be interpreted:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;First tune to a dummy load. Then, switch to the antenna and tune again.&lt;/li&gt;&#xA;&lt;li&gt;First tune your transmitter for a 50 ohm load, using a dummy load. Then tune your (separate) antenna tuner to present a 50 ohm load to the transmitter.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The first case, which is how I first understood it, doesn't make any sense unless you know the antenna is 50 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case where you have a transmitter that requires tuning (common for tube equipment) &lt;em&gt;and&lt;/em&gt; an antenna tuner, then the second sense makes sense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Though in either case I have a better solution: make a mark where the knobs should be set for a 50 ohm load: then you can return to this setting without any dummy load at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's what you need to know about tuning:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Try to do it on a clear frequency. Avoid doing it on recognized calling frequencies.&lt;/li&gt;&#xA;&lt;li&gt;Do it at low power, if possible.&lt;/li&gt;&#xA;&lt;li&gt;Keep it short by writing down the approximate settings for each band beforehand.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;More generally, I think half that document is absurd, and I wouldn't take anything it says too seriously. Consider the first sentence of &lt;a href=&quot;http://www.hamradio-operating-ethics.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hamradio-operating-ethics.org/&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Over the past decades, and not surprisingly together with the introduction and growth of the Internet, the behavior of the radio amateurs on the bands has significantly deteriorated.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Kids these days, am I right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would call it not so much a &quot;seminal work&quot;, rather than an overbearing, 68 page tirade by a couple people upset that not everyone does everything exactly how the authors do it. Half the work has legitimate information on basic procedure, but the other half is common sense or just the author's particular operating habits presented as authoritative procedure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Some subjects which are a &lt;strong&gt;no no&lt;/strong&gt; in amateur radio conversations on the air are:&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;religion&lt;/li&gt;&#xA;  &lt;li&gt;politics&lt;/li&gt;&#xA;  &lt;li&gt;business (you can talk about your profession, but you cannot advertise for your business);&lt;/li&gt;&#xA;  &lt;li&gt;derogatory remarks directed at any group (ethnic, religious, racial, sexual etc.).&lt;/li&gt;&#xA;  &lt;li&gt;bathroom humor: if you wouldn't tell the joke to your ten year old child, don't tell it on the radio;&lt;/li&gt;&#xA;  &lt;li&gt;any subject that has no relation whatsoever with the ham radio hobby.&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;People use ham radio to talk about the weather, their health problems, or to make plans to meet friends. I don't know what these things have to do with the ham radio hobby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another example:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Saying 'CQ from Victor Romeo two Oscar Portable' is not very clear. Either VR2OP calls SQ using an incorrect spelling phonetic, or VR2O/p calls CQ and omits to add the expression 'stroke' while calling CQ. This can lead to a lot of confusion.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is what's called a &lt;a href=&quot;https://en.wikipedia.org/wiki/False_dilemma&quot; rel=&quot;nofollow noreferrer&quot;&gt;false dilemma&lt;/a&gt;. There's a 3rd possibility: VR2O is portable. That's how I understand it, anyway. Sometimes people even say &quot;mobile&quot; instead of &quot;portable&quot;, but I don't find it confusing at all.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Call CQ: ‘CQ from G3ZZZ, G3ZZZ calling CQ, golf three zulu zulu zulu calling&#xA;  CQ and listening’. At the end you may say ‘...calling CQ and standing by’,&#xA;  instead of ‘...and listening’. One could also say: ‘...and standing by for any call’.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I just assume anyone calling CQ is standing by for any call. I just end with &quot;calling CQ&quot;, but reading this document makes me feel like I must be &quot;doing it wrong&quot; and the ham radio procedure police are probably going to arrest me.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If signals are not very strong and if the readability is not perfect, you can spell out your name etc. Example: 'My name is John, spelled juliett, oscar, hotel, november ...' Do NOT say '...juliett juliett, oscar oscar, hotel hotel, november november'. This is &lt;strong&gt;not&lt;/strong&gt; the way you spell the name &lt;strong&gt;John&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I have never once heard anyone doing this. Reminds me of &lt;a href=&quot;https://www.youtube.com/watch?v=xOrgLj9lOwk&quot; rel=&quot;nofollow noreferrer&quot;&gt;four shalt thou not count...&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-01-04T16:51:54.603" LastActivityDate="2019-01-04T16:51:54.603" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="12542" PostTypeId="2" ParentId="12539" CreationDate="2019-01-04T04:09:53.637" Score="5" Body="&lt;p&gt;We use a non-radiating dummy load at first &lt;em&gt;so that we minimize the chance of interfering with others&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When our tuning adjustments are as close as they can be using that, &lt;strong&gt;then&lt;/strong&gt; we can switch over to our antenna and make any needed adjustments. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The HF bands are full of annoying carriers because hams perform their entire tuneup procedure into their antennas.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-01-04T04:09:53.637" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12543" PostTypeId="1" AcceptedAnswerId="12545" CreationDate="2019-01-04T13:46:21.940" Score="5" ViewCount="111" Body="&lt;p&gt;In my city there is a local amateur radio &quot;club&quot;. People gather every morning on 7.135 and chat. I was invited by one of the members of this club to join. Turned out that people can chat on this frequency for a very long time without any pauses or naming their call signs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the most common way to let people know that I'm here and would like to join? Currently I briefly name my call sign and it seems to work. However I don't know whether this is the right way to do it.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-01-04T14:26:48.987" Title="How to interrupt a long discussion on HF politely?" Tags="&lt;procedure&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12544" PostTypeId="1" CreationDate="2019-01-04T03:03:30.030" Score="1" ViewCount="794" Body="&lt;p&gt;I'd like to increase personal security by receiving Wifi connections 50-100 km away from physical device location, with high decibel to milliwatts (dbm) reading to overcome path attenuation by foliage and other obstacles. This would allow me to avoid the geographical restrictions imposed by the local ISP's Wifi connections, because I would be able to access the internet wherever I please and at any point in the system (within a max 100 km radius). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm thinking of using a Yagi directional antenna or maybe a parabolic grid, but the ones I could find so far are significantly limited in range, at 15-20 km max, never in excess of 50 dbm. Where can I find a Yagi or parabolic grid with a range of 50-100 km? Do I need to purchase industrial-grade radio equipment for this kind of Wifi frequency range or is this a DIY project? If it's DIY, what equipment will be needed and are there any guides to building one? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not at all familiar with RF theory, but can a Wifi range be increased on say a parabolic grid from 15-20 km to 50-100 km?   &lt;/p&gt;&#xA;" OwnerDisplayName="piece0fshite" LastActivityDate="2019-01-04T14:41:40.100" Title="Where can I find a very long distance Wifi antenna with a range of 50-100 km? Or is it a DIY project?" Tags="&lt;wifi&gt;" AnswerCount="1" CommentCount="17" ContentLicense="CC BY-SA 4.0" />
  <row Id="12545" PostTypeId="2" ParentId="12543" CreationDate="2019-01-04T14:26:48.987" Score="7" Body="&lt;p&gt;Stating your call in the brief pause between transmissions is accepted procedure. It seems brief and rude by normal social convention, but it's necessary on the radio since anything longer might not be heard by the other stations involved in the conversation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the other stations should acknowledge you and give you an opportunity to speak. It's at that time you can say &quot;thanks&quot;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-01-04T14:26:48.987" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12546" PostTypeId="2" ParentId="12544" CreationDate="2019-01-04T14:41:40.100" Score="6" Body="&lt;p&gt;As the comments on the question suggest, there are regulatory concerns that may be relevant. But those are dependent on jurisdiction, so let's not get into that. A separate question, tagged with your location, would be appropriate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's focus just on the technical aspects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two concerns with getting a radio link over these distances: radio horizon and path loss.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Radio Horizon&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;The radio horizon is how far the antenna can &quot;see&quot; before the curvature of the earth gets in the way. Assuming flat terrain, it can be estimated by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{horizon in km} = 3.57 \sqrt{\text{height in meters}} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(For a result in miles and a height in feet, change the constant to 1.23.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The horizons on each end add. So if one antenna has a horizon of 20 km and the other 10 km, the antennas could be up to 30 km apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With this equation, you can see to have a chance at a link over a distance of 50 km, you'll need a tower at least 50 meters tall on each end. Unless you are lucky to have one or both of the stations on a hilltop, this alone probably precludes the possibility of a simple DIY solution.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Path Loss&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Path loss (assuming no obstructions) can be estimated with the &lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;Friis transmission equation&lt;/a&gt; to make a &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt;. For Wi-fi to have any chance of working at all, you'll need a received power of at least -85 dBm. To have it work well, -60 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The free space path loss at 2.4 GHz at a distance of 50 km is 134 dB. A Wi-fi transmitter is typically 100 mW or 20 dBm. 20 dBm - 134 dB = -114 dBm, which is 29 dB below the absolute minimum of -85 dBm. That shortfall will have to come from antenna gain and/or amplifiers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So one solution would be an antenna with 15 dB gain on each end, that would provide a total of 30 dB gain. This is a &lt;em&gt;bare minimum&lt;/em&gt;, at the lower end of your &quot;50-100 km&quot; range, and assuming no obstructions. You mention &quot;foliage and other obstacles&quot;, which will take additional power or gain to overcome, though realistically by the time you have the necessary 50 meter towers on each end as described above, foliage and obstacles may be much less of a concern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All kinds of parabolic reflector antennas would be able to provide the necessary gain. A well-built Yagi could work as well.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-01-04T14:41:40.100" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12547" PostTypeId="1" CreationDate="2019-01-04T22:42:05.983" Score="3" ViewCount="162" Body="&lt;p&gt;It seems a resonant dipole can be shortened by either loading coils near the center feed point or capacitive &quot;hats&quot; at the ends (and still be resonant).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say I run out of linear physical distance for a full-sized wire dipole by X.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be the difference (radiation pattern, radiation resistance, efficiency, SWR, etc.) if I use one of the above additions (loading coil or cap hat) to asymmetrically shorten only one side of the dipole by X, instead of symmetrically shortening both sides, each by X/2?  Or how about one side short by X/3, the other by 2/3rds X?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(in all cases, &quot;tweaking&quot; the L or C additions to the shortened partition to optimize for the desired resonant frequency).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I the case of a vertical dipole, would it make a difference whether the upper half, or half closer to the ground was shortened?  (in the extreme, replacing the bottom element with a large enough cap hat seems to be approaching being equivalent to a vertical over a ground plane).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-01-04T22:47:53.483" LastActivityDate="2019-01-06T05:26:14.450" Title="asymmetric shortened dipole" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12551" PostTypeId="2" ParentId="12042" CreationDate="2019-01-05T15:04:21.497" Score="-2" Body="&lt;p&gt;DVMega is more or less a protocol in this sense and any Jumbo/Zum/Openspot or any Pi-Star dongle...&lt;/p&gt;&#xA;" OwnerUserId="888" LastActivityDate="2019-01-05T15:04:21.497" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12552" PostTypeId="2" ParentId="12547" CreationDate="2019-01-06T05:26:14.450" Score="2" Body="&lt;p&gt;We have a lot of available information and knowledge on a certain type of asymmetric shortened dipole, i.e. mobile antennas which are standing wave antennas. The vehicle body can be thought of as 1/2 of the dipole and the vertical part of the antenna as the other half. Since the legal height limit is something like 13.5 feet from the ground, mobile antennas are necessarily shortened for any wavelength above ~15 meters. What we know about such antennas is that the maximum radiation is associated with the point of maximum current on the standing wave antenna which is usually at the feedpoint. From mobile shootouts we know that loading coils are most efficient when located as far away from the feedpoint as feasible but not too close to a large top hat - that increases the radiation efficiency while lowering the feedpoint impedance. &quot;The ARRL Antenna Book&quot; has a chart for eight-foot base-loaded and center-loaded mobile antennas with the feedpoint impedance and radiation resistance listed. Dividing the radiation resistance by the feedpoint impedance gives an idea of radiation efficiency. I have the results of three 80m shootouts from the 1990s on my web page at:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w5dxp.com/shootout.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w5dxp.com/shootout.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please note that because of the self-resonance of loading coils, antennas with loading coils do not usually make good multi-band antennas although self-resonance is sometimes used as a trap function on the self-resonant frequency.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-01-06T05:26:14.450" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12554" PostTypeId="1" AcceptedAnswerId="12571" CreationDate="2019-01-06T07:39:27.923" Score="13" ViewCount="272" Body="&lt;p&gt;I am a prospective HAM, and I recently began reading the ARRL's third edition of their Ham License Manual, published in 2014.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyhow, under &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;WHO CAN BE A HAM&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;They mention that there are ham operators who may have disabilities that might affect how they get licenced, or things like that, but also say that they can provide unique talents to the mixwith their experiences.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being completely blind, I would like to know how to go about taking the first technician licence exam.Would they either provide it in Braille, where I orally announced the number, followed by the letter for multiple choice? Or, would the proctor have to read aloud both the question and answers, and then I would respond with the answer?&lt;/p&gt;&#xA;" OwnerUserId="13927" LastEditorUserId="4665" LastEditDate="2020-01-29T22:19:55.763" LastActivityDate="2020-01-29T22:19:55.763" Title="Do volunteer exam coordinators provide accommodations for applicants with visual impairments?" Tags="&lt;license&gt;&lt;volunteer-examiners&gt;&lt;disability&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12556" PostTypeId="2" ParentId="12554" CreationDate="2019-01-06T14:29:10.680" Score="3" Body="&lt;p&gt;Blind operators typically end up being highly skilled CW operators which are highly valued in ham clubs that do contesting and are greatly appreciated and frequently treated as a VIP.  But as the hobby is largely reliant on listening and speaking, blind operators integrate well even without CW skills.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Testers do not typically have resources to accommodate blind participants, but if you contact the test group well in advance, they can get those resources.  The ARRL VEC does have braille exams, but local sessions typically do not stock them unless they are requested in advance.  The ARRL VEC manual recommends giving the exam orally, which would probably also have to be arranged in advance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you get your license, do your research when buying a radio.  Many radios have special accommodations for the blind, including spoken menus.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-01-06T14:29:10.680" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12557" PostTypeId="1" CreationDate="2019-01-06T18:33:44.480" Score="3" ViewCount="489" Body="&lt;p&gt;Because of space limitations, am purchasing a magnetic loop antenna.  Because of needing to move the antenna around, do i need a RFI choke in the feed line?&lt;/p&gt;&#xA;" OwnerUserId="13930" LastEditorUserId="8717" LastEditDate="2019-01-06T20:33:20.837" LastActivityDate="2020-09-09T01:20:08.077" Title="Magnetic Loop Antenna with RFI Choke" Tags="&lt;antenna&gt;&lt;magnetic-loop&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12558" PostTypeId="2" ParentId="12557" CreationDate="2019-01-06T21:28:17.257" Score="5" Body="&lt;p&gt;From my current experience of using Cha F-Loop 2.0:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Yes, you most definitely need an RFI choke to use a magnetic loop antenna, and a good one.&lt;/li&gt;&#xA;&lt;li&gt;Magnetic loops are not as good as you might think. Particularly they are very narrowband - you have to seat near it and tune the capacitor all the time. Or you need a remote tuning device.&lt;/li&gt;&#xA;&lt;li&gt;Despite the fact that some manufacturers may claim that their antennas work great indoor, they actually don't. For sure there is a chance to make a QSO even in this case, but this will be very tricky.&lt;/li&gt;&#xA;&lt;li&gt;Most magnetic loops have a power limitation 25W or so, which also reduces your chances for a successful QSO.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Simply put, I paid 400 GPB for a magnetic loop and now I can't use it. It doesn't work indoor, I can't use it outdoor because it's winter and I live in Russia. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is your first antenna I &lt;strong&gt;strongly&lt;/strong&gt; recommend to choose some other type of antenna. I made many QSO with shortened vertical antenna, OPEK HVT-400B, installed on a balcony. There is also a similar model, OPEK-600. These antennas are very simple to use. You need to connect one cointerpose wire (or better - a few, on the balcony I use two 5m long wires for both 40m and 20m bands) with length &lt;em&gt;about&lt;/em&gt; L/4, then you tune the length of the antenna itself to get minimum SWR, and you are ready to go. Unlike magnetic loops, these antennas 1) can handle more then 100W 2) are wideband. To get best results you still need an RFI choke, but it is optional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This being said, if you are an experienced ham and this is not your first antenna, go for it!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 de R2AUK&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-01-06T21:28:17.257" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12559" PostTypeId="1" CreationDate="2019-01-07T00:49:10.827" Score="5" ViewCount="1443" Body="&lt;p&gt;What kind of changes can be expected in the behavior (resonance, SWR, etc.) of a mobile vertical HF antenna between dry conditions and wet rainy weather? (assume a coax feed-line and low SWR in dry conditions)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is some form of weatherproofing required/recommended? (beyond that required to keep the upholstery or trunk dry)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added:  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The hollow core of a hamstick vertical, inside the loading windings, ended up filled with water after a couple days in heavy rain.  I unstopped the ends, drained and dried it in the sun, and the SWR inside 20M went from over 5 to under 1.5.  Could water inside the windings during the rainstorm have been part or all of the issue?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-02-22T17:33:24.200" LastActivityDate="2019-02-22T17:33:24.200" Title="antenna in the rain" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;hf&gt;&lt;mobile&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12560" PostTypeId="2" ParentId="12559" CreationDate="2019-01-07T02:54:05.610" Score="2" Body="&lt;p&gt;The SWR of the antenna should not be affected too much by rain, but you should do as much as possible to protect the connectors from water.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Water inside coaxial cable changes the characteristics of the cable, as well as corroding the copper.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many commercial antennas with a coaxial cable running from outside to inside, have heatshrink tubing around any external joints (antenna to base, or base to coax) for this reason.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-01-07T02:54:05.610" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12562" PostTypeId="1" AcceptedAnswerId="12566" CreationDate="2019-01-07T08:11:55.777" Score="1" ViewCount="71" Body="&lt;p&gt;If the transmitter and receiver are placed one centimeter apart, what would be the power at the receiving end if the tranmission power is 1dBm?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider an omnidirectional antenna. And if it is a directional antenna, how could I calculate based on the VSWR and directivity? I just want to know if the inverse square law can be applied here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am doing a study in which I used a stub antenna. The antenna is operating at 950MHz. The datasheet of the antenna is unknown. When gone through VNA S11[dB] is -20dB which conveys that 0.99mW is radiated from the transmitter, whereas the received power is -20dB which is 0.01mW. I placed both the antennae adjecent, still I didn't achieve. &lt;a href=&quot;https://physics.stackexchange.com/questions/451648/why-does-s11-seem-to-be-independent-of-transmission-media-in-this-rf-transmissio/451665?noredirect=1#comment1013221_451665&quot;&gt;Here's the link to earlier discussion&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I am trying to calculate the maximum and least possible powers to complete my work.&lt;/p&gt;&#xA;" OwnerUserId="13894" LastEditorUserId="8717" LastEditDate="2019-01-07T17:18:58.940" LastActivityDate="2019-01-07T17:18:58.940" Title="What would the power at output at a distance of 1cm when transmitted at a power of 1dBm from the transmitting antenna?" Tags="&lt;antenna-theory&gt;&lt;rf-power&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12563" PostTypeId="2" ParentId="12559" CreationDate="2019-01-07T11:56:31.303" Score="6" Body="&lt;p&gt;Water has a drastically different relative permittivity &lt;span class=&quot;math-container&quot;&gt;$\varepsilon$&lt;/span&gt; than air (water: ca 88, air: pretty much 1); it is, however, pretty non-conductive, just like air (being distilled and all).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a good approximation, uniform mixtures of substances with grain sizes significantly below wave length can be represented by a metamaterial with electrical properties defined by the weighted properties of the constituents. Weights are typically just the volume proportions!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, how much volume percent in air is &quot;moderate to heavy rain&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's define that rain to be 10 mm/hr, that is, on any given surface, in 1 hour, 10mm of water column precipitate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A large rain drop reaches 8 m/s, and has a diameter of 5 mm, thus a cross-section area of &lt;span class=&quot;math-container&quot;&gt;$(2.5\,\text{mm})^2\pi\approx 20\,\text{mm}^2$&lt;/span&gt;. Raindrops are pretty much spherical, and not at all &quot;drop-shaped&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On these 20 mm², in one hour, 10 mm or rain fall. Thus, 1 hr brings 200 mm³ (that's 0,20 ml) of rain if you were to put out a cyclinder where that &quot;standard&quot; raindrop fits exactly. Since the volume of a raindrop sphere is &lt;span class=&quot;math-container&quot;&gt;$\frac43\pi r^3\approx 65\,\text{mm}^3$&lt;/span&gt;, that's pretty much 3 raindrops an hour. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the 8 m/s that our standard raindrop has, it takes it 0.6 ms to trave 5mm, i.e. it's own height.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means that for any given point in the volume of the air surrounding your antenna, out of 3600 s in an hour, only 6 ten-thousandsth are occupied with rain being there. That's a concentration &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; of about &lt;span class=&quot;math-container&quot;&gt;$1.7 \cdot 10^{-7}$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, your relative permittivity of the rain-air medium surrounding your antenna would then be &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \varepsilon_\text{rainy air} = C \cdot \varepsilon_\text{water} + (1-C) \cdot \varepsilon_\text{air}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, as you can see, that's going to be damn irrelevant for your antenna, unless you match six digits after the comma!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-01-07T11:56:31.303" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12564" PostTypeId="2" ParentId="12559" CreationDate="2019-01-07T15:51:58.550" Score="9" Body="&lt;p&gt;The antenna itself won't be significantly affected by the water.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, waterproofing the coax connection is essential. If this is not done, water will creep inside the coax by capillary action and ruin the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several products that can be used, for some examples see &lt;a href=&quot;https://multimedia.3m.com/mws/media/937488O/3m-rubber-mastic-specialty-tape-application-guide-lr-print.pdf&quot; rel=&quot;noreferrer&quot;&gt;3M's application guide&lt;/a&gt;. However all have three elements:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;An underlying insulating layer which covers exposed conductors and/or facilitates removal of the outer layers of tape later.&lt;/li&gt;&#xA;&lt;li&gt;A sealing layer of rubber or mastic tape.&lt;/li&gt;&#xA;&lt;li&gt;An abrasion and UV protective top layer.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;h3&gt;Step 0: clean the connection&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;Remove any dirt or oil with a cloth and alcohol. You'll notice I skipped this step in my photos :)&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Step 1: Courtesy Wrap&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;This makes the waterproofing much easier to remove in the future. If this isn't done, over time the sealing tape will creep into the connector, making it nearly impossible to unscrew.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6Za1t.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6Za1t.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used Scotch Super 88 because it's what's on hand. Some people like to wrap with the adhesive side up so it doesn't leave goo on the connector. There are also tapes designed for specifically this application which remove cleanly. Stretch the tape to get it to conform to the connector. You'll find cheap electrical tape does not conform nearly as well.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Step 2: Sealing Layer&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;For this I used 3M 2228 rubber mastic tape: it's a sticky mastic with a UV protective layer on one side. The nonsticky side goes out. I prefer mastic tapes in permanent installations since it flows better into tiny cracks, though it can be quite difficult to remove.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FrtdG.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FrtdG.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oe2yg.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oe2yg.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An alternative to mastic tape is rubber tape. It's not sticky but still fuses to itself over time. I use it if I know I'll need to dismantle the connection in less than a year.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bAda4.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bAda4.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Proper application is important:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Stretch the tape as you wrap it such that its width is 75% or less of its original width.&lt;/li&gt;&#xA;&lt;li&gt;Be sure to get the tape really well into the exposed threads of the female connector.&lt;/li&gt;&#xA;&lt;li&gt;Each wrap should overlap the previous wrap by half the tape width.&lt;/li&gt;&#xA;&lt;li&gt;Extend the wrap past the connector, and if your connector has any kind of shrink wrap on it, past that as well.&lt;/li&gt;&#xA;&lt;li&gt;If this connection is going to be vertical with the coax coming from the bottom when installed, consider wrapping in the other direction such that water would have to travel upwards to get in.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h3&gt;Step 3: Protective Layer&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;3M 2228 has a UV protective layer built-in. It's the non-sticky side of the tape, so ensure that side is facing out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Had another kind of tape been used, or if extra protection is desired, a final wrap or two with some vinyl electrical tape would be appropriate. Don't use cheap electrical tape! It will turn brittle and peel off when exposed to the elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As before, stretch the tape to get good conformance, though a reduction in tension on the final wrap helps prevent the tape from peeling itself off. For the same reason, it's good practice to cut the tape, rather than to pull it until it breaks.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;Use N Connectors if Possible&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;The PL-259 / SO-259 or &quot;UHF&quot; connector common on ham equipment provides no waterproofing whatsoever, which is why it's so important to get the sealing tape into the threads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, male N connectors have a gasket inside which seals against the face of the female connector. It's the red thing inside:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/e4IHS.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/e4IHS.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This prevents moisture ingress through the threads.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;N connectors are often installed with what looks like heatshrink over the barrel that crimps over the shield. This should be not just ordinary heatshrink but one with a waterproofing adhesive. If done properly, this combined with the gasket should make an N connector waterproof with no taping. However I still tape them for extra protection unless it's a very temporary installation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a bonus, N connectors are good up to 11 GHz.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-01-07T17:11:04.420" LastActivityDate="2019-01-07T17:11:04.420" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12565" PostTypeId="2" ParentId="12562" CreationDate="2019-01-07T16:11:57.047" Score="2" Body="&lt;p&gt;At a distance of 1 cm and a frequency of 950 MHz, the two antennas will be coupled substantially by the &lt;a href=&quot;https://en.wikipedia.org/wiki/Near_and_far_field&quot; rel=&quot;nofollow noreferrer&quot;&gt;near field&lt;/a&gt;, and so the inverse square law is not applicable. Furthermore the inverse square law only works for point sources, and at these distances it is grossly inaccurate to approximate the antennas as points.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The actual power coupling will be highly dependent on the precise geometry of each antenna involved. I'm afraid no precise answer is possible without either performing an empirical measurement or modelling.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-01-07T16:11:57.047" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12566" PostTypeId="2" ParentId="12562" CreationDate="2019-01-07T17:10:35.450" Score="1" Body="&lt;p&gt;A couple of observations based on your post here and Physics SE.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your choice of antennas is a significant compromise. These are not balanced antennas so your coaxial cables will easily function as part of the antenna. This will cause stray RF and it will alter the receive and transmit patterns of the antennas. You would have more predictable results with a balanced antenna, such as a half wave, center fed dipole, and ensuring that your feedline length is an odd multiple of 1/4 of wavelength of 950 MHz. The directionality and impedance of the center fed, half wavelength &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;dipole&lt;/a&gt; is well understood and documented.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The intent of your experiment is not completely clear. If you are trying to determine the effect of the sample on the attenuation or reflection of RF, you should position your antennas at least 1 wavelength (~0.318 meters) apart and insert your sample material mid position. You can calculate the amount of transmit power required by using a &lt;a href=&quot;https://www.pasternack.com/t-calculator-link-budget.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;link budget calculator&lt;/a&gt; based on your receiver sensitivity, the antenna spacing, and the gain of the antennas. For dipole antennas, you can estimate the gain to be 2.15 dBi each. As a rough calculation, if your receiver has a -107 dBm (1 &lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;V at 50 ohms) sensitivity, the minimum transmit power would be approximately -90 dBm. You can of course determine this experimentally by simply stepping down the transmit power until the receiver no longer registers a signal and then bring it back up just a bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your test fixture should be in an &lt;a href=&quot;https://en.wikipedia.org/wiki/Anechoic_chamber&quot; rel=&quot;nofollow noreferrer&quot;&gt;anechoic chamber&lt;/a&gt; in order to eliminate unwanted reflections and standing waves. If you fail to take this step, you will likely find the results of your experiment to be inconsistent and unrepeatable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The screen shot you showed of the VNA in the Physics SE link shows that you have the bandwidth of your VNA set much too wide. You should have it set to perhaps +/- 50 kHz of the carrier frequency instead of multiple harmonics as shown. This will allow you to more easily see the effects of the change of scattering parameters on the plot.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-01-07T17:10:35.450" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12568" PostTypeId="1" CreationDate="2019-01-07T18:39:40.357" Score="5" ViewCount="432" Body="&lt;p&gt;I'm curious what is the legal limit for unlicensed TV signals being transmitted on the VHF Band I?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems ill defined. The part 15 FM rules I am assuming don't apply here. And I don't think it can be illegal at all power levels because even old VCRs and TV tuners will leak a little RF. So what is the limit?&lt;/p&gt;&#xA;" OwnerUserId="1817" LastActivityDate="2019-01-08T18:31:21.470" Title="Unlicensed TV broadcasting power limit (Band I)" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;vhf&gt;&lt;transmitter&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12569" PostTypeId="2" ParentId="12568" CreationDate="2019-01-07T20:22:36.213" Score="4" Body="&lt;p&gt;It's illegal at all power levels. If you &quot;leak a little RF&quot; then there is something in Part 15 that applies (e.g. &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/15.115&quot; rel=&quot;nofollow noreferrer&quot;&gt;this section&lt;/a&gt; for VCRs and cable boxes) &lt;em&gt;and&lt;/em&gt; the device needs to be certified. If you broadcast &lt;em&gt;intentionally&lt;/em&gt; then there isn't anything that allows it at all, at any power level.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-01-07T20:22:36.213" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12570" PostTypeId="2" ParentId="12568" CreationDate="2019-01-07T20:49:42.357" Score="5" Body="&lt;p&gt;Since you mentioned part 15, I'm guessing you're asking about the rules in the United States.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look at part 15 subpart C in detail, you'll see that the frequencies in the VHF I band (44 - 87.5 MHz) have some specific unlicensed uses, mostly related to audio transmissions (wireless microphones, cordless phones, etc.)  Since the question is about TV signals, most of those don't apply.  The only exception I can see is &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&amp;amp;SID=a645decedfab383f8e97585a503ee849&amp;amp;mc=true&amp;amp;n=pt47.1.15&amp;amp;r=PART&amp;amp;ty=HTML#se47.1.15_1235&quot; rel=&quot;nofollow noreferrer&quot;&gt;§15.235&lt;/a&gt;, which doesn't specify a specific application (except for saying that it can't be a cordless phone).  However, that section is for a very narrow band: 49.82-49.90 MHz.  Since NTSC signals require 6 MHz of bandwidth, that band isn't nearly big enough to accommodate a typical video application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That leaves &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&amp;amp;SID=a645decedfab383f8e97585a503ee849&amp;amp;mc=true&amp;amp;n=pt47.1.15&amp;amp;r=PART&amp;amp;ty=HTML#sp47.1.15.h&quot; rel=&quot;nofollow noreferrer&quot;&gt;white space devices&lt;/a&gt; as the last remaining option.  The rules for these devices are complicated.  The available frequencies vary by location and time.  The maximum allowed power levels vary depending on the frequency and the characteristics of the device.  It's possible to transmit with a range of &lt;a href=&quot;https://www.carlsonwireless.com/tv-white-space/&quot; rel=&quot;nofollow noreferrer&quot;&gt;several kilometers&lt;/a&gt; with the right gear, but you have to carefully follow some fairly complicated rules.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the question referenced unintentional leakage, I'll point out that it's covered by different rules.  &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&amp;amp;SID=a645decedfab383f8e97585a503ee849&amp;amp;mc=true&amp;amp;n=pt47.1.15&amp;amp;r=PART&amp;amp;ty=HTML#sp47.1.15.b&quot; rel=&quot;nofollow noreferrer&quot;&gt;Part 15 subpart B&lt;/a&gt; has the specifics.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2019-01-08T18:31:21.470" LastActivityDate="2019-01-08T18:31:21.470" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12571" PostTypeId="2" ParentId="12554" CreationDate="2019-01-07T23:41:53.660" Score="7" Body="&lt;p&gt;Yes, volunteer exam coordinators &lt;strong&gt;must&lt;/strong&gt; provide accommodations for applicants with visual impairments. For the best experience, please contact the test team in advance so they can best prepare for your needs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC's Part 97 regulations which govern the amateur radio service in the USA (you'll learn more about these as you study) cover this in &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.509&quot; rel=&quot;noreferrer&quot;&gt;section 97.509&lt;/a&gt;, titled &quot;Administering VE requirements&quot;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(k) The administering VEs must accommodate an examinee whose physical disabilities require a special examination procedure. The administering VEs may require a physician's certification indicating the nature of the disability before determining which, if any, special procedures must be used.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So by law, any examiners volunteering under &lt;em&gt;any&lt;/em&gt; of the VECs (ARRL, &lt;a href=&quot;http://www.w5yi-vec.org/&quot; rel=&quot;noreferrer&quot;&gt;W5YI&lt;/a&gt;, &lt;a href=&quot;https://www.laurelvec.com&quot; rel=&quot;noreferrer&quot;&gt;Laurel&lt;/a&gt;, etc.) are required to accommodate a disability like blindness — and I trust you will find they are happy to help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can take a look at the &lt;a href=&quot;http://www.arrl.org/ve-manual&quot; rel=&quot;noreferrer&quot;&gt;ARRL VE manual&lt;/a&gt; for the guidance they give to their volunteers:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The accommodations may include administering the examination at a place and time convenient and comfortable to the examinee, even at bedside. Other procedures can include reading or writing for candidates who can't do so themselves.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Further down on page 50 of the PDF there is a section with specific suggestions for accommodating those who are visually impaired:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The major modification usually needed for testing the visually impaired is that the tests are given orally. Read the exam questions and multiple-choice selections to the candidate and then record the candidate's response on the answer sheet. Try to allow the candidate the same opportunity sighted people enjoy: process of elimination; reading the&#xA;  questions and remaining answers again; narrowing down the possibilities, skipping a question and returning later; and guessing. This will require a much longer time than most exams so plan accordingly. If you use someone other than a VE or trusted ham to be the reader, be sure the reader is familiar with the correct pronunciation of amateur radio terms.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The ARRL/VEC has a supply of written-element examinations written in Braille; check with the ARRL/VEC for availability. It is HANDI-HAMS’ experience that it is more efficient and effective to read the test to an applicant, rather than to arrange for the Braille materials, unless there are special circumstances that require it.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'd encourage you to contact a local ham exam team and discuss with them directly ahead of when you would like to take it. They will appreciate the advance notice whether you'd like to join a regularly scheduled exam session, and/or can schedule a group of volunteers for a one-on-one session.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2019-01-07T23:46:57.407" LastActivityDate="2019-01-07T23:46:57.407" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12572" PostTypeId="1" CreationDate="2019-01-08T08:05:21.293" Score="5" ViewCount="93" Body="&lt;p&gt;So I started writing an antenna simulator program to design antennas for my needs.&#xA;To calculate the electric field vector at every point, I split the active element of the antenna into a large number of smaller parts and the calculate the electric field generated by each element at that point - taking into account speed of light. In the program I simulated a dipole antenna and it worked well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I'm thinking how could I add support for passive element? If I would like to simulate a yagi-uda antenna, I need to somehow take into account a passive element which does not fit into my model.&lt;/p&gt;&#xA;" OwnerUserId="13942" LastEditorUserId="8717" LastEditDate="2019-11-05T19:39:34.303" LastActivityDate="2019-11-05T19:39:34.303" Title="How to model passive elements when simulating an antenna?" Tags="&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12574" PostTypeId="1" AcceptedAnswerId="12577" CreationDate="2019-01-08T12:21:36.957" Score="3" ViewCount="295" Body="&lt;p&gt;I'm just getting into radio (inspired by YouTube videos), and like many, I plan to start by building a crystal set (or multiples) before moving up to vacuum tubes (which I prefer over transistors).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All the crystal set schematics I've seen, however, are aimed at AM Broadcast band (540-1610 kHz).  I'd like to build one that covers a broader band selection -- ideally, up to 80 m or even 40 m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I correct in understanding that simply tapping the main tuning coil isn't sufficient to extend the working frequency up into the 7 MHz range?  Is it even possible to do this without physically switching coils?  Or are signals in 40 m and 80 m likely to be too weak to receive with a crystal set, or impossible to separate without making a receiver as complex as a tube regen set?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-01-08T20:09:33.653" LastActivityDate="2019-01-08T20:50:32.920" Title="Multi-band Crystal Receiver?" Tags="&lt;equipment-design&gt;&lt;crystal-radio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12575" PostTypeId="1" AcceptedAnswerId="12580" CreationDate="2019-01-08T13:02:15.097" Score="5" ViewCount="439" Body="&lt;p&gt;I'm trying to incorporate several transceivers on my board design; I need&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;WiFi (2.4 GHz)&lt;/li&gt;&#xA;&lt;li&gt;SatCom (~1.6 GHz)&lt;/li&gt;&#xA;&lt;li&gt;RF (~900 MHz) and&lt;/li&gt;&#xA;&lt;li&gt;GNSS (~1.5 GHz). &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I need to combine them into one antenna. I found a wide band antenna that can    handle the 700 MHz to 5 GHz frequencies, but I'm not sure how to&#xA;   combine or mix the signals for transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm presuming that I&#xA;   won't need to worry about it for receiving - but what's the proper&#xA;   way to accomplish this combining?&lt;/p&gt;&#xA;" OwnerUserId="13948" LastEditorUserId="4076" LastEditDate="2019-01-08T19:10:57.280" LastActivityDate="2019-01-08T19:20:41.220" Title="Share wide band antenna with multiple transceivers" Tags="&lt;antenna&gt;&lt;transceiver&gt;&lt;antenna-system&gt;&lt;electronics&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12576" PostTypeId="2" ParentId="12575" CreationDate="2019-01-08T13:51:25.800" Score="8" Body="&lt;p&gt;The basic concept is to use RF bandpass filters for each frequency range. This is frequently done by hams for VHF and UHF applications. The common term for a grouping of these filters is diplexer, triplexer, or quadplexer as appropriate. Sometimes the term &quot;duplexer&quot; is used although this creates confusion with a different device that is typically much more expensive and used for repeater implimentations. &lt;a href=&quot;https://www.martinrfsupply.com/comet-cfx-324b-triplexer-br-1-3-150mhz-200-320mhz-390-500mhz-br-triplexer/combiner.aspx?feed=Froogle&amp;amp;gclid=Cj0KCQiAsdHhBRCwARIsAAhRhsmE8ISQhM4nxrLtghK5qpKioTMLWCc32ptAVACmVa2WGUypDUsoQM4aAlQbEALw_wcB&quot; rel=&quot;noreferrer&quot;&gt;Here&lt;/a&gt; is one example of a triplexer for the frequencies used by ham radio operators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The nice thing about these type of bandpass filters is that they work for transmit as well as receive. During receive, each received frequency range is routed to the correct receiver with minimal loss. This is advantageous compared to simple splitters or combiners that divide the receive power among all of the radio ports equally thereby effectively reducing the receive range of each radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is unlikely that you will find an off the shelf version of a quadplexer for your indicated frequencies. You can design and build such devices but in order to properly tune them, you will require some test equipment such as a spectrum analyzer with a tracking generator or a wide band vector network analyzer. If you have access to some of this type of equipment, please indicate so and I will update my answer with more specific design guidance. In the end, you may find that it is easier and less expensive to simply use separate antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would be concerned about an antenna that claims a 700 MHz to 5 GHz bandwidth as this suggests the antenna may not be very efficient. You may wish to update your question with a link to the antenna you are considering.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-01-08T13:51:25.800" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12577" PostTypeId="2" ParentId="12574" CreationDate="2019-01-08T14:11:17.843" Score="4" Body="&lt;p&gt;A crystal radio generally consists of a simple LC network and a diode detector. So in theory, altering the LC network would allow you to tune higher frequencies. The real issue is that signals you will find in the higher bands, simply do not have enough power to be detected without additional amplification.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You have an even larger obstacle, however. A CW signal will not be properly demodulated by a simple diode detector even if the signal is sufficiently strong. CW is simply the turning on and off of a carrier. If you were to listen to this with a simple diode detector you would hear the carrier when a dit or dah is being sent - this would be denoted by the absence of background noise. The space in between a dit or dah would be denoted by the sudden rise of background noise. So instead of a nice CW tone of 800 hertz or so, an &quot;S&quot; sent via CW would sound like Silence-Pffft-Silence-Pfft-Silence and then prolonged Pfft. To overcome this, a CW receiver creates a side tone through various techniques. This is beyond the scope of a simple crystal radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same problem exists for the SSB voice modes on 80 meters and 40 meters. Your best hope is to catch the occasional AM QSO and then only if the signals are strong enough - you will probably lose patience quickly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are interested in a simple CW receiver kit, for example, there are many on the market that are inexpensive and simple to build. &lt;a href=&quot;http://www.4sqrp.com/zzrx40.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt; is one example from Four State QRP Group:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zLZkD.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zLZkD.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;An Internet search will reveal many kits for SSB/CW receivers, transceivers, and multi-band versions with a wide variety of features and price ranges.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-08T20:50:32.920" LastActivityDate="2019-01-08T20:50:32.920" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12578" PostTypeId="2" ParentId="12572" CreationDate="2019-01-08T14:23:51.267" Score="3" Body="&lt;p&gt;Without any insight into the design of your program, I can only offer some basic guidance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The parasitic elements in a yagi design are shorted dipoles that can also be modeled as a collection of infinitesimal dipoles. A shorted dipole will re-radiate nearly all of the power that it intercepts. This re-radiation will interact with the driven element. The conditions of this interaction depend upon the relative spacial phase separation of the parasitic element from the driven element (and other elements).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The parasitic elements are also slightly shortened or lengthened compared to their resonant frequency. This is done so that the current to voltage phase relationship of the elements simulate the progressive spacial phase shift of a plane wave intercepting, or emanating from, the yagi antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would think you would find it beneficial to first understand the details of the design theory of a yagi type antenna. There are many references in text books on this subject as well as Internet resources. &lt;a href=&quot;http://www.antenna-theory.com/antennas/travelling/yagi.php#yagi&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here&lt;/a&gt; is one of many credible Internet sources.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-08T16:12:25.507" LastActivityDate="2019-01-08T16:12:25.507" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12579" PostTypeId="2" ParentId="12568" CreationDate="2019-01-08T14:40:11.347" Score="2" Body="&lt;p&gt;Yes, you may broadcast (called an &amp;quot;intentional radiator&amp;quot;) video transmissions but only on unused TV channels 14-51 (UHF, not VHF) as so called &amp;quot;white spaces&amp;quot;. Read Part 15 regulations part 701 and on for the requirements and restrictions. Here is the introduction to this section:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;This subpart sets forth the regulations for unlicensed white space devices. These devices are unlicensed intentional radiators that operate on available TV channels in the broadcast television frequency bands, the 600 MHz band (including the guard bands and duplex gap), and in 608-614 MHz (channel 37).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Also reference &lt;a href=&quot;https://www.fcc.gov/general/white-space-database-administrators-guide&quot; rel=&quot;nofollow noreferrer&quot;&gt;the FCC web site&lt;/a&gt; on this topic.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-01-08T15:39:27.597" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12580" PostTypeId="2" ParentId="12575" CreationDate="2019-01-08T19:20:41.220" Score="7" Body="&lt;p&gt;A wideband antenna is not what you're looking for – you really don't care about anything &lt;em&gt;between&lt;/em&gt; 900 and 1500 MHz, or between 1600 and 2400 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wideband antennas are inherently hard to make, and even harder, even impossible, to make uniformly good across their whole range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you much likely will rather want is a &lt;em&gt;multi-band&lt;/em&gt; antenna. For example, I'd assume that you can get 2400 + 900 MHz antennas commercially, as that is, due to ISM bands, a rather common combination.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something feels off about your presumption that you'll build a GNSS &lt;em&gt;transceiver&lt;/em&gt;; you definitely want a receiver, but I doubt you'll send data to a GNSS satellite ;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, honestly, what small multi-band devices like smart phones do is having separate PIFA antenna for the completely separate  GPS receiver (that luckily fall far above the 800/900 MHz GSM frequencies and far below UMTS at 1800 MHz), and then typically have some combined multi-band antenna for the rest, which is integrated into the mechanical design of the device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simple multi-band antennas I've seen look like connected dipoles for different wavelengths – but not really, the &quot;branches&quot; tend to be slightly offset (not periodically offset like in logper wideband antennas) and not quite exactly as long as they should be. My best guess is that someone started with an antenna that is just multiple dipoles for these frequencies connected to the same feedline, and then just simulated that, got the frequency response, and started randomly change lengths and positions until things worked out.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-01-08T19:20:41.220" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12582" PostTypeId="1" AcceptedAnswerId="12583" CreationDate="2019-01-09T17:55:33.590" Score="0" ViewCount="457" Body="&lt;p&gt;I've been reading about the history of telegraphy, and I knew that back then radio signals were produced in massive strength by using powerful dynamos and magnetos, with a telegraph key to interrupt this current, as described in Tom Swift and his Wireless Message, by Victor Appleton. I first read that book in eighth grade, and since then my fascination with radio grew.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that lots of technological advancements have been made since, which doesn't require as much energy to produce radio signals, especially when there are repeaters to carry on the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I'm wondering why a continuous wave will cause the transceiver to emit a 750 Hz tone in accordance to the signal's interruption. Wouldn't it sound like white noise, or mains hum, whose alternating frequency is 60 Hz, or a harmonic above that, 120 Hz? Of course, with the latter example, one would have to actually be connected to a power source. I also wondered what the mayday call sounded like on the Titanic, and it sounded like &lt;a href=&quot;https://www.youtube.com/watch?v=8E4wrcVQSgw&quot; rel=&quot;nofollow noreferrer&quot;&gt;this.&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13927" LastActivityDate="2019-01-10T12:14:12.657" Title="Why do CW signals get converted to pure sine wave tones at 750 Hz?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12583" PostTypeId="2" ParentId="12582" CreationDate="2019-01-09T18:04:53.810" Score="7" Body="&lt;p&gt;The tone you hear when receiving a CW signal is generated inside your receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Originally, a motor-driven variable capacitor or interrupter was used to put an AC component into the detector circuit, which sounded as a tone in the earpiece when the detector conducted the carrier.  &lt;a href=&quot;http://onetuberadio.com/2017/12/13/1917-cw-crystal-set/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here's a 1917 example&lt;/a&gt; on the OneTubeRadio blog.  Once active components were available, and electronic oscillator fulfilled this function.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Later, regenerative receivers could be adjusted to the edge of oscillation.   Oscillation is bad if you're receiving an AM audio signal, but for CW, it allowed the set to enter oscillation when the carrier was detected, and stop when the carrier shut off, thus generating a tone in the earpiece; the pitch was controlled by adjusting the regeneration coupling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern CW transceivers listen on a slightly offset frequency (typically between 400 and 1000 Hz difference, but usually operator adjustable) from their transmit setting; when the transmitter is tuned to the same frequency as the station you're receiving, that offset causes the internal oscillator to &quot;beat&quot; against the (nearly identical) received frequency; that beat produces the tone you hear, and the oscillation that produces it also produces the &quot;side tone&quot; that you hear when keying the transmitter.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-01-10T12:14:12.657" LastActivityDate="2019-01-10T12:14:12.657" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12584" PostTypeId="2" ParentId="12582" CreationDate="2019-01-09T18:20:32.283" Score="2" Body="&lt;p&gt;&quot;CW&quot; means &lt;a href=&quot;https://en.wikipedia.org/wiki/Continuous_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;continuous wave&lt;/a&gt;, that is a signal of constant amplitude and frequency which is switched on and off. The transmission itself has nothing to do with 60 Hz, 120 Hz, or 750 Hz. The transmission is simply a sine wave at whatever frequency the transmitter is tuned to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Sidetone&quot; rel=&quot;nofollow noreferrer&quot;&gt;sidetone&lt;/a&gt; that the transmitting operator hears is generated by the radio, and could be at any audible frequency. Most modern radios allow adjusting the sidetone frequency though a menu option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The receiver produces an audible tone by &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_mixer&quot; rel=&quot;nofollow noreferrer&quot;&gt;mixing&lt;/a&gt; the received signal with a locally generated carrier. According to the basic function of mixers, the resulting audible tone is at the difference between the two frequencies. So if the receiver's local oscillator is set to 10,000,000 Hz and the signal is at 10,000,500 Hz, the result is an audible 500 Hz tone. The receiver usually sets its oscillator to some fixed offset from the frequency shown on the dial, again often configurable in modern radios to suit the operator's preference. A slight mistuning of the receiver results in the tone being heard at a different frequency, as long as the frequency is still close enough to fall within the filter passband.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-01-09T18:20:32.283" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12585" PostTypeId="1" CreationDate="2019-01-09T20:51:36.893" Score="1" ViewCount="70" Body="&lt;p&gt;It's silent over there... USA is full of FT8 stations, in Canada you can count them on one hand and you don't even need all your fingers...&lt;/p&gt;&#xA;" OwnerUserId="13953" LastEditorUserId="218" LastEditDate="2019-01-10T18:55:18.903" LastActivityDate="2019-01-10T18:55:18.903" Title="How many HF (FT8/JT65/BPSK/RTTY etc) amateurs are active in Canada?" Tags="&lt;canada&gt;&lt;ft8&gt;" AnswerCount="1" CommentCount="7" ClosedDate="2019-01-10T01:27:09.887" ContentLicense="CC BY-SA 4.0" />
  <row Id="12586" PostTypeId="1" CreationDate="2019-01-10T00:19:09.667" Score="6" ViewCount="273" Body="&lt;p&gt;I'm planning on building a multi-band vacuum tube receiver.  I've got a circuit diagram in hand for a two triode twin reflex with optional regeneration (P.E. Edelman, &lt;em&gt;Reflex Radio Receivers&lt;/em&gt;, 1924, Fig. 35, also discussed &lt;a href=&quot;http://makearadio.com/others/regenrx5.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;), and expect to use modernized plug-in coils to cover broadcast AM through at least 40 m (possibly 15 m if I can get it to tune that high).  I will most likely also use regeneration drawn from one or the other RF stage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &quot;reflex&quot; circuit, in this context, makes one or both tubes do double duty; in this case, both tubes act as RF amplifiers (with tuned input and a tuned crystal detector), then the detector output is fed back to the first tube's grid, and from that plate to the second grid, with the (intended) result to get a radio with both the high sensitivity and selectivity of a two-staged tuned RF input, and the ability of a two-stage audio amp to directly drive a speaker.  Capacitors, chokes, and audio transformers are used to ensure the RF and AF get appropriately routed through the tubes.  Double tuning and separate regeneration control promise a &quot;three hands&quot; operation experience (and reflex receivers are also known as &quot;unstable&quot;, prone to oscillation and &quot;motorboating&quot;), but the final performance makes it worth attempting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've got a pair of tubes in hand: 1T4 miniature pentodes.  They use relatively low plate voltage (22.5 up to 90 V B+), compared to the older types, but with two amplification stages in RF and two more in AF, I should still get good results.  However, as noted, these are pentodes, and the original circuit (which dates from the 1920s) called for triodes.  The manufacturer documentation for this tube type calls it an RF &quot;remote shutoff&quot; -- apparently because the screen grid voltage can be manipulated to control gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The suppression grid in this type is internally connected to the filament/cathode, and I've seen a number of examples showing the screen grid connected to B+ (i.e. plate voltage), so that some portion of B+ acts to accelerate electrons after they pass the control grid.  The general rule is that a pentode can potentially produce much higher gain than an otherwise similar triode, without the &quot;kink&quot; in response seen in standard tetrodes and with almost zero screen current due suppression of secondary emission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there anything else I need to watch out for in converting this kind of reflex/regen receiver from triodes to pentodes?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-01-20T00:46:51.257" LastActivityDate="2019-04-02T14:25:10.670" Title="Pentode vs. Triode in Tuned RF Reflex Receiver" Tags="&lt;receiver&gt;&lt;equipment-design&gt;&lt;vacuum-tubes&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12587" PostTypeId="2" ParentId="12585" CreationDate="2019-01-10T00:28:50.227" Score="2" Body="&lt;p&gt;If there is any merit to your claim, consider that Canada has ~ 69,000 hams while the US has ~800,000 hams &lt;a href=&quot;https://wikipedia.org/wiki/Amateur_radio_operator&quot; rel=&quot;nofollow noreferrer&quot;&gt;according to Wikipedia&lt;/a&gt;. With less than 10% of the number of hams in Canada compared to the US, it is plausible that for any mode you will hear far less Canadian hams than US hams.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you then project that the population density of hams follows the general &lt;a href=&quot;https://wikipedia.org/wiki/List_of_Canadian_provinces_and_territories_by_population&quot; rel=&quot;nofollow noreferrer&quot;&gt;population density&lt;/a&gt;, Canada will have the majority of the ham population in the Quebec and Ontario provinces and then generally closer to the US border. If you are located within this region you are less likely to &quot;hear&quot; the majority of Canadian hams on HF frequencies due to propagation effects.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-10T00:45:25.507" LastActivityDate="2019-01-10T00:45:25.507" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12588" PostTypeId="1" CreationDate="2019-01-10T00:49:57.950" Score="1" ViewCount="879" Body="&lt;p&gt;I'm trying to null out vertical signals from a particular suburb which is about 40 kms away from my location by pointing a 4 element 10 m yagi such that the direction i want to null out is off to the side at about 90 deg to the direction of maximum gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The polarization of signals from the direction of the yagi's maximum gain isn't important because i'm interested in long distance via skip and then the polarization is always changing.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will the yagi provide the best side rejection for the vertical signals coming from the offending suburb if I mount it vertically or horizontally ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keeping in mind that in theory a yagi has little or no gain in the plane it isn't positioned in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To re-phrase, what provides more side rejection to vertically polarized received signals :&lt;/p&gt;&#xA;&#xA;&lt;p&gt;a.  The cross polarization attenuation provided by a horizontal yagi coupled with the minimal gain in the vertical plane and the associated minimal nulls in the vertical plane it has which can be used to null out vertical signals from some directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;b.  The fact that a vertical yagi has gain in the vertical plane and so then has definite nulls in the pattern which can be used to null out vertical signals from some directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When using a 4-element Yagi antenna, is there any other way I can best reject signals coming from a particular direction ? &lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-01-15T00:03:17.563" LastActivityDate="2019-01-15T00:03:17.563" Title="Which polarization for a Yagi antenna will have the best side rejection for received signals with vertical polarization?" Tags="&lt;antenna-theory&gt;&lt;polarization&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12592" PostTypeId="2" ParentId="11910" CreationDate="2019-01-10T13:45:22.357" Score="1" Body="&lt;p&gt;I see two coils in close proximity in the &quot;as built&quot; photo.  One coil is connected to the detector; the other to the antenna -- and their axes are colinear.  Whether this was the intent or not, your receiver is acting as a regenerative type -- detected signal in one coil is coupling to the other.  Without a control to limit current in the coil that's acting as a &quot;tickler&quot; or an adjustment to limit coupling (one classic method was to rotate the tickler -- one way it was maximum, rotated 180 degrees it was out of phase and minimum), the circuit can enter oscillation and there'll be no easy way to stop it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tiny disturbances, such as signal strength fluctuations, body capacitance, or stray inductance (from a wedding ring, for instance) can change the conditions enough to trigger this.  Once it starts, it's generally self sustaining, in that the regenerated signal will be enough stronger than the un-augmented to keep oscillating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding a variable resistance in series between the detector and its coil will allow you to reduce the coupling and control oscillation.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-01-10T13:45:22.357" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12593" PostTypeId="1" CreationDate="2019-01-10T14:40:41.507" Score="1" ViewCount="92" Body="&lt;p&gt;I am trying to make a wide scan from 24M to 1700M using HackRF One by using:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rx_power -f 24M:1700M:1000k -g 50 data.csv&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This gives me a nice output like this.&#xA;2019-01-10, 15:18:26, 24000000, 25000000, 1000000.00, 1, 38.42, 38.42&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I try to increase the resolution by decreasing the bin size like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rx_power -f 24M:1700M:500k -g 50 data.csv&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I get this result:&#xA;2019-01-10, 15:23:52, 24000000, 26797996, 349749.50, 2048, -64.47, -inf, -inf, -inf, -inf, -inf, -inf, -inf, -inf&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if I just decrease bin size by 1k like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rx_power -f 24M:1700M:999k -g 50 data.csv&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I get:&#xA;2019-01-10, 15:24:55, 24000000, 26797996, 699499.00, 4096, -inf, -inf, -inf, -inf, -inf&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like anything below 1000k gives this behaviour.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I go slightly higher to 1001k, output seems fine&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rx_power -f 24M:1700M:1001k -g 50 data.csv&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;gives&#xA;2019-01-10, 15:29:29, 24000000, 25001000, 1001000.00, 1, 39.29, 39.29&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would expect I would be able to decrease the bin size and get a higher resolution output. Instead I get a lot of -inf values. What could be the cause of this?&lt;/p&gt;&#xA;" OwnerUserId="13958" LastEditorUserId="76" LastEditDate="2019-01-10T16:38:10.407" LastActivityDate="2019-01-10T16:38:10.407" Title="unexpected output using HackRF One with rx_power" Tags="&lt;software&gt;&lt;hackrf&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12594" PostTypeId="2" ParentId="984" CreationDate="2019-01-11T06:42:08.517" Score="2" Body="&lt;p&gt;Get a two terminal GDT and call it a day, use very short low inductance leads to attach it between the center conductor and earth ground. GDT (Gas Discharge Tube), Bourns make them, Digikey or Mouser may have them. GDTs are high-impedance, very fast-acting, very high-energy devices for surge protection. MOV (Metal Oxide Varistor) devices may have low enough off-state leakage to parallel the GDT - pick a 600VDC device. These two together should really nail down any spikes.  You will find lots of application information at the Bourns and Little Fuse web sites.&lt;/p&gt;&#xA;" OwnerUserId="13965" LastEditorUserId="873" LastEditDate="2019-01-11T07:41:42.030" LastActivityDate="2019-01-11T07:41:42.030" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12595" PostTypeId="2" ParentId="1469" CreationDate="2019-01-11T11:15:09.493" Score="1" Body="&lt;p&gt;I have had no luck with alternative screw-on antennas, even the 771 seems to have less range than the included rubber duck. Magnetic mounts seem to be better but they are for cars or to use the HT as a table radio, not to carry around as HT.&lt;/p&gt;&#xA;" OwnerUserId="13968" LastActivityDate="2019-01-11T11:15:09.493" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12597" PostTypeId="1" CreationDate="2019-01-11T12:32:30.317" Score="1" ViewCount="73" Body="&lt;p&gt;I wanted to make an experimental simple 1296 MHz transmitter to have fun with my sdr dongle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But after hours of googling I realised that there is no such thing as &quot;simple 1296 MHz transmitter&quot;. Even though there is a &quot;x3 varactor multiplier&quot; it consists of old components that is rare and expensive. Which is strange since GSM uses multiple bands lower and higher than 32cm ham band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But then I spotted a circuit called &quot;diode odd-order frequency multiplier&quot; which looks very simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Immediately I thought that 868 MHz ISM band is 2·434 MHz which is upper part of LPD band in europe.&lt;br&gt;&#xA;So I can take my 70 cm radio, and connect this multiplier to its output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What diodes can survive 1W @ 433 MHz and how to calculate rest of components (inductors and capacitors) used in said multiplier?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or it also requires rare old components?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&#xA;I'm using SDR to RECEIVE the 868 MHz signal, not to transmit.&#xA;I want to create a 868 or 1296 MHz transmitter not create 868 mhz transmitter to use it as LO for 1296 MHz one.&#xA;I planned to use non-sdr handheld radio as my transmitter.&lt;/p&gt;&#xA;" OwnerUserId="13758" LastEditorUserId="13758" LastEditDate="2019-01-11T14:26:02.043" LastActivityDate="2019-01-11T14:26:02.043" Title="What circuit to use to multiply 434 MHz by two?" Tags="&lt;transmitter&gt;&lt;transverter&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12599" PostTypeId="2" ParentId="12597" CreationDate="2019-01-11T14:14:06.673" Score="2" Body="&lt;p&gt;You don't usually produce microwave frequencies using frequency-doubling diodes (or any other nonlinear component) like that, that's why you can't find an &quot;easy&quot; circuit to do that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyways, sure, any sufficiently robust semiconductor (all of which have nonlinear I/O curves) can do that. I'd frankly just go to e.g. mouser.com click through the semiconductors to the RF semiconductors and use a sufficiently fast transistor in a AC-coupled, biased common emitter configuration. 400something MHz isn't really &quot;fast&quot;! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea then would be that the mixing circuit itself behaves as an amplifier, greatly reducing the needed &quot;transport&quot; of energy from low to high frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question still would be how to pick values for any circuit. The rule here really is that you want to pick an operating point for your semiconductors (which, for their full range, are exponential) that fulfills the mathematical operation you want it to perform as nicely as possible – for example, for an amplifier, you want the whole thing to operate as linearly as possible, whereas for a frequency doubler, you want the second-order intermodulation products to happen, which means you need quadratic behaviour: you'd bias your semiconductor so that around that bias point, its curve looks as quadratic as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, again, that's not how you typically generate RF signals, especially not in an SDR context!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd typically have a separate frequency synthesizer and a mixer. In your example, you say you already have a 434 MHz transmitter, but want to operate at 1296 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you need to shift that up by (1296-434)MHz = 862 MHz (and now I see where that number is coming from). In fact, you're building a heterodyne transmitter. So, aside from your 434 MHz IF signal, you'll need a 862 MHz LO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And that is where things get more complicated than they need (at these frequencies) be if you use a high-powered IF:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For any mixer to work well, you'd want your LO to be at least at the same power as your IF signal – and suddenly you a) need to produce power at your LO frequency and b) need a mixer that can withstand at least twice the amount of power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After mixing, you'll always need filtering to get rid of the unwanted intermodulation products; and mixers are optimized to produce at least one intermodulation product, and it's nontrivial to build them so that the others are well suppressed. Now these  filters will also have to withstand power at unwanted frequencies! Power, that, by the way, you'll have produced only to have it dissipated in filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Compare that to a solution where you mix low-power signal + LO first, filter the result, and amplify the resulting RF signal (and then might not need to filter the PA output at all).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Which is strange since GSM uses multiple bands lower and higher than 32cm ham band.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;And that's where a few things come to together:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GSM requires devices to be able to hop frequencies rapidly, over a relatively large range compared to the accuracy that these frequencies still need to have.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's typically achieved using rational or fractional-N &lt;em&gt;synthesizers&lt;/em&gt;. The idea is simple:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead of relying on the nonlinearity of some amplifier to produce a multiple of an input frequency (effectively, by letting that input mix itself up by itself, or by a mixed-up version of itself), you run a VCO (voltage controlled oscillator) at about the target frequency. The benefit of that is that this oscillator will be relatively &quot;pure&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, you adjust your control voltage so that it's actually the frequency you want – and you do that simply by counting. For example, you want to generate 942 MHz for GSM operation. OK, so you take your 10 MHz reference source, and say: by the time this reference has fulfilled 10 cycles, the VCO has to have done 942 cycles (or, if you cancel out common factors: 10 cycles low should be 471 high). If the number of actual cycles is lower, increase the control voltage, and conversely, if its lower, decrease that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Throw a bit of algebra at the problem, and you end up specifying slightly less intuitive numbers than the rational ratio between in- and output frequency, but can get a huge number of additional frequencies that you can synthesize (fractional-N synthesis).&lt;br&gt;&#xA;Design an actual control loop (i.e. a PLL) instead of my vague &quot;decrease or increase&quot;, and you end up with a synthesizer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such synthesizers can cheaply be built using bog-normal silicon digital logic – and that's a great advantage, because suddenly you're not depending on the hard-to-manufacture-exactly nonlinearities of some semiconductor to do your mixing, and you can account for the nonlinearities in the VCO's frequency-vs-voltage curve simply with the control loop that you've got in there, anyways.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Jumping to another frequency becomes as easy as adjusting the numbers &quot;5&quot; and/or &quot;471&quot; (or their fractional-N equivalents); that can be really fast-settling, too!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look inside post-GSM phones (i.e. 3G/UMTS and 4G/LTE/LTE advange/5G), you'll find that these aren't even heterodyne systems, but quadrature mixers – the standards are designed for complex baseband processing! Still, these systems use said fractional-N synthesizers to generate their target frequencies, and they do so to great accuracy; a relatively simple synthesizer like described above allows you to  adjust frequencies on a very fine raster, so that you often don't even need correctable reference oscillators, which again decreases component cost in mass products.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So, you say, that's nice and all, but where do we go from here with my actual problem?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd say: whenever you're experimenting with mixing / frequency generation, the first thing you do is build a filter, as you don't want to get visited by your friendly neighbor, the national spectrum authorities (FCC, OFcom, BNetzA,…). You might be in luck, if distributors like mouser, digikey or arrow carry SAW filters, that might be easy to implement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Put your tone-generating device in the lowest power setting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, really, get a power rated transistor rated for bandwidths beyond your frequency of interest, and really just build a DC biasing network out of low-pass components (R's in series with L's) for that, so that you end up in an operation point of that transistor that has a quadratic curve. I find common-emitter circuits with NPNs to be easiest to build, so I'd go with that. Keep everything shorter than 1/10 of any wavelength involved, and matching becomes kinda optional¹. Make sure a mismatch can't damage your tone-generating device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Filter the collector voltage, and do a spectrum plot of the result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹ very kinda. It's just that it's actually hard to actually match semiconductor circuits, so we need to simply be as robust as possible against mismatch.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-01-11T14:14:06.673" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12600" PostTypeId="1" CreationDate="2019-01-11T14:36:33.857" Score="5" ViewCount="637" Body="&lt;p&gt;I have asked this quesion on other sites, but want to try to repeat it here. Also I have asked question about multiplier, and this is a different question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I discovered a 1296MHz beacon in my city that I can receive with SDR and got inspired by this band. Also I have build and played with simple FM and HF CW transmitters that consists of one transistor and a coil or a quartz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I want to create anything that can transmit on 1296MHz (and legal on ham band). Better if it's a FM transmitter, but a CW transmitter is also acceptable, since I can connect it to a microcontroller to transmit my callsign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want a simplest posible circuit but I can etch a PCB if it's necessary.&lt;/p&gt;&#xA;" OwnerUserId="13758" LastEditorUserId="13758" LastEditDate="2019-01-11T14:46:04.350" LastActivityDate="2019-01-12T10:50:57.690" Title="How to create a simple 1296MHz transmitter?" Tags="&lt;transmitter&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12602" PostTypeId="2" ParentId="12600" CreationDate="2019-01-12T10:50:57.690" Score="7" Body="&lt;p&gt;So, there's a bit of disappointment I'll have to spread here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Building microwave circuits like the one you need isn't per se as easy as just scaling up a circuit for, say 3 MHz or 100 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's assume we start with CW and hence just need an oscillator (and a switch). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, let's do, say, a Colpitts, right? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, sure, but the problem is that it's impossible to get or build really exact components. So, your Colpitts oscillator will be some say 2 to 5% off its nominal, calculated frequency from the start. And that is assuming that you've already taken the frequency derating of the capacitors into account, and inductances of resistors, and capacitances of inductors. Parasitic effects become important once you cross into microwave land :( Also, if you are actually building an oscillator, the phase shift and coupling behaviour of every single signal trace becomes important – you're suddenly starting to do microwave transmission line design. That's no fun to calculate, and you'll want a PCB that has nice exact trace width, substrate properties, quite a few ground stitching vias – in other words, you're out of self-etching territory there.¹&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 1.2 GHz, your 2 to 5% would be some 24 to 60 MHz. Sure, you'll first connect that oscillator to something you can use to find where the tone actually is, and then tune the thing till it works – but that will only take you so far. An old electrical engineering saying goes &quot;everything is a temperature sensor; some things can just also be used for other purposes&quot;; your oscillator will immediately start to wander. And again, a &lt;span class=&quot;math-container&quot;&gt;$\frac1{1000}$&lt;/span&gt; of drift means 1.2 MHz here...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you'd need compensation circuitry that compensates that drift itself; but then you'd need some way to measure drift, or at least temperature as a &quot;proxy&quot; for the frequency shift; you'll spend eternity calibrating stuff.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, direct oscillation at high frequency without a good standard for you to measure how exactly you're oscillating is inherently &lt;em&gt;hard&lt;/em&gt; to build. In fact, people that need to do that (high-power radar, for example) go the route of building &lt;em&gt;cavity resonators&lt;/em&gt; and the like – but that's not a circuit, that's a metal box of finely adjusted dimensions in a finely tuned amplifying loopback. Not easy to model nor cheap to build.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I explained in my previous &lt;a href=&quot;https://ham.stackexchange.com/a/12599/4076&quot;&gt;answer&lt;/a&gt;, the way to go here is having a reliable, precise oscillator at a low frequency, and using a control loop and a voltage-controlled oscillator to make a VCO run at a higher rate, controlled by the low frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, and since 1296 isn't an overly nice multiple of any standard frequency (&lt;span class=&quot;math-container&quot;&gt;$1296=2^4\cdot3^4$&lt;/span&gt;), going for a integer-n or fractional-n synthesizer is probably the way forward.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So, from my perspective: Design a small board that contains the decoupling capacitors, the in- and output matching circuitry, maybe a linear voltage regulator IC and aside from that only the loop filter, and of course a synthesizer IC. I've worked with the &lt;a href=&quot;https://www.maximintegrated.com/en/products/comms/wireless-rf/MAX2870.html&quot; rel=&quot;noreferrer&quot;&gt;MAX2870&lt;/a&gt; before. &lt;br&gt;&#xA;It needs a reference oscillation in between 10 and 200 MHz; if you don't have something like that at hand, building a 10, 12, or 20 MHz reference oscillator out of a sub-€ quartz and an inverter isn't hard, as these crystal frequencies are abundant on the market. &lt;br&gt;&#xA;The only microwave transmission line you'll need to design is the trace from chip to coax connector. That's a massive simplification over having to build everything that happens at microwave frequencies yourself.&#xA;&lt;br&gt;&#xA;For control, it uses SPI. Attach your favourite microcontroller, Raspberry Pi, or USB-to-SPI adapter. To know which settings to program, you don't even have to write code yourself: there's open source &lt;a href=&quot;https://github.com/EttusResearch/uhd/blob/UHD-3.9.LTS/host/lib/usrp/common/max287x.hpp&quot; rel=&quot;noreferrer&quot;&gt;MAX2870&lt;/a&gt; driver software, used by people that use it to control the same chip used in their commercial SDR RF frontends (&lt;a href=&quot;https://files.ettus.com/schematics/cbx/CBX.pdf&quot; rel=&quot;noreferrer&quot;&gt;schematic, p.3&lt;/a&gt;). So use the settings generated by that, or download Maxim's design software and let it calculate the right settings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JOKDo.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JOKDo.png&quot; alt=&quot;Typical application circuit from the MAX2870 datasheet&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&lt;hr&gt;&#xA;¹ But I'll be honest: I've etched exactly one board in my life myself. Services like OSHPark, elecrow, seeed and newly JLCPCB offer a round of PCBs manufactured and delivered to your door for &amp;lt; 10€ – my loss in material couldn't really keep up with that. And you actually get decent PCBs. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-01-12T10:50:57.690" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12603" PostTypeId="5" CreationDate="2019-01-12T12:04:24.120" Score="0" Body="&lt;p&gt;Despite having gained the moniker &quot;glow-FET&quot;, a vacuum tube is century-old technology in which electron flow is manipulated and controlled by grids, beam forming plates.  The first vacuum diodes (rectifiers and detectors) appeared in 1907, and by 1914 they were widely used in radio, both commercial transmitters and high-end receivers.  They figured heavily in science fiction as late as the 1960s, despite already beginning to be replaced by transistors for most applications.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-01-21T02:28:47.130" LastActivityDate="2019-01-21T02:28:47.130" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12604" PostTypeId="4" CreationDate="2019-01-12T12:04:24.120" Score="0" Body="This tag is for questions relevant to vacuum tubes, also known as thermionic valves or simply valves." OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-01-14T01:18:40.413" LastActivityDate="2019-01-14T01:18:40.413" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12605" PostTypeId="2" ParentId="6887" CreationDate="2019-01-12T12:34:56.563" Score="0" Body="&lt;p&gt;I'm a ham operator, and I have problems with my own radio interfering with my own internet connection, when I transmit on the 40 meter amateur band. I have fiber to the house, so the interference is probably being picked up by the in house internet wiring. If you are getting drop outs once a week, I suggest you speak to your neighbor, and find out what times he is on air, and see if it coincides with your dropouts. Most amateurs are also keep a log every transmission. If it doesn't, then there is probably another cause. Also, check to see if you are getting interference on your TV, at the same time. If the ham operator's station is interfering with your internet, it is likely to also interfere with your TV. Radio amateurs are legally required to take all measures to stop interference from their station. If you can establish that he is the cause, and is non compliant with fixing it, your next step is to take it up with your communication authority, i.e. FCC or equivalent. Also, keep a diary of your drop outs, showing date, time, and duration.&lt;/p&gt;&#xA;" OwnerUserId="13978" LastActivityDate="2019-01-12T12:34:56.563" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12610" PostTypeId="1" CreationDate="2019-01-13T12:42:47.633" Score="2" ViewCount="175" Body="&lt;p&gt;I have a faulty MFJ-259, the early model I believe.  When I power it up, the power light doesn’t illuminate, and the meter needles hit the right hand end stops.  I immediately power down as I guess this isn’t an encouraging sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before I take the thing apart in earnest, any ideas anyone what he problem might be? Anyone seen this kind of thing before with an MFJ-259? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any hints gratefully received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cheers Tim.&lt;/p&gt;&#xA;" OwnerUserId="11258" LastEditorUserId="8717" LastEditDate="2019-01-13T19:49:50.313" LastActivityDate="2019-01-13T20:08:32.910" Title="Faulty MFJ-259 - meter hits end stop on power up" Tags="&lt;equipment-troubleshooting&gt;&lt;antenna-analyzer&gt;" AnswerCount="1" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="12611" PostTypeId="2" ParentId="12610" CreationDate="2019-01-13T20:08:32.910" Score="5" Body="&lt;p&gt;No power light could just be a burned out bulb or dead LED (I have a 259B...don't recall if the power button ever lit up). If you don't have anything connected to the antenna connector, then it's perfectly normal for the SWR meter needle to go all the way to the right because it's indicating a high SWR. Put a 50 ohm dummy load on the analyzer and see what happens &lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2019-01-13T20:08:32.910" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12612" PostTypeId="1" AcceptedAnswerId="12614" CreationDate="2019-01-13T22:06:43.380" Score="2" ViewCount="206" Body="&lt;p&gt;I recently got a couple of very basic Zastone ZT-X6 2W UHF handheld radios. The actual brand seems to be WLN and the model KD-C1 (because the programming software I downloaded from Zastone is named after this WLN model? I know they have a number of different brand names for this one product). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking in that KD-C1 programming software, and Chirp as well, there's an option for this device called &quot;Embedded Message&quot; (in Chirp, it's under the Settings-tab on the left for this radio). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not familiar with this functionality and I've tried some googling, but thought this would be a better place to ask: what is the meaning of this &quot;Embedded Message&quot;?&lt;/p&gt;&#xA;" OwnerUserId="9016" LastEditorUserId="76" LastEditDate="2019-01-14T01:19:18.463" LastActivityDate="2019-01-14T01:19:18.463" Title="Embedded Message on Zastone ZT-X6 / WLN KD-C1" Tags="&lt;uhf&gt;&lt;equipment-operation&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12614" PostTypeId="2" ParentId="12612" CreationDate="2019-01-13T22:31:57.487" Score="2" Body="&lt;p&gt;An embedded message allows you to leave a user defined artifact in the memory of the radio that can be recalled by the programming software. This can be used for things such as to identify the specific radio, to identify the source file from which the radio was programmed, to identify the company or individual that programmed that radio, the time and date it was programmed, etc. Since it is user defined, any use is possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe this radio has two 32 character lines (line 1 and line 2) for its embedded message that can be programmed and recalled.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-01-13T22:31:57.487" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12616" PostTypeId="1" AcceptedAnswerId="12618" CreationDate="2019-01-14T03:02:56.450" Score="2" ViewCount="139" Body="&lt;p&gt;I have a 4 element 10 m yagi antenna. If I point it at the sky, will its azimuth radiation pattern then become the same as its elevation radiation pattern when horizontally polarized?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="4076" LastEditDate="2019-01-14T13:04:09.703" LastActivityDate="2019-01-14T23:37:25.807" Title="If I point a yagi antenna at the sky, what will its azimuth radiation pattern look like?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12618" PostTypeId="2" ParentId="12616" CreationDate="2019-01-14T12:17:35.837" Score="3" Body="&lt;p&gt;Short answer: yes, provided there are no ground effects in either orientation. That's how azimuth and elevation are defined.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there are ground effects in either orientation, then it is likely that the radiation patterns will change as the orientation of the antenna, in relation to ground, is changed. In this case it is likely that changing the orientation of the antenna will not cause the azimuth pattern to become to the elevation pattern and visa versa. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="9493" LastEditDate="2019-01-14T23:37:25.807" LastActivityDate="2019-01-14T23:37:25.807" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12619" PostTypeId="1" CreationDate="2019-01-14T13:31:11.423" Score="8" ViewCount="1752" Body="&lt;p&gt;I know that most amateur operators simply sign at the beginning or end of a message, like&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;The weather is good, Kz1XXY&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Would it also be customary to say that in phonetic form?&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Kilo zulu 1 X-ray X-ray Yankee&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="13927" LastEditorUserId="76" LastEditDate="2019-01-14T17:55:05.357" LastActivityDate="2021-04-17T08:25:03.960" Title="Is it conventional to sign using the phonetic alphabet like people do in the military or aviation?" Tags="&lt;procedure&gt;&lt;callsign&gt;&lt;phone&gt;" AnswerCount="6" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12621" PostTypeId="2" ParentId="12619" CreationDate="2019-01-14T14:33:04.457" Score="3" Body="&lt;p&gt;Yes, the standard phonetic alphabet is used by radio amateurs. Of course, some people use alternatives in some circumstances - but we are required to know the standard phonetic alphabet.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-01-14T14:33:04.457" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12622" PostTypeId="2" ParentId="12619" CreationDate="2019-01-14T17:54:49.630" Score="13" Body="&lt;p&gt;The choice of using phonetics ('alpha, bravo, charlie, …') versus plain alphabet sounds ('aye, bee, see, …') should be, and in my limited experience usually is, made based on how likely the recipient is to need them to understand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are two extreme cases:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;A contact made using a FM repeater at close range, among people who already know each other, does not need to use phonetics because there is little noise on the received audio and the people already know what they'll be hearing.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;On the other hand, someone calling CQ on simplex using SSB either for a contest or DXing will always use phonetics, because they're trying to call anyone they can, &lt;em&gt;particularly&lt;/em&gt; operators at the longest possible range, and so they want to maximize understandability when the recipient hears lots of noise and has never heard this particular call sign before.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If someone is doing, say, VHF FM simplex, you might hear either one. If someone is continuing a discussion rather than making the initial contact, they might not use phonetics because they're doing it for the legally required identification rather than to communicate to the other party. And so on.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-01-14T17:54:49.630" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12623" PostTypeId="2" ParentId="12619" CreationDate="2019-01-14T20:34:33.110" Score="5" Body="&lt;p&gt;In fact, hams use phonetic alphabet for their call signs (and also QTH) most of the time. The reason is simple - when you are establishing a QSO you don't know how well the other operator hears you. Maybe your signal is weak on her side, or maybe there is a QRM or QSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During an established QSO phonetic alphabet is used by two reasons. Firstly, you make sure that the other operator received your call sign correctly. I've been in a few situations when my suffix was recorded wrong (e.g. R2AU instead of R2AUK). Repeating your call sign is a polite way to say that it should be corrected. Secondly, all other hams may hear you as well, but you don't know how well they hear you. They may even hear only one of two hams. Repeating call signs using phonetic alphabet allows to specify who is talking and who she is talking to. Otherwise someone can think that, for instance, you are calling CQ, and intervene in the QSO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way (&lt;strong&gt;very important!&lt;/strong&gt;) you assumption that hams sign a message by telling a call sign is not quite correct. During the QSO hams use &lt;strong&gt;two&lt;/strong&gt; call signs - the first one is who you are taling to, and the second is your call sign, always in this order. The obvious exception is when you are calling CQ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This being said, during a long and stable QSO hams may get tired of repeating their call signs using phonetic alphabet all the time and start using regular letters, or even pronounce the call signs as if they were words. &lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-01-14T20:34:33.110" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12625" PostTypeId="2" ParentId="12588" CreationDate="2019-01-14T23:53:05.697" Score="1" Body="&lt;p&gt;It should be mounted horizontally. The deepest nulls would be ~90° off the sides. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-01-14T23:53:05.697" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12626" PostTypeId="1" CreationDate="2019-01-15T01:07:12.337" Score="0" ViewCount="297" Body="&lt;p&gt;This question is very similar &lt;a href=&quot;https://ham.stackexchange.com/questions/6439/yaesu-g-5400b-rotator-controller-problem&quot;&gt;Yaesu G-5400B rotator controller problem&lt;/a&gt;, with a bit of a twist.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm getting a consistent 5.84 VDC up to the rotators and the expected 0-5.84 VDC at terminals A1-3 and E1-3, and thence to VR2 and VR4. But tracing those voltages through the circuits to the eventual outputs at DIN pins 1 and 6 (to my computer interface - a K3NG device) I'm only seeing a maximum of 1.5 to 2 VDC if I rotate VR2 and VR4 to minimum. (The meters are reading just fine, and are stable.) Thoughts on this? Perhaps the OpAmps Q3 and Q4 have failed? They're obviously still passing voltage, just not 0-5.84 volts. I'm hoping it's something simpler.&lt;/p&gt;&#xA;" OwnerUserId="14001" LastEditorUserId="76" LastEditDate="2019-01-15T01:13:05.373" LastActivityDate="2019-01-15T16:40:58.517" Title="Another Yaesu G-5400B output voltage question" Tags="&lt;yaesu&gt;&lt;equipment-troubleshooting&gt;&lt;antenna-rotator&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12627" PostTypeId="2" ParentId="12626" CreationDate="2019-01-15T01:35:33.377" Score="1" Body="&lt;p&gt;It is unlikely that both op amps have failed, especially since the other half of each op amp drives the meters, which you stated are still working properly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am initially concerned that you are seeing 5.84 VDC at the rotor. The input to the range pots that are in the rotor should be ~8 volts. This may indicate that you have a wiring error or a high resistance wiring connection somewhere. Check the voltage at the rotor control box A1 and E1 with and without the rotor connected. It should stay at ~8 volts in both cases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If E1 an A1 are not at 8 volts with the rotor disconnected, this would indicate a problem with the 8 volt regulator circuit, including Q2. Given the age of the rotor, it could be that C1 is no longer up to spec. Check this with volt meter across the capacitor. It should read near 0 AC volts and near 12 DC volts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To adjust the output voltage on the DIN connector, you must adjust VR3 and VR4 (you stated VR2 and VR4). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remove the K3NG device from the DIN plug. Check that the op amp inputs (Q3 pin 3 and Q4 pin 3) follow the voltage output of VR3 and VR4 respectively. If they do not, then check the clamping diodes D12, D13, D24 and D25 for correct functioning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you find nothing amiss in the prior step, check the op amp outputs (Q3 pin 1 and Q4 pin 1) to see that they follow VR3 and VR4 respectively. If not, check the output clamping diodes D10, D11, D22 and D23 for correct functioning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you find nothing amiss in the prior step, then suspect a problem in the K3NG controller or the interconnect cable wiring. A common problem is incorrect pin numbering for the interface cable:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pE0UH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pE0UH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on the comments, here is a brief circuit description of the relative part of the circuit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Q2 is a voltage regulator that feeds 8 volts to the position sensing pots in the rotor. The resulting voltage back to the controller ranges from 0 to ~7.8 volts. The maximum voltage will be less due to the resistance of the wiring between the controller and the rotor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The output voltage from the rotor pots is fed into VR3 and VR4, each of which is in series with a 4.7k ohm resistor. The output voltage of VR3 and VR4 is conditioned, divided in half, and fed into an op amp circuit with a gain of ~2. The output of the amp amp is further conditioned and current limited by a 220 ohm resistor before being fed to the DIN jack on the back of the rotor controller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VR3 and VR4 set the maximum output voltage present on DIN pins 1 and 6 when the rotor is in its maximum position. They should be adjusted when the rotor is at its maximum position in both axes (both meters full right). The output adjustments (negating the wire resistance mentioned earlier) should range from ~2.5 volts to ~7.8 volts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the schematic for the az-el rotor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yymiG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yymiG.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-15T16:40:58.517" LastActivityDate="2019-01-15T16:40:58.517" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="12630" PostTypeId="1" AcceptedAnswerId="12631" CreationDate="2019-01-15T07:07:26.117" Score="1" ViewCount="97" Body="&lt;p&gt;I encountered the following question on a test, and I'm not sure of the theory behind it. Could someone please explain?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;When a signal with spectrum ranging from 13 MHz to 15 MHz is mixed with (i.e., multiplied by) a 14-MHz sine wave, which of the following frequency ranges does NOT contain frequencies of the resulting mixed signal?&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;(A) From 0 to 1 MHz&lt;/li&gt;&#xA;  &lt;li&gt;(B) From 13 to 14 MHz&lt;/li&gt;&#xA;  &lt;li&gt;(C) From 27 to 28 MHz&lt;/li&gt;&#xA;  &lt;li&gt;(D) From 28 to 29 MHz&lt;/li&gt;&#xA;  &lt;li&gt;(E) All of the above ranges contain frequencies of the resulting signal&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="14005" LastEditorUserId="76" LastEditDate="2019-01-15T15:36:56.673" LastActivityDate="2019-01-15T15:36:56.673" Title="Frequency mixing products" Tags="&lt;mixer&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12631" PostTypeId="2" ParentId="12630" CreationDate="2019-01-15T11:15:10.533" Score="7" Body="&lt;p&gt;When two sinusoidal signals are multiplied through a non-linear mixer circuit, it results in the sum and difference of the mixed frequencies:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$f_s=f_1+f_2 \tag 1$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$f_d=f_1-f_2 \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, negative frequencies are not possible so &lt;span class=&quot;math-container&quot;&gt;$f_1$&lt;/span&gt; should be the higher frequency in equation 2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This multiplying or mixing process is also called heterodyning and is the basis for most modern, analog radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So now you can work through the formulas to determine your homework answer. Take note that the question asks for a range that would &lt;strong&gt;not&lt;/strong&gt; be produced by the mixing action. If you care to work through the answer as a comment to this answer, I would be happy to comment on your conclusion.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-15T11:20:31.170" LastActivityDate="2019-01-15T11:20:31.170" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12634" PostTypeId="1" CreationDate="2019-01-15T21:11:38.387" Score="1" ViewCount="228" Body="&lt;p&gt;Can a generic SSB transceiver, together with an FSK modem, be used to receive FSK modulated digital signals?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, what considerations should be taken? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;and what kind of issues (AGC? Compression? Audio filtering? etc.) can occur when trying to inject audio to create a clean FSK RF output when transmitting?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, what is the max data rate allowed to stay with the 3khz bandwidth?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any help is appreciated. Best&lt;/p&gt;&#xA;" OwnerUserId="12902" LastActivityDate="2019-01-17T11:31:53.700" Title="Is it possible to transmit and receive FSK G3RUH using SSB transceiver operating on USB-D?" Tags="&lt;ssb&gt;&lt;icom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12636" PostTypeId="2" ParentId="8899" CreationDate="2019-01-16T10:19:35.567" Score="-2" Body="&lt;p&gt;Set the STE in menu to off that will add some repeater sound in the end of transmission&lt;/p&gt;&#xA;" OwnerUserId="14016" LastActivityDate="2019-01-16T10:19:35.567" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12638" PostTypeId="2" ParentId="12634" CreationDate="2019-01-16T12:10:27.850" Score="1" Body="&lt;p&gt;In short, this is generally not permitted on HF. The G3RUH FSK proposal dealt with sending 9600 baud packet data over a 4800 hertz wide channel. The envisioned application was on VHF and UHF FM radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many countries (including the US) restrict the data rates on HF frequencies to the equivalent bandwidth of an SSB voice channel or even less. SSB voice is typically considered to occupy a 2.4 kHz bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The major data mode on HF in the last few years is called FT8. This mode is designed for weak signal communications and is optimized to exchange data needed to qualify as a confirmed contact. It occupies a 50 hertz bandwidth. There is a software suite of digital modes that includes FT8 called &lt;a href=&quot;https://physics.princeton.edu/pulsar/k1jt/wsjtx.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSJT-X&lt;/a&gt;. The latest version is 2.0 with earlier versions depricated due to incompatibility. The success of FT8 is providing new insight into propagation conditions on HF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, newer transceivers can be directly interfaced to a computer through a direct USB connection that presents the transceiver as both a USB sound card and, through a separate channel on the same USB connection, allows full control of the transceivers features.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moving one generation back in HF radio technology, the rigs had a connection for rig control features (often through an RS-232 adapter) but did not emulate a sound card. To interface the sound channel to the computer, a special modem is used. A popular brand is &lt;a href=&quot;https://wikipedia.org/wiki/RIGblaster_Nomic&quot; rel=&quot;nofollow noreferrer&quot;&gt;RIGblaster&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stepping yet another generation back, the HF radio will have no facility for computer controlling any of its features. The modem can still be used, however for data modes that can be used with manual rig control. Even FT8 is possible with this generation of radios although many of the desirable FT8 features cannot be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Edit]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your IC-9100 requires audio to be supplied via the ACC or DATA2 jack on the back of the radio. Either connection supports connecting to the PC speaker/mic or the use of a modem. In FM mode, you can run up to 9600 baud (if your regulations permit this) so 4800 baud would also work. See pages 171-173 of the English language manual for details. 4800 baud is considered &quot;slow&quot; data in this context. In VHF/UHF FM, AGC and transmit bandwidth are generally not a limiting factor. Do make sure, however, to turn off any equalizers, etc. to basically run the a wide, undistorted audio path in both directions.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-17T11:31:53.700" LastActivityDate="2019-01-17T11:31:53.700" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12639" PostTypeId="2" ParentId="8899" CreationDate="2019-01-16T17:23:02.580" Score="1" Body="&lt;p&gt;I'll confirm what Steve said above, the ROGER menu item (adding tones at the end of the transmission) is probably the closest you'll get in a Baofeng.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I would also point out that if you're operating on a repeater, you're likely to draw some criticism because most repeaters already signal the end of their (re)transmission with a courtesy tone.  So the ROGER beep generated by the radio ends up being redundant.&lt;/p&gt;&#xA;" OwnerUserId="9350" LastEditorUserId="9350" LastEditDate="2019-01-16T17:48:43.650" LastActivityDate="2019-01-16T17:48:43.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12642" PostTypeId="1" AcceptedAnswerId="12645" CreationDate="2019-01-17T16:12:56.820" Score="-1" ViewCount="67" Body="&lt;p&gt;A direct current will be interrupted by a high frequency switch. It seems , that in a wire, connected to the source (the antenna rod), instead of pushed back- and forwards electrons, the electrons get pushed only in one direction and “fall” back in the other.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/cDw5Bm.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fcDw5Bm.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will where be a skin effect?&lt;br&gt;&#xA;Additional question: Is there an electromagnetic radiation produced?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit&lt;/strong&gt; After reading the comments a have to add that I thought, that in a wire, even if the circuit is open, some amount of electrons will be affected from the AC source.&lt;/p&gt;&#xA;" OwnerUserId="13834" LastEditorUserId="13834" LastEditDate="2019-01-17T16:52:35.117" LastActivityDate="2019-01-17T17:29:49.403" Title="Skin effect for a modified antenna with a high frequency pulsed DC" Tags="&lt;antenna-theory&gt;&lt;electronics&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12643" PostTypeId="1" CreationDate="2019-01-17T16:19:01.943" Score="1" ViewCount="157" Body="&lt;p&gt;&lt;strong&gt;Task: Path loss modelling&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Target frequency&lt;/strong&gt;: 433 MHz;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Laboratory environment&lt;/strong&gt;: in a basement where there were other equipment and metal shelves. A few acoustic absorbers were placed around the setup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Scenario 1&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;TX antenna sealed in a small bottle (diameter 3 cm, length 10 cm)&lt;/li&gt;&#xA;&lt;li&gt;TX antenna moving inside 50 L of a tissue-simulating liquid (held in a basin);&lt;/li&gt;&#xA;&lt;li&gt;RX antenna fixed outside of the basin; &lt;/li&gt;&#xA;&lt;li&gt;Both are connected to a Network Analyzer (very old, but calibrated before each measurement) that recorded the S parameters of different TX-RX distances;&lt;/li&gt;&#xA;&lt;li&gt;Addition: The coaxial cables seemed to be very sensitive. A gentle twist could result in big changes in the S-parameters' curves in the frequency domain.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Scenario 2&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;TX antenna integrated to an electronic system (MCU+RF module+battery)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The whole electronic system was sealed in the small bottle (diameter 3 cm, length 10 cm), placed inside the aforementioned basin, and moved along the same trail as in Scenario 1;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;RX antenna fixed outside of the basin and connected to a Spectrum Analyzer that recorded the received signal level at the same TX-RX separation distances as in Scenario 1;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;S21 is regarded as Tranmitter power level - Received signal level - cable loss;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Illustration of the setup&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bq0w5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bq0w5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Expected results&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;S21 increases (generally) as TX-RX distance increases&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Actual results&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Scenario 1&lt;/strong&gt;: S21 against distance fluctuated within a small range (the measurement was repeated many times)&#xA;&lt;a href=&quot;https://i.stack.imgur.com/T6k5G.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/T6k5G.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;S11 against frequency and S22 against frequency were normal reflection curves, and the values were reasonable.&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Scenario 2&lt;/strong&gt;: S21 increased with TX-RX distance&#xA;&lt;a href=&quot;https://i.stack.imgur.com/FJrL5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FJrL5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Questions&lt;/strong&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What could be the causes then? Is that because the network analyzer is too sensitive to the noises in the environment?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The network analyzer was supposed to work well as other people were using it for measurement as well. )&lt;/p&gt;&#xA;" OwnerUserId="11250" LastEditorUserId="11250" LastEditDate="2019-01-17T20:50:25.453" LastActivityDate="2019-01-17T20:50:25.453" Title="Measuring S21 against TX-RX distance (a.k.a path loss modelling) with a network analyzer didn't give expected results" Tags="&lt;rf-power&gt;&lt;measurement&gt;&lt;noise&gt;&lt;equipment&gt;&lt;path-loss&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12644" PostTypeId="2" ParentId="12643" CreationDate="2019-01-17T17:19:42.340" Score="1" Body="&lt;p&gt;I would suspect that the primary reason for the seemingly odd results is that you are likely operating the experiment in the near field of the antennas. As your distance changes, the &lt;a href=&quot;http://www.antenna-theory.com/definitions/mutualcoupling.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;mutual coupling &lt;/a&gt; of the antennas changes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As mutual coupling changes, antenna efficiencies, impedances, S11 and S22 parameters will change as well. You can execute experiments to confirm these effects. The result of this, however, is that your experiment has not isolated path loss but in fact has commingled other factors in the S21 measurement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you execute the test with at least 1 wavelength (i.e. &gt; 0.7 meters) between the antennas, you should see more predictable results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the lab environment, some of the observations could also be due to reflections of RF from nearby objects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will also need to take care that your transmission lines do not carry common mode currents as this will negatively impact the results. 1:1 choking baluns, or continuous ferrite sleeves consisting of the appropriate material, on double shielded coax is recommended.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as the effect of the lossy medium goes, the effect can be modeled as a loss within the transmitting antenna system as long as the medium is a homogeneous, non conducting medium (e.g. a dielectric). Thus the path loss, once outside of the medium and in the far fields of the antenna, will follow a classic free space path loss (FSPL) model.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-17T17:45:38.763" LastActivityDate="2019-01-17T17:45:38.763" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12645" PostTypeId="2" ParentId="12642" CreationDate="2019-01-17T17:29:49.403" Score="2" Body="&lt;p&gt;In the schematic you have shown, it is straightforward what will happen. During the periods in which the switch is closed, the DC source will transfer electrons through itself until the voltage difference between &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the left antenna element and&lt;/li&gt;&#xA;&lt;li&gt;all the conductors from the positive terminal to the capacitor plate, including the switch&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;is at the target voltage. (The right antenna element and the capacitor plate it is attached to are 'floating' — there is no way for electrons to enter or leave — so the voltage is unspecified, though even if everything starts out at equal voltage there may be a small voltage difference between the plate and the antenna due to &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrostatic_induction&quot; rel=&quot;nofollow noreferrer&quot;&gt;electrostatic induction&lt;/a&gt; across the capacitor.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, nothing further will happen, because there are no other paths for current to flow. When the switch is open, nothing happens because there are even fewer paths for current to flow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will this circuit radiate? Yes, a very tiny amount, when the DC source is powered on or when you start closing the switch for the first time. But it will not continue to do so, because there is no oscillation in voltage or current. You're opening and closing a switch where the two sides will be equal in voltage, and so no current flows as a consequence of the closing.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-01-17T17:29:49.403" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12647" PostTypeId="1" AcceptedAnswerId="12648" CreationDate="2019-01-17T21:58:13.567" Score="0" ViewCount="105" Body="&lt;p&gt;AM broadcast signal covering 995-1005 kHz radio frequency (RF) range is to be down-converted to an intermediate frequency (IF) range of 395-405 kHz where main amplification takes place in AM receivers.&#xA;I need to find the mixing frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;i solved it this way&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;IF=Fmixer-RF&#xA;fm-1005=405 .     fm=1410&#xA;fm-995=405        fm=1400&#xA;fm-1005=395 .      fm=1400&#xA;fm-995=395 .      fm=1390&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;so the mixing frequency is 1400. &#xA;I was just wondering if that the way of how to find the mixing frequency? &lt;/p&gt;&#xA;" OwnerUserId="14005" LastEditorUserId="76" LastEditDate="2019-01-17T22:47:39.360" LastActivityDate="2019-01-18T02:36:21.553" Title="mixing frequency of intermediate frequency (IF) and radio frequency (RF)" Tags="&lt;mixer&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12648" PostTypeId="2" ParentId="12647" CreationDate="2019-01-17T23:43:13.577" Score="3" Body="&lt;p&gt;Your answer in your question is not correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This question is solved in the same way as the last question you asked. The formulas are the same:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$f_s=f_1+f_2 \tag 1$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$f_d=f_1-f_2 \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This time, the sum and difference is called IF (intermediate frequency) - a common term in mixer circuits. Then rearrange to find the LO (local oscillator) frequency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$LO=| IF-Signal | \tag 3$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$LO=IF+Signal \tag 4$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Start with the low end of both ranges and plug them into the equations. There are two possible answers for the LO frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can then plug in the upper frequencies of the ranges in the same way to see that it works out to the same LO frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Spoiler alert! The answer follows:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$LO=| IF-Signal | = | 395 - 995 | = 600 \text{ kHz}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$LO=IF+Signal = 395 + 995 = 1390 \text{ kHz}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The issue with using the 1390 kHz LO is that the IF passband will be inverted compared to the original signal. Consider that 1390 kHz - 995 kHz = 395 kHz but 1390 - 1005 kHz = 385 kHz, so the frequency image is inverted. As a result, the correct LO is 600 kHz.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-18T02:36:21.553" LastActivityDate="2019-01-18T02:36:21.553" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12649" PostTypeId="1" CreationDate="2019-01-18T05:44:41.027" Score="10" ViewCount="218" Body="&lt;p&gt;In Russia hams use two phonetic alphabets - the regular one (Alpha, Beta, Charlie, ...) and a localized one (Анна, Борис, Цапля, ...). When a ham calls CQ in Russian (which by the way is pronounced not &quot;CQ&quot; but &quot;Всем-всем&quot;) she uses Russian phonetic alphabet. For instance, my call sign R2AUK is pronounced as Роман-Два-Анна-Ульяна-Константин.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The tricky part about the localized phonetic alphabet is how it maps to the regular one. For instance, since in Russian language there is no Q letter, and W and V both sound like В (Виктор), Q is mapped to Щ (Щука) and V is mapped to Ж (Жук).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Long story short - if you live in Russia you have to learn not only the international phonetic alphabet, but also the local one. The test for the amateur radio license includes corresponding questions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to know, whether there is a similar situation in other countries. For some reason I doubt that Europe uses two alphabets. But maybe there are alternative phonetic alphabets, for instance, in Japan or maybe Oman?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-01-18T05:50:01.513" LastActivityDate="2019-01-20T14:11:02.180" Title="Local phonetic alphabets" Tags="&lt;phonetic-alphabet&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12650" PostTypeId="1" CreationDate="2019-01-18T11:37:57.330" Score="6" ViewCount="358" Body="&lt;p&gt;Is it possible, and how can I setup communication between stations 1000km apart from each other by using just 1W of transmission power?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By communication, I mean:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It can be text based&lt;/li&gt;&#xA;&lt;li&gt;It can be very slow. It's okay if I receive a small message in few hours of time.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;What are the limitations:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I don't have an amateur license&lt;/li&gt;&#xA;&lt;li&gt;I can use only 27MHz CB radio band&lt;/li&gt;&#xA;&lt;li&gt;Maximum radiated power can't be more than 1W&lt;/li&gt;&#xA;&lt;li&gt;Many busy cities will be between the two stations, not just plain fields and seas.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;What I have/can do:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Use a directional antenna&lt;/li&gt;&#xA;&lt;li&gt;I like DIY&lt;/li&gt;&#xA;&lt;li&gt;I am planning to receive using an RTL-SDR&lt;/li&gt;&#xA;&lt;li&gt;I can use open-source software to decode signals and/or can write a script to do so, too.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I am from India and &lt;a href=&quot;http://www.wpc.dot.gov.in/DocFiles/CB%20Radio%20Delicensing.doc&quot; rel=&quot;nofollow noreferrer&quot;&gt;here is the latest&lt;/a&gt; I could find for CB radio band. Also, it seems I could use 5W of power, but no external antenna and no mention of data transfer policy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was amazed how far WSPR signals can go with very little power. Trying to achieve something like that. Not just beacons, but actual communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anything I asked doesn't make sense, I'll keep on editing the question as per the community's feedback, to be more specific. &lt;/p&gt;&#xA;" OwnerUserId="14026" LastEditorDisplayName="user4168" LastEditDate="2019-01-23T00:55:41.347" LastActivityDate="2019-01-23T00:55:41.347" Title="Long range communication with just 1W of power?" Tags="&lt;software-defined-radio&gt;&lt;hf&gt;&lt;transmitter&gt;&lt;india&gt;&lt;wspr&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12651" PostTypeId="2" ParentId="12650" CreationDate="2019-01-18T12:26:23.953" Score="4" Body="&lt;p&gt;At 27 MHz and a distance of 1000 km, propagation will be the main determinant of the possibility of communications. Propagation will primarily be a factor of time of day and the sun spot conditions. You can get a fairly accurate estimate by using propagation prediction sites such as &lt;a href=&quot;http://www.voacap.com/hf/&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your interest is exchanging messages between stations, one of the best weak signal modes is FT8 which is part of the free &lt;a href=&quot;https://physics.princeton.edu/pulsar/k1jt/wsjtx.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSJT-X&lt;/a&gt; software. A similar, derivative work is &lt;a href=&quot;https://groups.io/g/js8call&quot; rel=&quot;nofollow noreferrer&quot;&gt;JS8CALL&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take care, however, to check your local regulations to see if data modes are permitted on these frequencies. This would not be allowed in the US, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that being said, why don't you and your friend become ham radio operators? The effort and expense to get a license in India is not very much. For a &lt;a href=&quot;http://www.niar.org/how-to-be-a-ham.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;restricted grade license&lt;/a&gt; you don't even need to know morse code. It will give you the option for more power and many more frequencies, some of which are more suitable to reliable communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-18T23:06:21.130" LastActivityDate="2019-01-18T23:06:21.130" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12652" PostTypeId="2" ParentId="12649" CreationDate="2019-01-18T16:00:01.877" Score="4" Body="&lt;p&gt;I enjoyed your description of phonetics and the Russian language. Thank you for sharing that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a friend in Japan that mentioned this. A quick check on &lt;a href=&quot;https://wikipedia.org/wiki/Japanese_radiotelephony_alphabet&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt; yielded:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Japanese radiotelephony alphabet (和文通話表 wabuntsūwahyō, literally &quot;Japanese character telecommunication chart&quot;) is a radiotelephony spelling alphabet, similar in purpose to the NATO/ICAO radiotelephony alphabet, but designed to communicate Japanese kana rather than Latin letters. The alphabet was sponsored by the now-defunct Ministry for Posts and Telecommunications.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-18T17:05:27.870" LastActivityDate="2019-01-18T17:05:27.870" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12653" PostTypeId="1" AcceptedAnswerId="12655" CreationDate="2019-01-18T16:12:05.247" Score="1" ViewCount="172" Body="&lt;p&gt;CD-audio has a bandwidth of 22kHz. CW usually has a bandwidth between 3 to 5 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I am wondering what is the bandwidth my Icom IC-910H can listen to in both, the SSB and the FM mode?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, what is the Bandwidth, the Icom IC-910H can transmit in USB and in FM?&#xA;Can the bandwidth be adjusted somehow?&lt;/p&gt;&#xA;" OwnerUserId="14027" LastEditorDisplayName="user4168" LastEditDate="2019-01-23T00:57:51.700" LastActivityDate="2021-04-18T16:19:10.070" Title="ICOM IC-910h How much bandwidth does it listen when receiving USB and FM?" Tags="&lt;receiver&gt;&lt;fm&gt;&lt;ssb&gt;&lt;icom&gt;&lt;filter&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12654" PostTypeId="2" ParentId="12650" CreationDate="2019-01-18T16:24:05.863" Score="2" Body="&lt;p&gt;I would say, your task is a challenging one, but not unsolvable. 27 MHz CB radio band should work similar to 10m amateur radio band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest to start with simple experiments. For instance, solder a simple oscillator. In my experience Clapp oscillator is quite simple to solder, see schematic in this article &lt;a href=&quot;https://eax.me/clapp-oscillator/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://eax.me/clapp-oscillator/&lt;/a&gt; . Then add a 555 timer to turn it on and off. Now you have a simple CW beacon. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then use the beacon on transmitting side and RTL-SDR on receiving side. Experiment with antennas, power, observe the propagation during different time. If you receive a beacon, even a wery weak signal, &lt;em&gt;now&lt;/em&gt; you can start experimenting with different modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also I would like to note that in some countries it's illegal to use a directional antenna in CB.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-01-18T16:24:05.863" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12655" PostTypeId="2" ParentId="12653" CreationDate="2019-01-18T16:37:27.503" Score="1" Body="&lt;p&gt;According to &lt;a href=&quot;http://icomamerica.com/en/products/amateur/satellite/910h/specifications.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;Icom's description&lt;/a&gt;, the receiver's bandwidth is&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;Selectivity&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;SSB, CW&lt;/strong&gt;&#xA;  More than 2.8 kHz/-6dB;&#xA;  Less than 4.2 kHz/-60 dB&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;FM&lt;/strong&gt;&#xA;  More than 15.0 kHz/-6dB;&#xA;  Less than 30 kHz/-60 dB  &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;strong&gt;FM-N*2&lt;/strong&gt;&#xA;  More than 6.0 kHz/-6dB;&#xA;  Less than 18 kHz/-60 dB&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A CW signal has a bandwidth of about 200 Hz. Therefore, &lt;a href=&quot;http://icomamerica.com/en/products/amateur/satellite/910h/options.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;a narrower CW filter&lt;/a&gt; would significantly help the signal-to-noise ratio.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;FL-132/FL-133 &lt;strong&gt;CW NARROW FILTERS&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;FL-132 is for the main band;&#xA;  FL-133 is for the sub band operation. &#xA;  Center frequency: 10.8491 MHz (FL-132);&#xA;  10.9491 MHz (FL-133). &#xA;  Passband width: 500 Hz/-6dB.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The instructions for installing the filter is in &lt;a href=&quot;http://icomamerica.com/en/downloads/DownloadDocument.aspx?Document=32&quot; rel=&quot;nofollow noreferrer&quot;&gt;the instruction manual&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/C2sF1.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/C2sF1.jpg&quot; alt=&quot;Optional filter installation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-01-18T17:02:30.020" LastActivityDate="2019-01-18T17:02:30.020" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12659" PostTypeId="2" ParentId="12650" CreationDate="2019-01-20T01:06:54.330" Score="0" Body="&lt;p&gt;If you have the ability to use a different wavelength band, you might want to investigate (including your local licensing requirements) use of 20, 40, or 80 meter and CW (Morse code).  American QRP (low power) operators have a certificate for &quot;1000 miles per watt&quot; (that would be 1600 km per watt), which I've seen referred to as almost a joke, because it's so easy to do in the American CW bands.  In part, this is easy because 40m and 80m, especially, propagate well, and in part because CW makes more efficient use of radiated power by transmitting on a narrower bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you're proposing isn't impossible, at all, even in 27 MHz/11m band; during the American CB heyday of the late 1970s, I recall hearing transmitters that were limited by law to 5 watt input or 4 watt output (depending on date of manufacture) from several hundred miles away, with no real attempt to optimize transmission (i.e. using off the shelf antennas on mobile installations).  With single sideband rigs and optimized antennae, it was common to talk to other stations across the width of the North American central plains, from Montana to Florida (nearly 3000 miles, or around 4500 km) with that power level, at night when the &quot;skip&quot; was good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the limitations you have on radiated power and terrain, even if you're stuck in 27 MHz band, I'd seriously suggest investigating something akin to machine-sent and machine-received CW.  There's a Linux program called &lt;em&gt;fldigi&lt;/em&gt; that's free and open source, and is in the repositories for Ubuntu (at least 16.04, probably 14.04 and 18.04 as well) that can manage both sending and receiving International Morse at any reasonable rate -- even very slow, if that's what you need to make you connection work.  It also handles many other digital radio formats, though use of other than Morse may be limited by law to certain bands and licenses.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-01-20T01:06:54.330" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12661" PostTypeId="1" CreationDate="2019-01-20T07:57:18.580" Score="1" ViewCount="42" Body="&lt;p&gt;My answer to the question &lt;a href=&quot;https://space.stackexchange.com/q/33031/12102&quot;&gt;Where can I find the TLE of ExseedSat 1, India's first ever private LEO satellite?&lt;/a&gt; is currently that while 60+ objects are being tracked from this mutli-payload launch, ExseedSat has not yet been unambiguously identified, so it's impossible to know which TLE would belong to that satellite.&lt;/p&gt;&#xA;&lt;p&gt;According to the &lt;a href=&quot;https://www.exseedspace.com/exseed-sat-1&quot; rel=&quot;nofollow noreferrer&quot;&gt;ExseedSat1 webpage&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;As it orbits around the earth, every minute it will whistle out the letter ‘V’ in Morse code (remember Beethoven’s 5th symphony? Yes, those notes).&lt;/p&gt;&#xA;&lt;p&gt;This will be followed by telemetry in radio teletype format. Watch a simulated test: &lt;a href=&quot;https://youtu.be/da0y_InGffY&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://youtu.be/da0y_InGffY&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;NOTE:&lt;/strong&gt; if you watch the video, skip ahead to &lt;code&gt;05:14&lt;/code&gt; or 1h 45m 15s on the display in the video to see the tape-measure antenna unwind and the satellite send it's &amp;quot;V&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;The page goes on to identify the various teams involved, and many of the leads have callsigns.&lt;/p&gt;&#xA;&lt;p&gt;I can keep an eye on the satcat report, but I don't know where to look to find out if there have been any reports of receiving any signal from this satellite? Is there a good place to watch for one?&lt;/p&gt;&#xA;" OwnerUserId="8643" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-01-20T07:57:18.580" Title="Any reception reports from ExseedSAT1 yet?" Tags="&lt;satellites&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12662" PostTypeId="2" ParentId="12649" CreationDate="2019-01-20T14:11:02.180" Score="1" Body="&lt;p&gt;I'm from Serbia, and we have our own phonetic alphabet here. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as I can see, the early version of that phonetic alphabet was developed/used by the Yugoslav People's Army, and covered letters used in the Serbo-Croatian language, as well as the English letters which we didn't have. The local letters were mapped to mostly geographic names, while the foreign letters were mapped to their local pronunciation. This alphabet can still be heard on the waves. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A-А-Avala, B-Б-Beograd, C-Ц-Cetinje, Ć-Ћ-Ćuprija, Č-Ч-Čačak,&#xA;  D-Д-Drvar, Đ-Ђ-Đakovica, DŽ-Џ-Džep, E-Е-Evropa, F-Ф-Foča, G-Г-Gorica,&#xA;  H-Х-Heroj, I-И-Istra, J-Ј-Jadran, K-К-Kosovo, L-Л-Lika,&#xA;  LJ-Љ-Ljubljana, M-М-Mostar, N-Н-Niš, NJ-Њ-Njegoš, O-О-Osijek,&#xA;  P-П-Pirot, Q-/-Kvorum, R-Р-Ruma, S-С-Skopje, Š-Ш-Šibenik,T-Т-Tetovo,&#xA;  U-У-Užice, V-В-Valjevo, W-/-Duplove, X-/-Iks, Y-/-Ipsilon, Z-З-Zagreb,&#xA;  Ž-Ж-Žabljak, 1-Jedinica, 2-Dva, 3-Tri, 4-Četiri, 5-Petica, 6-Šest,&#xA;  7-Sedam, 8-Osam, 9-Devet, 0-Nula&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;After the civil war, the alphabet was split into several local versions. The usual change was that the now foreign geographic names were replaced with local ones. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The current Serbian one (official for amateur radio in Serbia, also used Serbian parts of Bosnia and Herzegovina) is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A-А-Avala, B-Б-Beograd, C-Ц-Cetinje, Ć-Ћ-Ćuprija, Č-Ч-Čačak,&#xA;  D-Д-Drina, Đ-Ђ-Đakovica, DŽ-Џ-Džep, E-Е-Evropa, F-Ф-Futog, G-Г-Golija,&#xA;  H-Х-Heroj, I-И-Igalo, J-Ј-Jadran, K-К-Kosovo, L-Л-Lovćen,&#xA;  LJ-Љ-Ljubovija, M-М-Morava, N-Н-Niš, NJ-Њ-Njegoš, O-О-Obilić,&#xA;  P-П-Pirot, Q-/-Kvorum, R-Р-Ruma, S-С-Sava, Š-Ш-Šabac,T-Т-Timok,&#xA;  U-У-Užice, V-В-Valjevo, W-/-Duplove, X-/-Iks, Y-/-Ipsilon, Z-З-Zemun,&#xA;  Ž-Ж-Žabljak, 1-Jedinica, 2-Dva, 3-Tri, 4-Četiri, 5-Petica, 6-Šest,&#xA;  7-Sedam, 8-Osam, 9-Devet, 0-Nula&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The upcoming (expected to come into use in 2019, and be shared with other services) Serbian one is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A-А-Avala, B-Б-Beograd, C-Ц-Cer, Ć-Ћ-Ćuprija, Č-Ч-Čačak, D-Д-Drina,&#xA;  Đ-Ђ-Đakovica, DŽ-Џ-Džep, E-Е-Evropa, F-Ф-Futog, G-Г-Golija, H-Х-Heroj, I-И-Ivanjica, J-Ј-Jadar, K-К-Kosovo, L-Л-Leskovac, LJ-Љ-Ljubovija,&#xA;  M-М-Morava, N-Н-Niš, NJ-Њ-Njegoš, O-О-Obilić, P-П-Pirot, Q-/-Kvorum,&#xA;  R-Р-Ruma, S-С-Sava, Š-Ш-Šabac, T-Т-Timok, U-У-Užice, V-В-Valjevo,&#xA;  W-/-Duplove, X-/-Iks, Y-/-Ipsilon, Z-З-Zemun, Ž-Ж-Žabalj, 1-Jedinica,&#xA;  2-Dva, 3-Tri, 4-Četiri, 5-Petica, 6-Šest, 7-Sedam, 8-Osam, 9-Devet,&#xA;  0-Nula&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Pronunciation background: C is always pronounced like say tz in English, or Z in German, and is never hard like k. The Ć and Č are similar to the ch in Charlie. DŽ and Đ are similar to j in Juliet. I is basically English ee. The J is like y in Yankee. U is always like English oo. E is like e in Echo. The Š is the sh in ship. The LJ and NJ don't have good English equivalents, and are pronounced something like combination of L or N followed by y as in yes. The Ž is something like Zh in English. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Political background notes: Some Yugoslav successor states have switched to the international phonetic alphabet completely, some retain their own, while others seem not to have a clear guidance on which phonetic alphabet should be used.&lt;br&gt;&#xA;Although amateur radio is supposed to be apolitical, in some areas selection of the phonetic alphabet (including wether or not to use the international one) is seen as a political statement, so using the inappropriate alphabet can result in less than friendly responses. So we not only have to know several versions of local alphabet, plus international, but also when to use which. &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2019-01-20T14:11:02.180" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12663" PostTypeId="2" ParentId="12463" CreationDate="2019-01-20T23:16:48.003" Score="4" Body="&lt;p&gt;See below a summary of what i did to remove most of the RFI coming from my house solar panel system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Problem = horrid RFI across the entire HF spectrum. It's only there when the sun's out. The RFI sounds like a lawn mower. I normally like the sound of lawn mowers but not in this case. If i point my yagi towards the solar panels the RFI signal strength goes up. My solar panels are not the type with inverters on the back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fix is to connect an RF choke between each solar panel array and the solar panel inverter right at the input to the inverter.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Turn off solar panel inverter to see if that stops the noise.&lt;/li&gt;&#xA;&lt;li&gt;Noise goes away so inverter is probably the source.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Then for each solar panel array (or for each postive/negative solar panel cable input pair on the inverter) :&lt;/p&gt;&#xA;&#xA;&lt;ol start=&quot;3&quot;&gt;&#xA;&lt;li&gt;Obtain 2 x type 43 ferrite rings from Element 14 FAIR-RITE  5943003801  FERRITE CORE, TOROID, 43.&lt;/li&gt;&#xA;&lt;li&gt;Obtain about 2 meters of 4mm2 solar panel extension cable and cut it in half.&lt;/li&gt;&#xA;&lt;li&gt;Obtain 2 pairs of IP67 MC4 solar panel plugs/sockets.&lt;/li&gt;&#xA;&lt;li&gt;Make 2 series RF chokes. Each choke has about 7 turns of two solar panel extension cables wound in a bifilar fashion (two cables next to each other) on one ferrite ring. Make the two chokes using the same two single 1 m pieces of cable such that the two chokes are in series with no joins in the middle. &lt;/li&gt;&#xA;&lt;li&gt;Fit the MC4 connectors to the chokes. The set of two chokes in series will have two connectors at one end and two connectors at the other end. The connector sex must be such as to preserve the original polarity of the solar panel array connections to the inverter.&lt;/li&gt;&#xA;&lt;li&gt;Follow your solar panel system's proper procedure to power down.&lt;/li&gt;&#xA;&lt;li&gt;Connect the chokes at the inverter between the inverter and the solar panel array. Make sure the polarity is correct. If you get it wrong your inverter will have a heart attack and die. Be careful as solar panel arrays output approx 300 - 500 VDC. If you're afraid like me do it at night.&lt;/li&gt;&#xA;&lt;li&gt;Follow your solar panel system's proper procedure to power up.&lt;/li&gt;&#xA;&lt;li&gt;Jump up and down (well that's what i did) as you tune across the bands and see that the noise is mostly gone.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Note that clip-on ferrite chokes won't do anything to cure solar panel inverter noise.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-01-22T02:25:17.050" LastActivityDate="2019-01-22T02:25:17.050" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12664" PostTypeId="1" AcceptedAnswerId="12666" CreationDate="2019-01-21T04:35:53.470" Score="1" ViewCount="138" Body="&lt;p&gt;I am interested to explore what a Yaesu VX-8DR radio can do and would like to add an amplifier to it. One of the AMPs that seems to work with a 5W input is KPA100, I am still doubtful how the Yaesu can key into the Amp. Of, course I plan to get a J-pole antenna to work with the radio + amp. Is this a good Amp for the Yaesu? Any advice on this idea of adding an Amp for a handleld? &lt;/p&gt;&#xA;" OwnerUserId="14044" LastActivityDate="2019-01-21T18:30:15.457" Title="is KPA100 a good amplifier for Yaesu Vx-8Dr" Tags="&lt;ht&gt;&lt;amplifier&gt;&lt;yaesu&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12666" PostTypeId="2" ParentId="12664" CreationDate="2019-01-21T18:30:15.457" Score="5" Body="&lt;p&gt;and welcome to ham.stackexchange.com!  Sorry, but the Elecraft KPA100 won't work at all with the Yaesu VX-8DR.  The VX-8DR is a handheld that runs on the 6m/2m/1.25m/70cm bands; the KPA100 works on the ham bands between 80m&amp;ndash;10m.  What's more, the KPA100 is really meant to be part of the Elecraft K2, and isn't meant to be a stand-alone amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You didn't say what your intentions are, but allow me to guess that you're shopping for your first radio, and you want both the convenience of an HT and also more power when you're operating from home.  I have an ancient Yaesu FT-470 handheld and a 30 W amplifier meant for it, which I got for cheap at a hamfest.  So amplifiers meant for handhelds aren't unknown, but they are fairly rare.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a question-and-answer site and not a forum-style site, so we usually shy away from giving personal advice; we want answers that will also be useful to other people in the future.  So instead here is some more generic advice.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;You might be surprised how much better an HT will do connected to a good antenna, especially one mounted up high (like the roof of a single-story building) will do compared to the &quot;rubber duck&quot; antenna that comes with the HT.  You might not need more power at all, especially if you're mainly interested in connecting to local repeaters.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Rather than spending a lot of effort and money finding an amplifier for an HT, most people would probably just buy another radio, like a mobile rig, with more power to supplement the HT.  (People use &quot;mobile&quot; rigs both in vehicles and at home.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Your local ham club could probably give you lots of advice, and might also be a good source of much less expensive used radios.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-01-21T18:30:15.457" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12667" PostTypeId="1" CreationDate="2019-01-22T07:24:09.183" Score="6" ViewCount="702" Body="&lt;p&gt;One explanation I found is that a signal reflected from ionosphere is always circularly polarized. Thus it can be received by both vertically and horizontally polarized antennas (naturally, with 3 dB attenuation). However I don't trust the source very much and thus decided to ask for a second opinion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this explanation accurate or is the truth a little more complicated?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="9493" LastEditDate="2019-01-22T17:15:49.280" LastActivityDate="2019-01-22T19:58:52.323" Title="Why can I receive a vertically polarized signal on a horizontally polarized antenna on HF and vice versa?" Tags="&lt;polarization&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12668" PostTypeId="2" ParentId="12667" CreationDate="2019-01-22T13:58:52.127" Score="4" Body="&lt;p&gt;Reflections from the ionosphere are randomly distorted from the original polarization - but not circular. Polarization matters for ground waves but not for most sky waves.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-01-22T13:58:52.127" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12669" PostTypeId="2" ParentId="12667" CreationDate="2019-01-22T16:01:22.450" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Why can I receive a vertically polarized signal on a horizontally polarized antenna on HF and vice versa?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Who says you can?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cross-polarization is a common source of path loss even on HF. &lt;a href=&quot;http://www.lz1aq.signacor.com/docs/hpsra/horizontally-polarized-small-active-receiving-antennas7.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;LZ1AQ has some experiments&lt;/a&gt; which show as much as a 25 dB difference between horizontal and vertical polarization. &lt;a href=&quot;https://ham.stackexchange.com/questions/6676/how-big-is-a-decibel&quot;&gt;25 dB is quite a lot&lt;/a&gt;, enough to make the difference between 100% copy and unintelligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, ionospheric propagation changes rapidly and unpredictably, and the polarization might be rotated 90 degrees one instant, and 30 seconds later, not rotated at all. As such, trying to match the other station's polarization is a futile game of chance. So it's not so much that the problems with opposite polarization don't exist on HF, but rather they are just unavoidable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unless of course you have both horizontally and vertically polarized antennas to choose from, and some mechanism to combine them dynamically in the best way in the moment. This is called &lt;em&gt;diversity reception&lt;/em&gt;, and it can greatly increase the robustness of a receiver. It could be as simple as a switch between two antennas, or two separate receivers and antennas driving different ears on headphones, or a pair of phase-coherent receivers and a &lt;a href=&quot;http://www.antenna-theory.com/arrays/weights/main.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;dynamic algorithm&lt;/a&gt; that finds the best combination for each moment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is the fading only 25 dB, and not much more? Theoretically, the coupling between cross-polarized antennas should be zero, but in practice there's always a bit of overlap. Polarization is not a binary choice between &quot;horizontal&quot; or &quot;vertical&quot;, but can be any angle. The coupling between antennas is proportional to the cosine of the difference between the angles, so there's infinite loss only when the polarization is exactly 90 degrees apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, most paths, and especially ionospheric paths, are not truly just one path: they are the combination of many paths. It is very unlikely all possible paths at any given time will be cross-polarized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, all real antennas are somewhat sensitive to the opposite polarization though imperfections in their design. For example, a horizontal dipole often has a vertical feedline. Although not an ideal behavior, the antenna will be somewhat sensitive to common-mode currents on this feedline which will be vertically polarized.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-01-22T19:58:52.323" LastActivityDate="2019-01-22T19:58:52.323" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12670" PostTypeId="1" AcceptedAnswerId="12678" CreationDate="2019-01-23T02:54:10.250" Score="8" ViewCount="424" Body="&lt;p&gt;I understand the idea that when we are targeting the electrical component  of the radio waves we need to have some form of a linear conductor that receives the electrical component, this creates a current in the circuit and thus induces a signal. But in antennas that are designed to capture the magnetic component we use loop antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the understanding of how radio waves are propagated, the electrical and the magnetic component are orthogonal to each other and are in phase, and therefore the wavelength must be the same as well (assumption). So I would expect the antenna that focuses on the magnetic component to be similar in design to the antennas that capture the electrical component.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But then, why do these two antennas look remarkably different? &lt;/p&gt;&#xA;" OwnerUserId="14044" LastActivityDate="2019-05-30T12:58:01.163" Title="Why are there differences in antennas that depend on electrical component and magnetic component of a radio wave?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;loop-antenna&gt;&lt;magnetic-loop&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12671" PostTypeId="1" AcceptedAnswerId="12672" CreationDate="2019-01-23T03:08:43.643" Score="2" ViewCount="97" Body="&lt;p&gt;I have a 25w radio running through a ~4.5db gain antenna. If I use a 4W HT indoors, I can hear a loud buzzing noise emmanating from my computer speakers. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I used the 25w mobile with the 4.5db gain antenna close (within 2-3ft) to any unshielded electronics, could they get damaged? Cliche, but the landlord says no antennas on the roof.&lt;/p&gt;&#xA;" OwnerUserId="13184" LastActivityDate="2019-01-23T03:38:29.813" Title="Can an indoor antenna damage unshielded electronics?" Tags="&lt;antenna&gt;&lt;rfi&gt;&lt;rf-power&gt;&lt;electronics&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12672" PostTypeId="2" ParentId="12671" CreationDate="2019-01-23T03:29:31.297" Score="4" Body="&lt;p&gt;Possible, but very unlikely unless you have some extremely sensitive electronics. If you did you'd know it, because cell phones and WiFi would also be hazards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The buzzing you hear is the RF current being picked up by the speaker wiring, then rectified and amplified by the speaker's electronics. It's no more damaging than plugging the audio input of the speakers into a recording of a similar noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To put your mind at ease, consider all the other RF radiators you likely have lying around: your cell phone, WiFi in your laptop, etc. These are probably somewhat less power, around 1W, but the difference isn't huge. Power density falls off with the square of distance, so if your HT has 25 times the power, it's similar to a 1W device at &lt;span class=&quot;math-container&quot;&gt;$1/\sqrt{25} = 1/5$&lt;/span&gt;th the distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So say you are worried your HT might damage something five feet away, ask yourself: would you worry about a cell phone damaging the same thing at one foot away? Probably not.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-01-23T03:38:29.813" LastActivityDate="2019-01-23T03:38:29.813" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12673" PostTypeId="1" AcceptedAnswerId="12675" CreationDate="2019-01-23T03:37:59.630" Score="3" ViewCount="130" Body="&lt;p&gt;I've recently had an MRI, and after studying chapter two and three of the ARRL manual, I've got a better understanding of how my MRI machine might have worked.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I am curious to know what would happen if I brought a transceiver within range of an MRI machine and tuned it to the frequency. Assuming it was CW, would I hear the same rise and fall of the pitch the way &lt;a href=&quot;http://www.aurora-service.eu/radio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;mentioned in this article.&lt;/a&gt; There was a guy by the name of Stephen Charlie, or something like that who recorded these phenomena, and in fact is another reason I want to experiment with radio.&lt;/p&gt;&#xA;" OwnerUserId="13927" LastActivityDate="2019-01-24T01:56:54.290" Title="Do MRI machines use the ISM band, and do they generate audible CW signals?" Tags="&lt;cw&gt;&lt;uhf&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12675" PostTypeId="2" ParentId="12673" CreationDate="2019-01-23T08:01:43.907" Score="6" Body="&lt;p&gt;Medical MRI looks for the nuclear magnetic resonance of hydrogen, at around 1 or 2 Tesla, at about 100 MHz.&#xA;NMR is a phenomenon of the nucleus, not the atom, it is different to anything involving ions or electrons moving in a magnetic field, like aurora and the ionosphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a table of &lt;a href=&quot;http://web.mit.edu/speclab/www/Facility/nmrfreq.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;NMR frequencies&lt;/a&gt; for somewhat higher magnetic field strengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MRI machines operate in shielded rooms, because they generate strong RF signals, perhaps 100 Watts, and they need to detect very weak signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think of it as a kind of through-meat radar, but using magnetic field gradients and different frequencies to probe different parts of you, not time delay and direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From outside the room you might hear a pulsed RF signal, scanning over a frequency range of 10% or so as the machine probes different regions of the magnetic field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, because of the large magnets, you wouldn't be allowed to take a transceiver, phone or even a belt buckle into the room.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-01-24T01:56:54.290" LastActivityDate="2019-01-24T01:56:54.290" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12676" PostTypeId="2" ParentId="12670" CreationDate="2019-01-23T13:23:54.087" Score="3" Body="&lt;p&gt;Whether an antenna is called an &quot;electrical&quot; or &quot;magnetic&quot; antenna, the generated and captured far-field electromagnetic photons of the same wavelength are identical. The difference in the two antennas occurs in the near-field where the electric field is dominant for electrical antennas and the magnetic field is dominant for magnetic antennas. The difference is most noticeable during receive in noisy environments. &lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-01-23T13:23:54.087" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12678" PostTypeId="2" ParentId="12670" CreationDate="2019-01-23T14:28:48.153" Score="8" Body="&lt;p&gt;In free space, the electric and magnetic fields are always in a fixed ratio, a physical constant called the &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;noreferrer&quot;&gt;impedance of free space&lt;/a&gt;, about 377 volts per ampere. The two are always in phase (and thus have identical wavelength) but in orthogonal angles. In fact, the magnetic field is &lt;a href=&quot;https://youtu.be/1TKSfAkWWN0&quot; rel=&quot;noreferrer&quot;&gt;explained by relativity&lt;/a&gt; to be the effect of length contraction of moving electric charges. Viewed in this light, the magnetic field doesn't really exist: there are just electric fields, and relativistic distortions of electric fields in moving reference frames. The &quot;magnetic field&quot; is an abstraction that accounts for relativistic effects as they apply to electric charges.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Point being, the two are quite inseparable: it's not possible to build an antenna which receives just the &quot;magnetic component&quot; of a radiated wave, because the magnetic and electric fields are the &lt;em&gt;same thing&lt;/em&gt;. So I think your intuition is on the right track.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Theoretically, an antenna could be described only in terms of Maxwell's equations, or even more modern science if you prefer. But this wouldn't be very practical. To be able to reason more intuitively about antennas, or any electrical device, we apply fundamental laws to derive abstractions which are less general but more practical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, a small loop can be described by &lt;a href=&quot;https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction&quot; rel=&quot;noreferrer&quot;&gt;Faraday's law of induction&lt;/a&gt;. But if the loop becomes longer that abstraction stops working, because we must account for differences in phase of the waves propagating around the loop. If the loop's perimeter grows to a full wavelength, it's easier to explain it as a &lt;a href=&quot;http://www.antenna-theory.com/antennas/foldeddipole.php&quot; rel=&quot;noreferrer&quot;&gt;folded dipole&lt;/a&gt;. A typical explanation of folded dipoles involves transmission lines and quarter-wave stubs, abstractions that have no particular association with magnetic or electric fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to answer your question, I'd say maybe you're thinking about it backwards. An antenna can't &quot;target&quot; the electric or magnetic field specifically: after all, for electromagnetic radiation the two are the same thing. But there are many possible ways to design an antenna, and there are many abstractions we may choose to use to explain how those antennas work, and some of those abstractions (like Faraday's law) are most conveniently phrased in terms of the magnetic field. It's not that loop antennas receive a different &quot;kind&quot; of radiation, just that the magnetic field happens to be the most accessible abstraction for conveying an intuitive sense of the approximate operation of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-01-23T14:28:48.153" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12679" PostTypeId="2" ParentId="12673" CreationDate="2019-01-23T19:47:38.087" Score="3" Body="&lt;p&gt;An MRI unit used for clinical imaging will be a 1.5T or 3T magnet.  Because of abundance, the receiving coils of most clinical magnets will be designed to pick up the induced RF signals from hydrogen, which has a Larmor frequency of about 42.6 MHz/T.  For a 1.5T magnet, it's listening around 63.87 MHz or so.  For a 3T magnet, it will be listening around 127.7 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RF shielding for MRI rooms is primarily to keep out external RF that would create artifacts in the images.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While you wouldn't be able to bring a receiver into the MRI room, outside the room would be doable.  Depending on the pulse sequence being used you might hear a pattern of chirps.  If anything was heard though, first thing I'd do is question the integrity of the room's RF shielding.&lt;/p&gt;&#xA;" OwnerUserId="73" LastActivityDate="2019-01-23T19:47:38.087" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12680" PostTypeId="1" AcceptedAnswerId="12683" CreationDate="2019-01-23T23:52:53.953" Score="0" ViewCount="64" Body="&lt;p&gt;Will the quantization noise be increased if the step level is increased? I was wondering about the relationship between the step size of the quantizer and quantization noise,&lt;/p&gt;&#xA;" OwnerUserId="14005" LastEditorDisplayName="user4168" LastEditDate="2019-01-24T01:32:34.187" LastActivityDate="2019-01-24T15:05:46.210" Title="Will the quantization noise be increased if the step level is increased?" Tags="&lt;dsp&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12681" PostTypeId="2" ParentId="11918" CreationDate="2019-01-24T04:10:55.763" Score="0" Body="&lt;p&gt;I installed a 40m dipole, having just enough space in my yard.  I cut it to length as per the formula, so resonance should have been close…  I used 12 gauge insulated wire.  As a test, I installed 4 x 18” wire radials on each end to see the effect.  Using an antenna analyzer, I was surprised to see that resonance was down around 6.200 mhz.  I replaced the 4 wire radials I improvised, with a larger 3 leaf clover shaped cap hats,  made with steel wire,  fastened the cap hat to the wire using split nut connectors and soldered the ends of the dipole to the cap hat.  The dipole resonated somewhere in the upper 5 mhz range.  I then shortened the wire from the middle to bring it close to resonance on 40m.   At the moment, the antenna resonates around 7.350 mhz , SWR is 1.2/1.3 @  R=50 ohms.  After I trim it a bit, the dipole should be about right.   On my first contact with a person I had spoken to before, he was surprised that I was now coming in 25+ over….   The overall length on my dipole, with the hats,  is now  roughly  50'ish ft.  The size and shape of the cap hats will determine the  final length of your dipole. With out over thinking capacitor hats, size, shape or equations, etc… just try it. I would say that in no way does using capacitor hats become a compromise to the signal in any way, if anything, it will likely greatly improve the efficiency of the dipole you have. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best regards,&#xA;Rene&#xA;VE6DAY&lt;/p&gt;&#xA;" OwnerUserId="14067" LastActivityDate="2019-01-24T04:10:55.763" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12683" PostTypeId="2" ParentId="12680" CreationDate="2019-01-24T06:59:28.860" Score="2" Body="&lt;p&gt;Quantization noise is highly dependent on the signal source distribution and its amplitude, the number of ADC bits, and the use of dithering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a high resolution ADC that is digitizing a full amplitude sine wave, the maximum noise contribution is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\text{SNQR}_\text{dB}=1.76+Q \cdot 6.02 \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; is the number of bits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here we can observe that increasing the number of bits increases the maximum SNQR by the 6.02 dB factor per bit. The 1.76 term simply accounts for the non-uniform distribution of the sine wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The origin of formula 1 is found in the formula for ideal noise contribution of the lower +/- 1/2 bit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\text{SNQR}_\text{dB}=20\log_{10}(2^Q) \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formula 1 generally remains true for complex signals being quantized by high resolution ADCs. Lower level signal  inputs or low bit ADCs will generally suffer from a higher noise contribution (lower SNQR)  unless appropriate counter measures are deployed.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-24T15:05:46.210" LastActivityDate="2019-01-24T15:05:46.210" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12686" PostTypeId="1" AcceptedAnswerId="12687" CreationDate="2019-01-24T07:45:21.417" Score="1" ViewCount="249" Body="&lt;p&gt;There are videos on YouTube that show how to make a 1:1 current balun. When the balun is done some people connect a 100W 50 Ohms resistor to the balun and measure SWR say in 7.000-7.200 MHz range. If SWR is low they conclude that the balun works as expected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why SWR, i.e. a measure of reflected power, has anything to do with common mode current that the balun suppose to cut off? Or maybe these hams just don't know what they are doing and the test is worthless?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to ask the authors of corresponding videos, but unfortunately they didn't reply.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-01-24T09:02:01.367" LastActivityDate="2019-01-24T15:32:41.230" Title="Why some hams test their baluns with an SWR meter?" Tags="&lt;balun&gt;&lt;swr-meter&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12687" PostTypeId="2" ParentId="12686" CreationDate="2019-01-24T13:44:28.960" Score="3" Body="&lt;p&gt;A balun has two functions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;present a high impedance to common-mode currents&lt;/li&gt;&#xA;&lt;li&gt;present a low impedance to differential-mode currents&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;A balun that does just the first but not the second is easy: an open circuit fits the bill.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Testing with an SWR meter doesn't test the first, but it does test the second. That does mean the balun is doing at least half its job. It means the balun has been constructed without any shorts, etc. It may not be a complete test of the balun, but it's better than no testing at all, and it doesn't require any advanced equipment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-01-24T13:44:28.960" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12688" PostTypeId="2" ParentId="12686" CreationDate="2019-01-24T15:18:44.560" Score="3" Body="&lt;p&gt;A 1:1 choke-balun has a design impedance, usually 50 ohms. It also has an electrical length, e.g. mine is 60 degrees long on 28 MHz (4 feet of RG58 on two FT240-52 cores). If I load it with a 50 ohm dummy load on 28 MHz, it will read ~50 ohms on the input because the SWR is 1:1. However, if I test it with a 600 ohm dummy load, it will read 5.8-j26 ohms on the input. A lot of hams would expect a 1:1 balun to read 600 ohms with a 600 ohm load. Here is a graphic of actual measurements made with an AIM4170D. The violet curve is the measured impedance at the balun output looking into the ladder line going to a ZS6BKW antenna. The green curve is the measured impedance seen by the transmitter through eight feet of RG8x connected to the balun input. I was surprised to learn that my &quot;1:1 balun&quot; is only 1:1 with a 50 ohm load.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/0pfmI.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0pfmI.gif&quot; alt=&quot;Input/Output Impedance for ZS6BKW 1:1 Choke-Balun&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-01-24T15:32:41.230" LastActivityDate="2019-01-24T15:32:41.230" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12689" PostTypeId="2" ParentId="12670" CreationDate="2019-01-24T16:49:20.070" Score="2" Body="&lt;p&gt;RE: &lt;em&gt;It's an oversimplification to say that antennas respond to E or H fields. Antennas respond to the electromagnetic wave. Loop antennas are just as &quot;electric&quot; as dipoles.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Following is some background on this topic from Johnson &amp;amp; Jasik's &quot;ANTENNA ENGINEERING HANDBOOK, 2nd Edition, Section 5-4:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;RECEIVING LOOP  When the electrically small loop is used as a receiving antenna, the voltage developed at its open-circuited terminals is proportional to the component of the &lt;strong&gt;incident magnetic flux density normal to the plane of the loop&lt;/strong&gt;, where the incident field is assumed to be uniform over the area of the loop. This simple relation makes the small loop useful as a probe for measuring the magnetic flux density.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note (1) that magnetic flux density is related to the r-f current component of a radiated e-m wave, and (2) that such a receive loop is insensitive to the E-field that accompanies that H-field.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Edit of 30 May 2019&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quoted from:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Proceedings of the Institute of Radio Engineers&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Volume 23, Number 4; April, 1935&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GENERAL CONSIDERATIONS OF TOWER ANTENNAS FOR BROADCAST USE&lt;/p&gt;&#xA;&#xA;&lt;p&gt;by H. E. GIHRING AND G. H. BROWN&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(RCA Victor Company, Inc., Camden, New Jersey)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*APPENDIX B&#xA;MAGNETIC FLUX DENSITY MEASUREMENTS WITH A LOOP ANTENNA&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;The ordinary field intensity measuring set makes use of a loop antenna. This device inherently measures the magnetic flux density of a radiated field, and really yields the electric intensity by virtue of the fact that at remote points from the source of radiation the magnitudes of the electric vector and the magnetic flux density vector are related in a constant ratio.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-05-30T12:58:01.163" LastActivityDate="2019-05-30T12:58:01.163" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12690" PostTypeId="1" CreationDate="2019-01-24T17:42:42.907" Score="5" ViewCount="3984" Body="&lt;p&gt;I have read that radio waves just keep traveling but the signal gets weaker because of how the wave spreads. OK, I get this, but what confuses me is that satellites emit signals from space that our phones and GPS modules pick up regardless of distance, versus walkie-talkies and WiFi routers whose signals don't travel nearly as far relative to GPS and phones. If GPS modules can pick up waves from space, why can't my laptop reach my WiFi Signal from far away? And why are walkie-talkies not able to transmit and receive at much further distances? Do all radio waves potentially travel the same distance? Or does the distance depend on the power of the signal? What determines the power of signal, wavelength or frequency?&lt;/p&gt;&#xA;" OwnerUserId="14075" LastEditorUserId="8713" LastEditDate="2019-04-07T14:27:02.263" LastActivityDate="2019-04-07T14:27:02.263" Title="How far do radio waves travel?" Tags="&lt;propagation&gt;&lt;physics&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12691" PostTypeId="2" ParentId="11631" CreationDate="2019-01-24T17:59:49.923" Score="2" Body="&lt;p&gt;An alternative impedance matching method for the magnetic loop is a series capacitance between each side of the feedline and each side of the the tuning capacitor.  Typically from 15 to 50 pF 6kV doorknobs per side has been found to work on my kilowatt transmitting loops for 20 through 160 meters respectively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your receive only case, a pair of small receiving air variables, adjusted for maximum signal, may work.  Readjusting the loop's main tuning capacitor will be necessary, as these adjustments interact.   &lt;/p&gt;&#xA;" OwnerUserId="13433" LastActivityDate="2019-01-24T17:59:49.923" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12692" PostTypeId="2" ParentId="12690" CreationDate="2019-01-24T18:37:02.567" Score="14" Body="&lt;p&gt;Radio waves don't stop at a distance, they just get weaker; you've read this correctly. The reason that communications stop working at some distance is that &lt;em&gt;the signals are too weak to be understood.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides distance (and being absorbed or reflected by objects in the path) causing the signal to be weak in an absolute sense (how much power there is), there is also the question of &lt;em&gt;signal-to-noise ratio&lt;/em&gt;. That is, there are other radio waves, from other transmitters, natural sources, and even unintentional noise sources inside the receiver itself, all of which “drown out” the desired signal just like acoustic noise can make it hard to hold a conversation.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Ok i get this but what confuses me is that satellites emit signals from space that our phones and GPS modules pick up regardless of distance versus; Walkie-talkies and WiFi routers whos siganls don't travel nearly as far relative to GPS and phones&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There are several factors here, including:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The GPS system is &lt;em&gt;predictable&lt;/em&gt; by the receivers. If you've ever used a dedicated GPS receiver, you may notice that it takes longer to get a location fix the first time it's turned on or if it's been off for a while. This is because it's using the information about &lt;em&gt;where it last was&lt;/em&gt;, and what time it is, and the last satellite-orbit information it copied from the transmissions, to make good guesses about what it expects to receive. This allows GPS to work with a very poor signal-to-noise ratio.&lt;/li&gt;&#xA;&lt;li&gt;(Almost) nobody else is transmitting on the GPS frequencies, because that's illegal. They're reserved for the purpose. In WiFi, there are lots and lots of devices all using the same few channels; if two transmit at the same time on the same channel (and distance/obstacles don't make one significantly stronger) then neither will get through, for that one packet.&lt;/li&gt;&#xA;&lt;li&gt;GPS is sending a lot less information per second than WiFi. &lt;a href=&quot;https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem&quot; rel=&quot;noreferrer&quot;&gt;The Shannon-Hartley theorem&lt;/a&gt; tells us that there is a maximum rate of information transfer across any channel (here, a limited range of radio frequencies) depending on the signal-to-noise ratio. So WiFi is doing a harder task.&lt;/li&gt;&#xA;&lt;li&gt;Your phone does not just use GPS to obtain its location; it also detects nearby WiFi devices and cell towers, and constructs a best guess from all of these information sources.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Do all radio waves potentially travel the same distance?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There is no limit on distance. In a vacuum, with nothing else around, a wave simply loses power with distance. On Earth, with atmosphere and trees and buildings and so on, different wavelengths/frequencies will be reflected and absorbed differently. Generally, longer wavelengths (lower frequencies) can be used at greater distances, because absorption generally tends to increase with frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, in the &quot;HF&quot; regions of the spectrum, below 30 MHz, signals are actually &lt;a href=&quot;https://en.wikipedia.org/wiki/Skywave&quot; rel=&quot;noreferrer&quot;&gt;refracted off the ionosphere&lt;/a&gt; allowing them to propagate around the curve of the earth, whereas higher frequencies usually pass through the ionosphere — which is better if you want to talk to satellites!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Or does the distance depend on the power of signal?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you increase power from the transmitter, then any receiver receives proportionally more power. Therefore, the signal-to-noise ratio improves (unless the power is so high as to cause overload). So more power means a larger &lt;em&gt;usable&lt;/em&gt; range.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What determines the power of signal, wavelength or frequency?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Neither; they're completely independent. If you have a transmitter that can produce a power of &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt; watts at a frequency of &lt;span class=&quot;math-container&quot;&gt;$y$&lt;/span&gt; MHz, then you can always reduce its power output to some lesser value. This is done routinely for any non-broadcast communication; reducing output power saves battery and lets other users use the same frequency at a distance without &quot;overhearing&quot; each other as much (just the same whether these are 'walkie-talkie' voice communications or several WiFi networks or anything else).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you get into fundamental physics, you may hear that the energy of a &lt;em&gt;photon&lt;/em&gt; is proportional to its frequency, and that radio waves are made of photons. This is all true, but practically useful radio transmissions are made up of &lt;em&gt;many&lt;/em&gt; photons. So changing the transmitter power changes the number of photons emitted per second, but each photon still has the same energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Also note that wavelength and frequency &lt;em&gt;are the same thing&lt;/em&gt; just measured reciprocally: you can convert one to the other using &lt;span class=&quot;math-container&quot;&gt;$\lambda = \frac{c}{f}$&lt;/span&gt;, where &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is the wavelength, &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is the frequency, and &lt;span class=&quot;math-container&quot;&gt;$c$&lt;/span&gt; is the constant speed of light.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-01-24T18:37:02.567" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12694" PostTypeId="1" CreationDate="2019-01-24T22:41:43.043" Score="5" ViewCount="412" Body="&lt;p&gt;I've grown up using SWR/power meters. They're &quot;simple&quot; devices: They show forward and reverse power, and show the standing wave ratio. They, however, do not show antenna efficiency. New hams are traditionally instructed to tune their antennas so as to minimize the SWR. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, I've been reading about the RF amperemeters. Older radio sets used to have them, and there are people who recommend tuning for maximum antenna current, instead of minimum SWR. Manuals for some of them have statements such as &quot;Tuning for maximum feedline current for any given antenna always gives&#xA;maximum radiated power.&quot;, without going into details why.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So with what extra information does the amperemeter provide me, compared to a regular SWR meter?&lt;/p&gt;&#xA;" OwnerUserId="77" LastEditorUserId="8717" LastEditDate="2019-01-24T23:08:17.913" LastActivityDate="2019-01-29T05:50:59.583" Title="What additional information do I get from an RF ammeter, as compared to a regular SWR/wattmeter?" Tags="&lt;rf-power&gt;&lt;antenna-system&gt;&lt;impedance-matching&gt;&lt;swr-meter&gt;&lt;history&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12695" PostTypeId="2" ParentId="12694" CreationDate="2019-01-24T23:06:36.863" Score="1" Body="&lt;p&gt;A VSWR meter does not tell you the current. An RF ammeter does.&#xA;Tuning for maximum current = maximum power to the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, if we have to choose between them the former is always the best choice. An ammeter cannot tell you the VSWR, and a low SWR reading is synonymous with the lowest transmission line losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RF ammeters can be placed &lt;em&gt;anywhere&lt;/em&gt;, because the current in a series circuit is always the same. However, if the SWR is not 1:1 &lt;em&gt;at the antenna&lt;/em&gt;, the reading will be inaccurate unless the feedline is exactly  one-half of an electrical wavelength long (or an even multiple thereof).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RF ammeters were invented before VSWR meters. See &lt;a href=&quot;https://ham.stackexchange.com/questions/11708/how-did-hams-manage-to-tune-their-antennas-before-vswr-meters/11709#11709&quot;&gt;How did hams manage to tune their antennas before VSWR meters?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-01-24T23:14:20.400" LastActivityDate="2019-01-24T23:14:20.400" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12696" PostTypeId="2" ParentId="11708" CreationDate="2019-01-25T12:53:30.473" Score="1" Body="&lt;p&gt;I can't say it was used historically, both because 50 ohm loads were not the norm they are today, and LEDs did not exist, or even solid state diodes if you go back far enough, but one way to tune an antenna without an SWR meter is given by example in &lt;a href=&quot;http://www.aa5tb.com/coupler.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;AA5TB's tuner&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UlCye.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UlCye.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;R1, R2, and R3 form a Wheatstone bridge, with the antenna making the fourth leg of the bridge. The LED is dimmest when the antenna impedance is near 50 ohms. I've explained the operation of the circuit in more detail in &lt;a href=&quot;https://ham.stackexchange.com/a/2404/218&quot;&gt;another answer&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is interesting in that there's no directional coupler, so it doesn't measure forward and reverse power like a typical SWR bridge. Instead it just measures how close you are to 50 ohms (or any other impedance, if you swap out the resistors) which accomplishes the same objective.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-07-01T23:26:37.000" LastActivityDate="2019-07-01T23:26:37.000" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12697" PostTypeId="1" AcceptedAnswerId="12698" CreationDate="2019-01-25T15:00:31.770" Score="0" ViewCount="158" Body="&lt;p&gt;I've recently come into possession of a Yaesu FT-1DR, and one of the first things I noticed is that it has a bluetooth icon on the screen! Turn up the contrast and look carefully at the line of icons...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JqBDP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JqBDP.jpg&quot; alt=&quot;FT-1DR display from https://www.youtube.com/watch?v=6V-sz2qBSjA&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;None of my research has turned up any bluetooth option or even a hint of built-in bluetooth functionality, but presumably Yaesu didn't repurpose someone else's display which just happened to include a bluetooth icon, so why is it even there? I assume they considered it seriously enough as an option early in development that it got on the display, but reconsidered at some later date. So what are the chances that there is untapped bluetooth potential, perhaps built into the GPS chipset or some such, that only requires someone to go to the considerable effort of reverse engineering the interface and writing a stack for it? More likely, the icon is a leftover of a consideration to keep options open early in the design process, because I'm guessing that if there was bluetooth hardware in there they would've made use of it, but I don't know much about how Yaesu designs things and whether there's a sister model that did include bluetooth and might have shared hardware (or at least the screen) with the FT-1D.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anyone has any insight I'd be most interested!&lt;/p&gt;&#xA;" OwnerUserId="4452" LastEditorUserId="4076" LastEditDate="2019-01-25T16:24:20.120" LastActivityDate="2019-01-29T05:53:46.073" Title="Bluetooth icon on Yaesu FT-1D display: Is there Bluetooth integrated?" Tags="&lt;yaesu&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12698" PostTypeId="2" ParentId="12697" CreationDate="2019-01-25T15:20:06.527" Score="3" Body="&lt;p&gt;Yaesu simply uses one LCD, which has a dot matrix display in the upper part, and a few fixed icons in the lower part, as can be seen in the picture in your question, for multiple handsets.&lt;/p&gt;&#xA;&lt;p&gt;Compare this photo of a VX-8R:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=HdS3EqRooN8&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CmdZA.jpg&quot; alt=&quot;VX-8R &quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;So, same display, different hardware.&lt;/p&gt;&#xA;&lt;p&gt;Chances that there's Bluetooth in the FT-1DR are basically zero. Bluetooth simply takes a more expensive microcontroller with integrated Bluetooth functionality, and I don't see a compelling reason to assume both devices use the same main PCB - meaning that even if they used the same bluetooth-containing microcontroller on the FT-1DR as on the VX-8R, then they wouldn't have routed the microwave trace from the chip to any antenna or header.&lt;/p&gt;&#xA;&lt;p&gt;Then again, the form factors &lt;em&gt;are&lt;/em&gt; similar, so maybe it's really just a matter of replacing the microcontroller and getting the right firmware image, but I'm not willing to call an endeavour like that a hobbyist project.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-01-25T16:47:56.340" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12699" PostTypeId="2" ParentId="3829" CreationDate="2019-01-25T20:03:18.743" Score="0" Body="&lt;p&gt;I unfortunately use google translate to write to you.&#xA;This design was published in April 2012 and is based on using a Dipole Fold antenna of reduced length (Lambda -10%), whose capacitive reactance is canceled by the inductive reactance produced from the coaxial balun of reduced length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The auto-cancellation of reactances is due to the fact that, when the frequency varies, the reactances vary in both components.&#xA;this configuration improves the impedance balance for 50 ohm systems and greater bandwidth, with respect to the standard Folded Dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Link: &lt;a href=&quot;http://yy5rm.blogspot.com/2012/02/antena-dipolo-11-metros-con-coaxial-41.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://yy5rm.blogspot.com/2012/02/antena-dipolo-11-metros-con-coaxial-41.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coaxial Balun of 171°, to generate + jX:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VmdF9.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VmdF9.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Folded Dipole antenna is 5% smaller than the standard, to generate -jX in the complex impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an image of the Folded Dipole antenna of 1/2λ -10% ( 5% less than standard ), for 50Ω systems and self-canceling reactance by the coaxial balun of reduced length by 171 ° ( The standard coaxial balun is 1/2λ = 180 ° ).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/boe7B.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/boe7B.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In VHF and UHF, the antenna height is generally higher than 3λ and the folded dipoles are around 280Ω → 300Ω.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In HF 20, 40 and 80 meters the antenna impedance generally approaches 240Ω → 430Ω and with any 4:1 balun it could achieve good balance in 50 ohm systems, therefore it will not always be necessary to reduce the length of the antenna to generate capacitive reactance, or use coaxial balun of reduced length (171°) to auto-cancel. Simply varying the height a bit will suffice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This antenna of 1/2λ -10%, have greater bandwidth and better coupling in 50Ω, but it is less efficient than the standard of 1/2λ -5%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the trials, this was the response of the virtual and field analysis, obtained from the approximate relationship, between the impedance &amp;amp; height of the Folded Dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/a0ypg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/a0ypg.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14083" LastEditorUserId="76" LastEditDate="2019-01-26T20:46:58.497" LastActivityDate="2019-01-26T20:46:58.497" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12703" PostTypeId="2" ParentId="12042" CreationDate="2019-01-26T05:44:56.427" Score="1" Body="&lt;p&gt;I doubt such a device will ever exist, I'm afraid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is the TNC-radio interface. Packet at 1200 bps is pretty forgiving, you can hold your radio up to a computer or phone's speaker or mic and it'll work, more or less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Packet at 9600 bps, on the other hand, requires a connection deeper inside the radio because there is circuitry (or nowadays, digital signal processing) in the radio that's designed to make voice sound better, but that same circuitry distorts digital signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The various digital voice modes use encoding in the range of 4800 to 9600 bps or more, so I expect that the same problem will make it practically impossible to engineer a dongle or soundcard interface without a radio capable of tapping in before the audio filtering circuitry/DSP.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastActivityDate="2019-01-26T05:44:56.427" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12704" PostTypeId="2" ParentId="12694" CreationDate="2019-01-26T16:32:25.953" Score="2" Body="&lt;p&gt;In a way, an SWR measures voltage and current simultaneously, and that's how it's able to separate forward and reverse power. &lt;a href=&quot;https://www.youtube.com/watch?v=byF1FLdbUiA&quot; rel=&quot;nofollow noreferrer&quot;&gt;W2AEW has an excellent video on how directional couplers work&lt;/a&gt;. One way to convert an SWR meter into an ammeter is to disconnect one of the transformers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Older equipment included an RF ammeter because that older equipment used vacuum tubes. Tube PAs have a characteristically high output impedance, and thus require a matching network to drive typical loads. Thus in practice tube equipment has what amounts to an antenna tuner built in. The ammeter is a useful tool for &lt;a href=&quot;https://www.w8ji.com/loading_amplifier.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;tuning the matching network&lt;/a&gt;, but the tuning procedure usually involves measuring currents within the PA, not just feedline current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would say an ammeter is of little to zero practical use if you already have an SWR meter. If you have tube equipment, there's likely already a ammeter built into it. And if you have solid-state equipment, it has a fixed matching network which is designed for a 50 ohm load. Deviating from 50 ohms will result in one or more of:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;activation of protection circuitry, reducing power output or shutting down the transmitter&lt;/li&gt;&#xA;&lt;li&gt;an increase in nonlinear distortion&lt;/li&gt;&#xA;&lt;li&gt;overheating and eventual destruction of the transmitter&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Measuring feedline current is a tricky business, since it depends on where the meter is placed. You probably know that a VSWR greater than 1:1 means there will be high and low voltage nodes on the feedline. Those high voltage nodes are also low current nodes, and vise-versa.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, an SWR meter indicates the same thing regardless of where it's placed&lt;sup&gt;1&lt;/sup&gt;. It can do this because it measures voltage as well as current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is true that if feedline length, meter position, and frequency are held constant, then more feedline current means more radiated power. However the SWR meter also measures forward power, and more forward power also means more power to the antenna. If you want to tune for maximum power without regard to anything else, the SWR meter allows that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But given the issues with improperly loading the transmitter above, I would not recommend it. Hams decades ago may have gotten away with it due to the generally more robust equipment and &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=d4b3c60d2d60000a147f885bdee88264&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5#se47.5.97_1307&quot; rel=&quot;nofollow noreferrer&quot;&gt;relaxed spurious emission regulation&lt;/a&gt; of era, but the times have changed, standards are higher, and there's newer equipment available.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt; modulo transmission line losses. As the line loss increases, more of the reflected power is absorbed by the line, and the indicated SWR approaches 1:1. For typical feedlines with low loss and moderate SWR the effect is negligible.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-01-26T16:32:25.953" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12706" PostTypeId="1" AcceptedAnswerId="12728" CreationDate="2019-01-26T20:52:13.567" Score="0" ViewCount="475" Body="&lt;p&gt;I want to build a generic multi-antenna switch using relays. Many projects on the web have done this but the relays have silver contacts.  This would be fine if I were to transmit to all antennas so the slowly forming silver oxide would be removed but this is not possible. I know I could use gold contacts or even a weird phasing scheme with two relays (gold and silver) so the gold contacts engage after the silver for &quot;make&quot; and before the silver for &quot;break&quot;.  In practice, how is this problem solved?  This device will be in an attic so humidity and heat will be a factor.  The desired frequency range is 3 to 30MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Silver contact relay examples: RT314F12 in relay switch (&lt;a href=&quot;https://www.hamradioworkbench.com/4-port-coax-relay.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.hamradioworkbench.com/4-port-coax-relay.html&lt;/a&gt;) or G2R-1-E-T130 DC12 (&lt;a href=&quot;http://www.ad5x.com/images/Articles/AntSwitch.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ad5x.com/images/Articles/AntSwitch.pdf&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A QEX project (&lt;a href=&quot;http://www.arrl.org/files/file/QEX_Next_Issue/2014/Mar-Apr_2014/Dzado.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/files/file/QEX_Next_Issue/2014/Mar-Apr_2014/Dzado.pdf&lt;/a&gt;) uses G6RN-1 relays that are gold plating on silver but I imagine the gold plating will not hold up to 1500W (I'm happy to be wrong about this because these relays are cheap.)&lt;/p&gt;&#xA;" OwnerUserId="13997" LastEditorUserId="9493" LastEditDate="2019-01-29T22:53:28.317" LastActivityDate="2019-01-29T23:13:46.233" Title="Antenna relay switch design" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12707" PostTypeId="2" ParentId="12110" CreationDate="2019-01-27T18:03:42.737" Score="0" Body="&lt;p&gt;nice to get back to communicate with you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my file &quot;Displacement of Resonance Frequency&quot;, I wrote that theoretical statement, but it was already corrected to avoid confusing readers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reality is how you explain it, when the physical length of the antenna is in resonance with the frequency, the current wave distributions in the antenna are in phase and the RF voltage waves are also in phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This condition in the antenna, determines its best radiation resistance and maximum efficiency of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To this answer, I added the updated link of the file &quot;Displacement of Resonance Frequency.pdf&quot;, which unfortunately has not yet updated its complement file &quot;Coaxial Cable Length and Node.pdf&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This file was written with the purpose of clarifying a reality, typically considered as an old myth and the scarce information that links themes of resonance lengths in optimization processes of antenna systems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that should not include links, because they probably will not work, but if required in the future, it is possible to locate it from the web.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Greetings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Displacement of Resonance Frequency.pd: &lt;a href=&quot;https://files.acrobat.com/a/preview/7021823f-839c-4122-bdb7-c41eede5891d&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://files.acrobat.com/a/preview/7021823f-839c-4122-bdb7-c41eede5891d&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14083" LastActivityDate="2019-01-27T18:03:42.737" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12708" PostTypeId="1" AcceptedAnswerId="12712" CreationDate="2019-01-28T06:38:03.413" Score="2" ViewCount="102" Body="&lt;p&gt;For a yagi antenna, for transmit, does the waveform traveling away from the driven element towards the reflector get cancelled out by the reflector and then simply disappear ? Or is that cancelled power then 'available' to be added to the power radiated in the opposite direction ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason i ask this question is this. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;If power radiated in a direction opposite to the direction of maximum gain is just cancelled out due to the interference between the incident wave and the re-radiated wave from the reflector, then the only advantage good front to back ratio gives is less noise and the ability to reduce the strength of signals from unwanted directions. Then a yagi could just be designed for maximum gain and front to back ratio ignored.&lt;/li&gt;&#xA;&lt;li&gt;If power radiated in a direction opposite to the direction of maximum gain is cancelled out but then 'added' to the rest of the lobes, then better front to back ratio means more gain in the forward direction because the power not radiated out the back is added to that radiated towards the front.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;And the above would also all be true for receive.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-01-29T05:43:43.193" Title="What happens to the transmitted power cancelled out by a yagi antenna's reflector?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12712" PostTypeId="2" ParentId="12708" CreationDate="2019-01-28T12:52:11.340" Score="6" Body="&lt;p&gt;Total radiated power is approximately the same in a low-loss beam antenna as it is in a dipole. The beaming effect is the result of constructive interference in one direction accompanied by destructive interference in other directions. Constructive interference energy equals destructive interference energy so the total energy remains the same. The energy &quot;lost&quot; to destructive interference, like squeezing a balloon, is added as constructive interference in the beaming direction. That's why a beam has gain over a dipole in the beaming direction. Energy cannot be lost. It can only be redirected or transformed, e.g. to heat. Any antenna with a gain higher than 0 dBi is undergoing constructive/destructive interference.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-01-28T13:10:40.697" LastActivityDate="2019-01-28T13:10:40.697" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12713" PostTypeId="2" ParentId="12690" CreationDate="2019-01-28T16:38:35.123" Score="3" Body="&lt;p&gt;The curvature of the Earth also makes a difference between how a signal will propagate near the ground versus in outer space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And at a large enough distance, the random quantum behavior of the atoms and electrons in your receiver radio will drown out their reaction to any incoming radio waves.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-01-28T16:38:35.123" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12714" PostTypeId="1" AcceptedAnswerId="12725" CreationDate="2019-01-28T22:22:42.477" Score="1" ViewCount="183" Body="&lt;p&gt;Using a Raspberry Pi 3B, Signalink, HT, direwolf and ax25-tools and ax15-apps. All up to date. Clean start.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Commands:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;sudo direwolf -p  &#xA;sudo kissattach /tmp/kisstnc wl2k&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;obtain assignment to ax0, then&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;beacon -s wl2k &quot;testing&quot;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;first attempt - direwolf reports: &lt;code&gt;Invalid transmit channel 8 from KISS client app.&lt;/code&gt;&lt;/li&gt;&#xA;&lt;li&gt;second attempt - direwolf report: &lt;code&gt;Invalid transmit channel 2 from KISS client app.&lt;/code&gt;&lt;/li&gt;&#xA;&lt;li&gt;third attempt - works just fine and the RPi transmits the &quot;testing&quot; perfectly.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I want to address the channel issue and can find nothing in documentation. What is going wrong, what can I do to fix this?&lt;/p&gt;&#xA;" OwnerUserId="14102" LastEditorUserId="9844" LastEditDate="2019-01-29T19:47:28.467" LastActivityDate="2019-01-30T00:02:37.713" Title="ax.25 error shown in direwolf. Fails on channel 8, then 2, then works" Tags="&lt;aprs&gt;&lt;software&gt;&lt;linux&gt;&lt;direwolf&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12724" PostTypeId="1" CreationDate="2019-01-29T14:11:10.080" Score="1" ViewCount="191" Body="&lt;p&gt;From a comment on &lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike#comment1724_51&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Most of the damage from nearby strikes comes from strong voltage&#xA;  gradients over the ground or between the ground and things near it,&#xA;  causing arcing, causing things near the ground to effectively be&#xA;  grounded. You don't need a whole Faraday cage to protect against this;&#xA;  just a ring of wide copper strap around a building will do, forming a&#xA;  sort of two-dimensional Faraday cage. Commercial broadcast stations do&#xA;  exactly this, and this is part of why they are able to stay on the air&#xA;  despite multiple strikes per year and never disconnecting the&#xA;  antennas. – Phil Frost - W8II Feb 27 '14 at 12:22&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;How wide?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the wide copper strap near the foundation?&lt;/p&gt;&#xA;" OwnerUserId="14114" LastEditorUserId="218" LastEditDate="2019-01-30T06:11:22.223" LastActivityDate="2019-03-01T12:01:20.250" Title="How large and where should a perimeter ground be installed?" Tags="&lt;lightning&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12725" PostTypeId="2" ParentId="12714" CreationDate="2019-01-29T19:33:56.823" Score="2" Body="&lt;p&gt;This is issue #42 on Direwolf's GitHub page.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://github.com/wb2osz/direwolf/issues/42&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/wb2osz/direwolf/issues/42&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To work around it, put the interface into CRC mode &quot;none&quot; with a command like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;# kissparms -c 1 -p radio&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="13390" LastActivityDate="2019-01-29T19:33:56.823" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12726" PostTypeId="2" ParentId="12670" CreationDate="2019-01-29T21:14:06.673" Score="1" Body="&lt;p&gt;Consider very small &quot;antennas&quot; (in relation to the wavelength.) You can for example consider a coil 1 m in diameter and feed it with 60 Hz. With an identical coil you can pick up the magnetic field at some distance - several meters easily, but if you make an electric dipole with a length of 1 m you would pick up nothing. If you send 60 Hz to such an electric dipole you can pick up the electric field with a similar dipole, but nothing with a coil. Very small antennas are useful for receive - but they should better be referred to as E-sensors and H-sensors. I once made a crystal receiver with a 1 m whip antenna. By use of good ferrites and carefully avoiding stray capacitances I could get a loaded Q of about 500 at about 1 MHz. (Unloaded Q was much higher.) The load was a rectifier diode into a very high impedance audio transformer. On the low impedance output of the transformer I could actually hear AM broadcast stations from Germany about 700 km from here in my headphones without any amplification. Surely this E-field sensor absorbs energy from the free wave and therefore affects both the electric and the magnetic component of the wave beyond the sensor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It should be noted that receiving whip antennas are typically NOT impedance matched, they have a high impedance FET amplifier that senses the voltage while drawing a very small current. They just sense the field while absorbing negligible energy. A receiving loop antenna should ideally have a current amplifier, one with near zero input impedance. Such a loop would distort the field locally like a shorted turn, but it would absorb negligible energy.from the field. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the near field (local QRM) E- and H- fields are separate. You can have one or the other or a combination at any arbitrary phase angle. One or the other might be best. A two channel radio with both an E-sensor and a H-sensor can be used to cancel local interference by phasing if the QRM is present both in the electric and magnetic field.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-01-29T21:14:06.673" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12727" PostTypeId="2" ParentId="12724" CreationDate="2019-01-29T22:52:11.313" Score="1" Body="&lt;p&gt;A copper ring that encompasses the entire room and is located near the ceiling of the room is typically referred to as a halo ground. This ring is bonded directly to the external, buried ground ring for the structure. The purpose of the halo ring is to protect the contents of the room from strong electromagnetic fields from an EMP (e.g. lightning) that may otherwise induce currents in enclosures and other metal in the room.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some installations, the halo ground is also used as the method to provide SPGS (single point ground system) connections since large equipment cabinetry is also subject to EMP induced currents. I was recently in a large state patrol communications room associated with a 200+ foot tower and more than 10 transmitters and repeaters that used this method of SPGS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One and one half inch (38 mm) wide, solid (not woven) copper strap, with a minimum thickness of 26 AWG (0.0159 inch / 0.405 mm) is commonly used as a halo ring or SPGS conductor as it has far less inductance than say #4/0 wire. Wider and/or thicker copper is acceptable as it will increase current handling and further reduce inductance. The copper strap also makes it much easier to fashion drop connections to the various equipment cabinets. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The halo system is bonded by a minimum of one #2 AWG solid copper wire for every 25 feet of halo. These wires drop straight down the interior wall, exit at the base of the wall and are bonded to the exterior buried building ring. For a halo of 100 feet or less. It is recommended that a drop wire be installed in each corner of the room.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are various standards and best practices documents pertaining to ground systems - some of which are in direct conflict with each other. You may enjoy reading &lt;a href=&quot;http://www.repeater-builder.com/ge/lbi-library/lbi-39067a.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Erickson's guidance&lt;/a&gt; in this area.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-30T11:48:51.073" LastActivityDate="2019-01-30T11:48:51.073" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12728" PostTypeId="2" ParentId="12706" CreationDate="2019-01-29T23:06:24.680" Score="2" Body="&lt;p&gt;The high temperature and humidity conditions of an attic are dwarfed by the environmental requirements of automotive applications. Picking relays that are rated for automotive use is therefore one way to overcome this design constraint. Many of the industrial relays are now supplied in a sealed form factor that will also sidestep any problems related to humidity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your application is for receive and low power transmit applications then pick relays for which the contacts are not excessively rated. Remember that relays are typically never switched while transmit power is applied so the extinguishing characteristics of the contacts are rarely a concern. With modern, small signal relays, contact corrosion is rarely reported. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a particularly sensitive receive application (e.g. very low radiation resistance antennas), you can include a second relay for each primary antenna relay that periodically passes the minimum required current and voltage through the antenna relay contacts to ensure proper contact cleansing. Several cycles of the relay are typically necessary for sufficient cleansing. Make certain to exclude the attached radios from this cleansing current, for example, through capacitive isolation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your relays must handle higher transmit power, then size relays according to the best practices in the articles you referenced. The relatively high current and voltage from the transmitter will typically be sufficient to clean the contacts.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-29T23:13:46.233" LastActivityDate="2019-01-29T23:13:46.233" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12730" PostTypeId="2" ParentId="5953" CreationDate="2019-01-30T05:16:09.437" Score="2" Body="&lt;p&gt;Try the airport “squawk technique”: run a speaker wire up to the top of the tower rotor box and place an outdoor speaker next to it and a PA system,  if your friends come around to annoy your antennas turn it on for a few seconds  with a good sharp popping sound to the mic  should do. The GRUMMAN Aerospace corporation used to use them at the end of the their airport runways to keep the birds and geese away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wrap or place fiberglass window screen mesh around your rotor plate or tower to prevent nesting. Wineries and farmers use this to keep birds and animals away from eating their grapes.&lt;/p&gt;&#xA;" OwnerUserId="14118" LastEditorUserId="76" LastEditDate="2019-01-30T16:26:19.653" LastActivityDate="2019-01-30T16:26:19.653" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12732" PostTypeId="2" ParentId="9324" CreationDate="2019-01-30T13:58:17.223" Score="4" Body="&lt;p&gt;While not using a computer in a hybrid configuration to decode high speed CW, I think the following method offers a viable alternative.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In his May 2017 QST Article, &quot;Increase Your CW Speed with Wordsworth&quot;, George Allison describes a method similar to Farnsworth but applied to learning words he describes as&quot;head copy&quot;. He uses a computer program, fldigi, to send words at speeds above what you can normally copy and adds large spaces between words. He suggests sending at speeds of 25wpm or higher.&#xA;I used an Android app, Morse Trainer by Wolphi, to test this method, but found I had to send words at 28-30wpm so as not to be able to hear individual dots and dashes. The author provides a list of 65 common ham words to get you started.&#xA;While my normal CW speed is about 18wpm, I am able to identify words from on the air higher speed QSOs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest one consider the Wordsworth method if one wants to increase his effective CW copying speed.&lt;/p&gt;&#xA;" OwnerUserId="14117" LastEditorUserId="14117" LastEditDate="2019-01-30T14:54:44.337" LastActivityDate="2019-01-30T14:54:44.337" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12733" PostTypeId="2" ParentId="5953" CreationDate="2019-01-30T17:44:11.953" Score="1" Body="&lt;p&gt;We had one at our last house to keep the birds out of our 16x16 vegetable garden. &lt;strong&gt;That one was effective&lt;/strong&gt;, as it had a motion sensor that triggered an owl sound and flashed the eyes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After some months, we noticed the birds were back. The problem was that a wasp had filled the deep motion sensor hole with mud. As soon as I cleaned that out, no birds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It was placed on a corner post with the sensor pointed at the opposite corner. We never moved it.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-01-30T17:44:11.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12735" PostTypeId="1" CreationDate="2019-01-30T23:06:20.240" Score="3" ViewCount="229" Body="&lt;p&gt;Just researching an outdoor long run shortwave antenna. I found &lt;a href=&quot;https://nz.rs-online.com/web/p/harsh-environment-wire/0359677/&quot; rel=&quot;nofollow noreferrer&quot;&gt;some cheap wire&lt;/a&gt; online but it said it is resistant to corona discharge:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Will satisfy a wide number of applications related to medical, electronic or electrical equipment which may be operated in environmental conditions where ozone, corona discharge, radiation, heat, weathering or the normally adverse effects of a wide range of oils, solvents, etc., may be encountered.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Would this be suitable or would it block the signal?&lt;/p&gt;&#xA;" OwnerUserId="14124" LastEditorUserId="218" LastEditDate="2019-01-31T17:48:57.960" LastActivityDate="2019-01-31T22:49:15.140" Title="Shortwave antenna wire — do I care about &quot;corona discharge&quot;?" Tags="&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12736" PostTypeId="1" CreationDate="2019-01-30T23:15:55.507" Score="0" ViewCount="91" Body="&lt;p&gt;From online directions, I made a MURS antenna. The 1:1 SWR is at 142.000 and I want to tune it for 146.500 (therebouts).  I know I need to shorten this antenna. I would like to confirm that I do NOT adjust the &quot;4 radials&quot; that project out horizontally, but only shorten each vertical.  The online photo can be seen by searching for &quot;High Gain Omni MURS jedsoft&quot;.  My antenna looks identical and I need to know which part(s) to adjust to get a higher resonant frequency.  Thanks!&lt;/p&gt;&#xA;" OwnerUserId="14125" LastActivityDate="2019-01-30T23:47:48.663" Title="Tuning a Homebrew MURS" Tags="&lt;murs&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12737" PostTypeId="1" AcceptedAnswerId="12740" CreationDate="2019-01-30T23:37:45.563" Score="1" ViewCount="86" Body="&lt;p&gt;I know that repeaters on VHF and UHF are primarily automatic, but there will be times when they will fail, or something is not working. The repeater may not respond to the remote control. In these situations, someone will have to climb the top of a building or go up to the top of a mountain and tinker with it. Who can do this?&lt;/p&gt;&#xA;" OwnerUserId="13927" LastEditorUserId="13927" LastEditDate="2019-01-30T23:43:43.770" LastActivityDate="2019-01-31T20:28:26.083" Title="Who has the ability to physically manipulate a repeater's controls?" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12738" PostTypeId="2" ParentId="12735" CreationDate="2019-01-30T23:38:08.043" Score="4" Body="&lt;p&gt;That is a bit of marketing speak that simply means the insulation on the wire will not permit current to flow under some unspecified differential voltage. The insulation is simply black silicone rubber and it is rated for a maximum working voltage of 750 volts. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an antenna, the silicone rubber insulation will have no practical effect on the efficiency or effectiveness of the antenna. If you are cutting the antenna to some specific length assuming a bare wire, you can take 3% or so off that length to account for the dielectric effect of the insulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unlike many wires insulated with common PVC (e.g. THHN  and XHHW), the black silicone rubber should not suffer from UV degradation. So unlike THHN, for example, you won't go out in your garden only to find pieces of insulation lying about. As @MikeWaters points out, the silicone rubber is also generally resistant to ozone which may help to keep the insulation intact if your antenna happens to be exposed to high ozone levels.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-31T20:31:51.693" LastActivityDate="2019-01-31T20:31:51.693" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12739" PostTypeId="2" ParentId="12736" CreationDate="2019-01-30T23:47:48.663" Score="1" Body="&lt;p&gt;The antenna you reference is referred to as a Moxon antenna. All dimensions of the two elements are frequency dependent. I recommend that you use the &lt;a href=&quot;https://ac6la.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;AC6LA&lt;/a&gt; software to calculate the correct dimensions for your target frequency.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-01-30T23:47:48.663" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12740" PostTypeId="2" ParentId="12737" CreationDate="2019-01-30T23:52:47.600" Score="4" Body="&lt;p&gt;The owner of the repeater is typically in control of who has physical access. Often the owner will permit the trustee of the station license (in the US) to have access in order to carry out their lawful responsibilities although the owner and trustee may be one in the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When a club maintains a repeater, there is often a technical committee that is charged with keeping the repeater in good working order.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also consider that in the US, from a legal perspective, the control point of the repeater may be remotely located from the repeater even if the repeater is normally automatically controlled.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-01-31T20:28:26.083" LastActivityDate="2019-01-31T20:28:26.083" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12741" PostTypeId="2" ParentId="12735" CreationDate="2019-01-31T22:20:11.433" Score="1" Body="&lt;p&gt;In industrial high voltage switchgear, corona creates ozone. And ozone can deteriorate rubber insulation, which in turn has historically caused catastrophic failures. Note that the wire specs also say that the insulation is resistant to ozone. I think that's the reason it is labeled as such.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regardless, that wire will work just fine as an antenna!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said all of this, if you have a loose strand of wire with a sharp end, you can still have a corona discharge &lt;em&gt;and that can cause noise in your receiver&lt;/em&gt;. But that's true of ANY kind of stranded wire.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-01-31T22:49:15.140" LastActivityDate="2019-01-31T22:49:15.140" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12742" PostTypeId="1" CreationDate="2019-02-01T03:11:36.130" Score="5" ViewCount="410" Body="&lt;p&gt;I've wondered if many of the abbreviations are empty, or if they are similar to the recursive acronym like PHP and GNU. For instance, I learned that CQ mimics the two syllables of a French word for Cequite, which means to secure. So, what does QRZ, and others, stand for, how did they originate?&lt;/p&gt;&#xA;" OwnerUserId="13927" LastEditorUserId="76" LastEditDate="2019-02-01T03:28:12.633" LastActivityDate="2019-02-04T15:02:04.267" Title="How did the terms like QRZ, QTH, and other forms of ham shorthand evolve?" Tags="&lt;history&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12743" PostTypeId="2" ParentId="12742" CreationDate="2019-02-01T03:29:33.300" Score="9" Body="&lt;p&gt;They were created to save time in Morse code communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Q_code&quot; rel=&quot;noreferrer&quot;&gt;https://en.m.wikipedia.org/wiki/Q_code&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Q code is a standardized collection of three-letter codes all of&#xA;  which start with the letter &quot;Q&quot;. It is an operating signal initially&#xA;  developed for commercial radiotelegraph communication and later&#xA;  adopted by other radio services, especially amateur radio. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Although Q codes were created when radio used Morse code exclusively,&#xA;  they continued to be employed after the introduction of voice&#xA;  transmissions. To avoid confusion, transmitter call signs are&#xA;  restricted; no country is ever issued an ITU prefix starting with &quot;Q&quot;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/Q_code#Q_codes_as_adapted_for_use_in_amateur_radio&quot; rel=&quot;noreferrer&quot;&gt;Here is a list of them&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-02-01T03:29:33.300" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12744" PostTypeId="1" AcceptedAnswerId="12745" CreationDate="2019-02-01T07:23:25.900" Score="5" ViewCount="885" Body="&lt;p&gt;Apparently there's a parking lot in which car key fobs are messing up:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Key fobs that suddenly won't unlock vehicles. Cars that won't start. Alarms that go off for no reason and can't be quieted. Something mysterious is thwarting drivers outside a grocery store in the small Alberta town of Carstairs — and it's sparking all kinds of theories.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The problems have been happening for weeks in the parking lot outside the Westview Co-op grocery store in Carstairs, a town of about 4,000 about 60 kilometres north of Calgary.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A longtime employee at the dollar store right across the street from the Co-op says it's all she hears some folks talk about when they come into her store to buy a battery for their fobs — and then discover that doesn't solve the problem.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&quot;I've been at the dollar store almost four years,&quot; Laura Strate said, with a laugh.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&quot;It's just bizarre. People are actually scared to go to the Co-op now because they don't know if their cars are going to start.&quot;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&amp;ndash;&lt;a href=&quot;https://www.cbc.ca/news/canada/calgary/carstairs-westview-co-op-grocery-car-key-fob-1.4999558&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;Something mysterious is blocking vehicle key fobs from working in a small Alberta town&quot;&lt;/a&gt; (2019-01-30)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Seems likely that the problem's radio interference, unless someone's &lt;a href=&quot;https://security.stackexchange.com/questions/202026/&quot;&gt;having fun&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a &lt;a href=&quot;https://news.ycombinator.com/item?id=19046475&quot; rel=&quot;nofollow noreferrer&quot;&gt;related discussion&lt;/a&gt; at HackerNews, someone &lt;a href=&quot;https://news.ycombinator.com/item?id=19048623&quot; rel=&quot;nofollow noreferrer&quot;&gt;commented&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Call in a couple of ham radio operators who like to foxhunt and they should be able to point you in the general direction of the problem within minutes. If the effects are as localized as they say it should be able to be pinpointed within an hour.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Question:&lt;/strong&gt;  How would a HAM radio operator go about finding the source of interference in a scenario like this, where car key fobs are malfunctioning across a parking lot?&lt;/p&gt;&#xA;" OwnerUserId="10051" LastEditorUserId="9493" LastEditDate="2019-02-01T23:59:32.697" LastActivityDate="2019-02-01T23:59:32.697" Title="How to find something disrupting car key fobs across a parking lot?" Tags="&lt;rfi&gt;&lt;fox-hunt&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12745" PostTypeId="2" ParentId="12744" CreationDate="2019-02-01T11:18:29.947" Score="7" Body="&lt;p&gt;There was a similar problem in the US a few years ago and it turned out to be a new shop sign that had a defective ballast that emitted a wide RF spectrum. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most key fob systems operate at frequencies of 315 MHz for North American made cars and 433.92 MHz for all others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The direction finding equipment would involve a programmable receiver or a portable spectrum analyzer, an attenuator, and a directional antenna. The spectrum analyzer may be more helpful in this situation because it allows a view of a broad range of frequencies at once.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The direction finding technique involves aiming the antenna in all directions to find the strongest signal. The operator then moves in that direction. As the signal gets stronger, it may be necessary to increase the attenuation so as to not overload the receiver with the signal and to have the peaks and nulls in the directional pattern of the antenna be more apparent. Sometimes it may be necessary to deliberately veer off course in order to get a different bearing on the signal, allowing the operator to effectively triangulate on the  location of the signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This sequence of turning the antenna and moving in the direction of the strongest signal continues as the operator zeroes in on the exact location of the signal. When the operator gets quite close, the operator may install a less sensitive antenna or even remove the antenna to further reduce the signal strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As @JonCuster points out sometimes you can use a much simpler kit of just a programmable radio and a basic antenna. You determine direction by using your body to block the signal. So it may work in a pinch but the earlier described equipment will generally be much more reliable and flexible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio (ham) operators frequently call this technique &quot;fox hunting&quot; in an obvious nod to the English sport. It is also known as radio orienteering or simply amateur radio direction finding (ARDF). Many ham clubs organize fox hunts as a fun and healthy outdoor activity for their members. These culminate in a world champion event known as the &lt;a href=&quot;http://www.homingin.com/intlfox.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;World ARDF Championship&lt;/a&gt; where the best from around the world meet to match their skills.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-01T16:22:27.697" LastActivityDate="2019-02-01T16:22:27.697" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12746" PostTypeId="1" CreationDate="2019-02-01T13:16:16.020" Score="1" ViewCount="256" Body="&lt;p&gt;I have a radio that does not support VOX, but then I got the idea that there might be a VOX mic that sends the PTT when VOX is activated?&#xA;Basically a mic that will &quot;push&quot; the button for me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does that exist, both wired (3.5 mm) and Bluetooth (phone headsets) versions work with this radio I have.&#xA;Ridingtoo RT1&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have tried to find something like it but don't know what to search for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sorry about the tags, didn't know what to choose.&lt;br&gt;&#xA;Maybe this is off topic here?&lt;/p&gt;&#xA;" OwnerUserId="14134" LastEditorUserId="9493" LastEditDate="2019-02-01T23:57:53.133" LastActivityDate="2019-02-01T23:57:53.133" Title="VOX mic that emulates PTT" Tags="&lt;microphone&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12747" PostTypeId="2" ParentId="12746" CreationDate="2019-02-01T15:17:41.970" Score="1" Body="&lt;p&gt;After a quick Google I wasn't able to find any devices on the commercial market but it doesn't sound too hard to DIY.  Here's one: &lt;a href=&quot;http://www.rason.org/Projects/basicvox/basicvox.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.rason.org/Projects/basicvox/basicvox.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically you amplify the audio, use it to charge a capacitor and then use the voltage across the capacitor to control a transistor which keys the transmitter.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2019-02-01T15:17:41.970" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12748" PostTypeId="2" ParentId="12746" CreationDate="2019-02-01T16:45:24.420" Score="1" Body="&lt;p&gt;Unfortunately your RT1 radio will not easily support VOX operation. The only control  of the PTT is on the main radio or the remote. There is no push to talk (PTT) connection brought out on the radio or the remote.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could conceivably hack into either unit to bring out a PTT connection that could be interfaced to a VOX circuit but the radio does not bring out a microphone connection so that you can complete the project. It only has an earphone jack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on our discussion in comments, you may have found some undocumented connections that could be usable for your VOX application. There is a &lt;a href=&quot;https://www.radioparts.com/icom-vs-1&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOX adapter&lt;/a&gt; for Icom headsets that might be adaptable to your situation if you can find the proper connections on your radio. You would probably have to add a battery to the VOX unit since the Icom connections normally carry an 8 volt supply on the jack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/A4upp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/A4upp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-01T23:31:40.300" LastActivityDate="2019-02-01T23:31:40.300" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12750" PostTypeId="2" ParentId="12742" CreationDate="2019-02-02T17:43:18.873" Score="3" Body="&lt;p&gt;Here's a quote from &lt;a href=&quot;https://en.wikipedia.org/wiki/Q_code&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Q_code&lt;/a&gt; .&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The original Q codes were created, circa 1909, by the British government as a &quot;list of abbreviations... prepared for the use of British ships and coast stations licensed by the Postmaster General&quot;.[citation needed] The Q codes facilitated communication between maritime radio operators speaking different languages, so they were soon adopted internationally. A total of forty-five Q codes appeared in the &quot;List of Abbreviations to be used in Radio Communications&quot;, which was included in the Service Regulations affixed to the Third International Radiotelegraph Convention in London (The Convention was signed on July 5, 1912, and became effective July 1, 1913.)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It is my understanding that the 'Q' was used as there were very few words that began with that letter , thus making it easy to discern by ear. Many of the 'Q' codes are pairs of interrogative and statement functions. Example , issuing a QRO is either asking the recipient to increase power or stating that the sender will increase power. Another , issuing QTH ( which follows from &quot;Question The House&quot; ) is either what is your home location or this is my home location. In all four cases , what follows the code determines the intent.&lt;/p&gt;&#xA;" OwnerUserId="14102" LastEditorUserId="76" LastEditDate="2019-02-04T15:02:04.267" LastActivityDate="2019-02-04T15:02:04.267" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12752" PostTypeId="1" AcceptedAnswerId="12754" CreationDate="2019-02-04T20:46:33.140" Score="3" ViewCount="1584" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/m4AHe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/m4AHe.png&quot; alt=&quot;print screen of CHIRP readout&quot;&gt;&lt;/a&gt;I got 2 Baofeng 888s off Amazon and reprogrammed them to the 16 legal channels (for unlicensed use) in Germany, up from 446.00625 MHz in 12.5 kHz steps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used both CHIRP and a software called ZT-V68 to make sure they are identically programmed. So both in CHIRP and in ZT-V68, when I download the settings from radio one and then compare them to the downloaded settings from radio two (making sure that it is actually downloading and showing me the new data from the other radio) — these software data files look identical. All the settings are the same. I disabled the &quot;scrambler&quot; in everywhere, and set all channels to &quot;low&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the radios are not communicating with each other. Why on earth can that be?&lt;/p&gt;&#xA;" OwnerUserId="14157" LastEditorUserId="14157" LastEditDate="2019-02-05T10:22:36.930" LastActivityDate="2020-07-24T01:05:19.003" Title="Pair of Baofeng BF-888s stopped communicating after reprogramming - what to do" Tags="&lt;baofeng&gt;&lt;radio-programming&gt;&lt;germany&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12753" PostTypeId="1" CreationDate="2019-02-04T22:54:48.087" Score="1" ViewCount="102" Body="&lt;p&gt;I have a new interest in RF modulation and read the O'Reilly book electronics cookbook. I understand that in FM you start out with a carrier wave and then it is modulated but I don't understand if both waves are sent out or if it combines to make one wave.&lt;/p&gt;&#xA;" OwnerUserId="14158" LastActivityDate="2019-02-06T09:30:11.037" Title="Modulation basics" Tags="&lt;fm&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12754" PostTypeId="2" ParentId="12752" CreationDate="2019-02-04T22:58:28.833" Score="5" Body="&lt;p&gt;One other setting for each channel that may be giving you problems is Duplex/Simplex. Make certain it is set to Simplex or equivalently &quot;no offset&quot;. This feature, when turned on, causes that channel to transmit and receive on different frequencies - typically for using the radio with a repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Viel Glück!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-02-04T22:58:28.833" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12755" PostTypeId="2" ParentId="12753" CreationDate="2019-02-04T23:15:07.053" Score="2" Body="&lt;p&gt;By &quot;both waves,&quot; I assume you mean both the unmodulated (carrier) wave and the modulated wave. Only the modulated wave is amplified and sent on to the antenna for outbound transmission. In the case of FM, the modulated wave includes some power dedicated to the carrier, which is also transmitted.&lt;/p&gt;&#xA;" OwnerUserId="14159" LastActivityDate="2019-02-04T23:15:07.053" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12757" PostTypeId="1" AcceptedAnswerId="12760" CreationDate="2019-02-05T09:34:35.243" Score="0" ViewCount="113" Body="&lt;p&gt;I went to the ARRL's band plan site at &lt;a href=&quot;https://clatsopauxcomm.org/index.php/technical/arrl-band-plan&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://clatsopauxcomm.org/index.php/technical/arrl-band-plan&lt;/a&gt;, and the first table began with the 60-metre band, which starts at 1.8MHz and ends at 2.0MHz. However, the next table shows the 80-metre band, which is 3.5 to 4.0MHz. This doesn't make sense. Shouldn't the wavelengths get shorter as frequencies increase?&lt;/p&gt;&#xA;" OwnerUserId="13927" LastActivityDate="2019-02-05T15:54:10.807" Title="Why do the metres seem to be increasing with frequency?" Tags="&lt;band-plan&gt;&lt;arrl&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12760" PostTypeId="2" ParentId="12757" CreationDate="2019-02-05T15:54:10.807" Score="8" Body="&lt;p&gt;It is simply an error or typo on that website. Take a look at the companion color chart on that page that is provided by the ARRL. It shows that frequency range as 160 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula for converting a frequency &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt;, in MHz, to wavelength, &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;, in meters is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\lambda=300/f \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is clear from inspection of the formula that wavelength is inversely related to frequency. So as frequency goes down, the wavelength increases.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-02-05T15:54:10.807" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12761" PostTypeId="2" ParentId="12753" CreationDate="2019-02-05T17:23:55.133" Score="3" Body="&lt;p&gt;To answer your question requires some definition of what it means to &quot;send a wave&quot;. So let's look at the problem more rigorously, with math. First let's consider amplitude modulation, since it's mathematically simpler.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the baseband signal (for example, audio from a microphone) is &lt;span class=&quot;math-container&quot;&gt;$x(t)$&lt;/span&gt;, and the carrier frequency is &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt;, and time is &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt;, then what's &quot;sent out&quot; is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ y(t) = [1 + x(t)] \cos(2\pi ft) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And by &quot;sent out&quot;, I mean the voltage at the antenna terminals at any time will be proportional to &lt;span class=&quot;math-container&quot;&gt;$y(t)$&lt;/span&gt;. The antenna voltage at the receiver will also be proportional to &lt;span class=&quot;math-container&quot;&gt;$y(t)$&lt;/span&gt;, except weaker, and with added noise and interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You asked if one or both waves are sent out, but without a definition of what &quot;a wave&quot; is, this question can't really be answered. What we can say is &lt;span class=&quot;math-container&quot;&gt;$y(t)$&lt;/span&gt; contains both a baseband signal term &lt;span class=&quot;math-container&quot;&gt;$x(t)$&lt;/span&gt; and a carrier term &lt;span class=&quot;math-container&quot;&gt;$\cos(2\pi ft)$&lt;/span&gt;, but at any given time the antenna terminal voltage can have only one value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frequency modulation is no different, except the math is a little more complicated. Using the same terms as before but with the additional parameter &lt;span class=&quot;math-container&quot;&gt;$f_{\Delta}$&lt;/span&gt; for the frequency deviation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ y(t)=\cos \left(2\pi ft +2\pi f_{\Delta} \int _{0}^{t}x(\tau )d\tau \right) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again you can see the baseband signal is in there, as is the carrier wave, except now the baseband signal is changing the frequency of the carrier, instead of the amplitude.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-02-05T17:23:55.133" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12763" PostTypeId="2" ParentId="12753" CreationDate="2019-02-06T09:30:11.037" Score="2" Body="&lt;p&gt;In simple terms, &lt;strong&gt;modulated wave&lt;/strong&gt; is sent out, which is what you get after modulating the &lt;strong&gt;carrier wave&lt;/strong&gt; with the &lt;strong&gt;modulating wave&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or some people also like to say that the carrier is sent with the message(modulating wave) modulated on it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Neither of the carrier and modulating waves are transmitted in their pure forms, because pure carrier(which is just a sinusoidal signal) doesn't contain any information and pure modulating wave(or usually called message) is normally very low in the frequency spectrum(around DC(0 Hz) mostly), which makes it almost impossible to transmit over air for some practical reasons.&lt;/p&gt;&#xA;" OwnerUserId="3016" LastActivityDate="2019-02-06T09:30:11.037" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12764" PostTypeId="1" AcceptedAnswerId="12778" CreationDate="2019-02-06T13:50:13.583" Score="3" ViewCount="234" Body="&lt;p&gt;I've recently purchased a Hallicrafters S-120 -- 4-tube superhet receiver from the 1960s, continuous tuning from 540 kHz to 30 MHz, bandspread control, and a regenerative IF that doubles as a BFO for SSB and CW reception.  Someone before me appears to have worked on the set, as the capacitors seem good (no hum, good reception for the antenna currently available).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I've learned since receiving it, however, is that this set lacks the selectivity, stability, and fineness of tuning to make a good communications receiver; that is, it's for listening, rather than the listening side of two-way operation.  While I have tuned in CW, digital, and SSB transmissions, the latter especially are hard to really clean up.  AM transmissions in any band come in very readily and clearly, assuming they're above the noise floor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a limited budget, however, I'm looking for a better receiver for use when I get on the air (likely mainly CW, as a CW transmitter can be had fairly cheaply).  I need to be able to tune across a band to search for calls, hear the spot tone to set the transmitter, have support for muting when the tranmitter key is down (or the ability add it), and by preference, I'd like it to use vacuum tubes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What do I need to look for (that can be identified from photos and eBay listings that usually are intended to hide the faults of a piece) to distinguish &quot;listening&quot; radios from &quot;communication&quot; receivers?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-02-09T12:08:10.613" Title="How to identify a practical HF communication receiver?" Tags="&lt;receiver&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12766" PostTypeId="2" ParentId="12764" CreationDate="2019-02-07T02:41:18.707" Score="1" Body="&lt;p&gt;When looking at legacy receivers, a key differentiator is often general coverage (shortwave) vs amateur radio coverage. Most shortwave receivers lack the band spread, selectivity, filtering and demodulation features needed for practical use as a receiver for a QSO. Receivers targeted primarily at the ham radio community tend to have better overall features for ham use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next major differentiator is the superheterodyne architecture that represents the epitome of legacy receiver architectures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having selectable filters such as 3000 and 300 hertz can help to cut adjacent QRM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A notch filter can help to cut an offending signal or noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a computer (even a Raspberry Pi 3) and are willing to invest $200, you can get a state of the art software defined receiver. An example of such a receiver is the &lt;a href=&quot;https://airspy.com/airspy-hf-plus/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Airspy HF+&lt;/a&gt;. It is an amazing piece of hardware for the price and will give superior performance to many heterodyne receivers. It even allows you to operate it over the Internet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For slightly more money, you can purchase an SDR transceiver such as the &lt;a href=&quot;https://wikipedia.org/wiki/HackRF_One&quot; rel=&quot;nofollow noreferrer&quot;&gt;HackRF One&lt;/a&gt;. This will eliminate the need for frequency spotting and transmit/receive relays or PIN diode switching that you would need to accommodate with a separate transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are not familiar with SDR receivers, there is a &lt;a href=&quot;http://www.websdr.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;network&lt;/a&gt; of them on the Internet that are free to use. &lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-07T11:58:00.760" LastActivityDate="2019-02-07T11:58:00.760" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12769" PostTypeId="1" AcceptedAnswerId="12770" CreationDate="2019-02-07T20:40:22.757" Score="12" ViewCount="542" Body="&lt;p&gt;I am currently studying for my Technician Exam and I am amazed at the sheer number of amateur radio satellites in orbit. Knowing how expensive it is to launch something into space, and assuming there is very little return on investment concerning these satellites (since they are free to use), who funded them? Don't get me wrong, I'm super happy they are there, I'm just perplexed as to how (in terms of money) they got there.&lt;/p&gt;&#xA;" OwnerUserId="14182" LastEditorUserId="76" LastEditDate="2019-02-07T20:58:14.770" LastActivityDate="2019-02-08T01:35:43.917" Title="Who funds amateur radio satellites?" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12770" PostTypeId="2" ParentId="12769" CreationDate="2019-02-07T21:25:04.400" Score="11" Body="&lt;p&gt;Many of the amateur radio satellites are built, owned, and operated by various AMSAT organizations around the world.  They typically get their funds from donations and organization membership fees.  They're able to keep their costs low by using commodity hardware when possible, utilizing volunteer labor, and sharing launch vehicles with other payloads (essentially carpooling to orbit).&lt;/p&gt;&#xA;&lt;p&gt;From &lt;a href=&quot;https://www.amsat.org/amsat-history/&quot; rel=&quot;noreferrer&quot;&gt;AMSAT-NA's history&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;AMSAT’s major source of operating revenue is obtained by offering yearly or lifetime memberships in the various international AMSAT organizations.  Membership is open to Radio Amateurs and to others interested in the amateur exploration of space.  Modest donations are also sought for tracking software and other satellite related publications at Amateur Radio gatherings.  In addition, specific spacecraft development funds are established from time to time to receive both individual and corporate donations to help fund major AMSAT spacecraft projects.&lt;/p&gt;&#xA;&lt;p&gt;However, in corporate terms, these funds usually yield operating capital that’s well below project budgets for comparable commercial satellite activities.  For example, AMSAT-North America’s entire operating budget for 2014, including all the development funding generated from member donations toward AMSAT’s latest satellite project (the FOX Project) amounts to just a little more than $250,000.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-02-07T21:41:57.473" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12773" PostTypeId="1" AcceptedAnswerId="12775" CreationDate="2019-02-08T16:42:09.980" Score="2" ViewCount="720" Body="&lt;p&gt;Numerous sources say that LW length shouldn't be a multiple of λ/2 for any frequency in interest. This will cause the antenna to have a high impedance at this frequency. Since the coax cable impedance is 50 Ohms, we will get a high SWR. I get this part.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I don't get is &lt;strong&gt;why&lt;/strong&gt; the antenna will have a high impedance in this case and low impedance otherwise. It is my understanding that it has something to do with standing waves and voltage nodes. However when I tried to investigate this question further I've found only a lot of formulas, and since I'm not a mathematician this is where I stuck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could you please explain why the antenna works this way as if I was 10 years old? Or maybe name a book or article that does this.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-02-11T16:28:25.010" Title="Why long wire antenna length shouldn't be a multiple of λ/2?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wire-antenna&gt;" AnswerCount="3" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12774" PostTypeId="2" ParentId="12773" CreationDate="2019-02-08T17:04:01.717" Score="4" Body="&lt;p&gt;Start with a standard 1/2 wave, center fed dipole. Close to earth, the impedance will be ~50 ohms with very little reactance. Now start moving the feedpoint towards either end of the antenna and the impedance begins to rise - both the resistive and reactive parts. If you continue towards the very end of the antenna, the resistive and reactive part of the impedance become very high - greater than several thousand ohms each.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DvoaU.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DvoaU.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem comes in when we finally get to the end of the wire - there are not two places to connect the feedline. But because we can see the impedance rising as we approach the end of the antenna, we can theorize that it is even higher at the very end of the antenna. This can be difficult to match to 50 ohm coax. Since the impedance is very high, for a given amount of applied power, the voltage is also very high in this area:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\text{Voltage}=\sqrt{PR} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So care must be taken. For example a 100 watt transmitter could develop more than 700 volts across a 5,000 ohm load when there would be only 70 volts present across a 50 ohm load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But a much more important consideration is if only one side of the feedline is connected to the end of the wire, how can the antenna radiate if their is no return path? The answer is that typically the exterior of the shield of the coax cable is acting as part of the antenna. This means that the antenna is not a 1/2 wavelength of wire but rather something longer. How long is highly installation dependent but we can say for certain it is longer than 1/2 wavelength. So all of the concern about a 1/2 wavelength antenna is a bit misplaced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Why So Many Impedances?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason a single piece of wire has different impedances along its length is due to reflections of RF energy that gives rise to standing waves. As RF current travels along the wire, it eventually reaches the end of the wire. Since the end is nearly an open circuit, the wave is reflected back toward whence it came. But when it starts its return trip, the phase of the wave is different from the original wave. So the peaks and troughs of the two waves do not line up to each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While there are now two waves traveling in opposite directions on the wire, when we take typical voltage or current measurements at any point on the wire, we are observing only the combined voltage or current of all of the traveling waves. Since impedance is simply voltage divided by current, the impedance therefore varies in accordance with the combination of the repective waves.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-08T19:33:48.000" LastActivityDate="2019-02-08T19:33:48.000" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12775" PostTypeId="2" ParentId="12773" CreationDate="2019-02-08T17:43:17.390" Score="5" Body="&lt;p&gt;A real antenna is more complicated, but I believe the insight you seek can be obtained by learning about a simpler case of transmission line stubs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider what happens when a DC voltage is applied at one end of a transmission line, and it's unknown what's connected at the other end. It this is a 50 ohm line, that means for every 50 volts applied, 1 ampere of current will flow initially. That voltage wave propagates down the line until reaching the other end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the initial wave reaches the other end, if the line isn't terminated by a 50 ohm resistor, then the initial 50 volts per ampere is &quot;wrong&quot; for that termination. Say it's a 100 ohm resistor. Ohm's law dictates that for every 100 volts across this resistor, 1 ampere must flow through it. But when the wave arrives, we have 50 volts, and 1 ampere. How can this be resolved?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens is a new wave begins at the resistor, and propagates back towards the voltage source. Eventually this reflected wave reaches the voltage source, and it will &quot;try&quot; to increase the voltage. But a voltage source by definition always has a fixed voltage, so it will respond by reducing current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This change then propagates back down the line towards the resistor. The superposition of all these waves that have happened now brings the conditions at that end closer to 100 volts per ampere, but we're still not there so another reflected wave is set up. The voltage source makes another adjustment to its output current, and these reflections continue on forever, each time approaching 100 volts per ampere. In practice they happen so fast that it's basically instant, and we just ignore this process of how voltage and current settle to equilibrium.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But when the voltage source is AC, and the transmission line is a significant fraction of the wavelength, now the time it takes to reach this equilibrium is no longer &quot;instant&quot; compared to how fast the voltage is changing, so we can't neglect it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A special case is when the transmission line is a half wavelength long. In this case, the time it takes a wave to travel from the source, to the other end, and back is exactly 1 cycle. If we assume the source is a sine wave infinitely repeating, a delay of 1 cycle is identical to no delay at all. So if the transmission line is open at the end, that means voltage must be zero, and all that excess voltage is reflected back at the source. And because the line is a half wavelength long, that means the crest of that reflected wave arrives at the same time the source is at its crest. The two voltages add, creating a very high voltage for a very low current. That is, a &lt;em&gt;high impedance&lt;/em&gt;. Ideally infinite, though in practice it will be limited by losses in the transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another special case is when the transmission line is a quarter-wave long. In this case, the delay to make a round-trip is a half cycle, so the reflected waves arrive in the opposite phase. This has the effect of &quot;inverting&quot; the impedance: if the quarter-wave line is open at the end, it &quot;looks&quot; like a short to the source. It looks like a short because however much voltage the source tries to generate, it's never enough because the reflected wave cancels the source wave exactly. A very low voltage even for a very high current is the definition of a short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's an example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Transient_to_standing_wave.gif#/media/File:Transient_to_standing_wave.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/7/70/Transient_to_standing_wave.gif&quot; alt=&quot;Transient to standing wave.gif&quot;&gt;&lt;/a&gt;&lt;br&gt;By &lt;a href=&quot;//commons.wikimedia.org/wiki/User:Davidjessop&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;User:Davidjessop&quot;&gt;Davidjessop&lt;/a&gt; - Own work, &lt;a href=&quot;https://creativecommons.org/licenses/by-sa/4.0&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Creative Commons Attribution-Share Alike 4.0&quot;&gt;CC BY-SA 4.0&lt;/a&gt;, &lt;a href=&quot;https://commons.wikimedia.org/w/index.php?curid=44429448&quot; rel=&quot;nofollow noreferrer&quot;&gt;Link&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can see a couple things going on here. Firstly, as the forward wave travels to the right, it's attenuated by loss. In an antenna, it could be attenuated by radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pay particular attention to the voltage at the ends. We can infer this particular example is terminated in a short, because the voltage at the right end is fixed at 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Initially, the source is able to develop some voltage into the line, looks like about ±0.5V at the peaks. But after the forward wave has reached the right, and then the reflected wave has reached back to the source, in the last moments of the animation, the voltage developed at the source is nearly zero. Were it not for the loss in the line, it would be exactly zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally note at 0.25 wavelengths on the horizontal axis, the peak voltage is almost ±1V, twice that of the initial wave from the source. This is because at this point, the forward and reverse waves are interfering constructively. That some points on the line have a very high RMS voltage, and other points have a very low RMS voltage indicates this line is operating with a &lt;em&gt;high SWR&lt;/em&gt;. The SWR is exactly the ratio of RMS voltages between these nodes and antinodes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas aren't exactly transmission lines, but the general principle still holds. The end of the antenna is like an open line: the current there must be zero because there's nowhere else to go. When center-feeding a half-wave dipole, each leg of the dipole is a quarter-wave long, so the high impedance ends of the antenna looks like a low impedance in the middle, a quarter wave away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if the leg(s) of the antenna are a half-wave, this impedance inversion doesn't occur. The source sees not a low impedance but a high one. Not infinite, since theoretically the antenna is still able to radiate. But such a high impedance does create issues in practice: it's hard to match if your transmitter expects a 50 ohm load.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-02-10T14:33:01.853" LastActivityDate="2019-02-10T14:33:01.853" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12776" PostTypeId="1" CreationDate="2019-02-08T21:01:36.293" Score="1" ViewCount="109" Body="&lt;p&gt;I'm looking for a reliable, however cheap solution for ground-space communication. I need at least 50W of transmitted power with 2GFSK modulation at 70cm band (433 MHz). Transmission will be done between earth's surface and a cubesat on LEO at 9600bps.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What should I be looking for?&lt;/li&gt;&#xA;&lt;li&gt;Is SDR + amplifier a good solution? &lt;/li&gt;&#xA;&lt;li&gt;Or should I aim at transceivers  with capability of transmitting 50W with 2GFSK modulation (if any like that exist), or &lt;/li&gt;&#xA;&lt;li&gt;maybe should I aim for creating my own solution?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13735" LastEditorUserId="13735" LastEditDate="2019-02-09T12:46:00.793" LastActivityDate="2019-02-09T12:46:00.793" Title="2GFSK 9600bps Transmitter and amplifier for 433 MHz" Tags="&lt;uhf&gt;&lt;transceiver&gt;&lt;transmitter&gt;&lt;amplifier&gt;" AnswerCount="0" CommentCount="13" ContentLicense="CC BY-SA 4.0" />
  <row Id="12778" PostTypeId="2" ParentId="12764" CreationDate="2019-02-09T12:08:10.613" Score="4" Body="&lt;p&gt;Since you plan to get licensed, I recommend that you purchase a transceiver, for two reasons. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;There is no &quot;modern&quot; transmitter to pair with a communications-grade receiver.&lt;/li&gt;&#xA;&lt;li&gt;A quick perusal of the classified ads reveals that, for similar receiver capability, the price of a receiver is not too different from the price of a transceiver.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The latest generation of ($$$!!) high-performance receivers appear to be &quot;cut downs&quot; of the same generation of transceiver. But, again, no mating transmitter is available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you still want to go the &quot;separates&quot; route, you will probably be relegated to the Drake &quot;twins&quot; or similar. Beware - the oscillators in these units may not be sufficiently stable to support digital modes beyond RTTY. If you want to operate FT8, for example, check with an expert to be sure you don't waste your time and treasure.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-02-09T12:08:10.613" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12779" PostTypeId="1" AcceptedAnswerId="12781" CreationDate="2019-02-09T17:17:40.020" Score="5" ViewCount="1223" Body="&lt;p&gt;My apt balcony is 1,812 feet exactly from my campus's Wifi access point behind a triple pane, brick, 4th floor building window. There is a clear line of sight. I was interested in seeing if I could use a Yagi or a Dish to connect to it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I ran this project idea past a campus network administrator and he said there wouldn't be any concern by the campus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the apartment is restricted to slow, overpriced Comcast internet. (Mentioning as this factors into the cost-benefit analysis of my setup) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would be the better antenna to try using? Is this even worth the electrical cost of keeping this broadcasting?&lt;/p&gt;&#xA;" OwnerUserId="14193" LastEditorUserId="4076" LastEditDate="2019-02-10T13:59:03.103" LastActivityDate="2019-02-10T13:59:03.103" Title="Yagi vs Parabolic Dish for 2.4GHz Campus Wifi from 1,800ft away?" Tags="&lt;united-states&gt;&lt;antenna-theory&gt;&lt;wifi&gt;&lt;yagi&gt;&lt;range&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12780" PostTypeId="2" ParentId="12779" CreationDate="2019-02-09T18:06:05.870" Score="6" Body="&lt;p&gt;Depends on the particular Yagi or dish. Look for a published gain. Beware of low-quality manufacturers that publish erroneous data. Higher gain will correlate with higher probability of working. Point-to-point links of 1812 feet are easily accomplished, with a clear line of sight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think you'll have 4 potential issues:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Attenuation by the building will have to be overcome by antenna gain. 1812 isn't so far, so that may be feasible. You might want to calculate a &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt; to estimate how much gain you'll need.&lt;/li&gt;&#xA;&lt;li&gt;Interference from other sources is another concern. A higher gain antenna will have a narrower beam, reducing interference.&lt;/li&gt;&#xA;&lt;li&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Hidden_node_problem&quot; rel=&quot;noreferrer&quot;&gt;hidden node problem&lt;/a&gt;. That you're using such a directional antenna makes it likely you will not hear other devices on the same AP. Your campus network administrator might have a change of heart after you get the project up and running.&lt;/li&gt;&#xA;&lt;li&gt;Regulations may limit antenna gain and/or power you can legally use.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In my area, electricity costs about \$0.13 per kilowatt-hour. Comcast is \$80/mo. That means for the price of Comcast for a month, I can purchase 615 kWh of energy. There are about 720 hours in a month, so roughly speaking, I'd have to burn 1,000 watts every hour of the month to keep pace with the price of Comcast. Electrical cost of a WiFi radio will be orders of magnitude less than that.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-02-09T18:06:05.870" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12781" PostTypeId="2" ParentId="12779" CreationDate="2019-02-10T06:35:10.210" Score="6" Body="&lt;p&gt;You can make a first order approximation by using typical WiFi ranges in combination with two &lt;a href=&quot;https://wikipedia.org/wiki/Free-space_path_loss&quot; rel=&quot;noreferrer&quot;&gt;free space path loss calculations&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;802.11b/g has a typical indoor range of 150 feet. By calculating the difference in FSPL between 150 feet and 1812 feet, the approximate antenna gain requirement can be determined. Using an &lt;a href=&quot;https://www.pasternack.com/t-calculator-fspl.aspx&quot; rel=&quot;noreferrer&quot;&gt;on-line FSPL calculator&lt;/a&gt;, we find 73 dB vs 95 dB of loss respectively for 0 dBi antennas. So your antenna must have at least 95 dB - 73dB = 22 dBi of gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a first order approximation that assumes the stock WiFi antennas have 0 dBi of gain, the normal working range is 150 feet,  the window coatings do not present any additional losses, and there are no other attenuating effects in the path. Given all of this, adding another 6 dB of antenna gain (28 dBi total) for good margin would put you at a reasonable starting point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna such as &lt;a href=&quot;http://www.l-com.com/tabbeditem_mobi.aspx?id=22203&quot; rel=&quot;noreferrer&quot;&gt;this one&lt;/a&gt; would meet the requirement. Don't forget adapter cables and keep them as short as possible as these too will introduce losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NRO1w.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NRO1w.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding the power usage requirements, &lt;a href=&quot;http://www.tpcdb.com/list.php?type=11&amp;amp;query=D-Link&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt; is a nice site that catalogs the power required for various WiFi access points. Based on this data, a budget of 15 watts would be generous. If you leave it on 24x7, it would use 15 watts * 24 hours per day * 365 days per year = 131.4 kilowatt-hours per year. According to &lt;a href=&quot;https://www.electricitylocal.com/states/south-carolina/clemson/&quot; rel=&quot;noreferrer&quot;&gt;Electricity Local&lt;/a&gt;, your residential electric rate is 0.0984 dollars per kilowatt-hour. This puts your worst case operating cost at $12.93 annually. That is well within the budget of even the most frugal grad student!&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-10T08:39:08.697" LastActivityDate="2019-02-10T08:39:08.697" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12784" PostTypeId="2" ParentId="12773" CreationDate="2019-02-10T21:48:57.477" Score="2" Body="&lt;p&gt;This discussion applies to standing wave antennas for which there is a forward wave traveling from the feedpoint to the open end of the antenna where a reflection takes place that creates a reflected wave traveling back toward the feedpoint. Since we know that the current is zero at the open end of a wire, it follows that the forward current undergoes a change of sign (&lt;span class=&quot;math-container&quot;&gt;$180^o$&lt;/span&gt; phase shift) when it is reflected such that &lt;span class=&quot;math-container&quot;&gt;$I_{for}-I_{ref}=\varnothing$&lt;/span&gt; where the wire ends. We also know that the voltage is maximum at the end of an antenna wire so it follows that the reflected voltage is in phase (&lt;span class=&quot;math-container&quot;&gt;$\varnothing^o$&lt;/span&gt; phase shift) with the forward voltage such that &lt;span class=&quot;math-container&quot;&gt;$V_{for}+V_{ref}=2(V_{for})$&lt;/span&gt; where the wire ends. The forward wave undergoes a &lt;span class=&quot;math-container&quot;&gt;$90^o$&lt;/span&gt; phase shift in 1/4 wavelength of wire and so does the reflected wave on its way back to the feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna is 1/4 wavelength between the feedpoint and the open end of the wire (e.g. one-half wavelength dipole) then the forward and reflected currents will be in phase at the antenna feedpoint such that &lt;span class=&quot;math-container&quot;&gt;$I_{for}+I_{ref}=high$&lt;/span&gt; &lt;span class=&quot;math-container&quot;&gt;$current$&lt;/span&gt;. The forward and reflected voltages will be &lt;span class=&quot;math-container&quot;&gt;$180^o$&lt;/span&gt; out of phase such that &lt;span class=&quot;math-container&quot;&gt;$V_{for}-V_{ref}=low$&lt;/span&gt; &lt;span class=&quot;math-container&quot;&gt;$voltage$&lt;/span&gt;. The result is a low resistance at the antenna feedpoint, e.g. &lt;span class=&quot;math-container&quot;&gt;$(V_{for}-V_{ref})/(I_{for}+I_{ref})=50$&lt;/span&gt; &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna is 1/2 wavelength between the feedpoint and the open end of the wire (e.g. one wavelength dipole) then the forward and reflected currents will be &lt;span class=&quot;math-container&quot;&gt;$180^o$&lt;/span&gt; out of phase at the antenna feedpoint such that &lt;span class=&quot;math-container&quot;&gt;$I_{for}-I_{ref}=low$&lt;/span&gt; &lt;span class=&quot;math-container&quot;&gt;$current$&lt;/span&gt;. The forward and reflected voltages will be in phase such that &lt;span class=&quot;math-container&quot;&gt;$V_{for}+V_{ref}=high$&lt;/span&gt; &lt;span class=&quot;math-container&quot;&gt;$voltage$&lt;/span&gt;. The result is a high resistance at the antenna feedpoint, e.g. &lt;span class=&quot;math-container&quot;&gt;$(V_{for}+V_{ref})/(I_{for}-I_{ref})=5000$&lt;/span&gt; &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This answer is deliberately simplified by limiting the math to in-phase and &lt;span class=&quot;math-container&quot;&gt;$180^o$&lt;/span&gt; out-of-phase signals. A more generalized discussion would require phasor (vector) math with which many hams are unfamiliar.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-02-11T16:28:25.010" LastActivityDate="2019-02-11T16:28:25.010" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12786" PostTypeId="1" CreationDate="2019-02-10T23:50:27.493" Score="0" ViewCount="187" Body="&lt;p&gt;I'm an Amateur Radio enthusiast from way back; mostly CB and 10 meters. I have a couple of hand-held Baofengs that I want to use for family communications and as a backup link in case of emergencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to get my Federal number and technician license so that I'm legal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been reading a lot of material on the Web, and it has been a little confusing as to where to start.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many local clubs to join where I live in Georgia; &lt;em&gt;I just need to know where to start.&lt;/em&gt; I know that I need a license from the FCC, but would appreciate help in what to do first and where is the best information on handheld programming of these little radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't want to just fire it up and start fumbling around without knowing what to do. Thanks for any help you all can provide.&lt;/p&gt;&#xA;" OwnerUserId="14202" LastEditorUserId="873" LastEditDate="2019-02-11T02:29:01.030" LastActivityDate="2019-02-11T16:14:50.220" Title="Amateur wanting to re-enter ham radio legally" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;procedure&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12791" PostTypeId="2" ParentId="12786" CreationDate="2019-02-11T14:44:04.760" Score="2" Body="&lt;p&gt;The traditional way to get licensed is to contact a local club, join up with an Elmer (ham-speak for a mentor), and get guidance to study for the license exam.  It's likely your local club also hosts several license exam sittings per year (in my area, there are at least three clubs that, between them, provide at least two exams each month within an hour's drive).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, the Technician license is a breeze compared to what even Novice was when I was a teen.  If you've had a license previously, Technician or higher, you can probably take the exam (written only -- no code required in almost twenty years) cold and pass -- you need 74% correct on thirty-five questions out of a pool of 432, and the entire pool is available at the ARRL web site, along with &quot;practice exams&quot; containing randomly selected questions from the pool, just like the exam you'll ultimately take.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pass the exam at an organized session, pay your fee, and wait a few weeks, and you'll have your license.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-02-11T14:44:04.760" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12792" PostTypeId="2" ParentId="12786" CreationDate="2019-02-11T16:14:50.220" Score="1" Body="&lt;p&gt;A starting point is :  &lt;a href=&quot;https://apps.fcc.gov/coresWeb/publicHome.do&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://apps.fcc.gov/coresWeb/publicHome.do&lt;/a&gt;  , click the button for &quot;Register&quot;. This will get you into the process for obtaining your FRN : Federal Registration Number. Once you have that you can take an exam. Do a web search for your area and look for VE ( Volunteer Examiner ) Exams , Technician Exams or just Amateur Radio clubs. You can also search for your Counties or your Cities ARES ( Amateur Radio Emergency Service ) group - these folks will know all the local information. There are a great number of online practice testing tools if you find that there is nothing to be had locally. All you'll need do then is travel once for the exam.&lt;/p&gt;&#xA;" OwnerUserId="14102" LastActivityDate="2019-02-11T16:14:50.220" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12793" PostTypeId="1" AcceptedAnswerId="12798" CreationDate="2019-02-11T19:43:37.280" Score="5" ViewCount="144" Body="&lt;p&gt;The answers to this &lt;a href=&quot;https://ham.stackexchange.com/questions/12773/why-long-wire-antenna-length-shouldnt-be-a-multiple-of-%CE%BB-2&quot;&gt;question&lt;/a&gt; explain why it's difficult to transfer power from a transmitter to an antenna that is λ/2 in length (or a multiple for long wires, or as half a dipole's length).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there reasons why this length would not work or be less efficient when used for a receive-only antenna?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-02-12T11:52:10.207" Title="Are there reasons why a receive-only wire antenna should not be λ/2 in length?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wire-antenna&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12794" PostTypeId="1" CreationDate="2019-02-11T20:41:01.100" Score="2" ViewCount="146" Body="&lt;p&gt;&lt;a href=&quot;https://streamable.com/zlun4&quot; rel=&quot;nofollow noreferrer&quot;&gt;Video&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was experimenting with different settings on my IC-7300 and trying out manually controlling the RF Gain with AGC off.  Too much gain for a moment caused audio clipping followed by the audio going into a weird state.  Even after flipping AGC back on it was still acting bizarre (you can see in the video).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this point I'm in a cold sweat-- did I just brick my new radio like an idiot?  I turned the radio off, said a quick prayer, and turned it back on.  Thank god the audio is back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently kicking myself right now.  I can't just leave well enough alone.  I always have to tinker.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could I have broken something in the ADC or elsewhere?&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="76" LastEditDate="2019-02-11T21:17:25.123" LastActivityDate="2019-02-12T01:33:03.340" Title="What did I just do to my rig? Audio went crazy and had to reboot" Tags="&lt;equipment-operation&gt;&lt;icom&gt;&lt;icom-ic-7300&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12795" PostTypeId="1" AcceptedAnswerId="12796" CreationDate="2019-02-11T20:56:15.553" Score="0" ViewCount="118" Body="&lt;p&gt;I have a chance to get a 1 kW amplifier with a 220V plug dirt cheap from a friend of mine, but I only have a 110 outlet.  The 110 outlet is on its very own 20A breaker with no other outlets.  Could I run a 110-220V step up converter with the amplifier with no issues?  Thanks&lt;/p&gt;&#xA;" OwnerUserId="9772" LastEditorUserId="873" LastEditDate="2019-02-14T04:11:27.763" LastActivityDate="2019-02-14T04:11:27.763" Title="Voltage Converter for Amp" Tags="&lt;united-states&gt;&lt;amplifier&gt;" AnswerCount="3" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12796" PostTypeId="2" ParentId="12795" CreationDate="2019-02-11T21:14:04.310" Score="5" Body="&lt;p&gt;120 volts times 20 amperes = 2400 watts. That would mean this amplifier would have to be more than 42% efficient to avoid popping the breaker. That's pretty unlikely. Check the specs for the amplifier to get its current requirements, then double it to account for the voltage conversion, and add some more for converter inefficiencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A voltage converter that can do 20 amps isn't going to be cheap anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is the only outlet on the circuit, I'd recommend rewiring the circuit for 240V. That will give you more available power and you won't need to buy any additional equipment to convert voltages. It's likely possible without pulling new wire, so shouldn't be too expensive even if you have to hire a professional electrician to do the work, as long as you can make room in the service panel.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-02-12T00:58:15.850" LastActivityDate="2019-02-12T00:58:15.850" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12797" PostTypeId="2" ParentId="12794" CreationDate="2019-02-12T01:33:03.340" Score="2" Body="&lt;p&gt;I think it's highly doubtful you could break anything by turning those knobs. At worst, you just end up with horrible clipping and distortion as you experienced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The IC-7300 is a direct-sampling SDR. It's possible you found some software bug. Or it could just be that the AGC wasn't on long enough to adjust the gain back down. Complicating matters is that tuned to exactly 10 MHz, the carrier of that AM station is at or very near DC, which might put the signal closer to the clipping threshold, without being audible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, I wouldn't worry too much.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-02-12T01:33:03.340" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12798" PostTypeId="2" ParentId="12793" CreationDate="2019-02-12T04:05:49.077" Score="4" Body="&lt;p&gt;The difference between transmitting and receiving is that a good receiver has a dynamic range in the neighborhood of 75-100 dB, i.e. very weak signals can be amplified to an acceptable level. An efficiency of 1% is terrible for a transmitting antenna system but may be hardly noticeable for a receiving antenna system. For instance, a Beverage antenna has a negative gain (-3dBi) but is a good receiving antenna because of the dynamic range of communications receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In defense of 1/2WL end-fed transmitting antennas, the famous Zepp antenna is a 1/2WL end-fed antenna that is reasonably efficient because of the 1/4WL parallel matching section.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-02-12T11:52:10.207" LastActivityDate="2019-02-12T11:52:10.207" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12799" PostTypeId="2" ParentId="4951" CreationDate="2019-02-12T04:44:17.217" Score="2" Body="&lt;p&gt;Have a 2018 Subaru Forester &#xA;Has a heavy 2nd wire from negative batter terminal&#xA;going to an ELD sensor...the wire from the sensor to the chassis ground is enclosed within aluminum tubing and cannot be easily accessed. The head tech for Subaru in my location went to my car opened the hood and pointed to the main chassis ground bolt between the fuse box and the shock mount...good enough for me..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SMBaB.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SMBaB.jpg&quot; alt=&quot;Main Chassis Ground Bolt&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/xRe6v.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xRe6v.jpg&quot; alt=&quot;Main Routing Scheme&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14209" LastActivityDate="2019-02-12T04:44:17.217" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12803" PostTypeId="1" AcceptedAnswerId="12804" CreationDate="2019-02-12T16:47:43.127" Score="1" ViewCount="104" Body="&lt;p&gt;Here is my schema. I would like to connect a device using SMA connector with RG 174 to an attenuator of 30 dB with SMA connector. On the other side the attenuator is connected to a SMA-UHF converter to connect another device. This last device use normally PL 259 connector with RG-58 cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think everything is good in this description, but I want to be sure. I forgot to specify that all the cables have a characteristic impedance of 50 Ohms.&lt;/p&gt;&#xA;" OwnerUserId="14207" LastEditorUserId="9493" LastEditDate="2019-03-06T13:13:05.287" LastActivityDate="2019-03-06T18:39:33.177" Title="Cabling question between two devices" Tags="&lt;coaxial-cable&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12804" PostTypeId="2" ParentId="12803" CreationDate="2019-02-12T17:30:29.833" Score="5" Body="&lt;p&gt;RG-174 cable does not offer very good shielding. This can be a significant problem when you are attempting relatively high levels of attenuation as the cable leakage may provide more signal than the attenuator is allowing. Here is an illustration of coaxial cable leakage from &lt;a href=&quot;https://wikipedia.org/wiki/Leaky_feeder&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/irl97.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/irl97.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There will be losses in the &quot;transport mode&quot; that are due to the RF resistance of the conductors and losses in the dielectric material between the two conductors. This is generally expressed as dB/100 feet or dB/100 meters at a given frequency by the cable manufacturer. The radiating loss is much smaller by comparison and is generally not specified by the manufacturer. This needs to be determined experimentally. Cable TV companies, for example, learned long ago that at least two shields were needed in order to prevent signal leakage that could either be used to pirate cable TV service using a simple antenna pointed at the cable or to not run afoul of regulatory requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider your situation. You wish to attenuate a signal from a higher power source so as to reduce it to a level suitable for a sensitive receiver input. If the coaxial cable leaks only 1/1000 of the power that is traveling through the cable, for example, that is a -30 dB signal source that is radiating from the cable. If you now place a 30 dB attenuator at the end of the cable, the leaked signal and the transported signal are at the nearly same power level. Depending on many other factors, this may or may not affect your measurements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A general rule for any well equipped RF lab is to use at least double shielded coaxial cables. As @ChrisK8NVH suggested, &lt;a href=&quot;https://www.timesmicrowave.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Times Microwave&lt;/a&gt; LMR-100 or LMR-195 would be good choices as they are both double shielded. The nice thing about Times Microwave is that they typically rate their shielding effectiveness - both cables are &gt; 90 dB. These cables are also suitable for SMA connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I am doing sensitive RF work, I will also include several ferrite toroid cores that the cable wraps around in order to reduce &lt;a href=&quot;https://www.w8ji.com/common_mode_current.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;common mode current&lt;/a&gt; that can also upset sensitive experiments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you get away with RG-174 cable for your experiments? Perhaps. But the results you observe may not be in line with your underlying assumptions.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-06T18:39:33.177" LastActivityDate="2019-03-06T18:39:33.177" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="12805" PostTypeId="1" CreationDate="2019-02-12T17:53:51.790" Score="5" ViewCount="257" Body="&lt;p&gt;I understand that in a half-wave center-fed antenna current distribution has a sinusoidal wave approximately, so the current in the center has max value and it has to become zero at the ends of dipole which are open. But since we change the feed point from center to one of the end points, the current in feed point (the end of antenna) is not zero this time right? So it seems that moving feed point from center to end change the current distribution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is how to calculate current distribution in theory in this new arrangement. I am familiar with Hallen integral equation and method of moment, but in this method we use boundary condition of current which is zero in both ends. However, in end-fed dipole it seems we do not have this boundary condition in one end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what should I do? Or in general how can I calculate current on dipole antenna?&lt;/p&gt;&#xA;" OwnerUserId="14218" LastEditorUserId="8717" LastEditDate="2019-02-12T18:34:40.427" LastActivityDate="2019-02-14T19:07:03.893" Title="How can I calculate current distribution on an end-fed dipole antenna in theory?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12806" PostTypeId="2" ParentId="12795" CreationDate="2019-02-12T21:57:36.850" Score="2" Body="&lt;p&gt;Most homes have 220v service, but many are not wired for it.  That is, there is 220 at your junction box, but not throughout the house.  You would be better off to have a licensed electrician come in and provide a 220 v circuit for your amp.&#xA;Warning about the amp - if it is an old, tube based amp, then you would want to get it looked at by a qualified repair person.  Is the amp in use currently (no pun intended) ?  If so, then you could just install it.  However, it seems that few people give away good equipment (&quot;dirt cheap&quot;), so I would imagine that the amp has been sitting in someone's basement for years.  Better get it looked at.  Maybe replace the electrolytics.  Ironically, I also have a SB220 for sale, thru my local ham club.  73, Joe&lt;/p&gt;&#xA;" OwnerUserId="8647" LastActivityDate="2019-02-12T21:57:36.850" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12807" PostTypeId="1" AcceptedAnswerId="12808" CreationDate="2019-02-13T02:23:46.043" Score="0" ViewCount="71" Body="&lt;p&gt;In analog-to-digital conversion, how independent is the Nyquist rate from the power of the signal?&lt;/p&gt;&#xA;" OwnerUserId="14005" LastEditorUserId="76" LastEditDate="2019-02-13T04:44:41.347" LastActivityDate="2019-02-13T16:57:17.877" Title="Is the Nyquist rate independent of the power of the analog signal being digitized?" Tags="&lt;dsp&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12808" PostTypeId="2" ParentId="12807" CreationDate="2019-02-13T04:03:26.023" Score="4" Body="&lt;p&gt;Completely independent. It is dependent on frequency only. The amplitude of the signal is only relevant when looking at the number of bits used (and the dynamic range).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;See here&lt;/a&gt; for more details.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-02-13T04:03:26.023" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12809" PostTypeId="5" CreationDate="2019-02-13T04:53:34.840" Score="0" Body="&lt;p&gt;The exact distinction between “portable” and “mobile” varies depending on who you ask. For the purposes of tagging questions on Amateur Radio Stack Exchange, “portable” refers to a station which will be set up temporarily in some location; as opposed to one which is a long-term installation whether, that be stationary or in a vehicle (&lt;a href=&quot;/questions/tagged/mobile&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;mobile&amp;#39;&quot; rel=&quot;tag&quot;&gt;mobile&lt;/a&gt;).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-02-13T04:53:34.840" LastActivityDate="2019-02-13T04:53:34.840" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12810" PostTypeId="4" CreationDate="2019-02-13T04:53:34.840" Score="0" Body="Transporting, setting up, and operating a temporary station. For operation from a vehicle, use [mobile] instead." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-02-13T04:53:34.840" LastActivityDate="2019-02-13T04:53:34.840" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12815" PostTypeId="2" ParentId="12807" CreationDate="2019-02-13T16:57:17.877" Score="2" Body="&lt;p&gt;Theoretically, the rate is independant.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In reality, exceeding certain power levels will cause real world digitizers to increase in non-linearities (clipping, saturation, thermal damage, and etc.), which will introduce harmonics and other spectra above any Nyquist rate based on linear system assumptions, if not complete system failure.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-02-13T16:57:17.877" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12816" PostTypeId="2" ParentId="12795" CreationDate="2019-02-14T00:58:54.723" Score="1" Body="&lt;p&gt;You could use a voltage converter, but like &lt;a href=&quot;https://ham.stackexchange.com/a/12796/&quot;&gt;Phil (W8II)&lt;/a&gt; is pointing out, the old &lt;span class=&quot;math-container&quot;&gt;$P = IE$&lt;/span&gt; formula means that for the same wattage, if you half the voltage, you double the amount of current needed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not sure which amplifier you have, but let's assume it is one like the Ameritron AL-80B. It is a 1KW amplifier. They claim it will put 1000 Watts on SSB (which usually means peak-to-peak) and 800 W on CW. You can get in either 120 or 240 VAC.&#xA;At 120 VAC, it draws 12 amps which is 1440 watts input power. Let's assume it is putting out 1000 W. That would be 70% efficient, which is exceptional! On CW, it puts out 800 W (more realistic), which would be 55% (800/1440) efficient and is more of the norm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a full 1000W on CW, that would be (at 55%) 1800 watts. 1800/120 = 15 amps. Now you are starting to push the limits of a 20A breaker (see circuit breaker ratings for more info on how they are rated). As you start to get without 80% of their ratings, you can start to get nuisance tripping because you current draw will pulsing with voice peaks or CW tones. These peaks with a heavy current draw will also start causing you house lights to dim or pulse - drove my wife nuts! I had to go to 240V! At 240V, you only need 7.5 Amps. Much, much less dimming of the lights also!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could do one of three things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;If you want to try the amp out, plug it into your clothes dryer outlet (if it is not too far away) and see how it affects the lights. That would let you see how happy it is running on a 240V circuit. You could &quot;share&quot; the connection, if you aren't drying clothes while you want to operate - or even better - you have a gas dryer!&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you are a good electrician or know a good one, wire a 240V line to your shack and make everyone happy.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What most of us do - get the 600-800 Watt version, which is usually 120V at about 8-10 amps. 800 W PEP is 8x power (over 100W), which is a 9db gain! Double again to 1600W output is only another 3 db (diminishing returns).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;But, I would have a really hard time turning down a &quot;cheap&quot; or nearly free 1kW amplifier. I'll bet the money you would save would easily pay for a licenced electrician to run a single 240V 15 or 30 amp outlet! So, I would recommend door #2!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ayway, hope to hear you on the air with a fine, strong signal!&lt;/p&gt;&#xA;" OwnerUserId="14234" LastEditorUserId="76" LastEditDate="2019-02-14T01:42:18.980" LastActivityDate="2019-02-14T01:42:18.980" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12820" PostTypeId="2" ParentId="12805" CreationDate="2019-02-14T12:09:50.800" Score="1" Body="&lt;p&gt;M-o-M software such as NEC (Numerical Electromagnetics Code) is capable of calculating the distribution and values of r-f currents along radiating conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The graphic below shows the distribution of such current along the conductors of an &quot;end-fed&quot; antenna &lt;em&gt;system&lt;/em&gt;, for the parameters and configuration described there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The value of r-f current at each segment of the antenna conductors is available from the calculated results, but that data is omitted in this post.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TafcK.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TafcK.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-02-14T12:09:50.800" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12822" PostTypeId="1" AcceptedAnswerId="12823" CreationDate="2019-02-14T13:28:11.623" Score="11" ViewCount="1606" Body="&lt;p&gt;I recently watched, on You Tube, a NOVA program about the British school masters and students who were the first to publish the news that the Soviets had started launching satellites from a new launch site back in 1958. (&lt;a href=&quot;https://www.youtube.com/watch?v=HQFmF9Gnp0A&quot; rel=&quot;noreferrer&quot;&gt;School Boys Who Cracked the Soviet Secret&lt;/a&gt;).  Early in the program (about 8:35, if you watch it), one schoolmaster asks another what he would need in order to receive and record the transmissions from the early Soviet satellites.  He was told three items were needed: a receiver, a tape recorder, and a signal generator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why would you need a signal generator?  The program is short on technical information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although interested in radio, I am not an expert, so please excuse me if I have asked a dumb question.&lt;/p&gt;&#xA;" OwnerUserId="14245" LastActivityDate="2019-02-14T16:35:33.443" Title="Why would you need a signal generator to receive early satellite transmissions?" Tags="&lt;receiver&gt;&lt;satellites&gt;&lt;oscillator&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12823" PostTypeId="2" ParentId="12822" CreationDate="2019-02-14T13:45:30.350" Score="15" Body="&lt;p&gt;The earliest Soviet satellites, like Sputnik 1, transmitted what amounted to a CW stream -- just pulsed RF at pretty low power (later Sputniks transmitted data by pulse width modulation, still essentially CW).  In order to hear it, you needed a Beat Frequency Oscillator -- a BFO -- and with a common radio receiver, the signal generator was standing in for the BFO.  If you had a ham receiver or transceiver that could tune the correct frequency, switching to CW mode would do the same job, and a few &quot;world&quot; radios (multiband AM/SW sets) had a BFO function.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The BFO makes the unmodulated signal audible by mixing it with another signal at a few hundred Hertz different frequency.  The two signals will reinforce and cancel, forming a &quot;beat&quot;, and they'll do it at a frequency equal to the difference between the two (or their sum, but the difference is chosen to be in the audio range, while the sum is radio frequency).  This &quot;beat frequency&quot; is then filtered out of the mixed RF and amplified by the receiver.  This is the same process used to make a radiotelegraphy signal audible, or to reconstruct a Single Side Band audio signal.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-02-14T16:35:33.443" LastActivityDate="2019-02-14T16:35:33.443" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12824" PostTypeId="1" AcceptedAnswerId="12826" CreationDate="2019-02-14T14:03:38.353" Score="2" ViewCount="271" Body="&lt;p&gt;I'm considering buying a Yaesu FT-857D for car mount and I'm now concerned the speaker is on the body and only the body and not on the head unit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where's the speaker? Can a mic contain the speaker too?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2019-02-14T15:03:14.687" Title="Where is the speaker on the Yaesu FT-857D?" Tags="&lt;yaesu&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12825" PostTypeId="2" ParentId="12805" CreationDate="2019-02-14T14:27:40.713" Score="0" Body="&lt;p&gt;Perhaps the following graph based on EZNEC simulation data will allow the development of an empirical curve-fitting formula. Note that the current envelope is very similar to one half of a Double Zepp. &lt;a href=&quot;https://i.stack.imgur.com/hiGXo.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hiGXo.png&quot; alt=&quot;Current Magnitude and Phase for an End Fed Dipole simulated in EZNEC&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-02-14T19:07:03.893" LastActivityDate="2019-02-14T19:07:03.893" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12826" PostTypeId="2" ParentId="12824" CreationDate="2019-02-14T15:03:14.687" Score="3" Body="&lt;p&gt;I don't have one handy to validate this, but &lt;a href=&quot;https://www.yaesu.com/downloadFile.cfm?FileID=12848&amp;amp;FileCatID=158&amp;amp;FileName=FT%2D857D%5FOM%5FENG%5FEH007M108.pdf&amp;amp;FileContentType=application%2Fpdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;in the manual&lt;/a&gt; you can see the speaker grille on top of the radio in the angled view on page 20. This is the same place it is on my FT-897. So, yes, the speaker is on the body.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The microphone connector pinout is unfortunately not described in the manual (it is in the FT-897's, which is largely identical), but it does not contain audio output, so no speaker-mic can be connected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, &lt;strong&gt;you can connect an external speaker to the EXT SPKR 3.5mm mono jack,&lt;/strong&gt; described on pages 34-35. You will have to mount it separately, but communications speakers with suitable mounting brackets and cables are a common item (if often expensive for the sound quality you get).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-02-14T15:03:14.687" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12827" PostTypeId="1" CreationDate="2019-02-14T16:16:08.027" Score="2" ViewCount="824" Body="&lt;p&gt;I made a simple linear power supply for my transceiver using 12V 30A transformer, four diodes RHRP3060 forming a rectifier and three 30_000 µF capacitors connected in parallel. I also used a 200 Ω 50W resistor to discharge capacitors in a few seconds after powering the device off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power supply works reasonably well and I already made a few QSOs using it. However if I transmit in FM using 100W the oscilloscope shows +/- 6 V ripple. It's not that bad in SSB though. In this mode I see 9-15V which is in safe range for my FT-891, which is 13.8 +/- 15%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What upsets me is that the cheapest switching 12V 29A LED driver I could find gives only +/- 1.3V ripple in FM mode. If anyone is interested, it's GDLI-350-IP20-12, the price is ~15$.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I reduce the ripple of my power supply to approximately the same level? Should I use even more capacitance, a high-pass filter, or maybe something else?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="4076" LastEditDate="2019-02-14T20:53:11.137" LastActivityDate="2021-02-01T20:10:22.353" Title="How to reduce voltage ripple of a linear power supply?" Tags="&lt;electronics&gt;&lt;power-supply&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12829" PostTypeId="2" ParentId="12827" CreationDate="2019-02-14T17:06:34.800" Score="9" Body="&lt;p&gt;Unless you haven't mentioned all the parts, you have built an &lt;strong&gt;unregulated&lt;/strong&gt; power supply. The output voltage of a transformer varies depending on load, and the other components will just follow that voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For electronic equipment you should use a &lt;strong&gt;regulated&lt;/strong&gt; power supply. This requires the rectifier to produce an output voltage somewhat &lt;em&gt;higher&lt;/em&gt; than the target 12 V, and a regulator circuit (or IC) which controls power transistors to drop it down to the exact target voltage, allowing the final output voltage to stay constant even as the transformer's output voltage varies. These transistors must have a heat sink (for all but the smallest linear supplies) as it will produce heat equal to the excess voltage times the load current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Arguably, your current power supply should not even be called “linear”, as it does not have the above-described “linear regulator” circuit in it. The common terminology usage is not entirely consistent, as sometimes “linear” is used to describe any non-switching power supply.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I cannot advise you on the detailed design of linear power supplies; this answer is just describing what is obviously missing.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-02-15T01:20:42.490" LastActivityDate="2019-02-15T01:20:42.490" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12830" PostTypeId="2" ParentId="12827" CreationDate="2019-02-14T17:07:04.167" Score="2" Body="&lt;p&gt;I'm surprised you haven't damaged your radio! You need a voltage regulated linear power supply to provide a stable DC voltage to the radio. Your 100 watt transmitter likely draws about 20 amperes of current in FM mode. A popular supply is the Astron  RS-35. If you examine the output of your current supply with an oscilloscope, you will see a lot of AC ripple or hum on the DC output. This will vary with load current being drawn. Your simple unregulated power supply output voltage will rise much higher during light load (receive) and drop to unacceptably low voltage during heavy load (transmit).&lt;/p&gt;&#xA;" OwnerDisplayName="user14247" LastEditorDisplayName="user14247" LastEditDate="2019-02-14T19:30:56.820" LastActivityDate="2019-02-14T19:30:56.820" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12832" PostTypeId="2" ParentId="606" CreationDate="2019-02-14T22:15:01.067" Score="0" Body="&lt;p&gt;I would try a portable receiver and go for a walk around your street.  In the U.K. short wave listening is almost impossible , there is so much noise everywhere.  I have come to the conclusion that using a desktop communications receiver at home even with a loop antenna in the garden is no longer possible due to the noise.  I bought a second hand Tecsun Pl660 and go mobile with it well away from houses and overhead wires.&lt;/p&gt;&#xA;" OwnerUserId="14251" LastActivityDate="2019-02-14T22:15:01.067" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12833" PostTypeId="1" AcceptedAnswerId="12837" CreationDate="2019-02-14T22:32:03.517" Score="4" ViewCount="920" Body="&lt;p&gt;Here is how the FM Receiver I made using the GNU Radio Companion.&lt;/p&gt;&#xA;&lt;p&gt;(Basically, I was following this tutorial by &lt;a href=&quot;https://www.youtube.com/watch?v=2Nd9BIYmKD8&quot; rel=&quot;nofollow noreferrer&quot;&gt;VYE6Y on youtube&lt;/a&gt;.)&lt;/p&gt;&#xA;&lt;h1&gt;FM Receiver&lt;/h1&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7dQNg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7dQNg.png&quot; alt=&quot;FM Receiver&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Problem: Unfortunately for me, the GNU Radio gives no output. It opens a window as you can show below but no matter what I click or change, there is nothing to be heard. I think, the signal is being processed as the Bandpass spectrum can be seen(as shown in the 2nd image below, which shows the characteristic peak at the center-frequency of the channel).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I am using &lt;em&gt;GNU Radio Companion 3.7.11.1&lt;/em&gt;, which is fairly new, on Windows 8.1.&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;What cannot be a problem:&lt;/em&gt;&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The RTL-SDR Dongle works. I can run it, for example, without any problems on CubicSDR, where it produces crisp clear sound.&lt;/li&gt;&#xA;&lt;li&gt;Also, I can run a different FM Receiver also made on GNU Radio Companion (though the parameters and scheme of the receiver are different and not quite tuned.)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GNRrv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GNRrv.png&quot; alt=&quot;Output&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Any ideas why there is no sound?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13000" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2020-02-16T13:09:43.217" Title="FM Receiver on GNU Radio with RTL-SDR fails to produce any output sound" Tags="&lt;rtl-sdr&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12836" PostTypeId="2" ParentId="12690" CreationDate="2019-02-15T15:00:54.200" Score="0" Body="&lt;p&gt;Light is a form of radio wave. That type of radio wave travels billions of light years before being received on earth by telescopes.&lt;/p&gt;&#xA;" OwnerUserId="13125" LastActivityDate="2019-02-15T15:00:54.200" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12837" PostTypeId="2" ParentId="12833" CreationDate="2019-02-15T22:40:26.243" Score="2" Body="&lt;p&gt;Indeed, as I suspected this morning, it was the &lt;code&gt;Multiply Const&lt;/code&gt; block. After changing it to accept&amp;amp;work with &lt;code&gt;float&lt;/code&gt;s instead of &lt;code&gt;int&lt;/code&gt;s, I can hear sound.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also as Marcus suggested, I changed the &lt;code&gt;Sample Rate&lt;/code&gt; for the &lt;code&gt;Audio Sink&lt;/code&gt; to &lt;code&gt;48KHz&lt;/code&gt; from &lt;code&gt;24KHz&lt;/code&gt;. But then I noticed that I could only hear every other second. I realized then that the &lt;code&gt;Rational Resampler&lt;/code&gt; &lt;code&gt;Interpolation&lt;/code&gt; rate nees to be double also from &lt;code&gt;24&lt;/code&gt; to &lt;code&gt;48&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Honestly, I don't hear a big difference between &lt;code&gt;48KHz&lt;/code&gt; and &lt;code&gt;24KHz&lt;/code&gt;, but then again, I am not much of an audiophile. :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/44UgI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/44UgI.png&quot; alt=&quot;Image of fixed flow-graph&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13000" LastActivityDate="2019-02-15T22:40:26.243" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12840" PostTypeId="2" ParentId="390" CreationDate="2019-02-16T14:25:48.423" Score="0" Body="&lt;p&gt;The following comments might be of interest to those using base-fed, vertical monopoles:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Medium-wave AM broadcast stations typically use an r-f ground path through a set of 120 x 1/4-wavelength, uninsulated, copper conductors buried radially in the earth, with their common point located directly below the base of their radiators. They also use a series-connected arc gap between the tower base and one or more ground rods buried near the tower base. The gap spacing is set to flash over when the radiator base voltage exceeds the normal value for the modulated peak power at the feedpoint, by a given amount. Also the tower base is connected directly to the ground rod(s) through an r-f choke at the operating frequency, to avoid d-c (static) buildup voltages on the tower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even though their vertical radiators can approach heights of 1,000 feet AGL, such AM broadcast stations continue to operate during nearby lightning events without component damage(s), and without loss of service except for the very short (x-millisecond) intervals when the arc gap flashes over, because protection circuits in their transmitter sense the arc event and kill their r-f output for that time interval. &lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-02-16T15:46:55.520" LastActivityDate="2019-02-16T15:46:55.520" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12844" PostTypeId="2" ParentId="12690" CreationDate="2019-02-18T12:20:34.010" Score="0" Body="&lt;p&gt;Signals that don't bounce or refract are also limited to line of sight propagation.   In other words, your walkie talkie held in your hand can only be heard by other walkie talkies about 3-5 miles away in general, because further than that, the two walkie talkies are over the horizon from each other (i.e., this big rock called the planet Earth is between them).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To overcome this limitation, the height of one or both has to be raised.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So distance is limited by all of these factors (some of these were described well in other answers):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;attenuation of the signal by absorption (air, trees, walls, rocks, etc.)&lt;/li&gt;&#xA;&lt;li&gt;attenuation of the signal by spreading&lt;/li&gt;&#xA;&lt;li&gt;signal to noise ratio (noise from other signals, natural and otherwise, on frequency and on close frequencies)&lt;/li&gt;&#xA;&lt;li&gt;propagation effects (multipath propagation, reflection, refraction, ducting, and horizon)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Each of these factors can be mathematically modeled with equations, but different effects dominate in different situations, so no one equation will give you a distance for all situations.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-02-18T12:20:34.010" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12845" PostTypeId="1" AcceptedAnswerId="12846" CreationDate="2019-02-18T15:28:59.927" Score="4" ViewCount="453" Body="&lt;p&gt;I came across &lt;a href=&quot;http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SolderCoax.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; article about torch soldering PL-259 coax connectors.  It seemed like a good idea since the body needs a lot of heat to get solder to flow into the holes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a little vague when describing the soldering technique for soldering the braid.  It says to heat the area between two holes and after about 10 seconds the solder will flow.  The problem is I can't get the solder near the holes before the flame of my little butane torch melts it away.  So then I tried pulling the torch away just before bringing the solder in.  But the solder won't melt unless the barrel is super hot.  And then it only flows for a second.  Afterwords I'm left with an overheated barrel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like a catch 22.  In order for the barrel to be hot enough to flow solder it also has to be hot enough to melt coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A large iron directly on the hole seems a little more focused.  But then the solder won't flow very far past the immediate opening of the hole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe I'm missing something about the technique.&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="8717" LastEditDate="2019-02-18T21:50:42.313" LastActivityDate="2019-12-15T15:31:50.423" Title="Soldering PL-259.. with a torch?" Tags="&lt;coaxial-cable&gt;&lt;pl259-so239-connector&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12846" PostTypeId="2" ParentId="12845" CreationDate="2019-02-18T17:16:18.557" Score="8" Body="&lt;p&gt;Our friends in the UK and other parts of the world are now wondering how you could even begin to solder a PL259 connector with a torch (aka flashlight)! But in their vernacular, you of course are referring to a burning torch. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, when you heat a metallic object with the hopes of applying solder, the heat will cause oxidation to form on the metallic surfaces. This will frustrate the application of solder. A better technique is to prepare the mating surfaces with a paste type electronics flux prior to heating the surfaces. Make certain to use a flux rated for electronic components to avoid conductivity, contamination or future corrosion. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The general issue of how to heat a PL259 connector body has been a topic for decades. There is a delicate balance between applying sufficient heat so as to allow the solder to flow into the holes and the braid without using so much heat so as to melt the dielectric material or the pin support insulator. It is a skill that takes practice to perfect. Be ready to sacrifice some coax and connectors to the learning process. I have had better success soldering silver plated connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One technique to avoid overheating the connector is to apply heat away from a hole while touching the solder to the hole area. As soon as the solder starts to melt, remove the heat and continue to apply solder. There is generally enough residual heat in the body of the connector to allow the solder to flow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people, including me, have had success with not soldering the braid at all. Instead the braid is folded back over the outer jacket of the coax and then the connector body is forcibly screwed on so as to pinch the braid between the outer jacket and the inner threaded part of the connector. This may not be a good solution if the braid is subjected to moisture or high humidity that would promote oxidation of the mating surfaces. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;More recently, crimp type coaxial connectors have overtaken most coaxial cable applications. These have the same or better reliability than solder type connectors. But the key to a successful installation is to have the correct tool, including the right die set, for the job. Here is a picture of such a tool from &lt;a href=&quot;https://www.dxengineering.com/search/part-type/coax-and-wire-connector-crimping-tools/product-line/dx-engineering-ultra-grip-2-crimp-connector-hand-tools-and-tool-kits?autoview=SKU&amp;amp;sortby=Default&amp;amp;sortorder=Ascending&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Engineering&lt;/a&gt; for the larger size coaxial cables:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/D3hOg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/D3hOg.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several vendors of these types of tools. The quality tools are of a ratcheting design with changeable die sets. The connectors that are used with these types of tools look like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Q5XNW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Q5XNW.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you are equipped with the right tools, you will never want to go back to soldered PL259 connectors again.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-18T20:18:16.313" LastActivityDate="2019-02-18T20:18:16.313" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12847" PostTypeId="2" ParentId="12845" CreationDate="2019-02-18T21:44:57.497" Score="5" Body="&lt;p&gt;I've often used a propane torch to quickly &lt;strong&gt;preheat&lt;/strong&gt; PL259s, but seldom for the actual soldering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once the connector is preheated, it is a quick and simple matter to flow solder into the holes and the &lt;em&gt;pre-tinned&lt;/em&gt; braid using a 50 watt soldering iron.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(These days I use a &lt;a href=&quot;http://www.steinel.net/Professional-Heat-Guns&quot; rel=&quot;noreferrer&quot;&gt;Steinl heat gun&lt;/a&gt; instead of the torch flame for preheating, as it gives much better control over the temperature.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This method minimizes the damage to the plastic dielectric and outer jacket.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-02-18T21:44:57.497" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12848" PostTypeId="1" AcceptedAnswerId="12849" CreationDate="2019-02-19T02:12:48.853" Score="7" ViewCount="248" Body="&lt;p&gt;If, as an amateur radio operator, you're licensed in one country with a callsign,  let's suppose, the US and you migrate to, say, Germany, will you have to reapply and obtain a new callsign?&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;What if your migration is temporary, and you're only living there for a few years — can you continue using your old callsign?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What if it's permanent? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="14220" LastEditDate="2019-02-19T22:12:24.780" LastActivityDate="2019-02-19T22:12:24.780" Title="What happens to your callsign if you migrate?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;callsign&gt;&lt;germany&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12849" PostTypeId="2" ParentId="12848" CreationDate="2019-02-19T10:19:15.303" Score="11" Body="&lt;p&gt;I have done exactly that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had a US amateur extra class license when I moved to Germany. As a legal resident of Germany, I applied for and received a reciprocal (no test required) German license with the call DJ0IQ. Yes, it was a requested/vanity call sign to match my US call. The good folks at &lt;a href=&quot;https://www.darc.de/home/&quot; rel=&quot;noreferrer&quot;&gt;DARC&lt;/a&gt; (the German equivalent to ARRL) helped me with that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;During the time I lived in Germany, I retained my US W9IQ license since the only requirement to do so was to have a valid US mailing address in my &lt;a href=&quot;https://apps.fcc.gov/coresWeb/simpleSearch.do&quot; rel=&quot;noreferrer&quot;&gt;FRN&lt;/a&gt; profile with the FCC. I could have retained my US license indefinitely this way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I would visit the US, the FCC regulations required me to use my US call sign. When I was travelling outside of Germany and the US, I could use the call sign most suitable to the situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I moved back to the US several years later, I again updated my mailing address in my FRN profile and resumed operating with my US call.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While living in Germany, look up your local ham radio club - DARC maintains a list. It is a great way to meet local hams and get into local ham radio activities. The are also a number of ham radio swapfests in Germany. Check out your local ham radio dealer as well. I lived within 30 minutes from &lt;a href=&quot;https://www.wimo.com/uebersicht-funkgeraete_d.html&quot; rel=&quot;noreferrer&quot;&gt;WiMo&lt;/a&gt; so I was a regular in their store. They even casually offered me a position at one point because they needed someone with strong English skills to support their international growth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A nice, technically oriented, monthly ham radio magazine in Germany is &lt;em&gt;&lt;a href=&quot;https://www.funkamateur.de&quot; rel=&quot;noreferrer&quot;&gt;FUNKAMATEUR&lt;/a&gt;&lt;/em&gt;. You can pick it up in all book/magazine shops in Germany.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oPw7q.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oPw7q.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More generally, anyone that can pass an authorized US amateur radio license exam may hold a US amateur radio license. There is no requirement to be, to become, or to ever have been, a resident of the US. You must, however, have a valid US mailing address in your FRN. Many non-residents simply use the mailing address of a friend, a colleague, or a mail forwarding service. I knew several European hams that held US amateur radio licenses under these circumstances.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-19T13:40:53.817" LastActivityDate="2019-02-19T13:40:53.817" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12850" PostTypeId="1" AcceptedAnswerId="12852" CreationDate="2019-02-19T19:37:16.997" Score="2" ViewCount="345" Body="&lt;p&gt;When I was watching television, especially when I was younger, I sometimes heard a loud noise, followed by either a test message, or a genuine emergency  broadcasts, like an Amber alert.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first signal sounded like short bursts of packets,  which usually lasted around 1100 ms.  Then there was another 1100 ms pause, and then it would repeat an additional two or three times.  Sometimes these bursts are shorter, like around 300 ms long, but the pause is about the same length.  Most of the time I would also hear a combination of 853 Hz and 960 Hz tones. I am assuming this is the attention signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since this was before June 12, 2009, I was using over the air analogue television, also known as the national television standards committee (NTSC). Also, I think the encoded marker is also known as a tail preamble.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What devices are able to read these messages and display them as text?     &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13927" LastEditorUserId="873" LastEditDate="2019-02-20T02:15:41.900" LastActivityDate="2020-12-25T05:29:26.290" Title="What devices are able to decode the EAS SAME headers, attention signal, and encoded marker?" Tags="&lt;united-states&gt;&lt;digital-modes&gt;&lt;emergency&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12851" PostTypeId="2" ParentId="6140" CreationDate="2019-02-20T01:42:57.980" Score="1" Body="&lt;p&gt;1:1 baluns or current chokes may be VERY important on receive and then there are many options. If an antenna should be used also for transmit there are fewer options.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Simply wind two conductors together over some sort of core&quot; is very good for&#xA;receive - but the bandwidth becomes limited.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look 9:55 here:&lt;a href=&quot;http://sm5bsz.com/videos/sensors-part3.mp4&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://sm5bsz.com/videos/sensors-part3.mp4&lt;/a&gt; until at&#xA;least 15 minutes into the video. A narrowband conversion from unbalanced&#xA;to balanced is trivial, but a wideband conversion is surely possible  -&#xA;although not quite as trivial.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case you want the antenna for transmit as well as for receive, a wideband&#xA;solution with high isolation against common mode currents over a very large&#xA;bandwidth is non-trivial.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question:&#xA;Do you really want the same antenna for receive as for transmit?&#xA;(The answer should be NO on all frequencies except for 144 MHz where&#xA;sky temperature is similar to room temperature.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For receive on HF, efficiency is insignificant while common-mode&#xA;suppression might be VERY important. For transmit, efficiency is all&#xA;that counts - although common-mode suppression could affect RFI in&#xA;HIFI equipment owned by neighbours.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On 1296 MHz you would want different feeds on your parabola for Rx&#xA;and Tx. For Tx you would want maximum gain, for Rx you would want&#xA;maximum G/T. It is not really difficult to arrange for this. On lower&#xA;frequencies one wants maximum far field on Tx (in a certain direction)&#xA;while one wants minimum interference pick-up from other directions&#xA;on receive. That is a very different problem because receiver noise&#xA;is a no-issue on receive - the sky temp is far above any decent&#xA;amplifier noise temp. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the serious operator it will be a good idea to use different&#xA;antennas for transmit and receive (on bands where the sky temperature&#xA;differs significantly from room temperature.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;/Leif&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a larger bandwidth one can connect two such current chokes in series.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-02-20T01:42:57.980" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12852" PostTypeId="2" ParentId="12850" CreationDate="2019-02-20T02:42:25.553" Score="5" Body="&lt;p&gt;Yes, what you are hearing is digital data encoded into the audio stream. These can be decoded by devices that understand the digital data, such as a dedicated &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B00176T9OY&quot; rel=&quot;noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;weather radio&lt;/a&gt; like this one that came up in an Amazon search:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4Av39.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4Av39.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The audio signal &lt;em&gt;does&lt;/em&gt; catch the attention of people because it sounds kind of like a warning buzz. But that is a secondary benefit, its primary purpose is to transmit the digital information about what kind of weather alert is coming up where.&lt;/p&gt;&#xA;" OwnerUserId="1183" LastActivityDate="2019-02-20T02:42:25.553" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12856" PostTypeId="1" CreationDate="2019-02-21T17:34:39.607" Score="2" ViewCount="917" Body="&lt;p&gt;I need dvbt2 transreceiver.&#xA;I tried gnuradio with &lt;a href=&quot;https://github.com/BogdanDIA/gr-dvbt&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/BogdanDIA/gr-dvbt&lt;/a&gt;.&#xA;The &quot;apps/dvbt_tx.grc&quot; is working.&#xA;But, video cannot transfer flexibly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On gnuradio flow, I adjust multiple const value, and &lt;strong&gt;tx gain&lt;/strong&gt; of limeSDR-mini sink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, video transfer is not good.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How I can convert &lt;strong&gt;video.mp4&lt;/strong&gt; to &lt;strong&gt;adv8dvbt34.ts&lt;/strong&gt;?&lt;/li&gt;&#xA;&lt;li&gt;Why &quot;multiple const&quot; used before LimeSdr sink?&lt;/li&gt;&#xA;&lt;li&gt;How do I transfer videos flexibly?&lt;/li&gt;&#xA;&lt;li&gt;Is there dvbt/dvbt-2 receiver?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="14307" LastEditorUserId="14307" LastEditDate="2019-02-21T17:40:22.097" LastActivityDate="2019-02-21T18:12:19.370" Title="How I can build dvb-t/dvb-t 2 transceiver?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="12857" PostTypeId="2" ParentId="12856" CreationDate="2019-02-21T17:59:52.210" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there dvbt/dvbt-2 receiver?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes and no: T2 reception is too computationally hard so far. It's work in progress, but it's almost certain that your average PC can't decode full standard T2 rates in real time on its CPU. The channel coding is just too involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transmission is always computationally easier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;code&gt;gnuradio/gr-dtv/&lt;/code&gt; example flowgraphs.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why &quot;multiple const&quot; used before LimeSdr sink?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;To adjust the amplitude – that's what the multiplication with a constant does.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How I can convert video.mp4 to adv8dvbt34.ts?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;FFMPEG can be used to convert video file containers to MPEG transport streams. You need to &lt;em&gt;exactly&lt;/em&gt; use the same bit rate as your DTV transmission chain uses for the transport stream.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How do I transfer videos flexibly?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Stretch multiple times daily and make sure to train hard so that you'll be the most flexible user of GNU Radio in existence. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;No seriously, &quot;flexibly&quot; doesn't tell me anything about what you need.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-02-21T18:12:19.370" LastActivityDate="2019-02-21T18:12:19.370" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12859" PostTypeId="1" AcceptedAnswerId="12860" CreationDate="2019-02-22T21:00:22.797" Score="0" ViewCount="60" Body="&lt;p&gt;Can a laser  be used as an antenna? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can a beam of any type extend transmission distance of an electromagnetic field? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://medium.com/starts-with-a-bang/this-is-why-the-2018-nobel-prize-in-physics-for-lasers-is-so-important-21bef2dab7d8&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://medium.com/starts-with-a-bang/this-is-why-the-2018-nobel-prize-in-physics-for-lasers-is-so-important-21bef2dab7d8&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5840" LastEditorUserId="5840" LastEditDate="2019-02-22T21:55:39.523" LastActivityDate="2019-02-22T22:19:50.887" Title="Can radio waves be made to travel as or along a particle beam?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;frequency&gt;&lt;transmitter&gt;&lt;physics&gt;" AnswerCount="1" CommentCount="14" ClosedDate="2019-02-22T21:19:30.597" ContentLicense="CC BY-SA 4.0" />
  <row Id="12860" PostTypeId="2" ParentId="12859" CreationDate="2019-02-22T22:19:50.887" Score="3" Body="&lt;p&gt;Light waves and RF waves are both electromagnetic radiation. The only difference is that we can see the narrow band of frequencies that we call light.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a common misconception that laser irradiance does not follow the inverse square law that describes the irradiance of an antenna. But in fact, they are exactly the same. The only difference is that the laser has a huge boost in initial intensity compared to an antenna. But thereafter, the laser irradiance decays following the same inverse square law.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The stark difference in initial intensity and the much higher frequency of the laser compared to typical RF systems makes it an attractive candidate to use for long distance, high speed communications. These facts have not escaped NASA's and the JPL's attention.   An experimental system, dubbed &lt;a href=&quot;https://www.nasa.gov/mission_pages/station/research/experiments/861.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;OPALS&lt;/a&gt; (optical payload for lasercom science) has been used to transmit images from a ground station to the ISS. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;OPALS used a simple 50 megabit OOK (on off keying) modulation with a forward error correction code to transmit video files. The signal is therefore a 50 MHz modulation of a 1,550 nanometer carrier. No different than an RF transmitter other than the use of much higher frequencies.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-02-22T22:19:50.887" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12861" PostTypeId="1" CreationDate="2019-02-23T00:17:45.037" Score="1" ViewCount="142" Body="&lt;p&gt;I am asking on behalf of my friend who is not on this site. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My friend wants to know the nomenclature behind the licence   Amateur extra, since they think that that term is misleading.  I think  my friend  means that the term amateur  in front of extra  is what makes  it sound as if it were less than what it was supposed to be.  General is somewhere in between, and technician sounds so advanced that somebody with that license would be able to repair radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My friend said that they liked the older licensing system better because the name corresponded with the level of expertise.   &lt;/p&gt;&#xA;" OwnerUserId="13927" LastActivityDate="2019-02-23T23:19:43.700" Title="Why do some of the amateur radio license names imply something different than what it actually is?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12862" PostTypeId="2" ParentId="12861" CreationDate="2019-02-23T02:07:11.860" Score="3" Body="&lt;p&gt;If your friend likes the &quot;old&quot; license classes, then he or she should like the Amateur Extra class because it has its origins in the earliest years of amateur radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the early 1920s, there were two classes of licenses, the highest of which was Amateur First Grade that required passing a basic code test and an essay type written test. Then in the mid 1920s, the Department of Commerce (pre FCC) started to issue a higher class of license that required a 20 WPM code test and a more comprehensive written test. The new license class was named Amateur Extra First Grade with the Extra cannoting more privileges. Thus began the &quot;Extra&quot; class license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the prevailing years, the First Grade designation was dropped as licenses were restructured but the Amateur Extra designation remained. I believe, however, there was a period where the top license was called Class A. To this day, &quot;Extra&quot; remains the highest class of license with the most privileges.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-23T02:32:00.060" LastActivityDate="2019-02-23T02:32:00.060" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12863" PostTypeId="2" ParentId="12827" CreationDate="2019-02-23T05:40:05.507" Score="2" Body="&lt;p&gt;You do have an unregulated supply .This issue has been raised by others .You can reduce hum by increasing Your total filter Capacitance .The ripple volts is inversly proportional to Total Capacitance .If you have Caps on hand then why not add these to what you already have .Large numbers of small caps will work fine .You could also resolve the Hum issue by using LC filtering which means a choke that will handle the current .&lt;/p&gt;&#xA;" OwnerUserId="6095" LastActivityDate="2019-02-23T05:40:05.507" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12865" PostTypeId="2" ParentId="12861" CreationDate="2019-02-23T15:53:21.677" Score="1" Body="&lt;p&gt;I believe that your friend is missing the definition of &quot;Amateur&quot;. With respect to all three classes currently available ( and now extinct classes who still have members ) , Amateur only refers to the fact that none of us can be paid to perform [ with very specific exceptions ]. It has absolutely nothing to do with the professionalism or lack thereof of the operator , just if they can get renumeration. I could use an analogy of Amateur sports v.s. Professional sports. A kid that can dazzle and shoot hoops can be just as skilled as a pro-player for a pro-team , he just doesn't get paid. For the kid , it's circumstance , for us it's in the rules.&lt;/p&gt;&#xA;" OwnerUserId="14102" LastActivityDate="2019-02-23T15:53:21.677" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12866" PostTypeId="1" CreationDate="2019-02-23T16:56:41.950" Score="9" ViewCount="625" Body="&lt;p&gt;I am currently studying for the Technician Exam and have come across an answer to a question I think is ridiculous. The question is: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why do VHF/UHF signals usually travel somewhat farther than visual line-of-sight distance between two stations?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The given &quot;correct&quot; answer is, &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Because the Earth seems less curved to radio waves than to light.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Come on, there are much better answers than that and one does not even have to go into the duality of particles and waves. My question is, asking a ham expert, what would be a better answer to this question?&lt;/p&gt;&#xA;" OwnerUserId="14182" LastEditorUserId="4076" LastEditDate="2019-02-23T21:12:33.160" LastActivityDate="2019-02-27T14:52:24.857" Title="Better explanation for beyond-line-of-sight VHF signal reach than &quot;lower curvature to radio waves&quot;" Tags="&lt;propagation&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12867" PostTypeId="2" ParentId="12866" CreationDate="2019-02-23T22:00:47.010" Score="7" Body="&lt;p&gt;The full question, and possible answers:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;T3 C11&lt;br&gt;&#xA;  Why do VHF and UHF radio signals usually travel somewhat farther than the visual line of sight distance between two stations?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;A. Radio signals move somewhat faster than the speed of light&lt;br&gt;&#xA;  B. Radio waves are not blocked by dust particles&lt;br&gt;&#xA;  C. The Earth seems less curved to radio waves than to light&lt;br&gt;&#xA;  D. Radio waves are blocked by dust particles&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Of these, &lt;em&gt;C&lt;/em&gt; is the only answer that makes any kind of sense. Arguably, one could take issue with the phrasing of the answer, because radio waves have no consciousness, and so nothing can &quot;seem&quot; anything to them. However, atmospheric refraction does bend the relatively low frequencies (compared to visible light) of VHF and UHF to a greater extent, and it's in human nature to transform our observations into impossible reference frames to more intuitively reason about the world. If your eyes could see in RF you would indeed see farther which means the Earth is effectively less curved, so even if it's an impossible scenario, it holds up to simple intuition and reason.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trying to simplify a complex interaction of atmospheric conditions and electrodynamics into a single sentence question and answer in simple language is bound to generate some degree of disagreement about the single &quot;best&quot; sentence that captures the situation, and going to require some reasonable assumptions to be made. The best we can hope is that one of the four proposed answers is obviously correct, while the other three are obviously wrong, and by that standard, this question seems fine to me.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-02-23T22:00:47.010" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12868" PostTypeId="1" CreationDate="2019-02-23T23:07:59.050" Score="3" ViewCount="1459" Body="&lt;p&gt;The screen reset to Chinese characters. How do I get it back to English? I haven’t found any information on this problem.&lt;/p&gt;&#xA;" OwnerUserId="14332" LastEditorUserId="4076" LastEditDate="2019-02-23T23:26:47.647" LastActivityDate="2021-03-28T23:44:54.510" Title="Baofeng DM-1801 DMR: Language switched to Chinese" Tags="&lt;baofeng&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12869" PostTypeId="2" ParentId="12866" CreationDate="2019-02-23T23:15:49.250" Score="7" Body="&lt;p&gt;Please accept Phil's answer. It's the sanest one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, however to answer:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;what would be a better answer to this question?&lt;/p&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;Why do VHF/UHF signals usually travel somewhat farther than visual line-of-sight distance between two stations?&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Because they are not the same as light; first of all, they aren't blocked by things like a thin cotton sheet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hear me muttering to myself:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Ok, you know exactly how that question was meant; don't be an arse:&lt;/p&gt;&#xA;  &#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;Why can VHF/UHF waves be detected when no straight line through an RF-transparent medium connects emitter and receiver?&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Because beam optics don't apply here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that the assumption that light forms perfectly straight beams is actually wrong; it just looks that way because the wavelength of visible light, which is an electromagnetic wave just like radio waves, is in the nanometers, and hence, most effects that we can observe in lights are well-modeled with a model of light following a straight beam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, that's just a justifiable simplification under the assumption that&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;all structures interacting with the wave are way, way larger than the wavelength&lt;/li&gt;&#xA;&lt;li&gt;the medium (air, for example) through which the wave travels is homogenous, and works the same no matter in which direction you travel through it&lt;/li&gt;&#xA;&lt;li&gt;the sensitivity with which we look at light phenomena is low enough for us to ignore the effects that can't be explained by the model (this applies to any model of the world, by the way)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;h1&gt;Large-scale-ness (Assumption 1)&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;To illustrate 1.: Maybe you've done slit experiments with light: Make a really, really narrow slit and place it between a source of light and a screen. You'll see that light really doesn't need a straight path to travel. Also, you'd ideally be able to observe interference effects on the screen, ie. not only light in places that should be dark, but also regular patterns of brightness fluctuating. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you need a &lt;em&gt;really&lt;/em&gt; narrow slit to make this work visibly well (or even better, a lot of identical slits in equal distance, to make the effect stronger).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Same applies to radio waves and the earth: Say your UHF signal has a wavelength in the order of &quot;single-digit meters&quot;. The earth has a radius of 6370 km. It's &quot;huge enough&quot; compared to the wavelength that radio waves, just like light, wouldn't &quot;reach beyond the horizon&quot;, **iff* there was no atmosphere around earth.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Homogenous, anisotropic Medium (Assumption 2)&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Now here's the thing: if the earth is really large-scale compared to UHF waves, the optical propagation model would work, and we shouldn't be able to receive things from a place to which a straight line goes through the earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the atmosphere doesn't play along here, at all: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the lower end, it's limited by earth, or actually, globally, more often by seawater, which is at least partially a pretty well-reflecting surface for radio waves. On the upper end, we get the ionosphere, and troposphere and whatsitcalledsphere; basically, you get a refraction that &quot;bends&quot; the beam towards the earth just enough to make it &quot;cling&quot; to earth's surface a little more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I've writtne an advanced high-school physics level explanation for that &lt;a href=&quot;https://ham.stackexchange.com/questions/9854/communications-ground-wave-propagation/9856#9856&quot;&gt;here&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what we see happen for microwave radio is similar to what happens in a (graded index multimode) optical fiber; the fiber doesn't have to run in a straight line, but a light beam can still pass relatively unhindered through it, by the simple fortune of always being refracted (and reflected) back towards the core of the fiber when it comes closer to the edge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That doesn't make the fiber (earth) any less curved; it's just that macroscopically, the beam follows the curvature. The fact that the curvature isn't &quot;eradicated&quot; by this refractive model can pretty simply be verified by realizing that light still has to travel a distance longer (and hence, for a time measurably longer) than the straight connection between the points. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, yes, I'd consider that answer wrong.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Sensitivity too low to detect the difference to the simpler model (assumption 3)&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;While our eyes are tremendous instruments that can be continuously and smoothly adjusted to different lightning situation, their instantaneous &lt;em&gt;dynamic range&lt;/em&gt; (the ratio of the weakest detectable to the strongest detectable light power) is limited: Numbers differ depending on who examined what, but it's fair to assume doesn't exceed the order of magnitude of 1:1,000,000 (or 60 dB). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With radio receivers, and transmitters, we can be a lot more sensitive by something that light waves don't allow us (because the waves aren't coherent):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can take an arbitrarily long observation and boil it down to a number. (We call the increase in sensitivity &lt;em&gt;processing gain&lt;/em&gt;. I find that name very fitting.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You won't be able to see a lighthouse's atmospherically refracted light at all if the ambient light outshone it, even if you stood right next to it – but with radio receivers, we can suppress the effect of ambient and receiver noise. You can do something like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let the transmitter transmit a &lt;span class=&quot;math-container&quot;&gt;$\cos(2\pi 200\,\text{MHz} t)$&lt;/span&gt; for 1 ms, then a &lt;span class=&quot;math-container&quot;&gt;$-\cos(2\pi 200\,\text{MHz} t)$&lt;/span&gt; (i.e. a 180° phase shifted, or inverted, version of the same carrier), and repeat that pattern for an hour (that's 3,600,000 ms).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If our receiver knows that pattern, it could take all signals from the odd-numbered milliseconds, record them and add them up. Do the same for all the even-numbered milliseconds, but in a separate accumulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you get two different &quot;sum-recordings&quot;, each with 1,800,000 summed up cosine segments, one with all the +cos, the other with all the -cos. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the two bins don't look like cosines at all, then you pretty certainly only noise with no cosines &quot;hidden&quot; in it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the one bin, however, looks like a cosine, and the other like a minus-cosine, then you can say with high certainty that you  received the transmitter's signal. The same-phase cosines just added up constructively – you made a cosine with amplitude of 1.8 million out of a cosine with amplitude 1. The noise can't add up as much; the math is relatively easy here: If we say a cosine with amplitude 1 has power &lt;span class=&quot;math-container&quot;&gt;$P$&lt;/span&gt;, then a cosine with an amplitude of &lt;span class=&quot;math-container&quot;&gt;$A\cdot 1$&lt;/span&gt; has power of &lt;span class=&quot;math-container&quot;&gt;$A^2 \cdot P$&lt;/span&gt;, i.e. you see a power increase in the sum signal of &lt;span class=&quot;math-container&quot;&gt;$1\,800\,000^2$&lt;/span&gt;. Uncorrelated noise's power adds up – so the power increase of the noise is &quot;only&quot; &lt;span class=&quot;math-container&quot;&gt;$A$&lt;/span&gt;, not &lt;span class=&quot;math-container&quot;&gt;$A^2$&lt;/span&gt;; hence, the signal-power-to-noise-power ration (SNR) of the sum is &lt;span class=&quot;math-container&quot;&gt;$\frac{A^2}{A}=A$&lt;/span&gt; times better than that of the original single observation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's a pretty crass thing – and it's the reason modes like WSPR or things like GPS work so robustly – your GPS receiver might work with a 4-bit ADC, that means the weakest-to-strongest instantaneously discriminatable signal rate, i.e. the dynamic range is just 16, even ignoring that one bit should actually be the sign of the received signal. GPS signals are usually significantly below noise floor – i.e., they have a negative SNR (in dB). Still, GPS works well! GPS receivers know the pattern in the signal sent by the satellites, and they add it up over a long time, which lifts the signal out of noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This all is just to illustrate that we have it much easier, because it's just such a standard thing to do, to detect sub-ambient RF signals than light signals; hence, it's easier to notice that things don't work like in the nice and simple optical (beam) model.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Answer&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Because we're breaking the assumptions necessary for modelling electromagnetic waves as beams, we can't make any statements based on a beam-based model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Especially, emitted energy does reach beyond the horizon due to &lt;em&gt;wave&lt;/em&gt; (as opposed to ray) propagation effects such as refraction, diffraction and reflection.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-02-24T00:22:12.787" LastActivityDate="2019-02-24T00:22:12.787" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12870" PostTypeId="2" ParentId="12861" CreationDate="2019-02-23T23:19:43.700" Score="2" Body="&lt;p&gt;A technician is someone trained to perform a set of procedures. Performing a procedure on a technological thing is not the same thing as understanding the technology.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, anyone can enlist in the Air Force and in less than a year, become an aircraft maintenance &lt;em&gt;technician&lt;/em&gt;. The job involves following prescribed test procedures, then turning bolts and screws in the proper direction to replace the parts that the procedure says require replacement. Job qualifications involve basic mechanical and deductive reasoning, but most importantly a capacity to &lt;em&gt;follow directions&lt;/em&gt;. It's superficially impressive that technicians get to work on the most technologically advanced flying killing machines in the world, but really it's mundane, uncreative work that's been developed and documented to be as simple as possible so any grunt can do it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But a technician is not an aeronautical engineer. The engineer will hold a higher degree, get paid more, have a deeper understanding of how the aircraft works, get to do creative things like design new aircraft, and create the service manual that tells the technicians what to do. One can't simply show up at an Air Force recruiting center and become an aeronautical engineer: it takes years of school, then even more years of job experience to be successful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most &quot;technician&quot; jobs don't even involve repairing things. A lab technician might spend their time loading fecal samples into a centrifuge, for example. Don't let the lab coat fool you: this is not highly advanced work: it's putting turds in tubes, loading them in a machine, and pressing a button while ensuring the labels don't get mixed up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So &quot;technician&quot; as a license class implies just what it is: the lowest possible qualification to operate amateur radio equipment. The technician exam is much more about operating procedures than it is about understanding how radios work, just like the lab technician's training is much more about how to spin turds really fast than it is understanding the biochemistry to develop a colon cancer treatment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for &lt;em&gt;amateur extra&lt;/em&gt;, the inclusion of &quot;amateur&quot; shouldn't diminish anything as all the classes in question are classes of &lt;em&gt;amateur&lt;/em&gt; radio license. As Glenn W9IQ notes, &quot;amateur&quot; is included in that title mostly for historic reasons. And as ASzy notes, &quot;amateur&quot; means unpaid, not sub-par.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-02-23T23:19:43.700" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12871" PostTypeId="1" AcceptedAnswerId="12876" CreationDate="2019-02-24T01:46:56.560" Score="1" ViewCount="1072" Body="&lt;p&gt;I have two 10-meter masts to support a 40-meter inverted L.  I have a decent enough sized yard that I have a few options for counterpoise/ground/radial.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could run 1/4 wave radials in several directions along the ground/just below the surface and feed the inverted L just a few feet off the ground, giving me a longer vertical section.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option I'm considering is feeding the inverted L at a height of about 10 feet, giving me a 20+ foot vertical section, along with elevated wires at about 10 feet to give me a handful of elevated radials.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, I could use a folded counterpoise, which, I admit, I am not very familiar with.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've heard that a few elevated radials is a better, or at least as good an option as many ground radials, and that seems to be the easier option too, and so I'm leaning toward that option.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thoughts?  Thanks.&lt;/p&gt;&#xA;" OwnerUserId="9772" LastEditorUserId="76" LastEditDate="2019-04-13T20:35:35.587" LastActivityDate="2019-04-13T20:35:35.587" Title="Counterpoise/ground/radial options for an Inverted L" Tags="&lt;wire-antenna&gt;&lt;grounding&gt;&lt;counterpoise&gt;&lt;earth&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12872" PostTypeId="2" ParentId="12868" CreationDate="2019-02-24T02:21:25.513" Score="4" Body="&lt;p&gt;According to the &lt;a href=&quot;https://fccid.io/2AJGM-DM1801/User-Manual/User-manual-4125309&quot; rel=&quot;nofollow noreferrer&quot;&gt;manual&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This radio supports both Chinese and English language. The menu functions as follows: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Press [MENU] to enter menu mode. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Press [ ]/ [ ] to set, then press [MENU] to select. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Press [ ]/ [ ] to the radio setting, then press [MENU] to select. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Press [ ]/ [ ] to language selection, then press [MENU] to select. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Press [ ]/ [ ] to select the corresponding language, then press [MENU] to select. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The screen shows the language selected and returns to the main screen.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="76" LastEditDate="2019-02-24T16:22:03.880" LastActivityDate="2019-02-24T16:22:03.880" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12874" PostTypeId="2" ParentId="12871" CreationDate="2019-02-24T12:01:58.093" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/9823/how-does-the-performance-of-elevated-radials-differ-from-that-of-buried-radials/9824#9824&quot;&gt;Here is another answer on this site about buried vs. elevated radials&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="8717" LastEditDate="2019-02-24T19:13:55.353" LastActivityDate="2019-02-24T19:13:55.353" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12875" PostTypeId="2" ParentId="6325" CreationDate="2019-02-24T13:28:05.937" Score="3" Body="&lt;p&gt;Please see my graphic below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A λ/2, center-fed dipole has about 0.7 dB more gain than a λ/4 ground plane, but otherwise their v-pol, free-space radiation patterns are very similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether the vertical conductor of a λ/4  ground plane is pointing to the zenith &lt;strong&gt;&lt;em&gt;or&lt;/em&gt;&lt;/strong&gt; the nadir, its radiation toward the earth would produce nearly the same reflections from the earth (other things equal).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So its net, far-field radiation patterns would be very similar for &lt;strong&gt;&lt;em&gt;both&lt;/em&gt;&lt;/strong&gt; installation configurations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MmJf0.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MmJf0.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-02-24T13:28:05.937" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12876" PostTypeId="2" ParentId="12871" CreationDate="2019-02-24T17:33:27.760" Score="1" Body="&lt;p&gt;Either elevated radials, or radials lying on the ground or buried just below the surface can work just fine. The difference usually comes down to what's more convenient to install.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would not recommend a folded counterpoise, or any other kind of counterpoise which is not simply a straight wire unless you are constrained by space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Elevated radials have the advantage of requiring fewer (as few as 2 can work pretty well) and being effective even if soil conductivity is extremely poor. They have the disadvantage of requiring something to support the ends, presenting a hazard to pedestrians or vehicles if they can't be mounted high enough, and they must be a quarter wavelength long to be effective, making them less desirable for multiband antennas. It's possible to have multiple sets of radials each tuned for a different band, but of course this negates some of the advantage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radials on the ground or buried have the advantage of not requiring any support structure, being out of the way and relatively protected from damage, and their length is not critical so they work for multiband antennas. However, at least 16 are typically required for good performance, and they require at least moderate soil conductivity so extremely rocky, dry areas may not perform well without a much higher number of radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You say you have two 10-meter masts for a 40-meter antenna. I'd like to point out these masts are probably tall enough for a straight, 1/4 wave monopole which will be more efficient than an inverted-L. If you can place the two masts a half-wavelength apart, you could also string a dipole between them and get good performance without any radials at all.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-02-24T17:33:27.760" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12877" PostTypeId="1" CreationDate="2019-02-25T00:11:35.020" Score="1" ViewCount="42" Body="&lt;p&gt;I can hear vertical local signals (not skip) on my horizontal yagi, and when i point it at them their signal goes up, so my horizontal yagi has some gain for vertical signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the vertical transmitting antennas in the distance were infinitely thin with no width, and my horizontal yagi was infinitely thin with no height, and there were no reflections, could i receive the vertical signals ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so there must be some attenuation so what is it ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the fact that i can hear vertical signals on my horizontal yagi only because it does have some height and therefore does respond a bit to vertical signals, and because it's probably receiving reflected signals which started out as being vertical but whos polarization changed along the way ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Someone please help before I become a once vertical dude who went horizontal because his brain exploded because he couldn't work it out !!!&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-02-25T18:46:05.100" Title="Would an infintely thin horitzontal yagi with zero height respond to vertical signals?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12878" PostTypeId="1" AcceptedAnswerId="12882" CreationDate="2019-02-25T00:24:25.950" Score="3" ViewCount="1887" Body="&lt;p&gt;How much difference does a metal pole make when it's sitting in the middle of all the lower elements of my beautiful new highly optimized to the max YO.EXE 10 m yagi ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I get it that the closeness of the pole will mess up the impedance a bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the elements are still there in the right place with the right length constructively adding to and destructively subtracting from the incoming signals (for example) and after a few tests it seems that a metal pole makes less difference that you might think.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it just affect the radiation pattern in the elevation plane ? Can anyone tell me if actually a metal pole which only goes up to the boom lowers the angle of radiation .. imagine that ! a rare case of owning an antenna cake and eating it at the same time :o&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-02-25T03:17:44.697" LastActivityDate="2019-02-27T17:08:49.250" Title="What happens to a vertical Yagi when you mount it on a vertical metal pole?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12879" PostTypeId="1" AcceptedAnswerId="12883" CreationDate="2019-02-25T00:34:21.053" Score="2" ViewCount="256" Body="&lt;p&gt;Can someone tell me what dB gain over an isotropic radiator means?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say I have a 3 element vertically polarized 10 m Yagi (which I do) which is meant to have 7.5 dBi gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which of the following is correct?&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;If I measure the signal strength 1 km away in line with the boom in the direction in which the Yagi is pointing, and in exactly the same plane as the elements, and then compare that to the signal from an isotropic radiator, the yagi will have a signal which is 7.5 dB stronger.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If I do a 3 dB azimuth plot of both antennas and then compute the surface area of both plots and relatively compare them in dB, then I get 7.5 dB difference.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If I do a 3 dB 3 dimensional plot of both antennas a then compute the Volume of both and compare them in a relative way then I get 7.5 dB.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some other method I don't know about yet.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-02-27T04:21:48.427" LastActivityDate="2019-02-27T17:40:33.490" Title="What does dBi mean?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12880" PostTypeId="1" CreationDate="2019-02-25T00:39:21.653" Score="0" ViewCount="881" Body="&lt;p&gt;For a yagi antenna for example, what does front to back ratio mean exactly ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it mean the reverse gain at 90 deg behind the antenna compared to the forward gain at 90 deg in front of the antenna ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or does it mean the average or combined gain from 0 - 180  deg behind compared to 0 - 180 deg in front of the antenna ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or the max gain in the forward direction regardless of angle compared to the maximum gain in the reverse direction regardless of angle ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or is it a 3 dimensional thing ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-02-25T05:43:36.700" LastActivityDate="2019-02-25T16:47:39.910" Title="What EXACTLY does front to back ratio mean?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12881" PostTypeId="2" ParentId="12879" CreationDate="2019-02-25T02:09:23.587" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I measure the signal strength 1 km away in line with the boom in the direction in which the Yagi is pointing, and in exactly the same plane as the elements, and then compare that to the signal from an isotropic radiator, the yagi will have a signal which is 7.5 dB stronger.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is correct. The others are incorrect; antenna gain is always considered in some specific direction, and if you sum it up all around then you have thrown out the information about directivity and the number you have left is only the antenna &lt;em&gt;efficiency&lt;/em&gt; (how much power it transmits vs. turning into heat).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-02-27T17:40:33.490" LastActivityDate="2019-02-27T17:40:33.490" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12882" PostTypeId="2" ParentId="12878" CreationDate="2019-02-25T03:13:35.753" Score="4" Body="&lt;p&gt;Mounting a vertically-polarized Yagi on a vertical conductive mast usually screws up the pattern. You either have to use a non-conductive mast, or offset them from it with a horizontal boom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;40 years ago, Cushcraft sold an 11 element beam designed for 146 MHz. Not realizing this, I (and countless other hams) mounted it on top of a steel mast. That caused so many extra lobes that it made a better omnidirectional antenna than my ground plane! It still had a useful forward lobe, but those that mounted it as described above had a much cleaner pattern.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-02-25T03:13:35.753" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12883" PostTypeId="2" ParentId="12879" CreationDate="2019-02-25T04:16:47.597" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I measure the signal strength 1 km away in line with the boom in the direction in which the Yagi is pointing, and in exactly the same plane as the elements, and then compare that to the signal from an isotropic radiator, the yagi will have a signal which is 7.5 dB higher.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Theoretically correct. In practice you'll have some trouble actually performing this measurement. Firstly, isotropic radiators don't exist. Secondly, if the specified gain of 7.5 dBi is in free space, the antenna installed over ground will have different characteristics. The location of the mast or tower on which the antenna is mounted, feedline, and other nearby antennas can also perturb the pattern, sometimes very significantly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your other two examples seem to involve in some way integrating the power radiated by the antenna over all possible directions. You'll find most antennas likely to be used for amateur radio transmitting will give about the same total power as an isotropic radiator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason should be fairly intuitive considering the law of conservation of energy: if a directional antenna radiates more strongly in a particular direction, it must radiate less strongly in some other direction. To do otherwise would require creating additional energy from somewhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The relevant metric comparing total power radiated in all directions is called antenna &lt;em&gt;efficiency&lt;/em&gt;. It's not difficult to achieve efficiencies above 99%. Consider a simple wire dipole: the wire has very low resistance, so there isn't anywhere for a significant amount of energy to be lost: it has nowhere to go but into electromagnetic radiation. A mobile HF antenna has lower efficiency: the electrical shortening increases the current in the antenna, making the resistive losses in the antenna and the loading coil much more significant. A vertical installed without radials has lower efficiency due to the high resistance of the soil. But antennas that aren't shortened, and are properly installed, can have efficiencies that are very nearly 100%.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-02-26T17:47:53.340" LastActivityDate="2019-02-26T17:47:53.340" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12885" PostTypeId="2" ParentId="12880" CreationDate="2019-02-25T10:42:12.917" Score="2" Body="&lt;p&gt;Antenna gain generally refers to the maximum gain of the antenna unless the context makes it clear that some specific elevation or azimuth angle is being considered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a directional antenna such as a yagi, the forward gain is therefore the maximum gain of the antenna unless otherwise qualified. The gain in the azimuth direction 180 degrees opposite of the maximum forward gain (and generally at the same elevation) is the rearward (back) gain of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the forward and rearward gain is expressed in dB (e.g. dBi or dBd), then the front to back ratio is the forward gain minus the rearward gain. The result is then expressed in dB. For example, if the forward gain is 10 dBi and the rearward gain is -3 dBi, then the front to back ratio is 13 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a practical perspective, you can measure the front to back ratio if you have a remote signal that you can monitor while propagation is constant. Turn the antenna to find the maximum signal strength of the remote signal and note the signal strength in dB form. Turn the antenna 180 degrees from that direction and again note the signal strength in dB form. Subtract the forward dB value from the reverse dB value to compute the front to back ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you only have an s-meter available to make comparative measurements, each s-unit is generally 6 dB so you can approximate the front to back ratio by making the appropriate measurements and conversions and then subtracting the two values as described above.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-25T16:47:39.910" LastActivityDate="2019-02-25T16:47:39.910" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12886" PostTypeId="2" ParentId="5848" CreationDate="2019-02-25T13:03:26.473" Score="2" Body="&lt;p&gt;Recall that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Antenna system &lt;strong&gt;gain&lt;/strong&gt; (efficiency) &lt;em&gt;includes&lt;/em&gt; system r-f losses.  If any exists, then a proportional amount of applied power from the transmitter is dissipated as heat in the lossy elements of that antenna system.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The shape of the radiated envelope (relative fields) of that antenna system remains the same for all &lt;em&gt;non-zero&lt;/em&gt; losses, but for other things equal, its radiated power is reduced.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For an example using 4nec2 with a NEC4.2 engine, the far-field study shown below illustrates that the E/E(max) relative fields of a vertical monopole remain the same for the two different configurations of a lossy ground plane connection to the earth, but &lt;strong&gt;not&lt;/strong&gt; their gains (efficiencies).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The blue trace there shows the pattern directivity if that system had zero losses, and in this configuration, antenna system radiation efficiency is 100%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UR1sq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UR1sq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-02-25T13:03:26.473" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12887" PostTypeId="1" CreationDate="2019-02-25T15:57:55.320" Score="0" ViewCount="483" Body="&lt;p&gt;I'm in Dominica working with a donated TM-741A. The internal memory backup battery lasted just long enough for me to learn three things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;there's a backup battery;&lt;/li&gt;&#xA;&lt;li&gt;it's dead; &lt;/li&gt;&#xA;&lt;li&gt;there's no manual describing where it is in the radio, what type of battery it is or how to replace it.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Can anyone tell me how to replace it? I'm hoping one of the spare &quot;watch&quot; batteries in our SCUBA dive computers will fit.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="8717" LastEditDate="2019-02-25T17:35:02.387" LastActivityDate="2019-02-25T18:22:34.817" Title="How do I replace the Li-ion battery in a Kenwood TM-741A?" Tags="&lt;kenwood&gt;&lt;battery&gt;&lt;repair&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12888" PostTypeId="1" AcceptedAnswerId="12889" CreationDate="2019-02-25T16:49:46.863" Score="1" ViewCount="94" Body="&lt;p&gt;I'm working on an old school VFO for the 15 meter band based on a JFET Hartley oscillator.  The plan is to follow the oscillator section with a JFET buffer, then a CB amplifier (for increased reverse isolation) and finally, a feedback amplifier for gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The oscillator and buffer stage are complete and working well. But, I'm having some issues with the CB amplifier.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/hucdZ.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fhucdZ.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the schematic above, the buffer output is represented by V1.  I measured it's output impedance to be ~80 ohms (it has quite a high trans-conductance).  The impedance seen at the CB emitter should be about 26mV/4mA||510 or ~ 6.7 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The (theoretical) gain of this amplifier should be (50 ohms x (n^2))/6.6 = 68 approximately.  So, you would expect to see 20mV p-p x (68/3) across the 50 ohm load or something just shy of 0.5 of a volt.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, having built the circuit and after taking some measurements, I get about 240mV or half the gain.  &lt;strong&gt;What seems to be happening is that the transformer is not &quot;transforming&quot; like it should&lt;/strong&gt;.  If I test the transformer using a signal generator, I get a transform ratio of 3:1, as expected.  However, in-circuit it's more like 1.66.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Interestingly, the BJT is fulfilling its duty nicely: if you consider that a turns ratio of 1.66 makes 50 ohm look like 138 ohm at the collector.  Then 138 / 6.6 = 21 approx.  Then (20mV x 21) / 1.66 = 250mV which is very close to what I see across the load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm just a bit stumped as to why the transformer is not behaving itself.  I've used these type 43 cores before without issues and I even tried a bigger core size (same material) and I experimented with bigger values of C2. No change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the transistor is not a BC546 but rather a high frequency transistor pulled from a radio front-end.  I've tried various HF transistors in its place with the same result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there something about the CB amplifier that I'm overlooking?&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="8717" LastEditDate="2019-02-25T17:31:25.617" LastActivityDate="2019-03-03T20:02:40.307" Title="Toroid Coupling Issue in Common-base Amplifier" Tags="&lt;equipment-design&gt;&lt;amplifier&gt;&lt;oscillator&gt;&lt;transformer&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12889" PostTypeId="2" ParentId="12888" CreationDate="2019-02-25T17:05:10.730" Score="5" Body="&lt;p&gt;The problem is most likely the type 43 core material. It is quite lossy at 21 MHz and is a poor choice for the auto-transformer. Unlike a transmission line transformer, the auto-transformer relies on the coupling of the two coils to partially occur by passing flux through the core. The complex permeability of type 43 material indicates high losses for this flux at 21 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The effect of this core loss can be modeled as a loss resistance in series with each winding of the transformer. This would account for the apparent poor transformation ratio you are observing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wUj2A.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wUj2A.png&quot; alt=&quot;Type 43 Material&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A much better core material selection would be type 61 which is suitable up to ~25 MHz. This material has a lower initial permeability (125 vs 850 for type 43) so you may wish to increase the number of turns in the correct proportions in order to ensure sufficient inductive reactance in the windings. Due to the low power involved, a large core geometry is not warranted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3Gb9p.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3Gb9p.png&quot; alt=&quot;Type 61 Material&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-25T18:21:04.387" LastActivityDate="2019-02-25T18:21:04.387" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12890" PostTypeId="2" ParentId="12887" CreationDate="2019-02-25T17:40:50.140" Score="3" Body="&lt;p&gt;I found the &lt;a href=&quot;http://www.repeater-builder.com/kenwood/pdfs/tm-641-741-svc-man.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;TM-741A service manual&lt;/a&gt;. As shown on page 106, the battery can be seen looking into the case from the front after the display panel is removed. Luckily, the spare batteries from my dive computer will work; now I just have to open the radio and solder in a replacement!&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9493" LastEditDate="2019-02-25T18:22:34.817" LastActivityDate="2019-02-25T18:22:34.817" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12891" PostTypeId="2" ParentId="12878" CreationDate="2019-02-25T18:40:53.737" Score="4" Body="&lt;p&gt;You definitely don't want to mount a long metal pole through a Yagi. My rule of thumb is that it at best cuts off the Yagi at that point, perhaps worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You have three options to avoid this.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Mount the Yagi at its back, perhaps supporting the front with a non-conductive rope. The mast can get quite close to the reflector, 1/8 wave is ok.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Offset it from the mast with a bracket that's perpendicular to the plane of the Yagi. Exact length required is hard to say, but at least half a wavelength, maybe more. The Yagi is a slow-wave structure, its capture area at the front is large, perhaps 1 wavelength square for a 10 dBi antenna. Halfway along the boom the sensitive region is smaller.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Use a non-conductive pole. I used many filament wound fiberglass poles for this purpose. Again, you probably want a half-wavelength clearance from the boom, but a third of a wavelength will work. The coax of course can't go in the tube, so it has to hang down from the very back, somewhat behind the director. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;It is possible to put the coax in the pole if it's adequately loaded with ferrites. At 30 MHz I'd use a string of about 50 beads, 1.5&quot; long, 1/2&quot; dia, 1/4&quot; hole, made of material 31, big enough for RG223 or RG58 to fit. You could also use three or four larger cores of 61 material, 1 m apart, wound with 6 turns of coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, as you're only looking for a narrow band, you might be able to design some sort of quarter wave trap, several of them in series, on the coax or even on the metal pole. This would need to be carefully designed in simulation, and I've never tried it in this application.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-02-26T06:41:55.947" LastActivityDate="2019-02-26T06:41:55.947" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12892" PostTypeId="2" ParentId="12877" CreationDate="2019-02-25T18:46:05.100" Score="1" Body="&lt;p&gt;Most likely the signals you're receiving aren't purely vertical anyway,. It doesn't take much angle on the other guy's to leak plenty of signal into the other pol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, your yagi is imperfect, even as it is. The feed line hangs down vertically - how is it connected? How good is the balun at balancing? The mast is vertical, is it exactly in the centre of the antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Making it thinner won't reduce any of these effects.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then as you say, reflections from any diagonal object or plane will scatter one polarisation into the other.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-02-25T18:46:05.100" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12895" PostTypeId="2" ParentId="11708" CreationDate="2019-02-26T20:55:44.177" Score="3" Body="&lt;p&gt;I have been a ham for 58 years. I used an incandescent light bulb for transmit and a fluorescent tube for antenna tuning. Later, I could afford a field strength meter. I have also used Lecher wires for UHF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Technical details? Go with the glow.&lt;/p&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="8717" LastEditDate="2019-10-12T01:37:03.933" LastActivityDate="2019-10-12T01:37:03.933" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12896" PostTypeId="1" AcceptedAnswerId="12902" CreationDate="2019-02-26T23:01:28.213" Score="3" ViewCount="657" Body="&lt;p&gt;I am building several types of radio antennas, and I would like to test which is the most effective. I am wondering: What is the best way to measure the strength of the received signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is at ~151 MHz and 2 watt transmission power, and I will be testing over a distance of at least a couple of hundred feet. The results don't have to be calibrated, only correct relative to one another. Any ideas?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks in advance&lt;/p&gt;&#xA;" OwnerUserId="14341" LastActivityDate="2019-02-27T12:50:22.780" Title="How to Measure Signal Strength" Tags="&lt;antenna&gt;&lt;rssi&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12897" PostTypeId="2" ParentId="12896" CreationDate="2019-02-26T23:37:49.487" Score="3" Body="&lt;p&gt;You could use a receiver with an S-meter or if you are not too close to commercial RF signals you could use a field strength meter.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-02-26T23:37:49.487" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12898" PostTypeId="2" ParentId="12866" CreationDate="2019-02-26T23:40:57.827" Score="5" Body="&lt;p&gt;From &lt;a href=&quot;https://www.electronics-notes.com/articles/antennas-propagation/tropospheric/tropospheric-propagation.php?fbclid=IwAR1NQLl3hHHYx1Ea2EdKKsyDDb0jk5Ufru6GfLoYoPTXsM0M_MapzsAIeio&quot; rel=&quot;nofollow noreferrer&quot;&gt;Electronics Notes&lt;/a&gt;, a British page.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Line of sight radio communications&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;It might be thought that most radio communications links at VHF and&#xA;  above follow a line of sight path. This is not strictly true and it is&#xA;  found that even under normal conditions radio signals are able to&#xA;  travel or propagate over distances that are greater than the line of&#xA;  sight.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The reason for the increase in distance travelled by the radio signals&#xA;  is that they are refracted by small changes that exist in the Earth's&#xA;  atmosphere close to the ground. It is found that the refractive index&#xA;  of the air close to the ground is very slightly higher than that&#xA;  higher up. As a result the radio signals are bent towards the area of&#xA;  higher refractive index, which is closer to the ground. It thereby&#xA;  extends the range of the radio signals.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The refractive index of the atmosphere varies according to a variety&#xA;  of factors. Temperature, atmospheric pressure and water vapour&#xA;  pressure all influence the value. Even small changes in these&#xA;  variables can make a significant difference because radio signals can&#xA;  be refracted over whole of the signal path and this may extend for&#xA;  many kilometres.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="8717" LastEditDate="2019-02-27T00:06:29.553" LastActivityDate="2019-02-27T00:06:29.553" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12899" PostTypeId="1" CreationDate="2019-02-27T00:31:56.640" Score="3" ViewCount="589" Body="&lt;p&gt;How are the conductors/radiators in the &lt;a href=&quot;https://en.wikipedia.org/wiki/Quad_antenna#The_E-Z-O_variation&quot; rel=&quot;nofollow noreferrer&quot;&gt;E-Z-O Antenna&lt;/a&gt; configured, and why is it described in Wikipedia's article &lt;a href=&quot;https://en.wikipedia.org/wiki/Quad_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Quad antenna&lt;/a&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see three circles and a spider web of wires inside each, but from an electrical point of view I can't understand what's going on, and the article doesn't help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is this a type of quad antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;below:&lt;/strong&gt; Cropped, contrast enhanced, monochromed for better visualization of the wires. &lt;a href=&quot;https://en.wikipedia.org/wiki/File:E-Z-O_Antenna.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;Original source&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JjqbR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JjqbR.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;below:&lt;/strong&gt; &lt;a href=&quot;https://en.wikipedia.org/wiki/File:E-Z-O_Antenna.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;Original image&lt;/a&gt; click image for full size or visit link.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uskR1.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/I5ibl.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8643" LastActivityDate="2020-08-17T22:25:32.070" Title="How does an E-Z-O Antenna work and why does it appear in Wikipedia's article on quad antennas?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12900" PostTypeId="2" ParentId="12899" CreationDate="2019-02-27T01:26:31.517" Score="5" Body="&lt;p&gt;It's basically 3 square/cubical quad elements bent into a circle. Though not really a &quot;quad&quot; because it doesn't have four sides, in principle it is electrically similar. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a boom and three circular metal elements: director, driven element, and reflector. Everything else you see are guy and support ropes.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-02-27T01:26:31.517" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12902" PostTypeId="2" ParentId="12896" CreationDate="2019-02-27T10:06:05.337" Score="2" Body="&lt;p&gt;For antennas, it's often interesting to know at which frequencies they work best and how far that is from the frequency you designed them for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if you have a broadband or adjustable tone transmitter, you can just plug your antenna into an RTL-SDR dongle (cheap!!) and observe the received spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That'll not only give you relative reception strength at a given design frequency, but also an understanding for which bandwidths the antenna works well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that passive antennas are reciprocal - i.e. what works good as receiver works just as well as a transmitter; this means you can swap the roles of transmitter and receiver, if that makes the measurement system easier.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-02-27T10:06:05.337" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12904" PostTypeId="2" ParentId="12896" CreationDate="2019-02-27T12:50:22.780" Score="2" Body="&lt;p&gt;Considerations when comparing the field intensities from different transmit antennas over a given terrestrial path, and assuming use of the same receive+antenna system and its siting/adjustment for all measurements:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Path distance from transmit antenna to receive antenna&lt;/li&gt;&#xA;&lt;li&gt;Height above the reflecting plane (Earth) of the radiation center of each transmit antenna&lt;/li&gt;&#xA;&lt;li&gt;Free-space radiation pattern of each transmit antenna toward the receive antenna, in the vertical plane&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The graphic below shows the variations in received field vs. elevation above a level ground plane, for the configuration and conditions stated in the graphic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The vertical axis (Z) = Height above Earth of the calculated field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The horizontal axis (E) = Field intensity in mV/m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yD5T5.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yD5T5.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-02-27T12:50:22.780" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12905" PostTypeId="2" ParentId="12866" CreationDate="2019-02-27T14:45:58.487" Score="2" Body="&lt;p&gt;From Marcus' answer of Feb 23, 2019:  ...&lt;em&gt;Especially, emitted energy does reach beyond the horizon due to wave (as opposed to ray) propagation effects such as &lt;strong&gt;refraction,&lt;/strong&gt; diffraction and reflection.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is an extreme example of refraction in the VHF range.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although the line-of-sight path there is severely shadowed by Earth curvature plus several terrain obstructions, enough radiated energy &lt;em&gt;may&lt;/em&gt; reach beyond those obstructions to provide a useful signal to a suitable receive system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/00SyY.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/00SyY.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-02-27T14:52:24.857" LastActivityDate="2019-02-27T14:52:24.857" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12906" PostTypeId="2" ParentId="12878" CreationDate="2019-02-27T17:08:49.250" Score="0" Body="&lt;p&gt;The best way of understanding what happens is to think in terms of currents on the mast as well as on the boom tube. The impedance on the boom tube varies along the tube. So does the impedance of the vertical mast. If both are low you can get high currents and an associated high amount of radiation from the mast as well as from the boom tube. Isolating the boom tube from the mast with a low capacitance while having a good current balun (ferrite cores) will make the current on the boom tube very low, but the free mast tube may pick up a large current because it can couple efficiently to the strong vertical electric field of the yagi. The best solution I know of is to put a half-wave horizontal tube at the point where the mast tube connects to the boom tube. That tube would create a low impedance point on the boom where it connects to the vertical mast. Then, 0.75 wl vertically down the mast, place another 0.25 wl long tube that is parallel to the yagi boom tube. That would create another low impedance point on the vertical mast. As a consequence the impedance at the top of the mast tube will be very high and the mis-match to the boom tube will be maximized. The current on the vertical mast would be very low so there would not be any radiation and no interaction with the yagi. For long yagis on 144 MHz I have seen degradations in the order of a few tenths of a dB. These things can be simulated. The elements of the yagi can be in metallic contact with the boom tube or they can be isolated. That may have a big influence on the impedances at various places along the boom tube. With this kind of solution there is no need for ferrites, just run the cable tight to the boom and mast tubes or maybe even inside.&#xA;These things can be simulated!!&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-02-27T17:08:49.250" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="12907" PostTypeId="2" ParentId="12899" CreationDate="2019-02-27T21:08:46.723" Score="4" Body="&lt;p&gt;It's described on the Wikipedia page because &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Quad_antenna&amp;amp;diff=271136628&amp;amp;oldid=245425072&quot; rel=&quot;nofollow noreferrer&quot;&gt;the creator of the antenna put it there in Feb 2009&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The E-Z-O section has subsequently been removed and re-added several times.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Quad_antenna&amp;amp;oldid=593034101&quot; rel=&quot;nofollow noreferrer&quot;&gt;Jan 2014&lt;/a&gt;, it was removed by an anonymous user with the explanation: &quot;False claim to fame because the EZO variation is nothing but a variation on a coaxial loop antenna with reflector and directors&quot;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Quad_antenna&amp;amp;oldid=847253116&quot; rel=&quot;nofollow noreferrer&quot;&gt;Jun 2018&lt;/a&gt; The section as restored by a user &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=User:Enix150&amp;amp;action=edit&amp;amp;redlink=1&quot; rel=&quot;nofollow noreferrer&quot;&gt;Enix150&lt;/a&gt; without any explanation.&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=User:Enix150&amp;amp;action=edit&amp;amp;redlink=1&quot; rel=&quot;nofollow noreferrer&quot;&gt;Feb 27, 2019&lt;/a&gt; (shortly after you posted this question) The section is removed again by an anonymous user.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ezoantennas.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ezoantennas.com/&lt;/a&gt;  claims:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In spite of its humble inception, this could be the biggest improvement in antenna design in over 50 years!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The site appears to be authored by N8PPQ, and the &lt;a href=&quot;https://www.godaddy.com/whois/results.aspx?domain=EZOANTENNAS.COM&quot; rel=&quot;nofollow noreferrer&quot;&gt;domain registration&lt;/a&gt; and &lt;a href=&quot;https://wireless2.fcc.gov/UlsApp/UlsSearch/license.jsp?licKey=746467&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC database&lt;/a&gt; corroborate the authenticity of the author.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A circular versus square element is only minorly significant, electrically. Most of the visible lines are nonconductive support structure, allowing the elements themselves to be flexible. ezoantennas.com explains:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The idea came after a Scouting event, and was inspired by the way tent design has changed, with flexible tubes replacing ridged [sic] poles.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is an interesting idea in construction technique, but not as revolutionary as the author claims. I don't believe the antenna is unique enough to merit inclusion in Wikipedia.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-03-01T15:35:35.723" LastActivityDate="2019-03-01T15:35:35.723" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12908" PostTypeId="1" CreationDate="2019-02-27T23:51:36.050" Score="0" ViewCount="185" Body="&lt;p&gt;My project is to monitor the power and the deviation of 3 radio FM stations, sending this values into a MySQL database.&#xA;I can't stream directly the audio of the station, due to limited bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I ask you if there is a method, command or Python script to get power level and deviation of an FM signal from an RTL SDR.&lt;/p&gt;&#xA;" OwnerUserId="13140" LastEditorUserId="8717" LastEditDate="2019-02-28T00:13:14.327" LastActivityDate="2019-03-01T12:34:05.083" Title="RTL-SDR: command or script to obtain power and deviation of an FM radio station" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12911" PostTypeId="2" ParentId="12908" CreationDate="2019-02-28T20:58:32.407" Score="1" Body="&lt;p&gt;You may wish to look into &lt;a href=&quot;https://wiki.gnuradio.org/index.php/Main_Page&quot; rel=&quot;nofollow noreferrer&quot;&gt;GNU Radio&lt;/a&gt; as the basic platform from which to develop your specific application. GNU Radio is based on the &lt;a href=&quot;https://www.python.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Python&lt;/a&gt; and &lt;a href=&quot;https://en.wikipedia.org/wiki/C_(programming_language)&quot; rel=&quot;nofollow noreferrer&quot;&gt;C&lt;/a&gt; programming languages using &lt;a href=&quot;http://www.swig.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;SWIG&lt;/a&gt; for the interface between the two. In GNU Radio you are essentially connecting various blocks (a functional processing unit with inputs and outputs) in a graphical form into &quot;flowgraphs&quot;  to build your application. You can do a great deal of &lt;a href=&quot;https://wiki.gnuradio.org/index.php/BlocksCodingGuide&quot; rel=&quot;nofollow noreferrer&quot;&gt;customization of blocks&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also add your own &quot;private&quot; extensions to GNU Radio using &lt;a href=&quot;https://wiki.gnuradio.org/index.php/OutOfTreeModules&quot; rel=&quot;nofollow noreferrer&quot;&gt;Out of Tree&lt;/a&gt; modules. You can do this by authoring in C or C++, for example. This perhaps would be a good approach for meeting your database interface requirements. You may find some ready made code on the Internet that you can use for this purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also be able to use the File Sink block to output binary data to a file for post processing into your database. The use of meta data headers may also prove helpful to your application. See the &lt;a href=&quot;https://www.gnuradio.org/doc/doxygen/classgr_1_1blocks_1_1file__meta__sink.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;file_meta_sink Class Reference&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-02-28T21:23:57.147" LastActivityDate="2019-02-28T21:23:57.147" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12913" PostTypeId="2" ParentId="12908" CreationDate="2019-03-01T12:34:05.083" Score="1" Body="&lt;p&gt;RE:  &lt;em&gt;My project is to monitor the power ...&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;em&gt;power&lt;/em&gt; present in a received e-m wave is highly dependent on the frequency, propagation path, the receive antenna pattern characteristics when installed, and other factors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Accurate measurement of such received power over most open-area propagation paths is difficult to achieve, requiring expensive receive equipment assembled as a system having known characteristics at each frequency tested.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SDR output likely will produce only &lt;strong&gt;relative&lt;/strong&gt; indications of received field/power, which due to the unknowns that are present can be deceptive as a basis to compare the performances of several radiating sources.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-03-01T12:34:05.083" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12914" PostTypeId="1" AcceptedAnswerId="12916" CreationDate="2019-03-01T16:23:41.857" Score="0" ViewCount="108" Body="&lt;p&gt;I have a Nissan Versa 2012 (hatchback).  It comes with one of those default antennas at the back/center of the roof, for listening to AM/FM radio stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a dual band mag-mount (TRAM 1185), which I placed right in the center of the roof, with the coax entering through the trunk.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is working OK.  But I am new to the hobby, so I am wondering if the exact center of the roof is the best place for an antenna, given the placement of the default AM/FM antenna.&lt;/p&gt;&#xA;" OwnerUserId="11385" LastEditorUserId="76" LastEditDate="2019-03-01T20:13:28.777" LastActivityDate="2019-03-01T20:26:19.513" Title="Proper magnetic mount placement on roof" Tags="&lt;antenna-construction&gt;&lt;mobile&gt;&lt;vertical-antenna&gt;&lt;2m-band&gt;&lt;70cm-band&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12915" PostTypeId="2" ParentId="12914" CreationDate="2019-03-01T17:27:19.400" Score="2" Body="&lt;p&gt;It's difficult to predict in the general case how a particular antenna placement will work because it's very sensitive to the particular geometry of the car. Most likely the center of the roof is just fine, and alternative placements would yield not very significant differences.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-01T17:27:19.400" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12916" PostTypeId="2" ParentId="12914" CreationDate="2019-03-01T17:40:42.667" Score="3" Body="&lt;p&gt;When dealing with UHF and VHF communications, height is often the determining factor of range for line of sight conditions. If there are obstructions that height cannot overcome, then more effective radiated power tends to be the determining factor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Exact placement on the roof won't have much effect on the pattern. If you place it way to one side of the roof, then you may have a signal that is a bit lopsided due to the lack of a ground plane in that direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question often comes up about any potential damage of your AM/FM radio by your ham radio, consider that your FM broadcast radio will have more than 0.5 volts of an in-band signal when you are within 1/2 mile of a 50 kW FM station and this doesn't cause any harm to the radio. The front end filters of the FM receiver will likely attenuate out of band signals by more than 40 dB. For your 2 meter transmitter to pass the equivalent voltage through the front end of the FM broadcast receiver when the antennas are located 2 feet apart would require more than 200 watts of power. So your 2 meter or 70 centimeter transmitter may cause some minor temporary overload of the broadcast receiver but it is unlikely to cause any harm. I regularly run 50 watts and have never had a problem.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-01T20:26:19.513" LastActivityDate="2019-03-01T20:26:19.513" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12917" PostTypeId="2" ParentId="769" CreationDate="2019-03-01T20:42:46.683" Score="1" Body="&lt;p&gt;I know this is an old thread but I thought I'd chime in anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lead-free solder is used for plumbing since the early eighties, because you don't want lead on contact with potable water.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For electronics, the danger from soldering is from inhaling the flux smoke. The temperatures used aren't high enough to vaporize the lead, so there is minimal lead exposure from soldering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, for electronics leaded solder is my preference unless I want to build something that is sold into the EU, where it is prohibited.&lt;/p&gt;&#xA;" OwnerUserId="14360" LastActivityDate="2019-03-01T20:42:46.683" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12918" PostTypeId="1" AcceptedAnswerId="12921" CreationDate="2019-03-01T22:49:40.737" Score="0" ViewCount="782" Body="&lt;p&gt;Can anyone tell me what the theoretical and actual cross polarization attenuation from horizontal to vertical polarization is ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason i ask is that i have the idea that for receive a vertical yagi has little gain for horizontal signals, and this idea seems to be backed up by the fact that a vertical 3 element yagi i have built does indeed seem to null out vertical signals much better then another 4 element horizontal yagi that i have. So i'm trying to work out what's going on and knowing the cross-polarization attenuation is a good start.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-03-01T23:24:09.790" LastActivityDate="2019-03-02T09:52:02.963" Title="What is the theoretical and actual cross polarization attenuation from horizontal to vertical polarization?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12919" PostTypeId="1" CreationDate="2019-03-01T22:56:07.290" Score="0" ViewCount="278" Body="&lt;p&gt;From a reply to a previous post I've been told that a horizontal tube half a wavelength long mounted right at the junction between the boom on a vertically mounted yagi and a vertical metal pole will present a high impedance on the mast and allow the Yagi to work properly despite the presence of the metal mast, can anyone shed any more light on this idea ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mounting a 10 m vertical Yagi on a non-metallic pole is not a good solution in my opinion and the only other way to do it is mount from the back (not easy if you have a rotator) or phase two yagis together just so they can be mounted on a horizontal connecting boom which balances out the weight,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or worst case I can make a combination horizontal / vertical Yagi with the vertical elements in front of the metal mast and the horizontal elements sprinkled behind and among those so it's balanced, but then the antenna will start to become pretty long and unwieldy.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-03-04T14:16:46.680" LastActivityDate="2020-05-26T17:25:09.433" Title="How can a vertical Yagi for 10 m be mounted on on a vertical metal mast and be made to work properly?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="0" ClosedDate="2020-05-28T09:47:29.047" ContentLicense="CC BY-SA 4.0" />
  <row Id="12920" PostTypeId="2" ParentId="12918" CreationDate="2019-03-02T00:29:08.037" Score="2" Body="&lt;p&gt;A yagi is a purely linearly polarized antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since H and E fields are orthogonal to each other, &lt;strong&gt;every&lt;/strong&gt; antenna has a theoretically infinite cross-polarization attenuation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The actual attenuation depends on factors like material thickness, production accuracy, and the reliability in which the signals are actually polarized in either direction, so there's no general formula that we could tell you for your 3 or 4 element yagi – but as a rule of thumb, if it's a good one, it's going to be high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another rule of thumb that I basically just came up with from my tummy: If it has many directors (i.e. non-driven elements), then chances are that if a wave incides even slightly slanted from a theoretically suppressed cross-polarization, the effects of the non-orthogonal part will be easier to measure – simply because it's harder to align four elements exactly than 3.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-03-02T09:52:02.963" LastActivityDate="2019-03-02T09:52:02.963" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12921" PostTypeId="2" ParentId="12918" CreationDate="2019-03-02T01:07:37.507" Score="3" Body="&lt;p&gt;Theoretically, cross-polarization loss is infinite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, both the receive and transmit antennas aren't exactly linearly polarized. They will have fields in the cross polarization to some extent due to imperfections in their construction, for example misaligned elements, or less than perfect isolation from common-mode currents on the feedline, mast, or tower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, some paths can alter polarization, for example by reflecting off slanted surfaces. Real environments thus introduce some degree of &quot;leakage&quot; into orthogonal polarizations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, cross polarization is probably between 15 and 40 dB, depending on the antennas and the environment.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-02T01:07:37.507" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12922" PostTypeId="2" ParentId="12919" CreationDate="2019-03-02T04:38:23.390" Score="0" Body="&lt;p&gt;You mentioned to &quot;mount from the back&quot;, which is not easy, but you can add an extension of the boom backward to act as a counter weight for the antenna. (Usually vertical polarization is for working a repeater!  Is that what you will be using the antenna for?)&lt;/p&gt;&#xA;" OwnerUserId="5252" LastActivityDate="2019-03-02T04:38:23.390" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12924" PostTypeId="2" ParentId="769" CreationDate="2019-03-02T16:20:49.760" Score="1" Body="&lt;p&gt;The best solder for Amateur and hobby use is &lt;a href=&quot;https://en.wikipedia.org/wiki/Solder&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;eutectic solder&lt;/strong&gt;&lt;/a&gt;, which solidifies without crystallizing regardless of the speed of cooling down. This eliminates so-called &lt;em&gt;&lt;a href=&quot;https://learn.adafruit.com/adafruit-guide-excellent-soldering/common-problems&quot; rel=&quot;nofollow noreferrer&quot;&gt;cold solder joints&lt;/a&gt;&lt;/em&gt;, which can sometimes appear to be solid, but may make poor electrical connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Traditionally, eutectic solder was made of 63% tin and 37% lead, and is easy to use because it has a very low melting point, but laws are tightening to eliminate lead, which is poisonous, from all electronics. An example replacement is made of Tin-Silver-Copper alloy.&lt;/p&gt;&#xA;" OwnerUserId="14362" LastActivityDate="2019-03-02T16:20:49.760" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12925" PostTypeId="1" CreationDate="2019-03-02T16:45:25.597" Score="1" ViewCount="125" Body="&lt;p&gt;I read &lt;a href=&quot;http://www.ukaranet.org.uk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; (in the &lt;a href=&quot;http://www.ukaranet.org.uk/ideas.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;ideas&lt;/a&gt; section) that an old shortwave radio can be used as a receiver for listening to Jupiter but am unsure about how to do it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;MY radio has both a whip and ferrite antenna, should I remove both which would I replace with my own antenna?&lt;/p&gt;&#xA;" OwnerUserId="10922" LastEditorUserId="4076" LastEditDate="2019-03-02T19:46:01.063" LastActivityDate="2021-05-23T19:33:29.713" Title="Using SW radio to detect Jupiter" Tags="&lt;receiver&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12926" PostTypeId="2" ParentId="12919" CreationDate="2019-03-02T16:58:26.653" Score="1" Body="&lt;p&gt;A very common approach that is used for satellite antennas is a solid, fiberglass mast. These are readily available from amateur radio distributors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fiberglass mast has sufficient rigidity that I have used it in a horizontal boom configuration with large, crossed polarized yagi antennas with preamps on each side and there was no noticable sag. You can certainly use it as a vertical mast so as to avoid any gain or impedance degradation of your vertical yagi. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may even find a hollow fiberglass mast would prove sufficiently stiff for the job although you may need a reinforcing material inside the tube at the clamp points to prevent crushing it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also fashion a hybrid metal / fiberglass mast using short fiberglass sections inserted into the metal mast to join the mast pieces so as to break up the electrical length of the mast to make it more nearly transparent on 10 meters.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-04T13:41:35.127" LastActivityDate="2019-03-04T13:41:35.127" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12927" PostTypeId="1" AcceptedAnswerId="12929" CreationDate="2019-03-02T17:25:59.490" Score="2" ViewCount="1288" Body="&lt;p&gt;In movie &quot;6 Below&quot;, based on a true history, a lost snowboarder at Mammoth Mountain (California) is located by search and recuse when they detect and triangulate a signal from his MP3 player that also had an FM radio tuner (not a phone nor a two-way-radio, just an FM tuner).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This event forms a essential part of the story, so it doesn't makes sense to me that they just made it up as a part of their theatrical license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I was very confused because in my understanding it should be impossible to detect a receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After some google search I &lt;a href=&quot;https://www.pugski.com/threads/search-and-rescue-technology-question.10216/&quot; rel=&quot;nofollow noreferrer&quot;&gt;found some info&lt;/a&gt; saying that: as the receiver internally amplifies the signal, this creates &quot;unintended emissions&quot;, and those emissions could be detected. Also &lt;a href=&quot;https://ieeexplore.ieee.org/document/5699393&quot; rel=&quot;nofollow noreferrer&quot;&gt;this fairly recent paper&lt;/a&gt; refer to such methods.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is this possible in practice?&lt;/strong&gt; If so. &lt;strong&gt;It is such technology actually used for Search &amp;amp; Rescue in California?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="14363" LastEditorUserId="9493" LastEditDate="2019-03-02T22:48:41.573" LastActivityDate="2019-03-03T19:43:39.753" Title="Can a FM tuner (receiver) be detected and triangulated?" Tags="&lt;receiver&gt;&lt;fm&gt;&lt;emergency&gt;&lt;location&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12928" PostTypeId="1" CreationDate="2019-03-02T17:49:05.940" Score="2" ViewCount="461" Body="&lt;p&gt;These are photos of the headphones that I use in my ham shack. As you can see, the dark gray foam rubber inside is deteriorating, and I need to replace it. It appears to be open-cell foam &quot;rubber&quot; between 1/8&quot; and 3/16&quot; thick.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the headphones has had little use (bought it as a spare) and shows the original size of the hole centered around the element's sound holes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are military surplus communications phones with just the right frequency response for SSB ham radio use. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;That foam is holding the elements in place.&lt;/strong&gt; Notice that one element where there is almost no foam left is loose. However, it is not particularly stiff. That may or may not be because it is so deteriorated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it matter what kind of foam is needed to replace this deteriorating stuff? Regardless, where can I get it? (It doesn't matter what color it is.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ey9Wa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ey9Wa.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/KDtjM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KDtjM.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JhxUZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JhxUZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/cZo8g.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cZo8g.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-12-05T20:04:55.307" LastActivityDate="2020-07-07T15:43:07.987" Title="Suitable acoustic foam rubber for headphones?" Tags="&lt;equipment&gt;&lt;audio&gt;&lt;military-surplus&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="12929" PostTypeId="2" ParentId="12927" CreationDate="2019-03-02T19:43:39.080" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is this [detection of a receiver through its amplification of received signals] possible in practice?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Aaaah, no. Not exactly like described in  that thread. In more general terms, yes, it is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, first of all: the point of &lt;em&gt;radio&lt;/em&gt; is that the transmitted energy &lt;em&gt;radiates&lt;/em&gt; away from the transmitter. That means that you can't know whether something absorbed that energy at the transmitter. The energy is gone either way, and there's no way for information to &quot;flow back&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we assumed that the receiver had an amplifier for the transmitted frequency (say, a tone of 100 MHz), and it &quot;leaked&quot; energy back out, and we'd need to detect that, we'd be in a bad spot:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the original transmitter was meant to transmit, its emission will be much stronger; and being on the exact same frequency, we couldn't reliably tell the leakage from a faint echo, e.g. from a reflection off a rock or metal surface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's another way of detecting radio receivers, and rumor has it used to be used in the 20th century by TV companies trying to detect unlicensed TV receivers: Receivers have to &lt;em&gt;mix down&lt;/em&gt; the RF signal to some fixed intermediate frequency. There was basically one fixed IF that all good ole TVs used – and if you built a sensitive receiver for those, you might have been able to locate &lt;em&gt;turned on, actively receiving TVs of the 1940s to 70s&lt;/em&gt;; not modern MP3 players. They don't all agree on a single IF, if they use an IF at all; and they won't be as leaky, and they won't be as powerful, and most importantly, probably turned off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;But:&lt;/strong&gt; Everything that actively deals with a signal is some kind of &lt;em&gt;non-linear&lt;/em&gt; device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What that means is that math is your friend: Without loss of generality, we can assume our tone to be a cosine of frequency &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt;, i.e. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$s(t) = \cos(2\pi ft)\text.$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, that cosine is picked up by an antenna (which in itself is undetectable from a position of the transmitter), and amplified; amplified means &quot;sent through something that multiplies the signal with a constant &lt;span class=&quot;math-container&quot;&gt;$&amp;gt;1$&lt;/span&gt;&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, such somethings are made from &lt;em&gt;active components&lt;/em&gt;, typically &lt;em&gt;transistors&lt;/em&gt;. And all these have a pretty important downside:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They don't actually multiply the signal with a constant. That is technically relatively hard to achieve.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, they have  &lt;a href=&quot;https://en.wikipedia.org/wiki/Exponential_function&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;exponential&lt;/em&gt; behaviour&lt;/a&gt;, something like&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$r(t) = e^{\alpha + \beta s(t)}\tag1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/Exp.svg/800px-Exp.svg.png&quot;&gt;&#xA;where &lt;span class=&quot;math-container&quot;&gt;$s$&lt;/span&gt; is the horizontal axis (input), and &lt;span class=&quot;math-container&quot;&gt;$r$&lt;/span&gt; would be on the vertical axis (output).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, that's not very alike to what we want, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\hat r(t) = a \cdot s(t),\quad a\gg 1\text, \tag2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;so how does that work out?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, you make sure that the &lt;span class=&quot;math-container&quot;&gt;$s(t)$&lt;/span&gt; is relatively small and is offset with a bit of DC voltage so that you pick a region on that curve that is pretty steep and looks &quot;flat enough&quot;, so that you land on the rightmost black dot in the below figure when &lt;span class=&quot;math-container&quot;&gt;$s=0$&lt;/span&gt;, and let &lt;span class=&quot;math-container&quot;&gt;$s$&lt;/span&gt; vary just a bit so that the difference between the steep red line and the blue exponential curve is small:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/c/c4/Exp_tangent.svg/491px-Exp_tangent.svg.png&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, you have something that has &lt;em&gt;approximately&lt;/em&gt; the linear behaviour from &lt;span class=&quot;math-container&quot;&gt;$(2)$&lt;/span&gt; that we wanted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But only approximately so. Maybe you've had some advanced math – if you did, you might know that the exponential function can be written as a series:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$e^x = \sum_{k=0}^\infty \frac{x^k}{k!} = 1 + x + \frac{x^2}2 + \frac{x^3}{6} + \cdots$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of that, we've only covered the first to terms with our approximation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$e^x  = \underbrace{1 + x}_{\text{red line approximation}} + \underbrace{\frac{x^2}2 + \frac{x^3}{6} + \cdots}_{\text{error terms}}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, when you mentally replace &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt; with your &lt;span class=&quot;math-container&quot;&gt;$s(t)$&lt;/span&gt; in that error term, you see that you get your signal squared, cubed, …⁵ and so on as error terms, albeit with less amplitude the higher the exponent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, let's look at one of these – the strongest, x². What happens to our cosine when we square it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;\begin{align}&#xA;\cos(2\pi ft)^2 &amp;amp;= \cos(2\pi ft)\cos(2\pi ft)\\&#xA;&amp;amp;= \frac12\left(\cos(2\pi ft+ 2\pi ft)+ \cos(2\pi ft-2\pi ft)\right)\\&#xA;&amp;amp;= \frac12\left(\cos(2\cdot2\pi ft)+ \cos(0)\right)\\&#xA;&amp;amp;= \frac12\left(\cos(2\pi (2f)t)+ 1\right)\\&#xA;&amp;amp;= \frac12\cos(2\pi (2f)t)+ \frac12\tag3&#xA;\end{align}&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, &lt;span class=&quot;math-container&quot;&gt;$(3)$&lt;/span&gt; is pretty spectacular: that's a &lt;em&gt;new&lt;/em&gt; cosine with twice the input frequency! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A sensitive receiver can look for signals at that specific double frequency; if you couple that with switching the transmitter of the original frequency on and off to test the hypothesis of energy there not just being random noise, you can make a pretty decent detector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's actually used in detection of semiconductor junctions by physicists experimenting with materials, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also been used in the past to detect simplistic bugging devices in e.g. embassies, but these are designed to be transmitters, so they are going to be a pretty solid bit easier to detect than just a radio receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I'd assume that since being not very close to the device makes the detection harder (actually, the hardness goes with the square of the distance), nope, that's not going to happen in an emergency location situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does work is if you are carrying something that is &lt;em&gt;meant&lt;/em&gt; to be excited by an external tone, then &quot;save&quot; that energy and continue to transmit for a few microseconds at least after the external tone has been shut off – that's exactly how these cheap anti-theft tags work, and it's how &lt;a href=&quot;https://www.sport-conrad.com/blog/en/what-is-recco-avalanche-rescue-system/&quot; rel=&quot;nofollow noreferrer&quot;&gt;radioresponders in ski clothing&lt;/a&gt; work.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If so. It is such technology actually used for Search &amp;amp; Rescue in California?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I don't know, but the passive tags mentioned above stand a high chance of being known to rescue teams and thus, there's a high chance they carry equipment to detect these. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the &quot;radiolocation through MP3 player&quot; will not be part of anyone but James Bond's avalanche rescue team, is my technical assessment.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-03-02T19:43:39.080" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="12930" PostTypeId="1" AcceptedAnswerId="12932" CreationDate="2019-03-03T11:31:35.753" Score="1" ViewCount="381" Body="&lt;p&gt;Sometimes in FT-8 mode I receive calls like this one:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yAmtH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yAmtH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It happens 2-3 times a week.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problems are: 1) I never could look up such call signs 2) I tried to reply, but never got answer 3) I don't know what /R means.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are these real calls or maybe just a noise that WSJT-X somehow managed to decode? So far I didn't log such events as QSO's. Maybe I should?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPD: As Marcus pointed out, the checksum collision in FT-8 is very unlikely. Also I managed to figure out that &quot;/R&quot; means a repeater &lt;a href=&quot;https://en.wikipedia.org/wiki/Amateur_radio_call_signs&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Amateur_radio_call_signs&lt;/a&gt; I believe it means that the signal was sent automatically by the device, not that the operators works through the repeater. Still I wonder - should I add repeaters to the logbook?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-03-03T13:01:51.073" LastActivityDate="2019-03-03T14:26:30.527" Title="Should I add call signs with /R suffix to the logbook?" Tags="&lt;repeater&gt;&lt;ft8&gt;&lt;wsjt-x&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="12932" PostTypeId="2" ParentId="12930" CreationDate="2019-03-03T14:17:50.007" Score="4" Body="&lt;p&gt;FT8 decoding can use a technique called &lt;em&gt;a priori&lt;/em&gt; (AP) whereby it uses naturally accumulating information for the purposes of increasing apparent sensitivity by about 4 dB. There is an increased chance of false decodes when AP is enabled since AP is essentially sophisticated guess work. The technique looks at its guessed result and compares it to the parity information and displays the guess if there is a specified level of confidence of it being correct. There is no assurance that it is correct. The term often used for these false AP decodes is &lt;em&gt;exotica&lt;/em&gt; - referring to a rare, decoded call sign that doesn't exist.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While it is entirely possible that the sender is a pirate station, the fact that the V0 prefix is not allocated by the &lt;a href=&quot;https://en.wikipedia.org/wiki/ITU_prefix&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU&lt;/a&gt; is a good indicator that you are experiencing exotica. The /R is likely part of the exotica decode - not an indication of a repeater. Another good indication of an exotica decode is a decode of an unlikely grid square.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the decoded call sign does not exist, when you respond, the other station does not recognize the exotica call as their call sign so no QSO takes place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wish to avoid exotica, at the expense of some loss of apparent sensitivity, simply disable the AP feature under the decode menu.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-03T14:26:30.527" LastActivityDate="2019-03-03T14:26:30.527" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12933" PostTypeId="2" ParentId="12928" CreationDate="2019-03-03T14:49:31.330" Score="3" Body="&lt;p&gt;Audiophiles like to replace those plastic and foam earpads with a velour product such as this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3tJPb.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3tJPb.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If red doesn't suit you, there are other choices. There are several vendors for this type of product, with &lt;a href=&quot;https://www.brainwavzaudio.com/products/velour-headphone-pad&quot; rel=&quot;nofollow noreferrer&quot;&gt;Brainwavz Audio&lt;/a&gt; as one example.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-03-03T14:49:31.330" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12934" PostTypeId="2" ParentId="12928" CreationDate="2019-03-03T15:05:01.207" Score="5" Body="&lt;p&gt;Out of left field - If function is the only cause and fashion isn't an issue, use a couple of black cotton socks. On my headphones the plastic outer pieces are removeable. I cut the ends off two socks, slid them over the phones and my wife sewed them in place. Comfortable, although the seams do show a little. I don't care! Cost nothing and works fine!&lt;/p&gt;&#xA;" OwnerUserId="14368" LastActivityDate="2019-03-03T15:05:01.207" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12935" PostTypeId="1" AcceptedAnswerId="12939" CreationDate="2019-03-03T16:55:57.527" Score="1" ViewCount="224" Body="&lt;p&gt;I received a few eQSL's from shortwave listeners.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I send an eQSL back or just archive these QSLs? Also, is it possible to receive a paper QSL card from a SWL?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPD: The reason why I asked this question is that eQSL.cc has certain rules regarding sending QSLs for QSOs that didn't happen. I'm not sure whether it will count as if I had a QSO with an SWL (which naturally couldn't happen) if I respond.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-03-03T20:58:34.300" LastActivityDate="2019-03-03T21:07:44.110" Title="QSL cards from shortwave listeners" Tags="&lt;qsl-card&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12936" PostTypeId="2" ParentId="12927" CreationDate="2019-03-03T19:43:39.753" Score="8" Body="&lt;p&gt;The story is about Eric LeMarque who got lost after snowboarding out of bounds in the Sierra Nevada mountains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio receivers usually contain some kind of oscillator. Detecting the unintentional radiation from the oscillator or the mixing products in the receiver is technically possible, but in modern receivers the power is so weak this power is so weak it is quite difficult to detect, even knowing the particular model of receiver and where it is. Consider what would happen if receivers produced conspicuous detectable signals: every radio would be a source of interference, and all kinds of radio communication wouldn't work through the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;LeMarque unsuccessfully tried using the screen of his MP3 player as a signaling device. He was instead &lt;a href=&quot;http://articles.latimes.com/2004/mar/04/local/me-survivor4&quot; rel=&quot;noreferrer&quot;&gt;found the usual way&lt;/a&gt;: search and rescue teams followed his trail in the snow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Search and rescue teams don't find people by their MP3 players, but they do use intentional transmitters like &lt;a href=&quot;https://www.rei.com/learn/expert-advice/avalanche-transceiver.html&quot; rel=&quot;noreferrer&quot;&gt;avalanche transceivers&lt;/a&gt; and &lt;a href=&quot;https://www.rei.com/learn/expert-advice/personal-locator-beacons.html&quot; rel=&quot;noreferrer&quot;&gt;personal locator beacons&lt;/a&gt; when people have the good sense to carry them. More ordinary radio communication devices like cell phones, portable FRS and amateur radios, etc. also factor into some operations.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-03T19:43:39.753" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12937" PostTypeId="2" ParentId="12935" CreationDate="2019-03-03T19:50:05.553" Score="1" Body="&lt;p&gt;I receive SWL QSL cards every few years. And I usually respond, especially if they include an SASE. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But why not also respond to eQSLs? In either case, you might make someone's day. :-)&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-03-03T19:50:05.553" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12938" PostTypeId="2" ParentId="12888" CreationDate="2019-03-03T20:02:40.307" Score="1" Body="&lt;p&gt;I thought I'd come back to this having discovered the real reason why I wasn't developing the expected voltage across the 50 ohm load.  Glenn's answer was good and is still very relevant, but I made a silly and simple mistake and I'd like to post it up as an answer in case someone else has the same issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, I had reversed the windings on the toroid.  This wasn't obvious on the schematic, but I had the major winding towards the power rail and the minor winding towards the collector.  Since the power rail is AC grounded, this puts the major winding (8 turns in my case) in parallel with the load and gives an impedance transform of 2.25 or a collector impedance of roughly 112 ohms.  This reduces the CB gain substantially.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is how I should have wired it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DDoGe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DDoGe.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a real &quot;trap for young players&quot; since it seems quite intuitive to have the minor winding where I had it.  I guess the golden rule is - always look for ground.  Cheers!&lt;/p&gt;&#xA;" OwnerUserId="11875" LastActivityDate="2019-03-03T20:02:40.307" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12939" PostTypeId="2" ParentId="12935" CreationDate="2019-03-03T21:02:36.907" Score="2" Body="&lt;p&gt;OK, I think I found an answer to my own question after Mike helped to word the right question :) The &lt;a href=&quot;http://www.eqsl.cc/qslcard/FAQ-Old.cfm&quot; rel=&quot;nofollow noreferrer&quot;&gt;eQSL.cc FAQ&lt;/a&gt; says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;How do I handle SWL cards?&lt;/strong&gt; When a user sets the SWL/HAM checkbox in&#xA;  his Profile to SWL, it automatically forces all incoming and outgoing&#xA;  cards to say 'Confirming SWL Reception' instead of the usual 'This&#xA;  Confirms Our 2-Way QSO'. If you are an SWL, just make sure to go to My&#xA;  Profile and set yourself up as an SWL. If you are a ham, when you send&#xA;  an eQSL to an SWL, it will automatically put the correct wording into&#xA;  the card.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Also according to &lt;a href=&quot;https://ham.stackexchange.com/questions/5104/minimal-info-on-a-swl-qsl&quot;&gt;this discussion&lt;/a&gt; SWLs do send paper QSL cards.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-03-03T21:07:44.110" LastActivityDate="2019-03-03T21:07:44.110" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12940" PostTypeId="1" CreationDate="2019-03-04T03:42:44.583" Score="5" ViewCount="109" Body="&lt;p&gt;I'm playing with an RTL-SDR dongle and an LNA, on Linux Mint with GQRX and DSD&#xA;A lot of frequencies show digital transmissions, which the DSD is not converting.  I don't whether it is a format DSD cannot convert, encrypted, or just distorted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a site were I can listen to how different digital transmission formats (DMR, D-Star, etc.) sound without converting, or any other strange transmissions?&lt;/p&gt;&#xA;" OwnerUserId="11385" LastActivityDate="2019-03-04T23:57:07.357" Title="Digital transmission sounds" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;digital-voice&gt;&lt;lna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12942" PostTypeId="2" ParentId="12940" CreationDate="2019-03-04T10:08:15.593" Score="5" Body="&lt;p&gt;See SigiWiki:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;This wiki is intended to help identify radio signals through example&#xA;  sounds and waterfall images. Most signals are received and recorded&#xA;  using a software defined radio such as the RTL-SDR, Airspy, SDRPlay,&#xA;  HackRF, BladeRF, Funcube Dongle, USRP or others.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.sigidwiki.com/&quot; rel=&quot;noreferrer&quot;&gt;https://www.sigidwiki.com/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-03-04T10:08:15.593" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12946" PostTypeId="2" ParentId="12940" CreationDate="2019-03-04T23:57:07.357" Score="3" Body="&lt;p&gt;Here's one from the designer of fldigi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w1hkj.com/modes/index.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w1hkj.com/modes/index.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-03-04T23:57:07.357" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12947" PostTypeId="1" CreationDate="2019-03-05T01:19:51.843" Score="2" ViewCount="510" Body="&lt;p&gt;I am brand new to AX25 on a Raspberry Pi with a TNC-Pi and Baofeng UV5R. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a BBS at WE1CT-4 which is line of sight at 3 miles. Do I just axcall 1 WE1CT-4. and the BBS will magically appear (if its active)?&lt;/p&gt;&#xA;" OwnerUserId="14381" LastEditorUserId="9493" LastEditDate="2019-03-05T23:11:41.853" LastActivityDate="2019-03-05T23:58:24.007" Title="Raspberry Pi with TNC-Pi - How to Connect to BBS" Tags="&lt;packet&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12951" PostTypeId="1" CreationDate="2019-03-05T19:44:05.347" Score="3" ViewCount="1651" Body="&lt;p&gt;I am reposting &lt;a href=&quot;https://ham.stackexchange.com/questions/6378/where-year-2016-falls-in-the-sun-spot-cycle-for-hf-propagation&quot;&gt;this question about the year 2016&lt;/a&gt; here. This is 2019.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Are we now at the good or bad portion of the 11 years cycle?&lt;/li&gt;&#xA;&lt;li&gt;What effect are we seeing now?&lt;/li&gt;&#xA;&lt;li&gt;How large (strong/deep) is the effect during the peak and bottom of cycle?&lt;/li&gt;&#xA;&lt;li&gt;What will change in coming years?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-03-05T20:04:04.287" LastActivityDate="2020-01-01T08:20:09.073" Title="Where does the year 2019 fall in the sunspot cycle for HF propagation?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;sunspots&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12952" PostTypeId="2" ParentId="12951" CreationDate="2019-03-05T19:58:59.947" Score="2" Body="&lt;p&gt;&lt;strong&gt;TL;DR: As of March 2019, we have not yet reached the minimum of the current solar cycle. But we are close.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://spaceweatherarchive.com/2018/09/27/the-chill-of-solar-minimum/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Spaceweather.com&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5h0be.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5h0be.png&quot; alt=&quot;Thermosphere climate index&quot;&gt;&lt;/a&gt;&#xA;Above: An historical record of the Thermosphere Climate Index. Mlynczak and colleagues recently published a paper on the TCI showing that the state of the thermosphere can be discussed using a set of five plain language terms: Cold, Cool, Neutral, Warm, and Hot.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;“Right now, it is very low indeed,” says Mlynczak. “SABER is currently&#xA;  measuring 33 billion Watts of infrared power from NO. That’s 10 times&#xA;  smaller than we see during more active phases of the solar cycle.”&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;As 2018 comes to an end, the Thermosphere Climate Index is on the&#xA;  verge of setting a Space Age record for Cold. “We’re not there quite&#xA;  yet,” says Mlynczak, “but it could happen in a matter of months.”&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-03-05T19:58:59.947" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12953" PostTypeId="2" ParentId="12947" CreationDate="2019-03-05T23:23:59.970" Score="3" Body="&lt;p&gt;Assuming that you have:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;correctly connected your Baofeng to the TNC&lt;/li&gt;&#xA;&lt;li&gt;installed the AX25-tools and AX25-apps&lt;/li&gt;&#xA;&lt;li&gt;configured /etc/ax25/axports with your call and the baud rate&lt;/li&gt;&#xA;&lt;li&gt;attached the serial port to the AX.25 system using kissattach&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;then you may first want to listen for AX25 traffic on that frequency by typing:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt; sudo axlisten –a&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Finally, you can connect to the BBC by typing:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt; axcall 1 WE1CT-4&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;There should be a short pause and then you will see the splash screen from the BBS.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-05T23:58:24.007" LastActivityDate="2019-03-05T23:58:24.007" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12954" PostTypeId="1" AcceptedAnswerId="12957" CreationDate="2019-03-06T07:53:06.693" Score="1" ViewCount="475" Body="&lt;p&gt;I imagine that a repeater atop a building for which the repeater owner has sought permission would be sharing the same power source as that of the building occupants, but:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What if the repeater is installed in a remote area on a mountaintop or hill?&lt;/li&gt;&#xA;&lt;li&gt;In general, how much would the repeater owner(s) be spending a month&#xA;on electricity?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13927" LastEditorUserId="13927" LastEditDate="2019-03-06T10:30:34.330" LastActivityDate="2019-03-06T13:11:02.043" Title="From where do repeaters get their power supply?" Tags="&lt;repeater&gt;&lt;power-supply&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12955" PostTypeId="2" ParentId="12954" CreationDate="2019-03-06T10:29:26.047" Score="0" Body="&lt;p&gt;According to &lt;a href=&quot;http://www.repeater-builder.com/rbtip/repeater101.html&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Repeater101&quot;&gt;Repeater 101,&lt;/a&gt; repeater owners can choose how to get their power supply. Most repeaters use commercial power lines, or they may employ a slew of power backup systems such as batteries or generators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not uncommon for repeaters to use alternative sources of power, but they are mostly built to primarily run from batteries and recharge them only as needed. This makes them extremely power-efficient.&lt;/p&gt;&#xA;" OwnerUserId="13927" LastActivityDate="2019-03-06T10:29:26.047" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12957" PostTypeId="2" ParentId="12954" CreationDate="2019-03-06T11:12:56.943" Score="9" Body="&lt;p&gt;You are correct that most repeaters that are on buildings or typical towers get their energy from the commercial grid. The repeaters that I own are all commercially powered. Repeaters that are installed in remote locations almost always use solar panels with storage batteries as their energy source. I have talked with one repeater group that supplemented their solar energy with wind energy but they did it as an experiment and didn't feel it was practical at their location to use it as the sole energy source.&lt;/p&gt;&#xA;&lt;p&gt;How much energy a repeater uses varies widely based upon the repeater construction, the amount of transmitter output power, and the duty cycle (idle vs. transmit) of the repeater. So we can put together a formula but many of the values vary according to the specifics of the repeater. I will use data from my repeaters to exemplify the formulas. The following examples and formulas are designed to be illustrative but not exhaustive.&lt;/p&gt;&#xA;&lt;p&gt;Most solid state repeaters run off of a 12 volt bus. If the repeater is powered from a commercial mains supply, then a mains to 12 volt power supply is involved. This power supply has a conversion efficiency as it steps the mains supply down to 12 volts. Let's call this efficiency &lt;span class=&quot;math-container&quot;&gt;$k_1$&lt;/span&gt;. If the supply is a linear design, &lt;span class=&quot;math-container&quot;&gt;$k_1$&lt;/span&gt; can typically range from 65% to 75%. If the supply is a switching supply, &lt;span class=&quot;math-container&quot;&gt;$k_1$&lt;/span&gt; will typically range from 85% to 95%. My repeaters use a linear supply that is about 70% efficient.&lt;/p&gt;&#xA;&lt;p&gt;Because a repeater must be always listening for a signal, the receiver of the repeater must always be powered on. In the repeaters that I own, the receiver draws about 0.5 amps off of the 12 volt supply. We can then calculate the required receiver power as:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$P_{rcvr}=EI/k_1=12*0.5/0.7=8.6 \text{ watts} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The transmitter in the repeater is generally turned off until the repeater is transmitting. The power output of a repeater transmitter will be anywhere from 10 watts to 250 watts. Above 250 watts is generally not used because even with a duplexer, the receiver desense becomes problematic. My repeaters put out about 80 watts. Power amplifiers in the transmitter have an efficiency factor that we will call &lt;span class=&quot;math-container&quot;&gt;$k_2$&lt;/span&gt;. Most FM and digital repeaters use a class C amplifier that will be about 80% efficient.&lt;/p&gt;&#xA;&lt;p&gt;Since the repeater is not transmitting all the time, we need to apply a duty cycle factor that we will call &lt;span class=&quot;math-container&quot;&gt;$k_3$&lt;/span&gt;. This factor should be a representative average over a 24 hour, 7 day cycle. For the purposes of this estimate, let's call this 10%. We can now calculate the average transmitter power as:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$P_{xmtr}=\frac{P_{out}k_3}{k_1k_2}=\frac{80*0.1}{0.7*0.8}=14.3 \text{ watts} \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The repeater also has a controller in it that monitors all the subsystems, turns on the transmitter, identifies the repeater, etc. On my repeaters, this draws about 0.5 amps. We can calculate the power required as:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$P_{cntl}=EI/k_1=12*0.5/0.7=8.6 \text{ watts} \tag 3$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;So if we add the three power terms from formulas 1, 2 and 3 together, we have an average power consumption of 31.5 watts.&lt;/p&gt;&#xA;&lt;p&gt;In the USA, we buy electricity by the kilowatt hour. There are ~731 hours in the average month, so the monthly energy requirement is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$kW⋅h=P_{watts}h/1000=31.5*731/1000=23 \text{ kW⋅h} \tag 4$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The &lt;a href=&quot;https://www.chooseenergy.com/electricity-rates-by-state/&quot; rel=&quot;noreferrer&quot;&gt;average electric energy rate in the US&lt;/a&gt; is 0.1247 US dollars per kilowatt hour. Using that as a basis, this example repeater owner would pay 2.87 dollars per month for the energy. In the USA, this may not tell the full story as there is often a minimum monthly billing or a facility charge that can come into play. At one of my repeater locations, for example, the energy charge is only 0.06851 dollars per kWh but there is an additional monthly facility charge of 24 dollars.&lt;/p&gt;&#xA;&lt;p&gt;In some installations, a cooling or heating system may also be required in order to keep the repeater within its allowable operating temperature range. It would not be unusual that this system would consume more energy than the repeater itself. As an example, a simple fan tray could in itself consume 80 watts which is 58 kWh per month.&lt;/p&gt;&#xA;&lt;p&gt;Note that if the repeater is running off of solar, the repeater owner will likely spend more time optimizing the energy consumption of the repeater. It will also likely be designed to run directly off of the 13.8 volt battery bus so there is no linear or switching supply efficiency factor. However, there is a charge controller between the solar panels and the battery that will have a comparable efficiency factor that affects the sizing of the required solar panels.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-03-06T13:11:02.043" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12960" PostTypeId="1" AcceptedAnswerId="12961" CreationDate="2019-03-06T17:43:31.720" Score="7" ViewCount="1503" Body="&lt;p&gt;Let's say I have a 25 W transmitter. First I transmit some SSB signal with 2500 Hz bandwidth (no audio compressor is used, etc...). Then I transmit a BPSK31 signal with at most 100 Hz bandwidth using the same power. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it accurate to say that BPSK31 signal is at least 2500/100 = 25 times stronger, e.g. it will be received as if an SSB signal was transmitted using 625 W? Or, in other words, if someone somewhere receives my SSB signal with some level, he or she will receive a BPSK31 signal transmitted using 1 W with the same level?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is false, what is the actual relation between the signal strength and its bandwidth, if there is any?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="76" LastEditDate="2019-03-06T18:12:56.000" LastActivityDate="2019-03-07T02:52:36.507" Title="How does signal strength relate to bandwidth?" Tags="&lt;digital-modes&gt;&lt;ssb&gt;&lt;theory&gt;&lt;bandwidth&gt;&lt;psk31&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12961" PostTypeId="2" ParentId="12960" CreationDate="2019-03-06T18:11:50.917" Score="12" Body="&lt;p&gt;It depends on what you mean by &quot;stronger&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ignoring actual limitations of your hardware and just considering the theory of communications, if you have 25 W of transmit power, then you can spread that over as much bandwidth as you want, and &lt;strong&gt;you're always transmitting 25 W of power.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The quantity which is 25 times higher in the 100 Hz case than the 2500 Hz case is called &lt;em&gt;power spectral density&lt;/em&gt; (PSD), which we can get by dividing the power by the bandwidth and measure in watts per hertz. &lt;strong&gt;In your two cases you're transmitting 0.25 W/Hz and 0.01 W/Hz;&lt;/strong&gt; that's how they are different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The place that PSD starts being interesting to calculate with is when you want to consider &lt;em&gt;noise&lt;/em&gt; — by which I mean here “all RF that is not your transmitter”. We can roughly approximate noise as having a constant PSD (this is true when it is primarily wideband natural or manmade noise as opposed to strong transmissions specifically on the same or a nearby frequency). From this we can conclude that if your receiver's filter is wider, it receives proportionally more noise power along with the desired transmission — making the signal-to-noise ratio (SNR) worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why — to compare two modes that are alike in that they are both decoded by ear — CW can get through where SSB cannot, because the signal-to-noise ratio is much higher in the narrow bandwidth of CW. (It also helps that the ear has to distinguish only the beginning and end of the tone rather than phonemes; in digital terminology, there are fewer &lt;em&gt;symbols&lt;/em&gt; the receiver must discriminate between. Of course, that means that information is being transmitted at a slower rate.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;However, you should not conclude that using the same power in less bandwidth &lt;em&gt;always&lt;/em&gt; improves SNR &lt;em&gt;after demodulation.&lt;/em&gt; For example, spread-spectrum transmissions use a very wide bandwidth without correspondingly worse performance. To see why this can be true, consider a simple frequency-hopping spread spectrum system: the receiver and the transmitter agree on a sequence of frequencies to rapidly jump between in sync with each other. Therefore, at any moment the receiver only uses the signal in that narrow bandwidth, with correspondingly low noise, even though overall the system occupies a wide bandwidth. This effect is called &lt;a href=&quot;https://en.wikipedia.org/wiki/Process_gain&quot; rel=&quot;nofollow noreferrer&quot;&gt;process gain&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-03-07T02:52:36.507" LastActivityDate="2019-03-07T02:52:36.507" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12962" PostTypeId="2" ParentId="12960" CreationDate="2019-03-07T02:36:00.210" Score="3" Body="&lt;p&gt;If by &quot;strength&quot; you mean &quot;subjective volume as determined by a human operator&quot;, then reducing the bandwidth of the transmission while keeping the transmitter power constant does indeed produce a &quot;stronger&quot; signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is because noise is typically assumed to have a constant power spectral density over some range of frequencies of interest. Meaning, every hertz of bandwidth has some amount of power in it. Double the bandwidth, and the noise power is doubled. However the signal has the same power regardless of bandwidth. Thus, narrowing the bandwidth reduces the noise power, and increases the signal to noise ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We could write this mathematically as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{subjective strength} \approx {S \over N_0 B} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$S$&lt;/span&gt; is the received signal power in watts&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$N_0$&lt;/span&gt; is the noise spectral power density in watts per hertz&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$B$&lt;/span&gt; is the channel bandwidth in hertz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If the transmitter power is fixed, and we can't increase the received power by upgrading the antennas, reducing the transmission distance, etc., and the noise power is fixed by the conditions at the time, then the only thing we can really change is &lt;span class=&quot;math-container&quot;&gt;$B$&lt;/span&gt; by choosing to transmit a wider or narrower modulation. We can then adjust the receiver filter bandwidth to remove noise outside the bandwidth also occupied by the signal, or even if we don't adjust the receiver filter the human auditory system is pretty good at doing this kind of filtering without any additional help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if your definition of a &quot;strong signal&quot; is &quot;could theoretically send more information per unit time&quot;, a narrow modulation is actually worse. You need the &lt;a href=&quot;https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;Shannon-Hartley theorem&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{channel capacity in bits/sec} = B \log_2\left( 1 + {S \over N_0 B} \right) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Shannon-Hartley theorem provides an upper theoretical limit on the rate at which information can be communicated in an &lt;a href=&quot;https://en.wikipedia.org/wiki/Additive_white_Gaussian_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;additive white Gaussian noise&lt;/a&gt; (AWGN) channel. Actual communication may occur at below this rate of course, but not above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, say the signal power (&lt;span class=&quot;math-container&quot;&gt;$S$&lt;/span&gt;) is 1 (the particular unit doesn't matter, as long as we use the same one for noise) and the noise density (&lt;span class=&quot;math-container&quot;&gt;$N_0$&lt;/span&gt;) is 0.000004. This gives a SNR of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {1 \over 0.000004 \cdot 2500} = 100 = 10\:\mathrm{dB} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a reasonable SNR for an intelligible SSB contact. The theoretical maximum channel capacity is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 2500 \log_2\left( 1 + {1 \over 0.000004 \cdot 2500} \right) = 16646\:\text{bits/sec} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a bit odd to think of spoken words in terms of bits per second, yet &lt;a href=&quot;http://people.seas.harvard.edu/~jones/cscie129/papers/stanford_info_paper/entropy_of_english_9.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;within information theory this is a valid thing to do&lt;/a&gt;. We could just as easily consider this example as any digital modulation that occupies 2500 Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now reducing the bandwidth to 100 Hz yields a channel capacity of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 100 \log_2\left( 1 + {1 \over 0.000004 \cdot 100} \right) = 1129\:\text{bits/sec} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is actually an order of magnitude &lt;em&gt;decrease&lt;/em&gt; in channel capacity. So in this sense, a narrower bandwidth is actually &lt;em&gt;weaker&lt;/em&gt;! Although the narrower channel may be easier to hear, its theoretical capacity to communicate information is less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can this be? Say the modulation is something really simple, like the transmitter is either on for 1 seconds transmitting a steady carrier, or it's off. The receiver has to decide for each 1 second interval if the transmitter is on or off. This can occupy a very small bandwidth, &lt;a href=&quot;https://en.wikipedia.org/wiki/Nyquist_rate#Nyquist_rate_relative_to_signaling&quot; rel=&quot;nofollow noreferrer&quot;&gt;0.5 Hz at a minimum&lt;/a&gt;. And let's further assume the transmitter power is high enough that the chance of an error is negligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this 0.5 Hz, one bit is communicated per second.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now say we have four receivers each tuned to a slightly different frequency, and in each interval, the transmitter will transmit on one of the 4 frequencies.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;If the first receiver detects the tone, we say this means 00.&lt;/li&gt;&#xA;&lt;li&gt;If the second receiver detects the tone, this means 01.&lt;/li&gt;&#xA;&lt;li&gt;The third receiver, 10, and...&lt;/li&gt;&#xA;&lt;li&gt;the fourth receiver, 11.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Adding more receivers doesn't make any one of them less reliable, so simply increasing the channel bandwidth also increases the channel capacity.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-03-07T02:49:38.347" LastActivityDate="2019-03-07T02:49:38.347" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12963" PostTypeId="1" CreationDate="2019-03-07T05:01:13.427" Score="2" ViewCount="189" Body="&lt;p&gt;This is a hobby project to learn more about GPS technology.&lt;/p&gt;&#xA;" OwnerUserId="14401" LastEditorUserId="7804" LastEditDate="2019-11-03T01:53:15.667" LastActivityDate="2019-11-03T01:53:15.667" Title="What equipment and software do I need to read raw civilian GPS signals on my Mac?" Tags="&lt;receiver&gt;&lt;gnss&gt;&lt;macos&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12966" PostTypeId="2" ParentId="12963" CreationDate="2019-03-07T08:45:23.443" Score="6" Body="&lt;p&gt;I will answer this question from a &quot;technology of radio&quot; perspective, because half of the question is very much related to the technology of radio. The other half is related to the decoding of a data stream from multiple GPS satellites, and that is beyond the scope of this site.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to receive the data from the GPS satellites, your best bet would be to have an outdoor antenna at a good height (to be able to see as much of the horizon as possible), tuned to the frequencies on which the GPS satellites transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to &lt;a href=&quot;https://en.wikipedia.org/wiki/GPS_signals&quot; rel=&quot;noreferrer&quot;&gt;the Wikipedia page on GPS signals&lt;/a&gt;, there are two frequencies: the so-called L1 frequency is 1575.42MHz, and the L2 frequency is 1227.60MHz. Your antenna would need to be able to receive both of these frequencies. Either a discount antenna designed for use up to 1.6GHz, or an actual GPS external antenna, would do nicely for this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Actually decoding and turning the received radio signals into data is something that is beyond the scope of this site (being specifically for &quot;amateur radio&quot; in the strictest sense), but in order to turn the received signals at radio frequencies (RF) into data that you can work on on your computer, your best bet would probably be an SDR receiver (these can be found very cheaply - search for RTL SDR for plenty of information) and some SDR software (perhaps GNU Radio or similar). Once you have turned the RF into a data stream, you can then work on decoding it in software.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-03-07T08:45:23.443" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12967" PostTypeId="1" AcceptedAnswerId="12971" CreationDate="2019-03-07T10:01:46.157" Score="8" ViewCount="1110" Body="&lt;p&gt;Recently I've build a trap dipole for 20/40/80m bands. I followed an &lt;a href=&quot;http://degood.org/coaxtrap/&quot; rel=&quot;nofollow noreferrer&quot;&gt;article&lt;/a&gt; by John DeGood, NU3E and got following measurements:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;From balun to 20m trap: 485 cm&lt;/li&gt;&#xA;&lt;li&gt;From 20m trap to 40m trap: 362 cm&lt;/li&gt;&#xA;&lt;li&gt;From 40m trap to the end of the arm: 530 cm&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;You can find a complete description of the antenna (including descriptions of the balun, used wire, etc) &lt;a href=&quot;https://eax.me/diy-dipole/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;https://eax.me/diy-trap-dipole/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; (in Russian, but Google Translate should manage; please email me if you got any questions).&lt;/p&gt;&#xA;&lt;p&gt;Since 20m trap acts as a loading coil on 40 and 80 meters and 40m trap acts as a loading coil on 80m the antenna turned out to be much shorter than a full-size 80m dipole, and thus probably less efficient on both 40m and 80m bands. I would like to estimate what is the efficiency of the antenna on these bands &lt;em&gt;relative&lt;/em&gt; to corresponding full-size dipoles (not an absolute efficiency). The problem is I'm not a mathematician and don't know much about antenna theory.&lt;/p&gt;&#xA;&lt;p&gt;I was thinking about the following method:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yE9Me.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yE9Me.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It is based on the fact that the current distribution in the antenna is sinusoidal; it radiates more in the proximity to the balun and almost doesn't radiate at the end of the arm. The radiation and size of the coil are considered neglectable.&lt;/p&gt;&#xA;&lt;p&gt;I used &lt;a href=&quot;https://www.scipy.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;SciPy&lt;/a&gt; to calculate an efficiency of the dipole on 40m band:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;&amp;gt;&amp;gt;&amp;gt; from scipy.integrate import quad as integrate&#xA;&amp;gt;&amp;gt;&amp;gt; from math import cos, pi&#xA;&amp;gt;&amp;gt;&amp;gt; wl = 40 # 40 m band&#xA;&amp;gt;&amp;gt;&amp;gt; bc = 4.85 # 485 cm before the coil&#xA;&amp;gt;&amp;gt;&amp;gt; ac = 3.62 # 362 cm after the coil&#xA;&amp;gt;&amp;gt;&amp;gt; integrate(cos, 0, ((bc)/(wl/4))*(pi/2))[0] + \&#xA;...         integrate(cos, ((wl/4 - ac)/(wl/4))*(pi/2), pi/2)[0]&#xA;0.847610828074005&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;... and got 84.76% efficiency comparing to a full-size 40m dipole. Naturally this is only a rough estimate, and I'm not interested in calculating a very-very accurate value.&lt;/p&gt;&#xA;&lt;p&gt;Now I have two questions. 1) Is this method more or less OK or is it completely wrong? If it's wrong could you please suggest a better method? 2) Can this method be generalized for 2 and more coils? The problem is that I don't know in which phase the current is between two coils. Thus currently I can only estimate an upper (70%) and lower (41.1%) bounds for 80m, by ignoring one of the coils, and tell that the actual efficiency is somewhere in between (55.5%).&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2021-05-19T07:53:49.510" LastActivityDate="2021-05-19T07:53:49.510" Title="Estimating the efficiency of a shortened (loaded) antenna" Tags="&lt;antenna-theory&gt;&lt;dipole&gt;&lt;efficiency&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12969" PostTypeId="1" CreationDate="2019-03-07T12:50:00.687" Score="3" ViewCount="81" Body="&lt;p&gt;Complete radio ignoramous here. I've been playing a game called &lt;a href=&quot;https://store.steampowered.com/app/599080/The_Blackout_Club/&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Blackout Club&lt;/a&gt;, and I'd quite like to make a 3D model of a radio set for it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The game is set around 2007 and, as in the picture below, features young teenagers (13-17 years old) monitoring the communications of a sinister conspiracy which uses radio to send commands to their field agents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/foEMF.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/foEMF.jpg&quot; alt=&quot;One of the tutorial texts from the game&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be nice if my 3D model fit the tone / period of the game as much as possible - and so I'm turning to you, the specialists! Can anybody suggest a suitable make and model for me? Something that would be suitable for a dispatcher at their home base? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was looking at military radios earlier, but I figure they'd probably be encrypted... this needs to be something that an average person could use, that could be intercepted by a teenager.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you reading my odd request!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;--Rev&lt;/p&gt;&#xA;" OwnerUserId="14407" LastActivityDate="2019-03-07T12:50:00.687" Title="Can anybody identify an appropriate radio for this game?" Tags="&lt;united-states&gt;&lt;transmitter&gt;&lt;fox-hunt&gt;" AnswerCount="0" CommentCount="8" ClosedDate="2019-03-07T15:11:10.043" ContentLicense="CC BY-SA 4.0" />
  <row Id="12970" PostTypeId="2" ParentId="12963" CreationDate="2019-03-07T13:55:13.143" Score="4" Body="&lt;p&gt;Start with a GPS receiver that outputs &lt;a href=&quot;https://www.gpsworld.com/what-exactly-is-gps-nmea-data/&quot; rel=&quot;nofollow noreferrer&quot;&gt;NMEA data&lt;/a&gt;. This data will be made available through a serial connection such as RS-232, USB, or Bluetooth. Pick a serial connection that you can use with your MAC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the MAC you will need a serial terminal emulation program (not to be confused with the MAC terminal program). A program such as &lt;a href=&quot;https://www.decisivetactics.com/products/serial/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Serial&lt;/a&gt; would do the job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Configure the Serial program to access the port to which the GPS receiver is connected. You will then begin to see the raw NMEA data from the GPS receiver in your Serial program. All sentences begin with a &quot;$&quot; sign and all fields are comma separated. Here is an example from the above link:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;$GPGGA,181908.00,3404.7041778,N,07044.3966270,W,4,13,1.00,495.144,M,29.200,M,0.10,0000&#xA;  *40&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This information in this string can be broken down as follows (again taken from the earlier link):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;GP&lt;/strong&gt; represent that it is a GPS position (GL would denote GLONASS).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;181908.00&lt;/strong&gt; is the time stamp: UTC time in hours, minutes and seconds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;3404.7041778&lt;/strong&gt; is the latitude in the DDMM.MMMMM format. Decimal places are variable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;N&lt;/strong&gt; denotes north latitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;07044.3966270&lt;/strong&gt; is the longitude in the DDDMM.MMMMM format. Decimal places are variable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;W&lt;/strong&gt; denotes west longitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;4&lt;/strong&gt; denotes the Quality Indicator:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;13&lt;/strong&gt; denotes number of satellites used in the coordinate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;1.0&lt;/strong&gt; denotes the HDOP (horizontal dilution of precision).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;495.144&lt;/strong&gt; denotes altitude of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;M&lt;/strong&gt; denotes units of altitude (eg. Meters or Feet)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;29.200&lt;/strong&gt; denotes the geoidal separation (subtract this from the altitude of the antenna to arrive at the Height Above Ellipsoid (HAE).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;M&lt;/strong&gt; denotes the units used by the geoidal separation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;1.0&lt;/strong&gt; denotes the age of the correction (if any).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;0000&lt;/strong&gt; denotes the correction station ID (if any).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;*40&lt;/strong&gt; denotes the checksum.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-07T15:08:28.153" LastActivityDate="2019-03-07T15:08:28.153" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12971" PostTypeId="2" ParentId="12967" CreationDate="2019-03-07T14:52:20.810" Score="6" Body="&lt;p&gt;I applaud you for diving into this topic. The notion of trap efficiency has been driven largely by antenna marketing FUD (Fear, Uncertainty, and Doubt) with implicative phrases such as &quot;no lossy traps&quot;. Since then, hams have been wringing their hands at the thought of all of those losses in their favorite trap antenna. Here is a current example of such an advertisement:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/z44co.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/z44co.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, your integral approach to the analysis of trap loss will not present usable results. You have effectively pieced together two different antennas while calling the missing current the loss. In order to understand the underlying issues, it pays to briefly explore wave mechanics as they apply to a dipole antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a wave mechanics perspective, when current initially begins to flow at the feedpoint of a dipole into one of the legs, it travels along the length of the wire until it hits the open end of the dipole. Because the wire has a finite thickness, there is a small amount of &lt;a href=&quot;https://wikipedia.org/wiki/Capacitance#Self_capacitance&quot; rel=&quot;nofollow noreferrer&quot;&gt;self capacitance&lt;/a&gt; present at the end. Since this capacitance does not present the same impedance at which the current was flowing, it forms an &lt;a href=&quot;http://physics.usask.ca/~hirose/ep225/animation/reflection/anim-reflection.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance discontinuity&lt;/a&gt;. Any impedance discontinuity forms a complex reflection coefficient that sends (in this case) all of the current traveling in the opposite direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/N6eLR.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/N6eLR.gif&quot; alt=&quot;Credit to http://physics.usask.ca/~hirose/ep225/animation/reflection/anim-reflection.htm&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once this reflected current reaches the feedpoint of the antenna, the current standing wave pattern on the antenna fully is established. It has a near sinusoidal shape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can repeat the above wave mechanics from the perspective of a voltage wave that will also develop a voltage standing wave. It is the ratio of the voltage standing wave to the current standing wave that determines the impedance at any point along the antenna wire. This is the mechanism by which the feedpoint impedance changes when moving from a center fed to an off center feed dipole arrangement, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When we insert a trap somewhere along the wire, consider what changes. The current starts from the feedpoint as before but when it reaches the trap, there is an impedance discontinuity that establishes a complex reflection coefficient. In this case, part of the current is reflected back toward the feedpoint and part of the current continues through the trap, toward the end of the wire. The portion of the current that reaches the end of the wire is reflected back as before. But when the reflected current reaches the trap, this is another impedance discontinuity. So part of the current passes through the trap and heads for the feedpoint and part is reflected back towards the end of the antenna. Clearly, the trap has significantly altered the wave mechanics compared to simple wire dipole and as a result, the analysis has become very complex.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Despite the very complex wave mechanics, we can still reason that any resistive losses attributable to the trap are largely due to the current passing through the trap. The challenge though is in describing the current profile associated with the trap. Most of the credible analysis you will find in this regard uses computer modeling based on NEC to assess the losses. Unfortunately, I have not found any credible field measurements that have validated the NEC modeling of trap loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the well constructed NEC models suggest that a reasonably constructed trap will have losses &amp;lt;&amp;lt; 0.5 dB. One such example is &lt;a href=&quot;https://www.w8ji.com/traps.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this analysis&lt;/a&gt; by W8JI. It is notable however, that through the use of bold type and lots of exclamation marks, there seems to be implicit surprises and contradictions noted by the author. Perhaps some of this is attributable to no apparent consideration of the underlying wave mechanics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then just when you start to get a grasp on the wave mechanics, it turns out that the inductor itself can have standing waves along its length. Here is an interesting lab picture from &lt;a href=&quot;http://g3ynh.info/zdocs/magnetics/appendix/self_res/gallery.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dr. David Knight&lt;/a&gt; that shows a wave traveling along an inductor is reflected at the impedance discontinuities that occur at the ends of the wire of the inductor. The picture shows a gas discharge tube in close proximity to an inductively excited coil:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mIy92.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mIy92.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This suggests that a more rigorous analysis should include any standing wave effects associated with the trap itself.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-07T15:57:09.920" LastActivityDate="2019-03-07T15:57:09.920" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="12972" PostTypeId="1" AcceptedAnswerId="12974" CreationDate="2019-03-07T17:52:39.733" Score="4" ViewCount="273" Body="&lt;p&gt;I'm currently studying for the General Exam and in looking at charts of the new frequency privileges have run across a restriction I would like to have further defined. In the 160 meter band the books all say &quot;1.90 MHz thru 2.0 MHz should be treated as a secondary allocation as we are required to avoid interfering with Radio-location Services in that range.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are Radio-location Services at 1.90-2.0 MHz?&lt;/p&gt;&#xA;" OwnerUserId="14182" LastEditorUserId="76" LastEditDate="2019-03-07T18:21:32.023" LastActivityDate="2019-03-08T13:57:05.357" Title="What are Radio-location Services in the 1.9-2.0 MHz range?" Tags="&lt;united-states&gt;&lt;hf&gt;&lt;frequency&gt;&lt;160m-band&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12973" PostTypeId="2" ParentId="12967" CreationDate="2019-03-07T17:56:49.137" Score="5" Body="&lt;p&gt;&quot;The ARRL Antenna Book&quot; uses the &lt;strong&gt;&lt;em&gt;lumped circuit model&lt;/em&gt;&lt;/strong&gt; for HF loading coils which is an inaccurate thing to do in a &lt;strong&gt;&lt;em&gt;distributed network&lt;/em&gt;&lt;/strong&gt; circuit with reflections. The helix model in EZNEC presents a much more accurate picture as does the distributed network model or Maxwell's Equations.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/QE2VH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QE2VH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My web page at &lt;a href=&quot;http://www.w5dxp.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;www.w5dxp.com&lt;/strong&gt;&lt;/a&gt; has a lot of information on HF loading coils, some that contradicts the conventional &quot;wisdom&quot; on the topic. In general, an HF loading coil can be treated somewhat like a transmission line with a characteristic impedance and electrical length. There is also a largely ignored current &quot;bulge&quot; inside a loading coil that affects losses in the coil. That &quot;bulge&quot; can cause the loading coil to have the highest &lt;strong&gt;&lt;em&gt;standing wave current&lt;/em&gt;&lt;/strong&gt; in the system. Notice how &quot;The ARRL Antenna Book&quot; has the current decreasing in the bottom section between the feedpoint and the bottom of the coil and a constant current through the coil while, in reality, &lt;strong&gt;&lt;em&gt;the standing wave current&lt;/em&gt;&lt;/strong&gt; actually increases in the bottom section and increases even more through the loading coil. There's just too much information to be included here. Please visit my web page at &lt;a href=&quot;http://www.w5dxp.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;www.w5dxp.com&lt;/strong&gt;&lt;/a&gt; and digest the articles on loading coils.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-03-08T13:57:00.847" LastActivityDate="2019-03-08T13:57:00.847" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12974" PostTypeId="2" ParentId="12972" CreationDate="2019-03-07T18:11:49.537" Score="6" Body="&lt;p&gt;I wish you well with the general test!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiolocation services in question are defined in CFR 47 §2.106: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;NG92   The band 1900-2000 kHz is also allocated on a primary basis to the maritime mobile service in Regions 2 and 3 and to the radiolocation service in Region 2, and on a secondary basis to the radiolocation service in Region 3. &lt;strong&gt;The use of these allocations is restricted to radio buoy operations on the open sea and the Great Lakes&lt;/strong&gt;. Stations in the amateur, maritime mobile, and radiolocation services in Region 2 shall be protected from harmful interference only to the extent that the offending station does not operate in compliance with the technical rules applicable to the service in which it operates.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;EDIT&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I got to thinking about the comment by @RichardFry and wondered, how likely would it be that a ham could interfere with a fisherman trying to locate one of these beacons? Here is a rough first order analysis. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The output power of the buoy beacons run from 4 watts to 15 watts. The buoy antenna is a relatively short whip. So if the fisherman is searching for a 4 watt buoy in a 10 statute mile (8.6 nautical mile) radius and we assume the gain of the whip antenna is -10 dBi, a ham with a 100 watt transmitter and a 3 dBi gain antenna would have to be less than 220 miles away to have a signal equal to the buoy. That is a free space path loss calculation and the real path loss is likely to be greater so the ham would have to be even closer or use more power. It also does not account for the directionality of the fisherman's receive antenna which statistically speaking would be pointed unfavorably with respect to the ham's location.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on that very rough estimate, it seems very unlikely that the right distance, location, frequency, and time factors would come together to cause any real interference to the fisherman's objective. And if these factors would happen to align, the interference would be quite temporary.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-08T13:57:05.357" LastActivityDate="2019-03-08T13:57:05.357" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12975" PostTypeId="2" ParentId="12967" CreationDate="2019-03-08T15:01:24.287" Score="1" Body="&lt;p&gt;Calculating the current distribution on the antenna might be a way to determine the radiation resistance, but to arrive at efficiency will require incorporating loss in the equation. It will be tricky: as Cecil notes the current in the trap could be quite high. Depending on the kind of trap there may be significant dielectric losses to take into account. Ground losses are also relevant and quite site-dependent. Ultimately the complexity is high enough an empirical approach may be more feasible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would note a low SWR across a wide band suggests low efficiency. A plain half-wave dipole made of thin wire should have a &lt;a href=&quot;https://ham.stackexchange.com/q/6481/218&quot;&gt;2:1 SWR fractional bandwidth in the neighborhood of 6%&lt;/a&gt; if losses are low. Loading coils should reduce that bandwidth. So if your trap dipole has a bandwidth wider than that, it's a fair inference that antenna efficiency isn't great.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-08T15:01:24.287" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12976" PostTypeId="1" AcceptedAnswerId="12979" CreationDate="2019-03-08T15:03:33.223" Score="5" ViewCount="881" Body="&lt;p&gt;When I work in FT8 mode I often see signals like these:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bkTYm.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bkTYm.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I couldn't identify these signals using SigiWiki nor managed I to decode them using WSJT-X. Though these signals seem to use 15 second frames. They don't seem to be a noise created by stations that use too much power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it look like any amateur radio digital mode to you?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-10-04T08:50:42.973" Title="Unidentified signals on FT8 frequencies" Tags="&lt;digital-modes&gt;&lt;signal-identification&gt;&lt;ft8&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12977" PostTypeId="2" ParentId="12976" CreationDate="2019-03-08T17:59:15.410" Score="3" Body="&lt;p&gt;Both marked signals follow an 8 tone MFSK pattern. The one on the left is about 125 hertz wide while the one on the right is about 100 hertz wide.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal on the left appears to follow the waterfall that would be expected from an &lt;a href=&quot;https://en.wikipedia.org/wiki/Olivia_MFSK&quot; rel=&quot;nofollow noreferrer&quot;&gt;Olivia&lt;/a&gt; 8/125 (8 tones with 125 hertz bandwidth) signal although this is not a common Olivia mode. Olivia is a free typing, teletype like mode, so the 15 second sequence wouldn't apply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I cannot offer any suggestions for the 100 hertz wide signal on the right of the waterfall.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-03-08T17:59:15.410" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12978" PostTypeId="1" CreationDate="2019-03-08T08:56:30.610" Score="4" ViewCount="233" Body="&lt;p&gt;I noticed this antenna park in &lt;a href=&quot;https://goo.gl/maps/mAVk6KSk28H2&quot; rel=&quot;nofollow noreferrer&quot;&gt;Heidmoosstrasse&lt;/a&gt;, Switzerland. What is it used for? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/YD97S.png&quot; alt=&quot;Photo&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="4102" OwnerDisplayName="Loreno Heer" LastEditorUserId="76" LastEditDate="2019-03-08T18:36:21.320" LastActivityDate="2019-09-24T15:40:37.663" Title="What are these antennas used for?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;frequency&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12979" PostTypeId="2" ParentId="12976" CreationDate="2019-03-08T21:08:54.250" Score="5" Body="&lt;p&gt;The fact that they align properly to the FT8 15-second period, and have 8 tones (the same as FT8) is a sign that these may be distorted FT8 signals, caused by AF harmonics in the transmitter or the receiver. The one on the right, being about 100Hz wide, is a second harmonic, and the one on the left, being about 150Hz wide, may be a third harmonic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But before you go looking for the offending signal at 1/2 or 1/3 of the audio frequency, remember that when the &quot;Split&quot; option in wsjtx is set to &quot;Rig&quot; or &quot;Fake It&quot;, the software will adjust the TX VFO in order to put the transmit audio somewhere between 1500 and 2000 Hz. e.g. if you're on 14.074.000 and you put your transmit cursor on 235Hz, wsjtx will actually tune the rig to 14.072.500 and send it audio at 1735Hz; if you put your transmit cursor on 2560Hz, wsjtx will tune the rig to 14.075.000 and send it audio at 1560Hz. If the distortion is being caused by the transmitter, therefore, the subharmonic will probably &lt;em&gt;not&lt;/em&gt; appear on the waterfall at 1/2 or 1/3 of the frequency of the harmonic product.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even with this offsetting, a third harmonic anywhere to the left of 3000Hz on the waterfall is hard to explain, but it may be caused by frequency aliasing in the receive path. Perhaps someone else has a more complete explanation.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-03-08T21:08:54.250" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12980" PostTypeId="1" AcceptedAnswerId="12991" CreationDate="2019-03-08T21:28:10.427" Score="3" ViewCount="80" Body="&lt;p&gt;I recently bought a couple SPF5189 low-noise amplifier boards via an online marketplace. One thing that struck me is that while nearly all the listings highlighted the LNA as having a noise figure of 0.6 dB, very few listings actually specified its gain (which datasheet I found says is 18.7 dB typical) at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe I shouldn't read too much into it [half of these listings were from sellers with screennames like &quot;toecare best ecogreen 2015&quot;] but is there a technical reason that the noise figure specification would be more important than the gain figure?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly the &quot;low noise&quot; aspect is important but isn't the &quot;amplification&quot; the first thing I should know when inserting a block into a signal chain?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2019-03-08T22:05:34.300" LastActivityDate="2019-03-09T16:58:33.347" Title="Is there a technical reason to sell an LNA without advertising its gain?" Tags="&lt;rf-power&gt;&lt;path-loss&gt;&lt;lna&gt;&lt;link-budget&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12981" PostTypeId="2" ParentId="12978" CreationDate="2019-03-08T21:29:15.003" Score="4" Body="&lt;p&gt;There are several antennas of different types.  Near the front looks like a discone  antenna and the beam on the tower looks like a Log Periodic antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such an antenna farm is typical of a government or military installation.  In the US, the regional FEMA (Federal Emergency Management Agency) sites have similar antenna farms.  These are designed to provide multi-frequency (HF, VHF, UHF) communications in times of emergency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not familiar though with Switzerland but likely it is a government site.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2019-03-08T21:29:15.003" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12982" PostTypeId="2" ParentId="12978" CreationDate="2019-03-08T22:18:55.310" Score="5" Body="&lt;p&gt;&lt;strong&gt;UPDATE&lt;/strong&gt;: I've started a followup question regarding the leftmost antenna, which I originally took to be a discone. See: &lt;a href=&quot;https://ham.stackexchange.com/questions/15374/what-sort-of-antenna-would-use-a-biconic-arrangement-of-vertical-wires&quot;&gt;What sort of antenna would use a bicone or lozenge-like arrangement of vertical wires?&lt;/a&gt; (Thanks @HK1A for noticing my error!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see at least four antennas in that picture: one &lt;del&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Discone_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;discone&lt;/a&gt;&lt;/del&gt; &lt;a href=&quot;https://ham.stackexchange.com/questions/15374/what-happens-to-a-discone-style-antenna-if-the-cones-are-flipped?noredirect=1#comment23369_15374&quot;&gt;mystery antenna&lt;/a&gt; on the left, two &lt;a href=&quot;https://en.wikipedia.org/wiki/Log-periodic_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;log-periodic&lt;/a&gt; on towers in the middle, and a &lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;dipole&lt;/a&gt; above the building. All look like they are designed to work best at relatively low frequencies, specifically (and confusingly) within the &lt;a href=&quot;https://en.wikipedia.org/wiki/High_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;High Frequency (HF)&lt;/a&gt; region.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The discone and the LPDAs [would be] interesting to compare and contrast [even though there's probably not a discone in the picture after all]:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Opposite: a discone is omni-directional (receives/transmits fairly equally all around), while a LPDA is directional (signals focused to/from one direction).&lt;/li&gt;&#xA;&lt;li&gt;Opposite: though the &lt;a href=&quot;https://ham.stackexchange.com/questions/146/should-i-chose-a-vertical-or-a-horizontal-hf-antenna&quot;&gt;polarization&lt;/a&gt; is not terribly critical for HF signals, note that the discone is mounted for the vertical component, while the LPDAs are mounted for horizontal signals.&lt;/li&gt;&#xA;&lt;li&gt;But alike: both the discone and the LPDA are &quot;wide-band&quot; antennas, which means they work well through a whole range of frequencies. Most antennas work best only within say ± 1% of a particular &lt;a href=&quot;https://ham.stackexchange.com/a/6744/1362&quot;&gt;frequency and/or some harmonics&lt;/a&gt;, whereas these antennas work continuously from their lowest frequency to something 5–10x higher than that.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The dipole here is the one that almost looks like a telegraph wire coming out of the shack on the right and then T-ing out above the fence in the picture's framing. That one works on one or a small handful of &quot;fixed&quot; frequencies. Coupling &quot;broadside&quot;, it's not really &lt;a href=&quot;https://ham.stackexchange.com/questions/12096/dipole-antenna-radiation-field-equation&quot;&gt;omni-directional&lt;/a&gt; but it's not particularly directional either. I shouldn't make it sound too boring, because dipole antennas are pretty much the fundamental concept within the rest of antenna theory. Just not nearly so versatile, or cool-looking, as the other two :-)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2019-09-24T00:04:04.467" LastActivityDate="2019-09-24T00:04:04.467" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12983" PostTypeId="2" ParentId="1215" CreationDate="2019-03-08T23:14:05.767" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;It seems like there will be very few audio waveform cycles in short&#xA;  QRQ dots when using a very low tone frequency at a very high WPM&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's true; &lt;strong&gt;&lt;em&gt;but the number of cycles are still enough to copy&lt;/em&gt;&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;b&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The lower the tone, the less fatiguing when operating CW for hours.&lt;/li&gt;&#xA;&lt;li&gt;The lower the tone, the better we are able to separate and copy stations that are very close together.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;/b&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A high-speed CW op who could copy 70 WPM (&lt;a href=&quot;https://www.qrz.com/lookup/w8ji&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI&lt;/a&gt;) told me that. I worked beside him during the 1980 &lt;a href=&quot;http://www.arrl.org/160-meter&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL 160 Contest&lt;/a&gt;, and can testify to the wisdom of that.&#xA;&lt;hr&gt;&#xA;On my IC-765, I have the CW pitch set almost as low as it can go. Others have theirs set as high as it will go. To each his own. However, how low the sidetone can go depends on the operator.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-03-08T23:58:49.323" LastActivityDate="2019-03-08T23:58:49.323" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12984" PostTypeId="1" CreationDate="2019-03-08T23:42:33.153" Score="2" ViewCount="72" Body="&lt;p&gt;I am constantly on the lookout for effective yet inexpensive means to generate SSB signals. Analog Devices' LTC5598 Direct Quadrature Modulator turns baseband analog I/Q signals into RF from 5MHz to 1.6GHz. Sadly, the performance falls off dramatically for the amateur radio bands below 60 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would happen, theoretically, if the output of the LTC5598 could be processed through some frequency-dividing means to cover lower frequencies? Would the spectrum of the modulation be preserved, distorted or destroyed?&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="76" LastEditDate="2019-03-10T19:29:32.083" LastActivityDate="2019-03-10T19:29:32.083" Title="Effect of frequency division on a signal's spectrum" Tags="&lt;ssb&gt;" AnswerCount="2" CommentCount="6" ClosedDate="2019-03-10T19:29:41.973" ContentLicense="CC BY-SA 4.0" />
  <row Id="12987" PostTypeId="2" ParentId="1215" CreationDate="2019-03-09T15:06:08.727" Score="-1" Body="&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Nyquist_rate#Nyquist_rate_relative_to_signaling&quot; rel=&quot;nofollow noreferrer&quot;&gt;Nyquist rate&lt;/a&gt; tells us in a frequency range of B cycles per second, a maximum of 2B code elements per second can be resolved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The length of a dit is the fundamental unit of time in Morse code. &quot;PARIS&quot; is commonly used word for determining speed, and it's 50 dits long. So at a speed of 70 words per minute, that's 3500 dits per minute, or 58.33 dits per second. The Nyquist rate requires a frequency bandwidth of at least 29.17 Hz to encode something at that rate. Let's call it 30 Hz for a round number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the lower limit of human hearing is 20 Hz, that would imply the lowest possible range is 20 to 50 Hz. That would imply a sidetone frequency in the middle: 35 Hz, with sidebands arising from the amplitude modulation of the sidetone on and off occupying the 15 Hz above and below that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for 70 WPM morse code, the theoretically lowest sidetone frequency which could be audible is 35 Hz. It could be as low as 15 Hz, but that would simply be below the audible range of humans.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;70 WPM is pretty fast already, and the biggest limiting factor isn't the speed of the code but rather the limits of human hearing. So to a first order approximation, the answer to your question, &quot;How low a sidetone frequency will allow QRQ CW to be copied?&quot; is &quot;as low as you can hear.&quot; Hearing loss, genetics, and the frequency response of the speakers or headphones in use will be more limiting factors than the speed of the code.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-09T15:06:08.727" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12988" PostTypeId="1" CreationDate="2019-03-09T15:10:28.110" Score="2" ViewCount="816" Body="&lt;p&gt;I live in the city, with 50’x 100’ lots.  I use an 80 meter doublet at 30 feet, fed with ladder line to a tuner.  My noise floor ranges from S5 to S9 depending on the time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would a coax feed reduce the noise level, while eliminating my ability to tune all the HF bands?  Or is this just the nature of city living and the HF bands?  I tried a loop antenna and it actually has more noise!  I miss the suburbs for my ham radio hobby!&lt;/p&gt;&#xA;" OwnerUserId="14421" LastEditorUserId="4076" LastEditDate="2019-03-09T19:13:21.477" LastActivityDate="2019-03-12T21:27:17.600" Title="Doublet with ladder line vs coax w.r.t. noise" Tags="&lt;dipole&gt;&lt;feed-line&gt;&lt;noise&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12989" PostTypeId="2" ParentId="12988" CreationDate="2019-03-09T15:22:44.840" Score="2" Body="&lt;p&gt;No, coax wouldn't be expected to improve the noise, unless your ladder line is running very close (within 1-2 times its conductor spacing) to a specific noise source, in which case you would be better off fixing &lt;em&gt;that&lt;/em&gt; by finding a way to provide better spacing. The only thing that will change with coax is that your losses will become quite a bit higher, and more of your transmit power will be spent on heating the coax instead of making radio waves, especially when operating the doublet far away from a match with the coax.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-03-09T15:22:44.840" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="12990" PostTypeId="2" ParentId="12984" CreationDate="2019-03-09T16:51:01.907" Score="3" Body="&lt;p&gt;The spectrum of the modulation would also be reduced. Imagine a 1MHz suppressed-carrier upper-sideband signal (so that we can talk about the carrier, as well) that has a single audio tone of 1kHz as its modulation. The result is two frequencies: The carrier (1MHz), and the carrier plus the tone (1.001MHz). Now divide that by two and you get 500.5kHz. If we demodulate that, we get a 500Hz tone. (Also note that a true analog frequency divider is more complicated than a digital divider.)&lt;/p&gt;&#xA;" OwnerUserId="5855" LastActivityDate="2019-03-09T16:51:01.907" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="12991" PostTypeId="2" ParentId="12980" CreationDate="2019-03-09T16:58:33.347" Score="4" Body="&lt;p&gt;The gain becomes an issue only if its ridiculously low. The main purpose of an LNA is to lift the signal well above any noise of the following stages, and often that can be done with a gain of several dB. However, the fact that they didn't advertise it, makes it suspect.&lt;/p&gt;&#xA;" OwnerUserId="5855" LastActivityDate="2019-03-09T16:58:33.347" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12992" PostTypeId="2" ParentId="12984" CreationDate="2019-03-09T17:11:28.013" Score="1" Body="&lt;p&gt;You could use a device known as a downconverter (or &quot;transverter&quot;), like &lt;a href=&quot;https://www.nuand.com/product/hf-vhf-transverter/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; (but there may be others that are cheaper and/or easier to setup and use). It can take a high-frequency signal and downconvert it (&quot;shift&quot; it down). In theory, the spectrum shape is not modified at all; it is just shifted from a larger to a smaller frequency.&lt;/p&gt;&#xA;" OwnerUserId="4637" LastActivityDate="2019-03-09T17:11:28.013" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12993" PostTypeId="2" ParentId="12988" CreationDate="2019-03-09T17:24:18.707" Score="3" Body="&lt;p&gt;There are a few things to think about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coaxial cable will likely not have a positive impact on your RFI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, urban locations are loaded with RFI. Antenna direction and distance are the primary ways of reducing the received noise. On a small lot, this is not always possible but improvements should at least be evaluated. For example, an electrically shortened antenna may allow the antenna to be located further away from local noise sources and oriented such that its directionality attenuates these noises.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't overlook the opportunity to identify and potentially eliminate noise sources. Start with your own house by powering your radio off of a battery and shutting down the house power and other battery powered devices within the house. If the noise level drops, start turning on individual breakers to help identify the sources of your local noise. Go RFI hunting in the neighborhood to identify other noise sources that might be correctable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna is not well balanced due to factors such as uneven heights or trees or buildings near the antenna then the feedline can become unbalanced and be a point of ingress for noise. A 1:1 balun at the feedpoint may help mitigate the noise ingress.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connecting a balanced feedline to an unbalanced tuner can also couple local RFI into the antenna system. The antenna side of an unbalanced tuner should have a 1:1 balun between it and the balanced line. A belts and suspenders approach is to also put a 1:1 balun on the coaxial side of the tuner going to the transceiver.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-09T19:24:44.313" LastActivityDate="2019-03-09T19:24:44.313" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12994" PostTypeId="1" AcceptedAnswerId="12995" CreationDate="2019-03-10T07:47:22.110" Score="5" ViewCount="249" Body="&lt;p&gt;FCC Regulation 97.113 (a) 4 states that:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;messages encoded for the purpose of obscuring their meaning&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are &quot;Prohibited transmissions&quot;, I believe this is the clause that is used to prohibit encryption over ham radios.&#xA;Are there any other clauses that are used to prohibit encryption.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, is &quot;signing&quot; of messages acceptable/legal over ham radios.&#xA;For example consider the following transmission:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A digitally transmitted message contains:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The callsign of the sender.&lt;/li&gt;&#xA;&lt;li&gt;The callsign of the intended recipient&lt;/li&gt;&#xA;&lt;li&gt;The public key of the sender&lt;/li&gt;&#xA;&lt;li&gt;The entire body of the message in plain text.&lt;/li&gt;&#xA;&lt;li&gt;A checksum/signature generated from the private key of the sender and the body of the message.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;In this case no encrypted information is sent.&#xA;Additionally any receiver of the message can verify both the integrity of the message (by validating the signature) and that no additional information has been sent, since the entire signature is used as part of the validation process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: I realize that sending the public key is superfluous, but I didn’t want to get into the details of key exchange protocols as part of this question.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Edit: 3/10/19&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you all, for the high quality responses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As pointed out by others in the comments, I had three concerns:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;That it would be possible to authenticate the generation of the message (this system cannot detect the retransmission of the message in full).&lt;/li&gt;&#xA;&lt;li&gt;That a third party can verify the message contains no encrypted information.&lt;/li&gt;&#xA;&lt;li&gt;That in the US, the only applicable regulation was 97.113 (a) 4&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I had read another article specifically on CRAM-MD5 over amateur radio, however my concern was that any system that uses a shared secret, will require the secret in order to prove that no encrypted information is present (if you don’t know the secret, the checksum might be an encrypted string).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This was the reason I based the question on public/private key crypto and why I included the public key in the transmission - I realize that any receiver that wishes to authenticate the transmission needs to obtain the public key via a secure channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However with the message formatted as it is, any receiver that knows the protocol, can verify that the message contains no encrypted data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I feel all these concerns have been addressed and I have accepted the answer.&lt;/p&gt;&#xA;" OwnerUserId="14424" LastEditorUserId="14424" LastEditDate="2019-03-10T20:52:14.120" LastActivityDate="2019-03-10T20:52:14.120" Title="Signing of messages transmitted over ham radio" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;encryption&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="12995" PostTypeId="2" ParentId="12994" CreationDate="2019-03-10T09:46:39.443" Score="3" Body="&lt;p&gt;Even though signing of a digest uses cryptographic techniques, this is permitted. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Part 97 regulations regarding obscuring clearly speaks of purpose/intent. The regulation you quoted is the only one that applies to this topic for amateur radio. The FCC has previously commented that encryption is prohibited under this regulation even if the algorithm is well published.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A signed digest is not intended, nor is its purpose, to obscure, rather it is used for authentication, integrity and non-repudiation. It would be wise to publically publish the protocol in order to avoid any misunderstandings. In order to minimize potential legal issues, I recommend that you make certain the digest only uses information derived from the clear text (no new or hidden information, no salting, etc.) and its derivation and the signing technique be based on a publicly available method or standard (e.g. SHA or DSA). Similarly, the public keys should be publicly obtainable from a recognized CA (certificate authority).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be aware that other countries may not permit this technique so it may not see world wide adaption or use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While I believe your comment regarding the sending of the public key was simply to clarify your question, in practice this is cryptographically weak and should be avoided.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-10T18:11:40.817" LastActivityDate="2019-03-10T18:11:40.817" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="12996" PostTypeId="1" CreationDate="2019-03-10T10:22:39.707" Score="1" ViewCount="424" Body="&lt;p&gt;I was operating under the impression that the arm length of a half dipole antenna is λ/4 while making one that operated at the 145Mhz frequency using a piece of 9.525 mm (3/8 inch) copper tubing, at a heigh of about 50 ft (15.24 meters)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, a friend of mine informed me that the velocity factor of the material plays a role and that the real equation of Vf * λ/4, where Vf is the Velocity Factor of the material.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does this work? Are there other variables in the equation? Does the amount of space between the arms play a role, since every NEC representation I've seen assumes there's no space in the middle of the arms?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the one true equation for the arm lengths of a dipole antenna?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="14220" LastEditDate="2019-04-20T22:40:04.780" LastActivityDate="2019-04-20T22:40:04.780" Title="What is the equation for the arm lengths of a half wavelength dipole antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="12997" PostTypeId="2" ParentId="12996" CreationDate="2019-03-10T11:11:33.917" Score="5" Body="&lt;p&gt;There are several factors that come into play in determining the length of a center fed 1/2 wavelength dipole - all of which center on the notion of a near resonant feedpoint impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To begin with, an infinitely thin, 1/2 wavelength center fed dipole in free space has a feedpoint impedance of 73+j42.5 ohms. By slightly shortening the antenna, the reactive component fades away and we are left with a ~73+j0 ohm feedpoint impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When we construct a practical version of this dipole near the surface of the earth with real wire, things change. The proximity to the earth changes the impedance as a function of &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; above the earth and the soil conditions. The wire ends create a small &lt;a href=&quot;https://wikipedia.org/wiki/Capacitance#Self_capacitance&quot; rel=&quot;nofollow noreferrer&quot;&gt;self capacitance&lt;/a&gt; due to their real thickness. The result is reflected in an empirically derived formula for the total length (both arms) of a 1/2 wavelength dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$l=142.6 \text{ meters}/f_{\text{MHz}} \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For imperial units, the numerator is replaced with 468 feet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formula 1 yields a starting point. A good practice is to start slightly longer and then symmetrically reduce the length while monitoring the complex impedance of the feedpoint. Depending upon the antenna height, the real part of the impedance can range from ~48 to 73 ohms when optimally tuned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Formula 1 assumes bare, copper wire. If the wire is insulated, then the velocity factor of the insulation must be considered. This will result in a reduction of the calculated length. For example, when household &lt;a href=&quot;https://wikipedia.org/wiki/Electrical_wiring_in_North_America#Wire_types&quot; rel=&quot;nofollow noreferrer&quot;&gt;THHN&lt;/a&gt; (Thermoplastic High Heat-resistant Nylon) wire is used, the velocity factor is approximately 97% according to most field reports. The result of formula 1 is therefore multiplied by 0.97.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, there are resistive losses due to the RF resistance of the conductors. While this will not alter formula 1, these losses will directly add to the real part of the idealized feedpoint impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding your question of the gap between the arms, this is assumed to be minimal compared to the wavelength. On HF frequencies (3-30 MHz) a gap of 5 cm is immaterial. At higher frequencies, this gap should be reduced. At 145 MHz, a gap of 2 cm or less should not pose a problem.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-10T17:11:01.373" LastActivityDate="2019-03-10T17:11:01.373" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="12999" PostTypeId="1" AcceptedAnswerId="13002" CreationDate="2019-03-11T09:04:48.333" Score="16" ViewCount="9169" Body="&lt;p&gt;My 5-year old son loves sending out an SOS signal using a toy Morse code generator (wired, don't worry about false alarms for real authorities).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He has learned to send the SOS signal and was asking me to send a response to him to let him know that help is on the way. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What Morse code should I respond with in a real life situation when I hear a distress call on radio?&lt;/p&gt;&#xA;" OwnerUserId="14430" LastEditorUserId="9493" LastEditDate="2019-03-11T22:10:01.173" LastActivityDate="2020-07-06T20:47:44.320" Title="If I receive an SOS signal, what is the proper response?" Tags="&lt;cw&gt;&lt;procedure&gt;&lt;emergency&gt;" AnswerCount="5" CommentCount="15" FavoriteCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13000" PostTypeId="2" ParentId="12999" CreationDate="2019-03-11T12:49:06.323" Score="3" Body="&lt;p&gt;To respond to a &lt;em&gt;received&lt;/em&gt; Morse SOS by radio requires a transmit system and operator able to do that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally a transmit station license issued by the appropriate regulating agency having jurisdiction for that receive location is required to operate such a transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If no such transmit capabilities are available, then relaying the details of the SOS message to an appropriate, emergency response organization is about the best recourse available.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-03-11T12:49:06.323" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13001" PostTypeId="1" CreationDate="2019-03-11T13:10:46.063" Score="4" ViewCount="97" Body="&lt;p&gt;The FCC publishes a map of estimated groundwave conductivity of the United States, but the resolution is quite low:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4selT.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4selT.png&quot; alt=&quot;FCC groundwave conductivity map&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any GIS datasets that include groundwave conductivity at a higher resolution and with more precision? For example, at the arcminute resolution?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've already converted the map into a shapefile, so I don't just need this map in GIS format.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;&#xA;I originally asked this question on the &lt;a href=&quot;https://opendata.stackexchange.com/q/13579/3565&quot;&gt;OpenData StackExchange&lt;/a&gt;, but it might be a better fit here because it's highly specific to radio.&#xA;&lt;/sub&gt;&lt;/p&gt;&#xA;" OwnerUserId="13271" LastEditorUserId="873" LastEditDate="2019-09-11T02:36:47.533" LastActivityDate="2019-09-11T02:36:47.533" Title="High-resolution GIS datasets of groundwave conductivity of the United States, besides the FCC?" Tags="&lt;united-states&gt;&lt;propagation&gt;&lt;earth&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13002" PostTypeId="2" ParentId="12999" CreationDate="2019-03-11T13:29:51.427" Score="11" Body="&lt;p&gt;Since you're simulating the situation with non-transmitting equipment, you get the play the part of actual emergency agencies.  You'd start by asking the SOS caller to identify themselves (call sign, ship name, etc.) and give their location and the nature of the emergency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, unless your 5 year old knows a lot more Morse than just SOS, that's where the exchange will end -- but this is a good way to get him interested in learning the whole alphabet (if he hasn't), getting his speed up, learning prosigns, and so forth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a real life situation, the FCC says you should respond to the caller and ask what assistance is needed -- pretty much what you'll do in simulation with your son.  Find out what's the emergency, where the caller is located (latitude and longitude, map grid, or town and address), etc.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-03-11T13:29:51.427" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13003" PostTypeId="2" ParentId="1142" CreationDate="2019-03-11T13:46:48.600" Score="0" Body="&lt;p&gt;A 5/8 wave provides a style of vertical radiation pattern which doesn't offer energy in some of the mid- upper angles but compresses that 1/4 wave donut like stepping on it, to being flatter but WIDER.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're attempting to contact a station 10 miles past the donut of energy created by the 1/4 wave, then you won't be heard, if you then switch to a 5/8 wave you will concentrate the transmitted power into a flatter-lower angle and wider donut pattern of energy and now you might be heard where you weren't making it before when using the 1/4 wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The downside is the lack of midrange energy at the medium upper angles and is where a 1/4 wave might be the better choice when attempting to transmit over a range of nearby hills which could block and deflect the low angle energy of a 5/8 but the upper angle energy of a 1/4 wave might propagate successfully over that range of hills or obstructions.&lt;/p&gt;&#xA;" OwnerUserId="14432" LastEditorUserId="76" LastEditDate="2019-03-11T14:02:32.720" LastActivityDate="2019-03-11T14:02:32.720" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13004" PostTypeId="2" ParentId="12999" CreationDate="2019-03-11T14:32:43.483" Score="6" Body="&lt;p&gt;Since this is all for a bit of fun, you could respond with the typical Morse Code response to indicate that the last transmission was successfully received: R:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;•-•&lt;/pre&gt; &#xA;&#xA;&lt;p&gt;Some operators stylize this as two R's sent consecutively. You could also use your &quot;Dad&quot; call sign by appending &quot;de DAD&quot;:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;-••  •    -••  •-  -••&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;which means this transmission is &quot;from Dad&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As others have pointed out, in a real situation the response would either be asking for clarifying information (e.g. a location or nature of emergency) or it would be a confirmation that help is on the way. If I were responding, I would end my transmission with &quot;de W9IQ&quot; to indicate my FCC assigned call.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-12T13:47:53.453" LastActivityDate="2019-03-12T13:47:53.453" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13005" PostTypeId="1" AcceptedAnswerId="13006" CreationDate="2019-03-11T15:11:59.163" Score="6" ViewCount="1310" Body="&lt;p&gt;Making a common mode choke out of bifilar windings has proven rather difficult.  For me the difficulty lies in getting the impedance to remain a constant 50 ohms from on the HF bands.  I've tried 14 gauge enameled and I've tried 18 gauge PTFE.  The wires seem very sensitive to any kind of change in position.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been modeling the choke after the one shown on &lt;a href=&quot;https://www.youtube.com/watch?v=JhAPJISUjB8&quot; rel=&quot;nofollow noreferrer&quot;&gt;this tutorial&lt;/a&gt;.  Also what's the deal with that design?  It's like someone took a 4:1 guanella and just cut the connection that makes it 4:1.  Turning it into to parallel 1:1 chokes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any disadvantage to simply using coax windings instead of bifilar?  Can I just wrap 11 or 12 turns of RG-316 around a toroid?  How much more choking impedance do you get from a bifilar choke?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The application here primarily on the 40m band.  I was looking to build a simple in-line choke (SO-239 on both ends) as well as choke &quot;balun&quot; (SO-239 on one end and balanced terminals on the other).  I was also entertaining the idea of a choke &quot;unun&quot; for use with an elevated quarter wave vertical.  I would have a top lug connected to the center conductor; the shield would split off to two side lugs.&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="76" LastEditDate="2019-03-15T00:29:30.660" LastActivityDate="2019-03-15T16:58:59.450" Title="Coax or bifilar windings for a choke?" Tags="&lt;impedance&gt;&lt;balun&gt;&lt;choke-balun&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13006" PostTypeId="2" ParentId="13005" CreationDate="2019-03-11T15:30:08.653" Score="7" Body="&lt;p&gt;In most multi-band balun applications, there is rarely a need to maintain a perfect 50 ohm impedance within the balun. The feedpoint or input impedance is varying widely so another impedance bump in the mix typically has no detrimental effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I highly recommend the use of coaxial wound over bifilar style for a 1:1 balun. Comparatively, the coaxial and bifilar design can be made to have equivalent common mode choking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bifilar style will couple some of the energy traveling on the parallel lines into the core - much like getting a parallel transmission line too close to metal objects. This creates an unnecessary loss and it promotes heating of the core due to the complex permeability of the core material.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also very difficult to fabricate a true bifilar 50 ohm line. The design is so touchy that even minor changes in the wire coating thickness or failure to keep the lines adjacent will cause impedance discontinuities. Due to this marginal construction, the voltage withstand rating of this type of transmission line is much lower than what can be attained through the application of a coaxial transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coaxial wound style will keep all but the common mode current from creating a flux in the core. This is the ideal behavior of a transmission line transformer of this type. Do estimate the losses in this length of transmission line in order to project the effect on core heating. If heating of the core due to coax loss is a design constraint, consider using higher impedance coaxial cable (e.g. 75 ohm) as this will reduce the loss compared to the same size/class of 50 ohm cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Selection of the correct core material is essential. Generally, type 31 is suitable for the lower HF bands and type 43 for the upper HF bands. Look at the complex permeability curves and use a material where the &lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;''&lt;sub&gt;s&lt;/sub&gt; is greater than &lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;'&lt;sub&gt;s&lt;/sub&gt; for the frequencies of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may find some practical information regarding the number of turns of coax vs the core material on the &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;G3TXQ&lt;/a&gt; (now an SK) site. Here are some examples of his analysis:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2Pwsu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2Pwsu.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SkTdu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SkTdu.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://audiosystemsgroup.com/2018Cookbook.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;K9YC 2018 Cookbook&lt;/a&gt; also features type 31 material balun designs.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-11T17:41:18.213" LastActivityDate="2019-03-11T17:41:18.213" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="13007" PostTypeId="2" ParentId="13001" CreationDate="2019-03-11T17:44:04.163" Score="1" Body="&lt;p&gt;You could get the data from e.g. the Sentinel-1 or possible the TerraSAR-X satellite missions, and look for the ground characteristics (much like for moisture estimation) that are beneficial to ground wave propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't know how much that actually helps – C-Band wave propagation is pretty different to HF, but I could imagine that conductivity estimates would still translate pretty well.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-03-11T17:44:04.163" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13008" PostTypeId="2" ParentId="13005" CreationDate="2019-03-11T18:40:07.017" Score="4" Body="&lt;p&gt;The advantage of using coax for a 1:1 choke-balun is the constant Z0 of 50 ohms. As can be seen in the following graphs, the only time a 1:1 choke-balun accomplishes a 1:1 transformation is when it sees 50 ohms at its output. Any other impedance at the output causes an impedance transformation because the SWR is not 1:1.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/bJtXf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bJtXf.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-03-11T18:40:07.017" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13009" PostTypeId="1" AcceptedAnswerId="13011" CreationDate="2019-03-11T18:48:01.050" Score="5" ViewCount="429" Body="&lt;p&gt;I read &lt;a href=&quot;https://ham.stackexchange.com/questions/12994/signing-of-messages-transmitted-over-ham-radio&quot;&gt;this question&lt;/a&gt; about digital signatures and FCC prohibitions on &quot;obscuring&quot; messages in amateur transmissions, and it cause me to think of something: the difference between encryption and compression is small.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I send a file in compressed form via digital radio (say, a Mesh running on firmware-modified wifi routers, to support data rates that don't make this silly), the contents are easily decompressed by anyone who receives the file in error-free form (and most compression systems include redundant error correction codes to reduce the likelihood that the file will fail decompression) -- but without attempting decompression, there's no simple way to tell whether the file is encrypted within the compressed archive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would obviously be a no-no to send an encrypted archive by amateur radio, I think, but where is the line drawn?  Does compression itself count as &quot;obscuring&quot; the contents?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="76" LastEditDate="2019-03-11T18:50:55.060" LastActivityDate="2019-04-12T04:22:12.243" Title="Is compression &quot;encryption&quot; under FCC regs?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;digital-modes&gt;&lt;encryption&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13010" PostTypeId="2" ParentId="13009" CreationDate="2019-03-11T19:33:32.183" Score="0" Body="&lt;p&gt;As long as your compression uses a standard compression method, it is legal and not considered encryption. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-03-11T19:33:32.183" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13011" PostTypeId="2" ParentId="13009" CreationDate="2019-03-11T21:35:26.277" Score="6" Body="&lt;p&gt;For governments around the world to continue to trust that amateur radio has no nefarious purpose, it is essential that everyone that wishes to, can &quot;listen in&quot; to any amateur radio communications. Anything that hints at eroding this capability will likely be struck down in time through regulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To pass the FCC legal hurdle regarding obfuscation, it must first be evident that the purpose is not to obscure the message. Part of this test would likely be that the technique must accomplish some useful level of compression if that is really its purpose. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The legal second test would likely be that can anyone readily decompress the message to return it to its clear text form. This must be very easily achievable due to broad publication or acceptance of the compression method.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both tests are important. For example, consider a symmetric encryption scheme using an industry standard and with the encryption key widely published on the web. This will possibly pass the second test but it would fail the first test because it doesn't actually compress the message in any real sense. It is also clear that the public standard is primarily for encryption (obscuring) and not compression (reducing).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, FT8 makes extensive use of compression. The standard is well published so that anyone wishing to decode the bits can do so. Even though the compression &quot;obscures&quot; the message - it is clear the purpose of the technique is compression. Furthermore, the software to copy FT8 transmissions is readily available for free. Everyone can &quot;listen in&quot;. So FT8 passes both tests. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even Morse Code uses a form of compression by using shorter symbol lengths for the more commonly used letters. Clearly it passes both tests.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-03-11T21:35:26.277" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13012" PostTypeId="1" AcceptedAnswerId="13015" CreationDate="2019-03-11T22:14:06.777" Score="3" ViewCount="150" Body="&lt;p&gt;When you look down on an isotropic radiator from above, ie : the azimuth view radiation pattern, it's a circle. The same as looking down on any omni directional antenna. So when comparing the gain of a yagi antenna in the azimuth view at 0 degrees elevation to an isotropic radiator's azimuth view gain at 0 degree, this gives a good practical indication of gain over a real omni directional antenna such as a 1/4 wave ground plane antenna, is that right ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="9493" LastEditDate="2019-03-12T13:04:16.707" LastActivityDate="2019-03-15T13:08:55.220" Title="Ham operators often tell me that comparing gain to an isotropic radiator isn't much use because it's only a theoretical antenna, is this true?" Tags="&lt;antenna-theory&gt;&lt;radiation-pattern&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13013" PostTypeId="2" ParentId="13009" CreationDate="2019-03-12T00:30:20.877" Score="0" Body="&lt;p&gt;Compression is not encryption.  You don't have to use a standard compression method.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By FCC rules, even encryption is not encryption if you publish the key (and the algorithm).  You could, for instance, use encrypted wifi but publish the ssid..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It doesn't matter how you encode the signal if you publish the method to decode it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you spoke plain words but used special words for special meanings in ways that is not published, that would be illegal, as it obscures the meaning.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2019-04-12T04:22:12.243" LastActivityDate="2019-04-12T04:22:12.243" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13014" PostTypeId="2" ParentId="13012" CreationDate="2019-03-12T02:51:24.733" Score="6" Body="&lt;p&gt;dBi is useful for comparing gains of real world antennas. For instance, an 80m mobile antenna may be -10 dbi, a 1/4WL vertical ground plane may be 0 dbi, a dipole may be 6 dbi, and a beam may be 10 dbi. So we can say that the beam has 20 dB gain over the 80m mobile antenna using dBi as the reference dimension.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-03-12T02:51:24.733" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13015" PostTypeId="2" ParentId="13012" CreationDate="2019-03-12T11:23:12.100" Score="9" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Ham operators often tell me that comparing gain to an isotropic radiator isn't much use because it's only a theoretical antenna, is this true?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, that is not true. I generally find that hams that denigrate or choose to ignore the isotropic antenna or references to it, simply don't understand its central place in antenna engineering. Certainly the isotropic antenna only exists theoretically but it is the basis for a great deal of the fundamentals principles of antenna engineering and the related formulas. It is a shame that more hams don't take the time as you are to strengthen their knowledge in this field. I applaud you for digging into this subject.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;So when comparing the gain of a yagi antenna in the azimuth view at 0 degrees elevation to an isotropic radiator's azimuth view gain at 0 degree, this gives a good practical indication of gain over a real omni directional antenna such as a 1/4 wave ground plane antenna, is that right ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There is a confusion in terminology in your question that is common place regarding omnidirectional for a vertical antenna and radiating equally in all directions for an isotropic antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An isotropic antenna radiates equally in all directions. The best way to think about this is to place the isotropic antenna inside, and at the center, of a large sphere. Then apply power to the isotropic antenna and imagine the power &quot;illuminating&quot; the surface of the sphere in the same way a light bulb might. Since the isotropic antenna radiates equally in all directions, the entire sphere would be uniformly lit - no bright spots and no dark spots.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now take the isotropic antenna out of the sphere and replace it with an omnidirectional vertical antenna. When we apply the same power to the vertical, we would not see a uniformly lit sphere. Instead, the &quot;poles&quot; of the sphere would be nearly dark and the &quot;equator&quot; of the sphere would be brightly lit. Clearly the &quot;omni&quot; part of the description is referring to the equal &quot;illumination&quot; in the area near and around the equator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since spheres are not the easiest to render in our 2D literature, we tend to take a slice through the sphere and talk about that. For ham radio, the two most common slices are azimuth (a slice parallel to the equator) and elevation (a slice parallel to the poles). The azimuth and the elevation plots for an isotropic antenna would always show a uniform and equal, circular radiation pattern for all such slices. By contrast the omnidirectional vertical would show uniform radiation in the azimuth plot but in the elevation plot, most of the power would be concentrated near the horizon with very little power near 90 degrees of elevation. So the omnidirectional term only applies to the azimuth pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Computer modeling has brought about the ability to more easily generate graphics that have a 3D appearance to them. Here is such a rendering of a 1/4 wave ground plane antenna with a relatively small ground plane from the &lt;a href=&quot;http://www.antenna-theory.com/antennas/monopole.php&quot; rel=&quot;noreferrer&quot;&gt;Antenna Theory&lt;/a&gt; website:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W3rYI.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W3rYI.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The correct technical term for the illumination of the surface of the sphere is &quot;irradiance&quot;. This is typically expressed as watts per square meter (W/m&lt;sup&gt;2&lt;/sup&gt;). So the isotropic antenna causes the entire surface of the sphere to have the same W/m&lt;sup&gt;2&lt;/sup&gt; but since the omnidirectional vertical focuses more of its power near the equator, the W/m&lt;sup&gt;2&lt;/sup&gt; in the equator region would be greater than at the poles. So the dBi gain of the omnidirectional vertical can be thought of as the comparison of its greatest irradiance value that is found near the equator compared to the irradiance value (at the same power level and same size of sphere) of the irradiance at any location for the isotropic antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Gain_\text{dBi}=10 \log \left(\frac{E_{e\text{ Omni}}}{E_{e\text{ Isotropic}}}\right) \tag 1$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where E&lt;sub&gt;e&lt;/sub&gt; is the irradiance in W/m&lt;sup&gt;2&lt;/sup&gt; for the respective antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unless specifically stated otherwise, dBi gain refers to the maximum irradiance of the antenna in question compared to that of the isotropic antenna. For example, a 1/2 wavelength dipole in free space has a 2.15 dBi gain. Our knowledge of the radiation pattern of a dipole would allow us to equate this gain to the direction that is perpendicular to the direction of the arms of the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, don't forget that the gain of an antenna includes the effect of any losses in the antenna. In fact gain (in linear form) is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Gain=Directivity*Efficiency \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So while the free space directivity of a small, &quot;magnetic&quot; loop antenna is nearly the same as a free space 1/2 wavelength dipole, the poor efficiency of the small loop compared to a dipole causes it to have much less gain than the dipole. The isotropic antenna is always considered to be 100% efficient.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastActivityDate="2019-03-12T11:23:12.100" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13016" PostTypeId="1" AcceptedAnswerId="13017" CreationDate="2019-03-12T12:15:55.453" Score="1" ViewCount="52" Body="&lt;p&gt;This came up in comments on &lt;a href=&quot;https://ham.stackexchange.com/questions/13009/is-compression-encryption-under-fcc-regs/13011?noredirect=1#comment19601_13011&quot;&gt;this question&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since before the Internet was widely available, it's been common to pass along files received from other users or downloaded from a server somewhere.  For amateur radio, however, the FCC has some rules concerning &quot;third party communications&quot;, where Alice sends a message to Bill on behalf of Charlie, who isn't part of the communication (for purposes of this question, Charlie isn't under a license revocation).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I send a downloaded file (one I didn't create) via a digital connection such as a mesh network, would this constitute &quot;third party communication&quot;?  I have the file already stored in my local system; I'm not downloading it from a server in real time as I transmit to the mesh.  I'm not being paid for the file, either as a condition to sending it, or on approval (like the old &quot;shareware&quot; concept).  All I get out of the exchange is a good feeling for sharing something I've enjoyed, and the likelihood that someone else on the mesh will share something I might want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With no &quot;fiduciary interest&quot; this ought to be legal (pending copyright etc. concerns), but does it in fact constitute &quot;third party communication&quot;?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-03-12T12:53:17.527" Title="Sending a downloaded file on digital: third party communication?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;digital-modes&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13017" PostTypeId="2" ParentId="13016" CreationDate="2019-03-12T12:47:09.900" Score="7" Body="&lt;p&gt;From a Part 97 perspective, the definition of third party communications is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Third party communications. A message from the control operator (first party) of an amateur station to another amateur station control operator (second party) on behalf of another person (third party).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you send a file to Bob because &lt;em&gt;you&lt;/em&gt; wish to share it with Bob, that is not a third party communication even though the file originated from somewhere else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if I gave you the same file and asked you to send it to Bob, I am the third party and you are conducting third party communications.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-12T12:53:17.527" LastActivityDate="2019-03-12T12:53:17.527" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13018" PostTypeId="1" CreationDate="2019-03-12T13:32:22.530" Score="3" ViewCount="55" Body="&lt;p&gt;I've recently (part of studying for Extra license exam) learned about &quot;mesh networks&quot;, where it's common to use repurposed wifi routers to connect at 2.4 or 4.8 GHz and form a network over a much wider area than wifi normally covers (10 W radiated power and high antenna gain adds a lot to range over the usual 100 feet or so).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I understand the way these routers operate, they'd be considered &quot;automatic control&quot; stations -- in that the mesh wouldn't stay up for any length of time if there had to be an operator in real-time control of each node at all times when connected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also recall reading that an automatic control station may not initiate contacts, but only respond to a contact from an operator-controlled or remote-controlled station.  This is clearly not the case for a mesh network that operates much like a home or office LAN.  Is this permissible because of the high communication band, or is there some other factor here I've missed?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-03-12T23:39:38.893" Title="Digital networks -- operator at control point, or automatic relay?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;digital-modes&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13019" PostTypeId="1" AcceptedAnswerId="13020" CreationDate="2019-03-12T14:40:36.620" Score="8" ViewCount="222" Body="&lt;p&gt;How are PL tones (CTSS, et.al.) typically removed from the audio of received VHF FM repeater signals?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it done with a fixed high-pass filter?  Or a notch, when using a transceiver with the PL tone configured correctly?  Or dynamically, by assuming any constant low tone detected is hum to be removed by an auto-adaptive notch?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or is it sometimes not removed by filtering because the tiny speakers on handheld receivers don't have sufficient low frequency response?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-03-12T16:47:30.807" Title="PL tone removal?" Tags="&lt;tone-squelch&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13020" PostTypeId="2" ParentId="13019" CreationDate="2019-03-12T16:47:30.807" Score="8" Body="&lt;p&gt;I would expect some low-frequency roll-off in the amp and the speaker. You could check by putting headphones on the speaker output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia says that a 300 Hz cutoff high-pass filter is common.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Continuous_Tone-Coded_Squelch_System&quot; rel=&quot;noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Continuous_Tone-Coded_Squelch_System&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the CTSS tone is injected at a lower level than the voice content, usually 15% of full deviation. That is about 8 dB below full modulation.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2019-03-12T16:47:30.807" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13021" PostTypeId="2" ParentId="12999" CreationDate="2019-03-12T17:08:16.847" Score="3" Body="&lt;p&gt;First, let's be very clear that making a false distress call is a federal crime carrying sanctions of up to six years imprisonment, and a fine of $250,000.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, there is no commercial or maritime use of Morse now, so distress calls use &quot;Mayday Mayday Mayday&quot; at the beginning and end. You are extremely unlikely to hear a Morse distress call or need to respond to one. Maritime Morse stations stopped operation on July 12, 1999, almost twenty years ago.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When someone who is not a first responder or dispatcher receives a distress call, they need to start writing down information to forward to first responders. If they don't provide it, and they may be scared and not thinking straight, you need to interview them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be calm and clear. If a better-prepared station steps in to help, let them do it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a maritime distress call, collect this information. A land call would be similar. This is a script for the person making the call, so you would walk them through this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, write down the local time (your own clock). If you have UTC, use that.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Distress signal &quot;MAYDAY&quot;, spoken three times.&lt;/li&gt;&#xA;&lt;li&gt;The words &quot;THIS IS&quot;, spoken once.&lt;/li&gt;&#xA;&lt;li&gt;Name of vessel in distress (spoken three times) and call sign or boat registration number, spoken once.&lt;/li&gt;&#xA;&lt;li&gt;Repeat &quot;MAYDAY&quot; and name of vessel, spoken once.&lt;/li&gt;&#xA;&lt;li&gt;Give position of vessel by latitude or longitude or by bearing (true or magnetic, state which) and distance to a well-known landmark such as a navigational aid or small island, or in any terms which will assist a responding station in locating the vessel in distress. Include any information on vessel movement such as course, speed and destination.&lt;/li&gt;&#xA;&lt;li&gt;Nature of distress (sinking, fire etc.).&lt;/li&gt;&#xA;&lt;li&gt;Kind of assistance desired.&lt;/li&gt;&#xA;&lt;li&gt;Number of persons onboard.&lt;/li&gt;&#xA;&lt;li&gt;Any other information which might facilitate rescue, such as length or tonnage of vessel, number of persons needing medical attention, color hull, cabin, masks, etc.&lt;/li&gt;&#xA;&lt;li&gt;The word &quot;OVER&quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;From: &lt;a href=&quot;https://www.navcen.uscg.gov/?pageName=mtBoater&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.navcen.uscg.gov/?pageName=mtBoater&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should practice copying text, including asking for repeats and phonetic spelling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best practice is participating in drills and public service events for your local ARES/RACES emergency communication group.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a recorded VHF marine distress call. You can find more of these on YouTube.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=kKHBWOXfGMM&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=kKHBWOXfGMM&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more information about maritime Morse, start with the Night of Nights, which runs maritime Morse one day per year on July 12. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.nps.gov/pore/planyourvisit/events_nightofnights.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.nps.gov/pore/planyourvisit/events_nightofnights.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2019-03-12T17:08:16.847" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13022" PostTypeId="2" ParentId="13012" CreationDate="2019-03-12T17:52:10.330" Score="4" Body="&lt;p&gt;Those that complain that dBi isn't useful because an isotropic antenna is only theoretical often advocate an alternate unit such as dBd, or decibels relative to a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a couple arguments that could be made from here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One argument is that a dBd is typically defined as 2.15 dBi, because that's the directive gain of a half-wavelength dipole in free space. That is, to convert dBi to dBb, just subtract 2.15. If you want to be pragmatic, this is hardly something to get worked up about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But wait a minute, a dipole in free space is &lt;em&gt;also&lt;/em&gt; a theoretical antenna. In practice, reflections from ground, ground losses, feed issues, interactions with the tower, misalignment of the antenna, and myriad other issues result in a dipole's gain being something other than 2.15 dBi. For any terrestrial communication scenario, interactions with the ground are relevant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some cases, especially on VHF and higher frequencies where the antenna can be many wavelengths high, it may be acceptable  to assume 2.15 dBi gain, and model the ground with a simple model like the &lt;a href=&quot;https://en.wikipedia.org/wiki/Two-ray_ground-reflection_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;two-ray reflection model&lt;/a&gt;. Or perhaps the link budget simply contains sufficient fade margin that it's not important to have a very precise model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But on HF it can become quite difficult to get the dipole more than a quarter wavelength high, and this means both that the ground has the potential to create constructive interference though the &lt;a href=&quot;https://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;image antenna&lt;/a&gt; created, and also reduce gain through ground losses. Depending on ground conductivity and height, it can make quite a difference for better &lt;em&gt;or&lt;/em&gt; worse.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, a dipole's gain even in free space isn't 2.15 dBi in all directions: that's only its gain in the most favorable direction. How frequently is the dipole rotated to the ideal angle for a given path? And even given a rotatable dipole, how frequently is the height of that dipole optimized to give the ideal takeoff angle?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You see, trying to distill antenna performance into a single number that's realistic in practice rapidly becomes a very complex problem. Wouldn't it be nice if we had a simpler number, something which was insensitive to direction, polarization, ground interactions, and all the other gotchas; something which is mathematically simple and universally applicable? Then we can use this as the starting point, and then add as many correcting factors to account for real-world effects as we desire until we are satisfied our model is sufficiently accurate to meet our needs?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That &quot;simple&quot; model is the isotropic antenna. To show why it's simple, I pose a simple question: if a 1 W transmitter is 10 km distant from the receiver, how much power is received?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we assume the transmitting antenna radiates equally in all directions, is in free space, and is 100% efficient, then this is a simple geometry problem. Simply imagine a sphere centered on the transmitter, with a radius of 10 km. Radiated power from the transmitter can only intersect the sphere, so the power flux of the entire sphere must be 1 W. Since the antenna radiates equally in all directions, the power flux density must be equal everywhere on the sphere. So calculating the surface area of this sphere, then dividing the transmit power by this quantity, yields the power flux density.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ { 1 \:\mathrm{W} \over 2 \pi (10 \:\mathrm{km})^2 } = 1.59 \:\mathrm{nW/m^2} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we want to know the power received then we only need to know how big of an &quot;energy net&quot; the receiving antenna presents. This is called the &lt;a href=&quot;https://ham.stackexchange.com/q/1530/218&quot;&gt;effective aperture&lt;/a&gt;, which as it turns out is just another way to express gain:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ A_e = {\lambda^2 \over 4\pi} G $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$A_e$&lt;/span&gt; is the effective aperture, &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is wavelength, and &lt;span class=&quot;math-container&quot;&gt;$G$&lt;/span&gt; is the antenna gain (as a linear number, not decibels).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the basis of the &lt;a href=&quot;https://ham.stackexchange.com/q/1530/218&quot;&gt;Friis transmission equation&lt;/a&gt; and finds practical application in calculating &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budgets&lt;/a&gt;. Granted, it's based on a theoretical antenna, the mathematical simplicity of the isotropic antenna allows the mathematics to be simple when simple is all we need, and more complex when necessary by adding additional terms to the equation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we were to eschew the isotropic antenna and use the dipole as the reference antenna, we would gain little. Some might argue the results are &quot;more realistic&quot;, but as previously stated the gain of a dipole is not constant. We'd have to add terms to the fundamental equations to account for at least the orientation of the dipole. And if the objective is realism, even that is insufficient. It's a slippery slope that has neither the mathematical simplicity of an isotropic reference nor the accuracy of a real-world model.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-12T17:52:10.330" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13024" PostTypeId="2" ParentId="12988" CreationDate="2019-03-12T21:27:17.600" Score="0" Body="&lt;p&gt;Coax with a good 1:1 current balun at the antenna feedpoint could reduce your received noise. The function of that balun is to provide a high impedance to common mode signal (mostly nearby noise) and a matched impedance to differential mode signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did a simple S-meter test when I put a balun on my dipole. The noise floor dropped by 6 dB on the 20 meter band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next step is to hunt down and eliminate nearby noise sources.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For understanding baluns and RF chokes, I highly recommend &quot;A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing&quot; by Jim Brown, K9YC. This is the best publication on the subject and it is free.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://audiosystemsgroup.com/RFI-Ham.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Jim Brown also wrote two good articles on &quot;killing receive noise&quot; for the National Contest Journal in 2016. Those are available here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://ncjweb.com/features/mayjun16feat.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://ncjweb.com/features/mayjun16feat.pdf&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;http://ncjweb.com/features/sepoct16feat.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://ncjweb.com/features/sepoct16feat.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, thinking of ladder line as &quot;balanced&quot; doesn't help understand the noise problem. Like coax, ladder line carries a mix of differential mode and common mode signals. Your goal is to reduce the noise generated near the antenna and reduce the noise on the feed line.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2019-03-12T21:27:17.600" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13025" PostTypeId="2" ParentId="13018" CreationDate="2019-03-12T22:52:46.973" Score="1" Body="&lt;p&gt;I decided to redo my original answer as I didn't formulate my response to what the question specifically asks and I neglected to consider the intent of the &amp;quot;message forwarding system&amp;quot; language in part 97. My apology for any confusion from my first answer.&lt;/p&gt;&#xA;&lt;p&gt;The following discussion specifically applies to amateur radio stations under FCC Part 97 regulations.&lt;/p&gt;&#xA;&lt;p&gt;An amateur radio station may be locally controlled, remotely controlled, or automatically controlled as defined by part 97:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Local control. The use of a control operator who directly manipulates the operating adjustments in the station to achieve compliance with the FCC Rules.&lt;/p&gt;&#xA;&lt;p&gt;Remote control. The use of a control operator who indirectly manipulates the operating adjustments in the station through a control link to achieve compliance with the FCC Rules.&lt;/p&gt;&#xA;&lt;p&gt;Automatic control. The use of devices and procedures for control of a station when it is transmitting so that compliance with the FCC Rules is achieved without the control operator being present at a control point.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Any station may be locally or remotely controlled. Automatic control is the most limited form of control in that only certain station activities are permitted: auxiliary station, repeater station, certain beacon stations, digital stations and message forwarding stations.&lt;/p&gt;&#xA;&lt;p&gt;It would be tempting to run with the automatic digital station concept for a node on a mesh network, but there are two major limitations that generally prevent this:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(1) The station is responding to interrogation by a station under local or remote control; and&lt;/p&gt;&#xA;&lt;p&gt;(2) No transmission from the automatically controlled station occupies a bandwidth of more than 500 Hz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;In March 30, 1994 the FCC adopted PR Docket No. 93-85 in recognition that with the regulations at that time &amp;quot;the potential for transmitting a high volume of messages cannot be achieved&amp;quot; and they sought to add specific language and restrictions that allowed the transmission of high volumes of messages.&lt;/p&gt;&#xA;&lt;p&gt;First, they added a new section defining message forward systems:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Message forwarding system. A group of amateur stations participating in a voluntary,&#xA;cooperative, interactive arrangement where communications are sent from the control operator of an originating station to the control operator of one or more destination stations by one or more forwarding stations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Then they relieved all forwarding stations of most legal responsibilities regarding the content of the message:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(b) For stations participating in a message forwarding system, the control operator of the station originating a message is primarily accountable for any violation of the rules in this part contained in the message.&lt;/p&gt;&#xA;&lt;p&gt;(c) Except as noted in (d) of this section, for stations participating in a message forwarding system, the control operators of forwarding stations that retransmit inadvertently communications that violate the rules in this part are not accountable for the violative communications. They are, however, responsible for discontinuing such communications once they become aware of their presence.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The originating station is primarily held responsible:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(d) For stations participating in a message forwarding system, the control operator of the first forwarding station must:&lt;/p&gt;&#xA;&lt;p&gt;(1) Authenticate the identity of the station from which it accepts communications on behalf of the system; or&lt;/p&gt;&#xA;&lt;p&gt;(2) Accept accountability for any violation of the rules in this part contained in messages it retransmits to the system.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;PR Docket No. 93-85 also changed the definition of an auxiliary station and a repeater station to clarify that they are not part of a message forwarding system:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Auxiliary station. An amateur station, other than in a message forwarding system, that is transmitting communications point-to-point within a system of cooperating amateur stations.&lt;/p&gt;&#xA;&lt;p&gt;Repeater. An amateur station that simultaneously retransmits the transmission of another amateur station on a different channel or channels.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The final significant addition resulting from PR Docket No. 93-85 was:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;No station may be automatically controlled while transmitting third party communications, except a station participating as a forwarding station in a message forwarding system.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This is a key paragraph as this not only grants the right of a message forwarding system to pass third party traffic, but it also grants the right for a message forwarding system to be automatically controlled.&lt;/p&gt;&#xA;&lt;p&gt;Finally, regarding your concern:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I also recall reading that an automatic control station may not initiate contacts, but only respond to a contact from an operator-controlled or remote-controlled station.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This language largely comes from the limitations of an automatic digital station. It does not apply to a station participating in a message forwarding system.&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-03-12T23:39:38.893" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13026" PostTypeId="2" ParentId="1394" CreationDate="2019-03-12T23:35:14.297" Score="0" Body="&lt;p&gt;Gold is fine, but gold plated pins in connectors is usually on a layer of nickel - and nickel is ferromagnetic. I have recently been studying sideband noise and as it turns out the limitation of my interferometric setup is noise due to nickel beneath the gold in BNC connectors. Have a look here: &lt;a href=&quot;https://www.youtube.com/watch?v=GCtJ1aQ5fek&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=GCtJ1aQ5fek&lt;/a&gt;&#xA;The problem might not exist on microwaves where the gold layer could be thick enough to carry most of the current. At modest frequencies the nickel would produce intermodulation and overtones.&#xA;I do not know why we can not have gold on brass or god on copper for connectors. In the old days we had silver on brass (I think) but silver is problebatix because&#xA;it forms silver sulphide on the surface.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-03-12T23:35:14.297" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13027" PostTypeId="5" CreationDate="2019-03-13T01:45:37.953" Score="0" Body="&lt;p&gt;&lt;strong&gt;GNSS&lt;/strong&gt; or &quot;global navigation satellite system&quot; is the generic term for a collection of satellites that may be used for determining position. The most well known system, whose name is often used interchangeably for it and the technology in general, is the United States' Global Positioning System (GPS).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In amateur radio, the most common use of GNSS / GPS technology is to report the location of a station over &lt;a href=&quot;/questions/tagged/aprs&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;aprs&amp;#39;&quot; rel=&quot;tag&quot;&gt;aprs&lt;/a&gt;. It may also be used to obtain accurate time information to coordinate operations between stations, such as agreed-upon transmission times or locating a transmitter by precisely measuring the time of reception at multiple receivers.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Satellite_navigation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Satellite navigation on Wikipedia&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-03-13T01:45:37.953" LastActivityDate="2019-03-13T01:45:37.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13028" PostTypeId="4" CreationDate="2019-03-13T01:45:37.953" Score="0" Body="Satellite navigation systems, including GPS. Questions should be related either to amateur radio operations (e.g. APRS tracking) or the theory of positioning using radio signals; questions merely about using GPS receivers are not on-topic." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-03-13T01:45:37.953" LastActivityDate="2019-03-13T01:45:37.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13030" PostTypeId="1" AcceptedAnswerId="13033" CreationDate="2019-03-13T14:53:07.513" Score="9" ViewCount="1634" Body="&lt;p&gt;It is well understood in the amateur radio community that ladder line, window line, etc. have lower losses per foot than say RG-213 or LMR400, particularly on HF frequencies. It is also understood that this loss is a function of the RF resistance of the conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you examine the size (surface area) of the conductors in LMR400, they are much larger than say the conductors in 450 ohm window line. This includes the LMR400 center conductor and certainly the shield is quite a bit larger. This would seem to suggest that the RF resistance of LMR400 would be lower than that of the 450 ohm ladder line. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, place 50+j0 ohm loads on 100 feet of LMR400 and 100 feet of 450 ohm window line and measure the losses on 20 meters. The 450 ohm window line will have lower losses even though the 450 ohm window line has a 9:1 SWR while the LMR400 has a 1:1 SWR. So even with the additional losses due to SWR, the 450 ohm window line has lower losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What then accounts for the typically lower losses on HF frequencies of parallel transmission lines compared to coaxial transmission lines?&lt;/p&gt;&#xA;" OwnerUserId="9493" LastEditorUserId="9493" LastEditDate="2019-03-13T18:39:08.513" LastActivityDate="2019-03-15T18:45:22.947" Title="Why does ladder line generally have a lower loss than coaxial cable?" Tags="&lt;coaxial-cable&gt;&lt;feed-line&gt;&lt;transmission-line&gt;" AnswerCount="4" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="13031" PostTypeId="2" ParentId="13030" CreationDate="2019-03-13T15:12:25.020" Score="1" Body="&lt;p&gt;In a flat 450 ohm line, there is significantly less current in the conductors than in 50 ohm coax. Therefore, the I^2*R losses are significantly lower as compared to commonly-used coaxial cables. The size of the conductors in each has a bearing on this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ohm's law (chart below) tells us that as we increase the impedance, the voltage increases while at the same time the current decreases. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/azwg9.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/azwg9.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-03-13T21:08:09.240" LastActivityDate="2019-03-13T21:08:09.240" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13032" PostTypeId="2" ParentId="13030" CreationDate="2019-03-13T16:10:58.237" Score="0" Body="&lt;p&gt;In &quot;true&quot; open wire line, the electromagnetic wave travels entirely in free space. Insulating spacers that establish the line's characteristic impedance, whether applied at intervals or are an integral part of the cable as in &quot;window line,&quot; depart from the free-space ideal and add loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coaxial cables use a dielectric material to establish the spacing between the center and outer conductors. Thus, the electromagnetic wave in coax travels in material that has higher loss than free space. &quot;Hardline&quot; replaces a uniform dielectric layer with periodic dielectric spacers to reduce dielectric losses.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-03-13T16:10:58.237" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13033" PostTypeId="2" ParentId="13030" CreationDate="2019-03-13T21:51:48.953" Score="6" Body="&lt;p&gt;When the SWR is 1:1, the matched line loss of ordinary ladder line is lower than the matched line loss of ordinary coax because at HF, most of the loss is &lt;span class=&quot;math-container&quot;&gt;$I^2R$&lt;/span&gt; loss, and the current magnitude is inversely proportional to the characteristic impedance of the feedline. Of course, a high SWR results in higher standing wave currents and thus increases the &lt;span class=&quot;math-container&quot;&gt;$I^2R$&lt;/span&gt; losses on a 1/2 wavelength (or longer) feedline. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ladder line is not always at a lower loss than coax. For instance, if the frequency is 10 MHz, the load is 20 ohms, and the length of the feedline is 100 feet, the loss in RG-213 is 1.524 dB according to TLDetails, while the loss in Wireman #551 ladder line is 2.236 dB. The SWR for the RG-213 is 2.5:1 while the SWR for the ladder line is about 22:1.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-03-13T21:51:48.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13034" PostTypeId="2" ParentId="13030" CreationDate="2019-03-14T02:12:26.417" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;It is well understood in the amateur radio community that ladder line, window line, etc. have lower losses per foot than say RG-213 or LMR400, particularly on HF frequencies.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Is it though? I'd say only sometimes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the &lt;a href=&quot;https://www.timesmicrowave.com/DataSheets/CableProducts/LMR-400.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;LMR-400 datasheet&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0muiR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0muiR.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://www.dxengineering.com/parts/dxe-ll300-1c/documentation&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Engineering's 300 ohm ladder line datasheet&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lFdtI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lFdtI.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Compare the loss at say, 30 MHz: 0.7 versus 0.668 dB/100 ft. For practical purposes, the same. If the ladder line is wet, or running in proximity to other things, the loss is much higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, not all ladder line is equal: there are examples both better and worse than this one. But the unqualified assumption that ladder line has lower loss is not true.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;OK then, but why is ladder line, at least in this example, able to deliver about the same loss, with less copper?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's the same reason power lines run at high voltages for long-distance distribution: higher impedance means for a given power less current and more voltage. Less current means less resistive loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power &lt;span class=&quot;math-container&quot;&gt;$P$&lt;/span&gt; is the product of current &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; and voltage &lt;span class=&quot;math-container&quot;&gt;$E$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ P = I E $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, 50 volts and 1 amp delivers the same power as 1 volt and 50 amps. The ratio of volts to amperes is the line impedance, which we get from Ohm's law:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ R = {E \over I} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Resistive losses are the square of current, times resistance &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ P = I^2 R $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So a higher impedance means more volts per amp, which means more power per amp, which means less amps are necessary for a given power, which means less resistive loss. Or we can just use less copper, thus increasing &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; but decreasing cost while keeping losses the same.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;As an example, place 50+j0 ohm loads on 100 feet of LMR400 and 100 feet of 450 ohm window line and measure the losses on 20 meters. The 450 ohm window line will have lower losses even though the 450 ohm window line has a 9:1 SWR while the LMR400 has a 1:1 SWR. So even with the additional losses due to SWR, the 450 ohm window line has lower losses.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That may be, however this one situation can not be generalized to conclude 450 ohm window line will have lower losses at other load impedances, feedline lengths, and frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The issue is the standing waves set up alternating nodes of high current, and high voltage. They are spaced a 1/4 wavelength apart, repeating every 1/2 wavelength. As explained above, a higher voltage is associated with lower loss, and conversely higher current with higher loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 20 meters, 100 feet is approximately 1.25 wavelengths, or enough for 5 nodes. If the load impedance is selected such that there are 3 high current nodes and 2 high voltage nodes, the loss will be greater than if there are 2 high current nodes and 3 high voltage nodes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The trouble is, &quot;ladder line has low loss&quot; is usually mentioned in an antenna proposal such as this: put a tuner in the shack, run &quot;low-loss&quot; ladder line up to a dipole of whatever length, &lt;em&gt;et voila:&lt;/em&gt; low-loss multiband antenna, easy to build, and cheap too! Right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But in this proposal, the feedline's physical length is dictated by the site, its electrical length varies with frequency, and the load impedance varies by frequency too. At any particular frequency, the standing waves may fall in a way that reduces loss or increases it, but what's the average case?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That can be calculated by &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;assuming the line has uniform loss throughout&lt;/a&gt;. Let's do that for the example provided.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The LMR-400 datasheet doesn't go to 14 MHz, but the &lt;a href=&quot;https://www.timesmicrowave.com/calculator/?Product=LMR-400&amp;amp;RunLength=100&amp;amp;Frequency=14&quot; rel=&quot;nofollow noreferrer&quot;&gt;Times Microwave calculator&lt;/a&gt; puts the matched loss at 0.5 dB for 100 feet at 14 MHz. No adjustment for SWR is required because the SWR is 1:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Very little ladder-line comes with a datasheet, but some &lt;a href=&quot;http://k6mhe.com/ladder_line.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;independent tests&lt;/a&gt; put the matched loss for &lt;a href=&quot;http://www.thewireman.com/balance.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Wireman type 553&lt;/a&gt; at .25 dB / 100 ft.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you say, the SWR is now 9:1; We first calculate the magnitude of the reflection coefficient:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ |\Gamma| = {9-1 \over 9+1} = 0.8 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And convert that 0.25 dB to a linear ratio:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L = 10^{-0.25/10} = 0.944 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now we can calculate the feedline loss:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ -10 \log \left(L {&#xA;  1 - |\Gamma|^2 \over&#xA;  1-L^2 \: |\Gamma|^2&#xA;}\right)&#xA;= 1.02\:\mathrm{dB} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even assuming no tuner losses, this 450 ohm ladder line has 1 dB more loss than LMR-400. So indeed, in the particular example given, the ladder line does have lower loss than LMR-400, even without matching the load to the line. However it was due to luck, not an inherent advantage of ladder line: in fact more often than not, LMR-400 will outperform this 450 ohm ladder line if used to feed a 50 ohm load without a matching device.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h1&gt;Conclusion&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Ladder line can be applied to good effect, but the often repeated, unqualified statement that it has lower loss than coax is demonstrably wrong in enough situations that I would not say it's &quot;generally true&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not all kinds of ladder line have lower loss than coax. Just like coax, ladder line loss varies. Look for specifications. Usually a datasheet is not available, and you have to find independent tests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If ladder line is used to feed a mismatched load, SWR losses can be substantial. Calculate it for the particular length and load impedance, if possible. If not, &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;use an estimation&lt;/a&gt;. Using ladder line to drive a load that's better matched to coax can often be a losing proposition.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-03-15T18:45:22.947" LastActivityDate="2019-03-15T18:45:22.947" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13035" PostTypeId="1" CreationDate="2019-03-14T05:10:42.023" Score="0" ViewCount="55" Body="&lt;p&gt;I would like a simple device which enables me to transmit a beep every second or so on a chosen frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is anyone aware of a product that can do this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, can anyone tell me what you would call this so I can work out how to make one? I have been searching for all sorts of terms, but I have no technical understanding of what I am trying to find.&lt;/p&gt;&#xA;" OwnerUserId="14467" LastActivityDate="2019-03-14T14:09:33.447" Title="Simplest way to transmit beep 5-10km (3-6 miles) using FM?" Tags="&lt;transmitter&gt;" AnswerCount="2" CommentCount="4" ClosedDate="2019-03-14T14:19:52.027" ContentLicense="CC BY-SA 4.0" />
  <row Id="13036" PostTypeId="1" CreationDate="2019-03-14T05:42:53.987" Score="5" ViewCount="1223" Body="&lt;p&gt;I am looking to design a dual conversion FM receiver/power meter for t-hunting similar to the MK4 sniffer using 10.5 MHz and 455 kHz IF.  In my research it appears that manufactures have stopped making 455 kHz ceramic filters.  I am in the U.S.A. and the only thing I can find still in production is in England.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is what can/is used for a very high Q if filter (Q of about 45 = 455 kHz / 10 kHz) at 455 kHz in the absence of ceramic filter/discriminators.&lt;/p&gt;&#xA;" OwnerUserId="14466" LastEditorUserId="8717" LastEditDate="2019-03-14T14:22:58.563" LastActivityDate="2020-02-05T22:50:38.150" Title="Substitute for 455 kHz Ceramic filters in new designs" Tags="&lt;receiver&gt;&lt;equipment-design&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13038" PostTypeId="2" ParentId="13035" CreationDate="2019-03-14T13:05:47.560" Score="1" Body="&lt;p&gt;In the U.S., FCC regulations limit unlicensed broadcast-band FM transmission to a range of about 100 to 200 feet.  Read about Part 15 Devices here:&#xA;&lt;a href=&quot;https://www.fcc.gov/media/radio/low-power-radio-general-information&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fcc.gov/media/radio/low-power-radio-general-information&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-03-14T13:05:47.560" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13039" PostTypeId="2" ParentId="13036" CreationDate="2019-03-14T13:14:16.110" Score="5" Body="&lt;p&gt;Since this platform considers questions asking for products as off-topic, I'll interpret your question as:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I have an IF receiver, but there's no good filters for the rather low IF it uses (455 kHz). What to do?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you're doing a new design, simply pick an IF that works with the filters you can get. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That, and pretty much nothing else, is what defines what IF is chosen in commercial detectors. Your high-sensitivity Spectrum Analyzer does that. Your cheap FM Radio receiver IC does that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand: If you're just reworking a superhet where the final receiver stage failed, then consider why you need the IF filter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Its purpose is to isolate the wanted spectrum from all the unwanted stuff, so that noise and interference has lesser influence on the receiver. That's why you want that IF filter to be sharp; and that's why you'd use an IF to fit your filter (and not the other way around). Adjusting an oscillator to a different LO frequency is easy, building a good filter for an arbitrary frequency band is not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, what if I tell you that 455 kHz is &quot;practically baseband&quot; in 2019. If you, say, build a very relaxed low-pass filter that lets through 0 to 550 kHz and a very relaxed high pass that lets through 400 to &lt;span class=&quot;math-container&quot;&gt;$\infty$&lt;/span&gt; kHz, and then digitized at more than 300 kS/s, then you could do the IF processing with digital filters (in software!), and these can be pretty much arbitrarily steep. You can modify them to your hearts delight (for example, to account for actual signal spectrum shape or LO inaccuracies), and that doesn't cost anything and has no risk of not working.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;People's classical argument is that a good IF filter is paramount to receiving weak signals between and especially near to strong ones – but that's no problem for a digital receiver, that is, as long as the dynamic range of the ADC can still &quot;see&quot; the weaker signal without clipping the stronger one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, say you want to be able to, without even using oversampling¹, detect a signal that is say 80 dB weaker than its neighbor. Your Superhet receiver with nice IF filter would require an IF filter with a suppression of at least 83 dB if you want your SNR to be still 3 dB, i.e. crosstalk to only be half as powerful as the signal of interest. In reality, you'd probably need more filter attenuation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I doubt the MK4 achieves that selectivity (I've not found two-tone test charts for it), but let's assume it did and you'd want to achieve the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your ADC would thus need to be able to not overflow on the 80 dB stronger signal, and still have at 3dB dynamic range to spare on resolving the weaker one; a 18 bit ADC gladly does that (and far more) and &lt;a href=&quot;https://www.digikey.com/product-detail/en/texas-instruments/ADS8695IPWR/296-50908-1-ND/9745272&quot; rel=&quot;nofollow noreferrer&quot;&gt;comes&lt;/a&gt; at less than 10 USD.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can accept only a DR of a little more than 60 dB (which will, for fox hunting and the like, more than suffice), a &amp;lt; 20 USD &lt;a href=&quot;https://www.arrow.com/en/products/nucleo-f446ze/stmicroelectronics&quot; rel=&quot;nofollow noreferrer&quot;&gt;Microcontroller eval board&lt;/a&gt;'s on-chip ADC will simply do. That microcontroller itself is so plenty fast enough at doing math that applying even a mean filter on a couple kHz of signal is no big deal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice that I'm an SDR guy – I really know that the time for narrowband filters under benign circumstances implemented as analog hardware components is over. You still need to do your anti-aliasing filtering, but seriously, instead of hoping you can calibrate your analog filtering to be acceptably steep and stable, digitally filter. Microcontrollers are plenty fast enough for the bandwidths you use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹ You can increase the SNR of signals by sampling faster than you need to. And this will have happened dramatically after your digital filter.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-03-15T07:31:45.540" LastActivityDate="2019-03-15T07:31:45.540" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13040" PostTypeId="2" ParentId="13035" CreationDate="2019-03-14T14:09:33.447" Score="0" Body="&lt;p&gt;Your question is unclear, but if you're talking about a Ham transmitter in the U.S. (and you're a licensed ham), then I'd look into the Ham shield for an Arduino.  It's a shield for an Arduino along with a (poorly documented) library that lets you control it.  With that you can program it to do pretty much whatever you'd like.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2019-03-14T14:09:33.447" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13041" PostTypeId="1" AcceptedAnswerId="13042" CreationDate="2019-03-14T16:35:49.520" Score="1" ViewCount="390" Body="&lt;p&gt;I'm building multiple antennas tuned to different amateur bands and would like them connected to my SDR for remote listening and analysis, and a handheld radio for transmission, which I may upgrade or supplement with another radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I build a solid state setup where I don't have to decouple antennas as I shift to a different frequency. Is there an equivalent of an ON-OFF switch that I can trigger remotely?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastActivityDate="2019-03-14T18:18:27.333" Title="How do I use multiple antennas with two or more radios?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13042" PostTypeId="2" ParentId="13041" CreationDate="2019-03-14T18:18:27.333" Score="3" Body="&lt;p&gt;You're looking for an antenna switch.  There are many different kinds of switches available.  Manual switches are the simplest and the cheapest, but they allow for the operator to make the common error of having the wrong antenna (or no antenna) connected, which can lead to equipment damage in some scenarios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a more automatic setup, then you'll want a system that uses relays to switch antennas.  Prices vary widely depending on the features that you want: number of coaxial connections, maximum frequency, power limit, amount of isolation (cross-talk can be a problem for some), rated for outdoor use or not, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next problem to be solved is how to switch antennas automatically.  Generally some software on a computer connected to the radio, or the radio firmware itself, switches antennas based on what the operator is doing.  The antenna switch is connected to the computer or the radio, of course.  Commercial ham radio rig control software such as &lt;a href=&quot;https://www.hamradiodeluxe.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ham Radio Deluxe&lt;/a&gt; can be programmed to switch antennas based on the band selected by the operator.  If the software that you use with your SDR can do that also, great; if not, you might have to write your own software.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-03-14T18:18:27.333" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13043" PostTypeId="1" CreationDate="2019-03-14T19:08:19.833" Score="9" ViewCount="837" Body="&lt;p&gt;At one time I was active in the local SKYWARN program, but then we moved and I find myself 10 miles from the local repeater. Given the various obstructions between it and me, I can't really hit it unless I'm up in the attic or on the roof. To make matters more challenging, the repeater is northeast of me, and normally our weather comes from the southwest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, I can put up an antenna, run the necessary cabling and hit the repeater, but that leaves me &lt;em&gt;stuck&lt;/em&gt; at the end of the cable, at times when mobility may be essential (I use a dual-band handheld).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution I have in mind is a repeater attached to the antenna which I can reach anywhere from inside the house. The house repeater (or reflector, or relay, or whatever the proper name would be) is attached to the external antenna where it won't have any problem hitting the SKYWARN repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will this work, and what equipment do I need?&lt;/p&gt;&#xA;" OwnerUserId="14473" LastEditorUserId="76" LastEditDate="2019-03-14T22:10:30.933" LastActivityDate="2019-03-19T19:06:30.243" Title="In-house repeater?" Tags="&lt;ht&gt;&lt;repeater&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13044" PostTypeId="2" ParentId="13043" CreationDate="2019-03-14T22:03:00.477" Score="9" Body="&lt;p&gt;The simplest way of accomplishing your goal doesn't require a conventional and expensive repeater system. It's completely passive (no electronics needed).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Put a Yagi on your roof pointed at the repeater. Put an upside-down ground plane in your living area. Connect the two antennas with coax. You now have a &lt;em&gt;passive&lt;/em&gt; repeater!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Signals picked up on the Yagi will be radiated by the ground plane, and signals from your HT will be picked up by the ground plane and be radiated by the Yagi.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;It goes without saying that:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The coax should be low loss and as short as possible&lt;/li&gt;&#xA;&lt;li&gt;The antennas should be tuned for a good match. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-03-14T22:13:24.240" LastActivityDate="2019-03-14T22:13:24.240" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13045" PostTypeId="1" AcceptedAnswerId="13058" CreationDate="2019-03-14T23:44:24.127" Score="0" ViewCount="169" Body="&lt;p&gt;I have a 3 element vertical Yagi mounted on a rotator, and in one direction the roof of the house gets pretty close and messes up the SWR a bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If i mash up a few type 43 material ferrite cores and mix them in some paint and paint the roof near my Yagi with that, will that make the roof 'invisible' to my Yagi?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="76" LastEditDate="2019-03-15T00:28:20.070" LastActivityDate="2019-03-16T03:49:07.580" Title="Can I make ferrite paint? Will it shield my antenna from my roof?" Tags="&lt;antenna-theory&gt;&lt;ferrite&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13046" PostTypeId="1" AcceptedAnswerId="13047" CreationDate="2019-03-15T01:30:55.563" Score="0" ViewCount="106" Body="&lt;p&gt;When terminating coax (e.g. RG-400) that has an outer braid over an inner braid onto an SO-239 chassis mount, do we want to solder both the inner and outer braids together onto the ground of the SO-239? I assume yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's obvious that the inner and outer shields are already coupled together at DC.  But I know that AC is a strange beast and sometimes complicates things.  I also have the idea that &quot;good&quot; differential current travels on the inside of the braid, and &quot;bad&quot; common mode travels on the outside.  Now, I'm pretty sure this happens because the differential currents get &quot;pulled together&quot; and the common mode currents &quot;repel&quot; one another- so it sort of happens on its own.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That being said- would it make sense to cut away the outer shield and only solder the inner shield at the termination?  I'm assuming that only the inner shield carries the signal (on the inner part) and that the outer shield is simply a passive shield to help reduce leakage.  &lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="12939" LastEditDate="2019-03-15T01:54:58.950" LastActivityDate="2019-03-15T01:54:58.950" Title="Terminating double-shielded coax" Tags="&lt;coaxial-cable&gt;&lt;connectors&gt;&lt;transmission-line&gt;&lt;pl259-so239-connector&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13047" PostTypeId="2" ParentId="13046" CreationDate="2019-03-15T01:50:25.690" Score="1" Body="&lt;p&gt;The short answer is yes, both shields must be connected together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many other connectors for this already connect the shields for you, providing that you follow the instructions. N connectors (at least the ones I've used) do. The snap-and-seal crimp connectors for my RG-6 (that's all that I use outdoors anymore) does this also.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-03-15T01:50:25.690" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13048" PostTypeId="1" AcceptedAnswerId="13057" CreationDate="2019-03-15T02:34:19.487" Score="2" ViewCount="623" Body="&lt;p&gt;How do you identify that a UHF Connector (PL-259 &amp;amp; SO-239) is of a high quality and build?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you identify specific materials in the construction, gold plating, or other characteristics? How will I be able to determine these at a glance when browsing through a sale bin?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="873" LastEditDate="2019-03-15T06:25:13.160" LastActivityDate="2019-03-16T12:32:28.857" Title="How to identify a high quality PL-259/SO-239 (so-called &quot;UHF&quot;) connector?" Tags="&lt;pl259-so239-connector&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13049" PostTypeId="1" CreationDate="2019-03-15T02:51:59.550" Score="4" ViewCount="92" Body="&lt;p&gt;I know the NATO/ICAO pronunciation of modifying 3, 4, 5, and 9 to &quot;tree&quot;, &quot;fower&quot;, &quot;fife&quot;, and &quot;niner&quot;, respectively, but I just discovered &lt;a href=&quot;https://life.itu.int/radioclub/rr/ap14.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;the ITU figure pronunciations are vastly different&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which are more common, and which should I learn as a prospective ham?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="14220" LastEditDate="2019-03-15T12:58:19.643" LastActivityDate="2019-03-15T17:53:34.577" Title="Is the NATO/ICAO or ITU figure pronunciation more common?" Tags="&lt;procedure&gt;&lt;phone&gt;&lt;phonetic-alphabet&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13050" PostTypeId="2" ParentId="13012" CreationDate="2019-03-15T11:43:42.000" Score="0" Body="&lt;p&gt;It is important to realize in the &quot;gain&quot; analysis of any antenna that the far-field radiation patterns and gains of antennas calculated by M-o-M software such as NEC typically include the effects of reflections of its intrinsic radiated energy when used near a large, reflecting surface such as the earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below are two far-field results for a ground plane antenna as calculated by NEC. The top one includes reflections from a nearby plane surface, and the other shows the intrinsic radiation from the ground plane antenna, itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W3rYI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W3rYI.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NOTE:  The gain in dBi of the antenna shown below is color-coded to the vertical scales adjacent to the patterns.  An enlarged view of that image is possible by left-clicking on the image.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those gain values may be converted to free space gain referred to a center-fed, 1/2-wave dipole (= dBd) by subtracting 2.15 from the dBi values shown in the graphic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MmJf0.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MmJf0.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-03-15T13:08:55.220" LastActivityDate="2019-03-15T13:08:55.220" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13051" PostTypeId="2" ParentId="13036" CreationDate="2019-03-15T12:53:27.743" Score="0" Body="&lt;p&gt;Murata makes the CERAFIL(R) line of ceramic filters, some of which are designed for use at 455kHz and 450kHz. For example, the SFPLA450KD1A-B0 has a -6dB bandwidth of 10kHz, designed for use with AM stereo receivers. A search of eBay for &quot;filter if 455&quot; turns up units like the AVX Kyocera KBF455R, which may be suitable for your project.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on your goals, you might consider building the Elenco AM/FM-108CK receiver kit. It is a superhet design, though it does not achieve the high selectivity of a ceramic or mechanical filter. This kit is an excellent hands-on educational project - being the focus of Elenco products - and you could learn a great deal by simulating the design with the free LTSpice from Analog Devices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your goal is a portable, low-drain FM receiver - as opposed to reproducing an arcane architecture for historical or nostalgia value - I agree with an earlier answer that recommends using a modern integrated circuit approach for a new design. There are many how-to articles online showing everything from standalone battery-powered units to &quot;shields&quot; for the current generation of single-board computers.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-03-15T12:53:27.743" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13052" PostTypeId="2" ParentId="13005" CreationDate="2019-03-15T13:46:54.880" Score="2" Body="&lt;p&gt;I strongly recommend &lt;a href=&quot;https://archive.org/details/UnderstandingBuildingAndUsingBalunsAndUnuns&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;Building and Using Baluns and Ununs&quot; by Jerry Sevick, W2FMI&lt;/a&gt;. I have built dozens of coaxial- and bifilar-wound transformers and chokes for use in high-power amplifiers and antenna systems based on the easy-to-understand information in this book. Specific mention is made of how to make reproducible bifilar-wound units over a wide range of impedance levels. They differ in important ways from the units shown in the &quot;splash screen&quot; of the video you cite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's certainly easier to use coax to build a 1:1 choke for use in a coax-based system. Rather than adding separate units to choke currents on the shield, I find it cheaper and more convenient to wind as many turns of the feedline as possible through stacks of &quot;large&quot; diameter ferrite toroids. This also avoids the possibility of water-intrusion and other failures that can occur at the coax-coax joints needed to insert separate units. K9AY describes this configuration in, &quot;Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the category of &quot;better is the enemy of good enough,&quot; it's important to understand the problem you're trying to solve. While operating recently in a DX location, I had to make do with a heavily compromised antenna installation. Observing unstable SWR readings and watching the mouse wander all over the screen of my laptop when transmitting, I surmised that RF was traveling down the outside of the coax shield. Simply winding a few turns of the coax feedline into a coil lying on the ground solved the problem.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="8717" LastEditDate="2019-03-15T16:58:59.450" LastActivityDate="2019-03-15T16:58:59.450" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13055" PostTypeId="2" ParentId="13049" CreationDate="2019-03-15T17:50:14.743" Score="-2" Body="&lt;p&gt;My suggestion is to learn the NATO/ICAO pronunciation. That's what is used by nearly every airline pilot and military group.&lt;/p&gt;&#xA;" OwnerUserId="14102" LastActivityDate="2019-03-15T17:50:14.743" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13056" PostTypeId="2" ParentId="13049" CreationDate="2019-03-15T17:53:34.577" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;3, 4, 5, and 9 to &quot;tree&quot;, &quot;fower&quot;, &quot;fife&quot;, and &quot;niner&quot;, respectively,&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Those pronunciations are not used on Amateur Radio.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-03-15T17:53:34.577" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13057" PostTypeId="2" ParentId="13048" CreationDate="2019-03-16T00:17:37.567" Score="7" Body="&lt;p&gt;UHF connectors are tricky, because they're not a very good connector by modern standards to begin. They have only a few redeeming qualities:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;They are common on amateur radio equipment&lt;/li&gt;&#xA;&lt;li&gt;The socket can accommodate a banana plug&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Due to their non-constant impedance design, an unavoidable consequence of being designed so long ago, they don't work well above 30 MHz. They're also inherently not weather-resistant on their own, so you have to be really good about taping them outside. Personally I only use them on the back of radios that come with them: every other connector I've installed is N (anything outside), BNC (anything inside I might connect/disconnect frequently), or SMA (small things).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, if you still want UHF connectors and want &quot;good&quot; quality, I'd look for two things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;A well-known brand, like Amphenol&lt;/li&gt;&#xA;&lt;li&gt;Silver plating&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;You may find silver plating in some sale bin, but it may be difficult to find something that's not made in China to the cheapest possible specifications. I've used these and sometimes they work well enough, but it would be prudent to test any cables you make with them by putting a dummy load on one end, an antenna analyzer on the other (or even just a transmitter and an SWR meter) and jiggling the connectors on each end to ensure the SWR stays at 1:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your best bet, counterintuitively, is to look for old, surplus equipment contemporary with the design of the connector. The silver will likely be oxidized and the connector will look terrible, but don't worry, it will work anyway. If the corrosion is really bad it's easy to clean off with a silver cleaner or any of the homemade concoctions you can find on the internet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Otherwise you'll have to order the connectors new from a reputable distributor (ie, not ebay), and they'll set you back several dollars each.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-03-16T12:32:28.857" LastActivityDate="2019-03-16T12:32:28.857" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13058" PostTypeId="2" ParentId="13045" CreationDate="2019-03-16T03:49:07.580" Score="4" Body="&lt;p&gt;No. At best it will do nothing; if it did something, it would probably turn your roof from a relatively good reflector (which may mess with your SWR, and may distort your pattern, but the energy that doesn't go where you expected it at least goes somewhere) to a relatively &lt;em&gt;bad&lt;/em&gt; reflector (which absorbs energy from your antenna and turns it into heat — ferrites are lossier than metals, and whatever you do to make it into &quot;paint&quot; will almost certainly increase that). What it won't do is make your wall RF-transparent.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-03-16T03:49:07.580" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13059" PostTypeId="1" CreationDate="2019-03-16T04:55:13.893" Score="2" ViewCount="1035" Body="&lt;p&gt;Aaronia released this ultra-wide-range antenna, that can measure up to 35GHz.  This was really impressive for only 3000 Euros, so I was considering purchasing it, when I figured I would look at the spec sheet to compare it with their previous model.  And that's when I realized that, above ~23GHz, the antenna's gain is all negative!&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/OJJu2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OJJu2.png&quot; alt=&quot;PrintScreen of spec sheet&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this mean that when I point the antenna toward the source of the signal, then the reading would actually decrease?&lt;/p&gt;&#xA;" OwnerUserId="14482" LastActivityDate="2019-03-17T08:54:08.287" Title="How can the gain of an antenna be negative?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13061" PostTypeId="1" AcceptedAnswerId="13062" CreationDate="2019-03-16T10:42:40.463" Score="2" ViewCount="7578" Body="&lt;p&gt;I understand that the:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;PL-259/SO-239&lt;/strong&gt; connector (so-called &quot;UHF connector&quot;) isn't great for UHF frequencies, but is very common&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;N type&lt;/strong&gt; connector is water-proof; and the&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;BNC&lt;/strong&gt; connector is quick to connect and disconnect&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;From James Eagleson's &lt;a href=&quot;https://www.youtube.com/watch?v=40ESujVdg7A&quot; rel=&quot;nofollow noreferrer&quot;&gt;YouTube video&lt;/a&gt; I can see that the PL-259/SO-239 (so-called UHF-connector) performs the worst over VHF, BNC is significantly better, with the N-type performance being comparable to the BNC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However I, as a ham-in-training building his own SWL rig, haven't been able to figure out when to use which as my primary coupling for antennas and switches as the cabling comes down to my rig.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I, personally, plan on creating antennas for a wide array of bands. My first antenna is for the 2m band, and I plan on creating some UHF antennas, but most of them will be for HF frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When do I use which is best connector to use when?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="76" LastEditDate="2019-03-16T15:09:13.590" LastActivityDate="2019-03-16T15:09:13.590" Title="PL-259/SO-239 vs N Type vs BNC which is best connector to use when?" Tags="&lt;connectors&gt;&lt;pl259-so239-connector&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13062" PostTypeId="2" ParentId="13061" CreationDate="2019-03-16T11:35:11.523" Score="10" Body="&lt;p&gt;For shortwave listening, it doesn't really matter – all these connectors are suitable for 30 MHz, and for reception you don't need to work with significant power.&lt;/p&gt;&#xA;&lt;h1&gt;PL-259&lt;/h1&gt;&#xA;&lt;h2&gt;2m-band&lt;/h2&gt;&#xA;&lt;p&gt;If you, however, plan to work in the 2m band (2m being the wavelength, so frequency is, &lt;span class=&quot;math-container&quot;&gt;$f=\frac c\lambda=\frac{3\cdot10^8\,\frac{\text m}{\text s}}{2\,\text{m}}=150\,\text{MHz}$&lt;/span&gt;), then PL-259 definitely reaches its limits. That connector was designed before going &amp;quot;so high&amp;quot; in frequency was expected to be common for civil/low-cost radio equipment, and thus, the shape creates impedance changes over frequency. And that gets worse with increasing frequency.&lt;/p&gt;&#xA;&lt;h2&gt;UHF&lt;/h2&gt;&#xA;&lt;p&gt;Just to cite Amphenol RF, which probably are the most important industrial player in RF connectors: They do offer PL-259 connectors, but even they say &amp;quot;Impedance: Non-Constant&amp;quot; on their product specifications, for example: &lt;a href=&quot;https://www.amphenolrf.com/083-1sp-15rfx.html&quot; rel=&quot;noreferrer&quot;&gt;https://www.amphenolrf.com/083-1sp-15rfx.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;That's not really an option, to be honest, when handling power. Your amplifier will not like seeing its power getting reflected back at him. You will not like getting less power at your antenna than your amplifier generates.&lt;/p&gt;&#xA;&lt;p&gt;Oh, and even they only say the connector works up to 0.3 GHz. UHF actually is defined to be 0.3 to 3 GHz, so nope:&lt;/p&gt;&#xA;&lt;p&gt;It's called UHF-connector, but it's not good for what we call UHF, at all.&lt;/p&gt;&#xA;&lt;h1&gt;BNC&lt;/h1&gt;&#xA;&lt;p&gt;The go-to connector for anything that is high-frequency, but not outright microwave, at least in labs. It can be manufactured to a high degree of precision, which allows frequencies above 1 GHz to be transported well. If you spend more money, you can even get connectors that work up to ~ 4.5 GHz. These expensive connectors don't make sense unless both sides of a connection have the same precision. And you don't want to go up that far in frequency, anyway, probably&lt;/p&gt;&#xA;&lt;p&gt;BNC is pretty nice for the lower UHF band, i.e. below ca 1.8 GHz. It's cheap, easy to buy from &lt;a href=&quot;https://www.digikey.com/products/en/connectors-interconnects/coaxial-connectors-rf/437?FV=c84001d%2Cffe001b5&amp;amp;quantity=10&amp;amp;ColumnSort=1000011&amp;amp;page=1&amp;amp;stock=1&amp;amp;nstock=1&amp;amp;pageSize=500&quot; rel=&quot;noreferrer&quot;&gt;multiple reliable manufacturers&lt;/a&gt; (I wouldn't go for &amp;quot;sale boxes&amp;quot; on connectors – if you save 1€ on a connector to 50€ on cabling, but end up with something flaky, or lossy, you'll be sad). Also, they are typically able to withstand 1 kV of voltage – enough for high-power transmitters.&lt;/p&gt;&#xA;&lt;p&gt;Cables that work with these connectors are cheap, and there's adaptors available to basically anything you want, from SMA over N-Type to Gardena garden hose.&lt;/p&gt;&#xA;&lt;p&gt;You have to pay a bit of attention: BNC systems and connectors exist in 75Ω and in 50Ω variants – you need to pick what is identical to your system! (50Ω is kind of standard in RF measurement and lower- to medium-power systems, but 75Ω has typically lower losses and thus is preferrable if you have long cables delivering much power – but the 75Ω cables and connectors typically don't work for frequencies as high as their optically nearly identical 50Ω counterparts, soooo... it depends on what you have, anyway, but don't buy BNC stuff that doesn't say whether it's 75 or 50 Ω.)&lt;/p&gt;&#xA;&lt;p&gt;BNC is also pretty nice as it's quick to connect and disconnect. It's, on the other hand, not as sturdy, and not outdoor-compatible.&lt;/p&gt;&#xA;&lt;h1&gt;N-Type&lt;/h1&gt;&#xA;&lt;p&gt;Kind of what you see the most in medium-power professional RF equipment's antenna connectors. Works up easily to 10 GHz (again, depends on the price, in the end), handles significant power, is sturdy, has low loss and excellent impedance match.&lt;/p&gt;&#xA;&lt;p&gt;It's a &lt;a href=&quot;https://www.digikey.com/products/en/connectors-interconnects/coaxial-connectors-rf/437?k=&amp;amp;pkeyword=&amp;amp;sv=0&amp;amp;pv801=32&amp;amp;sf=0&amp;amp;FV=ffe001b5&amp;amp;quantity=10&amp;amp;ColumnSort=1000011&amp;amp;page=1&amp;amp;stock=1&amp;amp;nstock=1&amp;amp;pageSize=500&quot; rel=&quot;noreferrer&quot;&gt;bit more expensive&lt;/a&gt; than BNC stuff.&lt;/p&gt;&#xA;&lt;p&gt;More of a hassle to connect, and disconnect, but very reliable once tightened (don't over-tighten!), and can be wrapped in self-vulcanizing tape to make a connection weatherproof.&lt;/p&gt;&#xA;&lt;p&gt;N-type is used in most sensitive RF measurement equipment when BNC doesn't go high enough in frequency – exactly because you can tighten it precisely enough to give a very reliable low-attenuation connection, which isn't easily degraded.&lt;/p&gt;&#xA;&lt;h1&gt;Conclusion&lt;/h1&gt;&#xA;&lt;p&gt;You're not starting with a 1 kW transmitter. You'll probably be happiest with using no connectors outside, and BNC inside.&lt;/p&gt;&#xA;&lt;p&gt;When aiming for higher frequencies as interconnects between low-power devices, SMA might be a better, because smaller, alternative to N-type. For high power, N-Type is pretty much your go-to choice.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-03-16T11:35:11.523" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13063" PostTypeId="2" ParentId="13059" CreationDate="2019-03-16T13:37:34.713" Score="4" Body="&lt;p&gt;The vertical axis is in dB, which indicates a ratio. The literature probably mentions that it's the ratio of the antenna's gain to that of an isotropic antenna, or a dipole for the frequency in question (i.e. which is 2.15dB more). So a negative dB means the gain is less than that of a dipole or isotropic antenna. As far as directionality goes, I'd say this is the gain at the boresight. Again, the literature should make this clear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: corrected gain of dipole to 2.15dB&lt;/p&gt;&#xA;" OwnerUserId="5855" LastEditorUserId="5855" LastEditDate="2019-03-17T08:54:08.287" LastActivityDate="2019-03-17T08:54:08.287" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13065" PostTypeId="1" AcceptedAnswerId="13070" CreationDate="2019-03-18T03:36:42.210" Score="6" ViewCount="151" Body="&lt;p&gt;I have this radio, with a rubber duck antenna, and a repeater twenty miles away to my north-northwest.  If I set my radio on the top of a cabinet in my bathroom, I receive the repeater fine.  I can't hit it from there, but I can hear it, which for now is good enough.  I can't receive that repeater anywhere else in the house, though, on that antenna.  My house is off-grade, so my floor is about three feet above the dirt below.  Therefore, on the bathroom cabinet, it's around ten feet above ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have also a 4-element yagi.  Currently, I have it on a makeshift 3/4-inch PVC mast shoved into a 5-gallon Firehouse Subs pickle bucket with a hole in the lid sitting beside my recliner in the den.  Keep laughing, but it works.  So, this thing is pointed pretty much right at that repeater, a foot from my ceiling, so about the same altitude as the rubber duck in the bathroom, and nothing.  I get bupkis.  But wait...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I take the antenna off of the radio, and put on the radio a BNC tee.  On one side of the tee, I put my antenna.  On the other side, I put another tee, which itself has a BNC 50-ohm Ethernet terminator on each side (scavenged from work's trash, old Thinnet cabling being tossed).  So, the antenna, and two BNC Ethernet terminators (dummy loads?) in parallel, and wouldn't you know it, I can now receive that repeater with almost zero static.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I'm confused by this.  ADDING load to the line IMPROVES reception?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The whole story is a lot more drawn out, and it's odd how I actually came to discover this phenomenon that seemingly improves reception (originally I had about eight of these tees all daisy-chained off of one another, just screwing around), but when I asked my father about it, he suggests that the antenna has such a high gain that it overpowers -- and desensitizes -- the receiver in my radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I trust my father, but does this sound feasible?  Why would I then not just be able to aim my antenna slightly off target and pick up the repeater equally well (or better)?&lt;/p&gt;&#xA;" OwnerUserId="14492" LastEditorUserId="76" LastEditDate="2019-03-18T03:56:28.457" LastActivityDate="2019-03-18T20:01:37.813" Title="Why does adding 50-ohm BNC Ethernet terminator(s) in parallel to my 4-element yagi improve my radio's reception? (70cm)" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;antenna-system&gt;&lt;path-loss&gt;&lt;dummy-load&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13067" PostTypeId="1" AcceptedAnswerId="13068" CreationDate="2019-03-18T09:07:07.830" Score="3" ViewCount="131" Body="&lt;p&gt;I live in a country that falls under ITU region three and recently joined my national amateur radio association. I learned that the frequencies for the repeaters run by the association were kept secret because they'd been facing cross-border abuse from neighboring countries when regional political relationships became...strained. Since the association runs all the repeaters in the country, that means all the repeaters are operated in secret.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found this odd because since all regional associations are &quot;member-societies&quot; of the International Amateur Radio Union as per its &lt;a href=&quot;http://www.iaru.org/constitution.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;constitution&lt;/a&gt;. Are there no safeguards to cross-border amateur radio abuse?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that I do not know the exact nature of the abuse, just that it was serious enough to cause this change.&lt;/p&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="8573" LastEditDate="2019-03-18T18:11:06.260" LastActivityDate="2019-03-19T13:31:41.977" Title="Safeguards against cross-border abuse?" Tags="&lt;legal&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13068" PostTypeId="2" ParentId="13067" CreationDate="2019-03-18T10:53:37.553" Score="4" Body="&lt;p&gt;There can't be physical &quot;safeguards&quot;; radio waves simply do not care about human borders.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There should be political safeguards, but these would require the regulatory bodies of two countries to cooperate. If cooperation fails, you get a political problem (not a technically solvable one, typically). If cooperation on a regulatory level between countries fails, the least they're probably going to worry about the constitution of some international organization that is occupied with coordinating a hobby internationally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, how would you even keep active repeater frequencies secret? It would take a person with an SDR transceiver seconds to scan all bands in question and minutes to figure out which frequencies get transposed to others. Keeping frequencies secret sounds more like a military thing to do (where you can actually make it illegal / punishable by localization and potential military counteraction to &quot;probe&quot; these frequencies) than something applicable to civil-access frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Extended Answer (from the comments)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Legally, nothing binds nations but international law (which not all countries feel bound by), only enforcable by action of the UN – and I'd assume it'll take a couple of decades to even reach a decision, and enforcement could typically only happen by means of violence; I doubt a halfway reasonable congregation of states will ever wage war because of IARU violations. So, no, there's no &quot;realistic&quot; legal ways to enforce things between non-cooperating states&#xA;Things look very different when states still feel bound by contracts they signed. But if tensions are high, like let's say between Pakistan and India, this commitment to contracts breaks down. Again, there's nothing legally binding states if states don't want to commit to that. International law very much is extremely only defined by the notion that it's&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;better for all if states adhere to that; and&lt;/li&gt;&#xA;&lt;li&gt;the relatively abstract assumption that violation of it can have&#xA;embargoes or war as consequence. Again, states won't wage war&#xA;because amateur radio rights are broken, realistically.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So, the legal safeguard you can get can only work if the worst case – war with a neighbor – is actually so unlikely that neither side risks that. If, like you say, &quot;tensions are high&quot;, then your best bet at getting a legal safeguard for the neighboring country not violating your rights is to make your own government find peace with its neighbors, and reinstantiate the rule of law on a basis of agreement. Sorry. There's no easier alternative.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="14220" LastEditDate="2019-03-19T13:31:41.977" LastActivityDate="2019-03-19T13:31:41.977" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="13069" PostTypeId="2" ParentId="13067" CreationDate="2019-03-18T15:36:22.747" Score="2" Body="&lt;p&gt;I post this response as a brainstorming idea. I don't know the law and I point out the weaknesses of the idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am surprised that keeping the repeater frequencies secret has worked. Static information like this is notoriously difficult to protect. I perceive the goal as being to reduce the frequency of unauthorized access to some tolerable level, with a means to monitor compliance and rapidly respond to breaches, without increasing equipment cost. As your &quot;legal&quot; tag suggests, this must be accomplished by means that pass muster with IARU.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because an in-band repeater might include a duplexer, changing the PL tones could be a more convenient and cost-effective way to limit access than changing repeater frequencies. For a cross-band repeater, it might be simpler to just change the frequencies inside each band, or even go so far as to implement frequency hopping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, even if you change the PL tones or frequencies, the problem is the same: protecting the new values. Perhaps you could use an algorithm that works like a &quot;security dongle,&quot; computing the current PL tone or repeater frequencies for use at any given time. When the details of the algorithm and its parameters leak out (which they will), you can change the algorithm and/or its parameters. This logic would have to be implemented in the repeater, authorized members would need to carry the computing means with them and the regulatory authorities would need to be informed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because there is a small number of PL tones available, it would not take very long for a determined abuser to identify the new PL tone, so it may be difficult to balance the convenience of authorized operators with security against abuse. Adding external tone-generating hardware could implement multi-tone and poly-tone means that would effectively increase the &quot;mean time to being hacked.&quot;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-03-18T17:51:33.093" LastActivityDate="2019-03-18T17:51:33.093" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13070" PostTypeId="2" ParentId="13065" CreationDate="2019-03-18T19:54:52.120" Score="2" Body="&lt;p&gt;A four element yagi shouldn't overload your receiver unless you're very close to the transmitter.  If you were close enough for that to be an issue, your rubber duck antenna would work just fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you added the tee to the cable, you created a &lt;a href=&quot;http://www.rfcafe.com/references/popular-electronics/kill-harmonics-october-1960-popular-electronics.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;quarter wave stub trap&lt;/a&gt; that would filter out certain frequencies.  It would probably work even better if you shorted the ends instead of using resistors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those tee connectors aren't that big, so I'm betting your problem is from interference that's somewhere around the microwave part of the spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe a different radio with better built-in filters would work better.  But, if you have a solution that already works, you may want to stick with it.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2019-03-18T20:01:37.813" LastActivityDate="2019-03-18T20:01:37.813" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="13071" PostTypeId="2" ParentId="13043" CreationDate="2019-03-19T13:39:21.723" Score="0" Body="&lt;p&gt;For what it's worth, I have essentially the same situation.  I can hear the repeater with my handheld, but access is spotty.  My solution was to use my IC-706 as a receiver tuned to a non-repeater frequency (because audio and squelch lines are easily accessible) and utilized a relay board (&lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B0057OC5O8&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amazon.com/SainSmart-101-70-101-4-Channel-Relay-Module/dp/B0057OC5O8&lt;/a&gt;) to use the squelch line to key my UV-3 tuned to the repeater's input frequency.  I just have to program my handheld to a split frequency with an odd offset. &#xA; It's not pretty, and I wouldn't recommend it for regular use, but it works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also for what it's worth, my first stab was to use the Ham Shield and an Arduino.  It worked, but the shield can't handle strong signals, so the audio was unintelligible.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2019-03-19T13:39:21.723" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13072" PostTypeId="1" CreationDate="2019-03-19T14:32:56.517" Score="1" ViewCount="161" Body="&lt;p&gt;I'm just about to get on the air for the first time as a ham.  It's been my understanding that it's good to log contacts with call sign, frequency, signal quality, and time of contact.  However, for some time (until I finish repairs on the &quot;technician special&quot; multiband transceiver and have an antenna up for it) I'll be &quot;on air&quot; only via a 2m, 1.25m, and 70cm handie-talkie.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a practical way to log contacts while using a mobile transceiver, or any strong reason to make the effort?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-03-19T15:39:25.413" LastActivityDate="2019-03-19T16:03:29.413" Title="How to log contacts when mobile?" Tags="&lt;united-states&gt;&lt;mobile&gt;&lt;logging&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13073" PostTypeId="2" ParentId="13072" CreationDate="2019-03-19T14:55:11.980" Score="0" Body="&lt;p&gt;I don't know for the rest of the world, but in Russia strictly speaking every ham is &lt;em&gt;obligated&lt;/em&gt; to keep a log and store it at least one year after the last logged QSO. The other question is that no one ever needed these logs :) Also from what I know there are no strict rules on the format these logs supposed to be in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try to use a portable recorder. I would also recommend to keep a digital log, just for yourself. &lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-03-19T14:55:11.980" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13074" PostTypeId="1" AcceptedAnswerId="13099" CreationDate="2019-03-19T15:00:10.593" Score="4" ViewCount="1334" Body="&lt;p&gt;Let's say for sake of example we are in the 40m band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've read articles and posts about riding the RF gain (or even just simply lowering it).  And I can see how it is useful in overload situations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I don't quite get is how lowering the RF gain can help dig a weak signal out of the noise.  A &quot;weak signal&quot; just means that it's not much stronger than the noise floor.  Lowering the RF gain will lower the noise floor.  But it will also lower the signal as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How is it possible that lowering the RF gain will attenuate the background noise faster than the desired signal.  If you lower the gain by 3dB.  Everything goes down by 3dB, right?  The SNR doesn't improve.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've also heard of &quot;riding the RF gain&quot; where you crank up the AF and use the RF as your volume control.  How does this help?  You are lowering the noise floor and the desired signal by the same amount with the RF gain.  And then making it loud again with the AF gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There must be something happening when going from the IF to audio then benefits from having an overall quieter signal I guess.  I just don't see how any of this can somehow know to attenuate static and amplify desired signal more. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is dynamic range an issue with weak signals?  I can see it being a problem with strong signals (hence the overload and need to attenuate).  But with a weak signal, unless your noise floor is S9, you have enough dynamic range right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Articles (i.e. forum posts)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.eham.net/reviews/review/148466&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.eham.net/reviews/review/148466&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Next, with the RF Gain still all of the way Counter-clockwise, so that the radio is nearly silent (don't move the RF Gain yet), we bring the AF Gain (volume) up to a quieted -- not quite normal listening level, where we cut hiss, but still just hear the signal clearly.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Once that AF Gain volume is set (about half for Icom 7300), you just leave it where it is, roughly, but you will twiddle it a bit up or down, to keep HISS down to lowest possible levels, as your slowly raise your RF Gain. You are now using your RF Gain as your volume control, by turning it clockwise to raise the volume, or counter-clockwise to lower the volume. While you are adjusting your RF Gain, you are looking for a happy medium between where signals are loudest, but the noise around them is quietest.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;…&#xA;   I also twiddle with the AF Gain a little bit, if that helps the signal -- it really depends. Experiment!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://forums.qrz.com/index.php?threads/rf-gain-more-powerful-than-nr.554997/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://forums.qrz.com/index.php?threads/rf-gain-more-powerful-than-nr.554997/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;With AF gain on full, while using the RF gain to control volume, and aggressive EQ settings on upper-middle frequencies, signals barely readable often rise to an easy 56 to 57.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://forums.qrz.com/index.php?threads/help-me-like-my-new-ic-7300-more.551169/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://forums.qrz.com/index.php?threads/help-me-like-my-new-ic-7300-more.551169/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My KX2's RF Gain, when used with either ATT or Pre-amp, and EQ, will dramatically cut hiss noise while digging out signals.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="12939" LastEditDate="2019-03-19T18:57:59.727" LastActivityDate="2021-04-06T12:41:30.520" Title="How does lowering the RF Gain help with SNR?" Tags="&lt;equipment-operation&gt;&lt;noise&gt;" AnswerCount="5" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13075" PostTypeId="2" ParentId="13074" CreationDate="2019-03-19T15:24:24.423" Score="1" Body="&lt;p&gt;There is some systemic noise created by the front end which is proportional to its gain. So, lowering the gain lowers that systemic noise, thus raising the SNR. Of course, the degree of improvement depends on the front end and the frequency. 'Riding the RF' simply keeps the front-end gain as low as possible. You're right, it isn't a dynamic range issue.&lt;/p&gt;&#xA;" OwnerUserId="5855" LastActivityDate="2019-03-19T15:24:24.423" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13076" PostTypeId="2" ParentId="13074" CreationDate="2019-03-19T15:30:10.607" Score="2" Body="&lt;p&gt;I've seen this argument before and never been entirely convinced by it either, but I &lt;em&gt;think&lt;/em&gt; the theory is that it comes down to nonlinearity. The silicon in the amplification and detection stages of your rig is never perfectly linear. Nonlinearity at the high end is what causes overload issues, but there's also nonlinearity at the low end, where a signal that is too small is greatly attenuated or causes no reaction at all. So if you can push the noise down far enough by reducing the input gain, the noise level in the output will suddenly fall off of a cliff, &quot;revealing&quot; your weak signal, or so the theory goes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, since the signal is (in this scenario) very close to the noise, we must be adding quite a bit of nonlinear distortion to it as well, and indeed the nonlinearity must be &lt;em&gt;multiplying&lt;/em&gt; the signal with the noise (since the gain in the nonlinear region is dependent on the sum of signal and noise), so it's not clear that the result is any better than what we started with. Perhaps, since the mixing means that even most of the distortion products we hear are somehow &lt;em&gt;correlated&lt;/em&gt; with the signal, copyability should improve even though the absolute fidelity doesn't?&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-03-19T15:30:10.607" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13078" PostTypeId="2" ParentId="13072" CreationDate="2019-03-19T16:03:29.413" Score="4" Body="&lt;p&gt;In the USA there is no longer any legal requirement to keep  a log. Many HAMs log HF contacts often for use in contests or applying for various awards. There are a few contests and awards for VHF / UHF so some HAMs will keep a log for these types of contacts, but most don't. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can always use paper logs, there are even small notebooks specifically for this purpose. You can also find some apps for you phone or tablet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another alternative is to use a small recorder, what used to be called tape recorders, and transcribe the contacts later. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2019-03-19T16:03:29.413" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13079" PostTypeId="2" ParentId="13043" CreationDate="2019-03-19T17:44:33.720" Score="3" Body="&lt;p&gt;My solution to your problem (that I also have) was to buy a mobile radio that will do cross band repeat mode, such as the Icom IC-2730A. It runs (at this time) about $280. It sounds expensive, but.... when you are not at home, you have a really nice dual band mobile radio for your car/truck that puts out 50W. It is a great mobile radio that is easy to install in any car. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I have it hooked up in my home QTH and I am sitting in my basement shack, I can listen to the local SKYWARN repeaters, flip over to listen to NOAA weather radio stations or the local police and fire services. When I want to move around the house or back yard, I put it into cross band repeat mode with my HT and it works fantastic. (Make sure you only enable cross band repeat with ham frequencies!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can make it do VHF -&gt; UHF or UHF -&gt; VHF. I put a nice dual band antenna (I used the Diamond X50A) up at the peak of the roof and it is very low profile that the HOA has not complained about. Plus it just looks cool!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another use is to cross band repeat from your car to the HT like the Highway Patrol cars do. A lot of them run VHF low-band to the car and UHF to their HT's. I always thought that was a really cool setup. When they transmit on their in-car radio, it goes out on VHF low band and does not repeat to the HT, so no feedback! When out of the car, the HT goes into the UHF side and out the VHF 110W low band side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is also a great setup if you are camping or hiking or running a public service event where you cannot quit reach the main repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope that gives up some ideas! 73&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PS - The Kenwood TM-V71A is a little bit more, but a lot easier to setup cross-band repeat. See this link for the Icom setup: &lt;a href=&quot;https://www.eham.net/ehamforum/smf/index.php?topic=115770.0&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.eham.net/ehamforum/smf/index.php?topic=115770.0&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14234" LastEditorUserId="14234" LastEditDate="2019-03-19T19:06:30.243" LastActivityDate="2019-03-19T19:06:30.243" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13080" PostTypeId="2" ParentId="9451" CreationDate="2019-03-19T21:46:49.287" Score="1" Body="&lt;p&gt;The simple answer is: There is no difference between copper and aluminium. Now, the simple answer is misleading because copper has to be coated in order to not form the badly conducting oxide while aluminium does not have to be coated because aluminium oxide is a good dielectric. The coating needed on copper can affect the electrical length slightly. Better would be gold plated copper. A VERY thin layer of gold would prevent oxidation and allow most of the current to flow in the copper. Even better, silver plated &quot;whatever&quot; with a very thin layer of gold on top. Silver forms a sulphide which is lossy while gold is inert.The silver layer&#xA;can be fairly thin and what is beneath does not matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Much better than optimizing conductivity is to make a design with larger element diameters:-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case you want an invisible antenna, a 144 MHz yagi with 1 mm piano wires as elements with appropriate silver/gold coating on a very thin boom tube could give very good performance while not frustrating neighbours.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-03-19T21:46:49.287" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13081" PostTypeId="1" AcceptedAnswerId="13088" CreationDate="2019-03-19T22:32:50.027" Score="2" ViewCount="235" Body="&lt;p&gt;I haven't been able to find NEC cards or pictures of radiations patterns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm used to seeing them as polar diagrams, however, the only description I've gotten is &quot;[t]he modification of the loop antenna produces a radiation pattern which is orthogonal to the loop.&quot; from &lt;a href=&quot;https://www.eh-antenna.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;eh-antenna.com&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the radiation pattern of a tubular EH antenna like in the picture below?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ryXQq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ryXQq.jpg&quot; alt=&quot;40m band EH antenna by WB5CXC&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Image from &lt;a href=&quot;https://www.youtube.com/watch?v=DWR5d7t0WAw&quot; rel=&quot;nofollow noreferrer&quot;&gt;video by WBGCXC&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bonus: What does the EH stand for?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastActivityDate="2019-06-12T16:45:13.450" Title="What is the radiation pattern of an EH antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="13082" PostTypeId="2" ParentId="9451" CreationDate="2019-03-19T23:08:44.467" Score="2" Body="&lt;p&gt;When an electromagnetic (EM) signal is traveling along a conductor at the speed of light, it is not traveling IN the conductor but is instead traveling in the medium that surrounds the conductor. If the conductors are bare copper and bare aluminum, the medium through which the EM signals travel is air so the velocity factor (VF) would be the same for both conductors. EM signals are not electrons traveling in a conductor but rather are photons traveling in the air (or insulation) surrounding the exterior surface of the conductor. Photons, not electrons, are what travel at the speed of light in the medium. EM signals require an ever changing electric field and that cannot happen inside the conductor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thing that slows down an EM signal is not the type of metal in the conductor but instead the type of medium surrounding the conductor, e.g. air or the type of insulation through which the photons must travel.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-03-19T23:08:44.467" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13083" PostTypeId="2" ParentId="11881" CreationDate="2019-03-20T01:29:13.703" Score="1" Body="&lt;p&gt;There’s another way according to Jason Ham Radio 2.0&#xA;Turn radio off. Press and hold the two buttons on both sides of the ptt button. Turn radio on and wait for boot up. Then release the two buttons. These radios are sold locked. This will unlock the radio. It worked for me. Mike K1MIC&lt;/p&gt;&#xA;" OwnerUserId="14503" LastActivityDate="2019-03-20T01:29:13.703" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13084" PostTypeId="1" AcceptedAnswerId="13089" CreationDate="2019-03-20T11:29:04.337" Score="1" ViewCount="1201" Body="&lt;p&gt;I just got this new 2m/70cm hand-held, my first ham rig.  I neglected to order the computer connection cable with the radio (it's on the way, and I've already installed the Chirp software on my Linux desktop computer).  Meantime, in case I need to transmit or there's a delivery delay for the cable, how do I set up the &quot;tone&quot; for the local repeaters?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I understand it, this is to ensure the squelch stays off while the repeater (or the HT) is transmitting, to prevent break-ups at the receiving end.  Various repeaters have different tone figures listed in repeaterbook.com -- for instance, 107.2 -- but the radio and its manual don't have clear instructions on what to do with that tone.  I see the menu entries related, not now how to set the correct value or ensure it gets sent or correctly processed when received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This may become clear or easy to set up when I can connect Chirp to the radio, but at present it's not very clear.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-03-20T13:40:07.730" LastActivityDate="2019-03-20T19:15:34.983" Title="How do I set the &quot;tone&quot; in my new BaoFeng BF-F8HP?" Tags="&lt;repeater&gt;&lt;baofeng&gt;&lt;equipment-operation&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13085" PostTypeId="1" AcceptedAnswerId="13098" CreationDate="2019-03-20T11:34:06.980" Score="2" ViewCount="2154" Body="&lt;p&gt;I just got this new 2m/70cm hand-held, and I'm working through programming the local repeaters into channels.  I've been able to set the repeater frequency in VFO mode, then save the settings to channel memories -- except that the offset doesn't save, even if I delete the channel, set the offset, and then re-save the channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've gone through the manual twice, and viewed the video linked in one of the answers below (which effectively mirrored what I had been doing, except I had voice on so could hear &quot;Receiving Memory&quot; and &quot;Transmitting Memory&quot; when saving a channel in Frequency Mode -- I don't see the &quot;scan&quot; button doing anything) -- yet every time I return to Channel Mode, the offset value is set to zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This happens regardless whether my band is set to UHF or VHF or whether that setting matches the actual frequency; regardless whether CTCSS is programmed for transmit or receive, and so forth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've found comments on a blog post suggesting this model and the very similar UV-5R have a firmware bug that does this.  Is there a known work-around to keep the offset?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-03-21T11:21:24.127" LastActivityDate="2020-11-14T21:08:28.553" Title="Brand new BaoFeng BF-F8HP -- how to save settings in a channel memory?" Tags="&lt;baofeng&gt;&lt;equipment-operation&gt;&lt;radio-programming&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13086" PostTypeId="1" AcceptedAnswerId="13087" CreationDate="2019-03-20T11:49:37.547" Score="4" ViewCount="2796" Body="&lt;p&gt;I'm just starting to use 2m and 70cm bands, which normally use repeaters to extend range beyond a mile or two (limited mostly by line of sight, as I understand it).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I'm at home, however, I'm not at all sure I have line of sight to any of the nearby repeaters (I live in a small, fairly steep ravine that causes issue with cell phone signal on some networks) -- assuming I get my radio programmed correctly (right frequency, offset, tone, etc.), how can I be sure my signal is actually getting to the repeater?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if I can hear activity on the repeater, it's highly likely they're running much more power than the 1/4/8 watts my hand-held puts out, so I might well be able to hear the repeater when the repeater can't hear me.  How can I be sure I'm getting out?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-08-22T04:44:16.673" Title="How can I be sure I'm actually hitting the repeater?" Tags="&lt;propagation&gt;&lt;repeater&gt;&lt;equipment-operation&gt;&lt;repeater-coverage&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13087" PostTypeId="2" ParentId="13086" CreationDate="2019-03-20T13:10:04.780" Score="6" Body="&lt;p&gt;The simple answer is to transmit on the repeater's input frequency, saying something like &quot; &amp;lt; &lt;strong&gt;&lt;em&gt;your callsign&lt;/em&gt;&lt;/strong&gt; &gt; &lt;strong&gt;&lt;em&gt;testing&lt;/em&gt;&lt;/strong&gt;&quot; and listen for the repeater's courtesy beep (assuming there is one) on its output.  If you've heard the beep, then you've hit the repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even without a &quot;beep&quot;, the repeater's &quot;presence&quot; will be audible - its carrier will remain for a brief (several hundred milliseconds at least) after you release your mic, thereby keeping your radio's squelch open for a moment. This is easy to hear. Compare to what you hear if you &quot;ID&quot; on a simplex channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need a few things right:  Repeater Output Frequency, Repeater Input Frequency (or offset from the output frequency) and CTCSS (or PL) tone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Added based on the comments:&lt;/em&gt; Whenever one keys up a repeater, one should wait a half-second or so to speak after pressing the PTT button - this allows the repeater to &quot;come up&quot;.  It's common to hear transmissions cut off at the start because the operator neglected to do this. The adage is &quot;Press first, then talk&quot;&lt;/p&gt;&#xA;" OwnerUserId="8573" LastEditorUserId="8573" LastEditDate="2019-03-21T12:27:02.553" LastActivityDate="2019-03-21T12:27:02.553" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13088" PostTypeId="2" ParentId="13081" CreationDate="2019-03-20T17:40:33.220" Score="5" Body="&lt;p&gt;Appendix A of, &quot;&lt;a href=&quot;http://www.physics.princeton.edu/~mcdonald/examples/crossedfield.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Crossed-Field” and 'EH' Antennas Including Radiation from the Feed Lines and Reflection from the Earth’s Surface&lt;/a&gt;,&quot; by &lt;a href=&quot;https://dof.princeton.edu/about/clerk-faculty/emeritus/kirk-t-mcdonald&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dr Kirk T. McDonald&lt;/a&gt;, Professor of Physics at Princeton University, provides a model and some pattern diagrams of an EH antenna. The paper also provides a list of useful references.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The paper concludes that, &quot;As-built EH antennas use arms that are cylindrical sleeves, one of which surrounds the coaxial feedline and provides good capacitive coupling to the outside [of] the outer conductor of the coax. This configuration leads to strong currents on the outside of the feedline, which then acts as the principal radiator of the antenna.&quot; Tom Rauch, W8JI, arrives at the same conclusion in his analysis of the &lt;a href=&quot;https://www.w8ji.com/e-h_antenna.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;E-H Antenna&lt;/a&gt;. This subject is discussed, but not resolved, on the web site of &lt;a href=&quot;http://www.eh-antenna.com/EH_coax.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;EH Antenna Systems&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From my reading of the &lt;a href=&quot;http://www.eh-antenna.com/EH_theory.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;theoretical basis for the EH antenna&lt;/a&gt;, the authors appear to claim that electric and magnetic fields, separately produced by the fringing fields from a capacitor and leakage flux from a solenoidal inductor, respectively, are equivalent to an electromagnetic field produced by accelerating charge. Derivations of antenna radiation in standard antenna texts, e.g., &quot;Antennas&quot; by Kraus, contradict this notion.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-03-20T19:03:53.977" LastActivityDate="2019-03-20T19:03:53.977" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13089" PostTypeId="2" ParentId="13084" CreationDate="2019-03-20T19:15:34.983" Score="3" Body="&lt;p&gt;See Appendix B of the &lt;a href=&quot;https://baofengtech.com/usermanual/BF-F8HP_Manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;User Manual&lt;/a&gt;. BaoFeng calls these &quot;CTCSS&quot; tones, more recently referred to as &quot;PL&quot; tones. Page 67 of the manual describes Menu 13, which allows you to set the value of the sub-audible tone according to table C.2 on page 78.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-03-20T19:15:34.983" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13090" PostTypeId="2" ParentId="13085" CreationDate="2019-03-20T19:32:02.490" Score="3" Body="&lt;p&gt;If you insist on manually programming the radio, this 10-minute &lt;a href=&quot;https://www.youtube.com/watch?v=gF38uLNKTkM&quot; rel=&quot;nofollow noreferrer&quot;&gt;YouTube video&lt;/a&gt; should help. The programming description begins about 4:20 into the video, but I recommend watching the introductory material because it affects the programming steps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note an error in the voice over at 7:46. The author says, &quot;Hit memory one more time,&quot; but he actually presses the MENU button.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Purchasing the &lt;a href=&quot;https://baofengtech.com/Programming-cable&quot; rel=&quot;nofollow noreferrer&quot;&gt;PC-03 programming cable&lt;/a&gt; and downloading the &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP software&lt;/a&gt; will dramatically improve the ease and management of programming.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-03-20T19:32:02.490" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="13091" PostTypeId="1" CreationDate="2019-03-20T22:38:20.753" Score="2" ViewCount="549" Body="&lt;p&gt;I recently purchased a Baofeng UV-82 from a seller that advertised it as an &lt;a href=&quot;https://s.click.aliexpress.com/e/bwDVXo7m&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;...Upgrade 8W&quot;&lt;/a&gt;. There are a fair number of these on Ali Express.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming it was a UV-82HP and the seller got the listing wrong, I ordered it anyways, but no, it really does say UV-82 8W on the back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WGPTC.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WGPTC.jpg&quot; alt=&quot;Radio model and power rating at the back&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's more is that the radio does indeed have 3 transmission power options (low, medium and high) in the settings, and when I spoke to a local seller and they say that they sell genuine 8W UV-82 radios that they import directly from Baofeng.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I've been unable to find any mention of this on the Baofeng website, and there aren't any genuine mentions of this online.&lt;/p&gt;&#xA;" OwnerUserId="14220" LastActivityDate="2019-03-22T19:28:54.430" Title="Is there an 8-Watt &quot;Upgraded&quot; Baofeng UV-82?" Tags="&lt;baofeng&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13092" PostTypeId="2" ParentId="13091" CreationDate="2019-03-21T00:00:49.200" Score="3" Body="&lt;p&gt;&lt;strong&gt;Update:&lt;/strong&gt; The seller tells me I contacted BaoFeng's US distributer that provided incorrect information and gave me the &lt;a href=&quot;http://baofengradio.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;manufacturer's website&lt;/a&gt;, as well as credentials purporting to prove his legitimate seller status. As of this time, BaoFeng has not replied to my emails, but I will update my answer if they do.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;BaoFeng support tells me that there is no such thing and that this radio is, in fact, counterfeit. Time for a refund request :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9Ynit.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9Ynit.png&quot; alt=&quot;Email conversation with Baofeng support&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="14220" LastEditDate="2019-03-22T19:28:54.430" LastActivityDate="2019-03-22T19:28:54.430" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13093" PostTypeId="2" ParentId="1399" CreationDate="2019-03-21T00:51:23.530" Score="1" Body="&lt;p&gt;Nickel is a magnetic material.  Magnetic fields traveling through it will react with it and create a non-linear system.  This will create radio noise in the form of intermodulation distortion.  Most of the time we just don't care because the noise is very low compared to the signal.  One place where we do care is in repeater use where the transmitter creates a high power and the intermodulation distortion creates noise that competes with the weak signal from the distant transmitter.  AKA de-sense.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any place where a transmitter and a receiver are operating at the same time may be subject to this noise. Could be a busy tower site, or perhaps you listen to the radio as you transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why we don't use nickel (otherwise an excellent plating material).  The reason we use silver is because it is not nickel and is also an excellent plating material.&lt;/p&gt;&#xA;" OwnerUserId="14510" LastEditorUserId="14510" LastEditDate="2019-03-21T00:56:53.720" LastActivityDate="2019-03-21T00:56:53.720" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13096" PostTypeId="2" ParentId="12142" CreationDate="2019-03-21T20:24:44.577" Score="1" Body="&lt;p&gt;The answer depends on the WPM and the sampling rate.  If the WPM is fixed and known, and/or the receiver can phase lock to the the WPM dot transition rate, and you sample the carrier amplitude only once per dot time, you get a binary representation which includes a fair amount of information redundancy (e.g. no tones 2 samples long, etc.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you dynamically vary the sampling to once per symbol transition at a fixed WPM, (dot,dash,gap,letter space,word space), then you get a quintic (5 symbol) coding, instead of binary, a little more compact, but less redundant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you allow varying the WPM, and sample all the transitions, then you have an additional analog coding on top of the quantized digital coding, as each tone length and gap length can carry information, the amount depending on the rise/fall times, which increase the spectral bandwidth, but still being Morse Code if the short term timing variations stay within some limit (dots don't randomly double in length within some short number of beeps, etc.), and/or the long term WPM speed drift rate isn't too high.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This analog timing channel can carry (encode) quite a bit of information, e.g. you might be able to ID a straight key operator by their &quot;fist&quot;, even without their callsign.  Or an operator's emotional state by how they vary their straight key keying.  This is common in practice (assuming they still make straight keys), and thus might be considered part of Morse Code encoding (in practice, not in the ITU spec.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suppose one could even vary the CW envelope rise and fall times to carry even more information over &quot;CW&quot;.  Although standard HF rigs can't do this, once could do this by using DSP/SDR radios (or SDR audio input to an SSB modulation).  Although this might be considered an obscuration code, illegal in some regions unless well documented publicly.  This form of &quot;CW&quot; might sound identical to Morse Code, but would really be a different modulation scheme.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-03-21T20:58:01.390" LastActivityDate="2019-03-21T20:58:01.390" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13097" PostTypeId="2" ParentId="1188" CreationDate="2019-03-21T20:50:38.407" Score="1" Body="&lt;p&gt;If you demodulate CW to audio by the same method (and frequency readout) as SSB, then swapping I &amp;amp; Q will often move the CW signal frequency by twice your chosen side tone (depending on how your receiver's CW frequency display algorithm works).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The CW audio side-tone, using direct conversion complex demodulation SDR methods, is produced by the rate of change in phase between the I near-sinusoid carrier and the Q near-sinusoid carrier.  If the phase between Q and I is, say, increasing, then the opposite part of the phase circle, the phase between I and Q will be decreasing, thus representing a different frequency. This will commonly move the side tone outside a SSB+CW filter's passband unless you retune the complex heterodyning frequency (DSP/SDR frequency synthesizer) of the receiver.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-03-21T20:55:39.117" LastActivityDate="2019-03-21T20:55:39.117" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13098" PostTypeId="2" ParentId="13085" CreationDate="2019-03-22T11:19:38.710" Score="2" Body="&lt;p&gt;I found an answer for this online.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apparently there's a bug in the firmware of the various BaoFeng handie-talkie models (UV-5R family, BF-F8HP, and others) that causes frequency offset to revert to zero when in channel mode, regardless what was saved in any channel memory.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found &lt;a href=&quot;http://wc5c.org/wp-content/uploads/2017/08/Manually-Programming-BaoFeng-HT-Radio-Channels.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this online document&lt;/a&gt; that gives the work around for it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One must program in Frequency Mode (VFO), preferably with Voice active.  One must delete the channel before saving (you can skip this if programming a previously unused or blank channel).  Program the radio's receive frequqency (the repeater's transmit frequency), offset off, set the correct transmit CTCSS/PL tone, and save the channel; radio will respond &quot;Receiving Memory.&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Exit menus, change displayed frequency to the repeater's receive frequency (manually add or subtract the correct offset, if this isn't supplied explicitly), changing no other settings.  Save the same channel again; radio will respond &quot;Transmitting Memory.&quot;  You're done, that channel will work correctly when in channel mode.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-03-22T11:19:38.710" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13099" PostTypeId="2" ParentId="13074" CreationDate="2019-03-22T13:34:25.383" Score="11" Body="&lt;p&gt;For an ideal, linear receiver, reducing the RF gain by 1 dB lowers signal and noise by 1 dB, so there would be no change in SNR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, receivers are not perfectly linear. This means that besides just amplifying inputs, they also &lt;em&gt;mix&lt;/em&gt; them to some extent. So any input to the receiver which contains more than just a single frequency will generate some intermodulation products, that is, new frequency components at frequencies based on the sums and differences of the input components, and harmonics thereof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason for this argument to reduce RF gain is that these intermodulation products aren't linear. For a 1 dB increase in gain, the 3rd order intermodulation products increase by 3 dB. Thus if intermodulation is contributing significantly to noise, decreasing gain improves SNR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see an example in the animation below. The two central markers M1 and M2 are the &quot;signal&quot; inputs, two tones from signal generators. D3 and D4 are the third-order distortion products, and outside of those we also see the fifth, seventh, and ninth order products rise above the noise floor. The animation shows in each frame a gain increase of 1 dB: note how the gain of the intermodulation products increases faster than 1 dB per frame. This is because as gain is increased, the amplifier becomes less linear, and thus generates disproportionately more distortion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Two_carrier_3rd_order_intermod_measurement.png#/media/File:Two_carrier_3rd_order_intermod_measurement.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/1/15/Two_carrier_3rd_order_intermod_measurement.png&quot; alt=&quot;Two carrier 3rd order intermod measurement.png&quot;&gt;&lt;/a&gt;&lt;br&gt;By &lt;a href=&quot;//commons.wikimedia.org/wiki/User:Ice_Ardor&quot; rel=&quot;noreferrer&quot; title=&quot;User:Ice Ardor&quot;&gt;Ice Ardor&lt;/a&gt; - I measured the intermodulation characteristics of an amplifier myself on a spectrum analyzer, &lt;a href=&quot;https://creativecommons.org/licenses/by-sa/4.0&quot; rel=&quot;noreferrer&quot; title=&quot;Creative Commons Attribution-Share Alike 4.0&quot;&gt;CC BY-SA 4.0&lt;/a&gt;, &lt;a href=&quot;https://commons.wikimedia.org/w/index.php?curid=76200513&quot; rel=&quot;noreferrer&quot;&gt;Link&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course in practice the input to the receiver isn't just two tones in an otherwise quiet spectrum, but rather a cacophony of many signals and external noise. As a result, the intermodulation distortion isn't tidy, regular spurs such as this, but rather a raising of the noise floor. The distortion can be generated in the receiver front-end, and also in mixer stages when very strong signals can have an effect even through the filter's stop-band attenuation. Digital modes like PSK31 present a particular challenge since many signals all fall in the receiver passband, and thus can intermodulate quite strongly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The extent to which this effect is significant depends significantly on the quality and design of the radio. In recent years, many radios have adopted direct-sampling or direct-conversion SDR architectures, and this has the effect of greatly reducing intermodulation distortion since there are very few analog stages to introduce such distortion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In contrast, superheterodyne receivers have several intermediate mixer stages, and each one can add some distortion. A very high quality design might have very effective filtering and very linear stages, approaching the performance of a direct-conversion SDR. But a cheaper design can be quite terrible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, I have a Softrock RXTX, and a Yaesu FT-897. The former is a direct-conversion SDR which costs under \$100, and the latter is a superheterodyne receiver that cost over \$900 when it was new. Decoding FT8 with WSJT-X on the Softrock I get easily twice the decodes compared to the FT-897. The FT-897 simply generates too much intermodulation distortion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reducing the RF gain on the FT-897 does help, though it's never as good as the Softrock. On the other hand, the Softrock is so linear, adjusting gain makes no relevant difference because the intermodulation products are always well below the noise floor.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-22T13:34:25.383" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13101" PostTypeId="1" CreationDate="2019-03-22T15:30:13.353" Score="3" ViewCount="588" Body="&lt;p&gt;I was following this &lt;a href=&quot;http://qso365.co.uk/2018/04/updated-guide-to-setting-up-an-aprs-rx-only-igate-using-a-raspberry-pi-rtl-sdr-dongle-and-a-pre-built-image/&quot; rel=&quot;nofollow noreferrer&quot;&gt;guide&lt;/a&gt; to setup an iGate using an RTL-SDR dongle and a Raspberry Pi. It worked, and I have been able to test it by seeing some APRS packets from a separate transmitter (Arduino+BaoFeng HT) I made be relayed through that IGate. However, when I moved the IGate to another room in my house, there was a significant decrease in the number of packets that were successfully received by the IGate. I am thinking that I should put a better antenna on the dongle. Currently the antenna I have on the IGate is some 4 inch rubber ducky antenna that I scavenged from an old 2G/3G cellular modem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you suggest what criteria I should use when shopping for a better antenna for the IGate?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am in the USA and so use frequency 144.390 MHz.&lt;/p&gt;&#xA;" OwnerUserId="1845" LastEditorUserId="8717" LastEditDate="2019-03-22T16:38:20.020" LastActivityDate="2019-03-26T12:41:10.733" Title="RTL-SDR dongle - what antenna should I use for APRS receive only?" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;rtl-sdr&gt;&lt;aprs&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13102" PostTypeId="2" ParentId="13101" CreationDate="2019-03-22T15:58:48.563" Score="4" Body="&lt;p&gt;Here are the fundamentals of improving VHF antennas from what you've got:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&quot;Rubber ducky&quot; (loading coil shortened) antennas are less efficient and more frequency-selective than un-shortened antennas. Choose an antenna which is a straight length of wire. (The exact length is not critical for receiving as long as it's in the neighborhood; you may get essentially as good results from a VHF &quot;scanner&quot; antenna as from a 144 MHz specific one.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Ordinarily, &quot;get the antenna better line of sight to the transmitter&quot; would be the first thing I'd list, but that's evidently not your first problem since you started in the same room. Still, in order to use it at longer range you should consider planning an outdoor antenna installation — this may mean either installing the electronics in a weather-shielded enclosure or using a feed line between the antenna and the electronics.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A monopole-type antenna depends on the &quot;ground&quot; provided by the objects it's attached to. This does not mean it needs to be attached to earth, rather, it means that the metal of the feed line, PCB and any attached cables function as part of the antenna structure. In order to get more predictable good performance, you should choose an antenna type that has its own ground plane, or paired elements in some other form. These can include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Vertical antenna with built-in &quot;radials&quot; (wires extending horizontally).&lt;/li&gt;&#xA;&lt;li&gt;Magnet-mount antenna on top of any handy metal structure or even a steel pizza pan.&lt;/li&gt;&#xA;&lt;li&gt;&quot;Whip&quot; wire antenna mounted onto a bulkhead connector (female-female coax coupler with threads and a nut for panel mounting) or NMO mount, installed in the middle of a horizontal sheet of metal. (This requires separate care to weatherproof but might be appropriate for temporary or experimental installations.)&lt;/li&gt;&#xA;&lt;li&gt;Vertical dipole (coaxial dipole, or standard dipole with horizontal center feed).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The common feature of all of these designs is that the antenna consists of/is attached to &lt;em&gt;two&lt;/em&gt; large conductive objects.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Finally, note that once you have a good antenna, you may find that the system &lt;em&gt;doesn't&lt;/em&gt; work when the transmitter is in the same room. This would be because the receiver is overloaded and cannot decode the signals properly. If you need to do short-range tests, you can install an attenuator on either the transmitter or receiver antenna connection, or install a dummy load on the transmitter (there'll still likely be enough leakage to get through).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-03-22T15:58:48.563" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13103" PostTypeId="2" ParentId="12142" CreationDate="2019-03-22T17:56:53.767" Score="0" Body="&lt;p&gt;Interesting question, which really depends on what one means by a &quot;binary&quot; encoding system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the lowest level, an International Morse encoded, continuous wave (CW) transmission the signal is either 0 or 1, energy present or not.  This is similar to the frequency-shift keying (FSK) encoding used by radioteletype (RTTY) transmission.  &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Aside: CW isn't as redundant as FSK, where the encoding is done by&#xA;shifting the frequency up and down.  With RTTY, three states can be&#xA;determined by the receiver:  0 (space), 1 (mark), or no signal.  With&#xA;CW, the &quot;no signal&quot; condition must be determined by noticing that an&#xA;excessive time has passed without detection the signal, or a 1.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Both RTTY and CW depend on time-domain decoding to convert the binary sequence into characters.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In RTTY, the time-domain decoding is performed by looking for a space condition (0) and using a fixed timer to sample the signal at specified times.  The samples are assembled into a multi-bit character.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In CW, the time-domain decoding is not based on a pre-fixed bit rate.  Instead, the receiver watches the binary data flow looking for patterns -- two distinct period durations in which the signal is 1 balanced with periods during which the signal is 0.  In a more modern system, we would consider that there is a clock recovery process looking at the 0-1 and 0-1 transition times.  Rather than assembling a fixed number of bits, there is a state machine that takes inputs of short-1, long-1, short-0, and long-0, as determined by the clock recovery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In American Morse, there are two more inputs to the state machine, the extra-long-1 &quot;L&quot;-dash, and the even longer &quot;0&quot;-dash.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I suggest that Morse code is a binary encoding system which depends on clock recovery to recover multi-bit symbol information.  In this way, it is similar to other digital encoding schemes such as Non-return to Zero Invert (NRZI), and Phase Modulation (PM), as well as more complex schemes such as HDMI, USB, and Ethernet.&lt;/p&gt;&#xA;" OwnerUserId="9109" LastActivityDate="2019-03-22T17:56:53.767" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13104" PostTypeId="1" CreationDate="2019-03-22T18:38:19.580" Score="4" ViewCount="273" Body="&lt;p&gt;One of my goals as a new ham is to homebrew my own transmitter (using vacuum tubes, aka valves).  Initially I'll stick with CW for the transmitter, though over time I might build an AM modulator or even attempt an SSB modulator/filter.  For the CW iteration, I plan to use a vacuum tube Hartley oscillator, with the tap on the oscillator coil positioned to minimize drift on key-down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've read of some CW transmitters with high voltage at the key, suggesting they were interrupting the B+ to the output tubes (for power levels above QRP, this may be several hundred volts; for higher power, it may run to several thousand).  Obviously, if I do this, I'd use a relay to keep the high voltage inside the case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For other designs, however, I've seen reference to keying the oscillator -- either interrupting the output of the oscillator before it reaches the first output tube's grid, or interrupting the plate or grid on the oscillator's own tube to completely stop the RF (potentially also leading to relatively high voltage at the key).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I understand it, both can work well enough to have survived until transistors replaced vacuum tubes for most applications, and obviously the quality of the keyed output depends on multiple other factors (stability of the oscillator, rise and fall time of the chosen keying control, etc.).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the standpoint of signal quality, however, is there a good reason to prefer one over the other?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-03-22T19:00:07.060" LastActivityDate="2019-03-22T20:50:25.013" Title="Will I get cleaner keying by keying the oscillator, or interrupting the amplifier B+?" Tags="&lt;diy&gt;&lt;cw&gt;&lt;transmitter&gt;&lt;equipment-design&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="13105" PostTypeId="2" ParentId="13104" CreationDate="2019-03-22T19:24:38.030" Score="6" Body="&lt;p&gt;Highest frequency stability is generally achieved when the oscillator is kept running while some following stage (or stages) is (are) keyed. However, the very high &lt;em&gt;Q&lt;/em&gt; of a crystal-controlled oscillator permits direct keying. While the cathode, grid or plate of any stage can be keyed depending on design goals and available parts, an oscillator should be keyed outside of the primary frequency-determining circuitry. Cathode keying does not place high AC or DC voltage on the key terminals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Chirp&quot; can also result when the &lt;em&gt;load&lt;/em&gt; on the oscillator output varies from key-up to key-down. This can be avoided by providing a &quot;buffer&quot; amplifier stage between the oscillator and the amplifier. For example, &lt;a href=&quot;https://www.qsl.net/k5dh/6ag7_807.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;K5DH's 807 CW Transmitter&lt;/a&gt; uses a 6AG7 pentode either as a cathode-keyed crystal-controlled oscillator &lt;em&gt;or&lt;/em&gt; as a cathode-keyed buffer amplifier according to the position of SW1, which brings the V1 cathode to AC ground through a .01uF bypass capacitor. Note that the cathodes of both the oscillator/buffer &lt;em&gt;and&lt;/em&gt; the amplifier stages are keyed to prevent oscillator feed-through to the antenna during key-up. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radios like the Heathkit &lt;a href=&quot;https://www.vintage-radio.info/download.php?id=505&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX-60&lt;/a&gt; and the &lt;a href=&quot;http://www.wb4hfn.com/DRAKE/DrakeManuals/2NT/Manual_2NT.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Drake 2-NT&lt;/a&gt; employed a similar architecture but used &lt;em&gt;grid block keying&lt;/em&gt;, which is thoroughly explained in the cited manuals, placing a high negative DC voltage on the key terminals. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-03-22T20:50:25.013" LastActivityDate="2019-03-22T20:50:25.013" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13106" PostTypeId="1" AcceptedAnswerId="13123" CreationDate="2019-03-22T19:44:45.483" Score="6" ViewCount="1542" Body="&lt;ol&gt;&#xA;&lt;li&gt;Which Baofeng website(s) in the USA is (are) official (that is, selling genuine Baofeng radios, programming cables, and accessories)? &lt;/li&gt;&#xA;&lt;li&gt;Which &quot;Baofeng&quot; websites are &lt;strong&gt;NOT&lt;/strong&gt;, allegedly selling &lt;a href=&quot;https://www.google.com/search?q=counterfeit&quot; rel=&quot;nofollow noreferrer&quot;&gt;counterfeit&lt;/a&gt; radios and programming cables?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.google.com/search?q=baofeng%20usa&quot; rel=&quot;nofollow noreferrer&quot;&gt;A Google search for &lt;em&gt;baofeng usa&lt;/em&gt;&lt;/a&gt; returns several websites, &lt;strong&gt;all of which claim to be &quot;official&quot;&lt;/strong&gt;.&#xA;It &lt;em&gt;could&lt;/em&gt; be that Baofeng USA has several genuine/official/bona fide domain names. But as &lt;a href=&quot;https://ham.stackexchange.com/questions/13091/is-there-an-8-watt-upgraded-baofeng-uv-82&quot;&gt;this question and the answers therein&lt;/a&gt; points out, there are apparently:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;counterfeit Baofeng radios&lt;/li&gt;&#xA;&lt;li&gt;counterfeit programming cables, and&lt;/li&gt;&#xA;&lt;li&gt;counterfeit Baofeng websites.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-03-23T23:10:17.367" LastActivityDate="2020-12-04T17:47:36.827" Title="What are the official Baofeng websites in the USA?" Tags="&lt;united-states&gt;&lt;baofeng&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13107" PostTypeId="1" AcceptedAnswerId="13111" CreationDate="2019-03-23T02:14:16.203" Score="1" ViewCount="1960" Body="&lt;p&gt;On a Raspberry Pi 3 B+ running Raspbian Stretch, when I run this command,&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;timeout 115 rtl_fm -d 0 -g 49 -M usb -s 32000  -r 32000 -F 1 -f 50.293M outfile.raw&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I get the following messages, the last line of which is an error:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Found 1 device(s):&#xA;  0:  Realtek, RTL2838UHIDIR, SN: 00000001&#xA;&#xA;Using device 0: Generic RTL2832U OEM&#xA;Found Rafael Micro R820T tuner&#xA;Tuner gain set to 49.60 dB.&#xA;rtl_fm: symbol lookup error: rtl_fm: undefined symbol: rtlsdr_set_bias_tee&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Does anyone know how to fix this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Internet says it is just a library issue and the following commands should fix it:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;LD_LIBRARY_PATH=/usr/local/lib&#xA;export LD_LIBRARY_PATH=$LD_LIBRARY_PATH&#xA;sudo ldconfig&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I did this and rebooted... same problem&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hardware:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Computer is a Raspberry Pi 3 B+ running the latest Raspbian Stretch.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;RTL-SDR dongle is V3 with the following printed on it:  RTL 2832U R820T2 TCX0 + Bias T + HF&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A note about the Bias T:  I am not using that function.  Not on purpose, anyway.  The antenna is a simple dipole and I have no need to feed power into the antenna line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Background:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using the RTL-SDR as part of a WSPR listening station.  A Kiwi-SDR is monitoring 7 other bands while the RTL-SDR is monitoring 6m.  The output from the RTL-SDR is sent into sox for processing and then over to wsprd for analysis.  The Pi seems to be able to handle quite a few channels like this; I am monitoring 7 total and the Pi handles it easily.  More channels will be added as time goes on; still tweaking the software and the signal processing.  This system has worked well for some months, however I thought it could be useful to change the command from&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;timeout 115 rtl_fm -d 0 -g 49 -M usb -s 32000  -r 32000 -F 1 -f 50.293M outfile.raw&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;to&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;timeout 115 rx_fm -d 0 -g 49 -M usb -s 32000  -r 32000 -F 1 -f 50.293M outfile.raw&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;At this point I have given up on that; rx_fm is a clone of rtl_fm with some improvements but I was never able to get it to work.  Along the way --adding software to try to get rx_fm to work-- I broke something.  For a week or so, I was getting the above error message when running rtl_fm as root (sudo) however not as a user (pi).  Today, it is now affecting the user and so the 6m listening segment is now off line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thing that changed today --strange as it seems-- was some of the flags as shown below.  With the new flags, the error message started.  Restoring the original flags, the error message remains.  The command with the new flags was&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;timeout 115 rtl_fm -d 0 -g 49 -M usb -s 96000  -r 96000 -F 1 -f 50.293M outfile.raw&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;(changed 32k to 96k, expecting some SNR benefits)  Once I saw the above-referenced error, I changed it back to 32k.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems like it should be fairly straightforward, but it has me confused.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I address the &quot;symbol lookup error&quot; so the RTL-SDR can start working again?  &lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2019-03-23T02:53:10.723" LastActivityDate="2019-03-23T15:42:58.060" Title="RTL-SDR - rtl_fm: undefined symbol: rtlsdr_set_bias_tee" Tags="&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13109" PostTypeId="2" ParentId="13106" CreationDate="2019-03-23T09:10:24.557" Score="2" Body="&lt;p&gt;What's &quot;official&quot; anyway? The address of the company producing the device? That company seems to be &quot;PO FUNG ELECTRONIC(HK) INTERNATIONAL GROUP COMPANY&quot;; the company importing to the US? That'd be &quot;SAIN3 LLC, Berkeley&quot;, I think. Is Baofeng a company or just a brand (hint: Nike produces zero shoes. They license logos. They are a brand company.)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, the officialst you'll get is probably whatever is known to the official positions – in this case, what is known to the FCC. A quick search on fccid.io for UV-5R yielded this document:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://fccid.io/2AJGM-UV5R/Letter/C2PC-letter-4057982&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://fccid.io/2AJGM-UV5R/Letter/C2PC-letter-4057982&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1zS6T.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1zS6T.png&quot; alt=&quot;Signature of company officer&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which answers the question of who's responsible from the point of view of the FCC: a Mr. Wang with a baofengradio.com address.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether that is the &lt;em&gt;US&lt;/em&gt; website – I don't know. Why should a Chinese manufacturer even have a specific US website? They produce goods for export. They have have an English website – that's probably it.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-03-23T10:12:57.237" LastActivityDate="2019-03-23T10:12:57.237" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13110" PostTypeId="1" CreationDate="2019-03-23T11:38:42.617" Score="1" ViewCount="89" Body="&lt;p&gt;I have a problem with recording SWS-morse using SDRSharp and RTL-SDR.&#xA;I want fixed gain, not audio automatic gain control.&#xA;The problem is that all signal but the weakest will cause the recorded audio to be saturated with disastrous result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When recording FM audio there is no problem&#xA;How do I adjust the recording level manually in SDRSharp?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have tried a recording addon: same bad result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MEmnX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MEmnX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14525" LastEditorUserId="8717" LastEditDate="2019-04-22T16:53:38.800" LastActivityDate="2019-04-22T16:53:38.800" Title="Problem recording morse with sdr#" Tags="&lt;software-defined-radio&gt;&lt;cw&gt;&lt;sdrsharp&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13111" PostTypeId="2" ParentId="13107" CreationDate="2019-03-23T15:42:58.060" Score="3" Body="&lt;p&gt;Based on the observations by @MarcusMüller I looked more closely at the installation.  I had, indeed, installed multiple versions.  &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;$ which -a rtl_fm&#xA;/usr/local/bin/rtl_fm&#xA;/usr/bin/rtl_fm&#xA;&#xA;$ ls -la /usr/local/bin/rtl_fm /usr/bin/rtl_fm &#xA;-rwxr-xr-x 1 root root 26836 Oct 11  2017 /usr/bin/rtl_fm&#xA;-rwxr-xr-x 1 root staff 39772 Mar 16 20:35 /usr/local/bin/rtl_fm&#xA;&#xA;$ sudo rm /usr/local/bin/rtl_fm&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;In other words, I found multiple instances of the executable rtl_fm and simply removed the newest one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Problem went away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this only makes the immediate problem go away.  There are other redundant executable files to be removed in that same directory and, likely, libraries as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My immediate issue is resolved.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2019-03-23T15:42:58.060" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13112" PostTypeId="2" ParentId="13110" CreationDate="2019-03-23T15:52:36.493" Score="1" Body="&lt;p&gt;You're pretty clearly experiencing numerical wraparound: the two numbers produced by the ADC combine to a complex number &lt;span class=&quot;math-container&quot;&gt;$z=I+jQ$&lt;/span&gt; with &lt;span class=&quot;math-container&quot;&gt;$|z|&amp;gt;1$&lt;/span&gt;, and thus, numerically, you suddenly get a switchover.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reduce the gain by 3 dB. This should give you enough headroom.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-03-23T15:52:36.493" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13113" PostTypeId="2" ParentId="10015" CreationDate="2019-03-23T19:01:34.847" Score="1" Body="&lt;p&gt;When faced with a question like this, I find it easiest to use the selection &quot;filters&quot; at the web sites of the major distributors. My favorites are &lt;a href=&quot;http://digikey.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;DigiKey&lt;/a&gt;, &lt;a href=&quot;http://mouser.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mouser&lt;/a&gt; and &lt;a href=&quot;http://arrow.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;Arrow&lt;/a&gt;, but there are others and your region may have different suppliers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the Mouser web site, I was able to find six (6) part numbers with &lt;span class=&quot;math-container&quot;&gt;$f_t$&lt;/span&gt; between 600MHz and 1200MHz, priced between 80 cents and 5 dollars.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-03-23T19:01:34.847" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13115" PostTypeId="2" ParentId="7325" CreationDate="2019-03-24T02:05:19.013" Score="0" Body="&lt;p&gt;It maybe that the tnc you are connecting to expects SABME (v2.2) AX.25.  Some TNCs are not able to accept the older ( V2) AX.25.  The comment about VOX is also correct. Usually the minimum VOX delay in a SignalLink will work.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a PI3 running Dire Wolf and connecting to the Pi on the house Lan.  Wife checks winlink via wireless LAN to Dire Wolf.  The Dire Wolf soft modem is set as a KISS TNC.  The UA7HO modem works but is about like a TNC2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 Ed KE3D&lt;/p&gt;&#xA;" OwnerUserId="14529" LastActivityDate="2019-03-24T02:05:19.013" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13116" PostTypeId="1" AcceptedAnswerId="13119" CreationDate="2019-03-24T07:34:02.117" Score="1" ViewCount="364" Body="&lt;p&gt;I am currently building a two element portative cubical quad with one reflector and one driven element. the conductors of the driven element and reflector are encased in pvc tubing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was wondering what tuning stub design I could use for the reflector. I didn't find a lot in the literature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently, I am thinking of a conductive bar bolted across two long screws. it would be quite precise for tuning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now for the choice of metal: it has to be a compromise between corrosion resistance, price and conductivity. I was thinking of corrosion resistant brass.&#xA;for a better and more expensive design a silver or gold plated stub would be better, I suppose ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway,  I have no idea of the best geometry for the stub. I suppose it has to have a decent spacing or it will behave like a transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ideas or references welcome.&lt;/p&gt;&#xA;" OwnerUserId="13081" LastEditorUserId="4076" LastEditDate="2019-03-24T09:11:03.253" LastActivityDate="2019-03-24T19:07:51.770" Title="cubical quad reflector tuning stub design" Tags="&lt;loop-antenna&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13119" PostTypeId="2" ParentId="13116" CreationDate="2019-03-24T19:07:51.770" Score="2" Body="&lt;p&gt;Using this &lt;a href=&quot;https://www.qsl.net/yt1vp/CUBICAL%20QUAD%20ANTENNA%20CALCULATOR.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Cubical Quad Antenna Calculator&lt;/a&gt;, it appears that the length of your driven element targets 95MHz operation. As you surmise in your comment, wire insulation and PVC housing will reduce the velocity factor of the elements, which in turn will make the elements &lt;em&gt;electrically&lt;/em&gt; longer and lower the antenna's operating frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning stubs are made from transmission lines; the word &lt;em&gt;stub&lt;/em&gt; refers colloquially to a short section of transmission line. The tuning stub acts as a reactance in series with the antenna conductor: series capacitive reactance will &lt;em&gt;shorten&lt;/em&gt; the electrical length, while inductive reactance will &lt;em&gt;lengthen&lt;/em&gt; it. Applying stubs to the driven element and to the reflector will both affect driving-point impedance; applying a stub to the reflector will also change the antenna's directional characteristics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Stub_(electronics)&quot; rel=&quot;nofollow noreferrer&quot;&gt;stub's reactance&lt;/a&gt; depends on its length, the characteristic impedance of the transmission line comprising the stub and whether the end of the stub is a short- or open-circuit. For short-circuited stubs:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$Z_{sc} = jZ_0 tan(\beta l)$$&lt;/span&gt;&#xA;while for open-circuited stubs:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$Z_{oc} = -jZ_0 tan(\beta l)$$&lt;/span&gt;&#xA;where &lt;span class=&quot;math-container&quot;&gt;$l$&lt;/span&gt; is the length of the stub and &lt;span class=&quot;math-container&quot;&gt;$\beta=\frac{2\pi}{\lambda}$&lt;/span&gt;. Since &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is the wavelength in the transmission line, the line's velocity factor must be figured into the calculation. Assuming you want the shortest practical stub, &lt;span class=&quot;math-container&quot;&gt;$\beta l$&lt;/span&gt; should be kept to less than &lt;span class=&quot;math-container&quot;&gt;$\frac{\pi}{2}$&lt;/span&gt;, the length at which the sign of the reactance changes, so &lt;span class=&quot;math-container&quot;&gt;$l$&lt;/span&gt; should be less than &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{4}$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you are operating in the vicinity of 100MHz and using only 10 watts of power, it will probably be most convenient to make your stub from an inexpensive RG-58 or RG-59 type of coax rather than making your own transmission line. 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; RG-58 coax is popular in amateur radio, while 75-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; RG-59 coax is commonly used in CATV installations. Using &lt;a href=&quot;https://en.wikipedia.org/wiki/Coaxial_cable&quot; rel=&quot;nofollow noreferrer&quot;&gt;RG-58/U&lt;/a&gt; as an example,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\lambda = \frac{v c}{f} = \frac{0.66 \times 3\times10^8 \left.\mathrm{m}\middle/\mathrm{s}\right.}{95\times10^6\mathrm{Hz}}= 2.08\mathrm{m}$$&lt;/span&gt;&#xA;and &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{4}\approx0.5\mathrm{m}$&lt;/span&gt;&#xA;Changing the length of an open-circuited line is simply a matter of cutting the line to different lengths. The length of a short-circuited line can be trialed by inserting a pin in the coaxial cable to short the braid to the center conductor.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-03-24T19:07:51.770" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13120" PostTypeId="1" CreationDate="2019-03-25T03:11:50.850" Score="2" ViewCount="860" Body="&lt;p&gt;I see on the internet that a radio amateur made bowtie antennas for transmitting and receiving on the 2 meter and 10 meter bands. They produced very good SWR bandwidth when fed with 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; coax. Why, then, are bow tie antennas for UHF TV connected to 75-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; coax through a 300-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;:75-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; stepdown balun? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Commercial 4-bay bow tie antennas connect the feedpoints of the bowties with ~14ga solid conductors and feed the antenna through a 300-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;:75-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; stepdown balun. If the impedance of a single bow tie is close to 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; or 75-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, then connecting four of them with half wave wires should result in an impedance around 12.5-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; or 18.75-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, which is a very poor match to the 300-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; input impedance of the balun. This situation would be even worse for an 8-bay antenna. How do these antennas work?&lt;/p&gt;&#xA;" OwnerUserId="14540" LastEditorUserId="8717" LastEditDate="2019-03-25T14:39:56.107" LastActivityDate="2019-08-20T16:35:29.763" Title="Bow Tie antennas impedance" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;phased-array&gt;&lt;parallel-dipole&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13121" PostTypeId="1" CreationDate="2019-03-25T10:46:10.170" Score="1" ViewCount="68" Body="&lt;p&gt;I have as source a bit frame, then I modulate it, to finally transmit it with my HackRF. I can receive and decode it normally with another HackRF.&#xA;However I would like to limit to a number of frame the transmission of this frame. &#xA;Currently, it works like a infinite loop. My expected behaviour would be to transmit it only once or twice but not that much.&#xA;My final objective is to change the source (modify the bit frame) after every transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I didn't find a way to limit my transmission. &#xA;Then, when I will achieve this first step, I will look into this second step.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is my Gnu Radio Graph &#xA;&lt;a href=&quot;https://i.stack.imgur.com/kNzOj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kNzOj.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14207" LastEditorUserId="8717" LastEditDate="2019-03-25T14:17:27.390" LastActivityDate="2019-03-25T14:17:27.390" Title="How to limit frame transfer in Gnu Radio Companion?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;hackrf&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13123" PostTypeId="2" ParentId="13106" CreationDate="2019-03-25T19:14:31.337" Score="2" Body="&lt;p&gt;I believe the answer by Marcus Müller correctly associates the name &quot;Po Fung&quot; with Baofeng radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found that baofengtech.com and baofengradio.com both have news from 2014 about their brand changing from Baofeng to Pofung. In both cases, the change was short lived. It sounds to me like they're two different importers using the same supplier.  You can find the posts &lt;a href=&quot;https://web.archive.org/web/20140731003542/http://www.baofengradio.com/en/shownews.asp?id=28&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;https://baofengtech.com/blog/Fr/Post/5/What-was-with-the-Confusing-Pofung-Hype&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The post from baofengradio.com lists some business partners: www.baofengtech.com, www.radioddity.com, www.baofengradio.us, and www.sainsonic.com.  If you buy from any of these sites, and if you're buying a model these sites have in common, it's likely that you're getting radios from the same manufacturer.  (At least until things change.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If any of these sites have links to online marketplaces such as Amazon, those links should lead to the right products, &lt;strong&gt;but you still need to verify the seller name!&lt;/strong&gt;  There's a chance the marketplace site will show you an identical looking product from a different seller if the product is out of stock or if the link you clicked is expired or otherwise defective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any Baofeng radios from other sources should be considered suspect unless you can verify their origin.  It's possible that they came from different manufacturers.  It's also possible that they're factory rejects (maybe sold without authorization) or they were made under a different contract with different specs.  There are a lot of possibilities and we can only guess about them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's interesting to note that baofengradio.com has an &lt;a href=&quot;http://www.baofengradio.com/enshowNews.asp?id=78&quot; rel=&quot;nofollow noreferrer&quot;&gt;updated version of the name change article&lt;/a&gt; referenced above that doesn't name any business partners.  Their site also has a &lt;a href=&quot;http://www.baofengradio.com/enshowNews.asp?id=78&quot; rel=&quot;nofollow noreferrer&quot;&gt;page about the Baofeng trademark&lt;/a&gt; that makes it clear that some companies are using the name with authorization, and others are violating the trademark.  It mentions the existence of authorized distributors, but doesn't name them.  The fact that these pages don't name any other companies suggests that it may be very difficult to obtain a more current list of authorized distributors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, I'm going to point out another interesting find.  Baofengtech.com uses two different brands on its radios: BaoFeng and BTECH.  Given the site's domain name, you might think the two brands are related.  But, they're not.  You'll notice that the BTECH radios aren't listed at baofengradio.com.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I asked John Miklor (of miklor.com) and he gave me some further information about BTECH:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Several years ago, BaofengTech (BTech) started as an authorized distributor of Baofeng products. Since then they have grown to become an ODM. They work with companies taking existing designs and having custom features added to meet their specifications.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Some of the companies they work with are Baofeng, Vero, Nagoya, Anytone, etc. directly. (No clones, fakes or copies). They still retain the original website identity as BaofengTech, as BTech is used by another company. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Long story short, they are a US distributor (not manufacturer) selling analog and DMR products mostly built to their specs.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2019-03-25T23:38:42.063" LastActivityDate="2019-03-25T23:38:42.063" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13124" PostTypeId="2" ParentId="13120" CreationDate="2019-03-25T23:03:47.627" Score="2" Body="&lt;p&gt;A &lt;strong&gt;single&lt;/strong&gt; bowtie dipole &lt;em&gt;does&lt;/em&gt; have an impedance of about 50 ohms. &lt;em&gt;However&lt;/em&gt;, stacking multiple dipoles with a properly-designed phasing system can change that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a TV antenna that I made and use, with four phased bowties. Notice the phasing lines running between them. At the feedpoint where the 4:1 balun is, the impedance is about 300 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QnmHO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QnmHO.jpg&quot; alt=&quot;Phased dipole array&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-08-20T16:35:29.763" LastActivityDate="2019-08-20T16:35:29.763" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13125" PostTypeId="1" AcceptedAnswerId="13128" CreationDate="2019-03-26T01:46:15.480" Score="6" ViewCount="213" Body="&lt;p&gt;I have a Daiwa CS-201A two position switch. The single side is connected to by quarter wave vertical (40m). The A and B sides are connected to an IC-7300 and TS-830S.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The switch is claimed to have 60dB of isolation. It also shorts the unused port to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I transmit 100W (50dBm) from the TS-830S to the antenna, am I correct in that about -10dBm will leak to the other side into the IC-7300?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried it and saw about +40 over S9 on the 7300. The service manual for the 7300 says never give it a signal over 20dBm (0.1W).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I safe doing this? How can I tell if it’s too much?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPDATE:&#xA;I did some testing with an Elecraft XG3 signal source.  It produces signals at -107dBm (1uV), -73dBm (S9), -33dBm (S9+40), and 0dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Following the instructions using the 1uV signal and a DMM on the speaker output, the MDS is around -135dBm and -142dBm with the preamp off and set to 1, respectively.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the -73dBm signal is showing just shy of S9 on the S meter.  That worried me a little, but I saw in the August 2016 QST magazine article that the ARRL test showed an S9 with a 70uV signal.  So there's an error of about 3dB (which is also the S unit increment on this rig's meter).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I think my receiver is still okay.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also tested the isolation of the switch by hooking the 7300 to port A, the signal generator to port B, and a dummy load to the common port.  With switch in the B position (allowing a direct path from the signal generator to the dummy load), I set the signal output to 0dBm and noted the S meter deflection on the 7300.  It was around S5.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know exactly what signal level that is, but it's less that what it read when I fed -73dBm directly into it.  So even if we overestimate the received signal at -73dBm, that's still at least 73dB of isolation- if I'm thinking this through correctly.  This was done on at a frequency of 7.020MHz.  I think the switch claims an isolation of 60dB at 600MHz.  It appears the isolation improves as you go down in frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added a bounty for feedback on the tests and the data.  Is it really possible for the switch to have that good of isolation?  Is there anything else I should look into?  Do the tests seem valid?  Am I in the clear running two rigs on this switch?&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="12939" LastEditDate="2019-04-16T23:02:47.667" LastActivityDate="2019-04-16T23:02:47.667" Title="Is it safe to run two barefoot rigs on one antenna with an AB switch?" Tags="&lt;rf-power&gt;&lt;antenna-system&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13126" PostTypeId="1" CreationDate="2019-03-26T12:16:34.120" Score="1" ViewCount="106" Body="&lt;p&gt;I hope this question is not out of bounds. I'm a EE with little RF and you guys seem to know a LOT about RF...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a small vehicle traveling in a straight line at low speed. I need to know when it crosses a line that is perpendicular to it's travel. I can't use the normal proximity or through beam sensors. I propose to embed an antenna in the &quot;finish line&quot; (which needs to span 25-30 feet), mount a receiver on the vehicle, and monitor something like RSSI to determine when it passes the finish line. The receiver would need to be about 3 feet above ground level where the antenna is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this possible? What frequencies would work best and are available for something like this?&lt;/p&gt;&#xA;" OwnerUserId="14552" LastActivityDate="2019-03-27T15:14:09.887" Title="Can I measure position with antenna/receiver?" Tags="&lt;antenna-theory&gt;&lt;rssi&gt;" AnswerCount="3" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="13128" PostTypeId="2" ParentId="13125" CreationDate="2019-03-26T12:24:29.673" Score="4" Body="&lt;p&gt;S9 corresponds to 50 microvolts or -73 dBm. Thus S9+40 is -33 dBm. In theory, since it's much less then 20dBm your 7300 should be fine. HOWEVER I believe that +40 is just a maximum level your transceiver can show. Given that the attenuation of your switch is 60 dB and you are using 100W (50 dBm), -10 dBm will leak. It's much more than -33 dBm but you are still in the safe range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From personal experience I used a DIY switch with measured 58.7 dB attenuation in the same manner with a 100W transceiver and an RTL-SDR, which maximum input is 10 dBm. RTL-SDR showed a large signal level as well, but worked just fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This being said I wouldn't recommend to trust the manufacturers claim regarding the attenuation level of the switch. It's always a good idea to measure it using a &lt;strong&gt;low-power&lt;/strong&gt; signal generator (if you don't have one you can solder a simple Clapp oscillator) and an oscilloscope (or your transceiver).&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-03-26T12:24:29.673" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13129" PostTypeId="2" ParentId="13101" CreationDate="2019-03-26T12:41:10.733" Score="3" Body="&lt;p&gt;Rubber ducky antennas are not very efficient indeed. Also for best performance they may require a ground plane or radials, which I guess you could omit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally I used &lt;a href=&quot;https://www.rtl-sdr.com/product/rtl-sdr-blog-multipurpose-dipole-antenna-kit/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTL-SDR Blog Multipurpose Antenna&lt;/a&gt; (i.e. a regular dipole) for this purpose quite successfully:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UXzUA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UXzUA.jpg&quot; alt=&quot;https://eax.me/files/2018/11/aprs-antenna.jpg&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One observation I made while experimenting with APRS is that using a broadcast FM filter helps a lot. I was using this one:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dRDHV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dRDHV.jpg&quot; alt=&quot;https://eax.me/files/2018/04/bandstop-filter.jpg&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-03-26T12:41:10.733" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13131" PostTypeId="2" ParentId="13126" CreationDate="2019-03-26T23:46:56.297" Score="0" Body="&lt;p&gt;It sounds like there are requirements that are not called out in the question but, since it invites some interesting &quot;spitballing,&quot; here's a thought: Doppler effect. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would propose to mount a small transmitter on the vehicle(s) and connecting the antenna to a receiver. As the transmitter approaches the antenna, the receiver will observe a higher carrier frequency than the one on which the transmitter is known to be operating. As it passes the antenna, the receiver's observation of the carrier frequency will coincide with the known frequency. As the transmitter travels away from the antenna, the received frequency will drop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The higher the carrier frequency, the greater the Doppler effect. It should be possible to operate in one of the ISM bands with an off-the-shelf transmitter. With narrow receiver bandwidth, the receiver will produce a &quot;blip&quot; indicating the arrival of the transmitter with arbitrary precision.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding a second receiving antenna, at some distance from the first, perpendicular to the direction of travel of the transmitter, creates opportunities for other algorithms to indicate the transmitter's position.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-03-26T23:46:56.297" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13132" PostTypeId="2" ParentId="13126" CreationDate="2019-03-27T04:49:18.530" Score="1" Body="&lt;p&gt;Use induction.  Bury conductors underground just below the surface or on the surface is conductive coating.  Run current thru the conductors which creates a fixed magnetic field (DC current).  Have a inductor coil of suitable size mounted on the front of the car to sense the magnetic field and create emf and current.  Use that current as an indicator to signal you have crossed the line.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2019-03-27T04:49:18.530" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13135" PostTypeId="2" ParentId="13126" CreationDate="2019-03-27T15:14:09.887" Score="0" Body="&lt;p&gt;How about a laser or other infrared transmitter/receiver similar to the safety device on your garage overhead doors?&lt;/p&gt;&#xA;" OwnerUserId="9076" LastActivityDate="2019-03-27T15:14:09.887" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13136" PostTypeId="1" CreationDate="2019-03-27T15:54:17.553" Score="3" ViewCount="170" Body="&lt;p&gt;I live in a draw, well below local average ground level.  There are two repeaters I want to be able to use (because they're in the network my club uses).  One is in the 440 band, thirty miles away but more than a thousand feet up in a pass, with a small mountain (a little lower than the repeater) directly between; the other, on 2m, is on a radio tower fifteen or so miles away, but with the ridge that forms one side of my draw blocking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Short of installing my own repeater or antenna on a tower high enough to get over the surrounding terrain, is there a trick for hearing and being heard by either of these repeaters while at home?  I have 8W of transmit power available on a 16&quot; Nagoya antenna that replaced the original on my BaoFeng BF-F8HP.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-02T19:12:08.370" Title="Is there a trick for reaching a repeater &quot;through&quot; terrain?" Tags="&lt;propagation&gt;&lt;2m-band&gt;&lt;70cm-band&gt;" AnswerCount="2" CommentCount="15" ContentLicense="CC BY-SA 4.0" />
  <row Id="13137" PostTypeId="2" ParentId="13136" CreationDate="2019-03-27T16:09:06.887" Score="3" Body="&lt;p&gt;Reaching a repeater 30 miles (48 km) away with a mountain in between, with a handheld, sounds nearly impossible.  Reaching a repeater 15 miles away with a ridge in the way with a handheld sounds very difficult.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could experiment with several improvements:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A better omnidirectional antenna up high, like on the roof&lt;/li&gt;&#xA;&lt;li&gt;A radio with more power, like a 50 W mobile rig&lt;/li&gt;&#xA;&lt;li&gt;A directional antenna like a yagi&lt;/li&gt;&#xA;&lt;li&gt;A passive repeater (a 1/2&amp;lambda; vertically-oriented conductor) on the ridge or mountain top&lt;/li&gt;&#xA;&lt;li&gt;A repeater on the ridge or mountain top that is linked to the other repeater(s)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-03-27T16:09:06.887" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13139" PostTypeId="1" AcceptedAnswerId="13141" CreationDate="2019-03-27T18:22:25.493" Score="3" ViewCount="897" Body="&lt;p&gt;I have line of sight issues with repeaters I want/need to use (it's a repeater network my club uses).  One of the options that might be available to me is to install a &quot;passive repeater&quot; in a location that has line of sight both to my home and to one or another of the repeaters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a public tool that can be used to plot line of sight from arbitrary heights above ground between selected points (say, using Google Maps data)?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="8717" LastEditDate="2019-03-27T19:54:59.200" LastActivityDate="2019-03-28T12:57:07.390" Title="Line of sight from geographic/map data?" Tags="&lt;propagation&gt;&lt;software&gt;&lt;line-of-sight&gt;&lt;repeater-coverage&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13140" PostTypeId="2" ParentId="13139" CreationDate="2019-03-27T18:41:33.937" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://www.heywhatsthat.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;HeyWhatsThat&lt;/a&gt; is a free web app that can show you the view from any location and elevation. From what I've seen (I haven't used it seriously), it's a bit clunky but it does the job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also see a plot of elevation between two points, which is useful if you want to consider Fresnel zones in your propagation analysis.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-03-27T18:41:33.937" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13141" PostTypeId="2" ParentId="13139" CreationDate="2019-03-27T19:52:55.607" Score="3" Body="&lt;p&gt;I've used &lt;a href=&quot;https://www.solwise.co.uk/wireless-elevationtool.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt; several times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;added:&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Go to the graphic under: Surface Elevation Tool. &lt;/li&gt;&#xA;&lt;li&gt;Scroll (zoom out to speed things up) OR use the search to get to your geographic area. Search somewhat reliably recognizes town,state names and zip codes.&lt;/li&gt;&#xA;&lt;li&gt;Zoom into and Click on a location to drop a balloon.&lt;/li&gt;&#xA;&lt;li&gt;Zoom out and scroll to other location - zoom in and click again to drop other balloon&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Click balloons to enter heights (in meters)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that for longer distances (where it matters!) the earth's curvature is NOT being taken into account.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="8573" LastEditorUserId="8573" LastEditDate="2019-03-28T12:18:26.597" LastActivityDate="2019-03-28T12:18:26.597" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13142" PostTypeId="2" ParentId="13139" CreationDate="2019-03-28T05:30:46.140" Score="3" Body="&lt;p&gt;Google Earth Pro (now free. $0) has a Viewshed tool.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;A viewshed is the geographical area that is visible from a location. It includes all surrounding points that are in line-of-sight with that location and excludes points that are beyond the horizon or obstructed by terrain and other features (e.g., buildings, trees).&quot; --&lt;a href=&quot;https://en.wikipedia.org/wiki/Viewshed&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://support.google.com/earth/answer/3064261&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://support.google.com/earth/answer/3064261&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.gearthblog.com/blog/archives/2015/02/google-earth-pro-viewshed-tool.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.gearthblog.com/blog/archives/2015/02/google-earth-pro-viewshed-tool.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=9SP1O8q2Lng&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=9SP1O8q2Lng&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=DcZ8hyHZnu0&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=DcZ8hyHZnu0&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://techcrunch.com/2013/04/22/google-launches-google-earth-pro-7-1-with-new-viewshed-visualization-tool-and-improved-printing-options/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://techcrunch.com/2013/04/22/google-launches-google-earth-pro-7-1-with-new-viewshed-visualization-tool-and-improved-printing-options/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.forbes.com/sites/amitchowdhry/2015/01/30/google-earth-pro-is-now-available-for-free/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.forbes.com/sites/amitchowdhry/2015/01/30/google-earth-pro-is-now-available-for-free/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14566" LastEditorUserId="14566" LastEditDate="2019-03-28T12:57:07.390" LastActivityDate="2019-03-28T12:57:07.390" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13143" PostTypeId="1" CreationDate="2019-03-28T05:46:02.483" Score="0" ViewCount="135" Body="&lt;p&gt;There are several cell towers on the hills around me.&#xA;Usually I just walk around their base in a circle with&#xA;&lt;a href=&quot;https://play.google.com/store/apps/details?id=com.parizene.netmonitor&quot; rel=&quot;nofollow noreferrer&quot;&gt;one&lt;/a&gt; of the many CellID apps&#xA;to get their ID. Then I can impress my friends, &quot;That's tower 4664! That's&#xA;tower 5995!&quot;. You know, a sort of hobby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But now I'm getting kind of old so I'm thinking can I just sit back in&#xA;my armchair and point some kind of homebrew antenna isolator cannon at them...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I put my cellphone in a long metal pipe aimed at one of them (I can see the hill with the target tower when looking down the &quot;barrel&quot; of my &quot;cannon&quot;), that&#xA;will eliminate the signals from the others, and my cellphone will surely&#xA;now just lock on the one I pointed at... or so I thought.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the correct dimensions to make it work? Putting my cellphone in&#xA;the middle of 1.3 meter length, 15 cm diameter pipe didn't give me any&#xA;different results than without the pipe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm talking about 4G LTE towers in the 900 and 1800 MHz bands. I put my&#xA;phone in the pipe pointed at tower A, even pushed the reboot button, but&#xA;it still ends up locking in to tower B. Hmmm, checking the &lt;a href=&quot;http://www.hottconsultants.com/techtips/freq-wavelength.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;wavelengths&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;900 MHz 33.3 cm&#xA;1.8 GHz 16.7 cm&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Do I simply need a wider pipe? (Certainly even more money down the drain!)&lt;/p&gt;&#xA;" OwnerUserId="14566" LastEditorUserId="8717" LastEditDate="2019-03-29T14:08:19.443" LastActivityDate="2019-03-29T19:17:35.830" Title="Cell tower identifier antenna isolator cannon" Tags="&lt;antenna-theory&gt;&lt;microwave&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13145" PostTypeId="2" ParentId="13143" CreationDate="2019-03-28T11:21:30.993" Score="0" Body="&lt;p&gt;You could try a parabolic reflector, such as an old satellite dish, with your phone at the focus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We think of radio waves as travelling in straight lines, but that's not quite right; they also need some open space &lt;em&gt;around&lt;/em&gt; the straight line, known as the &lt;a href=&quot;http://radiomobile.pe1mew.nl/?Calculations:Propagation_calculation:Fresnel_zones&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fresnel zone&lt;/a&gt;. A long metal pipe will interfere with the Fresnel zone, while a parabolic reflector stays out of the way.&lt;/p&gt;&#xA;" OwnerUserId="13390" LastEditorUserId="13390" LastEditDate="2019-03-29T14:04:47.060" LastActivityDate="2019-03-29T14:04:47.060" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13146" PostTypeId="1" AcceptedAnswerId="13148" CreationDate="2019-03-28T11:22:09.210" Score="5" ViewCount="1246" Body="&lt;p&gt;I saw a couple YouTube videos last night about setting up a repeater using a pair of cheap hand-held radios and, at its simplest, an audio patch cable to connect the speaker output of one radio to the mic input on the other.  Set frequencies correctly, turn VOX on, and what one HT receives will be retransmitted by the other -- potentially even cross-repeating between 2m and 70cm bands, or whatever bands your radios can use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are potential issues with doing this on a non-emergency basis -- protecting the radios from weather, keeping their batteries charged, preventing someone from finding the setup and saying &quot;Hey, free radios!&quot;  The one I'm concerned with at the moment, however, is FCC legality.  It's my understanding that periodic ID, at least when active, is legally required, but none of the other repeaters I've listened to seem to do this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the cheap HT sets don't have this capability, I'm concerned about the legality of operating a repeater that doesn't identify itself.  Just because another repeater doesn't (that I've heard), doesn't mean it's legal to do things that way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there an inexpensive way to insert an ID generator between the receive and transmit HT units in this kind of setup?  It would need to detect activity, wait some period of time, and then send an ID, as well as sending periodically if there's no activity.  Either voice or Morse is legal, but presuming this will be a digital playback system of some kind, either one is easy to set up.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-03-29T12:44:39.380" LastActivityDate="2019-04-09T11:16:52.983" Title="Call sign ID for a &quot;homebrew&quot; or improvised repeater?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;repeater&gt;&lt;callsign&gt;" AnswerCount="3" CommentCount="7" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13147" PostTypeId="2" ParentId="13146" CreationDate="2019-03-28T14:18:10.603" Score="3" Body="&lt;p&gt;Many repeaters are not based on radios with built-in ID or any other repeater functions, but rather an ordinary transmitter and receiver (each possibly a transceiver used only for one function, if that's the most economical option) connected by a &lt;strong&gt;repeater controller&lt;/strong&gt; through which the audio, PTT, etc. signals pass. The repeater controller knows how to ID (and to do so without interrupting usage of the repeater), generates the &quot;courtesy tone&quot; at the end of repeated transmissions, and may have remotely-controllable special functions (e.g. for repeater linking).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I haven't built a repeater I can't recommend any specific examples, but I hope that you can find suitable products or project plans now that you know what to call them.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-03-28T14:18:10.603" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13148" PostTypeId="2" ParentId="13146" CreationDate="2019-03-28T15:44:58.760" Score="6" Body="&lt;p&gt;Are you up to buying a Raspberry Pi, two USB sound cards, some assorted transistors and such, and making your own interface cable? If so, you can run &lt;a href=&quot;https://www.svxlink.org/&quot; rel=&quot;noreferrer&quot;&gt;svxlink&lt;/a&gt;. It supports all sorts of fancy things related to internet-linking, remote control, and automation, but you don't &lt;em&gt;need&lt;/em&gt; to use any of that; it will also function just fine as a repeater controller for a standalone repeater, and periodic ID is one of the built-in features.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-03-28T15:44:58.760" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13149" PostTypeId="1" AcceptedAnswerId="13152" CreationDate="2019-03-28T16:20:17.603" Score="1" ViewCount="141" Body="&lt;p&gt;I'm putting in a radial system for my inverted-L and am wondering if the hobby wire like the kind sold at Hobby Lobby or Home Depot for hanging pictures, which is 22-24 gauge copper or aluminum, would work for radials?  It's cheap, and I already happen to have a bunch.  Thanks.&lt;/p&gt;&#xA;" OwnerUserId="9772" LastActivityDate="2019-03-29T14:27:01.233" Title="Hobby Wire for Ground Radials" Tags="&lt;antenna&gt;&lt;radial&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13150" PostTypeId="2" ParentId="13143" CreationDate="2019-03-29T12:12:25.577" Score="0" Body="&lt;p&gt;If the pipe is tied to the antenna you're essentially using the whole pipe as part of the antenna, so it's no wonder it doesn't isolate the signal -- and there's no effective way to prevent this when the pipe is smaller than the signal wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, make sure your pipe is big enough (maybe use a metal garbage can, or a plastic one lined with foil, instead of a pipe?), and make sure it's grounded.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The pipe you have might work for range extension on wifi -- I've seen many reference to using Pringles cans as shotgun antennae for those (2.4 and 5 GHz, so around 6 and 12 cm wavelength).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-03-29T14:37:29.020" LastActivityDate="2019-03-29T14:37:29.020" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13151" PostTypeId="2" ParentId="13143" CreationDate="2019-03-29T14:07:10.333" Score="0" Body="&lt;p&gt;It would be nice if it were so simple to make a very narrow &quot;cylinder-shaped&quot; beam, but &lt;strong&gt;a pipe is simply not going to do that&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/13145/8717&quot;&gt;This answer&lt;/a&gt; has a considerably better chance of working than sticking a phone in a pipe.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-03-29T14:07:10.333" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13152" PostTypeId="2" ParentId="13149" CreationDate="2019-03-29T14:27:01.233" Score="3" Body="&lt;p&gt;Sure it will work. Metal wire is metal wire. The electrons don't care about the packaging.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;24 gauge wire is thin enough you might be concerned about the resistance of the wires, which will decrease antenna efficiency. Use some &lt;a href=&quot;https://chemandy.com/calculators/round-wire-ac-resistance-calculator.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;RF resistance calculator&lt;/a&gt; to get some estimate of the resistance, and remember if you have 16 radials, then the effective resistance is 1/16th that of a single wire. As a rule of thumb, I'd suggest aiming to keep the total resistance under 5 ohms, which should be no problem given a reasonable (at least 16) number of ground radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're going with elevated radials then you might have far fewer of them: in that case maybe you want to twist several strands together to effectively make a thicker wire with less resistance.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-03-29T14:27:01.233" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13153" PostTypeId="2" ParentId="13143" CreationDate="2019-03-29T19:17:35.830" Score="2" Body="&lt;p&gt;What you are describing is a directional antenna for your phone. You can do this by placing the phone Inside the antenna, or by connecting the antenna to the phone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The pipe you describe is actually used as an antenna - google for the Cantenna wifi antenna made from a pringles can.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A horn antenna like this might not be the most elegant antenna for a phone though.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, it isn't very directive. A simple tube has a beam about 60 degrees wide, meaning it's half power or -3 dB at +- 30 degrees. And it only falls to -10 dB at +-70 degrees. So it's not the cannon you imagine. 10 dB is probably only one bar on your phone's signal display. Making the tube longer doesn't make it more directive. &lt;a href=&quot;https://www.researchgate.net/figure/Cantenna-radiation-pattern-measurements_fig14_260515111&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here's an example of a radiation pattern&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An analogy, not too far fetched actually: Imagine using a pipe to blast sound waves in a certain direction - they spread out all over the place, they don't come out in a beam like a ray of light. (Try it by playing some music on your phone while it's in the tube).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, a cylindrical waveguide horn will only work properly for one cellphone band. If you size the tube for 900 MHz, it will not work well as a directional antenna at 1800 or 2100 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My suggestion is that you scratch around online for a cellphone booster antenna. These are commercially used by people who have marginal cell signal outdoors, and nothing indoors. They're a passive wideband antenna, usually an LPDA, connected to a cable that runs indoors, either directly to your phone if it has an antenna socket, or to a coupler gadget that sticks to the back of the phone.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My experience with these is that you can isolate individual cell towers by turning the antenna around, but it's a difficult, confusing process. &lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-03-29T19:17:35.830" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13157" PostTypeId="1" CreationDate="2019-03-30T18:02:35.870" Score="9" ViewCount="1203" Body="&lt;p&gt;I have a new RigExpert AA-35 antenna analyzer.  1st one I have had &amp;amp; 1st time trying to use an analyzer on an antenna.  My questions are very basic and general, but I am having difficulty in Googling for answers.  Hope someone can help, or direct me to a document that would explain the meaning of these figures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This analyzer produces many results when run.  I understand the simple ones: Frequency, SWR, Return Loss, Wave Length.  However there are several results, and some of those results that are presented in such a manner that I am not understanding what they are or what they mean.  Here are the 10 main results that are shown when a test is run, along with an example of those results:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;strong&gt;Freq in kHz&lt;/strong&gt; = 511.2&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;SWR&lt;/strong&gt; = 2.62&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;RL dB&lt;/strong&gt; = 6.98&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Z (Ohms)&lt;/strong&gt; = 167.19 - j63.91&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;|Z|&lt;/strong&gt; (Ohms) = 178.99&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;|rho|&lt;/strong&gt; = .045, phase = 19.95 (Degrees)&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;C (pF)&lt;/strong&gt; = 4871.47&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Zpar (Ohms)&lt;/strong&gt; = 191.62 - j501.28&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Cpar (pF)&lt;/strong&gt; = 621.08&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;1/4 Cable Length&lt;/strong&gt; = 317.47'&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The results I do not understand are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Z (Ohms)&lt;/strong&gt; = 167.19 - j63.91&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;|Z|&lt;/strong&gt; (Ohms) = 178.99&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;|rho|&lt;/strong&gt; = .045, phase = 19.95 (Degrees)&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Zpar (Ohms)&lt;/strong&gt; = 191.62 - j501.28&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Cpar (pF)&lt;/strong&gt; = 621.08&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Here are my questions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;em&gt;Why for Z &amp;amp; Zpar are there 2 numbers, one with a j in front.  What do those mean?&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;em&gt;What is the difference between Z &amp;amp; |Z| &amp;amp; Zpar?&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;em&gt;What is the difference between C &amp;amp; Cpar?&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;em&gt;What is rho?&lt;/em&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Thanks in advance.  At this time I am not looking for advice on this antenna itself, just on how I can interpret these figures.......&lt;/p&gt;&#xA;" OwnerUserId="14581" LastActivityDate="2020-01-09T18:19:47.210" Title="RigExpert AA-35 - Interpreting The Information" Tags="&lt;antenna-construction&gt;&lt;impedance-matching&gt;&lt;capacitance&gt;" AnswerCount="3" CommentCount="15" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13158" PostTypeId="2" ParentId="13157" CreationDate="2019-03-30T19:15:46.513" Score="5" Body="&lt;p&gt;Welcome to StackExchange. Your questions are natural for a new user of an instrument like the AA-35. Some of your questions are addressed in the item on &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Impedance&lt;/em&gt;&lt;/a&gt; in Wikipedia.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance, denoted as &lt;span class=&quot;math-container&quot;&gt;$Z$&lt;/span&gt;, describes two aspects of a circuit's behavior when stimulated with AC: resistance, &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt;, which dissipates energy, and reactance, &lt;span class=&quot;math-container&quot;&gt;$X$&lt;/span&gt;, which stores and releases it as the AC stimulus fluctuates. In mathematical shorthand, these two aspects are combined into a single &quot;complex&quot; number: &lt;span class=&quot;math-container&quot;&gt;$Z_s=R_s+jX_s$&lt;/span&gt;, where the &lt;span class=&quot;math-container&quot;&gt;$s$&lt;/span&gt; subscript denotes the &lt;em&gt;series equivalent&lt;/em&gt; description of the impedance. More on that later.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$R_s$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$X_s$&lt;/span&gt; can be plotted on an &lt;span class=&quot;math-container&quot;&gt;$xy$&lt;/span&gt;-coordinate axis, with &lt;span class=&quot;math-container&quot;&gt;$R_s$&lt;/span&gt; being plotted along the horizontal &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;-axis and &lt;span class=&quot;math-container&quot;&gt;$X_s$&lt;/span&gt; along the vertical &lt;span class=&quot;math-container&quot;&gt;$y$&lt;/span&gt;-axis. The distance from (0,0) to the point (&lt;span class=&quot;math-container&quot;&gt;$R_s$&lt;/span&gt;,&lt;span class=&quot;math-container&quot;&gt;$X_s$&lt;/span&gt;) is the magnitude of the impedance,&lt;span class=&quot;math-container&quot;&gt;$|Z_s|$&lt;/span&gt;, which is calculated as:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|Z_s|=\sqrt{R_s^2+X_s^2}$$&lt;/span&gt;&#xA;For the data in your question:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|Z_s|=\sqrt{167.19^2+63.91^2}=178.99\Omega$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We are perhaps most accustomed to describing the &lt;em&gt;series equivalent&lt;/em&gt; impedance of an AC circuit - &lt;span class=&quot;math-container&quot;&gt;$Z_s=R_s+jX_s$&lt;/span&gt; - but we may also describe it in terms of its &lt;em&gt;parallel equivalent&lt;/em&gt; - &lt;span class=&quot;math-container&quot;&gt;$Z_p=R_p||X_p$&lt;/span&gt;. Knowing the series and parallel equivalents is useful when one wants to combine the measured circuit with other components, e.g., to match the measured circuit to a specific value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since series and parallel AC circuits behave so differently as a function of frequency, this transformation can only be accomplished at a single frequency. The essential nature of the transformation requires the &lt;em&gt;Q&lt;/em&gt; of the series and parallel equivalents to be identical:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$Q_s=\frac{X_s}{R_s}$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$Q_p=\frac{R_p}{X_p}$$&lt;/span&gt;&#xA;equating &lt;span class=&quot;math-container&quot;&gt;$Q_s=Q_p$&lt;/span&gt; and rearranging,&#xA;&lt;span class=&quot;math-container&quot;&gt;$$R_p=R_s(1+Q^2)$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$X_p=X_s(1+\frac{1}{Q^2})$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The parallel equivalent impedance, &lt;span class=&quot;math-container&quot;&gt;$Z_p$&lt;/span&gt;, is:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|\frac{1}{Z_p}|=\sqrt{\frac{1}{R_p^2}+\frac{1}{X_p^2}}$$&lt;/span&gt;&#xA;which, of course, should equal &lt;span class=&quot;math-container&quot;&gt;$|Z_s|$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the data in your question:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$Q_s=\frac{63.91}{167.19}=0.3822$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$R_p=167.19(1+0.3822^2)=191.6\Omega$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$X_p=-63.91(1+\frac{1}{0.3822^2})=-501.4\Omega$$&lt;/span&gt;&#xA;substituting into the equation for &lt;span class=&quot;math-container&quot;&gt;$Z_p$&lt;/span&gt;,&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|\frac{1}{Z_p}|=\sqrt{\frac{1}{191.6^2}+\frac{1}{501.4^2}}$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|\frac{1}{Z_p}|=0.005587$$&lt;/span&gt;&#xA;so,&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|Z_p|178.98$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The value of &lt;span class=&quot;math-container&quot;&gt;$C_{par}$&lt;/span&gt; is calculated from the equation for capacitive reactance:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$X_c=\frac{1}{2\pi f C_{par}}$$&lt;/span&gt;&#xA;which is rearranged to provide &lt;span class=&quot;math-container&quot;&gt;$C_{par}$&lt;/span&gt;:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$C_{par}=\frac{1}{2\pi f X_c}$$&lt;/span&gt;&#xA;and, using the value of &lt;span class=&quot;math-container&quot;&gt;$X_p=-501.4\Omega$&lt;/span&gt; obtained above,&#xA;&lt;span class=&quot;math-container&quot;&gt;$$C_{par}=\frac{1}{2\pi\space 511.2kHz\space 501.4\Omega}=621pF$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Though you did not mention SWR in your question, I note that the SWR reported in your question is correct only if the reference impedance, &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt;, is 75&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, so I will use that value throughout.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I confirmed with Rig Expert support that &lt;span class=&quot;math-container&quot;&gt;$\rho$&lt;/span&gt; is the &lt;a href=&quot;http://www.antenna-theory.com/tutorial/txline/transmission3.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;reflection coefficient&lt;/a&gt;, sometimes denoted by &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt;:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\rho=\frac{Z_L-Z_0}{Z_L+Z_0}$$&lt;/span&gt;&#xA;Remembering that &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$Z_L$&lt;/span&gt; can be complex numbers - i.e., each can comprise resistance and reactance - &lt;span class=&quot;math-container&quot;&gt;$\rho$&lt;/span&gt; can be stated as a complex number or in terms of its magnitude and angle. For the example given in your question, this &lt;a href=&quot;https://leleivre.com/rf_gammatoz.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;online calculator&lt;/a&gt; gives:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|\rho|=0.4478, arg(\rho)=-19.95^\circ$$&lt;/span&gt;&#xA;Note that the values you reported in your question are different, which bears re-checking. And, just for completeness,&#xA;&lt;span class=&quot;math-container&quot;&gt;$$SWR=\frac{1+|\rho|}{1-|\rho|}$$&lt;/span&gt;&#xA;substituting from above:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$SWR=\frac{1+0.4478}{1-0.4478}=2.62$$&lt;/span&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-04-02T19:47:32.957" LastActivityDate="2019-04-02T19:47:32.957" CommentCount="14" ContentLicense="CC BY-SA 4.0" />
  <row Id="13159" PostTypeId="2" ParentId="13157" CreationDate="2019-03-30T19:22:44.620" Score="8" Body="&lt;p&gt;First, a general statement: the antenna analyzer has one &lt;em&gt;set&lt;/em&gt; parameter, the frequency, and one &lt;em&gt;measured&lt;/em&gt; parameter, the impedance (which is a complex number and therefore requires two real numbers to display).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Everything else can be derived,&lt;/strong&gt; one way or the other.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why for Z &amp;amp; Zpar are there 2 numbers, one with a j in front. What do those mean?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$Z$&lt;/span&gt; stands for &lt;strong&gt;impedance&lt;/strong&gt;, which is a &lt;strong&gt;complex number&lt;/strong&gt; and so has to be written as made up of two real numbers. (Mathematicians write complex numbers with an &lt;span class=&quot;math-container&quot;&gt;$i$&lt;/span&gt; instead of a &lt;span class=&quot;math-container&quot;&gt;$j$&lt;/span&gt;, but it means the same thing.) I won't explain complex numbers here — there's many different introductions and you should find one that makes sense to you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance is a quantity analogous to resistance which is useful in analyzing radio-frequency systems in the same way as resistance is useful in analyzing DC systems, and much of the math is the same; you just need to use complex arithmetic instead of real arithmetic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any time you see someone refer to the impedance of an RF device as, say, &lt;span class=&quot;math-container&quot;&gt;$50\,\Omega$&lt;/span&gt;, it's “really” &lt;span class=&quot;math-container&quot;&gt;$(50 + j0)\,\Omega$&lt;/span&gt; — that is, the complex number has a zero “imaginary part” and since it is zero we can leave it out (after all, anything multiplied by zero is zero and adding zero doesn't change a number, so &lt;span class=&quot;math-container&quot;&gt;$50 + j0 = 50 + 0 = 50$&lt;/span&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance corresponds to resistance whenever the imaginary part is zero; when it's nonzero, that means the thing that has that impedance resembles an inductor or a capacitor (it can't be both) at that frequency. The imaginary part is called &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_reactance&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;reactance.&lt;/em&gt;&lt;/a&gt; Reactance is like resistance except that instead of dissipating energy, it releases it later in some way.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The impedance of an ideal resistor is always &lt;span class=&quot;math-container&quot;&gt;$(x + j0)\,\Omega$&lt;/span&gt; for some &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;.&lt;/li&gt;&#xA;&lt;li&gt;The impedance of an ideal capacitor is always &lt;span class=&quot;math-container&quot;&gt;$(0 - jx)\,\Omega$&lt;/span&gt; for some &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;.&lt;/li&gt;&#xA;&lt;li&gt;The impedance of an ideal inductor is always &lt;span class=&quot;math-container&quot;&gt;$(0 + jx)\,\Omega$&lt;/span&gt; for some &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;When you get into more complex (and realistic) circuits, including an antenna at the end of a length of transmission line, both will be nonzero. (Or, a simple example: as you may know, if you put two resistors in series you add their resistances. The same implies to impedances: if you have an inductor with impedance &lt;span class=&quot;math-container&quot;&gt;$Z_L$&lt;/span&gt; and a resistor with impedance &lt;span class=&quot;math-container&quot;&gt;$Z_R$&lt;/span&gt; in series, the impedance will be &lt;span class=&quot;math-container&quot;&gt;$Z_L + Z_R = jx\,\Omega + y\,\Omega = (x + jy)\,\Omega$&lt;/span&gt; for the particular &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$y$&lt;/span&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the difference between Z &amp;amp; |Z| &amp;amp; Zpar?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$|Z|$&lt;/span&gt; is the &lt;em&gt;magnitude&lt;/em&gt; of the impedance. Imagine you take the two parts of the complex number and use them to mark a point on graph paper; the magnitude is the distance from the origin (i.e. the square root of the sum of the squares).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't offhand remember what &lt;span class=&quot;math-container&quot;&gt;$|Z|$&lt;/span&gt; is good for when analyzing antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_{\text{par}}$&lt;/span&gt; should be the same as &lt;span class=&quot;math-container&quot;&gt;$Z$&lt;/span&gt;, I would think, because there's only one impedance value regardless of the model (see below for explaining &quot;par&quot;).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the difference between C &amp;amp; Cpar?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; is capacitance, but the impedance (or reactance) of a capacitor is not only dependent on its capacitance, but also the frequency. But the analyzer knows the frequency being applied, so it can compute &quot;&lt;em&gt;If&lt;/em&gt; we assume the circuit under test is actually a resistor in series with a capacitor, what is the capacitance that would produce the observed impedance at this frequency?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$C_\text{par}$&lt;/span&gt; is the same, except that it is for the model of a resistor in parallel with a capacitor instead of in series.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the analyzer displays &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; values, they are the same except that the circuit is more like an inductor than a capacitor and it is displaying those values.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-01-09T18:19:47.210" LastActivityDate="2020-01-09T18:19:47.210" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13160" PostTypeId="2" ParentId="13157" CreationDate="2019-03-30T19:37:43.570" Score="0" Body="&lt;p&gt;Nearly all of these things are just the antenna impedance, expressed a different way.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why for Z &amp;amp; Zpar are there 2 numbers, one with a j in front. What do those mean?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Z&lt;/em&gt; represents &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance&lt;/a&gt;. It's essentially the concept of resistance, but extended to work for AC circuits. Impedance is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Complex_number&quot; rel=&quot;nofollow noreferrer&quot;&gt;complex number&lt;/a&gt;, which consists of two parts. The first part is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Real_number&quot; rel=&quot;nofollow noreferrer&quot;&gt;real number&lt;/a&gt;, and is the resistance. The second part is an &lt;a href=&quot;https://en.wikipedia.org/wiki/Imaginary_number&quot; rel=&quot;nofollow noreferrer&quot;&gt;imaginary number&lt;/a&gt; which represents &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_reactance&quot; rel=&quot;nofollow noreferrer&quot;&gt;reactance&lt;/a&gt;, which accounts for the effects of things like inductors and capacitors. The &lt;em&gt;j&lt;/em&gt; is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Imaginary_unit&quot; rel=&quot;nofollow noreferrer&quot;&gt;imaginary unit&lt;/a&gt;, which is just part of the notation for writing imaginary numbers.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the difference between C &amp;amp; Cpar?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;One way to represent an impedance is to come up with an equivalent circuit made of resistors and capacitors that would have the same impedance (though only at the single frequency tested). That can be done as a series or a parallel circuit:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/yJBLW.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fyJBLW.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; is the value required for the series circuit, and &lt;span class=&quot;math-container&quot;&gt;$Cpar$&lt;/span&gt; is for a parallel circuit. The RigExpert doesn't give a value for the resistor, because that's just the first part of the impedance, either &lt;em&gt;Z&lt;/em&gt; or &lt;em&gt;Zpar&lt;/em&gt; for the series or parallel circuits, respectively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some cases you will see the rigexpert report &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$Lpar$&lt;/span&gt; instead, this means the capacitor should be swapped for an inductor.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the difference between Z &amp;amp; |Z| &amp;amp; Zpar?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$Z$&lt;/span&gt; is just the resistance and capacitance of the series equivalent circuit above expressed in a different way. Rather than give the value of the capacitor (or inductor) required in farads (or henries), it gives the impedance, which is the resistance plus the reactance. Calculating the reactance of a capacitor is just some simple math:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ X = - {1 \over 2 \pi f C} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And likewise for an inductor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ X = 2 \pi f L $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$X$&lt;/span&gt; is the reactance, in ohms&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is the frequency, in hertz&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; is the capacitance, in farads&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; is the inductance, in henries&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So taking &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; and the frequency from your example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {1 \over 2 \pi \times 511200 \times 621.08 \times 10^{-12}} = 63.91 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note how this is the 2nd part of &lt;span class=&quot;math-container&quot;&gt;$Z$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Zpar&lt;/em&gt; is just the same thing, but with &lt;em&gt;Cpar&lt;/em&gt; instead. I would note this notion of &quot;parallel impedance&quot; is a bit of mathematical nonsense specific to the RigExpert. Because impedance is a single number, just one impedance can't be arranged &quot;in series&quot; or &quot;in parallel&quot;. &lt;em&gt;Zpar&lt;/em&gt; does tell you the equivalent parallel resistance, and the reactance of the equivalent parallel capacitor, but adding these numbers together doesn't make sense because &lt;a href=&quot;http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imped.html#c3&quot; rel=&quot;nofollow noreferrer&quot;&gt;parallel impedances don't combine by adding&lt;/a&gt;. Rather, they combine like parallel resistors: the reciprocal of the sum of the reciprocals. And you will find the result of combining the equivalent components in parallel yields the (actual) impedance given as &lt;em&gt;Z&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$|Z|$&lt;/span&gt; is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Complex_number#Modulus_and_argument&quot; rel=&quot;nofollow noreferrer&quot;&gt;magnitude&lt;/a&gt; of &lt;span class=&quot;math-container&quot;&gt;$Z$&lt;/span&gt;. Other terms for the same thing are the &quot;modulus&quot; or the &quot;absolute value&quot;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is rho?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It should be the &lt;a href=&quot;https://en.wikipedia.org/wiki/Reflection_coefficient&quot; rel=&quot;nofollow noreferrer&quot;&gt;reflection coefficient&lt;/a&gt;, which is just yet another way to express an impedance, but which also takes into account a characteristic impedance which the RigExpert is going to assume is 50 or 75 ohms, depending on the settings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the numbers you've provided, it looks like your RigExpert is currently set to 75 ohms, and there was an error in transcribing the magnitude which should be 0.45, not .045.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-04-02T13:36:08.563" LastActivityDate="2019-04-02T13:36:08.563" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13161" PostTypeId="1" AcceptedAnswerId="13162" CreationDate="2019-03-30T21:10:06.580" Score="7" ViewCount="925" Body="&lt;p&gt;I recently purchased a Nagoya NA-771 that I believe is counterfeit given the overall feel of the antenna. How do I identify a genuine Nagoya antenna vs. a counterfeit?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastActivityDate="2020-01-13T22:29:33.427" Title="How do I identify a genuine Nagoya antenna?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13162" PostTypeId="2" ParentId="13161" CreationDate="2019-03-30T21:10:06.580" Score="6" Body="&lt;p&gt;Nagoya has an &lt;a href=&quot;https://www.nagoya.com.tw/en/news-31478/%E3%80%8Elatest-updated%E3%80%8FHow-to-identify-the-genuine-and-fake-antenna.html&quot; rel=&quot;noreferrer&quot;&gt;official article&lt;/a&gt; listing the difference between genuine antennas and counterfeits, please refer to that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As of their January 15, 2015 update:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Genuine antennas come in a green bag&lt;/li&gt;&#xA;&lt;li&gt;Genuine antennas' bags have well-made rounded corners&lt;/li&gt;&#xA;&lt;li&gt;Genuine antennas come with a spacer&lt;/li&gt;&#xA;&lt;li&gt;Genuine antennas are straight&lt;/li&gt;&#xA;&lt;li&gt;Genuine antennas have a particular printed font (see pictures in the article)&lt;/li&gt;&#xA;&lt;li&gt;The QR code on genuine packaging goes all the way next to the Nagoya branding&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These are all illustrated in the article, I recommend reading it.&lt;/p&gt;&#xA;" OwnerUserId="14220" LastActivityDate="2019-03-30T21:10:06.580" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13163" PostTypeId="1" AcceptedAnswerId="13164" CreationDate="2019-03-30T22:32:53.973" Score="2" ViewCount="168" Body="&lt;p&gt;I decided to see what my ham transmissions look like on an SDR and was kind of shocked to see how much leaks out.  The waterfall display is split between two handhelds during transmit.  There are a couple large energy spikes at +/- 800kHz to the 431.5MHz transmitting frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that both radios spurious emissions are lined up and similar I'm guessing it is common and due to some sort of harmonic effect, possibly from implementing similar architecture.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any negative to the less dispersed transmission of the bottom device/waterfall?  The top half of the waterfall display is from a handheld transceiver that is much higher in quality than the one captured on the bottom half.  Interestingly the SDR picks up the better handhelds audio much better even though voice communication between handheld devices is fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Xe0ga.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Xe0ga.png&quot; alt=&quot;&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14582" LastActivityDate="2019-03-30T23:46:11.827" Title="Where does this common spurious transmission come from? Is there a quality difference?" Tags="&lt;software-defined-radio&gt;&lt;rfi&gt;&lt;transceiver&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13164" PostTypeId="2" ParentId="13163" CreationDate="2019-03-30T23:46:11.827" Score="7" Body="&lt;p&gt;This is very likely to be be due to overload of the receiver. A quick, rough way to tell the difference:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Tune your SDR receiver so the waterfall center frequency is &lt;em&gt;not&lt;/em&gt; the same as the transmitter's frequency.&lt;/li&gt;&#xA;&lt;li&gt;Transmit.&lt;/li&gt;&#xA;&lt;li&gt;Check whether the spurs you see are symmetric about the &lt;em&gt;transmitter's&lt;/em&gt; frequency or the &lt;em&gt;receiver's&lt;/em&gt; frequency. This tells you which side generated them.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Also, if transmitting causes the &lt;em&gt;entire&lt;/em&gt; waterfall to rise up then you definitely have an overload problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How to eliminate overload: First, make sure your receiver's RF gain is set to the minimum level, and AGC (if any) is off. Then try these things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Replace the transmitter's antenna with a dummy load.&lt;/li&gt;&#xA;&lt;li&gt;Replace the receiver's antenna with a dummy load or terminator, or if neither is available, just leave the antenna port unconnected.&lt;/li&gt;&#xA;&lt;li&gt;Get more distance.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-03-30T23:46:11.827" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13166" PostTypeId="1" AcceptedAnswerId="13168" CreationDate="2019-04-01T03:11:11.413" Score="8" ViewCount="404" Body="&lt;p&gt;When the other party sends &lt;code&gt;QSL&lt;/code&gt;, do they just want to know whether I received the previous message and expect &lt;code&gt;RR&lt;/code&gt; or &lt;code&gt;AGN?&lt;/code&gt; Or, are they asking for a &lt;code&gt;QSL Card&lt;/code&gt; to be sent to them?&lt;/p&gt;&#xA;" OwnerUserId="11364" LastActivityDate="2019-04-08T10:19:36.623" Title="What does QSL mean in a CW conversation?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13168" PostTypeId="2" ParentId="13166" CreationDate="2019-04-01T03:39:00.940" Score="12" Body="&lt;p&gt;Generally, QSL means &quot;I acknowledge receipt&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;QSL?&quot; (with a question mark) means &quot;please acknowledge&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sometimes when listening to QSOs you will hear someone say QSL VIA BURO or QSL DIRECT or similar, and those are instructions on how to send a QSL card. But QSL on its own just means &quot;acknowledged&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, if someone says PSE QSL then &lt;em&gt;that&lt;/em&gt; usually means that they would like a QSL card.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-04-01T03:39:00.940" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13169" PostTypeId="1" AcceptedAnswerId="13170" CreationDate="2019-04-01T05:03:45.467" Score="2" ViewCount="306" Body="&lt;p&gt;This is kind of odd. I just got my first SDR receiver and I noticed that one application (SDR#) sounds a &lt;strong&gt;lot&lt;/strong&gt; better than another (SDR Console) when listening to stereo FM broadcasts through the same antenna, in the same position, at the same time, with similar settings. I set up all of the configuration options as close as I could but the difference persists. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm totally new to radio and I don't have any idea where to start. Does anyone recognize the audio difference between the two clips, or have ideas about what could be causing it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://briangordon.github.io/images/31-Mar-2019%2021h48m57s%20-%2091.1%20MHz%2C%20BFM.mp3&quot; rel=&quot;nofollow noreferrer&quot;&gt;SDR console audio clip&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://briangordon.github.io/images/SDRSharp_20190401_044813Z_91100000Hz_AF.wav&quot; rel=&quot;nofollow noreferrer&quot;&gt;SDR# audio clip&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14593" LastActivityDate="2019-04-01T05:42:31.097" Title="Why does SDR# sound better than SDR console?" Tags="&lt;software-defined-radio&gt;&lt;fm&gt;&lt;sdrsharp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13170" PostTypeId="2" ParentId="13169" CreationDate="2019-04-01T05:42:31.097" Score="5" Body="&lt;p&gt;I'm not familiar with the behavior of the particular programs you've named, but the obvious (guessed by ear and confirmed with a spectrogram/waterfall tool) difference between these two clips is the audio bandwidth is different.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The clip from SDR Console has audio occupying about 5 kHz of bandwidth, in a file with a 12 kHz sample rate.&lt;/li&gt;&#xA;&lt;li&gt;The clip from SDR# has audio occupying about 15 kHz of bandwidth, in a file with a 39.062 kHz sample rate. (An odd rate for audio, presumably chosen for convenience given SDR#'s internal sample rates.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So, the clip from SDR# has more of the music's high-frequency content preserved. Also more background hiss — because of that, more bandwidth isn't necessarily going to sound better in all ways.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To see if you can get comparable results, look for terms like for audio bandwidth, filtering, or sample rate. (Ones specific to the WFM demodulator or the audio output section, not your RF input sample rate!) It's also possible that the recording function has its own limits.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-04-01T05:42:31.097" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13171" PostTypeId="2" ParentId="13166" CreationDate="2019-04-01T14:12:56.717" Score="8" Body="&lt;p&gt;Especially true in a contest, or noisy environment: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hearing a &quot;QSL?&quot; from someone can mean they want to know specifically if what &lt;em&gt;they've sent to you&lt;/em&gt; has been sent correctly. They may have been trying to pull your callsign out of the QRN or QRM and want to ONLY hear back from you a &quot;QSL&quot; or &quot;R&quot; so they can confidently log your call. If you hear correct information (say,  your call) followed by a &lt;strong&gt;QSL?&lt;/strong&gt; absolutely DO NOT SEND YOUR INFORMATION AGAIN. Doing so is a tacit indication that they DO NOT have the information correct.  And, yes, QSL is often used on phone regardless of what the purists might advise!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HIM  &lt;strong&gt;CQ CQ&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;YOU  &lt;strong&gt;W1^%&amp;amp;&lt;/strong&gt;   (as heard by HIM)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HIM &lt;strong&gt;W1? AGN?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;YOU  &lt;strong&gt;*&amp;amp;ABC&lt;/strong&gt;   (as heard by HIM)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HIM  &lt;strong&gt;W1ABC QSL QSL??&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;YOU  &lt;strong&gt;QSL QSL QSL&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="8573" LastEditorUserId="8573" LastEditDate="2019-04-08T10:19:36.623" LastActivityDate="2019-04-08T10:19:36.623" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13172" PostTypeId="2" ParentId="12586" CreationDate="2019-04-02T14:25:10.670" Score="3" Body="&lt;p&gt;It is a pleasure to follow your adventures with vacuum tubes. A number of references indicate that &quot;triode-strapped pentodes&quot; can be directly substituted in regenerative receiver circuits. In Sound Practices Issue 2 (Fall 1992), Herb Reichert of Eddy Electronic Inc. wrote in &lt;a href=&quot;http://www.enjoythemusic.com/magazine/sound_practices/2/triode_pentode.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Triode Connected Pentodes&lt;/em&gt;&lt;/a&gt;, &quot;The Williamson amp ... triode connected &lt;em&gt;[push-pull pentodes]&lt;/em&gt; gave ... the low-distortion loadline of triodes with some of the gain and efficiency of beam power tubes. This circuit and its siblings became the most popular tube amps of all time. It also created the most popular tube modification of all time: triode connecting multigrid power output tubes.&quot; While this reference pertains only to audio amplifiers, it does appear to support the idea of testing the configuration in reflex receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, there are numerous examples using pentodes in their native habitat. Sir Douglas Hall's &lt;a href=&quot;http://www.spontaflex.free-online.co.uk/quality/circuit.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Twin Pentode Receiver&lt;/em&gt;&lt;/a&gt; seems to be a good fit for the two pentodes you have on hand. Two simpler designs are found in &lt;a href=&quot;https://www.vintage-radio.info/download.php?id=740&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;One Valve Receivers&lt;/em&gt;, volume 99, number 1 (1951)&lt;/a&gt;: the &quot;Midget Pentode Receiver&quot; on pp. 8-9 and the &quot;Oscillodyne&quot; on pp. 12-13. The single-tube circuits might play better to your goals by allowing you to compare two designs side-by-side.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-02T14:25:10.670" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13173" PostTypeId="2" ParentId="13136" CreationDate="2019-04-02T19:12:08.370" Score="2" Body="&lt;p&gt;Regardless of where you live or what band you operate, the general rule is: &quot;If you can't hear 'em, you can't work 'em.&quot;  A secondary rule for repeaters is that if no one is there, it gets boring fast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first challenge is to listen for the repeaters.  If you do, you are most of the way there.  If not, verify that your rig is configured correctly by going near the repeater and listening.  If you hear nothing, try transmitting your callsign and seeing if you can key the repeater.  If you don't, step back and figure it out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you do hear the repeater, next determine where you can hear the repeater.  Can you hear it from the top of the ridge?  If yes, can you see the repeater and your QTH from the top of the ridge?  Maybe you can estimate how tall an antenna support structure you would need to be in line-of-sight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know your terrain, but the first antenna I put up for my son was a vertical antenna in a tree.  It included a counterpoise.  Rather than screw it to a base, I pulled it up with a rope.  It worked really well for repeaters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been advised that if you decide to install a yagi for better gain, it should be mounted with the elements vertical rather than horizontal.  Repeaters are usually vertically polarized, so the system gain is much high if the yagi is also vertically polarized.&lt;/p&gt;&#xA;" OwnerUserId="9109" LastActivityDate="2019-04-02T19:12:08.370" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13177" PostTypeId="2" ParentId="9598" CreationDate="2019-04-03T11:44:03.327" Score="1" Body="&lt;p&gt;66 years ago, my Elmer, W5OLV, told me that 'and' evolved into 'es' as a short form because it occurred so often. He said it started out as dit-dah dah-dit dah-dit-dit and for efficiency, the operators dropped the dahs and started sending dit dit dit-dit which then evolved into dit dit-dit-dit. But that might have just been Shorty's theory.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-04-03T11:44:03.327" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13179" PostTypeId="1" AcceptedAnswerId="13180" CreationDate="2019-04-03T12:01:39.797" Score="3" ViewCount="125" Body="&lt;p&gt;I am a UK licensed Amateur Radio operator with an Intermediate License.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a question surrounding the UK's (Ofcom's) definition of &quot;Remote Operation&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding is that for any Remote Operation you must not use any form of encryption on the links, and if you hold an Intermediate License, you must only use wireless links to communicate with your rig (which I think is limited to 500mW).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am considering building my own little rig using a Raspberry Pi. However, I would most likely be manipulating the Pi (within my house) using SSH, connected to wired Ethernet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given Ofcom's restrictions, does this mean I can't do that, as I would be violating both the encryption (using SSH) and wireless-only (by using wired Ethernet)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, have I interpreted the term &quot;Remote Operation&quot; too broadly, and as long as I was at my house, it would be fine as it wouldn't be considered &quot;Remote&quot;?&lt;/p&gt;&#xA;" OwnerUserId="14615" LastEditorUserId="218" LastEditDate="2019-04-03T12:33:07.067" LastActivityDate="2019-04-03T13:28:12.983" Title="UK &quot;Remote Operation&quot; defination" Tags="&lt;legal&gt;&lt;united-kingdom&gt;&lt;remote-control&gt;&lt;encryption&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13180" PostTypeId="2" ParentId="13179" CreationDate="2019-04-03T13:28:12.983" Score="1" Body="&lt;p&gt;According to clause 17(ff) in Ofcom publication, &lt;em&gt;&lt;a href=&quot;https://www.ofcom.org.uk/__data/assets/pdf_file/0027/62991/amateur-terms.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;UK AMATEUR RADIO LICENCE, Section2: Terms,conditions and limitations&lt;/a&gt;&lt;/em&gt;, &quot;Remote Control Operation&quot; applies, &quot;...where the Licensee has the ability to control the Radio Equipment from a different location to that where the Radio Equipment is located;&quot; Since your control means and your radio will both be located within your house, they are &lt;em&gt;not&lt;/em&gt; in different locations and none of the remote control regulations would seem to apply.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-03T13:28:12.983" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13181" PostTypeId="1" CreationDate="2019-04-03T14:29:28.617" Score="5" ViewCount="1667" Body="&lt;p&gt;I need some help interpreting some information from my antenna analyzer (RigExpert AA-35).  I want to use the information to impedance match my AM receiving antenna system to AM radios.  No transmitting, just receiving.  The data was captured at the point just before the feed-line enters the radio.  75Ω coax is used &amp;amp; was programmed into the analyzer.  Here is the data that the analyzer provided:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Freq in kHz = 511.2&lt;/li&gt;&#xA;&lt;li&gt;SWR = 2.62&lt;/li&gt;&#xA;&lt;li&gt;RL dB = 6.98&lt;/li&gt;&#xA;&lt;li&gt;Z (Ω) = 167.19 - j63.91&lt;/li&gt;&#xA;&lt;li&gt;|Z| (Ω) = 178.99&lt;/li&gt;&#xA;&lt;li&gt;|rho| = .045, phase = 19.95 (Degrees)&lt;/li&gt;&#xA;&lt;li&gt;C (pF) = 4871.47&lt;/li&gt;&#xA;&lt;li&gt;Zpar (Ω) = 191.62 - j501.28&lt;/li&gt;&#xA;&lt;li&gt;Cpar (pF) = 621.08&lt;/li&gt;&#xA;&lt;li&gt;1/4 Cable Length = 317.47'&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;Q1:&lt;/em&gt;&lt;/strong&gt; &lt;em&gt;How do I convert the above data to provide the impedance of my antenna, at this point, for this tested frequency?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;&lt;em&gt;Q2:&lt;/em&gt;&lt;/strong&gt; &lt;em&gt;Then, how many ohms, increase or decrease, would be required to “transform” from the antenna impedance, so it becomes the 75Ω expected for input to the radio?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How these two answers are arrived at using the figures provided by the analyzer and the known requirements of the radio would be most helpful, so I understand the process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was under the mistaken impression that this impedance number would be provided in ohms by the analyzer in the same simple manner in which say the SWR is given.  Trying to learn this process and hoping that being provided “how” this answer is achieved will help me understand how to use the analyzer for this purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just for reference, the antenna is an “IP33 MIni Whip Antenna”.  Connected to 75 Ω coax.  Connected to the systems small power amp for the whip (Unplugged).  Connected to another short length of the 75 coax.  The analyzer was at this point connected to the system.  The same point where the antenna lead is converted to enter the back of the radio.  I have measured at other points in the system.  Just used this point as the example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This question is not really about location placement of any actual transformer or Balun or Unun that might be installed.  I am just using the above example to understand the impedance data acquisition and conversion for use in impedance matching.  Thanks!&lt;/p&gt;&#xA;" OwnerUserId="14581" LastEditorUserId="8717" LastEditDate="2019-04-03T16:33:51.217" LastActivityDate="2019-04-03T17:05:31.430" Title="Determining Impedance With An Antenna Analyzer" Tags="&lt;antenna-theory&gt;&lt;balun&gt;&lt;impedance-matching&gt;&lt;measurement&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13182" PostTypeId="2" ParentId="13181" CreationDate="2019-04-03T15:56:25.907" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How do I convert the above data to provide the impedance of my antenna, at this point, for this tested frequency?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&quot;Z (Ω) = 167.19 - j63.91&quot; &lt;em&gt;is&lt;/em&gt; telling you the impedance. The impedance of your antenna is &lt;span class=&quot;math-container&quot;&gt;$(167.19 - j63.91)$&lt;/span&gt; ohms.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Then, how many ohms, increase or decrease, would be required to “transform” from the antenna impedance, so it becomes the 75Ω expected for input to the radio?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's not how impedance transformation works. You need a matching network, which may contain inductors, capacitors, transformers, chokes, transmission lines, or all of those. Impedance matching is a two-dimensional problem, just as we measure impedance as a complex number with two components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, we don't want to add ohms in the form of a resistor, because while that &lt;em&gt;would&lt;/em&gt;, technically, be able to help match the impedance (e.g. in the simple case where the antenna's impedance is too small), it would not improve the signal to the receiver, but merely throw away some of it (dissipated in the antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's many different ways to design matching networks; I should really link to an introduction to the topic here but I haven't found a good one at the moment.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-04-03T15:56:25.907" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13183" PostTypeId="2" ParentId="13181" CreationDate="2019-04-03T16:42:15.100" Score="4" Body="&lt;p&gt;Thanks for following up on your &lt;a href=&quot;https://ham.stackexchange.com/questions/13157/rigexpert-aa-35-interpreting-the-information&quot;&gt;earlier question&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All of the data you provide in your question represents the impedance the analyzer &quot;sees&quot; at the point you measured it. There is no need to convert anything, it's all there, the challenge is how to use it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the impedance you measured at the transmitter end of the feedline to your antenna includes both resistance (167.19&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;) and reactance (-63.91&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;), &quot;how many ohms, increase or decrease&quot; doesn't fully describe the process by which you transform it to the 75&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; (resistive) output impedance of your rig. Instead, a network of inductors and capacitors must be designed to perform the required transformation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A two-element &quot;L&quot; network is a simple circuit to accomplish the transformation. The easiest way to obtain the L-network values may be to use one of several calculators available on the internet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, let's use this &lt;a href=&quot;https://www.allaboutcircuits.com/tools/l-match-impedance-matching-circuits/&quot; rel=&quot;nofollow noreferrer&quot;&gt;calculator&lt;/a&gt;. From the data in your question, we enter the following information:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/sGWMs.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sGWMs.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which produces the following results:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/kShfb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kShfb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your matching network looks like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/VN5Yg.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fVN5Yg.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using &lt;a href=&quot;http://harriman.ddns.net/Smith_Charts.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;SimSmith&lt;/a&gt; to plot this transformation on a Smith chart:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/l4K50.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/l4K50.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;shows that the L-network provides a nearly perfect match to your transmitter.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-03T16:42:15.100" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13184" PostTypeId="2" ParentId="13181" CreationDate="2019-04-03T17:05:31.430" Score="4" Body="&lt;p&gt;Firstly, an SWR of 2.62 is probably acceptable for a receiver, and no additional matching is necessary. See &lt;a href=&quot;https://ham.stackexchange.com/q/382/218&quot;&gt;What is the relationship between SWR and receive performance?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the IP33 Mini Whip Antenna is an active antenna, meaning it has a preamplifier built-in. Antenna analyzers are good for looking at passive antennas, but looking into a preamplifier may not tell you anything about the preamplifier's output impedance. For that it would be best simply to consult the manual. In any case, that you're using an active antenna only reinforces the notion that matching isn't required here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But let's say you did want to match this impedance, if only as an exercise. You don't need to calculate the impedance, because the analyzer shows it directly:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Z (Ω) = 167.19 - j63.91&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's the impedance seen by the analyzer, which will also be the impedance seen by receiver. This is looking at the antenna, through the feedline. Your objective is to add some matching network to change that to some target impedance, probably 75+j0 or 50+j0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many ways to design such a matching network, but perhaps the most intuitive is using a Smith chart. I suggest trying an &lt;a href=&quot;https://www.fourier-series.com/rf-concepts/smithchart.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;interactive tutorial&lt;/a&gt; to get some intuition for how it works.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-03T17:05:31.430" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13185" PostTypeId="1" CreationDate="2019-04-03T17:46:40.397" Score="3" ViewCount="114" Body="&lt;p&gt;My back garden is very small - about 500sqft. I also live near an AM transmitter and requires an AM filter. I would appreciate some general tips on the best approach to receiving HF signals (Ham and Shortwave Radio) in such a small space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use an RTL-SDR with a Ham-It-Up converter v1.3 and a Raspberry Pi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What kind of wire antenna setup would someone suggest for such a small space? I current have a signal wire (speaker wire) coming out of a window about 10ft AGL going to the top of a shed that is about 8ft AGL. I use NooElec's &quot;Balun&quot; with the wire going into one hole, and the other going to the Raspberry Pi's ground. I was thinking of running some speaker wire around the perimeter of the garden, with each end of the wire going to each hole of the Balun. Would that help?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given my small height AGL I have, and the small size of the garden, I can't really do anything nice at all I don't think :(&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to increase the length of the above wire by twisting some more wire to the shed-end, and walk around the garden with the slack. I found that I got more noise with only the original piece of wire. More noise is generally a good thing for reception, as it means more signal is entering the device, right? Or am I totally off base?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any further tips would be appreciated.&lt;/p&gt;&#xA;" OwnerUserId="14615" LastEditorUserId="14615" LastEditDate="2019-04-04T14:30:08.283" LastActivityDate="2019-04-06T18:58:08.827" Title="Tips for HF Antenna with house near AM transmitter" Tags="&lt;hf&gt;&lt;wire-antenna&gt;&lt;rfi&gt;&lt;rtl-sdr&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13186" PostTypeId="1" CreationDate="2019-04-03T18:06:02.763" Score="1" ViewCount="155" Body="&lt;p&gt;&lt;strong&gt;TL;DR&lt;/strong&gt;: If I blast out a periodic SOS, what rescue action should I expect? Similar to if I activated an EPIRB, or something less?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This question is inspired by &lt;a href=&quot;https://ham.stackexchange.com/questions/12999/if-i-receive-an-sos-signal-what-is-the-proper-response&quot;&gt;If I receive an SOS signal, what is the proper response?&lt;/a&gt; Also by the fact that I recently read about the survival story of Jose Alvarenga, whose fishing boat was taken out to ocean by a storm - Alvarenga had a radio and used it to call for help, but the search team called off the search in the storm and the radio battery did not last until after the storm, but I wonder if he could have gotten more out of the battery sending periodic SOS instead of voice so they could keep tracking him.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am new to all this and am not licensed yet. My daughter knows even less about this, but she is interested, especially in Morse code. We have practiced it a little bit, and she quickly remembered the pattern for SOS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If someone has the ability to broadcast an SOS and does so, but nothing else (for whatever reason, whether lack of knowledge or otherwise), what would be the reaction by the amateur radio community and/or the government and their rescue services?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to think that it would be like in the movies, that someone would get a fix on my position and that search and rescue would start a search in that area. I am picturing in my head a few hams getting bearings on the SOS while one of them is contacting emergency services, who would likely have even better capability for triangulating. Basically, I'm envisioning that it would be treated similar to an &lt;a href=&quot;https://en.wikipedia.org/wiki/Emergency_position-indicating_radiobeacon_station&quot; rel=&quot;nofollow noreferrer&quot;&gt;EPIRB&lt;/a&gt; and that every reasonable effort would be made to mount a rescue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;But if all you do is blast out a periodic SOS in an appropriate range then what would the expected response be in reality?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For some context: I like to do a lot of outdoor activities, mostly hiking. I have been studying boating/sailing material and hope to be out on the water too within the next year or two. Of course I don't plan on anything bad happening, but I like to be prepared. I will probably get a PLB at some point (already should because of the hiking, but I haven't), but I'm still interested to know what response the SOS would get.&lt;/p&gt;&#xA;" OwnerUserId="14605" LastActivityDate="2019-04-04T17:27:36.087" Title="If I send periodic SOS and nothing else, what would be the response by hams and/or government?" Tags="&lt;cw&gt;&lt;emergency&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13188" PostTypeId="2" ParentId="13186" CreationDate="2019-04-03T22:42:19.540" Score="5" Body="&lt;p&gt;I'm not sure what you mean exactly by &quot;blasting out a periodic SOS&quot;.  Since you said SOS rather than Mayday, I presume that you're talking about Morse code, or another digital mode, rather than voice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you mean picking an HF band that is likely to have decent propagation to an area with a relatively large ham population, and picking a part of the band with decent activity, and then actively trying to get hams to answer with a decent antenna and a reasonable amount of power, then I think your odds are reasonable.  Rather than expecting people to guess at your emergency and triangulate your location, you'd probably do much better at telling whoever answers your SOS what your location is to the best of your knowledge, and describing your emergency in practical terms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The person who answers your SOS is likely to be an ordinary ham.  He or she might well suspect a hoax, especially if you're just repeatedly broadcasting a canned SOS message.  If instead for example you could give your call sign and mention that you're hiking in a particular national forest (in the US) in a particular state and you twisted your ankle, but you're in your tent and you have a sleeping bag, food, and water.  Or that you're in a 33' (10 m) sailboat in the Gulf of Mexico with no mast in a storm.  That would sound less like a hoax, and would also give the ham on the other end an idea of what agency to call, and give the responding agency an idea about how dire your situation is.  GPS coordinates would be a nice help also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The point I'm trying to get across is that a ham radio can be a very valuable tool in the wilderness, or in a boat in the middle of the ocean, or after a wide-ranging natural disaster, but please don't assume that simply having the radio makes you safe.  You would also need a good antenna, enough battery power, as well as practical knowledge and experience of antennas, propagation, operating techniques, and so on in order to best use the radio and get through to someone before your battery dies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having operators triangulate in on a weak &quot;SOS SOS SOS SOS SOS SOS SOS&quot; resulting in a helicopter being quickly dispatched, is something that only happens in the movies.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-04-03T22:42:19.540" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13189" PostTypeId="2" ParentId="13146" CreationDate="2019-04-04T01:18:23.700" Score="2" Body="&lt;p&gt;You're not required to have an independent controller providing an ID.&lt;br&gt;&#xA;As long as you can ensure the repeater does not transmit without IDing.  You could ID the repeater yourself by just saying your callsign.  When you ID the transmission on the input, the output provides identification as well.  Per §97.119, a crossband system would need an ID transmitted on each input (UHF and VHF) since a true crossband repeater is bidirectional and actually has two transmit frequencies.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: Automatic Control&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Repeater controllers provide several functions to a repeater system.  One is ID.  The other is they will implement a system to comply with §97.109(d). Part 97 no longer gives specific direction on how to accomplish automatic control. Alot of the things repeater controllers implement in terms of automatic control are leftovers from past revisions of Part 97.  This is detailed in &lt;a href=&quot;http://www.repeater-builder.com/fcc/repeater-control.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Repeater and Auxiliary Control&lt;/a&gt; on the Repeater-Builder website.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is generally accepted as a best practice to have an alternate means of turning off the system remotely.  This could easily be accomplished with a second receiver and a DTMF controller.  Alternatively, if your repeater location has internet access, you could use a WiFi controlled outlet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I should add that this only applies to the United States. &lt;/p&gt;&#xA;" OwnerUserId="97" LastEditorUserId="97" LastEditDate="2019-04-09T11:16:52.983" LastActivityDate="2019-04-09T11:16:52.983" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="13190" PostTypeId="2" ParentId="9993" CreationDate="2019-04-04T13:55:24.130" Score="1" Body="&lt;p&gt;Use a Duplexer and it will manage your issues that are described.  Not as cheap but a far better and safer solution.  Assuming that both antenna's are for separate bands.  If your trying to use both antenna on a single band, then a switch.  Leave the Tee fittings to the CB group.  Also, talk around your local radio club, the elmers are always willing to help!&lt;/p&gt;&#xA;" OwnerUserId="14624" LastActivityDate="2019-04-04T13:55:24.130" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13191" PostTypeId="1" AcceptedAnswerId="13193" CreationDate="2019-04-04T14:32:28.770" Score="2" ViewCount="74" Body="&lt;p&gt;I live near an AM transmitter, and the input of my RTL-SDR becomes overloaded. I've added an AM filter and it's really helped, however I still get a very strong AM signal with some IMD all over different bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would daisy chaining another AM filter help?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have to admit I'm concerned that the harmonics from the transmitter are strong enough to cause IMD also, which of course the AM filters wouldn't prevent.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My aim is to receive HF ham radio as well as shortwave radio from around the world.&lt;/p&gt;&#xA;" OwnerUserId="14615" LastEditorUserId="76" LastEditDate="2019-04-04T14:56:32.337" LastActivityDate="2019-04-04T15:45:05.207" Title="Daisy Chaining AM filters to help with IMD" Tags="&lt;filter&gt;&lt;am&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13192" PostTypeId="2" ParentId="13186" CreationDate="2019-04-04T14:35:43.913" Score="4" Body="&lt;p&gt;The only way you're likely to actually get help with this kind of signal is if you're noticed as &quot;interfering&quot; with other operators and do it for long enough, and with enough power, to get the &quot;fox&quot; hunters on your trail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is (in the USA) a corps of volunteers who specialize in finding stations that violate FCC regs.  I read a write-up just yesterday about a fox hunt that took &lt;em&gt;thirty years&lt;/em&gt; to finally track down a flagrant and continual violator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously, that kind of long term response isn't what you're after with an SOS call, so rather than just call for a few minutes every hour (or similar -- very good for maximizing battery life, not so much for getting responses quickly), you'd be ahead, as noted in another answer, to call on a commonly used CW frequency (in the US, you should ideally use the national calling frequency for one of the CW sub-bands, such as 7.050 on 40m, to maximize the likelihood of someone hearing and having the correct equipment and knowledge to copy and respond to the call), and keep calling until you get a response, followed by giving as many details as possible about your situation and location (and battery state, if that's an issue -- and it usually is, if you're in an emergency and running on battery).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only exception I can see to this is if you're transmitting blind -- that is, you have a (presumed) working transmitter, but no way to receive a response.  In that case, continual transmission (still on a CW calling frequency) until your battery power is gone is more likely to be useful than trying to ration your battery.  You should cycle through the SOS, call sign, location, and situation, including &quot;TX BLIND&quot;, as frequently as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's some difference of opinion whether its better to send slow (5-10 wpm) or faster (20+ wpm) to get through poor conditions -- it might make sense to send fast during one cycle of SOS etc., and then send slow the next time.  After all, even if fast code gets through noise and fade better, an operator who can't copy fast won't get past the SOS.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-04-04T17:27:36.087" LastActivityDate="2019-04-04T17:27:36.087" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13193" PostTypeId="2" ParentId="13191" CreationDate="2019-04-04T14:52:44.230" Score="2" Body="&lt;p&gt;Yes, multiple filters in series will combine “like they ought to”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You will also see more loss and ripple in the passband (all the imperfections of the filter design are also multiplied). This probably doesn't matter for your application; you're not designing a receiver or spectrum analyzer.&lt;/li&gt;&#xA;&lt;li&gt;Even a perfect filter doesn't help at all with interference that's not coming in through the antenna but directly impinging on the receiver itself, or the shield on the computer side of things, etc. If this is an issue, it may or may not help to ensure that your RTL-SDR is one of the metal-cased models.&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;No filter helps with interference that is within the passband, such as the harmonics you mention. However, from my own experience and understanding of RF standards, I would not expect there to be substantial harmonics (in the specific sense of multiples of the carrier frequency) from a properly operating AM transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Signals at the wrong frequency, whether harmonics or intermodulation products, appear due to the signal entering a nonlinear process/device. If that's your receiver, then the filter will help. If that's the transmitter, nothing will help for you but your local regulatory authority will care.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A third possibility is another object that happens to be in the vicinity, or bad connections in your receiving system, that act as nonlinear elements (the &quot;&lt;a href=&quot;https://en.wikipedia.org/wiki/Rusty_bolt_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;rusty bolt effect&lt;/a&gt;&quot;). Therefore, it can be useful to apply direction-finding techniques to try to locate undesired signals and eliminate their source.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-04-04T15:01:17.990" LastActivityDate="2019-04-04T15:01:17.990" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13194" PostTypeId="2" ParentId="13191" CreationDate="2019-04-04T15:45:05.207" Score="3" Body="&lt;p&gt;Cascading more filters may help. Also simply adding an attenuator may help, as long as the RF noise floor is above the receiver's internal noise floor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, spurious emissions from the station can also be an issue. In the US, spurious emissions are regulated by &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/73.44&quot; rel=&quot;nofollow noreferrer&quot;&gt;73.44&lt;/a&gt;, which states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Emissions removed by more than 75 kHz must be attenuated at least 43 + 10 Log (Power in watts) or 80 dB below the unmodulated carrier level, whichever is the lesser attenuation, except for transmitters having power less than 158 watts, where the attenuation must be at least 65 dB below carrier level.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Say this is a 1000W transmitter: that means spurious emissions more than 75 kHz (which would include all harmonics) would have to be attenuated by 46 dB. 46 dB less than 1000W is 25 mW, which is still quite a lot if you are very near the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, there's not much you can do about spurious emissions from the transmitter, except attempt to orient your antenna to null them out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can determine if a spurious signal is from the transmitter, or generated by your receiver, by switching an attenuator in and out. If you have a 3 dB attenuator, and it makes a 3 dB difference to a spurious signal, that's most likely something being received by the antenna. But if adding or removing the attenuator makes a 6 dB difference or more, that signal is generated by your receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-04T15:45:05.207" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13195" PostTypeId="1" CreationDate="2019-04-04T19:33:27.373" Score="1" ViewCount="82" Body="&lt;p&gt;I'm using RG-213 coaxial cable for two-way ham radio communication. But due to weather conditions, the metallic shield of my coaxial cable (RG-213) become rusty and carbonated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I use copper electrical cable 3/.029 as metallic shield with aforesaid (rusty metallic shield ) Coaxial Cable, what will be the result? Will it be the best solution for my damage metallic shield coaxial cable or not? Can i get the best two way communication with this method?&lt;/p&gt;&#xA;" OwnerUserId="14630" OwnerDisplayName="ajmal nawaz" LastEditorUserId="76" LastEditDate="2019-04-04T20:08:41.537" LastActivityDate="2019-04-04T21:10:08.260" Title="RG-213 Cable with electric strained wire as metallic shield of Coaxial cable" Tags="&lt;coaxial-cable&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13196" PostTypeId="2" ParentId="13195" CreationDate="2019-04-04T20:08:29.800" Score="2" Body="&lt;p&gt;You cannot repair a coaxial cable by wrapping or replacing the outer conductor (shield) with ordinary wire. The shape of the shield is critical to its functioning (determining the characteristic impedance) and the different impedance created by using differently shaped conductors will lead to reduced performance, and possibly damage your transmitter if it does not have high-SWR protection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Weather-damaged coaxial cable should be replaced with new coaxial cable. Be sure to apply suitable sealing tape (self-amalgamating tape) to the end connectors after tightening them down if they will be exposed to moisture.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The one thing you can do for damaged cable is to cut off the damaged section and install a connector (a proper coaxial connector, &lt;em&gt;not a splice&lt;/em&gt;) to join it to a new length. However, this is not a good idea for outdoor installations since it introduces more places for water to get in.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-04-04T20:50:03.860" LastActivityDate="2019-04-04T20:50:03.860" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="13197" PostTypeId="2" ParentId="13195" CreationDate="2019-04-04T20:53:33.027" Score="1" Body="&lt;p&gt;If part or all of the shield of your coax is corroded, &lt;em&gt;then that entire portion of the coaxial cable must be discarded&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The corrosion causes the individual strands of the shield to be isolated from one another, significantly reducing the shielding effect of the braid.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It also causes noise to be heard in your receiver.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And as Kevin correctly stated in another answer here:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;You cannot repair a coaxial cable by wrapping or replacing the outer conductor (shield) with ordinary wire. The shape of the shield is critical to its functioning (determining the characteristic impedance) and the different impedance created by using differently shaped conductors will lead to reduced performance, and possibly damage your transmitter ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-04T21:10:08.260" LastActivityDate="2019-04-04T21:10:08.260" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13198" PostTypeId="1" AcceptedAnswerId="13200" CreationDate="2019-04-05T10:23:17.250" Score="4" ViewCount="228" Body="&lt;p&gt;I would like to build a 100W T-network antenna tuner:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cdNWO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cdNWO.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a 12-pole wafer switch, 12.5 meters of enameled copper wire (d=1.5mm) and a pair of 12-365pF variable capacitors rated 200V DC (dielectric strength) 250MΩ (insulation resistance).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are some doubts regarding the capacitors. They are quite small (about 3x3x3 cm) and the plates are placed very close to each other. I have MFJ-971 tuner and it uses much larger capacitors which have much more space between the plates. Although this tuner is rated 200W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe there are three problems. The first one is that the capacitors voltage rate is provided only for DC, but I'm going to apply AC. I don't know whether it's possible to convert DC rate to AC rate. The second problem is that I don't know how to estimate the maximum AC voltage that will be applied to the capacitors in the T-network. Finally, I could just build a tuner and check whether the capacitors will arc, but I don't know how to do it without the risk of damaging the transceiver (Yaesu FT-891). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically my question is: how to determine (theoretically, experimentally or both) whether it's safe to use given capacitors in this network?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-04-05T10:31:36.217" LastActivityDate="2019-04-05T12:29:14.860" Title="What dielectric strength is required for a variable capacitors in a 100W T-network antenna tuner?" Tags="&lt;diy&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13199" PostTypeId="1" CreationDate="2019-04-05T11:03:10.673" Score="1" ViewCount="67" Body="&lt;p&gt;I spoke to a friend about what antennas I was using for PMR and the frequency range on them was only set to 170-430Mhz he said it could lead to a high SWR, So I decided to test it out for safety reasons I tried a few tests within the frequency range and they were reading 1.2 I then tried 446 and the needle didn't even move is this bad? &#xA;P.s. I'm pretty new in this field. &lt;/p&gt;&#xA;" OwnerUserId="14607" LastEditorUserId="14607" LastEditDate="2019-04-05T11:08:39.337" LastActivityDate="2019-05-06T18:01:25.803" Title="Really Low SWR Reading On PMR" Tags="&lt;swr-meter&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13200" PostTypeId="2" ParentId="13198" CreationDate="2019-04-05T12:29:14.860" Score="4" Body="&lt;p&gt;I made a NEC model of an antenna with the dimensions of your &quot;long wire&quot; on 14.2MHz, found the values of C1, L1 and C2 that produce a 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; match and simulated the network to observe the voltages across the capacitors with 100W dissipated in the load. The voltage across C1 was 220VRMS, over 300V peak. Given all the variables that I did not evaluate, plus good design practice to allow considerable margin, I would say that your capacitors will not support 100W transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Qualitatively, this result agrees with the 500VRMS, minimum, recommended in the 100W Z-match in the ARRL &lt;em&gt;Handbook&lt;/em&gt;. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-05T12:29:14.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13201" PostTypeId="2" ParentId="13185" CreationDate="2019-04-05T16:18:18.447" Score="3" Body="&lt;p&gt;Very possibly, the solution is not related to your antenna*, but to &lt;em&gt;find and eliminate nearby noise at its source&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may very well be coming from something in your house. A quick way of finding that out is to power your receiving setup from a battery and then turn off your main circuit breaker**. If the noise drops significantly, the next step is to figure out which appliances, etc. are radiating the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often, it's a &lt;a href=&quot;http://www.mastechpowersupplies.com/linear-power-supply-vs-switching-power-supply.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;switching power supply&lt;/a&gt;. They are both prolific and notorious for generating RFI (noise). They are in our computers, chargers, and power supplies such as &quot;wall-warts&quot;. Some are quiet, others not so much. A nearby ham friend's S9+20 noise on 20 meters dropped to S6 when we unplugged his son's laptop battery charger! I once had a computer that radiated noise even when it was powered off. I had to unplug it to stop the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another way of detecting noise is by carrying around a portable AM radio (a radio tuned to the VHF AM Aircraft Band is preferred to a BCB radio). Tune to a spot where there is no station, and see if the noise is louder as you approach a utility pole. If so, try shaking the pole and see if the noise changes. If it does, then you have nailed down the approximate source of the power line noise. However, noise can be carried to your pole from miles away. One arc last year was 8 miles south of me on the 7850 volt line that feeds my pole transformer. The engineer from the power company found and fixed it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*A small rotatable and tunable receiving loop is often useful for nulling out a single source of nearby noise, such as something in your neighbor's house, an arc on the overhead HV power lines, &lt;strong&gt;or a nearby AM broadcast station&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;** Properly shut down your computers first, of course.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-05T16:24:43.243" LastActivityDate="2019-04-05T16:24:43.243" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13202" PostTypeId="1" AcceptedAnswerId="13204" CreationDate="2019-04-05T18:36:46.317" Score="2" ViewCount="502" Body="&lt;p&gt;In my handbook it talks about keying the transmitter to produce the dots and dashes. Does this mean that the operator is turning the transmitter on and off, or does this mean that the key is turning the oscillator (within the transmitter) on and off?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&#xA;I am reading my 1976 handbook book&lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="12988" LastEditDate="2019-04-07T19:30:31.453" LastActivityDate="2019-04-07T19:47:23.847" Title="How does keying a CW transmitter work?" Tags="&lt;cw&gt;&lt;transmitter&gt;&lt;equipment-design&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13203" PostTypeId="2" ParentId="13202" CreationDate="2019-04-05T18:56:02.840" Score="1" Body="&lt;p&gt;In every case of correctly operating CW transmitters, the RF output is interrupted to produce the pauses between elements, letters, and words.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To a modern ear, the term &quot;Continuous Wave&quot; is slightly misleading -- it doesn't mean the transmitter operates continuously, but rather it's in opposition to the &quot;damped wave&quot; that was produced by spark gap transmitters -- each spark started a pulse of RF energy, which decayed rapidly as losses in the RC circuit sapped the energy.  With Continuous Wave, the oscillation has a constant amplitude while it operates; hold down the key, and you'll send a &quot;continuous wave&quot; until you release the key (or burn out something in the transmitter by exceeding its duty cycle limit).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other misunderstanding here is that there's some other way to send than turning the transmitter off and on.  If you stop the RF oscillator in a CW transmitter, you &lt;em&gt;have&lt;/em&gt; stopped the transmitter from transmitting, just as you would if you interrupt the signal path from oscillator to amplifier, or cut the power to the amplifier stage.  These will all reduce the RF output to zero, and it's switching the RF on and off that makes the &quot;dots and dashes&quot; of CW transmission.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-05T18:56:02.840" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13204" PostTypeId="2" ParentId="13202" CreationDate="2019-04-06T00:12:00.827" Score="4" Body="&lt;p&gt;This block diagram, from the &lt;a href=&quot;http://www.rfcafe.com/references/electrical/NEETS-Modules/NEETS-Module-17-2-1-2-10.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Navy Electricity and Electronics Training Series (NEETS)&lt;/a&gt;, shows that a &lt;em&gt;buffer amplifier&lt;/em&gt; is turned on and off to interrupt the signal from the oscillator to an optional power amplifier and thence to the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AiF3i.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AiF3i.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The buffer amplifier encourages a stable output frequency in two ways. First, by keying the buffer amplifier, the oscillator is always running, so the possibility of frequency instability (e.g., &lt;em&gt;drift&lt;/em&gt;) resulting from oscillator temperature changes is reduced. Second, the buffer amplifier provides a stable load to the oscillator output to prevent &quot;chirp&quot; - brief change of the oscillator frequency - when the key is opened/closed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, a &quot;transmitter&quot; could be as simple as an oscillator that is turned on and off, but such a circuit would be far more likely to suffer from various types of frequency instability, unless it used a very high-Q resonator like a quartz crystal.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-06T00:12:00.827" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13205" PostTypeId="1" CreationDate="2019-04-06T16:14:35.283" Score="1" ViewCount="119" Body="&lt;p&gt;I'm using an RTL-SDR to receive &lt;a href=&quot;https://amsat-uk.org/satellites/geo/eshail-2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Es'Hail 2&lt;/a&gt;. My chain is as follows in order:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;60 cm TV Satellite dish pointing 2 degrees off Es'Hail 2&lt;/li&gt;&#xA;&lt;li&gt;Universal LNB (from TV company, not really a stable frequency). This LNB downconverts the satellite to the 739Mhz band.&lt;/li&gt;&#xA;&lt;li&gt;Long RG6 coax run (involving a serious amount of adapters and sockets in order to feed to the correct room in my house). The run is about 20-25m&lt;/li&gt;&#xA;&lt;li&gt;RTL-SDR bias-t module&lt;/li&gt;&#xA;&lt;li&gt;RTL-SDR AM filter module&lt;/li&gt;&#xA;&lt;li&gt;NESDR Smart RTL-SDL (inside metal case)&lt;/li&gt;&#xA;&lt;li&gt;Raspberry Pi (running rtl_tcp)&lt;/li&gt;&#xA;&lt;li&gt;Windows laptop running SDR#&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The following is an image of my reception strength:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/jSNA1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jSNA1.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As long as I use SDR#'s audio noise filtering DSP, reception isn't too bad as long as the people transmitting are using a good amount of power. Weaker stations are quite hard to hear. Due to the unstable LNB, I have to keep re-tuning, but that's ok for now.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At this stage, installing a new, or re-aligning my satellite dish isn't an option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would appreciate any help on any tips in order to improve this reception. The RTL-SDR has quite a high noise floor compared to the satellite signal. FWIW, the noise doesn't drop much even with the antenna removed, indicated that the noise is internal to the device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My current train of thought is to add a LNA somewhere, but I'm not sure where. Given my LNB requires a 12v bias-t, I'm unsure i'd be able to install an LNA close to the dish, without have to move the bias-t injector even closer as well.&lt;/p&gt;&#xA;" OwnerUserId="14641" LastEditorUserId="76" LastEditDate="2019-04-07T14:26:00.923" LastActivityDate="2019-04-07T14:26:00.923" Title="How can I improve my Es'Hail 2 reception?" Tags="&lt;satellites&gt;&lt;rtl-sdr&gt;&lt;filter&gt;&lt;lna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13206" PostTypeId="1" CreationDate="2019-04-06T17:04:27.783" Score="7" ViewCount="2074" Body="&lt;p&gt;I live in a house that sits in the middle of the city, in a lot 10x20m in size.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first 6x10m are covered by a metal roof with a rather low angle (IIRC only 50cm difference between the highest and lowest point). The rest is concrete roofing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to set up an HF rig at this location again. Many years ago my dad had a 4 element yagi with a rotator for HF, and this metal roof did not exist. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What options do I have as far as antennas go? I'm severely limited by length to install dipoles. In practice I only have 10m &quot;wall to wall&quot; where I can bolt hooks to hang a dipole. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I thought of trying with a piece of iron pipe I have, it's about 63mm in diameter, 6m in length, attached to a wall with U bolts. I thought of moving to one side of the metal roof and see how it performs as a vertical antenna with the 6x10m roof as a ground plane. But I'm not sure if this would give any sort of reasonable result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, right now, I'm using some mobile vertical antennas on a tripod of sorts. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a top and side view of my house&#xA;&lt;a href=&quot;https://i.stack.imgur.com/XkMPG.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XkMPG.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are my options (ideally DIY but commercial solutions would be viable too) for this property? I don't have a particular band I want to operate.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="14642" LastEditDate="2019-04-07T03:31:58.630" LastActivityDate="2019-06-12T16:30:59.883" Title="Antenna options for a 10x20m property with a large metal roof?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;hf&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13207" PostTypeId="2" ParentId="13199" CreationDate="2019-04-06T17:20:59.687" Score="1" Body="&lt;p&gt;A low SWR is desirable and nothing to be concerned about. Any antenna operated at its design frequency should present a very low SWR.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-06T17:20:59.687" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13208" PostTypeId="2" ParentId="13205" CreationDate="2019-04-06T18:49:33.847" Score="2" Body="&lt;p&gt;20-25 meters of RG-6 coaxial cable has significant loss at 739 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RG-11 coax has significantly &lt;em&gt;lower&lt;/em&gt; loss than RG-6. Unless there is an issue with your LNA, I expect that replacing the RG-6 with RG-11 will give you the signal boost that you are looking for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you could do in lieu of replacing the coax is add a low-noise preamp right at the dish, to overcome the loss in the coax and improve the S/N ratio.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-06T21:59:35.207" LastActivityDate="2019-04-06T21:59:35.207" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13209" PostTypeId="2" ParentId="13185" CreationDate="2019-04-06T18:58:08.827" Score="0" Body="&lt;p&gt;As pointed out in another answer, enhanced reception can be a matter of improving the &quot;signal to junk&quot; ratio between the desired signal and everything else. By varying the relative amplitudes and the phase difference between signals arriving at two, physically separated antennas, a &quot;steerable null&quot; can be used to reduce interference from signal and/or noise sources. The two antennas need not be large or identical. Commercially built phaser/combiners are available from several outlets. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.rtl-sdr.com/using-a-quantum-phaser-to-null-out-interfering-signals/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTL-SDR&lt;/a&gt; points to the &lt;a href=&quot;http://www.dxtools.com/Phaser.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Quantum Phaser&lt;/a&gt; from &lt;a href=&quot;http://www.dxtools.com/index.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio Plus+ Electronics&lt;/a&gt;. The videos demonstrate the effective use of the product.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://www.mfjenterprises.com/Product.php?productid=MFJ-1026&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ-1026&lt;/a&gt; is used by ham radio operators to improve reception on the lower HF (aka MW) bands. The &lt;a href=&quot;https://www.mfjenterprises.com/Downloads/index.php?productid=MFJ-1026&amp;amp;filename=1026_3B.pdf&amp;amp;company=mfj&quot; rel=&quot;nofollow noreferrer&quot;&gt;manual for the MFJ-1026&lt;/a&gt; describes the theory of operation and includes a schematic diagram for your reference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have not used either of these products and I have no affiliation with their manufacturers.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-06T18:58:08.827" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13210" PostTypeId="1" CreationDate="2019-04-06T19:39:57.077" Score="3" ViewCount="1637" Body="&lt;p&gt;In the context of controlling a radio from a computer, what does CI-V stand for? I've noticed in relationship to a jack as well as USB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, from the Icom IC-7300 manual:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FCqqP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FCqqP.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2019-04-06T20:13:10.870" Title="What does CI-V stand for?" Tags="&lt;jargon&gt;&lt;ci-v&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13211" PostTypeId="2" ParentId="13210" CreationDate="2019-04-06T19:47:13.050" Score="1" Body="&lt;p&gt;From the &lt;a href=&quot;http://www.icom.co.jp/world/support/download/manual/pdf/IC-7610_ENG_CI-V_0a.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Icom IC-7610 Command Manual&lt;/a&gt;, CI-V stands for &quot;Computer Interface V&quot;.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-04-06T19:55:41.853" LastActivityDate="2019-04-06T19:55:41.853" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13212" PostTypeId="2" ParentId="13210" CreationDate="2019-04-06T19:55:04.770" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;CI-V stands for &lt;strong&gt;C&lt;/strong&gt;omputer &lt;strong&gt;I&lt;/strong&gt;nterface 5 [Roman numeral &quot;&lt;strong&gt;V&lt;/strong&gt;&quot;]&#xA;  and is ICOM's designation for their rig interface to a computer or to&#xA;  another rig. You can find it on most HF and some VHF rigs since the&#xA;  1980s and is has not changed in it's basic structure up to now. CI-V&#xA;  is a simple to use interface which allows --in contrast to other&#xA;  manufacturers' designs-- a &quot;daisy chaining&quot; of rigs.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;To connect &lt;em&gt;just two rigs&lt;/em&gt; you need nothing more than a cable with two&#xA;  3.5mm mini plugs. &lt;strong&gt;&lt;em&gt;For a connection to a computer&lt;/em&gt;&lt;/strong&gt;, you need an additional interface for most rigs.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Above quoted from &lt;a href=&quot;http://www.plicht.de/ekki/civ/civ-p0.html&quot; rel=&quot;noreferrer&quot;&gt;http://www.plicht.de/ekki/civ/civ-p0.html&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Icom CI-V interface is &lt;a href=&quot;https://www.kb6nu.com/ci-v/&quot; rel=&quot;noreferrer&quot;&gt;not a standard RS-232 type interface&lt;/a&gt;. The signals are TTL-level. It is a two-wire interface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CI-V rig-to-computer interfaces can either be purchased, or built &lt;a href=&quot;https://www.qsl.net/g3vgr/civ.html&quot; rel=&quot;noreferrer&quot;&gt;using a simple  two transistor circuit&lt;/a&gt; or the &lt;a href=&quot;http://www.ka1mda.org/ham/homebrew/civ/index.htm&quot; rel=&quot;noreferrer&quot;&gt;MAX-232&lt;/a&gt; chip.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-06T20:13:10.870" LastActivityDate="2019-04-06T20:13:10.870" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13214" PostTypeId="1" CreationDate="2019-04-06T21:11:37.247" Score="9" ViewCount="111" Body="&lt;p&gt;A set of utility lines, and above them some high voltage power lines, run almost directly over the backyard fence.  Some radio antennas are situated so that they can't fall onto the utility or power lines.  However the opposite is not true.  It appears that if one or two of the power poles were to collapse slightly towards each other, some of the high power lines could potentially fall almost anywhere on the property or house.  And the house is near a major fault line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna feedline shields are grounded to a deep ground stake directly behind the house.  Are they any additional safety precautions needed on the antennas, feed-lines, or radio equipment in the house?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I wanted to route a feedline to some very tall trees well past the power lines (by more than the height of either), are there any specific things I should do when routing under power lines for safety?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="8573" LastEditDate="2019-04-08T19:32:23.790" LastActivityDate="2019-05-09T17:01:45.680" Title="overhead power-line safety" Tags="&lt;coaxial-cable&gt;&lt;safety&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13215" PostTypeId="1" AcceptedAnswerId="13223" CreationDate="2019-04-06T23:14:30.543" Score="3" ViewCount="181" Body="&lt;p&gt;I'm playing with the new &lt;a href=&quot;http://js8call.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;JS8 mode&lt;/a&gt;. One feature I find particularly interesting is an ability to relay messages using rigs of other OP's. Though I'm not sure whether such QSOs should count as valid ones. Especially if it turns out that the station you try to contact runs in AUTO mode. I feel like I'm cheating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a particular example:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;22:37:31 - (2187) - R2AUK: HB9AVK STATUS? ⌁&#xA;22:37:59 - (2185) - HB9AVK: R2AUK STATUS HB AUTO RELAY SPOT 0M V1.0.0 ⌁ &#xA;22:38:49 - (2180) - R2AUK: HB9AVK SNR? ⌁ &#xA;22:39:29 - (2185) - HB9AVK: R2AUK SNR +05 ⌁ &#xA;22:39:37 - (2180) - R2AUK: HB9AVK HEARING? ⌁ &#xA;22:40:14 - (2184) - HB9AVK: R2AUK HEARING KD8UJG KB8HTU KK4WTI CO2DC ⌁ &#xA;22:41:24 - (2187) - R2AUK: HB9AVK&amp;gt; KD8UJG LETS QSO VIA RELAY HW CPY? EIH ⌁ &#xA;22:42:44 - (2185) - HB9AVK: KD8UJG&amp;gt; LETS QSO VIA RELAY HW CPY? VIA R2AUK -UR ⌁ &#xA;22:44:14 - (2184) - HB9AVK: R2AUK&amp;gt; ACK VIA KD8UJG ⌁ &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;In this case I got a response from KD8UJG, though the template 'ACK' response suggests that this station runs in AUTO mode. Unfortunately I got no response for a relayed 'STATUS?' message or any other messages to confirm this - it looks like the station disspeared.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Though technically there was a contact. I don't see how it differs from using a satellite or a repeater in UHF case except that HF were used here. Wikipedia &lt;a href=&quot;https://en.wikipedia.org/wiki/Contact_(amateur_radio)&quot; rel=&quot;nofollow noreferrer&quot;&gt;says&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;An amateur radio contact, more commonly referred to as simply a&#xA;  &quot;contact&quot;, is an exchange of information between two amateur radio&#xA;  stations. The exchange usually consists of an initial call, a response&#xA;  by another amateur radio operator at an amateur radio station, and&#xA;  possibly a signal report. A contact is often referred to by the Q code&#xA;  QSO. It is often limited to just a minimal exchange of such station&#xA;  IDs.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;According to this definition a QSO over a relay counts, even if one of the stations (besides the relay) runs in AUTO mode. The only problem is that I'm not sure whether this is a generally accepted definition of QSO. Is there any reason (like existence of other definitions of QSO, or any other) why described case may not counts as a QSO?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-04-07T09:43:44.070" LastActivityDate="2019-04-07T15:57:15.143" Title="JS8: does a QSO over a relay counts as a valid QSO?" Tags="&lt;digital-modes&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13218" PostTypeId="2" ParentId="13206" CreationDate="2019-04-07T09:30:07.163" Score="2" Body="&lt;p&gt;Generally speaking, I wouldn't recommend to work from the middle of the city at all. Because of the high noise level your experience with ham radio will be awful. If you have ANY option to work on HF in a suburb, I highly recommend to choose this path. Personally I travel 1.5 hours to the country house (35 km from the center of the city) every Friday and travel back to Moscow every Sunday. This being said I don't know what the noise level in your QTH actually is, maybe it's not that bad.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've experimented with some &quot;indoor&quot; (not actually indoor, see next) antennas and currently the results are following.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A shortened vertical antenna (I'm using OPEK HVT-400B) on a balcony works reasonably well and it's more or less effective on 10-40m bands. There is nothing to do with this type of antenna on 80m even if the manufacturer tells otherwise. You need place for one or two radials to make the antenna work. This type of antenna doesn't work indoor, I've tried.&lt;/li&gt;&#xA;&lt;li&gt;Magnetic loop antenna (I'm using CHA F-Loop 2.0) on the balcony works reasonably well on 10-20m bands. It's not very efficient on 40m, although it's possible to make a few QSOs. There is absolutely nothing to do with this type of antenna on 80m. Magnetic loops don't require radials but are very narrowband and usually handle only 10W in digital modes and 25W in SSB. You should be not far from the loop to tune it every time you change the frequency. Magnetic loops don't work indoor despite what the manufacturer may say. &lt;/li&gt;&#xA;&lt;li&gt;A shortened DIY dipole (&quot;Buddipole&quot;) didn't work well on a balcony, probably because of the proximity to metal objects. I'm going to test it outdoor in the nearest feature.&lt;/li&gt;&#xA;&lt;li&gt;A long wire antenna (23.5m) throwed from the window to a tree with a 8m counterpoise along the wall and MFJ-971 tuner works fine on 10-80m. The only problem with this antenna is that it's noisy comparing to a dipole or delta loop.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Please note that all these antennas are comprimise antennas. Their effectiveness cannot be compared to the effectiveness of non-comprimise antennas you can build in the suburb, like a (trap-)dipole or even more effective delta / quad loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case it's worth trying to build a vertical antenna on the metal roof. Personally I would attach a wire to a 7.2m long fishing rod, put an autotuner (like mAT-40 [1] or similar) in the bottom of the antenna and attach a few radials 5-10m long just in case metal roof will not work well as a ground.  Such antenna will be multiband and should work well on 10-40m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[1]: Hint - you can purchase a cheaper tuner, like mAT-30, designed for indoor usage, and make it suitable for using outdoor by filling it with silicon coating. Please note that mAT-30 is intended to be used only with Yaesu transceivers, but there are similar models for Kenwood and ICOM available on eBay.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-04-08T16:27:47.913" LastActivityDate="2019-04-08T16:27:47.913" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13221" PostTypeId="2" ParentId="1058" CreationDate="2019-04-07T11:42:58.180" Score="1" Body="&lt;p&gt;I'd say, if you plan on putting it in the attic /loft, then figure out where your wiring is, and in what orientations, and let that dictate the size and orientation of your antenna. Smaller might be better if it means you avoid closer interactions with noisy wiring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of my wiring runs horizontally EW along the loft and vertically down the house, and my lowest noise loft antenna was NS along the inside of the roof (actually at a diagonal) therfore at eight angles to most of the closest wiring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I put a horizontal wire in the garden and it picks up more local noise, probably due to orientation relative wiring in to the houses around...and the huge number of dishwashers and washing machines generating the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My property is small. All my antennas are tuned or loaded. The best receive I eve had though is on a small tuned loop. You can null out a particular source of noise, and it's pretty narrow bandwidth. You can make one out of cheap stuff if you're not planning to transmit. &lt;/p&gt;&#xA;" OwnerUserId="14650" LastActivityDate="2019-04-07T11:42:58.180" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13223" PostTypeId="2" ParentId="13215" CreationDate="2019-04-07T15:57:15.143" Score="3" Body="&lt;p&gt;Whether a contact &quot;counts&quot; depends on who does the counting. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, the rules for the &lt;a href=&quot;http://www.arrl.org/files/file/DXCC/DXCC%20Rules.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL DXCC Award&lt;/a&gt; state, &quot;Contacts made through 'repeater' devices or &lt;em&gt;any other power relay methods&lt;/em&gt; (other than satellites for Satellite DXCC) are &lt;strong&gt;invalid&lt;/strong&gt; for DXCC credit.&quot; Similarly for the &lt;a href=&quot;http://www.arrl.org/files/file/Worked%20All%20States/WAS%20Rules%202019%20with%20fees(1).pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Worked All States Award&lt;/a&gt; (WAS), &quot;Contacts made through repeaters or &lt;em&gt;any other power relay method&lt;/em&gt; &lt;strong&gt;cannot&lt;/strong&gt; be used for WAS credit.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There may, however, be reasons for organizations with different goals to count contacts on a different basis. For example, the &lt;a href=&quot;http://ranv.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio Amateurs of Northern Vermont&lt;/a&gt; (RANV) sponsored the &lt;a href=&quot;http://ranv.org/ranvqso.doc&quot; rel=&quot;nofollow noreferrer&quot;&gt;RANV QSO Party&lt;/a&gt; to, &quot;Bring life back to the FM repeater frequencies!&quot; In this case, valid event contacts were &lt;em&gt;required&lt;/em&gt; to be made through an analog or digital repeater.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-07T15:57:15.143" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13224" PostTypeId="2" ParentId="13206" CreationDate="2019-04-07T16:27:14.327" Score="2" Body="&lt;p&gt;&quot;If you can't fix it, feature it!&quot; As @R2AUK points out, the metal roofs &lt;em&gt;might&lt;/em&gt; act as a useful part of a vertical antenna. I recommend placing a mobile magnetic mount in the middle of the roof area:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OYgPA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OYgPA.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A skilled person could fashion such a mount from available materials. The radiator could take many different forms. A mount like this with an 11-ft long &quot;CB&quot; mobile whip worked well for me on the 40-10 meter bands, with a short run of coax and a match box (antenna tuner) at the radio. (Note: the high resistance of a telescoping stainless-steel whip probably makes it &lt;strong&gt;inappropriate&lt;/strong&gt; for transmitting.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &quot;screwdriver&quot; antenna uses a motor-driven variable inductor to match the vertical radiator to the feedline at the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y3PyI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y3PyI.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Searching the internet for &quot;homebrew screwdriver antenna&quot; turns up plenty of interesting design and construction ideas.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-07T16:27:14.327" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13225" PostTypeId="2" ParentId="1597" CreationDate="2019-04-07T19:26:33.760" Score="0" Body="&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Dual_in-line_package&quot; rel=&quot;nofollow noreferrer&quot;&gt;DIP = &lt;strong&gt;D&lt;/strong&gt;ual &lt;strong&gt;I&lt;/strong&gt;nline &lt;strong&gt;P&lt;/strong&gt;ackage&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-04-07T19:26:33.760" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13227" PostTypeId="1" AcceptedAnswerId="13228" CreationDate="2019-04-07T20:20:09.173" Score="3" ViewCount="356" Body="&lt;p&gt;Assume directional coupler is coupling with 16dB attenuation when signal is traveling from input to output. And directivity is let's say 20dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I understand correctly, when the RF signal is traveling from input to output the coupled port signal will be 16dB less than the input signal. And if any signal is reflected back from the output port to input direction then this reflected signal will be coupled with 16+20 = 36dB attenuation. &lt;a href=&quot;https://www.youtube.com/watch?v=iBK9ZIx9YaY&quot; rel=&quot;nofollow noreferrer&quot;&gt;(learned from this video)&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I use a directional coupler to measure an antenna's performance then signal generator will be connected to output port and the antenna will be connected to input. So the reflected signal from the antenna will be coupled with 16dB less to coupling port. And the main signal we sent from output to input will be coupled with 36dB attenuation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is: should I simply select a coupler with high directivity and low coupling attenuation? Because in my logic the directivity should be high enough so the main signal we sent traveling from output to input should not be coupled to couple port so much (we are not interested in it). And only the reflected signal should be coupled with as little attenuation as possible. Is this the correct approach?&lt;/p&gt;&#xA;" OwnerUserId="14653" LastEditorUserId="8573" LastEditDate="2019-04-08T18:05:26.593" LastActivityDate="2019-04-08T18:05:26.593" Title="Selecting Directional Coupler for VSWR Measurement" Tags="&lt;rf-power&gt;&lt;directional-coupler&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13228" PostTypeId="2" ParentId="13227" CreationDate="2019-04-08T05:01:15.013" Score="3" Body="&lt;p&gt;Yes, you understand it correctly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Directivity is the most important thing, as it limits how low a VSWR you can measure. In your example, 20 dB directivity, will show a constant ~20 dB return loss, or a VSWR of about 1.2, even with a perfect 50 Ohm load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coupling ratio is not as important. You can always adjust the input power to keep the detector in its sweet spot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Watch out, when measuring reflected power, that your readings aren't dominated by external transmitters. Any signal out there will be received, coupled and detected like reflected power. It helps to use a larger test signal, and to have a frequency selective detector.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-04-08T05:01:15.013" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13231" PostTypeId="2" ParentId="23" CreationDate="2019-04-08T19:56:04.797" Score="2" Body="&lt;p&gt;I'm at the fringe of the coverage area for the local DMR 70cm repeater. Using the &quot;extended&quot; dual-band antenna that came with my HT, the repeater typically reports received signal strength (RSSI) of about -123dBm and a loss rate between 10% and 20%, which is unacceptably high. I wanted a quick and cheap solution, preferably using items on hand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A mobile mag-mount on my large, metal roof did not improve the RSSI or loss rate reported by the repeater. Same with a friend's 5/8-wave base-station vertical about 10-ft above ground. Then it hit me: the repeater's 455MHz frequency is just below UHF TV channel 14 in the US - and I had an unused, 4-bay bow-tie antenna in the garage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the addition of two adapters to convert the F-type connector on the 75&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; cable to the radio's SMA female connector, this antenna - oriented for vertical polarization - increased the reported RSSI by 10dB and reduced the loss rate to near zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Eureka!&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-08T19:56:04.797" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13232" PostTypeId="1" CreationDate="2019-04-08T21:17:56.413" Score="2" ViewCount="432" Body="&lt;p&gt;I am about to build a new house with a ham shack incorporated in it. I am considering installing number 4 copper wire in the foundation around the perimeter as my ground ring.  Is it necessary to install ground rods every 16 to 20 feet around the perimeter also?  &lt;/p&gt;&#xA;" OwnerUserId="14663" LastActivityDate="2019-04-09T10:52:50.673" Title="Ufer ground and ground rods" Tags="&lt;grounding&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13233" PostTypeId="1" CreationDate="2019-04-08T22:31:11.473" Score="2" ViewCount="153" Body="&lt;p&gt;I would love to get involved with amateur radio, but I'm not sure how.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My community recreation center hosts a class to get a Technicians license for a reasonable price ($10), and I know a little bit of Morse Code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My Questions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How much will it cost to get entry-level equipment? (I can build if necessary, I am okay with using a soldering gun and uploading software)&lt;/li&gt;&#xA;&lt;li&gt;How can I find others to communicate with on the radio?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="14665" OwnerDisplayName="Ben Gubler" LastEditorUserId="8717" LastEditDate="2020-10-26T20:11:31.000" LastActivityDate="2020-10-26T20:11:31.000" Title="How can I get started with Amateur Radio?" Tags="&lt;license&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13234" PostTypeId="2" ParentId="13232" CreationDate="2019-04-09T10:52:50.673" Score="2" Body="&lt;p&gt;I'm going to make the assumption that you live in the United States.  With that assumption, I highly recommend you start with the National Electric Code (NEC) that applies to your area.  Different jurisdictions have adopted different years of the NEC as their standard.  You can access the &lt;a href=&quot;https://www.nfpa.org/NEC/About-the-NEC/Free-online-access-to-the-NEC-and-other-electrical-standards&quot; rel=&quot;nofollow noreferrer&quot;&gt;NEC Online For Free&lt;/a&gt;.  Your local library may have a copy you can use as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition to the NEC, &lt;a href=&quot;https://www.seapac.org/documents/seminars/2013/2013-Kuhlman-Applying%20the%20NEC%20to%20Amateur%20Radio.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Tim Kuhlman, KD7RUS&lt;/a&gt; has a good summary of the sections of the code that apply to amateur radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To specifically address the &lt;a href=&quot;https://en.wikipedia.org/wiki/Ufer_ground&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ufer&lt;/a&gt; connection; the 2017 version of the NEC covers the requirements for concrete-encased electrode (Ufer).  It does not mention a ground rod requirement for the ground ring.&lt;/p&gt;&#xA;" OwnerUserId="97" LastActivityDate="2019-04-09T10:52:50.673" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13236" PostTypeId="2" ParentId="13233" CreationDate="2019-04-09T11:33:05.743" Score="1" Body="&lt;p&gt;If you are willing to build equipment and don't specify what functionality you want, there is no lower or upper limit to cost.  Low quality commercial hardware that can transmit can be found for as low as \$25.  Low quality but broad band receivers can be found for as low as  \$7.  About double that for both will get a decent but minimum functionality commercial device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The easiest way to find people to talk to on the radio (after you get your license) is to call on the radio.  Also, there may be local clubs you can join, and very likely the technician class you already found is sponsored by such a club.  If you are in the United States, you can use &lt;a href=&quot;http://www.arrl.org/find-a-club&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/find-a-club&lt;/a&gt; to search for a local club.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-04-09T11:33:05.743" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13237" PostTypeId="1" AcceptedAnswerId="13270" CreationDate="2019-04-09T12:08:43.627" Score="1" ViewCount="110" Body="&lt;p&gt;Yes, obviously, it would be best if there's not an emission that doesn't include a call sign ID.  Part 97 seems to say this should never, ever occur (the law is often written in that kind of black-and-white view).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The real world isn't quite that cooperative, in my experience.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Especially with radio gear under repair or gear operated by internal firmware, it's very possible to accidentally transmit either without knowing it has occurred, or without any way to subsequently transmit a call sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say you're repairing a transceiver, and you power the station (connected to an antenna) to check receive functions -- and realize after a few seconds that it's transmitting.  You don't have a microphone or key connected, so it's not practical to transmit an ID.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you need to pick up your cell phone and turn yourself in to the FCC?  Or, realistically, what should you do in this kind of situation?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-10T18:00:18.923" Title="What to do when accidental emission can't be given a call sign ID?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;callsign&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13238" PostTypeId="2" ParentId="13237" CreationDate="2019-04-09T12:36:32.657" Score="1" Body="&lt;p&gt;Before connecting a radio to an antenna, you could test your repair procedure with a dummy load to prevent this from happening. It is good engineering practice to make off-the-air observations and measurements of the effects of any change to a regulated emitter to ensure compliance once the antenna is connected. Note that, since the impedance of an antenna can affect the behavior of a transmitter or amplifier, off-the-air testing ideally replicates the load presented to the transmitter by the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have not followed this procedure, however, there would seem to be no reason to, &quot;pick up your cell phone and turn yourself in to the FCC,&quot; if the unintended transmission was brief, within the ham bands and did not interfere with urgent operations.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-09T12:36:32.657" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13239" PostTypeId="2" ParentId="13233" CreationDate="2019-04-09T12:52:07.063" Score="5" Body="&lt;p&gt;My advice would be to start as a HF listener. There are a lot of fun things you can do without even having a license. As a listener you need only an RTL-SDR v3. This version has a direct sampling functionality which allows you to listen HF bands (3.5-30MHz) without any additional equipment (an upconverter). The price of RTL-SDR v3 is about 30$. Please make sure you buy it in the &lt;a href=&quot;https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/&quot; rel=&quot;nofollow noreferrer&quot;&gt;official rtl-sdr.com shop&lt;/a&gt;. Otherwise you can get a fake device without direct sampling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are a few things you can do with it:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Build a receive-only antenna an listen to SSB on HF bands&lt;/li&gt;&#xA;&lt;li&gt;Try to decode different amateur radio modes, like BPSK31, FT8, WSPR, SSTV, JS8 and others&lt;/li&gt;&#xA;&lt;li&gt;Receive a WeFax&lt;/li&gt;&#xA;&lt;li&gt;Figure out how to receive and decode ADS-B&lt;/li&gt;&#xA;&lt;li&gt;Receive and decode APRS signals&lt;/li&gt;&#xA;&lt;li&gt;Figure out how to use RTL-SDR as an spectrum analyzer&lt;/li&gt;&#xA;&lt;li&gt;After step (6) solder a simple filter and test it with RTL-SDR&lt;/li&gt;&#xA;&lt;li&gt;Receive images from weather satellites&lt;/li&gt;&#xA;&lt;li&gt;If you are not bored yet consider getting a ham license and bying a transceiver&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The process of getting a license in USA was &lt;a href=&quot;https://hackaday.com/2019/03/08/the-50-ham-getting-your-ticket-punched/&quot; rel=&quot;nofollow noreferrer&quot;&gt;described&lt;/a&gt; not a long time ago on hackaday.com by Dan Maloney, KC1DJT. In the comments to this article you can find links to the similar articles for different countries. I happened to be an author of &lt;a href=&quot;https://eax.me/amateur-radio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;such an article&lt;/a&gt; for Russia.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A transceiver is more expensive device than RTL-SDR. A brand new 100W transceiver like Yaesu FT-891 costs 680$ on Amazon. It could be more price-efficient to buy a second hand transceiver, though in this case there is a risk of buying a defected device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also worth noticing that there are a lot of channels on YouTube dedicated to ham radio. You might want to subscribe to some of them. Here is my current list of favorite channels:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/channel/UCiqd3GLTluk2s_IBt7p_LjA&quot; rel=&quot;nofollow noreferrer&quot;&gt;Alan Wolke, W2AEW&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/channel/UCjETc3psT6i7B5z6S1Y3ojQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mike Dahlhofer, K8MRD&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/user/loughkb&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kevin Loughin, KB9RLW&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/channel/UCQfwjjXcnW1hE4v2OTKgeFw&quot; rel=&quot;nofollow noreferrer&quot;&gt;Tommy Newcomb, N9YO&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/channel/UCuawHU2iYR_0tpYAIDyIH4Q&quot; rel=&quot;nofollow noreferrer&quot;&gt;Eric Hofer, KJ4YZI&lt;/a&gt; &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/channel/UC3xxr5EeFDtxnuHTWsDu2rA&quot; rel=&quot;nofollow noreferrer&quot;&gt;Julian, OH8STN&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;73 and see you on the bands!&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-04-12T16:47:58.960" LastActivityDate="2019-04-12T16:47:58.960" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13240" PostTypeId="1" AcceptedAnswerId="13241" CreationDate="2019-04-09T14:14:41.850" Score="1" ViewCount="415" Body="&lt;p&gt;I live close to an AM transmitter broadcasting in the kW of power. My RTL SDR dongle gets very overloaded. Using 2 AM broadcast filters, I have mostly managed to stop the overloading, at least from the main frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, generally on all bands, especially on HF, there is just a lot of noise. I assume this large amount of noise is due to the nearby AM transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is: given that I use a random long wire antenna going into my 9:1 &quot;balun&quot;, is there a way to reduce noise? Would a good ground rod help?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm quite new to antenna design, and I'm unsure that when I do different random things (e.g. increase/decrese length or move it) to my long wire, when the noise reduces, I'm not sure if I've just attenuated my overall signal, or somehow managed to reduce the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't understand if there is a distinction between noise and wanted signals when it comes to antenna design/placement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks&lt;/p&gt;&#xA;" OwnerUserId="14615" LastActivityDate="2019-10-30T01:37:56.120" Title="Noise reduction" Tags="&lt;hf&gt;&lt;wire-antenna&gt;&lt;noise&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13241" PostTypeId="2" ParentId="13240" CreationDate="2019-04-09T15:15:54.963" Score="1" Body="&lt;p&gt;Their are two types of sources that noise can come from. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Environmental &gt; What Nature doles out. &lt;/li&gt;&#xA;&lt;li&gt;interference from devices and electronics. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Electronics are big culprits, I had to turn off my computer monitor just to listen to commercial stations.    &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I would do is first make sure that no other electronics are near the equipment. first by turning off everything, then tune in and then turn things on one by one, their you can pin point where the noise is coming from, if you found the culprit then relocate the item. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then if that is not the problem check shielding on the cable to your radio antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;if anything else above does not remedy then I suspect something inside your radio equipment is emitting where it should not be. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;for the interest i did a little digging and found this: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.rtl-sdr.com/tip-effect-of-power-sources-on-the-ham-it-up-upconverter/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.rtl-sdr.com/tip-effect-of-power-sources-on-the-ham-it-up-upconverter/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="12988" LastEditDate="2019-10-30T01:37:56.120" LastActivityDate="2019-10-30T01:37:56.120" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13242" PostTypeId="1" CreationDate="2019-04-09T15:28:03.020" Score="8" ViewCount="2470" Body="&lt;p&gt;I was investigating about magnetic loop antennas. In a &lt;a href=&quot;https://www.nonstopsystems.com/radio/pdf-ant/article-antenna-mag-loop-2.pdf&quot; rel=&quot;noreferrer&quot;&gt;paper&lt;/a&gt; about them I found some bold claims:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fD9NU.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fD9NU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tf1bQ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tf1bQ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This almost sounds too good to be true, considering a lot of us hams are surronded by city noise and this paper claims the noise would be much lower with this design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the real performance of this kind of antennas, then?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="8717" LastEditDate="2019-04-09T15:45:19.737" LastActivityDate="2019-06-12T11:15:48.403" Title="Real world performance of magnetic loop antennas?" Tags="&lt;antenna&gt;&lt;rfi&gt;&lt;magnetic-loop&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13243" PostTypeId="2" ParentId="13242" CreationDate="2019-04-09T15:42:44.017" Score="4" Body="&lt;p&gt;Under &lt;em&gt;some&lt;/em&gt; circumstances, this can be true. What Leigh seems to be talking about is nulling out a &lt;strong&gt;local&lt;/strong&gt; noise source, which a rotatable loop excels at.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Between the loop and a vertical or dipole, in my experience the loop will often do what he says. But a loop compared to a beam? Not so much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have always respected the author, Leigh Turner VK5KLT for his technical knowledge. However, unless a rotatable beam (such as a tribander) is quite low (say, under 40 or 50 feet), I take exception to his statement that a loop will nearly always hear better than an HF beam. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-09T16:17:22.687" LastActivityDate="2019-04-09T16:17:22.687" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13244" PostTypeId="1" AcceptedAnswerId="13247" CreationDate="2019-04-09T16:03:53.537" Score="2" ViewCount="112" Body="&lt;p&gt;&lt;a href=&quot;https://www.mouser.com.tr/datasheet/2/392/Susumu_01192017_PAT-1206544.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;PAT1220-C-10DB-T5 is a 10dB attenuator.&lt;/a&gt; (This chip is just an example, it could be any other component as well). &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Can I simply connect 3 of them in series in a PCB design to make my cheap 30dB attenuator?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I have a few attenuator modules with an SMA connector. One of them is 20dB while others are 6dB and 10dB. Can I again connect them in series to get higher attenuation?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="14653" LastEditorUserId="8717" LastEditDate="2019-04-09T16:08:42.570" LastActivityDate="2019-04-09T17:00:09.433" Title="Attenuator Cascaded Connection" Tags="&lt;rf-power&gt;&lt;electronics&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13245" PostTypeId="2" ParentId="13214" CreationDate="2019-04-09T16:08:14.167" Score="2" Body="&lt;p&gt;Just make sure that supports are fully anchored and supported other than that check with local codes to make sure that wires that you are putting up are away a certain amount. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are in a major fault line try designing a Yugi antenna that way you do not need to deal with wire antenna&lt;/p&gt;&#xA;" OwnerUserId="12988" LastActivityDate="2019-04-09T16:08:14.167" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13246" PostTypeId="2" ParentId="13233" CreationDate="2019-04-09T16:49:34.050" Score="1" Body="&lt;p&gt;I concur that a good place to begin is with a local radio club. Ham radio can be as simple or as involved as you want it to be, but getting started on the air can be made easier by working with an experienced operator. It might also be helpful to interest siblings, friends, parents, teachers or scout leaders. Group members can help each other, contributing to the fun of exploration and discovery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since your profile indicates your interest in coding, you might consider exploring software-defined radio (SDR). With SDR, much of the radio's functionality is implemented on a &quot;computer,&quot; be it a PC/Mac, a single-board computer or a smartphone. &lt;a href=&quot;https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Receive-only USB &quot;dongles&quot;&lt;/a&gt; are an inexpensive path into this field and relatively inexpensive open-source transceiver hardware, like &lt;a href=&quot;http://www.hermeslite.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hermes-Lite&lt;/a&gt;, is becoming more available. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are numerous open-source SDR programs that run under Windows, MacOS, Linux and Android on their respective hardware platforms. Here, again, you can focus on the part of the &quot;radio&quot; that interests you: the top-level programs are built on open-source libraries that implement lower-level (and, often, deeply technical) functions, like DSP, graphics, hardware interfaces, etc. The only limit is your imagination!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you explore ham radio's many facets, you will also find lots of support in other areas of StackExchange. We look forward to hearing more from you!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have no affiliation with the companies whose products are cited in this answer.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-09T16:49:34.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13247" PostTypeId="2" ParentId="13244" CreationDate="2019-04-09T17:00:09.433" Score="4" Body="&lt;p&gt;Yes, you can cascade attenuators to realize more attenuation. Attenuation (in dB) will increase algebraically, as long as all individual attenuators are designed to operate at the same impedance and they are operating at that impedance. For example, mixing 75&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; and 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; attenuators may produce unexpected results. Same for using terminators in a system that doesn't terminate in the appropriate characteristic impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on what you're doing, be aware of the amount of power that each attenuator can dissipate. Putting 1W into a 30dB attenuator means only 1mW comes out - the attenuator has to dissipate the rest!&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-09T17:00:09.433" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13248" PostTypeId="2" ParentId="9044" CreationDate="2019-04-09T21:39:04.887" Score="-7" Body="&lt;p&gt;REPEAT AFTER ME; THERES NO SUCH THING AS AN ANTENNA TUNER. THERES NO SUCH THING AS AN ANTENNA TUNER. &#xA;LABEL BE DAMNED, ITS A LIE, A PLOT TO OIVERTHROW THE HAM COMMUNITY.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BUT WHAT ARE WE DOING??? LET US TUNE: AT 14.25MHZ, YOUR 1/2 WAVE DIPOLE IS &quot;TUNED&quot; WHEN YOU CUT IT TO THE LENGTH OF 32.842'&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IF YOU LIKE TO WORK C.W. AT THE BOTTOM OF THE BAND, SAY 14.05MHZ, YOUR DIPOLE WOULD NOW NEED TO BE 33.309' ABOUT 5 1/2&quot; LONGER.&#xA; ALSO ON THE 75 &amp;amp; 80 MTR BANDS: 3.975MHZ NEEDS 117.735'. - AT 3.6MHZ - 130' . ABOUT 12 ' LONGER.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;THOSE WOULD BE TUNED ANTENNAS.  NO TUNER DOES THAT. A &quot;BROOMSTICK&quot; TYPE WITH THE VARIABLE LOADED WHIP COMES PRETTY CLOSE IN THAT YOU ARE CHANGING THE ANTENNA'S PHYSICAL CHARACTERISTICS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;WHAT IS HE SAYING? THIS GUY IS NUTS YOU SAY.&#xA;WELL HERE IS THE DIFFERENCE YOU ARE NOT USING A TUNER, YOU ARE USING A &quot;MATCHING DEVICE&quot;. (OFTEN CALLED A MATCHBOX, TRANSMATCH, COUPLER, AMU) YOU ARE NOT DOING SQUAT TO THE ANTENNA, YOU ARE MATCHING THE ANTENNA - AND THIS IS KEY: SYSTEM - TO THE RIG. ALL YOU'RE DOING IS CHANGING THE DIFFERENT VALUE OF THAT SYSTEM (FEEDLINE, TRAPS, BALUNS, CHOKES ETC.) BETWEEN THE TX AND THE RADIATING ELEMENT.&#xA;REMEMBER: THERES NO SUCH THING AS AN ANTENNA TUNER. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;SO LET US MATCH.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HOPEFULLY I HAVEN'T BORED U W/ DETAILS, BUT AFTER 58 YRS AS A HAM, I HAD TO LEARN MANY THINGS THE HARD WAY. MOST OF THIS WAS FROM W1ICP LEW MCCOY.&#xA;'73 RICH KF9F&lt;/p&gt;&#xA;" OwnerUserId="8492" LastActivityDate="2019-04-09T21:39:04.887" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13249" PostTypeId="2" ParentId="7866" CreationDate="2019-04-09T21:48:49.620" Score="-4" Body="&lt;p&gt;FOR GOSH SAKES, YOU DON'T NEED TWO MATCHING DEVICES, (AKA TUNERS EVEN IF THEY'RE NOT). I WOULD BUY A GOOD ROLLER INDUCTANCE TYPE MATCHBOX AND BYPASS THE RIG'S &quot;AUTOTUNER&quot; WHY? BECAUSE ANYTHING WILL LOAD. YOU CAN MATCH THE LOAD TO THE SOURCE, OR YOU CAN REDUCE THE POWER OF THE SOURCE UNTIL IT IS WITHIN A SAFE OPERATING PARAMETER FOR THE SOURCE - TX. THE MORE STUFF BETWEEN U AND THE RADIATOR, THE MORE STUFF TO GO WRONG, CAUSE PROBLEMS ETC. KEEP IT SIMPLE AND BY USING AN EXTERNAL MATCHBOX, YOU KNOW FOR SURE WHAT YOYU'RE DOING TO UR RIG. '73 KF9F&lt;/p&gt;&#xA;" OwnerUserId="8492" LastActivityDate="2019-04-09T21:48:49.620" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13250" PostTypeId="1" CreationDate="2019-04-09T21:54:51.347" Score="0" ViewCount="72" Body="&lt;p&gt;Look at the title for the body because my question is short.&lt;/p&gt;&#xA;" OwnerUserId="14672" LastActivityDate="2019-04-10T12:35:45.897" Title="How old do you have to be to be a ARES volunteer?" Tags="&lt;united-states&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13251" PostTypeId="2" ParentId="13250" CreationDate="2019-04-09T22:01:42.470" Score="3" Body="&lt;p&gt;From &lt;a href=&quot;http://www.arrl.org/ares&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio Emergency Service&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Every licensed amateur, regardless of membership in ARRL or any other local or national organization is eligible to apply for membership in ARES.  &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, if you have an amateur FCC license, you may apply for ARES membership.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/amateur-radio-service&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio Service&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The amateur and amateur-satellite services are for qualified persons &lt;strong&gt;of any age&lt;/strong&gt; who are interested in radio technique solely with a personal aim and without pecuniary interest.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There is no age requirement for getting an amateur FCC license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that the ARES page also says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Please inquire at the local level for specific information.  &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, your local ARES organization may have an age requirement for participation, but you will have to ask.&lt;/p&gt;&#xA;" OwnerUserId="1183" LastActivityDate="2019-04-09T22:01:42.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13252" PostTypeId="2" ParentId="13242" CreationDate="2019-04-09T22:02:12.810" Score="3" Body="&lt;p&gt;I use a magnetic loop as my main antenna since I am a renter. It is outdoors about 10 feet from the building and about 10 feet above ground level. It is approximately 1 meter in diameter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Performance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;usable frequency range: 40 meters through 15 meters. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;15 meters similar to dipole you can rotate.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;20 meters similar to dipole you can rotate. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;30 meters about 3 to 6 db worse than dipole not very directional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;40 meters about 6 to 9 db worse than dipole not very directional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is not usable at all on 80 meters , not even for receive of local strong signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Overall mag loops have one significant problem: Extremely low usable bandwith (very high Q factor).  This is also the reason they work so well so this problem cannot be fixed, you have to work around it. If you want to change frequency more than 1 kHz (not MHz) you will need to re-tune. For this to be practical you will need a remote tuning device of some kind.&lt;/p&gt;&#xA;" OwnerUserId="14671" LastEditorUserId="9621" LastEditDate="2019-06-12T11:15:48.403" LastActivityDate="2019-06-12T11:15:48.403" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13253" PostTypeId="1" CreationDate="2019-04-09T23:25:49.953" Score="3" ViewCount="159" Body="&lt;p&gt;I don't consider myself an expert, but I have a fairly decent understanding of radio. I belong to a club that includes a number of people who have less theoretical background.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that reciprocity for an antenna means that we can calculate properties for an antenna when transmitting, when it is more intuitive and then we &quot;hand wave&quot; and say that reciprocity exists and because of that, we can apply the same parameters to an antenna being used in receive mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to explain this to someone with less experience without having to invoke reciprocity? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: the following is a secondary part of this question and is of lesser importance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, is there a way to explain it to someone with more experience at a higher level than Maxwell's equations or the like?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also I am not questioning Reciprocity, but it may not be intuitive to some. The comment by Brian K1LI may imply the best answer. &quot;Don't try to explain &lt;strong&gt;without&lt;/strong&gt; Reciprocity, but &lt;strong&gt;explain Reciprocity&lt;/strong&gt;, if necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clarification by a simple example: If I want to explain why a Yagi has a null on receive, I can invoke reciprocity and say there is a null in various places or gain in various places because that is what it looks like when it is transmitting. Some people may be fine with that, especially if I explain why the principle holds, but It may not be an obvious answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added April 17: I'm not sure what answer to accept. Most of them have some useful or interesting pieces, but none of them really provide a good answer to my question. What is the proper protocol on this site? I'm happy to write up an answer that is a combination of what was said by everyone, but I also want to give credit to those who have provided answers.&lt;/p&gt;&#xA;" OwnerUserId="5166" LastEditorUserId="5166" LastEditDate="2019-04-17T16:21:57.263" LastActivityDate="2019-04-17T16:21:57.263" Title="Is there a way to explain antenna radiation patterns on receive without reciprocity?" Tags="&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13254" PostTypeId="2" ParentId="13206" CreationDate="2019-04-09T23:49:20.037" Score="1" Body="&lt;p&gt;I consider this a very interesting problem. I would suggest that you first investigate various receive antennas. You might try E-sensors and H-sensors at different places on your property. The metal roof is a screen that you might take advantage of. &quot;in the middle of the city&quot; the bottleneck is likely to be the receive side. A two channel receiver with two sensors (E-field or H-field or one of&#xA;each) would allow cancellation of the dominant interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you know what you can receive reasonably well it is time to design a transmit&#xA;antenna with a reasonable efficiency for the desired radiation pattern and&#xA;polarization. A &quot;scientific approach&quot; in these cases is most helpful.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastEditorUserId="76" LastEditDate="2019-04-10T00:37:04.080" LastActivityDate="2019-04-10T00:37:04.080" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13255" PostTypeId="1" AcceptedAnswerId="13266" CreationDate="2019-04-10T02:19:54.753" Score="2" ViewCount="289" Body="&lt;p&gt;I am very confused about Standing Waves on transmission lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia says &quot;a standing wave, also known as a stationary wave, is a wave which oscillates in time but whose peak amplitude profile does not move in space&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm getting the time domain and wave amplitude confused, I think.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I understand that a standing wave is caused by the superposition of the amplitude of a wave traveling in one direction upon that of one traveling in the opposite direction. In other words, the resultant wave caused by the addition and subtraction of amplitudes or 'interference' between two waves traveling in opposite directions. And that even though no one says it, they always mean the special case of two waves of the same frequency because one is usually a reflected wave of the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the voltage amplitude of a standing wave a DC value which you could measure with a multi-meter (with a theoretically infinite input impedance) ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The pictures you normally see of standing waves which look like a sine wave, is this an instantaneous snapshot or does the amplitude of the standing wave actually stay fixed in space and time along say a transmission line ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does the amplitude of the actual standing waves in space oscillate in time at the same rate as the two waves traveling in opposite directions ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What else have I missed?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-04-10T12:49:54.243" LastActivityDate="2019-04-10T14:29:20.673" Title="Are standing waves on a transmission line RF or DC?" Tags="&lt;antenna-theory&gt;&lt;transmission-line&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13256" PostTypeId="1" AcceptedAnswerId="13265" CreationDate="2019-04-10T02:36:15.587" Score="5" ViewCount="211" Body="&lt;p&gt;I always get the feeling that an antenna which has a loop for the driven element such as a folded dipole or quad will pick up less static or 'high impedance' noise than an antenna that has free ends such as a dipole or long wire. Noting that atmospheric noise probably doesn't have an impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason I have this idea is as follows.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A short piece of thick wire 2 inches long which is used to short out the ends of a transmission line isn't going to pick up anything, right? It has a low DC resistance and at HF a low radiation resistance, and noise in the atmosphere is going to have a hard time inducing any current in it because it's a very low impedance short compared to the easily manipulated seemingly high impedance of the noise.  So a loop antenna is like a tame version of the 2 inch short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whereas in contrast, the ends of a dipole (for example) are high impedance because the current is zero (R = E / I) and so you get the feeling that noise will be able to have an effect or 'pull' the voltage at the ends of the dipole more easily because the dipole ends are not a low impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It this thinking correct?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-04-10T17:00:26.153" LastActivityDate="2019-04-10T17:00:26.153" Title="Does a loop antenna have less susceptibility to atmospheric noise than an open ended antenna?" Tags="&lt;antenna-theory&gt;&lt;dipole&gt;&lt;noise&gt;&lt;small-loop&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13257" PostTypeId="1" AcceptedAnswerId="13264" CreationDate="2019-04-10T03:48:57.787" Score="2" ViewCount="183" Body="&lt;p&gt;If i amplitude modulate an AM carrier with an audio signal, can i then feed that resultant AM waveform into another modulator and amplitude modulate the AM signal to give a signal which is amplitude modulated twice ? I think the answer is yes, then how would you demodulate that ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-04-10T05:34:41.847" LastActivityDate="2019-07-27T16:24:30.743" Title="Is double amplitude modulation useful?" Tags="&lt;modes&gt;&lt;electronics&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13258" PostTypeId="2" ParentId="13242" CreationDate="2019-04-10T10:01:53.943" Score="2" Body="&lt;p&gt;In practice there are a lot of other factors to consider. For instance you are not using a magnetic loop in the free space, it probably will be placed on the balcony. Thus you should consider the proximity of metal objects and the fact that half of the horizon will be closed by the building itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also beside of receiving a signal you should consider the transmission. Magnetic loops usually have power rating about 25W SSB 10W CW, thus the possibility to be heard by someone decreases. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally magnetic loops are directional and very narrowband. This means that you should be near the antenna and tune / rotate it all the time. Which is not only inconvenient but also reduces the time you TX or RX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an experience of using magnetic loop in the city. A 23m long wire antenna performs much better in the same conditions despite the fact that it's much more noisy than a dipole or a magnetic loop.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-04-10T10:01:53.943" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13259" PostTypeId="2" ParentId="13255" CreationDate="2019-04-10T11:41:14.670" Score="1" Body="&lt;p&gt;In this case, &lt;a href=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/1/10/Dipole_antenna_standing_waves_animation_461x217x150ms.gif/350px-Dipole_antenna_standing_waves_animation_461x217x150ms.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;a picture is worth a thousand words&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xiTPy.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xiTPy.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is usually shown as a standing wave is the envelope, not the wave itself. The wave oscillates at the frequency of operation between 100% magnetic energy (current) and 100% electric energy (voltage). Standing wave current is easy to measure. The lack of a reference point makes standing wave voltage harder to measure so the electric field may be measured instead and converted to voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Standing waves don't stand still. The energy in the two underlying waves on a standing wave antenna (forward and reflected) is traveling back and forth at the speed of light. Electromagnetic waves on an antenna cannot stand still. They must necessarily travel at the speed of light in the medium.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that all electromagnetic energy (including RF energy) is photonic, not electronic. The free electrons in the antenna conductor are simply oscillating in place while assisting the RF photons to travel at the speed of light back and forth on the standing wave antenna. Some of the photons are lost to radiation from the antenna. Antennas do not transmit or receive electrons! The exceptions to that statement are lightning and corona.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="8717" LastEditDate="2019-04-10T12:43:57.937" LastActivityDate="2019-04-10T12:43:57.937" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="13260" PostTypeId="2" ParentId="13256" CreationDate="2019-04-10T12:33:00.547" Score="2" Body="&lt;p&gt;An ungrounded antenna element is subject to precipitation static (P-static) buildup that can result in arcing. At least one element of a dipole is usually without a DC ground reference while if one conductor of the transmission line to a loop antenna is grounded, P-static cannot build up to cause an arc. P-static can be caused by dust, snow, or rain and usually occurs under low humidity conditions, e.g. the Arizona desert around Phoenix. For more information about P-static, please do a web search.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-04-10T12:33:00.547" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13261" PostTypeId="2" ParentId="13250" CreationDate="2019-04-10T12:35:45.897" Score="0" Body="&lt;p&gt;Many activities in ARES would probably require a legal age adult.  However, few of those activities would exclude someone younger if accompanied by their parent or guardian, and many activities are easier with two people.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A perfect example of this would be amateur radio communication for a hurricane storm shelter, where ideally one person sits with the radio and the other person acts as a runner to relay communications within the shelter.  If both people have sufficient training and licensing, the roles could even trade off.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-04-10T12:35:45.897" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13263" PostTypeId="2" ParentId="13255" CreationDate="2019-04-10T12:49:19.470" Score="2" Body="&lt;p&gt;If it was DC, there would be no wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the wave, you have AC power; RF merely means that the frequency of the AC is high enough to be considered radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can measure the voltage of the wave with a multimeter if it has an AC setting.  This will measure either RMS voltage or simulated RMS voltage; these two are the same if the wave is a sine wave.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-04-10T12:49:19.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13264" PostTypeId="2" ParentId="13257" CreationDate="2019-04-10T13:58:37.787" Score="6" Body="&lt;p&gt;Sure, it's technically possible. But I can't think of a reason it would be useful. The resulting modulation would be more complicated to implement, and occupy more bandwidth, than ordinary AM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Demodulation would be accomplished simply by cascading two demodulators together.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-10T13:58:37.787" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13265" PostTypeId="2" ParentId="13256" CreationDate="2019-04-10T14:26:07.150" Score="6" Body="&lt;p&gt;Your reasoning is not too far off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say you attach a signal generator to an antenna, and then probe the magnetic and electric fields at many places around this antenna in a test chamber. The ratio of the electric field strength to the magnetic field strength is called the &lt;em&gt;field impedance&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For &lt;em&gt;any&lt;/em&gt; antenna, several wavelengths away (in the far field), this ratio will be approximately 377 ohms (an ohm is a volt/ampere). This is a physical constant called the &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;noreferrer&quot;&gt;impedance of free space&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But closer to the antenna, the field impedance can vary by design. Let's compare a dipole that's small relative to wavelength, to a loop of similar size. Very close to the antenna, the field impedance for the dipole will be high, and low for the loop. And the intuitive explanation is as you expect: the loop is a short circuit, and the dipole an open circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By &lt;a href=&quot;https://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot; rel=&quot;noreferrer&quot;&gt;reciprocity&lt;/a&gt;, the field strength measured when the antenna is transmitting is also proportional to its sensitivity when receiving. So very close to the antenna, the short dipole will be better at detecting electric fields, and the small loop will be better at detecting magnetic fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Paradoxically, at some intermediate distance which isn't very near the antenna, but is also not far enough away to be in the far field, the situation reverses. &lt;a href=&quot;https://www.w8ji.com/magnetic_receiving_loops.htm&quot; rel=&quot;noreferrer&quot;&gt;W8JI has this great graph&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4f8bZ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4f8bZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the vertical axis were logarithmic, these two antennas would each have a field impedance that's the mirror of the other. This is an example of &lt;a href=&quot;https://en.wikipedia.org/wiki/Duality_(electricity_and_magnetism)&quot; rel=&quot;noreferrer&quot;&gt;duality&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You asked specifically if loops have reduced sensitivity to &lt;em&gt;atmospheric&lt;/em&gt; noise, and the answer is &lt;em&gt;no&lt;/em&gt;. Since such noise is in the far field of the antenna, a dipole and a loop will perform identically if all else (efficiency, polarization, feed arrangement, height above ground, etc) are equal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However especially on HF, there can be quite a lot of noise in the near field of the antenna. Since the near field impedance of these antennas are quite different and complementary, it is often the case that a loop does not pick up the same noise sources that a dipole does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also mention a &lt;em&gt;folded dipole&lt;/em&gt;, so I emphasize the above explanation works only for dipoles or loops which are &lt;em&gt;small&lt;/em&gt; relative to wavelength. Folded dipoles are often a half-wavelength long, that is, the size of resonant ordinary dipoles. Other than the higher feedpoint impedance, they work just like ordinary dipoles. Just why this is merits a question of its own: &lt;a href=&quot;https://ham.stackexchange.com/q/919/218&quot;&gt;How does a folded dipole work?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-04-10T14:31:13.030" LastActivityDate="2019-04-10T14:31:13.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13266" PostTypeId="2" ParentId="13255" CreationDate="2019-04-10T14:29:20.673" Score="3" Body="&lt;p&gt;Thanks for citing the &lt;a href=&quot;https://en.wikipedia.org/wiki/Standing_wave_ratio&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia item on SWR&lt;/a&gt;; as well as being a solid overview of the subject as presented in textbooks, the animations reveal much that is not obvious from a static description.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is the voltage amplitude of a standing wave a DC value which you could&#xA;  measure with a multi-meter (with a theoretically infinite input&#xA;  impedance) ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Wikipedia tells us that the voltages along the line are AC: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;For example, the VSWR value 1.2:1 denotes an &lt;strong&gt;AC voltage&lt;/strong&gt; due to&#xA;  standing waves along the transmission line reaching a &lt;em&gt;peak value&lt;/em&gt; 1.2&#xA;  times that of the &lt;em&gt;minimum&lt;/em&gt; AC voltage along that line.&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The RF voltage along the line could be measured with an ideal rectifier and smoothing filter connected to a DC multimeter. Non-ideal rectifiers may produce misleading measurements at low voltages because their response is not linear below their knee voltage.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The pictures you normally see of standing waves which look like a sine&#xA;  wave, is this an instantaneous snapshot or does the amplitude of the&#xA;  standing wave actually stay fixed in space and time along say a&#xA;  transmission line ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The &quot;picture you normally see of standing waves which look like a sine wave&quot; is borne out in the animation for the &lt;em&gt;special case&lt;/em&gt; of &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt;=-1:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/B4HfY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/B4HfY.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SWR=&lt;span class=&quot;math-container&quot;&gt;$\infty$&lt;/span&gt; results from dividing the peak value by the value of zero at the nodes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several noteworthy features in the subsequent graphs for SWR values of 4, 2 and 9, respectively:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/5k3KH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5k3KH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The superimposed forward and reflected waves form an envelope with &quot;peaks&quot; and &quot;valleys&quot;&lt;/li&gt;&#xA;&lt;li&gt;The peaks and valleys are stationary (&quot;standing&quot;) even though the underlying forward and reflected waves travel up and down the line&lt;/li&gt;&#xA;&lt;li&gt;The higher the SWR, the greater the ratio between the peak and valley values of the standing wave&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does the amplitude of the actual standing waves in space oscillate in&#xA;  time at the same rate as the two waves traveling in opposite&#xA;  directions ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Observing again the graphs, the forward and reflected waves have the same wavelength and, therefore, the same frequency, though they may be out of phase. While not explicitly stated in the Wikipedia item, the system is assumed to be linear, so there are no distortions which could introduce additional frequency components. Since linear combinations of signals of the same frequency can only produce resultant signals of the same frequency, the standing waves have the same frequency as the underlying RF signals that produce them.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-10T14:29:20.673" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13267" PostTypeId="2" ParentId="13253" CreationDate="2019-04-10T14:39:45.140" Score="2" Body="&lt;p&gt;Sure, you &quot;just&quot; have to calculate the electromagnetic waves generated by the transmitter, how these will interact with the receiving antenna and the mobile charges in them, and how this will result in transmitting electromagnetic forces through the antenna, ultimately to the feedline, and then the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's really a problem no different than transmitting, but in the other direction. Maxwell's equations already provide the mathematical basis for doing this, and software exists to numerically solve the problem. For example if you've ever modeled a Yagi in NEC, each of the parasitic elements is in a way a &quot;receiving&quot; the radiation from the other elements around it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in invoking reciprocity isn't necessary to explain radiation patterns, though it is often more practical. It's often easier, either in simulation or in a real test, to consider the antenna as transmitting then measure the field around the antenna, than it is to set up a transmitter and measure the received power, then move the transmitter and repeat the experiment dozens or hundreds of times until the antenna pattern is resolved with sufficient resolution.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-10T14:39:45.140" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13268" PostTypeId="2" ParentId="13253" CreationDate="2019-04-10T15:12:32.357" Score="2" Body="&lt;p&gt;According to Wikipedia, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;Lorentz Reciprocity theorem&lt;/a&gt; loosely states that:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;...the relationship between an oscillating current and the resulting&#xA;  electric field is unchanged if one interchanges the points where the&#xA;  current is placed and where the field is measured.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As shown in the citation, Maxwell's equations can be manipulated to show this is correct, but a simple experiment may help to understand it intuitively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Place two, center-fed, vertically oriented, half-wave dipoles 10 wavelengths apart:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/rgqqX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rgqqX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using antenna simulation software, driving dipole 1 with a 1A RF current source induces a peak current of 26mA in dipole 2. Conversely, driving dipole 2 with a 1A RF current source induces a peak current of 26mA in dipole 1. This demonstrates the effect of reciprocity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is nothing special about the nature or disposition of the two antennas in the example. Repeating the experiment with the two antennas in any arrangement produces the same reciprocal result, as long as the antennas are in each other's far field. You can measure the pattern of antenna 1 by moving antenna 2 throughout the space surrounding antenna 1, while keeping antenna 2 &quot;aimed at&quot; antenna 1. Using a very short dipole for antenna 2 approximates the pattern of an isotropic radiator, making such &quot;aiming&quot; less critical.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-04-10T15:29:45.953" LastActivityDate="2019-04-10T15:29:45.953" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13269" PostTypeId="2" ParentId="13257" CreationDate="2019-04-10T17:43:51.150" Score="7" Body="&lt;p&gt;One case where this might happen would be in the world of &lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_over_fiber&quot; rel=&quot;nofollow noreferrer&quot;&gt;RF over fiber&lt;/a&gt;. In this technique, a radio-frequency signal is used to modulate an optical (usually infrared) signal for transmission over optical fiber. Light is, after all, just really high frequency electromagnetic waves. To the best of my knowledge, the modulation used here is always AM, so if such a system is carrying an AM radio signal then you have AM-in-AM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other kinds of &quot;nested modulation&quot; occur from time to time, for instance &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency-shift_keying#Audio_FSK&quot; rel=&quot;nofollow noreferrer&quot;&gt;AFSK&lt;/a&gt; as used in the amateur radio VHF packet world is FSK-in-FM. &lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2019-07-26T16:09:24.123" LastActivityDate="2019-07-26T16:09:24.123" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13270" PostTypeId="2" ParentId="13237" CreationDate="2019-04-10T17:53:46.640" Score="4" Body="&lt;p&gt;Practically I think the answer is more or less as &lt;a href=&quot;https://ham.stackexchange.com/a/13238/1362&quot;&gt;Brian says&lt;/a&gt;. Mistakes happen and I think it's generally reasonable to simply move on:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;[…] if the unintended transmission was brief, within the ham bands and did not interfere with urgent operations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In fact, I imagine an argument could be made that this is the most reasonable decision, in accordance with §97.101:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(d) No amateur operator shall willfully or maliciously interfere with or cause interference to any radio communication or signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As soon as you &lt;em&gt;realize&lt;/em&gt; that you were unintentionally transmitting, the first and best thing to do would be to &lt;strong&gt;cease&lt;/strong&gt; transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The identification requirement &lt;em&gt;is&lt;/em&gt; a requirement. I'm not trying to downplay that. But let's say you're in a situation where you've just unintentionally transmitted and perhaps in an interfering matter. Now you have a choice. Which rule would you rather break next — flout the identification rule this time, or perpetuate against the &lt;em&gt;willful&lt;/em&gt; interference rule?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, I would rather go with &quot;least said soonest mended&quot;. Shut down and be prepared to apologize profusely for the initial unintended (and unidentified) transmission should the occasion arise. If I would willfully keep interfering, solely in an attempt to identify myself, that doesn't seem to help either party.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, to answer the original question more directly, I think there is nearly always a way to identify — if, &lt;em&gt;only if&lt;/em&gt;, and/or &lt;em&gt;when&lt;/em&gt; I am reasonably certain that I am able to transmit a clean and &lt;strong&gt;non-interfering&lt;/strong&gt; signal. The &quot;key&quot; (pun intended) is that there is no &lt;em&gt;lower&lt;/em&gt; limit to the speed of a CW emission. Quoting §97.119:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(b) The call sign must be transmitted with an emission authorized for the transmitting channel in one of the following ways:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(1) By a CW emission. When keyed by an automatic device used only for identification, the speed must not exceed 20 words per minute;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(2) […other potentially authorized options follow…]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I understand this to mean:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;it is always acceptable to identify by a CW emission, since CW is an &quot;emission authorized&quot; everywhere within the ham bands.&lt;/li&gt;&#xA;&lt;li&gt;there's a maximum speed limit when automatic keying, but…&lt;/li&gt;&#xA;&lt;li&gt;there's no regulation on speed for manual keying. Neither maximum, or…  &lt;strong&gt;minimum&lt;/strong&gt;!&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;To get to the point, if you have enough control to both start and stop your transmissions at any given time, you are able to identify in Morse Code! Maybe back in ham's heydey they called this &quot;&lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=History_of_electric_power_transmission&amp;amp;oldid=887893298#Transformers_and_alternating_current&quot; rel=&quot;nofollow noreferrer&quot;&gt;Westinghouse&lt;/a&gt; keying&quot; or something :-P&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2019-04-10T18:00:18.923" LastActivityDate="2019-04-10T18:00:18.923" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13271" PostTypeId="1" CreationDate="2019-04-10T19:01:52.100" Score="9" ViewCount="1632" Body="&lt;p&gt;I've heard older hams talk about &quot;aligning&quot; their equipment. E.g. &quot;I sent it to a guy for alignment&quot; or &quot;that rig probably needs to be completely aligned before you use it&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a kid, sometimes I remember broadcast AM/FM receiver dial indicators would get &quot;stuck&quot; and you'd have to fuss with the knob, like crank it all the way one direction for a while, to get it to properly line up with the rough tuning labels again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is &quot;alignment&quot; basically that only on a more precise VFO indicator? Or does it involve more tuning elsewhere, say re-adjusting to factory biases via trimpots? Or is it not really a physical adjustment thing at all, more like checking capacitors or replacing tubes?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2019-04-11T17:11:34.753" Title="What did it mean to &quot;align&quot; a radio?" Tags="&lt;history&gt;&lt;maintenance&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13272" PostTypeId="2" ParentId="13271" CreationDate="2019-04-10T19:25:06.890" Score="4" Body="&lt;p&gt;The process of alignment involves optimizing the settings of variable inductors and/or trimmer capacitors in the set to maximize sensitivity and selectivity.  It usually involves feeding the set a series of precise signals and adjusting particular components, in sequence, in each case to maximize output volume or voltage at a particular test point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This was mostly a procedure of the vacuum tube era, though solid state sets (even pocket transistor radios) could also be aligned.  Once set, however, only extreme conditions or a goodly number of years of operation (resulting, in either case, in value drift of components like capacitors and resistors) would generally require realignment.  One exception to this is that replacing a tube in a vacuum tube set might change some value (dependent on the replaced tube) enough that realignment would be of value.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are at least a couple YouTube videos that show the process (with a little compression, not to see all, in that case, 23 adjustments required) -- in one of them, the operator has to use an alternative alignment frequency to work around a very strong local AM broadcast station close to the recommended one.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-04-11T11:15:57.437" LastActivityDate="2019-04-11T11:15:57.437" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13273" PostTypeId="2" ParentId="13271" CreationDate="2019-04-10T19:30:37.987" Score="2" Body="&lt;p&gt;Alignment usually means to turn various built-in adjustable components to put the equipment back to factory specs. This is necessary because as some electronic components age, they change in value over time. That can and does cause reduced performance of the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two basic types of alignment. This is kind of tongue-in-cheek, but bear with me. ;-)&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Adjusting the adjustable adjustments&lt;/li&gt;&#xA;&lt;li&gt;Adjusting the non-adjustable &quot;adjustments&quot;.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;The &quot;adjustable adjustments&quot; are built-in adjustable components, such as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Trim pots (variable resistors)&lt;/li&gt;&#xA;&lt;li&gt;Variable capacitors&lt;/li&gt;&#xA;&lt;li&gt;Variable inductors&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These are found on IF cans (containing transformers).&#xA;&lt;hr&gt;&#xA;&quot;Non-adjustable&quot; adjustments are necessary when a component has drifted out of specs, and the technician must add a component in series or parallel with it. For example, I had to trim the BFO crystals in my Collins S-Line back to spec by adding a capacitor in parallel or in series with the crystal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mechanical adjustment of the pointer &lt;em&gt;could&lt;/em&gt; also be considered as alignment as well, I suppose; but that's not what is usually meant. A blind person would likely not be affected by that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's more that could be said, but basically, that is what it means to align a radio. I have done this many times over the years.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-11T17:11:34.753" LastActivityDate="2019-04-11T17:11:34.753" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13274" PostTypeId="2" ParentId="13253" CreationDate="2019-04-10T19:46:32.957" Score="1" Body="&lt;p&gt;For simple antennas it's easy to imagine how they are more sensitive in some directions, than in others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine a short dipole, with a resistor at the feedpoint, and have a travelling wave impinge on it from some direction. It should be fairly obvious, even if the maths isn't simple, that the voltage developed at the feedpoint will be largest when the dipole is aligned with the E-field of the travelling wave. End-on, it won't develop any voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same for thinking about its polarisation - when it is oriented perpendicular to the E-field, no voltage will be induced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This simplistic model works OK for a short dipole, which is basically a field probe. It seems to work for a half-wave dipole too, but the near fields are actually more complicated when significant current flows on the antenna, leading to scattered fields which add to the fields of the TEM wave. I think it's about as good as a transmitting model, when explaining the pattern of a dipole to a beginner. However it's not much use for explaining a yagi, or deriving input impedance etc.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-04-10T19:46:32.957" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13275" PostTypeId="2" ParentId="13271" CreationDate="2019-04-10T19:47:18.810" Score="2" Body="&lt;p&gt;As &lt;a href=&quot;http://www.ultraswank.net/television/mr-peabody-sherman-original-cartoon/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mr. Peabody&lt;/a&gt; would say in a cartoon of my youth, &quot;Sherman, set the WABAC machine!&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As shown in this block diagram of a double-conversion &lt;a href=&quot;https://en.wikipedia.org/wiki/Superheterodyne_receiver&quot; rel=&quot;nofollow noreferrer&quot;&gt;superheterodyne receiver&lt;/a&gt;, the signal from the antenna would be heterodyned - &lt;em&gt;mixed&lt;/em&gt; in modern parlance - down to successively lower &lt;em&gt;intermediate frequencies&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yKu3n.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yKu3n.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A primary purpose for the conversion steps was that the achievable bandwidth for a given filter &lt;a href=&quot;https://en.wikipedia.org/wiki/Q_factor&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt;&lt;/a&gt; becomes narrower as the cutoff frequency is decreased, improving &lt;em&gt;selectivity&lt;/em&gt;, the ability to reject unwanted signals on adjacent frequencies. Triple-conversion &quot;superhets&quot; were not unknown and the more recent trend of up-converting the antenna frequency to ~70MHz before downconverting it twice for single-signal filtering has only recently been seriously challenged in ham gear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Affordable bandpass filters in the 1st and 2nd IF stages were based on multisection &lt;em&gt;LC&lt;/em&gt; resonators, around which an entire field of study arose. Regardless of whether the sections were tuned to the same frequency or were &quot;stagger&quot; tuned, inevitable component variations required that a laborious &quot;alignment&quot; process be followed to optimize receiver performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As single &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;sideband, supressed-carrier modulation (SSB)&lt;/a&gt; supplanted AM, the superior performance of resonators based on &lt;a href=&quot;https://en.wikipedia.org/wiki/Crystal_filter&quot; rel=&quot;nofollow noreferrer&quot;&gt;piezoelectric&lt;/a&gt; and &lt;a href=&quot;https://en.wikipedia.org/wiki/Mechanical_filter&quot; rel=&quot;nofollow noreferrer&quot;&gt;mechanical filters&lt;/a&gt; over &lt;em&gt;LC&lt;/em&gt; phasing networks resulted in the dominance of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation#Bandpass_filtering&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;filter method&quot;&lt;/a&gt; of SSB generation. The great expense of these filters, in turn, was a driving force in the development of the &quot;transceiver,&quot; which combined the transmitter and receiver into a single unit. This allowed the very high-&lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; SSB generation filter(s) to be deployed in the receive chain. The elimination of multiple &lt;em&gt;LC&lt;/em&gt; resonators in two receiver stages all but eliminated the need for the receiver &quot;alignment&quot; process. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-10T19:47:18.810" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13276" PostTypeId="2" ParentId="13271" CreationDate="2019-04-10T20:06:33.430" Score="4" Body="&lt;p&gt;It's more complicated than that. &lt;em&gt;One of the things&lt;/em&gt; you do in an alignment is like what you describe, making sure that all of the fixed and adjustable frequencies inside the rig are correct and agree with what's on the dials. This might involve mechanical or electrical adjustment. But in addition to that you do things like&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Adjusting the tuned filters for different IF stages to make sure that they have the maximum response in the places where the signal ought to be&lt;/li&gt;&#xA;&lt;li&gt;Adjusting band pre-select filters to make sure that they admit as much of the desired band as possible, with a minimum of everything else&lt;/li&gt;&#xA;&lt;li&gt;Adjusting the gains and biases of various amplifiers so that they're operating in the ideal range, where they will pick up weak signals, but without saturating or distorting on strong signals&lt;/li&gt;&#xA;&lt;li&gt;Making sure that the receive and transmit sides of a transceiver are in good agreement, and the RIT offset is really 0 when that knob is at 0.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you have some time, I recommend &lt;a href=&quot;https://www.youtube.com/watch?v=z8k-h-g_8V8&quot; rel=&quot;nofollow noreferrer&quot;&gt;this Mr. Carlson's Lab&lt;/a&gt; video for a pretty detailed rundown of aligning a receiver; a few of his other restorations involve similar tuning-up.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-04-10T20:06:33.430" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13277" PostTypeId="2" ParentId="13253" CreationDate="2019-04-11T01:46:40.637" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I want to explain why a Yagi has a null on receive, I can invoke&#xA;  reciprocity and say there is a null in various places or gain in&#xA;  various places because that is what it looks like when it is&#xA;  transmitting.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You could take that approach, but it isn't the only approach you could take. As with any antenna, the explanation begins with the nature of the (transverse) &lt;a href=&quot;https://en.wikipedia.org/wiki/Electromagnetic_radiation&quot; rel=&quot;nofollow noreferrer&quot;&gt;electromagnetic wave&lt;/a&gt; that arrives at the antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/p7UlA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/p7UlA.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This linearly- and vertically-polarized wave - so called because of the orientation of the electric field vectors - will induce the largest currents in a conductor that is perfectly aligned with the &lt;span class=&quot;math-container&quot;&gt;$E$&lt;/span&gt; field: a &quot;vertical,&quot; in ham parlance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At a great distance from the transmitting antenna, each of the &lt;span class=&quot;math-container&quot;&gt;$E$&lt;/span&gt; field vectors extends to form an &lt;span class=&quot;math-container&quot;&gt;$xy$&lt;/span&gt; plane; this plane is a &lt;em&gt;wavefront&lt;/em&gt;, a plane on which the amplitude and phase of the &lt;span class=&quot;math-container&quot;&gt;$E$&lt;/span&gt; field is everywhere the same. Depending on the relative orientation of the transmitting and receiving antennas, the wavefront will arrive at an angle, &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt;, to the receiving antenna conductor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rDnWa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rDnWa.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At each point where the wavefront intersects the antenna, the &lt;span class=&quot;math-container&quot;&gt;$E$&lt;/span&gt; field will have a component along the direction of the antenna conductor which can induce a current in the antenna. As the wavefront proceeds to cut across the antenna conductor, the arrival time of the wavefront will be delayed from the earlier points of intersection, introducing a &lt;em&gt;phase difference&lt;/em&gt; between the currents induced at the successive points of intersection. Summing the amplitudes and phases of the individual interactions determines the total current on the conductor. Finding this response for all arrival angles establishes the pattern of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of a dipole - which, we should remember, may be an element of a yagi - the maximum induced current occurs when &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt;=0 because all of the &lt;span class=&quot;math-container&quot;&gt;$E$&lt;/span&gt; field vectors align perfectly with the antenna conductor and arrive at the same time (i.e., no phase differences). Conversely, when &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt;=90&lt;span class=&quot;math-container&quot;&gt;$^\circ$&lt;/span&gt; - that is, when the wave arrives &quot;off the side&quot; of the antenna - there is no component of the &lt;span class=&quot;math-container&quot;&gt;$E$&lt;/span&gt; field along the direction of the antenna, so no current is induced.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-11T01:46:40.637" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13278" PostTypeId="1" AcceptedAnswerId="13279" CreationDate="2019-04-11T03:15:12.147" Score="5" ViewCount="83" Body="&lt;p&gt;I was looking for a 2.4 GHz WiFi antenna to catch a weak free WiFi signal, and amplify it so I can use it.  I found &lt;a href=&quot;https://data.kommago.nl/files/pdf/ruckus_metroflex_2211_901-2211-eu25_datasheet.pdf&quot; rel=&quot;noreferrer&quot;&gt;Ruckus Metroflex NG&lt;/a&gt;, which can receive signals down to -108 dBm.  Which is amazingly weak; however, while searching for such an antenna, I couldn't help noticing that 900 MHz receivers, such as &lt;a href=&quot;http://www.libelium.com/development/waspmote/documentation/waspmote-lorawan-networking-guide/?action=download&quot; rel=&quot;noreferrer&quot;&gt;LoRaWAN&lt;/a&gt; have a sensitivity down to -136 dBm.  This is literally weak enough that at 1W transmission power, you can catch the 900 MHz signals of anything you can see on earth -- even of the highest planes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I thought, OK, the lower the frequency, the longer the waves, and the easier to catch them.  But apparently, that's not the case.  GPS receivers, which operate at the intermediate frequency of 1.575 GHz, go down to a whopping -164 dBm acquisition sensitivity for the&#xA;&lt;a href=&quot;https://www.mouser.com/ProductDetail/Linx-Technologies/RXM-GNSS-TM-B?qs=sGAEpiMZZMsjLMBIknjmkswlEeXPOvfiRjqnYDxKS%2F9P78qs%252B74sew%3D%3D&quot; rel=&quot;noreferrer&quot;&gt;RXM-GNSS-TM-B&lt;/a&gt; (and even lower tracking sensitivity).  So, what gives?  Why is there such a huge discrepancy in the required strength of a signal before it's detected?&lt;/p&gt;&#xA;" OwnerUserId="14482" LastEditorUserId="14482" LastEditDate="2019-04-11T03:21:49.230" LastActivityDate="2019-04-11T14:32:05.277" Title="Why do receiver sensitivities vary so much with frequency?" Tags="&lt;receiver&gt;&lt;frequency&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13279" PostTypeId="2" ParentId="13278" CreationDate="2019-04-11T13:00:17.763" Score="6" Body="&lt;p&gt;Detecting a signal is not a question of amplifying the signal: the problem is distinguishing the signal from the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Noise by nature is random: individual observations are unpredictable, but as more observations are made the average tends towards zero. By averaging more observations, the noise can be made arbitrarily close to zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Signals are not random. The presence of the signal introduces a predictable bias into the noise. As more observations are taken, these biases add. By sending the same &lt;em&gt;predictable&lt;/em&gt; signal for longer, more observations can be taken, and that accumulated bias representing the signal can be made arbitrarily large.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So one way to make a signal easier to detect is to send bits at a lower rate. All else equal, this means more energy is put into transmitting each bit, and thus its easier to know if a bit should be a 0 or a 1. Consequently the minimum detectable signal power can be lower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus there's a fundamental tradeoff between speed and sensitivity. WiFi can operate at multiple speeds, and the speed is negotiated dynamically to find the highest speed that's just barely detectable under the current conditions. Consequently you'll get higher speeds when the AP is only 3 meters away, and lower speeds when it's on the other side of a large building. At some point even the slowest WiFi speed (6,5000 kbit/s) is no longer detectable and communication fails entirely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;LoRaWAN is designed for low power and long range, and consequently it runs at a lower speed: 27 kbit/s. Being 240 times slower than even the slowest WiFi speed means it can be much more sensitive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GPS is designed for even lower power and longer range. GPS is somewhat unique in that its primary purpose isn't communication. This means the bitrate can be extremely low: 0.050 kbit/s. Consequently GPS receivers can be extremely sensitive.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-11T13:00:17.763" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13281" PostTypeId="1" CreationDate="2019-04-11T13:56:36.643" Score="3" ViewCount="140" Body="&lt;p&gt;Quote from Wikipedia, Photons: &quot;Nevertheless, all semiclassical theories were refuted definitively in the 1970s and 1980s by photon-correlation experiments. Hence, Einstein's hypothesis that quantization is a property of light itself is considered to be proven.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the Nobel archives: &quot;The photon is the field quantum (particle) acting as the communicator of force between charged particles.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For about a century, visible light waves have been known to be quantized into discrete packets of electromagnetic energy with each packet containing an energy level of &lt;span class=&quot;math-container&quot;&gt;$E = hc/\lambda$&lt;/span&gt; (where &lt;span class=&quot;math-container&quot;&gt;$h$&lt;/span&gt; is Planck's constant, &lt;span class=&quot;math-container&quot;&gt;$c$&lt;/span&gt; is the speed of light, and &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is the wavelength of the electromagnetic wave). Visible light waves and RF waves are both electromagnetic waves with different wavelengths. Are RF waves also quantized into packets of energy with each packet containing an energy level of &lt;span class=&quot;math-container&quot;&gt;$E = hc/\lambda$&lt;/span&gt;? If so, considering that a free copper electron driven by one amp at 10 MHz vibrates back and forth by less than 1% of the width of its copper atom (2mm diameter copper wire) how do most of those discrete packets of energy, generated by the transmitter, get to the antenna?&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-04-14T13:55:10.287" Title="Given the classical top down view, what does a bottom up view of RF waves look like?" Tags="&lt;propagation&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13282" PostTypeId="2" ParentId="13278" CreationDate="2019-04-11T14:32:05.277" Score="2" Body="&lt;p&gt;We can drill down a bit further into the answer given by &lt;a href=&quot;https://ham.stackexchange.com/users/218/phil-frost-w8ii&quot;&gt;Phil Frost - W8II&lt;/a&gt;. The datasheet for the &lt;a href=&quot;https://data.kommago.nl/files/pdf/ruckus_metroflex_2211_901-2211-eu25_datasheet.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ruckus Metroflex NG&lt;/a&gt; wireless router you cite quotes the receiver sensitivity vs. data rate:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eargs.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eargs.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We notice a logarithmic relationship between data rate and sensitivity:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\mathsf{10log(\frac{2Mbps}{1Mbps})=3.0dB}$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\mathsf{10log(\frac{5.5Mbps}{1Mbps})=7.4dB}$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\mathsf{10log(\frac{11Mbps}{1Mbps})=10.4dB}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which track the sensitivity differences between the various data rates quoted by the specs.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-11T14:32:05.277" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13283" PostTypeId="1" CreationDate="2019-04-11T15:22:12.870" Score="2" ViewCount="37" Body="&lt;p&gt;I'm currently trying to receive the Es'hail 2 satellite using a standard TV LNB, 60cm dish and RTL-SDR. My dish is slightly offset by 2 degrees, and my SNR is only about 15dB unfortunately.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My main issue is that there is a lot of noise. I can't figure out if the noise is coming from my LNB, or if it's due to a &quot;hump&quot; I think is coming from the satellite (which I think is just noise).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using RG6 coax, but the issue isn't really improved by reducing this to as little as 4m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amplifying the signal from the LNB just increases the noise also, so the SNR stays about the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could someone please provide me some advice on what to expect, noise wise, from this satellite based on their experience? Do I just have a low quality LNB, or is the signal just weak due to my offset dish/size of dish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks&lt;/p&gt;&#xA;" OwnerUserId="14615" LastActivityDate="2019-04-11T15:22:12.870" Title="Noise Floor when receiving Es'hail 2" Tags="&lt;satellites&gt;&lt;noise&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13284" PostTypeId="2" ParentId="13281" CreationDate="2019-04-11T15:36:17.413" Score="1" Body="&lt;p&gt;Yes, RF radiation is quantized. Yes, the photon is the quantum of electromagnetic radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this is not an excuse to revert to a &lt;a href=&quot;https://en.wikipedia.org/wiki/Corpuscular_theory_of_light&quot; rel=&quot;nofollow noreferrer&quot;&gt;particle theory of light&lt;/a&gt;. It is tempting to think of little &quot;light bullets&quot; shooting out of transmitters, through the air in straight lines, then hitting the receiving antenna. But you'd have difficulty explaining even basic radio phenomena with such a theory. How do you explain interference in antenna arrays? Or diffraction that limits the aperture efficiency of dish antennas? How do the &quot;light bullets&quot; change direction at the ionosphere?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to think of photons as particles that go from one point to another, then you have to consider all possible paths a photon can get from point A to point B, even paths that make no sense classically, including curved, circuitous paths that wander for no reason at all. &lt;em&gt;All&lt;/em&gt; possible paths must be considered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Zka5X.png&quot; alt=&quot;&quot;&gt;&#xA;&lt;br&gt;By &lt;a href=&quot;https://en.wikipedia.org/wiki/User:Matt_McIrvin&quot; rel=&quot;nofollow noreferrer&quot;&gt;Matt McIrvin&lt;/a&gt;, &lt;a href=&quot;http://creativecommons.org/licenses/by-sa/3.0/&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;Creative Commons Attribution-Share Alike 3.0&quot;&gt;CC BY-SA 3.0&lt;/a&gt;, &lt;a href=&quot;https://commons.wikimedia.org/w/index.php?curid=409445&quot; rel=&quot;nofollow noreferrer&quot;&gt;Link&lt;/a&gt;&lt;/p&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You must also account for the changing phase of the photon as it travels this path. Then all the possible paths combine in a &lt;a href=&quot;https://en.wikipedia.org/wiki/Path_integral_formulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;path integral&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since there are infinitely many possible paths, this is a very complicated problem, intractable except in the simplest cases. And while it does indeed explain how light can both be quantized while still exhibiting wave effects like interference and diffraction, it's extremely tedious, and we don't get the satisfaction of &quot;light bullets&quot; that travel in straight lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While this is an incredibly powerful tool for describing observable phenomena at very small scales, and it explains some things that classical electromagnetism could not such as the &lt;a href=&quot;https://en.wikipedia.org/wiki/Photovoltaic_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;photovoltaic effect&lt;/a&gt; and the &lt;a href=&quot;https://en.wikipedia.org/wiki/Ultraviolet_catastrophe&quot; rel=&quot;nofollow noreferrer&quot;&gt;ultraviolet catastrophe&lt;/a&gt;, Maxwell's equations remain consistent with experimental results at more practical scales such as those encountered in radio communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since QED provides none of a more intuitive understanding, a simpler mathematical model, or more accurate results for practical radio communication problems, I don't really see a reason to invoke it in any answer on this site.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-11T15:36:17.413" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="13285" PostTypeId="2" ParentId="13240" CreationDate="2019-04-11T17:01:41.313" Score="1" Body="&lt;p&gt;First try isolating your noise sources.  If you have a portable antenna and battery power system, move away from your house and all other structures with electric power, but the same distance from the AM station(s), and check the noise levels.  Then travel away from the AM station. If it's in your house, kill circuit breakers room-by-room to isolate powered interfering sources (sometimes LED lighting systems, or network routers, etc.).&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-04-11T17:01:41.313" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13286" PostTypeId="2" ParentId="13281" CreationDate="2019-04-11T18:49:37.667" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;... considering that a free copper electron driven by one amp at 10 MHz&#xA;  vibrates back and forth by less than 1% of the width of its copper&#xA;  atom (2mm diameter copper wire) how do most of those discrete packets&#xA;  of energy, generated by the transmitter, get to the antenna?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Just as the molecules of &lt;span class=&quot;math-container&quot;&gt;$\mathrm{H_2O}$&lt;/span&gt; carrying an (ideal) water wave aren't displaced in the direction the wave travels, so it is with the electrons whose oscillations give rise to electromagnetic waves. It is only the &lt;em&gt;disturbance&lt;/em&gt; that travels. According to the &lt;a href=&quot;https://en.wikipedia.org/wiki/Standard_Model&quot; rel=&quot;nofollow noreferrer&quot;&gt;Standard Model&lt;/a&gt; of particle physics, the energy that travels along a transmission line, along an antenna conductor and between two antennas is an electromagnetic wave, described by a field equation, that is carried by a messenger particle. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-11T18:49:37.667" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="13287" PostTypeId="1" AcceptedAnswerId="13288" CreationDate="2019-04-11T21:37:14.653" Score="5" ViewCount="223" Body="&lt;p&gt;The unit in question is an &lt;a href=&quot;https://elecraft.com/products/xg3&quot; rel=&quot;nofollow noreferrer&quot;&gt;Elecraft XG3 test signal generator&lt;/a&gt;.  It puts out anywhere from -107 dBm to 0 dBm.  Is it safe to have these signal generators on and transmitting while not connected to anything, or should they always be connected to a 50 ohm load?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to fire it up for the first time but I don't want it hooked up to my actual rig until I know everything's good.  Can I just hook it up to a dummy load?  Or is the power so minuscule that it doesn't matter?&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="76" LastEditDate="2019-09-28T23:11:09.073" LastActivityDate="2019-09-28T23:11:09.073" Title="Can I have a signal generator on while it's not connected?" Tags="&lt;rf-power&gt;&lt;transmitter&gt;&lt;impedance-matching&gt;&lt;testing&gt;&lt;elecraft&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13288" PostTypeId="2" ParentId="13287" CreationDate="2019-04-11T22:47:00.690" Score="4" Body="&lt;p&gt;It's not necessary to turn it off while it is not connected. Zero dBm is a power level of only 1 milliwatt, and no device will be damaged by that power level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it were, &lt;a href=&quot;https://elecraft.com/pages/xg3-sweep-and-signal-generator-manuals&quot; rel=&quot;nofollow noreferrer&quot;&gt;the manual&lt;/a&gt; would have said so.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-04-11T22:47:00.690" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13289" PostTypeId="1" AcceptedAnswerId="14457" CreationDate="2019-04-12T18:52:38.867" Score="5" ViewCount="1388" Body="&lt;p&gt;I've got, for the near term, limited resources to put up an HF antenna at my home.  One of the options I can manage without excessive cost is a loop, which would enclose the house.  I need to transmit on 80m, and likely up to 20m (I understand loops are very tolerant of shorter wavelengths). It wouldn't be as high as I'd like, so would probably perform more like an NVIS, with poor horizontal radiation (given I live in a draw, that's not entirely a bad thing, as less of my energy will go into the ground where it rises).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only thing is, the space I have pretty much requires the loop to enclose the house, if I'm to avoid entanglements in the dense pine/hardwood mix that covers more than half the lot.  How will the steel roof (about 5x20 meters) affect the radiation of an 80m loop (probably hexagonal), mounted close to roof height (roundly 3 meters above ground)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not certain of the grounding status of the roof panels; it was applied by a &quot;handyman&quot; who seems to do no better work than is expected of him (that is, if you don't know it's wrong, he won't do it right), before I lived in the house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the property aerial view; the bright white roof with two extensions is mine. The property line follows the fence parallel with the driveway, the near edge of the line of trees next to the plowed field North of the house, and loops into the heavily treed area S and SSE (mix of pines and hardwoods, tangled branches, difficult to run wire into).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YeQR5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YeQR5.png&quot; alt=&quot;Aerial view from Google Maps&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As requested in chat, &lt;a href=&quot;https://imgur.com/gallery/IkyHGx5&quot; rel=&quot;nofollow noreferrer&quot;&gt;here are photos&lt;/a&gt; of the trees that have reasonably open space nearby -- as noted, a mix of pines and hardwoods.  &lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-04-18T12:03:24.003" LastActivityDate="2019-10-09T09:02:35.987" Title="Loop antenna layout and radiation?" Tags="&lt;antenna-construction&gt;&lt;hf&gt;&lt;propagation&gt;&lt;wire-antenna&gt;&lt;loop-antenna&gt;" AnswerCount="5" CommentCount="13" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13290" PostTypeId="1" CreationDate="2019-04-13T06:24:56.603" Score="6" ViewCount="260" Body="&lt;p&gt;I am putting a 40m antenna in my attic and I was wondering would it be safe to have a shack in the room right below the attic (10ft of coax or less) or should I have my shack in the basement/ground level (50ft coax). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any health effects of sitting to close to the antenna. I am planning to operate max 100w on HF and 50w on VHF/UHF.&lt;/p&gt;&#xA;" OwnerUserId="14274" LastEditorUserId="8717" LastEditDate="2019-04-13T14:37:56.267" LastActivityDate="2019-04-15T15:01:40.137" Title="distance between shack and antenna" Tags="&lt;antenna&gt;&lt;rf-power&gt;&lt;safety&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13293" PostTypeId="2" ParentId="13290" CreationDate="2019-04-13T10:24:12.580" Score="1" Body="&lt;p&gt;The &lt;a href=&quot;https://www.fcc.gov/general/radio-frequency-safety-0&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC regulates RF exposure&lt;/a&gt; for safety and health. RF exposure must be evaluated on a station-by-station basis. As a free public service, the &lt;a href=&quot;http://www.arrl.org/rf-exposure&quot; rel=&quot;nofollow noreferrer&quot;&gt;American Radio Relay League&lt;/a&gt; (ARRL) makes available a free download of &lt;strong&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Technology/RFsafetyCommittee/RF+Exposure+and+You.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;RF Exposure and You&lt;/a&gt;&lt;/strong&gt; by staff member Ed Hare, W1RFI. &lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/RF%20Exposure%20Chapter%205.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Chapter 5&lt;/a&gt; contains the references needed to complete the &lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/rfex1_2.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;RF Exposure Station Evaluation and Exemption Worksheets&lt;/a&gt;. The League has published &lt;a href=&quot;http://www.arrl.org/rf-safety-publications&quot; rel=&quot;nofollow noreferrer&quot;&gt;numerous works&lt;/a&gt; over the years, including some that can help you interact with neighbors on the subject, if needed.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-13T10:24:12.580" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13295" PostTypeId="2" ParentId="9712" CreationDate="2019-04-13T16:51:44.967" Score="1" Body="&lt;p&gt;Hash is wide band radiated noise. But it doesn't have to be wide band. Radiated is the key word here. Which is why it's usually related to RF. It can also occur at audio frequency. &lt;/p&gt;&#xA;" OwnerUserId="14694" LastActivityDate="2019-04-13T16:51:44.967" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13296" PostTypeId="2" ParentId="13281" CreationDate="2019-04-13T18:30:00.230" Score="0" Body="&lt;p&gt;When I studied electromagnetic theory at Texas A&amp;amp;M during the 1950s, I was envious of my fellow classmates who could picture fields and waves in their mind's eye as I could never manage that feat. I noticed that my textbook used ink particles to illustrate fields and waves. The professor used chalk particles to illustrate fields and waves on a chalk board. I used carbon particles to illustrate fields and waves on a piece of paper. To this day, I have trouble picturing in my mind anything that doesn't consist of particles. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Particles do not necessarily contain matter. Anything, including pure energy, that has momentum is considered to be a particle. So I have finally been able to picture fields and waves as clouds of energy particles called photons. Just as each individual in a flock of birds or a school of fish does not have to be tracked, each individual photon doesn't have to be tracked to understand what the cloud of photons is doing, i.e. performing a path integral is not necessary. As long as coherent photons from a single source are being considered, knowing the phase of each photon is not necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We know that electromagnetic RF energy moves from the source to the antenna at the speed of light where it is radiated as radio waves traveling through the air. We know that free electrons in the conductors are somehow involved in the transfer of energy although they simply vibrate in place at RF. Knowing the abilities and limitations of electrons and photons enables one (me in particular) to understand what is going on at a particle collective level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only thing that electrons and photons have in common is that they are both quantum particles in the standard model. The characteristics of both particles are available on Wikipedia. The velocity of an electron driven by a current is called the drift velocity which is very low. The velocity of a photon is the speed of light in the medium. The electron is a charged particle with mass. The photon has zero charge and zero rest mass. Both particles can transfer energy but the photon transfers energy at the speed of light which the electron cannot do. Electromagnetic fields and waves consist of photons as does Maxwell's displacement current. Photons can go where electrons cannot go. This difference in capabilities is what is responsible for skin effect in RF conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the photons in the wave in a transmission line travel at an average velocity of VF(c) where VF is the velocity factor of the transmission line and c is the speed of lignt. Most of the photons travel through the air or insulation surrounding the conductor. The free electrons in the conductor act like a sort of bucket brigade while guiding the photons to the antenna. The differential nature of the coherent photon energy flow in the two conductors tends to prevent radiation of photons from the feedline. When the photons reach the antenna some are free to radiate while others are involved in maintaining the standing waves on the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people are satisfied with their mental picture of electromagnetic waves using field and waves and/or Maxwell's equations and I remain envious of them. For others, like me, who have trouble picturing that model, the photon model might help. It goes without saying that the way I choose to picture fields and waves in my mind doesn't have any effect on reality.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-04-14T13:55:10.287" LastActivityDate="2019-04-14T13:55:10.287" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="13297" PostTypeId="5" CreationDate="2019-04-13T20:29:31.127" Score="0" Body="&lt;p&gt;[This tag has been named &lt;a href=&quot;/questions/tagged/earth&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;earth&amp;#39;&quot; rel=&quot;tag&quot;&gt;earth&lt;/a&gt; to make it clearly distinct from forms of &lt;a href=&quot;/questions/tagged/grounding&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;grounding&amp;#39;&quot; rel=&quot;tag&quot;&gt;grounding&lt;/a&gt; that are not &quot;earth ground&quot;. This naming choice should be revisited if it is not succeeding at its goal.]&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-04-13T20:29:31.127" LastActivityDate="2019-04-13T20:29:31.127" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13298" PostTypeId="4" CreationDate="2019-04-13T20:29:31.127" Score="0" Body="Questions about the surface of the Earth as it affects radio propagation and antenna system design and installation. For questions about RF grounds and shields, counterpoises, virtual grounds, etc. use [grounding] instead unless the question is particularly about soil properties or similar details." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-04-13T20:37:56.787" LastActivityDate="2019-04-13T20:37:56.787" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13299" PostTypeId="2" ParentId="12494" CreationDate="2019-04-13T22:59:32.103" Score="1" Body="&lt;h1&gt;It is primarily an RF ground.&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Connecting that to an earth ground can invite damage from a lightning strike. See &lt;a href=&quot;http://w8ji.com/station_ground.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://w8ji.com/station_ground.htm&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used to have lots of annoying audio and CW feed back through my speakers, headphones, computers, etc. My voice and CW came through all of that whenever I transmitted. &#xA;But when I bonded my tuners, amplifiers, speakers, wattmeter, and other shack equipment  to that terminal on the back of my IC-765 transceiver, that put a screeching halt to that problem &lt;strong&gt;because all of that equipment is now at the same RF potential&lt;/strong&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-14T18:53:44.220" LastActivityDate="2019-04-14T18:53:44.220" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13300" PostTypeId="2" ParentId="1820" CreationDate="2019-04-14T06:17:48.940" Score="0" Body="&lt;p&gt;Yes. There's no such thing as a separation between RF and Safety ground. I highly recommend the book &lt;a href=&quot;https://amzn.to/2GoRTZh&quot; rel=&quot;nofollow noreferrer&quot;&gt;Grounding and Bonding for the Radio Amateur&lt;/a&gt;  that clarified a lot of the myths and issues I was having, including this separation of the two grounds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It makes sense to analyze a grounding system from the point of safety, RF and lightning protection but it's still one system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example: your ground cable could twist and bend and have no effect on safety, but reduce the lighting protection as those don't like bending.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another example: having your ground rod at 1 meter, 10 meters or 30 meters from your house will make very little difference for the safety, but it will affect how it behaves at different frequencies (and you might want them all if you operate at many different frequencies).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would actually say that trying to keep the safety and RF ground separate is probably dangerous, because both grounds will end up acting as both things and most likely your RF ground might not be safe enough (it might not have wire that is thick enough to dissipate a discharge for example).&lt;/p&gt;&#xA;" OwnerUserId="10431" LastActivityDate="2019-04-14T06:17:48.940" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13302" PostTypeId="2" ParentId="12928" CreationDate="2019-04-14T12:38:34.567" Score="2" Body="&lt;p&gt;To directly answer your question, the exact-replacement material would be open-celled polyurethane foam with a density of about 2.0 lb/ft^3 (30 kg/m^3).  This can be found at just about any foam outlet store.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatives:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;It does not have to be polyurethane but I have found polyurethane to be far more durable than other foams.  &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The density can be adjusted; heavier foams will provide a little more absorption at lower frequencies and a little less at higher frequencies. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Open-celled foam is better for sound absorption than closed celled foam&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Having said that, I understand the function is to reduce reverberation in the air space between the outer shell and the ear.  For that, the best sound absorbers are fibers rather than foams.  So a non-woven fiber such as Thinsulate or even a few cotton balls would work better than a foam.  Materials such as this can be found in old coats or gloves.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;@Doc 's suggestion of cotton socks is an excellent one.  A little bit of absorption is lost due to the woven nature of the fibers, but it is still a very good absorber.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2019-04-14T12:43:51.013" LastActivityDate="2019-04-14T12:43:51.013" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13303" PostTypeId="2" ParentId="13287" CreationDate="2019-04-14T14:51:07.930" Score="2" Body="&lt;p&gt;From Elecraft support:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;You do not have to connect a load to the XG3.  A signal generator is different from a transmitter.&quot; &lt;/p&gt;&#xA;" OwnerUserId="12939" LastActivityDate="2019-04-14T14:51:07.930" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13304" PostTypeId="1" CreationDate="2019-04-14T19:09:29.770" Score="6" ViewCount="161" Body="&lt;p&gt;I'm trying to design a low frequency dipole interferometer antenna array. I am realizing how little I know about radio antennae. I'm confused by the concept of effective area &lt;span class=&quot;math-container&quot;&gt;$A_e$&lt;/span&gt; and how it applies to arrays. I haven't been able to get a clear answer on that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say I'm using my array to receive 10MHz signals. That's &lt;span class=&quot;math-container&quot;&gt;$\lambda = 30\,\text{m}$&lt;/span&gt;, so is my effective area &lt;span class=&quot;math-container&quot;&gt;$A_e \approx \lambda^2/4\pi \approx 72\,\text{m}^2$&lt;/span&gt;? Is that for each dipole antenna? How does effective area change when I combine them?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What factors do I need (e.g. dipole length, spacing, baseline) to calculate the effective collecting area for the array as a whole?&lt;/p&gt;&#xA;" OwnerUserId="14703" LastEditorUserId="9621" LastEditDate="2019-04-15T14:10:18.220" LastActivityDate="2019-04-15T19:19:02.370" Title="Effective Area of Dipole Array" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;dipole&gt;&lt;phased-array&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13305" PostTypeId="1" CreationDate="2019-04-15T06:30:51.060" Score="2" ViewCount="72" Body="&lt;p&gt;Is it possible to setup up an interface from a PC to a digital radio that is able to communicate with a Hytera PD702 handheld (450-520MHz) or like type radio?  Or are there off the shelf radios that can manage this out of the box that have a USB connection and a software API?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The research I've done shows this is easily possible with non digital radios.  The information for digital is vague at best.  For example the West Mountain Radio/RIGblaster looked like it could be suitable but they don't support digital.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We are aiming to do 2 things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Send audio from the PC to the handheld&lt;/li&gt;&#xA;&lt;li&gt;Record transmissions from the handhelds&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;We could hack something together using a USB controlled relay to control the push to talk and route the mic and speaker through an audio card but I really think this has been done before and a lot more professionally.&lt;/p&gt;&#xA;" OwnerUserId="14705" LastEditorUserId="76" LastEditDate="2019-04-16T01:46:04.503" LastActivityDate="2019-04-16T01:46:04.503" Title="Is PC to Digital Radio possible, is there an existing solution?" Tags="&lt;ht&gt;&lt;audio-interface&gt;&lt;digital-voice&gt;&lt;computer-control&gt;" AnswerCount="0" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13307" PostTypeId="2" ParentId="13290" CreationDate="2019-04-15T15:01:40.137" Score="4" Body="&lt;p&gt;Various organizations have issued guidelines on maximum permissible exposure. Below a certain power, the station can be assumed harmless. Above that power, some more careful design is prudent. Your station is mostly below that threshold, except possibly on the upper HF bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/RF%20Exposure%20Chapter%205.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Thresholds below which a station does not need to be evaluated, according to the ARRL&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;40 meters and lower frequencies: 500 watts&lt;/li&gt;&#xA;&lt;li&gt;30 meters: 425 watts&lt;/li&gt;&#xA;&lt;li&gt;20 meters: 225 watts&lt;/li&gt;&#xA;&lt;li&gt;17 meters: 125 watts&lt;/li&gt;&#xA;&lt;li&gt;15 meters: 100 watts&lt;/li&gt;&#xA;&lt;li&gt;12 meters: 75 watts&lt;/li&gt;&#xA;&lt;li&gt;10 meters, and all VHF: 50 watts&lt;/li&gt;&#xA;&lt;li&gt;70 cm: 70 watts&lt;/li&gt;&#xA;&lt;li&gt;33 cm: 150 watts&lt;/li&gt;&#xA;&lt;li&gt;23 cm: 200 watts&lt;/li&gt;&#xA;&lt;li&gt;all higher frequencies: 250 watts&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The lower thresholds around VHF are due to the increased energy absorption of human tissue at those frequencies. The cornea is especially at risk because it's small and has no blood flow to cool it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you say you intend to operate 100 watts on HF, and 50 watts on VHF, you are below these thresholds except on 12 and 10 meters. So if you want to be safe, reduce power a little bit on these bands and there should be no issue at all having the shack near the antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-15T15:01:40.137" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13308" PostTypeId="2" ParentId="13304" CreationDate="2019-04-15T18:29:55.060" Score="1" Body="&lt;p&gt;The effective aperture can be expressed in terms of the antenna's gain:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$A_e=\frac{\lambda^2 G}{4\pi}$$&lt;/span&gt;&#xA;where G is the &quot;linear&quot; value of gain, not the logarithm of a ratio expressed in decibels.&#xA;Assuming you are able to obtain the gain of your dipole array, this may be a more workable expression.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-15T18:29:55.060" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13309" PostTypeId="2" ParentId="13304" CreationDate="2019-04-15T18:37:21.547" Score="2" Body="&lt;p&gt;For some context, the relevant part of the &lt;a href=&quot;https://www.cv.nrao.edu/course/astr534/AntennaTheory.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;cited source&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The average collecting area is defined by&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \langle A_e \rangle \equiv {\int_{4\pi} A_e d \over \int_{4\pi}d}.$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The effective collecting area of a receiving antenna is independent of its radiation environment, so this result applies for any type of radiation, not just blackbody radiation.  Without using Maxwell's equations we have obtained the remarkable result true for &lt;em&gt;all&lt;/em&gt; lossless antennas:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \langle A_e \rangle = {\lambda^2 \over 4 \pi} \tag{3A6} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Any antenna, from a short dipole to the 100-m diameter Green Bank Telescope, has the same average collecting area &lt;span class=&quot;math-container&quot;&gt;$\langle A_e \rangle$&lt;/span&gt;  that depends only on wavelength.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;In the case of an isotropic antenna, the effective collecting area in any direction equals the average collecting area:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ A_e(\theta, \phi) = \langle A_e \rangle = {\lambda^2 \over 4 \pi} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The description follows after a description about thermodynamic equilibrium and this illustration:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pVvgJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pVvgJ.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;A cavity in thermodynamic equilibrium at temperature &lt;span class=&quot;math-container&quot;&gt;$T$&lt;/span&gt; containing a resistor &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; is coupled to an antenna, also at temperature &lt;span class=&quot;math-container&quot;&gt;$T$&lt;/span&gt;, through a filter passing frequencies in the range &lt;span class=&quot;math-container&quot;&gt;$\nu$&lt;/span&gt; to &lt;span class=&quot;math-container&quot;&gt;$\nu+d \nu$&lt;/span&gt;.&lt;/em&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The discussion involves the thermodynamic equilibrium between the resistor and the antenna. This &amp;quot;average collecting area&amp;quot; is describing what should be fairly intuitive: this equilibrium holds regardless of what kind of antenna is put in the left cavity.&lt;/p&gt;&#xA;&lt;p&gt;In other words, the average collecting area has something to do with how the antenna responds, &lt;em&gt;on average&lt;/em&gt;, over all directions. It must be the same for all lossless antennas because anything else would violate conservation of energy.&lt;/p&gt;&#xA;&lt;p&gt;Note the average collecting area is &lt;span class=&quot;math-container&quot;&gt;$\langle A_e \rangle$&lt;/span&gt;. Just &lt;span class=&quot;math-container&quot;&gt;$A_e$&lt;/span&gt; on its own is &lt;em&gt;effective aperture&lt;/em&gt;, which has an additional term &lt;span class=&quot;math-container&quot;&gt;$G$&lt;/span&gt; added for gain:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ A_e = {\lambda^2 G \over 4 \pi} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Gain is often given as a single number, just the maximum gain for the antenna. But more completely, gain is defined as a function over direction and polarization. Since the average collecting area is the same for any lossless antenna design, and the effective aperture is the average collecting area multiplied by gain, it follows that if gain is to be increased in some direction, it must necessarily be decreased in some other direction if no laws of thermodynamics are to be broken.&lt;/p&gt;&#xA;&lt;p&gt;For an array of &lt;span class=&quot;math-container&quot;&gt;$N$&lt;/span&gt; antennas, the effective aperture is at best &lt;span class=&quot;math-container&quot;&gt;$N A_e$&lt;/span&gt; where &lt;span class=&quot;math-container&quot;&gt;$A_e$&lt;/span&gt; is the effective aperture of a single antenna. In practice it's less, due to either limited performance of the correlators, or due to overlap between the fields of the antennas.&lt;/p&gt;&#xA;&lt;p&gt;If the antennas are several wavelengths apart, then the interactions between them will be negligible and performance will be dominated by the correlators.&lt;/p&gt;&#xA;&lt;p&gt;If the antennas are closer than that, mutual coupling between them must be considered. The interactions are not simple or amenable to a closed form solution, so usually some &lt;a href=&quot;http://www.arrl.org/antenna-modeling&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna modelling software&lt;/a&gt; is used to solve the equations numerically.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-04-15T19:19:02.370" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="13313" PostTypeId="1" AcceptedAnswerId="14432" CreationDate="2019-04-16T12:38:24.137" Score="3" ViewCount="236" Body="&lt;p&gt;I have updated this question to make it simpler because i haven't seen an acceptable answer yet.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;New Question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance seen at any point on a transmission line is E/R. If the SWR isn't 1:1 then the impedance changes along the length of the line. Does the departure away from 50 +j0 ohms of the impedance on the transmission line caused by the SWR not being 1:1 affect the accuracy of a SWR meter which is designed to work at 50 + j0 ohms ?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;A swr meter is designed to work with a specific impedance transmission line, that usually being 50 ohms. The meter is calibrated to be correct for 50 ohms and it won't read correctly if the transmission line impedance isn't 50 ohms and won't read anything if there's no RF current flowing along the transmission line. And a 50 ohm transmission line has a characteristic impedance of 50 ohms. But the real impedance seen by the swr meter when there is RF current is E / I which is not the same as the characteristic impedance, in particular when there is a mismatch between transmission line and antenna where the impedance seen on the transmission line becomes a function of the frequency and changes along the length of the line. So then if the swr meter only reads accurately when the impedance is 50 ohms, it wont read correctly if the swr isn't perfect and the reading will change if you move the meter along the transmission line because the actual impedance seen by the meter and as determined by E / I is also changing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is that right ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does that also mean if the swr isn't perfect and E / I isn't 50 ohms at the swr meter then there will be secondary reflections at the swr meter ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-05-27T22:55:31.040" LastActivityDate="2020-12-21T22:02:11.380" Title="What is the main source of error for SWR meters?" Tags="&lt;transmission-line&gt;" AnswerCount="2" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="13314" PostTypeId="2" ParentId="13289" CreationDate="2019-04-16T15:36:58.817" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The space I have pretty much requires the loop to enclose the house [...] How will the steel roof (about 5x20 meters) affect the radiation of an 80m loop?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Although such antenna may work, personally I wouldn't expect it to have an overwhelming performance. From what I know a loop antenna radiates perpendicularly to the plane of the antenna which means it will radiate 50% of the energy to the ground and 50% - to zenith. Thus on 80m only short distance communication will be possible. Also I hope you are aware that a multiband loop antenna requires a tuner (you didn't mention whether you have one).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a tuner my advice would be to give up 80m (who needs 80m anyway? :D) and build a 40m vertically polarized vertically oriented delta loop. Unlike horizontally polarized delta, vertically polarized delta has to be placed only ~2m above the ground to be suitable for long-distance communication. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've &lt;a href=&quot;https://eax.me/delta-loop-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;tried&lt;/a&gt; such an antenna not a long time ago, here is a scheme:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iHRRQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iHRRQ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It works on HF bands from 80m to 10m, although it's not very efficient on 80m. I used a 10m fiberglass fishing rod as a mast which costs ~45$ on eBay. As I understood you have trees near your house thus probably you don't need a mast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Note: For 80m double the length of the loop, the distance from the ground and the mast height.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option that doesn't require a tuner is to &lt;a href=&quot;http://degood.org/coaxtrap/&quot; rel=&quot;nofollow noreferrer&quot;&gt;build a trap dipole&lt;/a&gt;. &lt;a href=&quot;https://eax.me/diy-trap-dipole/&quot; rel=&quot;nofollow noreferrer&quot;&gt;I've built&lt;/a&gt; such a dipole for 20, 40, 80m bands once. The antenna turned out to have total length 27.5m. It also worked on 10/12/15/17/30m bands with SWR about 2. It's enough to place the balun about 6-7 meters above the ground, although for better performance on 80m it's better to place it higher.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sbbFk.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sbbFk.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this will help. Good luck and 73!&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-10-09T09:02:35.987" LastActivityDate="2019-10-09T09:02:35.987" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="13315" PostTypeId="2" ParentId="7376" CreationDate="2019-04-16T19:40:07.037" Score="1" Body="&lt;p&gt;If you're wondering about the max RF input for your IC-706MK2G specifically, the &lt;a href=&quot;http://www.repeater-builder.com/icom/pdfs/ic-706mk2g-svc-man.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;service manual&lt;/a&gt; has a warning on the first page about it (not to exceed 20 dBm).&lt;/p&gt;&#xA;" OwnerUserId="12939" LastActivityDate="2019-04-16T19:40:07.037" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13316" PostTypeId="1" AcceptedAnswerId="13317" CreationDate="2019-04-17T11:28:22.173" Score="2" ViewCount="1232" Body="&lt;p&gt;I am new to amateur radio, and I'm trying to learn the basics of the hobby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to build a simple radio transceiver from scratch (i.e. not from a kit).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have searched the Internet for references, but most of them seem complicated and costly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what is the best kind of radio to look at building? From my searches I found that many people are recommending &lt;em&gt;QRP&lt;/em&gt; radios. But even in that area of the hobby there are many variants.&lt;/p&gt;&#xA;" OwnerUserId="14723" LastEditorUserId="8717" LastEditDate="2019-04-18T19:50:25.317" LastActivityDate="2019-04-19T20:23:50.687" Title="What is a simple kind of amateur radio transceiver I could try to build, as a beginner?" Tags="&lt;diy&gt;&lt;transceiver&gt;&lt;equipment-design&gt;&lt;equipment&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13317" PostTypeId="2" ParentId="13316" CreationDate="2019-04-17T12:01:16.187" Score="1" Body="&lt;p&gt;Assuming you want to build from a kit, the simplest kits will be those that use a minimum number of components, avoid having to wind coils, and have only through-hole component mounts.  On that basis, and from my own recent experience building one, I'd recommend a Cricket (QRP CW transceiver, includes a built-in key).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Cricket series (they've been available at various times on 80, 40, 30, and 20m bands) have the inductors etched directly on the circuit board, so you don't have to wind coils or mount toroids.  They're crystal controlled, using a common crystal type that's readily available.  They put out roughly 1W on a fresh 9V battery.  Mine took just about two hours to assemble, taking my time and working one component at a time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The instructions are very good, almost Heathkit quality (individual check boxes for each component), though not perfect (they left out the step of actually installing the crystal, for instance).  There's an option to install a connector in place of the simple key to use an external key or keyer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't been able to try mine on the air, yet (I don't have an antenna -- need a BNC connector and some coax to connect to the wire I have), but the tests I can make with a frequency counter seem to indicate it's working.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However: For a beginner to build a radio (transmitter/receiver or combined transceiver) from scratch without already knowing how they work is hardly different from building a kit, except with poorer odds of success. Build kits (plural/multiple) first, learn how they work, then build a radio from scratch.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-04-17T15:54:54.103" LastActivityDate="2019-04-17T15:54:54.103" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13318" PostTypeId="1" AcceptedAnswerId="13325" CreationDate="2019-04-17T12:11:19.850" Score="1" ViewCount="118" Body="&lt;p&gt;I'm a student and new to amateur radios. Is it legal to operate ham radios for educational purposes without any license?&lt;/p&gt;&#xA;" OwnerUserId="14723" LastEditorUserId="13598" LastEditDate="2019-04-17T16:21:50.360" LastActivityDate="2019-04-17T16:21:50.360" Title="Is it legal to operate Ham Radios for educational purposes" Tags="&lt;legal&gt;&lt;india&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13319" PostTypeId="1" CreationDate="2019-04-17T12:20:19.977" Score="1" ViewCount="436" Body="&lt;p&gt;Using &lt;code&gt;rpitx&lt;/code&gt;, we can transmit SSB using a single GPIO port from the Raspberry Pi. This of course uses square waves so creates a lot of harmonics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were to use a couple of daisy-chained 70 cm bandpass filters on the GPIO output, would there be any harm in using this output for ham radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My aim would be to either connect it up to a PA, or to an upconvertor to go to 2.4 GHz for Es'hail-2 usage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that it wouldn't be the &quot;cleanest&quot; signal, but would be be legal and usable?&lt;/p&gt;&#xA;" OwnerUserId="14615" LastEditorUserId="76" LastEditDate="2019-04-17T17:01:00.200" LastActivityDate="2019-04-24T20:08:23.467" Title="Raspberry Pi rpitx for SSB with filter?" Tags="&lt;equipment-design&gt;&lt;ssb&gt;&lt;filter&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13321" PostTypeId="2" ParentId="13318" CreationDate="2019-04-17T12:45:22.183" Score="1" Body="&lt;p&gt;Hmm, I want to say no. Here is why. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you answer is clear if you intended to operate and radiate then yes regardless if it is educational or not then you need to get a license. &lt;/p&gt;&#xA;" OwnerUserId="12988" LastActivityDate="2019-04-17T12:45:22.183" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13322" PostTypeId="2" ParentId="13318" CreationDate="2019-04-17T12:57:42.950" Score="3" Body="&lt;p&gt;The purpose for licensed ham radio in and of itself is education (whether for self or others), experimentation and for recreation. So yup, to transmit, you'll need a license (at least for the US and UK).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can, however, listen to ham broadcasts without a license (at least in the UK, where I'm familiar with the laws)&lt;/p&gt;&#xA;" OwnerUserId="14615" LastActivityDate="2019-04-17T12:57:42.950" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13323" PostTypeId="1" AcceptedAnswerId="13324" CreationDate="2019-04-17T14:53:43.077" Score="6" ViewCount="1324" Body="&lt;p&gt;My question is the title itself: what is homebrew (or home brewing)? And how do homebrews differ from ordinary ham radios?&lt;/p&gt;&#xA;" OwnerUserId="14723" LastEditorUserId="76" LastEditDate="2019-04-17T16:59:52.320" LastActivityDate="2019-07-04T05:29:26.413" Title="What is homebrew?" Tags="&lt;diy&gt;&lt;jargon&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13324" PostTypeId="2" ParentId="13323" CreationDate="2019-04-17T15:10:27.920" Score="12" Body="&lt;p&gt;Homebrew is (as the name suggests) when you make your equipment yourself, as opposed to buying it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An amateur setup consists of many components - the largest and most complicated of which are a radio transceiver (or separate receiver and transmitter), and the antenna. A power supply is also needed, but these are relatively inexpensive compared to the cost of other components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many people use a homebrew antenna, as it’s relatively straightforward to make a simple dipole and all it really costs is some wire and a balun. However, building a transceiver is a much more daunting task, unless you’re happy to stick with a single band and QRP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people became radio amateurs literally because they wanted the challenge of building large complex electronics projects that they could maintain and improve, while using the equipment on a daily basis. However, for us mere mortals it is beyond most people’s ability without a long time of research and learning, when you can spend money and get a reliable working radio.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-04-17T15:10:27.920" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13325" PostTypeId="2" ParentId="13318" CreationDate="2019-04-17T15:24:43.903" Score="3" Body="&lt;p&gt;As mentioned in a comment, if you ask a legal question you need to give us an idea of where you are. Please add a country tag.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However - this is one that’s not hard to answer without knowing where you are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, around the world, if you are to transmit as a radio amateur in any case apart from an actual emergency, then you need to be licensed in the country you are in when you transmit. Or have an amateur radio licence from a country that has agreements with the country you are in when you transmit that specifically allow you to do that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It’s not like software licensing where you have to buy an expensive license but it’s “free for educational purposes”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to transmit, you need a licence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many reasons for this, which you will learn in detail as part of the process of getting your licence.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-04-17T15:24:43.903" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13326" PostTypeId="1" CreationDate="2019-04-17T16:45:10.977" Score="4" ViewCount="114" Body="&lt;p&gt;I am in the United States.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The title pretty much says it all. I am really into to building transmitters. It's even more fun for me than using them. I really have a lot of skills and would like to sell my own broadcast transmitters. Yes, I have a spectrum analyzer and can check to make sure they comply with specifications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that there is compliance testing that would have to be done (IE the transmitter would need to be sent to a lab for specification testing, etc.). This part I am pretty sure on, however I have no idea whether I need a license to build such transmitters or can I just contact some testing house and if it passes, I have a licensed transmitter. Is it that simple or do I need other licenses?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the name of any testing facilities would be appreciated, but that is outside the scope of the question.&lt;/p&gt;&#xA;" OwnerUserId="1817" LastEditorUserId="4665" LastEditDate="2019-04-17T23:11:18.653" LastActivityDate="2019-04-17T23:52:00.820" Title="How can I get a license to build broadcast transmitters?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;fcc&gt;&lt;testing&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13329" PostTypeId="2" ParentId="13326" CreationDate="2019-04-17T19:11:17.357" Score="1" Body="&lt;p&gt;Building doesn't require a license (though if you're planning to do it commercially, as seems to be the case, you may need to meet government safety standards, especially for the high voltages required on the finals).  Actually transmitting &lt;em&gt;would&lt;/em&gt; require a license of some sort -- not an amateur license, because you're almost certainly talking about building hardware that won't work in the amateur bands and will exceed the legal power limits (1.5 kW for most bands) for amateurs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dummy load and sufficient shielding might ensure you don't radiate enough power to need a license, but that's a hard thing to test without actually applying the power.  Otherwise, you're asking someone (albeit a skilled and trained someone) to test a previously untested high power, high voltage device for you.  This will not be cheap.  It may not even be possible.  Companies that build transmitters for broadcasters typically have their own testing facilities and engineers; for that reason, you may not find anyone with the qualifications and equipment to can/will do the testing you want.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-17T19:11:17.357" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13330" PostTypeId="2" ParentId="13326" CreationDate="2019-04-17T23:10:33.463" Score="3" Body="&lt;p&gt;As implied in other comments and answers, this sounds like it would be legal to do (we’re all assuming you’re in the USA, given the fcc tag), since all you are doing is building equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you want to sell the equipment once you have built it, that is going to be more difficult.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would ask you the question - why &lt;em&gt;broadcast&lt;/em&gt; equipment specifically? You say in a comment that you really want to build high-quality exciters, and not multi-kilowatt behemoths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My suggestion to you would be to get an amateur radio licence (not difficult, especially if you’re already ‘into’ electronics and have an interest in radio) and build high-quality &lt;em&gt;amateur&lt;/em&gt; radio transmitters/amplifiers/etc. - that way, you could test them out yourself, use them in your own shack, and even sell them to other amateurs. There is no type-approval (as such) for amateur radio equipment, although the usual checks for spurious and out-of-band emissions that you mention would have to be done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It could be the start of a business - there are a few small companies that specialise in amateur radio transmitters and amplifiers already, but more are always welcome. Especially those that are made in the USA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Plus it would have the advantage that you would be able to get experience in building equipment across a huge range of frequencies, not just the usual broadcast frequencies currently in use.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-04-17T23:10:33.463" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13331" PostTypeId="2" ParentId="13326" CreationDate="2019-04-17T23:45:22.517" Score="3" Body="&lt;p&gt;No license is required to build broadcast transmitters in the United States.  To get approval to sell your transmitters in the US, you would most likely need FCC authorization.  The process to get that authorization is covered by &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=be7dbb5d84aa010f5ed384dea0fcf1cd&amp;amp;mc=true&amp;amp;node=pt47.1.2&amp;amp;rgn=div5&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR part 2&lt;/a&gt;, and is summarized on &lt;a href=&quot;https://www.fcc.gov/engineering-technology/laboratory-division/general/equipment-authorization&quot; rel=&quot;nofollow noreferrer&quot;&gt;this FCC web page&lt;/a&gt;.  I'll summarize further:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Determine FCC Rules that Apply.  Determine if device is a Radio Frequency (RF) device subject to the FCC rules.&lt;/li&gt;&#xA;&lt;li&gt;Equipment Authorization Procedures. If a device is subject to FCC rules, determine the specific type of equipment authorization that applies to the device.  Devices subject to the rules require either the Supplier’s Declaration of Conformity (SDoC) procedure, or the Certification procedure.&lt;/li&gt;&#xA;&lt;li&gt;Compliance Testing. SDoC-procedure devices don't need to be tested by an FCC-recognized accredited testing laboratory, but thorough records must be kept.  For Certification-procedure devices, an FCC-recognized and accredited testing laboratory must be used.  There is a search form for accredited testing laboratories &lt;a href=&quot;https://apps.fcc.gov/oetcf/eas/reports/TestFirmSearch.cfm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Approval.  Finalize the approval process based on the applicable approval procedure.  For the SDoC procedure, the manufacturer warrants that the devices comply with the rules, keeps all the applicable records, and prepares a compliance information statement to be supplied with the product at the time of marketing.  For the Certification procedure, the responsible party must apply for an FCC Registration Number (FRN).  Then the responsible party must apply for a Grantee Code by applying at the Grantee Registration website.  Then the responsible party files an application for a grant of certification with a Telecommunication Certification Body (TCB), which is a third party designated by the FCC.  Assuming all goes well, the TCB then issues a grant of certification on the FCC Equipment Authorization Electronic System (EAS) database.&lt;/li&gt;&#xA;&lt;li&gt;Label/Manual/Record Retention. Label the product and provide the required customer information, and keep all the records mandated by law.&lt;/li&gt;&#xA;&lt;li&gt;Manufacture/Import/Market.  Finally you get to sell stuff!&lt;/li&gt;&#xA;&lt;li&gt;Modifications to Approved Products. Changes to your product design may require  additional approval, which is covered by a separate process.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So there you have it.  Designing a product you'd like to sell is just the beginning.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-04-17T23:45:22.517" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13332" PostTypeId="2" ParentId="13316" CreationDate="2019-04-18T01:06:34.173" Score="3" Body="&lt;p&gt;You say you are &quot;not supposed to build with a kit&quot;. Who has set this limitation? This is beginning to sound like a homework assignment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are you actually expected to design and build a radio receiver and transmitter without looking at other people's prior work? And on top of this, you say in another question that you do not have an amateur radio licence, which means that while you can build and test a radio receiver (and use it on the air to make sure it works as expected), you would not be able to test a transmitter, outside of connecting it to a dummy load and making sure that no radio waves are actually transmitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My recommendation would be to get an amateur radio licence, and use the knowledge that you gain from that process to design a simple transmitter first. You only need to transmit a few milliwatts, to show a proof of concept. (Internally, this is what all commercial transmitters do - generate the signal at a very low level, then put it through a preamplifier and a final power amplifier [PA] stage).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recommend building a transmitter first, simply because it is &lt;strong&gt;much&lt;/strong&gt; easier to build a CW transmitter (that you would use to transmit Morse code) than it is to build even a simple receiver - a transmitter is basically an oscillator with a buffer, and some cleverness so it does not drift in a range of input voltage conditions. It can be a single frequency using a crystal for stability to start with, and you could later replace it with a VFO (a &lt;em&gt;variable frequency oscillator&lt;/em&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Building a receiver would be slightly more complicated, unless you wanted to try a TRF (Tuned Radio Frequency) receiver to receive AM. Unfortunately, receiving CW or SSB is a little more complicated, as they require mixers and the like. But again - build something simple first, and work your way up to something more usable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Limiting yourself to not using a kit really does make it more tricky, but if this is an assignment then you have to work within those parameters. If you really &lt;strong&gt;can't&lt;/strong&gt; use a kit, then how about looking at the circuit diagram of a kit, and see if you can redesign it slightly to fit your purposes. Technically it's probably cheating, but it could be argued that asking a load of people on the internet is cheating as well, so ...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; I noticed on your profile that you are a keen programmer. Another aspect of amateur radio that is becoming more popular, and now has mainstream hardware available, is that of the Software Defined Radio (SDR).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several commercially-built amateur radio transceiverss that have a traditional user interface (knobs and buttons), but underneath they are pure software. Good examples are the Icon IC-7300 and the Icom IC-7610. These radios are extremely popular, largely because of the flexibility that an SDR can provide, but still having a 'traditional' user interface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Building SDR receivers is so trivially simple, with such inexpensive parts, that I would recommend that you have a look at some of these just to see if there is anything you can learn from them. Transmitters are not horribly complicated, but there is a lot to do about filtering that would need some care.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2019-04-18T02:54:26.707" LastActivityDate="2019-04-18T02:54:26.707" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13334" PostTypeId="1" CreationDate="2019-04-18T05:24:48.033" Score="5" ViewCount="574" Body="&lt;p&gt;I am building the antenna for the first time and I have choosen to start with 40m inverted-v. I am almost done with the center insulator made of PVC piping elements, three eye hooks and SO 239 connector at the bottom. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I am getting ready to measure and attach legs and I have a bit of a question here. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found an online calculator and according to it, for 40m Inverted-V with 22 degrees angle from horizontal, each leg should be around 31ft 10inch. Now I am trying to figure is that the distance between the eye hook on center insulator and end insulator or that is the total length of wire that should be used. I am working on the theory that I will need around 10 inches of wire to tie it to both ends so if I were to use the exact length of wire, the distance between the center point and end insulator would be a bit shorter? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is my dipole leg length the actual length of wire used or the distance between the center point and end insulator.&lt;/p&gt;&#xA;" OwnerUserId="14274" LastActivityDate="2019-04-19T04:16:55.833" Title="How to measure wire for antenna leg | 40m inverted V" Tags="&lt;hf&gt;&lt;inverted-vee&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13335" PostTypeId="2" ParentId="13334" CreationDate="2019-04-18T06:02:12.940" Score="5" Body="&lt;p&gt;If I were making an antenna like that, I would add the extra 10&quot; (25cm) first anyway, because when you come to tune it it's much easier to trim the wire than it is to add wire to it later.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, because the antenna is an inverted V (a kind of dipole - a balanced antenna) and you are using coaxial cable to feed it, you should consider using a &lt;strong&gt;balun&lt;/strong&gt; at the feedpoint. This will effectively stop the outside of the coax from carrying unwanted (common-mode) currents and being part of the antenna, and will help keep RF out of the shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;: To answer the question, it is my understanding that it's basically the length of the wire between the centre and the tip of each leg, and any additional wire you use to tie it off or to wrap around an anchor does not count in the length calculation.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-04-18T06:02:12.940" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13336" PostTypeId="1" AcceptedAnswerId="13338" CreationDate="2019-04-18T08:31:50.333" Score="1" ViewCount="329" Body="&lt;p&gt;I want to use the *.ogg files available in &lt;a href=&quot;https://network.satnogs.org/observations/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Satnogs&lt;/a&gt;' database to test demodulation software for several satellites (using gnuradio).&lt;/p&gt;&#xA;&lt;p&gt;Can I use the &lt;strong&gt;ogg file source&lt;/strong&gt; (available in gr-satnogs module) and transform its output to complex data and then do the signal processing as if I were using raw IQ data coming from an SDR? And in this case, what sample rate is suitable in the &lt;strong&gt;throttle&lt;/strong&gt; block ?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y9PGB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y9PGB.png&quot; alt=&quot;gnuradio ogg file source&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Or, if not possible, should I convert the *.ogg file first to a *.raw file, using &lt;a href=&quot;http://sox.sourceforge.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;sox&lt;/a&gt; for example (Sound eXchange program) and then use it in GNU Radio? In this case, what are the parameters (input file sample rate, output file sample rate, encoding, sample size in bits, etc ...) i must use ?&lt;/p&gt;&#xA;" OwnerUserId="11517" LastEditorUserId="8573" LastEditDate="2020-12-18T00:45:23.360" LastActivityDate="2020-12-18T00:45:23.360" Title="Using Satnogs' *.ogg files in GNU Radio flowgraphs" Tags="&lt;software-defined-radio&gt;&lt;satellites&gt;&lt;gnuradio&gt;&lt;dsp&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13337" PostTypeId="2" ParentId="13316" CreationDate="2019-04-18T11:51:36.760" Score="1" Body="&lt;p&gt;Since you (based on comments) know your way around electronics and have built radios, building ham equipment should be a walk in the park -- and more or less parallels my own plans (which, due to personal preference, will use vacuum tubes, aka &quot;valves&quot;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What &lt;em&gt;I&lt;/em&gt; intend to do is to start with a simple one-tube regenerative receiver.  This can be built for any band you like, can use a transistor (or more than one) in place of the tube, and has the potential, if well built, to give excellent sensitivity and good selectivity (you can add a filter to the input if you find you need a narrower band for CW, for instance).  When operated at the edge of oscillation, a regen can receive CW or SSB without a separate BFO, and an RF preamp stage will prevent radiating on the tuned frequency when the set is in oscillation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once that's built, a simple one- or two-tube transmitter (again, alternatively with a small number of transistors) is easy to build -- for low power, it can be as simple as a tuned RF oscillator and keying circuit connected to your antenna.  All of this can potentially be done with three or four tubes or transistors -- RF and detector/regenerator for the receiver, oscillator and optional output buffer/amp for the transmitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look online for designs from the 1920s to 1930s; these will be simple radios that use triodes (though they can also be built with more modern tetrode or pentode tubes, FETs, or bipolar transistors, with a little modification).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-18T11:51:36.760" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13338" PostTypeId="2" ParentId="13336" CreationDate="2019-04-18T15:07:56.410" Score="2" Body="&lt;p&gt;(This answer is from the perspective of GNU Radio programming; I'm not familiar with what SatNOGS is doing.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two problems to solve to use a given data file. First, you need to decode the file format into samples of a signal. The OGG File Source presumably solves this problem for you. Converting the file to a raw format is also an option, but not necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, you need to &lt;em&gt;interpret the signal correctly.&lt;/em&gt; And here is where I can fairly confidently say you are going wrong:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Converting float to complex with a zero imaginary part (as seen in your proposed graph) results in a signal with a spectrum which is symmetric about 0 Hz. This is not necessarily wrong, but it is definitely &lt;em&gt;not&lt;/em&gt; an IQ / complex-baseband signal, which would be expected to have an asymmetric spectrum — and converting such a signal to real/float for storage would either destroy its content or require a frequency shift step to put all of the signal in positive frequencies. &lt;strong&gt;Converting float to complex is almost certainly not a correct processing step.&lt;/strong&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Ogg is a container for &lt;em&gt;audio&lt;/em&gt; data. It is theoretically possible but unlikely that it has been applied here to IQ RF signals; it is much more likely, whenever you see an audio-formatted radio recording, that it is a recording of the signal &lt;em&gt;after some demodulator&lt;/em&gt; — most commonly a FM demodulator. For example, a signal transmitted as FSK will show up in the &quot;audio&quot; data with varying level (a square wave / pulse train) instead of varying frequency.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;My recommendation would be to first &lt;em&gt;look at the signal&lt;/em&gt; (using for example the &quot;QT GUI Sink&quot; block connected after the Throttle) and identify the modulation (or lack thereof), and use that to decide what to add to your signal processing chain.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-04-18T15:07:56.410" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13339" PostTypeId="2" ParentId="13334" CreationDate="2019-04-18T16:08:44.873" Score="3" Body="&lt;p&gt;The length is measured between the center and the end insulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd further add: don't overthink it. Common practice is to cut the wire a bit long, then iteratively make it shorter until you get a good match at your target frequency. Things like proximity to ground or other conductive objects can cause some deviation from the idealized conditions used by generic calculators, so an iterative empirical approach is often best.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-18T16:08:44.873" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13340" PostTypeId="2" ParentId="13334" CreationDate="2019-04-18T16:43:11.870" Score="1" Body="&lt;p&gt;The formula for calculating the end-to-end length of a half-wavelength center-fed dipole is&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;in feet: 468÷f&lt;/li&gt;&#xA;&lt;li&gt;in meters: 143÷f&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;where f=frequency in MHz. That is measured &quot;from loop to loop&quot;; that is, after the extra wire you allow for the wire loops inside the end insulators is twisted back on itself and soldered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Between the &lt;em&gt;center of the center insulator to each end&lt;/em&gt; is 1/2 of this dimension, the &quot;leg&quot; as you asked.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using that has always got me very close to resonance, if not right on. However, as others have stated, you may want to leave extra. But I never have.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-18T19:44:30.107" LastActivityDate="2019-04-18T19:44:30.107" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13341" PostTypeId="2" ParentId="13319" CreationDate="2019-04-18T18:18:39.027" Score="3" Body="&lt;p&gt;Two daisy-chained bandpass filters might clean up your SSB signal enough to be legal, or they might not.  Much depends on the design of the bandpass filters, of course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you should do is to get help from someone with the equipment (a suitable dummy load and a spectrum analyzer, primarily) and expertise who can measure the important parameters of your signal to determine if it would be clean enough to be legal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You wouldn't want to just cross your fingers and hope that such a signal is clean enough, and then amplify it and point it at a satellite.  If your signal were dirty, then you would be a nuisance to everyone else using the satellite on the same band, and possibly to other people trying to use other bands as well.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-04-18T18:18:39.027" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13342" PostTypeId="2" ParentId="13313" CreationDate="2019-04-18T19:44:23.583" Score="1" Body="&lt;p&gt;If a properly designed (Bruene) and calibrated SWR meter is used in the Z0=50 ohms environment for which it is calibrated, it will read the actual SWR on 50 ohm coax (to a certain degree of accuracy). If it is used in a different Z0 environment, it will indicate the SWR that would exist if the environment was equal to the Z0 for which it is calibrated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the actual SWR on a piece of 300 ohm transmission line is 1:1, an SWR meter calibrated for 50 ohms will indicate an SWR of 6:1. If the V/I ratio at a point on a piece of 300 ohm transmission line is 50+j0 ohms, the 50 ohm SWR meter will read 1:1 at that point. Note that phasor addition and subtraction of the voltage and current samples are used in the process of obtaining the SWR reading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the SWR meter is properly designed and calibrated for 50 ohms, the assumption by the designer is that &lt;span class=&quot;math-container&quot;&gt;$Vfor/Ifor = 50+j0 ohms$&lt;/span&gt; and that &lt;span class=&quot;math-container&quot;&gt;$Vref/Iref = 50+j0 ohms$&lt;/span&gt;. Thus if a 50 ohm SWR meter is used in a 50 ohm environment, the SWR reading is &quot;accurate&quot;.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-04-19T13:04:33.713" LastActivityDate="2019-04-19T13:04:33.713" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13343" PostTypeId="1" AcceptedAnswerId="13359" CreationDate="2019-04-19T01:04:20.763" Score="5" ViewCount="115" Body="&lt;p&gt;I have an old TenTec Argosy II that hasn’t been powered up for 20 years. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How long can electronics go unpowered before I have to worry about the electrolytic needed a slow power up with a Variac? &lt;/p&gt;&#xA;" OwnerUserId="528" LastEditorUserId="4076" LastEditDate="2019-04-19T18:46:47.113" LastActivityDate="2019-04-22T21:00:20.763" Title="How long can a transceiver be unused before I have to use a variac?" Tags="&lt;transceiver&gt;&lt;equipment-operation&gt;&lt;maintenance&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="13344" PostTypeId="1" AcceptedAnswerId="13346" CreationDate="2019-04-19T01:45:17.820" Score="14" ViewCount="4300" Body="&lt;p&gt;I wonder, even in this modern generation why the outdated vacuum tubes are used. In other electronic circuits they have been replaced by more efficient (and small) transistors years ago. Why they are still used?&lt;/p&gt;&#xA;" OwnerUserId="14723" LastEditorUserId="76" LastEditDate="2019-04-19T02:03:12.383" LastActivityDate="2019-07-01T19:47:26.523" Title="Why are vacuum tubes still used in amateur radios?" Tags="&lt;equipment-design&gt;&lt;history&gt;&lt;vacuum-tubes&gt;" AnswerCount="6" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13345" PostTypeId="2" ParentId="13344" CreationDate="2019-04-19T02:15:16.910" Score="10" Body="&lt;p&gt;As far as I know, vacuum tubes are used in newly-manufactured radio equipment (as opposed to still-in-use old equipment) for one purpose: &lt;strong&gt;high-power amplifiers.&lt;/strong&gt; The advantages of vacuum tubes in this application are essentially from the fact that the tube can be built as a large and sturdy device.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Semiconductor devices may fail due to overheating which changes the properties of the semiconductor material in ways which lead to further heating and destruction; vacuum tubes can run hot and be made of large metal structures which are more robust against heat &lt;em&gt;and&lt;/em&gt; can conduct it away to external heat sinks more readily.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Semiconductor devices may fail due to excessive voltage across them, and improving voltage rating is a difficult engineering problem — vacuum tubes can have physically large elements which the high voltage would have to arc between (through vacuum) to cause failure. In RF applications, high voltages may arise at the output of an amplifier due to poor impedance matching — which can happen while in operation due to changing frequency or damage to the antenna or feed line.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-04-19T02:15:16.910" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13346" PostTypeId="2" ParentId="13344" CreationDate="2019-04-19T03:09:46.243" Score="15" Body="&lt;p&gt;The last mass-produced vacuum tube was the &lt;strong&gt;Cathode Ray Tube&lt;/strong&gt;, Thankfully those are now going the way of the dodo, replaced with much more practical LCD or OLED displays.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(&lt;strong&gt;Edit&lt;/strong&gt;: it turns out the magnetron is still mass-produced, for microwave ovens. Although apparently semiconductor replacements already exist, and soon the magnetron will go the way of the CRT.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, for some applications a vacuum tube is still more practical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Vacuum tubes are (by their nature) high voltage, low current devices; semiconductors are by contrast lower voltage, higher current devices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The failure mode for vacuum tubes in case of over-voltage is mostly arcing. This does damage the tube, but if it's caught in time it need not be catastrophic. Since the tube's components are made of metal, they tend to go up in resistance (thus limiting the current passing through them) as their temperature rises.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The failure mode for semiconductors tends to be self-destruction. Semiconductors have an awkward property that as they get hotter the resistance goes down, and this leads to thermal runaway, where the device gets hotter still, which lowers the resistance even more, until the device is destroyed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in a high-temperature environment, vacuum tubes can be more robust. And this especially applies in high-power applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where high-power amplifiers are made of semiconductors, they tend to run at around 50v and tens of amps. Where vacuum tubes are used, they tend to run in the hundreds of milliamps (which is a lot for a vacuum tube), but in the thousands of volts. The final result is the same because volts x amps makes watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this reason, you will still find transmitters around the world that use vacuum tubes (valves, as they are known in the UK), an example of which is highlighted in &lt;a href=&quot;https://www.theguardian.com/media/2011/oct/09/bbc-radio4-long-wave-goodbye&quot; rel=&quot;nofollow noreferrer&quot;&gt;this article about the BBC's long wave transmitters from 2011&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power semiconductors can be very expensive, especially ones that can work at high radio frequencies. It can still be cheaper to have an amplifier with one or two tubes as the 'final', with all the high voltage inside it, than it is to have a much lower voltage, safer semiconductor amplifier for amateur use. The tube amplifier will tend to be more robust, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wikipedia says something very similar about how tubes are more robust at higher powers, &lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_transmitter_design#Amplifying_the_signal&quot; rel=&quot;nofollow noreferrer&quot;&gt;on their page on radio transmitter design&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2019-04-21T01:17:17.457" LastActivityDate="2019-04-21T01:17:17.457" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="13349" PostTypeId="1" CreationDate="2019-04-19T07:05:02.927" Score="1" ViewCount="90" Body="&lt;p&gt;I was hit with a big arc of static from a metal door frame.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was a little over a foot away. It stung pretty good, then my coworker told me I was transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My baofeng uv5r will not stop transmitting unless I turn it off. I turn it on and as soon as it boots it starts transmitting again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All the buttons just make tones like a phone, but I can't get into menu or change channels or anything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After a little while she says &lt;em&gt;transmit overtime&lt;/em&gt; and cuts out, but I still can't unlock or access the menu.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried downloading with chirp but even that won't work. Vox is not on, and if I press the PTT button I can feel it click.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried a different battery too. De-soldering the PTT button doesn't solve the issue, either.&lt;/p&gt;&#xA;" OwnerUserId="14736" LastEditorUserId="4076" LastEditDate="2019-04-19T13:40:35.083" LastActivityDate="2019-04-19T13:40:35.083" Title="did static fry my uv5r?" Tags="&lt;baofeng&gt;&lt;transmitter&gt;&lt;uv-5r&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13351" PostTypeId="2" ParentId="13344" CreationDate="2019-04-19T11:18:21.850" Score="5" Body="&lt;p&gt;There's one more reason vacuum tubes are still used in &lt;em&gt;amateur&lt;/em&gt; radios: personal preference of the amateur building the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Speaking for myself, I understand what's going on inside a vacuum tube much more clearly and deeply than I do the internal physics of a transistor.  Further, it's much more comfortable (for me) to think in terms of increasing voltage to increase power output, than it is to find a way to increase current without burning something out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Put those factors together, and anything I build from scratch is almost certain to include tubes/valves, because that's where my comfort zone lies.  There's the possibility it will also include transistors, possibly even integrated circuits (because op amps and IC audio amps are so convenient and easy to use) -- but it will revolve around those triodes, tetrodes, and pentodes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Oh, one other reason for my preference for tubes: if a tube fails, you just wiggle it out of its socket and plug in a &quot;new&quot; one.  With transistors, it's hard to tell which one is bad, and you have to (at least) desolder the old one to replace it.  A new tube costs more than a new transistor, but to me, the ease of troubleshooting and replacement wins.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-19T11:18:21.850" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13353" PostTypeId="2" ParentId="13349" CreationDate="2019-04-19T11:26:30.600" Score="1" Body="&lt;p&gt;Sounds very much to me as if something connected to the PTT (the electronics that the physical switch activates) was damaged.  With what a BaoFeng costs, unless you're just curious, it's not worth putting much time into troubleshooting.  As a bonus, the battery you have appears to be okay, so you'll have a spare battery (which can be charged off the radio; it plugs into the desk charger just like the radio does).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-19T11:26:30.600" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13354" PostTypeId="2" ParentId="13344" CreationDate="2019-04-19T11:34:07.997" Score="9" Body="&lt;p&gt;Vacuum tubes are neither outdated nor less efficient.  See &lt;a href=&quot;https://spectrum.ieee.org/semiconductors/devices/the-quest-for-the-ultimate-vacuum-tube&quot; rel=&quot;noreferrer&quot;&gt;https://spectrum.ieee.org/semiconductors/devices/the-quest-for-the-ultimate-vacuum-tube&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above IEEE Spectrum article talks about a vacuum tube amplifier that is more efficient than any solid state amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is just one example of active research on vacuum tubes.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-04-19T11:34:07.997" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13356" PostTypeId="2" ParentId="7205" CreationDate="2019-04-19T14:04:47.157" Score="0" Body="&lt;p&gt;They can mount on surfaces a little thicker than 2.5mm, though I suspect the exact thickness varies by manufacturer. I was successful in mounting to a .125&quot; surface (3.2mm). The constraint was not so much the mounting surface thickness, but rather snaking the connector through the 0.75&quot; mounting hole in a too-thick plate. I had to add some cutouts to the mounting hole to get it to fit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question also asked if they can go as thick as 1/4&quot;.  For a &quot;common&quot; NMO antenna mount, no.  Thk 1/8&quot; is about the upper limit --and I do not recommend trying it-- due to the clearance in the non-adjustable section.  As mentioned by others, though, it is easy enough to buy NMO-compatible mounts which work with thicker surfaces.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2019-04-19T17:00:22.373" LastActivityDate="2019-04-19T17:00:22.373" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13357" PostTypeId="1" AcceptedAnswerId="13375" CreationDate="2019-04-19T14:24:31.580" Score="3" ViewCount="321" Body="&lt;p&gt;I built a bicycle antenna mount featuring an NMO connector to allow quick changes.  With a 2m 1/4 wave monopole it gives reasonable SWR results (1.4 or so in the band of interest), with a particular dual-band it gives reasonable SWR results (1.7 or so on 2m, 1.1 or so on 80cm), but with an 80cm 1/4 wave monopole SWR=3.2@450MHz, SWR=1.05@510MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 80cm 1/4 wave monopole has my attention.  It is a Childs Antenna Model QB 430.  It appears to be a well-made antenna and I believe it is operating properly.  The radiating element has a length of about 156mm which I think is about right for transmitting at 440MHz however with SWR ~=3 it seems odd.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My suspicion is that it has something to do with how the QB 430 antenna interfaces with the NMO mount, introducing some sort of capacitance at the feed point.  Photos are below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0v7qZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0v7qZ.png&quot; alt=&quot;Overall System&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1 - overall system.  The thick area around the feed line are ferrite beads, expected to provide 1000+ Ohms common mode impedance between 140MHz and 600MHz.  Feed line is apprx 480mm long, LMR 195 cable.  Feedline was moved for the photo so as to be more easily seen.  The implementation is that it runs along the center of the base plate staying in the plane of the wheels until under the rack, where it then runs to one side of the rack's bottom support.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qc9Z1.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qc9Z1.jpg&quot; alt=&quot;NMO mount with &amp;quot;problem&amp;quot; antenna on the left&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2 - NMO mount on the right, QB 430 antenna base on the left.  Because of the way the antenna interfaces with the mount, I use the brass disk for the interface; according the the NMO mount manufacturer, that disk is for HF antennas.  It is not obvious from the picture but the brass disk connects only to the center wire in the NMO mount however it is wide enough that perhaps capacitance is an issue.  At VHF and UHF there is a different mounting system (see Photo 3)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RkoeO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RkoeO.png&quot; alt=&quot;NMO mount with an antenna using a different interface&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3 - NMO mount on the right, dual-band antenna on the left.  This antenna uses an interface consistent with what the NMO mount manufacturer is expecting.  Notice the large brass disk is not present.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2qtLK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2qtLK.jpg&quot; alt=&quot;NMO mount with inverted brass disk&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4 - NMO mount with the brass disk (inverted, so the pin can be seen).  The pin fits in the center hole of the NMO, holding the brass disk in place.  The center hole mounting point is surrounded in plastic, this holds the brass disk 1 or 2 mm above the aluminum surroundings.  (EDIT:  I did not originally realize it, but there is an additional insulator I neglected to put on.  Sadly, putting it on does not make any difference.  The insulator is not shown in the photos.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could it really be the brass disk causing this problem?  If so, I guess it would be easy enough to just get a smaller one (where would I find one? There is a pin on the underside that mates to the NMO mount.)  If not, what else could be causing this?  Somehow the antenna seems to be electrically shortened, which points to a capacitance of some sort.  Maybe I can just add a matching network?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additional information:  The antenna analyzer shows some sort of resonance --presumably the feedline being a multiple of &lt;span class=&quot;math-container&quot;&gt;$\lambda/4$&lt;/span&gt;-- at 410MHz.  At 444MHz it seems to still be &quot;recovering&quot; from this resonance and the impedance is 36.2-j53&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;.  So maybe I just need to make the feedline longer or cut the antenna longer?  (I made small changes to the feedline; it does make a difference but none of the changes I made were big enough to make enough of a difference.)&lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2019-04-21T01:29:25.590" LastActivityDate="2019-08-11T00:27:30.423" Title="NMO bicycle mount antenna has unexpected SWR" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;transmission-line&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13358" PostTypeId="2" ParentId="13357" CreationDate="2019-04-19T17:23:24.210" Score="2" Body="&lt;p&gt;It appears that the coax is too close to at least one radial. That can and will detune it. Try moving the coax away from them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same thing could be true about the metal wheel and spokes. They could also be detuning the radials. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Raising the antenna would be one solution to the radial tuning, as might moving the radials if you can.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try elevating the antenna base plate --with the connector and radials-- higher with some threaded rod, nuts, and washers.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-19T20:02:51.263" LastActivityDate="2019-04-19T20:02:51.263" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13359" PostTypeId="2" ParentId="13343" CreationDate="2019-04-19T19:57:13.837" Score="2" Body="&lt;p&gt;There is no set time period. Play it safe, bring it up slowly and be done with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also put a ~100w incandescent lamp in series with the AC line (or better yet, a clamp-on AC current meter) as you bring up the voltage. If the capacitors are not bad, then the lamp should dim as the capacitors charge.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-04-22T21:00:20.763" LastActivityDate="2019-04-22T21:00:20.763" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13360" PostTypeId="2" ParentId="13316" CreationDate="2019-04-19T20:23:50.687" Score="1" Body="&lt;p&gt;Welcome to amateur radio! We hope that our hobby will form the basis for a long and enjoyable career in electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the most important factors when building your first radio is support, whether you are building from a kit or from &quot;scratch.&quot; In-person help from someone who has already built your project is the best, of course, while nearby or in-country support can be almost as helpful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In that spirit, I recommend the &lt;a href=&quot;http://www.hfsignals.com/index.php/ubitx/&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;BitX transceiver&lt;/a&gt; pioneered by &lt;a href=&quot;https://www.qrz.com/db/vu2ese&quot; rel=&quot;nofollow noreferrer&quot;&gt;VU2ESE&lt;/a&gt; in Hyderabad. I have several acquaintances who enjoyed building and &lt;em&gt;really&lt;/em&gt; enjoy using this rig.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To paraphrase Isaac Newton, &quot;If we see further, it is because we stand on the shoulders of Giants.&quot; Building a kit will help you learn practices for design and construction, which you can put to use when you decide how you can improve on what has come before.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck! &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-19T20:23:50.687" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13362" PostTypeId="2" ParentId="11776" CreationDate="2019-04-19T20:45:02.890" Score="1" Body="&lt;p&gt;This doesn't quite answer your question, but may get you closer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://store.mobilinkd.com/collections/tnc-cables/products/tnc-cable-for-yaesu-ft-25r-ft-65r&quot; rel=&quot;nofollow noreferrer&quot;&gt;This cable&lt;/a&gt; at Mobilinkd works on the FT-65R HT. They describe it as working with any radio that uses a uses a Motorola M1 style connector. You may be able to back into the information you want through that Motorola M1 lead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've actually had the same question myself, so I'll update this thread if I find more information.&lt;/p&gt;&#xA;" OwnerUserId="14089" LastActivityDate="2019-04-19T20:45:02.890" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13363" PostTypeId="1" AcceptedAnswerId="15394" CreationDate="2019-04-19T21:05:35.130" Score="2" ViewCount="1085" Body="&lt;p&gt;Hi I want to switch between tx and rx in a flow graph with my HackRF.&#xA;I found &lt;a href=&quot;https://www.youtube.com/watch?v=YTSI--d2UvQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;this video&lt;/a&gt; that shows how it could be done.&#xA;The key component is the Selector block which is now deprecated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is there a alternative way to the selector block method?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also found &lt;a href=&quot;https://github.com/mossmann/hackrf/issues/195&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; feature request. But the last comment is nearly 2 years old.&lt;/p&gt;&#xA;" OwnerUserId="6257" LastEditorUserId="873" LastEditDate="2019-04-22T02:49:59.270" LastActivityDate="2019-11-19T21:02:35.320" Title="GnuRadio alternative for Selector Block" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13364" PostTypeId="1" AcceptedAnswerId="13365" CreationDate="2019-04-19T23:43:22.520" Score="1" ViewCount="1037" Body="&lt;p&gt;If you look at the circuit diagram for a Colpitts crystal oscillator, it's pretty simple -- a crystal, load resistor, and capacitive voltage divider, with the positive supply feeding the control element (base of a transistor, or control grid of a vacuum tube) through a resistance, and the voltage between the capacitors tied to the negative supply side of the gain device (emitter of an NPN, or cathode/filament of a tube).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1ubay.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1ubay.gif&quot; alt=&quot;Colpitts Crystal Oscillator&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the equivalent of a crystal is a series inductance, resistance, and capacitance, in parallel with another capacitance -- a tuned circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/R9M4x.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/R9M4x.jpg&quot; alt=&quot;Crystal equivalent circuit&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems to me it ought to be possible to replace the crystal in a crystal oscillator circuit with a variable tuned circuit, to make a simple crystal-controlled radio work like one with a VFO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given I don't see a lot of people converting their Pixie or Cricket transceivers to be frequency mobile by doing this, I guess there's something I'm missing.  What prevents replacing the crystal with its equivalent circuit (containing variable induction and/or capacitance) to allow tuning an entire band with a radio made for crystal control?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-04-20T22:42:38.280" LastActivityDate="2019-04-20T22:42:38.280" Title="How to convert a crystal controlled tranceiver to VFO (aka Unbinding from the Rock)?" Tags="&lt;diy&gt;&lt;equipment-design&gt;&lt;vfo&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13365" PostTypeId="2" ParentId="13364" CreationDate="2019-04-20T02:14:58.493" Score="2" Body="&lt;p&gt;The &lt;a href=&quot;https://www.vintage-radio.info/download.php?id=141&quot; rel=&quot;nofollow noreferrer&quot;&gt;Heathkit HW-7&lt;/a&gt; offered the option of crystal or VFO control via front-panel pushbutton switch. Pierce crystal oscillator Q5 was repurposed as a buffer amplifier for use with a VFO by switching out the crystal in the feedback path from collector to base. Given all the modern options for generating stable signals, this seems like a good approach today, too.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-20T02:14:58.493" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="13366" PostTypeId="2" ParentId="13364" CreationDate="2019-04-20T06:47:17.310" Score="2" Body="&lt;p&gt;I'd frankly not replace the crystal with an oscillating circuit of adjustable resonance frequency, like you're recommending, but the whole oscillator: remove (the unlabeled) C3, and just insert the output of your complete VCO circuit there, AC coupled on its own.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just going from &quot;the crystal has a component-wise identical equivalent circuit&quot; to &quot;I can replace it with that circuit&quot; is a bit questionable: You're relying on a &lt;em&gt;simplified model&lt;/em&gt; of a crystal be functionally identical to the simplified model of a VCO – that might in many cases work, but it might require a lot of hand-tuning, or simply might not work. The phase response of a crystal is pretty sharp, and the lag you'll see in a RLC might simply not do it for the transistor together with C1,C2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, VCO circuits can be built that include an active part (e.g. at least one amplifying transistor) at little added complexity, but without the hoping and tuning. So, I'd do that, verify its operation in isolation, and then have a switch that switches between the original colpitts and the VCO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know this is not the &quot;market&quot; you're in, but I'd like to also point out how frequency-agile radios do it these days to have both crystal-grade frequency accuracy and VCO-grade adjustability whilst maintaining low harmonics: They use a fixed crystal as the primary source of frequency, then use adjustable frequency dividers (i.e. fast digital counters), fixed frequency multipliers (e.g. square the sine signal, e.g. with a diode, filter out harmonics) and adjustable frequency multipliers in control loops.&lt;br&gt;&#xA;The adjustable part is typically realized through having a VCO with a counter that counts the VCO cycles during reference cycles, and adjusts the VCO control voltage accordingly. For example: You have a 10 MHz crystal, you want to get a stable 88.88… MHz; you program your counter to count 9 crystal cycles until it emits one pulse at 1.11… MHz (that's 10 MHz / 9). Then your PLL is programmed to count the reference cycles in e.g. 80 VCO cycles; if that's less than 10, increase VCO voltage, if it's more, decrease.&lt;br&gt;&#xA;In reality, these devices can be even more complicated, and allow for non-rational ratios of in- to output frequency through the elegance of a bit of algebra.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-04-20T06:47:17.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13374" PostTypeId="2" ParentId="13344" CreationDate="2019-04-22T17:53:36.147" Score="0" Body="&lt;p&gt;Vacuum tubes are also used in audio amplifiers where some users feel that there is a better or more genuine sound from tube based amps. This is especially true in guitar amps where distortion tone and quality are highly sought after.&lt;/p&gt;&#xA;" OwnerUserId="14763" LastActivityDate="2019-04-22T17:53:36.147" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13375" PostTypeId="2" ParentId="13357" CreationDate="2019-04-22T22:23:37.340" Score="3" Body="&lt;p&gt;I'm just guessing here, but perhaps the problem is your ground plane.  Your Childs Antenna Model QB 430 is designed to be mounted to a motor vehicle that presumably offers a relatively-large ground plane perpendicular to the vertical antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your ground plane is different.  The main part of your ground plane, otherwise known as the bicycle frame, extends forward perpendicular to the antenna, but doesn't extend to the sides or to the back.  You have some elevated radials that do extend to the sides and the back a bit, but not perpendicularly; instead they seem to go more downward than outward.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wouldn't be surprised if the difference between a typical ground plane for that antenna and the ground plane that you're using explains the higher SWR.  You could test the theory by installing the antenna on a car or truck, and then measuring the SWR.  Perhaps someone at your local club has a car or truck with an NMO-mounted antenna that could be used for the test?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might consider trying an HT antenna, which is designed to operate with less of a ground plane.  An HT antenna would be less efficient than a mobile antenna of course, but I have a feeling that it would solve the SWR problem.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2019-04-23T13:20:16.883" LastActivityDate="2019-04-23T13:20:16.883" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="13376" PostTypeId="2" ParentId="9474" CreationDate="2019-04-23T00:13:54.710" Score="1" Body="&lt;p&gt;The UV-5R has a nominal battery voltage of 7.4V and the supplied charger provides 8.4V with 600mA current limit.  I believe this means the battery max charging voltage is 8.4 volts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Directly applying 9 volts would be risky.  Certainly make sure the current stays limited to a sane amount and certainly make sure the battery never gets charged above 8.4 volts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is easy enough to make a buck or boost circuit to transform 5 or 9 or 12 volts to 8.4.  This seems like a route you might want to go.  Google &quot;DIY Baofeng Charger&quot; for more ideas and check with EE Stack Exchange for safety information related to charging lithium batteries such as here: &lt;a href=&quot;https://electronics.stackexchange.com/questions/230155/why-is-there-so-much-fear-surrounding-lipo-batteries/230164#230164&quot;&gt;https://electronics.stackexchange.com/questions/230155/why-is-there-so-much-fear-surrounding-lipo-batteries/230164#230164&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2019-04-23T00:13:54.710" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13377" PostTypeId="1" AcceptedAnswerId="13381" CreationDate="2019-04-23T02:50:47.613" Score="7" ViewCount="144" Body="&lt;p&gt;For VHF and UHF, it seems reasonable to slip ferrite beads over a coaxial cable to act as a transmission line common mode choke.  It also seems reasonable to use beads with the smallest diameter possible.  This can lead to ferrite-over-cable lengths on the order of 250-400mm or more with a slip-fit ferrite cover.  Can this affect the cable's velocity factor or impedance?&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2019-04-23T12:40:19.387" Title="Can ferrite beads lower coax cable velocity factor?" Tags="&lt;coaxial-cable&gt;&lt;impedance&gt;&lt;transmission-line&gt;&lt;ferrite&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13378" PostTypeId="1" AcceptedAnswerId="13385" CreationDate="2019-04-23T04:24:09.693" Score="1" ViewCount="127" Body="&lt;p&gt;I have an &lt;a href=&quot;https://www.alphadeltaradio.com/pdf/DX-EE%20Jan%20QST-1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Alpha Delta DX-EE antenna&lt;/a&gt; in my attic. The antenna is 40 ft long and my attic is about 5ft high by 55 ft long. There's a lot of other stuff up there--a chimney, Romex, Cat 6 cable, RG-6 cable, a TV antenna, junction boxes, etc. It tried to place the antenna so anything metal was at least a foot away. I ran about 60 ft of LMR400 up to the attic (I soldered N connectors on it).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I borrowed a friend's brand new Icom IC-7300. He hadn't tried it before. I connected the chassis ground to the ground prong on an electrical outlet and connected the antenna to the radio with a PL259 to N adapter. We didn't have much success receiving any stations on any bands. I'm in the Pacific Northwest and the band conditions were roughly same as pictured below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/f61wA.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/f61wA.gif&quot; alt=&quot;band conditions&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Icom IC-7300 has a feature where it can make a bar-chart SWR plot. It transmits at 30W when doing so. I tried 10M and a believe a few other bands. No matter which frequencies I picked, all the bars in the chart were always pegged at an SWR of 3:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I recently tested my antenna (and feedline) with a &lt;a href=&quot;http://pocketvna.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;VNA&lt;/a&gt;. I only measured reflection on one port, however. These are my results (please ignore the phase plot--I got the feedline length compensation factor wrong):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Joisw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Joisw.png&quot; alt=&quot;return loss&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've marked the points with the lowest VSWR. The numbers are even better than in the review article I linked to above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why are my VSWR results so different between the radio and the VNA? Could a bad adapter cause this? I used a different N adapter for the VNA as opposed to the radio. Could this difference have anything to do with the radio operating at 30W and the VNA at -14 dBm?&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Edit - 23-Mar-2019&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;After reviewing K1LI's answer, here are zoomed in versions of the plot above that show his point. The house is a split-level with two stories at one end of the antenna and one story at the other. On the two-story end, the antenna is about 21 ft AGL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1fB50.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1fB50.png&quot; alt=&quot;40m&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/pf8Ma.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pf8Ma.png&quot; alt=&quot;20m&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/nEJ4j.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nEJ4j.png&quot; alt=&quot;15m&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/FTbSO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FTbSO.png&quot; alt=&quot;10m&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5820" LastEditorUserId="5820" LastEditDate="2019-04-23T15:42:14.790" LastActivityDate="2019-04-23T15:42:14.790" Title="How to interpret VSWR results for an attic antenna" Tags="&lt;hf&gt;&lt;wire-antenna&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="13379" PostTypeId="1" AcceptedAnswerId="13384" CreationDate="2019-04-23T05:54:59.440" Score="6" ViewCount="1145" Body="&lt;p&gt;I was just thinking about making a QRP transceiver, but are they only used for CW (Morse code) communication?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it is so, can I modify a QRP for two way audio communication?&lt;/p&gt;&#xA;" OwnerUserId="14723" LastEditorUserId="8717" LastEditDate="2019-04-23T19:26:30.997" LastActivityDate="2021-01-15T00:30:58.427" Title="Are QRP transceivers only meant for CW communication?" Tags="&lt;diy&gt;&lt;cw&gt;&lt;equipment-design&gt;&lt;qrp&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13380" PostTypeId="2" ParentId="13379" CreationDate="2019-04-23T06:56:40.733" Score="5" Body="&lt;p&gt;A QRP transceiver is just a transceiver that operates on low power (usually less than 5 watts). If you look at the international &lt;a href=&quot;https://en.wikipedia.org/wiki/Q_code&quot; rel=&quot;nofollow noreferrer&quot;&gt;Q Code&lt;/a&gt;, you will see that QRP simply means 'low power', and QRO means 'high power'.&lt;/p&gt;&#xA;&lt;p&gt;However, what you are talking about is a QRP transceiver &lt;strong&gt;kit&lt;/strong&gt;. Such kits are usually by necessity a fairly simple design, and the simplest transmitter is a CW transmitter. Transmitting CW is just a matter of keying on and off a signal from an oscillator and putting the signal through a power amplifier.&lt;/p&gt;&#xA;&lt;p&gt;If you were to build an AM transmitter and receiver, those are also relatively simple - but nobody (I know, &lt;em&gt;some&lt;/em&gt; people still use it) uses AM these days.&lt;/p&gt;&#xA;&lt;p&gt;I have seen kits that are based around an SDR design, that do CW/SSB/AM/FM, and cost in the order of \$300-\$400. But when someone says they are thinking of building a QRP kit, this is not usually the first thing that comes to mind. An example of such a device is &lt;a href=&quot;https://www.sdr-cube.com/ordering.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt; at \$209 for the 'kit' version.&lt;/p&gt;&#xA;&lt;p&gt;Most CW kits are small, and only do CW because of the simplicity of the design. An example is the &lt;a href=&quot;http://vakits.com/qrp-pixie-cw-transceiver-kit-7050-mhz&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRP Pixie&lt;/a&gt; kit at \$15.&lt;/p&gt;&#xA;&lt;p&gt;Having said all this about the complexity of SSB versus the simplicity of CW (when it comes to transmitting, at least), when it comes to operating the radio the SSB one is obviously much simpler if you don't know Morse code.&lt;/p&gt;&#xA;&lt;p&gt;If you were to learn Morse code, though ... then you can use the cheapest possible kits, and get all the benefits of a smaller, simpler device - with a lot of the complexity taking place in your own brain as you operate.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="18450" LastEditDate="2021-01-10T20:20:11.277" LastActivityDate="2021-01-10T20:20:11.277" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13381" PostTypeId="2" ParentId="13377" CreationDate="2019-04-23T12:35:42.747" Score="7" Body="&lt;p&gt;No, adding ferrite beads to choke currents on the outside of the shield of a coaxial cable does not affect its impedance or velocity factor. Impedance and velocity factor are determined by the &lt;em&gt;inside&lt;/em&gt; construction of the cable: the outside diameter of the inner conductor, d, the inside diameter of the outer conductor (shield), D, and the magnetic permeability, &lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;, and dielectric constant, &lt;span class=&quot;math-container&quot;&gt;$\epsilon$&lt;/span&gt;, of the material that separates them:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$Z_0=\frac{1}{2\pi}\sqrt{\frac{\mu}{\epsilon}}ln\frac{D}{d}$$&lt;/span&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-23T12:35:42.747" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13382" PostTypeId="2" ParentId="13377" CreationDate="2019-04-23T12:40:19.387" Score="6" Body="&lt;p&gt;For well-designed coax, the EM fields are confined to the space between the inside of the braid and the center conductor, i.e. the dielectric insulation region which affects the velocity factor. Therefore, those beads have negligible effect on the differential signals. They do have an effect on the common-mode signals on the outside of the braid which has very little to do with the differential velocity factor or characteristic impedance of the coax.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-04-23T12:40:19.387" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13383" PostTypeId="2" ParentId="13379" CreationDate="2019-04-23T12:54:31.137" Score="4" Body="&lt;p&gt;CW is preferred over SSB for low power (QRP) operation because CW delivers better signal-to-noise ratio (S/N or SNR) than SSB. Because a CW signal occupies about an order of magnitude less bandwidth than an SSB signal, a narrower receiving filter can be used, which admits all of the signal and a much smaller amount of noise energy than a wider SSB filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While QRP is often considered to be synonymous with CW for the cost and SNR reasons already pointed out, the challenge of QRP SSB is not without its adherents; many &quot;phone&quot; contests attract QRP entrants and QRP may satisfy the needs and constraints of a particular situation. The &lt;a href=&quot;http://www.hfsignals.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;BitX&lt;/a&gt;, &lt;a href=&quot;https://elecraft.com/collections/kx-line&quot; rel=&quot;nofollow noreferrer&quot;&gt;KX2/KX3&lt;/a&gt; and &lt;a href=&quot;http://www.qrp-labs.com/qsx&quot; rel=&quot;nofollow noreferrer&quot;&gt;QSX&lt;/a&gt; transceivers are all fine examples of QRP SSB/CW transceivers. Amplifiers are also available from several suppliers to boost the output power as conditions warrant. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-04-23T12:54:31.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13384" PostTypeId="2" ParentId="13379" CreationDate="2019-04-23T13:06:35.117" Score="9" Body="&lt;p&gt;QRP only means low power, often 1W or less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While you could technically have a 1W SSB transceiver and call it QRP, the practical range of such a radio would be limited. It is much easier to hear a single tone over the noise than it is to hear a voice which has its energy spread over a wide range of frequencies. Thus we say CW is a more &lt;em&gt;sensitive&lt;/em&gt; mode: it can be detected at a lower power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's try some simulations with &lt;a href=&quot;http://www.voacap.com/hf/&quot; rel=&quot;noreferrer&quot;&gt;VOACAP&lt;/a&gt;. In each case, the simulation is for UTC 20:00 for a transmitter in Michigan, USA (marked by the red dot) on 30 meters. The simulated antenna is a dipole 10 meters above ground at both receiver and transmitter, and the transmitter power is 1W. The colors on the map indicate the probability that communication will be possible, depending on conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the simulation for SSB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hTUUW.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hTUUW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looks like about a 40% chance of some contacts in an approximately 600 mile radius, and no chance of anything outside that. Neat, but not especially thrilling. On some days, it may be impossible to make contacts at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now CW:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VZCDd.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VZCDd.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Within that primary 600 mile radius, the reliability is 90%. There's now some small chance of much longer range contacts, including Europe, Asia, and the Western US. While these contacts will require some good luck, for many people this is the thrill and challenge of QRP operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are even more sensitive modes than CW. Here's a simulation for FT8:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/KUf38.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KUf38.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And WSPR:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OUWBN.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OUWBN.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While digital modes like FT8 and WSPR are more sensitive than CW, they require a computer to operate. Since CW is simple to implement electronically, and requires no computer, and is still sensitive enough to feasibly complete QRP contacts, many QRP kits are CW. For digital modes there are some QRP kits that are essentially the analog bits of an SDR which then interface to a computer soundcard to perform modulation and demodulation available for under $50 USD.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-23T13:06:35.117" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13385" PostTypeId="2" ParentId="13378" CreationDate="2019-04-23T13:11:14.630" Score="2" Body="&lt;p&gt;With the exception of 10 meters, the frequencies of lowest return loss (and SWR) measured with the VNA are below the ham bands on which you must have tested with the IC-7300. It's not easy to see on the graph, but the return loss within the ham bands appears to be about -5dB, which &lt;a href=&quot;https://www.amphenolrf.com/vswr-conversion-chart/&quot; rel=&quot;nofollow noreferrer&quot;&gt;corresponds to an SWR of over 3:1&lt;/a&gt;. It's important to compare apples to apples when performing measurements; i.e., SWR should be reported on the same frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna's resonant frequencies may be lower than expected because: it's close to the ground (you didn't say how high the attic is); it is being de-tuned by proximity to wiring and attic clutter; it is cut longer than required to permit tuning to higher frequencies by pruning; all of the above.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-04-23T15:02:06.967" LastActivityDate="2019-04-23T15:02:06.967" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13386" PostTypeId="1" AcceptedAnswerId="13387" CreationDate="2019-04-23T16:49:53.807" Score="1" ViewCount="72" Body="&lt;p&gt;I'm attempting to tune my &lt;a href=&quot;https://static.dxengineering.com/global/images/instructions/alf-dx-ee.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX-EE&lt;/a&gt; Alpha Delta multi-band wire antenna. The instructions state:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The 40 meter sections can be shortened to the SSB section of the band&#xA;  by pulling the wires through the end insulators an additional 3 inches&#xA;  each side, and twisted back on themselves. This length will vary due&#xA;  to the installation site, so check the SWR resonance first. The wires&#xA;  don’t have to be cut. Then, a wide range antenna tuner should be&#xA;  employed to broaden out its bandwidth.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I think what they're saying is, &quot;you can't cover the entire 40m band with this antenna, so trim it to the half you want to use (the upper half, where phone transmissions are allowed), and let your antenna tuner do the rest.&quot; Am I right in my interpretation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When trimming a wire antenna, should you trim it so the VSWR is lowest in the middle of the band of interest or should you trim it so it's lowest at one edge?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This question stems from &lt;a href=&quot;https://ham.stackexchange.com/questions/13378/how-to-interpret-vswr-results-for-an-attic-antenna&quot;&gt;a previous question&lt;/a&gt;. In those graphs you can see that all my wire segments aren't trimmed properly (I may not be able to fix 15m--I'll look in the attic and see if I can unfold some of the wire I folded back). &lt;/p&gt;&#xA;" OwnerUserId="5820" LastActivityDate="2019-04-23T18:20:16.460" Title="To which part of the band should I tune my Hi-Q wire antenna if my transceiver has an automatic antenna tuner?" Tags="&lt;wire-antenna&gt;&lt;swr-meter&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13387" PostTypeId="2" ParentId="13386" CreationDate="2019-04-23T18:07:15.070" Score="2" Body="&lt;p&gt;You should trim it so that the SWR is the same at each edge of your band segment of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you tune it for the lowest SWR in the middle, you likely will find that the the above condition does not occur and the SWR might be too high at one edge.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-04-23T18:07:15.070" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13388" PostTypeId="2" ParentId="13386" CreationDate="2019-04-23T18:20:16.460" Score="2" Body="&lt;p&gt;You can tune it like Mike Waters says, the idea being to minimize the worst case regardless of where you are in the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or perhaps you use one side of the band more than the other, in which case tune for the part of the band you use the most.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most likely, it doesn't matter too much either way. As long as the SWR is still within range of your transmitter's tuner, what you're trying to avoid is &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;additional loss due to SWR&lt;/a&gt;. Since the feedline to your attic is probably not very long, and the worst-case SWR is probably not that bad, the losses will probably be small.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-23T18:20:16.460" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="13389" PostTypeId="2" ParentId="13379" CreationDate="2019-04-23T18:40:38.540" Score="2" Body="&lt;p&gt;There's at least one video on YouTube concerning a Pixie (normally a 40m QRP CW-only transceiver, with rather questionable control of harmonics) converted to use the output audio amplifier IC as a modulator for AM transmission.  Another Pixie could be used as a receiver, as long as they have the same frequency crystal.  This is about as simple and cheap as you could get for voice QRP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, as other answers have noted, there are very good reasons why CW is a preferred mode for QRP -- but it's also worth noting that the ubiquitous BaoFeng UV-5R hand held is technically QRP, with a maximum output of 5W, and it's FM voice on either 2m (VHF) or 70cm (UHF) bands.  In my experience, this kind of radio is mainly useful for contacting a repeater, which retransmits at higher power from a higher elevation to allow communication over a wider area (there are a couple repeaters near my home that are high enough to nominally cover a fifty mile or 80 km radius).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a 5W CW transceiver on 20m, 40m, or 80m, and a correctly matched antenna, you can pretty readily cover a significant fraction of a continent -- in good conditions (we'll have those again in a couple years, after this solar minimum has run its course) you can make global contacts, at least along the Gray Line, with that kind of rig.  There are operators who have achieved a DXCC with 5W rigs (that's worked 100 foreign countries -- with 5 watts output).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-23T18:40:38.540" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="13390" PostTypeId="1" CreationDate="2019-04-23T23:46:18.907" Score="0" ViewCount="128" Body="&lt;p&gt;I got a power-supply gifted by my friend. When I powered ON, the main (120V) FUSE blows up. I started by disconnecting the transformer from the control circuit and powered ON. This time the fuse is NOT BLOWN. This points to the control circuit as the source of the short. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then I checked the bridge using the multi-meter and it looks good.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From here I don't know how to proceed...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is the link for the circuit &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.icom.co.jp/world/support/download/manual/pdf/IC-PS15.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.icom.co.jp/world/support/download/manual/pdf/IC-PS15.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10528" LastEditorUserId="12971" LastEditDate="2019-04-29T15:45:35.420" LastActivityDate="2019-04-29T15:45:35.420" Title="Troubleshooting ICOM PS15 Power Supply" Tags="&lt;icom&gt;&lt;equipment-troubleshooting&gt;&lt;dc-power&gt;&lt;power-supply&gt;" AnswerCount="0" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14390" PostTypeId="1" CreationDate="2019-04-24T15:34:27.447" Score="7" ViewCount="809" Body="&lt;p&gt;QRP doesn't have a strict definition, though 5W or less seems to be a common threshold. So would &quot;QRP operation&quot; usually be considered to include UHF/VHF handhelds?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-04-25T11:57:38.040" LastActivityDate="2019-04-25T11:57:38.040" Title="Is a 5 watt UHF/VHF handheld considered QRP?" Tags="&lt;qrp&gt;&lt;jargon&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14391" PostTypeId="2" ParentId="9474" CreationDate="2019-04-24T15:57:30.223" Score="1" Body="&lt;p&gt;The two extended batteries I have (for a BF-F8HP, but as far as I know, this model uses the same batteries as the UV-5R) have direct charging input socket &lt;em&gt;on the battery&lt;/em&gt;, separate from the contacts for the charging cradle.  The chargers made to plug into this socket (that I've seen advertised) are direct USB, suggesting that either the charge cable itself includes boost converter, or the battery does (the battery has much more room for this).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It might be worth contacting BTech's support address to verify this, but I suspect this is the solution to your need to run off plain 5V -- just get one of those USB charge cables that plugs into the battery's socket.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-24T15:57:30.223" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14392" PostTypeId="2" ParentId="14390" CreationDate="2019-04-24T16:07:22.590" Score="0" Body="&lt;p&gt;While most 2m and UHF hand held units are limited to 5W, not all are (I have one that offers a choice of 1W, 4W, or 8W) -- and this is done mainly to extend battery life with a radio that's normally only useful for the distance to the nearest repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, 2m/UHF mobile units mounted in vehicles routinely emit 50W or more (I'm looking at a Yaesu for my car that offers 5W, 30W, or 65W, for under $150), and base units can readily emit 100W, or with an amplifier up to 1500W legal limit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence, even though 5W is common for hand held VHF/UHF units, I still consider it QRP.  A hand held could easily be built to radiate ten times this power -- though battery life would be compromised.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-24T16:07:22.590" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14393" PostTypeId="2" ParentId="14390" CreationDate="2019-04-24T16:10:46.020" Score="8" Body="&lt;p&gt;My personal opinion is that QRP means using significantly less power than is customary for a given mode of operation. In that sense, a 5W HT would not be QRP because pretty much everybody else with an HT is also operating at (or near) 5W. 0.5W might be considered QRP in this case.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastActivityDate="2019-04-24T16:10:46.020" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14394" PostTypeId="1" AcceptedAnswerId="14395" CreationDate="2019-04-24T16:27:07.720" Score="1" ViewCount="166" Body="&lt;p&gt;What are smart antennas? How are they used in amateur radio, and how might they better than conventional antennas?&lt;/p&gt;&#xA;" OwnerUserId="14723" LastEditorUserId="6080" LastEditDate="2019-04-27T02:19:59.927" LastActivityDate="2019-04-27T02:19:59.927" Title="What are Smart Antennas?" Tags="&lt;antenna-theory&gt;&lt;equipment-design&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14395" PostTypeId="2" ParentId="14394" CreationDate="2019-04-24T16:59:54.770" Score="7" Body="&lt;p&gt;&quot;Smart antennas&quot; are antenna arrays with software-controlled phasing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna arrays are commonly used in the amateur radio hobby, such as in Yagis, four-square antennas, etc. However, the phasing for these arrays is either fixed (as in the Yagi) or sometimes selectable between a few configurations via a switch (as in the four-square). The individual antennas combine into a single feedline that runs to the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Traditionally these antennas are adjusted by manual control with a rotator, or by a manual switch. If this control is instead done by software, the antenna is said to be &quot;smart&quot;. Software control allows the adjustment to be performed automatically by feedback from the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible to run a feedline to each element of the array, and then combine the signals from each in software. This allows for a much higher degree of flexibility and complexity. This is called an &lt;em&gt;adaptive array&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One application is the development of software to dynamically determine the optimal weights for each array element. Numerous &lt;a href=&quot;http://www.antenna-theory.com/arrays/weights/main.php&quot; rel=&quot;noreferrer&quot;&gt;algorithms&lt;/a&gt; exist. In contrast with a four-square which typically allows selecting 1 of 4 possible arrangements to optimize reception in a specific direction, software phasing allows an infinite selection of weights which may not simply optimize gain in a particular direction. They may optimize to place a source of interference in a null, for example. Furthermore they are not limited to just one phasing at a time: the software demodulator may use one set of weights to receive a station in one direction, while simultaneously using a different set of weights for another station in a different direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another application is spatial multiplexing. Software can find several orthogonal paths between stations, a trivial one being vertical versus horizontal polarization, though in practice multipath propagation creates opportunities for even more orthogonal paths. This allows a reduction in spectrum usage by sending multiple streams on the same frequency at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These technologies are ubiquitous even in consumer equipment, for example cell phones and Wi-Fi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, application in the amateur radio hobby is not common. I've read of some people experimenting a little, for example &lt;a href=&quot;http://www.lz1aq.signacor.com/&quot; rel=&quot;noreferrer&quot;&gt;LZ1AQ&lt;/a&gt; has some &lt;a href=&quot;http://www.lz1aq.signacor.com/docs/antenna-performance/switching-technique-compare-receiving-antenna-performance.htm&quot; rel=&quot;noreferrer&quot;&gt;experiments switching between vertical and horizontal polarization&lt;/a&gt;. It should be possible to extend software like &lt;a href=&quot;http://www.w1hkj.com/&quot; rel=&quot;noreferrer&quot;&gt;fldigi&lt;/a&gt; and &lt;a href=&quot;https://physics.princeton.edu/pulsar/k1jt/&quot; rel=&quot;noreferrer&quot;&gt;wsjt&lt;/a&gt; to use inputs from multiple antennas to improve reception, though to my knowledge there's no commonly used amateur radio software that does so.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-04-24T17:13:07.137" LastActivityDate="2019-04-24T17:13:07.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14396" PostTypeId="2" ParentId="14390" CreationDate="2019-04-24T20:03:06.497" Score="8" Body="&lt;p&gt;My understanding of &quot;QRP&quot; is simply the use of as little power as possible to make contacts over interesting distances. There isn't a specific power level that equates to &quot;QRP&quot; - it is more a function of what's less than expected. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;1W on 2m/UHF for 10 mile simplex (or local/regional repeater communications) isn't QRP. 0.1W on 2m/UHF for 250 mile simplex would fit my definition of QRP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is a gray area, for sure. Like the Judge said, &quot;I know it when I see it.&quot;&lt;/p&gt;&#xA;" OwnerUserId="14772" LastEditorUserId="8717" LastEditDate="2019-04-24T20:26:21.813" LastActivityDate="2019-04-24T20:26:21.813" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14398" PostTypeId="2" ParentId="14390" CreationDate="2019-04-25T03:25:08.880" Score="3" Body="&lt;p&gt;Although it's highly opinionated, it may be defined as operating at 5% or less than standard 'barefoot' operating power on your band, by convention.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, for most HF, 100W is the standard power, 5W is considered QRP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For VHF, most handhelds (which are the most frequently used on that band) operate at 5W, so QRP would be 250mW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, that doesn't include whether you're counting power applied to your antenna system or your actual ERP :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's opinionated, and relative!&#xA;QRP historically means &quot;Should I reduce power?&quot; or &quot;Decrease Power&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would say: No, a 5W handheld does not count as QRP, since that's well within the standard expectation for transmitter power for that band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please see:&#xA;&lt;a href=&quot;http://www.arrl.org/qrp-low-power-operating&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/qrp-low-power-operating&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14773" LastActivityDate="2019-04-25T03:25:08.880" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14399" PostTypeId="2" ParentId="14394" CreationDate="2019-04-25T03:30:03.727" Score="1" Body="&lt;p&gt;Smart antennas, the software controlled ones with directional phased arrays, are typically too expensive for the radio amateur.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, benefits of a smart antenna for simplex communication typically does not outweigh the cost of implementing such an antenna system. Variable phase adjusters are extremely expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically they're used for detection purposes, since the beam is very quickly steerable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The closest I've ever seen, closest to amateur radio, is here: &lt;a href=&quot;https://hackaday.com/2015/04/07/build-a-phased-array-radar-in-your-garage-that-sees-through-walls/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hackaday.com/2015/04/07/build-a-phased-array-radar-in-your-garage-that-sees-through-walls/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14773" LastActivityDate="2019-04-25T03:30:03.727" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14400" PostTypeId="2" ParentId="14390" CreationDate="2019-04-25T09:03:21.187" Score="2" Body="&lt;p&gt;If you read contest rules, the QRP section is for those using 5W or less (sometimes 10W or less) no matter what type of transmitter you use. So you can enter the FM QRP section of a VHF or UHF contest when using a handheld on full (5w) power. &lt;/p&gt;&#xA;" OwnerUserId="14777" LastActivityDate="2019-04-25T09:03:21.187" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14401" PostTypeId="1" AcceptedAnswerId="14404" CreationDate="2019-04-25T23:46:11.710" Score="1" ViewCount="69" Body="&lt;p&gt;Trying to calculate 3rd order intermodulation for a frequency range (2110 to 2155). I know the answer is 1710 to 1755, but I don't know how to get there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;attempts:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;f1 = 2110&#xA;f2 = 2155&#xA;2*f1 - f2 = 2065&#xA;2*f2 - f1 = 2200&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;this doesn't seem to follow the equation. help!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;update:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My source of the frequency range info is from the website of a manufacturer of PIM analyzer equipment, Kaelus - (formerly Summitek): &lt;a href=&quot;https://www.kaelus.com/en/test-measurement-solutions/bench-pim-testing/iba-series&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.kaelus.com/en/test-measurement-solutions/bench-pim-testing/iba-series&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you go find their &lt;strong&gt;iBA-1921B&lt;/strong&gt; analyzer, you will see these frequency ranges in their specs.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/tDVOW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tDVOW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This was also confirmed on another site: &lt;a href=&quot;https://awt-global.com/wp3/resources/pim/intermodulation-products/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://awt-global.com/wp3/resources/pim/intermodulation-products/&lt;/a&gt;. From this other site, it appears as though the 9th im product is the problem, but the Kaelus PIM analyzer (iBA-1921B) returns im frequencies 1710-1755. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/69SZQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/69SZQ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question has not changed, but the reason I ask this is because I am trying to calculate how many data points I can expect to get back based on the sweep frequency ranges for carriers 1 &amp;amp; 2 and the receive band for the PIM analyzer. What is odd here is that the 3rd order IM products are not inside the receive band of the PIM analyzer, at all, and yet the analyzer returns 1710-1755 when taking measurements.&lt;/p&gt;&#xA;" OwnerUserId="14778" LastEditorUserId="14778" LastEditDate="2019-04-26T13:23:10.183" LastActivityDate="2019-04-26T19:42:02.237" Title="why is 3rd order intermodulation for 2110-2155 = 1710-1755?" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;&lt;antenna-analyzer&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14402" PostTypeId="2" ParentId="13357" CreationDate="2019-04-26T14:48:36.767" Score="2" Body="&lt;p&gt;I have a far less-optimized antenna mount on my bike (without the ground radials). Did you build the ground radials yourself, or was it a kit? You're bike mobile, it doesn't need to be perfect - in fact, do be more concerned about your safety (not injuring yourself with your antenna) than about minimal SWR. After all, if you're on the bike, you're a significant impact on your signal!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your driven element is a bit short for 430-450 MHz. Is the dual-band antenna providing a good SWR on 440 MHz? If so, I'd look at the antenna, not at the mount. Given the low SWR at frequencies higher than desired, I'd test with a slightly longer, single-band whip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dual-band antenna may or may not require a ground plane. I have a dual-band Diamond SG7900, and it doesn't need a ground plane. On the other hand, if your dual-band is 1/4 or 5/8 wave on each band, it will need a ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an aside, the brass insert gets removed when you are operating on HF. Leave it in for VHF/UHF.&#xA;I have several of these Larsen mounts, and they operate similarly:&#xA;&lt;a href=&quot;https://pulselarsenantennas.com/wp-content/uploads/2017/01/ASB11-Cable-Assemblies-Mounts-10.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://pulselarsenantennas.com/wp-content/uploads/2017/01/ASB11-Cable-Assemblies-Mounts-10.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14772" LastActivityDate="2019-04-26T14:48:36.767" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14403" PostTypeId="2" ParentId="1467" CreationDate="2019-04-26T15:04:57.423" Score="3" Body="&lt;p&gt;The &lt;strong&gt;&lt;em&gt;clarifier&lt;/em&gt;&lt;/strong&gt; is simply Yaesu's term for &lt;strong&gt;RIT&lt;/strong&gt; (receiver incremental tuning) and &lt;strong&gt;XIT&lt;/strong&gt; (transmitter incremental tuning), and can be used for either of those two adjustments, or turned off.&#xA;&lt;strong&gt;RIT&lt;/strong&gt; keeps your transmit frequency constant while you adjust your receive frequency. This way, when you're talking to a group (like in a net), you can more clearly hear the one ham who's off-frequency while everybody else in the group can hear you without detecting any change in your frequency.&#xA;&lt;strong&gt;XIT&lt;/strong&gt; performs the reverse function, in that it keeps your receive frequency constant while you adjust your transmit frequency.&#xA;In both cases, tuning with the big knob will adjust both the transmit and receive frequencies simultaneously, while tuning with the RIT or XIT will adjust only one of them.&lt;/p&gt;&#xA;" OwnerUserId="9166" LastActivityDate="2019-04-26T15:04:57.423" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14404" PostTypeId="2" ParentId="14401" CreationDate="2019-04-26T19:42:02.237" Score="1" Body="&lt;p&gt;The TX ranges supported by those units are the downlink ranges of recognized cellular allocations and the RX ranges are the corresponding uplink ranges — e.g. LTE Band 2 has downlink from 1930-1990 MHz and uplink from 1850-1910 MHz, and LTE Band 4 has downlink from 2110-2155 MHz and uplink from 1710-1755 MHz. Together they make up the ranges supported by the 1921B. Likewise the 1800B covers Band 3, the 0901B covers Band 8, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So they're not designed around looking for specific IMD products wherever they occur, but around looking at the corresponding uplink range and detecting whatever IMD from the downlink happens to land in that range. Presumably out of concerns of a transmitter raising the noise floor / desensitizing its own receiver. In particular, they have nothing to do with the specific placement of IMD3 products.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-04-26T19:42:02.237" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14405" PostTypeId="1" AcceptedAnswerId="14406" CreationDate="2019-04-26T19:57:50.353" Score="1" ViewCount="896" Body="&lt;p&gt;I've been reading about the D-STAR, and I've heard that there are these things called D-STAR reflectors, and that a repeater can be linked to a reflector. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On my Icom IC-9700, when I press and hold the CALL DR button, get into the Digital Radio mode, select a nearby D-STAR repeater, and press the TO button on the touch-screen, I get the menu, where I can select reflector operations. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vPEgG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vPEgG.png&quot; alt=&quot;IC-9700 reflector operations menu&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I click on Link to Reflector, and use Direct Input, I can only choose from REF and XRF reflectors. It's not possible to select a DCS or XLX reflector, and it's not possible to get a keyboard screen, to enter value manually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AP4kY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AP4kY.png&quot; alt=&quot;Reflector selection menu&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What can I do to select a different reflector on my friendly local repeater?&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2019-04-26T19:57:50.353" Title="How do I link a repeater on one of the DCS reflectors using IC-9700?" Tags="&lt;icom&gt;&lt;d-star&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14406" PostTypeId="2" ParentId="14405" CreationDate="2019-04-26T19:57:50.353" Score="1" Body="&lt;p&gt;As of firmware version 1.06, it seems that there is no way to use the actual Link to Reflector feature to link to non-REF or non-XRF reflectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the Link to Reflector option need not be used to establish a link. Instead, the linking can be done the old way, but putting the command in the Your Call Sign option, or by using the Direct Input (UR) option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, the radio thinks as if it were me: My callsign is the callsign of the current user of the radio, and your callsign is the callsign of whomever I want to talk to, and is placed in the UR field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, I can write the name of the reflector in the Your Callsign field followed by the command to link to the reflector.&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/WU9Mx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WU9Mx.png&quot; alt=&quot;Manual entry of UR field on IC-9700&quot;&gt;&lt;/a&gt;   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if I want to link to, for example, DCS001K, I would write DCS001KL in the UR field. Then I only need to press the transmit button, or key the microphone up, in order to send the command to the repeater.&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/PRgUJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PRgUJ.png&quot; alt=&quot;Your Call Sign field with manual command to link to a reflector&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The alternative option is to first go to menu, then page 2, and select the menu item DV/DD Memory. There, under the item Your Call Sign, I can add a Your Call Sign item, which I can name, for example, Link to DCS001K, and as callsign enter the above-mentioned DCS001KL.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/beto7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/beto7.png&quot; alt=&quot;Link to reflector memorized as Your Call Sign&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Afterwards, when I press on the TO field in the Digital Radio mode, I can use the Your Call Sign menu item, to select the Link to callsign I previously memorized, and not have to enter the link command by hand.&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/t9m17.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/t9m17.png&quot; alt=&quot;Link to reflector selected as Your Call Sign&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;In GUI, this option will appear a bit differently, since the radio will show a silhouette, instead of a computer when linking to a repeater, but seems to work fine.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2019-04-26T19:57:50.353" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14407" PostTypeId="1" CreationDate="2019-04-27T08:55:22.740" Score="1" ViewCount="129" Body="&lt;p&gt;I have a Yaesu FT101E which has low output because the final 6JS6C valves are old. If i increase the plate voltage on the final tubes from 600 to 800 VDC  by changing the mains transformer tapping from 240 V to 220 V will that increase the output power ? What else would that do ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-04-27T23:20:30.543" LastActivityDate="2020-03-14T05:19:37.580" Title="How can the output power of a Yaesu FT101E be increased?" Tags="&lt;electronics&gt;&lt;theory&gt;" AnswerCount="1" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="14409" PostTypeId="1" CreationDate="2019-04-27T15:25:46.057" Score="1" ViewCount="181" Body="&lt;p&gt;Yesterday I was trying to tune up the duplexers one can at a time as listed in this &lt;a href=&quot;https://www.youtube.com/watch?v=U7QZzzB2LZU&quot; rel=&quot;nofollow noreferrer&quot;&gt;Sinclair Youtube Video&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After tuning them my receive is awful and my transmit is somewhat not what it used to be. What could be the reasons?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is my last photo on the meter before hooking it up:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Zi3m8.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Zi3m8.jpg&quot; alt=&quot;Final tune..&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any advice on how to tune these things?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I notice I have to turn the screws to find the rods; since that is kind of weird I think I might be doing something wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically hooking the input into the antenna portion of the duplexer and then the output on either side with a dummy load on the other end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a &lt;a href=&quot;http://www.sinclairtechnologies.com/catalog/product.aspx?id=75&quot; rel=&quot;nofollow noreferrer&quot;&gt;Sinclair Duplexer Model Q2330E&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="5438" LastEditorUserId="76" LastEditDate="2020-02-14T01:22:01.873" LastActivityDate="2020-06-04T05:49:17.060" Title="Retuning 2m Duplexers (Q2330E) with Spectrum Analyzer and Tracking Generator" Tags="&lt;testing&gt;&lt;duplexer&gt;&lt;spectrum-analyzer&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14410" PostTypeId="1" AcceptedAnswerId="14420" CreationDate="2019-04-28T03:44:21.700" Score="2" ViewCount="98" Body="&lt;p&gt;I'm interested in a low frequency (10 MHz - 100 MHz) radio receiver array, made up of crossed dipole antennas. I'm working on a design project mainly focused on the mechanical engineering side of making a low mass array printed on thin polyimide sheets for deployability. So, as I am not too familiar with antenna theory, I was hoping for some guidance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First are the antennas. The goal is to keep everything small and light. The idea was to use thin copper or aluminum ribbons to make crossed dipoles on the polyimide sheets. The dipoles will be about 0.3m long to be &lt;span class=&quot;math-container&quot;&gt;$\ll \lambda$&lt;/span&gt; at all wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then there's the transmission lines. The maximum length of a transmission line for my setup is &lt;span class=&quot;math-container&quot;&gt;$\sim$&lt;/span&gt; 30 m. I haven't been able to learn much about transmission lines in this frequency range. Specifically, I'm interested in what the dimensions have to be (length vs. &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;, diameter or width, separation between lines) and what materials are good. Could it be as simple as more conductive wire?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will microstrips lines be applicable here? That would be ideal, since they are thin and very light and could actually be printed on the film. Could microstrips even be used for the antennas themselves?&lt;/p&gt;&#xA;" OwnerUserId="14703" LastEditorUserId="76" LastEditDate="2019-04-28T04:54:27.320" LastActivityDate="2019-04-30T12:40:53.780" Title="Low mass, low frequency transmission line" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;transmission-line&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14414" PostTypeId="2" ParentId="14410" CreationDate="2019-04-28T13:44:49.883" Score="2" Body="&lt;p&gt;Based on the little information you've given us, you might be able to use off-the-shelf Ethernet cable, like &lt;a href=&quot;http://www.nag.ru/goodies/tia/TIA-EIA-568-B.1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Category 5&lt;/a&gt; (aka Cat 5) cable. Owing to its ubiquity, it is probably the most inexpensive option available. Each cable comprises four (4) 100-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; unshielded twisted pair (UTP) transmission lines rated to 100-MHz. The loss at 100MHz is 21.6dB per 90m, so your 30m application would sustain about 7.2dB at the high end of your frequency range. Should you require shielding between pairs, shielded twisted pair (STP) cable is also available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you need more bandwidth, Cat 6, 6a, 7 and 8 provide up to 2GHz performance. These cables also include crosstalk specifications and may include shielding of individual pairs.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-04-28T20:06:06.430" LastActivityDate="2019-04-28T20:06:06.430" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14415" PostTypeId="1" AcceptedAnswerId="14416" CreationDate="2019-04-28T15:50:05.843" Score="3" ViewCount="2255" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8JH90.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8JH90.png&quot; alt=&quot;drawing of a fan dipole, taken from PDF file listed below&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I built a fan dipole according to the basic instructions in the &lt;a href=&quot;https://apps.dtic.mil/dtic/tr/fulltext/u2/684938.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;SRI publication&lt;/a&gt; describing the theory and basic design.&lt;/p&gt;&#xA;&lt;p&gt;My questions is about next steps in tuning for the various bands.  I am primarily interested in the phone / image range of the band as a General (KN4MIO).&lt;/p&gt;&#xA;&lt;p&gt;Specific questions are bold below.  I apologize for including multiple questions but I felt the topic of tuning and the context of the various bands were better presented in a single question.&lt;/p&gt;&#xA;&lt;p&gt;I did some basic tuning while on the ground and received some satisfactory results.  I then positioned the antenna approximately 85' off the ground suspended between two trees and took some additional measurements. The SWR across the 80 - 15 meter range was tested and the results were good for a first pass.  The shaded areas are the various bands.  The second from the left is 60m can can be ignored.&lt;/p&gt;&#xA;&lt;p&gt;Here is the SWR measured across the whole range from 80 - 15 meter&#xA;&lt;a href=&quot;https://i.stack.imgur.com/iaHSt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iaHSt.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The 80 Meter band is shown below scanning from 3.5 - 4.0 Mhz.&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Ee2UT.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ee2UT.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The SWR for this band is tuned at the low end of the phone / image area at 3.8 Mhz.  My understanding is that I can shorten the 80 meter antenna length to shift the SWR into the mid-range of the phone band.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Is there a way to flatten the SWR in this range or is this graph typical?&lt;/strong&gt;&lt;br /&gt;&#xA;&lt;strong&gt;Is shortening the antenna the proper way to shift the SWR to the right?&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;The 40 meter band is presented scanning from 7.0 Mhz - 7.3 Mhz.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/8diGI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8diGI.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&#xA;Before adjusting the 40 meter I would complete the tuning of the 80 meter first.&#xA;&lt;strong&gt;Given the lower SWR is to the left of my target shortening the antenna seems to be the means to shift the SWR to the right, correct?&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Following are the 20 and 15 meter SWR scans.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/JxZpK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JxZpK.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt; .&lt;br /&gt;&#xA;I was surprised that in the same way as the 40 meter being further to the left it seems like the 20 meter is following closely and shifting further to the left.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/N56iC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/N56iC.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&#xA;For the 15 meter band I was surprised to see this range but it looks very good.  Since 15 meter is really a harmonic of the 40 meter band it goes along for the ride.&lt;br /&gt;&#xA;&lt;strong&gt;Is the tuning for 15 meter primarily tied to the 40 meter dipole, or, is it more spread out amongst all dipoles?&lt;/strong&gt;&lt;br /&gt;&#xA;&lt;strong&gt;For antenna shortening, what are the pros and cons of shortening in terms of cutting versus folding back on itself and twisting?&lt;/strong&gt; .&lt;/p&gt;&#xA;&lt;p&gt;Thanks in advance for providing some insight on tuning the fan dipole.&lt;/p&gt;&#xA;" OwnerUserId="12971" LastEditorUserId="8717" LastEditDate="2021-01-26T19:20:00.507" LastActivityDate="2021-01-26T19:20:00.507" Title="3 Band (80-40-20 Meter) Fan Dipole Tuning Question" Tags="&lt;antenna-construction&gt;&lt;dipole&gt;&lt;bandwidth&gt;&lt;parallel-dipole&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14416" PostTypeId="2" ParentId="14415" CreationDate="2019-04-28T19:29:06.953" Score="6" Body="&lt;p&gt;Before getting to the questions you asked, an observation: the design doesn't appear to include a balun. Adding one is &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;probably a good idea&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there a way to flatten the SWR in this range [80m] or is this graph typical?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's typical. Because 80 meters is such a low frequency, the &lt;a href=&quot;http://www.antenna-theory.com/definitions/fractionalBW.php&quot; rel=&quot;noreferrer&quot;&gt;fractional bandwidth&lt;/a&gt; of the entire band is quite large. For this reason sometimes the upper portion of the band is called &quot;75 meters&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Getting a flatter SWR would require &lt;a href=&quot;http://www.antenna-theory.com/antennas/broaddipole.php&quot; rel=&quot;noreferrer&quot;&gt;making the antenna fatter&lt;/a&gt;, perhaps by adding more wires to the fan at an appropriate length for 80 meters. But since an 80 meter dipole is already quite large, few people bother. An antenna tuner is probably a more practical solution.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is shortening the antenna the proper way to shift the SWR to the right?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Given the lower SWR is to the left of my target shortening the antenna seems to be the means to shift the SWR to the right, correct?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is the tuning for 15 meter primarily tied to the 40 meter dipole, or, is it more spread out amongst all dipoles?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It is mostly tied to the 40 meter dipole, but on any fan dipole the elements do interact to some extent, so it can be a good idea to recheck the tuning on all bands periodically. The particular design you have has the elements separated at the center and the ends, which is good because it should mean their interaction is quite low.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For antenna shortening, what are the pros and cons of shortening in terms of cutting versus folding back on itself and twisting?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Electrically, either method is identical. You can't uncut a wire obviously, so it would be prudent to keep a little extra length available.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-28T19:29:06.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14418" PostTypeId="2" ParentId="6382" CreationDate="2019-04-29T22:41:50.610" Score="1" Body="&lt;p&gt;None of them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Baofeng UV-5RA &lt;em&gt;is&lt;/em&gt; legal to own, but they are not legal to transmit on here in the U.S. unless you get your license. &lt;/p&gt;&#xA;" OwnerUserId="14796" LastEditorUserId="8717" LastEditDate="2019-04-30T16:01:17.343" LastActivityDate="2019-04-30T16:01:17.343" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14420" PostTypeId="2" ParentId="14410" CreationDate="2019-04-30T12:40:53.780" Score="2" Body="&lt;p&gt;You would not want to use microstrip for the antennas. Microstrip is a kind of &lt;a href=&quot;https://en.wikipedia.org/wiki/Transmission_line&quot; rel=&quot;nofollow noreferrer&quot;&gt;transmission line&lt;/a&gt;, and transmission lines by design limit their electromagnetic fields to a small area in and around the transmission line. This means they do not radiate or receive, which is what allows them to transmit a signal from one end to the other without much loss or interference. The antennas could instead be made of simple, single conductors printed on the sheet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But for bringing the signal from the antennas to whatever processing unit you have, microstrip could work, as well as any number of other printed transmission lines. The particular geometry of the transmission line, and the electric and magnetic properties of the material its printed on will determine its characteristic impedance. Since you control the design of this system on both ends, there is a wide range of impedances that could work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The small dipoles will necessitate some kind of preamplifier at each antenna, which could likely be made quite small and printed on the sheet as well.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-04-30T12:40:53.780" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14421" PostTypeId="1" CreationDate="2019-04-30T13:32:32.497" Score="3" ViewCount="570" Body="&lt;p&gt;I have a networked remote HF receive-only receiver (Raspberry Pi with an SDR module).  When I transmit to myself (to the remote receiver on its listening frequency), say for antenna path testing, or for logging mobile location telemetry (etc.) to my fixed-base server, how should I identify my transmissions?  (U.S., amateur license, HF bands using Morse code)  What additional stuff (punctuation, etc.) besides a bare call-sign?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-04-30T15:22:12.790" LastActivityDate="2019-04-30T16:43:06.053" Title="Identifying a transmission to myself" Tags="&lt;station-identification&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14422" PostTypeId="2" ParentId="14421" CreationDate="2019-04-30T14:05:43.050" Score="2" Body="&lt;p&gt;As I understand it, the bare call sign in (English) voice or Morse (as appropriate for your license class and the band or sub-band you're transmitting in) is the minimum.  You can attach additional information if you wish -- for instance, a couple 2m repeaters I use regularly transmit Morse calls signs like &quot;W4NC RPT&quot;.  Your beacon could be something akin to that -- but it doesn't have to be.  It could be &lt;em&gt;just&lt;/em&gt; your call sign in Morse.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-04-30T14:05:43.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14423" PostTypeId="2" ParentId="14421" CreationDate="2019-04-30T14:14:21.990" Score="4" Body="&lt;p&gt;Identification is governed by &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=d4b3c60d2d60000a147f885bdee88264&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5#se47.5.97_1119&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.119&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(a) Each amateur station, except a space station or telecommand station, must transmit its assigned call sign on its transmitting channel at the end of each communication, and at least every 10 minutes during a communication, for the purpose of clearly making the source of the transmissions from the station known to those receiving the transmissions. No station may transmit unidentified communications or signals, or transmit as the station call sign, any call sign not authorized to the station.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There are further rules about special situations, but since you are both the control operator and the station licensee, operating with your normal license,  in quite ordinary circumstances, none of those apply. Remember the purpose of the identification is to identify the transmitter: who's receiving is irrelevant. So an ordinary &quot;DE [your call]&quot; would be sufficient.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And if the identification is keyed by an automated device used only for identification, keep it not above 20 WPM:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(1) By a CW emission. When keyed by an automatic device used only for identification, the speed must not exceed 20 words per minute;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-04-30T14:21:57.833" LastActivityDate="2019-04-30T14:21:57.833" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14424" PostTypeId="2" ParentId="14421" CreationDate="2019-04-30T16:43:06.053" Score="5" Body="&lt;p&gt;When doing a diagnostic self-reception, it's typically advantageous to give the receiver as much chance to identify the channel as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wouldn't it be cool if your identification could be used to measure the channel itself? That way, you'd stay on the air for as shortly as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you'd typically would want to send something that is spectrally white to sound the channel. Correlate with exactly the same white sequence at the receiver (yielding the autocorrelation of a white sequence, which is a dirac impulse, convolved with the channel impulse response; convolution with a dirac impulse is nothing but a time shift).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sadly, um, that's typically not allowed as a means of identification, although having a large registry of orthogonal white pseudorandom noise sequences would make for an &lt;strong&gt;excellent&lt;/strong&gt; ID database! Instead, identification must be done in a way that a (relatively uninformed) third party can understand (not to mention that in many bands you can't just send arbitrary signal at all, but must use predefined modulations).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Still, within the bandwidths and methods you're allowed to use, don't hesitate to optimize your transmitter identification signal for channel identification purposes!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example: You've got a 200 Hz wide channel on which you're only allowed to do morse with &lt;span class=&quot;math-container&quot;&gt;$\le 20\,\text{wpm}$&lt;/span&gt;, which leads to a dot length of ca 50 ms, which leads to an actually necessary bandwidth of about 40 Hz only – but we're not in the business of being as bandwidth efficient as possible! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unlike usually, if we want to get channel state information, we want to be as wide as legally possible – and that's exactly what you'd achieve by&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;generating a dot length of white noise, in your favourite programming language or audio program&lt;/li&gt;&#xA;&lt;li&gt;running that on repeat&lt;/li&gt;&#xA;&lt;li&gt;Gating that in a Morse fashion&lt;/li&gt;&#xA;&lt;li&gt;using a good band-pass filter (as in: Many taps, so that the passband is as wide and flat as possible, and the transition widths narrow, and after that the stopbands strongly attenuated) to get band-limited white noise&lt;/li&gt;&#xA;&lt;li&gt;Save the result to a file, and send that to your networked remote&lt;/li&gt;&#xA;&lt;li&gt;using AM / SSB to modulate that signal, so that it ends up occupying the channel your remote receiver is listening to&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;At the receiving end,&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;well, receive&lt;/li&gt;&#xA;&lt;li&gt;Correlate with the file from above &#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Hint: means filtering with the time-inverse!&lt;/li&gt;&#xA;&lt;li&gt;Another hint: just correlate with the original white noise dot-length sequence, you get an impulse for every dot period of signal coming in after doing the matched filter to the noise-bandlimiting filter (you've just built a matched filter! Yay!)&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Identify your own transmission by the impulse(s) you observe&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The beauty in that is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;you estimate signal power based on the power of what you've actually sent, not &quot;integral&quot;, including noise and interference (these are typically uncorrelated to your signal)&lt;/li&gt;&#xA;&lt;li&gt;you get a full-bandwidth signal, with which you can get a full-bandwidth estimate of the channel –  which means that if your channel is 200 Hz wide, you'll be able to get a more detailed impulse response, i.e. resolving different signal paths more clearly, than if you used say 40 Hz channel bandwidth, whilst still&lt;/li&gt;&#xA;&lt;li&gt;using an allowed mode (Morse; §97.305 says &quot;MCW, RTTY, DATA&quot;) for identification. A casual listener would hear a noisy (yet potentially strong) signal during your &quot;tone&quot; time; it doesn't disturb them more than an actual CW signal of low bandwidth, yet is more useful to you!&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Fun fact: that trick can even be used to (via self-assessment of the person doing that, so take with a grain of salt) operate a GSM base station in a ham band – you can simply pulse the transmit power of the control channel to CW out your station sign. (can't find the video link, sorry.)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-04-30T16:43:06.053" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14425" PostTypeId="1" CreationDate="2019-04-30T18:49:00.517" Score="3" ViewCount="934" Body="&lt;p&gt;I noticed a weird behavior of my Yaesu FT-891 transceiver. I'm using it with an external autotuner &lt;a href=&quot;http://www.mat-tuner.com/en/mAT-30.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;mAT-30&lt;/a&gt; (120W SSB/CW, 30W PSK31), which is compatible with Yaesu FC-50.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I connect a 100W 50 Ohm dummy load, switch to SSB mode and say &quot;aaaaah&quot; to the microphone the internal meter (MTR) shows SWR 1:1 and 100W transmit power, as expected. However, if instead of dummy load I connect a real antenna through mAT-30 tuner and enable the tuner by pressing TNR in the transceiver menu, the transmit power (according to MTR) drops to 50W while the SWR is about 1.5:1. I've found a few tables online (&lt;a href=&quot;http://www.firestik.com/Tech_Docs/SWRLOSS.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;the first one&lt;/a&gt;, &lt;a href=&quot;http://www.skyworksinc.com/uploads/documents/VSWRreturn.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;the second one&lt;/a&gt;) that say that SWR 1.5 correspond to only 4% power loss, thus I'm a little surprised.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At first I thought this might be some sort of bug in the firmware, thus I decided to re-check the readings using an external analog SWR/power meter. I have a second (manual) tuner MFJ-971, which has a build-in SWR/power meter. I bypassed the capacitors and the inductance of MFJ-971 using an alligator clip, which turned the device into just a SWR/power meter. Surprisingly it showed the same SWR 1.5:1 and only 50W of transmit power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then I decided to disconnect mAT-30 and tune the antenna using only MFJ-971. Now the transceiver works as expected - the transmit power is 100W despite the fact that SWR is about 1.5:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see two possible explanations. The first one is that FT-891 reduces the power when it sees an SWR higher then 1:1 and TNR is ON. Another possibility is that the protocol between the autotuner and the transceiver (over 8pin mini-DIN socket) supports some sort of back pressure (&quot;TRX DE ATU PSE DROP PWR&quot;), and the tuner is one to blame. Though I'm not familiar with this protocol and thus I don't know whether the tuner could be responsible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Did you ever encounter a similar behavior in other Yaesu products, or products by any other manufacturers? How would you suggest to bypass this limitation and transmit full 100W with my autotuner?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="76" LastEditDate="2019-04-30T21:29:44.620" LastActivityDate="2020-12-13T05:03:55.120" Title="Yaesu FT-891: power drops to 50% when TNR is ON and SWR is 1.5:1" Tags="&lt;rf-power&gt;&lt;equipment-operation&gt;&lt;yaesu&gt;&lt;antenna-tuner&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14426" PostTypeId="1" AcceptedAnswerId="14428" CreationDate="2019-05-01T10:42:53.103" Score="1" ViewCount="195" Body="&lt;p&gt;I have a GPS tracking device which was designed for inventory management, currently I'm using a GSM module to transmit the telemetry data (latitude and longitude only) to the base station. The problem in using GSM is it is not suitable to work in remote locations.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to use a QRP transmitter to send the same data to the base station?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit:&lt;/strong&gt; The current system is capable of sending the whole NMEA data with an interval of 1 minute, but I want only the latitude and longitude. Geographically, my locality (&lt;a href=&quot;https://en.m.wikipedia.org/wiki/Geography_of_Kerala&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kerala&lt;/a&gt;) is roughly divided into three climatically distinct regions. These include the eastern highlands (rugged and cool mountainous terrain), the central midlands (rolling hills), and the western lowlands (coastal plains).&lt;br&gt;&#xA;Since this is a hand held portable device and supposed to operate in remote areas, there may be obstacles in between the transmitter and receiver so Line of sight communication may not be possible.&lt;/p&gt;&#xA;" OwnerUserId="14723" LastEditorUserId="14723" LastEditDate="2019-05-01T16:35:01.690" LastActivityDate="2019-05-02T13:11:51.107" Title="Is it possible to transmit telemetry data (GPS) via QRP?" Tags="&lt;qrp&gt;&lt;gnss&gt;&lt;india&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14428" PostTypeId="2" ParentId="14426" CreationDate="2019-05-01T15:56:37.467" Score="3" Body="&lt;p&gt;When you ask if a QRP transmitter could be used to solve your problem, I presume that you mean a low-powered transmitter on HF, meaning roughly 3 &amp;ndash; 30 MHz.  That would solve the problem of limited range associated with the VHF and higher-frequency bands, but a large antenna would be necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that radio spectrum, especially in the HF bands, is very scarce.  Because there are so many uses for scarce bandwidth, governments require licenses to use the bandwidth, and often charge large fees for the privilege.  On the HF and lower-frequency bands, governments generally reserve most of the bandwidth for themselves.  The only reason that there is an allocation for amateur radio is that hams were there at the very beginning of radio, and have loudly campaigned for a share ever since.  Unfortunately for you, the amateur radio bands aren't available for business uses such as the one you describe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know of a frequency allocation for low-powered HF automated data transmission for business purposes, but if there were such an allocation, then licenses would surely be very expensive because the available bandwidth is so narrow.  Think how much mobile phone companies are willing to pay for allocations at much higher frequencies where there is much more bandwidth available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This fundamental problem of limited bandwidth has driven ingenious solutions to similar problems:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The global cellular network&lt;/li&gt;&#xA;&lt;li&gt;The Iridium satellite network&lt;/li&gt;&#xA;&lt;li&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/SNOTEL&quot; rel=&quot;nofollow noreferrer&quot;&gt;SNOTEL&lt;/a&gt; network in the Western US&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/International_Cospas-Sarsat_Programme&quot; rel=&quot;nofollow noreferrer&quot;&gt;COSPAS-SARSAT&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you could find another solution that would be inexpensive enough for inventory tracking and would work with handheld devices in remote locations, then fame and fortune would surely find you.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2019-05-01T19:05:30.607" LastActivityDate="2019-05-01T19:05:30.607" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14430" PostTypeId="1" AcceptedAnswerId="14431" CreationDate="2019-05-01T23:58:41.410" Score="1" ViewCount="45" Body="&lt;p&gt;I'm working on a project to design a space-based low frequency array. It will only be receiving signals, and it will operate between 10MHz - 100MHz. It is made of short wave crossed dipole antennas. I want to get an estimate for the power consumption and data rates, and my web searches have been unhelpful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I look for power needs, all I find is regarding transmitters. I know I will need to pass some current through the antennas along transmission lines, but I have no clue how much. This is more of a mechanical engineering project, so at the end of the day I need a wattage value. Is there a general equation that determines power needs, maybe based on wavelength and array geometry?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, I need some data rate estimate to size the onboard computing. Given that I'm clearly not an electrical engineer, this may not even be the right question to ask. What determines data output rates in a receiver system? Is it the antenna itself, the source, or the sampling of the computer?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks for any insight.&lt;/p&gt;&#xA;" OwnerUserId="14703" LastActivityDate="2019-05-02T11:59:16.870" Title="Passive receiver power needs &amp; data rate" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;dipole&gt;&lt;transmission-line&gt;&lt;power-supply&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14431" PostTypeId="2" ParentId="14430" CreationDate="2019-05-02T02:34:52.170" Score="1" Body="&lt;p&gt;The antenna itself doesn't require any power because it receives power from the transmitter. But you might need to power a preamplifier. The power consumption of the preamplifier will depend greatly on the design, but for ordinary designs it's very small, perhaps 25 mW. Much less, if you make low power a priority in the design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The data rate is limited by the Nyquist theorem: you must have at least 2 samples per second for every Hz of bandwidth, assuming you want to sample the signal and process it digitally. Often the sampling is done at a higher rate, then filtered and converted to a lower rate digitally (a process called &lt;em&gt;decimation&lt;/em&gt;) because it yields more flexibility and it can reduce the design requirements on the analog filtering which is more difficult to realize. If you're demodulating something digital, often after clock recovery the stream is further decimated to one sample per symbol.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-05-02T11:59:16.870" LastActivityDate="2019-05-02T11:59:16.870" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14432" PostTypeId="2" ParentId="13313" CreationDate="2019-05-02T04:22:39.633" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;Is the measurement accuracy made by an SWR meter affected by the fact&#xA;  that the actual impedance E/ I seen on the line during operation is&#xA;  not the same as the characteristic impedance if standing waves exist?&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Assuming your SWR meter employs a variant of the Bruene Coupler&lt;span class=&quot;math-container&quot;&gt;$^1$&lt;/span&gt;, perhaps the most popular topology in use today, the short answer to your question is, &quot;No,&quot; because your SWR meter is not measuring impedance. Rather, SWR is evaluated using the well-known relationship:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$SWR=\frac{V_f+V_r}{V_f-V_r}$$&lt;/span&gt;&#xA;where &lt;span class=&quot;math-container&quot;&gt;$V_f$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$V_r$&lt;/span&gt; &lt;em&gt;represent&lt;/em&gt; the forward and reverse voltages at the point of measurement. Developing the &lt;em&gt;representations&lt;/em&gt; of the forward and reverse voltages &lt;em&gt;does not&lt;/em&gt; require &quot;separating&quot; forward and reverse waves traveling on a transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As described in &lt;a href=&quot;http://www.collinsradio.org/wp-content/uploads/2015/05/Understanding-the-Bruene-Coupler-Transmission-Line-Bold.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Bruene Directional Coupler and Transmission Lines&lt;/a&gt; by Gary Bold, ZL1AN:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The operation of the Bruene coupler is traditionally derived as if it's inserted &lt;em&gt;in&lt;/em&gt; a &#xA;  transmission line, using the concepts of &quot;forward&quot; and &quot;reflected&quot; waves, which are &#xA;  assumed to exist on the line &lt;em&gt;before&lt;/em&gt; and &lt;em&gt;after&lt;/em&gt; it, and which flow &lt;em&gt;through&lt;/em&gt; it. But the &#xA;  coupler also works when connected to: the &lt;em&gt;input&lt;/em&gt; of a line; where there is no line on the &#xA;  &quot;input&quot; side; or when connected to a transmatch; or even to a pure resistance - which &#xA;  must always be done to calibrate it. There are no standing waves inside a transmatch or &#xA;  resistance, and the coupler itself doesn't contain a transmission line.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The Bruene Coupler - notice, it is not called a &quot;bridge&quot; - sums voltages to produce relative measurements of forward and reflected power. A capacitive divider (&lt;span class=&quot;math-container&quot;&gt;$C_1$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$C_2$&lt;/span&gt;, below) across the input develops a sample of the RF voltage. Samples of the RF current from two halves of the center-tapped secondary winding of the toroid transformer pass through a resistor (&lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt;) to develop corresponding voltage representations of the RF current:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wkRPO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wkRPO.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Note that the voltage induced by the current sample results from &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; rather than from &lt;span class=&quot;math-container&quot;&gt;$2R$&lt;/span&gt; because, by virtue of circuit symmetry, the potential at the &quot;center&quot; of resistor &lt;span class=&quot;math-container&quot;&gt;$2R$&lt;/span&gt; in the diagram is the same as the potential at the center tap of the transformer secondary. This connection is explicitly made in some designs.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$V_m$&lt;/span&gt;, the &quot;Reverse&quot; meter voltage being measured in the diagram, comprises the &lt;em&gt;difference&lt;/em&gt; between these two voltages. &lt;span class=&quot;math-container&quot;&gt;$V_m$&lt;/span&gt; on the &quot;Forward&quot; half of resistor &lt;span class=&quot;math-container&quot;&gt;$2R$&lt;/span&gt; comprises the &lt;em&gt;sum&lt;/em&gt; of the two voltages because the voltage induced in &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; by its half of the transformer secondary is &lt;span class=&quot;math-container&quot;&gt;$180^\circ$&lt;/span&gt; out of phase with the voltage induced on the &quot;Reverse&quot; half of &lt;span class=&quot;math-container&quot;&gt;$2R$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bold and David Knight, G3YNH, in his article on &lt;a href=&quot;http://www.g3ynh.info/zdocs/bridges/reflectom/part1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Reflectometry&lt;/a&gt;, discuss sources of error in SWR meters based on the capacitive divider.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Bruene, Warren, &quot;An Inside Picture of Directional Wattmeters,&quot; &lt;em&gt;QST&lt;/em&gt;, vol. 43 no. 4 (American Radio Relay League), April 1959, pp. 24-28&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-05-02T12:40:37.050" LastActivityDate="2019-05-02T12:40:37.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14433" PostTypeId="1" CreationDate="2019-05-02T07:28:25.510" Score="2" ViewCount="342" Body="&lt;p&gt;I am looking to buy a wifi antenna for a boat to connect to shore based wireless hotspots that may be &quot;far&quot; away. Due to the waves, I am assuming that the antenna mast sways +-15° from vertical. The antenna will be mounted approximately 18m above the water.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly if I choose an omni-directional antenna with too high gain, the swaying mast will lead to periodic drops of the the connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I choose the gain too low, I will not reach shore based access points.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can somebody advise me, what gain of an omni-directional antenna corresponds to an opening angle of 30°?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In principle it should be possible to define a relationship between gain and opening angle but all my internet searches for a graph showing this relationship have been in vain.&lt;/p&gt;&#xA;" OwnerUserId="14804" LastEditorUserId="9621" LastEditDate="2019-05-02T11:20:31.280" LastActivityDate="2019-06-12T13:36:35.357" Title="Beamwidth of omni-directional antenna with gain" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wifi&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14434" PostTypeId="2" ParentId="14433" CreationDate="2019-05-02T11:48:46.753" Score="4" Body="&lt;p&gt;According to Kraus&lt;span class=&quot;math-container&quot;&gt;$^1$&lt;/span&gt;, the directivity of an antenna with a given beamwidth can be &lt;strong&gt;&lt;em&gt;approximated&lt;/em&gt;&lt;/strong&gt; by:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$D\approx\frac{4\pi}{\theta_{HP} \phi_{HP}}$$&lt;/span&gt;&#xA;where &lt;span class=&quot;math-container&quot;&gt;$\theta_{HP}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\phi_{HP}$&lt;/span&gt; are the half-power beamwidths (in radians) in the azimuth and elevation planes. Simply put, this approximates the solid fraction of a sphere that is subtended by the antenna's half-power beamwidth. The approximation ignores the antenna's minor lobes and should be used in that context.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the beamwidths are expressed in degrees,&#xA;&lt;span class=&quot;math-container&quot;&gt;$$D\approx\frac{41000}{\theta^{\circ}_{HP} \phi^{\circ}_{HP}}$$&lt;/span&gt;&#xA;Thus, for an omnidirectional antenna with 30&lt;span class=&quot;math-container&quot;&gt;$^\circ$&lt;/span&gt; elevation beamwidth, &lt;span class=&quot;math-container&quot;&gt;$D\approx 3.8$&lt;/span&gt; or about 5.8dB gain over an isotropic source. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This gain can be provided by a &lt;a href=&quot;https://martybugs.net/wireless/collinear.cgi&quot; rel=&quot;nofollow noreferrer&quot;&gt;simple homemade collinear vertical antenna&lt;/a&gt;. Simulation indicates that such an antenna must be fed against a ground plane to provide low SWR to the WiFi radio. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;John D Kraus, &lt;em&gt;Antennas&lt;/em&gt;, McGraw-Hill, any edition&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-02T11:48:46.753" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="14435" PostTypeId="1" CreationDate="2019-05-02T13:08:02.200" Score="1" ViewCount="697" Body="&lt;p&gt;I'm going to be putting up a Comet GP6 UHF/VHF Ground Plane Antenna.  It will be chimney mounted to a mast, and the total height is around 40 ft.  The upper half of the chimney starts at the first story of the house and stands around 25-30 ft above the roof adding to the extra length of the coax.  I already own 80 ft of Tram RG213/U Mil-C-17G and was considering using that (they are split so I would have to use use connectors on them so they can be used together).  I also own a 82ft Belden RF400.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure what to use or if I should buy something else.  I'm also considering installing a feedline choke at the antenna side of the feed line similar to an HF antenna I'm setting up.  I know the RF400 would be a better feed line but I was hoping to use it on my HF setup 160m-6m end fed Balun 9:1 unun setup that's 100-120 ft away from my ham shack.  Same coax I'd like to use for my G5RV.  What would be the best type of feedline to use for the VHF/UHF antenna in this situation?   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do know there are a lot of variables. I will be using both digital &amp;amp; analog. The average distance to repeaters in my area is around 25-30 miles. I'm currently able to hit them with my 50W mobile rig without issue. I'm willing to buy different coax if needed. Leaving out the difficult to determine variables like obstacles (there is only 1 to my north but it has not hindered my contact to repeaters on my mobile in the driveway obstacles don't appear to be an issue). My rig will be a Yaesu FT-991a which runs 50W FTM UHF/VHF. I'm just trying to see if there is a preferable coax for my setup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="13303" LastEditorUserId="8713" LastEditDate="2020-05-09T18:49:55.327" LastActivityDate="2020-05-09T18:49:55.327" Title="What is the best type of feedline for a base UHF VHF ground plane antenna with a distance of around 50-75 feet of coax?" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14436" PostTypeId="2" ParentId="14426" CreationDate="2019-05-02T13:11:51.107" Score="1" Body="&lt;p&gt;If you are just transmitting GPS coordinates and at a slow rate and need a bandwidth of about 50kbps or less then have a look at LoRa technology.&#xA;It is low power, low data rate and spread spectrum but it is very reliable with a range over 10km (some as far as 50km) on licence free VHF and UHF bands. It is designed for IoT uses in a noisy environment it could be the solution to your problem depending on your exact requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;some details below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.rfsolutions.co.uk/radio-modules-c10/name-c49/lora-c218&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.rfsolutions.co.uk/radio-modules-c10/name-c49/lora-c218&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11749" LastActivityDate="2019-05-02T13:11:51.107" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14437" PostTypeId="2" ParentId="14435" CreationDate="2019-05-02T16:25:42.047" Score="1" Body="&lt;p&gt;Belden datasheets indicate RF400 has 2.7dB attenuation per 100ft at 450MHz; RG213 has 4.1dB at 400MHz. Given the lengths of the two cables you have on hand, it appears that the difference in attenuation between the two cables is on the order of 1dB, which is ordinarily insignificant given all the other variables involved.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-02T16:25:42.047" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14439" PostTypeId="2" ParentId="14435" CreationDate="2019-05-03T01:29:07.400" Score="1" Body="&lt;p&gt;LMR-1700 (*)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tend to shy away from questions of the form &quot;what is the best ...?&quot; because the answers tend to be subjective; they have to be, there are too many individual circumstances.  But this is a really good question because low-loss coax cable has some folklore associated with it and this is an opportunity to address some of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming you are restricting to 50 Ohm coaxial cable, the only parameter you are concerned with is loss, and there are no other considerations, I believe LMR-1700 is the cable you are looking for.  But it is expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If cost is a consideration and you are still restricting to 50 Ohm coaxial cable, check out the Times Microwave catalog.  They have multiple grades of low-loss cable and publish easy-to-understand specifications, including the equations used to compute loss at different frequencies.  If there are other considerations (say, ease of use or availability of connectors, for example), that is there too.  I suspect, after reading the spec sheets and checking prices, you will agree with @BrianK1LI that the RF400 you have on hand is &quot;good enough&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(*) There are good reasons to down-grade this answer.  If your reason is along the lines of &quot;there is a different cable with lower loss&quot; please add it in the comments.  I do not wish to spread misinformation. &lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2019-05-03T01:29:07.400" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14440" PostTypeId="2" ParentId="5930" CreationDate="2019-05-03T06:02:03.403" Score="3" Body="&lt;p&gt;We have been using traditional hf modes on a weekly 2 meter FM net for around 5 years. Participation varies from week to week. There is no weak signal advantage over a FM modulated signal. Our net is to encourage upgrading and to teach data modes. The local ARES group has recently  started adding message and forms transfer using the fldigi suite to our ARES group to encourage wider spread adoption of these forms in our radio community for the same reason. SSTV, hell, PSK31, RTTY, and Olivia are among the most popular modes. We are now seeing activity on 10 meter data sub band locally. Give people a reason to upgrade and they will. Ham radio is more fun when it is more than just voice. &lt;/p&gt;&#xA;" OwnerUserId="14810" LastActivityDate="2019-05-03T06:02:03.403" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14441" PostTypeId="1" AcceptedAnswerId="14446" CreationDate="2019-05-03T22:29:03.537" Score="5" ViewCount="178" Body="&lt;p&gt;There have been a number of questions regarding the issue of feed line loss and ladder line eventually gets discussed.  So I am curious, how does one begin to estimate the loss in ladder line?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, for the case of 2 bare wires &quot;somehow&quot; spaced an appropriate distance apart acting as a feedline with SWR=1.000, what loss could be expected?  (Loss due to SWR was very well covered here:  &lt;a href=&quot;https://ham.stackexchange.com/questions/7333/what-is-the-actual-loss-in-a-feed-line-with-high-swr&quot;&gt;What is the actual loss in a feed line with high SWR?&lt;/a&gt; )&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would think that spacing the wires farther apart would increase the impedance, lowering the current and thus the loss/100m (at a cost, perhaps, of more complicated and lossy impedance transformers at each end which I am ignoring).  I would think that adding an insulator would (1) lower the velocity factor --somewhat increasing the loss by somewhat increasing the number of wavelengths at a given frequency-- and (2) add some sort of additional loss mechanism in addition to that which could be attributed directly to the velocity factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to quantify any of this?&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2019-05-09T18:01:18.020" Title="How to estimate ladder line loss?" Tags="&lt;feed-line&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14442" PostTypeId="2" ParentId="14441" CreationDate="2019-05-03T23:31:43.710" Score="4" Body="&lt;p&gt;There is a program called TLDetails, available from &lt;a href=&quot;https://ac6la.com/tldetails1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ac6la.com/tldetails1.html&lt;/a&gt;, that will calculate the loss for many standard transmission lines. One enters the frequency, the type and length of transmission line, and the load impedance and TLDetails will calculate the line loss, SWR, and impedance seen at the source plus other parameters. More information on k0, k1, and k2 is covered under &lt;a href=&quot;https://ac6la.com/zplots1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ac6la.com/zplots1.html&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-05-04T03:57:37.877" LastActivityDate="2019-05-04T03:57:37.877" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14446" PostTypeId="2" ParentId="14441" CreationDate="2019-05-04T13:13:49.017" Score="5" Body="&lt;p&gt;For most feedlines, dielectric loss is very low, and at HF where ladder line is practical, negligible. So significant losses are due to resistance and associated Joule heating of the copper conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The characteristic impedance &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; gives the ratio of voltage to current in a matched line, so we can always find voltage if the current is known:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ E = Z_0 I \tag 1 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and the power &lt;span class=&quot;math-container&quot;&gt;$P$&lt;/span&gt; transmitted by the line is the product of current and voltage between the conductors:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ P_\text{tx} = IE $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;substituting equation 1 for &lt;span class=&quot;math-container&quot;&gt;$E$&lt;/span&gt;, we get&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ P_\text{tx} = I^2 Z_0 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and solving for &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; we can determine the current in a matched line as a function of power and characteristic impedance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ I = \sqrt{P_\text{tx} \over Z_0} \tag 2$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, Joule heating which is most of the loss is the product of resistance &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; and current squared:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ P_J = I^2 R $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;substituting equation 2 for &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; yields&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ P_J = {P_\text{tx} \over Z_0} R \tag 3 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;therefore as a first order approximation, we can say losses are inversely proportional to characteristic impedance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ P_J \propto {1 \over Z_0} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, doubling the impedance halves the power lost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind &quot;loss&quot; in transmission lines is actually the ratio of power in to power out: it's power &lt;em&gt;not&lt;/em&gt; lost. So don't make the mistake of thinking a feedline with 1dB of loss, if the impedance is doubled, becomes 3dB better with a result of 2dB of gain!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rather, a loss of 1dB means &lt;span class=&quot;math-container&quot;&gt;$ 1 - 10^{-1/10} = 20.6\% $&lt;/span&gt; of the power is lost. Doubling the impedance would change that loss to &lt;span class=&quot;math-container&quot;&gt;$ -10 \log_{10} (1- .103) = 0.47\:\mathrm{dB} $&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equation 3 provides a start for calculating the loss, but the devil is in the details, especially in calculating &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt;. Both the &lt;a href=&quot;https://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin effect&lt;/a&gt; and  &lt;a href=&quot;https://en.wikipedia.org/wiki/Proximity_effect_(electromagnetism)&quot; rel=&quot;nofollow noreferrer&quot;&gt;proximity effect&lt;/a&gt; must be taken into account, and the math is not nearly so simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For practical purposes I suspect the approximation is good enough to appreciate the potential benefits of a feedline change. If more precise loss numbers are required then perhaps an empirical method is easiest.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8717" LastEditDate="2019-05-09T18:01:18.020" LastActivityDate="2019-05-09T18:01:18.020" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14452" PostTypeId="1" CreationDate="2019-05-06T10:42:32.127" Score="2" ViewCount="233" Body="&lt;p&gt;This feature that some radios have seem to have various names:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;band scope&lt;/li&gt;&#xA;&lt;li&gt;spectrum scope&lt;/li&gt;&#xA;&lt;li&gt;water fall&lt;/li&gt;&#xA;&lt;li&gt;panadapter&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I understand the first three names, but not panadapter. Where does it come from?&lt;/p&gt;&#xA;" OwnerUserId="10431" LastEditorUserId="76" LastEditDate="2020-02-09T23:48:18.693" LastActivityDate="2020-02-09T23:48:18.693" Title="Why is the band scope called panadapter?" Tags="&lt;jargon&gt;&lt;panadapter-and-waterfall&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14453" PostTypeId="2" ParentId="14452" CreationDate="2019-05-06T10:53:34.900" Score="2" Body="&lt;p&gt;&quot;Panorama, an unobstructed and wide view of an extensive area in all directions.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &quot;panoramic adapter&quot; for implementing a &quot;wide view&quot; of the radio spectrum is abbreviated as &quot;panadapter&quot;.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-05-06T14:19:25.677" LastActivityDate="2019-05-06T14:19:25.677" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14455" PostTypeId="2" ParentId="14452" CreationDate="2019-05-06T12:12:04.253" Score="9" Body="&lt;p&gt;Marcel Wallace founded Panoramic Radio Corp. and details his &quot;Panoramic radio receiving system&quot; in patent &lt;a href=&quot;https://patents.google.com/patent/US2279151&quot; rel=&quot;nofollow noreferrer&quot;&gt;US2279151A&lt;/a&gt; (1938). Page 2, column 1, line 19 of the patent gives us a clue as to how the physical &quot;panoramic&quot; concept made its way into what we now consider to be a purely electrical phenomenon:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;...provide a panoramic radio compass system having visual indicating means operative in correlation to the radio compass system...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In &quot;One-Chip Panoramic Adpapter&quot; &lt;a href=&quot;https://www.americanradiohistory.com/Archive-Short-Wave-UK/90s/SWM-1995-01.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Shortwave Magazine for January 1995 pp. 18-25&lt;/a&gt;, Bill Wilson makes this attribution:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;To the best of my knowledge, the panoramic receiver was invented in the early thirties by a Marcel Wallace ... Dr. Wallace later devised the panoramic adapter which could be connected to a conventional superhet to permit a visual spectrum display, and, along with the Hallicrafters company, coined the term 'Panadapter'.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Figure 4 from Wilson's article shows that the &quot;adapter&quot; picked off its input before the IF signal was filtered by the receiver's high-selectivity stages. Comprising its own RF amp, mixer, oscillator, filter and detector, the panadapter is essentially a second receiver, but one who's output is meant to be displayed visually rather than decoded, audibly or otherwise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jjBTD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jjBTD.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-05-07T16:14:17.850" LastActivityDate="2019-05-07T16:14:17.850" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14456" PostTypeId="2" ParentId="13289" CreationDate="2019-05-06T19:24:26.707" Score="1" Body="&lt;p&gt;A horizontal loop of 283Ft circumference will work brilliantly. Feed it at any point with 300ohm flat twin window (slotted ) feeder and ideally use 60 feet of this back into a balanced tuner in the shack. Height will not be overly important. You will have high angle radiation on 80m but that will still work long distances after dark.&#xA;The angle of radiation will drop for 40m band use and get progressively lower still as you work your way towards the higher bands like 20  15 and 10m. At 10 metres you should have eight daisy petal lobes radiating as horizon kissers. It can be a rectangle, circle or heptagon as you like, but aim to keep as open a shape as possible. (Avoid &quot;Letter box&quot; slot shape for example !) &#xA;Mine was at an average height of 18 feet and was the &quot;best antenna I ever had&quot;. It won't break the bank either. Good luck ! Mike EA7JVZ. &lt;/p&gt;&#xA;" OwnerUserId="14834" LastActivityDate="2019-05-06T19:24:26.707" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14457" PostTypeId="2" ParentId="13289" CreationDate="2019-05-06T20:06:13.737" Score="5" Body="&lt;p&gt;Summary: substantial advantage can be realized for every meter increase in the height of the loop. Other parameters, including the metal roof, are much weaker factors in performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I simulated a 3.8MHz 1-&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; hexagonal loop (no wire loss) mounted 3-m above medium-conductivity ground, surrounding a 5m x 20m grid of wires as shown here:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/VDfKw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VDfKw.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the loop is so close to the ground (in wavelengths), the 0.2-dBi maximum radiation occurs at the zenith. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/L5i4w.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/L5i4w.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;dropping to -3-dBi at 45&lt;span class=&quot;math-container&quot;&gt;$^\circ$&lt;/span&gt; elevation angle. The gain increases less than 0.25-dB when the wire grid is removed, a small change as expected from the low currents reported in the grid wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SWR calculations show that the &quot;roof&quot; does have a meaningful effect on the loop's characteristics:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/koybi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/koybi.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feeding the loop at the mid-point of a side parallel to the long edge of the &quot;roof&quot; gives somewhat better SWR than feeding the mid-point of one of the &quot;angled&quot; sides, so the loop must indeed be exciting meaningful current in the grid wires. It's possible that the slight gain decrease with the wire grid is due to ground losses, which would couple into the loop, lowering the Q and the efficiency of the antenna. Conversely, feeding at a corner of the loop has minimal impact on the SWR curve, regardless of the presence of the wire grid. The antenna's feedpoint impedance varies considerably as the band is changed; a wide-range antenna matching network will probably be required. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Raising the loop just 1 meter increases the gain at the zenith by 2dB. Another meter increase adds another 1.5dB. The gain at 45&lt;span class=&quot;math-container&quot;&gt;$^\circ$&lt;/span&gt; elevation increases at about half the rate of the gain at the zenith.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the request of another SE member, here are 3D plots that show how the pattern evolves as the frequency is successively doubled:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;7.15MHz - maximum gain ~0dBi, impedance 152.6 - J 423.1 ohms&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5MShM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5MShM.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;14.2MHz - maximum gain 5dBi, impedance 439.3 - J 1106 ohms&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cmB8j.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cmB8j.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-05-10T17:17:18.833" LastActivityDate="2019-05-10T17:17:18.833" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14458" PostTypeId="1" AcceptedAnswerId="14499" CreationDate="2019-05-07T00:50:29.520" Score="4" ViewCount="831" Body="&lt;p&gt;I've got a Kenwood MC-59 microphone, which started fraying around the place where the mic cable goes into the body. I thought I'd cut it off and put a new RJ-45 jack on it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After cutting the cable, I discovered something completely unexpected. Although it looks as if the RJ-45 plug has 8 insulated connectors:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1Y0jn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1Y0jn.png&quot; alt=&quot;top view of jack with 8 wires connected&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;the cable itself has only 7 (plus a shield):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/HJKrA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HJKrA.png&quot; alt=&quot;end of cable with 7 wires + shield&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone ever repaired one of these cables before, and if so - what goes where? How did you do it?&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2019-05-13T07:06:11.420" LastActivityDate="2019-05-13T07:06:11.420" Title="How do I put an RJ-45 connector on to repair a Kenwood MC-59 microphone cable?" Tags="&lt;kenwood&gt;&lt;audio-interface&gt;&lt;repair&gt;&lt;microphone&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14459" PostTypeId="1" AcceptedAnswerId="14460" CreationDate="2019-05-07T09:48:27.863" Score="3" ViewCount="850" Body="&lt;p&gt;I have an LDG RBA-1:1 current balun, and I was wondering if it behaves as a common-mode choke that I can use for a ground-mounted quarter wave vertical w/ 16 radials. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other choice I have is a 4:1 unun (also LDG), but I think that would cut  down my impedance quite a lot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I currently do not have an antenna analyzer so that I can properly measure the performance.&lt;/p&gt;&#xA;" OwnerUserId="11474" LastEditorUserId="8717" LastEditDate="2019-05-07T18:56:25.533" LastActivityDate="2019-05-07T19:02:04.493" Title="Can I use a 1:1 current balun to feed a 1/4λ vertical?" Tags="&lt;balun&gt;&lt;vertical-antenna&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14460" PostTypeId="2" ParentId="14459" CreationDate="2019-05-07T10:52:41.917" Score="4" Body="&lt;p&gt;Looking at the pictures of the LDG RBA-1:1, it looks like the answer is yes. It is just a choke that can be used as either a balun or unun. Note that if the vertical has a resonant feedpoint resistance of 35 ohms, a 50 ohm unun will transform the 35 ohms to a slightly inductive impedance which will decrease the resonant frequency at the unun input terminal. Or if you want a perfect SWR, you can use a shunt capacitor at the unun input terminal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://www.radioexpert.ru/upload/iblock/4bb/4bb35fed728a4e6c2d81d47df7b37a52.jpg&quot; alt=&quot;LDG RBA-1:1&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-05-07T18:10:39.363" LastActivityDate="2019-05-07T18:10:39.363" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14461" PostTypeId="1" CreationDate="2019-05-07T18:15:28.453" Score="2" ViewCount="1931" Body="&lt;p&gt;I, just as a hobby project, am writing a program for decoding Morse code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not a ham, but generally interested in radio and programming.&#xA;I have a first version of the project, but it failed to decode the signal in &lt;a href=&quot;https://www.dropbox.com/sh/adoatd80zm0i37d/AADsdp7Az9SEgu5X7Vq6_yhIa?dl=0/StrangeMorse.mp3&quot; rel=&quot;nofollow noreferrer&quot;&gt;this recording&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The length relation between the dash and the dots is far from &quot;standard&quot; and the length of the dashes varies wildly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this type of signal common or should I say &quot;skip this, too weird&quot;? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also see &lt;code&gt;_....._&lt;/code&gt; in the recording, which I don't recognize as a character: does it have some special interpretation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:&#xA;Fun to read about the &quot;banana boat swing&quot;. And to get confirmation about my suspicion that a &quot;bug&quot; was used from the consistent length of the &quot;dits&quot;.&#xA;I once tried to learn Morse, but I gave it up. Was unable to get hang of reading. For sending I tried both straight key and bug. And according to my&#xA;mentor my &quot;fist&quot; was quite good.&#xA;The aim of the project is not only to read the charters. But also to decode all the prosigns to make the conversation more understandable for an outsider.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73   :)&lt;/p&gt;&#xA;" OwnerUserId="14525" LastEditorUserId="14525" LastEditDate="2019-05-08T09:42:12.907" LastActivityDate="2019-05-08T09:42:12.907" Title="Is this strange Morse signal type common?" Tags="&lt;cw&gt;" AnswerCount="6" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14462" PostTypeId="2" ParentId="14459" CreationDate="2019-05-07T19:02:04.493" Score="1" Body="&lt;p&gt;You can. In fact currently I'm doing some experiments with verticals and do exactly this - use a 1:1 current balun which I originally made for a dipole as an RFI choke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are interested in the subject, here are a few articles that will answer all your questions regarding baluns, RFI chokes and common mode current:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/AntComp1-Lewallen(1).pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Baluns: What They Do And How They Do It [PDF]&lt;/a&gt; by Roy Lewallen, W7EL&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Common-mode chokes&lt;/a&gt; by Steve Hunt, G3TXQ&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-05-07T19:02:04.493" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14463" PostTypeId="2" ParentId="14461" CreationDate="2019-05-07T19:10:41.713" Score="3" Body="&lt;p&gt;I'm not an expert but it sounds like a regular CW to me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem with decoding CW automatically is that it's synthesised by people. The speed (letters per minute) can change, the length of &quot;dits&quot; and &quot;dahs&quot; can change, etc. Whether you should support decoding such style of CW depends only on the time you are willing to invest in the project.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The code &lt;code&gt;.....&lt;/code&gt; is a regular code for number 5.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-05-07T19:10:41.713" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14464" PostTypeId="2" ParentId="14461" CreationDate="2019-05-07T19:11:34.837" Score="3" Body="&lt;p&gt;I can't listen to the recording at the moment, but what you describe sounds very much like a &quot;bad fist&quot; -- an operator whose sending isn't particularly standards compliant.  Incorrect dot-to-dash ratio and varying dash length are characteristic of sloppy sending (though it's barely possible you recorded someone using the old American Morse, which had two different dash lengths and different ratios and spacing from International Morse).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the biggest challenges of writing a Morse reader program is handling the inconsistencies of hand-sent Morse.  Even the best operator will have some variation in ratio and spacing -- this is the &quot;fist&quot; that lets an experienced operator recognize another ham from the sound of his Morse.  Even highly developed software doesn't always manage to interpret some fists that an experienced human operator will read without problems.  In some ways, it's like handwriting recognition in software (but at least without the image processing and need to handle both manuscript and cursive).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether you want to try to write your software to handle a broad range of fists, or only something close to the &quot;perfect code&quot; a machine would send, is up to you.  The latter is far easier -- but the former is more useful, and a much greater challenge.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-05-07T19:11:34.837" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14465" PostTypeId="2" ParentId="14461" CreationDate="2019-05-07T19:12:58.537" Score="2" Body="&lt;p&gt;To my ears, that's not all that strange. I was able to casually copy some words by ear. I would guess that it was sent using a hand key, rather than a computer or electronic keyer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some unfinished CW RX Pascal code here --somewhere-- that I wrote many years ago to compensate for variations in dit, dah, or spacing lengths. I suggest you think about writing something similar. It used if..then 'greater or less than' character length statements to correct and print the characters.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-05-07T19:31:28.310" LastActivityDate="2019-05-07T19:31:28.310" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14466" PostTypeId="1" CreationDate="2019-05-07T20:24:28.967" Score="2" ViewCount="322" Body="&lt;p&gt;I've build a verical for 40M band using a fishing rod as a mast, 6 radials and an RFI choke (FT240-31 ring, 8 turns of RG58, W1JR winding according to the &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;article&lt;/a&gt; by Steve Hunt).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I measure SWR right in the bottom of the antenna, using only 2-3 meters of RG58 as a feeder, I get this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Rc7fx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Rc7fx.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is pretty much what I would expect - a resonance around 7 Mhz + around 21 Mhz as a 3rd harmonic. The SWR meter is not well calibrated, thus it shows SWR 1.3:1 at 7 Mhz when it's in fact 1:1 according to two other SWR meters I have.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I add about 10 meters of RG58 to the feeder the picture changes, but not much in terms of SWR:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/romsk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/romsk.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, here is what I see if I measure SWR from the shack (about 30 meters of coax):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RLAn8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RLAn8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This I find quite surprising. I've found a few similar questions, including:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/5098/will-measuring-swr-through-a-feed-line-mislead-me&quot;&gt;Will measuring SWR through a feed line mislead me?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/12177/exactly-why-do-some-swr-meters-give-a-changing-reading-depending-on-the-length-o&quot;&gt;Exactly why do some SWR meters give a changing reading depending on the length of coax used to connect to an antenna?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It looks like usually people name two possible reasons of changes in SWR readings:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Common mode current, e.g. feeder radiates and works as a part of the antenna.&lt;/li&gt;&#xA;&lt;li&gt;Losses in the feeder, thus lower reflected power and lower SWR.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Although both explanations sound plausible 1) I'm quite conviced that common mode current is well suppressed in my case. I used this choke many times before under different conditions and with different power. Nothing indicated that the coax radiated anything. 2) Somehow I doubt that 10 or 30 meters of coax introduce significant losses. Also a 100W transceiver agrees with SWR readings I get.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any &lt;strong&gt;other&lt;/strong&gt; reasons why SWR could depend on the length of the feeder? For instance, can the feeder work as a matching device for the antenna on certain bands? If it's possible then how does it work?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-05-07T22:31:07.667" Title="Why SWR significantly changes with adding 10-30 meters of coax in presence of RFI choke?" Tags="&lt;antenna-theory&gt;&lt;vertical-antenna&gt;&lt;impedance-matching&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14467" PostTypeId="2" ParentId="14461" CreationDate="2019-05-07T20:52:08.360" Score="4" Body="&lt;p&gt;That sounds like code sent from a &lt;a href=&quot;https://en.wikipedia.org/wiki/Vibroplex&quot; rel=&quot;nofollow noreferrer&quot;&gt;bug&lt;/a&gt; to me: machine-generated dits, hand-generated dahs.  The operator seems fairly good actually; those things take lots of practice to use well, and I've definitely heard much worse code from bugs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can see how writing software to decode that would be challenging, but code like that won't seem unusual or more-difficult to copy to any long-time Morse operator.  This is one area where machine learning and software are only now just catching up to an ability skilled humans have had for over a century.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-05-07T20:52:08.360" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14468" PostTypeId="2" ParentId="14461" CreationDate="2019-05-07T21:15:54.560" Score="11" Body="&lt;p&gt;That is Morse code, in Norwegian, being sent with a &quot;bug&quot; (Vibroplex type mechanical key). The two operators are &lt;a href=&quot;https://www.qrz.com/db/la6uh&quot; rel=&quot;noreferrer&quot;&gt;LA6UH&lt;/a&gt; and &lt;a href=&quot;https://www.qrz.com/db/la7js&quot; rel=&quot;noreferrer&quot;&gt;LA7JS&lt;/a&gt;. Probably not something you want to figure out how to decode with a machine, but the ops' &quot;fists&quot; make them very recognizable to those who know them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;LA6UH gives a clue in his bio, where he writes:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I spent a couple of years of my youth roaming the seven seas as a radio officer.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I worked as a research assistant on the &lt;a href=&quot;https://www.google.com/maps/place/16%C2%B005&amp;#39;52.5%22N+86%C2%B055&amp;#39;58.9%22W/@16.0979189,-86.9680531,13z/data=!4m14!1m7!3m6!1s0x8f69b52e8defd67b:0x1be70667bd085710!2sUtila,+Honduras!3b1!8m2!3d16.0989148!4d-86.8960322!3m5!1s0x0:0x0!7e2!8m2!3d16.0979181!4d-86.9330337&quot; rel=&quot;noreferrer&quot;&gt;Honduran island of Utila&lt;/a&gt; the summer after graduating high school. The only reliable communications with the mainland were via the commercial radio shack a few hundred yards from our residence, from which they also served the Merchant Marine and security establishments. Those ops had the true &quot;banana boat swing,&quot; virtually indecipherable to my ears, even though I was already a Vibroplex veteran. The ops identified each other immediately by &quot;fist,&quot; much as any of us recognize people we know by the timbre and cadence of their speech.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-05-08T01:39:19.353" LastActivityDate="2019-05-08T01:39:19.353" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14469" PostTypeId="2" ParentId="1596" CreationDate="2019-05-07T22:22:14.463" Score="1" Body="&lt;p&gt;RC oscillators have high levels of sideband noise. I do not know whether one could mitigate that by connecting RC filters in series, but it seems unlikely to me. A good LC oscillator uses the fact that the impedance depends on the frequency. With a parallel crystal resonance, the amplifier would see a low impedance far from the resonance so the wideband noise floor would not be determined by the noise near the resonance where impedance is high. Likewise, an osscillator using a series resonant crystal would have a very low gain off resonance because it would use a grounded base/gate configuration where gain is inversionally proportional to signal source impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe this page can help to understand the problems:&#xA;&lt;a href=&quot;http://www.sm5bsz.com/osc/newref.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sm5bsz.com/osc/newref.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-05-07T22:22:14.463" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14470" PostTypeId="2" ParentId="14466" CreationDate="2019-05-07T22:31:07.667" Score="3" Body="&lt;p&gt;The repeating hi-Z measurements seen when SWR is measured with the 30m line suggest that it is defective. One needs to know the velocity factor and loss of the cable to determine the location of the defect. These should be determined from measurement, as actual lines can deviate significantly from published specifications and values can change as a result of electrical and environmental ageing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As shown on &lt;a href=&quot;https://www.daenotes.com/electronics/communication-system/open-circuited-transmission-line&quot; rel=&quot;nofollow noreferrer&quot;&gt;DAE Notes&lt;/a&gt;, the impedance measured at the input to an open-circuited transmission line will be high at frequencies at which the line's electrical length is an even multiple of a half-wavelengh:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uaZ25.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uaZ25.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact that you observe similar behavior with a different antenna as the load reinforces this conclusion.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-07T22:31:07.667" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14471" PostTypeId="2" ParentId="14461" CreationDate="2019-05-08T03:03:17.293" Score="1" Body="&lt;p&gt;Having just listened to the recording, I concur with the other answers that say this is Morse code generated by a mechanical &quot;bug&quot; key, where the dots are generated by the key, and the dashes are generated manually by the operator. I have never tried using one of these keys, but I would imagine that they take a bit of getting used to. But one day if you used one every day as your only way of communicating, you might be as proficient as these operators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are obviously very comfortable talking to each other, and very comfortable with each other's &quot;fists&quot;. I disagree with the answer saying this is a &quot;bad fist&quot;, since both operators seem fine talking to each other, and with a bit of practice you would easily be able to understand what they are saying (assuming you can read Norwegian, which I can't!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Interestingly, and counterintuitively, the mechanical &quot;bug&quot; is where the convention of using the 'thumb' paddle for the dots and the 'index finger' paddle for the dashes on a paddle key comes from - one would expect to use the index finger for the dots and the thumb for the dashes, as you need more precision for the shorter elements than you need for the longer ones. But on a mechanical &quot;bug&quot; you don't need much precision for the dots, since they are being generated by the key - and it is more important to use the extra precision for the dashes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, to answer the question about the &lt;code&gt;_...._&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two possible answers for this:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;it could be that the user is sending &lt;code&gt;_..._&lt;/code&gt; but missing the number of dots, so it comes out with four dots instead of three. The symbol &lt;code&gt;_..._&lt;/code&gt; is the &quot;equals sign&quot; &lt;code&gt;=&lt;/code&gt; and is commonly used as a 'break' in text, usually to indicate that there may be a pause following, but that you're not finished yet.&lt;/li&gt;&#xA;&lt;li&gt;It is also possible that the user intended to send &lt;code&gt;_...._&lt;/code&gt; which is a dash &lt;code&gt;-&lt;/code&gt; because he is a way more experienced operator than most, and actually knows most of the punctuation symbols that most people never use in standard conversation.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I tend to favour the second explanation, after listening to the audio.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-05-08T03:03:17.293" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14472" PostTypeId="1" AcceptedAnswerId="14474" CreationDate="2019-05-08T03:56:27.633" Score="1" ViewCount="261" Body="&lt;p&gt;Currently, I am running a semi-portable setup at home. I have a spool of 100ft of lmr400 coax outside in the porch where it free from most weather and rain. I only drag it out to the yard when I am setting up a portable antenna, and when I am not on the air it is in front porch. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not going to have it out when it is pouring rain outside, but I did notice a lot condensation on the antenna and coax when I left it out overnight to work on night bands. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I still imply some waterproof treatment or pl259 is water resistant enough? &#xA;I think that warp the connector in raincoat tape and cut it open every setup and take down is a little hassle.&lt;/p&gt;&#xA;" OwnerUserId="13362" LastActivityDate="2019-05-08T10:16:16.770" Title="Temporary/Portable station coax pl259 connector water proof?" Tags="&lt;pl259-so239-connector&gt;&lt;portable&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14474" PostTypeId="2" ParentId="14472" CreationDate="2019-05-08T05:29:47.350" Score="2" Body="&lt;p&gt;For temporary connections, there's small &quot;clamp on&quot; cable boxes, something like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/v8IFP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/v8IFP.jpg&quot; alt=&quot;waterproof box&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qfEdx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qfEdx.jpg&quot; alt=&quot;box2&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Definitely not &quot;condensation-proof&quot;, but &quot;should reduce quite significantly&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other than that, there's people that swear by the powers of the flexible LIDL or Aldi plastic radome, i.e. a plastic bag fastened with rubber bands or whatever around the parts to be protected. I can see how that would be even better, but look less professional.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-05-08T05:29:47.350" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14475" PostTypeId="1" CreationDate="2019-05-08T09:33:27.623" Score="2" ViewCount="151" Body="&lt;p&gt;Most resources around the Internet discuss common antenna types, classifying them between directive (like Yagi) and nondirective (like a simple dipole). Directive antennas are good when you know from which direction you are receiving a signal and would like to collect as much of it as possible. Nondirective antennas are good when you do not know from where you are receiving, or you want to receive from many directions at once without moving your antenna.&lt;/p&gt;&#xA;&lt;p&gt;I would like to build a weakly directive antenna: i.e., I don't know the direction from which I will be receiving, but I know it must be in a certain half plane or quadrant around my position (because in the other directions there are buildings that screen any interesting signal, and unfortunately I do not have easy access to an unobstructed position).&lt;/p&gt;&#xA;&lt;p&gt;I could use a nondirective antenna that also listens in the useless directions, but maybe I can squeeze some dB more if I can exclude them. What are good antenna types for this kind of application? Pointers to designing resources are welcome!&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt; As specified in the comments, my band of interest for this antenna in VHF/UHF. Mostly UHF, actually. I am looking for antennas whose radiation pattern is something like one of these two pictures.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/go1hB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/go1hB.png&quot; alt=&quot;90 degrees pattern&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ge8HY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ge8HY.png&quot; alt=&quot;180 degrees pattern&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I would consider an antenna nondirective when it has a radiation pattern more or less like a circle, and strongly directive when the radiation pattern is a circle sector with a small angle (and therefore a strong gain in that sector), like 10 degrees or less. Since this is intermediate between the two extremes, I would consider this weakly directive, but if this is non standard terminology just ignore it.&lt;/p&gt;&#xA;" OwnerUserId="1654" LastEditorUserId="8573" LastEditDate="2020-08-04T16:50:31.153" LastActivityDate="2020-08-04T16:50:31.153" Title="Weakly directive VHF/UHF antenna" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;uhf&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14476" PostTypeId="2" ParentId="14472" CreationDate="2019-05-08T09:52:08.270" Score="2" Body="&lt;p&gt;For temporary weatherproofing my coax connectors I use a piece of bicycle innertube and a few cable ties.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2019-05-08T09:52:08.270" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14477" PostTypeId="2" ParentId="14472" CreationDate="2019-05-08T10:16:16.770" Score="1" Body="&lt;p&gt;Your are rightly concerned about dew infiltrating the connector. This can cause corrosion over time and moisture can build up to the point that short circuits result. But, if you only leave the antenna outdoors for a day or two at a time and not in the rain, it's unlikely you need very much moisture protection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I treat the threads of all PL259/SO239 connectors - whether used indoors or out - with a thin layer of the Aluminum-loaded grease originally intended to prevent oxidation of Aluminum house wiring ... when that was still a thing. This is sold at most hardware and home improvement retailers as &quot;anti oxidant compound&quot; under trade names like NoAlOx, OxGard, etc. The pressure between the mating connector threads forces connection through the Aluminum particles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Especially if the connector is mounted in a vertical orientation, you may find that this provides enough moisture-repelling effect to protect your connection without adding external sealants. It also serves to prevent over-tightened connectors from seizing.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-08T10:16:16.770" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14478" PostTypeId="2" ParentId="14475" CreationDate="2019-05-08T10:32:49.717" Score="3" Body="&lt;p&gt;A center-fed half-wave dipole mounted a half-wavelength above ground isn't as directive as you might expect. The deep nulls off the ends of the antenna are not as pronounced as they are in free space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simulation with &lt;em&gt;&lt;a href=&quot;http://eznec.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC&lt;/a&gt;&lt;/em&gt; shows this azimuth pattern at the elevation angle of maximum radiation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/acNTH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/acNTH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Drooping the ends of the dipole to form an &quot;inverted V&quot; with a 90&lt;span class=&quot;math-container&quot;&gt;$^\circ$&lt;/span&gt; included angle further fills in the nulls:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3pBf4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3pBf4.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This antenna's low cost, simplicity, good SWR and relatively low directivity may satisfy your requirements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may want to consider downloading the free &lt;a href=&quot;https://www.qsl.net/4nec2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;4NEC2&lt;/a&gt; antenna modeling program. It comes with many antenna models, from simple verticals and dipoles to complex beams and arrays, which will give you a jump start, and its optimizer simplifies and accelerates the process of obtaining a useful based on your goals and constraints.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-05-08T10:42:17.447" LastActivityDate="2019-05-08T10:42:17.447" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14479" PostTypeId="1" AcceptedAnswerId="14480" CreationDate="2019-05-08T11:06:19.117" Score="3" ViewCount="232" Body="&lt;p&gt;The specification for a certain radio receiver says: Typically 12dB SINAD NBFM for 0.15uV at 145MHz.&#xA;If I understand correctly, this means that the received radio wave should have a voltage level of at least 0.15uV for the receiver to produce a signal with a quality of 12dB SINAD. I know how to calculate the signal power with the link equation, I can also calculate the electric field intensity of the EM wave, but I don't see how I can calculate the voltage level of a signal. How do I verify that my transmitted radio wave will meet this voltage requirement?&lt;/p&gt;&#xA;" OwnerUserId="14847" LastActivityDate="2019-05-08T23:19:54.370" Title="Determining whether signal meets the 12 dB SINAD voltage" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;wire-antenna&gt;&lt;rf-power&gt;&lt;voltage&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14480" PostTypeId="2" ParentId="14479" CreationDate="2019-05-08T12:17:05.913" Score="2" Body="&lt;p&gt;The specification means &lt;span class=&quot;math-container&quot;&gt;$0.15\ \mu\text{V}$&lt;/span&gt; at the input terminals of the receiver, so this voltage across a &lt;span class=&quot;math-container&quot;&gt;$50\ \Omega$&lt;/span&gt; load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power in a resistor can be calculated with&lt;br&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$P={V^2}/{R}$&lt;/span&gt;&lt;br&gt;&#xA;so &lt;span class=&quot;math-container&quot;&gt;$0.15\text{ }\mu\text{V}$&lt;/span&gt; is a power of &lt;span class=&quot;math-container&quot;&gt;${(0.15 \times 10^{-6})^2 } /{50} =  4.5 \times 10^{-16} \text{ W}$&lt;/span&gt; (&lt;a href=&quot;https://www.google.com/search?q=%280.15%20microvolts%29**2%2F%2850%20ohms%29%20in%20milliwatts&quot; rel=&quot;nofollow noreferrer&quot;&gt;or ask google&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is &lt;a href=&quot;https://www.google.com/search?q=10*log10%284.5e-16+Watts+%2F+%281+milliWatt%29%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;-123.5 dBm&lt;/a&gt; into the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For interest, if the receiver is 25 kHz wide, and needs about 6 dB S/N to achieve that SINAD, then the receiver noise figure is an amazing 3 dB. Put another way, thermal noise at room temperature, in 25 kHz, is already -127 dBm, so the receiver is about as sensitive as it could possibly be for terrestrial communications.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-05-08T20:12:11.177" LastActivityDate="2019-05-08T20:12:11.177" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14481" PostTypeId="2" ParentId="14479" CreationDate="2019-05-08T12:22:20.837" Score="1" Body="&lt;p&gt;You must also know the impedance of the receiver which is typically 50 ohms.&#xA;Convert the received signal from dBm to Watts.&#xA;Then the input voltage is sqrt ( P * R )&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We usually work this the other way around:&#xA;Convert 0.15 uV into 50 Ohms to dBm which is -123.5 dBm.&#xA;If your signal is greather than that you are Ok.&#xA;Say your received signal is -100 dBm you have a 23.5 dB fade margin.&lt;/p&gt;&#xA;" OwnerUserId="13732" LastEditorUserId="13732" LastEditDate="2019-05-08T23:19:54.370" LastActivityDate="2019-05-08T23:19:54.370" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14482" PostTypeId="2" ParentId="14475" CreationDate="2019-05-08T14:54:03.783" Score="2" Body="&lt;p&gt;I recall from one of the license exams that a double vertical, fed with a phase delay to one pole, will produce a cardiod radiation (and sensitivity) pattern.  As I recall (it's been a couple months since my exam, and I memorized this just long enough to pass the test), this requires a pair of half wave elements, separated by a half wave, and fed a half wave out of phase, with the main radiation going toward the undelayed element.  This is more or less like a Yagi with only the radiator and reflector elements, but no directors.  You'll get a strong null, but a very wide pattern otherwise.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-05-08T14:54:03.783" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14483" PostTypeId="2" ParentId="14475" CreationDate="2019-05-08T15:11:30.720" Score="3" Body="&lt;p&gt;With your expressed interest in &quot;listening,&quot; you might consider this &lt;a href=&quot;http://www.fvarc.org/sites/default/files/2%20Meter%20hand%20Beams.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;portable 2-element VHF yagi&lt;/a&gt; presented by K3MT:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oLgrJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oLgrJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;rabbit ears&quot; are collapsible whips taken from an indoor TV antenna, but they should be available from the usual electronics hobby retailers. Using the element dimensions on the web site - 37in driven element, 42in reflector - gives this free-space azimuth pattern with forward gain of 4.6-dBi:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vUyim.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vUyim.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Optimizing this antenna in 4NEC2 with equal weights on forward gain and front/rear ratio yields slightly different dimensions with 1/4in diameter elements:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;reflector: 38in&lt;/li&gt;&#xA;&lt;li&gt;driven element: 37in&lt;/li&gt;&#xA;&lt;li&gt;spacing 21.75in&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tadDJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tadDJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-08T15:11:30.720" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14484" PostTypeId="5" CreationDate="2019-05-08T15:20:45.920" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-05-08T15:20:45.920" LastActivityDate="2019-05-08T15:20:45.920" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14485" PostTypeId="4" CreationDate="2019-05-08T15:20:45.920" Score="0" Body="CI-V, Icom's radio/computer interface protocol." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-05-08T15:20:45.920" LastActivityDate="2019-05-08T15:20:45.920" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14486" PostTypeId="1" CreationDate="2019-05-09T01:20:20.903" Score="3" ViewCount="830" Body="&lt;p&gt;I'm pretty good at repairing broken regular coax, but I recently had an RG-174 cut and it's too small for me to solder the center wire and keep the braid away from it.  What's a good way to do this? Edits for clarity: this is for a feedline to an antenna, using for HF signals, so the repair method is important in keeping a clean signal.&lt;/p&gt;&#xA;" OwnerUserId="14852" LastEditorUserId="14852" LastEditDate="2019-05-15T23:02:46.933" LastActivityDate="2019-05-15T23:02:46.933" Title="How to splice RG-174 coax?" Tags="&lt;hf&gt;&lt;coaxial-cable&gt;&lt;repair&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14488" PostTypeId="2" ParentId="14486" CreationDate="2019-05-09T02:53:36.270" Score="1" Body="&lt;p&gt;Hmm. I've done this many times.  Would a magnifying headband and extra light help you? That's certainly helped me to do that. The same way as we would splice larger coax.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-05-09T02:53:36.270" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14489" PostTypeId="1" AcceptedAnswerId="14493" CreationDate="2019-05-09T17:12:06.987" Score="1" ViewCount="119" Body="&lt;p&gt;I've been playing around with RTL-SDR and Unitrunker attempting to get a police scanner working.  I followed the tutorial here: &lt;a href=&quot;https://sites.google.com/site/policescannerhowto/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://sites.google.com/site/policescannerhowto/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Everything works as expected until I run Unitrunker and try to add the two receivers.  When I do so I only see the top section as seen in this image:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9c22K.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9c22K.png&quot; alt=&quot;Unitrunker display&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This happens when I add the control receiver as well.  In the tutorial and all the other examples I've seen all over the net, there are many more fields underneath those which are necessary to get things working.  I know the RTL-SDR receiver is working, I am able to tune to various radio stations with SDR#.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What could be causing this?  And what steps can I take to fix it?&lt;/p&gt;&#xA;" OwnerUserId="14855" LastEditorUserId="14855" LastEditDate="2019-05-09T18:37:19.820" LastActivityDate="2019-05-10T03:07:50.087" Title="Unitrunker Receivers Not Displaying Fields" Tags="&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14492" PostTypeId="2" ParentId="1950" CreationDate="2019-05-10T01:35:43.603" Score="1" Body="&lt;p&gt;For the question of which frequencies can be used with an amateur licence, your amateur licence should tell you all this. You have tagged the question as &quot;Europe&quot;, but that is a large geographical area with many countries in it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are operating under the CEPT agreements, the CEPT documentation will also tell you all this. Anything I could look up for you using Google, you could just as easily have looked up yourself, especially since you know exactly what licence you have, and which countries this will apply to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(When you passed your amateur radio examinations, you were told what the bands are, and while you might have forgotten all this, your national radio society will have all the information. Furthermore, there are published national band plans - and the international IARU band plans show you what the 'maximum' range of frequencies are, that are allowed in each region. If you are operating in another country than your own, there are international agreements for which frequencies you can use. These are also available online.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the ISM bands, you should have a look at &lt;a href=&quot;https://en.wikipedia.org/wiki/ISM_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;the Wikipedia page here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-05-10T01:35:43.603" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14493" PostTypeId="2" ParentId="14489" CreationDate="2019-05-10T02:36:04.840" Score="2" Body="&lt;p&gt;The phrase &quot;Everything works as expected&quot; covers a lot of ground, so I'm going to assume that included:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Installing the Zadig drivers when you first plugged your RTL-SDR device(s) into your USB port rather than relying on the Plug-and-Play drivers that would've been installed automatically.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Running your RTL-SDR device(s) under a basic recever program such as HDSDR or SDRSharp and confirming that you can receive a simple FM signal such as NOAA weather broadcasts in the 162 MHz range.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Allowing your RTLSDR device(s) to warm up and stabilize by letting your basic receiver program such as HDSDR or SDRSharp run for a half hour or more and then calibrating your RTLSDR device's &quot;Frequency Correction&quot; parameter (ExtIO button on HDSDR or the gear icon on SDRSharp) to the dial frequency of the HDSDR/SDRSharp software.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Making note of the &quot;Frequency Correction&quot; parameter and writing it on a piece of tape that you affixed to your RTLSDR device(s).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If that has all been completed successfully then you click on the &quot;Type | Signal&quot; line in the screen shot you posted, then in the drop down menu select RTL2832U or the equivalent RTL device listing, enter your &quot;Frequency Correction&quot; parameter into Unitrunker's &quot;Correction&quot; line, selecting the &quot;Drift Correct&quot; option and pressing the PLAY button (right-pointing triangle).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ksGWS.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="14857" LastEditorUserId="76" LastEditDate="2019-05-10T03:07:50.087" LastActivityDate="2019-05-10T03:07:50.087" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14495" PostTypeId="1" CreationDate="2019-05-10T03:12:04.227" Score="1" ViewCount="75" Body="&lt;p&gt;I need to switch a bank of filters operating on bands from about 2MHz to 30MHz. The parasitic series inductance of the relay contact system will have an effect on the performance of my system. Manufacturers of small encapsulated relays, like this &lt;a href=&quot;https://omronfs.omron.com/en_US/ecb/products/pdf/en-g2rl.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Omron&lt;/a&gt; unit, don't specify this parasitic value. Has anyone done so?&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-10T03:12:04.227" Title="Parasitic inductance of relay contacts" Tags="&lt;hf&gt;&lt;rf-power&gt;&lt;transmitter&gt;&lt;amplifier&gt;&lt;measurement&gt;" AnswerCount="0" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="14497" PostTypeId="2" ParentId="13289" CreationDate="2019-05-10T21:34:36.623" Score="1" Body="&lt;p&gt;To add to &lt;a href=&quot;https://ham.stackexchange.com/a/14457/8717&quot;&gt;Brian's fine answer&lt;/a&gt;, I'd like to share some two-dimensional plots to complement his answer and 3D patterns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To me, &lt;strong&gt;2D plots are also necessary, because they show the actual takeoff angle vs. gain.&lt;/strong&gt; Generally speaking, &lt;em&gt;the lower the takeoff angle, the farther away that you can work DX&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;75 Meters&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;As was expected by most of us who have decades of experience on the HF bands, this is not an optimum antenna for DX on this band &lt;em&gt;because it is so low in terms of the ratio between its height and wavelength&lt;/em&gt;. On 75/80m, it's pretty much omnidirectional and most of the radiation goes straight up. It's an NVIS antenna. Depending upon the time of day, it can work well for stateside work within, say, 750 miles. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;75 meter 3D radiation pattern&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DI1rF.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DI1rF.gif&quot; alt=&quot;75 meter 3D pattern&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;75 meter 2D elevation pattern, gain vs. takeoff angle&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1TnLd.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1TnLd.gif&quot; alt=&quot;75m elevation pattern&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;75 meter 2D azimuthal pattern&lt;/strong&gt;, looking down on the antenna&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OJQPP.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OJQPP.gif&quot; alt=&quot;75m azimuth pattern&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;40 Meters&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;40 meter 3D radiation pattern&lt;/strong&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/wSnoZ.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wSnoZ.gif&quot; alt=&quot;40 meter 3D pattern&quot;&gt;&lt;/a&gt;&#xA;&lt;hr&gt;&#xA;&lt;strong&gt;40 meter 2D elevation pattern, gain vs. takeoff angle&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iduvz.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iduvz.gif&quot; alt=&quot;40m 2D elevation plot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;40 meter 2D azimuthal pattern&lt;/strong&gt;, looking down on the antenna&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/izb3f.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/izb3f.gif&quot; alt=&quot;40 meter 2D azimuthal pattern&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;20 Meters&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;20 meter 3D radiation patterns&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/emhM4.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/emhM4.gif&quot; alt=&quot;20 meter 3D radiation pattern&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/e60mJ.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/e60mJ.gif&quot; alt=&quot;20m 3d plot rotated&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;20 meter 2D elevation pattern, gain vs. takeoff angle&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3TZUW.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3TZUW.gif&quot; alt=&quot;20 meter 2D elevation pattern plot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;20 meter 2D azimuthal pattern&lt;/strong&gt;, looking down on the antenna&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pZOf7.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pZOf7.gif&quot; alt=&quot;20m azimuthal pattern plot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;These pattern plots are based on the same &lt;a href=&quot;http://www.eznec.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC&lt;/a&gt;+ model that Brian was kind enough to share with me.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;An important word about the gains&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Notice that the gains in these pattern plots are in &lt;strong&gt;dBi&lt;/strong&gt;. That means the gain over a theoretic isotropic antenna. &lt;strong&gt;A dipole has a peak gain significantly higher than an isotropic antenna,&lt;/strong&gt; at the expense of nulls off the ends.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;In summary, a ham should have more than one antenna. This loop would be good on some bands, and the vertical as Phil Frost suggested would be good on other bands and under some conditions. The same would be true with a dipole.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-05-11T23:44:16.123" LastActivityDate="2019-05-11T23:44:16.123" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14499" PostTypeId="2" ParentId="14458" CreationDate="2019-05-11T06:37:43.447" Score="8" Body="&lt;p&gt;Here's how to repair a Kenwood MC-59 microphone cable (ships with the TM-V71a, probably the 710, and a few LMR radios as well).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, if you didn’t know already, behind the rubber boot at the end of the Kenwood MC-59 mic cable is a regular RJ-45 jack:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vyzNn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vyzNn.png&quot; alt=&quot;Picture of MC-59 hand mic with the boot slid down, exposing the RJ-45 jack&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 0&lt;/strong&gt;. If you want to avoid all this, the cord is part &lt;a href=&quot;http://www.pacparts.com/part.cfm?sku=881H07%2D4210%2D85&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kenwood E30-7543-18 at PacParts.com&lt;/a&gt;. (They also carry Kenwood 881M59-7889-72, which might be the same, and is a lot cheaper.) Avoid the cables that sell for under $10 on eBay - they will work, but will sound awful. The Kenwood cable has a shield that covers the clock line. If your cable doesn't have that, you’ll get a terrible buzzing noise in your audio - as if cicadas have infested your mic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to repair the existing cable yourself, you’ll need:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;1/4 inch (6.35mm) heat shrink, about 2-3 inches (50-75mm)&lt;/li&gt;&#xA;&lt;li&gt;a network cable to sacrifice&lt;/li&gt;&#xA;&lt;li&gt;an EZ-RJ45 jack &lt;/li&gt;&#xA;&lt;li&gt;two paper clips&lt;/li&gt;&#xA;&lt;li&gt;soldering iron&lt;/li&gt;&#xA;&lt;li&gt;diagonal cutters&lt;/li&gt;&#xA;&lt;li&gt;RJ-45 crimpers&lt;/li&gt;&#xA;&lt;li&gt;utility knife (if your crimper doesn’t have a cutter)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 1&lt;/strong&gt;. I'll assume you're repairing the head because the mic cord is wearing where the bottom of the boot meets the wire. That's what happened with mine. First, pull the rubber boot down, then disconnect the RJ-45 jack from the mic head. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 2&lt;/strong&gt;. If it's still attached, cut the RJ-45 jack off the cable with diagonal cutters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 3&lt;/strong&gt;. Trim about 1 inch (25 mm) of the remaining jacket.  Carefully unweave the braid from the clock line (on mine it was the white wire), separate the copper braid from the cloth braid, and wind the copper braid into a wire. (Although my original RJ-45 jack had two black wires, they were not electrically connected.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/79zNh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/79zNh.jpg&quot; alt=&quot;Closeup of cable, with shield twisted to form a wire.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 4&lt;/strong&gt;. &lt;strong&gt;Very important&lt;/strong&gt;: now is the time to pull the boot down as far as it will go, and put the heat shrink on the wire. I ended up wishing I'd made my heat shrink longer - it fits, but exposes the same weak spot the cable originally had. If I'd added an extra inch (25 mm) or so, I'd have a stronger cable, I think. You can slide the boot partway down the curly part of the cord if you need more room.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qiI8e.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qiI8e.jpg&quot; alt=&quot;Closeup of heatshrink placed on the cable, but not yet shrunk&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 5&lt;/strong&gt;. Sacrifice the network cable and take out about 3 inches (75 mm) of one wire. (I used the white/brown, so I wouldn't confuse it with the other wires.) Strip the wire back on one end. Carefully tack-solder that end of it to the base of the copper braid. I tried not to solder the whole braid so I would have some flexibility.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/67Vw9.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/67Vw9.jpg&quot; alt=&quot;Image of brown/white wire from network cable tack-soldered to base of braid&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 6&lt;/strong&gt;. Feed the individual wires through the EZ-RJ45 jack. Order here is important. On my jack, it was:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;yellow&lt;/li&gt;&#xA;&lt;li&gt;grey &lt;/li&gt;&#xA;&lt;li&gt;white &lt;/li&gt;&#xA;&lt;li&gt;originally black connected to the shield, now white and brown&lt;/li&gt;&#xA;&lt;li&gt;blue&lt;/li&gt;&#xA;&lt;li&gt;black&lt;/li&gt;&#xA;&lt;li&gt;red&lt;/li&gt;&#xA;&lt;li&gt;green&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Leave the wires long to give you plenty of room to work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a face-on diagram of the jack:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pfKSi.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pfKSi.jpg&quot; alt=&quot;View of jack from front of jack. Yellow is on the left, then grey, white, black/shield, blue, black, red, then green on the right.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 7&lt;/strong&gt;. Adjust the EZ-RJ45 jack first so it's in position, then put the heat shrink where it needs to be. Slide the EZ-RJ45 jack so it no longer covers the heat shrink. Heat the heat shrink so it conforms to the wire. Slide the EZ-RJ45 jack back down over the heat shrink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gWsFi.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gWsFi.jpg&quot; alt=&quot;Heat shrink shrunk around cable, with EZ-RJ45 in position, not yet crimped&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 8&lt;/strong&gt;. Crimp the EZ-RJ45. I didn't have the official EZ-RJ45 crimper, so I used my RJ-45 crimper and then trimmed the wires off with a utility knife.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ztXgW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ztXgW.jpg&quot; alt=&quot;Picture of the crimper in action&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 9&lt;/strong&gt;. Check all the wires for continuity with the RJ-45 connector on the other end. I used an ohmmeter with a couple of sewing pins held by mini-grabber test leads as probes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CAIBq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CAIBq.jpg&quot; alt=&quot;Picture of probes (mini-grabbers grabbing sewing pins)&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Step 10&lt;/strong&gt;. You're almost done! (If the boot weren't so tight, you'd be done. But it's tight, and unless you're careful, it will push the heat shrink out of shape as you slide it up.) Deform two paperclips and slide them between the wire and the boot, and use those to wedge the boot around the heatshrink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/makGr.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/makGr.jpg&quot; alt=&quot;Paperclips unfolded and placed between wire and boot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note as you slide the boot up that it has an orientation. Make sure the cut in the molded boot matches the tab in the EZ-RJ45 jack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7zdTs.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7zdTs.jpg&quot; alt=&quot;Closeup of molded boot with cutout for RJ-45 tab&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connect the mic head to the EZ-RJ45 jack. Slide the boot up, and the repair is complete. The cable can now be reconnected to the radio.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2019-05-13T06:19:50.247" LastActivityDate="2019-05-13T06:19:50.247" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14501" PostTypeId="1" AcceptedAnswerId="14508" CreationDate="2019-05-11T17:20:43.660" Score="3" ViewCount="1155" Body="&lt;p&gt;So here is a strange thought.&#xA;If a vertical electrically speaking is a half dipole with the other half as a ground plane to balance out. Perhaps there are ways to make equivalent director and reflector make it into a vertical yagi? Is that a possibility?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that it might be difficult to do, but low take-off angle without height and with a directional gain is an advantage. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I heard that when you run radials into a general direction, you also get some gain into that direction, not sure how much that would effect. &lt;/p&gt;&#xA;" OwnerUserId="13362" LastActivityDate="2019-12-06T13:32:19.440" Title="Give vertical antenna directional gain?" Tags="&lt;antenna-theory&gt;&lt;vertical-antenna&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14502" PostTypeId="2" ParentId="13289" CreationDate="2019-05-11T22:45:50.060" Score="2" Body="&lt;p&gt;As other answers have established, the presence of the roof doesn't affect the loop pattern too much. However, the proximity to ground does make the antenna quite inefficient, and radiation is mostly upward.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moreover, I suspect the noise performance of such an antenna will be especially poor. A loop antenna around the house will make a very effective inductive pickup for every noise source inside the house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So let me propose an alternative design: a mobile antenna on the roof. It would be easy to install and cheap, probably more so than the loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The metal roof will make an excellent ground plane, and a vertical can take advantage of that. The roof need not be grounded in any particular way to be effective as an antenna: it merely needs to be conductive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna is grounded, the antenna can only reduce your risk of lightning related fire and structural damage. Lightning rods are installed on fire-prone buildings (like barns) so the bulk of the surge current travels through the lightning rod, ground rod, and conductor between. The result is some warm copper. Without a lighting rod the current may go through wood, bales of straw, or other flammable and not very conductive materials, the result is fire.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-05-11T22:45:50.060" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14505" PostTypeId="1" AcceptedAnswerId="14506" CreationDate="2019-05-12T15:33:54.043" Score="7" ViewCount="977" Body="&lt;p&gt;I will soon need an antenna impedance match (aka &quot;antenna tuner&quot;), because I'll initially only have a single antenna for my HF rig (needs to cover 80m, 40m, 20m, 15m, and 10m).  Obviously, in order to manage SWR, I'll need a matching network, quite likely with a wider capability than the pi network built into my Heathkit SB-102.  Even if the SB-102 can manage without help, I'll also need to match my portable antenna to my portable QRP rigs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the core components of any matching network -- L, T, SCS, or pi -- is a &quot;variable&quot; inductor.  Home builders seemingly usually use a tapped coil for this, giving discrete increments of inductance and depending on a variable capacitance to finalize the match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, variable caps are getting harder to find; they're no longer manufactured in the old &quot;interleaved plates, air spaced&quot; form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It occurred to me that what's needed is to adjust the &lt;em&gt;ratio&lt;/em&gt; of inductance to capacitance, not either one in particular; if one had an inductor with stepless adjustment over a wide range of value, one might be able to use common fixed capacitors, or possibly a switch-selected gang of parallel fixed capacitors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, adjustable inductors have been around for decades; aligning an old superheterodyne receiver involves tweaking up to a couple dozen components, of which roughly half are slug-tuned variable inductors.  I recall from studying for my license exam that a ferrite or iron slug will increase inductance when inserted into a coil, while a brass (or presumably copper or aluminum -- conductive but non-magnetic) slug decreases it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What wasn't covered in the study materials is how widely one can adjust the inductance with slugs.  Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="4665" LastEditDate="2019-05-13T14:11:14.823" LastActivityDate="2020-05-26T02:49:19.527" Title="Is it practical to use a slug-tuned variable inductor in an antenna matcher (aka &quot;antenna tuner&quot;)?" Tags="&lt;diy&gt;&lt;electronics&gt;&lt;antenna-system&gt;" AnswerCount="7" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14506" PostTypeId="2" ParentId="14505" CreationDate="2019-05-12T17:49:19.170" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What wasn't covered in the study materials is how widely one can adjust the inductance with slugs. Common variable capacitors out of old radio or TV tuners run from zero to several hundred picoFarad, and a tapped coil can likewise run near zero inductance when tapped down to two or three turns. What sort of range could I get with, say, a tuning slug that's iron on one end, brass on the other?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The inductivity of a coil is very much dominated by the magnetic permeability of its core – use a core with a twice as high a permeability, get (pretty much) twice the inductivity. A ferrite core can have a permeability a couple thousand times higher than that of air. So, by inserting a core into an otherwise air-core coil, you could achieve that factor of variability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Problem: Cores tend to saturate in strong fields. You'll have to dimension the core such that saturation does not occur at the powers you plan to use. That can be large, challenging and hence expensive! &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-05-12T17:49:19.170" CommentCount="14" ContentLicense="CC BY-SA 4.0" />
  <row Id="14507" PostTypeId="2" ParentId="14505" CreationDate="2019-05-12T18:17:43.910" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Variable caps are getting harder to find; they're no longer&#xA;  manufactured in the old &quot;interleaved plates, air spaced&quot; form.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;They are not hard to find. You &lt;em&gt;can&lt;/em&gt; buy those if you know where to look. I have managed to find more than enough for my uses. You just have to look elsewhere than those selling new components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have quite a stock of them (and even rotary inductors!) that I purchased very inexpensively from &lt;strong&gt;hamfests&lt;/strong&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Electronics and radio surplus companies&lt;/strong&gt; often have them. And have you looked on &lt;strong&gt;eBay&lt;/strong&gt;? I've seen some real bargains from time to time!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some places that sell surplus radio parts are &lt;a href=&quot;https://www.surplussales.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;Surplus Sales of Nebraska&lt;/strong&gt;&lt;/a&gt;, &lt;a href=&quot;https://www.rfparts.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;RF Parts&lt;/strong&gt;&lt;/a&gt;, and &lt;a href=&quot;https://fairradio.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;Fair Radio Sales&lt;/strong&gt;&lt;/a&gt;. And those are &lt;em&gt;only a few of them&lt;/em&gt;.&#xA;&lt;hr&gt;&#xA;In lieu of rotary (or ferrite-core) inductors, you could use a fixed air-wound coil with taps. One of the homebrew tuners at the base of my inverted-L uses that method (photos below); the other uses just two variable capacitors &lt;a href=&quot;http://www.w0btu.com/files/antenna/160m_inv-L/&quot; rel=&quot;nofollow noreferrer&quot;&gt;in an L-network (Omega match)&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/w4HdW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/w4HdW.jpg&quot; alt=&quot;Air Dux coil with alligator clip to select taps&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The red alligator clip shorts out the unused portion of this old Barker &amp;amp; Williamson Air Dux coil that I bought from eBay. If you can't find one, you can wind one yourself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/968Kc.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/968Kc.jpg&quot; alt=&quot;Air Dux coil with alligator clip to select taps&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is inside the tuner that I made to match my 160m inverted-L on 80 and 40 meters. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-05-16T19:07:23.813" LastActivityDate="2019-05-16T19:07:23.813" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14508" PostTypeId="2" ParentId="14501" CreationDate="2019-05-12T20:36:15.603" Score="4" Body="&lt;p&gt;I took the EZNEC VERT1.EZ 40m model and added an identical passive element 27 feet away connected to the same miniNEC ground. Here are the results. 4+ dBi gain at a TOA of 24 deg. But this leads to another question. How does one implement a miniNEC ground in the real world?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IHsyq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IHsyq.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To equal the above performance over high-accuracy ground, each element needs two radials elevated at 10 feet, one to the NW and one to the SW.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/saEnv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/saEnv.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the lowest SWR (1.6:1) occurs at 7.3 MHz but the highest gain occurs at 7.12 MHz where the SWR is 2.5:1.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-05-13T22:35:06.517" LastActivityDate="2019-05-13T22:35:06.517" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14509" PostTypeId="2" ParentId="14501" CreationDate="2019-05-12T21:45:12.020" Score="5" Body="&lt;p&gt;Sure, that can work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a monopole yagi I designed:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xgibV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xgibV.jpg&quot; alt=&quot;Photo of antenna&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;Photo: Alaris Antennas MONO-A0005.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a half-yagi for remote control of a mine locomotive, improving the control range by firing one way down the tunnel. The driven element is a half-folded-dipole, a good match for 50 Ohms. Also, it's welded up from solid 20 mm steel so it survives low ceilings, cable snags, etc. It's for 915 MHz but the principle is the same at HF. A good ground screen will be required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is also a half-log-periodic antenna, sometimes called an LPMA. It's a fairly standard thing at HF, but takes up a lot of room for hams. &lt;a href=&quot;https://www.rohde-schwarz.com/dk/product/hl210a3-productstartpage_63493-9370.html?rusprivacypolicy=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here's one from R&amp;amp;S for 1.5-30 MHz&lt;/a&gt;, 97 m long and needs a 90 m mast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll find designs for directors or reflectors for monopoles out there. One neat trick is that you can switch direction with some relays to jump between being the driven element and being the reflector.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-05-14T05:43:58.897" LastActivityDate="2019-05-14T05:43:58.897" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14510" PostTypeId="2" ParentId="14505" CreationDate="2019-05-13T01:24:10.930" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;...variable caps are ... no longer manufactured in the old &quot;interleaved plates, air spaced&quot; form, and the tiny plastic dielectric ones that are still available can't take much voltage (and are difficult to adjust precisely).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Thankfully, &lt;a href=&quot;http://www.orenelliottproducts.com/index-1.html&quot; rel=&quot;noreferrer&quot;&gt;Oren Elliott&lt;/a&gt; is a surprisingly affordable source of brand new air-variable capacitors. I have used them successfully in several projects.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-13T01:24:10.930" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14513" PostTypeId="2" ParentId="14501" CreationDate="2019-05-13T12:31:01.510" Score="2" Body="&lt;p&gt;Not a strange thought, at all, with several interesting solutions described over the years. The information below is &lt;strong&gt;not&lt;/strong&gt; presented as a construction idea: elements are #14 wire and lengths are approximate. The antenna is simulated over &quot;real&quot; ground of &quot;medium&quot; conductivity (Sommerfeld model), with the lower set of elevated radials .05&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; above ground and .01&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; vertical separation between the radial sets to prevent shorts. More engineering would have to be done to result in a practical design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just as you would with a horizontal yagi, a lengthened vertical parasitic reflector (wire 6) could be added to a driven vertical (wire 1):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VEZNp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VEZNp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The horizontal spacing between the vertical elements is 0.15&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;, the driven vertical and the radials (wires 2-4 and 7-10) are 0.24&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; long and the parasitic element (wire 6) is 9% longer than the driven element, producing some gain and useful directivity (elevation plane shown):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SaVAi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SaVAi.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, you could change the &lt;em&gt;electrical&lt;/em&gt; length of the parasitic element by adding reactance to it. Instead of changing the &lt;em&gt;physical&lt;/em&gt; length of the parasitic vertical, a 550nH inductor, similar to what one might use as a loading coil for a matching network, is added to the base (note the square at the base of element 6):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GGKrY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GGKrY.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;again with some gain and useful directivity (elevation plane shown here):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ypnt4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ypnt4.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sadly, modeling does not show useful directivity when replacing the inductive reactance with capacitance in an effort to make the loaded parasitic reflector into a director, so there is some limit to the flexibility of this approach. However, one could swap the driven and loaded connections to reverse the pattern.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-13T12:31:01.510" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14514" PostTypeId="2" ParentId="14505" CreationDate="2019-05-13T23:09:52.293" Score="5" Body="&lt;p&gt;&lt;a href=&quot;https://www.fair-rite.com&quot; rel=&quot;noreferrer&quot;&gt;Fair-Rite&lt;/a&gt; makes ferrite rods which would be suitable for HF applications. It should be possible to create or repurpose a screw-operated mechanism to move the rod into and out of a cylindrical coil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Preferably, the material will have steady permeability and low loss over the frequency range of interest. Loss is proportional to the ratio of the real and imaginary components of permeability, &lt;span class=&quot;math-container&quot;&gt;$\frac{\mu'}{\mu''}$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The properties of Material 61 are probably best, because:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\mu'$&lt;/span&gt; doesn't begin to drop off until past 30MHz&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\mu''$&lt;/span&gt; is relatively low and doesn't rise significantly until 20MHz&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3J7KJ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3J7KJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://www.fair-rite.com/product/rods-4061375411/&quot; rel=&quot;noreferrer&quot;&gt;relative permeability of a wound rod&lt;/a&gt; depends on the ratio of the rod's length to its diameter:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9brbJ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9brbJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you will have to make some preliminary calculations before deciding on turns count for &lt;a href=&quot;https://www.fair-rite.com/product-category/inductive-components/rods/low-permeability-61-ui125-material/&quot; rel=&quot;noreferrer&quot;&gt;rods using Material 61&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-13T23:09:52.293" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14515" PostTypeId="1" AcceptedAnswerId="14516" CreationDate="2019-05-13T23:49:58.360" Score="1" ViewCount="96" Body="&lt;p&gt;I'm working on a kite-supported antenna for an 80m QRP rig -- to be flown at beaches, on mountaintops, and possibly other places where I want to work HF but don't want to lug poles or give up efficiency with a sub-optimal antenna.  This will be a center-fed half wave dipole, so about 132 feet of wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have the kite already in hand, a carbon spar nylon sail conyne (aka French war kite, a hybrid of a box and a diamond) just over three feet in length.  It's stable, flies in a broad range of wind, and has good pull (so keeps the line taut).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To support the antenna wire, I plan to use 000 size locking snap-swivels (made for fishing) bent to the kite line with prusik knots.  The knots can be loosened and moved when adjusting the setup, and are light enough that they won't affect the kite if I'm not lifting the antenna.  Because they grip the line without forcing it into a sharp bend, they will have almost no effect on the line strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question concerns the snap swivels (similar to &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B01AJM23V2&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;these&lt;/a&gt;).  These are effectively tiny wire loops that will hold the antenna, one at each end, one in the middle, and two or three spread along each leg of the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to their small size, I wouldn't expect these loops to have any noticeable effect on the antenna's radiation in the 80m band, but I wanted to ask to be sure.  I'd hate to key up the transmitter and find out all the power I'm sending up the wire is going into heating the snap swivels.  &lt;strong&gt;Am I correct in thinking a stainless and brass snap swivel, with the snap loop about an inch long, will have no significant effect on the radiation of a half wave dipole on 80m band?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-05-14T16:14:06.700" Title="Will close-loop metal hangers affect antenna radiation?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;diy&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14516" PostTypeId="2" ParentId="14515" CreationDate="2019-05-14T00:07:55.517" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Am I correct in thinking a stainless and brass snap swivel, with the snap loop about an inch long, will have no significant effect on the radiation of a half wave dipole on 80m band?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. This object is over 1,500 times smaller than the wavelength; you can therefore conclude it will have much less effect than other features of your antenna system. The material and shape don't affect this conclusion.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-05-14T00:07:55.517" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14517" PostTypeId="1" AcceptedAnswerId="14518" CreationDate="2019-05-14T12:54:19.570" Score="2" ViewCount="70" Body="&lt;p&gt;I have to measure the S parameter for a  rectangular sample with an antenna that works from 2 to 18 GHz. I need to measure a large band from 5 to 15 GHz and I have a problem with the known F.F. (Far Field) formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$R = 2D^2/λ$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually with &lt;span class=&quot;math-container&quot;&gt;$D$&lt;/span&gt; is referred the aperture of the antenna, that in my case is 100 mm, while I found that for RCS the formula use as &lt;span class=&quot;math-container&quot;&gt;$D$&lt;/span&gt; value the dimension of the sample (300 mm).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Why can the F.F. formula be referred to the antenna or to the sample and&lt;/li&gt;&#xA;&lt;li&gt;when I need to use one or the other?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="14689" LastEditorUserId="14689" LastEditDate="2019-05-14T14:30:21.710" LastActivityDate="2019-05-14T18:18:35.607" Title="Measurements in far field for radar cross section" Tags="&lt;antenna-theory&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14518" PostTypeId="2" ParentId="14517" CreationDate="2019-05-14T14:35:01.597" Score="3" Body="&lt;p&gt;The far field formula is simply derived from a general idea that the phase error at the edge of the antenna aperture should be less than &lt;span class=&quot;math-container&quot;&gt;$22.5^\circ$&lt;/span&gt; which means that &lt;span class=&quot;math-container&quot;&gt;$r'-r &amp;lt; {1\over16}\lambda$&lt;/span&gt;.&lt;br&gt;&#xA;This figure is chosen because it gives gain errors of less than some small percentage, I can't remember the figure, it depends on the aperture field distribution too).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W8tb8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W8tb8.png&quot; alt=&quot;far field derivation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now draw a new diagram with the large target object, and the source antenna, and work out the difference in path length between a ray from the centre of the object, to the centre of the antenna, and a ray between the edge of the object and the opposite edge of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Mm4OD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Mm4OD.png&quot; alt=&quot;RCS measurement&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The whole path difference &lt;span class=&quot;math-container&quot;&gt;$r'-r$&lt;/span&gt; should be kept to below &lt;span class=&quot;math-container&quot;&gt;${1\over16}\lambda$&lt;/span&gt; for some level of accuracy.&lt;br&gt;&#xA;You can see from this diagram (slide &lt;span class=&quot;math-container&quot;&gt;$r'$&lt;/span&gt; up to make one triangle) that the &quot;safe&quot; far-field distance will be&lt;br&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;${2(D_{antenna}+D_{target})^2}\over\lambda$&lt;/span&gt;&lt;br&gt;&#xA;This will guarantee that phase errors from any part of the antenna aperture, to any part of the reflecting target, are kept below &lt;span class=&quot;math-container&quot;&gt;$22.5^\circ$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might be able to relax this criterion by half if you're willing to tolerate a larger error, or know something about the aperture distribution of the antenna, or the reflection properties of the target. A sphere, for example, might not reflect from the whole surface, only the middle. Unfortunately a horn antenna will have a fairly uniform field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; in all equations above needs to be calculated at the highest frequency you are measuring (but not the highest specified frequency of the horn).&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-05-14T18:18:35.607" LastActivityDate="2019-05-14T18:18:35.607" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14519" PostTypeId="2" ParentId="14515" CreationDate="2019-05-14T16:14:06.700" Score="1" Body="&lt;p&gt;I wouldn't worry about radiation pattern.  I might worry about metal to metal arcing, as ends of a dipole are a high-voltage RF node adjacent to whatever static charge the plastic kite string picks up from the wind.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See: &lt;a href=&quot;https://ham.stackexchange.com/questions/1410/what-is-the-peak-voltage-at-the-tips-of-a-dipole-antenna&quot;&gt;What is the peak voltage at the tips of a dipole antenna?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-05-14T16:14:06.700" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14520" PostTypeId="2" ParentId="14486" CreationDate="2019-05-14T17:00:26.837" Score="-1" Body="&lt;p&gt;Connectors.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Splicing without connectors will introduce an impedance &quot;bump&quot; which may or may not bother you.  The magnitude of the bump may be considerable.  The bump will cause reflections which may cause the spliced coax to act like a comb filter.  It gets pretty messy unless you are able to splice the coax perfectly, and you can't do that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connectors aren't perfect either, but they have a lot of design work behind them to minimize the bump and the problems caused by the bump.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At DC, none of this matters, but I have to assume you aren't using coax for DC.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2019-05-14T17:00:26.837" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14521" PostTypeId="1" CreationDate="2019-05-14T19:14:26.887" Score="13" ViewCount="338" Body="&lt;p&gt;My friend is blind and would like to take the amateur radio license exam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that the question and the four possible answers can be read to them, and that is fine. The one question that we are still not sure on is, &lt;em&gt;When it comes to block diagrams where the examinee is asked &quot;What is component three&quot;?&lt;/em&gt;, how would the reader get past this question?&lt;/p&gt;&#xA;" OwnerUserId="14889" LastEditorUserId="4665" LastEditDate="2020-01-29T22:18:02.690" LastActivityDate="2020-01-29T22:18:02.690" Title="Testing blind license applicants" Tags="&lt;united-states&gt;&lt;license&gt;&lt;volunteer-examiners&gt;&lt;disability&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14522" PostTypeId="2" ParentId="14486" CreationDate="2019-05-14T19:41:01.990" Score="2" Body="&lt;p&gt;At HF there are almost no limits on how bad your splice can be, as long as:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;there's no short circuit&lt;/li&gt;&#xA;&lt;li&gt;braid is connected to braid and inner to inner&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You could even use a &quot;chocolate block&quot; connector :) &#xA;&lt;a href=&quot;https://i.stack.imgur.com/6Ybl5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6Ybl5.png&quot; alt=&quot;chocolate&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;* photo from &lt;a href=&quot;https://www.flickr.com/photos/tudedude/15135903142&quot; rel=&quot;nofollow noreferrer&quot;&gt;Tudor Barker&lt;/a&gt;, cropped&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But to do a neat job:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;At each cut end, strip about 25 mm (1&quot;) of the outer sheath, and then about 7 mm (1/4&quot;) of the inner.&lt;/li&gt;&#xA;&lt;li&gt;open the braid out and lay it back on the jacket&lt;/li&gt;&#xA;&lt;li&gt;lay the inners overlapping and solder quickly and carefully. RG174 inner melts quickly, the trick is not to bend or force it until it sets again.&lt;/li&gt;&#xA;&lt;li&gt;insulate them with a 25 mm piece of electrical tape. (or more if you're &amp;lt; 200 MHz, less chance of a short circuit)&lt;/li&gt;&#xA;&lt;li&gt;fold the braids back, they will also overlap&lt;/li&gt;&#xA;&lt;li&gt;wind a bit of thin wire gently around the braid to keep it snug against the inner (but not so tight that it'll sink through the insulation&lt;/li&gt;&#xA;&lt;li&gt;solder the braids together carefully. Use a cool iron. Don't fully wet the joint - the RG174 insulation will melt and run out the ends! Just gently wet the bits of the braid where they meet, and tack the wrapping wire to the braid in a few places. The idea is to get just enough mechanical strength, not a solid tube of solder.&lt;/li&gt;&#xA;&lt;li&gt;insulate the whole thing with tape, or heatshrink if you remembered to put it on first...&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I'm comfortable splicing coax like this up to 1.5 GHz for GPS without unreasonable loss. Of course it won't be a first class measurement cable, but for radio transmission a tiny, short impedance mismatch won't hurt. At HF the whole joint is 1/1000 of a wavelength, it will be fine no matter how ugly it is.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-05-14T21:14:00.140" LastActivityDate="2019-05-14T21:14:00.140" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14523" PostTypeId="2" ParentId="14521" CreationDate="2019-05-14T20:45:47.793" Score="10" Body="&lt;p&gt;When testing applicants that are vision impaired we use versions of the test that do not include any diagrams. I am a VE and there is a state school for the deaf and blind near us so we have had several vision impaired applicants over the years. Please try to let us know ahead of time so we can ready with the test and so that we can have an extra VE to read the test to the applicant. We seat them away from other testers, but still in sight of the rest of the VE team. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="9425" LastEditDate="2019-05-17T20:20:03.560" LastActivityDate="2019-05-17T20:20:03.560" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14524" PostTypeId="2" ParentId="14505" CreationDate="2019-05-14T23:55:27.623" Score="2" Body="&lt;p&gt;For a variable inductor you can make two coils with a fairly large diameters. One diameter a bit larger than the other. Place the smaller one inside the larger one.&#xA;If you make the length of the inner coil fairly small you can rotate it so the coils will have the same or the opposite winding direction. This way you can get a large&#xA;tuning range for the inductance. Obviously, if you design for a very small minimum capacitance, Q will be poor since the series R will be much larger compared to a normal coil. Get inspiration from here: &#xA;&lt;a href=&quot;http://axotron.eu/photo/2013/2013-08-18_Rundradiomuseet/slides/DSC_1812.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://axotron.eu/photo/2013/2013-08-18_Rundradiomuseet/slides/DSC_1812.html&lt;/a&gt;&#xA;This one is to tune a 150 kW transmitter. Something similar, but much smaller....&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-05-14T23:55:27.623" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14529" PostTypeId="2" ParentId="14521" CreationDate="2019-05-15T11:55:59.253" Score="3" Body="&lt;p&gt;While a VE has answered definitively above, I'd also add another kind of answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I was studying for my license exam, the study site repeatedly pointed out that &quot;if you have trouble with math, you can skip all the math questions and still pass the exam.&quot;  They made the same point about certain other sub-classes of questions, such as band allocation. I'm certain the same is true for the diagram questions -- as long as you score near-perfect on the rest of the exam, you could skip all the diagrams and still pass.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is simple: while the test questions are randomly selected from a large pool, the selection process ensures there will be &lt;em&gt;some&lt;/em&gt; questions from each sub-class (antenna questions, circuit calculations, band allocation, etc.), and that no sub-class will dominate the test.  Because of that, there will be only a limited number of diagram questions on the test (something like three our four) -- and you can skip that many questions without issue, as long as you're confident on all the other subject matter.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-05-15T11:55:59.253" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14530" PostTypeId="2" ParentId="6864" CreationDate="2019-05-15T15:10:54.683" Score="2" Body="&lt;p&gt;The demise of the military CDAA is not an issue of capability, accuracy or even economics, but the primary driving factor is the change in mission, targets and technology.    HF; whether it's SSB, CW or even digital, is  simply not today's prevailing set of tactical or operational frequencies.   In addition, satellites and other passive technologies do not require the target to transmit a signal!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One comment:  By the late 1960's, CDAA target location was highly automated, including multiple computer generated bearings, and refined elyptical search areas with each bearing.  Fron the time of the automated bearing request, location times were better than 2min for NB, with WB better than 5min.  WB times were NOT dependent on the antenna or the recievers, but on the technology required to address the variation of the transmitter center frequency for the short duration signal.  New technology in mid 1970's solved this issue, automating WB bearings.  Repeated localizations provided target tracking data to commanders, supporting field observations and field data.  By the 1970's target tracking was part of a secure database including date, target, track and confidence included...&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Accuracy:  The CDAA design, technology and field implimentation means that the accuracy of each site's bearings are highly impacted by the level of maintenance and consistency of the antenna and the individual elements.  Without daily antenna and signal handling  maintenance, each site deviates from the &quot;best case&quot;, which  is listed in the classified tech documents and performance testing as much better than 2.5 degrees!!&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Typo:  CDAA. not CBAA&#xA;NB = Narrow Band. (CW, SSB, etc)&#xA;WB = Wide Band (Burst)  (Soviet Submarine)&lt;/p&gt;&#xA;" OwnerUserId="14895" LastEditorUserId="14895" LastEditDate="2019-05-18T01:05:38.577" LastActivityDate="2019-05-18T01:05:38.577" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14535" PostTypeId="1" AcceptedAnswerId="14536" CreationDate="2019-05-16T13:44:13.470" Score="3" ViewCount="75" Body="&lt;p&gt;I managed to successfully install Winlink on my Ubuntu operating system  but it is not completely functional yet. I don't know which COM my computer is set up to use, and there are a lot of them available.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's my question though, how to quickly find the right COM without going through each and every one individually. Thank you very much, and I look forward to hearing from you. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Iqj33.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Iqj33.png&quot; alt=&quot;Winlink&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1861" LastEditorUserId="873" LastEditDate="2019-05-17T00:41:59.010" LastActivityDate="2019-05-17T00:41:59.010" Title="Find the right COM to setup Winlink" Tags="&lt;packet&gt;&lt;linux&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14536" PostTypeId="2" ParentId="14535" CreationDate="2019-05-16T14:07:14.747" Score="1" Body="&lt;p&gt;If you're running under WINE, you can make the port whatever you want.  You need to know the Linux device name (like /dev/ttys0 or /dev/ttyUSB or whatever) the TNC is plugged into on the computer.  Then all you do is set up a symlink in ~/.wine/dosdevices that &quot;connects&quot; the two.  If you look in that directory, you can see the default devices already set up.  If you don't know how to set up a symlink, look for help on the ln command.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2019-05-16T14:07:14.747" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14539" PostTypeId="2" ParentId="14521" CreationDate="2019-05-17T01:41:29.150" Score="1" Body="&lt;p&gt;I don't like the answer &quot;just pass enough of the rest of the exam so it doesn't matter if you fall this one.&quot; That is doing a disservice to our blind friends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The point of the question is just to identify what the schematic symbol is for the electrical component. Just describe what you see in basic detail. Especially when we're talking about the Technician exam, these aren't super complex transistors and exotic components  we're talking about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;The component three schematic consists of two parallel lines that are perpendicular to the wire line in and out of it.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Component four is a solid black triangle with a solid black line at it's point.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Component five is a zig zag style line.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being knowledgeable hams, I hope you can recognize I'm describing a capacitor, diode, and resistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, you can do this question in reverse. Read them each answer choice and ask them to describe what the symbol looks like. If they can clearly answer that at the very least for the correct answer choice, I think it's a fair assumption to say they would recognize it if they were physically able to see it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, we're talking about an accommodation for a blind person to answer a question about what a paper schematic symbol looks like. There's a bit of irony there. As long as you make a good faith effort to give this person a chance to answer without giving the answer away, I don't feel you are committing any ethical violation as an exam proctor, nor are you cheapening the licensing process for anyone else.&lt;/p&gt;&#xA;" OwnerUserId="9450" LastEditorUserId="9450" LastEditDate="2019-05-17T01:50:02.697" LastActivityDate="2019-05-17T01:50:02.697" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14540" PostTypeId="1" AcceptedAnswerId="14544" CreationDate="2019-05-17T02:06:32.970" Score="5" ViewCount="1830" Body="&lt;p&gt;I am trying to put together a vertical pole style antenna with a loading coil housed at the base using a plan very similar to the one &lt;a href=&quot;https://www.arrl.org/files/file/Technology/tis/info/pdf/7806016.pdf&quot; rel=&quot;noreferrer&quot;&gt;described in this ARRL article&lt;/a&gt;. I am trying to understand how to electrically wire it though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For convenience, the wiring schematic from that article is shown here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GIw8H.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GIw8H.jpg&quot; alt=&quot;Loading Coil Electrical Wiring Schematic&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this build, the author used a switch to control where he tapped the coil to tune his antenna for the different bands as shown. Here's what I don't understand about this though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Why does the bottom of the coil bypass S1?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand generally that the 80 meter band needs more coil windings tapped than the 40/15 tuning, and the 10 meter band bypasses the coil altogether. But why have that connection from S1 to the first coil of L1 at all? Is that required for some reason?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the proper way to electrically wire in a loading coil to a vertical antenna?&lt;/p&gt;&#xA;" OwnerUserId="9450" LastEditorUserId="76" LastEditDate="2019-05-17T03:02:40.257" LastActivityDate="2019-05-17T14:53:00.663" Title="What is the proper way to electrically wire in a loading coil to a vertical antenna?" Tags="&lt;antenna-theory&gt;&lt;hf&gt;&lt;vertical-antenna&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14541" PostTypeId="2" ParentId="14540" CreationDate="2019-05-17T03:00:07.043" Score="3" Body="&lt;p&gt;This is similar to a common technique applicable to potentiometers used as variable resistors, and I'm guessing that it is done for similar reasons. However, it probably isn't a good idea to implement as drawn.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Consider a potentiometer connected like so:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/hIAaX.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fhIAaX.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally, the connection between the wiper and the left end of the potentiometer would do nothing, since the portion of the potentiometer to the left of the wiper is shorted out at all times, and without that connection would be open circuit at all times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, a potentiometer may lose connection between the wiper and track momentarily as it is turned, or an extremely worn one have “dead” spots of no connection even when not being turned. Therefore, the extra connection ensures that the resistance between A and B is always &lt;em&gt;no greater than&lt;/em&gt; the end-to-end resistance of the potentiometer. This is important if a too-high resistance or open circuit could damage the circuit (for example, if A is ground and B is connected to a voltage source would, by itself, raise point B to a voltage that would damage other components), and more generally means that the potentiometer's &quot;output&quot; cannot become &quot;out of range&quot; in the event of dead spots (unless the potentiometer's track/winding breaks entirely).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;In your case, you do not have a potentiometer but a switch — therefore, unless it is a make-before-break type (which might be a good choice anyway), it &lt;strong&gt;will always&lt;/strong&gt; behave like the worn potentiometer, causing J1 to become open-circuit as you make the change. Thus, the extra connection ensures that &lt;strong&gt;the antenna is always connected to J1, regardless of what is done with the switch.&lt;/strong&gt; It might present a poorly-matched load, but not a pure open circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, there's a catch — instead of shorting out portions of a resistor we're shorting out portions of an &lt;em&gt;inductor&lt;/em&gt;. All turns of an inductor are coupled together (though more separated ones less so), so there are now shorted turns, which will waste power in eddy currents rather than radiating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore, the presented design with a tapped inductor is not a good idea. You could fix it by using &lt;em&gt;separate&lt;/em&gt; inductors for each stage, arranged to minimize coupling between them (perpendicular axes, keeping them apart).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;To address your broader question of &lt;em&gt;what is the proper way to electrically wire in a loading coil to a vertical antenna&lt;/em&gt; — I don't have any personal recommendations, but I do think that the extra wire that you were puzzled by is plausibly a good idea. Whether it's worth the complications of implementation, I can't say.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-05-17T14:53:00.663" LastActivityDate="2019-05-17T14:53:00.663" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14542" PostTypeId="1" AcceptedAnswerId="14543" CreationDate="2019-05-17T03:21:20.663" Score="2" ViewCount="217" Body="&lt;p&gt;Not sure if in scope for ham SE. I'm very new to this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most wifi repeaters contain an actual router and two radios set up to receive and transmit at different frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why can't we have a wifi repeater that literally takes the wifi EM band, amplifies it, and spits it back out?&lt;/p&gt;&#xA;" OwnerUserId="14910" LastActivityDate="2019-05-17T16:37:47.563" Title="How come wifi repeaters aren't just amplifiers?" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14543" PostTypeId="2" ParentId="14542" CreationDate="2019-05-17T03:38:36.663" Score="7" Body="&lt;p&gt;This type of repeater is sometimes called a &lt;strong&gt;linear transponder&lt;/strong&gt;, particularly when it is installed on amateur radio satellites (I don't know of other uses). There are several problems with using it in the application you propose.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Such a repeater cannot &lt;em&gt;improve the signal quality&lt;/em&gt;. Whatever noise it receives, it transmits. Therefore, the signal-to-noise ratio coming out of it will always be worse than going into it. A repeater which demodulates/decodes the signal and re-modulates it can clean up the signal. Even an analog FM repeater as used by all sorts of two-way radios will do this — it inherently takes advantage of the “FM capture effect” to produce less RF noise than it received. Digital transmissions can do this even better because the received bits (more precisely, &lt;a href=&quot;https://en.wikipedia.org/wiki/Symbol_rate&quot; rel=&quot;nofollow noreferrer&quot;&gt;symbols&lt;/a&gt;) are detected and then re-modulated from scratch, so none of the received noise passes through the repeater at all (whereas in the analog FM case the audio will degrade somewhat).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, decoding and validating a digital packet ensures that &lt;em&gt;if&lt;/em&gt; it is unusable for any reason (too much noise or other transmissions to decode, or the transmitter was just not obeying the protocol) the repeater will not retransmit it, thus helping efficiently use the available spectrum.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;WiFi famously works in the same 2.4 GHz band as microwave ovens. Such a repeater would retransmit the leakage from any nearby microwave oven. (This is just a particular example of the general case of not being able to avoid retransmitting noise.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Retransmitting on another frequency requires that you have two separate frequencies designated for this purpose. If these are chosen arbitrarily for each network setup, then you could create a feedback loop between separately administered repeaters. If the protocol specifies pairs of frequencies, reserved for &quot;devices&quot; and &quot;repeaters&quot;, then multi-hop repeater networks wouldn't work.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Broadly speaking, simply repeating a band is &lt;strong&gt;not an efficient use of spectrum,&lt;/strong&gt; particularly when you have many devices and repeaters, uncoordinated, all trying to use the &lt;em&gt;same&lt;/em&gt; bands.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I mentioned above that this technique is used in some amateur radio satellites. In this case, the input and output frequencies are widely separated, and unlike WiFi there are no other nearby un-coordinated repeaters using the same frequencies, so there is no feedback loop problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantages (that I can recall) of a linear transponder are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Many users can use it at the same time — it just repeats a band of the RF spectrum it receives, so many signals can occupy different frequencies within that band. (As long as nobody transmits too strongly.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It can be used with any mode (modulation), even ones that were invented after the satellite was launched. Most amateur satellite repeaters are basically FM repeaters, and thus support only one voice channel.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-05-17T16:37:47.563" LastActivityDate="2019-05-17T16:37:47.563" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14544" PostTypeId="2" ParentId="14540" CreationDate="2019-05-17T05:50:02.947" Score="3" Body="&lt;p&gt;I don't think it's correct to connect the end of the coil to the common point of S1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shorted turns, because they're magnetically coupled to the active turns in the coil, increase the loss in the inductor. Loading coils need to be kept away from metals, and unused turns should be left open. I suggest that if you're building a new coil, you should tap it like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pvnIp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pvnIp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The extra turns on the inductor make sense for this reason: when making a loaded antenna like this, you don't know exactly how much inductance is required. You wind the coil so that it is definitely resonant &lt;em&gt;below&lt;/em&gt; 3.5 MHz, and then &lt;em&gt;on your particular ground system or vehicle&lt;/em&gt; find the correct tap positions for 80 m, 40 m, 20 m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bottom turns are wasted, but it's better to have too many than too few, so you have no choice but to build it like this.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-05-17T06:50:04.293" LastActivityDate="2019-05-17T06:50:04.293" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14545" PostTypeId="2" ParentId="14540" CreationDate="2019-05-17T12:10:33.793" Score="2" Body="&lt;p&gt;Simulation indicates that there is an error in the diagram.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shortened antennas exhibit capacitive reactance which can be compensated by adding series inductive reactance as shown in the diagram. However, shortened antennas also exhibit lower driving-point &lt;em&gt;resistance&lt;/em&gt;, for which compensating reactance is no cure. The &quot;cold&quot; end of the coil should be connected to the radial system. The feed point is then &quot;tapped up&quot; the coil to form an &quot;L&quot; network. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simulation shows that the driving-point impedance of a 25-ft 1&quot; diameter vertical with four (4) 25-ft #14 radials is 6.4-j609 ohms. (These values are only significant for purposes of illustration; actual measured values may vary substantially, but those effects are outside the scope of this question.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Entering these values into &lt;em&gt;&lt;a href=&quot;http://harriman.ddns.net/Smith_Charts.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;SimSmith&lt;/a&gt;&lt;/em&gt; and choosing appropriate inductance values shows that we can achieve a match on 80 meters by tapping up a ~27uH coil:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Bb7Bl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Bb7Bl.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A different &lt;em&gt;total&lt;/em&gt; inductance will be needed on each band and it is possible that a good match on some bands will require capacitance in the L network. A &lt;a href=&quot;http://p1k.arrl.org/pubs_archive/72101&quot; rel=&quot;nofollow noreferrer&quot;&gt;follow up item&lt;/a&gt; to this effect was published in &lt;em&gt;QST&lt;/em&gt;'s &quot;Technical Correspondence&quot; column a few months after the original article.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-17T12:10:33.793" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14546" PostTypeId="1" CreationDate="2019-05-17T13:19:59.563" Score="1" ViewCount="88" Body="&lt;p&gt;I wonder whether the source code of VE6YP (Tony Field) coaxtrap design program (&lt;a href=&quot;https://www.qsl.net/ve6yp/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;link 1&lt;/a&gt;, &lt;a href=&quot;http://www.cqham.ru/coaxtrap.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;link 2&lt;/a&gt;) was ever published or described. As a Mac user I'm having little difficulties using this software and I would like to rewrite it in Python. Or maybe there are similar calculators available online? Unfortunately I didn't manage to find one.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-05-17T13:19:59.563" Title="Looking for a formula used by VE6YP trap calculator" Tags="&lt;antenna-theory&gt;&lt;software&gt;&lt;software-development&gt;&lt;trap&gt;" AnswerCount="0" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14547" PostTypeId="1" AcceptedAnswerId="14548" CreationDate="2019-05-17T15:11:37.853" Score="2" ViewCount="959" Body="&lt;p&gt;lightning damage can be extensive and costly, its even life-threatening.&lt;br&gt;&#xA;If I have properly grounded the equipment and have a Surge protection device, do I have to disconnect the antennas during the thunderstorms?&lt;/p&gt;&#xA;" OwnerUserId="14723" LastActivityDate="2019-05-20T13:33:34.547" Title="Do I have to disconnect antennas during thunderstorms?" Tags="&lt;antenna&gt;&lt;grounding&gt;&lt;lightning&gt;&lt;security&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14548" PostTypeId="2" ParentId="14547" CreationDate="2019-05-17T15:52:45.473" Score="3" Body="&lt;p&gt;What is &quot;proper&quot; grounding and protection?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my experience, most amateur stations that have installed grounding and surge protection devices have not installed them properly. Surge protection devices are designed to handle relatively small voltage transients, not handle surge currents on the order of a lightning strike. And with the tremendous currents involved in a strike, even a few milliohms is enough impedance to generate voltages high enough to cause damage. As such, protection efficacy is much more about where and how grounds and protection devices are installed rather than if they are installed at all. See &lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is certainly possible for a well-designed station to reduce the lightning risk below the threshold necessary to justify the hassle of disconnecting the antennas. Consider commercial stations: the antennas are never disconnected. Although they do suffer damage occasionally, most times they are able to continue operating through a thunderstorm without incident.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-05-17T15:52:45.473" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14549" PostTypeId="2" ParentId="14547" CreationDate="2019-05-17T20:28:25.127" Score="2" Body="&lt;p&gt;While I completely agree with Phil on everything he wrote, antennas are not the only path to your equipment from a lightning strike.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to the map of &lt;a href=&quot;https://upload.wikimedia.org/wikipedia/commons/6/6d/United_States_Effective_Ground_Conductivity_Map.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;Estimated Effective Ground Conductivity in the United States&lt;/a&gt;, I enjoy the privilege of living in a rural area with 0.5mS/m of ground conductivity - the lowest value on the map. Low conductivity means large voltages induced in the Earth by lightning strikes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I note the rural location because the telephone and electrical utilities &quot;sometimes&quot; don't invest what they should to maintain the grounding integrity of their systems. Result: hundreds of dollars of losses of electrical and electronic equipment and appliances connected to the AC mains and/or to the phone lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, don't forget your rotor cable - another good pickup for the strong electric fields induced by nearby lightning strikes!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I disconnect EVERYTHING when not in use and haven't had a loss since I instituted this policy, despite some frighteningly close strikes.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-17T20:28:25.127" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14550" PostTypeId="2" ParentId="6864" CreationDate="2019-05-18T01:31:22.000" Score="1" Body="&lt;p&gt;Response times are not primarily driven by the antenna characteristics, but the data sampling rate (electro-mechanical, ecectronic, or otherwise), data transmission time (including both receiver's tuning and bearing response) and lastly the ABI calculation algorithms.&lt;br&gt;&#xA;So, beyond the fixed sampling rate, the biggest limitation is the confidence algorithm in the ABI calculation.  What signal quality and how many &quot;valid&quot; samples are necessary to satisfy and complete the calculation.   Obviously a marginal signal requires more time to satisfy the calculation. &#xA;ABI = Automatic Bearing Instrumentation &lt;/p&gt;&#xA;" OwnerUserId="14895" LastActivityDate="2019-05-18T01:31:22.000" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14552" PostTypeId="1" CreationDate="2019-05-18T06:44:10.593" Score="1" ViewCount="433" Body="&lt;p&gt;Are transmit antennas the same as receive ones? I am making a extended Wi-Fi comms CCTV camera.&lt;/p&gt;&#xA;" OwnerUserId="14912" LastEditorUserId="218" LastEditDate="2019-05-18T15:25:09.867" LastActivityDate="2019-06-28T11:18:25.953" Title="Are transmit antennas the same as receive ones?" Tags="&lt;antenna&gt;" AnswerCount="6" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14553" PostTypeId="2" ParentId="9295" CreationDate="2019-05-18T09:24:47.817" Score="0" Body="&lt;p&gt;144.6125 is the calling frequency for all Digital modes.&lt;/p&gt;&#xA;" OwnerUserId="14914" LastActivityDate="2019-05-18T09:24:47.817" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14554" PostTypeId="1" CreationDate="2019-05-18T14:42:58.980" Score="3" ViewCount="593" Body="&lt;p&gt;I'm new to amateur radio, and I would like to listen to those satellites in the orbit.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Where do I start?&lt;/li&gt;&#xA;&lt;li&gt;What types of amateur radio satellites exist?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="14723" LastEditorUserId="14723" LastEditDate="2019-05-29T14:02:55.530" LastActivityDate="2019-06-06T06:34:29.660" Title="How do I listen to the amateur radio satellites?" Tags="&lt;antenna-theory&gt;&lt;receiver&gt;&lt;satellites&gt;&lt;equipment&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14556" PostTypeId="2" ParentId="1950" CreationDate="2019-05-19T09:53:53.187" Score="0" Body="&lt;p&gt;Judging by your name, I think you must be Greek (I'm also from Greece) so the official band plan can be found here: &lt;a href=&quot;https://www.eett.gr/opencms/opencms/admin/downloads/Announcments/AP399_034.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.eett.gr/opencms/opencms/admin/downloads/Announcments/AP399_034.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14924" LastActivityDate="2019-05-19T09:53:53.187" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14557" PostTypeId="2" ParentId="14552" CreationDate="2019-05-19T21:46:32.900" Score="1" Body="&lt;p&gt;In short, yes. The nature of an antenna is that it is naturally resonant on one frequency. Now, that doesn't mean that you can't use an antenna if it isn't exactly at its resonant length (most in fact are not, but that is a different topic). Literally entire books are dedicated to that subject. However, for the question you asked, the only difference between a receive and transmit antenna is what is connected to the other end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you have a receiver connected to it, like your car radio? It's a receive antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you have a handheld transceiver like a &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B010LOI056&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;UV-5R&lt;/a&gt; connected? It's a transmit antenna when you're talking and a receive antenna when you're not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To use your Wifi question, take a look at your wireless router and think about what's going on. Sometimes you are sending data to the router, and sometimes you are getting data from it. The same antenna can be used to transmit or receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your question is, can I send and receive at the same time on the same antenna? Well, that is dependent on the transceiver you're using, not the antenna.&lt;/p&gt;&#xA;" OwnerUserId="9450" LastEditorUserId="9450" LastEditDate="2019-05-26T12:10:29.667" LastActivityDate="2019-05-26T12:10:29.667" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14558" PostTypeId="2" ParentId="14552" CreationDate="2019-05-20T11:25:44.700" Score="4" Body="&lt;p&gt;A transmit antenna for a frequency should work well for receiving that frequency, but the reverse may not be true.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, while an antenna meant for transmitting works much better when resonant on that frequency (e.g., a half wavelength for a dipole, a full wavelength for a loop), receive antennas are not necessarily resonant.  Although in most cases a resonant antenna may allow greater receive sensitivity, it isn't strictly necessary.  When receiving, signal to noise ratio is typically more important than sensitivity, and a more sensitive antenna might just receive more noise.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2019-06-28T11:18:25.953" LastActivityDate="2019-06-28T11:18:25.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14559" PostTypeId="2" ParentId="14547" CreationDate="2019-05-20T13:33:34.547" Score="3" Body="&lt;p&gt;As far as I know the probability of direct strike to the antenna is considered relatively small. And if it will happen it is unlikely that your antenna will survive anyway (or the protection will cost more than the antenna itself).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Static electricity which is formed in the antenna during storms represents the greater danger to the radio in practice. Although there are various ways to mitigate this danger (bleeder resistors, inductance between the shield and the core of the coax, ...), personally I follow two simple rules:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Never operate during the storm or if you see the lightning on the horizon.&lt;/li&gt;&#xA;&lt;li&gt;When not operating, disconned the antenna from the radio. Then connect the antenna to the 100W dummy load. The dummy load will prevent the static charge to be accumulated in the antenna.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-05-20T13:33:34.547" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14560" PostTypeId="2" ParentId="14552" CreationDate="2019-05-20T13:47:42.330" Score="1" Body="&lt;p&gt;From what I know there are two main differences between transmit and receive antennas:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Receive antenna may but doesn't have to be resonant (and thus effective) on any particular frequency. For instance, consider very wideband antennas, designed for monitoring, that may have SWR ~3 or greater. Or very small loop antennas designed for radio fox hunting. The small weight and directivity are more important for these antennas than effective transmission.&lt;/li&gt;&#xA;&lt;li&gt;Receive antennas may not be designed to transmit on high power.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-05-20T13:47:42.330" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14561" PostTypeId="1" CreationDate="2019-05-20T16:08:13.440" Score="1" ViewCount="105" Body="&lt;p&gt;I want to build an ladder SSB filter using 8 MHz quartz resonators.&#xA;I don't have frequency meter but I have &lt;a href=&quot;http://www.giga.co.za/ocart/index.php?route=product/product&amp;amp;product_id=226&quot; rel=&quot;nofollow noreferrer&quot;&gt;NWT-70&lt;/a&gt;.&#xA;How can I match crystals to build a good filter?&#xA;What kind of parameters should I take into account?&lt;/p&gt;&#xA;" OwnerUserId="11243" LastEditorUserId="11243" LastEditDate="2019-05-20T19:30:21.627" LastActivityDate="2019-05-20T19:30:21.627" Title="How to match crystals using NWT?" Tags="&lt;filter&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14562" PostTypeId="2" ParentId="14561" CreationDate="2019-05-20T16:28:59.897" Score="1" Body="&lt;p&gt;One good option here would be to buy and build a crystal tester and frequency counter kit.  These are available on eBay for under $20, and take less than two hours to assemble.  It's only a 4 digit counter, however, so if you need a closer match than 1 kHz you'll need one with more precision.  Still available as a kit, though likely without the direct crystal testing function, and the kit will cost a bit more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, if the control software lets you directly control the frequency on that sweep generator, you should be able to spot the amplitude peak when you hit the crystal's frequency; the peak will be a good bit wider than the 1 Hz resolution claimed for the NWT-70, but you if you can sweep a narrow range, you ought to be able to read the peak well enough to at least equal a 4-digit frequency counter, if not get down to a few tens of Hz.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-05-20T17:22:47.653" LastActivityDate="2019-05-20T17:22:47.653" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14565" PostTypeId="2" ParentId="10201" CreationDate="2019-05-21T11:16:21.870" Score="3" Body="&lt;p&gt;The beauty of the license exams is that they are not trying to trick you with material you've never seen before. In fact, they go out of their way to publicize the questions for you ahead of time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can actually see &lt;a href=&quot;http://www.arrl.org/question-pools&quot; rel=&quot;nofollow noreferrer&quot;&gt;all of the exam bank questions&lt;/a&gt; at the ARRL website. As of the time of this post, ARRL provides the following schedule for when the exam questions will change:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;TECHNICIAN Class (Element 2) Pool is effective July 1, 2018 and is &#xA;  valid until June 30, 2022.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;CURRENT GENERAL Class (Element 3) Pool is ONLY valid until June 30,&#xA;  2019.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;NEW GENERAL Class (Element 3) Pool will be effective July 1, 2019 and &#xA;  will be valid until June 30, 2023.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;EXTRA Class (Element 4) Pool is effective July 1, 2016 and is valid&#xA;  until June 30, 2020.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The Technician pool was revised in 2018. The General pool is scheduled&#xA;  for a revision in 2019.  The Extra pool is scheduled for a revision in&#xA;  2020.  No question pools will be updated or released in 2021. The question pools review is part of a regular process.  Each question&#xA;  pool is reviewed and updated on a four year rotation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's not to say paper books are worthless, they are actually very good instructional manuals for principles that don't really change. I have a paper copy of the study guide for all three classes that I refer to frequently. Just pay attention to that exam bank schedule when you're studying for the license exam to make sure you have the current list. No point in handicapping yourself with things you've never seen before!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I was studying for the exams, I personally used an app called &lt;a href=&quot;https://play.google.com/store/apps/details?id=com.iversoft.ham.test.prep&amp;amp;hl=en_US&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ham Test Prep&lt;/a&gt;. (I am not affiliated with the product in any way). It was a good way to get a bit of studying done while I was traveling.&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2019-05-21T11:16:21.870" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14566" PostTypeId="1" AcceptedAnswerId="14569" CreationDate="2019-05-21T20:35:11.743" Score="9" ViewCount="754" Body="&lt;p&gt;I'm asking this because of the comments &lt;a href=&quot;https://ham.stackexchange.com/a/14506/8717&quot;&gt;in this answer&lt;/a&gt;, that imply that steel (mostly iron) has similar characteristics to ferrite. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically, it is implied that inserting solid steel into a single-layer coil (as is commonly used in an antenna tuner) will significantly increase its inductance at HF, as some ferrite and powdered-iron rods do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this true under any circumstances? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are suitable materials for this purpose? &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-05-22T13:31:04.427" LastActivityDate="2019-05-22T15:25:35.407" Title="What types of materials increase the inductance of a coil when inserted inside it?" Tags="&lt;antenna-tuner&gt;&lt;inductor&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14567" PostTypeId="1" CreationDate="2019-05-21T21:12:27.990" Score="7" ViewCount="600" Body="&lt;p&gt;I want to base the output network for a 500W push-pull HF amplifier on &quot;A 250W Broadband Linear Amplifier&quot; described in Chapter 17 of the 2014 ARRL &lt;em&gt;Handbook&lt;/em&gt;. I need advice on whether and/or how the 1:4 impedance step-up transmission line transformer should be modified to handle twice the originally intended power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The long-form article included on the companion DVD shares the rationale for the transformer:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The advantage of the transmission line type of RF transformer is that it does not have the leakage reactance that plagues the tube-and-sleeve type of transformer used on many solid-state amplifiers.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Simulation documents the significance of this statement: even with compensation, the gain falls off with increasing frequency when the coupling factor of a conventional transformer is reduced from the ideal value of k=1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;T3, the output transformer for this 250W PA, comprises two (2) separate ferrite-loaded 25&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; transmission lines whose inputs are paralleled on the low-Z side and connected in series on the high-Z side:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JiNqY.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JiNqY.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transformer calls for miniature coax such as p/n &lt;a href=&quot;http://www.communication-concepts.com/d260-4118-0000-coax-wire-price-per-foot/&quot; rel=&quot;noreferrer&quot;&gt;D260-4118-0000&lt;/a&gt; wound on &lt;a href=&quot;https://www.fair-rite.com/product/multi-aperture-cores-2861010002/&quot; rel=&quot;noreferrer&quot;&gt;Fair-Rite 2861010002&lt;/a&gt; binocular cores. How can I determine, &lt;em&gt;a priori&lt;/em&gt;, whether this transformer can handle a 500W output level? If it can't handle 500W, how do I determine what changes I need to make to the coax and ferrite components?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is calculating power dissipation as simple as noting the resistance component of the impedance from the data sheet and multiplying that by the square of the product of the current and the number of turns? How do I convert that into temperature rise for the core? &lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-05-22T14:51:14.590" LastActivityDate="2019-05-24T09:01:28.053" Title="Double power-handling ability of RF amplifier output transformer" Tags="&lt;rf-power&gt;&lt;electronics&gt;&lt;equipment-design&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14568" PostTypeId="2" ParentId="14566" CreationDate="2019-05-21T22:20:52.363" Score="4" Body="&lt;p&gt;&lt;strong&gt;TL;DR:&lt;/strong&gt;&lt;br&gt;&#xA;It's NOT mild steel, brass, or aluminum. &#xA;&lt;hr&gt;&#xA;I connected two different inductors to an antenna analyzer, and all of the above materials &lt;em&gt;decreased&lt;/em&gt; the inductance as they were inserted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The larger the diameter of the steel I inserted, the lower the inductance and the greater the loss. It was the worst material I tried.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I inserted some powdered iron (a 2.4&quot; OD T-200-2 toroid core that I happened to have on hand), the inductance increased. The greatest increase by far was when I inserted a short piece of 1/2&quot; diameter ferrite (Amidon R61-050-750) which was left over from a grounded-grid amplifier cathode choke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://www.w8ji.com/steel_wool_balun.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.w8ji.com/steel_wool_balun.htm&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For example, inserting a solid iron slug inside a small RF coil shows a behavior almost identical to using brass or aluminum slugs. Inserting a solid slug of iron might increases the magnetic field concentration and inductance near direct current frequencies, but at some higher frequency eddy currents and the inability of the core to follow field changes cause the flux concentration to decrease.....eventually reaching zero. At some frequency, the counter MMF takes over. Inductance is actually reduced by the core. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-05-22T14:05:26.420" LastActivityDate="2019-05-22T14:05:26.420" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14569" PostTypeId="2" ParentId="14566" CreationDate="2019-05-22T15:25:35.407" Score="6" Body="&lt;p&gt;Any material with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Relative_permeability_and_magnetic_susceptibility&quot; rel=&quot;noreferrer&quot;&gt;relative permeability&lt;/a&gt; greater than 1 will increase inductance when inserted into a coil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that permeability is a complex number and frequency dependent. The imaginary part of permeability contributes to loss and appears as a resistance, so the addition of some material in the coil may increase inductance and also add resistance. Generally, the real part of permeability of materials decreases with frequency, while the imaginary part increases. Thus at some frequency, the material becomes useless for constructing inductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many magnetic materials are also non-linear. This is because they work by aligning internal magnetic domains within the material with the applied magnetic field of the core. At some magnetic flux density, the domains are all as aligned as they can be, and can become no more aligned, and thus can not respond to increasing magnetic flux density. This is called &quot;core saturation&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ferromagnetic material, such as iron, nickel, or cobalt, has a high permeability. &lt;a href=&quot;https://en.wikipedia.org/wiki/Paramagnetism&quot; rel=&quot;noreferrer&quot;&gt;Paramagnetic materials&lt;/a&gt;, such as liquid oxygen work as well. Generally, anything that will stick to a permanent magnet indicates a high permeability at 0 frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, ordinary lumps of metal do not make good cores for inductors because their real permeability decreases rapidly with frequency, and inserting them into a RF inductor just &lt;a href=&quot;https://en.wikipedia.org/wiki/Induction_heating&quot; rel=&quot;noreferrer&quot;&gt;makes them hot&lt;/a&gt;. A resistor is a much simpler and economical way to achieve the same electrical effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Powdered iron cores and ferrite cores are two common materials engineered to overcome these effects to produce useful inductors up to 10s or sometimes even 100s of MHz. Beyond those frequencies even these materials become ineffective. Fortunately higher frequencies also tend to require lower inductances, and thus air-core inductors become practical.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-05-22T15:25:35.407" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14570" PostTypeId="2" ParentId="14554" CreationDate="2019-05-22T15:46:01.060" Score="2" Body="&lt;p&gt;there's at least one you can listen to online: &lt;a href=&quot;https://eshail.batc.org.uk/nb/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Qatar-OSCAR 100&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2019-05-22T15:46:01.060" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14571" PostTypeId="2" ParentId="14505" CreationDate="2019-05-22T22:55:14.190" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it practical to use a slug-tuned variable inductor in an antenna matcher (aka “antenna tuner”)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As far as I have been able to determine after countless exhaustive searches, I believe that the answer is &lt;strong&gt;no&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While trying to minimize costs is certainly an admirable goal, I think that you should abandon this idea for a proven design. This could include tuners using only variable capacitors, or tuners using tapped or continously-variable rotary inductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No company makes antenna tuners with variable inductors using this method. And neither has any ham homebrewer. &lt;strong&gt;The inductance range is simply too narrow to be practical across a multiple bands, regardless of the tuner circuit design&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might ask this on one of the &lt;a href=&quot;https://www.eham.net/ehamforum/smf/&quot; rel=&quot;nofollow noreferrer&quot;&gt;eHam.net forums&lt;/a&gt; where Glenn W9IQ (and other experts not yet on hamSE) has historically spent most of his time.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-05-22T22:55:14.190" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14574" PostTypeId="1" CreationDate="2019-05-23T08:40:52.030" Score="2" ViewCount="130" Body="&lt;p&gt;Is it possible to set a gnuradio flowgraph to record with a File Sink a fixed number of samples? I would like to use this wave as a reference.&#xA;Thank you!&lt;/p&gt;&#xA;" OwnerUserId="14904" LastEditorUserId="14904" LastEditDate="2019-05-23T08:55:28.833" LastActivityDate="2019-05-23T10:52:43.510" Title="How to record fixed number of samples in gnuradio" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14576" PostTypeId="2" ParentId="14574" CreationDate="2019-05-23T10:52:43.510" Score="1" Body="&lt;p&gt;An epy block is a good solution.&#xA;It can be connected where the desired data flows and collect the desired samples.&#xA;Then, a pressed push button can trigger the save.&lt;/p&gt;&#xA;" OwnerUserId="14904" LastActivityDate="2019-05-23T10:52:43.510" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14577" PostTypeId="1" AcceptedAnswerId="14579" CreationDate="2019-05-24T00:17:29.480" Score="9" ViewCount="113" Body="&lt;p&gt;I have a couple of HTs with channel scanning features. I imagine setting the radio to scan mode takes more power than just listening to a single channel, but what rough order of magnitude? Will I lose 1%, 10% or 50% of my battery life? Are some brands or models notably better than others for power efficiency while scanning?&lt;/p&gt;&#xA;" OwnerUserId="14609" LastActivityDate="2019-05-25T18:31:47.567" Title="Does scanning take much more battery than listening on one channel?" Tags="&lt;battery&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14578" PostTypeId="2" ParentId="14567" CreationDate="2019-05-24T02:05:47.147" Score="3" Body="&lt;p&gt;Details on 25&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; coax are not easy to find. In addition to the coax called out in the Handbook design, Communication Concepts sells UT-141C-25. Sadly, CCI does not publish datasheets for many of the products they sell, but I was able to find a datasheet for UT-141C-25 at &lt;a href=&quot;https://www.microstock-inc.com/pdfshow01.php?item=UT-141C-15&quot; rel=&quot;nofollow noreferrer&quot;&gt;Microstock Inc&lt;/a&gt;. With 0.1dB/ft loss at &lt;em&gt;500&lt;/em&gt; MHz, the cable is rated to handle 470W, so it should dissipate about 5W running 500W at 30MHz and below. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cable diameter is 3.6mm, so three turns require a core with a 7.9mm opening. Fair-Rite &lt;a href=&quot;https://www.fair-rite.com/product/round-cable-emi-suppression-cores-2661801902/&quot; rel=&quot;nofollow noreferrer&quot;&gt;2661801902&lt;/a&gt; appears suitable, but with X&lt;span class=&quot;math-container&quot;&gt;$_L$&lt;/span&gt;=10&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; at 10MHz, three turns on two cores end-to-end would produce only 2.8&lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;H of inductance and X&lt;span class=&quot;math-container&quot;&gt;$_L$&lt;/span&gt;=32&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; of reactance at 1.8MHz, short of the 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next larger core is Fair-Rite &lt;a href=&quot;https://www.fair-rite.com/product/round-cable-emi-suppression-cores-2661665702/&quot; rel=&quot;nofollow noreferrer&quot;&gt;2661665702&lt;/a&gt;, which delivers X&lt;span class=&quot;math-container&quot;&gt;$_L$&lt;/span&gt;=35&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; at 10MHz with a single core. Three turns will produce 5&lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;H of inductance and X&lt;span class=&quot;math-container&quot;&gt;$_L$&lt;/span&gt;=57&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; at 1.8MHz, adequate for this design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Care must be taken when winding the coax. Since the minimum bend radius is 4.8mm, winding the coax tightly against the shoulder of the core could damage the coax.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-05-24T09:01:28.053" LastActivityDate="2019-05-24T09:01:28.053" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14579" PostTypeId="2" ParentId="14577" CreationDate="2019-05-24T09:31:52.627" Score="5" Body="&lt;p&gt;There are a few states of listening that you should think about:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;listening with the squelch closed, the receiver is probably off for 95% of the time, turned on a couple of times a second to check for a signal. This is the lowest power state.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;receiving a signal, squelch open, the receiver is fully on.&lt;br&gt;&#xA;Also the loudspeaker takes some power, not much if it's soft, but more than the receiver if the volume is loud.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;scanning at full speed, the receiver is on all the time.  Re-tuning won't increase its power consumption significantly (there is some time wasted while the tuner settles, but this is just part of scanning).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So I estimate that scanning, with the squelch closed, takes the same or less power than listening to a busy channel at low volume, but many times more than monitoring an empty channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why not do an experiment?  Disconnect the battery, power the HT from an external source, and monitor the current that it draws.&#xA;You might have to do some work to smooth out the pulses of current in monitoring mode, something like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/4vraJ.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f4vraJ.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-05-24T09:31:52.627" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14580" PostTypeId="2" ParentId="5138" CreationDate="2019-05-24T11:39:43.653" Score="1" Body="&lt;p&gt;I know this is an old question, but I recently had to setup Chirp again on a new computer and have long since lost the &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B00PBLDWD0&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;driver CD that came with my cable&lt;/a&gt;... thus I was having the same problem. The issue is that it's not really a USB cable per say. What your computer is doing is emulating an analog COM port through the USB cable, and it has to have special instructions (i.e. software drivers) that tell the hardware (the USB port) how to do that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I solved it by going directly to the &lt;a href=&quot;https://www.ftdichip.com/Drivers/VCP.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Baofeng website driver page&lt;/a&gt;. They only have one driver installation for Windows, and although I am using Windows 10 and you asked for Windows 7, they have this note:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;*Includes the following version of of the Windows operating system: Windows 7, Windows Server 2008 R2 and Windows 8, 8.1, Windows server 2012 R2, Windows Server 2016 and Windows 10&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What you will need to know is if your dad's computer is running off of 32 bit or 64 bit software. Your computer will not run the opposite type. Also, make sure you download the setup executable file (link on the righthand side) and not the link under the &quot;Processor Architecture&quot; table, as that file is really just the source code for the drivers. I doubt you want to compile the drivers yourself!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once I installed the drivers, I just restarted Chirp and the USB appeared as a COM port when I tried to export to the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2Q8V9.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2Q8V9.jpg&quot; alt=&quot;Chirp screenshot showing Emulated COM Port&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2019-05-24T11:39:43.653" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14581" PostTypeId="2" ParentId="302" CreationDate="2019-05-24T17:21:48.580" Score="0" Body="&lt;p&gt;According to &lt;a href=&quot;http://www.w6wgz.org/images/HAMS.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Florida Skip Magazine&lt;/a&gt; of 1959&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It goes like this: The word &quot;HAM&quot; as applied to 1908 was the station CALL of the first amateur wireless stations operated by some amateurs of the Harvard Radio Club. They were ALBERT S. HYMAN, BOB ALMY and POOGIE MURRAY. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At first they called their station &quot;HYMAN-ALMY-MURRAY&quot;. Tapping out such a long name in code soon became tiresome and called for a revision. They changed it to &quot;HY-AL-MU,&quot; using the first two letters of each of their names. Early in 1901 some confusion resulted between signals from amateur wireless station &quot;HYALMU&quot; and a Mexican ship named &quot;HYALMO.&quot; They then decided to use only the first letter of each name, and the station CALL became &quot;HAM.&quot;&lt;/p&gt;&#xA;" OwnerUserId="14723" LastActivityDate="2019-05-24T17:21:48.580" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14584" PostTypeId="2" ParentId="14577" CreationDate="2019-05-25T18:31:47.567" Score="2" Body="&lt;p&gt;I would not be surprised if the audio amp used more power than the rf front, tuner osc, and signal detect combined.  Thus listening at some reasonable speaker volume, and using energy to vibrate a physical mass, might consume more power than just retuning and monitoring some level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But measuring your particular radio is much better than guessing.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-05-25T18:31:47.567" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14585" PostTypeId="1" CreationDate="2019-05-25T18:44:54.420" Score="7" ViewCount="278" Body="&lt;p&gt;Would a disconnected wire or conductive mat below a low height antenna reduce ground losses?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A tuned length of wire under a wire antenna might be suitable for NVIS gain.  But would a bunch of space blankets or unconnected random length wires or mesh (gopher wire) on or slightly above the ground help reduce ground loss of a low dipole or a vertical with far too few counterpose radials? (e.g. maybe one).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-05-25T21:04:32.547" LastActivityDate="2019-06-07T09:44:01.393" Title="Passively reducing ground loss?" Tags="&lt;antenna-theory&gt;&lt;wire-antenna&gt;&lt;antenna-system&gt;&lt;earth&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14586" PostTypeId="2" ParentId="14552" CreationDate="2019-05-25T18:51:07.133" Score="0" Body="&lt;p&gt;There may be current carrying and legal requirements for transmit antennas (minimum 16 gauge wire size, insulators, separation distance from human bodies and heads, etc.) that do not apply to receive only antennas (invisible 30 gauge woven into your shirt , etc.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-05-25T18:51:07.133" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14587" PostTypeId="2" ParentId="14585" CreationDate="2019-05-25T20:09:47.253" Score="4" Body="&lt;p&gt;It is well-established that a wire reflector --on or just above the ground-- directly under a dipole can do just that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have a reference, but at a field day that I was present at years ago, a ham on 75m did that. Afterwards, as W8JI (who also was present) said, &quot;He was just 'killing people'&quot;, meaning that his QSO count immediately went way up. His reflector was directly under his center-fed dipole. IIRC, it was laying directly on the ground. Although the spacing between the wire and the dipole was not optimum, it certainly seemed to work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It was good and conductive soil, in NW Ohio near the Maumee River where Route 235 ends at a SW-NE road parallel with it. 200 years ago, that was part of the Great Black Swamp. Later, ditches were dug and tiles laid to drain it into the river, which turned all of Lucas and Wood county into fertile farmland. Still, adding that wire helped his signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps the band conditions improved at the same time, and the wire had little or nothing to do with it. But I've heard of too many similar experiences to discount that.&#xA;&lt;hr&gt;&#xA;As for a vertical as you describe, I'm leaving that for someone else to answer.&#xA;&lt;hr&gt;&#xA;&lt;a href=&quot;https://ham.stackexchange.com/a/14595/8717&quot;&gt;See this answer by R. Fry&lt;/a&gt;, which seems to disprove my anecdotal statements.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-05-26T18:32:54.493" LastActivityDate="2019-05-26T18:32:54.493" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14590" PostTypeId="1" CreationDate="2019-05-26T10:26:43.720" Score="6" ViewCount="867" Body="&lt;p&gt;We have a question about the algorithm for conversion from coordinates into grid squares &lt;a href=&quot;https://ham.stackexchange.com/q/221/77&quot;&gt;here&lt;/a&gt;, and this is an extension of that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've noticed that there are several web-sites (for example &lt;a href=&quot;http://www.sarl.org.za/public/QRA/Abt_Locators.asp&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;, or &lt;a href=&quot;https://k7fry.com/grid/&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;, or &lt;a href=&quot;http://rk1at.ru/WWWLOC/QTHLOC.html&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;) and Android applications which will happily show me my 8 or 10 character locator. However, I've been unable to find an exact specification for that extended system. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is: Is there a publicly available specification for the 8 and 10 character locator systems, and if yes, where?&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2019-07-20T19:04:18.493" Title="Is there a public standard for 8 and 10 character grid locators?" Tags="&lt;location&gt;&lt;maidenhead-locator&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14591" PostTypeId="2" ParentId="14590" CreationDate="2019-05-26T10:33:29.613" Score="3" Body="&lt;p&gt;The Maidenhead locator system (which you correctly tagged) is described in detail &lt;a href=&quot;https://en.wikipedia.org/wiki/Maidenhead_Locator_System&quot; rel=&quot;nofollow noreferrer&quot;&gt;in this Wikipedia page&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A short summary from that page is:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;To summarise:&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Character pairs encode longitude first, and then latitude.&lt;/li&gt;&#xA;  &lt;li&gt;The first pair (a field) encodes with base 18 and the letters &quot;A&quot; to &quot;R&quot;.&lt;/li&gt;&#xA;  &lt;li&gt;The second pair (square) encodes with base 10 and the digits &quot;0&quot; to &quot;9&quot;.&lt;/li&gt;&#xA;  &lt;li&gt;The third pair (subsquare) encodes with base 24 and the letters &quot;a&quot; to &quot;x&quot;.&lt;/li&gt;&#xA;  &lt;li&gt;The fourth pair (extended square) encodes with base 10 and the digits &quot;0&quot; to &quot;9&quot;.&lt;/li&gt;&#xA;  &lt;li&gt;The fifth and subsequent pairs are not formally defined, but recycling the third and fourth pair algorithms is one possible definition: BL11bh16oo66&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;  &#xA;  &lt;p&gt;On shortwave frequencies, positions are reported at square precision, and on VHF and UHF, subsquare precision is used. More precise position reports are very rarely used.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Note that this means the formal standard does not define anything past the first eight characters (four pairs), but that people tend to extend the system used in the third and fourth pair if they need to be more accurate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also note that this extension (only as far as five pairs, or ten characters) is the one used at the &lt;a href=&quot;https://aprs.fi/&quot; rel=&quot;nofollow noreferrer&quot;&gt;APRS website&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2019-05-26T10:46:59.027" LastActivityDate="2019-05-26T10:46:59.027" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14592" PostTypeId="2" ParentId="14585" CreationDate="2019-05-26T11:39:51.647" Score="2" Body="&lt;p&gt;Random long wires - probably will help. Especially if they're aligned with the dipole above them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Space blankets might not have a thick enough metal layer to be effective at HF, (though I know reflective window film is as good as wire mesh at 900 MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most importantly, things &amp;lt; &lt;span class=&quot;math-container&quot;&gt;${1\over2}\lambda$&lt;/span&gt;, not connected together, will make no difference, the fields will go right through them. There is no easy way of connecting space blankets to each other. Perhaps with a substantial overlap and some sandbags on that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, note that adding metal under an antenna, as it makes it more efficient, will also push its pattern up. Better for NVIS and worse for long distances. So depending on your ground conditions, dipole height and band, you might see a loss of performance on some paths.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-05-26T11:39:51.647" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14593" PostTypeId="1" AcceptedAnswerId="14596" CreationDate="2019-05-26T11:50:16.907" Score="4" ViewCount="176" Body="&lt;p&gt;I am working on my 80m and 40m CW transmitter and ran into a problem: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I need to match the high impedance of PL504 to 50ohm coax, a Pi match seems to be the best, but I don't know how to calculate the inductor - the calculators online give capacitor values of several nF, too big for tuning caps and sometimes they just say NaN.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Operation class is C and I'd like to get 20W of power at least. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What is the best value for plate RF choke?&lt;/li&gt;&#xA;&lt;li&gt;Can it be made with a SMPS power core rated for 200kHz?&lt;/li&gt;&#xA;&lt;li&gt;Are there any general errors?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://imgupload.pl/images/2019/05/26/received_2079405082168955.jpg&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="14961" LastEditorUserId="4076" LastEditDate="2019-05-26T12:16:22.430" LastActivityDate="2019-06-02T13:23:42.357" Title="Pi Matching circut for tube PA - what values?" Tags="&lt;impedance&gt;&lt;transmitter&gt;&lt;amplifier&gt;&lt;antenna-tuner&gt;&lt;vacuum-tubes&gt;" AnswerCount="2" CommentCount="12" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14594" PostTypeId="2" ParentId="14590" CreationDate="2019-05-26T12:34:09.297" Score="2" Body="&lt;p&gt;The Maidenhead system breaks down a grid into increasingly smaller chunks. The fourth pair is defined as an evenly spaced 100 square grid, or 10x10. &lt;a href=&quot;http://www.hamradio.in/circuits/grid_locator_system.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;This site&lt;/a&gt; has an excellent image that breaks that down for you:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/w265U.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/w265U.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this picture, the black box outline is MK80ht. You can see this box was further subdivided, and the user's location of Kalpathy, India is located in MK80ht80.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As noted by the &lt;a href=&quot;https://en.wikipedia.org/wiki/Maidenhead_Locator_System&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia article&lt;/a&gt;, there is no formal definition for anything smaller than that, however some users apparently recycle the formula for the third and fourth pairs if needed:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;The first pair (a field) encodes with base 18 and the letters &quot;A&quot; to &quot;R&quot;.&lt;/li&gt;&#xA;  &lt;li&gt;The second pair (square) encodes with base 10 and the digits &quot;0&quot; to &quot;9&quot;.&lt;/li&gt;&#xA;  &lt;li&gt;The third pair (subsquare) encodes with base 24 and the letters &quot;a&quot; to &quot;x&quot;.&lt;/li&gt;&#xA;  &lt;li&gt;The fourth pair (extended square) encodes with base 10 and the digits &quot;0&quot; to &quot;9&quot;.&lt;/li&gt;&#xA;  &lt;li&gt;The fifth and subsequent pairs are not formally defined, but recycling the third and fourth pair algorithms is one possible&#xA;  definition&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9450" LastEditorUserId="9450" LastEditDate="2019-05-26T12:43:42.650" LastActivityDate="2019-05-26T12:43:42.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14595" PostTypeId="2" ParentId="14585" CreationDate="2019-05-26T13:38:22.153" Score="2" Body="&lt;p&gt;Below is the result of a NEC4.2 comparison of a 75m, center-fed dipole at 10m elevation above 15 mS/m Earth, with and without a reflector on the surface of the earth directly under it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The gain improvement &lt;strong&gt;with&lt;/strong&gt; the reflector is about 0.03 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for adding a single wire on the surface of the earth or buried several inches below the surface to improve the performance of a vertical monopole -- its effect on antenna system radiation performance would be close to negligible, also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That single conductor, no matter how long it is, will be ineffective in collecting and re-radiating the r-f currents flowing on and just below the surface of the earth within a circle of 1/2WL radius from the base of a radiating monopole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/A4IlG.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/A4IlG.jpg&quot; alt=&quot;a&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-06-07T09:44:01.393" LastActivityDate="2019-06-07T09:44:01.393" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14596" PostTypeId="2" ParentId="14593" CreationDate="2019-05-27T00:11:19.377" Score="3" Body="&lt;p&gt;Inspection of figures 17.17 through 17.19 in the ARRL &lt;em&gt;Handbook&lt;/em&gt; suggest that the components in your Pi network might need to be adjusted:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eFtK5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eFtK5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Jim Tonne, W4ENE, wrote a utility called &lt;a href=&quot;http://tonnesoftware.com/piel.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;PIEL&lt;/a&gt; to calculate output tank values. A Pi-L network - a Pi network with an L-network extension - is frequently used to match a wider range of impedances than a Pi network alone can handle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To use the program, you must know the load represented by the plate of the tube. PIEL includes a &quot;Plate load help&quot; button to perform this calculation using your intended voltage swing, RMS output power and class of operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming you want the plate to swing over half the 100V supply to produce 20W in class C, PIEL calculates the plate impedance to be 62.5&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;. Entering this value in PIEL's main screen with an intermediate impedance of 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; to drop the L-section yields this Pi network:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OlTsd.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OlTsd.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Increasing the plate voltage swing and reducing the network Q reduces the capacitor values. You can experiment with these values until you find a network you can build with available components. For example, increasing the swing to 90V and reducing the Q to 3 produces this network:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bGK7s.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bGK7s.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, you need to keep in mind that the network may no longer provide the harmonic rejection required to comply with FCC rules.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-05-27T20:29:28.280" LastActivityDate="2019-05-27T20:29:28.280" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14597" PostTypeId="1" CreationDate="2019-05-27T02:59:21.317" Score="2" ViewCount="217" Body="&lt;p&gt;I just purchased a UV-5R to hopefully integrate into business class radios my company uses. Do I need a technician or other class FCC license to operate these only on the frequencies I already access with the business radios? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I do need a license then what class would this type of use fall under, it seems to be something that doesn’t qualify entirely under any of the FCC classes as I’ve read them so far.  &lt;/p&gt;&#xA;" OwnerUserId="14964" LastEditorUserId="1362" LastEditDate="2019-05-27T17:28:57.233" LastActivityDate="2019-05-30T16:49:47.050" Title="Would a ham license allow me to use an uncertified radio on other (non-ham) bands I have permission to use?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;uv-5r&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14600" PostTypeId="1" AcceptedAnswerId="14602" CreationDate="2019-05-27T19:25:16.623" Score="1" ViewCount="82" Body="&lt;p&gt;I was at Anaheim HRO and few guys there were talking about an MFJ all band vertical antenna that does not need radials. I forget what model number it is but it is one of those &quot;wife pleasing antennae&quot; looks not much more from a flag pole but one of the points a guy mentioned caught my attention. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;You have to run at least some coax on the ground, it is radialess and it uses the shield of coax as a counterpoise. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I don't think that is right. If that is the real case for that antenna then I don't think it is good design. &#xA;I did a test on an end fed long wire type antenna I have up today. Not much measurable change between run the coax on the ground and hang on the wall. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And now think about, if it does have significant changes, is that some sort of RF in the shack problem? As there will be current running on the shield of coax?&lt;/p&gt;&#xA;" OwnerUserId="13362" LastActivityDate="2019-05-27T22:04:52.920" Title="SWR characteristic changes when lifting coax off the ground?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14601" PostTypeId="2" ParentId="14597" CreationDate="2019-05-27T20:33:27.617" Score="10" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I just purchased a UV-5R to hopefully integrate into business class radios my company uses.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, this is not likely legal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Business radio is licensed under the FCC's Part 90 rules; those rules include &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/90.203&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR § 90.203 - Certification required&lt;/a&gt;: &quot;[…] each transmitter utilized for operation under this part […] must be of a type which has been certified for use under this part.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is, unless the FCC has approved your particular radio model for use on business bands, you can't use it there. And they will &lt;strong&gt;not&lt;/strong&gt; approve radios where the user can arbitrarily change the frequency. That's based on §90.203(e), which says transmitters &quot;shall not be certified […] if the operator can program and transmit on frequencies other than those programmed […]&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio you use on business bands has to be both:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;eligible for Part 90 certification&lt;/li&gt;&#xA;&lt;li&gt;have been granted that certification&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For example, the &lt;a href=&quot;http://www.miklor.com/COM/Review_UV82C.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;UV-82C&lt;/a&gt; is a special version of a similar radio to what you have. It has its frequency settings locked out &lt;strong&gt;and&lt;/strong&gt; then successfully went through the process to get an FCC-ID approval. As a result, it would be legal to use. It also looks a bit more expensive to buy!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Do I need a technician or other class FCC license to operate these only on the frequencies I already access with the business radios?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A Technician-class license under &lt;em&gt;would&lt;/em&gt; allow you to operate a UV-5R on the &quot;ham&quot; bands but &lt;strong&gt;not&lt;/strong&gt; on the &quot;business&quot; bands. There's no crossover between the Amateur Radio Service (&quot;ham radio&quot;, i.e. Part 97 rules) and the Private Land/Mobile Radio Service (&quot;business radio&quot;, i.e. Part 90 rules).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if you have multiple licenses, each time you use a radio you have to operate completely within &lt;strong&gt;one&lt;/strong&gt; of them:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;as a ham licensee you could use that radio on the 2m or 70cm frequencies, but you have to follow that license rules (saying your callsign frequently, not conducting business, etc.) and transmit &lt;strong&gt;only&lt;/strong&gt; on frequencies allowed to Technician class operators&lt;/li&gt;&#xA;&lt;li&gt;as a business licensee you could use certain other frequencies that hams can't, but unfortunately only using an approved (&quot;certified&quot;) radio&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This is similar to the situation with &lt;a href=&quot;https://ham.stackexchange.com/q/623/1362&quot;&gt;using a Baofeng on FRS or MURS frequencies&lt;/a&gt;, where they are technically not allowed due to lack of certification, even if used in an otherwise appropriate manner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ham license is fairly unique in allowing non-certified equipment. The trade-off is that you have to both pass a knowledge test to get the license, and also abide by a lot of communication restrictions once you have it. For the other services, they put the burden more on the equipment manufacturer than the end-user.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2019-05-30T16:49:47.050" LastActivityDate="2019-05-30T16:49:47.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14602" PostTypeId="2" ParentId="14600" CreationDate="2019-05-27T22:04:52.920" Score="2" Body="&lt;p&gt;Your reasoning is correct. If the antenna is affected by the positioning of the feed line, more than it would be by any other similar metallic object, then the feed line is radiating; one could say, &quot;is part of the antenna&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This does not necessarily mean you have an &quot;RF in the shack problem&quot;. For example, if you install a balun (more precisely, an unun) in the feed line and/or ground the coax (connect the shield to earth), at any point between the transmitter and the base of the antenna, then you will reduce (not perfectly eliminate) the common-mode signal traveling back, quite possibly low enough that it's no stronger than just the antenna's radiation through the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So you can certainly use such an antenna safely and effectively, if you choose to. But when thinking about, simulating, or testing how it will perform, you have to consider the coax as part of the antenna design.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-05-27T22:04:52.920" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14604" PostTypeId="1" AcceptedAnswerId="14667" CreationDate="2019-05-28T14:53:11.760" Score="2" ViewCount="652" Body="&lt;p&gt;I have a new TYT MD-380; it works well for DMR channels, but on analog, the squelch doesn't seem to open when it should. I'm relatively new to ham and my first suspicion is user error, but it's tempting to blame it on poor hardware quality control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I've observed is that if the squelch is on, I can listen on the MD-380 and an analog-only radio (a Baofeng UV-5R) and hear nothing on the MD-380. If I use monitor mode to turn the squelch off, I do hear audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried a number of combinations here:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Simplex and multiple repeaters&lt;/li&gt;&#xA;&lt;li&gt;Carrier squelch and CTCSS (haven't tried DCS yet)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;When testing against a repeater, I can transmit with either radio and be heard by others. The transmitting radio always drowns out RX on my non-transmitting one as expected, and I should be able to hear the roger beep from both radios, but I only ever hear it on the Baofeng, not the TYT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll add that I have installed the md380tools custom firmware, but I'm pretty sure the squelch was an issue before doing so. (Yes, that may have voided my warranty and was probably dumb.) I'm not sure whether firmware would affect the squelch's ability to function.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Update: I've seen at least &lt;a href=&quot;https://www.facebook.com/groups/KD4ZToolkit/permalink/397098334133129/&quot; rel=&quot;nofollow noreferrer&quot;&gt;one reference&lt;/a&gt; which says the md380tools custom firmware might be the cause, and it's not clear whether the firmware has been tested on my generation of MD380 hardware. I'm going to try to get back to the original stock firmware (D014.009) if TYT posts it for download.&lt;/p&gt;&#xA;" OwnerUserId="14609" LastEditorUserId="14609" LastEditDate="2019-05-29T19:30:31.343" LastActivityDate="2019-06-04T14:06:17.800" Title="Bad squelch on a TYT MD-380: user error or hardware?" Tags="&lt;uhf&gt;&lt;ht&gt;&lt;fm&gt;&lt;squelch&gt;&lt;tyt&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14605" PostTypeId="1" CreationDate="2019-05-28T15:15:15.507" Score="2" ViewCount="93" Body="&lt;p&gt;I'm running a feed line from the end of my amplifier to the antenna for HF transmissions. I'm using RG8x / mini 8. There's an existing pathway through my house I'd like to use that has a cat 5e ethernet cable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to just push the coax through the same conduit as the ethernet, they'll be laying on top of each other for maybe 10 feet, outer jackets touching. In a couple of areas they'll end up zip tied next to each other.  Does this create any interference that would be detectable? I'll be running up to max legal power (US / FCC). &lt;/p&gt;&#xA;" OwnerUserId="11284" LastActivityDate="2019-05-28T17:33:06.087" Title="Should I run RG8x / mini8 zip tied to a cat 5e ethernet cable?" Tags="&lt;antenna&gt;&lt;rfi&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14606" PostTypeId="2" ParentId="14605" CreationDate="2019-05-28T15:39:19.323" Score="3" Body="&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, you shouldn't use RG-8X at all. &lt;a href=&quot;http://static.dxengineering.com/pdf/Belden%20RG8X%20Date%209258.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Belden's specifications&lt;/a&gt; put the maximum power at 1000 W at 10 MHz, and 370 W at 50 MHz. The maximum power on most HF bands is 1500 W, so you'll be significantly exceeding the ratings of the cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also keep in mind a cable in an enclosed space will run hotter than one with natural convection, so some derating may be appropriate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Provided however you operate within the cable's specifications, use a high quality cable, and the cat 5 isn't connected to something extremely sensitive to RF, running other cables bundled with the coax is probably fine. See the datasheet for the isolation the shield provides: if there's not a datasheet then it's not a high quality cable. Do be sure to &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;check for common-mode current&lt;/a&gt;, and mitigate as necessary, as this is likely the more significant coupling mechanism compared to leakage through the shield.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-05-28T17:33:06.087" LastActivityDate="2019-05-28T17:33:06.087" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14607" PostTypeId="2" ParentId="14604" CreationDate="2019-05-28T20:17:46.743" Score="1" Body="&lt;p&gt;Whenever you can hear when monitoring analog but not in normal operation, start by suspecting the way the CTCSS tones are set up.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Make sure the Band Width setting is 25 kHz (for most analog repeaters, this corresponds to &quot;WIDE&quot; on the Baofeng).&lt;/li&gt;&#xA;&lt;li&gt;Make sure the CTCSS Decode is set to OFF or Carrier Squelch (CSQ).&lt;/li&gt;&#xA;&lt;li&gt;Make sure the CTCSS Encode is set to the value the repeater needs.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2019-05-28T20:25:23.000" LastActivityDate="2019-05-28T20:25:23.000" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14608" PostTypeId="5" CreationDate="2019-05-28T21:12:14.043" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-05-28T21:12:14.043" LastActivityDate="2019-05-28T21:12:14.043" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14609" PostTypeId="4" CreationDate="2019-05-28T21:12:14.043" Score="0" Body="TYT is a manufacturer of DMR and analog radios. Use this tag when the question is related to specific features of those models." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-05-28T21:12:14.043" LastActivityDate="2019-05-28T21:12:14.043" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14610" PostTypeId="1" AcceptedAnswerId="14612" CreationDate="2019-05-28T21:54:07.470" Score="2" ViewCount="757" Body="&lt;p&gt;I understand that Wi-Fi transmits on 2.4 GHz or 5 GHz whereas local ham repeaters transmit around 147 MHz or 450 MHz. What differences would be needed in antennas tuning into either of these frequencies, to account for the difference in frequencies, either Wi-Fi or the ham repeaters?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, let's say I'm getting or building a &lt;a href=&quot;https://en.wikipedia.org/wiki/Yagi%E2%80%93Uda_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yagi antenna&lt;/a&gt; to pick up a distant Wi-Fi signal better, and I also want a Yagi antenna to better listen to (even better if also transmit) a distant ham repeater station. Could I use the same Yagi antenna for both purposes, or if not, how should the two Yagi antennas differ to best work with the different purposes?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In that example, let's say for Wi-Fi I'd plug the antenna into a USB wireless adaptor in a PC, whereas for the ham repeaters I'd plug the antenna into a transceiver, e.g. a simple Baofeng HT.&lt;/p&gt;&#xA;" OwnerUserId="6634" LastEditorUserId="366" LastEditDate="2019-05-29T16:15:15.507" LastActivityDate="2019-05-29T16:15:15.507" Title="Difference between antennas for Wi-Fi vs. ham repeaters" Tags="&lt;antenna&gt;&lt;wifi&gt;&lt;range&gt;&lt;repeater-coverage&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14612" PostTypeId="2" ParentId="14610" CreationDate="2019-05-28T22:02:29.770" Score="11" Body="&lt;p&gt;In order to use the same antenna &lt;em&gt;design&lt;/em&gt; at different frequencies, &quot;all you need to do&quot; is scale all elements of the antenna proportionally to the difference in wavelength. For example, if you take a Yagi antenna designed for around 150 MHz, and scale all of the lengths in its design down by half, you will have a Yagi antenna good for 300 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, there's no “resize” button on physical objects, so you have to build two separate antennas instead. And there may be mechanical limitations (e.g. the thickness of sufficiently strong wires) that mean a design doesn't physically scale perfectly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use an antenna at a frequency/wavelength that is too far off from what it was designed for, two things will happen:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;It will have a different &lt;em&gt;impedance&lt;/em&gt; at the feed point (the connection to the transmitter). This means that the RF energy will not be efficiently transferred into/out of the antenna, and it may damage a transmitter. (For receivers, this is not usually critical.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The &lt;em&gt;radiation pattern&lt;/em&gt; will be not as designed. Generally, a directional antenna will not be as directional — instead of &quot;pointing&quot; in one direction, it will have a spiky pattern with many highs and lows.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It is not impossible to have a directional antenna which works for two different frequency bands. But it must be designed specifically for that pair. And unless physical space is an issue (as with HF antennas which work with long wavelengths and therefore are themselves quite large), it is simpler to use two separate antennas with standard designs, if a suitable multi-band design is not already available.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-05-28T22:02:29.770" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14617" PostTypeId="1" AcceptedAnswerId="14618" CreationDate="2019-05-29T14:31:16.470" Score="6" ViewCount="801" Body="&lt;p&gt;I've been looking at options for a high-gain directional antenna recently, and I've noted that there are commercially available parabolic antennae for the shorter bands -- specifically 70 cm, with an antenna that probably doubles as a UHF OTA television receiving antenna.  The size of these antennae, however, not much bigger than the microwave dishes used for satellite TV, makes me suspicious of their effectiveness.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's my understanding that a Yagi-Uda can pretty readily exceed a gain of 10 dBi in its forward lobe; I've seen commercial ones advertised at 13 dBi.  Even the seller's rating of these very small parabolics barely exceeds that figure, if at all, but can a parabolic antenna in the 440 band of manageable size (say, no more than 2 meters in any dimension) give enough additional forward gain to be worth the extra cost to purchase or effort to build?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-05-30T17:01:49.290" Title="Is there any practical advantage to a parabolic reflector over a high-gain beam antenna?" Tags="&lt;antenna&gt;&lt;uhf&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14618" PostTypeId="2" ParentId="14617" CreationDate="2019-05-29T15:16:54.553" Score="6" Body="&lt;p&gt;The issue with using a parabolic dish antenna at UHF is one of size. The 60cm dishes you see on the side of people’s houses are picking up signals at 10GHz, and if you scaled them up for the 70cm band you would have a dish around 14m across.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those satellite TV dishes have a gain of around 35-40dB (&lt;a href=&quot;https://en.wikipedia.org/wiki/Satellite_dish#Principle_of_operation&quot; rel=&quot;noreferrer&quot;&gt;source&lt;/a&gt;), which is very impressive - but you’re not going to build a 14-meter dish for use on 70cm (you’re really not).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many people use stacked and bayed arrays of multiple-element yagi antennas for EME (moonbounce) work, rather than a dish. With four 13dBi yagis you will get around 19dBi of gain, which is pretty good going. With eight you will get around 22dBi. Any more than that and you’ll probably wish you’d just built the 14-meter dish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: here is an array of eight stacked and bayed yagis for EME (moonbounce):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0eGLl.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0eGLl.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Source &lt;a href=&quot;http://spectrafold.com/quadrus/radio-software/receiving-moon-bounce-signals/&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2019-05-29T15:32:27.327" LastActivityDate="2019-05-29T15:32:27.327" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14619" PostTypeId="1" CreationDate="2019-05-29T17:10:45.777" Score="8" ViewCount="917" Body="&lt;p&gt;I noticed that the &lt;a href=&quot;https://ham.stackexchange.com/questions/1891/whats-the-pinout-for-kenwood-2-5mm-trs-3-5-mm-trs-connector&quot;&gt;pinout&lt;/a&gt; for cheap Baofeng connectors has +V available. I'm interested in powering some electronics directly from this connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When unloaded, this seems to have about 3.3V on it, but when I try to power my load (an ESP32), the voltage drops to 0.8V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How much current can this pin actually provide without significant voltage drop? Or, what does the voltage/current curve look like?&lt;/p&gt;&#xA;" OwnerUserId="13122" LastActivityDate="2019-05-30T21:55:31.497" Title="How much current can Baofeng UV-5R provide on +V pin?" Tags="&lt;baofeng&gt;&lt;audio-interface&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14620" PostTypeId="2" ParentId="14619" CreationDate="2019-05-29T22:01:18.687" Score="7" Body="&lt;p&gt;I would first measure the current draw of your ESP32 to rule out a fault there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The +V pin on the Baofeng microphone connection is probably intended to bias an electret microphone. These are essentially a capacitor, with sound pressure changing the spacing between the plates and thus the voltage. They contain a FET buffer since the capacitor could not drive a cable directly. The buffer requires power, but very little: the bias current is probably far less than 1 mA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus it's quite likely the +V pin is unable to supply even a small current. Adding a series resistance on such a pin would have no impact to the intended use of biasing a microphone, but is a cheap and effective way to protect the radio from all kinds of faults that could happen on such a connector.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-05-29T22:01:18.687" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14622" PostTypeId="2" ParentId="14619" CreationDate="2019-05-30T02:55:12.737" Score="8" Body="&lt;ul&gt;&#xA;&lt;li&gt;With no load, I measure 3.17V&lt;/li&gt;&#xA;&lt;li&gt;With 100kΩ load, 2.91V&lt;/li&gt;&#xA;&lt;li&gt;With 10kΩ load, 1.59V&lt;/li&gt;&#xA;&lt;li&gt;With 1kΩ load, 0.29V&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The math works out to a 10kΩ series resistance between +V and ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such the maximum power that can be drawn is at 1.59V/10kΩ load, or 0.25mW max power. Short circuit current would be about 0.3mA.&lt;/p&gt;&#xA;" OwnerUserId="13122" LastEditorUserId="4665" LastEditDate="2019-05-30T21:55:31.497" LastActivityDate="2019-05-30T21:55:31.497" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14625" PostTypeId="2" ParentId="14617" CreationDate="2019-05-30T17:01:49.290" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/1530/218&quot;&gt;Gain, wavelength, and effective aperture&lt;/a&gt; are related by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ A_\mathrm{eff} = {G \lambda^2 \over 4\pi} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, a gain of 10 dBi (&lt;span class=&quot;math-container&quot;&gt;$G = 100$&lt;/span&gt;) for 440 MHz (&lt;span class=&quot;math-container&quot;&gt;$\lambda = 0.68\:\mathrm m$&lt;/span&gt;) means an effective aperture of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {100 \times 0.68^2 \over 4\pi} = 3.68\:\mathrm m^2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming we could build reflector antennas with 100% &lt;a href=&quot;https://ham.stackexchange.com/q/3643/218&quot;&gt;aperture efficiency&lt;/a&gt;, this means you'd need a dish with an area of 3.68 square meters to achieve 10 dBi of gain at 440 MHz. This isn't impossible, but such an antenna would be heavy, expensive, and have quite a high wind load, so a Yagi might be a better choice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Moreover, aperture efficiency isn't 100%, so the dish would need to be somewhat larger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most real parabolic antennas have an aperture efficiency between 50% and 75%. One of the factors limiting the efficiency is diffraction around the edges of the dish. As the dish becomes smaller relative to wavelength, this diffraction becomes more significant. So in practice, the dish must be several times larger than the wavelength to achieve a decent aperture efficiency. This is another reason you won't see a common rooftop dish used for 440 MHz: the dish is simply too small to be effective at that wavelength.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-05-30T17:01:49.290" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14626" PostTypeId="1" AcceptedAnswerId="14628" CreationDate="2019-05-30T17:57:36.583" Score="1" ViewCount="107" Body="&lt;p&gt;I am new to RF field and trying to use an Archimedean Spiral Antenna design from &lt;a href=&quot;https://www.researchgate.net/publication/331812302_RF_Energy_Harvesting_System_Based_on_an_Archimedean_Spiral_Antenna_for_Low-Power_Sensor_Applications&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; paper to capture 915MHz RF for the &lt;a href=&quot;https://www.powercastco.com/wp-content/uploads/2016/12/P2110B-Datasheet-Rev-3.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;P2110B&lt;/a&gt; power harvester chip. The estimated antenna impedance is 188 Ohm (see page 5), whereas the chip's unbalanced RF input expects a 50 Ohm antenna (see page 4).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I match the impedance of the antenna to the RF input and how the antenna should be connected to the chip since it has no ground plane? Should one end of the antenna be connected to the GND pins on both sides of the RF pin?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There will be a dedicated directional RF power transmitter (not just ambient RF) emitting at 915MHz center frequency. The plan is to transfer energy across some surface (up to 2 inch thick), so, please, share your thoughts if you think there is a better approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QA0tE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QA0tE.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14991" LastEditorUserId="8717" LastEditDate="2019-05-30T18:31:19.937" LastActivityDate="2019-05-30T20:27:47.667" Title="Matching a 188 ohm antenna to an unbalanced input that expects a 50 ohm antenna" Tags="&lt;antenna-construction&gt;&lt;rf-power&gt;&lt;impedance&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14627" PostTypeId="2" ParentId="14626" CreationDate="2019-05-30T19:08:49.117" Score="1" Body="&lt;p&gt;188 Ohm is theoretical result. In practice think like 200 Ohm, and such can be connected via 2:1 balun (2:1 in voltage, 4:1 in impedance)&lt;/p&gt;&#xA;" OwnerUserId="6323" LastActivityDate="2019-05-30T19:08:49.117" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14628" PostTypeId="2" ParentId="14626" CreationDate="2019-05-30T20:27:47.667" Score="0" Body="&lt;p&gt;The P2110B datasheet quotes the maximum receiver input power as +23dBm, which is 200mW. You might be able to use an off-the-shelf surface-mount 4:1 balun such as the &lt;a href=&quot;https://www.minicircuits.com/pdfs/TC4-25+.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mini-Circuits TC4-25+&lt;/a&gt;, which is specified to handle 250mW with less than 0.4dB of insertion loss at 900MHz.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-05-30T20:27:47.667" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14629" PostTypeId="1" AcceptedAnswerId="14632" CreationDate="2019-05-30T22:02:42.460" Score="8" ViewCount="317" Body="&lt;p&gt;I recently bought this tube for use in an art project and would like to know what it is and what it was originally used for. Unfortunately, the silkscreen labelling on the glass envelope was worn off and unreadable and there are no other obvious identifying marks on it. The tape measure indicates scale (it's big!). I'd also like to find a source for more like this, since it has generated a lot of interest sitting on the shelf in my shop.&lt;br&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/bqGKU.jpg&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="10598" LastEditorUserId="14723" LastEditDate="2019-05-31T06:47:59.530" LastActivityDate="2020-06-20T21:48:29.020" Title="help identifying a vacuum tube" Tags="&lt;vacuum-tubes&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14630" PostTypeId="1" AcceptedAnswerId="14631" CreationDate="2019-05-31T03:02:52.273" Score="1" ViewCount="551" Body="&lt;p&gt;TL;DR  Laptop keeps switching between Signal Link audio output and speakers. Problem goes away when I turn TX knob down far enough on Signal Link.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just bought a SignalLink and have it connected between my laptop and my radio (a Yaesu FT-450D). I've successfully made a couple QSO's on FT8, but keep running in to a problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I tune the tx knob too high, the computer seems to change the audio output from the Signal Link back to the speakers on the laptop. As a result, the Signal Link doesn't get an audio signal any more and it turns off the PTT. After a moment (well less than a second), audio switches back to the Signal Link.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can avoid the problem by keeping the TX knob turned way down, but them my actual transmitted power is way lower than intended.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Details:&#xA;Radio: Yaesu FT-450D&#xA;Laptop: old Dell running Ubuntu 18.04&lt;/p&gt;&#xA;" OwnerUserId="10424" LastActivityDate="2019-05-31T03:52:58.890" Title="My radio and audio output keep changing using WSJTX on FT8" Tags="&lt;audio-interface&gt;&lt;wsjt-x&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14631" PostTypeId="2" ParentId="14630" CreationDate="2019-05-31T03:52:58.890" Score="3" Body="&lt;p&gt;I'm not familiar with the failure modes of SignaLink devices, but in general, a USB device disappearing temporarily likely means that its internal microprocessor or USB interface chip has been reset, or the USB connection itself failed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The obvious hypothesis, then, is that your transmitted RF power is itself causing the problem by interfering with the digital electronics when it gets too high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To collect evidence for whether or not this is true:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Check if the radio's transmit power setting also changes whether or not the problem occurs.&lt;/li&gt;&#xA;&lt;li&gt;Make a &lt;em&gt;manual&lt;/em&gt; transmission using your radio's own controls, not the computer (using CW or AM, not SSB, so that you don't need to change microphone connections to get any output power). If you observe your computer switching audio devices in the same way, this shows that the problem is triggered by the radio and not by the SignaLink unit.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;If this is the case, then solutions depend on how the problematic RF is getting in. That can be difficult to measure, so practically it's a matter of trying fixes in whatever order is convenient:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Problem: The transmitted power from the antenna is too high.&lt;br&gt;&#xA;Solution: Relocate your antenna farther from the rest of your station.&lt;/li&gt;&#xA;&lt;li&gt;Problem: The antenna is putting common-mode current onto the feed line.&lt;br&gt;&#xA;Solution: Ensure that it is fed properly (e.g. a dipole antenna fed by coax &lt;strong&gt;must&lt;/strong&gt; have a balun).&lt;/li&gt;&#xA;&lt;li&gt;Problem: The transmitter is leaking RF onto its audio/control cables.&lt;br&gt;&#xA;Solution: Add ferrites to the cables between the radio and the SignaLink.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-05-31T03:52:58.890" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14632" PostTypeId="2" ParentId="14629" CreationDate="2019-05-31T19:30:59.533" Score="6" Body="&lt;p&gt;This looks like a &lt;a href=&quot;http://lampes-et-tubes.info/th/th077.php?l=e&quot; rel=&quot;noreferrer&quot;&gt;JAN-CTL-5948A&lt;/a&gt;, found via images within the search results for &quot;huge vacuum tube&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://lampes-et-tubes.info/th/th077.php?l=e&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/b08PU.jpg&quot; alt=&quot;ITT Electron Tube Division JAN 5948A Hydrogen Thyratron image from Lamps &amp;amp; Tubes website&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to the linked site (from which the picture is also taken):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The primary application of this tube is in high power, high voltage radar modulators. The 5948A is capable of supplying 12 megawatt pulses in this service.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The datasheet indicates that it's a bit beyond a typical vacuum tube:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The special features of the 5948A include an internal hydrogen-reservoir capable of producing a wide range of hydrogen pressure […]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Some online listings title this as a &quot;Industrial High Power Early Warning Radar Military Hydrogen Thyratron Tube&quot;. I couldn't recommend trying to get it working ;-)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2019-05-31T19:39:13.290" LastActivityDate="2019-05-31T19:39:13.290" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="14633" PostTypeId="2" ParentId="117" CreationDate="2019-06-01T00:26:08.863" Score="2" Body="&lt;p&gt;Yes, you can.&#xA;If you are an amateur radio operator you can grab any radio including an American / Australian CB and use it as long as it has been modified to operate on the amateur bands. Australian / American 27 MHz. CB's were easy to modify to 28 MHz. Both crystal synthesis &amp;amp; PLL, However, I have only known of one that was modified to work on 21 MHz. &lt;/p&gt;&#xA;" OwnerUserId="14999" LastEditorUserId="8573" LastEditDate="2019-06-02T22:04:56.197" LastActivityDate="2019-06-02T22:04:56.197" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14634" PostTypeId="2" ParentId="14552" CreationDate="2019-06-01T01:56:39.533" Score="-1" Body="&lt;p&gt;The keyword here is tolerance. For receiving antenna you don't really have to have a match or low SWR with the receiving system unless for a high Q antenna like a mag loop. Tho if you have a very great unmatch you won't receive well too. I have received 70cm on a 40m dipole, it probably was received on the coax but it did receive well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if you try to transmit 70cm on a 40m dipole the mismatch well thru the roof, and almost all your power input will be reflected. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is why there are antennas for receive only. Active antenna uses an amplifier for the received signal and you will damage it if you transmit on it.  Some receive antenna just either don't have a good match for trasmitting or not build for power handleing or both. &lt;/p&gt;&#xA;" OwnerUserId="13362" LastActivityDate="2019-06-01T01:56:39.533" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14635" PostTypeId="1" AcceptedAnswerId="14680" CreationDate="2019-06-01T02:32:31.223" Score="1" ViewCount="101" Body="&lt;p&gt;If an antenna needs to be mounted on a metal structure what would be needed to avoid interference? Are there just some specific length to avoid or it is better to be separated by some insulator? &#xA;As I am looking at towers, are there any parts that insulate antenna from the tower and each element? I can't see it from pictures only, what it looks like?&lt;/p&gt;&#xA;" OwnerUserId="13362" LastActivityDate="2019-06-08T12:47:54.573" Title="Mounting antenna on a metal structure? Tower/Antenna insulator?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14636" PostTypeId="1" CreationDate="2019-06-01T03:18:26.123" Score="5" ViewCount="584" Body="&lt;p&gt;Last night there was a power outage at home. I was able to see a LOT of stations on 20M (FT8). As soon power returned, all of them disappeared. You can see in the waterfall very clearly when power returned:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/J1liF.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/J1liF.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The odd thing is, noise is around 7 here at home. But when power went out it dropped only to 6.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, today I went to my dad's and he was seeing lots and lots of stations. I left WSJT-X open, and when I came back, there were only two decodes, out of dozens at his place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure what's going on. My antenna is a dipole, tuned to the right frequency. Measures SWR 1.1. My rig is a Kenwood TS-450S. My dad's antenna is also a dipole, and his rig is an Icom IC-765. We're only 700m apart. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried adding a balun and a choke. The choke made a big difference by dropping the noise levels by 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What can I do to troubleshoot this?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2019-06-04T00:21:42.050" Title="Only noise, no signals whatsoever on HF" Tags="&lt;rfi&gt;&lt;ft8&gt;&lt;reception&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14637" PostTypeId="2" ParentId="14636" CreationDate="2019-06-01T05:16:53.460" Score="2" Body="&lt;p&gt;QRM is extremely common nowadays due to a great increase in switch-mode power supplies that tend to desensitize nearby receivers, hence the reason why many Hams put up a shack away from the house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simply because there isn't noise on the exact frequency you're on, doesn't mean you're not experiencing interference. You might want to try a band pass filter for 20M, and that may help compensate for your radio's poor selectivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if someone is blasting bass at 100Hz super loud, you may not be able to hear the 1000Hz you might normally be able to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally, where I'm at, I also cannot operate on 20M very well due to noise from my neighbors. Antenna polarization helps, but does not solve the problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is such a thing as RF noise cancellation, and MFJ makes such a component such as this, but I haven't tried it: &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-1026&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.mfjenterprises.com/Product.php?productid=MFJ-1026&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14773" LastActivityDate="2019-06-01T05:16:53.460" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14641" PostTypeId="2" ParentId="14636" CreationDate="2019-06-01T10:33:55.047" Score="4" Body="&lt;p&gt;There is a lot you haven't told us about the current situation that could be helpful. Since your dad lives so close, perhaps you can make various substitutions to identify the problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, what do you hear from the speaker or headphone jack of the TS-450S when using your station antenna? If you hear nothing, then you should expect to see nothing on the waterfall display; if you hear signals but don't see them on the waterfall, then the problem is probably in the radio-to-computer interface or in the computer's audio system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you hear nothing from the TS-450S, take it to your dad's and listen with his antenna. If you hear more signals, the problem is your antenna; if you still hear nothing with the TS-450S when he does hear signals with his transceiver, the problem is probably in the TS-450S.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-01T10:33:55.047" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14646" PostTypeId="2" ParentId="14593" CreationDate="2019-06-02T13:23:42.357" Score="3" Body="&lt;p&gt;DISCLAIMER: I offer these results only as a &lt;em&gt;possible&lt;/em&gt; solution. Completing this design may depend on many other factors, thermal and electrical, steady state and transient, component- and layout-dependent parasitics. This is the subject of, at least, sizeable chapters if not entire text books, which I will not reproduce here. Your mileage may vary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I entered the following values into the PiEl program:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Plate load help:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;- Plate voltage swing: 190 volts&#xA;- RF power: 12 watts, RMS&#xA;- Class C (k=2)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Plate load result: 1.504k ohms&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Main page&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;- Frequency: 3.5MHz&#xA;- Plate load: 1.504k&#xA;- Intermediate impedance: 1.504k&#xA;- Load impedance: 50 ohms&#xA;- Pi-section Q: 10&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Resulting output network:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/JQqoL.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JQqoL.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Resulting harmonic output:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/QZV2Q.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QZV2Q.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can do this yourself to settle on a set of parameters that best meets your particular constraints and requirements.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-02T13:23:42.357" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14647" PostTypeId="1" CreationDate="2019-06-02T20:44:20.680" Score="1" ViewCount="61" Body="&lt;p&gt;Are jammers relate to electronics or electrotechnics , why ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please ,tell me the main difference between electronics and electrotechins and &lt;strong&gt;why we can classify jammers as electrotechics or electronics ?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Indeed i didn&lt;span class=&quot;math-container&quot;&gt;`&lt;/span&gt;t found this information in Google&lt;/p&gt;&#xA;" OwnerUserId="15012" LastEditorUserId="15012" LastEditDate="2019-06-03T13:37:30.350" LastActivityDate="2019-06-03T13:37:30.350" Title="Are jammers relate to electronics or electrotechnics , why?" Tags="&lt;electronics&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2019-06-02T20:58:31.110" ContentLicense="CC BY-SA 4.0" />
  <row Id="14648" PostTypeId="2" ParentId="12868" CreationDate="2019-06-03T00:32:46.680" Score="1" Body="&lt;p&gt;Press [MENU] to enter menu mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Select the wrench, then press [MENU] to select.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Select 1, then press [MENU] to select.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should come up on a 2 character selection that is not selected, then press [MENU] to select.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The screen shows the language selected and returns to the main screen.&lt;/p&gt;&#xA;" OwnerUserId="15014" LastActivityDate="2019-06-03T00:32:46.680" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14649" PostTypeId="1" CreationDate="2019-06-03T01:40:24.317" Score="5" ViewCount="752" Body="&lt;p&gt;I can't find my Baofeng DM-5R in the CHIRP list of supported radios. I've been told that I should try by telling CHIRP to assume a different radio from the DM-5R - perhaps the UV-5R!? Do you know if this is a feasible option? I am able to manually program the DM-5R, but it's too onerous. Thank you.&lt;/p&gt;&#xA;" OwnerUserId="15015" LastEditorUserId="1362" LastEditDate="2019-06-03T22:51:58.770" LastActivityDate="2019-06-04T19:19:48.800" Title="Can I use CHIRP for programming a Baofeng DM-5R?" Tags="&lt;baofeng&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14650" PostTypeId="1" CreationDate="2019-06-03T05:39:15.273" Score="8" ViewCount="293" Body="&lt;p&gt;If I get a German &lt;em&gt;Amateurfunklizenz&lt;/em&gt;, will I be allowed to experiment with non-communication radio technologies like radar?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously, I'd still adhere to using allocated ham bands, stay within power budgets (solidly below), and identify.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The according &lt;a href=&quot;https://www.gesetze-im-internet.de/afug_1997/BJNR149400997.html&quot; rel=&quot;noreferrer&quot;&gt;law&lt;/a&gt; states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Im Sinne dieses Gesetzes ist&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;[…]&lt;/p&gt;&#xA;  &#xA;  &lt;ol start=&quot;2&quot;&gt;&#xA;  &lt;li&gt;Amateurfunkdienst ein Funkdienst, der von Funkamateuren untereinander, zu &lt;strong&gt;experimentellen&lt;/strong&gt; und technisch-wissenschaftlichen Studien, zur eigenen Weiterbildung, zur Völkerverständigung und zur Unterstützung von Hilfsaktionen in Not- und Katastrophenfällen wahrgenommen wird[…]&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;in English&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In the sense of this law,&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;[…]&lt;/p&gt;&#xA;  &#xA;  &lt;ol start=&quot;2&quot;&gt;&#xA;  &lt;li&gt;amateur radio service is a radio service utilized by radio amateurs among each other, for &lt;strong&gt;experimental&lt;/strong&gt; and technically-scientific studies, for their own education, for international understanding, and for support of aid endeavors in crisis and catastrophe cases […]&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;which seems to indicate that the German legislation intends on fostering the usage of amateur radio bands for the purpose of doing radio experiments.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-06-03T17:49:41.550" Title="Can I use a amateur license to experiment with radar?" Tags="&lt;legal&gt;&lt;license&gt;&lt;germany&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14652" PostTypeId="2" ParentId="14650" CreationDate="2019-06-03T11:26:13.913" Score="3" Body="&lt;p&gt;I can’t comment on the specifics of the German Licence, but the wording of the &lt;a href=&quot;https://www.ofcom.org.uk/__data/assets/pdf_file/0027/62991/amateur-terms.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;terms, conditions and limitations of the UK licence&lt;/a&gt; is such that it sounds exactly within the terms of the amateur licence.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;1. Purpose&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;1(1) The Licensee shall ensure that the Radio Equipment is only used:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) for the purpose of self-training in radio communications, including conducting technical investigations; and&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) as a leisure activity and not for commercial purposes of any kind`&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It’s that additional clause that makes me think that this is exactly within the terms of the amateur radio: “including conducting technical investigations”. What you are asking about is exactly that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, obviously this is the UK licence, but this iteration of the terms was written while the UK was an EU member state, regardless of what might happen later this year. My German is not good enough to go through a large legal document, but I would expect it to have similar intent.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="76" LastEditDate="2019-06-03T14:38:50.987" LastActivityDate="2019-06-03T14:38:50.987" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14653" PostTypeId="1" CreationDate="2019-06-03T17:48:56.023" Score="1" ViewCount="63" Body="&lt;p&gt;Phones will receive signal from many pRRus. Should I average the antenna gain and all the path-loss (both line of sight and no-line of sight)? Or should I sum them all together?  &lt;/p&gt;&#xA;" OwnerUserId="11738" LastEditorUserId="4076" LastEditDate="2019-06-08T02:14:20.180" LastActivityDate="2019-06-08T02:14:20.180" Title="Building a ray tracing path-loss propagation model of LTE for small cells (pRRus)" Tags="&lt;path-loss&gt;" AnswerCount="0" CommentCount="10" ClosedDate="2019-06-08T19:04:54.583" ContentLicense="CC BY-SA 4.0" />
  <row Id="14654" PostTypeId="2" ParentId="14650" CreationDate="2019-06-03T17:49:41.550" Score="2" Body="&lt;p&gt;In the USA, amateurs ARE allowed to use pulse modulation, which apparently includes radar pulses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&amp;amp;SID=336ab7469b61ecbfa15086dbf1bf2c59&amp;amp;rgn=div5&amp;amp;view=text&amp;amp;node=47:5.0.1.1.6&amp;amp;idno=47#se47.5.97_1113&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC allows pulse transmissions on and above the 33 cm band&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found nothing in Part 97 prohibiting radar. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-06-03T17:49:41.550" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14655" PostTypeId="2" ParentId="14552" CreationDate="2019-06-03T18:57:26.410" Score="1" Body="&lt;p&gt;Because of the general nature of your question and the likelihood that future questioners might find their way here, I wish to provide a general answer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible that a transmit antenna and a receive antenna may serve quite different purposes in a radio communication system. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A transmit antenna may have the primary purpose of &lt;em&gt;producing&lt;/em&gt; the strongest possible signal at a distant receive antenna within constraints of cost, space, technology, etc. Conversely, the performance of a receiving system may be optimized by using an antenna whose primary purpose is to &lt;em&gt;reject&lt;/em&gt; sources of unwanted noise and interfering signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This situation is commonly encountered on the longer-wavelength amateur bands, where an omnidirectional quarter-wave monopole could approach 40 meters in height with a radial system that occupies most of an acre of land. Such a monopole may stretch the financial- and real estate budget, making directional arrays of such antennas impossible. However, arrays of much smaller antennas can be used to increase the signal-to-noise ratio of a &lt;em&gt;receiving system&lt;/em&gt; by rejecting atmospheric noise in undesired directions. The &lt;a href=&quot;http://www.wa2wvl.net/pdf/03-Is%20this%20EWE%20for%20you0001.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;EWE&lt;/a&gt;, &lt;a href=&quot;https://www.aytechnologies.com/TechData/HowToBuild.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;K9AY Loop&lt;/a&gt;, &lt;a href=&quot;http://www.arrl.org/files/file/QEX_Next_Issue/Sep-Oct_2012/Bauman_QST_10_12.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Shared Apex Loop Array&lt;/a&gt; and &lt;a href=&quot;https://wwrof.org/webinar-archive/n4is-waller-flag-construction/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Waller Flag&lt;/a&gt; are examples.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-03T18:57:26.410" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14657" PostTypeId="2" ParentId="14636" CreationDate="2019-06-04T00:21:42.050" Score="1" Body="&lt;p&gt;I am really going to echo what @pappad said.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Get a large 12V battery and connect to your radio. &lt;/li&gt;&#xA;&lt;li&gt;Turn all the power off in the house - and check you can hear the stations on FT8/CW etc. This will be the quietest your environment can be. But if you are not hearing anything at this stage (note I am saying hearing... not visualising on a PC screen) then there is something wrong with your antenna/radio. You can verify this by calling your dad, and listening to the same frequency. &lt;/li&gt;&#xA;&lt;li&gt;Either section by section (not sure what type of fusing you have) or device by device re-power up your home. Starting first of all with your PC and it's monitor. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;You should be able to identify what device is causing your the trouble quite quickly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope that helps.&lt;/p&gt;&#xA;" OwnerUserId="4994" LastActivityDate="2019-06-04T00:21:42.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14659" PostTypeId="1" AcceptedAnswerId="14673" CreationDate="2019-06-04T08:53:23.463" Score="2" ViewCount="106" Body="&lt;p&gt;The solution for the voltage in a transmission line can be written as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V(z) = V_o^+ e^{-jkz} + V_o^- e^{jkz}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The voltage &lt;span class=&quot;math-container&quot;&gt;$V(z)$&lt;/span&gt; is the difference between the conductors of the line at a certain distance &lt;span class=&quot;math-container&quot;&gt;$z$&lt;/span&gt;. My question are now:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;What are exactly &lt;span class=&quot;math-container&quot;&gt;$V_o^+$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$V_o^-$&lt;/span&gt;? I know it is the voltage wave travelling forward and backward but exactly what are physically? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;How can I physically think about a connection between &lt;span class=&quot;math-container&quot;&gt;$V_o^+$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$V_o^-$&lt;/span&gt; and S parameters?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="14689" LastActivityDate="2019-06-04T21:30:13.520" Title="Voltage wave in transmission lines" Tags="&lt;transmission-line&gt;&lt;theory&gt;&lt;voltage&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14662" PostTypeId="2" ParentId="14659" CreationDate="2019-06-04T12:47:42.907" Score="0" Body="&lt;p&gt;The electromagnetic (EM) wave(s) on an antenna consist of an Electrical component manifested as the electric field associated with voltage and a Magnetic component manifested as the magnetic field associated with current. An EM antenna wave cannot exist without both components. If one divides the above voltage components by the characteristic impedance, Z0, one gets the equation for the current. A very good explanation of s-parameters appears in the following HP Ap Note 95-1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.sss-mag.com/pdf/an-95-1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sss-mag.com/pdf/an-95-1.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$b1 = s11(a1) + s12(a2)$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$b2 = s21(a1) + s22(a2)$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reflected wave(s) on the dipole antenna elements are simply obeying the laws of physics. When the forward wave coming from the antenna feedpoint reaches the open end of a dipole element, there is nothing it can do except undergo wave reflection in the opposite direction. The forward energy wave and the reflected energy wave superpose on the dipole elements to get the standing waves (on the standing wave antenna) but do not affect each other except at an impedance discontinuity and that is where the s-parameter equations can be applied. For a dipole, the discontinuity exists at the feedpoint where the transmission line Z0 may be 50 ohms. The Z0 of an ideal #14 wire horizontal dipole antenna 30 feet in the air is 600 ohms so s11 at the 50 ohm to 600 ohm junction of such an antenna is equal to 0.846. If the feedpoint impedance of the dipole is 50 ohms then &lt;span class=&quot;math-container&quot;&gt;$b1$&lt;/span&gt; in the first s-parameter equation is equal to zero, i.e. there are no reflections from the antenna feedpoint back down the 50 ohm transmission line. It follows that &lt;span class=&quot;math-container&quot;&gt;$s11(a1)$&lt;/span&gt; has to phasor sum to zero with &lt;span class=&quot;math-container&quot;&gt;$s12(a2)$&lt;/span&gt;. This can only happen when total destructive interference occurs at the feedpoint. The conservation of energy principle tells us that total destructive interference in one direction at an impedance discontinuity in a typical antenna system must be accompanied by total constructive interference in the opposite direction so all of the available energy winds up in the &lt;span class=&quot;math-container&quot;&gt;$b2$&lt;/span&gt; forward wave on the dipole antenna. These same principles apply to any impedance discontinuity in an antenna system including a change in Z0 between two sections of transmission line. Note that all elements of the s-parameter equations are phasors and have an associated phase angle. Luckily, for a resonant dipole, the phase angles are either zero or 180 degrees at the feedpoint so that ordinary math will suffice. More info available in an old magazine article of mine which uses the more common amateur radio terms rather than the s-parameter terms:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w5dxp.com/energy/energy.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w5dxp.com/energy/energy.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Somehow, before my first cup of coffee, I got the idea that the question was about the voltage on an antenna. Mea Culpa. Most of what I said applies to both antennas and transmission lines.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-06-04T18:56:42.483" LastActivityDate="2019-06-04T18:56:42.483" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14665" PostTypeId="1" AcceptedAnswerId="14668" CreationDate="2019-06-04T13:58:37.290" Score="9" ViewCount="1281" Body="&lt;p&gt;The specs of the Elecraft T1 tuner say, that it can match a 10:1 SWR.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What does that mean in terms of impedance ratio?&lt;/li&gt;&#xA;&lt;li&gt;What antenna impedance can it match to 50 Ohm then?&lt;/li&gt;&#xA;&lt;li&gt;Or is it not that easy?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="15019" LastEditorUserId="4076" LastEditDate="2019-06-04T14:02:51.460" LastActivityDate="2019-06-04T18:33:33.420" Title="Impedance ratio vs. SWR" Tags="&lt;impedance&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14666" PostTypeId="2" ParentId="14665" CreationDate="2019-06-04T14:04:02.667" Score="2" Body="&lt;p&gt;When a tuner in a radio says it can match 3:1 and below, they sometimes say that it can match 16.7-150 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would take this to mean that a tuner that can match 10:1 and below, can match 5-500 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is an example of a tuner that can match some bands to 10:1 on &lt;a href=&quot;https://qrznow.com/kat500-high-power-auto-tuner-smart-antenna-switch/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page.&lt;/a&gt; they specify:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Frequency&lt;/strong&gt;               &lt;strong&gt;Typical Matching Range and Power Limit&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3 — 30 MHz            600W into 5 to 500 Ohms (10:1 SWR)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;                                 1000W into 16 to 150 Ohms (3:1 SWR )&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-06-04T14:04:02.667" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14667" PostTypeId="2" ParentId="14604" CreationDate="2019-06-04T14:06:17.800" Score="2" Body="&lt;p&gt;Thanks all for the tips. Going back to stock firmware fixed the issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My radio reports hardware V05.01 and came from the factory loaded with firmware D014.009. I loaded md380tools onto it, which right now is based on D013, but I suspect that's incompatible with my hardware generation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;TYT sent me D015.001, which appears to fix the issue.&lt;/p&gt;&#xA;" OwnerUserId="14609" LastActivityDate="2019-06-04T14:06:17.800" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14668" PostTypeId="2" ParentId="14665" CreationDate="2019-06-04T14:18:08.893" Score="4" Body="&lt;p&gt;Short detour: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a so-called &lt;em&gt;reflection coefficient&lt;/em&gt; &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt; that says &quot;OK, for this mismatch, so and so much of the power is reflected back where it came from&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can calculate it as, based on load impedance &lt;span class=&quot;math-container&quot;&gt;$Z_L$&lt;/span&gt; and conduction line impedance &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \Gamma =\frac{Z_L - Z_0}{Z_L + Z_0}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the VSWR is a &lt;em&gt;result&lt;/em&gt; of things getting reflected back:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;\begin{align}&#xA;\DeclareMathOperator{\vswr}{VSWR}&#xA;\vswr  &amp;amp;= \frac{1+\lvert\Gamma\rvert}{1-\lvert\Gamma\rvert}\\&#xA;&amp;amp;\implies\\&#xA;\lvert\Gamma\rvert &amp;amp;= \frac{\vswr-1}{\vswr +1}\\&#xA;&amp;amp;\iff\\&#xA;\left\lvert\frac{Z_L - Z_0}{Z_L + Z_0} \right\rvert &amp;amp;=\frac{\vswr-1}{\vswr +1}&#xA;\end{align}&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming &lt;span class=&quot;math-container&quot;&gt;$Z_L&amp;gt;Z_0$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;\begin{align}&#xA;\frac{Z_L - Z_0}{Z_L + Z_0} &amp;amp;=\frac{\vswr-1}{\vswr +1}&amp;amp;&amp;amp; \lvert\vswr=10, Z_0 = 50\,\mathrm\Omega\\&#xA;&amp;amp;=\frac{9}{11}\\&#xA;&amp;amp;\implies\\&#xA;\frac{Z_L - Z_0}{Z_L + Z_0} - \frac9{11} &amp;amp;= 0 &amp;amp;&amp;amp; \lvert\cdot (Z_L+Z_0)\\&#xA;0 &amp;amp;=Z_L - Z_0 - \frac9{11}(Z_L + Z_0)  \\&#xA;&amp;amp;=\frac2{11}Z_L -\frac{20}{11}Z_0 &amp;amp;&amp;amp;\lvert\cdot11:2\\&#xA;&amp;amp;=Z_L -10 Z_0\\&#xA;Z_L&amp;amp;= 10 Z_0 \\&#xA;&amp;amp;= 500\,Ω&#xA;\end{align}&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming &lt;span class=&quot;math-container&quot;&gt;$Z_L&amp;lt;Z_0$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;\begin{align}&#xA;\frac{Z_0 - Z_L}{Z_L + Z_0} &amp;amp;=\frac{\vswr-1}{\vswr +1}&amp;amp;&amp;amp; \lvert\vswr=10, Z_0 = 50\,\mathrm\Omega\\&#xA;&amp;amp;=\frac{9}{11}\\&#xA;&amp;amp;\implies\\&#xA;\frac{Z_0 - Z_L}{Z_L + Z_0} - \frac9{11} &amp;amp;= 0 &amp;amp;&amp;amp; \lvert\cdot (Z_L+Z_0)\\&#xA;0 &amp;amp;=Z_0 - Z_L - \frac9{11}(Z_L + Z_0)  \\&#xA;&amp;amp;=\frac2{11}Z_0 -\frac{20}{11}Z_L &amp;amp;&amp;amp;\lvert\cdot11:2\\&#xA;&amp;amp;=Z_0 -10 Z_L\\&#xA;\frac1{10}Z_0&amp;amp;= Z_L \\&#xA;&amp;amp;= 5\,Ω&#xA;\end{align}&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, 5 Ω to  500 Ω are &quot;specification-wise&quot; matchable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is assuming a &lt;em&gt;real-valued&lt;/em&gt; antenna impedance. That's often not given. For the complete region of applicable values, see (and upvote!) Cecil's answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, impedance matching doesn't happen on a &quot;reflection coefficient level&quot;; it happens by having an adjustable matching network (typically takes the shape of an adjustable LC filter). Things actually get rather interesting there, because the matches you get from that typically aren't wideband and typically aren't all real and typically aren't all within a &quot;nice&quot; shape in the real world. So, assuming the best, the SWR range is but a thing that the manufacturer has tested to work, and special complex impedances outside the circle from Cecil's answer can be matched too.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-06-04T18:33:33.420" LastActivityDate="2019-06-04T18:33:33.420" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14669" PostTypeId="2" ParentId="14665" CreationDate="2019-06-04T14:31:33.133" Score="10" Body="&lt;p&gt;As you can see from the following equation, it is definitely not that easy. What I would do is draw a 10:1 SWR circle on a Smith Chart and assume that your tuner can match all of the infinite number of impedances inside that 10:1 SWR circle. If you don't know how to read impedances from a Smith Chart, it would be worth your while to learn how. The green area below on the Smith Chart normalized to 50 ohms is the advertised matching range for your tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xeY2K.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xeY2K.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IXBrN.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IXBrN.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-06-04T14:45:10.507" LastActivityDate="2019-06-04T14:45:10.507" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14670" PostTypeId="1" AcceptedAnswerId="14671" CreationDate="2019-06-04T18:45:43.037" Score="2" ViewCount="122" Body="&lt;p&gt;Using software defined radios I can generate and demodulate a DVB-S2 signal live. I'm wondering if I can use this to send single pictures over the air using as narrow BW as possible. Using QPSK and a symbol rate of 1 MSPS the signal is about 1 MHz wide, which isn't very practical. If I reduce the symbol rate, will the signal occupy less bandwidth?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JHLeV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JHLeV.jpg&quot; alt=&quot;DVB-S2 Signal&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14950" LastActivityDate="2019-06-04T19:07:46.107" Title="How narrow-band can a DVB-S2 signal be?" Tags="&lt;software-defined-radio&gt;&lt;dsp&gt;&lt;atv&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="14671" PostTypeId="2" ParentId="14670" CreationDate="2019-06-04T19:07:46.107" Score="3" Body="&lt;p&gt;I've heard that 2 days in the lab can save 2 hours of reading but in this case it turned out to be easy to test. It is the sample rate of the SDR which changes the bandwidth of the signal. Since I am using the PLUTO SDR I can't go below around 500ksps. So I tried with a symbol rate of 300 kbaud at a sample rate of 600k. Able to demod successfully. I asked because I thought this would be harder to figure out but I'll leave it for reference. &lt;a href=&quot;https://i.stack.imgur.com/gm47N.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gm47N.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14950" LastActivityDate="2019-06-04T19:07:46.107" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14672" PostTypeId="2" ParentId="14649" CreationDate="2019-06-04T19:19:48.800" Score="1" Body="&lt;p&gt;The &lt;a href=&quot;https://baofengtech.com/download&quot; rel=&quot;nofollow noreferrer&quot;&gt;Baofeng Tech download page&lt;/a&gt; says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;At this time our DMR radios are not compatible with CHIRP; you will need to use the OEM software to update and program your BTECH DMR radios.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Here's a &lt;a href=&quot;https://chirp.danplanet.com/issues/4507&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP &quot;issue&quot;&lt;/a&gt; (actually a feature request), which is open and not complete, to add support for the DM-5R.  It seems clear, unfortunately, that CHIRP doesn't yet support the DM-5R.  However, the Baofeng Tech download page does offer OEM software to program the radio.  I'd suggest trying that as an alternative.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-06-04T19:19:48.800" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14673" PostTypeId="2" ParentId="14659" CreationDate="2019-06-04T21:30:13.520" Score="4" Body="&lt;p&gt;A transmission line is linear, which means we can consider the voltage at any point to be the &lt;a href=&quot;https://en.wikipedia.org/wiki/Superposition_principle&quot; rel=&quot;nofollow noreferrer&quot;&gt;superposition&lt;/a&gt; of two other voltages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Asking what they are &quot;physically&quot; may or may not be a useful question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could for example define:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ V(z) = Ve^{jkz} + V_{DS}(t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$V_{DS}(t)$&lt;/span&gt; is a function corresponding to the normalized amplitude of Pink Floyd's &lt;em&gt;Dark Side of the Moon&lt;/em&gt; at time &lt;em&gt;t&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does this mean, &quot;physically&quot;? Nothing at all. It's math, and I can do what I want, as long as I follow the rules. And I have: the superposition principle says that I can take the voltage and define it as the sum of any terms I like.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So perhaps the answer to your question of what these terms are physically is the same: they aren't anything physically. They are mathematical abstractions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps the question you should be asking is why this particular superposition of forward and reverse waves is a &lt;em&gt;useful&lt;/em&gt; one (unlike my Pink Floyd superposition).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer is that by considering the waves divided in this way, we can say the forward and reverse waves independently exhibit the characteristic impedance of the transmission line. For example, if this is a (50+0j) ohm line, then considering just the forward wave, there will always be precisely 50 volts per ampere. The ratio will always be 50 and the two will always be in phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is useful, because it isn't generally true considering a transmission line in whole. If the line isn't terminated by its characteristic impedance, then the ratio of volts to amps may not be 50. And the two may not be in phase, indicating a reactive component to the impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So by defining the voltage to be a superposition of forward and reflected waves, the relationship between current and voltage becomes a simple fixed, real (for idealized lines) ratio. This makes analysis simpler. It also means when the line is terminated in a matched load (or at least, any mismatch is practically negligible), the reflected wave is zero and this cancels a lot of terms in a lot of equations related to transmission lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course we can't simply ignore reality either, but with this superposition defined that complexity can be factored as the reflection coefficient. And this is also real nice since the reflection coefficient can trivially be calculated if the (possibly mismatched) load impedance is known.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-06-04T21:30:13.520" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14674" PostTypeId="1" AcceptedAnswerId="16188" CreationDate="2019-06-05T13:52:32.277" Score="4" ViewCount="180" Body="&lt;p&gt;If I'm building a vacuum tube HF transmitter (say, 40 m band), obviously the simplest mode to build is CW; it's common to key the oscillator input to the final (in order to keep the oscillator running stably, minimizing chirp and drift).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I want to add AM to this simple transmitter, one method of modulating the output might be to use a saturable reactor, aka &quot;magnetic amplifier,&quot; to boost the output of a microphone to be added to the B+ plate voltage (coupled through a suitable capacitance, to keep high voltage DC off the microphone); the fluctuation of the plate voltage would control the gain of the PA, modulating the output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't see plate modulation used much in radio circuits I've found, so there must be some disadvantage, but I don't see offhand what that would be; I think it's just simpler in a &quot;normal&quot; circuit to feed the output of one stage to the grid of the next.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a big problem with using a magnetic amplifier to modulate the plate voltage this way?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="76" LastEditDate="2019-06-05T17:21:38.007" LastActivityDate="2020-03-03T13:18:08.547" Title="Is it practical to use a magnetic amplifier as an AM modulator in a transmitter?" Tags="&lt;modes&gt;&lt;electronics&gt;&lt;vacuum-tubes&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14675" PostTypeId="2" ParentId="14554" CreationDate="2019-06-06T06:34:29.660" Score="2" Body="&lt;p&gt;&lt;strong&gt;First Steps in Satellites&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As with trying anything new, it’s best to take small steps as you learn. Here’s a simple exercise to help you get started: listening for the AO-91 FM satellite.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Go to AMSAT or N2YO.com, or download one of the satellite tracking apps, and get the latest pass information on the FM satellite AO-91 (also known as Fox-1B). AO-91 has a downlink frequency of 145.960 MHz, so it won’t be as affected by Doppler as other satellites.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Use your current 2 meter radio and hook it up to the best antenna you have. If you’re trying this from your car with a mobile whip, try and go to a park or other area with as clear a horizon as possible. If you have a directional antenna, you will have to rotate your antenna to follow the satellite across the sky as it goes overhead.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;At AOS, open the squelch on your radio so you can hear static all the time. Start listening for signals through the static. With luck and experience, you will soon hear signals coming through the static as the pass progresses, until the pass is over.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Try several different passes at different elevations above the horizon.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.onallbands.com/satellite-basics-part-1-guide-to-ham-radio-satellite-operating/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Source&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="14723" LastActivityDate="2019-06-06T06:34:29.660" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14676" PostTypeId="1" CreationDate="2019-06-06T13:02:15.480" Score="1" ViewCount="141" Body="&lt;p&gt;What is the definition of these terms? Would a system with signal to noise ratios of uplink 100dBHz and downlink 80dBHz be downlink-limited?&lt;/p&gt;&#xA;" OwnerUserId="15035" LastActivityDate="2019-06-06T13:02:15.480" Title="Uplink-limited vs. Downlink-limited" Tags="&lt;noise&gt;&lt;link-budget&gt;" AnswerCount="0" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="14677" PostTypeId="1" CreationDate="2019-06-06T17:28:39.850" Score="3" ViewCount="380" Body="&lt;p&gt;What are the effects on signal propagation if this ground plane is just a metal object and what are the effects if the ground plane is actually grounded?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am asking this question because someone wants to put a storage container under my 40m antenna and I want to know what the effects of this large metal object will be. Will it harm my radiation pattern?&lt;/p&gt;&#xA;" OwnerUserId="1817" LastActivityDate="2019-06-06T17:45:57.093" Title="What are the effects of a ground plane under a horizontal dipole?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;radiation-pattern&gt;&lt;grounding&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14678" PostTypeId="2" ParentId="14677" CreationDate="2019-06-06T17:45:57.093" Score="5" Body="&lt;p&gt;If the container is small relative to wavelength, then it won't have much effect at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's very large (say, infinite) then it will reduce ground losses by providing a more conductive ground plane. It doesn't matter if it's actually connected to the soil or not. This is a good thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The container will be closer to the antenna, which will change the spacing of the dipole and the &lt;a href=&quot;https://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;noreferrer&quot;&gt;image antenna&lt;/a&gt; under it, which may move the elevation of the main lobe up or down depending on the height of the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since a storage container is probably neither very small nor very large relative to a 40m wavelength, you can expect effects somewhere between the extremes. In all, I'd say as long as the dipole isn't very close to the container you can expect no significant detrimental effects, and perhaps even some positive ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to know more exactly what will happen, of course the thing to do is model the precise geometry of your situation.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-06-06T17:45:57.093" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14679" PostTypeId="1" CreationDate="2019-06-08T08:53:44.410" Score="11" ViewCount="475" Body="&lt;p&gt;5 wpm is easy to learn and better than nothing in emergency.&#xA;Speed Morse Coding is fine for &quot;sport competition&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am trying to find out which is the typical speed for what I call &quot;conversation&quot; and define it with the following questions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Are there statistics about the speed distribution?&lt;/li&gt;&#xA;&lt;li&gt;Which is the most common speed in wpm for contacts over words in exchange?&lt;/li&gt;&#xA;&lt;li&gt;Which is the most common speed in wpm for communication with duration over 5 min?&lt;/li&gt;&#xA;&lt;li&gt;Which is the average speed in wpm used for morse coding?&lt;/li&gt;&#xA;&lt;li&gt;Which is the median of the speed in wpm for mose coding?&lt;/li&gt;&#xA;&lt;li&gt;Which are the terciles or quartiles of the speed for morse coding?&lt;/li&gt;&#xA;&lt;li&gt;Is there a standard speed used by NATO, UN or any national military?&lt;/li&gt;&#xA;&lt;li&gt;Which is the standard speed for messages sent by machine?&lt;/li&gt;&#xA;&lt;li&gt;At which speed starts &quot;speed coding&quot;?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The reason for this question:&#xA;Using the Koch method you train with the &quot;letter speed&quot; farnsworth compression in wpm which you want to achieve at the end, while step by step decreasing spacing and errors. If you choose a too high speed you may never reach the standard spacing by an acceptable number of errors, if you choose a too low speed, it is difficult to increase your speed later. Therefore one should know which speed is mostly used for longer communication between people who are experienced in sending morse code.&lt;/p&gt;&#xA;" OwnerUserId="15039" LastEditorUserId="15039" LastEditDate="2019-06-09T16:12:14.913" LastActivityDate="2019-06-09T16:12:14.913" Title="Dominant speeds of Morse Communications" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="14680" PostTypeId="2" ParentId="14635" CreationDate="2019-06-08T12:47:54.573" Score="2" Body="&lt;p&gt;This depends a great deal on the type of antenna, the shape of the metal structure, and the radiation pattern you want.  Ideally, you would want use the structure as part of the antenna, either as a ground plane, radiator, or reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It usually isn't necessary to insulate the antenna from the structure -- this might even be dangerous, as you may need to ground the antenna to the structure for lightning purposes.  If you are using an antenna designed for a tower, it is probably designed so that insulators are not necessary or are already part of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may need to put a spacer (usually metal, conducting) between the antenna and the structure so that reflections off the structure give you constructive interference rather than destructive interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible in extreme cases with a tower to &quot;tune&quot; part of the tower to make it transparent to the frequency of interest, but usually if the radiation pattern is blocked by a tower too much, instead multiple antennas are placed on different sides of the tower to overcome this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A specific answer to this question is not really possible without knowing the geometry of the antenna and tower and the frequency of interest.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-06-08T12:47:54.573" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14681" PostTypeId="2" ParentId="14679" CreationDate="2019-06-09T02:23:10.560" Score="10" Body="&lt;p&gt;Data from the &lt;a href=&quot;http://reversebeacon.net&quot; rel=&quot;noreferrer&quot;&gt;Reverse Beacon Network&lt;/a&gt; provides an answer. RBN receivers and computers decode CW (and other &quot;digital&quot; modes) to identify stations calling CQ and posts information about signal strength and operating speed. I think it's reasonable to assume that QSOs are conducted at the same speed as the op sends &quot;CQ.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Click on &quot;DX Spots&quot; followed by &quot;Download Raw Data&quot; to access files of &quot;comma separated values&quot; (.csv) for specific dates. For example, I downloaded 20190210.csv, a Saturday, from which I calculated an average CW speed of 24.6WPM. Performing the same analysis for 20181124 - the first day of the annual CQ WW CW contest - results in an average CW speed of 31.7WPM, a nearly 30% increase that reflects on the nature of contests and contesters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other possible analyses are limited only by the imagination of the questioner.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-06-09T12:30:53.763" LastActivityDate="2019-06-09T12:30:53.763" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14682" PostTypeId="1" CreationDate="2019-06-09T16:05:17.287" Score="6" ViewCount="690" Body="&lt;p&gt;I built a vertical out of a 5M aluminium pipe. It tunes fine (and wide!) on 20M.&#xA;I decided to add a loading coil to operate it on 40M, and it also worked fine, albeit not so wide.&#xA;While I was at it, I extended the coil for operation on 80M as well. It became super narrow! But it worked.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To test this, I used crocodile wires to bite into the coil. I decided make a remote switch out of relays. But it's not working as expected when operating 80M. The SWR jumps around like crazy on my meter, and at some point it just stays inifinite. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is what I built:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZB5vP.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZB5vP.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I suspect is that when both relays are off, there is a very high voltage across the relays and an arc forms, due to the high Q of the coil.&#xA;This does not happen when the 40 or 20M relays are activated. The antenna works more or less as expected when the 40 or 20M relays are active.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could this be the problem? Could it be solved somehow?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I thought of using traps instead of relays to make the antenna &quot;auto switching&quot;, but I'm not sure if traps would add more loss than the relays, or if they would whitstand the high voltages appearing on the coil.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="76" LastEditDate="2019-10-21T20:42:18.743" LastActivityDate="2019-10-21T20:42:18.743" Title="Multiband vertical antenna not working as expected" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14683" PostTypeId="2" ParentId="14682" CreationDate="2019-06-09T16:26:58.973" Score="1" Body="&lt;p&gt;Your suspicion is justified. Voltage increases (and current decreases) as you move toward the open-circuited end of the antenna. The most common solution is to situate the loading coil - and, perhaps, a resonating capacitor - at the base of the antenna. A base-loaded vertical only 5m tall will not be very efficient on 80m, but a center-loaded antenna will probably not be great either, as it's only about 1/4 the length of a resonant monopole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The voltage along the 5m radiator can be reduced and efficiency can be improved by effectively lengthening the radiator with &quot;top hat&quot; conductors. This will increase the current at the top of your 5m aluminum pipe and, depending on the size of the top hat, reduce the amount of inductive loading you need to add. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-09T16:26:58.973" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14684" PostTypeId="2" ParentId="14682" CreationDate="2019-06-09T17:29:04.217" Score="5" Body="&lt;p&gt;It may very well be that the open contacts are arcing, and I'm betting that's what is happening.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some possible solutions. How about using different relays that have less tendency to arc:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Open-frame relays with much wider contact spacing&lt;/li&gt;&#xA;&lt;li&gt;Vacuum relays&lt;/li&gt;&#xA;&lt;li&gt;Multiple relays in series&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Another &lt;em&gt;possibility&lt;/em&gt; might be that RF on the control lines may be activating the relays. Suitable RF chokes and bypass capacitors might help that.&#xA;&lt;hr&gt;&#xA;&lt;strong&gt;It's a myth that all traps are lossy&lt;/strong&gt;. If they don't get hot to the touch at sustained 100W or higher, then their loss is insignificant. Scroll to the bottom of &lt;a href=&quot;https://www.w8ji.com/traps.htm&quot; rel=&quot;noreferrer&quot;&gt;https://www.w8ji.com/traps.htm&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;3.) Do traps create noticeable loss, perhaps one dB per trap typically?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;NO! Even the worst traps (coaxial traps) in the worse possible condition of operation are only 1.6dB loss for BOTH traps!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-06-09T17:52:47.890" LastActivityDate="2019-06-09T17:52:47.890" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14685" PostTypeId="1" AcceptedAnswerId="14686" CreationDate="2019-06-09T20:01:43.973" Score="2" ViewCount="155" Body="&lt;p&gt;Why do line of sight communication links have a restricted range for a given tower height? Is it only because of the Earth's Curvature? &lt;/p&gt;&#xA;" OwnerUserId="15044" LastEditorUserId="8573" LastEditDate="2019-06-19T14:31:22.377" LastActivityDate="2019-06-19T14:31:22.377" Title="Restricted line-of-sight communication" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;line-of-sight&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14686" PostTypeId="2" ParentId="14685" CreationDate="2019-06-10T01:14:56.843" Score="5" Body="&lt;p&gt;As pointed to by Marcus' comment, &quot;line of sight&quot; communication is just that: if you can see it, you can communicate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are formulae that will calculate the distance to the horizon, given the height of the tower at each end, and it is because of the curvature of the Earth, as you suggested.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-06-10T01:14:56.843" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="14687" PostTypeId="1" CreationDate="2019-06-10T05:11:32.523" Score="3" ViewCount="105" Body="&lt;p&gt;There are a ton of old USSR Gunn diodes available on ebay and I'm looking for a cavity that can make use of them. I am willing to machine one myself if necessary, but I'm unable to find any decent schematics. They either leave info out or they look way too complicated and include something that doesn't even look like the correct design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it is possible to buy one to fit these, that'd be perfect, but I can't find it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see some gunnplexers on ebay, but I don't know if they will fit the diodes that I want to use. Are there any other variables aside from frequency and the actual mounting hole diameter for the diode itself? So maybe I could just hack it in place.&lt;/p&gt;&#xA;" OwnerUserId="1817" LastEditorUserId="8717" LastEditDate="2019-12-05T20:16:49.117" LastActivityDate="2019-12-05T20:16:49.117" Title="What are the parameters and necessary features of a Gunn diode oscillator cavity?" Tags="&lt;microwave&gt;&lt;military-surplus&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14691" PostTypeId="1" AcceptedAnswerId="14693" CreationDate="2019-06-10T15:21:33.063" Score="0" ViewCount="130" Body="&lt;p&gt;How hard and expensive would it be to send a file from my house in London to  a coastal area in Spain? It would most likely be software I want, so it must transfer perfectly, however if it is feasible then movies would also be great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am in a situation where it is impossible to get a telephone line and there is often only 2G mobile signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anything is better than nothing, so speed is not a huge concern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: &#xA;2G is too expensive.&#xA;Internet cafes are too far away.&#xA;The postal service is not reliable.&#xA;I have no car.&#xA;Satellite services are far too expensive and even if I wanted to they are always scams where I live.&lt;/p&gt;&#xA;" OwnerUserId="15050" LastEditorUserId="15050" LastEditDate="2019-06-12T14:23:57.203" LastActivityDate="2019-06-12T14:23:57.203" Title="How hard to send files" Tags="&lt;transmitter&gt;&lt;transmission&gt;" AnswerCount="1" CommentCount="3" ClosedDate="2019-06-10T21:18:09.097" ContentLicense="CC BY-SA 4.0" />
  <row Id="14692" PostTypeId="2" ParentId="14687" CreationDate="2019-06-10T16:16:48.423" Score="3" Body="&lt;p&gt;You might be able to use this mechanical drawing, from the ARRL's monthly &lt;em&gt;QST&lt;/em&gt; magazine for August 1974, to determine whether the available units are appropriate to your needs:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BQ68U.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BQ68U.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-10T16:16:48.423" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14693" PostTypeId="2" ParentId="14691" CreationDate="2019-06-10T16:58:29.193" Score="4" Body="&lt;p&gt;To get that distance, you're going to need to use an HF frequency, which means you won't have nearly as much bandwidth as Wi-Fi.  Transferring a movie could take a very long time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, you may have legal issues if the file is encrypted.  That's not allowed for amateur transmissions in the United States, anyway.  I'm not sure about your jurisdiction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And you might run into different legal issues if the file isn't encrypted.  (You could be accused of mass distribution of copyrighted content because anyone within range could receive the file.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's yet another potential legal issue if you send a movie that has music in it (i.e. nearly every movie).  Transmitting music generally isn't allowed.  But, again, the laws in your jurisdiction may vary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your best option might simply be to send DVDs or flash drives in the mail.  Or you could look for a place within driving distance that has a good internet connection and download your files there.  There are also satellite internet services available if you're willing to pay for them.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2019-06-10T17:04:37.603" LastActivityDate="2019-06-10T17:04:37.603" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14694" PostTypeId="2" ParentId="7664" CreationDate="2019-06-11T03:24:04.980" Score="1" Body="&lt;p&gt;A magnetic loop can work well if it has two qualities: enough power handling (a 5 kV vacuum variable will handle the 7300's 100 Watts); and a decent remote tuning setup.  Tuning is critical, as eHam reviews show the main difficulty is getting the SWR properly dipped.  Thanks to the popularity of robotics, low cost stepper motors are available, and do the job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While size isn't critical, efficiency goes rapidly downhill at diameters less than than about a 20th of a wavelength.  1/2&quot; or 3/4&quot; copper tubing is self supporting, low loss, and is easily flattened and drilled for low loss connections.  Paint it a dark color for stealth, and to avoid corrosion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dealing with high voltages and extreme narrow bandwidth are the price paid for an antenna that makes a magnetic near field, which seems to penetrate nearby conductors, such as trees, the ground, house wiring, powerlines, etc. almost as if they weren't there, because induced currents are in phase with the antenna's field.  Near field losses are reduced by an S unit in a typical urban location, when compared with a wire antenna or a vertical whose electrical near field induces out of phase re-radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stealth is achieved not only by small size, but also by suppression of RFI which does not emanate from the loop's matched feedline, since tuning and matching is done at the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further details are at &lt;a href=&quot;http://www.x44.cc&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.x44.cc&lt;/a&gt;, or by Googling my ham callsign, K1QAR&lt;/p&gt;&#xA;" OwnerUserId="15054" LastEditorUserId="8717" LastEditDate="2019-06-12T02:07:19.553" LastActivityDate="2019-06-12T02:07:19.553" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14695" PostTypeId="2" ParentId="11624" CreationDate="2019-06-11T12:01:56.780" Score="1" Body="&lt;p&gt;As a KWM-2 overhauler, I'm impressed with your knowledgeable attack on the problem.&#xA;Two suggestions:  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would look at the driver stage, and check voltages and the cathode and screen resistors  (like you did for the finals) to make sure their output is up to spec. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want meaningfully more output, an easy way is to get an amplifier in the 500 Watt class, such as a 30L1, can be had for short money.  Makes a huge difference in the quality of on-air conversation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, gettering generally takes of the order of 24 hours.  Time well spent, as you found out the hard way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;" OwnerUserId="15054" LastActivityDate="2019-06-11T12:01:56.780" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14698" PostTypeId="2" ParentId="13242" CreationDate="2019-06-12T03:01:50.310" Score="4" Body="&lt;p&gt;I've been using magnetic loops for 20 years&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A magnetic loop can work well if it has two qualities: enough power handling (a 5 kV vacuum variable will handle 100 Watts, 15kV will do a kW); and a decent remote tuning setup.  tuning is critical, as Eham reviews show the main dfficulty is getting the SWR properly dipped.  Thanks to the popularity of robotics, low cost stepper motors are available, and do the job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While size isn't critical, efficiency goes rapidly downhill at diameters less than than about a 20th of a wavelength.  1/2&quot; or 3/4&quot; copper tubing is self supporting, low loss, and is easily flattened and drilled for low loss connections.  Paint it a dark color for stealth, and to avoid corrosion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dealing with high voltages and extreme narrow bandwidth are the price paid for an antenna that makes a magnetic near field, which seems to penetrate nearby conductors, such as trees, the ground, house wiring, powerlines, etc. almost as if they weren't there, because induced currents are in phase with the antenna's field.  Near field losses are reduced by an S unit in a typical urban location, when compared with a wire antenna or a vertical whose electrical near field induces out of phase re-radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The statements about quiet receive are approximately correct.  In my experience, fixed local terrestrial noise sources (a pole pig with nesting squirrels, an LED streetlight)can be reduced typically by two S units (10 dB) by a vertically hung loop that is tied with a side line to keep the null lined up.  Unlike stations using an antenna tuner at the radio, received and transmitted RFI does not come from the loop's feedline because its matched all the way to the antenna, where tuning and matching is done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further details are at www.x44.cc, or by googling my ham callsign, K1QAR&lt;/p&gt;&#xA;" OwnerUserId="15054" LastActivityDate="2019-06-12T03:01:50.310" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14699" PostTypeId="2" ParentId="1866" CreationDate="2019-06-12T10:50:08.790" Score="1" Body="&lt;p&gt;Where practical I will pot the connection up permanently in resin. Auto body filler works well enough and can be purchased in gallon quantities and up. Just be mindful of the heat buildup that occurs with large cross sections and plan accordingly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once I built a N4UJW 2m/440 dipole using this method. The center feedpoint is potted using the above instead of hot glue. In vertical it still reaches stations 40mi distant after 4 years at modest PEP.&lt;/p&gt;&#xA;" OwnerUserId="15062" LastActivityDate="2019-06-12T10:50:08.790" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14700" PostTypeId="2" ParentId="14433" CreationDate="2019-06-12T13:36:35.357" Score="0" Body="&lt;p&gt;I used a loop yagi, rated at 15 dB gain, on my boat.   It had about a 30 degree beamwidth in both horizontal and vertical planes.  It had plenty of gain when used with an amplifier, as it still had lots of signal at TCP-IP drop out (at a distance of about a mile, the nanosecond propagation delay seems to be too much for typical WIFI)  I used it at a height of about 10 feet on a pole, since below that sihgnals die rapidly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would use trial and error to find a connection. I'd point it in a likely direction, see if there was service, then swing it 30 degrees, and try again.&#xA;Also, I'd put the amplifier at the antenna and use USB cable to get to the cabin, avoiding coax loss (which is considerable at 2 Gigs.)&lt;/p&gt;&#xA;" OwnerUserId="15054" LastActivityDate="2019-06-12T13:36:35.357" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14701" PostTypeId="2" ParentId="13206" CreationDate="2019-06-12T16:30:59.883" Score="2" Body="&lt;p&gt;I have just put up a magnetic loop on a metal aircraft hangar roof.  It plays! &#xA;The antenna is vertically mounted on a tripod, and is 4' by 6' using 3/4&quot; copper tubing. A dozen tests on 40 and 60M showed an average of 4- 6 dB better reports than a full wave delta loop at the same 20' height above ground using the same power.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The magnetic loop will also give you much quieter receive than a vertical or dipole, especially if it is rotated to null the worst local noise source on installation. Because the the null is within 20 degrees of the horizon, the loop is effectively omnidirectional for skywave, including NVIS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The metal roof acts as a shield, so RF exposure is a non issue.  For mounting, I'd leave the 18' pole alone.  A 5-6' tripod with cement block weighted legs and a 10' pole in the center of the roof would work, since the bottom of the antenna only needs a few feet of clearance.  Matching is done in the customary way, with the coax attached to a small loop opposite the tuning capacitor. Keep the control and feed lines symmetrical with the axis of the loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no reason to restrict power.  Tuned with a 15kV vacuum variable capacitor, It'll handle a kilowatt.  The tuning problem is easily solved with an off-the-shelf stepper motor, driver and encoder from a robotics supplier. No programming necessary, and easier than an antenna tuner (only one knob) Mount the motor at least 8&quot; away from the antenna; use an on/off switch for stepper power as they are noisy.&lt;/p&gt;&#xA;" OwnerUserId="15054" LastActivityDate="2019-06-12T16:30:59.883" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14703" PostTypeId="2" ParentId="59" CreationDate="2019-06-12T17:12:11.663" Score="3" Body="&lt;p&gt;I used the 14.300 maritime net frequency to undeclare an emergency.  My vessel was dismasted in the Gulf Stream during a Bermuda-Newport sailboat race in 2005.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Had the situation been both urgent and life threatening, a repeated 'mayday' would've been appropriate. If urgent but non-life threatening, then 'pan' or 'break' would have gotten everybody quickly in receive mode, at which point the customary information would be asked for. (location, souls on board, etc)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As this was neither a split second nor a life endangerment issue, I waited a few minutes for net control to issue a callup.  An onboard tracker and another vessel both had reported the situation, and the expected result would have been forced abandonment of my boat and a five figure rescue bill.  Luckily, a gentleman in Florida phone patched me into our home phone, where I requested they call off any rescue. To make sure, I also requested they phone to tell the Race Committee I was still competing under jury rig. &lt;/p&gt;&#xA;" OwnerUserId="15054" LastActivityDate="2019-06-12T17:12:11.663" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14704" PostTypeId="2" ParentId="936" CreationDate="2019-06-13T01:36:03.893" Score="3" Body="&lt;p&gt;Cut off a little extra and save some dielectric material. Then strip the outer sheath off and bend back the braid and carefully flip it inside out like a sock back over the sheath. Then cut back the exposed dielectric and core a little. This is so the braids can overlap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now strip the dielectric off the core and solder the 2 core ends together with about 1/8&quot; (5mm) of overlap for strength. Make sure it's a nice shiny joint with the right amount of solder so it doesn't ball up. Liquid flux and a clean iron tip really help. Then clean flux residue with some IPA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that dielectric material you saved? Cut a piece the length of the exposed core in your joint and slit it lengthwise with a razor like a hot dog bun. Take this and slip it over the core so it's covering as though the dielectric was continuous through the whole joint with as little exposed core as possible. Keep it all as short is you feel comfortable with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last step is to flip the braid back over the soldered core and your dielectric hot dog. The two ends of braid should slightly overlap and stay close against the dielectric. If there was foil under the braid wrap some around as well as it is in the rest of the coax. Keep in mind we are trying to recreate the conditions of the coax as closely as possible using pieces of itself. Then very carefully solder the braid all the way around using as little heat as possible. It is very easy to melt the dielectric and ruin the splice. This isn't the case so much with Teflon but other types can be difficult or impossible to solder without melting it. That is why industry only uses crimp connections on foam core. If you're using a soldering iron without temperature control, you should unplug it and let it cool, then plug it back in and quickly solder it up before it gets too hot. Heat shrink or tape over this and it should be a near perfect splice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This old trick has been used many times to join sections of coax without using connectors. &lt;/p&gt;&#xA;" OwnerUserId="15062" LastEditorUserId="9621" LastEditDate="2019-06-14T10:26:05.033" LastActivityDate="2019-06-14T10:26:05.033" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14707" PostTypeId="2" ParentId="7876" CreationDate="2019-06-14T18:19:06.197" Score="4" Body="&lt;p&gt;I tested your make/model antenna and others in various configurations with and without a tiger-tail on a small 2m HT with results in &lt;a href=&quot;https://www.hamradio.me/antennas/ht-antenna-comparisons.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this article&lt;/a&gt;. Here is the money graph...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://www.hamradio.me/wp-content/uploads/2018/10/ht_antenna_tests_ref_dipole.007.png&quot; alt=&quot;EIRP of Yaesu FT1D, 1/4 wave whip and “tiger tail.”&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Needless to say the extra bit of counterpoise helps A LOT and reveals why these 1/4 wave replacement whips on HTs often are no better than the well engineered stubby stock antenna as the above graph suggests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We took this concept a bit further using a 1/4 wave or so bit of braid strap on a shoulder mounted antenna atop a tactical vest. Needless to say, despite the existence of a lengthy coaxial feedline, the braid strap weaved in a serpentine fashion increased the EiRP also by about 10 dB. That's a mighty fine return on investment. Most of the tak vest is non-conductive ballistic stop material so didn't interfere with the &quot;hot&quot; end of the ground strap... and that's an important point about these 1/4 wave &quot;tiger tails&quot;... the high voltage end needs separation from other conductive and sometimes dielectric materials to perform their best. However we found there was lots of slop tolerable in this approach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You have that nice metal in your frame so, as others suggest, you may well be better off to tie your antenna &quot;ground&quot; point to the closest frame piece. The only caution I can give is the possibility your frame's connection points may not pass currents... or worse sometimes do resulting in scratchy radio performance. It's just something to keep in mind as you continue your cool project.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastActivityDate="2019-06-14T18:19:06.197" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14708" PostTypeId="2" ParentId="5305" CreationDate="2019-06-14T19:38:05.590" Score="0" Body="&lt;p&gt;Your posting is a good reminder how prevalent end-fed half-wave (EFHW) dipoles are in the commercial antenna biz. The marine VHF antenna industry seems to be the most obvious of the bunch given the need for an antenna to function &quot;well&quot; without benefit of a conductive structure to mount upon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My ham VHF/UHF mobile antenna is another EFHW example &lt;a href=&quot;https://www.hamradio.me/antennas/diamond-nr770hbnmo-vs-comet-ngc-m-24m.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;where measurements confirm&lt;/a&gt; improvement over its predecessor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking into the various EFHW offerings reveals an exemplar matching transformer at the base that looks something like this...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.hamradio.me/wp-content/uploads/2019/02/EFHW_Antenna_with_no_CP_an.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://www.hamradio.me/wp-content/uploads/2019/02/EFHW_Antenna_with_no_CP_an.png&quot; alt=&quot;The end-fed half-wave dipole antenna with magnified view of transformer.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More details available in this &lt;a href=&quot;https://www.hamradio.me/antennas/simulating-the-end-fed-halfwave-dipole-antenna.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;article&lt;/a&gt;. The above operates well, in simulation, without any need of the oft mentioned counterpoise, etc. &lt;a href=&quot;https://www.hamradio.me/antennas/electrically-isolated-end-fed-center-fed-dipole-radiation.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Measurements of an HF analog to the above&lt;/a&gt; reinforce the ability of an EFHW to operate independent of additional conductors albeit with a bit of loss in the slightly different transformer structure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qDlob.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qDlob.png&quot; alt=&quot;Difference between EFHW transformer configurations&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, feedlines are the norm so I am exploring the effects there as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following graph details the behavior of the VHF/UHF mobile EFHW above against varying lengths of feedline with a grounded end/radio. The frequency is 146 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.hamradio.me/wp-content/uploads/2019/02/HRM_03_EFHW_vs_CPLength_Gain_5m_overlay_p.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://www.hamradio.me/wp-content/uploads/2019/02/HRM_03_EFHW_vs_CPLength_Gain_5m_overlay_p.png&quot; alt=&quot;The peculiar 13.5′ feedline length of the Diamond K515 mount.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly there are certain lengths one should avoid lest we rob energy from the antenna, but the good news is most lengths seem to play well enough. One can only wonder if the unusually specific length of 13.5 feet was chosen by the maker of my mobile antenna to precisely avoid certain lengths that will entice current from the antenna down the feedline. More detail &lt;a href=&quot;https://www.hamradio.me/antennas/of-end-feds-and-feed-lines.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;in the article&lt;/a&gt;. This assertion is pure conjecture on my part, but I do wonder if the stock feedline lengths of the marine VHF mobile antennas are also of some specific and peculiar length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In summary, the longevity of the EFHW design in the world of radio, especially VHF marine, gives comfort the manufacturers know what they are doing and the notion feeding a half-wave dipole from the end = NBD.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastActivityDate="2019-06-14T19:38:05.590" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14709" PostTypeId="2" ParentId="9555" CreationDate="2019-06-14T21:53:28.837" Score="4" Body="&lt;p&gt;I entered your circuit into LTSpice and made some test runs to verify the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to get reasonably accurate Fourier analysis, you need to simulate at least 20 cycles. I prefer 50. And, you need to add a SPICE statement setting plotwinsize=0 to eliminate data compression that compromises Fourier analysis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;polarity&quot; of V6 needs to be PULSE(0 5 ...) rather than PULSE(5 0 ...) to match the 180 degree phase shift of V5 from V1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find that simulating a center-tapped transformer as two series-connected transformers produces more reliable results. There's no problem placing the 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; load across the transformer secondary in a balanced configuration, as shown below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/r4tUt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/r4tUt.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This circuit produces these currents:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aktWO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aktWO.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And so the RMS output power is a bit more than 3W (with k=1 on the transformer).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note the sharp frequency spike at the 236kHz carrier frequency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qE2zu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qE2zu.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only resistor I can imagine having trouble at this frequency is a wirewound. Any other type of resistor or pot should work fine. Your choice of DAC will depend on whether you want a serial or parallel data interface, as well as the &quot;usual&quot; parameters of bit depth, settling time, etc. The best way to choose is to search the web site of your favorite distributor.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-14T21:53:28.837" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14710" PostTypeId="1" AcceptedAnswerId="14751" CreationDate="2019-06-15T02:29:17.957" Score="3" ViewCount="982" Body="&lt;p&gt;I'm installing a new antenna mast to hold one or more antennas. The new mast will be strapped on to a chimney near the center of my house. Coax will run down the mast, across the roof, down the side, and enter the house within inches of ground level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A collection of several ground rods spaced several feet apart (and tied together) is already installed near where the coax enters the house, with one rod being less than a foot from the entry point. The coax will run through a lightning arrester (specifically &lt;a href=&quot;https://www.dxengineering.com/parts/DMN-SP3000W&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.dxengineering.com/parts/DMN-SP3000W&lt;/a&gt;) at the ground rods.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the mast itself will have no ground connection (except what a brick chimney provides), the coax should be the most likely path to ground. Is the lightning arrester sufficient for lightning/static discharge, or should I run a separate grounding wire from the mast down to the ground?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's relevant, station ground will come to a single point in the shack and then be a thick copper cable wire back out to the same ground rod system.&lt;/p&gt;&#xA;" OwnerUserId="10424" LastEditorUserId="76" LastEditDate="2019-06-15T02:37:03.943" LastActivityDate="2019-06-21T06:09:44.043" Title="Grounding a chimney mounted antenna" Tags="&lt;grounding&gt;&lt;lightning&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14713" PostTypeId="1" CreationDate="2019-06-15T16:21:05.263" Score="5" ViewCount="1195" Body="&lt;p&gt;Can I feed a folded dipole constructed of hollow tubing by threading coax through the element to create both an impedance transformation and balun?    I have fed coax through the tubing of the dipole from a point opposite the feed point and soldered directly to the open ends of the dipole from inside the tubing. SWR seems ok with 50 ohm cable but a I being fooled into thinking all is ok? A bit hard to explain, the coax is inside the element for 1/2 wavelength.&lt;/p&gt;&#xA;" OwnerUserId="15084" LastActivityDate="2019-06-17T21:05:25.547" Title="Feeding a folded dipole" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14714" PostTypeId="2" ParentId="14713" CreationDate="2019-06-15T17:52:39.907" Score="0" Body="&lt;p&gt;Here is the way I feed my half-square antenna. The choke is necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/faXXx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/faXXx.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13587" LastEditorUserId="13587" LastEditDate="2019-06-15T21:54:19.783" LastActivityDate="2019-06-15T21:54:19.783" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14715" PostTypeId="1" CreationDate="2019-06-16T00:51:50.150" Score="3" ViewCount="140" Body="&lt;p&gt;I have a GNU Radio Companion flow graph, where I have the following connections: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;440Hz cosine wave&lt;/li&gt;&#xA;&lt;li&gt;throttle block&lt;/li&gt;&#xA;&lt;li&gt;audio sink&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pEwiB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pEwiB.png&quot; alt=&quot;Flow Graph Screenshot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All of the above blocks use the same sample rate (48KHz). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I execute this flow graph, I don't get a continuous note, the way I expected. Instead, it pulses on and off, several times per second. Why is this? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I make it output a continuous 440Hz tone? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Removing the Throttle block makes it stop cutting in and out, but it sounds even worse when I do this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have tried this setup, with and without the Throttle block, at all common sample rates for sound cards.&lt;/p&gt;&#xA;" OwnerUserId="15086" LastEditorUserId="76" LastEditDate="2019-06-16T02:28:22.143" LastActivityDate="2019-06-16T02:28:22.143" Title="Why is GNU Radio &quot;stuttering&quot; with this flow graph?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14716" PostTypeId="1" AcceptedAnswerId="14717" CreationDate="2019-06-16T00:58:20.190" Score="1" ViewCount="71" Body="&lt;p&gt;Similar to &lt;a href=&quot;https://ham.stackexchange.com/questions/10365/will-stainless-steel-bolts-work-with-my-copper-antenna&quot;&gt;Will stainless steel bolts work with my copper antenna?&lt;/a&gt; however my concern here is with electrical properties.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With copper antennas I never gave it much thought... just solder the wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am finishing a loop antenna using aluminum tube and it seems to be a little tricky.  Easy enough is to use a steel or stainless steel stud for the feedline connection and crimp an appropriate terminal connector to the feedline wire.  Feedline will be something like 10-12 gage THHN going to a nearby auto-tuner.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I forgetting something important?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not much concerned with galvanic corrosion as this is going in an attic.  But still avoiding direct copper-aluminum connection anyhow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case it matters, this is for HF and low VHF (80 meters - 6 meters) and power is expected to be limited to 100 watts.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2019-06-16T01:16:09.850" Title="Are stainless steel studs acceptable as a feedpoint connector for an aluminum loop antenna?" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14717" PostTypeId="2" ParentId="14716" CreationDate="2019-06-16T01:16:09.850" Score="2" Body="&lt;p&gt;Using stainless steel hardware to connect copper to aluminum works well as long as the copper and the aluminum are not allowed to be in contact. Home Depot carries some connectors designed to interface copper to aluminum in their electrical section.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-06-16T01:16:09.850" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14718" PostTypeId="2" ParentId="14715" CreationDate="2019-06-16T01:42:53.200" Score="2" Body="&lt;p&gt;I ended up figuring it out. I had to do three things:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;remove the Throttle block&lt;/li&gt;&#xA;&lt;li&gt;enable the &quot;OK to Block&quot; option in the audio sink&lt;/li&gt;&#xA;&lt;li&gt;ensure the amplitude of the sine wave is less than 1&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="15086" LastActivityDate="2019-06-16T01:42:53.200" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14719" PostTypeId="1" CreationDate="2019-06-16T02:01:36.310" Score="3" ViewCount="161" Body="&lt;p&gt;I recently purchased a 500-foot roll of military surplus 14 AWG stranded copper wire at a hamfest for next to nothing .  It is Prestolite M13486/1-6 (&lt;a href=&quot;https://www.iewc.com/assets/specsheets/Prestolite%20M13486A.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;spec sheet&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has very thick chlorinated polyethylene (CPE) insulation.  The outside diameter is nearly 1/4 inch (.235 to be exact). My plan is to use it to lay out radials for a ground mounted vertical, and my assumption is that it should work just fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, my knowledge does not extend very far into dielectric constants (actually, my knowledge pretty much ends right after looking-up what the dielectric constant of chlorinated polyethylene is: 5.5  at 1kHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the past, as many do, I have used 14 AWG stranded copper THHN for radials in ground mounted verticals with good results.  As far as the copper conductors are concerned, THHN is identical to the Prestolite.  Both are comprised of 19 strands of 29 AWG wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference between the two products comes down to the insulation/jacketing:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Prestolite uses CPE that is 57 mils thick.  CPE has a dielectric constant of 5.5&lt;/li&gt;&#xA;&lt;li&gt;THHN uses PVC that is 4 mils thick.  PVC has a dielectric constant of 4.0&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So, there are obviously significant differences between the two in terms of insulation/jacketing and by definition, they will perform differently.  My question is: Will these differences result in any practical, discernable difference in performance?&lt;/p&gt;&#xA;" OwnerUserId="15087" LastEditorUserId="8717" LastEditDate="2019-12-05T20:04:14.093" LastActivityDate="2020-02-03T12:36:41.073" Title="Dielectric Constant of Insulation/RF Permeability" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;radial&gt;&lt;military-surplus&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14720" PostTypeId="2" ParentId="9281" CreationDate="2019-06-16T02:25:41.340" Score="0" Body="&lt;p&gt;The movement of the whip,will effect radition pattern more then location where it is mounted while traveling is my though. Grounding vs mag mount, when the coax is on the antenna and you have a grounded antenna thru the radio and negative lead for power is my though on this as well. So why would a seperate ground be necessary?&lt;/p&gt;&#xA;" OwnerUserId="15088" LastActivityDate="2019-06-16T02:25:41.340" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14721" PostTypeId="2" ParentId="14710" CreationDate="2019-06-16T12:16:29.233" Score="2" Body="&lt;p&gt;One definitive answer comes from the National Electric Code Section 810, which requires that both the coax &lt;strong&gt;&lt;em&gt;and&lt;/em&gt;&lt;/strong&gt; the mast itself be grounded.  However, in my experience, the vast majority of people do not bother.&lt;/p&gt;&#xA;" OwnerUserId="15087" LastActivityDate="2019-06-16T12:16:29.233" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14722" PostTypeId="2" ParentId="14719" CreationDate="2019-06-16T12:36:36.247" Score="1" Body="&lt;p&gt;Thanks for joining us on Ham.SE! Insulation on wires will affect performance if they are part of the antenna's system of resonance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just as with coaxial cable, adding insulation to a wire decreases the speed at which electromagnetic effects propagate:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\lambda=\frac{vc}{f}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$v$&lt;/span&gt; is the velocity factor of the insulation and is less than or equal to 1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get an idea of the effect of the two insulating media you cited, I simulated dipole antennas in NEC 2. With no insulation, the resonant frequency of a dipole in free space was 14.16 MHz. With the thin THHN insulation, the resonant frequency dropped to 14.08 MHz, a relatively modest but measurable decrease. With the thicker Prestolite insulation, the resonant frequency dropped to 13.36 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ratios of the resonant frequencies indicate the amounts by which you should shorten your radials if they are part of a resonant antenna system.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="76" LastEditDate="2019-06-16T15:00:54.823" LastActivityDate="2019-06-16T15:00:54.823" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14724" PostTypeId="2" ParentId="14713" CreationDate="2019-06-16T15:43:50.037" Score="2" Body="&lt;p&gt;It seems as though your configuration might represent something like the &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{2}$&lt;/span&gt; 4:1 coax balun shown in figure 5 on page 18-6 of the ARRL &lt;em&gt;Antenna Book&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/renK4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/renK4.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been unable to see the equivalence, but running your coax feedline through the tubing does result in two coaxial lines: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the center conductor and the inside of the shield of the feedline&lt;/li&gt;&#xA;&lt;li&gt;the outside of the shield of the feedline and the inside of the antenna tubing&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;This means that the feedline jacket and the air-space between the feedline jacket and the inside of the antenna tubing comprise the &quot;dielectric&quot; of the second coaxial line. We can't compute the impedance of this second coaxial line without knowing its dimensions &#xA;and the composition of the jacket material, but it seems as though it would be difficult to control this impedance unless the fit was fairly snug. Since you observe a strong effect on the SWR at the input to the feedling, it's possible that you've hit on a serendipitous combination of variables that produces your desired results, one of which could even be the feedline length back to the SWR meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As long as the resulting signal strength is what you expect, it sounds like you have what you need. Nice work!&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-16T15:43:50.037" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14725" PostTypeId="2" ParentId="14685" CreationDate="2019-06-16T22:19:43.840" Score="2" Body="&lt;p&gt;In addition to earth's curvature, obstacles in the various Fresnel Zones may reduce received signal strength, and hence lower effective range&lt;/p&gt;&#xA;" OwnerUserId="14159" LastActivityDate="2019-06-16T22:19:43.840" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14726" PostTypeId="1" AcceptedAnswerId="14744" CreationDate="2019-06-17T04:06:54.603" Score="2" ViewCount="464" Body="&lt;p&gt;So add inductor coil(loading coil) is to cancel out capacitive reactance to make the antenna electrically longer. But what if a capacitor is placed on the antenna, to make the antenna electrically shorter, would that increase the efficiency antenna due to its increase &lt;em&gt;&quot;radiating length&quot;&lt;/em&gt; ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, what it will like if you add a variable capacitor to a 20m whip, shorten it to match 10m? or even 2m?&lt;/p&gt;&#xA;" OwnerUserId="13362" LastActivityDate="2019-06-19T14:59:19.067" Title="Add capacitor to unload antenna?" Tags="&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14728" PostTypeId="2" ParentId="14726" CreationDate="2019-06-17T11:35:20.780" Score="2" Body="&lt;p&gt;Verticals can use a capacitive hat and/or a loading coil.&#xA;Small loops use a tuning capacitor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;length&quot; is not really correct, that's an oversimplification.  It's more like phase of the complex reactance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You aren't really making it shorter or longer, you're trying to get the complex portion of the reactance to be zero, and either an inductor or a capacitor can do that, but one or the other might be able to do it with a smaller value at a particular location on the antenna.  Some antennas use both in different places.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-06-17T11:35:20.780" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14730" PostTypeId="2" ParentId="14726" CreationDate="2019-06-17T13:55:24.887" Score="2" Body="&lt;p&gt;Fascinating question! I used NEC 2 to assess the gain change of a dipole in free space with capacitive center loading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The quasi-sinusoidal current distribution on a resonant 20 meter dipole produces the expected 2.0dBi maximum gain:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/op1C0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/op1C0.png&quot; alt=&quot;![enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding 10pF capacitors immediately on each side of the feedpoint raises the resonant frequency to 23.6MHz, raises feedpoint impedance to 734&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; and results in a current profile that produces a 1dB maximum gain increase to 3.0dBi:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/megzU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/megzU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impact this has on efficiency will depend on the loss characteristics of the rest of the antenna system.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-17T13:55:24.887" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14731" PostTypeId="1" CreationDate="2019-06-17T15:10:13.273" Score="3" ViewCount="128" Body="&lt;p&gt;I'm part of a small team that runs 3AB with a few Kx3 radios. We've been struggling a bit with logging. First year was all paper and that was messy. Next couple of years one of the guys put together something that runs on RaspPi and the operators use tablets for logging.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe I'm an old dog but I just cannot jump back and forth between a CW contact and a log on a tablet. I can't type quickly on a tablet and I feel like I lose the rhythm. I'd prefer to do it by paper but then we lose the dupe checking. I'm also concerned that we'll lose contacts on the home grown solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I love N1MM but I guess that's out. I think if there were windows laptops that lasted 12-24+ hours on a charge we'd be OK. I can run my old surface pro off a 12v marine battery for days but I guess most laptops can't do this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the question, what do multi-transmitter battery stations do for logging. Has it been successful for you or are you also looking for something better?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73,&#xA;Kev N4TT&lt;/p&gt;&#xA;" OwnerUserId="15097" LastActivityDate="2019-06-17T19:18:48.337" Title="FD Battery Stations... How Do You Log?" Tags="&lt;battery&gt;&lt;logging&gt;&lt;field-day&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14732" PostTypeId="2" ParentId="14731" CreationDate="2019-06-17T15:29:18.280" Score="2" Body="&lt;p&gt;You can get an inverter that will run a 35W, or even a 65W 120V laptop charger from a 12V source for around $25 at any auto parts store.  That won't get you internet, but it will get you all-day operation fairly cheaply.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-06-17T15:29:18.280" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14733" PostTypeId="1" AcceptedAnswerId="14753" CreationDate="2019-06-17T16:08:13.610" Score="1" ViewCount="163" Body="&lt;p&gt;As an Extra class licensee, I should probably know this... I am working on a web application for repeater owners.  I would like to include an estimated coverage area, provided they have entered all of the necessary information (power, DBi/Dbd, antenna gain, feedline loss, etc).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a formula in which I can use that information to estimate a coverage area?&lt;/p&gt;&#xA;" OwnerUserId="313" LastEditorUserId="218" LastEditDate="2019-06-18T15:28:52.567" LastActivityDate="2019-06-21T16:07:50.073" Title="How to plot transmitter coverage area?" Tags="&lt;repeater&gt;&lt;radiation-pattern&gt;&lt;repeater-coverage&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14734" PostTypeId="1" AcceptedAnswerId="14741" CreationDate="2019-06-17T17:59:39.670" Score="2" ViewCount="167" Body="&lt;p&gt;I am trying to intercept signals from a drone remote controller and decode them. Before I can do this I need to demodulate the signals. All I have is radio data from the transmitter's operating frequency. Is there any way for me to tell how the signal is modulated by looking at the radio data or some other source?&lt;/p&gt;&#xA;" OwnerUserId="15099" LastActivityDate="2019-06-18T17:46:47.927" Title="How does one know how a signal has been modulated" Tags="&lt;software-defined-radio&gt;&lt;transmitter&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14735" PostTypeId="2" ParentId="14731" CreationDate="2019-06-17T18:27:02.260" Score="0" Body="&lt;p&gt;Personally I'd go with an inverter to power a laptop running N1MM Logger.  But there's also the way that contesters did it for decades before computer logging was practical, and continue to do it when needed: the paper dupe sheet.  Below is an example from K4CHE.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The basic idea is that there is a sheet for every band/mode combination, such as 40m SSB.  When a contact is logged, the data is written on a regular log sheet, but the call sign is also written on the dupe sheet.  The dupe sheet has a grid of boxes.  To look up which box to write the call sign in, pick the row corresponding to the number in the call sign, and pick the row corresponding to the first letter of the suffix.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When a call sign is heard on the air, the call sign is quickly searched for on the dupe sheet: if found, you know that station has already been worked.  It's almost as fast as computer logging.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL has published a &lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2019/2018-Field-Day-2-page-dupesheet.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;blank dupe sheet for Field Day&lt;/a&gt; that you can print out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YN7fL.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YN7fL.jpg&quot; alt=&quot;paper dupe sheet example&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-06-17T18:27:02.260" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14737" PostTypeId="2" ParentId="14731" CreationDate="2019-06-17T19:18:48.337" Score="1" Body="&lt;p&gt;I built a voltage booster using a LT1270A for this purpose: &lt;a href=&quot;https://www.qsl.net/ve3lny/booster.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.qsl.net/ve3lny/booster.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15100" LastActivityDate="2019-06-17T19:18:48.337" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14738" PostTypeId="2" ParentId="14713" CreationDate="2019-06-17T21:05:25.547" Score="2" Body="&lt;p&gt;Running the coax through the folded dipole is one good way of feeding it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Advantages over the more traditional 1/2 wave coax balun:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;No balun required - unbalanced coax all the way to the feedpoint, with guaranteed symmetrical excitation&lt;/li&gt;&#xA;&lt;li&gt;Easier to waterproof the feed, as the connections are inside, and you can heatshrink over the feedpoint&lt;/li&gt;&#xA;&lt;li&gt;Only one side of the dipole touches anything, the other just hangs open&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Disadvantages:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Matching network may be less broadband than the 1/2 wave feed&lt;/li&gt;&#xA;&lt;li&gt;Manufacturing process is a little fiddly&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;To answer your questions directly:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Yes you can feed a folded dipole by passing the coax through the tube&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It doesn't really create any impedance transformation&lt;br&gt;&#xA;(but it does take care of the balancing that's otherwise required)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Your measured impedance seems suspiciously good - as you describe it I would expect you to find a 4:1 VSWR.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Let me draw a few diagrams&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) This is the case I believe you are describing:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/De2p1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/De2p1.png&quot; alt=&quot;coax feed no matching&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;The coax is hidden entirely inside the pipe, so it has the minimum effect on the patterns, and no balun is required to feed the balanced antenna from the unbalanced input. The coax should see the full 200-300 ohm impedance of the folded dipole, so a bad match without further work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) One of these probably describes what you did when you say&lt;br&gt;&#xA;&lt;em&gt;&quot;When I connect the coax to the folded dipole terminals directly I get an SWR of around 8:1&quot;&lt;/em&gt;:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/8wfIF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8wfIF.png&quot; alt=&quot;don&amp;#39;t do this&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/DOHZM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DOHZM.png&quot; alt=&quot;and definitely not this&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;You shouldn't really connect the coax like this, it's not even worth measuring. The effect of the feedline is so profound, especially on the higher impedance of the folded dipole, that you won't learn anything about the dipole impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) I recommend something like this:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/OHHwV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OHHwV.png&quot; alt=&quot;working folded dipole coax feeed&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;With the coax run through the pipe, the required balun action is taken care of.&lt;br&gt;&#xA;Some impedance transformation is required. In this drawing I've shown a piece of 100 Ohm cable, 1/4 wave long, when I built some of these I used a small PCB across the feed gap, which makes the connections more robust and takes care of the 100 Ohm line. You could also use an actual 4:1 Unun transformer, or even an LC network, though that will be quite narrow band and spoil the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see a photo of a commercial dipole fed &quot;through the pipe&quot; &lt;a href=&quot;https://www.telewave.com/product/ant50d-folded-dipole-antenna-45-54-mhz/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; (not mine!).&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-06-17T21:05:25.547" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="14739" PostTypeId="2" ParentId="14733" CreationDate="2019-06-17T21:46:49.513" Score="2" Body="&lt;p&gt;There is a web application already:&#xA;&lt;a href=&quot;https://www.ve2dbe.com/rmonline_s.asp&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ve2dbe.com/rmonline_s.asp&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73, Brian, ZL1IE&lt;/p&gt;&#xA;" OwnerUserId="15101" LastActivityDate="2019-06-17T21:46:49.513" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14740" PostTypeId="1" CreationDate="2019-06-18T02:31:37.020" Score="1" ViewCount="282" Body="&lt;p&gt;Textbook colinear vertical antenna designs show coax cable with alternating braid to centre configuration. Commercial whips seem to utilise a single wire as the radiating element with .66 velocity factor phasing shields along the radiator with no other connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does this work? I can copy the design but am intrigued as to the theory behind it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also how do you feed the antenna? A 1/4 wave stub like a j-pole (or something else)? This has to be up in the weather, so simple and robust is better!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd explain this better with diagrams but I don't know how to put up a picture?&lt;/p&gt;&#xA;" OwnerUserId="15084" LastEditorUserId="8717" LastEditDate="2019-06-20T18:31:44.860" LastActivityDate="2019-06-20T18:31:44.860" Title="Colinear Vhf antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vhf&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14741" PostTypeId="2" ParentId="14734" CreationDate="2019-06-18T07:41:30.140" Score="6" Body="&lt;p&gt;Yes, you'll have to look at it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't go into detail about every possible modulation, because there's just too many. But typically, a look at the spectral representation gives you an idea of whether you're dealing with&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;a straightforward single-carrier signal&lt;/li&gt;&#xA;&lt;li&gt;a spread-spectrum signal or&lt;/li&gt;&#xA;&lt;li&gt;a multicarrier signal.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;One place to see some examples is the Signal Identification Wiki's &lt;a href=&quot;https://www.sigidwiki.com/wiki/Database&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;All Identified Signals&quot; database&lt;/a&gt; page, paying attention mostly to the &quot;Modulation&quot; and &quot;Waterfall image&quot; columns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if the spectrum looks nearly like a rectangle, then you're most likely looking at an OFDM multicarrier system. If it's really wide, but not very powerful and typically has slight periodic sidelobes, that'd be typical for a direct-sequence spread-spectrum system. If it looks like a set of sub-100% duty cycle tones, it might be FSK. You'll need to play with the parameters of your spectrum display quite a bit to see that!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, you'd look at the signal autocorrelation statistics to figure out symbol rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, you'd often manually try very hard to correct any frequency offset. There's algorithms to do that, but they are not the same for all modulations. A FLL might be reasonably generic, but it's rather sensitive to noise and hard to parameterize optimally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Armed with that, you can have an attempt at things like trying to come with an eye diagram for I and Q; that can give you an idea of the number of discrete points in constellation space that you'll see. Another good option is to attempt a reasonable guess of symbol timing, based on the maxima of the signal shape in the eye diagram and generate a scatter plot showing the complex values at that point in a complex plane – a constellation plot! Ideally, you could already see the constellation in that, but in reality, noise and frequency error as well as remaining timing error will typically smear and distort that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you can often infer a lot from that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;All points on a circle: PSK or FSK&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;With that, you can apply clever higher-order statistics to get a very good frequency estimate. Correct that frequency, and analyze furhter&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Points with wildly varying amplitude, but not mostly on one or two lines: QAM&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Due to the multiple unknowns, this is very hard to recover other than trying. Try 16QAM, 64QAM; anything higher than that would be very hard to deal with later on.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Points straddling the 0+0j point, mostly looking like a cloud with a Gaussian intensity: sorry, you didn't quite manually synchronize enough. Try again!&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Start with short segments of signal; you'll not have succeeded at completely removing frequency error at this point, so everything will at least slightly rotate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's a very rich amount of knowledge on automated signal classification, mostly dating back to the cold war era. As you can imagine, it's not the easiest to access literature; there's plenty of companies that offer products and services related to classifying modulations; it's a nontrivial business. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One attempt at a half-automated classifier is SbMüller's &lt;a href=&quot;https://github.com/gnuradio/gr-inspector&quot; rel=&quot;nofollow noreferrer&quot;&gt;gr-inspector&lt;/a&gt;, a GNU Radio module using a lot of cool algorithms to take reasonable stabs at estimatimating the modulations and exact positions of transmitters. As you can imagine, it has to focus on a few very specific types of modulation. It does a very good job at estimating OFDM parameters, though!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;So, assume you now know that e.g. this is an OFDM system with 128 carriers, 1/8 symbol length cyclic prefix, Schmidl&amp;amp;Cox synchronization symbols and QPSK on each carrier, and you're able to correctly synchronize to that and receive the symbols.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Great! Now you've got symbols. That means that for any serious system you still have to figure out&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Mapping of symbols to code bits&lt;/li&gt;&#xA;&lt;li&gt;Scrambling/Whitening/Interleaving&lt;/li&gt;&#xA;&lt;li&gt;channel coding (very often: outer and inner coding)&lt;/li&gt;&#xA;&lt;li&gt;frame data structure and&lt;/li&gt;&#xA;&lt;li&gt;potentially cryptography.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So, that's really far from an easy task!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, many very cheap remote controllers for toys simply do idiotically simple and inefficient things like OOK, no interleaving, no whitening, a repetition code, and constant frame structure, meaning that pushing the same thing always results in the same transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not only are the parameters that realistically guessable, but you could just as well deal with this by &lt;em&gt;not&lt;/em&gt; decoding anything but simply linking your RF signal observation directly to the action that caused it via cross-correlation with reference signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have fun!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="1362" LastEditDate="2019-06-18T17:46:47.927" LastActivityDate="2019-06-18T17:46:47.927" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14742" PostTypeId="2" ParentId="1859" CreationDate="2019-06-19T08:58:47.080" Score="1" Body="&lt;p&gt;you may, in principle, use any wire length, foreseen you bring it to resonance with a suitable tuner.&#xA;A simple and versatile QRP tuner circuit was proposed by WB3GCK (&lt;a href=&quot;https://www.qsl.net/wb3gck/tuner.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.qsl.net/wb3gck/tuner.htm&lt;/a&gt;)&#xA;(when rebuilding this circuit, I recommend letting the coil end open, instead of closing it to the variable tap, in order to avoid any shorted induction coil).&#xA;This circuit works for capacitive and inductive load low impedance, as well as for&#xA;high impedance wire antennas. It needs a counterpoise (including the mantle of the&#xA;coax cable, the TX and the operator, hi).&#xA;A 40m long wire is about multiple half wave (i.e. high-impedance) &#xA;on 80m, 40m, 30m, 20m, 17m, 15m, 12m, and 10m&#xA;A 20m long wire is high-impedance on 40m, 20m, 15m and 10m, and low-impedance &#xA;on 80m, 30m, 17m, and 12m&#xA;A 27m long wire is of medium impedance on all bands.&#xA;A single strand of insulated outdoor telephone wire (comprising 3 copper and &#xA;3 steel wires in a double-layer insulation) makes a superb QRP antenna, &#xA;because it can be tended free-hanging over trees and rocks. &#xA;73 de Edgar, HB9TRU&lt;/p&gt;&#xA;" OwnerUserId="15106" LastActivityDate="2019-06-19T08:58:47.080" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14743" PostTypeId="2" ParentId="12389" CreationDate="2019-06-19T13:22:59.650" Score="3" Body="&lt;p&gt;Half wave end-fed has appr.  5k impedance, you need a 49:1 transformer to match 50Ohms cable.&#xA;As the impedance of the antenna is very high a small counterpoise of only 1/10 of a wavelenght does the trick. Do use some form of coax-choke at the antenna-end of your coax to stop RF current flowing in the coax-outside. Usually some 10 turns of coax with a diameter of say 5&quot; will be sufficient.&lt;/p&gt;&#xA;" OwnerUserId="15108" LastActivityDate="2019-06-19T13:22:59.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14744" PostTypeId="2" ParentId="14726" CreationDate="2019-06-19T14:59:19.067" Score="2" Body="&lt;p&gt;Changing the length of a dipole &lt;a href=&quot;https://ham.stackexchange.com/q/9021/218&quot;&gt;changes the radiation pattern&lt;/a&gt;. As the dipole gets much longer than 0.5 wavelength, the radiation pattern grows multiple lobes. Here's an animation from 0.1 to 5 wavelengths:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/T0LEv.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/T0LEv.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the &lt;em&gt;efficiency&lt;/em&gt; of the antenna isn't just a question of length. Consider conservation of energy: if energy isn't going into some sort of loss (usually being converted to heat) then it must be radiated. A dipole that is far from a resonant length (too long &lt;em&gt;or&lt;/em&gt; to short) has a very reactive feedpoint impedance, which must necessarily be accompanied by some sort of matching network. This matching network will have loss, to the detriment of the overall efficiency of the antenna system.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-06-19T14:59:19.067" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14746" PostTypeId="1" CreationDate="2019-06-19T15:41:16.880" Score="3" ViewCount="180" Body="&lt;p&gt;I was reading this &lt;a href=&quot;https://upcommons.upc.edu/bitstream/handle/2117/121278/LAWP2857856-revised.pdf?sequence=1&quot; rel=&quot;nofollow noreferrer&quot;&gt;paper&lt;/a&gt; and I found it very interesting and the following question came up,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the main applications (what is used for) 100 GHz band? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I couldn't find any reference on what is used nowadays.&lt;/p&gt;&#xA;" OwnerUserId="15096" LastEditorUserId="8717" LastEditDate="2019-06-19T15:59:11.077" LastActivityDate="2019-06-21T15:50:39.587" Title="Applications for 100 GHz band?" Tags="&lt;antenna&gt;&lt;frequency&gt;&lt;microwave&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14747" PostTypeId="2" ParentId="14746" CreationDate="2019-06-19T17:31:19.340" Score="2" Body="&lt;p&gt;A frequency of 100 GHz is equivalent to a 3 mm wavelength; these &quot;millimeter waves&quot; have been used for decades in airborne radars.  The short wavelength allows a narrow beam and excellent gain from a dish that can fit inside the nose of a fighter aircraft, allowing a forward-looking radar with mechanical sweep to be used without disturbing the aerodynamics of a potentially supersonic airplane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More modern radars use phased arrays (eliminating the need to physically move a dish, replacing it with an array of small flat panels and beam focusing and steering done by precisely delaying the signal to various portions of the array), but the same size limitations apply; shorter wavelengths allow smaller arrays to give required gain and beam spread for the application.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-06-19T17:31:19.340" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14748" PostTypeId="2" ParentId="14746" CreationDate="2019-06-19T20:41:24.813" Score="4" Body="&lt;p&gt;Aside from what Zeiss Ikon &lt;a href=&quot;https://ham.stackexchange.com/a/14747/4076&quot;&gt;wrote&lt;/a&gt;, these high frequencies are indeed also interesting for communications technology, for very high-rate and typically narrow-range links.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, in cellular mobile communications (&quot;phones&quot;), 5G specifies the &quot;New Radio&quot;, which includes using several mmWave bands, the highest among them spanning 37 – 40 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The motivation is actually a bit complex, but mostly&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The higher your band, the easier it is to get a large bandwidth (you can't get 50 MHz of bandwidth around 144 MHz; it's easy to get 500 MHz in mmWave bands, simply because there's &quot;more spectrum there&quot;)&lt;/li&gt;&#xA;&lt;li&gt;The higher your frequency, the shorter the wavelength, the smaller your antenna, the more antennas you can integrate in a device of a fixed size. This results in the feasibility of &lt;em&gt;massive MIMO&lt;/em&gt; techniques that basically use very many antennas per device, mathematically arguing that when you combine enough of the signals of these antennas, it's almost certain you get a few good usable transmissions.&lt;/li&gt;&#xA;&lt;li&gt;At mmWave frequencies, antennas are so small that they can actually be integrated into IC packages – and that's very important, because for the higher microwave frequencies, building boards that carry these reliably is already very complicated and expensive.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Also, for long range links in space, especially inter-satellite links, going as high as 100 GHz does make sense for exactly Zeiss' reasons: The smaller the bandwidth, the narrower the beam an antenna (array) of fixed size can achieve. The math works out that this effect is exactly the same in magnitude as the increase of free space path loss (if you keep antenna system size constant and just change wavelength). If you have a dynamic constellation of satellites, you'll need digitally steerable antennas – and then, going for higher frequencies simply gives you the freedom to do exactly that.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-06-20T13:06:47.100" LastActivityDate="2019-06-20T13:06:47.100" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14749" PostTypeId="2" ParentId="14740" CreationDate="2019-06-20T11:00:33.297" Score="5" Body="&lt;p&gt;The ideal dipole antenna is roughly a half wave long.&#xA;A monopole is half of that, with the other half in the conductive surface below the monopole.  The colinear antenna is a series of stacked and phased half wave dipoles with a quarter wave section at the top and bottom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your commercial whip is only a half wavelength long or less, then it is just a monopole whip, and not a colinear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to how the colinear works...  consider it as an antenna array rather than a single antenna.  Each antenna is separately fed, and it is phased so that the radiation emitted from the antenna is in phase with the radiation from the other antennas, causing constructive interference in the desired radiation direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several styles of colinear antennas.   A common commercial version uses folded dipoles (that look like flat/oval loops) mounted along a vertical rod.  The version you describe combines the phasing harness (the coax) with the antenna elements.  The shield and center conductor are swapped at half wavelength intervals to create the correct phase between each section.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Either way, the effect of this is to take the toroidal radiation pattern of the dipole and flatten it, to give decreased gain at higher elevation angles and increased gain horizontally.  Sometimes (typically for colinears on towers) the length of the phasing is adjusted to cause the flattened toroid to &quot;droop&quot; to make it better fit the curvature of the Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the advantages of using an array of antennas is that the radiation pattern can be &quot;steered&quot; by adjusting the phase between elements which shifts where the constructive and destructive interference occurs.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-06-20T11:00:33.297" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14751" PostTypeId="2" ParentId="14710" CreationDate="2019-06-21T05:28:58.130" Score="4" Body="&lt;p&gt;You should definitely ground the antenna to your earth system with a heavy conductor. The coax alone will not cope well with the lightning current. By carrying a share of the current, the earth wire also reduce the voltage transferred to the coaxial cable inner conductor, and hence the load on the lightning protection device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Better would be a metal cable tray, continuously bonded, carrying the coax and earth cable, and connected to the antenna and earth system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Grounding your shack at a single point sounds good. The lightning protection device is great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the LPD does only two things - it provides a solid ground point for the coax shield, and it prevents large differential voltage in the coax. It doesn't scare away lightning, and only makes a difference if it's part of a well designed grounding system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that &lt;em&gt;all&lt;/em&gt; cables entering the shack must be protected - coax you have taken care of, what about power? It should also go through a lightning arrestor at the single earth point. Otherwise a strike on a nearby utility pole could lift the mains up by a few thousand volts, which will travel through your shack to get to your nice earth.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-06-21T06:09:44.043" LastActivityDate="2019-06-21T06:09:44.043" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14752" PostTypeId="2" ParentId="14746" CreationDate="2019-06-21T15:50:39.587" Score="0" Body="&lt;p&gt;Emissions around this wavelength are used by &lt;a href=&quot;https://en.wikipedia.org/wiki/Millimeter_wave_scanner&quot; rel=&quot;nofollow noreferrer&quot;&gt;millimeter wave scanners&lt;/a&gt;, of the sort you may have encountered in airport security.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radiation in this band is useful because it penetrates clothing quite well, but skin not so much. This means the scanner can see contraband hidden under clothing.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-06-21T15:50:39.587" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14753" PostTypeId="2" ParentId="14733" CreationDate="2019-06-21T16:07:50.073" Score="2" Body="&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Longley%E2%80%93Rice_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;Longley-Rice model&lt;/a&gt; is a fairly common technique. However it's not a simple formula, and so requires some kind of software to implement. Unfortunately my favorite such tool, &lt;a href=&quot;http://lrcov.crc.ca/main/&quot; rel=&quot;nofollow noreferrer&quot;&gt;CRC CovWeb&lt;/a&gt;, has gone defunct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a more simplistic prediction, you can try making a simple &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt; based on the &lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;Friis transmission equation&lt;/a&gt;, or if you want to get a little more sophisticated, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Two-ray_ground-reflection_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;two-ray model&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should additionally consider the &lt;a href=&quot;https://en.wikipedia.org/wiki/Line-of-sight_propagation#Radio_horizon&quot; rel=&quot;nofollow noreferrer&quot;&gt;radio horizon&lt;/a&gt;, and you may perform some simple math to determine how far your antenna can &quot;see&quot; based on an idealized spherical Earth. Or you might use some source of topographic information like &lt;a href=&quot;https://www.heywhatsthat.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;heywhatsthat&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your estimated coverage area is then all the areas that are close enough that free space path loss hasn't attenuated the signal beyond usability, and where terrain isn't in the way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will typically find even for modest powers around 5W, terrain and antenna height are most often the limiting factor. Higher powers and antenna gains are typically only useful if the station can be well placed, such as on a large tower, building, or mountaintop.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-06-21T16:07:50.073" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14754" PostTypeId="1" AcceptedAnswerId="14755" CreationDate="2019-06-21T17:01:07.510" Score="6" ViewCount="120" Body="&lt;p&gt;I'm planning to attend Field Day this weekend, and the forecast calls for thunderstorms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can picture a serious issue with a bunch of temporary antennas set up in an open area when a thunderstorm sweeps through.  This seems to have the potential for multiple fatalities (it has happened under conditions without the lightning attractants, such as soccer games).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do field operators protect themselves (and secondarily their rigs) from lightning when a squall or storm passes over?  &lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-06-21T17:07:15.570" LastActivityDate="2019-06-21T19:36:11.100" Title="How do Field Day participants protect from lightning?" Tags="&lt;lightning&gt;&lt;field-day&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="14755" PostTypeId="2" ParentId="14754" CreationDate="2019-06-21T19:28:32.507" Score="6" Body="&lt;p&gt;They are not intending to keep operating in spite of a thunderstorm in the vicinity, are they? That would be very dangerous and foolish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well in advance of the storm, the group must unplug the equipment, antennas, and power and get into a suitable building or vehicles until the storm is well past.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There may be some good information &lt;a href=&quot;https://ham.stackexchange.com/search?q=Disconnect+lightning+&quot;&gt;in this search&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-06-21T19:36:11.100" LastActivityDate="2019-06-21T19:36:11.100" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14757" PostTypeId="1" AcceptedAnswerId="14758" CreationDate="2019-06-22T22:08:02.287" Score="6" ViewCount="488" Body="&lt;p&gt;I'm listening to the 40m band during Field Day and I keep hearing things like &quot;You are THREE ALPHA in Virginia,&quot; or &quot;do you hold me ONE ALPHA in Eastern Pennsylvania?&quot;, or &quot;you are TWO ALPHA Maine.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have no idea what they're talking about, can someone please explain?&lt;/p&gt;&#xA;" OwnerUserId="9450" LastEditorUserId="76" LastEditDate="2019-06-22T23:31:58.347" LastActivityDate="2019-06-22T23:46:25.340" Title="What does &quot;THREE ALPHA in Virginia&quot; mean?" Tags="&lt;procedure&gt;&lt;contest&gt;&lt;phone&gt;&lt;field-day&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14758" PostTypeId="2" ParentId="14757" CreationDate="2019-06-22T23:46:25.340" Score="10" Body="&lt;p&gt;First, some background on general amateur radio procedure:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Field Day &quot;is not a contest&quot;, but acts a lot like one. In any contest contact, the &quot;&lt;strong&gt;exchange&lt;/strong&gt;&quot; is whatever information is communicated, beyond the call signs of the participants and the procedure of making and confirming the contact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In many contests, but not Field Day, the exchange is a &lt;strong&gt;signal report&lt;/strong&gt; — telling the other station how well it is being received by the station sending the report. Standard signal reports have 2 digits, or 3 for CW; the best possible report is &quot;59&quot; or &quot;599&quot;, respectively.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is where the phrase &quot;You are&quot;, which is appropriate for a signal report but rather backwards in the case of Field Day, comes from — contest operators sticking to their practiced phrases.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2019/1_6-2019%20Rules.pdf&quot; rel=&quot;noreferrer&quot;&gt;In Field Day&lt;/a&gt;, the exchange consists of two pieces of information (per rule 5):&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The operating class (entry category) of the station transmitting, which consists of:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the number of simultaneous transmissions the station is using (essentially the number of radios/operators), and&lt;/li&gt;&#xA;&lt;li&gt;a letter denoting the type of station as defined in the rules.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For example, &quot;3A&quot; (&quot;three alpha&quot;) means that the station has three radios (and probably three or more operators) and that it was set up specifically for Field Day (&quot;must be located in places that are not regular station locations and must not use facilities installed for permanent station use&quot;).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The &quot;ARRL / RAC section&quot; in which the station transmitting is located. &lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2019/2019%20Section%20List.pdf&quot; rel=&quot;noreferrer&quot;&gt;Here is a list of them&lt;/a&gt;; they are generally no bigger than a US state but in many cases subdivide a state. The section is given either as its full name or its abbreviation in the list.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your examples, Virginia is one section, but Pennsylvania has two, hence specifying &quot;Eastern Pennsylvania&quot;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-06-22T23:46:25.340" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14760" PostTypeId="1" CreationDate="2019-06-23T09:36:51.487" Score="3" ViewCount="7688" Body="&lt;p&gt;Can I replace my old 50 Ω coax with RG6? It's cheaper and less loss at VHF/UHF. I would match by L/2 multiples of coax to repeat input and output impedance or L/C matching networks at each end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this a viable alternative to expensive 50 Ω coax and what problems could I have? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So far I have used this on UHF and found a 6dB improvement in received signal.&lt;/p&gt;&#xA;" OwnerUserId="15084" LastEditorUserId="76" LastEditDate="2019-06-23T16:20:42.630" LastActivityDate="2021-01-06T07:58:49.700" Title="Using 75 Ω instead of 50 Ω coax feed" Tags="&lt;coaxial-cable&gt;&lt;antenna-system&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14761" PostTypeId="2" ParentId="14760" CreationDate="2019-06-23T17:24:09.123" Score="3" Body="&lt;p&gt;Many, many hams use 75Ω coax. I have for decades. All of my outdoor coax is RG-6 or RG-11. In the past I have used larger 75Ω CATV hardline, which has even lower loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many hams just accept the 1.5:1 VSWR caused by the small impedance difference. I fed a 50Ω 2m array with 75Ω coax using a very simple matching arrangement, using two short pieces of coax at the feedpoint; one 50Ω and one 75Ω. (I can't think what it is called right now).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, the feedpoint impedance of a center-fed dipole is 75Ω! It is only 50Ω at one low height. Feed a resonant dipole with 50Ω coax, and you actually have a small mismatch!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power handing capability of RG-6 is almost identical to RG-213. And even at the legal limit, the voltage is still low enough that flashover will not occur between the center conductor and the shield even with a mismatch.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The thin copper plating on the RG6 cable centre conductor may be a problem at HF but for UHF it should be ok&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;K4KYV, myself, and others on the Topband reflector measured it. The consensus was that at 80 meters it made no difference, and at 160m it made a little difference but it was still insignificant. &#xA;&lt;hr&gt;&#xA;This &lt;em&gt;may&lt;/em&gt; be a duplicate question. In any case &lt;a href=&quot;https://ham.stackexchange.com/search?q=75+ohm+coax&quot;&gt;check out this search&lt;/a&gt; and see if you can find more answers there.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-06-25T16:54:05.070" LastActivityDate="2019-06-25T16:54:05.070" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="14762" PostTypeId="2" ParentId="14760" CreationDate="2019-06-24T20:13:38.330" Score="0" Body="&lt;p&gt;Jerry Sevick, W2FMI, described the use of multifilar-wound toroid cores to perform 1.56:1 transformations over wide HF frequency ranges. Given the vagaries of antennas as loads, this should provide a very close match between 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; and 75&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; coax - as long as the impedance at the input to the 75&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; coax is reasonably close to 75&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Page 65 of &lt;a href=&quot;https://archive.org/details/UnderstandingBuildingAndUsingBalunsAndUnuns/page/n74&quot; rel=&quot;nofollow noreferrer&quot;&gt;Understanding and Using Baluns and Ununs (2003)&lt;/a&gt; shows the implementation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rvSMe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rvSMe.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As shown in the photograph, four (4) quintafilar turns of thermaleze-coated wire are wound on a 1.4-in OD ferrite toroid core of &lt;span class=&quot;math-container&quot;&gt;$\mu_r=250$&lt;/span&gt; (e.g., &lt;a href=&quot;https://www.mouser.com/ProductDetail/Fair-Rite/5952020801?qs=%2Fha2pyFaduhcyrq4g9l206nL729Jk0IVAs01yKDR66xanGLz%252BsEtVg%3D%3D&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fair-Rite 5952020801&lt;/a&gt;). Winding 7-8 is #14; the other four windings are #16.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pcrJi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pcrJi.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The larger 1:1 Guanella balun in the upper portion of the photograph is not needed in unun applications, such as when matching a 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; system to 75&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; feedlines. Sevick measured this transformer to be essentially flat from 1.5MHz to 40MHz.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-24T20:13:38.330" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14763" PostTypeId="1" AcceptedAnswerId="14777" CreationDate="2019-06-24T22:08:01.893" Score="5" ViewCount="147" Body="&lt;p&gt;Is the ARRL Field Day a contest, or is it not a contest?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Kindly explain the reasoning behind your answer.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A non-ham could not tell the difference.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-06-27T20:17:32.277" LastActivityDate="2019-06-27T20:17:32.277" Title="Is Field Day a contest?" Tags="&lt;united-states&gt;&lt;contest&gt;&lt;field-day&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14764" PostTypeId="2" ParentId="14763" CreationDate="2019-06-24T23:04:02.290" Score="0" Body="&lt;p&gt;Yes, because score is kept and the rankings get published.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No, because no monetary prize is allowed and enforcement of rules is done by the &quot;contestants&quot; with no real verification.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-06-24T23:04:02.290" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14765" PostTypeId="1" CreationDate="2019-06-24T23:25:49.637" Score="10" ViewCount="196" Body="&lt;p&gt;Why do we have 50, 75, 62 and 92 Ω coaxial cable, to name a few? Why not just one standardised cable? Is there some technical reason or did Mr. Coax and Mr. Cable have a disagreement, like Mr. Tesla and Mr. Edison?&lt;/p&gt;&#xA;" OwnerUserId="15084" LastEditorUserId="76" LastEditDate="2019-06-25T00:13:09.577" LastActivityDate="2019-06-27T16:49:36.317" Title="Why are there so many coaxial cable impedances?" Tags="&lt;coaxial-cable&gt;&lt;impedance&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14766" PostTypeId="2" ParentId="14763" CreationDate="2019-06-25T01:03:26.493" Score="5" Body="&lt;p&gt;No, Field Day is not a contest, because stations do not submit logs for checking to validate the claimed scores. No plaques or other commemorations of competitive achievement are sponsored or awarded by ARRL, the sanctioning organization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That does not stop participants from &lt;em&gt;behaving&lt;/em&gt; as though Field Day is a contest. Inasmuch as a primary goal of the activity is to exercise hams' ability to communicate effectively under field conditions, the number of contacts made on various bands using various modes over a 24-hour period is a useful surrogate measurement of performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Experienced Field Day participants often develop specialized skills. These can include: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Planning: equipment, antennas, power, shelter, security, safety, RFI and powerline noise abatement, hospitality&lt;/li&gt;&#xA;&lt;li&gt;Construction and teardown: antenna supports, electrical distribution and communication networks, station habitats, chuck wagon&lt;/li&gt;&#xA;&lt;li&gt;Operation: band, mode and time-of-day specialties&lt;/li&gt;&#xA;&lt;li&gt;Recruiting, mentoring and organizing individuals into effective teams&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;While many Field Day operations may fall into broad categories, no two Field Day operations are identical, depending as they must on the skills of the individuals that are available to participate in any given year. It is this dynamic nature of the challenge that keeps so many of us coming back year after year.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-25T01:03:26.493" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14767" PostTypeId="2" ParentId="14765" CreationDate="2019-06-25T02:04:05.890" Score="5" Body="&lt;p&gt;Glad to see this question posted! This has a really interesting answer which I'm not qualified to write a comprehensive answer to, so here's a rather unsupported answer to help you along until someone writes a better one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several reasons why coaxial cable is used in several different impedances.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;On basic principles: if a device on one end of the cable inherently has a specific impedance, then using a cable matched to that impedance means you don't need a matching network at least at that end.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Different choices of impedance result in different characteristics of the cable, given the available choices of material and construction techniques.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is said (I don't have a citation) that 50 Ω was chosen as a compromise between power handling capability (lower impedance would be better) and attenuation per length (higher impedance would be better). In high-power applications, 50 Ω is used to allow use of the smallest cable possible for the power (minimizing cost and bulk).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if you are not intending to transfer significant power, i.e. your application is very low-power or receive-only, then you only care about attenuation and so you choose the higher 75 Ω to optimize for least attenuation.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Even if there was one best line impedance to use, you would still want to have available cables of other impedances. This is because RF circuits that use transmission lines as impedance transformers don't need any &lt;em&gt;specific&lt;/em&gt; impedance, but they do need to have an impedance that is &lt;em&gt;different than the impedance of the incoming/outgoing lines&lt;/em&gt;. For example, in this Wilkinson power divider implemented using coax:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/File:Wilkinson_divider.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dvVhJ.png&quot; alt=&quot;Wilkinson power divider&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;(Image credit: &lt;a href=&quot;http://en.wikipedia.org/wiki/File:Wilkinson_divider.png&quot; rel=&quot;noreferrer&quot;&gt;SpinningSpark on Wikimedia Commons&lt;/a&gt;)&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your lines are 50 Ω then you need 71 Ω in the divider. If your lines are &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt; Ω then you need &lt;span class=&quot;math-container&quot;&gt;$\sqrt{2}x$&lt;/span&gt; Ω in the divider. No single type of coax can do this.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-06-25T02:04:05.890" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14772" PostTypeId="1" AcceptedAnswerId="14774" CreationDate="2019-06-25T14:38:20.433" Score="1" ViewCount="369" Body="&lt;p&gt;Not being so fluent in RF, I decided to ask here if my current approach seems doable or how one would try to achieve something like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm doing research and deciding on an approach for my proto-board, to understand if and how combining signals from three different antennas into single coax and then splitting(filtering) them at the receiving end for different radio modules would even work (and for transmitting as well, so bidirectional).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;More precisely - let's say I have antennas for 1) GPS, 2) 2G/3G and 3) Bluetooth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the frequency bands for them are rather separated, based on the antennas I have: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Cellular: 800 - 960MHz / 1700 - 2170MHz&lt;/li&gt;&#xA;&lt;li&gt;GPS: 1560 - 1590 MHz (1575MHz center frequency).&lt;/li&gt;&#xA;&lt;li&gt;Bluetooth: 2400 - 2500MHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;so &lt;strong&gt;to me it seems it would be possible to join these into single coax,&lt;/strong&gt; without greatly disturbing the signals (they are not in the same bands thus interference should be minimal - especially with filtering). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This where my discussion on different approaches begin, so I currently plan to test two things:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;a)&lt;/strong&gt; Bluntly join antenna traces together into single coax after some impedance transforming and filtering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;b)&lt;/strong&gt; Use a passive combiner/splitter to join the antenna traces together - in hopes for better isolation when signal is transmitted the other way back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the receiving end I would mirror these blocks, before any ANT input on the chips.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/1j4s8.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f1j4s8.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SO basically:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;1) Does just joining antenna lines like that make sense or there's smth completely wrong with this idea?&lt;/strong&gt; (based on the proposed protocols)&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;2) Would using combiner/splitter make this approach more feasible ?&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;3) I'm completely off and I should try smth else&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In any way I believe I need filtering for each of those bands for sure - in order to get better SNR on my receiving end.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;GSM filtering is probably more complicated since there's two bands to deal with. That's why it's red on the schematic.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="15139" LastEditorUserId="4665" LastEditDate="2020-11-04T16:30:20.193" LastActivityDate="2020-11-04T16:30:20.193" Title="Combining/splitting three different RF signals" Tags="&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14774" PostTypeId="2" ParentId="14772" CreationDate="2019-06-25T15:14:25.467" Score="5" Body="&lt;p&gt;You should use a four-port multiplexer, more commonly known as a &lt;em&gt;&lt;a href=&quot;https://www.microwaves101.com/encyclopedias/multiplexers&quot; rel=&quot;noreferrer&quot;&gt;triplexer&lt;/a&gt;&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xtiyj.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xtiyj.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As shown in the diagram, a triplexer is a bidirectional device comprising three filters that separate (or combine) the signals from the input (or output) port into band-limited signals at the three output (or input) ports. A properly designed triplexer will present 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; at all four ports across the unit's usable frequency range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An alternative to the lowpass - bandpass - highpass architecture is to cascade two diplexers, each of which comprises a lowpass and a highpass filter, to produce the desired signal separation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The specifics of your solution will depend on the required power handling capability and implementation technology (e.g., lumped elements, microstrip, cavity, etc.) An internet search turns up commercial sources for these parts. If you wish to design your own microwave triplexer, you can download &lt;em&gt;Microwave Filters, Impedance-Matching Networks, and Coupling Structures&lt;/em&gt; by Matthaei, Young and Jones (&lt;a href=&quot;https://www.microwaves101.com/uploads/MYJ-part-1.pdf&quot; rel=&quot;noreferrer&quot;&gt;part 1&lt;/a&gt; and &lt;a href=&quot;https://www.microwaves101.com/uploads/MYJ-part-2.pdf&quot; rel=&quot;noreferrer&quot;&gt;part 2&lt;/a&gt;) from the Microwaves101 web site.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-25T15:14:25.467" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14775" PostTypeId="2" ParentId="14760" CreationDate="2019-06-25T22:34:19.860" Score="5" Body="&lt;p&gt;Sure, you can use 75 ohm coax instead of 50 ohm. In some cases (such as feeding a dipole), 75 ohm coax may be a better match to the load than 50 ohm. In other cases (such as feeding a vertical), it may be a worse match.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may not even need to do additional matching. A 75 ohm load on a transmitter designed for a 50 ohm load is only a 1.5:1 SWR, which isn't that bad.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do however keep in mind that in many cases 75 ohm coax is cheap not because 75 ohm coax is inherently cheaper, but because it's just plain &lt;em&gt;cheap coax&lt;/em&gt;. The common application of CATV means big-box stores are quick to carry cheap 75 ohm coax because their customers care primarily about cost, and for a short CATV run, the high loss and poor isolation of a cheap cable may not be especially critical or noticed by a typical consumer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a transmitting radio application, the consequences may not be so benign. It is usually cheaper to buy better coax than it is to buy a bigger amplifier. And a directional antenna in a receive application fed with coax with poor isolation may pick up enough external noise to negate the benefits of the antenna directivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;75 ohm coax will work, and you may be able to find good quality 75 ohm coax at a favorable price. But do try to make an informed decision.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-06-25T22:34:19.860" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14776" PostTypeId="1" AcceptedAnswerId="14781" CreationDate="2019-06-25T22:54:09.167" Score="2" ViewCount="86" Body="&lt;p&gt;A new vanity callsign will be granted to me (currently in pending level 2 stage). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I transfer my current soon to be cancelled callsign (vanity) to a club which I am trustee without waiting the two years for the club to apply for it?&lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="4665" LastEditDate="2019-06-25T23:23:57.577" LastActivityDate="2019-06-26T04:57:45.310" Title="Transferring old callsign to a club?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14777" PostTypeId="2" ParentId="14763" CreationDate="2019-06-25T23:11:54.237" Score="1" Body="&lt;p&gt;Based on &lt;a href=&quot;https://www.qsl.net/ta1dx/afet/fieldnedir.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this affiliated club document&lt;/a&gt;, yes, Field Day is a contest.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Field Day is a competitive event sponsored by the American Radio Relay&#xA;  League (ARRL). The objective is for participating individuals and&#xA;  organizations to:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;    Go to a location where there is normally no communications capability.&#xA;    Create one.&#xA;    Contact as many stations as possible during the operating period.&#xA;    Tear the site down, and pack it away for a real emergency.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The document goes on to discuss techniques for efficiently maximizing number of contacts by exchanging the minimum required information (call sign, station type, section) and &quot;moving on.&quot;  This document doesn't talk about scoring, but I've encountered many references to &quot;bonus points&quot; for this and that (for instance, if I were to operate for the club, my recent license would be worth extra points for each QSO; the visit we received from an ARRL official was, I was told, worth 100 bonus points).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's a competitive event, with scoring, it's a contest.  No awards, no plaques, etc. just make it a &quot;bragging rights&quot; contest.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-06-25T23:11:54.237" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14778" PostTypeId="1" CreationDate="2019-06-26T02:54:44.653" Score="1" ViewCount="49" Body="&lt;p&gt;Baofeng 888s, programed with chirp, worked good but maybe at change channels during pushing moni button or something else (I don't know), don't work. I tried to change side key options by programming, but don't effect. &#xA;When push it, no reflection. Is the side key burnt?  &lt;/p&gt;&#xA;" OwnerUserId="15146" LastActivityDate="2019-06-26T02:54:44.653" Title="Baofeng 888s sidekey (moni) don't work" Tags="&lt;baofeng&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14780" PostTypeId="2" ParentId="12752" CreationDate="2019-06-26T03:25:12.057" Score="0" Body="&lt;p&gt;When you want to load data to baofeng I think you must adjust both channel buttons (for two devices) on the same (first device on ch.1 and connect to pc and next device on ch.1). &lt;/p&gt;&#xA;" OwnerUserId="15146" LastActivityDate="2019-06-26T03:25:12.057" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14781" PostTypeId="2" ParentId="14776" CreationDate="2019-06-26T04:57:45.310" Score="4" Body="&lt;p&gt;No. Per the &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/amateur-radio-service/amateur-vanity-request-types-3&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC vanity callsign FAQs&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Q: Can I request that the call sign I vacated be assigned to my new club station under the former holder provision?&lt;/p&gt;&#xA;&lt;p&gt;A: No. Your club station was not the holder of the call sign you vacated. After two years, your club station license trustee might apply for it under the request-by-list provision.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-06-26T04:57:45.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14782" PostTypeId="1" AcceptedAnswerId="14786" CreationDate="2019-06-26T08:15:22.213" Score="1" ViewCount="49" Body="&lt;p&gt;&lt;strong&gt;Question&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does a band allocation to &quot;Amateur&quot;, &quot;Fixed&quot;, and &quot;Mobile&quot; mean that it's for amateur radio use by fixed and mobile services, or does it mean that all these services are separate but equal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it is the latter case, what kind of services fall under &quot;Fixed&quot; and &quot;Mobile&quot;, because it sounds very broad.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Background&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my country's &lt;a href=&quot;https://www.pta.gov.pk/media/Pakistan_Table_of_Frequency_Allocations.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;frequency allocation document&lt;/a&gt;, it has the following table for the amateur radio 2M band:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;|---------------------------------------------------------------------------|&#xA;|                         Allocation to Services                            |&#xA;|-----------|-----------------------------------|---------------------------|&#xA;| Frequency | ITU - Region 3                    | Pakistan’s Allocations    |&#xA;|-----------|-----------------------------------|---------------------------|&#xA;| 144 – 146 | AMATEUR                           | AMATEUR                   |&#xA;|           | AMATEUR-SATELLITE                 | AMATEUR-SATELLITE         |&#xA;|           | 5.216                             |                           |&#xA;|-----------|-----------------------------------|---------------------------|&#xA;| 146 – 148 | AMATEUR                           | AMATEUR                   |&#xA;|           | FIXED                             | FIXED                     |&#xA;|           | MOBILE                            | MOBILE                    |&#xA;|           | 5.217                             |                           |&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The same document contains the following definitions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&quot;Allocation (of a frequency band): Entry in the Table of Frequency Allocations of a given frequency band for the purpose of its use by one or more terrestrial or space Radiocommunication services or the radio astronomy service under specified conditions. This term shall also be applied to the frequency band concerned.&quot; (Page 6)&lt;/li&gt;&#xA;&lt;li&gt;&quot;Fixed service: A radiocommunication service between specified fixed points.&quot; (Page 6)&lt;/li&gt;&#xA;&lt;li&gt;&quot;Mobile service: A radiocommunication service between mobile and land stations, or between mobile stations.&quot; (Page 6)&lt;/li&gt;&#xA;&lt;li&gt;&quot;Amateur service: A radiocommunication service for the purpose of self-training, intercommunication and technical investigations carried out by amateurs, that is, by duly authorized persons interested in radio technique solely with a personal aim and without pecuniary interest.&quot; (Page 8)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;N.B. I could have tagged this as &lt;code&gt;ITU - Region 3&lt;/code&gt;, or &lt;code&gt;Pakistan&lt;/code&gt;, but I believe the question is broader than both these tags.&lt;/p&gt;&#xA;" OwnerUserId="14220" LastActivityDate="2019-06-26T15:23:42.557" Title="Clarification: What are Fixed and Mobile services intended for in frequency allocation documentation?" Tags="&lt;legal&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14783" PostTypeId="1" AcceptedAnswerId="14787" CreationDate="2019-06-26T11:02:58.123" Score="5" ViewCount="1904" Body="&lt;p&gt;I am reading about how radio communication works and I have an unanswered question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We have wideband channels with 25kHz of radio spectrum. The transmitter modulates a signal and sends it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The receiver that captures that particular channel and receives the signal.&#xA;But how does it know to which frequency it has to tune in?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a 25 kHz channel size, so there are so many different frequencies that it could be as the signal is modulated. How does the receiver decide?&lt;/p&gt;&#xA;" OwnerUserId="15147" LastEditorUserId="966" LastEditDate="2019-06-27T15:10:18.463" LastActivityDate="2019-06-28T11:13:03.563" Title="How does a receiver know the exact frequency in the channel to &quot;listen to&quot;?" Tags="&lt;frequency&gt;&lt;bandwidth&gt;" AnswerCount="4" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14785" PostTypeId="2" ParentId="14783" CreationDate="2019-06-26T13:52:18.697" Score="5" Body="&lt;p&gt;The receiver &quot;listens&quot; to any and all signals in its receive bandwidth (talking about AM, CW, or sideband here, FM handles everything differently).  Generally, there will be only one strong signal that gets through the receiver's filter, and that (plus atmospheric or man-made noise) is all you'll hear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there are two stations within the filter width, however, they'll get mixed together (you can sometimes hear this in AM broadcast, if stations in adjacent cities are on adjacent frequencies, or at night when the signals can propagate hundreds of miles).  In this case, your radio &lt;em&gt;doesn't&lt;/em&gt; &quot;know&quot; what signal to listen to -- it just detects and amplifies whatever signal it receives.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some radios have adjustable filters that let you narrow the receive band -- this is especially common with SSB and CW, where the signal you're after can be quite narrow (around 3 KHz for SSB and as little as 150 Hz for CW).  In this case, you can adjust filter width wider to make it easier to find a signal, then narrow it to ensure you can hear the one you're after.  Still and always, however, the radio just reproduces whatever signal comes in through the filter width.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-06-26T13:52:18.697" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14786" PostTypeId="2" ParentId="14782" CreationDate="2019-06-26T15:23:42.557" Score="1" Body="&lt;p&gt;The definitions already cover everything. Fixed and Mobile are separate from Amateur; Fixed is used for private/commercial/public safety/etc. uses where both ends of the link are in fixed locations, and Mobile is for communications between mobile stations (handhelds, vehicles, aircraft, etc.), or between fixed base stations and mobile stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Amateur service allows both fixed and mobile uses according to the laws of wherever you are, regardless of whether a band is also allocated to the Fixed or Mobile services (or both, or neither).&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-06-26T15:23:42.557" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14787" PostTypeId="2" ParentId="14783" CreationDate="2019-06-26T15:30:53.560" Score="9" Body="&lt;p&gt;The signal is not at exactly one frequency. The only signal that exists exactly at one frequency is an unmodulated carrier, and such a signal contains no information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As soon as the carrier is modulated, the signal's energy is spread over a wider bandwidth. So to receive any signal containing information, the receiver must listen to some range of frequencies, in your case a 25 kHz channel.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-06-26T15:30:53.560" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14788" PostTypeId="2" ParentId="14765" CreationDate="2019-06-26T15:47:42.933" Score="1" Body="&lt;p&gt;Nearly all coax is either 50 or 75 ohms. 50 ohms is standard for radio applications, and 75 ohms for CATV and video applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Everything else is a specialty item.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One use of odd impedance feedlines is to match impedances. Any two impedances can be matched by a 1/4 wavelength section of feedline having a characteristic impedance that is the geometric mean of the two to be matched. For example, to match 300 ohms to 50 ohms, a 1/4 wave selection of &lt;span class=&quot;math-container&quot;&gt;$\sqrt{300 \times 50} = 122$&lt;/span&gt; ohms can be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Certain devices, like a Wilkinson power divider, require transmission lines of peculiar impedances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or the application may be one where there's no particular need to accomodate any existing standard, and the system impedance is already set by some other design constraint. For example, antennas don't usually have a 50 ohm impedance feedpoint, and printed feedlines are not often 50 ohms either. The coax impedance is determined by its geometry, so perhaps for mechanical reasons a particular geometry is preferred and this dictates an unusual characteristic impedance.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-06-26T15:47:42.933" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14789" PostTypeId="2" ParentId="14765" CreationDate="2019-06-26T16:01:21.053" Score="5" Body="&lt;p&gt;&lt;a href=&quot;http://www.rfcafe.com/references/electrical/history-of-50-ohms.htm&quot; rel=&quot;noreferrer&quot;&gt;RF Cafe cites&lt;/a&gt; quotes Harmon Banning of W.L. Gore &amp;amp; Associates, Inc.:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In the early days of microwaves, around World War II, impedances were&#xA;  chosen depending on the application. For maximum power handling,&#xA;  somewhere between 30 and 44 Ω was used. On the other hand, lowest&#xA;  attenuation for an air filled line was around 93 Ω. In those days,&#xA;  there were no flexible cables, at least for higher frequencies, only&#xA;  rigid tubes with air dielectric. Semi-rigid cable came about in the&#xA;  early 50s, while real microwave flex cable was approximately 10 years&#xA;  later.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Somewhere along the way it was decided to standardize on a given&#xA;  impedance so that economy and convenience could be brought into the&#xA;  equation. In the US, 50 Ω was chosen as a compromise. There was a&#xA;  group known as JAN, which stood for Joint Army and Navy who took on&#xA;  these matters. They later became DESC, for Defense Electronic Supply&#xA;  Center, where the MIL specs evolved. Europe chose 60 Ω. In reality, in&#xA;  the U.S., since most of the &quot;tubes&quot; were actually existing materials&#xA;  consisting of standard rods and water pipes, 51.5 Ω was quite common.&#xA;  It was amazing to see and use adapter/converters to go from 50 to 51.5&#xA;  Ω. Eventually, 50 won out, and special tubing was created (or maybe&#xA;  the plumbers allowed their pipes to change dimension slightly).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Further along, the Europeans were forced to change because of the&#xA;  influence of companies such as Hewlett-Packard which dominated the&#xA;  world scene. 75 Ω is the telecommunications standard, because in a&#xA;  dielectric filled line, somewhere around 77 Ω gives the lowest loss.&#xA;  (Cable TV) 93 Ω is still used for short runs such as the connection&#xA;  between computers and their monitors because of low capacitance per&#xA;  foot which would reduce the loading on circuits and allow longer cable&#xA;  runs.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-06-26T16:01:21.053" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14790" PostTypeId="2" ParentId="14783" CreationDate="2019-06-26T23:27:08.283" Score="6" Body="&lt;p&gt;It may be easier to think of the receiver as receiving all frequencies. The job of the receiver is not to tune to a single frequency. Its job is to filter out everything that's not at that frequency, or in a band around it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So when you tune your FM receiver to 144.2500 with a 25 kHz bandwidth, you're telling it to reject all frequencies that are more than 12.5 kHz below 144.2500, and all frequencies that are more than 12.5 kHz above 144.2500.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other frequencies are still there, they still hit your antenna, and still show up (to some degree or another) at the antenna connector of your receiver. A big part of the receiver's job is to filter out all the frequencies you don't want to listen to - leaving only the signal that you do.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2019-06-26T23:54:13.233" LastActivityDate="2019-06-26T23:54:13.233" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14792" PostTypeId="1" AcceptedAnswerId="16184" CreationDate="2019-06-27T07:58:32.297" Score="4" ViewCount="440" Body="&lt;p&gt;The FCC has .seq &lt;a href=&quot;https://www.fcc.gov/media/radio/m3-ground-conductivity-map&quot; rel=&quot;nofollow noreferrer&quot;&gt;files that show ground conductivity&lt;/a&gt; which it makes available for download. Unfortunately, there doesn't appear to be any documentation that comes with the files, or even headers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can make an educated guess that there are two longitudes/latitudes for each record, and the last two numbers represent perhaps a range of ground conductivity. What is the meaning of each field? Is there anywhere I can learn more?&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="8717" LastEditDate="2020-02-17T21:49:47.960" LastActivityDate="2020-03-02T06:40:58.040" Title="How do I interpret the FCC ground conductivity map files?" Tags="&lt;grounding&gt;&lt;earth&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14793" PostTypeId="2" ParentId="14783" CreationDate="2019-06-27T11:38:49.263" Score="3" Body="&lt;p&gt;So everyone is talking about frequencies and almost nobody mentioned modulation mode.  This is important because how close you have to get in frequency depends on the mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A signal with information is not one frequency; it has a bandwidth, or a range of frequencies that contain the information being transmitted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio has filters that allow it to receive a slice of spectrum in the &quot;pass band&quot; which is usually slightly wider than the signal you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the mode is AM, the pass band is usually the same as the desired signal, the carrier is suppressed (hopefully), and the amplitude of the RF is converted to audio amplitude to demodulate the signal.  If multiple signals are present, they will all be present in the demodulated audio, like people in a room all talking at once.  If the pass band is not aligned with the transmitted signal, the audio will be clipped and distorted, although with commercial AM, the signal is so wide that you'd only notice that with loud music if it's just a little off. Also, if the frequency is not aligned, carrier suppression may fail which will add a whistle to the demodulated audio.  Some advanced AM receivers are able to lock onto the carrier or look for the symmetry in the signal to lock on, but most AM receivers (especially older ones) are built too cheaply to do this and just try to suppress the whistle in the demodulated audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the mode is SSB, the upper or lower range of frequencies is isolated, and the opposite side is reconstructed, and the result is then handled similarly to AM.  If the frequency is not aligned with the transmitted signal, the audio will be distorted badly and garbled, as the reconstructed portion will not be correct.  If it is only slightly off, the frequency of the audio will be higher or lower than the original along with some distortion, and it is sometimes possible to align the frequency by ear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the mode is FM, the FM signal is mostly symmetrical and the demodulation method has a capture effect that uses that symmetry to lock on to the signal. (This allows FM receivers to have sloppy frequency control while still having good quality demodulation.) If the signal is within the (usually larger) pass band, the demodulated signal won't be distorted; if it is not entirely in the pass band, it will be clipped.  If there are multiple signals present, only the strongest will be demodulated, although there may be buzzing as a result of the secondary signals.  If multiple signals are close to the same strength, the receiver may alternately lock on each of them in turn, which may make all of them unintelligible depending on how fast it switches between them.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2019-06-28T11:13:03.563" LastActivityDate="2019-06-28T11:13:03.563" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14795" PostTypeId="1" CreationDate="2019-06-27T14:29:13.007" Score="6" ViewCount="87" Body="&lt;p&gt;I know auroras are a propagation mode, but I was wondering with the recent outburst of noctilucent clouds (as reported on www.space.com) brings with it any interesting propagation modes, either on HF or VHF/UHF?&lt;/p&gt;&#xA;" OwnerUserId="9974" LastEditorUserId="76" LastEditDate="2019-07-03T00:17:47.930" LastActivityDate="2019-07-03T00:17:47.930" Title="Propagation effects of noctilucent clouds" Tags="&lt;propagation&gt;&lt;weather&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14796" PostTypeId="1" CreationDate="2019-06-27T16:01:57.300" Score="1" ViewCount="64" Body="&lt;p&gt;Thanks. Solved. Baofeng 888s, programmed with chirp, worked great. I hit the device with CHIRP many times, Everything was ok., but moni button after a month, didn't work. First I thought that the problem is for programming. I tried to change side key options by programming, but no effect. When push it, no reflection. Is the side key burnt? The device is new and I confused about this problem. I looked at the keys by magnifier but nothing was seen. I checked their connections by multi meter and I found the problem is in the key connection plates, not in other parts. I opened carefully stick ribbon over the &quot;moni&quot; key and saw a very small dust between two plates of the key, and remove it and the key acts very good and is ok.&lt;/p&gt;&#xA;" OwnerUserId="15160" LastActivityDate="2019-06-27T16:01:57.300" Title="Baofeng 888s side key didn't work and solved" Tags="&lt;baofeng&gt;" AnswerCount="0" CommentCount="1" ClosedDate="2019-06-27T16:27:19.243" ContentLicense="CC BY-SA 4.0" />
  <row Id="14797" PostTypeId="2" ParentId="14765" CreationDate="2019-06-27T16:49:36.317" Score="0" Body="&lt;p&gt;92Ω coax has been used for &lt;em&gt;many&lt;/em&gt; decades in cars and trucks between the radio and the non-resonant antenna. 75Ω or 50Ω coax would attenuate the signal more than 92Ω would.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason is the same: because of its lower capacitance per foot which helps minimize losses in the cable under such a mismatch.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-06-27T16:49:36.317" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14798" PostTypeId="1" CreationDate="2019-06-27T20:18:51.167" Score="1" ViewCount="684" Body="&lt;p&gt;I have some &lt;a href=&quot;https://en.wikipedia.org/wiki/LoRa&quot; rel=&quot;nofollow noreferrer&quot;&gt;LoRa&lt;/a&gt; &lt;a href=&quot;https://www.google.com/search?q=SX1278&quot; rel=&quot;nofollow noreferrer&quot;&gt;SX1278&lt;/a&gt; 433 MHz modules:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/41Zjx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/41Zjx.png&quot; alt=&quot;LoRa&quot;&gt;&lt;/a&gt; &lt;a href=&quot;https://i.stack.imgur.com/tHRK3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tHRK3.png&quot; alt=&quot;SX1278&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I don't have an antenna. My question is: what would be a good antenna option for longest range? I don't really care that much about transfer speed, I will only be sending commands and numbers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to build an effective antenna from inexpensive materials? For example, can I just solder a 34.5 cm (1/2 wavelength) wire to the &quot;ANT&quot; pin on the module? Or is there an easy way to make a dipole?&lt;/p&gt;&#xA;" OwnerUserId="15162" LastEditorUserId="8717" LastEditDate="2019-06-28T22:37:19.913" LastActivityDate="2019-07-01T09:21:09.047" Title="Simple antenna for LoRa 433 MHz module" Tags="&lt;antenna&gt;&lt;uhf&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="14799" PostTypeId="2" ParentId="14792" CreationDate="2019-06-27T20:29:40.433" Score="1" Body="&lt;p&gt;&lt;strong&gt;The figures on that map are &lt;em&gt;approximate&lt;/em&gt;.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They represent estimated ground conductivity in &lt;a href=&quot;https://en.wiktionary.org/wiki/millimho&quot; rel=&quot;nofollow noreferrer&quot;&gt;millimhos&lt;/a&gt; per meter. And it varies with (among other things) how wet or dry the soil is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UUuRT.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UUuRT.gif&quot; alt=&quot;FCC CONUS ground conductivity map&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live near a line where on one side it is 15, and on the other side it is 8. Driving across that line, the conductivity does not suddenly jump to the other number. Rather, it changes gradually. Having said that, there &lt;em&gt;are&lt;/em&gt; some places in the US where there is a drastic change between the soil types, which often are visible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Much more details can be found &lt;a href=&quot;http://lists.contesting.com/archives//cgi-bin/namazu.cgi?query=fcc+ground+map&amp;amp;submit=Search%21&amp;amp;idxname=Topband&amp;amp;max=20&amp;amp;result=normal&amp;amp;sort=score&quot; rel=&quot;nofollow noreferrer&quot;&gt;here on the Topband Reflector&lt;/a&gt;. In one of those threads, K2AV has a method for laying a dipole on the ground to measure it.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-02-17T20:22:59.410" LastActivityDate="2020-02-17T20:22:59.410" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14800" PostTypeId="1" AcceptedAnswerId="14859" CreationDate="2019-06-28T17:58:15.977" Score="3" ViewCount="379" Body="&lt;p&gt;Planning to go for a camping trip. According to &lt;a href=&quot;https://lovdata.no/dokument/SF/forskrift/2012-01-19-77/KAPITTEL_13#%C2%A740&quot; rel=&quot;nofollow noreferrer&quot;&gt;this document&lt;/a&gt; (in Norwegian but easy to understand), I can use a radio running PMR446 and KDR 444 freqs. Baofeng can do this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question is: is the Baofeng unit legal itself? And is it legal to take into the country?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I remember that some countries impose restrictions on taking your radios with you, and in some countries it's illegal to use a non-certified model.&#xA;Also note that Norway is not in the European Union and has separate laws.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE AND DETAILS&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;One small detail: I do not hold CEPT or any other amateur license.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks for the info and your answer SandPiper; it was exhaustive but I decided to dig a little bit more. I reached directly to the authorities and got this reply:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dear Alexander,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your radio, Baofeng UV-82 is a radio made for &lt;strong&gt;amateur radio usage only&lt;/strong&gt;.&#xA;It is not a radio made for use on frequencies where you need a licence from the authorities or general authorisations frequencies like PMR446 or KDR444.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PMR446 and KDR444 frequencies does have a general authorisation in Norway, but radios for use on these frequencies must be manufactured for this purpose. There are special rules/standards for these radios. Radios for use on PMR446 and KDR444 frequencies shall have a maximum output of 0,5W e.r.p. and shall have an integrated antenna. Increasing output power and use of external antenna must not be possible on such radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Baofeng UV-82 is only for use on Amateur radio frequencies and the user must hold an amateur radio licence.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have attached an english unauthorized version of general authorisations for the use of radio frequencies in Norway. See chapter XIII for information regarding KDR444 and PMR446. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best regards,  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tarjei Austegard&lt;br&gt;&#xA;Senior Engineer&lt;br&gt;&#xA;Spectrum Management Department&lt;br&gt;&#xA;Norwegian Communications Authority&lt;br&gt;&#xA;www.nkom.no  &lt;/p&gt;&#xA;" OwnerUserId="15165" LastEditorUserId="15165" LastEditDate="2019-08-13T10:28:52.017" LastActivityDate="2019-08-13T10:28:52.017" Title="Can I take and use Baofeng UV-82 in Norway?" Tags="&lt;legal&gt;&lt;baofeng&gt;&lt;europe&gt;&lt;international-operating&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14801" PostTypeId="1" CreationDate="2019-06-28T21:15:13.067" Score="4" ViewCount="153" Body="&lt;p&gt;In ideal free space, both arms of a tuned wire dipole will be of identical length.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the real world is not perfectly symmetric free space.  The support heights, ground levels, ground conductivity, parasitic buildings, wiring, feed lines, and metal towers might be close to one end and far from the other end of a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given very visible differences (such as the above) between the environments at the two ends of a dipole, should each arm of a &quot;center-fed&quot; wire dipole still be equal in length?  Or should the length of each half or arm be separately tuned (for lowest SWR, resonance at the desired frequency, etc.)?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, how?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-06-29T22:21:36.333" LastActivityDate="2019-07-01T08:59:06.253" Title="Dipole symmetry?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14805" PostTypeId="2" ParentId="421" CreationDate="2019-06-30T02:32:07.973" Score="2" Body="&lt;p&gt;I just read &lt;a href=&quot;https://repository.si.edu/bitstream/handle/10088/26620/201531CE.pdf?sequence=1&amp;amp;isAllowed=y&quot; rel=&quot;nofollow noreferrer&quot;&gt;the ionospheric sounding data obtained from MARSIS&lt;/a&gt; and it looks like Top Band (160 meters) would work great. Moreover:  zero atmospheric noise (no thunderstorms).&lt;/p&gt;&#xA;" OwnerUserId="15172" LastEditorUserId="76" LastEditDate="2019-07-07T14:44:21.373" LastActivityDate="2019-07-07T14:44:21.373" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14808" PostTypeId="2" ParentId="10348" CreationDate="2019-06-30T12:49:37.197" Score="2" Body="&lt;p&gt;Put ladder line on the system and feed it all the way to a balanced tuner or 1:1 current balun (or 4:1?). Put it high as a kite broadside it to the places you want to talk most on higher bands. You'll be surprised what you can do. &lt;/p&gt;&#xA;" OwnerUserId="15174" LastEditorUserId="8717" LastEditDate="2019-06-30T23:03:46.920" LastActivityDate="2019-06-30T23:03:46.920" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14811" PostTypeId="2" ParentId="14801" CreationDate="2019-07-01T08:59:06.253" Score="1" Body="&lt;p&gt;Net: given the difficulty of ascertaining the actual current distribution and the negligible improvement achieved by correcting any distortion of the current distribution, the additional effort is not warranted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Changing the lengths of a dipole on either side of the feedpoint results in an off-center fed dipole. In free space, off-center feeding of a &lt;span class=&quot;math-container&quot;&gt;$\lambda/2$&lt;/span&gt; dipole raises the feedpoint impedance, which could adversely affect the match to the feedline. The effect in a real-world scenario would be very difficult to predict and would most likely have to addressed through trial and error adjustment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I added an &quot;extra&quot; current source to a NEC2 model of a &lt;span class=&quot;math-container&quot;&gt;$\lambda/2$&lt;/span&gt; dipole in free space to examine the practical effect of distorting the current distribution. Even severe distortions like this:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/sqDGj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sqDGj.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;and this:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/lh1l5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lh1l5.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;produced less than 0.1dB difference in the radiation pattern. It's pretty clear that the minimal possible improvement doesn't warrant the effort that would be required to achieve it.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-07-01T08:59:06.253" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14812" PostTypeId="2" ParentId="14798" CreationDate="2019-07-01T09:21:09.047" Score="1" Body="&lt;p&gt;You can build an effective antenna with a &lt;em&gt;quarter wave&lt;/em&gt; of wire sticking out from the PCB. This is called a monopole antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 433 MHz, &lt;span class=&quot;math-container&quot;&gt;${1\over4}\lambda$&lt;/span&gt; is about 17 cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The wire should be oriented straight up, so that it radiates all around it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Monopoles require a ground plane. Your PCB and its wiring harnesses will function as a ground plane if they're fairly large - say a total of 30 cm diameter. If the board is very compact, then it will be better to build a dipole antenna instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dipole can be made by soldering a 17 cm wire to the ANT pin, and another 17 cm wire to the associated GND pin, with the ANT wire going straight up, and the GND wire going straight down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna like this, monopole or dipole, will give you pretty good performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should package your antenna in a way that no-one can accidentally touch the ANT wire - the module could easily be damaged by electrostatic discharge.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-07-01T09:21:09.047" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14813" PostTypeId="2" ParentId="13344" CreationDate="2019-07-01T19:47:26.523" Score="-1" Body="&lt;p&gt;Vacuum tubes produce cleaner transmitter signals more easily and vacuum tune receivers donlt overload on strong nearby signals as easily as tr&lt;/p&gt;&#xA;" OwnerUserId="15172" LastActivityDate="2019-07-01T19:47:26.523" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14814" PostTypeId="2" ParentId="11708" CreationDate="2019-07-01T20:04:38.843" Score="0" Body="&lt;p&gt;Tune Tx for maximum smoke LOL! This occurred when your anode choke was a bit under-specified for the PA voltage!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;ON HF it was easy because we didn't even try to get a 50 ohm match. Trying to get a match to a 50ohm feeder only became important at VHF and above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the technique on HF was to use a transmitter with Pi tank comprising a tuning capacitor and a loading capacitor. With loading capacitor at maximum capacitance, you tune the tuning capacitor for the bottom of the dip in PA supply current. Then you slowly reduce the loading capacitance while retuning for the dip, which gets shallower. You have got it right when the dip is shallowest but still discernible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I finally understood what was going on. The driven PA generates an RF anode (or collector or drain) current. When the tank is tuned to resonance, this develops a voltage in-phase with the current so that maximum current occurs at minimum PA anode (collector or drain) voltage, minimizing average DC consumption and causing the current dip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you want to then do is to increase the load on the output (by reducing the loading capacitance) so that the anode/collector/drain still swings as near as possible to 0 volts, but not so much that the anode/collector/drain voltage doesn't achieve the full voltage swing. When the latter happens, your power output is current limited and the dip won't happen. So it is when the dip just happens that you have it loaded just right.&lt;/p&gt;&#xA;" OwnerUserId="15172" LastEditorUserId="4665" LastEditDate="2019-07-01T21:15:15.277" LastActivityDate="2019-07-01T21:15:15.277" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14817" PostTypeId="1" CreationDate="2019-07-02T08:55:17.967" Score="3" ViewCount="133" Body="&lt;p&gt;I'm transmitting Z-Wave frames using HackRF One in loop, one frame every second. Has anyone clue why are some frames not transmitted? You can see  several too long gaps between frames on Waterfall (RTLSDR dongle + GQRX).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lnFSp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lnFSp.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm pretty sure the problem is not the receiver. I use GRC blocks for this transmission, but when I use different tool, it's more reliable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GgfYp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GgfYp.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I increase Interpolation on Rational Resampler (500, 750, ...) all frames are transmitted. However, these frames are not legitimate, because I Have to respect the formula:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QTOcY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QTOcY.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;40K sym/sec = data rate of Z-Wave&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2 samp/sym = min for HackRF One&lt;/p&gt;&#xA;&#xA;&lt;p&gt;20M samp/sym = max for HackRF One&lt;/p&gt;&#xA;&#xA;&lt;p&gt;250 (1/250) = resampling ratio&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this means the HackRF One is overloaded? I believe it should work somehow more reliable, because &lt;em&gt;hackrf_transfer&lt;/em&gt; transmit pre-modulated frames reliable.&lt;/p&gt;&#xA;" OwnerUserId="15186" LastActivityDate="2020-12-13T05:00:24.267" Title="HackRF One and IoT overloaded?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;gnuradio&gt;&lt;hackrf&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14818" PostTypeId="1" AcceptedAnswerId="14822" CreationDate="2019-07-02T11:49:22.580" Score="11" ViewCount="1730" Body="&lt;p&gt;I haven't seen this done, (which, after more than a century of amateur and professional radio development, is probably a bad sign), but I had an idea the other day for simplifying the setup and feed to cover more than one band without the compexity of traps or multiple feeds and RF switching.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were to build a pair of dipoles at right angles, on the same feed line, one sized for, say, 40m, the other for, in this case, 20m, would they act as one very poorly tuned antenna, or would they act like a wave trapped dipole (except with two different radiation patterns)?  I can think of arguments for either case, and I'm pretty fuzzy on antenna theory.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-05-23T02:26:27.623" Title="Will electrically joined dipoles of different lengths, at right angles, behave as a multiband antenna?" Tags="&lt;antenna-theory&gt;&lt;hf&gt;&lt;diy&gt;" AnswerCount="5" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14819" PostTypeId="2" ParentId="14818" CreationDate="2019-07-02T12:48:00.587" Score="4" Body="&lt;p&gt;The feedpoint current will take the path of least resistance (or least impedance) so it will always flow mainly into the center-fed resonant 1/2WL dipole rather than into any other higher impedance path.&lt;/p&gt;&#xA;" OwnerUserId="13587" LastActivityDate="2019-07-02T12:48:00.587" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14821" PostTypeId="2" ParentId="14818" CreationDate="2019-07-02T13:13:16.237" Score="2" Body="&lt;p&gt;Have a look at &lt;a href=&quot;https://en.wikipedia.org/wiki/Log-periodic_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Logper antennas&lt;/a&gt;!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/d/de/VHF_UHF_LP-antenna_closeup.JPG&quot; alt=&quot;Logper&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are not just &quot;joined dipoles for different wavelengths&quot;, but calculated to work in combination (otherwise they'd just be a mismatched piece of metal; still an antenna, but not a good one). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also of interest to you might very well be &lt;a href=&quot;https://en.wikipedia.org/wiki/Vivaldi_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Vivaldi antennas&lt;/a&gt;, but these will be hard to realize in HF:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/d/dc/Vivaldi-Antenna-Testing-In-Chamber.jpg&quot; alt=&quot;Vivaldi&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you'll sometimes find in both cases is that you duplicate the antenna, rotate it by 90° along the main direction, so that you get a second antenna in the orthogonal polarization plane; that way, you can generate (and receive!) arbitrary linear, circular and elliptic polarizations by phase shifting the input to either polarization.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-07-02T13:13:16.237" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="14822" PostTypeId="2" ParentId="14818" CreationDate="2019-07-02T13:56:23.887" Score="9" Body="&lt;p&gt;The results depend on the two bands you choose. Frequency ratios of 2:1 are a good choice because the longer dipole, which is a full wavelength at the higher frequency band, will show high impedance on that band, while the shorter dipole, which is only a quarter wavelength at the lower frequency band, will show a high (capacitive) impedance on that band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's use your example of crossed dipoles that are a half wavelength on 40m and 20m, respectively. In &lt;a href=&quot;http://eznec.com&quot; rel=&quot;noreferrer&quot;&gt;EZNEC&lt;/a&gt;, this is accomplished by connecting identical very short transmission lines from the center of each dipole to a virtual segment that hosts the single driving current source. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As shown below, the current at the center of the 20m dipole is about 8% of the current at the center of the 40m dipole when operated on 40m:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NwAkJ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NwAkJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The situation is reversed when operating on 20m, where the current at the center of the 40m dipole is about 1.4% of the current at the center of the 20m dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/C7OZ0.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/C7OZ0.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One might suspect that interactions between the the currents in the two antennas could adversely affect the SWR on each band, but these plots show that this is not the case:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/msX8m.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/msX8m.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/jwhdw.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jwhdw.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These SWR curves are virtually identical to the curves obtained when each dipole is swept after the other dipole is completely removed from the model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One reason this is not frequently done could be that more supports are needed and that the patterns of the two dipoles are orthogonal to each other, which might not serve the desired communicating directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Rotating one dipole to be parallel to the other requires the 20m dipole to be lengthened slightly to achieve resonance, but dramatically reduces the 20m SWR bandwidth. This design begins to look like a so-called open-sleeve dipole, in which the longer element is fed directly and excites the shorter dipole through close coupling, restoring much of the useful SWR bandwidth while preserving the directivity on both bands:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gjAm0.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gjAm0.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beginning on page 21 of &lt;a href=&quot;http://www.gfara.com/documents/Choosing_Your_First_Antenna-Hallas.pdf&quot; rel=&quot;noreferrer&quot;&gt;Choosing Your First HF Antenna&lt;/a&gt;, the ARRL's &lt;a href=&quot;https://www.qrz.com/db/w1zr&quot; rel=&quot;noreferrer&quot;&gt;Joel Hallas, W1ZR&lt;/a&gt;, describes Unfolded and Folded Skeleton Sleeve Dipoles for many band pairs. I have used these antennas at home, for DXpeditions and Field Days and can attest to their simple construction and reliable performance. A matching unit may be required to obtain the SWR required by your transmitter across an entire amateur band. A folded skeleton-sleeve dipole for the 40m and 20m bands would look like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cD1Ys.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cD1Ys.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-07-02T18:33:46.887" LastActivityDate="2019-07-02T18:33:46.887" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="14823" PostTypeId="2" ParentId="14818" CreationDate="2019-07-02T14:29:11.937" Score="2" Body="&lt;p&gt;I have done it for years, sometimes 2 bands (40-80m) at a 90° angle sometimes even 3 bands (40-80-160m) at 60° angles all 3 in inverted V dipole settings. It takes a bit of tweaking to get the VSWR OK but it definitely works pretty well.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2019-07-02T14:29:11.937" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14824" PostTypeId="2" ParentId="14818" CreationDate="2019-07-02T17:25:17.907" Score="7" Body="&lt;p&gt;What you describe is not far off from a common &lt;em&gt;fan dipole&lt;/em&gt;. This is a multiband antenna consisting of several dipoles in parallel, each cut to a different length. Only instead of orienting each dipole at right angles, they are simply spread apart with spacers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea is that the resonant dipole for the band will have a low impedance, while the non-resonant dipoles will have a higher impedance. By the basics of parallel impedances, most of the current ends up on the resonant dipole, and the addition of the higher-impedance non-resonant dipoles don't have a significant effect on the overall feedpoint impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The spacers reduce the interaction between the dipoles which makes the arrangement much easier to tune. Rotating the dipoles to be 90 degrees apart would reduce interaction even more, at the expense of doubling the number of supports required.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-07-02T17:25:17.907" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14825" PostTypeId="2" ParentId="14795" CreationDate="2019-07-02T20:59:31.980" Score="1" Body="&lt;p&gt;Noctilucent clouds are just clouds at a very high altitude. The temperature is low so they are formed by ice crystals. They are visible only when the sun is below the horizon but still shining on the clouds that are at very high altitudes. I can not imagine any effect on radio propagation. Maybe with visible light from a laser one could get reflections(??)&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-07-02T20:59:31.980" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14826" PostTypeId="2" ParentId="14795" CreationDate="2019-07-02T22:00:42.957" Score="4" Body="&lt;p&gt;NLCs may propagate radio waves, according to a 21 May 2019 article on &lt;a href=&quot;https://spaceweatherarchive.com/2019/05/21/polar-mesospheric-summer-echoes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Polar Mesospheric Summer Echoes&lt;/a&gt;: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The underlying physics of these echoes is still uncertain. A leading&#xA;  theory holds that the ice particles in noctilucent clouds are&#xA;  electrically charged, and this makes them good reflectors of radio&#xA;  waves. However, NLCs are not always visible when the radar echoes are&#xA;  observed and vice versa.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;According to Rob Stammes of the Polarlightcenter in Lofoten, Norway:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;“I detected these &lt;em&gt;[56.25MHz]&lt;/em&gt; VHF signals coming from transmitters in Eastern&#xA;  Europe. Before they reached my receiver in Norway, they bounced off&#xA;  something in the mesosphere. The patterns were recognizable and very&#xA;  strong.”&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-07-02T22:00:42.957" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14829" PostTypeId="1" AcceptedAnswerId="14832" CreationDate="2019-07-03T10:19:19.803" Score="5" ViewCount="589" Body="&lt;p&gt;Kenwood TH-D72A supports 3 types of tone: Tone, CTCSS and DCS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the difference between Tone and CTCSS?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as I know CTCSS is basically a continuous transmission of a given low frequency signal mixed with the voice. So it's basically a simple tone, isn't it?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-07-03T18:25:38.043" Title="Kenwood TH-D72A: what's the difference between Tone and CTCSS?" Tags="&lt;vhf&gt;&lt;kenwood&gt;&lt;tone-squelch&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14832" PostTypeId="2" ParentId="14829" CreationDate="2019-07-03T14:25:58.603" Score="7" Body="&lt;p&gt;&quot;Tone&quot;, displayed as &quot;T&quot; on the main screen, selects tone encoder + carrier squelch (your HT will send a tone, selected by the TONE Freq menu, and receive any strong-enough signal, regardless of whether it has a tone.) The transmitted tone is necessary to &quot;open up&quot; most repeaters so that you can talk on them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;CTCSS&quot;, displayed as &quot;CT&quot; on the main screen, selects tone encoder + tone squelch (your HT will send a tone, and only open the squelch on receive if the incoming signal contains the same tone).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The CTCSS option has some advantages, in that it will ignore interference, or a far-away repeater on the same frequency that uses the same tone, and on some repeaters will also silence the repeater ident. Especially helpful if you use scanning mode and you only want the scan to stop on actual conversations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there are also reasons to use the Tone option. Not every repeater has tone on its output. For the ones that don't, you can't use tone squelch, so Tone is the only valid option. Also, tone squelch might cut off a very weak signal that comes in too staticky for the tone to be heard clearly. In this case, switching to Tone might provide slightly better reception.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-07-03T14:25:58.603" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14834" PostTypeId="1" CreationDate="2019-07-04T04:30:39.070" Score="2" ViewCount="155" Body="&lt;p&gt;I have a Baofeng UV-82 with the charging cradle and switching power supply (wall wart). Tonight, I noticed a slick spot on the floor next to the couch, and saw some orange goo on a paper I had picked up from the floor. I saw the wall wart on the floor, and when I picked it up, I found that it was the source of the orange goo on the floor. It was not plugged up or anything, and the rig itself is only about two years old (it was not in the charging cradle at the time). Does anybody know why the wall wart would be leaking, and is the stuff that leaked out dangerous? This has never happened before. Thanks, Kate NK4TE &lt;/p&gt;&#xA;" OwnerUserId="15194" LastActivityDate="2019-07-04T11:57:37.373" Title="Orange Goop Leaking from Power Supply" Tags="&lt;baofeng&gt;&lt;battery-charging&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14835" PostTypeId="1" CreationDate="2019-07-04T04:35:09.840" Score="1" ViewCount="278" Body="&lt;p&gt;Any ideas on adjusting the low power output of the KT8900. The output tranny has a max rating of 12V and specs are centred on 7.5 volts. Yet they try to run it at 13.8V?? I want to reduce the output to about 5 watts, save the transistor some grief and run outboard amps on VHF and UHF instead, but there is no adjustment other than high and low which are just about the same anyway!&lt;/p&gt;&#xA;" OwnerUserId="15084" LastActivityDate="2019-07-04T09:04:55.453" Title="Power output of KT8900" Tags="&lt;transceiver&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14836" PostTypeId="2" ParentId="14834" CreationDate="2019-07-04T04:49:37.173" Score="2" Body="&lt;p&gt;That's very unusual. Modern electronics do not usually contain significant volumes of fluid that could leak out like that.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The most likely sort of leak one might find is an electrolytic capacitor losing its electrolyte, but that is more likely to make a circuit board corroded and stained in the vicinity than to manage to escape the housing. And the electrolyte would be mostly colorless/white appearing.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Another possibility is that the power adapter somehow got wet, something iron inside rusted (e.g. a transformer core) and the rusty water leaked out so that you have rusty water stains. If it seems to be an orange substance mixed with water, this seems plausible. But, I wouldn't expect to see &lt;em&gt;that much&lt;/em&gt; rust.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Finally, it's possible that the power supply is not the source and it simply got dunked in some other orange goop somehow. It can be hard to tell &quot;sat in a puddle&quot; from &quot;is the source of the substance&quot;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Well-lit pictures of the goop as it was found would help narrow things down; if you take one or two, please edit your question and upload them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the absence of further information, to be reasonably cautious, I would certainly discard the power supply (because if it &lt;em&gt;is&lt;/em&gt; from inside, something's gone wrong), and clean or discard the things the goop got on, but not take any more drastic measures.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-07-04T04:49:37.173" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14839" PostTypeId="2" ParentId="14835" CreationDate="2019-07-04T08:11:16.307" Score="1" Body="&lt;p&gt;The circuit diagram for the KT9800 can be found &lt;a href=&quot;https://dw1zws.com/schematic-diagram-qyt-kt8900_m-ver-1-0/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;, along with the specifications for the RF finals &lt;a href=&quot;https://dw1zws.com/qyt-kt-8900-and-variants-rf-finals-aft05ms006nt1/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking at the specifications sheet, the transistor's maximum drain-to-source voltage (Vdss in the spec sheet) is 30V, so I would not be worried about the finals unless you're using more than double the 13.8V you are worrying about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Vgs has a maximum of 12V, but it looks like the main IC (although I might be mistaken here) uses a supply voltage of 3.3V, so I would expect that to be the approximate level of the input to the finals. Way within the 12V maximum, anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: To try to answer the question as asked, there is no straightforward way of changing the power output, as the circuit does not look like it has any way of adjusting the level of the signal going into the finals. There are no variable components (e.g. a variable resistor) between the output of the RDA1846 and the final stage. So if the powers to be varied, it has to be done within the RDA1846 itself. And of course we don't have direct access to that because there is a control IC in the way.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2019-07-04T09:04:55.453" LastActivityDate="2019-07-04T09:04:55.453" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14840" PostTypeId="1" CreationDate="2019-07-04T10:35:26.737" Score="1" ViewCount="147" Body="&lt;p&gt;I am trying to setup FLDigi with my ICOM-7300 via the USB connection so I can start using digital modes. Everytime I try to &lt;a href=&quot;http://thestingyham.blogspot.com/2018/01/how-to-set-up-icom-7300-for-digital.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;follow the instructions here&lt;/a&gt;, it doesn't work. Specifically, everytime I try to load the .xml file, FLDigi hangs up and crashes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fsSuF.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fsSuF.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried using the Hamlib definition for the radio, and I can see it has made some kind of connection because whenever I rotate the VFO on the radio, the FLDigi frequency display changes, and vice versa when I change that frequency the radio changes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I am receiving nothing on the waterfall display, and when I center on digital signals in the low end of the 40m band FLDigi doesn't decode anything. Not even a garbled signal that might indicate I'm on the wrong encoding protocol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What am I doing wrong, and what do I need to do to get the radio data into FLDigi in addition to the rig control features?&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2019-07-04T10:35:26.737" Title="FLDigi Crashes When Trying to Load RigCAT Description File" Tags="&lt;digital-modes&gt;&lt;icom&gt;&lt;icom-ic-7300&gt;&lt;fldigi&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14841" PostTypeId="5" CreationDate="2019-07-04T10:40:26.020" Score="0" Body="&lt;p&gt;Download the software from &lt;a href=&quot;http://www.w1hkj.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is an open source software suite for Amateur Radio operators to control, receive, and transmit from the radio via a computer interface. General usage is supported for Linux, Unix, macOS.&lt;/p&gt;&#xA;" OwnerUserId="9450" LastEditorUserId="8713" LastEditDate="2020-05-04T12:36:36.347" LastActivityDate="2020-05-04T12:36:36.347" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14842" PostTypeId="4" CreationDate="2019-07-04T10:40:26.020" Score="0" Body="Use this tag for anything related to the FLDigi software suite. " OwnerUserId="9450" LastEditorUserId="9450" LastEditDate="2019-07-04T15:41:46.840" LastActivityDate="2019-07-04T15:41:46.840" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14843" PostTypeId="2" ParentId="14834" CreationDate="2019-07-04T11:57:37.373" Score="1" Body="&lt;p&gt;Wall warts aren't terribly complicated devices, they're just small transformers to convert the commercial AC into low voltage DC. There won't be any batteries in it, but there are likely capacitors. As noted &lt;a href=&quot;https://electronics.stackexchange.com/questions/169205/mechanically-damaged-capacitor-leaked-liquid-is-it-toxic&quot;&gt;here&lt;/a&gt;, the electrolyte is mildly toxic and corrosive, but not to the point where it's a significant HAZMAT issue. Just clean it up with a paper towel and wash your hands with soap and water.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two questions: &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Can you post a picture of it?&lt;/li&gt;&#xA;&lt;li&gt;Exactly how positive are you it was from the wall wart and not something else (e.g. child spilled orange juice)&lt;/li&gt;&#xA;&lt;li&gt;Was it plugged in at the time?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Electronics don't commonly &lt;em&gt;leak&lt;/em&gt;, especially not new ones. It is not unheard of though, particularly in &lt;a href=&quot;https://www.pcmag.com/feature/355587/how-to-preserve-vintage-electronics&quot; rel=&quot;nofollow noreferrer&quot;&gt;older electronics&lt;/a&gt;, like the capacitors in this article. But even then, they shouldn't produce enough fluid to run all over the floor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pending more data, if you are 100% positive it was coming from the wall wart I personally wouldn't plug it back in because I wouldn't want to risk an electrical short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/U92HA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/U92HA.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2019-07-04T11:57:37.373" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14845" PostTypeId="1" AcceptedAnswerId="14855" CreationDate="2019-07-04T14:24:07.530" Score="1" ViewCount="104" Body="&lt;p&gt;I want to make a radio antenna at home which will be able to receive all FM frequencies for my FM radio or Android FM.&#xA;How do I make it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Frequency it can catch : 88 - 108 MHz&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="15199" LastEditorUserId="15199" LastEditDate="2019-07-05T09:34:03.320" LastActivityDate="2019-07-05T15:08:55.593" Title="Radio antenna for my FM receiver / Android FM" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;receiver&gt;&lt;fm&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14846" PostTypeId="1" AcceptedAnswerId="14849" CreationDate="2019-07-04T17:18:25.977" Score="3" ViewCount="230" Body="&lt;p&gt;I understand that my local laws may differ but amateur radio satellites, by their very nature, orbit the earth going over several legal jurisdictions.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Are satellite bands the same internationally?&lt;/li&gt;&#xA;&lt;li&gt;If not, how do they keep track of which frequency to operate on?&lt;/li&gt;&#xA;&lt;li&gt;If a satellite is transmitting in a non-amateur band, do amateurs in the country just stay silent as it passes above?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="14220" LastEditDate="2019-07-04T17:25:47.533" LastActivityDate="2019-07-04T18:32:26.803" Title="How do amateur satellites stay consistently in the amateur-sat bands acoss the globe?" Tags="&lt;legal&gt;&lt;satellites&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14847" PostTypeId="1" AcceptedAnswerId="14851" CreationDate="2019-07-04T17:40:47.380" Score="1" ViewCount="445" Body="&lt;p&gt;I have seen sketches of 3-element 2m yagi antennas in which the driven dipole elements are staggered i.e., one element is positioned slightly in front of the other along the length of the (plastic) horizontal beam. these elements also &quot;overlap&quot; slightly, as they protrude through the beam pipe for an inch or so and the coax is connected directly to the elements at the ends of these protrusions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been told that the staggered elements raise the feedpoint impedance to furnish a correct impedance match to RG-58/U coax without requiring a balun transformer. Is this a true claim? And do the elements need to be driven at their overlapping ends? Or does this overlap matter at all? In short...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where can I find detailed design rules for staggered dipoles like this? I would like to try this design in a 5-element Yagi. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the image linked below, you can see the &quot;stagger&quot; (one element is in front of the other) and the &quot;overlap&quot; (the elements cross over the horizontal beam midpoint).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aAVt8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aAVt8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10598" LastEditorUserId="10598" LastEditDate="2019-07-04T18:56:36.563" LastActivityDate="2019-07-15T15:14:08.027" Title="2m 5-element yagi with staggered driven elements" Tags="&lt;antenna-construction&gt;&lt;2m-band&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14848" PostTypeId="1" CreationDate="2019-07-04T17:46:47.427" Score="2" ViewCount="73" Body="&lt;p&gt;I am new to Echolink and I have Hughes Net Satellite delivered Internet service. Can I use Echolink with my Satellite service since there is a longer delay involved. Thanks in advance for your response. Larry N4QDE.&lt;/p&gt;&#xA;" OwnerUserId="15200" LastActivityDate="2019-07-05T00:57:59.350" Title="Using EchoLink with Satellite delivered Internet" Tags="&lt;echolink&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14849" PostTypeId="2" ParentId="14846" CreationDate="2019-07-04T18:32:26.803" Score="5" Body="&lt;p&gt;A simple internet search turns up the IARU's &lt;a href=&quot;http://www.iaru.org/satellite.html&quot; rel=&quot;noreferrer&quot;&gt;Amateur Radio Satellite Frequency Coordination&lt;/a&gt; web page. There you will find an &lt;a href=&quot;http://www.iaru.org/uploads/1/3/0/7/13073366/short_info_paper.pdf&quot; rel=&quot;noreferrer&quot;&gt;Amateur Satellites Short Info Paper&lt;/a&gt; that answers your question: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Satellite frequencies in bands allocated to the amateur-satellite&#xA;  service are coordinated by the IARU Satellite Frequency Coordination&#xA;  Panel.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As an international body operating under the UN-chartered ITU, all of the regions over which a satellite will travel should be represented.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since frequency allocations are subject to change, I will not copy them here, but the current frequency allocations are shown by region starting on page 3 of the document.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-07-04T18:32:26.803" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14850" PostTypeId="2" ParentId="14847" CreationDate="2019-07-04T19:15:54.833" Score="1" Body="&lt;p&gt;The staggering in the drawing is small, 0.7&quot;, and the overlap is not specified. This makes me think it's done for mechanical reasons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feedpoint of a dipole or yagi is difficult to support mechanically - both halves need to be insulated but we'll supported. One neat solution to this is to stagger them somehow, so they can &lt;em&gt;both&lt;/em&gt; pass through the boom and be supported there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've built broomstick-and-wire-and-glue yagis and staggered the driven elements by 10 mm or so, just to provide mechanical strength. Both halves of the driven element can go through the boom. Then I can solder the coax on one side and its strong and neat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yagis can be designed for various feedpoint impedances. I can't simulate your one now, but it might well be designed for 50 Ohms. If you're planning to feed your yagi directly with coax, this is what you'd do. 15 to 25 Ohms is more common, and might give slightly better performance, but a yagi designed for 50 will work fine and is nice and simple to feed. Impedance is mostly affected by reflector spacing and length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There will be no significant impedance transformation from the feed staggering and overlap in your drawing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a direct coax connection you still need a balun. This could be a small coil of coax, or a 1/4 wave sleeve on the coax.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-07-04T19:15:54.833" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14851" PostTypeId="2" ParentId="14847" CreationDate="2019-07-04T19:51:35.223" Score="0" Body="&lt;p&gt;Thanks for bringing this technique to our attention. I applied the concept to a simple half-wave dipole to gauge the impact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Spacing the halves of a 1-inch diameter, 40m dipole &lt;span class=&quot;math-container&quot;&gt;$.001\lambda$&lt;/span&gt; apart (about 3.3-inches), overlapping them by 36 inches and feeding them with a segment that joined the staggered dipole halves at the midpoint of the antenna, the feedpoint impedance increased from &lt;span class=&quot;math-container&quot;&gt;$72\Omega$&lt;/span&gt; to &lt;span class=&quot;math-container&quot;&gt;$92\Omega$&lt;/span&gt; with no change in the resonant frequency. Note that each wire comprised a large number of identical-length segments to avoid possible computation errors. Reducing the element diameters to 1/2-inch reduced the impedance to &lt;span class=&quot;math-container&quot;&gt;$82\Omega$&lt;/span&gt;, again with no change in the resonant frequency. This could be used to raise the feedpoint impedance of the driven element of a parasitic array, which is ordinarily lowered by inducing currents in the parasitic elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know of any closed-form expression to calculate this behavior in pursuit of a working design. Since the resonant frequency wasn't affected by the staggered feed, it doesn't appear that the principle of a gamma match is applicable. It might be possible to build a traditional yagi design with the staggered driven element and simply trim the overlap until you reach your impedance target.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A balun will still be required to prevent unbalance currents from traveling down the outside of the coax shield.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-07-04T19:51:35.223" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14852" PostTypeId="2" ParentId="14848" CreationDate="2019-07-05T00:57:59.350" Score="3" Body="&lt;p&gt;The EchoLink site talks about using satellite Internet, so you should be able to. You may experience a slight delay, but it will really only be noticeable for each party while awaiting a response. If you've ever seen live news coverage from a scene you will get the same effect.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Anchor: &amp;quot;We're going to our reporter at the scene.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;Reporter at scene: &lt;em&gt;Abnormal 2-3 second pause&lt;/em&gt; &amp;quot;Here we are at...&amp;quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;As long as you're not stepping on each other, the signal will get there eventually.&lt;/p&gt;&#xA;&lt;p&gt;Of note, you might have some firewall settings you need to adjust per the &lt;a href=&quot;http://www.echolink.org/firewall-friendly.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;EchoLink documentation&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9450" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-07-05T00:57:59.350" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14854" PostTypeId="1" AcceptedAnswerId="14856" CreationDate="2019-07-05T11:35:22.463" Score="2" ViewCount="1097" Body="&lt;p&gt;Fairly regularly on the 40m band I hear a quick blip of a tone, and when I look at the waterfall I see these brief transmissions all across the band that look like little dots. What is causing that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5F2o6.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5F2o6.jpg&quot; alt=&quot;Burst transmissions across the full band, low to high&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9450" LastEditorUserId="76" LastEditDate="2019-07-05T15:19:02.753" LastActivityDate="2019-07-05T20:42:12.160" Title="What is this burst transmission sequence across the entire band?" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;signal-identification&gt;&lt;panadapter-and-waterfall&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14855" PostTypeId="2" ParentId="14845" CreationDate="2019-07-05T15:08:55.593" Score="2" Body="&lt;p&gt;Common receiver antennas for the FM broadcast band (88-108 MHz) are typically center-fed folded dipoles roundly 1.5 meters long (half wavelength for the ~100 MHz center frequency of the band); they're made from twin-lead (flat, like old fashioned TV antenna cable) cut to length, conductors joined at the ends, and one conductor cut at the center and joined to a similar length of twin-lead feed line -- at DC, this forms a simple loop.  In practice, a long wire, up to about ten wavelengths (thirty meters) will do at least as well, but isn't as compatible with an indoor installation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding an antenna to an Android device, however, isn't as simple as hooking up a wire antenna.  Most such devices have no provision for an external antenna, or any connector for one (in a phone designed more than five years ago or so) is likely to be hidden inside the back cover of the device.  Many modern Android devices use fractal antennas to give the effect of a resonant antenna for the cellular communication frequency (much higher than FM broadcast, though it varies by phone make/model and cell provider), and some of the more popular current models have deleted the FM radio receive capability in hardware (my first-gen Pixel, for instance, lacks the FM chip).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-07-05T15:08:55.593" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14856" PostTypeId="2" ParentId="14854" CreationDate="2019-07-05T15:18:26.357" Score="7" Body="&lt;p&gt;It's probably an &lt;a href=&quot;https://en.wikipedia.org/wiki/Ionosonde&quot; rel=&quot;nofollow noreferrer&quot;&gt;ionosonde&lt;/a&gt; — sending out HF radio signals not to communicate but to measure the reflections and thereby determine the current characteristics of the ionosphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal is probably not actually a series of brief transmissions, but a continuous &lt;a href=&quot;https://en.wikipedia.org/wiki/Chirp&quot; rel=&quot;nofollow noreferrer&quot;&gt;chirp&lt;/a&gt; transmission with continuously increasing frequency. Two reasons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;As far as I know, this is how ionosondes work, and I've heard many chirps on HF, but never a stepped transmission.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you look closely at the display, it appears that &lt;em&gt;only one pixel in each horizontal line is lit by this transmission&lt;/em&gt;. If it were short bursts on single frequencies, we would expect to either see the transmission either taking up multiple pixels in the vertical time axis occasionally, or for some of the transmissions to be missed entirely, rather than a constant-ish spacing along the spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It looks like a series of dots because your waterfall display is displaying a series of momentary snapshots over time, not using the entire period of the signal between one line of the display and the next. (This is possible, but requires more computation. If it did, you'd see a continuous slanted line, but much more faintly than the dots because you'd be looking at the power effectively averaged over a longer time period.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If this is a chirp, then if you catch the sound of it in SSB mode, you should hear a quickly increasing or decreasing tone, not a stable tone.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-07-05T20:42:12.160" LastActivityDate="2019-07-05T20:42:12.160" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="14857" PostTypeId="2" ParentId="14854" CreationDate="2019-07-05T15:19:01.647" Score="0" Body="&lt;p&gt;It appears from your photo that the pulses are not quite simultaneous; rather the transmitter sends a pulse, steps frequency up, sends another pulse, and so on.  That behavior is what I'd expect from a propagation test beacon system, checking for things like MUF over a variety of paths and distances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This kind of transmission would usually be received by a network of stations that would report back (by Internet, or before Internet via land lines or return radio transmission) on what frequencies pulses were received.  This data, in turn, is combined with that from a number of other beacons and converted to an &lt;a href=&quot;http://www.spacew.com/www/realtime.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;MUF path map&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-07-05T15:19:01.647" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14858" PostTypeId="1" CreationDate="2019-07-05T17:27:41.620" Score="3" ViewCount="240" Body="&lt;p&gt;There seem to be plenty of construction articles on center-fed wire fan dipoles with pairs of arms of different lengths, each pair dimensioned for a different band (e.g. half-wave 80M+40M+20M).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would a wire fan dipole work with arms of equal physical lengths, but each pair with a different loading coil configuration (perhaps none, plus other pairs of arms tuned for different bands/frequencies with different inductors)?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, is there a rule-of-thumb for how far apart the wire fan elements need to be spaced (say in degrees or radians)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or could an (insulated) wire fan element be fed coaxially through the loading coil of another fan element?  Or could a single loading coil be shared, with different taps for different top segments?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="9450" LastEditDate="2019-07-24T13:12:26.863" LastActivityDate="2019-07-24T13:12:26.863" Title="Fan dipole with loading coil(s)?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;parallel-dipole&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14859" PostTypeId="2" ParentId="14800" CreationDate="2019-07-06T13:30:24.937" Score="2" Body="&lt;p&gt;There was a bit of a kerfuffle last year over this very topic here in the states. See: &lt;a href=&quot;https://medium.com/@lucky225/did-the-fcc-just-make-baofengs-illegal-1fd4ba048194&quot; rel=&quot;nofollow noreferrer&quot;&gt;Did the FCC just make Baofengs Illegal?&lt;/a&gt; While that is ongoing, I wasn't able to find any literature on Norway banning the Baofeng radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, even though they aren't part of the EU, they still require you to have a &lt;a href=&quot;http://www.arrl.org/cept&quot; rel=&quot;nofollow noreferrer&quot;&gt;European Conference of Postal &amp;amp; Telecommunications Administrations (CEPT)&lt;/a&gt; radio-amateur license. This license:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;allows US Amateurs to travel to and operate from most European&#xA;  countries without obtaining an additional license or permit. For a US&#xA;  citizens to operate an amateur station in a CEPT country, certain&#xA;  requirements of the CEPT European Radio Committee (ERC) must be met&#xA;  for participation by non-CEPT Administrations (the US is a Non-CEPT&#xA;  administration who has obtained permission to allow its licensees the&#xA;  privilege of operation from CEPT countries).&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Under the CEPT Agreement, to activate operating authority, a traveler&#xA;  would have to carry credentials in English, French and German that the&#xA;  person, if a US citizen, and if a Commission-authorized amateur&#xA;  operator, is entitled to certain amateur station operating privileges&#xA;  in the specific countries that have implemented the CEPT Agreement.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Furthermore, digging further into the CEPT info, I found this on &lt;a href=&quot;http://www.arrl.org/select-countries-i-n&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL's operating permit page&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Norway (LA)&#xA;      ·         CEPT Radio Amateur License Recommendation T/R 61-01 allows US Amateur Extra and US Advanced class licensees to operate in&#xA;  European Union countries and their dependencies listed below under&#xA;  CEPT T/R 61-01.  The qualified US Amateur must carry a copy of the FCC&#xA;  CEPT Public Notice DA 11-221 (dated February 7, 2011), your US&#xA;  passport and your original FCC-issued license (not a photocopy).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In other words, if you don't have an Extra/Advanced license, the whole question is moot because you won't be allowed to operate anyway. Further information found on the &lt;a href=&quot;https://eng.nkom.no/leisure/radio-amateurs/radio-amateurs/information-for-visitors-to-norway&quot; rel=&quot;nofollow noreferrer&quot;&gt;Norwegian Communications Authority visitor's page&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2019-07-06T13:30:24.937" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14860" PostTypeId="2" ParentId="14858" CreationDate="2019-07-06T15:48:34.593" Score="2" Body="&lt;p&gt;This is already a commercially available antenna. Alpha-Delta makes several variations, with the DX-LB-Plus being the one I'm using. It covers 10,15, 20, 40, 80 and 160, with loading coils for 80 and 160, both shared on the longest legs. Overall length is 100 feet. The antenna works pretty well on 10, 15 and 20 and is excellent on 40! On 80 and 160 it's about what one would expect from a shortened dipole. On 160 on a good night I can get some DX during the winter, but Asia and Middle East won't happen for me!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you're asking sounds like it would be a very worthwhile project! Probably more so if you drop 160 and 80 from the design. Check out Alpha-Delta for more information, and I'm sure there are designs available under &quot;shortened dipoles&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 es GL&#xA;Dave - KB3MOW&lt;/p&gt;&#xA;" OwnerUserId="10286" LastActivityDate="2019-07-06T15:48:34.593" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14861" PostTypeId="2" ParentId="14800" CreationDate="2019-07-07T02:07:57.533" Score="1" Body="&lt;p&gt;This just in from Bjorn Myrvold, LB7ZG, at NRRL:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Yes, you can bring your Baofeng UV82 transceiver and use it in Norway.&#xA;  Remember to use the prefix LA/.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-07-07T02:07:57.533" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14862" PostTypeId="2" ParentId="11830" CreationDate="2019-07-07T03:04:41.547" Score="2" Body="&lt;p&gt;To answer each point in turn:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;DMR radios are different from &quot;normal&quot; ham radio equipment in that it uses a digital voice encoder/decoder rather than the more traditional FM analog voice mode that you're probably used to. &lt;em&gt;Fun fact: Kenwood makes DMR-capable radios in their NX series of digital (commercial land mobile) radios, and the mode was made popular in commercial circles by Motorola. So the voice mode has been around for a while, just more recently coming to amateurs via the explosion of Chinese-made models&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;As mentioned, this voice mode was originally found in commercial rigs. Two of the most appealing benefits of DMR (and generally, YSF/C4FM falls into this as well, D-STAR a bit less so) is that the voice quality is extraordinary, no background hiss that you get from analog FM; additionally, the range of DMR radios (for the same amount of power output) is far superior to analog FM radio. In fact, you'll generally get very listenable content up until you're right at the absolute range limit for the power level of the radio. There are more benefits (and a few drawbacks even) but this is a high-level overview, right?&lt;/li&gt;&#xA;&lt;li&gt;DMR radios these days very often come in dual-band VHF/UHF models. However, most of the big names (Kenwood and Moto) are UHF &lt;em&gt;or&lt;/em&gt; VHF, not both. Since Motorola was early on the scene with DMR, a fair number of repeaters use Motorola hardware, and use UHF frequencies. More recently, there are voice modems that you can patch into analog repeaters to bring digital voice modes like DMR to existing analog hardware. It's a pretty wild scene out there.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Bonus question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you asked about simplex in your comments, DMR can absolutely be used for simplex comms (this would be what people would call &quot;Tier 1&quot; DMR) and the general consensus for amateurs is as &lt;a href=&quot;https://ham.stackexchange.com/users/9493/glenn-w9iq&quot;&gt;Glenn W9IQ&lt;/a&gt; put it &lt;a href=&quot;https://ham.stackexchange.com/questions/11830/help-with-zastone-d900#comment17398_11831&quot;&gt;here&lt;/a&gt;: program your DMR radio to color code 1, time slot 1, and talk group 99.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All the vocabulary (color codes, time slots, talk groups, and the oft-misunderstood CPS software) are all challenges that await your interest or pleasure, depending on what you're into with this hobby.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have a great day!&lt;/p&gt;&#xA;" OwnerUserId="9523" LastActivityDate="2019-07-07T03:04:41.547" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14863" PostTypeId="1" CreationDate="2019-07-07T13:34:03.443" Score="3" ViewCount="110" Body="&lt;p&gt;I'm trying to run some transmit/receive RF examples that I found online using GNU Radio with USRP B200. I read and heard about some cautions in terms of transmitted frequencies here in the USA which made me slow down! What is the legal frequency signals that I can transmit in the USA as a hobbyist or a student? Kind of, I felt lost while looking at the following USA Frequency Allocations Chart:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eS0nJ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eS0nJ.jpg&quot; alt=&quot;link to USA Frequency Allocations Chart&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Assuming I know what is my ISM band allocation value, where I should input this value, I mean which block?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other issue is the safety issue. I don't want to fry my tools, so how and where I should set the power? Again, which block I should be looking at?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any hints, clues, or recommended resources would be highly appreciated.&lt;/p&gt;&#xA;" OwnerUserId="15206" LastEditorUserId="218" LastEditDate="2019-07-08T01:48:09.907" LastActivityDate="2019-07-08T01:48:09.907" Title="GnuRadio RF transmission, legal and safety issues" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;frequency&gt;&lt;gnuradio&gt;&lt;usrp&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14864" PostTypeId="1" AcceptedAnswerId="14867" CreationDate="2019-07-07T13:40:49.787" Score="2" ViewCount="865" Body="&lt;p&gt;I have a &lt;a href=&quot;https://www.radioworld.co.uk/rba-20-airband-antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;50 Ω VHF airband antenna&lt;/a&gt; which I’m planning to install in my loft, for use with a RaspberryPi-based RTLSDR scanner/receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I already have a UK-standard UHF/Freeview antenna using standard 75 Ω coaxial cabling running from the loft into the lounge and want to make use of this rather than running new cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not planning on transmitting on the VHF band, and the antenna will only be used for receiving/monitoring UK airband traffic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I correct in thinking that:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Running two antennae for two diverse frequency bands across the same coax is OK, providing that both antennae are RX only&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I will need a UHF/VHF diplexer on either end to suitably merge/split the signals from each antenna&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The loss resulting from using a 50 Ω antenna and a 75 Ω antenna/cable is negligible enough to make the setup viable&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="15207" LastEditorUserId="8717" LastEditDate="2019-07-07T21:46:50.027" LastActivityDate="2019-07-10T00:02:26.740" Title="VHF 50 Ω Antenna Over 75 Ω TV Coax" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;coaxial-cable&gt;&lt;antenna-system&gt;&lt;rtl-sdr&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14866" PostTypeId="2" ParentId="14864" CreationDate="2019-07-07T14:26:59.090" Score="3" Body="&lt;p&gt;To answer your questions in order:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;As long as you’re not transmitting, you can run as many signals as you want into a piece of coax. In fact, your receiving antenna is passing a whole band of frequencies into it already&lt;/li&gt;&#xA;&lt;li&gt;Ideally you would want a combiner at one end and a splitter at the other. These can be passive (a few coils and a capacitor or two), or active (with some electronics in, and power being supplied)&lt;/li&gt;&#xA;&lt;li&gt;Certainly for receive, you won’t notice anything from using 75ohm instead of 50ohm cable&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-07-07T14:26:59.090" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14867" PostTypeId="2" ParentId="14864" CreationDate="2019-07-07T14:27:49.280" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;I will need a UHF/VHF diplexer on either end to suitably merge/split the signals from each antenna&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, this is correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A tangent: If you wanted to save some money by using mass-market parts, you could use 75 Ω &lt;a href=&quot;https://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers&quot; rel=&quot;nofollow noreferrer&quot;&gt;power dividers&lt;/a&gt; (coax splitters) instead of diplexers. This has 3 dB loss because the signals are not directed exclusively to the intended receivers for each band, but evenly split between them.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Running two antennae for two diverse frequency bands across the same coax is OK, providing that both antennae are RX only&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This type of configuration can work for transmitting as well, provided the diplexers are rated for the transmit power and the receivers can tolerate the leakage through the wrong port of the diplexer.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;The loss resulting from using a 50 Ω antenna and a 75 Ω antenna/cable is negligible enough to make the setup viable&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, this is correct, unless you are seeking to receive extremely weak signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 75-50 Ω mismatch has a reflection coefficient of 0.2. That is, each point of mismatch will reflect 20% of the signal, or &lt;span class=&quot;math-container&quot;&gt;$10\log_{10}(1 - 0.2) \approx 0.96\,\text{dB}$&lt;/span&gt;. So (discounting secondary reflections), you'll have a total loss of 2 dB. That will most likely be fine.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-07-08T13:59:21.423" LastActivityDate="2019-07-08T13:59:21.423" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14869" PostTypeId="1" CreationDate="2019-07-07T16:02:55.600" Score="1" ViewCount="38" Body="&lt;p&gt;Have 23 foot &lt;a href=&quot;http://shakespeare-ce.com/marine/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Shakespeare&lt;/a&gt; SSB antenna.  Can not connect  through the side feed termination band? Antenna not working?  What is the band supposed to look like? Is the termination band supposed to be smooth on inside of band? How does the termination band connect to the antenna pole? Is there supposed to be a metal bead on the inside of the band??  I am NOT referring to where my lead connects to the band, as show in company diagram, how does the band connect to the antenna pole? Have sent emails to Shakespeare tech support. They do not answer. Can not find diagram or picture of &lt;strong&gt;actual&lt;/strong&gt; side feed termination band.&lt;/p&gt;&#xA;" OwnerUserId="15209" LastEditorUserId="76" LastEditDate="2019-07-07T16:25:59.933" LastActivityDate="2019-07-07T16:25:59.933" Title="Unsure how to assemble Shakespeare SSB antenna; not working" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;vhf&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2019-07-07T20:16:18.397" ContentLicense="CC BY-SA 4.0" />
  <row Id="14871" PostTypeId="1" CreationDate="2019-07-07T22:18:37.087" Score="1" ViewCount="245" Body="&lt;p&gt;I'm looking for some sort of simple and a beginner level instructions on how to build TX/RX loopback flowgraph using GnuRadio software and B200 USRP with an attenuator FW -10 + 10dB.&#xA;Kindly, help me with any available examples/resources you have.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Update:&#xA;What I meant by a loopback here is a simple flowgraph that has both: a transmitter and receiver, to transmit a signal and receive it by connecting the TR port to the RX on the USRP device.&lt;/p&gt;&#xA;" OwnerUserId="15206" LastEditorUserId="15206" LastEditDate="2019-07-08T11:58:15.983" LastActivityDate="2019-07-08T11:58:15.983" Title="Simple Gnuradio TX/RX loopback example/tutorial" Tags="&lt;gnuradio&gt;&lt;usrp&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14872" PostTypeId="2" ParentId="9533" CreationDate="2019-07-08T02:45:21.887" Score="3" Body="&lt;p&gt;I cannot speak to the off-center type dipole feeds that use the 1:9 (impedance) transformers, but for the truly end-fed dipoles fed with something like a 1:49 impedance ratio, the answer is, it depends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I performed &lt;a href=&quot;https://www.hamradio.me/antennas/of-end-feds-and-feed-lines.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;some simulations&lt;/a&gt; of an end-fed dipole system with an autotransformer and an additional wire representing the currents along the feed line. I did so with the wire open ended and with a couple 1/4 wave radials to represent both ungrounded and grounded situations. In the article I look at SWR, Return Loss and antenna gain in the axis of only the antenna radiator. All tell the same story, but gain gets the nod to view for this answer...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.hamradio.me/wp-content/uploads/2019/02/HRM_03_EFHW_vs_CPLength_Gain_p.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://www.hamradio.me/wp-content/uploads/2019/02/HRM_03_EFHW_vs_CPLength_Gain_p.png&quot; alt=&quot;Gain (Theta) of EFHW vs. feed line length&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Key points include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Feedline lengths up to near 1/4 wave do not cause much trouble for either case. This jives well with the many reports of successful portable operations using EFHW antennas with very short feed lines.&lt;/li&gt;&#xA;&lt;li&gt;Whenever the feedline presents a high impedance to the antenna feed, current is drawn from the primary radiator resulting in perturbed performance and lower gain.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So to answer your question if the feedline is under 1/4 wave in length, there appears to be no reason for a current choke. However, if you have lengths 1/4 wave or longer, it may be time to add one... but where?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If my simulations are correct, placing the high impedance of the choke 1/4 wave back should provide protection to the system for any length of feedline past the choke since the choke always forces a low impedance (1/4 wave transformer) at the feed point that is very dissimilar to the high impedance feedpoint. This odd phenomena is reverse of the case of a center-fed dipole or 1/4 wave monopole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is what simulations and a growing set of measured data suggests.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastEditorUserId="4306" LastEditDate="2019-07-08T11:29:34.600" LastActivityDate="2019-07-08T11:29:34.600" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14873" PostTypeId="1" AcceptedAnswerId="14876" CreationDate="2019-07-08T09:52:52.380" Score="2" ViewCount="311" Body="&lt;p&gt;I bought a pre-owned Yaesu FT-8900R. Sadly turned out that the radio doesn't turn on. When I hold the power button (the right bottom one) the speaker pops briefly but nothing else happening. The previous owner claims very persistently that it worked before shipping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that the device was not damaged during the shipping I would like to exclude any &quot;stupid&quot; reasons of malfunction before bringing it to the repair service. I'm hoping that there are some FT-8900R owners here who might observe the described behaviour before.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I already checked the fuses, re-soldered all connections on the power cable, opened the top door of the case to make sure there are no dust or any visible damage on the board. The multimeter shows that the board gets stable 13.8V from the SamplexPower SEC-1235M power supply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What else should I check?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-07-08T11:06:38.433" LastActivityDate="2019-07-09T13:18:48.020" Title="Presumably working FT-8900R doesn't turn on. What can be a reason?" Tags="&lt;yaesu&gt;&lt;repair&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14874" PostTypeId="1" CreationDate="2019-07-08T10:24:11.377" Score="5" ViewCount="209" Body="&lt;p&gt;I have been looking at the Buddipole, and I've seen the most popular configuration is as a standard dipole with the arms parallel to the ground. I've also seen it configured as an upright V, as well as configured in a sloped condition. But I haven't found anyone that uses it as an inverted V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It looks like there could be some advantages to it. Sloping the arms down at 45 degrees would relieve some of the mechanical strain on the arms as well as lower the center of gravity. The antenna would also be more omnidirectional (assuming you want that). Finally, I'm not an expert on impedance matching, but I think it would also bring the impedance closer to 50 ohms which would eliminate the balun requirement, right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I overlooking some key detail here? Why is this not a more popular configuration?&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2019-07-09T08:31:05.213" Title="Why does no one use a Buddipole as an Inverted V?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14875" PostTypeId="2" ParentId="14874" CreationDate="2019-07-08T13:44:44.370" Score="3" Body="&lt;p&gt;The 50 Ohm impedance doesn't eliminate the need of the balun. A balun prevents the feed line to work as a part of the antenna (eliminates common mode current). You can find more info on this topic in the article &lt;a href=&quot;http://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/AntComp1-Lewallen(1).pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Baluns: What They Do And How They Do It [PDF]&lt;/a&gt; by Roy Lewallen, W7EL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess the reason why most people don't use Buddipole as an inverted V is that if you want an inverted V you can erect a full-sized inverted V on a fishing rod. If you are using Buddipole which is a shortened (= less efficient) dipole, you probably want something else. Directivity for instance, i.e. a dipole configuration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also suspect that many users of Buddipole don't actually care about directivity or anything else and just experiment with different configurations for fun.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-07-08T14:28:21.290" LastActivityDate="2019-07-08T14:28:21.290" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14876" PostTypeId="2" ParentId="14873" CreationDate="2019-07-08T20:22:27.407" Score="4" Body="&lt;p&gt;OK, I figured it out. Turned out a little FFC cable disconnected inside the panel during the shipping. After fixing this the radio worked flawlessly! &lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-07-08T20:22:27.407" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14877" PostTypeId="2" ParentId="14874" CreationDate="2019-07-09T05:14:17.410" Score="2" Body="&lt;p&gt;A vee-dipole brings the impedance &lt;em&gt;down&lt;/em&gt; compared to the same dipole in &quot;straight&quot; configuration. If you've got that theoretical half-wave in free-space with its 72-ish ohms of impedance then sure, maybe you want to bring it down towards 50. But a Buddipole almost always has too &lt;em&gt;little&lt;/em&gt; impedance to start with, so you don't want to reduce it any further.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mechanically, the peak of a Buddipole is usually not very high up, so you can't tilt the elements down very much before you have to start worrying about them contacting the ground, or at least people's eyes. And even when you mount them straight, those whips flex towards the ground anyway.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-07-09T05:14:17.410" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14879" PostTypeId="2" ParentId="14874" CreationDate="2019-07-09T08:31:05.213" Score="3" Body="&lt;p&gt;There are 4 questions in the original post:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Why does no one use a Buddipole as an Inverted V?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I think it would also bring the impedance closer to 50 ohms which would eliminate the balun requirement, right?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Am I overlooking some key detail here?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Why is this not a more popular configuration?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;There are good answers given for question 2, but not for the others. Reason is probably that questions 1/3/4 are quite speculative.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;Why does no one use a Buddipole as an Inverted V?&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&quot;no one&quot; probably is an assumption which is speculative. However I must say that I have experience with the Buddipole. I have &quot;bended down&quot; the elements. I cannot recall if the results were any different then the elements horizontal. While never really experimented or measured it, I am not sure about either advandtages or disadvantages of such. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However to say that &quot;no one&quot; uses this, is probably an overstretch&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol start=&quot;3&quot;&gt;&#xA;  &lt;li&gt;Am I overlooking some key detail here?&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I believe that in order to answer that you need to experiment, measure, and probably apply complex math's to answer such a question. As the Buddipole itself is a compromise antenna, there are many design factors to take into account, which makes the math on detail even more complex.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Chances are that some detail is indeed overlooked, simplisticly speaking. (no disrespect to OP)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol start=&quot;4&quot;&gt;&#xA;  &lt;li&gt;Why is this not a more popular configuration?&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This would be speculative, but in my opinion; if you need an inverted V, you need to get the feedpoint up higher than traditionally done with the Buddipole. And while you have the feedpoint higher, you may as well run a half-wave (two quarter wave) wires, to have a &lt;em&gt;normal&lt;/em&gt; inverted V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have done it, I cannot recall any difference vs the normal dipole config. Saying that, I was not looking or executing any measurements either, so if there was a difference then I probably would not have noticed it. Other than that; I would guess you need to &quot;just try it&quot; and experience yourself.&lt;/p&gt;&#xA;" OwnerUserId="6079" LastActivityDate="2019-07-09T08:31:05.213" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14881" PostTypeId="1" AcceptedAnswerId="14882" CreationDate="2019-07-09T13:51:17.467" Score="1" ViewCount="204" Body="&lt;p&gt;Inspired by &lt;a href=&quot;https://chat.stackexchange.com/rooms/95673/discussion-between-zeiss-ikon-and-brian-k1li&quot;&gt;this discussion&lt;/a&gt;, I wanted to check if this is something I can get away with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've got an old FM Broadcast antenna that came with a home stereo receiver -- it's 75 ohm flat cable, in a T shape (not sure if it's a loop or folded dipole, but I'll check -- let's assume, for this question, that it's a folded dipole).  It's close to resonant length for the 3m approximate center of the FM Broadcast band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've read that antennae often work well if they're on a third harmonic of the transmit frequency.  This antenna is close to a third harmonic of the upper end of the 10m ham band (a little short, but not much).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I currently have it connected to a Heathkit SB-102; I was using it to test the receive functions.  It occurred to me that I might be able to transmit meaningfully (possibly at reduced power) on the highest 10m segment supported by this transceiver (29.5-29.8 MHz), or, if there's enough matching capability, on the rest of 10m band.  I'm concerned, however, not to damage anything while trying to adjust the transceiver's matching network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is that a realistic concern?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-07-11T18:25:48.150" Title="Will transmitting on this antenna cause problems?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14882" PostTypeId="2" ParentId="14881" CreationDate="2019-07-09T14:32:10.287" Score="8" Body="&lt;p&gt;It won't work very well.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;antennas often work well if they're on a third harmonic of the transmit frequency&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is calculating the third harmonic the wrong way around. A better statement would be something like&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;em&gt;dipole&lt;/em&gt; antennas often work well &lt;strong&gt;at the&lt;/strong&gt; third harmonic of the &lt;em&gt;design&lt;/em&gt; frequency&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A simple dipole antenna like an inverted-V, designed for 10 MHz will probably work at 30 MHz. The radiation pattern will be broken up into three beams, not one, but that doesn't matter much at HF. It might even help, as the middle lobe has a higher gain than a dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it doesn't work the other way around.  An antenna designed for 100 MHz will be extremely short for 30 MHz, and hardly radiate at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not certain that a &lt;em&gt;folded dipole&lt;/em&gt; will resonate nicely again at three times the design frequency, because of the interplay of the transmission line and antenna modes. This needs to be simulated to be sure.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-07-09T14:32:10.287" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="14883" PostTypeId="1" AcceptedAnswerId="14884" CreationDate="2019-07-09T20:09:54.210" Score="2" ViewCount="205" Body="&lt;p&gt;I am trying to figure out how I control a Software Defined Radio over a network, and stream the received baseband samples from my remote hardware back to the gnuradio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I'm trying to do here is, this Python code should be able to output a user selectable waveform which can be a CW tone, Broadband Noise, or an arbitrary waveform read from a file containing I/Q values.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I searched on the internet and the closest thing that I found was the BorIP and unfortunately couldn't get it set-up on my machine because the instructions I found were not helpful (at least for a beginner like me). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I created the Python web server using this script (which I found online):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;    import http.server&#xA;import socketserver&#xA;&#xA;PORT = 8080&#xA;Handler = http.server.SimpleHTTPRequestHandler&#xA;&#xA;with socketserver.TCPServer((&quot;&quot;, PORT), Handler) as httpd:&#xA;    print(&quot;serving at port&quot;, PORT)&#xA;    httpd.serve_forever()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;But didn't know how to merge the generated gnuradio python code into the Python web server.&lt;/p&gt;&#xA;" OwnerUserId="15206" LastEditorUserId="76" LastEditDate="2019-07-09T20:48:55.907" LastActivityDate="2019-07-17T02:23:32.870" Title="Merging gnuradio generated python code into the Python web server" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14884" PostTypeId="2" ParentId="14883" CreationDate="2019-07-09T20:47:47.153" Score="4" Body="&lt;p&gt;GNU Radio Companion (GRC) generates Python code that is something like this (not exact text). &lt;strong&gt;(Make sure you chose the &quot;No GUI&quot; option in GRC.)&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;class my_block(gr.top_block):&#xA;    # ...&#xA;&#xA;def main():&#xA;    tb = my_block()&#xA;    tb.run()&#xA;&#xA;if __name__ == '__main__':&#xA;    main()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;You can just &lt;code&gt;import&lt;/code&gt; this as a module in your Python program (the &lt;code&gt;if __name__&lt;/code&gt; check will skip running the code that wouldn't be appropriate). Once you've done that, the way you use it is to just create the top block and call &lt;code&gt;tb.start()&lt;/code&gt;. This will start the flow graph without also waiting for it to finish, which is exactly what you want when you have a separate main loop like a web server.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;import my_block&#xA;&#xA;tb = my_block.my_block()&#xA;tb.start()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;When you're shutting down, do this to stop the GNU Radio threads:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;tb.stop()&#xA;tb.wait()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Then you can also use the generated methods (a getter and setter per GRC &quot;Variable&quot;) to change parameters while the flow graph is running. For example, if you have a &quot;Variable&quot; block in GRC with ID &lt;code&gt;freq&lt;/code&gt;, then you can use &lt;code&gt;freq&lt;/code&gt; in other blocks' parameters, and &lt;strong&gt;GRC will generate&lt;/strong&gt; a getter and setter method like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;def get_freq(self):&#xA;    return self.freq&#xA;&#xA;def set_freq(self, freq):&#xA;    self.freq = freq&#xA;    self.freq_xlating_fir_filter_xxx_0.set_center_freq(self.freq)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And so from your controlling application, you call these methods, like &lt;code&gt;tb.set_freq(123e6)&lt;/code&gt; to change the frequency to 123 MHz, for example.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;There's a lot more that can be said about how to go beyond what GRC generates for you (which would best be asked as separate questions), but this is how you get started with integrating a GNU Radio flow graph into a larger program.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would recommend &lt;em&gt;expecting&lt;/em&gt; to eventually stop using GRC's code generation and write your own Python code. This is because GRC has quite a few limitations in what you can do with it — for example, if you want to decide at runtime which type of signal source block to create, you can't do that in GRC but it's easy when you write your own Python. You can always use GRC to generate examples to copy from, when you're unsure how to configure a block.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-07-17T02:23:32.870" LastActivityDate="2019-07-17T02:23:32.870" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14888" PostTypeId="2" ParentId="14864" CreationDate="2019-07-10T00:02:26.740" Score="1" Body="&lt;p&gt;For ultimate receive performance you would need a LNA at the antenna for UHF to avoid the losses of the coax and to improve the system noise figure. A LNA for VHF would not hurt (probably) and then you could use simple T-connectors to send the outputs through the same 70 ohm cable without loss of S/N. A receive only system is by far easier than a RX/TX system :-)&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-07-10T00:02:26.740" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14889" PostTypeId="1" AcceptedAnswerId="14891" CreationDate="2019-07-10T08:33:02.883" Score="5" ViewCount="117" Body="&lt;p&gt;An engineer working in the RF industry told me something which left me very confused: He said that a pair of emitter-receiver beacons get the clearest signal when loopstick antennas in the receiver and the emitter are parallel. That is, when both loopstick ferrite rods point at each other. (We are talking low MF band, with distances of 50-100 meters between antennas)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This left me confused for the following reasons:&lt;br&gt;&#xA;- I had been taught from multiple sources that a loopstick antenna has a null in the loop axis.&lt;br&gt;&#xA;- According to my limited knowledge of the Maxwell equations, near and far field, and antennas, the opposite should be true.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First off, a visualization of the EM field around a dipole antenna field is easy to find:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/7cvXu.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7cvXu.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I understand, the field around a loopstick antenna would look something like this:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/1FaJJ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1FaJJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is correct, I would assume that placing the loopstick antennas parallel but side by side would maximize the signal strength, and not placing them parallel on an axis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;( like this  ||     ||  VS  like this  =     = )&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what is the right answer?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(An extra question: this engineer mentioned that at distances 50+ meters away, it should still be considered as near-field. Wouldn't the near-field for a ~600m wavelength, loopstick antenna be much, much smaller?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="15228" LastEditorUserId="15228" LastEditDate="2019-07-10T08:38:42.927" LastActivityDate="2019-07-10T13:40:29.157" Title="How should two loopstick antennas be placed w.r.t each other to maximize transmission?" Tags="&lt;mf&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14891" PostTypeId="2" ParentId="14889" CreationDate="2019-07-10T13:40:29.157" Score="8" Body="&lt;p&gt;When they're very close together, aligning them end to end will give better coupling - think of them as coupled inductors or a transformer. You want the strongest magnetic field from one magnet, to pass through the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When they're very far apart, you're right, side to side, broad side, is best. Remember that you're free to think of an antenna as a magnetic or an electric device. A loop or coil is just a lot of little dipoles in series, and its far fields reflect this. From the end of a small loop, the (far) electric fields of all the little dipoles clearly cancel out, so there's a null.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the cross-over region it might be complicated.&lt;br&gt;&#xA;Near fields (the reactive fields that decay as &lt;span class=&quot;math-container&quot;&gt;$1\over{r^2}$&lt;/span&gt; ) and far fields (travelling wave components that decay as &lt;span class=&quot;math-container&quot;&gt;$1\over{r}$&lt;/span&gt;) are equal at approximately &lt;span class=&quot;math-container&quot;&gt;$\lambda\over{2\pi}$&lt;/span&gt; or 90 metres in your case, so the transformer type coupling might dominate over the antenna-type coupling.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-07-10T13:40:29.157" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14892" PostTypeId="1" AcceptedAnswerId="14919" CreationDate="2019-07-10T17:45:19.057" Score="2" ViewCount="4089" Body="&lt;p&gt;I encountered with the &quot;No module named 'gnuradio'&quot; error while I was trying to run GnuRadio python code in my python web server.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rm15U.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rm15U.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And this is my gnuRadio generated code:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;#!/usr/bin/env python2&#xA;# -*- coding: utf-8 -*-&#xA;##################################################&#xA;# GNU Radio Python Flow Graph&#xA;# Title: Exercise 1&#xA;# GNU Radio version: 3.7.13.5&#xA;##################################################&#xA;&#xA;from gnuradio import analog&#xA;from gnuradio import audio&#xA;from gnuradio import blocks&#xA;from gnuradio import eng_notation&#xA;from gnuradio import filter&#xA;from gnuradio import gr&#xA;from gnuradio.eng_option import eng_option&#xA;from gnuradio.filter import firdes&#xA;from optparse import OptionParser&#xA;import osmosdr&#xA;import time&#xA;&#xA;&#xA;class Exercise_1(gr.top_block):&#xA;&#xA;    def __init__(self):&#xA;        gr.top_block.__init__(self, &quot;Exercise 1&quot;)&#xA;&#xA;        ##################################################&#xA;        # Variables&#xA;        ##################################################&#xA;        self.samp_rate = samp_rate = 10000000&#xA;        self.channel_width = channel_width = 200e3&#xA;        self.channel_freq = channel_freq = 96.5e6&#xA;        self.center_freq = center_freq = 97.9e6&#xA;&#xA;        ##################################################&#xA;        # Blocks&#xA;        ##################################################&#xA;        self.rational_resampler_xxx_0 = filter.rational_resampler_ccc(&#xA;                interpolation=12,&#xA;                decimation=5,&#xA;                taps=None,&#xA;                fractional_bw=None,&#xA;        )&#xA;        self.osmosdr_source_0 = osmosdr.source( args=&quot;numchan=&quot; + str(1) + &quot; &quot; + '' )&#xA;        self.osmosdr_source_0.set_sample_rate(samp_rate)&#xA;        self.osmosdr_source_0.set_center_freq(center_freq, 0)&#xA;        self.osmosdr_source_0.set_freq_corr(0, 0)&#xA;        self.osmosdr_source_0.set_dc_offset_mode(0, 0)&#xA;        self.osmosdr_source_0.set_iq_balance_mode(0, 0)&#xA;        self.osmosdr_source_0.set_gain_mode(False, 0)&#xA;        self.osmosdr_source_0.set_gain(0, 0)&#xA;        self.osmosdr_source_0.set_if_gain(20, 0)&#xA;        self.osmosdr_source_0.set_bb_gain(20, 0)&#xA;        self.osmosdr_source_0.set_antenna('', 0)&#xA;        self.osmosdr_source_0.set_bandwidth(0, 0)&#xA;&#xA;        self.low_pass_filter_0 = filter.fir_filter_ccf(int(samp_rate / channel_width), firdes.low_pass(&#xA;            1, samp_rate, 75e3, 25e3, firdes.WIN_HAMMING, 6.76))&#xA;        self.blocks_multiply_xx_0 = blocks.multiply_vcc(1)&#xA;        self.audio_sink_0 = audio.sink(48000, '', True)&#xA;        self.analog_wfm_rcv_0 = analog.wfm_rcv(&#xA;            quad_rate=480e3,&#xA;            audio_decimation=10,&#xA;        )&#xA;        self.analog_sig_source_x_0 = analog.sig_source_c(samp_rate, analog.GR_COS_WAVE, center_freq - channel_freq, 1, 0)&#xA;&#xA;&#xA;&#xA;        ##################################################&#xA;        # Connections&#xA;        ##################################################&#xA;        self.connect((self.analog_sig_source_x_0, 0), (self.blocks_multiply_xx_0, 1))&#xA;        self.connect((self.analog_wfm_rcv_0, 0), (self.audio_sink_0, 0))&#xA;        self.connect((self.blocks_multiply_xx_0, 0), (self.low_pass_filter_0, 0))&#xA;        self.connect((self.low_pass_filter_0, 0), (self.rational_resampler_xxx_0, 0))&#xA;        self.connect((self.osmosdr_source_0, 0), (self.blocks_multiply_xx_0, 0))&#xA;        self.connect((self.rational_resampler_xxx_0, 0), (self.analog_wfm_rcv_0, 0))&#xA;&#xA;    def get_samp_rate(self):&#xA;        return self.samp_rate&#xA;&#xA;    def set_samp_rate(self, samp_rate):&#xA;        self.samp_rate = samp_rate&#xA;        self.osmosdr_source_0.set_sample_rate(self.samp_rate)&#xA;        self.low_pass_filter_0.set_taps(firdes.low_pass(1, self.samp_rate, 75e3, 25e3, firdes.WIN_HAMMING, 6.76))&#xA;        self.analog_sig_source_x_0.set_sampling_freq(self.samp_rate)&#xA;&#xA;    def get_channel_width(self):&#xA;        return self.channel_width&#xA;&#xA;    def set_channel_width(self, channel_width):&#xA;        self.channel_width = channel_width&#xA;&#xA;    def get_channel_freq(self):&#xA;        return self.channel_freq&#xA;&#xA;    def set_channel_freq(self, channel_freq):&#xA;        self.channel_freq = channel_freq&#xA;        self.analog_sig_source_x_0.set_frequency(self.center_freq - self.channel_freq)&#xA;&#xA;    def get_center_freq(self):&#xA;        return self.center_freq&#xA;&#xA;    def set_center_freq(self, center_freq):&#xA;        self.center_freq = center_freq&#xA;        self.osmosdr_source_0.set_center_freq(self.center_freq, 0)&#xA;        self.analog_sig_source_x_0.set_frequency(self.center_freq - self.channel_freq)&#xA;&#xA;&#xA;def main(top_block_cls=Exercise_1, options=None):&#xA;&#xA;    tb = top_block_cls()&#xA;    tb.start()&#xA;    try:&#xA;        raw_input('Press Enter to quit: ')&#xA;    except EOFError:&#xA;        pass&#xA;    tb.stop()&#xA;    tb.wait()&#xA;&#xA;&#xA;if __name__ == '__main__':&#xA;    main()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I tried to figure out the cause of this error but no luck. I even removed Pybombs and reinstall it again but kept getting the same error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any clues to solve this error would be highly appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Update:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I appreciate your help &quot;fmagno&quot;. Again, I removed/cleaned everything and tried to follow the instructions you recommended, but I am stuck with the below error whenever I run pybombs auto-config. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The error is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PyBOMBS.RecipeListManager - ERROR - '/home/fit-pc/.pybombs/recipes/gr-recipes' is not a directory. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4GFZb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4GFZb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Update:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fmagno, I just finished re-installation and made sure that pybombs prefix is activated by running source setup_env.sh before using gnuradio, but it did solve the main problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZEIYV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZEIYV.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9Mdmm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9Mdmm.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15206" LastEditorUserId="15206" LastEditDate="2019-07-11T18:47:15.710" LastActivityDate="2019-07-15T18:07:49.473" Title="No module named 'gnuradio'" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14893" PostTypeId="1" CreationDate="2019-07-10T21:19:05.793" Score="1" ViewCount="63" Body="&lt;p&gt;I have a winegard 8200 series antenna and it worked flawlessly in getting me reception of more than 70 stations. The wind blew it down and I couldn't replace it for about 6 months due to the fact that I couldn't get a suitable man lift into my yard because of the season and ground conditions. When I replaced it with a new one, my reception was seriously limited. I could receive signals in both the UHF and VHF ranges, however only a few in each. I have a rotor and tried every adjustment. I replaced the coaxial cable, my amplifier and the splitter card from winegard. Nothing worked. I was about to give up, when, out of the blue, my reception became flawless again! It only lasted a week and reverted to the limited reception that was unsatisfactory. I have discussed the issue with Winegard and they suggest that it is not an antenna issue. My neighbor is a Ham radio operator and his house is located between me and the broadcasting stations in the large metro area to the East of me approximately 60 miles away. I just learned that he is an amateur radio guy, because he has no large antenna on his property, which I thought was requisite for a Ham operator. My question is, can his equipment be somehow blocking my reception?&lt;/p&gt;&#xA;" OwnerUserId="15232" LastActivityDate="2019-07-10T21:19:05.793" Title="Can my neighbors ham radio station be preventing my TV antenna from proper reception?" Tags="&lt;rfi&gt;&lt;frequency&gt;&lt;equipment&gt;" AnswerCount="0" CommentCount="4" ClosedDate="2019-07-10T21:21:16.417" ContentLicense="CC BY-SA 4.0" />
  <row Id="14896" PostTypeId="2" ParentId="14892" CreationDate="2019-07-11T13:20:35.267" Score="2" Body="&lt;p&gt;@Hadad, maybe you are not activating your pybombs prefix by running  &lt;code&gt;source setup_env.sh&lt;/code&gt; before using gnuradio? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Documentation for details: &lt;a href=&quot;https://wiki.gnuradio.org/index.php/InstallingGR#Using_PyBOMBS&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wiki.gnuradio.org/index.php/InstallingGR#Using_PyBOMBS&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once activated you should be able to import gnuradio within a python console without errors:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;$ python&#xA;&amp;gt;&amp;gt;&amp;gt; import gnuradio&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="14674" LastActivityDate="2019-07-11T13:20:35.267" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14897" PostTypeId="2" ParentId="14881" CreationDate="2019-07-11T18:25:48.150" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Will transmitting on this antenna cause problems?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;It certainly can&lt;/strong&gt;! Forget that FM BCB antenna, my friend. You can damage your SB-102.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are not only wasting your time with it, but you may very well damage your 6146B PA tubes &lt;strong&gt;or related components&lt;/strong&gt; in the PA circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if you had an external tuner that &lt;em&gt;could&lt;/em&gt; match that antenna on 10m, you would have &lt;em&gt;enormous&lt;/em&gt; losses. You need a dipole in the air that's fairly close to resonance, say less than 5:1 SWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But before you go that far, I strongly suggest that you buy a 100 watt (or more) non-resonant 50 ohm dummy load. Once you can load that, &lt;em&gt;then&lt;/em&gt; you can build and connect a proper antenna.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-07-11T18:25:48.150" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14898" PostTypeId="2" ParentId="6631" CreationDate="2019-07-11T22:00:57.773" Score="3" Body="&lt;p&gt;The 3-volt plug that works with the Eton Mini portable reciever is the Philmore # 204.  Its stated dimensions are 1.3mm I.D. and 3.5mm O.D.  It works!&lt;/p&gt;&#xA;" OwnerUserId="15238" LastActivityDate="2019-07-11T22:00:57.773" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14899" PostTypeId="1" CreationDate="2019-07-12T16:01:23.260" Score="0" ViewCount="138" Body="&lt;p&gt;I am trying to run GnuRadio python code in my python web server and got the &quot;No module named _osmosdr_swig&quot; error. Please, what is the cause for this error? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know it sounds like so obvious that I need to have the 'osmosdr-swig' package but I searched online trying to figure out how to add it but no luck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/q5LGo.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/q5LGo.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My python code is:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;#!/usr/bin/env python2&#xA;# -*- coding: utf-8 -*-&#xA;##################################################&#xA;# GNU Radio Python Flow Graph&#xA;# Title: Exercise 1&#xA;# GNU Radio version: 3.7.13.5&#xA;##################################################&#xA;&#xA;from gnuradio import analog&#xA;from gnuradio import audio&#xA;from gnuradio import blocks&#xA;from gnuradio import eng_notation&#xA;from gnuradio import filter&#xA;from gnuradio import gr&#xA;from gnuradio.eng_option import eng_option&#xA;from gnuradio.filter import firdes&#xA;from optparse import OptionParser&#xA;import osmosdr&#xA;import time&#xA;&#xA;&#xA;&#xA;class Exercise_1(gr.top_block):&#xA;&#xA;    def __init__(self):&#xA;        gr.top_block.__init__(self, &quot;Exercise 1&quot;)&#xA;&#xA;        ##################################################&#xA;        # Variables&#xA;        ##################################################&#xA;        self.samp_rate = samp_rate = 10000000&#xA;        self.channel_width = channel_width = 200e3&#xA;        self.channel_freq = channel_freq = 96.5e6&#xA;        self.center_freq = center_freq = 97.9e6&#xA;&#xA;        ##################################################&#xA;        # Blocks&#xA;        ##################################################&#xA;        self.rational_resampler_xxx_0 = filter.rational_resampler_ccc(&#xA;                interpolation=12,&#xA;                decimation=5,&#xA;                taps=None,&#xA;                fractional_bw=None,&#xA;        )&#xA;        self.osmosdr_source_0 = osmosdr.source( args=&quot;numchan=&quot; + str(1) + &quot; &quot; + '' )&#xA;        self.osmosdr_source_0.set_sample_rate(samp_rate)&#xA;        self.osmosdr_source_0.set_center_freq(center_freq, 0)&#xA;        self.osmosdr_source_0.set_freq_corr(0, 0)&#xA;        self.osmosdr_source_0.set_dc_offset_mode(0, 0)&#xA;        self.osmosdr_source_0.set_iq_balance_mode(0, 0)&#xA;        self.osmosdr_source_0.set_gain_mode(False, 0)&#xA;        self.osmosdr_source_0.set_gain(0, 0)&#xA;        self.osmosdr_source_0.set_if_gain(20, 0)&#xA;        self.osmosdr_source_0.set_bb_gain(20, 0)&#xA;        self.osmosdr_source_0.set_antenna('', 0)&#xA;        self.osmosdr_source_0.set_bandwidth(0, 0)&#xA;&#xA;        self.low_pass_filter_0 = filter.fir_filter_ccf(int(samp_rate / channel_width), firdes.low_pass(&#xA;            1, samp_rate, 75e3, 25e3, firdes.WIN_HAMMING, 6.76))&#xA;        self.blocks_multiply_xx_0 = blocks.multiply_vcc(1)&#xA;        self.audio_sink_0 = audio.sink(48000, '', True)&#xA;        self.analog_wfm_rcv_0 = analog.wfm_rcv(&#xA;            quad_rate=480e3,&#xA;            audio_decimation=10,&#xA;        )&#xA;        self.analog_sig_source_x_0 = analog.sig_source_c(samp_rate, analog.GR_COS_WAVE, center_freq - channel_freq, 1, 0)&#xA;&#xA;&#xA;&#xA;        ##################################################&#xA;        # Connections&#xA;        ##################################################&#xA;        self.connect((self.analog_sig_source_x_0, 0), (self.blocks_multiply_xx_0, 1))&#xA;        self.connect((self.analog_wfm_rcv_0, 0), (self.audio_sink_0, 0))&#xA;        self.connect((self.blocks_multiply_xx_0, 0), (self.low_pass_filter_0, 0))&#xA;        self.connect((self.low_pass_filter_0, 0), (self.rational_resampler_xxx_0, 0))&#xA;        self.connect((self.osmosdr_source_0, 0), (self.blocks_multiply_xx_0, 0))&#xA;        self.connect((self.rational_resampler_xxx_0, 0), (self.analog_wfm_rcv_0, 0))&#xA;&#xA;    def get_samp_rate(self):&#xA;        return self.samp_rate&#xA;&#xA;    def set_samp_rate(self, samp_rate):&#xA;        self.samp_rate = samp_rate&#xA;        self.osmosdr_source_0.set_sample_rate(self.samp_rate)&#xA;        self.low_pass_filter_0.set_taps(firdes.low_pass(1, self.samp_rate, 75e3, 25e3, firdes.WIN_HAMMING, 6.76))&#xA;        self.analog_sig_source_x_0.set_sampling_freq(self.samp_rate)&#xA;&#xA;    def get_channel_width(self):&#xA;        return self.channel_width&#xA;&#xA;    def set_channel_width(self, channel_width):&#xA;        self.channel_width = channel_width&#xA;&#xA;    def get_channel_freq(self):&#xA;        return self.channel_freq&#xA;&#xA;    def set_channel_freq(self, channel_freq):&#xA;        self.channel_freq = channel_freq&#xA;        self.analog_sig_source_x_0.set_frequency(self.center_freq - self.channel_freq)&#xA;&#xA;    def get_center_freq(self):&#xA;        return self.center_freq&#xA;&#xA;    def set_center_freq(self, center_freq):&#xA;        self.center_freq = center_freq&#xA;        self.osmosdr_source_0.set_center_freq(self.center_freq, 0)&#xA;        self.analog_sig_source_x_0.set_frequency(self.center_freq - self.channel_freq)&#xA;&#xA;&#xA;def main(top_block_cls=Exercise_1, options=None):&#xA;&#xA;    tb = top_block_cls()&#xA;    tb.start()&#xA;    try:&#xA;        raw_input('Press Enter to quit: ')&#xA;    except EOFError:&#xA;        pass&#xA;    tb.stop()&#xA;    tb.wait()&#xA;&#xA;&#xA;if __name__ == '__main__':&#xA;    main()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="15206" LastEditorUserId="15206" LastEditDate="2019-07-12T16:17:38.347" LastActivityDate="2019-07-12T16:17:38.347" Title="No module named _osmosdr_swig" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;gnuradio&gt;&lt;usrp&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2019-07-15T17:00:17.830" ContentLicense="CC BY-SA 4.0" />
  <row Id="14900" PostTypeId="1" AcceptedAnswerId="14908" CreationDate="2019-07-12T20:32:49.597" Score="7" ViewCount="1485" Body="&lt;p&gt;If you search the Internet for Faraday cages, you'll find a lot of information about using homemade cages to protect radios from EMP damage while in storage.  A lot of that information is either contradictory or isn't backed up by satisfactory explanations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not my intent to debate the usefulness of storing equipment in Faraday cages.  There aren't a lot of nuclear wars or lightning strikes where I live, so odds are really good that I don't need to worry about it.  But, I am curious about the theory of operation and practical design considerations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I understand it, radio waves can't penetrate into a space that's fully enclosed by a sufficient thickness of conductive material.  The radio waves induce a current in the conductor, which results in the energy being re-released as a mix of radio waves and heat, right?  What stops the radio waves from being released to the inside of the container?  (I'm guessing it's related to the skin effect.)  Does it matter to any electronics inside the cage if they're in physical contact with the cage?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is a DIY Faraday cage as simple as using a metal suitcase or a foil-wrapped box, or is there more to it than that?&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="76" LastEditDate="2019-07-13T22:06:52.023" LastActivityDate="2019-07-13T23:43:29.893" Title="How does a Faraday cage block an EMP?" Tags="&lt;theory&gt;&lt;faraday-cage&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14901" PostTypeId="1" AcceptedAnswerId="14902" CreationDate="2019-07-12T20:48:17.273" Score="1" ViewCount="790" Body="&lt;p&gt;I understand that my question is not desireable for ham radio communication at all, but bear with me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to use long range walkie talkies whose microphone is attached to an underground acoustic sensor and bury it into the ground, it transmitting their acoustics on a specified channel constantly, in order to &quot;baby monitor&quot; a certain area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously a number of these devices would need to work in parallel to be effective. I'm just wondering if a number of these devices are transmitting on a specific channel, will a receiver walkie talkie be able to hear all the signals coming from the ground sensors?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not is there a radio setup/circuit that would allow for long range acoustic monitoring of all these sensors concurrently?&lt;/p&gt;&#xA;" OwnerUserId="10855" LastEditorUserId="76" LastEditDate="2019-07-12T21:32:32.633" LastActivityDate="2019-07-14T13:48:00.757" Title="Is it possible to have multiple people talking on the same radio channel at the same time?" Tags="&lt;modes&gt;&lt;transmission&gt;&lt;phone&gt;&lt;telemetry&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14902" PostTypeId="2" ParentId="14901" CreationDate="2019-07-12T21:31:41.537" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;if a number of these devices are transmitting on a specific channel, will a receiver walkie talkie be able to hear all the signals coming from the ground sensors?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The exact result depends on the modulation used, but in no case will it be all that useful.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;If they use FM (almost certain for any modern off-the-shelf equipment), you will hear mostly the strongest signal, and if two signals are of similar strength you will hear interference sounds as well as some of the other signal. This is known as the &lt;a href=&quot;https://en.wikipedia.org/wiki/Capture_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;capture effect&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;If they use AM, you will hear the audio from all of them, but mixed in proportion to the RF signal strength (&lt;em&gt;not&lt;/em&gt; the audio volume). So the one closest to the receiver will be much more audible.&lt;/li&gt;&#xA;&lt;li&gt;If they use a digital voice modulation, you will probably hear the strongest one and other transmissions will be entirely inaudible except as interference; degradation and drop-outs of the signal, not any of the other audio.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In order to get multiple audio signals through, you must use multiple channels (frequencies), or use a system that is intended to share a single channel (e.g. as cell phones do).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If not is there a radio setup/circuit that would allow for long range acoustic monitoring of all these sensors concurrently?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What comes to mind is some kind of digital mesh network. Since you're intending to spread sensors across an area of land, a mesh means that each sensor node can forward data from others so that you get your monitoring done with less total power needed. Using a suitable audio codec, or a simple noise gate, you can have the nodes which are not hearing any significant sound not send any data, thus saving power (again) and bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I'm not familiar with the field to recommend equipment, and it would probably require a bit of configuration and programming to set up the monitoring (though it is probably easier to make an inefficient prototype than something fit to run off batteries/solar permanently).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-07-12T21:31:41.537" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14903" PostTypeId="2" ParentId="14901" CreationDate="2019-07-13T12:13:21.903" Score="0" Body="&lt;p&gt;If it is a small number of sensors and they are relatively far apart, you could consider using a separate receiver for each transmitter, each receiver having a directional antenna pointing at its transmitter.  This still uses one channel but has multiple monitors.  You could use any number of summing methods to combine everything if you like.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several problems with this approach depending on how the sensors are laid out, the biggest being that &quot;directional antennas&quot; are not perfect and if the transmitters are close together (really this means small angular separation as seen at the receivers) this could have significant challenges.  But with a little imagination I think you can see how to address it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;multiple receiver&quot; thing adds some flexibility; receivers do not all need to be at a central location, they just need to be somewhere with alternate communication infrastructure (like an internet, for example).  SDR receivers are inexpensive and fun --fun is important when monitoring underground pressure sensors :-)  @KevinReidAG6YO 's observation that FM will only decode the dominant signal is a feature in this scenario.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One other suggestion...  Depending on the bandwidth you are monitoring, you could consider using an acoustic frequency shifting technique so each transmitter sends a unique acoustic band on that transmitter frequency.  Then AM would make more sense than FM and there would be no need of multiple receivers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck with your project!&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2019-07-13T12:13:21.903" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14905" PostTypeId="2" ParentId="14901" CreationDate="2019-07-13T15:49:26.623" Score="0" Body="&lt;p&gt;Modern digital cell phones share channels -- a cell site can service dozens of phones on a single channel.  Whether this is practical for your application is questionable, however.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For digital cell communications, the phone digitizes the speech and transmits the data in short bursts, tens of times a second.  The return transmission to the phone is handled similarly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each burst contains either the data since the last burst, or enough data to last until the next, when the sound is re-rendered to real time.  Since the transmission burst is a tiny fraction of the real time duration of the sound it encodes, this allows multiplexing on a time-sharing basis of, in the maximum case, many more than a dozen cell phones on a single tower channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The technology to do this, unfortunately, is expensive, and represents decades of research in digital voice transmission.  Further, parts of it are still covered by patents, so you can't just buy hardware that does this job (at least not at this level).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One way you might be able to emulate this, however, would be to use VOIP software.  Skype is a well known example that handles conferencing well (especially if you don't try to conference video, but voice only).  You'd need one VOIP device for each sensor site, and a continuous connection (ethernet, wifi, or connect through the internet cloud -- some software will work without a central server, some requires it), then set up a conference.  How well this would work over the long term (say, more than an hour or two) is a question left to the experimenter...&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-07-14T13:48:00.757" LastActivityDate="2019-07-14T13:48:00.757" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14906" PostTypeId="1" CreationDate="2019-07-13T21:51:31.310" Score="3" ViewCount="735" Body="&lt;p&gt;Can a SDR be used as a general purpose AC oscilloscope with appropriate attenuation at the front end. &#xA;Have in mind a capacitor to block DC voltages, large resistor say 10 Mohms to limit current and present a high impedance to a signal &amp;amp; a scope probe.&#xA;Then would need software to convert quadrature signals in to a scope like signal on my computer screen.&lt;/p&gt;&#xA;" OwnerUserId="15242" LastActivityDate="2019-07-13T22:05:52.887" Title="SDR as an oscilloscope" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14907" PostTypeId="2" ParentId="14906" CreationDate="2019-07-13T22:05:52.887" Score="2" Body="&lt;p&gt;I haven't looked into this concept myself, but here's some thoughts on problems you'll have:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The biggest architectural difference between a software-defined radio and a digital oscilloscope is that &lt;strong&gt;a SDR usually has a downconverter in it&lt;/strong&gt;. This might be exactly what you want, if you want to bring a RF signal down to baseband and look at the waveform/modulation. But if you're looking for a general-purpose oscilloscope, this means you can't look at the original signal without frequency shifting it back up to what you &lt;em&gt;assume&lt;/em&gt; is the correct frequency — and you will have lost phase information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SDRs intended for LF-MF-HF usage will often omit downconversion (performing all frequency shifting in software). But you might find their frequency response cuts off too low, if your &quot;AC&quot; signals are low frequency as RF goes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You also won't have any of the &lt;strong&gt;input conditioning&lt;/strong&gt; of an oscilloscope front-end, unless you build a circuit for that. With your 10 MΩ series impedance — while the SDR is expecting a 50 Ω or 75 Ω input — you may find that you're picking up more signal from other sources than your probe input. (&lt;em&gt;May.&lt;/em&gt; I'm not confident about this.) At a minimum, I'd expect it to function a lot better with a buffer amplifier (which would also give you a fairly good sacrificial component in case of bad input, if nothing else).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;On the other hand, &lt;em&gt;displaying&lt;/em&gt; the signal is no problem at all. For example, if the SDR you choose has a driver for GNU Radio, then you can launch GNU Radio Companion, connect the SDR source block to a scope block, and you can immediately see the signal. You can also add frequency shifts and other signal processing that might be useful.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-07-13T22:05:52.887" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14908" PostTypeId="2" ParentId="14900" CreationDate="2019-07-13T23:43:29.893" Score="7" Body="&lt;p&gt;Faraday cages block EMP in the same way they block all other time-varying electromagnetic fields. The only difference between blocking EMP versus blocking an ordinary radio transmission is the EMP is many orders of magnitude stronger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A Faraday cage works because metals consist of a &quot;sea&quot; of mobile electrons among the protons in the atomic nuclei. That is, metals are good conductors. When an electromagnetic field approaches the metal, the mobile electrons will be attracted to the locations where the electric potential is higher, leaving behind excess protons where the electric potential is lower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mobile electrons do this because they seek the lowest potential arrangement, just as a boulder rolls down a hill, or water in a vessel in any shape tends towards level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To the extent that the Faraday cage is made of a perfect conductor, the electrons will rearrange themselves such that the redistribution of the electrons and the external field cancel exactly, so there is no change to the electromagnetic field inside the cage. No energy is lost in the process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This animation absurdly exaggerates the distance the electrons travel (in practice they barely move, since if the protons were left all alone like that the box would tear itself apart into individual atoms), but it does a fair job of getting the idea across: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cD143.gif&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cD143.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice metals aren't perfect conductors so a little energy is lost to resistance and converted to heat, and the electrons are unable to perfectly cancel the field so some of the electromagnetic wave makes it inside the cage, so we just say the Faraday cage attenuates the external field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Skin effect does indeed limit the currents to the outside surface of the metal, but that's not really necessary to explain how a Faraday cage works. Consider: Faraday cages are also effective in blocking static electric fields, where skin effect does not apply. Insulating the protected contents from the cage is probably still a good idea if the very highest attenuation is required. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is essential that the cage forms a continuous conductive shield fully enclosing the device to be protected. For example, cutting a slot in a Faraday cage renders it ineffective if that slot is an appreciable fraction of wavelength. This is because the slot presents a barrier to the motion of the electrons, and consequently the electric field associated with the mobile electrons must &quot;flow around&quot; the slot, making it no longer able to cancel the external field. A &lt;a href=&quot;http://www.antenna-theory.com/antennas/aperture/slot.php&quot; rel=&quot;noreferrer&quot;&gt;slot antenna&lt;/a&gt; exploits this effect to make a waveguide (which is not so different from an inside-out Faraday cage) radiate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For this reason, metal boxes with lids don't always work as a Faraday cage, since often the lid does not make good electrical contact with the rest of the box.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Foil works OK as long as care is taken to make good electrical contact at all seams. And the thinness of foil means less attenuation, but depending on the power of the EMP and the sensitivity of the contents, perhaps it's sufficient.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-07-13T23:43:29.893" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14909" PostTypeId="1" AcceptedAnswerId="14914" CreationDate="2019-07-14T05:32:30.637" Score="5" ViewCount="112" Body="&lt;p&gt;Good day,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have a Kenwood TS-480HT with a Wolfriver coil and a stainless steel whip in my car.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find that on 40 meters I can get the SWR at around 1.4 (using an MFJ 269) at 7.1000 MHz. But the SWR goes high (2.5 to 3.0) very quickly if I go closer to 7.0000 and even higher if I go closer to 7.2000 (past 6.0).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This also happens on 80 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way I can increase the SWR bandwidth?&lt;/p&gt;&#xA;" OwnerUserId="5784" LastActivityDate="2019-07-14T18:59:39.033" Title="Better SWR bandwidth" Tags="&lt;mobile&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14910" PostTypeId="1" CreationDate="2019-07-14T08:53:41.097" Score="3" ViewCount="84" Body="&lt;p&gt;I'm not sure this question is appropriate for this site, but I feel that if anyone knows about a filter, a radio ham knows!&#xA;And as a ham myself I feel I need to understand this important area better. To that end, I've been reading various filter texts (Zverev and Dimopoulos mainly).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm at the point where the low-pass approximation has been developed (I'm going to chose a Butterworth for this question) and I'm moving to the transformation of a low-pass to other types (high-pass, band-pass, etc).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lets take a Butterworth low-pass given in the book by Dimopoulos:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$ \frac{17.5514}{s^3+3.2743\cdot s^2+5.3604 \cdot s+4.3878}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have Maxima installed, you can try it yourself:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;load(draw);&#xA;&#xA;maxima_tempdir:&quot;C:/maxima-5.41.0a&quot;;&#xA;&#xA;H_lpbut(s):=17.5514/(s^3+3.2743*s^2+5.3604*s+4.3878);&#xA;&#xA;G_lp(omega):=abs(subst([s=%i*omega],H_lpbut(s)));&#xA;&#xA;Omega_3dB(N):=(1/beta_m())^(1/N);&#xA;&#xA;draw2d(&#xA;        xlabel=&quot;Omega&quot; &#xA;        ,ylabel=&quot;Lowpass G(Omega)&quot;&#xA;        ,xaxis=true&#xA;        ,yaxis=true&#xA;        ,xrange=[-10,10]&#xA;        ,yrange=[0,5]&#xA;        ,explicit(G_lp(omega),&#xA;                    omega,-10,10&#xA;                    )&#xA;        ,color=red&#xA;        ,points([[Omega_3dB(3), G_lp(Omega_3dB(3))]])&#xA;        ,points_joined=true&#xA;        ,line_type=dashes&#xA;        ,points([&#xA;                [0,G_lp(Omega_3dB(3))]&#xA;                ,[Omega_3dB(3), G_lp(Omega_3dB(3))]&#xA;                ,[Omega_3dB(3), 0]&#xA;            ])&#xA;    );&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;As you can see, I get the magnitude of the transfer function and plot from the normalized frequencies -10 to 10.  Notice how wonderfully symmetrical the plot is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/B4ER8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/B4ER8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That sort of makes sense, we're plugging in negative frequencies (from -10 to zero) and we end up with a mirror image of the low-pass giving a band-pass shape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, that's pretty much how the lp to bp transform works, only this time they use a different function:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \frac{\omega ^{2}-\omega_0^{2}}{\omega\cdot BW} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, using Maxima we can explore how this function maps band-pass frequencies to normalized low-pass frequencies.  I've taken some liberties here to highlight it's properties (it uses a log scale and negative infinity is now positive infinity - but you get the idea).  The function goes to infinity at one end (omega=0) and takes a more leisurely trip to infinity at the other (omega=inf).  It converges at zero (or bp centre frequency), which is exactly what required for bp transformation - so I get that bit.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;bpt(omega,omega_0,BW):=(omega^2-omega_0^2)/(omega*BW);&#xA;&#xA;draw2d(&#xA;        xrange=[0,1000]&#xA;        ,yrange=[0.0001,1000]&#xA;        ,logy=true&#xA;        ,explicit(sqrt(bpt(2*%pi*f,2*%pi*500,2*%pi*100)^2),&#xA;                    f,0,1000&#xA;                    )&#xA;    );&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kHQWv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kHQWv.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and finally, here's the transformed band-pass using the standard lp-to-bp transform:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XXg1U.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XXg1U.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice it isn't as symmetrical as the previous plot (using -10 to 10).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;But, here's what I don't get...why would they use a function like this, which is obviously non-symmetrical, to produce the band-pass?  Why not use a function that works to produce the nice linear -10 to 10 input that we saw earlier?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="11875" LastEditDate="2019-07-15T10:18:25.533" LastActivityDate="2019-07-15T10:18:25.533" Title="Where did the LP to BP transformation $ \frac{\omega ^{2}-\omega_0^{2}}{\omega\cdot BW} $ come from?" Tags="&lt;filter&gt;" AnswerCount="0" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="14911" PostTypeId="2" ParentId="14909" CreationDate="2019-07-14T13:23:26.497" Score="3" Body="&lt;p&gt;Capacitive hats (spokes, discs, or loops) on the tops of vertical antennas are reported to increase SWR bandwidth, as well as increasing radiation resistance (the loading inductance or antenna length may need to be (re)adjusted for resonance). Downside is an increase in wind loading.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-07-14T18:59:39.033" LastActivityDate="2019-07-14T18:59:39.033" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14912" PostTypeId="1" AcceptedAnswerId="14913" CreationDate="2019-07-14T13:52:09.290" Score="2" ViewCount="249" Body="&lt;p&gt;When I set my sound device to record from the monitor/loopback source, I can capture the signal from WebSDR in my browser in an application like &lt;a href=&quot;https://www.audacityteam.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Audacity&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking at the captured signal more closely reveals that both the left and right channels of the stereo signal are identical. As a result, I cannot demodulate properly from the captured signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AV7BC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AV7BC.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this a limitation of WebSDR? I can capture stereo audio correctly from other websites (e.g. YouTube).&lt;/p&gt;&#xA;" OwnerDisplayName="user15245" LastActivityDate="2019-07-14T15:32:21.697" Title="Can I capture stereo IQ signals from WebSDR?" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14913" PostTypeId="2" ParentId="14912" CreationDate="2019-07-14T15:32:21.697" Score="3" Body="&lt;p&gt;You could call it a limitation of WebSDR, but WebSDR intends to give you &lt;em&gt;demodulated&lt;/em&gt; audio, audio for &lt;em&gt;listening&lt;/em&gt; to, which an IQ signal is not suitable for (even if the signal is audio-like as in SSB and CW, the 90° phase shift of the quadrature component will make for unpleasant listening).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, you &lt;strong&gt;can&lt;/strong&gt; take a SSB signal you've captured and turn it into an IQ signal. This does not add any useful bandwidth that wasn't present in the original, of course, but it could help if it's what the demodulator you want to use needs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Hilbert_transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hilbert transform&lt;/a&gt; takes a signal and creates a 90° phase shifted version; if you replace one of the stereo channels with the transformed signal, then you have an IQ signal — specifically an &lt;em&gt;analytic&lt;/em&gt; signal, one whose frequency content is entirely in the positive half of the spectrum. If you need it 'baseband' (centered around 0 Hz) then you frequency shift it downward after the transform.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both of these steps should be doable using any DSP tools suitable for SDR; here's how you might set it up in GNU Radio. (The value in the rotator block is &lt;span class=&quot;math-container&quot;&gt;$-\pi/2$&lt;/span&gt;, a frequency shift of one quarter of the sampling rate.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4sAiu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4sAiu.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;However, &lt;strong&gt;none of this is actually necessary&lt;/strong&gt; if the demodulator you are trying to use afterward either knows how to take SSB input (in which case your recording is just fine the way it is) or can be told to look for the signal it wants at an arbitrary frequency offset.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is because the spectrum of any 1-channel signal is just symmetric about zero. You can treat it as if it were IQ and as long as your next step is to apply a bandpass filter within one of the mirrored halves, there's no difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if your demodulator expects the recording to contain &lt;em&gt;only&lt;/em&gt; the intended signal (plus noise), rather than apply a channel filter itself, then you do need to use the transformations I described above.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-07-14T15:32:21.697" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14914" PostTypeId="2" ParentId="14909" CreationDate="2019-07-14T18:57:31.177" Score="6" Body="&lt;p&gt;A low SWR bandwidth is a consequence of shortening the antenna for mobile use. SWR bandwidth is related to the antenna system's Q factor, the ratio of energy stored to energy dissipated per cycle. A higher Q means less SWR bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Decreasing Q will increase SWR bandwidth. That can be done by decreasing the energy stored, or increasing the energy dissipated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A smaller loading coil will decrease energy stored, but will require a longer whip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Distributing more current over a longer length of the antenna will increase the energy dissipated by radiation. This can be done by moving the loading coil up, thus leaving a longer section of antenna below the loading coil with high current. Or a capacitive hat at the top of the antenna increases current overall. But in either case there's some cost to be paid: higher wind loading, a longer whip, or a bigger loading coil with associated loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course energy dissipated can also be increased by increasing losses, but that's not really desirable. So if it makes you feel better, a low SWR bandwidth suggests a good, efficient antenna!&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-07-14T18:57:31.177" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14915" PostTypeId="1" CreationDate="2019-07-14T21:36:01.127" Score="0" ViewCount="228" Body="&lt;p&gt;I know guys you gonna tell me tat there is something wrong about GnuRadio or Pybombs installation. Well, this is my third time during the past 48 hours I reformat the OS of my mini pc fitlet2 mint linux and reinstall the the OS which is mint 19.1 cinamon and reinstall gnuradio using apt-get or even using Pybombs and get this problem when I try Python3 to run my .py file. Please, I am in real need for your help, again, I am a real beginner and try to learn.&#xA;Here is how I installed Pybombs:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;sudo apt-get install python3-pip&#xA;sudo apt-get install python3-setuptools&#xA;sudo pip3 install wheel&#xA;sudo apt-get install python3-setuptools&#xA;sudo pip3 install pybombs&#xA;pybombs auto-config&#xA;pybombs recipes add-defaults&#xA;pybombs prefix init ~/gnuradio -R gnuradio-default&#xA;pybombs install gr-osmosdr&#xA;pip install analog&#xA;sudo uhd_images_downloader&#xA;. ~/gnuradio/setup_env.sh&#xA;gnuradio companion&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Later, I learned Kevin here on this community how to generate a python code from Gnuradion to run it through a python web server that I built based on simple script that I've found online. When I run it using python3 I get the &quot;ModuleNotFoundError: No module named 'gnuradio'&quot; error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/weDcV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/weDcV.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3hcK8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3hcK8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know you may say something again about editing the PYTHONPATH file, and that is the other problem to be honest. I mean I am not sure what I am suppose to change aboutthe steup_env.sh file? Shouldn't be set and ready to go! If not, then please, guide me on how to do it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is my setup_env.sh file:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GS6xm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GS6xm.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Update:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I just noticed that when I run 'Pybombs run gnuradio companion' the interface itself, it generated this error:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;lt;&amp;lt;&amp;lt; Welcome to GNU Radio Companion 3.7.13.5 &amp;gt;&amp;gt;&amp;gt;&#xA;&#xA;Block paths:&#xA;    /home/fit-pc/gnuradio/share/gnuradio/grc/blocks&#xA;    /home/fit-pc/gnuradio/share/gnuradio/grc/blocks&#xA;&#xA;Loading: &quot;/media/fit-pc/DA54CCFE54CCDDFF/Mint Linux stuff/mint backup/My-Projects/FM-Radio-Receiver/FM-Radio-Receiver.grc&quot;&#xA;&amp;gt;&amp;gt;&amp;gt; Done&#xA;&#xA;Generating: '/media/fit-pc/DA54CCFE54CCDDFF/Mint Linux stuff/mint backup/My-Projects/FM-Radio-Receiver/top_block.py'&#xA;&#xA;Executing: /usr/bin/python2 -u /media/fit-pc/DA54CCFE54CCDDFF/Mint Linux stuff/mint backup/My-Projects/FM-Radio-Receiver/top_block.py&#xA;&#xA;gr-osmosdr v0.1.4-127-g4d83c606 (0.1.5git) gnuradio 3.7.13.5&#xA;built-in source types: file osmosdr fcd rtl rtl_tcp uhd hackrf bladerf rfspace airspy soapy redpitaya &#xA;[0;32m[INFO] [UHD] [0;39mlinux; GNU C++ version 7.4.0; Boost_106501; UHD_3.15.0.git-16-gcad30dfe&#xA;Traceback (most recent call last):&#xA;  File &quot;/media/fit-pc/DA54CCFE54CCDDFF/Mint Linux stuff/mint backup/My-Projects/FM-Radio-Receiver/top_block.py&quot;, line 189, in &amp;lt;module&amp;gt;&#xA;    main()&#xA;  File &quot;/media/fit-pc/DA54CCFE54CCDDFF/Mint Linux stuff/mint backup/My-Projects/FM-Radio-Receiver/top_block.py&quot;, line 183, in main&#xA;    tb = top_block_cls()&#xA;  File &quot;/media/fit-pc/DA54CCFE54CCDDFF/Mint Linux stuff/mint backup/My-Projects/FM-Radio-Receiver/top_block.py&quot;, line 101, in __init__&#xA;    self.osmosdr_source_0 = osmosdr.source( args=&quot;numchan=&quot; + str(1) + &quot; &quot; + '' )&#xA;  File &quot;/home/fit-pc/gnuradio/lib/python2.7/dist-packages/osmosdr/osmosdr_swig.py&quot;, line 1170, in make&#xA;    return _osmosdr_swig.source_make(*args, **kwargs)&#xA;RuntimeError: No supported devices found (check the connection and/or udev rules).&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;The other thing that I just noticed is when I run the Pybombs GR in the terminal it shows warnings &quot;blocks already exist&quot;, but then the programs starts normally:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;fit-pc@fitpc-fitlet2:~$ pybombs run gnuradio-companion&#xA;PyBOMBS.ConfigManager - INFO - Prefix Python version is: 3.6.8&#xA;PyBOMBS - INFO - PyBOMBS Version 2.3.3&#xA;Warning: Block with key &quot;analog_agc2_xx&quot; already exists.&#xA;    Ignoring: /home/fit-pc/gnuradio/share/gnuradio/grc/blocks/analog_agc2_xx.xml&#xA;Warning: Block with key &quot;analog_agc3_xx&quot; already exists.&#xA;    Ignoring: /home/fit-pc/gnuradio/share/gnuradio/grc/blocks/analog_agc3_xx.xml&#xA;Warning: Block with key &quot;analog_agc_xx&quot; already exists.&#xA;    Ignoring: /home/fit-pc/gnuradio/share/gnuradio/grc/blocks/analog_agc_xx.xml&#xA;Warning: Block with key &quot;analog_am_demod_cf&quot; already exists.&#xA;    Ignoring: /home/fit-pc/gnuradio/share/gnuradio/grc/blocks/analog_am_demod_cf.xml&#xA;Warning: Block with key &quot;analog_const_source_x&quot; already exists.&#xA;    Ignoring: /home/fit-pc/gnuradio/share/gnuradio/grc/blocks/analog_const_source_x.xml&#xA;..&#xA;&#xA;..&#xA;&#xA;..&#xA;&#xA;..&#xA;Warning: Block with key &quot;zeromq_sub_msg_source&quot; already exists.&#xA;    Ignoring: /home/fit-pc/gnuradio/share/gnuradio/grc/blocks/zeromq_sub_msg_source.xml&#xA;Warning: Block with key &quot;zeromq_sub_source&quot; already exists.&#xA;    Ignoring: /home/fit-pc/gnuradio/share/gnuradio/grc/blocks/zeromq_sub_source.xml&#xA;&amp;lt;&amp;lt;&amp;lt; Welcome to GNU Radio Companion 3.7.13.5 &amp;gt;&amp;gt;&amp;gt;&#xA;&#xA;Block paths:&#xA;    /home/fit-pc/gnuradio/share/gnuradio/grc/blocks&#xA;    /home/fit-pc/gnuradio/share/gnuradio/grc/blocks&#xA;&#xA;Loading: &quot;/media/fit-pc/DA54CCFE54CCDDFF/Mint Linux stuff/mint backup/My-Projects/FM-Radio-Receiver/FM-Radio-Receiver.grc&quot;&#xA;&amp;gt;&amp;gt;&amp;gt; Done&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Update:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;NO supported devices ...&quot; error is fixed now after I run &quot;/home/fit-pc/gnuradio/lib/uhd/utils/uhd_images_downloader.py&quot;, so the gnuradio gui/interface works and generates output normally with the usrp. But &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I still have the original error there which is &quot;No module named 'analog_swig'&quot; whenever I run python3 /home/fit-pc/Desktop/python-web-server/serv.py  in the terminal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here i my original .grc file (the ID here is top_block and not Exercise_1 for demonstration purposes):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RRgmU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RRgmU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And to generate my python code to run it through the web server I had to remove the FFT sink, Multiply Const, and the Slider and run it as &quot;No Gui&quot; as I was instructed before:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SoOyW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SoOyW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My last Update:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I run it using python2.7 in the Terminal I get this and nothing happens:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ozfwb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ozfwb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15206" LastEditorUserId="15206" LastEditDate="2019-07-14T23:34:58.383" LastActivityDate="2019-07-14T23:34:58.383" Title="No module named 'analog_swig'" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;gnuradio&gt;&lt;usrp&gt;" AnswerCount="0" CommentCount="13" FavoriteCount="1" ClosedDate="2019-07-15T17:00:02.043" ContentLicense="CC BY-SA 4.0" />
  <row Id="14916" PostTypeId="1" CreationDate="2019-07-15T11:55:34.617" Score="2" ViewCount="83" Body="&lt;p&gt;I would like to analyze data from the &lt;a href=&quot;http://wspr.aprsinfo.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Weak Signal Propagation Reporter&lt;/a&gt; (WSPR) and/or the &lt;a href=&quot;http://www.reversebeacon.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Reverse Beacon Network&lt;/a&gt; to understand the propagation mode(s) of the recent welcome spate of CW and SSB contacts between North America and Europe on the 10 meter band. I was able to create a WSPR map of the past week's events, but I'd like to reduce the temporal granularity. Does anyone know of a site or tool that provides this ability?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dswwt.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dswwt.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-07-15T12:11:09.093" LastActivityDate="2019-07-15T13:49:00.837" Title="Propagation Analysis with WSPR / RBN" Tags="&lt;propagation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14917" PostTypeId="2" ParentId="14916" CreationDate="2019-07-15T13:13:42.263" Score="1" Body="&lt;p&gt;For WSPR, all spots are available for download at &lt;a href=&quot;http://wsprnet.org/drupal/downloads&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://wsprnet.org/drupal/downloads&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;The entire database of millions of WSPR spots is available for public download in comma-separated value (CSV) format compressed with the gzip and zip utilities. Each file contains the data for one calendar month of spots.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every spot is stored as a line in a CSV file, along with the time. Time is rounded off to two minutes, which is the finest it will get as the transmissions are on a 2-minute cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The columns are:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;SPOT#   Unix Time   Receive Grid    SNR Frequency   Transmit  Grid  Pwr Drift   Range   Head   Band  version    Errorcode&#xA;2397255 1228089600  K1JT    FN20    -11 3.594062    HB9CZF  JN47ch  37  0       6390    296     3   1.1_r1042   0&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Now your problem becomes how to aggregate gigabytes of text into a useful map.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-07-15T13:49:00.837" LastActivityDate="2019-07-15T13:49:00.837" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14918" PostTypeId="2" ParentId="14847" CreationDate="2019-07-15T15:14:08.027" Score="1" Body="&lt;p&gt;It is a design for a 3el yagi. the feed overlaps because the &quot;wires&quot; are metal rods thru the beam which allows for adjustments. there is a 4el design out there using this method &lt;/p&gt;&#xA;" OwnerUserId="11654" LastActivityDate="2019-07-15T15:14:08.027" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14919" PostTypeId="2" ParentId="14892" CreationDate="2019-07-15T18:07:49.473" Score="3" Body="&lt;p&gt;I found the solution to my problem. It was due to running my program using Python3, while as Marcus Muller stated in my other posting &quot;GNU Radio 3.7 is not python3 compatible&quot;. So, using Python2.7 instead was the solution.&lt;/p&gt;&#xA;" OwnerUserId="15206" LastActivityDate="2019-07-15T18:07:49.473" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14920" PostTypeId="1" AcceptedAnswerId="14925" CreationDate="2019-07-15T22:40:06.243" Score="4" ViewCount="66" Body="&lt;p&gt;What might be the relative computational performance requirements for the various popular digital modes? (FT, JT, WS, PSK31, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I seem to recall FSK modulation/demodulation being done with 1 or so MHz 8-bit CPUs.  By what factor or magnitude have the newer digital modes increased the processor requirements from this? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And what is taking up most of that computational requirement increase (CPU/FPU/GPU cycles) needed in the newer digital modes?  (filtering? FFTs? cross-correlation? convolution decoding? AI/ML?, or ???)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question is motivated because someone said their computer (GHz, multicore, with over 100X more performance than a Cray 1 supercomputer) couldn't handle receiving some popular HF digital mode, which surprised me.  After all, lots of deep space comms were done well before Cray 1's were obsolete.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-07-15T23:04:54.063" LastActivityDate="2019-07-16T08:31:50.623" Title="Relative computational requirement for various digital modes?" Tags="&lt;digital-modes&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14922" PostTypeId="1" AcceptedAnswerId="14924" CreationDate="2019-07-16T07:17:11.503" Score="5" ViewCount="1183" Body="&lt;p&gt;I'm an &lt;em&gt;amateur&lt;/em&gt; amateur radio enthusiast finally building my own antenna, and have decided on a double cross antenna, with the goal of pulling data from NOAA satellites.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/FscMu.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FscMu.jpg&quot; alt=&quot;Diagram of 50ohm coaxial connections to the four dipoles of the double cross antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Four coax cables, two of length x, and two of length x+λ/4. For 137 MHz, the wavelength is ~218.8cm, and a quarter of that is 54.7cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, everywhere I go online I see a quarter of the wavelength being ~36cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Eg, 2x79cm lengths and 2x115cm lengths, or 2x14.25in lengths and 2x28.5in lengths - they always come out to be ~36cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I overlooking something, or is this a case of everyone copying from an incorrect source?&#xA;I'm inclined to believe I'm wrong here because I'm quite new, but I don't see how.&lt;/p&gt;&#xA;" OwnerUserId="15256" LastActivityDate="2019-07-17T02:56:44.700" Title="Why is my calculation for added length of coax for a double cross antenna different to everyone else's?" Tags="&lt;antenna-theory&gt;&lt;coaxial-cable&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14924" PostTypeId="2" ParentId="14922" CreationDate="2019-07-16T07:29:52.243" Score="10" Body="&lt;p&gt;The difference is the &quot;Velocity factor&quot;. A 36cm long physical coax wire of this type is electrical 54.4cm long.&#xA;Different types of wire have different velocity factors.&#xA;&lt;a href=&quot;https://en.wikipedia.org/wiki/Velocity_factor&quot; rel=&quot;noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Velocity_factor&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15258" LastActivityDate="2019-07-16T07:29:52.243" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14925" PostTypeId="2" ParentId="14920" CreationDate="2019-07-16T08:31:50.623" Score="6" Body="&lt;h1&gt;Complexity of your question&lt;/h1&gt;&#xA;&lt;p&gt;It's hard to make general statements here, because computational complexity is a property of the &lt;em&gt;implementation&lt;/em&gt; of a receiver, which usually is a choice given the properties of the transmission.&lt;/p&gt;&#xA;&lt;p&gt;For example, assume you have 2-FSK. You can either demodulate that by having say, 2 bandpass filters applied to a passband signal, and a maximum-energy detector, or by averaging the phase error signal of a PLL, or by mixing to baseband and mutliplying each sample with the complex conjugate of the previous and making a sign decision.&lt;/p&gt;&#xA;&lt;p&gt;All these have their advantages and disadvantages, and will perform differently errorwise and computationally, and the latter especially considering that different platforms can do different kind of calculations more or less easily.&lt;/p&gt;&#xA;&lt;p&gt;But let's be honest here: the complexity of FSK demodulation (and in fact, most simple modulation schemes) will very likely be outshined by far four things:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;digital Filtering to isolate the signal&lt;/li&gt;&#xA;&lt;li&gt;synchronization in time, frequency (and phase)&lt;/li&gt;&#xA;&lt;li&gt;Equalization&lt;/li&gt;&#xA;&lt;li&gt;channel decoding&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;h1&gt;Channelization / Filtering&lt;/h1&gt;&#xA;&lt;p&gt;Assume you know where your signal is in spectrum. It'd be only logical to filter out anything that's not part of the occupied bandwidth as a first step.&lt;/p&gt;&#xA;&lt;p&gt;That usually would call for the well-known but impossible to realize brickwall filter. So, you live with what you can do and build a long filter.&lt;/p&gt;&#xA;&lt;p&gt;Now, we're talking classical HAM modes: A steep FIR applied to a &amp;quot;couple hundred kilosamples per second&amp;quot; signal (if at all that much bandwidth) with a couple hundred taps is ... &lt;a href=&quot;https://stackoverflow.com/questions/32916536/is-there-a-constant-time-algorithm-for-generating-a-bandlimited-sawtooth/32931019#32931019&quot;&gt;cute&lt;/a&gt; for modern hardware.&lt;/p&gt;&#xA;&lt;h1&gt;Synchronization&lt;/h1&gt;&#xA;&lt;p&gt;Then, we have the synchronization part.&lt;/p&gt;&#xA;&lt;p&gt;This is where things &lt;em&gt;really&lt;/em&gt; get system-specific. Does your transmitter just send a white-ish preamble? Then, you might just want to correlate for that preamble (which is nothing but a filter of length equal to preamble length), but on a grid of frequency hypotheses: If you're not frequency-corrected yet, your correlation will not be good, and you'll need to simply &amp;quot;try out&amp;quot; a lot of different frequency offsets.&lt;/p&gt;&#xA;&lt;p&gt;The complexity of that is typically in the order of &lt;span class=&quot;math-container&quot;&gt;$K\cdot L^2$&lt;/span&gt;, with &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; being the preamble length, and &lt;span class=&quot;math-container&quot;&gt;$K$&lt;/span&gt; being the number of different frequency offsets you need to try. You can reduce &lt;span class=&quot;math-container&quot;&gt;$L^2$&lt;/span&gt; to &lt;span class=&quot;math-container&quot;&gt;$L\log L$&lt;/span&gt; with FFT-based convolution, but that's it. &lt;br&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$K$&lt;/span&gt; is defined by how badly you want to detect the preamble: If &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; gets longer, a frequency offset leads to more phase rotation, leading to higher decorrelation (until you do more than &lt;span class=&quot;math-container&quot;&gt;$\pi$&lt;/span&gt; phase rotation over the whole length &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt;). So, sadly, &lt;span class=&quot;math-container&quot;&gt;$K$&lt;/span&gt; is a function that increases with &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt;, and only decreases if you can accept a higher probability of not detecting the preamble.&lt;/p&gt;&#xA;&lt;p&gt;Good thing is that after initial acquisition of the signal, complexity drops.&lt;/p&gt;&#xA;&lt;p&gt;If, on the other hand, your transmit signal is &amp;quot;modern&amp;quot; and uses e.g. OFDM with one of the well-known OFDM synchronization aids (just because it's so standard, and because the paper is really good: Schmidl&amp;amp;Cox is something you want to look at), then the structure of your signal allows simultaneous timing and frequency estimation with a single correlation (within bounds). Nice, because that means your complexity drops a lot.&lt;/p&gt;&#xA;&lt;p&gt;Phase sync is also very system-dependent: If you have short bursts, then, well, the preamble might be enough to estimate phase for the rest of the signal. If not, you'll have to go one of many routes, the most prevalent being&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;in case of PSK, or sufficiently PSK-alike modulations, costas loops, or&lt;/li&gt;&#xA;&lt;li&gt;in most cases, transmit data-aided methods like inserting pilot symbols periodically, which require a full demodulation chain afterwards, or&lt;/li&gt;&#xA;&lt;li&gt;fully data-aided methods like constantly regenerating the signal that the transmitter would have generated considering the received bits, and comparing the phase of that and the reception through simple correlation, which of course requires that correlation (&lt;span class=&quot;math-container&quot;&gt;${}^2$&lt;/span&gt;) and a full demodulation, decision, channel decoding and re-modulation chain&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h1&gt;Equalization&lt;/h1&gt;&#xA;&lt;p&gt;Ugh. Equalizers need some form of channel estimation to work, in order to reverse the effects of the multipath propagation.&lt;/p&gt;&#xA;&lt;p&gt;Again, there's more methods for this than there's modulations, but let's highlight a few.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;If you've got that preamble correlator from above, that might simply yield a reasonable estimate for the channel impulse response, if &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; was large enough to allow for feasible SNR. That'd come more or less free at the cost of having to have a pretty complex sync to begin with.&lt;br&gt;&#xA;You can then go and try to find an &amp;quot;inverse&amp;quot; of the channel, either by building a zero-forcing (simply transform the channel impulse response to frequency domain, take the inverse, transform back) filter (which has terrible noise amplification) or by building a MMSE filter (similar, but respect noise variance in the process). &lt;br&gt;&#xA;So, you'd get the channel estimation cost plus a running cost of about the square of the length of the channel for equalization.&lt;/li&gt;&#xA;&lt;li&gt;If you're looking at a multicarrier system (like OFDM, as used in FreeDV, DVB-T, LTE, WiFi…) then your signal giant multipath channel typically gets decomposed into many flat narrow channels with but a single complex channel coefficient each. That often reduces the complexity of estimation to a linear function of the number of subcarriers, and the cost of equalization to a single complex multiplication per subcarrier.&lt;/li&gt;&#xA;&lt;li&gt;You can do a decision-feedback equalizer, if you've got sufficiently low receiver block sizes to allow you to cancel the influence of the first symbol on the later second and so on. You incur the complexity of an IIR, plus estimation and full decision chain.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h1&gt;Channel Decoding&lt;/h1&gt;&#xA;&lt;p&gt;This is really where things go down.&lt;/p&gt;&#xA;&lt;p&gt;You mentioned deep space comms: Yeah, good point. You know that there's &amp;quot;daytime&amp;quot; and &amp;quot;nighttime&amp;quot; decoders on Voyager comms? Comparable signal, two different decoders, one better in performance than the other, so that one works more or less at live speeds, whereas the other runs overnight on a more beefy machine on an offline recording.&lt;/p&gt;&#xA;&lt;p&gt;Channel decoders can be built in different ways. You mention convolutional codes, and we'd often decode them with simple, and complexity-wise quite limited decoders like the Viterbi algorithm. Still uses a metric stuffton of memory and CPU for long depths, but can be made to decide early adaptively to signal quality.&lt;/p&gt;&#xA;&lt;p&gt;But that's not all there is. You can use iterative decoders, involving e.g. the Turbo principle. Now, all your complexity bounds go out the window. Want to have lower error probability? Just run another iteration.&lt;/p&gt;&#xA;&lt;p&gt;In more recent years, large block codes have become a favourite way of implementing very close-to-Shannon codes. Low-Density Parity Check (LDPC) matrices can (and will) be of multiple thousand columns in size, and the only way to realistically demodulate them is through iteratively improving the quality of the transmit data estimate by passing info through the check notes. That can, again, be done in very many ways, and LDPC codes are designed with specific hardware or software abilities in mind, having e.g. shifted-identity-matrix substructures or not. Like with most of the iterative decoders, you can abort decoding early, if acceptable error probability and SNR allow.&lt;/p&gt;&#xA;&lt;p&gt;But, seriously, PCs are not &lt;em&gt;good&lt;/em&gt; at juggling a lot of small-granularity distributed-memory operations. Both memory and CPU bandwidth get quickly exhausted. So, something that a cheap TV set-top box IC (not to mention smartphone chipsets) can do relatively nicely can be extremely harrowing to get to run sufficiently fast on CPU or GPU hardware.&lt;/p&gt;&#xA;&lt;h1&gt;Conclusion&lt;/h1&gt;&#xA;&lt;p&gt;One would have to look at the individual standards, but I'm willing to say that usually, modern methods are lower in complexity to demodulate at a desired symbol error rate than legacy digital modes, especially if OFDM is involved.&lt;/p&gt;&#xA;&lt;p&gt;As soon as we start to deal with bits, however, the full force of the desirable advances of the last 30 years of channel coding hits us in the face and you might end up with a code for which no commodity-CPU software decoder that is real-time capable exists. Of course, it's unlikely that someone specifying a ham mode will rely on custom hardware, unless they are a company that holds patents about that.&lt;/p&gt;&#xA;&lt;p&gt;For least-SNR modes like WSPR/FT8 both the low-power signal detection (see &amp;quot;synchronization&amp;quot; above) and the channel decoding dominate.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-07-16T08:31:50.623" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14926" PostTypeId="1" CreationDate="2019-07-16T11:12:32.003" Score="3" ViewCount="96" Body="&lt;p&gt;I have very little knowledge about antennas (I just read about simple dipoles and monopoles recently) and I need to buy a directional antenna for my wireless device. I have found a cheap antenna (I know cheap eBay antennas are not what the sellers claim) and I want to know more about the antenna before buying it. The seller listed that it has an 8dbi gain, &amp;lt;2 VSWR and they didn't provide the radiation pattern. I have an image of the antenna elements, can you please tell me the type of the antenna? Then, I can read some more about this specific type.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inside, it is formed by two plates. The driven element is a 40x50mm plate. The reflector is larger, curved, and grounded. A black plastic is there between the plates but there is a metal bolt in the center causing electrical contact between the plates.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: Is the metal bolt okay in this design? It is sorting the patch and the ground. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/As4Bw.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/As4Bw.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/iLW0T.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iLW0T.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/29qQN.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/29qQN.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please forgive me if this is a very common antenna. As I have said, I am very new to this. &lt;/p&gt;&#xA;" OwnerUserId="15259" LastEditorUserId="15259" LastEditDate="2019-07-16T12:05:19.057" LastActivityDate="2019-07-16T12:19:05.590" Title="What type of antenna is this?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14928" PostTypeId="2" ParentId="14926" CreationDate="2019-07-16T11:24:48.577" Score="1" Body="&lt;p&gt;This is a Planar or Patch Antenna.&#xA;&lt;a href=&quot;https://www.oreilly.com/library/view/rf-and-microwave/9781118349571/c07_level1_5.xhtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.oreilly.com/library/view/rf-and-microwave/9781118349571/c07_level1_5.xhtml&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15258" LastActivityDate="2019-07-16T11:24:48.577" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14930" PostTypeId="1" AcceptedAnswerId="14937" CreationDate="2019-07-16T19:37:17.687" Score="1" ViewCount="108" Body="&lt;p&gt;I just bought a &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B01MYY5JWF&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;QYT KT-8900D mobile radio&lt;/a&gt;. One of the first things I've noticed is that I cannot use my mixer to completely lower the volume of the radio's 3.5mm TRRS output. When the fader is all the way down, there's still a good amount of audio coming through. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After closer inspection by my friend on his identical radio, an audio signal is being sent over just the ground pin somehow. Tested it on 3 radios with the same result.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone know why this is happening and how to fix it?&lt;/p&gt;&#xA;" OwnerUserId="15265" LastEditorUserId="15265" LastEditDate="2019-07-17T14:34:09.000" LastActivityDate="2019-07-18T13:34:52.253" Title="Audio being sent over ground pin on audio jack" Tags="&lt;rfi&gt;&lt;mobile&gt;&lt;audio&gt;" AnswerCount="2" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="14931" PostTypeId="2" ParentId="283" CreationDate="2019-07-16T20:35:27.143" Score="1" Body="&lt;p&gt;I always use the 468 formula and have for the past 30 years and ALWAYS had a perfect SWR and matched antenna. I have made over 200 dipoles and I have NEVER had to trim to get a perfect antenna. I also have NEVER made an antenna too short or too long!&lt;/p&gt;&#xA;" OwnerUserId="15266" LastEditorUserId="76" LastEditDate="2019-07-16T20:42:27.533" LastActivityDate="2019-07-16T20:42:27.533" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14932" PostTypeId="1" CreationDate="2019-07-16T22:27:19.933" Score="1" ViewCount="778" Body="&lt;p&gt;I have been looking for an affordable yagi antenna to use with a dual band handheld radio and I came across some very inexpensive VHF/UHF (HDTV) antennas. They are all 75 ohm though. Is it ok to use a 75 ohm antenna on a tx/rx radio that uses 50 a ohm antenna, or do I need to spend more money and buy a 50 ohm to 75 ohm converter?&lt;img src=&quot;https://i.stack.imgur.com/JWVUL.jpg&quot; alt=&quot;Cheap 75 ohm TV antenna&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="15267" LastActivityDate="2019-07-16T22:44:33.830" Title="Can I connect a 75 ohm antenna to a 50 ohm radio?" Tags="&lt;antenna&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14933" PostTypeId="2" ParentId="14932" CreationDate="2019-07-16T22:44:33.830" Score="4" Body="&lt;p&gt;You &lt;em&gt;probably&lt;/em&gt; cannot use that antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 75 Ω-50 Ω mismatch is a SWR of 1.5, which is not intolerable for a handheld radio (which needs to tolerate a directly attached antenna being detuned by the body of the user or other objects). So the answer to the question in your title is &quot;yes&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, what you have posted is an &lt;strong&gt;amplified&lt;/strong&gt;, &lt;strong&gt;receiving&lt;/strong&gt; antenna for TV signals.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;An &quot;amplified antenna&quot; has an amplifier which will amplify signals &lt;em&gt;from&lt;/em&gt; the antenna &lt;em&gt;to&lt;/em&gt; the feed line to the radio receiver. If you try to transmit through it, at best nothing will happen and at worst the amplifier will be destroyed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(The amplifier &lt;strong&gt;might&lt;/strong&gt; be a separate module that you can simply not attach; it depends on the design.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Receiving is far more tolerant of impedance/SWR mismatch than transmitting so it's possible to declare an antenna is just &quot;VHF/UHF&quot;; transmitting needs a more precisely matched antenna. You will likely find that the antenna has a widely varying SWR which is very poor — for transmitting purposes — over most of the VHF range. It &lt;em&gt;might happen&lt;/em&gt; that the antenna has a good SWR at the amateur 2-meter (144 MHz) and 70-cm (440 MHz) bands, but you should not expect it.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Even if the antenna did not have an amplifier, it might contain unsuitable contents. A dipole antenna connected to coaxial feed line needs a &lt;a href=&quot;https://en.wikipedia.org/wiki/Balun&quot; rel=&quot;nofollow noreferrer&quot;&gt;balun&lt;/a&gt;, and a balun intended only for receiving can be made with small, cheap components which cannot handle the power of even a handheld transmitter.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-07-16T22:44:33.830" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14934" PostTypeId="2" ParentId="14930" CreationDate="2019-07-17T01:08:02.870" Score="2" Body="&lt;p&gt;Audio isn't send just over the ground pin, or the other pin. It's sent over both. If both weren't necessary, then why not just make audio connectors with one pin and audio cables with one wire?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The audio signal is represented by a voltage at the input. And the source of the signal manipulates that voltage by adding or removing electrons, what we usually call &quot;current&quot;. And since &lt;a href=&quot;https://en.wikipedia.org/wiki/Charge_conservation&quot; rel=&quot;nofollow noreferrer&quot;&gt;electrons aren't just magically created, but must come from somewhere&lt;/a&gt;, where are they obtained?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer is the signal source doesn't create or destroy electrons: if it wants to increase the voltage then it takes electrons from the &quot;audio&quot; pin and deposits electrons in the ground pin. And to decrease the voltage it does the opposite.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So naturally, if you try to measure &quot;just&quot; the ground pin, you're going to see something. Only what you see is going to be highly dependent on how you've connected the test equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The more likely reason your mixer can't totally eliminate the signal is probably just because mixers don't work like that. The faders only attenuate the signal, perhaps to the point where it's no longer audible. Or perhaps not, depending on how much amplification follows the mixer output, how good your ears are, and how quiet the room is.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-07-17T01:08:02.870" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14935" PostTypeId="2" ParentId="14922" CreationDate="2019-07-17T02:56:44.700" Score="1" Body="&lt;p&gt;A wavelength/4 in a vacuum at 137 mhz is about 300 / 137 / 4  = 54.7cm. However in coaxial cable the velocity of the radio wave is significantly less.In the case of RG 58 for example 66% of the speed of light in a vacuum. So! .66 x 54.7 = 36.1 cm. There fore to get the free space wave and the wave from the cable in phase the length of the cable has to be reduced by the velocity factor of the cable.&#xA;Often you will have a situation where you are trying to space two elements at say a quarter of  a wavelength apart. The cable between them will be too short because in your example the space between the elements will be 54 cm and the cable is only 36 cm long!&#xA;Just add a half wavelength to the cable. The additional length just repeats the input and output impedances and allows you to space the elements correctly. &#xA;This is a neat trick with antennas as you can match an antenna to a load with any impedance cable as long as it is a multiple of a half wavelength.&#xA;For instance you can have a 50 ohm antenna connected to a 50 ohm transceiver with 75 ohm cable that is a multiple of half wavelengths long. Great if you have a load of 75 ohm tv cable lying around!&lt;/p&gt;&#xA;" OwnerUserId="15084" LastActivityDate="2019-07-17T02:56:44.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14936" PostTypeId="1" CreationDate="2019-07-17T02:58:15.850" Score="2" ViewCount="58" Body="&lt;p&gt;New ham, here...getting motivated to build some antennas to experiment with and so far my research has shown that stainless steel is not a desirable metal for creating antenna elements - which is a shame because I have access to a LOT of long stainless piano-hinge pin stock.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would anyone be able to explain what it is about SS that makes it less ideal than aluminum or copper? &lt;/p&gt;&#xA;" OwnerDisplayName="user14945" LastEditorUserId="76" LastEditDate="2019-07-17T03:01:19.950" LastActivityDate="2019-07-17T03:01:19.950" Title="What's the issue with stainless steel antenna elements?" Tags="&lt;antenna-construction&gt;" AnswerCount="0" CommentCount="4" ClosedDate="2019-07-17T03:03:59.833" ContentLicense="CC BY-SA 4.0" />
  <row Id="14937" PostTypeId="2" ParentId="14930" CreationDate="2019-07-17T07:28:09.200" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;More info: the mixer takes 2 stereo unbalanced 3.5mm inputs. maybe the extra ring on the radio's output jack is actually for stereo? Some weird behavior I experienced with the mixer: When both faders for radio and bluetooth audio receiver are at negative infinity, there is no sound coming out. However, when I fade up only the BT audio receiver's level while keeping the radio at negative infinity, it increases the level of the radio's audio, and I can hear it in the background. It's not as loud as it would be if its fader were up, but it's definitely noticeable and only happens w/ radio. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Aha!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you've got cross-talk between the radio input and the other channels :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cross-talk between audio channels at a level this high is typically not because audio-frequency signals somehow couple into other conductors, but because higher-frequency components couple more easily. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My guess is that your radio might be leaking some IF signal into its audio outputs, which get transported along wires towards your mixer, influence some non-linear circuitry inside, and thus get mixed down to baseband involuntarily by your mixer acting like a radio receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have a ferrite clamp lying around (old computer cables?), that might be something you can try adding to your audio cable. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-07-17T12:16:39.700" LastActivityDate="2019-07-17T12:16:39.700" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14944" PostTypeId="1" AcceptedAnswerId="14945" CreationDate="2019-07-17T18:13:23.030" Score="2" ViewCount="507" Body="&lt;p&gt;I have a Hallicrafters S-120 1960s vintage vacuum tube receiver (an &quot;All American Five&quot; superhet with solid state rectifier replacing one of the &quot;five&quot; tubes).  It works well, doesn't have excessive internal noise, and seems very sensitive (with the regenerating IF used for &quot;exalted carrier&quot; on AM, and as a BFO for CW and SSB).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've considered using this as a secondary receiver, for some version of &quot;split&quot; operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem with that is that, while the tuning is plenty precise (with the Bandspread control allowing several turns of a secondary tuning knob to cover a few hundred kilohertz), the tuning indicator needle is significantly off the actual tuned frequency (correctable) and doesn't move at all when using the Bandspread.  I had the idea to connect a digital frequency display, which would allow me to see exactly where I'm tuned.  I have such a display on hand, built from a kit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only place I see to get current tuned frequency from a superhet receiver is to tap into the local oscillator.  Am I correct in thinking this will give a frequency 455 KHz &lt;em&gt;below&lt;/em&gt; the actual tuned frequency?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2021-04-16T20:13:02.470" Title="Frequency Display for Old Tube Radio" Tags="&lt;receiver&gt;&lt;diy&gt;&lt;modification&gt;&lt;superheterodyne&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14945" PostTypeId="2" ParentId="14944" CreationDate="2019-07-17T18:39:57.563" Score="3" Body="&lt;p&gt;Yes, attaching a general-purpose frequency counter to the local oscillator of a superheterodyne radio will result in displaying a frequency with an &lt;strong&gt;offset&lt;/strong&gt; either above or below (depending on the design of the radio) the nominal frequency of the signal being received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to account for this, apply the reverse offset numerically, between the frequency counter and its digit display.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This may or may not be practical with the counter module you already have.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A frequency counter intended for the purpose should have a programmable offset.&lt;/li&gt;&#xA;&lt;li&gt;If it is microcontroller-based and has open source firmware then you could reprogram it (this may or may not require special programming hardware and software).&lt;/li&gt;&#xA;&lt;li&gt;If it is based on discrete logic, then the circuit could be modified to include an adder/subtractor and the offset programmed using wiring or switches.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-07-17T18:39:57.563" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="14946" PostTypeId="2" ParentId="9882" CreationDate="2019-07-18T01:00:15.983" Score="0" Body="&lt;p&gt;It's a little late of a response, but my answer is try your idea of the slot cut into the bar stock and see if it works. Try it with a known repeater and turn the antenna to see the null off the side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try bending it into a hoop like a vhf squalo and see if that works. What is there to lose? &lt;/p&gt;&#xA;" OwnerUserId="15278" LastActivityDate="2019-07-18T01:00:15.983" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14947" PostTypeId="2" ParentId="9121" CreationDate="2019-07-18T10:19:06.550" Score="-1" Body="&lt;p&gt;I was also looking for a &quot;pure&quot; GNU/Linux solution to have (straight) morse keys generate sidetones, but unfortunately I gave up and I'm now using a Windows software which I installed with Wine on Ubuntu 19.04:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Adapter&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you already have a serial-to-USB adapter with FTDI chip plus a DB9-to-audio cable (like &lt;em&gt;SDsolar&lt;/em&gt; mentioned them) to connect your key to a PC, you're fine. If I connect the FTDI adapter to my PC's USB, a device &lt;code&gt;/dev/ttyUSB0&lt;/code&gt; shows up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my case, Wine provides several symbolic links &lt;code&gt;$HOME/.wine/dosdevices/com*&lt;/code&gt; pointing to the serial devices &lt;code&gt;/dev/ttyS*&lt;/code&gt;, and once I plug the adapter in, a symbolic link &lt;code&gt;com33&lt;/code&gt; is created which points to &lt;code&gt;/dev/ttyUSB0&lt;/code&gt;. I always rename that link to &lt;code&gt;com1&lt;/code&gt; to be able to use it in the emulated environment. Since Wine sometimes renames it back, there seems to be a configuration option in Wine for these links: (&lt;a href=&quot;https://wiki.winehq.org/Wine_User%27s_Guide#Serial_and_Parallel_Ports&quot; rel=&quot;nofollow noreferrer&quot;&gt;source&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;To override Wine's default device mapping, run &lt;code&gt;wine regedit&lt;/code&gt; and create string entries in &lt;code&gt;HKEY_LOCAL_MACHINE\Software\Wine\Ports&lt;/code&gt; where the entry name is the Windows device name and the entry value is the path to the Unix device. Continuing with the above example, to make COM1 the first USB-attached serial port, create an entry with the name &lt;code&gt;COM1&lt;/code&gt; and the value &lt;code&gt;/dev/ttyUSB0&lt;/code&gt;. [...] After editing the registry, shut down Wine with &lt;code&gt;wineserver -k&lt;/code&gt; and the next time Wine runs a program, your changes will take effect.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Practice software&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The actual CW practicing software I use then is CW Communicator or CWCom. This is an old and disappearing client to connect to an Ionosphere network to communicate in CW over the internet. However, it doesn't require network for practicing alone. In addition, it has a very good Morse decoder built in. You can find an &lt;a href=&quot;https://archive.org/details/cwcom&quot; rel=&quot;nofollow noreferrer&quot;&gt;archived download&lt;/a&gt; link or can also directly download from &lt;a href=&quot;https://www.oecwg.at/downloads/CWCom/cwcom_inst-1.51.exe&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. This second link is provided by the Austrian CW society, OECWG, who still use this software for teaching.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you launch the program, you should see a black rectangle in the upper left corner of the main window. If you click on it, you should be able to hear a sidetone while holding the mouse button down. You can configure its frequency in the settings. To trigger sidetones with your key, open the configuration window and go to tab &quot;Morse Key&quot;. Change the &quot;COM Port&quot; number to the one that points to your USB device, and then switch the &quot;Morse Input&quot; radio button to &quot;COM Port&quot;. If it stays selected, try triggering your key. You should hear a sidetone. The decoder and the statistics window will help you making your Morse characters right.&lt;/p&gt;&#xA;" OwnerUserId="14070" LastActivityDate="2019-07-18T10:19:06.550" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14950" PostTypeId="1" AcceptedAnswerId="14956" CreationDate="2019-07-19T01:44:12.693" Score="4" ViewCount="373" Body="&lt;p&gt;Im not sure if this is the best place to ask a question like this but its the best place i could find.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My goal is to build a dual band antenna similar to &lt;a href=&quot;https://www.telcoantennas.com.au/rfi-wideband-8-12dbi-3g-4g-4gx-lpda-antenna-700-30&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt;. That covers &lt;code&gt;694-1000MHz&lt;/code&gt; and &lt;code&gt;1500-3000MHz&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In theory the design seems fairly simple its just a high frequency antenna on the end of a low frequency antenna sharing the same core. Here is an image of a similar antenna where you can clearly see this &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://ss.brandon3055.com/a7793&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So borrowing from a diagram i found &lt;a href=&quot;https://hamwaves.com/lpda/en/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; The design seems to be as &quot;simple&quot; as this&#xA;&lt;img src=&quot;https://ss.brandon3055.com/f5592&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The only issue with this design is that &lt;em&gt;&quot;Zterm&quot;&lt;/em&gt; measurement. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;As far as I can tell the rails need to be terminated a specific distance from the last element. &lt;/li&gt;&#xA;&lt;li&gt;The way I suspect they get around this is maybe Zterm does not have to be a specific value but instead some multiple of the target wavelength or something? &lt;/li&gt;&#xA;&lt;li&gt;If that's the case then you could just design the high frequency antenna with a large enough Zterm to fit in the low frequency antenna behind it. &lt;/li&gt;&#xA;&lt;li&gt;The problem is I have no idea if thats how it actually works and if it is how to calculate the what Zterm values would work for the high frequency antenna. &lt;/li&gt;&#xA;&lt;li&gt;And then there's the possibility that simply slapping a low frequency antenna behind it would cause them to interfere with each other.&lt;/li&gt;&#xA;&lt;/ol&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So i am here hoping someone a little more knowledgeable than me would be happy to share their knowledge. It would be really nice to be able to build something like this prof scratch considering the price of the commercial versions.&lt;/p&gt;&#xA;" OwnerUserId="15286" LastEditorUserId="13000" LastEditDate="2019-07-24T13:11:28.317" LastActivityDate="2019-07-24T13:11:28.317" Title="How do I design a dual band LPDA antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14951" PostTypeId="1" CreationDate="2019-07-19T03:20:59.187" Score="3" ViewCount="387" Body="&lt;p&gt;The apartment I live in is a 1970s type without access to the outdoors. It does have a balcony. A 2m transceiver is the only radio which will enable me to reach the ham world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would be possible to use the electrical wiring for HF as it has already been used for TV and FM radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone managed to use the electrical house wiring for SSB at a low power antenna?&lt;/p&gt;&#xA;" OwnerUserId="15287" LastEditorUserId="8717" LastEditDate="2019-07-19T04:03:30.683" LastActivityDate="2019-07-20T05:07:06.177" Title="House wiring as an antenna on HF and 2 meters?" Tags="&lt;antenna-construction&gt;&lt;hf&gt;&lt;vhf&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="14952" PostTypeId="1" CreationDate="2019-07-19T05:41:45.027" Score="1" ViewCount="62" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;I am designing a portable antenna with a radiating element and a balun that are not close to each other. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The impedance has been designed to be close to &lt;code&gt;50 ohms&lt;/code&gt;. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;So I will feed the antenna with a twisted pair of enameled copper that should be close to &lt;code&gt;50 ohm&lt;/code&gt; too. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Q:&lt;/strong&gt; I was wondering however how to expose the balanced terminals on the balun enclosure so that they should be close to each other in order not to increase impedance. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;An obvious choice would be a &lt;code&gt;75 ohm&lt;/code&gt; twinax socket and fitting the custom twisted pair to a twinax male connector, but these connectors are expensive. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Q:&lt;/strong&gt; Any idea of what kind of terminals i could use, with limited separation while maintaining sufficient mechanical clearance to avoid shorting the terminals?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(That's why I am reluctant to use spade conectors that could rotate inadvertently). I thought of small banana plugs or RCA connectors. Any other idea ?&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It will handle limited power (&lt;code&gt;30W&lt;/code&gt; max at UHF, max &lt;code&gt;400MHz&lt;/code&gt;)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13081" LastEditorUserId="13000" LastEditDate="2019-07-26T14:38:50.993" LastActivityDate="2019-07-26T14:38:50.993" Title="advice needed for balanced line terminals" Tags="&lt;balun&gt;&lt;feed-line&gt;" AnswerCount="0" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14955" PostTypeId="2" ParentId="14951" CreationDate="2019-07-19T12:27:10.620" Score="5" Body="&lt;p&gt;Inductive coupling to &lt;em&gt;only&lt;/em&gt; the neutral wire &lt;em&gt;might&lt;/em&gt; be safe (if you can verify that the outlets are wired correctly).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's probably not a good idea, however, not only from a safety standpoint, but because house wiring will crosstalk to other wires in the same building, at least back to the breaker box and more likely all the way back to the service transformer -- and thus couple in all the noise generators all your neighbors use.  Small appliances.  Wall wart power supplies.  Cordless phones.  Etc.  You won't be happy with the reception you get, and there's also a strong possibility you'll generate interference on neighbors' TVs, radios and telephones (since, in effect, your antenna will be in their apartments).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you have a balcony, a 2 m vertical is simplicity itself to put up, and it's small and not very noticeable.  For 6 m, a quarter wave vertical is still only about five feet, and even a 12 m quarter wave is just about ten feet.  This is still a size that could pass as a flagpole, and has in many restricted locations.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-07-19T13:26:51.350" LastActivityDate="2019-07-19T13:26:51.350" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14956" PostTypeId="2" ParentId="14950" CreationDate="2019-07-19T13:26:59.723" Score="6" Body="&lt;p&gt;You're on the right track, just cut the middle out of an LPDA and see what happens.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The benefit of this design is that by eliminating the middle section of the antenna, you can get &lt;em&gt;slightly&lt;/em&gt; more gain in the bands of interest, for the same boom length. Or you can achieve a small shortening of the boom. It's ideal for dual-band cellular antennas, where the bit from 1 GHz - 1.7 GHz is (was) not really required. Doing this makes a mess in the middle frequencies, (the transitions can be improved by tweaking).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Its die-cast successor, the &lt;a href=&quot;https://www.inet.se/files/pdf/5401839_0.pdf&quot; rel=&quot;noreferrer&quot;&gt;LPDA-44&lt;/a&gt;, shows a gain graph like this:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/vXLgc.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vXLgc.png&quot; alt=&quot;gain&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;So you can see the hole between the bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should definitely simulate this one before you build. I did all of these in NEC-2, nothing fancy, then built and tested a few prototypes to decide on the exact number of elements needed at the front. You will need to write a custom program to generate the structure with the middle missing, and link up all the segments correctly. &lt;a href=&quot;http://www.w8io.com/nec-benchmarks.htm&quot; rel=&quot;noreferrer&quot;&gt;Here's a site&lt;/a&gt; with an example of a suitable simple NEC LPDA model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't try to make a gap-LPDA like this without simulating it in detail - if you're not going to simulate (or copy one) then you're probably better off with a simple LPDA - they're so forgiving it will almost certainly work first time. Trying this without simulation will probably be lower performance than just making a continuous LPDA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Termination of the boom is not really required on high gain / pointy LPDAs. Shorter fatter ones have many weird dips in gain when the boom and the longer elements resonate mysteriously, and sometimes the only way to improve this is with a resistor. In this case we short circuited it 1/4 wave from the back, which makes it mechanically strong, and prevents static build-up. You can also leave it open-circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are a &lt;a href=&quot;http://www.therfidshop.com/images/LPDA-A0021_BROC%20V5.2.pdf&quot; rel=&quot;noreferrer&quot;&gt;few more&lt;/a&gt; &lt;a href=&quot;https://fccid.io/ANATEL/02207-07-04248/Fotos-Externas-M2/C1D28C8F-36E4-475A-B3C5-E485F2C88554/PDF&quot; rel=&quot;noreferrer&quot;&gt;pictures&lt;/a&gt; of it, if you want to study the lengths.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-07-19T13:26:59.723" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14957" PostTypeId="2" ParentId="14951" CreationDate="2019-07-20T05:07:06.177" Score="0" Body="&lt;p&gt;For 2 m, get an Ed Fong dual-band J pole. It looks like a short length of PVC pipe because it is a short length of PVC pipe with an antenna inside. It has performance similar to a 1/4 wave ground plane, but does not need radials. It is a vertical half wave. It is a great deal at $30.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://edsantennas.weebly.com/about.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://edsantennas.weebly.com/about.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For HF, consider a magnetic loop antenna. These have good performance, but need to be retuned when the frequency changes, even if it is just 20 kHz or so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be efficient, a mag loop must be constructed with very low loss components, especially in the variable dipole. If a mag loop vendor doesn't talk about their capacitor choice, I would not buy from them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The W4OP loop from LNR appears to be a good design and well-constructed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.lnrprecision.com/loop-antennas/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.lnrprecision.com/loop-antennas/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Disclaimer: I don't personally use a mag loop, but I do understand the physics behind them.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2019-07-20T05:07:06.177" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14960" PostTypeId="1" CreationDate="2019-07-20T17:07:23.240" Score="4" ViewCount="209" Body="&lt;p&gt;A single inductive loading coil in a vertical or a pair of loading coils in a dipole are commonly used to match a given total antenna length parameter to a given frequency wavelength (where the ratio may not be a nice N/4) for either resonance or low SWR.  This question only concerns dipoles with a pair of loading coils or inductors, one in each leg.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a loading coil is of non-zero dimension and non-zero wire length, then the difference in standing wave current (forward + reverse) would be different across the inductor, which should cause the inductor to radiate a magnetic field (act as a mini loop antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given this, what should be the relative direction of windings of the two inductive loading coils be for a dipole?  Same or opposite winding directions?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will one winding relationship tend to cancel the (E)M fields and the other constructively add?  Or will the directional pattern change?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-07-20T18:01:07.430" LastActivityDate="2021-04-28T19:57:24.470" Title="Dipole loading coil winding directions?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14963" PostTypeId="2" ParentId="14590" CreationDate="2019-07-20T19:04:18.493" Score="1" Body="&lt;p&gt;A recommendation for a formal definition of the 10 character system is available in the &lt;a href=&quot;https://www.iaru-r1.org/index.php/downloads/func-startdown/1008/&quot; rel=&quot;nofollow noreferrer&quot;&gt;IARU-R1 VHF Handbook&lt;/a&gt;.&#xA;Here's the relevant quote:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3.7 Proposals to Clarify and Standardise the IARU Locator, including&#xA;higher Accuracy positioning   &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The definition of the existing 8-character scheme should be extended&#xA;by adding a further division into 24 lettered squares to give a&#xA;10-character locator allowing a positioning accuracy of around 13&#xA;metres. Even higher resolution use for future appli-cations should be&#xA;defined by successively sub-dividing in the same way; alternating 10&#xA;and 24 subdivisions using numbers and letter pairs.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;When the locator is specified at lower resolutions, e.g. 6 characters&#xA;such as in VHF contests, the centre of the squaroid at that&#xA;resolution should be taken. This is equivalent to, for example,&#xA;appending the 6-digit location IO90IV with the mid-range char-acters&#xA;44LL to give IO90IV44LL for the purposes of calculation. A quoted&#xA;locator of IO90IV58 would have “LL” appended for the calculation.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;That the WGS84 worldwide spheroid be the standard mapping be used for&#xA;all locator conversions.&lt;/li&gt;&#xA;&lt;li&gt;IARU Locators should always be quoted and used employing all Upper&#xA;Case (Capital) letters.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="77" LastActivityDate="2019-07-20T19:04:18.493" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14964" PostTypeId="1" CreationDate="2019-07-20T21:36:45.113" Score="1" ViewCount="193" Body="&lt;p&gt;I've got a Baofeng UV-5R and a &lt;a href=&quot;https://www.cobrafrs.com/products/acxt645&quot; rel=&quot;nofollow noreferrer&quot;&gt;Cobra ACXT 645&lt;/a&gt;, and I'm trying to get them to communicate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Cobra transmits and the Baofeng (programmed with CHIRP) receives, but not the other way around.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried different channels, different frequencies, and with the CTCSS and DCS on and off. I'm on day 3 now and have begun pulling my hair out.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What am I doing (or not doing) wrong here?&lt;/li&gt;&#xA;&lt;li&gt;Why aren't the radios working like they're supposed to?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm a beginner at all this.&lt;/p&gt;&#xA;" OwnerUserId="15302" LastEditorUserId="8717" LastEditDate="2019-07-21T22:37:10.327" LastActivityDate="2019-07-21T22:37:10.327" Title="Mismatched Radios: A Baofeng UV-5R &amp; a Cobra ACXT 645" Tags="&lt;united-states&gt;&lt;baofeng&gt;" AnswerCount="0" CommentCount="7" FavoriteCount="1" ClosedDate="2019-09-04T00:55:10.173" ContentLicense="CC BY-SA 4.0" />
  <row Id="14966" PostTypeId="1" CreationDate="2019-07-21T21:55:20.957" Score="3" ViewCount="78" Body="&lt;p&gt;I recently set up my own RTL-SDR-based ADS-B receiver. I live in a Manhattan high-rise with an eastern view, so I do not get any signals from behind the building (almost: I get the occasional reflection). A simple (azimuth-) omni antenna is a waste, nothing is coming from inside my apartment! Similarly, there are no planes flying below my window (if there are, I'll &lt;em&gt;hear&lt;/em&gt; them :) ), so I am only interested in the upper half of the radiation lobe. The receiver has an SMA connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Searching around I have found lots of omni designs for ADS-B receivers, but none that fit these requirements. The last time I thought about antenna design was in my undergraduate class on antenna design, &gt;35 years ago; can someone please point me to some appropriate resource? Ideally, something that I can render on PCBs and tape it to my window?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;/ji, KC2IER&lt;/p&gt;&#xA;" OwnerUserId="15253" LastActivityDate="2019-12-27T01:00:50.197" Title="Somewhat-directional (cardioid?) antenna for receiving ADS-B?" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14969" PostTypeId="1" CreationDate="2019-07-22T11:47:00.590" Score="0" ViewCount="99" Body="&lt;p&gt;It is commonly known that greater antenna heights usually improve the performance of these point-point terrestrial paths.  Here's a NEC study showing the relationship of receive antenna height AGL to its output signal. &lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-07-22T11:47:00.590" Title="How does the height above ground of a VHF/UHF receive antenna affect the r-f voltage at its output terminals?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14970" PostTypeId="2" ParentId="14969" CreationDate="2019-07-22T11:47:00.590" Score="1" Body="&lt;p&gt;Below is a graphic showing that an approximately linear relationship applies. That is, doubling the receive antenna height above ground ~doubles the r-f voltage existing across the output terminals of the receive antenna (other things equal).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Elevating the receive antenna sufficiently may provide more improvement than that, if it reduces the propagation losses resulting from obstructed paths such as possible from nearby buildings, hills, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/K8Z6T.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/K8Z6T.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-07-22T11:47:00.590" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14971" PostTypeId="1" CreationDate="2019-07-22T12:32:15.647" Score="4" ViewCount="291" Body="&lt;p&gt;I bought a &quot;technician special&quot; Heathkit SB-102 transceiver.  Everything seems to work well until I attach a dummy load and try to go through the &quot;initial tune up&quot; procedure in the manual.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the point where I switch the &quot;Mode&quot; to &quot;Tune&quot;, instead of showing 50-60 mA plate current, I'm seeing an initial switching spike and then the needle settles around 150-250 mA and begins to creep upward.  When it gets past 300 mA (as little as 10-15 seconds), the upward creep accelerates, and when it gets past 350 mA the breaker in the HP-23A power supply pops (presumably to protect various components).  During this time, grid current appears to be negative -- the needle goes past the zero point on the meter (which I've zeroed with the zeroing screw when power was off).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Output was to an MFJ 300W/30 second dry dummy load (derating graph shows 100W up to 90 seconds, and hasn't even gotten warm in any test). If there's any resonance going on, it's inside the transceiver's housing. Further, it does the same thing on bottom of 80 m, 40m, and top of 10m that I've checked (as a recommended check against self-oscillation in the final stage).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have very limited diagnostic tools -- a digital multimeter (cheap unit from Harbor Freight) and kit-built frequency counter (which I'm sure would need attenuation for use in this situation, even if it were likely to be useful).  I could build an oscilloscope probe to plug into the headphone jack of an Android device, but I doubt that would be any more useful than my multimeter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The manual doesn't ask for more than a VTVM -- but makes it clear this isn't the same as a VOM, specifically for resistance testing circuit segments with diodes, and as I understand it, for this type of testing, my DMM is more like a VOM (low test voltage) than a VTVM.  Comments have suggested that this modern digital meter is more like a VTVM than a VOM from the era when the SB-102 manual was printed, so should be okay for these tests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've replaced the mismatched 6146 and 6146A final tubes that were in the rig when I got it with actual 6146 tubes -- I now have three with varying date codes, and I'm using the closest-dated (on Internet advice), about a year apart.  No change.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not sure it's relevant, but turning down the variac (feeding the power supply ~100 V instead of ~120 V), thereby reducing plate voltage from 800+ to just under 700, has reduced this effect, lowering the initial settling point and slowing the upward creep in plate current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question is, at this point, what kind of failure do I need to look for?  Bad grid leak resistor on one of the 6146 tubes?  Failed capacitor in the final stage?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-09-20T12:09:09.287" LastActivityDate="2019-12-15T01:22:54.090" Title="Heathkit SB-102 Plate Current out of control" Tags="&lt;repair&gt;&lt;vacuum-tubes&gt;" AnswerCount="3" CommentCount="14" ContentLicense="CC BY-SA 4.0" />
  <row Id="14972" PostTypeId="1" AcceptedAnswerId="14973" CreationDate="2019-07-22T15:55:21.693" Score="0" ViewCount="70" Body="&lt;p&gt;I have a &lt;em&gt;Fortigate AP&lt;/em&gt;, and need to understand its radio pattern for optimal positioning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've already understood the &lt;em&gt;E-plane&lt;/em&gt; and &lt;em&gt;H-plane&lt;/em&gt; representations and also that number on the circumference of the circles are radiuses. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what are the values listed vertically down to the center of the circle and what do they mean, how can I equate that to any distance(in meters).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;-&#xA;&lt;a href=&quot;https://i.stack.imgur.com/GPttX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GPttX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15313" LastEditorUserId="13000" LastEditDate="2019-07-24T13:10:51.420" LastActivityDate="2019-07-24T13:10:51.420" Title="Understand Radio Pattern of a WIFI antenna" Tags="&lt;antenna&gt;&lt;wifi&gt;&lt;range&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14973" PostTypeId="2" ParentId="14972" CreationDate="2019-07-22T17:06:45.210" Score="2" Body="&lt;p&gt;The numbers arranged vertically are decibels. They tell you the relative &lt;a href=&quot;https://en.wikipedia.org/wiki/Radiant_intensity&quot; rel=&quot;nofollow noreferrer&quot;&gt;radiant intensity&lt;/a&gt; in each direction. For example if in one particular direction you read 0 on that scale, and in another direction you read -3, then the power in the latter direction is half what it is in the first direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Translating this into a range in meters depends on the &lt;a href=&quot;https://ham.stackexchange.com/questions/352/what-is-a-link-budget-and-how-do-i-make-one&quot;&gt;link budget&lt;/a&gt;, which would have to include things like additional attenuation due to walls and floors, and some margin for interference.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-07-22T17:06:45.210" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14974" PostTypeId="1" CreationDate="2019-07-22T18:07:56.773" Score="1" ViewCount="110" Body="&lt;p&gt;My understanding is that the value of the axis (like &lt;code&gt;-10 / 0 dB&lt;/code&gt;) refers to the maximum antenna gain (e.g. &lt;code&gt;12dbi&lt;/code&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, if a point on the figure is &lt;code&gt;-5dB&lt;/code&gt;, then antenna gain of that point is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;code&gt;12 - 5 = 7 dBi&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this correct? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The axes in the figure are in degrees and dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mXcqg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mXcqg.jpg&quot; alt=&quot;db&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15314" LastEditorUserId="13000" LastEditDate="2019-07-24T13:12:15.277" LastActivityDate="2019-07-24T13:12:15.277" Title="Need help understanding the gain on antenna pattern plots" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;radiation-pattern&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14975" PostTypeId="2" ParentId="14974" CreationDate="2019-07-22T19:35:57.670" Score="1" Body="&lt;p&gt;In your example, the outer ring in the polar plot would be 12 dBi. So you are correct in thinking that any point -5 dB from the outer ring would represent a gain of 7 dBi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It works the same for referencing dB, dBi (isotropic), and dBd (dipole).&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="873" LastEditDate="2019-07-23T07:01:19.640" LastActivityDate="2019-07-23T07:01:19.640" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14976" PostTypeId="1" CreationDate="2019-07-22T22:43:52.763" Score="3" ViewCount="185" Body="&lt;p&gt;Suppose that I am familiar with the safety procedures for working on 20 A 120 VAC 60 Hz household lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What should I be prepared for before working on high voltage DC circuits (say, 800 volts) as is commonly found on the anodes in tube transmitters?&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="76" LastEditDate="2019-07-22T23:05:46.820" LastActivityDate="2019-07-27T15:56:28.873" Title="How is working on DC high voltages as in a tube radio different from 120VAC?" Tags="&lt;electronics&gt;&lt;transmitter&gt;&lt;safety&gt;&lt;voltage&gt;&lt;vacuum-tubes&gt;" AnswerCount="4" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14977" PostTypeId="2" ParentId="14976" CreationDate="2019-07-23T07:17:57.503" Score="1" Body="&lt;p&gt;First of all, a voltage of 800VDC can be &lt;strong&gt;very&lt;/strong&gt; dangerous if you happen to be touching anything at ground potential. An 800V potential is REALLY eager to pass some current down to ground, compared to a 120V potential.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, because of Ohm's Law, if you were to touch something at a potential 6.66 higher (800V against 120V), you will get 6.66 times the current flowing through you, and we all know that it's current that kills!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Static electricity can be in the order of tens of thousands of volts, and can surprise us when we touch it - because it has no current (or such a ridiculously low current that we only feel it as a slight jolt). But if you touch 800VDC coming from a power supply that can give several milliamps you are going to be in real trouble.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To say a 120VAC circuit with a 20A breaker on it is more dangerous than an 800VDC power supply, is itself a very dangerous statement. Usually, domestic appliances are protected by a circuit breaker that will detect any current flowing to ground, and will trip the breaker very quickly before you do too much damage to yourself. And if they are not, you will still get a fraction of the current flowing through your body compared to what you would get from the 800VDC PSU.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have had a shock from mains voltage (240V AC) when I was a child, which threw me down a flight of stairs from the jolt. And I had a shock from the anode cap of a (thankfully black-and-white) television's CRT. That was WAY more painful (and to be fair, was several kilovolts, albeit at much lower current) - and I was extremely lucky that my dad had taught me that when you work inside a TV, you always work with one hand behind your back. The last thing you need is any current (even a few mA can be fatal) going between your arms and across your heart.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-07-23T07:17:57.503" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="14978" PostTypeId="2" ParentId="14976" CreationDate="2019-07-23T12:03:45.240" Score="-2" Body="&lt;p&gt;&lt;a href=&quot;https://www.brighthubengineering.com/power-plants/89792-ac-and-dc-shock-comparison/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Online references&lt;/a&gt; confirm my long standing understanding that 30 mA across the chest at 60 Hz is likely to be fatal, and state that it generally takes more than ten times that current of DC to have a similar effect:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Either AC or DC currents can cause fibrillation of the heart at high enough levels. This typically takes place at 30 mA of AC (rms, 60 Hz) or 300 – 500 mA of DC.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is the basis behind my understanding that, in general, 120 VAC 60 Hz is more dangerous than 800 VDC, even from a large capacitor.  Assuming similar skin and body resistance, it would take approximately 1200 VDC (ten times the RMS voltage of 120 VAC) to produce the same risk of fibrillation -- and it takes tens of times that again to quickly produce fatal levels of burns because the body is mostly water, and it takes a tremendous amount of energy to heat water compared to most other substances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not to say 800V from a capacitor can't kill you -- just that it's significantly less likely to do so than 120VAC at 60 Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, then, &lt;strong&gt;I'd need to avoid offering cross-chest paths to ground (the standard precaution has been &quot;keep one hand in your pocket&quot; for nearly a century), use insulated tools when I must make an adjustment with power on, check that energy storing capacitors (like the filter caps in the power supply) have drained through their bleed resistors before working with power down, and as an added precaution, manually short capacitors (preferably through a suitable resistance -- high wattage 1k ohm resistor, for instance) if I can't avoid touching their terminals or conductors connected to them.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of these are similar if not identical to the precautions I take daily in repairing 120V power tools that must often be tested while partly disassembled.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-07-23T23:22:31.357" LastActivityDate="2019-07-23T23:22:31.357" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14981" PostTypeId="1" AcceptedAnswerId="14989" CreationDate="2019-07-23T20:53:32.927" Score="2" ViewCount="2746" Body="&lt;p&gt;I'm a new radio amateur setting up a half-wave 10-meter inverted vee antenna fed by 50 ohm coax. I understand that the inverted vee lowers the normal 72 ohm dipole closer to 50 ohms, so I only need to choke the common mode signal from feeding back on the outside of the coax. I obtained an old Hy-Gain BN-86 1:1 3-30 MHz balun, which Hy-Gain literature calls a &lt;strong&gt;curren&lt;/strong&gt;t balun (notated in their literature below). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZDp71.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZDp71.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, opening the enclosure, the wiring turns out identical to references of a Ruthroff 1:1 &lt;strong&gt;voltage&lt;/strong&gt; balun (found on a several websites). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SCK8B.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SCK8B.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The diagram above from Marki Microwave shows that with one additional winding, a current balun with separate series windings (which seems proper for my use) becomes a voltage balun (an autotransformer).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Q: Will the third winding in my balun somehow help my inverted vee dipole or would an improvement be to remove the winding (rewind the balun) to convert this to a standard 2-winding current balun as a choke? I also wonder if the 30 MHz high limit is too close to 10 meters for this balun to be useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xn5Gt.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xn5Gt.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15325" LastEditorUserId="15325" LastEditDate="2019-07-24T15:55:01.133" LastActivityDate="2021-03-28T20:27:18.640" Title="Voltage vs. Current Balun for Dipole" Tags="&lt;electronics&gt;&lt;balun&gt;&lt;choke-balun&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14982" PostTypeId="2" ParentId="14976" CreationDate="2019-07-23T21:02:37.280" Score="3" Body="&lt;p&gt;&lt;strong&gt;800 volts is far more likely to burn you&lt;/strong&gt;. Just doubling the voltage from 120 to 240 will &lt;em&gt;quadruple&lt;/em&gt; the power heating your flesh.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is just basic Ohm's Law: [P=E*I]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://electronics.stackexchange.com/a/450196/134896&quot;&gt;DC is one nasty customer&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;It is easy to get complacent after spending a youth and a career working with docile, harmless 5-24 volts DC, or well-behaved 100 - 240 V AC voltages because of its frequent zero crossings.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;DC in that same range is a mean drunk. You may have been in very old houses and felt switches that had a definitive SNAP when switched on or off. Those are throwbacks to when house power was DC, and they snap the contacts quite wide, to assure an arc is snuffed. Above that, you need magnetic or pneumatic &quot;blowouts&quot; designed to pull the arc up into an arc chute to blow it out. ,&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;...&#xA;  Look at the &lt;a href=&quot;https://i.stack.imgur.com/ehvsl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;DC ratings for contactors and relays. You will see very different voltage ratings for DC than AC.&lt;/a&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;As a result, the various regulations treat higher voltage DC differently from low voltage, and allowable maximums are typically in the 30-50 volt range&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;And if RF is present, the burn will be even worse.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;A friend of mine was severely burned by 240V when his hand was momentarily inside a breaker panel, and &lt;em&gt;it took several months to heal and for the redness to go away&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, I watched an old electrician show off by testing for the presence of 120 volts at the ends of two wires using his old and dry thumb and forefinger. He would have been burned if he was touching 800 volts, either AC or DC.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-07-27T15:56:28.873" LastActivityDate="2019-07-27T15:56:28.873" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="14983" PostTypeId="1" AcceptedAnswerId="14984" CreationDate="2019-07-24T01:33:23.877" Score="2" ViewCount="104" Body="&lt;p&gt;I am looking for a few long range antennas that can pick up signals from recreational drones in the 2.4-2.5 GHz range. I have done a lot of looking online and most of the results I find are for WiFi antennas or other 2.4 GHz antennas. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;So I am wondering if the two antennas listed below, or other antennas listed as 2.4's or WiFi antennas could be used for other applications in 2.4-2.5 GHz range as well.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://www.alliedelec.com/product/l-com/hg2415y-nf/70126388/?gclid=CjwKCAjw4NrpBRBsEiwAUcLcDAUwo1SO6xxz6r1oFw1hFO9IrTm-OOrnrFYtwno4lg9yAo250MMVjRoCO5cQAvD_BwE&amp;amp;gclsrc=aw.ds&quot; rel=&quot;nofollow noreferrer&quot;&gt;Product 1&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://www.newegg.com/silverstone-sst-wa219-adapter/p/N82E16833965003?item=N82E16833965003&amp;amp;source=region&amp;amp;nm_mc=knc-googleadwords-pc&amp;amp;cm_mmc=knc-googleadwords-pc-_-pla-_-accessories+-+wireless-_-N82E16833965003&amp;amp;gclid=CjwKCAjw4NrpBRBsEiwAUcLcDKYuHkcz3a-DgFthZ72QX3PFqWgClvOydllFF6CM2LiTSKrgX3UtrBoC9H8QAvD_BwE&amp;amp;gclsrc=aw.ds&quot; rel=&quot;nofollow noreferrer&quot;&gt;Product 2&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="15099" LastEditorUserId="13000" LastEditDate="2019-07-24T15:01:16.577" LastActivityDate="2019-08-01T18:08:15.513" Title="Can a WiFi antenna be used for other 2.4 - 2.5 GHz applications?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14984" PostTypeId="2" ParentId="14983" CreationDate="2019-07-24T01:45:13.540" Score="5" Body="&lt;p&gt;Antennas in general are not specific to a modulation/protocol/mode, only the frequency range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible that a device which has &quot;antenna&quot; in the name might in fact be a receiver, or otherwise &quot;smart&quot;, but this is not the case for WiFi antennas, and in general anything with a single coaxial connector rather than something more computer-connector-ish is probably a normal antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some antennas contain built-in receive amplifiers (LNAs). These antennas cannot be used for transmitting, hence would not be suitable for WiFi, and if you did find one, it would be fine for your application but you would need to power the amplifier.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-07-24T01:45:13.540" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="14986" PostTypeId="2" ParentId="14976" CreationDate="2019-07-24T08:33:57.450" Score="-2" Body="&lt;p&gt;I'll answer your questions along the way in order of how they are asked. As well as giving some background information on this misunderstood topic. The 800 VDC is less dangerous on certain circumstances. Let me give examples of where it is dangerous and where it isn't. The most dangerous is when the output current is usually greater than 1.5 amps for your exact voltage. By output I am meaning the amperage that is avalible. Not the amperage that is going through your body. Now that seems like a lot. But given you're skin is dry and even if you touched both ends on purpose, it would feel weird and possibly possibly hurt a little. But it won't kill you on the first try. But if your hands are wet, well lets just make sure no one with wet hands touches something with that much amperage and voltage output. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the things that is very misunderstood by many is that 1 volt can kill or that amperage kills no matter what the voltage is. That is entirely wrong. Very very wrong. I'm sure a couple people reading and editing this will know this is true. And some won't and will try to edit it to say something different. The non dangerous conditions are if the amperage is 1 amp or below with the 800 VDC given. But this condition is strictly only for dry hands. Wet hands are a no no. The only time wet hands would equal the danger level of dry hands is if the amperage was 200 mA and below. It will hurt a little more than dry hands. And this is why I will say 50 mA is the best. But max is 200 mA. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your exact info that was given I will say to wear some class 1 electrician gloves. (With a radio you may not have very good flexibility with the electrician gloves, so thick rubber harbor freight gloves will be sufficient enough. If not then wrap 1 or 2 layers of electrical tape over the fingers of contact on the glove) Class 2 is nice to have, and covers up to 12.5 kVAC. AC is not equal to DC when it comes to insulation. For example, I had a 10 kV DC insulator. And 2.320 kV made the insulator breakdown and catch fire. So the lesson here is DC and AC insulation is never ever the same. So make sure you are using the right type and classification of electrician gloves. If you need more info on electrician gloves try to contact a HV linemen or a master electrician in your area. For the 800 VDC if you do not have the money or resources to get the class 1 electrician gloves, harbor freight or any local hardware store might have some thicker rubber gloves. Use those and a chicken stick. That will also work in certain circumstances. But I personally don't recommend it unless you can insulate the equipment or whatever it is good enough. A chicken stick is usually some insulator (PVC pipe) with a conductor on the end. Depending on what you need done, I would maybe use a plastic coat hanger and break off a straight end. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm just covering most of the variables but not all of them. Again if you can specify what kind of equipment or if its a circuit board or something I can help more. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I thought I would also add a couple corrections or suggestions. The outlet frequency you gave leads me to believe you're on the U.S power grid. Outlet power can be said as (in your case) 20 Amp 120 or 125 VAC 50-60 Hz. U.S power grids don't have just one set frequency. They tend to usually be in the 50-60 range with + or - 5 Hz. So they really are around 45-65 Hz. But it is usually said as 50-60 Hz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you could look on the device and post the input and output info. Such as the output and input voltage, amperage, wattage, VA or KVA. As well as  the operating frequency. I can then make a better judgement on what info I give. Those that want to edit this, please feel free to if I have missed any information that is important or that is a side note. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other Important Information:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your hands can easily be 100,000 ohms and at max 120,000 ohms generally speaking. By generally speaking I am covering humid climates up to 75 percent humidity and down to 3 percent humidity. 3 percent is as dry as Utah air is. 75 percent would be like California, Florida, Oregon and even Maui Hawaii. If you feel your hands becoming moist the resistance can drop to 50,000 ohms. In some cases if completely soaked will drop down to a very minimum of 100 ohms. But this is the resistance from the left arm to the right. Measurements for feet to hands will have a greater resistance. The values I have given are not based on formulas, these values are based on a real life experiment I did. The feet to hands resistance according to the data I've already gathered with my other data says the resistance will naturally be greater. But I haven't done the feet to hands resistance test myself. So I dont have real values for that yet.&lt;/p&gt;&#xA;" OwnerUserId="15329" LastEditorUserId="15329" LastEditDate="2019-07-26T00:07:51.977" LastActivityDate="2019-07-26T00:07:51.977" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14987" PostTypeId="2" ParentId="14981" CreationDate="2019-07-24T10:43:40.863" Score="0" Body="&lt;p&gt;Yes, it does appear that re-winding that balun would be a good idea, as the primary purpose of a 1:1 choke balun is to cut off common-mode currents on the transmission line.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-07-24T10:43:40.863" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="14988" PostTypeId="1" CreationDate="2019-07-24T17:26:10.190" Score="1" ViewCount="66" Body="&lt;p&gt;I am trying to choose a new antenna for the HackRf One, but there are several variables to consider, such as the frequency, threading, resistance etc. In general, what things should I take into account when choosing a new antenna to ensure compatibility.&lt;/p&gt;&#xA;" OwnerUserId="15099" LastActivityDate="2019-07-24T17:26:10.190" Title="What should I take into consideration when choosing a new antenna?" Tags="&lt;antenna&gt;&lt;hackrf&gt;" AnswerCount="0" CommentCount="4" ClosedDate="2019-07-26T03:53:07.163" ContentLicense="CC BY-SA 4.0" />
  <row Id="14989" PostTypeId="2" ParentId="14981" CreationDate="2019-07-24T21:11:34.397" Score="5" Body="&lt;p&gt;You could rewind it, but the result may not necessarily be better. This is because the core must be optimized for different needs in each balun design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In what you're calling a &quot;current balun&quot;, the idea is to maximize the impedance in the common mode. Ideally, that impedance is mostly resistive, meaning high loss. Saturation current isn't so important, because as long as the balun is working and common-mode current is low, the core won't saturate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a &quot;voltage balun&quot;, the objective for the core is to provide an efficient and effective coupling between windings. Unlike the current balun, the windings are such that the differential mode contributes a net magnetic flux to the core. Thus, the core must have &lt;em&gt;minimal&lt;/em&gt; loss, since any loss would degrade antenna efficiency and contribute to heating the core. Moreover, the core must not saturate at the current expected at maximum operating power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A single core design can not likely satisfy both use cases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll note that many current balun designs use ferrite materials and a closed toroid core. This closed magnetic circuit and the material properties of ferrite maximize impedance, but also offer a low saturation current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The balun you picture uses a rod core, which affords much less impedance but a much higher saturation current. It may also use a powdered iron rather than ferrite material. While these design choices allow the core to handle more power as a voltage balun, they would also make it ineffective as a current balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest you use the balun as-is. Voltage baluns aren't necessarily bad, and provided the dipole, feedline, and surroundings are reasonably symmetrical, a voltage balun could work just fine. You can give it a try and see how well it works:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;How to detect common-mode currents or “RF in the shack”?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/6153/218&quot;&gt;How to measure a balun for effectiveness?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If it doesn't work so well then you can try adding or replacing with a current balun, or perhaps you can make some adjustments to your installation to make it more symmetrical, giving the voltage balun a better chance to work.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-07-24T21:11:34.397" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="14991" PostTypeId="1" CreationDate="2019-07-25T21:35:10.820" Score="0" ViewCount="216" Body="&lt;p&gt;I'm new to amateur radio, and as a beginner project, I wanted to use some of the basic components I have to create an AM receiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, what I'm trying to do is create a simple AM receiver that simply detects if a radio station is transmitting, or not. I'm not interested in listening to that station, I just want my receiver to detect the radio waves (basically, I'm just trying to detect a carrier wave). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've spent a lot of time researching how to make what I'm trying to make, but all of the websites I visited explain how to make radio receivers with speakers (such as crystal radios, or very complicated AM receivers). For example, I tried building &lt;a href=&quot;https://www.petervis.com/Radios/one-transistor-radio/one-transistor-radio-9v.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; one by modifying it (aka replacing the speaker with an LED), but it doesn't work even after tinkering around for a couple days, so I thought I'd ask you guys for some help :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be more specific, I would like to receive the AM signal/carrierwave using an LC circuit to detect a specific frequency, and then amplify that signal to drive an LED (since the station's AM signals are too low: around 50-100 μV). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm pretty new to radio and circuitry, but I've done some research and I think I have a general understanding of what's going on. Regardless, I was hoping to make a detector that is &lt;strong&gt;super&lt;/strong&gt; simple, using basic components such as those used on the site I linked. Lastly, for the sake of simplicity, we can leave the LC circuit permanently tuned to, let's say, 1000 KHz (also because I don't have variable capacitors or inductors). I've struggled with this for a while, so I truly appreciate guidance from you guys!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT 1:&lt;/strong&gt; When I say that replacing this circuit with an LED didn't work, what actually happened was that the LED simply turned on the whole time, regardless of whether or not the receiver was picking up a signal (which was confirmed by disconnecting the antenna and LC part). I deduced that the reason for this to happen is that since there is a constant current running in the base of the NPN transistor, there is also a constant current running thorugh it's collector and emitter, and therefore the LED has current running through it, keeping it on. I haven't been able to solve this issue, so if anyone knows how to keep it off (until it receives a signal), let me know!!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a picture of the circuit I tried:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/u7W19.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/u7W19.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15337" LastEditorUserId="15337" LastEditDate="2019-07-25T21:48:32.270" LastActivityDate="2019-07-26T14:30:34.880" Title="How to make simple AM detector using an LED?" Tags="&lt;receiver&gt;&lt;amplifier&gt;&lt;am&gt;&lt;dc-power&gt;" AnswerCount="3" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="14992" PostTypeId="2" ParentId="14991" CreationDate="2019-07-25T22:40:35.277" Score="2" Body="&lt;p&gt;Partial answer (what's going on, but not a good recommendation for how to fix it):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the LED simply turned on the whole time&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This circuit puts DC across the speaker terminals. You don't need to analyze the amplifier at all to see this: just note that the power supply must pass through the node at the bottom side of the speaker (and the 22k resistor) and therefore the voltage drop across the 22k resistor also appears at the speaker.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is fine for a 'crystal earpiece' (piezoelectric crystal) because it is electrically like a capacitor, and does not pass DC and even if it did, does not make sound from it (other than a click on power-up). But your LED passes DC and lights up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(If you were to use a dynamic (magnetic coil based) speaker rather than a piezo speaker (such as normal headphones), the DC would pass through it, and this would change the characteristics of the circuit and waste power, but it would still not make sound other than a power-on click.)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I'm not well-versed in transistor amplifier circuits to tell you how to modify the circuit to provide carrier detection without a perpetual DC offset. If you were to add a high-pass filter before the LED, you could get a circuit which would detect the &lt;strong&gt;audio&lt;/strong&gt; signal, but that's not the same thing as detecting the carrier.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-07-25T22:40:35.277" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14993" PostTypeId="1" CreationDate="2019-07-26T05:12:31.750" Score="1" ViewCount="59" Body="&lt;p&gt;I am building a 1000W &lt;a href=&quot;https://www.google.com/search?q=microwave%20kiln%20for%20glass%20jewelry&quot; rel=&quot;nofollow noreferrer&quot;&gt;microwave kiln for glass jewelry&lt;/a&gt;. The internal capacity needs to be around 5 litres. &#xA;What internal dimensions of the cavity should I avoid, or strive for, to ensure even heating. &#xA;Where should I locate the feedpoint, and. &#xA;Would a magnetron feeding into such a small space be subject to an excessive load? &lt;/p&gt;&#xA;" OwnerUserId="15084" LastEditorUserId="8717" LastEditDate="2019-07-26T18:45:45.673" LastActivityDate="2019-07-26T18:45:45.673" Title="Microwave kiln for glass" Tags="&lt;diy&gt;&lt;microwave&gt;" AnswerCount="0" CommentCount="10" ClosedDate="2019-07-26T18:46:04.730" ContentLicense="CC BY-SA 4.0" />
  <row Id="14995" PostTypeId="2" ParentId="14991" CreationDate="2019-07-26T11:55:01.217" Score="1" Body="&lt;p&gt;My experience is that an LED doesn't act like a common diode -- that is, it's not much use as a rectifier, or especially as a detector, because it requires too much forward voltage and has too much drop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wanted to rectify something like 6 VAC, an LED might work, but when you're trying to detect a few microvolts, it won't do anything by itself; it'll act like an open circuit.  Your circuit above may be attempting to correct this problem with a DC bias (which needs to be critically close to, but below the LED's forward voltage drop, so the LED will &quot;switch on&quot; and &quot;switch off&quot; as the incoming RF voltage fluctuates).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beyond that problem, however, once the LED does &quot;switch on&quot;, so much of the energy it passes goes into light production that there's nothing left to drive your audio amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you change the LED to a low-bias germanium diode made for detector use, or zero-bias FET, and alter the biasing to suit the new component, you might get a functional radio (though your single transistor isn't well matched to the high impedance of a crystal earphone -- you'd be better with a low impedance headphone).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As noted in comments, however, if you're attempting to just give a visual indication whether the tuned station is in fact transmitting, you need the &lt;em&gt;output&lt;/em&gt; of the receiver to control the LED.  To do that, you need to start with a working receiver, in this case, using the original diode specified for the circuit you built.  Once you have that, you can experiment with replacing the speaker or earphone with an LED (using the level control to determine when it lights) or a circuit that will drive the LED.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-07-26T14:30:34.880" LastActivityDate="2019-07-26T14:30:34.880" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="14996" PostTypeId="1" AcceptedAnswerId="14997" CreationDate="2019-07-26T12:21:52.753" Score="0" ViewCount="64" Body="&lt;p&gt;I've been writing a SciFi story, and it calls for something very unusual to happen. I'd like to check this idea for plausibility, but as I'm not a radio ham myself, I don't know if this already exists (and if so under what name) or if it is totally impossible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I have a normal modulated radio signal that can, if broadcast, be picked up by a normal radio receiver — purely for example, let's say it's the normal broadcast from a typical 25 MHz AM radio station — can I use that modulated radio signal to itself modulate a much higher frequency carrier wave in such a way that the radio station's signal will come out of the speakers of a totally unmodified radio tuned to 25 MHz?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an illustration of my intention, where y_1 is the signal, y_2 is the signal modulated by the first carrier wave, and y_3 is y_2 modulated by the next carrier wave. (I chose the constants here purely for the visuals, don't take them to mean anything precise). To rephrase the question: Can y_1 come out of the speakers if y_3 is what's hitting the antenna, and the circuit was tuned for y_2?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eepCG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eepCG.png&quot; alt=&quot;illustrative example of intention&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The intention here is to cheat the normal rules about gain, given the transmitter is a fixed size and power and the receiver is a fixed size and frequency, and nobody was expecting them to be so far apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm still interested if the answer is in the form of &quot;yes, but&quot; for example &quot;yes, but that won't ever work for FM&quot; or &quot;yes, but there is an extra restriction on the frequencies, which is…&quot;&lt;/p&gt;&#xA;" OwnerUserId="15340" LastActivityDate="2019-07-26T12:49:44.620" Title="Unusual modulation" Tags="&lt;receiver&gt;&lt;transmitter&gt;&lt;theory&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14997" PostTypeId="2" ParentId="14996" CreationDate="2019-07-26T12:49:44.620" Score="1" Body="&lt;p&gt;In a word, no.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You &lt;em&gt;could&lt;/em&gt; impress a frequency &lt;em&gt;lower&lt;/em&gt; than 25 MHz onto your 25 MHz carrier with alternate modulation (say, FM), then the audio frequency signal in amplitude modulation, and an AM receiver tuned to 25 MHz would play the AM signal, while an FM radio would play the FM signal.  But any sub-carrier you might put on with FM would have to be lower frequency than the main carrier's 25 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're careful to limit the level of modulation on your FM sub-carrier, it wouldn't even significantly affect the fidelity of the AM signal.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-07-26T12:49:44.620" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="14998" PostTypeId="2" ParentId="14991" CreationDate="2019-07-26T13:29:25.750" Score="2" Body="&lt;p&gt;Good morning F-16Falcon, Immediately i read you question, I thought about a Roimeter, and lucking in internet i found this: &lt;a href=&quot;https://radioclubplacetas.cubava.cu/2016/11/17/medidor-de-roe-optico/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://radioclubplacetas.cubava.cu/2016/11/17/medidor-de-roe-optico/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's an optical Stationary waves meter.Its simple, cheap and do that you need.&#xA;What do you think?&lt;/p&gt;&#xA;" OwnerUserId="15341" LastActivityDate="2019-07-26T13:29:25.750" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="14999" PostTypeId="1" CreationDate="2019-07-26T17:55:31.640" Score="1" ViewCount="97" Body="&lt;p&gt;I'm having trouble running a simple flowgraph with an &lt;a href=&quot;https://osmocom.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;osmocom&lt;/a&gt; source and a qt gui sink. If I run the file with a waveform generator instead of the osmocom source, all is well, the plots appear as they should, no problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the osmocom source is hooked up, everything runs and there is no immediate error message... the gui window just never opens. If I run it from the terminal, I get the following:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;import 'osmosdr._osmosdr_swig' # &amp;lt;_frozen_importlib_external.ExtensionFileLoader object at 0x7f5e0cae23c8&amp;gt;&#xA;import 'osmosdr.osmosdr_swig' # &amp;lt;_frozen_importlib_external.SourceFileLoader object at 0x7f5e0cdda978&amp;gt;&#xA;import 'osmosdr' # &amp;lt;_frozen_importlib_external.SourceFileLoader object at 0x7f5e0cdc9dd8&amp;gt;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Not sure what those errors mean but it just hangs there. Eventually it ends up using 100% of CPU and I have to CTRL + \ it to get it to stop. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it a library maybe in the wrong place that it's not finding?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Please let me know if I can post any more info but:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;OS : Ubuntu 18.04&lt;/li&gt;&#xA;&lt;li&gt;Gnuradio-config-info -version : 3.8.0.0-rc2&lt;/li&gt;&#xA;&lt;li&gt;gr-osmosdr was installed from the git repo and the gr3.8 branch (which worked for me previously)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Any and all help is greatly appreciated, thanks!&lt;/p&gt;&#xA;" OwnerUserId="15343" LastEditorUserId="13000" LastEditDate="2019-07-29T02:01:18.400" LastActivityDate="2019-07-29T02:01:18.400" Title="Trouble with osmocom source" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;hackrf&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15000" PostTypeId="2" ParentId="11776" CreationDate="2019-07-26T23:55:21.423" Score="0" Body="&lt;p&gt;ok. so here's what i have figured out. the large jack (3.5mm) has the external speaker output at the tip of the jack.the last ring is the ground,obviously for that audio output. Now, for the mic/ptt switch i have found this :connected a bare bone 2.5mm stereo mini jack at the other input. I connected the GND (last ring) with the tip of the jack through a 1K resistor (for safety of not shorting anything) and VOILA..the tranceiver light went to red and transmission begun! eureka! .now if you connect in series with the switch a typical mic from a mobile handsfree headset instead of the 1k resistor as load, (mine was ~960 ohm) you get it working. The yaesu ft-25 i tested has a 3.3V voltage acros the head of the jack and the Gnd.&lt;/p&gt;&#xA;" OwnerUserId="15345" LastEditorUserId="15345" LastEditDate="2019-07-27T01:32:52.923" LastActivityDate="2019-07-27T01:32:52.923" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15004" PostTypeId="1" AcceptedAnswerId="15013" CreationDate="2019-07-27T15:30:50.727" Score="3" ViewCount="682" Body="&lt;p&gt;Long ago, it was fairly standard to provide lightning protection for outdoor radio antennas by installing a large double-throw knife switch -- antenna leads to the center, radio on one side, ground on the other.  Double pole for a two-wire feed, single for a plain long wire for a receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This, installed outdoors with suitable thermal protection between the switch/wires and house structure, seems like it ought to still be a good method, and one that's in reach of the cash-strapped starting amateur or SWL.  Just step outside and throw the switch before operating and after shutting down, and your antenna becomes a grounded wire (I've read fairly recent research that suggests lightning rods actually &lt;em&gt;repel&lt;/em&gt; lightning by grounding off charge build-up on high points of the protected structure; this would work the same way).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, heavy knife switches are less visible than they used to be, but they're still around -- look inside any industrial high-voltage or -current shutoff box, and you'll find a knife switch with copper bus bars as thick as a heavy chef's knife and as wide as your thumbnail; on three-phase, it'll be three pole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, knife switches are well within the capability of a hobbyist to build, though heavy gauge copper sheet and bar isn't as easy to find as it once was (and costs plenty) -- one could source all the needed materials in the plumbing section of the local Big Box home improvement store (copper pipe can be flattened to make bus bars and contact clips).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly, there's something missing from my picture of this kind of lightning protection, for it to have been replaced with (potentially sketchy and impossible to genuinely test at the consumer level) gas discharge systems and similar high voltage switching.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are knife switches to alternately connect my antenna to the radio or to ground obsolete for good electrical or safety reasons, or have they just fallen victim to profit motive on the part of equipment makers and sellers?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-07-28T22:20:10.243" Title="Why have knife switch storm grounds for antennas vanished?" Tags="&lt;diy&gt;&lt;antenna-system&gt;&lt;lightning&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15005" PostTypeId="2" ParentId="13257" CreationDate="2019-07-27T16:24:30.743" Score="0" Body="&lt;p&gt;This would be much less efficient, because the carrier is sent as part of the modulated signal. It also creates a very wide signal with no additional information, so it wastes bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lets assume our original audio is 3 kHz wide and our carrier is at 10 kHz. This is a very low RF frequency, in the audio band. The AM signal goes from 13 kHz to 7 kHz, like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;   USB Carrier LSB&#xA;  |               |&#xA;13 kHz           7 kHz  &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Now we modulate a 1 MHz carrier with that signal. We now have an audio signal that goes from 13 kHz to 7 kHz. That audio signal shows up as upper and lower sidebands of the new 1 MHz carrier. It is inverted on the LSB side.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;      [USB Carrier LSB]   Carrier   [LSB Carrier USB]&#xA;      new upper sideband            new lower sideband&#xA;     |                                                |&#xA;1.013 MHz                                        0.987 MHz&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;This new signal covers 26 kHz and uses 75% of the transmitter power in carriers and modulated carriers. In the original signal, 50% of the power is in the carrier. When that is modulated again, it only gets 50% of the power in the new signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a &quot;sideband stacking&quot; technique that is very useful called &quot;subcarriers&quot;. This is primarily used in FM broadcast. It is how we get FM stereo, RDS, and over the air Muzak.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FM broadcast audio feed is about 100 kHz, with bands for mono FM, stereo, and other services. The mono signal is at baseband and the others are translated (modulated) up in frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The diagram in this Wikipedia article shows several common subcarriers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/FM_broadcasting#Other_subcarrier_services&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/FM_broadcasting#Other_subcarrier_services&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2019-07-27T16:24:30.743" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15006" PostTypeId="2" ParentId="15004" CreationDate="2019-07-27T17:09:05.037" Score="0" Body="&lt;p&gt;A regular household light switch is actually an enclosed knife switch. Those are spring-loaded so they close completely every time. If you want to ground your antenna, put a SPDT light switch in a weather-resistant NEMA enclosure and wire it up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Classic open-air knife switches are hard to find and not that cheap to build. As you point out, copper is more expensive than it used to be. Home workshops are harder to find, too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Exposed to weather, copper will corrode quickly. Corroded or half-closed knife switch connections can have a lot of resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Exposed knife switches don't meet electrical safety standards from the past few decades, so good-quality ones just aren't made. Those &quot;mad scientist&quot; switches in the 1940s electrical labs just aren't available now. Electrical service shutoff enclosed knife switches are good, but don't ground and cost about $100.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Knife switches are a pain to use with coax, because you need to break out the coax to the knife switch, then go back to coax to get to the rig. The knife switch will add a big impedance discontinuity with associated reflections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This all assumes a good ground, which isn't cheap. I expect only a few hams actually have a quality safety ground where the RF enters the shack. That would be two 8-foot ground rods 4 feet apart, with 4 gauge wire run between them. For details, see the (great) ARRL book &quot;Grounding and Bonding for the Radio Amateur&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/shop/Grounding-and-Bonding-for-the-Radio-Amateur/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/shop/Grounding-and-Bonding-for-the-Radio-Amateur/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a coax feedline, it makes sense to spend your money on a coax switch that grounds unconnected feedlines. You can also use a lightning arrester with a gas tube and a DC blocking capacitor. Use the right voltage rating gas tube for the power level. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are going to walk outside, just disconnect the coax. This is much easier if you use BNC or even Type N connectors. Those connect and disconnect more reliably than UHF connectors. It is too easy to get a bad connection with a UHF connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Push-on UHF connectors are also popular. At $6, this one is a lot cheaper than any knife switch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.americanradiosupply.com/uhf-male-female-push-on-quick-coaxial-adapter-connector-pl-259/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.americanradiosupply.com/uhf-male-female-push-on-quick-coaxial-adapter-connector-pl-259/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Equipment doesn't disappear because of the &quot;profit motive&quot;. That actually keeps popular stuff available. Equipment disappears because not enough people want it.&lt;/p&gt;&#xA;" OwnerUserId="10" LastActivityDate="2019-07-27T17:09:05.037" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15007" PostTypeId="1" AcceptedAnswerId="15037" CreationDate="2019-07-27T22:42:00.653" Score="8" ViewCount="375" Body="&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Is there a legal (U.S. FCC) or a commonly accepted standard requirement for SSB opposite sideband and and carrier suppression for either manufactured or kit built transmitters?  &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Does the 43+ dB down spurious emissions CFR 97.307 rule apply?  Or some other metric?  (for new stuff, not pre-mid-70’s tube transmitters).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;How well did the old tube transmitters do in this regard?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Added: If there is no legal or regulatory requirement, what might be considered &quot;good practice&quot; on HF amateur bands when attempting to transmit SSB (e.g. not AM or DSB) from a home-built or experimental transmitter.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-02T21:48:47.220" LastActivityDate="2019-08-08T14:06:29.250" Title="Required SSB sideband and carrier suppression?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;ssb&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15009" PostTypeId="2" ParentId="1281" CreationDate="2019-07-28T08:24:47.317" Score="1" Body="&lt;p&gt;There are no official records for actual on-air contacts that I know if and it would be extremely difficult to establish them because (unlike at HST competitions where a team of judges is watching the competitor) it's impossible to detect cheating and there are no clear rules how to measure the speed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are some clubs dedicated to high speed CW operating without keyboards, namely the High Speed Club (HSC), Very High Speed Club (VHSC), Super High Speed Club (SHSC) and finally the Extremely High Speed Club (EHSC). The conditions to join these clubs are to receive a recommendation from existing members for Morse contacts without the help of decoders or encoders (other than standard keyers) at speeds of 25 wpm, 40 wpm, 50 wpm and 60 wpm respectively (125, 200, 250 and 300 characters per minute).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While the &quot;basic&quot; HSC speed of 25 wpm is something that many hams can easily achieve, at 40 wpm the air is getting quite thin: The VHSC has 421 members, SHSC 186 and EHSC 114.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://morsecode.nl/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://morsecode.nl/index.html&lt;/a&gt; (website for HSC-EHSC)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://hsc.dj1yfk.de/db/hsc_list_by_number.txt&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hsc.dj1yfk.de/db/hsc_list_by_number.txt&lt;/a&gt; (current member lists)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So there are some hams on the air who can send and receive at 60 wpm (at these speeds, the sending is the limiting factor for most operators - there are numerous hams who have shown that they can do head-copy at speeds of up to 100 wpm!) with a paddle (no keyboard).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is the official Guinness record (as cited in another answer, 216 letters per minute by Andrei Bindasov) so much lower than 60 wpm?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two major differences: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Those 216 letters were &lt;em&gt;real sent characters&lt;/em&gt;, not measured by the PARIS standard. When you use completely random letters (the record was done at a HST championship with random 5 letter groups), 216 letters &lt;em&gt;real&lt;/em&gt; are approximately 260 characters according to PARIS (52 wpm) due to the different distribution of character lengths.&lt;/li&gt;&#xA;&lt;li&gt;At the HST competition you have to transmit one minute of random 5 letter groups from a sheet of paper you have never seen before, which is more difficult than sending plain text in a language of your choice. If you make an error and have to repeat a group, the repetition of the wrong group does not count as additional sent letters.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In on-air contacts you may make mistakes which you don't even bother to correct, because an extra dit here or there will not make a difference for the receiving party. So comparing on-air contacts with HST competitions is comparing apples and oranges.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bottom line: Amateur radio Morse code contacts with manual keyers (not keyboards) at around 60 wpm are well documented.&lt;/p&gt;&#xA;" OwnerUserId="15352" LastActivityDate="2019-07-28T08:24:47.317" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15010" PostTypeId="2" ParentId="6439" CreationDate="2019-07-28T12:30:27.783" Score="2" Body="&lt;p&gt;I had the same issue. I adjust the Azimuth every day, then sometimes it fails between 15-20 degrees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then I replaced the regulator with a new one. Now it is ok.&lt;/p&gt;&#xA;" OwnerUserId="15354" LastEditorUserId="8717" LastEditDate="2019-07-28T19:04:00.637" LastActivityDate="2019-07-28T19:04:00.637" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15012" PostTypeId="2" ParentId="15004" CreationDate="2019-07-28T21:44:12.393" Score="1" Body="&lt;p&gt;Well ... IMHO, they have not &lt;em&gt;totally&lt;/em&gt; vanished.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Just because you don't see them for sale on the Web or in QST, doesn't necessarily mean that they are not in common use&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This ceramic knife switch and lightning arrestor were at my previous QTH, for my ladder-line-fed multiband 125' inverted-V dipole. I bought the knife switch at a local hardware store. Lots of these are for sale on eBay.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mR7I7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mR7I7.png&quot; alt=&quot;Ceramic knife switch&quot;&gt;&lt;/a&gt;&#xA;&lt;hr&gt;&#xA;&lt;strong&gt;Lightning arrestor&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The red wire in the center is ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I use this here again, I would put static drain resistors across the gaps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yI6X7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yI6X7.png&quot; alt=&quot;OWL lightning arrestor&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-07-28T22:20:10.243" LastActivityDate="2019-07-28T22:20:10.243" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15013" PostTypeId="2" ParentId="15004" CreationDate="2019-07-28T21:52:17.287" Score="3" Body="&lt;p&gt;The dimensions of a typical &quot;knife switch&quot; make it well suited to the high impedance of the open-wire or &quot;ladder&quot; transmission lines which were ubiquitous &quot;Long ago.&quot; While the wide spacing between the switch's &quot;protected&quot; and &quot;operating&quot; positions provides a significant level of lightning protection, it would also present a substantial impedance discontinuity to a low-impedance coaxial transmission line, which could create unwanted reflections.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-07-28T21:52:17.287" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15014" PostTypeId="1" AcceptedAnswerId="15016" CreationDate="2019-07-29T05:49:11.873" Score="3" ViewCount="173" Body="&lt;p&gt;For a modern rig, any rigs that come out within the last 20 years. How long would it last in storage? By that, I mean &quot;dust it off and plug and play&quot;.  Assume it is in a dry and cool place, without exposure to extreme temperature. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What component would likely go bad first? I would imagen capacitor might dry out or some weak solder joint fail.&lt;/p&gt;&#xA;" OwnerUserId="13362" LastActivityDate="2019-07-31T17:00:44.667" Title="How long would a radio last in storage?" Tags="&lt;equipment&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15016" PostTypeId="2" ParentId="15014" CreationDate="2019-07-29T10:41:18.887" Score="6" Body="&lt;p&gt;In modern, medium- to high-end equipment, chances of dry solder joints are slim to none, especially in radio equipment, where your solder process needs to be especially safe against this kind of failure to not inadvertedly add parasitic capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd agree, electrolyte capacitors are a prime aging suspect. They've gotten better, so in most cases, I wouldn't even expect a capacitor failure after 20 years from a device with medium density (i.e. enough room for mechanically large caps) that came out in the 2000s.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's typically not good after 20 years are batteries, which are still common to preserve volatile memory (e.g. channel settings) and by more more commonly to keep an internal timekeeper running.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some thermal greases (between electronic components and coolers) tend to deterioriate over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Dust and dirt are actually most likely to pose problems due to clogging cooling structures. So, a dustproof plastic bag might be a good idea. Make sure it's not 100% airtight, though, if the device is exposed to some thermal cycling: you don't want moisture to condense within the bag.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-07-29T10:41:18.887" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15018" PostTypeId="1" AcceptedAnswerId="15412" CreationDate="2019-07-29T16:55:34.013" Score="5" ViewCount="2702" Body="&lt;p&gt;I tried to build a multiband EFHW antenna as described in articles by &lt;a href=&quot;https://pa3hho.wordpress.com/end-fed-antennes/multiany-band-end-fed-english/&quot; rel=&quot;noreferrer&quot;&gt;PA3HHO&lt;/a&gt;, &lt;a href=&quot;http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html&quot; rel=&quot;noreferrer&quot;&gt;PD7MMA&lt;/a&gt;, &lt;a href=&quot;http://www.infotechcomms.net/downloads/Multi_band_EFHW.pdf&quot; rel=&quot;noreferrer&quot;&gt;G0KYA&lt;/a&gt; and many others. I decided to start with a short 40/20/(15?)/10 meters version without any loading coils. Surprisingly, no matter what I tried I didn't manage to make the antenna work on more than one band. I was hoping someone could explain where my mistake was.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used FT240-31 ferrite core for 64:1 (and later - 49:1) transformer, about 18 meters of wire (П274М, Russian equivalent of British &lt;a href=&quot;https://www.youtube.com/watch?v=0Xs3NxP5_Go&quot; rel=&quot;noreferrer&quot;&gt;D10&lt;/a&gt; - I've used it many times before for long wires, dipoles and delta loops) and 2 meters of RG58 as a feed line and counterpoise at the same time. The second end of the cable was connected to a 1:1 balun. The antenna was installed in inverted-L configuration on a 10 meters long fishing rod.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a photo of a transformer and 100 pF capacitor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IHjZy.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IHjZy.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I easily got SWR from 1.5:1 to 1:1 on 40m. However the best I could get on 20m is 4:1:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nWjoy.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nWjoy.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to get rid of the capacitor, to change it value with a variable capacitor, to change the 64:1 transformer to the 49:1 one, to change the length of the antenna, etc. Currently I spend three weekends on this project. No matter what I tried I get a single band antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It looks like I'm missing something. Maybe the loading coil is not optional in this antenna, maybe it's important to use mix 43 (not 31) as other authors did, maybe something else. What would you do to make the antenna work on 2+ bands?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-07-30T09:23:27.153" LastActivityDate="2021-01-06T01:21:59.943" Title="EFHW works only on one band - what am I missing?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;" AnswerCount="5" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="15019" PostTypeId="2" ParentId="14966" CreationDate="2019-07-29T23:58:41.340" Score="1" Body="&lt;p&gt;Moxon?  Patch?   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those are common models.  To get something more specific, you'd have to model it.  Maybe a genetic algorithm or something could find something that shaped.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-07-29T23:58:41.340" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15020" PostTypeId="1" CreationDate="2019-07-30T09:23:11.230" Score="5" ViewCount="836" Body="&lt;p&gt;I tried to understand the physics of Fuchs antenna and there is one thing that I don't quite understand. This is probably a very silly question, but I spent a lot of time looking for an answer (books, online) and didn't manage to find it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern Fuchs antenna looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JqIth.gif&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JqIth.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The L1,L2 is a transformer, typically 64:1 or 49:1. It is required because the end fed half wave wire has an impedance about 2500..3200 Ohm, assuming a counterpoise wire is about 0.05 lambda. OK, this is clear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also the L2,Cv circuit &lt;a href=&quot;https://m0ukd.com/homebrew/baluns-and-ununs/end-fed-half-wave-antenna-tuned-coupler-efhw/&quot; rel=&quot;noreferrer&quot;&gt;has to resonate&lt;/a&gt; on the frequency of interest (e.g. 7.1 Mhz for 40m band). This is the part I don't quite understand. Why using only a transformer is not enough to convert 2500..3200 Ohm to 50 Ohm of the feed line and feed the antenna as a regular dipole? Why we also need a capacitor to form a resonant circuit? Or, in other words, what happens if we remove Cv?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not an expert in antennas or physics. I would appreciate very much if you could explain it like I'm 10 years old.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-11-19T00:33:35.107" Title="Why a capacitor is needed in Fuchs antenna?" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15021" PostTypeId="2" ParentId="15020" CreationDate="2019-07-30T10:37:03.663" Score="1" Body="&lt;p&gt;L2 and Cv builds an resonant circuit (or tuned circuit) to the desired frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you remove the C or change it to a small fixed value and hold on this transformer ratio, you change the antenna &quot;type&quot; to an EFHW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally a transformer has an high bandwidth than an resonant circuit. It has a very small bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means a Fuchs antenna does some filtering on the used wire and a EFHW not so much. So the EFHW antenna should give more noise from differed frequencys to the output than a Fuchs antenna. But it needs not to tuned across the resonant ham bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case you will not feed the antenna like a dipole. The radiation diagram looks close like it but dipole means always an center-fed antenna. This antenna types are all end-fed.&lt;/p&gt;&#xA;" OwnerUserId="15261" LastEditorUserId="15261" LastEditDate="2019-07-30T11:46:43.083" LastActivityDate="2019-07-30T11:46:43.083" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15022" PostTypeId="2" ParentId="15020" CreationDate="2019-07-30T11:55:23.960" Score="3" Body="&lt;p&gt;It may be simpler to think of the matching network this way:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Mvuyt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Mvuyt.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The high-impedance antenna (in the example, R1 = &lt;span class=&quot;math-container&quot;&gt;$3500\Omega$&lt;/span&gt;) is connected to a parallel-resonant network consisting of an inductor (L1+L2: note the coupling indicated by the &quot;k1&quot; statement) in parallel with a capacitor (C1). L1 is, in reality, a &quot;tap&quot; on a single inductor comprising (L1+L2). As the &quot;tap&quot; approaches ground - that is, as L1 becomes a smaller part of the total L1+L2 - the impedance presented to the generator (V1) becomes smaller.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the impedance presented to the generator vs. frequency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XofCC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XofCC.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Judicious selection of components produces the desired match at the operating frequency. Air-spaced and vacuum-variable capacitors are often used to accommodate: the difficulty of knowing the antenna impedance at a particular frequency; the narrow operating bandwidth; the high voltages that come with high-impedance levels. This method, commonly referred to as &quot;voltage feed,&quot; is often used with end-fed antennas such as half-squares, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coupling link, L1, shown in your question is another way to &quot;tap&quot; down on the impedance across L2.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-07-30T11:55:23.960" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15024" PostTypeId="1" CreationDate="2019-07-30T17:43:44.013" Score="1" ViewCount="130" Body="&lt;p&gt;I want to buy an SDR RTL USB dongle and I'm looking for one on Amazon. I currently saw ones from 100 MHz to 1.7 GHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't decide and I know almost nothing about radio, but I want to experiment with this piece of hardware + the software. I see many come with an expansion that expands the frequency range even more. Should I get this expansion device from the start?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want this dongle to use it on PC, laptop or android devices, to be more specific I want it to be radio dongle, but I don't know if it can support TV as well and I'd like it to have the widest frequency range as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What things should I have in consideration when buying one of these dongles, taking in account the things I wrote before?&lt;/p&gt;&#xA;" OwnerUserId="15373" LastEditorUserId="4076" LastEditDate="2019-07-30T21:13:45.753" LastActivityDate="2019-08-01T02:28:16.747" Title="What to take in consideration when buying an RTL SDR dongle? (Amateur)" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15025" PostTypeId="1" AcceptedAnswerId="15026" CreationDate="2019-07-30T18:43:40.673" Score="1" ViewCount="140" Body="&lt;p&gt;I was wondering what happens when you directly electrically couple the transmitter antenna to the receiver antenna? Particularly I’d like to know what happens for FM radio broadcast. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since I don’t have an FM transmitter I cannot try this at home. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My intuitive guess is that the receiver will not get the intended signal. Is this correct? Why?&lt;/p&gt;&#xA;" OwnerUserId="15374" LastEditorUserId="76" LastEditDate="2019-07-30T20:10:45.213" LastActivityDate="2019-07-30T20:10:45.213" Title="What happens when you directly couple the transmitter antenna to the receiver antenna?" Tags="&lt;antenna-system&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15026" PostTypeId="2" ParentId="15025" CreationDate="2019-07-30T18:53:09.910" Score="5" Body="&lt;p&gt;If your transmitter emits enough power to be heard more than a few meters away, the likely result will be destruction of components in the receiver and possibly in the transmitter as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Receivers are designed to amplify, detect, and decode signals in the range of a few to a few tens of microvolts; transmitters as weak as a few watts will put tens of volts of RF onto their antenna.  The latter signal, applied to the receiver's components, will at a minimum overpower and desensitize the receiver, resulting in no reception at all. It's very likely that this level of power will damage components (transistors or integrated circuits) in the receiver RF amplifier or detector stages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, the receiver (at least after components start to burn) will appear as a grossly mismatched impedance to the transmitter, and the reflected power from that mismatch might well damage the final amplifier stage in the transmitter (burn out transistors, pop capacitors, etc.).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="8573" LastEditDate="2019-07-30T20:10:25.430" LastActivityDate="2019-07-30T20:10:25.430" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="15027" PostTypeId="2" ParentId="15024" CreationDate="2019-07-30T23:23:20.933" Score="0" Body="&lt;p&gt;The main consideration for me was price (~$20).  Also, it should connect via USB to a laptop or desktop and have a small (~5&quot;) antenna that plugs into it.  The idea for me was to use it w/a free SDR program to view a waterfall display of portions of the E&amp;amp;M spectrum, tune in a particular station, and listen to it.  The dongle's range should span from 25MHz up to 1.6GHz so that it covers the 2m &amp;amp; 70cm bands, the NOAA weather radio broadcast (162.4 MHz in my area), local airport tower transmissions, and the local radio stations.  I understand that higher priced dongles will allow for more resolution than my cheap one, but for me the inexpensive dongle approach has worked quite well.&lt;/p&gt;&#xA;" OwnerUserId="15377" LastActivityDate="2019-07-30T23:23:20.933" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15030" PostTypeId="2" ParentId="15014" CreationDate="2019-07-31T14:10:01.317" Score="1" Body="&lt;h1&gt;Capacitor Plague&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Also keep in mind the capacitor plague that afflicted many electronic devices built between 1999 and 2007. &lt;a href=&quot;https://en.wikipedia.org/wiki/Capacitor_plague&quot; rel=&quot;nofollow noreferrer&quot;&gt;Details on Wikipedia&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Short summary abstracted from the Wikipedia article:&lt;/h1&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A higher-than-expected failure rate of non-solid aluminum electrolytic capacitors, between 1999 and 2007, especially those from some Taiwanese manufacturers, due to faulty electrolyte composition that caused corrosion accompanied by gas generation, often rupturing the case of the capacitor from the build-up of pressure.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8886" LastEditorUserId="8717" LastEditDate="2019-07-31T17:00:44.667" LastActivityDate="2019-07-31T17:00:44.667" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15031" PostTypeId="2" ParentId="15024" CreationDate="2019-07-31T20:03:05.197" Score="1" Body="&lt;p&gt;Get one of the RTL-SDR USB devices marketed as &quot;V3&quot; or &quot;V.3&quot;, as they include direct sampling in the MF and HF bands as well as IQ sampling in VHF and UHF region.  Beware of the cheapest units, as some have been reported to use substandard components.  Beware the smallest models, as I've had one of them overheat, and have read other similar reports about them running hot.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-01T02:28:16.747" LastActivityDate="2019-08-01T02:28:16.747" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15032" PostTypeId="1" CreationDate="2019-08-01T14:06:45.193" Score="2" ViewCount="94" Body="&lt;p&gt;I'm planning to build a two-tube reflexed RF regen receiver soon.  I'm examining methods of controlling the regeneration — it needs to be possible to both initiate and halt oscillation in all bands (I plan to cover 500 kHz to 30 MHz, if I can manage it).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;what I keep reading as the &quot;best&quot; method of controlling regeneration is sometimes called a &lt;em&gt;variometer&lt;/em&gt; or &lt;em&gt;variocoupler&lt;/em&gt; — the tickler coil is mounted on a pivot, so it can rotate from aligned with the tuning coil (or in this case, the secondary of the RF coupler between the RF amp and detector), to opposite, so the field from the coil goes from maximum positive feedback to maximum negative feedback.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been mulling over for a couple weeks how to do this without the physical moving coil (which seems prone to issues in a portable set).  It came to me that I can use a double length tickler with a center tap, connect the arm of a potentiometer to the detector plate, and connect each end of the potentiometer track to one end of the tickler, with the return through the center tap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JSMg2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JSMg2.jpg&quot; alt=&quot;Split Tickler Regen Receiver&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This ought to allow me to vary the feedback continuously (if not linearly) from maximum negative to maximum positive without any mechanical parts.  What I'm uncertain of is whether the resistance that's always in the circuit (except at maximum positive or negative setting) will have a negative effect on sensitivity or tuning width.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can't find any reference to this method of controlling regeneration -- have I invented new, 85 year old technology, or was there a good reason this wasn't done?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-08-06T23:10:34.530" LastActivityDate="2019-08-06T23:10:34.530" Title="Has this regeneration control been done?" Tags="&lt;receiver&gt;&lt;diy&gt;&lt;vacuum-tubes&gt;" AnswerCount="0" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="15033" PostTypeId="1" AcceptedAnswerId="15703" CreationDate="2019-08-01T16:25:16.507" Score="6" ViewCount="1552" Body="&lt;p&gt;There is an unknown ferrite toroid. I would like to figure out whether it can be used in an audio transformer, or maybe in a 1:4 transformer on given HF frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The experiment I came up with is following. I can wind a 1:1 transformer using this core, connect one winding to a signal generator and the second winding to the oscilloscope with a 50 Ohm dummy load. Then I can measure Vpp vs frequency with and without the transformer and calculate power loss as 1 - (Vpp_with/Vpp_without)^2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this an adequate experiment? Using this method I could also estimate pase shift and temperature stability. Is there anything else I should be mindful of?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-10-09T15:00:18.310" Title="How to measuring ferrite core efficiency vs frequency" Tags="&lt;measurement&gt;&lt;ferrite&gt;&lt;transformer&gt;" AnswerCount="1" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15034" PostTypeId="2" ParentId="14983" CreationDate="2019-08-01T17:45:16.553" Score="3" Body="&lt;p&gt;Yes, if you're happy with the antenna's properties (physical size, resonant bandwidth, radiation pattern, feedpoint impedance, etc.), you can use it for other purposes--antennas don't know about &quot;applications&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two common &quot;gotchas&quot; to watch out for:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Regular Wifi antennas usually have reverse polarity (&quot;RP&quot;) connectors that won't mate with normal connectors (the US FCC wanted to make it hard for consumers to use higher-gain antennas on their home Wifi units, so manufacturers complied by using RP connectors). Of the two antennas you link to, one has a normal N connector that's common in RF work, but the other has a Wifi-specific RP-SMA connector that won't mate with standard SMA connectors. You can still use RP connectors, but may need an adapter.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some antennas have active electronics or other components in them that make them unusable for transmitting (I have a dipole antenna that has a resistor connecting the two halves of the dipole together to eliminate static buildup, for example--trying to transmit through it would be... spectacular...).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="14767" LastEditorUserId="76" LastEditDate="2019-08-01T18:08:15.513" LastActivityDate="2019-08-01T18:08:15.513" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15035" PostTypeId="1" AcceptedAnswerId="15051" CreationDate="2019-08-02T15:07:02.207" Score="4" ViewCount="1824" Body="&lt;p&gt;Have you used an SSTV decoding application on an up-to-date version of macOS? Which one, and if you built from source, can you share the steps you took to do so?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do not know of a single working macOS application for SSTV decoding. I've been playing SSTV signals over my Mac's speakers, captured with my RTL-SDR dongle, and using &lt;a href=&quot;https://play.google.com/store/apps/details?id=xdsopl.robot36&amp;amp;hl=en&quot; rel=&quot;nofollow noreferrer&quot;&gt;Robo36&lt;/a&gt; on an Android phone to decode the image, as has everyone else I know, but this comes with additional problems. There have been instances of engine-noise (or even the occasional donkey bray) introducing unwanted artifacts in the decoded image.&lt;/p&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="14220" LastEditDate="2019-08-03T22:32:28.793" LastActivityDate="2021-05-25T22:10:15.190" Title="How can I decode SSTV with only macOS software?" Tags="&lt;software&gt;&lt;sstv&gt;&lt;macos&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15036" PostTypeId="2" ParentId="15007" CreationDate="2019-08-02T18:06:13.793" Score="2" Body="&lt;p&gt;Answer (one example) to the third question:  How well did the old tube transmitters do in this regard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In summer after high-school I started building a Phasing type SSB exciter based on a circuit that appeared in the 1965 ARRL Handbook.  This exciter was of course tube based.  It used a set of coils and trimming capacitors for each band (80,40,20) and I only did the 20-meter band as it was the easiest to do.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I finally got it to work during the summer after my freshman year in college (summer of 1966).  One of the tests described in the article that appeared in the Handbook (and I still have my copy) says that the lower side band and carrier (20-meters operating on USB) should be down at least 30 dB from the tuned USB.  Assuming 6 dB per S-unit, that is about 5 S-units on my receiver's S-meter and I rememember looking at that and then adjusting the trimming capacitors for a deeper suppression of the signal.  I had work to do because I was not quite reaching 5 S-units.  My receiver was Hammarlund HQ-170AC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I never did finish that project as college got too busy and I dropped out of my ham radio hobby and either sold or gave away all my equipment.  Also, as I remember my time doing that, the accuracy of my testing experiments might have been compromised a little by having the cover off the SSB exciter and sitting on the work bench right next to my receiver.  So, I most likely was also hearing signals before the circuits designed to suppress carrier and opposite sideband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The article in 1965 ARRL Handbook (A Phased Single Sideband Exciter, page 286) does not refer to any official FCC requirements on carrier suppression or sideband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;P.S.  I have a photo of this exciter although it does not show much more than the front panel.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2019-08-02T18:06:13.793" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15037" PostTypeId="2" ParentId="15007" CreationDate="2019-08-02T18:06:21.387" Score="4" Body="&lt;p&gt;There is no such specific legal requirement, because AM and double-sideband suppressed carrier (DSBSC) are allowed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Different emission types occupy different bandwidths&lt;/em&gt;, as the FCC clearly acknowledges below.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;&lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.307&quot; rel=&quot;nofollow noreferrer&quot;&gt;§ 97.307 Emission standards&lt;/a&gt;.&lt;/strong&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) No amateur station transmission shall occupy more bandwidth than necessary for the information rate and &lt;strong&gt;emission type&lt;/strong&gt; being transmitted, in accordance with good amateur practice.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There is a vague phrase that says that an amateur's signals should conform to 'good engineering practices'. However, there are in fact very wide emissions such as ESSB (8 kHz wide), and the FCC does not cite stations for that.&#xA;&lt;hr&gt;&#xA;When I was in high school, I found plans in an amateur radio publication for converting a WWII surplus Command Set transmitter to DSBSC (which I successfully built). It is highly doubtful that the articles would have been published if that were an illegal mode.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-08-02T18:37:59.073" LastActivityDate="2019-08-02T18:37:59.073" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15038" PostTypeId="1" CreationDate="2019-08-03T02:23:15.867" Score="2" ViewCount="1073" Body="&lt;p&gt;Consider the picture below is design of half wave length (λ) dipole antenna. I read some explanations saying that it is the best design to get the optimum transmit power. Half wave length (λ) is from tip to the tip of the two elements (you know it).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But my concern here is, what is the minimum or maximum distance of the gap as in the picture? Gap between the two elements which the feeder line is connected? Some say that it should be as small as possible. But unfortunately, I don't have mathematical justification for that reason even it make sense. I expect that the explanation is in λ. But if you really need the used frequency, then just put 2,100 MHz. If needed, the feeder line is RG6 75 ohm.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/GQogp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GQogp.jpg&quot; alt=&quot;Hal λ dipole antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15393" LastActivityDate="2019-08-10T12:27:48.317" Title="What is the maximum and minimum of antenna gap of dipole antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;" AnswerCount="4" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15039" PostTypeId="2" ParentId="15038" CreationDate="2019-08-03T07:30:18.963" Score="0" Body="&lt;p&gt;Actually, that gap is fixed within cable. That is distance between inner conductor and shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part of the cable from the point where inner conductor exits out of the shield is actually part of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, it does not matter what is distance between antenna wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, minimum distance is important, as if wires are too close, it might cause sparking. It depends of transmitter power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8UJwP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8UJwP.png&quot; alt=&quot;Dipole antenna attachment to cable&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="306" LastEditorUserId="306" LastEditDate="2019-08-06T08:26:38.333" LastActivityDate="2019-08-06T08:26:38.333" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="15040" PostTypeId="1" CreationDate="2019-08-03T07:34:37.003" Score="1" ViewCount="2726" Body="&lt;p&gt;I would like to make a match half wave length (λ) dipole antenna (or probably a short dipole antenna). So I would like to make it by measure using LCR meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I am still confuse is about what is the correct formula of impedance (Z). Is in most explanations the formula is written that impedance (Z) = R + jX (Ω), which X is capacitance (and inductance if any). The resistance, the capacitance, and the inductance (if any). As there will be imaginary component there, then the unit will not be ohm (Ω). Then the question is, which one is the correct one for this two formulas (assuming no inductance)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Z = R + jX_C = R + j\frac{1}{2\pi fC} \qquad(1)$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Z = \sqrt{R^2 + (\frac{1}{2\pi fC})^2} \qquad(2)$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JnsG0.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JnsG0.jpg&quot; alt=&quot;LCR Meter&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15393" LastEditorUserId="4665" LastEditDate="2019-08-05T13:44:27.547" LastActivityDate="2019-08-05T13:44:27.547" Title="How to calculate impedance in antenna design's practice?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;balun&gt;" AnswerCount="3" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="15041" PostTypeId="2" ParentId="15040" CreationDate="2019-08-03T11:19:08.253" Score="0" Body="&lt;p&gt;In general, impedance consists of two parts: a &lt;em&gt;resistive&lt;/em&gt; part that dissipates energy and a &lt;em&gt;reactive&lt;/em&gt; part that stores energy in an electric or magnetic field. A &lt;em&gt;complex&lt;/em&gt; number that includes a &lt;em&gt;real&lt;/em&gt; part and an &lt;em&gt;imaginary&lt;/em&gt; part is a mathematical tool for keeping track of two related properties of a system. On a Cartesian graph, the real part (resistance) is plotted along the &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;-axis, while the imaginary part (reactance) is plotted along the &lt;span class=&quot;math-container&quot;&gt;$y$&lt;/span&gt;-axis. By convention, inductive reactance has a positive sign and capacitive reactance has a negative sign. The distance from the origin of the graph to the point &lt;span class=&quot;math-container&quot;&gt;$(x,y)$&lt;/span&gt; corresponding to the impedance of interest is the magnitude of the impedance, while the angle of a line segment from the origin to the point is the phase angle of the impedance, as shown in the diagram:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9ITwo.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9ITwo.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your first equation should read: &lt;span class=&quot;math-container&quot;&gt;$Z=R-j\frac{1}{2\pi fC}$&lt;/span&gt; (note the change of sign). If the reactive part of the impedance was inductive, the equation would be: &lt;span class=&quot;math-container&quot;&gt;$Z=R+j2\pi fL$&lt;/span&gt;. Your second equation is the &lt;em&gt;magnitude&lt;/em&gt; of the impedance: &lt;span class=&quot;math-container&quot;&gt;$|Z|=\sqrt{R^2+X^2}$&lt;/span&gt;, where &lt;span class=&quot;math-container&quot;&gt;$X$&lt;/span&gt; is the inductive or capacitive reactance calculated earlier. The companion of the magnitude of the impedance is its phase angle, which is &lt;span class=&quot;math-container&quot;&gt;$arctan\frac{X}{R}$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the simple example of a half-wave dipole, the impedance at the feed point would: be purely resistive at the resonant frequency &lt;span class=&quot;math-container&quot;&gt;$(R+j0)$&lt;/span&gt;; show capacitive reactance below the resonant frequency &lt;span class=&quot;math-container&quot;&gt;$(R-jX_C)$&lt;/span&gt;; show inductive reactance above the resonant frequency &lt;span class=&quot;math-container&quot;&gt;$(R+jX_L)$&lt;/span&gt;. The graph below illustrates this behavior for a half-wave dipole designed for the 20m amateur band (14.1MHz):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fqDHt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fqDHt.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Measuring the same dipole's feed point impedance with an &lt;span class=&quot;math-container&quot;&gt;$LCR$&lt;/span&gt; meter operating at 100kHz would produce a measurement of &lt;span class=&quot;math-container&quot;&gt;$0-j88184 \Omega$&lt;/span&gt;, which is equivalent to an 18pF capacitor. Why? At this very low frequency, the 20m dipole is only 0.003 wavelengths long, so it will only radiate (dissipate) a very small amount of energy; thus, the resistive part of the impedance is very small. The capacitive coupling between the two dipole legs dominates the small inductance of the short wires, so the reactance is capacitive.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-08-04T12:47:36.960" LastActivityDate="2019-08-04T12:47:36.960" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="15042" PostTypeId="2" ParentId="15040" CreationDate="2019-08-03T11:46:03.317" Score="0" Body="&lt;ul&gt;&#xA;&lt;li&gt;Formular (1) is correct for impedance. &lt;br&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Formular (2) calculates the magnitude of Z for e.g. the polar form representation.&lt;br&gt;&#xA;&lt;br&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;However with an LCR meter (as in your picture) you won't get the rf impedance of interest for an antenna because the impedance changes considerably between low frequencies (~DC) as measured by an LCR meter and rf frequencies &lt;br&gt;&#xA;&lt;br&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You would need an impedance analyzer or vector network analyzer (VNA) specified for the frequency of interest from your antenna.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;Here are links to 3 youtube videos from w2aew that show an example of such a measurement with the mentioned devices:&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=_Dlw_XheKl0&quot; rel=&quot;nofollow noreferrer&quot;&gt;#282: Part 1: How to measure complex impedance with MFJ-259B | determine sign of X&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=ON9htKshkIk&quot; rel=&quot;nofollow noreferrer&quot;&gt;#283: Part 2: Measuring Complex Impedance with MFJ-259B | Crossing the real axis...&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=f8wJ0io95RE&quot; rel=&quot;nofollow noreferrer&quot;&gt;#264: RF Fun: Visualize antenna tuner operation on Smith Chart, SWR &amp;amp; more with VNA&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="15355" LastEditorUserId="15355" LastEditDate="2019-08-03T11:51:34.503" LastActivityDate="2019-08-03T11:51:34.503" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15044" PostTypeId="1" CreationDate="2019-08-03T19:30:41.460" Score="1" ViewCount="112" Body="&lt;p&gt;The second R in AR&lt;strong&gt;R&lt;/strong&gt;L stands for &lt;em&gt;Relay&lt;/em&gt;, but is that still as relevant in the 21st century?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has it been relevant since broad damped-wave spark transmitters were supplanted with tube-generated CW, which covers far greater distances?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/a/15046/8717&quot;&gt;We still have NTS&lt;/a&gt; as one answer nicely points out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am &lt;em&gt;not&lt;/em&gt; suggesting that the ARRL should change their name.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-08-05T19:46:26.010" LastActivityDate="2019-08-05T20:47:38.063" Title="Is the Relay in ARRL still relevant?" Tags="&lt;history&gt;&lt;arrl&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15045" PostTypeId="2" ParentId="15038" CreationDate="2019-08-03T20:36:34.400" Score="0" Body="&lt;p&gt;The point where the feedline separates marks the center of the dipole.  That length of conductor matters.  It radiates, carries current, and effects the behavior of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the conductors feeding the &quot;dipole&quot; wires don't diverge at 90 degrees and are &quot;significantly long&quot;, it gets more complicated to calculate, and the NEC software many hams use can help to calculate the impact, and let you model variations.&lt;/p&gt;&#xA;" OwnerUserId="9109" LastActivityDate="2019-08-03T20:36:34.400" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15046" PostTypeId="2" ParentId="15044" CreationDate="2019-08-03T23:14:19.120" Score="6" Body="&lt;p&gt;The ARRL NTS (National Traffic System) is designed to operate from one local area to another local area (say, across the country) by the process of Relaying messages from one station to another.  I am a member of several section nets in the northwest area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I had a message that I wanted to originate from the Seattle area to a destination across the country (for example, Miami, Florida) several different stations are involved that operate at different levels of the relay schedule.  For example, I would post the message traffic to the CW section net called WSN (Washington State Net) with final destination to Miami (presume a phone number is the contact method).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In WSN the message would be taken from me by an operator who is scheduled to submit it to RN7 (area net).  Then, an RN7 station will take the message and probably submit it to PAN (Pacific Area Net) to make its way across the country via dedicated and scheduled operators who move that traffic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the east coast, the reverse process may happen, the message will be taken by the EAN (Eastern Area Net) operator and submitted to 4RN for delivery to a section net closest to the Miami destination.  The final operator who takes the message is usually local to Miami and makes the phone call to deliver the message.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For priority messages that must be delivered in a given time interval, this process can occur relatively fast assuming good propagation at each relay point.  Sometimes QRN or other propagation problems can halt the process until the message can be sent.  There are methods defined for handling messages that cannot be delivered on time which can include ACK or NAK messages relayed back the originating station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the US, virtually every ham radio operator has a local traffic net that they can join.  Evening nets on the 80 meter band are usually the section nets or area nets that handle message traffic.  Often, the PAN nets may pick up a message in the evening for cross country hop but wait until the next day for a scheduled hookup, usually on the 20 meter band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Operating as an NTS volunteer traffic handling station is good experience, there are both CW and SSB HF traffic nets and even the VHF/UHF repeater stations host traffic nets.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2019-08-03T23:14:19.120" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15047" PostTypeId="2" ParentId="1748" CreationDate="2019-08-04T03:48:24.030" Score="4" Body="&lt;p&gt;Both modes are FSK, and both have the same effective data rate (72 data bits in about 50 seconds), but there is one very big difference between them: bandwidth. JT9 is 20Hz wide. JT65A (the mode commonly used in HF) is 180Hz wide, JT65B (often used for 2m EME) is 360Hz wide, and JT65C (often used for 33cm and up) is 720Hz wide. Why does this matter and how does it relate to which one you would use on which band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first reason is noise. The power of the natural noise we receive is proportional to the width of our passband in Hz. If we can make a signal narrower, and the receiver filter narrower, while keeping the same signal power, the amount of noise goes down proportionally and the SNR goes up proportionally. This is basically free sensitivity!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second reason is stability. Given the first argument, you might think that JT9 is always going to be the best choice for a low-data-rate, high-sensitivity mode. But to receive a message using an FSK mode where the tones are only separated by 1.75Hz, the transmitter and the receiver had both better be stable to better than 1Hz. Even on HF, not everyone is that good. As the frequency goes up, it becomes borderline impossible. JT65A has a tone spacing of 2.7Hz, JT65B 5.4Hz, and JT65C 10.8Hz. That makes them approximately 1.5x, 3x, and 6x as forgiving to drift as JT9.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for MF and HF, where you want to be heard over the QRN and frequency stability isn't a big problem, JT9 works great. For higher frequencies, where the natural noise generally becomes less and less, and frequency stability becomes more and more of a challenge, JT65 is more suitable.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-08-04T03:48:24.030" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15050" PostTypeId="2" ParentId="15040" CreationDate="2019-08-04T16:36:56.350" Score="4" Body="&lt;p&gt;&lt;em&gt;Impedance&lt;/em&gt; is the sum of &lt;em&gt;resistance&lt;/em&gt; and &lt;em&gt;reactance&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z = R + jX $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$j$&lt;/span&gt; is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Imaginary_unit&quot; rel=&quot;nofollow noreferrer&quot;&gt;imaginary unit&lt;/a&gt;, equal to &lt;span class=&quot;math-container&quot;&gt;$\sqrt{-1}$&lt;/span&gt;. Some equations use &lt;span class=&quot;math-container&quot;&gt;$i$&lt;/span&gt; instead to mean the same thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reactance is a concept that describes the effects of capacitors and inductors, as well as other components that introduce a phase shift between voltage and current, but don't dissipate energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, the reactance of a capacitor is given by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ X_C = {-1 \over 2 \pi fC} \tag 1 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And for an inductor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ X_L = 2 \pi fL \tag 2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; is capacitance (farads), &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; is inductance (henrys), and &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is frequency (hertz). From this you can see for capacitors and inductors (and in practice, most other things) the reactance depends on frequency, and capacitors have negative reactance whereas inductors have positive reactance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The unit of impedance, resistance, and reactance is &lt;em&gt;ohms&lt;/em&gt; in each case. Impedance is represented by a &lt;a href=&quot;https://en.wikipedia.org/wiki/Complex_number&quot; rel=&quot;nofollow noreferrer&quot;&gt;complex number&lt;/a&gt;, but the unit is still ohms.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;That's the theory.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, you won't be able to measure the impedance of your antenna with an LCR meter. As you can see in equations 1 and 2, reactance (and thus impedance) depends on frequency. The LCR meter works by measuring the impedance at some frequency, then working backwards though equations 1 or 2 to find the inductance or capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This works OK for inductors and capacitors (at least, when operating at frequencies where parasitic effects are negligible), but an antenna is something else so equations 1 and 2 don't apply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, people use an &lt;em&gt;antenna analyzer&lt;/em&gt; to measure the impedance directly at the frequency where the antenna is intended to be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't have an antenna analyzer, you can use an &lt;em&gt;SWR bridge&lt;/em&gt;. This will tell you how close you are to 50 ohms, though not in what direction. There will be a dip in SWR around where the antenna is resonant. Making the antenna longer moves this dip lower in frequency, and making the antenna shorter moves it higher. By measuring SWR at several frequencies and iteratively adjusting the length of the antenna, it's possible to get the antenna to be the right length for the desired frequency.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-08-04T16:36:56.350" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="15051" PostTypeId="2" ParentId="15035" CreationDate="2019-08-04T18:37:35.237" Score="3" Body="&lt;p&gt;&lt;a href=&quot;https://www.qsl.net/kd6cji/&quot; rel=&quot;nofollow noreferrer&quot;&gt;MultiScan 3B&lt;/a&gt; works fine in terms of decoding. This being said I had some issues making it work with my external sound card for &lt;em&gt;transmitting&lt;/em&gt; SSTV. For some reason transmitted images turned out to be cropped. I accidentally figured this out using &lt;a href=&quot;http://max.cqsstv.com/HF20m-recent.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;cqsstv.com&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Eventually I ended up using a Linux laptop and QSSTV software. Still if you are interested only in decoding, MultiScan 3B should be OK.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-08-04T18:37:35.237" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15052" PostTypeId="1" CreationDate="2019-08-04T23:00:37.677" Score="1" ViewCount="62" Body="&lt;p&gt;I'm starting design work on a two-tube (two-valve, for those who prefer that term) reflex-regen receiver that I hope will cover AM broadcast through 160m-10m -- both amateur bands and those &quot;in between&quot; spectrum segments including SW broadcast bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Longer term, I'd like to build this into a transceiver, with at least CW transmit and possibly a later upgrade to AM or even SSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part of the definition of a transceiver is that parts count is kept under control by sharing parts of the circuits -- the audio amplifier in a receiver might be reconnected as the voice modulator for AM transmission, for instance, almost always the antenna is shared, and in older handy-talkies (especially the &quot;toy&quot; variety) the speaker becomes the microphone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I'm wondering is whether it's practical, without sacrificing desirable qualities like stability, to make the receiver's tuning tank circuit also act as the tuning section of the VFO for transmit.  It seems so, at first glance -- we've got a tuned network already set to resonance at the selected frequency; at most we might want (for CW, especially) to offset the transmitter by a small amount, easily done by switching in a low-value capacitance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the transceiver schematics I've looked at, however, were either very simple circuits that really only share the power supply and antenna, are crystal controlled without the ability to genuinely tune either receive or transmit, or are so complex I can't be sure I'm following the functions correctly (ex. the 22 tube Heathkit SB-102).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, is it practical or advisable to expect to use the same tuned circuit to control both receive and transmit frequency in a VFO-controlled transceiver?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-08-05T10:03:43.427" Title="Can the transmit and receive functions of a boat anchor transceiver share the tank circuit?" Tags="&lt;diy&gt;&lt;transceiver&gt;&lt;equipment-design&gt;&lt;vacuum-tubes&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15054" PostTypeId="2" ParentId="15052" CreationDate="2019-08-05T10:03:43.427" Score="1" Body="&lt;p&gt;You can use the tuning circut of the regen and, to be exact, the regen stage as a VFO for your transciever! Couple it to the separator amp with a 100pF cap between separator grid and the to of VFO tuning circut. Keying can be achieved by the key turning a relay on, the relay's contacts being connected to separator's cathode resistor and ground with a cap in the range of 100nF to 10nF for smooth keying in parralel. Another contact of relay switches some component to turn regen on to max - we could really use the schematic here. The third relay contact switches the antenna between the reciever input and power amp output. I suggest using two relays, fir the first we contacts you can use DPDT relay (two switches that switch between two contacts) or DPST (two switches that have only one contact), for the antenna switch you can use a SPDT. You can use the heater supply for powering them, the antenna relay should be faster than the first relay so the power output tube doesn't transmit into a open circut, if you can, use small relays here since smaller relay = faster relay. The separator and power output tube can be one of those triode-power pentode combos. Use a П network to tune tube to antenna and high quality mica capacitor between anode and П network. Remember to test VFO stability and screen each stage to separate them, especially the power supply and power amplifier.&lt;/p&gt;&#xA;" OwnerUserId="14961" LastActivityDate="2019-08-05T10:03:43.427" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15055" PostTypeId="1" CreationDate="2019-08-05T11:40:15.470" Score="1" ViewCount="39" Body="&lt;p&gt;Here is my C-Band parabolic tv digital receiver. As shown by the pictures, the incoming coax cable (INPUT) connected both the outer and the core. One goes to digital receiver 1 (receiver 1), and another goes to digital receiver 2 (receiver 2).&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;If BOTH receivers are turned ON, they are working fine.&lt;/li&gt;&#xA;&lt;li&gt;If receiver 1 is turned OFF, receiver 2 is working fine.&lt;/li&gt;&#xA;&lt;li&gt;But, if receiver 2 is turned OFF, the receiver 1 is NOT working.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;They are supposed to be connected by a spliter. Unfortunately, I don't have a suitable one. This is temporary until I get it. Then my question is, why is the receiver 1 can not be independent from digital receiver 2 (but not vice versa)? Which one is better in term of loss affected by the connection compared to if compared to use combiner?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uV8st.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uV8st.jpg&quot; alt=&quot;Co-axial&amp;#39;s connection&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/z62KB.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/z62KB.jpg&quot; alt=&quot;Digital receiver 1&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/9TCsP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9TCsP.jpg&quot; alt=&quot;Digital receiver 2&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15393" LastEditorUserId="15393" LastEditDate="2019-08-05T12:09:16.527" LastActivityDate="2019-08-05T12:09:16.527" Title="Problem to paralel tv digital reciever" Tags="&lt;antenna&gt;&lt;receiver&gt;" AnswerCount="0" CommentCount="11" ClosedDate="2019-08-05T18:15:30.343" ContentLicense="CC BY-SA 4.0" />
  <row Id="15056" PostTypeId="1" AcceptedAnswerId="15062" CreationDate="2019-08-05T13:25:08.353" Score="1" ViewCount="280" Body="&lt;p&gt;I’m trying to be less of an appliance operator.  To that end, I recently came up with a simple project that I thought I could figure out and build entirely on my own.  I was wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My goal was to create a splitter with an attenuator that would allow me to  connect the external speaker jack output from my Yaesu FT-8900 to the microphone input on an iPhone in order to record, while simultaneously listening to the live audio via headphones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’m doing this because I’d like to record FM satellite QSOs as they occur while I’m outside using a handheld yagi (thankfully, building the antenna was within my skillset!).  Currently, I just use an old Olympus DM-10 digital recorder Velcro’d next to the built-in speaker, which is less than optimal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My problem is I get lost in the calculations for resistor sizes needed to get from the higher voltage output on the FT-8900 speaker jack to the millivolt input on the iPhone, as well as well as how to physically wire everything from the mono TRS plug for the radio side to the stereo TRRS plug for the iPhone side, as well as splitting-off for a headphone jack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reference, the specs on the Yaesu output is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Maximum AF Output:   2 W @ 8 Ω for 5% THD&lt;/li&gt;&#xA;&lt;li&gt;AF Output Impedance: 4-16 Ω&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Any help would be greatly appreciated.  Thanks in advance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;To answer Chris K8NVH's questions:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as headphones always being plugged in:  The vast majority of the time, I would be using headphones.  However, it would be nice to have the ability to use the device both with and without headphones attached.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As far as line level drop: if the drop is such that it doesn't render the resulting audio unusable, it doesn't really matter to me.  I don't mind turning up the volume when playing back if that is the only consequence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wanted to go with the iPhone over the Olympus for a number of reasons:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;First and foremost, it is very easy to accidentally hit a button on the Olympus and cancel a recording.  This has happened to me in the past.  With the iPhone, this would not be a concern.&lt;/li&gt;&#xA;&lt;li&gt;I already use the iPhone when I'm working the satellites outdoors to see times, tracks across the sky, etc.  Using it over the Olympus would allow me to eliminate one piece of equipment&lt;/li&gt;&#xA;&lt;li&gt;The iPhone offers better battery life.  Its surprising how fast the Olympus goes through AAA batteries.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;But, in the end, simple is probably better.  If that means sticking with the Olympus and creating a circuit that is designed to be used only with the headphones plugged in, I can accept that for the time being.  I can always try a more involved design later.&lt;/p&gt;&#xA;" OwnerUserId="15087" LastEditorUserId="15087" LastEditDate="2019-08-09T11:04:22.040" LastActivityDate="2019-08-09T11:04:22.040" Title="Design/Build a DIY Audio Attenuator and Splitter" Tags="&lt;diy&gt;&lt;audio-interface&gt;&lt;audio&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15058" PostTypeId="1" AcceptedAnswerId="15061" CreationDate="2019-08-05T18:52:45.917" Score="2" ViewCount="550" Body="&lt;p&gt;I am traveling to El Salvador later this fall, and was wonder if there is any reciprocal agreement that would let me use a US callsign while there? If so, what privileges would I have there based on an Amateur Extra class license here? Would a Technician class licensee have any reciprocal privileges?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have already tried to contact the national &quot;Club de Radio Aficionados de El Salvador&quot; via their &lt;a href=&quot;http://www.ys1ys.org/home/nstroclub/contactenos&quot; rel=&quot;nofollow noreferrer&quot;&gt;YS1YS web contact form&lt;/a&gt; but I get a &quot;mailbox full&quot; response. I also tried to contact some of their club officers via their QRZ email addresses but got no response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That club website does host a &quot;MRS-GAJ-99&quot; document titled &lt;a href=&quot;http://www.ys1ys.org/descargas/docs/normativa_de_operacion.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Normas Para La Operación De Radioaficionados En El Salvador&lt;/a&gt; does mention I can apply via CRAS &quot;u &lt;strong&gt;otra Organización de radioaficionados&lt;/strong&gt; reconocida por la IARU (Unión Internacional de Radioaficionados) previamente autorizada por la SIGET&quot; [emphasis mine] but I'm not sure how to find out if either the FCC or ARRL VEC is authorized by SIGET,  or really what that would mean for the rest of the licensing rules that follow.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2019-08-06T01:17:20.280" Title="Can I use my US callsign to transmit while in El Salvador?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15059" PostTypeId="2" ParentId="15044" CreationDate="2019-08-05T20:47:38.063" Score="4" Body="&lt;p&gt;The challenging propagation experienced during the 2019 ARRL Field Day exercise answers your question with a resounding, &quot;Yes, Relay is still relevant!&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many hams are unable to erect directional antennas on tall towers and power them with legal-limit amplifiers. Others simply prefer to complete contacts with modest antennas and lower power. We will not be able to pick and choose which stations survive the challenges of any particular &quot;event,&quot; nor the band conditions at a particular time of day, annual season or point in the sunspot cycle. It could very well be essential for the average station - one like those deployed during Field Day - to be able to relay a message from one coast of North America to the other, particularly as our social circles have become so geographically dispersed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I had first hand experience with this situation in the wake of the devastation wrought by Hurricane Maria on the Caribbean island of Dominica. One might be tempted to say, &quot;That couldn't happen here,&quot; but threats from weather, fire, earthquakes, network crashes and power system failures could all create the same need for a robust alternative to mainstream commercial channels.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-08-05T20:47:38.063" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15060" PostTypeId="2" ParentId="15058" CreationDate="2019-08-05T21:00:20.733" Score="3" Body="&lt;p&gt;You may be able to obtain an &lt;a href=&quot;http://www.arrl.org/iarp&quot; rel=&quot;nofollow noreferrer&quot;&gt;International Amateur Radio Permit&lt;/a&gt; (IARP) from the ARRL. According to their web site, the IARP:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;... allows US amateurs to operate without seeking a special license or permit to enter and operate from that country...&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;According to the &lt;a href=&quot;http://www.oas.org/en/sla/dil/inter_american_treaties_A-62_radio_permit_signatories.asp&quot; rel=&quot;nofollow noreferrer&quot;&gt;Organization of American States&lt;/a&gt; (OAS), El Salvador is a &lt;a href=&quot;http://www.oas.org/en/sla/dil/inter_american_treaties_A-62_radio_permit_signatories.asp&quot; rel=&quot;nofollow noreferrer&quot;&gt;signatory to treaty A62&lt;/a&gt;. The &lt;a href=&quot;http://www.arrl.org/files/file/VEs/IARP%20Application%20March%202015%20interactive.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;IARP application&lt;/a&gt; is available from the ARRL web site.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-08-05T21:00:20.733" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15061" PostTypeId="2" ParentId="15058" CreationDate="2019-08-05T21:09:56.583" Score="4" Body="&lt;p&gt;The information on ARRL's &lt;a href=&quot;http://www.arrl.org/iarp&quot; rel=&quot;nofollow noreferrer&quot;&gt;IARP&lt;/a&gt; page and the &lt;a href=&quot;https://www.citel.oas.org/en/Pages/Inte-American-Conventions.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;CITEL&lt;/a&gt; page indicates that El Salvador allows operation on an International Amateur Radio Permit, without you getting a license from El Salvador. Similar to CEPT, it would allow you to operate using your home callsign together with an El Salvador prefix (YS/AF7TB).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the 1995 Convention, an IARP Class 1 permit (which allows the use of HF) is issued to &quot;amateurs who have proved their competence with Morse code to their own Administration in accordance with the requirements of the ITU Radio Regulations&quot;, while a Class 2 permit only allows bands above 30MHz. However, in a 2018 amendment (which doesn't seem to have been ratified yet by El Salvador), the text &quot;amateurs who have proved their competence with Morse code to their own Administration in accordance with the requirements of the ITU Radio Regulations&quot; is replaced with &quot;amateurs who have proved their advanced competence to their own Administration, where guidance for standards of competence may be found in the most recent version of Recommendation ITU-R M.1544.&quot; That would clearly open things up to an Extra. Regardless of the technicalities, ARRL will issue a Class 1 permit to anyone holding a General, Advanced, or Extra license, without requiring proof of Morse proficiency, since there hasn't been an avenue for US amateurs to get a Morse code endorsement on their license since 2006.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.arrl.org/files/file/VEs/IARP%20Application%20March%202015%20interactive.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;application form for an IARP&lt;/a&gt; is found on the ARRL website, and is filed by mail along with an application fee. The permit is mailed to you, and there is an additional fee for international or express delivery. All this means: don't wait until the last minute to apply!&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2019-08-06T01:17:20.280" LastActivityDate="2019-08-06T01:17:20.280" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15062" PostTypeId="2" ParentId="15056" CreationDate="2019-08-05T23:13:45.703" Score="1" Body="&lt;p&gt;Pulling some information from Electronics Stack Exchange,  &lt;a href=&quot;https://electronics.stackexchange.com/questions/38452/electronic-aspects-of-iphone-3-5mm-audio-output&quot;&gt;https://electronics.stackexchange.com/questions/38452/electronic-aspects-of-iphone-3-5mm-audio-output&lt;/a&gt; and &lt;a href=&quot;https://electronics.stackexchange.com/questions/30841/how-do-i-build-a-trrs-headphone-jack-with-a-jack-that-is-detectable-by-an-iphone&quot;&gt;https://electronics.stackexchange.com/questions/30841/how-do-i-build-a-trrs-headphone-jack-with-a-jack-that-is-detectable-by-an-iphone&lt;/a&gt; and Apple Stack Exchange, &lt;a href=&quot;https://apple.stackexchange.com/questions/326149/how-to-record-a-audio-with-iphone-via-input-cable-like-aux-from-laptop&quot;&gt;https://apple.stackexchange.com/questions/326149/how-to-record-a-audio-with-iphone-via-input-cable-like-aux-from-laptop&lt;/a&gt; here is my estimate of what such a circuit would look like.  There are some assumptions built in here, as will be explained.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/juOp0.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fjuOp0.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple voltage divider is 2 resistors.  The values are somewhat arbitrary, but the iPhone seems to need 1.6k Ohm input impedance to recognize the item as an input.  Additionally, one of the linked pages states full scale input is 4mA (I cannot verify).  The circuit below is expected to provide a max current to the iPhone of about 2mA (1), about 1/2 of full scale amplitude; 3.2 volts.  The iPhone needs to &quot;see&quot; 1.6k Ohm, the first resistor can be adjusted either up or down to get the amplitude right (either use a variable resistor or perhaps a small handful of larger resistors and keep adding more in parallel as needed) but that second resistor should stay close to 1.6k Ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, microphone input circuits often include a DC bias voltage to power the microphone.  To prevent that from causing any issues with the radio, best to place a small capacitor (say, 10 micro-Farads, though probably any capacitor you have laying around is &quot;good enough&quot;) in front of this voltage divider.  More about this below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The headphone jack can be wired in parallel to the voltage divider.  If your headphones are high impedance, it will have minimal effect on the circuit, though you will hear &quot;pops&quot; when you connect and disconnect.  If your headphones are lower impedance, a headphone amplifier would be appropriate (easy enough to buy or build).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Connecting to the iPhone seems tricky, but the steps to do it are outlined and/or linked to in the Electronics Stack Exchange links from earlier.  In particular, Wikipedia &lt;a href=&quot;https://en.wikipedia.org/wiki/Phone_connector_(audio)#TRRS_standards&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Phone_connector_(audio)#TRRS_standards&lt;/a&gt; seems to believe the iPhone TRRS connector has Sleeve=Microphone and Ring 2=Ground.  There is an odd note in a linked article ( &lt;a href=&quot;http://martinjohnsoncommunications.blogspot.com/2012/04/iphone-external-mic-connection-solved.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://martinjohnsoncommunications.blogspot.com/2012/04/iphone-external-mic-connection-solved.html&lt;/a&gt; ) stating that some TRRS connectors have a sleeve which will touch the phone case, causing problems --if your connector does that, add a small rubber washer to isolate it.  So connect the voltage divide output (that would be the space between the 2 resistors) to the TRRS Sleeve and Ground to Ring 2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said all of this, I am not sure this circuit is completely necessary.  Certainly C1 is a Good Idea and R2 seems Important, but R1 might be optional.  If 4mA really is full scale with an input impedance of 1.6k&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, that would mean the phone's max range is really 6.4V and R1=0.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One more pedagogical note.  Without knowing for certain what input the iPhone is looking for (+/-5 volts?  +/-4mA?) or its input impedance (1.6k&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;? 16k&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;?) or even the actual purpose of R2 (does that somehow signal that Sleeve is a microphone instead of a Line In, adding an additional amplifier to the signal chain, for example?) perhaps it makes some sense to do some quick error analysis.  What is the effect of changing the different resistors?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$V_{phone}={V R_2 R_3}/{(R_1 R_2+R_1 R_3+R_2 R_3)}$&lt;/span&gt; - signal voltage seen by the phone&#xA;&lt;span class=&quot;math-container&quot;&gt;$i_{phone}={V R_2 }/{(R_1 R_2+R_1 R_3+R_2 R_3)}$&lt;/span&gt; - signal current seen by the phone&lt;/p&gt;&#xA;&#xA;&lt;p&gt;...where V=5Volts, the signal voltage generated by the radio.  You can use these relationships to identify what happens if things change.  This might help you decide which high values for R1 to keep on hand in case things are not quite perfect the first time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Last item, I think.  The capacitor forms a high pass filter with the voltage divider and the load.  The cutoff frequency for a 10 micro-Farad capacitor and an 800&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; resistance --2x 1.6k&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; resistors in parallel-- is about 20 Hz.  A larger capacitor will decrease that frequency and a smaller one will increase that frequency.  Since you are using this for voice recordings, any cutoff below about 200Hz will work well; this corresponds to a 1 micro-F capacitor.  For signal processing reasons, there is an incentive to use the smallest capacitor you can get away with but such a discussion is beyond the scope of this answer :-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(1) Assuming the max voltage put out by the FT-8900 is about 5 volts and the internal impedance of the iPhone is about 1.6k Ohm (apparently Apple changes this with different models).&lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2019-08-06T23:04:07.060" LastActivityDate="2019-08-06T23:04:07.060" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15063" PostTypeId="2" ParentId="5769" CreationDate="2019-08-06T02:05:56.860" Score="0" Body="&lt;p&gt;You should be able to search for it via the FCC's licensing database.  Might also try Googling your callsign, many times that can take you right to the licensing page for your sign.&lt;/p&gt;&#xA;" OwnerUserId="15406" LastActivityDate="2019-08-06T02:05:56.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15064" PostTypeId="2" ParentId="15038" CreationDate="2019-08-06T09:36:37.143" Score="2" Body="&lt;p&gt;The gap is neglectable in terms of λ. Let's say you are making a 20m (14 MHz) dipole and you decided to use a large gap, let's say 10cm. This is only 0.0005λ. For 2m band (144Mhz) it's 0.005λ. If you choose an even larger gap it means there will be some wires that will connect the arms of the dipole to the feed line. These wires will just work as parts of the arms. Once again - there is no significant gap except the distance between the center of the coax and the shield of the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words just connect the arms to the coax the way it's comfortable and then trim the length of the arms to get minimum SWR in the center of the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Richard Fry is the author of the following paragraph and graphic.]  Below is a NEC4.2 study of a 40m, 1/2WL, center-fed, free space dipole with a 0.2m gap for an insulator at the feedpoint. NEC sources themselves are applied at a single point on a conductor, but this approach or a variation of it might lead to a reasonable, practical solution for most amateur radio operators and applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/J6OEc.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/J6OEc.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="10565" LastEditDate="2019-08-10T12:27:48.317" LastActivityDate="2019-08-10T12:27:48.317" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15065" PostTypeId="2" ParentId="15038" CreationDate="2019-08-06T10:40:17.397" Score="1" Body="&lt;p&gt;Looking at this sentence,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;But unfortunately, I don't have mathematical justification for that reason &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Here is a mathematical answer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The minimum gap is zero and the maximum gap is &lt;span class=&quot;math-container&quot;&gt;$\lambda/2$&lt;/span&gt;.  The mathematically ideal gap is 0, as explained in several books on antenna theory; there is an integral over the dipole length as charge is collected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any gap between 0 and &lt;span class=&quot;math-container&quot;&gt;$\lambda/2$&lt;/span&gt; will work, but it will work a little &quot;better&quot; if the gap is closer to --or equal to-- 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, with the way you are laying out your dipole, adding a zero gap will cause a short circuit and the dipole will not function.  Adding an infinitesimally small gap will allow sparks to jump across the gap, which is also bad.  So add a gap to prevent a short circuit and try to make it big enough to prevent sparks.  Mathematically, you want this gap to be as small as possible to maximize the aforementioned integral.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you accidentally make it too short, that is a problem, but an easy solution is to add some insulator to fill in the gap, or just make the gap bigger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It really is that simple.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2019-08-06T21:33:08.390" LastActivityDate="2019-08-06T21:33:08.390" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15066" PostTypeId="1" AcceptedAnswerId="15187" CreationDate="2019-08-06T11:11:21.200" Score="0" ViewCount="1202" Body="&lt;p&gt;Here is my measurement to a piece of RG6 cable. It is around 30cm cable. On the shield is written &lt;strong&gt;COAXIAL CABLE 5C-2V 75 ohm&lt;/strong&gt;. From my measurement I got data as below:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/5jLvy.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5jLvy.jpg&quot; alt=&quot;Electronic Measurement&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From that table, we can see that there is significant impedance of the cable. If we calculate the inner and the outer impedance using formula &lt;strong&gt;Z=R+j(XL-XC)&lt;/strong&gt;, where &lt;strong&gt;XL=j2pi&lt;em&gt;f&lt;/em&gt;L&lt;/strong&gt;, and &lt;strong&gt;XC=j/(2pi&lt;em&gt;f&lt;/em&gt;C)&lt;/strong&gt;, L in Henry, C in Farad, f in Hertz, and pi=3.14159265358979. Calculation with the data below and using 2,100 MHz frquency, I got as below:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;Z inner=5+j2638.9 ohm&lt;/strong&gt;, and&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Z outer=6+j1319.5 ohm&lt;/strong&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Then my question is:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What is the 75 ohm meaning (written at the the cable shield)?&lt;/li&gt;&#xA;&lt;li&gt;What is those two impedance meaning to the antenna?&lt;/li&gt;&#xA;&lt;li&gt;If we got data in real cable, what to do to match the impedance?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit:&lt;/strong&gt;&#xA;The cable was just used for C-Band parabolic antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PXT4v.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PXT4v.jpg&quot; alt=&quot;Measurement&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15393" LastEditorUserId="15393" LastEditDate="2019-08-06T11:52:29.463" LastActivityDate="2019-08-25T19:20:31.430" Title="Understanding RG6-75 ohm Cable Impedance" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;coaxial-cable&gt;&lt;antenna-system&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="15068" PostTypeId="2" ParentId="15007" CreationDate="2019-08-06T12:31:22.980" Score="3" Body="&lt;p&gt;Collins was the long-established &quot;gold standard&quot; for amateur radio equipment. The &lt;a href=&quot;http://collinsradio.org/archives/manuals/32S-3-_7th-ed-06-69_.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;32S-3&lt;/a&gt; quotes carrier and unwanted sideband suppression at -50dB; the later, solid-state &lt;a href=&quot;http://www.collinsradio.org/wp-content/uploads/2012/04/KWM-380-2nd-Edition-1-January-1981.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;KWM-380&lt;/a&gt; improved opposite-sideband suppression to -55dB. The &lt;a href=&quot;http://www.hamanuals.com/S1/CX7/Manuals/Thomas.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Signal/One CX-7&lt;/a&gt; made a big splash in the amateur market; carrier and unwanted-sideband suppression are listed at -60dB. Modern rigs like the &lt;a href=&quot;https://ftp.elecraft.com/KX3/Manuals%20Downloads/E740163%20KX3%20Owner&amp;#39;s%20man%20Rev%20C5.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Elecraft KX-3&lt;/a&gt; use less expensive modern digital and mixed-signal means to deliver 60dB or better suppression without using crystal or mechanical filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the era of the 32S-3, amateurs in the US were limited to 1000W DC &lt;em&gt;input&lt;/em&gt; power. At the roughly 50% practical efficiency of class AB amplification, the legal output limit would be around 500 watts. 50dB of suppression would have limited the opposite-sideband power to approximately 10 &lt;em&gt;milliwatts&lt;/em&gt;! This would have been extremely unlikely to disturb adjacent stations unless they were very close to the transmitter. In the current era, 60dB of suppression means that a 1500W legal-limit signal would be reduced to 1.5 &lt;em&gt;milliwatts&lt;/em&gt;!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;INRAD still produces crystal filters for such &quot;vintage&quot; equipment. In addition to the IF frequency, these units are characterized by &quot;shape factor,&quot; the ratio of the bandwidth at -60dBc to the bandwidth at -6dBc. A typical 8-pole, 2.1kHz filter exhibits a 1.5:1 shape factor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CHWRs.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CHWRs.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clearly, the attenuation continues past -60dBc, but this demonstrates the useful limit as perceived by companies' marketing departments!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For comparison, here is the shape of a 5-pole crystal filter shipped by one of today's leading amateur equipment manufacturers:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kyEkC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kyEkC.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note the much gentler &quot;skirts&quot; on the filter passband, resulting in a shape factor of about 3:1. &quot;Baseband&quot; filters, whether analog or DSP, may be used to combat interference and/or restricted emitted bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Despite the relatively high cost compared to &quot;phasing&quot; gear, nearly all SSB transmitting equipment used the filter method, to take advantage of its superior opposite-sideband suppression performance. (Note: carrier suppression results from the use of balanced modulators.) It  may be speculated that the &quot;transceiver&quot; owes its existence to the desire to control product cost and improve receiver performance by sharing the expense of the IF crystal or mechanical filter between transmitting and receiving duties. The low cost and high performance possible with modern digital and mixed-signal technologies may encourage a return to separate receiver and transmitter units to permit independent optimization of the respective signal chains.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-08-08T14:06:29.250" LastActivityDate="2019-08-08T14:06:29.250" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15069" PostTypeId="2" ParentId="15066" CreationDate="2019-08-06T13:01:50.610" Score="1" Body="&lt;p&gt;See a description of 50 vs 75 Ω here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.eham.net/ehamforum/smf/index.php/topic,98296.msg776787.html#msg776787&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.eham.net/ehamforum/smf/index.php/topic,98296.msg776787.html#msg776787&lt;/a&gt; :&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Here's a good high level summary of why (From Belden's site, with a little marketing):&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;a href=&quot;http://www.belden.com/blog/broadcastav/50-ohms-the-forgotten-impedance.cfm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.belden.com/blog/broadcastav/50-ohms-the-forgotten-impedance.cfm&lt;/a&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;If you play with coax, short for coaxial cable, you probably know this it is available in a number of different impedances. The most common is 75 ohm, like video cable or antenna cable, but in fact our products range from 32 ohms up to 124 ohms.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Why all these different numbers? It's not an accident of course, and there is a reason for each one. Today, we're going to take a quick look at 50 ohm coax cable.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Belden makes hundreds of 50 ohm cables, including a whole line of ultra-low loss versions (Belden 7805 to Belden 7977). The two largest versions are HUGE. The 7977 has a diameter of .600&quot; six-tenths of an inch! This is the largest coax cable that we make.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;But first of all, why 50, or any other number? The answer can be shown in the graph below. This was produced by two researchers, Lloyd Espenscheid and Herman Affel, working for Bell Labs in 1929.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;They were going to send RF signals (4 MHz) for hundred of miles carrying a thousand telephone calls. They needed a cable that would carry high voltage and high power. In the graph below, you can see the ideal rating for each. For high voltage, the perfect impedance is 60 ohms. For high power, the perfect impedance is 30 ohms.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;This means, clearly, that there is NO perfect impedance to do both. What they ended up with was a compromise number, and that number was 50 ohms.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;You will note that 50 ohms is closer to 60 than it is to 30, and that is because voltage is the factor that will kill your cable. Just ask any transmitter engineer. They talk about VSWR, voltage standing wave ratio, all the time. If their coax blows up, it is voltage that is the culprit.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;So why not 60 ohms? Just look at the power handling at 60 ohms - below 50%. It is horrible! At the compromise value of 50 ohms, the power has improved a little. So 50 ohm cables are intended to be used to carry power and voltage, like the output of a transmitter. If you have a small signal, like video, or receive antenna signals, the graph above shows that the lowest loss or attenuation is 75 ohms.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Still, I get a lot of feedback from people who use 50 ohms for small signals; you can see above that they are taking a 2-3 dB hit in attenuation. Excuses I hear are “It's too late to change now!” or “That's the impedance of the box itself.” This is especially true of most test gear, which is universally 50 ohms. You have to buy a matching network to use it at 75 ohms or any other impedance. But there are lots of applications where 50 ohms is the best choice.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Belden 7977 mentioned above, can carry more than 5 kW at 30 MHz and more than 600 watts at 6 GHz. So even a cable this small could be used for TV or FM low power, boosters, translators, two-way radios, life-safety such as police/fire, RPU, many ham frequencies, microwave transmitters up to 6 GHz, and probably hundreds of other applications where signal are being delivered with high voltage and high power.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Most often, these signals end up in antennas. For instance, the sections in transmitters where small output power sections, like an exciter, are fed to a larger power section also require 50 ohm cable. That might be where the physically smaller 50 ohm cable might be used.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;[...]&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;hr&gt;&#xA;  Now to really dig into the math, go here:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;a href=&quot;http://www.microwaves101.com/encyclopedias/458-why-fifty-ohms&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.microwaves101.com/encyclopedias/458-why-fifty-ohms&lt;/a&gt;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Additional information about using 75 ohm coax and how to compensate is here: &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;a href=&quot;http://www.w9xt.com/page_radio_gadgets_hardline.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w9xt.com/page_radio_gadgets_hardline.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="14508" LastEditorUserId="8717" LastEditDate="2019-08-25T19:20:31.430" LastActivityDate="2019-08-25T19:20:31.430" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15070" PostTypeId="1" AcceptedAnswerId="15073" CreationDate="2019-08-06T13:57:05.097" Score="1" ViewCount="301" Body="&lt;p&gt;I'm new to APRS and trying to setup a RaspberryPi APRS GPS Tracker. I've installed Direwolf and configured it, my transceiver transmits the signal, and I've decoded it with GQRX via an RTL-SDR and I get the following (i've substituted the actual GPS coordinates):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;fm KC1KAZ-0 to APDW15-0 UI PID=F0 !gpsCoordinatesHere;360/001&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And it isn't picked up by any of the local digipeaters. So I fired up my iPhone and used PocketPacket to check if I could get a signal out, it sent the following: &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;fm KC1KAZ-0 to APZP22-0 via WIDE1-1,WIDE2-1 UI PID=F0 =gpsCoordinatesHere;testMessage&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And that does get picked up by the local digipeater. Of course now that I write this all out, I'm thinking it's because I don't have the via=WIDE1-1,WIDE2-1 path defined in my configuration file. Though, I'm trying to take advantage of smartbeaconing and when I RTFM it says to use smart beaconing I should just have the following in my config:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;SMARTBEACONING 60 2:00 5 15:00 0:15 30 255&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Is the fix as simple as adding via=WIDE1-1,WIDE2-1 to the config line?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Also, curiously, and probably unrelated, if I use PulseModemA on my iPhone to try to get a signal out it isn't picked up and I get the following from GQRX:&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;&lt;code&gt;fm KC1KAZ-0 to APRS-0 via WIDE1-1,WIDE2-1 UI PID=F0 !/8grS&amp;lt;HOS;&lt;/code&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's my config file:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;ADEVICE  plughw:1,0&#xA;ACHANNELS 1&#xA;&#xA;MYCALL KC1KAZ&#xA;&#xA;MODEM 1200&#xA;&#xA;AGWPORT 8000&#xA;KISSPORT 8001&#xA;&#xA;GPSD&#xA;&#xA;SMARTBEACONING 60 2:00 5 15:00 0:15 30 255&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Thank you in advance for reading this and taking your time to help out.&lt;/p&gt;&#xA;" OwnerUserId="15409" LastEditorUserId="15409" LastEditDate="2019-08-09T17:45:29.240" LastActivityDate="2019-08-09T17:45:47.307" Title="Direwolf sends APRS transmission but it isn't being picked up by local digipeaters" Tags="&lt;aprs&gt;&lt;direwolf&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15071" PostTypeId="2" ParentId="15007" CreationDate="2019-08-06T14:30:50.153" Score="-1" Body="&lt;p&gt;The definition of a spurious emission seems clear enough in &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.3&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR § 97.3&lt;/a&gt;: &quot;An emission, or frequencies outside the necessary bandwidth of a transmission, the level of which may be reduced without affecting the information being transmitted.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As @MikeWaters points out, AM, DSBSC, and 8-kHz ESSB are all legal modes.  But let's consider an SSB transmitter with a badly-suppressed carrier that's only down 30 dB.  Clearly the carrier is a suppressed emission, because the carrier could be reduced further without affecting the intelligibility of the signal in an SSB receiver.  The manufacturer could try the argument that the transmitter isn't transmitting SSB, but rather a different mode: single-sideband with an intentional carrier.  I doubt that the FCC or the courts would look favorably upon such an argument, since such a mode would offer no technical advantages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.307&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR § 97.307&lt;/a&gt;: &quot;For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm no lawyer, but in my opinion the law should be interpreted that carriers and opposite sidebands in SSB transmitters should be suppressed by at least 43 dB.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2019-08-06T17:45:18.770" LastActivityDate="2019-08-06T17:45:18.770" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15072" PostTypeId="2" ParentId="606" CreationDate="2019-08-06T21:47:05.813" Score="0" Body="&lt;p&gt;At low frequencies local electric and magnetic fields are not coupled and they decay very rapidly with distance. Any metal structure would however distribute the interference as currents on electric cables or water pipes. I suggest you make yourself a battery powered H-field sensor (a transistor ratio with a ferrite antenna) and an E-field sensor (a car radio with a battery.) Walk around your&#xA;property and try to find good points. Once you have a place where magnetic or electric fields are low, place the appropriate sensor there and use common mode&#xA;chokes or other means to prevent interference to be conducted to the sensor. I suggest you have a look at these videos:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=ItLkn8r4s3E&amp;amp;t=11s&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=ItLkn8r4s3E&amp;amp;t=11s&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=zsZTX7MQSGQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=zsZTX7MQSGQ&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=kgMbaJDFu9M&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=kgMbaJDFu9M&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=C65u7Pmz7a0&amp;amp;t=3s&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=C65u7Pmz7a0&amp;amp;t=3s&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would take quite some time - hopefully it would be well spent time...&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-08-06T21:47:05.813" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15073" PostTypeId="2" ParentId="15070" CreationDate="2019-08-07T14:00:40.197" Score="3" Body="&lt;p&gt;Yes, the lack of WIDE1-1 and WIDE2-1 is why no other stations are picking up your beacon. For example a station (mine is n9ds) listens for a packet with &quot;WIDE1-1&quot; in the routing.  Since it's still &quot;WIDE1-1&quot;, the station knows it hasn't been retransmitted.  It then deducts 1 from the number after the dash (* means zero) and resends it. (I may have a detail or two slightly off, but that's the general idea.) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;WIDE1 are &quot;fill-in&quot; digis, smaller stations like mine where there may be gaps in coverage for mobile stations.  WIDE1s generally relay the packets to a WIDE2 somewhere.  WIDE2 are the bigger stations and frequently the IGates.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2019-08-07T14:00:40.197" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15074" PostTypeId="1" AcceptedAnswerId="15093" CreationDate="2019-08-07T20:19:14.360" Score="4" ViewCount="453" Body="&lt;p&gt;What are CW skimmers, especially with regard to spotting networks?  Are there more than one (of each)?  How do the skimmers interface with spotting networks?  (Or are they combined into a single application?)  Is there an open protocol?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a controversy regarding the use of CW skimmers and/or spotting networks for certain purposes? (e.g. contests, DX pile-ups, SKCC, etc.)  If so, what is the controversy?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-07T20:25:05.663" LastActivityDate="2021-03-25T22:56:37.803" Title="CW skimmers and spotting networks?" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15075" PostTypeId="1" CreationDate="2019-08-08T00:10:58.890" Score="1" ViewCount="88" Body="&lt;p&gt;I recently bought a cheap stereo amplifier with built in FM receiver from Amazon at the first link below. Testing it out today I found the FM reception to be sub-par. All of my local stations that I can pick up in my car sound fuzzy. The antenna is approximately 14 inches long and is simply a floppy cord. Pictures are at the second link below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to build a better antenna to get better reception. If I can get reception equal to the reception you find on an OEM economy box car radio, I'd be plenty happy. What is a simple path forward?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B07QKW2WMF&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amazon.com/gp/product/B07QKW2WMF/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&amp;amp;psc=1&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CrqIt.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CrqIt.jpg&quot; alt=&quot;Mini Wireless Bluetooth Power Amplifier, ARCHEER 2 x 45W&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15414" LastEditorUserId="4665" LastEditDate="2019-08-09T05:25:16.947" LastActivityDate="2019-08-09T05:25:16.947" Title="How do I Construct a Simple FM Antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;reception&gt;" AnswerCount="0" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15077" PostTypeId="1" CreationDate="2019-08-08T04:47:59.333" Score="0" ViewCount="81" Body="&lt;p&gt;Consider a situation as below. I am stay in a farm field, which my house is 9.4km distance from the nearest and the only one BTS (Base Transceiver System), a cellular antenna for transmit and receive signal of 2G/3G network. Measurement I did using Google. In between my house and the BTS, there is hill which block direct signal to the house. If I climb to a three near my house around 8 meter high, I will get signal around 93dBm (up and down). Then I think to make an outdoor parabolic antenna which will be connected by a coax cable to an indoor omni antenna which will serve 360 degree inside the house 5 meter radius. The diagram is as in the picture below. The outdoor antenna itself will compensate the cable loss plus will give more gain. I expect I will get around 90 dBm signal strength after installing the antenna. For now, forget about the antenna detail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get the signal in the house, I probably need an electronic device located in between outdoor (parabolic) and indoor (omni) antenna. That device is intended to receive that signal from outdoor and send to indoor without any modification or amplification, just to make the indoor antenna will radiate signal. And vice versa also will do, to send the received signal from indoor and delivered to the outdoor antenna and radiate to send it to the BTS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then,&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How can I do it? I need as simple as possible electronic device.&lt;/li&gt;&#xA;&lt;li&gt;Or, can I do it without any electronic (active) device?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit:&lt;/strong&gt; What is done in &lt;a href=&quot;https://www.youtube.com/watch?v=bHWrRG_kdn8&quot; rel=&quot;nofollow noreferrer&quot;&gt;this video&lt;/a&gt; is almost the same to my intention. This video makes an external Yagi antenna and attached to the back side of the phone. But I also don't how how it work. There supposed to be there is &quot;transformation&quot; or induction (?) so there is electric transfer from the coax-cable to the antenna. &lt;em&gt;Then, is any one here can guide me to do that way?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bIFQJ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bIFQJ.jpg&quot; alt=&quot;schematic diagram&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15393" LastEditorUserId="15393" LastEditDate="2019-08-08T11:39:45.373" LastActivityDate="2019-08-08T11:39:45.373" Title="Can I make a simple Tx/Rx antenna (Radio System) which will receive signal from BTS and broadcast/transmit it, and vice versa?" Tags="&lt;antenna&gt;&lt;transceiver&gt;&lt;transmitter&gt;&lt;transmission&gt;" AnswerCount="0" CommentCount="20" ClosedDate="2019-08-08T12:55:58.640" ContentLicense="CC BY-SA 4.0" />
  <row Id="15078" PostTypeId="1" AcceptedAnswerId="15082" CreationDate="2019-08-08T07:35:41.060" Score="0" ViewCount="381" Body="&lt;p&gt;&lt;strong&gt;Background:&lt;/strong&gt;&#xA;Last night (and the night before) I was playing with my RTL-SDR and GNU-Radio again. Working with &lt;a href=&quot;https://ham.stackexchange.com/questions/12833/fm-receiver-on-gnu-radio-with-rtl-sdr-fails-to-produce-any-output-sound/12837#12837&quot;&gt;my FM Receiver&lt;/a&gt;, (which was working previously by the way), I detected that last night I was not getting any output? No matter where I tuned, I only got noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This had me flummoxed! This GNU-Radio flow-graph was working not more than a couple of months ago. What changed since then? The version of GNU Radio is the same (&lt;em&gt;GNU Radio Companion 3.7.11&lt;/em&gt;). The Dongle is the same &lt;a href=&quot;https://www.amazon.de/NooElec-NESDR-Mini-USB-Empf%C3%A4nger-Set-Female-SMA-Adapter/dp/B00VZ1AWQA/ref=pd_lpo_sbs_147_t_0/261-3495567-7120661?_encoding=UTF8&amp;amp;psc=1&amp;amp;refRID=8CYVMTD0SC4KZ2F3YRR1&quot; rel=&quot;nofollow noreferrer&quot;&gt;NooElec RTL-SDR Dongle&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;CubicSDR:&lt;/strong&gt;&#xA;I then, just as a sanity check, decided to compare with &lt;a href=&quot;https://cubicsdr.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;CubicSDR&lt;/a&gt;. With Cubic-SDR and the same RTL-SDR Dongle connected to the same front panel USB, I immediately got an output when tuned to the right Radio-station frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Connect to Motherboard's USB:&lt;/strong&gt;&#xA;Then just to test, I turned off CubicSDR. Unplugged the RTL-SDR Dongle from the front panel of the PC and put it in one of the four USB sockets that are directly attached to the motherboard and can be reached from the backside of the PC. I restarted GNU Radio and executed the same flowgraph for the FM Radio. And this time I got an output. I could listen to some radio stations.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;So, it seems the front panel USB sockets are maybe not providing enough power for the Dongle to work? I googled &lt;a href=&quot;https://www.rtl-sdr.com/forum/viewtopic.php?t=1587&quot; rel=&quot;nofollow noreferrer&quot;&gt;how much power the Dongle draws?&lt;/a&gt; and apparently it varies from model to model.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Does running a GNU Radio flow graph stress the Dongle more, so that it has to draw more power from the USB? Because the CubicSDR was working without a problem when the RTL-SDR Dongle was connected to the same front panel USB where GNU Radio flowgraph was not giving any output. (The flowgraph is the same as in my first question, also shown below at the end of this post).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I am looking to buy, then, an USB extension set, to power the RTL-SDR externally. (As I am worried, it might be drawing too much power and could possibly damage the Motherboard, as &lt;a href=&quot;https://www.rtl-sdr.com/forum/viewtopic.php?t=2440&quot; rel=&quot;nofollow noreferrer&quot;&gt;happened to this guy's phone&lt;/a&gt;? And also to have the Dongle running stably.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;On a further note, if it is indeed a power issue, then it is a tricky little pitfall that a n00b like me can fall in. Because you get no error, no warning. The flowgraph runs. Everything seems to be working, except you get no output. You can never be really sure, if your flow graph has a bug or your Dongle is not working. How (IF it is even at all possible) can one be sure that the Dongle at least, is working correctly when testing different flowgraphs, applications, etc?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ePFut.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ePFut.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13000" LastEditorUserId="13000" LastEditDate="2019-08-08T07:41:53.423" LastActivityDate="2019-08-10T00:35:44.660" Title="How much power does an RTL-SDR draw?" Tags="&lt;rtl-sdr&gt;&lt;gnuradio&gt;&lt;power-supply&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15081" PostTypeId="2" ParentId="15078" CreationDate="2019-08-08T14:05:36.940" Score="4" Body="&lt;p&gt;I have used RTL-SDR USB peripherals from several vendors.  They run at different temperatures (implying different power draws), which suggests that your question does not have a single answer.  The power level also seems to vary with what the device is doing (idle, streaming, sample rate, etc.)  So you probably need to measure the USB current on your particular device, perhaps using a USB power meter (commonly available from Amazon, eBay, etc.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-10T00:35:44.660" LastActivityDate="2019-08-10T00:35:44.660" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15082" PostTypeId="2" ParentId="15078" CreationDate="2019-08-08T14:56:36.380" Score="4" Body="&lt;p&gt;To extend what hotpaw2 said:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;So, it seems the front panel USB sockets are maybe not providing enough power for the Dongle to work? I googled how much power the Dongle draws? and apparently it varies from model to model.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Exactly, different models use different tuners, some additional amplifiers, and some use linear power supplies only, others mix linear and switch-mode power supplies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The actual power draw depends on frequency, sampling rate, gain, and a few other factors. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does running a GNU Radio flow graph stress the Dongle more, so that it has to draw more power from the USB? Because the CubicSDR was working without a problem when the RTL-SDR Dongle was connected to the same front panel USB where GNU Radio flowgraph was not giving any output. (The flowgraph is the same as in my first question, also shown below at the end of this post).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The software using the rtlsdr driver to get the same amount of data at the same gain from the same frequency shouldn't matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it might very well be that e.g. you're using GNU Radio to sample at 2MS/s and Cubic for 250 kS/s, and that makes a difference.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I am looking to buy, then, an USB extension set, to power the RTL-SDR externally. (As I am worried, it might be drawing too much power and could possibly damage the Motherboard, as happened to this guy's phone? And also to have the Dongle running stably.)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I've never seen that happen. USB ports are generally protected against overcurrent, and you'll really need a &lt;em&gt;lot&lt;/em&gt; of bad luck or malicious intent to damage one electrically.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;On a further note, if it is indeed a power issue, then it is a tricky little pitfall that a n00b like me can fall in. Because you get no error, no warning. The flowgraph runs. Everything seems to be working, except you get no output. You can never be really sure, if your flow graph has a bug or your Dongle is not working. How (IF it is even at all possible) can one be sure that the Dongle at least, is working correctly when testing different flowgraphs, applications, etc?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The console output of gr-osmosdr usually contains info on that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;general remarks:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;gr-wxgui is deprecated. We've removed it, after repeating this sentence for four years, from the current version of GNU Radio. Use Qt GUI instead. It's more efficient, more stable, and we're able to fix it when it breaks.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-08-08T14:56:36.380" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15083" PostTypeId="1" CreationDate="2019-08-09T06:10:35.483" Score="1" ViewCount="96" Body="&lt;p&gt;I &lt;a href=&quot;https://ham.stackexchange.com/questions/15077/can-i-make-a-simple-tx-rx-antenna-radio-system-which-will-receive-signal-from&quot;&gt;posted&lt;/a&gt; yesterday asking how can I have signal inside my house which my house is obstructed by a hill from direct signal from the cellular's operator' Base Transceiver System (BTS). The schema of the system will be something like the first picture, but could be with additional electronic device in between the two antennas to make the system become active. But one commented and shared a link &lt;a href=&quot;https://ham.stackexchange.com/questions/2146/wifi-passive-repeater-antenna-to-antenna-connection&quot;&gt;here&lt;/a&gt; which asked the similar question which from my understanding, the schema should be like first picture.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also searched in Youtube if any can help and solve my problem. Then I got these two videos (&lt;a href=&quot;https://www.youtube.com/watch?v=2L914NBasXY&quot; rel=&quot;nofollow noreferrer&quot;&gt;video 1: 850mhz cell phone signal booster Yagi antenna&lt;/a&gt; and &lt;a href=&quot;https://www.youtube.com/watch?v=bHWrRG_kdn8&quot; rel=&quot;nofollow noreferrer&quot;&gt;video 2: Homemade portable 1800mhz 4g LTE signal booster&lt;/a&gt;). The schema are something like the second picture. From the two videos, the folded cable at another end are acting like antenna to the attached mobile phone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the &lt;a href=&quot;https://ham.stackexchange.com/questions/2146/wifi-passive-repeater-antenna-to-antenna-connection&quot;&gt;schema 1&lt;/a&gt;, one commented quite comprehensive. If I didn't understand it wrongly, he recognized that the system is working but with some limitations and he recommended that rather than to make himself, better to buy with only $100. Then my question for both the schematic:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Are they really work?&lt;/li&gt;&#xA;&lt;li&gt;If they are really work, how they work without any active device?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The second schema (the two videos) I tried and both are didn't work. But my failure could be due to wrong design/installation. That's why I ask here. And I appreciate any helping comment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8BSui.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8BSui.jpg&quot; alt=&quot;Antenna System1, Rx/Tx-Tx/Rx omni&quot;&gt;&lt;/a&gt;&#xA;&lt;em&gt;First picture&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/o3jSW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/o3jSW.jpg&quot; alt=&quot;Antenna System2, Rx/Tx-Tx/Rx induction&quot;&gt;&lt;/a&gt;&#xA;&lt;em&gt;Second picture&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="15393" LastEditorUserId="15393" LastEditDate="2019-08-09T06:17:47.200" LastActivityDate="2019-08-10T12:11:28.643" Title="Is this antenna &quot;system&quot; really work?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;antenna-system&gt;&lt;feed-line&gt;" AnswerCount="1" CommentCount="6" ClosedDate="2019-08-13T21:17:50.167" ContentLicense="CC BY-SA 4.0" />
  <row Id="15084" PostTypeId="1" CreationDate="2019-08-09T06:43:32.357" Score="2" ViewCount="179" Body="&lt;p&gt;I am new to GNU Radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I need some reference to how to use FEC block in GNURadio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I try to make encoder and decoder without modulation, its work as well, but when I using modulation and add some noise, there is a problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Received bit are not same with transmitted bit and make a decoder not working as well. Say I have k=40 bit and encoded c=64 bit ready to transmit, but I receive extra bit c=96 bit, so decoder can't recognize and decode all c received data as &lt;strong&gt;zeros&lt;/strong&gt;. Find pictures of my simulation system below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jVHqu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;TX&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/v5J93.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;RX+Noise&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/RL1Ae.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;Python_read_data&lt;/a&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/jVHqu.png&quot;&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/v5J93.png&quot;&gt;&#xA;&lt;img src=&quot;https://i.stack.imgur.com/RL1Ae.png&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="15334" LastEditorUserId="4076" LastEditDate="2019-08-09T09:23:01.150" LastActivityDate="2019-08-09T09:23:01.150" Title="How FEC works on GNU Radio" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="0" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15085" PostTypeId="1" AcceptedAnswerId="15087" CreationDate="2019-08-09T13:24:11.800" Score="0" ViewCount="245" Body="&lt;p&gt;Kindly, can anyone show me how to output CW tone or a Broadband Noise in GnuRadio in a sort of simple flowgraph if possible?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Update:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what I did is I tried not to overthink the whole issue here and followed @Kevin's advice and came up with two simple CW tone flowgraph and another simple Broadband Noise flowgraph (as seen below). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;CW_Tone Flowgraph:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/O4uYU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O4uYU.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Broadband_Noise Flowgraph:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ievhs.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ievhs.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question now, if you think that these are legit CW tone and Broadband Noise flowgraphs, what should I do to make them transmit the generated signals? Just connect the UHD-USRP Sink block to the output?&lt;/p&gt;&#xA;" OwnerUserId="15206" LastEditorUserId="15206" LastEditDate="2019-08-09T15:34:22.560" LastActivityDate="2019-09-28T00:30:08.487" Title="How to output a CW tone or a Broadband Noise in GnuRadio?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15086" PostTypeId="1" CreationDate="2019-08-09T14:13:10.337" Score="0" ViewCount="51" Body="&lt;p&gt;I am trying to figure out how to create a gnuradio program that can output some arbitrary waveform read from a file containing I/Q values. &#xA;I would highly appreciate any guidance in this topic. Simple example would be a great help for a beginner like me.&lt;/p&gt;&#xA;" OwnerUserId="15206" LastActivityDate="2019-08-09T14:13:10.337" Title="A gnuradio program that can output some arbitrary waveform read from a file containing I/Q values" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15087" PostTypeId="2" ParentId="15085" CreationDate="2019-08-09T15:51:47.037" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;what should I do to make them transmit the generated signals? Just connect the UHD-USRP Sink block to the output?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You need to do that, but there are a couple more points:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Make sure that you &lt;strong&gt;remove the throttle block.&lt;/strong&gt; Using a throttle as well as a hardware device sink (whether USRP or audio) will potentially cause stuttering. The rule is that you should ideally have only one block that &quot;has a clock&quot; in the flow graph: in your case the clock will be the USRP because it decides how fast it wants to consume the samples based on its DAC clocking.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;You must change the sample rate&lt;/strong&gt; from 32 kHz to a sample rate that is supported by the USRP — probably a higher one. Read the documentation for your specific USRP model to find out what is supported.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-08-09T15:51:47.037" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15088" PostTypeId="2" ParentId="15070" CreationDate="2019-08-09T17:45:47.307" Score="0" Body="&lt;p&gt;So it seems like Duston's answer below was correct, adding the via=WIDE1-1,WIDE2-1 to the config file under the beaconing properties seemed to fix it. Full config file below:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;#############################################################&#xA;#               Configuration file for Dire Wolf            #&#xA;#                   Linux version                           #&#xA;#############################################################&#xA;#&#xA;#############################################################&#xA;#               FIRST AUDIO DEVICE PROPERTIES               #&#xA;#               (Channel 0 + 1 if in stereo)                #&#xA;#############################################################&#xA;ADEVICE - plughw:1,0&#xA;ACHANNELS 1&#xA;#############################################################&#xA;#               CHANNEL 0 PROPERTIES                        #&#xA;#############################################################&#xA;CHANNEL 0&#xA;MYCALL KC1KAZ&#xA;MODEM 1200&#xA;#############################################################&#xA;#               VIRTUAL TNC SERVER PROPERTIES               #&#xA;#############################################################&#xA;AGWPORT 8000&#xA;KISSPORT 8001&#xA;#############################################################&#xA;#               BEACONING PROPERTIES                        #&#xA;#############################################################&#xA;GPSD&#xA;TBEACON EVERY=60 SYMBOL=car via=WIDE1-1,WIDE2-1&#xA;SMARTBEACONING 60 2:00 5 15:00 0:15 30 255 via=WIDE1-1,WIDE2-1&#xA;#############################################################&#xA;#               INTERNET GATEWAY                            #&#xA;#############################################################&#xA;IGTXLIMIT 6 10&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I left both TBEACON and SMARTBEACONING uncommented, I think I'm only getting results from the TBEACON though. My U-Blox7 USB GPS module seems to have a lot of issues getting a fix on my position. Outside and in a static position it seems to work, as soon as I start moving though, it just can't get a fix. I'm sure it's because it's a cheapo USB GPS, I'm just a little disappointed because multiple online resources heaped a lot of praise on it.&lt;/p&gt;&#xA;" OwnerUserId="15409" LastActivityDate="2019-08-09T17:45:47.307" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15089" PostTypeId="1" AcceptedAnswerId="15091" CreationDate="2019-08-09T20:16:39.457" Score="1" ViewCount="317" Body="&lt;p&gt;I've seen a lot of videos and tutorials on using the &lt;a href=&quot;http://jcoppens.com/ant/qfh/index.en.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Quadrifilar Helix Antenna &lt;/a&gt; for receiving signals, but I haven't seen any material for transmitters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm just starting right now, but can a QFH antenna be used to transmit? Will it make sense for me to make one right now for receiving and then transmit from the same once I have my license?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastActivityDate="2019-08-10T07:46:07.183" Title="Can I use a QFH antenna for transmission?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15090" PostTypeId="2" ParentId="15018" CreationDate="2019-08-09T21:19:37.523" Score="0" Body="&lt;p&gt;I used a 2 to 14 wrap on a T240-31. Close wrap first 7 turns and run cross turn close to the first 7 then close wrap the last turns. You can adjust the spacing and it will lower or raise your SWR. Works for me, only had to adjust it once. Then I hot glued the turns so they wouldn't move. Also check out &lt;a href=&quot;https://youtu.be/N_o0jneBEh0&quot; rel=&quot;nofollow noreferrer&quot;&gt;Steve Ellington video&lt;/a&gt;s on his research. This was his idea.&#xA;Anything is worth a try.&lt;/p&gt;&#xA;" OwnerUserId="15424" LastEditorUserId="8717" LastEditDate="2019-09-30T19:07:21.113" LastActivityDate="2019-09-30T19:07:21.113" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15091" PostTypeId="2" ParentId="15089" CreationDate="2019-08-09T21:52:57.513" Score="4" Body="&lt;p&gt;A key characteristic of antennas is that they are &lt;a href=&quot;http://www.antenna-theory.com/definitions/reciprocity.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;reciprocal&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means it does not matter if you consider them in receive or transmit mode because both have the same characteristics. Changing that view often helps when wrapping your head around antenna topics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That also means you can use &lt;strong&gt;any&lt;/strong&gt; (passive) antenna for both, receiving and transmitting.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Some boundary conditions to keep in mind:&#xA;&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;At circular polarized antennas when they are used in the receive as well as the transmit path that the polarization is aligned (otherwise there are considerable losses), see e.g. &lt;a href=&quot;https://ham.stackexchange.com/a/2210/15355&quot;&gt;answer from jcoppens&lt;/a&gt; &lt;br&gt;&#xA;When one of them is linear polarized you get the advantage of not bothering with orientation.&lt;/li&gt;&#xA;&lt;li&gt;&quot;Some receive antennas can't be used for transmit because they can't handle the power or their SWR is poor (which is not as important for receiving).&quot; - contributed by user10489 in the comments.&lt;/li&gt;&#xA;&lt;li&gt;High gain antennas may yield to exceed the allowed &lt;a href=&quot;https://en.wikipedia.org/wiki/Effective_radiated_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;EIRP&lt;/a&gt; in transmit mode (when the amplification is not aligned accordingly), whereas at receiving they can be used legally.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="15355" LastEditorUserId="15355" LastEditDate="2019-08-10T07:46:07.183" LastActivityDate="2019-08-10T07:46:07.183" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15093" PostTypeId="2" ParentId="15074" CreationDate="2019-08-10T04:00:01.020" Score="4" Body="&lt;p&gt;Computerized Morse decoders have been around for quite a while, but until recently they had many limitations.  The original style of decoder, what one might call the &quot;first generation&quot;, listens to a very narrow frequency range of a few hertz at most, and tries to interpret whether a single signal's carrier is present or not.  Such decoders work fairly well for well-formed code when conditions on the bands are good and there is no man-made interference (QRM).  Noise on the bands (QRN), fading (QSB), interference, or badly-formed code from a straight key or a &quot;bug&quot; tends to quickly destroy the intelligibility of the decoded text from such a first-generation decoder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please note that deciding if a signal is present or not is a difficult problem for a simple decoder circuit or algorithm.  Radioteletype, RTTY, is much, much easier for such a circuit or algorithm to decode: instead of deciding whether a weak signal in a noisy environment is present or not, the algorithm has only to decide if the signal at one particular frequency is louder than the signal at another frequency, because an RTTY signal constantly alternates between two different tones at a 100% duty cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hams used such first-generation Morse decoders in contests, but their use wasn't very controversial, because such decoders work on only a single signal, and are easily out-performed by the ear of a skilled operator, especially in typical HF contest conditions where QRN, QRM, and QSB are rife.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then Alex Shovkoplyas VE3NEA changed everything, when he released his software &lt;a href=&quot;http://www.dxatlas.com/CwSkimmer/&quot; rel=&quot;nofollow noreferrer&quot;&gt;CW Skimmer&lt;/a&gt;.  CW Skimmer uses DSP (digital signal processing) techniques and more advanced algorithms to decode every Morse signal in a receiver's entire passband.  And because the software can be passed the receiver's entire passband in I and Q format, simple and inexpensive SDR receivers can be used that have enough bandwidth to cover the entire Morse code part of an HF band.  The decoding isn't perfect, but it's very good, an enormous improvement over first-generation decoders.  The software also estimates the signal-to-noise ratio, which gives a fairly good estimate of how accurate the decoding might be, which is important when an operator is trying to decide if CW Skimmer really did hear the incredibly-rare DX prefix in a call sign or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I should mention that CW Skimmer has a built-in telnet spotting server, so it interfaces with contesting software just like a spotting network.  Really, it &lt;em&gt;is&lt;/em&gt; a built-in spotting network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer another question that was asked, no, there is no public CW Skimmer protocol, other than the well-known telnet protocol used by internet spotting networks.  CW Skimmer is closed-source proprietary software.  It's shareware, which allows users to try the software for free for 30 days before deciding whether or not to buy it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This revolutionary improvement in machine decoding quickly became controversial in the contesting community, which was just settling down after a long public discussion about how contests should handle hams using spotting networks.  (Should there be separate categories for operators using spotting networks?  How should the inevitable cheaters be caught?  And so on.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fortunately, the controversy over spotting networks that had recently been largely resolved lead to guidelines that could be applied to the new controversy.  Most contest committees quickly decided that using CW Skimmer during a contest meant that the operator or operators are in the &quot;assisted&quot; category, the same category that operators using spotting networks are in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there's one particularly controversial technique: operators can monitor the output of a CW Skimmer connected to a remote receiver at a different location.  Some contests, like the CQ WW CW contest, simply don't allow remote receivers, which makes that technique cheating in that contest.  Other contests, like the ARRL DX CW, allow operators to listen to remote receivers as long as they are &lt;em&gt;public&lt;/em&gt;; it's not cheating unless the operator is listening to a &lt;em&gt;private&lt;/em&gt; remote CW Skimmer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CW Skimmer isn't controversial for DXing, because there's no way to police whether operators use it or not.  Operators use it and they can't be stopped, so it has changed DXing forever, like it or not, and has generally been grudgingly accepted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You didn't ask about the Reverse Beacon Network, but no discussion of CW Skimmer is complete without talking about the RBN.  What is the reverse beacon network, and why is it &quot;reverse&quot;?  Well a normal beacon &quot;network&quot; consists of several beacons transmitting from different locations.  An operator can tune in to the beacons, and which beacons can be heard gives a good idea of where the band may be open to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Reverse Beacon Network is simply a network of stations running receivers connected to computers running CW Skimmer in different places.  To test the RBN, one transmits a quick CQ, and then checks to see which RBN locations heard the signal.  Using a typical beacon involves listening, but using the RBN involves transmitting, which is why it's the &quot;reverse&quot; beacon network.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-08-10T04:00:01.020" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15094" PostTypeId="2" ParentId="15083" CreationDate="2019-08-10T12:11:28.643" Score="0" Body="&lt;p&gt;We used to use a similar set up for 2G GSM/DCS and pagers many years ago, where rx levels were marginal and we wanted to 'reach around corners'. We called them 'passive repeaters'. Results were mixed to say the least but we did have some successes.&lt;/p&gt;&#xA;" OwnerUserId="15224" LastActivityDate="2019-08-10T12:11:28.643" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15095" PostTypeId="1" AcceptedAnswerId="15096" CreationDate="2019-08-10T15:45:47.627" Score="1" ViewCount="678" Body="&lt;p&gt;I’m super new to radio with nobody I know knowing it, so noob alert - plus some extraneous details in case you can comment on any of those.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I got a pair of BaoFeng BF-F8HP radios with recommended antenna upgrades with the idea that my brother and I can eventually get licensed and talk over the 5 miles between our houses in dense suburbs.  Seems plausible from the reviews, but haven’t tested yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, we’re just listening for now and there are a few emergency services I found through radioreference.  Most in my area are encrypted and some are at like 700+Mhz that are beyond this radio’s uhf &amp;amp; vhf bands.  (I think I can pick up P25 and FM, but not other modes).  I was able reach more stations by decreasing the Freq Step size to the minimum 2.5khz, and also going to Narrowband mode for easier scanning (although scanning has been fruitless).  Infrequently I hear morse go out on the otherwise vox channel.  Perhaps they’re different bands and my narrow-band is still too wide?  I haven’t found any broadcasts that sound like anything but regular old walkie talkies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Main question:  Why don’t these unencrypted FM emergency services seem to use any call signs or ham codes?  Are they not required to because they aren’t operating as “amateur”s?  And if not, why wouldn’t that type of activity get isolated bands instead of mixing two different vocal protocols in the same bands?  And if I broadcast on any of the vast empty areas of the spectrum as a range test, who would know I wasn’t just some emergency/government service?&lt;/p&gt;&#xA;" OwnerUserId="15427" LastEditorUserId="76" LastEditDate="2019-08-10T19:42:12.253" LastActivityDate="2019-08-11T01:12:58.740" Title="Why aren’t emergency services using callsigns?" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;procedure&gt;&lt;callsign&gt;&lt;phone&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15096" PostTypeId="2" ParentId="15095" CreationDate="2019-08-10T20:03:48.383" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;… Why don’t these unencrypted FM emergency services seem to use any call signs … ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;They aren't required to and don't find it useful in their procedures. Also, they don't &lt;em&gt;have&lt;/em&gt; call signs in the sense amateurs do — they may have names for different groups in a transmission (&quot;Car #3&quot; or whatever) which are &lt;em&gt;call signs&lt;/em&gt; in the sense that they play the same role in radio procedure, but they're not related to radio licensing at all — they're made up for the organization's purposes.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Are they not required to because they aren’t operating as “amateur”s?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. Amateur licensing is completely unrelated to licensing for commercial or government two-way radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio licenses are granted to a person for their operations, with whatever equipment they like. Commercial and government licenses (in the US, and I would expect similarly elsewhere) are granted &lt;strong&gt;to an organization — the individual users do not use any license of their own in order to participate.&lt;/strong&gt; The organization purchases or rents radios and, usually, &quot;programs&quot; them to operate only on the frequencies they have a license to (so the individual users cannot violate the license &lt;em&gt;and&lt;/em&gt; don't have to think about frequencies, just a small list of preset channels).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And if not, why wouldn’t that type of activity get isolated bands instead of mixing two different vocal protocols in the same bands?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;They &lt;em&gt;are&lt;/em&gt; isolated. The transmissions you are listening to are not in the amateur frequency allocations (bands). Your local radio licensing authority keeps track of the licenses/allocations. (For the FCC in the US: here's &lt;a href=&quot;http://transition.fcc.gov/oet/spectrum/table/fcctable.pdf&quot; rel=&quot;noreferrer&quot;&gt;the table of allocations&lt;/a&gt; and &lt;a href=&quot;https://wireless2.fcc.gov/UlsApp/UlsSearch/searchAdvanced.jsp&quot; rel=&quot;noreferrer&quot;&gt;the search engine for individual licenses — including by frequency&lt;/a&gt;.) &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And if I broadcast on any of the vast empty areas of the spectrum as a range test, who would know I wasn’t just some emergency/government service?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Whatever frequency you pick probably belongs to somebody. They'll have expectations about how their licensed allocation is used, and possibly recognize you as not anyone they know and not following any procedures they have. Or, it could be that the allocation in question is used for an incompatible mode (digital something-or-other) in which case you're just another source of RFI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would you &quot;get caught&quot;? Often not, but think of it like trespassing on someone's land — they often might not notice, and they often might not care — or they might care a whole lot. And it's rude, too.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-08-10T20:45:44.540" LastActivityDate="2019-08-10T20:45:44.540" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15097" PostTypeId="2" ParentId="15095" CreationDate="2019-08-10T20:51:07.750" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;who would know I wasn’t just some emergency/government service?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;There's national regulations agencies that monitor the spectrum, and come when someone notifies them of an interference. They can fine you! (And: Typically &lt;em&gt;will&lt;/em&gt; fine you if they find you in &lt;em&gt;intentional&lt;/em&gt; abuse of spectrum.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, be a bit careful about not accidentally using a military allotment. Depending on the service, your country's attitude towards that and the mood of whoever is in charge of the military devices you're interfering with: Visits by these guys will probably not be overly pleasant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Location of a radio emitter is a lot easier than you might think, especially if you're an agency not afraid of spending a couple dozen kilodollar on radiolocation systems (which are commercially available).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I fully agree with everything Kevin wrote: don't test your luck, and don't interefere with someone's potentially life-critical systems. It's plain rude and inconsiderate!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-08-10T20:51:07.750" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15098" PostTypeId="2" ParentId="15095" CreationDate="2019-08-10T21:44:53.907" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Why don’t these unencrypted FM emergency services seem to use any call signs or ham codes? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;They are required to identify periodically and they do.  That is the Morse code you heard.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Emergency services (police, fire, EMS) along with taxicabs, tow trucks, anything else that moves on land, is licensed under part 90, Private Land Mobile Service, of the FCC regulations (in the US, other countries similar).  The FCC issues a station license with a call sign to the agency.  The license generally covers one (or more) base station and some number of mobile units.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the past operation was simplex, base station to mobile, and the base station operator would periodically announce the call sign by voice.  Now, most operation in via repeater.  The repeater will automatically send the station ID by Morse code so the human operator does not have to bother with it. Only the base station has to identify.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most FM systems will use CTCSS.  They leave the tone off when identifying so anyone monitoring the channel with tone squelch enabled will not be bothered by the ID.  I don't really know how P25 systems identify.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: CTCSS = &quot;Continuous Tone Coded Squelch System&quot; = PL (a trade mark).  A system that adds a low frequency audio tone to a transmission.  Receivers may enable tone access so they will only hear transmissions with the proper tone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Addendum: I can see some potential for confusion between answers.  Just keep in mind that a land mobile system (e.g. county fire/EMS dispatch) operates as a isolated system.  The FCC license and callsign applies to the entire system.  Units within the system only talk between units in that system.  They don't make random contacts like hams do nor travel outside their jurisdiction.  Identifiers for individual units (or people) are assigned by the agency (e.g. &quot;Engine 27&quot;, &quot;Chief 15&quot;, &quot;Ambulance 498&quot;).  That is what they use when communicating within the system.  (Then there are some variations such as mutual aid, but let's not get any more complicated).&lt;/p&gt;&#xA;" OwnerUserId="15428" LastEditorUserId="15428" LastEditDate="2019-08-11T01:12:58.740" LastActivityDate="2019-08-11T01:12:58.740" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15099" PostTypeId="2" ParentId="13357" CreationDate="2019-08-11T00:12:16.527" Score="3" Body="&lt;p&gt;This Bruce, the guy who sold you that antenna. A good ground plane is key to a 1/4 wave like that. Another fix would be a shunted antenna. I make those too. I make a 5/8 wave, it is little bigger and longer, but requires very little to no ground plane. &lt;/p&gt;&#xA;" OwnerUserId="15429" LastEditorUserId="15429" LastEditDate="2019-08-11T00:27:30.423" LastActivityDate="2019-08-11T00:27:30.423" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15100" PostTypeId="1" CreationDate="2019-08-11T02:30:07.523" Score="5" ViewCount="251" Body="&lt;p&gt;Hoping someone can identify the following military radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/i3Aa4.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/i3Aa4.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I spotted it at the curb and decided to make it a land-fill diversion project...&lt;/p&gt;&#xA;" OwnerUserId="15430" LastEditorUserId="8717" LastEditDate="2019-12-05T20:06:41.507" LastActivityDate="2019-12-05T20:06:41.507" Title="Can anyone identify this military radio?" Tags="&lt;united-states&gt;&lt;transceiver&gt;&lt;military-surplus&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15102" PostTypeId="1" CreationDate="2019-08-11T10:16:55.153" Score="1" ViewCount="2732" Body="&lt;p&gt;I am sorry but yet again a question about GNU Radio. &lt;em&gt;(I just started following some tutorials a couple of months ago and am learning about it. I am unfortunately not that proficient in it yet, but I am getting there).&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Background:&lt;/strong&gt;&#xA;So here at the end of the post is my (infamous) FM Receiver flow graph (my hello world in GNU Radio). Nothing has changed. Everything's still as it was (in my first two posts). In fact the problem appears independent of which flow graph I run (as long as it does not contain any bugs), no matter whether I use &lt;code&gt;Qt GUI&lt;/code&gt; or &lt;code&gt;WX GUI&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I upgraded to Windows 10 and also updated to the latest binary &lt;strong&gt;(v3.7.13.5/v1.6)&lt;/strong&gt; for GNU Radio from &lt;a href=&quot;http://www.gcndevelopment.com/gnuradio/downloads.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Problem Observed:&lt;/strong&gt;&#xA;The problem is the flow graph appears to start, and stops immediately. No errors. The flow graph window appears, but all I see is the titlebar, and the &lt;em&gt;close&lt;/em&gt;, &lt;em&gt;minimize&lt;/em&gt; and &lt;em&gt;maximize&lt;/em&gt; icons. The rest of the window never appears. The only output I see in the terminal window down in the bottom left corner is the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Terminal Log&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;lt;&amp;lt;&amp;lt; Welcome to GNU Radio Companion 3.7.13.5 &amp;gt;&amp;gt;&amp;gt;&#xA;&#xA;Block paths:&#xA;    C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks&#xA;    C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks&#xA;&#xA;Loading: &quot;D:\projects\gnuradio\projects\FM_RX_1a.grc&quot;&#xA;&amp;gt;&amp;gt;&amp;gt; Done&#xA;&#xA;Loading: &quot;D:\projects\gnuradio\projects\AM_RX_1.grc&quot;&#xA;&amp;gt;&amp;gt;&amp;gt; Done&#xA;&#xA;Loading: &quot;D:\projects\gnuradio\projects\fm_receiver_qt.grc&quot;&#xA;&amp;gt;&amp;gt;&amp;gt; Done&#xA;&#xA;Generating: 'D:\\projects\\gnuradio\\projects\\fm_receiver.py'&#xA;&#xA;Executing: C:\Program Files\GNURadio-3.7\gr-python27\python.exe -u D:\projects\gnuradio\projects\fm_receiver.py&#xA;&#xA;gr-osmosdr 4d83c606 (0.1.5git) gnuradio 3.7.13.5&#xA;built-in source types: file osmosdr fcd rtl rtl_tcp uhd hackrf bladerf airspy redpitaya &#xA;[INFO] [UHD] Win32; Microsoft Visual C++ version 14.0; Boost_106000; UHD_3.14.1.HEAD-0-g5491b80e&#xA;&#xA;&amp;gt;&amp;gt;&amp;gt; Done&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I also get a ton of warnings when launching the GNU Radio as shown below (I had to remove some lines here as I was hitting the post size limit):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Startup log&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;setting gnuradio environment&#xA;Warning: Block with key &quot;acars2_decode&quot; already exists.&#xA;        Ignoring: C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks\acars2_decode.xml&#xA;.... &#xA;*(a lot of similar lines -&amp;gt; I guess nearly all the blocks/modules in GNU Radio)*&#xA;....&#xA;Warning: Block with key &quot;zeromq_sub_source&quot; already exists.&#xA;        Ignoring: C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks\zeromq_sub_source.xml&#xA;&amp;lt;&amp;lt;&amp;lt; Welcome to GNU Radio Companion 3.7.13.5 &amp;gt;&amp;gt;&amp;gt;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;I thought maybe it is some permissions problem. I tried launching GNU Radio as administrator (just to test). &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;GNU Radio just failed to start. &lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Anyways, as always, the Dongle works. I compared it, by running CubicSDR.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;After I had posted this question on HAM.SE, I downgraded to version &lt;strong&gt;3.7.11.1&lt;/strong&gt; from &lt;a href=&quot;http://www.gcndevelopment.com/gnuradio/downloads.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; and it was able to launch the Flow graph.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Even though, only &lt;code&gt;Qt GUI&lt;/code&gt; worked. When a flow graph made with &lt;code&gt;WX GUI&lt;/code&gt; is run, it would start a little and then the window would freeze. Which is strange. As with this GNU Radio version, this flowgraph used to work on &lt;code&gt;Windows 8.1&lt;/code&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Then after @MarcusMüller hinted that I may possibly have two GNU Radio installations [possibly conflicting with each other], &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I removed the GNU Radio version &lt;em&gt;3.7.11.1&lt;/em&gt;, &lt;/li&gt;&#xA;&lt;li&gt;restarted the computer &lt;/li&gt;&#xA;&lt;li&gt;and thoroughly checked that there are no GNU Radio installations anywhere. &lt;/li&gt;&#xA;&lt;li&gt;I reinstalled the latest version of GNU Radio &lt;strong&gt;3.7.13.5&lt;/strong&gt; and the same problematic behavior was observed as explained above. &lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;What one can see though is that due to some reason (some setting or bug), this version &lt;strong&gt;3.7.13.5&lt;/strong&gt; of GNU Radio includes the &lt;strong&gt;blockpath&lt;/strong&gt; twice, as shown below.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;lt;&amp;lt;&amp;lt; Welcome to GNU Radio Companion 3.7.13.5 &amp;gt;&amp;gt;&amp;gt;&#xA;&#xA;Block paths:&#xA;    C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks&#xA;    C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks&#xA;&#xA;Loading: &quot;D:\projects\gnuradio\projects\FM_RX_1a.grc&quot;&#xA;&amp;gt;&amp;gt;&amp;gt; Done&#xA;&#xA;Loading: &quot;D:\projects\gnuradio\projects\AM_RX_1.grc&quot;&#xA;&amp;gt;&amp;gt;&amp;gt; Done&#xA;&#xA;Loading: &quot;D:\projects\gnuradio\projects\fm_receiver_qt.grc&quot;&#xA;&amp;gt;&amp;gt;&amp;gt; Done&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And from there come all the warnings, I guess. (I have NOT made any such changes. The installation was done with default settings, just like for the other version of GNU Radio &lt;strong&gt;v3.7.11.1&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;One of the (otherwise working) flowgraphs:&lt;/strong&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/bIzvS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bIzvS.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;My tentative Conclusion:&lt;/strong&gt; As far as I can see, the Windows build for GNU Radio &lt;strong&gt;v3.7.13.5/v1.6)&lt;/strong&gt; is buggy &lt;a href=&quot;http://www.gcndevelopment.com/gnuradio/downloads.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13000" LastEditorUserId="13000" LastEditDate="2019-08-14T07:53:59.437" LastActivityDate="2021-01-18T08:21:00.330" Title="GNU Radio does not run flow graph" Tags="&lt;rtl-sdr&gt;&lt;gnuradio&gt;" AnswerCount="2" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="15104" PostTypeId="1" CreationDate="2019-08-11T12:56:19.093" Score="5" ViewCount="125" Body="&lt;p&gt;Some receivers contain a noise reduction button or function. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What does this noise reduction do?&lt;/li&gt;&#xA;&lt;li&gt;Is there more than one type of noise reduction? &lt;/li&gt;&#xA;&lt;li&gt;How does the circuit or software know what part of the signal to reduce as noise and what part to not attenuate? (e.g. the stuff the operator wants to hear)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-11T17:24:03.437" LastActivityDate="2019-08-12T08:52:06.350" Title="What does a receiver's noise reduction function do?" Tags="&lt;equipment-operation&gt;&lt;noise&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15105" PostTypeId="1" AcceptedAnswerId="15113" CreationDate="2019-08-11T16:23:50.303" Score="0" ViewCount="126" Body="&lt;p&gt;Premise: I had a Baofeng GT-3 TP Mark III 8W stored and never used, this morning my nephew has found It and He tried to &quot;play with It&quot; transmitting at maximum power(8 Watt) despite antenna wasn't attached, (seems He has transmitted for several minutes).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I have tried the radio in a near range indoor transmission and in &lt;em&gt;channel mode&lt;/em&gt; apparently seems working, but in &lt;em&gt;frequency mode&lt;/em&gt; It activates on all frequencies, as there is an incoming transmission, but It receives noise on all frequencies even at maximum squelch level (9).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since I haven't tried this radio before, I don't know if this depends on local radio pollution and bad factory squelch parameters, that eventually I can adjust with CHIRP(you can see the current parameters in the image), or this could be caused by some noise filtering component that has been burned during the transmission without antenna making It more sensitive to any radio disturbance.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/bm5xF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bm5xF.png&quot; alt=&quot;the squelch levels setting currently on the radio&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How could I determine the possible damages of transmission with detached antenna in portable ham radios?&#xA;(consider that I haven't any special testing equipment)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the kinds of damages that could occur? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case the damage occur, is It something of the kind radio totally stop to receive and transmit or could happens even kinds of damages that make the radio performing worse?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks to everyone help me.&lt;/p&gt;&#xA;" OwnerUserId="15439" LastEditorUserId="15439" LastEditDate="2019-08-11T17:39:25.290" LastActivityDate="2019-08-12T14:51:42.213" Title="How can I determine the possible damages of transmission with detached antenna in portable ham radios?" Tags="&lt;baofeng&gt;&lt;testing&gt;&lt;squelch&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15106" PostTypeId="2" ParentId="15100" CreationDate="2019-08-11T17:13:13.283" Score="7" Body="&lt;p&gt;One of the fine folks from &lt;a href=&quot;https://mmrcg.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;MMRCG&lt;/a&gt; identified this as model R-1484/PRR-15&lt;/p&gt;&#xA;" OwnerUserId="15430" LastEditorUserId="8717" LastEditDate="2019-08-11T19:40:04.450" LastActivityDate="2019-08-11T19:40:04.450" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15107" PostTypeId="1" AcceptedAnswerId="15130" CreationDate="2019-08-11T17:14:00.347" Score="3" ViewCount="806" Body="&lt;p&gt;Another question (&lt;a href=&quot;https://ham.stackexchange.com/questions/133/metal-for-antenna-construction&quot;&gt;Metal for antenna construction?&lt;/a&gt;) covered some aspected of this question, but the answers didn't exactly answer it, so I'll make it specific.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given 2 dipole antennas, resonant at the 2-meter band (146 MHz) exactly, differing in their construction:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Uncoated copper tubing with an outer diameter of 19.05 mm (0.75 inches), something like a &lt;a href=&quot;https://en.wikipedia.org/wiki/Copper_tubing#United_States,_Canada_and_India&quot; rel=&quot;nofollow noreferrer&quot;&gt;3/8 copper tube&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Uninsulated copper wire with an outer diameter of 2.053 mm (0.0808 inches), something like &lt;a href=&quot;https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes&quot; rel=&quot;nofollow noreferrer&quot;&gt;12 AWG copper wire&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Wherein would the difference between them lie?&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Since I don't know the answer: I'm wondering if, for example, there would be a difference between their effectiveness, arm lengths, or something else?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="14220" LastEditDate="2019-08-11T17:19:53.057" LastActivityDate="2019-08-14T19:54:41.140" Title="How does the thickness of the radiator affect an antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15108" PostTypeId="2" ParentId="15107" CreationDate="2019-08-11T20:02:35.033" Score="1" Body="&lt;p&gt;Of the many factors, the skin effect depth at 146 MHz is on the order of 5 microns, so the vastly greater surface area of the tube will reduce resistive losses.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-08-11T20:02:35.033" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15109" PostTypeId="2" ParentId="15107" CreationDate="2019-08-12T04:25:27.920" Score="3" Body="&lt;p&gt;The bandwidth of the thicker antenna will be slightly wider &#xA;Just like for instance on 80 meters people build cage antennas to increase bandwidth on that band, up on 146 the effect will be the same as the percentage of diameter as it relates to the length will be comparable.  Not that it will be all that big of a deal at 146 because the entire band while 4 mhz wide is not as wide as the .5 mhz on 80 meters as a percentage. The .5 Mhz of 4 mhz is 12.5% while the 4 Mhz width of 148 Mhz is only 2.7%&lt;/p&gt;&#xA;" OwnerUserId="15443" LastEditorUserId="9621" LastEditDate="2019-08-12T17:17:02.540" LastActivityDate="2019-08-12T17:17:02.540" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15110" PostTypeId="2" ParentId="15104" CreationDate="2019-08-12T08:34:40.567" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What does this noise reduction do?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That should depend on the device. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, it's to be assumed that it applies (analog and/or digital) signal processing to improve the &lt;em&gt;perceived Signal-to-Noise ratio&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In simple cases, this might simply mean reducing the bandwidth of an analog receiver. Sure, voice will not sound as crisp, but if that buys one a reduction in 75% of noise, that might be worth it.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How does the circuit or software know what part of the signal to reduce as noise and what part to not attenuate? (e.g. the stuff the operator wants to hear)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In more complex cases, DSP will be used to find and isolate the components in the signal that match a mathematical model of what constitutes intelligible speech. This is not unlike the vocoder problem, where you'd want to condense the wholeness of audio data to only the parts that define the contained speech just well enough to reproduce it reliably.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, this becomes an estimation problem: What's the speech content that led to the observed, noise signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An intuitive approach is: If you had all possible speech signals to choose from, which one has the least quadratic difference to the noisy signal you're observing? Pick that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, since you can't wait forever, this is not viable. What indeed is viable is trying to estimate a very limited set of speech model parameters, and then continuously updating that, predicting what would happen next, comparing that to the next freshly received bit of noisy signal, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think of that as a speech synthesizer (that for example mimics the human mechanics of producing sound, by having different coefficients for different things your mouth and vocal chords could do), continuously just being fed the coefficients that someone estimated based on the noisy reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That brings me to&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there more than one type of noise reduction? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes! not only are there many ways the above can be implemented, you also have different kinds of noises you might want to reduce:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While the bandwidth reduction most certainly pays for e.g. low-SNR FM and AM subject to stationary wideband noise, it won't do much against impulse noise (e.g. from spark plugs), since that just means a potentially huge spike with a lot of energy all over the spectrum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's easy to zero out that impulse. That would already improve the situation, but: you'd really want the uttering in progress when the impulse noise started to be continued, extrapolated for the duration of the impulse. Then, it becomes incredibly helpful if you're already using a predictive model coder, because you can just let it run freely without continously adjusting it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let me add one last question you didn't ask but that I'd like to answer:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What would be the best noise cancelling system, including a transmitter that cooperates?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, if the transmitter knows about the characteristics of the noise you're expecting, it could spend its transmit power on transmitting only what you really use to reconstruct, and not on the rest of what you spoke into your mic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the simple narrower-filter case above, that would simply mean it'd use a filter that is matched to what you use in the receiver on the transmit side. (And, yes, that is actually the same thing as &lt;em&gt;matched filtering&lt;/em&gt; known from comms theory.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the voice-model case, it's not hard to see that it'd be way cleverer to just use the transmit power to transmit the coefficients needed to reconstruct voice and nothing else. Make sure the whole bandwidth you get is filled as much power put into these. Furthermore, the more important a specific coefficient is for intelligible reconstruction, the more power should be spent on encoding it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's exactly what vocoders due. It's intuitively not hard to see, thus, that digital voice comms with receiver RF SNR knowledge at the transmitter will be better than analog comms (especially AM). The often stressed argument of &quot;digital doesn't do gradual degradation, it just fails&quot; really isn't true for modern vocoders; there's a lot of channel coding going on that distributes errors as well as possible, and joint source/channel coding that makes sure that the remaining bit errors would have least possible effect on intelligibility. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can actually make use of that with an SSB radio: just use the SSB audio in/output as bandwidth carrying digital signals. &lt;a href=&quot;https://freedv.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV&lt;/a&gt; does exactly that!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-08-12T08:52:06.350" LastActivityDate="2019-08-12T08:52:06.350" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15111" PostTypeId="2" ParentId="690" CreationDate="2019-08-12T14:13:27.000" Score="0" Body="&lt;p&gt;Two suggestions. First coordinate with other EOCs in your state. I know in SC there is a DMR network set up to provide communications between EOC in different parts of the state. You can also see if they have a commonly used HF frequency that is shared.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second make contacts with the local HAM community, If they is a club, contact them. Get to know the people who run the local repeaters. Contact your State ARES coordinator. If you are not sure who any of those people are contact the ARRL and they can put you in contact. If there is currently no ARES or RACES group you be able to find a local HAM who would be willing to set one up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know locally our HAM club works closely with CERT, the Red Cross, and our local EOC. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2019-08-12T14:13:27.000" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15112" PostTypeId="2" ParentId="1310" CreationDate="2019-08-12T14:22:25.590" Score="1" Body="&lt;p&gt;Your local HAM club will almost certainly have HAMs who are contesters. Most will be happy to help you. Many contests have website that will explain their rules and procedures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While not officially a contest, even though they keep score and post the &quot;winners&quot;, ARRL field day is a good way to get started. You can find out more at the ARRL website as well as many other places on the web. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The goal for most contests is to make as many contacts was possible within a certain time period. A contact will be defined differently for different contest. Most include your call sign and a signal report. Other might require your state if in the USA or maidenhead grid square. Some assign you a specific identifier you have to use in addition to your call sign. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For scoring it is usually the number of contacts, but often there are modifiers. Operating low power, QRP or less than 5 watts, may add to or even double your score. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most contests will have various limitations. A CW contest will only accept contacts made using morse code. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL does publish a contacting journal. It can be a good source of information. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2019-08-12T14:22:25.590" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15113" PostTypeId="2" ParentId="15105" CreationDate="2019-08-12T14:51:42.213" Score="3" Body="&lt;p&gt;If your nephew damaged the Baofeng GT-3TP Mark III, the damage is likely to the transmitting circuits of the radio, and not to the receive side.  I don't have that model of Baofeng, but I do have a different model, which is notorious for having difficult-to-adjust squelch.  On several channels I can't get the squelch to stop the radio from playing static.  It could be that the squelch hasn't been improved much in the GT-3TP Mark III.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the radio has been damaged, the most likely symptoms are low transmit power (perhaps none) and/or high current usage.  The best way to test the radio would be to compare the transmit power and current draw to a unit that hasn't been transmitted without an antenna.  If you don't have access to a second radio and test equipment, then you could try asking for a radio check on a local repeater or your local 2m FM simplex calling frequency (146.52 MHz in the US and Canada).  You could also keep an eye on how long the battery lasts, and compare that to other operators' experience.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-08-12T14:51:42.213" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15114" PostTypeId="2" ParentId="15107" CreationDate="2019-08-12T15:31:40.893" Score="5" Body="&lt;p&gt;Generally, the thicker an antenna is, the wider its bandwidth. So the copper tubing will have slightly higher bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, the copper tubing will have much more surface area, thus lower resistance, and lower loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll probably find the length necessary to achieve resonance is slightly different in each case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But overall, these effects are pretty small. Their more significant differences are cost and mechanical properties.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-08-12T15:31:40.893" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15115" PostTypeId="1" AcceptedAnswerId="15119" CreationDate="2019-08-12T18:24:36.663" Score="3" ViewCount="355" Body="&lt;p&gt;I'm having little difficulties understanding the following schematic:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SC23k.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SC23k.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand the part regarding current distribution. I understand why this schematic suppresses common mode current. Also I realize that if Z1 = V/2I was 50 Ohm than the balun converts the impedance to Z2 = 2V/I, 200 Ohm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I don't understand is the voltage part on this schematic. Why the voltage is +3V/2 and -V/2 in the right part (2V in total), where V/2 came from in the middle part and what does it mean?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-08-12T22:04:43.843" LastActivityDate="2019-08-13T00:04:32.687" Title="How does a 1:4 current balun work?" Tags="&lt;balun&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15117" PostTypeId="1" CreationDate="2019-08-12T21:24:42.773" Score="2" ViewCount="506" Body="&lt;p&gt;I have an old Philips walkman that has AM/FM radio. I tried AM radio. Really I can get clearly 2 country radios. I catched very poorly 4 foreign radios or different countries, but they do lots of noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I plug in headphones with quite a long cable, and those headphones are pluged into the splitter that came with it, so that it can connect to headphones input and mic input since it's a cpmplete headset. However this does not improve much the quality.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency range in this walkman is from 530 to 1180 Khz I believe, since the lowest number says 53 and the highest number says 118 and below it says &quot;10x&quot;. I guess it means you have to multiplay those numbers by 10 so that you have the Khz number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The walkman doesn't have any external attached antena, since I guess headphones do that function, however is that an easy way of improving the reception of AM signal?&#xA;Is there a headphones cord optimal length?&lt;/p&gt;&#xA;" OwnerUserId="15373" LastActivityDate="2019-08-13T17:46:04.803" Title="Improve AM reception on an old Walkman that has no external antenna" Tags="&lt;antenna&gt;&lt;am&gt;&lt;reception&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15118" PostTypeId="2" ParentId="15117" CreationDate="2019-08-12T23:11:55.693" Score="3" Body="&lt;p&gt;The genuine Sony Walkman, and most of the Walkman-style radios from other makers, did indeed use the headphone cable for their antenna.  My experience (with an early 1980s Sony model) was very good on FM, and even then AM was mostly talk, news, and sports, so I didn't listen much on that band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, AM radio isn't what it used to be.  Fewer stations broadcasting at lower power means you may not nave a broad selection of strong local stations.  Further, many AM stations (at least in America) now broadcast a digital sideband (which carries station and track ID information as well as the HD/stereo signal if offered) that can come through as a &quot;buzz&quot; or similar distortion in the analog signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you note, most &quot;pocket&quot; size AM sets have a tuner that covers the whole band with less than half a turn of a small wheel; these are almost impossible to tune with high precision.  Add that to the relatively poor discrimination of many less expensive pocket AM sets, and it's fairly likely your antenna isn't the problem.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-08-12T23:11:55.693" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15119" PostTypeId="2" ParentId="15115" CreationDate="2019-08-12T23:48:07.907" Score="6" Body="&lt;p&gt;It's a confusing diagram.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of the voltages are differences between points you might intuitively assume. For example, the &lt;span class=&quot;math-container&quot;&gt;$2V$&lt;/span&gt; at the right is the voltage across the entire load (which also confusingly, is modeled by two identically named series resistors).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the other voltages are implicitly relative to the ground symbol attached to the connector shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lemma: the voltage across any winding must be the same since we are considering only the differential mode and the transformers are the same. Hopefully that's intuitive enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The voltage across any winding must be &lt;span class=&quot;math-container&quot;&gt;$V/2$&lt;/span&gt; (though the polarity may differ). Consider this circuit:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CON5Y.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CON5Y.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the &lt;a href=&quot;https://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws#Kirchhoff&amp;#39;s_voltage_law_(KVL)&quot; rel=&quot;noreferrer&quot;&gt;KVL&lt;/a&gt;, the voltages around this circuit must add to zero. Since the voltage across the connector is &lt;span class=&quot;math-container&quot;&gt;$V$&lt;/span&gt; by definition, the windings must each be half that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now start at the point labeled &lt;span class=&quot;math-container&quot;&gt;$-V/2$&lt;/span&gt; and follow back to ground:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/M6ER6.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/M6ER6.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having gone through one winding (minding polarity) the voltage is one times the winding voltage, or &lt;span class=&quot;math-container&quot;&gt;$-V/2$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the other point labeled &lt;span class=&quot;math-container&quot;&gt;$3V/2$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xHTJH.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xHTJH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This way goes through a winding and the connector, so the voltage is &lt;span class=&quot;math-container&quot;&gt;$V + V/2 = 3V/2$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference between these points is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 3V/2 - (-V/2) = 2V $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which is the output voltage you'd expect considering conservation of energy or just what a 4:1 balun is supposed to do.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-08-13T00:04:32.687" LastActivityDate="2019-08-13T00:04:32.687" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15120" PostTypeId="2" ParentId="15117" CreationDate="2019-08-13T03:21:40.777" Score="2" Body="&lt;p&gt;I would recommend getting a multi band radio that can receive these and other frequencies. In the late 1980s I used to listen to AM radio using an old FRG-7 communications receiver. I &lt;strong&gt;loved&lt;/strong&gt; that thing - it was a joy to use. Even its power switch was big and red, just like they should be! The only problem with that was that it worked best with a large external antenna. But you could make a ferrite bar antenna (effectively a magnetic loop antenna for LF/VLF) that would work well enough to pick up some distant long- and medium-wave stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The world has moved on, however, and many stations have now closed down and moved to the internet or VHF (usually on FM). A communications receiver and a decent antenna will help you find the long-, medium- and short-wave stations that are still broadcasting, as well as the many radio amateurs out there across the globe. Maybe one day you might even hear me! :)&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-08-13T03:21:40.777" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15121" PostTypeId="1" CreationDate="2019-08-13T04:53:19.863" Score="1" ViewCount="412" Body="&lt;p&gt;I am using four HackRF One devices that will be situated ~1000ft apart, and that must be synchronized. Running 4000ft of cable to connect their clocks is obviously not feasible. I am wondering what sort of solutions are available for synchronizing their clocks through wireless means. I have done some research on this, but all I could find was a method using GPS, which required hardware mods. I would like to avoid modding if possible. These HRF's will also be connected to Raspberry Pi's with internet access. Perhaps there is a way to use internet time servers to sync them? They all operate at 10MHz, just need phase alignment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: I am trying to locate some transmitters using time difference of arrivals. So highly accurate event timing is necessary. If any other SDRs besides the HackRF would be more suitable I'm open to switching over to something else if necessary.&lt;/p&gt;&#xA;" OwnerUserId="15099" LastEditorUserId="15099" LastEditDate="2019-08-21T01:45:39.160" LastActivityDate="2019-08-21T01:45:39.160" Title="Synchronizing HackRF Ones at a distance" Tags="&lt;hackrf&gt;" AnswerCount="3" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="15122" PostTypeId="1" CreationDate="2019-08-13T09:17:47.363" Score="4" ViewCount="49" Body="&lt;p&gt;An antenna system often consists of more than the feedline and radiating wires: such as fixed or tapped loading coils, LC traps, baluns, toroids, air variable capacitors, roller inductors, feed horns, reflector dishes, poles, standoffs, mounting hardware, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens when this stuff gets wet?  Which parts requires waterproofing and which do not?  When does the entire antenna system need to go in an enclosed dome?  And when will it all just work on the roof of a truck in a downpour?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-13T17:27:02.363" LastActivityDate="2019-08-13T17:27:02.363" Title="Antenna system components in the rain" Tags="&lt;antenna-system&gt;&lt;weather&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15123" PostTypeId="1" CreationDate="2019-08-13T13:17:33.047" Score="3" ViewCount="110" Body="&lt;p&gt;I need to simulate 2 helix antennae placed side by side, and see the resultant radiation pattern. But after adding the second antenna with a separate and when I try to simulate 4nec2, only simulated the 1st antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any thoughts on how to simulate both antennas?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/z1TjA.png&quot; alt=&quot;two helix&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/4X271.png&quot; alt=&quot;Only one is getting simulated&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="15447" LastEditorUserId="8717" LastEditDate="2019-11-05T21:35:46.577" LastActivityDate="2020-10-16T17:31:01.937" Title="How to simulate two antennas in 4nec2" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vhf&gt;&lt;antenna-system&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15124" PostTypeId="2" ParentId="15122" CreationDate="2019-08-13T16:02:37.250" Score="4" Body="&lt;p&gt;A lot of things will work electrically when wet, as long as the water film is thin relative to the size of the thing. For example, a wet dipole, no problem. A tiny coil where water droplets can short adjacent turns, not so much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Water getting in coax, either the feedline, or as part of a balun or trap, is a problem. The water will wick down the shield, causing corrosion and dielectric loss. The coax is ruined. Best practice is to terminate the coax with connectors, then waterproof the connections with mastic or rubber tape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Water facilitates corrosion. Galvanic corrosion between dissimilar metals happens faster with water. Sticking to one kind of metal (don't connect aluminium and copper), or using corrosion resistant metals (stainless steel), or protective coatings (paint) are often easier than avoiding all water.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Water is only part of the problem: in many climates snow and ice must also be considered. A coil may not be a problem in rain, but may be sufficient for sticky snow to accumulate in it. A thin film of water may not be significant, but packing a coil with wet snow could be a problem. Furthermore, freeze-thaw cycles can cause mechanical stress and eventual failure, especially in ferrite which is slightly porous. Accumulated snow and ice can increase the weight of antenna systems beyond the structure's capacity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At microwave frequencies, the dielectric loss of water is more significant, and the dimensions of a water droplet approach something significant relative to wavelength.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="6080" LastEditDate="2019-08-13T16:17:53.447" LastActivityDate="2019-08-13T16:17:53.447" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15125" PostTypeId="2" ParentId="15121" CreationDate="2019-08-13T16:11:51.703" Score="1" Body="&lt;p&gt;Synchronizing clocks without wires usually involves radio. But since you're building a radio, &quot;just use a radio&quot; is probably not a useful solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, it's unlikely NTP (the most common protocol for synchronizing time over IP) is able to provide sufficient precision to keep the receiver's phase coherent enough to be useful. The jitter in network delay and even Raspberry Pi processing is simply orders of magnitude too great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GPS is probably the best option. You don't necessarily have to modify the hardware: the HackRF One has &lt;a href=&quot;https://github.com/mossmann/hackrf/wiki/HackRF-One#external-clock-interface-clkin-and-clkout&quot; rel=&quot;nofollow noreferrer&quot;&gt;a clock input that expects a 10 MHz reference signal&lt;/a&gt;. And there are external devices that &lt;a href=&quot;https://www.sdr-kits.net/GPS-Disciplined-Reference-Oscillator-for-DG8SAQ-VNWA&quot; rel=&quot;nofollow noreferrer&quot;&gt;generate the 10 MHz reference from GPS&lt;/a&gt; for precisely this purpose. You just need two such devices, and a clear(ish) view of the sky.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-08-13T16:11:51.703" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15126" PostTypeId="2" ParentId="15117" CreationDate="2019-08-13T17:38:35.270" Score="2" Body="&lt;p&gt;A tunable high-Q loop antenna, such as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B001KC579Q&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amazon.com/Kaito-Tunable-Passive-Antenna-Panasonic/dp/B001KC579Q/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;placed near your small AM radio can inductively couple into the internal ferrite antenna or RF front-end, and add to their gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's an example of one built around a crate than you can put your radio inside:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://swling.com/blog/2017/06/how-to-build-a-milk-crate-am-broadcast-loop-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://swling.com/blog/2017/06/how-to-build-a-milk-crate-am-broadcast-loop-antenna/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, you construct a large (larger than your radio), multi-turn air-core inductor, and tune to stations in the AM band using an air variable capacitor.  The much higher Q of the large air-core inductor and air variable capacitor can also help separate adjacent frequency AM stations better than the tiny dial on your pocket radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you just want to add a long wire antenna, and have a large enough yard or field to put it in, around 250 to 750 feet of wire suspended above ground might be suitable for improving AM broadcast band reception.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-13T17:46:04.803" LastActivityDate="2019-08-13T17:46:04.803" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15127" PostTypeId="2" ParentId="15121" CreationDate="2019-08-13T20:08:09.043" Score="3" Body="&lt;p&gt;If you're using four independent GPS receivers as your time synchronisation source, you may be able to feed some version of the GPS 1PPS signal into the receiver, and recover it later in the data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's possible to synchronise two A/Ds, usually by time tagging the samples and resetting the counter in the FPGA using an external sync signal like GPS, but this requires support in hardware and gateware. Fancier A/D converters have a secondary 1-bit A/D that's completely synchronised with the main sampler, for this exact purpose. I don't know the HackRF but you say it requires a hardware modification.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feeding the time signal into the front end simplifies all that, if you can tolerate some occasional interference. A CW tone or noise source, switched on for a very short time by the 1PPS, would be one kind of signal you could use. I've also had some success simply passing the pulse through a high-pass filter and detecting the resultant small RF burst - this depends on the rise time of the PPS and the frequency and bandwidth of your receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your receivers are only 1000' apart, GPS probably won't be good enough for good TDOA. Off the shelf modules probably don't do better than a few hundred nanoseconds time error from each other, depending on your luck and the ionosphere, and your baseline is only 1000 ns long, so the position errors will be large. The uBlox F9T can apparently be set up to share clock data between receivers in real time, to offer a claimed 15 ns time offset between receivers, this might work better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the space between the receivers is clear, the idea in the comments might be simplest - place a transmitter at a known position, compute its time offset to each receiver, and use this to find the offset of a signal from an unknown position.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-08-13T20:08:09.043" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15128" PostTypeId="2" ParentId="15121" CreationDate="2019-08-13T21:14:50.317" Score="2" Body="&lt;p&gt;First synchronize all 4 clock generators in frequency using an external source (say, GPS or atomic clock derived into the 10MHz ref input).  Start receiving continuously on all 4, and use the received sample counts as your Raspberry Pi timer time bases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, place a reference source (such as a cheap FM transmitter, FMRS, HT, et.al.) in the center of the constellation of your 4 radios.  Record some transmission (you saying &quot;hello&quot;) in all 4 receivers.  Find the peak cross-correlation time-stamp for each pair of receivers and use these cross-correlation time lags to adjust a sample count offset in the time stamps of each unit until all 4 cross-correlation lags between units go to zero (or sub-1-sample).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-13T21:27:56.097" LastActivityDate="2019-08-13T21:27:56.097" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15129" PostTypeId="1" AcceptedAnswerId="15144" CreationDate="2019-08-13T22:03:11.603" Score="4" ViewCount="235" Body="&lt;p&gt;I have operated at several stations - including my own - where a 40m beam is stacked above a tribander. During a rain storm, there is so much QRN on the 40m beam that the band is unusable, but the tribander seems unaffected. Conversely, a nearby tribander without a beam stacked above it is similarly useless due to QRN.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are precipitation discharges being re-radiated out of phase from the upper antenna in the stack and cancelling the discharges in the lower antenna?&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="4665" LastEditDate="2021-03-17T16:24:02.167" LastActivityDate="2021-03-17T16:24:02.167" Title="How does a higher antenna reduce rain static on a lower antenna?" Tags="&lt;antenna&gt;&lt;antenna-system&gt;&lt;qrn&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15130" PostTypeId="2" ParentId="15107" CreationDate="2019-08-13T22:27:48.760" Score="1" Body="&lt;p&gt;Some rf aspects that could be taken into account.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Summary: no considerable impact&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;but feel free to read the long version below&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Check the answers that have covered the important physical and bandwidth aspects already.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;1. Skin effect&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;rf current concentration at the surface are described by the &lt;a href=&quot;https://en.wikipedia.org/wiki/Skin_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;skin effect&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a rule of thumb the material thickness should be  &lt;span class=&quot;math-container&quot;&gt;$&amp;gt;5* skin \, depth$&lt;/span&gt;. &#xA;Then the majority of the concentrated current (skin effect) is within the available material. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;current density follows a &lt;span class=&quot;math-container&quot;&gt;$e^{-z/\delta}$&lt;/span&gt; relation, so with &lt;span class=&quot;math-container&quot;&gt;$z=5*\delta$&lt;/span&gt; that's  &lt;span class=&quot;math-container&quot;&gt;$&amp;lt;1\%$&lt;/span&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;thicker material has no more considerable impact on losses&lt;/li&gt;&#xA;&lt;li&gt;for thinner material losses increase&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Skin depth: &#xA;&lt;span class=&quot;math-container&quot;&gt;$\delta \, [m]= \sqrt{\frac{2\rho}{\omega\mu}}$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Angular_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;angular frequency&lt;/a&gt;: &lt;span class=&quot;math-container&quot;&gt;$\omega=2\pi f =2\pi * 146 MHz=917*10^6$&lt;/span&gt; &lt;span class=&quot;math-container&quot;&gt;$\frac{1}{s}$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;permeability&lt;/a&gt;: &lt;span class=&quot;math-container&quot;&gt;$\mu \, [H/m = \Omega s /m]$&lt;/span&gt; (&lt;a href=&quot;https://en.wikipedia.org/wiki/Henry_%28unit%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;Henry unit&lt;/a&gt;)&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;copper: &lt;span class=&quot;math-container&quot;&gt;$1.26*10^{-6} H/m$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity&quot; rel=&quot;nofollow noreferrer&quot;&gt;resistivity&lt;/a&gt;: &lt;span class=&quot;math-container&quot;&gt;$\rho \, [\Omega m]$&lt;/span&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;copper: &lt;span class=&quot;math-container&quot;&gt;$1.68*10^{-8} \Omega m$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\delta_{copper\_146MHz} = 5.4 \, \mu m$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your example &lt;span class=&quot;math-container&quot;&gt;$&amp;gt;5* skin \, depth$&lt;/span&gt; is &lt;strong&gt;well fulfilled&lt;/strong&gt;, so the tube / wire has no difference.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;2. Losses&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;By considering a two-wire transmission line &lt;a href=&quot;https://math.stackexchange.com/a/935458&quot;&gt;analytical&lt;/a&gt; formulas provided by rf textbooks can be applied to assess the losses impact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For sure that two-wire line isn't the same as a dipole antenna, but it can be used to provide some perspective without electromagnetic simulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Surface resistance: &lt;span class=&quot;math-container&quot;&gt;$R_s = \sqrt{\frac{\omega\mu\rho}{2}} = 3.1 \, m\Omega$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Series resistance in unit length of a two-wire line: &lt;span class=&quot;math-container&quot;&gt;$R' [\Omega/m]=\frac{R_s}{\pi * radius}$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;19mm tube: &lt;span class=&quot;math-container&quot;&gt;$R'=104  \, m\Omega/m$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;2mm wire: &lt;span class=&quot;math-container&quot;&gt;$R'= 992  \, m\Omega/m$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There is a considerable relative difference, but absolute it's still small especially concerning that not even a full wavelength is applied on a &lt;span class=&quot;math-container&quot;&gt;$\lambda/2 \, dipole$&lt;/span&gt; (compared to a transmission line that's usually &lt;span class=&quot;math-container&quot;&gt;${&amp;gt;&amp;gt; \lambda}$&lt;/span&gt;)&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For effectiveness that consideration also applies.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;h3&gt;2.1 Putting it into perspective&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;With an arbitrary made up two-wire line example.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;assumptions: air with 0 conductane, 2mm wire, d&gt;&gt;a simplifaction&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;distance: &lt;span class=&quot;math-container&quot;&gt;$d=0,01m$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;radius: &lt;span class=&quot;math-container&quot;&gt;$a=0,001m$&lt;/span&gt; (2mm wire)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$j\omega C' = \frac{\pi \epsilon_0}{ln \,d/a}=0,011 \frac{F}{m}$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$j\omega L' = \frac{\mu_0}{\pi} \, ln \frac{d}{a}= 845 \frac{H}{m}$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$R'= 0.992  \, \Omega/m$&lt;/span&gt; (from above 2mm wire)&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;2.1.1 Lossless&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_0=\sqrt{\frac{L'}{C'}} = 276.12 \, \Omega$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\lambda=2.0533731 \, m$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;2.1.2 Lossy line&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_0=\sqrt{\frac{R'+j\omega L'}{G'+j\omega C'}} = 276.12 -j 0.16 \, \Omega$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\lambda=2.0533727 \, m$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Length of line to have &lt;span class=&quot;math-container&quot;&gt;$0.1 \, dB$&lt;/span&gt; attenuation: &lt;span class=&quot;math-container&quot;&gt;$3.2 \lambda$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even the 'higher' series resistance of the 2mm wire has a negligible effect on the impedance of a two-wire line compared to the lossless case (for short lenght like the case of a &lt;span class=&quot;math-container&quot;&gt;$\lambda / 2 dipole$&lt;/span&gt;). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the difference in between tube / wire will be also negligible.&lt;/p&gt;&#xA;&#xA;&lt;h3&gt;2.2 Losses impact on radiation pattern&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;The losses will affect the current distribution along the dipole length and therefore the radiation pattern. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway based on the previous assessments I won't expect a recognizable impact.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;3. Diameter impact on radiation pattern&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;To assess this without electromagnetic simulation programs: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case the air &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is &lt;span class=&quot;math-container&quot;&gt;$2.05 \, m$&lt;/span&gt; and therefore even the &lt;span class=&quot;math-container&quot;&gt;$19 \, mm$&lt;/span&gt; tube diameter is &lt;span class=&quot;math-container&quot;&gt;$&amp;lt; 1\%$&lt;/span&gt; of the wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antenna elements that are applied to impact the radiation pattern usually are in the magnitude of the wavelength (&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$\lambda /2$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$\lambda /4$&lt;/span&gt; - but not &lt;span class=&quot;math-container&quot;&gt;$\lambda /10$&lt;/span&gt; or &lt;span class=&quot;math-container&quot;&gt;$\lambda /100$&lt;/span&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Therefore I won't expect a recognizable impact on radiation pattern for your application.&lt;/p&gt;&#xA;" OwnerUserId="15355" LastEditorUserId="15355" LastEditDate="2019-08-14T19:54:41.140" LastActivityDate="2019-08-14T19:54:41.140" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15132" PostTypeId="1" AcceptedAnswerId="15146" CreationDate="2019-08-14T18:20:07.270" Score="2" ViewCount="259" Body="&lt;p&gt;In my ongoing process of building up to a homebrewed general coverage receiver/transceiver, a first step might reasonably be a crystal set, where a tuned circuit and simple, or even improvised, rectifier extract enough power from the transmitted signal to power an earphone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Crystal radios usually can only receive strong local stations.  It occurred to me, however, that I'd gain a lot of sensitivity if I were to connect an RF amplifier stage between the antenna and the tuning RC circuit.  This would also let me test the RF stage of my future two-tube receiver in a way I don't have the instruments to do otherwise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this case, an untuned RF amp will just amount to making a small antenna do the job of a very long wire, and then some -- but the output of even a very basic RF amp will be far more power than an ordinary germanium detector needs.  Burning out the detector isn't desirable, obviously.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One way I can foresee to avoid destroying the detector diode is to use a different diode, with higher power tolerance -- after all, I don't need the very low forward voltage of a germanium part, since I'll have a signal measurable in volts, not microvolts (or millivolts after resonance boosts it a bit).  Am I correct in thinking nearly any rectifier part with suitable voltage ratings could be used as the detector in this kind of circuit?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-08-16T17:04:47.320" LastActivityDate="2019-08-18T01:11:05.543" Title="Will a &quot;crystal set&quot; work with an untuned RF amp stage?" Tags="&lt;receiver&gt;&lt;diy&gt;&lt;vacuum-tubes&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15133" PostTypeId="2" ParentId="15132" CreationDate="2019-08-14T18:45:34.597" Score="1" Body="&lt;p&gt;Many radios do include a preamp that amplifiers the RF signal coming from the antenna. However there are many issues to consider. A truly broad amplifier will not only amplifier the radio signal you want, it will also amplify noise and even other radio signals on other frequencies. Most preamps are therefore some what narrow in bandwidth and their tuning is part of the radio tuning. This is complicated and limits the usefulness of a preamp in most homebrew radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are also correct that if the output of the preamp is too high it can damage the next stage of your radio. A limiter is often need which again can get complicated. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="8717" LastEditDate="2019-08-14T19:33:11.723" LastActivityDate="2019-08-14T19:33:11.723" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15134" PostTypeId="2" ParentId="15132" CreationDate="2019-08-14T19:26:58.390" Score="2" Body="&lt;p&gt;A &lt;a href=&quot;http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=1N3409&quot; rel=&quot;nofollow noreferrer&quot;&gt;1N3409&lt;/a&gt; is a 39 volt Zener, completely unusable in a crystal radio (unless you are sitting at the base of the broadcast tower. ;-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Historically, 1N34 germanium diodes have been used because of the low voltage drop and therefore high sensitivity. They are a dime a dozen, so you can afford to blow up a lot of them.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-08-14T19:26:58.390" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15135" PostTypeId="1" CreationDate="2019-08-15T05:57:09.723" Score="0" ViewCount="77" Body="&lt;p&gt;gnuradio packetize using access code for start sync packet, but another example attach the preamblee, so what the differences preamble and access code ?&lt;/p&gt;&#xA;" OwnerUserId="15334" LastActivityDate="2019-08-15T05:57:09.723" Title="What the difference preamble and access code?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15137" PostTypeId="1" CreationDate="2019-08-15T16:41:29.980" Score="3" ViewCount="137" Body="&lt;p&gt;Assume that one does not have access to a multi-million-dollar RF anechoic chamber.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When testing an amateur radio HF or VHF antenna, how would one absolutely minimize the amount of any RF radiation from the feedline, tower, and/or any other parasitic elements, such as power supply cords, AC wiring, computer cables, gutters, or any other nearby antennas?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assume the antenna is (claimed to be) an imperfect dummy load, and you want to make sure the vast majority of any RF radiation is convincingly coming from the &lt;strike&gt;dummy load&lt;/strike&gt; antenna, and not elsewhere.  &lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-15T21:21:16.730" LastActivityDate="2019-09-06T21:17:31.207" Title="Antenna testing, minimizing feed-line radiation?" Tags="&lt;antenna&gt;&lt;feed-line&gt;&lt;testing&gt;" AnswerCount="3" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15138" PostTypeId="2" ParentId="15137" CreationDate="2019-08-15T17:36:35.120" Score="2" Body="&lt;p&gt;The proper mix of ferrite for your frequency of interest in a properly-designed common-mode current choke is your friend.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look no further than Jim Brown's latest PDF on this subject at &lt;a href=&quot;http://k9yc.com/publish.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;k9yc.com&lt;/a&gt; There is no better source of information anywhere else.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;strong&gt;&lt;a href=&quot;http://k9yc.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;RFI, Ferrites, and Common Mode Chokes For Hams&lt;/a&gt;&lt;/strong&gt;&#xA;  &lt;strong&gt;Most recent update April 2019.&lt;/strong&gt; &#xA;  This tutorial is directed specifically to RFI in ham radio applications. It includes an extended discussion of the use of common mode chokes in antenna systems and for suppression of RFI. A chapter on audio and computer interconnections in ham stations shows how to make bulletproof connections between a computer sound card and ham rigs for SSB, RTTY, PSK31, and SO2R contesting without expensive interface boxes, using nothing more than simple cables with the right connectors on each end. There's also a chapter on grounding and bonding.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Of course, the unun or balun would be mounted right at the antenna feedpoint; right where the power cord meets the power supply, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://k9yc.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://k9yc.com/RFI-Ham.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Also see &lt;a href=&quot;http://www.karinya.net/g3txq/chokes&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.karinya.net/g3txq/chokes&lt;/a&gt;. Although he recently passed away, his expertise lives on.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-08-27T20:10:05.817" LastActivityDate="2019-08-27T20:10:05.817" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15139" PostTypeId="2" ParentId="283" CreationDate="2019-08-15T19:29:42.410" Score="1" Body="&lt;p&gt;Need to get a few things out of the way to understand why some things are.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Velocity Factor - speed of a electromagnetic (EM) wave through ANY material.&lt;/li&gt;&#xA;&lt;li&gt;Frequency - Speed in Hz of a (EM) wave. 20Hz to 20kHz is Audio, 100kHz and above is considered Radio until nanometers then it's visible then on to other types. We are referring to RF.&lt;/li&gt;&#xA;&lt;li&gt;Antenna - item for receiving and transmitting an electromagnetic wave.&lt;/li&gt;&#xA;&lt;li&gt;Transmission Line/Coax - item to convey electromagnetic wave to/from antenna and radio.&lt;/li&gt;&#xA;&lt;li&gt;Skin Effect - the tendency of (EM) wave to migrate to the outside edge of a conductor.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;A. Velocity factor in antenna building does NOT matter unless &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;You are using coax or transmission line as part or all of the antenna. &lt;/li&gt;&#xA;&lt;li&gt;You are calculating an antenna for use under 50 MHz. &#xA;Only then does the velocity factor of the line need be known. And usually it is LESS than 1. This factors into the size of the antenna as well. Very important to those co-linear antennas everyone wants to build for the gain. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;B. Personally, use the L(feet)=234/f in MHz for 1/4 wave and 468/f in MHz for 1/2 wave antennas. &#xA;   This works for all antennas used to about 2 GHz, After that a gnat hair changes the tuned frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;C. An antenna that is broadband is NOT going to have a large amount of gain, and is better suited to receiving, i.e., scanner antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;D. An antenna that is narrow-banded can exhibit a large amount of gain, but operate in a narrower bandwidth. These are best suited for repeater antennas, as the repeater transmits on ONE frequency. Some can be engineered with electrical down-tilt to increase coverage below the horizon of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;E. An antenna uses tubing for two purposes, the first is fairly obvious, weight. A tube is much lighter than a solid rod of the same length and diameter. Tubing is usually the choice when building any antenna that has multiple elements usually a beam antenna and used in large single- and multi-band verticals. Wire for antennas can be found that uses a stronger inner core coated with a variety of materials to make it conduct better on the outside circumference making it ideally suited for long wire use.  &lt;/p&gt;&#xA;" OwnerUserId="15460" LastEditorUserId="76" LastEditDate="2019-09-04T00:56:24.357" LastActivityDate="2019-09-04T00:56:24.357" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15142" PostTypeId="1" CreationDate="2019-08-16T22:09:17.870" Score="1" ViewCount="1832" Body="&lt;p&gt;Approximately what frequency should my UHF Pi-Star be set on in the US? Is there a standard?&lt;/p&gt;&#xA;" OwnerUserId="15465" LastEditorUserId="4665" LastEditDate="2019-08-18T19:30:11.390" LastActivityDate="2019-08-22T09:11:06.750" Title="Frequency for UHF hot spot in the US" Tags="&lt;united-states&gt;&lt;d-star&gt;&lt;digital-voice&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15144" PostTypeId="2" ParentId="15129" CreationDate="2019-08-17T14:05:28.787" Score="4" Body="&lt;p&gt;Among other things, rain and cloud droplets interacting with each other causes a &lt;a href=&quot;https://www.corrosionpedia.com/definition/6248/voltage-gradient&quot; rel=&quot;nofollow noreferrer&quot;&gt;voltage gradient&lt;/a&gt; in the air, similar to the Kelvin water drop experiment explained &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Kelvin_water_dropper&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;http://amasci.com/emotor/kelvin.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;), with the earth being the lowest potential and increasing with height.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The noise on the highest antenna is because there is a corona (like &lt;a href=&quot;https://en.m.wikipedia.org/wiki/St._Elmo%27s_fire&quot; rel=&quot;nofollow noreferrer&quot;&gt;St. Elmo's fire&lt;/a&gt;) emanating from sharp points on that highest antenna -which is at ground potential- to the higher voltage gradient in the air.  Therefore, eliminating or covering those sharp points or edges will reduce or eliminate the corona noise. A &lt;em&gt;sharp point&lt;/em&gt; could be threads, the ends of metal tubing, or sharp edges. Ideally, the ends of the boom and elements would have metal spheres or insulating caps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But there's a better way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As W8JI points out in &lt;a href=&quot;https://www.w8ji.com/pecipitation_static.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;his page about precipitation static&lt;/a&gt;, there should be a sharp, grounded point above the highest antenna, like a &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Talk:Lightning_rod&quot; rel=&quot;nofollow noreferrer&quot;&gt;lightning rod&lt;/a&gt;. &#xA;Afraid that it will attract lightning? :&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;My physics teacher taught that if a lightning conductor actually did &quot;conduct&quot; a lightning strike then it would have failed in its job. Its job, he taught, was to prevent a strike from ever occurring by dissipating the charge in the atmosphere above the conductor, thereby causing the lightning to strike elsewhere. ...&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;It does dissipate the charge from the ground to the atmosphere. This is fact as current can be measured flowing up through the lightning rod to the atmosphere. Any current flow will reduce the potential difference between the ground and charges in the sky thus lessening the probability of a strike. This reduction in potential also will weaken any strike that does occur (not by much but it will weaken it none the less).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;TL;DR:&lt;/strong&gt; Put up a &quot;lightning rod&quot; above your highest antenna to eliminate the noise; that will now become your &quot;highest antenna&quot;.&#xA;&lt;hr&gt;&#xA;&lt;strong&gt;REF:&lt;/strong&gt; &lt;a href=&quot;https://physics.stackexchange.com/questions/65825/does-a-lightning-rod-prevent-lightning-strikes&quot;&gt;https://physics.stackexchange.com/questions/65825/does-a-lightning-rod-prevent-lightning-strikes&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-08-29T19:33:30.587" LastActivityDate="2019-08-29T19:33:30.587" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="15145" PostTypeId="2" ParentId="4938" CreationDate="2019-08-17T23:42:34.493" Score="1" Body="&lt;p&gt;Blocking the tx is actually very simple.&#xA;Remove the ptt button (from the outside) with a small narrow screwdriver.&#xA;Remove all tabs from the inside of the button&#xA;and put it back carefully.&#xA;Ready.&#xA;It's not necessary to open the baofeng in this way ...&lt;/p&gt;&#xA;" OwnerUserId="15471" LastActivityDate="2019-08-17T23:42:34.493" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15146" PostTypeId="2" ParentId="15132" CreationDate="2019-08-18T01:11:05.543" Score="0" Body="&lt;p&gt;After some additional thought, I recalled I'd seen designs for single-tube &quot;reflex&quot; radios, where the tube acts as both an RF amp and, after detection of the audio modulation, as the AF amp to provide enough gain to drive a speaker.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is actually the next step in the &quot;build up from simple to complex&quot; process I've set myself -- in my question, I was asking about this without the AF amplification (the audio signal would require an earphone, lacking enough power to drive a loudspeaker).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And when I searched for &quot;single tube reflex receiver&quot; I found this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hdwme.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hdwme.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A single tube receiver with a pentode RF amp (differing from the tube I intend to use mainly in filament voltage), albeit in a tuned RF configuration, and a 1N34 germanium diode detector.  Which answers my original question: yes, any diode with suitable ratings could be used, but the 1N34 family is &quot;tough enough&quot; to be used in a preamplified receiver and I needn't look further for a more suitable detector diode.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-08-18T01:11:05.543" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15147" PostTypeId="2" ParentId="15142" CreationDate="2019-08-18T19:27:40.777" Score="1" Body="&lt;p&gt;A web search revealed nothing, so I would suspect that there is no standard UHF frequency for D-STAR hot spots, in Kansas or anywhere else.  The &lt;a href=&quot;http://www.arrl.org/band-plan&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL Band Plan&lt;/a&gt; for the 70cm band reveals that 433&amp;ndash;435 MHz is for &quot;Auxiliary/repeater links&quot;, which seems like the category that hot spots would fall in.  Typical UHF/VHF channel spacing is 20 kHz, and you wouldn't want your signal to bleed into another channel outside the 433&amp;ndash;435 sub-band, so I'd pick a frequency somewhere in the range of 433.02&amp;ndash;434.98 Mhz, on a multiple of 20 kHz.  (433.02, 433.04, 433.06, ..., 434.94, 433.96, 433.98)  That gives quite a few possibilities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That advice is for the US.  You didn't ask about Canada, but just to make this a more complete answer I checked the &lt;a href=&quot;https://wp.rac.ca/432-mhz-70-cm-page/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RAC UHF band plan&lt;/a&gt;, which says that 433&amp;ndash;434.8 MHz is for digital modes, including links, and that the recommended channel spacing there is 25 kHz.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-08-18T19:27:40.777" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15148" PostTypeId="2" ParentId="15142" CreationDate="2019-08-19T03:59:25.617" Score="2" Body="&lt;p&gt;Given that it has been established that there is no 'standard', the main criteria for picking a frequency are:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Find a frequency where the mode you are using is permitted&lt;/li&gt;&#xA;&lt;li&gt;Find a frequency where you will not interfere with an existing user of the band&lt;/li&gt;&#xA;&lt;li&gt;Make sure you use as little power on your handheld as necessary to get into your hotspot. The hotspot is already probably only using around 10mW or similar, so it is not really the problem.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So the thing you are most worried about is that your handheld is going to be interfering with other users of the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would recommend finding a frequency in the 'digital modes' portion of the band, and see if there are any people already using it. If so, pick another, until you find one where your handheld transmitting on 500mW will not bother anyone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember to turn your handheld power down as low as it will go, while still being able to get into your hotspot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt; It should be obvious, but in case it isn't ... please avoid the part of any band that is allocated to satellite operation. Satellites are very low signal devices (due to power and size constraints), and so even a very low signal transmission can ruin someone's day if they are trying to communicate with a satellite.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2019-08-22T09:11:06.750" LastActivityDate="2019-08-22T09:11:06.750" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15149" PostTypeId="1" AcceptedAnswerId="15152" CreationDate="2019-08-19T09:01:23.403" Score="1" ViewCount="66" Body="&lt;p&gt;The question came up during a club event, and obviously we checked the regulations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;references:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.comreg.ie/publication-download/amateur-station-licence-guidelines&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;Amateur Station Licence Guidelines&quot; page 22&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;From this document the details in regards to required logbook keeping:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;dates of transmission;&lt;/li&gt;&#xA;&lt;li&gt;the times (in UTC standard time), during each day of the first and&#xA;last transmissions from the Station and changes made to the&#xA;frequency band, mode of emission or power;&lt;/li&gt;&#xA;&lt;li&gt;frequency band of transmission;&lt;/li&gt;&#xA;&lt;li&gt;mode of transmission;&lt;/li&gt;&#xA;&lt;li&gt;power level (dBW or W);&lt;/li&gt;&#xA;&lt;li&gt;initial calls (&quot;CQ&quot; calls) whether or not they are answered; and&lt;/li&gt;&#xA;&lt;li&gt;the call-sign of licensed Amateur Stations with which&#xA;communications have been established.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;All this is clear, except item 3.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question here is, what is meant by &quot;&lt;em&gt;frequency band of transmission&lt;/em&gt;&quot;&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the frequency, e.g. &quot;7.123 MHz&quot;&lt;/li&gt;&#xA;&lt;li&gt;the band, e.g. &quot;40m&quot;&lt;/li&gt;&#xA;&lt;li&gt;both the band and frequency, e.g. &quot;7.123 MHz 40m&quot;&lt;/li&gt;&#xA;&lt;li&gt;either the band or frequency, e.g. &quot;7.123 MHz&quot; |or| &quot;40m&quot;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;My question:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is &lt;strong&gt;&lt;em&gt;minimum&lt;/em&gt;&lt;/strong&gt; required here, in regards to &quot;&lt;em&gt;frequency band of&#xA;  transmission&lt;/em&gt;&quot; ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;In my own interpretation of this, I would believe the requirement is logging the &quot;band&quot; as the minimum requirement, e.g &quot;40 meter&quot; or &quot;40m&quot;&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="6079" LastEditorUserId="6079" LastEditDate="2019-08-19T09:53:52.733" LastActivityDate="2019-08-19T15:52:18.220" Title="What is the minimum legal requirement for logbook keeping in Ireland?" Tags="&lt;legal&gt;&lt;logging&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15151" PostTypeId="1" CreationDate="2019-08-19T13:12:45.353" Score="3" ViewCount="206" Body="&lt;p&gt;I was looking at some Stereo FM demodulators on the Internet, and I can't understand&#xA;the use of the complex to real block for demodulation of the L-R signal (DSBSC-AM)&#xA;which can be seen in different projects, for example:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/gnuradio/gnuradio/blob/master/gr-analog/python/analog/wfm_rcv_pll.py#L145-L147&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/gnuradio/gnuradio/blob/master/gr-analog/python/analog/wfm_rcv_pll.py#L145-L147&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://github.com/vsergeev/luaradio/blob/master/radio/composites/wbfmstereodemodulator.lua#L36-L39&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/vsergeev/luaradio/blob/master/radio/composites/wbfmstereodemodulator.lua#L36-L39&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;My (possibly flawed) understanding is that complex to real can be used here only because in both&#xA;cases there is a PLL which accurately tracks the phase.  Is this correct?  Because I also explored the gr-rds project, and I can't&#xA;understand how it works without a PLL block.  There were PLL blocks until&#xA;&lt;a href=&quot;https://github.com/bastibl/gr-rds/commit/2500f7ef926fc82e0b5e0b219931efac93cc864f?diff=unified&quot; rel=&quot;nofollow noreferrer&quot;&gt;this commit&lt;/a&gt;&#xA;but they were removed.  Another example is the&#xA;&lt;a href=&quot;https://github.com/vsergeev/luaradio/blob/master/radio/composites/ssbdemodulator.lua#L32&quot; rel=&quot;nofollow noreferrer&quot;&gt;luaradio SSB demodulator&lt;/a&gt;&#xA;which again uses complex to real without some type of carrier recovery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, my question is: what is the right way to demodulate a DSBSC-AM signal (with and without a pilot tone)&#xA;and how is the complex to real (not complex to magnitude) block able to do it, even without a PLL in the rds_rx flowgraph?&lt;/p&gt;&#xA;" OwnerUserId="10631" LastEditorUserId="10631" LastEditDate="2020-06-05T07:31:00.587" LastActivityDate="2020-06-05T07:31:00.587" Title="I/Q demodulation of DSBSC-AM signals" Tags="&lt;gnuradio&gt;&lt;am&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15152" PostTypeId="2" ParentId="15149" CreationDate="2019-08-19T15:32:35.247" Score="1" Body="&lt;p&gt;I'm neither from Ireland nor involved in legal issues, so please take this answer with a grain of salt.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;From the document you had linked I would argue that 'frequency band' can be referred to Annex A1.3 table 1 as that states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The &lt;code&gt;frequency bands&lt;/code&gt; &lt;code&gt;specified in Table 1&lt;/code&gt; below ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So it's something like:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;7100-7200 kHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;That corresponds also to my rf engineering point of view that a 'band' represents a frequency range and not a single frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But as long as an abbreviation is unambiguous my personal guess is that it should be ok as well.&lt;/p&gt;&#xA;" OwnerUserId="15355" LastEditorUserId="15355" LastEditDate="2019-08-19T15:52:18.220" LastActivityDate="2019-08-19T15:52:18.220" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15153" PostTypeId="2" ParentId="15142" CreationDate="2019-08-19T17:41:59.453" Score="0" Body="&lt;p&gt;Be in a legal band allowed by your license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Follow any band plan that has been published for your area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do not use a frequency that interferes with others. I want to emphasize this one. There have been reports of interference between hotspots and satellite links. Just because you don't hear anyone on the frequency this instant does not mean someone does't already use it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before I get a large number of comments, &quot;no one owns any frequency&quot;, that is true, but it is also true that you don't have to be a self center jerk believing you can interfere with others any time you feel like it. I'd like to think that most Amateur Radio operators are considerate. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2019-08-19T17:41:59.453" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15155" PostTypeId="1" AcceptedAnswerId="15156" CreationDate="2019-08-19T20:25:06.970" Score="2" ViewCount="111" Body="&lt;p&gt;I received a QSL card with the signal reports transposed, at least according to my log of the contact. He says I sent a 44 and that he sent a 55, but I wrote down the opposite in my log.&#xA;If I send a QSL card to him, should I just confirm his account of the exchange? Or should I just use the received/sent numbers as recorded in my log? Does it matter? Is it still a “good contact”? What’s the protocol here?&lt;/p&gt;&#xA;" OwnerUserId="15126" LastActivityDate="2019-08-19T21:17:06.393" Title="Received a QSL card with signal reports transposed. What to do?" Tags="&lt;qsl-card&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15156" PostTypeId="2" ParentId="15155" CreationDate="2019-08-19T21:17:06.393" Score="3" Body="&lt;p&gt;Regarding your question about whether it matters if the RS numbers in a QSL card you received match the numbers in your log, that's mainly up to you, unless you want to use the contact for something, like for DXCC credit or as part of a contest entry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most contest rules require that for you to get credit for the contact, you must correctly copy everything sent by the other station.  In a contest, if his log said that he sent a 55 report and your log reported that you copied 44, then you typically wouldn't get credit for the contact and might also lose points for the mistake.  In a phone contest almost everyone sends 100% 59 reports to simplify things, but newbies and stubborn holdouts still send real reports.  If you were sending in a contest entry, which is &lt;a href=&quot;https://ham.stackexchange.com/questions/6714/what-happens-if-a-station-did-not-submit-a-contest-log&quot;&gt;optional&lt;/a&gt;, your contest log would typically be sent in electronically long before a paper QSL card confirming a contact in the contest is received by snail mail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The DXCC program, on the other hand, doesn't care about the signal report in contacts submitted for DXCC credit.  Specifically, in the &lt;a href=&quot;http://www.arrl.org/dxcc-rules&quot; rel=&quot;nofollow noreferrer&quot;&gt;DXCC rules&lt;/a&gt;, rule #4 says, &quot;Confirmation data for two-way communications must include the call signs of both stations, the entity name as shown in the DXCC List, mode, date, time and band.&quot;  Note that the signal report isn't mentioned.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding whether you should send the RS numbers in your log or matching the QSL card you received, I think you should send the signal reports in your log, but that's just my opinion.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-08-19T21:17:06.393" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15157" PostTypeId="1" AcceptedAnswerId="15169" CreationDate="2019-08-20T05:18:43.080" Score="4" ViewCount="677" Body="&lt;p&gt;Exactly why does an RF output transistor fail if the SWR is bad ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it A because the impedance mismatch between the transmission line and the antenna results in maximum power not being transferred to the antenna but rather being converted to heat inside the transistor ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or is it B because the reflected AC current caused by the impedance mismatch from the antenna goes back into the transistor output somehow ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the answer is B, then what stops the output signal produced by the RF output transistor from going back into the transistor in the same way as the reflected signal caused by a bad SWR ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-08-27T21:59:03.977" LastActivityDate="2019-08-27T22:33:52.973" Title="Why does an RF Amplifier fail when the SWR is high?" Tags="&lt;antenna-theory&gt;&lt;electronics&gt;&lt;amplifier&gt;&lt;transmission-line&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15158" PostTypeId="1" CreationDate="2019-08-20T05:22:25.597" Score="1" ViewCount="439" Body="&lt;p&gt;The Maximum Power Transfer Theorem says that maximum power transfer occurs when the source impedance equals the load impedance, when the power transferred to the load is 50%, the other 50% being converted to heat inside the source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The output impedance of a transistor in an RF power amp is very low before it's converted to 50 ohms by the various matching networks in a transmitter, so how does that work?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="76" LastEditDate="2019-08-20T14:14:10.513" LastActivityDate="2019-08-21T19:29:50.513" Title="How does the Maximum Power Transfer Theorem relate to RF power amplifiers?" Tags="&lt;rf-power&gt;&lt;antenna-system&gt;&lt;electronics&gt;&lt;impedance-matching&gt;&lt;amplifier&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15159" PostTypeId="1" CreationDate="2019-08-20T06:00:34.060" Score="1" ViewCount="107" Body="&lt;p&gt;I have a meter that will analyze limited RF spectrum in my area. One frequency that keeps coming up is &lt;strong&gt;2.498 kHz&lt;/strong&gt;. An FCC site listed that as the frequency used to communicate with underground mines. Is that correct, and if so, why would it be in my neighborhood? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There were a series of repeating frequencies, I'll list the most prominent, and hopefully you can tell me what most likely are producing them: &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;2.502 GHz, &lt;/li&gt;&#xA;  &lt;li&gt;672 MHz, &lt;/li&gt;&#xA;  &lt;li&gt;640 and 624 MHz, &lt;/li&gt;&#xA;  &lt;li&gt;72 MHz, &lt;/li&gt;&#xA;  &lt;li&gt;2.623 MHz is a constant, &lt;/li&gt;&#xA;  &lt;li&gt;550 kHz is a constant at -30 dbm, &lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;then &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;159, &lt;/li&gt;&#xA;  &lt;li&gt;168,&lt;/li&gt;&#xA;  &lt;li&gt;172,&lt;/li&gt;&#xA;  &lt;li&gt;219,&lt;/li&gt;&#xA;  &lt;li&gt;378, and&lt;/li&gt;&#xA;  &lt;li&gt;471 kHz, all averaging -40 dBm. &lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's a limited piece of data, but even that seems like alot. What&#xA;     are these coming from, and especially, is that 2.498 kHz really for&#xA;     communicating with mines? Thanks for your help.&lt;/p&gt;&#xA;" OwnerUserId="15483" LastEditorUserId="4665" LastEditDate="2019-08-21T17:09:03.950" LastActivityDate="2019-08-21T17:09:03.950" Title="communication with underground mines?" Tags="&lt;frequency&gt;" AnswerCount="0" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="15162" PostTypeId="2" ParentId="15158" CreationDate="2019-08-20T14:13:13.437" Score="2" Body="&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Maximum_power_transfer_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;maximum power transfer theorem&lt;/a&gt; tells you &lt;strong&gt;how to design a load to extract the maximum possible power from a given source.&lt;/strong&gt; It does &lt;em&gt;not&lt;/em&gt; tell you that the source will survive this treatment, and it does not tell you &lt;strong&gt;how to best design a source given a load.&lt;/strong&gt; If you apply the maximum power transfer theorem to a typical solid-state RF transmitter, it will overheat (or reduce output to protect itself).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a radio transmitter or amplifier, we design the output to operate &lt;em&gt;efficiently&lt;/em&gt;, sending RF to the antenna and not heating itself up unnecessarily. A low impedance works fine for this purpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The maximum &lt;em&gt;practical&lt;/em&gt; power is achieved at the point where the transmitter has reached its heat-dissipation limit (would overheat) or its circuits can no longer deliver more current to the output (would distort).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;You may wonder: but don't we always make sure the antenna system is 50 Ω (or whatever impedance) everywhere? Aren't impedance mismatches really bad?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is true — everywhere but at the transmitter/amplifier output! What we want to avoid is &lt;em&gt;reflections that cause phase shifts&lt;/em&gt;. At the transmitter, there is not yet any length for the reflection to travel over, so there cannot be any phase shift. The output device is interacting instantaneously with (the matching network connected to) the 50 Ω line, and so the output can be designed as a &lt;a href=&quot;https://en.wikipedia.org/wiki/Lumped_element_model&quot; rel=&quot;nofollow noreferrer&quot;&gt;lumped circuit&lt;/a&gt; driving a 50 Ω resistive load without transmission-line effects.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Another point is that this reasoning does not apply to receivers. In receivers, the incoming signal has already been traveling when it gets to the antenna and there is no active device driving it. An impedance mismatch at any point in the entire free space→antenna→feed line→receiver system will reflect some of the signal back out, making the received signal that much weaker.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or, to say the same thing differently: &lt;strong&gt;the maximum power transfer theorem &lt;em&gt;does&lt;/em&gt; apply to receivers&lt;/strong&gt;, because your source (radio waves in free space) is unchangeable and so you match its impedance to extract as much signal power as possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Unless, I suppose, you're operating in an environment of &lt;em&gt;too much&lt;/em&gt; RF power, like some kind of RF-heating system or physics experiment. Then a deliberate mismatch could allow you to sample a calibrated fraction of the signal without overloading the receiver and without dissipating the RF in an attenuator.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-08-20T14:13:13.437" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15163" PostTypeId="2" ParentId="13120" CreationDate="2019-08-20T14:33:05.930" Score="0" Body="&lt;p&gt;A bowtie is in fact a full wave dipole so it's impedance&#xA;is very high which is why they require a 4 to 1 balun.&lt;/p&gt;&#xA;" OwnerUserId="15487" LastActivityDate="2019-08-20T14:33:05.930" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15164" PostTypeId="1" CreationDate="2019-08-20T16:17:55.553" Score="2" ViewCount="195" Body="&lt;p&gt;I would like to fetch the data transmitted by a specific radio station from &lt;a href=&quot;http://www.aprs-is.net/Connecting.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;APRS-IS.net servers&lt;/a&gt;. I've read the documentation on their site and it is not clear how you would do it, if you are fetching the data instead of transmitting it. It is mentioned to use a callsign and password, but I'm not sure where to get them from.&lt;/p&gt;&#xA;" OwnerUserId="15488" LastEditorUserId="15488" LastEditDate="2019-08-20T16:29:27.147" LastActivityDate="2019-11-16T07:29:44.570" Title="Fetching data from APRS-IS.net" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15165" PostTypeId="2" ParentId="15158" CreationDate="2019-08-20T17:08:28.757" Score="2" Body="&lt;p&gt;The objective of specifying a 50 ohm load isn't to generate maximum power per se. The transmitter is subject to damage from excessive current or voltage. The currents and voltages will depend on the attached load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the load is specified as 50 ohms then it's possible to calculate what will happen in the transmitter and design it such that the specified device can operate to its maximum potential while staying within it's ratings (thermal, voltage, and current). If the load isn't 50 ohms then the transmitter may have protection circuitry to reduce power, or it may simply self-destruct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the load could be anything, the design will have to be more conservative to accommodate the worst case without damage. This means either a more expensive and robust transistors, or reduced performance.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-08-20T17:08:28.757" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15166" PostTypeId="1" CreationDate="2019-08-21T02:29:38.070" Score="2" ViewCount="84" Body="&lt;p&gt;I have decided to build my own linear regulated power supply to provide the power for an upcoming build. Since I'm no pro, I was hoping I could get some feedback on my design before building it, just in case I made some catastrophic mistakes in my design or anything like that. Its pretty simple and based off the LM317 adjustable voltage regulator. Most of the schematic is based on the information found in the LM317 datasheet. The requirements I have for this build is a clean source of about 30VDC at the output. I did the calculations and came up with the details and design listed on the attached photo of the schematic. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anyone has a moment to look the schematic over for any mistakes or to give any feedback or criticisms of the design, I would be immensely grateful. Thanks&lt;img src=&quot;https://i.stack.imgur.com/Y2R3Y.jpg&quot; alt=&quot;![enter image description here&quot;&gt;]&lt;a href=&quot;https://i.stack.imgur.com/Y2R3Y.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;1&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15490" LastActivityDate="2019-08-21T02:29:38.070" Title="First linear power supply build - design questions" Tags="&lt;power-supply&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15167" PostTypeId="2" ParentId="15157" CreationDate="2019-08-21T03:03:50.390" Score="1" Body="&lt;p&gt;When there is a mismatch between the output stage and the antenna, a certain amount of power is reflected back to the transistor. As the mismatch becomes larger, so does the reflected power, and this generates heat in the transistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you put a large heatsink on the transistor, and keep liquid nitrogen circulating around the heatsink, you might be able to operate for an indefinite time with an infinite SWR, as the heat generated by the reflected power is being taken away by the heatsink surrounded by liquid nitrogen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The main problem with semiconductors in this scenario is that if you heat them up, their internal resistance goes down, which causes more current to flow for a given voltage (which in turn generates more heat, etc.). This can lead to thermal runaway, which itself usually results in the destruction of the transistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Related - see also this answer: &lt;a href=&quot;https://ham.stackexchange.com/questions/13344/why-are-vacuum-tubes-still-used-in-amateur-radios&quot;&gt;Why are vacuum tubes still used in amateur radios?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;To answer the question directly&lt;/strong&gt;, though: an RF transistor fails when the SWR is too high because it can not dissipate the heat generated by the reflected power, and this can cause the thermal breakdown of the transistor. Usually with a bang, and letting out the magic smoke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some radios have a heat sensor and shut down the PA stage when the PA transistors reach a threshold temperature.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-08-21T03:03:50.390" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="15169" PostTypeId="2" ParentId="15157" CreationDate="2019-08-21T16:07:14.703" Score="4" Body="&lt;p&gt;A high SWR implies the load impedance is significantly different from 50 ohms, violating the design specifications of the amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, there is power reflected in a feedline. But it's not this power per se that causes problems, it's simply that the impedance seen by the transmitter isn't the 50 ohms it was designed for. In other words, the transmitter can't tell the difference between reflected power and simply the wrong impedance connected directly at the antenna connector with no feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the design assumptions violated, all the design specifications (like not catching fire) are off the table. Excessive current may lead to overheating. Or there may be too much voltage across them leading to &lt;a href=&quot;https://www.vishay.com/docs/90160/an1005.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;avalanche breakdown&lt;/a&gt;. These are just examples: other failure modes are possible depending on the design of the amplifier.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-08-21T16:07:14.703" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15170" PostTypeId="2" ParentId="15157" CreationDate="2019-08-21T18:20:04.600" Score="2" Body="&lt;p&gt;I like to turn the question around.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why does a transmitter amplifier not burn up or fail?  There's power coming into the transmitter from the power supply.  Why doesn't it melt the transmitter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Well, some of that energy (power over some period of time) goes into warming up heat sinks and eventually the air around your locale.  But a transmitter isn't (designed as) a toaster or room heater.  It's designed as part of a system to radiate RF energy.  So a transmitter is designed for (a large fraction of) the energy to exit your locale as electromagnetic radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But a high SWR means a large portion of the power being sent up the feedline isn't being electromagnetically radiated.  Thus, energy has to be dissipated somewhere.  So, if the transmitter doesn't fold back the power level to below what the feedline and the heatsinks can radiate away, something will melt or otherwise stop functioning due to overheating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added: Alternatively the power reflected back by a high SWR can be reflected back up the transmission line by yet another impedance mismatch at the transmitter.  But that reflection will either increase the voltage or current at the reflection point, depending on the impedance mismatch. So again, you either dissipate, arc, or melt something.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, a non-resonant antenna system is a reactive load.  One thing about reactive systems is that they store energy.  If you pump more power into a reactive system than it dissipates, the system will store energy in the form of increasing voltages and/or currents across or within components.  If you keep on increasing voltages or currents without bound, eventually something will melt or arc over.  An antenna system with a nice low SWR and moderate resistance will radiate most of that energy away (as RF or heat), rather than turning the transmitter into a blown fuse.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-23T15:41:11.280" LastActivityDate="2019-08-23T15:41:11.280" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15171" PostTypeId="2" ParentId="15158" CreationDate="2019-08-21T19:29:50.513" Score="0" Body="&lt;p&gt;It's true that at maximum power transfer 50% of the power are lost to heat inside the source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However often maximum power &lt;strong&gt;efficiency&lt;/strong&gt; is intended instead of maximum power transfer to prevent overheating of the source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And maximum power efficiency is achieved by a low source resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;br&gt;&#xA;Some links concerning max power transfer / effiency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Maximum_power_transfer_theorem#Maximizing_power_transfer_versus_power_efficiency&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia - Maximizing power transfer versus power efficiency&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.allaboutcircuits.com/textbook/direct-current/chpt-10/maximum-power-transfer-theorem/&quot; rel=&quot;nofollow noreferrer&quot;&gt;allaboutcircuits - Maximum Power Doesn’t Mean Maximum Efficiency&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://electronics.stackexchange.com/questions/435140/contradictionmaximum-power-transfer-and-high-resistance-of-load&quot;&gt;electronics.stackexchange - answer from mkeith&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15355" LastActivityDate="2019-08-21T19:29:50.513" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15172" PostTypeId="1" CreationDate="2019-08-21T20:12:07.110" Score="1" ViewCount="1507" Body="&lt;p&gt;I'm searching the pinout of the Baofeng UV-9R to programm it with Chirp.&lt;/p&gt;&#xA;" OwnerUserId="15494" LastActivityDate="2019-08-21T20:39:38.783" Title="Baofeng UV-9R Chirp Pinout" Tags="&lt;baofeng&gt;&lt;radio-programming&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15173" PostTypeId="2" ParentId="15172" CreationDate="2019-08-21T20:12:07.110" Score="2" Body="&lt;p&gt;The Pinout is as in the following Picture:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SHmlv.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SHmlv.jpg&quot; alt=&quot;Baofeng UV-9R pinout photo&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used a cheap USB&amp;lt;-&gt;RS232 Adapter with 5V TTL voltage level.&#xA;In Chirp I used the UV-82WP Model. &lt;/p&gt;&#xA;" OwnerUserId="15494" LastEditorUserId="4665" LastEditDate="2019-08-21T20:39:38.783" LastActivityDate="2019-08-21T20:39:38.783" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15176" PostTypeId="1" CreationDate="2019-08-22T11:07:17.600" Score="1" ViewCount="375" Body="&lt;p&gt;I have a question, right before purchasing SDR for some tests:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Commercial hardware for bluetooth (even Ubertooth) allows you to receive packets on a 1MHz channel. Which practicaly means that if you, and the transmitter, are not listening to the same channel, you will not see the transmittion. pretty clear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions is this. if by the spec, for example USRP - can listen to 160MHz channel, does it mean it can listen in parellel and collect packets for more than one bluetooth channel?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If not, why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks Jen&lt;/p&gt;&#xA;" OwnerUserId="15500" LastActivityDate="2019-08-22T11:20:41.587" Title="Capturing Bluetooth / WiFi on an SDR" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;usrp&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15179" PostTypeId="1" CreationDate="2019-08-23T09:47:05.127" Score="1" ViewCount="57" Body="&lt;p&gt;I was trying to set up packet communication using examples in gr-digital/examples/uhd_packet_tx and rx. uhd_packet_tx is doing fine, but on receiver side(uhd_packet_rx) is freeze when i check up the dialog button(). What should i do for running this examples ? &lt;/p&gt;&#xA;" OwnerUserId="15334" LastEditorUserId="15334" LastEditDate="2019-08-23T10:13:02.793" LastActivityDate="2019-08-23T10:13:02.793" Title="uhd_packet_rx do not work" Tags="&lt;gnuradio&gt;&lt;usrp&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15181" PostTypeId="1" AcceptedAnswerId="15183" CreationDate="2019-08-23T19:12:37.850" Score="4" ViewCount="208" Body="&lt;p&gt;My 20 meter inverted vee dipole is fed with 56 feet of 50-ohm coax. The SWR measures 1.2 at the center of the band. According to &lt;a href=&quot;http://arrl.org/grounding&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://arrl.org/grounding&lt;/a&gt; a balanced antenna doesn't need a ground, so my transceiver is not grounded. I've read that an inverted vee lowers the 73 ohm dipole impedance closer to the 50-ohm coax impedance but connecting a coax unbalances the antenna, so I wanted also to test using a current choke balun. I studied &lt;a href=&quot;https://ham.stackexchange.com/questions/12395/how-to-determine-number-of-turns-for-a-11-balun&quot;&gt;How to determine number of turns for a 1:1 balun?&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Within that post, I found &lt;a href=&quot;https://ham.stackexchange.com/questions/1271/how-to-detect-common-mode-currents-or-rf-in-the-shack&quot;&gt;How to detect common-mode currents or “RF in the shack”?&lt;/a&gt;. I constructed a snap-on ferrite detector with analog meter. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/eb8yX.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eb8yX.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without any balun, the CM meter clipped on the coax near the output of the transceiver just barely deflected when transmitting. That was encouraging but I wanted to compare it using a choke balun. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I made a choke balun on a ferrite rod 3&quot; x 1/2&quot; (scavenged from a Hy-Gain 1:1 balun) by wrapping a bifilar winding of 12 turns of #16 magnet wire, each winding in series with a dipole element. I inserted this balun at the antenna feed point. The SWR measured about the same as without the balun, but this time the CM meter showed about 10 times more current than without the balun. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does that mean that the antenna doesn't need a choke balun, or the balun is not designed right, or both? Even if a wrong number of turns (I planned to test it empirically as Phil Frost suggested), I don't understand how it apparently &lt;strong&gt;increased&lt;/strong&gt; the common mode current. Could my testing be bogus because the transceiver is not grounded? (I don't have a ground rod installed yet to connect). I haven't had a chance to transmit to someone but the antenna receives distant signals well so it seems correct in that respect.&lt;/p&gt;&#xA;" OwnerUserId="15325" LastEditorUserId="15325" LastEditDate="2019-08-24T18:37:59.657" LastActivityDate="2019-08-24T18:37:59.657" Title="Dipole increased CM current using choke balun" Tags="&lt;electronics&gt;&lt;dipole&gt;&lt;balun&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15182" PostTypeId="2" ParentId="15157" CreationDate="2019-08-23T23:21:55.837" Score="1" Body="&lt;p&gt;When an amplifier of a fixed output impedance (50 ohms) is tuned for minimum VSWR into a load (your antenna), then maximum power is transferred from that device to be radiated into the ionosphere. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's assume that our RF amplifier feeding  our antenna (and in the interest of simplification is 100% efficient) has 5 volts applied to it, and the current is 20 amps. 5 * 20, that's 100 watts. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SWR is 1:1, so in this ideal amplifier there are 100 watts delivered to the antenna, and the RF power amplifier transistor doesn't get hot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(But, of course, in the real world, &lt;em&gt;there is no such thing as an RF amplifier device (either transistor or vacuum tube) that is 100% efficient&lt;/em&gt;. Therefore, those devices will get warm to some degree, even when perfectly matched at a 1:1 VSWR.)&#xA;&lt;hr&gt;&#xA;Now, suppose that we deliberately change things and mistune our antenna so that its feedpoint impedance is lower or higher than 50 ohms. &lt;/p&gt;&#xA;&#xA;&lt;p&gt; - Less power will be radiated by the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt; - The current through the output transistor &lt;em&gt;may&lt;/em&gt; change up or down slightly, but now more power will be dissipated in the transistor, making it hotter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt; - As we continue to detune our antenna, even less power will make it to the antenna and more power will be dissipated in the transistor. Eventually, so much power will heat up the device to the point where it is destroyed. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Higher SWR = less power to the antenna to be radiated into space = &lt;strong&gt;more power to heat up and destroy our device&lt;/strong&gt; .&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-08-27T22:33:52.973" LastActivityDate="2019-08-27T22:33:52.973" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15183" PostTypeId="2" ParentId="15181" CreationDate="2019-08-24T17:03:50.027" Score="4" Body="&lt;p&gt;I'm answering my own question after seemingly solving the problem, thanks to the helpful comments I received. Evidently, the ferrite rod core that I salvaged from a Hy-Gain balun was the culprit. I couldn't find any information on what kind of ferrite it is but it was manufactured about 30 years ago. I don't know much about baluns yet but earlier questions I had about that same stock Hy-Gain balun prompted me to post &lt;a href=&quot;https://ham.stackexchange.com/questions/14981/voltage-vs-current-balun-for-dipole&quot;&gt;Voltage vs. Current Balun for Dipole&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the solution is, I wound a new balun per info in &lt;a href=&quot;http://audiosystemsgroup.com/2018Cookbook.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://audiosystemsgroup.com/2018Cookbook.pdf&lt;/a&gt;. Although the document says to use a 2.4&quot; #31 torroid core, I had a 1.4&quot; #43 core so I wound it with #20 wire just to test if it would work. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/Mevza.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Mevza.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;Now there is no increase in common mode current as was measured before, and the SWR is only 0.1 higher than without the balun, so I think this qualifies as solved. Hopefully this post can somehow help others with similar questions.&lt;/p&gt;&#xA;" OwnerUserId="15325" LastActivityDate="2019-08-24T17:03:50.027" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15184" PostTypeId="2" ParentId="15181" CreationDate="2019-08-24T18:19:26.247" Score="1" Body="&lt;p&gt;You might want to try a choke balun on the coax itself, as the outside of the shield  of the coax can couple to the antenna even if the currents on your wound wire pair or internal to the coax are balanced.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-08-24T18:19:26.247" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15185" PostTypeId="2" ParentId="11638" CreationDate="2019-08-25T00:31:52.837" Score="4" Body="&lt;p&gt;The normal answer is no.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is one exception however, in that if the Foundation holder is directly &quot;operating under the supervision of a Full Licence holder&quot;.  See Clause 7, para 2.76 and 2.77 of Ofcom's &quot;Guidance for licensees&quot; document.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find this document at: &lt;a href=&quot;https://www.ofcom.org.uk/__data/assets/pdf_file/0026/82637/amateur_radio_licence_guidance_for_licensees.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Guidance for licensees&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14873" LastActivityDate="2019-08-25T00:31:52.837" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15187" PostTypeId="2" ParentId="15066" CreationDate="2019-08-25T07:21:56.687" Score="5" Body="&lt;p&gt;You have mixed up the characteristic impedance of a coaxial cable with the DC impedance measured from a piece of that cable. So I'll tell you what you measured and then what you could have done instead.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;First of all, I have no idea what does it mean to measure a&#xA;capacitance with a multimeter when you have connected both&#xA;measurement leads to the same piece of wire. Probably your multimeter doesn't know either and that's why you got the wildy swinging numbers. Capacitance is a measure&#xA;of how much electric charge (electrons) is stored in a capacitor. If&#xA;you would have a bit of ripple in any voltage, this charge could be&#xA;used to &quot;even out&quot; the variations. If you measure the capacitance between the inner and outer wire, it would be more useful. I would forget your measurement&#xA;results completely.&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The inductance measurement already makes more sense: it tells you how&#xA;strongly anything (your cable in this case) fights against the&#xA;current from changing. Again, inductance can be useful in a filter. Longer cable means more inductance. In your measurement, probably a great deal of measured inductance is created by the fact that the measurement leads form a loop. If you repeat the &quot;L outer&quot; measurement and start turning the cable in all kinds of crazy shapes, you'll get much higher inductances.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The resistance you have measured tells us about the losses in your&#xA;circuit. It basically tells you how much is the voltage loss along&#xA;the cable if a known current goes through the cable. If you have a longer cable, there will be more losses.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So that's what you measured, and I'm sorry to say but all of that was nonsense. When we are talking about characteristic impedance of a coaxial cable, we mean the ratio of current going along the wire and the voltage between the inner and outer conductor. Although the wire has impedance of &lt;span class=&quot;math-container&quot;&gt;$75 \Omega$&lt;/span&gt;, this doesn't say anything about losses. As others have pointed out, you can measure the capacitance per unit length and the inductance per unit length and then calculate the characteristic impedance of the cable from &lt;span class=&quot;math-container&quot;&gt;$Z=\sqrt{L/C}$&lt;/span&gt;, but the multimeter accuracy is just not enough.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;What is the 75 ohm meaning (written at the the cable shield)?&lt;/strong&gt; The characteristic impedance is a property of the raw cable that tells you the ratio of voltage and current of a wave travelling through the cable.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;What is those two impedance meaning to the antenna?&lt;/strong&gt; In this case (I assume you have a commercial satellite TV dish antenna) the only importance is that all components in the chain must have the same impedance: the antenna has been &quot;matched&quot; so that the output impedance is &lt;span class=&quot;math-container&quot;&gt;$75 \Omega$&lt;/span&gt;, your cable is &lt;span class=&quot;math-container&quot;&gt;$75 \Omega$&lt;/span&gt;, and finally the actual receiver is designed so that it works best when it sees &lt;span class=&quot;math-container&quot;&gt;$75 \Omega$&lt;/span&gt; impedance. Changes in impedance mean that power is reflected (and then lost).&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;If we got data in real cable, what to do to match the impedance?&lt;/strong&gt; You can trust the impedance written in the cable jacket. You don't match impedance of the cable, you must match the impedance of the antenna as seen through the cable. If you can measure the actual impedance (at RF frequency, not multimeter) of the system of antenna and cable, maybe you can ask a new question on how to match that to &lt;span class=&quot;math-container&quot;&gt;$75 \Omega$&lt;/span&gt; or &lt;span class=&quot;math-container&quot;&gt;$50 \Omega$&lt;/span&gt; (or what ever impedance you choose to use in your system).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="194" LastActivityDate="2019-08-25T07:21:56.687" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15188" PostTypeId="1" AcceptedAnswerId="15189" CreationDate="2019-08-25T10:37:12.197" Score="3" ViewCount="158" Body="&lt;p&gt;I've designed a two element UHF cubical quad. It was designed to resonate at 385 Mhz. I used 0.1mm thick and 1cm wide copper tape instead of wire to lower the antenna Q. I used PVC electrical conduit as a radome. Durapipe (ABS) would be better but i haven't that at hand.&#xA;I used a 50 to 90 ohm balun (two stage design: trifilar followed by a guanella, based on Jerry Sevick W2FMI design).&#xA;The transmission line to the balun uses two coaxial cables (using only the center conductor to make the loop legs, the shield is connect on the balun side to the center tap of the guanella). This feedline design part is experimental.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The analysis results are promising but the resonance is way off. (405 MHz instead of 380 and then a near perfect SWR at 460 MHz) the driven element loop is 0.79m long. I know that lowest SWR and resonance are not always matched — frankly i don't know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I wonder what may be the cause.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;velocity factor issue ?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;balun related ? (i used two turns around 37 cores (61 material), which is VHF UHF optimized it seems)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;related to the conductor geometry (a copper tape)?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;related to measure (done on a wood table inside a building) ?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;the experimental transmission line made of coax ?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;a mix of all these factors ?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Any ideas? I have not tested the balun itself on two 50 ohm dummy loads yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Schematic of the balun and antenna pics attached.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pMrwP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pMrwP.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/pAnay.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pAnay.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/rW4mD.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rW4mD.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13081" LastEditorUserId="76" LastEditDate="2019-08-25T16:20:28.623" LastActivityDate="2019-08-25T20:43:58.760" Title="UHF cubical quad VNA analysis interpretation" Tags="&lt;antenna-construction&gt;&lt;balun&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15189" PostTypeId="2" ParentId="15188" CreationDate="2019-08-25T17:59:07.047" Score="5" Body="&lt;p&gt;&lt;strong&gt;1. You need to re-think your balun&lt;/strong&gt;.&lt;br&gt;&#xA;At UHF we don't use toroids and wire, it's always done with transmission lines of varying impedance, on PCB or maybe thin coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are transformers for UHF, mini-circuits sells them, but they're tiny - the cores are say 2 x 4 mm and the wires hair-thin. Power handling is 0.25 Watts.&#xA;Here's a photo/rendering - the pads are at 0.1&quot; pitch:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/TWtzU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TWtzU.png&quot; alt=&quot;minicircuits&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;Remember 433 MHz is at least 20 times HF frequencies, so you need to scale the balun down 20 times. Yours doesn't look small enough.&#xA;With microstrip you can make a balun or transformer for hundreds of watts. &lt;a href=&quot;https://www.mwrf.com/active-components/what-techniques-boost-pa-efficiency&quot; rel=&quot;nofollow noreferrer&quot;&gt;This link&lt;/a&gt; has tons of photos of microwave and UHF stripline impedance matching.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can measure your balun separately. Does your VNA have two ports?&lt;br&gt;&#xA;Two 50-ohm coaxes make a valid 100-ohm transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;2. You should measure the impedance right at the feedpoint&lt;/strong&gt;.&lt;br&gt;&#xA;Solder an SMA-F directly at the feed.&lt;br&gt;&#xA;Make a thin SMA test lead (say RG316 or RG174), with a very effective choke balun: the last metre completely covered with small beads (say 12 mm long, 7 mm OD 3.5 mm ID, material 43 or 46).&lt;br&gt;&#xA;Calibrate your VNA, connect the cable.&lt;br&gt;&#xA;Now short out the SMA with a screwdriver and adjust the port extension to get a nice small ball on the left of the chart. Now you can see your feed impedance alone.&lt;br&gt;&#xA;Here's a photo of a VNA with a port extension to achieve a (very good) short circuit:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/VhZxM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VhZxM.png&quot; alt=&quot;vna&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;(from &lt;a href=&quot;http://www.eryptick.net/unisold/loop.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this very relevant article about measuring impedance of loops&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;By the way, unless you have done a port extension like this, it's meaningless to talk about the impedance, resonance, etc - the only valid quantity is reflection magnitude, or SWR. An unknown length of cable &quot;winds up&quot; the impedance on the Smith chart, so you can't actually say if it's high or low, capacitive or inductive. This obsession with &quot;resonance&quot; on a test instrument at the end of a cable.... /rant&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;3. Measure outdoors&lt;/strong&gt;&lt;br&gt;&#xA;At UHF the reflections from the room will spoil the measurement.&#xA;Try two things:&lt;br&gt;&#xA;- Run your hand down the RF cable (at the VNA end) to see if the SWR changes. It should be stable, indicating that the balun is working.&#xA;- Also, wave the antenna around, and observe the fast-moving wrinkles run down the SWR chart. These are from reflections in the environment. They give you an idea of the size of the error they're causing, and also an idea of the gain of the antenna. Bring it close to a metal sheet and look at what happens.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;4. 10 mm copper tape isn't particularly fat.&lt;/strong&gt;&lt;br&gt;&#xA;At 380 MHz, 25 mm diameter copper pipe would be considered fat. The effective diameter of your copper tape is only a few mm, so you could stick with wire.&lt;br&gt;&#xA;But the impedance bandwidth and gain bandwidth of a yagi or quad is usually not dominated by the self-impedance bandwidth of the feed. The Yagi combination has a narrower bandwidth than its parts, so don't overthink the wire fatness. Put another way, amateurs use 2 mm wire to make quads, at a 20 times lower frequency, and achieve reasonable bandwidth...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck, and come back and ask more questions as you go along.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-08-25T20:43:58.760" LastActivityDate="2019-08-25T20:43:58.760" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15190" PostTypeId="1" CreationDate="2019-08-26T01:47:48.390" Score="3" ViewCount="506" Body="&lt;p&gt;I previously asked a &lt;a href=&quot;https://ham.stackexchange.com/questions/15104/what-does-a-receivers-noise-reduction-function-do&quot;&gt;general question about noise reduction&lt;/a&gt;, but none of the answers mentioned this specific method or algorithm.  (the noise reduction button on some radios and DSP software seems to enable spectral subtraction, rather than just blanking, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does Spectral Subtraction reduce noise in receiver audio?  Why does this method or algorithm of noise &lt;strong&gt;reduction&lt;/strong&gt; possibly create the problem of (reportedly) &lt;strong&gt;adding&lt;/strong&gt; musical noise?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-26T13:57:28.820" LastActivityDate="2019-08-26T13:57:28.820" Title="What is Spectral Subtraction for noise reduction?" Tags="&lt;noise&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15191" PostTypeId="2" ParentId="15190" CreationDate="2019-08-26T02:54:41.070" Score="5" Body="&lt;p&gt;From &lt;a href=&quot;https://link.springer.com/chapter/10.1007/978-3-322-92773-6_9&quot; rel=&quot;noreferrer&quot;&gt;https://link.springer.com/chapter/10.1007/978-3-322-92773-6_9&lt;/a&gt; :&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;em&gt;Spectral subtraction&lt;/em&gt; is a method for restoration of the power or the magnitude spectrum of a signal observed in additive noise, through subtraction of an estimate of the average noise spectrum from the noisy signal spectrum. The noise spectrum is estimated, and updated, from the periods when the signal is absent and only the noise is present.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The assumption is that the noise is a stationary or a slowly varying process, and that the noise spectrum does not change significantly in-between the update periods. For restoration of time-domain signals, an estimate of the instantaneous magnitude spectrum is combined with the phase of the noisy signal, and then transformed via an inverse discrete Fourier transform to the time domain. In terms of computational complexity spectral subtraction is relatively inexpensive.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-08-26T02:54:41.070" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15192" PostTypeId="1" AcceptedAnswerId="15200" CreationDate="2019-08-26T04:49:40.987" Score="2" ViewCount="273" Body="&lt;p&gt;I'm reading about using software-defined radio for picking up ADS-B signals at 1090MHz. There is &lt;a href=&quot;http://adsbfilter.blogspot.com/2015/01/make-your-ads-b-reception-even-better.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this blog&lt;/a&gt; which considers (among others) a setup as follows:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Antenna -&amp;gt; coax -&amp;gt; low noise amplifier (LNA) -&amp;gt; filter -&amp;gt; software-defined radio dongle&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;After that, it mentions swapping the LNA and the filter with the following note:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;At some point a very strong &quot;Blockers&quot; signals will push any LNA into the saturation where IMD products will be created spoiling the reception. To avoid that, the filter should be placed in front the LNA protecting the system from the unwanted signals leaving only the targeted signal. Such a filtered signal is then amplified in the chain. Both the LNA and filter are close to the receiver (indoor).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I found that &lt;em&gt;&quot;IMD products&quot;&lt;/em&gt; refers to &lt;a href=&quot;https://en.wikipedia.org/wiki/Intermodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;intermodulation&lt;/a&gt;, but the blog is not detailed enough to go into the circumstances under which this becomes an issue. Since they mention both options, I assume there is some trade-off going on, possibly based on some of the following factors (these are just factors I can think of, there may be more and these may not be factor after all):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;how well out of band signals are filtered out by the filter&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;how much the LNA amplifies in-band signals&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;initial signal to noise ratio&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;signal to noise ratio after the filter&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Which of these factors play a role, and what's the theory behind choosing between the one option over the other? I'm aware that one can simply try both and compare the results in any specific setup, but I'm really looking for the theoretical idea behind it.&lt;/p&gt;&#xA;" OwnerUserId="13385" LastActivityDate="2019-08-26T20:44:45.237" Title="Under what circumstances does intermodulation become an issue in a filter after LNA setup?" Tags="&lt;software-defined-radio&gt;&lt;amplifier&gt;&lt;filter&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15195" PostTypeId="2" ParentId="15192" CreationDate="2019-08-26T15:15:58.790" Score="2" Body="&lt;p&gt;I believe this blog post is trying to show the evolution of a good setup, rather than present a number of equally appropriate setups.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might want to first read &lt;a href=&quot;https://ham.stackexchange.com/q/9832/218&quot;&gt;How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming the LNA is good enough to justify using, you want to:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;minimize losses between the LNA and the antenna, and&lt;/li&gt;&#xA;&lt;li&gt;keep the LNA as linear as possible.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Two the first point, this means putting the LNA at the antenna so you don't have the loss from a long coax run between the antenna and the LNA introducing noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually the filter would then be between the LNA and the antenna. By reducing the power going into the LNA that isn't even in the band you care about, the LNA can operate in a more linear region. Theoretically it's possible with a really terrible filter and a really good LNA that the filter would introduce more noise than it would eliminate distortion, but in practice if you're using filters and amplifiers of comparable quality it's always better to filter first.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-08-26T15:15:58.790" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15196" PostTypeId="1" AcceptedAnswerId="16150" CreationDate="2019-08-26T15:44:49.137" Score="1" ViewCount="78" Body="&lt;p&gt;I was reading these lecture slides: &lt;a href=&quot;https://web.mit.edu/6.02/www/f2006/handouts/Lec9.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://web.mit.edu/6.02/www/f2006/handouts/Lec9.pdf&lt;/a&gt;&#xA;and I tried to implement some of the schematics shown there in GNU Radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On page 3 the author describes how using a single LO is suboptimal, because in the worst case, when the transmitter's and the receiver's LOs are orthogonal, the output will be zero. I implemented this in the following flowgraph: &lt;a href=&quot;https://gist.github.com/ardavast/45b3fa0fb6e8ee9f3489a15a732549a9&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://gist.github.com/ardavast/45b3fa0fb6e8ee9f3489a15a732549a9&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/i3C1r.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/i3C1r.png&quot; alt=&quot;lo.grc&quot;&gt;&lt;/a&gt;&#xA;It behaves as expected, if I move the sliders so that the phase difference is &lt;span class=&quot;math-container&quot;&gt;$\pm \frac{\pi}{2}$&lt;/span&gt; the output is zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After that, on page 10, there is an explanation on how this can be prevented by using quadrature signals. I implemented this one too: &lt;a href=&quot;https://gist.github.com/ardavast/f1c2f0296382bbc005e72ee034117e6a&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://gist.github.com/ardavast/f1c2f0296382bbc005e72ee034117e6a&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/7ZO9a.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7ZO9a.png&quot; alt=&quot;loiq.grc&quot;&gt;&lt;/a&gt;&#xA;After I start it, I move the rx_phase slider to about 1.57 (&lt;span class=&quot;math-container&quot;&gt;$\approx \frac{\pi}{2}$&lt;/span&gt;) - this should make the rx_lo_i and rx_lo_q signals which are originally cos and sin, equal to, respectively, sin and -cos, exactly as shown in the diagram on page 10, the one on the right side. But contrary to what's written there, the signal vanishes completely, as in the single LO example. Where is the error in my flowgraph?&lt;/p&gt;&#xA;" OwnerUserId="10631" LastActivityDate="2020-02-23T17:21:19.903" Title="Error in an attempt to simulate SDR frontend hardware in GRC" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15197" PostTypeId="2" ParentId="15192" CreationDate="2019-08-26T16:47:33.613" Score="4" Body="&lt;p&gt;Simply put, the LNA amplifies everything that comes into it. If you think about it, it's actually kind of amazing. It's dragging its output value up and down in response to nanosecond-by-nanosecond changes in its input, reproducing signals at &lt;em&gt;every&lt;/em&gt; frequency up to its bandwidth limit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good amplifier is as linear as possible (meaning its output is precisely  proportional to its input) but nothing is perfectly linear, and non-linearities result in distortion. For our purposes, distortion means that part of the amplifier's response to an input signal will be on a different frequency from the input signal. Mainly we're interested in harmonic distortion (where output energy is present on multiples of the input frequency) and intermodulation distortion (where two different frequencies combine to make an output frequency that is the sum or difference of the input frequencies, or the sum or difference of multiples of the input frequencies).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Out of all of these distortion products of all of the signals coming into the amplifier, some of them will end up on the same frequency as the signal you're trying to receive. All of that junk constitutes noise, and we say that it's lowered the signal-to-noise ratio, or raised the noise floor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By filtering out frequencies that you're not interested in before they get to the amplifier, you're denying the amplifier the chance to amplify those signals, which means you're denying it the chance to create those distortion products, which means that most of what the amplifier outputs on your desired frequency will be what it &lt;em&gt;received&lt;/em&gt; on that frequency, and you will have an improved signal-to-noise ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the filter can't do anything at all about noise that's actually &lt;em&gt;received by the antenna&lt;/em&gt; at 1090MHz; no amount of magic will remove that. What it's doing is decreasing the amount of noise that's &lt;em&gt;added to the system&lt;/em&gt; by imperfections in the amplifier. When this noise reduction is greater than the signal reduction, your SNR improves and you get more decoded signals.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2019-08-26T20:44:45.237" LastActivityDate="2019-08-26T20:44:45.237" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15198" PostTypeId="1" CreationDate="2019-08-26T17:57:03.397" Score="1" ViewCount="205" Body="&lt;p&gt;Some transceivers come with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Phone_connector_(audio)&quot; rel=&quot;nofollow noreferrer&quot;&gt;TRS plug&lt;/a&gt; input labeled &quot;key&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When wiring my paddle or a straight key for these TRS connector inputs, is there any current standard for which key connection goes to which portion of the TRS? (tip, ring, or sleeve; left or right paddle closure; straight key closure).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or do I need to make custom cables or a patch board for each radio at which I might find myself operating?  (bring my own key + field day guest possibilities: Icom, Yaesu, Kenwood, Elecraft, et.al.)  Or do some of these radios have a (panel or software) selectable key input configuration setting?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/3572/wiring-a-cw-paddle/3574#3574&quot;&gt;This question&lt;/a&gt; only has an incomplete answer for only one model of radio.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2019-08-26T20:56:12.023" LastActivityDate="2019-08-26T20:56:12.023" Title="Wiring a CW paddle and straight key to a TRS connector?" Tags="&lt;cw&gt;&lt;wiring&gt;&lt;paddles&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15199" PostTypeId="2" ParentId="15198" CreationDate="2019-08-26T18:10:24.003" Score="3" Body="&lt;p&gt;The sleeve/shield contact is always &quot;common&quot; between the two switch contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't had extensive experience, but the two radios with key inputs I have used both had settings for whether tip and ring were dot and dash or vice versa (or if a straight key was connected, disabling the internal keyer). Note that this setting isn't just useful for compensating for lack of standards — it also means you can swap the &quot;handedness&quot; of a paddle to your preference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, if you're planning to use your key as a guest operator, it might make sense to have a hardware switch just so you can make it work the way you want without having to learn how the radio's settings menu works. A common DPDT toggle switch, suitably wired, will suffice to reverse the tip and ring connections — or you could have a box with two differently wired jacks and you plug a TRS-TRS cable into the appropriate jack.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-08-26T18:10:24.003" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15200" PostTypeId="2" ParentId="15192" CreationDate="2019-08-26T18:33:43.760" Score="2" Body="&lt;p&gt;I see two main factors about the options in the blog.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;IMD&lt;/li&gt;&#xA;&lt;li&gt;Noise figure&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Option 4 is just option 2 but for a considerable cable length along with distortions and recommending to put the filter after the cable. Which is a good point for that case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Option 1 is the basis as the blog discusses the application of a filter.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;From there we have:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;a) Amplifier -&gt; Filter&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Advantage: lower noise figure&lt;/li&gt;&#xA;&lt;li&gt;Disadvantage: IMD &lt;strong&gt;if&lt;/strong&gt; there are &lt;strong&gt;very strong&lt;/strong&gt; blockers  &lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;b) Filter -&gt; Amplifier&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Advantage: &lt;strong&gt;very strong&lt;/strong&gt; blockers don't impact the amplifier (&lt;strong&gt;if&lt;/strong&gt; they are present)&lt;/li&gt;&#xA;&lt;li&gt;Disadvantage: higher noise figure  &lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In receiving environments blockers usually are low power, that means &amp;lt;&amp;lt; 0 dBm (except you are located close to a high power transmitter). &lt;br&gt;&#xA;And I would expect most receiver amplifiers 1dB compression point to be &gt;10dBm.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The theory behind the noise figure is &lt;a href=&quot;https://en.wikipedia.org/wiki/Friis_formulas_for_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Friis formula for noise factor - Wikipedia&lt;/a&gt;, in a nutshell:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the 1st elements noise figure is the most important one and therefore should be as low as possible&lt;/li&gt;&#xA;&lt;li&gt;attenuation, like the insertion loss of a filter, is the same as noise figure&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The concern behind considering IMD is most likely &lt;a href=&quot;https://en.wikipedia.org/wiki/Third-order_intercept_point&quot; rel=&quot;nofollow noreferrer&quot;&gt;third Order Intermodulation - Wikipedia&lt;/a&gt;, in a nutshell:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Intermodulation causes unwanted additional frequencies&lt;/li&gt;&#xA;&lt;li&gt;The 3rd order products are more critical than the 2nd order products as they fall close to the intended frequency (e.g &lt;span class=&quot;math-container&quot;&gt;$2 * f_1 - f_2$&lt;/span&gt;) when they are nearby and therefore can't be filtered as easily as the 2nd order ones (e.g &lt;span class=&quot;math-container&quot;&gt;$f_1 + f_2$&lt;/span&gt;) .&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Concerning your points:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;blockquote&gt;&#xA;  &lt;p&gt;how well out of band signals are filtered out by the filter&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;When saturation is not of concern the filter/amplifier position has no impact on that item.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;blockquote&gt;&#xA;  &lt;p&gt;how much the LNA amplifies in-band signals&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;In the context of the blog I would say no. Because you can drive any single signal into saturation with enough amplification, but that's general and neither related to filter/amplifier positions nor discussed in the blog.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;blockquote&gt;&#xA;  &lt;p&gt;initial signal to noise ratio&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You can't impact that one, but you can receive lower signals with a lower noise figure in your setup.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;blockquote&gt;&#xA;  &lt;p&gt;signal to noise ratio after the filter&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Yes, to be able to receive low signals (from further away).&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;In summary:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;a) Amplifier -&gt; Filter&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For best reception of low signals (far away sources) due to the better noise figure&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;b) Filter -&gt; Amplifier&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Only &lt;strong&gt;if&lt;/strong&gt; there are &lt;strong&gt;very strong&lt;/strong&gt; blockers&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;When in doubt I would go with a) as strong blockers that actually drive a common amplifier into compression are rare and also as the applications (receiver behavior) that are very critical to IMD are not very common.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To note an actual case where IMD could be of concern is for example when you transmit at the same time in a nearby frequency, e.g. in a cellphone call, and the isolation is poor.&lt;/p&gt;&#xA;" OwnerUserId="15355" LastActivityDate="2019-08-26T18:33:43.760" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15201" PostTypeId="1" CreationDate="2019-08-26T18:41:35.007" Score="1" ViewCount="136" Body="&lt;p&gt;One of the things I need to do to put my Heathkit SB-102 into service is connect a microphone.  I've got a suitable crystal mic, with four conductors in the cable -- two for the mic element, and two for the Push To Talk (PTT) switch.  The PTT switch is to be connected to short one of the pins in the connector to the shell (chassis ground), which closes the transmit relay(s).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is identifying the unmarked pins in the radio's mic connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By examination of the circuit schematic, it appears one pin connects to the first stage voice amplifier; the other connects to the low B+ (300V DC).  When I test the pins with a voltmeter to the shell, however, I find around 30V on one, and no potential on the other.  I'm not savvy enough on electronics to be confident shorting either one to the chassis to check if it keys the transmitter; further, I don't see how that will do anything on the pin with no voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also don't have the original assembly manual, only the testing and operation section and schematic -- the manual would have told me which wire was which (I do have an SB-101 manual, this is likely to be the same on both, but I hadn't thought of that possibility until just now).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm pretty confident the low B+ isn't completely dead, as the set receives well.  How can I determine reliably which pin should get the PTT and which the mic element?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-08-26T19:11:03.330" LastActivityDate="2020-03-09T22:16:49.270" Title="How to identify the mic connection pins in Heathkit SB-102?" Tags="&lt;repair&gt;&lt;vacuum-tubes&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15204" PostTypeId="2" ParentId="11721" CreationDate="2019-08-27T16:45:00.477" Score="2" Body="&lt;p&gt;What you are looking for does not 100% exist yet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However there is something close to it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;AREDN  , Amateur Radio Emergency Data Network&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.arednmesh.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.arednmesh.org/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is mesh networking using Wifi protocol. Range is about 13 miles. It is under active development.   &lt;/p&gt;&#xA;" OwnerUserId="15538" LastActivityDate="2019-08-27T16:45:00.477" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15205" PostTypeId="1" AcceptedAnswerId="15208" CreationDate="2019-08-27T17:13:12.507" Score="1" ViewCount="61" Body="&lt;p&gt;In the below simple &lt;code&gt;qpsk_tx_uhd&lt;/code&gt; flowgraph I am trying to create a slider to control the number of samples but got a bit confused with which parameter I should be looking at: the &lt;code&gt;Num samples&lt;/code&gt; in the Random source block, the &lt;code&gt;Samples/symbol&lt;/code&gt; in the PSK block, or the &lt;code&gt;Number of points&lt;/code&gt; in the Constellation Sink block!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any help with this issue would be highly appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Flowgraph image:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/71y66.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/71y66.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15206" LastActivityDate="2019-08-27T20:27:22.563" Title="Controlling the number of samples" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15207" PostTypeId="1" CreationDate="2019-08-27T20:16:28.717" Score="2" ViewCount="114" Body="&lt;p&gt;Using a sensor and procedure discussed &lt;a href=&quot;https://www.hamradio.me/antennas/electrically-isolated-end-fed-center-fed-dipole-radiation.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;in my article&lt;/a&gt;, I made the following plot comparing the magnetic field strength along a 30m-band half-wave dipole fed at center and one end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.hamradio.me/wp-content/uploads/2019/06/center-fed_vs_end-feds_magfield.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://www.hamradio.me/wp-content/uploads/2019/06/center-fed_vs_end-feds_magfield.png&quot; alt=&quot;Measured magnetic field in vicinity of no-feedline end-fed and center-fed 10 MHz dipoles.&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Key points include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;No feed lines (just a small transmitter WiFi controlled)&lt;/li&gt;&#xA;&lt;li&gt;No wires to magnetic sensor (WiFi controlled)&lt;/li&gt;&#xA;&lt;li&gt;Center-fed has direct connection while the two end-fed variations have a transformer&lt;/li&gt;&#xA;&lt;li&gt;VSWR presented to transmitter is 1.5 or less&lt;/li&gt;&#xA;&lt;li&gt;Just a dipole hanging in free space (or as close as I could get for this test)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;More questions&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have I proven one can feed a dipole from its end without need for something to electrically &quot;push against&quot; such as a strategic counterpoise wire or the usual feedline? Or, as quite a few reviewers suggest, is the capacitive coupling to ground still a large player in making the end-fed case work? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I ask because I plan on repeating the experiment with the antenna much further away from ground to confirm what I think I'm seeing in the data and to ascertain the role of capacitive coupling to ground. Tips for the next test are welcome and appreciated.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastEditorUserId="4306" LastEditDate="2019-08-28T11:41:17.257" LastActivityDate="2019-08-29T17:39:03.280" Title="Do these magnetic field measurements of end-fed and center-fed half-wave dipoles corroborate measurements made by antenna experimenters?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;end-fed-antenna&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15208" PostTypeId="2" ParentId="15205" CreationDate="2019-08-27T20:27:22.563" Score="0" Body="&lt;p&gt;A digital modulator block takes &lt;em&gt;symbols&lt;/em&gt; (discrete digital values) and produces &lt;em&gt;samples&lt;/em&gt; (of an RF signal). Therefore, if you want to transmit, say, 1000 samples, and you have 2 samples/symbol set in your modulator, you must feed 1000/2 = 500 values into the modulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Change your Random Source block so that its number of samples (values) is the number of samples you want divided by the modulator's samples/symbol setting. You will also need to change the random source's “Repeat” option to &quot;No&quot;, otherwise it will repeat those samples forever.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-08-27T20:27:22.563" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15210" PostTypeId="1" AcceptedAnswerId="15223" CreationDate="2019-08-27T22:28:14.980" Score="1" ViewCount="125" Body="&lt;p&gt;Will the bandwidth be doubled ?&#xA;And will the impedance be halved ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-08-27T22:45:52.587" LastActivityDate="2019-09-03T02:48:27.607" Title="If I parallel two crystal filters together, will that double the bandwidth?" Tags="&lt;electronics&gt;&lt;transceiver&gt;&lt;filter&gt;&lt;bandwidth&gt;" AnswerCount="2" CommentCount="1" ClosedDate="2019-09-04T13:01:35.303" ContentLicense="CC BY-SA 4.0" />
  <row Id="15211" PostTypeId="2" ParentId="7008" CreationDate="2019-08-28T01:01:00.883" Score="-1" Body="&lt;p&gt;The places where such a rig might be useful are in emergency areas with civil strife, wildfires, post storm ravaged landscapes. Of course this assumes the residents of the broadcast area would have receivers as well.  Using such a setup might help in directing crowds to safety, to food and shelter, or other concerns re: public safety.... all for at most a couple of weeks.&lt;/p&gt;&#xA;" OwnerUserId="15539" LastActivityDate="2019-08-28T01:01:00.883" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15212" PostTypeId="2" ParentId="15137" CreationDate="2019-08-28T01:39:34.617" Score="1" Body="&lt;p&gt;I'm breaking your question into the two major parts within.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Antenna system&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;When testing an amateur radio HF or VHF antenna, how would one&#xA;  absolutely minimize the amount of any RF radiation from the feedline...&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I agree with Mike Waters about the judicious use of proper ferrites near the feedpoint and every 1/4 wave down the feedline to help quell any induction between feedline and antenna under test.&lt;/li&gt;&#xA;&lt;li&gt;Perform some sort of EiRP test using as small a transmitter as possible to simply eliminate any feedlines. Perhaps a small HT for VHF and a Tiny Tin assembly for HF. Yeah you still need a way to receive the power, but if you compare the test antenna with a reference dipole or equiv. the results are often quite revealing.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Parasitic conductors and dielectrics&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;...tower, and/or any other parasitic elements, such as power supply cords, AC&#xA;  wiring, computer cables, gutters, or any other nearby antennas?&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The goal here is to detune anything that might resonate at the frequency of interest. Ferrites often help with this. Sometimes the lengths are already non-resonate to mess with your goals and you might actually cause a resonance with a ferrite. Best if possible to remove these objects from the near field of the antenna or just test with them as part of your overall antenna &quot;system.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;It's what we do at the antenna lab&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Eliminating the feedline is job number one when we perform testing at work. The EiRP test, such as &lt;a href=&quot;https://www.hamradio.me/antennas/ht-antenna-comparisons.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one testing HT Antennas&lt;/a&gt;, is our favorite way to really see how things work without benefit of additional conductors. We get our fair share of snake oil antennas that completely rely on feedline radiation to work. Our test snags them and quick.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastActivityDate="2019-08-28T01:39:34.617" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15216" PostTypeId="1" AcceptedAnswerId="15218" CreationDate="2019-08-28T14:07:59.790" Score="4" ViewCount="155" Body="&lt;p&gt;I have designed PCB's in the past, but need to draw a constant 50 ohm impedance track on the project I'm planning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know the calculations for (for example) a coplanar wave and how to get a &lt;strong&gt;straight&lt;/strong&gt; PCB track around 50 ohms. (I can recommend the free &lt;a href=&quot;http://www.saturnpcb.com/pcb_toolkit/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Saturn PCB design software&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But how do I create a track that has 45/90 degree angles or something like this while keeping impedance fairly constant?&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ssD8l.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ssD8l.jpg&quot; alt=&quot;Constant impedance track&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using Diptrace, which does not support this by itself. The PCB above however is (at least) 25 years old, so I cannot imagine you absolutely &lt;em&gt;need&lt;/em&gt; state-of-the-art PCB layout software...&lt;/p&gt;&#xA;" OwnerUserId="8263" LastEditorUserId="8713" LastEditDate="2020-03-03T10:39:53.817" LastActivityDate="2020-03-03T10:39:53.817" Title="How to design constant impedance tracks on PCB?" Tags="&lt;diy&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15218" PostTypeId="2" ParentId="15216" CreationDate="2019-08-28T23:09:41.307" Score="6" Body="&lt;p&gt;Besides not knowing about the dimensions, substrate &lt;a href=&quot;https://en.wikipedia.org/wiki/Permittivity&quot; rel=&quot;noreferrer&quot;&gt;relative permittivity&lt;/a&gt; &lt;span class=&quot;math-container&quot;&gt;$e_r$&lt;/span&gt; and backside ground yes/no my guess from the picture is that the transmission line is a &lt;strong&gt;microstrip&lt;/strong&gt; line and not a &lt;strong&gt;coplanar&lt;/strong&gt; line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Front sides of the microstrip line printed circuit boards often also have ground metal, but that's for shielding or just practical etching reasons and does not impact the transversal electromagnetic wave mode. &lt;br&gt;&#xA;However just from the front side these may be mistaken as coplanar lines. I would always check the backside for that reason (still there is no definite prove, but another clue).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Anyway for both transmission lines at bends you get a parallel capacitance to ground due to the fringing fields causes by the sharp inner and outer edges. &lt;br&gt;&#xA;That capacitance can to be compensated by adding inductance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hHn7Y.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hHn7Y.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The compensating inductance can be achieved by a narrowed line, e.g. phase cutting the outer edge.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For &lt;strong&gt;microstrip&lt;/strong&gt; lines you can either simulate the compensated bend with e.g. &lt;a href=&quot;https://www.sonnetsoftware.com/products/lite/&quot; rel=&quot;noreferrer&quot;&gt;sonnet lite&lt;/a&gt; or calculate it with an approximation formula as given by e.g. &lt;a href=&quot;https://www.microwaves101.com/encyclopedias/mitered-bends&quot; rel=&quot;noreferrer&quot;&gt;Microwaves101 Mitered bends&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/09NUO.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/09NUO.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$D = W* \sqrt{2}$&lt;/span&gt; (the diagonal of a &quot;square&quot; miter)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$X= D* (0.52 + 0.65 e^{-1.35 * (W/H)})$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$A = ( X- D/2) * \sqrt{2}$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;W, H being width and height of the microstrip line.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For actual &lt;strong&gt;coplanar&lt;/strong&gt; lines the compensation is more complex as you have to make sure  the slot mode is not excited.&#xA;Here are two links describing such an option:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.semanticscholar.org/paper/Wire-Bond-Free-Technique-for-Right-Angle-Coplanar-Kim-Franklin-Drayton/5c4a9375fdf3b41291b3fa2756c5b64592aba7e7&quot; rel=&quot;noreferrer&quot;&gt;Wire-Bond Free Technique for Right-Angle Coplanar Waveguide Bend Structures&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.researchgate.net/publication/3355568_Coplanar_waveguide_bend_with_radial_compensation&quot; rel=&quot;noreferrer&quot;&gt;Coplanar waveguide bend with radial compensation&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For these I presume EM simulation is mandatory and you won't get good approximation formulas.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Finally, when there is enough area you can also form a wide radius circle segment to smoothly bend without having to compensate - for both lines. &lt;br&gt;&#xA;But that is often prevented due to cost and losses by the additional line length.&lt;/p&gt;&#xA;" OwnerUserId="15355" LastActivityDate="2019-08-28T23:09:41.307" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15221" PostTypeId="2" ParentId="7008" CreationDate="2019-08-29T11:49:16.740" Score="3" Body="&lt;p&gt;Please reconsider your weather balloon hoisting scheme, at least if you plan to use helium as your lifting gas.  Helium is a non-renewable resource derived from fossil fuel (natural gas wells are the only source).  It migrates through all materials light enough to make good balloons, and can't be recaptured even if the balloon is recovered before significant leakage has taken place -- and helium lost into the atmosphere is effectively gone forever, no longer available for no-substitute applications like chilling superconducting coils in MRI machines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can do the ground handling safely (requires care, but not at the level of rocket propellants), hydrogen will lift slightly more wire for the same balloon size, costs less than helium, and is renewable (commercially, it's made by electrolyzing water).  As a bonus, it's not a greenhouse gas (as methane, the other alternative lifting gas, is), nor is its combustion product (water vapor) a significant greenhouse factor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hydrogen can be purchased from industrial gas suppliers -- you local welding shop can order it.  It can also be made by a number of methods that predate wide use of electricity -- zinc dropped into acid produces hydrogen, and forcing steam past red hot iron will also produce the gas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Safe handling mainly revolves around ignition control -- hydrogen will ignite/explode at concentrations from 4% to 95% (as I recall) in air, so during hydrogen handling and generation, one must take similar precautions to working around natural gas leaks or similar flammable/explosive gases.  The good news is that hydrogen is so much lighter than air that leaked gas rises out of the work area very quickly.  Worth noting that German zeppelins were lifted by hydrogen from before WWI until almost WWII with few accidents (zeppelins were destroyed by gunfire with incendiary bullets, and there was the Hindenburg, but those weren't mainly hydrogen problems).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-08-29T16:34:53.333" LastActivityDate="2019-08-29T16:34:53.333" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15222" PostTypeId="2" ParentId="15207" CreationDate="2019-08-29T16:06:31.490" Score="2" Body="&lt;p&gt;It looks to be a well done experiment. We see a sinusoidal current distribution in either case, and the current tapers off to (approximately) zero at the ends. But this is what we'd expect of any standing wave on a wire of this length. Where its fed doesn't matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem with end-fed dipoles was never that they are impossible, but that they are &lt;em&gt;impractical&lt;/em&gt;. As you know, the impedance of a center-fed dipole is in the neighborhood of 75 ohms. To feed such a dipole &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;we will want a balun&lt;/a&gt;, with the objective of making the common-mode impedance much higher than the differential-mode impedance (75 ohms).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we can construct a balun with an impedance of say, 4000 ohms, then considering this impedance and the differential feedpoint impedance of 75 ohms as a voltage divider we can see most of the current will go to the differential mode and very little current will remain on the feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the feedpoint moves towards the end of the half-wave the differential feedpoint impedance becomes higher. We can see this in your experiment with the magnetic field decreasing. As this differential impedance becomes higher, the common-mode impedance of the balun becomes relatively smaller, and thus the choking less effective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not &lt;em&gt;impossible&lt;/em&gt; of course, but increasingly difficult. Of course one way to make the common mode impedance extremely high is to eliminate the feedline, as you've done in your experiment. Or one can simply accept the increased common mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your objective is to experimentally explore the consequences of an end-fed design, I'd suggest repeating the experiment with a &quot;feedline&quot; added to the feedpoint. The feedline can be a simple piece of wire, and you can include a current transformer on it to &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measure the common-mode current&lt;/a&gt; on it. Repeat the experiment with different feedline lengths (I suspect a quarter wavelength is especially interesting), and with and without a balun, and compare the results.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-08-29T17:39:03.280" LastActivityDate="2019-08-29T17:39:03.280" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15223" PostTypeId="2" ParentId="15210" CreationDate="2019-08-29T16:36:42.293" Score="3" Body="&lt;p&gt;As pointed out, the short answer is no. The Q value for the series resonance of a crystal can be calculated from &lt;span class=&quot;math-container&quot;&gt;$Q = \frac{2\pi f_s L_m}{r_m}$&lt;/span&gt;. Q value is of course related to the bandwidth: &lt;span class=&quot;math-container&quot;&gt;$Q = \frac{f_s}{BW}$&lt;/span&gt;. If you take the equivalent circuit for a crystal, add another similar next to it, and then simplify the circuit as far as you can, you can see that both &lt;span class=&quot;math-container&quot;&gt;$L_m$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$r_s$&lt;/span&gt; are halved and the &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; is not affected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/r5IBL.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/r5IBL.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="194" LastEditDate="2019-08-29T16:52:23.103" LastActivityDate="2019-08-29T16:52:23.103" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15224" PostTypeId="1" AcceptedAnswerId="15227" CreationDate="2019-08-29T17:09:50.043" Score="0" ViewCount="138" Body="&lt;p&gt;I have just changed from a ground mounted Vertical antenna , to a &lt;a href=&quot;https://www.mfjenterprises.com/Product.php?productid=MFJ-1796&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ-1796 Vertical antenna&lt;/a&gt;, due to not having big enough ground to bury as many verticals &#xA;as recommended. So far what I have found is on FT8 the incoming signals are from &#xA;the US as well as Western Europe … ie Spain , France , Italy etc., yet they never respond to my coming back to them. Since FT8 is low power usage , its not like the stations in Europe are using amps , so what gives ? One way propagation???&lt;/p&gt;&#xA;" OwnerUserId="15556" LastEditorUserId="8717" LastEditDate="2019-08-29T22:18:00.543" LastActivityDate="2019-08-29T22:18:00.543" Title="Vertical Antennas" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;vertical-antenna&gt;&lt;radial&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15225" PostTypeId="2" ParentId="15216" CreationDate="2019-08-29T17:23:50.713" Score="4" Body="&lt;p&gt;At 145/445MHz, things are not so hard. As a rule of thumb, anything under 1/10th of a wavelength doesn't even count as a transmission line. At 445MHz that's about 6.7cm. At 145 MHz, 21cm. Anything shorter than this length and you probably don't even need constant impedance traces.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do need such traces (or you just want to do things &quot;right&quot;), you can make mitered bends, like MagnusO_O suggests. But if your design software doesn't support that, you'd probably do just fine making &quot;gentle&quot; bends, with two 45-degree turns. At these low (by today's standards) frequencies you probably won't notice the difference.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-08-29T17:23:50.713" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15226" PostTypeId="1" CreationDate="2019-08-29T17:53:54.860" Score="8" ViewCount="251" Body="&lt;p&gt;I'd read that the current theory of how lightning rods protect a house, antenna tower, or other structure is by &lt;em&gt;preventing&lt;/em&gt; lightning from striking -- that is, the sharply pointed rod lets charge dissipate from the structure, so that it doesn't build up a potential opposite that of the cloud and attract strikes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've also read (in older references, mostly) that lightning rods attract lightning and actually &lt;em&gt;increase&lt;/em&gt; the risk of a strike, by offering a higher path for the stepped leader (and hence the main bolt) to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can easily see how either situation could be argued -- put up something to attract lightning and route the strike harmlessly to ground, or put up something that makes the strike less likely.  It's been well known for a couple hundred years that lightning rods do appear to protect structures where they're correctly installed.  What's the up to date theory on how?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="8717" LastEditDate="2019-08-29T19:25:21.080" LastActivityDate="2020-09-14T06:24:08.650" Title="Do lightning rods attract or do they help prevent lightning?" Tags="&lt;lightning&gt;&lt;safety&gt;&lt;equipment-protection&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15227" PostTypeId="2" ParentId="15224" CreationDate="2019-08-29T21:42:06.900" Score="6" Body="&lt;p&gt;First: do you know about &lt;a href=&quot;https://pskreporter.info&quot; rel=&quot;noreferrer&quot;&gt;pskreporter&lt;/a&gt;? You're &lt;a href=&quot;https://i.imgur.com/9DCnK49.png&quot; rel=&quot;noreferrer&quot;&gt;definitely getting heard, including one spot on 40m from New Zealand&lt;/a&gt;. Sometimes FT8 takes some patience, and it seems like no one wants to come back to you for long periods of time, but pskreporter can at least provide some reassurance that your equipment and the ionosphere are actually in working order.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, your antenna is dreadfully short. It's a multi-band &quot;half-wave&quot; vertical that's about 12 feet (4m) long. That's about 20% the length of a real half-wave for 40m, and 30% the length of a reasonable 4-band vertical (if you could imagine stacking two 4BTVs end-to-end to make a half wave and eliminate the need for radials, the contraption would be 43 feet tall). So it's not as efficient as it could be. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that want to stick with this antenna, you might want to try to maximize the efficiency as much as you can. Remove the 2m and 6m stubs if you don't use them. Tune meticulously for minimum SWR. Make sure that all connections are made firmly and free of oxidation. Use the best feedline you can get, and not a foot more of it than you need. Clear the space around the antenna of conductive objects as well as you can. Consider measuring the loading coils and seeing if you can wind better ones... you get the idea. Most of those changes are probably fractional-dB improvements, but enough of them &lt;em&gt;can&lt;/em&gt; make a noticeable improvement, and sometimes small reductions in loss have a surprising impact on shortened antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, I'd put my money on a ground-mounted vertical with &quot;not really enough&quot; radials still being a better performer than a 1796.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-08-29T21:42:06.900" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15228" PostTypeId="1" AcceptedAnswerId="15303" CreationDate="2019-08-30T05:58:37.080" Score="4" ViewCount="189" Body="&lt;p&gt;I am a licensed ham looking for a UHF/VHF handheld transceiver kit. Unfortunately so far I was only able to find broken links, i.e. Ten-Tec used to produce exactly such a thing but they just don't anymore. I'm looking for a kit, not a finished product. My search has not been successful so far.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there &lt;strong&gt;any&lt;/strong&gt; such kits in current production?&lt;/p&gt;&#xA;" OwnerUserId="10691" LastEditorUserId="76" LastEditDate="2019-08-31T15:13:24.080" LastActivityDate="2019-09-09T10:21:48.080" Title="Does a UHF/VHF handheld transceiver kit exist?" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;ht&gt;&lt;transceiver&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15230" PostTypeId="1" AcceptedAnswerId="15232" CreationDate="2019-08-31T01:29:23.647" Score="10" ViewCount="437" Body="&lt;p&gt;The ITU's International Morse Code recommendation &lt;a href=&quot;https://www.itu.int/rec/R-REC-M.1677-1-200910-I/&quot; rel=&quot;noreferrer&quot;&gt;ITU-R M.1677-1&lt;/a&gt; specifies a &quot;Full stop (period)&quot; as &quot;.−.−.−&quot;, however it falls short of specifying a decimal point. Even the examples, though they illustrate fractional numbers, don't show decimal usage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;ITU's Phonetic Alphabet and Figures regulations (&lt;a href=&quot;http://life.itu.int/radioclub/rr/ap14.pdf&quot; rel=&quot;noreferrer&quot;&gt;AP14&lt;/a&gt;), however, define a &quot;Decimal point&quot; and require it to be spoken as &quot;DAY-SEE-MAL&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What then is the decimal in Morse code, and where is it defined?&lt;/p&gt;&#xA;" OwnerUserId="14220" LastEditorUserId="4076" LastEditDate="2019-08-31T09:12:20.597" LastActivityDate="2019-09-02T21:00:04.363" Title="What is the decimal in Morse Code?" Tags="&lt;cw&gt;&lt;encoding&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15232" PostTypeId="2" ParentId="15230" CreationDate="2019-08-31T15:14:21.607" Score="10" Body="&lt;p&gt;In the &lt;a href=&quot;http://www.seasources.net/PDF/PUB102.pdf&quot; rel=&quot;noreferrer&quot;&gt;International Code of Signals&lt;/a&gt; (&lt;a href=&quot;https://en.wikipedia.org/wiki/International_Code_of_Signals&quot; rel=&quot;noreferrer&quot;&gt;an International system of maritime communication&lt;/a&gt;, including radiotelegraphy), AAA (over-bar) is designated for &lt;strong&gt;both&lt;/strong&gt; full stop and for decimal point.  (See flashing light procedure signaling, page 20.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-08-31T16:08:01.183" LastActivityDate="2019-08-31T16:08:01.183" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="15233" PostTypeId="1" CreationDate="2019-08-31T17:05:46.573" Score="2" ViewCount="136" Body="&lt;p&gt;I'm thinking about buying a 70' self supporting tower that I can see had a little rust here and there.  Besides minor rust is there anything I should ask the seller before I buy?  &lt;/p&gt;&#xA;" OwnerUserId="15550" LastActivityDate="2021-01-30T21:44:28.220" Title="Buying used tower" Tags="&lt;tower&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15234" PostTypeId="2" ParentId="15233" CreationDate="2019-08-31T17:50:23.007" Score="3" Body="&lt;p&gt;You should first ask &lt;em&gt;the manufacturer&lt;/em&gt;. They should be able to provide the all-important safety, erection, and guying information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Study the manual and relevant info first, which probably is available on the manufacturer's website.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-08-31T17:50:23.007" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15235" PostTypeId="1" CreationDate="2019-09-01T12:30:55.213" Score="2" ViewCount="824" Body="&lt;p&gt;I have a raspberry pi 3b on my roof (in a plastic box) with two SDR sticks attached to it.&#xA;On the raspberry pi the &quot;soapysdr&quot; program runs.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;root@antenne:/# lsusb &#xA;Bus 001 Device 005: ID 0bda:2838 Realtek Semiconductor Corp. RTL2838 DVB-T&#xA;Bus 001 Device 004: ID 0bda:2838 Realtek Semiconductor Corp. RTL2838 DVB-T&#xA;&#xA;root@antenne:/# rtl_fm -f 123M -d 1 | more&#xA;Found 2 device(s):&#xA;  0:  Realtek, RTL2838UHIDIR, SN: 00000001&#xA;  1:  Realtek, RTL2838UHIDIR, SN: &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Now from my laptop running GQRX, I can connect to the first SDR module attached to the rpi by using the following device string:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;soapy=0,driver=remote,remote:driver=rtlsdr&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;My question now is: how do I select the second device? (from within gqrx)&lt;/p&gt;&#xA;" OwnerUserId="15420" LastActivityDate="2019-09-01T12:42:02.840" Title="how to select an SDR stick remotely from gqrx via soapysdr" Tags="&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15236" PostTypeId="2" ParentId="15235" CreationDate="2019-09-01T12:42:02.840" Score="1" Body="&lt;p&gt;I was looking for days for an answer for this problem and then suddenly I realised it is quite simple:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use rtl_eeprom to give the the stick without serial a serial number:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rtl_eeprom -d 1 -s 66666666&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Then it is only a matter of adding &quot;,serial=66666666&quot; to the device string in gqrx:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;soapy=0,driver=remote,remote:driver=rtlsdr,serial=66666666&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="15420" LastActivityDate="2019-09-01T12:42:02.840" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15240" PostTypeId="1" AcceptedAnswerId="15241" CreationDate="2019-09-02T20:26:53.847" Score="0" ViewCount="98" Body="&lt;p&gt;I want to locate a small ball in the air 1000 times a second. The ball is thrown from the ground and then flies in the air for 0.5 seconds until it lands. Distance from the location instrument is 1 meter. I was thinking of a radio beacon inside the ball and 2 phased arrays on the ground. Is it possible to do? And if yes what signal should it be (sine?), what radio frequency should I use and what circuit should I use to generate the signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal should not necessarily be processed in real-time. Post-processing is also ok, but I do not know how high should be the sampling rate to make a phased array calculations in a software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My end goal is to detect where the ball lands before it moves again (rolls or bounces). An augmented reality game like &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Artillery_game&quot; rel=&quot;nofollow noreferrer&quot;&gt;an artillery game&lt;/a&gt; where a robotic gun fires a round pebble and based on the position of the hit the program changes the environment or just checks hit or miss. It is played somewhere in a park where wind and terrain are random. Round pebbles have low precision and launch from the barrel with a bit randomized direction, see paintball and air soft.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was also thinking about cameras but they are expensive for this high sampling rate frequency.&lt;/p&gt;&#xA;" OwnerUserId="15575" LastEditorUserId="15575" LastEditDate="2019-09-02T22:14:32.587" LastActivityDate="2019-09-03T17:15:19.610" Title="Locate a ball 1000 times a second" Tags="&lt;receiver&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15241" PostTypeId="2" ParentId="15240" CreationDate="2019-09-02T20:57:59.747" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I want to locate a small ball in the air 1000 times a second. The ball is thrown from the ground and then flies in the air for 0.5 seconds until it lands. Distance from the location instrument is 1 meter&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That probably means you're not satisfied with a range resolution of a couple meters – you need a much finer measurement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That means your system must have a very high bandwidth to allow for sufficient localization accuracy.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And if yes what signal should it be (sine?), &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;lol, no. A sine's foremost property is that it repeats – so you can't do location with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need a high-bandwidth signal that is as aperiodic as possible – white noise would be perfect, but there's technical and legal limits to how white noise can be.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;what radio frequency should I use&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You'd need to use a high frequency, because&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The higher the frequency, the smaller the antennas&lt;/li&gt;&#xA;&lt;li&gt;The higher the frequency, the easier it is to get a high bandwidth around that frequency&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;and what circuit should I use to generate the signal?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Since you'd need to produce a high-bandwidth signal that should be easy to detec by your receivers, probably a well-conditioned noise source, the legally required band filter, power supply … you're trying to build a very complex system! This question is HUGE!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That quickly becomes very complicated to build, even if you don't make your life unnecessarily hard by putting the transmitter (instead of a reflector) inside the ball.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd really rather want a monostatic or bistatic radar instead of a triangulating a transmitter, and a bit of target tracking.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Anyway, wrong technology at this point (there's excellent microwave radars in the 24 to 200 GHz range, but they are most certainly out of your price and complexity range, if you think image processing is hard).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a handful dollars you can get ultrasonic transducers. These are usually used for industrial ranging applications. Getting 1 kS/s for multiple receivers might be a challenge with the cheap boards you can get from China, but really, a megasample multi-channel receiver isn't that hard to build (compared to the radio system you were sketching).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;By the way, I'd heavily contest your &quot;1000 measurements per second&quot; number. That sounds &lt;em&gt;very&lt;/em&gt; unnecessary; the system you're observing is physically not able to change its state unpredictably 500 times per second, making this number of measurement unnecessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an engineer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're trying to solve something. Don't start that by finding a technology and then trying to roughly match the problem to it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, write down what you need to achieve. What is it that you want to achieve with that measurement? Is it predicting where the ball will land? Is it estimating side winds? Estimating irregularities in the ball's weight distribution? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From that follows which parameters you &lt;em&gt;actually&lt;/em&gt; care about – for example, in a windstill room with balls of known mass and air drag, you really only care about exit velocity and angle of the ball – the rest of the ball's trajectory is fully defined by these two parameters. No need to 1000s of measurements, at all!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a less well-isolated situation, you might need to figure out the parameters of a more complex physical model, and incorporate distortion and measurement noise. In any case, I really do not see your measurement requirement come out of that, anywhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Explicitly &lt;em&gt;deriving&lt;/em&gt; your measurement requirements is the first, &lt;strong&gt;necessary&lt;/strong&gt; step in system design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Based on that, you'd then sit down again and consider how you can estimate these parameters. That will make your system way, way, way easier than what you're planning to do now!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If dealing with uncertainty and disturbances, you'll want to track/update your estimation. There's many state modelling tools that are employed for such tasks – a classic would be the &lt;a href=&quot;http://www.bzarg.com/p/how-a-kalman-filter-works-in-pictures/&quot; rel=&quot;noreferrer&quot;&gt;Kalman Filter&lt;/a&gt;, which you'll see can work with very sparse updates and can predict complex trajectories from few noisy measurements.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-09-02T21:11:45.720" LastActivityDate="2019-09-02T21:11:45.720" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15242" PostTypeId="2" ParentId="15230" CreationDate="2019-09-02T21:00:04.363" Score="6" Body="&lt;p&gt;The web sites of &lt;a href=&quot;http://www.kent-engineers.com/abbreviations.htm&quot; rel=&quot;noreferrer&quot;&gt;Kent Morse Keys&lt;/a&gt; and of the &lt;a href=&quot;http://ac6v.com/morseaids.php#CW&quot; rel=&quot;noreferrer&quot;&gt;AC6V&lt;/a&gt; reference compendium document use of the Morse letter 'R' (dit-dah-dit) as an abbreviation for 'decimal point.' 'R' can have other meanings, of course, but I have used and heard it used to represent a decimal point in numbers - particularly when specifying a frequency - for 50 years.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-09-02T21:00:04.363" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15243" PostTypeId="1" CreationDate="2019-09-03T00:08:01.463" Score="0" ViewCount="70" Body="&lt;p&gt;I found the below uhd_two_tone_loopback example (which is one of the gnuradio provided examples) and I am trying to run it, it runs but I can't receive signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I mean when I run the program I cannot hear the audio tone at all. If I connect an audio sink to the TX side I hear the audio. But when the audio sink is connected to the output port of the USRP source I can't hear the audio tone. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, I have the b200 mini usrp and I am connecting the TX to the RX using an FW-10+ 10 dB attenuator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What could be the problem that I can't get the loop working? Thanks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Flowgraph:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MYczd.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MYczd.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15206" LastEditorUserId="15206" LastEditDate="2019-09-03T01:34:02.620" LastActivityDate="2019-09-03T01:34:02.620" Title="Gnuradio loopback flowgraph is not working" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15244" PostTypeId="2" ParentId="15210" CreationDate="2019-09-03T02:48:27.607" Score="1" Body="&lt;p&gt;The answer about bandwidth is &quot;not doubled, but not the same&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As demonstrated in a previous answer, Q of two identical crystals in parallel remains the same. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But BW of the  filter is determined not only by crystals' Q (unloaded Q) but also by generator and load impedances. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If those are &amp;lt;&amp;lt; than Rm (xtal series R at series resonance) then BW with 2 xtals is the same. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if &gt;&gt; then it tends to 2x because they are lowering the &quot;loaded Q&quot; of the filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are your design needs?&lt;/p&gt;&#xA;" OwnerUserId="15576" LastActivityDate="2019-09-03T02:48:27.607" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15246" PostTypeId="2" ParentId="9407" CreationDate="2019-09-03T09:54:44.487" Score="4" Body="&lt;p&gt;The effects of using unequal length buried radials on the radiation patterns of a monopole are not very significant, as shown by the NEC4.2 analysis below.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/kClrp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kClrp.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-09-03T09:54:44.487" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15248" PostTypeId="1" CreationDate="2019-09-03T14:28:14.427" Score="2" ViewCount="212" Body="&lt;p&gt;Resonance in electronic means: reactance of zero. (maybe wrongly/correctly someone's calling the minimum VSWR, the resonance of antenna! and this cause confusion)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've heard in Antenna Design for Mobile Devices book: &quot;If your antenna does not have good resonator then matching circuit will not really help&quot;. Or look at this question on stackexchange-ham : &quot;What is the best resonator in Yagi antennas?&quot;. I think they must say &quot;radiator&quot; instead of resonator! isn't that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the resonance is not important in hypothetical radiator if we have no limitation in value of feeding/source impedance. For example: Radiator con have any reactive/resistive impedance, who care about it, if our source have impedance conjugate to radiator impedance, since there is not reflection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But maybe the resistive impedance of radiator is physical characteristic of good radiator, but why? (and this is philosophy of calling the radiator, resonator!). Any idea about it? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or maybe this (resonators are equal to good radiator) is conflicting concept, because if we use conjugate of pure reactive radiator, all of energy will transfer and we then have no reflection, then all energy have to radiate, isn't that? (If this is really conflicting then the quote from &quot;Antenna Design for Mobile Devices&quot; from Zhijun Zhang must be wrong!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if we deny the equality, more confusion will occur, since in this manner everything can radiate in our band of interest efficiently, (through matched source/line) and there is no lambda/2 limitation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I need idea to stop being confused!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question in glance:&#xA;1.Is there a different between definition of resonance in electronic and antenna?&#xA;2.Is the resonance is the characteristic of good antenna? why?&#xA;3.If yes, then what will happen to the signal, that transferred to antenna completely, through conjugate matching? Since it have to radiate but you told it is not a good radiator, what's different.&#xA;4.Is radiating efficiently mean having no reflection from antenna?&lt;/p&gt;&#xA;" OwnerUserId="15580" LastEditorUserId="15580" LastEditDate="2019-09-03T15:18:09.750" LastActivityDate="2019-09-06T15:20:17.887" Title="resonance vs resonator in antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15250" PostTypeId="2" ParentId="15248" CreationDate="2019-09-03T18:24:05.207" Score="2" Body="&lt;p&gt;The word Resonator is used to mean the loading coil in a short vertical whip antenna, that makes it resonate at the frequency of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Hustler brand, for example, calls its coils resonators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know or any other meaning of a resonator in antennas. I've never heard of it in a yagi or other &quot;full size&quot; antenna. I would use *resonant circuit&quot; for anything made of discrete components. There is a Dielectric Resonator Oscillator in a satellite TV LNB, and it has a characteristic resonant circuit response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now for efficiency and matching of antennas, what matters is the amount of current you can drive into the &lt;em&gt;radiation resistance&lt;/em&gt; of the antenna. All the capacitive or inductive impedance just has to be cancelled out by a conjugate matching network, otherwise it reduces the current flow. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The matching components will have some loss, so if they can be kept as small as possible the antenna will be more efficient. Often, making the antenna the right size and shape will result in a radiation resistance closer to the driving impedance, making the matching circuit's job easier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, if you try to match a highly reactive antenna with another large reactance, the bandwidth of the antenna will be small. Again, an antenna with a smaller reactance to start with, will generally have a wider bandwidth when matched.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-09-03T18:24:05.207" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15251" PostTypeId="2" ParentId="15248" CreationDate="2019-09-03T22:12:24.097" Score="1" Body="&lt;p&gt;A &quot;resonator&quot; may be used in a &quot;resonant&quot; circuit. A resonator is a circuit; resonance is a condition that exists at the natural frequency of the resonator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to resonate, a resonator, whether it contains &quot;lumped&quot; circuit elements (e.g, resistors, capacitors, inductors, etc.) or distributed circuit elements (e.g., transmission lines, antennas, etc.) must comprise positive and negative reactances which cancel at the resonant frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, a simple &lt;em&gt;series&lt;/em&gt; resonant circuit comprises a capacitor (negative &lt;em&gt;reactance&lt;/em&gt;) and an inductor (positive &lt;em&gt;reactance&lt;/em&gt;) which resonates where the values of the capacitive and inductive reactances are equal and opposite, so they cancel to zero. At the resonant frequency, such a perfect circuit passes the input signal without attenuation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Conversely, a simple &lt;em&gt;parallel&lt;/em&gt; resonant circuit comprises a capacitor (positive &lt;em&gt;susceptance&lt;/em&gt;) and an inductor (negative &lt;em&gt;susceptance&lt;/em&gt;) which resonates where the values of the capacitive and inductive susceptances are equal and opposite, so they cancel to zero, equivalent to infinite reactance. At the resonant frequency, such a perfect circuit completely blocks the input signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some hams refer to the frequency at which an antenna system presents the lowest SWR to a transmitter as the antenna's resonant frequency. This is a colloquial generalization of the term. As indicated in the question, a &quot;resonator&quot; added to a non-resonant antenna will change the impedance measured at the driving point, but it can also change the current distribution on the radiator and the current induced in nearby objects (like ground, radials, vehicle body, etc.), which can effect efficiency and other parameters. Whether it produces &quot;resonance&quot; in the purest sense of the word is up to the discretion of the designer.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-09-06T15:20:17.887" LastActivityDate="2019-09-06T15:20:17.887" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15252" PostTypeId="2" ParentId="15226" CreationDate="2019-09-04T00:47:53.970" Score="-1" Body="&lt;p&gt;One of the best demonstrations, that I've seen anyway, of the effect of pointed &quot;air terminals&quot; begins at 17:25 of this rather old video...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=2sSqzLPMb4s&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=2sSqzLPMb4s&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The whole video is well worth the time as the demonstrations are very compelling, but your answer awaits at 18:04.&lt;/p&gt;&#xA;" OwnerUserId="4306" LastActivityDate="2019-09-04T00:47:53.970" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15253" PostTypeId="1" AcceptedAnswerId="15254" CreationDate="2019-09-04T01:29:16.590" Score="5" ViewCount="341" Body="&lt;p&gt;What is the algorithm or circuit needed to generate a (vintage?, retro?) crossed-ellipse display from RTTY and/or 2FSK signals?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(as per the (obsolete?) questions in some FCC exam pool)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(assume already down-converted from HF RF to either/or a baseband IQ data stream, or audible AFSK)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-04-29T17:33:24.160" Title="How is a crossed-ellipse display generated from FSK?" Tags="&lt;software-defined-radio&gt;&lt;rtty&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15254" PostTypeId="2" ParentId="15253" CreationDate="2019-09-04T03:14:41.417" Score="4" Body="&lt;p&gt;Judging by &lt;a href=&quot;http://blog.templaro.com/the-crossed-bananas-display/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this blog post from AI4SV&lt;/a&gt; and an inspection of the source code for fldigi (which supports such a scope in its RTTY mode), it's pretty simple — you just run the AF signal through two narrow filters at the mark and space frequencies (exactly as you would normally do when decoding RTTY), and then use the mark signal to drive the X axis and the space signal to drive the Y axis (or vice versa). You should AC-couple each signal (digitally, subtract it from a lowpassed version of itself) so that the display remains centered regardless of the signal strength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also downmix each signal, after filtering, to a lower frequency and use the downmixed signals to drive the scope axes. Fldigi does this, apparently as a digital convenience to make it so that there will be a whole number of ellipse-cycles per audio block / per display update, which makes the digital nature of the scope a little bit less obvious.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-09-04T03:14:41.417" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15255" PostTypeId="2" ParentId="15253" CreationDate="2019-09-04T03:17:14.733" Score="6" Body="&lt;p&gt;The display is simple:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Pass the incoming signal through two band-pass filters, one at the mark frequency and one at the space frequency.&lt;/li&gt;&#xA;&lt;li&gt;Use the two filters' output signals as the X and Y coordinates of the plot.&lt;/li&gt;&#xA;&lt;li&gt;(Since you are in the SDR domain:) Do as much as you want to make a nice-looking digital oscilloscope display of that signal. The simplest accurate way to do it is to keep a buffer of the last however-many filtered samples and draw them as dots (&lt;strong&gt;not&lt;/strong&gt; lines).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;If you had perfect signals and perfect filters, the display would not display ellipses but a straight line on one axis or the other. Since instead filters have roll-off, the signal is merely highly attenuated in the other axis, and an elliptical trace (for an input signal at a single frequency) results. The sharper your filters, the narrower the ellipses will be. The exact shape of the ellipse depends on the phase response of the filters (for example, an ellipse that is perfectly axis-aligned implies a 90° phase shift).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;crossed&quot; ellipses result from the modulated signal alternating between the mark and space frequencies and thus between the two possible displayed ellipses. A signal between the two frequencies will appear as a severely off-axis ellipse or a circle (because both filters are passing the signal), and one outside them will appear as an attenuated ellipse. Thus, you can tune a RTTY receiver by changing the receive frequency until the distinct horizontal and vertical ellipses appear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Disclaimer: I have neither used or implemented one. All of the details in this answer are based on reasoning from signal processing theory.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-04-29T17:33:24.160" LastActivityDate="2020-04-29T17:33:24.160" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15257" PostTypeId="1" AcceptedAnswerId="15258" CreationDate="2019-09-04T08:38:24.530" Score="4" ViewCount="385" Body="&lt;p&gt;Does an antenna tuner remove standing waves from a transmission line ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="11434" LastEditDate="2019-09-04T14:59:04.353" LastActivityDate="2019-09-04T14:59:04.353" Title="Does an antenna tuner remove standing waves from a transmission line?" Tags="&lt;transmission-line&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15258" PostTypeId="2" ParentId="15257" CreationDate="2019-09-04T10:59:19.380" Score="10" Body="&lt;p&gt;An antenna matching network (aka &quot;tuner&quot;) does not affect the conditions of the load (antenna) or the transmission line between the load and the matching network. The matching network transforms the impedance &quot;looking into&quot; the transmission line to a more desirable value, typically 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; for ham applications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the network manages to achieve such a &quot;perfect match,&quot; then there will be no standing waves on the transmission line between the transmitter and the matching network and there will be no additional mismatch loss in that line. This is the primary reason that &quot;remote tuners&quot; have gained some popularity in the marketplace. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-09-04T10:59:19.380" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15259" PostTypeId="1" CreationDate="2019-09-04T15:44:28.393" Score="4" ViewCount="172" Body="&lt;p&gt;Do resonant antennas actually resonate (in the lumped circuit sense, exchanging stored energy between inductive and capacitive elements at a natural oscillation frequency)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If so, can this resonance be observed directly?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;By adding wire between the inductive and capacitive portions of a short but resonant antenna (while adjusting things to keep the natural oscillation frequency the same), will that wire radiate stored energy as well as energy supplied by the transmitter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a high Q resonant antenna is &quot;hard keyed&quot;, say by a fast digital output, will the resonant impulse response radiate at that resonant frequency (and potentially harmonics) instead of just generating flat broadband noise?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If, say, a transmitter is tuned to near a high SWR band edge, after the transmitter is keyed off will the antenna continue to resonate and thus radiate, but closer to its true resonant frequency ?  e.g. will a high Q resonant antenna &quot;chirp&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And lastly, if SWR is measured carefully, will the SWR minimum be at the antenna system's self resonant or natural frequency of oscillation?  Or at some other slightly different frequency?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="1362" LastEditDate="2019-09-04T21:17:54.997" LastActivityDate="2019-09-05T12:03:59.657" Title="Do resonant antennas actually resonate?" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15260" PostTypeId="2" ParentId="15259" CreationDate="2019-09-04T16:21:12.663" Score="1" Body="&lt;p&gt;I've seen small devices that consist of a toroid with a few turns of wire around it and an LED, forming a loop wrapped on the toroid; these are slipped on the antenna and when transmitting, the LED lights where the antenna &lt;em&gt;at the point where the toroid rests&lt;/em&gt; has RF current, with brightness proportional to the current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This device can then be slid along an antenna to see what points along the conductor have higher and lower currents; on a center-fed half-wave dipole one can easily see the current peak at the feed point of the wire, and dropoff toward the end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fact that this high and low current region remains fixed on the antenna is demonstration that the RF forms a standing wave, which is an indicator of resonance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Resonance can be demonstrated other ways, but this simple little visual tool is one of the simplest and most striking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another confirmation of resonance is a measurement of RF voltage at the low-current point on the antenna -- which will exceed the voltage at the transmitter's final amplifier stage, possible only if the antenna system exhibits resonance.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-09-05T12:03:59.657" LastActivityDate="2019-09-05T12:03:59.657" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15261" PostTypeId="1" CreationDate="2019-09-04T17:50:31.137" Score="5" ViewCount="663" Body="&lt;p&gt;Last year, I planned to make a double-balanced mixer covering the entire 3-30 MHz band as an upconverter for my RTL-SDR receiver, mainly for learning RF circuits and ham radio. Naturally, it requires two RF transformers as baluns, possible 4:1 or 9:1 baluns.&lt;/p&gt;&#xA;&lt;p&gt;In the United States, it appears that Type 43 and Type 61 toroids are the most commonly used cores among the entire ham radio community. One can find a lot of existing designs and materials. Unfortunately, they are not widely available outside US. It seems unworthy to purchase some toroidals cores from the US via Digikey when the local industry at home has something to offer. Or so I thought.&lt;/p&gt;&#xA;&lt;p&gt;When I received some large toroidal cores, I realized I don't have any knowledge nor experience - a balun is much more difficult than I thought, a lot of electromagnetism terminology and tricky parameters to consider. I tried winding three baluns but it seemed none worked, and none of the rule-of-thumbs or spreadsheet calculator could help me because I wasn't using a well-known core. I didn't even have a signal generator to test it properly. So I finally abondoned the project and built a single-ended mixer instead, with poor LO rejection.&lt;/p&gt;&#xA;&lt;p&gt;I recently got a signal generator for my bench, and I regain the courage to try it again. Could anyone help me explaining my questions?&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The toroidal core manufacturer claims it's suitable for HF applications and provided tho following data:&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;Model&lt;/strong&gt;: NXO-40&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Outer diameter&lt;/strong&gt;: 31 mm&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Inner diameter&lt;/strong&gt;: 18 mm&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Height&lt;/strong&gt;: 7mm&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Initial permeability (&lt;span class=&quot;math-container&quot;&gt;$\mu_i$&lt;/span&gt;)&lt;/strong&gt;: 40 ± 20%&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Relative loss factor (&lt;span class=&quot;math-container&quot;&gt;$\tan \delta / \mu_{i}$&lt;/span&gt;)&lt;/strong&gt; : 8MHz, 92 (&lt;span class=&quot;math-container&quot;&gt;$\times 10^{-6}$&lt;/span&gt;)&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Temp. Coefficient (&lt;span class=&quot;math-container&quot;&gt;$\alpha_{\mu}$&lt;/span&gt;)&lt;/strong&gt;: 1200 (20-60 °C, &lt;span class=&quot;math-container&quot;&gt;$\times 10^{-6}$&lt;/span&gt; / °C)&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Curie Temperature (&lt;span class=&quot;math-container&quot;&gt;$T_{c}$&lt;/span&gt;)&lt;/strong&gt;: 300 °C&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Resistivity (&lt;span class=&quot;math-container&quot;&gt;$\rho$&lt;/span&gt;)&lt;/strong&gt;: &lt;span class=&quot;math-container&quot;&gt;$10 \times 10^6$&lt;/span&gt; Ω cm&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Saturation Flux Density (&lt;span class=&quot;math-container&quot;&gt;$B_s$&lt;/span&gt;)&lt;/strong&gt;: 290 mT&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Remanent Induction (&lt;span class=&quot;math-container&quot;&gt;$B_r$&lt;/span&gt;)&lt;/strong&gt;: 90 mT&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Coercive Force (&lt;span class=&quot;math-container&quot;&gt;$H_c$&lt;/span&gt;)&lt;/strong&gt;: 0.32 KA/m&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Applied Frequency (&lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt;)&lt;/strong&gt;: 40 MHz&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;What information can I learn from these parameters? Is it a good toroidal core to use for a HF receiver? A good balun for transmitters? What about using it as a EMI/RFI chock? A low-wattage 50 Hz power transformer?&lt;/p&gt;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;&lt;p&gt;It's common to characterize toroidal cores in terms of &lt;span class=&quot;math-container&quot;&gt;$A_{L}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$u_H$&lt;/span&gt;. What are they useful for (obviously, useful for calculating the inductance, but what purposes do it serve for RF transformers)? They are not given by the manufacturer, how can I calculate them from the known parameters of the core?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If I need to replace a toroidial core from an American design in the future, for example, FT37-43, which parameters should I look, and what calculations should I do to find an equivalent substitution?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What measurements can I take with an 100 MHz oscilloscope (w/ FFT) and a 10 MHz signal generator to test whether my balun is working as intended after I winded it?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Are there any resources for beginners like me to get started?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="15589" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-10-27T16:02:20.333" Title="How do I evaluate and use a toroidial core for my HF double-balanced mixer?" Tags="&lt;hf&gt;&lt;ferrite&gt;&lt;toroid&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15262" PostTypeId="1" CreationDate="2019-09-04T17:57:20.963" Score="8" ViewCount="3449" Body="&lt;p&gt;I found out a while back that, as things currently stand with the FCC, if you take and pass all three license class exams in the same sitting, you get a so-called &quot;two by two&quot; or 2x2 call -- two letter prefix, region/district number, and two letter suffix.  Regularly issued Technician and General licenses at this time are 2x3.  In the past, there have been times when call signs would change with license upgrades (for instance, when N was inserted in a Novice licensee's call, then replaced with the then-current second prefix letter when they upgraded), but upgrading to Extra class doesn't now, as far as I can see, result in snipping a letter out of your call.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also still possible to request a new call on license upgrade, though only Advanced (no longer offered, but still renewed) and Extra are eligible for 2x2 calls.  This will get a serially assigned call.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there's another way to get a 2x2 call: buy it (though apparently the FCC dropped the fees for vanity call applications).  Any licensee in the USA can apply for a so-called &quot;vanity&quot; call, which can be any currently valid (for their license class) format call not currently issued (1x2, 2x2, 2x1, 1x3, etc.).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which brings up the curiosity question: about what fraction of 2x2 call signs in the USA are vanity calls, as opposed to originally issued in that format?  Is this information even public?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-09-05T11:26:22.347" LastActivityDate="2019-09-06T19:48:14.867" Title="What fraction of 2x2 USA call signs are vanity calls?" Tags="&lt;united-states&gt;&lt;callsign&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15263" PostTypeId="2" ParentId="15259" CreationDate="2019-09-04T18:34:50.470" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;By adding wire between the inductive and capacitive portions of a short but resonant antenna (while adjusting things to keep the natural oscillation frequency the same), will that wire radiate stored energy as well as energy supplied by the transmitter?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, normally you don't have to add that wire, because you already have one and call it &quot;the antenna&quot;, and it's radiating. The antenna element might also be serving as the capacitive element at the same time. But yes. Keep in mind that even a &quot;high-Q&quot; transmitting antenna probably has a Q of around 500, which means that the oscillation has a decay time in the microseconds at HF. More reasonable antennas have a lower Q (an antenna's goal in life is to lose energy as radiation), so they ring-down even faster.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If, say, a transmitter is tuned to near a high SWR band edge, after the transmitter is keyed off will the antenna continue to resonate and thus radiate, but closer to its true resonant frequency ? e.g. will a high Q resonant antenna &quot;chirp&quot;?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I've never seen this demonstrated but I would assume so. Again, rapid decay makes it hard to spot, or to separate from the turn-off transient itself.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-09-04T18:34:50.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15264" PostTypeId="2" ParentId="15262" CreationDate="2019-09-04T19:17:14.850" Score="5" Body="&lt;p&gt;An amateur licensee of any class can request a vanity call sign.  Also, only Amateur Extra operators are eligible for 1x2 or 2x1 call signs; only Advanced and Amateur Extra operators are eligible for 2x2 call signs.  See &lt;a href=&quot;https://www.govinfo.gov/content/pkg/CFR-2018-title47-vol5/xml/CFR-2018-title47-vol5-sec97-19.xml&quot; rel=&quot;noreferrer&quot;&gt;US Title 47 CFR §97.19&lt;/a&gt; and the FCC's &lt;a href=&quot;https://www.fcc.gov/amateur-call-sign-systems&quot; rel=&quot;noreferrer&quot;&gt;Amateur Call Sign Systems&lt;/a&gt; page.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether a current call sign is sequentially-issued or vanity is easy to see in the FCC's Universal Licensing System (ULS) database: if the service is &quot;HA&quot;, the call sign was sequentially issued; if &quot;HV&quot;, it's a vanity call.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fraction of 2x2 call signs that are vanity is public information, since the ULS is public information.  To answer it would require downloading the entire database (instructions on how to do so are &lt;a href=&quot;https://www.fcc.gov/wireless/data/public-access-files-database-downloads&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;) and then analyzing the data.  Several organizations, such as qrz.com, have already downloaded the data, so you might ask one of them.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-09-04T19:17:14.850" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15265" PostTypeId="2" ParentId="15262" CreationDate="2019-09-04T22:38:08.733" Score="9" Body="&lt;p&gt;According to my calculations, about &lt;strong&gt;20%&lt;/strong&gt; of active 2x2 callsigns in the FCC's amateur radio service database are vanity callsigns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For comparison…&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;75% of active 1x2 ham licenses&lt;/li&gt;&#xA;&lt;li&gt;nearly 50% of active 2x1 licenses&lt;/li&gt;&#xA;&lt;li&gt;only 3.5% of active 2x3 licenses&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;…are vanity callsigns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you'd like to check my work or make further refinements, I determined these stats using a Python script available at &lt;a href=&quot;https://gist.github.com/natevw/3ddfe7aef454c345f68464048ad52ee2&quot; rel=&quot;noreferrer&quot;&gt;https://gist.github.com/natevw/3ddfe7aef454c345f68464048ad52ee2&lt;/a&gt; against the &lt;a href=&quot;ftp://wirelessftp.fcc.gov/pub/uls/complete/l_amat.zip&quot; rel=&quot;noreferrer&quot;&gt;ftp://wirelessftp.fcc.gov/pub/uls/complete/l_amat.zip&lt;/a&gt; file downloaded on 2019 September 4.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that as @rclocher3 points out in his answer, two of your question's premises regarding vanity callsigns are a bit off:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;em&gt;any&lt;/em&gt; class licensee can request a vanity callsign, not just General and Extra&lt;/li&gt;&#xA;&lt;li&gt;but only &lt;em&gt;Extra&lt;/em&gt; (or Advanced) class licensees can request most 2x2 callsigns&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The last point requires a bit of qualification: there are some regions like Alaska, Hawaii, and other US possessions which generate 2x2 patterns within &lt;strong&gt;Group C&lt;/strong&gt; and therefore would be available to Technician and General class — that said, unless I'm mistaken you &lt;em&gt;would&lt;/em&gt; need a mailing address within the region to be eligible. See &lt;a href=&quot;https://www.fcc.gov/amateur-call-sign-systems&quot; rel=&quot;noreferrer&quot;&gt;https://www.fcc.gov/amateur-call-sign-systems&lt;/a&gt; for more details of all the callsign groups corresponding to the license classes. (Note that the script used for the stats above does &lt;strong&gt;not&lt;/strong&gt; distinguish between callsign &lt;em&gt;groups&lt;/em&gt;, only the raw letter/number &lt;em&gt;pattern&lt;/em&gt;.)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2019-09-04T22:38:08.733" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15266" PostTypeId="2" ParentId="15259" CreationDate="2019-09-04T22:59:36.847" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;By adding wire between the inductive and capacitive portions of a short but resonant antenna (while adjusting things to keep the natural oscillation frequency the same), will that wire radiate stored energy as well as energy supplied by the transmitter?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That would be tricky, since the length of this wire would have non-zero length, and would be part of the antenna. Can another wire be added to an antenna, I suppose so. Does this somehow demonstrate the antenna resonating? Probably not any more than the antenna already does.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If a high Q resonant antenna is &quot;hard keyed&quot;, say by a fast digital output, will the resonant impulse response radiate at that resonant frequency (and potentially harmonics) instead of just generating flat broadband noise?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It sure will. You don't even need a fast digital output to perform this experiment: simply an antenna analyzer will do. If you generate a plot of return loss over frequency, you will see some frequencies are absorbed by the antenna because that energy is radiated, while other frequencies are reflected by the antenna. What happens to the reflected energy depends on the source, if it's a 50 ohm source then all that energy is dissipated in the source impedance and feedline losses.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If, say, a transmitter is tuned to near a high SWR band edge, after the transmitter is keyed off will the antenna continue to resonate and thus radiate, but closer to its true resonant frequency ? e.g. will a high Q resonant antenna &quot;chirp&quot;?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes. Q is &lt;em&gt;by definition&lt;/em&gt; proportional to the ratio of energy stored to energy dissipated per cycle. If the Q is non-zero, some of the energy must &lt;em&gt;not&lt;/em&gt; be dissipated in one cycle. Since there is no other place for the energy to go, it must necessarily make another cycle, with each cycle having diminishing amplitude.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And lastly, if SWR is measured carefully, will the SWR minimum be at the antenna system's self resonant or natural frequency of oscillation? Or at some other slightly different frequency?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not necessarily: the SWR is at a minimum where the magnitude of the reflection coefficient is at a minimum, which might occur at an impedance with a nonzero reactantance, which is by definition not the resonant frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference is evident if the antenna impedance is plotted on a Smith chart, such as this example from &lt;a href=&quot;https://www.semanticscholar.org/paper/A-wideband-printed-dipole-antenna-with-optimized-Vasiliadis-Vaitsopoulos/3c8cbce79907d21e83a5e605ec57fd82048d2b54&quot; rel=&quot;nofollow noreferrer&quot;&gt;A wideband printed dipole antenna with optimized tapered feeding balun for ISM and FWA bands&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ci9hF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ci9hF.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The minimum SWR points are where the curves are closest to the center of the chart, whereas the resonant points are where the curves pass through the horizontal center line. In some cases (like the solid line on the right) they appear to be nearly the same. In others they appear to be very different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, a perfect match is exactly (50+0j) ohms, so any antenna that achieves a perfect match must necessarily do so at a point of resonance. But any antenna with a less than perfect minimum SWR has some potential for resonance and minimum SWR to be at difference frequencies.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-09-04T22:59:36.847" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15267" PostTypeId="2" ParentId="15262" CreationDate="2019-09-04T23:15:46.017" Score="4" Body="&lt;p&gt;natevw has already answered the primary question, but there are some secondary points in your question to address.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although passing the Extra exam doesn't immediately grant you a new call, you do become eligible to request a new one, which will be a 2x2 and sequentially allocated just as it would be for a first-time ham that tested straight to Extra.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible to request a new call if you move to a &lt;a href=&quot;https://www.fcc.gov/amateur-call-sign-systems&quot; rel=&quot;nofollow noreferrer&quot;&gt;region subject to a different numbering scheme&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the past this was mandatory, but now it's optional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, vanity calls are now free. The FCC determined they spent more money administering the fees than they made from them, so they just dropped the fee.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-09-04T23:15:46.017" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15268" PostTypeId="1" CreationDate="2019-09-04T23:30:37.937" Score="1" ViewCount="444" Body="&lt;p&gt;Around my location, there is an odd signal near 50.145MHz (at this moment it seems centered around 50.14735MHz but that changes as the day progresses).  Other amateur radio operators in this city also hear it; apparently it started about a year ago.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am curious where it is coming from but do not have equipment for 6m fox-hunting.  There was something written once about using existing web-SDR stations to triangulate signals.  Is such a thing really practical?  If so, how would one go about doing that?&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2019-09-05T00:21:59.177" Title="Is there a practical way to triangulate a signal?" Tags="&lt;fox-hunt&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15269" PostTypeId="2" ParentId="15268" CreationDate="2019-09-05T00:21:59.177" Score="3" Body="&lt;p&gt;I suppose that a very rough estimate of the general location of the transmitter could be made by comparing signal strengths of several receivers with omnidirectional antennas without knowing exact details of the antenna systems of the receivers, but the estimate will be very approximate.  That's not a very practical technique.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A better technique is to have several fixed stations point directional antennas at the transmitter as best they can, and then triangulate.  However this technique can be fooled by reflections, interference, etc., and it's still not exact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to locate a transmitter is to use &quot;fox hunting&quot; techniques with a portable antenna, a portable receiver, and other such equipment.  (An attenuator can be a great help.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-09-05T00:21:59.177" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15273" PostTypeId="1" CreationDate="2019-09-05T09:58:15.027" Score="0" ViewCount="109" Body="&lt;p&gt;I am wondering if I can use &lt;a href=&quot;https://www.hepsiburada.com/gob2c-usb-2-0-mini-dijital-dvb-t-hdtv-uzaktan-kumanda-p-HBV00000LDJXT?magaza=GOB2C%20Global&quot; rel=&quot;nofollow noreferrer&quot;&gt;that&lt;/a&gt; dvb-t device to listen 48-836 mhz?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/C8uDP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/C8uDP.png&quot; alt=&quot;product&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/M5wXg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/M5wXg.png&quot; alt=&quot;frequence&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;if it's no, why?&#xA;thanks..&lt;/p&gt;&#xA;" OwnerUserId="15596" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-09-05T16:30:12.800" Title="Using dvb-t device as rtl-sdr" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15276" PostTypeId="1" CreationDate="2019-09-05T12:20:26.403" Score="2" ViewCount="120" Body="&lt;p&gt;This is a rather common belief among amateur radio operators, but is it true?  A NEC analysis provides some insight on this concept.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-09-05T21:45:12.620" LastActivityDate="2019-09-05T21:45:12.620" Title="Do Buried Radials for Vertical Monopoles Need to be No Longer than the Monopole Itself?" Tags="&lt;vertical-antenna&gt;&lt;radial&gt;&lt;efficiency&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15277" PostTypeId="2" ParentId="15276" CreationDate="2019-09-05T12:20:26.403" Score="2" Body="&lt;p&gt;Below is a NEC4.2 study comparing the fields radiated by an eighth-wave, series-fed vertical monopole driven against sets of thirty buried radials of 1/4 and 1/8 wavelength (other things equal).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The X axis shows field intensity (E), and the Y axis shows elevation (Z) above a flat Earth ground plane, at a horizontal distance of 100 meters from the base of the monopole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna system with 1/4-wave radial lengths generates a maximum field intensity 12.5% greater than the system with 1/8-wave radials.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The corresponding improvement in radiated power is 1.125² x 100% = 26.6% (approximately).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The increased radiation efficiency is the result of collecting more of the r-f currents flowing on and below the surface of the earth within a 1/2-wavelength radius from the base of the monopole, as a result of its radiation.  The r-f resistance of the set of buried radials is a series circuit element whose I^2R loss reduces the r-f current that flows along the monopole, itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jYh4i.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jYh4i.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-09-05T17:34:44.343" LastActivityDate="2019-09-05T17:34:44.343" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15278" PostTypeId="2" ParentId="15273" CreationDate="2019-09-05T14:31:21.707" Score="4" Body="&lt;p&gt;&lt;em&gt;If&lt;/em&gt; the specific device is built around the Realtek RTL2832U chip, then the &lt;code&gt;rtl-sdr&lt;/code&gt; driver software will be able to use it as an SDR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it uses a different chip, then that driver will not work. It &lt;em&gt;might&lt;/em&gt; still be possible to use that hardware, but would require writing new driver software and possibly reverse-engineering (the same as the original RTL-SDR development project).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is also worth noticing that &lt;code&gt;rtl-sdr&lt;/code&gt; actually does not use the DVB-T capabilities of the devices it works with at all — the raw-samples mode of the chip is narrow-band compared to what is required to receive DVB-T and was used by the original software to receive FM radio, not video. Hardware that &lt;em&gt;only&lt;/em&gt; has a DVB-T mode &lt;em&gt;cannot&lt;/em&gt; be used as a SDR.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-09-05T16:30:12.800" LastActivityDate="2019-09-05T16:30:12.800" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15279" PostTypeId="2" ParentId="12391" CreationDate="2019-09-05T16:25:49.513" Score="2" Body="&lt;p&gt;There's confusion about counterpoise because there's two kinds of end fed antennas.  Both are multi-band, but different approaches to achieve this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first kind is deliberately non-resonant, uses a 9:1 unun and requires a tuner.  It may require a good tuner if you want to work the low bands on a short wire.  Some suggest a counterpoise of .05 or .1.  Common lengths are 44' 53' etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second kind is EFHW which is half wave resonant on the lowest band but is also resonant on all harmonics.  This requires a 49:1 unun or similar and if built and installed right, should not require a tuner, except to cover all of 80m.  If you use a 0.05 counterpoise here, you will likely need a tuner.  With my installation, a ground rod was excellent to sufficient for most bands and 2 rods were slightly better for SWR.  You may try adding additional .25 counterpoise wires for problem bands if you really don't want to use a tuner.  I've noticed that adding to the counterpoise system always seems to help and never hurts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A DC ground is desirable for lighting and static electricity, but not required if your counterpoise wire(s) is effective.  Though ground rods are forbidden with 1/4 wave verticals due to resistance, they're not a problem for EFHW since much less current flows through the rod than when driving a 1/4 wave.  For non-resonant wires using 9:1 unun, ground losses will be greater than EFHW and will become a problem when trying to load up lower bands on short wires.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For either antenna, I recommend using a common mode filter at the antenna and use a separate counterpoise system instead of the coax shield.&lt;/p&gt;&#xA;" OwnerUserId="15602" LastEditorUserId="15602" LastEditDate="2019-09-05T17:03:40.867" LastActivityDate="2019-09-05T17:03:40.867" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15280" PostTypeId="2" ParentId="15262" CreationDate="2019-09-05T23:37:10.560" Score="2" Body="&lt;p&gt;There's already an excellent answer from natevw, but I wanted to slice and dice the numbers in a few more ways, so I downloaded the ULS database (on September 4, 2019) and imported it into PostgreSQL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the original question seemed to show an interest in people who pass all three exams in one sitting, I tried to incorporate that into the results.  When a license is obtained this way, the &lt;code&gt;Prev. Op Class&lt;/code&gt; and &lt;code&gt;Prev. Call Sign&lt;/code&gt; fields are both blank in ULS.  I can't rule out the possibility that other situations would cause these fields to be blank, but it's the best indicator I have available, so I'm going with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The database queries I used are available at &lt;a href=&quot;https://gist.github.com/mrog/f0a64d8a4c9cb70d79ccba1d7caab1e5&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://gist.github.com/mrog/f0a64d8a4c9cb70d79ccba1d7caab1e5&lt;/a&gt;.  The good news for both natevw and me is that our answers are in agreement about the percentage of 2x2, 1X2, 2x1, and 2x3 vanity callsigns.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&#xA;+--------------------------------------------+&#xA;|      Active Callsigns for Individuals      |&#xA;+--------------------------+--------+--------+&#xA;| Total number             | 810715 |        |&#xA;+--------------------------+--------+--------+&#xA;| 2x2 vanity callsigns     | 10610  | 1.31%  |&#xA;+--------------------------+--------+--------+&#xA;| 2x2 non-vanity callsigns | 47686  | 5.88%  |&#xA;+--------------------------+--------+--------+&#xA;| 1x2 vanity callsigns     | 13854  | 1.71%  |&#xA;+--------------------------+--------+--------+&#xA;| 1x2 non-vanity callsigns | 4727   | 0.58%  |&#xA;+--------------------------+--------+--------+&#xA;| 2x1 vanity callsigns     | 9608   | 1.19%  |&#xA;+--------------------------+--------+--------+&#xA;| 2x1 non-vanity callsigns | 10947  | 1.35%  |&#xA;+--------------------------+--------+--------+&#xA;| 2x3 vanity callsigns     | 17748  | 2.19%  |&#xA;+--------------------------+--------+--------+&#xA;| 2x3 non-vanity callsigns | 526625 | 64.96% |&#xA;+--------------------------+--------+--------+&#xA;| 1x3 vanity callsigns     | 78484  | 9.68%  |&#xA;+--------------------------+--------+--------+&#xA;| 1x3 non-vanity callsigns | 90426  | 11.15% |&#xA;+--------------------------+--------+--------+&#xA;&lt;/pre&gt;&#xA;&#xA;&lt;pre&gt;&#xA;+-----------------------------------------------------------------------------+&#xA;|                     Active 2x2 Callsigns for Individuals                    |&#xA;+--------------------------------------------------------+-------+------------+&#xA;|                                                        | Count | Percentage |&#xA;+--------------------------------------------------------+-------+------------+&#xA;| Total number                                           | 58296 |            |&#xA;+--------------------------------------------------------+-------+------------+&#xA;| Vanity                                                 | 10610 | 18.20%     |&#xA;+--------------------------------------------------------+-------+------------+&#xA;| Non-vanity                                             | 47686 | 81.80%     |&#xA;+--------------------------------------------------------+-------+------------+&#xA;| With no previous callsign or operator class            | 16514 | 28.33%     |&#xA;+--------------------------------------------------------+-------+------------+&#xA;| Vanity with no previous callsign or operator class     | 3     | 0.01%      |&#xA;+--------------------------------------------------------+-------+------------+&#xA;| Non-vanity with no previous callsign or operator class | 16511 | 28.32%     |&#xA;+--------------------------------------------------------+-------+------------+&#xA;&lt;/pre&gt;&#xA;&#xA;&lt;pre&gt;&#xA;+---------------------------------------------------------------------------------------+&#xA;|                   Active Extra or Advanced Licenses for Individuals                   |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;|                                                                 | Count  | Percentage |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| Total number                                                    | 197033 |            |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| Vanity callsigns                                                | 61364  | 31.14%     |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| Non-vanity callsigns                                            | 135669 | 68.86%     |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| No previous callsign or operator class                          | 47976  | 24.35%     |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| Vanity callsigns and no previous callsign or operator class     | 44     | 0.02%      |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| Non-vanity callsigns and no previous callsign or operator class | 47932  | 24.33%     |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| 2x2 callsigns                                                   | 51844  | 26.31%     |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| Vanity 2x2 callsigns                                            | 10000  | 5.08%      |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| Non-vanity 2x2 callsigns                                        | 41844  | 21.24%     |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;| 2x2 callsigns and no previous callsign or operator class        | 12608  | 6.40%      |&#xA;+-----------------------------------------------------------------+--------+------------+&#xA;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;UPDATE (September 6, 2019): I filtered out clubs, businesses, etc., so the results now only reflect licenses for individuals.  This reduced the total callsign count from 823,438 to 810,715.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2019-09-06T19:48:14.867" LastActivityDate="2019-09-06T19:48:14.867" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15281" PostTypeId="1" CreationDate="2019-09-06T07:27:55.870" Score="0" ViewCount="73" Body="&lt;p&gt;So i want to build my very own transceiver, not looking for anything worldwide, just local but i do have a background in arduino and &lt;em&gt;some&lt;/em&gt; electrical engineering, what tutorials would you recommend?&lt;/p&gt;&#xA;" OwnerUserId="15606" LastActivityDate="2019-09-06T18:40:45.413" Title="How should i go about building my first transceiver?" Tags="&lt;diy&gt;&lt;transceiver&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15283" PostTypeId="2" ParentId="15226" CreationDate="2019-09-06T11:42:56.833" Score="1" Body="&lt;p&gt;As with most argued questions like this, there is some truth to both sides.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lightning rods can dissipate small charges if they have sharp tips, but when that doesn't work, their real purpose is to conduct the lightning around your house instead of through it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the current standard (recently changed?) for lightning rods is round tips.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lightning rods are one of three parts of a good protection system.&#xA;The other two parts are ground rods (connected to the lightning rods) and surge protectors at each device connected to an external wire.  (If you have a direct strike on a wire, the lightning rods only reduce the spike voltage there to a manageable level, not elminiate it entirely.  Lightning doesn't take the shortest path -- it takes ALL paths, but follows the voltage divider rule with some paths getting more.)&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="6080" LastEditDate="2019-09-07T13:21:01.333" LastActivityDate="2019-09-07T13:21:01.333" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15284" PostTypeId="2" ParentId="15281" CreationDate="2019-09-06T15:02:29.103" Score="4" Body="&lt;p&gt;You might want to first assemble a kit, perhaps an inexpensive one for QRP (many mail-order QRP transceiver kits seem to exist for under $100 USD).  This will allow you to experience component recognition, assembly tools and practices, bring-up, instrumentation, calibration, test procedures, and repairs, etc. before doing this on a design of your own that hasn't been &quot;pre-flighted&quot; with known results (as least according to kit reviews).&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-09-06T15:02:29.103" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15285" PostTypeId="2" ParentId="15281" CreationDate="2019-09-06T18:40:45.413" Score="0" Body="&lt;p&gt;You can find many designs for homebrew amateur radios on the internet. A couple I am somewhat familiar with include the BITX radios made famous by HfSignals with their BITX40 and uBITX radio kits and Bob Heil's Pine Board Transmitter that used vacuum tubes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do suggest starting small with just a section like a local oscillator, mixer, or amplifier. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As mentioned by others buying and assembling a kit is a good way to get started. If you buy two kits you can build the first one following the instructions and then use the second kit to experiment by trying different components or designs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If time and expertise is limited, get a commercial or kit radio but make your own antennas. Antennas are much easier to make and experiment with than radios them selves. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2019-09-06T18:40:45.413" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15286" PostTypeId="2" ParentId="5445" CreationDate="2019-09-06T20:24:22.890" Score="2" Body="&lt;p&gt;None of your formulas will mean anything because you are not considering the path loose. What is the SWR on the J-poles at the frequency you are using? How high are they?  If they are in your basement instead of on the roof, that's a problem. J-poles that have good SWR, at 30 ft, with flat ground between them should easily work 10 miles apart with 8 watts.&lt;/p&gt;&#xA;" OwnerUserId="15612" LastActivityDate="2019-09-06T20:24:22.890" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15287" PostTypeId="2" ParentId="15137" CreationDate="2019-09-06T21:11:57.093" Score="0" Body="&lt;p&gt;To add a partial answer to my own question, I realized I have at least one interesting test tool available, a tiny transmitter (TAPR WSPR board), controlled via a small computer (a Raspberry Pi Zero), smaller than the test antenna.  Both can be run (for short periods) from a small battery, and the Pi can be either remotely controlled or run a timer-based CW beacon script.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using a transmitter smaller than the antenna and directly connected at the antenna feed-point should eliminate feed-line radiation almost entirely.  A battery supply and remote operation of the transmitter allows complete ground wire and control wire isolation as well.  Perhaps a small toroidal common-mode choke between the transmitter and the antenna, even though lengthening the feed-line by a few centimeters, might help eliminate the transmitter from becoming part of the antenna.  The setup would likely need be be placed maybe 2 wavelengths or more away from any metallic structures or wires to prevent re-radiation in the near field from distorting RF measurements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps a useful idea only for &quot;lightbulb&quot; antenna's that are larger than a Raspberry Pi.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-09-06T21:17:31.207" LastActivityDate="2019-09-06T21:17:31.207" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15288" PostTypeId="1" AcceptedAnswerId="15305" CreationDate="2019-09-06T23:51:56.380" Score="3" ViewCount="282" Body="&lt;p&gt;What are the advantages for a receiver that uses an IF compared to direct conversion ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-09-10T02:38:17.057" Title="What are the advantages for a receiver that uses an IF compared to direct conversion?" Tags="&lt;electronics&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15289" PostTypeId="1" CreationDate="2019-09-06T23:55:06.933" Score="1" ViewCount="89" Body="&lt;p&gt;How is frequency selection (tuning) accomplished in a direct conversion receiver ? A crystal filter can't be used is that correct ? Because there is no IF to mix with the incoming frequency band ...&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-09-07T19:11:35.027" LastActivityDate="2019-09-08T03:08:37.617" Title="How is frequency selection (tuning) accomplished in a direct conversion receiver?" Tags="&lt;receiver&gt;&lt;electronics&gt;&lt;direct-conversion&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15290" PostTypeId="1" AcceptedAnswerId="15297" CreationDate="2019-09-07T01:12:59.197" Score="1" ViewCount="234" Body="&lt;p&gt;I know the characteristic impedance can't change because it's determined by the physical properties of a transmission line. But the impedance seen when there are standing waves changes along the length, is that correct?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then my SWR meter won't be accurate because the impedance isn't 50 ohms, is that right? So, the higher the SWR the more inaccurate by SWR meter will be?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-09-07T19:25:16.243" LastActivityDate="2019-09-08T13:55:31.950" Title="Does the impedance along a transmission line change when there are standing waves?" Tags="&lt;transmission-line&gt;&lt;swr-meter&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15291" PostTypeId="2" ParentId="15290" CreationDate="2019-09-07T05:05:41.503" Score="2" Body="&lt;p&gt;Yes, the characteristic impedance of the transmission line &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; does not change (it is a property of the cable itself), but the impedance seen from the end of the cable depends on the length of the cable. But also no, your VSWR meter will work just fine. VSWR is a measurement of how far the measured impedance is from &lt;span class=&quot;math-container&quot;&gt;$50\Omega$&lt;/span&gt; (or whatever is the impedance of your system).&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;VSWR, impedance, and cable length&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;If you terminate your &lt;span class=&quot;math-container&quot;&gt;$50\Omega$&lt;/span&gt; coax line with an antenna whose input impedance is something else, like &lt;span class=&quot;math-container&quot;&gt;$75\Omega$&lt;/span&gt;, some of the power transmitted reflects when it hits the antenna. This is because both current (along the transmission line) and the voltage between your outer and inner conductors must remain continuous at all points. The amount (and phase) of reflected signal is called reflection coefficient &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\Gamma = {Z_L - Z_O\over Z_L + Z_O}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Voltage Standing Wave Ratio is just an another way of expressing the magnitude (so we don't care about the phase of the reflected signal) of the &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$VSWR = \frac{1 + |\Gamma|}{1 - |\Gamma|}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the length of your transmission line changes, you don't affect the amount of reflected signal (assuming lossless transmission line), only its phase. The simplest example is openly terminated coaxial cable (&lt;span class=&quot;math-container&quot;&gt;$Z_l = \infty$&lt;/span&gt;): A short open ended coax acts as a capacitor and a bit over quarter wavelength long cable (&lt;span class=&quot;math-container&quot;&gt;$l &amp;gt; \lambda/4$&lt;/span&gt;) acts as an inductor. If you have long enough coax, the losses will dissipate some of the reflected signal, leading to improved VSWR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you know the complex propagation constant &lt;span class=&quot;math-container&quot;&gt;$\gamma$&lt;/span&gt; (so you know both how fast the wave travels and how much there are losses), you can calculate the input impedance &lt;span class=&quot;math-container&quot;&gt;$Z_{in}$&lt;/span&gt; that is seen from the end of the coaxial cable:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_{in}(l )=Z_{0}\,{\frac {Z_L+Z_{0}\tanh (\gamma l )}{Z_{0}+Z_L\,\tanh (\gamma l )}}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Standing waves&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;When ever there is a impedance mismatch in the end of the cable, that is, your antenna is not exactly &lt;span class=&quot;math-container&quot;&gt;$50 \Omega$&lt;/span&gt;, a wave is reflected back. If you look at the animation below (from Wikipedia), you can see the blue wave is transmitted from left, hits a short on the right, and is reflected to left as red wave. The black curve is the sum of these two waves. In some locations the red and blue cancel each other out and a &lt;span class=&quot;math-container&quot;&gt;$\lambda/4$&lt;/span&gt; away from those points they amplify each others. In this animation the load impedance is &lt;span class=&quot;math-container&quot;&gt;$Z_l=0\Omega$&lt;/span&gt;, but the graph is similar with other impedances as well, except that the minimum voltage is not exactly zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/7/7d/Standing_wave_2.gif&quot; alt=&quot;Standing wave&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This sum wave is called as standing wave and the ratio of the minimum and maximum voltage along this transmission line is called the Voltage Standing Wave Ratio (VSWR). Your VSWR meter measures the amplitudes from red and blue curves for example through a &lt;a href=&quot;https://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers&quot; rel=&quot;nofollow noreferrer&quot;&gt;directional coupler&lt;/a&gt;. If you had a suitable waveguide where you can move a probe along the transmission line, you could also measure the minimum and maximum amplitude from the waveguide itself. I don't think this measurement method has any practical uses outside of demonstrating the phenomenon.&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="9621" LastEditDate="2019-09-07T15:32:45.963" LastActivityDate="2019-09-07T15:32:45.963" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15295" PostTypeId="1" CreationDate="2019-09-07T14:25:07.037" Score="0" ViewCount="143" Body="&lt;p&gt;I conducted an experiment today using a prototype copper wire 2m dipole at a ground level base station (noted on images) and a FT2D HT with an SRH77CA antenna. I recorded my transmissions using a laptop at the base station, and recorded my GPS coordinates as I moved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The base station received all of my transmissions up to ~2km at a signal strength of ~S9. However, after 0.5km the signal became unreadable (signal report would be 1/5). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What might be the cause of this lack of readability, but strong reception? Could it be the dense steel/glass/concrete disrupting propagation path? I would have guessed that this would cause the signal strength to be diminished in proportion to the readability. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What kind of things could I do to improve readability of my signal (Maybe it's really just getting an antenna on the roof instead of on ground floor)? - Thanks! KC9PPX/HB3XRS&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Weather condition: clear skies&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dEp1A.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dEp1A.jpg&quot; alt=&quot;3D view of GPS&quot;&gt;&lt;/a&gt;&lt;a href=&quot;https://i.stack.imgur.com/KW2av.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KW2av.jpg&quot; alt=&quot;Overhead View&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Update 10-SEP-2019&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I repeated the experiment again today, but this time I connected the FT2D to my homebrew dipole to act as my base station instead of my FT857.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This time I carried an FT-4X HT with a factory rubber duck. Again inside my pack next to a bag of water. The signal was still unreadable for all transmissions beyond the first checkpoint (same as before). But I can hear one or two words in some of the static, which is an improvement over the last time I ran the experiment. Could have something to do with putting my homebrew dipole on the FT2D!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Weather condition: clear skies.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the next time I run this experiment I will put my antenna, radio and computer on the roof of my building. I hadn't thought of using the FT2D as a base station before, it's much more portable and easier to hide than the 857. My guess is this will make a massive difference in readability, but let's see. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm using Audacity to evaluate signal strength. I would still guess S9 for each transmission. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/hCgRg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hCgRg.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15618" LastEditorUserId="15618" LastEditDate="2019-09-10T17:21:44.890" LastActivityDate="2019-09-10T17:21:44.890" Title="Strong but unreadable signal received on 2m FM voice, transmitter less than 2km away. What could be the cause of the readability problem?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;ht&gt;&lt;2m-band&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15297" PostTypeId="2" ParentId="15290" CreationDate="2019-09-07T16:12:05.160" Score="5" Body="&lt;p&gt;VSWR is related to the magnitude of the reflection coefficient &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{VSWR} = {1+|\Gamma| \over 1-|\Gamma|} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reflection coefficient can be calculated from the load impedance &lt;span class=&quot;math-container&quot;&gt;$Z_L$&lt;/span&gt; and the characteristic impedance &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \Gamma = {Z_L - Z_0 \over Z_L + Z_0} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reflection coefficient, like the load impedance, a complex number with a magnitude and phase. But only the magnitude of the reflection coefficient is relevant to the calculation of VSWR. Changing the length of the transmission line between the SWR meter and the load alters the phase of the reflected wave, but assuming a lossless line it does not alter the magnitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, while the impedance seen looking into the line varies depending on the length of the line, the VSWR remains constant on a lossless line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice transmission lines have some loss, and this has the effect of decreasing the magnitude of the reflection coefficient with increasing line length, which means the VSWR will approach 1:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is difficult to say where the SWR meter is most &quot;accurate&quot; since the VSWR is not a constant but varies along the transmission line. If your transmitter is specified to work into a VSWR of 1.6:1 or below, then placing the SWR meter next to the transmitter is most accurate as that measures the VSWR seen by the transmitter. On the other hand if your objective is to measure the SWR bandwidth of an antenna, placing the meter at the antenna will be more accurate because the transmission line loss would otherwise result in increasing the measured bandwidth. Then again, in many applications the transmission line losses are low enough that the difference is of no practical significance.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-09-07T16:12:05.160" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15298" PostTypeId="2" ParentId="15289" CreationDate="2019-09-07T19:08:37.593" Score="2" Body="&lt;p&gt;For single-channel direct-conversion to baseband, tuning is done by setting the heterodyne or mixer oscillator frequency, and possibly by tuning band-pass filters, if any, in front of the direct-down-converter mixer. For AM or SSB, the oscillator is tuned to zero-beat with the carrier or suppressed carrier. For CW, the mixing oscillator is tuned slightly higher or lower than the CW signal frequency of interest to produce an audio side-tone.  For digital modes a similar offset is used to mix the signal of interest into the audio input bandwidth of a computer sound-card or mono audio input interface.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The upper and lower sidebands around the tuned frequency end up aliased, so cannot be separated.  But audio or baseband low-pass filtering can be applied to the resulting aliased baseband signal.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For dual-channel direct-conversion to quadrature/complex/IQ sampled data, DSP processing on the IQ data stream can separate out the upper and lower sidebands, and filter out (via FFT or otherwise) multiple signals somewhat offset from the mixer oscillator frequency, but sufficiently below half the sample rate in offset.  This offset acts as a very low IF.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-09-07T19:18:36.693" LastActivityDate="2019-09-07T19:18:36.693" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15299" PostTypeId="1" CreationDate="2019-09-07T20:55:55.343" Score="2" ViewCount="83" Body="&lt;p&gt;I was wondering what calculations would need to be performed to find out if a receiver will blow out in the given conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Portable AM receiver with ferrite rod antenna 200 ft away from MW antenna producing 1kW RMS into 1/4 wave GP antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know there is no clear cut answer due to different receiver tolerances, but I need to know if it is just way off and nearly impossible to happen or if it is very likely.&lt;/p&gt;&#xA;" OwnerUserId="1817" LastActivityDate="2019-09-08T17:00:39.300" Title="How much field strength to blow out a receiver?" Tags="&lt;receiver&gt;&lt;vertical-antenna&gt;&lt;am&gt;&lt;mf&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15300" PostTypeId="2" ParentId="15299" CreationDate="2019-09-07T22:02:02.633" Score="1" Body="&lt;p&gt;A major edit to my original answer to capture the comments below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Friis equation, that I originally suggested, does not apply in this situation since the receiving antenna is only around one wavelength away from the transmitting antenna, meaning that it is still in the near field. At these low frequencies, also the conductive ground plays a major role. Accurate results can be obtained from simulations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can test the withstanding of your receiver by gradually moving closer and observing what happens. As the ferrite core antennas have somewhat high losses in the ferrite, the first sign might be that the antenna starts to heat up. On the other hand, if you are listening to the TX antenna, I think the first effect will be that the sound starts to clip when the output voltage from your pre-amplifier reaches the DC bias voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My gut feeling is unchanged, I don't think the receiver will break down.  Please let us know if I'm wrong.&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="194" LastEditDate="2019-09-08T17:00:39.300" LastActivityDate="2019-09-08T17:00:39.300" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15301" PostTypeId="2" ParentId="15289" CreationDate="2019-09-08T03:08:37.617" Score="1" Body="&lt;p&gt;The IF (intermediate frequency) is not mixed with the incoming signal, but the LO (local oscillator).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning in a direct conversion receiver is achieved just as it is with a superhet: by varying the LO frequency. A direct conversion receiver simply has an &quot;IF&quot; of 0 Hz. In fact another name for a direct-conversion receiver is a &quot;zero-IF receiver&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A crystal filter would not be used because with the signal mixed down to baseband, typically the frequencies of interest are too low for a crystal filter to be applicable. Furthermore, the lower frequency means the fractional bandwidth required to get an acceptably steep roll-off is obtainable with a simple RC filter. And in common modern practice the analog filtering is limited to antialising for an ADC, with the final channel selection being performed by digital filters.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-09-08T03:08:37.617" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15302" PostTypeId="2" ParentId="15290" CreationDate="2019-09-08T13:49:35.103" Score="1" Body="&lt;p&gt;In an ideal system, the VSWR is not changed by the coax length.  However, in the real world, two factors affect this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, the coax is lossy, and high SWR magnifies the loss, causing swr to appear to approach 1:1 at the transmitter.  If you are measuring complex swr (i.e., with a network analyzer), and your goal is to determine if the antenna is well matched and your coax is not so long as to absorb too much of the high SWR, then this is not of great consequence and you can still see the mismatch, although perhaps with a smaller magnitude than it is at the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, if you are measuring a balanced antenna connected via coax with no balun or a balun that is unable to block all the common mode current, then the coax becomes part of the antenna, and the SWR measured at the transmitter may actually be raised by the coax, and may actually appear to change randomly if you move the coax with respect to the antenna, as the geometry between the antenna and the coax can change the common mode coupling with the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This second effect can be minimized with a good balun at the antenna (and perhaps at the transmitter).  It can also be minimized by cutting your coax to an electrical multiple of 1/4 wavelength (i.e., consider VF of the coax), which will at least make common mode radiation not add more of the complex component to your SWR -- but realize that your coax is still part of the antenna and may be radiating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few antennas intentionally take advantage of this to either soften directionality of the antenna by radiating from the coax, or with careful placement of a  un-un on the coax, tune a section of the coax for a band not otherwise supported by the rest of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2019-09-08T13:55:31.950" LastActivityDate="2019-09-08T13:55:31.950" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15303" PostTypeId="2" ParentId="15228" CreationDate="2019-09-08T15:23:41.240" Score="2" Body="&lt;p&gt;&lt;a href=&quot;http://fofio.blogspot.com/2015/07/radio-kit-guide.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;This&lt;/a&gt; site lists several kits and is the most current and complete list I could find (list is reproduced here).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Disclaimer: operation of devices linked depends on your jurisdiction. In any case you need the proper license to operate these devices.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://stores.ebay.com/24hrsradioshop&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://stores.ebay.com/24hrsradioshop&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://ae9rb.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://ae9rb.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.ebay.com/usr/ag6bd&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ebay.com/usr/ag6bd&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://amateurradiokits.in/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://amateurradiokits.in/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.amateurradioreceivers.net/index.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.amateurradioreceivers.net/index.htm&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://bit.ly/2OYINVm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://bit.ly/2OYINVm&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://breadboardradio.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://breadboardradio.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.crkits.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.crkits.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.cumbriadesigns.co.uk/kits.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.cumbriadesigns.co.uk/kits.htm&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://cycle24kits.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://cycle24kits.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.danssmallpartsandkits.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.danssmallpartsandkits.net/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.dzkit.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.dzkit.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.qrphamradiokits.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.qrphamradiokits.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://emtech.steadynet.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://emtech.steadynet.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.etherkit.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.etherkit.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.4sqrp.com/kitIndex.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.4sqrp.com/kitIndex.php&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://products.foxdelta.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://products.foxdelta.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.genesisradio.com.au/order.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.genesisradio.com.au/order.html&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.gqrp.com/sudden.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.gqrp.com/sudden.htm&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hamgadgets.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hamgadgets.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hamtronics.com/menu_products.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hamtronics.com/menu_products.htm&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hanssummers.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hanssummers.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.qrp-labs.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.qrp-labs.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://heathkit.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://heathkit.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://hfprojects2.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hfprojects2.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://hfsignals.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://hfsignals.com/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.hobbypcb.com/amateur-radio&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hobbypcb.com/amateur-radio&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://wb9kzy.com/ham.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://wb9kzy.com/ham.htm&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.jumaradio.com/juma/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.jumaradio.com/juma/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://kc9on.com/shop/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://kc9on.com/shop/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.qsl.net/k5bcq/Kits/Kits.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.qsl.net/k5bcq/Kits/Kits.html&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.kanga-products.co.uk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.kanga-products.co.uk/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.kitradio.co.uk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.kitradio.co.uk/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.kitsandparts.com/index.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.kitsandparts.com/index.php&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10691" LastEditorUserId="10691" LastEditDate="2019-09-09T10:21:48.080" LastActivityDate="2019-09-09T10:21:48.080" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15304" PostTypeId="2" ParentId="15295" CreationDate="2019-09-08T20:03:22.653" Score="2" Body="&lt;p&gt;Not an expert here, but since I don't see any answers yet these might be possible reasons:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;during the first leg of the trip, it seems like you had more or less line of sight. After that, there seem to be more buildings in between you and the base station. Maybe you had lots of reflections/multipath towards the receiver (the receiver receiving the signal not just directly from the source/ht, but also from reflections from buildings/... These have a phase shift depending on the reflection and additional transmission path length. Mix all that together and you might end up with a strong but possibly useless signal.)&lt;/li&gt;&#xA;&lt;li&gt;was the signal reception back as it should during the last part of the trip? So, did you have a similar transmission quality when you moved away from the base station as when you got back closer to it? If not, a drained battery in the handheld might be a possible cause...&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;-edit: after looking up your ht, I doubt the battery could be the cause. I noticed this behaviour with a simple old Kenwood th22e. I think the empty battery voltage dropped on each transmit, triggering a brown out reset, starting transmit again and so on. On your ht you would see the screen going blank and you would notice the restart so not a likely cause...&lt;/p&gt;&#xA;" OwnerUserId="8263" LastEditorUserId="8263" LastEditDate="2019-09-08T20:24:14.317" LastActivityDate="2019-09-08T20:24:14.317" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15305" PostTypeId="2" ParentId="15288" CreationDate="2019-09-08T20:08:25.310" Score="6" Body="&lt;p&gt;A superhet has two distinct &lt;em&gt;properties&lt;/em&gt;, which may or may not be advantages:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The image frequency is far away, and&lt;/li&gt;&#xA;&lt;li&gt;The IF is not DC&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;In a typical superhet design, the LO and signal frequencies will be quite far apart, making the image frequency in an entirely different band. Thus it's not difficult to exclude the image frequency with a simple analog filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a direct conversion receiver, the LO is at or very near the signal frequency, and thus the image frequency is immediately adjacent. Obtaining a sufficiently selective filter at the signal frequency is often impractical: it would require a very small fractional bandwidth, and would need to be tunable over the operating band of the receiver. Contrast with a superhet design which allows the channel filter to be tuned at just one frequency: the IF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, a direct conversion receiver must typically perform channel selection &lt;em&gt;after&lt;/em&gt; the mixer, typically with a quadrature mixer. Dealing with quadrature signals in the analog domain requires more circuitry since there are twice as many signals to process, which must each be treated carefully to maintain coherence. Furthermore, it is difficult to minimize DC offset and 60 or 50 Hz hum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These issues are largely mitigated in modern times by digital electronics. Many (perhaps most?) modern HF amateur rigs now utilize either direct sampling (example: Icom IC-7300, FlexRadio, Hermes), running an ADC fast enough to sample RF with no mixing at all, or direct conversion with a quadrature mixer (example: Softrock, QRP Labs QCX, everything from Elecraft).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern VHF+ applications tend to use direct conversion and digital demodulation as well. For examples, consider the ubiquitous, cheap RTL-SDR receivers, and BaoFeng handhelds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often, the digital solution not only performs better but is cheaper too, especially when the modulation in question is a digital one that already requires digital hardware. So arguably, there is not much modern advantage to a superhet design, except possibly cost when a very simple analog demodulation circuit is possible, for example AM.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-09-09T15:01:30.923" LastActivityDate="2019-09-09T15:01:30.923" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15306" PostTypeId="2" ParentId="15233" CreationDate="2019-09-08T20:08:31.960" Score="0" Body="&lt;p&gt;I'd be more inclined to ask a local (metal) engineering workshop. I have one near me (Surrey UK) that do a large amount of work for a nearby amusement park. They would be well used to assessing the state of the steel-work underneath the galvanising (I guess it is galvanised). If you pay for their advise you should then have some come-back if things go wrong. &#xA;I would also take into account where I was going to site it, in particular where and on what it would fall should the worst happen.&#xA;Also - it is described as self-supporting - does this classification apply to all geographical areas? I am thinking here of wind-loading?&#xA;A point relevenat for when you put aerials up there.&#xA;Oh, and don't forget the base/foundation; the size of which is dependent on the last factor together with the type of soil in your area.&lt;/p&gt;&#xA;" OwnerUserId="9323" LastActivityDate="2019-09-08T20:08:31.960" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15307" PostTypeId="2" ParentId="15295" CreationDate="2019-09-09T01:14:37.330" Score="0" Body="&lt;p&gt;Because you had a strong signal, I am thinking this is either a measurement error (clipping, for example) or a transmission error (high volume background noise, for example) of some sort.  I will keep asking &quot;dumb questions&quot; in comments and update this answer as appropriate. &lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2019-09-09T01:14:37.330" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15309" PostTypeId="2" ParentId="15261" CreationDate="2019-09-09T22:33:33.770" Score="1" Body="&lt;p&gt;My biggest mistake was keeping my search on everything about ferrite and balun online, and receiving various piece of confusing information of mixed quality. Meawhile, I didn't even take a look at the most basic and authoritative reference material: &lt;em&gt;The ARRL Handbook for Radio Communication&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Today, I just obtained a copy of the 2014 edition, and immediately even before open the book, I saw six toroidial cores on the hardcover, aha! I think I can answer most of my questions now. If you are reading this, please help me to check whether my answer is correct, thanks.&lt;/p&gt;&#xA;&lt;p&gt;First, we assume the transformer required is (1) for reception only, so temperature/heat dissipation is not an issue, and (2) not a transmission-line transformer, but a conventional transformer, which should be enough for our purpose [Note 1] as a beginner's project.&lt;/p&gt;&#xA;&lt;h2&gt;1. Is it a good toroidal core to use?&lt;/h2&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What information can I learn from these parameters? Is it a good toroidal core to use for a HF receiver?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The most important parameter is the initial permeability, μi = 40. In &lt;em&gt;Chapter 5: RF Techniques&lt;/em&gt; of the &lt;em&gt;ARRL Handbook&lt;/em&gt;, it advice that...&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;5.7.3 Broadband Ferrite RF Transformers&lt;/strong&gt;: [...] The core-material permeability plays a vital role in designing a good broadband transformer. The effective permeability of the core must be high enough to provide ample winding reactance at the low end of the operating range. As the operating frequency is increased, the effects of the core tend to disappear until there are scarcely any core effects at the upper limit of the operating range. The limiting factors for high frequency response are distributed capacitance and leakage inductance due to uncoupled flux. A high-permeability core minimizes the number of turns needed for a given reactance and therefore also minimizes the distributed capacitance at high frequencies.&lt;/p&gt;&#xA;&lt;p&gt;One of the most common ferromagnetic transformers used in amateur circuits is the conventional broadband transformer. Broadband transformers with losses of less than 1 dB are employed in circuits that must have a uniform response over a substantial frequency range, such as a 2 to 30 MHz broadband amplifier. In applications of this sort, the reactance of the windings should be at least four times the impedance that the winding is designed to look into at the lowest design frequency.&lt;/p&gt;&#xA;&lt;p&gt;[...] Ferrite cores with a permeability of 850 are common choices for transformers used between 2 and 30 MHz. Lower frequency ranges, for example, 1 kHz to 1 MHz, may require cores with permeabilities up to 2000. Permeabilities from 40 to 125 are useful for VHF transformers.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;In principle, there's &lt;strong&gt;nothing&lt;/strong&gt; to prevent one from constructing a RF transformer for HF using a core with μi = 40, however, due to its low permeability...&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;It requires one to wind &lt;strong&gt;much more turns than necessary&lt;/strong&gt; to obtain the same inductance required, which is a a quite labor-intensive process.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;As the number of turns increases, distributed capacitance and leakage inductance increases, which cause &lt;em&gt;the high-frequency response of transformer to deteriorate.&lt;/em&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Given the same number of turns, a lower permeability implies poorer low-frequency performance, because it provide lower inductance.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Furthermore, the vendor claims the operating frequency of the core is 3-100 MHz, which is consistent with &lt;em&gt;The ARRL Handbook&lt;/em&gt;'s advise that &amp;quot;Permeabilities from 40 to 125 are useful for VHF transformers&amp;quot;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;A good balun for transmitters?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Unlike receivers, transformers used for transmitters must handle significant power (and temperature rise). Cores with low permeabilities often have a much higher Curie temperature. Thus, transmitters have to use cores with much lower permeabilities. A presentation from &lt;a href=&quot;http://www.arnsw.org.au/html/ARNSW%20Balun%20Day.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio New South Wales (ARNSW)&lt;/a&gt; claims &amp;quot;permeability above 250 is not recommended as this will degrade high frequency performance&amp;quot;, and that the T200-2 iron powder core with μi = 10 can well be used for &amp;quot;baluns from about 7 MHz to 50 MHz&amp;quot;, but recommends FT240-61 (μi = 125) for 3 MHz to 30MHz.&lt;/p&gt;&#xA;&lt;p&gt;Also, &lt;em&gt;Transmission Line Transformers, 4th Edition&lt;/em&gt; by &lt;em&gt;Jerry Sevick, W2FMI&lt;/em&gt; suggests in Chapter 11,&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Generally, the lowest-permeability nickel-zinc ferrites yield the highest efficiencies. These have permeabilities in the range of 40 to 50. But, these ferrites can limit the low-frequency response. [...] Limited measurements on 4C4 material (μi = 125) [...] showed the best efficiency at the 200-ohm level. Table 11-2 lists some suggested power ratings [...] These ratings should generally  hold for permeability below 300.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It is quite consistent with ARNSW's recommendations, shows their claims should be reliable.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;What about using it as a EMI/RFI chock?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Not a good option. The material from Fair-Rite's Type #67, a similar core, shows they are only useful for suppressing interference above 1 GHz.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;A low-wattage 50 Hz power transformer?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Absolutely not. A power transformer requires large inductance.&lt;/p&gt;&#xA;&lt;p&gt;In &lt;em&gt;Chapter 7: Power Transformer Design&lt;/em&gt; of the book &lt;em&gt;Transformer and Inductor Design Handbook, Third Edition&lt;/em&gt; by &lt;em&gt;Colonel McLyman&lt;/em&gt; showed various candidates for transformer cores. The 50 Hz transformer candidates all have permeabilities greater than 1500.&lt;/p&gt;&#xA;&lt;h3&gt;Remarks 1.1&lt;/h3&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;This toroidal ferrite core is only suitable for winding high-Q inductors. It can be used as a wideband transformer, but best be used for VHF, not HF.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It's not a good EMI/RFI choke.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In general, do not use build a transformer with ferrite cores that have permeabilities lower than 125 for transmitters, 850 for receivers.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;In conclusion, the local vendor of the MXO series of ferrite offers cores of higher permeabilities, better cores should be purchased from the vendor for building a balun for the double-balanced mixer.&lt;/p&gt;&#xA;&lt;h2&gt;2. Calculating Inductance&lt;/h2&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;It's common to characterize toroidal cores in terms of AL and uH. What are they useful for (obviously, useful for calculating the inductance, but what purposes do it serve for RF transformers)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Already mentioned and explained, and the ARRL Handbook continued to show...&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Example: What should be the winding reactances of a transformer that has a 300-Ω primary and a 50-Ω secondary load? Relative to the 50-Ω secondary load:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ X_{S} = 4 Z_{S} = 4 \times 50 \Omega = 200 \Omega $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;and the primary winding reactance (&lt;span class=&quot;math-container&quot;&gt;$X_{P}$&lt;/span&gt;) is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ X_{P} = 4 Z_{P} = 4 \times 300 \Omega = 1200 \Omega $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;They are not given by the manufacturer, how can I calculate them from the known parameters of the core?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The article &lt;em&gt;&lt;a href=&quot;http://www.highfreqelec.summittechmedia.com/Jan05/HFE0105_Sevick.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Magnetic Materials for Broadband Transmission Line Transformers&lt;/a&gt;&lt;/em&gt; from &lt;em&gt;High Frequency Electronics, January 2005&lt;/em&gt;, by &lt;em&gt;Jerry Sevick&lt;/em&gt; says...&lt;/p&gt;&#xA;&lt;p&gt;If a toroid is used for the core, the magnetizing inductance &lt;span class=&quot;math-container&quot;&gt;$L_{m}$&lt;/span&gt; (in henrys) is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L_m = 0.4 \pi N^2 \mu \frac{A_e}{L_e} \times 10^{-8} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Where &lt;span class=&quot;math-container&quot;&gt;$N$&lt;/span&gt; is the number of turns, &lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt; is the permeability of the core, &lt;span class=&quot;math-container&quot;&gt;$A_e$&lt;/span&gt; (in square centimeter) is the effective cross-sectional area of the core, and &lt;span class=&quot;math-container&quot;&gt;$L_e$&lt;/span&gt;  (in centimeter) is the average magnetic path length in the core.&lt;/p&gt;&#xA;&lt;p&gt;And according to &lt;a href=&quot;https://www.cwsbytemark.com/CatalogSheets/MPP%20PDF%20files/13.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page&lt;/a&gt;, the cross-sectional area of a toroidial core is...&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ A_e = \frac{(D_{out} - D_{in})}{2} H $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Where &lt;span class=&quot;math-container&quot;&gt;$D_{out}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$D_{in}$&lt;/span&gt; are outer diameter and inner diameter in centimeter, &lt;span class=&quot;math-container&quot;&gt;$H$&lt;/span&gt; is the height in centimeter, and the average magnetic path length of a toroidial core is...&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L_e = \frac{\pi (D_{out} - D_{in})}{\ln (\frac{D_{out}}{D_{in}})}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus,&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ A_L = \frac{L_m}{N^2} = 0.2 \mu \ln (\frac{D_{out}}{D_{in}}) H \times 10^{-8}  \space \text{H}/\text{Turn}^2$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Where &lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt; is the permeability of the core, &lt;span class=&quot;math-container&quot;&gt;$\ln$&lt;/span&gt; is natural logarithm, &lt;span class=&quot;math-container&quot;&gt;$D_{out}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$D_{in}$&lt;/span&gt; are outer diameter and inner diameter in centimeter, &lt;span class=&quot;math-container&quot;&gt;$H$&lt;/span&gt; is the height in centimeter.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.fuantronics.net/PicFile/201462014515.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;For example&lt;/a&gt;, there's a 141-35 core, &lt;span class=&quot;math-container&quot;&gt;$D_{out} = 3.58 \space \text{cm}$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$D_{in} = 2.24 \space \text{cm}$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$H = 1.05 \space \text{cm}$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$\mu_{i} = 35$&lt;/span&gt;,&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ A_L = 0.2 \times 35 \times \ln (\frac{3.58}{2.24}) \times 1.05 \times 10^{-8} \space \text{H}/\text{Turn}^2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ A_L = 3.446 \times 10^{-8} = 34.4 \space \text{nH}/\text{Turn}^2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The listed &lt;span class=&quot;math-container&quot;&gt;$ A_L $&lt;/span&gt; in the datasheet is &lt;span class=&quot;math-container&quot;&gt;$ 33\space \text{nH}/\text{Turn}^2 $&lt;/span&gt;, showing our calculation only has an error of 5%.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;TODO: recheck the calculation tomorrow, don't trust my formula until this notice is removed.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;h3&gt;Remarks 2.1&lt;/h3&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The reactance of the windings should be at least four times the impedance that the winding is designed to look into at the lowest design frequency.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A formula for calculating the inductance of a toroidal ferrite core from its geometric dimensions and the number of turns is given. Plug the numbers in, inductance per turn can be calculated.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Alternatively, wrapping a few turns of wires on the core and measure the inductance directly using an LCR meter is a solution.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h2&gt;3. Core Replacement&lt;/h2&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;If I need to replace a toroidial core from an American design in the future, for example, FT37-43, which parameters should I look, and what calculations should I do to find an equivalent substitution?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Finding a core made of the same material with similar permeability shouldn't be hard. The question &lt;a href=&quot;https://ham.stackexchange.com/questions/1159/how-does-one-read-a-ferrite-datasheet&quot;&gt;How does one read a ferrite datasheet?&lt;/a&gt; also gives good references.&lt;/p&gt;&#xA;&lt;h2&gt;4. Measurements&lt;/h2&gt;&#xA;&lt;p&gt;&lt;strong&gt;TODO: misleading instructions, only suitable for 1:1 balun, need to fix this section.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;What measurements can I take with an 100 MHz oscilloscope (w/ FFT) and a 10 MHz signal generator to test whether my balun is working as intended after I winded it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;del&gt;Turn on the signal generator, switch it to 10 MHz. Connect the primary side of the balun to the signal generator. Probe the primary side with an oscilloscope and save the waveform.&lt;/del&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;del&gt;Disconnect the probe. Probe the secondary side of the balun. You should see a AC signal (without DC bias), with minimum attenuation of its amplitudes. This check confirms whether the balun is working as a transformer correctly as expected.&lt;/del&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;del&gt;Possibly, feeding a tracking generator or a noise source to the primary side and checking the attenuation of the secondary side with a spectrum analyzer or oscilloscope FFT is also an option. &lt;/del&gt;&lt;/p&gt;&#xA;&lt;p&gt;However, for an authoritative characterization, a Vector Network Analyzer should be used to measure the S-parameter of the balun. Currently, there are a lot of low-cost options such as MiniVNA and NanoVNA on the market, which should do its job to a reasonable level of certainty, and not out-of-reach for most people. The measurement should be done on a test rig (e.g. a copper board with all components soldered, SMD resistors) to minimize parasitic inductance and capacitance.&lt;/p&gt;&#xA;&lt;h2&gt;5. How to get started?&lt;/h2&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Are there any resources for beginners like me to get started?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Read the entire &lt;em&gt;ARRL Handbook&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;h3&gt;Remark 5.1&lt;/h3&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;em&gt;ARRL Handbook&lt;/em&gt; has much more information and pointers to even more references than most beginners believes.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h3&gt;Notes&lt;/h3&gt;&#xA;&lt;p&gt;[Note 1] &amp;quot;Conventional transformers have been constructed to perform over wide bandwidths. Losses on the order of one decibel can exist over a range from a few kiloherz to over 200 MHz. Throughout a considerable portion of this band, the losses are only 0.2 dB. On the other hand, transimission line transformers exhibit far wider bandwidths and much greater efficiencies.&amp;quot; - &lt;em&gt;Transmission Line Transformers, 4th Edition&lt;/em&gt; by Jerry Sevick, W2FMI&lt;/p&gt;&#xA;" OwnerUserId="15589" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-09-27T15:39:30.037" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15310" PostTypeId="2" ParentId="15288" CreationDate="2019-09-10T02:38:17.057" Score="4" Body="&lt;p&gt;There are several advantages to converting to an IF. These include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It is easier to make a multi-band receiver, as you just need to change the RF stage for each band, and everything after the IF is the same. It is cheaper to have one set of expensive filters in the IF path with a high-quality audio path, and then use it for every band.&lt;/li&gt;&#xA;&lt;li&gt;If the IF is a lower frequency than the RF stage, then filters can be much cheaper. Also, the tuning circuitry can be made much simpler. Imagine trying to tune accurately a microwave receiver to separate two signals 500Hz apart.&lt;/li&gt;&#xA;&lt;li&gt;Some receivers use multiple (two or three, sometimes four) intermediate frequencies, in an attempt to get around the disadvantages of a superhet design (image rejection is the big one).&lt;/li&gt;&#xA;&lt;li&gt;As mentioned in another answer, there can be issues with 50Hz/60Hz hum from mains electricity in a direct-conversion receiver. This is a complete non-issue in a superhet receiver, assuming that the final conversion to baseband and the audio path are designed properly to avoid it.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Of course there are also disadvantages - the big one is of course image rejection, but careful selection of an IF and some basic filtering can make that go away. Another one is the display of the frequency being tuned.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-09-10T02:38:17.057" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15311" PostTypeId="1" CreationDate="2019-09-10T11:30:39.567" Score="2" ViewCount="83" Body="&lt;p&gt;I'm looking for info on demodulating both sides of an ISO14443 communication using a cheap SDR, preferably an RTL-SDR (R820T2+RTL2832U). The application is passively monitoring an &lt;a href=&quot;https://en.wikipedia.org/wiki/Near-field_communication&quot; rel=&quot;nofollow noreferrer&quot;&gt;NFC&lt;/a&gt; exchange for debugging purposes (like &lt;a href=&quot;https://github.com/Proxmark/proxmark3/wiki&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; or &lt;a href=&quot;http://www.keolabs.com/SC-ProxiSPY__product__smart-card-testing.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; specialized tools allow), using a pickup coil next to the devices. I'm restricting to ISO/IEC&amp;nbsp;14443-2:2010 (which covers some of the most-used NFC modes).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Operation uses magnetic induction at f&lt;sub&gt;c&lt;/sub&gt;=13.56MHz (an ISM band). The field is generated by the reader (aka PCD), with a TRP often up to 1W. It is picked-up by a card (aka PICC) at like up to 100mm. The PICC's antenna is typically a coil (like 60mm diameter, 3 turns), connected to an (integrated) capacitor forming an L(R)C tuned slightly above f&lt;sub&gt;c&lt;/sub&gt;, followed by a rectifier for power extraction. The PICC transmits by load modulation of a sub-carrier at f&lt;sub&gt;s&lt;/sub&gt;=f&lt;sub&gt;c&lt;/sub&gt;/16=847.5kHz. That creates sidebands (e.g. at f&lt;sub&gt;c&lt;/sub&gt;&amp;pm;f&lt;sub&gt;s&lt;/sub&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PCD transmission is ASK &amp;approx;10% NRZ-L (or [*] ASK &amp;approx;100% modified Miller). PICC transmission is BPSK NRZ-L (or [*] OOK Manchester). Bit rates are f&lt;sub&gt;s&lt;/sub&gt;/8, f&lt;sub&gt;s&lt;/sub&gt;/4, f&lt;sub&gt;s&lt;/sub&gt;/2, sometime f&lt;sub&gt;s&lt;/sub&gt; (&amp;approx;106, 212, 424, sometime 848 kbit/s), negotiated independently in each direction.&lt;br&gt;&#xA;[*] These modes are for the so-called &quot;type A&quot; at f&lt;sub&gt;s&lt;/sub&gt;/8 bit rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Issues designing a circuit between the pickup coil and SDR:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the 13.56MHz field can be strong (&gt;4V RMS for each turn of an unloaded 60mm diameter pickup coil) and should not fry the SDR&lt;/li&gt;&#xA;&lt;li&gt;that 13.56MHz field varies enormously (?-25dB) depending PCD, PICC, and position of a pickup coil (and to a lesser degree according to internal activity in the PICC, which varies between communication bursts).&lt;/li&gt;&#xA;&lt;li&gt;the 847.5kHz sub-carrier is comparatively very weak (?-40dB), and also very variable depending on devices and placement of a pickup coil.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Info, links, ideas (even half-baked) welcome.&lt;/p&gt;&#xA;" OwnerUserId="15638" LastEditorUserId="15638" LastEditDate="2019-09-10T12:07:46.053" LastActivityDate="2019-09-10T12:07:46.053" Title="Demodulating ISO14443 (part of NFC) using SDR?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15312" PostTypeId="1" AcceptedAnswerId="15313" CreationDate="2019-09-10T19:26:50.970" Score="1" ViewCount="90" Body="&lt;p&gt;I've got a week-old TYT TH-9800, a quad-band (10/6/2/70cm) mobile, Chinese knock-off of a Yaesu HT-8900.  So far, I love it -- several times the power of my HT, and a better antenna actually outside the car, I can stay on a single repeater for my whole commute (does get a little scratchy in the bottoms of draws at 40+ miles out, of course).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've noticed a couple times, however, that the &quot;right half&quot; of the radio will receive while I'm transmitting, either on the right half as well or on the left half.  When it's done it while the left half was transmitting, the left half was on &lt;em&gt;6m&lt;/em&gt; -- and it's only ever done it on one frequency,  right half on a repeater setting, 145.470 (standard offset, don't recall the tone but PL enabled).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first time I heard this, my own voice was intelligible from the speaker while transmitting on the right half, and the left half tuned to, as I recall, a 6m repeater.  The other time, I heard pretty garbled signal exactly when I keyed the mic while tranmitting on 6m on the other half of the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can switch the right half to another nearby channel, 145.250, and no more cross-talk.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this just a consequence of a cheap radio, or is it something that just happens sometimes?  &lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-09-11T11:10:21.710" LastActivityDate="2019-09-11T15:55:23.603" Title="New quad-band mobile receives while transmitting?" Tags="&lt;rfi&gt;&lt;mobile&gt;&lt;repeater&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15313" PostTypeId="2" ParentId="15312" CreationDate="2019-09-10T21:00:56.563" Score="3" Body="&lt;p&gt;It's something that happens sometimes. Perfect isolation is hard, and harmonics are a thing, so you're most likely to see an issue while transmitting on a lower-frequency band and receiving on a higher-frequency band — but any band combination is possible, due to images.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difficulty of doing this right is why full-duplex radios are somewhat rare — most dual-receive radios, even if you could mod them to leave the receiver on, wouldn't have enough isolation between the two sides for the receiver to be useful anyway. So it's not entirely surprising that sometimes there are minor issues even on a radio that is specced for full-duplex.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2019-09-11T15:55:23.603" LastActivityDate="2019-09-11T15:55:23.603" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15314" PostTypeId="1" AcceptedAnswerId="15330" CreationDate="2019-09-10T21:40:43.447" Score="5" ViewCount="266" Body="&lt;p&gt;Looking to take up learning understanding everything from basic electronics to how today's wideband radios work, so that I can build my own radio systems (not just ham radios), and talk radio concepts better. Would ARRL Handbook be a good enough guide to learn from? Or are there any missing pieces to that book which can be done with other sources?&lt;/p&gt;&#xA;" OwnerUserId="6722" LastEditorUserId="76" LastEditDate="2019-09-12T02:14:30.007" LastActivityDate="2019-09-13T21:27:07.120" Title="ARRL handbook as a reference for all your radio learning needs?" Tags="&lt;antenna-theory&gt;&lt;software-defined-radio&gt;&lt;electronics&gt;&lt;equipment-design&gt;&lt;arrl&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15315" PostTypeId="1" CreationDate="2019-09-12T05:31:24.573" Score="1" ViewCount="82" Body="&lt;p&gt;My Hy-Gain TH6DXX antenna has been up on a tower about 20 years, with excellent results.   Suddenly, the gain of the antenna is off the side; in other words, when the boom is broadside to the transmitting station, and the element ends are pointing at it.  Just 90 degrees off of where it has been and where it should work. This is verified in any direction. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SWR of the antenna is excellent. I have tried different frequencies in the different bands and the results are the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone have any guesses to what has happened?&lt;/p&gt;&#xA;" OwnerUserId="15650" LastEditorUserId="8717" LastEditDate="2019-09-12T17:30:48.033" LastActivityDate="2019-09-12T17:40:17.660" Title="Beam antenna changed directivity" Tags="&lt;antenna&gt;&lt;theory&gt;&lt;yagi&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15316" PostTypeId="2" ParentId="15315" CreationDate="2019-09-12T06:38:12.997" Score="3" Body="&lt;p&gt;I would suggest that one of the transmission line connections to the antenna, probably the earth if you are using coax, has become disconnected at the antenna feed point, and it's just a coincidence that the SWR is still ok.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-09-12T06:38:12.997" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15317" PostTypeId="1" AcceptedAnswerId="15318" CreationDate="2019-09-12T08:46:42.400" Score="3" ViewCount="81" Body="&lt;p&gt;I was trying to DIY a VHF/UHF diplexer, and got some weird readings from the VNA.&lt;br&gt;&#xA;By debugging I reached this trivial circuit:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/qpjGf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qpjGf.jpg&quot; alt=&quot;circuit&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which has the following frequency response:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/dQ9nq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dQ9nq.png&quot; alt=&quot;response&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm trying to figure out where the parasitic elements come from and why they are of such magnitude that I get -9dB in UHF. Any help or pointers would be awesome.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT: To be more precise, I've calculated the stray inductance at around 60nH and capacitance at less than 1pF for this specific scenario (wire above ground plane). What makes me uncomfortable is that the simulated cutoff is earlier and less aggressive than what I measure.&lt;/p&gt;&#xA;" OwnerUserId="11474" LastEditorUserId="2988" LastEditDate="2019-09-12T11:12:29.437" LastActivityDate="2019-09-13T06:01:17.317" Title="Help understanding transmission loss of trivial circuit" Tags="&lt;diy&gt;&lt;uhf&gt;&lt;filter&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15318" PostTypeId="2" ParentId="15317" CreationDate="2019-09-12T11:34:14.333" Score="3" Body="&lt;p&gt;Your measurement looks about right.  I think your circuit looks like a loop antenna, of about 20 cm in circumference, so it will start to radiate well when the wavelength gets below ~ 80 cm, about 400 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The loss you see is radiation - the circuit/antenna is radiating the signal into space, not absorbing it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stray inductance calculations don't work when the circuit is a good fraction of a wavelength, but if you like, 60 nH is 170 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; at 450 MHz, which is a lot more than 50 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a circuit to work at UHF, keep the wire lengths shorter than 1 or 2 cm, or better, use 50 ohm track on the circuit board. For starters, solder the SMA connectors directly to the board. You could place them on edge, or better, use a single sided board, and solder them flat on to the copper side, with their pins sticking through, ready for inventing your circuit on the clean side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a picture of a good looking DIY UHF construction method (from &lt;a href=&quot;https://xtronic.org/circuit/amplifier/wideband-dtv-uhf-antenna-tv-amplifier-circuit/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;)&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Z0iTG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Z0iTG.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2019-09-13T06:01:17.317" LastActivityDate="2019-09-13T06:01:17.317" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15319" PostTypeId="1" CreationDate="2019-09-12T12:17:42.190" Score="0" ViewCount="191" Body="&lt;p&gt;I want to extend WiFi signal using a passive repeater between two isolated boxes (have to make both box wireless).&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Transmitter antenna from box A is placed in the gap between box A and B.&lt;/li&gt;&#xA;&lt;li&gt;In the same gap at distance of about 10cm receiving antenna for box B which will be connected through coax to a computer in box B.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For link budget calculation:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Receiver antenna gain 0db.&lt;/li&gt;&#xA;&lt;li&gt;Max Transmitter power for wifi 20dBm&lt;/li&gt;&#xA;&lt;li&gt;Propagation loss in free space for 10 cm is -16db&lt;/li&gt;&#xA;&lt;li&gt;Wire loss is 0.3dbi/m for 3m - 0.9db.&lt;/li&gt;&#xA;&lt;li&gt;Prx = 20dbm - 16db -0.9db = 3.1dbm.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is this calcuation correct?&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, if free space is very less, can I couple all signal to receiving antenna?&lt;/p&gt;&#xA;" OwnerUserId="15644" LastEditorUserId="8717" LastEditDate="2019-09-12T17:15:31.313" LastActivityDate="2019-09-12T20:13:38.197" Title="Passive antenna system as a Wi-Fi repeater" Tags="&lt;antenna-theory&gt;&lt;rf-power&gt;&lt;wifi&gt;&lt;microwave&gt;&lt;link-budget&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2019-09-13T08:35:10.640" ContentLicense="CC BY-SA 4.0" />
  <row Id="15320" PostTypeId="1" CreationDate="2019-09-12T13:25:28.203" Score="-4" ViewCount="102" Body="&lt;p&gt;I want to understand, as most rocket uses LAN cable and switches to communicate between stages. Is it possible to replace with WiFi? Although it's will be complex system but one idea to make each stages wireless. How can I improve reliability? With combination of wireless and wireless can we communicate within its structure. How to improve coupling between antennas?&lt;/p&gt;&#xA;" OwnerUserId="15644" LastEditorUserId="15644" LastEditDate="2019-09-15T21:22:07.857" LastActivityDate="2019-09-15T21:22:07.857" Title="Wifi inside a rocket" Tags="&lt;rf-power&gt;&lt;wifi&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15321" PostTypeId="2" ParentId="15320" CreationDate="2019-09-12T13:56:45.373" Score="3" Body="&lt;p&gt;The biggest issue between stages is that wifi doesn't penetrate metal well.  Engine bells and plumbing are generally metal, even if tanks and exterior airframe skin aren't.  Since cables are highly reliable, it's worth having the weight to avoid dropouts when flight conditions add enough interference on top of the signal blockage to cut off your guidance at just the wrong time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Too, signal wires needn't be heavy gauge; therefore, they can be fairly light (though the conduit they run in usually can't be lightened as much, it has to stand up to stresses of one kind or another).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-09-12T13:56:45.373" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15322" PostTypeId="2" ParentId="15315" CreationDate="2019-09-12T17:40:17.660" Score="0" Body="&lt;p&gt;I can think of two possibilities.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The antenna and/or mast slipped 90° in relation to the rotor&lt;/li&gt;&#xA;&lt;li&gt;The rotator control box direction indication is 90° off. This could be caused by the pot in the rotor itself, or something inside the control in your shack.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-09-12T17:40:17.660" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15323" PostTypeId="2" ParentId="15319" CreationDate="2019-09-12T18:02:02.703" Score="1" Body="&lt;p&gt;Your math seems correct, but you're making some assumptions that might not work out in practice.  First, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Friis_transmission_equation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Friis transmission equation&lt;/a&gt; assumes that the transmitting and receiving antennas are in each others' far fields, but the 10 cm distance you specify is less than a wavelength (12.2 cm at a typical WiFi frequency of 2.45 GHz), which puts you in the &quot;&lt;a href=&quot;https://en.wikipedia.org/wiki/Near_and_far_field#Transition_zone&quot; rel=&quot;nofollow noreferrer&quot;&gt;transition zone&lt;/a&gt;&quot; between the near field and the far field, which means that your path loss may be different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, your antenna gain of 0 dB basically assumes that your antennas are isotropic, which means that they radiate and receive equally in all directions.  There is no such thing as an isotropic antenna in the real world, although there are real antennas that have 0 dB gain in specific directions.  A &quot;lossless&quot; dipole antenna (another antenna that doesn't exist) has a gain of about 2.15 dB.  So if you were using two dipoles in free space that were broadside to each other, far enough that they are in each others' far fields, then you would have antenna gain of about 4.3 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it's not possible to give an exact estimate of the gain you would see in real life from the information that you have given us.  I'm not an electrical engineer, but I think that you would have better coupling (more gain) than your calculations say.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2019-09-12T20:13:38.197" LastActivityDate="2019-09-12T20:13:38.197" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15324" PostTypeId="2" ParentId="15314" CreationDate="2019-09-12T18:42:43.773" Score="4" Body="&lt;p&gt;While it is useful to have, &lt;strong&gt;NO&lt;/strong&gt; single book contains everything that you want or need to know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the &lt;em&gt;ARRL Handbook&lt;/em&gt; is published every year, and each year contains different information. But even if you owned every Handbook that was ever published, inevitably something you want to know will still be missing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last Handbook that I bought was because arrl.org advertised it as having a new and featured section about something that I really wanted to learn about. However, after I received it in the mail, there were only a couple of pages about it. I had to use Google to find the information that I wanted.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-09-12T20:22:49.543" LastActivityDate="2019-09-12T20:22:49.543" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15325" PostTypeId="2" ParentId="15314" CreationDate="2019-09-12T19:01:54.973" Score="4" Body="&lt;p&gt;The &lt;em&gt;ARRL Handbook&lt;/em&gt; is a useful reference, but it's just that: a &lt;strong&gt;reference&lt;/strong&gt;.  It's not written as a text.  It's useful for looking up forgotten details of stuff you almost mostly know, but it's not in a good form for learning things like electronics, antenna theory, an the like.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A text aimed at self-study would be much more useful -- one written to be learned from.  An updated version of &lt;em&gt;Elements of Radio&lt;/em&gt; (Marcus and Marcus, last edition 1959) would be just about exactly right; it's a learning text that is intended that the learner build along, working from a basic crystal set receiver up to sophisticated receiving and transmitting circuits.  It's even useful for the self-learner, with review questions and circuits that include component values (if not tubes that are still easy to get).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, in 1959, transistors were new and cost as much as tubes, if not more (but were much more delicate); its emphasis was almost entirely on vacuum tubes and there's little if any solid state circuity (I haven't gotten completely through it, because I stopped well along the receiver section, planning to start building the circuits to better understand what was happening).  Sure, it's possible to do anything with solid state that a vacuum tube circuit will do (except possibly handling very high power, from hundreds of watts into the kilowatts range), but the conversion isn't at all obvious since tubes generally run on voltage, and transistors mostly on current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The learning path you describe is hard to follow even in college level courses today -- at a minimum, you'd be looking at a full four-year course in electronic engineering.  You'll probably get more satisfaction choosing some intermediate goals and working toward them before committing yourself to go as far as radio can go.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-09-12T19:01:54.973" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15327" PostTypeId="1" CreationDate="2019-09-13T14:23:38.000" Score="0" ViewCount="57" Body="&lt;p&gt;On our local Relay there are from time to time transmissions, where only static can be heard. Most transmissions via relay can be heard clearly. What could be the cause of this?&lt;/p&gt;&#xA;" OwnerUserId="10691" LastEditorUserId="8717" LastEditDate="2019-09-13T14:43:57.673" LastActivityDate="2019-09-17T14:58:43.373" Title="Local Relay with static" Tags="&lt;vhf&gt;&lt;repeater&gt;&lt;signal-identification&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15328" PostTypeId="2" ParentId="15327" CreationDate="2019-09-13T14:38:37.003" Score="3" Body="&lt;p&gt;Could very well be someone who is bored and opens the repeater without actually transmitting anything useful. Happens on a lot of repeaters. You only need one person to do this to bother all users of the relay...&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2019-09-13T14:38:37.003" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15329" PostTypeId="2" ParentId="15327" CreationDate="2019-09-13T18:39:07.380" Score="0" Body="&lt;p&gt;I hear this from time to time on more than one of my local repeaters -- especially on one that has a significant height advantage over most (1400 feet up a TV transmitting tower).  Given the length of some of the static-only transmissions, and their timing (about when I regularly hear two or three local hams have their morning conversation), I have a hypothesis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hear this from time to time when I'm driving (I only listen to repeaters when driving; I've got too much other stuff to do at home, and don't own a fixed location radio that can access repeaters in any case).  &lt;em&gt;When&lt;/em&gt; I hear it is when I'm driving though a local terrain depression -- a small valley -- in a location far enough from the repeater to produce at least a partial signal blockage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I encountered this again this morning on my way to work, and was able to verify that the S-meter bargraph on my radio's display was showing its minimum level -- yet the squelch was open with no audible signal.  I took this as confirmation of my hypothesis below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I believe is happening when this occurs is that someone transmits and keys the repeater; the repeater opens and sends its CTCSS tone, which my radio detects and opens its squelch -- but the signal from the repeater is attenuated enough by terrain that instead of clear voice, I hear only the noise floor that would always be present without squelch.  The CTCSS tone is &quot;subaudible&quot; -- below most radios' frequency response limit -- but it can also be detected in pretty heavy noise because the receiver is filtering for a single, narrow audio frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not to say you can't hear static-only when someone &quot;kerchunks&quot; the repeater (illegally makes a short unidentified transmission), but in my experience, what I get then is a short period of &quot;full quiet&quot;, followed by the repeater's courtesy tone and the very short static burst before my radio's squelch closes.  That's very different from a long period of static with the squelch open.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-09-17T14:58:43.373" LastActivityDate="2019-09-17T14:58:43.373" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15330" PostTypeId="2" ParentId="15314" CreationDate="2019-09-13T21:27:07.120" Score="2" Body="&lt;p&gt;You might consider the following two books useful in learning more about radio design and the details of various circuits used in transceivers.  These two are not equal in their coverage -- the first considers the electronics of radio technology and the second is more focused on the science and mathematics governing the application of various radio circuits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First suggestion:  The Electronics of Radio, by David B. Rutledge, published by Cambridge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This book is used by the author as a text book for a radio/electronics course given to undergraduate (mostly) students at Caltech.  I also know that it has been taught at other universities too.  This book uses a novel approach to teach about radio electronics.  It uses a kit, popular at the time of its original publication, The Norcal 40A, a 40-meter CW Transceiver, in presenting the material.  Students would put the transceiver together but along the way lab courses (outlined in the book) would be used to perform measurements or tests on various circuit elements in isolation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although the Norcal 40A is no longer available (at least the last time I looked it was not available), you can still get a lot out of this book even without building the radio.  You can still do many of the suggested &quot;labs&quot; and you can still do most of the problem sets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After preliminary chapters on electronics and electronic components used in the 40A, the chapters cover: Transmission Lines, Filters, Transformers, Acoustics, Transistor Switches, Transistor Amplifiers, Power Amplifiers, Oscillators, Mixers, Audio Circuits, Noise &amp;amp; Intermodulation, and Antennas &amp;amp; Propagation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second Suggestion: The Science of Radio by Paul J. Nahin, published by AIP Press.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I own every book Paul Nahin has written and I have read them all.  This one on the Science of Radio is one of my favorites.  This book can be used as a text book as well, it has problem sets for each chapter.  It also makes use of MATLAB and Electronics Workbench for various lab type exercises.  If you do not own a copy of MATLAB, you could probably get by with the trial demo copy.  But, then again you don't actually need MATLAB, I did all computation and graphics using Mathematica instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This book is a bit more focused on the mathematics of Radio as it gets into the use of Calculus and a few Differential Equations and Fourier Analysis in describing the workings of various radio circuits.  This book asks the reader to spend more time working through the mathematical theory as a means of understanding the content.  Thus, is is less of an armchair read than the Rutledge book but honestly both require study and a sharp pencil (or, whatever you choose to use).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The chapter headings are not that useful in understanding the content so I have not included them here.  Instead, I submit you consider Amazon or other resources on-line that include a detailed table of contents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good study of both of these books with dedication to doing the problem sets and lab exercises provides a very good education on radio technology, the electronics used by radios (both transmitters and receivers), and the science &amp;amp; math (or, Engineering) background to know the theory.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2019-09-13T21:27:07.120" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15331" PostTypeId="2" ParentId="1052" CreationDate="2019-09-15T06:22:42.423" Score="-3" Body="&lt;p&gt;NO  where I live the house heating is electric in the ceiling acting as a faraday cage   no cell service in center of area and barely any on perimeter of building 2mtr and 70 cm same no service  on HF lower freqs but marginal&lt;/p&gt;&#xA;" OwnerUserId="15663" LastActivityDate="2019-09-15T06:22:42.423" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15332" PostTypeId="1" CreationDate="2019-09-15T13:50:25.580" Score="3" ViewCount="364" Body="&lt;p&gt;In Portugal, to transmit, one must take the category 3 exam, then wait for 2 years to take the category 2 exam. While these 2 years go by, one cannot emit on his station. I find this rather annoying.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any EU country where I can go and get my license and then use it to operate in Portugal? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.anacom.pt/render.jsp?contentId=978436&amp;amp;languageId=1&quot; rel=&quot;nofollow noreferrer&quot;&gt;Portuguese Law on the matter, check article 5&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Article 5 Amateur categories&lt;/p&gt;&#xA;  &#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;&lt;p&gt;There are six amateur categories: 1, 2, 3, A, B and C; the first&#xA;  three categories - 1, 2 and 3 - correspond to the ranking of amateurs&#xA;  after they have taken the ability exam pursuant to this Decree-Law and&#xA;  procedures set out herein; the other three categories - A, B and C -&#xA;  correspond to existing categories, which are maintained.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Category 3 is accessed to where the respective exam is passed.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Without prejudice to paragraphs 8 and 9 of article 6, access to&#xA;  category 2 requires:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;a) Passing the respective exam, to which may apply amateurs over 16&#xA;  years of age who remained in category 3 for at least two years, and&#xA;  amateurs of category C;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;b) An application for this purpose submitted by holders of valid&#xA;  qualifying documents issued by CEPT, ITU or a country with which&#xA;  Portugal has a reciprocity agreement.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Without prejudice to paragraphs 8 and 9 of article 6, access to&#xA;  category 1 requires:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;a) Passing the respective exam, to which may apply amateurs who&#xA;  remained in category 2 for at least one year and amateurs of category &#xA;  A and B;&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;b) An application for this purpose submitted by holders of valid&#xA;  qualifying documents issued by CEPT, ITU or a country with which&#xA;  Portugal has a reciprocity agreement.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Amateurs who were subject to any sanction for infringement of&#xA;  obligations provided for herein in the two preceding years may not&#xA;  apply to any exam.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;ICP - ANACOM shall define and publicise procedures to be followed&#xA;  as regards access to amateur categories by holders of valid qualifying&#xA;  documents issued by CEPT, ITU or a country with which Portugal has a&#xA;  reciprocity agreement.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="15665" LastEditorUserId="7804" LastEditDate="2019-10-03T14:22:56.783" LastActivityDate="2019-10-03T14:22:56.783" Title="Can a person in Portugal get an amateur radio license in another country?" Tags="&lt;license&gt;&lt;europe&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15333" PostTypeId="2" ParentId="15332" CreationDate="2019-09-15T16:39:30.507" Score="4" Body="&lt;p&gt;I don't have the full answer, but I hope I can give you some pointers on where to search.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you get a HAREC (Harmonised Amateur Radio Examination Certificate) &#xA;license in any country that complies with HAREC, i.e, the license test covers a certain set of topics, you should be able to transfer the license to another country. Most European countries are in HAREC one way or other. You have to find one where the licensing doesn't take as long, at least in Finland there are no wait times.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another related acronym is CEPT (European Conference of Postal and Telecommunications Administrations) that allows you to obtain a license in one country and then temporarily use it elsewhere. However, this doesn't help in your case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Amateur_radio_international_operation&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Amateur_radio_international_operation&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/reciprocal-permit-faqs&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/reciprocal-permit-faqs&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="194" LastActivityDate="2019-09-15T16:39:30.507" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15334" PostTypeId="1" CreationDate="2019-09-15T19:25:03.037" Score="3" ViewCount="59" Body="&lt;p&gt;I am working on space-ground networking for a Cube Satellite, and one of our candidate Layer 2 protocols is AX.25. We haven't settled on a physical layer, but it's likely to be some form of quadrature-encoded PSK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we were using Cubesat Space Protocol (CSP) as a Layer 3/4 protocol, what would go in the PID field for I and UI type frames? Would we just pick a random number out of the YY11YYYY and YY00YYYY values other than those listed, or is that a no-no? Would we treat it as 0xF0 &quot;No layer 3 protocol implemented.&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or alternatively, does it not matter in the end? Does the PID field for I and UI frames do anything?&lt;/p&gt;&#xA;" OwnerUserId="15667" LastEditorUserId="76" LastEditDate="2019-09-15T19:49:19.817" LastActivityDate="2019-09-15T19:49:19.817" Title="What value goes in the AX.25 PID field if the Layer 3 protocol is not defined in the standard?" Tags="&lt;digital-modes&gt;&lt;satellites&gt;&lt;software&gt;&lt;software-development&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15335" PostTypeId="1" CreationDate="2019-09-16T00:20:04.803" Score="10" ViewCount="256" Body="&lt;p&gt;Lately I've been thinking about weak signal communication on HF. &lt;em&gt;Very&lt;/em&gt; weak, like weaker than even WSPR could achieve.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be nice if one could simply take any existing modulation and slow it down to achieve an arbitrarily high Eb/N0 and thus, given sufficient time, communicate with arbitrarily low power. However I understand ionospheric conditions introduce distortions which make this not really work in practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, there exists a WSPR-15 mode, which is like WSPR-2 but uses 15-minute instead of 2-minute intervals. This should mean WSPR-15 is about 9 dB more sensitive, but &lt;a href=&quot;http://wsprnet.org/drupal/node/3891&quot; rel=&quot;nofollow noreferrer&quot;&gt;the documentation states&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;WSPR-15 is not recommended for use at HF: the tone spacing is only 0.183 Hz, less than the Doppler spreading typical of many HF paths&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, what is &quot;Doppler spreading&quot;, and how much of it is there on HF paths, and what can be done to overcome this challenge? More broadly, are there other properties of HF channels that limit the attainable sensitivity?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-09-16T20:23:52.777" LastActivityDate="2020-01-22T00:28:54.300" Title="Practical limits to maintaining coherence in an HF channel" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;modes&gt;&lt;qrp&gt;" AnswerCount="6" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15337" PostTypeId="2" ParentId="15335" CreationDate="2019-09-16T06:09:38.997" Score="1" Body="&lt;p&gt;Any transmissive data channel will hit a lower power limit for readability when the signal no longer exceeds the noise floor of the transmission mode. This is another way of saying that the minimum-required signal strength for establishing data exchange is dependent on the position of the noise floor. So understanding the physics and math behind S/N ratios is needed to work on this problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition, it is at least theoretically possible to obtain very low noise interference if the signal bandwidth is extremely narrow. However, the narrower the bandwidth, the lower the theoretical maximum data rate will become, which means as the bandwidth approaches zero, so does the data rate. Working in this arena hence requires you to understand the relationship between bandwidth and data rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Data rate limits in narrow-band data transmission can be mitigated by data compression, in which some portion of the signal is discarded by an encoding algorithm so as to reduce the bandwidth needed to meet the data rate requirement, but there are information-theory based limits to how much compression can be applied to a signal before it stops being a signal. An information theory background will be helpful in this context. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, the integrity of a transmitted signal can be enhanced in weak-signal applications by adding redundancy into the transmission- in the simplest form, this would mean transmitting every bit in the data stream twice to ensure it gets received at least once. In this simple model, adding full redundancy cuts the data rate in half. It is possible to do better than this using data encoding that incorporates things like checksum exchange to improve integrity without drastically decreasing the data rate. This falls into the realm of digital signal processing as practiced in the computer world, which is another thing you'd need to master in order to work in this field. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I invite the experts here to add their perspectives. &lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2019-09-16T06:09:38.997" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15338" PostTypeId="2" ParentId="1052" CreationDate="2019-09-16T11:16:27.113" Score="0" Body="&lt;p&gt;Legalities aside, what I would see as a significant caution in this case is that unless you have constant monitoring and an automatic shutdown in place, you have no immediate way to be sure your Faraday cage hasn't failed.  If your enclosure is damaged and you transmit, your transmission will propagate according to frequency and conditions -- and may cause &quot;harmful interference&quot; without you even being aware you're violating the law.  Note that you are also bound by requirements to perform an RF exposure evaluation to ensure that your experiments are safe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The microwave oven mentioned in comments is a bad example, because if (say) a door seal or the mesh in the window is damaged, it may leak enough microwave RF to cause significant problems without the operator being aware of it -- and even when in good condition, certain sensitive devices (older pacemakers, for instance) may receive harmful interference from the leakage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Further, I would question what can be learned by transmitting at significant power inside a reasonably sized shielding enclosure -- reflections from the enclosure itself will swamp anything you might be studying as far as propagation, and will tend to amplify spurious emissions like harmonics (you'll detect the harmonic and its reflection from each wall of the cage, out of phase by some number of nanoseconds).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-09-16T11:16:27.113" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15339" PostTypeId="2" ParentId="1052" CreationDate="2019-09-16T16:24:28.993" Score="1" Body="&lt;p&gt;The practical answer is &lt;strong&gt;&lt;em&gt;yes&lt;/em&gt;&lt;/strong&gt;, as long as (as others have nicely answered here) your signal cannot be detected outside the cage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you might damage your transmitter. As an example, let's say you have a Faraday cage that's not much larger than your antenna. It might be impossible to tune the vswr for a good match, thereby heating the RF output stage beyond safe limits.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-09-16T17:06:02.883" LastActivityDate="2019-09-16T17:06:02.883" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15340" PostTypeId="1" AcceptedAnswerId="15344" CreationDate="2019-09-16T18:00:51.703" Score="0" ViewCount="114" Body="&lt;p&gt;Can I add a center-frequency parameter for my noise generator flowgraph, is there a different noise source that has this parameter other than the generic noise source block?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GKi8j.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GKi8j.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15206" LastActivityDate="2019-09-17T15:29:47.933" Title="Center-frequency parameter for gnuradio noise generator flowgraph" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15341" PostTypeId="2" ParentId="15335" CreationDate="2019-09-16T20:08:45.987" Score="-1" Body="&lt;p&gt;As Neils mentions, I don't see any better technique other than incorporating checksum exchange. This would be true regardless of the modulation technique.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, both stations could be half-duplex and constantly exchanging ACK/NOACK data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;strong&gt;NOACK&lt;/strong&gt;[nowledge] would cause the data to be repeated until an ACK is received.&#xA;An &lt;strong&gt;ACK&lt;/strong&gt;[nowledge] from the receiving station would tell the transmitting station to send the next data packet.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-09-16T20:08:45.987" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15342" PostTypeId="2" ParentId="1052" CreationDate="2019-09-16T22:40:59.160" Score="0" Body="&lt;p&gt;The answer to this question is really simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You cannot legally transmit using radio equipment that you are not licensed to operate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact in some cases you are not even allowed to own equipment that you are not licensed to operate.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-09-16T22:40:59.160" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15343" PostTypeId="2" ParentId="15335" CreationDate="2019-09-17T02:25:48.610" Score="3" Body="&lt;p&gt;If a transmitter is moving toward or away from you, the received frequency will get shifted up or down, depending on direction and rate of movement.  Even if the transmitter and receiver are not moving relative to each other, but a reflector, reflecting the signal between them, is moving, the you can get the same Doppler effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's well known (at minimum, from the license exam question pool) that non-line-of-sight HF propagation is made possible by refraction and reflection off of the ionosphere.  But the ionosphere changes in many aspects, including height, not only with time-of-day, but with high altitude weather, solar radiation, and etc., lots of things.  As the ionosphere altitude changes, you get a moving mirror, thus a bit of doppler shift of your HF signal frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But that's not all.  The ionospheric reflector is nowhere near flat.  Thus you get multiple reflections (or refractive “bounces”), much like a fun house mirror.  As the shape and layering changes, the directions and amplitudes of the different multi-path paths move around; and different combinations of paths constructively and destructively interfere in a (unpredictably?) changing pattern.  Since each path has a different distance, its reflection likely has a different phase from other paths.  Thus, depending on how the combinations of multiple reflection paths changes, you get phase modulation on top of frequency modulation of your signal.&#xA;And fading with increasing phase cancellations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your demodulation scheme is using a DFT or FFT (or similar filter) on a strong signal, but half of the FFT window sees one phase and the other half sees the opposite phase, that signal will be invisible to the FFT result bin where you might expect to find your signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The statistics are such that the likelihood of a phase and frequency change of dF over time T increases with T.  (I don't know where to find those statistics.  Anybody?)  There appear to be papers from the 70's and 80's on research in this area.  Maybe earlier research papers as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, any narrowband communication scheme should either:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) track the doppler with a PLL or other adaptation, or&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) finish before the doppler shift and phase shifts are likely to be greater than the demodulation filter width and carrier lock delta-F.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;wspr-2 likely finishes fast enough often enough. wspr-15 possibly might not over typical HF ionospheric paths.  Neither wspr seems to have an internal PLL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The equivalent of a PLL might be a signal re-acquisition.  So perhaps repeating something the same length as a wspr-2 data transmission 7 or 8 times (or more) might provide more reliable coding gain than wspr-15, since each repeat would require a new fresh frequency and phase acquisition by the receiver, similar to a slow-motion step-function PLL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added: &#xA;Here’s an ITU document recommending an HF channel simulation model that includes Doppler shift/spreading : &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.itu.int/rec/R-REC-F.1487/en&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.itu.int/rec/R-REC-F.1487/en&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-09-19T23:36:32.430" LastActivityDate="2019-09-19T23:36:32.430" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15344" PostTypeId="2" ParentId="15340" CreationDate="2019-09-17T15:29:47.933" Score="1" Body="&lt;p&gt;The noise from that block doesn't have a center frequency because it's &quot;white&quot; — it has an equal power at &lt;em&gt;any&lt;/em&gt; frequency (up to the half the sample rate, anyway, and you can extend that as far as you need). You can &lt;em&gt;give&lt;/em&gt; it a shape by filtering it. Whatever the shape of the filter is, will be the shape of the resulting noise power. If you run it through a bandpass filter with a given center frequency, then the noise will have that center frequency.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-09-17T15:29:47.933" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15345" PostTypeId="2" ParentId="15332" CreationDate="2019-09-17T16:46:39.117" Score="1" Body="&lt;p&gt;The same conditions are applied in Portugal as in the other CEPT countries.&#xA;&lt;a href=&quot;https://www.anacom.pt/render.jsp?contentId=956629&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.anacom.pt/render.jsp?contentId=956629&lt;/a&gt;&#xA;I am not sure where you received your information, check with ANACOM.&#xA;This can be done by email, by post or im person.&#xA;Email: info@anacom.pt&#xA;&lt;a href=&quot;https://www.google.com/maps/place/ANACOM+-+Autoridade+Nacional+de+Comunica%C3%A7%C3%B5es/@38.73728,-9.163151,14z/data=!4m5!3m4!1s0xd1933141c4c82b7:0x2e94c673216a09ed!8m2!3d38.7373143!4d-9.1630645?hl=en&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.google.com/maps/place/ANACOM+-+Autoridade+Nacional+de+Comunica%C3%A7%C3%B5es/@38.73728,-9.163151,14z/data=!4m5!3m4!1s0xd1933141c4c82b7:0x2e94c673216a09ed!8m2!3d38.7373143!4d-9.1630645?hl=en&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15676" LastActivityDate="2019-09-17T16:46:39.117" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15347" PostTypeId="1" CreationDate="2019-09-17T21:14:55.843" Score="6" ViewCount="78" Body="&lt;p&gt;Recently, &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Ultra-wideband&amp;amp;oldid=915782881&quot; rel=&quot;noreferrer&quot;&gt;ultra-wideband&lt;/a&gt; technology has been in the news again. From the Wikipedia article:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;UWB transmissions transmit information by generating radio energy at specific time intervals and occupying a large bandwidth, thus enabling pulse-position or time modulation.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;From other reading I've done, I've gotten the impression that UWB signals can be used in a way quite similar to radar which makes sense. (In that it seems relatively plausible that one could send out a &lt;em&gt;known&lt;/em&gt; broad-spectrum signal and look for reflected returns that correlate well to what was sent.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But how would UWB work for transmitting data between two transceivers? My impression is that the transmit power is weak enough and spread out enough that these devices are allowed by the FCC as ± a Part 15 &lt;strong&gt;un&lt;/strong&gt;intentional radiator. Without sharing an exact timebase [at least, not initially?] how would a receiver discern signal pulses it should be interested in, versus other random broad-spectrum noise? And how many devices could be communicating simultaneously in a given area before the strategy falls apart?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2019-09-18T21:54:14.847" Title="Can an ultra-wideband system transfer data at high speed without precise clock synchronization?" Tags="&lt;rfi&gt;&lt;modes&gt;&lt;dsp&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15348" PostTypeId="2" ParentId="15335" CreationDate="2019-09-17T21:58:20.187" Score="0" Body="&lt;p&gt;This is an interesting topic, as I operate CW only (for 60 yrs) , &#xA;and now only QRP,&#xA;and commonly copy signals down to  SNR=1. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I certainly employ several different CW Filters &#xA;which reduce the sideband noise power &#xA;and limiter methods to quench QSB. &#xA;...&#xA;Recently I did a research project, published on ResearchGate.net &#xA;and also my own website www.GeoCities.WS/glene77is/ &#xA;This project utilizes phased-filtering to produce two -60 dB notches &#xA;surrounding the central f(0) band pass audio signal. &#xA;This greatly helps attenuate the sideband noise power. &#xA;Using this filter, I have consistently worked stations at SNR=1  and lower &#xA;( depending on just how much band-noise, static, QSB are present. &#xA;...&#xA;But the OQ was not about CW nor &quot;Navigating-by-the-Stars&quot;.&#xA;rather &#xA;the OQ was about &lt;strong&gt;computerized methods for Weak Signal Communication&lt;/strong&gt;. &#xA;...&#xA;So, I return to the original topic,&lt;br&gt;&#xA;which was &lt;strong&gt;&quot;weak signal communication on HF&quot; using computerized methods ** .&lt;br&gt;&#xA;...&#xA;**To Mike Waters&lt;/strong&gt;, &#xA;I like your suggestion about the 'original' error detection scheme which was &#xA;the   &quot;ACK/NOACK&quot;  data exchange control, very popular in 1976 for me.&lt;br&gt;&#xA;This Communication is still within the bounds of Father Nature &gt; SNR=1. &#xA;...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;(1)&lt;/strong&gt;&#xA;I would like your comments &#xA;about a technique which comes from a QST article &#xA;dated in 1976 (as I recall).  ---&#xA;&lt;strong&gt;Coherent CW&lt;/strong&gt; was the name of the method.   ---&#xA;It required a timing co-ordination scheme (very un-attainable in 1976) . &#xA;The original Coherent CW methods may be feasible ( 2019 ) &#xA;using Global Position Time signals, &#xA;but, by that same standard, would provide very slow and un-interesting communication &#xA;to the current crop of ham operators.&#xA;...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;(2)&lt;/strong&gt;&#xA;It appears to me that &lt;strong&gt;PSK-31&lt;/strong&gt; has incorporated this &quot;clock&quot; information &#xA;in its phase-shifting (+/- 15.25 Hz) .&lt;br&gt;&#xA;In our club, our operators have demonstrated accurate copy of PSK-31 at -9 dB.&#xA;PSK-31 methods are useful for ordinary Weak Signal HF communication and the speed is aprox 33 wpm, and allows good two-way conversation style communication.&lt;br&gt;&#xA;...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;(3)&lt;/strong&gt;&#xA;It appears to me that the extreme of these techniques &#xA;is the technology developed by &quot;JT&quot;  for ham use (&lt;strong&gt;JT-65&lt;/strong&gt;). &#xA;A step further is a similar Weak Signal method employed to communicate &#xA;with the several Space Probes. &#xA;Space Probe signals are in the hundreds of dB  below Johnson Noise levels. &#xA;With these methods, DSP and  statistical analysis is a key technique. &#xA;Space Probe methods are not practical for ordinary use.&lt;br&gt;&#xA;...&#xA;This is an interesting topic. &#xA;... Glen Ellis, K4KKQ &lt;/p&gt;&#xA;" OwnerUserId="8402" LastActivityDate="2019-09-17T21:58:20.187" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15349" PostTypeId="2" ParentId="15347" CreationDate="2019-09-17T22:25:07.307" Score="3" Body="&lt;p&gt;Even if all the transmitted UWB pulses are identical, and initially start at an unknown time, the pattern variations in the delta time between pulses could be used to code information.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As with any spread (spectrum or otherwise) system, a longer sequence with more coding might allow more (orthogonality coded?) signals to occupy a channel at some given reliability probability level.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-09-17T22:31:57.037" LastActivityDate="2019-09-17T22:31:57.037" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15350" PostTypeId="1" CreationDate="2019-09-18T11:49:13.017" Score="5" ViewCount="852" Body="&lt;p&gt;I just got a 100W HF radio and I am new at this. What is the cheapest antenna I can hook up without burning up my radio or shocking myself?&lt;/p&gt;&#xA;" OwnerUserId="15201" LastActivityDate="2019-09-18T15:26:17.617" Title="Cheap antenna for new HF HAM" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;rf-power&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15351" PostTypeId="2" ParentId="15350" CreationDate="2019-09-18T13:45:19.293" Score="3" Body="&lt;p&gt;Hello and welcome to the hobby!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally speaking, it depends on your conditions and area available. Assuming it's not a problem (e.g. you live in a suburb area and have a backyard or are willing to travel to the nearest forest) the simplest, cheapest and quite efficient antenna you can build is a dipole / inverted-V. There are a few ways to build one. I believe there is little sense to describe them here because there is a lot of information on this topic online and in the literature as well. I would like only to leave a few hints here:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A 10-meters long fishing rod is a good and cheap mast for a 7Mhz or 14Mhz dipole. Use three ropes and screwdrivers to make guys. &lt;/li&gt;&#xA;&lt;li&gt;A 1:1 balun made of 8 turns of RG58 coax on FT240-31 or FT240-43 ferrite core will improve the performance of the antenna.&lt;/li&gt;&#xA;&lt;li&gt;You can build a multiband antenna, so called fan dipole, if you connect multiple arms for each band&lt;/li&gt;&#xA;&lt;li&gt;&quot;ARRL Handbook&quot; and &quot;ARRL Antenna Handbook&quot; are great source of information on antennas.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-09-18T13:45:19.293" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15352" PostTypeId="2" ParentId="15350" CreationDate="2019-09-18T13:53:36.237" Score="9" Body="&lt;p&gt;The cheapest antenna you can set up is a speaker wire dipole.  A spool of speaker wire long enough to split the conductors and make a center fed half wave dipole ought to cost around ten dollars US (or less).  You can get useful radiation with supports made from cheap stud lumber from the home improvement store (8-10 dollars per support to get 5 meters off ground -- low for an HF dipole, but it will work).  Insulators can be made from bungee cord or zip ties (since the poles aren't conductive).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only thing you have to spend real money on is a suitable length of 50 ohm coaxial cable and an adapter to connect the antenna wires.  You most likely don't even need a balun with a center fed dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This close to the ground, you won't get the very low takeoff angle for DX, but you'll get plenty of ground wave contacts -- when 40 and 80 m are behaving a little (gray line or at night) you should be able to cover a few hundred miles, anyway.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-09-18T13:53:36.237" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15354" PostTypeId="2" ParentId="15350" CreationDate="2019-09-18T15:26:17.617" Score="3" Body="&lt;p&gt;Wire antenna are usually the easiest for beginners. The standard is a dipole with 1/4 wavelengths on each side connected in the center to your coax. Another easy antenna is a end fed half wave. It requires a bit more equipment as you need a transformer to match the high impedance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can buy or make your antennas. Home brew antennas are a popular way to get started in making equipment instead of buying. While there are many web resources with information on making EFHW antenna, here is good presentation that is relatively recent, &lt;a href=&quot;http://gnarc.org/wp-content/uploads/The-End-Fed-Half-Wave-Antenna.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://gnarc.org/wp-content/uploads/The-End-Fed-Half-Wave-Antenna.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I made a 40 meter end fed half wave antenna with a 49:1 transformer with 2 type 43 cores. I have made over 2500 contacts using it, primarily digital modes like FT8 and FT4, using mostly 40 meter, a few 30 meter, some 20 meter,a couple of 17 meter and 15 meter. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2019-09-18T15:26:17.617" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15355" PostTypeId="1" AcceptedAnswerId="15358" CreationDate="2019-09-18T16:14:26.443" Score="1" ViewCount="124" Body="&lt;p&gt;The event I'm currently attending hosts Ham exams, and it's kind of likely that the student would pass on first attempt; would it make sense for him to take the exam? Can he just go home to China and use the license to transmit on amateur bands?&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-09-20T19:23:08.097" Title="Can a foreign student take a US license exam in the US and use that license in China?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;china&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15356" PostTypeId="2" ParentId="15355" CreationDate="2019-09-18T17:21:28.403" Score="2" Body="&lt;p&gt;This would depend on what if any reciprocity agreements are in place between the USA and China.  If I (a US Amateur Extra license holder) were to travel to Europe as a tourist, I'd need to print a specific document and carry it with me, along with a printed copy of my license (and passport, but I should have that anyway).  If I were to travel to most of Latin America, I wouldn't have to do anything special.  There are places where I'd have to effectively get a local license (if they'd even issue one to a foreigner) to operate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One might be able to find out with a call, email, or paper letter to a local Chinese consulate.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-09-20T19:23:08.097" LastActivityDate="2019-09-20T19:23:08.097" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15357" PostTypeId="2" ParentId="15347" CreationDate="2019-09-18T21:46:39.573" Score="3" Body="&lt;p&gt;As hotpaw2 said, the thing is that while it looks like random noise, the actual UWB signal &lt;em&gt;is&lt;/em&gt; correlated, in &lt;em&gt;some specific way&lt;/em&gt; known to the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll explain this using an example (keeping it short, I'm at GRCon):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine your UWB transmitter using a scheme where it generates a wideband noise signal. The way it encodes a &quot;0&quot; bit is that it turns on the noise for exactly 1 ms, and then off for exactly 1 ms. To encode a &quot;1&quot;, it turns off the noise first, then on, same 1ms+1ms timing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your receiver would now always aggregate the noise power it sees for 1 ms, and for the following 1 ms; it would then compare these two, e.g. by dividing the first by the second energy value. If their difference is significant enough, it would be fairly sure that a) there is a transmitter operating, and b) what the transmitted bit was.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it was just noise, it would be unlikely that it'd be on only in the first millisecond, but not in the second.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In reality, you probably wouldn't do a 1 ms on, 1 ms off scheme (that only gives you 500 symbols per seconds, and each symbol only carries one bit. Not a lot of data speed!). Instead, for UWB, the typical times would more be in the nanosecond scale. Then, you wouldn't do a simple on-off or off-on method, but more likely a more complex sequence, dividing the symbol time in way more &lt;em&gt;chips&lt;/em&gt;, allowing for way more orthogonal sequences (&quot;orthogonal&quot; means that if you add two sequences, you can still detect the presence of both sequences from the sum). That would allow for more bits per symbol, or for multiple simultaneously operating transmitting devices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I didn't address clock synchronization here so far:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Especially for power-detection-only systems like UWB, symbol timing recovery is necessary; you'd often counter that by using short packets to avoid that clocks run out of sync, and start these short packets with a specially crafted sequence that has an autocorrelation that allows you to estimate the chip rate easily.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-09-18T21:54:14.847" LastActivityDate="2019-09-18T21:54:14.847" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15358" PostTypeId="2" ParentId="15355" CreationDate="2019-09-19T03:58:34.773" Score="3" Body="&lt;p&gt;A bit of Googling led me here: &lt;a href=&quot;http://www.crac.org.cn/?p=1646&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.crac.org.cn/?p=1646&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to that page, a visitor to China would need to submit an application for an &quot;AMATEUR RADIO OPERATOR’S CERTIFICATE FOR VISITORS&quot;, along with their foreign licence, their foreign passport and their Chinese visa.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The implication here is that if a Chinese national wants to get a US licence and then operate in China, they can not do that (since they have a Chinese passport and don't have a visa to enter China, obviously).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounds like they should take the exam in China to get their local amateur radio licence.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-09-19T03:58:34.773" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15359" PostTypeId="2" ParentId="15355" CreationDate="2019-09-19T04:35:55.293" Score="0" Body="&lt;p&gt;The answer to this question is very simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unless a special arrangement has been made, Amateur licenses are generally valid only for operation in the country that the license was issued in. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can't use a USA issued ham license in China.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-09-19T04:49:03.347" LastActivityDate="2019-09-19T04:49:03.347" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15360" PostTypeId="1" CreationDate="2019-09-20T14:25:54.857" Score="5" ViewCount="1706" Body="&lt;p&gt;I currently use a homebrew 40/60/80m vertical consisting of a 5M aluminium tube with a multi tapped coil at the base. The ground plane is the metal roof at my house, and the antenna is not centered in it, but it's next to one of the edges.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I read that for center loading, the coil needs to be twice as big as for base loading. So I was thinking of adding another 5M length of aluminium tube and raising the loading coil to the center of the antenna. Since the required coil will be twice as big, but the antenna is now twice as long, the coil will be the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I'd like to know is if there will be significant benefit of center loading the antenna, considering the hassle of raising a 10m tall radiator with a coil in the middle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, how is the radiation pattern affected by not centering the antenna in the ground plane?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2019-09-23T20:09:53.267" Title="Base vs center loading a vertical antenna" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15361" PostTypeId="2" ParentId="15360" CreationDate="2019-09-20T18:24:58.137" Score="3" Body="&lt;p&gt;In this context, loading is used to make an electrically short antenna resonant.&#xA;&lt;hr&gt;&#xA;In an electrically short vertical, moving the loading higher is almost always an improvement because it raises the point of maximum current, &lt;em&gt;where the majority of the radiation takes place&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Center is better than base loading and top loading is superior to center loading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Top loading is usually accomplished by adding capacitance to the top, rather than inductance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you move the loading, don't expect the taps to be in the right place. You'll need some other way of tuning the antenna at the base, and not the tapped coil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case, with the vertical all the way to the end of your metal roof peak, the gain will be strongest towards the roof and weakest away from the roof.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-09-23T20:09:53.267" LastActivityDate="2019-09-23T20:09:53.267" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15362" PostTypeId="2" ParentId="15355" CreationDate="2019-09-20T18:42:27.077" Score="0" Body="&lt;p&gt;As long they have a valid mailing address and are not representing a foreign government they can take the test, and if the pass get a US license and operate in the USA. There is a agreement with China for &quot;visitors&quot; to China to use their US license after approval, but I don't believe that would let a Chinese national or citizen to do so. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2019-09-20T18:42:27.077" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15364" PostTypeId="2" ParentId="15360" CreationDate="2019-09-21T06:07:29.390" Score="0" Body="&lt;p&gt;As a rough rule of thumb, moving inductive loading from near the feed point to near halfway up an antenna of the same dimension might improve radiation resistance by somewhere around 2X, minus added resistive losses. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But for antenna’s much shorter than lambda/4, radiation resistance goes up with roughly somewhere proportional to the square of the length.  So your biggest gain will be from the 2X taller vertical, not the repositioning of the loading inductor.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-09-21T21:11:18.957" LastActivityDate="2019-09-21T21:11:18.957" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15365" PostTypeId="1" CreationDate="2019-09-21T06:52:34.600" Score="1" ViewCount="83" Body="&lt;p&gt;I am in a process of making a &lt;a href=&quot;https://www.nanosats.eu/cubesat&quot; rel=&quot;nofollow noreferrer&quot;&gt;nanosatellite&lt;/a&gt; on which I am considering putting an APRS digipeater. I know about micro-modem based on &lt;a href=&quot;https://www.microchip.com/wwwproducts/en/ATmega328p&quot; rel=&quot;nofollow noreferrer&quot;&gt;ATmega 328P&lt;/a&gt; but it is pretty power hungry. MX614 has really good power stats; however, I am unable to find any clear documentation on how to implement it with a radio. Rather I am only getting the circuitry for line connection. Please help on connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.sv1afn.com/dra818.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;DRA818 info&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15694" LastEditorUserId="15694" LastEditDate="2019-09-22T15:03:21.157" LastActivityDate="2019-10-30T01:01:20.153" Title="How to connect MX614 to an ATmega 328p and a DRA818V to make an APRS transceiver" Tags="&lt;digital-modes&gt;&lt;aprs&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15366" PostTypeId="1" CreationDate="2019-09-21T08:01:16.653" Score="1" ViewCount="166" Body="&lt;p&gt;I want to compare field strength with an RTL-SDR dongle or HackRF One. With comparing I mean being correct relative to one another, like if I know field strength of one in mW/m^2 then I know the other. I am pretty sure this works for a fixed bandwidth (&lt;a href=&quot;https://ham.stackexchange.com/questions/12896/how-to-measure-signal-strength&quot;&gt;How to Measure Signal Strength&lt;/a&gt;). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My remaining question is: Can I compare field strength of 145Mhzish to 900Mhzish? I wouldn't mind an inaccuracy of factor 3.&lt;/p&gt;&#xA;" OwnerUserId="15696" LastActivityDate="2019-09-21T08:01:16.653" Title="Compare signal strength with Software Defined Radio" Tags="&lt;rtl-sdr&gt;&lt;hackrf&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15371" PostTypeId="2" ParentId="15335" CreationDate="2019-09-23T00:19:03.317" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://www.itu.int/rec/R-REC-F.1487-0-200005-I/en&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU Recommendation F.1487-0&lt;/a&gt; defines methods for testing HF ionospheric paths for bandwidths up to 12 kHz. While ionospheric propagation can be complex, this document provides a starting point for the widely applicable basics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It characterizes an HF channel with two parameters:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;multipath differential time delay, and&lt;/li&gt;&#xA;&lt;li&gt;Doppler spread.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The multipath differential time delay is the maximum difference in time of arrival between multipath components. Put another way, it's the length of the channel impulse response. When the length of a symbol is very long compared to this value, differential time delay has negligible effect on demodulation performance. The ITU document states that the differential time delay exceeds 5 ms 5% of the time. Given that most very weak signal communication modes will have symbols much longer than this, differential time delay is not likely a major detriment to performance in this case.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other parameter, Doppler spread, quantifies how &quot;spread out&quot; the power spectra of the signal will become due to each path having a randomly changing Doppler shift. The worst environment described is &quot;disturbed conditions at high latitudes&quot;, with a Doppler shift of 30 Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the objective is coherently detecting a very long symbol, Doppler spread may better be understood by its dual, &lt;em&gt;coherence time&lt;/em&gt;. Coherence time &lt;span class=&quot;math-container&quot;&gt;$T_C$&lt;/span&gt; can be defined as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ T_c = {9 \over 16 \pi f_m} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$f_m$&lt;/span&gt; is the Doppler spread. This definition of coherence time gives the time where the correlation of the channel impulse response will be above 0.5. In other words, if one were to receive a signal at some time, and then an identical signal &lt;span class=&quot;math-container&quot;&gt;$T_c$&lt;/span&gt; later, the correlation of those received signals will be on average 0.5.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the worst case of 30 Hz, this works out to a coherence time of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {9 \over 16 \pi\ 30\:\mathrm{Hz}} = 5.97\:\mathrm{ms} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, detecting a 6 ms symbol might work OK, but doubling the symbol length to 12 ms doesn't make the symbol twice as easy to detect since the second half of the symbol doesn't correlate perfectly with the first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why polar paths are so challenging: Doppler spread can be extremely high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;WSPR-15 has a symbol rate of 0.1831 baud, whereas the ITU document gives a differential time delay of 0.5 Hz for &quot;quiet conditions&quot; at mid and low latitudes. From this we can already see the challenge: considered in the time domain, we can't count on an individual tone to maintain the same phase long enough that it won't start to cancel itself out. Or considered in the frequency domain, it's a challenge for WSPR-15 to resolve individual tones since the Doppler spread smears them together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What can be done about it? I'm not entirely sure: I am after all answering my own question. But if the challenge is to establish communication even when slowing the symbol rate enough to approach the coherence time is insufficient, and transmitter power can't be increased, I'd guess the approach must be to take many shorter samples and add them noncoherently over a long time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider the bad polar case where the coherence time is 6 ms: one could calculate an FFT every 6 ms and accumulate the magnitudes of each bin over a longer time. The Doppler spread means the received phase will be effectively random but a constant carrier, given enough time, will accumulate enough bias in the magnitude to become detectable above the noise. The short FFT duration will also mean the bins will be wider than necessary, which will introduce additional noise and require a wider tone spacing, but then if it was easy everyone would do it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-09-23T00:19:03.317" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15372" PostTypeId="1" AcceptedAnswerId="15375" CreationDate="2019-09-23T03:44:02.247" Score="2" ViewCount="210" Body="&lt;p&gt;Will using a 1:1 balun at the feedpoint of a center-fed dipole when using coax result in no common mode current on the outside of the coax ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-09-24T21:11:24.403" LastActivityDate="2019-09-25T00:12:48.430" Title="Will using a 1:1 balun at the feedpoint of a center feed dipole result in no common mode current on the outside of the coax?" Tags="&lt;antenna-theory&gt;&lt;coaxial-cable&gt;&lt;dipole&gt;&lt;balun&gt;&lt;transmission-line&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15373" PostTypeId="2" ParentId="15372" CreationDate="2019-09-23T13:59:29.963" Score="4" Body="&lt;p&gt;Yes. If the balun is properly designed, there will be little to no common mode current on the outside of the shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is almost always good practice to use an effective choke balun at the feedpoint of any center-fed balanced dipole. The exception would be if some vertical radiation was helpful &lt;em&gt;and&lt;/em&gt; the coax was not picking up RFI.&#xA;&lt;hr&gt;&#xA;&lt;a href=&quot;https://ham.stackexchange.com/a/15375/8717&quot;&gt;Hotpaw2 makes some excellent points about being symmetrical&lt;/a&gt; in his answer. I doubt whether a &quot;small&quot; amount of asymmetry would cause a significant amount of common-mode, but that would have to be determined by either experimenting or modeling.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regardless of the amount of asymmetry, the choke balun would help; however, at some point it would become necessary to add a choke farther away from the feedpoint.&#xA;&lt;hr&gt;&#xA;&lt;a href=&quot;https://ham.stackexchange.com/search?q=Balun+center+dipole&quot;&gt;Here are some past questions and answers I found searching for &lt;em&gt;Balun center dipole&lt;/em&gt;&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-09-24T21:08:42.113" LastActivityDate="2019-09-24T21:08:42.113" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15374" PostTypeId="1" AcceptedAnswerId="15376" CreationDate="2019-09-23T17:42:06.990" Score="2" ViewCount="79" Body="&lt;p&gt;In another QA here, there's a picture of an antenna I identified as a &quot;discone&quot;: &lt;a href=&quot;https://ham.stackexchange.com/questions/12978/what-are-these-antennas-used-for/12982&quot;&gt;What are these antennas used for?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One commenter noticed that antenna was actually a &quot;Discone, but no disc, just the cone...&quot; so I gave it a second look:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/5lWGm.jpg&quot; alt=&quot;View of antenna in question near Heidmoosstrasse&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sure enough, no &quot;disc&quot;. But now I don't even see &quot;the cone&quot; either!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There seem to be two things going on around this mast:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Wires going from the mast to the ground. I count two sets of four such wires. These wires have a number of &quot;bumps&quot; on them. Probably guy wires to support the tower; with the bumps being insulators which split them up electrically so they don't mess with the pattern as much?&lt;/li&gt;&#xA;&lt;li&gt;Some eight or ten wires all around, running from the top of the mast, passing over a hoop halfway down the mast, and then gathering again at the bottom of the mast. These must be the active elements?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Unlike a discone, which is derived from a &lt;a href=&quot;https://en.wikipedia.org/wiki/Biconical_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;biconical antenna&lt;/a&gt; where two cones meet at their point, this antenna seems to be shaped more like a geometric &lt;a href=&quot;https://en.wikipedia.org/wiki/Bicone&quot; rel=&quot;nofollow noreferrer&quot;&gt;bicone&lt;/a&gt; where two cones are joined base-to-base instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What type of antenna — or, antenna &lt;em&gt;array&lt;/em&gt; — is this?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2019-09-24T16:50:16.277" LastActivityDate="2019-09-24T16:50:16.277" Title="What sort of antenna would use a bicone or lozenge-like arrangement of vertical wires?" Tags="&lt;antenna-theory&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15375" PostTypeId="2" ParentId="15372" CreationDate="2019-09-24T02:07:57.667" Score="5" Body="&lt;p&gt;Depends on how much current you mean by no current.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But in general, unless the dipole is actually perfectly symmetrical, in a perfectly symmetric environment, above a symmetric ground, with the feed line at exactly 90 degrees all the way into the far field, and/or with the radio equipment and their ground connections also exactly 90 degrees perpendicular to the dipole, any of those could cause asymmetry in the RF field around the antenna, which could then couple into the outer coax (and any other nearby conductive objects).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It might be possible to reduce that coupled current into the coax shield by positioning chokes which can increase the impedance to asymmetric RF fields, if any.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But odds are that if you were to place a short receive antenna anywhere along your coax, exactly parallel to it, you would pick up the transmitted signal.  And if that short receive antenna is picking up RF, so is the much longer coax.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-09-25T00:12:48.430" LastActivityDate="2019-09-25T00:12:48.430" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15376" PostTypeId="2" ParentId="15374" CreationDate="2019-09-24T09:49:26.860" Score="3" Body="&lt;p&gt;This is probably a conical monopole antenna, as described by E.W. Pappenfus,  WB6LOH, in &lt;a href=&quot;http://www.rfcafe.com/references/qst/conical-monopole-antenna-november-1966-qst.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;QST&lt;/em&gt; for November 1966&lt;/a&gt;. Antennas of the size order shown in the OP are probably for use from 4MHz and higher in the medium-wave band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Paul Lee, N6PL, describes the &quot;discage&quot; in, &quot;&lt;a href=&quot;https://www.universal-radio.com/catalog/books/0043.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Amateur Radio Vertical Antenna Handbook&lt;/a&gt;&quot; , which could explain the &quot;disk&quot; one may observe atop such antennas. &#xA;The top disk is fed separately against the wire cage to provide improved coverage of the shortwave frequencies.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2019-09-24T14:11:07.007" LastActivityDate="2019-09-24T14:11:07.007" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15377" PostTypeId="2" ParentId="12978" CreationDate="2019-09-24T15:40:37.663" Score="1" Body="&lt;p&gt;The antenna in the left foreground is probably a conical monopole, as described by E.W. Pappenfus,  WB6LOH, in &lt;a href=&quot;http://www.rfcafe.com/references/qst/conical-monopole-antenna-november-1966-qst.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;QST&lt;/em&gt; for November 1966&lt;/a&gt;. Antennas of the size order shown in the OP are probably for use from 4MHz and higher in the medium-wave band.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-09-24T15:40:37.663" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15378" PostTypeId="1" AcceptedAnswerId="16173" CreationDate="2019-09-24T17:17:01.867" Score="5" ViewCount="290" Body="&lt;p&gt;What dot near country means in JTDX? Maybe LOTW?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CPv4K.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CPv4K.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15712" LastEditorUserId="5222" LastEditDate="2019-09-24T22:48:27.513" LastActivityDate="2020-02-26T18:00:02.713" Title="What dot means in JTDX FT8 received messages?" Tags="&lt;software&gt;&lt;ft8&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15379" PostTypeId="1" CreationDate="2019-09-24T17:55:39.007" Score="1" ViewCount="97" Body="&lt;p&gt;I recently received my technician license, with the purpose of sending FPV video (on 5.8GHz) when flying model aircraft. However, I cannot figure out how to perform station identification when transmission is complete (flights with quadcopters last less than 10 minutes at this point, so the end of the flight is what I'm primarily concerned with.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume that this situation does not fall under the clause that states the following: &quot;Amateur station may transmit without identifying only when transmitting signals to control a model craft.&quot; This would be because the FPV feed is not specifically controlling the craft, but I could be wrong.&lt;/p&gt;&#xA;" OwnerUserId="15713" LastActivityDate="2019-09-25T11:16:51.753" Title="How does one identify the transmitting station at the end of an FPV video transmission?" Tags="&lt;station-identification&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15381" PostTypeId="2" ParentId="15379" CreationDate="2019-09-25T11:16:51.753" Score="1" Body="&lt;p&gt;More or less any way you want...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some options are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Mix the call sign into the video as an overlay in a corner&lt;/li&gt;&#xA;&lt;li&gt;voice or morse code in the audio track&lt;/li&gt;&#xA;&lt;li&gt;Call sign slide at end of transmission&lt;/li&gt;&#xA;&lt;li&gt;morse code in CW or MFM after video modulation stops (this is rare)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Audio track is probably the simplest.  The video overlay is frequently used with NTSC video, but might be more difficult (requiring more computing power) in digital video.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-09-25T11:16:51.753" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15382" PostTypeId="1" AcceptedAnswerId="15399" CreationDate="2019-09-25T15:20:31.690" Score="4" ViewCount="80" Body="&lt;p&gt;This &lt;a href=&quot;https://ham.stackexchange.com/questions/1410/what-is-the-peak-voltage-at-the-tips-of-a-dipole-antenna&quot;&gt;question&lt;/a&gt; has good answers for the voltages reached in portions of a dipole antenna during transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a beam (Yagi or Yagi-Uda) antenna, do points along passive or parasitic elements (reflectors and directors, etc.) also reach similarly high peak voltages?  If so, by what relationship to the driven element?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-09-26T02:28:48.490" LastActivityDate="2019-09-27T12:06:00.687" Title="Voltages in a beam antenna's passive elements?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15383" PostTypeId="1" CreationDate="2019-09-26T05:02:16.633" Score="4" ViewCount="66" Body="&lt;p&gt;FM seems to be the most popular in the 144 to 148 MHz  Amateur  Band      .Narrow band is used for spectrum conservation .   SSB is also used but is more common on the HF bands .Would SSB provide any  range advantage when taking VHF propagation into Account ?&lt;/p&gt;&#xA;" OwnerUserId="6095" LastActivityDate="2019-09-27T11:14:00.090" Title="2 meter Mode Options" Tags="&lt;vhf&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15384" PostTypeId="1" AcceptedAnswerId="15391" CreationDate="2019-09-26T09:39:34.033" Score="3" ViewCount="476" Body="&lt;p&gt;It's well-known that the signal processing of an SDR adds a significantly amount of latency, the SDR software on the computer adds more latency due to data buffering, FFT, decoding, demolutaion, audio buffering, etc, not to mention that most computer systems aren't a real time system and have unpredictable delays as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's usually not a concern, but can be a problem when one wants to extract the precise time-mark of a signal. To elaborate the question, imagine a SDR running on a typical desktop computer, operated by a program powered by GNU/Radio, and consider two scenarios:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;em&gt;Time Synchronization&lt;/em&gt; - SDR is tuned to a frequency and listens for an incoming pulse. A pulse is generated at 00:00:00 UTC. Upon receiving it, the SDR immediately set the system's real-time clock to 00:00:00 UTC (for example, in a time synchronization experiment). What would be the error between UTC and system's real-time clock now? Ignore all insignificant sources of errors.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;em&gt;Time-mark extraction&lt;/em&gt; - SDR is tuned to a frequency and listens for an incoming pulse. As soon as the pulse is generated, the SDR records the wall-clock time (for example, in a propagation-delay experiment). Assume the system's real-time clock has no error, what would be the error of the time measurable by the program?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Both questions ask for a simple parameter: The typical total delay/latency in the entire signal path of the an SDR setup on a desktop computer. We also assume the latency is not predetermined and calibrated to zero prior to these experiments. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I expect the latency is much worse than what the operating system on a desktop computer is capable of. For example, protocols like NTP uses a PLL-like algorithm and finish the time synchronization in multiple steps, an final error of less than 10 milliseconds over the Internet is not impossible given a datacenter network with symmetric routes (see &lt;a href=&quot;https://www.pool.ntp.org/scores/161.53.131.133&quot; rel=&quot;nofollow noreferrer&quot;&gt;this statistics&lt;/a&gt;), but extracting the time-mark of an one-off event is harder for a desktop computer with SDR, and I expect the delay of an unoptimized implementation has a latency of a dozen of milliseconds. If an accuracy comparable to NTP is required, it's better use a specialized circuit, not a SDR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That all being said, while I can find some research papers and projects on the architecture of a low-latency SDR, I cannot find a solid measurement or analysis of latency/delay of a typical SDR, such as a RTL-SDR, HackRF, LimeSDR, with gqrx or GNU Radio. I was inspirited by Dan Luu's experiments on the &lt;a href=&quot;https://danluu.com/input-lag/&quot; rel=&quot;nofollow noreferrer&quot;&gt;typical latency between entering a keystroke and a screen update on various computer hardware&lt;/a&gt;, or the &lt;a href=&quot;https://danluu.com/keyboard-latency/&quot; rel=&quot;nofollow noreferrer&quot;&gt;typical latency of latency between a keystroke and a keyboard scancode using a logic analyzer&lt;/a&gt;, some experiments for SDR software and hardware would be greatly useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe this can be an useful reference question. Any data, analysis, and measurements are appropriated. I think I could do some measurements in the future. &lt;/p&gt;&#xA;" OwnerUserId="15589" LastEditorUserId="15589" LastEditDate="2019-09-27T15:10:59.547" LastActivityDate="2019-09-27T15:10:59.547" Title="What is the typical latency of a SDR setup running on a desktop computer?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="3" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="15386" PostTypeId="2" ParentId="15383" CreationDate="2019-09-26T10:49:24.233" Score="0" Body="&lt;p&gt;From personal experience it will be not easy to find someone who uses CW or SSB on 2 meters on regular basis. Contests are a noticable exception. On the other hand you can find people on a local repeater who might be interested in experimenting not only with CW or SSB, but also with such digital modes as D-STAR, C4FM and DMR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I know SSB doesn't give any advantage in terms of range. In fact FM might have an advantage since the noise usually is amplitude modulated and FM is more immune to it.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-09-27T11:14:00.090" LastActivityDate="2019-09-27T11:14:00.090" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15388" PostTypeId="2" ParentId="15384" CreationDate="2019-09-26T11:34:04.963" Score="2" Body="&lt;p&gt;It's difficult to give an exact number, because the overall latency involves at least:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Processing of the signal on the given SDR&lt;/li&gt;&#xA;&lt;li&gt;Transferring data over USB 2.0 / USB 3.0 / PCIe (depending on what is used)&lt;/li&gt;&#xA;&lt;li&gt;Latencies on USB controllers on both SDR and PC (+ USB hubs, if used)&lt;/li&gt;&#xA;&lt;li&gt;Latency caused  by other USB devices (keyboard, touchpad, webcam, ...) on the bus. Note that USB devices are always pulled by the PC, USB device can't just push data over the bus without being asking for it.&lt;/li&gt;&#xA;&lt;li&gt;Latency in the device driver&lt;/li&gt;&#xA;&lt;li&gt;Latency between ring0 and ring3 levels in the particular operating system (involves process switching, data copying =&gt; memory latancy, etc)&lt;/li&gt;&#xA;&lt;li&gt;Processing of the data by the given software (GNU Radio / Python / C++)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;My rough approximation would be that all this chain typically takes no more than 10 ms (probably much less). But it's difficult to give a more accurate number because there are too many unknown variables.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also difficult to measure this number experimentally. You could write an application that receives a signal, somehow replies to it, measure the time between sending request and receiving response (roundtrip time) and divide it by two. The problem is - where you can find a measuring equipment with near-zero internal latency? I can only think of using an analog transmitter and receiver and measure the roundtrip time using an oscilloscope.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-09-26T11:41:35.980" LastActivityDate="2019-09-26T11:41:35.980" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15389" PostTypeId="2" ParentId="15383" CreationDate="2019-09-26T11:36:41.817" Score="5" Body="&lt;p&gt;As you can read in this answer: &lt;a href=&quot;https://ham.stackexchange.com/questions/6847/single-side-band-am-vs-fm&quot;&gt;Single Side Band AM vs FM&lt;/a&gt;, SSB is more power efficient than FM so normally you should get a greater range using the same power from your transmitter.&#xA;But as R2AUK stated you probably will find a lot more people to talk to on 2m FM than on 2m SSB.&lt;/p&gt;&#xA;" OwnerUserId="9532" LastActivityDate="2019-09-26T11:36:41.817" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15390" PostTypeId="2" ParentId="15085" CreationDate="2019-09-26T13:15:03.003" Score="0" Body="&lt;p&gt;If you want to transmit Morse code, or just to learn more about flowgraphs, you might be interested in &lt;a href=&quot;https://github.com/duggabe/gr-morse-code-gen&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/duggabe/gr-morse-code-gen&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: if you change the output rate to something other than 48khz, you will need to change the parameter calculations as well.&lt;/p&gt;&#xA;" OwnerUserId="15011" LastEditorUserId="15011" LastEditDate="2019-09-28T00:30:08.487" LastActivityDate="2019-09-28T00:30:08.487" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15391" PostTypeId="2" ParentId="15384" CreationDate="2019-09-26T14:47:28.160" Score="3" Body="&lt;p&gt;The answer is that the SDR hardware devices are all very different, so is the optimization quality of the SDR code.  So one pretty much needs to calibrate for their specific setup: device, current method of connection, OS, and software running.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find network latency between the SDR hardware server and the software client to be one of the biggest variables, especially over multiple WiFi hops.  But in general, there could be ADC buffering, FPGA buffering, hardware filtering and downsampling buffering, USB output buffering (depending on USB transfer block size), USB driver input buffering, OS network buffering  (depending on MTU size), Ethernet buffering, WiFi access point buffering, OS driver IO buffering, application network buffering, SDR software filtering buffering, SDR demodulation buffering, audio processing buffering, OS audio driver output buffering, audio DAC DMA buffering, and etc.  All these buffers are covering for latency jitter in the various interfaces, caused by asynchronous timing and contention for various buses, WiFi bandwidth, OS processes, and etc., which vary widely between setups.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that an SDR radio can shortcut many of these latencies by having all this hardware and software on a single board or a single chip running a real-time OS or even no OS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I test SDR total system latency by keying a QRP transmitter (preferably fully analog) into a dummy load, then listening to the delay between my keyer sidetone and when I hear the sidetone out of one of my SDR apps.  You can record these two in stereo and view the waveform rise-time deltas for a more precise measurement.  Depending on which SDR device I'm using, and whether the data is hardwired or from an SDR server over WiFi. I can hear latencies of from around 100 mS to over 1 Second.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-09-26T15:33:19.317" LastActivityDate="2019-09-26T15:33:19.317" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15392" PostTypeId="1" AcceptedAnswerId="15396" CreationDate="2019-09-26T15:44:26.817" Score="2" ViewCount="115" Body="&lt;p&gt;I am occasionally using an extremely simple shortwave portable setup consisting of a battery, the transceiver, a short coax feedline and a vertical half-wavelength vertical antenna with a transforming ladder-type feedline. &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;                        |&#xA;                        |&#xA;                        | λ/2&#xA;                        |&#xA;                        H&#xA;                        H ladder&#xA;                        H&#xA;------  -----           H&#xA;|Batt|--|TRX|XooooooooooX  &#xA;------  -----&#xA;&#xA;X .. Connector&#xA;H .. two-wire ladder&#xA;o .. coax&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;My goals are both to optimize the system's efficiency and to minimize uncontrolled radiation from the feedline and transceiver itself. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would normally try to ground both the transceiver and the connection point between my arbitrary-length coax feedline and the antenna's connector. However, this resulted in bad performance, and indeed, the antenna's description encourages keeping the feedline mechanically far from the ground and &quot;free-floating&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should a setup like this be grounded using just ground spikes, should I rather provide a defined ground using wire or would it be best to not care and rely on the fact that the antenna is resonant?&lt;/p&gt;&#xA;" OwnerUserId="15707" LastEditorUserId="8717" LastEditDate="2019-09-26T17:50:04.767" LastActivityDate="2019-09-27T16:48:03.320" Title="Grounding of a portable setup" Tags="&lt;antenna-system&gt;&lt;grounding&gt;&lt;portable&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15393" PostTypeId="1" AcceptedAnswerId="15395" CreationDate="2019-09-26T19:24:58.047" Score="2" ViewCount="100" Body="&lt;p&gt;I'm a newly licensed amateur and have decided to start out by trying WSPR on a Raspberry Pi equipped with TAPR's 20m QRPi. The QRPi write-ups I've read always talk about long wire antennas but I'd like to try to connect it to my Elecraft AX1. But I can't, for the life of me, find anything that specifies the output impedance of the QRPi. I'm assuming that some sort of matching will be required, for best results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anybody know what the QRPi's output impedance is? If I must measure it myself, would my &quot;Nano VNA&quot; be of any use?&lt;/p&gt;&#xA;" OwnerUserId="15474" LastActivityDate="2019-09-26T20:24:39.197" Title="Output impedance of TAPR QRPi?" Tags="&lt;impedance-matching&gt;&lt;qrp&gt;&lt;wspr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15394" PostTypeId="2" ParentId="13363" CreationDate="2019-09-26T20:23:00.327" Score="0" Body="&lt;p&gt;You can use a QT GUI Chooser as an alternative to the Selector Block when you want a tx/rx switch. The two multiply blocks (not counting the volume control) gate the transmit and receive signals.&lt;br&gt;&#xA;This image is also available at &lt;a href=&quot;https://wiki.gnuradio.org/index.php/File:Selector_demo.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wiki.gnuradio.org/index.php/File:Selector_demo.png&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4j3jn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4j3jn.png&quot; alt=&quot;Transmit/Receive switch&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15011" LastEditorUserId="15011" LastEditDate="2019-10-20T20:14:10.140" LastActivityDate="2019-10-20T20:14:10.140" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15395" PostTypeId="2" ParentId="15393" CreationDate="2019-09-26T20:24:39.197" Score="4" Body="&lt;p&gt;The output impedance isn't especially important: in fact I believe it uses a nonlinear amplifier so the concept doesn't really apply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does matter is the intended load impedance, which for any amateur radio application you can assume to be 50 ohms unless otherwise specified.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To verify, I modelled the low-pass filter part of the circuit from &lt;a href=&quot;https://www.tapr.org/pdf/DCC2015-QRPi-HA7DCD.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;the manual&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/K9rOn.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fK9rOn.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Running a frequency domain analysis we can see this provides a nice low-pass response with a cutoff just above the 20m band, with a pretty flat passband except for some minor ripple we can expect inherent to the Chebyshev design and rounding errors in selecting common values for the components:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/T1zdL.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/T1zdL.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the load impedance is changed to 5,000 ohms, the response no longer looks so nice:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qqgSK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qqgSK.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you aren't actually going to get an additional 40 dB of output power where the frequency response spikes because the real circuit isn't built of ideal components, but what this tells us is the person designing that filter assumed the attached load would be about 50 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens if the load isn't 50 ohms is somewhat undefined. It could be fine. It could just make less power. Or it overstress the transistor and damage it. &lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-09-26T20:24:39.197" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15396" PostTypeId="2" ParentId="15392" CreationDate="2019-09-26T23:26:29.203" Score="4" Body="&lt;p&gt;An antenna design that requires grounding to suppress the common-mode or improve efficiency is a poor antenna design, unless significant effort is made to make a low-loss ground. For example, a quarter-wave monopole above a ground plane of radials or saltwater works well. A quarter-wave monopole with just a ground rod is as much a dummy load as it is an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, many amateur antennas are poorly designed in this way. The details of your antenna are not entirely clear, but if the &quot;antenna's description encourages keeping the feedline mechanically far from the ground and &quot;free-floating&quot; that almost certainly means this design &lt;em&gt;requires&lt;/em&gt; a radiating feedline to function.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If grounding is your solution to common-mode currents, some portion (perhaps a very large portion) of the transmitter's power is going towards warming the soil rather than radiating.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since installing a low-loss ground is not feasible for most mobile setups, you should look for an antenna design that does not have a common-mode issue. It could be as simple as a &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;dipole with a balun&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having addressed the common-mode issue though an effective antenna design, there's no reason to ground the station because there are no common-mode currents that would use it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, you can just accept that the common-mode currents are going to happen. If transmit powers are low and the receiver and feedline aren't in noisy environment compared to the rest of the antenna (because the feedline &lt;em&gt;is&lt;/em&gt; the antenna), nothing especially terrible will happen, and you can just write it off as a compromise that's been made to make the antenna simpler, more portable, or easier to erect.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-09-26T23:26:29.203" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15397" PostTypeId="1" AcceptedAnswerId="15398" CreationDate="2019-09-27T01:30:16.770" Score="0" ViewCount="378" Body="&lt;p&gt;It seems like a gaming headset is a cheap option for my radio, considering I have a 3.5mm to XLR adapter, along with an adapter for the Yaesu mic input (from XLR).  However, what I'm not sure about is power requirements for the microphone on the headset.  What microphone element type should I be looking for in a headset?  Has anyone used a gaming headset with their radios with any success?  Thanks. &lt;/p&gt;&#xA;" OwnerUserId="9772" LastActivityDate="2019-09-30T17:48:43.903" Title="Using Gaming Headset on FTDX3000" Tags="&lt;microphone&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15398" PostTypeId="2" ParentId="15397" CreationDate="2019-09-27T02:31:15.280" Score="1" Body="&lt;p&gt;&lt;strong&gt;This answer has details that are not appropriately relevant because it does not match the actual features of the FTDX3000 microphone port.&lt;/strong&gt; Update to come.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I'm not familiar with the FTDX3000, but PC headset microphones, and most microphones for &lt;em&gt;handheld&lt;/em&gt; radios, are both &lt;strong&gt;electret&lt;/strong&gt; microphones. Electret microphones require a small DC voltage &lt;em&gt;across their terminals&lt;/em&gt; (not on separate pins) to operate, because they have an internal amplifier circuit. (The scheme for PC microphones is called &quot;plug-in power&quot;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the good news is that the microphones themselves should be electrically compatible. The bad news is, you may not have the right cables to hook it up, because XLR microphone connections typically do &lt;em&gt;not&lt;/em&gt; have &quot;plug-in power&quot;; they have &quot;phantom power&quot;, which is much higher voltage and connects differently. Therefore, it is &lt;em&gt;possible&lt;/em&gt; that one or both of your XLR adapters has internal capacitors or transformers to block the &lt;em&gt;other&lt;/em&gt; power standard from interfering.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, it might just work. If it doesn't work, figure out a cable adapter that is &lt;em&gt;not&lt;/em&gt; going through XLR. As long as the right two pins are connected, &lt;strong&gt;with the right polarity&lt;/strong&gt;, the microphone should work.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Some more details in case of wiring confusion: The PC microphone plug-in-power standard &lt;em&gt;nominally&lt;/em&gt; separates power supply from microphone: on the TRS plug/jack, the tip is audio, ring is power (+3 to +5 V) and sleeve is common for both. However, most microphones just wire the tip and ring together to go to the electret, and many microphone jacks also combine them (with a capacitor for audio coupling and a resistor for current-limiting the power output), particularly in order to enable stereo input (so the tip and ring are left power+audio and right power+audio).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio will probably not have this extra feature, and have a single contact for audio and power. This is OK — just use the tip contact of the headset microphone plug for the side with positive voltage, and the sleeve for the other.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-09-30T17:48:43.903" LastActivityDate="2019-09-30T17:48:43.903" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15399" PostTypeId="2" ParentId="15382" CreationDate="2019-09-27T12:06:00.687" Score="2" Body="&lt;p&gt;I used EZNEC (NEC2) to model a λ/2 dipole in free space. The program reports the voltage very close to the end of the dipole as 3910 volts with 100 watts of driving power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resonant frequency of this dipole was 14.27MHz. Moving to 14MHz resulted in 5392 volts at the end for the same 100W power input to the feedpoint. Moving to 14.54MHz resulted in 4536 volts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EZNEC includes an example 5-element 20m yagi design. The currents on the first two directors are surprisingly close in magnitude to the current in the driven element, while the current in the reflector is about 30% of the driven. These figures correlate with the deviations of the element lengths from the antenna's design frequency: the closer an element's resonance to the design frequency, the higher the current. These should give you an idea of the voltages at the ends of those elements.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-09-27T12:06:00.687" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15400" PostTypeId="2" ParentId="15384" CreationDate="2019-09-27T12:18:36.033" Score="1" Body="&lt;p&gt;Dr Warren Pratt, NR0V, introduced low-latency FIR filters to the &lt;a href=&quot;https://www.youtube.com/watch?v=THPjQV3I81g&quot; rel=&quot;nofollow noreferrer&quot;&gt;2018 SDR Academy&lt;/a&gt;. Dr Pratt reminded the audience that &lt;em&gt;mimimum phase&lt;/em&gt; FIR filters deliver much lower latency than &lt;em&gt;linear phase&lt;/em&gt; filters and opined that ease of design has driven the persistence of linear phase filters. I have observed a dramatic reduction in latency by switching to Dr Pratt's &lt;a href=&quot;https://github.com/NR0V/wdsp&quot; rel=&quot;nofollow noreferrer&quot;&gt;WDSP library&lt;/a&gt; in the SDRs I employ.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-09-27T12:18:36.033" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15401" PostTypeId="2" ParentId="15392" CreationDate="2019-09-27T16:48:03.320" Score="1" Body="&lt;p&gt;In your diagram you show 1/2 wavelength vertical and using a combination of ladder line and coax to do impedance matching. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means usual advice about 1/4 wave vertical does not apply here. Imagine this antenna as a half wave dipole that has been flipped from horizontal to vertical. Dipoles do not need an RF ground. You do not need a ground spike or an RF ground system with this antenna.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The real problem with this antenna is that it would be very hard to match the impedance using just a cable and then you get high SWR on your coax and bad performance. I have never seen a vertical half wave antenna that did not have an impedance transformer at the feed point. This is because the impedance of end fed half wave is very high. &lt;/p&gt;&#xA;" OwnerUserId="14671" LastActivityDate="2019-09-27T16:48:03.320" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15403" PostTypeId="1" CreationDate="2019-09-27T21:12:49.547" Score="5" ViewCount="185" Body="&lt;p&gt;One practice which seems common when operating temporary or portable QRP, SOTA, etc., is to throw a counterpoise wire out on the park lawn or shrubbery, mountaintop or hillside or parking lot ground, etc., not buried or wetted, connected to either the (ungrounded) transmitter or an antenna tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, continuing on with the subject raised about &lt;a href=&quot;https://ham.stackexchange.com/questions/1410/what-is-the-peak-voltage-at-the-tips-of-a-dipole-antenna&quot;&gt;voltages in dipoles&lt;/a&gt;, and &lt;a href=&quot;https://ham.stackexchange.com/questions/15382/voltages-in-a-beam-antennas-passive-elements&quot;&gt;voltages in beam/Yagi-Uda directors/reflectors&lt;/a&gt;, assume an insulated or near-ground counterpoise wire that is roughly a quarter wavelength in length, and a transmitter power in the range of 5 to 10 Watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What kind of voltages might appear on such a counterpoise wire?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it make a difference whether the antenna is a lambda/4 resonant or non-resonant vertical or a balun-end-fed half wave?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do these voltages raise any safety concerns?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="8717" LastEditDate="2019-09-27T21:27:31.370" LastActivityDate="2019-10-01T21:35:21.607" Title="Counterpoise wire voltages?" Tags="&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;counterpoise&gt;&lt;portable&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15405" PostTypeId="2" ParentId="10305" CreationDate="2019-09-28T10:24:19.450" Score="1" Body="&lt;p&gt;As others pointed out, the shorter the antenna, the lower its efficiency. Trying to use short wire in combination with a QRP transmitter is very likely to be a very frustrating experience (I know this from my own experience). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I simplify, it is the current in the antenna that causes RF transmission. Therefore, if your antenna is a short wire, it will always be inefficient. This is because the current at the far end of the wire is always zero (obviously, it has nowhere else to go...) and it grows gradually towards the feedpoint and it reaches its maximum at quarter wavelength from the end. Short wire (less than 1/4 wl) is always too short to develop sufficiently high current at the feed point. (The coil shown in the first answer will only match the antenna impedance to the output impedance of your transmitter, but it does not create more current in the antenna, it is physically impossible).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, using a small magnetic loop antenna tuned to your transmitting frequency, made of high-quality materials (copper tube at least 1/8 inch in diameter, vacuum or air capacitors able to withstand high RF current) may be a better option, because its efficiency can be much higher (compared to very short wire). The reason is that in small MLA (which is in fact just a physically big resonant circuit) you can achieve high RF current thanks to high Q of such antenna, whereas with a short wire you have absolutely no chance to push more current into the antenna than its physical length (relative to wavelength) allows.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However - the small MLA also has a problem. It is highly sensitive to any electrically  conductive objects in its vicinity. They could detune the antenna or even absorb some of the RF energy by electromagnetic induction caused by the high RF current in the antenna, or by capacitive coupling. MLA is actually very similar to the induction ovens used to heat vacuum tubes before sealing.&lt;/p&gt;&#xA;" OwnerUserId="11232" LastActivityDate="2019-09-28T10:24:19.450" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15406" PostTypeId="1" AcceptedAnswerId="15884" CreationDate="2019-09-28T10:46:23.847" Score="2" ViewCount="175" Body="&lt;p&gt;The original microphone for KX-3, Elecraft MH-3, is insanely expensive. What changes would be necessary to convert a cheaper speaker/microphone for a FM handheld transceiver? Is there any ready-to-buy adaptor?&lt;/p&gt;&#xA;" OwnerUserId="11232" LastEditorUserId="76" LastEditDate="2019-09-28T23:10:05.863" LastActivityDate="2020-01-05T22:28:38.543" Title="How to use HT microphone with two jacks (Kenwood connector) as a substitue for KX-3 microphone?" Tags="&lt;ht&gt;&lt;audio-interface&gt;&lt;microphone&gt;&lt;elecraft&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15407" PostTypeId="2" ParentId="15406" CreationDate="2019-09-28T13:59:53.783" Score="4" Body="&lt;p&gt;The Elecraft rigs have flexible interfaces for alternate microphone settings.  However, there is only the single TRRS plug for a Microphone on the KX3.  You should be able to wire up your own microphone to the diagram I have included here (extracted from the User Guide).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eFGEZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eFGEZ.png&quot; alt=&quot;Elecraft KX3 User Manual, page 5&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2019-09-28T13:59:53.783" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15408" PostTypeId="2" ParentId="15102" CreationDate="2019-09-29T08:40:51.467" Score="1" Body="&lt;p&gt;I had a similar problem for GRC v3.7.13.5/v1.6 and got it to work finally. The flow graph problem may be because that the RTL-SDR Source can't find the SDR device. I'm using HackRF hardware, and my WX GUI shows up after specifying the index number of the device by &lt;strong&gt;adding &quot;hackrf=0&quot; to the &quot;Device Arguments&quot; line in RTL-SDR Source properties&lt;/strong&gt;. For HackRF, the index can be shown by executing &quot;GNURadio-3.7\bin\hackrf_info.exe&quot; and GRC provides tools for other hardware in the same directory. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we don't specify the device index number, GRC may not work. The earlier release of v3.7.13.4 outputs error messages for that case but v3.7.13.5 doesn't. The windows build v3.7.13.5 may not be buggy but does not provide adequate messages.&lt;/p&gt;&#xA;" OwnerUserId="15732" LastEditorUserId="15732" LastEditDate="2019-10-01T07:13:51.593" LastActivityDate="2019-10-01T07:13:51.593" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15410" PostTypeId="1" CreationDate="2019-09-29T10:10:57.380" Score="2" ViewCount="1638" Body="&lt;p&gt;I would like to build a Yagi antenna for my Baofeng UV-5R, but I'm a total newbie when it comes to amateur radios. The antenna will be for UHF and shouldn't be too long (like 1.5 meters max).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my questions are: how many elements should I use? I'm little bit worried about Baofeng getting overloaded, I don't want to build an antenna that won't be usable with the Baofeng.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How exactly do you connect it to the Baofeng? &lt;/p&gt;&#xA;" OwnerUserId="15734" LastEditorUserId="8717" LastEditDate="2019-10-04T01:43:41.743" LastActivityDate="2019-12-06T23:00:27.753" Title="Can I build a Yagi antenna for my Baofeng UV-5R?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;baofeng&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15411" PostTypeId="2" ParentId="15410" CreationDate="2019-09-29T12:49:32.547" Score="1" Body="&lt;p&gt;From personal experience UV-5R doesn't work well with external antennas. I'm not sure what is the reason, but from what I know it has something to do with the fact that most of RF part of this radio is implemented in one chip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an experience of using a 3 element yagi with another 5W radio, Kenwood TH-D72A. 3 elements for 2m band and 5 elements for 70cm band is enough for making SAT QSOs. Kenwood TH-D72A is a little difficult to find these days, also this is not the cheapest radio. Something like Yaesu FT-60R or Yaesu FT-65R should work well with a yagi antenna, are not too expensive an are easy to find.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-09-29T12:49:32.547" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15412" PostTypeId="2" ParentId="15018" CreationDate="2019-09-29T13:26:03.203" Score="3" Body="&lt;p&gt;Eventually I managed to make the antenna work on more than one band. I used a modeller (CocoaNEC) to approximately determine the impedance on each band of interest for my antenna configuration (inverted-V on a 10m long fishing rod). The impedance was about 2450 Ohm. Thus I rewinded the transformer to 1:49. Also I used a 1:1 balun (8 turns of RG58 on FT240-31 core) to eliminate any common mode current. Using a variable capacitor I've found a capacitance (138 pF in my case) that gives the best SWR plot:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LhkqI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LhkqI.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No counterpoise was needed since it's role was played by the coax in the 1:1 balun. Then I replaced a variable capacitor with a constant NP0 capacitors. You can find a little more details &lt;a href=&quot;https://eax.me/end-fed-half-wave/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. The article is in Russian, but Google Translate should manage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna was tested on all band where it has SWR &amp;lt; 3: from 80m to 15m. QSOs were made on all these band. However, subjectively the overall performance of the antenna is not great comparing to the performance of a regular dipole. I wouldn't recommend trying to repeat it, at least definitelyly not with cores I've used.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-09-30T06:59:55.813" LastActivityDate="2019-09-30T06:59:55.813" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15413" PostTypeId="2" ParentId="15365" CreationDate="2019-09-30T00:34:29.067" Score="1" Body="&lt;p&gt;The atmega or any microcontroller worth their salt has built in serial ports just a matter of reading the datasheet and programming the controller as such. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your asking how to implement it as a radio. It is rather straight forward. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Carefully read the controller datasheet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take note that the controller has fuses  to determine which pin in each port behaves, this should be in your code that sets it up. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After that rhen set up each pin to your desire again read the datasheet for the controller. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thing about microcontrollers they are depdent on fuse and register settings. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pay particular attention to the USART section or the 2 wire serial section those pins that they are on. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It looks like you want to built something remote, implament something that sits and listens to the input allow you to have control that way you can change the way the transeciver behaves. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Take a high frequency that is beyond the speech and have it filtered out from the voice stream and have it converted into a data stream their you have remote control over the device. &lt;/p&gt;&#xA;" OwnerUserId="12988" LastActivityDate="2019-09-30T00:34:29.067" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15414" PostTypeId="2" ParentId="9683" CreationDate="2019-09-30T00:42:13.130" Score="0" Body="&lt;p&gt;You are overthinking this. You are using a CHARGER, not an AC power supply. Most chargers are meant for charging batteries, not running the radio. They are not well filtered (if at all) and probably not rated at enough current actually power the radio. Get a REAL AC power supply. &lt;/p&gt;&#xA;" OwnerUserId="15738" LastActivityDate="2019-09-30T00:42:13.130" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15417" PostTypeId="2" ParentId="15403" CreationDate="2019-09-30T20:44:57.423" Score="3" Body="&lt;p&gt;There are a lot of variables involved in calculating the voltage on an antenna. If you require an accurate answer, the solution is to model or empirically measure the particular antenna in question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But for a very rough estimate, a 1/4 wave &quot;counterpoise wire&quot; is effectively one leg of a half-wave dipole, so you can treat it as such to get some number. In practice voltage will probably be less due to ground losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, it's very difficult to create any kind of shock or RF hazard with a transmitter of only 10 watts. I wouldn't worry.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-09-30T20:44:57.423" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15422" PostTypeId="1" CreationDate="2019-10-01T22:40:59.790" Score="1" ViewCount="529" Body="&lt;p&gt;I have read that the new laws regarding FRS radios state that you may use up to 2 watts power, yet I can't find a single 2 way radio that advertises 2 watts power; only .5 watt, or they don't state anything at all. &lt;strong&gt;Why are no 2w FRS walkie talkies on the market?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every single forum and google search that pops up is 10 years old. Its driving me insane, its like google is deliberately making this research extremely difficult. ANY help is appreciated.&lt;/p&gt;&#xA;" OwnerUserId="15751" LastEditorUserId="873" LastEditDate="2019-10-02T07:12:14.347" LastActivityDate="2020-10-20T14:16:56.517" Title="Why are no 2w FRS walkie talkies on the market?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;ht&gt;&lt;frs&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15423" PostTypeId="2" ParentId="15422" CreationDate="2019-10-02T01:42:37.467" Score="0" Body="&lt;p&gt;&lt;strong&gt;It appears that 2 watt FRS radios are still available.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Click on &lt;a href=&quot;https://www.google.com/search?newwindow=1&amp;amp;safe=active&amp;amp;q=&amp;quot;2+watt&amp;quot;+&amp;quot;frs&amp;quot;+&amp;quot;radio&amp;quot;+-gmrs+-dmr+-ham&amp;amp;oq=&amp;quot;2+watt&amp;quot;+&amp;quot;frs&amp;quot;+&amp;quot;radio&amp;quot;+-gmrs+-dmr+-ham&quot; rel=&quot;nofollow noreferrer&quot;&gt;this custom Google search&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.google.com/search?q=&amp;quot;2+watt&amp;quot;+&amp;quot;frs&amp;quot;+&amp;quot;radio&amp;quot;+-gmrs+-dmr+-ham&amp;amp;newwindow=1&amp;amp;safe=active&amp;amp;prmd=sivn&amp;amp;sxsrf=ACYBGNRtH5J913nkUVM2injQHogM1rw1Dg:1569980223008&amp;amp;source=lnt&amp;amp;tbs=qdr:m&amp;amp;sa=X&amp;amp;ved=2ahUKEwi_lPyLuPzkAhWC9Z4KHdKrBDQQpwV6BAgNEBE&amp;amp;biw=768&amp;amp;bih=1024&quot; rel=&quot;nofollow noreferrer&quot;&gt;This should also work&lt;/a&gt;, which limited the search results to the past 30 days for me. &#xA;There was at least one refurbished one from Newegg. There appeared to be others selling them.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-10-02T01:42:37.467" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15424" PostTypeId="1" CreationDate="2019-10-02T02:29:03.633" Score="1" ViewCount="95" Body="&lt;p&gt;Is there any data anywhere showing if amateur radio operators are more likely to get cancer from exposure to RF?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="1362" LastEditDate="2020-05-01T00:35:28.170" LastActivityDate="2020-05-01T11:16:42.920" Title="Are amateur radio operators more likely to get cancer from exposure to RF?" Tags="&lt;safety&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15425" PostTypeId="2" ParentId="15422" CreationDate="2019-10-02T07:32:30.973" Score="0" Body="&lt;p&gt;Disclaimer: I am not in the USA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I do know how to use Google, and that came up with lots of products that claim to be FRS radios. But most of them are not (because they are mostly Baofengs that put out 8W, which is obviously out of spec for FRS in the USA). I suspect that this is the main source of your frustration - people lie in advertising. Advertise as &quot;FRS! Long range!&quot; But it turns out that it's too high a power for FRS, and as such a licence is required to use it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did find two manufacturers that are not too shy to say they make 2W FRS radios: Retevis have a few models, and I found another called Ansoko.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Shopping&quot; questions (such as which model is best for a particular situation, where to buy stuff, which sells for the best price) are not permitted on this site for good reason - the site would get clogged very quickly with simple questions that help nobody and that can be answered by looking in the usual places (start with Google).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I am answering this question basically to say that such things do seem to exist, and they can be found on the internet quite easily. The search I did was for: 2 watt frs radio - and it turned up a few promising leads. Just avoid the Baofengs, because they are all at least 5W and mostly 8W.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-10-02T07:32:30.973" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15430" PostTypeId="2" ParentId="1845" CreationDate="2019-10-02T11:30:04.203" Score="-8" Body="&lt;p&gt;Keying up is keying up -to a repeater- not to any individual.  If you key up and do not speak then you are merely checking to verify a connection to the -repeater-.  It actually -is- proper etiquette to merely key-up.  You would speak when you want a conversation.  Lets not confuse wanting a conversation with verifying your system is connecting with the repeater system.  Proper etiquette is to keep conversation to a minimum in an emergency.  The statute is not intended to clarify keying up or establishing a connection between a radio operator and a repeater.  the law pertains to when people communicate generally speaking. There is nothing rude about keying up.  It is not a personal assault on anyone else.  When someone keys up they -should- be merely establishing a connection.  They are allowed to listen &amp;amp; not communicate.  That is part of the allowance permitted by our licenses; being a good -listener.  Please don't confuse the above reference statute.  Please enjoy the hobby.  KM4FZQ&lt;/p&gt;&#xA;" OwnerUserId="15756" LastActivityDate="2019-10-02T11:30:04.203" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15432" PostTypeId="2" ParentId="15332" CreationDate="2019-10-02T16:22:06.700" Score="0" Body="&lt;p&gt;I have the same problem for taking CS in Portugal. I will live there and would like to take a local CS. I am a ham since 1962. Looking on the banks of USA qualification questions under CEPT agreement, I considered that my extra category should be accepted for granting  the CS (call sign) without questions. However, I have the clear e-mail from ANACOM:&#xA;As you do not have a HAREC certificate or a Brazilian COER it is not possible to grant a national amateur certificate with a portuguese call sign as according to the law in force those are the only documents we accept for this purpose.&#xA;The ARRL says: explain that you have not have HAREC. It is absolutely defenseless advice. We are not competitive in Europe, because the VEC certification  does not have a simple phrase &quot;Complaint with HAREC&quot;. Why? At the same time any organization including ARRL may joint to HAREC.&lt;/p&gt;&#xA;" OwnerUserId="15760" LastActivityDate="2019-10-02T16:22:06.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15437" PostTypeId="1" AcceptedAnswerId="15440" CreationDate="2019-10-03T17:53:04.363" Score="1" ViewCount="295" Body="&lt;p&gt;Is there a way where I can take a single frequency and subdivide it into channels so theoretically I can transmit multiple voice channels on the other?&lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="218" LastEditDate="2019-10-03T23:28:54.660" LastActivityDate="2019-10-04T00:01:23.613" Title="Is there a way to split a frequency into channels?" Tags="&lt;transmitter&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15438" PostTypeId="2" ParentId="15422" CreationDate="2019-10-03T19:10:07.277" Score="3" Body="&lt;p&gt;In fact, almost everything that was previously sold as an FRS/GMRS radio is now an FRS radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;In 2017, the FCC changed its rules to stop equipment authorization of FRS dual-service radios and it changed the rules for both FRS and GMRS such that existing radios would be reclassified as either FRS or GMRS to remove the confusion of whether a license was needed for legal operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically, if you have a radio that was sold as a dual-service FRS/GMRS radio and it is limited to the channels and power limits provided... then that device can be operated as an FRS device without a licensing requirement.&quot; (from &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/family-radio-service-frs&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/family-radio-service-frs&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The channel and power limits for FRS are 2W for channels 1-7, and 0.5W for channels 8-14 - so most radios that are officially FRS can do 2W, as do all the old &quot;FRS/GMRS&quot; radios, which are now classified as FRS.&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2019-10-03T19:10:07.277" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15439" PostTypeId="2" ParentId="15437" CreationDate="2019-10-03T19:13:11.720" Score="0" Body="&lt;p&gt;There are different ways to allow two signal sources to share the same frequency, although I wouldn't call them channels because that word implies different carrier frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could use time-division multiplexing (&lt;a href=&quot;https://en.wikipedia.org/wiki/Time-division_multiplexing&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Time-division_multiplexing&lt;/a&gt;).  This is the approach used by DMR radios.  It's much better suited for digital signals than for analog signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another possibility is frequency-division multiplexing (&lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency-division_multiplexing&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Frequency-division_multiplexing&lt;/a&gt;).  You could, for example, use lower frequencies for one voice and higher frequencies for another voice in your audio stream.  This would require electronically altering the pitch of at least one voice.  The combined audio would be used to modulate the carrier, and the process would be reversed on the receiving end.  This works great for analog signals, but it can greatly increase the bandwidth of the signal.  This trick was sometimes used in analog phone networks to reduce the number of wires needed to carry multiple phone calls.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option is to rely on polarization.  You could use vertically polarized antennas for one conversation and horizontally polarized antennas for another conversation.  This doesn't provide perfect separation, but it could be good enough if you're working within line of sight.  If you're trying to bounce the signal off the ionosphere, the polarization can be changed significantly.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2019-10-03T19:29:26.837" LastActivityDate="2019-10-03T19:29:26.837" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15440" PostTypeId="2" ParentId="15437" CreationDate="2019-10-03T20:42:41.613" Score="0" Body="&lt;p&gt;I agree with the previous answer that &quot;channel&quot; typically refers to a carrier frequency. For example, each Citizen's Band, marine FM and Family Radio System channel is assigned a unique frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Independent Sideband (ISB) is a method of modulating two &lt;em&gt;different&lt;/em&gt; signals onto a &lt;em&gt;single&lt;/em&gt; carrier. From &lt;a href=&quot;https://en.wikipedia.org/wiki/Independent_sideband&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Independent sideband (ISB) ... modulates two different input signals —&#xA;  one on the upper sideband, the other on the lower sideband. This is&#xA;  used in some kinds of AM stereo (sometimes known as the Kahn system).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;According to page 50 of &lt;a href=&quot;https://www.fritz.dellsperger.net/downloads/V7a_2.1-Amplitudemodulation_en.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dellsperger's treatise on Amplitude Modulation&lt;/a&gt;,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The practical implementation is realized by addition of an LSB and a USB signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is similar to &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency-division_multiplexing&quot; rel=&quot;nofollow noreferrer&quot;&gt;frequency-division multiplexing&lt;/a&gt;,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;... a technique by which the total bandwidth available in a&#xA;  communication medium is divided into a series of non-overlapping&#xA;  frequency bands, each of which is used to carry a separate signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-10-03T20:42:41.613" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15441" PostTypeId="2" ParentId="15410" CreationDate="2019-10-04T00:01:05.760" Score="0" Body="&lt;p&gt;The yagi will not hurt your radio if it is made for the right frequency. I would recommend making a small 3 element yagi that you hold in your hand.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You remove the antenna that comes with the radio and then plug a cable in. The other end of the cable goes to the Yagi. &lt;/p&gt;&#xA;" OwnerUserId="14671" LastActivityDate="2019-10-04T00:01:05.760" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15442" PostTypeId="2" ParentId="15437" CreationDate="2019-10-04T00:01:23.613" Score="3" Body="&lt;p&gt;What you are looking for is called a &lt;a href=&quot;https://en.wikipedia.org/wiki/Channel_access_method&quot; rel=&quot;nofollow noreferrer&quot;&gt;multiple access method&lt;/a&gt;: a way for two or more users to share the capacity of a single channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common ways to do it include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;frequency division: divide the channel into narrower channels, each user gets a sub-channel&lt;/li&gt;&#xA;&lt;li&gt;time division: divide the channel into time slots, users take turns&lt;/li&gt;&#xA;&lt;li&gt;code division: each user uses a different spreading code with a low correlation&lt;/li&gt;&#xA;&lt;li&gt;space division: each user gets a directional antenna (perhaps a dynamic one, with beamforming techniques) pointed at just them&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-10-04T00:01:23.613" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15443" PostTypeId="2" ParentId="1845" CreationDate="2019-10-04T00:45:47.123" Score="1" Body="&lt;p&gt;Transmitting without identifying is illegal in nearly all circumstances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One exception to this is when you make a transmission of type TEST on a band that allows such.  TEST is defined as an unmodulated CW signal (since it is unmodulated, it can't include an ID).  TEST is only allowed on HF bands (and a few other areas) where you might use SSB or CW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, it is legal to tune up on HF without identifying.&#xA;But repeater bands (which use FM) do not allow TEST, so you must identify there, and if you key up on FM, it is modulated, even if you don't speak.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-10-04T00:45:47.123" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15444" PostTypeId="1" CreationDate="2019-10-04T07:38:57.490" Score="3" ViewCount="90" Body="&lt;p&gt;We all know that the ionosphere — when charged — refracts RF energy, but why?  In other words, what is actually occurring at a molecular level to cause radio waves to bend back to earth because of charged particles in the atmosphere? Is it a collision of some type between waves and particles?&lt;/p&gt;&#xA;" OwnerUserId="14182" LastEditorUserId="7804" LastEditDate="2019-10-04T14:17:28.580" LastActivityDate="2019-10-04T16:17:40.233" Title="What is really happening during RF ionospheric refraction?" Tags="&lt;propagation&gt;&lt;ionosphere&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15445" PostTypeId="2" ParentId="15444" CreationDate="2019-10-04T07:47:12.430" Score="2" Body="&lt;p&gt;The ionosphere contains freely moving charged particles that act like a conducting &quot;plate&quot;. When a radio wave traveling up reaches the ionosphere, the electric field of the wave starts to move the electrons. This movement that happens at the RF frequency acts like a current and the current acts a bit like an antenna creating its own wave that is now traveling back to earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The original wave is mostly cancelled out by the radiation from this new current sheet in the region above the ionosphere.&lt;/p&gt;&#xA;" OwnerUserId="194" LastActivityDate="2019-10-04T07:47:12.430" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15446" PostTypeId="2" ParentId="15444" CreationDate="2019-10-04T16:17:40.233" Score="6" Body="&lt;p&gt;Solar radiation ionizes the atmospheric gas, creating a plasma with free electrons. The density of these free electrons varies by height, time of day, and solar conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the electrons are free to move in the plasma, they will be displaced by an electromagnetic wave. If you want a rigorous mathematical treatment, &lt;a href=&quot;http://www.waves.utoronto.ca/prof/svhum/ece422/notes/20c-ionosphere.pdf&quot; rel=&quot;noreferrer&quot;&gt;The University of Toronto has a great paper&lt;/a&gt;. In summary, the presence of these free electrons has the effect of altering the &lt;a href=&quot;https://en.wikipedia.org/wiki/Relative_permittivity&quot; rel=&quot;noreferrer&quot;&gt;relative permittivity&lt;/a&gt; of the medium.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Relative permittivity is also known as the dielectric constant, and is related to the refractive index:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ n = \sqrt{\varepsilon_\mathrm r \mu_\mathrm r} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$n$&lt;/span&gt; is the refractive index,&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\varepsilon_\mathrm r$&lt;/span&gt; is the relative permittivity, and&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\mu_\mathrm r $&lt;/span&gt; is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Permeability_(electromagnetism)&quot; rel=&quot;noreferrer&quot;&gt;relative permeability&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you have some experience engineering magnetic circuits, you may understand relative permeability in terms of magnetic dipoles within a material such as iron or ferrite which are able to align themselves with an applied magnetic field: this is why putting a core in an inductor increases the inductance. Relative permittivity is the same thing only for electric fields, and it's those free electrons in the atmosphere responsible for the change in permittivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, different layers of the ionosphere have different refractive indexes, which means at the interface between different layers an electromagnetic wave will be bent. The degree of bending is proportional to the difference between the refractive indexes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the wave skims the ionosphere at a shallow enough angle, the refraction will be sufficient to reflect the wave back out of the ionosphere. This phenomenon is called &lt;a href=&quot;https://en.wikipedia.org/wiki/Total_internal_reflection&quot; rel=&quot;noreferrer&quot;&gt;total internal reflection&lt;/a&gt;. You've probably seen it at the interface between water and air, which when viewed at a shallow angle appears to be a mirror:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Pi2BT.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Pi2BT.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;Brocken Inaglory [&lt;a href=&quot;https://creativecommons.org/licenses/by-sa/4.0&quot; rel=&quot;noreferrer&quot;&gt;CC BY-SA 4.0&lt;/a&gt;], &lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Total_internal_reflection_of_Chelonia_mydas.jpg&quot; rel=&quot;noreferrer&quot;&gt;via Wikimedia Commons&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In this example there are two media with a distinct boundary between them, which can make it a little hard to accept. In reality, the electron density (and thus the refractive index) of the atmosphere varies smoothly with altitude. But total internal reflection can still occur. Think of it as a stack of infinitesimally thin layers, with each layer having a very slightly different index of refraction. Each interface bends the wave just a little bit, with the net effect of making the wave travel in a curved line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A visible example of this is &lt;em&gt;mirage&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gMCxN.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gMCxN.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;Brocken Inaglory [Public domain], &lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Desertmirage.jpg&quot; rel=&quot;noreferrer&quot;&gt;via Wikimedia Commons&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice the inverted image of the tent. This is caused due to the temperature gradient of the air: the lower air is hotter, and the refractive index of air varies with temperature. Ionospheric refraction works the same way, only upside-down and the frequency is much lower.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-10-04T16:17:40.233" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15447" PostTypeId="1" CreationDate="2019-10-05T07:34:58.093" Score="1" ViewCount="144" Body="&lt;p&gt;I'm experimenting with SDR on MacOS High Sierra. Trying both CubeSDR and GQRX and experiencing similar issues with both. The applications seem to work, but the audio is choppy and chipmunk-like. Obviously a problem with buffering and sample-rate conversion. Both apps use SoapySDR.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm currently using a HackRF device, but will test with a stock RTL-SDR device and try and isolate the problem further.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anyone has any ideas as to how to resolve this, I would be grateful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;update: the chipmunking has been solved by rolling back the HackRF firmware to API version 1.02 from API version 1.03. Audio is still choppy after a few seconds though. suspecting a hackrf library issue.&lt;/p&gt;&#xA;" OwnerUserId="6084" LastEditorUserId="7804" LastEditDate="2019-10-05T14:01:20.403" LastActivityDate="2019-11-04T16:01:40.227" Title="audio problem with SDR on MacOS" Tags="&lt;software-defined-radio&gt;&lt;hackrf&gt;&lt;macos&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15448" PostTypeId="2" ParentId="5672" CreationDate="2019-10-05T07:50:05.880" Score="0" Body="&lt;p&gt;BaoFeng BF-F8HP 100% backwards compatibility claim:&#xA;In the document referenced above,&#xA;&lt;em&gt;&quot;Check point no 6.7 on this page - &lt;a href=&quot;http://www.miklor.com/uv5r/UV5R-FAQ.php#Batteries&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.miklor.com/uv5r/UV5R-FAQ.php#Batteries&lt;/a&gt;&quot;&lt;/em&gt;&#xA;it's inferred that since 3800mAh battery pack is compatible with UV-5R it's also compatible with BF-F8HP (based on BaoFeng claims BF-F8HP is 100% backward compatible with UV5R accessories, I suspect)...however...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are ads on ebay that &lt;strong&gt;specifically stipulate their BL-5L 3800mAh is NOT compatible with BF-F8HP even though compatible with UV-5R&lt;/strong&gt;. So, BF-F8HP compatibility is not 100% backwards compatible with UV-5R fitting accessories. I verified this by purchasing and checking. While slightly more difficult to slip onto a UV-5RTP case than the 1800mAh pack that came with the radio, the BL-5L battery packs definitely had to be firmly pushed to engage the eject tab on the F8HP.&#xA;I wrote baofengtech.com and they insist BF-F8HP is 100% compatible with all UV-5R accessories. I realize we're talking a non-Baofeng accessory, but if an accessory fits a UV-5R many folks would think &quot;backwards compatibility&quot; would ensure it fits an F8HP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the lesson of this is...don't ASSUME compatibility based on model numbers and Baofeng-ish claims...read every product description fully. The warning on this UV-5R=compatible, but BF-F8HP=incompatible was listed WAY down on the product page.&lt;/p&gt;&#xA;" OwnerUserId="15774" LastActivityDate="2019-10-05T07:50:05.880" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15449" PostTypeId="1" CreationDate="2019-10-05T14:35:17.807" Score="2" ViewCount="268" Body="&lt;p&gt;I would like to know, what I can legally do with SDR / a Hack RF One in Switzerland?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the limitations concerning sending and receiving?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I need any licenses for that? If so, which ones, and for what are they usable?&lt;/p&gt;&#xA;" OwnerUserId="15778" LastEditorUserId="8717" LastEditDate="2019-10-05T17:21:52.183" LastActivityDate="2019-10-05T17:38:17.627" Title="Legal aspects of the HackRF one / SDR in Switzerland?" Tags="&lt;legal&gt;&lt;rf-power&gt;&lt;hackrf&gt;&lt;europe&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15450" PostTypeId="2" ParentId="15447" CreationDate="2019-10-05T15:14:56.167" Score="1" Body="&lt;p&gt;Check the sample rate configuration in the software&#xA;you are using.  Older Apple products used a hardware sample rate of 44.1 ksps, whereas newer Apple products all seem to use a hardware audio sample rate of 48k (or a multiple thereof).&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-10-05T15:14:56.167" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15451" PostTypeId="2" ParentId="15449" CreationDate="2019-10-05T17:05:51.717" Score="3" Body="&lt;p&gt;The device usually doesn't have anything to do with legality, it's what you do. So, rule of thumb: Without a license, you can't transmit – full stop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not quite sure about federal Swiss law, but chances are you can only receive broadcast transmissions (meant for everyone to receive) and transmissions especially meant for you, and everything else is eavesdropping / invasion of privacy. Amateur radio transmissions are by definition broadcast, so always OK to receive, but you can't transmit in these bands without an amateur license. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-10-05T17:38:17.627" LastActivityDate="2019-10-05T17:38:17.627" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15452" PostTypeId="1" AcceptedAnswerId="15453" CreationDate="2019-10-05T18:19:42.437" Score="5" ViewCount="803" Body="&lt;p&gt;I want to match a 50-ohm coax feed wire to a 40-meter NVIS half-wave dipole. NVIS antenna examples I've found are usually based on a regular dipole (72 ohms in free air). However the impedance drops by a factor of four (to 12 ohms) when it is lowered to 7 feet (&lt;a href=&quot;https://www.w9xt.com/page_radio_gadgets_nvis_antenna.html&quot; rel=&quot;noreferrer&quot;&gt;https://www.w9xt.com/page_radio_gadgets_nvis_antenna.html&lt;/a&gt;).&#xA;(Note: the author's numbers seem not to correlate with his factor, but at any rate the impedance drops very low).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just for reference, a folded dipole in free air is between 200 and 300 ohms (&lt;a href=&quot;https://www.w8ji.com/folded_dipole.htm&quot; rel=&quot;noreferrer&quot;&gt;https://www.w8ji.com/folded_dipole.htm&lt;/a&gt;). Therefore, its impedance would drop by a factor of four to 50-75 ohms, making it closely match 50 ohm coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My idea was for a regular dipole (not a folded dipole) and use a 4:1 balun to raise the antenna impedance by a factor of four from 12.5 ohms to 50) to match the coax and transmitter impedance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Problem: Maybe some baluns are not designed to be reversed because the side designed to be high impedance balanced antenna would then be on the unbalanced coax, and vice versa with the low impedance side. Furthermore, transferring power the side driving the low impedance antenna might draw more current than the balun wire was designed for. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have not found answers in any Radio Amateur's Handbook (I have six ranging from 1956 through 2012), or on the Internet. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;So what is the proper way to match 50-ohm unbalanced coax to 12.5 ohm balanced dipole?&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="15325" LastEditorUserId="15325" LastEditDate="2019-10-07T03:10:58.177" LastActivityDate="2020-10-05T03:21:43.567" Title="How to match low impedance of NVIS Dipole?" Tags="&lt;antenna-system&gt;&lt;balun&gt;&lt;impedance-matching&gt;" AnswerCount="6" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15453" PostTypeId="2" ParentId="15452" CreationDate="2019-10-05T19:22:50.663" Score="2" Body="&lt;p&gt;Where did you hear that a 40m center-fed dipole λ/4 high has a feedpoint impedance of only 12.5Ω? It will be 75Ω or more. &lt;em&gt;A center-fed λ/2 dipole is only 50Ω at one height.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are some graphs. As you can see, you don't need a 4:1 balun.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Ignore the top graph in this first image.&lt;/h2&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RrEmq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RrEmq.jpg&quot; alt=&quot;Dipole impedance vs height&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;The graph below is based on theoretical values&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ezy1J.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ezy1J.jpg&quot; alt=&quot;Dipole impedance vs height&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;75Ω coax will be a better match, and the worst case VSWR mismatch to your rig will be only 1.5:1.&lt;/h2&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-10-05T23:02:40.737" LastActivityDate="2019-10-05T23:02:40.737" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15454" PostTypeId="2" ParentId="15452" CreationDate="2019-10-05T22:30:30.183" Score="4" Body="&lt;p&gt;From personal experience, a good 1:4 balun (50 to 200 Ohm) doesn't necessary work as a good 4:1 balun (50 Ohm to 12.5 Ohm). You can wind just a 4:1 transformer and use it with a 1:1 balun though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another simple way to match any impedance is to use an LC-network. There are a lot of online calculators. Personally I particularly like &lt;a href=&quot;https://leleivre.com/rf_lcmatch.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt;. Using this approach I matched my 40m delta loop antenna to all bands from 10m to 80m using a separate LC-network for each band.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-10-14T15:57:54.847" LastActivityDate="2019-10-14T15:57:54.847" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15455" PostTypeId="1" AcceptedAnswerId="15457" CreationDate="2019-10-05T23:16:45.610" Score="1" ViewCount="153" Body="&lt;p&gt;I'm learning to build radio receivers and transmitters. I've successfully build some oscillators, amplifiers and filters before and decided that to build a simple crystal radio would be a logical step further. I wanted to build a crystal radio for ~7-8 MHz because I have a good antenna for 40 m band and during the night there are always many strong AM signals (typically S9+30 and even above) around 7.200-7.300 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is how my radio looks like:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/J68oJ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/J68oJ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The inductance of the coil is about 8 uH. It has 12 taps with 6th tap around 3.7 uH. The capacitor is 12..365 pF, the diode - 1N34 and the resistor - 51 kOhm. One way or another (considering stray capacitance, not exact inductance of the coil, etc) it supposed to tune somewhere around the frequency of interest:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;gt;&amp;gt;&amp;gt; from math import pi, sqrt&#xA;&amp;gt;&amp;gt;&amp;gt; L = 3/1000/1000 # 3 uH&#xA;&amp;gt;&amp;gt;&amp;gt; C = 130 / 1000/1000/1000/1000 # 130 pF&#xA;&amp;gt;&amp;gt;&amp;gt; 1/(2*pi*sqrt(L*C))&#xA;8059123.816756153&#xA;&amp;gt;&amp;gt;&amp;gt; C = 170 / 1000/1000/1000/1000 # 170 pF&#xA;&amp;gt;&amp;gt;&amp;gt; 1/(2*pi*sqrt(L*C))&#xA;7047499.335473463&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I tested the radio using a signal generator and an oscilloscope and confirmed that the BPF (LC-network) works as expected. The radio is also capable to receive a 5 W CW signal from my transmitter with the transmitting antenna placed about 20 meters away from the receiving antenna. The radio doesn't receive anything when I transmit on 20 m band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However no matter how I tried I didn't manage to receive any AM stations. I've noticed though that if I briefly transmit an 5 W AM carrier on the frequency of the AM station (not something I supposed to do...) I can hear this particular station reasonably well while I'm transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to change the coil, the resistor and add/remove capacitors in series and parallel to the variable capacitor for quite some time. At this point I doubt that I will get any better results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What brings me to the question I have. I don't know whether such a low sensitivity of a crystal radio is expected for this band (maybe this is the reason why most people make crystal radios for 0.5-1.6 MHz?) or maybe I did something wrong. Is it worth trying to make any further tests or improvements to the radio (in this case, which one?) or it's as good as a simple crystal radio will be and I should move forward to other types of receivers (e.g. superheterodyne)?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="4076" LastEditDate="2019-10-06T09:41:35.117" LastActivityDate="2019-10-06T09:41:35.117" Title="What is an expected sensitivity of a crystal radio for 7 MHz band?" Tags="&lt;crystal-radio&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15456" PostTypeId="1" CreationDate="2019-10-05T23:51:39.950" Score="0" ViewCount="68" Body="&lt;p&gt;I have a copper wire antenna about 100 feet long that I have relocated and now need about 75 feet of lead in wire. What type &amp;amp; size of wire should I use?&lt;/p&gt;&#xA;" OwnerUserId="15629" LastActivityDate="2019-10-07T00:50:44.187" Title="Lead in wire size" Tags="&lt;antenna&gt;&lt;diy&gt;" AnswerCount="1" CommentCount="4" ClosedDate="2019-10-10T23:09:22.253" ContentLicense="CC BY-SA 4.0" />
  <row Id="15457" PostTypeId="2" ParentId="15455" CreationDate="2019-10-06T00:01:07.443" Score="4" Body="&lt;p&gt;I notice you have a BNC antenna socket, so I wonder if you're having the same problem I once had. I built a crystal radio kit, attached it to my HF antenna, and got essentially nothing. I then followed the kit instructions for a long-wire antenna connected directly to the terminals of the kit, and got much better results even though that antenna was strung up indoors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, consider whether you have an &lt;strong&gt;impedance matching&lt;/strong&gt; problem between the antenna and the radio. Try an impedance transformer or a different antenna with much higher impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, I don't have the theoretical background to tell you how to &lt;em&gt;calculate&lt;/em&gt; the input impedance of your radio — I once wondered about what the input impedance of a diode rectifier was, and found an lengthy article explaining that the effective impedance depended complicatedly on the details of the surrounding circuit. (A diode is a nonlinear device, so the rectifier doesn't &lt;em&gt;strictly&lt;/em&gt; have a consistent impedance at all.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-10-06T00:01:07.443" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15458" PostTypeId="2" ParentId="15456" CreationDate="2019-10-06T14:27:31.210" Score="2" Body="&lt;p&gt;Your question does not have enough information to give a specific answer, so here are some general guidelines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The type and size of wire needed is unrelated to the antenna.&#xA;The factors that are important here needed to answer your question are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the maximum power you will transmit with&lt;/li&gt;&#xA;&lt;li&gt;the amount of loss you can tolerate (greater distance has more loss)&lt;/li&gt;&#xA;&lt;li&gt;the frequencies in use&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Higher power needs heavier wire to handle the power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Low loss requires some type of transmission line with an impedance matched to the radio and antenna.  Typical choices are parallel line (such as twin lead or ladder line), coax, and wave guide.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wave guide is typically used for very short distances at high frequencies (1GHz and up); since your antenna is 100ft long, it's probably safe to assume you are working at much lower frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Parallel transmission line is typically extremely low loss even if the antenna is unmatched with high SWR, but is sensitive to surrounding metal objects.  This works well outside, but if the transmission line has to enter a building, it may couple to wiring and other metal and the building and have high loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coax works well in buildings and near other metal objects, but has high loss if the antenna is not well matched enough to have low SWR, and may have moderate loss (typically measured in dB per 100 feet) even with good SWR.  Different grades (i.e., more expensive) of coax have better shielding or better dielectric to reduce loss.  Loss in coax is also frequency dependent, with higher bands (above 1GHz) needing different coax than lower bands.  In extreme cases where either long distance is involved (more than 100 ft) or extremely low loss is desired, coax typically called hardline can be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both parallel line and coax have power ratings that can also be used as a guide when choosing transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For amateur radio use, the size of the transmission line is typically not a concern, as your choices in transmission line come first with the above concerns, and there are limited choices to increase wire size.  However, in commercial broadcast radio where the power may exceed 10Kw and loss becomes critical, hardline can have large diameters and come in the form of pipes with a diameter measured in feet.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2019-10-07T00:50:44.187" LastActivityDate="2019-10-07T00:50:44.187" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15459" PostTypeId="1" AcceptedAnswerId="15460" CreationDate="2019-10-06T16:08:50.407" Score="0" ViewCount="118" Body="&lt;p&gt;I'm sorry if my title seems weird but I just started to learn about signal transmitting and I don't know where to start &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm searching about simple ways to make diy radio but I can't really understand something without making it and all the circuits I saw seemed very complicated &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is can I make a simple circuit , like ne555 can produce 1-10khz signal so if I connect ne555's output into antenna , antenna will transmit the signal into air and if I know right I can receive that signal with some kind of coil but I tried several circuits and none of them achieve any progress &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm really sorry if my question is hard to read or off topic &lt;/p&gt;&#xA;" OwnerUserId="15786" LastEditorUserId="8717" LastEditDate="2019-10-06T18:47:53.263" LastActivityDate="2019-11-22T06:54:30.287" Title="Can I make signal transmitter without decoder?" Tags="&lt;antenna-theory&gt;&lt;diy&gt;&lt;transmitter&gt;" AnswerCount="4" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15460" PostTypeId="2" ParentId="15459" CreationDate="2019-10-06T18:46:00.733" Score="4" Body="&lt;p&gt;Just about anything that has rapidly varying current or voltage radiates some degree of electromagnetic energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Creating a transmitter which is efficient, legal, useful, and reliable on the other hand is an entirely different matter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna at 1-10 kHz would be extremely large. 1 kHz has a wavelength of about 300 km, 10 kHz about 30 km. Antennas are typically on the order of 1/4 or 1/2 wavelength. They can be made smaller, for a cost in efficiency. So whatever antenna you will conceivably attach to a 555 will be extremely small and inefficient. Communication at these frequencies &lt;a href=&quot;https://en.wikipedia.org/wiki/Very_low_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;is possible&lt;/a&gt;, but only with very large antennas and much higher powers than you'll get from a simple 555.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, you're probably not licensed to transmit on these frequencies, so if you did manage to build a working transmitter it would be illegal.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-10-06T18:46:00.733" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15461" PostTypeId="1" AcceptedAnswerId="15471" CreationDate="2019-10-06T19:51:32.947" Score="1" ViewCount="73" Body="&lt;p&gt;I have a Diamond HFV-5 (rotatable dipole) in the attic fed by ~30ft of coax. The antenna system comes with a Balun at the feedpoint. Would it be worthwhile to add an inline RF Choke (Unun) in addition or is that covered by the Balun?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.diamondantenna.net/HFV-5.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.diamondantenna.net/HFV-5.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="606" LastActivityDate="2019-10-08T01:52:32.410" Title="Rotatable Dipole &amp; RF Choke" Tags="&lt;dipole&gt;&lt;balun&gt;&lt;choke-balun&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15462" PostTypeId="1" AcceptedAnswerId="15463" CreationDate="2019-10-06T20:17:17.707" Score="1" ViewCount="85" Body="&lt;p&gt;I'm just getting started using amateur satellites and would like to subscribe to an email reflector, but I can't find one. Is there anything out there? &lt;/p&gt;&#xA;" OwnerUserId="15710" LastActivityDate="2019-10-07T00:12:44.787" Title="Are there any satellite email reflectors?" Tags="&lt;vhf&gt;&lt;satellites&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15463" PostTypeId="2" ParentId="15462" CreationDate="2019-10-06T21:38:54.370" Score="2" Body="&lt;p&gt;Yes there are. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.amsat.org/mailman/listinfo/amsat-bb&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amsat.org/mailman/listinfo/amsat-bb&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.google.com/search?q=amateur+satellite+email+reflector&quot; rel=&quot;nofollow noreferrer&quot;&gt;There are others&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-10-07T00:12:44.787" LastActivityDate="2019-10-07T00:12:44.787" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15466" PostTypeId="2" ParentId="15100" CreationDate="2019-10-07T13:35:50.470" Score="0" Body="&lt;p&gt;This is indeed a R-1484/PRR-15, also known as AN/PRR-15. Made by Zenith, circa 1969 for USMC sigint use in Viet Nam. Probably fewer than 100 made. &lt;/p&gt;&#xA;" OwnerUserId="15795" LastActivityDate="2019-10-07T13:35:50.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15467" PostTypeId="2" ParentId="15459" CreationDate="2019-10-07T15:33:53.960" Score="3" Body="&lt;p&gt;Every oscillator is a transmitter, and every wire is an antenna, mostly extremely inefficient at low frequencies.  Many wall plug type power supplies (USB, LED lighting, etc.) have an internal digital oscillator with an output waveform similar to a 555.  If you hold an old AM pocket radio with an internal ferrite loopstick antenna close and tune between AM stations, you can hear a buzz from the radiated RF if you hold it close to the power brick (or LED lighting) and plug the power brick in to AC.  Same with a 555 and a loop of wire (from the square wave harmonics).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To send RF farther, you need more efficient antennas.  But check what power levels are legal for whatever frequencies your antenna will radiate (FCC part 15 in the US, for hobby digital electronics “unintentional” radiators).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You actually don’t need more power.  With the proper radio license, you can occasionally send a 3.3V digital pin output from a Raspberry Pi plus a low pass filter and large high antenna a 1000 km or more (using WSPR or QRSS CW modulation).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="4076" LastEditDate="2019-10-08T11:51:40.047" LastActivityDate="2019-10-08T11:51:40.047" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15468" PostTypeId="2" ParentId="15452" CreationDate="2019-10-07T15:35:45.553" Score="6" Body="&lt;p&gt;Many baluns will work just fine in either direction, though there isn't just one kind of &quot;4:1 balun&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This kind is wound on two cores, and works as a common-mode choke:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/utxjg.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2futxjg.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A common-mode choke works in either direction, so it matters not which end is balanced and which is unbalanced (or if both ends are unbalanced, or both balanced, for that matter.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However this kind is wound on a single core and relies on ground potential being at the midpoint of the balanced terminals:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/cKLDD.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fcKLDD.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can work OK given a well-balanced load on the right, and an unbalanced load on the left. But flipped the other way (with the balanced load on the left) it will try driving each terminal of the balanced load to different voltages relative to ground, so you'll get quite a lot of common-mode current.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-10-07T15:35:45.553" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15469" PostTypeId="2" ParentId="15452" CreationDate="2019-10-07T17:09:35.943" Score="2" Body="&lt;p&gt;How to match a 12.5 ohm balanced antenna to a 50 ohm unbalanced line...  I think that has been well answered but one point worth mentioning, and a relevant anecdote...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are 2 books by Jerry Sevick directly addressing how to do this:&#xA; - Sevick's Transmission Line Transformers, Theory and Practice, 5th Edition (2014), by Mack and Sevick&#xA; - Understanding, Building and Using Baluns and Ununs (2002), by Sevick&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first book is very theoretical, the second --which I have not yet read-- is said to be more hands-on.  Both are worth reading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I happen to have a 12.5 ohm 40m balanced dipole (short dipole, not NVIS).  A lot of work went into designing and building, including the 4:1 balun (wound using 25 ohm coax; not easy to find).  When I finished and took measurements, I found the impedance was closer to 50 than 12.5 ohms.  It works better without the 4:1 balun!  Of course it certainly has a strong 1:1 common mode choke.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My point is that you might consider building the antenna first.  Measure the actual impedance, then build the balun.  You might find that a matching network may work better for you, as mentioned already by @alexanderalekseev-r2auk&lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="11434" LastEditDate="2019-10-08T23:02:04.370" LastActivityDate="2019-10-08T23:02:04.370" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15470" PostTypeId="2" ParentId="15452" CreationDate="2019-10-07T23:51:29.417" Score="1" Body="&lt;p&gt;Today I made the antenna and included some data, for what it's worth, although this isn't really an answer because the other answers helped me to get to this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is a dipole with 33 feet per leg (untrimmed) of insulated #14 stranded wire, with a ceramic insulator and about 10 feet of polyester rope at each end. The height is 10 feet. There are three 8-foot metal T-posts with 3 feet of 1&quot; PVC pipe clamped to the top for RF isolation. I laid 70 feet of extension cord on the ground below the antenna to act as one reflector (more are recommended). The center post holds a plastic box with a current choke made of 13 turns bifilar on an FT140-61 torroid. The feed cable is 66 feet long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tested it for SWR in the 40-meter band at 10 watts and was able to get SWR of 4:1 at 7.280 MHz, 2:1 at 7.150, and 1.3 at 7.000 MHz. That indicates to me that the resonance is slightly low so it needs to be trimmed. So it looks like it will tune with good SWR as soon as I can trim it. I believe the height of 10 feet is approximately 0.073 wavelength, so the graph of impedance vs. height indicates that it might be about 12 ohms. I'm concerned that my SWR readings are not right if that's the case. More experimenting is in store.&lt;/p&gt;&#xA;" OwnerUserId="15325" LastEditorUserId="15325" LastEditDate="2019-10-08T19:20:56.980" LastActivityDate="2019-10-08T19:20:56.980" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15471" PostTypeId="2" ParentId="15461" CreationDate="2019-10-08T01:52:32.410" Score="1" Body="&lt;p&gt;A balun effectively allows you to connect a balanced antenna (such as a dipole) to an unbalanced feeder (such as coax). You have a balun at the feed point of the antenna, with a coax socket on it, which means that the feeder going from the radio to the antenna is unbalanced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The HFV-5 is an antenna that presents a 50Ω impedance on its coax socket and it already has a balun. Your radio's impedance at the antenna socket is presumably also 50Ω, and I am assuming that you are using 50Ω coax as the feeder.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am puzzled as to what good the unun would do in this system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(So to answer your question - I don't think it would be worthwhile to put an unun in addition to what you already have).&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-10-08T01:52:32.410" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15472" PostTypeId="1" CreationDate="2019-10-08T11:00:45.610" Score="0" ViewCount="34" Body="&lt;p&gt;This is the follow up to:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/15188/uhf-cubical-quad-vna-analysis-interpretation&quot;&gt;UHF cubical quad VNA analysis interpretation&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a S21 and S31 analysis of an oversized 385 Mhz 50 Ohm to 90 Ohm balun between 100 Mhz and 600 Mhz&#xA;I tested phase separation and transmission loss for both ports.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I interpret the results correctly, phase separation is pretty good over the 300 - 400 Mhz range.&#xA;Transmission loss however is not good (more than 6dB loss, ideal should be 3dB loss) with one port more lossy than the other.&#xA;I did not compute the common-mode rejection yet, I know there is a simple formula to calculate it from the VNA data.&#xA;I did not test port isolation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I will rethink the balun from scratch and scale it down.&#xA;My questions are :&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Do smaller 43 ferrite cores (10 mm OD, 7mm ID, height 3mm) will have acceptable performance at 400 Mhz ? (currently using 61 material 23 mm OD, 14 mm ID)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Also, port 1 ground and port 2 and 3 center tap are grounded to their respective PCB bottom layers. The PCB is split in two to prevent the grounds from contacting.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it acceptable practice to use a ground layer in baluns ? or should I discard grounds and connect grounded leads to their respective connector leads ?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For a detailed schematic, please refer to the previous post linked atop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/URFpC.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/URFpC.jpg&quot; alt=&quot;phase separation between port 2 and port 3&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0uGs3.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0uGs3.jpg&quot; alt=&quot;transmission loss in db for port 2 and port 3&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13081" LastEditorUserId="13081" LastEditDate="2019-10-09T06:36:17.187" LastActivityDate="2019-10-09T06:36:17.187" Title="UHF cubical quad VNA analysis interpretation (part2)" Tags="&lt;balun&gt;&lt;ferrite&gt;&lt;antenna-analyzer&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15474" PostTypeId="1" CreationDate="2019-10-08T18:35:07.130" Score="2" ViewCount="272" Body="&lt;p&gt;An ideal dipole, at resonance, will have an impedance around 73 ohms. A folded dipole, around 280 ohms. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I calculate the impedances when not at resonance? Let's assume I have a span of 15M in my property where I can hang a dipole. Ideally, and very roughly, a folded dipole would give me about 280 ohms impedance at 10MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I estimate what the impedance will be at 160, 80, 40, 30, 20, 17, 15, 10 M will be?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to build a balanced matchbox and I want to estimate the required L and C sizes, to figure out what the range of matching would be.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2019-10-09T17:49:25.940" Title="How to estimate a dipole feedpoint impedance?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;&lt;impedance-matching&gt;&lt;folded-dipole&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15475" PostTypeId="1" CreationDate="2019-10-08T20:12:30.123" Score="1" ViewCount="167" Body="&lt;p&gt;My shack is on the second floor, 4m from the ground. My main antenna is a base loaded vertical, using the metal roof (10x6m) as a ground plane.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I operate in 20 and 40 meters, it's pretty acceptable. I don't seem to have RF in the shack. But on 80m I do: I have a small power supply with a digital readout and I see the current indicator go wild when I transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this mean my earthing is not good enough? What can be done to improve it? Will grounding the roof with the shortest possible ground strap help with this situation?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="4665" LastEditDate="2019-10-08T20:33:19.523" LastActivityDate="2019-10-09T17:46:46.227" Title="Grounding for an upper floor shack" Tags="&lt;grounding&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="15476" PostTypeId="2" ParentId="15474" CreationDate="2019-10-09T01:14:50.063" Score="2" Body="&lt;p&gt;Read it off this chart:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VxaQH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VxaQH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;Interferometrist [&lt;a href=&quot;https://creativecommons.org/licenses/by-sa/4.0&quot; rel=&quot;nofollow noreferrer&quot;&gt;CC BY-SA 4.0&lt;/a&gt;], &lt;a href=&quot;https://commons.wikimedia.org/wiki/File:DipoleImpedance-wide.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;via Wikimedia Commons&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A folded dipole with equal-sized conductors has 4x the impedance of an ordinary dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance repeats every wavelength, so for example if you're interested in the impedance at 2.5 wavelengths (off the chart) it won't be far off from the impedance at 1.5 wavelengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Height above ground, conductor diameter, and non-straightness of the dipole elements can alter the impedance, but if you just want a rough estimation this will do just fine.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-10-09T17:49:25.940" LastActivityDate="2019-10-09T17:49:25.940" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15477" PostTypeId="2" ParentId="15474" CreationDate="2019-10-09T08:56:24.627" Score="1" Body="&lt;p&gt;There are at least two ways. Firstly, you can use the antenna modeller (I prefer cocoaNEC) to estimate an impedance of the antenna at given frequency. From personal experience it doesn't work that well though. The real antenna will differ quite a bit from the model because of unknown ground properties, various metal object near antenna, etc. This method may still be useful, e.g. if the antenna is erected very high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, you can use an antenna analyzer (I use EU1KY antenna analyzer, model &lt;a href=&quot;https://www.elekitsorparts.com/product/faa-450-antenna-analyzer-eu1ky&quot; rel=&quot;nofollow noreferrer&quot;&gt;FFA-450&lt;/a&gt;) to measure the impedance. This method is not perfect as well, especially if impedance is high, but it gives numbers that are close to reality. I choose L and C using the impedance measured buy the antenna analyzer and wind a few extra turns in the coil. Then I tune L by stretching the coil until I get SWR close to 1:1. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(UPD: By the way, I have a very pleasant experience of using a delta loop  under similar conditions. You can find a diagram &lt;a href=&quot;https://ham.stackexchange.com/a/13314/13598&quot;&gt;here&lt;/a&gt; and the full description in Russian &lt;a href=&quot;https://eax.me/delta-loop-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;).&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-10-09T08:56:24.627" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15478" PostTypeId="2" ParentId="15475" CreationDate="2019-10-09T17:41:21.843" Score="3" Body="&lt;p&gt;Very similar question to &lt;a href=&quot;https://ham.stackexchange.com/questions/1227/what-are-some-ways-to-ground-a-transmitterantenna-in-an-enclosed-attic&quot;&gt;this one&lt;/a&gt;.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference might be the size of your metal roof.  The RF field from your vertical antenna element is &quot;looking&quot; for a counterpose element.  If your metal roof is too small for the transmitted wavelength to act as a semi-resonant counterpose, the vertical RF field might try to use something else for its counterpose: the wiring in your shack, the A/C power line, ground, internet or telephone wiring to your shack, etc.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I might try adding some longer counterpose wires, suitable lengths for 80M, to your metal roof, so the vertical antenna is more likely to use those, instead of stuff nearer to you, for its primary counterpose.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, you might want to try to &quot;cut&quot; the feed line, A/C power wiring, etc., at the RF frequency, by adding RF chokes spaced so the distance between the chokes makes those wire segments an unsuitable length to act as good counterposes or as nicely resonant director or reflector parasitic antenna elements.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-10-09T17:46:46.227" LastActivityDate="2019-10-09T17:46:46.227" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15479" PostTypeId="1" CreationDate="2019-10-09T19:42:39.470" Score="4" ViewCount="145" Body="&lt;p&gt;I'm fairly new to antenna matching, other than having built a base loaded vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm also new to EZNEC and I tried to simulate an horizontal loop. I arbitrarily chose a 10x10M loop, so I added 4 wires, 10M each, 5 segments each (20 segments max on the free eznec version), 9M above ground. I configured the alternate feedpoint impedance at 300, 450 and 600 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SWR sweep at 300 ohms shows SWR &gt;100 up to about 7MHz, and it decreases and stays between 3 and 10 as frequency increases. Does this mean this antenna can't be tuned to the 160M band, or does this just mean that the impedance is so different from 300 ohms that the SWR is useless?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to feed this loop with a balanced L network tuner. Series inductance, and shunt capacitance. At 2MHz, EZNEC shows an impedance of 23 + 2000j. Does this mean that I need to use a capacitor with -2000 ohms impedance at 1.8MHz, which would to compensate for the +2000 j in my loop?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or in short, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;can a 10x10M loop, 9 meters above ground, be matched to work on the 160M band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I suppose this will be a &quot;cloud warmer&quot; at this band, but still)&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="8717" LastEditDate="2019-11-05T21:30:30.917" LastActivityDate="2019-11-05T21:30:30.917" Title="Basic antenna matching theory?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;loop-antenna&gt;&lt;antenna-modeling&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15480" PostTypeId="2" ParentId="15479" CreationDate="2019-10-09T23:11:38.080" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Does this mean this antenna can't be tuned to the 160M band, or does this just mean that the impedance is so different from 300 ohms that the SWR is useless?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A little bit of both. If you get an off-the-shelf matchbox, which is usually advertised as being good for a 10:1 range or even less, then you can expect that it won't be able to make this antenna do 160m. If you build your own matching network you can &quot;tune&quot; pretty much anything, but the high SWR does give you some indication that the resulting system may be inefficient, narrow-band, or both.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I replicated your model in 4nec2 (except with more segments), and came up with a pretty similar frequency sweep to yours. But the feed impedance at 2MHz comes up as 0.12 + 1129j, not 23 + 2000j. This aligns with my expectations; a loop that size shouldn't have anywhere near 23 ohms of resistive component near 160m. In fact, the real part is &amp;lt;1 ohm on my plot up until 2.5MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But let's say we want to tune it out. Lucky for me, my tool has an automatic network calculator, so I select &quot;high pass L&quot;, and a 50-ohm Z0 (no point making things harder by trying to bring it all the way to 300). It suggests me a 70.3pF series cap (which is indeed about -1130j ohms at 2MHz) and a 195nH shunt impedance... hmm, something's off here, there's a precision problem. That's a bad sign, but let's press on. Okay, if I tweak the values to 69.98pF and 635nH, it tells me that I get 48.1 - 0.75j ohms at 2.0MHz, for an SWR of 1.04, which should make anyone happy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;But&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MdgKP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MdgKP.png&quot; alt=&quot;network loss&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;this is a problem... assuming typical values of Q for capacitors and inductors, this matching network will eat up more than 90% of the power going into the antenna. Not only is that bad for your actual output power, it means that your matching network has to be built to dissipate all of that heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AvmOW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AvmOW.png&quot; alt=&quot;SWR graph&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and &lt;em&gt;this&lt;/em&gt; is a problem as well... we adjusted the network with fiddly precision for a good match at 2.0MHz, and we got that, but the system 2:1 SWR bandwidth is from 1.999 to 2.001 MHz. 2kHz! Not even enough for a decent SSB signal. The 10:1 SWR bandwidth is only 8kHz wide.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So yeah, maybe that does mean that the antenna &quot;can't be tuned&quot;... at least in a practical sense. I'm not an expert in this stuff but I don't think that changing the matching topology would improve things by any significant amount.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And by the way, yes, it's a cloud warmer, with a predicted maximum gain at 65° elevation.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-10-09T23:11:38.080" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15481" PostTypeId="1" AcceptedAnswerId="15483" CreationDate="2019-10-10T08:25:37.610" Score="1" ViewCount="178" Body="&lt;p&gt;I am seeing a repeater on &lt;a href=&quot;https://www.repeaterbook.com/repeaters/Display_SS.php?state_id=41&amp;amp;band=4&amp;amp;loc=%&amp;amp;call=%&amp;amp;use=%&quot; rel=&quot;nofollow noreferrer&quot;&gt;RepeaterBook&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;444.8375&#xA;+5 MHz&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;CC 7&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Portland, Providence Portland Medical Center&#xA;Multnomah&#xA;WA7HAA&#xA;OPEN&#xA;ON-AIR&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to programme this on my Baofeng UV5R.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="13927" LastActivityDate="2019-10-10T18:35:41.910" Title="What is meant by CC 7?" Tags="&lt;ht&gt;&lt;repeater&gt;&lt;uv-5r&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15483" PostTypeId="2" ParentId="15481" CreationDate="2019-10-10T18:35:41.910" Score="2" Body="&lt;p&gt;According to the &lt;em&gt;&lt;a href=&quot;http://www.raqi.ca/~ve2rae/dmr/Amateur_Radio_Guide_to_DMR.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio Guide to Digital Mobile Radio&lt;/a&gt;&lt;/em&gt; by W2AXB, CC is the DMR programming &quot;Color Code.&quot;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-10-10T18:35:41.910" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15484" PostTypeId="2" ParentId="15479" CreationDate="2019-10-10T19:20:33.693" Score="1" Body="&lt;p&gt;Using a closed loop whose circumference is only about &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;/4 puts it in the regime of a &quot;small&quot; transmitting loop. This online &lt;a href=&quot;http://www.66pacific.com/calculators/small-transmitting-loop-antenna-calculator.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;Small Transmitting Loop Antenna Calculator&lt;/a&gt; gives remarkably similar results to NEC simulation using only formulae from the &lt;em&gt;ARRL Antenna Book&lt;/em&gt;. It's particularly interesting to observe the effects of increasing conductor diameter: higher efficiency through reduced ohmic loss, resulting in much narrower bandwidth resulting from increased &lt;em&gt;Q&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many printed and online references describing construction of small transmitting loop antennae.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-10-10T19:20:33.693" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15485" PostTypeId="1" CreationDate="2019-10-10T20:51:36.533" Score="2" ViewCount="214" Body="&lt;p&gt;I am trying to build an antenna for receiving NOAA satellites and I need to build two 137,5MHz dipoles. When I enter the frequency and width of the wires in a calculator, I obtain that &lt;span class=&quot;math-container&quot;&gt;$λ/2=1.09\,\mathrm{m}$&lt;/span&gt; and the length of the dipole should be 1.05 m. (It would be great if by the way someone could explain why this difference occurs.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, does that mean that the total length of the antenna must be that or that each leg must be 1.05/2 m? And does the separation between the legs affect the antenna measurements in a noticeable way? If so, is it the smaller the better?&lt;/p&gt;&#xA;" OwnerUserId="14937" LastEditorUserId="76" LastEditDate="2019-10-10T21:20:03.987" LastActivityDate="2019-10-11T00:14:23.397" Title="When I am told that a dipole must have a determined length, does that include the space between both elements?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15486" PostTypeId="2" ParentId="15485" CreationDate="2019-10-10T21:18:52.653" Score="4" Body="&lt;p&gt;The &lt;em&gt;most general&lt;/em&gt; answer to this question is that you neither include nor exclude the gap between the elements. Rather, whatever is going on there is &lt;strong&gt;part of the antenna design.&lt;/strong&gt; Physics doesn't care which things we call “antenna elements” and which things we call “wiring” — the shape of all conducting elements matter. To match theory and reality thoroughly, we would calculate using an antenna model which includes not just the gap but the shape of the wires that come from “across” that gap to the feed-line. Simulation tools can do this quite well, insofar as you can enter an accurate model and spend the computation time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, for amateur-built antennas, you should use construction techniques which allow the feed point (the gap and wiring I referred to above, and everything that is neither antenna elements nor feed line) to be made &lt;strong&gt;much smaller than the wavelength&lt;/strong&gt;. At HF this can be bolts and wires; at low UHF you might solder carefully shaped rigid wires and matching components directly to a connector; at higher frequencies the antenna and feed might be a single unit using printed circuit manufacturing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As long as the feed point is small in this way, the effect of choosing different answers to the question of where to measure from will be just one small part of the &lt;strong&gt;many&lt;/strong&gt; effects which cause real antenna performance to deviate from simple models. At which point the practical answer is to make your antenna a bit long, measure it with an analyzer, and trim it down to hit your target.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-10-11T00:14:23.397" LastActivityDate="2019-10-11T00:14:23.397" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15487" PostTypeId="1" AcceptedAnswerId="15494" CreationDate="2019-10-10T23:21:32.373" Score="2" ViewCount="68" Body="&lt;p&gt;If i mount my vertical 10 m 4 element yagi directly on a metal pole so that the pole is between the elements and so messes up the radiation pattern and input impedance, if i put lots of type 43 material ferrite rings around the pole will that 'hide' the pole from the antenna in an RF sense ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-10-11T10:27:45.550" Title="Will ferrite rings around a metal pole hide it in an RF sense from my vertical 10 m Yagi?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15488" PostTypeId="1" AcceptedAnswerId="15491" CreationDate="2019-10-10T23:26:08.983" Score="1" ViewCount="106" Body="&lt;p&gt;Does anyone know if a non-metallic pole approx. 4 m long is available that i can use to mount a vertical 10 m 4 element yagi ? that is not wood, PVC or fiber glass as these are either too heavy or not strong enough. My location is Melbourne in Australia.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-10-11T05:50:45.967" Title="Is there a suitable alternative to using a metal pole to mount a vertical yagi apart from wood and fiber glass?" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15489" PostTypeId="1" CreationDate="2019-10-11T00:09:12.307" Score="2" ViewCount="339" Body="&lt;p&gt;I visited a &quot;small loop antenna&quot; calculator web site today and fed in my horizontal loop gepmetry, curious to see what it would say.  2&quot; dia wire, 72' circumference, 3.935MHz.  Interesting results, though it mentioned avoiding lambda/4 lengths due to self resonance and recommended wire circumference be under about 60'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why is self resonance bad?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FWIW, the antenna seems okay-ish at 3.935 MHz.  There is a net on that frequency and on a good day I can sometimes check in.  &lt;/p&gt;&#xA;" OwnerUserId="11434" LastEditorUserId="8717" LastEditDate="2019-11-25T17:19:24.327" LastActivityDate="2019-11-25T20:11:57.043" Title="Why is self-resonance important in a loop antenna?" Tags="&lt;antenna-theory&gt;&lt;loop-antenna&gt;&lt;small-loop&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15490" PostTypeId="1" AcceptedAnswerId="15493" CreationDate="2019-10-11T05:14:22.257" Score="4" ViewCount="241" Body="&lt;p&gt;Will painting a 4 element yagi using conductive paint onto the side of a &#xA;building work? &lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="4076" LastEditDate="2019-10-11T08:29:58.280" LastActivityDate="2019-10-11T08:45:05.020" Title="Will painting a 4 element 10 m yagi using conductive paint onto the side of a building work?" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15491" PostTypeId="2" ParentId="15488" CreationDate="2019-10-11T05:50:45.967" Score="2" Body="&lt;p&gt;You could use a metal pole broken up with a few insulators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One at the boom itself, and one near the ends of the elements, perhaps one more 2.5 m below the antenna, or at the base of the pole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't forget to route the feed cable out around the back of the antenna far from the reflector, or cover it in ferrite beads if it runs down the pole.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-10-11T05:50:45.967" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15492" PostTypeId="2" ParentId="15487" CreationDate="2019-10-11T06:13:20.807" Score="1" Body="&lt;p&gt;For the whole pole they will be too heavy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I made lots of LPDAs with feed cables in the middle. They had about 50 beads on the cables, each of them about 35x30 mm, with a 12 mm hole. This sort of bead has about 100 Ohm impedance, at HF you might get a bit more and so need fewer beads.&lt;br&gt;&#xA;For a 50 mm pipe an equivalent bead would have a 120 mm OD, 150 mm long, and weigh several kg. You would need many of them.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-10-11T06:13:20.807" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15493" PostTypeId="2" ParentId="15490" CreationDate="2019-10-11T08:45:05.020" Score="3" Body="&lt;p&gt;ah, at 10m wavelengths, building aren't really RF transparent, but one can abstract a wall to something relatively homogenous with RF properties defined by the wall material.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(That's because the feature sizes are much smaller than the wavelength)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What's your building made of?&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;If that contains steel reinforcements, or metal window panes, or cables running far, then these will effect the RF property of your paint-wall-combination far more than a bit of conductive paint.&lt;/li&gt;&#xA;&lt;li&gt;If, on the other hand, your building is made of wood, or a 17th century limestone wall&#xA;without steel reinforcements, chances are good that it'll be&#xA;something that works. But barely so: Conductive paint isn't very conductive, and your paint would be very thin, and your wall not perfectly flat (roughness below the thickness of paint!), so that this will be a very inefficient antenna. I don't think you'd do much better than a random piece of wire hung from the top of the wall down.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Aluminium foil might work way better; conductive paint is conductive, but not nearly as good as a continuous stripe of metal. Even better would be thin wires glued/nailed to that wall – you'd be surprised how good a piece of copper wire is as conductor compared to foil (and of course compared to conductive paint). Thin wires have the downside of leading to the yagi antenna being only pretty narrow in bandwidth – the combination of foil at the ends of the elements (to make them more &quot;butterfly-y&quot; and thus slightly wider matched) might help, but to be honest here: this is speculation and could only be realistically answered in simulation; due to the wall probably not being even nearly well-known enough geometrically and RF-wise for such a simulation to be meaningful:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd have to try with your specific wall.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-10-11T08:45:05.020" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15494" PostTypeId="2" ParentId="15487" CreationDate="2019-10-11T10:27:45.550" Score="4" Body="&lt;p&gt;W8JI's article on &lt;a href=&quot;https://www.w8ji.com/detuning_towers.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Detuning Towers&lt;/em&gt;&lt;/a&gt; shows how to add a resonated loop to a conductive structure in order to make it &quot;vanish&quot; electrically:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YbXsk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YbXsk.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the capacitor is tuned to resonate at the frequency of interest, the loop comprising sections A and B carries &lt;em&gt;maximum&lt;/em&gt; current, analogous to a tank circuit. Because the currents in A and B are equal but flow in opposite directions, the radiation from the two sections cancels. And, just like a tank circuit, the resonated A-B loop acts as a high impedance that breaks up the continuous conductor comprising sections C, A and D into smaller conductors section C and section D. By properly positioning, sizing and tuning the loop, you can use your vertically-oriented antenna on a conductive vertical support.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-10-11T10:27:45.550" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15495" PostTypeId="1" AcceptedAnswerId="15496" CreationDate="2019-10-11T13:30:26.433" Score="3" ViewCount="199" Body="&lt;p&gt;The extra book (11-9) safety section mentions that a &quot;large diameter wire, or even better, a wide flat strap, has the lowest inductance and makes the best ground connection.&quot; Does anyone actually have conductive wire in that shape to reduce inductance or am I getting something mixed up here?&lt;/p&gt;&#xA;" OwnerDisplayName="user15628" LastActivityDate="2019-10-11T15:19:27.173" Title="Does copper wire get sold as flat straps to reduce inductance?" Tags="&lt;grounding&gt;&lt;safety&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15496" PostTypeId="2" ParentId="15495" CreationDate="2019-10-11T14:42:02.997" Score="3" Body="&lt;p&gt;You can buy copper strap at &lt;a href=&quot;https://www.gacopper.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;Georgia Copper&lt;/a&gt;. There are other sources, such as &lt;a href=&quot;https://www.dxengineering.com/search/brand/georgia-copper&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Engineering's Georgia Copper page&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GoyZx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GoyZx.jpg&quot; alt=&quot;1 inch wide copper grounding strap&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For RF, it is better to use this copper sheet metal strap wherever possible. The flexible braided stuff eventually becomes more lossy as corrosion and oxidation sets in and the small wires become significantly insulated from each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;http://www.w8ji.com/ground_systems.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w8ji.com/ground_systems.htm&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;... A good [lightning] ground must have a very low impedance over a very wide frequency range. This rules out thin wires, and loosely woven braided conductors should be avoided. The very best ground leads are solid wide smooth surfaces, although braiding sometimes must be used in areas that demand conductor flexibility.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-10-11T15:19:27.173" LastActivityDate="2019-10-11T15:19:27.173" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15497" PostTypeId="1" CreationDate="2019-10-11T15:21:56.253" Score="1" ViewCount="74" Body="&lt;p&gt;I am using RTLSDR on macOS with Cubic SDR, it works great and is very intuitive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I want to do a frequency envelope analysis where I need to basically 3-d plot intensity versus frequency and time. I can probably figure out the math to do that part (or get help). But I need data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The data I need is 1-second samples across the entire frequency range.&#xA;What tools are available for loop over the frequency range and save the samples for each band?&lt;/p&gt;&#xA;" OwnerUserId="15810" LastActivityDate="2019-11-13T00:44:42.417" Title="Batch sampling SDR" Tags="&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15498" PostTypeId="2" ParentId="15497" CreationDate="2019-10-11T15:43:35.660" Score="2" Body="&lt;p&gt;It depends on what you mean by &quot;the entire frequency range&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you mean the bandwidth supported by the rtlsdr (2.4 MHz), then all you need is the raw output (IQ samples). Performing a &lt;a href=&quot;https://en.wikipedia.org/wiki/Window_function&quot; rel=&quot;nofollow noreferrer&quot;&gt;windowed&lt;/a&gt; &lt;a href=&quot;https://en.wikipedia.org/wiki/Fast_Fourier_transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;FFT&lt;/a&gt; on the data, moving the window forward in time, and converting the samples to squared magnitude (power), will get you &quot;intensity versus frequency and time&quot;. This is what every SDR application's &quot;waterfall plot&quot; does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to cover the entire &lt;em&gt;tunable&lt;/em&gt; frequency range, you cannot do this all at once — the hardware is not capable of that. Instead, you must tune, take some data, and repeat, stepping across the range. Conveniently, there is already a tool which will do this for you in the rtl_sdr driver package — it is called &lt;code&gt;rtl_power&lt;/code&gt;. It will output a CSV file with the data already arranged in columns by frequency and rows by time.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-10-11T15:43:35.660" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15501" PostTypeId="2" ParentId="15497" CreationDate="2019-10-11T19:08:59.960" Score="0" Body="&lt;p&gt;The &lt;a href=&quot;https://github.com/osmocom/rtl-sdr/blob/master/src/rtl_sdr.c&quot; rel=&quot;nofollow noreferrer&quot;&gt;rtl_sdr command-line tool&lt;/a&gt; can capture a file of IQ samples of a specified (&lt;a href=&quot;http://manpages.ubuntu.com/manpages/trusty/man1/rtl_sdr.1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;on the command line&lt;/a&gt;) duration, file name, center frequency, gain, and sampling bandwidth, from a connected RTL-SDR device.  You could write a script to step between your frequency limits by a delta frequency step slightly less than the bandwidth or sample rate, sequentially execute the rtl_sdr command with that set of parameters, and thus capture a set of IQ files covering your full desired frequency range.  Rinse and repeat to cover a larger time range as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another method might be to use a bunch of RTL-SDR peripherals (maybe connected to a farm of Raspberry Pi's) and collect IQ samples from a range of frequency bands at the same time.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-11-13T00:44:42.417" LastActivityDate="2019-11-13T00:44:42.417" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15502" PostTypeId="1" AcceptedAnswerId="15505" CreationDate="2019-10-13T03:35:12.457" Score="1" ViewCount="409" Body="&lt;p&gt;I am a beginner in ham radio and am trying to program repeater data into my Alinco DR-635T/E VHF/UHF mobile radio. The manual that came with the radio is so poorly written that I could not successfully enter data using the steps in the manual and had to experiment around until I found the missing step by random chance which caused the radio to accept it. This is very discouraging. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use CHIRP to program my Baofeng/B-Tech 2m handheld and thereby get around the similarly sucky manual, so I wind up using the B-Tech with CHIRP and ignoring the Alinco. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Alinco has a &quot;clone&quot; cable which allows two DR-635's to be connected together and the programming in one to be downloaded into the other- but the manual makes no mention of downloading from a computer running CHIRP. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone know if this is possible? I'd like to put the Alinco into service and using CHIRP would be infinitely better than struggling with the user interface and the manual. &lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2020-07-23T18:08:32.800" Title="CHIRP-programmability of the Alinco DR-635T/E" Tags="&lt;radio-programming&gt;&lt;alinco&gt;&lt;chirp&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15503" PostTypeId="1" AcceptedAnswerId="15509" CreationDate="2019-10-13T04:05:14.393" Score="4" ViewCount="1497" Body="&lt;p&gt;If I were to mount my 10 m vertical Yagi on a pole with a motor attached at the bottom with the appropriate fastening and coax mounted via electrical brushes, if the Yagi is spun at say 1000 RPM would that make it have its rated gain in all directions ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2019-10-13T17:34:40.633" LastActivityDate="2020-04-23T05:42:31.847" Title="Vertical Yagi spun at 1000 RPM: gain properties?" Tags="&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="6" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15504" PostTypeId="1" CreationDate="2019-10-13T04:58:59.357" Score="0" ViewCount="111" Body="&lt;p&gt;I bought a hackrf one and I don't think it works.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before I return it can someone show me a grc flowchart on how to send text or a text file from a hackrf to a rtlsdr?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have been told you can do it. I have tried all of the flowcharts online and on youtube. Packet Decoder/Encoder no longer works. I have been trying to get this working for weeks and I'm about to send the hackrf back.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;right now its a $569 paper weight&lt;/p&gt;&#xA;" OwnerUserId="15818" LastEditorUserId="4076" LastEditDate="2019-10-13T11:52:38.720" LastActivityDate="2019-10-13T11:52:38.720" Title="Text transfer From/To SDR" Tags="&lt;gnuradio&gt;" AnswerCount="0" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15505" PostTypeId="2" ParentId="15502" CreationDate="2019-10-13T12:29:13.557" Score="1" Body="&lt;h1&gt;Yes, it'll probably work with CHIRP&lt;/h1&gt;&#xA;&lt;p&gt;Of course, the first place you'd look would be the &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP project page&lt;/a&gt;. That doesn't list the DR-635, but it does list the DR-135, DR-235 and DR-435, and that might be a good sign (but clearly not a guarantee, since the hardware might simply be different). In fact, &lt;a href=&quot;http://d-rats.com/hg/hgwebdir.cgi/chirp.hg/file/bb8427488942/chirp/drivers/alinco.py#l268&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP's alinco driver&lt;/a&gt; has a common DR-x35 base class, indicating that they expect x35 devices to be similar enough!&lt;/p&gt;&#xA;&lt;p&gt;The fact that you can program your radio according to the &lt;a href=&quot;http://www.alinco.com/pdffiles/Instruction/Mobile/dr635insweb.zip&quot; rel=&quot;nofollow noreferrer&quot;&gt;official device manual&lt;/a&gt; to be in slave mode for cloning is also a good sign, along with the fact that the manual specifies pinout!&lt;/p&gt;&#xA;&lt;p&gt;Not quite sure CHIRP does much but channel programming though, and I thus don't know whether &amp;quot;repeater data&amp;quot; programming is covered by it, but I'll leave that up to your experience!&lt;/p&gt;&#xA;&lt;p&gt;Regarding cabling, the same wiki has an &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/CableGuide#Alinco-Radios&quot; rel=&quot;nofollow noreferrer&quot;&gt;entry&lt;/a&gt; that states that the 3pin plug seems to be common among all Alinco radios.&lt;/p&gt;&#xA;&lt;h1&gt;But it's not directly supported by CHIRP, so that's something you'll want to change&lt;/h1&gt;&#xA;&lt;p&gt;Looking through the source code, you'd want to try the DR-435 driver first, as it seems to be the most similar. That won't let you do all frequencies of the DR-635T, but that's just adding a copy of the &lt;a href=&quot;http://d-rats.com/hg/hgwebdir.cgi/chirp.hg/file/bb8427488942/chirp/drivers/alinco.py#l468&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;code&gt;DR435Radio&lt;/code&gt; class&lt;/a&gt; with adjusted device naming and frequency ranges to that python file, which is text editing (really, aside from copy and pasting text, no programming skills required; but you can then share that addition with the CHIRP community and become a Free &amp;amp; Open Source contributor – how cool is that!).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-10-13T12:29:13.557" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15506" PostTypeId="2" ParentId="15503" CreationDate="2019-10-13T14:39:18.930" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;rated gain in all directions ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. And a lot more problems. Primarily, for any thinkable use case, this is a bad idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What rotating the antenna will do is of course rotate the antenna pattern, &quot;averaging out&quot; (over the curse of a multiple of a rotation period) the antenna pattern to look like a circle, i.e. equally good (or bad) in all directions; the &lt;strong&gt;average&lt;/strong&gt; gain of the original Yagi's radiation pattern, not the &lt;strong&gt;maximum&lt;/strong&gt; gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you wanted that, using a high-gain antenna type like a Yagi would be a terrible idea – just use the dipole (the driven element in your yagi), and you'd instantly have an omnidirectional antenna for a fraction of the effort, cost, maintenance, complexity and hazard!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1000 rpm = 116.7 Hz would be far too slow for anything useful: Let's focus on the transmit side for a second here; since antennas are reciprocal, the exact same things apply to receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, you're transmitting with your antenna. That means that your antenna's main beam sweeps around. A receiver in a specific direction will hence see &quot;strong signal&quot; when he's in the main beam's direction 16.7 times per second, and all the other times they'd see little signal power at all. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For any signal that has a bandwidth significantly larger than 16.7 Hz, this simply constitutes slow fading over a cyclostationary signal: The &quot;very strong for short, bad rest of the time, 16.7 times per second&quot; is typically harder to solve than an averagely moderately low receive power, because it contains an element of temporal change in addition to the majority-of-time-bad receive power. In essence, for a &lt;strong&gt;looooong&lt;/strong&gt; duration, your signal will be unusable, if you needed any gain to begin with, and from the short duration where it's good, you'd need to reconstruct the lost part. &lt;/li&gt;&#xA;&lt;li&gt;For any signal that has a bandwidth lower than 16.7 Hz, this constitutes fast fading, i.e. the channel changes within the duration of one &lt;em&gt;symbol&lt;/em&gt;; for anything that requires coherency (FM, PSK, most FSK, QAM, …), that simply means broken transmission. For power-detection only systems (e.g. AM, OOK, PPM), that might be workable by averaging out, but still not really desirable.&lt;/li&gt;&#xA;&lt;li&gt;For any system that has a signal bandwidth of roundabout 16.7 Hz, this is kind of neither and kind of both, and you'd really want to avoid that situation, because your rotation influence becomes statistically indistinguishable from your signal, and then no communication will be possible.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Basically all useful communication systems fall in the first category.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can also look at this from the perspective of Doppler: by rotating the antenna, you'd constantly be shifting the phase center of the antenna, relative to a fixed direction. That means that you're modulating the phase of the signal with a periodic function – and that's a frequency shift, just like a Doppler effect caused by your communication partner moving rapidly towards you and away from your 16.7 times per second. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;The only use case I could make out for this is in an indoor scenario with a lot of multipath propagation, you could get some temporal diversity for a diversity combination scheme. But that wouldn't incorporate &quot;masts&quot;, and it would be at much higher frequencies (2 GHz and upwards), and it would happen at not about 17, but 100,0000 to 1 million rotations per second, and it wouldn't happen through rotating a physical antenna, but through digital beamforming or antenna switching.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-10-13T16:06:04.853" LastActivityDate="2019-10-13T16:06:04.853" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15507" PostTypeId="2" ParentId="15503" CreationDate="2019-10-13T15:28:01.117" Score="6" Body="&lt;p&gt;Depending on the gain characteristics of your Yagi antenna, you’ll be adding an amplitude modulation of 16.7 or 33.3 Hz to your signal, plus a similar phase modulation.  These added modulation sidebands will also add to the bandwidth used.  This rotational modulation will have different phases to your original signal modulation in different directions, so your resulting signal will likely not be symmetric in all directions.  If you want, control and/or synchronize to this asymmetry, you could use this for some sort of directional beacon or radar.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-04-23T05:42:31.847" LastActivityDate="2020-04-23T05:42:31.847" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15508" PostTypeId="1" AcceptedAnswerId="15516" CreationDate="2019-10-13T17:41:03.363" Score="7" ViewCount="168" Body="&lt;p&gt;In amateur radio, we care about impedance matching when we need to keep the load within the equipment's specification (for best performance, or just to avoid damaging a transmitter), when we want to maximize the power delivered into the load, or when a minimum noise figure is desiable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the reasons above are not a concern, impedance matching can be ignored. For example, in the question &lt;a href=&quot;https://ham.stackexchange.com/questions/382/what-is-the-relationship-between-swr-and-receive-performance/905#905&quot;&gt;What is the relationship between SWR and receive performance&lt;/a&gt;, Phil Frost answered that &quot;There is no relationship between SWR and receive performance&quot;. Surely, modern electronics have a lot of gain, and on HF, the inherent noise from the environment is often already much greater than noise floor of the radio receiver, as long as the SNR is reasonable, a HF receiver will happily receive everything coupled into it, even a random wire works, in this case, matching is pointless or sometimes counterproductive. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nevertheless, they are not the only reasons for wanting a matched impedance or low SWR. In video engineering and high-speed digital systems, impedance termination (often by a resistor) is usually &lt;strong&gt;mandatory&lt;/strong&gt;, even if it decreases the power delivered into the load, because of another reason: the reflection on the transmission line causes signal distortion. In analog video, the reflection causes &quot;ghosting&quot; on a TV screen. In digital systems, the reflection causes intersymbol interference that increases the error rate of the transmission, or creates unacceptable overshoot and ringing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I don't see this issue discussed by any amateur radio publication. Why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume it's not important, either because it's &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Only relevant for higher-frequency signals above HF. Within HF, the wavelength is long, so these adversary transmission line effects don't show up.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It's only the case for high speed, wide bandwidth (a few megahertz or more) signals. On HF, bandwidth of a signal is measured in kilohertz. We never use wide-bandwidth signal on HF.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;But I'm not sure which one is the case.&lt;/p&gt;&#xA;" OwnerUserId="15589" LastEditorUserId="9621" LastEditDate="2019-10-14T20:44:09.637" LastActivityDate="2021-02-10T15:31:35.847" Title="Why aren't &quot;ghosts&quot; and intersymbol interference due to unmatched impedance (high SWR) a concern for HF receivers?" Tags="&lt;hf&gt;&lt;receiver&gt;&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15509" PostTypeId="2" ParentId="15503" CreationDate="2019-10-13T18:01:57.163" Score="13" Body="&lt;p&gt;As has already been stated, this will add amplitude modulation to your signal — you will &quot;achieve its rated gain in all directions&quot; but only at the &lt;em&gt;peak&lt;/em&gt; of the modulation; the &lt;em&gt;average&lt;/em&gt; will be much less, equivalent to an antenna with no azimuth gain but a similar elevation gain pattern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You and other readers might be interested to learn that &lt;strong&gt;this modulation has actually been used &lt;em&gt;intentionally&lt;/em&gt;, in the aircraft navigation system &lt;a href=&quot;https://en.wikipedia.org/wiki/VHF_omnidirectional_range&quot; rel=&quot;noreferrer&quot;&gt;VHF Omnidirectional Range (VOR)&lt;/a&gt;.&lt;/strong&gt; This system allows an aircraft to, by receiving signals from a ground station, determine the compass direction in which the aircraft lies relative to the ground station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The system in its original form worked by spinning a directional antenna at 30 Hz, causing amplitude modulation of the signal. The station also transmits, on the same carrier frequency but from a non-directional antenna, a subcarrier also frequency modulated at 30 Hz (like FM stereo encoding or AFSK). By comparing the phase of the amplitude modulation (varies with direction of the receiver) to the phase of the frequency modulation (does not vary), the direction can be obtained.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Later VOR stations replaced the rotating antenna with a circular phased array, so that the mechanical rotation could be replaced with electronic, but the signal is received and decoded the same way.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-10-13T18:01:57.163" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15510" PostTypeId="2" ParentId="15508" CreationDate="2019-10-13T22:29:21.380" Score="3" Body="&lt;p&gt;Some of both, but I think the second effect is dominant. The rest of this post is all my analysis from scratch as a non-EE, so hopefully it makes sense.&lt;/p&gt;&#xA;&lt;p&gt;Let's say we have an antenna at the end of a 100-meter (electrical length) lossless transmission line that's mismatched to the antenna by a 10:1 SWR. We'll assume that there's perfect reflection at the transmitter end of the feedline (so the transmitter is a perfect current source, doesn't dissipate anything, and can withstand whatever voltage is necessary).&lt;/p&gt;&#xA;&lt;p&gt;10:1 VSWR is an 0.82 voltage reflection coefficient, which amounts to a 0.67 power reflection coefficient. If we send a pulse from the transmitter, 33% of power goes into the antenna and 67% of power gets reflected down the feedline, reflected again, and comes back for another try, 33% of that 67% is absorbed by the antenna, etc. etc. Those two trips along the feedline take 667 nanoseconds. &lt;span class=&quot;math-container&quot;&gt;$ 0.67^2 \approx 0.45 $&lt;/span&gt;, so after 1.5 round trips, over half of the power has made it into the antenna. Those 1.5 round trips take 1 microsecond, so any modulating signal with a bandwidth less than 1MHz will survive pretty much intact. &lt;span class=&quot;math-container&quot;&gt;$ 0.67^{12} &amp;lt; 0.01 $&lt;/span&gt;, so after 11.5 round-trips, more than 99% of the power has been delivered, and anything under 130kHz is going to have pretty much undetectable distortion. Since our signals on HF are almost always under 6kHz wide (and usually under 3kHz) this seems pretty safe.&lt;/p&gt;&#xA;&lt;p&gt;Modifying our simplified system by adding loss in any part of it, or making the mismatched section shorter than 100m, or making the SWR lower than 10:1, all make the reflections die down that much faster, giving a more favorable result.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2021-02-10T15:31:35.847" LastActivityDate="2021-02-10T15:31:35.847" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15513" PostTypeId="1" CreationDate="2019-10-14T08:03:24.370" Score="-1" ViewCount="219" Body="&lt;p&gt;How to calculate &lt;a href=&quot;https://ham.stackexchange.com/questions/3643/what-is-the-aperture-efficiency-of-an-antenna&quot;&gt;aperture efficiency&lt;/a&gt; for an antenna with the following parameters:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Big reflector diameter= 24 mm&lt;/li&gt;&#xA;&lt;li&gt;Gain= 9.265 dbi&lt;/li&gt;&#xA;&lt;li&gt;Frequency= 11.60 GHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="15825" LastEditorUserId="8717" LastEditDate="2019-10-14T15:36:23.983" LastActivityDate="2021-01-06T17:03:15.287" Title="How would I calculate aperture efficiency for an antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15514" PostTypeId="2" ParentId="15513" CreationDate="2019-10-14T08:38:19.067" Score="1" Body="&lt;p&gt;For any antenna, also for wire antennas, you can calculate so called effective area with &lt;span class=&quot;math-container&quot;&gt;$A_{eff} = \frac{\lambda^2}{(4\pi)}G$&lt;/span&gt;. An ideal antenna with surface area of &lt;span class=&quot;math-container&quot;&gt;$A_{eff}$&lt;/span&gt; absorbs the same amount of power from the plane wave as that antenna.&#xA;Aperture efficiency is defined as ratio of effective and physical surface area &lt;span class=&quot;math-container&quot;&gt;$\eta_{ap} = A_{eff}/A_{phys}$&lt;/span&gt;. For a circular reflector antenna the physical size is the area of your antenna facing the incoming plane wave &lt;span class=&quot;math-container&quot;&gt;$ A_{phys} = \pi(d/2)^2$&lt;/span&gt;.&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="194" LastEditDate="2019-10-14T11:14:49.327" LastActivityDate="2019-10-14T11:14:49.327" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15516" PostTypeId="2" ParentId="15508" CreationDate="2019-10-14T16:33:41.423" Score="10" Body="&lt;p&gt;Intersymbol Interference (ISI) — or analog equivalents, like ghosting — are relevant only when the difference in time of arrival between the primary and reflected signal are significant compared to the symbol duration.&lt;/p&gt;&#xA;&lt;p&gt;For example, PSK 31 has a symbol rate of 31.25 baud, meaning each symbol is 32 ms long. If the difference in arrival time is significantly less than 32 ms, the reflection will arrive before the next symbol, so there's no significant ISI.&lt;/p&gt;&#xA;&lt;p&gt;100 meters of feedline, with a 65% velocity factor, introduces a round-trip delay of about 0.001 ms. Being much less than 32 ms, this wouldn't introduce any significant ISI for PSK31.&lt;/p&gt;&#xA;&lt;p&gt;What about modes with a faster symbol rate?&lt;/p&gt;&#xA;&lt;p&gt;Generally, they don't get too much faster on HF. This is because the typical HF skywave channel is already a multipath channel. Unlike a line-of-sight channel where there's just one path from receiver to transmitter, an ionospheric channel has multiple paths, each with a different lengths. This is because the ionosphere isn't a smooth mirror, but rather an undulating, multi-layer ionized gas.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.itu.int/rec/R-REC-F.1487-0-200005-I/en&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU Recommendation F.1487&lt;/a&gt; quantifies the &lt;em&gt;differential time delay&lt;/em&gt; for various HF channels, that is the time difference between the first arrival of the signal and the last. It's 0.5 ms under the very best conditions, and as high as 7 ms under poor conditions.&lt;/p&gt;&#xA;&lt;p&gt;HF modems typically cope with this issue by using a slow symbol rate. For example, &lt;a href=&quot;https://freedv.org/freedv-specification/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV&lt;/a&gt; uses a 1450 bit/s modem, quite fast by amateur HF standards. But it does so at a symbol rate of 50 baud, meaning each symbol is 20 ms long. &lt;a href=&quot;https://en.wikipedia.org/wiki/Digital_Radio_Mondiale&quot; rel=&quot;nofollow noreferrer&quot;&gt;DRM broadcasts&lt;/a&gt; have several modes, with the fastest symbol duration being 16.66 ms.&lt;/p&gt;&#xA;&lt;p&gt;These long symbol durations make the differential time delay of the HF channel, as well as any additional delay added by feedline reflections, relatively insignificant.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-02-09T23:36:10.913" LastActivityDate="2021-02-09T23:36:10.913" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15517" PostTypeId="1" AcceptedAnswerId="15536" CreationDate="2019-10-15T04:16:47.423" Score="1" ViewCount="119" Body="&lt;p&gt;I want to null out a particular direction so that i can't receive some vertically polarized interference on 10 m coming from that direction. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Which 10 m antenna will give the most rejection in one direction in the azimuth plane for received signals which are vertically polarized ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've already tried 3 and 4 element horizontal and vertical yagis and these don't provide enough rejection in the nulls in their patterns. I need 40 dB of rejection or more. Can i use parasitic elements to somehow cancel out in one direction only ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-10-15T04:25:42.453" LastActivityDate="2019-10-17T16:30:22.230" Title="Which 10 m antenna will give the most rejection in one direction for received signals which are vertically polarized?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15518" PostTypeId="2" ParentId="15517" CreationDate="2019-10-15T06:11:43.477" Score="3" Body="&lt;p&gt;You might want to try not one, but 2 identical vertical dipoles spaced a half wavelength apart in line with the noise source and fed to an active noise cancelation box or a coherent dual-input SDR.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-10-15T06:11:43.477" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15520" PostTypeId="2" ParentId="15517" CreationDate="2019-10-15T08:06:04.430" Score="4" Body="&lt;h1&gt;Constructive and Destructive Interference, Directivity&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;This is an excellent time to point you towards antenna arrays!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, maybe you remember the double-slit experiment from school. In case you never did that, or need a refresher:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine having e.g. a laser, that is, something emitting a plane wavefront (from the left in the below picture). You shine that light on a plane with two small slits:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Double-slit_experiment#/media/File:Doubleslit.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;from wikipedia&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/4/4e/Doubleslit.svg&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You've got two very small slits, emitting (half-) circular wavefronts that have the same phase (in the plane of the slits); when you look from a distance, you'll see that these wavefronts overlay constructively, whenever the run length difference of both waves is 0 or any other multiple of a wavelength. They interfere destructively, i.e. they cancel out, whenever the run length difference is an odd multiply of half the wavelength. These things line up in directions from the centre between the two slits, so that we can talk of directivity!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can imagine, adding more slots in the same spacing just makes the 0-difference direction &quot;stronger&quot; and all suppressed directions even more suppressed.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Light's just slightly higher-frequent radio&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;So, light is just electromagnetic waves, just as 10m radio waves. The latter are just slightly easier to handle – we don't need to build something that makes a plane wave front and then have some opaque material with slits in there. We can just put antennas with circular emission pattern at the point of the slits!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The whole idea of &quot;we add delayed versions of the same RF wave up&quot; is what makes multi-element antennas (and any aperture antenna) work: The elements of the Yagi are just sized and spaced that way, that they re-emit energy just in the right moment to lead to constructive interference of the radio wave in the main direction of the Yagi antenna. By the way, what works in TX works exactly the same in RX.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the geometry of the antenna system defining that main direction this way, Yagis are fixed-direction (unless you rotate them). That's fine for many applications, but I think you need something with which you can find a good direction to receive from.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Enter: Antenna Arrays&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Now, what would you have to change in the above double-slit experiment to change the direction(s) in which the main maximum occurs? You'd simply change the distance between the slots. Or, you could find a &quot;magic&quot; device that you install in one of these slots that delays the phase of the wave coming from that slot by some adjustable fraction of the full wave cycle, and with that you could &lt;em&gt;steer the beam&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While that's nontrivial for photonics, it's relatively easy for the relatively narrowband HF signals: We call such a device a phase shifter:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;                                                       v&#xA;                              +----------------------&amp;gt; |   Antenna 1 &#xA;Transmitter amplifier ---&amp;gt; splitter&#xA;                              |                        v&#xA;                              +-----&amp;gt; Phase shifter--&amp;gt; |   Antenna 2&#xA;                                         ^&#xA;                                         |&#xA;                                    Direction control&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Tadah, by adjusting the phase shift, you adjust in which direction your transmitted radio waves constructively add up; that's your antenna system's main direction! And you get a gain in that direction. If you want better directivity, repeat the above scheme; &lt;a href=&quot;https://en.wikipedia.org/wiki/File:Phased_array_animation_with_arrow_10frames_371x400px_100ms.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;from wikipedia&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/4/4a/Phased_array_animation_with_arrow_10frames_371x400px_100ms.gif&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember, what works in TX works in RX, too! Adjust the phase of the received wave of one antenna, add the electric signals up, and get a signal where the reception is good from one direction, and worse from the others.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;How to Shift your Phases (All your Phase are belong to us)&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;For most of the previous century, using (mechanical!) analog phase shifters was state of the art for  beam forming, and it's been extensively used, especially in radio sensing applications; and since that's something that military people like to do (for example, to have knowledge of where someone's transmitter is standing, or to build a radar with which you can look very far in a very specific direction), cost was …… less of an issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That changed around the turn of the millennium, when Software-Defined Radio (SDR) became a viable thing. Idea is simple: Take your RF signal, digitize it (like a sound card converts electrical signals from a microphone to digital numbers), and do the phase shifting and adding up in software. Done! Computers are cheap, and fast enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what you'd need is&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;a set of omnidirectional antennas in the polarization of your choice&lt;/li&gt;&#xA;&lt;li&gt;a place to set them up in a line, in typically quarter- or half-wavelength distances&lt;/li&gt;&#xA;&lt;li&gt;a SDR receiver for each of them&lt;/li&gt;&#xA;&lt;li&gt;a way to &quot;null&quot; the phases of these receivers (otherwise they'll just be random)&lt;/li&gt;&#xA;&lt;li&gt;a computer (seems like you have one!)&lt;/li&gt;&#xA;&lt;li&gt;and a tiny bit of software to add up these streams&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;For 1., antennas: The easiest and – perpendicular to its conductors – omnidirectional antenna is the dipole. And in fact, many &lt;em&gt;laaaaarge&lt;/em&gt; antenna arrays are simply made of dipoles, or similarly low-gain antennas. See &lt;a href=&quot;https://en.wikipedia.org/wiki/EISCAT#/media/File:Ramfjordmoen_forskningsstasjon_winter_1.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;EISCAT&lt;/a&gt;, for example, which I know hams that were involved with:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/4/42/Ramfjordmoen_forskningsstasjon_winter_1.jpg&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For 3. Receivers: For 30 MHz, basically all &lt;a href=&quot;https://osmocom.org/projects/rtl-sdr/wiki/Rtl-sdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTL-SDR dongles&lt;/a&gt; will do their job. Depending on where, in which quality and in which quantities you buy them, 6 to USD 40 a piece.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(from the OSMOcom wiki linked above:)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0u7zz.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0u7zz.jpg&quot; alt=&quot;cracked open RTL-SDR dongle of an early generation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For 4., you'll just need something to calibrate your receivers. A transmitter in a known direction would work – you can calculate the phase shifts that the antennas &lt;em&gt;should&lt;/em&gt; have with easy trigonometrics, and then just adjust their phases to have that, in doubt, manually. It'd be good idea to feed all receivers from the same reference oscillator source, so that you don't have continuously readjust (because the phases will drift away pretty quickly if they run from different reference oscillators), and that'll involve a bit of soldering (unsolder the oscillator from all but one dongle, add an amplifier and clock distributor to that one dongle, solder in cable to where the oscillator(s) used to be).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For 6., software: a tiny bit of GNU Radio, and pipe the result (e.g. via network) to the SDR receiver software of your choice (GQRX, SDR#, HDSDR, LinRad, I don't know a tenth of the candidates) to do the demodulation. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-10-15T08:06:04.430" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15521" PostTypeId="1" AcceptedAnswerId="15535" CreationDate="2019-10-15T22:39:32.650" Score="1" ViewCount="497" Body="&lt;p&gt;I am curious how much CW power an N connector or SO-239 connector will handle on such a low frequency like 160m band. I know on VHF they will probably handle about 800W before getting too warm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have made a high powered transmitter for this band, and I've always used cables with either N or SO-239 in the past. I know something like DIN is recommended for over 1kW, but at these frequencies, I would think the others could handle it. I know the voltage handling of the N connector is 1500 volts peak which is plenty for several kilowatts, but will it get too warm?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.amphenolrf.com/connectors/n-type.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amphenolrf.com/connectors/n-type.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am partial to the SO-239 because the center conductor is so much larger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone have personal experience using either of these connectors over 1kW? BTW my coax is fine as it's LMR400.&lt;/p&gt;&#xA;" OwnerUserId="1817" LastActivityDate="2019-10-17T20:05:26.153" Title="SO-239 (UHF) vs N connector power handling on 160m" Tags="&lt;hf&gt;&lt;rf-power&gt;&lt;coaxial-cable&gt;&lt;connectors&gt;&lt;pl259-so239-connector&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15522" PostTypeId="2" ParentId="15517" CreationDate="2019-10-16T01:58:31.600" Score="4" Body="&lt;p&gt;I might be missing something here, but one of the antennas in common use that has a very sharp null in one direction (and its opposite, so I guess two directions) is the one used by ARDF enthusiasts the world over - the magnetic loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can design and use a magnetic loop at 28MHz, which would be surprisingly compact, and would do a reasonable job of receiving in all other directions - but be aware that it also has a very sharp pass-band, so you would want to make it tunable. This means if you were to mount one outside, you would have to come up with a remote tuning capability (a motor to drive the variable capacitor, for example).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a transmit antenna, the magnetic loop is not particularly efficient, but it works fine as a receiver. In fact, if you open a regular domestic medium wave radio (so-called &quot;AM&quot; radio receiver), you will find one in there wound on a ferrite rod. You will find that you can turn the radio while listening to a strong station on the &quot;AM&quot; band and find a position where the station all but disappears. Similarly, if you build a magnetic loop antenna for 28MHz, you could turn it to reject the signal you are trying to avoid, and you simply won't hear it.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-10-16T01:58:31.600" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15524" PostTypeId="1" AcceptedAnswerId="15525" CreationDate="2019-10-16T08:13:21.903" Score="0" ViewCount="78" Body="&lt;p&gt;Can i use an analogue IC switch being triggered at the same frequency I am receiving on to change a 10 m yagi's directivity by somehow combining received signals with different variable phase either from the same driven element or two or more driven elements?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="4076" LastEditDate="2019-10-16T11:17:44.267" LastActivityDate="2019-10-18T09:42:49.903" Title="Can i use an anaolgue IC switch to change a 10 m yagi's directivity by somehow combining received signals with different variable phase?" Tags="&lt;antenna-theory&gt;&lt;electronics&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15525" PostTypeId="2" ParentId="15524" CreationDate="2019-10-16T11:45:29.900" Score="2" Body="&lt;p&gt;No, you can't; what you're building by switching something at its carrier frequency is a mixer to twice, four, six,… times the carrier frequency and to a broken 0 Hz baseband, so that's not useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The math is simple:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just as your normal mixer multiplies with a cosine to mix the signal to the sum of the cosine and signal frequencies, and to their difference, the same happens when you multiply with a square wave instead of a cosine. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A square wave can be mathematically represented as sum of cosines of the fundamental frequency of the wave, and every odd harmonic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ergo, switching with some frequency &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; just produces mixing products at your signal's frequency &lt;span class=&quot;math-container&quot;&gt;$\pm f$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's a standard mixer type, the &lt;em&gt;switching&lt;/em&gt; or &lt;em&gt;chopping&lt;/em&gt; mixer, but it's not a way of combining things with an adjustable phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking at that: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you &lt;em&gt;can&lt;/em&gt; do is use a switching mixers for each of two signals, where one square wave has a time (and hence: phase) offset; these mixers would produce a sum-frequency signal each, but with different phases. Then, add these and you get a phase-shifted sum. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll have a lot of unwanted harmonics to filter, and your phase adjustments of your square wave can be a bit hard to achieve, and you wouldn't want to use the carrier frequency of your signal, but a higher, adjustable frequency so that you end up on a useful IF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, technically, this is fun thing to consider, and whilst I'm pretty sure you didn't think it'd work like that, yes, you can use switching to phase adjust – but only in the context of using it as mixer.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-10-18T09:42:49.903" LastActivityDate="2019-10-18T09:42:49.903" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15526" PostTypeId="1" AcceptedAnswerId="15527" CreationDate="2019-10-16T12:28:06.920" Score="0" ViewCount="969" Body="&lt;p&gt;I've been using Repeater Book to manually programme some repeaters in my area, up to fifteen miles. I later started programming some FRS, GMR, and MURS frequencies based on the CSV file that someone had given me. I've been having to do this because Chirp either doesn't recognise the Baofeng UV5R because the only option I see is Baofeng UV5R3, or because I have a Prolific cable instead of a Chipset one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, the FRS channels have some odd channel spacing that I can't figure out. For example, one of them is 462.5625. So, I'm guessing I need to set the frequency step (menu 1) and set it to 6.25 kHz (option 2), or enter 462.500, and press up arrow?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meanwhile, the last column says TStep, which is set to 5 on all frequencies. Does this mean I have to set the frequency step to 5 (menu 1, option 1?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, I noticed that all the frequencies have a RTone and CTone of 88.5, but when I programmed the weather channel, I discovered that I needed to set the CTCSS tone (menu 11) to 0 so that I could hear the weather forecast, because if it I set it at 88.5, I'd hear nothing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, all the frequencies had a single DTSCode of 23, and all had the DTS Polarity set to NN.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think I programmed some of the GMR and MURS frequencies because they all ended in zeros, so I didn't have to worry about spacing. I just found it odd how all the them had five as the TStep, plus all of the aforementioned characteristics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, how would I go about manually programming these memory channels using the CSV file this person gave me&lt;/p&gt;&#xA;" OwnerUserId="13927" LastActivityDate="2019-10-16T23:39:03.557" Title="How can I manually programme these FRS channels onto my Baofeng UV5R?" Tags="&lt;ht&gt;&lt;radio-programming&gt;&lt;uv-5r&gt;&lt;chirp&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15527" PostTypeId="2" ParentId="15526" CreationDate="2019-10-16T13:01:27.853" Score="2" Body="&lt;p&gt;There are online instructions and YouTube videos on how to program a BaoFeng radio -- it's the same for all or almost all of their HT models, so if you find instructions for a BF-F8HP, for instance, they'll work for the UV-5R.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio, however, doesn't really support half-kilohertz precision in frequency entry from the keypad, so you'd be ahead to spend the $20 or so to get the correct programming cable (from BaoFeng USA) and use CHIRP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that, like most amateur radio hardware, it's up to the operator to ensure transmit compliance -- and that radio isn't type accepted for FRS or GMR (probably not for MURS, either).  Those bands are &quot;licensed by type&quot; and it's legal to transmit on them only from radios that are &quot;type accepted&quot; -- and the UV-5R isn't for those bands.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2019-10-16T13:01:27.853" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15528" PostTypeId="1" CreationDate="2019-10-16T16:01:53.953" Score="2" ViewCount="91" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;We have a VHF Omni directional antenna, 2.5 W and 119 MHZ (approximate) mounted on top of a commercial hanger. Access to the antenna is out of the question because of the lack of fall protection. Service personnel have expressed apprehension over accessing the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/87ie0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/87ie0.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;We’re trying to come up with a solution that minimizes the risk to service personnel&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;One idea is using two VHF antennas mounted at 8 feet elevation at diagonally opposite sides of the hanger with a Wilkinson Power-Divider at the VHF transmitter to ensure that the two antennas are properly phased. The VHF Antennas would be mounted at a much lower elevation (8’) on each side of the Hanger.   &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;Two antennas are used because of the obstruction caused by the hanger when mounting them at 10'&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;a.  Do you have any thoughts on this? &#xA;b.  Do we have a reasonable chance of success? &#xA;c.  Is this idea of any merit?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZCbJX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZCbJX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15837" LastActivityDate="2019-10-23T01:56:51.180" Title="Using two VHF antennas vs one because of a large obstruction" Tags="&lt;antenna-theory&gt;&lt;antenna-system&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15529" PostTypeId="2" ParentId="12110" CreationDate="2019-10-16T17:52:16.707" Score="5" Body="&lt;p&gt;Andrew, the typical graphics showing standing waves are showing voltage and current &lt;em&gt;distribution&lt;/em&gt; along the wire, not phase shift from each other. Voltage and current are always in-phase at every point, they are syncronized in time, so there are no reactive components in the impedance. The instant of time when voltage is at its max peak also current is at the same value. The same is true at the zero crossing instant or at any other time.&#xA;This happens at the center of the antenna, at its extremes, and at all the points in between.&#xA;This fact is useful in the off-center feed dipole (aka OCF dipole), which is feed at a point where it has about 200 ohms with a 4:1 balun. This points have about the same impedance at several bands, making it a multi-band antenna.&lt;/p&gt;&#xA;" OwnerUserId="15838" LastActivityDate="2019-10-16T17:52:16.707" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15530" PostTypeId="2" ParentId="15528" CreationDate="2019-10-16T18:57:17.753" Score="3" Body="&lt;p&gt;It sounds like the current antenna isn't working, and you want to replace it without climbing on the roof, right?  I recommend installing a single antenna on the highest point you can reach using a lift or tall ladder, without setting foot on the roof.  If needed, you can use a tall mast to elevate the antenna so it's higher than the roof peak.  This would avoid the potential pitfalls of using two antennas (including reduced gain and destructive interference).&lt;/p&gt;&#xA;" OwnerUserId="6080" LastActivityDate="2019-10-16T18:57:17.753" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15531" PostTypeId="1" AcceptedAnswerId="15532" CreationDate="2019-10-16T18:59:08.470" Score="3" ViewCount="105" Body="&lt;p&gt;I would be interested in receiving weather satellites (NOAA and Meteor) with my Icom 910. It has very good filters and could be a better solution than a simple SDR. However, its manual specifies that its -6dB BW for FM is 15kHz, and NOAA's BW is 36kHz and Meteors', 90kHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any way to solve this issue (disabling the bandpass filter maybe?) without hard-modding the rig?&lt;/p&gt;&#xA;" OwnerUserId="14937" LastEditorUserId="218" LastEditDate="2019-10-16T22:25:22.740" LastActivityDate="2019-10-16T22:25:22.740" Title="Is it possible to receive weather satellites with a ham radio rig? (Icom 910)" Tags="&lt;satellites&gt;&lt;icom&gt;&lt;bandwidth&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15532" PostTypeId="2" ParentId="15531" CreationDate="2019-10-16T22:24:49.973" Score="3" Body="&lt;p&gt;The filtering in an SDR is nearly always superior to the filtering in any analog receiver. This is because it's very inexpensive to implement a digital filter which can rapidly approach ideal behavior, whereas good analog filters are quite expensive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only analog filtering required by an SDR is that required to avoid aliasing and overload. Since these filters don't need to have a sharp transition to select a particular channel they can be quite cheap without compromising performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The issue with a very cheap SDR, like some $20 RTL-SDR stick, is noise, aliasing, and overload. But even a modestly better SDR, something with a modicum of engineering effort put towards anything but reducing cost, will probably outperform any analog radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a cursory read of the product literature, it looks like there's an option to add a narrow CW filter. The most straightforward modification is probably to build a filter with the desired wider bandwidth and insert in place of this CW module. I'm not sure if it's possible to use the &quot;CW&quot; filter in FM, if not you could always operate in SSB mode and perform the demodulation in software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Though at this point, you've essentially made an expensive, low-performance SDR. I'd suggest considering the SDR route: the cost won't be too much more than building a custom filter, the effort will be less, and the resulting performance superior.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-10-16T22:24:49.973" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15535" PostTypeId="2" ParentId="15521" CreationDate="2019-10-17T14:14:41.793" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The average power rating is determined by overheating of the centre&#xA;  contact and is a function of frequency, as heating depends on the&#xA;  resistive insertion loss. Typical makers curves for a new clean&#xA;  connector with a perfect load such as page 275 of [2] for example&#xA;  imply ~5000 watts at 20 MHz and ~500watts at 2 GHz, i.e. a square root&#xA;  frequency derating law as might be expected from skin depth decreasing&#xA;  with frequency.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(From &lt;a href=&quot;http://www.terminalblock-elinker.com/news/detail.php/id-345.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.terminalblock-elinker.com/news/detail.php/id-345.html&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since he sites 5kW at 20 MHz, and power handling decreasing with increasing frequency, I think it's safe to say that 2kW at 1.8MHz is no problem.&#xA;(Edit: Corrected the power rating at 20MHz)&lt;/p&gt;&#xA;" OwnerUserId="9974" LastEditorUserId="8717" LastEditDate="2019-10-17T20:05:26.153" LastActivityDate="2019-10-17T20:05:26.153" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15536" PostTypeId="2" ParentId="15517" CreationDate="2019-10-17T16:30:22.230" Score="2" Body="&lt;p&gt;There are several commercial units that work with a pair of antennas to reduce signals from a specific direction. These products are typically called &quot;noise canceller&quot;, &quot;signal enhancer&quot; or &quot;receive antenna phasing system&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The block diagram of a typical product is shown below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/HdbiO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HdbiO.png&quot; alt=&quot;NCC-2 block diagram&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By adjusting the &lt;em&gt;relative&lt;/em&gt; amplitudes and phases of received signals arriving from two antennas, unwanted signals arriving from particular directions may be attenuated. Note that one of the two input antennas may also be the station transmitting antenna and some units include a collapsible whip antenna, potentially obviating the need for additional structures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The adjustable nature of these designs makes it possible to achieve substantial interference reduction over a wide range of frequencies - though probably only over a relatively narrow range of frequencies for any specific set of amplitude and phase adjustments. Product documentation includes antenna recommendations for signal enhancement, signal rejection and noise rejection. One product manual includes a complete schematic diagram of the unit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The OP seeks to achieve a very substantial amount of interference reduction. The choice of receiving antenna(s), their spacing and height above ground may substantially affect rejection of signals arriving at specific elevation angles. It may be useful to model candidate antenna systems to evaluate performance before construction.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-10-17T16:30:22.230" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15537" PostTypeId="1" AcceptedAnswerId="15543" CreationDate="2019-10-19T00:53:10.153" Score="0" ViewCount="145" Body="&lt;p&gt;I have this antenna &lt;a href=&quot;https://www.ebay.com/itm/End-Fed-Half-Wave-Antenna-40-10-meters-1-5-KW-No-Tuner-Needed-65-ft/173740911341?hash=item2873c3eaed:g:DAsAAOSwFGNcKrFh&quot; rel=&quot;nofollow noreferrer&quot;&gt;EFHW 40-10&lt;/a&gt; from Maple Leaf Studios.  My current configuration:  Inverted L with feed point 3m above ground, with &quot;L&quot; at 9m.  I have 45 20-foot in-ground radials just below the feed point, as well as two ground rods connected to the radial plate, and the ground of the match box is  connected to the radial plate.  My question is:  Will lowering the feed point all the way to the ground hurt the performance in any way?  The manufacturer recommended that the antenna be at least six feet above the ground, which most of it would be.  I'd like to extend the vertical as far as possible (I'm limited as to how far I can go up, due to my mast), and reduce the length of my antenna ground.  Any help is appreciated.  Thanks.  I like the performance and versatility of the inverted-L and, given my limited yard size, feel that this is the best all-around multiband option. &lt;/p&gt;&#xA;" OwnerUserId="9772" LastActivityDate="2019-10-20T19:09:30.957" Title="Inverted L Feedpoint Height" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15538" PostTypeId="1" AcceptedAnswerId="15539" CreationDate="2019-10-19T05:50:53.947" Score="1" ViewCount="121" Body="&lt;p&gt;I am trying to build a simple superhet receiver for listening SSB signals.&#xA;I read several articles about SSB and got confused so I am looking for some practical explanation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have 2 mixers, quartz filter between them. &#xA;So there are 2 conversions. First, from HF to IF, second from IF to audio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say I want to receive LSB in range 3747-3750 KHz. If I understood LSB concept correctly 3750 KHz will become 0Hz in audio and 3747Khz will be 3kHz. Some sort of inversion. Am I wrong here?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If my intermediate frequency is 8MHz and I have some ideal filter in range 8000-8003KHz what should be first oscillator frequency?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think like this: &lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;8000 + 3750 = 11750 // I set DDS above the received frequency&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;so the lower part HF frequency will be on the high side of IF filter&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;11750 - 3747 = 8003&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And second oscillator frequency then has to be 8003 for LSB (highest edge of the IF filter):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;8003 - 8003 = 0&#xA;8000 - 8003 = 3&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And if I had USB I had to set to the starting IF filter frequency (8000kHz). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I getting it all wrong?&#xA;Can somebody give a good explanation with examples? Or good article to read.&lt;/p&gt;&#xA;" OwnerUserId="11243" LastActivityDate="2019-10-19T16:24:28.500" Title="How to calculate VFO/IFO frequencies?" Tags="&lt;diy&gt;&lt;ssb&gt;&lt;math&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15539" PostTypeId="2" ParentId="15538" CreationDate="2019-10-19T16:24:28.500" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Let's say I want to receive LSB in range 3747-3750 KHz. If I understood LSB concept correctly 3750 KHz will become 0Hz in audio and 3747Khz will be 3kHz. Some sort of inversion. Am I wrong here?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You're exactly right. LSB maps a 1 Hz baseband input to 1 Hz below the carrier frequency, 20 Hz to 20 Hz below the carrier, and so on. USB is the same but the modulated frequencies are above rather than below the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, in LSB the carrier frequency is the highest frequency in the transmission, and in USB it is the lowest.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;A frequency mixer has two inputs, the signal you'd like to demodulate, and the VFO. Each is at a frequency &lt;span class=&quot;math-container&quot;&gt;$f_1$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$f_2$&lt;/span&gt;, respectively. The mixer then outputs:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ f_\text{out} = \begin{cases}&#xA;f_1 \pm f_2 &amp;amp; \text{if } f_1 &amp;gt; f_2\\&#xA;f_2 \pm f_1 &amp;amp; \text{if } f_2 &amp;gt; f_1&#xA;\end{cases} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are demodulating LSB, you want the signal's carrier frequency (3750 kHz) to fall at the &lt;em&gt;top end&lt;/em&gt; (not the bottom, as in your example) of the filter (8003 kHz). So, you could tune your VFO to 4253 kHz, because 4253 + 3750 = 8003. Or, you could tune the VFO to 11753 kHz, because 11753 - 3750 = 8003.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Either will work, but you must also consider the &lt;em&gt;image frequency&lt;/em&gt;. Say you tune the VFO to 4253 kHz. Your signal at 3750 kHz does get mixed to the IF as desired, but there is another solution to the equation: 12256 - 4253 = 8003. So if there is another signal or noise present at 12256 kHz also present at the input to the mixer, that &lt;em&gt;also&lt;/em&gt; gets mixed to the IF and thus interferes with your desired signal. Alternately with the VFO tuned to 11753 kHz, the image frequency becomes 19756 kHz, because 19756 - 11753 = 8003.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, either choice works. Your design choices must balance the capabilities of the VFO, potential interference at the image frequency, and the requirements of the filter to remove the image frequency.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-10-19T16:24:28.500" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15540" PostTypeId="1" CreationDate="2019-10-20T05:38:59.837" Score="2" ViewCount="446" Body="&lt;p&gt;This is a very simple question and I'm sure if I had a bit more background knowledge, I could figure it out myself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say I have a 1/4 wave vertical antenna that is slightly too long, but it is impractical to cut shorter or fold back on itself. What do I need to add to raise the resonant frequency slightly higher (10 - 100kHz) without using a full-fledged tuner? To put it simply, I can't use a tuner. Can I do it with one or two components?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With electrically short antennas, I know I can add an inductor in series with the antenna to lower the resonant frequency, but how do I do the opposite?&lt;/p&gt;&#xA;" OwnerUserId="1817" LastActivityDate="2019-10-30T01:46:33.733" Title="Tweak antenna resonant frequency higher" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;wire-antenna&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15541" PostTypeId="2" ParentId="15540" CreationDate="2019-10-20T12:34:00.957" Score="5" Body="&lt;p&gt;An antenna which is electrically long at the desired frequency usually presents inductive series reactance at the feedpoint. This inductive reactance can be compensated by adding series capacitive reactance - a single capacitor - between the feedline and the antenna at the feedpoint. This will probably be a relatively narrow-band solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be sure to use a capacitor which can withstand the RF current flowing through it and the RF voltage that will appear across it. You must use a capacitor that presents high Q (low loss) at the operating frequency. I know from sad experience that using a &quot;transmitting&quot; or &quot;doorknob&quot; capacitor is no guarantee of success. To avoid converting your capacitor into smoke, start by applying very low power and, at the very least, measuring the capacitor's temperature before increasing the power. Duty factor will also affect heating; extended application of a steady carrier - for example, tuning, AM, FT8, etc. - will produce more heating than CW or SSB.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-10-20T12:34:00.957" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15542" PostTypeId="2" ParentId="15540" CreationDate="2019-10-20T13:46:08.760" Score="0" Body="&lt;p&gt;If adding an inductive load half way up each leg of a dipole “lengthens” it, I might try the opposite to “shorten” it.  Add a capacitive non-hat part way (half?) up each leg. This might partially shield the tips of the dipole, and make them seem shorter.  Vary the size of the non-hat to vary the effect.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2019-10-20T13:46:08.760" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15543" PostTypeId="2" ParentId="15537" CreationDate="2019-10-20T19:09:30.957" Score="3" Body="&lt;p&gt;RE: &quot;&lt;em&gt;The manufacturer recommended that the antenna be at least six feet above the ground, ...&lt;/em&gt;&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason probably is related to the r-f current flowing along ~six feet of &quot;ground&quot; wire, and/or along the outer diameter of the shield of the coax line connected to the input transformer. Those paths form the 2nd radiating conductor/section of this antenna system, and complete the conditions needed to enable its radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Greatly reducing those conductor lengths likely will reduce the radiation efficiency of that antenna system configuration. &lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-10-20T19:09:30.957" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15544" PostTypeId="1" CreationDate="2019-10-21T06:41:18.173" Score="0" ViewCount="62" Body="&lt;p&gt;I have tried mount ham sticks on SUV and a convertible use trunk lid mount, especially on 40m on the convertible I notice the SWR changes from opening the door and close the door. &#xA;Now I am quite interested to find out how much radials a car would present to the antenna. &#xA;Are there any ways to measure or give a somewhat quantified indication of how much radials an HF vertical is lacking? Something that indicates the &quot;unblancy&quot;? Maybe on a network analyzer? &lt;/p&gt;&#xA;" OwnerUserId="13362" LastActivityDate="2019-10-21T12:03:54.303" Title="Can you measure how much radials you are lacking for HF vertical?" Tags="&lt;antenna-theory&gt;&lt;testing&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15545" PostTypeId="1" CreationDate="2019-10-21T08:36:26.503" Score="0" ViewCount="58" Body="&lt;p&gt;I am using a TYT TH-9800 with a 10 m half dipole antenna on low power (5 W) to connect to a WIN linked repeater (+5.0 MHz offset and 123.0 tone).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I made contact with two other stations and was told that &quot;my audio was overloading and cutting out parts of my signal&quot; and &quot;my audio was high&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How should I fix this? &lt;/p&gt;&#xA;" OwnerUserId="15858" LastEditorUserId="4076" LastEditDate="2019-10-21T11:47:25.107" LastActivityDate="2019-10-21T12:07:15.390" Title="Audio too high, how to troubleshoot" Tags="&lt;repeater&gt;&lt;transceiver&gt;&lt;audio&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15546" PostTypeId="1" AcceptedAnswerId="15559" CreationDate="2019-10-21T09:33:03.390" Score="0" ViewCount="150" Body="&lt;p&gt;I've an AnyTone 878uv pluss and I want to know if roaming is only a DMR feature or if it can be used with analog repeaters?&lt;/p&gt;&#xA;" OwnerUserId="15859" LastActivityDate="2020-03-17T17:32:37.177" Title="Is roaming strictly a DMR feature or does it also relate to analog?" Tags="&lt;dmr&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15547" PostTypeId="2" ParentId="15544" CreationDate="2019-10-21T12:03:54.303" Score="1" Body="&lt;p&gt;An &quot;analyzer&quot; would indicate the impedance at the feedpoint. You could model the antenna and some radials in 4NEC2 or another program to learn what radials produce the equivalent feedpoint impedance.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-10-21T12:03:54.303" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15548" PostTypeId="2" ParentId="15545" CreationDate="2019-10-21T12:07:15.390" Score="2" Body="&lt;p&gt;Hold the HT/mic farther from your mouth and speak in a normal voice. I made this mistake when I first started using an HT. You &lt;em&gt;must not&lt;/em&gt; &quot;close talk&quot; the mic the way you might have done with a handheld mic in the &quot;olde days.&quot;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-10-21T12:07:15.390" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15549" PostTypeId="1" AcceptedAnswerId="15561" CreationDate="2019-10-21T14:12:49.910" Score="2" ViewCount="115" Body="&lt;p&gt;I am currently working on a system to communicate with amateur CubeSats. I have decided to use the turnstile crossed-dipole style yagi because it is relatively easy to construct and uses circular polarization. However, I cannot find resources on how to calculate the gain for such an antenna. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/FpLrY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FpLrY.png&quot; alt=&quot;Turnstile Yagi Antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suspect the gain would be equivalent to that of a typical yagi with the same characteristics. Is this correct?&lt;/p&gt;&#xA;" OwnerUserId="15861" LastActivityDate="2019-10-23T17:37:46.563" Title="Gain of Yagi turnstile?" Tags="&lt;antenna-theory&gt;&lt;satellites&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15550" PostTypeId="2" ParentId="15546" CreationDate="2019-10-21T20:11:21.440" Score="2" Body="&lt;p&gt;The radio can be programmed for DMR operation, or for standard analog repeater (or analog simplex) transmissions; you do not gain any DMR features while using analog.&lt;/p&gt;&#xA;" OwnerUserId="15862" LastActivityDate="2019-10-21T20:11:21.440" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15551" PostTypeId="1" CreationDate="2019-10-21T20:23:20.070" Score="0" ViewCount="159" Body="&lt;p&gt;I know, a dipole is the way to go, but cannot fit one, only a&#xA;    'birdhouse' antenna like the 75m 80m Isotron antenna.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it better to put at 15 feet Above Ground Level outside, or 20 feet AGL inside my attic? Is there the chance of a fire from the high voltage on the Isotron in the attic? Does the outside location improve performance?&lt;/li&gt;&#xA;&lt;li&gt;How about a giant decoupling coil (1 foot diameter x 12 turns) at the Isotron antenna from after the antenna feed line coax?&lt;/li&gt;&#xA;&lt;li&gt;Also, if in the attic, what should I use to ground my mounting post?&lt;/li&gt;&#xA;&lt;li&gt;Ground cable to top of 2nd floor copper water line, or go all the way to the ground? Ham shack is on 2nd floor.&lt;/li&gt;&#xA;&lt;li&gt;Likewise, ground if outside on garage roof?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I have to compromise, but would like to get into my state ARES net.&lt;/p&gt;&#xA;" OwnerUserId="15862" LastEditorUserId="8717" LastEditDate="2019-10-21T23:47:28.337" LastActivityDate="2019-10-26T23:01:55.843" Title="ISOTRON 80m 75m Antenna Position" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;antenna-system&gt;&lt;grounding&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15552" PostTypeId="5" CreationDate="2019-10-21T20:45:25.090" Score="0" Body="" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-10-21T20:45:25.090" LastActivityDate="2019-10-21T20:45:25.090" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15553" PostTypeId="4" CreationDate="2019-10-21T20:45:25.090" Score="0" Body="Questions specific to rules, regulations, and practices in China." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-10-21T20:45:25.090" LastActivityDate="2019-10-21T20:45:25.090" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15554" PostTypeId="5" CreationDate="2019-10-21T20:47:24.530" Score="0" Body="&lt;ul&gt;&#xA;&lt;li&gt;Web site: &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://chirp.danplanet.com/projects/chirp/wiki/Home&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-10-21T20:47:24.530" LastActivityDate="2019-10-21T20:47:24.530" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15555" PostTypeId="4" CreationDate="2019-10-21T20:47:24.530" Score="0" Body="For questions about CHIRP, the open-source software for programming (editing the frequency memories of) radios." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-10-21T20:47:24.530" LastActivityDate="2019-10-21T20:47:24.530" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15556" PostTypeId="1" CreationDate="2019-10-22T00:23:01.300" Score="-4" ViewCount="70" Body="&lt;p&gt;I took the test last week but I failed it I was in a program that went through all the chapters but I just very bad at taking tests is there a way to go around the test&lt;/p&gt;&#xA;" OwnerUserId="15863" LastEditorUserId="76" LastEditDate="2019-10-22T02:05:39.393" LastActivityDate="2019-10-24T21:17:50.383" Title="what is a good way to study for the tech test" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15557" PostTypeId="2" ParentId="15556" CreationDate="2019-10-22T00:34:46.917" Score="3" Body="&lt;p&gt;Have you considered taking practice exams?  Consider the following link which is a set of practice exams that iterate through the question pool on subsequent retakes of the test.  Exam link: &lt;a href=&quot;https://www.qrz.com/hamtest/&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRZ Practice Ham Tests&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would suggest you consider the following method:&#xA;(1) answer questions you are confident in knowing the right answer.&#xA;(2) research other areas until you understand the material gaining the confidence in the material.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the second part, some times the correct answer is just common sense based on knowing the FCC regulations.  Don't guess on these, try to understand why that answer is the correct one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Continue retaking the practice exams using a method like that outlined above until you score 100 percent over and over again.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2019-10-22T00:34:46.917" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15558" PostTypeId="2" ParentId="15556" CreationDate="2019-10-22T02:39:30.317" Score="0" Body="&lt;p&gt;It sounds like you are asking if you can get an amateur radio license without passing the test. Sorry, the answer to that is no.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, there are ways to take the test if one has special needs such as a physical handicap or perhaps something like dyslexia. The VEC that administered your test --or the ARRL-- should be able to provide you with such exceptions to a regular written exam, such as giving you the test orally.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-10-22T02:39:30.317" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15559" PostTypeId="2" ParentId="15546" CreationDate="2019-10-22T21:06:21.347" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;This handheld radio requires you program in all the repeaters you want to use, so it already knows what is available and could, in theory, check GPS or it could check to see if there's a usable signal on a given channel. ...but it already knows the channels. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, that'd be nice and all, but that wouldn't be enough to be useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine this: you're in coverage area of one repeater. Now you're getting closer to a different repeater and want to use that instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be useful, you need a lot more than switch your radio's own channel: &#xA;the moment you roam, you don't want to become &quot;disconnected&quot; from your original communication partner, and that means that you either need to stay on the same relay &quot;output channel&quot; on these two different relays, or you need to tell your partner that you're now on a different channel. Both impossible with an analog system, because:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Staying on the same relay output channel&lt;/strong&gt; is impossible, because these two relays are analog and hence shouldn't share the same channel if they're so close to each other.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Signalling that you'll be receivable on a different channel&lt;/strong&gt; is impossible because an analog network doesn't have the signaling backend for that.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Auto-discovery would be one Hell of a feature, though, huh?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not very complex to implement if your signal was digital. So anyone would do that with a digital signalling protocol, because: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To implement such a complex system as hand-off between relays, you'd need to have all the &lt;em&gt;tools&lt;/em&gt; to do digital speech. So you'd do just that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To give you a bit of historical insight:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Germany used to have &lt;em&gt;C-Netz&lt;/em&gt;, from around 1984 to 1990, with about 750000 subscribers. That was the third generation of analog telephony networks, and the first one to support handover between different relays (which would be called base stations in cellular telephony parlay).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It was also the the last analog cellular network (that was 29 years ago, so we can safely assume it's pretty obsolete, even by ham standards). And it was the only generation to support handover – because you really needed digital signalling to achieve that, and as soon as Siemens and others really had that technology figured out, it became obvious that a digital system would be vastly superior. So, C-Netz became a tremendously popular, but quickly superseded (only after six years – imagine that speed for a behemoth like the German Postal service, which run it) system. Simply because that if you have the digital signal processing capability to do the call management in a handset, you'd really want to make use of that and do digital voice, which has several advantages over analog.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;TL;DR:&lt;/strong&gt; You want to build something like a trunked/cellular analog network. You need to go digital to achieve that. So you usually drop the analog speech in the process. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Hence, your handset is unlikely to support anything like that. It's not a feature of DMR alone (any cell phone standard does that since '90), but it's certainly not an analog thing.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-10-22T21:06:21.347" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15560" PostTypeId="2" ParentId="15528" CreationDate="2019-10-23T01:56:51.180" Score="2" Body="&lt;p&gt;When you feed two antennas with equal power and the separation is large you would create a pattern with very deep nulls at points where both antennas are visible.With the proposed arrangement that would be two 90 degree sectors with problematic coverage. A better solution would be to use the hanger as a screen to minimize the sectors where both antennas are seen equally well. That would be at the midpoints of the long sides and close to the vertical wall. Maybe below the lower roof in case you do not need the range associated with more antenna height. Cable lengths do not matter and you should use a simple power splitter because in case there is any unbalance there is nothing to gain by heating the resistor in a Wilkinson splitter/combiner. 119 MHz seems to me like aeronautical. If that is the case so the signal arrives from some elevation, use a low height and do your best to minimize the directions from which both antennas are visible - but of course high enough to avoid obstacles that might screen the signal.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-10-23T01:56:51.180" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15561" PostTypeId="2" ParentId="15549" CreationDate="2019-10-23T17:37:46.563" Score="3" Body="&lt;p&gt;The answer to calculating the gain of any antenna is usually to model it. EZNEC is a common solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Absent modelling, you are correct that a circularly polarized Yagi will have gain approximately equal to an similar linearly polarized one.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-10-23T17:37:46.563" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15562" PostTypeId="2" ParentId="15556" CreationDate="2019-10-23T19:14:14.783" Score="0" Body="&lt;p&gt;Many people initially fail the test. Some fail it several times. You can keep trying.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most &quot;study&quot; guides and apps simply give you the questions and tell the correct answer. For tech there is a pool of about 350 questions. Its actually fewer, but 350 is close enough. With enough repetition you will eventually memorize enough of the answers to pass the test. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other guides and training material will teach you the material. For example how to use Ohm's law to calculate current when voltage and resistance are known. Many people do better when they understand how to get the answers instead of just memorizing the answers. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For some questions like questions on regulations, the only practical way to do it to memorize the answers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The test material is grouped by subjects. Most practice tests will show which subjects you are having trouble with and which subject you are doing good in. Focus on the subjects you are having trouble with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use a exam practice app on the iphone. There are many of them available in the app store, most are free. do a few practice tests each day until you are pass most of them. The you will be ready to test.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you get a exam preparation book from your library, make sure it is current. The tests are revised every 5 years. They don't change all of the questions, but they do change some of them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am a part of volunteer examiner group that gives the tests. We had a mother and son come in to test and both failed. Talking to them, they had used a book from their local library that was 15 or 20 years old.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Study and practice, you can pass the test. . &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2019-10-23T19:14:14.783" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15563" PostTypeId="2" ParentId="15556" CreationDate="2019-10-24T21:17:50.383" Score="1" Body="&lt;p&gt;No way around it, you have to earn it. It's easy. Just takes a little time and dedication. Repetition of practice tests, study the questions with the correct answers.  If you don't understand the question or the reason for that answer, google it.  There are apps for your smart phone as well as internet websites. www.eham.net/exams  hamstudy.org  arrlexamreview.appspot.com  When you are getting 85-90% on the practice exams you will pass the official exam. My point is, if you are bad at taking tests then practice taking the test.&lt;/p&gt;&#xA;" OwnerUserId="15874" LastActivityDate="2019-10-24T21:17:50.383" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15564" PostTypeId="1" CreationDate="2019-10-25T07:06:00.373" Score="2" ViewCount="105" Body="&lt;p&gt;I might have a bit of a problem with my groundplane, but I am unsure.&#xA;I am using a ground screen instead of radials. The problem is the ground screen is made of galvanized metal, but I can see that a white layer of corrosion has formed. The connection to the groundplane at the base of the antenna is no problem; however, the way that each individual sheet of screen contacts another is simply by being a little overlapped and then stapled to the ground.&#xA;Is this good enough? Let's say the oxide did form between them, does it even matter? I read that RF travels on the surface. Will it just permeate this layer?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know this is a hard question to answer without seeing the situation, but maybe you could just answer in regards to if RF does permeate corrosion to any degree.&lt;/p&gt;&#xA;" OwnerUserId="1817" LastActivityDate="2019-10-26T19:52:24.020" Title="Does RF go through thin corrosion better than DC?" Tags="&lt;antenna-construction&gt;&lt;antenna-system&gt;&lt;grounding&gt;&lt;counterpoise&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15565" PostTypeId="2" ParentId="15564" CreationDate="2019-10-25T15:59:16.787" Score="3" Body="&lt;p&gt;A layer of corrosion between two metals forms a &lt;strong&gt;capacitor&lt;/strong&gt; (or, sometimes, a &lt;strong&gt;diode&lt;/strong&gt;). RF will go through it better than DC, because RF can go through capacitors and DC can't. However, that doesn't mean it's an acceptable substitute for metal-to-metal contact, because the antenna wasn't designed to have an impedance (capacitance) there!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your specific case, it isn't likely a problem in &lt;em&gt;that&lt;/em&gt; way because, after all, both radials and ground plane work for a vertical antenna, and so does any intermediate form between those two designs. However, you must make sure that the ground plane is in fact well-attached &lt;em&gt;to the feed point&lt;/em&gt; and that the screen is oriented so that there are single wires running radially, otherwise there may be current paths through the corroded parts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there is another reason why it is a bad idea to have any such poor connection in an antenna: &lt;a href=&quot;https://en.wikipedia.org/wiki/Rusty_bolt_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;passive intermodulation, a.k.a. the rusty bolt effect&lt;/a&gt; occurs due to some corroded connections within an antenna acting in an electrically nonlinear fashion (like diodes) and therefore creating unwanted harmonics in transmission. Or, in a loose connection with sufficient transmit power, there could be arcing — another nonlinear phenomenon &lt;a href=&quot;https://en.wikipedia.org/wiki/Spark-gap_transmitter&quot; rel=&quot;nofollow noreferrer&quot;&gt;famous for creating harmonics&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your case, there shouldn't usually be any significant voltage difference between two points at the same distance from the feed point horizontally, so these effects would be unlikely to be significant — unless another fault develops such as a portion of the ground plane being disconnected from the base!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In conclusion: &lt;strong&gt;Antennas should never contain loose or oxidized connections between conductors.&lt;/strong&gt; You should make sure that all metal-to-metal connections are clean and clamped, crimped, or soldered so that any oxide layer that could be between the metals is removed and prevented from reforming.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-10-26T14:49:52.547" LastActivityDate="2019-10-26T14:49:52.547" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15566" PostTypeId="1" CreationDate="2019-10-25T17:06:30.807" Score="3" ViewCount="159" Body="&lt;p&gt;I've got a Heathkit SB-102 that I'm working on making operational (problems with transmit, receiver works just fine).  This model radio has a 9-pin Molex connector in the back, intended to connect an external auxiliary VFO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By design, this feature is intended to support &quot;split&quot; operation -- listening on a different frequency from the transmit setting (much more different than the usual 1 KHz offset of the CW setting in this model family).  It occurred to me to wonder, however, whether this external frequency input could be used to operate on bands outside the radio's normal complement of 80, 40, 20, 15, and 10m amateur bands.  There are a number of other amateur bands available within this freuqency range (30m, for instance, as well as 17m and 12m) as well as bands outside this range that might be within the capability of the hardware (160m and 6m come to mind).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to use the external VFO connector on an SB family radio to transmit and receive on amateur bands outside the 80-10m range, or unsupported bands within that range?  Would it become possible if a bypass for the internal VFO (aka LMO) were installed, so the &quot;primary&quot; operation was controlled by the external VFO?&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2019-10-27T13:43:53.783" LastActivityDate="2020-03-09T09:42:02.380" Title="Can the external VFO input in a Heathkit SB-(100, 101, 102) be used to operate on frequencies outside the radio's normal range?" Tags="&lt;hf&gt;&lt;transceiver&gt;&lt;modification&gt;" AnswerCount="1" CommentCount="17" ContentLicense="CC BY-SA 4.0" />
  <row Id="15567" PostTypeId="1" AcceptedAnswerId="15581" CreationDate="2019-10-26T01:39:16.373" Score="1" ViewCount="126" Body="&lt;p&gt;I have been trying to build a gnuradio AM broadcast receiver, but without success. I have tried a lot of combinations, but all of them produce a very distorted audio. I have an NBFM receiver using the same FunCube input and USB audio output which works very well, so they don't  seem to be the problem. Below are two flowgraphs of my attempts. Any help will be appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tzocC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tzocC.png&quot; alt=&quot;gnuradio AM broadcast rcvr&quot;&gt;&lt;/a&gt;&#xA;&lt;hr&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Ib5dK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ib5dK.png&quot; alt=&quot;gnuradio AM broadcast rcvr 2&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15011" LastEditorUserId="15011" LastEditDate="2019-10-28T11:16:02.933" LastActivityDate="2019-10-28T11:18:19.260" Title="Gnuradio AM broadcast receiver distorted audio" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15568" PostTypeId="1" AcceptedAnswerId="15569" CreationDate="2019-10-26T14:10:10.590" Score="1" ViewCount="352" Body="&lt;p&gt;I live next to a 100 kW FM transmitter, 600 feet away transmitting on 103.7 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is south east and most other station I want to listen to are in other directions.  This station comes though most of the FM band interfering with other stations. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a way to block or weaken this station on regular FM radios with internal antennas and pick up other stations?&lt;/p&gt;&#xA;" OwnerUserId="15881" LastEditorUserId="4076" LastEditDate="2019-10-27T10:55:54.620" LastActivityDate="2019-11-21T21:52:42.960" Title="Any way to block one FM station" Tags="&lt;receiver&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15569" PostTypeId="2" ParentId="15568" CreationDate="2019-10-26T15:31:02.793" Score="5" Body="&lt;p&gt;&lt;em&gt;Theoretically,&lt;/em&gt; it is possible: you need to buy or build a “notch” filter tuned exactly to 103.7 MHz, and insert this in line with the receiver's antenna port.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if the receiver has only an internal antenna then it is inconvenient to connect the filter. Furthermore, any such receiver (even many &lt;em&gt;with&lt;/em&gt; an external antenna port) will not actually have enough shielding to prevent the strong station from entering the circuit through paths other than the nominal antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were trying to solve this problem, I would start by looking only at receivers with a &lt;strong&gt;metal enclosure&lt;/strong&gt; (which will also have an external antenna port) to ensure that the circuit is properly shielded. Then the remaining questions are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is the enclosure actually complete without gaps or slots of significant length? (Can be fixed cheaply with foil tape or tidily by installing &quot;RF gasket&quot; strips.)&lt;/li&gt;&#xA;&lt;li&gt;Are the shields of all input/output sockets or cables actually connected to the enclosure? (Can be fixed by soldering in short wires for the signal shields — if this doesn't prevent reassembly or cause the circuit to malfunction. And if one of the cables is an AC power cord then you need a line filter module instead of a simple wire.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The receiver should also have a high &lt;strong&gt;selectivity&lt;/strong&gt; — this measures how good it is at tuning in one station without also receiving adjacent stations.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Some other possibilities:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A directional antenna pointed at a distant station will receive it better and the local station worse. But this will be a large antenna, and again, it doesn't do much good if the receiver isn't shielded.&lt;/li&gt;&#xA;&lt;li&gt;Even a receiver with ordinarily good selectivity may have trouble with a strong station due to &lt;strong&gt;overload&lt;/strong&gt;. If this is the problem, then a filter will help by lowering the strong signal, but also just an &lt;em&gt;attenuator&lt;/em&gt;, which reduces the level of &lt;em&gt;all&lt;/em&gt; signals, may help, making it easier for the receiver to handle them precisely. But in your case the level difference may be just too much for this strategy.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-10-26T15:31:02.793" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15570" PostTypeId="2" ParentId="6300" CreationDate="2019-10-26T16:32:43.007" Score="0" Body="&lt;p&gt;The questioner mentioned &quot;If you have room for a proper radial system...,&quot; which is generally 500 radials (well, maybe that's an exaggeration), buried, and at least 1/4 wavelength long at the lowest intended frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if the vertical's feedpoint is raised -- like 6 feet off the ground, or way up on the rooftop, it only needs 3 or 4 radials, which is at least simpler than dozens of buried radials when ground-mounted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Someone mentioned 1/2 wavelength vertical.  A traditional vertical is 1/4 wavelength, with 1/4 wavelength radials.  A halfwave vertical is a possibility, such as a vertical dipole.  Then the question might be, if you're going to center feed it, how you're going to deal with the coax slapping against the bottom half and radiation from the bottom half interacting in a bothersome fashion with the lower half of the vertical.  Or if you're going to feed the vertical 1/2-wave at its bottom, how are you going to match the 50 ohm coax to the 2000 ohm bottom-feedpoint.  The advantage of the halfwave vertical is that it doesn't require radials.  A major disadvantage would be that it's twice as high as a quarter wave.&lt;/p&gt;&#xA;" OwnerUserId="15882" LastEditorUserId="15882" LastEditDate="2019-10-26T18:47:25.860" LastActivityDate="2019-10-26T18:47:25.860" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15571" PostTypeId="1" CreationDate="2019-10-26T18:40:42.470" Score="1" ViewCount="94" Body="&lt;p&gt;Our church had a Verizon Cellular site until about 6 months ago when Verizon cancelled the lease. After they left we negotiated for them to leave the cabling between the cell site and the antenna located in the church steeple and the antenna itself in the steeple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone know of any uses for the cabling and the antenna or if it would be worth it to try to recover it and if it would be worth anything?&lt;/p&gt;&#xA;" OwnerUserId="15883" LastEditorUserId="4076" LastEditDate="2019-10-27T10:34:00.590" LastActivityDate="2019-10-27T11:07:07.903" Title="Use for Verizon 4G tower antenna" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15572" PostTypeId="2" ParentId="15564" CreationDate="2019-10-26T19:52:24.020" Score="0" Body="&lt;p&gt;I know StackExchange wrote &quot;But avoid responding to other answers.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sorry, but great answer from AG6YO.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;arcing — another nonlinear phenomenon famous for creating harmonics&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;... or setting your lawn on fire&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the arcs are big enough, you'll hear them in an AM transistor radio while you transmit, such as on voice peaks.  You'd be able to hear the staticy sound through the transistor radio's front-end overload.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And I think you'd see your SWR jump around, especially on power-peaks, if the ground plane is arcing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ham radio antennas are often a compromise: bent, shortened, less-than-textbook radials, not high enough, etc.  If there's a voltage difference between two points that are the same distance from the feedpoint, I guess the first question to ask would be &quot;How different?&quot;  (Not that I'd know what to do with the answer.)  A difference would indicate that the groundplane isn't perfect. But if you're not arcing and sparking when you transmit, then your antenna is certainly better than many others'.  Perfection is overrated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm also thinking of DeoxIT, Amazon item # B00006LVEU.&#xA;Deoxit dissolves corrosion, and then puts down a protective layer that prevents future corrosion.  It's a nice thing to dab onto the edge-connectors of PC boards.  I've never used it outdoors on the lawn, but I imagine treating connections with DeoxIT, clamping or crimping them, maybe spraying on a 2nd layer so the clamps don't corrode, and then being good for a long time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Adding a clamp around every point on chicken fencing where the wires cross sounds like an arduous task.  Maybe we could get rich inventing chicken fencing especially for ground planes where all the crossover points are electrically secure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few decades ago, you could have depended on neighbors complaining about TVI as an indicator that sparking and rectification is occurring in or around your antenna.  But now that everyone has cable TV, you can't depend on them, anymore.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hTf0f.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hTf0f.png&quot; alt=&quot;Googling for chicken fencing ground plane&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15882" LastActivityDate="2019-10-26T19:52:24.020" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15573" PostTypeId="2" ParentId="15551" CreationDate="2019-10-26T21:37:15.397" Score="1" Body="&lt;p&gt;CW 4ever.  On 80 Meters, not much difference between 15 or 20 feet AGL.  The resulting near-vertical radiation would be good for communications around your region.  Experience will show beyond what distance the antenna can't reach.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you're done with net business, you can get a couple of thousand additional miles by going on 7 MHz and up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My first antenna in 1974 was an indoor end-fed wire, about 50 feet long stapled to the ceiling of a room in almost a loop-shape on the 2nd floor (the top floor).  That was also where the radios were and the operator's seating position, so I guess I broke the law regarding the FCC's RF-exposure limits.  Mostly 80 meters, I got up and down the east coast from NYC with 75 watts out, DX-60B, HG-10B NC-303, HT32-B.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Be warned: Today, my code speed is about 18 to 20 wpm.  If it weren't for all that RF exposure, I might be up to 40 wpm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That was a brick house, wooden beams.  Foil backing on fiberglass insulation inside the ceiling I tried not to think about.  In newer building construction with steel, there's a lot of attenuation of signals trying to get through the walls of the building.  Moving from just a few inches inside the window to a few inches outside the window could pick you up 10 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know about the decoupling coil.  In my experience, if you and your radio are inside the main RF field, a decoupling coil is like locking the barn doors after the horses have all run off.  Coming from NYC, I don't know what that means, but I think it might be apropos.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For grounding in the attic, if you're pestered with RF voltage shocks when you touch your straight key, or if your antenna tuner is too squirrley when you bring your hand close to it, you can throw 1/4 wavelength wire around the floor to move the voltage node away from your equipment.  MFJ also sells a &quot;ground tuner,&quot; &lt;a href=&quot;https://www.mfjenterprises.com/Product.php?productid=MFJ-931&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.mfjenterprises.com/Product.php?productid=MFJ-931&lt;/a&gt;.  Looks like their ground tuner would allow you to use a shorter length of wire for the same benefit.  That's RF ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For DC ground, on the 2nd floor, all hope is lost.  Get one of those dongles to check the quality of your electrical ground -- the third wire.  That's all you can do.  Search Amazon for  &quot;ac socket tester.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll find advice on the internet insisting that the Ham station must be on the ground floor, with just a few feet of heavy copper ground-wire drilled through the wall running between your radio and a ground rod (outside).  Easier if you don't read the instructions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For grounding on the roof, the antenna should provide the RF ground, whether it's the other half of a dipole or the ground plane of a vertical.  Aluminum ground wire (Amazon item # B0751YB21D) should be run from the antenna's mounting hardware to a ground rod directly vertically straight down from the mounting hardware.  (If the antenna is hit by lightning, it wants to go straight down; it's not polite to ask lightning to follow curves or zig-zags).  You can put a lightning arrestor just below the coax-feedpoint of the antenna (if there is a coax feedpoint), Amazon item # B01LYK5TU5.  The ground rod can accept both ground wires.  Even better is two or more ground rods, so-many-feet apart (that's your homework), tied together with heavy copper wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, read up on grounding and bonding.  Bonding ties the grounds of all of your electrical services (AC, phone, cable TV) together.  Theory is that if one service is hit by lightning and goes up to 1000 volts, but if their grounds are not especially tied together, then for instance when your antenna is hit, the electrical ground (and Hot and Neutral) will go up to 1000 volts, but with the telephone and cable remaining at 0 volts, your TV could blow up, and your cable box, and your cordless telephone base, etc.  Instead, by making a conscious effort to tie all the services' grounds together, if any of them are hit by lightning, then at least all the services will jump up to 1000 volts, which will at least save a lot of your electronics.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My favorite power strip surge protector is Amazon item # B000JE9LD4.  In case of high voltage surprise on any of the three AC leads, the surge protection will short all three leads together.  They may all go up to 1000 volts, but at least the voltage between the wires will be about 0 volts, which helps prevent a lot of damage.  Even better to disconnect your transceiver from EVERYTHING before the thunderstorm gets here.  On the other hand, if your antenna is indoors, then you might be able to stay on the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I almost forgot -- grounding the antenna mounting hardware will help bleed off static from the antenna, which will help keep from attracting static charge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reeling in the antenna before a thunderstorm arrives can help.  Leave the antenna up, but disconnect the coax from the antenna before the storm arrives is a 2nd option.  Lots of grounding strategies on the internet to read.  &lt;a href=&quot;https://www.polyphaser.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.polyphaser.com&lt;/a&gt; Polyphaser is a lightning protection company.  They always have lots of lightning protection advice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I confess my father had a CB antenna.  It had a coax lightning arrestor, but the mounting hardware wasn't grounded.  The lightning arrestor and a lot of the coax cable must have vaporized when the antenna was hit. But apparently, the lighting wasn't finished.  Because the mounting hardware wasn't grounded, the lightning came into the wall, much to my sister's dismay, and a carpenter had to close up the hole.&lt;/p&gt;&#xA;" OwnerUserId="15882" LastActivityDate="2019-10-26T21:37:15.397" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15574" PostTypeId="2" ParentId="15551" CreationDate="2019-10-26T22:02:17.127" Score="1" Body="&lt;h2&gt;Location and Height&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://isotronantennas.com/index.php?main_page=page&amp;amp;id=23&amp;amp;zenid=bclvjvfk8kddrat2vmnu4e4ro0&quot; rel=&quot;nofollow noreferrer&quot;&gt;The manual&lt;/a&gt; seems to suggest that it would be better mounted outside on a mast.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Grounding&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;The manual (page 14) implies that no separate ground wire is necessary.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Choke decoupling&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;An Isotron antenna generally should not have any type of choke balun at the feedpoint, even though the feedline carries some common-mode current (and radiates along with the antenna).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I heard that directly from its inventor (&quot;It makes the antenna extremely narrow-banded&quot;). But you could certainly try it. :-)&#xA;&lt;hr&gt;&#xA;Note that an air-wound choke works over a much narrower bandwidth than ferrite chokes do. See &lt;a href=&quot;http://www.karinya.net/g3txq/chokes&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.karinya.net/g3txq/chokes&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vFPb4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vFPb4.png&quot; alt=&quot;Air-wound vs. Ferrite common mode chokes&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-10-26T23:01:55.843" LastActivityDate="2019-10-26T23:01:55.843" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15575" PostTypeId="2" ParentId="15571" CreationDate="2019-10-27T10:55:17.083" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Anyone know of any uses for the cabling &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The cabling in cellular sites is usually relatively high-quality relatively high-power (for the microwave frequencies 4G uses).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If this is actually 4G, Verizon (I think) uses 1900 MHz, 1700 MHz and maybe 700 MHz; it's possible the antenna is multi-band and supports all three, and they'd definitely use cable that covers all that frequency range (climbing up a tower and exchanging an antenna if one wants to upgrade a cell site is financially less frightening than having to run cable through a building structure, again, just because you saved $100 on the first cable you installed; tore down cables are hard to re-sell or use somewhere else within a professional context).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, first of all, you've got yourself a good quality of cabling to a tower – pretty much for anything above VHF frequency, likely, and in any case for any cellular frequency (700 MHz to  2.3 GHz). You'll want to find the cable, and take a photograph on the printings you'll find on it, and google (or ask here) to find out the type and frequency range of that!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If nothing else, you'd have the best TV antenna or sat dish cabling in the neighborhood if you decide to just use it for that. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;and the antenna&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The antennas themselves: as said, they are specific to the bands they are designed for. Maybe that's even printed on them – otherwise, same deal: Photos of antennas, and type labels, and google or us. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a bit of luck, the antenna you've got there might be feasible for the 13 cm ham band, or the 33 cm ham band, in addition to the 4G bands used commercially in your country (you're not allowed to use these, for obvious reasons).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that's the case, and with an appropriate amateur license, you could do cool things – like running your own amateur 4G network (laws apply, don't do this without asking someone who knows your local laws – I don't). The software exists, and the hardware necessary to set up a base station isn't that expensive!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you could do other things with the same antenna, too, but since the antenna defines the frequencies, and these define the path loss, it'd be &quot;short reach&quot; in amateur terms, since cellular antennas aren't &quot;point-to-point link&quot; directive antennas (i.e. little gain).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;or if it would be worth it to try to recover it and if it would be worth anything?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, check ebay for prices of used &quot;basestation antennas&quot; for antennas of comparable size and shape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's possible this antenna can be sold to someone, but don't expect buyers to invest large sums of money for antennas that the seller can't characterize; maybe one of the reasons for Verizon's cancellation was that there was something wrong with the site, and the investigation/repair costs would have outweighed the revenue that this site was able to generate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After all, the only way you can make money with such an antenna is by running a 4G network, and you need to buy a government license for that, and the companies who did that buy them by the thousands in new condition, only, because flying someone to Backcountry Somewhere, USA, to climb a tower and check an antenna simply isn't worth the savings of buying used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cabling: Since there's a general need for good coax cabling, you could have luck selling that to amateur radio enthusiast, after you've figured out the type, and made sure that the length you're selling doesn't have any visible defects.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-10-27T11:07:07.903" LastActivityDate="2019-10-27T11:07:07.903" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15576" PostTypeId="1" AcceptedAnswerId="15579" CreationDate="2019-10-27T20:58:44.270" Score="1" ViewCount="1728" Body="&lt;p&gt;I saw &lt;a href=&quot;https://www.livescience.com/33453-iss-astronauts-ham-radio.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this article&lt;/a&gt; but I can't imagine the power output, (eight watts max) would be enough to be picked up by the ISS at 200 miles above me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, I don't know if the preamp on the receiver would be sensitive enough to pick up the signal, unless they put up the full 1,500' ERP for it to be picked up.&lt;/p&gt;&#xA;" OwnerUserId="13927" LastActivityDate="2019-11-01T20:18:07.327" Title="Can I contact the International Space Station using my Baofeng UV5R?" Tags="&lt;vhf&gt;&lt;uv-5r&gt;&lt;transmission&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15577" PostTypeId="2" ParentId="15576" CreationDate="2019-10-27T22:16:01.953" Score="0" Body="&lt;p&gt;You don't need to imagine it, because it's true. Many amateur satellites have around &lt;em&gt;half&lt;/em&gt; a watt of output, and they're easily received on the ground with only a modest antenna (a 3-element yagi helps, but I've worked AO-91 and AO-92 with quarter-wave verticals). 8 watts is far more than enough. It doesn't take that much power to get above the noise floor even at hundreds or thousands of miles of distance. The reason terrestrial VHF/UHF are distance-limited is because some obstruction (like the earth itself) always gets in the way sooner or later, but satellites are conveniently located in the sky, where there is generally a whole lot of nothing between us and them.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-10-27T22:16:01.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15578" PostTypeId="2" ParentId="15576" CreationDate="2019-10-27T23:39:52.873" Score="0" Body="&lt;p&gt;Radio waves will travel for billions and billions of miles through space if they're not interfered by matter.  Consider the New Horizons Interplanetary Space Probe that did a fly-by of Pluto in 2015.  I am not sure how far that was but Pluto is about 2.6 Billion miles from Earth at its closest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The transmitters have a power of 12 watts!  One of the antennas on the probe has a gain of 42 dBi with about a 1 degree beam width.  Earth bound antenna dishes used for communications though are huge, 70 meter dishes part of the NASA Deep Space antenna network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use the Friis transmission formula to compute the free-space path loss of the signal and get an estimate of the power of the signal when it reaches the earth.  I have not done the computation but you can do it as a homework assignment.  Of course, there are likely unknowns that you will merely have to guess at to fill in the blanks of the formula.  Or, maybe a diligent internet search can find the necessary parameter values.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2019-10-27T23:39:52.873" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15579" PostTypeId="2" ParentId="15576" CreationDate="2019-10-28T01:40:35.043" Score="3" Body="&lt;p&gt;In theory, yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, &quot;probably not&quot;. In my experience, the front end on Baofengs is not very good. We have a UV-82, and it just did not work when we tried to use it for amateur satellites (AO-91, AO-92, etc). When we replaced it with a Yaesu FT-60R we were finally able to receive the &quot;birds&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So while theoretically you &lt;em&gt;should&lt;/em&gt; be able to receive LEO (low earth orbit) satellites (and the ISS), in reality your Baofeng is being overloaded by everything surrounding you. The same goes for cheap &quot;RTL SDRs&quot;, which need some filtering to get a usable signal: Baofengs &lt;em&gt;ARE&lt;/em&gt; SDRs, and cheap ones at that. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't tried it, but &lt;em&gt;maybe&lt;/em&gt;  in the &quot;middle of nowhere&quot;, far from broadcast stations, you would be able to receive the ISS. Or maybe if you use a suitable filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if you want to experiment with ISS, amateur FM satellites, and NOAA APT (while they last), you should get a second hand &quot;traditional&quot; (analog, superheterodyne, etc) receiver, which will save you a lot of headache.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2019-10-28T01:40:35.043" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15580" PostTypeId="1" AcceptedAnswerId="15582" CreationDate="2019-10-28T01:59:29.497" Score="0" ViewCount="311" Body="&lt;p&gt;I currently operate a 20M half-wave dipole with a balun. It's a little lower than ideal, but it gets me on the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've read about folded dipoles. But I've found contradicting information about them. So here are a few questions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Does a folded dipole really have &quot;wider bandwidth&quot;? Some sources say &quot;yes&quot; because that's what the textbooks say, others say &quot;no&quot;, based on their real wold experience&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is a folded dipole less succeptible to QRM? Would it work better in a city, compared to a regular dipole?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What's its impedance? The theory says it's closer to 300 ohms, but this number can vary wildly and even be much lower. If it's &quot;much lower&quot; than 300 ohms, will feeding it with 300 ohms line have significant loss from mismatch?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What is required to feed it?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is it a &quot;miracle antenna&quot; that will work in any band when tuned with a suitable balanced tuner?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is a folded dipole just a waste of time and money, giving diminishing returns over a regular dipole?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2019-10-29T03:06:39.533" Title="To folded dipole, or not to folded dipole?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;folded-dipole&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15581" PostTypeId="2" ParentId="15567" CreationDate="2019-10-28T11:18:19.260" Score="1" Body="&lt;p&gt;OK, I have found the answer: the tuning is critical. Similar to tuning a SSB signal which shifts the voice frequencies, tuning an AM signal not only shifts the voice frequencies, but distorts the audio until you get right on the carrier frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another minor issue is audio overload. Turning down the volume eliminates that problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;@Kevin Reid AG6YO I looked at the source code for the AM Demod block, and the Complex to Mag -&gt; Add Const(-1) -&gt; Low Pass Filter combination is what is inside the AM Demod block. I was just experimenting with making them separate.&lt;/p&gt;&#xA;" OwnerUserId="15011" LastActivityDate="2019-10-28T11:18:19.260" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15582" PostTypeId="2" ParentId="15580" CreationDate="2019-10-28T11:53:47.957" Score="0" Body="&lt;p&gt;Recently Kevin Loughin, KB9RLW &lt;a href=&quot;https://www.youtube.com/user/loughkb/search?query=folded%20dipole&quot; rel=&quot;nofollow noreferrer&quot;&gt;made a few videos&lt;/a&gt; about folded dipoles and how they perform comparing to regular dipoles. I believe these videos will answer all your questions.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-10-28T11:53:47.957" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15583" PostTypeId="1" CreationDate="2019-10-28T14:40:17.347" Score="2" ViewCount="769" Body="&lt;p&gt;If I build a folded dipole, it will have an impedance close to 300 ohms. I have to match this impedance to the 50 ohms of my transceiver. I know many people match that impedance with varying lengths and combinations of ladder lines, 75 ohm coax, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But let's assume I use a balun. I suppose the balun should be a 6 to 1 type, since it will be matching 300 to 50 ohms. &lt;strong&gt;Is this correct?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For most designs I've seen, the balun is placed at the antenna feedpoint, so there is only coax going from the receiver to the antenna, and this is most likely the way I'm going to implement it. What would happen if ladder line is used instead? &lt;strong&gt;If I use ladder line, could the balun be placed anywhere, and the rest be coax?&lt;/strong&gt; I would assume there should be no problem as long as the antenna and feed line are 300 ohms, and the coax is 50 ohms, a 6:1 balun could be placed anywhere and it would not change performance. Probably even have less loss because of ladder line.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2019-10-29T15:48:36.333" Title="300 ohm to 50 Balun at antenna feedpoint, or near receiver?" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;&lt;balun&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15584" PostTypeId="2" ParentId="15580" CreationDate="2019-10-28T18:12:17.913" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Does a folded dipole really have &quot;wider bandwidth&quot;? Some sources say &quot;yes&quot; because that's what the textbooks say, others say &quot;no&quot;, based on their real wold experience&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;A little more, yes, mostly just because they are thicker than a simple dipole. The same increase in bandwidth could be achieved by making an ordinary dipole out of sections of ladder line with both conductors shorted.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is a folded dipole less succeptible to QRM?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. I'd expect behavior exactly like a similar dipole.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What's its impedance?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;When constructed of two equally sized conductors, 4 times that of a dipole. So if an ordinary dipole has an impedance of 75 ohms, a folded dipole will be 300 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As with any antenna, the actual impedance can be influenced by proximity to ground, straightness or bending of the conductors, losses, and feedline isolation.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is required to feed it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As with any dipole, if you intend to feed it with an unbalanced feedline (like coax) then &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;you'll want a balun&lt;/a&gt;. Additionally, some kind of impedance matching may be desired if the feedline's characteristic impedance does not match the folded dipole, otherwise the feedline will operate with a higher SWR, &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;increasing losses&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both concerns can be addressed by constructing the dipole from tubing, and running the feedline inside the dipole, and matching with a 1/4 wavelength of 121 ohm coax. &lt;a href=&quot;http://ve2azx.net/technical/CustomImpedanceCoax.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;VE2AZX has a nice writeup&lt;/a&gt;. Many VHF commercial stations use this construction method.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it a &quot;miracle antenna&quot; that will work in any band when tuned with a suitable balanced tuner?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is a folded dipole just a waste of time and money, giving diminishing returns over a regular dipole?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Demonstrably no, since there are commercial applications of folded dipoles, and commercial applications care very much about not wasting time or money.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-10-28T22:04:46.733" LastActivityDate="2019-10-28T22:04:46.733" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15585" PostTypeId="2" ParentId="15580" CreationDate="2019-10-29T00:34:22.027" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it a &quot;miracle antenna&quot; that will work in any band when tuned with a suitable balanced tuner?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No more than a regular dipole. A dipole of an appropriate length, fed by ladder line to reduce the standing wave losses (often called a &quot;doublet&quot;) &lt;em&gt;can&lt;/em&gt; be pretty close to a miraculous all-band antenna with a little care, a little luck, and a big tuner. A &quot;folded doublet&quot; with an insulator at the center where the two ends meet behaves pretty much the same, only with 4x the impedance. This may be good, bad, or indifferent (depending on lots of factors) but as tuners are generally a bit better at matching high impedances than low ones, perhaps it's a slight win.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also the &lt;em&gt;terminated&lt;/em&gt; folded dipole, which is commonly advertised as an all-band antenna with an SWR &amp;lt; 2 across several octaves of frequency — and it &lt;em&gt;is&lt;/em&gt;, but only because of the terminating resistor that's placed at the center where the two ends meet. This resistor takes whatever voltage is left at the ends of the elements and dissipates it, turning it into heat. So you get a consistent &quot;all-band&quot; impedance, but the cost is that your antenna is literally part dummy load, with the efficiency varying very much with frequency.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2019-10-29T03:06:39.533" LastActivityDate="2019-10-29T03:06:39.533" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15586" PostTypeId="2" ParentId="15583" CreationDate="2019-10-29T14:57:51.977" Score="2" Body="&lt;p&gt;Yes, you need a 6:1 balun to feed a folded dipole. It might be a good idea to measure the real impedance of the antenna before making or buying a balun though. The real impedance can be anywhere between 200 and 300 Ohm depending on the exact shape of the antenna, the height of the mast, etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are going to feed an antenna using a coax cable you should place a balun at the feed point. If instead of a coax cable you are going to use a 300 Ohm ladder line a balun should be placed at the end of this ladder line. The balun can be connected to the transceiver directly or using a 50 Ohm coax cable of any length.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-10-29T15:48:36.333" LastActivityDate="2019-10-29T15:48:36.333" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15587" PostTypeId="2" ParentId="15576" CreationDate="2019-10-29T17:02:19.623" Score="1" Body="&lt;p&gt;You definitely can, but would benefit a lot from a dual band directional antenna.&#xA;There are plenty of examples of self-built yagi antennas that are perfect for satellite work (such as &lt;a href=&quot;https://hackaday.io/project/25143-wa5vjb-ultra-portable-dual-vhfuhf-yagi&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hackaday.io/project/25143-wa5vjb-ultra-portable-dual-vhfuhf-yagi&lt;/a&gt; but there are lots of others in varying degree of sophistication and effectiveness). &#xA;I particularly like the idea of using tape measure parts since you can easily fold them (see &lt;a href=&quot;https://www.instructables.com/id/The-Tape-Measure-Antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.instructables.com/id/The-Tape-Measure-Antenna/&lt;/a&gt; for an example). The idea is the same as above. For an &quot;ideal&quot; antenna you would probably want the wire version instead of the flat metal but you are trying to have fun and not make a commercial product.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The front end of those radios is not great, but you can quite easily make a filter yourself for that. It all depends on how much you want to make things yourself and experiment, or rather buy a product that you know (should) work...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, have fun with it...&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2019-10-29T17:02:19.623" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15588" PostTypeId="2" ParentId="15540" CreationDate="2019-10-30T01:46:33.733" Score="-1" Body="&lt;p&gt;Cut down your ground plane radials or counterpoise.&lt;/p&gt;&#xA;" OwnerUserId="15907" LastActivityDate="2019-10-30T01:46:33.733" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15589" PostTypeId="1" CreationDate="2019-10-30T03:42:25.840" Score="4" ViewCount="536" Body="&lt;p&gt;Dipoles ideally have 72 ohms impedance. I know most of the time this isn't what one gets and it can vary a lot. But let's assume we can build this perfect dipole that exhibits this impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why do most designs just suggest a 1:1 balun for coax, if coax is usually 50 ohms? Wouldn't it be better to use a 1.5:1 balun? What would be the loss if we connect a 72 ohm antenna to a 50 ohm line without matching it?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2019-10-30T16:59:20.980" Title="Does a dipole require a 1.5:1 balun?" Tags="&lt;balun&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15590" PostTypeId="2" ParentId="15589" CreationDate="2019-10-30T14:41:07.067" Score="3" Body="&lt;p&gt;In you are feeding an antenna which has an impedance 72 Ohm, you will &lt;a href=&quot;https://en.wikipedia.org/wiki/Standing_wave_ratio&quot; rel=&quot;nofollow noreferrer&quot;&gt;get&lt;/a&gt; SWR:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;72 / 50 == 1.44&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;... which &lt;a href=&quot;http://www.firestik.com/Tech_Docs/SWRLOSS.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;corresponds&lt;/a&gt; to ~3% power loss. Considering that the transformer may cause power losses of similar order personally I wouldn't use one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This being said in reality a dipole can be bent to inverted-V shape. Inverted-V has an impedance about 50 Ohm.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-10-30T14:41:07.067" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15591" PostTypeId="2" ParentId="15589" CreationDate="2019-10-30T16:59:20.980" Score="4" Body="&lt;p&gt;A &quot;1:1 balun&quot; in this application is usually a common-mode choke. Its function is primarily to &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;reduce common-mode current&lt;/a&gt;, rather than to perform any impedance transformation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such baluns are easy and inexpensive to fabricate, work on many bands, can handle a lot of power, and have low loss; all because in the differential mode they just look like a length of transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there were a trivial way to achieve a 1.5:1 impedance transformation additionally, that would be great. Unfortunately there is not. One could use a transformer with an appropriate turns ratio, but that would involve transferring power through the core with associated loss and other issues. Or an L matching network could be used, but again this comes with loss and other engineering challenges.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, any SWR under 1.6:1 is acceptable for most applications. The &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;SWR losses&lt;/a&gt; due to such a mismatch are most likely less than the loss that would be introduced by a matching network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SWR loss can be eliminated by using 75 ohm coax. Of course the transmitter will still see a 75 ohm load, but this is within the specifications of most transmitters.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-10-30T16:59:20.980" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15593" PostTypeId="1" CreationDate="2019-10-30T18:35:39.797" Score="0" ViewCount="51" Body="&lt;p&gt;Basically, I connected +5VDC to the ground of a GPS receiver, and now have no power from the power source.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to mess something up by doing this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I feel like this is more of a basic electronics question, but it is specific to this radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Here's the full backstory:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the back the Yaesu FT-2600M, there's a DSUB9 port for packet radio data. One nice thing they include in those pins is +5VDC for an accessory.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Pin 8&lt;/strong&gt; is &lt;strong&gt;+5 VDC&lt;/strong&gt; switched and regulated with a max current of 50mA according to the manual.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Pin 5&lt;/strong&gt; is &lt;strong&gt;Ground&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was trying to supply power to a GPS receiver using this 5 volt output. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm using a DB9 to terminal block connector for this as well as interfacing with  a TNC, so the housing for the connector would have 2 cables coming out of it - one to the TNC for PTT, audio I/O, the other carrying GPS power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The GPS receiver power inlet is a 6 pin mini DIN. &#xA;Mini DIN pinout:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Pin 2&lt;/strong&gt; - &lt;strong&gt;ground&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;pin 5&lt;/strong&gt; - &lt;strong&gt;+5VDC&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(GPS data goes through a separate DSUB9.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I checked the voltage on pin 8 of the Yaesu, and it was 8 volts. No problem, right? At least it wasn't low.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I soldered a 2 conductor cable to what I thought were the proper pins on a female mini DIN, then connected the other end to the DB9 terminal block at the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No power to the GPS. Weird, I thought.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I put the meter on the terminal block again to see if it was still reading 8V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nothing. Hmmm...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To troubleshoot, I took the ends of the female mini DIN out of the terminal block, put a USB-A on the end, and it and stuck it in my computer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Still no power to the GPS, but I was reading 5VDC at the connection, so the only other explanation was that I got the +5 and ground backwards at the mini DIN.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the kind where the housing is a one-shot deal so I had to destroy the housing/boot part to take it apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did wire it backwards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Pin 8&lt;/strong&gt; from the &lt;strong&gt;Yaesu&lt;/strong&gt; was going to &lt;strong&gt;Pin 2&lt;/strong&gt; of the mini &lt;strong&gt;DIN&lt;/strong&gt; when it &lt;em&gt;should have&lt;/em&gt; gone to &lt;strong&gt;Pin 5&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Could I have possibly blown a tiny fuse or ruined some other part in the radio somewhere by hooking this up to the load backwards?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't see anything in the manual about a setting within the radio that would turn this power on or off.&lt;/p&gt;&#xA;" OwnerUserId="15911" LastActivityDate="2019-10-31T01:30:25.057" Title="Had +5VDC and GND swapped, feeding a GPS receiver. Source is +5VDC output @ DB9 port on Yaesu FT-2600M, now showing 0V. Did I fry something?" Tags="&lt;electronics&gt;&lt;aprs&gt;&lt;yaesu&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15594" PostTypeId="2" ParentId="15593" CreationDate="2019-10-31T01:30:25.057" Score="1" Body="&lt;p&gt;It is quite probable that you blew a tiny fuse on the board of the radio. Sometimes these are &lt;a href=&quot;https://en.wikipedia.org/wiki/Resettable_fuse&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;resettable fuses&quot;&lt;/a&gt;, which will 'heal' themselves after some time, but sometimes they are actual fuses which would need to be replaced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, in some unlucky cases there is no fuse and it simply burns out a transistor or a diode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there is still no voltage after a few days, I would suggest taking the radio to be checked, and ask if it can be fixed. You can not be the first person in the world to have done this.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-10-31T01:30:25.057" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15596" PostTypeId="2" ParentId="12868" CreationDate="2019-10-31T04:20:57.223" Score="1" Body="&lt;p&gt;Select the wrench, then press [MENU] to select.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Select 1, then press [MENU] to select.&#xA;Select 17, then press [MENU] to select.&#xA;Then select English, then press [MENU] to select. &lt;/p&gt;&#xA;" OwnerUserId="15917" LastActivityDate="2019-10-31T04:20:57.223" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15597" PostTypeId="1" AcceptedAnswerId="15602" CreationDate="2019-10-31T12:06:28.940" Score="3" ViewCount="504" Body="&lt;p&gt;Let's consider the following picture (&lt;a href=&quot;http://www.hbphoto.com/Radio/Baluns_101.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;source&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/m3ZKd.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/m3ZKd.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When current passes the half-wavelength matching section it changes the phase to the opposite, this is why we get +V and -V in the feed point, 2V difference in total. Also I understand that the current splits to 2 x I/2, this is why we get ( R = 2V/[I/2] )  1:4 impedance matching.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I'm not sure about is what happens to the current in the shield of the half-wavelength coax. The current in the shield of the feed line should flow somewhere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it flow to the half-wavelength coax and cancels itself because of the phase shift? What prevents it from jumping over the beginning of the half-wavelength section and flowing from the end to the beginning of this section? Could you please explain this part in a little more details.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Update:&lt;/strong&gt; Or there is no current in the shield at all? After all it has no connection to the center part of the cable.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2019-11-01T09:38:53.283" LastActivityDate="2020-10-27T08:51:16.343" Title="Trying to understand the work of 4:1 coax balun" Tags="&lt;coaxial-cable&gt;&lt;balun&gt;&lt;impedance-matching&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15598" PostTypeId="1" AcceptedAnswerId="15599" CreationDate="2019-10-31T20:40:44.573" Score="2" ViewCount="586" Body="&lt;p&gt;I'm designing a weather balloon with a club at college. We want to build the antenna from scratch to learn more about antennas but are at a loss as to which antenna design would actually work for high altitude balloons.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reference, we are using an HX-1 as our transmitter and will be picking up APRS packets from the ground using a Baofeng UV-5R. I've read a lot about quarter wave dipole antennas being used in high altitude balloons, but someone also told me that they need connection to a ground plane. Is this true?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, we're considering using a 2m dipole antenna. What is the difference between these two antennas? Is one better than the other? I know the wavelength of 144.390 is 2m, but is there any advantage to using a 2m antenna over a quarter wave dipole antenna?   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And since the 2m dipole antenna isn't omnidirectional, would this be a problem for transmit range?&lt;/p&gt;&#xA;" OwnerUserId="15922" OwnerDisplayName="elbecker" LastEditorUserId="8717" LastEditDate="2019-10-31T21:18:39.127" LastActivityDate="2019-11-21T20:04:43.507" Title="High Altitude Balloon Antenna Design" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;vhf&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15599" PostTypeId="2" ParentId="15598" CreationDate="2019-10-31T21:16:51.683" Score="1" Body="&lt;p&gt;A quarter length antenna needs a ground plane, correct. Or at least large conducting plane. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiation pattern of dipole antenna is just the double (like mirrored) as a quarter length antenna.  The RC planes usually have two dipole antennas, that are positioned 90 degrees with respect to each other, so it can cover almost any angle. But for a baloon, this might not be necessary, if you use gravity to position the antenna. Maybe a better antenna is a directional antenna, like helix or some other, because everything you will transmit in sky is wasted, so think about using directional antenna with a pattern like semi sphere. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IMO, simplest way is to make a folded dipole antenna with a BALUN and one solid tube as reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.electroschematics.com/folded-dipole-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Link&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uMiOy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uMiOy.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://duo.com/labs/tech-notes/the-yagi-uda-antenna-an-illustrated-primer&quot; rel=&quot;nofollow noreferrer&quot;&gt;Link2&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/a60rQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/a60rQ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15919" LastEditorUserId="15919" LastEditDate="2019-10-31T21:54:14.637" LastActivityDate="2019-10-31T21:54:14.637" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15600" PostTypeId="2" ParentId="15598" CreationDate="2019-11-01T06:43:37.210" Score="2" Body="&lt;p&gt;Some friends of mine and I launched a balloon a couple of years ago. We used an antenna based on the design shown here: &lt;a href=&quot;http://www.trackuino.org/2010/04/trash-digging-at-its-finest-111-swr-vhf.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.trackuino.org/2010/04/trash-digging-at-its-finest-111-swr-vhf.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, the links are rotting. That page still exists, but the linked photos don't, nor the original reference they used. But the latter was captured by archive.org: &lt;a href=&quot;https://web.archive.org/web/20160509134815/http://ccarc.org/_misc/so-239_ant.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://web.archive.org/web/20160509134815/http://ccarc.org/_misc/so-239_ant.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The basic idea is a vertical radiator wire and four radials. The radials are directed at a 135 degree angle away from the radiator, at 90 degrees from each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, we were all neophytes (still are) and so much of our work was basically &quot;cargo cult&quot;. I can't tell you whether this design would have worked better or worse than a dipole or other design. I can't even say whether we configured it correctly; we had the option to point the radiator up or down, and chose down. For all I know, we would've gotten better performance the other way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The source material actually says that the impedance of the antenna can be adjusted by varying the vertical angle of the radials, but as you can see below, we didn't bother to do that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, it did work, and quite well. The balloon reached its intended altitude of roughly 110,000 feet, and we had a good signal for the entire flight, except at the lowest altitudes where it couldn't reach a repeater. We also had a direct receiver, which worked fine at launch, but we were having trouble following the balloon's flight track on the ground and so weren't close enough to receive at the last thousand feet or so when the repeaters also weren't receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The biggest problem we had was due to mounting the radiator wire pointed downward. That put the antenna in the most vulnerable spot. Our parachute didn't fully deploy, and the subsequent hard landing bent the antenna, so we didn't have any signal after the landing. It took a bit of searching, extrapolating from the last known position and general horizontal velocity, to find the package after it landed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, it turns out none of us took a decent photo of the antenna itself. Here's the best one I could find, showing the antenna separate from the package before it was attached (we 3D-printed struts to support the antenna near its base):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SKFr7.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SKFr7.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's hard to see in the photo, but we neglected to use the overlapping attachment for the radials as suggested in the source material. I think that would've been more useful/important had we not had the plastic bracing to keep the radials in place.&lt;/p&gt;&#xA;" OwnerUserId="15920" LastActivityDate="2019-11-01T06:43:37.210" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15601" PostTypeId="1" AcceptedAnswerId="15610" CreationDate="2019-11-01T18:12:22.593" Score="2" ViewCount="96" Body="&lt;p&gt;I've just wrote a NEC Antenna file of my longwire with xnec2c on Ubuntu. To calculate protection distance with &lt;a href=&quot;https://emf3.bundesnetzagentur.de/wattw%C3%A4chter.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wattwächter&lt;/a&gt;, I need an .out-file. Protection distance means the safety distance for human where the limits for electric field strength were kept as described in ICNIRP DIN VDE 0848 (&lt;a href=&quot;https://www.darc.de/fileadmin/filemounts/referate/ajw/Onlinelehrgang/a19/Tabelle_Personenschutz.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;overview table&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I generate/convert?&lt;/p&gt;&#xA;" OwnerUserId="15923" LastEditorUserId="8717" LastEditDate="2019-11-05T15:31:37.507" LastActivityDate="2019-11-05T15:31:37.507" Title="Convert NEC antenna file to .out-file for Wattwächter" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15602" PostTypeId="2" ParentId="15597" CreationDate="2019-11-01T18:28:55.463" Score="7" Body="&lt;p&gt;Think of it first without the feedline:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Z0t3X.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Z0t3X.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The half-wavelength of transmission line provides a 180 degree phase shift, and the (short) connection between the shield ends is &quot;ground&quot;. That means it's at 0V relative to the environment, and also the voltage at the open ends of the coax center conductor will be equal in magnitude but opposite in sign relative to this ground point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assume now this is somehow magically fed: there must indeed be an induced current on the shield, equal but opposite to the current on the center conductor. This shield current is also subject to the phase inversion, so if it's going in the coax on one end it's not coming out the other end because it's been inverted: it's also going in. Equal but opposite currents cancel. Which is good, since we said this was ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now if you've read about coax you may know this is exactly the kind of place we want to attach the shield end of a feedline: we want to attach it at a place where the voltage is unchanging relative to the environment, otherwise we get common-mode current that causes the feedline to radiate. And examining the original diagram, this is indeed where the coax is attached.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But still, where does the shield current go? If you like, you can imagine that it splits equally into each half of the 1/2 wave loop:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hgn7M.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hgn7M.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each half then independently travels around the loop where it's inverted then cancels itself.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-11-01T18:28:55.463" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15603" PostTypeId="2" ParentId="15576" CreationDate="2019-11-01T20:18:07.327" Score="0" Body="&lt;p&gt;I've received the ISS during a school contact as described in the linked article on my UV5R using its supplied helical antenna. Copy was good from a high pass but held up for a long time. A beam should give better results for a low elevation pass. The ground station was 150 miles away so I couldn't hear that, of course.&#xA;I've not tried sending to the ISS e.g. to the packet node.&lt;/p&gt;&#xA;" OwnerUserId="15924" LastActivityDate="2019-11-01T20:18:07.327" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15604" PostTypeId="1" CreationDate="2019-11-01T20:28:55.393" Score="2" ViewCount="90" Body="&lt;p&gt;I want to design a PCB for a diplexer for Satellite operations. I want to use SMD capacitors and possible inductors to get some experience with soldering SMD components. What should the voltage rating be for the components? Satellite operations are usually low power, 5 to 15 watts, but RF filters should be able to handle 100 watts or more. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="8717" LastEditDate="2019-11-01T21:14:34.970" LastActivityDate="2019-12-01T22:01:10.127" Title="voltage rating for RF filter components" Tags="&lt;electronics&gt;&lt;equipment-design&gt;&lt;filter&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15605" PostTypeId="2" ParentId="15604" CreationDate="2019-11-01T21:29:40.360" Score="1" Body="&lt;p&gt;Calculate of simulate the RF volts across your filter caps .Remember that The voltage rating of most caps falls with applied frequency .You have your RF volts and your cap value so calc your ripple current and check the ratings .This is why the voltage rating of the caps will be higher than what you think .&lt;/p&gt;&#xA;" OwnerUserId="6095" LastActivityDate="2019-11-01T21:29:40.360" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15607" PostTypeId="2" ParentId="10310" CreationDate="2019-11-02T23:08:16.467" Score="1" Body="&lt;p&gt;I just went through the exact same thing with my own new-to-me DJ-500T (second generation). After a day of poking around, I solved the problem through a hidden menu thanks to some useful posts at the &lt;a href=&quot;https://forums.radioreference.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio Reference Forums&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my case, I was trying to transmit on UHF (70cm) at 452.5625 MHz, which is a Part 90 channel used for local emergency response. When I pressed the PTT button to transmit, the unit made five beeps in rapid succession and displayed &quot;OFF&quot; on the screen. This led me to believe that I had been administratively barred from transmitting, even though I could receive just fine. Changing the offset did not work, since a 5.000 MHz offset is normal for the 70cm band; 0.6 is normal for the 2m band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A number of sites suggested that you needed a programming cable to unlock transmit, but weren't clear on how you would program the radio once you had the ERW-7 cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I finally solved the problem by changing the mode of the radio. The mode change function does not seem to be documented anywhere that I found except &lt;a href=&quot;http://forums.radioreference.com/threads/review-alinco-dj-500t-2nd-generation.294991/post-2482943&quot; rel=&quot;nofollow noreferrer&quot;&gt;in a forum&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;NOTE: This process functionally does a factory reset, erasing all stored channels.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To start, locate PF2 (the button with two squares on it directly under the PTT button) and &quot;D&quot; (lower right hand corner of the keypad).&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Power off the unit.&lt;/li&gt;&#xA;&lt;li&gt;Press and hold PF2 + D together&lt;/li&gt;&#xA;&lt;li&gt;Power on the unit and wait for MODE to appear on screen&lt;/li&gt;&#xA;&lt;li&gt;Release all buttons&lt;/li&gt;&#xA;&lt;li&gt;MODE and a number should be visible. &lt;/li&gt;&#xA;&lt;li&gt;Twist the tuning knob to set the desired mode. 01 is what worked for me.&lt;/li&gt;&#xA;&lt;li&gt;Press D to finalize the setting. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;My device was somehow set to Mode 02 (Mode 2). Switching it to Mode 1 removed my restrictions for transmitting on my desired frequency. There are 4 modes to choose from.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apparently, &lt;a href=&quot;http://forums.radioreference.com/threads/review-alinco-dj-500t-2nd-generation.294991/post-2536595&quot; rel=&quot;nofollow noreferrer&quot;&gt;they are&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;MODE 1 (DJ-500TB) Tx &amp;amp; Rx: 136 - 174 / 400 - 480 Rx on FM radio&#xA;  frequencies&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;MODE 2 (DJ-500T) Tx: 144 - 148 / 420 - 450 Rx: 136 - 174 / 400 - 480 /&#xA;  FM radio frequencies&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;MODE 3 (DJ-500E) Tx &amp;amp; Rx: 144 - 146 / 430 - 440 Rx on FM radio&#xA;  frequencies&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;MODE 4 (Fully Open) TX &amp;amp; Rx: 136 - 174 / 400 - 523 Rx on FM radio&#xA;  frequencies&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="15929" LastEditorUserId="15929" LastEditDate="2019-11-03T04:04:57.990" LastActivityDate="2019-11-03T04:04:57.990" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15608" PostTypeId="1" AcceptedAnswerId="15609" CreationDate="2019-11-03T11:18:24.653" Score="0" ViewCount="429" Body="&lt;p&gt;My file is a simple raw data 32 bit floats sampled at 384 kHz. No metadata or anything alike. The file is some 10+ GB. I am looking for a method of isolating a certain group of signals from it into a new raw data file. I know where the group starts and how long it lasts. How do I extract these few MB from the 10GB file ?&lt;/p&gt;&#xA;" OwnerUserId="8811" LastEditorUserId="8811" LastEditDate="2019-11-03T11:53:57.900" LastActivityDate="2019-11-03T12:35:11.160" Title="GNU radio companion raw captured data file split" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15609" PostTypeId="2" ParentId="15608" CreationDate="2019-11-03T12:35:11.160" Score="1" Body="&lt;p&gt;Basically, beacause you know how large your single sample is (32 bit = 4 B), and since you know where your signal of interest starts and how long it lasts, this is just a matter of&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Converting that position and length knowledge to sample numbers (if you know it in &lt;em&gt;time&lt;/em&gt; rather than samples; but it's easy; &lt;span class=&quot;math-container&quot;&gt;$n_{sample}= t_{sample}\cdot f_{sample}$&lt;/span&gt;)&lt;/li&gt;&#xA;&lt;li&gt;Multiplying that with the sample size&lt;/li&gt;&#xA;&lt;li&gt;Cutting the file at the appropriate places&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;If you're on a unixoid (or have &lt;code&gt;dd&lt;/code&gt; for windows), then &lt;code&gt;dd&lt;/code&gt; can do that for you, with the &lt;code&gt;bs&lt;/code&gt; (blocksize), with &lt;code&gt;skip&lt;/code&gt; you can skip the start of the input, and with &lt;code&gt;count=&lt;/code&gt; you can define how much you want. So, something like, if you want the 1 million samples, starting at sample 12345678:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt; dd if=/your/large/sample/file of=/path/to/output/file bs=4 skip=12345677 count=1000000&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Of course, there's other ways, too. If you like Python, you could use &lt;code&gt;numpy&lt;/code&gt; to open that file using &lt;code&gt;numpy.memmap&lt;/code&gt;, which acts as if you could directly deal with the data on disk as if it was in RAM; that alleviates the need to have 10 GB of spare RAM just to skip the first 9 GB. &lt;code&gt;memmap&lt;/code&gt; takes an offset argument and hence doesn't require seeking through the unintersting beginning, and &lt;code&gt;shape&lt;/code&gt; can be set to the length you're interested in:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;import numpy as np&#xA;arr = np.memmap(&quot;/path/to/input&quot;, dtype=np.float32, offset=12345678, shape(1,1000000))&#xA;# maybe you'd even want to do some signal processing here?&#xA;arr.tofile(&quot;/path/to/output&quot;) &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Of course, within GNU Radio:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Open the file with &lt;code&gt;file_source&lt;/code&gt;, skip the beginning with the &lt;code&gt;skip_head&lt;/code&gt; block, keep only what you want with the &lt;code&gt;head&lt;/code&gt; block.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-11-03T12:35:11.160" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15610" PostTypeId="2" ParentId="15601" CreationDate="2019-11-03T17:21:25.567" Score="2" Body="&lt;p&gt;Now I'm using the software 4nec2 (with wine) with the description from &lt;a href=&quot;http://dl6gl.de/anzeige-nach-bemfv/1-antennenmodellierung-mit-4nec2&quot; rel=&quot;nofollow noreferrer&quot;&gt;DL6GL&lt;/a&gt;. With this software you can generate the .out files. I hope to succeed.&lt;/p&gt;&#xA;" OwnerUserId="15923" LastEditorUserId="4076" LastEditDate="2019-11-04T14:28:53.210" LastActivityDate="2019-11-04T14:28:53.210" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15611" PostTypeId="1" CreationDate="2019-11-04T14:58:08.433" Score="3" ViewCount="133" Body="&lt;p&gt;Judging from posts on the Internet, this belief commonly is considered to be valid.  But what is the correct answer?&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="8717" LastEditDate="2019-11-05T19:46:00.687" LastActivityDate="2019-11-29T12:50:47.503" Title="Do Far-Field Radiation Patterns/Gains of NEC Software Accurately and Always Show the E-M Fields &quot;Launched&quot; by Vertical Monopoles?" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;&lt;radiation-pattern&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15612" PostTypeId="2" ParentId="15611" CreationDate="2019-11-04T14:58:08.433" Score="2" Body="&lt;p&gt;The NEC4.2 analysis below compares the intrinsic fields/gains of the same monopole for the definitions and conditions shown in that graphic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the monopole having a 10 Ω path connecting it to the ground plane does not display zero gain in the horizontal plane, then gradually rising to more positive values for greater elevation angles above the horizontal — as is shown by a NEC &quot;far-field&quot; analysis.  The analysis below shows that the greatest field/gain reduction actually &quot;launched&quot; by that monopole using the 10 Ω path to r-f ground is about 1 dB (in the horizontal plane), relative to using a perfect ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Propagation losses beyond a few wavelengths away from these monopoles affect their intrinsic radiation patterns.  However when an imperfect ground plane is present, the losses existing beyond that radius distance produce more attenuation for low-angle, radiated fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is this phenomenon that produces the zero and relatively low-amplitude, low elevation angle fields/gains shown by a far-field analysis using NEC (MoM software), from vertical monopoles using imperfect ground planes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However that doesn't mean that those fields/gains first launched by a vertical monopole using imperfect ground planes did not have much higher values closer to the antenna site.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2cUFS.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2cUFS.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;In response to the comments of tomnexus, this edit to my answer adds a new graphic (below), which better illustrates these issues and observations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio operators tend to use the NEC-calculated far-field analysis almost exclusively.  However the far field as defined in antenna engineering textbooks begins at a distance of about 2L²/λ meters [L = Radiator Length(Height), in meters; λ = wavelength, in meters].&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that at the distance of 1 kilometer specified for the e-fields of these NEC calculations, both the far-field &lt;em&gt;and&lt;/em&gt; the surface wave values lie in far-field of that radiator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using only the NEC far-field pattern to analyze the performance of a vertical monopole antenna system driven against a lossy ground plane can lead to a belief that it has zero radiation in the horizontal plane, and not much more than zero at very low elevation angles.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However that is not always the case, when NEC analyzes the surface wave at ranges within distances of 30 miles or even more from the antenna site (depending on radiated power, frequency, ground plane conductivity etc).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OWB8z.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OWB8z.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Added November 29, 2019&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is an expansion of my answer to address the concept that the radiation pattern of a vertical monopole requires a circular ground plane having a radius of some 10 to 100 wavelengths in order to reach its final form.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The graphic below shows the radiated fields of a vertical monopole for the conditions shown in the graphic, calculated using NEC4.2. Elevation AGL is shown on the left Y axis; field intensity 0.1 km from the radiator vs. elevation angle are shown by the X axis and the right Y axis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Observations, for these conditions:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;» The fields for Earth conductivities ranging from sea water (5,000 mS/m) to very poor (1 mS/m) all have nearly the same relative values (E/Emax)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;» All of these radiated fields are maximum in the horizontal plane&lt;/p&gt;&#xA;&#xA;&lt;p&gt;» These radiation patterns did not require &quot;10 to 100 wavelengths&quot; to form; the 0.1 km horizontal distance used in this analysis is only 0.617 wavelengths away from the radiator&lt;/p&gt;&#xA;&#xA;&lt;p&gt;» Low values of Earth conductivity do not produce zero v-pol radiation in the horizontal plane, as shown by a NEC far-field (only) analysis&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For reference, the field at 0.1 km radiated by this transmit/antenna system using a perfect ground plane is 0.992 V/m, an improvement of only 0.19 dB when compared to sea water.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/YNybr.jpg&quot; alt=&quot;enter image description here&quot;&gt;]&lt;a href=&quot;https://i.stack.imgur.com/YNybr.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;3&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-11-29T12:50:47.503" LastActivityDate="2019-11-29T12:50:47.503" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15613" PostTypeId="2" ParentId="5209" CreationDate="2019-11-04T18:50:42.623" Score="1" Body="&lt;p&gt;Yes when you update your SD card change percent box of FM repeaters to a much higher number. It will locate them by zip code and give you a very complete list once imported. If you travel far just have that SD card ready plug in and download. Doesn’t affect your memory channels etc. Very easy to search and scan.&lt;/p&gt;&#xA;" OwnerUserId="15934" LastActivityDate="2019-11-04T18:50:42.623" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15614" PostTypeId="5" CreationDate="2019-11-05T19:29:02.113" Score="0" Body="&lt;p&gt;The correct spelling in English-speaking countries outside the US is antenna-&lt;strong&gt;modelling&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;With modeling software, you can determine the pattern, feed point impedance and even the SWR of your antenna system before cutting one piece of wire or one tube of aluminum. This can save an awful lot of tree and tower climbing.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Antenna modeling used to be the domain of scientists and engineers with very expensive antenna ranges covering acres and acres of land strewn with expensive equipment. However, with the proliferation of personal computers and affordable (even free) software, antenna modeling has become a popular amateur activity.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;http://www.arrl.org/antenna-modeling&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/antenna-modeling&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;h2&gt;Popular antenna modeling software&lt;/h2&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://eznec.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC&lt;/a&gt; and &lt;a href=&quot;https://ac6la.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;AUTO-EZ&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.qsl.net/4nec2&quot; rel=&quot;nofollow noreferrer&quot;&gt;4NEC2&lt;/a&gt;; &lt;a href=&quot;https://labsdl.wordpress.com/2017/04/30/menjalankan-4nec2-dalam-ubuntu/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Running in Linux&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://hamsoft.ca/pages/mmana-gal.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;MMNANA-GAL&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-11-05T22:09:19.717" LastActivityDate="2019-11-05T22:09:19.717" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15615" PostTypeId="4" CreationDate="2019-11-05T19:29:02.113" Score="0" Body="Use for questions about using antenna modeling software to simulate an antenna system and determine its gain and radiation pattern." OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-11-05T19:29:02.113" LastActivityDate="2019-11-05T19:29:02.113" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15616" PostTypeId="2" ParentId="10347" CreationDate="2019-11-05T20:17:21.030" Score="2" Body="&lt;p&gt;Over the last few years, there have been many changes in Amateur Radio licensing law and practice in Taiwan.  One of the major changes is the abolition of the Morse Code proficiency requirement in order to obtain a Second-Class (rough FCC General equivalence) operator license.  Another is using FCC pool questions in all relevant sections down to the wording and answer choices literally translated.  Not sure whether the questions will be updated when then FCC pool for the license classes are updated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One may bring in amateur radio equipment provided that accompanying paperwork is completed and is not allowed to be operated until it is inspected and approved at the NCC (National Communications Commission) office.  It may not matter anyway to a foreign guest operator, because they cannot use their own equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What has not changed is that Taiwan (including Kinmen, Matsu and Penghu outlying islands) does not share operating authority with any other jurisdiction, period.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Operators licensed in their home jurisdiction may apply for temporary operating authority at a local sponsor station:  &lt;a href=&quot;http://www.ctarl.org.tw/bv5ya/2009-10/VSTR-op.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ctarl.org.tw/bv5ya/2009-10/VSTR-op.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While the link is dated 2009-10, my understanding is that the link is current as of this posting.  A list of guest operator permit grants may be found here:  &lt;a href=&quot;http://www.ctarl.org.tw/bv5ya/outnews.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ctarl.org.tw/bv5ya/outnews.htm&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What has also not changed is that one must possess a valid Alien Residence Certificate (ARC) or Passport issued by the Republic of China (Taiwan) to apply for an Amateur Radio Operator License and sit for the exam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The CTARL face book page is limited to news feed of their activities.  Current general information remains on their web site.  Actually all the information is there, it just may not be presented in the manner you expect.&lt;/p&gt;&#xA;" OwnerUserId="15937" LastEditorUserId="15937" LastEditDate="2019-11-05T21:37:58.270" LastActivityDate="2019-11-05T21:37:58.270" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15617" PostTypeId="2" ParentId="7771" CreationDate="2019-11-05T21:01:17.157" Score="1" Body="&lt;p&gt;Amateur Radio operators licensed in Taiwan find they cannot use their license outside their jurisdiction so they are eager to be licensed where there are reciprocal agreements for maximum flexibility during their overseas travel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To that end, there appears to be an active VE group in Taipei that administers FCC licensing exams as well as providing VE services.  The exam that was conducted earlier this year may be found here and one may be able to find out whether an upcoming session is scheduled or provide VE services upon request:  &lt;a href=&quot;http://www.arrl.org/exam_sessions/taiwan-fg-00000-3&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/exam_sessions/taiwan-fg-00000-3&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this helps!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73, BM2NHC&lt;/p&gt;&#xA;" OwnerUserId="15937" LastActivityDate="2019-11-05T21:01:17.157" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15618" PostTypeId="2" ParentId="1388" CreationDate="2019-11-06T03:46:52.150" Score="2" Body="&lt;p&gt;If you are interested in space communications (EME and satellites) even small losses are important since losses have room temperature. The sky as well as a good preamp should be well below 100K while losses are about 3 times warmer which makes them 3 times more destructive. When one designs a yagi one can trade between gain/pattern and element losses. The way elements are mounted on a boom tube does matter. Through hole with Starlock washers can cause severe losses to the extent one can feel the heat on the boom tube by hand after running 1 kW power for 5 minutes (a day with no wind that would cool the antenna.)&#xA;For details look here: &lt;a href=&quot;http://sm5bsz.com/antennas/sa/losses413.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://sm5bsz.com/antennas/sa/losses413.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2019-11-06T03:46:52.150" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15619" PostTypeId="2" ParentId="490" CreationDate="2019-11-06T16:15:00.307" Score="5" Body="&lt;p&gt;There are currently products from multiple major and minor DMR equipment manufacturers to support single frequency repeater (SFR) function.  They may have different names but essentially do the same thing:  Repeater input on time slot 1 and output on time slot 2.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is not certain is whether SFR is interoperable between different manufacturer equipment.  From the description by each manufacturer it appears to be interoperable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://cwh050.blogspot.com/2017/01/extended-range-direct-mode.html&quot; rel=&quot;noreferrer&quot;&gt;Motorola:&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Extended Range Direct Mode enables repeater operation on a simplex radio channel. Radios on an ERDM channel transmit on one slot and receive on another slot - the frequency is the same.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;With this you get:&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;Repeater-like coverage&lt;/li&gt;&#xA;  &lt;li&gt;No need for a 2nd frequency - your simplex channel can be reused.&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;In this configuration, dual slot operation is not possible and you need to be using a SLR series repeater. IP based dispatch solutions, like SmartPTT Plus and TRBONET Plus, are supported. It also only supports single site conventional operation so no trunking or IPSC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This feature requires R2.7.0 firmware and is supported on all current generation MOTOTRBO radios. My understanding is that this feature will also work on other makes of DMR radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://hytera.co.uk/news/md785i-hyteras-new-dmr-mobile-radio&quot; rel=&quot;noreferrer&quot;&gt;Hytera:&lt;/a&gt;   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Full Duplex and Single Frequency Repeater&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The UHF model variants of the MD785i are also available with Full-Duplex function and can thus also be used as Single Frequency Repeaters (SFR). In Repeater Mode the mobile radio boosts the range of a direct connection between conventional DMR devices without having to use a base station or repeater. In very concrete terms for users this means they now have more freedom of movement and considerably more flexibility.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.belfone.com/bf-sfr600-single-frequency-repeater_p66.html&quot; rel=&quot;noreferrer&quot;&gt;Belfone:&lt;/a&gt;  Repeater and Base Station&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BF-SFR600 is our new single frequency repeater solution which is also able to function as a base station within a system. As a single frequency repeater, BF-SFR600 allocates one timeslot to receive a signal and the other to transmit it at the same frequency, using DMO mode to extend radio coverage. &lt;/p&gt;&#xA;" OwnerUserId="15937" LastEditorUserId="8717" LastEditDate="2019-11-06T22:00:32.873" LastActivityDate="2019-11-06T22:00:32.873" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15620" PostTypeId="2" ParentId="6022" CreationDate="2019-11-06T21:25:54.797" Score="1" Body="&lt;p&gt;Antenna performance is not dependent on service or modulation type (waveform).  As long as your waveform is inside resonant frequency and bandwidth, the antenna will perform as constructed.&lt;/p&gt;&#xA;" OwnerUserId="15937" LastActivityDate="2019-11-06T21:25:54.797" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15621" PostTypeId="2" ParentId="1909" CreationDate="2019-11-06T21:51:24.967" Score="1" Body="&lt;p&gt;Often they are the same antenna electrically.  What sets them apart are aesthetics, material and price (unfortunately) as well as other factors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, I have a &quot;genuine&quot; antenna purchased from manufacturer-authorized distributor and a &quot;counterfeit&quot; antenna purchased online.  I am unable to distinguish performance between the two in a blind comparison test.  That said, the genuine antenna looks more visually appealing and the counterfeit antenna feels rough and does not attach/detach smoothly from the radio.  In another example, I have two stubby flexible antennas.  The rubber covering on the counterfeit antenna disintegrated after three months, exposing the loosely wound metal coil underneath.  The rubber covering on the genuine antenna remains intact after 3+ years of occasional abuse.  Both antennas seem to perform similarly; however, I am unable to use the former because I am afraid that the exposed coil will catch something and attach itself, causing damage when I pull away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bottom line for HT antennas, buy what suits you.&lt;/p&gt;&#xA;" OwnerUserId="15937" LastActivityDate="2019-11-06T21:51:24.967" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15622" PostTypeId="2" ParentId="15410" CreationDate="2019-11-06T22:11:48.770" Score="0" Body="&lt;p&gt;The antenna on &lt;a href=&quot;https://www.instructables.com/id/Yagi-Antenna-for-the-70-Cm-Band-430-440-MHz-by-F4H/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page&lt;/a&gt; seems doable and does not appear to require soldering.&lt;/p&gt;&#xA;" OwnerUserId="15937" LastActivityDate="2019-11-06T22:11:48.770" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15623" PostTypeId="2" ParentId="6545" CreationDate="2019-11-07T05:21:46.000" Score="1" Body="&lt;p&gt;Save time and aggravation. Get a Mobilinkd TNC-3 with cables and a ferrite bead for less than $200. The AFSK cables don't work well with VOX since (at least my cheap UV-5R) adds a hang of a few seconds after the tx ends. Not so with the Mobilinkd. UV-5R works pretty flawlessly with the TNC-3 and APRSdroid as well as MixW on my laptop. It is well worth the dough.&lt;/p&gt;&#xA;" OwnerUserId="15939" LastActivityDate="2019-11-07T05:21:46.000" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15624" PostTypeId="1" AcceptedAnswerId="15625" CreationDate="2019-11-08T07:53:54.293" Score="5" ViewCount="471" Body="&lt;p&gt;Are any of you guys familiar with a &quot;Viper&quot; antenna?  It came up in a recent discussion with club members for higher frequency bands (6m, 4m, 2m).  I hadn't heard of it before and internet searches suggest it's a brand as opposed to a type.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it seems the one thing they have in common is the coil (large or small) somewhere along the shaft.  So, how do these antennas work electrically and do they have advantages over better known antenna types - or are they just snake oil (sorry, just couldn't resist!!)&lt;/p&gt;&#xA;" OwnerUserId="11875" LastActivityDate="2019-11-08T15:31:09.527" Title="How does a Viper Antenna work?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15625" PostTypeId="2" ParentId="15624" CreationDate="2019-11-08T15:31:09.527" Score="5" Body="&lt;p&gt;As far as I know Viper antenna looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/81HpR.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/81HpR.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here we see an antenna for 2m band. It's well described by &lt;a href=&quot;https://vk2zoi.com/articles/half-wave-flower-pot/&quot; rel=&quot;noreferrer&quot;&gt;John, VK2ZOI&lt;/a&gt; and &lt;a href=&quot;https://vk1nam.wordpress.com/2018/02/10/portable-2m-144-mhz-coaxial-dipole-antenna/&quot; rel=&quot;noreferrer&quot;&gt;Andrew, VK1NAM&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically it's a vertical dipole. The inner part of the coax in the top is one arm and the shield in the bottom is a second arm. The antenna is fed from the bottom. 9 turns of the coax cable work as a balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've used this antenna on 2m and it works very well. If properly tuned it also works on 70cm as a 3 lambda dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BSRIX.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BSRIX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although the balun is probably not designed for 70cm band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find a little more details (in Russian) and pictures &lt;a href=&quot;https://eax.me/ham-radio-vhf-uhf-bands/&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2019-11-08T15:31:09.527" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15626" PostTypeId="1" CreationDate="2019-11-08T17:33:33.760" Score="5" ViewCount="1098" Body="&lt;p&gt;This question regards erroneous SWR measurements of K6BEZ antenna analyzer (links gone from Internet now) design from 2013 using Arduino and AD9850 DDS modules. There have been many variations of it by other people over the years. Good details to make it work right seem hard to find. Here is my circuit for just the bridge section (the FWD and REV go out to the Arduino).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8iJkH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8iJkH.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;While testing it for SWR with resistors, it only reads correctly at 50 ohms. 100 ohms and 25 ohms both measure about 1.3 SWR and should be 2:1. I believe the problem is the way the bridge drives the op amps. The op amp circuit and onward work fine and calculate the SWR properly if I simulate the supposed bridge detector output using DC voltages. Although the 300mV DDS wave is rather low, the 1N5817 diodes have only 134mV forward voltage drop. Two helpful resources I used to check the bridge operation, were:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://ludens.cl/Electron/swr/swr.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wideband SWR meter&lt;/a&gt;, using an identical bridge and analog meters (which I built), and&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/2399/adapting-an-antenna-coupler/2404#2404&quot;&gt;Adapting an Antenna Coupler&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Below are photos showing my wiring to mount the RF components as close together as possible.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uZNB0.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uZNB0.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/47lxA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/47lxA.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Below is a graph of SWR on a 20-meter dipole. I monitored the Arduino on the PC serial COM port, capturing its text file output of the SWR at 100 frequency points between 4-30 MHz. Then I graphed the data in Excel.&lt;/p&gt;&#xA;&lt;p&gt;The analyzer does seem to show something meaningful but but the valleys are too wide. The red line at 14.250 MHz is where I measured the lowest SWR (resonance?) using the Wideband SWR meter (mentioned above) and it was a sharp dip, unlike the graph from the Arduino analyzer.&lt;/p&gt;&#xA;&lt;p&gt;Any &lt;strong&gt;comments or suggestions&lt;/strong&gt; would be much appreciated.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YJRqt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YJRqt.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15325" LastEditorUserId="15325" LastEditDate="2021-02-26T17:46:22.800" LastActivityDate="2021-02-26T17:46:22.800" Title="RF Bridge Problem - K6BEZ Antenna Analyzer" Tags="&lt;hf&gt;&lt;diy&gt;&lt;measurement&gt;&lt;swr-meter&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15627" PostTypeId="2" ParentId="7014" CreationDate="2019-11-08T19:24:47.393" Score="7" Body="&lt;p&gt;Land line telegraph keys are fitted with a circuit closer switch. Radio telegraph keys were not but many radio operators used land line keys because they were so readily available. This includes the rather ubiquitous J-38 about which more will be found below. The arcing that occurred at the key contacts of the early spark radios caused radio stations to switch to purpose made keys which had more robust contacts and in some cases arc shields. In North American practice the idle condition of a land telegraph line was with a current of ~60 - 90 Milliamperes flowing continuously and the ferrous metal armatures of all Relays, Main Line Sounders, and Registers, were used, pulled to their energized position by the magnetic flux of the Electromagnet which is part of all Land Line telegraph receiving apparatus. As others have indicated the receiving apparatus were in series in the lines which passed through each station. When the line was idle the continuous current flowing through the line had to pass through each set of Relay or Main Line Sounder electromagnet coils in series. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The earliest batteries used in land line telegraphy were Gravity Cells, so called because the only thing separating the two liquids that made up the batteries electrolyte were the difference in their specific gravity. In order for those Gravity Cells to remain functional they had to be making current continuously. If the circuit was opened for any long period of time the specific gravity of the 2 liquids would become too similar and they would then mix rendering the battery useless until the output was reestablished and the two liquids would separate after the passage of sufficient time. That was the largest factor in telegraph lines in the North America being normally closed constant current systems because they started out that way. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If any telegrapher left their circuit closer open while they were not transmitting it would cripple the line. Without all other circuit closers being closed no operator could take control of the current flow to transmit a message. By opening the circuit closer switch the telegrapher took control of the line and caused all of the other sounders on the line to de-energize. The absence of current flow through the electromagnets of all of the Relays and Main Line Sounders, connected in series in the line, would result in the loss of the magnetic flux generated by each set of coils thus releasing the armature of the Relays and Main Line Sounders to be pushed, in the case of sounders, or pulled in the case of ralays, to their relaxed condition by their return springs. The single click made by the Sounders when the return spring pushed the hammer bar up against the limit stop of their frame alerted the other stations' operators to listen for their station's call to see if the message was for them. If they heard their stations call they would open their keys circuit closer and the operator who was sending their call would know that because the sending operators sounder would go silent in the up posotion. The telegrapher who called the station would then close their circuit closer to allow the other operator to respond. Occasionally the operator who opened the line would be someone other than the station called. This might be done by a telegrapher with urgent traffic such as a railway dispatcher controlling the movement of trains or, especially during World War Two, an operator who needed to send an Army Flash message.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The J-38 Telegraph Key is a US Army Signal Corps LAND LINE key that was already in use when the United States entered World War Two.  Every permanent Army post had a telegraph office to send and receive messages which could not wait for the US Mail.  The fact that it was a line key can be deduced from the presence of a shunt bar for the other side of the line and the markings on the base plate that indicate that the LINE is to be connected to one shunt terminal and one key terminal and the Relay or Main Line Sounder was to be connected to the shunt terminal and key terminal on the other side of the base plate labeled TEL for telegraph equipment. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the J-38 was already designed, prototyped, tested, tooled, and in production at the outbreak of WW2 it was quicker to use the J-38 for many applications than it would have been to wait for purpose made telegraph keys for individual uses to become available.  As a consequence many thousands of J-38 keys were made during the early years of the war until the keys which were made for those other uses became available.  When those other keys, such as the J-43 et al, became available their were already thousands of J-38 keys in the supply chain which became surplus after the war. That is why the J-38 is by far the most commonly available military surplus key.  &lt;/p&gt;&#xA;" OwnerUserId="277" LastEditorUserId="76" LastEditDate="2019-11-10T19:19:39.773" LastActivityDate="2019-11-10T19:19:39.773" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15628" PostTypeId="1" CreationDate="2019-11-08T22:09:19.607" Score="4" ViewCount="354" Body="&lt;p&gt;I am using a Folded Dipole which I bought when I first got my General License. It was advertised as an all band antenna. My results with it were less than the claims made by the makers to say the least. At a height of about 40 feet above local ground level and a manufactured length of 90 feet I could not make many contacts on any band. I began to believe that what the ad meant when it described the antenna as &quot;Quiet&quot; was actually deaf. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was given a Yaesu FT-1000 by a member of my radio club after a field day during which I logged for him whenever he was operating. I read the manual even though that is supposed to be some sort of violation of some sacred rule and found out that it had an internal antenna tuner. The manual and other sources said the internal tuner would bring any SWR up to 3:1 down to 1.5:1 or better. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since much of what I read about the Terminated Folded Dipole called them by such uncomplimentary names as &quot;Bird foot warmers&quot; and my experience with mine had been so unrewarding I thought I would give the tuner in the FT-1000 a try at making the beastie perform more effectively. I did some reading and took it as gospel that the impedance of a folded dipole without the 600 Ohm resister and the 12:1 balun would be 300 Ohms at resonance. I then ran the usual formula for Resonance and got ~5.464 MHz for my 90 foot long folded dipole. I knew that wouldn't be exactly right because the antenna is not strung at quite &gt;45 feet but I thought it might be close enough to try the FT-1000 internal tuner on. The tuner would not match the antenna anywhere I tried it. I concluded that the SWR had to be greater than 3:1 and thus beyond the tuners limit. I figured I could get the antenna to an actual 50 Ohm load with 300 Ohm window line down to a 6:1 balun. Suddenly the tuner likes the antenna from 160 Meters to 6 meters because the indicators said the the tuner was getting a match. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As it is know there is ~25 feet of Times Microwave Systems LMR-400, 1:6 balun, ~30 feet 300 Ohm window line, feed point of 90 foot long folded dipole. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is the heart of my question. Does it seem at all likely to those of you with more theoretical acumen that the tuner is getting a match through that wide a range of Wavelengths?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I take my club's AEA HF Analyzer and hook it up to the 6:1 balun will it show me what the tuner is actually seeing? Would their be any benefit to using the more recently designed RigExpert AA-200 instead? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the proper technique to measure the impedance of an antenna with a balanced feed line using an analyzer with in imbalanced input?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would be grateful for any help that anyone cares to offer.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;-- &#xA;Tom Horne W3TDH &lt;/p&gt;&#xA;" OwnerUserId="277" LastEditorUserId="8717" LastEditDate="2019-11-16T17:41:17.393" LastActivityDate="2019-11-16T17:41:17.393" Title="Actual Impedance of a folded dipole at resonance" Tags="&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15629" PostTypeId="2" ParentId="5859" CreationDate="2019-11-09T08:22:11.303" Score="0" Body="&lt;p&gt;you can install &lt;strong&gt;gr-baz&lt;/strong&gt; from &lt;a href=&quot;https://github.com/balint256/gr-baz&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/balint256/gr-baz&lt;/a&gt; (just do according to its readme file), after that u will have the &lt;strong&gt;&lt;em&gt;baudline sink block&lt;/em&gt;&lt;/strong&gt; in Gnuradio. &lt;/p&gt;&#xA;" OwnerUserId="15946" LastActivityDate="2019-11-09T08:22:11.303" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15631" PostTypeId="2" ParentId="15626" CreationDate="2019-11-10T05:04:33.750" Score="7" Body="&lt;p&gt;(See updated information further down)&lt;/p&gt;&#xA;&lt;p&gt;I found an article to address the problems all in one place in &lt;strong&gt;QST, September 2019&lt;/strong&gt;. The author addresses the same problems in the question, and explains his fixes for a similar bridge-circuit-based Arduino analyzer originally published in QST, November 2017. I realize I am a newcomer and many have already figured out fixes, but their information is so scattered, so the above article was great.&lt;/p&gt;&#xA;&lt;p&gt;After days of searching and hitting dozens of dead links, I have dug up some meaningful and linkable documents on the history and evolution of AD9850 Antenna Analyzers. It has been very time-consuming, but educational to find and organize all these as bookmarks and I want to share what I found.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.njqrp.club/dds/&quot; rel=&quot;nofollow noreferrer&quot;&gt;NJQRP DDS Daughtercard Kit&lt;/a&gt;, site last updated in 2005, is the earliest mention I've found of a DDS measuring project, although in their page they link to AARL publication - Original DDSVFO Article by Curtis Pruess WB2V, QEX 1997, which was a PIC/AD9850 VFO, essentially the same circuit as an analyzer but without the RF bridge. The daughtercard version, however, included an RF amplifier for the DDS, addressing the low output level even at that time.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://midnightdesignsolutions.com/dds60/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;DDS-60 Kit from the AmQRP&lt;/a&gt; is a current web page with a 2014 upgraded version of the same daughtercard, with history and lots of detail about the daughtercard evolution.&lt;/p&gt;&#xA;&lt;p&gt;Related to the above daughter cards is &lt;a href=&quot;http://www.midnightdesignsolutions.com/sweepgen/&quot; rel=&quot;nofollow noreferrer&quot;&gt;WØPCE &amp;quot;Sweep Gen&amp;quot; - Automated DDS Sweep Generator Measurement System&lt;/a&gt; that had a dead link to original article by Sam Green, WØPCE (in QEX for Nov-Dec 2008) but which by searching I found mention of a version II in QEX September/October 2012.&lt;/p&gt;&#xA;&lt;p&gt;I couldn't find mention of early DDS projects used for an antenna analyzer until 2013. The first one seems to be Beric Dunn's K6BEZ Antenna Analyzer. After that, many other analyzers seem to be offshoots of his, including some using the Si5351 DDS. Beric's version did not use an RF amplifier, which I believe is one key problem prompting me to post my question.&lt;/p&gt;&#xA;&lt;p&gt;Another related project is &lt;a href=&quot;http://www.tyler.net/wa5bdu/PHSNA_QQ_Spring_14.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;The Poor Ham's Scalar Network Analyzer (PHSNA)&lt;/a&gt; by Nick Kennedy—WA5BDU from 2014. It uses DDS, and also an AD8307 log detector (which I've read can be used instead of the diodes as an improved detector in the bridge.)&lt;/p&gt;&#xA;&lt;p&gt;In conclusion, a website with files originating from 2016, &lt;a href=&quot;http://www.farrukhzia.com/analyzer/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna Analyzer for Ham Bands&lt;/a&gt; by Jack Purdum (W8TEE), Farrukh Zia (K2ZIA) is their project that they published in QST, November 2017. Lots of documentation here! This one uses a nearly identical bridge circuit that Beric's did, but includes an RF amplifier for the DDS. This seems to be the most sophisticated and documented source of all, especially with the mods and customizing mentioned in QST, September 2019.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;3/12/2020 Update&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;It's disappointing to report that I can't make this project work accurately, when others claim to have made theirs work. I've tried every suggested modification that I've found: correcting DDS generator output filter impedance, add a MAR-65M MMIC to boost DDS output, tested with various diodes, germanium and Schottky, in the bridge and added in the op-amp feedback to correct below diode threshold voltage, etc. I've hand-matched the resistors and diodes use in the bridge. Below is the current schematic. Note: the FWD and REV outputs go to MCP6002 op-amps as in the schematic in the posted question.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/EpEib.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EpEib.jpg&quot; alt=&quot;new-schematic&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I've made special code tests to check FWD and REV amplitudes coming from the bridge at individual frequencies (prior to the SWR calculation formula). The formula used in the code to calculate SWR is VSWR = (FWD + REV) / (FWD - REV).  Below are four different test load results of the Arduino output on the COM port, graphed in Excel showing SWR with A/D units that go into the formula:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GocPN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GocPN.png&quot; alt=&quot;view1&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/BQxNs.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BQxNs.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Each different load strangely has its own unique characteristic, but they are repeatably the same every time I test them. The red circles show the correct SWR and the A/D units calculate properly in the formula. All modifications I mentioned above don't change the basic patterns of SWR calculated for each resistor; they only affect the absolute RF levels involved, but the proportions stay basically the same going into the formula, thus the same SWR numbers coming out.&lt;/p&gt;&#xA;&lt;p&gt;One thing I have noticed is that the high-frequency end of the RF sine wave has an average DC offset of about +50 mV after AC-coupling at the bridge, so that may indicate distortion, if that matters. Regardless of the wrong SWR readings, the resonant point of any dipole I've tried is detected and matches up with that of a NanoVNA and also an MFJ noise bridge. While researching on this site, I noticed in an answer of a somewhat related post, &lt;a href=&quot;https://ham.stackexchange.com/questions/2400/antenna-tuning-while-receiving&quot;&gt;Antenna tuning while receiving&lt;/a&gt;, that this type of bridge doesn't really measure SWR.&lt;/p&gt;&#xA;&lt;p&gt;I've also considered that my breadboarded construction may cause errors, but I've seen worse on the Internet that claim to work, and besides, it isn't really that high a frequency spectrum I'm working with.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Last update - 3/16/2020&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I suspected the metal film resistors causing a lot of problems at high frequencies, since I believe they are spiral-trimmed and therefore inductive. I made a whole new bridge using SMT resistors, capacitors, and Schottky diodes (BAT-54A). That made the measurements much more consistent and nearly level on the charts (and exactly level for 50 ohms).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5GwgU.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5GwgU.jpg&quot; alt=&quot;SMT Bridge&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now, all parts are as close together as possible and in a logical layout and there is a grounded backplane. The resistors all measure exactly the same on my ohmmeter. The diodes are in a dual package, so probably closely matched. Also I made a section with SMT load resistors to use for tests, since my others were the metal film type. I used pin jumpers to switch between test loads and antenna.&lt;/p&gt;&#xA;&lt;p&gt;So I got some positive results. Now, a 50 ohm resistor measures exactly 1.000 SWR from 1 MHz to 30 MHz. The single problem that still exists is that at 25, 100, and 150 ohms, the SWR is not what it should be. However it is close, and more important, they chart very close to one value from 1 MHz to 30 MHz. So 25 ohms measures 1.52 to 1.41 (should be 2.0), 100 ohms is 1.54 to 1.39 (should be 2.0), and 150 ohms is 2.27 to 2.02 (should be 3.0). I'm willing to live with that as long as 50 ohms is 1:1 as it is now. It is very much improved (less erratic) compared to the charts I posted above recently before switching to SMT.&lt;/p&gt;&#xA;&lt;p&gt;I also left space on the PCB to add capacitors successively as a test. C1 and C2 attached to the diodes are 1 nF in the schematic. I wondered if that value was correct so I first tested the new PCB with those, then I added 10 nF, and finally, 100 nF in parallel and with any of those values, the results were essentially the same, so that answered my question on that.&lt;/p&gt;&#xA;&lt;p&gt;To check one more area, I tested the FWD and REV op-amp sections with DC from 0 to +5V and both channels' outputs tracked the inputs within a few millivolts with a gain of 1 so it seems that isn't part of the problem. As I mentioned before, the code calculating the SWR from the FWD and REV is correct, so I can't think of any other reasons for the SWR readings being off. The analyzer works very well finding the SWR dip on antennas, so I think it's now working as well as I can make it work.&lt;/p&gt;&#xA;&lt;p&gt;So my answer now is that SMT parts on a PCB are much better than the discreet parts I had tacked together for an RF bridge.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/xq9we.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xq9we.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15325" LastEditorUserId="15325" LastEditDate="2020-08-01T17:46:53.233" LastActivityDate="2020-08-01T17:46:53.233" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15633" PostTypeId="2" ParentId="15628" CreationDate="2019-11-10T17:00:53.697" Score="5" Body="&lt;p&gt;Since you say &quot;Terminated Folded Dipole&quot; and mention a resistor, it sounds like you are talking about a &lt;a href=&quot;https://en.wikipedia.org/wiki/T2FD_antenna&quot; rel=&quot;noreferrer&quot;&gt;T2FD&lt;/a&gt;. This is a significantly different antenna from a vanilla folded dipole, which does not have a resistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A T2FD can indeed provide a flat-ish impedance over a wide band, however this comes at the expense of efficiency. A significant fraction of the power is absorbed in the resistor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feedpoint impedance of a T2FD is usually around 300 ohms, so a 6:1 balun is indeed a good choice if you intend to operate this antenna with a radio designed for a 50 ohm load, such as the FT-1000. An antenna analyzer would indeed be useful to get a more precise answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, none of this will address the inefficiency inherent to the design of the antenna. In a receive application the inefficiency may not be too much of a problem since both signal and noise are attenuated. But in a transmitting application, an inefficient antenna wastes transmitter power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Height above ground is also a factor. If you want long-distance communication, a dipole of any sort should be at least a half-wavelength above ground. Any lower than this and most of the radiation tends to go straight up rather than towards the horizon, and you lose significant power in the resistance of the soil. At 40 feet, 20 meters should work, but as frequency decreases you'll find your antenna limited to local contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would suggest building a simple 20 meter wire dipole at least as a point of reference. It's cheap and performs very well at 40 feet above ground. It only works for one band, but it will at least give you an idea of what's possible with a good antenna before you explore other designs.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-11-10T17:00:53.697" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15634" PostTypeId="2" ParentId="140" CreationDate="2019-11-11T03:06:41.227" Score="1" Body="&lt;p&gt;There are two properties you care about for antenna wire:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) Will it conduct well&#xA;2) Can it support its own weight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to skin effect, cost, conductivity, etc., the best material for conduction is copper.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best material to support its own weight is steel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use a large gauge (say, 14-12) of copper wire which will work.  For short wires that won't bend, solid copper will work.  If you are going to attach it to a support structure that won't flex, finer than 14 would work.  If this is a long wire that will move in the wind, etc., stranded is best to reduce fatigue issues.  Be aware, however, that long copper wires that are hung will stretch over time, which can affect tuning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could use solid steel wire but it doesn't conduct well; so a very good compromise is to use copper clad steel.  This can be a very small gauge because the steel portion can be thin and still support it, and it doesn't need a very thick copper layer on the outside to conduct well.  The disadvantages of copper clad steel is that it needs special tools to cut it and it tends to either curl up or refuse to stay curled, depending on how it is made.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2019-11-12T12:33:57.047" LastActivityDate="2019-11-12T12:33:57.047" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15635" PostTypeId="2" ParentId="15628" CreationDate="2019-11-11T17:16:01.963" Score="3" Body="&lt;p&gt;Below for further discussion is a NEC4.2 study for the folded dipole antenna description provided in earlier posts in this thread.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course its input SWR and radiation patterns vary with frequency.  The patterns at the two ends of the HF amateur bands and the input SWR across that spectrum are shown in the study.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The NEC wire model showed no segment or geometry errors at runtime.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vKmBc.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vKmBc.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;.&#xA;&lt;em&gt;Added 16 Nov:&lt;/em&gt;  To partially address the comments of W3TDH, below are the NEC4.2-calulated R and j values at the feedpoint terminals of that folded dipole, across the 3-30 MHz band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SWR match to R300 j0 ohms is best at/near 5 MHz, where it has a value of about 1.08:1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll limit this edit to add this graphic, only, as I have not kept up to date on the test equipment and procedures commonly used by amateur radio operators to measure impedance these days.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AJy5b.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AJy5b.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-11-16T12:56:56.103" LastActivityDate="2019-11-16T12:56:56.103" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15636" PostTypeId="1" CreationDate="2019-11-12T00:28:21.897" Score="3" ViewCount="147" Body="&lt;p&gt;At the bottom of webpages in the advertisement swamps I keep seeing this image of an antenna, accompanied by an offer &lt;em&gt;that I won't be clicking on.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But the antenna itself looks quite intriguing. It's a circular, horizontal loop of copper with the ground braid of a coaxial cable connected at one point. The center conductor connects to what looks like tap that runs a short distance around the loop, connecting to it just shy of 90 degrees away from where the braid connects to it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that this is a legitimate antenna design (and it might not be):&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What kind of loop antenna is it? What is it called?&lt;/li&gt;&#xA;&lt;li&gt;What is the relationship between the diameter of the loop and the wavelength at which it is used?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CGnT3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CGnT3.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8643" LastEditorUserId="8717" LastEditDate="2019-11-12T20:13:20.413" LastActivityDate="2019-11-12T23:36:41.777" Title="What kind of loop antenna is this, and what is the relationship between its diameter and wavelength?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15637" PostTypeId="2" ParentId="15636" CreationDate="2019-11-12T00:46:13.600" Score="4" Body="&lt;p&gt;That is a horizontally polarized omnidirectional &lt;strong&gt;halo antenna&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The relationship between the diameter and length (λ/2) is simply diameter÷&lt;em&gt;π&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some halos have a series capacitor to the right (where the &lt;a href=&quot;https://i.stack.imgur.com/CGnT3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;picture&lt;/a&gt; is cut off). Others are open. &lt;a href=&quot;https://www.google.com/search?q=halo+antenna&amp;amp;newwindow=1&amp;amp;safe=active&amp;amp;prmd=sinv&amp;amp;sxsrf=ACYBGNSQ-Cdh21R55heNZWb8BHMkPN-QhQ:1573587936092&amp;amp;source=lnms&amp;amp;tbm=isch&amp;amp;sa=X&amp;amp;ved=2ahUKEwiKitDvt-XlAhW0On0KHXs9AvAQ_AUoAnoECA8QAg&amp;amp;biw=768&amp;amp;bih=1024&quot; rel=&quot;nofollow noreferrer&quot;&gt;Pictures from Google search&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They were in common use on automobiles back when 6 and 2 meter AM was popular in the 50s and 60s. However, they are not that common now, since FM is now vertically polarized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, they would be an excellent choice in areas where VHF SSB is used, since that is mostly horizontal polarization. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-11-12T21:02:00.520" LastActivityDate="2019-11-12T21:02:00.520" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15638" PostTypeId="1" AcceptedAnswerId="15643" CreationDate="2019-11-12T01:20:25.040" Score="3" ViewCount="95" Body="&lt;p&gt;I apologize if this question is a little out of scope for the amateur radio stack exchange but I feel like it fit better here than over in any other forum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have successfully parsed raw PCM data out of a WAV file representing the signal received from one of NOAA's satellites in APT format. Since its bit rate is 16 bit I combined sequential pairs of bytes into 16 bits using simple bit shifting. I understand these values represent sampled amplitudes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I am trying to figure out is where to go from here. I don't really want to use a normal application as most of them are proprietary, and being  a ham operator I feel like programming an APT demodulator would be a useful exercise as a rite of passage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've done some digging around and have read the APT specification, but it doesn't quite give any clues on what I need to do to transform the signal into the appropriate image. I've read around on other forums, and it seems I need an AM demodulator and some form of an FFT to get it to where I need to be - however I am brand new to this stuff. I come from a computer science and math background so I can definitely handle the learning curve. I'm just about through with my amateur extra exam and the knowledge in there seems have left me with little to work with in this regard. I am willing to dig in but I have to know where to start!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone provide me any resources on how I can begin to learn how to transform these signals in the raw PCM data to the images I need? . I'd really appreciate it!&lt;/p&gt;&#xA;" OwnerUserId="15957" LastEditorUserId="76" LastEditDate="2019-11-12T03:21:01.213" LastActivityDate="2019-11-13T05:00:28.827" Title="Turning raw APT data into an image" Tags="&lt;software-defined-radio&gt;&lt;software-development&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15640" PostTypeId="2" ParentId="140" CreationDate="2019-11-12T07:53:23.353" Score="2" Body="&lt;p&gt;Don't believe the many myths in circulation concerning which wire to use for an antenna. Most of the myths over complicate this very simple subject. In reality, it doesn't make much if any difference what type of wire you use, so long as it's strong enough to hold it's own weight and isn't too thin,  you should be ok. I've used copper, stranded, solid, fencing wire and even insulated speaker wire and they all work about the same.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-11-16T05:22:19.440" LastActivityDate="2019-11-16T05:22:19.440" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15641" PostTypeId="2" ParentId="15636" CreationDate="2019-11-12T19:17:35.883" Score="7" Body="&lt;p&gt;It is a 2-meter halo antenna as built by Mike Fedler N6TWW: the image appears to have been lifted from &lt;a href=&quot;http://fedler.com/radio/2m_loop.htm&quot; rel=&quot;noreferrer&quot;&gt;his page describing the build&lt;/a&gt;. It's 40&quot; in circumference, and the boom length (slightly more than the diameter) is 14.5&quot; long. It's tuned for 144.25 MHz. The name &quot;halo&quot; comes from a combination of the antenna's appearance and an abbreviation for &lt;strong&gt;ha&lt;/strong&gt;lf wave &lt;strong&gt;lo&lt;/strong&gt;op.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2019-11-12T20:20:19.827" LastActivityDate="2019-11-12T20:20:19.827" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15643" PostTypeId="2" ParentId="15638" CreationDate="2019-11-13T04:52:26.040" Score="2" Body="&lt;p&gt;The data is AM modulated on the 2.4 kHz subcarrier, with 256 different levels representing a single value from 0 to 255. It's a scanline every 1/2 second from the cameras with sync and telemetry data added to the beginning and end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each line is 2080 data points (words) long, so it broadcasts at 4160 baud. The sync lines at the beginning let you know when a line starts, and helps the decoder to adjust its baud rate if needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Channel A starts its 39 word sync with 7 square wave pulses at 1040 Hz, with each pulse being 2 words wide with 2 word spacing, and the remainder blank. Then the space and minute marker at 47 words long. Then the raw 256 value picture data. And then 45 words of telemetry data used to calibrate the range values of the sensor and determine which sensor is transmitting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Channel B is exactly the same, except its sync is 7 pulses at 832 Hz, making its pulses 3 words wide with 2 word spacing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: Others around the web have pointed out that you can sample the audio at 9.6 kHz and get 4 samples per wave, take any two consecutive samples &lt;span class=&quot;math-container&quot;&gt;$x_{_1}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$x_{_2}$&lt;/span&gt;, and get the carrier amplitude with &lt;span class=&quot;math-container&quot;&gt;$A = \sqrt{{x_{_1}}^2 + {x_{_2}}^2}$&lt;/span&gt; .&lt;/p&gt;&#xA;" OwnerUserId="15722" LastEditorUserId="15722" LastEditDate="2019-11-13T05:00:28.827" LastActivityDate="2019-11-13T05:00:28.827" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15644" PostTypeId="2" ParentId="10015" CreationDate="2019-11-13T22:58:19.540" Score="0" Body="&lt;p&gt;The very common BC547 and the 2SC945 will both work in your FM receiver.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-11-13T22:58:19.540" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15645" PostTypeId="1" CreationDate="2019-11-14T05:52:26.570" Score="0" ViewCount="40" Body="&lt;p&gt;I know the major components of rectenna should be &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Receiving antenna - Patch Antenna &lt;/li&gt;&#xA;&lt;li&gt;Matching circuit&lt;/li&gt;&#xA;&lt;li&gt;Low pass filter  &lt;/li&gt;&#xA;&lt;li&gt;Rectifier - Schottky diode &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;but I could not visualize how can we put all these things together. Can anyone help, please? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For number 1(Rx): I have found some information saying that the gain wouldn't be important for Rx so if I were to build a system to transfer power wirelessly for 1meter with 2.45GHz, should I just use a patch antenna with a single element which will have around 5dbi gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For number 3(LPF): I have found another article on &lt;a href=&quot;https://www.researchgate.net/publication/266872359_Designing_Microstrip_Low_Pass_Filter_In_ISM_Band_For_Rectenna_System&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.researchgate.net/publication/266872359_Designing_Microstrip_Low_Pass_Filter_In_ISM_Band_For_Rectenna_System&lt;/a&gt; that connects the LPF with patch antenna by using microstrip. My idea of LPF was by using RC or LC and when I see that my mind was blown away lol. According to the complex calculation on the article, I am not sure can I follow that? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For number 2: Apparently almost every component will have its resistance so how can I calculate the optimum matching circuit? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have to create a chart that has all the voltage i/o, current i/o, gain i/o, power i/o for all the components, how am I able to calculate those for antenna, matching circuit, LPF and diode? It looks like impossible to me now.. &lt;/p&gt;&#xA;" OwnerUserId="15968" LastEditorUserId="15968" LastEditDate="2019-11-14T06:26:05.713" LastActivityDate="2019-11-14T10:42:04.593" Title="How can I design a microstrip patch rectenna that can power up 1W of payload?" Tags="&lt;antenna-system&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15646" PostTypeId="2" ParentId="15645" CreationDate="2019-11-14T10:42:04.593" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I know the major components of rectenna should be &lt;/p&gt;&#xA;  &#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;Receiving antenna - Patch Antenna &lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It needs to be an antenna. Not necessarily a patch antenna.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol start=&quot;2&quot;&gt;&#xA;  &lt;li&gt;Matching circuit&lt;/li&gt;&#xA;  &lt;li&gt;Low pass filter&lt;/li&gt;&#xA;  &lt;li&gt;Rectifier - Schottky diode&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The Low Pass Filter needs to come after the diode! Otherwise, there'd be no more signal energy to rectify.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For number 1(Rx): I have found some information saying that the gain wouldn't be important for Rx &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That information is very misleading, probably even wrong. The effective area of your antenna defines how much power you'll be able to extract from the electromagnetic field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you'd want is an antenna with a high effective area. That usually comes with high gain.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For number 3(LPF): I have found another article on &lt;a href=&quot;https://www.researchgate.net/publication/266872359_Designing_Microstrip_Low_Pass_Filter_In_ISM_Band_For_Rectenna_System&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.researchgate.net/publication/266872359_Designing_Microstrip_Low_Pass_Filter_In_ISM_Band_For_Rectenna_System&lt;/a&gt; that connects the LPF with patch antenna by using microstrip. My idea of LPF was by using RC or LC and when I see that my mind was blown away lol. According to the complex calculation on the article, I am not sure can I follow that? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You're using microwave frequencies. Your Ls and Cs don't look like components there, anymore. You need to use microstrip lines (and other types of waveguides) to even just transport the signal – a cable won't do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you understand none of the equations there, that's pretty normal, but that also means that you won't be designing an efficient rectenna soon.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For number 2: Apparently almost every component will have its resistance so how can I calculate the optimum matching circuit? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Sorry, that is far too broad. If you really want to use a patch antenna, then the matching of the patch to the microstrip line is done by calculating/simulating the optimum recessed feed inlet length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then you'd need to somehow match the diode to the microstrip line, which is mathematically impossible (the diode being very nonlinear), but you can get &quot;good enough&quot; for ranges of amplitude that you care about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, you'd need to have a sink for the high-frequency content that the diode produced, (the low pass filter + termination) to avoid that getting re-emitted by your antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are three pretty hard problems, and it'll probably take someone with a lot of experience and equipment quite a while to figure out a satisfying way.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I have to create a chart that has all the voltage i/o, current i/o, gain i/o, power i/o for all the components, how am I able to calculate those for antenna, matching circuit, LPF and diode? It looks like impossible to me now.. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm sorry, I think it &lt;em&gt;is&lt;/em&gt; impossible for you right now. You probably need a lot of Electrical Engineering basics, and then very specific knowledge of working with nonlinear RF elements.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-11-14T10:42:04.593" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15648" PostTypeId="1" CreationDate="2019-11-15T19:10:09.967" Score="1" ViewCount="59" Body="&lt;p&gt;What is the limit of a transmitter in the GSM1800 band (~1830 MHz)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ETSI GSM specification states a limit of -47dBm between 1GHz and 12.75GHz (&lt;a href=&quot;https://www.etsi.org/deliver/etsi_gts/05/0505/05.00.00_60/gsmts_0505v050000p.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.etsi.org/deliver/etsi_gts/05/0505/05.00.00_60/gsmts_0505v050000p.pdf&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, to my understanding these are spurious emissions from the transmitter itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am wondering about a non-GSM transmitter leaking into the GSM1800 and whether these limits can be derived from the above document in the first place.&lt;/p&gt;&#xA;" OwnerUserId="15972" LastActivityDate="2019-12-15T20:02:50.417" Title="Limit of transmission in GSM 1800 band" Tags="&lt;legal&gt;&lt;europe&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15649" PostTypeId="2" ParentId="15648" CreationDate="2019-11-15T19:22:37.140" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I am wondering about a non-GSM transmitter leaking into the GSM1800 and whether these limits can be derived from the above document in the first place.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;They can't. This is subject to local laws, not communication standards – and usually formulated and enforced by the regulatory body of a country (FCC in the US, OFCOM in UK, BNetzA in Germany, MIC in Japan, …) with laws governing the guidelines for that regulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a general &quot;rule of why things are legislated&quot;: These laws exist to protect services (in your case, cellular telephony and data transfer) from interference from other services and unintentional radiators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, it's realistic to assume that local laws are written so that the interference levels do not mitigate normal operation even in the low signal strength regimes of the protected services.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GSM handsets need to work down to -120 dBm per standard. That kind of implies that you might get into trouble if your out-of-band radiation is significantly more that; the definition of &quot;significantly&quot; will heavily vary between countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words, if you can measure it when using the smallest resolution bandwidth of your spectrum analyzer, chaaaaaances are it's too much. Again, for more information, you'll need to refer to your local regulator.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-11-15T19:27:38.403" LastActivityDate="2019-11-15T19:27:38.403" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15650" PostTypeId="1" CreationDate="2019-11-15T19:48:13.903" Score="2" ViewCount="86" Body="&lt;p&gt;Assume a computer (Raspberry Pi, Mac, etc.) is used to connect to a radio (HF transceiver, etc.) via audio cable(s), USB port, or GPIO, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What contemporary computer DSP/digital modes, of those popular and useful for low signal-to-noise ratio channels, can be used to communicate via just an ASCII text terminal for the computer? (e.g. no OpenGL GUI, Windows, VNC, RDP, CocoaTouch, no PPP/SLIP, etc., required)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, there exists a &lt;a href=&quot;https://github.com/JamesP6000/WsprryPi&quot; rel=&quot;nofollow noreferrer&quot;&gt;utility&lt;/a&gt; for the Raspberry Pi that allows transmitting WSPR, controlled from either a serial port connection or an ssh terminal command-line.  Any others?  Any receivers?  Any FT or JT or similar modes suitable for a full text-terminal-only QSO?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added for completeness: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do any of the recent modern software digital modes have existing specifications sufficient for implementation of the mode (e.g. writing DSP code rather than acquiring a &quot;product&quot;), and as part of the documentation, indicate how a QSO can be completely accomplished using just a terminal console (e.g. serial port connected dumb terminal)?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-11-16T18:56:58.747" LastActivityDate="2019-11-16T18:56:58.747" Title="What contemporary digital modes do not require a GUI?" Tags="&lt;digital-modes&gt;&lt;computer-control&gt;" AnswerCount="2" CommentCount="9" ClosedDate="2019-11-19T23:20:29.300" ContentLicense="CC BY-SA 4.0" />
  <row Id="15651" PostTypeId="2" ParentId="15650" CreationDate="2019-11-15T20:03:14.350" Score="0" Body="&lt;p&gt;Here's one example:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;&lt;a href=&quot;https://www.nue-psk.com/doc/NUE-PSK(DCC%202007).pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;NUE-PSK&lt;/a&gt; is a standalone, battery-operated digital modem using a&#xA;  Microchip dsPIC microcontroller. The project includes a character&#xA;  display for transmit and receive text data, and a graphic display&#xA;  showing band spectrum and tuning indicator. Using GPL open source&#xA;  software, the modem can be homebrewed for less than $60 parts cost.&#xA;  When coupled with an SSB-capable transceiver or with a popular PSK-xx&#xA;  transceiver board from Small Wonder Labs, you too can have an&#xA;  effective portable PSK31 station.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Note that the &quot;graphic display&quot; is another dot-matrix unit, like the multi-line text display.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4hfZJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4hfZJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-11-15T20:03:14.350" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15652" PostTypeId="2" ParentId="15650" CreationDate="2019-11-16T00:39:54.867" Score="3" Body="&lt;p&gt;You're confusing the transceiver implementation with mode as is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every single mode, as long as it's not used to transported to transport graphics, can be operated without a GUI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether or not an implementation without a GUI exists is a different question, but honestly, coming from a world that's not Windows, this is basically the standard – be it FreeDV, WSPR, JT65... all these modes have libraries implementing them with which you can interact programmatically (typically: C bindings, although the original WSPR code is FORTRAN, IIRC), and thus especially with a shell.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-11-16T00:39:54.867" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15653" PostTypeId="2" ParentId="15164" CreationDate="2019-11-16T07:29:44.570" Score="1" Body="&lt;p&gt;I am using firenet.aprs2.net and euro.aprs2.net for APRS-IS data.&#xA;If you need to fetch packets you have to connect to a server on a specific port.&#xA;Usually port 14580 is the one to use. Once a connection is established you are&#xA;supposed to authorize yourself using your callsign and password. Password is&#xA;a hash algorithm based on your callsign.&#xA;Here is an example of how to request packets from a APRS-IS server:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;user {your_callsign} pass {password_hash} vers {your_software_name} filter r/{latitude}/{longitude}/{range}\n&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;for example: your GPS location is 50.000N by 20.000E and you want to request packets within 200km range, use the following packet filter:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;... filter /r/50.000/20.000/200&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Please bear in mind that you need to add LF (&quot;\n&quot;) char to the end of your request.&#xA;If you need more details please contact me via my website &lt;a href=&quot;http://www.so6agj.pl&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.so6agj.pl&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;" OwnerUserId="11289" LastActivityDate="2019-11-16T07:29:44.570" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15654" PostTypeId="1" CreationDate="2019-11-16T14:54:06.423" Score="3" ViewCount="236" Body="&lt;p&gt;In an earlier question, there seemed to be some surprise when I (indirectly) asked about radio modes accessible to a blind operator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First question: So how do blind hams operate?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I were to be blind-folded, I could not operate any of my radios, HF or VHF, as I could not even tell if the rig was tuned to a proper legal frequency, as all the radio info is only output via LEDs or LCD displays.  I can use a few iPhone apps blindfolded (I've actually written a couple iOS apps for just that use case); the macOS command-line Terminal is usable via VoiceOver; but all of my Mac and Linux SDR apps (and thus digital modes) would be completely unusable, AFAIK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second question: If one were to design radios or SDR applications or digital modes or an operating station targeted for vision impaired amateur radio operators, what would be a good set of requirements to optimize for that use case?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance: perhaps voice (or Morse Code?) readout for all &quot;front panel&quot; information displays, and some form of feedback for all radio control settings; connector ports that could all be identified by touch. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any other necessary or beneficial requirements?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="8717" LastEditDate="2020-01-29T21:33:35.213" LastActivityDate="2020-01-29T21:33:35.213" Title="How do blind hams operate?" Tags="&lt;software&gt;&lt;equipment-operation&gt;&lt;software-development&gt;&lt;disability&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15655" PostTypeId="2" ParentId="15654" CreationDate="2019-11-16T17:03:25.133" Score="3" Body="&lt;p&gt;I'll answer the first part of your question, Ronald.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I once witnessed a blind ham (WD8PIC) operate. His solid-state transceiver had a speech synthesizer that audibly spoke the frequency when the front-panel SPEECH button was pressed. What is more, he had everything on the front and back panels memorized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It was simply amazing how much he was able to do for himself. I built him a custom crystal calibrator, and handed him the power plug. He had that plugged in and connected faster than I could. It did not have Braille on the rotary selector switch, but he quickly memorized its different positions before I left.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many blind hams are helped to erect antennas and set up their station by other hams that can see, and he was no exception. There are also automatic antenna tuners, either built-in or external.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Although he lost his sight at an early age, he attended a school for the blind. They taught him how to do many things for himself.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-11-16T17:03:25.133" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15656" PostTypeId="1" CreationDate="2019-11-16T23:24:28.717" Score="3" ViewCount="269" Body="&lt;p&gt;The ferrite rod is a reasonably effective receiving antenna for LW, MW, and lower HF spectrum. It is well known that a ferrite rod is much more effective than an air cored coil of the same dimensions. An array of ferrite rods would receive more power if tuned and phased properly. If all the rods were bundled together would they act as one large diameter rod? If the rods were spaced many diameters apart they would be independent. How far apart is reasonable? Would a spaced array be better than bundled rods due to a bigger capture area?&lt;/p&gt;&#xA;" OwnerUserId="6095" LastEditorUserId="10859" LastEditDate="2020-04-29T00:50:16.673" LastActivityDate="2020-04-29T00:50:16.673" Title="Ferrite Rod Antenna Array?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15658" PostTypeId="1" AcceptedAnswerId="15669" CreationDate="2019-11-17T18:58:58.470" Score="0" ViewCount="140" Body="&lt;p&gt;I am building an out building ham shack. I am planning to install an 8 foot ground rod for the antenna. Does the radio require an additional ground to the rod as well or do I need to install a lightning arrestor between the radio and the antenna coax?&lt;/p&gt;&#xA;" OwnerUserId="15980" LastEditorUserId="873" LastEditDate="2019-11-18T06:50:44.177" LastActivityDate="2019-11-19T16:36:55.810" Title="Is a lightning arrestor required with a ground rod?" Tags="&lt;grounding&gt;&lt;lightning&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15659" PostTypeId="1" AcceptedAnswerId="15660" CreationDate="2019-11-18T04:20:17.897" Score="3" ViewCount="385" Body="&lt;p&gt;I understand that an antenna is resonant at the frequency where the capacitive and inductive reactance cancel out to 0. Only the resistive impedance remains at resonance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this mean that the impedance is lowest at the frequency where only the resistive impedance remains? Can we find the resonant frequency of an antenna by looking for the lowest point on it's impedance curve?&lt;/p&gt;&#xA;" OwnerUserId="15981" LastActivityDate="2019-11-19T00:45:02.607" Title="Is an antenna resonant at the frequency of lowest impedance?" Tags="&lt;antenna-theory&gt;&lt;impedance&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15660" PostTypeId="2" ParentId="15659" CreationDate="2019-11-18T07:53:42.430" Score="3" Body="&lt;p&gt;Marcin, as you have alluded to, an antenna is resonant when there is no reactance present in the impedance seen at the feed point for the frequency you are using. There is no reactance because at resonance the antenna voltage and current are in phase, not because the inductive and capacitive reactances cancel out. When the antenna is not resonant, the voltage and current are not in phase which results in the impedance containing some reactance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming you are not changing the antenna or it's feed point and you are changing the frequency, the frequency at which the impedance has the lowest resistance (ignoring if there is any reactance present) does not however always match up with resonance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The value of the resistive or real part of the impedance does not determine whether or not the antenna is resonant. At resonance there is no reactance, not least resistance.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-11-19T00:45:02.607" LastActivityDate="2019-11-19T00:45:02.607" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15661" PostTypeId="2" ParentId="15659" CreationDate="2019-11-18T10:58:03.097" Score="4" Body="&lt;p&gt;A point to remember here is: A transmit antenna does not need to be &lt;strong&gt;self&lt;/strong&gt;-resonant at the operating frequency to be a very efficient radiator of e-m energy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A matching network at the antenna input terminals may be used to match the impedance of that antenna (including its non-zero reactive term) to the impedance of the transmission line connected there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such antenna &lt;em&gt;systems&lt;/em&gt; are commonly used by medium-wave AM broadcast stations, and may radiate &gt;95% of the r-f energy at the input of their matching network(s).&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-11-18T10:58:03.097" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15663" PostTypeId="2" ParentId="15654" CreationDate="2019-11-18T14:49:26.673" Score="2" Body="&lt;p&gt;There are accessories for some radios that provide a speech capability. Here is a link to a web site, HamRadioAndVision, that has some information. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.hamradioandvision.com/accessible-transceivers-vision/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.hamradioandvision.com/accessible-transceivers-vision/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also keep in mind that a person can be legally blind but still have some sight. I believe that a person with 20/100 vision is considered to be blind. 20/100 sight means they see at 20 feet the same amount of detail that someone with normal vision sees at 100 feet. Often with magnify aids they can read dials and displays. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also by using remote control software on a PC with a large monitor they can more easily see.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I cannot find a link, but I remember reading about some small QRP homebrew or kit CW radios that announced the frequency with Morse code as they were tuned.  &lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="9425" LastEditDate="2019-11-19T18:44:39.370" LastActivityDate="2019-11-19T18:44:39.370" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15664" PostTypeId="2" ParentId="15020" CreationDate="2019-11-19T00:33:35.107" Score="0" Body="&lt;p&gt;I think that Brian's answer is very helpful. In this case the tapped inductors do the matching, and the inductor resonates the circuit to remove the net inductance. (The same thing could be done with tapped capacitors and an inductor replacing the capacitor.) This does not assume or require any flux linkage between L1 and L2. If L1 and L2 were windings of an ideal transformer, with no flux leakage , then I think that you would not need the capacitor. I suspect that the reality depends upon how you wind the inductor. The amount of mutual inductance would I guess give a circuit equivalent to that given by Brian, but L1 and L2 would be modified by the mutual inductance. &lt;/p&gt;&#xA;" OwnerUserId="15986" LastActivityDate="2019-11-19T00:33:35.107" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15665" PostTypeId="2" ParentId="1388" CreationDate="2019-11-19T03:31:54.957" Score="0" Body="&lt;p&gt;Skyler, don't believe the myths which over stress and over complicate the importance of the type of metal used for the elements of a yagi antenna for instance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For all the common types of suitable metal available with which to make an antenna, excluding for very high powered transmitters, in reality it makes little if no noticeable difference which metal you use, especially below 30 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, it makes sense that the less resistance the better, but the small differences in resistance between metals never seems to affect the operation of an antenna in any significant way if at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For receive, i would argue that due to the extremely low currents involved, within reason, the metal type makes no difference whatsoever. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Excluding the effects of environmental conditions, for fixed installations, aluminium is no doubt the best thing to use in just about all cases and you can ignore it's resistance.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-11-19T11:14:28.273" LastActivityDate="2019-11-19T11:14:28.273" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15666" PostTypeId="1" AcceptedAnswerId="15668" CreationDate="2019-11-19T03:37:22.933" Score="4" ViewCount="310" Body="&lt;p&gt;I'm populating a CSV file to import into &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Download&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP&lt;/a&gt;. In the &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Documentation&quot; rel=&quot;nofollow noreferrer&quot;&gt;documentation&lt;/a&gt;, there's a list of &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/MemoryEditorColumns&quot; rel=&quot;nofollow noreferrer&quot;&gt;CSV columns&lt;/a&gt;. However, that list doesn't cover URCALL, RPT1CALL, and RPT2CALL. Can anyone tell me what those columns are for and how they're used in radios?&lt;/p&gt;&#xA;" OwnerUserId="5820" LastEditorUserId="76" LastEditDate="2019-11-19T03:50:35.490" LastActivityDate="2019-11-19T14:25:51.957" Title="What are the columns URCALL, RPT1CALL, and RPT2CALL in CHIRP?" Tags="&lt;radio-programming&gt;&lt;chirp&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15667" PostTypeId="2" ParentId="1710" CreationDate="2019-11-19T12:33:17.923" Score="0" Body="&lt;p&gt;While it is true that you do not need to have a repeater coordinated with one of the local repeater coordinators, they exist to minimize interference with others.  Think of them as a traffic cop at an intersection with a signal malfunctioning.&#xA;I do believe there are shared frequency pairs for testing and low power operation.  I can not remember the pairings.&#xA;I'm going through the same process myself for 70cm.&lt;/p&gt;&#xA;" OwnerUserId="15988" LastActivityDate="2019-11-19T12:33:17.923" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15668" PostTypeId="2" ParentId="15666" CreationDate="2019-11-19T14:25:51.957" Score="5" Body="&lt;p&gt;&quot;MYCALL&quot;, &quot;URCALL&quot;, &quot;RPT1CALL&quot;, and &quot;RPT2CALL&quot; are used to program D-STAR channels in D-STAR-capable radios.  Those columns should be left blank for analog FM channels.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;MYCALL is your own call sign, eight characters maximum; &quot;/&quot; and suffixes are allowed, as long as everything fits in eight characters.&lt;/li&gt;&#xA;&lt;li&gt;URCALL is ostensibly for the call sign of the station you're trying to call, or &quot;CQCQCQ&quot; for calling any station or to talk on a repeater; URCALL can also be used to hold routing information or linking commands.&lt;/li&gt;&#xA;&lt;li&gt;RPT1 (&quot;RPT1CALL&quot; in CHIRP) should be set to the local repeater and module that you're trying to access.  (The setting doesn't matter for D-STAR simplex.)&lt;/li&gt;&#xA;&lt;li&gt;RPT2 (&quot;RPT2CALL&quot; in CHIRP) designates where you want your signal to be routed on your local repeater; normally RPT2 is set to the call sign of the local repeater, followed by &quot;G&quot;.  (The setting doesn't matter for D-STAR simplex.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Exactly how to use D-STAR is beyond the scope of a single answer.  There's an article &lt;a href=&quot;http://www.roblocher.com/whitepapers/dstar.html&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt; that goes over the basics.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-11-19T14:25:51.957" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15669" PostTypeId="2" ParentId="15658" CreationDate="2019-11-19T16:36:55.810" Score="-1" Body="&lt;p&gt;I will explain lightning before giving my answer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lighting takes the path of least resistance, it dont matter whats it is. Lighting is a hammer, everything is a nail. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your antenna is prime real estate for its path. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A. Its metal and it covers a good deal of surface area. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;B. Its the quickest path to the ground. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my answer is this: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes install the lighting arrestor but at the same time protect your equipment with additional measures like lighting rods that provides a straight forward path to the ground thats not your atenna It is better to be safe than sorry. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because, lighting can hit that antenna and fry &lt;span class=&quot;math-container&quot;&gt;$$$$&lt;/span&gt;$ worth of equipment. &lt;/p&gt;&#xA;" OwnerUserId="12988" LastActivityDate="2019-11-19T16:36:55.810" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15670" PostTypeId="2" ParentId="822" CreationDate="2019-11-19T23:40:41.860" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What topics should the holder of a Technician, General, or Extra license have knowledge of? What would be the content of the question pool if test-takers had infinite patience, and could be tested on every fact rather than a sampling?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I recently passed my extra exam. From my perspective the following are common on all exams:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Knowledge of best practices&lt;/li&gt;&#xA;&lt;li&gt;Knowledge of laws regarding ham radio&lt;/li&gt;&#xA;&lt;li&gt;Some very basic knowledge on VECs/VEs&lt;/li&gt;&#xA;&lt;li&gt;Electrical safety (in particular safety with AC)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;You can quite literally pass each exam not knowing any math at all. Will you be effective? Yes, probably. The amount of work you have to do today to get on the air is significantly less than when ham radio first started. Should you learn the math? Yeah, if you like math or are interested in electronics or why things work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Specifically For the Technician&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has been a while since I've seen this exam but from what I remember there was a lot of emphasis on basic electronics (capacitors and resistors, ohms law, I think there was some mention of KVL/KCL related to this but nothing on the test). There were some soft-pitched questions on AC voltage, RMS, etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The vast majority of the technician was just regurgitating rules and regulations for each question. Perfect cramming material. I wouldn't feel bad about cramming for this exam. It's very simple.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Specifically for the General&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same requirements for the technician with some added electrical engineering stuff. I really only remember having to actually study the antenna portion and some of the line matching, SWR, etc stuff. Everything else was slightly more questions on rules and regulations (in particular bands you can and can't operate in) and some questions on ham equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Specifically for the Extra&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This exam was significantly harder, and required more dedicated study. About half the questions are crammable (basically all the rules and regs from technician and general, what acronyms are, etc) but the rest was basically uncrammable and required some significant study.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Basic reactance/impedence/frequency calculations&lt;/li&gt;&#xA;&lt;li&gt;Polar coordinates, plotting reactances and resistances on a graph&lt;/li&gt;&#xA;&lt;li&gt;Phase angle/Phasor diagram stuff. Trigonometry.&lt;/li&gt;&#xA;&lt;li&gt;Knowing some deeper knowledge on antennas including ground reflections, etc&lt;/li&gt;&#xA;&lt;li&gt;Knowing more about what protocols are useful for various kinds of transmission types&lt;/li&gt;&#xA;&lt;li&gt;Knowing current/voltage relationships through inductors&lt;/li&gt;&#xA;&lt;li&gt;SWR matching, impedence matching&lt;/li&gt;&#xA;&lt;li&gt;Atmospheric conditions, knowing why radio waves are reflected/bent/amplified in various conditions (more or less really, really basic electromagnetism)&lt;/li&gt;&#xA;&lt;li&gt;Op-Amp calculations, how they work, etc&lt;/li&gt;&#xA;&lt;li&gt;Some basic stuff on microwave radio (nothing complicated, but generally how it works and what is special about the circuits for microwave)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;There's more, but that's all that I can remember having to really study for. By the end of the extra you should have a decent grasp on basic DC and AC electronics stuff as it relates to radios. You should also know all of the major rules and regulations for ham radio, operating overseas, and other stuff related to that.  &lt;/p&gt;&#xA;" OwnerUserId="15957" LastEditorUserId="15957" LastEditDate="2019-11-20T20:48:47.040" LastActivityDate="2019-11-20T20:48:47.040" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15671" PostTypeId="2" ParentId="1710" CreationDate="2019-11-20T06:42:38.353" Score="0" Body="&lt;p&gt;There is no need to request a coordinated pair when using dead or quiet frequencies in 432.100 to 433.00 and 442.00 to 450.00 - huge sub-bands to choose within without causing QRM with a 15KHz bandwidth. Make sure no repeater use is taking place for continuous 20 minutes on the output freq (per ARRL Operation Manual) over a sensible sample of time frames. Ensure that none of the NON-Amateur first priority allocations (e.g. Radiolocation) are QRL on the freq. Check a current repeater database to avoid frequencies already coordinated in the coverage area.  Before repeater access is granted, do a test phase where the repeater automatically makes itself heard every 15 minutes at low power at first (25w) then increased in steps to 100w (keeping it local to the district). Announce with &quot;This is WA0XXX the Central High School official student party line repeater, yo, in test mode currently. PL tone is 131.8, and we're all about the positivity on input! Control Operator or Station Licensee can be reached or left a message at (xxx)xxx-xxxx&quot;. Since you don't want the repeater used by non-students and non-faculty, the PL tone could be left out, to at least delay LID intrusion. Remaining uncoordinated and out of the database will assist in this regard. However once established, then is a good time to become coordinated.&lt;/p&gt;&#xA;" OwnerUserId="15913" LastEditorUserId="15913" LastEditDate="2019-11-20T07:00:31.773" LastActivityDate="2019-11-20T07:00:31.773" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15672" PostTypeId="2" ParentId="1807" CreationDate="2019-11-20T07:20:27.703" Score="0" Body="&lt;p&gt;This just happened to me with a new UV-82HP purchased from Btech through Amazon. Btech support will send you a youtube link (&lt;a href=&quot;https://youtu.be/CrG0El1KkIM&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://youtu.be/CrG0El1KkIM&lt;/a&gt;) with a demonstration on how to program. Follow it exactly (assuming you have an HP).  When Btech became a problem, I took it to Amazon support linked in the Help side menu choice. I'd avoid CHirp for the time being. The FT-2900 issue (rendering radios inoperative) and my UV-82's blowup scare me.&lt;/p&gt;&#xA;" OwnerUserId="15913" LastEditorUserId="15913" LastEditDate="2019-11-20T07:31:04.137" LastActivityDate="2019-11-20T07:31:04.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15675" PostTypeId="1" CreationDate="2019-11-20T20:58:12.230" Score="0" ViewCount="66" Body="&lt;p&gt;I'm looking for a circuit topology that has unity gain, a 50 Ohm resistive input impedance, a 50 Ohm resistive output impedance, and here is the kicker, at least 60 dBm OIP3 over a 2 - 30 MHz HF bandwidth. I have tried a VMOS FET in a common gate configuration, and by adjusting the drain current to give a Gm of 20 mmhos, I get my 50 Ohm input impedance, but I only see 47 dBm of IP3. This circuit will terminate a Norton HF LNA preamp. Thanks for any suggestions - W6DSR&lt;/p&gt;&#xA;" OwnerUserId="15991" LastActivityDate="2019-11-20T20:58:12.230" Title="50 Ohm Active Termination" Tags="&lt;hf&gt;&lt;lna&gt;" AnswerCount="0" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15676" PostTypeId="2" ParentId="12073" CreationDate="2019-11-21T09:26:54.343" Score="-1" Body="&lt;p&gt;data cable not required - it actually works very well with with microphone to loudspeaker. I actually use my iPhone earbuds, connect them to the radio and hang them on the screen of the laptop (my laptop has the microphone near the middle of the top of the screen). Radio mike I just put on the laptop. Radio in VOX mode. Works like a charm. (Just remember to switch VOX off when you finish or else all your later conversations with your wife may go on air ...)&lt;/p&gt;&#xA;" OwnerUserId="15993" LastActivityDate="2019-11-21T09:26:54.343" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15678" PostTypeId="2" ParentId="15598" CreationDate="2019-11-21T20:04:43.507" Score="2" Body="&lt;p&gt;First - your &quot;2m dipole&quot; antenna and &quot;quarter wave&quot; antenna are almost the same thing. A &quot;quarter-wave&quot; antenna is really just a &quot;dipole antenna&quot; with the bottom/ground element bent at an angle - usually 90 degrees.  This might also be referred to as a &quot;ground plane&quot; antenna.  If you took this &quot;bent&quot; antenna, and straightened it out, it would be a &quot;dipole antenna&quot;. =)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second - both a &quot;2m dipole&quot; and &quot;quater wave&quot; (or ground plane) antenna are, indeed, omnidirectional.  Your high altitude balloon (HAB) payload should have absolutely no trouble being heard on APRS once it reaches about 300-500 feet above the local terrain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My suggestion for which antenna to use on your HAB is to use a simple wire dipole antenna.  For 2 meter APRS on 144.390 MHz this would be two, 19-1/2 inch pieces of wire (AWG 28 enameled copper wire works fine), with the driven element (the one connected to the radio's RF output/connector center pin) pointing DOWN towards the earth, and the other element (the one connected to the radio's ground) pointing UP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The element hanging down (driven element) does not need any support - gravity will do the trick.  You can use some tape to secure the element pointing UP to the rigging lines that attach the payload to the parachute/balloon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You want the DRIVEN element pointing DOWN so that when the balloon pops, all the rigging lines between the payload and the parachute/balloon don't tangle up and bend the DRIVEN element.  Don't be concerned about the tangling or twisting/breaking of the ground wire for the antenna - the radio signal will still get out!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pointing the DRIVEN element DOWN from the payload gives your payload a much better chance of continuing to transmit data during the descent - especially if your HAB traverses the thinner portions of the atmosphere (e.g. anything above 40,000 feet), where the drag effects of the parachute are not yet significant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can afford the payload weight, you may even chose to use a 2 meter &quot;rubber duckie&quot; antenna, coupled with a single 19-1/2&quot; AWG 28 ground wire.  My colleague and I have launched multiple HAB APRS payloads using this configuration, and have had no trouble being heard on 2m APRS using only 1/4 watt!  Again - if you can afford the weight, using a &quot;rubber duckie&quot; may be a good compromise between potentially losing the antenna due to tangling with the rigging (or impact with the ground), and good signal reception at APRS distances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the &quot;rubber duckie&quot; and a wire ground element, my colleague and I were able to directly receive our 1/4 watt 2m APRS signal from a distance of over 125 miles, and at no time during our HAB's 500 mile journey was it ever out of range of the APRS network.  The website aprs.fi reported that our payload could be heard out to a distance of 250 miles (a 500 mile diameter ground circle!) when we were transmitting 2m APRS from 60,000+ feet! (Don't forget to change your APRS path to WIDE2-1 while at altitude!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, we chose to implement two-way commanding over APRS (using APRS directed messages) between the ground and our balloon, and the APRS network faithfully relayed all of our commands/messages to the payload throughout its flight.  The payload had no problems receiving our commands over both the wire dipole and the &quot;rubber duckie&quot; antennas.  So omnidirectional / signal strength issues were not of concern to us.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck!&lt;/p&gt;&#xA;" OwnerUserId="15999" LastActivityDate="2019-11-21T20:04:43.507" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15679" PostTypeId="2" ParentId="15568" CreationDate="2019-11-21T20:40:34.297" Score="0" Body="&lt;p&gt;One thing you could try is to add a &quot;shorting stub&quot; tuned to 103.7 MHz to the antenna of your receiver.  The point of this shorting stub is to &quot;short out&quot; (attenuate) the 103.7 MHz signal, and leave the rest of the frequencies (somewhat) untouched.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This configuration works best when you use an external antenna with your radio.  If your radio only uses an internal antenna (such as a collapsible metal antenna), then this procedure may not work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For now, I'll assume you can use an external antenna, and that your radio has two screw lugs for attaching one to the radio.  We will want to connect this &quot;shorting stub&quot; directly across these two terminals for best results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A piece of 300 ohm twin-lead, which you can probably still find at your local hardware store, should work best to make the shorting stub.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One end of this twin-lead will need to be attached to the radio (antenna and ground lugs).  The other end of the twin-lead will be shorted together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Start by shorting together the free end of the twin-lead.  (Just strip and twist the two sides of the twin-lead together.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Measure up from this now-shorted end exactly 3 foot 10 and 11/16 inches.  Mark this point (don't cut it yet!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now figure out how much extra wire you will need to attach this stub to the radio's antenna and ground screw lugs.  It is very important that you do your best to minimize the &quot;extra&quot; or &quot;slack&quot; here.  Use the least &quot;extra&quot; wire as you can.  Add the smallest practical amount of wire you need to connect to these lugs as you can to the stub you have made so far.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you make a mistake, twin-lead is cheap, so start over.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you attach this stub to your radio, move your FM antenna around to see what position works best to null out the 103.7 MHz signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a strong possibility that your stub will reduce other signals on the FM band, but you might be surprised to find that you have at least some that will still work for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good Luck!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Edited to correct length. I used &quot;low-pass&quot; formula, needed &quot;fundamental&quot; formula: (492 / f(MHz)) * 0.82 - Where 0.82 = Velocity factor of 300 ohm twin-lead]&lt;/p&gt;&#xA;" OwnerUserId="15999" LastEditorUserId="15999" LastEditDate="2019-11-21T21:52:42.960" LastActivityDate="2019-11-21T21:52:42.960" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15680" PostTypeId="2" ParentId="15459" CreationDate="2019-11-21T21:00:09.053" Score="0" Body="&lt;p&gt;Something like this comes to mind - &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.learningaboutelectronics.com/Articles/7414-schmitt-trigger-oscillator-circuit.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.learningaboutelectronics.com/Articles/7414-schmitt-trigger-oscillator-circuit.php&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Attach your antenna to pin 2, and there you go!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XLAo0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XLAo0.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15999" LastActivityDate="2019-11-21T21:00:09.053" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15681" PostTypeId="2" ParentId="15459" CreationDate="2019-11-22T04:32:00.553" Score="0" Body="&lt;p&gt;Mordecai, your question has two parts which can be answered separately.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Can you make a signal transmitter without a decoder ? &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The answer is yes. Transmitters and decoders are two separate things and they don't necessarily have to be used together. A radio transmitter for example is a high frequency oscillator which sends out a signal into the air using an antenna. A decoder can be used to un-encode or decode a radio signal that was previously encoded by an encoder before being sent by a transmitter.&lt;/p&gt;&#xA;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;Can you use a 555 to make a 1-10 kHz transmitter ? &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Your idea with the 555 is on the right track except for two things. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, a radio signal should start off as a sine wave and a 555 will probably output a square wave which isn't much use to anyone. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, a radio signal is usually a much higher frequency than 1 - 10 kHz. For a radio signal to work well, it needs to be far above 10 kHz. Lets say at least 500 kHz or higher is much better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to make a simple transmitter with 1 transistor and a few other parts, have a look at the link below. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.buildcircuit.com/simple-steps-for-making-fm-transmitter/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.buildcircuit.com/simple-steps-for-making-fm-transmitter/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It shows you how to make a 100 MHz transmitter, which doesn't have a decoder but it does use a process called modulation which superimposes the audio signal from the microphone onto the 100 MHz radio signal. This circuit will work very well and you will learn a lot. You can receive it on your standard FM radio.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-11-22T06:54:30.287" LastActivityDate="2019-11-22T06:54:30.287" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15682" PostTypeId="1" CreationDate="2019-11-22T10:13:25.163" Score="2" ViewCount="192" Body="&lt;p&gt;I am an &lt;strong&gt;ELECTRONICS&lt;/strong&gt; final year student and I am working on a project, &quot;Full Duplex Radio On a Single Frequency&quot;. So is it possible to design such a project. If so then give me the idea about it, how can i design such a circuit, what do i need for it (mircrontroller, raspberry pi etc)? I have some idea about it but i don't know how to implement it.&lt;/p&gt;&#xA;" OwnerUserId="16001" LastActivityDate="2019-11-27T19:53:43.770" Title="Full Duplex Radio Communication On a Single Frequency" Tags="&lt;frequency&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15683" PostTypeId="2" ParentId="15682" CreationDate="2019-11-22T12:35:33.907" Score="2" Body="&lt;p&gt;If you have a single frequency with a single antenna, the best you can do is half duplex on the RF side -- you can't transmit and receive at the same time on the same frequency.   If you have two antennas sufficiently separated (on both ends), you might be able to use signal diversity and geometry to separate signals; this would work better on higher frequencies (&gt;5GHz?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, an easier way to do this would be to do timed half duplex (the two ends take turns transmitting), and digitize, compress, and packetize audio so that the audio is full duplex, even though the RF is only half duplex.  TDMA?&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-11-22T12:35:33.907" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15684" PostTypeId="1" AcceptedAnswerId="15685" CreationDate="2019-11-23T11:36:54.410" Score="0" ViewCount="94" Body="&lt;p&gt;in GRC for this source block ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/j6StC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/j6StC.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8811" LastActivityDate="2019-11-23T21:41:12.497" Title="what is the center frequency" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15685" PostTypeId="2" ParentId="15684" CreationDate="2019-11-23T16:34:48.133" Score="1" Body="&lt;p&gt;The &quot;Frequency&quot; is the center frequency of the signal the block produces.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;Freq. Corr.&quot; is a value in &quot;parts per million&quot; that the frequency is multiplied by, to correct for tuning inaccuracy separately from specifying the intended frequency. That is, the frequency sent to the hardware is &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\text{Frequency} \times \left(1 + \frac{\text{FreqCorr}}{1000000}\right)$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to adjust this correction is to use a program like Gqrx which lets you set it and see the effects — find a continuous transmission of stable known frequency (such as NOAA weather radio in the US) and adjust the correction value until the displayed peak lines up with the number.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-11-23T21:41:12.497" LastActivityDate="2019-11-23T21:41:12.497" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15686" PostTypeId="1" CreationDate="2019-11-24T19:40:32.043" Score="0" ViewCount="149" Body="&lt;p&gt;For older receivers with a fixed (crystal?) audio filter for CW, what is the usual center frequency of the audio bandpass of the filter?  Or cut-off frequency for low-pass CW filters?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For newer receivers (and external audio DSP boxes) with configurable narrow audio filters for CW, what is the usual default or factory configured center frequency for the narrowest audio filter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do experienced operators more commonly increase or decrease the narrow CW filter factory frequency setting?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I’m especially interested in old radios with fixed frequency (crystal or ???) audio CW filters.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-11-26T04:43:29.367" LastActivityDate="2019-11-26T04:43:29.367" Title="What is the most common CW audio filter center frequency?" Tags="&lt;cw&gt;&lt;filter&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15687" PostTypeId="1" CreationDate="2019-11-24T21:06:36.567" Score="2" ViewCount="1518" Body="&lt;p&gt;Is there considered an ideal / optimum length for a doublet for use on 160-10 meters when fed with open-wire feedline and a balanced tuner in the shack? &lt;/p&gt;&#xA;" OwnerUserId="16010" LastEditorUserId="16010" LastEditDate="2019-11-25T19:16:37.310" LastActivityDate="2019-11-25T22:17:39.323" Title="Ideal Doublet Size 160-10 Meters" Tags="&lt;antenna-system&gt;&lt;antenna-tuner&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15688" PostTypeId="2" ParentId="15489" CreationDate="2019-11-25T02:02:48.677" Score="1" Body="&lt;p&gt;As the circumference approaches 1/4 wavelength, it becomes increasingly difficult to tune it, as it is no longer a small loop and starts taking on properties of a a resonant loop, which is tuned differently and has a different radiation pattern.  The primary principle of a small loop is that it is small enough that the RF in the loop is nearly all the same phase.  As you approach 1/4wl, it will be 90 degrees out of phase by the time it goes around the loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A resonant monopole is 1/4wl long.  A typical (resonant) open loop (like a halo) is 1/2wl, and a resonant closed loop is 1wl or more.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2019-11-25T02:09:23.580" LastActivityDate="2019-11-25T02:09:23.580" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15689" PostTypeId="2" ParentId="3518" CreationDate="2019-11-25T13:50:46.270" Score="2" Body="&lt;p&gt;The region around the antenna where metallic objects will have the most impact is within the &quot;near field&quot;.  This distance is directly proportional to wavelength, and varies depending on if the antenna is electrically short or long.  The energy reflections in the near field will have a direct impact on the source, impacting the impedance seen and the loss experienced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is a good description of Near Field vs. Far Field here:  &lt;a href=&quot;https://en.wikipedia.org/wiki/Near_and_far_field&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Near_and_far_field&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16010" LastActivityDate="2019-11-25T13:50:46.270" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15690" PostTypeId="2" ParentId="15489" CreationDate="2019-11-25T15:41:12.683" Score="3" Body="&lt;p&gt;&lt;a href=&quot;https://owenduffy.net/blog/?p=1693&quot; rel=&quot;nofollow noreferrer&quot;&gt;VK1OD&lt;/a&gt; compared several small transmitting loop antenna calculators. The author concludes that there are &lt;a href=&quot;https://owenduffy.net/blog/?p=1682&quot; rel=&quot;nofollow noreferrer&quot;&gt;serious errors in the ARRL analysis&lt;/a&gt; which have made their way into some (most?) of these calculators. He buttresses these claims with a detailed &lt;a href=&quot;https://owenduffy.net/blog/?p=10648&quot; rel=&quot;nofollow noreferrer&quot;&gt;NEC model&lt;/a&gt; to estimate the structure, capacitor and ground losses which are so crucial to proper calculation of Q, efficiency, etc. He goes on to &lt;a href=&quot;https://owenduffy.net/blog/?p=14227#more-14227&quot; rel=&quot;nofollow noreferrer&quot;&gt;compare his modeling results with measurements made on a commercial antenna&lt;/a&gt;, lending credence to the models. These articles are all worth reading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While it is certainly true that the main lobe moves from &quot;end fire&quot; to &quot;broadside&quot; as one crosses the quarter-wave circumference boundary, evidence of flaws in the theoretical basis for the &quot;calculators&quot; may indicate that it would be worthwhile to re-evaluate the &quot;quarter wave circumference&quot; advice, particularly with respect to efficiency and Q.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-11-25T15:41:12.683" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15691" PostTypeId="2" ParentId="15687" CreationDate="2019-11-25T16:03:14.760" Score="1" Body="&lt;p&gt;While studying this question enroute to writing an article on &quot;A Slightly Off-Center-Fed Diople&quot; in &lt;em&gt;QST&lt;/em&gt; for September 2019, I learned that connecting the feedline to the antenna at a current node will essentially prevent the antenna from taking power at that frequency. Center-fed dipoles experience current nodes when the feedpoint is any even multiple of the frequency on which the length equates to an electrical half-wave. Since you ask for coverage from the 160 meter band and up, here's an 200&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; SWR plot of a 266-ft long center-fed dipole in free space:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sFuEi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sFuEi.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note the SWR dips near odd multiples of the half-wave resonant frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simply moving the feedpoint to 45% from either end doubles the number of SWR dips, indicating more opportunities for successfully coupling energy from the line into the antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qC1mK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qC1mK.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-11-25T16:03:14.760" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15692" PostTypeId="2" ParentId="15687" CreationDate="2019-11-25T16:47:16.937" Score="3" Body="&lt;p&gt;A single antenna that functions over such a wide band will necessarily be less than ideal. Compromises must be made to achieve such wideband performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna will have to be at least big enough for the lowest band, so anything significantly than 259 feet will be quite difficult to get working on 160 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, you especially want to avoid any length where the antenna is an even multiple of half-wavelengths: it's at these lengths that SWR is at a maximum and you'll probably be unable to match the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could plot or calculate these points for every band and pick a length to avoid them, but you will likely find this fails to take into account confounding variables:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;rotation of the feedpoint impedance by the mismatched feedline&lt;/li&gt;&#xA;&lt;li&gt;height above ground&lt;/li&gt;&#xA;&lt;li&gt;surroundings&lt;/li&gt;&#xA;&lt;li&gt;feedline position and common-mode suppression&lt;/li&gt;&#xA;&lt;li&gt;straightness (or lack thereof) of the antenna&lt;/li&gt;&#xA;&lt;li&gt;capabilities and efficiency of your tuner&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You could try modelling your antenna and feedline, and adjusting the length by trial and error. Or you could simply build it and find a good length empirically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind, changing the length by a few inches will be very significant for the higher frequencies, but relatively insignificant for the lower frequencies. So in picking your initial length, getting a reasonable match on the lower bands will be most critical. From there taking it a few inches longer or shorter you can find something that works for the higher bands while keeping the lower bands good enough.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-11-25T16:47:16.937" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15693" PostTypeId="2" ParentId="15489" CreationDate="2019-11-25T20:11:57.043" Score="3" Body="&lt;p&gt;&quot;self-resonance&quot; sounds like not quite the way to describe the issue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is more simply that if the circumference is not very small relative to the wavelength, the antenna is no longer a &lt;em&gt;small&lt;/em&gt; loop. As a rule of thumb, electrical engineers consider anything smaller than &lt;span class=&quot;math-container&quot;&gt;$\lambda/10$&lt;/span&gt; to be &quot;small&quot;. When things are &quot;small&quot; the analysis can be simplified with an approximation: current is equal everywhere in the loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no hard boundary where this approximation suddenly becomes invalid: in only becomes progressively worse. By &lt;span class=&quot;math-container&quot;&gt;$\lambda / 4$&lt;/span&gt; it's certainly no longer a very good approximation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As the loop becomes less &quot;small&quot;, it becomes more like a folded dipole, and thus will have a substantially different feedpoint impedance and radiation pattern than a &quot;small loop&quot;. It's possible to match such an antenna, but calculation of the necessary capacitance is different since the approximation of constant current is no longer valid.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-11-25T20:11:57.043" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15694" PostTypeId="1" AcceptedAnswerId="15696" CreationDate="2019-11-25T20:46:37.663" Score="5" ViewCount="186" Body="&lt;p&gt;There are a lot of videos on YouTube from people who have built high voltage sources and are sending electric arcs from one place to another. Although they have no intention to emit radio waves, they are probably creating a lot of noise. I have known DC motors to be bad just because of arcing across the commutator, and it is not too hard for someone's science project to send foot-long bolts flying through the air. Does the FCC have any regulations limiting that practice?&lt;/p&gt;&#xA;" OwnerUserId="16017" LastActivityDate="2019-11-25T22:28:50.037" Title="Does the FCC care about electrical arcs?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15695" PostTypeId="2" ParentId="15687" CreationDate="2019-11-25T22:17:39.323" Score="0" Body="&lt;p&gt;Make yourself a multiband antenna &lt;strong&gt;with many doublets in parallel&lt;/strong&gt;, fed with just one feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;a href=&quot;https://ham.stackexchange.com/search?q=Fan+dipole&quot;&gt;fan dipole&lt;/a&gt; is very likely a much better choice of multiband antenna for you, for both (1) easy impedance matching &lt;em&gt;and&lt;/em&gt; (2) similar patterns on each band. You can make one with many doublets in parallel, spaced apart and fed with just one feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You won't need open wire line. Contrary to popular myth, LMR-400 (or inexpensive, low-loss 75Ω CATV coax) &lt;em&gt;will actually have significantly less loss than even the best parallel conductor line available&lt;/em&gt;, which Phil Frost nicely explained here (somewhere) a few years ago. For paralleled λ/2 dipoles like this, coax just has lower loss than ladder line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume you asked your question based on commonly available tuners which incorporate a ferrite core balun for feeding balanced line. That type is really difficult (if not impossible) to match a single dipole on all of those bands, since the impedance and complex reactance varies so widely for each band.&#xA;However, if you are determined to use a ladder-line-fed 160m doublet: with the right type of tuner and low-loss open-wire line, you can match a center-fed dipole on any band. But you may have to build a custom balanced tuner yourself (as I did years ago using old junk parts).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, a custom balanced tuner will not change the radiation patterns of your 160m doublet. The higher you go in frequency, the more lobes and nulls you'll have. (That can actually be a good thing, but it depends on where you want to work.)&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-11-25T22:17:39.323" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15696" PostTypeId="2" ParentId="15694" CreationDate="2019-11-25T22:28:50.037" Score="9" Body="&lt;p&gt;Absolutely! &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/part-15&quot; rel=&quot;noreferrer&quot;&gt;FCC Part 15&lt;/a&gt; defines three broad classes of devices:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;em&gt;Intentional radadiator.&lt;/em&gt; A device that intentionally generates and emits radio frequency energy by radiation or induction.&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;Unintentional radiator.&lt;/em&gt; A device that intentionally generates radio frequency energy for use within the device, or that sends radio frequency signals by conduction to associated equipment via connecting wiring, but which is not intended to emit RF energy by radiation or induction.&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;Incidental radiator.&lt;/em&gt; A device that generates radio frequency energy during the course of its operation although the device is not intentionally designed to generate or emit radio frequency energy. Examples of incidental radiators are dc motors, mechanical light switches, etc.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;and a few other definitions that we'll want for later are&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;em&gt;Radio frequency (RF) energy.&lt;/em&gt; Electromagnetic energy at any frequency in the radio spectrum between 9 kHz and 3,000,000 MHz.&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;Harmful interference.&lt;/em&gt; Any emission, radiation or induction that endangers the functioning of a radio navigation service or of other safety services or seriously degrades, obstructs or repeatedly interrupts a radiocommunications service operating in accordance with this chapter.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Although most of the time when we talk about Part 15 we're thinking about unlicensed intentional radiators, or unintentional radiators, incidental radiators are &lt;em&gt;also&lt;/em&gt; regulated. 15.1(a) says&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;This part sets out the regulations under which an intentional, unintentional, or incidental radiator may be operated without an individual license.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;If it makes radio waves between 9kHz and 3THz, intentionally or not, it needs to either follow the rules in Part 15, or be licensed according to the rules in some other Part.&lt;/p&gt;&#xA;&lt;p&gt;So which sections of Part 15 apply to incidental radiators? Well, almost none of them. Most of them are dedicated to specific types of intentional or unintentional radiators. But one section that applies to &lt;em&gt;all&lt;/em&gt; kinds of radiators is section 15.5, &amp;quot;General conditions of operation&amp;quot;, which contains some text that you've probably seen on a label somewhere:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(b) Operation of an intentional, unintentional, or incidental radiator is subject to the conditions that no harmful interference is caused and that interference must be accepted that may be caused by the operation of an authorized radio station, by another intentional or unintentional radiator, by industrial, scientific and medical (ISM) equipment, or by an incidental radiator.&lt;/p&gt;&#xA;&lt;p&gt;(c) The operator of a radio frequency device shall be required to cease operating the device upon notification by a Commission representative that the device is causing harmful interference. Operation shall not resume until the condition causing the harmful interference has been corrected.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;So there are no specific frequency bands, field strength measurements, or other technical standards prescribed (as there are for intentional and unintentional radiators). The conditions for operating an incidental radiator are that you don't cause harmful interference to licensed users (navigation, public safety, broadcast, hams, or anything else), and that upon receiving proper notification that your device is causing interference, you stop using that device until the interference is mitigated.&lt;/p&gt;&#xA;&lt;p&gt;Also relevant is section 15.23, &amp;quot;Home-built devices&amp;quot; which states&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(a) Equipment authorization is not required for devices that are not marketed, are not constructed from a kit, and are built in quantities of five or less for personal use.&lt;/p&gt;&#xA;&lt;p&gt;(b) It is recognized that the individual builder of home-built equipment may not possess the means to perform the measurements for determining compliance with the regulations. In this case, the builder is expected to employ good engineering practices to meet the specified technical standards to the greatest extent practicable. The provisions of §15.5 apply to this equipment.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;which says that if you build it yourself, you're exempt from certification requirements but you're &lt;em&gt;not exempt from following the rules&lt;/em&gt; about interference.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-11-25T22:28:50.037" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15697" PostTypeId="1" CreationDate="2019-11-25T23:03:08.383" Score="-3" ViewCount="147" Body="&lt;p&gt;In amature radio, users can use what is called a phone patch to enable them to use a phone to establish connection to another party or user. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Phones are usually two wire and dont lend themselves to easy connection to the both the receiver and the transmitter so a hub is required. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe this curcuit bellow is the hub, the input connects to the receiver and the output to the transmitter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/LEaF4.jpg&quot; alt=&quot;loss is 3&amp;gt;=4db&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However their is an issue with using this curcuit. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Their is no curcuit protection that keeps oncoming received voice from hitting the transmitter and echoing back out. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I am looking for a better explanation on how this curcuit can work in feild radio  and in facilitating a 2 to 4 atachment and how it can be used to inter connecting the required componets in amature radio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This has been taken from my refrence data for radio engineering. &lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="12988" LastEditDate="2019-12-04T20:27:55.417" LastActivityDate="2019-12-04T20:46:06.727" Title="Carrier telephone system adaptation" Tags="&lt;transceiver&gt;&lt;transformer&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15698" PostTypeId="2" ParentId="15686" CreationDate="2019-11-26T03:49:18.137" Score="1" Body="&lt;p&gt;I have seen default centre frequencies of between 600Hz and 800Hz depending on the manufacturer. These have always been configurable though, sometimes using a knob, and sometimes with a menu setting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not everyone's hearing is the same, and so this should always be configurable. But if I were designing such a system, I would use a default of 700Hz, and allow it to be configurable between 200-2000Hz or so.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-11-26T03:49:18.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15700" PostTypeId="2" ParentId="15682" CreationDate="2019-11-27T02:52:17.437" Score="2" Body="&lt;p&gt;Until the last 20 or so years, this would have been extremely difficult to accomplish in the analog domain.  With advances in processing power applied to DSP however, Spatial Multiplexing is a reality -- that is, the ability to send different signals on the same channel simultaneously.   It is done by having separate, and multiple TX/RX radio chains -- each carrying different information -- separated by some distance causing different &quot;paths&quot; through reflection, refraction, etc of each link... processing is able to distinguish one stream of data from another through characterizing each path-channel, yet they occupy the same frequency.   It is not entirely an intuitive concept.  Lots of math.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of us have already experienced something similar (though not exactly the same) with MIMO (multiple in multiple out) technology that came with the 802.11n standard for WiFi.   Those routers you may have with multiple antennas (like 4, or 6, or 8....) are using a form of MIMO.  This significantly increases channel capacity, and hence throughput on a single frequency -- so you can happily watch Netflix on your laptop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is an example of a project done by Stanford on employing this technique on Full Duplex / Same channel.  Its a bit of a slog to read, but you're a student -- so you might actually like it :)   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://web.stanford.edu/~skatti/pubs/nsdi14-mimo.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://web.stanford.edu/~skatti/pubs/nsdi14-mimo.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, here is a brief tutorial on MIMO -- implemented for WiFi -- discussing some of the basics around spatial multiplexing.   Cool stuff.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.electronics-notes.com/articles/antennas-propagation/mimo/what-is-mimo-multiple-input-multiple-output-wireless-technology.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.electronics-notes.com/articles/antennas-propagation/mimo/what-is-mimo-multiple-input-multiple-output-wireless-technology.php&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16010" LastEditorUserId="16010" LastEditDate="2019-11-27T19:53:43.770" LastActivityDate="2019-11-27T19:53:43.770" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15701" PostTypeId="1" AcceptedAnswerId="15706" CreationDate="2019-11-27T18:57:41.467" Score="4" ViewCount="334" Body="&lt;p&gt;While monitoring the 40-meter band (among others) throughout a typical day/night as propagation changes I have noticed there are often bands of very low noise (black area) and others with much higher noise (some color) in the waterfall display. These are much too consistent, persistent, and wide bandwidth to be intentional signals of any type.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My two-part question is:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;What causes those light and dark bands in the waterfall? (More specifically, what causes there to be background noise patterns like that. They are just easier to see on the waterfall obviously.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If I was looking for a clear frequency transmit on and there was a spot in a dark band and one in a light band would one expect a better signal propagation in one over the other?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Hypothesis:&#xA;My best guess is that this is something do with signals being absorbed, reflected, transmitted or not transmitted from a distance by or through one of the ionosphere layers. Still, I'm wondering if there is something more specific and how the phenomenon relates to the second part of this question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Requested example screenshots:&lt;/strong&gt; &#xA;I know the WSJT-x &quot;waterfall&quot; is not technically the same as the waterfall display of an SDR but I don't have that hooked up right now. However, the visual effect is similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example running FT8 on 40M&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Hs48c.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Hs48c.jpg&quot; alt=&quot;FT8&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example running WSPR on 20M&#xA;&lt;a href=&quot;https://i.stack.imgur.com/60Yvy.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/60Yvy.jpg&quot; alt=&quot;WSPR&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16025" LastEditorUserId="16025" LastEditDate="2019-11-27T22:11:34.517" LastActivityDate="2021-03-12T22:39:27.200" Title="What causes the light and dark bands (of background noise) in an HF waterfall display?" Tags="&lt;propagation&gt;&lt;frequency&gt;&lt;noise&gt;&lt;panadapter-and-waterfall&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15702" PostTypeId="1" AcceptedAnswerId="15704" CreationDate="2019-11-27T20:59:26.347" Score="0" ViewCount="111" Body="&lt;p&gt;I am trying to use Gnuradio to build QPSK transmission with satellites simulation for educational purposes. &#xA;Unfortunately, I am unable to add new blocks after &quot;find blocks&quot; (blue magnifier icon) button of Gnuradio stopped functioning. It was working fine till yesterday, but somehow it suddenly stopped responding to my clicks. But I can execute flowgraphs. Just can`t use find blocks buton. &#xA;I have tried to uninstall and install with following commands:&#xA;1) sudo apt-get purge --auto-remove gnuradio&lt;br&gt;&#xA;2) sudo apt-get install gnuradio&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But problem still persists. &#xA;By the way, after reinstalling, when I open the gnuradio, it still opens last opened flowgraph. Why would it remember last flowgraph if I uninstalled config/data files(...purge --auto-remove...)?&#xA;Anyways, I am providing overall screenshot, maybe there is something wrong that I am missing.&#xA;I need to fix this and continue workign asap, so any help is hugely appreciated! &#xA; &lt;a href=&quot;https://i.stack.imgur.com/1dyCh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1dyCh.png&quot; alt=&quot;Current screenshot of the Gnuradio&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="16026" LastActivityDate="2019-11-27T23:17:17.080" Title="Find blocks function on Gnuradio does not work" Tags="&lt;gnuradio&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15703" PostTypeId="2" ParentId="15033" CreationDate="2019-11-27T21:39:23.243" Score="8" Body="&lt;p&gt;To help identify a mystery ferrite core mix, the most common method is to take some measurements to determine the initial permeability (µi). Then compare your results to a table of µi for common core materials. This will put you in the ballpark and likely more than close enough to make an educated guess about the application(s) the ferrite core would be usable in.&lt;/p&gt;&#xA;&lt;p&gt;The ferrite core's suitability for use at RF depends more on complex permeability at radio frequencies than on audio frequencies. For this reason, it is important to take your measurements using as few turns as necessary to give reliable and accurate readings. More turns relate to increased stray capacitance, which will affect the complex impedance and skew your readings.&lt;/p&gt;&#xA;&lt;p&gt;How to measure (one method):&#xA;I will be testing a known Fare-Rite 43 Toroid part number 5943003801 as an example.&lt;/p&gt;&#xA;&lt;p&gt;Test setup using a cheap LCR meter to measure the inductance of our toroid. I have found that 10-15 tight turns will yield acceptable measurements of most ferrite toroids.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tUTWX.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tUTWX.jpg&quot; alt=&quot;Test setup&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;11 turns (blue wire) yielded a measurement of 120uH.&lt;/p&gt;&#xA;&lt;p&gt;Next, we enter our measured inductance into a calculator like &lt;a href=&quot;https://coil32.net/online-calculators/determine-toroid-core-permeability.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt; along with our toroid dimensions.&lt;/p&gt;&#xA;&lt;p&gt;In this test, my results were the following:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/syOEg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/syOEg.png&quot; alt=&quot;Results&quot; /&gt;&lt;/a&gt;&#xA;As you can see, we are almost dead on for initial permeability and well within the &lt;a href=&quot;https://www.fair-rite.com/product/toroids-5943003801/&quot; rel=&quot;nofollow noreferrer&quot;&gt;datasheet specs&lt;/a&gt; for AL(nH) = 1075 ±20%. Once you know the core material type, you can then use that to reference it's usable application.&lt;/p&gt;&#xA;&lt;p&gt;Ferrite materials can be classified as soft ferrites and hard ferrites. Soft ferrites can handle reversals in their magnetic direction without losing a great deal of energy. The notable feature of these materials is that they resist any current in the core, making them &lt;strong&gt;more efficient&lt;/strong&gt;. Hard ferrites hold on to their magnetization very well and are very good at conducting magnetic flux, even at lower frequencies. These are quite inexpensive and not what you want in an efficient high-frequency design.&lt;/p&gt;&#xA;&lt;p&gt;--&lt;/p&gt;&#xA;&lt;p&gt;We can perform other simple tests such as testing what frequencies are passed or blocked in configurations like this to help determine if the unknown core will work for our application. Here are a couple of examples.&lt;/p&gt;&#xA;&lt;p&gt;Here we are injecting a 4Vpp sine wave on one coil of 5 turns around our type 43 core and viewing that signal at both sides of the winding. Notice as we sweep from 25MHz to 1MHz the changes that take place. Most notably, we can see a phase shift as the output signal (blue) lags the input (yellow) more as we go up in frequency (less as we go down). Also, note the output's amplitude is lowest at 25HMz, highest around 8MHz, and matches the input as we approach 1MHz. These are both useful to know in determining what this chunk of ceramic might be good for.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yLNcq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yLNcq.jpg&quot; alt=&quot;Test setup 2&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/CwzPa.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CwzPa.jpg&quot; alt=&quot;Core winding and connections&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Ka2eD.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ka2eD.gif&quot; alt=&quot;25 to 1MHz sweep&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I hope this helps and gives you a simple way to check out your box of inedible donuts! BTW you can pick up cheap LCR meters online or make your own. You might even be able to finagle an antenna analyzer to help you out here, but that is a topic for another post.&lt;/p&gt;&#xA;&lt;p&gt;73 - NC0H&lt;/p&gt;&#xA;" OwnerUserId="16025" LastEditorUserId="16025" LastEditDate="2020-10-09T15:00:18.310" LastActivityDate="2020-10-09T15:00:18.310" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15704" PostTypeId="2" ParentId="15702" CreationDate="2019-11-27T23:17:17.080" Score="1" Body="&lt;p&gt;It looks like the right sidebar, where the list of blocks is, is collapsed. Try dragging from where the faint dots in the middle of the right edge of the window are.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-11-27T23:17:17.080" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15705" PostTypeId="2" ParentId="15701" CreationDate="2019-11-28T02:39:41.723" Score="2" Body="&lt;p&gt;Often, the source of bands of noise in an SDR spectrum is locally generated RFI or EMI.  During a neighborhood power outage, one might notice a large number of these bands disappear.  Sharper bands in the waterfall can sometimes be mitigated by reducing or choking EMI sources in your &quot;shack&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other possible sources for these bands can be ripple in passband of the various digital filters in the DSP signal chain (for anti-aliasing, decimation, FFT windowing, audio, etc.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet another possible source might be antenna gain and pattern, which can vary with frequency.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-11-28T02:48:53.290" LastActivityDate="2019-11-28T02:48:53.290" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15706" PostTypeId="2" ParentId="15701" CreationDate="2019-11-28T02:40:04.477" Score="2" Body="&lt;p&gt;What you are seeing there is the frequency response of your receiver's audio stage (or possibly even the input of your computer's sound card). It is amplifying frequencies around 300Hz and 2500Hz much more strongly than it is amplifying frequencies less than 100Hz, and those between 800Hz and 1700Hz. It's clear on both those screenshots, even though you are (presumably - you don't do FT8 on the same frequencies as WSPR) tuned to different RF frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not something you need to worry about, as the digital modes in question don't depend on absolute signal strength at a specific frequency as much as they rely on signal-to-noise ratios.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-11-28T02:40:04.477" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15707" PostTypeId="1" CreationDate="2019-11-28T14:58:26.307" Score="0" ViewCount="135" Body="&lt;p&gt;I have a hackrf one sdr, which i use to transmit test signals.&#xA;I am using ISM bands, so I can omit transmitting my callsign, checking correct sub band (FM, digital) etc.&#xA;And one of most interesting bands is 2.4 GHz, the wifi band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that i have only one SDR device capable of operation in that band - the hackrf itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But recently I have discovered a MAX2121(b) IC which I saw in a sat top box circuit diagram. And this chip is what I think I need - it downconverts frequencies from 800-2100 mhz to IQ signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that this chip's upper band limit is 2100 MHz, which is below 2400 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to google &quot;S band tuner ic&quot; and found one which band starts from 2600 - still outside desired band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the question is: is there any 2.4 ghz tuner ICs for SDR receivers?&lt;/p&gt;&#xA;" OwnerUserId="13758" LastEditorUserId="4076" LastEditDate="2019-11-28T15:18:16.993" LastActivityDate="2019-11-28T15:18:16.993" Title="Is there any 2.4 GHz tuner ICs for SDR receivers?" Tags="&lt;software-defined-radio&gt;&lt;receiver&gt;&lt;microwave&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15708" PostTypeId="1" AcceptedAnswerId="15709" CreationDate="2019-11-29T01:23:53.110" Score="0" ViewCount="57" Body="&lt;p&gt;I made a small yagi, with the driven element being a coil loaded dipole. What is the effect of coil Q in this situation?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coils I built are 18 turns of 1.2mm enameled wire wound tightly with a calculated Q of about 400 on 14mhz. What benefit would I get from going to, say, a 100mm coil with thicker wire, with a Q of about 2000?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="8717" LastEditDate="2019-11-29T02:43:42.590" LastActivityDate="2019-11-29T02:53:55.017" Title="What is the effect of coil Q on a shortened dipole?" Tags="&lt;antenna-theory&gt;&lt;dipole&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15709" PostTypeId="2" ParentId="15708" CreationDate="2019-11-29T02:47:46.040" Score="1" Body="&lt;p&gt;Increased Q generally decreases both the losses and the usable bandwidth. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can expect:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The coil not to get as warm at the design frequency at a given power&lt;/li&gt;&#xA;&lt;li&gt;Your usable 2:1 VSWR bandwidth to be narrower&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Exactly how much is another matter.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-11-29T02:53:55.017" LastActivityDate="2019-11-29T02:53:55.017" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15710" PostTypeId="1" AcceptedAnswerId="15731" CreationDate="2019-11-29T04:41:58.153" Score="2" ViewCount="110" Body="&lt;p&gt;For transmit, the voltage at the center of a dipole not cut in the center and fed with coax and a gamma match is zero in the center at the resonant frequency. This is why apparently a 'plumbers delight' yagi with the driven element connected to the boom works ok, because the voltage in the middle is zero. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And then if the voltage is zero in the middle you don't have to worry about common mode current flowing down the outside of the coax because at the point where the outer of the coax joins to the middle of the driven element the voltage is zero and no current can flow anywhere. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what about when you move the frequency of the signal applied to the feed point away from resonance, then :&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Do you get current on the outside of the coax now because now the voltage in the middle isn't zero anymore ? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;And if you are outputting harmonics then will these result in corresponding current on the outside of the coax because voltage in the antenna caused by the harmonics are not at the resonant frequency and so that voltage won't be zero in the middle at the harmonic frequencies ? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;And also does this all help to make the antenna want to have a narrow bandwidth ?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-11-29T05:31:11.287" LastActivityDate="2019-12-03T03:20:04.227" Title="Is the voltage at the centre of a dipole zero only at it's resonant frequency?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15711" PostTypeId="1" CreationDate="2019-11-29T05:56:16.633" Score="1" ViewCount="192" Body="&lt;p&gt;I am trying to homebrew a cobweb antenna and need some help understanding the guanella balun used as described here: &lt;a href=&quot;http://www.karinya.net/g3txq/cobweb/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.karinya.net/g3txq/cobweb/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This author used RG316 coax around the ferrites, but I'm having a hard time stripping the delicate wires. I then found this balun with single strand wire: &lt;a href=&quot;http://www.m0pzt.com/blog/4to1-current-balun/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.m0pzt.com/blog/4to1-current-balun/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can I use this design to match the 50 ohm coax impedance to the 12 ohm cobweb antenna impedance?&lt;/p&gt;&#xA;" OwnerUserId="9450" LastEditorUserId="9450" LastEditDate="2019-11-30T16:26:29.283" LastActivityDate="2019-12-03T02:49:03.860" Title="Can I build a guanella balun using single strand wire instead of coax?" Tags="&lt;antenna-construction&gt;&lt;balun&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15712" PostTypeId="1" AcceptedAnswerId="15729" CreationDate="2019-11-29T08:32:12.250" Score="0" ViewCount="52" Body="&lt;p&gt;In theory when i need to shift some frequency i just multiply that signal by some sin or cos wave with the right frequency and than apply LPF or HPF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But when there is a wideband complex signal with the central frequency on for example 500MHz, bandwidth 3 MHz and 6Msps sample rate, i captured using SDR, how can i shift any harmonic inside of this band to much lower frequency like 50MHz i.e. far outside of the bandwidth? &lt;/p&gt;&#xA;" OwnerUserId="16030" LastActivityDate="2019-12-03T02:34:49.760" Title="Shifting frequency outside of the band" Tags="&lt;software-defined-radio&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15714" PostTypeId="1" AcceptedAnswerId="15882" CreationDate="2019-11-29T13:17:33.277" Score="7" ViewCount="706" Body="&lt;p&gt;I recently built a SA612 mixer for HF reception. I used an USB-frequency oscilator to shift the incoming frequency up by 28.8 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used a random wire antenna outside my balcony and connected it to the center-pin of a car antenna mount, and used a long coax to guide the signal in the room to my DIY low-pass filter, then connected it to my DIY SA612 mixer, and its output to my RTL-SDR, and finally connected everything to my battery-powered laptop. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reception was not the best, but its performance just allowed me to be able to pick up a lot of the high-power shortwave and mediumwave radio stations with low distortion, I was pretty satisfied with my device (although I was unable to hear anything from any amateur radio bands due to its limited dynamic range facing these strong stations). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nSETa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nSETa.png&quot; alt=&quot;Mediumwave Reception on Laptop&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, sitting inside the balcony on a tiny seat with a laptop is extremely uncomfortable, so I decided to hook up my Raspberry Pi for remote operation. Unfortunately, as soon as I connect my SDR to my Raspberry Pi, huge wideband noise is received all over the spectrum, killing MW and HF beyond recognition! I'm using the mediumwave as an example, but HF is also the case as well (note: this is upconverted signal, the actual IF is around 30 MHz). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FmGCZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FmGCZ.png&quot; alt=&quot;Mediumwave Reception on Raspberry Pi&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There must be a strong interference that was driving the SA612 to saturation. Initially, I thought the noise was coming from the switiched-mode power supply, so I powered the Raspberry Pi from a benchtop linear power supply, and I also powered the SA612 mixer from a 9-volt battery instead. See the following block diagram.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6UqZ5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6UqZ5.png&quot; alt=&quot;Block Diagram of my SDR Shack&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it had little effect. Although number of spurious interference was somewhat reduced, but the SA612 is still being overdriven, and I still see &quot;machine-gun&quot; like interference at fixed intervals, some are sweeping back and forth around its carrier like a wobbulator. Also, the noise floor of the signal of the entire band kept moving up and down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And strangely, if I power my SA612 via Raspberry Pi and use the RTL-SDR on my laptop, I see almost no interference. I also tried listening to the radio on my laptop while running an Ethernet speed test on the Raspberry Pi, but I see nothing at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And I finally found if I disconnect the coax input of my SA612 mixer, almost all the interference would be gone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my best guess of the situation is that the interference was generated inside the Raspberry Pi, its internal USB bus, or the Ethernet, and the EMI was traveling across the ground/shield, and/or somewhat the signal was being picked up at the input side of the mixer. Another possibility is that the Raspberry Pi has switched-mode power supply of its own to generate the 3.3 V and 1.8 V rails, perhaps this is the source of the interference. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it a correct conclusion? And what can do I to fix the interference?&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Edit 1&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;I realized that my benchtop power supply was actually a switched-mode power supply, oops... And I did more experiments.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Charging the laptop while listening to the radio can completely wipe out MW and HF using its own power supply. Although my benchtop supply was a switched-mode power supply, but I expect better performance.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Laptop + Battery: Clean spectrum.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Laptop + OEM power supply: &quot;Ultra-wideband&quot; interference at MW and HF.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Laptop + benchtop power supply: Wideband interference at MW and HF below and around 5 MHz, but the interference is weaker at 7 MHz and 10 MHz.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Laptop + unpowered benchtop power supply: strong interference at MW. But low interference at HF.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Laptop + unplugged benchtop power supply: No interference.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Using an old transformer and a LDO, I made my own linear power supply to power the Raspberry Pi. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Raspberry Pi + DIY linear power supply: mild interference at MW, but strong interference across HF. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Raspberry Pi + additional 1:1 isolation transformer + DIY linear power supply: low interference at MW, but strong interference across HF. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;h3&gt;Conclusion&lt;/h3&gt;&#xA;&#xA;&lt;p&gt;It doesn't change the conclusion of my original question, it seems the Raspberry Pi was responsible for most interference. But conducted EMI from the powerlines was also a culprit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll try isolating the ground plane between RTL-SDR and SA612 using an RF transformer to see if it improves its immunity of EMI/RFI.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Edit 2&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;I tried to use 10+ ferrite to chock every single cables, but it has absolutely no effect on reducing interference, the machine guns are still everywhere. And I'm already using a metal chassis on the Pi (&lt;em&gt;although I doubt it's effective as a shield since the case is painted and all the screw holes on the Pi doesn't have exposed copper to ground&lt;/em&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think the problem is that my SA612 mixer has poor immunity (built on a copper board with dead-bug construction). Better filtering and shielding for the mixer is probably the only potential solution to the problem.&lt;/p&gt;&#xA;" OwnerUserId="15589" LastEditorUserId="15589" LastEditDate="2019-12-01T13:47:24.727" LastActivityDate="2020-01-05T19:09:39.180" Title="DIY SA612 + RTL-SDR HF receiver: good on laptop, but huge wideband noise on Raspberry Pi" Tags="&lt;software-defined-radio&gt;&lt;rfi&gt;&lt;rtl-sdr&gt;&lt;mixer&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15716" PostTypeId="2" ParentId="2160" CreationDate="2019-11-29T20:49:44.537" Score="5" Body="&lt;p&gt;Yes. Detecting a receiver is VERY VERY VERY hard to do. Since it is only an absorber rather than transmitter of RF energy, it requires a signal strength meter to detect a dip in RF energy. It requires a very directional antenna, and circuitry to detect subtle changes in the signal. This is compounded by the fact that the receiver has a high-gain amplifier inside, so it &quot;steals&quot; very little RF energy. I would stake my bets that one would have better luck if there were a local oscillator inside. Personally, I'll stick to detecting transmitters. AM radios may be easier to detect than FM radios because of the local oscillator. &lt;/p&gt;&#xA;" OwnerUserId="16035" LastEditorUserId="8573" LastEditDate="2019-11-30T02:34:00.847" LastActivityDate="2019-11-30T02:34:00.847" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15717" PostTypeId="2" ParentId="15714" CreationDate="2019-11-30T15:57:27.523" Score="0" Body="&lt;p&gt;If the question is about how to solve this RFI/EMI issue, here's what I did to partially reduce the problem:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I put chokes (multiple turns thru ferrite toroids) on every wire and cable connected to the Raspberry Pi(s) being used for HF (AirSpy HF+, SDRPlay, Lime Mini, et.al.).  These cables are possibly being used as antennas by the on-board DC-to-DC voltage converter(s) near the IO chips (USB and ethernet, HDMI, etc.). Those parasitic antennas might radiate into every other wire nearby, including feedlines, antennas, up-converters, other radios, etc. The RTL-SDR is placed away from the Pi at the end of a heavy USB cable with toroid chokes at both ends.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Place an old vintage AM radio on top of your Pi and you might hear the buzzing from RFI/EMI.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A grounded metal case for the Pi may also help, but note that this kills WiFi and BLE range. I use a metal base and gigantic heat sink that covers nearly the entire top of the PCB on a Pi 4.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2019-11-30T16:10:36.393" LastActivityDate="2019-11-30T16:10:36.393" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15718" PostTypeId="1" AcceptedAnswerId="15726" CreationDate="2019-11-30T16:03:06.790" Score="0" ViewCount="74" Body="&lt;h1&gt;Context&lt;/h1&gt;&#xA;&lt;p&gt;I'm launching a series of weather balloons as a capstone graduation project.&#xA;Right now I am in the process of building the payload.&lt;/p&gt;&#xA;&lt;p&gt;I have been going over the different components of the mission and mapping out the different parts that I am going to need to build. For tracking / storing data I'm using OLHZN's Data Logger and Radio Position tracker (&lt;a href=&quot;https://github.com/OverlookHorizon/OLHZN_Track/blob/master/Documentation/OLHZN_PCB_Assembly_MEGA_V5.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;OLHZN Instructions&lt;/a&gt;) This system uses a HX-1 Radio Transmitter (&lt;a href=&quot;http://www.radiometrix.com/files/additional/hx1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;DATA&lt;/a&gt;) (144.390 Mhz) &amp;amp; a NEO-6M GPS Module (&lt;a href=&quot;https://www.electroschematics.com/neo-6m-gps-module/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DATA&lt;/a&gt;).&lt;/p&gt;&#xA;&lt;h1&gt;Questions&lt;/h1&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I understand that the HX-1 Radio Transmitter is an APRS, but how can I receive transmissions from this system? Could I track this with a RTL-SDR dongle?&lt;/li&gt;&#xA;&lt;li&gt;Also, with the NEO-6M GPS how do I receive these signals?. If I understand correctly the two work in tandem sending out information on telemetry and other data.&lt;/li&gt;&#xA;&lt;li&gt;Is there a standalone system that I would need to build to receive these signals? Or should I just rely on websites like APRS.fi? Or if I do need to build a standalone system (Antenna / Receiver) I would appreciate any guidance on how to construct one.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16037" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2019-12-02T07:40:01.260" Title="Required receiver for HX-1 (144.390 MHz) &amp; NEO-6M GPS Module?" Tags="&lt;transmitter&gt;&lt;aprs&gt;&lt;gnss&gt;&lt;telemetry&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15719" PostTypeId="2" ParentId="15711" CreationDate="2019-11-30T19:13:06.747" Score="2" Body="&lt;p&gt;At the end of section 2.4 of &quot;Building and Using Baluns and Ununs&quot; by Jerry Sevick, W2FMI, he uses parallel 14-gauge Thermaleze-coated wire in a transformer to match &lt;span class=&quot;math-container&quot;&gt;$50\Omega$&lt;/span&gt; to &lt;span class=&quot;math-container&quot;&gt;$12.5\Omega$&lt;/span&gt; as described in the article you cite. This wire is available in short lengths from &lt;a href=&quot;http://www.amidoncorp.com/awg-14-hapt/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amidon&lt;/a&gt;. Since the relative permittivity of wire coatings varies widely, using wire with a different coating may produce different results.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-11-30T19:13:06.747" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15720" PostTypeId="5" CreationDate="2019-11-30T21:33:31.100" Score="0" Body="&lt;ul&gt;&#xA;&lt;li&gt;Radio frequency impedance matching transformers&lt;/li&gt;&#xA;&lt;li&gt;Transceiver microphone; modulation; balanced modulator; audio-stage transformers&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-11-30T21:33:31.100" LastActivityDate="2019-11-30T21:33:31.100" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15721" PostTypeId="4" CreationDate="2019-11-30T21:33:31.100" Score="0" Body=" Impedance matching transformers as related to amateur radio." OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-11-30T21:33:31.100" LastActivityDate="2019-11-30T21:33:31.100" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15722" PostTypeId="2" ParentId="15697" CreationDate="2019-12-01T01:32:15.713" Score="2" Body="&lt;p&gt;I am still of the opinion that it is “unclear what you are asking”. But I will try to answer the two questions that you actually wrote:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Q. &lt;strong&gt;How does the carrier telophone system works on the conext of radio and most important how does this circuit work in establishing a connection between the receiver and the transmitter.&lt;/strong&gt; [sic]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A. It doesn’t. There is no radio in the picture - it is a simple diagram of how to mix incoming and outgoing audio signals over a two-wire telephone line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Q. &lt;strong&gt;Following it, is their additional passive or active componets place to keep the transmitted energy from over loading the receiver.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A. Following what? Still no radio in the picture, which means no transmitter or receiver, as such.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without further clarification of what you are actually trying to achieve (rather than an out-of-context portion of a picture that describes something that seems to work in a similar way to how you imagine it could work in a radio environment), I still think the question as framed is not answerable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I have posted this as an answer in order to explain why I think this question is not answerable. And I still think it is “unclear what you are asking”.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-12-01T01:32:15.713" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15723" PostTypeId="2" ParentId="15711" CreationDate="2019-12-01T13:47:15.790" Score="1" Body="&lt;p&gt;The balun in the &lt;a href=&quot;http://www.m0pzt.com/blog/4to1-current-balun/&quot; rel=&quot;nofollow noreferrer&quot;&gt;article by M0PZT&lt;/a&gt; does not accomplish the transformation you desire. The Cobweb antenna requires that &lt;span class=&quot;math-container&quot;&gt;$12.5\Omega$&lt;/span&gt; balanced be transformed &lt;em&gt;up&lt;/em&gt; to &lt;span class=&quot;math-container&quot;&gt;$50\Omega$&lt;/span&gt; unbalanced, while the M0PZT balun transforms &lt;span class=&quot;math-container&quot;&gt;$200\Omega$&lt;/span&gt; balanced &lt;em&gt;down&lt;/em&gt; to &lt;span class=&quot;math-container&quot;&gt;$50\Omega$&lt;/span&gt; unbalanced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The optimum impedance for the transmission line in such a transformer is the geometric mean of the primary and secondary impedances, i.e., the square-root of the product of the primary and secondary impedances. This is why the optimum transmission line impedance for the Cobweb transformer is &lt;span class=&quot;math-container&quot;&gt;$25\Omega$&lt;/span&gt; - as noted in G3TXQ's article - while for the M0PZT design it is &lt;span class=&quot;math-container&quot;&gt;$100\Omega$&lt;/span&gt;. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-12-01T13:47:15.790" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15724" PostTypeId="2" ParentId="15718" CreationDate="2019-12-01T14:43:50.833" Score="0" Body="&lt;p&gt;One reason why APRS is perfectly suited for such an experiment is that there is a physical network of receivers set up across the world. If your balloon is high up and transmitting its location on 144.390MHz, the chances are good that as long as it is near land where there is a certain density of amateur radio enthusiasts, someone will hear it and log it to the internet, where it can be seen on aprs.fi - and possibly some other sites.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have APRS in my car, and whenever I drive across Bangkok to go to work, I am tracked for my entire journey. If I go upcountry, then there are gaps in the logged journey until I get near a large town, but there isn’t a large number of APRS enthusiasts in Thailand. Most of Europe and the Americas are covered, though - and the densely-populated bits of most countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer your questions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;if you need to receive the transmitted signals directly yourself, consider a portable yagi antenna and something like an APRS receiver or an SDR with an APRS decoder.&lt;/li&gt;&#xA;&lt;li&gt;I am not familiar with this system, and will defer to someone with more knowledge about how it works.&lt;/li&gt;&#xA;&lt;li&gt;See the answer to point 1 if you want to receive the signals yourself, but bear in mind that the range will be a few tens of kilometres (or miles) at the most. But you can use the APRS network to do the listening for you. Bear in mind though that if the balloon goes over a large ocean (e.g. the Atlantic or the Pacific) there won’t be anyone to receive its signals until it reaches a populated area.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;There have been weather balloons that have gone all the way round the world with an APRS transmitter on board, and it was fascinating to track them as they went over populated areas - from the US over the Pacific to Asia, then all the way over through Europe to the Atlantic and back to the US. It was very interesting to follow them on aprs.fi see the routes they took!&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-12-01T14:43:50.833" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15726" PostTypeId="2" ParentId="15718" CreationDate="2019-12-01T15:47:52.820" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I understand that the HX-1 Radio Transmitter is an APRS, but how can I receive transmissions from this system? Could I track this with a RTL-SDR dongle?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, an RTL-SDR dongle and &lt;a href=&quot;https://github.com/wb2osz/direwolf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Direwolf&lt;/a&gt; is one good way to receive APRS; there are many others. You can also rely on existing receivers passing data to the &lt;a href=&quot;http://www.aprs-is.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;APRS-IS&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Also, with the NEO-6M GPS how do I receive these signals?. If I understand correctly the two work in tandem sending out information on telemetry and other data.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The GPS is a receiver, not a transmitter, you don't receive anything from it. The GPS &lt;em&gt;gets&lt;/em&gt; your position, the APRS transmitter &lt;em&gt;sends&lt;/em&gt; it (along with whatever telemetry you include).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there a standalone system that I would need to build to receive these signals? Or should I just rely on websites like APRS.fi? Or if I do need to build a standalone system (Antenna / Receiver) I would appreciate any guidance on how to construct one.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Your choice. Are you going to send out a car to chase this thing? Then you have a good reason to build a receiver for the tracking vehicle. Is your launch site far away from existing receivers? Then you have a good reason to build a receiver to track the launch phase. Otherwise, if you're just staying at home and letting it go, your receiver might not add very much to the network that's already out there.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2019-12-02T07:40:01.260" LastActivityDate="2019-12-02T07:40:01.260" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15727" PostTypeId="1" AcceptedAnswerId="15728" CreationDate="2019-12-02T11:56:00.733" Score="0" ViewCount="439" Body="&lt;p&gt;I'm trying to understand way which &lt;a href=&quot;https://wiki.gnuradio.org/index.php/Frequency_Mod&quot; rel=&quot;nofollow noreferrer&quot;&gt;Frequency Mod&lt;/a&gt; block works in gnuradio. According to my intuition there should be at least two inputs:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;signal to encode&lt;/li&gt;&#xA;&lt;li&gt;base frequency / carrier signal&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Instead there are some mysterious input signal and sensitivity parameter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems that I don't got the main point of it, can you fix my thinking please.&lt;/p&gt;&#xA;" OwnerUserId="16045" LastActivityDate="2019-12-02T14:52:37.377" Title="Frequency modulation with gnuradio" Tags="&lt;gnuradio&gt;&lt;fm&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15728" PostTypeId="2" ParentId="15727" CreationDate="2019-12-02T14:52:37.377" Score="0" Body="&lt;p&gt;The FM modulator in GnuRadio (as well as other modulator blocks) work in baseband: the carrier frequency is 0 Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe you should recall that, when working with SDR, you work with complex-valued samples. This means that positive and negative frequencies are distinguishable, and having a carrier frecuency of 0 Hz is perfectly valid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you send this signal to an actual SDR hardware, you specify at which frequency will the baseband signal be modulated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, to sum up, the carrier frequency is specified in the SDR (source or sink) blocks. The FM modulator only needs the input samples (real-valued), and the sensitivity (which is proportional to &lt;span class=&quot;math-container&quot;&gt;$f_\Delta$&lt;/span&gt;, according to the documentation).&lt;/p&gt;&#xA;" OwnerUserId="830" LastActivityDate="2019-12-02T14:52:37.377" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15729" PostTypeId="2" ParentId="15712" CreationDate="2019-12-03T02:34:49.760" Score="1" Body="&lt;p&gt;If your signal was at 500 MHz, and you successfully captured it with a 6 Msps sample rate, the signal is no longer &quot;at&quot; 500 MHz. Indeed it was transmitted there, but either:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;your receiver has an analog mixer, and mixed this signal down to baseband such that it could be sampled at 6 Msps, or&lt;/li&gt;&#xA;&lt;li&gt;the digital signal was originally sampled at a much higher rate, but has since been mixed to a lower frequency and decimated to a lower sample rate.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A 6 Msps complex-valued stream can represent frequencies from -3 MHz to +3 MHz. At this sample rate it is impossible to represent 500 MHz due to the &lt;a href=&quot;https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;Nyquist-Shannon sampling theorem&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, I suspect you will find that what was 500 MHz (the center frequency of your receiver at time of capture) is represented in the data as 0 Hz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to shift this around your certainly can, simply multiply it by a complex sinusoid: this will have the effect of &quot;rotating&quot; the frequency spectrum. Unlike multiplying a real-valued signal with a real-valued sinusoid (as done in many analog mixers) this does not generate two sidebands, so no additional filtering is required.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-12-03T02:34:49.760" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15730" PostTypeId="2" ParentId="15711" CreationDate="2019-12-03T02:49:03.860" Score="1" Body="&lt;p&gt;Sure, common-mode chokes such as a guanella balun can be made with coax or balanced transmission lines. Two parallel (in the geometric, rather than electric sense) strands of plain wire make a balanced transmission line, so there you go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Theoretically, there's some disadvantage to the transmission line used in the balun not being &quot;optimal&quot;, in the sense that it won't match the characteristic impedance of the rest of the system. Consequently there will be some additional SWR loss and some additional impedance transformation besides the 4:1 intention.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However as long as the length of the transmission line is small relative to wavelength (rule of thumb, less than &lt;span class=&quot;math-container&quot;&gt;$\lambda / 10$&lt;/span&gt;) the significance of these effects is negligible. It should be pretty plain to see that a 4:1 balun can't be made with &quot;matched&quot; transmission line throughout anyway: should it match the high impedance end, or the low impedance end?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So use whatever you have on hand. PTFE (teflon) insulation is a good choice: it can handle high temperatures (helps with soldering), and has low dielectric loss. But if you have something else on hand and don't want to spring for some new wire, just about anything will work fine enough unless you are trying to put 2 kW through this balun.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-12-03T02:49:03.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15731" PostTypeId="2" ParentId="15710" CreationDate="2019-12-03T03:20:04.227" Score="3" Body="&lt;p&gt;First let's clear up a misconception:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And then if the voltage is zero in the middle you don't have to worry about common mode current flowing down the outside of the coax&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This doesn't seem quite right. Indeed, &lt;em&gt;if&lt;/em&gt; the voltage in the middle of the dipole is zero and the boom and/or coax shield are attached there, then there won't be any common mode currents. Likewise if there aren't any common mode currents on the boom or coax, then wherever those things are attached must have zero voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But one does not guarantee the other. For example, take a vertical monopole, and put a horizontal bar across the top such that it makes a &quot;T&quot;. Now arguably, this added top bar could be considered an &quot;uncut dipole&quot;, but does that mean there's no voltage in the middle? Given that voltage is highest at the tip of a monopole, how can both these things be true?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now back to your original question; if the voltage at the center of a dipole is zero volts, you could say it's because (by design) there are no common-mode currents. The dipole is symmetrical, and any current is (again by design) only differential-mode, so at the center the voltage must be zero since there's no way to be both symmetrical about this point and have zero common-mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this still true if the dipole is off resonance? Well, I suppose that depends on what's ensuring common-mode current is zero, and if it still works off resonance. If common-mode current is zero (or at least, negligible) because of a broad-band common-mode choke, then probably yes, voltage at the center of the dipole is still zero at least over the effective range of the balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, if the antenna relies on something like a sleeve balun, this works only at a particular frequency, probably the same one or close to where the dipole is resonant. Away from this frequency the balun will be less effective and we'll start seeing common-mode currents, and this means the center of the dipole will no longer be at zero volts, much like the &quot;dipole&quot; attached to the top of a vertical.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-12-03T03:20:04.227" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="15732" PostTypeId="1" CreationDate="2019-12-03T05:58:40.187" Score="1" ViewCount="85" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Djnco.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Djnco.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I read in some text books that &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;E-plane is formed by taking constant azimuth angle  and scanning elevation angle from -90:90.&lt;/li&gt;&#xA;&lt;li&gt;H-plane is formed by taking a plane perpendicular to E-plane.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;What is the meaning of taking a plane perpendicular to E-plane?? Is it to take constant elevation angle  and scan azimuth angle from -90:90?&lt;/p&gt;&#xA;" OwnerUserId="16049" LastEditorUserId="16049" LastEditDate="2019-12-05T10:08:54.040" LastActivityDate="2019-12-05T10:08:54.040" Title="Can any one explain E,H plane definitions?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15733" PostTypeId="2" ParentId="15732" CreationDate="2019-12-03T09:18:42.757" Score="4" Body="&lt;p&gt;Those definition are false.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The E-plane is defined as the plane in which the E-field varies over time. The H-plane is the plane in which the H-field varies over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's nothing more to it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Logically, the definition of planes only makes sense for linearly polarized antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In isotropic (meaning: behaving the same from every angle) media (e.g., air), the H-plane is always perpendicular to the E-plane. &lt;em&gt;Perpendicular&lt;/em&gt; is when two planes are at a right angle to each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether the E-plane is in azimuth or elevation or somewhere in between depends on the direction of polarization of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-12-04T10:37:25.260" LastActivityDate="2019-12-04T10:37:25.260" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15734" PostTypeId="1" CreationDate="2019-12-03T17:05:39.860" Score="1" ViewCount="782" Body="&lt;p&gt;I recently got my GMRS license from the FCC, and I wanted to try out a couple radios for hiking and emergency communication.  I have two tenway UV-5R pro radios (these do have an FCC ID) that are set to narrowband, 8 watts and squelch at 5 with a tenway VHF/UHF NA-771 antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I gave one to my wife and I drove approx .5 miles from our home and tried to test them out.  All we got was silence or static when one of us tried to key up.  We were transmitting on 462.550.  When i scanned through the MGRS/FRS channels for a couple hours I didn't get anything either. Note that we live in the suburbs outside of a large city in Ohio. Any advice or constructive criticism?&lt;/p&gt;&#xA;" OwnerUserId="16052" LastEditorUserId="8717" LastEditDate="2019-12-03T20:45:26.003" LastActivityDate="2019-12-05T22:09:38.070" Title="GMRS not transmitting within a half mile" Tags="&lt;united-states&gt;&lt;uhf&gt;&lt;baofeng&gt;&lt;mobile&gt;&lt;frequency&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15735" PostTypeId="2" ParentId="15734" CreationDate="2019-12-03T20:07:11.787" Score="4" Body="&lt;p&gt;First, the legal issue: in the US, it's not legal to transmit on &lt;a href=&quot;https://en.wikipedia.org/wiki/General_Mobile_Radio_Service&quot; rel=&quot;nofollow noreferrer&quot;&gt;GMRS&lt;/a&gt; frequencies on a radio not type-accepted for GMRS.  Having an FCC ID doesn't mean that a radio is type-accepted for GMRS; UV-5Rs aren't.  Also, 462.55 MHz is slightly below GMRS channel 1, so you were transmitting out of the band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 8 W, you should have been able to easily have a conversation when 0.5 miles apart.  If you couldn't hear each other, your radios probably weren't set up right.  UV-5R radios are notoriously difficult to set up by following the procedure in the manual; most hams use the CHIRP software or the Baofeng software to program channels in their UV-5Rs, which is much easier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One possibility might be that you may have accidentally programmed the radio to require signals on the channel to have a &lt;a href=&quot;https://en.wikipedia.org/wiki/Continuous_Tone-Coded_Squelch_System&quot; rel=&quot;nofollow noreferrer&quot;&gt;CTCSS&lt;/a&gt; (PL) tone or a CDCSS (DCS) code in order to open the squelch.  (Setting a CTCSS tone or CDCSS code from the front panel is difficult on a Baofeng, so it's unlikely in this case, but someone in the future might have this problem so it's worth mentioning.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider earning ham licenses.  You'll have more people to talk to, you can use repeaters to greatly expand your range, and you could use your UV-5Rs legally.  There is a test, but there are &lt;a href=&quot;http://www.arrl.org/find-an-amateur-radio-license-class&quot; rel=&quot;nofollow noreferrer&quot;&gt;preparation classes&lt;/a&gt; and free online practice tests.  Your local ham club can help.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2019-12-05T22:09:38.070" LastActivityDate="2019-12-05T22:09:38.070" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15736" PostTypeId="1" AcceptedAnswerId="15737" CreationDate="2019-12-04T01:57:56.577" Score="1" ViewCount="100" Body="&lt;p&gt;Antenna theory it seems is always described assuming that the transmitted or received signal being talked about is a pure sine wave usually at the resonant frequency. Standing waves for example are always depicted as perfect sine waves. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So everyone gets the impression that the waveforms on our antennas and transmission lines are all perfect sine waves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it seems to me that the signals on an antenna including standing waves are hardly ever a perfect sine wave and are usually not exactly at the resonant frequency. For example, an LSB voice signal does not look like a perfect sine wave at all.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do antennas work differently for perfect sine waves than for the far more usual messy looking waveforms i see on my oscilloscope ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-12-04T21:44:35.463" LastActivityDate="2019-12-04T21:44:35.463" Title="Does an antenna work the same for pure sine waves as compared to other waveforms?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15737" PostTypeId="2" ParentId="15736" CreationDate="2019-12-04T02:18:26.123" Score="6" Body="&lt;p&gt;No, because of the superposition principle. Every signal that isn't a sine wave is expressible as a &lt;em&gt;sum&lt;/em&gt; of sine waves, and an antenna's response to the sum of two signals is the sum of its responses to the separate signals. This property is called &quot;linearity&quot; and it's true as long as you don't run excessively large amounts of power through the antenna (approaching power levels that would destroy it anyway).&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-12-04T02:18:26.123" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15740" PostTypeId="2" ParentId="15734" CreationDate="2019-12-04T22:07:28.037" Score="3" Body="&lt;p&gt;You've already been apprised of the legal issues, so let me ask you a few questions...&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How did you program the radios?&lt;/li&gt;&#xA;&lt;li&gt;Were the antennas screwed all the way in?&lt;/li&gt;&#xA;&lt;li&gt;What was the terrain like where you were testing these things? Trees, houses?&lt;/li&gt;&#xA;&lt;li&gt;How did you decide on squelch level 5?&lt;/li&gt;&#xA;&lt;li&gt;Did you modify the CTCSS settings on either of the radios? This seems like the most likely issue.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;For future reference, though, an FCC ID is just a confirmation that the FCC knows what the device is (not really, but that's a different issue). It's NECESSARY for a device to have an FCC ID to be type-accepted for a service like GMRS, but not &lt;em&gt;sufficient.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your Ham license, check out hamstudy.org. Don't overblow the studying part. The technician test is so fall-off-a-log easy that eight year-olds routinely pass it, and the general test is still pretty much child's play to anyone with even a modicum of electrical knowledge.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some of the old guys will tell you &quot;You've got to &lt;em&gt;learn the material!&lt;/em&gt;,&quot; and while that's true in principle,* you can only understand so much of the actual physics and engineering stuff before you get deep into serious electrical-engineering territory. It's the kind of stuff that you just can't understand without either a long time of tinkering and experimenting and fooling around, or dedicated academic study, or both. So just focus on learning the rules and safety procedures, and just drill-and-kill the rest of it. You'll learn it later as you go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a matter of fact, these are the four most important rules in electrical engineering:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;E = IR&#xA;P = IE&#xA;For capacitive circuits, the current leads the voltage.&#xA;For inductive circuits, the voltage leads the current.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;In the words of Hillel the Elder, that's the whole Torah, the rest is the explanation; go and learn.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;* No disrespect intended to the Old Guys; they're the keepers of The Ancient Knowledge, but a lot of them are, by training and profession, &lt;em&gt;hyper&lt;/em&gt;-experts in &lt;strong&gt;&lt;em&gt;extremely&lt;/em&gt;&lt;/strong&gt; abstruse and arcane fields like RF propagation physics or microwave circuit engineering, so &quot;learning the material&quot; by their standards is an extremely high bar by almost anyone else's.&lt;/p&gt;&#xA;" OwnerUserId="16058" LastActivityDate="2019-12-04T22:07:28.037" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15741" PostTypeId="1" CreationDate="2019-12-05T13:13:30.297" Score="0" ViewCount="87" Body="&lt;p&gt;I am using a Pixie transceiver, giving 1 W power and 7 MHz frequency. A 40-meter band dipole antenna, providing 5 dBi gain at high angles, has been designed and connected at the output of the circuit to transmit. We are using the concept of reflection from the ionosphere to receive a signal at a distance of 200 km from the transmitter. Our antenna is in the inverted-V configuration. We have designed the same antenna for the transmitter as well as the receiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First of all, we have tested it for almost a 15-meter region. We transmitted the signal from the same Pixie transceiver from the transmitter then to receiver and successfully received that signal at the receiver. Now, we tried to perform the same experiment by keeping a distance of 15 km between transmitter and receiver. We received only noise and the original signal was not received.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What modifications are required in my overall system as explained above so that we can receive our signal at a longer range?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: Keep in mind I want to receive skywaves, so for that reason, the actual distance is the distance from the earth to the ionosphere and then back to earth.&lt;/p&gt;&#xA;" OwnerUserId="16061" LastEditorUserId="4076" LastEditDate="2019-12-05T15:57:12.983" LastActivityDate="2019-12-05T16:22:56.417" Title="40 meter band Dipole antenna designed is not receiving any signal at 2 km distance" Tags="&lt;dipole&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15742" PostTypeId="2" ParentId="15741" CreationDate="2019-12-05T16:10:28.963" Score="3" Body="&lt;p&gt;At 15km you may be too far for line-of-sight or groundwave, and too close for skywave — you're in the &quot;skip zone&quot;. You should conduct your test from further away, or else use a lower frequency (80 meters). This is because the highest frequency that will reflect off of the ionosphere depends not only on the ionozation of the ionosphere at that moment, but also on the &lt;em&gt;angle&lt;/em&gt; at which the signal reaches the ionosphere. The shallower the angle, the higher the frequency that will work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Under the current solar conditions it is &lt;em&gt;not&lt;/em&gt; possible for a 7 MHz signal to go straight up and come straight down (NVIS) in most times and locations. 200km distance brings the usable frequency up by about a factor of 1.2 - 1.25, which &lt;em&gt;might&lt;/em&gt; be enough, at your latitude, for some parts of the day. But 3.5 MHz will usually work during daylight for most places in the world.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2019-12-05T16:22:56.417" LastActivityDate="2019-12-05T16:22:56.417" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15743" PostTypeId="1" CreationDate="2019-12-05T18:40:51.737" Score="3" ViewCount="144" Body="&lt;p&gt;Please help me identify this piece of equipment. It looks military spec, but don't know anything about it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to look up some history about what it was used for. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Hyd2y.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Hyd2y.jpg&quot; alt=&quot;Front&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/iRWwh.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iRWwh.jpg&quot; alt=&quot;Controls&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Eeim7.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Eeim7.jpg&quot; alt=&quot;Handset&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/wkzUL.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wkzUL.jpg&quot; alt=&quot;Label&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://photos.app.goo.gl/xepC1aYx2FJP5h5t5&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here are more photos.&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16064" LastEditorUserId="76" LastEditDate="2019-12-11T03:56:56.980" LastActivityDate="2019-12-11T03:56:56.980" Title="What is this military radio?" Tags="&lt;transceiver&gt;&lt;history&gt;&lt;military-surplus&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15744" PostTypeId="5" CreationDate="2019-12-05T20:01:12.310" Score="0" Body="" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-12-05T20:01:12.310" LastActivityDate="2019-12-05T20:01:12.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15745" PostTypeId="4" CreationDate="2019-12-05T20:01:12.310" Score="0" Body="Questions about military surplus radio equipment, especially related to converting them for amateur radio use." OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-12-05T20:01:12.310" LastActivityDate="2019-12-05T20:01:12.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15746" PostTypeId="1" AcceptedAnswerId="15769" CreationDate="2019-12-05T20:40:22.030" Score="1" ViewCount="128" Body="&lt;p&gt;I am just starting to learn CW, and for practice I have been recording and transcribing repeater identifications that I hear. This is what I heard today:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;DE W9KIC/R BBG&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the meaning of &quot;BBG&quot;?&lt;/p&gt;&#xA;" OwnerUserId="15816" LastEditorUserId="8717" LastEditDate="2020-10-26T20:11:15.340" LastActivityDate="2020-10-26T20:11:15.340" Title="Repeater identification ending (CW)" Tags="&lt;cw&gt;&lt;jargon&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15747" PostTypeId="1" CreationDate="2019-12-05T21:40:54.197" Score="16" ViewCount="2322" Body="&lt;p&gt;When using a balanced antenna such as a half wave dipole, with an unbalanced feed line such as coax, an RF choke can be used to block RF current emitted by the transmitter from splitting up at the antenna feed point and traveling along the antenna and also down the outside of the coax. Without the choke, the outer shield of the coax becomes a radiating part of the antenna, which is usually not desirable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why do amateur radio operators refer to the RF choke in this instance as a balun?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To me it seems that the RF choke isn't a balun and doesn't convert an unbalanced transmission line to a balanced system at all, but rather just removes one of the effects of connecting an unbalanced transmission line to a balanced antenna, that being the unwanted current traveling on the outside of the shield of the coax, by blocking it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Isn't a real balun for example a ferrite ring with wires arranged such that common mode current is cancelled out in the same way that a transmission line operates while at the same time allowing differential mode current to pass?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-12-06T00:31:42.743" LastActivityDate="2020-08-20T14:54:05.953" Title="Why do amateur radio operators call an RF choke a balun?" Tags="&lt;antenna-theory&gt;&lt;balun&gt;&lt;choke-balun&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15748" PostTypeId="2" ParentId="15747" CreationDate="2019-12-05T22:47:32.920" Score="25" Body="&lt;p&gt;&amp;quot;Balun&amp;quot; is a portmanteau of &amp;quot;balanced&amp;quot; and &amp;quot;unbalanced&amp;quot;. Anything made to interconnect a balanced and unbalanced load can be called a balun.&lt;/p&gt;&#xA;&lt;p&gt;A common-mode choke (like a length of coax wound over a ferrite ring) works as a balun because it inserts a high impedance in the common-mode without affecting the differential-mode. By action similar to a voltage divider, most of the current will then favor the differential-mode.&lt;/p&gt;&#xA;&lt;p&gt;Typically the differential-mode impedance will be something like 50 or 75 ohms: it's simply the design feedpoint impedance of the antenna. A decent choke can provide a common-mode impedance of 4000 ohms. Because the differential-mode impedance is so much lower, the common-mode current will be very low, practically negligible.&lt;/p&gt;&#xA;&lt;p&gt;A common-mode choke like this accomplishes the objective of converting between a balanced and unbalanced load. It's easy to manufacture, has low loss, high power handling, can be effective over a wide band, is inexpensive, and works even if the &amp;quot;balanced&amp;quot; load isn't quite perfectly balanced.&lt;/p&gt;&#xA;&lt;p&gt;This is by no means the only way to make a balun, but for HF and lower this particular design has a lot of advantages, making it very popular. It is very much a proper balun, and with an appropriate design and application is can be a superb solution.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-08-20T14:54:05.953" LastActivityDate="2020-08-20T14:54:05.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15750" PostTypeId="1" AcceptedAnswerId="15757" CreationDate="2019-12-06T01:57:13.010" Score="1" ViewCount="139" Body="&lt;p&gt;Actual standing waves have nothing to do with causing the output device in a transmitter to fail, in fact it's the reverse or reflected current which helped to create the standing waves which is flowing into the output device that causes the failure, is this true ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-12-29T14:56:08.563" Title="Is it true that standing waves on a transmission line don't cause failure of transmitting devices?" Tags="&lt;transmission-line&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15752" PostTypeId="1" AcceptedAnswerId="15756" CreationDate="2019-12-06T02:23:01.930" Score="0" ViewCount="96" Body="&lt;p&gt;If i were to use a passive transmit coupler to connect two transmitters of equal power output to the same antenna, and connect one microphone to both transmitters, and then transmit on both at the same time on the same frequency, will that be the same as using one transmitter but with twice the power ? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will a distant receiver see the two signals as one ? or as two separate signals just as if they were coming from completely separate stations ...&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="76" LastEditDate="2019-12-06T04:54:58.127" LastActivityDate="2019-12-06T23:19:16.027" Title="If i transmit on the same frequency using two separate transmitters joined together will they both add up in a reciever to produce a stronger signal?" Tags="&lt;antenna-theory&gt;&lt;propagation&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2019-12-12T01:23:48.360" ContentLicense="CC BY-SA 4.0" />
  <row Id="15753" PostTypeId="1" AcceptedAnswerId="15755" CreationDate="2019-12-06T03:51:38.037" Score="1" ViewCount="37" Body="&lt;p&gt;Standing waves are seen on a transmission line when for example there is a change in impedance and a transmitted wave is reflected back from one end and then the incident wave and reflected wave superimpose on each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And as far as i understand for a standing wave to exist there needs to be two or more wave forms on the same medium which have a fixed phase relationship with each other and are of the same frequency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If an AC current induced in an antenna from a received EMF signal happened to be exactly the same frequency and phase as a transmitted signal on the same antenna, would this produce standing waves ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Noting of course that the transmitted signal will probably be much higher in amplitude than the received signal.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-12-06T04:01:23.043" LastActivityDate="2019-12-06T04:30:59.253" Title="Can received and transmitted signals on the same antenna combine to produce standing waves?" Tags="&lt;antenna-theory&gt;&lt;transmission-line&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15754" PostTypeId="1" AcceptedAnswerId="15758" CreationDate="2019-12-06T03:58:06.703" Score="2" ViewCount="53" Body="&lt;p&gt;Is there any kind of directional coupler device such as you find in a SWR meter that only allows traveling AC waves of one direction to pass which i could use to block the reflected wave from my badly matched antenna and therefore save the output devices in my transmitter from failing ? I would then short the coupler out when receiving ...&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-12-06T04:32:59.037" LastActivityDate="2019-12-06T05:31:47.137" Title="Can I use a directional coupler to block reflected AC current from a mismatched antenna?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15755" PostTypeId="2" ParentId="15753" CreationDate="2019-12-06T04:30:59.253" Score="1" Body="&lt;p&gt;Yes, received signals can form standing waves, and there is a very easy way for this to happen:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;An object in the environment reflects some of your transmitted signal back to you.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may have heard that antennas are influenced by their environment, and may need to be fine-tuned for that (rather than being exactly the shape that is specified by theory or simulation of an antenna in free space). This is &lt;strong&gt;exactly the same phenomenon, with a different description.&lt;/strong&gt; Every such influence can be thought of as a partial reflection (in some direction, with some phase/polarization). An object separate from your antenna that is not fundamentally different from an element of your antenna — it's just usually farther away and thus has a lesser influence, but that's because we like to mount antennas in locations that maintain that separation and give &lt;em&gt;predictable&lt;/em&gt; performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can say that antennas are impedance matching devices, between your feed line &lt;em&gt;and the environment&lt;/em&gt;. To have perfect SWR, an antenna must be adapted to the environment, and if the environment changes so will the SWR.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;It might also be interesting to think about what happens when your antenna receives a signal that &lt;em&gt;isn't&lt;/em&gt; identical to your transmitted signal. That will not be a standing wave, by definition. But, it is still traveling &quot;in reverse&quot; on your feed line, and your SWR meter will read it as &quot;reflected&quot; power because the meter doesn't care what the signal's frequency is, thus showing a SWR that is higher while not technically being due to a standing wave. This is usually insignificant because received signals are usually much weaker than transmitted signals, but we could hypothetically imagine pointing two nearby transmitters' antennas at each other (or just connecting them with a cable), in which case you've got possible damage to the final amplifier even though the signals need not be similar at all (no standing waves).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My point is that what matters, mostly, is not that the returning signal has the same frequency and phase (and so forms standing waves), but that there &lt;em&gt;is a returning signal&lt;/em&gt; of significant power. Standing waves are just how we describe the condition in the feed line in the most practically relevant case, where there are reflections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, standing waves in particular do have some effects:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The theory of standing waves tells us what impedance the transmitter will observe, for a given length of line before the reflection. This could determine whether the transmitter will tolerate the reflections or not. (But in practice, we'd rather just avoid that case and the accompanying signal loss, hence why we care about low SWR.)&lt;/li&gt;&#xA;&lt;li&gt;Standing waves imply voltage and current peaks at stable locations on the feed line, which could overheat the line or break down insulation. (But in amateur applications, this is usually not a concern before the health of the transmitter.)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-12-06T04:30:59.253" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15756" PostTypeId="2" ParentId="15752" CreationDate="2019-12-06T04:43:57.883" Score="6" Body="&lt;p&gt;You certainly can, in theory, use multiple transmitters together to produce a signal of higher total power. However, there is a catch: the signals must be &lt;em&gt;in phase&lt;/em&gt; with each other. Otherwise they will cancel each other out instead of adding, half the time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To have the same phase, they would have to share the same RF oscillator (or be coupled to a master oscillator, perhaps), and the feed line lengths between each transmitter and the combiner must be equal. A more practical way to look at it is that you can build one transmitter which has many &lt;strong&gt;amplifiers&lt;/strong&gt; that work together to produce a high power signal. This can even be a particularly useful technique if your amplifier components cannot tolerate the voltage, or heat, that would result from the total RF power you want to transmit — each individual amplifier works with a lower voltage and can have its own heat sink.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;A related technique is &lt;a href=&quot;https://en.wikipedia.org/wiki/Beamforming&quot; rel=&quot;nofollow noreferrer&quot;&gt;beamforming&lt;/a&gt;, where you use multiple amplifiers &lt;em&gt;and multiple antennas.&lt;/em&gt; The waves from each antenna interfere with each other, constructively or destructively; by controlling the amplitude and phase of the signals transmitted via each antenna, the antenna array can be “steered” to transmit signals in a desired direction, without need for any mechanical rotation.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2019-12-06T23:19:16.027" LastActivityDate="2019-12-06T23:19:16.027" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15757" PostTypeId="2" ParentId="15750" CreationDate="2019-12-06T04:50:42.940" Score="3" Body="&lt;p&gt;&lt;strong&gt;Yes.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we say there is a standing wave on a feed line, we are saying that the voltage and current &lt;em&gt;along the length of&lt;/em&gt; the line have a certain shape in space and over time. But the transmitter doesn't care about any part of the line except the part it's connected to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can use the idea of standing waves to help &lt;em&gt;understand and calculate&lt;/em&gt; how the end of the line at the transmitter will behave — and in particular, it matters what phase the reflections have, not just that there is reflected power at all — but once you have your answer in terms of current and voltage over time &lt;em&gt;at that point&lt;/em&gt; that's all that matters, not what it might be some distance down the line.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-12-06T04:50:42.940" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15758" PostTypeId="2" ParentId="15754" CreationDate="2019-12-06T05:31:47.137" Score="5" Body="&lt;p&gt;There is a device that does this, but it's not a directional coupler. Rather, it's a &lt;a href=&quot;https://en.wikipedia.org/wiki/Circulator&quot; rel=&quot;noreferrer&quot;&gt;circulator&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A directional coupler isn't suitable since the forward and reflected ports merely &quot;sample&quot; the power in each direction. Most of the power just passes through the coupler, so at best you'd only reduce the reflected power reaching your transmitter by some insignificant amount.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, a typical directional coupler might have a &lt;em&gt;coupling factor&lt;/em&gt; of -20 dB, meaning if there are 100 watts reverse then -20 dB of that (1 watt) makes it to the reverse coupled port. The remaining 99 watts just pass through the coupler (or are lost to heat).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is good for driving an SWR meter with negligible impact to the signal but not so much if your objective is to absorb the reflected power in a dummy load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Attempting to solve this by increasing the coupling factor means increasing the forward power lost. A directional coupler is inherently a 4-port device, and the coupling factor is the same in forward and reverse directions. So if the coupling factor is increased to 0 dB the coupler would indeed be able to absorb all reflected power, however it would also absorb all forward power. Not a very useful device.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-12-06T05:31:47.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15759" PostTypeId="2" ParentId="15750" CreationDate="2019-12-06T05:38:00.317" Score="7" Body="&lt;p&gt;This is a bit like saying, &quot;it's not the fall that kills you, but the sudden stop at the end.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Technically, it's not the standing waves &lt;em&gt;per se&lt;/em&gt; that cause the damage. However, standing waves imply a mismatched load possibly outside the transmitter's specifications, which implies a potential for excessive heating or voltage in the transmitters, which can lead to damage. Therefore, standing waves imply a potential for damage, even if they aren't the direct cause.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2019-12-06T17:32:22.333" LastActivityDate="2019-12-06T17:32:22.333" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="15760" PostTypeId="1" AcceptedAnswerId="15765" CreationDate="2019-12-06T10:11:46.477" Score="2" ViewCount="185" Body="&lt;p&gt;I noticed that watches with GPS signal receivers made by Seiko and Citizen have an airplane mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's a GPS &lt;strong&gt;receiver&lt;/strong&gt;, it shouldn't cause interference, right?&lt;/p&gt;&#xA;" OwnerUserId="16068" LastActivityDate="2019-12-06T14:06:02.517" Title="Why do watches with GPS receivers have an &quot;airplane mode&quot;?" Tags="&lt;gnss&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15761" PostTypeId="2" ParentId="15760" CreationDate="2019-12-06T12:22:48.753" Score="0" Body="&lt;p&gt;I have no authorative answer – but my guess would actually be &quot;for power-saving reasons&quot;: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Especially during high-altitude flights, GPS might not work well anyways (for both technical and legal reasons). Successlessly trying to acquire a fix (which on top of that only has very limited validity, what with places often crossing time zone boundaries) consumes a lot of power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, even more likely: it's a user- or authority-demanded feature that has no technical reason. &quot;It's a radio device, it needs to be switched off. Why would a 1000€ thing not have an off button?!&quot;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-12-06T12:22:48.753" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15762" PostTypeId="2" ParentId="15760" CreationDate="2019-12-06T12:33:29.050" Score="1" Body="&lt;p&gt;If the watch has a GPS, it may also have bluetooth or wifi, and typically the function of the airplane mode is to turn these transmitters off.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2019-12-06T12:33:29.050" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15763" PostTypeId="2" ParentId="15750" CreationDate="2019-12-06T12:48:09.193" Score="-2" Body="&lt;p&gt;Standing waves are not what causes the damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Heat buildup in the transmitter from accepting some of the reflected power may cause the transmitter to overheat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But tubes are typically less vulnerable to this and can withstand a higher SWR, and solid state devices typically drop power until the heat buildup is not an issue.  Also, it is possible to block the incoming power so the transmitter is not affected.  (For instance, a tuner can do this.)  Under these conditions, swr around 10 might be acceptable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another reason we avoid high swr is to avoid inefficiency.  If you have high swr in a feed line with less than perfect efficiency, it will absorb some fraction of the power on each bounce (and heat up slightly) and this will result in less transmitted power.  This power drop may or may not be a concern depending on the power level and the feed line efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if you have a transmitter that is able to reflect the power back, and transmission line (like windowed ladder line) that is low loss, then the high swr is less of an issue, and eventually the reflected power will reflect again and get into the antenna (perhaps after several reflections).  The reflections themselves might cause issues (like ghosting) if the frequency is high enough or the feed line long enough, but at HF this is usually not an issue.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2019-12-29T14:56:08.563" LastActivityDate="2019-12-29T14:56:08.563" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15764" PostTypeId="2" ParentId="14501" CreationDate="2019-12-06T13:32:19.440" Score="0" Body="&lt;p&gt;Below is a NEC4.2 study of a 2-radiator, v-pol, parasitic array for the 40-meter band. Details for the configuration are shown within the red-outlined area on the left side of the graphic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The study excludes the loss of a matching network at the feedpoint to produce a nominal 50 j0 Ω match to a transmission line connected to the input terminals of that network.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no need to use a Mininec ground in this study, as NEC4.x is able to model antenna system conductors on, or buried in a lossy ground plane (Earth, in this case).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This NEC model reported no geometry or segment errors at runtime.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/G4niV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/G4niV.jpg&quot; alt=&quot;NEC4.2 Study:&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2019-12-06T13:32:19.440" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15765" PostTypeId="2" ParentId="15760" CreationDate="2019-12-06T14:06:02.517" Score="2" Body="&lt;p&gt;Some years ago when electronics on planes were still a big deal, I remember GPS receivers, portable CD players and radio receivers being singled out as Not Allowed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This could be because radio receivers can radiate some of their LO, and this could be at an unwanted frequency and interfere with the aircraft communications or navigation. GPS receivers are no exception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Scratching around I found &lt;a href=&quot;http://www.gpsinformation.net/airgps/gpsrfi.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page&lt;/a&gt; and this &lt;a href=&quot;http://gpsinformation.net/airgps/airgps.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;list of airlines&lt;/a&gt; which allow and do not allow GPS receivers on their planes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Presumably if one were flying on Lufthansa in 2010, such a GPS-only watch would need to be in flight mode to comply with the airline regulations. In practice it would be forgotten or ignored, like so many mobile phones, but the watch manufacturer couldn't ignore the airlines' requests.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-12-06T14:06:02.517" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15766" PostTypeId="1" AcceptedAnswerId="15772" CreationDate="2019-12-06T17:38:52.087" Score="2" ViewCount="114" Body="&lt;p&gt;I need to estimate the signal delay through the 1:4 Guanella balun shown here:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/oWdwV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oWdwV.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the delay simply the delay through the winding on CORE1 or CORE2?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, assume each winding comprises 0.1-m of coax with velocity factor of 0.78, is the delay:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$delay = \frac{0.1 \text{-m}}{0.78 \;\text x \;3\text x 10^8 \text{-m/s}} = 0.43 \text{ns}$$&lt;/span&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-12-09T03:48:11.047" Title="What is the delay through a 1:4 Guanella balun?" Tags="&lt;balun&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15768" PostTypeId="1" CreationDate="2019-12-07T09:12:44.887" Score="1" ViewCount="60" Body="&lt;p&gt;I have been under medically supervised treatment for the past few years.  I have been on heavy meds.  I presently am showing signs of improvement from cognitive issues which were troubling me.  I discovered that my license is expired past the two year renewal period.  Is there any way that my license can be salvaged?&lt;/p&gt;&#xA;" OwnerUserId="16077" LastEditorUserId="8717" LastEditDate="2019-12-07T14:02:14.630" LastActivityDate="2019-12-09T02:51:22.233" Title="To obtain operating privileges after the 2 year grace" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15769" PostTypeId="2" ParentId="15746" CreationDate="2019-12-07T21:48:40.320" Score="4" Body="&lt;p&gt;The repeater is in Blacksburg according to an internet search, so BBG is almost definitely an abbreviation of that.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-12-07T21:48:40.320" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15770" PostTypeId="1" AcceptedAnswerId="15771" CreationDate="2019-12-08T15:12:26.020" Score="1" ViewCount="352" Body="&lt;p&gt;I'm trying to get into SDR and was planning on buying an RTL-SDR. For an antenna, I was thinking of using an old set of bunny ears I have lying around. However, I first want to make sure that they'll work with the dongle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm only planning on receiving in the 10's to 100's of MHz which is in the listed range of the RTL. In addition, it looks like TV stations broadcast in similar ranges so the antenna should be built for receiving them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is my logic correct or is there something I have overlooked that would make the antenna not work with the dongle?&lt;/p&gt;&#xA;" OwnerUserId="16081" LastEditorUserId="76" LastEditDate="2019-12-08T16:03:30.047" LastActivityDate="2019-12-10T16:55:23.737" Title="Can I use a “bunny ears” TV antenna for RTL-SDR?" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15771" PostTypeId="2" ParentId="15770" CreationDate="2019-12-08T16:03:01.270" Score="2" Body="&lt;p&gt;First of all, the properties of an antenna are far less important for &lt;em&gt;receiving&lt;/em&gt; than &lt;em&gt;transmitting&lt;/em&gt;. To receive anything at all, just about any piece of metal will do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, the lower the frequency (longer wavelength) you want to receive, the larger the antenna should be for it to work well. Once you get into the “HF” range (below 30 MHz, formally, but that's an arbitrary division not a physics-based one), you want the sort of antenna that, practically implemented, is often less like a stiff metal rod sticking up and more like a wire strung out between supports. This is both because the wavelengths are larger, and because the signals people are often interested in (e.g. shortwave radio stations) are weaker.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be precise, the length of an antenna “element” (the distance from the receiver or coax to the end of the rod or wire), should be one-quarter of the wavelength, or&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\frac{1}{4}\times\frac{c}{f}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is the frequency and &lt;span class=&quot;math-container&quot;&gt;$c$&lt;/span&gt; is the speed of light (the idealized conversion factor between wavelength and frequency for radio waves).  For making these calculations it can be handy to use Wolfram Alpha (&lt;a href=&quot;https://www.wolframalpha.com/input/?i=1%2F4+*+c%2F%28100+MHz%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;example&lt;/a&gt;) or any other calculator that understands physical units and knows what &lt;span class=&quot;math-container&quot;&gt;$c$&lt;/span&gt; is. There are also various web pages with dedicated calculators for specific antenna designs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the example I linked above, we see that 100 MHz corresponds to 0.75 meters or 2'6&quot;; so assuming your “rabbit ears” are telescoping, then for good reception at 100 MHz, you should extend each of the two elements to that length. &lt;strong&gt;This is a simplification,&lt;/strong&gt; because all sorts of secondary effects and details of the antenna construction; use this number as a rough guide, and then adjust the antenna to see what gets you good reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If for some frequency you find your antenna can't be that size, that's a sign that you might want a different antenna. But it's still worth trying, because as I said to start with, receiving antennas can work well enough despite being “totally wrong” for the application. &lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-12-08T16:03:01.270" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15772" PostTypeId="2" ParentId="15766" CreationDate="2019-12-08T17:23:33.363" Score="1" Body="&lt;p&gt;A colleague used a 2-port vector network analyzer (VNWA) to perform a useful measurement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After calibrating the instrument to set the phase of S21 to zero at 20-MHz - no delay - he measured the phase added by about a meter of small diameter coax as 28.49 degrees. He then wrapped the entire length of the same coax on a large toroidal ferrite core, FT240-43 (2.4-in O.D., 43-mix ferrite) and measured the phase as 28.43 degrees, indicating that &quot;ferrite loading&quot; of the coax added no discernible delay. This is not surprising, in hindsight, but the experimental verification is worthwhile.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I modeled a Guanella balun using &lt;em&gt;&lt;a href=&quot;http://www.ae6ty.com/Smith_Charts.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;SimSmith&lt;/a&gt;&lt;/em&gt;. As shown, I used the resistance and reactance specified for a &lt;a href=&quot;https://www.fair-rite.com/product/multi-aperture-cores-2843010302/&quot; rel=&quot;nofollow noreferrer&quot;&gt;binocular type-43 ferrite core&lt;/a&gt; to establish the impedance to currents on the outside of the coax shield at 2-MHz: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lHIr7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lHIr7.png&quot; alt=&quot;SimSmith RUSE block for Guanella balun&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As shown by &lt;em&gt;SimSmith&lt;/em&gt;'s &lt;strong&gt;Wave&lt;/strong&gt; function:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/00ghR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/00ghR.png&quot; alt=&quot;SimSmith balun delay measurement&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;the delay from the input to the output of the balun is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;17.97ns - 17.54ns = 0.43ns&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which is the delay expected from the length of coax used to wind each of T1 and T2:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\text{delay} = \frac{\text{4-in x .0254-m/in}}{\text{0.78 x 3x}10^8 \text{m/sec}} = \text{0.43-ns}$&lt;/span&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-12-08T17:23:33.363" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15773" PostTypeId="2" ParentId="15768" CreationDate="2019-12-09T02:51:22.233" Score="2" Body="&lt;p&gt;To reclaim a license expired more than 2 years one must retake element 2 (Technician).  If you were a General or Advanced previously, you will be granted General privileges.  If you were an Amateur Extra, you will be granted Extra privileges.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were previously licensed as a Tech then not really, because you have to retake the Tech and will be granted Tech privileges.  Once you do this however, you can request your old call sign as a vanity and get it back that way.&lt;/p&gt;&#xA;" OwnerUserId="4748" LastActivityDate="2019-12-09T02:51:22.233" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15775" PostTypeId="1" AcceptedAnswerId="16917" CreationDate="2019-12-09T04:30:29.853" Score="-3" ViewCount="301" Body="&lt;p&gt;Is it true that for a half wave dipole, cancelling out reactance using for example a gamma match does not make the antenna resonant at all, but rather just cancels out the reactance of what is actually a non-resonant antenna which has an impedance when fed from the center of 73 + j43 ohms ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-12-10T12:34:31.427" LastActivityDate="2020-07-09T22:41:32.910" Title="How can a half wave dipole which has an impedance of 73 + j43 ohms ever be resonant?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15777" PostTypeId="1" AcceptedAnswerId="15778" CreationDate="2019-12-09T16:29:31.597" Score="2" ViewCount="136" Body="&lt;p&gt;When constructing a new radio, what should your step resolution  be and what is considered too much in resolution in frequency tuning and transmitting? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm talking about capacitor type tunning. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normal radios go in steps of .5 before going to the next band:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;100.0&lt;/li&gt;&#xA;&lt;li&gt;100.5&lt;/li&gt;&#xA;&lt;li&gt;Etc, Etc. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Capacitor types allow you get more inbetween which offers a better resolution:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;100.1 &lt;/li&gt;&#xA;&lt;li&gt;100.2 &lt;/li&gt;&#xA;&lt;li&gt;100.3 &lt;/li&gt;&#xA;&lt;li&gt;100.4 &lt;/li&gt;&#xA;&lt;li&gt;100.5 &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="4076" LastEditDate="2019-12-09T21:41:23.163" LastActivityDate="2019-12-10T02:30:39.060" Title="What is a good step resolution in tuning and transmitting?" Tags="&lt;transceiver&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15778" PostTypeId="2" ParentId="15777" CreationDate="2019-12-09T17:31:48.523" Score="2" Body="&lt;p&gt;I'm assuming you're building a digitally-controlled tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, there is no such thing as too much resolution. Think first about usability — choose an encoder (assuming you are using a knob for a physical tuning control) which has a high counts-per-revolution value (but not so high that you're entering the realm of overly expensive parts, whatever that means to you), and then let the user adjust the ratio of encoder steps to frequency. (The Elecraft KX3, for example, has both a permanent speed setting and a front-panel control for quickly switching between coarse or fine tuning.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fine steps are most obviously valuable in a SSB receiver — the closer to exact frequency, even within a few Hz, the better the audio can sound. But even for other modes that are not so frequency-sensitive, in a crowded band it can be valuable to tweak your receive tuning to help filter out an unwanted adjacent signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For VHF/UHF FM operation (among others), you should offer the option of tuning in discrete steps, which is useful for quickly finding well-known channel frequencies that are “round numbers”. But you should provide an &lt;em&gt;option&lt;/em&gt; as to what the tuning step is because it may vary depending on local practice. Furthermore, such a tuning step should definitely not be a single encoder step, because that would be much too fast, unless this is the &lt;em&gt;only&lt;/em&gt; mode of operation your transceiver supports and the encoder is detented (clicky).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I plan to update this answer with some more concrete numbers based on the transceivers I have available, but right now they're not in front of me.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-12-09T17:31:48.523" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15779" PostTypeId="2" ParentId="15777" CreationDate="2019-12-09T21:50:49.133" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;what is considered too much in resolution in frequency tuning and transmitting? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Nothing. You physically can't get arbitrary exact frequency  within finite time (Heisenberg won't let you), but that's far from where you are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the contrary: since oscillators aren't perfect and have frequency error, you'd always want to be able to tune. There's no downside to that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question what's &lt;em&gt;practical&lt;/em&gt; when someone turns a knob is a different one: If I was to build a radio, there'd be numeric buttons to key in the frequency I want. I'd simply stop typing digits when I think I'd be right.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Normal radios go in steps of .5 before going to the next band:&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;.5 of what &lt;em&gt;unit&lt;/em&gt;? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, I don't think that claim is true. Radios have very different ways of selecting frequencies. For some applications, a 75 kHz channel raster is right. For others some other.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Capacitor types allow you get more inbetween which offers a better resolution&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's simply not true. Fractional frequency synthesizers have a very high resolution, and the remaining offset is trivially compensatable with numerically controlled oscillators of various architectures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An electrically tunable capacitor only has as many settings as the DAC controlling it has possible output values. It's still a relatively inaccurate way of generating frequencies, so although you might think you have a high resolution, you actually just got many steps of relatively random frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A mechanically tunable capacitor is typically hard to actually tune very reproducibly and exact. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For these technical reasons, modern radio devices don't use undisciplined capacitor-based synthesizers at all – instead, they use the aforementioned fractional frequency synths (which can, in some instances, include an electronically tunable capacitor, but not necessarily).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, wrong claim: If you actually want good &lt;em&gt;resolution&lt;/em&gt;, then you need good &lt;em&gt;accuracy&lt;/em&gt;, otherwise your resolution is largely meaningless. You get excellent accuracy with things that are &lt;em&gt;not&lt;/em&gt; tunable capacitors.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-12-09T21:57:58.047" LastActivityDate="2019-12-09T21:57:58.047" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15782" PostTypeId="2" ParentId="15775" CreationDate="2019-12-10T05:27:53.153" Score="4" Body="&lt;p&gt;A &lt;em&gt;physically&lt;/em&gt; half-wave dipole isn't resonant. As you say, it has an impedance around 73+j43 ohms. Since the reactance is non-zero, it is by definition not resonant.&lt;/p&gt;&#xA;&lt;p&gt;Any manner of matching devices could be added to the antenna, and considered as a whole, they would make a resonant system. But that's not what people usually mean when they say &amp;quot;resonant antenna&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Instead, the antenna can be made just a little shorter. At slightly less than a half-wavelength the reactance drops to zero and the antenna becomes resonant, no matching device required.&lt;/p&gt;&#xA;&lt;p&gt;In practice this is almost always done, so unless writing in a context where very strict language is required, a &amp;quot;half-wave dipole&amp;quot; really means &amp;quot;a dipole of approximately a half-wave, adjusted to achieve resonance.&amp;quot; This means the dipole is &lt;em&gt;electrically&lt;/em&gt; a half-wave long.&lt;/p&gt;&#xA;&lt;p&gt;This is a convention that goes beyond dipoles. For example, a &lt;a href=&quot;https://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer&quot; rel=&quot;nofollow noreferrer&quot;&gt;quarter-wave transformer&lt;/a&gt; is understood to be a length of transmission line not physically the length of a quarter-wavelength in free space, but whatever length is a quarter-wavelength at the propagation velocity within the transmission line.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-07-09T13:08:34.463" LastActivityDate="2020-07-09T13:08:34.463" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15783" PostTypeId="2" ParentId="15743" CreationDate="2019-12-10T07:53:15.640" Score="2" Body="&lt;p&gt;The construction does not look appropriate for military service. Coast guard, Civil Aviation, emergency services or industry looks more likely. Photographs of the interior may yield more clues. A fixed squelch control may be a clue this was designed for VHF or UHF. It was not common to totally enclose radio equipment without ventilation so this may only contain the remote control circuit.&lt;/p&gt;&#xA;" OwnerUserId="16086" LastActivityDate="2019-12-10T07:53:15.640" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15784" PostTypeId="1" CreationDate="2019-12-10T15:09:02.020" Score="3" ViewCount="183" Body="&lt;p&gt;I'm sure this seems like a Google question, but I've BTDT and come up empty.&lt;/p&gt;&#xA;&lt;p&gt;The problem I'm trying to solve is to obtain cables that are as &amp;quot;leak proof&amp;quot; as possible.  Tried Pasternak &amp;quot;100% shield&amp;quot; and they leak like a sieve.   Tried Andrew FSJ1-50 (F1B-PNMBM-1M) which is pretty good, but leaks at both ends, apparently due to the joining to the connectors.&lt;/p&gt;&#xA;&lt;p&gt;Given that a commercially made cable isn't good enough here, I'm tempted to make my own, and if I'm going to that much trouble I want the best.  I keep seeing references to &amp;quot;Superscreened&amp;quot; or &amp;quot;double Superscreened&amp;quot; coax, which has braid and mu-metal, but I can't find anywhere that sells such cable.&lt;/p&gt;&#xA;&lt;p&gt;I'm hoping someone here knows where I can find it, and the appropriate BNC ends so I can fab some quality cables.  I'm not too concerned about cost.&lt;/p&gt;&#xA;&lt;p&gt;Premade 1m cables, BNC male to BNC male would be best, but only if the connectors are put on so that they don't leak.&lt;/p&gt;&#xA;&lt;p&gt;I am working inside a faraday cage sending test signals to multiple antennas, and I don't want the coax radiating anything significant. The ferrite bar antennas have a gain on the order of -80db so leakage from the cables can dominate the signal at the receiver, and I can't use any other type of antenna here.&lt;/p&gt;&#xA;&lt;p&gt;If there's another way to solve this, that would be great.&lt;/p&gt;&#xA;&lt;p&gt;Frequency of interest is &amp;lt;1MHz.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastEditorUserId="8573" LastEditDate="2020-07-15T15:44:42.063" LastActivityDate="2020-07-15T15:44:42.063" Title="Supershield or Superscreen coax: Does it exist? What is its common name?" Tags="&lt;coaxial-cable&gt;&lt;testing&gt;&lt;mf&gt;" AnswerCount="2" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="15785" PostTypeId="2" ParentId="15770" CreationDate="2019-12-10T16:55:23.737" Score="0" Body="&lt;p&gt;Yes , if it can work with a TV it can work with the dongle. You will want an adapter for the connection. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TV rabbit ears has a Type F connector.&#xA;The RTLSDR will have either an MCX or an SMA connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't try to buy just one adapter , buy a variety pack.  &lt;/p&gt;&#xA;" OwnerUserId="14671" LastActivityDate="2019-12-10T16:55:23.737" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15786" PostTypeId="2" ParentId="15714" CreationDate="2019-12-10T17:47:07.263" Score="0" Body="&lt;p&gt;Just some Suggestions: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could have a &quot;ground loop&quot; , try making a common ground for everything. &lt;a href=&quot;https://en.wikipedia.org/wiki/Ground_loop_%28electricity%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Ground_loop_%28electricity%29&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need type 31 material Ferrites for HF frequencies. If they don't list the core material assume it is not type 31.  &lt;/p&gt;&#xA;" OwnerUserId="14671" LastActivityDate="2019-12-10T17:47:07.263" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15788" PostTypeId="1" CreationDate="2019-12-10T19:40:11.513" Score="1" ViewCount="71" Body="&lt;p&gt;I have the Tecsun PL-310ET and PL-660 SW portables which are spec’d for 5V and 6V power sources respectively. Would it damage them if I tried to power them with a 9V Bioenno battery (actual steady voltage ~9.6V)?&lt;/p&gt;&#xA;" OwnerUserId="16090" LastActivityDate="2020-02-19T01:51:53.100" Title="Power supply for shortwave portables" Tags="&lt;power-supply&gt;&lt;dc-power&gt;&lt;battery&gt;&lt;voltage&gt;&lt;portable&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15790" PostTypeId="2" ParentId="12285" CreationDate="2019-12-10T20:42:48.073" Score="0" Body="&lt;p&gt;I'm trying to solve a problem right now that bears on your situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming we know what frequencies you're interested in using the cable for, and that you have a signal generator, receiver (CW is best) and a terminator of the appropriate impedance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Set up the signal generator on a frequency roughly in the middle of your range, output 0dBm or higher.&#xA;Terminate the far end of the cable.&#xA;Tune the reciever to the same frequency.&#xA;Run the reciever along the coax, defects in the shield (or really bad shields) will show up as a loud signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &quot;perfect&quot; cable would have no detectable leakage other than that dictated by its transfer impedance: &lt;a href=&quot;https://www.araconfiber.com/what-is-transfer-impedance/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.araconfiber.com/what-is-transfer-impedance/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's not a quantative test, but it's informative.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some Pasternak RG-58 &quot;100% shield&quot; cables here that are VERY leaky.&#xA;I have some Andrew RSJ1-50 cables with leakage that's almost undetectable except where the connectors attach to the cable (factory mounted, not my work)&#xA;Very noticeable difference between the two.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2019-12-10T20:42:48.073" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15793" PostTypeId="1" AcceptedAnswerId="15801" CreationDate="2019-12-10T22:56:27.803" Score="0" ViewCount="132" Body="&lt;p&gt;When an antenna is resonant, the impedance seen at the feed point is purely resistive and has no reactance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the physical properties of an antenna that actually make it resonant  and how do these properties relate to the frequency at which resonance occurs ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-12-10T23:02:50.293" LastActivityDate="2019-12-11T21:54:14.363" Title="What exactly makes an antenna resonant?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15795" PostTypeId="2" ParentId="15793" CreationDate="2019-12-11T04:33:49.193" Score="3" Body="&lt;p&gt;The antenna has inductance and capacitance, which is the same thing a tank circuit has.  A current traveling along the antenna creates a magnetic field; the field and the current interact with each other, thus it will be subject to inductance.  The charges that accumulate on the conductors creates an electrostatic field that causes them to interact with each other (or with conductive objects nearby).  The conductors thus behave like the plates of a capacitor.  The combination is resonant at the frequency where the inductive and capacitive reactances are equal.&lt;/p&gt;&#xA;" OwnerUserId="1087" LastActivityDate="2019-12-11T04:33:49.193" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15796" PostTypeId="1" CreationDate="2019-12-11T06:26:04.330" Score="5" ViewCount="403" Body="&lt;p&gt;I am looking at using NEC to model a &lt;span class=&quot;math-container&quot;&gt;$0.5\lambda$&lt;/span&gt; rectangular folded dipole, for closely spaced larger sides (choosing a separation of &lt;span class=&quot;math-container&quot;&gt;$0.01\lambda$&lt;/span&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In &lt;em&gt;Antenna Theory, Analysis and Design&lt;/em&gt; by &lt;em&gt;Balanis&lt;/em&gt;, the folded dipole is touched upon, and an equivalent antenna mode circuit is presented:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gvB6U.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gvB6U.png&quot; alt=&quot;balanis-figure-9.14&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I created a NEC model for this to show the geometry and pattern. Auto-segmentation is used with 20 segments/&lt;span class=&quot;math-container&quot;&gt;$0.5\lambda$&lt;/span&gt;. The larger sides of the model point in the same direction, so the voltage source matches the antenna mode circuit. The magnitude of the impedance is &lt;span class=&quot;math-container&quot;&gt;$213\Omega$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DPeXy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DPeXy.png&quot; alt=&quot;folded-dipole-model&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some questions I have:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How can I verify this model? The pattern and peak gain is very similar to the standard dipole. Are there any limitations due to NEC?&lt;/li&gt;&#xA;&lt;li&gt;Is the purpose of using 1 voltage source on each of the larger sides is to ensure to current is identical in each?&lt;/li&gt;&#xA;&lt;li&gt;The gain of a standard 0.5&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; dipole can be theoretically derived as &lt;span class=&quot;math-container&quot;&gt;$2.15$&lt;/span&gt; &lt;span class=&quot;math-container&quot;&gt;$dBi$&lt;/span&gt;. Does a similar derivation exist for a folded dipole, taking into account the separation length?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit:&lt;/strong&gt; As suggested, I have made the following updates:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Updated segmentation to 10 segments/0.5&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;. &lt;/li&gt;&#xA;&lt;li&gt;Wire radius at &lt;span class=&quot;math-container&quot;&gt;$0.001\lambda$&lt;/span&gt;, which satisfies &lt;span class=&quot;math-container&quot;&gt;$r &amp;lt; L/10$&lt;/span&gt; before/now.&lt;/li&gt;&#xA;&lt;li&gt;Using only a single source, in the &lt;span class=&quot;math-container&quot;&gt;$+\hat{x}$&lt;/span&gt; direction.&lt;/li&gt;&#xA;&lt;li&gt;Simulate for separation of &lt;span class=&quot;math-container&quot;&gt;$0.01\lambda$&lt;/span&gt; (left) and &lt;span class=&quot;math-container&quot;&gt;$0.1\lambda$&lt;/span&gt; (right).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JeiAs.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JeiAs.png&quot; alt=&quot;folded-dipole-model-seperation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The single source makes the elevation pattern non-constant, peaking at &lt;span class=&quot;math-container&quot;&gt;$\pm 15\deg$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\pm 55\deg$&lt;/span&gt; respectively to broadside. The magnitude of the impedance is &lt;span class=&quot;math-container&quot;&gt;$417\Omega$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$647\Omega$&lt;/span&gt; respective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The standard dipole impedance was &lt;span class=&quot;math-container&quot;&gt;$95\Omega$&lt;/span&gt;. In &lt;em&gt;Balanis&lt;/em&gt; it was stated the impedance of a short-separation folded dipole is 4 times the impedance of the standard dipole, which is approximately true in this model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some follow up questions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How can I know if the pattern and gain of my folded dipole is correct? I was under the impression a folded dipole pattern/gain is very similar to the standard dipole.&lt;/li&gt;&#xA;&lt;li&gt;If I feed from the &lt;span class=&quot;math-container&quot;&gt;$-\hat{x}$&lt;/span&gt; direction as shown in &lt;em&gt;Balanis&lt;/em&gt;, my front lobe is smaller than my back lobe. Why is this the case?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16087" LastEditorUserId="16087" LastEditDate="2019-12-11T10:03:55.897" LastActivityDate="2019-12-16T19:42:16.150" Title="Modelling a folded dipole" Tags="&lt;antenna-theory&gt;&lt;antenna-modeling&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15797" PostTypeId="2" ParentId="15796" CreationDate="2019-12-11T12:14:05.253" Score="2" Body="&lt;p&gt;Good simulation work - your results look pretty realistic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A note about patterns - when you talk about Azimuth and Elevation patterns, with the antenna lying on its side, it's not completely clear which they are. Normally a folded dipole is installed standing up, so it's omnidirectional. In your model there are two elevation patterns: one at &lt;span class=&quot;math-container&quot;&gt;$\phi=0$&lt;/span&gt; (the XZ plane cut) which is what we'd normally call the azimuth pattern, and one at &lt;span class=&quot;math-container&quot;&gt;$\phi=90$&lt;/span&gt; (the XY plane cut) which is the classic elevation pattern. It's usually obvious from the graph which is which, but not from the descriptions.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How can I verify this model? The pattern and peak gain is very similar to the standard dipole. Are there any limitations due to NEC?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;NEC has lots of limitations... first respect the design rules, that helps. Then you can do some sanity checks: Are the results similar when you change segmentation? Are they smooth over frequency? Finally NEC can do an integrated total power check - this tells you if the current in the feed segment is accurate, and gives a clue about the overall accuracy.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is the purpose of using 1 voltage source on each of the larger sides is to ensure to current is identical in each?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;As you've found in Balanis - the purpose of two sources is to allow you to separate and investigate the superimposed antenna and transmission line modes. One is just a (thicker) dipole &lt;span class=&quot;math-container&quot;&gt;$r_{eff}=\sqrt{as} $&lt;/span&gt;, the other is just a pair of short-circuit transmission lines.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does a similar derivation exist for a folded dipole, taking into account the separation length?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;For a thin folded dipole, the gain should be the same as an equivalent dipole. If you're getting more than this, remember that your dipole is a bit longer than resonance, so its gain is still going up (remember NEC gain doesn't include mismatch). A rule of thumb for me is that the total circumference should be included, i.e. its effective length is &lt;span class=&quot;math-container&quot;&gt;$l+s$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If I feed from the &lt;span class=&quot;math-container&quot;&gt;$−x$&lt;/span&gt; direction as shown in Balanis, my front lobe is smaller than my back lobe. Why is this the case?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's hard to analyse the whole structure in your head. Quite likely it's because you are on the long side of resonance - frequency too high. Try simulating it from 250-320 MHz and see how the pattern changes over frequency.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="8016" LastEditDate="2019-12-16T19:42:16.150" LastActivityDate="2019-12-16T19:42:16.150" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15798" PostTypeId="2" ParentId="15796" CreationDate="2019-12-11T13:33:15.573" Score="2" Body="&lt;p&gt;@pymekrolimus:  Below is a clip showing the details of a quick study of a model based on your posts so far. The NEC4.2 engine was used for the calculations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The results look close to what might be expected.  The wire model showed no geometry or segment errors at runtime, and the AGT test returned a result of &quot;perfect.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The wire table is shown, should you want to experiment with this model definition.  The source is placed on Segment 16 of Wire(Tag) 4.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6DAa2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6DAa2.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2019-12-11T13:39:48.097" LastActivityDate="2019-12-11T13:39:48.097" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15799" PostTypeId="2" ParentId="6217" CreationDate="2019-12-11T14:27:16.717" Score="0" Body="&lt;p&gt;As others have said, using coax for a long wire is workable but it's a waste of money.&#xA;There are antennas that specifically use coaxial cable to advantage though&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.rason.org/Projects/collant/collant.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.rason.org/Projects/collant/collant.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2019-12-11T14:27:16.717" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15800" PostTypeId="1" CreationDate="2019-12-11T15:17:20.313" Score="5" ViewCount="100" Body="&lt;p&gt;Why are the shapes of the impedance curves different for cores made of the same ferrite material?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://www.fair-rite.com/wp-content/uploads/2015/08/CUP-Paper.pdf&quot; rel=&quot;noreferrer&quot;&gt;impedance (Z) of an inductor wound on a ferrimagnetic core&lt;/a&gt; is:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$Z=j\omega L_s + R_s = j\omega L_0 (\mu_{s}^{'} -j\mu_{s}^{&quot;})$$&lt;/span&gt;&#xA;where &lt;span class=&quot;math-container&quot;&gt;$L_0$&lt;/span&gt; is the inductance of the winding in vaccuum and &lt;span class=&quot;math-container&quot;&gt;$\mu_{s}^{'}$&lt;/span&gt;,&lt;span class=&quot;math-container&quot;&gt;$\mu_{s}^{&quot;}$&lt;/span&gt; comprise the material's complex permeability, representing a core's lossless reactance and resistive dissipation, respectively. The variation of &lt;span class=&quot;math-container&quot;&gt;$\mu_{s}^{'}$&lt;/span&gt;,&lt;span class=&quot;math-container&quot;&gt;$\mu_{s}^{&quot;}$&lt;/span&gt; for a material vs. frequency is provided by the core's manufacturer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Px3SE.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Px3SE.png&quot; alt=&quot;43 material complex permeability&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$L_0$&lt;/span&gt; is calculated as:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$L_0 = \frac{4 \pi N^2 10^{-9}}{C_1}$$&lt;/span&gt;&#xA;where N is the number of winding turns and &lt;span class=&quot;math-container&quot;&gt;$C_1$&lt;/span&gt; is the core's &quot;structure constant&quot; or &quot;form factor&quot;. &lt;a href=&quot;https://www.tdk-electronics.tdk.com/download/531568/419f8df165fa780842566ab55510a8ce/pdf-generaldefinitions.pdf&quot; rel=&quot;noreferrer&quot;&gt;&lt;span class=&quot;math-container&quot;&gt;$C_1$&lt;/span&gt; is &lt;span class=&quot;math-container&quot;&gt;$\frac{l_e}{A_e}$&lt;/span&gt;&lt;/a&gt;, the ratio of the effective magnetic path length to the effective magnetic cross-sectional area of the core, physical characteristics that are constants for a given core's geometry. Since all of the parameters are constant, &lt;span class=&quot;math-container&quot;&gt;$L_0$&lt;/span&gt; should also be a constant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since &lt;span class=&quot;math-container&quot;&gt;$L_0$&lt;/span&gt; is a constant for a given core geometry and &lt;span class=&quot;math-container&quot;&gt;$\mu_{s}^{'}$&lt;/span&gt;,&lt;span class=&quot;math-container&quot;&gt;$\mu_{s}^{&quot;}$&lt;/span&gt; are inherent properties of the core material, the &lt;em&gt;shapes&lt;/em&gt; of the reactance, resistance and impedance curves vs. frequency should be the same for all cores of the same material, but this is not the case as shown below for two 43-material cores from Fair-Rite:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EJyPk.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EJyPk.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the cause of the differences in the shapes of the two sets of curves? &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-02-10T08:32:42.447" Title="What causes differences in properties of ferrite cores from same material?" Tags="&lt;balun&gt;&lt;ferrite&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15801" PostTypeId="2" ParentId="15793" CreationDate="2019-12-11T17:32:11.267" Score="3" Body="&lt;p&gt;A resonant antenna produces feedback that is in phase with the applied signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a more intuitive example, consider a mechanically resonant structure, like a tuning fork. If the fork is struck, a mechanical wave travels through the fork's structure. Some of the energy in this wave is lost as sound to the air, but most of that kinetic energy eventually propagates back to the point where the fork was initially struck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The time it takes for this to happen determines the resonant frequency of the tuning fork and the note you'll hear when its struck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were to repeatedly strike the tuning fork at this frequency, you'd find it would be &quot;softer&quot; than it would be at other frequency because right at the instant you're striking it, the fork is vibrating away from the striker. That is, the feedback is in phase with the applied signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Resonant antennas are analogous for electromagnetic waves. Consider a resonant dipole: each leg is tuned to be electrically a quarter wavelength long. The time it takes for the wavefront to travel from the feedpoint to the end is a delay of 90 degrees, and back from the end to the feedback another 90 degrees for 180 degrees in total. The time it takes this to happen is the time it takes the phase of the driving signal to move 180 degrees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because the feedback from reflections within the antenna is in phase with the applied signal at the feedpoint, the antenna is resonant.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8016" LastEditDate="2019-12-11T21:54:14.363" LastActivityDate="2019-12-11T21:54:14.363" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15802" PostTypeId="2" ParentId="12845" CreationDate="2019-12-11T17:48:25.367" Score="1" Body="&lt;p&gt;The torch method seems prone to problems as you can't control the heat all that well. Even silver-teflon connectors have their limits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've had good success using the old solder gun, much more heat available than most solder irons.  A Metcal iron with the right tip would probably work well also.  I just used an SP-200 with broad chisel tip to solder together some tin shielding plates which certainly have more &quot;heatsink&quot; potential than a PL-259. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might find this interesting:&#xA;&lt;a href=&quot;https://www.ntms.org/files/FSJ1-50%20Connector%20Application.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ntms.org/files/FSJ1-50%20Connector%20Application.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2019-12-11T17:48:25.367" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15803" PostTypeId="1" AcceptedAnswerId="15804" CreationDate="2019-12-12T09:11:42.353" Score="2" ViewCount="41" Body="&lt;p&gt;I am looking for ways to improve reception between two of my devices. The communicate on the 868 MHz ISM band with a 2-GFSK modulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that one of them is heavily shielded by metal (and I cannot change that) so reception is pretty bad.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using the CC1310 from TI and they recommend their CC1190 as a front-end to improve performance. In the reference schematic of the LAUNCHXL-CC13-90EU which uses a CC1310 and a CC1190 they added a SAW filter (&lt;a href=&quot;https://rffe.qualcomm.com/inf/40/ds/ae/B3725.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;B3725 from Qualcomm&lt;/a&gt;) between the CC1310 and the CC1190 RF front-end. I suppose to improve selectivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is: When do you use SAW filters? I can see that they improve selectivity a lot, but they also add insertion loss. So the overall signal is even weaker. Does it only help when there is a lot of noise on nearby frequencies or does a filter like that improve always performance?&lt;/p&gt;&#xA;" OwnerUserId="16096" LastActivityDate="2019-12-12T11:04:47.017" Title="In which cases do SAW filters improve performance?" Tags="&lt;filter&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15804" PostTypeId="2" ParentId="15803" CreationDate="2019-12-12T11:04:47.017" Score="4" Body="&lt;p&gt;You've got it right already:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does it only help when there is a lot of noise on nearby frequencies or does a filter like that improve always performance?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It helps by attenuating strong out-of-band signals.  In your case, cellphone signals from 880 MHz upwards are the problem, and in an office or factory these could be much stronger than the signal of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The filter is designed specifically for this, according to its data sheet:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/g6sqB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/g6sqB.png&quot; alt=&quot;filter transmisison&quot;&gt;&lt;/a&gt;  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It doesn't always help. In a quiet environment adding these filters will cost 5 dB of link margin and make things worse. But in a noisy environment where the receiver is being overloaded, they could make a big difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Before building a new board just to test this, have a look at the environment, 800-960 MHz, with a spectrum analyser set to max hold, and see how noisy it is. Turn off the one you're testing, leave the other end of the link turned on. If the unwanted signals are more than ?20 dB? stronger than the remote end, then the filters might help.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2019-12-12T11:04:47.017" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15805" PostTypeId="2" ParentId="425" CreationDate="2019-12-12T11:48:46.873" Score="3" Body="&lt;p&gt;Well, I operate daily from an old copper mine - where the main mineral is iron!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The comment about iron oxide are not correct.  In places such as here, and where the OP mentions, the ground is highly acidic.  Consequently, iron is in the FE2+ (ferric) state, not the FE3+ (ferrous/rust) state.  This may or may not affect conductivity.  You will have to consult a number of detailed academic papers on that, probably none of which are in the context of RF operations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When one comes across 'red water' (pH above 4, and so iron in the precipitatable, Fe3+ state), then you know you are likely in an area with lots of different types of mineralisation. Picking out the role of each, and when geological layering and water in and through these is present, is a task that quickly leads to madness!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are you better off with highly conductive ground under your antenna?  Yes!  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Gfq1e.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Gfq1e.jpg&quot; alt=&quot;Parys Mountain, a Kuroko-type mineral deposit&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16097" LastActivityDate="2019-12-12T11:48:46.873" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15806" PostTypeId="1" CreationDate="2019-12-12T21:45:34.213" Score="0" ViewCount="97" Body="&lt;p&gt;Starting sometimes after 2nd sometimes after 3th times.&#xA;Just now PC fresh booted, then console and fldigi started.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;and 2. start hangs after the two messages &quot;Silicon_Labs_CP2105_Dual_....&quot;&lt;/li&gt;&#xA;&lt;li&gt;start works, see now the successful ended start sequence below (in parts).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;It has something to do with the ALSA Sound.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;hb9fih@hb9fih-HP-EliteBook-840-G1:~$ fldigi&#xA;I: main: appname: fldigi&#xA;I: main: HomeDir: /home/hb9fih/.fldigi/&#xA;I: main: RigsDir: /home/hb9fih/.fldigi/rigs/&#xA;I: main: ScriptsDir: /home/hb9fih/.fldigi/scripts/&#xA;I: main: PalettesDir: /home/hb9fih/.fldigi/palettes/&#xA;I: main: LogsDir: /home/hb9fih/.fldigi/logs/&#xA;I: main: PicsDir: /home/hb9fih/.fldigi/images/&#xA;I: main: HelpDir: /home/hb9fih/.fldigi/help/&#xA;I: main: MacrosDir: /home/hb9fih/.fldigi/macros/&#xA;I: main: WrapDir: /home/hb9fih/.fldigi/wrap/&#xA;I: main: TalkDir: /home/hb9fih/.fldigi/talk/&#xA;I: main: TempDir: /home/hb9fih/.fldigi/temp/&#xA;I: main: LoTWDir: /home/hb9fih/.fldigi/LOTW/&#xA;I: main: KmlDir: /home/hb9fih/.fldigi/kml/&#xA;I: main: PskMailDir: /home/hb9fih/&#xA;I: main: DATA_dir: /home/hb9fih/.fldigi/data/&#xA;I: main: NBEMS_dir: /home/hb9fih/.nbems/&#xA;I: main: ARQ_dir: /home/hb9fih/.nbems/ARQ/&#xA;I: main: ARQ_files_dir: /home/hb9fih/.nbems/ARQ/files/&#xA;I: main: ARQ_recv_dir: /home/hb9fih/.nbems/ARQ/recv/&#xA;I: main: ARQ_send: /home/hb9fih/.nbems/ARQ/send/&#xA;I: main: WRAP_dir: /home/hb9fih/.nbems/WRAP/&#xA;I: main: WRAP_recv_dir: /home/hb9fih/.nbems/WRAP/recv/&#xA;I: main: WRAP_send_dir: /home/hb9fih/.nbems/WRAP/send/&#xA;I: main: WRAP_auto_dir: /home/hb9fih/.nbems/WRAP/auto/&#xA;I: main: ICS_dir: /home/hb9fih/.nbems/ICS/&#xA;I: main: ICS_msg_dir: /home/hb9fih/.nbems/ICS/messages/&#xA;I: main: ICS_tmp_dir: /home/hb9fih/.nbems/ICS/templates/&#xA;I: main: FLMSG_dir: /home/hb9fih/.nbems/&#xA;I: main: FLMSG_dir_default: /home/hb9fih/.nbems/&#xA;I: main: FLMSG_WRAP_dir: /home/hb9fih/.nbems/WRAP/&#xA;I: main: FLMSG_WRAP_recv_dir: /home/hb9fih/.nbems/WRAP/recv/&#xA;I: main: FLMSG_WRAP_send_dir: /home/hb9fih/.nbems/WRAP/send/&#xA;I: main: FLMSG_WRAP_auto_dir: /home/hb9fih/.nbems/WRAP/auto/&#xA;I: main: FLMSG_ICS_dir: /home/hb9fih/.nbems/ICS/&#xA;I: main: FLMSG_ICS_msg_dir: /home/hb9fih/.nbems/ICS/messages/&#xA;I: main: FLMSG_ICS_tmp_dir: /home/hb9fih/.nbems/ICS/templates/&#xA;I: testCommPorts: Found serial port /dev/serial/by-id/usb-Silicon_Labs_CP2105_Dual_USB_to_UART_Bridge_Controller_00733873-if00-port0&#xA;I: testCommPorts: Found serial port /dev/serial/by-id/usb-Silicon_Labs_CP2105_Dual_USB_to_UART_Bridge_Controller_00733873-if01-port0&#xA;**ALSA lib pcm_dsnoop.c:618:(snd_pcm_dsnoop_open) unable to open slave&#xA;ALSA lib pcm_dmix.c:1052:(snd_pcm_dmix_open) unable to open slave&#xA;ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear&#xA;ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe&#xA;ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side&#xA;ALSA lib pcm_dmix.c:1052:(snd_pcm_dmix_open) unable to open slave&#xA;Cannot connect to server socket err = Datei oder Verzeichnis nicht gefunden&#xA;Cannot connect to server request channel&#xA;jack server is not running or cannot be started&#xA;JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock&#xA;JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock**&#xA;I: rigCAT_init: &#xA;Serial port parameters:&#xA;device   : /dev/serial/by-id/usb-Silicon_Labs_CP2105_Dual_USB_to_UART_Bridge_Controller_00733873-if00-port0&#xA;baudrate   : 19200&#xA;stopbits   : 1&#xA;retries : 2&#xA;timeout : 500&#xA;wait       : 5&#xA;initial rts: -12&#xA;use rts ptt: F&#xA;initial dtr: -12&#xA;use dtr ptt: F&#xA;restore tio: T&#xA;flowcontrol: T&#xA;echo       : F&#xA;&#xA;I: rigCAT_init: Passed serial port test&#xA;I: rigCAT_init: Created rigCAT thread&#xA;initOptionMenus()&#xA;adding mode: LSB&#xA;adding mode: USB&#xA;adding mode: CW-USB&#xA;adding mode: FM&#xA;adding mode: AM&#xA;adding mode: RTTY-LSB&#xA;adding mode: CW-LSB&#xA;adding mode: DATA-LSB&#xA;adding mode: RTTY-USB&#xA;adding mode: DATA-FM&#xA;adding mode: FM-N&#xA;adding mode: DATA-USB&#xA;adding mode: AM-N&#xA;I: initInterface: using rigCAT xcvr control&#xA;I: readFreqList: # rfcarrier rig_mode carrier mode usage&#xA;I: readFreqList: 1000500 USB 800 CW &#xA;I: readFreqList: 1807000 USB 1000 BPSK31 &#xA;I: readFreqList: 3505000 USB 800 CW &#xA;I: readFreqList: 3580000 USB 1000 BPSK31 &#xA;I: readFreqList: 7005000 USB 800 CW &#xA;I: readFreqList: 7030000 USB 1000 BPSK31 &#xA;I: readFreqList: 7070000 USB 1000 BPSK31 &#xA;I: readFreqList: 10135000 USB 1000 BPSK31 &#xA;I: readFreqList: 14005000 USB 800 CW &#xA;I: readFreqList: 14070000 USB 1000 BPSK31 &#xA;I: readFreqList: 18100000 USB 1000 BPSK31 &#xA;I: readFreqList: 21005000 USB 800 CW &#xA;I: readFreqList: 21070000 USB 1000 BPSK31 &#xA;I: readFreqList: 24920000 USB 1000 BPSK31 &#xA;I: readFreqList: 28005000 USB 800 CW &#xA;I: readFreqList: 28120000 USB 1000 BPSK31 &#xA;**Expression 'alsa_snd_pcm_hw_params_set_format( pcm, hwParams, Pa2AlsaFormat( hostFormat ) )' failed in 'src/hostapi/alsa/pa_linux_alsa.c', line: 1789**&#xA;I: loadDefault: macro file name: /home/hb9fih/.fldigi/macros/macros.mdf&#xA;I: loadDefault: loading: /home/hb9fih/.fldigi/macros/macros.mdf&#xA;I: loadDefault: /home/hb9fih/.fldigi/macros/macros.mdf&#xA;I: n3fjp_init: N3FJP logger thread started&#xA;I: open: Trying [127.0.0.1]:7322&#xA;I: do_readfile: logfile: /home/hb9fih/.fldigi/logs/logbook.adif, read 3 records in  0.0 seconds&#xA;I: FD_init: fdserver thread started&#xA;I: DXcluster_init: dxserver thread started&#xA;I: open: Trying [127.0.0.1]:1100&#xA;I: n3fjp_start: Client socket 51&#xA;I: delayed_startup: &#xA;Portaudio devices:&#xA;HDA Intel HDMI: 0 (hw:0,3)&#xA;HDA Intel HDMI: 1 (hw:0,7)&#xA;HDA Intel HDMI: 2 (hw:0,8)&#xA;HDA Intel HDMI: 3 (hw:0,9)&#xA;HDA Intel HDMI: 4 (hw:0,10)&#xA;HDA Intel PCH: 92HD91BXX Analog (hw:1,0)&#xA;USB Audio CODEC: - (hw:3,0)&#xA;hdmi&#xA;pulse&#xA;default&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;When I start it the first time and it fails:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;I: testCommPorts: Found serial port /dev/serial/by-id/usb-Silicon_Labs_CP2105_Dual_USB_to_UART_Bridge_Controller_00733873-if00-port0&#xA;I: testCommPorts: Found serial port /dev/serial/by-id/usb-Silicon_Labs_CP2105_Dual_USB_to_UART_Bridge_Controller_00733873-if01-port0&#xA;ALSA lib pcm_dsnoop.c:618:(snd_pcm_dsnoop_open) unable to open slave&#xA;ALSA lib pcm_dmix.c:1052:(snd_pcm_dmix_open) unable to open slave&#xA;ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear&#xA;ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe&#xA;ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side&#xA;ALSA lib pcm_dmix.c:1052:(snd_pcm_dmix_open) unable to open slave&#xA;Cannot connect to server socket err = Datei oder Verzeichnis nicht gefunden&#xA;Cannot connect to server request channel&#xA;jack server is not running or cannot be started&#xA;JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock&#xA;JackShmReadWritePtr::~JackShmReadWritePtr - Init not done for -1, skipping unlock&#xA;I: rigCAT_init: &#xA;.......................................&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="16098" LastEditorUserId="4076" LastEditDate="2019-12-14T12:47:04.597" LastActivityDate="2020-01-13T13:03:05.343" Title="fldigi will only start the second/third time" Tags="&lt;fldigi&gt;" AnswerCount="1" CommentCount="18" ContentLicense="CC BY-SA 4.0" />
  <row Id="15807" PostTypeId="2" ParentId="15806" CreationDate="2019-12-12T23:57:30.927" Score="1" Body="&lt;p&gt;This question appears to be answered on stack overflow here :&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://stackoverflow.com/questions/31603555/unknown-pcm-cards-pcm-rear-pyaudio&quot;&gt;https://stackoverflow.com/questions/31603555/unknown-pcm-cards-pcm-rear-pyaudio&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-12-12T23:57:30.927" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15808" PostTypeId="2" ParentId="14971" CreationDate="2019-12-14T04:14:38.470" Score="1" Body="&lt;p&gt;The creap could be a bad capacitor or the circuit is over loaded due to excessive voltage on the plate. This sounds systematic of a component failure and requiring component isolation and L-C meters. You could have any number of bad components.  You should be using a VTVM however the main reason is the level of the reading, milli.  Sounds simple but first look for broken or discolored components and solder fractures. Make sure you are grounding the radio properly as well. The mixer is critical of that. If it’s a hot chassis don’t use the house wiring as a counterpoise. Many of the older manuals note this and how it may trip breakers.&lt;/p&gt;&#xA;" OwnerUserId="16101" LastEditorUserId="16101" LastEditDate="2019-12-14T13:54:19.003" LastActivityDate="2019-12-14T13:54:19.003" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15809" PostTypeId="1" CreationDate="2019-12-14T13:48:47.950" Score="3" ViewCount="108" Body="&lt;p&gt;I decided to check the linearity of my Yaesu FT-891 signal using an RF sampler and an oscilloscope. To generate two-tone (1550 Hz, 2150 Hz) signal I used Audacity. To connect the transceiver to the PC (MacBook Pro 2018) I used SignaLink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Surprisingly turned out that the signal is not quite linear:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CSLgy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CSLgy.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No matter how I change to output volume this is the best I can get. For a comparison, here is the exact same signal when another (DIY) digital interface is used:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wVKm1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wVKm1.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus I'm quite sure that the problem is with SignaLink. However I have little idea what exactly is causing it or even where to start from. I wonder whether this is a known problem and  maybe someone already described a mod to fix it (I didn't manage to find one). If there is no known solution a little piece of advice on how to debug the issue would be much appreciated.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="8717" LastEditDate="2019-12-17T20:16:04.233" LastActivityDate="2019-12-17T20:16:04.233" Title="How to fix SignaLink non-linearity problem?" Tags="&lt;digital-modes&gt;&lt;testing&gt;&lt;linearity&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15810" PostTypeId="2" ParentId="14971" CreationDate="2019-12-14T15:28:05.713" Score="0" Body="&lt;p&gt;In response to tuning the finals and grid dip: I’ve tuned a lot of IF strips as a Navaids Tech. VORs and Tacans mostly. Ham later. The procedure was always to start at the first IF and work to the final. Dip the plate and max the grid. All done with VTVM.  These days I use a audio sig gen and a usb dongle o’scope. &#xA;Like you said not much more effective for voltage but it is another way. I do find the o’scope useful for looking at the the audio. That and a usb spectrum analyzer. Yes attenuators! Id look at spectrum purity before i ever transmitted on an old radio like that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’m sure you started with the simple. The most likely to fail in those older radios (other than tubes) are the capacitors. Then dirty tube sockets, trim components and rotary contacts. Power off, unplug and ohm out the rotary contacts, milli. Be very careful what you clean with. Some contact cleaners eat the wafer material. Not sure of your knowledge base so I wanted to add that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look closely at the first IF tank circuit and try to isolate the components and verify values. Then work out to the final. There are LC meters on eBay for under $30. &lt;/p&gt;&#xA;" OwnerUserId="16101" LastActivityDate="2019-12-14T15:28:05.713" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="15812" PostTypeId="2" ParentId="12845" CreationDate="2019-12-14T18:14:57.910" Score="1" Body="&lt;p&gt;I’ve never had to preheat. Pre-tinning the wire and using the appropriate wattage iron or gun has always worked.  That and liquid flux. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’ve used swedging irons as well as guns. 60 watt isn’t too much. Once you tin and flux it shouldn’t be that difficult. I was taught in an Air Force tech school and torches just aren’t an option.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider the melting point of your solder and the iron tip temperature. If you have an IR thermometer place the iron tip to the solder barrel a few seconds and get a temperature. Ideally you should be 25-35F higher to allow for a good flow. Too hot or too long of heat can cause the lead and tin to start to separate. We always used liquid flux and 60/40.&lt;/p&gt;&#xA;" OwnerUserId="16101" LastEditorUserId="8717" LastEditDate="2019-12-15T15:31:50.423" LastActivityDate="2019-12-15T15:31:50.423" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15813" PostTypeId="2" ParentId="14971" CreationDate="2019-12-14T21:55:37.410" Score="1" Body="&lt;p&gt;Zeiss, the first step in fixing any radio is usually to check the power supply levels. If the power supplies are wrong then nothing will work properly. I would do that first before doing anything else. Also, when the plate current goes up does one or both of the valves glow brighter and brighter ? These two things will give clues to the fault. The fact that the dummy load doesn't get hot of course means that the high plate current isn't getting transferred to the output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your fault is never caused by faulty valves. In radios with valves you can almost always use the rule of thumb that the problem isn't the valves as it hardly ever is. The fault is probably also not caused by bad tuning or 'resonance' and it is very highly unlikely that it's caused by dirty contacts in the tube sockets, switches, relays or dials. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The fault is almost definitely caused by one or more capacitors or resistors in the transmit output stage which have HV on them that have failed due to age. The fault you describe cannot be caused by any stages preceding the transmit output stages such as in the IF as a fault in these stages cannot cause high plate current in the TX output stages while at the same time causing no output at the antenna socket, unless something is pulling down a supply rail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would replace all the high voltage coupling capacitors around the transmit driver and output stages first, as these capacitors can and very often do go leaky and turn into a temperature dependent resistors or go short circuit which can cause the symptoms you are seeing. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also replace all of the resistors in the biasing circuits around the transmit driver and output valves which have high voltage on them. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I bet if you do all this the problem will go away. I can add the component numbers to this post if you need.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also point out that if there are components failed due to age causing your problems in the transmit output stages, there is a high chance that there are components in other parts of the radio that also need changing, and another good rule of thumb when fixing old radios with valves in them is to change all the capacitors in the radio which have HV (&gt; 20 V) on them.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-12-15T01:22:54.090" LastActivityDate="2019-12-15T01:22:54.090" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15814" PostTypeId="1" CreationDate="2019-12-15T16:57:39.217" Score="0" ViewCount="38" Body="&lt;p&gt;If I have 1 amplifier running at 95%, and another identical one running at 60%, how may I calculate the output power of the combiner? I believe this combiner is a &quot;Magic T&quot;, but if there is a different formula for each type of combiner, please enlighten me. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that them both running at 95% would produce an output of 95%, and that running one at 90% and one at 60% does not produce an output of 75%. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume, based on this document, this process involves combining phasors: &lt;a href=&quot;https://www.ramayes.com/Data%20Files/Communications%20Power%20Industries/500-Watt%20Pwr-Phase%20Combiner.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ramayes.com/Data%20Files/Communications%20Power%20Industries/500-Watt%20Pwr-Phase%20Combiner.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user15517" LastActivityDate="2019-12-15T16:57:39.217" Title="How to calculate combined power of two amplifiers" Tags="&lt;amplifier&gt;&lt;theory&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15815" PostTypeId="1" CreationDate="2019-12-15T19:04:33.513" Score="0" ViewCount="173" Body="&lt;p&gt;I have a wall clock from the 1980s or early 1990s. Probably 1980s. It has a black box behind/&quot;inside&quot; it which powers the whole thing. It's made by Quartz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the black box, it says &quot;HF-QUARTZ 4.19 MHz&quot;. What do they mean by &quot;HF&quot; and &quot;4.19 MHz&quot;? Does it use radio signals? Can it be told to keep the time automatically by using radio signals at 4.19 MHz? Is that some kind of time-sync radio frequency?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found no button to press to activate its &quot;auto-time-keeping&quot; feature, if such a thing exists. I first thought that a little black button might be it, but it doesn't seem to be a button after all. It only has &quot;on/off&quot; (called start/stop) and a little wheel you use to manually set the time, mechanically. And a battery, of course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does this mean something completely different? Why mention a number of megahertz at all for a wall clock? What kind of significance does it have? Why does the user need to know that it uses &quot;4.19 MHz&quot; for something? What is that something?&lt;/p&gt;&#xA;" OwnerUserId="16110" LastActivityDate="2019-12-15T19:55:16.693" Title="What does &quot;HF-QUARTZ 4.19 MHz&quot; on a ~1980s wall clock mean?" Tags="&lt;electronics&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15816" PostTypeId="2" ParentId="15815" CreationDate="2019-12-15T19:55:16.693" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Can it be told to keep the time automatically by using radio signals at 4.19 MHz? Is that some kind of time-sync radio frequency?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm not aware of any timekeeping signals broadcasting on 4.19 MHz. However, web searching for &quot;4.19 MHz&quot; turned up a number of mentions of clocks whose timekeeping &lt;em&gt;oscillators&lt;/em&gt; used a 4.19 MHz quartz crystal (as opposed to the more usual 32.768 kHz), and that this might be a more accurate (for its time) mechanism.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This also explains why they brand it &quot;HF-QUARTZ&quot; — it's the quartz that's high frequency.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why mention a number of megahertz at all for a wall clock? What kind of significance does it have? Why does the user need to know that it uses &quot;4.19 MHz&quot; for something?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Advertising! &quot;Our clock is SUPER HIGH TECH and therefore better.&quot;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I found no button to press to activate its &quot;auto-time-keeping&quot; feature, if such a thing exists. I first thought that a little black button might be it, but it doesn't seem to be a button after all.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm pretty sure this &lt;em&gt;isn't&lt;/em&gt; a radio controlled clock, but if it were, I expect there would not be a button to activate it. Rather, such clocks do so automatically; for clocks using the WWVB 60 kHz signal, usually at night when signal propagation is better. There could be a switch to &lt;em&gt;disable&lt;/em&gt; the radio timekeeping but it would likely be a slider rather than a pushbutton.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2019-12-15T19:55:16.693" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15817" PostTypeId="1" CreationDate="2019-12-15T22:47:18.437" Score="0" ViewCount="114" Body="&lt;p&gt;I am using an USRP X310 which is unfortunately not calibrated and the specs given are only very vague.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence I would want characterize the device with first-order measurements. Unfortunately I only have a cheap spectrm analyzer and scope (Gw Instek GSP-730 and Hantek DSO5072P). I am aware that all this depends on frequency, gain etc and none of these devices are meant to be &quot;power meters&quot;. For the beginning, I am only interested in ~900 MHz and I would like to obtain a correct &quot;first-order&quot; 1dB/1dB plot for USRP output (as defined by amplitude and TX gain) and measured power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once I would have this, I would use the USRP in a loop config and match input power (measured using RMS) versus output power in dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am generating a pure CW with a certain setting (e.g. amplitude and TX gain) and then measure the power with the GSP-730.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, depending on which options I choose on the Spectrum Analyzer, my measurements are different by up to 6-10 dB(!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At first, I just used a fairly wide span and &quot;Peak Search&quot; which showed me the signal power in dBm. However, the peak search doesn't seem to be very accurate: Repeating with different settings (or just re-pushing &quot;Peak Find&quot;) gives different results. Zooming closely into it, the signal widens significantly due to leakage. Hence I started an ACPR measurement, basically defining the main channel as very wide (10 MHz) and reading off the Channel Power. The results are up to 8 dB different than using any peak method.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, depending on which signal power range I choose and which &quot;Ref Level&quot; I choose, the results again differ by up to 5dB. Interestingly for RefLevel=0dBm and RefLevel=20dBm the results seem somewhat consistent but RefLevel=10dBm is off.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is the method with peak search more accurate or the ACPR measurement (even though I am receiving a pure CW)?&lt;/li&gt;&#xA;&lt;li&gt;Should I try to use higher RefLevels or lower ones (assuming my signal is much lower than this level so that no clipping/significant distortion occurs)?&lt;/li&gt;&#xA;&lt;li&gt;Shall I try to use 1dBm/dec or 10dB/dec? Would it make a difference?&lt;/li&gt;&#xA;&lt;li&gt;Should I try to zoom into my CW as much as possible (high RBW, low span) or not?&lt;/li&gt;&#xA;&lt;li&gt;Any other recommendations when it comes to measuring signal power with a SA?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="15972" LastEditorUserId="76" LastEditDate="2020-02-15T17:05:22.817" LastActivityDate="2020-02-15T17:05:22.817" Title="Most accurate way to measure signal power with (cheap) Spectrum Analyzer" Tags="&lt;software-defined-radio&gt;&lt;measurement&gt;&lt;usrp&gt;&lt;spectrum-analyzer&gt;&lt;calibration&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15818" PostTypeId="2" ParentId="15817" CreationDate="2019-12-15T23:22:36.863" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;However, depending on which options I choose on the Spectrum Analyzer, my measurements are different by up to 6-10 dB(!).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Using a spectrum analyzer needs a bit of understanding what it does: it sweeps a filter across the spectrum and measures the power passing through that filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I didn't know how to properly use a spectrum analyzer when I first did, and none of the students I've met did – so, a spectrum analyzer is a mighty tool, that can easily mislead!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example: Depending on the settings, you might not actually &quot;hit&quot; the tone with the passband center of your filter (and see less energy), or you might have a setting that divides the observed power by the filter bandwidth to give you a power density estimate, or a lot of other settings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the first time I hear of that specific spectrum analyzer – and it's the first measurement device where the specifications are a microsoft word file. It specifies 50 kHz frequency accuracy — that's not really a great frequency standard, so you might be thinking you're tuning right onto the tone, but still be 50 kHz off (by the way, proper spectrum analyzers go through great lengths to more accurately describe the distribution of the frequency error, which is a thing relative to the center frequency – but assuming the spec means a standard deviation of 50 kHz error at 2.6 GHz, we can with a lot of good intentions hope for around 19 kHz at 900 MHz). &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;At first, I just used a fairly wide span and &quot;Peak Search&quot; which showed me the signal power in dBm. However, the peak search doesn't seem to be very accurate: Repeating with different settings (or just re-pushing &quot;Peak Find&quot;) gives different results. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yeah, sounds like the peak search functionality isn't great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That might compound with the bad frequency accuracy and the fact that the tuning steps are very rough – a distance between possible frequencies of 100 kHz (&quot;Settings Resolution&quot;) makes it hard to properly find the signals you're looking for, and also, if one can only tune in multiples of 100 kHz, the 30 kHz minimum resolution bandwidth means you're missing 70% of spectrum!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, stay away from that peak-finding tool, and don't use any resolution bandwidth smaller than the tuning steps – that leads to &quot;holes&quot; in your spectrum observation, which the SA then &quot;incorrectly&quot; interpolates with a line. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Interestingly for RefLevel=0dBm and RefLevel=20dBm the results seem somewhat consistent but RefLevel=10dBm is off.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Hm, that sounds wrong. If you don't change anything about the source of your power, i.e. don't move any cables, configure the X310 differently or send a different signal, that would be an indication of a measurement device error, or perhaps of some hidden setting (like an assumed probe attenuation or something).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, maybe that's all in the tolerances of your system: the spec sheet only says an error of 3 dB (that's a factor of 2!!!) is to be expected within 300 MHz to 2.6 GHz. Wow.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Zooming closely into it, the signal widens significantly due to leakage. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, that's just the resolution bandwidth of your filter!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is the method with peak search more accurate or the ACPR measurement (even though I am receiving a pure CW)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Since there's no point in doing an ACPR in a single-tone test:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No, this all sounds like you really need to learn what a spectrum analyzer does and how to use it – don't fret, there's great tutorials out there.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Any other recommendations when it comes to measuring signal power with a SA?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Generally, start as basic as possible – if you know you're only (or nearly only) emitting a single tone, use a wide filter and a long dwell time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use a measurement strategy that uses the fact that the daughterboards of the X310 are generally very linear for long swaths of their gain – see the &lt;a href=&quot;https://files.ettus.com/performance_data/&quot; rel=&quot;nofollow noreferrer&quot;&gt;performance metrics&lt;/a&gt; for your daughterboard to see what that range is for your frequencies and gains of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, you'll need a &lt;em&gt;measurement strategy&lt;/em&gt; – and that depends on what you want to actually know! It doesn't seem like your interest actually lies in generating tones of a specific power, but probably in more complex signals, so when setting up said strategy, make sure you actually deal with that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd start by using generating a uniformly distributed white noise signal, and passing it through a relatively sharp low-pass filter, so to generate say 10 MHz of band-limited white noise out of 25 MHz Nyquist rate (which is identical to sampling rate, since complex sampling). That's trivial to do with GNU Radio, and you can easily also visualize an average digital magnitude squared of that in GNU Radio; that's the digital domain power of the signal!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, when you successfully generate that broadband signal somewhere in the avg mag² region of 0.4, you send it using your USRP (the power limitation is a good idea to avoid USRP clipping). Now, you have 10 MHz that contain a known amount of digital power; use the 1 MHz wide resolution bandwidth on your SA, and you'll be able to, without having to think a lot about frequency errors, read the power that you see in that 1 MHz bandwidth; since that's 1/10 of the total power sent by the USRP, you get your physical power per digital power mapping.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;But, honestly: Your measurement device's spec are really bad. You'll be better off just using Ettus'/National Instruments &lt;a href=&quot;https://files.ettus.com/performance_data/&quot; rel=&quot;nofollow noreferrer&quot;&gt;performance data&lt;/a&gt; measurements, they have less uncertainty than 3 dB.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-12-15T23:47:07.780" LastActivityDate="2019-12-15T23:47:07.780" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15819" PostTypeId="1" AcceptedAnswerId="15823" CreationDate="2019-12-16T23:36:20.460" Score="0" ViewCount="125" Body="&lt;p&gt;For a 100 % efficient antenna, the real part of the impedance is equal to the radiation resistance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna were a dead short with zero impedance then the radiation resistance would be zero. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And at the other end of the scale an antenna with an infinite impedance (ie: no antenna) and so infinite radiation resistance also probably won't work that well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So somewhere in between those two extremes there must be an optimal radiation resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming a matched transmission line and transmitter, and ignoring the transmission line impedance values available (eg: 50, 75, 300 ohms), and all other things equal, what is that optimum radiation resistance for an antenna ? &lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2019-12-16T23:59:51.623" LastActivityDate="2019-12-18T02:38:39.980" Title="For an antenna when used for transmittiing, what is the optimum radiation resistance?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="15820" PostTypeId="2" ParentId="15819" CreationDate="2019-12-16T23:53:06.380" Score="1" Body="&lt;p&gt;No. What matters is if the radiation resistance (or do you mean feedpoint impedance?) of the antenna is matched to the feedline. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-12-18T02:38:39.980" LastActivityDate="2019-12-18T02:38:39.980" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15821" PostTypeId="2" ParentId="425" CreationDate="2019-12-16T23:57:48.173" Score="2" Body="&lt;p&gt;I did find a reference in MCRP 6-22D, Marine Corp Antenna Handbook page 1-10.  It talks specifically to ground wave.  “At high frequencies, 3 to 30 MHz, the ground’s conductivity is extremely important, especially above 10 MHz where the dielectric constant or conductivity of the Earth’s surface determines how much signal absorption occurs. In general, the signal is strongest at the lower frequencies when the surface over which it travels has a high dielectric constant and conductivity.”  I don’t see a case in LOS or sky wave.&lt;/p&gt;&#xA;" OwnerUserId="16101" LastActivityDate="2019-12-16T23:57:48.173" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15823" PostTypeId="2" ParentId="15819" CreationDate="2019-12-17T04:32:16.260" Score="3" Body="&lt;p&gt;Any non-zero radiation resistance will do. What matters is not the radiation resistance, but the ratio of energy radiated to energy lost to other means, such as ohmic losses in the feedline, antenna, or soil.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna system is made of ideal, lossless components, then any nonzero radiation resistance is 100% efficient. While somewhat counterintuitive it's easy to prove: the antenna must be 100% efficient because by definition there is no loss, so by the law of conservation of energy 100% of the energy must go to radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is this equation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{efficiency} = {R_\text{radiation} \over R_\text{radiation} + R_\text{loss}} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which would suggest that higher radiation resistance means higher efficiency. But it is important when using this equation to pick a single point to measure radiation resistance and loss resistance, and normalize all values to that point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider that a typical antenna system consists of numerous devices which transform impedances. They may be simple transformers, but also transmission lines and even antennas themselves (which are effectively transformers between the feedpoint impedance and the impedance of free space) do transformer impedances. So a resistance of a particular value may appear to have a different value when viewed from another perspective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, a folded dipole has 4x the impedance of a similar not-folded dipole, and thus 4x the radiation efficiency if your definition for radiation resistance is to measure it at the feedpoint. (There are other definitions!) But that does not mean a folded dipole is 4x as efficient, because the ohmic losses in the antenna conductors are also 4x bigger. And if this folded dipole is fed with coax it will be a poor match, and the antenna system is subject to additional &lt;a href=&quot;https://ham.stackexchange.com/questions/7333/what-is-the-actual-loss-in-a-feed-line-with-high-swr&quot;&gt;SWR loss&lt;/a&gt; as well.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-12-17T04:32:16.260" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15824" PostTypeId="1" AcceptedAnswerId="15825" CreationDate="2019-12-17T08:15:04.200" Score="0" ViewCount="196" Body="&lt;p&gt;A dipole which is exactly one half wave length allows reflections within the antenna to be in phase with the applied signal. To me it seems that this situation gives an antenna which will produce the most output for a given input signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna is not exactly one half wave length then the reflections won't be in phase exactly with the applied signal and the antenna output will drop because the reflections are subtracting from the applied signal for some duration of the waveform cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, in order to make the antenna resonant, wouldn't it be a better idea to not shorten a half wave dipole to remove the inherent inductive reactance but rather leave it at exactly half a wave length and cancel out the reactance with series capacitance ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2019-12-17T18:28:21.977" Title="Is shortening a half wave dipole to make it resonant by removing the inductive reactance a good idea?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15825" PostTypeId="2" ParentId="15824" CreationDate="2019-12-17T18:28:21.977" Score="2" Body="&lt;p&gt;A dipole can be &lt;em&gt;physically&lt;/em&gt; a half wave, or &lt;em&gt;electrically&lt;/em&gt; a half wave.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A dipole that's physically a half wave has a nonzero reactance at the feedpoint. This means it is &lt;em&gt;not&lt;/em&gt; resonant, and that the reflections within the antenna are &lt;em&gt;not&lt;/em&gt; precisely in phase with the signal. (These are two ways of saying the same thing.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The electrical length is determined by the time taken for the wave to traverse the antenna. Making the dipole a little shorter until the reactance is zero makes the dipole &lt;em&gt;electrically&lt;/em&gt; a half wave. Now it &lt;em&gt;is&lt;/em&gt; resonant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Making the antenna resonant doesn't make it better per se, but since any low-loss feedline (like, any one you'd use in practice) has a negligible reactance to its characteristic impedance, an antenna that is not resonant (which means a non-zero reactance at the feedpoint) must necessarily be mismatched to some extent. A mismatch means additional &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;SWR loss&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna that is resonant is not necessarily matched to the feedline, or even at minimum SWR, unless it just so happens the feedpoint impedance and feedline's characteristic impedance happen to be the same. Resonant dipoles typically have an impedance around 75 ohms; bending the dipole into a &quot;V&quot; decreases the feedpoint impedance and it's usually possible to get it down to 50 ohms. So it's usually possible to match a dipole to 50 or 75 ohm coax without any additional matching devices, though you'd still &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;want a balun in there&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you could always match the antenna some other way, but most ways you might do it (like adding discrete capacitors or inductors) would introduce additional loss, usually more than is saved by reducing the mismatch losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice on HF, all this is more theoretical than practical because the feedline losses, and thus the mismatch losses, are low. Any SWR under 1.6:1 is within the specifications of most transmitters and &quot;plenty good enough&quot; for most HF applications. The advantage to twiddling with the dipole shape to get closer to 50 ohms is really just that you then have a wider band where you're under 1.6:1.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2019-12-17T18:28:21.977" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="15826" PostTypeId="2" ParentId="15809" CreationDate="2019-12-17T19:55:43.350" Score="2" Body="&lt;p&gt;It might be the transformers frequency response is not flat. Try replacing them with reputable units that have a published frequency response such as &lt;a href=&quot;https://www.digikey.co.uk/product-detail/en/tamura/TTC-105/MT4134-ND/285701&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. See more signalink tweaks &lt;a href=&quot;http://www.frenning.dk/OZ1PIF_HOMEPAGE/SignaLinkUSB-mods.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. &lt;/p&gt;&#xA;" OwnerUserId="1098" LastActivityDate="2019-12-17T19:55:43.350" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15827" PostTypeId="1" AcceptedAnswerId="15829" CreationDate="2019-12-17T23:39:43.737" Score="5" ViewCount="149" Body="&lt;p&gt;Is it possible to transmit a short message across the Atlantic ocean from the UK to the US via shortwave? From what I understand, long-distance shortwave communication has lower bandwidth than other forms of communication such as microwave which uses line-of-sight. So by a short message, I mean maybe around three bytes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please excuse any poor phrasing of my questions/lack of knowledge. I am new to Amateur Radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Some questions:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;1.&lt;/strong&gt; To send a message of around three bytes over such a long distance, would this require an antenna that uses alot of power?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;2.&lt;/strong&gt; Are there companies that enable users to rent space on antennas that would be capable of transmitting messages over such long distances? Or would this require a completely custom infastructure(e.g. buying land and building a tower(s) with the necessary antennas)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;3.&lt;/strong&gt; How reliable would this be? I am aware that messages transmitted via shortwave may be subject to scrambling/interference due to sunspot activity/ionosphere conditions and poor weather.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If there are any other things to consider for this theoretical scenario (e.g. licensing, costs etc), I would appreciate any information on them.&lt;/p&gt;&#xA;" OwnerUserId="16117" LastEditorUserId="4665" LastEditDate="2019-12-17T23:46:31.287" LastActivityDate="2019-12-18T02:23:15.837" Title="Using shortwave communication, how difficult is it to transmit messages from the UK to the US?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15828" PostTypeId="1" CreationDate="2019-12-17T23:52:05.927" Score="8" ViewCount="146" Body="&lt;p&gt;I recently came into possession of number of old ham radio and a variety of old test equipment.  Items from to 1960s to the 1980s.  Several of the items have a strong musty smell.  What can I do to get rid of the smell without damaging the items?&lt;/p&gt;&#xA;" OwnerUserId="16118" LastActivityDate="2019-12-19T12:04:25.757" Title="Musty smell in old equipment" Tags="&lt;maintenance&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15829" PostTypeId="2" ParentId="15827" CreationDate="2019-12-18T02:23:15.837" Score="10" Body="&lt;blockquote&gt;&#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;To send a message of around three bytes over such a long distance, would this require an antenna that uses alot of power?&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. There's a huge variety of tradeoffs here, but as a quick calibration, &lt;a href=&quot;https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software)&quot; rel=&quot;noreferrer&quot;&gt;WSPR&lt;/a&gt; sends 50 bit messages (so, a bit more than twice what you're asking) all around the world using power levels usually ranging from several milliwatts to ten watts. Its main disadvantage is that it takes almost two minutes to send such a message. There are digital modes that are quite a bit faster, that can still do the job with less than 100 watts (which is considered an &quot;ordinary&quot; amount of power for an amateur).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Are there companies that enable users to rent space on antennas that would be capable of transmitting messages over such long distances? Or would this require a completely custom infastructure(e.g. buying land and building a tower(s) with the necessary antennas)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Hmm, maybe? I'm not familiar with rental, but I imagine it's possible. However, you might need far less in the way of land and antennas than you think, and no towers at all. It's hard to get into specifics without knowing details of your situation, but a simple wire antenna on a rooftop or a &quot;small transmitting loop&quot; antenna could potentially get the job done.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How reliable would this be? I am aware that messages transmitted via shortwave may be subject to scrambling/interference due to sunspot activity/ionosphere conditions and poor weather.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Less than 100% reliable — sometimes solar flares and the like make HF pretty close to completely unusable. But on &lt;em&gt;most&lt;/em&gt; days, there will be at least several hours a day when there is at least a 90%-reliability path from the UK to a given part of the US. When those hours occur and which bands they occur on depend on solar cycle, time of year, and location (the US is a big place).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If there are any other things to consider for this theoretical scenario (e.g. licensing, costs etc), I would appreciate any information on them.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Licensing is probably the sticking point. I imagine the communications you want to do are probably &lt;em&gt;not&lt;/em&gt; within the rules of amateur radio, so another form of licensing will be necessary. I'm not especially familiar with the UK but it seems like there's no out-of-the-box license type for this kind of use, and requests are handled case-by-case by Ofcom. In this regard, working with a third party is probably to your benefit.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-12-18T02:23:15.837" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15830" PostTypeId="1" AcceptedAnswerId="15832" CreationDate="2019-12-18T03:39:28.353" Score="6" ViewCount="207" Body="&lt;p&gt;For a resonant 1/2 wave dipole when used for transmitting, does the fact that the reflected waves on the antenna are in phase with the applied signal result in zero reactance at the feed point, or does zero reactance happen for some other reason ?&lt;/p&gt;&#xA;&lt;p&gt;This question isn't answered in explanations found on Wikipedia, in the ARRL handbook and a in few other antenna books i've read.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-06-20T11:28:01.793" LastActivityDate="2020-06-20T11:28:01.793" Title="For a resonant 1/2 wave dipole, does the reflections being in phase with the applied signal cause the zero reactance seen in the feedpoint impedance?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15831" PostTypeId="2" ParentId="183" CreationDate="2019-12-18T15:04:24.997" Score="9" Body="&lt;p&gt;I keep these &quot;Q&quot; signals in line with this :&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;QRN is &quot;N&quot;atural band noise ( lightning )   &lt;/li&gt;&#xA;&lt;li&gt;QRM is &quot;M&quot;an-made band noise ( crowded signals )    &lt;/li&gt;&#xA;&lt;li&gt;QSB is &quot;B&quot;utterfly effect from Ionosphere in-stability.    &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8402" LastEditorUserId="8717" LastEditDate="2019-12-18T19:10:53.497" LastActivityDate="2019-12-18T19:10:53.497" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15832" PostTypeId="2" ParentId="15830" CreationDate="2019-12-18T22:53:24.530" Score="2" Body="&lt;p&gt;Basically yes. One of the ways to view reactance is in terms of the phase relationship between voltage and current at a given point. When there is an inductive reactance, voltage leads current. When there is a capacitive reactance, voltage lags current. When there is zero reactance, voltage and current are in phase.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resonance condition means that a reflected wave comes back to the feedpoint with the same phase relationship as it had when it left, and therefore it doesn't contribute any reactance.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-12-18T22:53:24.530" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15833" PostTypeId="2" ParentId="15828" CreationDate="2019-12-19T12:04:25.757" Score="5" Body="&lt;p&gt;Welcome to hamSE! These recommendations from the &lt;a href=&quot;http://www.arrl.org/forum/topics/view/132&quot; rel=&quot;noreferrer&quot;&gt;ARRL Forum&lt;/a&gt; and &lt;a href=&quot;https://www.tdpri.com/threads/removing-musty-smell-from-an-amp.977574/&quot; rel=&quot;noreferrer&quot;&gt;Telecaster fans&lt;/a&gt; suggest activated charcoal, kitty litter, ground coffee (not used coffee grounds!), baking soda, sunshine (UV light) and dryer sheets as potential odor remedies. Warm, dry, fresh air and time are also important. What works best for you may depend on the nature of the odor and what you have on hand to fight it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Did you know you can post an answer to your own question?! Once you've had a chance to try to remove the odor, please let us know what worked and what didn't.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2019-12-19T12:04:25.757" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15834" PostTypeId="2" ParentId="15784" CreationDate="2019-12-19T13:07:44.670" Score="5" Body="&lt;p&gt;It turns out that these cables were made by TE Connectivity.&#xA;Some time back, they sold that business to Commscope.&#xA;After talking to Commscope, it looks like those cables no longer are made.  :(&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Their recommendation is to use FSJ1-50, even though RG-214 has a lower transfer impedance at this frequency, because the shield coverage is better.&#xA;So I will have to fight the leakage at the joints of the connectors and cables.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyway, if someone else can benefit from this info, here it is. &lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2019-12-19T13:07:44.670" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15835" PostTypeId="2" ParentId="11847" CreationDate="2019-12-19T14:48:59.080" Score="2" Body="&lt;p&gt;Actually, the answer is &quot;it depends&quot;.&lt;br&gt;&#xA;Polydoroff did some work on this in the 60's and documented it in his book:&#xA;&lt;a href=&quot;https://books.google.com/books/about/High_frequency_Magnetic_Materials.html?id=GC4jAAAAMAAJ&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://books.google.com/books/about/High_frequency_Magnetic_Materials.html?id=GC4jAAAAMAAJ&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd quote the relevant part but my copy isn't with me at the moment. &#xA;He showed significant shortening of the antenna with the ferrites he tested.&#xA;He used ferrites of very low permeability, something like 8 or 10 if I remember correctly.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastActivityDate="2019-12-19T14:48:59.080" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15836" PostTypeId="2" ParentId="15784" CreationDate="2019-12-19T18:48:31.537" Score="0" Body="&lt;p&gt;What you are looking for is Andrew Heliax®. &lt;a href=&quot;https://www.google.com/url?sa=t&amp;amp;source=web&amp;amp;rct=j&amp;amp;url=http://www.repeater-builder.com/antenna/andrew/andrew-shielding-effectiveness.pdf&amp;amp;ved=2ahUKEwjIh8zkp8LmAhWPU80KHYGKDnkQFjAJegQIAxAB&amp;amp;usg=AOvVaw08YWNpdBNqImqckOK2K24U&quot; rel=&quot;nofollow noreferrer&quot;&gt;This page from the full PDF&lt;/a&gt; indicates that it has &lt;strong&gt;in excess of 120 dB&lt;/strong&gt; of isolation from 10 MHz to 10 GHz. It has a solid yet somewhat flexible copper shield.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/d8wzM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/d8wzM.jpg&quot; alt=&quot;Andrew HELIAX leakage vs. frequency&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Have you looked at double- or quad-shielded coax &lt;em&gt;with the inner foil bonded to the dielectric&lt;/em&gt;? It is more flexible than Heliax®.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unless you are willing to give up on BNC connectors, you will likely need solid adapters at each end of the cable. However, perhaps you can find BNC connectors for this cable.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2019-12-19T18:48:31.537" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15839" PostTypeId="1" CreationDate="2019-12-25T18:18:41.723" Score="2" ViewCount="130" Body="&lt;p&gt;I got a Kenwood HT and using it with the Elk Antenna&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the radio, there is Tone and I set it to 67 Hz. I wasn’t able to break thru to the satellite and had it in Full Duplex mode. I can hear everyone on the satellite very well and the Signal meter was high. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there another setting other than Tone to set? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On my Baofeng, I used to set CTCSS and that is what the sites call for AO-91/92.&lt;/p&gt;&#xA;" OwnerUserId="16152" LastEditorUserId="8717" LastEditDate="2019-12-25T19:08:08.790" LastActivityDate="2020-01-26T03:03:45.453" Title="Kenwood TH-D72A and AO-91/92" Tags="&lt;satellites&gt;&lt;ht&gt;&lt;kenwood&gt;&lt;tone-squelch&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15840" PostTypeId="1" CreationDate="2019-12-25T20:11:13.760" Score="2" ViewCount="311" Body="&lt;p&gt;Linux Mint MATE 64 (system is up to date)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I installed qsstv &#xA;first it runs normally but no CAT ..&#xA;then I installed hamlib and put in the same string for the USB Device like in FlDigi which runs now UFB!  (&lt;code&gt;/dev/serial/by-id/usb-Silicon_Labs_CP2105_Dual_USB_to_UART_Bridge_Controller_00733873-if00-port0&lt;/code&gt;) &#xA;Also chose the FT-991 for my FT-991A &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Now if I start qsstv (without error) it is very slow (needs 12% from systemtime)..nearly not possible to do something else with my PC.&#xA;? I have no idea why...&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;For the device &lt;code&gt;/dev/serial/by-id/usb-Silicon_Labs_CP2105_Dual_USB_to_UART_Bridge_Controller_00733873-if00-port0&lt;/code&gt;, I made a sym link eg 991a - but after I restart Mint the sym Link is gone. Why ?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="16098" LastEditorUserId="76" LastEditDate="2019-12-25T21:59:48.990" LastActivityDate="2019-12-26T19:45:41.003" Title="QSSTV on Linux Mint" Tags="&lt;software&gt;&lt;linux&gt;&lt;sstv&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15841" PostTypeId="2" ParentId="10293" CreationDate="2019-12-25T20:52:53.497" Score="-4" Body="&lt;p&gt;I have a 35 amp Astron linear supply and the heat generated at 25 watts is negligible. So I beg to differ with the answer that linear power supplies run hot.&lt;/p&gt;&#xA;" OwnerUserId="16154" LastEditorUserId="16154" LastEditDate="2019-12-25T21:04:02.283" LastActivityDate="2019-12-25T21:04:02.283" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15842" PostTypeId="2" ParentId="15840" CreationDate="2019-12-25T22:28:17.247" Score="1" Body="&lt;p&gt;I once successfully used QSSTV on Linux Mint for displaying digital pictures. However, at some point after upgrading LM it ceased working correctly. It would just not lock onto a signal anymore. But I did not have &lt;a href=&quot;http://users.telenet.be/on4qz/qsstv/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;the latest version&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to try getting it working, I suggest that you forget the symlink until after you get the software working right.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try increasing qsstv's priority to something a little less than 100%, say 80%. An easy way to do that is from within htop (&lt;code&gt;sudo apt-install htop&lt;/code&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I suggest that you search on on the Debian-based Linux forums for QSSTV. If you find a solution, then by all means post it as an answer here! :-)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you install an earlier version of LM in a virtual machine as a guest OS, QSSTV might very well work.  Virtualbox and Mint MATE 18.1 should do it. Just don't upgrade LM 18.1, or you risk having the same problem that you do now. Don't install Virtualbox using Synaptic, etc. Instead, download everything from &lt;a href=&quot;https://www.oracle.com/virtualization/technologies/vm/downloads/virtualbox-downloads.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Oracle&lt;/a&gt;. And afterwards, be sure you install the guest extensions.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-12-26T19:45:41.003" LastActivityDate="2019-12-26T19:45:41.003" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15843" PostTypeId="2" ParentId="10401" CreationDate="2019-12-26T14:01:06.903" Score="0" Body="&lt;p&gt;You might want to take a look at the HC_12 433Mhz devices, they have a range of 1Km. Cheap and dead easy to use. Build your test setup using these units, and iron out your bugs. Then move over to LoRa once you are comfortable that your system is functioning well. Then longer range will be possable.&lt;/p&gt;&#xA;" OwnerUserId="16156" LastActivityDate="2019-12-26T14:01:06.903" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15844" PostTypeId="2" ParentId="15714" CreationDate="2019-12-26T14:51:33.400" Score="2" Body="&lt;p&gt;It looks to me like you've put a lot of effort into tracking this down. I believe you are on the right track as far as the Pi creating a lot of broadband noise. But I'm wondering if you've tried putting the SDR on a extension USB cable so that you can move it as far from the Pi as possible? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've found that getting farther from a noise source helps a lot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are feeding the SDR via a external antenna that is fed by coax, you could embed the SDR in a all metal project box (grounded), that has the coax passing on on one side for the antenna input, and a USB extension cord running to the Pi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best of luck!&lt;/p&gt;&#xA;" OwnerUserId="16157" LastActivityDate="2019-12-26T14:51:33.400" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15845" PostTypeId="2" ParentId="15839" CreationDate="2019-12-27T02:35:55.947" Score="1" Body="&lt;p&gt;This might be crazy, but you were on the TX band when you attempted to TX? You should have continued to hear the downlink of you were. Sinfulness it is the simple things. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, if it was during the last few days, you could have been doing everything correctly but being stomped out by stronger stations.  I assume you are just starting out with satellites, if this is correct, try to get on a pass late at night when there are fewer people on. Makes it easier to get into the birds. &lt;/p&gt;&#xA;" OwnerUserId="9550" LastActivityDate="2019-12-27T02:35:55.947" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15846" PostTypeId="1" CreationDate="2019-12-28T06:59:54.810" Score="1" ViewCount="107" Body="&lt;p&gt;I'm trying to get a ham radio listener working with RTLSDR on an old Pentium 4. Unfortunately it is playing for a few seconds, then not playing for a split second, very split up. Is there a way I can adjust this line for better throughput? The odd thing is it wasn't showing all memory used or excessive load (1.37)&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;rtl_fm -M fm -f 440.72M -l 22 | play -r 24k -t raw -e s -b16 -c 1 -V1 -&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Is there a minimum requirement for RTLSDR on XUbuntu or is there a better way I need to tune rtl_fm or play - pipe output?&lt;/p&gt;&#xA;" OwnerUserId="14201" LastActivityDate="2019-12-30T15:41:58.590" Title="Ham radio listener is split up on old hardware" Tags="&lt;rtl-sdr&gt;&lt;linux&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15847" PostTypeId="2" ParentId="15035" CreationDate="2019-12-28T08:33:37.230" Score="0" Body="&lt;p&gt;MMSSTV seems to work well if installed using Wine.&lt;/p&gt;&#xA;" OwnerUserId="16166" LastActivityDate="2019-12-28T08:33:37.230" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15849" PostTypeId="1" CreationDate="2019-12-28T18:17:26.530" Score="5" ViewCount="143" Body="&lt;p&gt;What does this mean:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;CQ de KYHP QTC? K&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;My father-in-law was a radio operator in the merchant marines during WWII — this was his last writing.&lt;/p&gt;&#xA;" OwnerUserId="16171" LastEditorUserId="1362" LastEditDate="2019-12-30T15:48:54.197" LastActivityDate="2019-12-30T15:48:54.197" Title="Last Morse call for Thomas?" Tags="&lt;cw&gt;&lt;q-codes&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15850" PostTypeId="2" ParentId="15849" CreationDate="2019-12-28T19:21:46.907" Score="5" Body="&lt;p&gt;That was a Morse code message, using common abbreviations to save time. Here it is translated into plain language:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;[CQ=] Calling any station, [de=] from radio station KYHP.  [QTC?=] How many telegrams have you to send? [K=] Go ahead, I'm listening.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The first letter K means that the station was a US station; however, it may or may not have actually been located there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The call sign KYHP has apparently been reassigned to a commercial TV station.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2019-12-28T19:50:43.877" LastActivityDate="2019-12-28T19:50:43.877" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15851" PostTypeId="2" ParentId="15846" CreationDate="2019-12-29T22:49:35.590" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The odd thing is it wasn't showing all memory used or excessive load (1.37)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If I remember correctly, the Pentium IV is a single-core architecture with the option for &lt;em&gt;Hyperthreading&lt;/em&gt;, which really is just one core with nearly two pipelines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, a load &gt; 1 is actually a heavy load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would have estimated the load of an RTL-FM reception to be low, but obviously, you're using more than one full core at full speed; that means you're very likely running into dropped samples on the RTL dongle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Aside from the Pentium IV burning power like a stove, it seems to be too slow for the task at hand. Maybe it's busy with something else? Maybe the inefficient 2000s-era USB host hardware is to blame? Or the inefficient sound card interface? Who knows.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pentium IV predates a lot of really useful processor instructions for signal processing (it's stuck in the SSE2 era...), so even a NEON-enabled ARM of similar clock speed would often beat it in such loads (e.g. a gen3/gen4 Raspberry Pi executing an ARM64 Debian (not Raspbian, which only uses &quot;old&quot; instructions to stay compatible with the original Raspberry Pi)).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="1362" LastEditDate="2019-12-30T15:41:58.590" LastActivityDate="2019-12-30T15:41:58.590" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="15853" PostTypeId="1" AcceptedAnswerId="15855" CreationDate="2019-12-30T10:59:40.690" Score="0" ViewCount="574" Body="&lt;p&gt;I am building the T/R switching circuit for an HF linear amplifier covering 80m band to 20m band. The current circuit takes a potential-free contact from the  exciter and use this contact to turn on/off the relay. When PTT is pushed relay contacts connect the RF output from exciter to HF linear amp input and output of HF linear amp to antenna.  When PTT is disengaged the linear amplifier is bypassed to connect the antenna directly to the exciter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I like to avoid the PTT connection from the exciter to HF linear amp, by sensing HF  carrier from exciter output and using this input to switch the relay.&#xA;Problem with this approach is that when using SSB modulation, relay opens briefly as carrier is absent when audio is briefly at a low level. How to get around this problem? &lt;/p&gt;&#xA;" OwnerUserId="16129" LastActivityDate="2020-06-29T22:35:09.893" Title="Can a carrier operated relay be used for T/R switching in a HF linear amplifier?" Tags="&lt;hf&gt;&lt;rf-power&gt;&lt;ssb&gt;" AnswerCount="3" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15854" PostTypeId="2" ParentId="15853" CreationDate="2019-12-30T19:27:34.870" Score="0" Body="&lt;p&gt;As I understand you, your amplifier looks for a certain level of RF power at the input.  If it is there, then the amplifier switches to active mode; if the RF power isn't at the input, then the amplifier switches to standby/bypass mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The advantage of using that switching method must be that no secondary connection for a switching signal between the exciter and the amplifier is necessary.  The disadvantage is that in SSB, when the audio input level is low, the RF power from the exciter is so low that the amplifier doesn't go into active mode.  Also, when the audio input level rises, then there is a switching delay.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could try adjusting the threshold level, so that the your amplifier kicks on a little sooner, or work on making the amplifier switch on faster to reduce the switching delay.  (Vacuum relays, or PIN diode switching perhaps?)  If that doesn't work, then it seems to me that you need to either accept things the way they are, or else design your amplifier to include a separate switching input.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2019-12-30T19:27:34.870" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15855" PostTypeId="2" ParentId="15853" CreationDate="2019-12-31T03:22:33.753" Score="1" Body="&lt;p&gt;If you rely on detecting RF output to activate the T/R relay, you will be switching it while there is already RF output (obvious, I know...) this leads to two problems: the switching can cause a transient high SWR that may damage the exciter, and switching under power can cause arcing which damages the T/R relay itself. Even if it doesn't cause an immediate failure it can put more stress on the equipment leading to premature failure. This is why best practice is to use a separate keying line to engage the T/R relay slightly &lt;em&gt;before&lt;/em&gt; the exciter starts making power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But to answer your question directly, equipment that does T/R switching for SSB usually has a circuit which adds a short delay before un-keying, usually a hundred to a few hundred milliseconds, and usually user-adjustable. This avoids excessive switching during speech.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2019-12-31T03:22:33.753" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15856" PostTypeId="1" CreationDate="2019-12-31T10:23:49.600" Score="3" ViewCount="111" Body="&lt;p&gt;If I understand things right if you go &quot;down&quot; to &quot;lower bands&quot; you eventually get to &quot;top band&quot;, which is 160 meter band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since this doesn't make any sense to me, is there something I'm missing? You keep going lower until you get to the top?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do I get it right that &quot;up/down&quot; and &quot;higher/lower&quot; (unless qualified with the word &quot;wavelength&quot;) refer to higher/lower &lt;em&gt;frequency&lt;/em&gt;, but &quot;top band&quot; is just an outlier that for some reason doesn't follow this convention but is just defined to be 160 meter?&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="76" LastEditDate="2019-12-31T17:11:31.983" LastActivityDate="2019-12-31T17:11:31.983" Title="What is &quot;up&quot; and &quot;down&quot;, and is it consistent with &quot;top band&quot;?" Tags="&lt;hf&gt;&lt;frequency&gt;&lt;jargon&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15857" PostTypeId="1" CreationDate="2019-12-31T11:45:46.097" Score="0" ViewCount="495" Body="&lt;p&gt;I am looking for a output filter to use with a HF linear amplifier called miniPA70 which is available through several online auction sites. The circuit is available here : &lt;a href=&quot;http://iu3idf.blogspot.com/2017/04/a-small-power-amplifier.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://iu3idf.blogspot.com/2017/04/a-small-power-amplifier.html&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am intending to use this amplifier in 80m, 40m and 20m bands. So i need filters for these bands. Most of the filters i saw online were LPF pi-section LC filters. LC filters make sense as they don't dissipate energy. Having a LPF also makes sense as the harmonics will be having frequency as multiples of the useful amplified signal( for 40m band, i can have a LPF of 7.3MHz cutoff; and harmonics will be 14MHz, 21Mhz etc which are filtered out by LPF).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have the following questions regarding selection of LPF - &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The LPF filters out the harmonics whereas it allows the fundamental to pass unattenuated into the antenna. Where is the energy from these harmonics dissipated? (if i use a good quality inductors and capacitors, these components wont be able to dissipate much energy)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Does the energy of harmonics get reflected back to the final MOSFETs and damage them? (If it is so, i should be able to see a high VSWR between PA output and LPF input)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In practice, how much percentage of the energy contained in the harmonics with respect to the fundamental? (I think this depends on what device is used in final. But for a MOSFET, how much should i expect)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is it a good idea to create a Band Pass filter rather than Low Pass Filter. This filter should be such that all the harmonics will be terminated at a dummy load and filtered output will go to the antenna. (Does this make the MOSFET see less reflections from filter?)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="16129" LastActivityDate="2020-01-03T13:15:51.217" Title="What kind of filter should be used at the output of HF linear amplifier?" Tags="&lt;rf-power&gt;&lt;impedance-matching&gt;&lt;filter&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15858" PostTypeId="2" ParentId="15856" CreationDate="2019-12-31T11:52:14.737" Score="4" Body="&lt;p&gt;These are just conventions. Back in the day of wavelengths determining the band you are in, the “highest” (i.e. the longest wavelength) band was the 160m band. This is of course not true any more, with many countries having access to bands with much longer wavelengths. But the 160m band is still known as “top band”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since then, it has become the convention to talk about frequencies rather than wavelengths. But when referring to a frequency &lt;strong&gt;band&lt;/strong&gt;, we still refer to them by their approximate wavelengths. Hardly anyone talks about the 21MHz band, but everyone knows where the 15m band is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you hear someone in a pileup who says “listening up 10-15” then they mean they are listening to frequencies between 10kHz and 15kHz &lt;em&gt;higher&lt;/em&gt; than the one they are transmitting on.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2019-12-31T11:52:14.737" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15859" PostTypeId="1" CreationDate="2019-12-31T11:56:56.313" Score="3" ViewCount="83" Body="&lt;p&gt;What is so special about a low noise amplifier? If I were to design an amplifier, I would always design an amplifier with low noise anyway.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Why is it emphasised as being “Low Noise”?&lt;/li&gt;&#xA;&lt;li&gt;What are the design features that makes an amplifier “low noise”?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="5349" LastEditorUserId="76" LastEditDate="2019-12-31T17:13:08.537" LastActivityDate="2019-12-31T18:05:12.983" Title="What is unique about a Low Noise Amplifier (LNA)?" Tags="&lt;electronics&gt;&lt;amplifier&gt;&lt;lna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15860" PostTypeId="2" ParentId="15859" CreationDate="2019-12-31T18:05:12.983" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If I were to design an amplifier, I would always design an amplifier with low noise anyway.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Nope! For a power amplifier, you'd do a different tradeoff; the noise figure of that amplifier nearly doesn't matter at all, whereas the capability to produce a high output power does very much.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Same goes for other aspects of amplifiers, things like linearity/fidelity, power-efficiency (&lt;em&gt;immensely&lt;/em&gt; important both in the portable radio as well as in the higher-power regime, since cooling is a hard technical problem)…&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why is it emphasised as being “Low Noise”?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Because, as explained above, the design tradeoffs made for that amplifier led to it being low in noise, rather than power-efficient, powerful-output, low in cost, small, …&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What are the design features that makes an amplifier “low noise”?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Good question! That's actually a hard one and it involves more than just the way you connect the components of an amplifier:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Achieving a low noise figure requires your amplifier to be operated in a manner that its input impedance can be &lt;em&gt;low&lt;/em&gt; (which is unusual for amplifiers, if you think about it), because that means that thermal noise doesn't induce high voltages on the input. This can be achieved via various means – appropriate input resistors, biasing of transistors, feedback mechanisms, carefully matched transistor pairs...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, you'll want to have few transistor stages doing the majority of the gain; more transistors will just increase the noise figure, and this being a low-noise amplifier, that's undesirable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Obviously, that single transistor can't have incredibly high gain – and its gain needs to be especially stable, since there's no supporting circuitry to compensate anything. Also, you'd want the transistor gain to be as high as possible, because the gain of the LNA defines, together with its noise figure, the whole signal chain's noise figure (Friis' Noise Formula; you definitely want to read up on that!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, that requires your semiconductor manufacturer to very carefully select the wafer dies that make it into  LNAs. As you can imagine, that leads to discarded parts and thus cost – and thus, another reason why not every amplifier is an LNA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll want to design your amplifier circuit so that the central transistor is very robustly biased in a high-gain region of its IO curve; that wastes power, since it implies that &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;more than a minimal current is always flowing to keep up that bias&lt;/li&gt;&#xA;&lt;li&gt;you're not operating the amplifier close to its maximum output, where it's most effective&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2019-12-31T18:05:12.983" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15861" PostTypeId="2" ParentId="15857" CreationDate="2019-12-31T18:16:56.897" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;LC filters make sense as they don't dissipate energy. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Hm, that's kind of true (at least theoretically), but guess what: that energy that doesn't reach the antenna still has to go somewhere, and will eventually be converted to heat. In the case of LC filters, that might be in some ohmic resistances in components and traces, or in the amplifier output stage.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Does the energy of harmonics get reflected back to the final MOSFETs &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Effectively, yes, a LPF like that simply looks like a large resistance, i.e. a mismatch, to higher frequencies.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;and damage them? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, that doesn't necessarily damage your amplifier: Often, amplifiers are designed to be able to dissipate the harmonics it produces themselves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If they aren't (can't tell you about your specific amp), an option would be to have a high pass &quot;shorten&quot; out the harmonics to a dummy load / ground.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(If it is so, i should be able to see a high VSWR between PA output and LPF input)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm not a fan of VSWR as measure. Standing waves aren't measurable &quot;at a single point&quot;, the whole point of standing waves is that there's locations of high and low amplitude on the transmission line.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In practice, how much percentage of the energy contained in the harmonics with respect to the fundamental? (I think this depends on what device is used in final. But for a MOSFET, how much should i expect)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That &lt;em&gt;really&lt;/em&gt; depends. There's nothing that limits that number in either direction for a MOSFET – you can build a good mixer with MOSFETs (which means that basically &lt;em&gt;all&lt;/em&gt; energy is moved to harmonics) or you can build a very linear amplifier (which means that nearly none of the energy is in harmonics).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, you're buying a linear amplifier – and that should come with very clear datasheets telling you things like second- and third-order intercept points, or acceptable output power ranges for which nonlinearity is limited to a low figure.  Nonlinearity is what causes the harmonics!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can't get such a datasheet (you &lt;strong&gt;really&lt;/strong&gt; should when buying electronics that someone built – they need to have the measurement equipment to know how well the device is built, and they must tell you, else buy somewhere else), because you're building this yourself, then you'll have to be able to measure the harmonics you get from single- and dual-tone tests yourself. From that, you can calculate the amount of power in the most significant harmonics yourself, and that will allow you to decide what kind of filtering you need – or whether you want to avoid overly complex filtering by &lt;em&gt;predistorting&lt;/em&gt; your input so that the output looks linear. (yay, SDR beats classical radio once again.)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it a good idea to create a Band Pass filter rather than Low Pass Filter. This filter should be such that all the harmonics will be terminated at a dummy load and filtered output will go to the antenna. (Does this make the MOSFET see less reflections from filter?)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Depends. Usually, that's not necessary or desirable, since band pass filters are hard to design and get right reliably if you need to defined both the passband impedance as well as the stopband impedance over small frequency differences. &lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2019-12-31T18:23:39.707" LastActivityDate="2019-12-31T18:23:39.707" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15863" PostTypeId="1" AcceptedAnswerId="15865" CreationDate="2020-01-01T03:23:41.440" Score="2" ViewCount="61" Body="&lt;p&gt;I'm using a commonly available imbedded firmware implementation of FreeDV with an SSB HF transceiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems that FreeDV encodes the input audio signal in both the frequency and time domains, which means that the output signal amplitude doesn't follow the input signal amplitude, but rather the output level from FreeDV is always high, even with no input audio. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a real problem for some SSB transmitters and amplifiers which are designed to not operate at constant 100 % output, and the continuous high output can cause them to overheat. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also the continuous 100 % output causes batteries in portable SSB equipment to go flat much quicker. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition, an SSB signal that is always close to 100 % modulation level doesn't help with conservation of bandwidth or with reducing interference to other operators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To me it seems that FreeDV results in wasted energy when used with SSB. I'm surprised that FreeDV would operate this way, especially when it's advertised for SSB usage, which makes me think i'm missing something.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any way to make FreeDV encode the input audio signal only in the frequency domain so that the input signal level is preserved ie: no audio input produces no output from FreeDV ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="76" LastEditDate="2020-01-01T05:59:06.723" LastActivityDate="2020-01-01T11:24:54.810" Title="Is there a way to get FreeDV output level to follow the input audio amplitude?" Tags="&lt;digital-modes&gt;&lt;software&gt;&lt;ssb&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15865" PostTypeId="2" ParentId="15863" CreationDate="2020-01-01T11:24:54.810" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;It seems that FreeDV encodes the input audio signal in both the frequency and time domains, which means that the output signal amplitude doesn't follow the input signal amplitude, but rather the output level from FreeDV is always high, even with no input audio.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Nah, that's not really the case. FreeDV uses a multicarrier scheme with 14 orthogonal carriers. Each of these carriers a (differential) PSK signal – i.e. one with constant envelope. Math (to be specific, the Central Limit Theorem) says that if you add up &quot;many&quot; independent, but identically distributed random variables (combining the 14 carriers into one signal),  you end up with a (approximately) Gaussian distribution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And that is &lt;em&gt;good&lt;/em&gt;. It means we get the most information across, given a fixed output power. Any other amplitude distribution is worse (for the continuous-amplitude case, at least; see: &lt;a href=&quot;https://en.wikipedia.org/wiki/Differential_entropy&quot; rel=&quot;noreferrer&quot;&gt;Differential Entropy&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More info with same amplitude means we have, within the same bandwidth, more &quot;room&quot; to make our transmission robust. That's one of the reasons why FreeDV under low-SNR scenarios is usually better than analog SSB.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;This is a real problem for some SSB transmitters and amplifiers which are designed to not operate at constant 100 % output, and the continuous high output can cause them to overheat. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;These things will overheat because of the &lt;em&gt;power&lt;/em&gt; put through them. So, we can find a power that they can continuous work with, and just work with that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Scale down your amplitude. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Also the continuous 100 % output causes batteries in portable SSB equipment to go flat much quicker. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Whether you transmit an average of 1W of SSB AM audio or 1W of FreeDV digital data should make little to no difference to the amplifier current consumption. Notice that you'll need &lt;em&gt;higher&lt;/em&gt; peak power to reach an average SSB power of 1W, because FreeDV is more evenly distributing the power. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other words: by using a mode that has a more constant power, you're making the most of your amplifier. The other mode is the one &quot;wasting&quot; power – it's only transmitting at full power when you make a very loud sound!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is there any way to make FreeDV encode the input audio signal only in the frequency domain so that the input signal level is preserved ie: no audio input produces no output from FreeDV ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No, and that would be highly undesirable, because it would negate the positive aspects!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;So, you're misinterpreting an advantage as a misadvantage; FreeDV makes &lt;em&gt;use&lt;/em&gt; of the power you have. Of course, you're totally free to just reduce the output you feed into your modulator (simply scale it with a factor &amp;lt; 1), and thus reduce the output power of your amp. That will still be more reliable than a full-power AM SSB transmission.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-01-01T11:24:54.810" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15866" PostTypeId="1" CreationDate="2020-01-02T02:15:01.990" Score="1" ViewCount="118" Body="&lt;p&gt;I'm trying to listen in to the telemetry frequency for Wallops Island which is 411.325 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I punch this into my radio (Baofeng UV-5R), the closest I can get is 411.320 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will I still be able to pick this up?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I read I may have to adjust the squelch. &lt;/p&gt;&#xA;" OwnerUserId="16186" LastEditorUserId="4076" LastEditDate="2020-01-02T11:33:50.543" LastActivityDate="2020-01-03T21:52:56.657" Title="can I still hear a frequency if I can only tune in 5 kHz off?" Tags="&lt;uhf&gt;&lt;baofeng&gt;&lt;frequency&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15868" PostTypeId="1" CreationDate="2020-01-02T04:07:20.753" Score="0" ViewCount="119" Body="&lt;p&gt;I am DIYing a class-AB HF Linear Power amplifier. How to quantify the non-linearity of this amplifier. What are the common measures of non-linearity as applicable to RF power amplifiers? How to measure them? Any good reference on these parameters would be really helpful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;20MHz dual trace oscilloscope,&lt;/li&gt;&#xA;&lt;li&gt;RTL SDR dongle,&lt;/li&gt;&#xA;&lt;li&gt;ubitx transciever,&lt;/li&gt;&#xA;&lt;li&gt;30V/20A power supply. &lt;/li&gt;&#xA;&lt;li&gt;I am planning to get hold of a nanoVNA as well&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16129" LastEditorUserId="4076" LastEditDate="2020-01-03T14:15:06.237" LastActivityDate="2020-01-07T07:04:23.310" Title="measures for quantifying non-linearity of a HF linear power amplifier" Tags="&lt;hf&gt;&lt;rf-power&gt;&lt;dc-power&gt;&lt;linearity&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15869" PostTypeId="2" ParentId="15866" CreationDate="2020-01-02T11:46:49.823" Score="0" Body="&lt;p&gt;That's a frequency error of about 10 parts per million. That is very much in the order of frequency uncertainty of your handheld's oscillator, anyway!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;As different oscillators not being &lt;em&gt;exactly&lt;/em&gt; the same is a problem for &lt;em&gt;every&lt;/em&gt; radio communication, every communication standard is built in a way that allows for a receiver to deal with small frequency errors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Small&quot;, here, depends &lt;em&gt;very&lt;/em&gt; much on the specific mode. A wideband FM speech signal can be dozens of kilohertz off, considering that what is most important is the derivative of the carrier's frequency over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're having an satellite phone: These satellites tend to fly around this blue marble at a rather high speed. High speed means high Doppler shift, and your phone would need to deal with that, anyway. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think about the about 2€ worth of wifi chipset in a cheap wifi lightswitch: That thing has, with good luck, a 20 ppm-accurate oscillator. That means that the nominal 2.45 GHz frequency it wants to use is off by +- 49 kHz to begin with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think of any old AM radio, especially in the pre-PLL era: Do you think you'd be &lt;em&gt;instantly&lt;/em&gt; able to set the frequency of the device &lt;em&gt;exactly&lt;/em&gt; within, say, 20 kHz bounds, using a greasy knob pulling a rubber string connected to a dusty air+grime-core capacitor? You can do that, but because you are a great feedback loop, and can simultaneuously listen for the sound you're expecting and watch for the position of the needle on the frequency scale! (you're a closed-loop system compensating the inaccuracy of the knob frequency-setting mechanism)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No, all these devices rely on at least some tolerance in tuning, and on the ability to correct a detected frequency error.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-01-02T21:27:37.913" LastActivityDate="2020-01-02T21:27:37.913" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15870" PostTypeId="1" CreationDate="2020-01-03T01:27:10.293" Score="4" ViewCount="485" Body="&lt;p&gt;When my university encouraged me to apply for an amateur radio license, they never mentioned the fact that my address would be listed on the public FCC database, for anyone who Googles my name to easily see in the first few links.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that now that it's out there, it's probably already cached and can't be removed from the internet, because that's how the internet works. If someone wants to find my address, I want them to at least have to do &lt;em&gt;a little bit&lt;/em&gt; of work, though. If I cancel my radio license, would the page listing my information, address included, at least be removed from the FCC website?&lt;/p&gt;&#xA;" OwnerUserId="16189" LastEditorUserId="76" LastEditDate="2020-01-03T04:08:48.867" LastActivityDate="2020-01-08T22:02:44.863" Title="If I cancel my amateur license, will my address be removed from the FCC database?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15871" PostTypeId="2" ParentId="15866" CreationDate="2020-01-03T03:48:11.193" Score="1" Body="&lt;p&gt;Jefferey, this is a very easy question to answer, and the answer is no. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Wallops Island telemetry transmitter is probably going to be a narrow band FM signal, and 5 kHz off is too far to be able to hear it on your Bofeng receiver which is also a narrow band receiver. You would normally need to be within 1 - 3 kHz of the frequency to hear it properly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also the squelch control has nothing to do with the frequency, but you would turn the squelch off when testing if you can receive a signal and then only turn it on to get rid of the FM hiss between stations once you have steady reception.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if the transmitter is AM or some other mode, 5 kHZ would generally still be too far off frequency to hear properly.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-01-03T21:52:56.657" LastActivityDate="2020-01-03T21:52:56.657" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15872" PostTypeId="1" AcceptedAnswerId="15875" CreationDate="2020-01-03T11:39:01.967" Score="0" ViewCount="46" Body="&lt;p&gt;My gas burning heating unit takes its temperature readings from a 433 MHz thermostat, which is emitting precisely the same data packets in a packet train at some ~100 ms interval like this: 2 x OOK and 4 x FSK. The trains are emitted once a minute. What does this technique have to gain as opposed to emitting only in FSK ?&lt;/p&gt;&#xA;" OwnerUserId="8811" LastActivityDate="2020-01-03T14:07:49.450" Title="Both OOK and FSK used in the same transmission" Tags="&lt;cw&gt;&lt;modes&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15873" PostTypeId="2" ParentId="15857" CreationDate="2020-01-03T13:15:51.217" Score="0" Body="&lt;p&gt;&lt;a href=&quot;https://sites.google.com/site/rfpowertools/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RF Power Tools&lt;/a&gt; sells &lt;a href=&quot;https://sites.google.com/site/rfpowertools/home/low-pass-filters&quot; rel=&quot;nofollow noreferrer&quot;&gt;3-band and 7-band low-pass filters modules&lt;/a&gt;. You can purchase &lt;a href=&quot;https://rfpowertools.ecwid.com/100W-Low-Pass-Filter-Boards-p152266605&quot; rel=&quot;nofollow noreferrer&quot;&gt;bare boards to stuff yourself or assembled and tested units&lt;/a&gt;. You might also consider using their &lt;a href=&quot;https://rfpowertools.ecwid.com/MRF-101A-Eval-Board-p151153877&quot; rel=&quot;nofollow noreferrer&quot;&gt;100W MRF101 amplifier board&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do not attest to the specs for the products and I am not affiliated in any way with RF Power Tools.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-01-03T13:15:51.217" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15874" PostTypeId="2" ParentId="15868" CreationDate="2020-01-03T14:04:36.977" Score="2" Body="&lt;h1&gt;Super-Light intro to nonlinearities&lt;/h1&gt;&#xA;&#xA;&lt;h2&gt;Amplifier model&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Ideally, an amplifier has this output function &lt;span class=&quot;math-container&quot;&gt;$f(x)$&lt;/span&gt;, where &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt; is the input amplitude:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$f_\text{ideal}(x) = a_1 x\text,$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and we call &lt;span class=&quot;math-container&quot;&gt;$a_1$&lt;/span&gt; the amplitude gain (which is inherently the square root of the power gain).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sadly, real amplifiers don't have ideal behaviour, instead they have:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$f(x) = a_1 x\text + a_2 x^2 + a_3 x^3 + a_4 x^4 + \ldots$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;span class=&quot;math-container&quot;&gt;$a_i$&lt;/span&gt; can be positive, negative, whatever the physics of the amplifier makes them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A good amplifier has a &lt;span class=&quot;math-container&quot;&gt;$|a_1|\gg |a_2| ,|a_3| , |a_4|,\ldots$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a general rule of thumb, a sensibly designed amplifier &lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Intermodulation products&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Now, why is &lt;span class=&quot;math-container&quot;&gt;$a_2$&lt;/span&gt;, for example, a problem? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's look at &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$f_{2}(x) = a_2 x^2\text,$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where we've simply set all &lt;span class=&quot;math-container&quot;&gt;$a_i=0$&lt;/span&gt; except &lt;span class=&quot;math-container&quot;&gt;$a_2&amp;gt; 0$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's feed in a single tone, &lt;span class=&quot;math-container&quot;&gt;$x=\cos(\omega t)$&lt;/span&gt; at frequency &lt;span class=&quot;math-container&quot;&gt;$f = \frac{\omega}{2\pi}$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;\begin{align}&#xA;f_2(\cos(\omega t)) &amp;amp;= a_2\left(\cos(\omega t)\right)^2\\&#xA;&amp;amp;=a_2\cos(\omega t)\cos(\omega t)&amp;amp;\hspace{-8em}\text{trigonometrics: }\cos(a)\cos(b) &amp;amp;= \frac12\left(\cos(a+b)+\cos(a-b)\right)\\&#xA;&amp;amp;=a_2\frac12\left(\cos(\omega t + \omega t) + \cos(\omega t - \omega t)\right)\\&#xA;&amp;amp;=\frac{a_2}2 \left(\cos(2\omega t) + \underbrace{\cos(0)}_{=1}\right)\\&#xA;&amp;amp;= \frac{a_2}2 \cos(2\omega t) + \frac{a_2}{2}&#xA;\end{align}&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Oooops! We've built a frequency doubler! That's where the harmonics on even multiples of the fundamental frequency come from: from &lt;span class=&quot;math-container&quot;&gt;$a_i\ne 0$&lt;/span&gt; where &lt;span class=&quot;math-container&quot;&gt;$i$&lt;/span&gt; even. And the fact that the double frequency is far away from the input frequency allows us to cancel that effect with a simple low-pass filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, what happens if we have two tones, e.g. &lt;span class=&quot;math-container&quot;&gt;$x=\cos(\omega_1 t) + \cos(\omega_2 t)$&lt;/span&gt;?&#xA;We get harmonics at &lt;span class=&quot;math-container&quot;&gt;$2\omega_1$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$2\omega_2$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$\omega_1 + \omega_2$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$|\omega_1\omega_2|$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good news is, if &lt;span class=&quot;math-container&quot;&gt;$\omega_1$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\omega_2$&lt;/span&gt; are close together (relative to their value, e.g. &lt;span class=&quot;math-container&quot;&gt;$\frac{\omega_1}{2\pi} = 14.1\,\text{MHz}$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$\frac{\omega_2}{2\pi} = 14.2\,\text{MHz}$&lt;/span&gt;), then these intermodulation products will also be &quot;far away&quot; from the frequencies we care about, and we can filter them away. By the way, that's the difference between an amplifier and an active mixer: The amplifier has large &lt;span class=&quot;math-container&quot;&gt;$a_1$&lt;/span&gt; and small &lt;span class=&quot;math-container&quot;&gt;$a_2$&lt;/span&gt;, and the mixer has large &lt;span class=&quot;math-container&quot;&gt;$a_2$&lt;/span&gt; and small &lt;span class=&quot;math-container&quot;&gt;$a_1$&lt;/span&gt;. All amplifiers are (bad) mixers!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The math becomes longer, but also stays boring (and that's why I'm leaving it as an exercise for the reader) for &lt;span class=&quot;math-container&quot;&gt;$a_3\ne0$&lt;/span&gt;: You get intermodulation products that are &lt;em&gt;close&lt;/em&gt; to the original frequencies, namely at &lt;span class=&quot;math-container&quot;&gt;$\omega_1 \pm |\omega_2-\omega_1|$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\omega_1 \pm |\omega_2-\omega_1|$&lt;/span&gt;, and since that frequency difference was small to begin with, these products land in our band of interest and can't be simply filtered out.&lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Practical measurements&lt;/h1&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I have:&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;20MHz dual trace oscilloscope,&lt;/li&gt;&#xA;  &lt;li&gt;RTL SDR dongle,&lt;/li&gt;&#xA;  &lt;li&gt;ubitx transciever,&lt;/li&gt;&#xA;  &lt;li&gt;30V/20A power supply. &lt;/li&gt;&#xA;  &lt;li&gt;I am planning to get hold of a nanoVNA as well&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's not half bad; I'd say, get a few attenuators, too, and you've got a basic setup!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;None of the following is done over-the-air, but with cabling in between devices.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know the UBITX, but you say it's a transceiver. &lt;strong&gt;If&lt;/strong&gt; you can use TX at the same time as RX on that device, you can replace the RTL-SDR below all with the RX side of your UBITX.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Use the ubitx (-&gt; somewhere between 16 and 20 MHz low-pass filter) -&gt; attenuator -&gt; RTL-SDR to calibrate:&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Make sure all cables are reliable (this is like embedded debugging – you wouldn't guess how much headache unreliable connections cause), and all connectors are screwed on to a proper connection (don't overtighten them. Coax connectors can be damaged by too much force.)&lt;/li&gt;&#xA;&lt;li&gt;Start with a strong attenuator to avoid frying the RTL-SDR.&lt;/li&gt;&#xA;&lt;li&gt;Disable any AGC on the RTL-SDR.&lt;/li&gt;&#xA;&lt;li&gt;Send a pure tune at say 1/8 of the max digital amplitude, at medium TX gain, at say 14.00 MHz using your UBITX (if you can, use offset tuning – I don't know the ubitx, but you want to have LO leakage, if existent, to be out of band)&lt;/li&gt;&#xA;&lt;li&gt;Tune the RTL-SDR to let's say 14.35 MHz, sampling rate 1 MHz. &lt;/li&gt;&#xA;&lt;li&gt;Use a spectrum plot (in a pinch, a high-length FFT display will do!) and note down the &quot;digital&quot; power for the one tone you see. (better: Use a parametric spectrum estimator that finds the N strongest tones)&lt;br&gt; You should see a very dominant peak at 14.00 MHz; verify that you're far away from Full Scale of the RTL-SDR (or that will be what introduces your nonlinearities).&lt;br&gt; If you see more than one peak (higher than say -45 dB of the main peak), try reducing the gain of the RTL-SDR.&lt;/li&gt;&#xA;&lt;li&gt;A good rule of thumb is that the time domain signal (i.e. as if you hooked up an oscilloscope to the baseband signal) should be -10 dB from full scale (i.e. typically &quot;1/10&quot;).&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Write down all the settings&lt;/strong&gt;: TX gain, TX amplitude, frequencies, the attenuator you used, the RX gain, sample rate, FFT length... Everything you can configure must be reproducible. (This is like debugging an embedded system!)&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;You now have a relatively calibrated transceiver pair, i.e. when you increase the amplitude or power on the transmitter by x dB , you see the same x dB on the receiving end. Great! Test whether that's true, and for which range of transmit powers. This gives you the range over which this measurement setup works linearly and can be used.&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Note down what you see on 14.00 MHz. Tune to 28.35 MHz; note down what you see at 28.00 MHz. Since the RTL-Dongle isn't calibrated to have the same amplitude response over the whole frequency band, this doesn't say much as it – but we'll compare this number later! (The filter should eliminate the 28 MHz spurs from your transmitter completely – these thus are effects of the RTL-SDR, so we need to ignore them later on). Optimally, you see nothing but noise floor here.&lt;/li&gt;&#xA;&lt;li&gt;That means that when you send two tones in a small frequency distance on the UBITX, you'll also only see these two tones on the receiving end. And they should have the same amplitude. Test that! If you see new tones appearing: That's the intermodulation of one tone with the other. Reduce amplitude / gains.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;add the amplifier and enough attenuation to (at least) compensate its gain between the UBITX (-&gt; filter)-&gt; and the attenuator we used so far. Power it.&lt;/li&gt;&#xA;&lt;li&gt;If the amplifier is perfectly linear, then gain + attenuation would cancel out, and we'd just see the input at the output (plus maybe a little more attenuation, because you probably don't have &lt;em&gt;exactly&lt;/em&gt; the same attenuator as your amplifier has gain, but that doesn't matter at all).&lt;/li&gt;&#xA;&lt;li&gt;Send a single, low-power tone. Make sure that your RTL-SDR is far from saturation (e.g. via time domain signal). If not, add more attenuation.&lt;/li&gt;&#xA;&lt;li&gt;SLOWLY increase the tone's power. You'll observe that over the range that was our measurement range above, the x dB input power increase -&gt; x dB output power increase doesn't hold. You might need to add more attenuation at some point. That simply gives you two measurement curves; one with, and one without the extra attenuation.&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;This is one figure of merit: You now know how much, on your frequency that you'll be using, the amplifier really amplifies for a given output power. At some point, pumping more power into the amplifier has diminishing returns!&lt;/li&gt;&#xA;&lt;li&gt;When you plot the output vs input power graph, you'll be able to read the 1 dB compression point from that. Save that graph! You'll need the curve later on&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Do the same – but do it for the 28 MHz frequency! That's the &lt;em&gt;second order intermodulation product&lt;/em&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Make a curve for second order output vs input power. Save that graph.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Find the second order intercept point:  Figure borrowed from &lt;a href=&quot;https://www.rfwireless-world.com/Terminology/second-order-intercept-point-vs-third-order-intercept-point.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;RF Wireless world&lt;/a&gt;, which I've never heard of before asking google just now.  You combine the two graphs above into one and find the intercept point if you &quot;extend&quot; your curves with a straight line. &lt;a href=&quot;https://i.stack.imgur.com/O1UAx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O1UAx.jpg&quot; alt=&quot;IIP2 construction&quot;&gt;&lt;/a&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;rule of thumb: stay 10 dB away from IIP2 for acceptable linearity&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;Same, but with two tones, and just looking at the spurs in the 14 MHz band; gives you IIP3.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;These are the two main figures you usually use to describe how (non)linear an amplifier is. &lt;/p&gt;&#xA;&#xA;&lt;h1&gt;Now what?&lt;/h1&gt;&#xA;&#xA;&lt;p&gt;Armed with knowledge of IIP2 and IIP3, you know how much you can put into your amplifier until it becomes very nonlinear, and can, through extrapolating your curves, also estimate how much power you'll see on the even and odd harmonics. That helps you decide on filters!&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Predistortion&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;However, that's kind of a sad thing: our amplifier uses its power to produce unwanted frequency components, that we then have to put effort into suppressing. Sad!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What if we could take the &lt;span class=&quot;math-container&quot;&gt;$f(x)$&lt;/span&gt; equation, measure the &lt;span class=&quot;math-container&quot;&gt;$a_i$&lt;/span&gt;, and find something like a &quot;good&quot; inverse function &lt;span class=&quot;math-container&quot;&gt;$g(x) \approx {f^{-1}(x)}{a_1}$&lt;/span&gt;, so that we can apply that function &lt;span class=&quot;math-container&quot;&gt;$g$&lt;/span&gt; to the signal we actually want to send:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$f(g(x)) \approx a_1 x$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That would be awesome, because now we're just using our amplifier to produce the signal we want, and none of the intermodulation products.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This technique exists, it's called &lt;em&gt;predistortion&lt;/em&gt; (which makes sense, since &lt;span class=&quot;math-container&quot;&gt;$g$&lt;/span&gt; definitely distorts &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;, but only in a manner that &quot;pre-reverts&quot; the distortion of &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt;). And, good news, your UBITX is a software defined radio, so you can calculate &lt;span class=&quot;math-container&quot;&gt;$g(x)$&lt;/span&gt; on your PC and send it to your UBITX instead of sending &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;. Yay!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Caveats:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Needs software to do that&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$f(x)$&lt;/span&gt; isn't actually fully invertible – so perfect predistortion won't happen, but you can significantly reduce out-of-band radiation. Professional radio equipment does predistortion for that very reason.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Here's a &lt;a href=&quot;http://bofh.nikhef.nl/events/FOSDEM/2019/AW1.120/sdr_dpd.webm&quot; rel=&quot;nofollow noreferrer&quot;&gt;talk&lt;/a&gt; by a friend of mine, MW0LNA on doing exactly that: predistortion in the digital domain.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-01-07T07:04:23.310" LastActivityDate="2020-01-07T07:04:23.310" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15875" PostTypeId="2" ParentId="15872" CreationDate="2020-01-03T14:07:49.450" Score="4" Body="&lt;p&gt;Probably ease of detection, or using the known OOK signal as kind of a frequency-synchronization and rate-synchronization method.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's hard to tell – in low-power and least-cost electronics, the emphasis often is not on RF signal optimality, but in ease of production and power usage, things you won't find out without knowing the silicon design process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It could also simply be a compatibility thing: maybe that thermostat is supposed to work with two different systems, one of which understands OOK, the other FSK.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-01-03T14:07:49.450" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15876" PostTypeId="2" ParentId="15868" CreationDate="2020-01-03T18:03:07.107" Score="2" Body="&lt;p&gt;You can do quite a lot with the RTL-SDR as a &quot;spectrum analyzer&quot;. A proper spectrum analyzer will be accurately calibrated to measure absolute power, but if you can fix the gain of the RTL-SDR and the receiving software you can use it to make relative power measurements which are sufficient if you only want to roughly quantify linearity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could dump the transmitter into an attenuator and hook it straight into the RTL-SDR. Of course you'll have to ensure the attenuation is sufficient so as to not damage the RTL-SDR, and your attenuator will have to be able to handle the output power and consequent heat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it's likely with this approach you'll encounter a problem with leakage. Unless the shielding on your transmitter, RTL-SDR, and all the cables and such between them is superb, you'll end up receiving a lot of leakage that isn't actually making it to the output: the LO of the radios, mixing products which are removed by filters, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One solution is to invest in a suite of lab-grade equipment. But a cheaper solution is to just hook up an antenna to the amplifier, and take the RTL-SDR outside at least some hundreds of feet away. Whereas an inline attenuator will attenuate the &quot;transmitted&quot; signal but not the leakage, simply adding distance attenuates both signal and leakage equally, rendering the leakage relatively insignificant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With your measurement apparatus set up, good things to measure are the 1dB compression point and 3rd order distortion.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To measure 1dB compression, you apply some input power and measure the output power. Comparing the two yields some gain. Then you increase the input power. For an ideal linear amplifier, the gain remains the same regardless of the input power. But with a real amplifier, you'll find at some level of input power, the gain starts to decrease. The point at which gain is 1dB less than it was at lower powers is the 1dB compression point. This gives you some idea of how hard the amplifier can be driven before it becomes nonlinear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To measure 3rd order distortion, you feed it two tones. (Protip: psk31 and variants in idle state is such a signal, so you can use psk31 software to generate the signal.) An ideal amplifier would produce the same two output tones, but a nonlinear amplifier produces sidebands spaced at regular intervals equal to the tone spacing. As input power increases, these sidebands grow faster than the intended signal. By measuring the difference in power between the sidebands and the main signal over a range of input powers, you can plot the third order intercept point, and oft-quoted measure of linearity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The final challenge is validating your measurements, since they will include distortion from the transmitter and the receiver, and the RTL-SDR isn't exactly certified. You'll note all these distortions get worse with increasing power, so a quick sanity check is to insert an attenuator at the input to the RTL-SDR and see if the distortion decreases. If so, the distortion you are seeing is predominately from the RTL-SDR, and you should add more attenuation. If not, the distortion is being generated from the transmitter and your measurements are good.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-01-03T18:03:07.107" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15877" PostTypeId="2" ParentId="15866" CreationDate="2020-01-03T20:04:52.997" Score="2" Body="&lt;p&gt;You might want to look in the manual of your radio. A lot of radios can be set up to tune in 6.25kHz steps, allowing you to tune to frequencies which are in between the frequencies you can tune to with the default 5kHz steps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have the same model radio so I can't verify this would allow you to tune to the frequency you want exactly, but it might be useful to know (and not limited to this radio but a lot of handhelds).&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2020-01-03T20:04:52.997" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15878" PostTypeId="1" CreationDate="2020-01-03T21:00:10.720" Score="7" ViewCount="134" Body="&lt;p&gt;In &lt;a href=&quot;https://nvlpubs.nist.gov/nistpubs/jres/124/jres.124.025.pdf&quot; rel=&quot;noreferrer&quot;&gt;A Century of WWV&lt;/a&gt;, I found this mention of an unusual sounding instrument that may have once been commonplace:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Calibration work was mainly focused on decremeters, instruments designed for measuring the decay, or decrement, of a pulsed radio signal, such as that generated by a spark transmitter typical of the day. Decremeters were essential in minimizing the interference produced as much as possible.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Another (much older) NIST publication titled &lt;a href=&quot;https://tf.boulder.nist.gov/general/pdf/2409.pdf&quot; rel=&quot;noreferrer&quot;&gt;A Direct-reading Decremeter and Wave&#xA;Meter&lt;/a&gt; describes the motiviation for these devices:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;[…] when&#xA;  persistent oscillations of single frequency are emitted from a&#xA;  radio transmitting station much more selective receiving apparatus may be employed with advantage at receiving stations,&#xA;  permitting sharp tuning with consequent minimizing of interference caused by stations other than those with which communication is desired.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;These devices were used either in the days of, or during the transition away from, &lt;a href=&quot;https://en.wikipedia.org/wiki/Spark-gap_transmitter&quot; rel=&quot;noreferrer&quot;&gt;spark-gap transmitters&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some notes on the &lt;a href=&quot;http://www.wdrcobg.com/decremeter.html&quot; rel=&quot;noreferrer&quot;&gt;Doolittle Decremeter&lt;/a&gt; describe that implementation as a &quot;transmitter antenna tuner&quot; and indeed the circuit diagram from the NIST decremeter paper looks to be in that vein as well:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Kv9J6.png&quot; alt=&quot;Simple circuit diagram from decremeter paper&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I right to understand that rather than measuring a signal directly, a decremeter essentially measured what we would now call the &lt;a href=&quot;https://en.wikipedia.org/wiki/Q_factor&quot; rel=&quot;noreferrer&quot;&gt;&quot;Q&quot;&lt;/a&gt; of an antenna, and in that way — indirectly — would determine how long that particular antenna would let a transmitted pulse ring?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-01-06T16:05:24.860" Title="What exactly was a decremeter and how did they work?" Tags="&lt;measurement&gt;&lt;equipment&gt;&lt;history&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15879" PostTypeId="2" ParentId="15878" CreationDate="2020-01-03T21:17:27.697" Score="2" Body="&lt;p&gt;Not only the antenna. It would also include the antenna, the tuned LC circuits, and how tightly the antenna was coupled to the latter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Spark transmitters produced a &lt;a href=&quot;https://en.wikipedia.org/wiki/Damped_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;damped wave&lt;/a&gt;. This edited &lt;a href=&quot;https://en.wikipedia.org/wiki/Damped_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;graph from Wikipedia&lt;/a&gt; shows one with desirable longer duration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The longer the system &quot;rang&quot;, the higher the average power --which is what the decremeter measured-- and the better the signal could be copied over longer distances. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eGsbC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eGsbC.png&quot; alt=&quot;Damped wave - courtesy Wikipedia&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-01-06T16:05:24.860" LastActivityDate="2020-01-06T16:05:24.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15880" PostTypeId="1" CreationDate="2020-01-04T15:20:37.587" Score="2" ViewCount="115" Body="&lt;p&gt;When my father - who became a ham years after I did - passed away, I found an unstarted project (board + components), which I only re-discovered again years later. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The board is marked DK0TV-001, and uses three ICs (as marked on the silk layer) SO42P, TCA1047 and TAA611. Apparently it converts 30 MHz to 10.7 MHz using the SO42P (with a 40.7 MHz crystal), then demodulates and amplifies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking over the internet DK0TV barely pops up, a little strange considering this seems to have been the club callsign of a german broadcast station (ZDF2?).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even though this call/kit probably pre-dates the internet, I am somewhat saddened I could find so little, and somewhat intrigued what this kit was about. Anyone remembers this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Added images&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1uAtc.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1uAtc.jpg&quot; alt=&quot;PC board&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/B4kaH.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/B4kaH.jpg&quot; alt=&quot;Components&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1290" LastEditorUserId="1290" LastEditDate="2020-01-07T14:29:30.637" LastActivityDate="2020-01-07T14:29:30.637" Title="Unknown kit from DK0TV" Tags="&lt;receiver&gt;&lt;diy&gt;&lt;electronics&gt;" AnswerCount="0" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="15881" PostTypeId="1" CreationDate="2020-01-04T20:21:15.607" Score="2" ViewCount="103" Body="&lt;p&gt;What's causing these horizontal bands of noise?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's the middle of the day here in a low density city neighborhood.&#xA;They were not present about 20 minutes ago; now they are even stronger and filling in the space between the lines.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Cannot hear any lawnmowers or other engine equipment, very quiet outside.&lt;/li&gt;&#xA;&lt;li&gt;Shut off all the power to the house, ran off a battery, still see the same thing.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;How do I figure out what these horizontal lines are?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sKihc.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sKihc.png&quot; alt=&quot;IC-7300 spectrum with periodic wideband noise&quot;&gt;&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="16196" LastEditorUserId="8717" LastEditDate="2020-01-04T21:03:39.797" LastActivityDate="2020-01-05T20:33:56.527" Title="Icom 7300 low frequency broad-spectrum noise" Tags="&lt;hf&gt;&lt;noise&gt;&lt;signal-identification&gt;&lt;icom-ic-7300&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15882" PostTypeId="2" ParentId="15714" CreationDate="2020-01-05T19:09:39.180" Score="1" Body="&lt;p&gt;I believe my problem is created by common-mode noise. I redesigned my homemade SA612 mixer. I isolated the antenna ground from the mixer ground, and I also isolated the mixer ground from the output RTL-SDR ground, and now the problem is fixed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's how I solved the problem. Since I only have very limited knowledge of electronics and radio, it may contain error, corrections and suggestions of improvement of this answer is welcomed.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Identify the Noise Sources&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;From the first observations, we can draw several educated guesses about the sources of the noise. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Unfortunately, as soon as I connect my SDR to my Raspberry Pi, huge wideband noise is received all over the spectrum&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The radio works well on a laptop, but receives huge wideband noise on a Raspberry Pi.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;So I powered the Raspberry Pi from a benchtop linear power supply, But it had little effect. Although number of spurious interference was somewhat reduced, but the SA612 is still being overdriven, and I still see &quot;machine-gun&quot; like interference at fixed intervals.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Using different power sources does make a difference, and somewhat reduce the noise on the spectrum, but not much.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;It indicates that the noise was certainly coming from external sources, and it's likely that the noise was coupled by conduction, not radiation.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Identify how the noise is coupled into the receiver&lt;/h2&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And strangely, if I power my SA612 via Raspberry Pi and use the RTL-SDR on my laptop, I see almost no interference. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The noise is not detected when the SA612 mixer frontend is connected to the Raspberry Pi, which is our suspected noise source. It means the noise was not coupled into the system by its power supply.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I also tried listening to the radio on my laptop while running an Ethernet speed test on the Raspberry Pi, but I see nothing at all.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The noise is not detected by the SDR if the laptop is used, even if the radio is at the same physical location, which indicates the noise was not coupled into the system by radiation. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;And I finally found if I disconnect the coax input of my SA612 mixer, almost all the interference would be gone.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;This is a critical observation: Disconnecting the antenna input makes the noise to disappear immediately, which means the noise must have found a way to travel all the way from the SDR to the mixer frontend, it's possible that the problem is created by common-mode noise. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;And from the block diagram...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6UqZ5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6UqZ5.png&quot; alt=&quot;Block Diagram of my SDR Shack&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only conductive path is the coax cables, which connects the input of the mixer, output of the mixer, and the input of the RTL-SDR together.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Hypothesis&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;So the hypothesis is that the EMI was traveling across the ground/shield, and finally being picked up at the input side of the mixer.&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Mixer&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Here's how the mixer was designed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/K1cXU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/K1cXU.png&quot; alt=&quot;Mixer Schematics&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An input balun transformer converts the single-ended signal from the antenna to a balanced signal, the incoming signal is mixed with an externally injected local oscillator, and the balanced output to converted back to a single-ended signal and connected to the RTL-SDR receiver. The baluns used were Mini-Circuit ADT16-1T, which is a high-performance RF transformer, combined with a double-balanced mixer, we should have a reasonable common-mode rejection and port isolation. Thus, the noise is unlikely to travel across the system through the ports.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the input, output, and the mixer are all connected to a common ground plane. Naturally, it becomes our suspect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another warning sign is the use of a random-wire antenna - the coax shield and any ground connected directly to it becomes the counterpoise of the antenna. The antenna is extremely vulnerable to interference if common-mode current is not suppressed. &lt;/p&gt;&#xA;&#xA;&lt;h2&gt;Redesign&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;The solution is to cut the conductive path between the input and output. The input transformer and output transformer should only be connected to the coax, but not be tied to common ground. Although separating the ground plane into pieces is normally not recommended, I believe it should work to solve the specific problem in my case. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W6vMtm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W6vMtm.png&quot; alt=&quot;Removing the connection to common ground&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On a single-layer PCB, I used three copper fills.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EwGtL.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EwGtL.png&quot; alt=&quot;PCB layout&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After etching and soldering the board, the mediumwave and shortwave spectrum are crystal clear now!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8966f.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8966f.png&quot; alt=&quot;gqrx screenshot&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15589" LastActivityDate="2020-01-05T19:09:39.180" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15884" PostTypeId="2" ParentId="15406" CreationDate="2020-01-05T22:28:38.543" Score="3" Body="&lt;p&gt;In the end I decided to build a simple adapter. Most handheld microphones available at cheap prices have two-jack &quot;Kenwood compatible&quot; interface. They have 3.5mm TRS jack and 2.5mm TRS jack. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The sleeve on 2.5mm jack provides ground contact. PTT contact is on 3.5mm jack sleeve and microphone contact is on 3.5mm ring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I bought two jack plugs, soldered the respective contacts on a single 3.5mm jack and, while the plugs were on the handheld microphone connector, fixed everything in a chunk of sugru.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Everything works fine. It is necessary to choose the right microphone. Wouxun microphone purchased in a local ham radio store has nice modulation, while &quot;Baofeng&quot; mike purchased on eBay is noisy and the modulation is unpleasant.&lt;/p&gt;&#xA;" OwnerUserId="11232" LastActivityDate="2020-01-05T22:28:38.543" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15885" PostTypeId="1" AcceptedAnswerId="15905" CreationDate="2020-01-06T22:16:55.033" Score="3" ViewCount="98" Body="&lt;p&gt;I have an analog 27 MHz transceiver which i am planning to convert to 10 m. The radio is an AM / SSB unit with a single conversion superhet receiver with an IF of 7.8 MHz using a crystal filter. This radio does not have any faults due to component failure, and I'm trying to align the receiver and have a problem understanding one aspect of the alignment. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally with other radios of this type, alignment of the IF strip generally involves connecting a signal generator to the antenna socket and then peaking coils and transformers for maximum signal level. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However when i do that with this model radio (i have 4 and they all do the same thing), the local oscillator used to inject carrier into the product detector used for SSB receive seems to appear as a signal on the S meter. I have to adjust the first transformer in the IP strip off to the side of the point where i see maximum signal generator level on the meter and then it seems to work properly, however with reduced receiver sensitivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other radios I have aligned don't show this behavior and you just set the alignments in the IF strip for maximum signal and you never see the local BFO appear as a signal on the S meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone explain to me what is going on when I am aligning this radio ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the schematic below, the 7.8 MHz IF strip is Q201, Q202, Q203, and you can see the IF output from the IF transformer T203 at the top middle going to T401 and then to the SSB product detector Q405 and Q406  at the lower right. The product detector has an input from a 7.8 MHz local oscillator which you can't see in the picture at the junction of Q405 and Q406 emitters. The 7.8 MHz crystal filter FL-1 is at the top left. The separate detector for AM are the diodes at the top right. The audio outputs from the 2 detectors are connected to R419 which connects to the audio amp input.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/spWkZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/spWkZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-01-08T23:08:43.900" LastActivityDate="2020-01-11T00:48:51.557" Title="How can i adjust the IF strip in a single conversion SSB receiver which has a product detector?" Tags="&lt;electronics&gt;&lt;ssb&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15886" PostTypeId="1" AcceptedAnswerId="15899" CreationDate="2020-01-07T00:45:35.877" Score="9" ViewCount="444" Body="&lt;p&gt;How is the signal-to-noise ratio for received CW and QRSS CW (and/or other ultra narrow-band DSP digital modes) typically computed?  e.g. What noise bandwidth should be used to measure the spectrum power against the narrow CW &quot;on&quot; signal power? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should one use the DSP detection bandwidth (roughly 1X the WPM), the human decode bandwidth (approximately 3X to 5X the WPM according to an ISO or ITU document), the actual bandwidth used by the transmitter rise time, or some other standard radio bandwidth (SSB LSB filter width?)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How should the CW S/N be computed to compare its data rate (at a given WPM) against the theoretical Shannon limit for that S/N?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the same S/N number meaningful depending on whether the noise is mostly Gaussian noise, white noise, or 1/f RF noise?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="4665" LastEditDate="2020-11-04T16:29:46.997" LastActivityDate="2020-11-04T16:29:46.997" Title="Calculating the signal-to-noise ratio for CW (Morse Code) signals?" Tags="&lt;cw&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15888" PostTypeId="2" ParentId="15870" CreationDate="2020-01-07T19:58:43.813" Score="3" Body="&lt;p&gt;Unfortunately your license is a matter of public record. As other have noted you can rent a PO box and use it as your address with the FCC. You required to maintain a postal address where the FCC can contact you. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of us use our home address. A few use a PO box. I have also heard of people who use a relative or friends address. I am not a lawyer and I am not 100% certain that the last option is legal, but as long as any letters from the FCC make their way to you in a timely fashion, I believe that it is OK.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On related note, when most people apply for their amateur radio license they put their Social Security Number on the application. While your SSN is not published like your address is, many people are not comfortable with handing their SSN to a group of strangers at the testing site. You can apply ahead of time to get a FRN number you can use instead. A FRN is assigned by FCC when you get your license, but you can get them ahead of time. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a link, &lt;a href=&quot;https://www.fcc.gov/wireless/support/universal-licensing-system-uls-resources/getting-fcc-registration-number-frn&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fcc.gov/wireless/support/universal-licensing-system-uls-resources/getting-fcc-registration-number-frn&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;by the way I am a Volunteer Examiner, one of those strange people you give you SSN to on your application. I have never heard of any VE using your SSN for anything except applying for your license. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-01-07T19:58:43.813" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15889" PostTypeId="1" CreationDate="2020-01-07T23:01:10.717" Score="4" ViewCount="2063" Body="&lt;p&gt;I am in rural Alaska and I am very far from anywhere that gives Ham Exams. I got a Ham Radio and I want to operate it and talk to people. However, I read that frequencies are not allowed to be transmitted on by people who don't have a license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So am I able to transmit on any frequency, or only allowed to receive?&lt;/p&gt;&#xA;" OwnerUserId="16212" LastEditorUserId="4665" LastEditDate="2020-01-07T23:20:34.320" LastActivityDate="2020-02-21T04:26:18.973" Title="What Frequencies Are Open To People Without A License?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15890" PostTypeId="2" ParentId="15889" CreationDate="2020-01-07T23:46:22.830" Score="5" Body="&lt;p&gt;Sorry, but you're legally not allowed to transmit on amateur radio frequencies without a license.  I'd recommend that you work on earning your ham license.  Not only would you be legal, but you would also learn how to operate a radio effectively, and how to deal with problems that come up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find a ham club &lt;a href=&quot;http://www.arrl.org/find-a-club&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;.  Most ham clubs have license classes and &quot;elmers&quot;, that is people who are willing to help new folks get set up.  Most ham clubs also offer license exams.  Maybe you could talk a club into coming to you to hold a special exam session; I think two examiners are required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you really are so far in the bush that you can't contact a ham club, then you could order a license study guide (the ARRL and W5YI guides are the most popular), study up, and schedule your next trip into a larger town to coincide with an &lt;a href=&quot;http://www.arrl.org/find-an-amateur-radio-license-exam-session&quot; rel=&quot;noreferrer&quot;&gt;exam session&lt;/a&gt;.  Online practice exams are available.  Good luck.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-01-07T23:46:22.830" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15891" PostTypeId="2" ParentId="15889" CreationDate="2020-01-08T05:25:02.413" Score="8" Body="&lt;p&gt;The Anchorage ARC VEC administers &lt;a href=&quot;https://kl7aa.org/vec/remote-testing/&quot; rel=&quot;nofollow noreferrer&quot;&gt;remote amateur radio license examinations&lt;/a&gt; to interested people living in the US and Canada who can't attend an in-person test because they're too far away from a location with a sufficient number of examiners. If you can secure a proctor, and access to an internet connection good enough to run a video chat, you can get your license without having to travel an excessive distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC opened the possibility of remote testing in 2014 following petitions from the Anchorage ARC VEC and the National Conference of Volunteer Examiner Coordinators, and Anchorage &lt;a href=&quot;https://kl7aa.org/anchorage-arc-vec-rolls-out-web-based-license-testing/&quot; rel=&quot;nofollow noreferrer&quot;&gt;launched their web-based testing system in October 2019&lt;/a&gt;, so you're just in time to participate! As of February 2020 they've &lt;a href=&quot;https://kl7aa.org/remote-testing-expanded/&quot; rel=&quot;nofollow noreferrer&quot;&gt;expanded the program to eligible candidates anywhere in the US and Canada&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-02-21T04:26:18.973" LastActivityDate="2020-02-21T04:26:18.973" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15892" PostTypeId="2" ParentId="15889" CreationDate="2020-01-08T13:17:01.953" Score="3" Body="&lt;p&gt;With appropriate equipment (which &lt;em&gt;does not&lt;/em&gt; include a ham rig) a non-licensed person in the USA is allowed to transmit in frequency bands which are &quot;licensed by type&quot; -- this includes CB channels 1 to 40, AM or SSB, Family Radio Bands (aka FMRS), and unlicensed business bands (GMR), but &lt;em&gt;only with type certified equipment specific to each band&lt;/em&gt;.  Use of WiFi, Bluetooth, and satellite internet fall in this category, also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone may also transmit under Part 15 regulations, which mainly limit output power to a small fraction of a watt.  Within that regulation, you may transmit on nearly any frequency -- including commercial broadcast and FM broadcast bands.  Generally, this will require either commercially made units like FM microphones (for speakers and performers) or homebrewed equipment -- and the low power limit makes it impractical for communication beyond a few hundred meters.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-01-08T13:17:01.953" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15893" PostTypeId="1" CreationDate="2020-01-08T13:57:59.710" Score="1" ViewCount="138" Body="&lt;p&gt;I am buying a house in the UK and the property next door has two poles for antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next door lady seems to be very nice person and said her husband is an RF engineer and he used these on weekends. My basic question: will it effect any of my internet or TV or telephone?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am planning to have fiber broad band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/g0T19.jpg&quot; alt=&quot;One tall antenna mast behind a house with smaller antennas on roof&quot;&gt;&lt;/p&gt;&#xA;" OwnerUserId="16216" LastEditorUserId="1362" LastEditDate="2020-01-08T17:42:20.760" LastActivityDate="2020-01-08T17:45:08.900" Title="Will my neighbor's amateur RF antennas effect my own utilities?" Tags="&lt;rfi&gt;&lt;united-kingdom&gt;&lt;safety&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15894" PostTypeId="2" ParentId="15893" CreationDate="2020-01-08T14:09:56.557" Score="1" Body="&lt;p&gt;No, this will affect nothing. Otherwise, the neighbor would not have gotten the right to operate these antennas.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-01-08T14:09:56.557" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15895" PostTypeId="1" CreationDate="2020-01-08T14:19:13.017" Score="3" ViewCount="254" Body="&lt;p&gt;If something bad goes down (state-wide or nationwide), what frequencies should I be tuning into?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I did see &lt;a href=&quot;https://ham.stackexchange.com/a/106/16217&quot;&gt;this answer&lt;/a&gt;, but I have a BaoFeng UV-82HP which cannot do HF at all, so what are my options?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Related question: if I wanted to hop on the radio and get in touch with someone during an emergency, what frequencies should I be aware of?&lt;/p&gt;&#xA;" OwnerUserId="16217" LastEditorUserId="4665" LastEditDate="2020-01-08T14:42:22.233" LastActivityDate="2020-01-08T15:17:59.250" Title="What VHF &amp; UHF frequencies are important during an emergency?" Tags="&lt;united-states&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;emergency&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15897" PostTypeId="2" ParentId="15895" CreationDate="2020-01-08T15:00:34.397" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If something bad goes down (state-wide or nationwide), what frequencies should I be tuning into?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Broadcast radio! Obviously, if your emergency services tried to let a lot of people know something is wrong, they'd do that on a frequency that most people actually have a receiver for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For emergency &lt;em&gt;communications&lt;/em&gt; (i.e. you want to actually transmit), things are a bit different:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;It's usually a good idea to keep the spectrum clean while distress communications are going on&lt;/li&gt;&#xA;&lt;li&gt;If you're on a maritime vessel, 156.8 MHz would be where you listen or set off distress/urgency signals&lt;/li&gt;&#xA;&lt;li&gt;I &lt;em&gt;think&lt;/em&gt; in most countries channels designated as &lt;em&gt;Simplex communications&lt;/em&gt; channel used in the default mode for that band are the optimal choice.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-01-08T15:00:34.397" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15898" PostTypeId="2" ParentId="15895" CreationDate="2020-01-08T15:17:59.250" Score="3" Body="&lt;p&gt;The most important frequencies to have programmed into your VHF/UHF radio would be the VHF simplex calling frequency, and the frequencies of the more important local repeaters, especially the ones that have emergency power such as solar panels.  BaoFeng radios are notoriously difficult to program channels into using the front panel buttons.  There is software available, &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP&lt;/a&gt; being the most notable example, that can make programming the radio much easier.  Your local ham club can help you program the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you don't have a ham license, then I can't recommend enough that you get your license and get on the radio and make contacts, enough that you are familiar with the radio and its features, and how to use a repeater or simplex frequency efficiently, and how to make a contact in an emergency situation (on both the end needing help, and the end rendering assistance).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the last decade or so, inexpensive ham radio HTs (&quot;handheld transceivers&quot;, aka walkie-talkies) have been available online from sites that don't worry about whether or not the customer has a license.  Millions of such radios have been bought by non-hams and people who got their licenses but never practiced using the radios.  The problem is that in a big emergency, big enough that the telephone network and the internet are down, then repeaters and the usual simplex frequencies could be swamped by panicky people who don't know what they're doing.  When that happens, the repeaters handling emergency traffic will probably be forced to switch frequencies, CTCSS tones, or DCS codes, and those not knowing how to reprogram their radios will be ignored.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-01-08T15:17:59.250" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15899" PostTypeId="2" ParentId="15886" CreationDate="2020-01-08T15:58:48.597" Score="4" Body="&lt;p&gt;The answer can be fond in The ARRL Handbook 2019, Vol 3, although it's spreaded across different chapters. In short, SNR is typically calculated for the noise floor of 2500 Hz SSB signal. Particularly this is how WSJT-X calculates negative SNRs for FT8 and other modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the trick is that by deviding the bandwidth in half you decrease the noise floor by 3 dB assuming the noise is distributed evenly. When I use 500 Hz wide DSP filter in my Yaesu FT-891 I typically see S2-S3 noise floor on 20m, and S4 when 2500 Hz bandwidth is used. Now keeping in mind that one S-unit is approximately 6 dB we get:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;gt;&amp;gt;&amp;gt; from math import log2&#xA;&amp;gt;&amp;gt;&amp;gt; 3*log2(3000/500)/6&#xA;1.292481250360578&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;And we really see 1-2 less S-units, as expected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now back to CW. The ARRL Handbook claims with the reference to &quot;The ITU Classification of Emission Standards&quot; that the bandwidth of CW signal can be estimated as:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;BW = WPM * 0.8 * 5&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;For instance, a 17WPM signal has a bandwidth about 68Hz. This means that the signal can be received:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;gt;&amp;gt;&amp;gt; 3*log2(2500/68)&#xA;15.600748614897329&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;... 15.6 dB &quot;under the noise floor&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please note,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) This assumes that there is a 68 Hz bandpass filter on the receiver side. This in fact is a reasonable assumption in the era of DSP filters. For instance, FT-891 has a very narrow-band audio peak filter (APF).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) When you compare the decoding threshold of different modes (e.g. FT8 and CW) there are many other factors to consider. In case of FT8: 1) it's not a &quot;chat mode&quot; as CW 2) FT8 frequencies are often crowded (read - QRM) thus the decoding threshold doesn't matter &lt;em&gt;that&lt;/em&gt; match 3) sadly many people who use digital modes don't &lt;a href=&quot;https://ham.stackexchange.com/questions/15809/how-to-fix-signalink-non-linearity-problem&quot;&gt;check the IMD of their sound card and transceiver combo&lt;/a&gt; which gives even more QRM, etc.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-01-08T16:05:44.110" LastActivityDate="2020-01-08T16:05:44.110" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15900" PostTypeId="1" AcceptedAnswerId="15902" CreationDate="2020-01-08T16:18:27.283" Score="7" ViewCount="571" Body="&lt;p&gt;I'm new to CW and one thing I couldn't figure out is when I supposed to send &quot;E E&quot;. Let's say I'm calling CQ and somebody answers me. The QSO is almost over. Should it be ended like this:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;- TNX FER NICE QSO 73 &amp;lt;SK&amp;gt; E E&#xA;- GDX 73 &amp;lt;SK&amp;gt; E E&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;... or:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;- TNX FER NICE QSO 73 &amp;lt;SK&amp;gt;&#xA;- GDX 73 &amp;lt;SK&amp;gt; E E&#xA;- E E&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Or maybe both options are OK, or maybe none? In other words how to use &quot;E E&quot; properly?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-01-08T18:13:23.023" Title="CW: when I supposed to send &quot;E E&quot;?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15901" PostTypeId="2" ParentId="15900" CreationDate="2020-01-08T17:33:55.997" Score="6" Body="&lt;p&gt;The dit dit that is sometimes (not all the time) sent at the end of a QSO is a derivitive of the old time &quot;shave and a haircut -- two bits&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back when I was a novice on the 40-m band in the 1960s it was quite common for the final signoff (whomever that might be) to send &quot;dit di-di-dit dit&quot; and the other operator would then respond with &quot;dit dit&quot;.  However today, it is almost universal that both ends (or all parties of a QSO) merely send dit dit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I participate in several CW Traffic nets and in one of those nets the net control always ends with dit dit as the final signoff.  Since there are a dozen or more other operators participating in the net, you can here all of these individual dit dits being signed by each operator spaced over about five seconds of time.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2020-01-08T17:33:55.997" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15902" PostTypeId="2" ParentId="15900" CreationDate="2020-01-08T17:43:58.817" Score="10" Body="&lt;p&gt;First, some history.  As I understand it, the &quot;dit-dit&quot; (E E) comes from an old practice.  There is a short tune in popular music that was often used to end a musical performance in a humorous way, called &quot;shave and a haircut, two bits&quot;.  The &lt;a href=&quot;https://en.wikipedia.org/wiki/Shave_and_a_Haircut&quot; rel=&quot;noreferrer&quot;&gt;Wikipedia article&lt;/a&gt; has a recording of the tune.  For older people, the rhythm of the notes in the tune is instantly recognized in a knock on a door; the person on one side of the door traditionally knocks the &quot;shave and a haircut&quot; rhythm, and the person on the other side knocks the &quot;two bits&quot; rhythm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the early 20th century, this practice carried over to Morse code.  At the end of a QSO, one party would tap out the &quot;shave and a haircut&quot; rhythm, and the other would tap out the &quot;two bits&quot; rhythm, hopefully leaving a smile on both faces.  In the more recent era, the &quot;shave and a haircut&quot; part has been dropped, possibly because it's harder to get the rhythm right with an electronic keyer, but the &quot;two bits&quot; part has survived.  The &quot;two bits&quot; rhythm is what you describe as &quot;E E&quot;.  (By the way, I've never heard &quot;shave and a haircut&quot; as &quot;dah-di-di-dah-di&quot; as it says in the Wikipedia article; I've only ever heard it as &quot;dit didi dit dit&quot;, or &quot;E I E E&quot; if you prefer.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer your question, I don't remember ever seeing advice anywhere on how to use &quot;E E&quot; at the end of a QSO, because it is such an informal ritual.  So I don't think it really matters, but I personally do it at the very end.  From time to time I still do the &quot;shave and a haircut&quot; rhythm, and when an old-timer (old person) answers me with &quot;two bits&quot; (E E), it still puts a smile on my face.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-01-08T17:43:58.817" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15903" PostTypeId="2" ParentId="15893" CreationDate="2020-01-08T17:45:08.900" Score="4" Body="&lt;p&gt;The frequencies your neighbor would be transmitting are different than the ones your own communications would use. They should not interfere with your utilities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Occasionally, funny things like old metal connections can end up re-broadcasting related frequencies instead of the original one, but this is usually accounted for as well when the allocations are made between TV/amateur/cellular/etc. bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is encouraging that the neighbor not only appears to be a &quot;ham&quot; (trained and licensed hobby radio operator) but is also a professional RF engineer, so I doubly doubt you should have any problem. A big antenna like that would used for frequencies no where near the frequency of your WiFi. And it would be extremely unlikely for a wireless radio signal to interfere with an optical fiber internet connection itself.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-01-08T17:45:08.900" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15905" PostTypeId="2" ParentId="15885" CreationDate="2020-01-08T21:06:29.140" Score="2" Body="&lt;p&gt;It looks like no one is going to answer this question and in the mean time i've found out was what wrong anyway so i am posting my own answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly after some more thinking it became obvious to me that the local oscillator has nothing to do with what the S meter reads, as the BFO injection is done in the product detector which outputs an audio signal and this circuit doesn't impact on RF reception, the AGC circuit or anything else that affects the S meter reading.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It became apparent that this particular radio has a mechanical design fault whereby the output from the local 7.8 MHz oscillator is erroneously coupled via various wires, PCB tracks, stray capacitance or lack of proper RF shielding into the path of the 7.8 MHz IF. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The design of this transceiver uses the local 7.8 MHz oscillator for the single receive IF, the AM transmit carrier oscillator and for the BFO injection for SSB reception. While this design minimizes the number of components used and aids in keeping everything on the correct frequency, it also allows for this fault where the local oscillator output is picked up or received by the radio's IF because the IF was chosen to be the same frequency as the local oscillator for that reason of simplifying transceiver design. Because of the erroneous or stray IF pickup, the local oscillator signal appears as a real signal which shows on the S meter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I solved the problem by adding a 100 nF ceramic capacitor between a point on the PCB where an incoming + 9V supply connects via a red wire to the IF circuitry, and a nearby ground pad. That got rid of the signal completely, so the 7.8 MHZ was getting in via the IF + 9 V supply rail. Now i can adjust the IF strip for maximum sensitivity as per usual.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm surprised that this radio got to production and units were actually sold in large numbers while having this fault, but there you go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Almost forgot to mention the radio model, which is an SBE Sidebander V 27 MHz CB AM/SSB transceiver made by NDC of Japan in about 1978.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-01-11T00:48:51.557" LastActivityDate="2020-01-11T00:48:51.557" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15906" PostTypeId="1" CreationDate="2020-01-08T21:14:52.113" Score="1" ViewCount="224" Body="&lt;p&gt;What is the best way to get an amateur radio license &lt;strong&gt;in different countries?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;This question is a &lt;a href=&quot;https://meta.stackexchange.com/questions/11740/what-are-community-wiki-posts&quot;&gt;&lt;em&gt;community wiki&lt;/em&gt;&lt;/a&gt;, which means that it's sort of a placeholder, an index of answers. &lt;a href=&quot;https://stackoverflow.blog/2011/08/19/the-future-of-community-wiki/&quot;&gt;More info&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Answers are automatically community wikis also.&lt;/li&gt;&#xA;&lt;li&gt;Anyone with 100 reputation points can edit the question or the answers.   -  &lt;/li&gt;&#xA;&lt;li&gt;Nobody earns or loses any reputation for votes on community wiki questions or answers.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Answers should be for specific countries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not asking for myself, but rather for anyone in any country who wants to be a ham.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="8717" LastEditDate="2020-11-07T00:14:18.407" LastActivityDate="2020-11-07T00:14:18.407" Title="How do I get a ham radio license in my country?" Tags="&lt;license&gt;" AnswerCount="4" CommentCount="4" FavoriteCount="1" CommunityOwnedDate="2020-01-08T21:17:17.877" ContentLicense="CC BY-SA 4.0" />
  <row Id="15907" PostTypeId="2" ParentId="15870" CreationDate="2020-01-08T22:02:44.863" Score="3" Body="&lt;p&gt;No.  As stated by @Jim your license is a matter of public record.  In fact, you can get a list of the names and addresses of all canceled amateur radio licenses at the FCC website: &lt;a href=&quot;https://wireless2.fcc.gov/UlsApp/UlsSearch/searchAdvanced.jsp&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wireless2.fcc.gov/UlsApp/UlsSearch/searchAdvanced.jsp&lt;/a&gt; (choose Service Group &quot;Amateur&quot; and Status &quot;Canceled&quot;).&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2020-01-08T22:02:44.863" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15908" PostTypeId="2" ParentId="15906" CreationDate="2020-01-08T22:03:30.483" Score="4" Body="&lt;p&gt;In the United States, the process of obtaining an amateur radio license is overseen by the Federal Communications Commission, better known as the FCC.  The FCC has outsourced the process to several organizations known as &lt;a href=&quot;https://www.fcc.gov/volunteer-examiner-coordinators-vecs&quot; rel=&quot;nofollow noreferrer&quot;&gt;Volunteer Examiner Coordinators&lt;/a&gt;, or VECs.  To get an amateur radio license, you must pass an exam given by a VEC.  You can find an upcoming exam in your area &lt;a href=&quot;http://www.arrl.org/find-an-amateur-radio-license-exam-session&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are three license classes in the US: Technician, General, and Amateur Extra.  (There are also two more license classes, Novice and Advanced, but new licensees can't qualify for those classes.)  Technician is the easiest test to pass, but has the least privileges; Amateur Extra has the hardest test and the most privileges.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, in order to pass the exam, one must know the material.  The traditional route to learn is to take a class, and/or read a license manual.  Classes and manuals are offered by the &lt;a href=&quot;http://www.arrl.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio Relay League&lt;/a&gt; (ARRL), the national association for amateur radio operators, and also &lt;a href=&quot;http://www.w5yi-vec.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;W5YI-VEC&lt;/a&gt;.  You can find upcoming classes &lt;a href=&quot;http://www.arrl.org/find-an-amateur-radio-license-class&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio clubs are a great resource for getting a license.  Many clubs offer license classes and license exams (for a VEC such as the ARRL).  You can find an ARRL-affiliated club close to you &lt;a href=&quot;http://www.arrl.org/find-a-club&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question pools for the exams are public, and so there are online practice exams, like &lt;a href=&quot;https://www.qrz.com/hamtest/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt;.  The practice exams are a great way to study for the exam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't have to be a citizen, or even live in the US, in order to hold a US license; but you may not be an agent of a foreign government.  You must be able to receive domestic US mail, but that territory includes FPO/APO addresses and US territories.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You must pass element 2 to get a &lt;strong&gt;Technician&lt;/strong&gt; license.&lt;/li&gt;&#xA;&lt;li&gt;You must take and pass elements 2 and 3 to get a &lt;strong&gt;General&lt;/strong&gt; license.&lt;/li&gt;&#xA;&lt;li&gt;You must take and pass elements 2, 3 and 4 to get an &lt;strong&gt;Amateur Extra&lt;/strong&gt; license.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You can take all three tests the same night, but most testing teams require you take an pass them in order. If you fail element 2, then you would not get a license even if you pass the other.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="8717" LastEditDate="2020-02-13T20:46:11.237" LastActivityDate="2020-02-13T20:46:11.237" CommentCount="4" CommunityOwnedDate="2020-01-08T22:03:30.483" ContentLicense="CC BY-SA 4.0" />
  <row Id="15909" PostTypeId="1" CreationDate="2020-01-09T07:28:23.693" Score="2" ViewCount="44" Body="&lt;p&gt;In an effort to &quot;up my game&quot; attempting to build a VFO for my DIY transceiver, I've been looking at PLL theory and circuits.  Many of my research references are quite old and I understand that many of the concepts I'll talk about here are no longer popular and have been replaced by integrated solutions and DDS.  So, this question is about &quot;How did they do that?&quot; and &quot;How might you do that nowadays?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More specifically, many of the PLL circuits for high frequency VFOs would use some kind of dual-modulus prescaler to divide down the VFO frequency before the phase comparator.  The &lt;a href=&quot;https://en.wikipedia.org/wiki/Dual-modulus_prescaler&quot; rel=&quot;nofollow noreferrer&quot;&gt;wikipedia link&lt;/a&gt; offers a fair description of how these &quot;fractional-N&quot; type prescalers work and I'm speaking about the discrete ICs - not the ones integrated into the PLL itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lets take the &lt;a href=&quot;https://www.qsl.net/n9zia/mc145158/mb501.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;MB501&lt;/a&gt; used in the wikipedia article.  This IC is just about still available (if you look hard enough!) and has a nice lower end frequency of 10MHz (many currently available ICs have much higher lower end frequencies).  It looks to me that to use this IC for fractional division, you'll need additional A and N counters.  If you take the example given in wikipedia, it seems like those additional counters will need to operate at over 7MHz (918MHz / 128).  That figure would be higher if you chose a lower M or had a higher VFO frequency.  My point is, the clock frequency might be on the high side for a uP or discrete counting logic.  &lt;strong&gt;So, how did they implement the A and N counters for this solution?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an additional &quot;bonus&quot; question, if someone more familiar with this stuff than I am were to build a PLL circuit in the spirit of the more discrete designs (i.e., basic PLL, maybe 4046 with separate prescaler), how would you go about it?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPDATE: a bit more research seems to show that discrete prescalers like the MB501 were driven by the PLL ICs themselves.  Not all PLL ICs had this capability. Seems that you programmed a N and A into the PLL and it did the counting for you.  I suppose that makes some sense, since it's the output of the N divider that gets presented to the phase comparator.  Anyway, I'm guessing (hoping?) someone out there has done this with a less specialized PLL, like the 4046.&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="76" LastEditDate="2020-01-09T16:16:26.930" LastActivityDate="2020-01-09T16:16:26.930" Title="Clocking A and N in a Dual-modulus PLL Prescaler" Tags="&lt;electronics&gt;&lt;vfo&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15910" PostTypeId="1" CreationDate="2020-01-09T17:23:27.183" Score="2" ViewCount="84" Body="&lt;p&gt;Which currently popular digital/SDR modes do not require a pre-compiled library or pre-written source code?  (e.g. has actually been used for QSOs as implemented from specification or sufficiently complete description by other than the original developer?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(For purposes of this question, C source code is not considered a specification, unless the comments alone allow re-implementation in another programming language.  Automatic translation of FORTRAN to C is not considered a specification.  The possibility of reverse engineering some software library is also not considered a specification of the digital mode.  Assuming an non-existent spec could potentially be written is not considered a specification (unless you can and have written it!).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-01-10T19:25:49.537" LastActivityDate="2020-01-10T19:25:49.537" Title="Which digital modes are formally specified sufficiently to be implemented?" Tags="&lt;digital-modes&gt;&lt;dsp&gt;" AnswerCount="0" CommentCount="20" ContentLicense="CC BY-SA 4.0" />
  <row Id="15911" PostTypeId="1" CreationDate="2020-01-09T19:20:41.427" Score="1" ViewCount="76" Body="&lt;p&gt;Anyone out there know of or developed s/w to predict HF conditions using ML?&lt;/p&gt;&#xA;" OwnerUserId="16225" LastEditorUserId="8717" LastEditDate="2020-01-10T01:34:29.027" LastActivityDate="2020-01-10T01:34:29.027" Title="HF propagation prediction using machine learning" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;software&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15912" PostTypeId="2" ParentId="15906" CreationDate="2020-01-11T12:36:59.057" Score="0" Body="&lt;p&gt;In Germany the DARC , the german Radio Club offers preparation courses for interested persons. The BNetzA, a subsidiary of the federal ministry for economics, offers license tests, which consist of a written and and a personal exam. After successful completion, a license is issued. Just as in most other jurisdictions, there is a “full “ CEPT and a novice license. A class A (full) allows up to 750 W on all ham bands. Because of international regulatory approval, the license is also valid in dozens of other countries. &lt;/p&gt;&#xA;" OwnerUserId="10691" LastActivityDate="2020-01-11T12:36:59.057" CommentCount="0" CommunityOwnedDate="2020-01-11T12:36:59.057" ContentLicense="CC BY-SA 4.0" />
  <row Id="15913" PostTypeId="2" ParentId="2095" CreationDate="2020-01-11T14:04:02.063" Score="2" Body="&lt;p&gt;The &lt;em&gt;Band Activity&lt;/em&gt; chart at &lt;a href=&quot;https://dxheat.com/dxc/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Heat&lt;/a&gt; is a good way to evaluate propagation from the standpoint of &quot;who is working whom, right now.&quot; Combining the color coded activity depiction with your general knowledge of when bands are more likely to be open can guide you as to what bands are opening and which are closing. The filtering tools allow you to target specific bands, modes, regions and DXCC entities.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://wsprnet.org/drupal/wsprnet/map&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSPRNet&lt;/a&gt; displays automated connections between stations around the world. While not quite as convenient to use as DX Heat, station automation doesn't rely on individuals to be active on a band for propagation information to be available.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-01-11T14:04:02.063" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15914" PostTypeId="1" CreationDate="2020-01-11T17:05:32.920" Score="0" ViewCount="389" Body="&lt;p&gt;My use case is intercontinental HF radio, and I am frequently traveling. Lugging a big rig is inconvenient and expensive ones get you into customs trouble all the time. So, I'm looking for a low cost portable rig that can be driven to at least 100 W output. ICOM IC-78 is the baseline, is there anything that can beat it in price and portability? Most portable rigs I find are UHV/VHF rigs. I know people frown on cheap Chinese stuff but they sometimes produce pretty market-disrupting stuff, anything like the &quot;Baofeng of HF&quot;? HF is too much of a niche right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Yaesu FT-857 has the small form factor and same output power, but it is even more expensive, so constant hassle by customs as airports are guaranteed. The Kenwood 480HX is a 200W rig, and smaller than the ICOM IC-718, but it is also more expensive, so giving me the same headache. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Xiegu X5105 is at same price as ICOM IC-78 but it needs an external RF amp to drive 125W and that's another box for the same price again. So it doesn't really beat the FT-857 and Kenwood 480HX in portability or price.&lt;/p&gt;&#xA;" OwnerUserId="16238" LastEditorUserId="16238" LastEditDate="2020-01-11T17:54:09.903" LastActivityDate="2020-01-13T15:31:27.547" Title="Lowest cost portable HF radio with at least 100 W output?" Tags="&lt;hf&gt;&lt;transceiver&gt;&lt;portable&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15916" PostTypeId="2" ParentId="121" CreationDate="2020-01-11T20:13:51.683" Score="0" Body="&lt;p&gt;I would always just plan for car battery. Ubiquitous, high current output, easy to charge. Probably overall the cheapest solution. Perfect for stationary backup and always on hand when driving with a car.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But yes, for back packing, weight concerns Li-Ion is of course the best choice. And you can get the Li-Ion as standard round cells, and create your own charging unit. Problem with the chargers is they cannot supply the 10 Amps you would need for a good transceiver during transmission. But I would think that the battery itself serves as a buffer to supply the high current when needed.&lt;/p&gt;&#xA;" OwnerUserId="16238" LastActivityDate="2020-01-11T20:13:51.683" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15917" PostTypeId="2" ParentId="3752" CreationDate="2020-01-11T20:22:55.313" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm looking to buy a shortwave to listen to &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you want to listen only I would use an SDR box on the computer. It is a total game changer. Seeing the waterfall visualization you can survey the bands at a glance and zoom in quickly where you find interesting action.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;either solely at home or perhaps if possible in a vehicle when traveling. &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Again, for listening it's SDR and all you need is decent antennas and a way to adapt them to your target bands. Loops seem pretty flexible and great for SDR, aren't they?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What should I look for when looking them over? I recall many years ago the ability to listen to Quito Ecuador from South Central Canada, as well as many Russian propaganda stations. I had purchased a radio from a Garage sale WWII vintage all tube, but boy did it work well (after it warmed up)!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Nice. I grew up in Europe and we had so much action there. One vintage mode that I just love (but is going away) is the Long Wave radio. It is a very far reaching terrestrial wave. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I'm sure today's radios are very good, but would rather some of you experts tell me about things to look for.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I think for you an SDR box is the best. You can also just tune into WebSDR or Kiwi SDR boxes around the world through the internet. That's a nice thing because you can pick up local stations in India or wherever your curiosity leads you.&lt;/p&gt;&#xA;" OwnerUserId="16238" LastEditorUserId="16238" LastEditDate="2020-01-11T23:01:21.933" LastActivityDate="2020-01-11T23:01:21.933" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15918" PostTypeId="2" ParentId="5465" CreationDate="2020-01-11T20:29:01.560" Score="0" Body="&lt;p&gt;UHF/VHF is your bands for this application. You can talk to the International Space Station on VHF. Line of sight is no issue in a flying object. You need to choose a band that is used for digital transmissions and then have a digital receiver. Set up packet radio and then control whatever you want and get your camera image and telemetry streamed down. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have tested the cell phone reception in airplanes during take-off, and that works fine for drones. But as you want to go into the stratosphere, you lose the cell tower connection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The key for very high flights is decent antennas of course. &lt;/p&gt;&#xA;" OwnerUserId="16238" LastActivityDate="2020-01-11T20:29:01.560" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15919" PostTypeId="2" ParentId="15906" CreationDate="2020-01-11T20:37:29.660" Score="0" Body="&lt;p&gt;In Brazil it is LABRE.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In all countries it is always the amateur radio association of that country. You can find them as members of the International Amateur Radio Union.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every country then has its own rules of course, but that is best figured out by talking with the local amateur radio association.&lt;/p&gt;&#xA;" OwnerUserId="16238" LastActivityDate="2020-01-11T20:37:29.660" CommentCount="0" CommunityOwnedDate="2020-01-11T20:37:29.660" ContentLicense="CC BY-SA 4.0" />
  <row Id="15920" PostTypeId="1" CreationDate="2020-01-11T20:46:41.600" Score="-3" ViewCount="133" Body="&lt;p&gt;What if I wanted to run a radio broadcast station on a commercial SW band? Say, I am on a boat in international waters. Or say I am in a free country. I monitor the frequency for months and I check the records seeing nothing is assigned to it. Then I start transmitting. I know there are all these draconian laws by the governments, but when I am out on a boat I am subject to no government. And when I'm in a free country and I'm not stepping on anybody's toes, what's the harm?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are the practical risks? Realistically? Are the governments really wasting that much tax payer money to be monitoring the waves and triangulate you and hunt you down for speaking your mind on the mostly deserted commercial SW bands?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A corollary question would be how much it would cost to put up an SW broadcast station legally? Searching the FCC directly brings up exactly nothing: &lt;a href=&quot;https://www.fcc.gov/media/radio/how-to-apply&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fcc.gov/media/radio/how-to-apply&lt;/a&gt; the only mention is AM radio in the MW band. So, that might mean that the commercial HF bands are essentially abandoned by the FCC?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PS: It seems I am having a discussion with myself. I wish that others chimed in. But people down voting my question or not responding doesn't deter me from researching and discussing it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PPS: I think I need to clarify, even for myself, a little better what the purpose of this thought exercise is. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I am asking out of curiosity&lt;/li&gt;&#xA;&lt;li&gt;Ham radio is fine and all, but you are constrained on just idle private chatting, what if instead I wanted to speak my mind to a larger audience, and do on SW what many people do on YouTube?&lt;/li&gt;&#xA;&lt;li&gt;Imagining life without Internet, how could we recreate the format of world wide citizens interactions? What about a YouTube live hangout on air (literally) using a group of Hams discussing but with the ability of commercial SW radios listening in?&lt;/li&gt;&#xA;&lt;li&gt;A full blown radio program on SSB with music and all? &quot;Amateur radio&quot; rules are too restrictive for that.&lt;/li&gt;&#xA;&lt;li&gt;Clearly, a 50kW or highers transmitter is a &lt;a href=&quot;https://www.researchgate.net/publication/233850660_Design_and_Characterization_of_50_kW_Solid-State_RF_Amplifier&quot; rel=&quot;nofollow noreferrer&quot;&gt;piece of massive engineering effort&lt;/a&gt; so probably out of reach, but who knows, I've been picking up old big iron computers decades ago, which previously sold for millions, I might come across a government auction that sells a 10 kW RF amplifier which I might use as a SSB broadcast station and reach quite far with it.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16238" LastEditorUserId="16238" LastEditDate="2020-01-13T15:04:03.380" LastActivityDate="2020-01-14T14:40:02.440" Title="Transmitting as SW AM station, not ham" Tags="&lt;hf&gt;&lt;am&gt;" AnswerCount="4" CommentCount="0" ClosedDate="2020-01-14T02:00:54.267" ContentLicense="CC BY-SA 4.0" />
  <row Id="15921" PostTypeId="1" AcceptedAnswerId="15926" CreationDate="2020-01-11T21:24:23.060" Score="1" ViewCount="96" Body="&lt;p&gt;It's my understanding that FM is used for UHF, VHF, and SSB is generally reserved for other bands.&lt;br&gt;&#xA;From my understanding, &lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;better audio quality when reception is good&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;SSB:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;more efficient (can transmit farther with the same amount of power as fm or the same distance as fm with less power)\&lt;/li&gt;&#xA;&lt;li&gt;more understandable when the quality is low &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Are there other, more efficient audio modes other than the most common two?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If my above understanding is correct, why aren't there any SSB HT's that operate in the UHF or VHF range, especially considering that efficiency is so important for battery life?&lt;/p&gt;&#xA;" OwnerDisplayName="user15628" LastActivityDate="2020-09-20T07:56:48.413" Title="What are the practical differences between the different voice modes (and why aren't there any SSB Handheld Transceivers (HT's))?" Tags="&lt;ht&gt;&lt;fm&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15922" PostTypeId="1" AcceptedAnswerId="15927" CreationDate="2020-01-11T22:31:58.293" Score="0" ViewCount="48" Body="&lt;p&gt;Ferrite beaded cords, and especially double-sided ferrite beaded cords, seem especially uncommon.  Are there other, perhaps more effective ways, which I should be minimizing the EMI of my overcrowded workstation?&lt;/p&gt;&#xA;" OwnerDisplayName="user15628" LastActivityDate="2020-01-12T05:56:55.140" Title="What are the most common EMI blockers for household computer cords, monitors, etc.?" Tags="&lt;rfi&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15923" PostTypeId="2" ParentId="15920" CreationDate="2020-01-11T22:38:43.550" Score="1" Body="&lt;p&gt;As for the USA, the FCC has a database of enforcement actions here: &lt;a href=&quot;https://www.fcc.gov/reports-research/maps/fcc-enforcement-actions-against-pirate-radio-location/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fcc.gov/reports-research/maps/fcc-enforcement-actions-against-pirate-radio-location/&lt;/a&gt;. Casual sampling of this information leaves the impression that the majority of the enforcement actions concern the commercial FM band and are generally initiated not by any systematic FCC surveillance but by complaints from license holders in the commercial FM band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since commercial SW radio is almost dead, I doubt the risk is very high. But then, as soon as a station becomes more famous, the likelihood for someone to initiate a complaint would grow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC has a special page on shortwave radio broadcasting &lt;a href=&quot;https://www.fcc.gov/general/high-frequency-broadcasting&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fcc.gov/general/high-frequency-broadcasting&lt;/a&gt; and a fact sheet &lt;a href=&quot;https://www.fcc.gov/reports-research/guides/fact-sheet-building-high-frequency-shortwave-international-broadcasting-station&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fcc.gov/reports-research/guides/fact-sheet-building-high-frequency-shortwave-international-broadcasting-station&lt;/a&gt;. But the whole issue is very unclear from there. It's a good example of regulatory overreach. For example, they say that you need a minimum output of 50 kW. OK. So what if I have an output of 200 W? Then I can't even apply. But the waves are empty, so why does the government block me from broadcasting at a signal strength too low? And I have tried to find what the actual application and maintenance fees are that they demand, but there is no direct way to find this information. Only publications about publications and proposed rule making with 400 pages and no occurrence of the words &quot;high frequency&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a very short list of FCC Authorized High Frequency Stations:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;KHBN Medorn, Aimeliik, Palau - Since gaining independence, licensed locally as T8BZ, and, by treaty, frequency coordination by FCC&lt;/li&gt;&#xA;&lt;li&gt;KNLS Anchor Point, AK&lt;/li&gt;&#xA;&lt;li&gt;KSDA Agat, GU&lt;/li&gt;&#xA;&lt;li&gt;KTWR Agana, GU&lt;/li&gt;&#xA;&lt;li&gt;KVOH Rancho Simi, CA&lt;/li&gt;&#xA;&lt;li&gt;WBCQ Monticello, ME&lt;/li&gt;&#xA;&lt;li&gt;WEWN Vandiver, AL&lt;/li&gt;&#xA;&lt;li&gt;WHRI Furman, SC&lt;/li&gt;&#xA;&lt;li&gt;WINB Red Lion, PA&lt;/li&gt;&#xA;&lt;li&gt;WJHR Milton, FL&lt;/li&gt;&#xA;&lt;li&gt;WMLK Bethel, PA&lt;/li&gt;&#xA;&lt;li&gt;WRMI Okeechobee, FL&lt;/li&gt;&#xA;&lt;li&gt;WRNO New Orleans, LA&lt;/li&gt;&#xA;&lt;li&gt;WTWW Lebanon, TN&lt;/li&gt;&#xA;&lt;li&gt;WWCR Nashville, TN&lt;/li&gt;&#xA;&lt;li&gt;WWRB Morrison, TN&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;This is it! 16 stations only! And a large proportion are on outlying island like Palau and Guam, etc. Now the list of frequencies can be found here: &lt;a href=&quot;https://transition.fcc.gov/ib/sand/neg/hf_web/B19FCC01.TXT&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://transition.fcc.gov/ib/sand/neg/hf_web/B19FCC01.TXT&lt;/a&gt; it is quite a complex schedule different seasons different frequencies, different days of the week and times of day.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given that the SW bands are so quiet in the continental US, I am amazed by the FCC's statement that:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Most existing stations have a transmitter power greater than 50 kW and an antenna gain greater than 10 db in an attempt to overcome the increasing congestion and interference in the limited frequency spectrum allocated to this service.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Congestion? What congestion?&lt;/p&gt;&#xA;" OwnerUserId="16238" LastEditorUserId="16238" LastEditDate="2020-01-12T17:49:10.200" LastActivityDate="2020-01-12T17:49:10.200" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15924" PostTypeId="2" ParentId="6515" CreationDate="2020-01-11T22:58:56.780" Score="0" Body="&lt;p&gt;Growing up in Europe and hanging on the SW dial, there were lots of stations received in cities without even any special antenna gear. At a maximum a totally non-tuned wire thrown anywhere along an inner wall was all that was had. Lots of stuff was received even so. But that was Europe, Europe is crowded and small, and the stations were perhaps less than 500 miles away. I think there is just very little commercial SW radio going on in the USA these days. If you want to hear the hams talk, you need to get a SSB receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have confirmed my suspicion by using a simple WebSDR receiver &lt;a href=&quot;http://108.53.131.186:8901/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://108.53.131.186:8901/&lt;/a&gt; somewhere in New Jersey. There isn't much going on.&lt;/p&gt;&#xA;" OwnerUserId="16238" LastActivityDate="2020-01-11T22:58:56.780" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15925" PostTypeId="2" ParentId="2095" CreationDate="2020-01-12T00:52:17.237" Score="1" Body="&lt;p&gt;The &lt;a href=&quot;http://dxlabsuite.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DXLab Suite&lt;/a&gt; includes &lt;em&gt;PropView&lt;/em&gt;, a convenient front-end to VOACAP, which makes current and near-term propagation predictions. &lt;em&gt;PropView&lt;/em&gt; works in conjunction with the other components of the DXLab Suite, so it works best when you use DXLab for all of your logging and operating functions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can download N6BV's Propagation Prediction Files with the purchase of the 2019 ARRL &lt;em&gt;Antenna Book&lt;/em&gt;. The files predict the strength of communication (in S-units) over virtually any path as a function of frequency and sun spot number. Instructions are given to &quot;discount&quot; the S-units to account for stations' output power and antenna gain.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-01-12T00:52:17.237" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15926" PostTypeId="2" ParentId="15921" CreationDate="2020-01-12T00:59:24.030" Score="5" Body="&lt;p&gt;SSB phone requires good frequency stability to be intelligible. Anything over 10Hz of frequency difference between transmitter and receiver and the signal starts to sound funny; beyond 50-70 Hz of error, intelligibility starts to drop. Hitting that target is more difficult at higher frequencies than at low frequencies. In the HF bands, getting within 10Hz requires 1 part per million (order of magnitude) relative frequency accuracy. For VHF it's more like 0.1 ppm, UHF is 0.01 ppm, and microwave we start thinking about GPS-locked oscillators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM, on the other hand, is pretty insensitive to frequency errors. For an FM signal with a deviation of 5kHz, a frequency offset of 1kHz between transmitter and receiver is almost unnoticeable, and even 2 kHz doesn't impair communications too much. So for practical purposes, let's say FM is 50 times as forgiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even base station and mobile VHF/UHF rigs are much more likely to have FM than SSB for this reason — it's simply much easier to get acceptable FM at those frequencies than acceptable SSB. &quot;All-mode&quot; rigs are usually (though not always) the more expensive ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HTs have the same problems to contend with &lt;em&gt;plus&lt;/em&gt; they're generally lower-cost, need to be smaller and lighter, and generally use unregulated battery power that tends to droop over the course of a transmission. All of those negatively impact frequency regulation, and keeping a signal accurate to within a few tens of Hz under those conditions is simply impractical.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-01-12T00:59:24.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15927" PostTypeId="2" ParentId="15922" CreationDate="2020-01-12T01:15:48.680" Score="1" Body="&lt;p&gt;First thing to do is determine the EMI source(s).  Chargers for mobile devices, LED room lighting, and/or rooftop solar panels, etc., can easily generate a noise floor above that of your workstation.  Neighbors can generate EMI closer to your antenna(s) than your office.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I cut the main circuit breaker to my house, and turned things on one at a time to find the worst RF noise sources.  A printer in another room was one.  However I found the noise floor went down even lower when there was a neighborhood wide power outage, so some of the RFI is out of my control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the worst random power cords, cables (USB, ethernet, video, 12V, etc.), and coax feed lines near my radio receivers, I wrapped a few to several turns (often limited by how many turns fit), thru type 31 or type 43 ferrite toroids.  I saw little to no effect from using single no-name clamp-on ferrite beads, or cables that came with them (but use them anyway).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-01-12T05:56:55.140" LastActivityDate="2020-01-12T05:56:55.140" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15928" PostTypeId="1" AcceptedAnswerId="15937" CreationDate="2020-01-12T15:54:36.860" Score="0" ViewCount="129" Body="&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/INmGM.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why does this band have special operating characteristics and what do they mean. &lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="76" LastEditDate="2020-01-13T00:05:31.080" LastActivityDate="2020-01-13T19:48:39.677" Title="Why does the 60 meter band have special operating characteristics?" Tags="&lt;united-states&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15929" PostTypeId="1" CreationDate="2020-01-12T21:40:17.750" Score="2" ViewCount="109" Body="&lt;p&gt;I'm looking for an amateur radio license class in central Iowa, near Des Moines.  I've been unable to locate anything through web searches.&lt;/p&gt;&#xA;" OwnerUserId="16248" LastEditorUserId="4076" LastEditDate="2020-01-12T22:50:37.363" LastActivityDate="2020-02-13T03:03:30.423" Title="Amateur Radio License classes in Central Iowa" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15930" PostTypeId="2" ParentId="15920" CreationDate="2020-01-13T12:28:40.267" Score="2" Body="&lt;p&gt;I don't know that commercial class HF transmitters are still being built, but it shouldn't be very difficult to put one together.  You'd need the audio mixing and control equipment that goes with any radio broadcasting station (this would be the same as a commercial MW AM or FM broadcast station), an HF transmitter that can be tuned to your chosen/assigned frequency, one or more stages of amplifiers to reach your chosen output power, transmission line and an antenna suitable for your chosen frequency and power level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This isn't going to be cheap -- your final, at least, will use high power tubes (far beyond a 6146 class) that cost thousands of dollars each; your transmission line will have a cost measured in hundreds to thousands of dollar per meter, your antenna will need a tower high enough to get half a wave above ground, in addition to the cost of a high power antenna itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Typically, to set up a licensed station in AM or FM at &quot;low power&quot; (a few hundred watts for a college campus station, say), from scratch, will cost tens of thousands of dollars for equipment.  Add the tower, amplifiers, and feed line needed for a station with enough range to cover a significant geographic footprint, and you can multiply that figure by at least ten (likely more).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your offshore location, of course, you'd add the cost of generating equipment, ongoing fuel and maintenance costs, and the ship itself with the necessary equipment (anchors or thrusters) for station keeping to ensure you &lt;em&gt;remain&lt;/em&gt; in international waters -- or the cost to buy you own private island (or &quot;private nation&quot; platform -- there are a couple for sale, last I heard, one with much of the radio equipment you'd need), plus the generating equipment.  Best plan to start with a good size suitcase of C notes...&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-01-13T12:28:40.267" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15931" PostTypeId="2" ParentId="15929" CreationDate="2020-01-13T14:51:31.283" Score="1" Body="&lt;p&gt;The ARRL's &lt;a href=&quot;http://www.arrl.org/find-an-amateur-radio-license-class&quot; rel=&quot;nofollow noreferrer&quot;&gt;License Class Finder&lt;/a&gt; should be able to help you; it says that there's a class in Indianola starting on the 8th of February.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-01-13T14:51:31.283" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15932" PostTypeId="2" ParentId="15906" CreationDate="2020-01-13T15:01:20.837" Score="0" Body="&lt;p&gt;in FRANCE on must pass a radio operator certificate which includes a technical part and a legislative part. Only when you have passed this exam can ask the administration for a call sign. Since January 2019 there is no more emission tax.&lt;/p&gt;&#xA;" OwnerUserId="16251" LastActivityDate="2020-01-13T15:01:20.837" CommentCount="0" CommunityOwnedDate="2020-01-13T15:01:20.837" ContentLicense="CC BY-SA 4.0" />
  <row Id="15933" PostTypeId="2" ParentId="15914" CreationDate="2020-01-13T15:31:27.547" Score="1" Body="&lt;p&gt;You might find it more cost effective to buy a relatively inexpensive, lower power radio (even QRP class), and couple it with an amplifier to get your desired power level.  There is a fairly broad selection of lower power &quot;all-band&quot; portable/mobile HF rigs available, some in &quot;some assembly&quot; form for under US$200.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For only 100W output, you ought to be able to find a solid state amplifier to do the job, which would be more compact than a vacuum tube unit for higher power (and require less bulky/heavy power supply, likely run off the same supply as the actual transceiver).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-01-13T15:31:27.547" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15935" PostTypeId="2" ParentId="15920" CreationDate="2020-01-13T16:39:58.143" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What if I wanted to run a radio broadcast station on a commercial SW band? Say, I am on a boat in international waters.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What you're suggesting is known as &lt;a href=&quot;https://en.wikipedia.org/wiki/Pirate_radio#Examples_of_pirate_radio_stations&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;pirate radio&lt;/strong&gt;&lt;/a&gt;. That Wikipedia page provides plenty of examples of unlicensed stations, many of which operated for years before either being shut down or getting licensed. Many of those stations operated from ships or platforms outside territorial waters. Although you're asking specifically about shortwave frequencies and most of these examples are in the commercial FM or AM broadcast bands, I don't think the frequency makes a difference. A station such as you describe is surely in the realm of pirate radio.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;...and I'm not stepping on anybody's toes, what's the harm?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That you don't hear anything when you listen on a given frequency doesn't mean that your high-power transmissions on that frequency won't cause problems. There aren't any empty spaces in the HF range on the FCC's &lt;a href=&quot;https://en.wikipedia.org/wiki/File:United_States_Frequency_Allocations_Chart_2016_-_The_Radio_Spectrum.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;spectrum allocation chart&lt;/a&gt;, so there's a strong chance that the signal you're thinking of blasting out will cause problems for people operating on your chosen frequency at power too low for you to hear.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;It seems I am having a discussion with myself.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The hypothetical nature of the question might have something to do with the lack of response.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Are the governments really wasting that much tax payer money to be monitoring the waves and triangulate you and hunt you down for speaking your mind on the mostly deserted commercial SW bands?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not for speaking your mind... you're free to say whatever you want, especially if you're outside the jurisdiction of any country. You can jump up and down on your transmitter-ship and shout your opinion. You can email your opinion to the New York Times, post it on Twitter, create your own web site, post it on billboards. The content isn't the issue, so don't conflate that with the actual problem. Broadcasting on frequencies that you're not authorized to use, and potentially interfering with other users, is the problem.&lt;/p&gt;&#xA;" OwnerUserId="11226" LastEditorUserId="11226" LastEditDate="2020-01-14T14:40:02.440" LastActivityDate="2020-01-14T14:40:02.440" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15936" PostTypeId="1" CreationDate="2020-01-13T16:47:20.037" Score="5" ViewCount="326" Body="&lt;p&gt;I want to share the same antenna for VHF (TX/RX 144-148 MHz) and for Airband RX-only (116-136 MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I live on a very congested area where filter is a must, so I'm looking for the best solution for my needs:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Wide bandwidth (~30 MHz)&lt;/li&gt;&#xA;&lt;li&gt;Transmit capable (&gt; 20W power handle with low return loss/SWR)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Currently I use a DIY helical filter for TX and a low-power LC filter for airband, but switching them everytime is very combersome. I like the high &quot;Q&quot; of the helical filter, but its bandwidth is very limited (~5 MHz) and I believe they cant be streteched to cover such bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My primary source of interference are strong FM stations in the neighborhood, so I need a high Q, sharp filter with a good degree of attenuation between 108 and 116 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any advice in the best filter design? My simulations shows a LC band-pass filter (Butterworth/Chebyshev) would meet my &quot;sharpness&quot; requirements, but they tend to have high return loss (SWR) as well, which could compromise my TX requiriments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some soldering skills and a NanoVNA, tuning the helical filter wasn't a big deal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I finally had time to build a LC filter, looks like it's still the best option to go.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First attempt was building a band-pass filter, but it showed to by tricky to tune. Then I went by a highpass + lowpass 5th-order Elliptic as calculated by &lt;a href=&quot;https://rf-tools.com/lc-filter/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://rf-tools.com/lc-filter/&lt;/a&gt;. to allow individual tuning.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The results can be seen on thes imgur post: &lt;a href=&quot;https://imgur.com/a/og9AsII&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://imgur.com/a/og9AsII&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The overall results are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;-11dB on 110Mhz (very important to attenuate strong FM station on 107Mhz)&lt;/li&gt;&#xA;&lt;li&gt;-40dB on FM band&lt;/li&gt;&#xA;&lt;li&gt;1,5dB insertion loss beteen 117-150Mhz &lt;/li&gt;&#xA;&lt;li&gt;SWR &amp;lt; 1:1,5 between 130-150Mhz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Since I had no high voltage variable capacitors in hand, I had to find the correct capacitor values using low voltage ones, then replacing by fixed value 1KV ceramic capacitor. As you might imagine that was a very time consuming exercise. The good thing is that there is no moving parts on the filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sharpness on the lower end is good. On the upper side I didn't push too much the sharpness, since looks like there is a tradeoff between sharpness and return loss. I wanted good SWR and the upper band is not a big source of interference, so a left it a bit soft.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Results are very good. Identical noise compared to a commercial airband filter I had in hand, but extended to 150Mhz. Completely blank airband spectrum, no sign of FM stations spurs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I wont post schematic or component values because this is a trial and error process. If you want to build something like this, you must have a VNA. Take the values calculated by rf-tools.com as a starting point then tweak to suit your needs.&lt;/p&gt;&#xA;" OwnerUserId="16252" LastEditorUserId="16252" LastEditDate="2020-02-23T23:15:13.860" LastActivityDate="2020-03-14T12:08:11.557" Title="Wide band TX capable band-pass filter for VHF and Airband" Tags="&lt;vhf&gt;&lt;rfi&gt;&lt;filter&gt;&lt;airband&gt;" AnswerCount="2" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="15937" PostTypeId="2" ParentId="15928" CreationDate="2020-01-13T17:55:50.570" Score="4" Body="&lt;p&gt;The ARRL has &lt;a href=&quot;http://www.arrl.org/60-meter-faq&quot; rel=&quot;nofollow noreferrer&quot;&gt;a good FAQ page&lt;/a&gt; about the 60 meter band.  The special rules in the United States for the 60 meter band aren't due to any technical limitations.  Instead, they're a compromise to allow amateur use of the band without interfering with government use.  The primary users of the band are government agencies, and they were using it long before amateurs were granted access.  As secondary users, amateurs are required to stop transmitting when asked to do so by another user, or if they detect non-amateur transmissions on the channel.  The channels were selected because they're lightly used frequencies that are least likely to cause interference with the primary users.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2020-01-13T19:48:39.677" LastActivityDate="2020-01-13T19:48:39.677" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15939" PostTypeId="1" AcceptedAnswerId="15941" CreationDate="2020-01-13T19:55:55.090" Score="3" ViewCount="381" Body="&lt;p&gt;Our local repeater is severely sabotaged by unknown parties. For example, broadcast radio transmissions are repeated. Other times someone will send a transmission, when a qso is in progress. Local authorities were informed but they apparently are ignoring this. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What can be done?&lt;/li&gt;&#xA;&lt;li&gt;Could they be triangulated?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10691" LastEditorUserId="76" LastEditDate="2020-01-13T22:21:52.983" LastActivityDate="2020-01-16T23:20:26.417" Title="Malicious interference to repeater" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;repeater&gt;" AnswerCount="5" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15940" PostTypeId="2" ParentId="15939" CreationDate="2020-01-13T20:26:34.807" Score="2" Body="&lt;p&gt;One of my local repeaters has a sound bleed from the (very high power) TV transmission on the same tower, and all the repeaters I use exhibit signal problems and interference that might or might not be intentional.  For instance, the same one that has the TV bleed also sometimes (re)transmits a Morse code station ID for another station.  My Morse is pretty bad, so I'm not certain what the other ID is, and I can't depend on it to record or concentrate on it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All of this is just part of using the 2 meter band.  The FCC has limited funding and personnel for enforcement on individual repeater interference, and even if they're actively investigating, it sometimes takes &lt;em&gt;years&lt;/em&gt; to trace down &lt;em&gt;intentional&lt;/em&gt; interference, never mind something accidental.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best I can suggest is either try to work around it, move to another repeater, or listen carefully for identifying information when the interference occurs and pass that information to your local FCC and Official Observer(s).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-01-13T20:26:34.807" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15941" PostTypeId="2" ParentId="15939" CreationDate="2020-01-13T21:42:49.037" Score="4" Body="&lt;p&gt;The first thing to do is to listen on the repeater's input frequency.  If you hear the interfering signal on the input frequency, then you're probably dealing with deliberate interference; otherwise, you most likely have a technical problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your problem is deliberate interference, then if I were in your shoes I would absolutely use radio direction finding (RDF) techniques to locate the source of the interfering transmission.  I've done a few fox hunts, and the best simple technique technique is to travel around with a directional antenna (a yagi is nice but the antenna doesn't have to be that directional), an attenuator (your body in between the transmitter and your antenna sometimes works well enough for a weak signal), and a radio that ideally has a signal strength meter.  An offset attenuator, containing an oscillator running at a few MHz and a mixer, offers better attenuation for this purpose much more cheaply than a typical laboratory attenuator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Triangulation doesn't seem to work very well for precise location because of reflected signals, at least in the mountainous area where I live; it might work better in flat lands, but I'd think it's still not accurate enough to positively identify the building or vehicle with the antenna.  With a directional antenna and a good attenuator, you could walk or drive a loop completely around the suspected location of the transmitter and prove that the transmission comes from inside the looped area.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Document your results thoroughly, hopefully with video, and turn your results over to the relevant government officials, which in the US are the FCC and Official Observers like @ZeissIcon says, and then you'll have done all that you can.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-01-16T16:46:08.303" LastActivityDate="2020-01-16T16:46:08.303" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15942" PostTypeId="1" CreationDate="2020-01-13T23:55:20.187" Score="3" ViewCount="171" Body="&lt;p&gt;TL/DR: How does someone make a good horn antenna system without using expensively made parts? &#xA;Welding thin steel for this is not something even pro welders can do (it's a specialty app.) What are DIY options then for joining sheet metal. What is the most careless thing that could still function, even fn well (like 300 sheet metal screws poking inside.)  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Beware, this is long:&#xA;I don't expect to match the efficiency of radar components. I made one out of copper/solder about 20 years ago using 2 pieces of copper and it had a short waveguide section for a probe or loop antenna. It was maybe 22&quot; aperture, I remember getting all the dimensions using a C++ program, drawing the piece in autocad and hijacking the plotting machine to print it out at work lol (it wound up being far from the printed accuracy) ... Copper has skyrocketed in cost since then and it's heavy and deforms easily. ... On the other hand, thin steel requires an exceptional welder I don't even know where to find, and have asked all around before. For very narrow gauge, as in the sheet metal used for the waveguide in a microwave oven I think it's a process involving a roller disc inside the waveguide making spot welds at the closest interval possible and doing multiple passes until it's continuous.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Literature(s) about horn antennas and waveguides just say &quot;smooth&quot; and &quot;continuous&quot;, no dings or warpage either. Not what a little bit of that might do. What for example would a rivet's profile do to the inside of an otherwise mirrorlike inside wall with exact angles. Not that getting it right the 1st attempt is ever expected, but I seek thoughts and advice from others before wanting to invest my time and resources into a project. I've seen an example of someone making a horns joining a corner with adhesive backed foil tape (?! they had no seeming concern about this nor data on performance, Maybe they even knew what they were doing I just doubt it.) I don't have any good examples for reference or really any examples of similar steel horn antennae. I think of all the such things involved with how the steel overlaps and maybe using a brazing technique (no familiarity with brazing) or something like closely drilled pairs of holes with twisted wire clamping edges/faces together. L shaped edges and the like create a problem inside with a valley/furrow that could be mitigated maybe a little by filling it with conductive epoxy or solder (solder in reality would be hard to do, it running all over the place or being lumpy.) I've never seen a homemade antenna that was any good besides ones made from copper, and those 2 were smaller than the one I did.&lt;/p&gt;&#xA;" OwnerUserId="16255" LastEditorUserId="76" LastEditDate="2020-01-14T01:07:17.830" LastActivityDate="2020-01-21T20:04:32.593" Title="2.45GHz: constructing a horn of *thin* steel, what are good ways to join the edges (at least one joint along corner?)" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;microwave&gt;" AnswerCount="5" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15943" PostTypeId="2" ParentId="15942" CreationDate="2020-01-14T01:06:21.277" Score="3" Body="&lt;p&gt;I'm no expert on sheet metal fabrication and hopefully someone will come along with a more confident one, but in general I would expect that soldering/brazing is the correct answer.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(solder in reality would be hard to do, it running all over the place or being lumpy.)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;From what I have seen of soldering large metal parts (with a torch, not an iron), with the proper flux and temperature for the materials involved, solder should not be lumpy — it should flow into the joint and make smooth junctions under surface tension. (At least as long as you don't have drips of solder running away from the heated work area into a cold area; and if that does happen, you can then either apply heat to melt the drip, or grind it off.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-01-14T01:06:21.277" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15944" PostTypeId="2" ParentId="15939" CreationDate="2020-01-14T01:22:27.857" Score="3" Body="&lt;p&gt;In the U.S., if you can foxhunt the interfering transmitter's location, then you might try sending this information to the ARRL: &lt;a href=&quot;http://www.arrl.org/amateur-auxiliary&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/amateur-auxiliary&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ARRL has access to lawyers who can send a polite letter informing the source of the potential Federal law violation, and the potential monetary penalties for such.  This kind of letter from a lawyer can often get the attention of the RFI source’s operator.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-01-16T16:38:01.657" LastActivityDate="2020-01-16T16:38:01.657" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15945" PostTypeId="2" ParentId="15920" CreationDate="2020-01-14T01:33:42.763" Score="-1" Body="&lt;p&gt;Well this is my first answer on Amateur Radio Beta, so be gentle. While I'm a new ham and liable to be ignorant on some subjects, I'm also a 10 year veteran software developer. However, if I'm wrong about something, please enlighten me. :-) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I might be off-base here in that I interpret &quot;not ham&quot; to mean &quot;not necessarily ham&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HamNet might be what you are looking for although IDK if it precisely matches what you are thinking of.  HamNet is a mesh WiFi net operated by hams. That may not sound very impressive but then again the Cellular system is similar in function if not design. Further, one should keep in mind that a standard WiFi router uses milliwatts whereas hams are authorized up to 1500 watts on some bands. Couple this with the Tor protocol and you have something fairly interesting and fairly hard to defeat. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, encryption is a concern when ever you start talking about computer networks. Hams aren't, generally speaking, permitted any encryption. In order to make something like that legal, it would have to happen a connection or two down the pipe, or so I'm told. I had occasion to ask around since it was quite bewildering to myself as to how Hams can live without encryption. I suspect that this restriction may be lifted one day soon although I could be wrong. The more computerized Ham becomes the more vulnerable it will be without encryption. The first time there's a major hack wherein the perpetrators use an unsecured Ham connection to get in or obfuscate the trail, I expect the FCC will be drug into the future like it or not. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For those hams who find this objectionable, consider that network connectivity is an increasingly anticipated service such that some might consider it an essential utility such as phone service. Who fills in the gaps where that doesn't exist or if it becomes unusable in an emergency? Apparently not us, if no encryption is permitted and people have to check their bank accounts, for example, without it. Especially if commercial wireless TV and Radio eventually go the way of the Dodo bird. &lt;/p&gt;&#xA;" OwnerUserId="15859" LastEditorUserId="15859" LastEditDate="2020-01-14T01:51:54.263" LastActivityDate="2020-01-14T01:51:54.263" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15946" PostTypeId="2" ParentId="15939" CreationDate="2020-01-14T02:01:37.707" Score="1" Body="&lt;ol&gt;&#xA;&lt;li&gt;Find and use a different repeater for the interim. &lt;/li&gt;&#xA;&lt;li&gt;Hold a regular fund raiser to fund #3 below. &lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Make finding the culprit or culprits an ongoing contest with a reward in your club. In other words:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Put a big fat bounty on em! ;-)&lt;/strong&gt; &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Once you've ID'ed them, the rest will be much easier. &#xA;If your club is unable to find em, add more clubs!&lt;/p&gt;&#xA;" OwnerUserId="15859" LastActivityDate="2020-01-14T02:01:37.707" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15947" PostTypeId="2" ParentId="15929" CreationDate="2020-01-14T02:18:34.130" Score="0" Body="&lt;p&gt;It's not a class but my brother and I have had quite a lot of success with &#xA;&lt;a href=&quot;https://www.hamradiolicenseexam.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.hamradiolicenseexam.com&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;He completed his Extra class exam a week or two ago and I'm at like 38% for my own Extra class exam.  You just spend some time every day hitting the multiple choice questions and for the times when you don't get it, you can click and get the text again. The machine doesn't care if you have to read the text 40 times. The machine tells you when you are ready for the exam and you can take a practice exam any time you like. It's cheap, too. :-) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I like doing them one at a time as it's easier for me to notice my own progress that way. After I did Technician, I started with General and Extra class at the same time but didn't like how slow it was going by. One at a time was a perfect cadence for me though. :-)&lt;/p&gt;&#xA;" OwnerUserId="15859" LastActivityDate="2020-01-14T02:18:34.130" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15948" PostTypeId="1" CreationDate="2020-01-14T03:42:20.203" Score="0" ViewCount="108" Body="&lt;p&gt;I need a directional antenna for 10 m that is less than half the size of a yagi or quad with more than about 7 dBi of gain, does anyone know if such a thing exists ? &lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-01-14T21:13:02.300" LastActivityDate="2020-02-13T00:31:21.067" Title="Small size vertical 10 m antenna with high gain" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15949" PostTypeId="2" ParentId="15942" CreationDate="2020-01-14T14:16:15.277" Score="2" Body="&lt;p&gt;For really fine control of soldering, use a soldering gun as a resistance welder. Just cut off the end of the heating tip, so that instead of a loop you have two big copper wires coming out of the gun. Press them onto either side of the joint and pull the trigger. The current passing through the metal will quickly heat it to the point where it will melt the solder. It's much easier to control than a torch.&lt;/p&gt;&#xA;" OwnerUserId="105" LastActivityDate="2020-01-14T14:16:15.277" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15950" PostTypeId="1" AcceptedAnswerId="15956" CreationDate="2020-01-14T14:41:48.870" Score="1" ViewCount="305" Body="&lt;p&gt;So I have the misfortune of being an apartment dweller. I know that 50 watts is pretty safe as it is what first responders use on 2 meters. Am I really going to have to run around with an analyzer checking safety? That is likely to cause some probably unwarranted alarm. I can't use more than 200 watts anyway as my gear isn't rated for higher nor does it make sense to purchase such with other human beings in such close proximity. My radio itself won't do more than 100 watts without an amp. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that my first Ham goal is to reach my Elmer (My brother, actually) in the lower thumb area of Michigan from the Ohio river. &lt;/p&gt;&#xA;" OwnerUserId="15859" LastEditorUserId="4665" LastEditDate="2020-01-14T17:24:17.000" LastActivityDate="2020-01-14T17:24:17.000" Title="How safe is 100 watts on 2-40 meters?" Tags="&lt;united-states&gt;&lt;rf-power&gt;&lt;safety&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15951" PostTypeId="2" ParentId="15942" CreationDate="2020-01-14T15:08:51.190" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;For very narrow gauge, as in the sheet metal used for the waveguide in a microwave oven I think it's a process involving a roller disc inside the waveguide making spot welds at the closest interval possible and doing multiple passes until it's continuous.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;People reviewing TIG welders on YouTube routinely &lt;a href=&quot;https://youtu.be/No3YHZfgClM&quot; rel=&quot;nofollow noreferrer&quot;&gt;weld razor blades&lt;/a&gt; together. Any thin steel that's heavy enough to hold a horn shape without deforming under its own weight can surely be welded by a skilled welder with a decent machine. TIG welds can be quite flat right off the machine, but if you need it absolutely smooth you can grind/sand/polish the seam until it's smooth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look around for a metal fabrication shop in your area — if you're not sure where to start, stop by an auto body shop and ask them to point you in the right direction.&lt;/p&gt;&#xA;" OwnerUserId="11226" LastActivityDate="2020-01-14T15:08:51.190" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15952" PostTypeId="2" ParentId="15950" CreationDate="2020-01-14T15:10:10.707" Score="1" Body="&lt;p&gt;As I recall, you're under no obligation to do RF field safety checks for radiated power up to 100 W.  The only significant safety concern (assuming you're running solid state, as opposed to old vacuum tube equipment) is RF burns from actually touching the antenna other radiating element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a concern, but it's worth noting that an antenna radiates just as well if made from insulated wire as it does in bare metal, so the touch exposure can be limited to connectors and cut wire ends (which can all be enclosed in heat shrink or otherwise insulated).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FWIW, if you have an antenna that's halfway efficient and reasonably well matched, your main contact range limitation on 20 and 40 meters is band conditions (which suck just now, early 2020, with the solar minimum).  Even so, either of those bands should be able to reach hundreds of kilometers with 100 W and an omni antenna, so long as you aren't sending almost all of your power upward.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-01-14T15:10:10.707" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15953" PostTypeId="2" ParentId="15950" CreationDate="2020-01-14T15:10:47.853" Score="0" Body="&lt;p&gt;As far as radiated energy, you're safe.  At 100W on 40m, if you touch the antenna wire, you run the risk of RF burns (ask me how I know), and perhaps similar on 2m.  But as far as problems from the RF floating around the room, it's a non-issue.  The other thing that might come up is RFI, your signal getting into their TVs and stereos and such.  But that's just an annoyance, not a safety issue.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2020-01-14T15:10:47.853" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15954" PostTypeId="1" CreationDate="2020-01-14T15:16:01.203" Score="-1" ViewCount="78" Body="&lt;p&gt;As I am settling on a design for a radio I need to figure out one thing:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Should I modulate on low power and boost it up with a post amp, or should I go on full power right out of the gate? &lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="4076" LastEditDate="2020-01-14T21:03:35.360" LastActivityDate="2020-01-14T21:13:38.740" Title="What is an optimal amplifier arrangement with ham radios?" Tags="&lt;amplifier&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15955" PostTypeId="1" CreationDate="2020-01-14T16:12:19.147" Score="1" ViewCount="201" Body="&lt;p&gt;I bought a FE-5650A rubidium standard reference from eBay in the hope I can readily use it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ebay.com/itm/142361240786&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ebay.com/itm/142361240786&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately this is far from &quot;reasily useable&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First and foremost, there is no RF connector (SMA, BNC, ...). Where is the 10 MHz output? (I hope it doesn't come out via the pin header, as it would result in significant interference&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, the attached picture says there is a 9 pin connector:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/92d9t.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/92d9t.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there is only a 2x10=20 pin connector on my device. How to connect a simple 15V benchtop supply to this?&lt;/p&gt;&#xA;" OwnerUserId="15972" LastActivityDate="2020-01-15T03:02:22.940" Title="How to use FE-5650A rubidium frequency standard?" Tags="&lt;frequency&gt;&lt;oscillator&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15956" PostTypeId="2" ParentId="15950" CreationDate="2020-01-14T16:17:14.650" Score="4" Body="&lt;p&gt;The FCC has published a bulletin OET 65B that has a table showing for VHF you don't need to evaluate the RF hazard if your effective power is 50 watts or below. For 70 cm UHF the limit is 70 watts. This does not mean it is not safe above those limits, it just means you must do an evaluation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://transition.fcc.gov/bureaus/oet/info/documents/bulletins/oet65/oet65b.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://transition.fcc.gov/bureaus/oet/info/documents/bulletins/oet65/oet65b.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another table shows safe distances from antennas. It distinguishes between uncontrolled access (outside) and controlled (in your house or fenced in yard). For VHF with a 0 gain antenna in a uncontrolled environment you need a separation of 3.2 meters. So if the antenna is on a 12 foot pole you are ok.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FCC is amending part 97 with regards to exposure limits. This will require radio operators to perform RF exposure evaluations regardless of power levels. Previous low power stations were not required to do this. The ARRL is working with the FCC to develop easy to use online RF calculators to make this task easier. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-01-14T16:17:14.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15957" PostTypeId="2" ParentId="15942" CreationDate="2020-01-14T16:20:53.867" Score="0" Body="&lt;p&gt;I would suggest overlapping the edges and using a adhesive such as JB weld. after the adhesive has set you can sand or file the seam to smooth out any squeeze out.  &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-01-14T16:20:53.867" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15958" PostTypeId="2" ParentId="15954" CreationDate="2020-01-14T16:59:41.597" Score="2" Body="&lt;p&gt;Pretty much every design I've looked at in detail (I'm not a radio engineer or electronic designer, but I've looked at circuits with an eye to building them) does the modulation before any power amplification.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way I understand it, the modulator can be less costly when its modulating a milliwatt signal than if you try to modulate, say, a hundred watts -- but the amplifier (if well designed) doesn't care if it's boosting a pure RF sine wave or a modulated signal.  That means, for the simple case of an AM transmitter, you'd generate the RF in the oscillator stage, modulate the output of the oscillator, then amplify the result.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-01-14T16:59:41.597" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15959" PostTypeId="2" ParentId="15955" CreationDate="2020-01-14T17:30:48.300" Score="0" Body="&lt;p&gt;The datasheet that I found online has a picture of what looks like an F-connector on the same side as the multi-pin connector. That's where your output should be.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-01-14T17:30:48.300" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15960" PostTypeId="1" CreationDate="2020-01-14T18:00:03.693" Score="0" ViewCount="28" Body="&lt;p&gt;Some time ago, I set up my Hytera PD785G. Unfortunately, I can't remember whether I have only requested my digital ID (I can look it up &lt;a href=&quot;https://ham-digital.org/dmr-userreg.php?callsign=dk3tu&quot; rel=&quot;nofollow noreferrer&quot;&gt;on ham-digital.org&lt;/a&gt;) or whether I have also entered it into the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do I look up the digital ID in order to find out whether it's entered and entered correctly? If it can't be looked up, where would I enter it?&lt;/p&gt;&#xA;" OwnerUserId="890" LastActivityDate="2020-03-17T17:25:08.907" Title="Did I enter my digital ID in Hytera PD785G?" Tags="&lt;dmr&gt;&lt;hytera&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15962" PostTypeId="2" ParentId="15954" CreationDate="2020-01-14T21:06:29.023" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;All modes @ Mike Waters&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, clearly, then your only choice is to modulate at low powers and then amplify the modulated signal:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Devices that affect a high-power signal do exist (for example, high-powered frequency mixers), but they are inherently somewhat mode-specific. (or very high in loss, which means you'd never want to use them at high powers.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You might want to share your design so far in future questions!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, there might be a few exceptions to the above rule, but only for very specific power/frequency/flexibility/complexity/cost tradeoffs, which I don't think apply to you (and which to discuss out of blue air would be far too open-ended).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-01-14T21:13:38.740" LastActivityDate="2020-01-14T21:13:38.740" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15963" PostTypeId="1" AcceptedAnswerId="15966" CreationDate="2020-01-14T22:09:30.567" Score="5" ViewCount="135" Body="&lt;p&gt;I have Kenwood TH-D72 2m/70cm HT. According to the &lt;a href=&quot;https://www.kenwood.com/usa/com/amateur/th-d72a/spec.html&quot; rel=&quot;noreferrer&quot;&gt;manufacturer&lt;/a&gt; the sensitivity is &quot;Less than 0.18 uV&quot;. I would like to check this, since the radio is not new and I'm not it's first owner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To do this I decided to use the tracking generator of my Rigol DSA815-TG and a bunch of SMA attenuators (120 dB in total), because I don't have any other way to reliably generate a few uV signal. Naturally, zero span was used. I discovered that a -127 dBm signal opens the squelch on both 2m and 70cm and with squelch turned off I can hear the presence of -133..-134 dBm signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What surprises me is that if my calculations are correct -127 dBm is &lt;strong&gt;much less&lt;/strong&gt; than 0.18 uV RMS:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;gt;&amp;gt;&amp;gt; from math import pow, log10&#xA;&amp;gt;&amp;gt;&amp;gt; 10*log10(1000*pow((0.18/1000/1000),2)/50)&#xA;-121.88424994129406&#xA;&amp;gt;&amp;gt;&amp;gt; 10*log10(1000*pow((0.05/1000/1000),2)/50)&#xA;-133.0102999566398&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I decided to check my HF QRP transceiver Xiegu X5105 as well and got similar results - the sensitivity is about 0.05 uV although the manufacturer promises only 0.25 uV.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are my measurements wrong? Or maybe it's a common practice among radio manufacturers to specify worst-case sensitivity? According to the spectrum analyzer attenuators are fine. Also a -73 dBm signal gives S9 level on a S-meter as expected.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-01-15T20:15:47.490" Title="How to properly measure sensitivity of the receiver?" Tags="&lt;measurement&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15964" PostTypeId="2" ParentId="15955" CreationDate="2020-01-15T01:20:40.923" Score="2" Body="&lt;p&gt;See &lt;a href=&quot;http://www.leapsecond.com/museum/fei5650a/FE5650A-pin-out.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.leapsecond.com/museum/fei5650a/FE5650A-pin-out.gif&lt;/a&gt;&#xA;for the pin out of option 58.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gNKAW.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gNKAW.gif&quot; alt=&quot;FE5650A pinout&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.leapsecond.com/museum/fei5650a/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.leapsecond.com/museum/fei5650a/&lt;/a&gt;  supplies more detail.&lt;/p&gt;&#xA;" OwnerUserId="15497" LastEditorUserId="8717" LastEditDate="2020-01-15T03:02:22.940" LastActivityDate="2020-01-15T03:02:22.940" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15965" PostTypeId="1" CreationDate="2020-01-15T04:11:38.243" Score="0" ViewCount="695" Body="&lt;p&gt;I'm having the following problem with my FT-817:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;1) Receives fine on all bands&lt;/p&gt;&#xA;&#xA;&lt;p&gt;2) Transmits fine on 2m and 70cm&lt;/p&gt;&#xA;&#xA;&lt;p&gt;3) Doesn't transmit at all on 160m through to 6m&lt;/p&gt;&#xA;&#xA;&lt;p&gt;4) Keying the MIC on 160m to 6m, gives me the red Tx light and I can hear the click of a relay engaging, but no power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Questions&lt;/p&gt;&#xA;&#xA;&lt;p&gt;a) Tried all the config settings, tried a full reset, but just on the off chance I have missed something, could this be a config issue? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;b) Fact that I get transmit on 2m and 70com I guess indicates no problem with the finals (?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;c) Has anyone seen this specific failure before?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;d) Any hints on what it might be?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess if it's nothing obvious, I'll have to print out the block and circuit diagrams, plan size like Alan W2AEW, and go through the signal path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hoping someone can help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tim &lt;/p&gt;&#xA;" OwnerUserId="11258" LastActivityDate="2020-10-19T23:52:19.973" Title="Yaesu FT-817 Won't transmit on 160m to 6m" Tags="&lt;yaesu&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15966" PostTypeId="2" ParentId="15963" CreationDate="2020-01-15T04:47:35.693" Score="5" Body="&lt;p&gt;Quite likely the signal generator, and the radio, are too leaky to do this experiment on one bench top. So the signal received by the radio is not as small as you think it is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution would be to eliminate the leak path, by shielding one or both ends. You'll get good results with aluminium foil: Power the HT from its battery only. Connect some of the attenuators directly to the HT. Wrap the whole thing tightly in foil, a few layers. Where the attenuators stick out, put a tight cable tie or wrap of wire twisted so the foil makes good contact with the attenuator body. Repeat the cable tie in two more places. Poke some small holes if you need to hear or see the LED.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also try more distance, with a cable between Tx and Rx, but&lt;br&gt;&#xA;a) watch out for leakage through the cable - it must be double-screened like RG214, RG223, etc, otherwise the signal will just leak in there instead, and&lt;br&gt;&#xA;b) watch out for currents on the outside, carrying RF from the leaky generator to be picked up by the leaky receiver. Some ferries distributed over its length will help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if you can't fix all the leakage, trying one of these tests will show you if there is a leakage problem or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible that the squelch opens at a lower power than is required for intelligible speech. A professional radio test box uses a frequency modulated RF signal, and evaluates the signal-to-noise ratio of the audio output. This wouldn't be a whole 10 dB different from what you're measuring though.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-01-15T19:10:58.193" LastActivityDate="2020-01-15T19:10:58.193" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15967" PostTypeId="1" CreationDate="2020-01-15T11:36:04.420" Score="1" ViewCount="768" Body="&lt;p&gt;I have a baofeng DMR radio with SMS feature, and since there is not much DMR radio owners in my area I want to do something myself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The easiest thing I can do I thought is to send myself some SMS as I did with a POCSAG pager using my hackrf one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I haven't found any software to do that. All I found is MMDVM-SDR program on github which acts as a MMDVM modem utilizing a fake serial port. It allows to get commands from the MMDVM-Host and modulate them as IQ WAV file.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is one problem: that MMDVM modem protocol has no commands to send DMR SMS. It only accepts &quot;DMR DATA packet&quot; at different rates. I tried to google for &quot;DMR AIR interface&quot; but it also has no mentions of SMS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By that time I learned that DMR SMS is a non-standartized thing which leaves me with this questions (one is part of the another):&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What format all those TYT and Baofeng radios is using, where I can get it's datasheet.&lt;/li&gt;&#xA;&lt;li&gt;How to make a DMR SMS packet for my radio and send it to a MMDVM modem emulator or directly to the SDR using some other modem software?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;PS: I tried to record my radio's signal with SDR and play it back. With voice it works, I can hear myself, but with SMS it doesn't work for some reason: my radio just ignores them (maybe that is because it's number in both from and to fields?)&lt;/p&gt;&#xA;" OwnerUserId="13758" LastActivityDate="2021-04-11T18:07:05.693" Title="How to send DMR SMS using MMDVM modem or hackrf?" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;&lt;dsp&gt;&lt;dmr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15968" PostTypeId="2" ParentId="15963" CreationDate="2020-01-15T16:58:30.627" Score="3" Body="&lt;p&gt;To reduce direct coupling between chassis (generator and DUT), I use a long antenna coax (10 to 20 meters or more), and put the RF source plus attenuators on the far side of the building, with the attenuator chain some distance from the RF source on another coax.  You may or may not need to take into account the loss on the coax (which might be less than the tolerances on your attenuators).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-01-15T20:15:47.490" LastActivityDate="2020-01-15T20:15:47.490" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15969" PostTypeId="2" ParentId="15965" CreationDate="2020-01-15T21:25:23.230" Score="3" Body="&lt;p&gt;Tim, what you have said provides a few clues to the problem you are seeing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that someone has not accessed the hidden menu which allows factory alignment of the radio, your problem is not a config issue. If someone has messed with the alignment settings, ignore what follows, because what to do for that is a different answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm guessing that you are deciding on whether or not the FT817 is outputting power by looking at the power meter bar graph on the FT817 screen or by looking at an external power meter. I would use an external power meter connected to a dummy load to be sure. I'm also assuming that the problem you are seeing occurs on AM, FM and SSB. If there is no TX output only on one mode, then the diagnosis given in this answer does not apply.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a radio that doesn't have any faults, the kind of antenna you are connected to makes no difference as to whether or not the FT817 will try to output TX power. For a working radio, ff the antenna is bad or missing you will still see TX power output shown on the power meter bar graph on the FT817 screen but the high SWR icon will show.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are no menu options for the FT817 which can cause output to be present on VHF/UHF and not on HF/6m. Also, there are no options which would cause no SSB transmit audio (and seemingly no TX output power because SSB only has power when you talk) only on some bands. So if there is SSB transmit audio on VHF/UHF then the SSB audio circuitry will  be working on the lower bands as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, the only power control for the FT817 is provided by the menu keys under the display, and this sets power for all bands from low to high but does not allow the output power to be turned down to zero or adjusted separately for individual bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So your problem is not being caused by incorrectly set menu options.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FT817 has a separate output stage including final transistors for HF/6m and VHF/UHF. It seems to me that the most probable explanation for what you are seeing is that the HF/6m output stage has failed, and this is most likely (not definitely) going to be caused by a failed output FET 2Sk2975 in the HF section of the PA output module. This device can be replaced but you need a high powered soldering iron and good soldering skills as there is a large area of heat-sink around the device which makes removal difficult. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;See this link &lt;a href=&quot;http://www.ka7oei.com/FT817-finals.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ka7oei.com/FT817-finals.pdf&lt;/a&gt; for an explanation on how to replace FT817 finals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the fault isn't the HF output FET, then fault finding will become more involved and complex.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the reason for a failure is another whole subject. If the FT817 does actually have a fault, I think you should try and determine why the FT817 has failed, for example transmitting using an antenna with a bad SWR, so that you can prevent a recurrence.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-01-16T05:30:17.327" LastActivityDate="2020-01-16T05:30:17.327" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15970" PostTypeId="1" AcceptedAnswerId="17561" CreationDate="2020-01-16T09:44:11.920" Score="6" ViewCount="108" Body="&lt;p&gt;When designing a waveform for packet radio usage, it'd be helpful to know a few things, mainly &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;distribution of coherency bandwidths&lt;/li&gt;&#xA;&lt;li&gt;distribution of coherency times&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Whilst such statistics are reasonably possible to generate for higher frequencies based on own measurements, for terrestrial HF propagation, due to the large distances involved and the low useable bandwidths, a sufficient measurement campaign would be infeasible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;HF propagation models are very light on details or vary wildly when it comes to the relevant aspects that would allow for simulation of the same (that being delay spread and doppler spread). Mostly, they're early cold war studies that care only about amplitude attenuation. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Are there more modern channel models for HF propagation?&lt;/li&gt;&#xA;&lt;li&gt;Alternatively, statistics over the coherency properties?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-01-16T09:56:47.090" LastActivityDate="2020-11-01T20:35:18.940" Title="Where to find HF channel models or statistics?" Tags="&lt;hf&gt;&lt;doppler&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="15971" PostTypeId="1" CreationDate="2020-01-16T21:44:05.387" Score="-1" ViewCount="174" Body="&lt;p&gt;In my working design, I have a transceiver TX on low power; Then boost it in a preamp phase in the back. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way I'm sending the signals (RX and TX) through the radio is by a network of 1/8 to 1/4 inch wide copper strips. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first network is from the TX side of the Transceiver to the input of the preamp in the rear. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second network branches to the RX of the transceiver and a secondary RX chip.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here then lays a problem before me, at what watt level will cause my TX network to start emitting and cause interference in my RX network. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is that okay, or should I invest in something else or just use wire? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason why I'm asking about the khz and Mhz is that the transceiver chip is going to handle all that is offered in both the khz and Mhz bands so talking about one specific band is going to limit what i can do. &lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="12988" LastEditDate="2020-01-19T00:17:10.907" LastActivityDate="2020-01-19T21:36:20.053" Title="At what watt level is it safe to use metal strips for modulated signals?" Tags="&lt;transceiver&gt;&lt;equipment-design&gt;&lt;transmission-line&gt;" AnswerCount="2" CommentCount="4" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15972" PostTypeId="2" ParentId="15939" CreationDate="2020-01-16T23:20:26.417" Score="2" Body="&lt;p&gt;To add to some already great answers here, the very first thing you should do is &lt;strong&gt;listen on the repeater's &lt;em&gt;input frequency&lt;/em&gt;&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Do you hear it then? If not, then drive fairly close to the repeater site. &lt;em&gt;Note that an off-frequency signal that overloads the repeater's receiver might also overload your HT&lt;/em&gt;. If that happens, then it would be prudent to attenuate the signal to determine if it suddenly disappears at some point or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to do that would be to use a step attenuator between your antenna and transceiver, but it could also be done by gradually covering the antenna with aluminium foil*. Or, you could simply drive a little farther away from the repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the signal suddenly disappears at some point as the attenuation is gradually increased, then it likely is only a spurious &quot;phantom&quot; signal due to the input preamps overloading, and not malicious QRM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can examine those signals using a spectrum analyzer. It could also be a product of two signals mixing. But I'll leave the details of that for someone else to expound upon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Only after doing this should you proceed to triangulate the interference source, assuming that is feasible.&#xA;&lt;hr&gt;&#xA;*Don't transmit with your HT's antenna covered! It might damage your HT's output circuit.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-01-16T23:20:26.417" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15974" PostTypeId="1" AcceptedAnswerId="15976" CreationDate="2020-01-17T07:42:21.723" Score="5" ViewCount="401" Body="&lt;p&gt;Recently I've been reading about EME and there was one thing that surprised me. Many sources claim that EME has path loss for 2m band about 252 dB. In the same time they claim (&lt;a href=&quot;https://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Earth_communication#Current_EME_communications&quot; rel=&quot;noreferrer&quot;&gt;one&lt;/a&gt;, &lt;a href=&quot;https://www.qsl.net/sterling/Activities/20151007_Paul_K4MSG_Small_Station_EME/EME%20Presentation_07-2015-h+.pdf&quot; rel=&quot;noreferrer&quot;&gt;two&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Recent advances in digital signal processing have allowed EME&#xA;  contacts, admittedly with low data rate, to take place with powers in&#xA;  the order of 100 Watts and a single Yagi–Uda antenna. [About 8-9 elements according to other sources.]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;100W is 50 dBm and the common sensitivity of the receiver is about 0.11 uV (the number for &lt;a href=&quot;https://www.hamoperator.com/Fusion/FusionFiles/FT-991_Technical_Supplement.pdf&quot; rel=&quot;noreferrer&quot;&gt;Yaesu FT-991A&lt;/a&gt;, SSB @ 2m band) or:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;gt;&amp;gt;&amp;gt; from math import pow, log10&#xA;&amp;gt;&amp;gt;&amp;gt; 10*log10(1000*pow((0.11/1000/1000),2)/50)&#xA;-126.16184634019568&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;... -126 dB. Assuming that all 50 dBm are radiated straight to the moon (ideal radiation pattern of the antenna):&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;gt;&amp;gt;&amp;gt; 50-252&#xA;-202&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;... we are not even close to -126 dB. So what is actual relation between path loss, receiver sensitivity, and also used power and antennas gain?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-01-17T21:32:19.440" Title="Why EME with 100W and a single Yagi-Uda antenna is possible?" Tags="&lt;math&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15975" PostTypeId="2" ParentId="15974" CreationDate="2020-01-17T09:30:41.590" Score="3" Body="&lt;p&gt;RE: &lt;em&gt;...So what is actual relation between path loss, receiver sensitivity, and also used power and antennas gain?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Friis transmission equation is useful to determine such for a free-space, far-field propagation path (see the example below).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wD8Wo.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wD8Wo.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-01-17T09:30:41.590" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15976" PostTypeId="2" ParentId="15974" CreationDate="2020-01-17T09:57:29.327" Score="15" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;You didn't include antenna gain at all. That number for the path loss is a starting point assuming &lt;em&gt;zero&lt;/em&gt; gain (isotropic antennas) on both ends. This isn't a realistic situation, because of course the vast majority of the signal from an isotropic antenna doesn't reach the moon at all, but it's conventional for calculating link budgets. A 9-element Yagi has a gain of about 13.4 dBi, so one of these on each end gives an improvement of 26.8 dB.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A receive pre-amplifier at the antenna makes the minimum discernable signal of the receiver basically irrelevant. With enough gain, we can bring any signal above the receiver's MDS. Instead we're concerned about the noise floor, which is characterized by something called &quot;system noise temperature&quot;. An achievable value of noise temperature for 144MHz, without any heroic measures, is 300 K, which equals a noise-in-2500Hz of -228.6 + 10*log(300 * 2500) = -169.8 dBW = -139.8 dBm (&lt;a href=&quot;https://www.physics.princeton.edu/pulsar/K1JT/Optimized_Small-Station_EME.pdf&quot; rel=&quot;noreferrer&quot;&gt;ref&lt;/a&gt;).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;JT65 decodes at 27dB below the noise-in-2500Hz, so our target is -167.8 dBm.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Now adding it all up we have 50dBm (transmit power) + 13.4dB (tx ant gain) - 252 dB (path loss) + 13.4 dB (rx ant gain) = -175.2 dBm. Compared to our JT65 receive threshold of -167.8 dBm we're still 7.4 dB short. So close, but still very far! How do we resolve this? Well... the truth is that a small station can't be heard by another small station. But a small station can be heard by a &lt;em&gt;larger&lt;/em&gt; station, with a bigger antenna. So let's replace one of the 13.4 dB, 9-element yagis with a 2x2 array of 10-element yagis as described by &lt;a href=&quot;http://www.kl7uw.com/eme144.htm&quot; rel=&quot;noreferrer&quot;&gt;KL7UW&lt;/a&gt;. These have a gain of 21.3 dBi. Now we're at 50 + 13.4 - 252 + 21.3 = -167.3 dBm, just squeaking in at half a dB above the JT65 decode threshold.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;There's a lot of variables here... there's room to improve things slightly (lower noise preamps, maybe a 200W transmitter, maybe some &quot;ground gain&quot; with the moon near the horizon), and also room for things to get worse (if cables aren't done very carefully, if the moon is in a &quot;noisier&quot; part of the sky, if the moon is further away than usual), but I think this goes to show that a &quot;small&quot; 100W-and-9-elements station is right in the ballpark of being decoded by a medium-sized station, under good conditions, which is exactly what people are reporting, and that it isn't 75dB away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the other end is a &lt;em&gt;really big&lt;/em&gt; station (HB9Q, KP4AO, DL7APV, or the like) it becomes possible for a smaller station to work them even under less-than-ideal conditions, and there are even people who have worked them with 2 elements, or a dipole. Antenna gain is a very powerful thing.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-01-17T10:21:07.707" LastActivityDate="2020-01-17T10:21:07.707" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15978" PostTypeId="2" ParentId="15974" CreationDate="2020-01-17T21:32:19.440" Score="3" Body="&lt;p&gt;From the linked manual:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dDMjZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dDMjZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice these sensitivities each specify a mode, and some threshold (10 dB S+N/N, 12 dB SINAD). For digital modes a bit error rate (BER) would be specified.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some modes are more sensitive than others. For example, WSPR takes 2 minutes to send a call, transmit power, and grid square, whereas the SSB transmission of the same information would take perhaps five seconds. If each is transmitted at 10 W, the WSPR signal contains a total energy of:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 120\:\mathrm s \times 10\:\mathrm W = 1200\:\mathrm J $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;whereas the SSB signal contains:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 5\:\mathrm s \times 10\:\mathrm W = 50\:\mathrm J $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Detecting 1200 joules of radiated energy is much easier than 50 joules. Even though they each have the same amplitude, the WSPR signal is transmitted over a longer time. The noise which obscures the signal is random: over time it averages to zero. The signal is not: the longer it is measured, the more bias it introduces into the detection. Thus, given a sufficiently low data rate (&quot;admittedly with low data rate&quot;) and sufficient attention to the details of propagation effects and appropriate engineering to overcome them (&quot;Recent advances in digital signal processing&quot;) it's possible to establish communication at lower amplitudes.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-01-17T21:32:19.440" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="15979" PostTypeId="1" AcceptedAnswerId="16158" CreationDate="2020-01-18T05:19:52.793" Score="3" ViewCount="297" Body="&lt;p&gt;The well-known repeater listings/apps don't provide a database that you can download and use freely for any use in building your own app.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there a such a freely accessible repeater listing database online for amateur radio?&lt;/p&gt;&#xA;" OwnerUserId="14201" LastEditorUserId="8717" LastEditDate="2020-01-18T21:47:59.173" LastActivityDate="2020-03-18T14:54:17.500" Title="Is there a freely accessible repeater database?" Tags="&lt;repeater&gt;&lt;software&gt;" AnswerCount="4" CommentCount="7" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15981" PostTypeId="1" CreationDate="2020-01-18T21:57:29.303" Score="0" ViewCount="104" Body="&lt;p&gt;I would like to understand how to calculate receive wattage given the following (excluding feeder loss and SWR):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transmit 50 dBm (100W) =&gt;&#xA;24 dBi directional antenna =&gt;&#xA;30 dB path loss =&gt;&#xA;24 dBi directional antenna (receive) =&gt; wattage?&lt;/p&gt;&#xA;" OwnerUserId="16278" LastActivityDate="2020-01-18T22:59:21.877" Title="Calculating receive wattage given transmit power, antennae dBi and path loss" Tags="&lt;receiver&gt;&lt;rf-power&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15984" PostTypeId="2" ParentId="15981" CreationDate="2020-01-18T22:46:33.610" Score="3" Body="&lt;p&gt;On the one hand: just add the numbers. 50 dBm + 24 dB - 30 dB + 24 dB = 68 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand: that's more power out than in! What that's telling you is that you will &lt;em&gt;never&lt;/em&gt; have path loss as low as 30 dB and a pair of 24 dB gain antennas at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For instance, say we're working at a wavelength of 2 meters. The Friis formula tells us that the path loss will be &lt;span class=&quot;math-container&quot;&gt;$ 20 \log \left( \frac{4\pi d}{2 m} \right) $&lt;/span&gt;. Setting that equal to 30, we get &lt;span class=&quot;math-container&quot;&gt;$d$&lt;/span&gt; = 5.03 meters. But a gain of 24 dB for a 2 meter wavelength requires a parabolic dish at least 10 meters in diameter, for which the far field begins (and the Friis equation is valid) only at a distance of at least 100 meters! No matter how you slice it, the laws of physics won't let you do that. So your example numbers don't represent a physically possible system.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-01-18T22:59:21.877" LastActivityDate="2020-01-18T22:59:21.877" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="15985" PostTypeId="1" CreationDate="2020-01-19T01:58:06.163" Score="1" ViewCount="48" Body="&lt;p&gt;I'm 99.9% certain that this will be OK, but independent verification would be reassuring.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am an &quot;Intermediate&quot; licence holder in the UK.  This means that I am authorised to design and build my own transmitters, or buy one, to a maximum TX power of 50 Watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an &quot;Intermediate&quot; though, I am not authorised to supervise an unqualified &quot;Foundation Candidate&quot; (novice).  I don't get that privilege until passing the final exam.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does it seem OK to practice CQ calls on the &quot;public licence&quot; PMR 500mW channels (with a pair of supermarket walkie talkies) to get my friend trained up.  The friend can't make it to the radio club/exam centre on a regular basis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I will also take my friend to a hilltop and demonstrate it for real... we can get repeaters 40 miles away from Dunkery Beacon on a little 5W Baofeng UV-5R.&lt;/p&gt;&#xA;" OwnerUserId="14873" LastActivityDate="2020-01-19T01:58:06.163" Title="UK Intermediate training a not qualified newbie" Tags="&lt;legal&gt;&lt;united-kingdom&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15986" PostTypeId="2" ParentId="15971" CreationDate="2020-01-19T03:30:31.870" Score="6" Body="&lt;p&gt;There is no such thing as a minimum power level at which a conductor will &lt;em&gt;start radiating.&lt;/em&gt; If it radiates at all, then the radiation will be proportional to the power applied. Therefore, the maximum usable power in this circumstance is the power at which such radiation will interfere with (or damage) the receiver, and in order to know it you must test empirically or use electromagnetic simulation software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there are two facts about radio design which you should consider before proceeding with the above principle.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;First:&lt;/strong&gt; You should not use brass strips. Not only that, you should not use wire either. In any RF system beyond the most basic, RF signals should be carried between modules or circuits through &lt;strong&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Transmission_line&quot; rel=&quot;noreferrer&quot;&gt;transmission lines&lt;/a&gt;&lt;/strong&gt;, which prevent (or more precisely, greatly reduce) radiation away from the line. This prevents interference among the parts of your system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(&lt;em&gt;Within&lt;/em&gt; individual circuits, where transmission lines are neither possible nor relevant (since the point of the circuit is to do something other than carrying the signal unchanged), wiring between components should be short, to prevent radiation and other undesired effects. This is usually accomplished in modern radios using a printed circuit board and surface-mount components, but various techniques can be used depending on the desired operating frequency range.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most commonly known type of transmission line is &lt;a href=&quot;https://en.wikipedia.org/wiki/Coaxial_cable&quot; rel=&quot;noreferrer&quot;&gt;coaxial cable&lt;/a&gt;, which is used to connect transceivers to antennas and also to route RF signals between boards/modules within them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On printed circuit boards, carefully designed copper traces function as &lt;a href=&quot;https://en.wikipedia.org/wiki/Planar_transmission_line&quot; rel=&quot;noreferrer&quot;&gt;planar transmission lines&lt;/a&gt; (&lt;a href=&quot;https://en.wikipedia.org/wiki/Microstrip&quot; rel=&quot;noreferrer&quot;&gt;microstrip&lt;/a&gt; being a common design).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides preventing radiation, correctly designed transmission lines also support &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_matching&quot; rel=&quot;noreferrer&quot;&gt;impedance matching&lt;/a&gt;, which is required to ensure radio signals are efficently transferred from the transmitter to the antenna; mismatches cause inefficiency and often cause destruction of the transmitter due to reflected high-power signals.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Second:&lt;/strong&gt; Most transceivers do not transmit and receive on the same frequency at the same time. This is because it is extremely difficult to prevent the transmitted signal from being partly reflected back and overwhelming the receiver, &lt;em&gt;even if you build everything correctly&lt;/em&gt;. Changes in the antenna due to weather, birds, etc. can disturb it enough to cause lots of reflected power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, a transceiver does one of the following:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Transmits and receives at separate times, known as &lt;em&gt;half-duplex&lt;/em&gt; operation. In traditional amateur radio this is accomplished with an obvious PTT button, but digital packet radio systems such as cell phones and WiFi switch back and forth many times per second.&lt;/li&gt;&#xA;&lt;li&gt;Transmits on a &lt;em&gt;different frequency&lt;/em&gt; than it receives. In amateur radio this can be seen in repeater systems. This requires either using widely separated frequencies (&quot;cross-band repeaters&quot;), or using a and precisely adjusted &quot;duplexer&quot; which is a pair of filters adjusted precisely to the transmit and receive frequencies — and the transmitter and receiver must be well-designed with appropriate shielding and transmission lines so that the signal which goes through the air and bypasses the filter does not interfere.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-01-19T06:35:00.450" LastActivityDate="2020-01-19T06:35:00.450" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15987" PostTypeId="1" AcceptedAnswerId="15988" CreationDate="2020-01-19T19:15:37.033" Score="4" ViewCount="86" Body="&lt;p&gt;I finished building my &lt;a href=&quot;http://www.qrpme.com/?p=product&amp;amp;id=RM4&quot; rel=&quot;noreferrer&quot;&gt;Rockmite ][&lt;/a&gt;. It's running off of 3x 18650s, or 12v. I connected it to a &lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-1840T&quot; rel=&quot;noreferrer&quot;&gt;MFJ-1840T&lt;/a&gt; and held the antenna horizontally in the air (also tried vertically) with my hand. I tried calling &lt;a href=&quot;https://hamprojects.info/Mortty/&quot; rel=&quot;noreferrer&quot;&gt;clean&lt;/a&gt; CQ on 7.030 mHz and get no response. I tried with and without a counterpoise attached to the MFJ. My &lt;a href=&quot;https://m.alibaba.com/product/62342877955/Hugen-NanoVNA-H-New-item-Original.html&quot; rel=&quot;noreferrer&quot;&gt;nanoVNA&lt;/a&gt; tells me the antenna has an SWR of ~2. I tried seeing my signal on a websdr 100 miles away to no avail. I'm in a suburb.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have lots of questions. I also don't know which of the following are necessary or not, or where to start.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;because I'm holding the antenna, should I be expecting nvis contacts only?&lt;/li&gt;&#xA;&lt;li&gt;is my hand wrapped around the antenna base heat shrink hurting things? What's the better way?&lt;/li&gt;&#xA;&lt;li&gt;how sensitive is my setup to time of day?&lt;/li&gt;&#xA;&lt;li&gt;would building a G5RV instead of the MFJ be the thing to get me some contacts? Thus focusing on the antenna instead of more watts.&lt;/li&gt;&#xA;&lt;li&gt;would investing in a QRP SDR such as the &lt;a href=&quot;https://www.hobbypcb.com/index.php/products/hf-radio/rs-hfiq&quot; rel=&quot;noreferrer&quot;&gt;RS-HFIQ&lt;/a&gt; make it possible to chase down band activity and move to more active frequencies to make a contact? Would this help me deduce receiver capability of my antenna setup?&lt;/li&gt;&#xA;&lt;li&gt;are newer digital modes other than cw required to be successful in QRP?&lt;/li&gt;&#xA;&lt;li&gt;should I join a club and being my setup to others to help me figure it all out with?&lt;/li&gt;&#xA;&lt;li&gt;should I climb a mountain peak and try the same thing again?&lt;/li&gt;&#xA;&lt;li&gt;do I need to figure out how to get the swr down?&lt;/li&gt;&#xA;&lt;li&gt;I type for 2-5 minutes before giving up. How long would it take to get a typical bite (response)?&lt;/li&gt;&#xA;&lt;li&gt;do I just need more watts? Am I attempting the rare or impossible? Is the rockmite just not usable in this part of the solar cycle without an amplifier?&lt;/li&gt;&#xA;&lt;li&gt;is there something else I'm not thinking of that is making it impossible for me to make a contact?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16062" LastEditorUserId="8717" LastEditDate="2020-01-19T20:21:52.903" LastActivityDate="2020-01-19T20:45:58.080" Title="no contacts with Rockmite" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;qrp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15988" PostTypeId="2" ParentId="15987" CreationDate="2020-01-19T20:45:58.080" Score="4" Body="&lt;p&gt;I see what your problem is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.mfjenterprises.com/Product.php?productid=MFJ-1840T&quot; rel=&quot;nofollow noreferrer&quot;&gt;That's a 1.4 meter long, based-loaded, telescoping, end-fed vertical antenna&lt;/a&gt;. &#xA;It has &lt;em&gt;significant&lt;/em&gt; losses on 40 meters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, all end-fed antennas require a good RF return, such as a resonant elevated radial or counterpoise. Since you don't mention that, that indicates to me that very little of your signal is actually being radiated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A full-size, center-fed, 40 meter dipole cut for 7.03 MHz is a little bit more than 67 feet long, and no counterpoise is required. I can almost guarantee you that you'll get some answers with one of those!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;I strongly discourage using a G5RV&lt;/strong&gt; for the reasons listed &lt;a href=&quot;http://www.karinya.net/g3txq/g5rv/&quot; rel=&quot;nofollow noreferrer&quot;&gt;on the G3TXQ page about them&lt;/a&gt;. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-01-19T20:45:58.080" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15989" PostTypeId="2" ParentId="15971" CreationDate="2020-01-19T21:36:20.053" Score="4" Body="&lt;p&gt;More critical than power is &lt;em&gt;length&lt;/em&gt;. As a rule of thumb, over distances less than 1/10th the wavelength, metal strips, ordinary wire, or anything you might use to conduct electricity is probably fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Longer than 1/10th the wavelength, and the &quot;wires&quot; start to look more like &quot;antennas&quot;, leading to unintentional reception or radiation. In these cases it's better to use some kind of &lt;em&gt;transmission line&lt;/em&gt;, which is some specific physical arrangement of conductors designed to have a controlled characteristic impedance and minimize radiation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power level is another concern, but not due to radiation: rather the concern is either overheating and efficiency. Thicker conductors will have a lower resistance and thus lower loss, thus generating less waste heat and being more efficient. The maximum power a conductor can handle depends on factors such as the insulation surrounding it, the maximum temperature of the surrounding materials, and your design's tolerance for loss. Due to the large number of variables involved I can't give a general answer here, but usually an online calculator or a manufacturer's datasheet can provide more specific guidelines for a particular situation.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-01-19T21:36:20.053" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15992" PostTypeId="1" AcceptedAnswerId="15993" CreationDate="2020-01-20T20:29:45.463" Score="1" ViewCount="209" Body="&lt;p&gt;Last night was my first night on the air as a General licensee and at HF. I've got an IC-7300 with the built-in antenna tuner. I'm pretty sure I understand how to operate the radio, for the most part. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My antenna is an MFJ-1625. It's one of those telescoping apartment window whips with a big coil and an alligator clip. It has a tuner mounted on it also. Problem is that I can't reach the dang thing where I'm deploying it out on the deck. I'm fairly certain that the 12 foot whip will be verboten the first time management sees it. Anyway, after I figured out how to read the SWR, it seemed pretty close to 1:1 but that is reading it from the transceiver, of course.  I was able to listen to AM radio stations without much trouble. I didn't hear much of anything on other bands though although there were spot sources of RFI. Of course, having found an RF source, I would naturally cycle through the modes to see if I was just in the wrong mode. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that my brother is a Ham up in the thumb area of Michigan and I live near the Ohio river. We were unable to reach each other regardless of the tricks that we tried. He is checking his gear as he hasn't hammed it up in quite a while. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now to the question. I was thinking of replacing the antenna tuner on the whip with an automatic one such that I don't need to reach it, but reviewing the options in the market so far, and looking at what specific antenna tuners's appear to be designed for, makes me think that maybe a whip doesn't need two tuners, one at each end of the transition line. Is this the case?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Request enlightenment. &lt;/p&gt;&#xA;" OwnerUserId="15859" LastEditorUserId="76" LastEditDate="2020-01-20T21:02:26.957" LastActivityDate="2020-01-22T19:24:48.103" Title="Do I always need a tuner at both ends of the transmission line or is that only for certain types of antennas/circumstances?" Tags="&lt;antenna&gt;&lt;feed-line&gt;&lt;antenna-tuner&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15993" PostTypeId="2" ParentId="15992" CreationDate="2020-01-20T21:22:20.337" Score="4" Body="&lt;p&gt;It is &lt;strong&gt;not&lt;/strong&gt; normal to have &lt;em&gt;and use&lt;/em&gt; tuners on both ends of a feed line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The purpose of an antenna tuner is to provide an adjustable impedance transformation. The reason we want that transformation is so that the transmitter can work into the (usually) 50 Ω load it was designed for.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;If you have an antenna tuner located (only) at the antenna, then this is the ideal condition; the transmitter transmits onto the matched-by-design feed line, and the tuner transforms that impedance to the antenna's feed point impedance.&lt;/li&gt;&#xA;&lt;li&gt;If you have an antenna tuner located at the transmitter, this is usable but results in additional losses, because the impedance of the feed line does not match the antenna, so the transmitted signal reflects off that mismatch, and reflects back and forth (standing waves), losing some power to the resistance of the line each time. This can be a good compromise &lt;strong&gt;when your feed line is short&lt;/strong&gt;, or made of a low-loss type of line such as ladder line.&lt;/li&gt;&#xA;&lt;li&gt;If you have antenna tuners in &lt;em&gt;both&lt;/em&gt; locations then at a minimum you have unnecessary components (which all add some loss to the system), but it's also likely that you're &lt;em&gt;unnecessarily&lt;/em&gt; mismatching with the line and adding standing waves to the system (more loss).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;In your case, you have an antenna &lt;em&gt;and&lt;/em&gt; a transmitter with built-in tuners; therefore, the ideal approach to using this system would be to &lt;strong&gt;set the tuner built into your radio in bypass mode&lt;/strong&gt;, and use only the tuner at the antenna (case 1 above). This is also the case if you buy an automatic or remote-controlled tuner to install at the antenna — the best configuration is to use that tuner &lt;strong&gt;only&lt;/strong&gt;, and set your radio's tuner to bypass mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do not get a remote controlled tuner and your antenna is positioned such that you cannot practically adjust the tuner at the antenna when operating, then using tuners at both ends (case 3 above) makes some sense; the one at the antenna can be set to give the best match feasible over the entire range you want to use and the one at the radio can be set for the frequency you're actually using at the moment. But that's a compromise, and it could be improved on by using a &lt;strong&gt;fixed&lt;/strong&gt; matching network at the antenna, designed once and left in place, rather than a tuner whose adjustable components aren't being used. If you do this, make sure to &lt;strong&gt;adjust the antenna's tuner with the radio's tuner bypassed, or with a separate tuner&lt;/strong&gt;; otherwise you're not getting the best match with the feed line.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-01-20T21:34:02.297" LastActivityDate="2020-01-20T21:34:02.297" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="15994" PostTypeId="2" ParentId="15992" CreationDate="2020-01-20T21:45:56.450" Score="2" Body="&lt;p&gt;First, I'd say that using both the tuner for the antenna and your built-in antenna tuner probably didn't hurt anything, but was most likely unnecessary.  You would have a bit more efficiency if you put your internal tuner on bypass.  Of course if you adjusted the whip's tuner at a particular frequency, and then changed the frequency, then you might have had higher losses that were somewhat disguised by the 1:1 SWR you saw.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your antenna is not very efficient for transmitting, and the lower the frequency gets, the worse the problem becomes.  The counterpoise wires are essential for getting the most out of a monopole antenna, so I hope that you had them installed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You didn't mention what band you were on, but it's possible that you were inside each other's &lt;a href=&quot;https://en.wikipedia.org/wiki/Skip_zone&quot; rel=&quot;nofollow noreferrer&quot;&gt;skip zone&lt;/a&gt;.  The closer your frequency is to the maximum usable frequency (MUF), the longer the skip zone is.  I've had the skip zone extend out a couple hundred miles or more at night on 40m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd recommend enlisting help from someone at the local ham club.  You could try a contact with your brother from a station with a known-good antenna, which would help explain if your problem is just propagation and noise; or propagation, noise, and the antenna.  If you can't find an experienced ham to help, you might try a different antenna, such as a dipole hung in the trees of a local park.  (Best to inform the people in charge of the park of your intentions beforehand.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-01-20T21:45:56.450" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="15996" PostTypeId="1" CreationDate="2020-01-21T04:54:16.867" Score="0" ViewCount="106" Body="&lt;p&gt;The solid angle formula calculates the surface area on a unit sphere, from projecting a rectangular patch onto the surface of a sphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oDAUam.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oDAUam.png&quot; alt=&quot;Solid angle for rectangular patch&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;http://www.texample.net/tikz/examples/spherical-and-cartesian-grids/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Image source&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is calculated using the azimuth angle &lt;span class=&quot;math-container&quot;&gt;$\phi$&lt;/span&gt; and the elevation angle &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\Omega = \int_{0}^{\phi} \int_{0}^{\theta} \sin{\theta'} d\theta' d\phi $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However an antenna beam pattern will project a curved patch onto a sphere. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Case 1: Circle projection&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First consider a linearly polarized, symmetrical parabolic dish antenna. This ideal geometry ensures the E/H planes have the same beamwidth. A circle is projected onto the unit sphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QZ1Ozm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QZ1Ozm.png&quot; alt=&quot;Solid angle for circular patch&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note this is equivalent to the surface area of a hemisphere between the circle and the sphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\Omega = \int_{0}^{2\pi} \int_{0}^{\theta} \sin{\theta'} d\theta' d\phi &#xA;= 2\pi(1-\cos{\theta})$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Case 2: Ellipse projection&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now consider any linearly polarized antenna, such that the E/H planes have different beamwidths. I presume this would be projecting an ellipse onto the unit sphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RoJaFm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RoJaFm.png&quot; alt=&quot;Solid angle for elliptical patch&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strike&gt;I presume the solid angle can be calculated from the surface area of a semi-ellipsoid.&lt;/strike&gt; A solid angle is a fraction of the surface area of the unit sphere, the ellipsoid is not coincident with a sphere (other than the trivial case), so this can't be correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Some questions:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How can the solid angle formula be used to derive the (elliptical) solid angle of an antenna with a beamwidth of &lt;span class=&quot;math-container&quot;&gt;$\phi$&lt;/span&gt; degrees in the E-plane and &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt; degrees in the H-plane?&lt;/li&gt;&#xA;&lt;li&gt;Are there any approximations to this?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16087" LastEditorUserId="16087" LastEditDate="2020-01-21T06:58:57.837" LastActivityDate="2020-01-23T20:18:16.333" Title="Solid angle for different E/H plane beamwidths" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;math&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="15998" PostTypeId="2" ParentId="15335" CreationDate="2020-01-21T19:20:56.853" Score="5" Body="&lt;p&gt;Doppler spreading is the change in received frequency from a distance transmitter due to the rise and fall of the ionosphere along the signal path. When the effective height of the ionosphere rises, this lengthens the path and causes the received frequency to drop; when it falls the path decreases and the frequency rises.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can measure this frequency change yourself in real time using simple equipment and, making some simple assumptions, compute the change in ionospheric height. The equipment and technique are both described in my Sept 2018 QEX article available &lt;a href=&quot;https://www.clearskyinstitute.com/ham/gps/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. The idea is to use a digital frequency synthesizer synchronized to GPS, then record the difference between the locally generated signal and a signal with a well-known frequency such as WWV. Then assuming the path is a simple triangular up-reflect-down profile, the change in frequency can be used to compute the change in path length and thence the change in ionospheric effective height.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My measurements suggest a 5 MHz frequency measured over a 1000 km path changes a few tenths of Hz during stable day and night periods, but can change up to half a Hz or more during twilight when ionospheric recombination (dusk) or excitation (dawn) is changing rapidly as the sun sets and rises over the path. These correspond to changes in the effective ionospheric height of a few tens of km.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NzNDp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NzNDp.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1157" LastEditorUserId="1157" LastEditDate="2020-01-22T00:28:54.300" LastActivityDate="2020-01-22T00:28:54.300" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="15999" PostTypeId="2" ParentId="15942" CreationDate="2020-01-21T20:04:32.593" Score="1" Body="&lt;p&gt;I recommend trying solder first, as suggested by a couple of other answers.  That should give you a good electrical connection as well as some mechanical strength.  If it doesn't go as well as you planned, put some foil HVAC tape over the joint.  You should have enough inductive coupling that you won't need to worry about the conductivity of the adhesive.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastActivityDate="2020-01-21T20:04:32.593" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16000" PostTypeId="2" ParentId="15979" CreationDate="2020-01-21T22:00:30.180" Score="2" Body="&lt;p&gt;There are several web sites, mobile phone apps, and printed books offering repeater lists.  The hearts of these sites, apps, and books are surely databases.  However, as @K7PEH says, collecting the information and making it easily available to the public costs time and money.  Every example of such a site, app, or book that I've seen is trying to make money from the information, if only from advertising.  I could be wrong, but I doubt that anybody would give away such a database for free, or keep it updated for free, at the present time.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-01-21T22:00:30.180" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16001" PostTypeId="2" ParentId="15979" CreationDate="2020-01-21T23:57:56.877" Score="2" Body="&lt;p&gt;There is a JSON formatted data base at:  &lt;a href=&quot;https://www.radioid.net/static/rptrs.json&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.radioid.net/static/rptrs.json&lt;/a&gt;&#xA;This database is accessible from the main page by clicking on 'Database', then 'Database Dump Files', so I assume it is intended for public viewing.  I don't know contents of these files or the license, but the Chirp software uses an old broken link for this repeater database.&lt;/p&gt;&#xA;" OwnerUserId="16297" LastActivityDate="2020-01-21T23:57:56.877" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16003" PostTypeId="2" ParentId="15979" CreationDate="2020-01-22T13:06:50.070" Score="1" Body="&lt;p&gt;I've been using RepeaterBook.  There's an app for Android or iOS, as well as a web site accessible with any modern browser.  The app is free, to download and to use, though both the app and the web site request donations.  Repeaterbook lists 10m, 6m, 2m, 1.25m, and 70cm repeaters in FM, DMR, and possibly other modes, and is searchable by band, call sign, or distance from a location.  It also includes notations for networked repeaters and those that support services like Echolink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;RepeaterBook is also an option for Chirp software to automatically obtain repeater lists, and I've used it that way as well (when programming my mobile for the repeaters along my usual route to a coastal vacation spot).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-01-22T13:06:50.070" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16004" PostTypeId="2" ParentId="15992" CreationDate="2020-01-22T19:24:48.103" Score="-2" Body="&lt;p&gt;AS A HAM FOR 59 YRS, 1. BYPASS THE INTERNAL &quot;TUNER&quot;, AND USE A MANUAL (MATCHBOX, TRANSMATCH, COUPLER ETC) BOTH THE BOX ON UR DESK AND / OR THE ONE BUILT INTO YOUR RIG ARE NOT, ARE NOT, ANTENNA TUNERS.&#xA;WHEN  YOU CUT A DIPOLE FOR 7.25 MHZ AT 64.55' YOU HAVE &quot;TUNED&quot; THAT ANTENNA. CHANGE YOUR FREQUENCY, YOU MUST CHANGE THE LENGTH OF YOUR DIPOLE. - THATS TUNING.&#xA;THE INTERNAL TUNERS OR BOXES WITH DIALS AND SWITCHES LABELED AS TUNER, ARE BOTH ANTENNA MATCHING DEVICES (TRANSMATCH OR MATCHBOX). THEIR JOB IS TO ACCOMODATE THE IMPEDANCE LOAD GIVEN TO YOUR TX BY THE ANTENNA (AND THIS IS IMPORTANT) &quot;SYSTEM&quot;.&#xA;REMEMBER MAXIMUM POWER TRANSFER OCCURS WHEN ZL = ZS.&#xA;PERSONALLY I USE ONE TRANSMATCH, AND ONE SWR BRIDGE&#xA;BOTH AT THE TX END. ONCE YOUR ANTENNA IS PROPERLY TUNED. - THE RADIATING ELEMENT IS RESONANT AT THE DESIRED FREQUENCY, CHANCES ARE SLIM YOU ARE GOING TO RAISE AND LOWER, ADD AND SUBTRACT LENGTH. YOUR GOING TO MATCH THE CHANGE IN IMPEDANCE TO YOUR RIG. '73 AND GL KF9F&lt;/p&gt;&#xA;" OwnerUserId="8492" LastActivityDate="2020-01-22T19:24:48.103" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16005" PostTypeId="2" ParentId="8963" CreationDate="2020-01-22T19:44:16.510" Score="-3" Body="&lt;p&gt;I use an SPC (series parallel capacitor) matchbox, or transmatch as designed by Lew McCoy W1ICP (SK).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're not tuning squat. You're matching the transmitter to the antenna system. - Feedline, traps, baluns - everything between TX out to antenna input. The antenna is or should be tuned, cut to frequency, resonant. So whats the problem simple change frequency - change the radiating element - make the dipole longer or shorter whether that dipole is a wire strung between trees or the one on your tribander. What to do? Put a transmatch on the feedline at the TX output and make Zs = Zl - or as close as you can. And don't worry theres no such thing as a 1 : 1 SWR, that would mean 100% efficiency. You are going to have to waste power in the form of heat (3412 BTU per kW) GI and '73 KF9F  &lt;/p&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="4665" LastEditDate="2020-01-22T20:57:53.657" LastActivityDate="2020-01-22T20:57:53.657" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16009" PostTypeId="2" ParentId="15996" CreationDate="2020-01-23T18:44:42.340" Score="1" Body="&lt;p&gt;If you're OK with an approximation, the solid angle can be calculated with much simpler math.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An isotropic antenna must radiate over a solid angle of 4π because it radiates in all directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna with a gain of (for example) 20 dBi has a gain of 100x, which means in the direction that gain is quoted, the power flux density must be 100x what it would have been for an isotropic antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we assume the antenna achieves its gain by an ideal beam which has some equal intensity within the beam, and no radiation outside the beam, then calculating the solid angle is a simple matter of division:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {4 \pi \over 100} = {0.04 \pi} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice a real antenna will have some sidelobes, meaning this method overestimates the beam solid angle. But also the quoted gain is at the peak, whereas the power flux density will on average be less than that, meaning this method underestimates the solid angle. A practical approach could call these errors a wash.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-01-23T20:18:16.333" LastActivityDate="2020-01-23T20:18:16.333" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16011" PostTypeId="1" AcceptedAnswerId="16014" CreationDate="2020-01-25T04:46:51.987" Score="4" ViewCount="142" Body="&lt;p&gt;Is there some simple utility, or published set of charts, or suite of formulae, where one can approach the situation by inputting a space weather summary, (sunspots, various indexes, etc), the receive frequency (band), half power beam width and gain of antenna, and arc distance from max gain main lobe vector to the sun disk (using the az el of the rotators), where the noise floor will rise enough to make signal detection unlikely, everything else being equal?  Yes, that might be too broad a brush.  Please educate my ignorance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Stated differently: If I am working a satellite or the ISS digipeater with a two meter beam or helical, and the sun is up, and the satellite (ISS) pass comes close to or even transits the sun disk, then at what arc distance to the sun (center?) will the sun  likely cause enough RFI to black out the attempted communication with the satellite (ISS), on two meter, 70 cm, 23 cm bands?  I understand it will depend on the main lobe of the antenna, and its half power beam width?  Let's use as an example, the average 3 element yagi maximized for gain, such that it gives about a 40 degree half power beam width... if those numbers are unrealistic, still, you get the idea of what I am looking for, yes?  I'd like an announced expectation of a sun causes comm black out.  It already says 'eye protection' when the antenna is pointed within 45 degrees arc distance of the sun.  Why?  When portable, or in power conserving situations, the rotator(s) might be strong-arm, aligning with a big plywood compass (az) rose on the ground, and an elevation scale, while looking somewhat along the antenna.  With az and el announcements every four seconds, strong-arm alignment should be plenty good enough.  People are making contacts with less accuracy than that, roadside, on youtube.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm thinking there must be some utilities already out there without my re-inventing the wheel, for the sun related noise floor increases.  Hopefully source code available, opensource, so I can write them into my python script(s), honoring any licensing terms and conditions of course.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My Antenna handbook is from 1988, and I figure there is a lot more data and experimentation since then, particularly in this context.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've got a python program using pyephem, that runs continuous, and gives periodic voice announcements of the status of upcoming passes and 'in progress' passes, grabbing TLE updates each day, internet connection dependent at least once per week.  It runs on a raspberry pi or an android device (since pyephem is easily installed on either of them).  I would like it to also give a caution regarding possible noise floor related black out(s) when the pass is closely aligned with the sun (risen of course).  For that, I need this additional RFI noise floor based on the sun/space-weather information, so it can be appropriately coded.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe the EME folks have already worked something like this out?  The geostationary commercial bird operators know when there is a higher probability for a blackout, briefly, twice per year, when the orbital position basically transits the sun for certain geographic regions.  I am looking to know if for the HAM sats, this would only happen if there is a literal transit, or if it develops into happening as the main lobe of the receive antenna gets within a certain threshold arc distance of the sun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Comments please if you need more clarification.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Update 2-23-2020:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have selected the post from tomnexus as the answer, but I wish to be clear.  Phil Frost - W8II 's post was just as valuable as the answer.  As is often the case here, there is not always a &lt;em&gt;best&lt;/em&gt; answer, but instead, several postings that form the more complete answer for which an OP was hoping.  Some of the comments and comment exchanges were also essential toward an &lt;em&gt;answer&lt;/em&gt; that would give me what I need to form a project decision.  If you can, imagine that both these posts have been selected as the answer.  If there are more posts that I miss later on, I trust they will be in some way helpful to someone with a similar question(s).  Thank you to all the contributors.&lt;/p&gt;&#xA;" OwnerUserId="15083" LastEditorUserId="15083" LastEditDate="2020-02-23T17:26:26.663" LastActivityDate="2020-02-23T17:26:26.663" Title="Working satellite on 2 meters, at what arc distance to sun (center) will noise floor be problematic to a disruption of a communication path?" Tags="&lt;antenna&gt;&lt;satellites&gt;&lt;noise&gt;&lt;solar&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16014" PostTypeId="2" ParentId="16011" CreationDate="2020-01-25T17:37:12.477" Score="2" Body="&lt;p&gt;It depends on the gain of your receive antenna, your system noise temperature, and how much link margin you had in the first place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The moonbounce (EME) community use Sun Noise as a measure of their system performance, so the sun is certainly detectable by a modest amateur station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A quick Google search for &quot;sun noise EME 144&quot; yields this interesting result from SM7SJR: &#xA;&lt;em&gt;2m noise measurement: 2 x 15 el LFA. Stacked vertically. LNA 0,36dB NF. Aimed at the sun: 5,3dB sun noise.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So with this fairly large station with a very good preamp, the noise floor rises 5 dB when pointed at the sun. Can your link budget afford this much additional noise?&lt;br&gt;&#xA;If you have no LNA or say one 5-element yagi (6 dB less gain, 10+ dB more system noise) then the sun will only contribute &amp;lt;&amp;lt;1 dB of noise, not enough to worry about. If you have both a small antenna and no fancy pre-amp then you definitely won't be able to detect sun noise. If you can hear the satellite at night, you'll be able to hear it in the day even as it transits the sun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For detailed, more general predictions, you can look up measurements of the solar flux at your frequency - it depends on the sunspot number. Then with the rest of the system parameters - gain (pattern), noise temperature - you can predict the rise in noise due to the sun in the beam. The sun  raises the system temperature depending simply on the pattern of the receive antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several EME system calculator programs which can predict sun noise for a particular system. The &lt;a href=&quot;https://www.google.com/search?q=eme+calculator+sun+noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;first many results for &quot;eme calculator sun noise&quot; look useful&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-01-27T18:38:11.763" LastActivityDate="2020-01-27T18:38:11.763" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16015" PostTypeId="1" AcceptedAnswerId="16016" CreationDate="2020-01-25T21:50:11.737" Score="1" ViewCount="161" Body="&lt;p&gt;How exactly is &lt;a href=&quot;http://gqrx.dk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;GQRX&lt;/a&gt; converting signal in any frequency to produce audio output?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it actually done by gqrx or some other element of the stack?&lt;/p&gt;&#xA;" OwnerUserId="16319" LastEditorUserId="8717" LastEditDate="2020-01-25T22:36:45.373" LastActivityDate="2020-01-25T23:57:49.707" Title="How is gqrx producing audio?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16016" PostTypeId="2" ParentId="16015" CreationDate="2020-01-25T23:45:19.343" Score="4" Body="&lt;p&gt;GQRX contains signal processing code, mostly executed in the shape of GNU Radio flow graphs, that convert the complex baseband representation of the RF signal that you get from your SDR device, to audio samples, which are then handed off to your operating system's sound system, which then hands them to the sound card, which converts them to analog, and speakers finally produce the audio output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, total flow:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Antenna picks of RF electric or magnetic field, converts to conducted wave&lt;/li&gt;&#xA;&lt;li&gt;SDR device takes said wave, amplifies, mixes, filters down to low IF or IQ baseband&lt;/li&gt;&#xA;&lt;li&gt;SDR device has an ADC (analog-to-digital converter) that converts the electrical signal to digital numbers, so-called samples&lt;/li&gt;&#xA;&lt;li&gt;If they aren't already, they're typically mixed down to complex baseband.&lt;/li&gt;&#xA;&lt;li&gt;The complex baseband samples are sent to your PC&lt;/li&gt;&#xA;&lt;li&gt;The operating system handles the data transfer between the SDR device hardware and its software driver&lt;/li&gt;&#xA;&lt;li&gt;The SDR device driver hands them off to gqrx (which under the hood uses GNU Radio to deal with the sample processing)&lt;/li&gt;&#xA;&lt;li&gt;gqrx mixes, filters and decimates the high-rate complex samples to select the channel you care about into a typically lower-rate string&lt;/li&gt;&#xA;&lt;li&gt;gqrx applies a demodulator algorithm to these, resulting in real-valued audio samples&lt;/li&gt;&#xA;&lt;li&gt;gqrx further processes the audio samples (filtering, de-emphasis, gain…)&lt;/li&gt;&#xA;&lt;li&gt;gqrx uses your operating system's audio system interface to hand these samples off&lt;/li&gt;&#xA;&lt;li&gt;that sound system might resample them to a sampling rate that works with the sound card, and/or add in other audio streams&lt;/li&gt;&#xA;&lt;li&gt;the sound system converts the audio samples into the format the sound card understands and makes sure that a new buffer of samples is present whenever the sound card is done with the last one&lt;/li&gt;&#xA;&lt;li&gt;the sound card takes the audio samples and converts them to analog domain&lt;/li&gt;&#xA;&lt;li&gt;the analog audio signal gets filtered and amplified&lt;/li&gt;&#xA;&lt;li&gt;the resulting audio-frequency analog voltage signal can be fed to a speaker&lt;/li&gt;&#xA;&lt;li&gt;the speaker converts the electrical signal to audible output&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Thus, I can't quite pinpoint where the &quot;conversion to audio output&quot; happens, specifically. I'd argue that strictly speaking it's in the speaker, but you probably mean &quot;conversion to some representation of the resultant audible signal&quot;, and that would probably be part of the GNU Radio flow graphs that gqrx sets up. If you mean &quot;where is the analog audio-frequency electrical signal produced&quot;, it's in the sound card.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-01-25T23:57:49.707" LastActivityDate="2020-01-25T23:57:49.707" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16018" PostTypeId="1" CreationDate="2020-01-26T14:10:18.023" Score="0" ViewCount="113" Body="&lt;p&gt;Is there a tool or some other way that would allow me to find out the type of modulation of a specific signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I specifically try to do is to decode signal from this remote control: &lt;a href=&quot;http://www.telran.co.il/images/980305%20QK-M04%20TECH%20SPECS.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.telran.co.il/images/980305%20QK-M04%20TECH%20SPECS.pdf&lt;/a&gt; mostly for learning purposes (later I probably will try to recreate it, to learn this way fundamentals of signal processing).&lt;/p&gt;&#xA;" OwnerUserId="16319" LastEditorUserId="4076" LastEditDate="2020-04-26T13:35:34.393" LastActivityDate="2020-04-26T13:35:34.393" Title="How to identify type of modulation from recording done by gqrx or gnu radio?" Tags="&lt;gnuradio&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16019" PostTypeId="1" CreationDate="2020-01-26T16:42:58.473" Score="2" ViewCount="660" Body="&lt;p&gt;I am making a Direct conversion receiver &lt;a href=&quot;https://www.qsl.net/pa2ohh/07swrx1.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;from this circuit at this website&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9YSAC.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9YSAC.gif&quot; alt=&quot;direct conversion receiver schematic&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I made it for the 80m band and I changed:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The frequency of VFO to about 1.75 MHz&lt;/li&gt;&#xA;&lt;li&gt;L1 and L2 to a bandpass filter for 80m&lt;/li&gt;&#xA;&lt;li&gt;and the VFO coil is not like the one in this circuit.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Everything works very well, but on some frequencies I hear loud AM broadcast stations. I think this is caused by harmonics from the VFO, but I am not sure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I get rid of this AM broadcast interference? Find out what frequency the AM broadcast is on, and try to filter it?&lt;/p&gt;&#xA;" OwnerUserId="16322" LastEditorUserId="8717" LastEditDate="2020-01-26T18:12:27.170" LastActivityDate="2020-02-01T16:15:42.967" Title="What causes my direct conversion 80m receiver to receive AM broadcasts?" Tags="&lt;receiver&gt;&lt;rfi&gt;&lt;equipment-troubleshooting&gt;&lt;direct-conversion&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16021" PostTypeId="2" ParentId="16019" CreationDate="2020-01-26T22:08:53.733" Score="4" Body="&lt;p&gt;It might be harmonics of the oscillator, as you suppose, but it also might be that any mixer doesn't only produce the difference frequency of its two inputs (&lt;span class=&quot;math-container&quot;&gt;$|f_\text{RF}-f_\text{local oscillator}|$&lt;/span&gt;, here), but also higher-order intermodulation products (like &lt;span class=&quot;math-container&quot;&gt;$|2f_\text{RF}-f_\text{LO}|$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$|f_\text{RF}-2f_\text{LO}|$&lt;/span&gt;).&#xA;&lt;br&gt;&#xA;I think I've posted multiple introductions to intermodulation product/mixing here, but the one I can find right now is &lt;a href=&quot;https://ham.stackexchange.com/a/15874/4076&quot;&gt;this&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Either way, since you can't change that your mixer somehow mixes a station outside your band of interest into your baseband or onto your IF, the only way to stop it is, as you proposed, to filter it out before it reaches the mixer stage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Luckily, that's a very sensible thing to do: Since you're designing your radio to use the second order intermodulation in your mixer, the &lt;em&gt;lowest&lt;/em&gt; frequency that gets mixed down is also the one that is of interest to you. So, low pass filter your signal!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That could happen at the output of your RF preamplifier¹, so, you could just add a series resistor followed by a capacitor to ground after the &quot;100&quot; capacitor (hope there's some document stating what the unit of &quot;100&quot; is). That'd form an &lt;a href=&quot;http://sim.okawa-denshi.jp/en/CRlowkeisan.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;RC low pass&lt;/a&gt;. However, that would limit the mixing performance of the two 1N4148 diodes², making a second preamplification state desirable – ugh, complexity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could also experiment with a capacitor in parallel to the 470 kΩ resistor between T1's base and collector (though that can lead to stability problems), or you very simply add a capacitor from base to ground. That's probably the stablest method of getting higher frequencies out of your input, but requires a bit of experimentation when it comes to figuring out the optimal capacitor value – it's  a bit hard for me to estimate the source impedance for the signal coming out of L2. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, reduce that 470 kΩ to maybe 100 kΩ from Base of T1 to ground, anyway – the 470 kΩ is there for the purpose of negative feedback making this thing more stable, but at these resistances and without a ground path, that's negligible. Use the 470 kΩ as second half of the voltage divider from base to ground. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, looking at that circuit: you can definitely improve the rejection of EMI by adding more stabilizing ceramic capacitors here and there; placing a 10 nF – 100 nF with short leads close to the top of the 4.7 kΩ of your preamplifier stage would swallow quite a bit of HF noise. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;¹: Sadly, the schematic doesn't label any of its passives, or most of its active components, that would make it much easier to talk about it, and also make it easier to understand what one is doing while building it – sigh, let's explain this nonetheless. Notice that &quot;label your components&quot; is really what EE students learn in their first lecture that actually deals with circuits in their first week of university. There's no good excuse not to label your components!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;²:  generally, interesting choice in this application: these are typically used as switching diodes, so you get a lot of your higher-order intermodulation products, because they are significantly nonlinear beyond a quadratic term. However, this is not subject of your post. If in doubt, try using a diode whose &quot;knee&quot; in the I/V curve is further out.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-01-26T22:08:53.733" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16023" PostTypeId="2" ParentId="16019" CreationDate="2020-01-26T23:11:38.740" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Everything works very well, but on some frequencies I hear loud AM broadcast stations. I think this is caused by harmonics from the VFO, but I am not sure.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What you're possibly hearing is intermodulation distortions created by your receiver from the mixer and amplifier. A local AM broadcasting station has high radiated power, making the problem even worse. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first trouble is when you apply a pure sine wave and a pure oscillator to a mixer. In an ideal mixer, when an RF input (e.g. an RF signal from the antenna), and a LO input (e.g. a VFO) are applied to a mixer, the sum and difference frequencies appears at its output.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$ f_\text{RF} \pm f_\text{LO} $&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;But in a real mixer, due to its nonlinearity, a wide range of frequency products appear at its output,&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$ m f_\text{RF} \pm n f_\text{LO} $&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Two RF signals, &lt;span class=&quot;math-container&quot;&gt;$ f_\text{RF1} $&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$ f_\text{RF2} $&lt;/span&gt; (e.g. signals from two radio stations) at different frequencies can create similar troubles. Due to the nonlinearity of amplifiers and mixers, they also create unwanted modulation between themselves. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$ m f_\text{RF1} \pm n f_\text{RF2} $&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In a receiver, the intermodulation from two RF input signals created by an amplifier can be modulated further by the local oscillator, creating even more unwanted frequencies. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$ c(a f_\text{RF1} \pm b f_\text{RF2}) \pm d f_\text{LO}$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;These higher-order intermodulation products always exist, but normally as the order goes up, their power decreases rapidly. The worst situation occurs when an amplifier or a mixer is overwhelmed by a powerful signal, these otherwise hard-to-see intermodulation products suddenly appear all over the spectrum. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following example is a two-tone test of a RF amplifier, showing how it will create significant intermodulation when the input signal power is excessive. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/C1l1G.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/C1l1G.png&quot; alt=&quot;An example of a two-tone test&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;Source: &lt;a href=&quot;https://en.wikipedia.org/wiki/File:Two_carrier_3rd_order_intermod_measurement.png#/media/File:Two_carrier_3rd_order_intermod_measurement.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikimedia Commons&lt;/a&gt;, by &lt;a href=&quot;https://commons.wikimedia.org/wiki/User:Ice_Ardor&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ice Ardor&lt;/a&gt;, License: CC BY-SA 4.0&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In amateur radio, powerful radio stations at different bands often create a lot of troubles. The three common culprits are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Local AM, Mediumwave radio stations&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Local FM, VHF radio stations&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Local/Remote AM, Shortwave Radio stations&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In general, all radio receivers are vulnerable to this problem, especially when a bandpass filter or preselector is not used. A ultra-wideband direct-conversion software defined radio, like a RTL-SDR, is the most vulnerable radio receiver. Severe interference from a &quot;blocker&quot; radio station it can make a radio receiver become utterly useless, you'll see radio stations everywhere, and nothing else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first step to solve the problem is making a bandpass filter for your band-of-interest to protect your receiver from being overloaded by unwanted out-of-band signals. You can make a bandpass filter for the 80-meter band, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But in this case, only the AM stations are creating the troubles, you can as well making a high-pass filter to remove all frequencies below 2 MHz, it's easier to make than a bandpass filter, as lower-Q inductors are acceptable. &lt;/p&gt;&#xA;" OwnerUserId="15589" LastEditorUserId="15589" LastEditDate="2020-01-26T23:17:28.423" LastActivityDate="2020-01-26T23:17:28.423" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16025" PostTypeId="2" ParentId="16018" CreationDate="2020-01-27T05:54:20.250" Score="1" Body="&lt;p&gt;Without looking at the specific device, I'll give a generic answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have the manual for the device, rarely it will tell you how it is modulated or what frequency it uses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The next place to check would be the FCC.  If the device is type accepted, it should have a FCC registration number, and you can look up technical documentation on FCC's website using that number.  This should at least give you a frequency and bandwidth, and usually a description of the modulation in broad strokes.  (Sometimes, in more detial.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, and possibly using the results from above (or maybe not, if you don't have or know about the device), there are several SDR software packages designed specifically to help with reverse engineering modulations.  These are described in the rtl-sdr.com blog and possibly in the software review section, as well as links to some tutorials and examples.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal identification wiki &lt;a href=&quot;https://www.sigidwiki.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.sigidwiki.com/&lt;/a&gt; may also help, with lots of examples of identified and unidentified signals.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-01-27T05:54:20.250" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16026" PostTypeId="2" ParentId="7817" CreationDate="2020-01-27T22:18:56.053" Score="4" Body="&lt;p&gt;You can experimentally 'ball park' the location of the focus, visually, several ways, by using sunlight.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One example -- some have temporarily attached (double-sided tape?) about a dozen one inch square mirrors in the dish, or reflective tape, from rim to center, and along say four radial lines from the center (if by the clock, at 12, 3, 6, 9 o'clock).  Then put a small white card where you think your antenna should be positioned, and aim the dish at the sun, and note where the bright square reflections (or two lines from the reflective tape) converge on the card as you shift the card around the imagined focus.  MacGyver probably would have used the reflective tape, and some gum, and a paper clip.  Also note what happens to those bright indicators as you correct your aiming at the sun.  The point is that there is a visual method available to you that can get you very close for the RF trials. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;a href=&quot;https://twitter.com/SP9UOB/status/1132567410777755648&quot; rel=&quot;nofollow noreferrer&quot;&gt;link from Twitter&lt;/a&gt; of someone using this method.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course &lt;a href=&quot;https://twitter.com/M0NWK/status/1136521119974998017&quot; rel=&quot;nofollow noreferrer&quot;&gt;the sun needs to be shining on the dish&lt;/a&gt; to do this.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;CAUTION!!&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When doing any sort of experiment that focuses light, particularly sunlight, the heating, or damage, or burning of body tissue or other materials, is possible!  Even a dozen one inch &lt;em&gt;ideal reflective&lt;/em&gt; square mirrors focused on one single square inch spot is now 12x the solar radiation of any sort of radiation that can be reflected by those mirrors, that would normally be on only one square inch!  Similarly, when testing or focusing or aligning any sort of RF link that uses a parabolic dish antenna, exercise proper RF safety practices, and do not allow anyone to be in front of a focused microwave (wifi) transmitting antenna system or open waveguide, particularly the head and eyes!  There are body parts that are naturally resonant to certain microwave frequencies and may suffer more damage due to that resonance, particularly in the head.  Experimenting with any sort of parabolic reflecting dish requires a functional knowledge of at least minimal safety considerations, for others as well as oneself, and property.  Understand the radiation frequencies and potential power levels involved!&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;If using reflective tape, be very careful to lay down the tape exactly on two 'diameters' that are 90 degrees to one another, and pass through the center of the dish.  If you are not sure if this is a prime focus dish, try some additional pieces of tape and experiment with the position of the card, until they all in some way intersect at one point, which is what a parabolic reflector is ultimately supposed to do. Two bright bars centered on your target focus point 'card' might not mean what you think it means.  Ultimately, the key to this is where the brightest portion of the reflected line(s) intersect on the card.  If it is a prime focus dish, then if you are careful to have the tape(s) pass through the center of the dish, the result will be more helpful, but again, what matters is where the brightest portions of the reflection lines intersect or converge, as crisply as possible.  (Remember, if you use wider tape, very reflective, and more pieces of it, you will be focusing that much more sunlight energy to the focus point, and it becomes damgerous as a burn hazard during your visual focusing efforts!  Mind the caution earlier in this posting!).  Think of the example of using a magnifying glass to focus the sun to a pinpoint, to burn a piece of dry wood.  One moves the glass closer and further away to find that focus distance where the &lt;em&gt;dot&lt;/em&gt; of the sun is smallest (and hottest).  If the glass is way too close or far, it may still show a big white spot &lt;em&gt;the size of the glass itself&lt;/em&gt;.  That is what the reflection lines alone are like, ie, they may not yet be focused on your target card, even though they may produce intersecting lines on the test focus card or surface, so you must move the card closer and farther away to get the intersection point strong, bright, minimal in its brighter 'size' compared to the rest of the lines that will appear.  If your dish is an offset dish, it is a little trickier.  Again, you don't just want to see all the lines from many pieces of tape 'intersecting'.  You also want to find the brightest intersection point by moving the card closer and then farther away. Let each of those extra pieces of tape be 'rim to rim', even if they don't span through the center of the dish.  If they project a curved line on your 'card', at least one point of the line should touch the other reflective tape produced lines on the card.  And again, the more tape strips you use, the more dangerous it may become if using sunlight.  A secondary benefit of this method, when done safely, is, it can be fun.  I'm pretty sure it will work on an offset dish.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mount your test focus 'card' on the same structure on which you intend to mount the antenna module, ideally one that is adjustable.  This will help your results be more stable (no jitters from shaking or shifting hands), and will let your hands be free to tweak the dish aiming at the sun.  Have fun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you find that best spot of strongest convergence on your card, and you find your dish's rim is not anywhere near perpendicular to the position of the sun, then you may indeed have an offset dish, instead of prime focus.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One might think that this could be done at night, more safely, with a bright spotlight instead of the sun.  If the dish is a prime focus dish, then the problem... can you guess... is that your focus card will be blocking much of the light source.  The sun, even though it appears almost like a point source of light in the sky, is many times larger than the earth, and your dish, which means that much solar radiation is coming into that tiny (relatively speaking) dish area, straight into it, beyond the edges of the focusing card.  Don't let the tiny dot of the sun in the sky skew your physics understanding.  Whereas with a bright flashlight, the rays of light from it are coming into the dish at an angle, at best &lt;em&gt;straight&lt;/em&gt; from the outer rim of the flashlight's outer edge of its own parabolic reflective.  So aligning the focal point with the light from a nearby flashlight, at night, or in a dark room, will not give the same results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your final adjusting should of course be done with the RF signal itself.  Be aware of, and respect the laws governing wifi antenna system output in your region, usually well thought out, by smart people, for good reasons.  If you are running a linux system, there are many ways to check your signal quality and strength with commandline based utilities.  Try an internet search, with your favorite search site, of this &lt;/p&gt;&#xA;&#xA;&lt;p&gt;terminal based wifi signal strength utility &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Something like this can give you a continuously updated overview:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;watch -n 1 cat /proc/net/wireless&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;That was taken &lt;a href=&quot;https://www.cyberciti.biz/tips/linux-find-out-wireless-network-speed-signal-strength.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;from this link&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are plenty of other links as well.  Of course, always be mindful of any security risks of your software sources, and the software itself. &#xA; I am not your source for a professional review of such security issues. &#xA; Personally, I &lt;a href=&quot;https://www.raspberrypi-spy.co.uk/2014/10/how-to-use-wavemon-to-monitor-your-wifi-connection/&quot; rel=&quot;nofollow noreferrer&quot;&gt;have used the wavemon utility&lt;/a&gt;, which you may likely need to install first, (it does what its name says) on any current raspberry pi system (Stretch or Buster on Pi2 through Pi4B).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Very important:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once you have found your focus visually, and RF'ally, remove the reflective tape, just in case you are coincidentally aiming at the sun one day.  Don't want to overheat your antenna module, whatever you finally decide that module to be.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, first test, in a very small area, maybe on the back of the dish, a weak solvent that is sufficient to remove any residue from the reflective tape, without removing the paint on the dish.  Maybe 70% iso propyl alchohol will be enough without removing paint, but I can't predict what is painted on your dish, or what solvent will be ideal.  Maybe the tape will peel off without leaving any residue at all, or, maybe it will peel the paint off.  What you don't want is a final result of a shiney aluminum 'light mirror', unless you want to cook hotdogs with it.  If you need to touchup some areas, maybe a light gray spray paint will do it, as long as it isn't formulated with the military's secret stealth RF absorbing materials, which would be, needless to say, counter productive, in perhaps more ways than one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Final:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am sure I have left out many details.  This wasn't intended to be a comprehensive wiki, but only a pointing out of another method, visual, to determine a dish's focus point.&lt;/p&gt;&#xA;" OwnerUserId="15083" LastEditorUserId="15083" LastEditDate="2020-02-01T03:43:16.160" LastActivityDate="2020-02-01T03:43:16.160" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16027" PostTypeId="2" ParentId="16011" CreationDate="2020-01-27T23:23:38.557" Score="2" Body="&lt;p&gt;The answer will depend on many factors. You've not given sufficient information to yield an answer, but the following concepts should help you arrive at your own answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly you must start with a link budget. The link budget determines how much power from the transmitter will arrive at the receiver. See &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;What is a link budget, and how do I make one?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ultimately it's not the power received that determines whether a signal is decodable or not, but rather the signal to noise ratio. So you will want to evaluate the noise performance of your receiver(s), see &lt;a href=&quot;https://ham.stackexchange.com/q/9832/218&quot;&gt;How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?&lt;/a&gt; Linked in that answer is &lt;a href=&quot;https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-13-201609-I!!PDF-E.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU-R P.372-13&lt;/a&gt; which will give you some estimation of the noise temperature of the sun, sky, and terrestrial noise in various conditions and frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll have to combine all these noise sources, weighted by the sensitivity of the antenna in every direction. That is, an extremely directional antenna will have a noise temperature nearly identical to just the thing it's pointed at, whereas a weakly directional antenna (like a 2 element Yagi) will pick up more noise from the sides, back, and other directions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally compare the estimated signal to noise ratio with the sensitivity of the mode you'll be using, and you should have some estimation of whether communication will work or won't.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-01-27T23:23:38.557" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16028" PostTypeId="1" AcceptedAnswerId="16035" CreationDate="2020-01-28T03:24:41.217" Score="3" ViewCount="285" Body="&lt;p&gt;What might be the advantages, if any, of HF SDR architectures that use a mixer between the ADC/DAC and RF, versus those that sample or generate RF directly (at 0 Hz on up) with a fast ADC or DAC?&lt;/p&gt;&#xA;&lt;p&gt;Are the advantages/disadvantages different depending on target use (QRP/SOTA vs. multi-operator contesting, etc.)?&lt;/p&gt;&#xA;&lt;p&gt;Both types of HF radios and rigs seem to be currently marketed, and/or offered as kits, and at least one vendor offers both as an (expensive?) add-on option.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-15T17:50:12.030" LastActivityDate="2021-03-15T17:50:12.030" Title="Advantages of IQ mixer versus direct sampling SDR architectures?" Tags="&lt;software-defined-radio&gt;&lt;receiver&gt;&lt;transceiver&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16029" PostTypeId="1" AcceptedAnswerId="16030" CreationDate="2020-01-28T09:19:48.187" Score="5" ViewCount="71" Body="&lt;p&gt;Do external signals affect the S11/SWR measurement of an antenna?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if I try measuring the S11/SWR of an HF antenna with a SWR meter or a Vector Network Analyzer in the middle of a field day with many transmitters near the antenna, or try measuring a 2.4 GHz dipole at a lab with many wireless access points, is it possible that the instrument sees a higher reflected power, thus giving me invalid S11/SWR results?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's a possibility, what can I do to reduce the measurement error? Shielding is often impractical for a large HF antenna. Is a SWR meter less vulnerable to this problem than a VNA due to its higher output power?&lt;/p&gt;&#xA;" OwnerUserId="15589" LastActivityDate="2020-01-28T14:09:59.447" Title="Do External Signals Affect Antenna S11/SWR Measurement?" Tags="&lt;antenna&gt;&lt;measurement&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16030" PostTypeId="2" ParentId="16029" CreationDate="2020-01-28T14:09:59.447" Score="4" Body="&lt;p&gt;Yes, in my experience antenna measurements on a VNA are affected by external transmissions. They look like &quot;noise&quot; on the graph.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Usually you can exclude them by eye - they're narrow and sharp while the antenna response is smooth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To make them smaller it helps to:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;increase the output power of the VNA&lt;/li&gt;&#xA;&lt;li&gt;reduce the measurement bandwidth&lt;/li&gt;&#xA;&lt;li&gt;turn on averaging. VNAs average coherently - i.e. the real and imaginary parts of the response are averaged separately. Because the interfering signal is almost certainly not coherent with the VNA, it averages to zero over some time.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A scalar measurement like an SWR meter will be worse affected, and there's no way to average it down, the effect will always be to increase the SWR. Worse, an SWR meter may have no preselector, so it might consider &lt;em&gt;all&lt;/em&gt; power coming in to be a reflection of its transmitted signal. In this case, for example, a single strong transmitter at 143.500 MHz could spoil the measurement of the whole 2 m band. A band-specific filter would help a lot in this case.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-01-28T14:09:59.447" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16031" PostTypeId="1" AcceptedAnswerId="16032" CreationDate="2020-01-28T15:25:46.017" Score="1" ViewCount="120" Body="&lt;p&gt;I want to take a non demodulate audio signal from webSDR portals (&lt;a href=&quot;http://www.websdr.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.websdr.org/&lt;/a&gt;). In order to try to feed these in DREAM DRM Radio software or GNURADIO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could be cool almost try it for educational purposes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A Youtube video very informational about I/Q could be see at:&#xA;&lt;a href=&quot;https://www.youtube.com/watch?v=h_7d-m1ehoY&amp;amp;t=150s&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=h_7d-m1ehoY&amp;amp;t=150s&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16333" LastEditorUserId="16333" LastEditDate="2020-01-28T18:39:14.900" LastActivityDate="2020-01-31T04:11:12.520" Title="Can I get non demodulate IQ signals from WebSDR" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16032" PostTypeId="2" ParentId="16031" CreationDate="2020-01-28T18:16:33.080" Score="2" Body="&lt;p&gt;Any radio in upper-sideband (USB) mode is effectively a frequency down-converter, WebSDR included. That is, USB simply shifts frequencies down, not changing the modulation other than the frequency shift. This is why digital modes such as PSK31, JT9, WSPR, etc can be implemented by an audio connection to an ordinary USB radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So simply tune in the frequency of interest in USB mode, and feed the resulting audio into GNU Radio. If you want it in IQ form you can use either the Hilbert transform block, or use &quot;float to complex&quot; and simply ignore or filter out all the negative frequencies, which will be a mirror of the positive frequencies.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-01-31T04:11:12.520" LastActivityDate="2020-01-31T04:11:12.520" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16033" PostTypeId="2" ParentId="16028" CreationDate="2020-01-28T18:34:18.400" Score="4" Body="&lt;p&gt;A direct-sampling SDR doesn't require a mixer, which can simplify the design. Also, provided the receiver has sufficient dynamic range and processing power, a direct-sampling receiver can monitor all the bands at once.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, a direct-sampling SDR must have an ADC and DAC at a sample rate above twice the maximum frequency. So for an SDR that covers all HF, the sampling rate must be at least 60 MHz, in practice more to provide some room for the filter roll-off.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;High-frequency ADCs are expensive. The resulting data is also computationally expensive to process, usually often an FPGA to do the initial digital filtering and decimation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In contrast, the addition of a mixer allows a much cheaper ADC and lower bandwidth digital stream: the ADC sample rate needs only to be wide enough to accommodate the widest bandwidth signal of interest. For amateur HF this is usually less than 4 kHz, within the capabilities of any audio interface and easily processed by any PC made in the last decade.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Theoretically the mixer adds distortion and eliminating it should could lead to better performance, but in practice designing a good mixer with modern components is neither difficult nor expensive. For example, the &lt;a href=&quot;http://fivedash.com/index.php?main_page=product_info&amp;amp;cPath=1&amp;amp;products_id=5&quot; rel=&quot;nofollow noreferrer&quot;&gt;SoftRock Lite II&lt;/a&gt; sells for $21 USD and includes anti-aliasing filters, a mixer, and a fixed-frequency oscillator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A mixer also allows for more flexible analog filtering options, which might be of some value in situations where the ADC lacks sufficient dynamic range due to a strong adjacent signal. In a direct sampling architecture you'll typically have a bank of &lt;em&gt;preselector&lt;/em&gt; filters which isolate a particular band with the objective of reducing the input power to the subsequent stages and thus the required dynamic range. However these filters will be fixed in frequency, and if you don't have the filter to isolate a strong interfering signal, you're just out of luck.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A mixing architecture will also have some fixed filters to eliminate mixing products, but then will have another filter at the IF, which is probably 0 Hz in most SDRs. This filter must at least be sufficient to avoid aliasing at the ADC, but the radio may offer a selection of filters of a few widths which will be selected according to the bandwidth of the signal of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a mixing architecture this filter can effectively be moved in frequency, and it's likely to be narrower than the preselector filters as well. This makes it more likely this filter can be used to exclude a nearby, strong interfering station which would otherwise overload the ADC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While this may be a useful capability in the right circumstance, it may not ever be useful unless your receiver is near another transmitter. Also keep in mind all the stages before this filter (so: the mixer, and any filters and buffers between it and the antenna) are still subject to the full power of the interfering signal, so any nonlinearities in these components will still be problematic. Very difficult interfering signals are best addressed, if possible, with a passive filter before any active components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I would say the most important practical differences come down to cost and maximum bandwidth. If you want to monitor 80 meters and 10 meters at the same time with the same radio, you'll need a direct sampling receiver. But it will cost more, on account of the high-speed ADC and FPGA.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're content monitoring less than 100 kHz of bandwidth at a time, then a cheap mixer-based SDR will be much more affordable. If it's of the variety that uses the computer's audio interface, then it's worth spending a little money on getting a good one since this is the main determinant in the receiver's performance, and the built-in audio interfaces in most computers are terrible.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-01-30T00:13:47.340" LastActivityDate="2020-01-30T00:13:47.340" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16034" PostTypeId="1" AcceptedAnswerId="16037" CreationDate="2020-01-28T21:17:22.300" Score="0" ViewCount="104" Body="&lt;p&gt;Looking to stack these 8 folded dipoles on my 100ft tower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can not find any information whatsoever on these. I have 4 consecutive serial numbered boxes.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Bluewave Marathon&lt;br&gt;&#xA;  BME139FN1H0&lt;br&gt;&#xA;  138 - 174 MHz&lt;br&gt;&#xA;  Gain  5.5dBd&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Looking for information on an appropriate phasing harness and spacing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gFD9t.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gFD9t.jpg&quot; alt=&quot;Photo of antenna in packaging&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16335" LastEditorUserId="76" LastEditDate="2020-01-29T02:38:05.413" LastActivityDate="2020-01-29T14:55:57.387" Title="How should I stack these folded dipoles?" Tags="&lt;vhf&gt;&lt;antenna-system&gt;&lt;dipole&gt;&lt;phased-array&gt;&lt;folded-dipole&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16035" PostTypeId="2" ParentId="16028" CreationDate="2020-01-29T06:26:06.450" Score="3" Body="&lt;p&gt;Direct conversion with lower distortion vs mixers with inexpensive ADC is only the first differentiation between the two methods.&lt;/p&gt;&#xA;&lt;p&gt;The original advantage of using a mixer is that you could vary the intermediate frequency used by the mixer to change the frequency of interest and have a fixed frequency output from the mixer to feed to second stage filters, amplifiers, and demodulators.  It is difficult and expensive to make filters that can change frequency, so this is a huge advantage.  SDR eliminates the need for fixed frequency demodulation, as it's all math, and can work equally well at any frequency the hardware supports.&lt;/p&gt;&#xA;&lt;p&gt;The remaining question is if it is still useful to have fixed frequency hardware filters on the output side of a mixer.  For a well isolated strong signal, these hardware filters are not better than what can easily be done in software.  However, if the signal of interest is either close in strength to the neighboring signals and noise, or if there is a strong signal near in frequency to a weak signal of interest, then hardware filters can significantly attenuate surrounding signals while passing through the weak signal of interest.  (This is called &amp;quot;sensitivity&amp;quot;.  I'm also glossing over details such as AGC, and multiple amplifier+filter+mixer stages.)&lt;/p&gt;&#xA;&lt;p&gt;How useful this is depends on the signal to noise ratio between these signals, and the sharpness of the analog filter vs. the dynamic range of the A/D converters in the SDR.  If the SDR has a wide dynamic range (which translates to bit depth of the samples on the software side), it can easily exceed the sharpness of a hardware filter, but maybe not the attenuation (in decibels).  For instance, a cheap 8 bit A/D converter has 48 decibels of dynamic range.  A good (but expensive) analog filter might have 60db of attenuation of noise, and a (large) cavity filter might have 120db of attenuation and isolation.&lt;/p&gt;&#xA;&lt;p&gt;Some high end radios made in the last 10 years take advantage of both good hardware filters and good SDR front ends (with more than 8 bits of depth) and get the best of both worlds.  However, in the last several years, the quality of good A/D converters has gone up and the cost gone down to the point where the dynamic range of SDRs and their software filters are starting to exceed the capability of small hardware filters so that the same manufacturers are discontinuing the hardware filters.&lt;/p&gt;&#xA;&lt;p&gt;We are currently in a transition period to a new mode of radio technology.&#xA;This is the third or fourth such transition since the inception of radio, converting parts of the radio from analog to digital while improving quality.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-03-13T13:33:44.423" LastActivityDate="2021-03-13T13:33:44.423" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16037" PostTypeId="2" ParentId="16034" CreationDate="2020-01-29T14:55:57.387" Score="2" Body="&lt;p&gt;The info is in the model number &lt;/p&gt;&#xA;&#xA;&lt;p&gt;BM - Bluewave Marathon&lt;br&gt;&#xA;E  - Exposed offset&lt;br&gt;&#xA;139- Frequency&lt;br&gt;&#xA;F  - Gain 5.5dBd&lt;br&gt;&#xA;N1 - Connector Type&lt;br&gt;&#xA;H  - Horizontal Polarized&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.scribd.com/document/31276153/Yagi-From-Pctel&quot; rel=&quot;nofollow noreferrer&quot;&gt;More info can be found here&lt;/a&gt; - Please note you may have to download the whole book for all info.&lt;/p&gt;&#xA;" OwnerUserId="15387" LastActivityDate="2020-01-29T14:55:57.387" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16038" PostTypeId="1" CreationDate="2020-01-29T18:53:33.837" Score="0" ViewCount="40" Body="&lt;p&gt;I'm about to axe the display on my radio in pursuit of cheapness.  However, I need to know, how do blind hams with older rigs tune to a station?&lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="4665" LastEditDate="2020-01-29T20:05:01.870" LastActivityDate="2020-01-29T20:05:01.870" Title="how do you tune blind?" Tags="&lt;transceiver&gt;&lt;disability&gt;" AnswerCount="0" CommentCount="4" ClosedDate="2020-01-29T21:32:48.077" ContentLicense="CC BY-SA 4.0" />
  <row Id="16039" PostTypeId="5" CreationDate="2020-01-29T20:13:19.910" Score="0" Body="" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-01-29T20:13:19.910" LastActivityDate="2020-01-29T20:13:19.910" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16040" PostTypeId="4" CreationDate="2020-01-29T20:13:19.910" Score="0" Body="Questions about amateur radio for operators with disabilities, especially how to adapt radios and other equipment to suit operators' capabilities." OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-01-29T20:13:19.910" LastActivityDate="2020-01-29T20:13:19.910" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16041" PostTypeId="1" CreationDate="2020-01-30T04:09:44.727" Score="4" ViewCount="126" Body="&lt;p&gt;I am an electrical engineer working on a product that needs a loopstick antenna.&lt;/p&gt;&#xA;&lt;p&gt;I had thought that AM radios were so commoditized that I'd be able to find an off-the-shelf vendor. However the closest thing I found was a recommendation in silicon labs AN602 app note for some shady Chinese company.&lt;/p&gt;&#xA;&lt;p&gt;Can anyone point me to a reliable supplier that I could purchase from in quantity? I have familiarity working with magnetics suppliers to build custom magnetics but was hoping to avoid that route.&lt;/p&gt;&#xA;" OwnerUserId="16344" LastEditorUserId="8717" LastEditDate="2020-07-16T05:04:41.460" LastActivityDate="2020-07-16T05:04:41.460" Title="Commercial Loopstick Antenna Manufacturers?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;receiver&gt;&lt;ferrite&gt;&lt;mf&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16042" PostTypeId="1" AcceptedAnswerId="16045" CreationDate="2020-01-30T19:14:37.587" Score="9" ViewCount="1054" Body="&lt;p&gt;I came across an &lt;a href=&quot;https://ham.stackexchange.com/a/1378/1362&quot;&gt;old answer&lt;/a&gt; on this site which makes the claim:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;It would take an act of Congress to change this [FCC Part 97] rule.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Is that correct? I was under the impression that United States Congress had delegated authority over civilian communications &lt;strong&gt;to&lt;/strong&gt; the FCC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Must Congress approve every change to &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/technologies-systems-and-innovation-division/rules-regulations-title-47&quot; rel=&quot;noreferrer&quot;&gt;Title 47&lt;/a&gt;, or does the FCC have the authority to determine those rules and regulations directly, as it sees fit (within its mandate)?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2020-01-30T23:04:29.443" LastActivityDate="2020-01-31T18:55:41.067" Title="Who enacts the FCC's rules and regulations?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16043" PostTypeId="2" ParentId="16042" CreationDate="2020-01-30T21:06:22.880" Score="6" Body="&lt;p&gt;Most of the time that I have heard or read that statement: &quot;It would take an act of Congress...&quot; it is usually referring to an impossible or very difficult act.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the answer is &quot;no&quot; it does not take an act of congress to affect rule making or rules change within the FCC.  Straight from the fcc.gov web site we have:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Most FCC rules are adopted by a process known as &quot;notice and comment&quot; rulemaking.  Under that process, the FCC gives the public notice that it is considering adopting or modifying rules on a particular subject and seeks the public's comment.  The Commission considers the comments in developing final rules.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;However, congress can also pass laws that affect the FCC and may also result in rule changes.  This usually happens when there is a subject or act that is in opposition to the politics and policies of the FCC or something that the FCC considers to be the responsibility of congress and not its own rulemaking facilities.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2020-01-30T21:06:22.880" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16045" PostTypeId="2" ParentId="16042" CreationDate="2020-01-31T02:32:28.323" Score="12" Body="&lt;p&gt;There are two different &quot;Title 47&quot;s in play here. &lt;a href=&quot;https://www.law.cornell.edu/uscode/text/47&quot; rel=&quot;noreferrer&quot;&gt;Title 47 of the US Code&lt;/a&gt;, as referred to by rclocher3, contains laws passed by Congress on the subject of telecommunications. Most interesting for our purposes is &lt;a href=&quot;https://www.law.cornell.edu/uscode/text/47/chapter-5/subchapter-I&quot; rel=&quot;noreferrer&quot;&gt;Chapter 5, Subchapter 1&lt;/a&gt; which establishes the FCC. It sets the compositon and appointment rules of the FCC, regulates how the FCC can spend money and how it can obtain revenue, and most importantly, in 47 USC 154(i), says that&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The Commission may perform any and all acts, make such rules and regulations, and issue such orders, not inconsistent with this chapter, as may be necessary in the execution of its functions.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Which basically incorporates any rules the FCC makes as part of the law, given that they are within the &lt;em&gt;purpose&lt;/em&gt; of the FCC as defined in the chapter preamble, and they don't conflict with the remainder of the law.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those rules are cataloged and collected in &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47&quot; rel=&quot;noreferrer&quot;&gt;Title 47 of the Code of Federal Regulations&lt;/a&gt;, which is what you linked to in your question. These are &lt;em&gt;not&lt;/em&gt; established by acts of Congress, they're &lt;em&gt;enabled&lt;/em&gt; by the act of congress that gives rulemaking power to the FCC. All of Part 97 is contained within 47 CFR. To change it, the FCC only needs to follow its &lt;em&gt;own&lt;/em&gt; rules about how regulations are made. So you're correct about how the delegation works, and with few exceptions, it doesn't take an act of Congress. However, Congress &lt;em&gt;can&lt;/em&gt; act by either passing a law mandating that the FCC takes a certain action, or by passing a law which directly overrides the FCC rules.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-01-31T18:55:41.067" LastActivityDate="2020-01-31T18:55:41.067" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16046" PostTypeId="1" AcceptedAnswerId="16085" CreationDate="2020-01-31T14:21:19.137" Score="1" ViewCount="157" Body="&lt;p&gt;I am transmitting a continuous wave and using one USRP B210 with the kitchen_sink tool in order to save the received samples from two RX channels (v.3.15.0)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I look into the received signal on both channels, it seems that the Gain factor is only being applied to one of the channels as shown below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9jqwO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9jqwO.png&quot; alt=&quot;Blue line is from channel 0 and orange line is from channel 1&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is the command that I am sending when executing kitchen_sink:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;./kitchen_sink --rx-freq=868000000 --rx-gain=76 --rate=1e6&#xA;  --rx-channels=0,1 --rx-ant=TX/RX --rx-file=data/_%1%_usrp.dat --clock=external --time=external --rx-start-delay=3 --rx-freq-delay=0.5&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;My UHD version is 3.15.0&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What could be causing the difference in the signal between the two channels?&lt;/p&gt;&#xA;" OwnerUserId="16350" LastActivityDate="2020-02-10T15:52:25.637" Title="Receiving different gain values on two RX channels on Ettus USRP B210" Tags="&lt;software-defined-radio&gt;&lt;usrp&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16047" PostTypeId="2" ParentId="15936" CreationDate="2020-02-01T01:46:55.770" Score="2" Body="&lt;p&gt;The basic idea is a high-pass filter to separate FM broadcast from Aircraft band. You need quite a wide passband, including aircraft, up to top of 2M ham band. So start with a 5-element high pass of the form:&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/NGnGW.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fNGnGW.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&#xA;&lt;br&gt;Then add some traps to take out more of the FM broadcast band, without impacting the passband. Somewhat Chebyshev-like. If you've got some tools like VNA, it can be hand-tweaked. I did the tweaking in LTSPICE, but probably gave up too soon:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Dvb6a.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Dvb6a.png&quot; alt=&quot;Chebyshev stopband&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/1p53o.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1p53o.png&quot; alt=&quot;voltage across R3 (output)&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11132" LastActivityDate="2020-02-01T01:46:55.770" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16048" PostTypeId="2" ParentId="16019" CreationDate="2020-02-01T15:49:05.957" Score="1" Body="&lt;p&gt;That's an oddball receiver, employing a so-called &lt;strong&gt;Polyakov mixer&lt;/strong&gt;. Its local oscillator is supposed to run at half the received frequency. For 80M, the local oscillator runs at about 1.8 MHz.&lt;br&gt;&#xA;The RF amplifier ahead of the mixer should be very linear...this one is biased weakly, and could easily distort when presented with strong input signals.&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This type mixer is &lt;em&gt;supposed to&lt;/em&gt; work well in this application. One can only guess at possible causes:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Local oscillator doesn't drive mixer with 50%/50% duty cycle&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Mixer input signals not balanced on +ve swing versus -ve swing.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Local oscillator feeds into audio amplifier, making it &lt;strong&gt;into a conventional mixer&lt;/strong&gt;.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;RF amplifier is distorting on strong signals.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;wrong local oscillator amplitude: you should not over-drive nor under-drive this mixer.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Balance for this mixer is key. Diodes should be matched, but more important: both local oscillator and RF amplifier input signals to this mixer must be symmetric on +ve swing and -ve swing.&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At these low RF frequencies, it is also important that the audio amplifier sees &lt;em&gt;audio input signals&lt;/em&gt;. A more aggressive filter that attenuates RF might be used between mixer and audio input.&lt;/p&gt;&#xA;" OwnerUserId="11132" LastEditorUserId="11132" LastEditDate="2020-02-01T16:15:42.967" LastActivityDate="2020-02-01T16:15:42.967" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16049" PostTypeId="2" ParentId="15830" CreationDate="2020-02-01T17:42:08.677" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;&quot;Does the fact that the reflected waves on the antenna are in phase&#xA;  with the applied signal result in zero reactance at the feed point, or&#xA;  does zero reactance happen for some other reason?&quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The short answer to your question is, &quot;Yes.&quot; It is helpful to think of the dipole antenna as an open-circuited two-wire transmission line whose conductors have been separated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Owing to reflections from the open end of a transmission line, its input impedance vs. frequency is zero when the line's electrical length is an odd multiple of &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{4}$&lt;/span&gt; at the operating frequency. For a lossless line that is &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{4}$&lt;/span&gt; at 10MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VTXIH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VTXIH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the two &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{4}$&lt;/span&gt; wires that comprise the transmission line are &quot;unzipped&quot; to form a &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{2}$&lt;/span&gt; dipole, its input impedance repeats in a similar way:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iEM0Z.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iEM0Z.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-02-01T17:42:08.677" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16050" PostTypeId="1" CreationDate="2020-02-01T20:24:27.657" Score="1" ViewCount="33" Body="&lt;p&gt;I am building a &quot;toy&quot; radio station as a teaching tool for high school students to work with. I intend to use a small (short-range) wireless FM microphone module as the transmitter. What is the legal limit for the transmitting power of an FM wireless mic that operates in the 88-108 MHz broadcast band?&lt;/p&gt;&#xA;" OwnerUserId="10598" LastEditorUserId="8717" LastEditDate="2020-02-01T20:33:23.063" LastActivityDate="2020-02-01T20:33:23.063" Title="power limit on wireless FM microphone transmitters" Tags="&lt;transmitter&gt;&lt;fm&gt;&lt;fcc&gt;&lt;microphone&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2020-02-01T21:03:33.860" ContentLicense="CC BY-SA 4.0" />
  <row Id="16051" PostTypeId="1" CreationDate="2020-02-02T00:26:49.240" Score="1" ViewCount="240" Body="&lt;p&gt;I'm new to SDR. Is it possible to transmit on more than one frequency, and if so what do I need?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;more on computer type network &#xA;side one for each 800, 2.4, 5, 60&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I get more than one SDR to work together?&#xA;trunking, handoff&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm dyslexic and dysgraphic&lt;/p&gt;&#xA;&#xA;&lt;p&gt;so my write not all and all ok not it sucks&lt;/p&gt;&#xA;" OwnerUserId="16356" LastEditorUserId="16356" LastEditDate="2020-02-03T16:47:11.353" LastActivityDate="2020-02-04T14:26:53.810" Title="SDR transmit on more than one frequency" Tags="&lt;software-defined-radio&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16052" PostTypeId="2" ParentId="16051" CreationDate="2020-02-02T12:24:06.717" Score="1" Body="&lt;p&gt;Since you are new to SDR (Software Defined Radio), I will assume that you're wondering why one can &lt;em&gt;receive&lt;/em&gt; more than one signal but &lt;em&gt;transmit&lt;/em&gt; only a single signal with off-the-shelf SDR units. Note that an &quot;SDR&quot; comprises the hardware, some companion software and the means for the software to operate on information supplied by the hardware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An SDR &lt;em&gt;receiver&lt;/em&gt; samples a band of frequencies and digitally demodulates those samples into a form that a human or machine can decode to recreate the original information. In general, the band of frequencies results from the mixing of band-limited signals from an antenna with a single oscillator, followed by a filter to restrict the frequency range of the resulting signals. High sample rates allow sampling of large bands of frequencies that comprise numerous signals. Faster digital processors - whether hardware, software, or a combination - may allow more than one of the signals in the sampled band of frequencies to be demodulated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An SDR &lt;em&gt;transmitter&lt;/em&gt; digitally modulates information onto a carrier generated by an oscillator. The modulated carrier signal will occupy a range of frequencies corresponding to the content of the source information and the way the carrier is modulated. An SDR transmitter may transmit on more than one frequency by appropriately combining multiple sources of information and modulating them onto the carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A simple and practical example is the two-tone test commonly used to characterize an SSB transmitter. Two audio frequencies are fed into the transmitter, which produces an RF signal comprising two carriers separated by the difference in frequency between the two audio tones. This is entirely equivalent to simultaneously transmitting two signals. One could encode different information sources into each of the two tones. Generalizing this process with appropriate software and adequately fast hardware, one could transmit an arbitrarily large number of signals at selected frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, as long as the transmitter is &quot;on&quot; for any of the information sources, the receiver on that frequency might have to be &quot;off&quot; to prevent destructive overload. This could seriously compromise the utility of such a system in a two-way communications application.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-02-02T12:24:06.717" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16053" PostTypeId="2" ParentId="16051" CreationDate="2020-02-02T16:07:15.753" Score="1" Body="&lt;p&gt;Yes it is possible to transmit on multiple frequencies with an SDR, assuming it can transmit, and those frequencies are all within the bandwith of the SDR's transmit bandwidth at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many SDR based modes do this, such as freedv (which uses multiple adjacent carriers with gaps between them) and js8call, ft8, etc., which use contiguous frequencies.  Technically, these are emitting a single signal with a particular bandwidth, but practically, these are using multiple frequencies at the same time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's nothing to prevent the frequencies in use to be separated widely.  However, you do have to realize that the transmit power will be spread over the frequencies, and legal requirements to filter spurious emissions still apply.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, it is possible to get more than one SDR to work together.&#xA;However, typically to make this work, the SDRs are all part of the same device and share an oscillator so they can be phase coherent.  Look for SDRs that support MIMO.  I know of two currently available.  I've also seen projects to modify SDR receivers to share oscillators.  Both the MIMO SDRs and the modification projects can be found at rtl-sdr.com&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-02-02T16:07:15.753" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16054" PostTypeId="2" ParentId="16051" CreationDate="2020-02-02T19:39:36.567" Score="2" Body="&lt;p&gt;Yes.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A direct conversion SDR (one with an ADC and DAC that covers the entire HF band, for instance) might be able to transmit not only on multiple frequencies, but with custom firmware/gateware, possibly on multiple bands at the same time.  But you might have to design a very unusual custom low-pass plus notch filter to make sure the harmonics of all the bands and frequencies used are properly suppressed to stay within legal limits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A non-custom IQ SDR transceiver (LimeSDR Mini, Hermes Lite 2, et.al.) can transmit on any number of frequencies that all fit under the bandwidth of the IQ data input, possibly an entire HF band, or CW segment thereof.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A non-custom sound card SDR transceiver can transmit on any number of frequencies that all fit under half the audio sample rate or audio bandwidth allowed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are lots of articles and web pages on wiring multiple RTL-SDRs together modified to share one clock for synchronous or diversity receive.  The TAPR/Hermes line of SDRs often have clock out/in ports for the same for transmit as well as receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or you can do non-synchronous simultaneous SDR QSOs just hooking up multiple SDRs to one console (PC, Raspberry Pi, et.al.). You need to check (spec, benchmark, etc.) to make sure the total bandwidth required (USB, network, memory, page-out to storage, FLOPS, GPU visualization, etc.) do not exceed the max stable load for the system.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-02-04T14:26:53.810" LastActivityDate="2020-02-04T14:26:53.810" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16055" PostTypeId="2" ParentId="14719" CreationDate="2020-02-03T12:36:41.073" Score="3" Body="&lt;p&gt;Developing this comment of W2ASC (above): &lt;em&gt;But, given the fact that radials are effective even when buried in a few inches of soil, my assumption was (and still is) that whatever difference exists between the two insulation types is - for all practical purposes - negligible. So, my question is probably a bit academic. I still believe my initial assumption was probably correct, I just don’t know how to do the math to confirm it. Can anyone confirm or refute?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is a comparison that might be useful, showing the effects of bare vs. insulated buried radials (other things equal).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Qq1w8.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Qq1w8.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-02-03T12:36:41.073" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16056" PostTypeId="1" CreationDate="2020-02-03T17:00:17.203" Score="0" ViewCount="142" Body="&lt;p&gt;Thanks to rclocher3 for helping edit more to English&lt;/p&gt;&#xA;&#xA;&lt;p&gt;why closed&#xA;so&#xA;my struggle to get thought to English&#xA;thank rclocher3&#xA;I round back too&#xA;best I put&#xA;in avuenue what I was asking&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;why closed&lt;/strong&gt;&#xA;i tryed&#xA;so&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SDR's are low power output, as I know it&lt;/p&gt;&#xA;&#xA;&lt;p&gt;can you control the watts out on an SDR&lt;/p&gt;&#xA;&#xA;&lt;p&gt;is if you like more output power&#xA;use an amplifier&lt;/p&gt;&#xA;&#xA;&lt;p&gt;as if you respect max power watt output to fcc band plan,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way I'm good in math not writing(dyslexia dysgraphia, that not excess, I do try to do better next time)&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;[sdr out put] watts * [amplifier gain]db = [to antenna]watts &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="16356" LastEditorUserId="16356" LastEditDate="2020-02-09T06:43:10.747" LastActivityDate="2020-02-09T06:43:10.747" Title="sdr as watts and amps" Tags="&lt;transmitter&gt;&lt;amplifier&gt;" AnswerCount="2" CommentCount="7" ClosedDate="2020-02-08T07:56:38.410" ContentLicense="CC BY-SA 4.0" />
  <row Id="16057" PostTypeId="1" AcceptedAnswerId="16060" CreationDate="2020-02-04T07:21:21.090" Score="4" ViewCount="212" Body="&lt;p&gt;Some time ago, when I just started with amateur radio, a few more experienced hams told me that an inverted-V works better in the forest than a ground plane, and that it has something to do with the orientation of liquids in the trunks of trees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since then I've read plenty of books on antennas and didn't find a single mention of anything like this. I wonder whether there was any research on the subject or maybe it's just another street legend?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="873" LastEditDate="2020-02-04T07:56:36.763" LastActivityDate="2020-02-04T11:48:32.610" Title="Is a ground plane antenna a poor choice to use in a forest?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16058" PostTypeId="2" ParentId="16056" CreationDate="2020-02-04T07:31:18.657" Score="3" Body="&lt;p&gt;You have forgotten that decibels are a way of expressing the difference of two things &lt;strong&gt;logarithmically&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;20dB is a gain of 100.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So with 1W in you get 100W out, and with 2W in you get 200W.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also remember that many commercial amplifiers talk a good talk about what gain they can provide, but they won't always walk the walk, if you see what I mean. That is to say that an amplifier sold as having a 20dB gain might only give 80W out for 1W in.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, since you are thinking in watts, make sure you don't overload the amplifier. Just because it says it gives a 20dB gain, you won't get 200W out for a 2W input if the amplifier itself is rated at 100W maximum output.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-02-04T07:31:18.657" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16059" PostTypeId="1" AcceptedAnswerId="16062" CreationDate="2020-02-04T11:30:37.947" Score="5" ViewCount="196" Body="&lt;p&gt;I would like to practice in CW on 2m/70cm bands when and if there will be a tropospheric or sporadic-E propagation. However I don't have mush space for the antenna. There is a possibility to install 3+5 el Uda-Yagi antenna on the balcony (the height is ~20 meters), which has 9.5 dBi gain on 2m and 11.15 dBi gain on 70cm in free space according to the manufacturer. Previously I successfully used this antenna to make SAT QSOs in FM. My QTH is Russia, Moscow, the balcony looks southwest (i.e. to Europe), the horizon is quite clear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming that I'm going to use 50W of power (e.g. Yaesu FT-991A), will the antenna be adequate for making CW QSOs? If not, what gain approximately is required? Would it help to use a 200W power amplifier on 2m?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-02-04T18:35:11.503" LastActivityDate="2021-02-08T11:00:38.877" Title="What gain and power are required for successful DX contacts on 2m/70cm bands in CW?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;cw&gt;&lt;2m-band&gt;&lt;70cm-band&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16060" PostTypeId="2" ParentId="16057" CreationDate="2020-02-04T11:48:32.610" Score="4" Body="&lt;p&gt;From my informal results based on the reception of medium-wave AM broadcast stations on a Tecsun PL-310 &quot;Ultralight&quot; receiver, the dBµ signal strengths displayed on the receiver were over 6 dB greater when the receiver was held at ~5' AGL next to the trunk of a large, isolated oak tree than when 10+ feet away from it.  In all test locations the physical orientation of the receive antenna was set to optimize vertical polarization, as is used by AM broadcast stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These results show that an antenna must be in the extreme near field of re-radiating trees in order for any significant amount of mutual coupling to exist between them.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-02-04T11:48:32.610" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16061" PostTypeId="1" CreationDate="2020-02-05T03:43:11.487" Score="0" ViewCount="101" Body="&lt;p&gt;I was wondering If I could use an Arduino to find the direction of a vehicle using radio. I want the Arduino to find the orientation of the radio/where the object is detected (North, South, East, West) and activate a bit of code. Based on the orientation and if there is an object it will run a bit of code. &lt;/p&gt;&#xA;" OwnerUserId="16375" LastEditorUserId="4076" LastEditDate="2020-02-05T21:10:44.743" LastActivityDate="2020-02-05T21:21:46.260" Title="Is there a way to find the direction of a vehicle using radio?" Tags="&lt;direction-finding&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16062" PostTypeId="2" ParentId="16059" CreationDate="2020-02-05T07:41:45.143" Score="4" Body="&lt;p&gt;I will talk about my experiences with 2m here - 70cm is similar, except (and anybody who knows better than me please correct me) there is no sporadic-E at all ever on 70cm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It all depends on conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I was living in the UK, I used to have a 9-element Yagi for 2m, and was into SSB DXing. I used 2.5W because that was all the power I had from my FT-290.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was in the south of England, and in winter when there were temperature inversions and tropospheric propagation I would easily work into GM, F, ON, PA, EI, GD, GJ, GU ...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I loved 2m SSB - the only problem is that the 2m band only gets sporadic-E extremely rarely during absolute solar maximum, and tropospheric propagation only happens in winter under exceptional circumstances. For anything else, you are waiting for meteor showers, or you are doing line-of-sight contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for the most part if you want to work DX on 2m, you would be waiting for winter and keeping your fingers crossed. We are currently at the absolute bottom of the solar cycle, with the new one having just started - so don't expect any sporadic E for another 5 years.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There was a recent extremely deep occurrence of tropospheric propagation, where a GM station was able to make an FT8 contact with a D4 station on 70cms - a new world record&lt;a href=&quot;https://ei7gl.blogspot.com/2019/12/excellent-end-of-year-tropo-opening.html&quot; rel=&quot;nofollow noreferrer&quot;&gt; [link here]&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-02-05T07:41:45.143" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16064" PostTypeId="2" ParentId="16061" CreationDate="2020-02-05T20:36:45.653" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I was wondering If I could use an Arduino to find the location of a vehicle using radio.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Radio&lt;/em&gt; is a pretty big topic, so yes, of course there are ways to use radio technologies to locate a vehicle. There are commercial solutions, but it could also be as simple as leaving a smartphone in the vehicle and using another phone to track it. Whether any of these make sense for your application is a different story, but here are some examples:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;GPS:&lt;/strong&gt; The Global Positioning System uses radio signals from an array of satellites to let receivers calculate their position. There are many GPS chips available that can interface with an Arduino, so if the goal is to know where the vehicle is while you're in it, that could work. It's also possible to connect an Arduino to a radio transmitter, so there are various ways that you could receive the location and then transmit it to receivers. One of those ways is...&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;APRS:&lt;/strong&gt; Automatic Packet Reporting System is a widely-used scheme for transmitting position and other information through a network of nodes so that it can be recovered by anyone interested. Take a look at &lt;a href=&quot;https://aprs.fi&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://aprs.fi&lt;/a&gt; for more information.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;RADAR:&lt;/strong&gt; The term &lt;em&gt;RADAR&lt;/em&gt; is an acronym for Radio Detection and Ranging -- you transmit a signal using radio waves, and then listen for any reflected signals. The orientation of the receiver and the delay between transmission and reception tell you the direction and distance of the thing that reflected the signal. You'll probably want something more capable than an Arduino for this application, but perhaps you could make it work for a very limited problem.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;radio beacon:&lt;/strong&gt; A simple transmitter that emits a periodic signal can be tracked by several receivers, and the position determined by triangulation.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm sure there are lots of other approaches as well. Your requirements aren't very clear, and without knowing more it's hard to point you in one direction. Here are some things you'll need to consider:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Do you want to track the vehicle's position inside the vehicle, or from some remote spot?&lt;/li&gt;&#xA;&lt;li&gt;Do you have an amateur radio license?&lt;/li&gt;&#xA;&lt;li&gt;Do you want to track the vehicle in an urban, suburban, or rural setting?&lt;/li&gt;&#xA;&lt;li&gt;Do you have access to the vehicle, and if so can you install tracking hardware in it?&lt;/li&gt;&#xA;&lt;li&gt;What's your budget?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="11226" LastActivityDate="2020-02-05T20:36:45.653" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16065" PostTypeId="2" ParentId="16061" CreationDate="2020-02-05T21:21:46.260" Score="1" Body="&lt;p&gt;You have two different use cases. Position reporting and direction finding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Position reporting would be using something like APRS, Automatic packet reporting system. While APRS can transmit different types of data, it is most often used to report positions. A vehicle with a APRS radio will periodically send it position. with a receiver you can get the data.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see real time APRS data at web sites like &lt;a href=&quot;https://www.aprsdirect.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.aprsdirect.com/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With direction finding you use directional antennas to find the bearing to transmitter. Some antennas such as Yagis have lobes with higher gains in certain directions. You rotate the antenna until the signal is the strongest. Other antennas have a sharp null in one direction. You rotate the antenna until you lose the signal. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;if you need a location instead of a direction, then you will have to get bearings from two different locations.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For more information on directional antennas do a search on &quot;fox hunting&quot; a popular radio competition. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-02-05T21:21:46.260" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16066" PostTypeId="2" ParentId="13036" CreationDate="2020-02-05T22:00:17.157" Score="1" Body="&lt;p&gt;&lt;a href=&quot;http://www.oscilent.com/catalog/Category/ceramic_filter.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Oscilent in Nevada&lt;/a&gt; stocks a number of these.&lt;/p&gt;&#xA;" OwnerUserId="9575" LastEditorUserId="8717" LastEditDate="2020-02-05T22:50:38.150" LastActivityDate="2020-02-05T22:50:38.150" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16068" PostTypeId="1" CreationDate="2020-02-06T03:56:28.227" Score="3" ViewCount="135" Body="&lt;p&gt;I am currently using a Baofeng BF-F9V2+ radio. I have found the when listening, my squelch won't stay open, despite getting a good clean signal. I am using a homemade verticle dipole antenna for 2-meter band. Compared to the rubber duck, it gets excellent reception signal, except for this unreliable squelch problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have also found that when I turn the squelch off, I get a continuous signal, so I do not believe that it is a problem with my antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there variables that could cause something like this other than an issue with the radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks,&#xA;Addison&lt;/p&gt;&#xA;" OwnerUserId="16018" LastEditorUserId="873" LastEditDate="2020-02-06T07:19:34.990" LastActivityDate="2021-02-01T04:45:55.910" Title="Squelch won't stay open on FM 2 meter band" Tags="&lt;antenna&gt;&lt;baofeng&gt;&lt;2m-band&gt;&lt;squelch&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16069" PostTypeId="2" ParentId="16068" CreationDate="2020-02-06T18:55:26.050" Score="3" Body="&lt;p&gt;I can think of two possible issues, but both of them are &quot;something to do with the radio&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first is that something in the signal you're listening to is tweaking the &lt;a href=&quot;https://ham.stackexchange.com/questions/3771/how-does-the-baofeng-radio-eliminate-squelch-tail&quot;&gt;Baofeng squelch tail eliminator&lt;/a&gt;. The answer to that question describes menu options that can stop a radio from &lt;em&gt;transmitting&lt;/em&gt; the STE tones, but my understanding is that there is no way at all to stop the receiver from muting when it &lt;em&gt;hears&lt;/em&gt; the tones. If the signal you're listening to contains content at those frequencies, your radio might decide to drop squelch intermittently.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The second possibility is the well-known susceptibility of Baofeng front-ends to overload, prompted by your mention of an external antenna. Working against this is the fact that you say everything is fine with squelch disabled, but it's still possible that some other strong signal is interfering with the squelch tracking, without causing audible distortion. If your reception gets &lt;em&gt;better&lt;/em&gt; with the stock rubber-duck antenna fitted, then overload is a likely culprit.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-02-06T18:55:26.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16070" PostTypeId="1" AcceptedAnswerId="16091" CreationDate="2020-02-07T07:45:05.147" Score="1" ViewCount="311" Body="&lt;p&gt;I have purchased a high quality ZS6BKW from the U.K. I have it suspended up about 40' between 2 trees. There is 30' of coax from the ladder line to the radio (Kenwood TS-870).SWR on the MFJ269 shows below 1.5 from 80m all the way up to 10m. SWR on the radio shows below 1.5 too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I cannot hear anything on any band. Nothing whatsoever. On 40m I get some voice VERY faint on 7.070.00 and 7.095.00. As far as I have read on google I can use any length of coax from the ladder line (which is a specific length) to the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ideas?&lt;/p&gt;&#xA;" OwnerUserId="5784" LastActivityDate="2020-02-12T20:54:33.340" Title="ZS6BKW deaf on all bands except 40" Tags="&lt;antenna&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16071" PostTypeId="1" AcceptedAnswerId="16072" CreationDate="2020-02-07T08:48:51.047" Score="3" ViewCount="889" Body="&lt;p&gt;I would like to communicate with someone 1000 miles (1600 km) away. I'm not sure how to target a specific distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SjwMV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SjwMV.jpg&quot; alt=&quot;skipdistance&quot;&gt;&lt;/a&gt;&#xA;&lt;sub&gt;(&lt;a href=&quot;https://www.eeeguide.com/sky-wave-propagation/&quot; rel=&quot;nofollow noreferrer&quot;&gt;image source&lt;/a&gt;)&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume it's an interrelation of the following factors:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Which frequency I'm using&lt;/li&gt;&#xA;&lt;li&gt;Which ionospheric layer I'm reflecting from (and its height)&lt;/li&gt;&#xA;&lt;li&gt;The launch angle of the antenna&lt;/li&gt;&#xA;&lt;li&gt;The maximum usable frequency for these conditions&lt;/li&gt;&#xA;&lt;li&gt;More stuff I don't know about yet&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;This distance is too far for groundwave or &lt;a href=&quot;https://en.wikipedia.org/wiki/Near_vertical_incidence_skywave&quot; rel=&quot;nofollow noreferrer&quot;&gt;NVIS&lt;/a&gt;, but it seems awfully close for skywave communications.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How do you figure all of this out? Can you estimate where the skip zone (dead zone between skips) is? And can you change the effective skip zone distance by selecting an different band?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specifically, I'm trying to reach from Portland, Oregon to Phoenix, Arizona (USA). Thank you for any insight you can give me.&lt;/p&gt;&#xA;" OwnerUserId="16390" LastEditorUserId="16390" LastEditDate="2020-02-07T09:01:51.663" LastActivityDate="2020-02-19T16:36:08.863" Title="How to determine frequency and launch angle given a target skip distance?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16072" PostTypeId="2" ParentId="16071" CreationDate="2020-02-07T10:28:03.067" Score="6" Body="&lt;p&gt;The actual math here is annoying enough that you will hardly ever want to use it (it requires knowing the incidence angle of the signal on the ionosphere, which is dependent on the height of the F-layer and the distance between the stations &lt;em&gt;taking into account the curvature of the Earth&lt;/em&gt;). &lt;a href=&quot;https://link.springer.com/book/10.1007/978-3-642-38430-1&quot; rel=&quot;nofollow noreferrer&quot;&gt;Zolesi and Cander&lt;/a&gt; gives the formula for incidence angle as &lt;span class=&quot;math-container&quot;&gt;$\varphi_0 = \arctan \frac{\sin\frac{\theta}{2}}{1+\frac{h'}{R}-\cos\frac{\theta}{2}}$&lt;/span&gt;, where &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt; is the angular distance between the two points on the surface of the Earth, &lt;span class=&quot;math-container&quot;&gt;$h'$&lt;/span&gt; is the virtual height of the F-layer, and &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; is the radius of the Earth. Then the formula &lt;span class=&quot;math-container&quot;&gt;$MUF(D) = f_0 \sec \varphi_0 $&lt;/span&gt; can be used to figure out the path MUF given the critical frequency at the midpoint of the path.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But that's pretty hard, so let's fudge it. First off, let's assume that &lt;span class=&quot;math-container&quot;&gt;$h' = 300 \,\mathrm{km}$&lt;/span&gt;, which is pretty reasonable, especially in the daytime. Then we can precompute some values of MUF(D) for different distances.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;D (km) | MUF(D) / foF2 | MUF(D) / MUF(3000)&#xA;0      | 1             | 0.305&#xA;500    | 1.29          | 0.394&#xA;1000   | 1.85          | 0.565&#xA;1500   | 2.39          | 0.729&#xA;2000   | 2.81          | 0.858&#xA;2500   | 3.10          | 0.947&#xA;3000   | 3.28          | 1&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;So for a 1500km path, if you have a map of foF2, then your MUF should be around 2.4 times the foF2 at the midpoint of the path. If you have a map of MUF(3000), then your MUF should be around 73% of the MUF(3000) at the midpoint of the path. If you want to remember this as &quot;MUF(1500) is about three-quarters of MUF(3000)&quot;, that would be perfectly acceptable. This is good enough that you could probably work 20 meters in mid-afternoon even under solar minimum conditions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;skip zone&quot; is simply the areas which are too far away for line-of-sight or groundwave, but close enough that the effective MUF at that distance is lower than the chosen frequency. As such, it's completely dependent on the frequency you're using. For frequencies less than the &quot;critical frequency&quot; (foF2), there is no skip zone (these are the NVIS frequencies). As the frequency increases beyond the MUF for longer and longer distances, the skip zone grows, until no propagation is possible. Because the Earth is curved, the incidence angle can't be arbitrarily low — even a signal that leaves the Earth completely horizontal is going to reach the ionosphere at an angle of 15-20°, after travelling 1500 - 2000 km. For this reason, the longest possible single hop between points on the Earth is around 3000 - 4000 km in distance, and that's why we use MUF(3000) as a practical upper limit for skywave frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for choosing a launch angle, very few people have any practical ability to fine tune their launch angle. If anything, they might be able to choose between a &quot;DX antenna&quot; which favors low-angle radiation over high-angle, or a &quot;NVIS antenna&quot; which favors high-angle over low-angle. A 1500km hop involves a launch angle in the neighborhood of 20° above the horizon, which is much more on the &quot;DX&quot; end of things.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-02-19T16:36:08.863" LastActivityDate="2020-02-19T16:36:08.863" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16073" PostTypeId="2" ParentId="16071" CreationDate="2020-02-07T10:46:36.550" Score="6" Body="&lt;p&gt;As an alternative to figuring all of this stuff by hand, you can use a tool like ITURHFPROP which does the math for you, based on statistical models of what the MUF and other variables will be for a given sunspot number, time of year, time of day, and location. I've chosen &lt;a href=&quot;http://www.predtest.uk/p2p.html&quot; rel=&quot;noreferrer&quot;&gt;predtest.uk&lt;/a&gt; because it allows me to direct-link to results. After setting the TX location to Portland, the RX location to Phoenix, both antennas to &quot;Dipole&quot;, power to 100W, and mode to SSB, the &lt;a href=&quot;http://www.predtest.uk/p2p.html?month=2&amp;amp;year=2020&amp;amp;txLat=45.4245&amp;amp;txLng=-122.6648&amp;amp;rxLat=33.3722&amp;amp;rxLng=-112.0444&amp;amp;txPower=-10&amp;amp;modulation=ANALOG&amp;amp;path=SHORTPATH&amp;amp;noise=RURAL&amp;amp;rxgos=0&amp;amp;txgos=0&amp;amp;bw=3000&amp;amp;snrr=24&quot; rel=&quot;noreferrer&quot;&gt;output&lt;/a&gt; should look something like &lt;a href=&quot;https://i.stack.imgur.com/lDPh7.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lDPh7.png&quot; alt=&quot;graph of usable frequencies vs time&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which shows the performance of different frequencies vs. UTC hour, for the month of February 2020. It indicates that your &lt;em&gt;best&lt;/em&gt; prop is likely to be on 40 meters around sunrise, but also that 20 meters should work well from the morning until the late afternoon, 40 meters should be acceptable (if not great) at any time of day, and 80 meters may be usable at night.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-02-07T10:46:36.550" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16074" PostTypeId="2" ParentId="16056" CreationDate="2020-02-07T20:00:51.927" Score="1" Body="&lt;p&gt;I know you want watts, and in this case since you are adding just one stage (the amplifier) it is a little bit annoying that the amplifier's gain is in decibels. The reason for that is because when you have a lot of things to add, for example…&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;SDR + amplifier - coax loss + antenna gain = &lt;a href=&quot;https://en.wikipedia.org/wiki/Effective_radiated_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;Effective radiated power&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;…then decibels becomes very handy. The trick I use is to start with my power (watts) in decibels too!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Think of a plain decibel &lt;code&gt;dB&lt;/code&gt; unit like an increase/decrease &lt;em&gt;ratio&lt;/em&gt;. But there are also &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Decibel&amp;amp;oldid=938548507#Suffixes_and_reference_values&quot; rel=&quot;nofollow noreferrer&quot;&gt;decibel-with-reference&lt;/a&gt; units, like &lt;code&gt;dBm&lt;/code&gt; (power relative to a milliwatt) and &lt;code&gt;dBuV&lt;/code&gt; (voltage relative to a microvolt).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can think of numbers with these &quot;reference decibels&quot; as &lt;em&gt;absolute values&lt;/em&gt; — e.g. &lt;code&gt;0 dBm&lt;/code&gt; is the same as &lt;code&gt;1 milliwatt&lt;/code&gt;. That's because it's the reference &lt;strong&gt;m&lt;/strong&gt;illiwatt (the &lt;code&gt;…m&lt;/code&gt; part) with no increase or decrease (the &lt;code&gt;0 dB…&lt;/code&gt; part).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's say your SDR is 0.1W. That is &lt;code&gt;20 dBm&lt;/code&gt;, because 100 mW (0.1W) is a 20 dB increase from the &lt;code&gt;…m&lt;/code&gt; reference unit of 1 mW. I made myself a little &quot;dBm ↔︎ watts converter&quot; that's available here &lt;a href=&quot;https://utils.ipcalf.com/#dbm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://utils.ipcalf.com/#dbm&lt;/a&gt; and you can type in your actual SDR watt in the right hand (watts) box and the dBM will show up in the left box.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll continue with a 100 mW transmitter for example, into an amplifier that has 35 dB gain for example. You can replace with your actual numbers. We know 100 mW is the same as 20 dBm. So now we can do your math:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;SDR output (20 dBm) + amplifier gain (35 dB) = to antenna (55 dBm)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;So you get &lt;code&gt;55 dBm&lt;/code&gt; to the antenna. But the FCC safety limits and some band restrictions are given in watts on most charts. So we don't want &lt;code&gt;dBm&lt;/code&gt; but &lt;code&gt;W&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I put that back into the left box (dBm) of my calculator and it shows &lt;code&gt;316.2277660168379&lt;/code&gt; on the watts side. So our example SDR plus example amplifier together output about 316 watts total!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or to get Effective Radiated Power, we keep it in dBm for a little longer:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;20 dBm (SDR) + 35 dB (amplifier) - 5 dB (coax loss) + 3 dB (antenna gain) = 53 dBm (ERP)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Converting to watts again, &lt;code&gt;53 dBm&lt;/code&gt; is approximately &lt;code&gt;200 W&lt;/code&gt; (199.5…). But it was very handy to add in more steps while it was still in decibels. You can even add more &lt;code&gt;dB&lt;/code&gt; things, like your &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Path_loss&amp;amp;oldid=936914768#Prediction&quot; rel=&quot;nofollow noreferrer&quot;&gt;predicted path loss&lt;/a&gt; and a &lt;strong&gt;receiver&lt;/strong&gt; antenna gain to &lt;a href=&quot;https://en.wikipedia.org/wiki/Link_budget&quot; rel=&quot;nofollow noreferrer&quot;&gt;predict whether communication is possible&lt;/a&gt;…&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2020-02-07T20:28:06.570" LastActivityDate="2020-02-07T20:28:06.570" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16075" PostTypeId="1" CreationDate="2020-02-08T10:06:49.017" Score="5" ViewCount="614" Body="&lt;p&gt;I would like to build a simple HF, VHF or UHF circulator to get a better understanding of how these devices work. Sadly at the moment I'm unaware of any articles or books that provide corresponding schematics and description. Could you please recommend a good source on the subject or maybe share a schematic?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-02-08T10:43:34.440" LastActivityDate="2021-01-01T16:22:50.573" Title="Looking for a schematic of a DIY circulator" Tags="&lt;filter&gt;&lt;duplexer&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16076" PostTypeId="2" ParentId="16075" CreationDate="2020-02-08T11:35:32.187" Score="6" Body="&lt;p&gt;Puh! That's a big one you're planning: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most circulators are &lt;em&gt;passive, magnetic material circulators&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These circulators are basically a three-port resonant cavity in a cylindric shape, where the cavity is filled with ferr&lt;em&gt;i&lt;/em&gt;magnetic material, typically special ferrite disks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The electromagnetic properties of magnetized ferrite are used to break up the geometric symmetry – now energy flows more in one direction (say, counterclockwise) than in the other (cw).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, the magnetic properties of the circulator material become pretty crucial for it to work at all; it sounds like a bit of a daunting task to build one from scratch, but since you're not afraid to do so: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pozar's &lt;em&gt;Microwave Engineering&lt;/em&gt; has a short section on magnetic circulators (section 9.6 in the third edition); it's rather advanced. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;corresponding schematics &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Not being a component that is representable in electronics, but only in field/wave propagation terms, there's no electric schematic that you could find.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a drawing of how a stripline Y-junction circulator might be built, from a book titled &lt;a href=&quot;https://books.google.de/books?id=tgFlBGfSpHcC&amp;amp;lpg=PA179&amp;amp;ots=SUiVEM3Go7&amp;amp;dq=Yoshida%3A%20The%20X%20Circulator&amp;amp;pg=PA174#v=onepage&amp;amp;q&amp;amp;f=false&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Ferrites at Microwave Frequencies&lt;/em&gt;&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/h7u1f.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/h7u1f.png&quot; alt=&quot;y-junction circulator&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll notice that circulators are inherently frequency-selective due to their cavity nature. So, you'll need the tools to build a well-defined cavity for your frequencies of interest, access to the raw ferrimagnetic discs, the ability to fix, shift them very finely, and potentially to rework them without them losing ferrimagnetism.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you put all this into a case that holds the elements into place and ensures all the dimensions, you end up with something like &lt;a href=&quot;https://mcli.com/documents/MC-90.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;source pdf&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/I08to.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/I08to.png&quot; alt=&quot;circulator package drawing&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-02-08T19:13:33.080" LastActivityDate="2020-02-08T19:13:33.080" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16077" PostTypeId="2" ParentId="16075" CreationDate="2020-02-09T00:31:59.400" Score="5" Body="&lt;p&gt;A &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Circulator&quot; rel=&quot;nofollow noreferrer&quot;&gt;circulator&lt;/a&gt; can probably be constructed from coaxial cable. However, you will also need ferrite and magnets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From &lt;a href=&quot;https://wa8dbw.ifip.com/Circulator.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wa8dbw.ifip.com/Circulator.html&lt;/a&gt; :&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A circulator is best thought of as a &quot;Magic Box&quot; containing three transmission lines spaced 120 degrees apart. These transmission lines are placed between two disks of ferrite material. On the other side of the ferrite is a non-ferrous ground plane and then a magnet followed by a ferrous pole piece that shields the unit from external magnetic fields.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Usually on circulators designed for the VHF/UHF (50 - 512 MHz) frequencies will have a means of tuning each transmission line so that insertion loss and isolation can be optimized at the desired center frequency range.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;From &lt;a href=&quot;http://www.e-meca.com/rf-microwave-blog/isolator-circulator-basics&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.e-meca.com/rf-microwave-blog/isolator-circulator-basics&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;An RF circulator is a three-port ferromagnetic passive device used to control the direction of signal flow in a circuit and is a very effective, low-cost alternative to expensive cavity duplexers in base station and in-building mesh networks. Examples of both applications will be covered later in this article.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;To understand how these components control the signal flow, think of a cup of water into which you place a spoon and stir in a clockwise motion. If you sprinkle some pepper into the cup and continue to stir, you will notice that the pepper easily follows the circular motion of the water. You can also see that it would be impossible for the pepper to move in a counterclockwise direction because the water motion is just too strong. The interaction of the magnetic field to the ferrite material inside isolators and circulators creates magnetic fields similar to the water flow in the cup. The rotary field is very strong and will cause any RF/microwave signals in the frequency band of interest at one port to follow the magnetic flow to the adjacent port and not in the opposite direction.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VPZua.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VPZua.jpg&quot; alt=&quot;Isolator and circulator&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Description of &lt;em&gt;circulator&lt;/em&gt;&lt;/strong&gt;, from &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Circulator&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia article&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A circulator is a passive, non-reciprocal three- or four-port device, in which a microwave or radio-frequency signal entering any port is transmitted to the next port in rotation (only). &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;&lt;a href=&quot;https://ieeexplore.ieee.org/document/1444937&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here's a &lt;strong&gt;circulator using transmission lines&lt;/strong&gt;&lt;/a&gt;. Per Marcus Müller:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;... It's really nice, kind of a circular bucket-brigade device made of &quot;signal storage&quot; delay lines. That's an elegant active way to build a circulator.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;This &lt;a href=&quot;https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Low_Frequency_Active_Isolator-Circulator-Wenzel.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;circulator schematic&lt;/strong&gt; from VA3IUL&lt;/a&gt; uses CLC406 op-amps and covers DC to 100 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UTJGC.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UTJGC.gif&quot; alt=&quot;Circulator schematic from VA3IUL&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Found at the &lt;a href=&quot;https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Homebrew_RF_Circuit_Design_Ideas.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;YO3DAC VA3IUL Homebrew RF Circuit Design Ideas website&lt;/a&gt;.&#xA;&lt;hr&gt;&#xA;&lt;a href=&quot;https://www.nature.com/articles/nphys3134&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here's a circulator using &lt;strong&gt;no magnets&lt;/strong&gt; based on parametrically-modulated coupled-resonator loops&lt;/a&gt; behind a $9 paywall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found that by Googling &lt;code&gt;homemade rf circulator -vector&lt;/code&gt;. There are information and construction articles and even a video there. (I did not follow many of those links in the Google search results.)&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-02-10T15:42:23.367" LastActivityDate="2020-02-10T15:42:23.367" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16078" PostTypeId="1" CreationDate="2020-02-09T11:44:28.027" Score="-3" ViewCount="50" Body="&lt;p&gt;Some SDR transmitters have a very low power output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can their output be adjusted? &lt;/p&gt;&#xA;" OwnerUserId="16356" LastEditorUserId="8717" LastEditDate="2020-02-09T18:07:29.637" LastActivityDate="2020-02-09T20:30:57.630" Title="Can the power output of a software defined radio be adjusted?" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="2" ClosedDate="2020-02-10T19:17:23.240" ContentLicense="CC BY-SA 4.0" />
  <row Id="16079" PostTypeId="2" ParentId="16078" CreationDate="2020-02-09T20:22:15.733" Score="1" Body="&lt;p&gt;All radio transmitters can adjust power within some limits, that's how they modulate the information they are sending.  Most solid state radios start with a very low power output modulation stage which then goes to one or more amplifier stages.  SDR is not different.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case of an SDR, it converts voltage on the antenna to an integer value from the A/D converter when receiving, or converts the integer value to an analog voltage in the D/A converter when transmitting.  Technically, this adjusts power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want more power, you need an amplifier, which could be in the device or external to the device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any more specific answer would require a device model to see what its maximum power output is and if it has an amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Theoretically, you can have any transmitter transmit at any power, through either of attenuators or amplifiers.  Asking if a non-specific transmitter power can be adjusted is not really a very good question. &lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-02-09T20:30:57.630" LastActivityDate="2020-02-09T20:30:57.630" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16080" PostTypeId="5" CreationDate="2020-02-09T22:51:26.577" Score="0" Body="&lt;p&gt;A &lt;strong&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/7183/what-is-a-panadapter&quot;&gt;panadapter&lt;/a&gt;, &lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_spectrum_scope&quot; rel=&quot;nofollow noreferrer&quot;&gt;spectrum scope&lt;/a&gt;, or band scope,&lt;/strong&gt; is a device used with, or built into, a radio receiver, which displays the amount of RF power received across a range of frequencies, for the purpose of observing finding signals to receive (or to avoid when transmitting).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Panadapters generally work by processing the downconverted intermediate-frequency signal from a &lt;a href=&quot;https://en.wikipedia.org/wiki/Superheterodyne_receiver&quot; rel=&quot;nofollow noreferrer&quot;&gt;superheterodyne receiver&lt;/a&gt; (or IQ baseband from a &lt;a href=&quot;https://en.wikipedia.org/wiki/Direct-conversion_receiver&quot; rel=&quot;nofollow noreferrer&quot;&gt;direct conversion&lt;/a&gt; receiver); an added output for a panadapter is sometimes known as an “IF tap”.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two common visual representations of the data, often presented together:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;A line chart, in which frequency is on the horizontal axis and logarithmic (dB) RF power is on the vertical axis.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A &lt;strong&gt;waterfall display&lt;/strong&gt;, or &lt;a href=&quot;https://en.wikipedia.org/wiki/Spectrogram&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;spectrogram&lt;/strong&gt;&lt;/a&gt;, which displays power as brightness (or color) instead of position and uses the vertical axis for time, displaying the presence of signals over a short time period. It usually moves downward (present time at the top, history below), hence the name “waterfall”, and may be accompanied by a line chart using the same frequency scale.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A &lt;a href=&quot;/questions/tagged/spectrum-analyzer&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;spectrum-analyzer&amp;#39;&quot; rel=&quot;tag&quot;&gt;spectrum-analyzer&lt;/a&gt; is RF test equipment whose primary function is to display the spectrum in the same way, but is &lt;em&gt;calibrated&lt;/em&gt; (displaying accurate absolute power level), and may have additional features for measuring or demodulating signals, but is not primarily intended as a receiver.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-02-14T01:19:32.370" LastActivityDate="2020-02-14T01:19:32.370" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16081" PostTypeId="4" CreationDate="2020-02-09T22:51:26.577" Score="0" Body="Questions about panadapters, waterfall displays, band scopes, or any other equipment that displays a plot of RF power vs. frequency. For test equipment, use the specific tag [spectrum-analyzer]." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-02-15T16:50:23.440" LastActivityDate="2020-02-15T16:50:23.440" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16082" PostTypeId="2" ParentId="7183" CreationDate="2020-02-10T02:06:31.163" Score="2" Body="&lt;p&gt;Is a panadapter hardware or software?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use a hardware spectrum analyzer and a scope, it's hardware.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the panadapter is based on an SDR, then it requires both the SDR hardware and software.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The difference between a waterfall and a panadapter is that the waterfall shows the spectrum analysis of a range of frequencies over time, which may include just the 3-4KHz audio pass band of the receiver, where the panadapter usually shows at least 12KHz, and more likely at least 1-5MHz (all of one or more bands).  Also, the panadapter might only show the instantaneous spectrum analysis, or it could show a wide band waterfall. &lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-02-10T02:06:31.163" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16083" PostTypeId="2" ParentId="15948" CreationDate="2020-02-10T02:16:27.727" Score="1" Body="&lt;p&gt;I use a 10m moxon, which when vertically polarized is about 6ft wide.&#xA;It's probably 80% the height of a similar yagi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you use Cebik's model, it should have gain similar to a 3 element yagi, and at least 7dbd gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can control the bandwidth by picking the correct diameter elements.&#xA;For instance, you could use the outer shield of coax or copper pipe and get some pretty good bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anything smaller will probably need loading coils, and might not have the gain you want.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-02-10T02:16:27.727" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16085" PostTypeId="2" ParentId="16046" CreationDate="2020-02-10T15:52:25.637" Score="1" Body="&lt;p&gt;The difference was caused by the splitter I was using to send the signal to both channels. &lt;/p&gt;&#xA;" OwnerUserId="16350" LastActivityDate="2020-02-10T15:52:25.637" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16086" PostTypeId="1" CreationDate="2020-02-10T17:33:31.717" Score="2" ViewCount="133" Body="&lt;p&gt;I have been a ham for almost 20 years, and when on CW I have always sent my call, name, RST, and full QTH.  I have noticed that now many operators send NR 5280 or something similar instead of their QTH.  What does this number represent?  I know for sure it is not a Grid Square.&lt;/p&gt;&#xA;" OwnerUserId="16406" LastEditorUserId="76" LastEditDate="2020-02-10T18:36:20.093" LastActivityDate="2020-02-11T16:03:42.577" Title="What is NR and a number instead of city and state after my QTH?" Tags="&lt;cw&gt;&lt;procedure&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16087" PostTypeId="2" ParentId="16086" CreationDate="2020-02-10T21:33:29.463" Score="4" Body="&lt;p&gt;I found a reasonable-looking answer here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://forums.qrz.com/index.php?threads/qso-party-question.156343/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://forums.qrz.com/index.php?threads/qso-party-question.156343/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As @Mike Waters said, it's probably the sequence number for a contest, i.e. the number of contest stations they've worked.&lt;/p&gt;&#xA;" OwnerUserId="16387" LastActivityDate="2020-02-10T21:33:29.463" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16088" PostTypeId="2" ParentId="16086" CreationDate="2020-02-11T16:03:42.577" Score="2" Body="&lt;p&gt;&quot;NR&quot; has double meaning in CW - its both &quot;near&quot; and &quot;number&quot;. 5280 in your example is most likely a number in a contest. Also it might be a club number, e.g. SKCC NR 123, depending on a context.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-02-11T16:03:42.577" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16089" PostTypeId="1" AcceptedAnswerId="16090" CreationDate="2020-02-11T18:42:21.670" Score="0" ViewCount="298" Body="&lt;p&gt;Currently I'm trying to make my radios (Baofeng UV-82 and Baofeng DM-860) friends with my Windows 7 and Chirp. My computer has only USB ports and no COM; Google adviced the Profilic driver (PL2303/PL23**) could help, but still no progress. Baofeng UV-82 LCD keeps blinking (blue and orange), being connected to the computer (and would not stop until the cable is put off), and no PnP sound is heard as well; Baofeng DM-860 (or DM-1801 - these two are just different names of the one model, as I can judge), surprisingly works (with their official app), but only allows reading from the radio, and the app crashes on trying to write to it. What can I do to get the stuff working? I have never had any drivers issues before, the USB ports all work properly for 'simple' devices (like mice, keyboards, flash drives).&lt;/p&gt;&#xA;" OwnerUserId="16411" LastActivityDate="2020-02-11T19:32:53.647" Title="Baofeng UV-82 and DM-860 drivers Windows 7" Tags="&lt;baofeng&gt;&lt;chirp&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16090" PostTypeId="2" ParentId="16089" CreationDate="2020-02-11T19:32:53.647" Score="2" Body="&lt;p&gt;You don't mention what programming cable that you're using.  The programming cable has a very important job: it interacts with the OS as a USB device, and acts as a &quot;virtual serial port&quot;, which means that the radio talks to the chip in the cable using a serial communications protocol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is that many inexpensive programming cables contain a USB-to-serial chip that's a close copy (a clone really) of a chip made by Prolific, so much so that Windows identifies them as Prolific chips. Windows Update will try to download the latest Prolific driver for the clone chips. Unfortunately for unsuspecting owners, Prolific responded to the flood of cloned chips by changing their driver to only work with genuine Prolific chips, so if you have the latest driver, a programming cable based on a cloned chip won't work. There is a work-around described &lt;a href=&quot;http://www.miklor.com/COM/UV_Drivers.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;, which involves disabling automatic hardware driver updates, uninstalling any driver that's already installed, and then manually installing an old driver version.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But before you do anything drastic with drivers, go to the Windows Device Manager, by pressing the Windows key on your keyboard and then typing &quot;device manager&quot; and hitting &lt;code&gt;&amp;lt;Enter&amp;gt;&lt;/code&gt;.  All the devices that the OS can see in the computer or connected to it are listed there.  If you unplug your cable, that &quot;device&quot; in the list will disappear, and if you plug the cable back in, then the device will reappear in the Device Manager list.  Find the device that way, and see how the Device Manager describes it.  If it's an &quot;unknown device&quot;, then Windows doesn't even know what it is.  If there's a problem with the driver then there is usually an exclamation point symbol next to the device, and right-clicking the device and then clicking &quot;Properties&quot; will usually give some explanation of the problem.  If the Device Manager thinks that the device is fine, but the Properties dialog mentions &quot;Prolific&quot; somewhere, then you &lt;em&gt;might&lt;/em&gt; have one of the programming cables with the clone chip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you could be doing something wrong in the software.  I've successfully used the Baofeng software in the past, but I much prefer &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP&lt;/a&gt;, because it's well thought out and it works for just about any radio that can be programmed with a computer.  So you might want to try CHIRP, which has a mailing list with people who can help with problems.  There is documentation; here's the &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Beginners_Guide&quot; rel=&quot;nofollow noreferrer&quot;&gt;Beginners' Guide&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-02-11T19:32:53.647" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16091" PostTypeId="2" ParentId="16070" CreationDate="2020-02-12T19:17:42.850" Score="4" Body="&lt;p&gt;I have a homemade ZS6BKW antenna so I might be able to provide some insight, even though I've only used it for a few weeks now. I get good reception on 40m and 20m with it (when conditions are favorable), and have not spent much time on the other bands. No tuner except for the built-in one on the IC-7300. With it in a less-than-ideal inverted V formation, and with my QTH laying between mountains in Colorado, USA, I've still reached Antarctica and Australia on WSPR, and around North America on FT8 and SSB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first thing that makes me think something is wrong is that you're seeing a 1.5:1 SWR on 80m. The ZS6BKW is not an 80m antenna without a tuner. Mine shows 5.5:1, and the &quot;standard&quot; design should be north of 4:1 unless you've got some relay-controlled stuff going on. I think you're seeing some kind of fake resonance (akin to a dummy load), unless perhaps your feedline is resonant which is also not good. You also should see very, very high (&gt; 5:1) SWR on 60, 30, and 15m. If you're seeing low SWR on those bands, I guarantee you something is wrong with the antenna or your feedline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would recommend picking up a NanoVNA and adapters or some other antenna analyzer. You should see clear dips below 3:1 for 40, 20, 17, and 12m, with part of 10 and 6m bands covered, and a slight dip for 80m that would require a tuner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do see the proper dips in SWR, and you've tested your feedline, then I would try doing something like WSPR and see who reports you on the other bands, or trying to reach a friend at an agreed upon time and frequency, or tune in to a nearby WebSDR to listen for yourself. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it helps, here is what the NanoVNA shows as SWR for my ZS6BKW antenna, as measured at the feedpoint, when I was in the process of trimming it (it was a little long here for 20m). Notice the 80m dip on the far left edge of the chart is about 6:1 (each horizontal line is about 1 SWR with the bottom edge being 1:1).&#xA;&lt;a href=&quot;https://i.stack.imgur.com/modWg.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/modWg.jpg&quot; alt=&quot;ZS6BKW NanoVNA&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Edit:&lt;/strong&gt; I missed from your question that the MFJ-269 is an antenna analyzer, I assumed it was some kind of inline SWR meter in the shack. I would confirm with it that you have high SWR at the feedpoint on 80/60/30/15, and that you do not have a short (low-Z). I think it might be possible that a short at the end of the ladder line where it meets the dipole legs might result in a false low SWR reading, but someone with more experience with antenna modeling might be able to confirm or deny that.&lt;/p&gt;&#xA;" OwnerUserId="15973" LastEditorUserId="15973" LastEditDate="2020-02-12T20:54:33.340" LastActivityDate="2020-02-12T20:54:33.340" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16092" PostTypeId="2" ParentId="15948" CreationDate="2020-02-13T00:31:21.067" Score="0" Body="&lt;p&gt;Look into “Hentenna antenna”.&#xA;Also there is an approximately half size version with a bit less gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like the Moxon, the Hentenna is composed of two superimposed resonances when perfectly tuned. A sight detuning of either type antenna broadens the bandwidth.&lt;/p&gt;&#xA;" OwnerUserId="8229" LastActivityDate="2020-02-13T00:31:21.067" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16093" PostTypeId="1" AcceptedAnswerId="16094" CreationDate="2020-02-13T01:02:38.040" Score="2" ViewCount="415" Body="&lt;p&gt;I have a BTech UV-25x2 that I'm using as a portable base station. This radio has a &quot;TRRS&quot; connection (GND/SP/MIC/PTT) which I would like to get a headset for. I'm relatively new to ham radio, so don't know if there is standardization on connectors or the like, but in my searches online so far, I've not been able to figure out what might work with this transceiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm fine with it being just for audio out and needing to use the hand-held mic for talking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What are some recommended headsets to look at that will work with this radio? Alternatively, how can I tell if a headset is compatible with this radio?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sbrcH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sbrcH.png&quot; alt=&quot; picture of the plug that fits the PTT/mic/audio out jack on the back of the UV-25X2&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16373" LastEditorUserId="4665" LastEditDate="2020-02-13T14:57:31.040" LastActivityDate="2021-01-15T04:45:42.790" Title="Looking for headset to use with BTech UV-25x2" Tags="&lt;equipment&gt;&lt;audio-interface&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16094" PostTypeId="2" ParentId="16093" CreationDate="2020-02-13T15:27:04.050" Score="3" Body="&lt;p&gt;There are standard connectors for microphones, speakers, and headsets, but unfortunately the pinout diagram (schematic) changes very frequently.  There is no guarantee that a headset with a 3.5mm TRRS plug that works with one radio will work with a radio from a different manufacturer, or even a different model radio of the same manufacturer.  &lt;a href=&quot;https://www.qsl.net/g4wpw/date.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;G4WPW's site&lt;/a&gt; tries to keep up with microphone connectors; have a look at it and you'll see the scope of the problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;BTech has made things more complicated by defining yet another &quot;standard&quot;; even their brother company Baofeng seems to use a different pinout for the UV-3R PLUS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, nobody seems to make a headset with a plug and pinout to match the UV-25X2, not even BTech, probably because not many people expect to plug headsets into mobile or base VHF/UHF rigs.  People will likely want to use that same jack for APRS though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most speakers with a 3.5 mm plug (I assume that's a 3.5 mm jack) have the speaker connection on the tip, where the UV-25X2 has the PTT connection, so most commercially-available speakers won't work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to find a headset or speaker to work with your radio, you'll need to verify that the pinout diagram is correct by comparing its specifications to the pinout diagram from your manual.  (Don't just take somebody's word for it from an internet review.)  If there is no commercially-made speaker or headset that has the correct connector and pinout, then you have two remaining options: rewire the headset's or speaker's plug to work, or create some sort of adapter.  If I had your problem I'd probably try to make a &quot;pigtail&quot; by connecting a 3.5 mm TRRS jack, wired for your chosen speaker or headset, to a 3.5 mm plug wired for your UV-25X2.  Plugs and jacks that you can wire yourself with a soldering iron are available from several vendors, such as Jameco, Mouser, Digi-Key, and Newark.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-02-13T15:27:04.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16095" PostTypeId="5" CreationDate="2020-02-14T01:11:13.193" Score="0" Body="&lt;p&gt;A &lt;a href=&quot;https://en.wikipedia.org/wiki/Spectrum_analyzer&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;spectrum analyzer&lt;/strong&gt;&lt;/a&gt; is RF test equipment which displays the amount of RF power versus frequency received on its input ports. Spectrum analyzers may operate on the principle of automatically sweeping a receiver across the desired display range of frequencies, or by performing a &lt;a href=&quot;https://en.wikipedia.org/wiki/Discrete_Fourier_transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;discrete Fourier transform&lt;/a&gt; on the entire bandwidth to be visualized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &lt;strong&gt;tracking generator&lt;/strong&gt; is a component of a spectrum analyzer which produces a swept signal in sync with the frequency the spectrum analyzer is currently receiving; this is one method to test the frequency response of filters and other RF components.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;See also &lt;a href=&quot;/questions/tagged/panadapter-and-waterfall&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;panadapter-and-waterfall&amp;#39;&quot; rel=&quot;tag&quot;&gt;panadapter-and-waterfall&lt;/a&gt; for the similar but often less precise instruments incorporated into radio receivers to find and view signals.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-02-14T01:11:13.193" LastActivityDate="2020-02-14T01:11:13.193" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16096" PostTypeId="4" CreationDate="2020-02-14T01:11:13.193" Score="0" Body="Questions about the use and theory of spectrum analyzers. For spectrum displays that are not test equipment, use [panadapter-and-waterfall] instead." OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-02-14T01:11:13.193" LastActivityDate="2020-02-14T01:11:13.193" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16097" PostTypeId="1" AcceptedAnswerId="16099" CreationDate="2020-02-14T02:17:47.963" Score="5" ViewCount="152" Body="&lt;p&gt;What is a QSL card?  Why would I ever receive one?  Why would I ever bother to send one?  If so, when?  Is it rude not to?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are they postcards sent by physical postal mail, or are they now digital thingys?  &lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="5222" LastEditDate="2020-02-14T18:55:49.947" LastActivityDate="2020-03-14T12:27:39.513" Title="What is a QSL card?" Tags="&lt;jargon&gt;&lt;qsl-card&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16098" PostTypeId="1" AcceptedAnswerId="16101" CreationDate="2020-02-14T18:23:29.583" Score="4" ViewCount="577" Body="&lt;p&gt;My radio manual says its current draw is 22A.  But in my naivety I would have calculated as follows:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the radio 'put out' 100W and I have a 13.8V supply then (using the formula power = VxI) 100W/13.8V = 7.2A.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, it looks that I'm way out (comparing 22A with 7.2A).  Is my transceiver terribly inefficient or is this normal?&lt;/p&gt;&#xA;" OwnerUserId="13777" LastEditorUserId="4076" LastEditDate="2020-02-14T20:33:51.820" LastActivityDate="2020-03-14T11:48:09.900" Title="Calculation of transceiver current draw" Tags="&lt;power-supply&gt;&lt;efficiency&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16099" PostTypeId="2" ParentId="16097" CreationDate="2020-02-14T18:33:49.980" Score="6" Body="&lt;p&gt;A QSL card is a physical card usually the size of a postcard. They are sent to verify a contact known as a QSL. To get various awards like Worked All States or DXCC (worked 100 entities) you need to verfiy the contacts. The main way this used to be done was to take the QSL cards you had received to a &quot;card checker&quot; who would verify them.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The card should have your information including call sign, the call sign of the person you contacted, the date and time of the contact, band or frequency, mode (SSB, FM, etc), and a signal report.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Today most verification is done using online services like Logbook Of The World or LOTW, but some people still like to use QSL cards.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Within a country they are usually mailed directly. I contacted you so I send a QSL card with the contact information. You can then send me back your QSL card confirming the contact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Outside of the country we often use a QSL Bureau. we send our cards to them. they gather all of the card going to a country and send them to bureau in that country that then send them to individuals. To receive QSL cards from your bureau you need to supply with stamped self addressed envelopes. Cards often arrive months after the contact, but this is the least expensive way to send them and receive them. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not every country has a QSL service Bureau. With the disappearance of international reply coupons you could use for postage it is more difficult to send QSL cards directly to people outside of your country. Some suggest sending a 'green stamp', a US Dollar, to help cover postage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many QSL cards have colorful art work or photographs. Others are very plain. They can be a way for you to creatively identify yourself. Many Hams keep a book or board with QSL cards they have received.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TV show &quot;last man standing&quot; features Ham radio from time to time. You will on the wall QSL cards that people have sent to the show after making a contact with the cast or crew using the station. People watch the show to see if they can spot their card. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-02-14T18:33:49.980" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16100" PostTypeId="1" CreationDate="2020-02-14T19:20:55.047" Score="1" ViewCount="223" Body="&lt;p&gt;An answer to &lt;a href=&quot;https://ham.stackexchange.com/questions/16097/what-is-a-qsl-card/16099#16099&quot;&gt;this question&lt;/a&gt; on QSL cards refers to something called Logbook Of The World or LOTW.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is LOTW?  What is its history?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What problem does LOTW solve? (that isn't solved by plain QSL cards or email confirmation)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why does taking part in LOTW seem so complex (digital certificates and signatures with custom library code, etc.)?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-02-17T15:29:55.670" Title="What is Logbook Of The World or LOTW?" Tags="&lt;jargon&gt;&lt;qsl-card&gt;&lt;lotw&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16101" PostTypeId="2" ParentId="16098" CreationDate="2020-02-14T19:25:47.740" Score="6" Body="&lt;p&gt;The rest (of the current) is why your transmitter requires heat sinks (and/or airflow for thermal dissipation).  Linear amplifiers are usually not anywhere close to 100% efficient.  A high SWR might reduce the efficiency even further.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's a transceiver, then the receive circuitry, front panel, and transmit idle bias also takes some wattage to run.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-02-14T19:25:47.740" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16102" PostTypeId="2" ParentId="16100" CreationDate="2020-02-14T20:08:17.027" Score="3" Body="&lt;p&gt;LOTW is a service provide by the American Radio Relay League or ARRL. It started in 2003. it allows a secure upload of your ham radio contacts to an online database. By matching your records with those turned in by the people you contacted the contact can be verified in minutes instead of months or even years which is how long it took with paper QSL cards. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are other groups that offer similar services, like eQSL or club log, LOTW is the most popular. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently over 1 billion contacts have been recorded in LOTW. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;LOTW records can qualify you for several award such as Worked all States (WAS) for making a contact in each of the 50 US states, or DXCC for making 100 contacts with different entities across the world. Man entities are countries, but some countries have several entities. For example besides the US mainland there is Alaska, Hawaii, the US virgin Islands, Puerto Rico, Guam, and American Samoa all of which count as separate entities. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many users upload their data to LOTW world after every day they operate. Other many do so only occasionally and of course not all ham radio operators even use LOTW. I recently made a contact with a person in the Falkland Islands. This would have been another country toward my DXCC, but he does not use LOTW or even QSL Bureaus. I will at some point send him a QSL card, but I may or may not get one back from him and it will not be soon. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-02-14T20:08:17.027" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16103" PostTypeId="2" ParentId="16098" CreationDate="2020-02-14T20:23:22.360" Score="8" Body="&lt;p&gt;Some of both!&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;It's normal for a linear power amplifier for HF to be something like 50% - 60% efficient. So to make 100W, the radio probably needs 170 - 200 W.&lt;/li&gt;&#xA;&lt;li&gt;There are other power draws in the radio, let's say about 20W if it's a fancy modern rig with lots of electronics and a backlit LCD.&lt;/li&gt;&#xA;&lt;li&gt;Your radio is 13.8V nominal, but it's probably rated for 13.8V +/- 15% (11.73 - 15.87 V) and it probably makes rated power at 12V (people tend to be unhappy otherwise). Combining the previous two points, assuming it pulls 220W at 12V, that could be more than 18A of steady-state draw for key-down 100W out.&lt;/li&gt;&#xA;&lt;li&gt;Add a little bit for transients (maybe inrush current for fans starting up, or relays switching), accessories (if supported, e.g. the Icom tuner port), and a little bit of fudge factor just to be safe, and 22A doesn't sound outlandish as a maximum rating.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;All that said, you should expect the &lt;em&gt;average&lt;/em&gt; to be quite a bit less. You're not transmitting 100% of the time; if you're doing SSB phone or any other non-constant-power mode your average power output will be significantly less than 100W; transients aren't happening all the time by definition, etc. But when choosing power supply, wire, etc. you should still plan for 22A at least.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-02-14T20:38:28.000" LastActivityDate="2020-02-14T20:38:28.000" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16104" PostTypeId="2" ParentId="7132" CreationDate="2020-02-15T11:08:13.213" Score="0" Body="&lt;p&gt;It's possible and there are tools out there to aid you in this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Please see &lt;a href=&quot;https://eartoearoak.com/software/rtlsdr-scanner&quot; rel=&quot;nofollow noreferrer&quot;&gt;RTLSDR-Scanner&lt;/a&gt; which describes itself perfectly:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;A cross platform Python frequency scanning GUI for USB TV dongles,&#xA;  using the OsmoSDR rtl-sdr library.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;In other words a cheap, simple Spectrum Analyser.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;The scanner attempts to overcome the tuner's frequency response by&#xA;  averaging scans from both the positive and negative frequency offsets&#xA;  of the baseband data.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It comes &lt;a href=&quot;https://tools.kali.org/wireless-attacks/rtlsdr-scanner&quot; rel=&quot;nofollow noreferrer&quot;&gt;preinstalled with Kali Linux&lt;/a&gt; if you have a copy, and will looks like this (taken from the linked page):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/elOzE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/elOzE.png&quot; alt=&quot;Kali Linux installation of RTLSDR-Scanner&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, I'm not sure if it supports direct sampling. If you plan on doing that, though, I'd consider chaining an upconverter.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If I were to choose one with an upconverter, should I worry about it&#xA;  creating spurious harmonics?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The RTL-SDR is a receive-only SDR, so no, you won't be transmitting. If you plan on transmitting as well—after checking which bands you can legally transmit on—you should consider getting another SDR like the HackRF One or something. It can operate between 1 MHz to 6000 MHz. That said, I'm not sure if it's compatible with the RTLSDR-Scanner since I've never used a HackRF One.&lt;/p&gt;&#xA;" OwnerUserId="14220" LastActivityDate="2020-02-15T11:08:13.213" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16105" PostTypeId="1" CreationDate="2020-02-15T15:21:40.490" Score="1" ViewCount="90" Body="&lt;p&gt;I'm installing a vertical antenna in back yard.  About 20 feet in height and using 1 counterpoise wire 16 feet for 20 meters.  Does installing two or more counterpoise wires help?&lt;/p&gt;&#xA;" OwnerUserId="16428" LastEditorUserId="8717" LastEditDate="2020-02-15T16:30:14.277" LastActivityDate="2020-02-15T23:36:23.763" Title="Vertical antenna" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;&lt;counterpoise&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16106" PostTypeId="2" ParentId="16105" CreationDate="2020-02-15T15:52:22.593" Score="0" Body="&lt;p&gt;A single counterpose wire makes the antenna pattern directional, usually in the direction of the counterpose.  Two or more counterposes in a symmetrical arrangement makes the antenna pattern more horizontally omnidirectional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The asymmetry of a single counterpose also makes it more difficult to arrange the feed line so that the antenna's radiation pattern doesn't couple to the feedline and generate common mode currents (potential RF in the shack, plus a further distortion of pattern).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The above are rules of thumb.  Best analysis would be to put your particular antenna geometry into an antenna modeling program (NEC2, MININEC, et.al.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-02-15T15:52:22.593" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16107" PostTypeId="1" CreationDate="2020-02-15T16:13:54.840" Score="1" ViewCount="550" Body="&lt;p&gt;Is there a distinction between a call sign for a General vs. Technician? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recently upgraded to general, I am curious about changing call sign to reflect license upgrade?&lt;/p&gt;&#xA;" OwnerUserId="16430" LastEditorUserId="4076" LastEditDate="2020-02-17T07:11:05.927" LastActivityDate="2020-02-17T14:51:41.220" Title="General Vs Technician Call Sign?" Tags="&lt;united-states&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16109" PostTypeId="2" ParentId="16105" CreationDate="2020-02-15T23:36:23.763" Score="1" Body="&lt;p&gt;As a start, below is a NEC analysis of the system described in the OP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The horizontal radials lie along the +Y &lt;em&gt;or&lt;/em&gt; the + and -Y axes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JtGu9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JtGu9.png&quot; alt=&quot;,,&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-02-15T23:36:23.763" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16111" PostTypeId="1" CreationDate="2020-02-17T05:26:40.870" Score="1" ViewCount="68" Body="&lt;p&gt;I've been trying to find manufacturing date info on the J.H. Bunnell key (&quot;J.H. Bunnell&amp;amp;Co&quot; is stamped on top of the frame), but it seems to be somewhat unique. Most J-38 keys that I've found online have a binding strap that is bolted to the top of the frame, but this one is bound by the LINE binding post instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the bottom is a white stamp that seems to show &quot;SC 16 k&quot;, I'm not sure about the &quot;k&quot;. So maybe 1916, or maybe this key has a bakelite base stolen from another manufacturer?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Appreciate any help identifying this key.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IMtv9.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IMtv9.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/haV32.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/haV32.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/HVSUV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HVSUV.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/wiO27.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wiO27.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16442" LastActivityDate="2020-02-22T06:27:53.127" Title="Info on this Bunnell J-38 key" Tags="&lt;cw&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16112" PostTypeId="2" ParentId="16107" CreationDate="2020-02-17T14:51:41.220" Score="4" Body="&lt;p&gt;According to the &lt;a href=&quot;https://www.fcc.gov/amateur-call-sign-systems&quot; rel=&quot;nofollow noreferrer&quot;&gt;FCC's Amateur Call Sign Systems page&lt;/a&gt;, Technician and General class operators are in the same group for call signs, so your call sign has a prefix of K, N, or W with a three-letter suffix, or a KL, NL, WL, NP, WP, KH, NH, or WH prefix with a two-letter suffix.  Because you've upgraded your license but are in the same call sign group, you're not entitled to any call sign format that you weren't already entitled to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a shorter call sign, you could always apply for a 1x3 license that isn't in current use through the &quot;vanity&quot; system.  Or you could study up for the Extra class license exam and pass it.  As an Extra-class licensee you could then request a new sequentially-issued license, which would be issued from the Extra call sign group, or apply for a &quot;vanity&quot; call sign from the Extra call sign group.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-02-17T14:51:41.220" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16113" PostTypeId="2" ParentId="16100" CreationDate="2020-02-17T15:29:55.670" Score="3" Body="&lt;p&gt;To add to Jim's answer, one of the goals of Logbook of the World is to be a secure system (&lt;a href=&quot;https://lotw.arrl.org/lotw-help/MissionObjectives/&quot; rel=&quot;nofollow noreferrer&quot;&gt;reference&lt;/a&gt;).  This presumably was necessary because contacts with some DXCC entities or other stations are very rare, and such contacts are very sought-after by many people.  The American Radio Relay League's rules about certificates follow security practices that are commonly used for secure computerized transactions over the internet.  The rules can be cumbersome because the League wants proof that that the person requesting the certificate is actually the operator in charge of the call sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other similar services exist where operators upload their logs, but they have different goals.  &lt;a href=&quot;https://www.eqsl.cc/&quot; rel=&quot;nofollow noreferrer&quot;&gt;eQSL&lt;/a&gt; is designed to be easy to use, and to be like paper QSL cards in that users can share a graphic picture; however it's not as secure as LOTW, and so the ARRL doesn't accept eQSL confirmations for DXCC awards.  (Also surely the ARRL is somewhat biased towards their own system.)  &lt;a href=&quot;https://clublog.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Club Log&lt;/a&gt; was designed as an electronic system to allow people to check if they are in the log of a DX station, and has since expanded to be a computerized toolkit for DXers.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-02-17T15:29:55.670" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16114" PostTypeId="1" CreationDate="2020-02-17T18:48:29.030" Score="1" ViewCount="61" Body="&lt;p&gt;I'm planning on installing a Hustler 4-BTV vertical by the house. There's already a 12 ft. steel pole mounted in cement, so I'm going to mount it on that pole about 10 feet up (sort of small mini tower). Because of another house next door and being close near corner of my house, not much room for ground radials. But being the steel pole is already in cement and in ground I shouldn't need any radials? What would you think?&lt;/p&gt;&#xA;" OwnerUserId="16431" LastEditorUserId="8717" LastEditDate="2020-02-17T19:44:46.000" LastActivityDate="2020-02-17T19:44:46.000" Title="Vertical Hustler - do I need any radials?" Tags="&lt;antenna-system&gt;&lt;vertical-antenna&gt;&lt;counterpoise&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16115" PostTypeId="2" ParentId="16114" CreationDate="2020-02-17T19:12:29.073" Score="2" Body="&lt;p&gt;The Hustler web site says: &quot;For optimal performance, radial wires should be used.&quot;  Somewhere else, there is a recommendation for sets of 3 tuned radials per band on which you plan to operate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A short metal pole in the ground does not act as a proper RF counterpose for HF bands, nor does it prevent ground losses, and will very likely not allow the best impedance match at the feed point.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-02-17T19:22:22.727" LastActivityDate="2020-02-17T19:22:22.727" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16116" PostTypeId="1" AcceptedAnswerId="16119" CreationDate="2020-02-17T20:02:14.990" Score="4" ViewCount="650" Body="&lt;p&gt;I bought a second-hand Yaesu FT-991A. It works pretty well and by the look of it's internals I don't believe it was ever repaired.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However I noticed one weird thing. When I try to use FM or C4FM on HF bands (including 28 MHz and 50 Mhz), FT-991A transmits for about half a second, then the green speaker icon blinks 3 times and the transceiver returns to receive mode. There is no such problem on 2m and 70cm bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question is - is this a well-known behavior and maybe I just need to check some settings, or this unit is defective? All settings related to VOX and operation using a repeater I could find are disabled.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPD1: It worth noticing that the manual of this transceiver is in Japanese, and maybe it's behavior differs from EU/US versions. As I understood using Google Translate, the manual implicitly says that FM and C4FM can be used only on 28 Mhz, 50 Mhz, 2m and 70cm bands. The manual in English doesn't seem to say that. I tried to take into account IARU Region 3 band plan and possible power limitations, but it didn't help. Also it seems that the unit was subjected to MARS/CAP mod, because it's possible to transmit outside of amateur bands, e.g. on 6 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;UPD2: I've checked that the latest available firmware is used (MAIN v02-01, TFT v02-00, DSP v01-11). Also I thought maybe PTT wires could catch an RFI, but using MOX has the same effect. Resetting the transceiver to factory defaults didn't help.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-02-18T18:45:37.817" LastActivityDate="2021-01-05T16:34:39.503" Title="Yaesu FT-991A: FM and C4FM modes don't work on HF bands" Tags="&lt;transceiver&gt;&lt;fm&gt;&lt;equipment-operation&gt;&lt;yaesu&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16117" PostTypeId="2" ParentId="6325" CreationDate="2020-02-18T11:42:02.333" Score="1" Body="&lt;p&gt;UHF inverted ground plane antennas on balloons and other aircraft are used for this very reason.  The radiation pattern gives the most gain at low radiation angles (which are at greatest distance to ground), less vertically down (closest) and theoretically none above.  I'd be interested in the calculated radiation pattern of a ground plane with sloping radials (e.g. &lt;a href=&quot;https://m0ukd.com/static/calculators/Quarter_Wave_Ground_Plane/Quarter_Wave_Drawing.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;ground plane sloping radials&lt;/a&gt; ) which I expect is somewhere between a dipole and ground plane.&lt;/p&gt;&#xA;" OwnerUserId="16448" LastActivityDate="2020-02-18T11:42:02.333" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16118" PostTypeId="2" ParentId="15788" CreationDate="2020-02-18T19:18:56.417" Score="4" Body="&lt;p&gt;I wouldn't risk directly connecting a 9.6v battery to a radio that expects 5-6v.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest solution would probably be the diodes mentioned in the comment to your question, but as the battery voltage dropped the voltage reaching the radio would drop as well, and as the battery got low the output voltage after the diodes might be too low to power the radio, wasting the last bit of the battery that could otherwise be used.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would recommend a linear regulator such as a 7805 (for 5v) or 7806 (for 6v). Here's how it's wired, and if you don't have them you can leave out the capacitors for this sort of application:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y99sd.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y99sd.png&quot; alt=&quot;circuit diagram for 7805 regulator from https://www.electronicshub.org/understanding-7805-ic-voltage-regulator/&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a 78xx regulator the voltage to the radio won't drop until the battery has reached the regulator's drop-out voltage, and the battery will likely be dead before that happens, at least for the 7805. For the 6v radio, you might consider an LDO (low drop-out) version of the 7806 regulator to squeeze every last bit out of the battery, or just use a 7805, which is much more common and easier to find than a 7806 anyway, as the 6v radio can probably run fine on 5v.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's worth keeping in mind that either the diodes or the linear regulator will waste a significant amount of battery power as heat. Their main advantages are that they are simple to build and won't introduce noise into the radio. More efficient regulators are commonly available but tend to be noisy, especially for sensitive radio receivers, but if you need to conserve battery you should do some further research into switching regulators and buck converters, or just use a battery the radio can handle directly.&lt;/p&gt;&#xA;" OwnerUserId="4452" LastEditorUserId="4452" LastEditDate="2020-02-19T01:51:53.100" LastActivityDate="2020-02-19T01:51:53.100" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16119" PostTypeId="2" ParentId="16116" CreationDate="2020-02-18T21:34:26.030" Score="2" Body="&lt;p&gt;After reverting MARS/CAP mod everything works as expected. I don't know whether the problem was caused by the mod per se or maybe just one of FCC cables was a little bit misplaced when the mod was made.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-02-18T22:02:55.913" LastActivityDate="2020-02-18T22:02:55.913" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16120" PostTypeId="1" CreationDate="2020-02-18T22:20:10.113" Score="7" ViewCount="565" Body="&lt;p&gt;Suppose I have a coax-fed half-wave dipole antenna. The coax shield goes to one side of the antenna, the center conductor to the other side. The transceiver's chassis is connected (via the coax connector) to both one side of the dipole and to Earth ground via the chassis to Earth ground wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm confused by having one-half of the dipole tied to the RF transmitter output and to Earth ground. Can anyone explain the electronics behind what is going on? &lt;/p&gt;&#xA;" OwnerUserId="16450" LastEditorUserId="8717" LastEditDate="2020-02-18T22:41:32.313" LastActivityDate="2020-04-02T08:29:51.917" Title="Coax fed dipole: shield goes to one side, yet is grounded via chassis line to Earth" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;&lt;dipole&gt;&lt;grounding&gt;" AnswerCount="5" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16121" PostTypeId="2" ParentId="16120" CreationDate="2020-02-18T23:16:17.923" Score="0" Body="&lt;p&gt;The part of the dipole that is connected to the shield is NOT grounded &lt;em&gt;at RF&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are common-mode RF signals on the outside of the coax caused by the junction of the unbalanced coax and the balanced dipole. This is why we use &lt;a href=&quot;http://Is:question%20dipole%20balun%20-increased&quot; rel=&quot;nofollow noreferrer&quot;&gt;choke baluns at the feedpoint&lt;/a&gt;: to force all the power present on the center conductor and the inside of the shield onto the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same is true for received signals. Without a proper balun, the outside of the coax can pick up unwanted noise.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-02-18T23:35:22.047" LastActivityDate="2020-02-18T23:35:22.047" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16122" PostTypeId="1" CreationDate="2020-02-19T00:15:27.023" Score="4" ViewCount="149" Body="&lt;p&gt;Twinax (shielded controlled impedance balanced line pairs) is said to be used in 10G ethernet signaling for greater noise immunity that other cabling types.  Why isn't twinax (or similar) commonly used for amateur radio antenna feed lines, where noise immunity on receive is also quite important?  Rather than unbalanced coax or unshielded twin-lead?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Added: Especially when dealing with a balanced antenna (dipole), balanced differential inputs, or balanced push-pull final RF amplifier stage.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-02-19T03:10:54.523" LastActivityDate="2020-02-20T12:11:53.433" Title="Why isn't some form of twinax commonly used for antenna feed lines?" Tags="&lt;feed-line&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16123" PostTypeId="2" ParentId="16122" CreationDate="2020-02-19T05:42:01.337" Score="3" Body="&lt;p&gt;Why coax or twin lead or ladder line?&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Because the others are traditional.&lt;/li&gt;&#xA;&lt;li&gt;Because twinax is relatively rare and expensive.&lt;/li&gt;&#xA;&lt;li&gt;Because unless you are dealing with high frequencies (&gt;5GHz) twinax is overkill.  Most amateur radio is &amp;lt;1GHz where coax and twin lead make more sense.  Above 5GHz, more commonly I see wave guide and hardline used.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Having said that, I have seen twinax used for short runs in situations where twin lead was inappropriate — like passing through a metal window frame.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, it has been pointed out (in another question) that twinlead is not better (lower loss) than high end coax, so I suspect that twinax may also not be better, and possibly waveguide and hardline are better than twinax already.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-02-20T12:11:53.433" LastActivityDate="2020-02-20T12:11:53.433" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16124" PostTypeId="2" ParentId="16122" CreationDate="2020-02-19T05:51:11.510" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Why isn't twinax (or similar) commonly used for amateur radio antenna feed lines&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It's always hard to say why something &lt;em&gt;isn't&lt;/em&gt; done, but after looking around at the options I'd say cost has to be one factor. A 100' spool of 18AWG or 20AWG twinaxial cable costs around $220, which is five or six times the cost of coax or ladder line. The connectors are also much more expensive than typical coax connectors.&lt;/p&gt;&#xA;" OwnerUserId="11226" LastActivityDate="2020-02-19T05:51:11.510" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16125" PostTypeId="2" ParentId="16120" CreationDate="2020-02-19T13:02:32.790" Score="1" Body="&lt;p&gt;Welcome to the world of RF (radio frequency) and AC power, where the obvious rules of DC power don't work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In RF electronics, just because two wires are DC shorted doesn't mean they are RF shorted.   In RF, a transmission line (like coax) can be shorted at one end and measure as RF open at the other end if it is an odd multiple of quarter wavelengths between the shorted end and the end you are measuring.  Even more confusing, change the shorted end to open and you can measure a short at the other end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So just because you have the shield connected to &quot;ground&quot; in one or more places doesn't mean the antenna is shorted.  The ground can be used to absorb (or induce!) common mode current.   If the coax is not symmetrical with respect to the dipole near the feedpoint, it will couple with the dipole and encourage common mode currents.   A balun or unun in the right place(s) can reduce this.  The simplest version of a choke balun would be a coil of a few loops (typically at least 5) of coax with the loops tightly bound to each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In transmission line like coax, currents are suppose to oppose, so that their magnetic fields cancel and the wire doesn't leak RF.  Common mode current (where some portion of the currents flow the same direction in both sides of the coax) cause the coax to leak and radiate.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-02-19T13:02:32.790" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16126" PostTypeId="2" ParentId="16120" CreationDate="2020-02-19T13:57:13.953" Score="1" Body="&lt;p&gt;RE (from the OP):  &lt;em&gt;I'm confused by having one-half of the dipole tied to the RF transmitter output and to Earth ground. Can anyone explain the electronics behind what is going on?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just to note that &lt;strong&gt;all&lt;/strong&gt; antenna systems are two-terminal devices — no r-f energy will flow on one &quot;leg&quot; of a dipole without an equal amount of r-f energy flowing on the other leg.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A coaxial cable carries the same amount of r-f energy on the OD of its inner conductor as it carries on the ID of its outer conductor. The r-f current on the outer conductor is confined to its inner diameter due to &quot;skin effect,&quot; that isolates the two surfaces of the outer conductor along its length.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At each end of the coax, a path exists between the inner and outer surfaces of the coax outer conductor. So a portion of the r-f energy on the ID of the outer conductor can appear on, and propagate along the outer surface of its outer conductor (or &quot;shield&quot;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This phenomenon occurs whether or not the coax shield has either a direct or an indirect conducting path to a true r-f ground reference such as the earth.  IOW, the coax shield does not have the same characteristics for the flow of a-c/r-f current that it has for direct current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;R-F current flowing along a conductor exposed to free space will produce e-m radiation, just as it does when it flows along the two legs of a dipole.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-02-19T13:57:13.953" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16127" PostTypeId="1" CreationDate="2020-02-19T14:17:03.917" Score="2" ViewCount="214" Body="&lt;p&gt;Many threads posted on various websites over the years have included statements/beliefs on this subject, but support there for the accuracy of those statements sometimes is minimal.  An accurate reference would be  useful.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-02-20T14:34:36.537" Title="Which is Better to Use with Vertical Monopoles: Buried Radials or Ground Screens?" Tags="&lt;grounding&gt;&lt;vertical-antenna&gt;&lt;radial&gt;&lt;buried&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16128" PostTypeId="2" ParentId="16127" CreationDate="2020-02-19T14:17:03.917" Score="3" Body="&lt;p&gt;The information below is extracted from the &quot;benchmark&quot; 1937 I.R.E. paper* of Brown, Lewis &amp;amp; Epstein of RCA Laboratories, and is based on their accurately measured data for these systems.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IMO, the outlined and underlined text at the bottom of this clip is worth remembering, and deserves greater access/acceptance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*Proceedings of the Institute of Radio Engineers&#xA;Volume 25, Number 6 June, 1937&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GROUND SYSTEMS AS A FACTOR IN ANTENNA&#xA;EFFICIENCY&lt;/p&gt;&#xA;&#xA;&lt;p&gt;by&lt;/p&gt;&#xA;&#xA;&lt;p&gt;G. H. BROWN, R. F. LEWIS, AND J. EPSTEIN&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(RCA Manufacturing Company, Inc., Camden, N. J.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iSlvI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iSlvI.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;blockquote&gt;&#xA;    &lt;p&gt;Added Feb 20, 2020 in response to the comments of Mike Waters:&lt;/p&gt;&#xA;  &lt;/blockquote&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Recently I was referred by a poster on another website to a paper published in 1977 in &lt;strong&gt;Ham Radio&lt;/strong&gt; (&lt;a href=&quot;http://nc0b.com/documents/GroundScreen-sm.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://nc0b.com/documents/GroundScreen-sm.pdf&lt;/a&gt;). I had been unaware of that paper prior to this.  The author's test equipment and test methods were of a professional level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From my POV though, his conclusions would have been more accurate if one of the closing sentences in his paper had included the edit now shown between the brackets below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;\The next time you erect a new vertical, or plan to improve an existing one, consider a ground screen as either a substitute for radials, or as an adjunct to an existing [but poorly performing] radial ground system./&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reason? Regardless of their number and physical length, if a set of radials is performing well when buried in the earth around the base of a vertical monopole, there is no compelling reason to add a ground screen to it that does not significantly improve the performance of that antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The graphic below illustrates this by including the ESR at the operating frequency of a rather sparse set of short, buried radials used with an electrically short vertical monopole. The ESR of those buried radials vs. the conductivity of the soil they are buried in is shown by the red trace and the scale on the left vertical axis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This study shows that even for this short radiator with only 32 short radials, the ESR for about 6 mS/m (~&quot;average&quot;) or better Earth is about 2 ohms or less, without the use of a ground screen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It also shows that reducing the ESR of the buried radial set for this scenario doesn't change the radiation efficiency of that antenna system very much over the span of Earth conductivities ranging from ~6 mS/m to 30 mS/m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/teuuV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/teuuV.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-02-20T14:34:36.537" LastActivityDate="2020-02-20T14:34:36.537" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16129" PostTypeId="2" ParentId="15970" CreationDate="2020-02-19T15:52:53.297" Score="0" Body="&lt;p&gt;There are plenty of modern studies of HF propagation.  For instance, in the last 10 years, I have seen new models for both sporatic E and selective fading.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For selective fading, the new models look at how faraday rotation causes circular polarization.  The modem used by freedv is specifically designed to resist this, so they must have a model for selective fading.  I believe that the group designing freedv have published several scholarly papers from their research.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may also want to research the various HF beacon networks such as wspr, many of which are designed specifically to research propagation.  There may also be isosonde data available, but I couldn't find any with a quick search.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-02-19T15:52:53.297" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16130" PostTypeId="1" AcceptedAnswerId="16134" CreationDate="2020-02-19T17:51:02.750" Score="2" ViewCount="106" Body="&lt;p&gt;I'm experimenting with low frequencies, but due to the inherent nature of LF, I strive for more transmit power and bigger antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now of course I want to comply with regulations, which allow (in my country) an average exposure of 80 V/m at this frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I'd have a T-antenna that was 15m high and 20m wide. How do I calculate/estimate at which distance I would expect this field strength? &#xA;Let's say 100W PEP, and an estimated radiated power of 10 mW EIRP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The formula that I've found applies only to the far-field, I think:&#xA;&lt;a href=&quot;https://ham.stackexchange.com/a/10078/16455&quot;&gt;https://ham.stackexchange.com/a/10078/16455&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="16455" LastEditorUserId="8717" LastEditDate="2020-02-19T20:44:02.453" LastActivityDate="2020-02-20T16:09:04.140" Title="Estimating near-field electric field strength at LF (137 kHz)" Tags="&lt;antenna-theory&gt;&lt;rf-power&gt;&lt;safety&gt;&lt;vlf&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16131" PostTypeId="2" ParentId="16130" CreationDate="2020-02-19T21:44:45.553" Score="3" Body="&lt;p&gt;Estimating the near field is best done with modeling software or empirical measurement. The details of the antenna construction and environment (the ground and any nearby conductive objects in particular) can significantly impact the near field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, 100W is not much, and often regulations specify that no particular evaluation need be done if the power is below some threshold. Furthermore, low frequencies are generally safer, as sensitive parts of the body (such as the cornea) don't readily absorb the radiation. For example in the US, &lt;a href=&quot;http://www.arrl.org/fcc-rf-exposure-regulations-the-station-evaluation&quot; rel=&quot;nofollow noreferrer&quot;&gt;no evaluation is necessary below 500W PEP on the 160 meter band&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-02-19T21:44:45.553" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16132" PostTypeId="1" CreationDate="2020-02-19T22:18:56.640" Score="3" ViewCount="110" Body="&lt;p&gt;With an OCF dipole, does it matter which leg, short or long, is connected to which side of the 4:1 balun, hot(coax center) or shield?  How can you tell which is which, the balun is not marked.  Thank you. &lt;/p&gt;&#xA;" OwnerUserId="16456" LastEditorUserId="8717" LastEditDate="2020-02-20T03:29:11.487" LastActivityDate="2020-02-21T22:15:10.630" Title="4:1 Balun question" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;dipole&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16133" PostTypeId="2" ParentId="16132" CreationDate="2020-02-20T09:33:55.587" Score="4" Body="&lt;p&gt;It doesn't matter. If you change the connection of the OCF dipole nothing will change from the current and voltage flow or distribution points of view.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-02-20T09:33:55.587" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16134" PostTypeId="2" ParentId="16130" CreationDate="2020-02-20T16:09:04.140" Score="3" Body="&lt;p&gt;Below is a rough estimate of the &lt;strong&gt;near fields&lt;/strong&gt; calculated by NEC4.2 for an elevation of 3 meters above level Earth from a transmit antenna and system as generally described in the OP, and the followup comments of the OP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Use with due diligence.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0FKlm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0FKlm.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-02-20T16:09:04.140" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16135" PostTypeId="1" CreationDate="2020-02-20T18:04:48.067" Score="12" ViewCount="129" Body="&lt;p&gt;An ionosonde is a special HF radio transmitter that periodically transmits a signal that sweeps across a large portion or the entire HF spectrum to identify the propagation of radio signal in the ionosphere, currently they are operated by various institutions around the world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To my knowledge, in order to legally operate a radio transmitter at a frequency/band, the frequency must be allocated by regulatory agencies for use by the type of service that the transmitter belongs to. Ultimately, all radio transmissions must be legal under the ITU Radio Regulations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How does the ITU Radio Regulations apply to an ionosonde? Why is it legal for an ionosonde to use a huge portion of the spectrum, which otherwise wouldn't be possible for conventional radio communication services?&lt;/p&gt;&#xA;" OwnerUserId="15589" LastEditorUserId="8717" LastEditDate="2020-08-20T19:46:26.820" LastActivityDate="2020-08-20T19:46:26.820" Title="How do Radio Regulations and Frequency Allocations Apply to an Ionosonde?" Tags="&lt;legal&gt;&lt;international-operating&gt;&lt;ionosphere&gt;&lt;itu-zones&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16136" PostTypeId="1" CreationDate="2020-02-20T20:54:42.457" Score="3" ViewCount="334" Body="&lt;p&gt;I need to build another 9:1 unun and I start searching for my toroids... (I have build 2-3 something like 4 years ago)...&#xA;In parallel I checked on Google about the correct toroid etc so I found 2-3 pages with designs. My focus is on power loss as I run QRP on batteries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://vk6ysf.com/unun_9-1_v2.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;9:1  voltage unun using a L15 ferrite core&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://g8jnj.webs.com/balunsandtuners.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;9:1 Voltage Unun - FT240-61&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://vk6ysf.com/unun_9-1.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;9:1  voltage unun using a T-200-2 powdered iron toroid core&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What do you think regarding power losses and materials?&#xA;Which toroid should I use? (I already have the *-61 and the *-2).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding wires for the turns, some use enameled copper wire, some 3-colour for like a power socket.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The unun is not for portable. So a size 200-240 is okay for some future proofing.&#xA;&lt;hr&gt;&#xA;If I can get ok losses down to 80m, I'll be very happy, I mainly use 15 to 40m.&#xA;&lt;hr&gt;&#xA;It's for a “random wire” end fed. Probably around 58ft max. Or maybe 53ft (space restricted)&lt;/p&gt;&#xA;" OwnerUserId="16460" LastEditorUserId="8717" LastEditDate="2020-02-21T13:54:19.323" LastActivityDate="2020-02-21T13:54:19.323" Title="9:1 unun material and power loss" Tags="&lt;balun&gt;&lt;ferrite&gt;&lt;end-fed-antenna&gt;&lt;transformer&gt;" AnswerCount="0" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16137" PostTypeId="1" AcceptedAnswerId="16139" CreationDate="2020-02-20T21:07:11.140" Score="10" ViewCount="1733" Body="&lt;p&gt;It's well-known that under certain conditions verticals and dipoles can gather static charge, which is a common reason of transceiver damage. There are several ways to solve this issue. Some hams suggest to place a 100 kΩ high-power resistor to the feed point (not an ideal solution, because the charge dissipates slowly). Others suggest to use a coil with inductance about 200 µH instead of the resistor. The inductance works as a short circuit for DC and has little effect (high resistance) on HF.&lt;/p&gt;&#xA;&lt;p&gt;Here is what surprises me. I don't believe I ever encountered an advice to use a regular 1:1 transformer, nor could I find such an advice online. It isolates the feed line from the antenna and works as a short circuit for DC. This is probably the simplest solution I can think of.&lt;/p&gt;&#xA;&lt;p&gt;Assuming that power losses in the transformer are acceptable, and that it's placed after 1:1 current balun (which eliminates common-mode current), is there any reason why it might be a poor solution?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="4665" LastEditDate="2020-07-09T21:01:45.703" LastActivityDate="2020-07-09T21:01:45.703" Title="Can a 1:1 transformer be used as a protection from static electricity?" Tags="&lt;dipole&gt;&lt;vertical-antenna&gt;&lt;transformer&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16139" PostTypeId="2" ParentId="16137" CreationDate="2020-02-21T01:48:18.933" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Assuming that power losses in the transformer are acceptable, and that it's placed after 1:1 current balun (which eliminates common-mode current), is there any reason why it might be a poor solution?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, the assumption about loss may not be a great assumption to make. It takes a substantial core to avoid saturation and overheating even at modest transmit powers, and then you've necessarily introduced some amount of loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course designing a suitable transformer isn't impossible, some might not even consider it difficult. It's just costly compared to other solutions, which I suspect is why it's not often recommended.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-02-21T01:48:18.933" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16140" PostTypeId="1" AcceptedAnswerId="16166" CreationDate="2020-02-21T04:39:56.757" Score="1" ViewCount="128" Body="&lt;p&gt;Where does the ground of the audio path go in this schematic?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Qber0.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Qber0.jpg&quot; alt=&quot;Schematic&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="76" LastEditDate="2020-02-21T15:14:01.433" LastActivityDate="2020-02-25T20:24:24.890" Title="Where am i supposed to ground the audio path?" Tags="&lt;electronics&gt;&lt;grounding&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16141" PostTypeId="2" ParentId="16137" CreationDate="2020-02-21T09:40:24.397" Score="10" Body="&lt;p&gt;A transformer can help and could also make things worse. I have some bad experience with this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way that a radio is damaged by &lt;em&gt;static&lt;/em&gt; is simple:&lt;br&gt;&#xA;&lt;strong&gt;Something charges up to a high voltage, and then there's a sudden breakdown resulting in a high voltage on the first transistor of the receiver.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This can happen in a few ways:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;A long-wire or monopole type antenna is not grounded, and the radio has a decoupling capacitor before the front-end amplifier. When the antenna charges up to a few hundred volts, the capacitor breaks down and the charge surges into the transistor.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A dipole type antenna is connected with a transformer, where the antenna side of the transformer, and the antenna itself, are not grounded. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Someone already charged, walks up to the antenna and touches it.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/D80Jm.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fD80Jm.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In both cases, even if the receiver has an inductor or resistor for DC grounding, it will be damaged because the impulse caused by the breakdown or spark is so fast.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;It isolates the feed line from the antenna...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;You can see that there are cases that adding a transformer could actually make things worse&lt;/strong&gt;, by isolating a the antenna and allowing it to charge up. Eventually it will jump across the transformer insulation...&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;... and works as a short circuit for DC.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If there is something isolated that can be charged up, then the DC short on the radio side will mean nothing. The breakdown is an impulse and its initial peak will go right past the DC short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The solution in cases 1 and 2 is to &lt;em&gt;prevent anything in or near the antenna from becoming charged up&lt;/em&gt;. This could be done with a resistor or inductor to ground, or by shorting the centre tap of the transformer. Transmission-line transformers are generally DC short throughout, so that solves it completely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In case 3, someone touching the antenna, the grounding is of limited use. You can add fast limiter diodes to the input - these are widely available, have low capacitance (0.2 pF maybe) and can handle the full current of a human body discharge. They clamp at just a few volts though, so aren't appropriate for transmitting antennas. A bandpass or highpass filter will also help to reduce the energy that reaches the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;None of this is advice about &lt;em&gt;lightning&lt;/em&gt; protection, though some of it may help a bit in the case of distant lightning.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-02-21T09:48:50.653" LastActivityDate="2020-02-21T09:48:50.653" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16143" PostTypeId="2" ParentId="12389" CreationDate="2020-02-21T15:43:01.650" Score="1" Body="&lt;p&gt;a 49:1 transformer with a bit of capacitance will help you more. for a 9:1 UNUN its better to choose a &quot;random length&quot;.&#xA;Like: 29  35.5  41  58  71  84  107  119  148 all in feet!&lt;/p&gt;&#xA;" OwnerUserId="16460" LastActivityDate="2020-02-21T15:43:01.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16144" PostTypeId="1" CreationDate="2020-02-21T18:48:11.067" Score="2" ViewCount="439" Body="&lt;p&gt;Say I have a shortened HF dipole (with significant inductive loading and/or capacitive hats), and can only mount it very close to ground level (but not touching), over lossy ground, and with no radials or counterposes.  (situation is temporary portable operation in an extremely constrained area).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To minimize ground losses and/or maximize radiation efficiency (what little is possible given the constraints), would it be better to orient the low short dipole horizontally or vertically?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-02-22T12:58:32.753" Title="Short low dipole, better if horizontal or vertical?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16145" PostTypeId="2" ParentId="16132" CreationDate="2020-02-21T20:11:50.333" Score="1" Body="&lt;h2&gt;Phase&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;The only difference will be the RF phase.   A &quot;balun&quot; is a transformer that goes between balanced and unbalanced sources and sinks of energy.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unless you are trying to use two dipoles as an array, the phase doesn't matter. &lt;/p&gt;&#xA;" OwnerUserId="9109" LastEditorUserId="8717" LastEditDate="2020-02-21T22:15:10.630" LastActivityDate="2020-02-21T22:15:10.630" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16146" PostTypeId="2" ParentId="16144" CreationDate="2020-02-21T22:22:42.340" Score="3" Body="&lt;p&gt;Generally, a low horizontal dipole doesn't do a good job of radiating power to where you want it. I found an &lt;a href=&quot;https://www.qsl.net/aa3rl/ant2.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;interesting analysis&lt;/a&gt; of horizontal dipole height, which ran a number of simulations and found that at low heights (less than 1 wavelength, roughly) the dipole's radiation pattern has a significant vertical lobe. At heights of 0.2 wavelengths or less off the ground, the direction of maximum gain is straight up.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have read elsewhere that low dipoles also tend to radiate a lot of power into the ground. So, you would be spending a lot of your power heating the ground and space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I believe polarization is important for groundwave propagation, but for skywave propagation it is minimally important unless you have a specific QRM issue that you need to work around. So, for the purposes of this answer, I will assume that polarization is not an important consideration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With that in mind, a vertical dipole is likely to be more effective. In practice it's likely to be similar to a monopole with radials, which is an antenna configuration that is widely used with positive results.&lt;/p&gt;&#xA;" OwnerUserId="10859" LastActivityDate="2020-02-21T22:22:42.340" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16147" PostTypeId="2" ParentId="16111" CreationDate="2020-02-22T06:27:53.127" Score="1" Body="&lt;p&gt;It appears to be an inspector's stamp.  It's not uncommon for such a stamp to include the inspector's initials along with a plant number, date code, or lot number.  Guessing it was stamped by someone whose initials are &quot;SC.&quot;  &lt;/p&gt;&#xA;" OwnerUserId="11094" LastActivityDate="2020-02-22T06:27:53.127" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16148" PostTypeId="2" ParentId="16144" CreationDate="2020-02-22T12:58:32.753" Score="2" Body="&lt;p&gt;Below is an analysis that may be useful in answering this question.  It shows the complete radiated fields from the horizontal dipole and the vertical monopole defined there, for elevation angles from zero (the horizontal plane) to 5.7° above it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The space wave and groundwave of the h-pol radiator are out of phase near the surface of the earth, and tend to cancel each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That does not occur for vertical polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/l841p.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/l841p.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-02-22T12:58:32.753" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16149" PostTypeId="1" CreationDate="2020-02-23T04:10:11.433" Score="5" ViewCount="111" Body="&lt;p&gt;I saw a design for a walkie talkie that used a mixer that mixed the TX freq to the RX path before demod. Looking at the SA616 chip, demod is acomplished by Gilbert cell  quadrature detector that is downstream from this. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest FM detector is a phase locked loop but the issue is that injection of the TX frequency at the demod stage rather than the mixer stage in this case I cannot do. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I want to use the TX frequency to demodulate the on incoming signal, thus reducing the complex circuitry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My first inclination is to go with the SA616 offered by NXP but I cannot inject the TX frequency. If I go the PLL route I need to somehow translate the frequency to an equivalent resistance in order to control the VCO that resides with in the Phase locked loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Im trying to work with 1.8Mhz to 222Mhz band ranges. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Relevent datasheet&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.nxp.com/part/SA616BS#/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.nxp.com/part/SA616BS#/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I doing something wrong or am I overthinking things?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is a diagram &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ceapy.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ceapy.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="12988" LastEditDate="2020-02-24T05:15:07.550" LastActivityDate="2020-02-26T16:35:52.267" Title="Demodulation based on external frequency source" Tags="&lt;equipment-design&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16150" PostTypeId="2" ParentId="15196" CreationDate="2020-02-23T17:21:19.903" Score="1" Body="&lt;p&gt;It turns out that I misunderstood how complex signal source blocks work.  For example, I was expecting that a flowgraph like this one: &lt;a href=&quot;https://gist.github.com/ardavast/2be4cc6db04622d65eca88531ca750ff&quot; rel=&quot;nofollow noreferrer&quot;&gt;phase_diff.grc&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/xbXN1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xbXN1.png&quot; alt=&quot;phase_diff.grc.png&quot;&gt;&lt;/a&gt;&#xA;will produce two signals 90° out of phase with each other - but it produces two signals that are exactly the same.  If I multiply the lower signal source by 1j, however: &lt;a href=&quot;https://gist.github.com/ardavast/5e6d70e3eaacbb93f2b5d14e0a4128ee&quot; rel=&quot;nofollow noreferrer&quot;&gt;phase_diff2.grc&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/RRs74.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RRs74.png&quot; alt=&quot;phase_diff2.grc.png&quot;&gt;&lt;/a&gt;&#xA;it works - and it doesn't matter if the lower signal source is set to sine or cosine.  Indeed, unexpectedly for me, a flowgraph like this one returns zero: &lt;a href=&quot;https://gist.github.com/ardavast/4b7b2d337505569d6730416dee691f19&quot; rel=&quot;nofollow noreferrer&quot;&gt;phase_diff3.grc&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/6xNAG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6xNAG.png&quot; alt=&quot;phase_diff3.grc.png&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if I change my original flowgraph to look like this - it works exactly as expected, and it produces the effect that was described in the lecture slides: &lt;a href=&quot;https://gist.github.com/ardavast/0fb52b541791829527d49e13a6116e32&quot; rel=&quot;nofollow noreferrer&quot;&gt;loiq2.grc&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/YuqHL.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YuqHL.png&quot; alt=&quot;loiq2.grc.png&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10631" LastActivityDate="2020-02-23T17:21:19.903" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16151" PostTypeId="1" AcceptedAnswerId="16153" CreationDate="2020-02-23T17:52:22.817" Score="3" ViewCount="58" Body="&lt;p&gt;On average, is there a chart, or formula, which shows an expected signal attenuation due to the elevation angle to the satellite's position?  I understand that range (distance) is also going to affect the signal path, so in order to simplify the problem, consider this in the context of a LEO circular orbit OSCAR, or, the ISS, where the height above the earth is very near unchanging, and the only thing changing the signal strength is the elevation angle.  (Assume also the optimal antenna orientation and polarization).  Yes, of course, a low elevation angle typically means the bird is further away, but what I am looking for is the effect of the signal needing to travel through much more atmosphere as the elevation angle is further from the zenith, and closer to the horizon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When such a chart or formula is then combined with losses due to distance, the hope is a result that is fairly reliable for predicting signal path strength.  I imagine height above the earth's surface is also very important. since, for example, a signal from Mars is not going to be changing much in strength due to a change in distance on the same day, compared to the atmospheric attenuation at the zenith compared to at 5 degrees above the horizon.  This is why I specified the context of a LEO OSCAR in a circular orbit, or the ISS (ARISS).  In such cases, all else being equal and optimal, the signal strength will be more greatly attenuated if it has to travel through  more atmosphere because of a low elevation angle.  So the question is, &lt;em&gt;by how much, based on the elevation angle (and band)?&lt;/em&gt;, and, &lt;em&gt;is there a chart or formula for predicting this attentuation, based on elevation angle (and band)?&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="15083" LastEditorUserId="15083" LastEditDate="2020-02-23T18:21:48.763" LastActivityDate="2020-02-24T02:13:09.410" Title="2 meter and 70cm OSCAR expected signal attenuation by topocentric elevation angle, chart?" Tags="&lt;satellites&gt;&lt;path-loss&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16152" PostTypeId="1" AcceptedAnswerId="16180" CreationDate="2020-02-24T01:00:11.470" Score="4" ViewCount="178" Body="&lt;p&gt;My favorite receiver used for 40 m AM broadcasts has a cracked valve, but the valve type normally printed on the glass has rubbed away. Can anyone tell me what the numbers for this valve are ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio is mid - late 40's, made in Australia and has no brand or model on it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The valve is the one audio output valve in the radio.&#xA;The valve has &quot;Philips Miniwatt Australia&quot; printed on the black base.&#xA;You can just see the crack in the 3rd picture at the lower left of the valve glass.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Clues are that it has 7 pins and they all seem connected when you look inside so 2 for the heater and 5 left over probably makes it a Pentode. CORRECTON, -&gt; there are 7 pins but only 6 pins are connected, so i'm not sure if it is a pentode now. - It's a Tetrode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The heater voltage is : 6  VAC.&#xA;The cathode resistor is : 240 ohms.&#xA;The G1 resistor is : 543 k ohms&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That should narrow it down a bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See the pictures of the radio, chassis and valve.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can see how clean the glass on the front dial is, that took a while to get it like that, i hardly ever clean the valves like that any more.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/miSPt.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/miSPt.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Zikuc.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Zikuc.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/c5Q0b.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/c5Q0b.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/v7Nvu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/v7Nvu.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/4sasc.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4sasc.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/79k29.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/79k29.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-02-28T22:19:58.737" LastActivityDate="2020-03-02T01:26:29.997" Title="Identification of valve" Tags="&lt;electronics&gt;&lt;repair&gt;&lt;vacuum-tubes&gt;" AnswerCount="1" CommentCount="21" ContentLicense="CC BY-SA 4.0" />
  <row Id="16153" PostTypeId="2" ParentId="16151" CreationDate="2020-02-24T02:13:09.410" Score="5" Body="&lt;p&gt;It's close enough to zero at 2m and 70cm that I wouldn't bother computing it. Judging by &lt;a href=&quot;https://www.itu.int/rec/R-REC-P.676-12-201908-I/en&quot; rel=&quot;noreferrer&quot;&gt;ITU-R P.676&lt;/a&gt; the attenuation due to the atmosphere is less than 0.01 dB/km for all frequencies below 1 GHz, and the contribution of water vapor is negligible below 3 GHz. Figure 6 shows that the attenuation at the zenith is 0.03 dB at 1 GHz, and equation 28 says that for elevations between 5 and 90 degrees, it's valid to get the path attenuation by just dividing the zenith attenuation by the sine of the elevation angle. That gives a loss of about 0.35 dB at 5°. So the difference in atmospheric loss between the satellite being straight up and almost on the horizon is about 0.3dB, but the difference in free-space loss due to distance is more than 10dB. &lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-02-24T02:13:09.410" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16155" PostTypeId="1" CreationDate="2020-02-24T19:33:07.627" Score="9" ViewCount="170" Body="&lt;p&gt;I solely learned to copy cw via a computer program using the Koch - method&#xA;(&lt;a href=&quot;http://f6dqm.free.fr/soft/cwplayer/en/cwplayer.htm&quot; rel=&quot;noreferrer&quot;&gt;http://f6dqm.free.fr/soft/cwplayer/en/cwplayer.htm&lt;/a&gt;)&#xA;I never learned how to send and if it is no big disadvantage, I would prefer to learn this at the end, when I am comfortable with copying. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I listen and write down exercises with 15wpm (standard spacing) I get a bit over 90% correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My problems:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;On lower speeds, I get even 95% right, but I am not able to pass the cw - test that requires not more than four faults within three minutes on speed 12 wpm. Even with 10 wpm I can't make it.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I am far away from copying in my head. Even with 10 wpm I catch not more than 30% of the letters. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;My final aim is a speed of 20 to 25 wpm. I could continue like in the past, each time I reach 90 - 95% to increase the speed... But it took me very long to reach 15 wpm and I am still not feeling &quot;secure&quot;. Currently I have doubts whether increasing speed is wise for improving my cw-copy-skills in general.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What would you recommend as a next step?&lt;/p&gt;&#xA;" OwnerUserId="15039" LastActivityDate="2020-02-25T23:15:47.270" Title="I can copy 15wpm how to to continue?" Tags="&lt;cw&gt;" AnswerCount="5" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16156" PostTypeId="2" ParentId="16155" CreationDate="2020-02-24T20:08:42.380" Score="1" Body="&lt;p&gt;&lt;em&gt;The Art &amp;amp; Skill of Radio Telegraphy&lt;/em&gt; by N0HFF is available as &lt;a href=&quot;https://www.google.com/search?q=the+art+and+skill+of+radio+telegraphy&quot; rel=&quot;nofollow noreferrer&quot;&gt;a PDF download&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;That's what I highly recommend as a next step&lt;/strong&gt;. I'm not posting an excerpt in this answer because it would probably exceed the character limit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It was so good and so highly motivating that I had my wife print and bind it. I found that it is not necessary to read the entire book to benefit from it.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-02-24T20:08:42.380" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16157" PostTypeId="2" ParentId="16155" CreationDate="2020-02-25T04:27:02.520" Score="2" Body="&lt;p&gt;Some random untested ideas:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Don't get stuck using just standard spacing/timing.  Variation (data augmentation or novelty) proves effective for both machine learning and human learning. It's also more realistic to what you will hear on the air.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Use Farnsworth timing, with the character WPM set at different speeds each session, but always at least at or slightly above your target goal WPM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then change the letter and word spacing a few times per session, from really easy to full speed (non-Farnsworth).  Don't just copy stuff you feel secure copying, occasionally try speeds where you can only copy 50%.  Maybe note the characters you always fail to copy fast, and at the next session try a set of mostly those characters at an extra super slow spacing to regenerate your confidence.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-02-25T23:15:47.270" LastActivityDate="2020-02-25T23:15:47.270" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16158" PostTypeId="2" ParentId="15979" CreationDate="2020-02-25T05:22:48.720" Score="3" Body="&lt;p&gt;Since there was no such repeater listing out there, I started my own database:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://hearham.com/repeaters&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hearham.com/repeaters&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a bonus, there is a service to comment on, and favorite to get status notifications about a repeater, something I haven't seen in other listings. Also, a topo map showing where each of the nearby repeaters is, is now available in &lt;a href=&quot;https://sourceforge.net/projects/repeater-start/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Repeater-START&lt;/a&gt; for Linux.&lt;/p&gt;&#xA;" OwnerUserId="14201" LastEditorUserId="14201" LastEditDate="2020-03-18T14:54:17.500" LastActivityDate="2020-03-18T14:54:17.500" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16161" PostTypeId="2" ParentId="16155" CreationDate="2020-02-25T12:17:11.603" Score="4" Body="&lt;p&gt;I've been working in CW only for about two months. But during this time I made over 200 QSOs (I'm on the air only during weekends) and made a progress from 15 WPM to 18 WPM. Thus I hope my advice might be useful.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you reached 15 WPM, it's time to start making your first QSOs. The first few will probably be a little bit embarrassing, but that's OK. Don't think too much about it and continue to work in CW. When calling CQ, use &lt;a href=&quot;https://www.iaru-r1.org/wp-content/uploads/2019/08/hf_r1_bandplan.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRS frequencies&lt;/a&gt;, around 14.055 MHz and (unofficial) 7.035 MHz. (At least for IARU Region 1, find a corresponding file for you region if necessary). Don't be afraid to make mistakes. When you are using 15 WPM everyone realizes that you are new to CW. Don't be shy to ask for QRS when necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are different opinions on whether you should start with a straight key or a modern one-paddle or two-paddle keys. Personally I choose a two-paddle key. uniHAM UNI-730A is not a bad option to start with. It's not the best key on the market, but it works quite well for a price. You can learn to transmit at 15 WPM with it in no time, and it doesn't create an unnecessary stress on your wrist (I'm a software developer and I already have some issues with my wrists). Later you can learn to use straight key as well. It will be much easier when you know how proper CW sounds like.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Soon you will notice that your current speed is not challenging anymore. Personally I start to notice it when I start losing dots in the beginning of the letters, because I expect that they should be transmitted faster. This is a good sign that it's time to increase the speed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are interested, you can also read my &lt;a href=&quot;https://eax.me/morse-code/&quot; rel=&quot;nofollow noreferrer&quot;&gt;blog post&lt;/a&gt; on how I learned CW. It's in Russian, but I believe Google Translate should manage.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-02-25T12:17:11.603" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16162" PostTypeId="1" AcceptedAnswerId="16169" CreationDate="2020-02-25T12:35:31.647" Score="4" ViewCount="113" Body="&lt;p&gt;Recently I've read &lt;a href=&quot;https://www.qsl.net/ik0ygj/enu/index.html&quot; rel=&quot;noreferrer&quot;&gt;Zen And The Art Of Radiotelegraphy&lt;/a&gt; by Carlo Consoli, IK0YGJ. I must say, it's a great book, and as a new CW operator I've found plenty of useful information in it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What especially catched my attention was:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;This  freedom  of  manipulating  a  telegraph  key  produces  very &#xA;  interesting phenomena: the laughter, HI, for example, is not&#xA;  transmitted accurately H (four dots), followed with the proper spacing&#xA;  by the I (two dots), it but is transmitted as four-dots, a  light &#xA;  syncope,  a  dot,  another  syncope  and  a  final  dot.  The &#xA;  resulting  sound  is incredibly similar to that of a real laugh.  Once&#xA;  heard, it cannot be forgot.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Sadly I couldn't find a recording of a proper HIHI sound, nor I encountered it on the air. Maybe someone knows a video on YouTube that demonstrates how HIHI supposed to sound? Or, if it's not too much trouble, could you please record this sound?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-02-25T22:59:11.757" Title="How proper HIHI sounds like?" Tags="&lt;cw&gt;&lt;jargon&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16163" PostTypeId="1" CreationDate="2020-02-25T13:06:18.900" Score="6" ViewCount="163" Body="&lt;p&gt;I want to extend functionality of some open-source programs which decode APT and LRPT images (wxapt and glrpt). More specifically I want to add possibility to overlay geographical data such as land borders, administrative borders, rivers etc on the resulting images after rectification. The same functionality exists in WXtoIMG software and it works only if you have updated Keplers list. I assume that received APT data (e. g. recorded with GQRX and then processes in Audacity) contains some timestamps (or may be GPS coordinates) and smart programs like WXtoIMG are possible to process this hidden metadata together with TLE data and draw geo objects in overlay.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However I can't find very much info about APT/LRPT protocols. The only thing that I found is that LRPT packets could contain APID 70 data which is satellite's onboard time. Does APT suggests the same data or I should rely on exact computer time and updated TLE?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another problem is that I can't figure out (yet) how to bind together timestamp info, TLE data and get geographical data for pixels. My suggestion is to find one basis point/pixel on my image which is my ground station (GPS coordinates for ground station are always available) and then, knowing rectified image dimensions and resolution, I could draw geographical data (for example from &lt;a href=&quot;https://gadm.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;GADM&lt;/a&gt;) in overlay. Is it right approach? I think I can catch moment when satellite transmits image line for my latitude (may be derive it from TLE parameters) but I don't know how to find longitude...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone suggest something?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT 1.&lt;/strong&gt; Here is my thoughts about how to perform pixel geotagging. Let's assume the following:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ukv48.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ukv48.png&quot; alt=&quot;flight scheme&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Let's take that satellite is passing from South to North at certain angle. It scans Earth surface and sends data as image lines with even interval. So at every time moment &lt;span class=&quot;math-container&quot;&gt;$t_i$&lt;/span&gt; we obtain a bunch of image lines, let's say that for time interval &lt;span class=&quot;math-container&quot;&gt;$\Delta t = t_{i+1}-t_i$&lt;/span&gt; we have four rows of pixels. This resolution should stay constant during satellite working cycle (I believe it's 4 km/px for NOAA and 1 km/px for Meteor-M series). After image rectification procedure we should get image with even pixel spacing so every pixel shift in image corresponds to the same distance shift in kilometers on Earth surface. Pixels which are nearest to the satellite's pass track projection (dashed red line with &quot;Flight direction&quot; label) will stay (almost) untouched during rectification. Knowing exact timestamps &lt;span class=&quot;math-container&quot;&gt;$t_i$&lt;/span&gt; and TLE data we can calculate latitude and longitude of satellite projection on Earth (green pixels on scheme). Then we can calculate latitude and longitude for every pixel in image (orange pixels) with respect to our basis pixels (satellite's projection) and map coordinates to them. After that we just take geographical objects for this area from database and draw borders, rivers etc by just mapping geo coordinates to pixel coordinates. Am i right in these suggestions?&lt;/p&gt;&#xA;" OwnerUserId="14179" LastEditorUserId="14179" LastEditDate="2020-02-27T11:28:19.710" LastActivityDate="2020-02-27T16:50:11.670" Title="APT/LRPT images geotagging" Tags="&lt;satellites&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16164" PostTypeId="2" ParentId="16163" CreationDate="2020-02-25T13:48:57.240" Score="3" Body="&lt;p&gt;First of all, I would like to applaud your desire to work on this project. I've been using both wxapt and glrpt before and having functionality you've described would be great.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not an expert in APT or LRPT but hopefully some information I have will help you a little. Firstly, there is a free e-book &lt;a href=&quot;http://www.sstv-handbook.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Image Communication on Short Waves&lt;/a&gt; by Martin Bruchanov, OK2MNM. If I remember correctly it has some details on APT. Also it worth trying to contact the author. Secondly, not a long time ago Andrew @dernasherbrezon wrote a complete LRPT decoder in Java. His &lt;a href=&quot;https://dernasherbrezon.com/posts/dsp-java/&quot; rel=&quot;nofollow noreferrer&quot;&gt;article&lt;/a&gt; is in Russian but I believe Google Translate should translate it quite well. Andrew seems to be very interested in decoding images from sattelites in general, it worth trying to e-mail him directly. Also you might find useful the article &lt;a href=&quot;http://jmfriedt.free.fr/glmf_meteor_eng.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Decoding digital weather satellite images: the LRPT protocol from Meteor-M2&lt;/a&gt; and the sources it references.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It might happen than nor APT or LRPT has any information that might help to draw a land borders on the image. In this case you can use the location of the receiver and the trajectory of the satellite to approximate which countries should be seen on the image. The information about borders, rivers etc is available in OpenStreetMap. Using edge detection algorithms might help to find shores, although if image contains little but clouds this approach might not work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case I wish you good luck with the project!&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-02-25T13:48:57.240" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16165" PostTypeId="2" ParentId="16163" CreationDate="2020-02-25T19:35:51.797" Score="4" Body="&lt;p&gt;Two resources that might be of use to you: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, &lt;a href=&quot;https://www1.ncdc.noaa.gov/pub/data/satellite/publications/podguides/N-15%20thru%20N-19/pdf/0.0%20NOAA%20KLM%20Users%20Guide.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;NOAA KLM User's Guide&lt;/a&gt; Section 4.2, beginning on page 4-51 (PDF page 225) covers APT. Judging from figure 4.2.2.1, there is no absolute timing or positioning information included in the telemetry data; just some calibration values and the channel ID. The &quot;space and marker&quot; contains a 4-line marker every 1 minute (120 lines). The document doesn't specify what, if anything, the marker is synchronized to, but I would guess that the start of the minute marker corresponds to the start of the UTC minute&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, there is &lt;a href=&quot;https://apps.dtic.mil/dtic/tr/fulltext/u2/a216041.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Spatial Registration of TIROS-N Weather Satellite Data&lt;/a&gt;, a thesis from the Air Force Institute of Technology. This states (page 35) &quot;Minute markers are also included in four consecutive lines (two white, two black). While the time of each mark is not specified, limited observation found the start of each minute indistinguishable from the first white line in the four-line sequence&quot;, which confirms my guess. This means that you can use the computer clock to &lt;em&gt;roughly&lt;/em&gt; timestamp the image (so long as the computer is kept within 1 minute of accurate time, which isn't that hard), and use the minute marker from the received signal to refine that timestamp to pixel precision.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've only scanned the remainder of the thesis, but it looks like it contains all of the math needed to answer your second question — how to transform the satellite ephemeris, the time, and the pixel number within a line to a position on the earth.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-02-26T00:10:14.343" LastActivityDate="2020-02-26T00:10:14.343" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16166" PostTypeId="2" ParentId="16140" CreationDate="2020-02-25T20:24:24.890" Score="3" Body="&lt;p&gt;If the schematic doesn't show a separate audio signal ground, then the audio input ground is clearly meant to be connected to chassis ground.  The power supply ground is also not shown, which means that it too should be tied to chassis ground.  All the ground symbols in the schematic are chassis &lt;a href=&quot;https://en.wikipedia.org/wiki/Ground_(electricity)&quot; rel=&quot;nofollow noreferrer&quot;&gt;ground&lt;/a&gt;, rather than earth ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the circuit is an RF circuit, you should probably build it in a shielded enclosure (aka chassis), which would be the chassis ground.  The RF input and output connectors should be RF coaxial connectors, grounded to the chassis of course.  The enclosure should be connected to the station ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(A comment with essentially the same information as this answer was posted several days before.  This answer was posted mainly so that the question officially has an answer, in the hope that the question won't keep popping up again and again on the &quot;home&quot; page.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-02-25T20:24:24.890" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16167" PostTypeId="2" ParentId="16155" CreationDate="2020-02-25T21:18:27.380" Score="2" Body="&lt;p&gt;First, do learn how to send.  Learning to send is much easier than learning to copy.  One mistake I made when I was first starting was to send faster than I could copy, which is surprisingly easy to do with a straight key.  If you send faster than you can receive, then you risk the other operator sending at the same rate you are, which can lead to disaster.  (I terminated my very first DX QSO by switching off the rig in the middle of the QSO because the other op sent faster and faster, and I couldn't copy at all eventually.  What a memory!)  If you start with a keyer, then you won't have that problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I echo Aleksander's advice to start making QSOs, assuming that you're licensed to do so, and to not be shy about asking the other operator to QRS when necessary.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to learn to copy faster and better is to make QSOs.  Not only will your receiving speed increase naturally, but you'll also learn how to deal with noise and bad fists, which aren't as common these days as they were when I started.  By the way, I recommend not avoiding QSOs with operators with bad fists, once you learn to copy them; some of my most memorable QSOs (and favorite QSL cards) have been with old-timers whose fists weren't the greatest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another way to learn to copy faster is to teach yourself to &quot;throw away the pencil&quot;, as my Elmer put it, which means to learn how to copy in your head.  I taught myself how by listening to Morse code recordings &lt;a href=&quot;http://www.arrl.org/code-practice-files&quot; rel=&quot;nofollow noreferrer&quot;&gt;from the ARRL&lt;/a&gt; with no pencil handy, and just trying to copy in my head.  What is surprisingly effective is to listen to code that is faster than you can comfortably copy.  (I discovered an interesting thing when listening to these recordings in the car: when the sound source comes from several speakers, but the sound is all at a single frequency, then there are nodes, places where the sound is louder, and anti-nodes, places where the sound is weaker, which you can explore by moving your head around.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A fantastic way to practice copying call signs and numbers is to use &lt;a href=&quot;http://www.dxatlas.com/MorseRunner/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Morse Runner&lt;/a&gt;, the Morse code contest simulator by Alex Shovkoplyas, VE3NEA.  Thanks to Morse Runner I can copy contest QSOs much faster than I can copy ragchew QSOs.  (This too can lead to disaster in a contest, so be careful.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-02-25T21:18:27.380" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16168" PostTypeId="2" ParentId="16155" CreationDate="2020-02-25T21:48:23.110" Score="0" Body="&lt;p&gt;I know a dozen hams who have quickly learned to send and receive 20WPM CW using &lt;a href=&quot;http://www.morserino.info/morserino-32.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Morserino&lt;/a&gt;. The beauty of Morserino is that it uses &lt;em&gt;sending&lt;/em&gt; to reinforce &lt;em&gt;copying&lt;/em&gt; by completing the feedback loop in your brain. There are demonstration videos on YouTube. Looks to me like the fastest way to become &quot;on the air&quot; proficient.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-02-25T21:48:23.110" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16169" PostTypeId="2" ParentId="16162" CreationDate="2020-02-25T22:59:11.757" Score="4" Body="&lt;p&gt;People sending &lt;code&gt;HI&lt;/code&gt; tend to fall into two camps. Some people send a correct &lt;code&gt;HI&lt;/code&gt;, as if they learned that &lt;code&gt;HI&lt;/code&gt; means laughter, and they want to send that accurately at all times. The second camp learned by listening, and they tend to send something that sounds more like &lt;code&gt;HEE&lt;/code&gt;. This latter version is the one being described in the text you quoted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;code&gt;HEE&lt;/code&gt; version sounds more ‘playful’ than the &lt;code&gt;HI&lt;/code&gt; version, to my ears, and I think that was the original intention.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can find examples of this by listening to the bands - especially the lower bands such as 80m, where you can usually still find a good rag chew on CW between old-timers.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-02-25T22:59:11.757" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16170" PostTypeId="1" CreationDate="2020-02-26T15:13:25.383" Score="3" ViewCount="243" Body="&lt;p&gt;(sorry for my English)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm using the HDMI to VGA adapter on my pc, and receiving weather satellites on ~137 MHz with RTL-SDR V3. There was a problem: my VGA adapter creates a powerful signal, who pollutes the 137 MHz band, with carrier wave on 138.5 MHz.&lt;a href=&quot;https://i.stack.imgur.com/XJde6.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XJde6.jpg&quot; alt=&quot;VGA adapter interference&quot;&gt;&lt;/a&gt;&#xA;This signal receivable anywhere in the house. I tried to use VGA cable with ferrites and shielding, and shielded the VGA adapter with aluminum foil, but it did not give any result. If I connect SDR to another device, I still can receive this signal. The signal disappears when I unplugging VGA adapter or turning off pc. With VGA graphics card (respectively without VGA adapter), there was not any interference. What should I do to mitigate this interference?&lt;/p&gt;&#xA;" OwnerUserId="16498" LastActivityDate="2020-02-28T23:47:57.987" Title="HDMI to VGA adapter interference with 138.5 MHz carrier" Tags="&lt;rfi&gt;&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16171" PostTypeId="2" ParentId="16170" CreationDate="2020-02-26T15:36:41.760" Score="2" Body="&lt;p&gt;It sounds like you have two options:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Buy a new HDMI monitor&lt;/li&gt;&#xA;&lt;li&gt;Use a VGA card&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;You say it was fine when you used a VGA card. So why change?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounds like the HDMI-to-VGA adapter is a generator of much noise, especially in the band you need to use. To me, this means you have to remove it from the equation. Either get an HDMI monitor (these are kind of standard these days), or get a display card that has a VGA port. eBay should be full of those. Of course, I would recommend getting a digital monitor, because VGA is old and analogue, where HDMI is digital.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Heck, I remember using VGA cards over thirty years ago.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-02-26T15:36:41.760" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16172" PostTypeId="2" ParentId="16149" CreationDate="2020-02-26T16:05:36.393" Score="3" Body="&lt;p&gt;One of the problems with a superheterodyne design is you need two frequency generators: one for Tx that operates at the intended Tx frequency, and one that operates at (the intended Rx frequency plus-or-minus the IF).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As suggested by Brian K1LI in the comments, if you take the received signal and mix it with the intended receive frequency, you end up with ‘baseband’ out, and you just made a &lt;a href=&quot;https://en.wikipedia.org/wiki/Direct-conversion_receiver&quot; rel=&quot;nofollow noreferrer&quot;&gt;direct-conversion receiver&lt;/a&gt;. This can be made to work, but it’s probably trickier at FM than it is for AM or even SSB (it would be a nightmare for CW!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I am confused as to why you would have a superheterodyne receiver design and then skip the IF altogether.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EDIT:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I added in my comment below, I now understand that you actually are asking about how to bypass the whole idea of using an IF, thus creating a direct conversion receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’m not saying that this is a bad idea in itself, but if you read about the history of radio, you will see that the direct-conversion receiver was one of the earliest receiver designs, followed by the regenerative receiver. After that came the superheterodyne receiver, and then that became the standard for about a century.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While I’m not trying to discourage you from your design (it would be interesting to see how well it performs), I would take a lesson from history and have a look at &lt;em&gt;why&lt;/em&gt; the superheterodyne design was used for so long (and still is today).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has the advantage that you can have multiple bands in a single receiver, although you have to pick your first IF carefully for that, simply by having switched front-ends, and all the heavy lifting of the filtering etc. is done at the first IF, and that is the same for all bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has the advantage that demodulating more esoteric modes (such as FM, which requires more work than AM) is relatively straightforward at the last IF (which can be the same as the first IF in a single-conversion superheterodyne design) - a simple PLL will do the job nicely for demodulating FM, rather than having to have a much more complex PLL to demodulate at baseband.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only real disadvantage is that it requires two mixing stages and two local oscillators (although the IF oscillator is fixed, and in your diagram is implemented with a very simple crystal oscillator - so that’s just a couple of extra components).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So why did the superheterodyne design ‘win’? And effectively win for an entire century? Its advantages outweigh its disadvantages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Today, if you’re not going to make a superheterodyne receiver, it’s probably because you will do it in software. Because that is what will cause the demise of the superhet: the SDR.&lt;/p&gt;&#xA;" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2020-02-26T16:35:52.267" LastActivityDate="2020-02-26T16:35:52.267" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16173" PostTypeId="2" ParentId="15378" CreationDate="2020-02-26T18:00:02.713" Score="5" Body="&lt;p&gt;Found on the &lt;a href=&quot;https://jtdx.groups.io/g/main/message/6797?p=,,,20,0,0,0::relevance,,new+symbols,20,2,0,28993897&quot; rel=&quot;noreferrer&quot;&gt;JTDX groups.io&lt;/a&gt; (link won't work without login, unfortunately):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;sybmol • - this operator loaded his log into LoTW&lt;br&gt;&#xA;  symbol ° - this operator loaded his log into LoTW and this is Hint decode (FT8 AP or matched filter based decoder in JT65 JT9 T10 modes)&lt;br&gt;&#xA;  symbol * - Hint decode (FT8 AP or matched filter based decoder in JT65 JT9 T10 modes)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So the solid dot and the open dot both mean LoTW user. Star doesn't (it means the same thing that it does in wsjt-x).&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-02-26T18:00:02.713" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16174" PostTypeId="2" ParentId="16163" CreationDate="2020-02-27T16:44:12.670" Score="1" Body="&lt;p&gt;Overlay mapping to APT images is complicated by at least two factors:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Each scan line (0.25 seconds) is pre-distorted to &quot;approximate&quot; a linear surface rather than a spherical surface&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The earth rotates during a satellite pass (perhaps 15 minutes)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In addition to these two factors, some demodulators don't account for doppler shift, which adds a noticeable skew to an image. A Costa's loop AM demodulator phase-locks to the 2400 Hz carrier, which can solve this problem.&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;APT predistortion...&lt;br&gt;&#xA;NOAA's &lt;code&gt;NOAA KLM Users Guide&lt;/code&gt; shows how each transmitted APT horizontal scan line is pre-distorted so as to &quot;linearize&quot; the resulting image. It is crudely divided into ten segments, but your eye accepts the image to be sorta map-like (figure 4.2.3-1 APT Linearization):&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ASwwn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ASwwn.png&quot; alt=&quot;from NOAA KLM USERS GUIDE&quot;&gt;&lt;/a&gt;&#xA;&lt;br&gt;This figure refers to &quot;data points&quot;...these are HRPT 1 km pixels. So at the satellite sub-point in zone 1, each 4 km APT pixel is comprised of four averaged HRPT 1 km pixels.&lt;/p&gt;&#xA;" OwnerUserId="11132" LastEditorUserId="11132" LastEditDate="2020-02-27T16:50:11.670" LastActivityDate="2020-02-27T16:50:11.670" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16175" PostTypeId="2" ParentId="12508" CreationDate="2020-02-28T08:34:57.063" Score="1" Body="&lt;p&gt;I carry a resonant end fed half wave monoband antenna with matching stub (window line) for portable operations.  Its huge advantage is that I need not carry an antenna tuner. One less piece of electronics to carry along, one less point of fail, one less thing to break or get lost.  It works for me.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;End fed antennas are also easy to deploy.  I usually work 20 meters, a good daytime band.  I don't do portable at night.  It can hang easily from a tree or some other support.&lt;/p&gt;&#xA;" OwnerUserId="16506" LastActivityDate="2020-02-28T08:34:57.063" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16176" PostTypeId="2" ParentId="16170" CreationDate="2020-02-28T23:47:57.987" Score="0" Body="&lt;p&gt;I agree with Mr. Earle. Remove the VGA adapter and use what does not cause the interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides, in my experience, aluminum foil doesn't do very much for shielding. Copper or silver foil do better, but can be more costly and not readily available to you. I'm surprised the VGA cable with ferrite beads didn't help, or maybe just didn't help enough. If you have some extra snap-on ferrite beads, you might try adding one (or a few) more before running out to buy a new monitor. In one interference issue at my QTH, I had to use 5, yes five, snap-on ferrites to squelch the noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, while I do like to recycle old stuff (like your VGA monitor), sometimes it is better to upgrade. In this case, the HDMI monitor will also save electricity over time. Will it be a lot? It depends on what you're using now and what HDMI monitor you may choose to obtain - but probably, yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You took the right steps to identify the problem. Now it is up to you, based on options presented, to decide what is best for you (financially, or otherwise) to get rid of the noise.&lt;/p&gt;&#xA;" OwnerUserId="16511" LastActivityDate="2020-02-28T23:47:57.987" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16178" PostTypeId="1" AcceptedAnswerId="16185" CreationDate="2020-02-29T22:52:43.030" Score="1" ViewCount="123" Body="&lt;p&gt;When I tune on 40 m (7.074 MHz USB as test frequency for there's FT8) and turn on my PC with a monitor that's 144 Hz refresh rate and has freesync on, it starts to make noise and makes signals almost impossible to listen.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Measuring the audio output with a simple audio spectrum analyzer on the pc, the noise is around 1.5 kHz and whenever I change the monitor's refresh rate (59, 60, 100 and 120 Hz are the other possible options) the noise changes frequency (729-772 Hz) and is lower, and when I turn off freesync on the monitor the noise ceases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I noticed that if I put my hand touching or almost touching the screen, the noise becomes a bit louder and so does the audio analyzer on the specified frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can this noise be eliminated?&lt;/p&gt;&#xA;" OwnerUserId="16500" LastEditorUserId="8717" LastEditDate="2020-03-03T03:56:05.377" LastActivityDate="2020-03-03T03:56:05.377" Title="144Hz monitor with freesync noise on 40m" Tags="&lt;hf&gt;&lt;rfi&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16179" PostTypeId="1" AcceptedAnswerId="16182" CreationDate="2020-03-01T01:56:35.223" Score="5" ViewCount="154" Body="&lt;p&gt;In &lt;a href=&quot;https://earthscience.stackexchange.com/questions/19349/earths-electricity#comment43006_19349&quot;&gt;this comment&lt;/a&gt; in Earth Science SE I've said:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;This is a really cool question! I remember (a long time ago) reading about electromagnetic waves inside conductive soil &lt;em&gt;that travelled near but below the Earth's surface&lt;/em&gt; for at least a few miles, and remember seeing a circuit for such a receiver in a book about ham radio circuits.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'm thinking of a paperback book from the late 1960's or early 1970's white cover with a title perhaps something roughly like &lt;em&gt;75 circuits for amateur radio operators.&lt;/em&gt; Just for example one was &lt;em&gt;A Watt and a Half on 80 Meters&lt;/em&gt;. Circuits were mostly if not completely using transistors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The circuit I'm thinking of was for receiving possible signals that were propagating just under the surface of the Earth. It wasn't saying that this was necessarily &quot;a thing&quot; but did suggest it might be fun to try.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Does this circuit and/or book sound familliar? Any recommendations how to track it down? &lt;/li&gt;&#xA;&lt;li&gt;Was this actually ever &quot;a thing&quot;? Did people try this? If so, roughly what frequencies might have been looked at?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="8643" LastEditorUserId="8717" LastEditDate="2020-03-01T21:26:26.280" LastActivityDate="2020-03-01T21:55:34.730" Title="Looking for a book that contained a circuit for receiving (literally) underground amateur radio transmissions" Tags="&lt;receiver&gt;&lt;propagation&gt;&lt;equipment-design&gt;&lt;history&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16180" PostTypeId="2" ParentId="16152" CreationDate="2020-03-01T11:33:27.773" Score="3" Body="&lt;p&gt;Are you sure that you are correct in the comments about your pin 2 and pin 7? (The conventional numbering for these tubes is as in your drawing, so conventionally pins 8 and 5).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look very carefully or use an ohm meter you might find that your pin2 is actually the cathode and your pin8 is G1, as in your drawing of the 6L6. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would be more normal for an octal beam pentode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the drawing is correct for your valve then it's likely a 6v6 (lower power but same pinouts as the 6L6).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a 10 watt max audio output tube used in lots of radios from that era.&#xA;Grid 3 is internally connected to the cathode, so doesn't have a pin.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Max rating currents of 45 mA anode + 5mA G2 would give max 12v across the 240 ohm cathode resistor, approximately right for self biased class A1 operation (6v6 has -12.5v G1 cutoff voltage). &#xA;Should be probably sitting around 5 or 6v across the cathode resistor at no signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd give a 6v6 a go if the pinouts are correct, check the quiescent anode and G2 currents (by measuring cathode voltage, I'd expect somewhere around 1/2 max or less) and that the peaks never exceed the max ratings. If there's any distortion find out why. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Capacitors, particularly electrolytics, can fail or change value in sets of this age so worth checking they are good where possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your pinout description in the comments is actually correct then it's a valve I'm not familiar with, sorry.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck.&lt;/p&gt;&#xA;" OwnerUserId="9531" LastEditorUserId="9531" LastEditDate="2020-03-02T01:26:29.997" LastActivityDate="2020-03-02T01:26:29.997" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16181" PostTypeId="2" ParentId="12508" CreationDate="2020-03-01T15:34:03.313" Score="4" Body="&lt;h1&gt;Bandwidth&lt;/h1&gt;&#xA;&lt;p&gt;&lt;strong&gt;Non-resonant antennas&lt;/strong&gt; typically have a high input reactance &lt;span class=&quot;math-container&quot;&gt;$X_\text{in}$&lt;/span&gt;.&#xA;This results in a higher loaded &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; and, by consequence, a reduced bandwidth &lt;span class=&quot;math-container&quot;&gt;$BW$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$${Q_\text{loaded}\uparrow}\equiv\frac{X_\text{in}\uparrow}{R_\text{in}+R_\text{source}}\quad\textrm{and}\quad Q_\text{loaded}=\frac{f_\text{res}}{BW}\quad\Rightarrow\quad{BW\downarrow}\,=\frac{f_\text{res}}{Q_\text{loaded}\uparrow}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;However, for &lt;strong&gt;extremely short, active receiving antennas&lt;/strong&gt; this does not matter as these are matched against an extremely high load impedance of a MOSFET RF amplifier. In this case, the loaded &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; hardly changes.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$${Q_\text{loaded}}\equiv\frac{X_\text{in}\uparrow\uparrow}{R_\text{in}+R_\text{load}\uparrow\uparrow}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Resonant off-center fed dipole (OCFD) antennas&lt;/strong&gt; exploit this effect by being fed at a higher input resistance &lt;span class=&quot;math-container&quot;&gt;$R_\text{in}$&lt;/span&gt; from a source with a higher internal resistance &lt;span class=&quot;math-container&quot;&gt;$R_\text{source}$&lt;/span&gt;. Consequently, OCFDs achieve much broader bandwidths at their fundamental resonant frequency than their center-fed counterparts.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$${Q_\text{loaded}\downarrow}\equiv\frac{X_\text{in}}{R_\text{in}\uparrow+R_\text{source}\uparrow}\quad\textrm{and}\quad Q_\text{loaded}=\frac{f_\text{res}}{BW}\quad\Rightarrow\quad{BW\uparrow}\,=\frac{f_\text{res}}{Q_\text{loaded}\downarrow}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;For example, here is a graph of the 80m VSWR bandwidth of &lt;a href=&quot;https://hamwaves.com/cl-ocfd/en/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;my multiband CL-OCFD&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.imgur.com/THtZDbW.png&quot; alt=&quot;ON4AA CL-OCFD 80m VSWR bandwidth&quot; /&gt;&lt;/p&gt;&#xA;" OwnerUserId="250" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2020-03-02T12:25:44.347" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16182" PostTypeId="2" ParentId="16179" CreationDate="2020-03-01T20:41:36.633" Score="7" Body="&lt;p&gt;&lt;strong&gt;Yes, this most certainly &lt;em&gt;was&lt;/em&gt; a thing, and people actually did it.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This type of communication has been done at &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Extremely_low_frequency&quot; rel=&quot;noreferrer&quot;&gt;ELF frequencies&lt;/a&gt; in the 3-30 kHz range. Their linear amplifiers were ordinary Hi-Fi audio amps. &lt;br&gt;I don't know if &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Low_frequency&quot; rel=&quot;noreferrer&quot;&gt;LF frequencies&lt;/a&gt; higher than that are useful for that, but the hams on the 2200m band (137 KHz) use above-ground antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A lot of ham stations used those frequencies during WWII when amateur radio was prohibited. They transmitted and received signals by using two ground rods as widely separated as possible. I used to have an old amateur radio magazine that described this in detail, along with limited distance &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Carrier_current&quot; rel=&quot;noreferrer&quot;&gt;carrier-current communications&lt;/a&gt; through power lines (&lt;em&gt;not recommended!&lt;/em&gt;).&lt;b&gt;*&lt;/b&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may very well be able to find radio and electronics magazine articles about this at &lt;a href=&quot;https://www.americanradiohistory.com/&quot; rel=&quot;noreferrer&quot;&gt;americanradiohistory.com&lt;/a&gt;. For example, I found a complete index to all the articles ever published in W1HR's (SK) &lt;em&gt;Ham Radio&lt;/em&gt; magazine, and then downloaded the PDF of the magazine that I wanted from that site. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some other related Wikipedia articles:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/Project_Sanguine#How_ELF_communication_works&quot; rel=&quot;noreferrer&quot;&gt;How ELF communication works&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/Through-the-earth_mine_communications&quot; rel=&quot;noreferrer&quot;&gt;Through-the-earth mine communications&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5701283/&quot; rel=&quot;noreferrer&quot;&gt;Simulation and Measurement of Through-the-Earth, Extremely Low-Frequency Signals Using Copper-Clad Steel Ground Rods&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://www.eevblog.com/forum/projects/how-can-i-communicate-with-elfvlf-ground-waves/&quot; rel=&quot;noreferrer&quot;&gt;How can I communicate with ELF/VLF ground waves?&lt;/a&gt;. &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://electronics.stackexchange.com/questions/81584/can-earth-be-used-for-communication&quot;&gt;https://electronics.stackexchange.com/questions/81584/can-earth-be-used-for-communication&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://sites.google.com/site/g3xbmqrp3/antennas/earth-electrode-antennas&quot; rel=&quot;noreferrer&quot;&gt;Earth electrode antennas&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://sites.google.com/site/sub9khz/&quot; rel=&quot;noreferrer&quot;&gt;Sub 9kHz Amateur Radio&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://sites.google.com/site/sub9khz/earthmode&quot; rel=&quot;noreferrer&quot;&gt;VLF Using Earth Mode&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://sites.google.com/site/sub9khz/earthmode/vlf-xbm-blog&quot; rel=&quot;noreferrer&quot;&gt;G3XBM Earth Mode Blog&lt;/a&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;&lt;b&gt;*&lt;/b&gt; It might have been an old QST, and ARRL members have free access to all the QSTs ever published. The ARRL's TIS (Technical Information Service) may be able to help you. If you are not an ARRL member, you can buy printed individual articles from them at a reasonable cost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.americanradiohistory.com/QST.htm&quot; rel=&quot;noreferrer&quot;&gt;Older QST magazines&lt;/a&gt; can be downloaded from americanradiohistory.com here.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-03-01T21:55:34.730" LastActivityDate="2020-03-01T21:55:34.730" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16184" PostTypeId="2" ParentId="14792" CreationDate="2020-03-02T05:57:33.727" Score="4" Body="&lt;p&gt;Here are the fields for AM_conductivity_m3.seq_.txt and AM_conductivity_m3hw.seq_.txt files:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;4001   21.5750  158.2760   21.5840  158.1900    2.00 5000.00&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Fields, left to right:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The number of the line segment.&lt;/li&gt;&#xA;&lt;li&gt;The north latitude of the start of the segment.&lt;/li&gt;&#xA;&lt;li&gt;The west longitude of the start of the segment.&lt;/li&gt;&#xA;&lt;li&gt;The north latitude of the end of the segment.&lt;/li&gt;&#xA;&lt;li&gt;The west longitude of the end of the segment.&lt;/li&gt;&#xA;&lt;li&gt;The immediate ground conductivity east of this segment (north conductivity for exact east-west lines) in mS/m.&lt;/li&gt;&#xA;&lt;li&gt;The immediate ground conductivity west of this segment (south conductivity for exact east-west lines) in mS/m.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I think I also understand the 9999 lines:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;9999  466.0000   19.0000  160.0000   24.0000  152.00   98.00&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Fields, left to right:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The number 9999 indicates the start of a region.&lt;/li&gt;&#xA;&lt;li&gt;The number of records (excluding the 9999) for that region.&lt;/li&gt;&#xA;&lt;li&gt;The north latitude of the lower left corner of a box bounding the region.&lt;/li&gt;&#xA;&lt;li&gt;The west longitude of the lower left corner of a box bounding the region.&lt;/li&gt;&#xA;&lt;li&gt;The north latitude of the upper right corner of a box bounding the region.&lt;/li&gt;&#xA;&lt;li&gt;The west longitude of the upper right corner of a box bounding the region.&lt;/li&gt;&#xA;&lt;li&gt;The index number of the region (1.00, 2.00, 3.00...etc.). The file AM_conductivity_m3.seq_.txt contains regions 1-97, and the Hawaii file AM_conductivity_m3hw.seq_.txt has region 98.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Just for completeness, 9998:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;9998    1.0000    1.0000    1.0000    1.0000    1.00    1.00&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;9998 is indeed an end-of-file, with dummy values of 1 in all fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are the fields for AM_conductivity_r2.seq_.txt file:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;  11   2  5000.0    1.0  BROCK ISLAND&#xA;  77.873115.027  77.905115.060  77.930115.181  77.935115.192  77.942115.126&#xA;  77.940115.071    .000   .000    .000   .000    .000   .000    .000   .000&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Region number.&lt;/li&gt;&#xA;&lt;li&gt;Number of following lines containing points for that region.&lt;/li&gt;&#xA;&lt;li&gt;Conductivity on one side of the line defined by the points (mS/m).&lt;/li&gt;&#xA;&lt;li&gt;Conductivity on the other side of the line defined by the points (mS/m).&lt;/li&gt;&#xA;&lt;li&gt;Name of the region.&lt;/li&gt;&#xA;&lt;li&gt;List of points in XX.XXX north latitude, YY.YYY west longitude. (So 77.101120.133 means 77.101 N, 120.133 W.) Points with value .000 should be ignored. Negative values are S or E.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2020-03-02T06:40:58.040" LastActivityDate="2020-03-02T06:40:58.040" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16185" PostTypeId="2" ParentId="16178" CreationDate="2020-03-03T03:40:37.747" Score="0" Body="&lt;p&gt;It sounds very much to me like you should turn off freesync, and only turn it on when you actually need it (while playing games, presumably), at which point you probably won't be playing radio anyway - so it will have little effect.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-03-03T03:40:37.747" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16186" PostTypeId="1" CreationDate="2020-03-03T12:47:23.517" Score="2" ViewCount="50" Body="&lt;p&gt;Their performance differences may be less than sometimes expected.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-03-03T12:47:23.517" Title="How Do Ground-Mounted Verticals Compare to Elevated Verticals?" Tags="&lt;vertical-antenna&gt;&lt;radial&gt;&lt;counterpoise&gt;&lt;buried&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2020-03-11T13:26:49.163" ContentLicense="CC BY-SA 4.0" />
  <row Id="16187" PostTypeId="2" ParentId="16186" CreationDate="2020-03-03T12:47:23.517" Score="1" Body="&lt;p&gt;Below is a graphic comparing some of the operational parameters of ground-mounted and elevated vertical radiators for the 40-meter band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Their performance when installed at sites with relatively poor Earth conductivity is fairly similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bcGuB.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bcGuB.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-03-03T12:47:23.517" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16188" PostTypeId="2" ParentId="14674" CreationDate="2020-03-03T13:18:08.547" Score="3" Body="&lt;p&gt;An interesting question. Not sure I can properly answer it but I'll contribute what I know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;AM modulation methods&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Changing the RF output tube plate voltage was a very common way of producing AM when I was learning about ham radio in the 1960s. It was usually achieved by using a modulation transformer driven by an audio amp of the same output power as the unmodulated RF carrier, and should give symmetrical upwards and downwards modulation.&#xA;This works extremely well with a final RF amp operating in the simple and efficient class C mode. There are other methods that eliminate the transformer but they have various disadvantages.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem with modulating an earlier stage is that the following RF stages must be linear amplifiers (less efficient, more difficult to achieve) or the transmission becomes spread across the spectrum in a very undesirable way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the rising popularity of SSB, where the SSB signal is produced at a low level and then amplified to output power using linear amplifier stages, transmitters already had the linear amp, so AM could be produced in a similar way with no extra complication.&#xA;So your statement &quot;I don't see plate modulation used much in radio circuits I've found&quot;, which was slightly surprising to me, might be the result of linear amplifiers becoming common... &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Magnetic Amplifiers&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A magnetic amplifier uses the change in inductance that occurs when an inductor's core is magnetically saturated (with a relatively small DC current through a high number of turns on the same core) to control an AC current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This works because the inductor (L1) is designed to have high impedance at the frequency of the current that it is required to control when no control current is flowing, and low impedance if sufficient DC control current is flowing. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Due to the use of a core material with the right saturation characteristics it is possible to reduce or remove the magnetic effect of the core by passing a DC control current through a second winding and progressively saturating the core, so that the core contributes less and less to the inductance of L1. This lowers the inductance of L1 and therefore the impedance to the controlled ac. The resistance of L1 to DC is not changed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several ways to stop induced emf from the (controlled) ac current from feeding back into the control circuit, all involving 2 magnetic fields or 2 emfs cancelling each other&lt;br&gt;&#xA;e.g. 2 identical magnetically separate saturable core inductors with the control windings in series and oppositely phased.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For in depth information about mag amps to control RF see the (pdf) thesis submitted by  E. W. Steffen, Jr. Lieutenant Commander, United States Navy in 1948, found at &lt;a href=&quot;https://calhoun.nps.edu/handle/10945/31621&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://calhoun.nps.edu/handle/10945/31621&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Controlling RF output amplitude&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I understand it is possible to use a mag amp to vary (at audio frequencies) the output power of an RF output stage. This requires a magnetic amplifier that can control the RF current flowing through the anode circuit and/or the power being coupled to the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This will present a varying anode load impedance which could cause other complications (e.g. instability) if not done carefully.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would guess that placing L1 in the cathode circuit might also be worth a bit of good old amateur radio experimentation. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The magnetic amp would not be able to supply extra energy to the RF output (as a transformer coupled modulator can) so it would need to be carefully set up if symmetrical upwards/ downwards modulation is to be achieved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the disadvantages of this modulation method is noted as the inefficiency due to losses in the core.&#xA;Availability of suitable core material to work effectively at the carrier frequency limits the maximum useful operating frequency, but mag amps have been used to modulate high power &lt;strong&gt;long wave&lt;/strong&gt; transmissions in the past (&lt;a href=&quot;https://en.wikipedia.org/wiki/Magnetic_amplifier#Applications&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Magnetic_amplifier#Applications&lt;/a&gt;). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With robust high power solid state devices becoming available and cheap the advantages of mag amps (reliability, robustness, high voltage/current/power handling, good isolation) have diminished and the disadvantages (bulk, weight, cost) have comparatively increased, so it seems it would not be a competitive method of modulating a final. &lt;/p&gt;&#xA;" OwnerUserId="9531" LastActivityDate="2020-03-03T13:18:08.547" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16189" PostTypeId="1" AcceptedAnswerId="16191" CreationDate="2020-03-03T13:46:31.763" Score="10" ViewCount="5102" Body="&lt;p&gt;I've been tasked to help update my organization's emergency contingencies and ham radios were brought up. We provide residential services to the mentally handicapped and we are looking at ways to make sure the staffed houses can talk to each other as well as the administration team in case all other forms of communication were down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've just started researching the subject and I'm a bit confused as to what qualifies as &quot;commercial&quot; use under the statues. We &lt;em&gt;are&lt;/em&gt; providing services to the community, but we're a non-profit, so I'm unsure if that changes things. Also, would we need to have each house have someone licensed or just the centralized point of contact on the administrative side (which would likely be me)?&lt;/p&gt;&#xA;" OwnerUserId="16528" LastEditorUserId="366" LastEditDate="2020-03-04T14:48:55.887" LastActivityDate="2020-03-05T02:22:42.187" Title="Is it legal for a non-profit to use ham radios for emergency purposes?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;" AnswerCount="3" CommentCount="11" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16190" PostTypeId="2" ParentId="16189" CreationDate="2020-03-03T13:58:33.623" Score="13" Body="&lt;p&gt;As I understand it, it's legal under FCC rules for &lt;em&gt;anyone&lt;/em&gt;, licensed or not, to use &lt;em&gt;any&lt;/em&gt; frequency or mode of radio communication as necessary in an emergency.  This includes, but is not limited to, police/fire/EMS radios, CB, ham (even tuned outside legal ham bands, if the hardware has the capability), using voice in digital-only or CW-only sub-bands, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, a key to emergency preparedness is &lt;em&gt;practice&lt;/em&gt; -- and since your practice isn't a real emergency, anyone transmitting during a practice scenario must be properly licensed and using legal equipment and permitted bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the case you describe, I don't see that your goal is different from S&amp;amp;R groups, run/bicycle road race groups, and others who routinely either enlist local hams for their event communications (unquestionably legal, as long as the event isn't a business operation), or go through the process of licensing their own members.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Technician licenses are surprisingly easy and cheap to earn, and the bands that permit Technician licensees to use voice have convenient repeaters available to ensure adequate communication range.  As long as the communications aren't being used for the purposes of a for-profit business (no dispatching pizza deliveries or courier services, for instance), there should be no legal problems with licensed operators and certified equipment (which is also not very expensive; a 50 W dual-band mobile/base rig and antenna installation can run under $300 per station).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where you may run into a snag is the provision in Title 47, §97.113 about &quot;Communications, on a regular basis, which could reasonably be furnished alternatively through other radio services.&quot;  This &lt;em&gt;could&lt;/em&gt; be interpreted to mean that since your organization could obtain a business licensed communication setup (private/shared repeater and licensed-by-group station radios, like a taxi company dispatch system), that you are required to do so for actual business communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ambiguity here is that you're proposing to use these radios only during communication breakdowns (phone and cell service out, for instance).  I'd recommend starting by checking with your ARRL local rep (the local ham club can most likely put you in touch).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2020-03-03T15:51:36.720" LastActivityDate="2020-03-03T15:51:36.720" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16191" PostTypeId="2" ParentId="16189" CreationDate="2020-03-03T15:22:45.697" Score="19" Body="&lt;p&gt;In the United States, Under the Code of Federal Regulations, Title 47, §97.113 &quot;Prohibited transmissions&quot;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;(a) No amateur station shall transmit&lt;br&gt;&#xA;  (2) Communications for hire or for material compensation, direct or      indirect, paid or promised, except as otherwise provided in these rules;&lt;br&gt;&#xA;  (3) Communications in which the station licensee or control operator has a pecuniary interest, including communications on behalf of an employer.&lt;br&gt;&#xA;  (5) Communications, on a regular basis, which could reasonably be furnished alternatively through other radio services.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;(That quote omitted some parts for the sake of shortness; &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.113&quot; rel=&quot;noreferrer&quot;&gt;here's&lt;/a&gt; the whole thing.) So in the US the standard is not whether or not the business that you work for is a non-profit.  If you're being paid to use the radio, then you can't use amateur radio bands in ordinary usage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, §97.403 &quot;Safety of life and protection of property&quot; says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;No provision of these rules prevents the use by an amateur station of any means of radiocommunication at its disposal to provide essential communication needs in connection with the immediate safety of human life and immediate protection of property when normal communication systems are not available.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So it seems to me, a non-lawyer whose advice should be taken with a generous helping of salt, that if you're in the US, then you and your fellow employees couldn't use amateur radio for your employer under any circumstances outside of an emergency, except for emergency drills not to exceed one hour per week (see &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.113&quot; rel=&quot;noreferrer&quot;&gt;47 C.F.R § 97.113&lt;/a&gt; (a)(3)(i)).  But that being said, it might not be a bad idea for you and other employees to get ham radio licenses and radios, and create an emergency plan for when all other electronic forms of communication are down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll echo @ZeissIcon's advice to say that in an emergency, it's not enough to have a license and a radio.  You should also have plenty of practice, and you should regularly test the radios to make sure that they'll work when you need them.  So if you do decide to pursue ham radio for emergency communication, get buy-in from your fellow employees, and all of you use the radios to check into your local club's weekly net at a minimum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The American Radio Relay League has published some helpful guidelines on appropriate usage of amateur radio &lt;a href=&quot;http://www.arrl.org/files/media/News/ARRL%20appropriate%20use%20guidelines.pdf&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="16546" LastEditDate="2020-03-04T20:44:19.783" LastActivityDate="2020-03-04T20:44:19.783" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16192" PostTypeId="1" CreationDate="2020-03-03T16:32:12.200" Score="1" ViewCount="76" Body="&lt;p&gt;I want to know if one can upgrade the hardware chips/ the CPU/DSP inside police scanners to do Phase II.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know they cannot do Phase II due to hardware/software limits but if whistler can upgrade these other legacy scanners from RS and GRE to do DMR/NXDN and Phase II they can do it with this as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There has to be a way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whistler has chosen NOT to upgrade these models.  Now the PSR800 uses a DSP CPU combo of part numbers &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://wiki.radioreference.com/index.php/PSR-800&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wiki.radioreference.com/index.php/PSR-800&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;CPU:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.digikey.com/product-detail/en/renesas-electronics-america/M30626FHPGP-U5C/M30626FHPGP-U5C-ND/964955&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.digikey.com/product-detail/en/renesas-electronics-america/M30626FHPGP-U5C/M30626FHPGP-U5C-ND/964955&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;DSP:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.digikey.com/product-detail/en/TMS320VC5507PGE/296-17287-ND/680421&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.digikey.com/product-detail/en/TMS320VC5507PGE/296-17287-ND/680421&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Will these parts FIT into the Pro 106?  Are the pinouts the same?  What about the Reneasas flash loader?  What about any other AMBE chip?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.ytimg.com/vi/EASmyA6F29s/maxresdefault.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://i.ytimg.com/vi/EASmyA6F29s/maxresdefault.jpg&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TGID displayed is a Phase I only.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now I have used google, I have used that easier to read manual for all those radios, I have asked RR and Youtube and various HAMs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not looking to do SDR at this time. I know all about TP4 and Tapping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The programming in the radio is python based I think. &lt;/p&gt;&#xA;" OwnerUserId="16529" LastEditorUserId="8717" LastEditDate="2020-03-03T16:41:54.330" LastActivityDate="2020-04-02T17:01:55.187" Title="PSR500/Pro106/WS1040 Phase II Upgrade?" Tags="&lt;receiver&gt;&lt;diy&gt;&lt;equipment-design&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16193" PostTypeId="2" ParentId="16192" CreationDate="2020-03-03T16:37:52.550" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;if whistler can upgrade these other legacy scanners from RS and GRE to do DMR/NXDN and Phase II they can do it with this as well.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Says someone with technical insight into the engineering of these radios?&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;There has to be a way.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That's unfounded wishful thinking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, exchanging the CPU and DSP in any board pretty much means a redesign of at least the software. So, if you have access to the source code of the software they run on that device, extensive knowledge in PCB rework (doesn't sound like it), and access to their development tools, maybe that's possible. I can't tell.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you have none of that, an &quot;upgrade&quot; will be impossible. (I'm having a hard time calling this an upgrade; what you're describing is mainly a replacement keeping a few parts of the radio.)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-03-03T16:37:52.550" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16194" PostTypeId="1" CreationDate="2020-03-03T17:09:15.787" Score="1" ViewCount="448" Body="&lt;p&gt;I recently purchased a Yaesu FT-65 handheld radio and quickly discovered it had no 12 VDC power port like other handheld radios I've seen.  The charging cradle uses a 12 VDC wall wart for power, and the radio sits in the cradle to charge, there's no power input port on the radio itself.  At least I couldn't find one.  I went looking for a  cable to plug the charging cradle into an automotive accessory power outlet, AKA cigarette lighter, from the manufacturer and found none.  The manual makes no mention of this as an option.  I contacted Yaesu using their website and didn't get a response, not yet anyway.  This leads me to think that I should not attempt to make a cable to connect the charger base to an automotive accessory port, at least not without some voltage regulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just how sensitive is the Yaesu FT-65 charging cradle to voltage variation from the 12 volts specified?  It's typical for Amateur radio gear to be able to take in a fairly wide range, such as the 11.5 to 15 volts seen from a healthy automotive battery that's under load and while charging.  I'd like to be able to charge the radio while traveling from an automotive accessory port but not damage anything while doing so.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Anyone know what voltage range the Yaesu FT-65 charging cradle will safely take?  Is there a third party adapter for this that will regulate the voltage from an automotive accessory outlet to a &quot;clean&quot; 12 volts?&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2020-03-10T11:16:09.847" Title="Can Yaesu FT-65 be charged from a 12 VDC automotive accessory outlet?" Tags="&lt;ht&gt;&lt;mobile&gt;&lt;yaesu&gt;&lt;equipment-protection&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16195" PostTypeId="2" ParentId="16194" CreationDate="2020-03-03T17:37:45.253" Score="1" Body="&lt;p&gt;The battery inside the radio is almost certainly a lithium-ion type (one to three cells, most likely one or two), which requires the device to manage its charge (for safety, as well as for battery cycle life purposes).  That means that not only is there most likely some regulation in the charging cradle (even if the cable from the wall wart is DC -- and it might well be 12VAC), but the radio itself is managing the charge going to the actual battery.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All that to say that if the wall wart is marked with output of 12.0 V DC, it should be fine to make up a cable with the correct polarity to connect to your vehicle 12V outlet.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are also various &quot;universal&quot; power supplies that run on 12V outlet power and produce (more or less) regulated output at various user selectable voltages -- and generally also include an assortment of connectors.  You'll usually find these at auto parts stores, in my experience (I've bought them at Radio Shack, but that's been a while).  Select the correct voltage, match the polarity (should show on either the cradle or wall wart), plug and go.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;From comments, &quot;Looking at the bottom of the cradle it lists the input as simply 12 VDC @ 1 A, and output as 8.4 VDC @ 800 mA.&quot;  First, that output voltage strongly implies a 2-cell battery.  Second, the voltage difference from input to output says there's almost certainly a regulator in the cradle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the question becomes whether the cradle can handle an input variation of 10-ish V during start up to peaks of 14.6V, depending how your vehicle handles voltage regulation.  If the components are particularly lightweight (as they might be if the wall wart is itself regulated), it's possible it may drop out during a start (not a big deal, generally, when powering a battery device), or burn out a component on a peak of 14.6V (more likely to occur if the device is drawing near maximum to charge a deeply discharged battery).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One possible way to deal with Yaesu's intransigence on what you can plug the cradle into would be to purchase a small inverter to run on your vehicle's 12V outlet, to give 120VAC to power the cradle's wall wart.  For the low draw you need, these can be had for around $20 at parts stores, and might well be the easy way out for this situation.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2020-03-10T11:16:09.847" LastActivityDate="2020-03-10T11:16:09.847" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16196" PostTypeId="2" ParentId="16120" CreationDate="2020-03-03T17:38:43.777" Score="0" Body="&lt;p&gt;As others have pointed out in their answers there's a distinction between RF and DC which makes this use of coax still an effective feed line for a dipole antenna.  There's going to be plenty of people that consider this bad form as it is feeding a balanced antenna with an unbalanced line.  Even so I checked my ARRL Antenna Book and they show a dipole being fed directly with 50 and 75 ohm coax, but they do point out that using a 1:1 balun might be a good idea.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why this works can be explained by many different theories.  One theory I'd use is to point out that the coax is a waveguide and grounding the coax at the source isn't going to have an effect on the RF being transmitted down what is the path of least resistance.  A copper strap to ground is not in fact the path of least resistance because the matched load of the dipole is going to have the lower SWR for the frequencies of concern, assuming the dipole is cut correctly.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2020-03-03T17:38:43.777" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16197" PostTypeId="1" CreationDate="2020-03-03T18:27:36.843" Score="1" ViewCount="559" Body="&lt;p&gt;My wife doesn't think that having tall antennas is acceptable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does anyone have a solution for this?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Our house is 16 meter long and 10 meter wide.&#xA;I have an antenna tuner (if it can help).&lt;/p&gt;&#xA;" OwnerUserId="16530" LastEditorUserId="4076" LastEditDate="2020-03-03T19:11:49.267" LastActivityDate="2020-03-05T16:19:49.223" Title="Indoor HF/VHF/UHF antenna, have someone an Idea?" Tags="&lt;antenna-theory&gt;&lt;diy&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16198" PostTypeId="2" ParentId="16197" CreationDate="2020-03-03T19:42:13.233" Score="2" Body="&lt;p&gt;Even though you're asking about &quot;tall antennas,&quot; I'm guessing that your wife is more concerned about the appearance of an antenna than its actual height.  Search the Internet for &quot;stealth antennas&quot; and you'll find a lot of options for outdoor antennas that aren't very noticeable.  Another option is to put an antenna in your attic, if you have one.  Either of these options would likely be preferable to putting an HF antenna in your living space because HF antennas tend to be rather large and unpleasant to touch.  Also, you'll get better performance if you can get them up high and/or outdoors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF/UHF antennas are a lot easier to fit in your living space, so you could use a J-pole or quarter wave vertical fairly easily.  But, there again, you'll get much better performance if you can move them up high and/or outdoors.  I put a quarter wave ground plane antenna in my attic that works well, but it would be even better on top of the roof.  I hear the VHF/UHF Ventenna antennas work very well without being conspicuous.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another good resource is ARRL's book &lt;a href=&quot;http://www.arrl.org/arrl-s-small-antennas-for-small-spaces&quot; rel=&quot;nofollow noreferrer&quot;&gt;Small Antennas for Small Spaces&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2020-03-03T19:56:08.030" LastActivityDate="2020-03-03T19:56:08.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16199" PostTypeId="2" ParentId="16189" CreationDate="2020-03-04T01:56:55.673" Score="4" Body="&lt;p&gt;In the case you outline, it probably wouldn't be legal.   The other answers give the rules in terms of what can be done in an actual emergency.  However, to be able to respond to an actual emergency you need to&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Have radio equipment on hand at each location&lt;/li&gt;&#xA;&lt;li&gt;Have employees at each location trained in the usage of that equipment (and licensed for any non-emergency traffic)&lt;/li&gt;&#xA;&lt;li&gt;Include radio communication as part of larger safety drills on how to respond in an emergency&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I don't know about paying employees to get a license, &lt;em&gt;edit&lt;/em&gt; some training is allowed on the employers time, however I've heard of one case where an emergency organization donating some equipment and providing meeting space was seen as a form of compensation (I wouldn't have thought it either, but the club corrected it by removing the equipment and meeting elsewhere). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since you're proposing use by regular employees another license type would be more appropriate. &lt;/p&gt;&#xA;" OwnerUserId="16533" LastEditorUserId="16533" LastEditDate="2020-03-05T02:22:42.187" LastActivityDate="2020-03-05T02:22:42.187" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16200" PostTypeId="2" ParentId="16197" CreationDate="2020-03-04T02:17:04.027" Score="0" Body="&lt;p&gt;For VHF/UHF, I did some J-pole's made out of twinlead (old style flat 300 ohm TV antenna cable.)  Just google Twinlead J-pole. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For HF, the attic trick is a good one, as is the use of stealth antennas. Flagpoles make good verticals :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I lived in the apartment (sometimes called a flat) I had a 40m/15m coaxial dipole strung around the living room.  I found the article in the 73 magazine archive. URL below.  It was great for CW, and I used it to get my code speed from 5 to 13 WPM so I could upgrade my license.  This was back in the early 90s.  I had to put ferrite chokes on various things, but I got it to work, and not bother my neighbors.  I ran about 10 watts into it and made contact with 20 or so states and canadian provinces. My longest hop was 1000 nautical miles from San Jose CA to Edmonton, AL. Not sure this is the best way, but I wanted to mention it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best,&#xA;Ed Greenberg&#xA;KM6CG&#xA;Queensbury, NY USA&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://archive.org/stream/73-magazine-1981-05/05_May_1981#page/n80/mode/1up&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://archive.org/stream/73-magazine-1981-05/05_May_1981#page/n80/mode/1up&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9456" LastEditorUserId="9456" LastEditDate="2020-03-05T16:19:49.223" LastActivityDate="2020-03-05T16:19:49.223" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16201" PostTypeId="1" AcceptedAnswerId="16217" CreationDate="2020-03-04T09:12:26.183" Score="0" ViewCount="113" Body="&lt;p&gt;Is it possible to image bones and tissues with radio waves (2.7GHz-5GHz) with a tiny radio frequency source and on one side and a receiver on other side which can image the data through a PC mediated software (eg:with sdr) and printing out like an X-Ray ? (Not exactly, but similar to that) &lt;/p&gt;&#xA;" OwnerUserId="16370" LastEditorUserId="8717" LastEditDate="2020-03-04T16:03:25.600" LastActivityDate="2020-03-06T17:41:09.470" Title="Imaging with radio Frequency" Tags="&lt;software-defined-radio&gt;&lt;equipment-design&gt;&lt;microwave&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16202" PostTypeId="1" CreationDate="2020-03-04T14:36:07.373" Score="2" ViewCount="113" Body="&lt;p&gt;I have a code that sends a beacon every 1 minute with a data-rate of 1200bps (BPSK-G3RUH). I do receive the signal using a custom software defined ground station that also decodes the beacon. After a couple of minutes (10 - 30 minutes), my software defined ground station stops receiving the signal. Thus I used &lt;a href=&quot;https://airspy.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Airspy SDR&lt;/a&gt; to have a visual on the signal. &#xA;&lt;a href=&quot;https://filebin.net/hub14gt80uq13gqh/WhatsApp_Video_2020-03-04_at_5.58.51_PM__1_.mp4?t=00sctohw&quot; rel=&quot;nofollow noreferrer&quot;&gt;This is the signal&lt;/a&gt; I see when I perfectly receive the signal.&#xA;&lt;a href=&quot;https://filebin.net/hub14gt80uq13gqh/WhatsApp_Video_2020-03-04_at_5.58.51_PM.mp4?t=cberh74k&quot; rel=&quot;nofollow noreferrer&quot;&gt;This is the signal&lt;/a&gt; I see after a few minutes. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The perfect signal has a higher peak and a longer duration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wkbNW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wkbNW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While the one I cant decode has a flatter peak and 2 other smaller peaks to the right and to the left. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/ugOLZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ugOLZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, what caused the signal to change like this? Could it possibly be a hardware problem from the transceivers or the antenna? &lt;/p&gt;&#xA;" OwnerUserId="16540" LastActivityDate="2020-03-05T02:42:44.390" Title="Whats wrong with this radio signal?" Tags="&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16203" PostTypeId="2" ParentId="16201" CreationDate="2020-03-04T15:23:55.917" Score="2" Body="&lt;p&gt;Yes, microwave imaging is a thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Technically, it's basically radar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, as always, your radar resolution is proportional to the bandwidth you're using and the carrier frequency (=inverse to the wavelength).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, 2.7 GHz to 5 GHz is probably not going to give you a very nice spatial resolution, simply because their wavelengths are in the 6 to 11 cm region. Wave physics will make the body act like a non-uniform, wavelength scale body, leading to diffuse diffraction and refraction patterns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the result will not be &lt;em&gt;anything&lt;/em&gt; like X-Ray, where the wavelengths are far, far shorter than anything you'd want to image. Instead, you're setting yourself up for trying to solve a very high-dimensional, very complicated inverse problem for which, to my understanding of the matter, no unique solution exists if you just have a single emitter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could try very complicated synthetic aperture radar interferometric approaches to gain better resolution, but that would not completely solve the mathematical ambiguity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the effort you'll have to take in terms of measurement bandwidth, and oscillator coherency, will be pretty significant (as a matter of fact, I don't think I'd start implementing that without access to a Rubidium atomic clock).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is it possible to image bones and tissues with radio waves (2.7GHz-5GHz)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, in the &gt; 10 k€ setup region, maybe,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;with a tiny radio frequency source &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&quot;tiny&quot; is relative, and a single source won't do,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;a receiver on other side which can image the data through a PC mediated software (eg:with sdr) and printing out like an X-Ray &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;... assuming you have extensive knowledge in RF electronics, SDR, wave physics, and inverse problems as well as writing software, yes, maybe?&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-03-04T15:23:55.917" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16204" PostTypeId="2" ParentId="16202" CreationDate="2020-03-04T16:03:28.643" Score="1" Body="&lt;p&gt;I agree with @MarcusMüller - that could be anything. I would fistly look for some kind of overheating in the circuit. Also it's worth checking the SWR of the antenna. If your antenna uses some kind of transformer it might be overheating. Something can be wrong with the coax as well, e.g. poor connection, whater inside the coax, etc.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-03-04T16:03:28.643" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16205" PostTypeId="2" ParentId="16197" CreationDate="2020-03-04T16:23:54.547" Score="2" Body="&lt;p&gt;J-Pole or vertical dipole are good choices for VHF/UHF. There are good chances that you can reach a local repeater with an antenna right in your shack:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Vq3Uw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Vq3Uw.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RnYpT.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RnYpT.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my case the repeater is ~10 km away and I have no problems reaching it with 5W and a cheap antenna, Nagoya NA-771. Please note that there are many fake NA-771's, see &lt;a href=&quot;https://www.nagoya.com.tw/en/news-31478/%E3%80%8Elatest-updated%E3%80%8FHow-to-identify-the-genuine-and-fake-antenna.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;How to identify the genuine and fake antenna?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Speaking of HF you will find many options online. For instance there are shortened vertical antennas (OPEK HVT-400B, OPEK HVT-600, Harvest RH10M, ...) that are no more than 2.5 meters tall. Although these antennas are not most efficient onces, I made plenty of QSOs on my OPEK HVT-400B.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also have a great experience with antennas described in articles &lt;a href=&quot;http://www.sgcworld.com/Publications/Articles/237qst0502.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;One Stealthy Delta&lt;/a&gt; by Steve Ford, WB8IMY and &lt;a href=&quot;http://www.hamuniverse.com/kl7jreasyvertloop.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;An Easy to Install Vertical Loop for 80-6 Meters&lt;/a&gt; by John Reisenauer, KL7JR. Here is my version of &quot;stealthy delta&quot; (&lt;a href=&quot;https://eax.me/delta-loop-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;full description in Russian&lt;/a&gt;):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BsrKX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BsrKX.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that it's only 6.2 meters tall. This is very little for an antenna that covers 40-10 meters (and 80m too although the antenna doesn't work especially well on this band), doesn't require any counterpoise wires. I made plenty of contacts on 40m and 20m with this antenna, including some transatlantic. The main drawback of my version is that it gathers some QRM from the house on 40m and 80m. I'm going to move it farther from the house.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are many other options as well, e.g. end-fed antennas. I've been using long wire and Fuchs antenna and they turned out to be quite good. I strongly recommend to read The ARRL Antenna Book for more details.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-03-04T16:23:54.547" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16206" PostTypeId="1" AcceptedAnswerId="16209" CreationDate="2020-03-04T17:00:11.120" Score="1" ViewCount="579" Body="&lt;p&gt;I'm having little issues understanding what S.A.S.E and S.A.E. mean exactly. &lt;a href=&quot;https://en.wikipedia.org/wiki/Self-addressed_stamped_envelope&quot; rel=&quot;nofollow noreferrer&quot;&gt;The description on Wikipedia&lt;/a&gt; is a little bit confusing because it says that it's literally the same. But from the context on some qrz.com pages I get an impression that there is a difference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I understand, S.A.S.E means a filled envelope where I'm a receiver and the OP I had QSO with is a sender, also the envelope has the postage stamps that would be accepted by the postal service in OP's country. The obvious issue here is that it's unlikely that Russian postage stamps will be accepted by US postal service, not mentioning that service prices differ. I asked this question in a local post office - there is no other way (at least in Russia) to pay for a reply mail except postage stamps, and they can't promise that Russian postage stamps will be accepted worldwide or even specifically in US. In other words, if OP accepts &lt;em&gt;only&lt;/em&gt; S.A.S.E there is no way for me to receive his QSL card.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;S.A.E, as I understand it, is the same but without postage stamps. In other words, OP asks only to include a filled envelope. To put a few &quot;green stamps&quot; (US dollars) might be a good idea, but it's not strictly necessary unless it's mentioned explicitly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are a few examples from qrz.com:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;If you want a paper QSL it will be necessary for you to send me your card via Direct Mail with either a S.A.S.E. or a S.A.E.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;My understanding is that just to include a S.A.E will be OK. OP doesn't ask for any &quot;green stamps&quot; but to include 1 or 2 GS might be a good idea nevertheless. (Is there any chance that including green stamps in this case may offence him or her?)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;For direct QSLs, send SASE or SAE w/green stamps.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;OP asks for S.A.E. and green stamps, in plural. Thus I have to send S.A.E and at least two green stamps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is my understanding of S.A.S.E and S.A.E. right or there is something I got not exactly right?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-03-05T16:20:33.277" Title="An exact meaning of S.A.S.E and S.A.E in the context of QSL cards" Tags="&lt;qsl-card&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16207" PostTypeId="2" ParentId="16202" CreationDate="2020-03-04T17:31:07.237" Score="1" Body="&lt;p&gt;Look for a buffer overflow, integer overflow, or numeric out-of-range error in your software.  Are you trying to compute the sine or cosine of some massive huge number?  (causing range reduction loss of precision due to some number you've been incrementing for 30 minutes).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-03-05T02:42:44.390" LastActivityDate="2020-03-05T02:42:44.390" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16208" PostTypeId="2" ParentId="16197" CreationDate="2020-03-04T17:52:40.360" Score="1" Body="&lt;p&gt;For HF, a loop antenna doesn't require being tall.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For UHF/VHF, you commonly want something vertically polarized.  But they can be short enough that you might be able to hide one inside something (attic, etc.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-03-04T17:52:40.360" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16209" PostTypeId="2" ParentId="16206" CreationDate="2020-03-04T18:19:37.630" Score="6" Body="&lt;p&gt;In my opinion, wikipedia is wrong on their definition of SAE, despite their reference in the footnote. In fact, even that reference gives two definitions of SAE.  Perhaps their are regional differences which I'm not aware.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since my childhood SAE has always meant &quot;self addressed envelope&quot;.  You put your own address on an envelope, in the recipient's portion of the envelope (the center).  You might also but your address as the return address as well.  It was the expectation the person or company you were sending the SAE would attach the proper postage.  In my experience, you sent an SAE usually to a company, as they had the financial resources to pay the postage.  And the returned item might require odd postage you might not know about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A SASE was then a SAE with a stamp attached: self addressed stamped envelope. &lt;/p&gt;&#xA;" OwnerUserId="9876" LastActivityDate="2020-03-04T18:19:37.630" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16210" PostTypeId="2" ParentId="16206" CreationDate="2020-03-04T18:20:13.913" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/S%26H_Green_Stamps&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;Green stamps&quot; originally meant something else&lt;/a&gt;. In this context, it's slang.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since &lt;a href=&quot;https://en.m.wikipedia.org/wiki/International_reply_coupon&quot; rel=&quot;nofollow noreferrer&quot;&gt;International Reply Coupons&lt;/a&gt; are no longer sold or accepted, it could mean postage stamps or money.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In some countries it is illegal to possess foreign currency etc., and you'll have to find out whether that is the case in your country.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-03-05T16:20:33.277" LastActivityDate="2020-03-05T16:20:33.277" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16211" PostTypeId="2" ParentId="6014" CreationDate="2020-03-04T18:55:01.003" Score="1" Body="&lt;p&gt;There is an effect on the of the conducting boom on the parasitic elements (directors), see&#xA;the pdf, which is downloadable:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.govinfo.gov/content/pkg/GOVPUB-C13-abad4b77cb9f7a5c73277d0d4b8b1f7d/pdf/GOVPUB-C13-abad4b77cb9f7a5c73277d0d4b8b1f7d.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.govinfo.gov/content/pkg/GOVPUB-C13-abad4b77cb9f7a5c73277d0d4b8b1f7d/pdf/GOVPUB-C13-abad4b77cb9f7a5c73277d0d4b8b1f7d.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Section 3.4 shows experimental result on optimum length of the parasitic elements in wavelength as a function of the boom's diameter to wavelength ratio. The results is shown in Figure 10. The result show a linear increase of the parasitic elements' length with increase in the boom diameter.&#xA;However, Balanis on &quot;Antenna Theory Analysis&quot; does not include the effect of boon in his derivations, see the following link for the download.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.technicalbookspdf.com/antenna-theory-analysis-and-design-4th-edition-by-constantine-a-balanis-books-free-download/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.technicalbookspdf.com/antenna-theory-analysis-and-design-4th-edition-by-constantine-a-balanis-books-free-download/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this helps&lt;/p&gt;&#xA;" OwnerUserId="16544" LastActivityDate="2020-03-04T18:55:01.003" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16213" PostTypeId="2" ParentId="2080" CreationDate="2020-03-06T04:58:32.407" Score="1" Body="&lt;p&gt;I would completely agree with the comment about the Canadian exam being very tough without an electronics background. I've wanted to get my license for years, but I'm really only interested in that so I can have something in the vehicle. I have zero interest in building my own antenna towers or building my own radios. I have no interest in competitions or trying to make as many contacts as possible around the world.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the several-week course I took, there were people with years of electronics experience that were surprised how much electrical theory there was in the course and on the exam. The vast majority of the questions (I think there 120 questions) were related to electrical theory, components, diagrams and formulas. Needless to say, even after two attempts I never managed to get a passing grade. It was the same for a number of other people in the course who wrote the test. There were also a number that just dropped out after a few weeks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think it's a shame that there's no Technician equivalent in Canada. I often hear &quot;old hams&quot; lamenting the dwindling numbers of licensed hams up here. I think if the regulations provided an entry level, there would be many more people getting into the hobby.&lt;/p&gt;&#xA;" OwnerUserId="16559" LastActivityDate="2020-03-06T04:58:32.407" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16214" PostTypeId="1" CreationDate="2020-03-06T05:37:26.990" Score="0" ViewCount="171" Body="&lt;p&gt;I was ham surfing on the 2 meter FM band on my C Crane 2E Radio and occasionally I come across these frequencys that are &quot;live&quot; but no Audio came through. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way I know that a frequency is dead is that their is static, when a round table or someone drops out the frequency goes out and static comes in. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Im listening to one it has static hiss in the background with some static the reception bar read about 1/3rd. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So why do these frequencys appear to have a carrier going but nothing is their or am i miss interpreting this as good reception. &lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="12988" LastEditDate="2020-03-08T13:34:08.827" LastActivityDate="2020-03-16T11:32:02.853" Title="Why are some frequencies &quot;live&quot; where is nothing" Tags="&lt;frequency&gt;&lt;station-identification&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="16215" PostTypeId="1" CreationDate="2020-03-06T13:18:09.800" Score="2" ViewCount="83" Body="&lt;p&gt;I had a 100cm prime focus dish laying around and I thought of making a circularly polarized feed for it, since it seemed pretty straightforward from what I've been reading. Helical feeds are supposed to be very wide and forgiving. &#xA;So I built this feed:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/6MdNl.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6MdNl.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;The problem I have is, even though the feed and signal are circularly polarized, if I rotate the feed or the antenna 90 degrees, the signal completely disappears. &#xA;I was told I'm losing a lot of signal due to the fact that this antenna is for a linear feed and so it's turning my CP signal into LP, and then the feed is losing signal again due to the fact that it's CP again. &#xA;What I tried was to cover my antenna with fine aluminium wire mesh (the kind you would use on a screen door), so the antenna ended up looking like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/R7CRQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/R7CRQ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But again I have the problem that rotating either the antenna or feed make it lose signal. &#xA;I don't have a VNA to analyze the feed (frequency of interest is 1.7GHz). So the best I can do is point it at a known satellite (in my case, GOES-16. I have a working system for it to which I can compare results,  but it's a slightly larger antenna with a linear feed. GOES LRIT is linear).&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Does the wire mesh I added help with preventing the antenna from linearizing my circular polarized signal?&lt;/li&gt;&#xA;&lt;li&gt;What can be causing the problem of losing signal as I rotate the feed or antenna?&lt;/li&gt;&#xA;&lt;li&gt;If the signal is linear and my antenna and feed are circular, I'm supposed to get the same signal level regardless of rotation, right? I'll be losing 3dB due to polarization mismatch but it should be the same regardless.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="8717" LastEditDate="2020-03-06T16:05:36.500" LastActivityDate="2020-03-06T16:05:36.500" Title="Circular polarized antenna feed changes as I rotate it?" Tags="&lt;antenna-theory&gt;&lt;satellites&gt;&lt;microwave&gt;&lt;polarization&gt;" AnswerCount="0" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16216" PostTypeId="1" AcceptedAnswerId="16218" CreationDate="2020-03-06T15:11:22.123" Score="8" ViewCount="199" Body="&lt;p&gt;I have set myself a challenge to write a Matlab script as proof of concept to send an FT8 CQ call (not necessarily for live transmissions yet, but I may extend the project). So far I have:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Generated and appended 14-bit CRC to precomputed message bits (from ft8code.exe utility in WSJT-X) &lt;/li&gt;&#xA;&lt;li&gt;Generated and appended 83-bit LDPC parity bits to give 174-bit channel symbols&lt;/li&gt;&#xA;&lt;li&gt;Implemented tone synthesis and audio-carrier modulation in Matlab for 8 FSK channel symbols&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;What I am missing is that I'd like to generate the message bits myself in Matlab from the callsign/grid locator. I understand that the callsign is converted to 2*28=56 bit field, locator is converted to a 15 bit field, and there are 6 message type bits giving 77 bits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question therefore is &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How do I convert the callsign to a 56-bit binary value and the locator to 15 bits?&lt;/li&gt;&#xA;&lt;li&gt;Does it use an ASCII table? Presumably it uses a 0-9, A-Z, space character set.&lt;/li&gt;&#xA;&lt;li&gt;What kind of compression is used to squeeze 4-character locator into 15 bits etc? I know the last 6 bits for CQ messages as these do not change so that's one piece of the puzzle. &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16562" LastEditorUserId="8717" LastEditDate="2020-03-06T15:50:55.553" LastActivityDate="2020-09-23T14:14:07.810" Title="FT8 callsign/maidenhead compression encoding" Tags="&lt;software&gt;&lt;callsign&gt;&lt;math&gt;&lt;ft8&gt;&lt;encoding&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16217" PostTypeId="2" ParentId="16201" CreationDate="2020-03-06T17:41:09.470" Score="1" Body="&lt;p&gt;With a wavelength on the order of 10 cm, you might be able to use radar get some blurry inside imaging of very large beached whales (or maybe large dinosaurs, in conjunction with a suitable time machine).&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-03-06T17:41:09.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16218" PostTypeId="2" ParentId="16216" CreationDate="2020-03-06T20:22:49.960" Score="8" Body="&lt;p&gt;You can find the code in &lt;a href=&quot;https://github.com/pavel-demin/ft8d/blob/master/packjt77.f90&quot; rel=&quot;nofollow noreferrer&quot;&gt;packjt77.f90&lt;/a&gt;. Callsign encoding (for &amp;quot;standard&amp;quot; callsigns that don't require hashing) is in function &lt;code&gt;pack28&lt;/code&gt;. A quick summary:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Adjust a few strange prefixes that don't follow the usual arrangement of letters and numbers. Swaziland &lt;code&gt;3DA0*&lt;/code&gt; will be encoded as if it was &lt;code&gt;3D0*&lt;/code&gt; instead, and Guinea &lt;code&gt;3XA1A&lt;/code&gt; will be encoded as if it was &lt;code&gt;QA1A&lt;/code&gt; instead. This adjustment is reversed in the decoder, which is possible because it maps to unused parts of the callsign space.&lt;/li&gt;&#xA;&lt;li&gt;&amp;quot;Align&amp;quot; the callsign into a 6-character field by identifying the last (or only) digit, and placing it in the third position. If there are fewer than two characters before the digit, or fewer than three characters after the digit, pad with spaces. If there are more than two characters before, or more than three characters after, this is a &amp;quot;nonstandard&amp;quot; callsign and has to be encoded by hashing. Example: my callsign KC2G becomes &lt;code&gt;&amp;quot;KC2G  &amp;quot;&lt;/code&gt;, N2XYZ becomes &lt;code&gt;&amp;quot; N2XYZ&amp;quot;&lt;/code&gt;, and 4U1ITU stays &lt;code&gt;&amp;quot;4U1ITU&amp;quot;&lt;/code&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Map the first character to its position (zero-indexed) in the list&lt;br /&gt;&#xA;&lt;code&gt;&amp;quot; 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ&amp;quot;&lt;/code&gt; (37 possibilities), the second to its position in the list &lt;code&gt;&amp;quot;0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ&amp;quot;&lt;/code&gt; (36), the third to its position in the list &lt;code&gt;&amp;quot;0123456789&amp;quot;&lt;/code&gt; (10), and the fourth through sixth to their positions in the list&lt;br /&gt;&#xA;&lt;code&gt;&amp;quot; ABCDEFGHIJKLMNOPQRSTUVWXYZ&amp;quot;&lt;/code&gt; (27). Example: &lt;code&gt;&amp;quot; K1BC &amp;quot;&lt;/code&gt; becomes &lt;code&gt;(0, 20, 1, 2, 3, 0)&lt;/code&gt;&lt;/li&gt;&#xA;&lt;li&gt;Read this off as a variable-base-(37, 36, 10, 27, 27, 27) integer, e.g.&lt;br /&gt;&#xA;((((0*36 + 20)*10 + 1)*27 + 2)*27 + 3)*27 + 0 = 3957822, or equivalently&lt;br /&gt;&#xA;36*10*27*27*27*0 + 10*27*27*27*20 + 27*27*27*1 + 27*27*2 + 27*3 + 0 = 3957822.&lt;/li&gt;&#xA;&lt;li&gt;Add 6257896. The first 2,063,592 codes are used by CQ/QRZ calls, and the next 4,194,304 are used by 22-bit hashed callsigns; regular callsigns start after that. 3957822 + 6257896 = 10215718.&lt;/li&gt;&#xA;&lt;li&gt;Encode the number as 28-bit binary, big-endian; 10215718 = 0000100110111110000100100110.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;For grid squares, the encoding is similar except there's no alignment necessary, and it's a base-(18,18,10,10) integer, so FN20 becomes (5, 13, 2, 0), which becomes the integer 5*18*10*10 + 13*10*10 + 2*10 + 0 = 10320. This is then packed into 15 bits. Note that the &amp;quot;RR73&amp;quot; message is actually encoded as a callsign pair plus the grid RR73 (which is valid, but in an uninhabited bit of arctic ocean north of Siberia), and that reception reports are encoded as the values above RR99 (32480).&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-09-23T14:14:07.810" LastActivityDate="2020-09-23T14:14:07.810" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16219" PostTypeId="1" CreationDate="2020-03-07T16:57:14.520" Score="2" ViewCount="148" Body="&lt;p&gt;We have a local radio shop that started selling us &lt;a href=&quot;https://www.ameradio.com/product/180285/description.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Relm P150&lt;/a&gt;s with a high gain 9 inch antenna, and those are ok. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;He also has thrown in longer 15 to 14 inch dual band antennas saying use those in rural areas for 155 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I thought the 144/430 MHz split meant it performance best and only at those tuned splits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm no expert, just a public safety user. While I can tell the repeater does catch it with this antenna, it is a backup repeater in no man's land and nobody monitors it unless they have to or know there is operations going on; as being a small entity, we only have 1 console and getting dispatch to go off from the 16 channels going elsewhere is a arm break. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounded clear when I keyed in with truck radio volume all the way up and I was a good 20 miles in hilltop terrain from the repeater. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So while it works, is this bad for the radio since the antenna says 144/430 to transmit on 155 MHz? If not and they work well, why do most not recommend these?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I figure ham radio operators would best answer my question, as them radio shops try to sell anything to counties with clueless commissions leaving us the users at mercy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thought crossed my mind they are trying to cheap fix some issues with this antenna over installing a new repeater or another.&lt;/p&gt;&#xA;" OwnerUserId="16571" LastEditorUserId="4076" LastEditDate="2020-03-07T23:42:50.327" LastActivityDate="2020-03-07T23:42:50.327" Title="144/430 MHz antenna on 155 MHz?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vhf&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16220" PostTypeId="2" ParentId="16219" CreationDate="2020-03-07T19:18:16.863" Score="2" Body="&lt;p&gt;Ask the radio shop to show you the &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Standing_wave_ratio&quot; rel=&quot;nofollow noreferrer&quot;&gt;VSWR&lt;/a&gt; of the antennas at the frequencies you use. Have them do it in front of you. That will likely tell you whether the antennas are suitable or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To ensure an accurate measurement, the antenna must be plugged directly into a &lt;a href=&quot;https://www.google.com/search?q=&amp;quot;vhf&amp;quot;+swr+meter&amp;amp;newwindow=1&amp;amp;prmd=sivn&amp;amp;source=lnms&amp;amp;tbm=isch&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;VHF&lt;/strong&gt;&lt;/a&gt; (not CB) &lt;a href=&quot;https://en.m.wikipedia.org/wiki/SWR_meter&quot; rel=&quot;nofollow noreferrer&quot;&gt;SWR meter&lt;/a&gt; with no coaxial cable jumper between the antenna and the meter. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A perfect match would be 1:1. (That is, the forward reading should be adjusted for a full-scale meter reading and the reverse reading would read zero.) If the VSWR is less than 1.5:1, it's probably not a cause for concern&lt;b&gt;*&lt;/b&gt;. A higher SWR than that would likely cause the power output of the radio to drop. As for damaging the radio, well, &lt;em&gt;it's possible&lt;/em&gt;, but most radios have built-in mismatch protection circuits.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;b&gt;*&lt;/b&gt; A low SWR reading &lt;em&gt;could&lt;/em&gt; also mean that the antenna has unacceptable losses. If that's the case, you &lt;em&gt;might&lt;/em&gt; feel the antenna grow slightly warm on an extended key-down. However, if you don't have any problems communicating, that's probably a moot point. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-03-07T19:18:16.863" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16221" PostTypeId="2" ParentId="15566" CreationDate="2020-03-09T06:46:54.100" Score="4" Body="&lt;p&gt;&lt;strong&gt;My answer&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It looks to me like you could probably go further outside the limits of the band you're switched to by using an external VFO with a wider tuning range than the inbuilt LMO (5.0 to 5.5 MHz) but the pass-band tuned circuits will limit the amount you can do this by. I'm fairly sure the WARC bands would be too far away from the original fitted bands to work well or at all. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Off frequency tank circuits can result in unexpected out of spec anode currents or voltages, which can do damage or cause parasitic oscillations, etc. They will at least severely limit the desired signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To tune to the other ham bands you would have to add suitable tuned circuits and crystals to the band selector circuits rather than just use a different VFO frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While this is not really difficult, it would require some careful adjustment of inductors and/or capacitors, and correct crystal frequencies to mix the 8.395 to 8.895 MHz signal into/from the desired band (in the 2nd Tx mixer / 1st Rx mixer). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could probably pull the tuning of the nearest higher band down to the correct tuning for some bands (e.g. 20m setting to work on 30m) by adding suitable high quality caps and/or trimmer caps across the 4 tuned circuits (across C607, C704, C802, C923 for example) through a multi-pole switch when required, simultaneously switching to the appropriate crystal at Y503&lt;br&gt;&#xA;e.g. 18.6MHz xtal would put 10.1MHz operating frequency in the 8.395 to 8.895 pass band at 8.5MHz. The transceiver would certainly be capable of operating either side of the 10.1 to 10.15MHz ham band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could possibly use some of the 10m band switch positions for new bands if you don't need all 4. However looking at the circuitry and the wafers of the band selector switch it seems that this could not easily be done without changing the switch wafers a bit (or using relays perhaps?).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The tubes will probably all work ok up to 6m. The 6146 was commonly used as a final in VHF mobile &quot;radiotelephones&quot; fitted to fleet vehicles and operating through commercial repeaters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Obscurely related to the question&lt;/strong&gt; (but possibly interesting to some): &lt;/p&gt;&#xA;&#xA;&lt;p&gt;After reading the comments I feel it is probably ok to add some extra notes about my experience with valves (tubes). Stop reading here if you don't like anything not entirely related to the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I initially learnt about electronics as a child, when almost everything electronic used valves or relays. WW2 surplus equipment and old radio receivers were relatively plentiful and could be and were converted to work on ham bands, with a bit of DIY coil winding and tweaking and alignment. A grid dip meter helped. And some trial and error. Easy enough really and lots of fun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transistors were still rare, easily destroyed, expensive, mostly germanium, and rather mysterious things.&lt;br&gt;&#xA;By contrast you could still get useful activity out of a valve that you had seen a &quot;flash-over&quot; happen inside of, or had biased badly and had got the anode glowing red hot for a moment (both of which I have done while learning).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I could clearly picture the &quot;electron cloud&quot; around the cathode and the negative electric field around G1 repelling these electrons, preventing most of them from getting past. Once past. they are strongly attracted to the highly positive anode. As G1 becomes less negative, more and more electrons get past it so more anode current flows, which is then seen as voltage across the plate load. Everything fairly high impedance.&lt;br&gt;&#xA;And high voltages everywhere. (Seems you can survive a pretty big shock if it doesn't go past your heart...)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It took a while for me to even begin to understand how bipolar junction transistors actually work, with &quot;electron carriers&quot; and &quot;holes&quot; etc.&lt;br&gt;&#xA;Current at the base rather than voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So looking at the circuit diagram of the SB102 is like going back in time to something that I was quite familiar with once.&lt;br&gt;&#xA;Several thoughts come to mind that I find useful in tracing and understanding valve circuits:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Valves are similar to FETs in operation. The extra grids in tetrodes, pentodes, etc. were added to decrease anode to G1 capacitance and improve linearity but can mostly be ignored when working out what's happening to the signal.&lt;br&gt;&#xA;There are exceptions to this so it's not always true e.g. SB102 V2 and V4 appear to be turned on/off by their G2 voltage.&lt;br&gt;&#xA;It was common to use some of the valves and circuitry in transceivers for both receive and transmit as seen in the 1st IF V3, and the bandpass filter T202, because valves cost a lot more than transistors in both space and (particularly heater) power drain. This can certainly appear to complicate the circuit, and can make understanding the signal path tricky.&lt;br&gt;&#xA;Valves can effectively be removed from the circuit (e.g. between Rx and Tx) by changing the G1 bias or G2 volts (e.g. V5A,V6,V7,V8,V9, or V2,V4).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hope this helps.&lt;/p&gt;&#xA;" OwnerUserId="9531" LastEditorUserId="9531" LastEditDate="2020-03-09T09:42:02.380" LastActivityDate="2020-03-09T09:42:02.380" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16222" PostTypeId="1" CreationDate="2020-03-09T09:55:09.370" Score="3" ViewCount="537" Body="&lt;p&gt;I happened across a discussion on building repeaters for Amateur radio, which lead to looking at GMRS repeaters (because apparently this is a potential source for inexpensive 70 cm Amateur repeaters), and that lead to seeing some discussion on illegal &quot;parrot&quot; repeaters for FRS.  This made me think that maybe I might want to build a repeater.  Not being committed to this in any way I be willing to spend kilobucks to this end but I could be convinced to spend a few hundred.  Certainly if I can repurpose this investment for something else if I lose interest in a repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For most every UHF and VHF Amateur radio band one can find a repeater for sale.  These look to cost many kilobucks, far more than I'd want to spend on playing with a repeater.  Even repurposing a GMRS repeater for this is not all that low cost, maybe lower cost than many other options but still more than a kilobuck.  These repeaters often use special purpose radios, not really useful for anything other than a repeater.  These are of course very popular because for the users it takes only a single band transceiver to use.  The cost for the repeater is large to keep costs low for the users.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's mobile transceivers out there that can do cross-band repeat.  This sounds interesting because such a radio can be used as anyone might use any mobile transceiver, but can be put into use as a repeater with very little setup.  After the need for a repeater has passed it can then returned to service as a mobile transceiver again.  Using this as a cross band repeater for a large number of users (with &quot;large&quot; being more than two) means the users will need dual band transceivers, or two radios.  This means low cost for the repeater but more expense for the users.  What seems to be a popular radio for this is the Yaesu FT-8900, and with new radios selling for about $300 this is attractive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is where my seeing these illegal FRS and CB &quot;parrot&quot; repeaters come in.  These are certainly illegal on FRS and CB but this should be legal on Amateur radio.  That is unless I'm missing something.  I did some searching on this and I will find people using parrot repeaters on Amateur radio but no description on how they were built.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For those unfamiliar with a parrot repeater they will wait for a signal on it's assigned frequency like any other repeater but instead of re-trasmitting it simultaneously on a different frequency they will record the audio.  When the transmission ends, or the audio buffer is full, it will playback the received audio on the same frequency.  These work for FRS and CB because the user radios do not need to be modified, and users do not need need two radios, to be useful.  The drawback is this doesn't make for the most natural conversation because it means waiting for the &quot;parrot&quot; to repeat everything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Has anyone built parrot repeater software for Amateur radio?  The kind that would make use of a common personal computer and computer-radio interface?  I'm thinking this might be useful for people that want to use an inexpensive single band mobile or base station radio as a repeater, and then the users of the repeater would only need an inexpensive single band radio as well.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perhaps this just isn't considered all that useful since mobile transceivers capable of acting as a cross band repeater are not all that expensive, and dual band transceivers to make use of them aren't all that expensive either.  If there isn't software for a parrot repeater then maybe there's software for turning a common PC, interfaced with a pair of suitable Amateur radios, into a repeater for people like myself that wants to keep a repeater &quot;in a back pocket&quot; in case a need to build one on short notice comes up.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2021-04-24T12:10:15.897" Title="Are there any &quot;parrot&quot; repeater software projects out there?" Tags="&lt;repeater&gt;&lt;software&gt;&lt;crossband-repeat&gt;" AnswerCount="2" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16223" PostTypeId="2" ParentId="5439" CreationDate="2020-03-09T10:43:15.893" Score="1" Body="&lt;p&gt;The radiation efficiency of all antenna systems is the quotient of its radiation resistance and the sum of the &lt;strong&gt;real&lt;/strong&gt; (energy-dissipating) resistive losses comprising that system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some M-o-M software using NEC (Numerical Electromagnetics Code) reports values identified/expected to be radiation efficiency, but including the effects of propagation loss in those values.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is an example of a customized study where the radiation efficiency excludes propagation losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PbXmK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PbXmK.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-03-09T10:43:15.893" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16224" PostTypeId="1" CreationDate="2020-03-09T10:50:00.800" Score="2" ViewCount="191" Body="&lt;p&gt;can you explain me what is happening with RF in a iron gutter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've tried to simulate with nec2, but I'm just a beginner and doesn't really know all the parameters to come close to reality. This is also for transmission and not receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The gutter looks like on the images.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've also &lt;strong&gt;connected a 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; coax&lt;/strong&gt; around 4-5 meters over ground at the vertical part with a short copper wire around it. Coax ground goes to a short wire radial.&#xA;The ending of the vertical iron gutter part is in tar. I don't know if there is plastic down there.&#xA;I've measured this with a VNA. And it doesn't look so bad as I've imagined before.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd like to use it for SWL. At the moment I have very &lt;strong&gt;weak signals of HAM&lt;/strong&gt; stations. Only &lt;strong&gt;HF AM radio&lt;/strong&gt; broadcast has &lt;strong&gt;power&lt;/strong&gt;. Although I receive some &lt;strong&gt;WSPR bacons&lt;/strong&gt; over 1000km, but only in noise level with application. The strongest 80m HAM LSB or CW was maybe 12-15db over noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it useful to try a &lt;strong&gt;unun/balun&lt;/strong&gt;? Does this change anything on receiving? How can I find out if the gutter is balanced or unbalanced? I think it might be unbalanced. But how do I know for sure?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The VNA tells me that it is quite &lt;strong&gt;resonant around 6 MHz&lt;/strong&gt;. There are a few more areas with resonance up to UHF.&lt;br&gt;&#xA;So would I receive stronger signals if I match it better with an &lt;strong&gt;1:2 or 1:2.5 unun&lt;/strong&gt; to come from 10-20&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; near 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or should I try a &lt;strong&gt;band filter&lt;/strong&gt; at the gutter?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or are the signals weak, because the gutter is &lt;strong&gt;grounded too good&lt;/strong&gt;? Would it make sense to strip an &lt;strong&gt;isolated wire&lt;/strong&gt; next to the gutter (all the way along). And a longer radial down to 1m over ground? Coming closer to a dipole.&lt;br&gt;&#xA;My possibilities are limited. I've no idea how to get a cable to the roof without annoying the neighbors. My balcony is roofed. The garden is small and also used by neighbors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YVhMC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YVhMC.png&quot; alt=&quot;nec2 simulation&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/QaJTK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QaJTK.png&quot; alt=&quot;nec2 radiation simulation&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16579" LastActivityDate="2020-03-10T08:01:53.240" Title="What is happening in a gutter &quot;antenna&quot;?" Tags="&lt;antenna&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16226" PostTypeId="1" AcceptedAnswerId="16228" CreationDate="2020-03-09T18:20:15.883" Score="2" ViewCount="299" Body="&lt;p&gt;I have only a small amount of time each week when I can get on the air. Frequently I turn on the radio and hear numerous operators participating in one contest or another. Is there some way to indicate I am not participating in the contest? That I am just getting on the air to rag chew or maybe log a few new DX entities? &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-03-10T02:14:59.307" Title="Not participating in contests" Tags="&lt;contest&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16227" PostTypeId="1" AcceptedAnswerId="16234" CreationDate="2020-03-09T18:40:28.970" Score="2" ViewCount="158" Body="&lt;p&gt;There's a lot of information available about how to block common mode current originating at the antenna end of a coax cable.  But, I haven't seen any reference to common mode current originating at the transmitter.  If common mode current is on the outside of the cable's shield (as many people describe it), and both the inside and outside of the cable braid are connected to the same wire in the radio (which they are), and the feed line is the right length to be an effective radiator (which could happen), wouldn't the shielding be radiating like crazy?  That doesn't seem to happen in real life, so I feel like I'm missing a crucial piece of information here.  What's stopping common mode current from originating at the transmitter?&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="76" LastEditDate="2020-03-09T19:48:07.293" LastActivityDate="2020-04-06T15:40:28.050" Title="Why do we talk about common mode current from an antenna, but not from a transmitter?" Tags="&lt;antenna-system&gt;&lt;feed-line&gt;&lt;theory&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16228" PostTypeId="2" ParentId="16226" CreationDate="2020-03-09T19:15:44.813" Score="4" Body="&lt;p&gt;If you're asking if adding &quot;/NPC&quot; (for &quot;Not Participating in Contest&quot;) to the end of your call sign or something like that will help, then I'm sorry to tell you that there is no commonly-recognized way of designating yourself as someone not interested in making contest QSOs.  But don't lose heart, contest activity can be avoided: see &quot;&lt;a href=&quot;https://ham.stackexchange.com/questions/1132/i-hate-contests-how-can-i-avoid-them&quot;&gt;I hate contests. How can I avoid them?&lt;/a&gt;&quot;  One of the easiest ways to avoid a contest is to head to the &quot;WARC bands&quot;: 12m, 17m, and 30m.  Contest rules generally don't allow contacts on those bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition to finding bands, frequencies, or modes where contest activity is not allowed or scarce: If you're answering a CQ, just don't answer a contester's CQ.  They're easily distinguished by &quot;CQ contest&quot;, &quot;CQ TEST&quot; (on Morse code), or &quot;CQ [contest name]&quot;.  On the weekend, it helps to know what contests are happening; maybe bookmark a contest calendar like &lt;a href=&quot;https://www.contestcalendar.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt; in your browser, and learn the names of the major contests, since the major ones are harder to avoid than the smaller ones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're sending CQ, it can't hurt to say &quot;CQ RAGCHEW&quot; on Morse code, or something like &quot;CQ, looking for a ragchew&quot; on phone.  In Morse code, sending CQ slowly will strongly discourage most contesters; typical speeds in major contests are 30 WPM+, so 20 WPM or less will make most contest operators who are looking for a QSO want to keep spinning the big knob.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're looking for new DX entities, you can of course always call &quot;CQ DX&quot; instead of &quot;CQ contest&quot;, although a few clueless contesters might try and work you anyway.  (Be kind; some contesters try and operate for 48 hours straight in the big contests, and that kind of fatigue can make one do funny things.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But you might also consider joining in DX contests, even if you only have a few minutes to spare; lots of semi-rare entities are much easier to get in DX contests, and lots of DXpeditions make a point of planning their operations around the big DX contests.  I would highly advise waiting until the last hours of a DX contest, usually Sunday, because contesters calling CQ get much more patient and accommodating toward the end of the contest when their CQs would otherwise go unanswered.  Remember, a contester wants every QSO that can possibly be made, even yours.  It helps to know the rules of the contest to know what information is passed in the QSO, which is called &quot;the exchange&quot; in the contest rules, but such an accommodating contester will usually be happy to ask you for the information one item at a time.  If they ask you for your serial number, just start with 1 for the first contest QSO, 2 for the second, and so on.  You are under no obligation to submit an official entry in the contest.  It's fine to make just one QSO in a contest, although &lt;a href=&quot;https://ham.stackexchange.com/questions/6714/what-happens-if-a-station-did-not-submit-a-contest-log&quot;&gt;it's polite to make two or more QSOs&lt;/a&gt; if that's not impractical for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, most contest stations are very good about confirming the QSO, either by Logbook of the World or by QSL card.  The reason is, if a contest station isn't polite about confirming QSOs, then other contest operators will remember and refuse a QSO with the rude operator the next time around, which would hurt the rude operator's efforts in future contests.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-03-09T19:15:44.813" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16229" PostTypeId="2" ParentId="15201" CreationDate="2020-03-09T21:49:06.947" Score="2" Body="&lt;p&gt;Referring to the circuit diagram for this set&lt;br&gt;&#xA;&lt;a href=&quot;http://www.nostalgickitscentral.com/heath/schematics/heathkit_schema_sb102.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;www.nostalgickitscentral.com/heath/schematics/heathkit_schema_sb102.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mic connector has 2 pins and the grounded body as the 3 connections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you have guessed the 2 pins are mic input (measured at 0 volts) and PTT switch (measured 30 volts). Both return to the body of the connector. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The PTT pin is connected to the cathode of the Rx/Tx relay driver (V12B) which is pulled up by the 470k resistor R219 (using the 300V low B+) and should be limited to +15V max by the 15V zener D202.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Shorting this pin to ground will operate the Rx/Tx relays so make sure you have a dummy load connected to the antenna and/or disable the finals to avoid doing any damage. There should only be power at the output if there is some audio input (SSB) or if it's key down on CW, but you never know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you have 30V at this point it's probably worth replacing the the zener.&lt;br&gt;&#xA;It only has 0.6mA flowing through it (300/470000) when V12B is biased off but might have enough current through it when using the VOX to have changed its value. Measure the current through the relays (30v pin to earth PTT current) to know what the zener current max is, use something capable of much more to avoid it getting hot. &lt;/p&gt;&#xA;" OwnerUserId="9531" LastEditorUserId="4665" LastEditDate="2020-03-09T22:16:49.270" LastActivityDate="2020-03-09T22:16:49.270" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16230" PostTypeId="2" ParentId="16227" CreationDate="2020-03-09T23:54:45.040" Score="0" Body="&lt;p&gt;The outside shield of a coax can “radiate like crazy”, depending on the antenna and feedline configuration. This effect is sometimes noticed when shifting a feedline noticeably changes the SWR and/or radiation pattern, or causes “RF in the shack”.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a feedline in the nearfield is not oriented at exactly 90 degrees from a balanced radiation pattern, the projection parallel to the antenna’s polarization can act like a director or reflector element, or raised counter pose, which can pick up a portion of voltage from the EM field and re-radiate it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This effect can occur even if the feedline (or a second feedline or wire of the same length and in the same orientation) is disconnected from the antenna (thus a choke balun won't help).  This is also why it's recommended the the feedline be routed away at close to 90 degrees from a dipole, in its near field; so that there's little or no geometric projection parallel to the dipole.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-03-14T23:05:05.637" LastActivityDate="2020-03-14T23:05:05.637" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16232" PostTypeId="2" ParentId="16226" CreationDate="2020-03-10T02:14:59.307" Score="2" Body="&lt;p&gt;If you are calling CQ, then there are a few ways to make sure you don't sound like a contest station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, if you are calling CQ:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For SSB, a contest station might call &quot;CQ contest, CQ contest, HS0ZLW CQ contest&quot; or if they are busy, just &quot;HS0ZLW CQ contest&quot;. This is sent as quickly as possible while still remaining intelligible. So you just try saying &quot;CQ CQ CQ, HS0ZLW calling CQ CQ 20 metres CQ CQ HS0ZLW calling CQ and standing by&quot; or similar. And you do it at normal pace. Do not mention the word &quot;contest&quot;, as a contest operator might glom on to that and think you're calling CQ contest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For CW, a contest station will be calling at at least 24wpm &quot;CQ HS0ZLW TEST&quot; or just &quot;HS0ZLW TEST&quot; if they are busy. So you call &quot;CQ CQ CQ HS0ZLW HS0ZLW HS0ZLW CQ CQ K&quot; at a slower speed. Contest stations will hear your pace, and not hear TEST at all, and will just go straight past.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, if you are listening to people to call:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Avoid people calling very quickly &quot;CQ contest&quot;, or in CW &quot;TEST&quot;. This bit is easy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thirdly, how about you mix it up a bit?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;12m is a very quiet band at the moment. It's probably the least used of the WARC bands. And the way propagation is at the moment, there's not much to be found there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;17m is an amazing band. I was once scanning around and heard the huge Heard Island DXpedition calling CQ on there in CW with no takers. Worked them first call. There is usually activity on 17m at all times of day and night, as its propagation characteristics are somewhere between those of 20m and 15m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are into CW, then have I got a secret for you! The 30m band is a band with characteristics somewhere between 20m and 40m, and it's not affected too much by the D layer like 40m is, so there is good DX to be found there during the day.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And finally:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the main contests of the weekend are focusing on CW or SSB or RTTY, then simply use another mode for those days. Or you can use FT8 or JS8CALL and still have a lot of fun. If you are a CW person, but the CW portions of every band are full of contest stations, then blow the dust off the microphone and give your vocal cords a tryout! Or if you are an SSB person, dust the key off and remind yourself how much fun can be had on CW (even a QRS CW contact can be very rewarding if you are not used to the mode!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Basically, the contesters are on the bands for a limited time. If you stay out of their way, they will not bother you. It's just another aspect of this fantastic hobby we call ham radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Disclaimer: I used my own callsign as the example in the text above]&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-03-10T02:14:59.307" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16233" PostTypeId="1" CreationDate="2020-03-10T02:39:01.650" Score="1" ViewCount="161" Body="&lt;p&gt;I don't usually operate in 2 m, save for FM satellites. I usually go to a nearby park when I do this, for better view of the horizon. But I tried working them from home for the past couple of days, and found there is massive QRM around 145.650 MHz. So strong, I can hear it on my handheld with the antenna detached. It sounds like a motor. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the SDR, with no antenna attached and the input gain set to zero, I see it at -45 with a noise floor of -60. The signal looks like a hump with the sides wobbling left to right (as if you were rocking a glass of water on a table). Yesterday, it looked like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3XrNk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3XrNk.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This QRM appears all around the neighborhood. It's difficult to pinpoint since it's so strong (it's so strong I don't need to open my squelch to hear it). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The signal stays mostly at 145.650 but from time to time it shifts up and down. Yesterday it was at 145.850.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What on earth could be causing such strong interference? Could it be power line related?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power here is 220 V 50 Hz. Overhead 220 V wires and buried 13.2 kV lines. On HF I have the usual S7 to S9 city noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was able to take a screen capture of SDRsharp during the two &quot;moments&quot; the noise has.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=THyrpk0yXGI&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=THyrpk0yXGI&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="14642" LastEditDate="2020-03-12T00:18:12.603" LastActivityDate="2020-03-12T00:18:12.603" Title="Extremely strong QRM on VHF?" Tags="&lt;vhf&gt;&lt;noise&gt;" AnswerCount="0" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="16234" PostTypeId="2" ParentId="16227" CreationDate="2020-03-10T07:29:24.620" Score="6" Body="&lt;p&gt;The short answer is that it can't.&lt;br&gt;&#xA;A shielded transmitter, connected to an ideal piece of coax, does not generate common mode currents.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The inner and the outer of the cable look connected (and for Direct Current they are), but high frequency currents really cannot pass through the thick metal, they are confined to the inside or the outside.&lt;br&gt;&#xA;Real coax can leak, but in practice it's very little.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Here are some examples.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First - a simple coaxial cable connecting a transmitter to a dummy load. See how the Inside and the Outside of the coax never meet - they really are separate worlds. No RF current can reach the outside of the coax. There are no common-mode currents.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/JwuHI.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fJwuHI.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, a shielded transmitter feeding a length of coax, connected to a balanced antenna without a balun, which creates the unbalanced currents.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/9z00A.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f9z00A.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Balanced lines&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I should mention that it is not only coax that can be used to generate balanced currents, it's just the example you asked about.&lt;br&gt;&#xA;If the transmitter drives a balanced line with equal and opposite voltages, say with a transformer, there will be no unbalanced voltage, and no common-mode current. Ethernet cables are like this (CAT5 etc, before they were shielded). There is very little radiation from the pair, even though it is carrying significant RF power, because the transformer that feeds it has a high common-mode impedance, and the other end is an identical circuit, not an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Generating common-mode currents on purpose&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible to generate common mode currents at the transmitter, but generally we take pains to avoid doing that. Here is an example where it is desirable - I have a bluetooth-receiver-FM-transmitter gadget in my car, which works best if there's a USB cable plugged in. It uses the USB cable &lt;em&gt;in common mode&lt;/em&gt; as the antenna. Separately, inside the shielding, the USB D+ and D-, and 5V and 0V, are available as differential signals to the phone. The same is done in phones that have FM radio receivers, using the headphone cords.&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/0ilhm.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f0ilhm.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-03-10T07:29:24.620" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16237" PostTypeId="2" ParentId="16222" CreationDate="2020-03-10T14:19:30.810" Score="0" Body="&lt;p&gt;Digging into this further I found something that might be what I'm looking for, SvxLink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://github.com/sm0svx/svxlink/wiki&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/sm0svx/svxlink/wiki&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While this might work I'm still curious about other options.  Once I clean up some computer and network issues about the house I'll play with this.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2020-03-10T14:19:30.810" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16238" PostTypeId="2" ParentId="16227" CreationDate="2020-03-10T18:25:35.483" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I haven't seen any reference to common mode current originating at the transmitter.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Likely, you won't. As &lt;a href=&quot;https://ham.stackexchange.com/a/16234/8717&quot;&gt;Tom pointed out&lt;/a&gt;, transceivers use unbalanced to unbalanced connections (where the coax plugs into the rig).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It could be argued that the common-mode currents on the outside of the shield do originate at the transmitter, but it is unbalanced to balanced connections at the antenna which can cause the RF from the transmitter to appear on the outside of the shield. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-03-10T18:25:35.483" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16240" PostTypeId="1" AcceptedAnswerId="16241" CreationDate="2020-03-11T20:46:38.327" Score="11" ViewCount="1434" Body="&lt;p&gt;I use RG-58 for all my HF antennas, since it's light, flexible, convenient, and cheap. And super easy to choke. Whenever I have a problem I just loop a few turns of it on a ferrite core and the problem goes away. Since I operate 100W max and all my antennas are properly matched, I don't think power loss is a concern.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But in a recent discussion I was told by a ham that he &quot;doesn't bother with anything less than RG213&quot;. I looked up the specs for the cable I'm using and the loss is 10.5dB every 100m at 50MHz. My interconnects are 10-12m max and for now I only operate 40 and 20m.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't see a reason to upgrade my RG58 to something better (LMR400 is what I would go with), but maybe I'm missing something?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do see a benefit in going with lower loss for VHF and especially UHF and up. But is there a reason, other than pushing kilowatts, to go with lower loss cable?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="8717" LastEditDate="2020-03-12T18:38:59.817" LastActivityDate="2020-03-15T23:04:18.497" Title="Is &quot;low loss&quot; cable required for HF?" Tags="&lt;hf&gt;&lt;coaxial-cable&gt;&lt;feed-line&gt;" AnswerCount="4" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16241" PostTypeId="2" ParentId="16240" CreationDate="2020-03-11T21:19:00.967" Score="9" Body="&lt;p&gt;Your question seems as much about psychology as much as technical concerns.  We mainly favor the technical questions, but I'll take a stab at the psychological aspects also.  All of you, please feel free to disagree with my conclusions!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coaxial cable is fairly inexpensive for many, compared to our time, even for LMR400.  (Your mileage may vary.)  For many, it's easier to buy and install the more-expensive coaxial cable and not have to worry about the power loss or the power handling capability and just install the cable once, rather than opting for cheaper cable initially and then deciding to replace it later, after buying an amplifier perhaps.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course statements like &quot;I don't bother with anything less than RG213&quot; sound as though they are less about the utility of various grades of cable, and more about how the operator just likes to go with the highest-quality, most-expensive option every time because of the way it makes him or her feel.  Or, as @Mast says, perhaps the operator had a bad experience with poorly-made less-expensive coaxial cable once, and is determined to not let that happen again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were a contester, you might be concerned about the ~1 dB loss in your coaxial cable, because every decibel counts to a contester; 1 dB can easily be the difference between getting the rare multiplier or not in a contest.  If you're just a casual operator with short coaxial runs and you're not about to buy an amplifier soon, then 1 dB is just one-sixth of an S unit that you'll likely never miss, and I'd say that there's no reason to upgrade your RG-58, and that makes you no less of a ham than the operator with all-RG-213 or better.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-03-12T14:55:13.473" LastActivityDate="2020-03-12T14:55:13.473" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16242" PostTypeId="2" ParentId="16240" CreationDate="2020-03-12T17:28:47.450" Score="1" Body="&lt;p&gt;The loses with RG 58 for HF are fairly small unless you have a long run of coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The losses are higher for VHF and much higher for UHF, but as most VHF/UHF is short range, often to a repeater, the loss of power usually does not have much of an impact. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personally I prefer to use LMR400 instead of RG58, as it has lower losses especially on VHF and UFH. It does cost more, but not much more. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-03-12T17:28:47.450" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16243" PostTypeId="1" CreationDate="2020-03-13T11:39:37.437" Score="1" ViewCount="61" Body="&lt;p&gt;Long time maritime operator now semi-retired and messin' about with radios. Family in NL and want to bring my little QRP 40-meter rig this summer. I'd like to operate in Canada, specifically VO1 while shooting some video. Will also be sailing on a friend's sailboat. Last trip home I talked to the operators at Signal Hill and have made some contacts. In 1997 I was reporting for Radio Australia and Australian Broadcasting Commission for the Matthew and Queen's visit for the 500 years. I sailed with the flotilla from Royal NL Yacht Club to Bonavista for the welcome.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because my home country Australia is not a CEPT country, I'm a bit unsure about how to get legal permission to operate in Canada.  Do I need a Canadian license?  What should I do to get started?&lt;/p&gt;&#xA;" OwnerUserId="16607" LastEditorUserId="4665" LastEditDate="2020-03-16T14:18:00.050" LastActivityDate="2020-03-17T23:32:42.443" Title="How can a ham from a non-CEPT country operate in Canada?" Tags="&lt;legal&gt;&lt;canada&gt;&lt;australia&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16244" PostTypeId="2" ParentId="14407" CreationDate="2020-03-14T05:19:37.580" Score="3" Body="&lt;p&gt;Should it be confirmed that the old finals are responsible for the low output then there could be only one solution i.e to replace the old finals with new tubes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thermionic emission from an old vacuum tube cannot be improved by increasing the plate voltage.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-03-14T05:19:37.580" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16249" PostTypeId="2" ParentId="15936" CreationDate="2020-03-14T12:08:11.557" Score="0" Body="&lt;p&gt;In my opinion either a ¼ λ ground plane antenna or a ½ λ J-pole antenna, cut for the centre of the Airband, would be a better choice for reception of ground stations.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-03-14T12:08:11.557" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16250" PostTypeId="2" ParentId="16097" CreationDate="2020-03-14T12:27:39.513" Score="1" Body="&lt;p&gt;It should also be noted that many hams now upload their logs to Log of the World, or other services, and that contest award providers can use these services to match up contacts, making QSL cards a bit less required than they previously were.  Nonetheless, they are still very nice to have as a tangible reminder of an accomplishment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also good to know that non-US hams may not be able to afford to keep up with QSL requests without being sent several dollars to cover costs.  &lt;/p&gt;&#xA;" OwnerUserId="9456" LastActivityDate="2020-03-14T12:27:39.513" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16251" PostTypeId="2" ParentId="16240" CreationDate="2020-03-14T16:36:51.650" Score="0" Body="&lt;p&gt;Your question leaves too many unknown variables to give a specific answer.  Resonant or non-resonant antenna, feedline length, operating frequencies, power levels, your station hardware, and your budget are all important considerations.  There is a wealth of information in various ARRL publications that will provide a lot of guidance.  The &quot;Antenna Book&quot; is probably the most comprehensive source but it can be heavy reading for a rookie.  Versions of the book a few years old can be had cheaply and for a beginner will be more than adequate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck&#xA;KD0ZGW &lt;/p&gt;&#xA;" OwnerUserId="16609" LastActivityDate="2020-03-14T16:36:51.650" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16252" PostTypeId="1" AcceptedAnswerId="16269" CreationDate="2020-03-14T22:41:25.763" Score="3" ViewCount="305" Body="&lt;p&gt;Computer generated and decoded Morse Code seems to be a not-uncommon operating practice in the HF bands.  Given this, and that there's no reason why Morse/CW signals can't be synthesized and decoded at at many 100s or even 1000s of WPM (perhaps with Gaussian pulse shaping at the higher rates), is there a maximum legal (in the U.S.) CW/Morse QRQ WPM in the HF bands?  How about even higher WPM rates in the higher amateur UHF bands? (10e6 WPM?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or does CW plausibly have to be human copiable?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, does QRQ CW require the operator to slow down to 20 WPM every 10 minutes to ID?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="4665" LastEditDate="2020-03-16T14:26:53.820" LastActivityDate="2020-03-17T21:47:04.517" Title="Maximum legal QRQ CW speed?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;cw&gt;&lt;bandwidth&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16253" PostTypeId="2" ParentId="7642" CreationDate="2020-03-14T23:26:25.003" Score="-1" Body="&lt;ol&gt;&#xA;&lt;li&gt;All antennas are dipoles.&lt;/li&gt;&#xA;&lt;li&gt;This means that a 1/4 wave vertical requires a 1/4 wave addition. That 1/4 wave is developed in the earth (hence the term earthing your rig, antenna etc). A signal applied to an antenna will seek out the first and best for it, to replace the earth if it is not available.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Consider a satellite. The scrawny little spike, parabola, conical, whatever is hanging on it, uses the body of the satellite as a ground. Oh you say; what if the satellite body was made of nonconductive material? The pcb ground would do the best it could to make the ground, this is why the shield or ground connection (like the barrel of an SO-239 must - &lt;em&gt;must&lt;/em&gt;, have a very good coupling to the antenna's ground). Best explained as if the SO-239 was soldered to the pcb or the satellite's case - or both. And the antenna also secure electrically as possible.&lt;/p&gt;&#xA;" OwnerUserId="8492" LastEditorUserId="8717" LastEditDate="2020-11-26T19:58:27.343" LastActivityDate="2020-11-26T19:58:27.343" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16255" PostTypeId="2" ParentId="16252" CreationDate="2020-03-15T18:15:54.537" Score="0" Body="&lt;p&gt;&lt;strong&gt;Yes, there is a maximum legal WPM for CW.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The higher the data rate, the more bandwidth a signal occupies. Thus, the &lt;a href=&quot;/questions/tagged/bandwidth&quot; class=&quot;post-tag&quot; title=&quot;show questions tagged &amp;#39;bandwidth&amp;#39;&quot; rel=&quot;tag&quot;&gt;bandwidth&lt;/a&gt; tag.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That also applies to CW. As the WPM is increased, the wider the signal will be. And at some point, the bandwidth of the signal will be so great that it &lt;a href=&quot;https://ham.stackexchange.com/questions/10556/do-fcc-regulations-limit-digital-data-rate&quot;&gt;violates FCC regulations&lt;/a&gt;. According to &lt;a href=&quot;https://ham.stackexchange.com/questions/16252/maximum-legal-qrq-cw-speed/16255#comment25093_16252&quot;&gt;Scott&lt;/a&gt;, the maximum legal speed would be about 360 wpm.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Or does CW plausibly have to be human copiable?&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Also, does QRQ CW require the operator to slow down to 20 WPM every 10 minutes to ID?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The answer to both of those points is no. Think of all the CW signals on the bands that are 40 WPM and higher. There are no present laws that require them to periodically ID at a lower speed. &lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-03-15T18:29:48.050" LastActivityDate="2020-03-15T18:29:48.050" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16256" PostTypeId="2" ParentId="16240" CreationDate="2020-03-15T23:04:18.497" Score="2" Body="&lt;p&gt;There are two reasons you might want to upgrade coax:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;lower loss&lt;/li&gt;&#xA;&lt;li&gt;other reasons&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&quot;Other reasons&quot; include durability, weather resistance, and absolute maximum ratings. Usually the coax either meets these requirements or it doesn't. If it meets these requirements then you'd only upgrade to reduce loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You say your cable has a loss at 50 MHz of 10.5 dB per 100 meters. Do be sure you got this from your specific cable, as not all cable sold as RG-58 is identical. Some of it is quite cheap, and losses are relatively high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your longest run is 12 meters, that's a loss of 1.26 dB at 50 MHz. And you don't operate at 50 MHz, so losses are probably half that, so 0.63 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's nearly nothing. The difference between these two images is 1 dB:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Gxl8N.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Gxl8N.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Jmk3U.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Jmk3U.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;See &lt;a href=&quot;https://ham.stackexchange.com/questions/6676/how-big-is-a-decibel&quot;&gt;How big is a decibel?&lt;/a&gt; for more of this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your situation, money is better spent elsewhere. Consider performance improvement per dollar. Money spent upgrading the feedline could instead be spent upgrading the antenna or transmitter. Other ways you might improve performance include:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Installing more/longer radials under a vertical, reducing ground losses&lt;/li&gt;&#xA;&lt;li&gt;Increasing the height of a dipole, reducing ground losses&lt;/li&gt;&#xA;&lt;li&gt;Installing a Yagi or other more directive antenna, increasing EIRP and also improving your station's receive performance&lt;/li&gt;&#xA;&lt;li&gt;Buying an amplifier or higher power transmitter&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A 1 dB improvement in any part of the &lt;a href=&quot;https://ham.stackexchange.com/questions/352/what-is-a-link-budget-and-how-do-i-make-one&quot;&gt;link budget&lt;/a&gt; is the same, so spend your money where it yields the biggest improvement per cost. On HF with runs under 100 feet, that area is not usually the feedline unless your point of reference is exceptionally low-quality coax.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-03-15T23:04:18.497" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16257" PostTypeId="2" ParentId="495" CreationDate="2020-03-16T11:23:11.620" Score="1" Body="&lt;p&gt;If you are using a monopole antenna, when you hold the radio, your body acts as the image of the antenna to make a full dipole.  This works for both transmit and receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are receiving a strong signal, it doesn't make a lot of difference, but if you have a marginal signal, you will notice that it gets a lot worse if you set the radio down or put it on your backpack.  However, if you set it down on a piece of metal, like a metal table, it'll be about as good as when you are holding it, because the radio can capacitively couple to the metal.  (It doesn't have to make conductive contact to do this.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you put an antenna on the radio that is a full dipole, like an end fed half wave whip, a loop, or coax going to a J-pole, you'll find that this matters a lot less.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, you can add a counterpoise to the monopole and it should help.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-03-16T11:23:11.620" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16258" PostTypeId="2" ParentId="16214" CreationDate="2020-03-16T11:32:02.853" Score="1" Body="&lt;p&gt;Probably you are seeing the results of the AGC on your radio adjusting the front end gain of your radio between when there is no signal and when there is a strong signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just because you hear static does not mean that there is a carrier.&#xA;It just means that your radio is trying very hard to find a signal and has demodulated noise into white noise.  If this bothers you, adjust the squelch on your radio, or if you are listening to a repeater that transmits it, enable tone squelch.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-03-16T11:32:02.853" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16259" PostTypeId="2" ParentId="2414" CreationDate="2020-03-16T23:52:26.717" Score="0" Body="&lt;p&gt;There are actually two types of helical antennas.  The other answers talk about a directional helical antenna, also called an end fire helical antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, there is also a broadside helical antenna, which is essentially a compromised (shortened) monopole.  This antenna is omnidirectional.   However, it is still not special (by itself at least) in receiving signals from multiple sources, beoyind being omnidirectional (like many other antennas are).  You would still need to separate the signals, either by frequency or time.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-03-16T23:52:26.717" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16260" PostTypeId="2" ParentId="16137" CreationDate="2020-03-17T06:50:44.680" Score="3" Body="&lt;p&gt;The answer is no.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best way to protect against static build-up would be to have both antenna elements DC-connected to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This would be automatically ensured with a 1:1 voltage balun.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cJ6qz.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cJ6qz.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With a 1:1 current balun, only one element would be DC-connected to ground. Hence a resistor would be required to be connected between the two elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WUyxD.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WUyxD.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the 1:1 transformer suggested, both the elements would not be DC-connected to ground.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RJBkq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RJBkq.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hence it would offer no protection.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-03-17T08:45:13.770" LastActivityDate="2020-03-17T08:45:13.770" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16261" PostTypeId="2" ParentId="15967" CreationDate="2020-03-17T16:57:48.040" Score="0" Body="&lt;p&gt;Message sending is not part of DMR standard. Messages are transmitted in CSBKs, Control Signalling Blocks&lt;/p&gt;&#xA;" OwnerUserId="16634" LastActivityDate="2020-03-17T16:57:48.040" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16262" PostTypeId="2" ParentId="7327" CreationDate="2020-03-17T17:23:04.803" Score="1" Body="&lt;p&gt;I don't know any radio firmware that would support blocking a specific ID.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It would be easy to implement in MMDMHost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Call Alert is a ringer function. If a radio receives a call alert signal then it rings and sends back an answer to the caller and the caller radio shows a message about the successful delivery.&lt;/p&gt;&#xA;" OwnerUserId="16634" LastActivityDate="2020-03-17T17:23:04.803" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16263" PostTypeId="2" ParentId="15960" CreationDate="2020-03-17T17:25:08.907" Score="1" Body="&lt;p&gt;The easiest way is if you send a private call to 9990 (parrot) in brandmaister network and see the actual traffic on brandmaister's site.&lt;/p&gt;&#xA;" OwnerUserId="16634" LastActivityDate="2020-03-17T17:25:08.907" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16264" PostTypeId="2" ParentId="15546" CreationDate="2020-03-17T17:32:37.177" Score="-1" Body="&lt;p&gt;DMR. It scans DMR signals on the available channels and selects the channel with the best signal&lt;/p&gt;&#xA;" OwnerUserId="16634" LastActivityDate="2020-03-17T17:32:37.177" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16265" PostTypeId="1" CreationDate="2020-03-17T17:45:43.517" Score="0" ViewCount="54" Body="&lt;p&gt;Such characteristics are described in Answer 1 below, as sourced in a study of antenna engineering textbooks, and by generating NEC4.2 studies.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-03-17T17:50:55.850" LastActivityDate="2020-04-16T18:03:00.337" Title="What Are Some of the Most Important Characteristics Applying to the Radiation of Monopole Antenna Systems?" Tags="&lt;antenna-system&gt;&lt;vertical-antenna&gt;&lt;radiation-pattern&gt;&lt;radial&gt;&lt;efficiency&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16266" PostTypeId="2" ParentId="16265" CreationDate="2020-03-17T17:45:43.517" Score="3" Body="&lt;pre&gt;&lt;code&gt;           VERTICAL MONOPOLE, EARTH, and BURIED RADIALS&#xA;         as FACTORS in ANTENNA SYSTEM RADIATION EFFICIENCY&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Considerations:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The components shown in the graphic below, and the soil where they&#xA;are located/buried are elements of the complete antenna system.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;R-F currents flowing on/in the earth within a radius of 1/2&#xA;wavelength from the monopole as a result of its radiation must be collected and returned to the 2nd terminal of the transmit/antenna system. The sum of those currents is equal to the current flowing along the monopole, itself.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The r-f resistance of the Earth+radial path through which those&#xA;currents travel is a series element of the transmit system. Reducing&#xA;the r-f resistance of that path increases the radiation efficiency&#xA;(gain) of the antenna system.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;em&gt;R-F currents flowing in the earth beyond a radius of 1/2 wavelength   from the monopole are not collected by buried radials of any length(s),and so do not affect the radiation efficiency of the antenna system.&lt;/em&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The e-m fields existing just beyond 1/2-wavelength from the monopole are&#xA;fully formed, and will propagate outward into space.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Fields radiated by the monopole toward higher* elevation angles decay at an inverse distance (1/r) rate.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Fields radiated by the monopole toward lower* elevation angles decay at a rate greater than 1/r, due to the effects of their (lossy) interface with the earth.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;em&gt;The radiation efficiency/gain of a monopole antenna system is independent of the conductivity values of the earth existing in the areas beyond 1/2 wavelength from the radiator.&lt;/em&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;em&gt;Received fields beyond a 1/2-wavelength radius of the monopole do vary as a functions of frequency, length of the propagation paths, and the physical conditions along and near those paths (earth conductivity, ionospheric reflection, obstructions etc).&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*The elevation angle separating lower from higher elevation angle        radiation is arbitrary, but generally thought of as ranging from 5 to 10 degrees.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/p3WBt.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/p3WBt.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Author:  Richard Fry - March 2020&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-03-17T17:45:43.517" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16267" PostTypeId="1" CreationDate="2020-03-17T19:01:24.380" Score="0" ViewCount="174" Body="&lt;p&gt;Is the HAM Radio License exam conducted in English in any of the western European Countries?&lt;/p&gt;&#xA;" OwnerUserId="16311" LastActivityDate="2020-03-22T15:55:25.080" Title="HAM Radio Exam in English in West Europe" Tags="&lt;license&gt;&lt;europe&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16268" PostTypeId="1" AcceptedAnswerId="16272" CreationDate="2020-03-17T21:32:36.400" Score="3" ViewCount="872" Body="&lt;p&gt;In particular when ham-sters are using the VHF  or UHF bands and talking to each other through repeaters(as well as local radio nets). But also what about DXing? Do FCC obscenity regulations apply equally to all amateur radio bands?&lt;/p&gt;&#xA;" OwnerUserId="16636" LastActivityDate="2020-04-22T15:45:53.943" Title="Do FCC obscenity regulations apply to ham radio transmissions?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;&lt;etiquette&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16269" PostTypeId="2" ParentId="16252" CreationDate="2020-03-17T21:47:04.517" Score="3" Body="&lt;p&gt;I have noticed that hams using CW, PSK31, RTTY, etc, use different equations to describe their bandwidth requirements.&lt;br&gt;&#xA;Over the years, I have used an equation which combines &#xA;the &quot;k&quot; and the &quot;baud&quot; and the &quot;freq shift&quot; : BW = (k) (baud) (delta freq) .&#xA;This has worked well with various forms of pulse signals, &#xA;and matches spectragraph samples of RF signals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(1)  &quot;k&quot; is the squareness shape from 1 (sine) to above 10 (requires much odd harmonic energy to produce a very 'square' shaped waveform ). &#xA;Sharply shaped Squared CW pulses require much Odd Harmonics energy &#xA;and this produce sideband 'splatter' for CW pulses. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(2)  &quot;baud&quot; is the repitition rate, the number of square pulses produced per second.&#xA;The more square pulses per second, the more 'sideband' required. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(3)  &quot;freq shift&quot; related directly to the FSK signals of PSK31 and RTTY.  Here we should note that even a Pierce crystal oscillator has 'jitter' of 3 to 10 Hz, but this is so close to zero shift that we notate it as &quot;1&quot;.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thus, my personal CW bandwidth is calculated at BW= (3) (15) (1) = 45 Hz. &#xA;Speeds of a K=10 squared signal at 360 wpm would be BW= (10) (360) (1) = 3600 Hz. &#xA;We should note that at higher speeds, the 'ear' requires a crisper defined wave-form in order to be 'heard'.  A soft ( K=1.2 as per PSK31 ) CW waveform would require a slower wpm rate.   A harder ( K=5 ) CW waveform would be intelligible at 25 wpm. &#xA;A harder ( K=7 ) CW waveform would be intelligible at 45 wpm. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using a SDR approach and DSP, software phase-locked loop algorithms, &#xA;a computer could 'copy' CW at very high speeds, but might also require some clocking signals.  PSK31 has clocking markers embedded in the waveform design ( this is the +/- shift of 15.25 Hz between elements. )  The JT65, et al, also rely on inherent clock signals, either for reasons of speed in decoding or in identifying a weak signal below noise level.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Still, &#xA;to the question at hand, Faster Speeds require More Band-Width, &#xA;and there are good equation descriptors of this electrical phenomenom. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have calculated this for PSK31 hams and inspected RF spectrographs , and it fits well. PSK31 at a K= 1.2 always occupies a BW of 67 Hz, measured -27dB down (per FCC). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Same goes for RTTY, where the FreqShift is d=200 or d=1200 ( depending on your country and operating system. ) In RTTY, the delta(F) swamps the other factors.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, with regards to CW band-width restrictions, &#xA;we can , in general , see that high speed and squared-wave-shape &#xA;can possibly require a potentially illegal bandwidth.&lt;br&gt;&#xA;The suggested limit of 360 wpm fits in this equations description. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are generalizations, &#xA;based on my engineering and personal experience, and 62 years of CW experience. &#xA;Please note the Caveat &quot; Y M M V &quot; [ Your Milage May Vary ] &#xA;always applies when evaluating our own experiences. &#xA;We do NOT invite a casual debate on the issues of CW pulse shape and human 'hearing'&#xA;in this forum, at least NOT with me.   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note:   Mike Waters has some good insight into the electrical requirements &#xA;of producing a 'clear' CW signal.  My first experience 'hearing' fast CW &#xA;was ... In our Navy Ham Club,  N.A.S. Norfolk, 1957, &#xA;our chiefs from WWII  operated  CW at 65 wpm !!! &#xA;You have not heard &quot;real CW&quot; &#xA;until you have listened in awe &#xA;as real Navy CW ops play ball at high speed !&#xA;Bugs &amp;amp; head-copy &amp;amp; a rattling mill ... &#xA; ... amazing.&#xA;Just imaagine how very short the 'dit' signal was, &#xA;and imagine just how much 'crispness' that 'dit' must have to be 'heard' ! &#xA;My 'dit' length is about 18 mS at 17wpm, and would be about 4 mS at 65 wpm. &#xA;At 65wpm,  the RF bandwidth could be more than 320 Hz at -27 dB (FCC). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck with your discussions, I am going back to listening to CW on 20M &#xA;and see who is up today !&lt;br&gt;&#xA;Glen Ellis, K4KKQ  ( see QRZ.com )&lt;/p&gt;&#xA;" OwnerUserId="8402" LastActivityDate="2020-03-17T21:47:04.517" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16270" PostTypeId="2" ParentId="16267" CreationDate="2020-03-17T22:02:26.027" Score="2" Body="&lt;p&gt;The UK is a western European Country - aside from Brexit. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The exams are conducted in English language (multiple choice test).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the &quot;Full Licence&quot; you will receive the HAREC (Harmonized Amateur Radio Examination Certificate) according CEPT recommendation T/R 61-02. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A person who holds a HAREC issued by a country that participates in recommendation T/R 61-02 may apply for a licence in a lot of other countries on production of that HAREC. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;See also: &#xA;&lt;a href=&quot;https://rsgb.org/main/clubs-training/for-students/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://rsgb.org/main/clubs-training/for-students/&lt;/a&gt;&#xA;and&#xA;&lt;a href=&quot;https://www.ofcom.org.uk/__data/assets/pdf_file/0026/82637/amateur_radio_licence_guidance_for_licensees.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ofcom.org.uk/__data/assets/pdf_file/0026/82637/amateur_radio_licence_guidance_for_licensees.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15497" LastActivityDate="2020-03-17T22:02:26.027" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16271" PostTypeId="2" ParentId="16268" CreationDate="2020-03-17T22:23:03.547" Score="3" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;FCC obscenity regulations &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;no such thing. It's US Code, and the FCC is only the enforcing organ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the FCC themselves say they enforce things on a &lt;a href=&quot;https://www.fcc.gov/consumers/guides/obscene-indecent-and-profane-broadcasts&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;we know when we see it&quot;&lt;/a&gt; basis, which, for me not coming from a US background, is a pretty strange way of regulating things fairly, since that basically means there's mostly &lt;em&gt;case law&lt;/em&gt;, ie. previous decisions to base one's rights on. ugh; especially, ugh, because that's a &quot;random range of decisions&quot; applied to the constitutional right to free speech (and there's high-publicity cases about exactly that).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the law in question: &lt;a href=&quot;https://www.law.cornell.edu/uscode/text/18/1464&quot; rel=&quot;nofollow noreferrer&quot;&gt;18 US Code §1464&lt;/a&gt; says¹ in verbatim:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Whoever utters any obscene, indecent, or profane language by means of radio communication shall be fined under this title or imprisoned not more than two years, or both.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;So, that doesn't deal with ham radio any different than with ABC news. Now, again, this is all case-law based, so only the judge in your case will be the authority to tell you what applies and what doesn't.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is an &lt;em&gt;extreme&lt;/em&gt; case of &quot;&lt;em&gt;you'll have a bad time if you solely rely on free online legal advice&lt;/em&gt;&quot;, so file a complaint if you want to, and if a complaint is filed against you, it's probably time to get a lawyer. Good luck! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;hr&gt;&#xA;Notice how it's not even a very well-stated law: &quot;radio communication&quot; could be the best-encrypted exchange between you and your lover, with &lt;em&gt;very&lt;/em&gt; personal, &lt;em&gt;very&lt;/em&gt; indecent, &lt;em&gt;very&lt;/em&gt; obscene content. Only the title of that paragraph, &quot;&lt;em&gt;Broadcasting obscene language&lt;/em&gt;&quot; lets the reader in on the original intent to limit this to broadcasting, which again is a broad term – technically, all ham radio communications is broadcast. Morally, the point of the law was to restrict free speech in a way that protects e.g. minors from indecency that they have little choice in receiving, so little sense in regulating ham radio as strictly as nationwide radio syndication.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-03-17T22:28:33.427" LastActivityDate="2020-03-17T22:28:33.427" CommentCount="13" ContentLicense="CC BY-SA 4.0" />
  <row Id="16272" PostTypeId="2" ParentId="16268" CreationDate="2020-03-17T23:18:26.610" Score="3" Body="&lt;p&gt;The amateur radio community is largely self regulated.  So violations of amateur radio rules are rarely directly directly observed by the FCC.  Usually it requires complaints from the amateur radio community for the FCC to initiate action.  Typically, for FCC to make a direct observation of a violation, it would have to be a repeat violation, very flagrant, or so severe as to interfere with other radio services.  Typically, amateurs try peer pressure to fix violations before attempting to get FCC to start enforcement actions.  ARRL recently published an &lt;a href=&quot;http://www.arrl.org/news/view/new-volunteer-monitor-program-is-up-and-running&quot; rel=&quot;nofollow noreferrer&quot;&gt;article about this&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The rules governing amateur radio are actually a bit tighter than for broadcast radio, as amateur radio transmissions are suppose to be family friendly.  However, enforcement of them is more lax than with commercial radio, and penalties are at least initially much lower.  The amateur community would probably complain about commercial use of amateur radio (which is explicitly illegal) before they complained about profanity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, there have been cases where amateur radio operators got in trouble with the FCC, usually because other amateur operators complained.   The results of such violations eventually result in loss of the amateur license. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Continued transmitting without a license is a serious violation that can result in very large fines and in extreme cases, jail time.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-04-22T15:45:53.943" LastActivityDate="2020-04-22T15:45:53.943" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16273" PostTypeId="2" ParentId="16243" CreationDate="2020-03-17T23:19:37.883" Score="1" Body="&lt;p&gt;From &lt;a href=&quot;https://www.ic.gc.ca/eic/site/025.nsf/eng/h_00006.html#tao4&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ic.gc.ca/eic/site/025.nsf/eng/h_00006.html#tao4&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;'...you must bring your amateur radio operator’s certificate/licence and have obtained a CEPT certificate from your home administration. &lt;strong&gt;If your country is not part of the CEPT agreement you must obtain a letter of authority from the &lt;a href=&quot;https://www.ic.gc.ca/eic/site/025.nsf/eng/h_00010.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio Service Centre (ARSC)&lt;/a&gt;&lt;/strong&gt;. Visiting amateurs must include the prefix of the geographical location, and the area of operation with the identification of their station. Therefore, an amateur from the United Kingdom with the call sign G**** who will be operating in Winnipeg, Manitoba, would append the prefix “Portable VE4” or “/VE4” to their home call sign, and transmit “Winnipeg” at least once during each communication.'&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short: to get started, send an email to ic.spectrumamateur-spectreamateur.ic@canada.ca and they should tell you how to proceed.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2020-03-17T23:32:42.443" LastActivityDate="2020-03-17T23:32:42.443" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16275" PostTypeId="1" AcceptedAnswerId="16276" CreationDate="2020-03-18T08:43:30.937" Score="0" ViewCount="202" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BYRNo.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BYRNo.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Warning: Noob question. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm new to Software Defined Radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My aim is to write a program that tells me the signal strength of a radio emitting source (I'll use three such sources and then try to triangulate the location).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've stumbled upon GNU Radio for this purpose (I am using r820t2 dongle -nooElec to receive and  fs1000A with arduino pronmini to transmit on 499 MHz).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've looked into some of GNU Radio docs and found out I can use the companion application to select a source block (osmosdr source for dongle) and direct it to a QT GUI Sink, except that I'd want the output from the source block and do some rssi/signal-strength/decibells to distance calculation on them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I finally found out about probe-blocks(preferred them over custom blocks, correct me if my approach is wrong), and now I'm using a probe block to get the value from source and simply printing it on a qtlabel for now. Its a complex value and usually goes like (-0.003435435353535345+0.00424234242423424234). I need to know what this value is and if either of them is the decibell/signalstrength/rssi.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any resource where I can find my answer? &lt;/p&gt;&#xA;" OwnerUserId="16642" LastEditorUserId="4076" LastEditDate="2020-03-18T09:53:41.700" LastActivityDate="2020-03-18T10:17:02.497" Title="GNURADIO: What does the complex output of an osmosdr source translate to?" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;gnuradio&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16276" PostTypeId="2" ParentId="16275" CreationDate="2020-03-18T10:17:02.497" Score="2" Body="&lt;p&gt;Ok, the probe blocks are not really what you should be using here. In fact, we (I, as architect) should have deprecated them a long time ago – they are really more of a debugging crutch than a signal processing tool.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could have used the QT GUI Number Sink instead.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then: yes, your received signal is a complex value – it's complex baseband. (An &lt;a href=&quot;https://greatscottgadgets.com/sdr/&quot; rel=&quot;nofollow noreferrer&quot;&gt;intro&lt;/a&gt; to that. If you're much more math-affine, &lt;a href=&quot;https://www.afidc.ethz.ch/A_Foundation_in_Digital_Communication/Getting_the_Book.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; book is theory-heavy, good and free. If you're less interested in the theory, and familiar with math at a third-semester engineering level, &lt;a href=&quot;https://www.analog.com/en/education/education-library/software-defined-radio-for-engineers.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Software Defined Radio for Engineers&lt;/a&gt; is good, and I very strongly suggest it over a lot of the tech-affine SDR literature that's floating around in the amateur radio space.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power of that signal is proportional to the squared absolute value. In GNU Radio, there's a block called &quot;Complex to Mag^2&quot;, and that is exactly that operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can convert the result to power by using the logarithm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, downer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Proportional&lt;/strong&gt; means really only that: For any given frequency, gain, sample rate setting of your RTL dongle, there's a fixed factor between power at your antenna and magnitude square of the complex numbers. (Assuming temperature and other environmental factors affecting the analog signal chain don't change.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To know actual physical units, you'll have to first &lt;em&gt;calibrate&lt;/em&gt; your receiver with a source of known power. You don't have one, so you can't.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your application, however, you don't need that at all – you just need to know &lt;em&gt;relative&lt;/em&gt; distances; i.e. it's enough to know that you're e.g. &lt;em&gt;half as far&lt;/em&gt; from the transmitter at point B as you were at point A. Add point C and D, and you can calculate a position.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's possible without calibration: In free-space propagation, power drops with the square of distance, so if your average magnitude square at point A was &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;, it would be &lt;span class=&quot;math-container&quot;&gt;$x\cdot\sqrt{2}$&lt;/span&gt; at point B. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Next downer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;499 MHz typically doesn't see a free-space propagation channel; it's already slightly attenuated through foliage, it reflects well off buildings and even better off cars and other metal surfaces, and so you don't really get a reliable square-law when it comes to power drop with distance. So, unless you really have a high-elevated receiver antenna and thus can guarantee a dominant line of sight to the transmitter, this will get pretty inaccurate, and you'll have to use a lot of different measurements and some algorithmic smarts to figure out the true transmitter location based on that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's whole industries that sell nothing but solutions for that problem – for way easier things, like estimating where in a mountain range a kW TV transmitter is. So, on level field, this is quite doable, on more complex terrain, you're moving into heavy inverse problem math, and would want a propagation map of the terrain as input :)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-03-18T10:17:02.497" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16277" PostTypeId="2" ParentId="16268" CreationDate="2020-03-18T19:04:29.077" Score="9" Body="&lt;p&gt;&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=d4b3c60d2d60000a147f885bdee88264&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5#se47.5.97_1113&quot; rel=&quot;noreferrer&quot;&gt;§97.113&lt;/a&gt;(a)(4) states:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;No amateur station shall transmit [...] obscene or indecent words or language&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;These are not the same regulations that prohibit TV stations from broadcasting obscene or indecent content. However, the above language applies specifically to amateur radio in its entirety.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To my knowledge, the U.S. Code does not explicitly state what is &quot;obscene&quot; or &quot;indecent&quot;, but the FCC is responsible for enforcement and has &lt;a href=&quot;https://www.fcc.gov/consumers/guides/obscene-indecent-and-profane-broadcasts&quot; rel=&quot;noreferrer&quot;&gt;issued some guidance&lt;/a&gt;, which is in turn based on &lt;a href=&quot;https://en.wikipedia.org/wiki/Jacobellis_v._Ohio&quot; rel=&quot;noreferrer&quot;&gt;legal precedent&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-03-18T19:11:34.087" LastActivityDate="2020-03-18T19:11:34.087" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16278" PostTypeId="2" ParentId="6281" CreationDate="2020-03-18T20:42:24.793" Score="4" Body="&lt;p&gt;Assuming the systems have no internal loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reflected power ratio for system 1 is 0.1, for system 2 is 0.01.&#xA;&lt;span class=&quot;math-container&quot;&gt;$ = \Gamma^2 = 10^{-RL/10}$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Power transmitted ratio for system 1 is 0.9, for system 2 is 0.99 &lt;span class=&quot;math-container&quot;&gt;$ = 1-\Gamma^2$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first reflection back from each system will be the largest and subsequent reflections will be heavily attenuated, so we approximate by only considering the first reflections.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we take A to be the power incident on system 1:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;first reflection from system 1 will be &lt;span class=&quot;math-container&quot;&gt;$0.1*A$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;incident power on system 2 will be &lt;span class=&quot;math-container&quot;&gt;$(1-0.1)*A = 0.9*A$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;reflected power from system 2 will be &lt;span class=&quot;math-container&quot;&gt;$(0.01)*(0.9)*A$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;reverse-transmission of system 2 reflected power through system 1 will be &lt;span class=&quot;math-container&quot;&gt;$(0.9)*(0.01)*(0.9)*A$&lt;/span&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;total power reflected (B) from both systems (first reflection only)&#xA;&lt;span class=&quot;math-container&quot;&gt;$B = 0.1*A + (0.9)*(0.01)*(0.9)*A = 0.1081*A$&lt;/span&gt;&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;return loss of total system&#xA;&lt;span class=&quot;math-container&quot;&gt;$RL = 10*log_{10}(0.1081) = -9.66dB$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16646" LastActivityDate="2020-03-18T20:42:24.793" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16279" PostTypeId="2" ParentId="6375" CreationDate="2020-03-18T22:04:31.457" Score="1" Body="&lt;p&gt;On most of TNCs you can dump the monitor settings by the &quot;display monitor&quot; (or &quot;display m&quot;) command&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;cmd:display monitor&#xA;BUDLIST  OFF NONE&#xA;CSTAMP   ON&#xA;DAYSTR   mm/dd/yy hh:mm:ss&#xA;FILTER   OFF&#xA;HEADERLN ON&#xA;LLIST    OFF NONE&#xA;MONITOR  ON&#xA;MALL     ON&#xA;MBEACON  ON  &amp;lt;---- If on, monitors packets addressed to BEACON and ID&#xA;MCON     ON&#xA;MCOM     ON&#xA;MHEADER  ON&#xA;MRESP    ON&#xA;MRPT     ON&#xA;MSTAMP   ON&#xA;MXMIT    ON&#xA;PID      ON&#xA;SUPLIST  OFF NONE&#xA;TRACE    OFF&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="16634" LastEditorUserId="16634" LastEditDate="2020-03-19T12:03:15.707" LastActivityDate="2020-03-19T12:03:15.707" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16280" PostTypeId="1" AcceptedAnswerId="16285" CreationDate="2020-03-19T18:23:53.007" Score="4" ViewCount="201" Body="&lt;p&gt;I got my HAM Radio License (Grade-One) License issued on 2005 year (New Delhi, India). Unfortunately Date of Termination of the license is missing. Tried reaching Helpdesk via E-Mail but not much help.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is my Amateur Radio license still valid? If not, how to get it renewed?&lt;/li&gt;&#xA;&lt;li&gt;My residence address got changed. How to update new address?&lt;/li&gt;&#xA;&lt;li&gt;Is there an online portal from Department of Telecommunication (India) where license can be renewed?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CuxpN.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CuxpN.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11347" LastEditorUserId="4665" LastEditDate="2020-03-19T20:34:50.657" LastActivityDate="2021-03-02T08:22:30.323" Title="How to check HAM license status - India - Grade One License?" Tags="&lt;license&gt;&lt;india&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16281" PostTypeId="1" CreationDate="2020-03-20T18:45:51.843" Score="1" ViewCount="129" Body="&lt;p&gt;I've built FM CCIR/OIRT downconverter based on Sanyo LA1185 IC. I've used most famous schematics for it with slight modification (added DC blocking capacitor 1 nF rated on the output)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UyrtA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UyrtA.png&quot; alt=&quot;schematics&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Coils L1 and L2 are made of 0.8 mm thick copper wire and have 4 turns with internal diameter of 4.5 mm. Coil L3 have almost the same params; the only exception is it have 6 turns. I've made and ordered PCB and soldered all components. However I observe some weird glitches.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I use 22 MHz quartz oscillator then I'm able to receive 88-96 MHz on my old FM OIRT radio: [88; 96] MHz - 22 MHz = [66; 74] MHz. All stations within that range can be heared just fine. The same is true for 29 MHz quartz: [95; 103] MHz - 29 MHz = [66; 74] MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem arises when I try to use 35 MHz quartz oscillator. Reception is fine within [101; 105] MHz range - I can hear stations clearly and signal indicator on receiver behaves normally. However when I try to receive higher frequencies I observe weird glitches. Within the range of approx [105; 106] MHz receiver plays just nothing - I can't even hear usual static noise. It seems like it plays &quot;loud silence&quot;. Signal indicator shows very strong signal during this but speaker just doesn't play anything! If I go even higher after ~106 MHz silence goes away, I can hear static noise and barely hear stations which works in [106; 108] MHz range. However reception is very weak. Moreover, I can hear ghost stations within the range [101; 104] but in mirrored order (e. g., for 106 MHz I receive station at 104.5 MHz, for 107.2 I receive 103.2 MHz and so on).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll try to summarize it all below:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;[88  --- 96  MHz] (22 MHz quartz, brilliant quality)&#xA;[95  --- 103 MHz] (29 MHz quartz, brilliant quality)&#xA;[101 --- 105 MHz] (35 MHz quartz, brilliant quality)&#xA;[105 --- 106 MHz] (35 MHz quartz, NOTHING is played, &quot;loud silence&quot;, unusually very strong signal)&#xA;[106 --- 108 MHz] (35 MHz quartz, barely audible 106-108 MHz stations, 101-105 stations in mirror order)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I can't figure out what the heck is taking place here. I suspect two things: quartz and LA1185. But if my quartz is defective I expect [101; 109] MHz range to not work at all but I observe incosistent behavior. I tried to find some info about LA1185 quirks but with no success.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you advice me where I should start? May be I made some obvious flaw in design...&#xA;I've uploaded my whole project to the &lt;a href=&quot;https://github.com/dvdesolve/ccir2oirt&quot; rel=&quot;nofollow noreferrer&quot;&gt;GitHub&lt;/a&gt; if someone is interested in actual schematics and layout.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;EDIT 1:&lt;/strong&gt; schematics available as separate PDF &lt;a href=&quot;https://ftp.desolve.ru/ftp/viktor/schematics.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. Don't be surprised with it - I made version for 3 selectable subranges. Also it have negative power regulator because the receiver itself have negative regulated PSU.&lt;/p&gt;&#xA;" OwnerUserId="14179" LastEditorUserId="14179" LastEditDate="2020-03-20T21:31:00.710" LastActivityDate="2020-03-20T21:31:00.710" Title="LA1185 FM downconverter shows weird behavior" Tags="&lt;equipment-design&gt;&lt;fm&gt;&lt;transverter&gt;" AnswerCount="0" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16282" PostTypeId="1" CreationDate="2020-03-21T00:53:55.923" Score="1" ViewCount="186" Body="&lt;p&gt;I have a Kenwood TM-261. It has the frequencies from 118 to 173 MHz. What frequencies can I transmit on without a licence? &lt;/p&gt;&#xA;" OwnerUserId="16656" LastEditorUserId="76" LastEditDate="2020-03-21T01:30:48.913" LastActivityDate="2020-03-27T02:26:59.700" Title="What frequencies in 118–173 MHz can I transmit on without a license in Canada?" Tags="&lt;legal&gt;&lt;frequency&gt;&lt;2m-band&gt;&lt;canada&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16283" PostTypeId="2" ParentId="16282" CreationDate="2020-03-21T09:54:40.170" Score="6" Body="&lt;p&gt;None. Basically, aside from a few ISM bands, none of which are covered by your radio, you can transmit &lt;strong&gt;nowhere&lt;/strong&gt; without a license, unless you're using hardware that restricts you to legal usage (e.g. DECT phones; you don't need a license to operate a wireless indoor phone, but the phone has to be built in a way that prohibits any other usage).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-03-21T09:54:40.170" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16284" PostTypeId="1" CreationDate="2020-03-21T10:02:55.463" Score="0" ViewCount="79" Body="&lt;p&gt;FT450D in cw mode does not transmit unless PTT is actuated.  &quot;BK-IN&quot; not in display despite pressing function followed by vox/store button.&lt;/p&gt;&#xA;" OwnerUserId="16657" LastActivityDate="2020-04-25T15:08:50.897" Title="FT450D no cw tx unless ppt is held" Tags="&lt;cw&gt;&lt;transmitter&gt;" AnswerCount="1" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16285" PostTypeId="2" ParentId="16280" CreationDate="2020-03-21T11:19:03.873" Score="3" Body="&lt;p&gt;For renewal of Amateur Radio Transmitting licence the following are required:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A letter requesting renewal of licence&lt;/li&gt;&#xA;&lt;li&gt;Copy of original license along with copy of last renewed intimation (if it has been renewed before)&lt;/li&gt;&#xA;&lt;li&gt;Proof of age&lt;/li&gt;&#xA;&lt;li&gt;Proof of address&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Licence fee Rs. 1000.00 for a 20 year license and Rs. 2000.00 for a Life Time License. Payments to be made through the Non Tax Receipt Portal (NTRP).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A copy of the online payment receipt is to be enclosed with your other documents.&#xA;A large self-addressed envelope (no stamps required) also to be enclosed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note:&#xA;WPC does not charge any fee for licence renewals beyond 80 years of age. The applicant only needs to submit an application requesting renewal along with a copy of the licence. The licence is then renewed for a period of 10 years.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It can be renewed for another 10 years after the licencee completes 90 years of age.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All these to be sent by courier to&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Asst. Wireless Advisor to GOI,&#xA;608 Sanchar Bhavan, 20 Ashoka Road,&#xA;New Delhi-110 001.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;More information at&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://arsi.info/faq/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://arsi.info/faq/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-03-24T03:19:07.643" LastActivityDate="2020-03-24T03:19:07.643" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16286" PostTypeId="1" CreationDate="2020-03-21T18:39:00.433" Score="1" ViewCount="23" Body="&lt;p&gt;Cannot connect to Raspberry Pi with Fldigi, ttyusb0 does not show up in any cat control functions. I can connect my TS590S to the Pi and I can connect the Ten Tec to any window machine. But I cannot connect the Pi to the Ten Tec,any ideas as to a solution??&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you,&lt;/p&gt;&#xA;&#xA;&lt;p&gt;John&lt;/p&gt;&#xA;" OwnerUserId="16661" LastEditorUserId="873" LastEditDate="2020-03-22T00:05:35.807" LastActivityDate="2020-03-22T00:05:35.807" Title="Ten Tec Argo IV wont connect to Fldigi on R Pi" Tags="&lt;linux&gt;&lt;computer-control&gt;&lt;fldigi&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16287" PostTypeId="2" ParentId="16286" CreationDate="2020-03-22T00:05:14.593" Score="1" Body="&lt;p&gt;If you don’t see ttyusb0 when you plug the radio into a Linux machine, but the COM port appears when you plug it into a Windows machine, then it sounds like you need to find a Linux driver for the USB-to-serial chipset inside the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This means finding out which chipset it uses, then trying to find a driver for that chipset. You can use &lt;code&gt;lsusb&lt;/code&gt; to find the chipset’s IDs, and then use those to search for a driver.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-03-22T00:05:14.593" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16288" PostTypeId="1" CreationDate="2020-03-22T04:24:38.553" Score="2" ViewCount="71" Body="&lt;p&gt;I programmed my Baofang UV-5RA radio to my local repeater about less than a 1/4 mile away. When I cue the mic and release, I get a signal from the repeater. However, I can only hear people if I have the moni button pressed. They can hear me clear but I can’t hear them unless I press the moni button.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also have another baofang uv-5ra radio that I set up to the same repeater, and I can’t transmit to it from my other baofang radio. Same thing happens I have to press the moni button and I can barley hear it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I programmed my radio to a repeater in San Francisco and I heard them loud and clear.  &lt;/p&gt;&#xA;" OwnerUserId="16664" LastEditorUserId="8717" LastEditDate="2020-03-24T00:11:15.123" LastActivityDate="2020-03-24T00:11:15.123" Title="Baofang uv-5rA/ repeater trouble" Tags="&lt;receiver&gt;&lt;baofeng&gt;&lt;repeater&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16289" PostTypeId="2" ParentId="16282" CreationDate="2020-03-22T10:47:37.223" Score="2" Body="&lt;p&gt;In addition to the answer from @Marcus, I'd like to point out that (since you already have the radio) it's just a small step to get a basic ham radio license. Not familiar with the classes as used in Canada, but surely there is a &quot;basic&quot; class which shouldn't take too much effort to get. While pretty basic, the knowledge required is rather interesting (basic propagation, transmission and technical/electronic knowledge as well as common radio operator do's and don't and practices). It's likely rather cheap as well. It will get you your own call sign and privileges to transmit and have conversations on a couple of bands, one which is the 2-meter band around 145 MHz which you can do with your radio. Add a cheap SDR dongle and some wire to receive and you could just as well contact and talk with/over the international space station.&#xA;Just in case you have the idea that the &quot;average&quot; radio operators are not the kind of group you relate to (I had that idea), you might be right. HOWEVER: the last few years, an amazing amount of new possibilities have come up, leading to a whole new group of amateurs doing really cool things with new technology. Just take a look at &lt;a href=&quot;https://hackaday.com/?s=Radio&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hackaday.com/?s=Radio&lt;/a&gt; to get an idea... &lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2020-03-22T10:47:37.223" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16291" PostTypeId="2" ParentId="16267" CreationDate="2020-03-22T15:55:25.080" Score="0" Body="&lt;p&gt;As already mentioned, the UK conducts test in English. Ireland does also - &lt;a href=&quot;https://www.irts.ie/cgi/st.cgi?applying&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.irts.ie/cgi/st.cgi?applying&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition you can sometimes sit the US FCC exam in various locations through Europe. This can then be used to apply for a US license. The ARRL lists some/most/all dates: &lt;a href=&quot;http://www.arrl.org/find-an-amateur-radio-license-exam-session&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/find-an-amateur-radio-license-exam-session&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am assuming you are a European resident trying to get a local license without speaking the local language. If so then check the rules carefully with regard obtaining a local license before proceeding. The FCC don't issue HAREC certificates and this might complicate matters when applying for a local license. Others will know more on this if Google doesn't help.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doing the exam in the UK is how I got my German license though so I know that definitely works! Note that, maybe depending on your local country, you probably have to qualify for the full UK license to be able to apply for a local license. That means passing the Foundation, Intermediate and Full exams (and there is a practical assessment as well). I'm not sure about Ireland so maybe its simpler there.&lt;/p&gt;&#xA;" OwnerUserId="865" LastActivityDate="2020-03-22T15:55:25.080" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16292" PostTypeId="1" AcceptedAnswerId="16371" CreationDate="2020-03-22T18:00:33.643" Score="4" ViewCount="92" Body="&lt;p&gt;While studying for a HAM license exam I ran into a question that I am having trouble with answering. There are two aspects that I cannot explain, given my current admittedly little understanding of the subject.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the following statement in the exam text...&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The damping between two vertical half-wave dipoles is measured at a certain frequency.&#xA;  The antennas are set up in free space.&#xA;  If the frequency is doubled and the dimensions of the half-wave dipoles are adjusted accordingly, the damping will increase by 6 dB. &lt;em&gt;(Translation is my own, original is in Dutch)&lt;/em&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;... I have the following questions:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Why does damping &lt;em&gt;increase&lt;/em&gt; rather than decrease with increasing frequency, with their relative distance of the antennae being (assumed) constant?&lt;/li&gt;&#xA;&lt;li&gt;What is the appropriate logic or formula to apply here that explains why there is a 6 dB increase rather than (say) 3 dB?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Should you wish to look at the original dutch wording, it's question 37 in the &lt;a href=&quot;https://cdn.ham-radio.nl/pdf/2019/F6-11-2019.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;6 November 2019&lt;/a&gt; full-license exam. The &lt;a href=&quot;https://cdn.ham-radio.nl/pdf/2019/F6-11-2019-ant.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;answer table&lt;/a&gt; lists answer A (6 dB increase) as being correct.&lt;/p&gt;&#xA;" OwnerUserId="16576" LastActivityDate="2020-04-02T15:31:21.930" Title="Why does damping between two antennas increase with frequency?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="7" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16293" PostTypeId="2" ParentId="16288" CreationDate="2020-03-23T12:13:22.253" Score="2" Body="&lt;p&gt;I am guessing that you programmed a receive tone requirement. Try programming only the transmit tone and leaving the receive tone not required. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't have Chirp available right now so I can't give you the names of these fields. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Best, &#xA;Ed Greenberg&#xA;KM6CG&lt;/p&gt;&#xA;" OwnerUserId="9456" LastActivityDate="2020-03-23T12:13:22.253" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16295" PostTypeId="1" AcceptedAnswerId="16296" CreationDate="2020-03-24T07:36:18.593" Score="3" ViewCount="1238" Body="&lt;p&gt;I am not sure if this question fits better in physics.stackexchange or ham.stackexchange, feel free to correct me. I am new to studying RF and SDR in general, I was looking up how modulation works and FM by definition encodes information to carrier frequency by modifying the frequency of wave. Considering this, it doesnt make sense how you can tune into an fm frequency, say 101, 101 being the carrier frequency makes sense but once information/music is encoded to this shouldn't the frequency change to something else? &lt;/p&gt;&#xA;" OwnerUserId="16642" LastActivityDate="2020-03-25T12:02:18.013" Title="How does FM station have fixed frequency when FM modulation changes the frequency?" Tags="&lt;rfi&gt;&lt;fm&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16296" PostTypeId="2" ParentId="16295" CreationDate="2020-03-24T07:49:27.157" Score="7" Body="&lt;p&gt;&quot;Tuning&quot; an FM receiver sets the &lt;em&gt;center&lt;/em&gt; frequency of the receiver, but its internal circuitry is designed to pass enough of the Bessel sidebands produced by frequency modulation of that waveform to be demodulated with low noise and distortion.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-03-24T07:49:27.157" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16297" PostTypeId="2" ParentId="16295" CreationDate="2020-03-24T12:32:11.773" Score="5" Body="&lt;p&gt;There are two ways to look at this: center frequency and bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In FM, the frequency varies as the amplitude of the audio varies.  If the audio was a sinusoidal tone, the frequency would vary symmetrically around a center frequency, which is constant.  More complex audio is generally still symmetrical.   The FM receiver actually locks on to that center frequency using the symmetry, so even if your tuning is a bit off (but still within the radio's pass band), it will lock on to the signal.  This is a fundamental defining feature of FM.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All transmissions containing information are assigned not just a frequency, but a bandwidth. (Without bandwidth, it can't contain any information.)  The bandwidth of the FM transmission is tied with a fixed ratio (frequency modulation index) to the maximum amplitude range of the audio.  If the audio has a dynamic range large enough to cause the FM to exceed its assigned bandwidth, it will be clipped before being modulated into FM.  The maximum range of amplitude variation of the audio is sometimes called &quot;envelope&quot;. &lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-03-25T12:02:18.013" LastActivityDate="2020-03-25T12:02:18.013" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16298" PostTypeId="1" CreationDate="2020-03-24T17:45:13.133" Score="2" ViewCount="1369" Body="&lt;p&gt;I see folding antennas of various lengths that people are using for for their HT. My question is about the optimal length. I know it may &quot;depend&quot; on many factors so let me know if I need to provide more information. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know that many antennas are actually a coil of a particular length (quarter wavelength perhaps), so maybe these are actually all the same coil length. I'm not sure. But I'm wondering what factors should determine the length that one chooses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't own anything outside of FRS and CB yet however I'm doing research ahead of time. To have an example, let's say I'm using the dual band UV-5R for communication on both VHF and UHF (2m and 70cm), and in an urban environment. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several lengths available:&lt;br&gt;&#xA;33cm=13in&lt;br&gt;&#xA;47cm=18in&lt;br&gt;&#xA;72cm=28in&lt;br&gt;&#xA;108cm=42.5in&lt;br&gt;&#xA;124cm=49in&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just look at this beast:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/auxJnm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/auxJnm.png&quot; alt=&quot;Example antenna&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;(Image from &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B07V315N3P&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amazon.com&lt;/a&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could it be too long and actually hurt gain or pickup too much noise? Or in general, the longer the better? If that's the case, perhaps there is diminishing return and the extra length becomes just an annoyance after 47cm/18in. How should one decide?&lt;/p&gt;&#xA;" OwnerUserId="16673" LastActivityDate="2021-03-29T14:57:44.097" Title="Optimal length of HT antenna for VHF UHF and diminishing return" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;ht&gt;" AnswerCount="6" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16299" PostTypeId="2" ParentId="16298" CreationDate="2020-03-24T19:27:26.300" Score="0" Body="&lt;p&gt;Typical HT antennas are very much a compromise.  What would be considered a &quot;basic&quot; antenna at other bands would be a half-wave dipole, or a quarter-wave vertical with a ground plane or quarter-wave elevated radials.  Polarization for FM is vertical, so a horizontal dipole won't work.  Ordinary vertical dipoles are not very practical for portable use (the coax must be led away from the center of the antenna at right angles for a ways), but a J-pole antenna is essentially an end-fed vertical dipole that uses some impedance matching tricks.  A 2m J-pole is about 60&quot; / 1.5 m long.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've used a 2m J-pole at HT power levels, and it makes a great antenna.  It doesn't suffer reduced gain or increased noise; people on the repeater thought I was using a mobile rig rather than an HT.  Generally speaking, any antenna smaller than a half-wave dipole or quarter-wave vertical (with ground plane or elevated quarter-wave radials) will suffer reduced performance.  In the reduced-performance category, which typical HT antennas are definitely in, anything larger is better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So finding the best antenna for you is an exercise in adjusting the compromise to find out what is best for you.  If you're close to the repeaters you usually use, and the noise isn't too terrible, then the &quot;rubber ducky&quot; antenna that came with the HT might be fine.  If you're in the woods far outside of town and you're trying to report an emergency, then you probably want the largest antenna you can get.  Personally I have the antenna that came with my HT that is about 10&quot; / 25 cm long, a slightly larger one about 18&quot; / 45 cm long, and I mean to get a roll-up J-pole from Ed Fong WB6IQN for hiking.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice would be to try the antenna that comes with the HT, and if that isn't long enough, then get a longer one.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-03-24T19:27:26.300" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16300" PostTypeId="2" ParentId="16298" CreationDate="2020-03-24T23:29:01.793" Score="1" Body="&lt;p&gt;I had a 15&quot; whip for my 2m HT that I thought performed quite well. Unfortunately I dropped my radio and that managed to snap the antenna. I have yet to replace it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You're gain isn't really proportional to the length. Rather, it's about the electrical resonance of that length. Think about humming an A really loudly next to a guitar. You can make the A string start vibrating, but the other strings won't vibrate. A resonant quarter-wave at 146 MHz (right in the middle of 2m) will be about 19&quot; long. But that's assuming there aren't any loading coils or anything else like that in the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My favorite 2m antenna though is a roll-up J-pole I made myself. Instructions &lt;a href=&quot;http://www.n1uec.org/n1uec/2meterjpole.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. I throws up anywhere and performs really well. I've been able to get signals about 11 miles on half a watt with it.&lt;/p&gt;&#xA;" OwnerUserId="16387" LastActivityDate="2020-03-24T23:29:01.793" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16302" PostTypeId="2" ParentId="1034" CreationDate="2020-03-25T03:08:56.970" Score="0" Body="&lt;p&gt;I have this hunch that using a standard Cat-5e networking cable to replace the speaker wires would work because wikipedia &lt;a href=&quot;https://en.wikipedia.org/wiki/Twisted_pair&quot; rel=&quot;nofollow noreferrer&quot;&gt;Twisted-pair&lt;/a&gt; says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;twisted pair reduces electromagnetic radiation from the pair and&#xA;  crosstalk between neighboring pairs and &lt;strong&gt;improves rejection of external&lt;/strong&gt;&#xA;  &lt;strong&gt;electromagnetic interference.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Also, instead of just using one pair, you could use all of them in parallel for better conductivity. An additional benefit is, if one wire breaks, the others remain. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last sentence in this &lt;a href=&quot;https://en.wikipedia.org/wiki/Twisted_pair#Unshielded_twisted_pair&quot; rel=&quot;nofollow noreferrer&quot;&gt;section on Unshielded-twisted-pair (UTP) at Wikipedia&lt;/a&gt; says a balun is needed, though.  Still learning about that...  Would this application require a balun?&lt;/p&gt;&#xA;" OwnerUserId="16674" LastActivityDate="2020-03-25T03:08:56.970" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16304" PostTypeId="2" ParentId="16298" CreationDate="2020-03-25T12:39:03.440" Score="3" Body="&lt;p&gt;To directly answer your question, the ideal antenna length for maximum radiation is dependent on the wavelength.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, CB wavelength is approximately 11m.  The ideal antenna is half of that for a dipole antenna.  However, most CB (and HT) antennas are monopoles, which split the antenna in half and use its mount as the other half, so the ideal CB antenna would be approximately 2.75m, or just under 9 ft, using the vehicle body as the other half of the antenna.  (A vehicle with less than 9ft of metal may not work well with such an antenna.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, the ideal 2m antenna for an HT would be approximately 0.5m with you holding the radio for the other half of the antenna, although you can also get a 1m antenna (&quot;half wave&quot;) that will work somewhat better, as this is an end fed dipole instead of a monopole, and doesn't rely on you holding the radio to make the other half of the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the antenna is a full 1/4 wavelength, it is typically not a coil.  Shorter antennas probably are, but the length of the wire in the coil changes as the antenna gets physically shorter, so it is not direct relationship, but electrically, it will still measure as 1/4 or 1/2 wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The higher frequencies like 2m and 70cm are very dependent on line of sight between the receiver and transmitter, and thus height of the antenna is a huge factor in antenna effectiveness.  Thus, the size of the antenna may increase effectiveness not because of better radiation, but because of better height, and you might get the same effect with a smaller antenna raised higher.  This is one of the advantages of external antennas like the J-pole -- you can separate it from the radio with coax and raise it higher.  (The j-pole is also an end fed dipole. )&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Lastly, when considering the &quot;optimal&quot; antenna, you need to take mechanical factors into consideration.  In other words, larger HT antennas are heavier and can become a huge lever arm, and put more stress on the radio's antenna connector, and have a higher chance of breaking it. Half wave antennas typically also include an impedance matching coil, which makes them even heavier.  When using large antennas, some care must be taken to minimize stress on the radio's antenna connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible to get a &quot;better&quot; antenna that is longer than 1/2 wavelength, but it would no longer be a dipole.  For instance, a colinear antenna is a stacked phased array of dipoles and can be many multiples of 1/4 wavenlength.  This describes some larger wifi antennas and possibly some vehicle antennas or antennas mounted to buildings, but you won't find a 70cm HT colinear, its just too big.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-03-25T12:45:09.997" LastActivityDate="2020-03-25T12:45:09.997" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16305" PostTypeId="1" AcceptedAnswerId="16306" CreationDate="2020-03-25T14:29:01.667" Score="1" ViewCount="156" Body="&lt;p&gt;I have a radio with a nominal output of 1-30mW (frequency dependent) and amplify this with a 21.8dB capable amplifier (frequency dependent, but should be ~150mW). The signal output then passes through a -20dB attenuator to my frequency counter. The frequency counter reads 121mV/-5.3dBm. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I calculate my amplified signal output, before -20dB attenuation? I understand -20dB is a reduction by a factor of 100. How do I calculate dBm/mW output?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone provide clarity?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: This frequency counter reads 2.2dBm/287mV when I transmit with a UV5R (~2W) 5cm from it. I guess this could be a problem, since it sees only 1.7mW. This UV5R transmits &gt;25km easily. The frequency counter is a Surecom SF-103.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Update: The Surecom SF-103 frequency counter cannot react quickly enough to changes in frequency (within a range of ~5KHz), and so it displays nothing. The solution was to output a stable signal, then it works fine. Signal strength is still not displayed correctly, even with the right shielded cable for UHF.&lt;/p&gt;&#xA;" OwnerUserId="9583" LastEditorUserId="9583" LastEditDate="2020-03-30T10:44:38.660" LastActivityDate="2020-03-30T10:44:38.660" Title="Signal power measurement" Tags="&lt;rf-power&gt;&lt;amplifier&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16306" PostTypeId="2" ParentId="16305" CreationDate="2020-03-25T14:43:43.780" Score="6" Body="&lt;p&gt;If the frequency counter is measuring -5.3 dBm, then before 20 dB of attenuation the power was 20 dB more than that, so 14.7 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;dBm&quot; means &lt;a href=&quot;https://en.wikipedia.org/wiki/Decibel&quot; rel=&quot;noreferrer&quot;&gt;decibels&lt;/a&gt; relative to 1 milliwatt. 14.7 decibels can be converted to a ratio like so:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 10^{14.7/10} = 29.5 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So 14.7 dBm is 29.5 milliwatts.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-03-25T14:43:43.780" CommentCount="14" ContentLicense="CC BY-SA 4.0" />
  <row Id="16307" PostTypeId="1" CreationDate="2020-03-25T14:56:32.143" Score="0" ViewCount="452" Body="&lt;p&gt;I am making an AM radio with the specifications of: Part 1. Design a circuit with an antenna for tuning your receiver to a signal of a specific carrier radio frequency so that you can select a certain radio station. The frequency range is from 526 kHz and 1706 kHz at 10 kHz intervals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found a site with some information about a resonator &lt;a href=&quot;https://www.instructables.com/id/How-to-Build-and-Tune-an-AM-Radio/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.instructables.com/id/How-to-Build-and-Tune-an-AM-Radio/&lt;/a&gt; and I have read some stuff about the detector, antenna, tuner, etc. &lt;img src=&quot;https://cdn.hswstatic.com/gif/radio-am-radio.gif&quot; alt=&quot;Parts of an AM Radio&quot;&gt;, but I don't know what kind of tuner, detector, or amplifier I need for my circuit specifically. I'll start with asking what kind of tuner would I need for my specifications(&lt;strong&gt;Answered&lt;/strong&gt;)? Also, is a tuner and a resonator the same thing(&lt;strong&gt;Answered&lt;/strong&gt;)? Can someone explain the detector and/or amplifier part of the am radio with regards to my specifications?&lt;/p&gt;&#xA;" OwnerUserId="16680" LastEditorUserId="873" LastEditDate="2020-03-26T02:03:27.323" LastActivityDate="2020-03-29T17:25:21.813" Title="Building an AM Radio receiver" Tags="&lt;antenna&gt;&lt;amplifier&gt;&lt;am&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16308" PostTypeId="2" ParentId="16307" CreationDate="2020-03-25T15:09:08.807" Score="2" Body="&lt;p&gt;The tuner is whatever allows the frequency to be selected. Tuners usually involve some kind of resonant circuit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a very basic AM receiver like you describe, the tuner is probably nothing more than an LC circuit, with one or both of the inductor or capacitor being variable.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-03-25T15:09:08.807" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16310" PostTypeId="2" ParentId="16307" CreationDate="2020-03-25T15:52:02.223" Score="0" Body="&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/klE2V.png&quot; alt=&quot;Simple crystal radio schematic.&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The way I understand it, the tuner is an LC circuit forming a parallel tank that is designed to give maximum impedance at the desired frequency. This mean at that frequency, more current will flow through the detector and headphones than through the tank. At other frequencies, the tank circuit presents a low impedance and those signals are sent to ground through the tank, bypassing the detector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The selected frequency is given by 1/(2*pi*sqrt(LC)). Making either your capacitor or inductor adjustable lets you tune around.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The diode acts as the detector. This circuit has no amplifier, so it'll only be good for picking up strong signals. The amplifier would come after the detector/diode.&lt;/p&gt;&#xA;" OwnerUserId="16387" LastEditorUserId="16387" LastEditDate="2020-03-26T19:29:16.390" LastActivityDate="2020-03-26T19:29:16.390" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16311" PostTypeId="1" AcceptedAnswerId="16314" CreationDate="2020-03-25T16:00:17.293" Score="2" ViewCount="956" Body="&lt;p&gt;Typical SWR meters don't measure forward power very accurately at the lower end of the scale, which can be a real problem at QRP power levels.  Better power meters like the Bird model 43 are expensive, and the calibration of used models can be very uncertain.  However, I've heard that an RF probe, a dummy load, and a multimeter can be used to make a power meter.  I've also heard that such a power meter can be more accurate, if an oscilloscope is available for calibration.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can one make an RF probe, and how does one use an RF probe for accurate power measurement?&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-03-25T20:30:15.617" LastActivityDate="2020-12-22T17:44:02.540" Title="How to make an RF probe for accurate power measurement at QRP power levels?" Tags="&lt;rf-power&gt;&lt;measurement&gt;" AnswerCount="6" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16312" PostTypeId="2" ParentId="16311" CreationDate="2020-03-25T18:16:40.990" Score="1" Body="&lt;p&gt;Especially for narrowband (by modern standards, I'd call that anything &amp;lt; 50 kHz bandwidth) signals, the oversampling that you can do with even the cheapest SDR devices (e.g. RTL-SDR dongles) gives you excellent detectability, down to thermal noise. (Make sure you turn of any AGC, though.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, assuming you just want to know what the power of that single tone is, which has low phase noise (and hence very low actual bandwidth), you'd tune your SDR such that the LO of the mixer doesn't lay over your signal of interest, then filter your signal drastically in the digital domain to restrict the observed power to really your band of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then magnitude-squaring and averaging gives you the digital power. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But, what's the physical power? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the SDR alone, you couldn't say – SDR devices are not calibrated measurement devices. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you have a source of known physical power, you can measure that, and calculate a factor between digital and physical power. Easy!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, the task has just been reduced to:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Build a digital-power-detection system: RTL-SDR, and GNU Radio companion (osmocom Source -&gt; complex to mag^2 -&gt; moving average -&gt; Qt number sink; done!).&lt;/li&gt;&#xA;&lt;li&gt;Build a way to switch between your reference power source and your device under test; in a pinch, reliable screw connections like SMA can be unscrewed and rescrewed without incurring significantly different losses&lt;/li&gt;&#xA;&lt;li&gt;Build a reference source of power. &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The third point is probably the only thing you'd need to build; in interest of good performance, a lab would usually &lt;strong&gt;buy a calibrated&lt;/strong&gt; noise source (&lt;a href=&quot;https://www.pasternack.com/rf-noise-sources-category.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;examples&lt;/a&gt;), or use a calibrated spectrum analyzer to calibrate one, but seeing you probably are running low on lab-grade RF equipment...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, that's not your only option. For example, an oscillator can relatively reliably be built with a known output power in the HF ranges; you'd only need an oscilloscope to trim the gain on an opamp until the amplitude over a 50Ω load is exactly, say, 5 mV, and the rest is math :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For higher frequencies, there's really no way around building something with a &lt;em&gt;constant&lt;/em&gt; power, and getting it somewhere that can measure it. If you're building a semiconductor-based 800 MHz noise source to compare your other devices too, but it turns out your build is 3dB off in power, then all your measurements would be invalid.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-03-25T18:16:40.990" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16313" PostTypeId="2" ParentId="16311" CreationDate="2020-03-25T20:21:16.957" Score="0" Body="&lt;p&gt;Most homebrew RF probes use a diode with low voltage drop to rectify the RF. You then measure the resulting pulsed DC voltage to determine the power. Most people use a germanium diode like a 1N34, but these can be hard to find. You can use a schottky diode instead. You want the voltage drop across the diode to be as low as possible. A diode with a high voltage drop like the 0.7 volts of most silicon diode will distort the reading. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Add a high value resistor, 4.7 megaohm works well, and small capacitor, 0.01 microfarad for example. Connect them up as shown. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is still going to be distortion cause by the voltage drop of the components, especially the diode. This will be noticeable at QRP power levels. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some dummy loads include a rectifying diode that lets you measure the voltage to determine the power going into the dummy load. They basically are including a RF probe in the dummy load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bmNn7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bmNn7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-03-25T20:21:16.957" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16314" PostTypeId="2" ParentId="16311" CreationDate="2020-03-25T22:16:31.280" Score="3" Body="&lt;p&gt;A basic probe looks something like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/Q1GOC.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fQ1GOC.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally the diode has a low voltage drop, like a Schottky diode. But any ordinary silicon diode will work in a pinch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The capacitor and resistor values aren't really critical as long as the time constant (the resistance times the capacitance) is much greater than the period between cycles. Something like 1nF and 10kΩ would be fine. I usually use whatever I have laying on the bench.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The circuit works because when the input voltage is positive, C1 can charge through D1 up to the peak RF voltage (less the forward voltage drop of D1). But when the input voltage is less, C1 can discharge only relatively slowly through R1.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To use, set up your transmitter to dump power in a dummy load or whatever, and then place this probe in parallel. VM1 can be an ordinary digital multimeter because this voltage changes only as fast as the RF output power, which for an unmodulated carrier, will be DC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's important that the leads on everything left of C1 are kept short. Otherwise the added inductance of the long leads will introduce significant errors in the measurement. This becomes more critical with increasing frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To convert the measured voltage to power:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;add the forward voltage of D1&lt;/li&gt;&#xA;&lt;li&gt;divide by &lt;span class=&quot;math-container&quot;&gt;$2 \sqrt 2$&lt;/span&gt;, converting peak-to-peak to RMS&lt;/li&gt;&#xA;&lt;li&gt;use Ohm's law to calculate power for this voltage, assuming some load impedance&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Assuming a 50Ω load impedance, the calculation is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{power} = { \left(V_\text{measured} + V_{D1} \over 2\sqrt 2 \right)^2 / 50\Omega } $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For low power levels where the forward voltage drop of D1 represents a significant fraction of the output voltage of the transmitter, accurately characterizing that voltage drop is critical for accuracy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simplest method for determining the voltage drop is to read it from the data sheet, but behavior at RF may not be accurately characterized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more sophisticated approach could bias the diode to compensate for the forward voltage drop:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/KQojU.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fKQojU.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To use, temporarily short the input terminals, providing an input of 0V. Adjust the pot for minimum voltage, then turn it up to the point where the meter just starts to measure some voltage. You've now biased the diode so it will turn on at 0V, at least for DC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bias can be further tuned if you have or can build an attenuator of known value. Say you have a 3dB attenuator: this represents a halving of power, and because power is proportional to the square of voltage, a reduction in voltage by a factor of &lt;span class=&quot;math-container&quot;&gt;$\sqrt 2$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Perform one measurement, then again with the same input power but with the attenuator. If the diode is properly biased, the voltages measured by the meter should differ by a factor of &lt;span class=&quot;math-container&quot;&gt;$\sqrt 2$&lt;/span&gt;: any difference is likely due to uncompensated diode voltage drop. Correct it by adjusting the pot or by manually adding a correction factor in the calculation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Accuracy could be further improved by adding a transformer on the input to increase the voltage, thus rendering error due to the diode less significant.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-03-26T18:13:42.893" LastActivityDate="2020-03-26T18:13:42.893" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16315" PostTypeId="2" ParentId="16307" CreationDate="2020-03-26T02:13:58.180" Score="2" Body="&lt;p&gt;To answer the last part of the question, the detector for an AM receiver is basically a rectifier, which rectifies the RF and the signal that it was modulated with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Once the RF has been rectified, it has superimposed on it the original signal that the carrier was modulated with. This is then usually put through a low-pass filter to turn the &quot;rectified RF modulated with a signal&quot; into just the signal, by removing the RF. The lazy man's low pass filter in these cases is our ears, but it doesn't hurt to put a tiny capacitor across the signal going to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the last stage is an amplifier - there are many amplifiers you could use for this. A simple transistor would do the trick, or you could use an LM386 IC if you wanted a decent sound out of a speaker or a pair of headphones.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-03-26T02:13:58.180" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16316" PostTypeId="2" ParentId="16311" CreationDate="2020-03-26T10:31:48.833" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;How to make an RF probe for &lt;strong&gt;accurate&lt;/strong&gt; power measurement at QRP power levels?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;&amp;emsp;(emphasis mine)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, accurate measurement of RF power is actually pretty hard once you cross over into bands that your oscilloscope can't measure directly anymore. Say, you want to measure what your 21 cm LNA does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sure, you'd rectify the signal, first, like in Phil's excellent answer, but that assumes you know the frequency behaviour of your diode – which you &lt;em&gt;really&lt;/em&gt; do not at higher frequencies. If you even &lt;em&gt;could&lt;/em&gt; know the frequency-dependent behaviour of all your semiconductors, you'd have little need to measure the output power of your amplifier, you could just calculate it on paper (it's really nothing but a single transistor, &lt;a href=&quot;https://docs.broadcom.com/docs/AV02-1237EN&quot; rel=&quot;nofollow noreferrer&quot;&gt;seriously&lt;/a&gt;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DRcpY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DRcpY.png&quot; alt=&quot;Minicircuits LNA&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;&lt;a href=&quot;https://www.minicircuits.com/WebStore/dashboard.html?model=ZX60-53LN%2B&quot; rel=&quot;nofollow noreferrer&quot;&gt;This&lt;/a&gt; LNA is really just a transistor, plus a few passives to reliably bias it, plus a few passives to impedance-match. If we knew how semiconductors like diodes and transistors behave at high frequencies, there'd be no need for the manufacturer to measure and calibrate these.&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, long story short, you need to build a detection system (like Phil's!) and then calibrate it; get the nonlinear effects out of there, and the effects that depend on frequency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A diode is not only the perfect diode you've read about (&quot;current through the diode is exponential to voltage across the diode yadda yadda&quot;), but when looked at with dynamic signals, also a capacitor, meaning that it does, in fact, pass higher-frequency AC signals pretty well, especially in low-voltage situations, where charge carriers get &quot;dangerously close&quot; to each other and the diode &quot;looks&quot; like a plate capacitor with very close-by plates. (By the way, that's what a varicap is: a voltage-adjustable capacitor, which is just a normal diode in reverse operation, optimized for high capacitance shift.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bR73D.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bR73D.png&quot; alt=&quot;Diode Capacitance over reverse voltage&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;&lt;a href=&quot;https://www.mouser.de/ProductDetail/Toshiba/1SV305L3F?qs=sGAEpiMZZMutXGli8Ay4kO3ds8Te0Ticp9Se%2FcDoFUU%3D&quot; rel=&quot;nofollow noreferrer&quot;&gt;This&lt;/a&gt; diode has a bit of a voltage-dependent capacitance and hence acts differently on different frequencies, depending on the voltage, just to make things less easy&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Soooo, you'll go, build your first measurement circuit, buy a USD 100,000 spectrum analyzer and start calibrating. Or maybe you just buy a used one, spend a lot less, not like you need to go up to 60 GHz or anything, but still&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2X4Ka.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2X4Ka.jpg&quot; alt=&quot;R&amp;amp;S FSC-3&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;New: a proper boat. Used: A car. Or the financial &lt;a href=&quot;https://www.rohde-schwarz.com/cz/product/fsc-productstartpage_63493-10891.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;equivalent&lt;/a&gt;.&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then you go get a coffee, leave the lab door open, the room cools down, you go back in, notice that everything changed, sigh, add a temperature probe to your measurement circuit board, note down the temperature, and spend the next four days calibrating your board. Then a friend comes over, sees what cool stuff you can do with your self-built power meter, and asks that you make him one, too. So, you take your spare parts, assemble another one, and sit another three days in the lab, calibrating that board, because at microwave frequencies no two semiconductors are identical, and especially not yours...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ex4FR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ex4FR.png&quot; alt=&quot;Diode Capacitance Change over Temperature&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;The same diode obviously also has a temperature dependency. You get the feeling physics doesn't like you... and that's a diode already partially optimized for temperature-stable behaviour&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doesn't sound tempting, right? If only there were companies that sold small circuits that they built, and tested, and calibrated themselves for this purpose...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good news, everyone!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They do. For example, Analog Devices (ADI) has a few of them. This demo board stuck out:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sJ4sX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sJ4sX.png&quot; alt=&quot;Analog Devices CN0399&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;&lt;a href=&quot;https://www.analog.com/en/design-center/reference-designs/circuits-from-the-lab/cn0399.html#rd-overview&quot; rel=&quot;nofollow noreferrer&quot;&gt;ADI CNO399&lt;/a&gt; evaluation board for the &lt;a href=&quot;https://www.analog.com/en/products/adl5904.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;ADL5904&lt;/a&gt; power meter IC&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What it does is relatively straightforward:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;There's an envelope detector, like in Phil's answer, but with a lot of compensation built-in &lt;/li&gt;&#xA;&lt;li&gt;There's an analog-to-digital converter, because, well, something's actually got to &lt;em&gt;measure&lt;/em&gt; the output&lt;/li&gt;&#xA;&lt;li&gt;and there's a bit of clean, stable voltage supply circuitry and input matching on there&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/j7f26.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/j7f26.png&quot; alt=&quot;Eval board block schematics&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;CN0399 Block diagram&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you can shell out USD 150, just buying that eval board, and then talking SPI to the ADC (e.g. from a microcontroller board like an Arduino, or from a Raspberry Pi), that's a working solution; the &quot;what the ADC says vs what was on the input curves&quot; do look pretty nice:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vaZ5d.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vaZ5d.png&quot; alt=&quot;ADC output over input power graph&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;CN0399 ADC output over input power graph&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, you can also just download the board layout files, have them &lt;a href=&quot;https://oshpark.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;manufactured&lt;/a&gt; for cheap, buy the components, solder them on and probably come out cheaper (but not as well-tested, probably, and on a different FR4 substrate, so the matching might be slightly off).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The purpose of such boards, however, is not production usage; it's to encourage you to use the schematics to build your own power meters from. Maybe the ADC is not what you're looking for? You'd be better off with an Opamp non-inverting amplifier that drives a simple analog voltage gauge? Sure! Just do that, replace the ADC, design your own board. Really, the &lt;a href=&quot;https://www.analog.com/en/products/adl5904.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;ADL5904&lt;/a&gt; isn't such a complicated beast to use in a minimal RMS detection setup:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xyW2H.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xyW2H.png&quot; alt=&quot;fig. 44 from ADL5904 Datasheet&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sub&gt;From the ADL5904 &lt;a href=&quot;https://www.analog.com/media/en/technical-documentation/data-sheets/ADL5904.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;datasheet&lt;/a&gt;: Figure 44, &lt;em&gt;Basic Connections for RMS Power Measurement&lt;/em&gt;&lt;/sub&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Counting that: One IC, four capacitors, two resistors; one coax connector for the input, and a stabilized 3.3 V supply IC, plus probably two more caps for that. Done! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a starting point, this will be quite a bit more accurate over quite a larger frequency range than a much simpler single-diode envelope detector. If you can actually verify your input matching and use your oscilloscope on a low-frequency oscillation to input a known power to the detector, you'll be able to put a high degree in certainty in your power measurements.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-03-26T10:31:48.833" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16317" PostTypeId="2" ParentId="16284" CreationDate="2020-03-26T14:06:44.700" Score="1" Body="&lt;p&gt;According to page 46 of the manual, you must press the &lt;code&gt;F&lt;/code&gt; button followed by the &lt;code&gt;STO/VOX&lt;/code&gt; button to put the rig in break-in mode, which is indicated by the &quot;BK-IN&quot; icon in the display.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-03-26T14:06:44.700" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16318" PostTypeId="1" CreationDate="2020-03-26T15:32:19.953" Score="3" ViewCount="108" Body="&lt;p&gt;I could relatively easily take the feeder down and use a tape measure but it’s more of a challenge to learn how to measure the length using my oscilloscope -Red Pitaya - but I have to admit I have no idea how to go about it.&lt;/p&gt;&#xA;" OwnerUserId="9323" LastActivityDate="2020-09-08T13:31:01.383" Title="How do I use a signal generator + oscilloscope to measure feeder length?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;feed-line&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16319" PostTypeId="2" ParentId="6778" CreationDate="2020-03-26T21:52:02.190" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://www.futurlec.com/Linear/LM387Npr.shtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.futurlec.com/Linear/LM387Npr.shtml&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This site claims to sell them. I do not know anything about the company, just the first source that came up.&lt;/p&gt;&#xA;" OwnerUserId="16687" LastActivityDate="2020-03-26T21:52:02.190" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16321" PostTypeId="1" CreationDate="2020-03-27T17:13:04.483" Score="0" ViewCount="117" Body="&lt;p&gt;With an FM signal, it takes up more room in the radio spectrum presumedly because the carrier frequency is changed. On average what's the width of the FM sidebands?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does the deviation from the center frequency depend on the frequency of the audio/information signal applied to the carrier?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2020-03-27T17:24:58.310" LastActivityDate="2020-03-27T17:27:14.457" Title="What determines the bandwidth of an FM signal?" Tags="&lt;modes&gt;&lt;fm&gt;&lt;spectrum-analyzer&gt;&lt;panadapter-and-waterfall&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16322" PostTypeId="2" ParentId="16321" CreationDate="2020-03-27T17:13:04.483" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;Does the deviation from the center frequency depend on the frequency of the audio/information signal applied to the carrier?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;No. In FM terminology, the &quot;deviation&quot; is &lt;strong&gt;chosen&lt;/strong&gt; by the designer (or mandated by regulation) and determines the amount by which the carrier itself is modulated at the &quot;peaks&quot; of the input signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, if the deviation is 2.5 kHz (NFM) then at the moment when a line level input is +1.736V, the output frequency will be 2.5 kHz more than the center frequency. At 0V the carrier will be at that instant &lt;em&gt;at&lt;/em&gt; the center frequency. And at -1.736V the carrier will be deviated from its center by -2.5 kHz. (For broadcast FM the deviation is usually closer to 75 kHz.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So it might seem that the input signal has no effect on the bandwidth, just the deviation, then? But that can't be!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that were the case then we could use, say, a 1 kHz deviation to encode a lovely audio signal up to 20 kHz. And if we could do that, why couldn't we keep extending that even further and use, say, a 100 Hz deviation to encode a 1 Gbps internet signal?! There's a reason that FM broadcast uses a channel spacing of 200 kHz, i.e. &lt;em&gt;more than&lt;/em&gt; double the 75 kHz deviation.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;On average whats the width of the FM sidebands?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Because of the maths of having a signal that's essentially a cosine of another sinusoidal function, it's a bit complicated. And there's no real stopping point either! Imagine something like a bell curve — or in this case, a &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Frequency_modulation&amp;amp;oldid=946676097#Bessel_functions&quot; rel=&quot;nofollow noreferrer&quot;&gt;Bessel function&lt;/a&gt; — that gets gradually less significant away from its peak but never actually goes to precisely zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So FM broadcast uses an approximation known as the &lt;a href=&quot;https://en.wikipedia.org/wiki/Carson_bandwidth_rule&quot; rel=&quot;nofollow noreferrer&quot;&gt;Carson Bandwidth Rule&lt;/a&gt; which says that the bandwidth needed is roughly &lt;span class=&quot;math-container&quot;&gt;$2 (\Delta f + f_m)$&lt;/span&gt; where &lt;span class=&quot;math-container&quot;&gt;$\Delta f$&lt;/span&gt; is the deviation and &lt;span class=&quot;math-container&quot;&gt;$f_m$&lt;/span&gt; is the highest frequency of the &lt;em&gt;input&lt;/em&gt; signal. Each sideband would be half of this overall bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So that's the catch! The deviation itself isn't affected by the signals transmitted &lt;em&gt;but&lt;/em&gt; the bandwidth used ends up being roughly the deviation &lt;strong&gt;plus&lt;/strong&gt; the frequency sent (and then double that combined sum, since there's both an upper and a lower sideband). Using only 1 kHz FM deviation to transmit a 20 kHz audio signal still results in a bandwidth of about 42 kHz ignoring ~2% of the signal power (which ends up even farther from the center frequency).&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Finally, note that an AM signal has sidebands too! Even though think only of the carrier &lt;em&gt;amplitude&lt;/em&gt; changing and not its &lt;em&gt;frequency&lt;/em&gt;, the change (modulation) itself adds information to the signal and necessarily increases its bandwidth. This is counter-intuitive at first, so when thinking about that it might help to remember the above. In FM the bandwidth is wider than just the deviation, too!&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2020-03-27T17:27:14.457" LastActivityDate="2020-03-27T17:27:14.457" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16324" PostTypeId="2" ParentId="6778" CreationDate="2020-03-27T17:43:57.557" Score="0" Body="&lt;p&gt;You may find the SA612 chip more readily available than SA602. I believe the SA602 is an identical chip with slightly tighter specs than SA612. SA612 is pin-compatible replacement.&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for the LM387 (IC2) low-noise preamp - you might substitute a two-transistor amplifier instead, shown below. It will give better low-noise performance, with similar gain (about 30 dB). It has better low-noises performance because its input impedance is tailored to be 1500 ohms. Note that R11 (1500 ohms) is not present...replaced by the amplifier's input Z of 1500 ohms. You can substitute many NPN transistors for the 2N3904's shown (2n2222, 2n4401).&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/FfFtz.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fFfFtz.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&#xA;&lt;br&gt;&#xA;As others have stated, the following LM387 (IC3) circuit can be replaced with a standard linear amplifier using any one of many opamps - it &lt;em&gt;need not&lt;/em&gt; be low-noise. A SA5534 is shown, could be NE5534.&lt;br&gt;&#xA; Driving a 8-ohm loudspeaker is really not necessary - a standard opamp can drive 32-ohm speakers with a 56-ohm series resistors added. You really only need to listen to ensure that it is extra-terrestrial noise that you're receiving, and not interfering man-made signals.&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/EhCcV.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fEhCcV.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="11132" LastEditorUserId="11132" LastEditDate="2020-03-27T19:29:43.910" LastActivityDate="2020-03-27T19:29:43.910" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16325" PostTypeId="1" CreationDate="2020-03-27T20:10:03.340" Score="2" ViewCount="127" Body="&lt;p&gt;Like many hams I have several radios and several antennas. instead of constantly connecting and disconnecting coax cables I would like to feed several antennas in to some type of switch so I can select which antenna. Unused antennas should connect to ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally a second switch could select which radio to connect to. For now assume I will only use 1 radio at a time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are commercial coax switches, but they seem to be expensive. Is there an inexpensive switch or relay I could use to home brew my own switching system? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know UHF and even VHF can be challenging to switch so I will primarily be concerned with H, but one that would also work with VHF and possible UHF would be good as long as they are not too expensive.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-03-28T07:10:04.527" Title="coax switches for HF" Tags="&lt;diy&gt;&lt;coaxial-cable&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16326" PostTypeId="1" AcceptedAnswerId="16409" CreationDate="2020-03-28T03:01:20.427" Score="4" ViewCount="57" Body="&lt;p&gt;Several months ago, before I had a Transceiver that worked, I  configured FLDIGI to graphically display  the letters QC 13P in the waterfall as a preamble to my PSK31 transmission. I remember I was looking into Reed Solomon identifiers or Hellschreiber or something else to tell hams what mode I was using.  I would like to remove this from my PSK31 signal.  The only problem is I forgot how I did it and I can't find where I configured FLDIGI to work like this. Is it time to reinstall FLDIGI?  Will that configuration persist through the reinstall?  How do I undo what I did?  &lt;/p&gt;&#xA;" OwnerUserId="16702" LastActivityDate="2020-04-09T19:49:15.287" Title="I configured FlDIGI to dislay letters before my PSK31 signal and then I forgot how I did it" Tags="&lt;digital-modes&gt;&lt;fldigi&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16327" PostTypeId="2" ParentId="16325" CreationDate="2020-03-28T05:56:03.567" Score="3" Body="&lt;p&gt;RF-specific parts aren't really required at HF. The physical dimensions of ordinary switches and relays are so small relative to the wavelengths involved that as long as you make a reasonable attempt to keep the leads short, it will work just fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Specific product recommendations are off topic, but there's really no need. Just be mindful of current and voltage ratings (which won't be difficult for powers up to 100W) and you're set.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-03-28T05:56:03.567" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16328" PostTypeId="2" ParentId="16325" CreationDate="2020-03-28T06:50:16.537" Score="0" Body="&lt;p&gt;Here's one you could homebrew, using a diode matrix, push button switches magnetic latch relays and SO-239s. The schematic shown is for 3 antennas but it's extendable. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Freewheeling diodes for the relay coils and LED indicators are not shown. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The SO-239 bodies are to be mounted on the aluminium enclosure, interconnected and earthed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reliable operation would be ensured with the use of relays having gold-plated contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/05z5Z.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/05z5Z.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/T9OZI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/T9OZI.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pushing a button selects an antenna and an indicator LED lights up. Unused antennas are grounded by the relay NC contacts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An identical unit could be used to select the radio.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-03-28T07:10:04.527" LastActivityDate="2020-03-28T07:10:04.527" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16329" PostTypeId="2" ParentId="16318" CreationDate="2020-03-28T18:14:19.407" Score="3" Body="&lt;p&gt;A quarter wavelength of coax (shortened by its velocity factor) is a notch filter if the far end is left open.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So leave the far end open; and try feeding the coax from a frequency generator voltage source plus a series resistor at the near end; and sweep the frequency across a slightly wider range than is appropriate for an adjusted quarter wavelength to be your min to max estimate of your coax length.  Use two scope probes on points before and after the series resistor, and look for the frequency causing the maximum drop in the ratio of waveform levels between the two scope inputs.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-03-28T18:14:19.407" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16330" PostTypeId="1" CreationDate="2020-03-29T03:46:18.207" Score="2" ViewCount="190" Body="&lt;p&gt;A few months ago I built a coil loaded vertical, and put it on my rooftop. My roof is made of corrugated metal, so I connected GND to it, to act as a ground plane (or is it a counterpoise?). With some shunt matching I got a decent antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Out of curiosity, I tried to simulate it on 4NEC2. I started with one of the example files included wih it, the GndScreen.NEC file. This file has 16 radials spreading out. I assume &quot;a ridiculous amount of radials&quot; would be the same as a solid ground plane, at least for HF. So I sized the radials to the shorter side of my roof, changed the radiator to match my radiator length, copied the radials and shortened, to emulate a capacitive hat, and added a load 3/4 of the way up, like I have with my vertical, and elevated it 6M off the ground, like my roof is. The end result looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kLQtb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kLQtb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequency plot matched my empirical tests very closely. But when I tried running the Far field analysis for 3.5MHz, I got this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NbnMG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NbnMG.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This antenna is showing only 30% radiation efficiency. What causes it to be so low? The radiator is about 8M long and it has a 30uH coil 3/4 of the way up. The radiator for a full-sized quarter wave monopole would need to be 20M tall. Mine is 8M. Is a radiation efficiency of only 30% the expected result for a radiator slightly less than half its ideal size?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's my NEC file:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;CM &#xA;CE&#xA;SY len=8.8  'Total wire length&#xA;SY hgh=9    'Tower heigth&#xA;SY segV=int(hgh)*5  'Vertical nr of segments&#xA;SY segH=int(len-hgh)    'Horizontal nr of segments&#xA;SY ra=360/16, radl=10   'Nr radials, radial length&#xA;SY radh =6  'radial height sabove ground&#xA;SY rseg = int(radl) '(integer) number of segments&#xA;SY cu=5.8e7, fe=1.39e6  'Wire loading for Copper, Steel&#xA;SY wrad =.0015  '1.5 mm2 house-wiring&#xA;SY RL=0.5&#xA;SY lenf=7.5&#xA;GW  1   10  0   0   radh    0   0   lenf+radh   .015&#xA;GW  11  rseg    0   0   radh    radl*cos(1*ra)  radl*sin(1*ra)  radh-0.6    wrad    'Ground screen&#xA;GW  12  rseg    0   0   radh    radl*cos(2*ra)  radl*sin(2*ra)  radh-0.6    wrad&#xA;GW  13  rseg    0   0   radh    radl*cos(3*ra)  radl*sin(3*ra)  radh-0.6    wrad&#xA;GW  14  rseg    0   0   radh    radl*cos(4*ra)  radl*sin(4*ra)  radh-0.6    wrad&#xA;GW  15  rseg    0   0   radh    radl*cos(5*ra)  radl*sin(5*ra)  radh-0.6    wrad&#xA;GW  16  rseg    0   0   radh    radl*cos(6*ra)  radl*sin(6*ra)  radh-0.6    wrad&#xA;GW  17  rseg    0   0   radh    radl*cos(7*ra)  radl*sin(7*ra)  radh-0.6    wrad&#xA;GW  18  rseg    0   0   radh    radl*cos(8*ra)  radl*sin(8*ra)  radh-0.6    wrad&#xA;GW  19  rseg    0   0   radh    radl*cos(9*ra)  radl*sin(9*ra)  radh-0.6    wrad&#xA;GW  20  rseg    0   0   radh    radl*cos(10*ra) radl*sin(10*ra) radh-0.6    wrad&#xA;GW  21  rseg    0   0   radh    radl*cos(11*ra) radl*sin(11*ra) radh-0.6    wrad&#xA;GW  22  rseg    0   0   radh    radl*cos(12*ra) radl*sin(12*ra) radh-0.6    wrad&#xA;GW  23  rseg    0   0   radh    radl*cos(13*ra) radl*sin(13*ra) radh-0.6    wrad&#xA;GW  24  rseg    0   0   radh    radl*cos(14*ra) radl*sin(14*ra) radh-0.6    wrad&#xA;GW  25  rseg    0   0   radh    radl*cos(15*ra) radl*sin(15*ra) radh-0.6    wrad&#xA;GW  26  rseg    0   0   radh    radl*cos(16*ra) radl*sin(16*ra) radh-0.6    wrad&#xA;GW  11  3   0   0   lenf+radh   RL*cos(1*ra)    RL*sin(1*ra)    lenf+radh   wrad    'Ground screen&#xA;GW  12  3   0   0   lenf+radh   RL*cos(2*ra)    RL*sin(2*ra)    lenf+radh   wrad&#xA;GW  13  3   0   0   lenf+radh   RL*cos(3*ra)    RL*sin(3*ra)    lenf+radh   wrad&#xA;GW  14  3   0   0   lenf+radh   RL*cos(4*ra)    RL*sin(4*ra)    lenf+radh   wrad&#xA;GW  15  3   0   0   lenf+radh   RL*cos(5*ra)    RL*sin(5*ra)    lenf+radh   wrad&#xA;GW  16  3   0   0   lenf+radh   RL*cos(6*ra)    RL*sin(6*ra)    lenf+radh   wrad&#xA;GW  17  3   0   0   lenf+radh   RL*cos(7*ra)    RL*sin(7*ra)    lenf+radh   wrad&#xA;GW  18  3   0   0   lenf+radh   RL*cos(8*ra)    RL*sin(8*ra)    lenf+radh   wrad&#xA;GW  19  3   0   0   lenf+radh   RL*cos(9*ra)    RL*sin(9*ra)    lenf+radh   wrad&#xA;GW  20  3   0   0   lenf+radh   RL*cos(10*ra)   RL*sin(10*ra)   lenf+radh   wrad&#xA;GW  21  3   0   0   lenf+radh   RL*cos(11*ra)   RL*sin(11*ra)   lenf+radh   wrad&#xA;GW  22  3   0   0   lenf+radh   RL*cos(12*ra)   RL*sin(12*ra)   lenf+radh   wrad&#xA;GW  23  3   0   0   lenf+radh   RL*cos(13*ra)   RL*sin(13*ra)   lenf+radh   wrad&#xA;GW  24  3   0   0   lenf+radh   RL*cos(14*ra)   RL*sin(14*ra)   lenf+radh   wrad&#xA;GW  25  3   0   0   lenf+radh   RL*cos(15*ra)   RL*sin(15*ra)   lenf+radh   wrad&#xA;GW  26  3   0   0   lenf+radh   RL*cos(16*ra)   RL*sin(16*ra)   lenf+radh   wrad&#xA;GE  -1&#xA;LD  5   1   0   40  37700000    'Left wire&#xA;LD  0   1   6   6   0   30e-6   0&#xA;GN  2   0   0   0   13  0.005&#xA;EK&#xA;EX  0   1   1   0   1   0   0&#xA;FR  0   0   0   0   3.5 0&#xA;EN&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-03-30T09:19:09.960" Title="How to model my rooftop vertical on 4NEC2?" Tags="&lt;antenna&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16331" PostTypeId="2" ParentId="16298" CreationDate="2020-03-29T05:43:06.743" Score="2" Body="&lt;p&gt;It depends on the &lt;a href=&quot;http://www.antenna-theory.com/antennas/main.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;type of the antenna&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mobile antennas are often &lt;a href=&quot;http://www.antenna-theory.com/antennas/monopole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;monopoles&lt;/a&gt;. A monopole is self-resonant when it's a quarter wavelength long. A quarter wavelength is good:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;smaller, and the feedpoint impedance will be capacitave and may require a matching network. Matching networks introduce loss.&lt;/li&gt;&#xA;&lt;li&gt;larger, and the radiation pattern grows lobes that go up towards the sky and down towards the ground when the antenna is held in the typical vertical way. The law of conservation of energy dictates that any energy sent in a direction where there's not likely another station means less energy is sent at the target receiver (or received from the desired transmitter).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Monopoles require a ground plane, which is omitted in mobile antennas to make them smaller at the cost of performance. If space allows, a &lt;a href=&quot;http://www.antenna-theory.com/antennas/dipole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;dipole&lt;/a&gt; is essentially two monopoles back-to-back, and does not require a ground plane. But a dipole is self-resonant around a half-wavelength, so it's twice the size, all else equal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An even longer antenna can be made with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Collinear_antenna_array&quot; rel=&quot;nofollow noreferrer&quot;&gt;collinear array&lt;/a&gt; of some other kind of antenna, often dipoles. An array allows the antenna designer to &quot;compress&quot; the radiation pattern, sending more of the radiation at the horizon by sending less in other directions. Provided the array is properly designed, and the other station is in a direction perpendicular to the antenna, this can improve performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Though I wouldn't expect much from a $24 antenna from Amazon. It's likely little to no engineering has gone into the design and it may not even be an array.)&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-03-29T05:43:06.743" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16332" PostTypeId="2" ParentId="16330" CreationDate="2020-03-29T08:29:58.313" Score="1" Body="&lt;p&gt;RE:  &lt;em&gt;This antenna is showing only 30% radiation efficiency. What causes it to be so low? ... Is a radiation efficiency of only 30% the expected result for a radiator slightly less than half its ideal size?&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The value for the Radiat-eff. result in the 4nec2 display includes losses based on the amount of the originally-radiated  r-f energy remaining after propagating along an infinite, flat  ground plane having the conductivity defined for the wire model &lt;strong&gt;as analyzed.&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using 4nec2 and running your unedited .nec file after selecting the &quot;Run Average Gain Test&quot; choice when setting up the NEC engine returns its true radiation efficiency (see below):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ak1IY.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ak1IY.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit of 30 March 2020 w.r.t. the comment of hjf this date:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna defined in your NEC model radiates nearly 100% of the Z-matched power across its feedpoint terminals.  After that its radiated fields are reduced by the losses of the propagation environment, but those losses are not attributes of the antenna system, itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following graphic from 4nec2 shows the radiated fields vs. height AGL at a horizontal distance of 50 meters from the antenna defined by your NEC model.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There &lt;strong&gt;&lt;em&gt;is&lt;/em&gt;&lt;/strong&gt; significant attenuation in its fields due to the lossy ground plane, even at that short distance.  However it is &lt;em&gt;far&lt;/em&gt; less than implied by the ~31% value for Radiat-Eff reported by a NEC &quot;Far Field&quot; (only) analysis.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/a2R4U.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/a2R4U.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-03-30T09:19:09.960" LastActivityDate="2020-03-30T09:19:09.960" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16334" PostTypeId="2" ParentId="16307" CreationDate="2020-03-29T13:47:50.633" Score="0" Body="&lt;p&gt;You would need the following:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Antenna - an inverted 'L' antenna using insulated wire strung between supports about 30' apart and 30' high.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Earth - an underground metallic water pipe would make a good earth connection.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Tuner - a parallel-tuned circuit (a coil with a variable capacitor across it) tuneable across the medium wave broadcast band.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Detector - a Germanium diode, a capacitor and a resistor to rectify and demodulate the signal. It is the process of extracting the audio from the modulated signal.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Audio amplifier - requiring a transistor, a resistor, a capacitor, audio output transformer and a battery to amplify the audio.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Speaker - for audio output.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UXnVH.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UXnVH.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A representative schematic of the radio is shown above.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-03-29T17:25:21.813" LastActivityDate="2020-03-29T17:25:21.813" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16335" PostTypeId="1" AcceptedAnswerId="17625" CreationDate="2020-03-30T16:24:11.177" Score="3" ViewCount="506" Body="&lt;p&gt;On the AnyTone 878UV I can choose to display the frequency or the channel name or frequency (Settings-&amp;gt;Radio Set-&amp;gt;4 Ch.Name). But seems to me like there's enough screen real estate to be able to show both. Is there a way?&lt;/p&gt;&#xA;&lt;p&gt;I've also looked for a way to map a PF button to switching between Channel and Frequency being displayed, but so far have had no luck.&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="9636" LastEditDate="2020-11-12T22:06:00.073" LastActivityDate="2020-11-22T22:32:31.090" Title="Is it possible to show frequency and channel name at the same time on AnyTone 878UV?" Tags="&lt;ht&gt;&lt;equipment-operation&gt;&lt;anytone&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16336" PostTypeId="1" CreationDate="2020-03-30T22:43:26.503" Score="-1" ViewCount="104" Body="&lt;p&gt;I am trying to gain a better grasp of how to build an AM radio receiver. Can you direct me to some books (or other information) that will help?&lt;/p&gt;&#xA;" OwnerUserId="16680" LastActivityDate="2020-04-07T06:51:12.727" Title="Recommended Books For AM/FM (especially AM) Radio Design" Tags="&lt;fm&gt;&lt;am&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16337" PostTypeId="1" CreationDate="2020-03-30T22:55:00.537" Score="0" ViewCount="39" Body="&lt;p&gt;Can I put two of these cheap (less than 3USD) and common CFU455IT +/-2kHz (4kHz bandwith -6dB ) ceramic filters in series to get a lower bandwidth good for SSB TX? If I'm correct I will get -12dB at +/-2kHz so the bandwidth will be reduced a bit, I can trim the rest by adding a trimmer in parallel to the filters and playing with the loading resistor. What about CFU455HT? They are even more easy to get and cost 1.25USD. It sure beats paying 50USD for a factory made one and I have only so much crystals to put in filters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When making an SSB superhet RX are lightly loaded (100k ohms) LC resonant circuits and RC lowpass audio filters good on their own or do I really need that filter?&#xA;&lt;a href=&quot;https://i.stack.imgur.com/71GZS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/71GZS.png&quot; alt=&quot;filter datasheet&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;73 de SO9LEK&lt;/p&gt;&#xA;" OwnerUserId="14961" LastActivityDate="2020-05-12T19:20:02.047" Title="Combining two CFU455IT +/-2kHz (4kHz) ceramic filters to get a +/-1.25kHz (2.5kHz) filter for SSB" Tags="&lt;receiver&gt;&lt;filter&gt;&lt;ssb&gt;&lt;superheterodyne&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16338" PostTypeId="2" ParentId="16336" CreationDate="2020-03-30T23:55:12.367" Score="2" Body="&lt;p&gt;A great textbook for building a receiver or transmitter from scratch is Solid State Design for the Radio Amateur, by Wes Hayward W7ZOI and Doug DeMaw W1FB, published by the American Radio Relay League in 1986.  (If you were hoping to build a receiver that uses tubes, then this book would only be indirectly useful.)  Unfortunately it's been out of print for many years, and ridiculous prices are asked for used copies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it can be found on archive.org &lt;a href=&quot;https://archive.org/details/SolidStateDesignForTheRadioAmateur1986&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.  Thanks to the ARRL for apparently allowing the book to be read online!  What's more, the ARRL also seem to have shared several editions of the Radio Amateur's Handbook / the ARRL Handbook, which are also excellent resources.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-03-30T23:55:12.367" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16339" PostTypeId="2" ParentId="16298" CreationDate="2020-03-31T03:41:41.750" Score="1" Body="&lt;p&gt;The optimal length for a HT whip antenna would be ¼ λ. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The smaller rubber ducky, with its comparable performance, would win hands down for its convenience and ease of use. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The performance of either would be enhanced by adding a ¼ λ flexible-wire counterpoise, popularly known as a 'rat tail' or 'tiger tail'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A ring-type lug, attached at one end of the counterpoise, would need to be slid over the HT BNC connector before connecting the whip or rubber ducky antenna.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-03-31T04:02:43.963" LastActivityDate="2020-03-31T04:02:43.963" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16340" PostTypeId="1" CreationDate="2020-03-31T04:21:12.670" Score="1" ViewCount="689" Body="&lt;p&gt;I have a GMRS License and currently studying for my Technician’s License. Once I pass the exam, can I use my GMRS “Call Sign?”&lt;/p&gt;&#xA;" OwnerUserId="16716" LastEditorUserId="873" LastEditDate="2020-04-01T07:09:34.323" LastActivityDate="2020-04-01T18:48:47.043" Title="GMRS Call Sign for Technician" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16341" PostTypeId="2" ParentId="16340" CreationDate="2020-03-31T05:26:43.670" Score="2" Body="&lt;p&gt;Only on GMRS frequencies.  And technically only with GMRS radio gear.&#xA;Wait until your ham call is issued to use it.  It will be available in CORES.&lt;/p&gt;&#xA;" OwnerUserId="16717" LastActivityDate="2020-03-31T05:26:43.670" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16342" PostTypeId="1" AcceptedAnswerId="16400" CreationDate="2020-03-31T10:12:50.733" Score="4" ViewCount="116" Body="&lt;p&gt;What's the difference between an APRS &quot;item&quot; and an APRS &quot;object&quot;?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.kenwood.com/i/products/info/amateur/pdf/TH-D74AE_IDM.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;A kenwood manual says Objects have timestamps&lt;/a&gt;, items do not. What does that mean, and how should it be used?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also in general: What is a good resource for learning about APRS? aprs.org is not one, since it only has angry rants about implementations doing it wrong, and no explanations about what's right.&lt;/p&gt;&#xA;" OwnerUserId="9636" LastActivityDate="2020-04-07T02:56:34.490" Title="What's the difference between an APRS &quot;item&quot; and an APRS &quot;object&quot;?" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16343" PostTypeId="1" AcceptedAnswerId="16364" CreationDate="2020-03-31T10:15:15.630" Score="2" ViewCount="65" Body="&lt;p&gt;In every description I've found of &lt;code&gt;WIDEn-N&lt;/code&gt;, the capital &lt;code&gt;N&lt;/code&gt; is described as the &quot;hop count&quot; / &quot;ttl&quot; (comparable to internet packets). But the lower case &lt;code&gt;n&lt;/code&gt; I've never found defined.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looks like &quot;higher number means wider reach&quot;, but what does that mean for who digipeats it, how often, and how widely?&lt;/p&gt;&#xA;" OwnerUserId="9636" LastActivityDate="2020-04-01T16:21:07.300" Title="APRS: What's the `n` in WIDEn-N?" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16344" PostTypeId="1" AcceptedAnswerId="16357" CreationDate="2020-03-31T12:29:41.263" Score="13" ViewCount="1021" Body="&lt;p&gt;Can someone please help clarify. I have tried searching all over, but almost all of the examples you find online and in books are for calling CQ on HF. I am new to ham radio, and recently got a few of my buddies licensed as well. I am confused over the recommended syntax when calling to a friend over simplex or a local repeater. Can someone please give me a few examples of how you personally call?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, would this be acceptable:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;&amp;lt;My call&amp;gt; &amp;lt;Friends call&amp;gt; blah blah blah.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;I get confused over the order (My call first or his call first) and also the position. Does my call go at the end? Also is there some common phase or sentence used when trying to reach someone? For example, &quot;come back&quot; or &quot;do you read&quot;. These seem more like CB/Hollywood radio terms and I use them here only for context.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you please give me a few examples to put my mind at ease. Thank you!&lt;/p&gt;&#xA;" OwnerUserId="16722" LastActivityDate="2020-04-07T06:28:54.500" Title="Calling a friend on simplex" Tags="&lt;simplex&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16345" PostTypeId="2" ParentId="16344" CreationDate="2020-03-31T12:37:20.410" Score="6" Body="&lt;p&gt;Common practice is to give your own call sign last.  So, if KA1ABC is calling KZ8ZYX, they'd call &quot;Kay zed eight zed wye ex, kay aeh one aeh bee cee.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regulations, however, don't &lt;em&gt;require&lt;/em&gt; doing it this way.  What US regs require is that you give your own call sign at least every ten minutes during an ongoing &quot;communication&quot; and at the end of the &quot;communication&quot;.  Obviously, you need to give the sign of the station you're calling, or they won't know they need to answer back (unless it's a sched QSO) -- but otherwise, if it's just &quot;Hey, buddy, just checking if you're awake,&quot; you could give your call only when you sign off and be perfectly legal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doing it the common way is just a matter of convention.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-03-31T12:37:20.410" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16346" PostTypeId="2" ParentId="16344" CreationDate="2020-03-31T13:06:49.243" Score="3" Body="&lt;p&gt;I'd recommend saying something like this, &quot;This is KA1ABC calling KZ8ZYX&quot;. HAM radio can be very conversational. We call it &quot;rag chewing&quot; but that term is just part of the jargon that evolves in almost every hobby or profession. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Outside some contests where people are trying to make as many contacts as possible with in a time limit using a specific verbiage you don't have to be overly rigid in your communications. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you should know the regulations require you to give your call sign at least every 10 minutes and at the end of every conversation. Most people find it works better if they also give it at the beginning of the conversation so we know who is talking. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would avoid the stereotypical &quot;CB lingo&quot; that we some times run into. Most people find it incredibly annoying and at least a few will make those feelings known. The same goes for the &quot;10 codes&quot; that public service sometimes uses. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd even be careful about Q codes that HAM radio operators do use. You can always ask, &quot;where do you live&quot; instead of &quot;what is your QTH&quot;.  &lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="9425" LastEditDate="2020-04-02T13:01:47.230" LastActivityDate="2020-04-02T13:01:47.230" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16347" PostTypeId="2" ParentId="5282" CreationDate="2020-03-31T13:12:22.410" Score="1" Body="&lt;p&gt;In some areas where there are a lot of active HAMs you might hear some traffic. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also if you want contacts you do need to call. Just listening for some else to call is seldom a good strategy. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Keep in mind that VHF is fairly sort range especially with a low antenna mount like a car driving down the road in a valley. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;if you are looking for conversations when travelling, you might have better luck finding the information on local repeater for the are you are travelling in.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-03-31T13:12:22.410" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16348" PostTypeId="2" ParentId="16340" CreationDate="2020-03-31T13:21:37.343" Score="5" Body="&lt;p&gt;You will need to continue to use your GMRS on GRMS frequencies with GMRS radios and once you get it your ham call sign on ham frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The call signs for GMRS have a different format than ham radio call signs. From what I can see GMRS call signs are 3 or 4 letters followed by 4 numbers. Ham radio call signs are 1 or 2 letters, 1 number, and 1 to 3 letters. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="1362" LastEditDate="2020-03-31T17:26:15.293" LastActivityDate="2020-03-31T17:26:15.293" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16349" PostTypeId="2" ParentId="16336" CreationDate="2020-03-31T13:32:06.840" Score="1" Body="&lt;p&gt;If you want to learn how a radio works one good source of information is Bob Heil's pine board radio project. It is a tube type radio, but even if you don't build it you will learn a lot about radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://heilhamradio.com/amateur-radio-post/the-pine-board-project/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://heilhamradio.com/amateur-radio-post/the-pine-board-project/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most HAM HF radios are SSB or CW instead of FM, but there are many books on all types of radios. On Amazon do a search for books published by the ARRL or if a ARRL member you can purchase them for the website.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;ARRL also publishes a magazine, QSX, for radio experimenters. At the moment it is a separate subscription, but they plan to  offer a digital subscription to all ARRL members in near future. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-03-31T13:32:06.840" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16350" PostTypeId="1" CreationDate="2020-03-31T13:38:18.880" Score="1" ViewCount="1043" Body="&lt;p&gt;so i have just received today a baofeng uv-5r that i had ordered, i already had the 888s&lt;/p&gt;&#xA;&#xA;&lt;p&gt;after programming the uv-5r to the same frequency as the 888s, i am able to recieve transmission&lt;/p&gt;&#xA;&#xA;&lt;p&gt;all LEDs work as i would expect them to under normal operating circumstances&lt;/p&gt;&#xA;&#xA;&lt;p&gt;however, the 888s will only receive transmission if i am holding down the &quot;mon&quot; button which is obviously impractical - if i transmit normally the LED does indeed light up green to suggest it is receiving a transmission but there is no actual audio (unless holding &quot;mon&quot;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;i am an amateur at this sort of thing, please help me&lt;/p&gt;&#xA;" OwnerUserId="16723" LastActivityDate="2020-04-30T14:22:12.283" Title="Baofeng UV-5R transmitting to Baofeng BF888s - 888s will not receive transmission unless holding &quot;mon&quot;" Tags="&lt;baofeng&gt;&lt;transmission&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16351" PostTypeId="2" ParentId="16350" CreationDate="2020-03-31T13:41:01.057" Score="2" Body="&lt;p&gt;Most likely the 888s are set up to require a &quot;tone&quot; to break squelch.  This is very common for a radio that's been used with repeaters, and almost all repeaters use CTCSS, aka PL tone, to minimize interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;mon&quot; button disables squelch momentarily, allowing the signal from the UV-5R to get through.  You can avoid this by finding out what tone the 888 is expecting and programming the UV-5R to send that tone, or alternatively (for simplex) disable tone squelch in the 888s.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-03-31T13:41:01.057" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16353" PostTypeId="1" CreationDate="2020-03-31T14:08:22.133" Score="0" ViewCount="149" Body="&lt;p&gt;I have a commercially manufactured ground plane antenna for 2 meters. It will be fed with about 150 feet of RG 8/U . I've seen pictures of a coil of the feed line going to a 2 meter ground plane; this is used as a balun. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm wondering if anyone can give me the suggested number of turns and diameter of the coax coil?&lt;/p&gt;&#xA;" OwnerUserId="16724" LastEditorUserId="218" LastEditDate="2020-03-31T15:22:21.263" LastActivityDate="2020-03-31T15:22:21.263" Title="2 meter coax cable balun dimensions for use with a ground plane?" Tags="&lt;balun&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16354" PostTypeId="1" AcceptedAnswerId="16358" CreationDate="2020-03-31T15:02:29.080" Score="5" ViewCount="1421" Body="&lt;p&gt;When I try to find information on the requirements to run a repeater, I just see a lot of results related to building one. But I'm wondering about USA regulations. &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Does one need a particular license?  &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Which frequencies are allowed?  &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Can/should the station have its own call sign, or the call sign of the owner? How does one get another callsign?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What is required of a station that is not being monitored by the&#xA;owner (Automated by a controller)? Does it have to broadcast its call sign every X minutes? &lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What other limitations/requirements are there?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16673" LastEditorUserId="16673" LastEditDate="2020-04-01T18:37:12.003" LastActivityDate="2020-04-01T18:37:12.003" Title="What are the regulation requirements for running a repeater?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;repeater&gt;&lt;callsign&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16355" PostTypeId="2" ParentId="16353" CreationDate="2020-03-31T15:15:49.030" Score="2" Body="&lt;p&gt;Having a 50Ω unbalanced output radio feeding a 50Ω unbalanced ground plane antenna through a 50Ω unbalanced coax feeder, there is nothing more you would need to do other than raise the antenna height for improved performance.   &lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-03-31T15:15:49.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16356" PostTypeId="2" ParentId="16353" CreationDate="2020-03-31T15:21:23.747" Score="2" Body="&lt;p&gt;Attempting to make a balun by coiling coax is a tricky business.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea with these baluns is to make an inductor with the coil. Because an inductor has an impedance that increases with frequency, it's hoped they will look like a high impedance to common-mode currents on the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, a real coil also has capacitance between the turns which counters this effect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, this approach does not take into account the common-mode impedance of the feedline, which could take all kinds of values depending on the length and placement of the feedline. Adding a reactive impedance in series with this unknown impedance might actually make things &lt;em&gt;worse&lt;/em&gt; by creating a resonant LC circuit with a &lt;em&gt;lower&lt;/em&gt; impedance at the operating frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As such, I would first recommend you do nothing. The ground plane already presents a low impedance to the common mode. If the feedline exits below the ground plane and away from the antenna, common mode current on the feedline should be low without taking any particular action.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After installing the antenna, you can measure the common-mode current. See &lt;a href=&quot;https://ham.stackexchange.com/questions/1271/how-to-detect-common-mode-currents-or-rf-in-the-shack&quot;&gt;How to detect common-mode currents or “RF in the shack”?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If then you still have issues, you can try adding a balun. And because you have a mechanism for measuring the common mode current, you can find the ideal number of turns by trial and error. If you can't get that to work sufficiently well, you can try &lt;a href=&quot;https://ham.stackexchange.com/questions/7225/where-are-the-baluns-for-vhf-and-higher-how-can-one-be-made&quot;&gt;other balun designs which may be more suited to VHF&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-03-31T15:21:23.747" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16357" PostTypeId="2" ParentId="16344" CreationDate="2020-03-31T15:28:52.380" Score="11" Body="&lt;p&gt;&amp;lt; friend's call sign &gt; &amp;lt; your call sign &gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&amp;lt; friend's call sign &gt; this is  &amp;lt; your call sign &gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&amp;lt; friend's call sign &gt;  &amp;lt; your call sign &gt; calling&lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-03-31T15:28:52.380" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16358" PostTypeId="2" ParentId="16354" CreationDate="2020-03-31T15:50:08.010" Score="11" Body="&lt;p&gt;The regulations for an amateur radio repeater are fairly minimal.  To answer your specific questions:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Does one need a particular license?&quot;  Your license must permit transmissions on the repeater output frequency.  That is, general or higher for 10m, technician or higher for higher frequency bands.  There is no special repeater license. (There used to be.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Which frequencies are allowed?&quot;  Repeaters are only allowed on the 10m and higher frequency bands.  Within those bands there are subranges where repeaters are not allowed (neither receive nor transmit).  These are spelled out in &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.205&quot; rel=&quot;noreferrer&quot;&gt;97.205(b) of the regulations&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;What other limitations are there?&quot;  Not much.  For the most part the regulations for power, modes, etc. are the same for repeaters as for other stations.  You should get coordinated with your local repeater coordination council.  That is not an FCC requirement, but if you don't you might have to protect a coordinated repeater from interference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most of the rules are fairly simple and can be found in Part 97 of the FCC regulations.  The ARRL web site has a &lt;a href=&quot;https://www.arrl.org/part-97-amateur-radio&quot; rel=&quot;noreferrer&quot;&gt;link&lt;/a&gt; to the official rules website plus it has a PDF.  Just search for &quot;repeater&quot; and you'll find the information you need.&lt;/p&gt;&#xA;" OwnerUserId="15428" LastEditorUserId="16673" LastEditDate="2020-04-01T02:48:17.907" LastActivityDate="2020-04-01T02:48:17.907" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16360" PostTypeId="2" ParentId="16354" CreationDate="2020-03-31T18:24:08.140" Score="9" Body="&lt;p&gt;WA9ZZZ's answer missed the issue of control of the repeater.  The repeater must be under control of one or more control operators, or under automatic control, at all times when the repeater is on.  There are three types of control:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Primary control, where a control operator is physically near the equipment and monitoring the repeater, ready to intervene as necessary, the whole time it's on.&lt;/li&gt;&#xA;&lt;li&gt;Remote control, where the control operator(s) is/are monitoring the repeater remotely and also controlling it remotely through a control link, typically a telephone line or a radio link.&lt;/li&gt;&#xA;&lt;li&gt;Automatic control, where devices and procedures are used to ensure that the repeater is operating in compliance with FCC rules.  For instance, a repeater controller can time out and stop transmitting if someone has been talking continuously through the repeater for too long.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Most repeaters in the US have a repeater controller, which is a device that provides automatic control.  Typically the repeater controller also allows some remote control to turn functions of the repeater on and off; for instance, a sequence of DTMF tones can be sent to turn the repeater off if someone is transmitting profanity through the repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If remote control and not automatic control is used (no repeater controller), then the control link has to be usable 100% of the time the repeater is running.  In my opinion this rule would preclude DTMF tones on the repeater input frequency being used for control, because a malicious operator with a bigger signal could block out the control operator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To sum up, if you're not planning on babysitting your repeater locally or remotely, then you'll need a repeater controller so your repeater will legally be under automatic control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found much of this information on the ARRL's &lt;a href=&quot;http://www.arrl.org/auxiliary-station-faq&quot; rel=&quot;noreferrer&quot;&gt;Auxiliary Station FAQ&lt;/a&gt; page.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the repeater must identify itself periodically, like any other station.  Repeater controllers can typically be programmed to do this, or I suppose a control operator could identify for the repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Someone asked if a repeater needs its own call sign, because the owner of the call sign, the licensee, might be operating on a different frequency at the same time.  As I understand, a repeater doesn't need its own call sign.  Furthermore, an operator can be on several frequencies at once, from several different physical locations, as long as he or she is exercising control over all the stations.  (Hat tip to @hobbs-KC2G.)  Many repeaters identify using Morse code, and the nearly-universal practice is to put the suffix &quot;/R&quot; on the end of the call sign, which identifies that the call sign is for a repeater.  If the identification is by voice, either by a recording or a live control operator, then I'd think the identification would be something like &quot;this is W1AW, repeater&quot;.  So the &quot;/R&quot; or &quot;repeater&quot; suffix on the call sign clearly identifies the call sign as being for a repeater, so there should be no need for a separate call sign.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the United States, the only way that I know of to get a new separate call sign for a repeater is to use a club call sign.  This process apparently was frequently abused in the past, because the rules have been tightened down considerably.  First, there must be a club with at least four members, and the club must have a document of organization (typically a charter) and several officers, and it must have regular meetings.  The club must designate a person to serve as trustee for the club call sign in a document signed by club officers.  A person can serve as trustee for only one club call sign.  A club can have multiple club call signs (and therefore multiple trustees), but only one call sign can be a &quot;vanity&quot; call sign.  More information about club call signs can be found on the &lt;a href=&quot;http://www.arrl.org/club-call-signs&quot; rel=&quot;noreferrer&quot;&gt;ARRL's Club Call Signs page&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-04-01T15:32:03.727" LastActivityDate="2020-04-01T15:32:03.727" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16361" PostTypeId="2" ParentId="16311" CreationDate="2020-03-31T20:14:30.147" Score="0" Body="&lt;p&gt;Building is educational and fun or you could just bye the W1 from Electraft (disclosure: I own one and love it) &lt;a href=&quot;https://elecraft.com/collections/test-equipment/products/w1-100w-wattmeter-kit-1&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://elecraft.com/collections/test-equipment/products/w1-100w-wattmeter-kit-1&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1098" LastActivityDate="2020-03-31T20:14:30.147" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16364" PostTypeId="2" ParentId="16343" CreationDate="2020-04-01T16:21:07.300" Score="3" Body="&lt;p&gt;Ultimately, it's just a name, but you're right, the convention is 2 is &quot;bigger&quot; than 1.  Let me explain.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;WIDE2 stations tend to cover a wide area and often have Internet connections to send the reports along.  WIDE1 stations usually cover a smaller area fill in the gaps between WIDE2s (there can be lots more of them.)  They typically pass the packets along to a WIDE2.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A reporting station will have a routing path.  A path for a fixed station will typically be WIDE2-2 because it will usually be within reach of a WIDE2. Passing its packet to a WIDE1 would just add useless traffic.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mobile stations may not be so lucky to reach a WIDE2, but could likely reach one of the WIDE1s.  With a path of WIDE1,WIDE2, the mobile stands a much better chance of having his packet passed along.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for &quot;who digipeats it&quot;, any station configured to handle WIDE2 packets will repeat it.  Usually the community at large will agree on which stations are the WIDE2s so you don't have a channel full of them.  &quot;How often&quot; is a configuration setting, and &quot;How far&quot; depends on its RF reach and whether the station is connected to the Internet.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2020-04-01T16:21:07.300" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16366" PostTypeId="2" ParentId="16340" CreationDate="2020-04-01T18:48:47.043" Score="1" Body="&lt;p&gt;Your GMRS license is only good on GMRS allocated frequency bands using GMRS equipment. Similarly, your Amateur Radio Service (ARS) license is only good on ARS allocated frequency bands using ARS equipment. When you pass your ARS Tech exam, wait until the FCC issue you (via the CORES) your unique ARS callsign before getting on air. You can't use your GMRS callsign on ARS frequencies and vice versa. Have fun!&lt;/p&gt;&#xA;" OwnerUserId="16735" LastActivityDate="2020-04-01T18:48:47.043" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16367" PostTypeId="1" CreationDate="2020-04-01T23:33:13.647" Score="2" ViewCount="555" Body="&lt;p&gt;I purchased my first radio, and of course I reset it to factory defaults soon after I received it. (I think that wasn't the best thing to do)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What options do I have to restore the radio to as-shipped configuration, and/or define a &quot;channel&quot; so that they can easily be navigated to with the up down arrow keys.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is my first radio, so beginner tips and directions most appreciated. &lt;/p&gt;&#xA;" OwnerUserId="16737" LastActivityDate="2020-04-07T22:28:48.770" Title="Lost all pre-programmed channels in BaoFeng UV-5R V2+ after reset. What were they and how do I restore?" Tags="&lt;baofeng&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16368" PostTypeId="2" ParentId="4951" CreationDate="2020-04-02T00:43:50.667" Score="2" Body="&lt;p&gt;Very simple. Never connect Negative directly to battery and never fuse the Negative as doing so is extremely dangerous. Doing so puts your radio in Parallel with the Battery Bonding Strap to the chassis. That means a portion of all the automobile electronics systems current is flowing through your radio including the Starter. Secondly will bypass the vehicle HFE current sensor in the vehicle battery bonding jumper. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anything were to happen to the vehicle bonding jumper, means your radio is now the bonding jumper. Put your key in the ignition, all the lights, bells, and whistles come as normal. Turn the key to crank your engine, and your car fills with smoke and fire. All that starter current flowed right down the Radio Negative Battery lead, through radio chassis and circuitry, and out the coax shield completing the circuit burning it all up along the way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Not only is it dangerous, with a portion of all vehicle current flowing through you radio is called Common Mode Noise, Can be bad enough to render your radio useless. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The proper termination points for Positive and Ground. For Positive directly to the Battery Term post with a fuse as close as possible to battery. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the Ground aka negative circuit conductor, locate the factory Battery Bonding Jumper to chassis. Cannot miss it, it is the cable on the Battery Negative Term Post. Typically bonded to Wheel Well, or Fire Wall. Remove factory bolt. Clean any paint, grease, dirt off and make sure you have bright shinny metal. Use an anti-oxidant. Place your radio negative cable Ring Terminal on TOP, not below Factory Rind Terminal. Replace factory bolt and Locking hardware. Same effect as directly to battery post with respect to low voltage loss, but takes your radio out of a Nasty Nasty Ground Loop. Anyone tells you different, tell them to pound rocks, they do not know what they are talking about. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1GDPC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1GDPC.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16738" LastEditorUserId="16738" LastEditDate="2020-04-02T00:51:05.930" LastActivityDate="2020-04-02T00:51:05.930" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16369" PostTypeId="2" ParentId="5282" CreationDate="2020-04-02T01:19:49.883" Score="0" Body="&lt;p&gt;To answer part of the original question that hasn't yet been answered, duplex (a.k.a. offset, meaning repeater mode) isn't used on the VHF calling frequency used in the US and Canada, 146.52 MHz.  Neither is a tone squelch code, a.k.a. a &quot;PL&quot; tone, properly called a CTCSS tone.  Just plain old FM simplex.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would think that the calling frequency tends to be used more in rural areas than in big cities.  I live in a rural area, and I hear occasional traffic on it, which is more than I can say for most of the repeaters.  Someone is as likely to be monitoring the calling frequency as the major repeaters in a small town, which makes it a good resource for travelers just passing through; no need to grab the directory and guess which repeater is the one that people actually use.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-04-02T01:19:49.883" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16370" PostTypeId="2" ParentId="16120" CreationDate="2020-04-02T08:24:47.557" Score="0" Body="&lt;p&gt;In a coax-fed dipole, the coax core is connected to one element of the dipole and the braid to the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the rig, the coax core is connected to the hot end of its output and the braid to the chassis, which is the common or cold end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Incidentally, the chassis is connected to shack earth which is bonded to mains safety earth. This serves 2 purposes - as safety earthing for all equipment in the shack and as a means to discharge static charges on the antenna (more on this later). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dipole antenna is a balanced load connected to the unbalanced output of the rig through unbalanced coax cable. The result of this imbalance is common mode current flowing on the outer surface of the coax braid, making it a radiating part of the antenna system, which is undesirable. The solution is a 1:1 voltage balun, at the feed point of the dipole, which eliminates common mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Without the balun, the coax braid would have provided a DC path to ground only for the dipole element to which it was connected. With the balun, both the dipole elements have a DC path to ground and static charges are thus effectively dissipated. &lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-04-02T08:29:51.917" LastActivityDate="2020-04-02T08:29:51.917" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16371" PostTypeId="2" ParentId="16292" CreationDate="2020-04-02T15:31:21.930" Score="0" Body="&lt;p&gt;As explained in the Wikipedia&#xA;article on &lt;a href=&quot;https://en.wikipedia.org/wiki/Link_budget&quot; rel=&quot;nofollow noreferrer&quot;&gt;Link budget&lt;/a&gt;, 'the loss due to propagation between the&#xA;transmitting and receiving antennas, often called the path loss, can be written in dimensionless form by normalizing&#xA;the distance to the wavelength:'&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$ L_\text{FS}\text{(dB)}=20\log_{10}\left(4\pi{\text{distance}\over\text{wavelength}}\right) $&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This equation shows that when you reduce the wavelength by a dB, &lt;span class=&quot;math-container&quot;&gt;$L_\text{FS}$&lt;/span&gt; will increase by twice that many dB. So if&#xA;we halve the wavelength (cut in half = -3 dB) the loss will increase 6 dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The comment about the Friis transmission equation set me on the right path to the answer.&lt;/p&gt;&#xA;" OwnerUserId="16576" LastActivityDate="2020-04-02T15:31:21.930" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16372" PostTypeId="1" CreationDate="2020-04-02T15:50:29.303" Score="5" ViewCount="120" Body="&lt;p&gt;There are mutliple ways to couple antennas. It is said that an antenna is capacitive loose coupled if a small capacitor is used between the antenna and the parallel resonant circuit (like &lt;strong&gt;C2&lt;/strong&gt; in the image below). &#xA;Such a loose coupling will increase the selectivity of the following parallel resonant circuit. That means, the bandwith of the parallel resonant circuit will be smaller. Therefore frequency parts of the signal which are more far away from the resonant frequency of the parallel resonant circuit will be &quot;filtered out&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand, that a smaller capacitor means a more loose coupling. The smaller the capacitor, the less energy will be transferred to the resonant circuit (therefore it is &quot;loose&quot; rather than &quot;tight&quot; coupled), due to an increasing capacitive reactance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is:&#xA;How can the increase of selectivity physically explained?&#xA;It seems as if the capacitor suddenly acts like a bandpass. But why is that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I googled a lot, but unfortunately everything I found just says &quot;it is like that&quot; or &quot;do it like that&quot; but not why this penomenon is observed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3O9im.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3O9im.png&quot; alt=&quot;Antenna coupled to parallel resonant circuit with a small capacitor&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16743" LastEditorUserId="8717" LastEditDate="2020-04-02T21:15:02.103" LastActivityDate="2020-04-06T13:55:54.397" Title="Why does capacitive loose coupling increase selectivity?" Tags="&lt;equipment-design&gt;&lt;antenna-tuner&gt;&lt;crystal-radio&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16373" PostTypeId="2" ParentId="11865" CreationDate="2020-04-02T17:06:19.970" Score="1" Body="&lt;p&gt;Although reciprocity and conjugate matching are physics facts there are certainly examples where an antenna system that is poorly matched will suffice for receive only use, ie on an HF band with high noise levels where the receiver is nowhere near it's limits of sensitivity and the receivers own noise levels are swamped by the received noise. Personally I often use nearly 20dB of attenuation in the receive path, on VHF/UHF I worry about small accidental losses in the feeder etc. The impedance of very short dipoles tends to have a very low resistive content and a huge reactive content, tricky to match with any efficiency. &lt;/p&gt;&#xA;" OwnerUserId="16744" LastActivityDate="2020-04-02T17:06:19.970" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16374" PostTypeId="2" ParentId="16372" CreationDate="2020-04-02T17:09:38.990" Score="1" Body="&lt;p&gt;Really short answer, since I'm just passing by:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you state (narrow bandwidth for small capacitor) is not generally true, but &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;low bandwidth means &quot;there's a narrow peak of strong resonance*&lt;/li&gt;&#xA;&lt;li&gt;that's equivalent to &quot;this is a very high-quality resonator&quot;&lt;/li&gt;&#xA;&lt;li&gt;In a series RLC resonator with a fixed resistive component (whether that is really a resistor), the damping factor goes with the square root of the capacitance; the less dampened a circuit is, the higher the quality of oscillation, the lower thus the bandwidth.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-04-02T17:09:38.990" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16375" PostTypeId="1" CreationDate="2020-04-02T22:00:28.520" Score="2" ViewCount="1242" Body="&lt;p&gt;I have a magnetic loop antenna for T/R with remote tuning. I would like to mount this in the attic horizontally. Will I loose much performance between mounting it horizontally verses vertical?&lt;/p&gt;&#xA;" OwnerUserId="16745" LastEditorUserId="8717" LastEditDate="2020-04-03T00:33:03.343" LastActivityDate="2020-09-09T02:30:06.090" Title="Magnetic loop antenna: vertical vs horizontal" Tags="&lt;antenna&gt;&lt;magnetic-loop&gt;&lt;polarization&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16376" PostTypeId="2" ParentId="16372" CreationDate="2020-04-02T22:05:09.243" Score="1" Body="&lt;p&gt;I think if we were able to use perfect components, it would not matter. However, your antenna is not a perfect component. Is has many losses which result in a resistor R in its replacement diagram, in serial to C2. Now you can consider your antenna system as one resonant circuit consisting of: L/C of the wire, C2, L1, C1 and R. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking at the circuit this way helps me to understand why a looser coupling of the lossy C2/R component helps to increase the all over Q of the circuit. Because the smaller C2 gets, the more the high Q of C1, L1 comes into position.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We should keep in mind that having a small C2 will help to get a higher Q, which is desirable for active antennas (receiving antennas). On the other hand loose coupling will reduce the efficiency, if C2 does not match the L/C of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="13317" LastEditorUserId="8573" LastEditDate="2020-04-06T13:55:54.397" LastActivityDate="2020-04-06T13:55:54.397" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16377" PostTypeId="2" ParentId="16375" CreationDate="2020-04-03T05:03:48.713" Score="1" Body="&lt;p&gt;If you mount it horizontally, it will be omnidirectional horizontally polarized.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because it loses its directionality, you also lose some of the gain, although this may not be all that significant.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-04-03T05:03:48.713" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16378" PostTypeId="2" ParentId="16375" CreationDate="2020-04-03T15:44:37.293" Score="2" Body="&lt;p&gt;A small horizontal loop will have two sharp nulls: one pointing straight up and one pointing straight down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That &lt;em&gt;may&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Help reduce losses in the soil directly beneath it&lt;/li&gt;&#xA;&lt;li&gt;Reduce the NVIS radiation directly overhead. On the lower bands, that could be a disadvantage if you want to work nearby stations, say, within a couple hundred miles.&lt;/li&gt;&#xA;&lt;li&gt;Lower the radiation angle&lt;/li&gt;&#xA;&lt;li&gt;Lower the gain at some angles and increase it at others&lt;/li&gt;&#xA;&lt;li&gt;However, you will lose the ability to null local sources of RFI by rotating it.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The best way to view the actual pattern is to model one. &lt;a href=&quot;https://www.qsl.net/kp4md/magloop.htm#horizontal&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here is a 4nec2 NEC file for a horizontal loop&lt;/a&gt;. You can compare that to &lt;a href=&quot;https://www.qsl.net/kp4md/magloop.htm#vertical&quot; rel=&quot;nofollow noreferrer&quot;&gt;this model of a vertical loop&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;Someone who &lt;em&gt;really&lt;/em&gt; knows &lt;a href=&quot;https://owenduffy.net/blog/?cat=31&quot; rel=&quot;nofollow noreferrer&quot;&gt;small transmitting loops&lt;/a&gt; is Owen, ex-VK1OD.&lt;br&gt;&#xA;&lt;a href=&quot;https://web.archive.org/web/20181014192354/http://www.w0btu.com/magnetic_loops.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Links on my old STL page&lt;/a&gt;&#xA;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-04-03T16:40:50.033" LastActivityDate="2020-04-03T16:40:50.033" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16379" PostTypeId="1" AcceptedAnswerId="16383" CreationDate="2020-04-03T16:01:44.727" Score="1" ViewCount="72" Body="&lt;p&gt;So a clock can listen to a station WWVB to update time. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could you use the time code to mark your logs in conjunction with a recorder thus doing away with paper logs all together. &lt;/p&gt;&#xA;" OwnerUserId="12988" LastEditorUserId="4076" LastEditDate="2020-04-04T01:46:27.457" LastActivityDate="2020-04-04T01:46:27.457" Title="Is the time code a way to reduce paper work when it comes to logs?" Tags="&lt;fcc&gt;&lt;logging&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16380" PostTypeId="2" ParentId="16375" CreationDate="2020-04-03T16:18:31.293" Score="1" Body="&lt;p&gt;Another possible side effect is that a horizontal transmit loop antenna in the attic might couple more strongly into the house's AC wiring below it than a vertical loop or monopole.  The house wiring might or might not distort the antenna's pattern much; but you may have to be more careful with regards to RFI getting into household appliances and electronics.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-04-03T16:18:31.293" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16381" PostTypeId="2" ParentId="16379" CreationDate="2020-04-03T17:46:42.650" Score="0" Body="&lt;p&gt;The times in your log needs to be approximate. having a few minutes of error is not usually issue. Many software logging programs will automatically use the time from your PC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When logs are used to confirm contacts a few minutes difference is accepted. The exact difference allowed will vary depending on the service being used. I believe Logbook Of the World will accept up to a 10 minute difference and still confirm the contact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, some digital modes like FT8 and FT4 require time to be accurate to within a couple of seconds. as these are digital modes that require a PC, it usually more convenient to use software to synchronize to network time servers instead of sources like WWVB. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For portable digital mode some operators use GPS timing signals.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-04-03T17:46:42.650" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16382" PostTypeId="2" ParentId="7494" CreationDate="2020-04-03T20:21:58.810" Score="4" Body="&lt;p&gt;Troposcatter is the common mode for beyond line of sight on the 10 GHz ham band when the band is not otherwise open, good for 100's of miles.   A radio with just a few watts output power and a moderate sized dish (60cm or more) gets enough ERP for troposcatter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a few random references, check out:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Pages 64-70 of &lt;a href=&quot;http://www.mike-willis.com/Tutorial/RT%20Propagation%20Lecture.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.mike-willis.com/Tutorial/RT%20Propagation%20Lecture.pdf&lt;/a&gt;  &lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://bobatkins.com/radio/troposcatter.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://bobatkins.com/radio/troposcatter.html&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.nitehawk.com/w3sz/W3SZ-PackRatsConference2014.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.nitehawk.com/w3sz/W3SZ-PackRatsConference2014.pdf&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.mgef.org/wa2aau/uWaveUp9.PDF&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.mgef.org/wa2aau/uWaveUp9.PDF&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="16752" LastEditorUserId="8717" LastEditDate="2020-04-03T22:39:06.760" LastActivityDate="2020-04-03T22:39:06.760" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16383" PostTypeId="2" ParentId="16379" CreationDate="2020-04-04T00:17:04.487" Score="3" Body="&lt;p&gt;The FCC no longer requires amateur stations to keep a log. So if you wish to reduce paperwork, a trash can is probably the best piece of equipment to employ.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;People that keep logs for other reasons (often contesting, or just personal interest) these days often use some software to do it which will automatically populate the time based on the computer's clock. The computer's clock is often set by NTP: network time protocol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GPS receivers provide another possible source of time, especially useful when the station won't have internet access. GPS receivers are more ubiquitous, cheaper, and more accurate than WWVB receivers. Many people carry one in their pocket in the form of a smartphone, which conveniently can also run logging software.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-04T00:17:04.487" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16384" PostTypeId="2" ParentId="16375" CreationDate="2020-04-04T00:27:22.140" Score="2" Body="&lt;p&gt;There is no issue with a horizontal small loop &lt;em&gt;per se&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fact, if you want a horizontally polarized antenna with equal gain in the horizontal plane, a horizontal small loop is a great way to do it. A horizontally polarized dipole by comparison would have two nulls off the ends of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The nulls may or may not be useful for you. Nulls can be useful to exclude sources of interference. But if you can't rotate the antenna they can also exclude stations you want to contact.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Horizontal polarization is less effective for ground wave propagation. If your primary concern is DX contacts on 20 meters, this is irrelevant as these contacts happen through skywave paths where any polarization works equally well (or poorly, depending on conditions). If you are more interested in local rag-chewing on 80 meters you may have more of an issue, both due to the reduced propagation range of your own signal, and the likely case that most other people are using vertically polarized antennas.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-04T00:27:22.140" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16385" PostTypeId="1" CreationDate="2020-04-04T04:48:49.907" Score="3" ViewCount="432" Body="&lt;p&gt;I live in a retirement center.  The rule here is “Never do anything anywhere at anytime.”  That translates to “No Antennas” which I have been told means I can put out an antenna as long as it is unobtrusive and is immediately taken down when not in use or when told to do so. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an ~60 foot piece of 22ga wire fed through 33 feet of coax and a 9:1 unun.  It’s mounted on the ground (that’s right, no masts and no trees)  when run north (0 degrees magnetic = 344 degrees true), what is my radiation pattern, if any?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The coax/wire connection is on a hook ~8’ in the air. The end of the wire is connected to the top of a 4’ fiberglass rod driven 1’ into the ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Depending on how far I can get it from my doorway, the center can be up to a foot off the ground, but can also be on the ground for &gt;⅔ of its length. &#xA;&lt;hr&gt;&#xA;OK, a couple of updates based on your answers.&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Yes, I use the antenna mostly for 40 meters, although, if I can get away with it, I might lengthen to permit use on 80 meters.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I added a better 9:1 unun and a 1:1 choke.  I have tested the swr at 40 meters and, surprisingly, it is less than 2:1.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I have a ground floor apartment.  All of my neighbors, and I mean ALL, are so araid of radiation that I gave been requested to not use my iPhone in the common areas (yes, they’re that paranoid).  I could terminate the antenna in the one tree within 100 yards of my apartment, but, if anyone saw it, stuff would hit the fan.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;This town is built on a strawberry bog, filled with rocks and covered with topsoil.  The wire is on grass which, because of our climate, is usually damp.  I have sealed the end of the insulated wire to prevent the conductor coming into contact with the ground.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;And finally, YES, I want to move.  This is not a retirement housing complex; it is a gulag!&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="16756" LastEditorUserId="8717" LastEditDate="2020-04-09T16:19:22.947" LastActivityDate="2020-04-09T16:19:22.947" Title="What is the radiation pattern of an ~60 foot end fed wire antenna used for 40 meters?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16386" PostTypeId="2" ParentId="16385" CreationDate="2020-04-04T19:37:52.803" Score="2" Body="&lt;p&gt;The radiation pattern of an antenna laying on the ground can be easily approximated for the transmit case: it's roughly equivalent to a dummy load. Unless of course you are &lt;a href=&quot;https://www.qrz.com/lookup/dp0gvn&quot; rel=&quot;nofollow noreferrer&quot;&gt;in Antarcitca&lt;/a&gt;: ice is transparent enough to HF that it's basically invisible. But I don't think there are any retirement centers in Antarctica.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a receive application, you might hear some things. There are antennas that deliberately work near or on the ground, such as the &lt;a href=&quot;https://en.wikipedia.org/wiki/Beverage_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Beverage antenna&lt;/a&gt;. Beverage antennas actually make great receive antennas on the low HF bands and below, but a proper Beverage antenna involves terminating one end of the antenna and installing a low-impedance ground.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's likely as installed that you get as much radiation from the feedline and the electrical wiring in the building as you do from the wire on the ground, so trying to determine the radiation pattern is a futile effort. In any case, it won't be of much use for transmitting, I'm afraid. The antenna really has to be away from the ground at least a little bit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your situation, you might look at a &quot;small transmitting loop&quot; antenna. These have a very narrow bandwidth and require some careful construction to handle more than a couple watts, but they're small and unobtrusive.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-04T19:37:52.803" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16387" PostTypeId="2" ParentId="3716" CreationDate="2020-04-05T16:37:48.843" Score="2" Body="&lt;p&gt;The HM-98 uses a couple resistors for the up/down buttons, while the 133 uses digital signalling along with the rest of the keypad. It is MOSTLY compatible. For normal operation, it will work just fine. The only issue will be when it comes to putting the radio in programming mode. The HM-98 uses a couple resistors for up/down, while the 133 uses digital signals just like the rest of the keypad. The up/down buttons on the 133 will still change memory channels, or vfo frequencies just like the 98. As far as programming, you can make a simple &quot;programming plug&quot; from a RJ-45 jack. IIRC, it's as simple as shorting pins 2 and 7. You could use a pushbutton on that so it's not acting like it's constantly held. &lt;/p&gt;&#xA;" OwnerUserId="16763" LastActivityDate="2020-04-05T16:37:48.843" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16388" PostTypeId="1" AcceptedAnswerId="16389" CreationDate="2020-04-05T17:10:10.467" Score="0" ViewCount="266" Body="&lt;p&gt;If a large horizontal loop antenna, insulated but laying at ground level, works as an MF and low HF receive antenna, why (even though it has very high ground losses) can't it be used for transmit (to the stations it can hear) via the reciprocity theorem?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-04-05T20:59:59.150" Title="Loop on ground for transmit?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16389" PostTypeId="2" ParentId="16388" CreationDate="2020-04-05T20:37:21.113" Score="3" Body="&lt;p&gt;You can transmit, and it might work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the magic things about HF is that the path loss is often so low, because of the reflection from the ionophere, that even &lt;em&gt;terrible&lt;/em&gt; antennas work OK. You'll find tons of stories of people working the whole of europe with a loop of wire around their desk, or a coathanger, or something.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is not to answer directly, but to warn about applying reciprocity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While it's true that (passive) antennas transmit and receive with the same efficiency, and same radiation pattern, you also need to consider the effects of external noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Receiving:&lt;/strong&gt; At the bottom of HF, and MW, a receiver is very much externally noise limited, which means that the signal fades into the noise not because the receive antenna is too small, but because the background noise is too strong. Because the noise (and the signal) are so strong, the receive antenna can be made very, very small before it starts to matter how poor it is. For example, in typical conditions, a little transistor radio is externally noise limited, with its 1 m whip or 20 cm loopstick for MW. The key thing to remember is that within reason, &lt;em&gt;the signal sounds the same, whether the receive antenna is small and inefficient, or full size.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;When transmitting&lt;/strong&gt;, things are very different. A full-length dipole will have at least 20 dB more gain than a little 1 m whip, which means the radiated power is 100 times larger. This makes the signal strength at any receiver 100 times better, and hence the signal-to-noise ratio, and the quality of the signal. So the key thing here is that &lt;em&gt;when transmitting, every dB of gain results in a stronger-sounding signal&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For any given Tx-Rx path, there will be a minimum ERP which will make the transmitted signal stronger than the noise, as seen at the receiver. Drop below this and you won't be heard by that station. If the other guy is transmitting with a full-size dipole, you might hear them with any antenna, but you'll only overcome the noise if you also transmit with an antenna of similar efficiency.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-04-05T20:37:21.113" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16390" PostTypeId="2" ParentId="16388" CreationDate="2020-04-05T20:59:59.150" Score="2" Body="&lt;p&gt;Ground losses introduce additional attenuation in the path between the stations. Reciprocity applies, but this additional attenuation is more of a practical problem for transmitting than it is receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say the ground losses amount to an additional 20 dB of attenuation. To offset this additional loss, you can add a 20 dB amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For receiving, you'll need to handle powers on the order of microwatts or even less. Any transistor can handle this power, so components are cheap.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Overcoming antenna inefficiency with additional gain in the receiver is feasible as long as the amplifier's noise floor is significantly below the RF noise floor. In practice this is trivially accomplished for HF and lower frequencies because the RF noise floor is so high. See &lt;a href=&quot;https://ham.stackexchange.com/q/9832/218&quot;&gt;How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For transmitting, you'll probably want much more power. If you want the radiated performance of a 100 W station with an efficient antenna, you'll need an amplifier capable of 70 dBm or 10,000 W. This is not a cheap proposition.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-05T20:59:59.150" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16391" PostTypeId="1" AcceptedAnswerId="16392" CreationDate="2020-04-06T08:53:08.043" Score="0" ViewCount="42" Body="&lt;p&gt;I have a number of ear guards with two way radio communication. They can only be set to send and receive on the same channel, and they have the option of dividing themselves according to the ctcss standard.&#xA;The tricky thing, is that I wish to setup a second channel, that will broadcast music. This would only those on that channel hear, though at the same time have full communication between the two channels. &#xA;Do anyone have any idea of how to pull this off? Is there a way to detect when someone tries to speak in the second channel and then stop the music? Because it's critical that the first, original channel does not get to hear music. &#xA;It would be dead easy if the ear guards could transmit and receive on different channels. Though sadly, they can't.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit: I have a number of disgarded ear guards I can hack and modify to my own whim, as well as a Baofeng radio at my disposal. &lt;/p&gt;&#xA;" OwnerUserId="16771" LastActivityDate="2020-04-06T14:12:46.837" Title="Detect multiple broadcast on same channel" Tags="&lt;diy&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16392" PostTypeId="2" ParentId="16391" CreationDate="2020-04-06T14:12:46.837" Score="2" Body="&lt;p&gt;Unfortunately, your idea is unlikely to work.  First, in most countries broadcasting music on amateur radio bands or business communication bands is illegal.  Second, using the FM mode there is no good way to have a receiver ignore one signal when another signal arrives on the same channel, even with CTCSS.  With FM, when two signals arrive on the same channel, then the receiver picks up the louder signal, or a combination of both signals that sounds like noise.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were an electronics expert, it might be possible to modify the circuit of your receiver to play music from an external source, which would be cut off when a signal arrived.  But this would not be easy.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-04-06T14:12:46.837" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16394" PostTypeId="1" CreationDate="2020-04-06T14:48:54.567" Score="3" ViewCount="460" Body="&lt;p&gt;I read that using narrow band (NFM) when you should be using normal(FM)/wide-band(WFM) can result in the a reduced volume at the receiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;What happens in the opposite situation? (What if you are transmitting with FM and the receiver is expecting NFM? Is the received audio extra loud, clipped/distorted, or perhaps quieter (because the information outside of the narrow band is being discarded?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example: FRS and GMRS have some overlapping channel frequencies. All FRS channels are NFM, and GMRS channel 1 uses FM. So if both an FRS and GMRS transceiver are set to channel 1, what is the result? &lt;/p&gt;&#xA;" OwnerUserId="16673" LastEditorUserId="16673" LastEditDate="2020-05-07T01:54:43.163" LastActivityDate="2020-05-07T01:54:43.163" Title="NFM and FM compatibility" Tags="&lt;modes&gt;&lt;bandwidth&gt;&lt;frs&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16395" PostTypeId="2" ParentId="16227" CreationDate="2020-04-06T15:40:28.050" Score="0" Body="&lt;p&gt;It is to be noted that the terms 'differential mode current' and 'common mode current' relate to two-conductor transmission lines. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider a transmitter, with balanced output, feeding a balanced dipole antenna, through a balanced ladder line feeder, perpendicular to it. Also the ladder line and the antenna elements being away from any metal structures that may upset the balance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In such a balanced system, the electromagnetic fields emanating from the differential mode currents in the feeder cancel out and there is no radiation from the feeder. Likewise, radiating antenna elements also do not induce common mode currents in the feeder. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A transmitter with unbalanced output, feeding a balanced dipole antenna, through an unbalanced coaxial cable feeder, is an unbalanced system in which the electromagnetic fields from the differential mode currents in the feeder cancel out but the common mode current, induced on the braid of the coaxial cable by radiation from the antenna elements, causes the braid also to radiate. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Common mode current cannot be induced on the coaxial feeder by the transmitter by itself since there is no radiation at the transmitter end of the feeder.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-04-06T15:40:28.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16396" PostTypeId="2" ParentId="16394" CreationDate="2020-04-06T15:59:44.450" Score="0" Body="&lt;p&gt;The quality of an NBFM transmission will be good on a wide band FM receiver. But selectivity will not be good since the band width of an NBFM transmission is 6 kHz as compared to 200kHz for wide band FM and result in a number of NBFM transmissions being received simultaneously.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The quality of a wide band FM transmission on an NBFM receiver will be highly distorted for the same reasons. &lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-04-06T15:59:44.450" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16397" PostTypeId="1" CreationDate="2020-04-06T16:07:10.883" Score="3" ViewCount="228" Body="&lt;p&gt;I recently built a vertical. It's 6M radiator, a coil, and 1.2M more of radiator. It sits on my roof, which is metal, and acts as a ground plane (GND from the feedline is connected to it). There is a choke right at the feedpoint. The impedance is matched (with a LC circuit) from 36 ohms to 50 (49.9, for a SWR of 1.02:1 according to my VNA).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But whenever I transmit more than 50W, my internet and the neighbor's, drop. Sometimes it's a small packet loss, other times is continuous over several seconds.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This doesn't happen when I use the dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dipole is located about 15M from the street (where the cable companies cables are located, overhead), and the vertical is only 5M away from it. My cable drop rests on the metal roof that acts as a ground plane (I lifted it about 50cm but nothing changed).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What can I do to avoid this situation? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also have a problem with strange interference near 145mhz that doesn't go away even when the power goes out. I suspect it's CATV related, so I'm thinking a leaky CATV amplifier is causing interference, and I'm causing interference to it as well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried choking the cable to the modem but nothing changed.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-04-06T16:07:10.883" Title="The whole neighborhood's internet drops when I transmit on 40M" Tags="&lt;rfi&gt;" AnswerCount="0" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="16398" PostTypeId="2" ParentId="16367" CreationDate="2020-04-06T21:06:19.027" Score="3" Body="&lt;p&gt;While I do not know for sure which frequencies were programmed into your radio (as in my experience baofeng products tend to come with empty memories), my first guess would be the unlicenced LPD and PMR channels on the 70-cm band. These are useful to avoid the math/table lookup when talking to unlicenced handhelds, which lack a proper frequency setting at all, using channel numbers &#xA;instead, and thus would make sense to a non-ham user.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In any case, unless you've gotten used to particular memory entries out of that set for regular contacts and can't remember their frequencies, I don't think you actually &lt;strong&gt;need&lt;/strong&gt; the preset memory back, for reasons I'll cover below; better start from that clean slate you've now got and gradually add your own &quot;channels&quot; to memory.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In order to do that on Baofengs, you'll have to:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;First tune your radio (in the regular, non-memory mode) to the corresponding frequency and set all the options as you need and/or prefer. &lt;/li&gt;&#xA;&lt;li&gt;After tuning everything to your liking, and if you think you're going to return to this setup later, you can then save the current settings as follows:&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Go to the menu (via the MENU button) and navigate to the MEM-CH page (page #27 on my UVB2+; you can input the page number via the keyboard to avoid paging the up-down buttons)&lt;/li&gt;&#xA;&lt;li&gt;MENU to change the value below, &#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Input the memory slot (channel) number where you want to store the current settings, then &lt;/li&gt;&#xA;&lt;li&gt;MENU again to save (or EXIT to return to the menu without saving if you messed something up and don't want to save) &lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;li&gt;EXIT the menu.&lt;/li&gt;&#xA;&lt;li&gt;You can also clear saved slots via the DEL-CH (#28) page using the same MENU-input-MENU procedure as for saving (it's the same for all settings in the  menu) or overwrite them by saving to the same slot.&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Now, the reason why you probably don't need that preset is that a radio's memory is a very personal thing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The memory function itself is intended to make it faster for you to recall the combinations of settings that &lt;em&gt;you&lt;/em&gt; use most often and thus don't want to spend the time to set up before each session. Those, in turn, vary strongly by location, habits and personal preference. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say, at some point you find that you really like talking through the local repeater on 145.425 with a -600KHz offset and a CTCSS 88.5 subtone for access, you won't want to input all that every time you want to access the repeater and then turn it all back off when switching to other frequencies. In that case you'd save all the settings to memory and just access them by choosing the saved preset. After you've done, though, you'd usually switch back to the free-tune (non-memory) mode of the radio to have the whole band (two, actually) to explore and play with! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The hypothetical preset from the previous paragraph would be totally useless to another person who lives outside this particular repeater's coverage area (unless they have one with the &lt;em&gt;exact same settings&lt;/em&gt; in their vicinity, which is not too likely).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a corollary, another person's radio presets would likely be useless to you, unless you live next door to them and &lt;em&gt;know what each of them is for&lt;/em&gt; (it might be, say, a particular satellite which you have to specifically track and wait to come overhead to be able to talk through it).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Especially for a new ham, there's a big benefit to spending lots of time just aimlessly scanning around the bands and tinkering with the settings (figuring out hands-on what they do in the process) without the crutches of preset channels limiting you to just a handful of options.&#xA;After some time of doing that there will come a point when you'll realise you've now got some favorites that you really like hanging out at, have written down and keep coming to (by the way, write &lt;em&gt;any&lt;/em&gt; useful information you've gained from your exploring down in a journal, it's like having a second brain). It might be a local repeater, a frequency that a friendly group/net hangs out on, one with a nice daily evening ragchew, the ISS, your personal phone-home frequency, or something else entirely. And after the second or third or fifth time it's becoming tedious to put in the frequency and subtones and repeater offset and whatever other settings you use for those instances. &lt;em&gt;Then&lt;/em&gt; you save all that in your receiver's memory and write the memory slot number into the journal too, so you remember which channel is for what.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are some exceptions to the locality/personal-preference nature of the memory function, i.e. settings that are likely to be useful anywhere (though still not to everyone). The biggest of them by far are, the LPD and PMR unlicenced frequency ranges mentioned in the beginning of my reply, with their corresponding (worldwide standardized) channels. Some ham operators may find saving those channels to their radio's memory useful if they communicate a lot with unlicenced radio users who operate on those frequencies and refer to channel number only, to avoid remembering (or looking up all the time) the channel-number-to-frequency mapping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some other semi-universal (at least in a somewhat large area) frequencies would be the national calling frequency and frequencies of emergency responders, which are handy to keep stored just in case so that you don't have to remember them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Everything else, however, is either very personal, or very local, or both. &lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;To recap, &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Ditch those memory slots, you probably didn't need them anyway. Populate the memory with your own channels: &lt;/li&gt;&#xA;&lt;li&gt;Spend time just scanning the bands in the &quot;pure&quot;, non-memory mode and maybe tinkering with the settings.&lt;/li&gt;&#xA;&lt;li&gt;When you've got some favorites, save them!&lt;/li&gt;&#xA;&lt;li&gt;Good things you might want to save for quick access besides personal favorites (and ideas as to what those favorites might be) are:&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;LPD/PMR/other numbered channels that you might want to switch quickly to communicate on with non-hams. Just google them (and use corresponding channel numbers for your memory slots for best results). Do note that these can easily occupy half of your radio's memory slots right away!&lt;/li&gt;&#xA;&lt;li&gt;Repeaters reachable from your and adjacent areas (even those you don't usually use) are sometimes even more useful in that regard due to the larger covered area provided by more sensitive receivers, powerful transmitters and various additional functions. They might come really handy in emergencies or other situations where you don't have the time or resources to look them up. Repeaters are also slower to tune into, requiring two more settings in addition to the frequency itself, set up through the menu, making them a prime candidate for memorizing just for convenience if you hang out there a lot. &lt;/li&gt;&#xA;&lt;li&gt;Locally popular simplex frequencies are also a good candidate, even ones you don't usually enjoy hanging out on.&lt;/li&gt;&#xA;&lt;li&gt;The locally-accepted calling frequency (frequencies) of your area in particular can be quite useful to snap to whenever you're up for a random ham contact or need to reach out to other hams in a time of need.&lt;/li&gt;&#xA;&lt;li&gt;If available, frequencies of emergency responders in your area (same reasons as repeaters).&lt;/li&gt;&#xA;&lt;li&gt;Simplex frequencies and repeaters frequented by local nets that you participate in, a dude you like talking to, your dedicated family frequency etc etc..&lt;/li&gt;&#xA;&lt;li&gt;&quot;interesting&quot; but relatively rarely seen frequencies: Satellites, the ISS, faraway stations/repeaters that are accessible only in certain atmospheric conditions, etc&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I hope that was helpful and not too patronizing, 73, and good luck in the hobby!&lt;/p&gt;&#xA;" OwnerUserId="13775" LastEditorUserId="13775" LastEditDate="2020-04-07T22:28:48.770" LastActivityDate="2020-04-07T22:28:48.770" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16400" PostTypeId="2" ParentId="16342" CreationDate="2020-04-07T02:56:34.490" Score="7" Body="&lt;p&gt;Per &lt;a href=&quot;http://www.aprs.org/doc/APRS101.PDF&quot; rel=&quot;noreferrer&quot;&gt;the spec&lt;/a&gt;, which unsurprisingly is found at aprs.org, objects are intended for moving or animate objects of the same nature as a station beacon (people, vehicles, storms, etc.) while items are meant for permanent points of interest (they may come and go, but they're not expected to move) such as hospitals. However, there's no real difference between them, other than the fact that, as Kenwood says, object reports contain timestamps. In practice, clients seem to display them and age them out identically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Both of them are almost completely equivalent to ordinary position beacons (which can have a timestamp or not), except that an object or item has a name which is different from the callsign of the originating station. &lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-04-07T02:56:34.490" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16401" PostTypeId="2" ParentId="16344" CreationDate="2020-04-07T06:28:54.500" Score="0" Body="&lt;p&gt;I believe it is conventional to do as they do with HF transmissions. You should give your call sign last and their call sign before -from-. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;[content of the message] [their call sign] from [your call sign]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;so something very similar to: &quot;Is this simplex frequency in use? [Friend's call] from [your call]?&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember that on simplex calling(checking a supposedly empty band) you should turn your squelch down or off.&lt;/p&gt;&#xA;" OwnerUserId="16784" LastActivityDate="2020-04-07T06:28:54.500" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16402" PostTypeId="2" ParentId="16336" CreationDate="2020-04-07T06:43:10.437" Score="1" Body="&lt;p&gt;I have a copy of &lt;em&gt;The ARRL Handbook for Radio Communications&lt;/em&gt; from 2014 but they make a copy every year. The 2014 copy i have is one large hard cover book but they also make it in soft cover. The last few editions have been broken down in to a set of 6 soft cover books. It is a bit pricey but it is available used for fairly cheap(around $5 for copies from the early 2000's) online. &#xA;If you have a good local library they may have an electronic copy you can &quot;check out.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found this copy of the 2019 edition online:&#xA;&lt;a href=&quot;http://web.archive.org/web/20200407064826/https://3v8hb.files.wordpress.com/2019/04/the-arrl-handbook-for-radio-communication-2019-v2.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://web.archive.org/web/20200407064826/https://3v8hb.files.wordpress.com/2019/04/the-arrl-handbook-for-radio-communication-2019-v2.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16784" LastEditorUserId="16784" LastEditDate="2020-04-07T06:51:12.727" LastActivityDate="2020-04-07T06:51:12.727" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16403" PostTypeId="1" AcceptedAnswerId="16406" CreationDate="2020-04-07T07:25:26.860" Score="3" ViewCount="298" Body="&lt;p&gt;I have an end fed random wire antenna about 50 feet from my shack into an antenna tuner. I do not have the option to install a ground rod at the house entrance but I do at the antenna feed point. The antenna tuner requires a very good ground so I installed a ground rod there. The question is: should I run a 60 foot 10 gauge wire from the shack to the same ground rod or is it a better idea to get an isolated ground at the entrance to the shack. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I currently have installed a 10 gauge bare copper wire buried 1 foot deep in the clay soil for 20 feet outside the house as my shack ground. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I feel that this improvised ground is better than grounding the radio chassis to the antenna feed point.   &lt;/p&gt;&#xA;" OwnerUserId="16784" LastEditorUserId="16784" LastEditDate="2020-04-07T07:58:42.497" LastActivityDate="2020-04-07T17:19:22.487" Title="Should I use the same grounding rod to ground my radio and my random wire antenna?" Tags="&lt;grounding&gt;&lt;end-fed-antenna&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16404" PostTypeId="2" ParentId="16385" CreationDate="2020-04-07T08:27:31.800" Score="0" Body="&lt;p&gt;See if you can make a connection to a rainwater downspout near your window. downspouts and gutters can sometimes make decent &quot;invisible&quot; antennas of the end-fed random wire type; as such you'll need an antenna matching device to load your transmitter correctly. &lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2020-04-07T08:27:31.800" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16405" PostTypeId="2" ParentId="891" CreationDate="2020-04-07T13:56:28.887" Score="3" Body="&lt;p&gt;When they installed solar on my house, I lamented how Hurricane Sandy came, and yet all of the people having solar on their house could not use it because of the anti-islanding law(s) which say that your solar system, which usually pumps its excess power into the grid, must not do so when the grid is down, to prevent from electrocuting electric company personnel working on the lines.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I lamented how all of that solar power was on their roofs, and yet they couldn't use it.  The guy installing my solar system actually listened to me, and found another way!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an SMA inverter (Sunny Boy, I think), and this particular model of SMA inverter comes with (or allows) an outlet that attaches directly to the inverter, and from which you can extract power if the grid is down -- potentially running your refrigerator long enough to preserve your food, and of course it should deliver enough power to run many ham setups.  And to charge one or more lead-acid batteries -- I bought the biggest marine battery I could find.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The key to this setup is that, when the grid is down, the inverter does not supply AC power to the house, and therefore does not violate the anti-islanding law that protects electrician linemen.  But the inverter &lt;strong&gt;does&lt;/strong&gt; still supply power directly to the two outlets directly attached to the box.  An extension cord allows you to bring it to what needs it.  I will try to bring more specific information back later about which specific Sunny Boy I have, and what the attachment is, because I spent some time on the SMA America site to try to find the outlet attachment and couldn't find it.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;EDIT:  I just had an opportunity to use the outlet.  When the grid is down and I'm extracting power through the special attached outlets, it displays a message &quot;P: nnnnW   SPS-mode active&quot; where nnnnW is how many watts is being delivered.  I was using a heat gun with lots of settings to extract power, slowly increasing the wattage until it finally choked.  In the storm, because of cloudiness, the power that I was able to extract ranged from about 1,000W all the way down to about 200W (dark like twilight).  When you draw more power than can be delivered, the inverter cycles on and off (on for short times) and the inverter keeps turning back on to try to deliver what you're asking of it.  I did not get the opportunity to test it under full sun.  We have 20 panels. Inverter (utility interactive 1-phase) is Sunny Boy Model &quot;SB5.0-1SP-US-40&quot; mfd. 9-2016.&lt;/p&gt;&#xA;" OwnerUserId="16674" LastEditorUserId="16674" LastEditDate="2020-04-13T17:19:48.740" LastActivityDate="2020-04-13T17:19:48.740" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16406" PostTypeId="2" ParentId="16403" CreationDate="2020-04-07T17:19:22.487" Score="2" Body="&lt;p&gt;If at all possible, the feed line should go through a panel that is connected by a short cable, or directly connected, to a ground rod.  A lightning arrester is a good idea also.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All earth grounds should be connected, including the ground rod connected to the service panel, the ground rod connected to the coax shield, and your station ground.  In the US, the National Electric Code requires it.  I believe 6 AWG or better is recommended.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's more information in these other questions:&lt;br&gt;&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/9526/antenna-input-and-ground-bonding&quot;&gt;Antenna, input and ground bonding&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-04-07T17:19:22.487" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16407" PostTypeId="1" CreationDate="2020-04-08T02:20:07.283" Score="5" ViewCount="433" Body="&lt;p&gt;I'm going to start this off by saying I'm very new to this and I don't really know a lot so any detailed information would be much appreciated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have just started using an SDR (a cheap RTL model) with my MacBook Pro laptop.  The laptop itself is a 2012 and the power supply is a bit older, I bought neither new.  I've discovered that while the computer is on battery power I get very little or no interference on 1-30 MHz bands.  I will also note, I'm using a Ham It Up upconverter to get access to the HF bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I plug the computer into its power adapter I get a ton of interference, so much so it makes it difficult to actually receive even local AM stations.  When the computer is on battery, no such interference.  I do have a travel-charger which is a lower wattage for the computer, and when I connect it there is an uptake in interference but it is manageable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, what can I do to the power supply to reduce its interference?  I'm not sure if the interference is coming in to the system via the line or if the interference is coming in to the radio via the air.  I'm not even sure if that makes sense, but I hope it does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, any help would be appreciated.  I don't have / want to sink a ton of money into this as a project, for right now I can take the easy way out and unplug the laptop from the wall outlet and play around for a 2-4 hours before plugging it back in again.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks in advance.&lt;/p&gt;&#xA;" OwnerUserId="16787" LastEditorUserId="4665" LastEditDate="2020-04-08T15:14:49.117" LastActivityDate="2020-05-07T04:47:45.287" Title="Using an SDR on a Laptop with Noisy Power Supply" Tags="&lt;rfi&gt;&lt;power-supply&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16408" PostTypeId="2" ParentId="16407" CreationDate="2020-04-08T03:50:42.047" Score="4" Body="&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;This may or may not help your particular situation, but when using a laptop power adapter, it can help to use one that is &lt;em&gt;grounded.&lt;/em&gt; For Apple power supplies in the USA, this means swapping out the folding plug for a &lt;a href=&quot;https://www.apple.com/shop/product/MK122LL/A/power-adapter-extension-cable&quot; rel=&quot;nofollow noreferrer&quot;&gt;cord&lt;/a&gt; (which on recent models may not be a stock item, but should have been original equipment with yours).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any ungrounded computer power supply will add AC line noise to the chassis and signal ground of the computer, compared to no adapter or a grounded adapter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Note that this change will do nothing if your outlets are missing the actual ground wiring. If you find out that's the case, you can consult our local &lt;a href=&quot;https://diy.stackexchange.com/&quot;&gt;Home Improvement Stack Exchange&lt;/a&gt; on options for fixing that.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;You can also try adding a choke to the cable between the power supply and the laptop. Get a ferrite ring (not a snap-on &quot;bead&quot;) of a ferrite material suitable for suppressing noise on the frequencies you want to receive, then wind several turns of the DC power supply cord through the center of the ring (as if you are making a toroidal inductor, which you are), as close to the power supply as possible. (But don't make it so tight as to damage the cable!)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Try connecting a USB extension cable between the receiver and the laptop. This adds distance from any any &lt;em&gt;radiated&lt;/em&gt; noise (radio waves as opposed to noise carried on cable shields or USB power).&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Variant: Try using a USB hub with its own power supply. Being a digital device, this will be a noise source on its own, but may be a simpler and less troublesome one. (Its stock power supply might be a noise generator itself, but you can add a choke and even try replacing it with a better supply — even a linear one, if you don't mind the heat.)&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Variant: Use an &lt;em&gt;active USB extension&lt;/em&gt;. This is basically a one-port USB hub with an extra-long cable — because it is an active device it can be longer than a passive extension cable while still maintaining signal integrity. You can even get converters to optical fiber, for complete electrical isolation (though I haven't priced those out, only heard they exist).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-04-08T03:50:42.047" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16409" PostTypeId="2" ParentId="16326" CreationDate="2020-04-08T07:37:24.140" Score="6" Body="&lt;p&gt;I figured it out. In FLDIGI I had video IDS check marked under Configure/IDS/Video.&#xA;Here is the link to a video on YouTube that clearly explains what I needed to know.&#xA;&lt;a href=&quot;https://youtu.be/nwkz0GNpA0I&quot; rel=&quot;noreferrer&quot;&gt;https://youtu.be/nwkz0GNpA0I&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16702" LastEditorUserId="16702" LastEditDate="2020-04-09T19:49:15.287" LastActivityDate="2020-04-09T19:49:15.287" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16410" PostTypeId="2" ParentId="3575" CreationDate="2020-04-09T04:42:42.663" Score="0" Body="&lt;p&gt;An easy way to do this is rather than dividing frequency by 300, use 280.  The frequency in this case is the whole number that people generally think of to represent the band.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The numbers come out to match the band names (not the real wavelengths) perfectly:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;280/3.5 MHz = 80 (meters)&lt;br&gt;&#xA;280/7 Mhz = 40 (meters)&lt;br&gt;&#xA;280/14 Mhz = 20 (meters)&lt;br&gt;&#xA;280/20 Mhz = 14 (meters)&lt;br&gt;&#xA;280/28 Mhz = 10 (meters)&lt;br&gt;&lt;/p&gt;&#xA;" OwnerUserId="16794" LastActivityDate="2020-04-09T04:42:42.663" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16411" PostTypeId="1" CreationDate="2020-04-09T15:05:05.160" Score="1" ViewCount="114" Body="&lt;p&gt;I live in a spot where I would be useful for weather spotting, but I can't reach the repeater with a handheld (I can hear just fine, but they can't hear me.)  My base is in a detached garage, and I'd like to be able to use it to transmit during periods of severe weather.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have bare pairs running from the house to the garage, and I know back in the Dark Ages, you could control a radio remotely over the telco using a 20mA loop or something similar.  I also have a battery backup for the radio.  What I'd like to do is have some gizmo that is powered by the battery in the garage that lets me transmit from inside the house.  (I don't need to control the rig, just key the transmitter and send audio.)  All the searches I've done wind up involving computers or Ethernet ports or CI-V and what not.  What did they call the thing that would sit on the desk to control the radio?  Is there a schematic or an article I can refer to?&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2020-04-10T15:18:21.813" Title="&quot;Remote&quot; two-wire PTT and audio for rig" Tags="&lt;remote-control&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16412" PostTypeId="1" CreationDate="2020-04-09T16:59:40.117" Score="0" ViewCount="71" Body="&lt;p&gt;If I mount an HF vertical antenna at say a 45 degree angle to avoid a balcony ceiling, what do you suppose might happen?&lt;/p&gt;&#xA;" OwnerUserId="16796" LastActivityDate="2020-04-09T17:09:37.270" Title="I have a hf vertical antenna I'd like to put on my high-rise balcony" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16413" PostTypeId="2" ParentId="16412" CreationDate="2020-04-09T17:09:37.270" Score="2" Body="&lt;p&gt;The polarization plane will be rotated by 45 degrees, and the radiation pattern will be slightly altered.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's probably no problem in practice. Dipoles make popular HF antennas, and those are usually installed fully horizontal.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-09T17:09:37.270" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16415" PostTypeId="2" ParentId="16411" CreationDate="2020-04-10T03:50:08.260" Score="1" Body="&lt;p&gt;Well, the minimum you need is just... a cable. You can get mic input, PTT, +8V, and ground off of the mic or accessory connectors on the radio, and audio output (if needed; I gather you just want to listen on your HT) from either of those or the external speaker jack. If you put each signal, along with ground, on one pair of the CAT6, and wire up to a microphone connector in the house, it might work 100% okay.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the cable is too long, the voltage drop might be too much to allow the PTT to key reliably. In that case, you can use a simple NPN transistor switch to help it out — collector to the radio's PTT pin, emitter to ground, one side of your PTT pair to base, and the other side to the radio's +8V through a suitable resistor (small enough that your PTT works, large enough to keep the current reasonable. Maybe 0 for a very long run.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If your transmit audio is too noisy, or just too low, then you might need to boost the levels on the cable. This is somewhat of a pain, because it appears the 706mkIIg comes with, and expects, a condenser-type microphone. Two routes suggest themselves:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Switch to a dynamic microphone, buy or make a simple mic preamplifier, and connect it between the mic and the cable at the house end. On the radio end, use the MOD input of the accessory jack, and not the mic jack. Crank the preamp level up to a point which brings your voice well above any noise, and then if that level is too much (overmodulates the radio), use a resistor divider to ground to bring it down as needed.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Keep using a condenser mic. Use audio transformers at each end of the cable for isolation. Provide 8V bias for the mic, and a DC-blocking capacitor in series with the microphone. You may or may not still need a preamp.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Speaker (if you choose to wire it) will probably be fine, but if the levels off of the mic or accessory jack are too low, then the rig's &quot;external speaker&quot; jack should provide considerably higher ones :)&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-04-10T03:50:08.260" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16416" PostTypeId="2" ParentId="16411" CreationDate="2020-04-10T15:18:21.813" Score="2" Body="&lt;p&gt;A fair number of base radios can function as a cross-band repeater. If this is the case, and your local regulations allow it, you might not need any cable or gizmo at all.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-10T15:18:21.813" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16417" PostTypeId="1" CreationDate="2020-04-10T19:35:03.637" Score="2" ViewCount="190" Body="&lt;p&gt;My  call KP4CSJ (general) I will like to get a copy or duplicate of my license. I lost my and i will like to to hang it in may shack. I am an old timer ham radio over 50 years.&#xA;Thanks for your help &lt;/p&gt;&#xA;" OwnerUserId="16803" LastEditorUserId="218" LastEditDate="2020-04-10T20:53:32.853" LastActivityDate="2020-04-10T21:01:57.290" Title="how do get a duplicate of my radio amateur license KP4CSJ" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16418" PostTypeId="2" ParentId="16417" CreationDate="2020-04-10T21:00:18.840" Score="4" Body="&lt;p&gt;If you don't mind a watermark that says &quot;Reference Copy&quot;, you can go to the &lt;a href=&quot;https://wireless2.fcc.gov/UlsApp/UlsSearch/searchLicense.jsp&quot; rel=&quot;nofollow noreferrer&quot;&gt;ULS license search&lt;/a&gt;, find yourself, and click the &quot;Reference Copy&quot; link at the top. This will download a PDF you can print.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want a copy without the watermark, see the &lt;a href=&quot;https://www.fcc.gov/requesting-duplicate-license-universal-licensing-system-uls&quot; rel=&quot;nofollow noreferrer&quot;&gt;instructions from the FCC&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ol&gt;&#xA;  &lt;li&gt;&lt;p&gt;Log in to &lt;a href=&quot;https://wireless2.fcc.gov/UlsEntry/licManager/login.jsp&quot; rel=&quot;nofollow noreferrer&quot;&gt;ULS Online Filing&lt;/a&gt; with your FCC Registration Number (FRN) and Password. &lt;br&gt;&lt;br&gt;&#xA;  &lt;em&gt;Note: If you are taken to the My Applications page, click My Licenses to begin the steps below.&lt;/em&gt;&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;On the left-hand side of the screen, click Request Duplicates.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Select the licenses and click Add.&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;Click Continue to navigate through the application.&#xA;  Sign your application and click Submit Application. &lt;/p&gt;&lt;/li&gt;&#xA;  &lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-10T21:00:18.840" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16419" PostTypeId="2" ParentId="16417" CreationDate="2020-04-10T21:01:57.290" Score="2" Body="&lt;p&gt;Go to the FCC web page and locate licensing there input your CALL SIGN and print out a copy of your license. The FCC stopped mailing out these as per the web page.&lt;/p&gt;&#xA;" OwnerUserId="16804" LastActivityDate="2020-04-10T21:01:57.290" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16420" PostTypeId="1" AcceptedAnswerId="16424" CreationDate="2020-04-11T03:55:38.620" Score="2" ViewCount="283" Body="&lt;p&gt;I've built 2-turn magnetic loop RX antenna using 5 meters of 6.5mm copper tube. I was able to tune it with a variable air-spaced capacitor in the range of 1.8-10Mhz, but I noticed that as tuning frequency goes to 7MHz and above - selectivity gets less significantly, reception peak gets wider and much less visible (around 300-500kHz wide, which is extremely wide for magloop as far as I understand). Tried 2 different variable capacitors - result is the same. Everything is soldered. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume there is an optimal length of the loop / number of turns to get the highest selectivity. But how to identify this optimal number of loops / length of 1 loop?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What causes this drop of Q-factor / selectivity at higher frequencies, where capacitor value gets smaller than ~20pF?&lt;/p&gt;&#xA;" OwnerUserId="546" LastActivityDate="2020-04-11T13:06:07.777" Title="Magnetic loop antenna : loops vs selectivity" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;magnetic-loop&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16421" PostTypeId="2" ParentId="16420" CreationDate="2020-04-11T05:03:23.630" Score="5" Body="&lt;p&gt;Two factors explain the wider bandwith:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly, as the frequency increases, bandwidth will necessarily increase even if the Q factor remains constant. There are a number of ways to define Q factor, but the result is the same so consider this definition:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Q = {f_r \over \Delta f} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;rearranged:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \Delta f = {f_r \over Q} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So as &lt;span class=&quot;math-container&quot;&gt;$f_r$&lt;/span&gt; (the resonant frequency) increases, &lt;span class=&quot;math-container&quot;&gt;$\Delta f$&lt;/span&gt; (the bandwidth) must increase as well if &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; is constant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, as frequency increases the loop becomes larger relative to the wavelength. This increases the radiation resistance, which increases the damping, reduces &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt;, and increases bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Intuitively, consider what happens as the loop continues to get larger: eventually it becomes a full-wave loop or some kind of stretched-out folded dipole, and at this point the bandwidth is relatively large.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the objective is maximum selectivity, the theoretically optimal size of the loop is infinitesimal, because this maximizes the reactance of the antenna and minimizes the damping. Of course practial issues in utilizing infinitesimal antennas, so in practice the optimal size is &quot;as small as possible.&quot;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-11T05:03:23.630" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16422" PostTypeId="1" CreationDate="2020-04-11T11:11:16.803" Score="3" ViewCount="127" Body="&lt;p&gt;A NEC4.2 analysis of this configuration may reveal an unexpected truth about this... &lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-04-11T19:52:31.040" Title="Do the Horizontal Conductors of a Ground Plane Antenna Adequately Decouple Its Feedline?" Tags="&lt;coaxial-cable&gt;&lt;feed-line&gt;&lt;radiation-pattern&gt;&lt;radial&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16423" PostTypeId="2" ParentId="16422" CreationDate="2020-04-11T11:11:16.803" Score="3" Body="&lt;p&gt;Below is a NEC4.2 comparison of the v-plane patterns of a 1/4-wave ground plane antenna mounted 5m above level Earth and using 4 x 1/4-wave, horizontal radials, with / without a coax transmission line having the OD of the shield &quot;grounded&quot; to the Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two observations:   &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The 4 x 1/4-wave horizontal conductors do not effectively decouple&#xA;the transmission line from currents flowing along the vertical&#xA;conductor of the ground plane, and&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The net, peak radiation pattern gain of the ground plane antenna is reduced&#xA;by about 1.8 dB for these conditions, due to the effects of the radiation from the OD of the outer conductor of that transmission line.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CPPZD.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CPPZD.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Added below are my comments and a graphic in response to the comment of hotpaw2:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feedpoints for the GP as modeled attach the center conductor of the coax feedline to the base of the vertical conductor, and the feedline shield to the common-point of the four radials. The vertical conductor is one pole of the antenna system; the radials are the other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the radials are attached to the base of the vertical conductor and then driven together by the center conductor of the coax feedline, that would force all of the r-f current flowing on the ID of the shield to migrate to the OD of the shield at the top of the feedline, and produce radiation from its outer surface.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wDJbD.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wDJbD.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-04-11T19:52:31.040" LastActivityDate="2020-04-11T19:52:31.040" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16424" PostTypeId="2" ParentId="16420" CreationDate="2020-04-11T12:55:29.620" Score="2" Body="&lt;p&gt;The ideal length of a small loop is 1/10 wavelength to 1/4 wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below 1/10 wavelength, the gain drops too much and the bandwidth starts to become unreasonably narrow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Above 1/4 wavelength, the antenna stops acting like a small loop and becomes more like a halfwave or full wave loop and the selectivity drops and the radiation pattern changes drastically and the impedance changes drastically.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;7MHz is roughly 40m, making a 5m loop 1/8 of a wavelength.&#xA;10MHz is roughtly 30m, 5m is 1/6 wavelength.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-04-11T13:06:07.777" LastActivityDate="2020-04-11T13:06:07.777" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16425" PostTypeId="1" CreationDate="2020-04-11T18:29:57.513" Score="4" ViewCount="286" Body="&lt;p&gt;What are the best times in early April to contact Japan on 40M and 20M from Pennsylvania?&lt;/p&gt;&#xA;" OwnerUserId="16808" LastEditorUserId="8717" LastEditDate="2020-04-11T18:57:15.033" LastActivityDate="2021-05-07T19:44:51.173" Title="What is the best time of day to contact Japan from the east coast?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16426" PostTypeId="1" AcceptedAnswerId="16431" CreationDate="2020-04-11T19:48:58.533" Score="2" ViewCount="832" Body="&lt;p&gt;How long does it take for the FCC to process vanity callsign applications?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My application shows as Pending in &lt;a href=&quot;https://wireless2.fcc.gov/UlsEntry/licManager/applicationsSummary.jsp&quot; rel=&quot;nofollow noreferrer&quot;&gt;license manager&lt;/a&gt; but oddly does not show up at all in &lt;a href=&quot;https://wireless2.fcc.gov/UlsApp/ApplicationSearch/searchAppl.jsp&quot; rel=&quot;nofollow noreferrer&quot;&gt;Application Search&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="16809" LastEditorUserId="16809" LastEditDate="2020-04-11T23:16:39.050" LastActivityDate="2020-04-13T01:18:15.597" Title="How long does it take the FCC to process vanity requests?" Tags="&lt;license&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16427" PostTypeId="2" ParentId="16426" CreationDate="2020-04-11T23:10:32.033" Score="-2" Body="&lt;p&gt;The FCC waits 18 days before rendering a judgement re a vanity request. Who knows why that would be the case in the 21st century, but that's what they do. The Feds take their own sweet time about everything they do.&lt;/p&gt;&#xA;" OwnerUserId="16811" LastActivityDate="2020-04-11T23:10:32.033" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16428" PostTypeId="1" CreationDate="2020-04-12T16:46:02.487" Score="3" ViewCount="81" Body="&lt;p&gt;I want my n/ac Wi-Fi card to operate in a spatially directional manner.&#xA;To achieve that I want to use a directional antenna(s). There is a slight complication though, because my &lt;a href=&quot;https://www.alfa.com.tw/products_detail/1.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Alfa AWUS036ACH&lt;/a&gt; network card has two omni-directional antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Because of that, I'm confused on how I should connect a directional antenna to such a setup. I can imagine a few options, but I don't have the experience to judge what would give me the optimal gain in dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can see the following options:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Connecting two directional antennas and pointing them in one direction&lt;/strong&gt;. The problem here is that the antenna connectors are very close to each other and two directional antenna would not fit that close together. So, I would have to extend connector using cables and build some frame to hold the antennas. A lot of work, and cables incure signal loss.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Disconnecting one omni and connecting one directional&lt;/strong&gt;. Problem here&#xA;is that I don't know if the NIC can work using one antenna.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;Connecting multipatch antenna&lt;/strong&gt; -- quite expensive, but if that is the only option then I have to go with that.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Or maybe some other option? &lt;/p&gt;&#xA;" OwnerUserId="16819" LastEditorUserId="8717" LastEditDate="2020-04-12T18:45:05.683" LastActivityDate="2020-04-12T19:33:33.353" Title="Connecting Directional Antenna To Two Antenna Ports on NIC" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wifi&gt;&lt;microwave&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16429" PostTypeId="2" ParentId="16428" CreationDate="2020-04-12T19:19:18.760" Score="0" Body="&lt;p&gt;Looking at &lt;a href=&quot;https://www.alfa.com.tw/products_detail/1.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;this information about your 802.11ac USB antenna&lt;/a&gt;, those two antennas are not on the same frequency. One antenna is for 2.4 GHz, and the other for 5 GHz. Since they are independent of each other, this is not a phased array of two verticals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FMh94.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FMh94.jpg&quot; alt=&quot;Dual band WiFi antennas&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you only need one of those bands, I suggest that you only remove the one that you want the directional antenna attached to, and leave the other antenna alone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since they have RP-SMA female connectors, those antennas can be disconnected. But I'll leave the details of the antenna and feedline to others here that are experienced in these WiFi frequencies.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-04-12T19:25:10.163" LastActivityDate="2020-04-12T19:25:10.163" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16430" PostTypeId="2" ParentId="16428" CreationDate="2020-04-12T19:33:33.353" Score="2" Body="&lt;p&gt;Wireless NICs and APs have multiple antennas for &lt;a href=&quot;https://en.wikipedia.org/wiki/MIMO&quot; rel=&quot;nofollow noreferrer&quot;&gt;MIMO&lt;/a&gt;. This means the device dynamically determines the coefficients for each antenna to combine them in the best way.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Often that means phasing the antennas to make an array with greater gain towards the other station and/or less gain towards interference sources. This is called &lt;em&gt;beamforming&lt;/em&gt;. So your NIC is already &quot;spatially directional&quot; in a way. A device with more antennas could be even more directional.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Additionally, the device can find two sets of orthogonal coefficients and use this to double the data rate. This is called &lt;em&gt;spatial multiplexing&lt;/em&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One solution to your issues may be to simply upgrade the NIC. Higher end devices may have 4 or even more antennas, and with more antennas in the array comes the potential for a more directional array. NICs are cheap enough this may be cheaper than buying antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, attaching two directional antennas would work well. This allows the NIC to still gains the benefits of MIMO, while adding gain in the direction where you need it the most. Unless the cables are going to be very long, it's likely the cable loss will be more than offset by the additional gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even if you attach just one directional antenna and leave the other omnidirectional antenna attached, the NIC will likely weight the directional antenna more heavily. Though this does mean you are less likely to get the higher data rates associated with spatial multiplexing.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-12T19:33:33.353" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16431" PostTypeId="2" ParentId="16426" CreationDate="2020-04-13T01:18:15.597" Score="6" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;If you submit your application online on a federal workday (Monday to Friday, except holidays), even after hours, it is considered received that day. If you submit it on a weekday or a holiday, it will be considered received on the next federal workday.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;There is a waiting period of 17 days, during which applications aren't processed. This allows time for mailed-in applications to be processed (yes, they're still allowed).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If the 18th day (inclusive) is a federal workday, your application will be queued for processing that night. Otherwise, it will be queued for processing on the night of the next federal workday.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The results of your application will be posted early in the morning of the following day (regardless of whether it is a federal workday).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Because the receipt date and the processing date must both be federal workdays, and be separated by 17 days, it works out that processing will only happen on Monday (if the receipt date was Wednesday through Friday), Thursday (if the receipt date was Monday), or Friday (if the receipt date was Tuesday), and the results will show on Tuesday, Friday, or Saturday mornings. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Normally, this works out to an 18-20 day wait, but holidays may increase it to 21. I don't think any two federal holidays are perfectly spaced to create the perfect storm of a 24-day wait.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most information in this answer sourced from &lt;a href=&quot;http://ae7q.com/query/text/Vanity.php&quot; rel=&quot;noreferrer&quot;&gt;AE7Q&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-04-13T01:18:15.597" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16433" PostTypeId="1" CreationDate="2020-04-13T13:34:10.097" Score="2" ViewCount="320" Body="&lt;p&gt;Short question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;What are the advantages and disadvantages of using gamma (solid element) or beta (split element) matching a yagi?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Long question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A while ago I built a coil loaded yagi for the 20M band, with a small coil in the middle, for a total element length of 6M (3M to each side). This element is split, center fed, like any traditional dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yesterday I added a second element, for the 10M band. I didn't have enough material to add a reflector, so basically I have a rotatable 10M dipole sharing the boom. The match was good enough, though, to provide a reasonable SWR of 1:1.5. It's a little too long, but I don't want to trim it until I add the reflector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3NAdy.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3NAdy.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand that, when I add the reflector, the feedpoint impedance at resonance may drop. I've been considering the options for matching a low impedance to 50 ohms, which so far I've only done with simple LC networks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From my understanding it comes down to:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Use a split element (like any traditional dipole), and match it, if necessary, with a &quot;hairpin&quot; or &quot;beta&quot; match&lt;/li&gt;&#xA;&lt;li&gt;Use a solid element, and drive it with a &quot;gamma&quot; match&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I couldn't find any information information, other than anecdotical &quot;I would never do it this way&quot;, on the advantages and disadvantages of both types of matches. The great benefit from solid + gamma, is that it makes design of the antenna much easier and stronger, since you don't need to cut the tube in the center. But apparently the gamma match isn't as broadband as a hairpin (that's all anecdotical info I found on different forums).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I solved the boom isolation by using strong L shaped alu pieces (6mm thick, 100mm flange length), and the element is sandwiched between two 3D printed insulators, bolted to this L (PETG is an amazing 3D print material). So I don't mind doing it this way if split elements have any significant advantage over a solid element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3y7dF.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3y7dF.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Environmental factors to conside at my location are winds, which are not often but once or twice a year, very strong (250km/h gusts are not unheard of). I need to design the yagi so I can drop it to a safe parking location, but that's a different issue. There is no snow, ice, or freezing rain to worry about.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="8717" LastEditDate="2020-04-13T15:20:14.457" LastActivityDate="2020-04-14T16:01:03.157" Title="Yagi: split or solid driven element?" Tags="&lt;antenna-construction&gt;&lt;yagi&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16434" PostTypeId="2" ParentId="16425" CreationDate="2020-04-13T15:44:02.157" Score="6" Body="&lt;p&gt;Around sunrise and sunset (both yours and theirs), to take advantage of &quot;grayline&quot; propagation, which has lower loss than daytime propagation, at higher frequencies than nighttime propagation. In April, Japanese sunset comes a few hours before your sunrise, around 5am. 40 meters may open around that time, and 20 meters may open right around your sunrise. At around 7pm, the sun will be rising in Japan, and there is a good chance of another 20m opening until your sunset.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Surprisingly, you might find better luck between October and February. Although northern-hemisphere propagation is overall less during those months, the shorter length of day means that your sunset and Japan's sunrise align more favorably, and your entire path will be &quot;in grayline&quot;. There is also a brief period in June where your sunrise and Japan's sunset align well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A nice tool to get an idea for these questions is &lt;a href=&quot;https://www.voacap.com/&quot; rel=&quot;noreferrer&quot;&gt;VOACAP&lt;/a&gt;. If you go to their newly redesigned &lt;a href=&quot;https://www.voacap.com/hf/&quot; rel=&quot;noreferrer&quot;&gt;HF planner&lt;/a&gt;, you can drag the red marker to your location, and the blue marker to where you want to talk to (or select &quot;W Harrisburg PA&quot; and &quot;JA Tokyo&quot; in the TX and RX QTH dropdowns). You may also adjust the mode, power, and antenna dropdowns. Then scroll to the bottom and click &quot;All Year&quot; for a month-by-month chart of bands and times, and you will see what I mean.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-04-13T15:44:02.157" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16435" PostTypeId="2" ParentId="16425" CreationDate="2020-04-13T22:31:44.517" Score="5" Body="&lt;p&gt;This is a great use case for &lt;a href=&quot;https://www.voacap.com/hf/&quot; rel=&quot;noreferrer&quot;&gt;VOACAP&lt;/a&gt;. You tell it where the stations are:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Yt3tv.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Yt3tv.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And then you can click the &quot;Prop Wheel&quot; button to see what times on what bands are good:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ViXch.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ViXch.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here we can see from 20:00 to 03:00 UTC are OK on 20 meters, and 40 meters is good from 08:00 to 11:00 UTC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VOACAP takes into account your power, mode, antennas, time of day, and time of year, all of which can significantly alter your chances of making a contact. For this run I used CW at 100 watts, and the default antennas which include a dipole 33 feet off the ground on 40m, and a 3 element Yagi at the same height for 20 meters, on April 13, 2020.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-13T22:31:44.517" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16436" PostTypeId="1" AcceptedAnswerId="16437" CreationDate="2020-04-14T00:05:35.447" Score="4" ViewCount="75" Body="&lt;p&gt;How do you choose the values of the capacitor and the resistor in an envelope detector circuit? In my case, the frequency range is from&#xA;20 Hz to 20,000 Hz. Also, am I correct in understanding that usually Schottky diodes are used in the circuit instead of other types of diodes because they have a lower turn-on voltage?&lt;/p&gt;&#xA;" OwnerUserId="16680" LastEditorUserId="16680" LastEditDate="2020-04-14T00:17:38.657" LastActivityDate="2020-04-15T01:16:32.960" Title="AM Radio Envelope Dectector" Tags="&lt;am&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16437" PostTypeId="2" ParentId="16436" CreationDate="2020-04-14T00:54:58.687" Score="7" Body="&lt;p&gt;The capacitor and resistor make a low-pass &lt;a href=&quot;https://en.wikipedia.org/wiki/RC_circuit&quot; rel=&quot;nofollow noreferrer&quot;&gt;RC filter&lt;/a&gt;, with a frequency cutoff around &lt;span class=&quot;math-container&quot;&gt;$\frac{1}{2\pi RC}$&lt;/span&gt; (in hertz). Do keep in mind &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; is not just the value of the resistor, but rather the entire load on the circuit which includes the input impedance of the next stage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea is to strip out the RF component, while passing the baseband component.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the cutoff is too high, the rectified RF gets through, so you're not making an envelope detector anymore.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the cutoff is too low, it means the envelope detector is slow to respond to changes in envelope amplitude. In an AM receiver this means high frequencies in the demodulated audio will be attenuated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the baseband signal is usually something audible to humans, it's not above 20 kHz. And the RF signal is usually at least an order of magnitude higher than that. So there is a very wide range of values that will work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You are correct, Schottky diodes are often selected for their lower turn-on voltage and fast switching speed.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-04-15T01:16:32.960" LastActivityDate="2020-04-15T01:16:32.960" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16438" PostTypeId="1" CreationDate="2020-04-14T02:37:19.373" Score="0" ViewCount="53" Body="&lt;p&gt;I get a 0X1C error in APRS.FI and my beacon does not show on ui-view32. I am totally lost. Any idea what I am doing wrong?&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;2020-04-13 19:19:38 CDT: W5CCL-10&amp;gt;TVRX0X,WIDE*,WIDE2-1,qAR,W0RC:'yVel &amp;lt;0x1c&amp;gt;Y\]=&#xA;2020-04-13 19:29:54 CDT: W5CCL-10&amp;gt;TVRX0X,WIDE1-1,WIDE2-1,qAR,W0KGW-10:'yVel &amp;lt;0x1c&amp;gt;Y\]=&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="16834" LastEditorUserId="76" LastEditDate="2020-04-14T16:01:27.870" LastActivityDate="2020-05-16T11:00:45.157" Title="0X1C error on APRS.FI" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16439" PostTypeId="1" CreationDate="2020-04-14T07:27:54.010" Score="0" ViewCount="50" Body="&lt;p&gt;am new to this forum, so tell me if this question is out of place - as it concerns a scanner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have an old radioshack pro-651 (same model as pro 106, and whistler 1040) that I am trying to program with the &lt;a href=&quot;https://www.radioreference.com/apps/db/?sid=7021&quot; rel=&quot;nofollow noreferrer&quot;&gt;NJICS TRS&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have added the TSYS object as follows, using the frequencies of West Orange Simulcast site.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;    Type:MOT VHF/UHF&#xA;    Frequencies:&#xA;            769.19375&#xA;            769.45625&#xA;            769.66875&#xA;            769.96875&#xA;            770.44375&#xA;            770.66875&#xA;            770.91875&#xA;            773.34375&#xA;            773.79375&#xA;            774.31875&#xA;            774.54375&#xA;            774.78125&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Everything else is on the default setting.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I added a TGRP object with id: &lt;code&gt;Wildcard&lt;/code&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However after consistent monitoring, I fail to pick up anything.&#xA;Am not sure if I'm leaving out any important fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can this be accomplished?&lt;/p&gt;&#xA;" OwnerUserId="16835" LastActivityDate="2020-04-14T07:27:54.010" Title="How to program a trunked System into radioshack pro 651?" Tags="&lt;radio-programming&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16441" PostTypeId="2" ParentId="16433" CreationDate="2020-04-14T15:34:58.767" Score="1" Body="&lt;p&gt;Providing a single, simple answer to your question requires the design to be more completely specified. Designers who are unhappy with their antenna's performance may have unrealistic expectations. For a given feed strategy, coupling between parasitic elements can dramatically affect the match bandwidth, as well as gain, directivity and feedpoint impedance. Conversely, adding a secondary &quot;sleeve&quot; to the driven element (a la WA3FET's &quot;Optimized Wideband Antenna&quot; concept) can substantially restore match bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition to the options you identified, the T-match is a &lt;em&gt;balanced&lt;/em&gt; version of the Gamma match, for use with solid elements. If you plan to feed the antenna with coax, it's important to add a balun at the feedpoint to balance the currents.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-04-14T15:34:58.767" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16442" PostTypeId="2" ParentId="16433" CreationDate="2020-04-14T16:01:03.157" Score="3" Body="&lt;p&gt;I'd say you're overthinking it. Mechanical issues, like ease of construction and strength are the biggest differences. Different matching arrangements may yield more or less flexibility in adjustment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The hairpin match is simply a parallel inductance. The idea is to make the driven element a bit short so it presents a capacitive impedance, then that inductance cancels it. On a Smith chart it looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oBafb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oBafb.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The green dot is the starting impedance of the feedpoint without the match. Changing the length of the hairpin adjusts the length of that arrow.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The hairpin match doesn't offer many options for adjustment. Provided the starting impedance is capacitive, it's always possible to find some hairpin length that cancels the reactance, but the resulting resistance might be too high or too low. There's nothing you can do about that besides change the length of the element, which might involve a redesign of the entire antenna. And let's hope you need to make the element shorter, not longer...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To its advantage, if you make the hairpin from tubing it can double as a &lt;a href=&quot;https://ham.stackexchange.com/questions/3591/how-does-a-folded-balun-work&quot;&gt;folded balun&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://ham.stackexchange.com/questions/1804/what-is-a-gamma-match-in-the-context-of-the-driven-element-of-a-yagi-antenna&quot;&gt;gamma match&lt;/a&gt; by comparison is much more flexible, having three things to adjust. Well maybe 2½, because changing the diameter of the tubing is a bit tricky, though not as tricky as changing the length of the element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the Smith chart, the gamma match looks like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/KCq2f.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The Gamma match isn't super effective as a balun: it only increases the common-mode impedance by the factor of the impedance step-up it provides, which is probably in the neighborhood of 4 to 10. To avoid turning the Yagi into a vertical, some additional choking is probably a good idea.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-14T16:01:03.157" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16443" PostTypeId="1" CreationDate="2020-04-14T18:38:33.893" Score="1" ViewCount="136" Body="&lt;p&gt;A very specific issue this one. I bought one of these radios on an impulse because it was cheap but never really used it. Now, during lockdown my club has a nightly net on 2m so I built an antenna and started using it.&#xA;The reception was patchy at best on all but the closest people with faint reception and a lot of static.&#xA;Then I nudged the power button and it cleared up instantly, crystal audio and very low static. The power button is  a momentary switch that switches on and off with a long press but I cannot find out in the manual what the short press is and if I there is a setting in the menu that will fix this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Long shot but does anyone know anything about the QYT?&lt;/p&gt;&#xA;" OwnerUserId="11749" LastActivityDate="2021-02-18T07:29:45.390" Title="QYT KT8900D issue" Tags="&lt;transceiver&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16444" PostTypeId="1" AcceptedAnswerId="16445" CreationDate="2020-04-14T20:09:43.990" Score="5" ViewCount="172" Body="&lt;p&gt;If I have a too short dipole, or vertical, I can add a coil to lenghten in electrically. But it's my understanding that I could also do this with any other kind of match: given the complex impedance at the frequency of interest, I could calculate, for example, a LC network that will match my radiator to present 50 ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So what's the difference between doing it one or the other way? Is a &quot;loading coil&quot; a type of match or does it behave differently?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-04-21T19:10:50.010" Title="Is &quot;coil loading&quot; a type of impedance match?" Tags="&lt;antenna&gt;&lt;impedance-matching&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16445" PostTypeId="2" ParentId="16444" CreationDate="2020-04-15T00:33:58.560" Score="4" Body="&lt;p&gt;The short answer to your question is, &quot;Yes.&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every change made to an antenna is likely to change the feedpoint impedance: lengths, diameters and configurations of driven and parasitic conductors; positions, values and parasitic characteristics of &quot;loading&quot; circuits; distance from ground and &quot;nearby&quot; conductive structures, including near-resonant feedlines; etc., etc., etc. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The approach used to maximize power transfer from the transmitter to the antenna may or may not include impedance matching circuitry at the feedpoint or as part of the antenna structure, depending on the losses incurred in the feedline as a result of any mismatch. In typical ham antenna applications, resources of time and treasure are relatively limited, so the need for and implementation of impedance matching means are driven by higher-order design constraints.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-04-15T00:33:58.560" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16446" PostTypeId="1" CreationDate="2020-04-15T02:41:36.127" Score="4" ViewCount="104" Body="&lt;p&gt;I have a Kenwood TH-D72 and I just got an old Radio Shack HTA-20 2m amplifier to use with it. They're both powered from a sizeable 3S2P Li-Ion battery pack and they work great together for the most part, but I recently noticed something odd. I connected a meter to measure the current draw of the amp, and with it turned off it still seemed to be drawing about 100mA. After a bit of head scratching as the amp has a physical power switch and so shouldn't draw anything when off, I concluded that when they're both connected to the same battery the radio must be getting a much lower resistance connection to the power supply ground/negative through the coax braid and the 12 gauge wire I've run to the amp than through its own comparatively dinky power lead; when I unplug the radio from the shared external battery or disconnect the coax from the radio to the amp, the current draw at the powered-off amp goes away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using the coax as a power supply lead just doesn't seem like a good thing to me, but is this really a big deal? The amp starts acting up when the battery gets below about 10.7V in this configuration, which is what got me hooking up meters and testing things in the first place, but it does the same thing when the battery gets a bit lower even when the radio is running on its internal battery, so I think this amp just doesn't handle undervoltage well and the extra voltage drop to the amp when its cabling is also partly powering the radio (which itself pulls a couple of amps on TX) causes it to misbehave sooner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, do I need to stop the radio from using the coax braid as its primary negative power supply connection and if so, how? Some sort of balun/unun/other transformerish isolator?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="4452" LastEditorUserId="4452" LastEditDate="2020-04-15T20:22:20.423" LastActivityDate="2020-04-15T23:46:07.213" Title="Coax braid acting as power supply ground between radio and amplifier connected to the same supply, is this a problem?" Tags="&lt;amplifier&gt;&lt;dc-power&gt;&lt;battery&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16447" PostTypeId="2" ParentId="16444" CreationDate="2020-04-15T06:43:01.250" Score="1" Body="&lt;p&gt;Yes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A vertical antenna element shorter than λ/4 at the required frequency would be capacitive. The inductive reactance of the loading coil at the base of the antenna would offset the capacitive reactance of the short antenna and make it resonant at the required frequency. Likewise with two loading coils at the feed point of a short dipole.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A tuner would be useful when a vertical ground plane antenna or a dipole is to be matched to work on different bands.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-04-15T10:14:21.617" LastActivityDate="2020-04-15T10:14:21.617" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16448" PostTypeId="2" ParentId="16443" CreationDate="2020-04-15T14:31:45.337" Score="1" Body="&lt;p&gt;I don't own a KYT8900D, but I did download the manual, and I went over it to see if the power button has a short-press function.  If there is such a function, I wasn't able to find it in the manual.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I find the notion that the radio has a function associated with the power button, not mentioned in the manual, that clears up the reception to be very unlikely.  If there were a function that improves reception for weak signals, then the manual would surely emphasize it for marketing purposes.  I also find the notion of the power button having a secondary function to be unlikely, unless the radio is so crammed with functions that there is no other button to hold the function.  Putting multiple functions on the power button is bad design; hold the button too long, and the radio switches off, which would annoy operators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm just guessing here, but I think that there's an intermittent connection somewhere in your setup, and pressing the button fixes the intermittent connection temporarily.  I suppose that it's possible that the bad connection is in your PL-259 coaxial connector, especially if you soldered it yourself and you don't have much practice soldering PL-259s, but that seems unlikely because pressing one place on the front panel would be unlikely to flex the connection between the coaxial cable and the connector.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The most likely explanation seems to me to be an intermittent connection inside the radio.  The problem could be a cracked surface-mount component, a corroded connector pin, a poor solder joint, etc.  Good quality control can prevent such defects from leaving the factory, but QYT seems to be a company that is new to making radios, and their reputation for quality control seems to be mostly unknown.  You could try pushing on the front panel near the power button.  If that improves the reception, then that would support the intermittent-connection theory.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-04-15T14:31:45.337" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16449" PostTypeId="2" ParentId="16444" CreationDate="2020-04-15T14:59:01.980" Score="3" Body="&lt;p&gt;Anything done to get the antenna impedance closer to 50 ohms (or whatever the design might call for) can be called an impedance match, loading coils included.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However I would note: many loading coils aren't exactly equivalent to an inductor at the feedpoint.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quite often, the loading coil is not at the base of the antenna but rather somewhere in the middle. This requires the inductance to be larger, but it also increases the current in the section of the antenna below the coil. Getting more current over a longer length increases radiation efficiency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's an optimal place to put it: too high and the inductance required is so high that the resistance of the additional wire required offsets the other gains.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also possible to &quot;stretch out&quot; the coil which distributes the inductance over the entire length. For example consider the &lt;a href=&quot;https://en.wikipedia.org/wiki/Rubber_ducky_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;rubber ducky antenna&lt;/a&gt;, ubiquitous on handheld radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Or consider the &lt;a href=&quot;https://mfjenterprises.com/collections/mfj-enterprises/products/mfj-1620t&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ hamstick&lt;/a&gt; which has a lower section of loosely wound coil like a rubber ducky, a tightly wound loading coil in the middle, and a simple whip at the top.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So yes, loading coils are a matching technique. And it's true it's possible, with ideal lossless components, to make a matching network from inductors, capacitors, and transmission line stubs that will match any load.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But when you start to consider real components with loss that can impact performance, the reasons for one matching technique over another become more apparent. For example, an air-core loading coil in the middle of an antenna performs differently than an inductor wound on a lossy ferrite core at the feedpoint.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-15T14:59:01.980" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16451" PostTypeId="2" ParentId="16446" CreationDate="2020-04-15T19:43:30.087" Score="1" Body="&lt;p&gt;Should a 'a not so good contact' at the HT's external jack/plug be ruled out as a contributory factor, the only way to avoid DC current in the coax braid would be to have a separate battery pack for the HT.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The moot point is whether DC current in the braid does matter.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-04-15T19:43:30.087" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16452" PostTypeId="2" ParentId="16446" CreationDate="2020-04-15T20:29:01.000" Score="4" Body="&lt;p&gt;An anecdote: I had problems with my station which included computer-radio interconnections; some of my devices (RTL-SDRs) would lock up when I powered on my Yaesu FT-897. I eventually tracked this down to the power-on inrush currrent of the radio passing through coax shields and the chassis of the antenna switch that both were connected to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I solved the problem by replacing the fuse (an element with resistance, after all) in the negative power lead of the FT-897 with a jumper (keeping the fuse in the positive side). This way, the negative power wire's impedance has been reduced compared to the paths not intended for power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the above is an example of one kind of problem that can happen, and a general precaution to take: &lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Make sure your power wires are fat and securely connected.&lt;/li&gt;&#xA;&lt;li&gt;Make sure there is no way to have a positive connection without a negative.&lt;/li&gt;&#xA;&lt;li&gt;Don't use an ammeter or current shunt on the negative lead, except where there is no other negative-side path (e.g. the battery terminals, or an otherwise-isolated load, but not interconnected components). Not only will it cause shield currents, it will read inaccurately since some current is bypassing it.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Adding galvanic isolation by a transformer (&quot;voltage balun&quot; in this context) could work, and will completely eliminate rather than reduce the stray current, but would be an expensive and heavy component (typical baluns are &quot;current baluns&quot;, which do not isolate, because that way they can avoid needing a magnetic core sized for the full RF power being carried). I've never heard of someone using one.&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2020-04-15T21:54:34.607" LastActivityDate="2020-04-15T21:54:34.607" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16453" PostTypeId="2" ParentId="16446" CreationDate="2020-04-15T23:46:07.213" Score="6" Body="&lt;p&gt;If I understand the description correctly:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/TDg01.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fTDg01.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that's all it is, I wouldn't say it's any big deal. Whenever you have multiple paths to ground, current will split between them. It's these currents that keep &quot;ground&quot; approximately the same voltage everywhere: an essential assumption in the design of most electronic equipment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some DC on the coax won't cause any issue. In fact putting a DC bias on coax is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Bias_tee&quot; rel=&quot;noreferrer&quot;&gt;common way to power an active antenna&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It could be the power leads for the radio are simply too light. The ground lead may not be a problem since the coax provides a low impedance connection, but the positive lead is equally small. Try eliminating the coax by attaching a dummy load to the radio. Then while transmitting, compare the battery voltage to the voltage at the radio's terminals. It shouldn't drop more than a volt, preferably less. You can also multiply that difference times the supply current and calculate the power wasted in the power leads, which might be of concern if you're trying to maximize the battery life of this station.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Out of an abundance of caution, I should also mention the possibility that this current has some more dangerous origin involving a fault in your mains wiring. You didn't describe anything not powered by the battery, but if you have for example a connection from the radio to a computer, and there's a ground fault in the computer, that ground current you are measuring could be the only thing keeping the chassis of your equipment from being an electrocution hazard. It's unlikely but possible, so be careful.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-15T23:46:07.213" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16454" PostTypeId="2" ParentId="10410" CreationDate="2020-04-15T23:48:01.920" Score="4" Body="&lt;p&gt;Remember the time-honored engineering adage: Better is the enemy of Good Enough.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is difficult to imagine any practical value to inserting a matching network between your generator or feedline and your antenna: 49.4 - j8.1 ohms equates to an SWR of less than 1.2:1 on a 50&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; line, already a very good match. Given the relatively large tolerances and potential losses of the components you would use in a matching network, whether lumped or distributed, it is likely that adding a matching network would actually &lt;em&gt;reduce&lt;/em&gt; the amount of power that is radiated by the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If, however, you need to increase the match &lt;em&gt;bandwidth&lt;/em&gt; - the range of frequencies over which the match does not exceed an upper limit on SWR - a properly engineered matching network could deliver improvement.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-04-18T00:08:35.630" LastActivityDate="2020-04-18T00:08:35.630" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16455" PostTypeId="2" ParentId="16438" CreationDate="2020-04-16T10:38:02.890" Score="1" Body="&lt;p&gt;There is nothing wrong with your packet and &lt;code&gt;&amp;lt;0x1c&amp;gt;&lt;/code&gt; is not an error. Your packet is a neatly formed Mic-E packet with a position of 46°28'08&quot; N, 93°58'73&quot; W, a speed/course of 0 (not moving), a status message of &quot;Off Duty&quot;, a symbol of &quot;radio or APRS device&quot;, and a type/version code of Kenwood D710. The &lt;code&gt;&amp;lt;0x1c&amp;gt;&lt;/code&gt; character is part of the encoding of the zero speed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't think there's adequate information in your post to guess why your position doesn't display in UI-View32; aprs.fi and APRS Direct were perfectly happy with it. It's worth noting that the author of UI-View32 passed away more than 15 years ago, so any bugs it may have are pretty well &quot;frozen in&quot; at this point. You may want to investigate other options.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-04-16T10:38:02.890" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16456" PostTypeId="2" ParentId="16444" CreationDate="2020-04-16T10:40:38.093" Score="1" Body="&lt;p&gt;A &quot;loading coil&quot; in series with its feedpoint terminals can offset the capacitive reactance of an electrically short set of radiating wires (where the &lt;em&gt;jX&lt;/em&gt; term of the feedpoint impedance &lt;em&gt;R -jX&lt;/em&gt; is zero ohms at the operating frequency).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However the loading coil value and its physical location in the antenna system have much less affect on matching the R term of the feedpoint impedance to the Zo of the transmission line connecting it back to the source (transmitter).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An electrically short antenna system still can have &lt;strong&gt;very&lt;/strong&gt; low radiation resistance, even though a loading coil has reduced the j term to zero ohms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radiation resistance is the only dissipative resistance that produces useful e-m radiation into space.  With very short radiators using only a loading coil, the radiation resistance can be only a few tenths of an ohm, even though the feedpoint Z has zero reactance (i.e., it is &quot;resonant&quot;).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A more complex matching network can match both the R and jX terms of the feedpoint Z of a short antenna to the Zo of a transmission line connected to its input terminals. However the radiation efficiency of that antenna system will be relatively poor.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radiation efficiency = Radiation Resistance / Total Dissipative Resistance of the Antenna System.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So for example, if a very short, center-fed dipole antenna has a radiation resistance of 1 Ω, and the ESR of the matching network used to produce a 50 Ω feedpoint impedance to it is 9 Ω, then the radiation efficiency of that system is 1/10 = 0.1, or 10%.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Not&lt;/strong&gt; matching both the R term and the j term to the source impedance reduces the radiation efficiency of that antenna system even further.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-04-16T10:40:38.093" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16457" PostTypeId="1" CreationDate="2020-04-17T02:48:28.710" Score="4" ViewCount="233" Body="&lt;p&gt;What is IQ, in the context of software-defined radios (SDRs)?&lt;/p&gt;&#xA;" OwnerUserId="8805" LastActivityDate="2020-04-21T17:23:33.620" Title="What is IQ in the context of SDRs?" Tags="&lt;software-defined-radio&gt;&lt;jargon&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16458" PostTypeId="1" CreationDate="2020-04-17T02:49:20.887" Score="4" ViewCount="75" Body="&lt;p&gt;I would like to monitor NCDXF beacons, and WSPR. What kind of antenna would be good for reception in the bands of 6, 10, 12, 15, 17 and 20M?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some antennas I considered:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A trapped dipole, with traps for each band. This could get tricky with the close proximity of the frequencies.&lt;/li&gt;&#xA;&lt;li&gt;A fan dipole. Doable, but I've tried a couple of times to build one without success.&lt;/li&gt;&#xA;&lt;li&gt;A vertical with an active tuner: a bunch of coils and capacitors, to match the multiple bands. I can build this with some relays and arduino, but I'd rather have a passive receiver.&lt;/li&gt;&#xA;&lt;li&gt;A loop, but as far as I know, these are single band and very narrow.&lt;/li&gt;&#xA;&lt;li&gt;A Random Wire: tried one, with a 1:9 balun. Reception wasn't great anywhere.&lt;/li&gt;&#xA;&lt;li&gt;That 20M dipole I no longer use, and hope for the best&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;My goal is to be able to monitor propagation at my QTH, and have a reasonable idea of the conditions, without relying on propagation report websites like WSPRnet or similar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If possible, I'd also like to be able to transmit WSPR, that's why a resonant antenna with reasonable SWR would be desired, but this isn't a priority for me.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-04-19T23:23:30.117" Title="What kind of antenna for an automatic high bands monitoring station?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;wspr&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16459" PostTypeId="1" CreationDate="2020-04-17T02:54:33.430" Score="0" ViewCount="42" Body="&lt;p&gt;Does digital coded squelch (DCS) interfere with the analog-to-digital conversion in software-defined radios (SDRs)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I noticed that I can receive normal transmissions with my SDR just fine, but I have trouble demodulating DCS-encoded ones; I have to set the IF to 2+ kHz for some reason (in &lt;a href=&quot;http://cubicsdr.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;CubicSDR&lt;/a&gt;) in order to make the audio somewhat intelligible. Why would this be?&lt;/p&gt;&#xA;" OwnerUserId="8805" LastActivityDate="2020-04-17T07:40:51.763" Title="Does DCS intefere with SDR reception?" Tags="&lt;software-defined-radio&gt;&lt;tone-squelch&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16460" PostTypeId="2" ParentId="16459" CreationDate="2020-04-17T07:40:51.763" Score="3" Body="&lt;p&gt;Short answer: No. The whole point of SDR is that the physical receiver doesn't &lt;em&gt;care&lt;/em&gt; what the kind of signal is it's receiving as long is bandwidth-wise narrow enough and amplitude-wise not overdriving.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-04-17T07:40:51.763" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16461" PostTypeId="2" ParentId="16458" CreationDate="2020-04-17T15:34:07.833" Score="2" Body="&lt;p&gt;A short dipole or small loop is a good choice for a receive-only antenna that works over many bands simultaneously.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The trick is to make an antenna that's equally bad everywhere. If you try to match a short dipole with a loading coil, or a small loop with a tuning capacitor, you end up with a very narrow-band antenna. So instead you don't try to match it at all, and just focus on extracting the maximum signal possible. For receiving you don't necessarily need optimal power transfer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a short dipole, that means having a preamplifier with an extremely high input impedance. And for a loop, an extremely low input impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, &lt;a href=&quot;http://www.lz1aq.signacor.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;LZ1AQ has such a preamplifier kit&lt;/a&gt;. There are many others available, sold as &quot;active antennas&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you also want to transmit, your ideas of traps, fans, and switchable matching networks all sound like viable options, perhaps even in combination. You can for example have a trap dipole or monopole, but with stubs added for bands not covered by the traps. For example, DX engineering makes a &lt;a href=&quot;https://www.dxengineering.com/parts/dxe-aokb-17m?seid=dxese1&amp;amp;gclid=CjwKCAjwp-X0BRAFEiwAheRui3XD74PXFoWzjuAGCU_eOB1T6fzaypX26oix_WOu7vp1sy04XrBtjhoCJx0QAvD_BwE&quot; rel=&quot;nofollow noreferrer&quot;&gt;17 meter add-on for the Huster BTV&lt;/a&gt; that works like this. You can find commercial kits, or you can make your own with a little trial and error.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-17T15:34:07.833" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16462" PostTypeId="2" ParentId="16457" CreationDate="2020-04-17T15:38:01.900" Score="0" Body="&lt;p&gt;IQ is a type of sampled data.  Sampled data (a vector of numbers) allows digital processing (a bunch of arithmetic on finite size numbers), instead of using analog circuits (inductors, capacitors, etc.), to produce some signal transform (for instance: filtering or demodulation, etc.).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;IQ usually describes pairs of unequally spaced or offset heterodyned samples taken at a sample rate (per pair) frequency related to the frequency bandwidth of interest, often well below the actual RF frequency of the signal of interest.  Regular (non-IQ) sampling is taking equally spaced samples at a rate above (often well above) the high end of a (radio or audio) frequency band of interest.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To be considered a good IQ signal, the pair of samples need to be taken in quadrature (1/4, 3/4 time spacing), or be samples of a pair of waveforms that result from heterodyning by a quadrature mixer.  This allows the IQ data to be fed to a complex FFT, where the positive and &quot;negative&quot; frequency halves of the FFT result will not just degenerate to complex conjugate mirrors of each other, as would be the FFT result if the FFT was fed, real component only, with equally spaced samples.  Thus you get twice a much useful &quot;stuff&quot; out of a given length IQ FFT.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-04-17T15:50:06.547" LastActivityDate="2020-04-17T15:50:06.547" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16463" PostTypeId="2" ParentId="16457" CreationDate="2020-04-17T15:59:39.410" Score="5" Body="&lt;p&gt;&quot;IQ&quot; refers to the practice of having two mixers with their oscillator phase 90 degrees apart, and then the digitization and processing of those two streams of data.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One practical problem is in a superheterodyne receiver, the LO must be selected and the filters designed for the best &lt;a href=&quot;https://en.wikipedia.org/wiki/Image_response&quot; rel=&quot;nofollow noreferrer&quot;&gt;image response&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem can be understood intuitively like this: say there is a spinning disk, with a mark on its diameter. The disk is spinning so quickly it's a blur, but you can use a &lt;a href=&quot;https://en.wikipedia.org/wiki/Stroboscope&quot; rel=&quot;nofollow noreferrer&quot;&gt;strobeoscope&lt;/a&gt; to observe it. You know approximately how fast the disk is spinning, and you set the strobeoscope to this frequency. It will then appear the disk is spinning slowly, with the speed corresponding to the difference in speed between the strobeoscope and the disk. Depending on the direction of spin, you can tell if the disk is spinning faster or slower than the strobescope.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you separate the horizontal and vertical positions of the mark into functions, you will find they are the trigonometric functions &lt;span class=&quot;math-container&quot;&gt;$\sin()$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\cos()$&lt;/span&gt;, which are the same function but 90 degrees apart:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TWl6L.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TWl6L.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem is a single RF mixer operates like a stroboscope that only gives you the position of the mark in one dimension. With just one dimension you can tell the difference in speed, but you can't tell if that difference is positive or negative.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mathematics of how this works is elegantly expressed in &lt;a href=&quot;https://en.wikipedia.org/wiki/Euler%27s_formula&quot; rel=&quot;nofollow noreferrer&quot;&gt;Euler's formula&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{ix} = \cos x + i \sin x $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It turns out this is really useful. The reason a frequency mixer has sum and difference frequency products is because&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(x) = \cos(-x) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But if we allow the calculations to have complex values we can write signals not like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ s(t) = \cos(\omega t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;but instead like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ s(t) = e^{i \omega t} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and because&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{ix} \ne e^{-ix} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;we no longer have that pesky issue of dealing with images at every mixing stage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In analog hardware this is implemented by having two mixers. They each get the same RF signal, but their local oscillators are 90 degrees out of phase. This means one mixer (call it &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt;) produces the &lt;span class=&quot;math-container&quot;&gt;$\cos$&lt;/span&gt; component in Euler's formula, and the other mixer (&lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt;) produces the &lt;span class=&quot;math-container&quot;&gt;$\sin$&lt;/span&gt; component. After these signals have been digitized we can treat each pair of samples and the real and imaginary part of a complex number, and then go on processing them as if it's a single, complex-valued signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It turns out complex numbers show up in all kinds of DSP math. For example, the &lt;a href=&quot;https://en.wikipedia.org/wiki/Discrete_Fourier_transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;discrete Fourier transform&lt;/a&gt; (DFT) can be thought of as calculating the correlation of the input with a &lt;span class=&quot;math-container&quot;&gt;$\sin$&lt;/span&gt; and a &lt;span class=&quot;math-container&quot;&gt;$\cos$&lt;/span&gt; function at each bin. That means with Euler's formula we can consider the DFT to operate on complex numbers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, many demodulation algorithms will involve shifting things up and down in frequency, and in the digital domain, just like the analog domain, if we do this only with real numbers then we have to be concerned with rejecting image frequencies at every step.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are just a few examples. The point is generally IQ processing simplifies both the analog and digital implementations of an SDR.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-04-21T17:23:33.620" LastActivityDate="2020-04-21T17:23:33.620" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16464" PostTypeId="2" ParentId="16457" CreationDate="2020-04-17T17:21:13.553" Score="1" Body="&lt;p&gt;If you're looking for just a basic definition, I/Q data is the result of a special form of sampling. Unlike &quot;normal&quot; sampling which takes a single measurement of a signal at each division of the sample rate, I/Q sampling gathers &lt;em&gt;two&lt;/em&gt; measurements for each sample: both an &lt;a href=&quot;https://en.wikipedia.org/wiki/In-phase_and_quadrature_components&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;In phase&quot; &lt;strong&gt;and&lt;/strong&gt; a &quot;Quadrature&quot;&lt;/a&gt; component — thus the acronym.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;quadrature&quot; part only makes sense in a context where you are &lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=Superheterodyne_receiver&amp;amp;oldid=951757807#Local_oscillator_and_mixer&quot; rel=&quot;nofollow noreferrer&quot;&gt;mixing&lt;/a&gt; the signals before sampling them. Although the ultimate signal of interest may be chosen selectively via software only, a typical SDR still gets &quot;tuned&quot; to a particular range of frequencies to start with. This is done by multiplying the incoming RF with an &quot;LO&quot; signal, similar to the first stage of an analog heterodyning receiver. The center frequency of the tuned-in range is determined by the frequency of that &quot;LO&quot; signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now you can think of the in-phase component as the &quot;normal&quot; sample, and the quadrature component is equivalent to a second sample taken &quot;90º later&quot; &lt;strong&gt;in terms of the tuning frequency&lt;/strong&gt; (i.e. delayed in time by 1/4 of the LO's period). In practice, both the I and Q &quot;&lt;a href=&quot;https://en.wikipedia.org/wiki/Analog-to-digital_converter&quot; rel=&quot;nofollow noreferrer&quot;&gt;ADC inputs&lt;/a&gt;&quot; would be provided simultaneously as separate signals from the mixer circuit, and the two components are taken together as a single &quot;vector&quot; sample at each point in time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Capturing a two-component I/Q sample is more useful than just doubling the acquisition rate of &quot;normal&quot; [scalar] sampling. The vector I/Q samples are better for DSP processing because they avoid some ambiguity issues that come about in the mixer/heterodyning process. See Phil's comments below in response to an earlier version of this answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found Whiteboard Web's &lt;a href=&quot;http://whiteboard.ping.se/SDR/IQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;I/Q Data for Dummies&lt;/a&gt; to be a great intro to the concept personally, as it works through questions like &quot;why isn't normal sampling good enough?&quot; at least from a processing perspective. (Especially now that other posters here have provided greater clarity on what it is trying to say… ;-)&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2020-04-20T20:23:21.713" LastActivityDate="2020-04-20T20:23:21.713" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16465" PostTypeId="2" ParentId="16457" CreationDate="2020-04-18T00:04:45.293" Score="1" Body="&lt;p&gt;A &lt;a href=&quot;https://en.wikipedia.org/wiki/Fourier_series&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fourier series&lt;/a&gt; can represent a real-world signal as a weighted sum of harmonically-related sine and cosine waves. Sine and cosine waves are out of phase by one-quarter of a cycle and so are said to be in quadrature to each other. Thus, the weighted sums are known as the In-phase (I) and Quadrature (Q) components.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;single sideband modulation (SSB)&lt;/a&gt; comprises a Q component weighted by the Hilbert transform of the weight of the I component.  Digital signal processors (DSP) &quot;do the math&quot; to calculate the weights needed to produced the desired results.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-04-18T17:29:30.747" LastActivityDate="2020-04-18T17:29:30.747" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16466" PostTypeId="1" AcceptedAnswerId="16473" CreationDate="2020-04-18T18:29:02.133" Score="1" ViewCount="95" Body="&lt;p&gt;I live half a mile from my volunteer fire station. We are toned out on a VHF frequency by a neighboring municipality, and we provide mutual aid for their fire department that is toned out on an 800-meter frequency. I am not able to monitor their frequency because I don't have equipment that can do that, but if I could do that I would have advanced notice when we would likely be toned for mutual aid and could improve our response times. (This is worth doing for me since I live so close. If we end up not being toned it's a short drive back to my house.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to be able to monitor both frequencies with one handheld radio and be able to at least transmit on the VHF frequency &lt;em&gt;and&lt;/em&gt; do my ham stuff on the same handheld. I don't want to have to keep up with and charge 2 radios all the time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I own a Wouxun KG-UVD1P that allows me to monitor frequencies for our department (VHF) and some UHF frequencies, just not in the range to catch the neighboring departments dispatches. I have also been issued a 'Vertex Standard' that also allows me to also monitor our own frequencies but it cannot reach the municipality from some parts of our district (don't want to sound ungrateful, just being honest).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Does such a handheld radio exist that covers that range of frequencies, and can also take a small beating?&lt;/p&gt;&#xA;" OwnerUserId="1027" LastEditorUserId="8717" LastEditDate="2020-04-18T20:39:54.877" LastActivityDate="2020-04-19T01:37:17.823" Title="Handheld multiband radio for a ham firefighter?" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;ht&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16468" PostTypeId="2" ParentId="16457" CreationDate="2020-04-18T22:20:59.930" Score="4" Body="&lt;p&gt;To just answer the literal question:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;I&lt;/strong&gt; stands for &lt;em&gt;Inphase&lt;/em&gt; and &lt;strong&gt;Q&lt;/strong&gt; stands for quadrature.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are the two baseband signals you get when you mix the RF signal with a cosine of the carrier frequency, and with a 90° shifted version of that cosine, respectively (and properly low-pass filter afterwards).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We call the first the inphase component, because it is literally what you get &lt;em&gt;in phase&lt;/em&gt; with the cosine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mathematically, mixing-and-filtering is an &lt;em&gt;inner product&lt;/em&gt; on the vector space of &lt;em&gt;&lt;span class=&quot;math-container&quot;&gt;$L^2$&lt;/span&gt; signals&lt;/em&gt; (it's effectively the integral of the point-wise multiplication of two functions – the RF signal and the local oscillator). That is: it's a projection, very much in the geometric sense! That explains the name of the quadrature component, as it's &lt;em&gt;orthogonal&lt;/em&gt; to the inphase component. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being orthogonal also means, just like in geometry: no matter which length you have orthogonal to the other vector, the projection on that vector is going to be 0.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is very important – it means that I and Q, respectively, are two signals that are, together, equivalent to the RF signal in what they contain in signal &quot;content&quot;, but they are independent; no matter what you do to the I part, it doesn't change the Q part.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That gives us a way of understanding &lt;em&gt;any&lt;/em&gt; RF signal around &lt;em&gt;any&lt;/em&gt; carrier frequency by describing the &lt;em&gt;equivalent baseband&lt;/em&gt; signal in terms of I and Q signals, which individually have half the bandwidth of the RF signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is the strength of it – no matter to which carrier frequency your transmitter mixes its signal, the equivalent IQ baseband doesn't change (only the LO frequency).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And the same applies to all the nice linear channel models we have: You could describe what happens to your signal between your transmitter and your receiver by describing what happens at the carrier frequency – or you could do the same directly in baseband, and &lt;em&gt;ignore&lt;/em&gt; the fact that you have a mixer to go up from baseband to RF, then some amplifier, an antenna, the air, another antenna, an LNA, a mixer in between and just describe all this as a channel on the baseband, mathematically (and SDR, being software, is very good at math).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, to do things mathematically with the baseband, it has proven elegant to associate complex numbers with the I and Q components: The complex baseband signal at any time &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt; is just &lt;span class=&quot;math-container&quot;&gt;$I(t) + jQ(t)$&lt;/span&gt;, with &lt;span class=&quot;math-container&quot;&gt;$j=\sqrt{-1}$&lt;/span&gt;, the imaginary unit.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-04-18T22:20:59.930" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16469" PostTypeId="1" AcceptedAnswerId="16471" CreationDate="2020-04-18T22:32:33.380" Score="2" ViewCount="55" Body="&lt;p&gt;Does Mexico have a time transmitter like NIST's &lt;a href=&quot;https://www.nist.gov/pml/time-and-frequency-division/radio-stations/wwv&quot; rel=&quot;nofollow noreferrer&quot;&gt;WWV&lt;/a&gt; in the United States?&lt;/p&gt;&#xA;" OwnerUserId="8805" LastEditorUserId="8717" LastEditDate="2020-04-18T23:53:37.957" LastActivityDate="2020-04-18T23:57:59.030" Title="Mexican version of WWV?" Tags="&lt;wwv&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16470" PostTypeId="1" CreationDate="2020-04-18T23:46:53.517" Score="1" ViewCount="183" Body="&lt;p&gt;A 10 watt transmitter is transmitting a 700 hz tone in a 3 kHz wide band. If the power is increased to 1000 watts will that not increase the bandwidth if the data (700Hz tone) remains constant? &#xA;What I am asking is this. Does the bandwidth become wider if the power is increased and the data transmitted stays the same? It seems to me like it must become wider. If the power is increased with the data remaining constant the power must go somewhere and I contend that it goes into increasing the bandwidth of the signal. I do not want to factor in noise or any changes in receiver characteristics. Just power vs. bandwidth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simply a 3kHz wide bandwidth saturated with 700 Hz tone and the power is increased from 10 watts to 1000 watts. Thank you.&lt;/p&gt;&#xA;" OwnerUserId="9004" LastEditorUserId="8717" LastEditDate="2020-04-18T23:59:45.487" LastActivityDate="2020-04-19T13:17:16.253" Title="Power vs. Bandwidth" Tags="&lt;rf-power&gt;&lt;bandwidth&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16471" PostTypeId="2" ParentId="16469" CreationDate="2020-04-18T23:52:14.323" Score="3" Body="&lt;p&gt;No, there are no radio stations that broadcast time and/or accurate frequencies in Mexico. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to these webpages, here are no time or frequency stations &lt;em&gt;anywhere&lt;/em&gt; in Central America.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.smeter.net/stations/hf-time-frequency.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.smeter.net/stations/hf-time-frequency.php&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/Radio_clock#&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.m.wikipedia.org/wiki/Radio_clock#&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/Radio_clock#List_of_radio_time_signal_stations&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.m.wikipedia.org/wiki/Radio_clock#List_of_radio_time_signal_stations&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;According to the last link above, there are some in South America if that helps you.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-04-18T23:57:59.030" LastActivityDate="2020-04-18T23:57:59.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16472" PostTypeId="2" ParentId="16470" CreationDate="2020-04-19T00:05:55.313" Score="4" Body="&lt;p&gt;Unless there is a defect in the transmitting station, &lt;em&gt;the transmitted bandwidth always stays the same when the power is increased&lt;/em&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That is true even if the power is increased from 1 microwatt to 1 megawatt, if that were possible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having said that, when you or I are listening to a 10 watt station and its power increases to 1000 watts (or more), its bandwidth may &lt;em&gt;appear&lt;/em&gt; to increase. This could be due to several reasons, and I'll list only a few here.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A linear amplifier is switched on, and it introduces more distortion than the 10W transmitter.&lt;/li&gt;&#xA;&lt;li&gt;Portions of the signal that were below your receiver's noise threshold are now audible.&lt;/li&gt;&#xA;&lt;li&gt;Due to the increased signal power at your preamp or receiver, the latter overloads and the bandwidth &lt;em&gt;in your receiver&lt;/em&gt; increases. Same thing can happen in your noise blanker&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-04-19T00:16:03.503" LastActivityDate="2020-04-19T00:16:03.503" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16473" PostTypeId="2" ParentId="16466" CreationDate="2020-04-19T01:04:58.620" Score="3" Body="&lt;p&gt;If you mean 800MHz not 800 meters, the Motorola APX-8000 Will give you the solution to talk on both the VHF Ham band, UHF Ham band, VHF fire band, UHF Fire band, and 800Mhz fire band on P25 Digital or Analog FM. Lots of firefighters use these radios for dual Ham and Fire. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radio specs 136-174 MHz, 380-470 MHz, 764-776, 794-806 MHz 806-825, 851-870 MHz&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.motorolasolutions.com/en_us/products/two-way-radios/project-25-radios/portable-radios/apx-8000.html#tabproductinfo&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.motorolasolutions.com/en_us/products/two-way-radios/project-25-radios/portable-radios/apx-8000.html#tabproductinfo&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you just want to receive analog on the 800 band, you might want to look into the Kenwood th-f6 or the icom ic92ad. There are a number of radios that have a wide band receiver in addition to the UHF/VHF transceiver. &lt;/p&gt;&#xA;" OwnerUserId="174" LastEditorUserId="174" LastEditDate="2020-04-19T01:37:17.823" LastActivityDate="2020-04-19T01:37:17.823" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="16475" PostTypeId="2" ParentId="16470" CreationDate="2020-04-19T10:51:46.037" Score="1" Body="&lt;p&gt;&quot;A rising tide lifts all boats equally.&quot; Since bandwidth is measured in relation to the signal's peak amplitude, linear amplification alone should not increase the signal's bandwidth. Generally speaking, all frequencies produced by your source that fall in the amplifier bandwidth will increase by at least the gain of the amplifier. The amplifier's inherent nonlinearity will distort the input to some degree, which may increase some noise components more than others and even produce new noise components that will increase the signal bandwidth. Of course, operating the amplifier outside its specified limits will produce undesired products like &quot;splatter.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We must be careful with our terms when talking about signals and bandwidth. The generator and the detector each has its own &quot;bandwidth.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In theory, a &quot;700Hz tone&quot; has zero bandwidth. In reality, all processes are subject to random fluctuations and nonlinear behaviors that increase the bandwidth from this ideal. Inasmuch as an oscillator is an (imperfect) amplifier with positive feedback, noises that appear in the output are fed back to the input, resulting in self-mixing products that appear as noise in a spectrogram. (In fact, the &quot;noise&quot; of random fluctuations is what gets the oscillation process going in the first place!) Even a crystal oscillator produces &quot;noise sidebands&quot; that generally diminish with frequency difference from the carrier. The &quot;bandwidth&quot; of this real world &quot;pure tone&quot; depends on many factors including: component selection and construction; circuit design and implementation; environmental noises like vibration and power supply variations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The detector measures the power that is present in its bandwidth. A wider detector will capture more of the generator's noise power than will a narrowband detector. Combining the properties of the generator with the properties of the detector gives meaning to your statement, re: &quot;700Hz tone in a 3kHz bandwidth&quot; but doesn't relate to the signal's bandwidth as a function of its amplitude.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-04-19T13:17:16.253" LastActivityDate="2020-04-19T13:17:16.253" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16476" PostTypeId="2" ParentId="16458" CreationDate="2020-04-19T13:34:02.913" Score="3" Body="&lt;p&gt;I’m going to throw the HF vertical’s hat in the ring, too. Something like an R5 or R7 (or HF9V or similar), that can be used on the higher HF bands and 6m. They’re omnidirectional, which is either a good thing or a bad thing, and with a good set of radials they perform well for both receive and transmit. They might be a little expensive for a simple multiband receiver, but you could also use them as reasonable DX antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I’d say that by the criteria given in Phil’s answer (equally bad on all bands), a multiband HF vertical is an excellent fit.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-04-19T13:34:02.913" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16477" PostTypeId="1" AcceptedAnswerId="16492" CreationDate="2020-04-19T13:53:42.677" Score="0" ViewCount="49" Body="&lt;p&gt;I am new in this group, and I would first like to say thanks to this community, I have used the Stack groups to solve many many questions I have, so it is a powerful knowledge place. So thanks for this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am using a &lt;a href=&quot;https://www.hoperf.com/modules/lora/RFM98P.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;RFM98PW&lt;/a&gt; module, and I would use it in narrow band, 12.5 kHz. I am able to work with it in 25 kHz bandwidth, but when I try to use it in 12.5 kHz, something doesn't work.&#xA;I tried with 5 kHz Fdev, and 20.8 kHz BWRx,and 19.2 kbps and I need to down to 12.5 kHz, but when I set the Fdev to lower values, I can see it perfectly in the Spectrum analyzer, but the link with other module doesn't seem to get any packets. (Fdev 3.05 kHz, BWRx 12.5, Bitrate 9.6kbps).&#xA;Does anybody tried it? If so, I will have a deeper look into my settings.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many thanks in advance&#xA;Jordi&lt;/p&gt;&#xA;" OwnerUserId="16870" LastEditorUserId="4665" LastEditDate="2020-04-20T13:52:08.140" LastActivityDate="2020-04-20T22:16:36.130" Title="HopeRF in Narrow Band" Tags="&lt;uhf&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16478" PostTypeId="2" ParentId="7169" CreationDate="2020-04-19T14:07:37.497" Score="0" Body="&lt;p&gt;Avoid the 300 ohm ladderline if possible. DX Engineering recommends a strong 1:1 current balun to join the ladderline and the coax. The losses you will get in the coax will be as you get on up toward 15 and 28 mhz, but they may not be as bad as you think. Another option is to examine your SWR sweep across the band at the radio end, of course, and figure out which current balun would best serve your purposes. I have a tall 165 foot dipole fed with about 62 foot of ladderline and it is resonant or close on several bands using a 6:1 balun. Do your measurements with a 1:1 and go from there. Fine tuning can be done for your favorite band by trimming or lengthening the ladderline. If you just want to get up and going use 400 or 600 ohm ladderline to 1:1 balun and coax to tuner and enjoy. Should tune most if not all bands depending on the tuner. As implied earlier, your losses won't be noticable until you hit 15 meter, 10 or 6 meters. I operate mine on 6 too. I think we all make too big a deal over swr. Plug and play and enjoy and perfect the system a little at a time to your liking. I know too many hams who plan a project and won't move until they get it perfect in their minds and waste precious time looking at a sheet of paper with drawing and telling the same old plans to their ham friends over and over and never do anything. Just do it. You'll be glad you did. At the high height, you will be a winner.&lt;/p&gt;&#xA;" OwnerUserId="16872" LastActivityDate="2020-04-19T14:07:37.497" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16479" PostTypeId="1" CreationDate="2020-04-19T14:19:32.430" Score="1" ViewCount="353" Body="&lt;p&gt;A USB signal is basically a baseband signal shifted up in frequency. However, an LSB signal is the mirror image of a baseband signal then shifted up in frequency. How is this 'mirroring' modulation done in a transmitter and its demodulation done in a receiver? Also why is LSB preferred below 9 MHz and USB preferred above 9 MHz.&lt;/p&gt;&#xA;" OwnerUserId="16871" LastEditorUserId="4665" LastEditDate="2020-04-23T14:04:36.497" LastActivityDate="2020-12-17T20:07:35.270" Title="LSB modulation and demodulation" Tags="&lt;ssb&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16480" PostTypeId="2" ParentId="16479" CreationDate="2020-04-19T15:01:47.360" Score="4" Body="&lt;p&gt;USB is basically AM with the carrier suppressed and the lower sideband filtered out. LSB is basically AM with the carrier suppressed and the upper side and filtered out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To demodulate either, you need to reinsert a carrier, and the signal becomes intelligible. To demodulate USB you insert the carrier below the signal, and for LSB you insert the carrier above.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to why LSB is used below 10MHz and USB above, it’s basically a convention. Nothing more than that. There are other questions on this site where this is addressed. Here is one: &lt;a href=&quot;https://ham.stackexchange.com/questions/1336/why-do-we-use-lsb-below-10-mhz-and-usb-above-10-mhz-when-operating-ssb-hf&quot;&gt;Why do we use LSB below 10 MHz and USB above 10 MHz when operating SSB HF?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-04-19T15:01:47.360" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16481" PostTypeId="2" ParentId="16479" CreationDate="2020-04-19T16:05:50.617" Score="2" Body="&lt;p&gt;The mirroring is achieved through negative frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This seems like a bit of magic, but the math checks out. We can represent an unmodulated carrier with angular frequency &lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt; as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ s(t) = \cos(\omega t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If &lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt; is negative, the result is the same as if it's positive due to the basic trigonometric identity:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos (x) = \cos (-x) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Weird but true: negative frequencies work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So to demodulate LSB you just select the LO frequency such that the carrier frequency ends up at zero and the lower sideband ends up at the negative frequencies just below zero. Then as a consequence of the trig identity above, the spectrum gets &quot;flipped&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course you also have to design everything so other mixing products don't interfere, but that's all the same things you would to do to design an upper sideband demodulator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To drive the point home, consider how a frequency mixer works. Usually it's described like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ f_\text{out} = \begin{cases}&#xA;f_1 \pm f_2 &amp;amp; (f_1 &amp;gt; f_2)\\&#xA;f_2 \pm f_1 &amp;amp; (f_2 &amp;gt; f_1)&#xA;\end{cases} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we say &lt;span class=&quot;math-container&quot;&gt;$f_1$&lt;/span&gt; is 9999 kHz and &lt;span class=&quot;math-container&quot;&gt;$f_2$&lt;/span&gt; is 10,000 kHz, we choose the second case and we end up with mixing products at 1 kHz and 19,999 kHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But wait, how does the frequency mixer &quot;know&quot; which case to choose?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Say we instead pick the first case, we instead end up with mixing products at -1 kHz and 19,999 kHz. If you accept that negative frequencies work just like positive frequencies, it means that don't the two cases because it doesn't matter which one you pick.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modulation is the same, in reverse. If you want to transmit LSB at 10 MHz, you can think of it as mixing the baseband signal to -10 MHz.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-04-19T16:18:49.637" LastActivityDate="2020-04-19T16:18:49.637" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16482" PostTypeId="2" ParentId="16458" CreationDate="2020-04-19T18:07:15.047" Score="2" Body="&lt;p&gt;This sounds like a perfect application for the Discone antenna:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CURGj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CURGj.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Skeletonizing&quot; the disc and the skirt make it amenable to construction with wire and/or tubular elements. The skirt is insulated from the disc and is angled downward from the horizontal plane; this insulator is the location of the feedpoint. There are several commercial suppliers of similar antennas which may work for you.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to an article in &lt;em&gt;&lt;a href=&quot;https://i.stack.imgur.com/CURGj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;Electronics Notes&lt;/a&gt;&lt;/em&gt;, the element lengths should be 0.175&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; for the disc and 0.25&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; for the skirt, at the lowest frequency of operation and the skirt should be angled at 60&lt;span class=&quot;math-container&quot;&gt;$^{\circ}$&lt;/span&gt; from the plane of the disc. Using 13MHz, this results in element lengths of 79.4-inches for the disc and 227-inches for the skirt. I simulated this antenna in NEC2 with 1-inch elements:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BFiXO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BFiXO.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the feedpoint 0.5&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; above &quot;real&quot;, medium-conductivity ground the SWR is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iobk7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iobk7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Section 10.4.6 of the &lt;em&gt;&lt;a href=&quot;http://www.arrl.org/arrl-antenna-book&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL Antenna Book&lt;/a&gt;&lt;/em&gt; gives different equations for the dimensions: &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;/4 for the &lt;em&gt;height&lt;/em&gt; of the cone and disc width &lt;em&gt;0.7 times the width of the base of the skirt&lt;/em&gt;. At a lower frequency of 13MHz, these equations result in element lengths of 90.8-inches for the disc and 263-inches for the skirt. This improves the match over the frequency range:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/air4h.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/air4h.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Replacing the elements with 14-gauge wire further &quot;skeletonizes&quot; the antenna, adversely affecting the SWR, but it is still more than adequate for monitoring:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PHM0d.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PHM0d.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Doubling the number of wires smooths out the SWR curve at nearly 2.5:1 from 14MHz to 30MHz.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-04-19T23:23:30.117" LastActivityDate="2020-04-19T23:23:30.117" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16483" PostTypeId="2" ParentId="16479" CreationDate="2020-04-19T18:44:26.740" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;A USB signal is basically a baseband signal shifted up in frequency.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is not accurate. &lt;a href=&quot;https://ham.stackexchange.com/users/873/scott-earle&quot;&gt;@ScottEarle&lt;/a&gt; points out that SSB can be produced by filtering out the carrier and undesired sideband from an AM signal, but that AM signal was generated at an intermediate frequency (IF), not at baseband; the baseband signal was used to modulate an IF carrier to produce the AM which was filtered to produce SSB at the IF before being heterodyned to the final signal frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition to the &quot;filter method&quot; described earlier, SSB can be generated by the &quot;phasing method.&quot; As such, it is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;special case of quadrature amplitude modulation&lt;/a&gt; (QAM). This implementation - adding or substracting quadrature versions of a signal to produce upper or lower sideband - may more clearly illustrate the distinction between the two.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-04-19T18:44:26.740" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16484" PostTypeId="1" AcceptedAnswerId="16485" CreationDate="2020-04-19T21:43:04.867" Score="1" ViewCount="303" Body="&lt;p&gt;I am so new to ham radio that I don't even have a transceiver or a certification study unit yet. Just learning all I can right now. So, I'm looking at &lt;a href=&quot;https://repeaterbook.com/repeaters/details.php?state_id=02&amp;amp;ID=53&quot; rel=&quot;nofollow noreferrer&quot;&gt;a repeater&lt;/a&gt; that I might be able to reach with a 5-watt Yaesu or something. On one frequency, the repeater offers autopatch, e-power, and link.&#xA;I'm pretty sure I know that autopatch is a way for a ham radio to talk to a phone. I'm impressed since I didn't know that was possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My question is, what is e-power and what is link?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you to all. Hope to get my license and join what seems to be an awesome community.&lt;/p&gt;&#xA;" OwnerUserId="16868" LastEditorUserId="76" LastEditDate="2020-04-19T21:51:54.633" LastActivityDate="2020-04-19T21:51:54.633" Title="Repeater Features: What is e-power and link?" Tags="&lt;repeater&gt;&lt;jargon&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16485" PostTypeId="2" ParentId="16484" CreationDate="2020-04-19T21:50:25.280" Score="3" Body="&lt;p&gt;&quot;E-power&quot; is probably an abbreviation for &quot;emergency power&quot;, meaning that the repeater is able to function (for some amount of time) even if grid power to the repeater site fails.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A &quot;link&quot; is when two repeaters are connected (over radio, internet, or phone) so that they repeat transmissions heard by either repeater, thus having a larger coverage area or even connecting repeaters in widely separated areas. Some repeaters are permanently linked, but others have a link mode that can be turned on or off. With some Internet linking services like EchoLink, individual users can join the &quot;conference call&quot; without even using a radio — sort of a hybrid of a simple repeater link and a phone patch.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-04-19T21:50:25.280" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16486" PostTypeId="1" CreationDate="2020-04-19T23:51:54.400" Score="1" ViewCount="59" Body="&lt;p&gt;I am attempting to design an antenna similar to a TTFD, double zepp or array of end fed wires, with a sinusoidal, with the period of the wavelength, spacing that causes additive waves on the target frequency(assume proper phase alignment,180 degrees, and a constant velocity factor for this question).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LgWQA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LgWQA.png&quot; alt=&quot;drawing of 2 vertical sine waves one of them is phase shifted 180 degrees&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assume the image is a top down view of the wires forming perfect sine waves :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feed point locations should be at +90 and -90 degrees offset. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I barking up the wrong tree?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thought process behind this: Invert the phase of half of the signal to null the desired frequency, and correct the phase disparity through the physical spacing of the wires. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This design would probably be very low bandwidth and thus impractical for most uses, but would it work at all? And what about noise reduction?&lt;/p&gt;&#xA;" OwnerUserId="16873" LastEditorUserId="16873" LastEditDate="2020-04-21T23:02:12.180" LastActivityDate="2020-04-21T23:02:12.180" Title="Would a phase compensated sinusoidally spaced folded dipole present less noise to a receiver?" Tags="&lt;antenna-theory&gt;" AnswerCount="0" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16487" PostTypeId="1" CreationDate="2020-04-20T12:27:32.390" Score="1" ViewCount="36" Body="&lt;p&gt;I recently bought 2 Baofeng UV5RAs from the same vendor. Neither of the charging stations work. They both flash green/red immediately upon plugging them in--before any battery is seated! When I seat the battery they continue to blink the error code. I have swapped A/C connectors and even tried different outlets. Same problem.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And no, the batteries do not charge despite the error codes. They continue to discharge while in the cradle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am assuming defective charging stations -- but what are the odds both units would have the same defective parts? Am I doing something wrong?&lt;/p&gt;&#xA;" OwnerUserId="16876" LastEditorUserId="8717" LastEditDate="2020-04-20T14:19:47.370" LastActivityDate="2020-04-20T14:19:47.370" Title="Baofeng UV5RA charger station error" Tags="&lt;baofeng&gt;&lt;uv-5r&gt;&lt;battery-charging&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16488" PostTypeId="1" AcceptedAnswerId="16616" CreationDate="2020-04-20T14:33:50.267" Score="2" ViewCount="318" Body="&lt;p&gt;I own an RTL-SDR v3 USB dongle (official version from rtl-sdr.com). I've successfully used it for decoding weather satellites past year. I use (GQRX + Audacity)/(Arch Linux 64bit) + (WXtoIMG)/(Windows 10 64bit) combination to receive and decode NOAA images and (glrpt)/(Arch Linux 64bit) to receive and decode images from Meteor-M sats. However now I observe strange behavior. I've tried to record about a dozen of NOAA passes but with no luck - my images are slanted and WXtoIMG can't do anything with that (see picture below).&#xA;&lt;a href=&quot;https://i.stack.imgur.com/tLmPV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tLmPV.jpg&quot; alt=&quot;NOAA 19&quot;&gt;&lt;/a&gt;&#xA;Also it says that it can't find telemetry data or complains about poor SNR ratio. This is strange because I constantly get about 40 dB SNR in GQRX for most prominent APT peaks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In &lt;code&gt;glrpt&lt;/code&gt; I observe issue with PLL locking. Signal level is awesome, AGC works fine, but PLL never locks even if satellite is flying right above my head. Previous summer I was able to start decoding from 2--4 degrees above the horizon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the same time I use GQRX quite well and can clearly hear FM broadcasting, NFM chatting and even AM broadcasting with the use of SpyVerter upconverter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't know what can cause such issues as non-lockable PLL and troubles with NOAA reception (I think they are related to each other). I suppose my dongle become damaged somehow but don't know exactly how. It has protection diode on the input and I handle it with care so it shouldn't be ESD-smashed (I suppose it will not work at all after discharge).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;May be someone has already faced such a problem and could give me some advice? Or how can I test my hypothesis on 3rd-party test?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE 1:&lt;/strong&gt;&#xA;I've tried with using LTS 5.4.32 kernel on Arch Linux, compiling &lt;code&gt;glrpt&lt;/code&gt; with GCC 8.4.0, clang but still getting the same issue. WXtoIMG works fine - when I feed old recording to it then it gives me nice images. Moreover, I've found that its is impossible to decode DRM HF stations with DReaM decoder in realtime at all - it fails to get all three CRCs good. Only sometimes it's able to say me station name and show list of channels. At the same time feeding sample audio from other users works just fine. I suppose it's all related to the dongle - APT, LRPT, DRM fails while simple audio works fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE 2:&lt;/strong&gt;&#xA;I've analyzed audio spectra for two files: good recording from last year and a bad one from past week. Here are the results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Good&lt;/em&gt;. I can see main 2.4 kHz peak, 4.8 kHz multiple and minor peaks. Frequency drift @2400 Hz is negligible.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/uRWCO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uRWCO.jpg&quot; alt=&quot;good, full spectrum&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/dkUZA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dkUZA.jpg&quot; alt=&quot;good, around 2.4 kHz&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/cbGcK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cbGcK.jpg&quot; alt=&quot;good, peak of interest&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Bad&lt;/em&gt;. There is no multiple of 4.8 KHz, main peak is very broad. I can't see minor frequencies. Also there is a quite significant drift from 2400 Hz.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/06U8X.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/06U8X.jpg&quot; alt=&quot;bad, full spectrum&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/MU128.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MU128.jpg&quot; alt=&quot;bad, around 2.4 kHz&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/usDKq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/usDKq.jpg&quot; alt=&quot;bad, peak of interest&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE 3:&lt;/strong&gt;&#xA;Yesterday I got another dongle (simple blue from AliExpress). The problem is still here! I observe the same symptoms as with RTL SDR blog v3 dongle. Even spectra are the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE 4:&lt;/strong&gt;&#xA;I've found the cause of the problem - it's VOLK who ruined decoding. Filed &lt;a href=&quot;https://github.com/csete/gqrx/issues/791&quot; rel=&quot;nofollow noreferrer&quot;&gt;an issue&lt;/a&gt; on GQRX GitHub. Seems like there are some serious bugs with VOLK's DSP, will recheck soon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also both dongles - cheap &quot;blue Chinese&quot; and RTL SDR v3 works just fine! So there is definitely no problem with crystals inside them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE 5:&lt;/strong&gt;&#xA;I've investigated the problem even further and this is not a bug with a VOLK. GQRX's frequency correction seems to ruin decoding. See my answer for full details.&lt;/p&gt;&#xA;" OwnerUserId="14179" LastEditorUserId="14179" LastEditDate="2020-05-07T06:52:51.217" LastActivityDate="2020-05-07T06:52:51.217" Title="Problem with RTL-SDR v3 dongle - unusable PLL" Tags="&lt;rtl-sdr&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16490" PostTypeId="1" CreationDate="2020-04-20T20:26:21.140" Score="2" ViewCount="273" Body="&lt;p&gt;I'm new in radio, so I started with seemingly easy task - receive and decode &lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_Data_System&quot; rel=&quot;nofollow noreferrer&quot;&gt;RDS&lt;/a&gt; data. I use GnuRadio to understand the concept of working with RF signals. So according to standard RDS receiver looks this way:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/jHt3u.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jHt3u.png&quot; alt=&quot;RDS decoder scheme&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I really would love to see how people actually do this in digital systems. I tried to apply a part of this scheme in GnuRadio, so I have this:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/cPa0Q.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cPa0Q.png&quot; alt=&quot;GnuRadio RDS decoder first part&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you can see I took 57kHz signal source to shift RDS spectrum to lower frequencies as in the standard, but what really confuses me is that in standard they use subcarrier recovery module. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As I understand if I don't use subcarrier recovery there will be a phase error in 2.4kHz signal so further demodulating will be impossible. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I tried to use costas loop, PLL carrier Tracking and PLL ref out blocks to recover this 57kHz carrier but I couldn't get any decent output after 2.4kHz low pass filter. Also these blocks have complex inputs but after WBFM receiver the signal is real. I tried to use Hilbert filter, but seems that is wrong.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Summarizing everything up, there are several questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Am I on the right way to decode RDS signal?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;How can I use carrier recovery blocks when my signal is real?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What do I need to do next after 2.4kHz lowpass filtering? What blocks do I need to use to get a bitstream?&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Thank you in advance!&lt;/p&gt;&#xA;" OwnerUserId="16030" LastEditorUserId="4665" LastEditDate="2020-04-20T21:13:14.577" LastActivityDate="2020-04-20T21:13:14.577" Title="Receiving and decoding RDS in GnuRadio" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="0" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16491" PostTypeId="1" CreationDate="2020-04-20T20:39:54.320" Score="2" ViewCount="253" Body="&lt;p&gt;I think I understand the basic principles of a collinear antenna. &lt;a href=&quot;https://ham.stackexchange.com/questions/7076/how-the-coaxial-collinear-antenna-works/7249#7249&quot;&gt;How the Coaxial Collinear Antenna Works?&lt;/a&gt; seems to describe it well.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, I've just repaired a 1090MHz (ADS-B receive only) antenna I built some time ago. Or at least I thought I'd repaired it, turns out I've left the final 1/4 wave still blu-tacked to the window! &lt;strong&gt;What purpose does this half-length section serve?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure exactly what design I used when I first built it, but they do seem to vary a little:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;N1HFX's &lt;a href=&quot;http://www.rason.org/Projects/collant/collant.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Build a 9 dB, 70cm, Collinear antenna from coax&lt;/a&gt; includes a 1/4 wave element at each end.&lt;/li&gt;&#xA;&lt;li&gt;Dusan Balara's &lt;a href=&quot;https://www.balarad.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Coaxial Collinear antenna for ADS-B receiver&lt;/a&gt; doesn't bother, but does have a 50/75 Ohm resistor on the end.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16880" LastActivityDate="2020-04-22T05:18:36.573" Title="Why do some 1/2 wave collinear designs have a 1/4 wave element?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16492" PostTypeId="2" ParentId="16477" CreationDate="2020-04-20T22:16:36.130" Score="1" Body="&lt;p&gt;Most likely, the device's crystal isn't stable/accurate enough for such a small bandwidth. Those little modules often have cheap crystals that are specced to be within +/- 50 ppm of correct. At 450MHz that's +/- 22.5 kHz. With two such modules, one's transmissions could be as far as 45kHz away from where the other is listening. Even with AFC magic, that's not going to work to bring in a 12.5kHz-wide signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It sounds like yours aren't worst-case, since they agree well enough for 25kHz to work... but they still aren't good enough for 12.5. Most applications of these things use wider modes for this reason.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-04-20T22:16:36.130" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16493" PostTypeId="1" CreationDate="2020-04-21T11:03:29.160" Score="0" ViewCount="52" Body="&lt;p&gt;Does &lt;a href=&quot;http://www.mat-tuner.com/en/mAT-30.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;this tuner&lt;/a&gt; work with this transceiver? Would appreciate response as I cannot get it to work!&lt;/p&gt;&#xA;" OwnerUserId="16883" LastEditorUserId="8717" LastEditDate="2020-04-22T02:40:53.387" LastActivityDate="2020-04-23T19:47:57.080" Title="Problem with mAT30 ATU and FT-450D transceiver" Tags="&lt;transceiver&gt;&lt;yaesu&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16494" PostTypeId="2" ParentId="16488" CreationDate="2020-04-21T16:06:30.883" Score="2" Body="&lt;p&gt;One common thread in all those dis-similar softwares is ADC sampling rate. It might be worthwhile to do a frequency calibration run to see if there's a problem there.&lt;br&gt;&#xA;NOAA's APT signal provides a convenient and very, very accurate frequency calibration reference: 2400 Hz audio carrier. If it's frequency is any other than 2400.00 Hz, then either samples have been dropped, or sampling rate is inaccurate. It might be worthwhile to examine a xxx.wav file and take a close look at carrier frequency.&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To provide you a benchmark, an old xxx.wav file was pulled for examination. It was captured by &lt;strong&gt;Wxtoimg&lt;/strong&gt; and saved. Sampling was done by WINDOWS 7 16-bit soundcard at 11025 samples-per-second. Wolf's &lt;strong&gt;SpectrumLab&lt;/strong&gt; was used to track 2400 Hz carrier frequency using its maximum 524288-point FFT. Bin resolution is 0.021 Hz, and its peak-frequency tracking is excellent. FFT window span is about 47 seconds of audio:&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;At signal acquisition, carrier frequency was high, at 2400.047 Hz&lt;/li&gt;&#xA;&lt;li&gt;At signal loss about 12 min. later, carrier frequency was low, at 2399.94 Hz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Carrier frequency variation is mostly due to doppler shift, nevertheless it would appear that sampling is a tiny bit off (mean frequency is 2399.9935 Hz). This does not cause a problem for the WXtoimg software.&lt;br&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/N18js.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/N18js.png&quot; alt=&quot;SpectrumLab plot of APT&amp;#39;s 2400Hz carrier (12min)&quot;&gt;&lt;/a&gt;&lt;br&gt;Using other software with PLL-tracking turned off, the same PC soundcard yields a decent vertical image, with a bit of doppler skew top and bottom.&lt;br&gt;&#xA;Take care to ensure that sample processing doesn't drop samples. Your image skew direction suggests that this is a possible cause instead of PLL-mistracking.&lt;/p&gt;&#xA;" OwnerUserId="11132" LastEditorUserId="11132" LastEditDate="2020-04-21T18:55:45.297" LastActivityDate="2020-04-21T18:55:45.297" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16495" PostTypeId="1" AcceptedAnswerId="16507" CreationDate="2020-04-21T18:53:41.183" Score="6" ViewCount="450" Body="&lt;p&gt;This came up in some feedback I got when I tried to answer &lt;a href=&quot;https://ham.stackexchange.com/questions/16457/what-is-iq-in-the-context-of-sdrs&quot;&gt;What is IQ in the context of SDRs?&lt;/a&gt; and revealed some of my own misunderstanding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Initially, I gave an answer something like (paraphrasing):&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;You could collect I/Q data by taking a second sample delayed by 1/4th of the sample rate&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That is, I had been imagining that the &quot;quadrature&quot; phase was related to a time offset relative to the &lt;strong&gt;sampling&lt;/strong&gt; rate. But with some feedback I came to think that instead it was related to a time offset relative to a &lt;strong&gt;local oscillator&lt;/strong&gt; and applicable only in the context of a mixer. So I said:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the quadrature component is equivalent to a second sample taken &quot;90º later&quot; in terms of the tuning frequency (i.e. delayed in time by 1/4 of the LO's period). &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;But even that explanation &lt;a href=&quot;https://ham.stackexchange.com/questions/16457/what-is-iq-in-the-context-of-sdrs/16464#comment26524_16464&quot;&gt;was disputed&lt;/a&gt; by someone with a better understanding, who said:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the phase shift is 90 degrees for &lt;em&gt;all&lt;/em&gt; frequencies, because it's achieved not by adding a delay, but by changing the LO phase&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;How can that happen? What modulates the LO? How can all sorts of simple mixer circuits — and I've seen some that were just XOR logic chips?? — introduce just the right phase delay across the spectrum of one of its inputs as it multiplies it with the other? Or taken another way, assuming that a mixer is indeed necessary, does a mixer enable something that a scalar sampling process cannot accomplish alone?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feel free to pick more convenient numbers, but let's say I have a ADC that can capture scalar samples all a generous rate of 1 GSPS. We are interested in receiving signals at 720 kHz and 1040 kHz and can optionally mix that RF input with a 1 MHz LO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Originally I would have said: let's treat this stream of 1 GSPS scalar samples as a vector of 4 components coming in at a rate of 250 MSPS instead. Then the first component would be the &quot;I&quot; value, the second component would be the &quot;Q&quot; value and we'll just toss the other two. Thus the second component is 90º out of phase with the first. But apparently this is &lt;strong&gt;not&lt;/strong&gt; what quadrature sampling means?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Trying again, what if we sample after mixing with the local oscillator (which I'll assume is phase-locked to the ADC)? With the input signals at &lt;code&gt;A1 = 720 kHz&lt;/code&gt; and &lt;code&gt;A2 = 1040 kHz&lt;/code&gt; and the LO of &lt;code&gt;B = 1 MHz&lt;/code&gt;, we'll get the famed sum (&lt;code&gt;A + B&lt;/code&gt;) and difference (&lt;code&gt;|A - B|&lt;/code&gt;) products out for each and our ADC will see signals at 1720 kHz, 280 kHz, 2040 kHz, 40 kHz. We could now group our 1 GSPS sample stream so that it matches up with our 1 MHz LO, taking the first of every 10 samples as the &quot;I&quot; value and perhaps interpolate the second and third to get the &quot;2.5th&quot; sample for the &quot;Q&quot; value, 90º later relative to the LO.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would I be able to feed those samples into a DSP unit as if it were I/Q data and get meaningful results out? Is there &lt;em&gt;any&lt;/em&gt; sort of processing I could do to convert a stream of 1 GSPS scalar samples to &quot;true&quot; I/Q samples at 500 MSPS or even say 50 kSPS?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2020-04-21T18:58:47.447" LastActivityDate="2020-04-23T05:29:55.773" Title="How can quadrature mixing adjust the phase of all frequencies by the same amount? Can it be done in the digital domain?" Tags="&lt;software-defined-radio&gt;&lt;mixer&gt;&lt;dsp&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16496" PostTypeId="2" ParentId="13336" CreationDate="2020-04-21T19:00:19.157" Score="1" Body="&lt;p&gt;You need to convert the .ogg file into something usable by the flowgraph. &lt;a href=&quot;https://community.libre.space/t/how-to-open-satnogs-iq-dat-files/3793&quot; rel=&quot;nofollow noreferrer&quot;&gt;How to open satnogs iq.dat files&lt;/a&gt; covers a similar issue for IQ files.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, an APT recording with &lt;code&gt;noaa_apt_decoder.grc&lt;/code&gt; resamples outside the normal demodulation chain before saving to the .ogg file:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/spQ17.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/spQ17.png&quot; alt=&quot;SatNOGS APT OGG file sink flowgraph&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You need to reverse this resampling and possibly add a throttle depending on what you're trying to do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ANcgD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ANcgD.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This assumes you want to run it through the existing GnuRadio flowgraph. If you want to feed into some other tool, you'll need to convert into a format that will take. You won't get back to the original IQ if it's not recorded but you could remix it with a carrier to recreate an equivalent, acceptable signal but it's probably not worth the effort.&lt;/p&gt;&#xA;" OwnerUserId="16880" LastActivityDate="2020-04-21T19:00:19.157" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16497" PostTypeId="2" ParentId="16444" CreationDate="2020-04-21T19:10:50.010" Score="0" Body="&lt;p&gt;AN EXAMPLE - A 5λ/8 MAG MOUNT ANTENNA USES A COIL TO BRING ITS LENGTH TO THE NEAREST ODD MULTIPLE OF A λ/4. IN MOST CASES; A 3λ/4.&#xA;THATS THE COIL'S PRIMARY PURPOSE. DO YOU NOT STILL FEED EITHER ONE WITH 52 OHM COAX?&#xA; THE COIL'S FUNCTION IS TO ALTER THE ELECTRICAL LENGTH.&lt;/p&gt;&#xA;" OwnerUserId="8492" LastActivityDate="2020-04-21T19:10:50.010" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16498" PostTypeId="2" ParentId="16495" CreationDate="2020-04-21T19:40:00.150" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;...it looks like a &quot;quadrature mixer&quot; is really just two separate mixers, with one fed by an LO to which a [constant] phase delay has been applied relative to the other's LO.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes ... and. Quadrature versions of the &lt;em&gt;modulating&lt;/em&gt; signal may comprise the &quot;baseband&quot; inputs to the quadrature mixers:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8Ti2k.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8Ti2k.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's where &quot;the phase shift is 90 degrees for all frequencies&quot; becomes more challenging, because the baseband input may simultaneously include any number of frequencies superimposed on each other; think of how the strings of a musical instrument produce harmonics and extend that concept to the human voicebox to get an idea of the spectral complexity of the modulating signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Quadrature versions of the modulating signal can be produced by analog circuits, but the accuracy is limited by component tolerances. Jim Tonne's &lt;em&gt;&lt;a href=&quot;http://tonnesoftware.com/quad.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;QuadNet&lt;/a&gt;&lt;/em&gt; applet gives an idea of the complexity and limitations of these circuits. Conversely, a digital computer can be used to apply a &lt;a href=&quot;https://en.wikipedia.org/wiki/Hilbert_transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hilbert transform&lt;/a&gt; to the input, producing a much more accurate and reproducible result with modern A/D and DSP technologies.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-04-21T19:40:00.150" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16499" PostTypeId="1" CreationDate="2020-04-21T19:59:14.567" Score="4" ViewCount="116" Body="&lt;p&gt;I'm currently trying to build my own SWR power Meter. This design is based on the so known HT detector with schottky diode BAS70. For my understanding, and for easy purpose, I'm currently focusing on 50 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, I found a nice theory called &quot;The Square Law Region&quot; which can be found here on page 115 of the book &lt;a href=&quot;https://books.google.fr/books?id=VIj9yAdKMbsC&amp;amp;printsec=frontcover&amp;amp;hl=fr&amp;amp;source=gbs_ge_summary_r&amp;amp;cad=0#v=onepage&amp;amp;q&amp;amp;f=false&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio Frequency &amp;amp; Microwave power measurement&lt;/a&gt;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It says that voltage out of the HF detector is&#xA;&lt;span class=&quot;math-container&quot;&gt;$$V=\frac{25e}{kTn}P_{RF}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$e$&lt;/span&gt; is the charge of an electron (&lt;span class=&quot;math-container&quot;&gt;$-1.602 \times 10^{-19}$&lt;/span&gt; C), &lt;span class=&quot;math-container&quot;&gt;$k$&lt;/span&gt; is the Boltzmann constant &lt;span class=&quot;math-container&quot;&gt;$1.38064852 \times 10^{-23} m^2 kg \cdot s^{-2} K^{-1}$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$T$&lt;/span&gt; the temperature in degrees Kelvin, &lt;span class=&quot;math-container&quot;&gt;$n$&lt;/span&gt; the ideality factor, and &lt;span class=&quot;math-container&quot;&gt;$P_{RF}$&lt;/span&gt; the power in Watts.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found that Spice says &lt;span class=&quot;math-container&quot;&gt;$n=1.018$&lt;/span&gt; for BAS70 diode.&#xA;If my calculation is correct, for P = -30dBm (1µW) lead to out voltage to 950µV. Is that correct?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At 50MHz, with BAS70, 47nF, it tried this set up...my measure leads to about 10mV...wich is far away for...let's say 1mV of theory. Is this theory correct ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then I also tried to set up in simulation with Qucs. I faced another problem: Qucs failed to simulate this situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, I must say that I see different delay of response regarding the input level. For +10dBm, voltage out tends to 1.5V in about 300µS.&#xA;For -30dBm, voltage is not stable before 1mS (see jpg joined file). I understand that it could come from the time needed by capacitor...but also, timing response should not depend on the input level for a basic RC filter. Right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What should I do to simulate my HF detector at low level?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UG8pI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UG8pI.jpg&quot; alt=&quot;out voltage for -30dBm input&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16886" LastEditorUserId="4665" LastEditDate="2020-04-22T23:15:05.327" LastActivityDate="2020-06-05T16:08:16.060" Title="Problem with theory of HF detector" Tags="&lt;diy&gt;&lt;measurement&gt;&lt;theory&gt;&lt;swr-meter&gt;" AnswerCount="0" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16500" PostTypeId="2" ParentId="16495" CreationDate="2020-04-21T21:21:39.810" Score="7" Body="&lt;p&gt;Let's first start by developing some intuition of what a complex signal looks like. We can use GNU Radio to generate a signal that's just an unmodulated carrier, and then put that into a UI that will display the real and imaginary components over time:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LVVKH.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LVVKH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The result for 80 Hz is this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yCULs.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yCULs.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how the real part is 90 degrees behind the imaginary part. If you were to plot this on the &lt;a href=&quot;https://en.wikipedia.org/wiki/Complex_plane&quot; rel=&quot;noreferrer&quot;&gt;complex plane&lt;/a&gt;, it would trace a circle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we change the frequency to -80 Hz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CksOC.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CksOC.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the phase difference is still 90 degrees, but it's the imaginary part that's lagging. Plotted on the complex plane it still traces a circle, but it spins in the opposite direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's this property that allows complex signals to represent positive and negative frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now importantly, this 90 degree phase shift holds for any frequency. If we change the frequency to 160 Hz but keep the sample rate the same:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AnK6o.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AnK6o.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The oscillation speed has doubled, as expected, but the phase difference between the real and imaginary parts is &lt;em&gt;still&lt;/em&gt; 90 degrees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is why IQ data isn't equivalent to sampling twice as fast: the 90 degree phase relationship between real and imaginary components must exist for &lt;em&gt;every&lt;/em&gt; frequency. By sampling the signal twice with some delay between samples, you can indeed introduce a 90 degree phase shift for &lt;em&gt;some&lt;/em&gt; frequencies. But 90 degrees is a different amount of time for each frequency, so generating the imaginary component with just a delay will generate the correct results for only one frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the imaginary component is just the real component +/- 90 degrees, if we had some kind of filter that could introduce a 90 degree phase shift for every frequency we could use that to convert from a real signal to a complex one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mathematically, that &quot;filter&quot; is called the &lt;a href=&quot;https://en.wikipedia.org/wiki/Hilbert_transform&quot; rel=&quot;noreferrer&quot;&gt;Hilbert transform&lt;/a&gt;. It can be realized as an &lt;a href=&quot;http://qrp-labs.com/polyphase&quot; rel=&quot;noreferrer&quot;&gt;analog filter&lt;/a&gt; or a &lt;a href=&quot;https://github.com/gnuradio/gnuradio/blob/a130486a5dd7d3cae81d376a37e37d4192b90b61/gr-filter/lib/firdes.cc#L491-L518&quot; rel=&quot;noreferrer&quot;&gt;digital filter&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;GNU Radio provides a &quot;Hilbert&quot; block which has a real input and complex output. It uses the Hilbert transform to create the imaginary part, where the real part is just the input passed through, with appropriate delay to match the delay added by the filter. We can use this block to take a real-valued signal and produce the equivalent complex-valued signal. The complex signal has (ideally) no negative frequencies present: it is an &lt;a href=&quot;https://en.wikipedia.org/wiki/Analytic_signal&quot; rel=&quot;noreferrer&quot;&gt;analytic signal&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is interesting then to see what happens if we present this block with an input that contains more than one frequency, like a square wave:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8sa9I.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8sa9I.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nPdPR.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nPdPR.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note how the real component is the square wave we expect, but the imaginary part certainly isn't just a delayed square wave. Once the real component is not a single frequency the 90 degree relationship between real and imaginary parts is no longer visually obvious from the time domain plot.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can see however that the frequency domain is just what we'd expect for a square wave: a fundamental at 640 Hz and then a series of odd harmonics of that. Ideally there would be no negative frequencies present, but the ideal Hilbert filter has an infinite impulse response: truncating it introduces some imaging.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally we can take the complex value and split it into real and imaginary parts. We've already seen them in the time domain, but looking at them in the frequency domain we can see that really all the same frequency components are in both real and imaginary parts, just 90 degrees apart:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zGCTh.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zGCTh.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CT2XZ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CT2XZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This visualization shows only the frequency magnitude but not phase, so the real and imaginary parts are drawn right on top of each other. We can also see that the &lt;a href=&quot;https://en.wikipedia.org/wiki/Discrete_Fourier_transform&quot; rel=&quot;noreferrer&quot;&gt;discrete Fourier transform&lt;/a&gt; inherently produces complex results, but since we gave it real inputs the negative frequencies are exactly a mirror of the positive ones.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Perhaps now with a better intuition of what we're trying to accomplish with IQ sampling, how might we go about generating the digital stream of complex numbers from an analog signal which can have only real values?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One way would be implement an analog Hilbert filter, and feed that into the 2nd channel of an ADC. We can then treat one channel as the real part, and the other channel as the imaginary part.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However there would be little point in that: to realize an analog Hilbert filter that provides an accurate 90 degree phase shift over a wide range of frequencies requires a large number of components, and the filter can't add any information. This approach is used in some analog SSB transceivers for sideband cancellation, but if you're going to be digitizing the signal then a digital implementation would be cheaper and perform better.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Instead, we can feed the RF signal to not one but &lt;em&gt;two&lt;/em&gt; frequency mixers:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/jg1DV.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fjg1DV.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You've probably read about how frequency mixers produce outputs with the sum and difference of the frequency components at the inputs. That's true, but what's the phase of the outputs? Turns out if you change the phase of the LO, then the phase of all the outputs is changed by the same amount. And unlike a delay, modulating the phase in this way makes the same phase shift for &lt;em&gt;all&lt;/em&gt; frequencies, just what we need to generate both real and imaginary parts for a complex signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is simple (in terms of component complexity) to create this phase shift with a mixer because the mixer is a nonlinear device. That means it has access to mathematical operators that linear devices (capacitors, inductors, resistors, transmission lines) don't, namely the multiplication of two functions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, since both real and imaginary parts are available digitally, we don't need analog filters to deal with image cancellation. What would be considered &quot;images frequencies&quot; in an analog design are instead just negative frequencies in the digital domain, and since the signal can be manipulated as a complex number these negative frequencies don't present any ambiguity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is also why you can find direct-sampling SDRs that work up to a few hundred MHz, but they get pricey because an ADC operating at 1 Gsps isn't cheap, nor is the FPGA you'll need to process that data rate. Once the frequency becomes high enough that a mixer is required, SDRs are almost exclusively use an IQ architecture since it's simpler to implement.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-04-21T23:29:48.653" LastActivityDate="2020-04-21T23:29:48.653" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16502" PostTypeId="2" ParentId="16488" CreationDate="2020-04-22T03:40:29.150" Score="2" Body="&lt;p&gt;This sounds like the TCXO, or thermally corrected oscillator, crystal has failed in the dongle. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my experience the dongles heat up during use. This heating (and cooling) can over time can deform the crystal beyond the tolerances that can be corrected by by the factory calibration of the TXCO. This may cause over and under corrections to the clock(bounces between the maximum and minimum).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Precise PLL locking is dependent on a stable local clock signal, any jitter, the amount of variation of non-uniform timing pulses, produced by the local oscillator disrupts the ability of the PLL to stabilize.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the PLL by definition compares the phase difference based on the local oscillator, a large jitter, the same value, but in this context the amount of phase difference from one pulse to the next, amount will disrupt the locking process.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the jitter consistently exceeds the bandwidth and then does not, it will cause the received frequency to move slightly up and/or down. This shift would be so minor as to be imperceptible by the human ear, when listening to audio. Since the small corrections are happening very fast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Analog audio(AM or FM) data only has to be close to the frequency not be rejected. The shifts are not noticeable.  Digital data requires precise timing to be decoded precisely and accurately.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The sample rate which maxes out at 2.4MHz on most dongles, definitely plays a factor, as does the 8-bit resolution, hence the loop around the offset frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The only test is to compare a your received time from radio digital non-moving time sources, such as the time beacons, and compare the offset with a GPS receiver. I cannot tell you how to do that with the precision required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This damage could also be caused by an electrostatic charge or lightning strike nearby, if it were a direct hit the dongle would be gone.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now after all of that, I would recommend replacing your your dongle and adding additional external heat-sinks and a fan, and a static discharge circuit to your antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This entire answer is created upon my own experiences with these dongles. I cannot discount the oscillator on the computer theory, but the probability of fault leans to the dongle, due to the major temperature fluctuations in the dongle making this the more likely source of the issue.&lt;/p&gt;&#xA;" OwnerUserId="16873" LastEditorUserId="16873" LastEditDate="2020-04-22T04:35:28.640" LastActivityDate="2020-04-22T04:35:28.640" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16503" PostTypeId="2" ParentId="16491" CreationDate="2020-04-22T05:18:36.573" Score="3" Body="&lt;p&gt;The quarter wave element compensates for the ground plane (as in a J-Pole). In many designs this same function is served through a counterpoise; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;On transmitters the antenna of an HT, a wire, the vehicle ground. No matter the form, the effect is the same, bleed off, either through radiation or termination to ground, to disperse the &quot;excess power&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On receive, the quarter wave element or section acts as the ground eliminating(reducing in practical terms) the need for a ground plane to function optimally.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you are not placing your antenna on a ground plane, with radials for optimal function, then the quarter wave portion is needed for optimal reception. &lt;/p&gt;&#xA;" OwnerUserId="16873" LastActivityDate="2020-04-22T05:18:36.573" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16504" PostTypeId="2" ParentId="6723" CreationDate="2020-04-22T07:20:41.007" Score="2" Body="&lt;p&gt;The prime reason that antennas electrically small in terms of wave length &lt;strong&gt;also&lt;/strong&gt; have useful SWR bandwidths that are relatively small is due to the low value of capacitance of those small antennas to the radiation environment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That low capacitance results in relatively higher capacitive reactance across their feedpoint terminals, which changes more rapidly for each unit change of operating frequency.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-04-22T07:20:41.007" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16506" PostTypeId="1" CreationDate="2020-04-22T15:32:07.580" Score="4" ViewCount="370" Body="&lt;p&gt;I am building an HF backpack rig using an Icom IC-706MkIIG with a Opek HVT-400B antenna. The specifications on the radio say 20 A draw at high power, so what size and type batteries would be suitable for a backpack operation?&lt;/p&gt;&#xA;" OwnerUserId="16895" LastEditorUserId="366" LastEditDate="2020-04-26T18:51:55.760" LastActivityDate="2020-04-26T18:51:55.760" Title="Need batteries for backpack operation" Tags="&lt;transceiver&gt;&lt;mobile&gt;&lt;dc-power&gt;&lt;portable&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16507" PostTypeId="2" ParentId="16495" CreationDate="2020-04-22T16:22:05.973" Score="2" Body="&lt;p&gt;An ideal frequency mixer simply multiplies its inputs. One input is the RF signal we wish to shift in frequency, and the other is the local oscillator (LO). For the moment, let's consider just an ideal frequency mixer where the LO is a pure sinusoid.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since mixers are used to shift frequencies, we can use the &lt;a href=&quot;https://en.wikipedia.org/wiki/Fourier_transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fourier transform&lt;/a&gt; to better understand their behavior in the frequency domain. I'm going to define the Fourier transform as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \hat f(\nu) = \int_{-\infty}^\infty f(x)e^{-i \nu x} dx \tag 1 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a bit dense, so breaking it down:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$f(x)$&lt;/span&gt; is the function to transform. In our case this is some function of time where &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt; is seconds,&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$e$&lt;/span&gt; is the base of the natural logarithm (about 2.718), and&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$i$&lt;/span&gt; is the imaginary unit, &lt;span class=&quot;math-container&quot;&gt;$\sqrt{-1}$&lt;/span&gt;,&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\hat f(\nu)$&lt;/span&gt; is the transformed function, where &lt;span class=&quot;math-container&quot;&gt;$\nu$&lt;/span&gt; is frequency in radians per second.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The &lt;span class=&quot;math-container&quot;&gt;$e^{-i \nu x}$&lt;/span&gt; term is a bit magic, but we can connect it to something more relatable with &lt;a href=&quot;https://en.wikipedia.org/wiki/Euler%27s_formula&quot; rel=&quot;nofollow noreferrer&quot;&gt;Euler's formula&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{ix} = \cos x + i \sin x \tag 2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So whenever you see &lt;span class=&quot;math-container&quot;&gt;$e$&lt;/span&gt; raised to some imaginary power, think of this as simultaneously two sinusoids, one 90 degrees apart from the other. So, this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ f(x)e^{-i \nu x} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;takes our signal at time &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt; and multiplies it with both a sine and a cosine of frequency &lt;span class=&quot;math-container&quot;&gt;$\nu$&lt;/span&gt;, also at time &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then we throw this integrator operator around it all, which says that to find the value of the transformed function at one frequency &lt;span class=&quot;math-container&quot;&gt;$\nu$&lt;/span&gt;, sum the product of the function and those two sinusoids over all points in time. That is, &lt;a href=&quot;https://en.wikipedia.org/wiki/Convolution&quot; rel=&quot;nofollow noreferrer&quot;&gt;convolve&lt;/a&gt; the function with a sine and a cosine for the frequency you want to know about.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Why a sine &lt;em&gt;and&lt;/em&gt; a cosine? With the Fourier transform we are &quot;probing&quot; (with convolution) for something in the signal at every possible frequency. If we probe with just one sinusoid and the signal is 90 degrees out of phase with that, the result of the convolution is 0. Probing with both a sine and  a cosine is sure to catch a signal of any phase, with the result being some complex number simultaneously representing sine and cosine parts. The &lt;a href=&quot;https://en.wikipedia.org/wiki/Argument_(complex_analysis)&quot; rel=&quot;nofollow noreferrer&quot;&gt;argument&lt;/a&gt; of that complex number tells us the phase, and the &lt;a href=&quot;https://en.wikipedia.org/wiki/Absolute_value#Complex_numbers&quot; rel=&quot;nofollow noreferrer&quot;&gt;modulus&lt;/a&gt; tells us the magnitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now with a mixer, we are multiplying the signal with a cosine. So the mixer calculates:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ f(x) \times \cos(2\pi f_\text{lo} x) \tag 3 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and we want to know what the mixer does in the frequency domain, so we can do that by calculating the Fourier transform of this expression. And by calculate I mean we can &lt;a href=&quot;https://en.wikipedia.org/wiki/Fourier_transform#Tables_of_important_Fourier_transforms&quot; rel=&quot;nofollow noreferrer&quot;&gt;look it up in a table&lt;/a&gt; and just take for granted that someone else has done the mathematical proof. The Fourier transform of two functions like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ f(x) g(x) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {1 \over 2 \pi} \left(\hat f * \hat g\right)(\nu) \tag 4 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$*$&lt;/span&gt; denotes convolution, and the hat denotes the Fourier transform. So to find the Fourier transform of two functions multiplied together, you can take the Fourier transform of each function and then convolve them. And then divide by &lt;span class=&quot;math-container&quot;&gt;$2\pi$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One of the functions is just a cosine, so we can look that up in the table too, and see that the Fourier transform of &lt;span class=&quot;math-container&quot;&gt;$\cos(ax)$&lt;/span&gt; is&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \pi (\delta(\nu - a) + \delta(\nu + a)) \tag 5 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\delta$&lt;/span&gt; is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Dirac_delta_function&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dirac delta function&lt;/a&gt;, which is 1 at 0 and 0 everywhere else. So this expression is a fancy way of saying &lt;span class=&quot;math-container&quot;&gt;$\pi$&lt;/span&gt; at &lt;span class=&quot;math-container&quot;&gt;$\pm a$&lt;/span&gt; and 0 everywhere else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Convolution of a function with an impulse is simple: it shifts the function left or right. That there are two impulses explains &lt;a href=&quot;https://en.wikipedia.org/wiki/Image_response&quot; rel=&quot;nofollow noreferrer&quot;&gt;image frequencies&lt;/a&gt;. So there you go, that's the mathematical basis for a common RF mixer that produces sum and difference outputs. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can then look up &lt;span class=&quot;math-container&quot;&gt;$\sin(ax)$&lt;/span&gt; in the table to see how things are different if we change the phase of the LO by 90 degrees:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ -i\pi (\delta(\nu - a) + \delta(\nu + a)) \tag 6 $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's the same thing, but multiplied by &lt;span class=&quot;math-container&quot;&gt;$-i$&lt;/span&gt;. The &lt;span class=&quot;math-container&quot;&gt;$i$&lt;/span&gt; term comes from the &lt;span class=&quot;math-container&quot;&gt;$i \sin x$&lt;/span&gt; term in equation 2 above. In other words, the result is rotated 90 degrees around the &lt;a href=&quot;https://en.wikipedia.org/wiki/Complex_plane&quot; rel=&quot;nofollow noreferrer&quot;&gt;complex plane&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that the rotation is 90 degrees for all frequencies. This isn't something that can be accomplished by adding a time delay, because a 90 degree delay is a different time for every frequency. Mixers can do this &quot;magic&quot; because they are nonlinear components. Linear components can't multiply two functions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Hopefully from here it's intuitively obvious that if changing the phase of the LO by 90 degrees changes the output of the mixer by 90 degrees, then this works for really any phase change as a superposition of these two cases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a bit funny but it really does work. To demonstrate, try graphing these equations:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ y = \cos(50x) \cos(51x) \\&#xA;   y = \cos(50x) \sin(51x) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We know the results will contain a high frequency component and a low frequency component, and they will both be in quadrature. Zooming in on a small part of the graph we can see the high frequency component, and indeed they are in quadrature:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ci3sa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ci3sa.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Zooming out we can see the low frequency component, and that too is in quadrature:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JsUpq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JsUpq.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It doesn't matter at all what the function on the left is: multiplying it by a sine and a cosine will always yield two functions with the same frequency spectra, but with the phases 90 degrees apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bringing this theory to implementation, it's pretty difficult to make an analog component that exactly multiplies an arbitrary signal by a sinusoid. However it's not so hard to multiply a signal by a square wave: that's just an XOR gate or a switch. Analog implementations of switches can be pretty close to ideal especially when we're talking about relatively low frequencies. Changing the LO from a sinusoid to a square wave the function is much the same, except adding the odd harmonics to the LO means odd harmonics in the input will also be mixed down to baseband. In practice this is addressed by passing the signal through a low-pass filter to remove all those harmonics before the mixer.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-04-23T05:29:55.773" LastActivityDate="2020-04-23T05:29:55.773" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16508" PostTypeId="2" ParentId="16506" CreationDate="2020-04-22T18:23:15.077" Score="1" Body="&lt;p&gt;If you want 20 A, then lead-acid batteries will be too heavy.  You would want some kind of lithium-ion battery.  Lithium ion phosphate batteries are popular for this sort of application, like the kind that &lt;a href=&quot;https://www.buddipole.com/portablepower.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Buddipole sells&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A few caveats: all this stuff will be really heavy by backpacking standards: the radio alone weighs 2.45 kg (5.4 lbs).  Of course there's nothing wrong with having 100 W on tap if you're willing to tote the load!  But, many backpackers do Morse code with 5 W QRP radios, which are cheaper, lots lighter, and use cheaper and lighter batteries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the antenna you've chosen is a vertical antenna that needs a ground plane, either the body of a vehicle or radial wires laid out on the ground.  &lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-04-22T18:23:15.077" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16509" PostTypeId="2" ParentId="16506" CreationDate="2020-04-22T18:54:45.587" Score="3" Body="&lt;p&gt;Sealed lead acid batteries are heavy. I would not recommend them. lithium phosphate or lipo are lighter, but can be hazardous. in case of physical damage to the battery they can burst into flames or even explode. Lithium Iron Phosphate batteries are also light weight and are much safer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bioenno is a well known battery vendor that has a wide selection of batteries and have several designed for HAM radio operators that even come with Anderson Power Pole connectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like most good backpacking gear they can be expensive. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;you also might want to look at a portable solar panel to supplement the battery. the solar panel will not provide enough current to run the radio during transmit, but it can extend the battery especially if you are just receiving. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also agree with rclocher3, the radio and antenna you have listed are not the best for backpacking. there are lighter radio and more effective antennas. I admit I like ICOM and I have been waiting for the ICOM 705 to become available in the USA. I also like end fed half wave antennas. They are multiband and only require a single wire and matching transformer. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-04-22T18:54:45.587" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16510" PostTypeId="2" ParentId="16495" CreationDate="2020-04-22T21:42:38.147" Score="-1" Body="&lt;p&gt;The LO quadrature isn't modulated to produce the correct phase relationship between the I and Q signals at the LO sample rate.  Instead, the low-pass filter (for down-sampling anti-aliasing) does the phase correction to allow producing a new set of I and Q signals with less phase error.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;90 degrees is important to get the correct complex vector representation in the Fourier transform of a sinusoid.  90 degrees is not relative to the time when the IQ samples are taken in the time domain with respect to the input signal sinusoid's frequency or period.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Start with the representation of a complex sinusoid in the frequency domain.  If the sinusoid frequency is identical to the sample rate, that aliases to 0 Hz, and the IFFT results in a constant, or an alias at the sample frequency if high pass filtered instead of low pass.  The real and imaginary components of the complex time domain signal will be 90 degrees apart.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bump that FT representation tick mark up a bit in the frequency domain, then IFFT, and you get not a constant anymore, but a vector of complex time domain samples that rotate at some rate relative to frequency delta.  Take the first two out of every four samples.  Is the rotation between them 90 degrees?  No.  Not any more. The rotation is 1/4th that of every 4 samples, which is not 2*pi, given you bumped the sinusoidal frequency up a bit, and the time domain vector is rotating over time.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But change the phase of the FT tick mark by 90 degrees, and all the time domain samples (both I and Q) will rotate by that amount, even though the difference between the I and Q samples is not 90 degrees.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the phase between successive I and Q samples at the LO frequency need not be 90 degrees at the frequency of some input sinusoid to an FFT, but different by an amount that depends on the difference between the spectrum and the sample rate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, even though the waveform is sampled at the LO frequency by the mixer (by a Tayloe switch or by 2 non-linear analog circuits), and the IQ phase is thus distorted by the fixed quadrature delay, these aren't the samples digitized and fed to the SDR.  Instead, these samples are usually low-pass filtered (usually by an analog LC filtering).  So what happens to the distorted phases in the low pass filter.  Well the slightly late-in-phase Q samples after an I sample are summed in the low pass filter with some prior early-in-phase Q samples.  The earlier Q samples are more distorted in phase relative to an I sample because they are half a sample duration farther from the I sample than the later Q samples.  The weighting of the low pass filter then does the equivalent of a weighted sum of lesser distorted Q samples with a higher weight plus the sum of greater distorted-in-phase Q samples with a lower weight (being farther from the I sample).  When the low pass filter result is then sampled (a new I and Q now sampled at the same time) by an 2 channel ADC, the phase of the new Q samples will have been corrected as if much less distorted in phase (depending on the quality of the low-pass filter) than the initial Q samples at the LO sample rate taken in quadrature offset timing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then samples at a reduced sample rate from the simultaneous 2 channel ADC is fed to the SDR FFT.  With little or none of the phase distortion resulting from the fixed LO offset between quadrature waveforms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So if you were to take your two 10 GHz samples, one being a 2.5th index interpolation, low pass filter both pairs, then (re)sample both low-pass filtered signal results at a simultaneous index (perhaps by interpolating one of the low-pass filtered results), you would get a phase corrected IQ signal.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-04-23T04:29:05.520" LastActivityDate="2020-04-23T04:29:05.520" CommentCount="13" ContentLicense="CC BY-SA 4.0" />
  <row Id="16511" PostTypeId="1" AcceptedAnswerId="16513" CreationDate="2020-04-22T21:45:40.583" Score="1" ViewCount="525" Body="&lt;p&gt;I have an Icom AH-4 with a random wire antenna. I have a fence around my property that is 60 feet long by 70 feet wide. The outdoor tuner is placed at the begining of the 60 foot section which leads to the 70 foot section. I intend to both receive and transmit. I would like to be able to tune 80 through 10 meters and have used a &lt;a href=&quot;https://udel.edu/~mm/ham/randomWire/&quot; rel=&quot;nofollow noreferrer&quot;&gt;webpage&lt;/a&gt; with a chart which suggests that I use between 134-136, 140-142, 150-152 or 169-171 feet of wire to make my antenna. &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;I can only buy outdoor wire in 100 or 500 feet lengths. Can I buy 2 X 100 feet of 16 guage PTFE cable and splice them with solder in the middle? I don't really need 350 extra feet of wire.&lt;/li&gt;&#xA;&lt;li&gt;Does it &lt;em&gt;really&lt;/em&gt; matter if I make the right angle turns at the corners and go around the fence? &lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I do &lt;strong&gt;not&lt;/strong&gt; need suggestions about other types of antennas unless they are shorter in height than 6 feet. HOA rules.&lt;/p&gt;&#xA;" OwnerUserId="16784" LastActivityDate="2020-04-25T17:06:11.293" Title="Can I splice a random wire antenna?" Tags="&lt;wire-antenna&gt;&lt;antenna-tuner&gt;&lt;icom&gt;&lt;icom-ic-7300&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16512" PostTypeId="2" ParentId="16506" CreationDate="2020-04-22T23:04:00.870" Score="6" Body="&lt;p&gt;I used LiFePO4 (read: Lithium Iron Phosphate) for my dad's FT-891. The big advantages of LiFePo4 are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Very power dense, almost as much as Li-Ion, IIRC twice as much Wh/kg than Lead-acid&lt;/li&gt;&#xA;&lt;li&gt;Extremely safe: they don't short circuit themselves to flames, like Li-Ion does&lt;/li&gt;&#xA;&lt;li&gt;Flat voltage discharge characteristics: their nominal voltage is 3.2V and they stay at 3.2V until they suddenly start dropping. &lt;/li&gt;&#xA;&lt;li&gt;Handles overcharging much better than Li-Ion: will not be damaged or catch fire from overchariging.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Disadvantages are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Rarer than Li-Ion. &lt;/li&gt;&#xA;&lt;li&gt;Current limited by chemistry&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;A series of 4 3.2V give you a convenient 12.8V. You actually need to charge to 3.65V per cell, 14.6V total. But don't worry, after you remove the battery from the charger, the voltage will drop to 12.8V.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The current limit is irrelevant for 100W operation since you will be pulling 20A max. I got cells for 30A discharge current and put two in parallel. Works just fine.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I bought mine from Aliexpress from a chinese supplier that makes them into nice rectangular shapes. Very easy to make a pack. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I used 8 3.2 10Ah batteries, connected as 4S2P, that is, two parallel packs of 4 battery series. From the same seller you need to also buy a BMS, which is a charge controller that will keep them balanced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In our experience, the battery lasts a very respectable 2-4 hours of 100W SSB ragchewing. My dad goes mobile on weekends and his pack lasts him for the weekend. Unlike the car battery, the voltage stays constant. Often my dad has to start the engine to recharge the battery after half an hour of operation. The LiFePO4 stays rock solid at 12.8V, and unlike the car battery, the voltage does NOT drop when you PTT. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I can provide links to the Ali seller I got them from, if you want. But if you're in the USA I suppose there are US sellers available. Don't be fooled by the high prices of other LiFePO4 packs you'll see. Those are giant batteries for use with solar systems at home (they're safe enough that they will not set your house on fire).&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="14642" LastEditDate="2020-04-23T17:07:37.457" LastActivityDate="2020-04-23T17:07:37.457" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16513" PostTypeId="2" ParentId="16511" CreationDate="2020-04-22T23:35:51.150" Score="3" Body="&lt;p&gt;A spliced joint makes very little difference to an HF antenna electrically, but if you do solder it then you should protect the solder joint from the weather, because the solder will corrode faster than the wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Right-angle turns in the wire will affect the radiation pattern, but since the radiation pattern of a &quot;random&quot; length wire antenna is funny-looking anyway, you're not likely to notice the difference from a bend or two.  The wire bends will probably change the antenna's impedance somewhat, but since you plan to use an antenna tuner, you probably won't notice that difference either.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could simulate the antenna to get a more exact idea of the radiation pattern and the impedance, but if I were in your shoes I'd just try it.  You might find that a particular length makes trouble for the antenna tuner on one or more bends; if so, just change the length of the antenna a bit and then try again.  If you double the wire back on itself, then electrically the doubled-back part of the wire vanishes.  (OK, really it couples to the wire it's laid against and radiates along with it, making a slightly thicker wire electrically, which makes no difference.)  So if you have extra wire you could double the extra part back on itself, and then if you want to lengthen the antenna later then you could just straighten part of the wire out, and then you wouldn't have to splice wire again.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-04-22T23:35:51.150" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16514" PostTypeId="2" ParentId="16511" CreationDate="2020-04-23T00:08:32.610" Score="2" Body="&lt;p&gt;Splicing the wire is just fine electrically, but if you're using multistranded cable you probably won't want to solder it. Soldering makes a stiff section which concentrates the stress at the joint, leading to premature failure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Swaging&quot; rel=&quot;nofollow noreferrer&quot;&gt;Swaging&lt;/a&gt; is ideal, but if you don't have the necessary tool then &lt;a href=&quot;https://blog.uscargocontrol.com/how-to-use-wire-rope-clips/&quot; rel=&quot;nofollow noreferrer&quot;&gt;rope clips&lt;/a&gt; are an acceptable alternative.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-04-25T17:06:11.293" LastActivityDate="2020-04-25T17:06:11.293" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16515" PostTypeId="1" CreationDate="2020-04-23T03:34:09.183" Score="3" ViewCount="164" Body="&lt;p&gt;My understanding is that the ground plane radials used on, for example, a free standing 5/8 wave 10 m vertical antenna mounted on a metal pole, are actually 1/4 wave length decoupling stubs, the function of which is to present a high impedance at the frequency being used to isolate in an RF sense the metal mounting pole from the antenna and stop the pole from becoming part of the antenna and radiating / receiving.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether this is true or not, can i use the decoupling stub idea to enable a 10 m vertical yagi to be mounted on a metal pole with the pole in between the elements and not have the metal pole upset the operation / radiation pattern / impedance of the yagi ?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anyone knows about this, any chance of getting details on construction or pointing in the right direction for more information ? &lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="9621" LastEditDate="2020-04-30T12:48:55.797" LastActivityDate="2020-04-30T12:48:55.797" Title="Can I use a 1/4 wave decoupling stub to enable mounting of a vertical yagi on a metal pole?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vertical-antenna&gt;" AnswerCount="5" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16516" PostTypeId="2" ParentId="16515" CreationDate="2020-04-23T08:27:31.250" Score="4" Body="&lt;p&gt;&lt;strong&gt;RE:&lt;/strong&gt; &lt;em&gt;...understanding...that...ground plane radials are...used to isolate...the metal mounting pole from the antenna and stop the pole from becoming part of the antenna and radiating / receiving.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately (for an example), even a set of 4 x 1/4WL radials of a 1/4WL v-pol &quot;Ground Plane&quot; antenna does not prevent r-f current from flowing along the outer diameter of the outer conductor/shield of coaxial transmission line connecting it to the source (the transmitter), even though the coax shield outer conductor is connected to and at the surface of the Earth.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;R-F current flowing along the coax shield OD (and/or the OD of a metallic tower/pole etc used to support the antenna) produces e-m radiation into space just as it does when flowing along the vertical conductor of the ground plane antenna, itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The following NEC4.2 analysis is an illustration of this.  The red lines surrounding the wire model at the right side of the graphic show the relative amplitude and phase of the r-f currents flowing along those conductors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cz80q.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cz80q.gif&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-04-23T08:27:31.250" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16517" PostTypeId="2" ParentId="16511" CreationDate="2020-04-23T13:21:41.723" Score="2" Body="&lt;p&gt;Ham radio is about experimenting, Wire antennas are relatively cheap to make. Go ahead and try it and see how well it works. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am not sating you should not read about various antennas and ask other people's opinions. You should, but at the end of day go ahead and try it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my experience splicing wires should not be an issue. mechanically fasten the wire together by twisting them around each other then solder them. I would also protect the spice from the environment by wrapping with tape or maybe  plastic sleeve filled with silicone.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Look up the Western Union splice, &lt;a href=&quot;https://en.wikipedia.org/wiki/Western_Union_splice&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Western_Union_splice&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-04-23T13:21:41.723" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16518" PostTypeId="1" CreationDate="2020-04-23T16:51:03.623" Score="3" ViewCount="205" Body="&lt;p&gt;I would like to know whether increasing the size of the antenna help increase its gain. Does this hold only for certain kinds of antennas like parabolic or horn antennas? And if it is true, can you please provide a solid paper reference?&lt;/p&gt;&#xA;" OwnerUserId="16906" LastActivityDate="2020-05-01T22:40:00.903" Title="Relation between antenna physical size and gain" Tags="&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16519" PostTypeId="2" ParentId="16518" CreationDate="2020-04-23T17:02:37.513" Score="1" Body="&lt;p&gt;TANSTAAFL. There is no such thing as a free lunch. Signals aren't multiplied by antennas, the only devices capable of adding &quot;gain&quot; are amplifiers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the antenna world, &quot;gain&quot; means &quot;directivity&quot;. If an antenna has a lot of &quot;gain&quot; it means the pattern of the antenna makes it radiate towards one direction more than others.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best analogy I found for an antenna is: consider a half inflated balloon. It's round (ish). Now squeeze it with your hand. Depending on how you squeeze it, you will create lobes: all forwards, forward and backwards, etc. The power coming out of your radio is the air inside the balloon. Your hand didn't add any more air, but directed it towards a preferred direction. Thats what an antenna does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you mentioned parabolics and horns, consider that neither are antennas. The parabolic &quot;antenna&quot; is a parabolic REFLECTOR. The actual antenna is the focus point of the reflector. It can be any number of designs, such as a helix, a monopole, a dipole, etc. The same is true for the horn. The horn is just a waveguide. The actual antenna is inside it.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-04-23T17:02:37.513" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16520" PostTypeId="1" AcceptedAnswerId="16521" CreationDate="2020-04-23T17:18:08.943" Score="5" ViewCount="373" Body="&lt;p&gt;I'm interested in a dish antenna with an axial mode helical feed for receiving video. My target frequency is about 1280 MHz or the 1.2/1.3GHz range.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've been able to figure out helical basics, like circumference equals wavelength, more turns is more gain, spacing is 1/4 wavelength, etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, when designing the antenna as a feed for a dish, I can't figure out optimal parameters for the design of the feed to maximize performance (directionality.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My best guess would be to have the angle of the outside edge of the dish from the focal point equal the &lt;em&gt;half power beam width&lt;/em&gt; of the helical (fancy words I learned &lt;a href=&quot;http://www.jpier.org/PIERC/pierc44/13.13061305.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;So basically my question is how many turns to put in a helical given dimensions of a parabolic reflector.&#xA;Are there any tried and tested rules for something like this?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best example I can find of this online is &lt;a href=&quot;https://fpvlab.com/forums/showthread.php?3008-Researching-a-100Km-video-link&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;, but I can't figure out how the OP decided on the number of turns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7o33D.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7o33D.jpg&quot; alt=&quot;a 1.3GHz dish antenna&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16907" LastEditorUserId="8717" LastEditDate="2020-04-23T18:20:18.353" LastActivityDate="2020-04-29T04:08:38.003" Title="Designing a helical antenna for a dish" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;microwave&gt;&lt;reflector&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16521" PostTypeId="2" ParentId="16520" CreationDate="2020-04-23T19:35:29.480" Score="8" Body="&lt;p&gt;I haven't built one of these myself, but one of the best resources I know of for the theory is &lt;a href=&quot;http://www.antenna-theory.com/antennas/reflectors/dish.php&quot; rel=&quot;noreferrer&quot;&gt;antenna-theory&lt;/a&gt;. The second page mostly discusses gain. There it talks about optimizing the distance between the feed antenna and the dish, given a fixed pattern for the feed antenna, but basically the same thing applies to narrowing or widening the pattern of the feed antenna for a fixed distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There isn't a lot of worked out math there, but it discusses what the tradeoff is. The more obvious component is &quot;spillover loss&quot; — any part of the feed antenna pattern that doesn't hit the dish is wasted power on transmit (and a source of noise on receive), so you want to minimize that. The slightly less obvious component is &quot;taper loss&quot; — the dish is most efficient when you're using &lt;em&gt;all&lt;/em&gt; of it. If you concentrate 99% of your pattern within half of the diameter of the dish, you might as well just use a dish half as big (with accordingly lower gain).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can work backwards from &lt;a href=&quot;http://www.antenna-theory.com/antennas/reflectors/apertureEfficiency.jpg&quot; rel=&quot;noreferrer&quot;&gt;this graph&lt;/a&gt; which shows the efficiency of different values of the angular size of the dish given a pattern that's shaped like &lt;span class=&quot;math-container&quot;&gt;$\cos^{n} \theta$&lt;/span&gt;, for different values of &lt;em&gt;n&lt;/em&gt;. The trick is to figure out what half-power beamwidths those &lt;em&gt;n&lt;/em&gt;s correspond to, which is a simple matter of solving &lt;span class=&quot;math-container&quot;&gt;$\cos^{n} \theta = 0.5$&lt;/span&gt;, or &lt;span class=&quot;math-container&quot;&gt;$\theta = \arccos \sqrt[n]{0.5}$&lt;/span&gt;. This works out to&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ &#xA;\begin{align}&#xA;n = 2 &amp;amp;&amp;amp; \theta_{HP} = 45^\circ &amp;amp;&amp;amp; \theta_{maxEff} = 67^\circ\\&#xA;n = 4 &amp;amp;&amp;amp; \theta_{HP} = 32.76^\circ &amp;amp;&amp;amp; \theta_{maxEff} = 52^\circ \\&#xA;n = 6 &amp;amp;&amp;amp; \theta_{HP} = 27^\circ &amp;amp;&amp;amp; \theta_{maxEff} = 45^\circ \\&#xA;n = 8 &amp;amp;&amp;amp; \theta_{HP} = 23.5^\circ &amp;amp;&amp;amp; \theta_{maxEff} = 40^\circ&#xA;\end{align}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$\theta_{HP}$&lt;/span&gt; is really a half-power &lt;em&gt;half&lt;/em&gt;-beamwidth, and &lt;span class=&quot;math-container&quot;&gt;$\theta_{maxEff}$&lt;/span&gt; is me eyeballing the peak efficiency values off of that graph.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This indicates that your guess was not terrible, but it loses a little too much power off the edges of the dish. The ideal seems to a half-power beamwidth between 55% of the angular diameter of the dish (for feeds fairly far from the dish) to two-thirds the angular diameter of the dish (for feeds fairly close). Having it be 100% of the dish diameter is 1-2 dB worse.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-04-23T19:42:45.290" LastActivityDate="2020-04-23T19:42:45.290" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16522" PostTypeId="2" ParentId="16493" CreationDate="2020-04-23T19:47:57.080" Score="1" Body="&lt;p&gt;yes went into external autotuner program on the FT450D, my problem was not leaving the buttons depressed for long enough!! managed to tune 1-1.5 on 20m but 1-4 on other bands--time to scrap the antenna and erect something that works! Thank you for pointing me in the right direction G4DIC.&lt;/p&gt;&#xA;" OwnerUserId="16883" LastActivityDate="2020-04-23T19:47:57.080" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16523" PostTypeId="2" ParentId="16511" CreationDate="2020-04-23T21:57:38.887" Score="1" Body="&lt;p&gt;Yes, you can. If you want it to stand up physically for a long time, you should&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Make a good, strong splice. To make a &quot;lineman splice&quot; you strip several inches of each wire, overlap them, and closely wrap each one around the other one, as in &lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Western_Union_splice.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;this diagram&lt;/a&gt; (A through D are the four steps of one variation; E and F are other variations with slightly wider spacing. Any of them are fine).&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Solder thoroughly and evenly. You want solder to flow &lt;em&gt;throughout&lt;/em&gt; the splice, not just cover up the outside. This needs consistent heating.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Protect it from the elements. Use heat-shrink tubing, or self-amalgamating tape wrapped over with vinyl tape, and cover at least an inch of insulation on either side to avoid water creeping in.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;If you're just throwing it over a tree for a summer, feel free to ignore all of this and do whatever. &lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-04-23T21:57:38.887" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16524" PostTypeId="1" AcceptedAnswerId="16536" CreationDate="2020-04-24T00:06:10.317" Score="3" ViewCount="95" Body="&lt;p&gt;I would like to have a go at measuring PIM. ( Passive Intermodulation ) in UHF.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To test my ability to measure PIM, I need to find something that generates PIM. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I either envision a 50Ω device that generates PIM, or a 2-port thru device which can be terminated on one end. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If anybody has any links to PIM sources, or home-brew build ideas, let me know. &lt;/p&gt;&#xA;" OwnerUserId="174" LastActivityDate="2020-04-29T11:15:55.010" Title="Method to generate PIM" Tags="&lt;rfi&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16525" PostTypeId="1" AcceptedAnswerId="16532" CreationDate="2020-04-24T00:54:41.247" Score="4" ViewCount="242" Body="&lt;p&gt;Here's why I wonder about this: I would love to be able to reach an Echolink-enabled repeater or similar, but I live on the other side of a ridge that would probably block a transmission to the nearest one. BUT I can likely reach a different repeater that would probably reach to the Echolink-enabled repeater.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know very little about ham radio so far. Hope to get my license and get on the air sometime.&lt;/p&gt;&#xA;" OwnerUserId="16868" LastActivityDate="2020-04-27T10:40:25.597" Title="Can one repeater be used to hit another repeater?" Tags="&lt;repeater&gt;" AnswerCount="3" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16526" PostTypeId="2" ParentId="16518" CreationDate="2020-04-24T01:05:43.513" Score="5" Body="&lt;p&gt;Gain and size are correlated, but not rigorously.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, a &lt;a href=&quot;https://en.wikipedia.org/wiki/Beverage_antenna&quot; rel=&quot;noreferrer&quot;&gt;Beverage antenna&lt;/a&gt; is larger than a half-wavelength dipole, but has lower gain. The Beverage does however have higher directivity.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another example, a &lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna#Hertzian_dipole&quot; rel=&quot;noreferrer&quot;&gt;Hertzian dipole&lt;/a&gt; is a theoretical antenna that's infinitesimal, and yet has only very slightly less gain than a half-wave dipole. It's efficiency however is a different story: as a dipole gets smaller its impedance becomes more reactive, thus necessitating a matching network that must deal with more reactive power and associated loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Extending a dipole beyond a half-wavelength does increase gain, but not usually in a very useful way: the pattern grows a bunch of lobes pointing in weird directions. For most antennas we want orderly lobes pointing in useful directions, maybe one specific direction or maybe we want to direct radiation at the horizon but not so much up or down.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These are examples that are contrary to the typical correlation. A final example that is more typical is a phased array, like a Yagi. Adding more elements to a Yagi increases the gain, and the Yagi is usually designed so all the gain goes towards a large forward lobe with minimum gain in any other direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is however important that the elements are correctly positioned and phased. Adding more elements to an array and incorrectly phasing them can result in an array that's no better than, or perhaps worse than a single element.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's worth considering two points:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Gain is the product of directivity and efficiency. A Beverage has low gain and high directivity because it has low efficiency.&lt;/li&gt;&#xA;&lt;li&gt;If the efficiency is already as high as it can be made practically, then the only way to increase gain is to increase directivity, and that usually requires making the antenna larger. A higher directivity means higher gain in the intended direction, but necessarily a lower gain in some other direction. This is a simple consequence of energy conservation.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-24T01:05:43.513" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16527" PostTypeId="2" ParentId="16525" CreationDate="2020-04-24T04:39:05.783" Score="4" Body="&lt;p&gt;They often do set them up to link to various repeaters. &lt;a href=&quot;https://www.w7pra.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;PRA&lt;/a&gt; for example. If those repeaters are linked it may work. If not it would not. Are you in contact with the repeater owner?&lt;/p&gt;&#xA;" OwnerUserId="14201" LastActivityDate="2020-04-24T04:39:05.783" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16528" PostTypeId="1" AcceptedAnswerId="16531" CreationDate="2020-04-24T14:01:54.520" Score="1" ViewCount="88" Body="&lt;p&gt;I tried to model a multiband yagi. I added radiators for 10-15-20M, and reflectors spaced .15 wavelenghts away. This gave a nice result with three sharp dips in SWR in the 10-15-20M center frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For some limitation of NEC2, I had to make equal wires for all the bands and then extend them with more wires (NEC2 wanted parallel wires to have segments aligned)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I then tried shortening the elements with coils. I shortened these extension wires, and put a series L at the first segment, in the 15 and 20m driven elements and reflectors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When doing a frequency sweep, the 20 and 15M bands show acceptable dips, but the 10M band does a strange thing: it has a wide SWR dip from 27 to 28mhz, then a spike at 28.1mhz, and then comes back down at 28.2mhz&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is this spike an artifact of simulation, or is it real interaction between the elements altering the frequency?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the NEC file:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;CM Back yard dipole, converted with 4nec2 on 26-mar-20 9:20&#xA;CE&#xA;SY DIEZmdrlen=5.03  '2.66&#xA;SY QUINmdrlen=7.07  '7.07&#xA;SY VEINmdrlen=10.63 '10.63&#xA;SY DIEZmdrpos=0.8   '0&#xA;SY QUINmdrpos=1.06  '1.06&#xA;SY VEINmdrpos=1.7   '1.7&#xA;SY h=8  '8&#xA;SY d=.019/2 '.019/2&#xA;GW  2121    2   .03 QUINmdrpos  h   -.03    QUINmdrpos  h   d&#xA;GW  1   20  .03 DIEZmdrpos  h   DIEZmdrlen/2    DIEZmdrpos  h   d&#xA;GW  2   20  .03 QUINmdrpos  h   DIEZmdrlen/2    QUINmdrpos  h   d&#xA;GW  3   20  .03 VEINmdrpos  h   DIEZmdrlen/2    VEINmdrpos  h   d&#xA;GW  111 20  -.03    DIEZmdrpos  h   -(DIEZmdrlen/2) DIEZmdrpos  h   d&#xA;GW  112 20  -.03    QUINmdrpos  h   -(DIEZmdrlen/2) QUINmdrpos  h   d&#xA;GW  113 20  -.03    VEINmdrpos  h   -(DIEZmdrlen/2) VEINmdrpos  h   d&#xA;GW  1111    5   -.03    DIEZmdrpos  h   -.03    QUINmdrpos  h   d/2&#xA;GW  1112    5   -.03    QUINmdrpos  h   -.03    VEINmdrpos  h   d/2&#xA;GW  2111    5   .03 DIEZmdrpos  h   .03 QUINmdrpos  h   d/2&#xA;GW  2112    5   .03 QUINmdrpos  h   .03 VEINmdrpos  h   d/2&#xA;GW  4   4   DIEZmdrlen/2    QUINmdrpos  h   DIEZmdrlen/2+.5 QUINmdrpos  h   d&#xA;GW  5   4   -DIEZmdrlen/2   QUINmdrpos  h   -(DIEZmdrlen/2+.5)  QUINmdrpos  h   d&#xA;GW  6   4   DIEZmdrlen/2    VEINmdrpos  h   (DIEZmdrlen/2+.8)   VEINmdrpos  h   d&#xA;GW  7   4   -DIEZmdrlen/2   VEINmdrpos  h   -(DIEZmdrlen/2+.8)  VEINmdrpos  h   d&#xA;GW  31  15  (DIEZmdrlen*1.05/2) -DIEZmdrpos h   -((DIEZmdrlen*1.05/2))  -DIEZmdrpos h   d&#xA;GW  51  15  (DIEZmdrlen*1.05/2) -QUINmdrpos h   -((DIEZmdrlen*1.05/2))  -QUINmdrpos h   d&#xA;GW  61  15  (DIEZmdrlen*1.05/2) -VEINmdrpos h   -((DIEZmdrlen*1.05/2))  -VEINmdrpos h   d&#xA;GW  32  5   (DIEZmdrlen*1.05/2) -QUINmdrpos h   (DIEZmdrlen/2+.5)   -QUINmdrpos h   d&#xA;GW  33  5   -(DIEZmdrlen*1.05/2)    -QUINmdrpos h   -(DIEZmdrlen/2+.5)  -QUINmdrpos h   d&#xA;GW  34  5   (DIEZmdrlen*1.05/2) -VEINmdrpos h   (DIEZmdrlen/2+.8)   -VEINmdrpos h   d&#xA;GW  35  5   -(DIEZmdrlen*1.05/2)    -VEINmdrpos h   -(DIEZmdrlen/2+.8)  -VEINmdrpos h   d&#xA;GE  1&#xA;LD  0   6   1   1   0   15.5e-6&#xA;LD  0   7   1   1   0   15.5e-6&#xA;LD  0   4   1   1   0   3e-6&#xA;LD  0   5   1   1   0   3e-6&#xA;LD  0   34  1   1   0   15.5e-6&#xA;LD  0   35  1   1   0   15.5e-6&#xA;LD  0   32  1   1   0   3.5e-6&#xA;LD  0   33  1   1   0   3.5e-6&#xA;&#xA;&#xA;&#xA;GN  2   0   0   0   13  0.005&#xA;EK&#xA;EX  0   2121    2   0   0   0   0&#xA;&#xA;FR  0   0   0   0   14.1    0&#xA;EN&#xA;&#xA;&lt;span class=&quot;math-container&quot;&gt;```&lt;/span&gt;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-04-25T01:22:56.683" Title="Modeling a multiband Yagi in 4NEC2?" Tags="&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16529" PostTypeId="2" ParentId="16524" CreationDate="2020-04-24T15:03:48.953" Score="0" Body="&lt;p&gt;Any non-linear device can work.  But a good physical analog might be to find a crystal radio kit with a point contact crystal, and use the point contact detector inductively or capacitively coupled to the ends of your terminator.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-04-24T15:03:48.953" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16530" PostTypeId="2" ParentId="16518" CreationDate="2020-04-24T15:18:54.810" Score="0" Body="&lt;p&gt;The angular resolution of an EM imager is in inverse proportion to its &lt;a href=&quot;https://www.sciencedirect.com/topics/earth-and-planetary-sciences/radio-telescope&quot; rel=&quot;nofollow noreferrer&quot;&gt;effective aperture&lt;/a&gt;. See &lt;a href=&quot;https://en.wikipedia.org/wiki/Angular_resolution&quot; rel=&quot;nofollow noreferrer&quot;&gt;Rayleigh criteria&lt;/a&gt;.  A parabolic dish antenna can be thought of as an EM imager, similar to a radio telescope.  The larger the dish aperture, the higher the potential resolution.  Large phased arrays can also have a large effective aperture.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And a finer resolution allows a higher gain in some targeted direction (where the imager's focus is aimed), as well as a reduction in sensitivity to some portion of off-axis noise.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-04-24T15:25:23.170" LastActivityDate="2020-04-24T15:25:23.170" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16531" PostTypeId="2" ParentId="16528" CreationDate="2020-04-25T01:22:56.683" Score="1" Body="&lt;p&gt;From the information presented below, I believe the &quot;problem&quot; with your model arises from the parallel wires that couple the forward elements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I made a reasonable facsimile of the antenna in your NEC model with the changes I described in my comment:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Each element consists of a single, segmented &quot;wire&quot; &lt;/li&gt;&#xA;&lt;li&gt;Loads are placed as close to the positions you specified as possible &lt;/li&gt;&#xA;&lt;li&gt;A 50-ohm transmission line replaces the parallel wires that couple the forward&#xA;elements&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Here are the element currents at the resonant frequency of 28.2-MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/POb9Z.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/POb9Z.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These produce useful directivity at the maximum radiation angle of 18-degrees above the horizon:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/R22BB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/R22BB.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and the SWR plot:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vNtLo.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vNtLo.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Changing the impedance of the transmission line to 200-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; produced an SWR curve quite similar to your original NEC model, but I believe it's still advisable to use NEC's native transmission line facility.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-04-25T01:22:56.683" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16532" PostTypeId="2" ParentId="16525" CreationDate="2020-04-25T01:46:00.333" Score="5" Body="&lt;p&gt;A repeater simply listens on one frequency, and retransmits what it receives on another frequency. If one repeater happened to listen on the frequency another was transmitting, theoretically you could exploit this to extend your range in one direction at least.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately as a user you have no control over these frequencies. To avoid interference with each other, repeater operators usually coordinate to not use the same frequencies. Some jurisdictions legally require this coordination.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is possible to link repeaters through the internet (this is how Echolink works) or though a point-to-point microwave link. Some clubs operate networks of repeaters in this way. They may be linked all the time or require some user command to bring up the link. This however does require deliberate setup on the part of the repeater owner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So unless the owner(s) of the repeaters in question have cooperated to link the repeaters though some means, unfortunately you can not use one repeater to hit another. Your best bet is to find the owner of the repeaters you can hit, see if they have any documentation on what links they provide, and if no such documentation exists contact them and inquire.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-25T01:46:00.333" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16533" PostTypeId="2" ParentId="5742" CreationDate="2020-04-25T21:20:42.683" Score="1" Body="&lt;p&gt;Tecsun PL660 antenna is connected to the gate of the J-FET for frequency range 1700 kHz to 30 MHz. This is a high impedance. The measured graph can't be correct. The measurement signal voltage must be low enough to prevent switching diodes to go in conductive state.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FET transistors in the diagram have non-consistent gate-drain-source connections. The diode D3 without dc-current is also a simplification in the schematic. The signal for frequency range 100 kHz to 1710 kHz comes from the ferroceptor. The gate from the FET is connected to the (about) 1 mH ferroceptor inductance, and the drain is connected to a feedback-current winding and to diode D0. The noise matching is not affected by this feedback. The conversion from field strength to output signal can be made frequency-independent with this feedback. For frequency range 1710 kHz to 30 MHz the signal path is via D1 to the low-pass filter just before the first balanced mixer with the two J-FETs. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;When you want to see a real and correct diagram, different from the PL660, that makes use of similar techniques look into Philips (Magnavox) D2935 schematic diagram: more complex but also a lot more sensitive. In 1980 I did the design of this &quot;portable&quot; receiver, which was planned to be better than the finally produced Philips radio :)&lt;br&gt;&#xA;PA0FSB &#xA;Brightnoise&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-04-25T21:20:42.683" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16534" PostTypeId="1" CreationDate="2020-04-25T22:16:38.083" Score="3" ViewCount="143" Body="&lt;p&gt;The Yaesu FT3D can send photos, but only if taken with the optional external mic that has a camera. I want to be able to send photos that come from elsewhere, by putting them on the SD card.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But it seems that in addition to putting the jpeg (320x240, max size 40kB, says the video below) on the SD card, you also have to put these into two index files, named &lt;code&gt;QSOPCTDIR.dat&lt;/code&gt; and &lt;code&gt;QSOPCTFAT.dat&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is supposedly possible to do this if you run Windows, with a free of cost program. See &lt;a href=&quot;https://www.youtube.com/watch?v=KhrKTsHd6Fw&quot; rel=&quot;nofollow noreferrer&quot;&gt;this video&lt;/a&gt;. I see comments on that video of people failing to use this method even on Windows with the FT3D, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's probably the same format as for audio recordings, which I have examples of:&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;$ od -txC /mnt/tmp/QSOLOG/QSOWAVDIR.dat&#xA;0000000 00 00 00 00 20 20 20 20 20 20 20 20 20 20 20 20&#xA;0000020 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20&#xA;0000040 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 03&#xA;0000060 06 19 19 00 00 00 00 00 00 00 00 00 00 00 00 00&#xA;0000100 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20&#xA;0000120 00 00 00 00 32 30 30 33 30 36 31 39 31 39 33 39&#xA;0000140 2e 77 61 76 ff ff ff ff ff ff ff ff ff ff ff ff&#xA;0000160 ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00&#xA;0000200 00 00 00 00 20 20 20 20 20 20 20 20 20 20 20 20&#xA;0000220 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20&#xA;0000240 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 03&#xA;0000260 17 20 33 00 00 00 00 00 00 00 00 00 00 00 00 00&#xA;0000300 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20&#xA;0000320 00 00 00 00 32 30 30 33 31 37 32 30 33 33 30 31&#xA;0000340 2e 77 61 76 ff ff ff ff ff ff ff ff ff ff ff ff&#xA;0000360 ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00&#xA;0000400&#xA;$ od -txC /mnt/tmp/QSOLOG/QSOWAVFAT.dat&#xA;0000000 40 00 00 00 40 00 00 80&#xA;0000010&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Clearly the &lt;code&gt;QSOxxxDIR.dat&lt;/code&gt; file contains the file name, but what could the rest be? And that's even assuming the &lt;code&gt;QSOPCTDIR.*&lt;/code&gt; files look like &lt;code&gt;QSOWAVDIR.*&lt;/code&gt; files. Since I have no photos (nor the optional external Yaesu camera), I have no example files. Both files are 0 bytes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What could this file format be? Given specs I could easily make a tool to create them.&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="76" LastEditDate="2020-04-25T22:22:35.213" LastActivityDate="2020-09-05T10:47:19.173" Title="What is the format of Yaesu FT3D's QSOPCTDIR.dat and QSOPCTFAT.dat files?" Tags="&lt;digital-modes&gt;&lt;yaesu&gt;&lt;software-development&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16536" PostTypeId="2" ParentId="16524" CreationDate="2020-04-26T05:40:11.743" Score="3" Body="&lt;p&gt;For generating PIM - for testing and calibration, you want a known level signal at the expected intermodulation frequency. This will let you calibrate the whole setup though the losses of the various combiners and filters, and by switching it on and off, measure the level of PIM in your measurement system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'd recommend using a signal generator at the correct frequency, feeding that in through a suitable attenuator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You probably don't want to use a non-linear device to actually generate PIM. Connecting a diode or something to the test point (with an attenuator, and some DC bias) will generate plenty of PIM, but at an unknown level, so you'll have to start by fully characterising your non-linear device.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can make a low-PIM high power attenuator with a roll of very thin coax. In a 30+30 watt, 900 MHz test set, we used something like this 1.19 mm diameter &lt;a href=&quot;https://www.ezform.com/product/ez-47-cu-2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZ-47&lt;/a&gt; which has 32 dB/100' attenuation. 50 feet is not a large roll of this cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You will need a low-PIM termination for the other side of your device under test, this gives you a way to upgrade your ordinary 50 Ohm termination. Combined with some ordinary attenuators, it also provides a way to measure the final incident power and apply your fake PIM signal.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-04-26T05:40:11.743" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16537" PostTypeId="2" ParentId="16515" CreationDate="2020-04-26T14:06:31.317" Score="3" Body="&lt;p&gt;I modeled a &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{2}$&lt;/span&gt; vertical dipole located &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{10}$&lt;/span&gt; from the top of a grounded &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; conductive pole. Numerous NEC2 simulations with four (4) &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{4}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{2}$&lt;/span&gt; radials at locations up and down the conductive support did meaningfully reduce currents in the support.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Reducing currents in the conductive pole requires breaking it up into lengths that won't support current at the operating frequency. Shown below is the first example that showed meaningful current reduction, requiring the pole to be broken into three sections. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fwFP1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fwFP1.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each of the upper sections is &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{5}$&lt;/span&gt; long and they are separated by &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{20}$&lt;/span&gt;, but the separation was just for convenience in simulation. This can be accomplished with insulators, of course, but also using de-tuning &quot;loops&quot; a la &lt;a href=&quot;https://www.w8ji.com/detuning_towers.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI&lt;/a&gt; and others:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vdn4Q.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vdn4Q.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maximizing the current through the capacitor-tuned loop sections A and B minimizes the currents in the adjacent sections C and D.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-04-26T17:57:54.290" LastActivityDate="2020-04-26T17:57:54.290" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16538" PostTypeId="1" AcceptedAnswerId="16541" CreationDate="2020-04-26T17:38:53.123" Score="-1" ViewCount="118" Body="&lt;p&gt;I wanted to build a small drone of my own as a &lt;em&gt;hobby project&lt;/em&gt;. My old drones were broken so I wanted to salvage as much as I could to build a small indoor one. I wanted to use an Arduino, however, I am facing a small problem.     &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, my drone controller is broadcasting at a frequency of 2.4 GHz which I want to capture through my Arduino. However, &lt;em&gt;every&lt;/em&gt; tutorial online uses a small specialized module to capture those signals.      &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So my question is - why can't I use a simple wire as a 2.4 GHz antenna? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I guess I would have left it alone but my drone has a small wire as an antenna (it is an indoor one). So how come that drones use a small piece of wire for receiving those signals while MicroControllers have to use a full-on module?&lt;/p&gt;&#xA;" OwnerUserId="16932" LastEditorUserId="4076" LastEditDate="2020-04-27T05:52:58.563" LastActivityDate="2020-04-27T05:52:58.563" Title="Why can't we use a simple wire for receiving 2.4 GHz signals?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;transceiver&gt;&lt;microwave&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16540" PostTypeId="2" ParentId="16538" CreationDate="2020-04-26T19:27:44.507" Score="6" Body="&lt;p&gt;It might be a good idea to start by trying to make a block diagram of what you have inside of each of those controllers...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Namely, the drone controller is most likely some sort of a system on a chip, which on its own chip, in addition to having a microcontroller also has the radio interface built in.&lt;br&gt;&#xA;Those are two separate things, but in one package. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio modules usually only communicate over radio, and need a extra digital electronics to drive them (today commonly implemented using microcontroller), which lead to the popularity of specialized microcontrollers with integrated radio interfaces. There are also many other types of specialized microcontrollers, with Bluetooth radios integrated, with audio amplifiers integrated, with FM and DAB radio receivers integrated and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, Arduino is a platform for rapid prototyping, which is based on Atmel's (now Microchip's) ATmega series general purpose microcontrollers. Its main selling point is not that it's especially cheap, or that it has integrated modules for something, but that it's super simple and relatively easy to understand, and therefore attractive to beginners. &#xA;As I mentioned, the ATmegas are general purpose micro controllers. They do not include the radio interface in them. Therefore, you need to use an external radio interface. That interface, depending on its complexity, will most likely converts the signal into data, which the microcontroller can easily process. However, since the interface chip doesn't know what is it actually going to be talking to, it needs to implement a lot of intelligence on its own, in order to covers the radio signal to data, which drives the cost of such modules up. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, let's go to the &quot;piece of wire&quot; statement. The piece of wire is almost certainly not just some piece of wire, but a wire antenna, hopefully cut to the appropriate length. The drone controller's PCB also most likely has tuning elements on it, which should allow it to properly drive the wire antenna you have. &#xA;The radio interface module for the microcontroller will also have its own antenna, either on the PCB, or perhaps externally, and needed electronics to drive it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And finally, one important thing to keep in mind: In order to have any hope of capturing the drone's signal, you need to actually figure out which protocol the drone uses in its controller, and to know which modules can work with them, so that you can select an appropriate one for your microcontroller. Just picking one up at random is not going to work, since the protocols running at 2.4 GHz tend to be very complicated.  &lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2020-04-26T19:27:44.507" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16541" PostTypeId="2" ParentId="16538" CreationDate="2020-04-26T23:53:36.927" Score="6" Body="&lt;p&gt;A wire will pick up a GHz signal, as well as a ton of other RF signals, all mixed together.  Some sort of filtering is required to separate out your desired radio signals.  An Arduino has none of filtering required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sampling a 2.4 GHz signal requires a sample rate above 5 billion samples per second.  The A/D on an Arduino samples at a rate of about 9000 samples per second, which is a few hundred thousand times too slow.  To say nothing about the CPU being able to store or process that amount of data.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-04-26T23:53:36.927" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="16543" PostTypeId="2" ParentId="16525" CreationDate="2020-04-27T10:40:25.597" Score="0" Body="&lt;p&gt;A licensed radio amateur, who is a validated user of Echolink and has an access problem similar to yours, would have absolutely no problem working through that repeater, via the internet, using Echolink. The question of accessing that repeater through another one does not arise, since Echolink would provide that very access for which it is intended.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio amateurs, who have no access to a local repeater or even a transceiver, easily work through repeaters on the other side of the world using Echolink.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer to your title question is no. The repeater-pair frequencies, assigned in band plans, would ensure that that would not be possible and thereby prevent unwanted interference.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-04-27T10:40:25.597" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16544" PostTypeId="2" ParentId="16524" CreationDate="2020-04-27T11:07:16.613" Score="0" Body="&lt;p&gt;I've confirmed generation of PIM within the 2m band and across 2m/70cm bands using a point contact diode as a mixer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Two 2m rubber ducky antennas were interconnected by a OA5 diode, with the junction fed by a 600kHz crystal oscillator. The passive setup could intercept a 145.1MHz signal, transmitted by a 2m HT in the vicinity, and retransmit it after mixing it with the 600kHz signal. This was confirmed by the resulting 145.7 MHz signal being received on a second 2m HT nearby. A 145.7 MHz signal transmitted by the second HT was also received at 145.1MHz on the first.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same test was done using a 2m and a 70cm rubber ducky, interconnected by a OA5 diode, with the junction fed by a 290MHz signal. A 145.5MHz signal transmitted from the 2m HT was received at 435.5Mhz on the 70cm HT and vice versa.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may go through my blog post, '&lt;a href=&quot;http://nandustips.blogspot.in/2013/07/simple-low-cost-demo-repeater.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Simple Low-cost Demo Repeater&lt;/a&gt;', for more details.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-04-29T11:15:55.010" LastActivityDate="2020-04-29T11:15:55.010" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16545" PostTypeId="1" CreationDate="2020-04-27T15:50:09.960" Score="0" ViewCount="88" Body="&lt;p&gt;If I obtain a license to a chunk of spectrum, are there any limitations on what I can do in that spectrum?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, would I need to declare to the FCC my intentions for using the spectrum (e.g. point-to-point links, mesh networks, etc), or can I use it for whatever? Can whoever I authorize transmit on this chunk of spectrum? If I lease the spectrum to another user, do I need to declare this sub-lease to the FCC? Are there any transmit power limitations?&lt;/p&gt;&#xA;" OwnerUserId="9672" LastActivityDate="2020-04-28T12:16:05.363" Title="Are there restrictions placed on transmissions in licensed spectrum in the United States?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;" AnswerCount="2" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="16546" PostTypeId="2" ParentId="16545" CreationDate="2020-04-27T19:43:08.273" Score="9" Body="&lt;p&gt;The FCC issues licenses for a particular service (e.g. broadcast, amateur, land mobile, common carrier, etc.).  Each service is regulated by a specific part of the FCC regulations (e.g., Part 97 for Amateur Radio Service).  These regulations determine the limitations on a licensees use of spectrum.  There may also be license specific limitations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In effect, when you apply for a license in a specific service, you are declaring the type of use you intend.  In the Amateur Service, as long as you follow the regulations, you do not normally need to notify the FCC of any particular use as long the use is allowed by Part 97.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether you can authorize others to use the frequencies you are licensed for depends on the service.  A Land Mobile (Part 90) license will allow for a number of mobile units.  The licensee (e.g. a fire department) gets to decide who can operate radios under that license.  But the use has to be appropriate to the license (e.g., fire dispatch).  An Amateur Radio licensee has no authority to allow others to use radio spectrum.  Each operator needs their own license.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;License term, power limits, etc. are determined by the service and possibly the specific license.  Cost of applying for and getting a license also depends on the service.  Costs: Amateur Service - a few dollars for test and time for study; Land Mobile - maybe a couple hundred for coordination or maybe more for big systems; common carrier (cell phone)- Megabucks, maybe Gigabucks (I don't know).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note: Spectrum auctions mostly (AFAIK) apply to spectrum allocated for common carrier use.  And large sums of money are involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What you really need to do is think about what you want to do with any radio spectrum, then come back and ask a &quot;How do I...&quot; question.&lt;/p&gt;&#xA;" OwnerUserId="15428" LastEditorUserId="15428" LastEditDate="2020-04-27T19:53:29.987" LastActivityDate="2020-04-27T19:53:29.987" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16547" PostTypeId="2" ParentId="14425" CreationDate="2020-04-27T21:48:20.647" Score="1" Body="&lt;p&gt;Common practice is to tune with low power. The FT-891 can do that automatically with SOME tuners. My DIY-tuner does not, so I have to reduce power from the FT-891 down to 5 watt, switch to FM for a constant envelope/carrier signal and match the antenna to lowest SWR-reading in the display, or in my (manual) tuner SWR-readout. When I try to tune WITHOUT power reduction, I see the message &quot;high SWR&quot; in the FT-891 and, as already mentioned in the thread, the power fold-back protection is/becomes active. &#xA;That is rather close to your observation, I think. And when tuning is succesfull, switch to SSB and adjust the power to 100 Watt or what you need for the QSO. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The conversion tables for SWR and loss in dB as found on the internet and in documents are ONLY VALID FOR 50 Ohm source and load systems! An SWR of 1:2 results from 25 Ohm or from 100 Ohm load impedance (or from other complex mismatch). SWR is RELATIVE mismatch. In transmitter systems there is no power loss as with mismatched 50 Ohm-intended laboratory systems. My FT-891 can deliver more than 100 Watt with output load 40 Ohm, but that is close to the survival-limit of the power amplifier..... Compare it with a mains outlet: for a certain power you need a certain resistive load. The system is designed for use with that load. The output impedance of a transmitter can range from zero (voltage source) to infinite (current source). Mismatch will lead to a high current or a high voltage and destroy your power amplifier. That is why there is an SWR-protection that reduces power at mismatch.&#xA;PA0FSB&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-04-27T21:48:20.647" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16548" PostTypeId="1" AcceptedAnswerId="16685" CreationDate="2020-04-28T09:55:54.023" Score="5" ViewCount="881" Body="&lt;p&gt;currently I am involved in a project were a data link is needed to communicate different devices. This is in one to many configuration and the devices are stand alone. &#xA;For this project there is need 9.2Kbps, even less, and the expected coverage is not so huge, is just about 500 mts in a rural environment (trees, hills) and the worst part... this device should work around the globe. The problem here is with the approvals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;LoRa could be a solution, but there is some differences in the regions (868/915/923) and the FCC rules and EU rules regarding duty cycle and dwell time are quite different.&#xA;I thought to use a NarrowBand radio, at 403-470MHz, using licensed channels (no problem to request a license), but these modules are quite expensive.&#xA;Do you have any idea? do you know any radio module transceiver for world wide?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many thanks in advance.&lt;/p&gt;&#xA;" OwnerUserId="16870" LastActivityDate="2020-05-15T07:08:44.943" Title="World wide Radio Module" Tags="&lt;legal&gt;&lt;uhf&gt;&lt;transceiver&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16549" PostTypeId="2" ParentId="16545" CreationDate="2020-04-28T12:16:05.363" Score="0" Body="&lt;p&gt;Short answer: yes, there are limitations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'll actually be applying for a license for &lt;strong&gt;spectrum&lt;/strong&gt; in a &lt;strong&gt;particular service&lt;/strong&gt; each of which has use requirements and/or restrictions.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2020-04-28T12:16:05.363" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16551" PostTypeId="2" ParentId="16548" CreationDate="2020-04-28T13:41:01.897" Score="12" Body="&lt;p&gt;Your problem is that there's really but one globally usable unlicensed band, and that's the 2.4 GHz band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But that doesn't sound so bad. People think &quot;high frequency = short reach&quot;, stemming from the well-known Free-Space Path loss formula&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$P_r = P_t \cdot G_t G_r \left( \frac{c_0}{4 \pi fd} \right)^2\text,$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where the received power &lt;span class=&quot;math-container&quot;&gt;$P_r$&lt;/span&gt; falls with the square of the  frequency &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; (for a fixed distance &lt;span class=&quot;math-container&quot;&gt;$d$&lt;/span&gt;), assuming you keep the transmit power constant and use antennas that have the same gain &lt;span class=&quot;math-container&quot;&gt;$G$&lt;/span&gt; on transmit- and receive-side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, what people tend to forget: your antenna directivity at constant antenna area also grows quadratically with frequency, so that it's typically a zero-sum game, if, and that is the great if here, you can have a directive link: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to keep the size of your system the same, this works out, because you can point the antennas at each other, and make a directive link.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If either side needs to be able to move, you usually can't just realign the antennas all the time, and this doesn't work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, is this really a problem? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming a gain for one antenna of 6 dB (which is somewhat logical, you don't build an antenna that illuminates the sky if you want to talk to things on the ground, nor do you let it illuminate the ground directly below it), and the other with 0 dB gain, and stay within the world-wide limit of 100 mW (= 20 dBm) for the 2.4 GHz band, your received power at 500 m becomes is 83 dB lower than your transmit power, so -63 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's not at all bad! Say, you're using a cheap 1 MS/s device, so you can only do 1 MHz of bandwidth at once, you get a noise power of &lt;span class=&quot;math-container&quot;&gt;$N_{[\text{dBm}]}=-174+B_{[\text{dBHz}]}=-114$&lt;/span&gt; dBm (1 MHz = 60 dBHz). That gives you a very comfortable SNR! You should pretty trivially be able to communicate at your rates over that.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-04-28T14:47:20.273" LastActivityDate="2020-04-28T14:47:20.273" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16552" PostTypeId="2" ParentId="16407" CreationDate="2020-04-28T14:30:36.500" Score="2" Body="&lt;p&gt;The common-mode isolator helps. For lower frequencies (&amp;lt; 1 MHz) it is almost impossible to have high isolation with just one or more ferrite rings. May be this helps: a common mode isolator specially for high-sensitivity outdoor E-field antennas. See picture. My receiver is RSP1A and/or RTL-SDR and I have not any noise from computer and/or power supply, nor from switch-mode supplies in my house. Remote antenna, free standing, 10 meters coax. Technical info: 3 uH * N^2 for the toroid, so 50 wdg makes 7500 uH. Isolation max 5 kOhm at 2 MHz. Signal loss &amp;lt; 1 dB up to 30 MHz (use twisted Cupper-enamel!). PA0FSB&lt;a href=&quot;https://i.stack.imgur.com/IAKti.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IAKti.jpg&quot; alt=&quot;Common mode interference isolator for SDR connected to noisy supply environment&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-04-28T14:30:36.500" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16553" PostTypeId="2" ParentId="15656" CreationDate="2020-04-28T17:10:29.597" Score="4" Body="&lt;p&gt;Ferrite rods are smaller than loop antennas, but since the &lt;span class=&quot;math-container&quot;&gt;$Q_u$&lt;/span&gt;  (unloaded &lt;em&gt;Q&lt;/em&gt;) is lower (200 is already very good as maximum) a copper or aluminium loop with same effective diameter (&lt;span class=&quot;math-container&quot;&gt;$\mu_r$&lt;/span&gt; of ferrox material is about 130) and &lt;span class=&quot;math-container&quot;&gt;$Q_u$&lt;/span&gt; of 500 for the loop is better. Dimension is indeed a factor larger; diameter goes factor &lt;span class=&quot;math-container&quot;&gt;$\sqrt {130}$&lt;/span&gt; = factor 11,4 up for same aperture of H-field. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And to go back to your question: it makes a difference wheter the antenna is tuned or not. When tuned loops are within the range where coupling comes in the region of &lt;span class=&quot;math-container&quot;&gt;$k*\sqrt {Q_l}$&lt;/span&gt; = 1 then the antennas have unwanted mutual effects. (&lt;span class=&quot;math-container&quot;&gt;$Q_l$&lt;/span&gt; is loaded &lt;em&gt;Q&lt;/em&gt;.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When more loopsticks antennas are coupled with single tuning capacitor then you created a larger ferroceptor antenna: higher effective height and better reception, better sensitivity and lower noise floor. Noise floor on medium wave 1 MHz is seldom lower than 3&lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;V/m in RBW = 3 kHz (&quot;radio bandwidth&quot;). Finally, when you make separate wideband antennas (no resonance, wideband noise matching) loop and ferroceptor loopstick antennas can be placed closer together.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Spaced array: coherence of signal is high within a wavelength separation. Local interference can vary. Last week I did a test with RSP-duo and 2 antennas and found only decorrelation for separation beyond 0,7&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;; probably only beam forming from an array. &#xA;PA0FSB &lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="9621" LastEditDate="2020-04-28T17:21:25.253" LastActivityDate="2020-04-28T17:21:25.253" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16554" PostTypeId="1" AcceptedAnswerId="16555" CreationDate="2020-04-28T21:50:39.157" Score="1" ViewCount="254" Body="&lt;p&gt;Regardless of the mode: digital or analog, the radios always transmit sinusoidal EM waves. So wouldn't a regular analog repeater be able to rebroadcast that EM signal regardless of its encoding?&lt;/p&gt;&#xA;" OwnerUserId="15878" LastActivityDate="2020-08-07T21:18:11.790" Title="Why is a separate repeater required for digital modes? Why can't an analog repeater be used for digital modes?" Tags="&lt;digital-modes&gt;&lt;repeater&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16555" PostTypeId="2" ParentId="16554" CreationDate="2020-04-28T22:52:25.413" Score="9" Body="&lt;p&gt;There is a kind of repeater that can repeat any kind of transmission: it's called a &lt;em&gt;linear translator&lt;/em&gt;. It's technically equivalent to an SSB receiver linked to an SSB transmitter. It works for any mode because SSB is simply a shift in frequency. Other than the change in frequency, the baseband and RF signals are linearly related. This is also why an SSB tranciever can be used to implement any digital mode, like PSK-31, FT8, and so on. The only requirement is the SSB radio's bandwidth needs to be wide enough to accommodate the mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This linear relationship does not exist for FM. For FM, only the phase of the input is relevant, and so as part of the demodulation process information about amplitude is lost. This means an analog FM repeater can't repeat any mode: it can only repeat modes that don't rely on changes in amplitude.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Theoretically this means an FM repeater could be used for some but not all digital modes. In FM demodulation, higher deviation in the RF signal relates to higher amplitude in the baseband signal. If the repeater includes any kind of AGC this will result in the input and output RF signals differing in deviation. Some digital modulations rely on the deviation to be some precise value, and so this further reduces the set of possible digital modulations that an analog repeater can repeat.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Besides AGC, an analog repeater might have additional filtering which distorts the digital modulation in ways that prevent demodulating it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, even for modulations that can still pass successfully through this repeater, there are significant technical advantages to using a purpose-engineered digital repeater. An analog repeater, with no knowledge of the modulation or coding of the signal, can only repeat exactly what it received, noise included. A digital repeater however can demodulate and decode the signal to recover the original digital message, then re-encode and re-modulate it, re-transmitting an equivalent signal with no noise. This significantly extends the useful range of the repeater.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-04-28T23:05:53.023" LastActivityDate="2020-04-28T23:05:53.023" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16557" PostTypeId="2" ParentId="16520" CreationDate="2020-04-29T04:08:38.003" Score="2" Body="&lt;p&gt;The information on Dish illumination is Correct.  That is... the Angle of the&#xA;waves from the Dish to the Feed Antenna ( helical ) at the Widest (rim) point. Using an off-center point feed makes it Vary Hard to design.   the next thing is the Focal Point.&#xA;this is the Exact Point the Waves are Concentrated at, to set the Helical at.&#xA;It is like taking a magnifying Glass and finding the Focus point to Burn something.&#xA;I would look for a UHF /VHF handbook, and find Satellite communications, and Parabolic&#xA;Dish design information. ray     &lt;/p&gt;&#xA;" OwnerUserId="16946" LastActivityDate="2020-04-29T04:08:38.003" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16558" PostTypeId="2" ParentId="7705" CreationDate="2020-04-29T11:31:31.110" Score="0" Body="&lt;p&gt;To add to Kevin's excellent answer above, look at &lt;a href=&quot;https://wiki.gnuradio.org/index.php/Tutorials&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wiki.gnuradio.org/index.php/Tutorials&lt;/a&gt; (GNU Radio tutorials for every user level) and in particular &lt;a href=&quot;https://wiki.gnuradio.org/index.php/Guided_Tutorial_Hardware_Considerations&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wiki.gnuradio.org/index.php/Guided_Tutorial_Hardware_Considerations&lt;/a&gt; (which includes building a working Software Radio Broadcast FM Receiver with GNU Radio).&lt;/p&gt;&#xA;" OwnerUserId="15011" LastEditorUserId="15011" LastEditDate="2020-04-29T16:18:36.860" LastActivityDate="2020-04-29T16:18:36.860" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16559" PostTypeId="1" AcceptedAnswerId="16560" CreationDate="2020-04-29T12:53:19.370" Score="5" ViewCount="386" Body="&lt;p&gt;I'm 13 years old. I hear all the fuss about ham radio how awesome it is. I really want to join, but I hear you have to get a certification.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How much does it cost?&lt;/li&gt;&#xA;&lt;li&gt;How long does it take?&lt;/li&gt;&#xA;&lt;li&gt;How much does a ham radio cost?&lt;/li&gt;&#xA;&lt;li&gt;What could you do with it?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="8717" LastEditDate="2020-10-26T20:10:57.283" LastActivityDate="2020-10-26T20:10:57.283" Title="Getting Started In Ham Radio" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16560" PostTypeId="2" ParentId="16559" CreationDate="2020-04-29T14:08:18.640" Score="3" Body="&lt;p&gt;You do have to be licensed to transmit on amateur (ham) radio frequencies. This requires passing a test, but it is not a hard test. There are many websites, Phone apps, and books that can help you study for the test. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The tests sessions are done by volunteers. The largest group of Volunteer Examiners is the American Radio Relay League or ARRL. On thier web site they list when and where tests will be held. As of April 2020 not many tests are being conducted due to the stay at home orders due to the COVID 2019 situation, but we expect this to change as restrictions are eased. The ARRL charges $15 for the test session. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first license class is technician which lets you use relatively short range VHF and UHF radios.  The other licenses are general and extra. These let you use HF frequencies which can travel great distances and you can communicate around the world. Each license requires passing an additional test. If you have studied all three test you actually can take and pass all three licenses the same day and go straight to extra.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many HAM start with an Handheld Transceiver or HT. These start at around 30 - 40 dollars, but these cheap ones are not very good and if you can afford it it is better to look in $100 price range. The price of HF radio for general and extras can vary greatly. Some are a few hundred others can be many thousands. For HF I started with a ICOM IC 7300 that cost me about 900 dollars. For most HF radios you also need a separate power supply and an antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some HAMs like to build kits instead of buying. simple CW kits may only cost 10 - 20 dollars, but you must know Morse code to use them. other more elaborate kits can cost as much as an radio.I would suggest getting some experience first before trying to build kits. They can be somewhat difficult to get working correctly. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My advice would be to try an find a local HAM club. there are clubs in most areas. Again due to the COVID 19 restrictions many are not meeting, but once they resume meetings go visit a club and talk to the people there. Most HAMs will gladly talk about their &quot;shacks&quot; where they have their radios and other equipment.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="4076" LastEditDate="2020-05-01T14:43:38.773" LastActivityDate="2020-05-01T14:43:38.773" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16561" PostTypeId="2" ParentId="16515" CreationDate="2020-04-29T14:41:56.237" Score="2" Body="&lt;p&gt;Modeling indicates that there are two steps you can take to reduce the interaction between the antenna and a conductive support:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Remove the conductive portion of the support from the space between the elements&lt;/li&gt;&#xA;&lt;li&gt;Insulate the support from ground&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;The image on the left, below, has a conductive element connected to ground; the image on the right does not. Note the substantial current in the support on the left and the near absence of current in the support on the right. The vertical radiation pattern from the antenna on the right loses about 0.25-dB of gain and about 2-dB of F/B compared to the same antenna without the support.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EOuam.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EOuam.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note that simply insulating a &quot;full length&quot; support from ground does not provide any relief, nor does it suffice to insulate a top section of metallic support from a bottom section.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-04-29T14:41:56.237" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16562" PostTypeId="2" ParentId="16515" CreationDate="2020-04-29T16:16:04.170" Score="3" Body="&lt;p&gt;The radials are there to present a low impedance, not a high one. The idea is to make the radials the lowest impedance thing around, though whether that's true or not depends on the mast, feedline, and other environmental factors beyond the antenna designer's control.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Mounting a vertical Yagi on a vertical mast is necessarily going to alter the antenna's behavior since the mast is essentially an additional element. You will want to minimize the interaction between the antenna and the mast since the contribution of the mast to the radiation pattern will probably not be a desirable one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other answers have demonstrated some models which show potential scenarios. It's tempting to overgeneralize these results, but keep in mind the way the antenna interacts with the mast is highly dependent on the geometry between the two. You'll have to model or empirically evaluate your specific situation to know what can work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately the only sure way to minimize interaction between the antenna and the boom is to get them apart, either through a horizontal member or a non-conductive one.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-04-29T16:16:04.170" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16563" PostTypeId="1" AcceptedAnswerId="16617" CreationDate="2020-04-29T21:20:07.943" Score="2" ViewCount="88" Body="&lt;p&gt;In my future shack I will have glass block windows consisting of 6 x 8 blocks and a 6 x 16 vent. I've been searching, but cannot find the best solution to pass coax through the windows.  I've thought about machining a plastic block to insert in the vent and insert bulkheads through the plastic block, and I've thought about replacing a glass block with a dryer vent, but that is unsatisfactory.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm looking for ideas to pass coax through a glass block window. Thanks in advance.&lt;/p&gt;&#xA;" OwnerUserId="9772" LastActivityDate="2020-05-04T10:38:45.670" Title="Glass Block Pass Through" Tags="&lt;coaxial-cable&gt;&lt;feed-line&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16564" PostTypeId="2" ParentId="16515" CreationDate="2020-04-30T12:48:36.577" Score="0" Body="&lt;p&gt;Here is some out-of-the-box thinking: rotate the yagi elements 45&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2x8xP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2x8xP.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The interaction with the (grounded) mast is virtually eliminated, plus the ground-reflection gain at least partially compensates for any polarization loss you might experience.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-04-30T12:48:36.577" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16565" PostTypeId="1" AcceptedAnswerId="16577" CreationDate="2020-04-30T13:36:15.017" Score="4" ViewCount="84" Body="&lt;p&gt;I am wondering about the exact pricing of kits. What is the range of each radio? How long do they last? Should I buy a portable or not? My complete budget is $100.&lt;/p&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="4076" LastEditDate="2020-05-01T14:17:05.900" LastActivityDate="2020-05-01T14:17:05.900" Title="Equipment Pricing" Tags="&lt;united-states&gt;&lt;jargon&gt;&lt;equipment&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16566" PostTypeId="1" AcceptedAnswerId="16579" CreationDate="2020-04-30T14:25:13.780" Score="11" ViewCount="3206" Body="&lt;p&gt;If you get a ham license, can you, later on, get a job with that license, or at least display it on a resume? Or are there further licenses after ham radio licenses?&lt;/p&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="4076" LastEditDate="2020-05-01T14:17:54.980" LastActivityDate="2020-05-01T14:17:54.980" Title="Can a ham license be used for a job?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16567" PostTypeId="1" AcceptedAnswerId="16569" CreationDate="2020-04-30T15:07:17.900" Score="5" ViewCount="110" Body="&lt;p&gt;What does the HAM license look like?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it a card? A document?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All I could find on google is &lt;em&gt;ham radio license plates&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="4076" LastEditDate="2020-05-01T14:18:44.400" LastActivityDate="2020-05-01T14:18:44.400" Title="What does a License look like?" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16568" PostTypeId="2" ParentId="16566" CreationDate="2020-04-30T15:25:06.430" Score="7" Body="&lt;p&gt;&lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=d4b3c60d2d60000a147f885bdee88264&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5#se47.5.97_1113&quot; rel=&quot;noreferrer&quot;&gt;§97.113 Prohibited transmissions&lt;/a&gt; states:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(a) No amateur station shall transmit:&lt;/p&gt;&#xA;&lt;p&gt;(1) Communications specifically prohibited elsewhere in this part;&lt;/p&gt;&#xA;&lt;p&gt;(2) Communications for hire or for material compensation, direct or indirect, paid or promised, except as otherwise provided in these rules;&lt;/p&gt;&#xA;&lt;p&gt;(3) Communications in which the station licensee or control operator has a pecuniary interest, including communications on behalf of an employer, with the following exceptions:&lt;/p&gt;&#xA;&lt;p&gt;(i) A station licensee or station control operator may participate on behalf of an employer in an emergency preparedness or disaster readiness test or drill, limited to the duration and scope of such test or drill, and operational testing immediately prior to such test or drill. Tests or drills that are not government-sponsored are limited to a total time of one hour per week; except that no more than twice in any calendar year, they may be conducted for a period not to exceed 72 hours.&lt;/p&gt;&#xA;&lt;p&gt;(ii) An amateur operator may notify other amateur operators of the availability for sale or trade of apparatus normally used in an amateur station, provided that such activity is not conducted on a regular basis.&lt;/p&gt;&#xA;&lt;p&gt;(iii) A control operator may accept compensation as an incident of a teaching position during periods of time when an amateur station is used by that teacher as a part of classroom instruction at an educational institution.&lt;/p&gt;&#xA;&lt;p&gt;(iv) The control operator of a club station may accept compensation for the periods of time when the station is transmitting telegraphy practice or information bulletins, provided that the station transmits such telegraphy practice and bulletins for at least 40 hours per week; schedules operations on at least six amateur service MF and HF bands using reasonable measures to maximize coverage; where the schedule of normal operating times and frequencies is published at least 30 days in advance of the actual transmissions; and where the control operator does not accept any direct or indirect compensation for any other service as a control operator.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The underlying principle here is &amp;quot;pecuniary interest&amp;quot;, which is reflected in &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=d4b3c60d2d60000a147f885bdee88264&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5#se47.5.97_13&quot; rel=&quot;noreferrer&quot;&gt;§97.3 Definitions&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(4) Amateur service. A radiocommunication service for the purpose of self-training, intercommunication and technical investigations carried out by amateurs, that is, duly authorized persons interested in radio technique solely with a personal aim and without pecuniary interest.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The only thing that trumps &amp;quot;without pecuniary interest&amp;quot; is emergency situations. During an emergency, you may use any means of communication possible to obtain help.&lt;/p&gt;&#xA;&lt;p&gt;And if your job involves ham radio as a possible emergency communication method, you can do the occasional drill as part of your job. For example, if you are employed by the Red Cross, and were conducting a drill for how you might respond to a natural disaster, that could be allowed.&lt;/p&gt;&#xA;&lt;p&gt;But you can't otherwise use the amateur service for your job. For example, you can't use it to dispatch trucks. For that you will need to use a commercial service.&lt;/p&gt;&#xA;&lt;p&gt;You can however use it to talk about your job, when you have no pecuniary interest in doing so. For example, you can talk with a friend after work about what a hard day you had at work. You can also (if your employer doesn't mind) use your ham radio while at work, if you're not doing work with the radio. For example if you were a parking lot attendant and had a lot of idle time to pass, you could talk about non-work stuff with other amateurs, or work on making FT8 contacts to complete some certification.&lt;/p&gt;&#xA;&lt;p&gt;And note, these regulations apply to what you &lt;em&gt;transmit&lt;/em&gt;. The FCC does not regulate in any way what you can put on your resume. If you think showing your license to an employer makes you a more valuable candidate, for example by showing your personal interest in radio, you can do that.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2020-04-30T15:25:06.430" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16569" PostTypeId="2" ParentId="16567" CreationDate="2020-04-30T15:54:36.763" Score="5" Body="&lt;p&gt;For most purposes, there is no &quot;official&quot; paper license in the United States anymore. Your record in the FCC's online database is what gives you a license to operate. However, if you like, you may download and print a PDF from their system. It looks like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1mphE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1mphE.png&quot; alt=&quot;FCC Amateur License Reference Copy&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;except that, for your own license, you can download one that says &quot;OFFICIAL COPY&quot; instead of &quot;REFERENCE COPY&quot;. As you can see, they provide cut-out marks for a certificate version that looks like it should fit a 5x6&quot; frame, and a &quot;wallet&quot; version that folds to the size of a standard ID card. Each one provides a place for you to affix a signature if you would like.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-04-30T16:02:46.657" LastActivityDate="2020-04-30T16:02:46.657" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16570" PostTypeId="2" ParentId="16565" CreationDate="2020-04-30T16:44:59.833" Score="3" Body="&lt;p&gt;There's really not a upper or lower limit to price -- it entirely depends on what capabilities you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;At the low end, you can get a receive only SDR for $20; several suggestions can be found at rtl-sdr.com&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several hand held UHF/VHF tranceivers available for under $50.  The quality of these are questionable, but they usually last at least 2 years.  Be sure to buy from a vendor that supplies a warranty.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are several single band HF kit radios that can be built for under $50 from an ARRL design contest several years ago.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Decent handheld FM UHF/VHF typically start at about $120.  Features to look for include: bands supported, dual or single receive, cross band capability, digital modes.  Usually each feature adds to the cost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Decent mobile UHF/VHF rigs also start at about $120.  Features to look for include the above features, and maximum transmit power (5w, 50w, 100w), and additional modes (AM, SSB).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A decent all mode all band HF radio might cost &lt;span class=&quot;math-container&quot;&gt;$900-$&lt;/span&gt;1500 new, but older models can be found used for half of that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These prices have been stable for more than 5 years (some more than 20 years), but the capabilities of the radios have shifted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a starting point.  Do your research, figure out what you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And I can't stress enough the power of building your own equipment, especially antennas!  $10 will go a long way for a self built antenna that can beat any bought antenna at 100x the cost.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-05-01T05:38:09.553" LastActivityDate="2020-05-01T05:38:09.553" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16571" PostTypeId="2" ParentId="16566" CreationDate="2020-04-30T16:59:39.073" Score="6" Body="&lt;p&gt;Amateur radio prohibits being paid to transmit.&#xA;However, nothing in the amateur radio rules prohibits you from using skills developed as an amateur radio operator in a professional setting.  Part of the purpose of amateur radio is to encourage development of such skills for professional use. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Putting amateur radio on your resume is an indicator that you have a certain level of technical ability and interest.  At the very least, it indicates you understand the radio terminology well enough to pass the test.  Some employers look for this and appreciate it on a resume, especially if your profession is not directly radio related but could involve interfacing with radios and electrical engineers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As to licenses beyond amateur radio -- there are many radio license types and certifications and degrees indicating competence in these areas.  Amateur radio may be a good gateway into these other areas as it introduces you to the foundation material needed for them.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-04-30T17:05:45.617" LastActivityDate="2020-04-30T17:05:45.617" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16572" PostTypeId="1" AcceptedAnswerId="16574" CreationDate="2020-04-30T18:29:44.390" Score="6" ViewCount="201" Body="&lt;p&gt;As I progress in my path to getting a ham license I notice that a lot of radio enthusiasts avidly talk about their radio shacks (or do they call it cabins?).&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Do I need that much space to start?&lt;/li&gt;&#xA;&lt;li&gt;Do I have to set up an antenna outside?&lt;/li&gt;&#xA;&lt;li&gt;Will it work if I have an  inside antenna?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;From what I hear they have handheld ham radios, but I'm guessing they don't have much range.&lt;/p&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="8717" LastEditDate="2020-10-26T20:10:38.520" LastActivityDate="2020-10-26T20:10:38.520" Title="Space Requirements" Tags="&lt;antenna&gt;&lt;united-states&gt;&lt;equipment&gt;" AnswerCount="7" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16573" PostTypeId="2" ParentId="16566" CreationDate="2020-04-30T18:40:34.213" Score="8" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;If you get a ham license, can you, later on, get a job with that license, or at least display it on a resume. Is that possible.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The other answers already cover this pretty thoroughly, so in short:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;it's fine to include it on your résumé as an educational/certification accomplishment, but…&lt;/li&gt;&#xA;&lt;li&gt;…you may not earn money for operating a ham radio station [with a few exceptions].&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Or is there further licenses after ham radio licenses.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The FCC issues many, many types of licenses. Which ones are &quot;further&quot; or &quot;better&quot; depends on your goals and perspective.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Without passing any sort of test, you can pay a fee and get a &lt;a href=&quot;https://www.fcc.gov/general-mobile-radio-service-gmrs&quot; rel=&quot;noreferrer&quot;&gt;GMRS license&lt;/a&gt; for a ten-year term. This is like an in-game purchase for &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/family-radio-service-frs&quot; rel=&quot;noreferrer&quot;&gt;FRS walkie-talkies&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;To carefully test a new idea, you might be able to get an &lt;a href=&quot;https://www.fcc.gov/news-events/blog/2017/04/14/open-business-fccs-new-experimental-licensing-system-accepting-new&quot; rel=&quot;noreferrer&quot;&gt;experimental license&lt;/a&gt; application approved.&lt;/li&gt;&#xA;&lt;li&gt;If you have a decent chunk of money and go through some paperwork, you can get a &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/industrial-business/industrial-business-licensing&quot; rel=&quot;noreferrer&quot;&gt;business license&lt;/a&gt; that e.g. your employees could use as they earn money.&lt;/li&gt;&#xA;&lt;li&gt;If you have an even bigger downpayment, and can fill out lots of technical and legal paperwork you could apply for a TV/radio &lt;a href=&quot;https://www.fcc.gov/media/radio/how-to-apply&quot; rel=&quot;noreferrer&quot;&gt;broadcast license&lt;/a&gt;; if you are friends with a high-level diplomat/ambassador you might even be able to get permission to set up a &lt;a href=&quot;https://www.fcc.gov/general/high-frequency-broadcasting&quot; rel=&quot;noreferrer&quot;&gt;shortwave broadcast&lt;/a&gt; station.&lt;/li&gt;&#xA;&lt;li&gt;If you have billions of dollars you could lease some spectrum and set up a &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/800-mhz-cellular-service&quot; rel=&quot;noreferrer&quot;&gt;cellular service&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Getting permission to run a &lt;a href=&quot;https://en.wikipedia.org/wiki/CubeSat&quot; rel=&quot;noreferrer&quot;&gt;CubeSat&lt;/a&gt; transponder is apparently in reach of many clubs/universities and is literally the &quot;highest&quot; radio license I can think of, if we're measuring in sea level terms &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'm sure there's at least several other types of licenses I've missed. For example, an FAA-licensed pilot basically gets an automatic &lt;a href=&quot;https://www.aopa.org/travel/international-travel/aircraft-radio-station-licenses-and-pilot-radio-operator-certificates&quot; rel=&quot;noreferrer&quot;&gt;radio license for their plane&lt;/a&gt;, and it's a bit similar with the radios on recreational boats.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;All that said, there is &lt;strong&gt;one particular license&lt;/strong&gt; that comes to mind, and that is the &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/commercial-radio-operator-license-program&quot; rel=&quot;noreferrer&quot;&gt;Commercial Operator License&lt;/a&gt;, better known to hams as the &lt;a href=&quot;https://en.wikipedia.org/wiki/General_radiotelephone_operator_license&quot; rel=&quot;noreferrer&quot;&gt;&lt;strong&gt;GROL license&lt;/strong&gt;&lt;/a&gt;. Informally, it's kind of considered the &quot;next step&quot; after earning an Amateur Extra and is potentially more valuable on a résumé because:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;You need a commercial operator license to operate, and/or to repair and maintain, specified ship, and aircraft radio communication stations.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Note however that you no longer need this license to work on the probably more lucrative business/cell radio equipment, although having it would presumably be a plus to someone hiring in those industries too. The state-of-the-art that powers $$$ things like 5G and 802.11ax and Ultra-wideband is more in the digital (signal processing) realm, not in memorizing the frequencies used to send faxes about the weather to seafarers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get to the point:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're interested in radio, a Technician-class license in the Amateur Radio Service is a &lt;em&gt;really really great place to start&lt;/em&gt;. That's your &quot;ticket&quot; to a whole lot of things. From there you can decide if you want to go for sport/social (upgrade to General/Amateur Extra) or as a radio officer/technician (earn the GROL) or as an RF engineer (learn SDR/DSP/EE).&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2020-04-30T18:57:00.833" LastActivityDate="2020-04-30T18:57:00.833" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16574" PostTypeId="2" ParentId="16572" CreationDate="2020-04-30T19:44:23.110" Score="2" Body="&lt;p&gt;You do not need a lot of space for ham radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I started with a Baofeng handheld radio. Then added a &lt;a href=&quot;https://ham.stackexchange.com/questions/1695/are-there-any-real-advantages-to-an-aftermarket-na-701-over-the-baofeng-stock-an&quot;&gt;slightly better antenna&lt;/a&gt;. That all fits in a drawer at home and a backpack while traveling. It works great in flat terrain and when on top of hilly terrain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What I needed for a bit more reliable communication was an external antenna that was both more efficient and could be placed higher. So I bought a nicely handmade &lt;a href=&quot;https://ham.stackexchange.com/questions/11730/is-a-copper-j-pole-antenna-better-than-a-slim-jim-for-transmitting&quot;&gt;&quot;slim jim&quot;&lt;/a&gt; antenna off eBay that had about 10' cable attached. I can hang that from a tree or even the ceiling inside and reach repeaters a few towns away that I couldn't even hear before. But even this antenna itself is flexible (made of old school television &quot;bunny ear&quot; cable), and so it rolls up and fits in the same drawer/backpack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you get into lower-frequency (HF) radio you usually need a bit more space, but it can be as little as some speaker wire you hang out across your yard or  &quot;loop&quot; antenna you can set in the corner of your room.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-04-30T19:44:23.110" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16575" PostTypeId="2" ParentId="16572" CreationDate="2020-04-30T19:45:44.133" Score="2" Body="&lt;p&gt;A handheld radio needs hardly any space, and is a great way to get started. A handheld with a decent antenna can easily communicate over 20+ miles, depending on terrain. It's good for local area communications. Most handhelds operate on VHF/UHF ham bands, most commonly the 2 m and 70 cm bands. These bands usually require line of sight. I've used mine indoors with a simple off-the-shelf antenna and have been given good signal reports at over 20 miles away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The HF bands (10-80 m) are the ones typically used for long distance communication. With the right conditions, you can communicate all the way around the world with these bands. Transceivers that can use these bands are typically larger than handhelds (with a few exceptions), and the antenna systems that are required are more involved. This is mainly because the size of an ideal antenna increases proportionally with the wavelength. So, for example, a dipole antenna for the 20 m band would be 10 times larger than one for the 2 m band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For these transceivers, it's best if you can set up an antenna outside, but it's not mandatory. Few amateurs have ideal setups; in practice we are all making compromises. Some people put antennas in their attics, which reportedly works fairly well. Personally, I don't have any way to set up a permanent antenna system, so I will sometimes put a vertical out my window. I certainly don't have any sort of a ham shack. If space is limited where you live, you might consider some portable options. Portable operation from summits or parks is a popular sub-discipline of amateur radio, and by necessity the gear that is used for that is small and lightweight. This might be a good option if space is limited where you live.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short, we all make compromises with our setups. You definitely do not need large amounts of space or an outdoor antenna to be involved with ham radio.&lt;/p&gt;&#xA;" OwnerUserId="10859" LastActivityDate="2020-04-30T19:45:44.133" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16576" PostTypeId="1" AcceptedAnswerId="16578" CreationDate="2020-04-30T20:21:14.623" Score="4" ViewCount="77" Body="&lt;p&gt;If I would buy a ham radio with an outdoor antenna, what would I need to do to make it work (e.g can I just stick it outside) especially because I live in Miami and Miami doesn't exactly have the best weather?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would putting an outdoor antenna require making an enclosure (including a roof)?&lt;/p&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="4076" LastEditDate="2020-05-01T14:19:46.567" LastActivityDate="2020-05-01T14:19:46.567" Title="Setting up an Outdoor Antenna" Tags="&lt;antenna&gt;&lt;equipment-protection&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16577" PostTypeId="2" ParentId="16565" CreationDate="2020-04-30T20:24:35.037" Score="1" Body="&lt;p&gt;Financially, \$100 isn't out of the question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the technician part of my own experience:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I paid about \$25 for &lt;a href=&quot;https://www.w5yi.org/catalog_details.php?pid=79&amp;amp;sort=4&quot; rel=&quot;nofollow noreferrer&quot;&gt;a Technician study guide&lt;/a&gt; (also available on Amazon) which might be helpful if &lt;a href=&quot;https://www.kb6nu.com/study-guides/&quot; rel=&quot;nofollow noreferrer&quot;&gt;one of the free options&lt;/a&gt; doesn't give enough background&lt;/li&gt;&#xA;&lt;li&gt;It usually costs just \$15 for each exam attempt, which includes the license application fee too assuming you pass. There are free &lt;a href=&quot;http://aa9pw.com/technician-license/&quot; rel=&quot;nofollow noreferrer&quot;&gt;practice tests&lt;/a&gt; available online to see if you're ready.&lt;/li&gt;&#xA;&lt;li&gt;I paid around \$35 for my first Baofeng/BTech handheld, and found it to be well built. Have someone help you program it right for ham usage, and limit the frequencies so you you can't accidentally mess with business/emergency channels.&lt;/li&gt;&#xA;&lt;li&gt;It was about \$15 to upgrade to longer whip antenna which might be a bit better than the one that comes with the radio. But see the next item…&lt;/li&gt;&#xA;&lt;li&gt;iirc I paid about \$25 or \$30 for an external roll up &quot;slim jim&quot; antenna with a built-in cable, from someone selling handmade ones on eBay. If you have to choose only one &quot;extra&quot; antenna, invest in this rather than a longer whip antenna since you can hang this up higher and the signal improvement is very obvious.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;You might also budget \$15–20 for a USB programming cable which hooks the radio to your computer so you can change settings with &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;Chirp&lt;/a&gt;, but probably someone in your local ham club could help you get it set up the radio anyway.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You'd be pushing your luck but there's a chance you could contact the International Space Station with not much more than the above equipment that fits in a drawer. (Don't count on it though without adding a $40–80 directional antenna which is gonna need a bigger drawer or a hook in the garage.) With just a license and a cheap handheld, you'll already have a good chance of using local VHF/UHF repeaters, make new contacts while traveling, try out EchoLink, etc. etc.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When my son (who is now 10yrs old) got his Technician license, we said we would buy him a handheld radio as a reward for the hard work he put into studying even when it was frustrating, and he was nervous to take the test in a room full of (very friendly!) grownups. Then some of those same grownups bought him a similar HT since they were glad to welcome a new young ham too!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So even if you buy all new equipment on your own, the Technician level is pretty affordable and I think it's a very good investment.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;If you upgrade to General class, however, that's another book and (if taking the test on a separate day) another exam fee. The equipment also gets a lot more expensive, plan on \$500 for a &quot;real&quot; (100W) HF transceiver and \$150 for an antenna matcher/SWR meter and maybe $25 for some cheap coax and a length of speaker wire. But if you're patient someone might sell you a spare setup for less. Especially once you pass your Technician you might find some older local hams who will help you invest in this next level.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another option is to assemble lower-power (&quot;QRP&quot;) kits like the &lt;a href=&quot;https://oz9aec.net/radios/omnia-sdr/omnia-sdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;Omnia SDR&lt;/a&gt; or the &lt;a href=&quot;https://www.hfsignals.com/index.php/ubitx-v6/&quot; rel=&quot;nofollow noreferrer&quot;&gt;BitX&lt;/a&gt; for a few hundred dollars (plus a \$10–20 power adapter, \$15 soldering iron, and a \$25 multimeter) and combine it with a ~\$75 tuneable loop antenna and tripod. These &quot;QRP&quot; kits are a bit safer too, but by the time you take your General exam you'll know how to avoid the risks.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2020-04-30T20:32:30.453" LastActivityDate="2020-04-30T20:32:30.453" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16578" PostTypeId="2" ParentId="16576" CreationDate="2020-04-30T20:36:07.287" Score="3" Body="&lt;p&gt;Antennas meant to be permanently installed are designed to withstand the elements. A proper installation would definitely not require an enclosure around the antenna. Pay attention to rated wind speeds when shopping around. There are even some antennas that are designed to withstand hurricane-force winds. For a permanent installation, you'll also need to carefully consider grounding and lightning protection, especially in an area prone to frequent thunderstorms.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I saw in some of your other questions that you are on a tight budget. With that in mind, it might be a better idea to buy, or even build, a cheaper antenna that you can put outside when you plan to operate. You can make a simple wire dipole with only speaker wire, and connect it to your radio with a binding post adapter. This way, you wouldn't have to pay a premium for a robust antenna system, since you would keep it indoors most of the time.&lt;/p&gt;&#xA;" OwnerUserId="10859" LastEditorUserId="10859" LastEditDate="2020-04-30T20:49:10.890" LastActivityDate="2020-04-30T20:49:10.890" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16579" PostTypeId="2" ParentId="16566" CreationDate="2020-04-30T20:40:47.123" Score="11" Body="&lt;p&gt;The answer is &lt;strong&gt;YES!&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Nothing in the rules prevents you from using the existence of your license to help you get a job.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you plan on going into a radio/TV/Cable engineering job, a amateur radio license(at the Extra level or Advanced Qualifications in Canada) can be very helpful to your career.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Study learn the concepts and &lt;strong&gt;understand&lt;/strong&gt; the math to pass the Extra exam.  During my studies, I worked out the how and why for each problem and developed similar problems to be worked out. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Having a &quot;photographic memory&quot; helps but it only goes so far. The intermediate steps are important, even if you have to work them out backwards(You may not see this now, but in the future, it will help).   &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Simply memorizing the answers does a disservice to you and the Amateur Community as a whole. You need to have a firm understanding of complex numbers, sine and cosine waves, phasor diagrams, AC theory, LC and RLC circuit design, Euler's equation, Smith charts, wave propagation, Electric fields and Magnetic flux fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer your question on licenses beyond Amateur Radio, the FCC offers the &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/commercial-radio-operator-license-program&quot; rel=&quot;noreferrer&quot;&gt;Commercial Radio Operator License Program&lt;/a&gt; This program is somewhat parallel to the amateur licensing, but is more oriented to commercial operators.(There are multiple levels of qualifications)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://www.sbe.org&quot; rel=&quot;noreferrer&quot;&gt;Society of Broadcast Engineers&lt;/a&gt; offers the &lt;a href=&quot;https://www.sbe.org/sections/CBT.php&quot; rel=&quot;noreferrer&quot;&gt;Certified Broadcast Technologist&lt;/a&gt; certification to Extra certified hams with two years of satisfactory experience in the broadcast field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope this post both encourages you and challenges you to learn what you didn't know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The more I learn; The more I learn that I do not know. After decades of experience, I can tell you that this is true, and even now: What I don't know exceeds that which I do know.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes, you cannot use your Amateur License for commercial purposes, but that restriction does not effect your ability to use it to get a job.&lt;/p&gt;&#xA;" OwnerUserId="16873" LastActivityDate="2020-04-30T20:40:47.123" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16580" PostTypeId="1" AcceptedAnswerId="16583" CreationDate="2020-04-30T21:05:10.907" Score="3" ViewCount="224" Body="&lt;p&gt;I hear a lot of people talking about getting in contact with space with their ham radio.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What do you hear?&lt;/li&gt;&#xA;&lt;li&gt;Do you talk to astronauts?&lt;/li&gt;&#xA;&lt;li&gt;Or: Is it just an expression?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="9621" LastEditDate="2020-05-04T13:26:08.777" LastActivityDate="2021-04-10T14:15:33.323" Title="Ham Radio and Space Communications" Tags="&lt;satellites&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16582" PostTypeId="2" ParentId="15424" CreationDate="2020-05-01T00:17:43.377" Score="4" Body="&lt;p&gt;FCC's page on this at &lt;a href=&quot;https://www.fcc.gov/general/fcc-policy-human-exposure&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fcc.gov/general/fcc-policy-human-exposure&lt;/a&gt; which links to several other documents including FCC OET Bulletin 56, &quot;Questions and Answers about&#xA;Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields&quot;, last updated 1999.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This document very carefully explains RF radiation and how ionizing radiation (UV and higher) causes DNA damage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It then explains the types of known effects of non-ionizing radiation (mostly heating which can result in burns) and the mechanisms involved.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It then goes into detail about how effects and damage other than heating have been reported, but that no conclusive evidence of this damage has been found. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, it is also very careful to say that just because evidence has not been found, there is no proof that there is no damage either, and that further research is both needed and being done.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This 36 page document is full of detail and includes additional more detailed references.  If you have unanswered questions on this topic, it is worth the read.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Short answer: we're not sure, but probably not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Longer answer: RF energy at any frequency is dangerous if power levels are high enough.  Different frequencies cause different damage.  Part of getting an amateur radio license is learning this so you know how to operate safely, both for you and those around your equipment.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-05-01T00:25:29.637" LastActivityDate="2020-05-01T00:25:29.637" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16583" PostTypeId="2" ParentId="16580" CreationDate="2020-05-01T00:48:02.220" Score="5" Body="&lt;p&gt;ISS has amateur radios on board.  Sometimes they even work.  Sometimes they're on.   Sometimes when they are on, there is an astronaut talking on it.   Details, schedules, frequencies, etc., can be found on the &lt;a href=&quot;https://www.ariss.org/contact-the-iss.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARISS contact page&lt;/a&gt;   (credit Greg Hewgill, thanks!)&lt;/p&gt;&#xA;&lt;p&gt;Over the years, the amateur radio equipment on ISS has been replaced, repaired, and broken repeatedly, but usually there's something there that works.  (My impression is that the most common damage is the memory in the radio being scrambled by cumulative space radiation.)&lt;/p&gt;&#xA;&lt;p&gt;When the radios are working, and the astronauts remember to leave them in the right mode, it is possible to contact the radio and get an automatic response.  Occasionally they are put in a transmit mode, repeating an automated message (such as SSTV images).&lt;/p&gt;&#xA;&lt;p&gt;When astronauts with amateur radio licenses have downtime and want to talk to someone in the real world other than NASA controllers and their family, sometimes they will talk to people through the ARISS equipment.&lt;/p&gt;&#xA;&lt;p&gt;ISS is in what is called a low Earth orbit.  As a consequence of this, it is only within radio contact with a location on the surface for about 9 minutes at a time before it goes over the horizon.  Longer contacts require relays.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-04-10T14:15:33.323" LastActivityDate="2021-04-10T14:15:33.323" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16584" PostTypeId="2" ParentId="16572" CreationDate="2020-05-01T05:50:44.913" Score="1" Body="&lt;p&gt;Hams like to talk about their &quot;shack&quot; because it's a dream to have one.  My &quot;shack&quot; is an extra shelf I added to my desk.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But a real ham shack is separate from the main house, to get away from all the noise like cheap noisy wall wart switching power supplies, plasma TVs, running brush motors, and similar.  Actually, this is a luxury and only a minor benefit.  Good antenna placement is more important.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The club version of the shack is a place to gather more than anything else.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Inside antennas are easy as long as you don't have a metal roof or rebar in your walls or aluminum siding or metal tinted windows.  Having said that, if you are transmitting more than 5 watts, you probably want your antenna outside, or at least 10-20 feet away from any people (or speakers), about as much as you want the antennas away from cheap power supplies, and for the same reason.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The other reason you want your antenna outside is to get it as high as possible.  If you're already on the third or fourth floor (or top floor) of a building that isn't metal shielded, maybe you already have that height inside.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But none of that is important for a beginner who just wants to do UHF/VHF, because you'll probably mostly be using repeaters, and the repeater is high so you don't have to be.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-05-01T05:50:44.913" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16585" PostTypeId="1" AcceptedAnswerId="16586" CreationDate="2020-05-01T11:15:56.927" Score="5" ViewCount="84" Body="&lt;p&gt;I started learning for my technician test and I noticed one of the FCC guidelines is that you have to &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Transmit your callsign at the beginning of radio contact, and every 10 minutes&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How does transmitting your callsign every 10 minutes work?&lt;/li&gt;&#xA;&lt;li&gt;What are you supposed to say? What does it sound like?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;So you're like talking to someone on the radio and then ten minutes later you say your callsign again?  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it go like&lt;/p&gt;&#xA;&#xA;&lt;p&gt;J: &lt;em&gt;&quot;Hey Bill.&quot;&lt;/em&gt; &lt;br&gt;&#xA;B: &lt;em&gt;&quot;Hey John&quot;&lt;/em&gt;&lt;br&gt;&#xA;…&lt;br&gt;&#xA;&lt;em&gt;Ten Minutes later:&lt;/em&gt;&lt;br&gt;&#xA;J: &quot;&lt;em&gt;By the way my callsign is KDSF12&lt;/em&gt;&quot;&lt;/p&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="4076" LastEditDate="2020-05-01T14:22:25.817" LastActivityDate="2020-05-01T14:22:25.817" Title="Transmitting Callsigns" Tags="&lt;united-states&gt;&lt;fcc&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16586" PostTypeId="2" ParentId="16585" CreationDate="2020-05-01T12:03:35.397" Score="7" Body="&lt;p&gt;Better double check.  There's no requirement to identify at the beginning of a communication (though it's common practice, and &lt;em&gt;was&lt;/em&gt; required at one time), only every ten minutes and &lt;em&gt;at the end&lt;/em&gt; of the communication.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;every ten minutes&quot; is often handled (say, on 2 meter or 440 band repeaters, which is where Technician licensees most commonly use voice communication) by identifying each time the repeater automatically does so.  So, if I were in conversation with another local ham on my nearest repeater, a listener might hear:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Okay, Donald, I'll try putting my antenna up in the oak tree when I&#xA;have time.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;W-4-N-C Repeater!&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;K-X-4-Q-P.  Yep, that antenna will work a lot better if you can get it even twenty feet up.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;W-N-4-Zed-P-H.  Oh, I don't doubt that, but I thought it was supposed&#xA;to work better than it is even just on the roof; I saw where someone&#xA;had one in their attic and they were getting out okay.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And communication continues.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also regularly hear things like &quot;For ID, this is [call sign]&quot;, again, often prompted by the repeater ID or by the other party identifying.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-05-01T12:03:35.397" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16587" PostTypeId="2" ParentId="16576" CreationDate="2020-05-01T13:44:36.593" Score="1" Body="&lt;p&gt;If you are doing VHF and UHF a simple antenna like a J pole can easily be made or if your prefer purchased. I have also liked making my own antennas. For HF frequencies a dipole  is also easily made form wire. I made a end feed half wave that also require winding a toroid to make the matching transformer, but that is not difficult to do. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;All antennas will be affected by weather and you should check them periodically looking for corroded connections and other issues. Most HAMS will get years out of their antennas. I try to use an antenna analyzer about once a month. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You should protect all connections from the weather. I wrap my coax connections in self sealing tape to prevent water form getting into them. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also be careful with home owners associations. their bylaws usually prohibit antennas, thought often simple wire antennas are not visible and don't get noticed.  &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-05-01T13:44:36.593" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16588" PostTypeId="2" ParentId="16572" CreationDate="2020-05-01T13:51:24.640" Score="1" Body="&lt;p&gt;My shack is a pair of short bookcases setting on top of desk next to my computer. On it is a power supply, an ICOM IC 7300 for HF and a TYT 9800 quad band mobile for UHF VHF. I also have 2 or 3 HTs and their chargers. I put a few certificates on the wall.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't need a lot of space to start, but I do notice the number of radios does somehow keep growing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it be nice to have several hundred square feet with dozens of radios and multiple operating stations all connected to several square miles of tower mounted antennas for all bands. Yes it would be, but the people keep drawing the wrong lottery numbers every time I buy a ticket, which admittedly is not very often. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-05-01T13:51:24.640" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16589" PostTypeId="2" ParentId="16572" CreationDate="2020-05-01T14:42:26.627" Score="1" Body="&lt;p&gt;Note that the actual radios can pretty much be arbitrarily small – in the end, your phone is a fully fledged radio too, just for other bands and other modes than amateur radio uses! (And technically, it does things that are way more impressive than any amateur radio you can buy does.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, once you want a radio that has very much output power (some amateur radios do 100 W or more of RF power – to me as a communications engineer, that is &lt;em&gt;crazy&lt;/em&gt; much power.), that power also unfortunately produces heat, and that heat needs to go somewhere, so these higher-power radios needs some heatsinks, fans and whatnot to keep them cool.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But technically, your radio can really without problem fit in your hand.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The thing that can't technically be made arbitrarily small is the antenna. An effective antenna is always in length somewhere in the &lt;em&gt;order of magnitude&lt;/em&gt; of a quarter of a wavelength – you can build smaller ones or larger ones, but the smaller, the more trade-offs the antenna has to do. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's why people in amateur radio also don't usually say &quot;the 14 MHz band&quot;, they say &quot;the 20m band&quot;, even if you put in the frequency in your radio in Hz, not in m. 20 m is roughly the wavelength for that band. So, if you see someone with an antenna in their yard that's say 4 to 20 m in size, chances are they are trying to have a very good antenna for the 20m band. Of course, again, a smaller antenna works, but it &quot;costs&quot; you received signal quality, and that means you can't successfully receive transmissions from further away or with lower power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many amateur radio users use very low-frequency bands, and through the speed of light, the frequency and the wavelength are linked (&lt;span class=&quot;math-container&quot;&gt;$\lambda = \frac cf$&lt;/span&gt;); the lower the frequency, the larger the wavelength. But, really, the 2m band (144 MHz and around) takes you very far – and an antenna for that isn't necessarily cumbersome.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-05-01T15:00:50.157" LastActivityDate="2020-05-01T15:00:50.157" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16590" PostTypeId="2" ParentId="16559" CreationDate="2020-05-01T14:58:45.377" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;How much does it cost?&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Depends on who's taking your exam, but 15$ is what ARRL takes, IIRC.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;How long does it take?&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The exam itself: not very long. Learning: depends on how familiar you already are with a bit of the technology, and how fast you can learn about operating and laws.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, since you're 13, you're generally in school, I'd guess, so you're &lt;em&gt;used to learning&lt;/em&gt;, and that's a big advantage you have over adults! (life pro tip: never stop learning, it's really hard to start again once you haven't done it a while)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then again, being young means you haven't had all of the physics courses in school, and that means you'll certainly spend an extra day or week on the physics stuff, but that really depends! Some things are easy for some people, others aren't :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, there's a lot of websites to study the basics, good place to start!&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;How much does a ham radio cost?&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Well, a device can be really cheap, I think you've already got an answer to that in another question of yours, but basically: you really don't have to spend 100s of dollars. Start small. If you can't wait to play with a radio before you have your license, spend 10 to 30 $ on a &quot;RTL dongle&quot;, that is a receiver only, which you plug into your computer's USB port, and then run some software on that computer to extract the audio that's transmitted by someone else, or the digital data. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;What could you do with it?&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;An application very popular with &quot;hams&quot; is to actually talk over their radio. Often, the thrill is that you talk to someone very far away – without having a cable run there, like you have in most internet communications. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;But that's far from all you can do:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, most communications these days on the HF band aren't Morse or speech, they are things like FT-8, a digital mode that is incredibly robust – meaning, you can receive it with a &quot;not very good antenna&quot;, and transmit it with &quot;not much&quot; power, and someone far away can still receive it! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Other amateur radio enthusiast use their license to experiment with radio communications more than for communication itself – for example, there's people that are using the undersides of airplanes as they pass over them as &quot;radio signal mirrors&quot; to talk to people &quot;hidden&quot; behind a mountain that they otherwise couldn't reach. You can also do things like Radar with your transmitter, as long as you don't disturb the others and clearly identify yourself (see your callsigns question!).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet other amateurs build up data communication networks – think WiFi, but with lower rate, but connecting local ham networks to far away networks. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people are part of a network of devices that talk to each other – APRS. That is basically what is &quot;IoT&quot; today, long before the buzzword &quot;internet of things&quot; was a thing – and started back when the internet still wasn't something anyone outside universities had.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I, personally, take general interest in the technologies used, and how people employ them, and how to make inefficient systems be better. (For example, APRS is, from a scientist's point of view, incredibly stupid in a lot of ways. It works well – and I enjoy that – but it would be very cool if within the next couple of years, better things would become the usual way of doing the same and more!)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-05-01T14:58:45.377" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16591" PostTypeId="2" ParentId="16559" CreationDate="2020-05-01T15:39:27.390" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What could you do with it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I believe this is the most important question of all. Within the the regulations, the answer is, &quot;Your imagination is the only limit!&quot; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can you use it for your job? Yes - if you want to dream up, prototype, build, market and/or sell radios, antennas and their many accessories! This is no joke - all the products you see in magazines and on the web had to come from somewhere and all the people who contributed to them feel the personal success of creating a useful and valuable product. Many features of ham gear apply to products for commercial, professional, emergency service and other markets, so the skills are all transferable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can it &lt;em&gt;apply&lt;/em&gt; to your job? Again, yes, especially if your job includes communicating with people of diverse interests and backgrounds. In my experience, this is especially true as the business world becomes ever more international; ham radio experiences allow you to feel as if you're in the conference room with people half a world away, and make them feel your presence, too. &quot;DXing&quot; - making contact with people around the globe - is a great way to develop these skills.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Want to help out in your community? Ham radio was conceived for exactly this purpose. Sure, cell phones are great for one-on-one conversations, but not so much for many-to-many communications over even modest areas, especially places that are &quot;off the grid&quot; - which includes many of the most beautiful places on Earth. How about providing communications for a competitive amateur race through the mountains or a fundraiser in the city?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You can even help people in other parts of the world who are suffering from the effects of natural disasters. Whether it's an earthquake, tsunami, wildfire or hurricane, radio amateurs are always there to provide emergency communications, help friends and families monitor the condition of their loved ones, and get equipment to their fellow hams to complete the mission. Annual events like ARRL &lt;em&gt;Field Day&lt;/em&gt; test our mettle by challenging us to set up and operate outdoor stations for a continuous 24-hour period every year, forcing us to confront the challenges we might expect to face after a natural disaster and helping us empathize with their unfortunate victims.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, if all that's not enough, you can use ham radio to investigate the physical world around you. How radio waves propagate long distances by bouncing off the ionosphere and even off the trails of ionized particles left in the wakes of meteors. How radio waves reflect off of or are absorbed by earth, water and man-made structures. How electromagnetic disturbances propagate along conductors to produce radio waves and how those waves can be focused to improve signal strength in a particular direction. Listen to emanations from the cosmos, even the remnants of the Big Bang believed to be the origin of our universe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what &lt;em&gt;can't&lt;/em&gt; you do with ham radio?&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-05-01T16:17:51.660" LastActivityDate="2020-05-01T16:17:51.660" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16592" PostTypeId="2" ParentId="16572" CreationDate="2020-05-01T17:46:23.433" Score="0" Body="&lt;p&gt;Not much space at all is required for basic radio equipment.  There are many handheld, portable, QRP, and kit radios that will easily fit in a small backpack or drawer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For HF antennas, big, outdoors, and high up is almost always better.  With indoor antenna's you have to be careful about coupling and interference (RFI &amp;amp; EMI) with and from the house wiring, lighting, and appliances.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;VHF, you can do with stuff that fits in your coat pocket.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-05-01T17:46:23.433" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16593" PostTypeId="2" ParentId="16572" CreationDate="2020-05-01T18:59:13.753" Score="1" Body="&lt;p&gt;My shack is a desk in my den/library:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/y9juA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/y9juA.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2020-05-01T18:59:13.753" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16594" PostTypeId="1" AcceptedAnswerId="16595" CreationDate="2020-05-01T20:00:48.127" Score="8" ViewCount="5522" Body="&lt;p&gt;Can I use a satellite dish as a ham radio antenna? I was thinking that because there are two unused, working satellite dishes that have all appropriate wires attached conveniently to the roof of my house. Would there be a way to use the dish as a ham antenna? Maybe it cn be used with a few modifications. All google searches came up blank. &lt;/p&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="16949" LastEditDate="2020-05-01T20:28:14.283" LastActivityDate="2021-05-22T13:07:58.790" Title="Can you use a satellite dish for a ham radio antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;equipment-design&gt;&lt;equipment&gt;&lt;improvised&gt;" AnswerCount="6" CommentCount="2" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16595" PostTypeId="2" ParentId="16594" CreationDate="2020-05-01T20:35:55.753" Score="0" Body="&lt;p&gt;Most TV satellite signals are between 915-MHz and 2.1-GHz. The 23-cm band (1240-MHz to 1300-MHz) does fall in this range, and a few hams have repurposed dishes for things like EME (Earth-Moon-Earth or &quot;moon bounce&quot;) operation, but it's not a band many hams use.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The feed line for TV is usually 75-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, not the 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; typically used with ham radios. The LNB (Low Noise Block, TV downconverter) probably has filters that reject most ham frequencies to cut down on interference. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In short, for traditional 2-meter VHF and 440-MHz UHF it would not work and would require extensive modification. It would be far simpler to put a J pole or maybe a Yagi if you want a directional antenna. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="9621" LastEditDate="2020-05-04T12:36:02.390" LastActivityDate="2020-05-04T12:36:02.390" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16596" PostTypeId="2" ParentId="16594" CreationDate="2020-05-01T21:01:40.213" Score="2" Body="&lt;p&gt;It appears that the contemporary-sized satellite dish is popular with X-band operators - that's the 10GHz band! See this &lt;a href=&quot;http://www.ham-radio.com/sbms/presentations/AF6NA/exciting_10ghz_world-af6na.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;presentation&lt;/a&gt; from the &lt;a href=&quot;http://www.ham-radio.com/sbms/&quot; rel=&quot;nofollow noreferrer&quot;&gt;San Bernardino Microwave Society&lt;/a&gt; for some examples.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-01T21:01:40.213" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16598" PostTypeId="2" ParentId="16594" CreationDate="2020-05-01T22:10:40.563" Score="13" Body="&lt;p&gt;You can use a satellite TV dish antenna for amateur radio use but how you use it depends on what frequency you want to operate on.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The satellite dish antenna is two basic parts, the parabolic reflector and the feed (at the focal point of the parabola).  The gain of the dish depends on what frequency you are using and the diameter of the dish.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A typical satellite TV dish probably has a LNA (low noise amplifier) at the focal point, along with a block down converter to change the received TV signal down to around 1 GHz so that it can be sent over a long coax cable to the TV with less loss (losses in cheap coax at 10 Ghz are pretty high).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately you can't easily reuse the satellite TV LNA and down converter (LNB) because it is designed for receive only and you will want be able to transmit.  So you will have to build your own feed for the dish.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Those satellite TV dishes are about 20 inches in diameter, too small to use for 220 or 144 Mhz VHF (unless you want to make a slot antenna, more below).  It could work for 440 Mhz UHF but the gain would be so low (~6 dB @440 Mhz) that it would be easier to just build a yagi.  It's much better at 1200 Mhz, where the gain would be around 14 db, or at 2.4 Ghz about 20 db.  A small dish works great at 10 Ghz where you get about 32 db of gain.  There is a gain chart is &lt;a href=&quot;https://ham.stackexchange.com/a/16599/13625&quot;&gt;this answer here&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are articles explaining how to convert a satellite TV antenna to a stealth 2m (146 Mhz) slot antenna, such as &lt;a href=&quot;https://w6nbc.com/articles/20xx-dishslot.pdf&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;https://www.dxzone.com/dx33256/dish-antenna-for-2-meters-band.html&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;.  You cut a slot in the parabolic dish which changes the dish from a passive reflector into the active element of the antenna.  A horizontal slot gives you a vertically polarized antenna.  Search for &quot;ham radio slot antenna satellite dish&quot; to find other examples and instructions.&lt;/p&gt;&#xA;" OwnerUserId="13625" LastEditorUserId="13625" LastEditDate="2020-05-02T18:56:24.763" LastActivityDate="2020-05-02T18:56:24.763" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16599" PostTypeId="2" ParentId="16518" CreationDate="2020-05-01T22:40:00.903" Score="0" Body="&lt;p&gt;For parabolic reflectors the larger the reflector the higher the gain (assuming the feed is illuminating the entire reflector).  Here is a nomogram from &quot;Reference Data for Radio Engineers&quot;.  You draw a line from the frequency to the diameter and the middle column gives you the gain.  As diameter goes up, so does the gain.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the example line at 3000 Mhz, with a 6 foot dish, you get 32 db of gain.  Go up to a 10 foot dish and you get 36 db of gain.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sPKbv.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sPKbv.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13625" LastActivityDate="2020-05-01T22:40:00.903" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16600" PostTypeId="2" ParentId="16594" CreationDate="2020-05-02T08:52:59.760" Score="5" Body="&lt;p&gt;Apart from using it as a ham radio satellite antenna (eg. for QO-100) or a microwave terrestrial antenna, you can turn it into a VHF slot antenna. Here is an example: &lt;a href=&quot;https://w6nbc.com/articles/20xx-dishslot.pdf&quot; rel=&quot;noreferrer&quot;&gt;https://w6nbc.com/articles/20xx-dishslot.pdf&lt;/a&gt; (keyword: &quot;satellite dish slot antenna&quot;).&lt;/p&gt;&#xA;" OwnerUserId="6699" LastActivityDate="2020-05-02T08:52:59.760" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16601" PostTypeId="2" ParentId="16594" CreationDate="2020-05-02T12:39:24.120" Score="4" Body="&lt;p&gt;The dish itself is pretty much universal - it will reflect and focus any radio waves that are short enough not to go around (say, 1/4 of the dish radius) and long enough not to be scattered off the paint (say, centimeter and up, but the particular dish may be good down to 1mm).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This interval contains few amateur bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is up to you to fit some transmitter and/or receiver at the focus.&lt;/p&gt;&#xA;" OwnerUserId="16981" LastActivityDate="2020-05-02T12:39:24.120" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16602" PostTypeId="2" ParentId="10556" CreationDate="2020-05-02T18:29:42.917" Score="1" Body="&lt;h2&gt;No.&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;Part 97 (FCC rules for amateur radio) place limits on &lt;em&gt;width of spectrum usage&lt;/em&gt;. For frequency/phase oriented modes such as AFSK, FSK, and PSK they are specified in symbol rate since increasing symbol rates (bauds) result in a widening of the sidebands created by these modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Symbol rates / baud figures are not data rates&lt;/strong&gt;. Multiple bits can be packed into a single symbol. It is up to the mode involved and the available signal-to-noise ratio to determine the number of bits per symbol.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For other means of modulation such as OFDM where the sidebands/spillover is very small and sharp, the FCC limitations are directly specified as the maximum width of spectrum used by the mode. For example, on 70cm and 1.25m this is 100khz.&lt;/p&gt;&#xA;" OwnerUserId="14335" LastActivityDate="2020-05-02T18:29:42.917" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16604" PostTypeId="1" CreationDate="2020-05-03T01:03:32.427" Score="3" ViewCount="1328" Body="&lt;p&gt;Can you pick up police signals with ham radio? Secondly, are you able to contact emergency services with ham radio. For example: In the middle of a hurricane, with no power, can you technically use a battery-powered radio to contact the police in an emergency (like for flooding or injuries), or is it illegal/impossible. Thanks.&lt;/p&gt;&#xA;" OwnerUserId="16949" LastActivityDate="2020-05-03T04:59:50.060" Title="Can a ham radio pickup police signals?" Tags="&lt;emergency&gt;&lt;transmission&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16605" PostTypeId="1" CreationDate="2020-05-03T01:21:21.470" Score="2" ViewCount="182" Body="&lt;p&gt;I'm new to ham and I'm wondering how to find test locations/study guides. I heard about this from a friend.&lt;/p&gt;&#xA;" OwnerUserId="16960" LastActivityDate="2020-05-04T14:28:48.213" Title="How do you find a test location?" Tags="&lt;license&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16606" PostTypeId="2" ParentId="16605" CreationDate="2020-05-03T01:22:34.067" Score="2" Body="&lt;p&gt;I actually found the website. &lt;a href=&quot;http://www.arrl.org/find-an-amateur-radio-license-exam-session&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/find-an-amateur-radio-license-exam-session&lt;/a&gt; Thanks.&lt;/p&gt;&#xA;" OwnerUserId="16960" LastActivityDate="2020-05-03T01:22:34.067" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16607" PostTypeId="2" ParentId="16605" CreationDate="2020-05-03T02:10:01.870" Score="2" Body="&lt;p&gt;You can also use this link &lt;a href=&quot;https://www.hamradiolicenseexam.com/where-to-take-amateur-radio-exam.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.hamradiolicenseexam.com/where-to-take-amateur-radio-exam.htm&lt;/a&gt; Hope this was helpful&lt;/p&gt;&#xA;" OwnerUserId="16988" LastActivityDate="2020-05-03T02:10:01.870" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16608" PostTypeId="2" ParentId="16605" CreationDate="2020-05-03T02:43:16.797" Score="2" Body="&lt;p&gt;Assuming you are in the US, start with the ARRL License Manual, it costs $32.95 &lt;a href=&quot;https://www.arrl.org/shop/Ham-Radio-License-Manual/&quot; rel=&quot;nofollow noreferrer&quot;&gt;from the ARRL&lt;/a&gt; or you can find it at any bookseller. The ARRL, or the American Radio Relay League, is the national association for amateur radio and their web site also has a wealth of information for the aspiring ham, including a &lt;a href=&quot;http://www.arrl.org/find-an-amateur-radio-license-exam-session&quot; rel=&quot;nofollow noreferrer&quot;&gt;search for exam sessions&lt;/a&gt;. Also, the FCC recently posted a &lt;a href=&quot;https://docs.fcc.gov/public/attachments/DA-20-467A1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;public notice (PDF)&lt;/a&gt; stating that &quot;nothing in the FCC’s rules prohibits remote testing&quot; so once you locate a local VE (Volunteer Examiner) you can ask them about whether they offer that if you're concerned about testing in person during the current pandemic. The ARRL has some &lt;a href=&quot;http://www.arrl.org/news/remotely-administered-amateur-exam-systems-showing-promise&quot; rel=&quot;nofollow noreferrer&quot;&gt;more information&lt;/a&gt; on the topic of remote testing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The best study guide I have found is the KB6NU No-Nonsense guides; the Technician guide is available &lt;a href=&quot;https://www.kb6nu.com/study-guides/&quot; rel=&quot;nofollow noreferrer&quot;&gt;as a PDF for free&lt;/a&gt;. Technician is the first level of licensing and is also what the ARRL book prepares you for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These two resources work together, you will want both of them. The License Manual goes in depth into the topics you will need to learn and is essential to get an understanding of all you need to know to not only pass the test but to set up and operate your station safely and effectively. The KB6NU study guide is the refresher you'll want to cram just before the test, as it includes every test question and its answer with just enough context to get the gist, without any of the multiple-choice wrong answers to distract you - but it doesn't explain anything in depth so without having first studied the manual you'll quickly be lost.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, you'll want to take some practice tests. A popular resource is HamStudy.org. The website has &lt;a href=&quot;https://hamstudy.org/tech2018&quot; rel=&quot;nofollow noreferrer&quot;&gt;flashcards and practice tests&lt;/a&gt; along with condensed explanations, similar to KB6NU's guides, and can keep track of your progress as you take the practice tests as many times as you want until you feel comfortable that you can pass the test. They also have an app for $3.99 that lets you do all of that offline.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Good luck! It's a very rewarding hobby and I'm glad you're interested in joining us on the air!&lt;/p&gt;&#xA;" OwnerUserId="4452" LastEditorUserId="4452" LastEditDate="2020-05-04T14:28:48.213" LastActivityDate="2020-05-04T14:28:48.213" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16609" PostTypeId="2" ParentId="16604" CreationDate="2020-05-03T03:17:09.963" Score="1" Body="&lt;p&gt;Some ham radios are capable of receiving many signals outside of the ham bands, including in some cases police or emergency services. Some are even capable of transmitting on those frequencies. And there is one and only one circumstance in which it's legal for a ham to transmit on any frequency, licensed or not: during an immediate emergency &lt;em&gt;when no other communication method is available&lt;/em&gt; and attempts to get help via proper ham bands have failed.&lt;/p&gt;&#xA;&lt;p&gt;Specifically, &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/amateur-radio-service/amateur-communications-operations#operations-in-emergencies&quot; rel=&quot;nofollow noreferrer&quot;&gt;the FCC's FAQ&lt;/a&gt; on the topic says:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Section 97.403 states that no provision of the Rules prevents the use by an amateur station of any means of radiocommunication at its disposal to provide essential communications in connection with the immediate safety of human life and immediate protection of property when normal communication systems are not available.&lt;/p&gt;&#xA;&lt;p&gt;Section 97.405 states that no provision of the Rules prevents the use by an amateur station in distress of any means at its disposal to attract attention, make known its condition and location, and obtain assistance. A sinking ship is a good example. It further states that no provision of the Rules prevents the use by a station, in that exceptional circumstance, of any means of radiocommunications at its disposal to assist a station in distress.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;So, in your example, in the middle of a hurricane your ham license would allow you to use your radio on any frequency it can transmit on, to talk to anybody who can help, &lt;strong&gt;only&lt;/strong&gt; if there is an immediate danger and you've exhausted all other means of communication. If everyone's phones have washed away and you're on the roof with flood waters lapping at your feet and you've gotten no response on your local repeaters and the calling frequencies, by all means call the police on their own frequency if you can - but be prepared for some serious questions as they don't generally tolerate that sort of thing.&lt;/p&gt;&#xA;&lt;p&gt;And if it isn't an absolute emergency, you not only risk your license but you may disrupt the very services others are relying on who are in such an emergency!&lt;/p&gt;&#xA;" OwnerUserId="4452" LastEditorUserId="-1" LastEditDate="2020-06-18T08:29:26.797" LastActivityDate="2020-05-03T03:34:05.510" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16610" PostTypeId="1" CreationDate="2020-05-03T04:03:43.367" Score="7" ViewCount="322" Body="&lt;p&gt;&lt;strong&gt;&lt;em&gt;Note: more measurements added after graphs below&lt;/em&gt;&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I recently acquired a RigExpert antenna analyzer and I am trying to learn how to use it to test cables.  I took two cables to start with to try and understand what it shows and what the graphs mean.  &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;LMR-240, 7.9m long (2 months old)&lt;/li&gt;&#xA;&lt;li&gt;RG-8/U, 18.3m long (&gt;25 years old)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I thought I would use these two cables to learn how this works.  I ran the TDR (Time Domain Reflectometer) sweep on both cables, with an open circuit at the far end. The LMR-240 matches one of the book's SR (Step Response) graph samples, the RG-8/U does not match any of the samples.  The book doesn't really explain much about what they mean and I haven't been able to find anything online that explains how to interpret the SR graph.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I get that reflections show up as peaks on the IR graph, is that it?  Since there is an open circuit at the end of these cables, I can see the electrical length from the IR graph, about 6.5m (21 ft).  The physical length is 7.9m (26 ft), so the velocity factor is 6.5/7.9 or 83% for the LMR-240.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What does the SR (Step Response) graph actually display and what does it mean?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't understand what it means when the SR goes negative on the RG-8 cable.  The cable is inductive?  I tried testing from the other end of the RG-8 cable instead and I got the exact same SR graph, so it's not that something is wrong with that end of the cable.  I'm thinking the capacitance of the dielectric is low, making the cable more inductive, messing up the cable's impedance, but that's just a guess based on sample graph for an Inductive Terminated cable.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The detail data for the RG-8/U shows that the impedance is only 20.8 at 16.96m down the cable.  Obviously it should be 50 ohms, but perhaps the dielectric is dried out or something like that is bad.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;* New Information *&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I measured the characteristic impedance for the RG-8 cable and it comes out to 32 ohms, off from the expected 50 ohm impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I also reran the TDR scan using the AntScope2 software (PC software provided by RigExpert) and the graph is quite different.  First the IR graph is the same, but the SR graph is different, instead of going negative it stays flat.  A more normal graph similar to the LMR-240 cable's graph.  The odd part though is that it shows the cable end at 4.2 meters instead of at 18.4 meters.  For some reason AntScope2 thinks the cable is much shorter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;LMR-240:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CfNv5.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CfNv5.jpg&quot; alt=&quot;IR/SR graph for LMR-240&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;RG-8/U:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DudVd.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DudVd.jpg&quot; alt=&quot;IR/SR graph for RG-8/U&quot;&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/0WZUm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0WZUm.jpg&quot; alt=&quot;Data for RG-8/U at 16.96m down the cable&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;AntScope2 graph&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;&lt;a href=&quot;https://i.stack.imgur.com/JP3NF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JP3NF.png&quot; alt=&quot;AntScope2 Graph for RG-8/U&quot;&gt;&lt;/a&gt;&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;SR graph samples:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7kohq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7kohq.jpg&quot; alt=&quot;SR graph samples from RigExpert&amp;#39;s manual&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13625" LastEditorUserId="13625" LastEditDate="2020-05-07T18:37:12.023" LastActivityDate="2020-05-07T18:37:12.023" Title="What does an antenna analyzer tell me about these coaxial cables?" Tags="&lt;coaxial-cable&gt;&lt;measurement&gt;&lt;transmission-line&gt;&lt;testing&gt;&lt;antenna-analyzer&gt;" AnswerCount="2" CommentCount="8" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16611" PostTypeId="2" ParentId="16604" CreationDate="2020-05-03T04:53:59.720" Score="0" Body="&lt;p&gt;Can a ham radio pick up police signals?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yes and no -- many ham radios are &quot;wide band receive&quot; capable, meaning they can receive outside of the ham bands.  These extra receive frequencies sometimes include police frequencies.  In some states, it is illegal to listen on those frequencies, but an exception is made for amateur radio operators and some others.  However, many police frequencies are now encrypted, and there is no way to decrypt them without the encryption key.  All of this varies wildly based on your location and what the local police do with their radios.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can a ham radio contact emergency services during a hurricane?  Again, yes and no.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio by itself does not give you the ability to contact emergency services typically.  However, there is a national organization called ARES with local branches that are typically directly involved with the local police on a volunteer basis.  Many counties have ARES clubs, and members of those clubs are deployed to hurricane shelters specifically so the county and the shelter can  still communicate if other means of communication fail.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, can you contact emergency services in a hurricane?  If you are an ARES member, you essentially become part of emergency services.  But as an individual at home, you can listen in on that channel but probably should not interfere with it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, the Red Cross, Salvation Army, Hurricane Watch Net, and several other organizations activate over ham radio during hurricanes.  Most are looking to serve large groups, but interest in individuals varies between these organizations.  All of these groups need trained local amateur radio volunteers. &lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-05-03T04:59:50.060" LastActivityDate="2020-05-03T04:59:50.060" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16612" PostTypeId="2" ParentId="16594" CreationDate="2020-05-03T05:14:05.203" Score="5" Body="&lt;p&gt;I want to point out an important aspect that is only implicit in the other answers. At the frequencies at which they can be efficiently used, dish antennas are (by design) &lt;em&gt;highly directional&lt;/em&gt;. That is, you have to point them quite precisely in the direction you want to transmit and/or receive; the benefit is that less power is needed for communication because power isn't &quot;wasted&quot; sending radiation in other directions. This is what it means to have high gain (mentioned in progrmr's answer).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Such antennas are convenient for receiving satellite TV because the signal is from a &lt;em&gt;geostationary&lt;/em&gt; satellite, so the dish can be accurately pointed once and then left in place. (The satellite transmits in many directions, but as seen by each individual receiver it is a distant, weak source in a fixed direction.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While ham radio antennas are often somewhat directional (somewhat high-gain) in order to work better with less power, taking this to an extreme can make them very difficult to get pointed right, especially if you don't know in advance exactly where you're trying to talk to. In the presentation linked by Brian K1LI about dish communication, note the statement &quot;Making a QSO [a contact] is a very special event.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In other, lower frequency bands, it is normal to make many contacts in various places with a low-gain (more omnidirectional) antenna that does not have to be re-aimed as much or at all. That is the type of ham radio experience that may be more appealing to beginners.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the big picture is that use of a satellite dish is a niche area of ham radio, for those looking for more of an exotic challenge.&lt;/p&gt;&#xA;" OwnerUserId="16991" LastActivityDate="2020-05-03T05:14:05.203" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16615" PostTypeId="2" ParentId="16580" CreationDate="2020-05-03T11:42:44.860" Score="-1" Body="&lt;p&gt;You can try &lt;a href=&quot;https://www.n2yo.com/?s=25544&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.n2yo.com/?s=25544&lt;/a&gt; to track the satellite. But I see in your posts that you live in Miami, and the ISS doesn't usually pass over there, so it might not be possible&lt;/p&gt;&#xA;" OwnerUserId="16993" LastActivityDate="2020-05-03T11:42:44.860" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16616" PostTypeId="2" ParentId="16488" CreationDate="2020-05-04T08:00:19.230" Score="2" Body="&lt;p&gt;Seems like finally I was able to solve the problem!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some time ago I've generated VOLK optimized profile according to the &lt;a href=&quot;https://github.com/csete/gqrx/blob/master/README.md#usage&quot; rel=&quot;nofollow noreferrer&quot;&gt;developer recommendations&lt;/a&gt;. After that I haven't been using real SDR receptions for several months and then faced a problem described in first post. Now I've remembered it and just deleted this optimal profile. Once that was done I was able to receive and decode APT transmissions just perfectly! Moreover, DRM radio works fine too! I think I'll file a bug for GQRX about this issue with VOLK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding LRPT reception: I've tried &lt;code&gt;mlrpt&lt;/code&gt; software and it works brilliant while &lt;code&gt;glrpt&lt;/code&gt; still shows me very strong signal and gives no PLL lock. I think my dongle is getting overloaded by some strong signal and auto AGC setting makes things even worser in this case. I can't figure out the exact cause of it right now. Should recheck with manual gain settings, though.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many thanks to everyone participated in the discussion! Here was a lot of useful info for personal education and experience.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE 1:&lt;/strong&gt;&#xA;I've investigated the situation even further and found that actually this is not the VOLK to blame! When I removed VOLK config last time I also set Frequency Correction in GQRX to zero again (was -1.6 ppm). Then I thought that it's VOLK who ruins further decoding. However, I've re-generated VOLK profile again while leaving freq. correction at zero and things work just fine! After that I've stashed VOLK config and set freq. correction to -1.6 ppm again and all of my APT/DRM decoding failed again! Setting it to zero solves the problem. Seems like there is a bug with the GQRX itself. I've done some tests and you see the results on the corresponding &lt;a href=&quot;https://github.com/csete/gqrx/issues/791#issuecomment-623924434&quot; rel=&quot;nofollow noreferrer&quot;&gt;issue page&lt;/a&gt; on GitHub.&lt;/p&gt;&#xA;" OwnerUserId="14179" LastEditorUserId="14179" LastEditDate="2020-05-07T06:51:21.910" LastActivityDate="2020-05-07T06:51:21.910" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16617" PostTypeId="2" ParentId="16563" CreationDate="2020-05-04T10:38:45.670" Score="2" Body="&lt;p&gt;You could use a short jumper of a thin cable, pushed through a hole drilled in the grout between the blocks, or next to them in the plaster.&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/938q5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/938q5.png&quot; alt=&quot;141 semi-rigid coaxial cable&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;A 141-size cable is 3.6 mm in diameter, and the base model with teflon / copper &lt;a href=&quot;https://www.ezform.com/product/ez-141-tpm17/&quot; rel=&quot;nofollow noreferrer&quot;&gt;claims to handle 600 W up to 500 MHz&lt;/a&gt; so that might be an option. You'd need some N-type connectors for the thin cable on both sides of the window, it's not flexible enough to go to your rig.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The power limit is a thermal limit, so must be derated for SWR &gt; 1:1, but if it's 600 W PEP then it will be be OK with 1.5:1 SWR. If the SWR is very high and you have a tuner inside, then it might only cope with 100-200 W.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-05-04T10:38:45.670" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16618" PostTypeId="1" CreationDate="2020-05-04T18:13:21.730" Score="2" ViewCount="58" Body="&lt;p&gt;Is there a podcast to listen to that teaches in-depth the technician class questions? All I could find is podcasts that just read the questions and answers. Is there a podcast that goes in-depth to every question and actually teaches the formulas/concepts?&lt;/p&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="10859" LastEditDate="2020-05-04T18:15:29.250" LastActivityDate="2020-05-07T13:38:40.080" Title="Podcasts for Technician Test" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16619" PostTypeId="5" CreationDate="2020-05-04T18:17:43.840" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2020-05-04T18:17:43.840" LastActivityDate="2020-05-04T18:17:43.840" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16620" PostTypeId="4" CreationDate="2020-05-04T18:17:43.840" Score="0" Body="Building, modifying or repairing radio equipment without proper tools/materials. " OwnerUserId="16949" LastEditorUserId="873" LastEditDate="2020-07-09T03:01:32.607" LastActivityDate="2020-07-09T03:01:32.607" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16621" PostTypeId="2" ParentId="16580" CreationDate="2020-05-04T18:26:36.563" Score="2" Body="&lt;p&gt;The only astronauts that currently have amateur radio on board are the ones on the International Space Station (ISS).  The MIR Space Station and the Space Shuttle used to have ham radio but they are no longer operational.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's rare that you can talk to the astronauts, for several reasons, but it is possible.  They have a full schedule of work and are very busy.  From time to time they do arrange a schedule to &lt;a href=&quot;https://www.ariss.org/submit-a-contact-proposal.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;talk to schools&lt;/a&gt; and do question and answer sessions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If they have free time in between their work hours and sleep hours, they may choose to &lt;a href=&quot;https://youtu.be/h73EYcyszf8?t=638&quot; rel=&quot;nofollow noreferrer&quot;&gt;operate the radio&lt;/a&gt; and chat with people.  It doesn't happen often and you won't be able to talk to them unless they happen to by flying overhead at that time.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;As explain on the &lt;a href=&quot;https://www.ariss.org/contact-the-iss.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARISS web site&lt;/a&gt;, when they do get on the radio, the astronauts operate split frequency, where you transmit your voice signal to them on 144.49 Mhz (the uplink for you in region 2) and you listen for their reply on the voice frequency 145.80 Mhz (the downlink).  This is a normal FM voice signal that any handheld 2 meter radio can do.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In theory you could talk to them with a 5 watt FM handheld radio, but in actual practice it is probably not enough.  With FM radio they will only hear the strongest signal (called capture effect).  A lot of hams monitor the 145.80 download frequency and if they hear the astronauts are on, they will call them.  The astronauts will only hear the strongest signal, about a 500 mile diameter circle below them.  If 50 hams in that area all call them at once, only the strongest signal will be heard.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to monitor the downlink frequency and listen for them, you need to know when they are passing over.  It's only for a maximum of 9 minutes, probably 2 or 3 times per day.  Miami is about 28.2 degrees N latitude and 80.2 degrees W longitude, so you can use a web site like &lt;a href=&quot;https://www.amsat.org/track/&quot; rel=&quot;nofollow noreferrer&quot;&gt;AMSAT's Online Pass Predictions&lt;/a&gt; to find out when to listen.  Select ISS, enter 28.2 North latitude, enter 80.2 West longitude, elevation 0, and get predictions.  Look for the passes where the elevation is at least 10 degrees (below 10 is a short pass, weak signal since they are too close to the horizon).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your best chance would be to find passes over you that coincide with their &lt;a href=&quot;https://www.nasa.gov/audience/foreducators/stem-on-station/ditl_free_time&quot; rel=&quot;nofollow noreferrer&quot;&gt;free time periods&lt;/a&gt; and listen for them then.  Keep up with ARISS news to know what is happening with &lt;a href=&quot;https://www.ariss.org/current-status-of-iss-stations.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;their radio equipment&lt;/a&gt; and &lt;a href=&quot;https://www.ariss.org/current-iss-crew.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;who is on board&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="13625" LastEditorUserId="13625" LastEditDate="2020-05-04T18:41:28.873" LastActivityDate="2020-05-04T18:41:28.873" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16622" PostTypeId="1" CreationDate="2020-05-05T06:07:58.207" Score="9" ViewCount="911" Body="&lt;p&gt;I'm trying to create a diplexer for the 2m and 70cm bands so that two antennas can share a feedline to my &quot;shack&quot;. My radio is a Yaesu FT60 handheld, 5W max. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have home made a j-pole for 2m, and a neat little ground plane antenna for 70cm, both of which show an SWR under 1.2:1 throughout their respective band, according to my Rig Expert. Both antennas have been analysed under various different feedline and mounting arrangements, with SWR curves staying very consistent - pretty confident about these results.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I found this circuit on the internet:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/bIP23.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bIP23.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I simulated it in LTspice out of curiousity and the response looked legit, so I whipped up a little single-sided PCB and soldered the components on. (without my magnifiers and with a very wonky tip, sorry)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I put this PCB in a stylish aluminium alloy box, with short stubs of RG58 connecting the I/O solder pads on the board with SO-239s mounted to the box.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3KzUu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3KzUu.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Unfortunately, with the diplexer installed on my main feedline (~25 feet of LMR-240) and each antenna connected to its respective SO-239 with about 3 feet of RG58, I'm looking at between 3:1 and 4:1 across both bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have carefully examined and electrically tested the PCB and the RG58 stubs/connectors for dead shorts or other issues but can find none.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there something &lt;em&gt;obviously&lt;/em&gt; &quot;wrong&quot; about what I've done here?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(not sure what tags are most appropriate for this question, suggestions welcome)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Cheers!!&lt;/p&gt;&#xA;" OwnerDisplayName="user14945" LastEditorDisplayName="user14945" LastEditDate="2020-05-07T03:56:15.220" LastActivityDate="2020-05-09T12:38:33.023" Title="Why is my diplexer such a spectacular failure?" Tags="&lt;diy&gt;&lt;swr-meter&gt;&lt;duplexer&gt;" AnswerCount="3" CommentCount="14" ContentLicense="CC BY-SA 4.0" />
  <row Id="16624" PostTypeId="2" ParentId="16622" CreationDate="2020-05-05T10:41:02.743" Score="5" Body="&lt;p&gt;You have soldered a 68nH inductor instead of 100nH!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maybe the layout and the wiring also play a key role.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a vintage commercial one.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8I7xw.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8I7xw.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's quite compact. The size, inclusive of the coaxial sockets, is 4&quot; x 2&quot; x 1&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's the schematic.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PVQyK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PVQyK.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tin plating is observed inside the enclosure.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no PCB and the wiring is point-to-point. Connections to the coaxial socket centre pins are direct (coaxial cables are not used). 'Common' connection to the coaxial socket bodies is via the enclosure itself.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Capacitors are miniature disc ceramic. The ground end of C1 and C3 are directly soldered to the enclosure.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-05-06T09:20:28.220" LastActivityDate="2020-05-06T09:20:28.220" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16625" PostTypeId="2" ParentId="16622" CreationDate="2020-05-05T10:48:57.563" Score="5" Body="&lt;p&gt;Like you, I modeled your diplexer in LTSpice, but I don't find the results to be acceptable. At 147-MHz, the input impedance is 87&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;; at 443-MHz, it's 24&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;. Also, the crossover frequency is about 350-MHz, which seems too high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://tonnesoftware.com/&quot; rel=&quot;noreferrer&quot;&gt;Tonne Software&lt;/a&gt; offers &lt;a href=&quot;http://tonnesoftware.com/diplexer.html&quot; rel=&quot;noreferrer&quot;&gt;Diplexer Designer&lt;/a&gt; to address your requirement. Creating a low-pass / high-pass design with a crossover frequency of &lt;span class=&quot;math-container&quot;&gt;$f_{cross} = \sqrt{147*435}$&lt;/span&gt; = 253-MHz delivers better results:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aKo8x.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aKo8x.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ~33-dB rejection shown by Diplexer Designer's plot function are confirmed by LTSpice:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aXZ5L.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aXZ5L.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and the 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; impedance presented to the generator on each band is well-controlled:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xRE8Y.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xRE8Y.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These plots were made possible by performing an AC analysis on the LTSpice circuit and taking advantage of the &quot;.net&quot; LTSpice directive, as shown in the LTSpice diagram below:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/V8ag2.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/V8ag2.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-05T10:48:57.563" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16626" PostTypeId="1" AcceptedAnswerId="16627" CreationDate="2020-05-05T13:34:04.850" Score="10" ViewCount="9366" Body="&lt;p&gt;Having a low price budget, my search for my first ham radio to buy has led me towards Baofeng. A quick Google search on baofeng showed a lot of results that said that certain model baofeng handhelds are illegal in the US. Is that true?&lt;/p&gt;&#xA;" OwnerUserId="16949" LastEditorUserId="-1" LastEditDate="2020-05-07T11:28:01.300" LastActivityDate="2020-05-12T19:42:22.667" Title="Are Baofeng radios illegal in the U.S?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;baofeng&gt;&lt;ht&gt;&lt;fcc&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16627" PostTypeId="2" ParentId="16626" CreationDate="2020-05-05T15:12:20.253" Score="17" Body="&lt;p&gt;They are legal to use, but &lt;em&gt;only&lt;/em&gt; on the amateur bands. (Of course, you'll need to get a license first).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There was a lot of debate on whether they were legal, but the FCC finally stated that they were. Thus the older search results you found, such as &lt;a href=&quot;http://www.arrl.org/news/fcc-cites-baofeng-importer-for-illegally-marketing-unauthorized-rf-devices&quot; rel=&quot;noreferrer&quot;&gt;this one&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since they are not type-accepted, they are not legal to use on other bands such as &lt;a href=&quot;https://ham.stackexchange.com/questions/3679/can-a-baofeng-uv-5r-be-used-on-frs-gmrs-and-murs&quot;&gt;FRS&lt;/a&gt;, &lt;a href=&quot;https://ham.stackexchange.com/a/15735/8717&quot;&gt;GMRS&lt;/a&gt;, etc.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-05-05T16:05:19.283" LastActivityDate="2020-05-05T16:05:19.283" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16628" PostTypeId="2" ParentId="16610" CreationDate="2020-05-05T15:29:04.110" Score="4" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;I get that reflections show up as peaks on the IR graph, is that it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, that's essentially it. Note that the reflections can be negative or positive: for example if you try it with a short at the end rather than an open you should get a negative spike in the impulse response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Falstad makes (I think) a pretty intuitive way to demonstrate the concept:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20496%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0Ao%204%2016%200%204098%205%200.025%200%202%204%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;open termination&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/9NQ3Q.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9NQ3Q.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20496%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0Aw%20544%20192%20544%20272%200%0Ao%204%2016%200%204098%205%200.025%200%202%204%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;short termination&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/tUHRR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tUHRR.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note as these simulations are set up, you do see in the graph the initial impulse created by the signal source. In the RigExpert, that's not present: all you see is the reflection (if any).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What does the SR (Step Response) graph actually display and what does it mean?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The step response is simply the integral of the impulse response.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So in the 2nd example, we see this downward trend in the step response. That means the impulse response throughout the entire length is some negative value. It must be a small one, because the cursor says the impulse response is 0.00. Perhaps -0.003 is rounded to 0.00. Or it's a bug in the RigExpert, or an artifact introduced by stray RF pickup.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Assuming it's not a bug, this indicates that throughout the length of the coax, there is something producing a small negative impulse response. Recall that a transmission line model consists of infinitely many segments like this:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/13xU7.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f13xU7.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In a lossless line, R' and G' are zero. (G' is &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_resistance_and_conductance&quot; rel=&quot;nofollow noreferrer&quot;&gt;conductance&lt;/a&gt;, so zero conductance means a perfect insulator, or infinite resistance.) The square root of the ratio of L' to C' then determines the characteristic impedance of the transmission line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice R' and G' are only very small enough to be negligible. But what if the transmission line isn't very good, or broken somehow? A &lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20304%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0A171%20368%20192%20496%20192%200%202e-9%20300%2080%200%0Ar%20544%20192%20544%20272%200%20300%0Ar%20336%20192%20336%20272%200%20500%0Aw%20304%20192%20336%20192%200%0Aw%20336%20192%20368%20192%200%0Aw%20368%20272%20336%20272%200%0Aw%20336%20272%20304%20272%200%0Ao%204%2016%200%204098%205%200.025%200%202%204%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;conductance fault simulates what happens&lt;/a&gt; when the insulation is less than perfect at one spot in the transmission line:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yAANP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yAANP.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice the small, negative impulse as a result. If we instead imagine not just one spot where this happens, but infinitely many such spots across the entire length of the line, we get a likely explanation for what you are seeing in the 2nd case: a small but constant negative impulse response over the length of the line.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So I would guess something (water intrusion? UV exposure? Cheap manufacturing and time?) has degraded the dielectric of your old coax such that it's no longer a good insulator. I'd wager if you measure the loss of this piece of coax you'll feel OK about throwing it in the trash.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of note, the RigExpert manual gives an example of a lossy line, which has an increasing step response. This is what happens when the problem is &lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20304%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0A171%20368%20192%20496%20192%200%202e-9%20300%2080%200%0Ar%20544%20192%20544%20272%200%20300%0Ar%20304%20192%20368%20192%200%20500%0Aw%20304%20272%20368%20272%200%0Ag%20304%20272%20304%20288%200%0Ao%204%2016%200%204098%205%200.025%200%202%204%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;significant resistance in the conductors&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/jbTDK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jbTDK.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Essentially the same situation, except the polarity of the impulse is reversed.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;For further exploration, I've assembled Falstad simulations of other cases you might consider:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20496%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0Al%20544%20192%20544%20272%200%201.0000000000000001e-7%204.4651918219930954e-11%0Ao%204%2016%200%204098%205%200.025%200%202%204%203%0Ao%208%2016%200%204099%200.15625%200.000390625%201%202%208%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;inductive termination&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/RvxsE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RvxsE.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20496%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0A209%20544%20192%20544%20272%200%201e-12%202.656944995198298e-7%201%0Ao%204%2016%200%204098%205%200.025%200%202%204%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;capacitive termination&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/a5gKD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/a5gKD.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20304%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0A171%20368%20192%20496%20192%200%202e-9%20300%2080%200%0Ar%20544%20192%20544%20272%200%20300%0Aw%20304%20272%20336%20272%200%0Ag%20304%20272%20304%20288%200%0Aw%20336%20272%20368%20272%200%0Ac%20304%20192%20368%20192%200%201e-13%20-7.954292071017043e-21%0Ao%204%2016%200%204098%205%200.025%200%202%204%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;series capacitance discontinuity&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/gBHUk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gBHUk.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20304%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0A171%20368%20192%20496%20192%200%202e-9%20300%2080%200%0Ar%20544%20192%20544%20272%200%20300%0Aw%20304%20272%20336%20272%200%0Ag%20304%20272%20304%20288%200%0Aw%20336%20272%20368%20272%200%0Al%20304%20192%20368%20192%200%201.0000000000000001e-7%205.328107453720753e-19%0Ao%204%2016%200%204098%205%200.025%200%202%204%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;series inductance discontinuity&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/6TMHO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6TMHO.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20304%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0A171%20368%20192%20496%20192%200%202e-9%20300%2080%200%0Ar%20544%20192%20544%20272%200%20300%0Aw%20304%20272%20336%20272%200%0Ag%20304%20272%20304%20288%200%0Aw%20336%20272%20368%20272%200%0Aw%20368%20192%20336%20192%200%0Aw%20336%20192%20304%20192%200%0Ac%20336%20192%20336%20272%200%201e-12%201.3811455832905268e-12%0Ao%204%2016%200%204098%202.5%200.025%200%202%204%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;shunt capacitance discontinuity&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ietEZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ietEZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.falstad.com/circuit/circuitjs.html?cct=%24%201%201e-12%202.688763906446752%2050%205%2050%0A171%20176%20192%20304%20192%200%202e-9%20300%2080%200%0Aw%20128%20272%20176%20272%200%0Aw%20496%20192%20544%20192%200%0Aw%20496%20272%20544%20272%200%0Ar%20176%20192%20128%20192%200%20300%0Ag%20544%20272%20544%20288%200%0Ag%20128%20272%20128%20288%200%0AR%20128%20192%2096%20192%204%205%20150000000%205%200%200%200.01%0A171%20368%20192%20496%20192%200%202e-9%20300%2080%200%0Ar%20544%20192%20544%20272%200%20300%0Aw%20304%20272%20336%20272%200%0Ag%20304%20272%20304%20288%200%0Aw%20336%20272%20368%20272%200%0Aw%20368%20192%20336%20192%200%0Aw%20336%20192%20304%20192%200%0Al%20336%20192%20336%20272%200%201e-8%206.885776709373006e-30%0Ao%204%2016%200%204098%205%200.025%200%202%204%203%0A&quot; rel=&quot;nofollow noreferrer&quot;&gt;shunt inductance discontinuity&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/13QKE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/13QKE.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-05-05T15:29:04.110" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16629" PostTypeId="2" ParentId="16626" CreationDate="2020-05-05T20:17:26.613" Score="18" Body="&lt;p&gt;The ARRL runs a booth at Dayton Hamvention since 2012 where people can submit their HTs to be tested for spectral purity. Over the years 2016-2019, 100% of the Alinco, Icom, Kenwood, and Yaesu HTs they tested were compliant with the standards laid out in Section 97.307. Only 7.5% of the Baofeng HTs they tested were compliant, with 27% being &quot;borderline&quot; (violating the limits by less than 3dB) and the remaining two thirds being more than 3dB out of spec (Source: QST January 2020, pp. 60-61).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FgM46.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FgM46.png&quot; alt=&quot;HT testing results&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur equipment isn't type-certified; the operator is responsible for the compliance of their equipment. With a fairly reliable source showing 92.5% of Baofeng HTs in the wild failing to meet the standards of Part 97, anyone without access to a calibrated spectral analyzer can reasonably assume that any given Baofeng is &lt;strong&gt;not&lt;/strong&gt; legal to use on the amateur bands.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-05-06T18:56:05.147" LastActivityDate="2020-05-06T18:56:05.147" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="16630" PostTypeId="1" AcceptedAnswerId="16635" CreationDate="2020-05-05T22:37:47.633" Score="3" ViewCount="125" Body="&lt;p&gt;I am quite interested in buying the Alinco DJMD5TGP as it seems like a full-featured radio for a low price. And I have already started studying for my Technician license so I can transmit. And then I ran across &lt;a href=&quot;https://radioaficion.com/news/alinco-dj-md5-illegal-in-the-united-states/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this article&lt;/a&gt;, which seems to state that the radio does not comply with everything it should. Granted, the article is almost two years old, so maybe it's not relevant anymore. Should I be concerned about buying this? Even &lt;a href=&quot;http://www.alinco.com/global.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Alinco's website&lt;/a&gt; says in red text that the DJMD5TGP &quot;is not an amateur radio equipment.&quot; Would I be alright as long as I stick to the frequencies allowed by a technician license? Anything else I should know about so that I don't unknowingly break the law?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;By the way, this question may be a duplicate of &lt;a href=&quot;https://ham.stackexchange.com/questions/16626/is-baofeng-illegal-in-the-u-s&quot;&gt;Is Baofeng illegal in the U.S?&lt;/a&gt; If so, I would appreciate an explanation as to how it will answer my question. I have a lot to learn.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thank you for your time.&lt;/p&gt;&#xA;" OwnerUserId="16868" LastActivityDate="2020-05-06T03:20:31.760" Title="Is the Alinco DJMD5 illegal for ham use?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;fcc&gt;&lt;alinco&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16631" PostTypeId="1" AcceptedAnswerId="16641" CreationDate="2020-05-06T00:41:33.480" Score="2" ViewCount="439" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Duykl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Duykl.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a reading from my RigExpert AA-35 ZOOM of my EFHW 40-10 inverted L with radials, and feedpoint 2 feet above the ground.  Any thoughts as to how I can tune or move this antenna to get the lowest SWR in the 40, 20 and 15 meter bands?   Thanks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An update:  I disconnected the ground lug on the box and moved the feed point up to 10 ft.  Big difference.  Hope to make more of a difference by increasing the antenna length. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gjC8N.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gjC8N.png&quot; alt=&quot;SWR of EFHW 40-10 inverted L&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Yet Another Update:&#xA;Connected a 10 foot ground wire to the radial plate and got slightly better results (in green).   If I ever care about 30 meters, I'll disconnect the ground. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/vnJok.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vnJok.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And yet another update.  Extended my antenna by 2.5 feet and get the following (red is longer wire, green is shorter wire):&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/hsQvD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hsQvD.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Final update:  Antenna is in its &quot;final&quot; state, spliced with PosiLock connector and crimped with an aluminum sleeve at the end.  10 meters is a compromise for better SWR elsewhere.&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ojsvv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ojsvv.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9772" LastEditorUserId="9772" LastEditDate="2020-05-23T20:11:16.713" LastActivityDate="2020-05-23T20:11:16.713" Title="How do I tune my EFHW 40-10 to have the lowest SWR in the 40, 20 and 15 meter bands?" Tags="&lt;antenna-theory&gt;&lt;hf&gt;&lt;wire-antenna&gt;&lt;impedance-matching&gt;&lt;end-fed-antenna&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16632" PostTypeId="1" AcceptedAnswerId="16642" CreationDate="2020-05-06T01:03:15.970" Score="3" ViewCount="104" Body="&lt;p&gt;I have connected my brand new RigExpert AA-35 to my Windows 10 PC via the provided USB cable, but the AA-35 does not show up in Device Manager.  There is no COM port assigned to it, nor does it show up in USB devices. Also, and this is very strange:  I can install AntScope2 (in its default directory) and read data from the AA-35 when I first run the AntScope2 after installing it.  After closing and then reopening AntScope2, however, AntScope2 does not see the AA-35.  I have to reinstall the software in order to see the AA-35 again.  I have to reinstall the software every time I want to get data from the AA-35.  Please advise.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Edit:  after email conversation with RigExpert (heard from them the very next morning!) it turns out I was looking in the wrong place for the device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sbMR1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sbMR1.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9772" LastEditorUserId="9772" LastEditDate="2020-05-07T23:04:12.587" LastActivityDate="2020-05-07T23:04:12.587" Title="How do I get my Windows 10 PC to consistently recognize my RigExpert AA-35 ZOOM?" Tags="&lt;antenna-analyzer&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16633" PostTypeId="2" ParentId="16630" CreationDate="2020-05-06T01:20:48.013" Score="0" Body="&lt;p&gt;I looked at the data sheet and saw nothing to indicate that that transceiver would be useful on any amateur radio band, with commonly deployed amateur radio repeaters.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The frequencies, modulation (FM, typically), access undertones, and (if digital) encoding all must be compatible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio operators are personally responsible for the correct operation of their equipment.  Manufacturers work with the FCC to have equipment pre-checked, or type accepted, by the FCC to assure that the equipment operates correctly and reduce the load on the operator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There may be a way to operate that transceiver in an manner compatible with amateur radio, but as an operator, the onus would he on you to assure compliant operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a ham, you can operate an electric dryer modulated by a hand mixer, but you are 100% responsible.  That is one of the beauties of amateur radio -- the innovation is in your hands, which, to me, justifies the additional responsibility.&lt;/p&gt;&#xA;" OwnerUserId="9109" LastActivityDate="2020-05-06T01:20:48.013" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16634" PostTypeId="1" AcceptedAnswerId="16665" CreationDate="2020-05-06T02:25:30.343" Score="2" ViewCount="822" Body="&lt;p&gt;I was looking for a cheap and easy to build 2M/70cm vertical. I found this: &lt;a href=&quot;http://vk2zoi.com/articles/dual-band-high-gain-flower-pot/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://vk2zoi.com/articles/dual-band-high-gain-flower-pot/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here are the plans to build it:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dXpzI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dXpzI.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I don't really understand how it works. Here are my doubts, starting from the bottom:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the lower coil seems to be an &quot;ugly balun&quot;, a choke made out of coax, is this it?&lt;/li&gt;&#xA;&lt;li&gt;the 447/457mm section, I don't understand. The 457mm section seems to be a radiator. According to some calculator, this should resonate at around 156mhz, which is what I observed when I built this antenna. Lengthening this 457mm section by 32mm helped me lower the resonance to 146mhz. What is the 447mm &quot;covered&quot; section, though? Is it some sort of quarter-wave matching? should it also be extended if i try to match the antenna to a lower frequency?&lt;/li&gt;&#xA;&lt;li&gt;the 7 turns middle coil, what does it do? I have read about phasing coils, but I've seen them implemented as coils that are part of the antenna. this is just a section of coax, like a choke balun. does this also work as a phasing coil?&lt;/li&gt;&#xA;&lt;li&gt;now there is a 920mm section of radiator. why is this different from the bottom part, not &quot;half covered&quot;? it also seems related to a half-wavelength. when trying to make this antenna resonant for 146mhz, I also extended this section by 60mm&lt;/li&gt;&#xA;&lt;li&gt;finally the sleeves. what are they? they do work, though, for UHF frequencies. moving them up and down makes the UHF resonance (and SWR) move. I was able to tune the antenna in UHF by moving these sleeves and got a very good match in the 70cm band, withouth affecting the 2M match&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;This antenna promises 6dBd of gain in 70cm and 3dBd in 2M. Is this realistic? What would be the pattern for this?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-05-10T09:44:28.620" Title="how does this collinear antenna work?" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;vertical-antenna&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16635" PostTypeId="2" ParentId="16630" CreationDate="2020-05-06T03:20:31.760" Score="3" Body="&lt;p&gt;The article is mistaken about at least one thing. It &lt;em&gt;may&lt;/em&gt; be illegal to market that radio in the US (I honestly don't care to read the tea leaves to find out if that's true or not, but it's certainly possible), but that has no bearing at all on whether you can legally operate one in the US as an amateur. Amateur transcievers don't have to be certified in any way, including Part 15 certification. Part 97 is more-or-less unique in that amateurs are allowed to build, buy, or modify anything that will radiate, and it becomes &lt;em&gt;their&lt;/em&gt; responsibility to operate the device in a way that is legal. Some hams enjoy operating everything from WWII military radios, to modified AM broadcast transmitters, to Motorola business-band handhelds. If the device &lt;em&gt;can't&lt;/em&gt; be operated in a legal way, of course, it's their responsibility not to push that transmit button. But you are allowed to own, and operate, a device that is capable of doing all kinds of bad things — your license is supposed to indicate that you have the sense not to do them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part 15 certification can be a barrier to &lt;em&gt;selling&lt;/em&gt; a radio in the US, but if there's a problem on that front, and the FCC decides to care about it, they will go after the manufacturers and importers of the noncompliant radios, not amateurs who own them.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-05-06T03:20:31.760" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16636" PostTypeId="1" AcceptedAnswerId="16660" CreationDate="2020-05-06T05:44:56.913" Score="3" ViewCount="43" Body="&lt;p&gt;When I series two SAW filter, why the attenuation less than sum both of them in stop band region. Each of them (in stop band) have 60dB attenuation but when series them, the attenuation is equal to 85dB.&#xA;What happening? Why didn't reach to 120dB?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Then, I put a 20dB attenuation between them ( SG --&gt; SAW1 --&gt; 20dB attenuation --&gt; SAW2--&gt; SA ), and the attenuation is equal to 90dB, this meaning only 5dB attenuate with 20dB attenuation.&#xA;What happening again?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the insertion loss is true when series. Each of the have 8dB insertion loss and when both of them is series the insertion loss equal to 16dB.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks in advanced&lt;/p&gt;&#xA;" OwnerUserId="17016" LastActivityDate="2020-05-09T05:03:15.887" Title="Problem of two SAW fitler?" Tags="&lt;filter&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16637" PostTypeId="2" ParentId="16636" CreationDate="2020-05-06T09:19:26.430" Score="4" Body="&lt;p&gt;So, probably a combination of different things:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You physically can't isolate things arbitrarily much. My experience with well-designed RF PCBs is that they have -60 dB to -49 dB crosstalk – simply through the board, shields, grounds, power supplies&lt;/li&gt;&#xA;&lt;li&gt;You're not telling us how you're measuring isolation. Measuring more than 90 dB in dynamic range is tricky, and requires you think a lot about signal leakage.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I'd mostly chalk this up to measurement error, because if an attenuator doesn't attenuate according to your measurements, then it's probably your measurements.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-05-06T09:19:26.430" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16638" PostTypeId="2" ParentId="16610" CreationDate="2020-05-06T10:58:00.090" Score="7" Body="&lt;p&gt;My name is Alex, I'm the head of technical support at RigExpert.&#xA;This is actually an interesting question.&#xA;Our engineers could not give an exact answer why the schedule in the second case behaves strangely.&#xA;I can offer to perform another experiment - to measure the parameters of the RG-8/U coax cable using the analyzer and the AntScope and AntScope2 software. In all three cases (analyzer and two programs), a bit different algorithm for the operation of the TDR function is used.&#xA;It will be very interesting to compare the three results obtained. Thus, you can get closer to solving the puzzle.&#xA;Link: &lt;a href=&quot;https://rigexpert.com/files/software/Antscope/&quot; rel=&quot;noreferrer&quot;&gt;https://rigexpert.com/files/software/Antscope/&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;Best regards, Alex Antonov UR4MCB&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="17019" LastActivityDate="2020-05-06T10:58:00.090" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16639" PostTypeId="1" CreationDate="2020-05-06T11:32:01.823" Score="5" ViewCount="223" Body="&lt;p&gt;Consider a center-fed dipole antenna. It‘s well understood how the bottom element can be replaced by a ground plane (in practice, generally a few rods but in principle a conducting plate would work as well), creating a „groundplane antenna“.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Iqhmd.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Iqhmd.png&quot; alt=&quot;From a dipole to a ground plane&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was wondering whether it would be possible to do the same transformation for directional antannas with either parasitic (Yagi-Uda) or active (HB9CV) directors.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cM9l8.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cM9l8.png&quot; alt=&quot;Illustration of suggested Yagi transformation &quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any publications out there discussing this idea? What consequences would this change have in terms of antenna properties, and how would antenna theory explain radiation?&lt;/p&gt;&#xA;" OwnerUserId="15707" LastActivityDate="2020-10-22T22:56:23.983" Title="Can half of a directional antenna (Yagi-Uda, HB9CV) be replaced by a ground plane?" Tags="&lt;antenna-theory&gt;&lt;yagi&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16640" PostTypeId="2" ParentId="16639" CreationDate="2020-05-06T12:04:31.313" Score="6" Body="&lt;p&gt;Yes, this is a time-honored practice, particularly at the longer wavelengths where horizontal antennas need to be mounted quite high to provide low-angle radiation for DX work. Callum, M0MCX, presents a nice gallery of information about his &lt;a href=&quot;https://www.m0mcx.co.uk/3-element-40m-vertical-parasitic-array-vpa/&quot; rel=&quot;nofollow noreferrer&quot;&gt;three-element parasitic array for 40-m&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mNRZ8.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mNRZ8.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The radiating elements are the three black verticals in the foreground behind the fence.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;While a &quot;vertical yagi&quot; can be an effective solution for low-angle radiation, it's important to remember:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the ground screen consumes considerable area&lt;/li&gt;&#xA;&lt;li&gt;you lose the reflection gain attendant upon horizontal antennas&lt;/li&gt;&#xA;&lt;li&gt;ground conductivity near the antenna strongly affects efficiency and feedpoint impedance&lt;/li&gt;&#xA;&lt;li&gt;ground conductivity out to several wavelengths from the antenna determines how low the radiation angle will be&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;M0MCX demonstrates the advantage he hopes to achieve:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/k0vdF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/k0vdF.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;but this comparison doesn't tell the whole story:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the text says the feedpoint shows a very low SWR across the entire 40-m band without any matching circuitry, indicating substantial losses in the system which may reduce radiation more for a vertical than for a horizontal antenna&lt;/li&gt;&#xA;&lt;li&gt;the comparison puts a dipole at 20-ft, while the vertical elements are at least 50% taller&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I point this out only to illustrate the complexity of an antenna system in the real world, not to criticize the efforts of M0MCX, who is obviously enjoying his fine antenna. All antennas require compromises, so carefully consider your goals and resources, then set your expectations accordingly.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-05-06T15:10:20.187" LastActivityDate="2020-05-06T15:10:20.187" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16641" PostTypeId="2" ParentId="16631" CreationDate="2020-05-06T13:27:47.820" Score="4" Body="&lt;p&gt;First you don't necessarily have to do anything. The SWR is below 3 for the bands and most transceivers can handle that OK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you want to try to get the resonate points inside the bands you will need to lengthen the wire. it is usually a good idea to start with too much wire and trim the length to bring the resonance down, but in your case it look like the wire is too short.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Ideally solder additional wire on the end and cover it heat shrink, then cover that with water proofing sealant. However you could get very similar results with a simple crimp splice or even just mechanically connecting the wire. If you don't provide some protection from the elements the connect will eventually corrode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In theory you should be able to calculate the exact length of wire you need. In practice it is difficult to account for all of the factors. Everyone I know of doing wire antennas makes them long and trims them as need to get the resonance. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Currently the antenna is resonate at about 7.7 Mhz. You would like it to be resonate at 7.1 Mhz. Take the old resonate frequency divided by the new resonate frequency and multiply by the original length, (7.7/7.1)*65 = 70.5 or so. The result is about 70.5 feet which would have you adding 5.5 feet to the existing antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would probably add about 7 feet and trim as needed to get the resonates where i want it. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="9425" LastEditDate="2020-05-06T20:26:58.877" LastActivityDate="2020-05-06T20:26:58.877" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16642" PostTypeId="2" ParentId="16632" CreationDate="2020-05-06T14:40:11.557" Score="3" Body="&lt;p&gt;After much troubleshooting, I was able to resolve the above behavior by running AntScope2 in compatibility mode for &quot;Windows XP (Service Pack 3)&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the record, I am running Windows 10 1909.  &lt;/p&gt;&#xA;" OwnerUserId="9772" LastActivityDate="2020-05-06T14:40:11.557" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16643" PostTypeId="2" ParentId="16394" CreationDate="2020-05-06T19:21:02.860" Score="4" Body="&lt;p&gt;A wide FM transmission in a narrow FM receiver is effectively &lt;a href=&quot;https://en.wikipedia.org/wiki/Overmodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;overmodulation&lt;/a&gt;: the excessive deviation of the transmitter results in the instantaneous frequency of the transmission deviating outside the bounds of what the receiver is designed for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A practical FM receiver will pass the signal through a channel filter before demodulation. The objective of this filtering is to remove adjacent signals and noise, while passing the desired signal with minimal distortion. Theoretically FM results in an infinitely wide spectrum, but &lt;a href=&quot;https://en.wikipedia.org/wiki/Carson_bandwidth_rule&quot; rel=&quot;nofollow noreferrer&quot;&gt;Carson's rule&lt;/a&gt; can be used to estimate the channel bandwidth where most of the signal energy exists:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{channel bandwidth} = 2(\Delta f + f_m) $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\Delta f$&lt;/span&gt; is the peak frequency deviation, and &lt;span class=&quot;math-container&quot;&gt;$f_m$&lt;/span&gt; is the highest frequency component in the baseband input. For narrow FM, &lt;span class=&quot;math-container&quot;&gt;$\Delta f$&lt;/span&gt; will typically be 5 kHz or less, and for voice communications &lt;span class=&quot;math-container&quot;&gt;$f_m$&lt;/span&gt; will be 4 kHz or less. The choice of these parameters will dictate the design of the receiver's channel filter and minimum channel spacing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If the deviation is excessive, as would be the case with a wide FM transmitter and a narrow receiver, the receiver's filter will truncate the FM sidebands. Because FM is a nonlinear operation this distorts the demodulated baseband audio in a nonlinear way, and the result is some pretty nasty sounding distortion at the receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-05-06T19:21:02.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16644" PostTypeId="2" ParentId="16394" CreationDate="2020-05-07T00:40:05.643" Score="2" Body="&lt;p&gt;As Phil Frost's answer already said, if the audio is at full amplitude the modulated signal will exceed the channel filter's bandwidth and the resulting audio will be distorted.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From a time-domain audio processing perspective, we could describe the effect approximately as if the signal &lt;em&gt;fades out&lt;/em&gt; whenever the modulation exceeds the passband of the channel filter. Thus, the (audio) peaks are replaced with (RF and also audio) noise; the strength of this effect will depend on how sharp the channel filter is.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is similar to an FM receiver tuned off the correct frequency, except that the off-center receiver will replace only &lt;em&gt;half&lt;/em&gt; the audio waveform peaks (those of one polarity, depending on which way it is detuned) with noise; whereas a too-narrow but centered filter will replace all peaks.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An extreme case of this is attempting to receive a broadcast FM (wideband FM, 75 kHz deviation) signal with a communications receiver — you will hear almost entirely noise, because unless the program is very quiet, all but the zero-crossings of the original audio signal will be lost.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-05-07T00:40:05.643" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16645" PostTypeId="1" CreationDate="2020-05-07T01:40:49.010" Score="3" ViewCount="222" Body="&lt;p&gt;I have a homebrew remote antenna switch. It uses relays and it has a nRF24L01-based wireless link to the band selector (Arduino, taps into CAT and switches antennas accordingly).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would like to power this device without running a separate power cable. I thought of using a bias tee with about 100 to 470nF capacitors, KV rated, several in parallel, and big inductors for DC injection and extraction. Some sources online recommended using a ferrite rod to make the coil, which should provide an inductance into the millihenries.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The questions are:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Is this a good idea?&lt;/li&gt;&#xA;&lt;li&gt;Will this introduce significant losses into the system?&lt;/li&gt;&#xA;&lt;li&gt;Will this introduce significant noise into the system?&lt;/li&gt;&#xA;&lt;li&gt;Is there anything else I should be concerned about?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;I've seen at least one supplier of this sort of &quot;bias tee&quot; circutry for HF, but at a price exceeding $250 (which I'm not willing to spend), so I believe it &quot;should work&quot;.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-05-07T10:49:42.137" Title="Bias Tee for HF: noise and losses?" Tags="&lt;hf&gt;&lt;dc-power&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16648" PostTypeId="2" ParentId="16645" CreationDate="2020-05-07T10:49:42.137" Score="1" Body="&lt;p&gt;You might be guided by the circuit for the &lt;a href=&quot;https://mfjenterprises.com/collections/ameritron/products/rcs-4#product-manuals&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ameritron RCS-4 Remote Antenna Switch&lt;/a&gt;. I have used this unit on HF for decades without any noticeably deleterious effects, though I have never performed any measurements.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://cdn.shopify.com/s/files/1/0289/7782/3843/files/RCS-4.pdf?v=1586882717&quot; rel=&quot;nofollow noreferrer&quot;&gt;manual&lt;/a&gt; shows L201 and C203 filtering the supply to the relay coils. L201, p/n &lt;a href=&quot;http://m.ameritron.com/Product.php?productid=401-4090-1&quot; rel=&quot;nofollow noreferrer&quot;&gt;409-2150&lt;/a&gt;, is a 1A 90uH choke. At 1.8-MHz, this provides about 1K&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; of inductive reactance, which will effectively isolate the RF and DC/low-frequency parts of the system. Of course, this isolation increases with operating frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Off-the-shelf components with these or similar specs (e.g., 1A 100uH) are available in unit quantities for less than US$1 from the usual suppliers (DigiKey, Mouser, Newark, etc.). It's difficult to imagine doing better by winding your own inductor.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-07T10:49:42.137" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16649" PostTypeId="2" ParentId="16618" CreationDate="2020-05-07T13:38:40.080" Score="2" Body="&lt;p&gt;I downloaded the youtube video of Dan Romanchik with the slideshow that's based on the No-Nonsense Guide (by KB6NU). I downloaded it as an mp3 and it's the perfect &quot;podcast&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I listen to the whole thing every day and now, 3 days later, I'm almost ready for the test!&lt;/p&gt;&#xA;" OwnerUserId="16949" LastActivityDate="2020-05-07T13:38:40.080" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16650" PostTypeId="1" AcceptedAnswerId="16651" CreationDate="2020-05-07T15:21:42.717" Score="3" ViewCount="153" Body="&lt;p&gt;I have some UHF, microwave antennas and an antenna rotator on a roof mounted mast. The &quot;radio room&quot; is in the second floor just below the antennas. Also the service entrance for building electricity comes up the outer wall and &lt;strong&gt;enters the building in the second floor&lt;/strong&gt; near the cables for the roof mounted antennas. The location of the service entrance is quite different from most descriptions I find on the web, which makes me a bit confused about how to best connect things for best protection.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I do not want to propagate the coaxial cables for UHF and microwave all the way down to ground to protect them before propagating them up again because of cable loss. My thinking was that I should add a single point ground panel on the outside wall on the second floor, connect the mast and all antenna and rotator cables through it and ground the panel with a wide copper conductor all the way to ground. At ground level I connect it to a new grid of ground rods + the electricity safety ground rod. Since the service entrance for building electricity is very close to where the ground panel on the second floor will be, I was thinking to bind the ground wires together also at this point. This means there will be two ground conductors going on that outer wall quite close to each other all the way to ground - one thick new one, and the existing one from the electricity provider. They are connected to each other in both ends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are there any problems associated with having two down conductors for grounding close to each other - vertically like 7 meters? Should I ensure a maximum/minimum distance between the two? Is it correct to connect them together also in the top? I am mainly thinking in terms of lightning safety + and also not screw up the building electrical safety.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I hope someone with more experience can answer these questions.&lt;/p&gt;&#xA;" OwnerUserId="17027" LastEditorUserId="17027" LastEditDate="2020-05-11T07:18:57.657" LastActivityDate="2020-05-11T07:18:57.657" Title="Grounding for lightning safety - upper floor (UHF/microwave antennas)" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;grounding&gt;&lt;lightning&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16651" PostTypeId="2" ParentId="16650" CreationDate="2020-05-07T16:54:21.617" Score="4" Body="&lt;p&gt;Your two ground conductors must be connected at both ends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They must be connected at the bottom because that's where the ground is and they aren't ground conductors if they aren't connected there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And they must be connected at the top because if they are not, you don't have a single point ground. Without a single point ground the potentials between the two ground conductors will be different, and the lightning protection will not be effective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would route them as closely together as possible. The idea is to minimize the area of the loop they create. A larger loop area means higher inductance, meaning more induced voltage due to changing magnetic fields, and &lt;a href=&quot;https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction&quot; rel=&quot;nofollow noreferrer&quot;&gt;higher voltages with changing current&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Remember the goal of a lightning protection scheme is to divert as much as possible of the strike current away from the protected equipment, and to ensure everything within the protected equipment stays at about the same voltage. If you haven't already, see &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-05-07T16:54:21.617" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16652" PostTypeId="1" CreationDate="2020-05-08T11:11:21.143" Score="2" ViewCount="415" Body="&lt;p&gt;I am in the process of designing a small receiving loop antenna for the lower HF bands. By small I mean a circumference of less than &lt;span class=&quot;math-container&quot;&gt;$0.2\lambda$&lt;/span&gt;. Thus, a uniform current distribution can rightly be assumed. If we forget about impedance matching and tuning at the moment, would we really need a balun for this antenna? It seems to me that there are no paths for a common mode current to flow. Because of the small electrical size and hence uniform current distribution of the loop, KCL applies, and the current flowing on the inner coax conductor has to equal the current flowing on the (inner side of the) shield. No current on the outside of the shield should exist, because where would it come from?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Am I right?&lt;/p&gt;&#xA;" OwnerUserId="17036" LastEditorUserId="17036" LastEditDate="2020-05-08T11:24:50.567" LastActivityDate="2020-05-08T17:09:36.183" Title="Is a balun really necessary for a small loop antenna?" Tags="&lt;balun&gt;&lt;loop-antenna&gt;&lt;magnetic-loop&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16653" PostTypeId="1" AcceptedAnswerId="16657" CreationDate="2020-05-08T13:07:14.730" Score="0" ViewCount="149" Body="&lt;p&gt;How would testing be done on Zoom? Or would testing be pushed off until after COVID-19?&lt;/p&gt;&#xA;" OwnerUserId="16949" LastActivityDate="2020-05-08T15:03:44.783" Title="Virtual Testing | How would it be done" Tags="&lt;united-states&gt;&lt;license&gt;&lt;fcc&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16654" PostTypeId="2" ParentId="16653" CreationDate="2020-05-08T13:59:10.550" Score="3" Body="&lt;p&gt;On April 30, 2020, the FCC issued a Public Notice, &quot;&lt;a href=&quot;https://docs.fcc.gov/public/attachments/DA-20-467A1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;WIRELESS TELECOMMUNICATIONS BUREAU CONFIRMS THAT AMATEUR RADIO SERVICE OPERATOR LICENSE EXAMINATIONS MAY BE HELD REMOTELY&lt;/a&gt;.&quot; According to the &lt;a href=&quot;http://www.arrl.org/arrlletter?issue=2020-05-07#toc01&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;ARRL Letter&lt;/em&gt; for May 7, 2020&lt;/a&gt;,&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The FCC opened the door to remotely administered examinations in a June 5, 2014, FCC &lt;a href=&quot;https://transition.fcc.gov/Daily_Releases/Daily_Business/2014/db0609/FCC-14-74A1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Report and Order&lt;/em&gt;&lt;/a&gt;, noting that, since the VE system was established, &quot;remote testing methods have been developed, including audio and video links, either hard-wired to a site or available through internet or satellite technologies, which would allow a VE team to observe an examinee from afar.&quot; The FCC ruled that allowing VEs and VECs the option of administering examinations remotely was warranted. The FCC declined to incorporate any specific requirements or conditions for remote testing into the rules, and made it clear that VECs and VEs were not required to offer remote testing.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;You may be able to &lt;a href=&quot;http://www.arrl.org/find-an-amateur-radio-license-exam-session&quot; rel=&quot;nofollow noreferrer&quot;&gt;find an examiner&lt;/a&gt; who can remotely administer a test. Groups like &lt;a href=&quot;https://blog.hamstudy.org/2020/04/fully-remote-amateur-radio-license-exam-administration/&quot; rel=&quot;nofollow noreferrer&quot;&gt;HamStudy&lt;/a&gt; may also be able to help. Searching the internet for &quot;remote ham radio examination&quot; turns up a variety of responses, from &quot;Yes, we can!&quot; to &quot;We're developing plans&quot; to &quot;Sorry, we're closed.&quot;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-08T13:59:10.550" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16655" PostTypeId="2" ParentId="16653" CreationDate="2020-05-08T14:24:09.830" Score="2" Body="&lt;p&gt;There is not a universal answer for this.  Each VE testing group is handling it differently.  Some groups are suspending operations.  You would need to search for a group doing virtual testing to determine how it works.  ARRL and FCC have only stated that nothing prevents virtual testing, and have not given specific guidance on how to do it.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-05-08T14:24:09.830" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16656" PostTypeId="2" ParentId="16652" CreationDate="2020-05-08T14:37:11.817" Score="0" Body="&lt;p&gt;There are two purposes for a balun:  impedance matching transformer, and blocking common mode current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A small loop shouldn't need impedance matching, as the built in tuning capacitor should handle that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would a balun be needed on any antenna, including a small loop? Adding balun typically doesn't hurt if it isn't needed, especially if it's just a few loops of coax (&quot;air balun&quot;).  Common mode current isn't guaranteed even when a balun is recommended, so you can frequently leave it out.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Where would current on the shield of the coax come from?  Usually it is induced by coupling with the antenna due to the geometry between the coax and the antenna and has little to do with any electrical path within the antenna.   Sometimes you can eliminate the need for a balun just by making sure this geometry is symmetrical.  Or, the balun can help make this geometry less critical.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-05-08T16:04:50.360" LastActivityDate="2020-05-08T16:04:50.360" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16657" PostTypeId="2" ParentId="16653" CreationDate="2020-05-08T15:03:44.783" Score="2" Body="&lt;p&gt;Online testing has been done in the past and is currently being done, but there are issues and only a few VE teams are currently doing remote tests.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The first issue is to prevent cheating on the exam. Previously during remote exams, examiners would require another HAM to sit the person being tested to act as a proctor. Some examiners today are requiring several cameras so they can view the entire room the person is in. Other require you to have a movable camera and will periodically ask you to sweep the room. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition most will not let you have a cell phone in room, no notes, books, or documents of any type. Basically they want you in an empty room, just you and the PC. You can have only 1 PC with a single monitor and you must be using software with a remote desktop feature that allow them to control your PC.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Each team seems to to be using different software to fill out the forms and actually conduct the test. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is very time consuming as each 3 person team can only monitor a single person testing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I know many think online testing will the way of future, but I know most VE teams will not be able to do online testing. I hope many VE teams will be able to conduct in person testing sessions in the near future. The VE team I am part of is currently not able to conduct test sessions because our meeting place was a fire station and currently no one from outside the fire department is allowed in the station.  So far we have not been able to find an alternative location.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-05-08T15:03:44.783" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16658" PostTypeId="2" ParentId="16652" CreationDate="2020-05-08T16:20:40.477" Score="3" Body="&lt;p&gt;You may be overlooking that the feedline is itself an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If signals came only from the loop, then sure, there would be no need for a balun. But the feedline is also effectively a big vertical antenna in the common-mode, and is going to pick up signals as such. Again by the KCL, the currents picked up by this vertical, at the end of the coax where the loop is attached, can travel right around the loop and enter the center conductor where we know they will affect the receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The purpose of the balun is to insert a large impedance at this point so that can't happen. To retain the desired radiation pattern of the loop and to avoid having the radiation pattern of a vertical superimposed upon it, you must show that common-mode currents from the feedline can't couple into the differential-mode.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, you can consider what happens to the loop in transmitting when the coax is represented as a superposition of its differential and common modes:&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/KN6yM.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fKN6yM.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$V_{dm}$&lt;/span&gt; is the differential-mode voltage generated by the transmitter. &lt;span class=&quot;math-container&quot;&gt;$Z_{ant}$&lt;/span&gt; is the antenna impedance. And &lt;span class=&quot;math-container&quot;&gt;$Z_{cm}$&lt;/span&gt; is the common-mode impedance which is unknown: it depends on the length of the feedline and the environment.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From this it should be clear that unless &lt;span class=&quot;math-container&quot;&gt;$Z_{cm}$&lt;/span&gt; is very large, than the current in &lt;span class=&quot;math-container&quot;&gt;$Z_{cm}$&lt;/span&gt; due to the voltage source is significant, and therefore there exist common-mode currents on the feedline which will radiate. And by reciprocity, you can conclude the feedline also acts as an antenna on receive.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The addition of a balun makes &lt;span class=&quot;math-container&quot;&gt;$Z_{cm}$&lt;/span&gt; very large, thus reducing the common-mode currents through impedance divider action to a negligible amount.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-05-08T17:09:36.183" LastActivityDate="2020-05-08T17:09:36.183" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16660" PostTypeId="2" ParentId="16636" CreationDate="2020-05-09T05:03:15.887" Score="0" Body="&lt;p&gt;First, I measure it by RG316 cable.The test structure following blow:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;SG --&gt; RG316 --&gt; SAW1 --&gt; Thru male SMA --&gt; SAW2 --&gt; RG316 --&gt; SA&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Signal Generator output power is 0dBm and when applied to SAWs, only 85dB~90dB attenuated. So, change RG316 cable to N Type cable and measure again and achieve to 120 dB attenuation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It was cable leakage and measurement error.&lt;/p&gt;&#xA;" OwnerUserId="17016" LastActivityDate="2020-05-09T05:03:15.887" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16661" PostTypeId="2" ParentId="16622" CreationDate="2020-05-09T12:38:33.023" Score="2" Body="&lt;p&gt;The added capacitance of the RG58 stubs may also be an issue. I suggest using flat copper strip instead between the port connectors and the PCB. While you can probably get away with SO239's for just 2m, N connectors (or similar UHF connectors) are really mandatory here. &lt;/p&gt;&#xA;" OwnerUserId="17043" LastActivityDate="2020-05-09T12:38:33.023" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16662" PostTypeId="1" CreationDate="2020-05-09T14:59:38.873" Score="0" ViewCount="351" Body="&lt;p&gt;I have a problem with my Yaesu FT-817 it Won't transmit Dig, SSB or CW, But it does transmit AM, FM and Pkt on all bands. Does anyone know what the problem might be. The Radio receives fine on all bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When I press the ptt the transmit light comes on but there is no power being sent to the Antenna. On AM FM I get power readings on my Meter on all bands HF and VHF but On SSB and CW there is no power leaving the radio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume if the finals where blown I would not be getting any output what so ever. I am hoping someone else that owns this radio as seen this issue in the past.&lt;/p&gt;&#xA;" OwnerUserId="17045" LastEditorUserId="76" LastEditDate="2020-05-10T21:03:10.917" LastActivityDate="2021-01-06T10:37:14.457" Title="Yaesu FT-817 Won't transmit Dig, SSB or CW" Tags="&lt;transceiver&gt;&lt;mobile&gt;&lt;yaesu&gt;&lt;equipment-troubleshooting&gt;&lt;repair&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16663" PostTypeId="2" ParentId="14981" CreationDate="2020-05-09T23:20:38.797" Score="0" Body="&lt;p&gt;Peter Buxton, you are right. The ferrite rod used here is most probably mix #43, the one commonly found in the BC Radio receivers. The one with the 3 windings is an 1:1 voltage BalUn, the center (blue) winding being the magnetising winding. If you removed this Blue winding you get 1:1 current balun or CMC choke that is what you require to suppress the CMC that tends to flow on the outer surface of the coax braid. Phil Frost has mistaken the core material as iron carbonyl mix #2 but whatever he said about the #2 is correct; and it is used mainly as high Q inductor as in harmonics filter below 10 MHz. But the CMC has nothing to do with the SWR you happen to observe in your antenna. SWR arises due to mismatch of impedance at the feed point of the dipole and the coax cable.&lt;/p&gt;&#xA;" OwnerUserId="17048" LastActivityDate="2020-05-09T23:20:38.797" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16664" PostTypeId="1" AcceptedAnswerId="16669" CreationDate="2020-05-10T07:27:15.693" Score="1" ViewCount="1177" Body="&lt;p&gt;How does a single FM antenna length work in the entire FM frequency band range, when there are theories which state that the antenna size should always be close to wavelength/4 for proper reception &amp;amp; transmission?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example: The FM frequency band ranges from 88 MHz to 108 MHz. How will an FM antenna length will match all the frequencies from 88 MHz to 108 MHz? Does the antenna length scale itself within that range or how does it work?&lt;/p&gt;&#xA;" OwnerUserId="17049" LastEditorUserId="8717" LastEditDate="2020-05-14T21:25:19.280" LastActivityDate="2020-05-15T09:14:13.540" Title="Determining one exact antenna length for a whole band (e.g. FM/AM broadcast, Bluetooth and others)" Tags="&lt;antenna&gt;&lt;bandwidth&gt;" AnswerCount="4" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16665" PostTypeId="2" ParentId="16634" CreationDate="2020-05-10T09:44:28.620" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;the lower coil seems to be an &quot;ugly balun&quot;, a choke made out of coax, is this it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Sure looks like it.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What is the 447mm &quot;covered&quot; section, though? Is it some sort of quarter-wave matching? should it also be extended if i try to match the antenna to a lower frequency?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, it's definitely intended as a kind of quarter-wave transformer akin to the lower segment of a J-pole. The fact that it's a little shorter than expected might have something to do with the physical extent of the &quot;ugly balun&quot;, or something to do with the mystery &quot;sleeves&quot;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;the 7 turns middle coil, what does it do? I have read about phasing coils, but I've seen them implemented as coils that are part of the antenna. this is just a section of coax, like a choke balun. does this also work as a phasing coil?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yes, it's a phasing coil. At a guess, the braid and jacket are left on this section to give the coil the right spacing or the right amount of parasitic capacitance. It's not &quot;working like coax&quot; since the braid is left unconnected at both ends.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;now there is a 920mm section of radiator. why is this different from the bottom part, not &quot;half covered&quot;?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Because it is what it is, just a half wavelength of radiator.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;finally the sleeves. what are they?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I have no idea what the theory on these is supposed to be. Obviously they have some effect on the impedance of the antenna in the area where they're placed, and moving them between lower- and higher- impedance points along the length of the antenna. But the author doesn't offer any real explanation of what they're doing, and I can't come up with one on my own.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-05-10T09:44:28.620" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16667" PostTypeId="1" AcceptedAnswerId="16671" CreationDate="2020-05-10T22:13:25.517" Score="2" ViewCount="112" Body="&lt;p&gt;I'm putting together a 2m NBFM transmitter/receiver combo using rpitx and rtl-sdr. During testing my low-pass filter I discovered that rpitx is generating spurious signals within and around the band (see screenshot below). They're only about -30dBc so I need to remove them before transmitting. Removing them with a band-pass filter would be difficult and restrict the frequency range. &lt;strong&gt;What could be causing these spurs, and can anything be done to clean up the signal?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've overlayed two screenshots, one with no signal (green), and one with the rpitx signal at 146MHz (red), taken from GQRX+RTLSDR which show some of the spurs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uxJYq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uxJYq.png&quot; alt=&quot;FFT of 2m band&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The spurs are frequency-dependent and generally span +/-5MHz or so. I've ruled out the rtl-sdr as the problem as I can see them on my scope too. The signal is generated with &lt;code&gt;rpitx/tune -f 146000000&lt;/code&gt; and is on the BCM4 GPIO. My Pi is a 3B+.&lt;/p&gt;&#xA;" OwnerUserId="9103" LastEditorUserId="76" LastEditDate="2020-05-10T22:27:24.767" LastActivityDate="2020-05-11T17:42:48.927" Title="Can these in-band spurs from rpitx be eliminated somehow?" Tags="&lt;software-defined-radio&gt;&lt;diy&gt;&lt;transmitter&gt;&lt;2m-band&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16668" PostTypeId="2" ParentId="16664" CreationDate="2020-05-11T05:47:02.813" Score="3" Body="&lt;p&gt;FM antennas (the sort that come with your receiver) are trimmed for best performance in the middle of the FM band. Because that band is not very wide, and the signals they receive are generally not weak, they work adequately well at the low and high ends of the band. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For picking up weak signals, you'll use a &lt;em&gt;broadbanded&lt;/em&gt; FM antenna on a mast, where there are enough antenna elements in the design to allow adequate operation all the way across the band. &lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2020-05-11T05:47:02.813" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16669" PostTypeId="2" ParentId="16664" CreationDate="2020-05-11T14:26:45.860" Score="3" Body="&lt;p&gt;Design goals for a receiving antenna and a transmitting antenna can be very different.  For transmitting antennas, the goals are generally efficient power transfer, directivity (a.k.a. &quot;gain&quot;), and efficiency.  Directivity has to do with the radiation pattern of the antenna (omnidirectional or aimed in a certain direction); efficiency generally has to do with the size of the antenna relative to the wavelength of the transmitted signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For efficient power transfer, the impedance of the transmission line and the load have to be &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_matching&quot; rel=&quot;nofollow noreferrer&quot;&gt;matched&lt;/a&gt; to the output impedance of the transmitter.  In ham radio terms, the SWR should be as close to 1:1 as possible.  If the load (the transmission line and antenna) is not perfectly matched to the source (the transmitter), then reflected power makes the output current and voltage rise.  Transmitters can often tolerate a certain degree of mismatch, but beyond that the output power must be reduced, or the transmitter may be damaged.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance of an antenna varies with frequency.  Transmitting antennas are typically tuned so that the mismatch is lowest at the center of the frequency band of interest.  The changing impedance of the antenna, combined with the degree of mismatch that the transmitter will tolerate, gives a range of frequencies that the transmitter, feed line, and antenna can be used to transmit at full power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For receive-only antennas, efficient power transfer is not necessarily a concern.  Impedance bridging, where the load impedance (of the receiver) is chosen to be much larger than the source impedance (of the antenna and transmission line), may be enough.  Impedance bridging maximizes the signal &lt;em&gt;voltage&lt;/em&gt; rather than the signal &lt;em&gt;power&lt;/em&gt;.  Maximum power transfer is generally unnecessary in a broadcast receiver because amplifier circuits can usually be designed to have as much gain as necessary.  (The limiting factor in how much gain can be used generally has to do with noise generated by the receiver itself, which is usually not a concern for a broadcast receiver.)  In an impedance bridging situation, as used by a typical FM broadcast antenna and receiver, small changes in the impedance of the antenna don't matter very much, because the input impedance of the receiver is much larger than that of the antenna and feed line anyway.  So a receive-only antenna can have a much broader bandwidth than a transmitting antenna, which needs to be concerned with efficient power transfer.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-05-11T14:26:45.860" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16670" PostTypeId="2" ParentId="1058" CreationDate="2020-05-11T17:18:02.790" Score="1" Body="&lt;p&gt;The &quot;LoG&quot; or &quot;Loop on Ground&quot; is a simple antenna to get you going. &lt;a href=&quot;http://www.kk5jy.net/LoG/?fbclid=IwAR0dDk21M6XqZg7IwQ5NE7ggmS5Ux6Ivc_-_gtSZpE9Qbeu4EB9h5T4NGyU&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.kk5jy.net/LoG/?fbclid=IwAR0dDk21M6XqZg7IwQ5NE7ggmS5Ux6Ivc_-_gtSZpE9Qbeu4EB9h5T4NGyU&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Like you, I have limited space in my yard, so the LoG works out nicely at a perimeter of 60 feet.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;You don't have to build the transformer yourself, as Black Cat Systems makes one for receiving already:  &lt;a href=&quot;https://www.blackcatsystems.com/rf-products/cyclops_rf_ham_shortwave_radio_matching_transformer.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.blackcatsystems.com/rf-products/cyclops_rf_ham_shortwave_radio_matching_transformer.html&lt;/a&gt;.  Chris at Black Cat is a Jedi Master of HF receiving antennas and can get you squared away.   &lt;/p&gt;&#xA;" OwnerUserId="9772" LastActivityDate="2020-05-11T17:18:02.790" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16671" PostTypeId="2" ParentId="16667" CreationDate="2020-05-11T17:42:48.927" Score="7" Body="&lt;p&gt;I can't dig up my source for this, but I'm pretty sure these spurs are just the result of rpitx using a fractional-N PLL (that isn't in any way optimized for phase noise) to generate a square wave. You get pulses of different (discrete) widths, which means you get spurs at predictable intervals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There isn't really anything you can do to make them go away, but their relative strength will be dependent on your chosen frequency and its relationship to the master oscillator frequency (which I believe is 19.2 MHz). If you're willing to do some trial-and-error, you can scan through the band hoping to find a center frequency where all of the spurs are at acceptable levels (unlikely, but possible) or one where all of the significant spurs are far enough away from the carrier that using a bandpass filter becomes practical.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-05-11T17:42:48.927" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16672" PostTypeId="2" ParentId="16664" CreationDate="2020-05-12T08:33:10.717" Score="2" Body="&lt;p&gt;It appears that only reception on the 88 -108 MHz FM is being referred to.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With high power FM transmitters located in the heart of a city, a 75 cm length of wire would suffice to receive stations across the band. In the case of a receiver with a telescopic antenna, it's length could be adjusted, if required, to receive weaker signals.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In fringe areas, a broadband log-periodic antenna, covering 88-108 MHz, would be the right solution.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The answer to your question would be that reception across the 88-108 MHz FM band would be possible using a single log-periodic antenna specifically designed for the FM band and having a bandwidth of 20 MHz. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;More details on log-periodic antennas at&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Log-periodic_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Log-periodic_antenna&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-05-12T08:33:10.717" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16673" PostTypeId="1" AcceptedAnswerId="16674" CreationDate="2020-05-12T13:13:52.943" Score="4" ViewCount="249" Body="&lt;p&gt;I have a vertical antenna, about 7M total length, with a loading coil at 6M height. This is just because aluminium tubing is sold in 6 meter lengths. The loading coil is used to make it resonate at 7.1 MHz. Here's a SWR plot of the antenna (simulated):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Aky1i.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Aky1i.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I was wondering if it would be possible to replace the loading coil for a trap, for example at 8.5MHz, so the antenna would work in both the 30 and 40M band. Here's my idea:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;At below 8.5MHz, the capacitor will present a high impedance, and the RF would flow through the coil, and will resonate at 7.1MHz&lt;/li&gt;&#xA;&lt;li&gt;At above 8.5MHz, the capacitor will present a low impedance, and RF would bypass the coil, making the antenna also resonate at 10MHz&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I don't know the exact value of my loading coil. It was calculated around 18uH but I had to remove one turn to raise the frequency to 7.1MHz. 4NEC2 is happy with a 16uH loading coil (as shown by the previous SWR plot). So I calculated a LC network for 8.5MHz with a 16uH inductance. The resulting value is 21.9pF. Here's the plot of said LC network:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/KFDaJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KFDaJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Definitely not good I did not find any capacitance values that will satisfy my requirements, so instead I used a coaxial trap calculator to calculate a 8.5MHz trap. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The problem with this is that the values seem to become extremely critical. When testing the different frequencies, the required inductance was within 2.8 to 3uH, and the capacitance between 120 and 130pf. Every picofarad matters, which makes me think thermal expansion effects will alter the trap. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's a SWR plot of the same antenna with a trap made with 3uH and 131pf, instead of the 16uH coil:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nySvH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nySvH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Definitely much more promising. Let's add a matching network with 4NEC2 and try to take the impedance to 50+0j:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bsC6e.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bsC6e.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The concept seems to be working, but the SWR bandwidth at the 7MHz section is extrmely narrow. Let's zoom in into the 7 MHz band:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uSg0F.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uSg0F.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can see the 1.5 to 1.5 SWR bandwidth goes from 7.18 to 7.22MHz. Only 40KHz! This is unusable and most likely will shift wildly with weather, and will be a nightmare to tune. So to recap:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Is it possible to replace my loading coil for a trap, and make my 7.2M vertical resonate both &quot;naturally&quot; (for the 30M band at 10.1MHz) and &quot;loaded&quot; (for the 40M band at 7.1MHz)?&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The lower portion of my vertical I'd prefer to stay 6M as not to cut the alu tubing (this is both radiator and structural support. The upper part I can shorten or extend as needed.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="14642" LastEditDate="2020-05-12T13:53:41.093" LastActivityDate="2020-05-13T12:56:19.557" Title="Using a trap out of its resonance frequency?" Tags="&lt;antenna&gt;&lt;trap&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16674" PostTypeId="2" ParentId="16673" CreationDate="2020-05-12T16:18:01.073" Score="4" Body="&lt;p&gt;While your specific implementation will include numerous variables which are difficult to account for, I ran a NEC-2 model to illustrate the direction of a solution:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Vertical element: 8.5-m tall 2-in diameter conductor, elevated 0.1-m above ground&lt;/li&gt;&#xA;&lt;li&gt;Radials: 8 x #14 wires, elevated 0.1-m above ground, that are &lt;span class=&quot;math-container&quot;&gt;$\frac{\lambda}{4}$&lt;/span&gt;-wave on 40m (10.5-m)&lt;/li&gt;&#xA;&lt;li&gt;Trap: 5uH in parallel with 50pF placed 85% of the way to the top of the conductor&lt;/li&gt;&#xA;&lt;li&gt;Ground: Sommerfeld-Norton model with &quot;medium&quot; conductivity (.005-S/m, &lt;span class=&quot;math-container&quot;&gt;$\epsilon_r$&lt;/span&gt;=13)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Varying any of these parameters will affect the driving point impedance. Here's a picture of the model:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/buEFA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/buEFA.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This produces a 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; SWR curve that should be a reasonable starting point for further optimization:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aolbZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aolbZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resonant frequencies are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;7.375-MHz with 300-kHz of 2:1 SWR bandwidth&lt;/li&gt;&#xA;&lt;li&gt;9.75-MHz with 250-kHz of 2:1 SWR bandwidth &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Adding a broadband transformer to match 35-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; improves the SWR:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UTQFw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UTQFw.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I observed that increasing trap capacitance and reducing inductance tended to produce more SWR bandwidth on 40m, so the L/C ratio is an important parameter to vary as you search for your solution. You may well have to spend hours or days tuning your model and more hours or days tuning your implementation, but it's a time-honored solution.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-05-13T12:56:19.557" LastActivityDate="2020-05-13T12:56:19.557" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16675" PostTypeId="2" ParentId="7192" CreationDate="2020-05-12T17:54:36.123" Score="1" Body="&lt;p&gt;We, ARES, send files often via VHF packet and via several HF digital modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My favorite HF digital is based on the many modes of FLDigi, but set up the files (like ICS-213 form) using Winlink Express.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On VHF, my station is part of a packet network, running 24/7. www.midgadata.net. The net also supports DRATS on the same frequency; so we can use the DRATS software to send either packet or DRATS mode. Both have collision avoidance.&lt;/p&gt;&#xA;" OwnerUserId="17057" LastActivityDate="2020-05-12T17:54:36.123" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16676" PostTypeId="2" ParentId="16337" CreationDate="2020-05-12T19:20:02.047" Score="1" Body="&lt;p&gt;Putting multiple ceramic filters in series is common practice. There is additional loss; twice as many filters equals twice a much loss, may have to adjust the amplifier a bit.&lt;/p&gt;&#xA;" OwnerUserId="17058" LastActivityDate="2020-05-12T19:20:02.047" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16677" PostTypeId="2" ParentId="16626" CreationDate="2020-05-12T19:42:22.667" Score="2" Body="&lt;p&gt;Since one aspect of amateur radio is &quot;home brew&quot; ... anything that transmits a &quot;suitable signal&quot; in an amateur band operated by a licensed amateur radio operator, is legal. The key part of the &quot;suitable signal&quot; is power level and spurious signal levels, and includes permitted modulations in the portion of the band wherein the transmission occurs.&lt;/p&gt;&#xA;" OwnerUserId="17058" LastActivityDate="2020-05-12T19:42:22.667" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16678" PostTypeId="2" ParentId="16662" CreationDate="2020-05-12T21:53:32.220" Score="1" Body="&lt;p&gt;SSB requires a signal from the microphone: only when you are talking there is a signal generated. For CW you need to connect a morse key or paddle to have output signal. When FM and AM are operational there is nothing wrong with your power amplifier. In case of a defect: check the microphone by listening to the AM or FM output signal and when that is ok and ssb still doesn't work, check the menu settings for SSB gain, audio, filter, etc. PA0FSB &lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-05-12T21:53:32.220" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16679" PostTypeId="1" AcceptedAnswerId="16682" CreationDate="2020-05-13T01:16:15.123" Score="1" ViewCount="141" Body="&lt;p&gt;I am doing some temporary FM broadcasting for car events such as COVID-safe car parades and drive-in movies. The terrain is horrible, urban areas with lots of buildings. The cars snake around a city, with the transmit car in the middle. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Understandably, there are not many purpose-built, car-mounted FM radio transmission antennas.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I have a 1/4λ &lt;a href=&quot;https://www.pulselarsenantennas.com/product/nmoq88c-2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Pulse Larsen PulseLarsen NMOQ88C&lt;/a&gt; on a 5&quot; NMO mag mount.(tuned by instructions) It works okay, but I wonder if there are better options.&lt;/li&gt;&#xA;&lt;li&gt;It seems there aren't any 5/8λ antennas with NMO mounts in this range, would it be possible to modify a 102&quot; CB Whip into a 5/8λ antenna at 88mhz? Can I use a base loaded coil from a 144-174MHz NMO 5/8λ system with a longer whip? &lt;/li&gt;&#xA;&lt;li&gt;Is a 1/2λ worth exploring?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I am transmitting with 30W. I have no antenna analyzer nor an SWR meter. &#xA;I am most interested in what I realize is mostly impossible, better NLOS (Non line-of-sight) transmission so cars can continue to hear after they have turned a corner.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is the 1/4λ as good as it gets for my application?&lt;/p&gt;&#xA;" OwnerUserId="17067" LastEditorUserId="17067" LastEditDate="2020-05-15T04:36:58.500" LastActivityDate="2020-05-15T04:36:58.500" Title="Need antenna for mobile mag-mount LPFM broadcast 88.3 MHz" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;mobile&gt;&lt;vertical-antenna&gt;&lt;fm&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16680" PostTypeId="2" ParentId="16679" CreationDate="2020-05-13T07:32:09.847" Score="2" Body="&lt;p&gt;A quick note:  If the transmit system described in the OP will be or is unlicensed by the regulating body having jurisdiction for such (e.g. the FCC in the USA), then some risk will be involved in its use.  In the US, such unlicensed systems in the FM broadcast band &lt;em&gt;are&lt;/em&gt; authorized under title 47CFR §15.239, but limit the maximum field intensity 3 meters in all directions from the transmit antenna to &lt;strong&gt;250 µV/m&lt;/strong&gt;.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;That free space field at that distance is produced by a simple 1/2-wave dipole radiating about 11 nanowatts (0.000 000 011 watts).  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The maximum useful range of such an FCC-compliant system to a good FM receive system on an interference-free FM channel is on the order of 300-500 feet.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-05-13T07:32:09.847" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16681" PostTypeId="2" ParentId="919" CreationDate="2020-05-13T09:47:45.213" Score="1" Body="&lt;p&gt;“&#xA;If you want an electric dipole antenna (because that is the desired radiation pattern) folded or straight dipoles should be equivalent if they use the same number of wires with the same spacing. It is probably best to use a straight dipole (maybe with many parallel wires for bandwidth) because the lower feed impedance makes it easier to eliminate common mode interference on the cable with balun or common mode choke.”&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Per the above; although correct based on a free space dipole impedance of 73 ohms, I would suggest that very few practical dipoles are close to this based on the typical proximity to ground and the slanting, inverting or angle of placement; especially on 160m and 80m. If the dipole is less than 1/8WL high, in an inverted v configuration or angled, it can be significantly less than even 50 ohms. Sometimes as low as 12 ohms. In those cases the impedance transformation of a folded dipole can in fact aid in getting a good match. &lt;/p&gt;&#xA;" OwnerUserId="17069" LastActivityDate="2020-05-13T09:47:45.213" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16682" PostTypeId="2" ParentId="16679" CreationDate="2020-05-13T18:00:30.983" Score="3" Body="&lt;p&gt;First, some technical information.  &lt;a href=&quot;https://www.w8ji.com/VHF%20mobile%20vertical.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;According to W8JI&lt;/a&gt;, who knows more about antennas than I likely ever will, a 5/8λ vertical antenna potentially offers a few decibels of horizontal gain over a 1/4λ vertical, if you have a large-enough ground plane; specifically, a ground plane with a radius of about 1.5 m or larger.  That's a ground plane 10' across, in imperial units, which means a big vehicle.  It might be possible to home-brew such a 5/8λ vertical or some other fancy antenna, but not without essential tools, including an SWR meter at a bare minimum.  An antenna analyzer is really helpful if you're trying to do home-brew any antenna, especially a tricky one like the one you describe.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I question your desire for fancy antennas that might get you a couple more decibels of horizontal gain.  30 W broadcast through a 1/4λ vertical would give you a fairly large broadcast area, much larger than a drive-in movie theater, even in urban terrain.  Also I think you underestimate the tendency of signals to get around obstacles such as found in cities; signals diffract, reflect, and pass around and through many obstacles like buildings.  When I'm in a city, I hear FM broadcast signals through my car radio quite well, even when I'm in an alley between tall buildings, unless the signal is weak to begin with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It is quite illegal to operate a 30 W FM broadcast station from a vehicle in the US, but I see that you are in Namibia, where rules may be very different.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-05-13T18:05:52.650" LastActivityDate="2020-05-13T18:05:52.650" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16683" PostTypeId="2" ParentId="16679" CreationDate="2020-05-15T01:06:29.633" Score="0" Body="&lt;p&gt;Height is king in urban environments; the higher the better.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;A 5/8 wavelength antenna will reduce the vertical beam-width, not what you want.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The optimal antenna for your application is a vertical dipole(folded or not) with a flat reflector, located well above and slightly behind the screen as high as possible with a very slight forward tilt(assuming there is a building opposite of the transmitter building to bounce off of, the primary users should receive the first bounce) downward at the top to aim the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume you want the viewers to hear the movie, this tends to indicate line of sight, not the whole town. Your 7 watt transmitter will work perfectly, assuming a good impedance match(and decent coax) to the antenna. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using a flat reflector behind will give you a &gt;2db gain in the forward direction with a wide,160 to 180 degree, pattern on the front of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Make sure you use a good bandpass filter to make sure you are not interfering with other adjacent stations.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="16873" LastActivityDate="2020-05-15T01:06:29.633" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="16684" PostTypeId="2" ParentId="1352" CreationDate="2020-05-15T02:00:31.297" Score="2" Body="&lt;p&gt;For United States Amateur Radio Call Signs I use this.&lt;/p&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;Regex TheCallSignRegex = new Regex(@&quot;^(A[A-L]|K[A-Z]|N[A-Z]|W[A-Z]|K|N|W){1}\d{1}[A-Z]{1,3}&quot;, RegexOptions.Compiled | RegexOptions.IgnoreCase);&#xA;&#xA;String Call = &quot;w6am&quot;; // Trailing spaces in the string 'Call' will return a failed match &#xA;Match  TheMatch = TheCallSignRegex.Match(Call);&#xA;&#xA;Boolean ItLooksLikeAUSACallSign = (TheMatch.Success &amp;amp;&amp;amp; TheMatch.Index == 0 &amp;amp;&amp;amp; TheMatch.Value.Length == Call.Length);&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;Note : Since I used RegexOption.Compiled it is preferred that this Regix &quot;TheCallSignRegex&quot; object be created in a static constructor so it is only executed once during the run of a program.&lt;/p&gt;&#xA;" OwnerUserId="17081" LastEditorUserId="4665" LastEditDate="2020-05-15T20:01:45.480" LastActivityDate="2020-05-15T20:01:45.480" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16685" PostTypeId="2" ParentId="16548" CreationDate="2020-05-15T07:08:44.943" Score="0" Body="&lt;p&gt;I found a LoRa &lt;a href=&quot;https://www.murata.com/en-global/products/connectivitymodule/lpwa&quot; rel=&quot;nofollow noreferrer&quot;&gt;device&lt;/a&gt; which covers all the frequencies and I prepared a matching network to cover all range, and after some tests the results were so good, so the problem is solved.&#xA;Many thanks&lt;/p&gt;&#xA;" OwnerUserId="16870" LastActivityDate="2020-05-15T07:08:44.943" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16686" PostTypeId="2" ParentId="16664" CreationDate="2020-05-15T09:14:13.540" Score="1" Body="&lt;p&gt;Bandwidth of an antenna is primarily dependent on the design of the antenna and the electrical radius of the active element(s). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;With FM radio stations, the high power 1 - 100+ kilowatt transmitters, allows a lot of loss with respect to the receive antennas: any approximately eighth wavelength wire or longer will adequately receive any station in range(20 to 150 miles depending on terrain and antenna gain or loss).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most car antennas are given a length the corresponds close to the center of the FM band. The power output of the stations make up the difference. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the AM band the output power tends to be lower overall( .01 - 5KW+), since the band will travel longer distances. AM Reception is done in car radios through the use of loading coils applied to the FM antenna. The efficiency of the antenna + loading coils is about 5 to 60 percent of the power available in the airwaves. Reception depends on propagation factors. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Bluetooth is a whole different story, it operates on the 2.4 GHZ spectrum with a power in the milliwatt power range. To minimize interference with WiFi occupying the same bands, it produces a signal that hops through all of the allocated frequencies in such a way to cause the minimal amount of disruption to the WiFi channels it conflicts with.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now back to antenna bandwidth:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are very wide designs based on angles like the rhombic design (high gain, highly directional, 1+ decade of 3db bandwidth)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The length specified wideband: (each band must be represented as a length in the elements of the design)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;log-periodic(Medium gain and directional)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;fan dipole&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would be failing to represent all widebands, I am sure I skipped many, if I did not include the End-Fed-Half-Wave(EFWH). The high impedance of an EFWH makes it a perfect longwire antenna for evenly divisible frequencies.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back to the electrical radius(where surface area dominates):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bowtie UHF, similar in concept to VHF rabbit ears:&#xA;    Four, or two, short sticks emanating from a common point and spaced appropriately. &#xA;The bounding frequencies of this design are dependent on the length and size of the elements. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For a dipole, the bandwidth is most dependent on the size of the conductor, but may be extended by introducing a second(or more wires) of the same length using (relative to wavelength) small spacers.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For microwave frequencies like 2.4GHz when space is a consideration, microstrip fractals tend to replace conventional antennas. The fractals offer a wider bandwidth and more electrical length, therefore more bandwidth for a smaller design.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Maximizing surface area leads to a higher bandwidth antenna.&lt;/p&gt;&#xA;" OwnerUserId="16873" LastActivityDate="2020-05-15T09:14:13.540" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16687" PostTypeId="1" CreationDate="2020-05-15T16:09:22.243" Score="2" ViewCount="1093" Body="&lt;p&gt;I am a new to the radio design field.&lt;/p&gt;&#xA;&lt;p&gt;My question is, 'What is so significant about 1/4 wavelength with respect to antennas.'&lt;/p&gt;&#xA;&lt;p&gt;From the information I have gathered from various sources, it is my impression that a 1/4 wavelength antenna is the most used on account of its performance.&lt;/p&gt;&#xA;&lt;p&gt;I am looking forward to an answer, elucidating the significance in simple terms that I could understand.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.electronics-notes.com/articles/antennas-propagation/vertical-antennas/quarter-wave-vertical.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Referred Link&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17049" LastEditorUserId="16873" LastEditDate="2020-09-05T17:05:42.113" LastActivityDate="2020-09-05T17:05:42.113" Title="Significance of 1/4 wavelength with respect to antennas" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;electronics&gt;" AnswerCount="5" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16689" PostTypeId="2" ParentId="16687" CreationDate="2020-05-16T20:36:43.960" Score="1" Body="&lt;p&gt;Dangerous to start this sequence of answers, but I do.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any conducting object can be used as antenna. From reciprocity (transmit versus receive) it can be deduced that when power is fed to such an antenna AND there is no loss, that all the power is transmitted. Must be transmitted, since without loss there is no conversion in heat (calories). There are however two important things for this antenna. 1: what is the directivity of the antenna (directivity pattern) and 2: what is the impedance of this antenna. That second aspect, the matching impedance, is a practical problem with limits: when the antenna feedpoint impedance deviates far from real impedance, there is need for complex matching network. And such network is realised with inductors and capacitances and these components do add to losses. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;To come back to your question: any resonant antenna is a practical solution to minimise the matching network losses. A resonant quarter wavelength with a dedicated counterpoise or earth system results in a feeding point impedance between 35 and (say) 60 Ohm pure resistive. That is an impedance that can be matched with simple means to most transmitter systems that require 50 Ohm real impedance. Most simple antenna systems are based on quarter wavelength antennas.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And, for next-step or future thoughts: a receiving antenna can be as small as you can imagine, without loss of signal to noise. At least at the antenna output terminal. Of course: noise is added in the amplifier or receiver that is connected to that antenna, so there is a practical limitation to the reduction of the dimensions. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example: a small telescope antenna used on shortwave for reception of signals with a simple (J-FET) LNA can have a sensitivity (own noise contribution) better than the received atmospheric noise, since the atmospheric noise is relatively high. Transmitting with such small telecope antenna requires series inductance to make impedance real AND impedance matching from that small few-Ohms impedance to the common 50-Ohms wanted load impedance for tranmitters. Also the requirements for the grounding are very different: for reception it is far less important, noise limitation only, than for transmitting, where the efficiency is affected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;PA0FSB&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-05-16T20:36:43.960" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16690" PostTypeId="2" ParentId="16687" CreationDate="2020-05-16T21:51:10.943" Score="1" Body="&lt;p&gt;Welcome to Ham SE, @Newbie, and thanks for your question.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you break a length of wire to create two terminals and apply an AC voltage across the terminals, you will excite an alternating current on the wire. Some wire lengths will accept more power from the generator than other lengths.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna cited in your reference has two terminals but, because Ground has some electrical conductivity, one of the two terminals is actually the Ground under the &quot;&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;\4 radiating element&quot;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/87SA6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/87SA6.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The ability of the &quot;antenna&quot; - in this case, the combination of the radiating element and the ground underneath it - to accept power from the generator depends on how much the antenna resists the flow of current. When speaking of AC voltages, we call this Impedance, symbolized by the letter Z and measured in ohms just like resistance for DC. For a given generator voltage, more current flows on the antenna when the Impedance is lower. When more current flows on the antenna, stronger electromagnetic waves are radiated. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance at the terminals - the &quot;feedpoint&quot; - varies with frequency. If we make the antenna 5-meters tall, the impedance seen by the generator will follow the green curve in the graph below as we change the frequency of the generator:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fa3kF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fa3kF.png&quot; alt=&quot;![![enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice that the antenna has the least resistance to the flow of current - the lowest impedance - at about 14.35-MHz, so this is the frequency at which the most current will flow and the strongest electromagnetic waves will be radiated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In free space, the length of an electromagnetic wave, &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;, is:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\lambda = \frac{c}{f}$$&lt;/span&gt;&#xA;where &lt;span class=&quot;math-container&quot;&gt;$c$&lt;/span&gt; is the speed of light (300 million meters/sec) and &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is the frequency of the generator (Hz). At &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt;=14.35MHz:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\lambda = \frac{3*10^8}{14.35*10^6} = 20.9-meters$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, our 5-m tall antenna is approximately 1/4 of the free-space wavelength of the 20.9-meter signal applied to the antenna terminals. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reasons the antenna is not &lt;em&gt;exactly&lt;/em&gt; &lt;span class=&quot;math-container&quot;&gt;$\lambda/4$&lt;/span&gt; are beyond the scope of your question. Antennas like this &quot;quarter wave vertical&quot; are indeed popular, but often for a complex set of reasons - cost, available space, materials on hand, stealth, etc. - not simply its &quot;performance.&quot;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-16T21:51:10.943" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16691" PostTypeId="1" AcceptedAnswerId="16692" CreationDate="2020-05-17T03:18:56.320" Score="1" ViewCount="117" Body="&lt;p&gt;&lt;strong&gt;What I am trying to do&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Radio is an IC-271, ~ 20 years old. I want to run it with a 12 V lead acid battery. I need to connect the battery to the radio. The radio's DC power connector is a 6-pin molex(?). The radio is designed to be used with power supply IC-PS15. On page 4 of the &lt;a href=&quot;https://www.manualslib.com/download/1036052/Icom-Ic-Ps15.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;power supply manual&lt;/a&gt;, it shows what the power connector pins are.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pins 2, 5 are ground. &amp;lt;- I understand this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pin 6 is for 110 or 240 V?? &amp;lt;- I don't understand this.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pins 1, 3, 4 &amp;lt;- I don't know what these are by looking at the diagram.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;Question&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;How can I connect a 12 V battery to the power connector? What should I do with each pin?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;My level&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am getting started with ham radio and have basic electronics knowledge.&lt;/p&gt;&#xA;" OwnerUserId="17050" LastEditorUserId="17050" LastEditDate="2020-05-17T03:43:39.877" LastActivityDate="2020-05-17T04:09:36.800" Title="How to connect IC-271 DC power connector to 12 V battery" Tags="&lt;power-supply&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16692" PostTypeId="2" ParentId="16691" CreationDate="2020-05-17T03:54:49.043" Score="1" Body="&lt;p&gt;I assume you're looking at this schematic:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/99Y5q.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/99Y5q.jpg&quot; alt=&quot;Schematic&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pins 2 and 5 are ground, as indicated by the chassis-ground symbol they're wired to. Since 1 and 4 also come from the power supply's low-voltage side, they must be the +12V output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, Pin 6 is going to the AC power cord, which is odd. But, if we follow the wire on pin 3 that is drawn parallel to it, we see that it goes to the transformer. So, there's a simple explanation for this: this is a circuit that &lt;strong&gt;allows the power supply to be turned on or off by a switch on the radio&lt;/strong&gt;. If pins 3 and 6 are not connected, the power supply gets no power, and if they are it does.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, there is no need to worry about those two pins if you are supplying battery power — you &lt;em&gt;could&lt;/em&gt; wire a switch across them to be able to use the switch that is somewhere on the radio, or you can also ignore them entirely.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(Incidentally, the &quot;110 or 240 V&quot; description is referring to selecting the right current rating for the &lt;em&gt;fuse&lt;/em&gt; given the supply voltage; it's not intended as a description of the function of the wire, but it did give you a hint!)&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;That was how to understand the pins, but if I identify this right, there's a much simpler &lt;em&gt;solution to your problem:&lt;/em&gt; &lt;strong&gt;this looks like the de-facto-standard 6-pin power connector used on many HF radios.&lt;/strong&gt; You can get a premade adapter from amateur radio accessory suppliers such as &lt;a href=&quot;https://powerwerx.com/hf6-molex-to-powerpole-adapter&quot; rel=&quot;nofollow noreferrer&quot;&gt;Powerwerx HF6-PP&lt;/a&gt; or &lt;a href=&quot;https://mfjenterprises.com/products/mfj-5535m&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ MFJ-5535M&lt;/a&gt;. That simplifies things down to the two pins of an Anderson PowerPole connector, a very common connector to use for attaching batteries to amateur radio gear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course, this requires a matching Anderson PowerPole plug on the battery, but you can also get such premade cables, or make your own — if you're at all interested in getting into portable or backup power, solar power systems, or just having several pieces of radio gear, it's quite useful to be able to make your own power cables to adapt various things to a common standard and to interoperate with other hams' gear and other equipment built for PowerPole connectors (e.g. including power meters and distribution boards), so getting a crimping tool for installing PowerPole connectors is a much more worthwhile investment than getting one for assembling one of those 6-pin plugs.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-05-17T03:54:49.043" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16693" PostTypeId="2" ParentId="16691" CreationDate="2020-05-17T04:09:36.800" Score="1" Body="&lt;p&gt;From the IC-271A/E manual, page 3:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zx4bS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zx4bS.png&quot; alt=&quot;diagram of DC power plug&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Pins 1 and 4 are both positive (12V or 13.8V or whatever), 2 and 5 are both ground, and 3 and 6 are left unconnected. This is the common six-pin power connector found on many HF rigs (but more recently replaced by a four-pin connector in Icom's case).&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-05-17T04:09:36.800" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16694" PostTypeId="2" ParentId="16687" CreationDate="2020-05-17T04:20:49.843" Score="-2" Body="&lt;p&gt;This explanation might be more intuitive, and thus not completely accurate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;EM fields (the RF someone might be trying to transmit using the antenna) are generated by accelerating charges (electrons, or maybe the lack thereof), over some distance.  For a particular transmit frequency, one wants to alter the direction of acceleration at some rate.  So, 1/(2*f) later, whatever is driving charges in one direction should probably try be trying to drive them in the opposite direction (for a frequency of f).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now the EM field driving the electrons can't go faster than the speed of light. So the acceleration of electrons gets to the end of a wire (tip of the antenna) after a certain amount of time, and then gets reflected back.  If the distance to and fro is half a cycle, the the charges rushing back get there at the same time the driver is also reversing direction.  Thus the two effects reinforce, instead of canceling out.  This reinforcement is usually a good thing, as it doesn't heat up the transmitter and/or the feedline as much.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-05-17T04:20:49.843" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16695" PostTypeId="2" ParentId="1804" CreationDate="2020-05-17T04:34:04.420" Score="0" Body="&lt;p&gt;I make legal limit power mag-loops with a gamma match and no capacitor.   It is my impression that the cap makes the match more frequency dependent and limits the ability to use the antenna on more than one band.    The cap does make fine tuning easier. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have also used the gamma match to match vertical poles up to 125 ft with good effect even when the pole was a height adverse to the usual vertical antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;These impressions are based on having matched dozens of antennas of various types.&lt;/p&gt;&#xA;" OwnerUserId="17089" LastActivityDate="2020-05-17T04:34:04.420" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16698" PostTypeId="1" AcceptedAnswerId="16705" CreationDate="2020-05-17T16:42:01.470" Score="2" ViewCount="350" Body="&lt;p&gt;I plan to put up a &quot;fan inverted vee&quot; but for various reasons I will not be able to take it down, adjust wire lengths, put it up, test, etc: I will basically have to cut the wires, put it up and leave it up there.  So given I sort of have one shot, I want to get the most accurate estimate by doing some modelling of my actual geometry, which I am able to do in the excellent EZNEC package. I note that I do have an antenna tuner (MFJ Intellituner).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But here is the problem: when I create such an antenna with the inverted vees from different bands physically far apart, I get a good result (low SWR in desired part of band), but when I create something that looks a lot more like the fan dipole/vee antennas you see described in numerous places, I see the shorter wavelength antenna having a swr like 10+. I expect this is the wrong answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It may be that I have done something wrong in creating the model in EZNEC.  I took the two band case (40m/20m) and created the basic antenna by using a short (one foot) central wire on which I place the source.  Then I have 40m and 20m wires coming out from the ends of the one foot section.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When the 40m section is a dipole (straight line) and the 20m section drops 35 degrees from each end, the swr looks very good for both bands (well under 2:1 in the desired band segments).  But if I then drop the 40m wires by 30 degrees on each side (so they are close-ish to the 20m wires), the 40m swr looks fine but the 20m swr is in between 10 and infinity in the region of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being a beginner with EZNEC, I suspect it is me doing something wrong! Below I attach from EZNEC 1) the dipole configuration 2) the source set-up  3) the &quot;fan inverted V&quot; configuration and a diagram showing the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I note that I am using the &quot;demo&quot; version with a maximum of 20 elements. Might this be why the antenna seems to not &quot;work&quot; in EZNEC?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CdRmC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CdRmC.png&quot; alt=&quot;fan inv v puzzle&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17088" LastEditorUserId="8717" LastEditDate="2020-05-18T21:36:07.300" LastActivityDate="2020-05-18T22:11:36.053" Title="Modelling a &quot;fan dipole&quot; or &quot;fan inverted vee&quot; using EZNEC - unexpected result" Tags="&lt;hf&gt;&lt;wire-antenna&gt;&lt;antenna-modeling&gt;&lt;parallel-dipole&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16699" PostTypeId="1" CreationDate="2020-05-18T03:07:22.847" Score="0" ViewCount="393" Body="&lt;p&gt;I am beginner in the Antenna theory and I have a few basic questions.&#xA;Please help me to clarify my understandings related to the basics which I have read.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And this question has 3 basic questions. Since, all are quite related and just basics, I have categorized all the below questions into a single umbrella question which could benefit both the answer provided and other people who would face the same doubts. If it is not right, I will ask a separate question. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My Understanding 1 - Antenna is just a piece of a metal conductor. &quot;Antenna is an OPEN CIRCUIT, and not a SHORT CIRCUIT&quot;.&#xA;Is my understanding correct that the Antenna is an open circuit and not a short circuit? Or is it different in different cases.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question 1 - Antenna being a just a single piece of wire/metal conductor, it can Either TRANSMIT or RECEIVE at a single time. Since, Antenna comprises of only one conductor, it can transmit or receive. In other words - Antenna is always a Half-duplex system, right? And not a Full-duplex system. This half duplex system is applicable for Antennas working at all frequency bands , example, Bluetooth, WiFi, GSM, etc. , right?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Question 2 - Without going into deep understanding, I am just understanding that for proper reception of antenna, the antenna length should be of half wavelength or quarter wavelength for proper reception of the transmitted signals. Why? - Without diving deep, I am just understand it as RESONANCE. Am I right in doing so?&lt;/p&gt;&#xA;" OwnerUserId="17049" LastActivityDate="2020-05-19T11:57:58.960" Title="Antenna Basics - Open/Short Circuit &amp; Half-Duplex/Full-Duplex" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;antenna-system&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16700" PostTypeId="2" ParentId="16699" CreationDate="2020-05-18T03:29:37.107" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;My Understanding 1 - Antenna is just a piece of a metal conductor. &quot;Antenna is an OPEN CIRCUIT, and not a SHORT CIRCUIT&quot;. Is my understanding correct that the Antenna is an open circuit and not a short circuit? Or is it different in different cases.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is not correct. There's a simple counterexample and a harder answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The simple counterexample is that, whereas &quot;dipole&quot;, &quot;monopole&quot;, or &quot;whip&quot; antennas consist of one or two separate conductors, &lt;em&gt;loop&lt;/em&gt; antennas consist of a single conductor — a loop — that is connected to the radio at both ends. (Antennas for AM broadcast receivers are commonly loop antennas — either wound on a ferrite rod inside the receiver, or an external wire loop that you might have seen packed in with a &quot;receiver&quot; in the home-theater sense.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The longer story is that in order to &lt;em&gt;understand&lt;/em&gt; antennas you need to understand &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_impedance&quot; rel=&quot;noreferrer&quot;&gt;impedance&lt;/a&gt;. Impedance is a generalization of resistance — any component with resistance also has impedance — that is an important tool when working with radio-frequency circuits that can resonate, or, more generally, that &lt;em&gt;react differently to different frequencies.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Given the concepts of impedance, we learn that an antenna (or any other component) has an impedance that &lt;em&gt;is different depending on the frequency your are considering.&lt;/em&gt; When we talk about something being an open or short circuit as measured with a multimeter, we're talking about its impedance as measured &lt;em&gt;with DC applied to it.&lt;/em&gt; DC has a frequency — zero hertz. On the other hand, if we measure an antenna with a tool that applies a radio-frequency signal, we will find (if it is a good antenna) an impedance that is &lt;em&gt;neither&lt;/em&gt; zero — an &quot;RF short circuit&quot; — nor infinity — an &quot;RF open circuit&quot;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, antennas can be designed such that they &quot;look like&quot; open circuits or short circuits to our usual understanding or wires, but still perform well as antennas. Both designs have their uses.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Antenna being a just a single piece of wire/metal conductor, it can Either TRANSMIT or RECEIVE at a single time. Since, Antenna comprises of only one conductor, it can transmit or receive. In other words - Antenna is always a Half-duplex system, right?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;False. Radio waves don't care. The foundation of this is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Superposition_principle&quot; rel=&quot;noreferrer&quot;&gt;superposition principle&lt;/a&gt;, which is true of the electromagnetic field whether it is in space or interacting with a radio or a transmission line or even just being the flow of current in an ordinary electric circuit. The principle tells us that you can have waves going both ways and they do not interfere with each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, in practice, in order to do full-duplex you have to either:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;use a device called a &lt;em&gt;diplexer&lt;/em&gt; or &lt;em&gt;duplexer&lt;/em&gt; (which is usually made of a pair of very good filters) to prevent the receiver from picking up the very strong signal from the adjacent transmitter,&lt;/li&gt;&#xA;&lt;li&gt;use very different frequencies, or&lt;/li&gt;&#xA;&lt;li&gt;do half-duplex but switch between transmitting and receiving very fast so it feels like it's full duplex (WiFi devices do this, for example).&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;But none of these are about properties of the antenna; rather, they are due to practical limitations on designing transmitters and receivers. (And also the fact that if you transmit on the same frequency you're receiving, objects in the environment will reflect the signal back to the receiver. Which is &lt;em&gt;great&lt;/em&gt; if you're building a radar, but not if you're building a communications device.)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I am just understanding that for proper reception of antenna, the antenna length should be of half wavelength or quarter wavelength for proper reception of the transmitted signals. Why? - Without diving deep, I am just understand it as RESONANCE.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Sort of. My advice would be, again, to study impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The impedance of an antenna changes depending on the frequency you are calculating or measuring with. If you use just the wrong frequency for the length, or just the wrong length for the frequency, your antenna will be an &quot;open&quot; or &quot;short&quot; circuit for RF purposes, and will therefore not transfer any signal into your receiver or out of your transmitter. So, you need to avoid those lengths. The quarter-wavelength is, in a sense, the length that is &lt;em&gt;most distant from&lt;/em&gt; the open circuit condition, so it is the one that is the easiest to actually get signal into or out of.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(For loop antennas, you need to be distant from the &lt;em&gt;short&lt;/em&gt; circuit condition, but it's basically a mirror-image situation, the same structure with different numbers. Also, for all of these lengths, there are longer lengths that are also usable, but we often use the shortest length because small is convenient and because the longer lengths have additional problems.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(There's some complications that I'm skipping over because I think it wouldn't be useful to talk about &quot;system impedances&quot;, say, until you know what an impedance is.)&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-05-18T03:29:37.107" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16701" PostTypeId="2" ParentId="16687" CreationDate="2020-05-18T12:36:43.960" Score="1" Body="&lt;p&gt;In reality, &lt;strong&gt;any&lt;/strong&gt; length/height of a conductor along which r-f current is present can produce e-m radiation into space.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, some antenna configurations and systems are more effective in generating e-m radiation from a given applied power than others.  This is shown in the graphic below by the reduced fields that antenna system produces when radiation resistance is low relative to &lt;strong&gt;non-radiating&lt;/strong&gt;, but resistive elements of the antenna system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The flow of r-f current in/along a non-radiating resistance produces heat, rather than the radiation of e-m waves.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/h3XnK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/h3XnK.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-05-23T08:42:34.087" LastActivityDate="2020-05-23T08:42:34.087" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16702" PostTypeId="2" ParentId="16687" CreationDate="2020-05-18T17:52:07.237" Score="6" Body="&lt;p&gt;The first part of why a quarter wavelength is special is actually understanding that it's not a quarter wavelength, but a half wavelength.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Consider a quarter-wavelength monopole. If a wavefront originates at the feedpoint, a quarter-cycle later it will have reached the end of the monopole. Here &quot;something interesting&quot; happens, because the antenna ends. That &quot;interesting event&quot; must then propagate back down the antenna to the feedpoint before it can affect the feedpoint impedance. So a quarter-wave element is a half-wavelength round trip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What then is the &quot;interesting thing&quot; that happens at the end of the antenna? The thing to realize is at the first instant something happens at the feedpoint, the feedpoint doesn't &quot;know&quot; the antenna is going to abruptly end some distance away. Even though the antenna is an open circuit, some current will initially flow, starting a wave propagating down the length of the antenna. When this wave reaches the end of the antenna, another wave starts in the opposite direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To develop some intuition for how this works, I suggest reading &lt;a href=&quot;https://electronics.stackexchange.com/q/19759/17608&quot;&gt;How does the current know how much to flow, before having seen the resistor?&lt;/a&gt; and these excellent &lt;a href=&quot;https://www.acs.psu.edu/drussell/Demos/reflect/reflect.html&quot; rel=&quot;noreferrer&quot;&gt;animations by Daniel Russell&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reflections take a half cycle to make their round trip, so by the time the reflection (of opposite polarity) reaches the feedpoint, the feedpoint has also reversed polarity. Thus the current in the reflected wave reinforces the current driven by the feedpoint. This current reinforcement means the feedpoint can drive a larger current with a lower voltage. In other words, it has a low impedance. And this is why an antenna which is an open circuit at DC can be a low impedance around 50 ohms at RF.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-05-18T17:52:07.237" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16703" PostTypeId="2" ParentId="16698" CreationDate="2020-05-18T20:42:32.193" Score="2" Body="&lt;p&gt;I doubt that the segment limits of the program is your main problem. You should get accurate enough details in spite of that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Part of the problem is at the feedpoint. You need to build your fan dipole so that there are insulating spreaders* to keep the wires for the different bands parallel and farther apart from each other for most of their length. &lt;em&gt;As it is, the wires are too close together for most of their length&lt;/em&gt;, and thus they are interacting with each other too much. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here's an easy solution: Add some short, steeply angled wires on each side --between the feedpoint insulator and the existing wires-- to get them away from each other. (Commercial multiband fan dipoles do this.) After that, you can adjust the length of each dipole to compensate for their interaction with each other.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9yeA2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9yeA2.jpg&quot; alt=&quot;Multiband dipole&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This design has a spreader as the center insulator:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Vf8EL.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Vf8EL.jpg&quot; alt=&quot;Fan dipole&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;*The spreaders could be rigid strips of plastic with holes drilled every 6 inches, and one should be as close to the feedpoint as practical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The alternative would be to not worry about being parallel with each other, and greatly increase the angle between them. One example of this might be to have two dipoles 90° to each other, or three dipoles 60° apart. It's often better not to do it this way due to the directional pattern of dipoles, but that's another story. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I once asked about the same thing here, but I can't find the question.)&#xA;&lt;hr&gt;&#xA;&lt;sup&gt;Photo credits: &lt;a href=&quot;https://wb4iuy.blogspot.com/2011/11/great-fan-dipole-diagram.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;First&lt;/a&gt; &#xA;&lt;a href=&quot;http://www.angelfire.com/mb/amandx/dipole.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Second&lt;/a&gt; &lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;h2&gt;TL;DR:&lt;/h2&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;The wires are too close&lt;/strong&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-05-18T21:30:50.037" LastActivityDate="2020-05-18T21:30:50.037" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16704" PostTypeId="1" CreationDate="2020-05-18T21:06:54.753" Score="1" ViewCount="123" Body="&lt;p&gt;Forgive me if this is not the proper forum, but I am an electrical engineer and a total radio novice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am designing a product that may contain off-the-shelf industrial radios that act as repeater devices. I recently spoke with an engineer at an industrial radio manufacturer, and he said that &quot;almost certainly&quot; a license is required if I am planning to use a 900 MHz repeater, even if I had intended for the rest of the system to be 900 ISM/unlicensed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can anyone confirm or deny this? I cannot find anything definitive, but I am probably not googling with the right terminology.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(I am in the United States, but I am working on a device that may be sold in the EU and/or Australia.)&lt;/p&gt;&#xA;" OwnerUserId="17096" LastEditorUserId="4665" LastEditDate="2020-05-19T14:58:28.103" LastActivityDate="2020-05-19T14:58:28.103" Title="When are licenses required for 900 MHz operation in the US? When are they not required?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;&lt;repeater&gt;" AnswerCount="1" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="16705" PostTypeId="2" ParentId="16698" CreationDate="2020-05-18T22:11:36.053" Score="4" Body="&lt;p&gt;Yes, being limited to 20 total segments for two dipoles is likely to be a problem, especially because of your hope / plan / expectation to have the model accurately predict what is built. I created an EZNEC model of a fan dipole for 40 and 20 meters; even the minimum segmentation - which, don't forget, must suffice at the highest operating frequency - required 21 total segments, which produced a somewhat different SWR curve than was obtained with more segments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Feedpoint geometry, as mentioned by another poster, is critical when simulating a design where two pairs of wires are meant to meet at a single set of terminals. I modeled the antenna thus:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qTz9r.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qTz9r.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;with this geometry at the feedpoint:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Swwby.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Swwby.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;All&lt;/strong&gt; segments are 1-ft long, for a total of 51 segments.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The resulting SWR curve, over medium-conductivity &quot;Real&quot; ground, is well behaved, with resonances at 7.1-MHz and 14.175-MHz:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/utEjW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/utEjW.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For your reference, here are the wire descriptions:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0AOYH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0AOYH.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-18T22:11:36.053" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16706" PostTypeId="1" CreationDate="2020-05-19T09:30:37.083" Score="2" ViewCount="115" Body="&lt;p&gt;This NEC4.2 analysis shows one example of such variation.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-05-20T08:26:06.613" Title="How Much Does the Radiation Pattern of an &quot;EFHW&quot; Antenna System Vary Across its Bands?" Tags="&lt;radiation-pattern&gt;&lt;efhw&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16707" PostTypeId="2" ParentId="16706" CreationDate="2020-05-19T09:32:43.630" Score="2" Body="&lt;p&gt;The analyses shown below provide one example of the difference in the radiation patterns of the EFHW system described there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Ih0fR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ih0fR.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;pre&gt;&lt;code&gt;              **RADIATION ENVELOPE at 3.9MHz**&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/chI65.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/chI65.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-05-20T08:26:06.613" LastActivityDate="2020-05-20T08:26:06.613" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16708" PostTypeId="2" ParentId="16699" CreationDate="2020-05-19T11:57:58.960" Score="2" Body="&lt;p&gt;The concept of open-circuit / short-circuit in DC circuits is not applicable to RF circuits. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;One example would be a 1/4 λ feeder, though left open at both ends, appearing as a short-circuit at either end for RF. The same line, when shorted at one end, would appear as an open circuit at the other end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An antenna used in a full duplex system receives and transmits simultaneously. A repeater antenna is an example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Half wavelength and quarter wavelength antennas are resonant antennas. A half wavelength antenna is analogous to a string, fixed at both ends and plucked in the middle, generating a similar standing wave. &lt;/p&gt;&#xA;" OwnerUserId="1569" LastActivityDate="2020-05-19T11:57:58.960" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16709" PostTypeId="2" ParentId="16704" CreationDate="2020-05-19T14:09:37.840" Score="1" Body="&lt;p&gt;the industrial, scientific, medical or ISM for region 2 (the Americas) is 902 to 928 MHz. Power is limited to no more than 1 watt without a license. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many consumer devices such as cordless phones use this band as well as industrial networks like ZIGBEE. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio operators in region 2 are secondary users of this band also know as the 33 CM band. While HAMS could transmit at 1.5 KW, we are not allowed to cause interference to other users which transmitting at that level certainly would. There are HAM radio repeaters that operate on this band, but they are not common.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-05-19T14:09:37.840" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16710" PostTypeId="1" CreationDate="2020-05-19T19:59:37.047" Score="2" ViewCount="66" Body="&lt;p&gt;I have noticed that participants in an HF exchange will often give number and a letter followed by a state, e.g. 1E Wisconsin. What does this mean?&lt;/p&gt;&#xA;" OwnerUserId="17100" LastEditorUserId="8717" LastEditDate="2020-05-19T21:44:41.320" LastActivityDate="2020-05-19T21:44:41.320" Title="Contesting dialog" Tags="&lt;procedure&gt;&lt;contest&gt;&lt;field-day&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16711" PostTypeId="2" ParentId="16710" CreationDate="2020-05-19T21:18:32.820" Score="3" Body="&lt;p&gt;So in a radio contest, there are definite rules about what information must be sent and received for the contact to be valid for contest points.  The information that must be traded is known as the &quot;exchange&quot;, in contesting lingo.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The example you gave sounds like the ARRL's &lt;a href=&quot;http://www.arrl.org/field-day&quot; rel=&quot;nofollow noreferrer&quot;&gt;Field Day&lt;/a&gt;.  The ARRL don't describe Field Day as a contest; they describe it as &quot;a local event and an opportunity for local amateur radio clubs to showcase the skills, science and technologies that make radio communication such a wonderful hobby and a valuable public service.&quot;  However, in the course of this event, contacts are made according to rules.  To many contesters, if it looks like an elephant, acts like an elephant, and smells like an elephant, then it's probably an elephant; in other words, many contesters view Field Day as a contest, and treat it as such.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;According to the &lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2020/1_61-2020%20Rules.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Field Day 2020 Rules&lt;/a&gt; (PDF), the exchange is the Field Day operating class and the ARRL or RAC section.  In your example, &quot;1E&quot; is the operating class, which means a single-transmitter station running from a permanent location (i.e. home), but on emergency power.  The ARRL section in your example is Wisconsin.  Many ARRL sections have the same borders as US states, but not all; some states include several sections.  Here's a &lt;a href=&quot;https://www.mapability.com/ei8ic/maps/sections.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;web page&lt;/a&gt; that has several ARRL and RAC section maps.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-05-19T21:18:32.820" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16714" PostTypeId="1" CreationDate="2020-05-21T10:59:22.910" Score="0" ViewCount="39" Body="&lt;p&gt;Base of loop will be about 6 feet above ground. RG-8 or 213 will be used for the feed wire.  Ugly balun as well.&lt;/p&gt;&#xA;" OwnerUserId="17107" LastEditorUserId="8717" LastEditDate="2020-05-21T17:41:42.210" LastActivityDate="2020-05-21T20:44:35.863" Title="On a horizontally setup 20m delta loop I am looking to determine the calculations for the proper length of a feed wire" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;hf&gt;&lt;feed-line&gt;&lt;loop-antenna&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16715" PostTypeId="1" AcceptedAnswerId="16722" CreationDate="2020-05-21T15:49:06.500" Score="6" ViewCount="793" Body="&lt;p&gt;We are setting up a all-band radio in an emergency com center that's intended most for amateur band use, but since its' for emergency use will also be used in the public safety bands; (150-170)MHz, (470-512)MHz, (700/800)MHz, and possibly others if needed.&#xA;We have a small tower to mount the antenna to.  The person in charge of the project wanted to use a PCTEL PCTWSLMR Multiband mobile antenna, since its commonly used in the local police vehicles that are outfitted with this radio.  I'm against using a mobile antenna on a tower, so researching I found TELEWAVE ANT280S Discone antenna.  I was told that we shouldn't use a Discone for transmit because of poor performance, but I'm not sure why.  The mobile antenna lists gain as unity and VSWR as 2:1 typical and 2.5:1 max.  The specs for the discone are unity gain with a maximum VSWR or 1.5:1 accross 132 Mhz - 3 GHz. So I don't understand why the discone would be considered inferior to the mobile antenna in this case.  I know that common wisdom is that a discone is for scanner type applications, but it seems that in this case that it would out perform the &quot;out of the box&quot; solution, which in this case is the Multiband mobile antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, is there anything I'm overlooking here as to why I shouldn't just use the discone for TX/RX applications?&#xA;Thanks    &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/J7GYJ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/J7GYJ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lwO4h.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lwO4h.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17109" LastEditorUserId="8717" LastEditDate="2020-05-21T17:36:16.827" LastActivityDate="2020-05-22T11:44:22.550" Title="Any reason not to choose a discone antenna over a Wide/ MultiBand mobile antenna for TX/RX operations" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;antenna-system&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16716" PostTypeId="2" ParentId="16715" CreationDate="2020-05-21T17:57:56.580" Score="2" Body="&lt;p&gt;Discone antennas have a very wide bandwidth. Many HAMs like them for this reason for receiving. You can have one antenna and use it for 440, 200 and 2 meter. Some will also do 6 meter. You can also use them with non HAM frequencies like Weather, marine, and aircraft. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The downside is that for transmitting they have 0 gain at best and often have a slight negative gain. There are many far simpler antennas that easily out preform them for transmitting. Some HAMs will say they cannot be used for transmitting. For most discone antennas that is not true, You can transit using them, just not very well. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Personnal I'd prefer something like a J pole for omnidirectional or a simple Yagi if I want gain in one direction such as trying to reach a distant repeater. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-05-21T17:57:56.580" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16717" PostTypeId="2" ParentId="16715" CreationDate="2020-05-21T19:19:09.577" Score="5" Body="&lt;p&gt;The discone antenna that you mention cites &quot;effective&quot; gain of 0 dBd.  I don't know what they mean by effective gain, but dBd means decibels compared to a dipole; 0 dBd would mean that the discone has the same gain as a dipole.  That's OK gain, but certainly not great.  Lots of other antennas would give you a few more decibels for not very much money.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I looked at the price of the TELEWAVE ANT280S, and the cheapest price I could find was $1,700.  Wow!  That's an expensive antenna!  I'd think that you could buy very nice rugged base station antennas for the three bands you mention, and diplexers as needed, for a lot less than the cost of that discone.  (&lt;a href=&quot;https://en.wikipedia.org/wiki/Diplexer&quot; rel=&quot;noreferrer&quot;&gt;Diplexers&lt;/a&gt; are used to connect two antennas to one radio, or two radios to one antenna.  Triplexers, quadruplexers, etc. are also available.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In my opinion, that's what you should do.  You'd save money, and get more gain.  The additional expense of the discone would only be justified, in my mind, if you had a definite need for the broad frequency coverage that is its main selling point.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A mobile antenna on a tower is a bad idea.  A mobile antenna depends on a ground plane, like the roof of a car.  You could jury-rig elevated radials to a mobile antenna to replace the ground plane, but why?  A good base station antenna is far more rugged, is designed to be mounted on a tower, and needs no ground plane.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-05-21T19:19:09.577" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16718" PostTypeId="2" ParentId="16714" CreationDate="2020-05-21T20:44:35.863" Score="1" Body="&lt;p&gt;Best solution is with an antenna tuner for impedance matching. Cheap-try is quarter lambda 70 Ohm cable (to convert 100 Ohm to nearby 50 Ohm) AND common-mode isolator. I assume your loop is NOT parallel to the ground, since it makes no sense at 14 MHz to have your radiation straight upward. PA0FSB&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-05-21T20:44:35.863" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16719" PostTypeId="1" CreationDate="2020-05-21T22:35:24.147" Score="2" ViewCount="98" Body="&lt;p&gt;I have a 40M vertical on top of my roof. When I transmit at 100W, my internet drops. My neighbor's internet too (different cable company). At 50W it seems to be OK.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an expermient, I used a smaller vertical (Hustler 40M mobile), clamped to a yagi's boom. It uses my 10-15-20M yagi as radials of sorts (gamma matched so all elements are shorted to the boom). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &quot;large&quot; vertical is about 4M away from overhead power and cable wires. The smaller one is about 15M away from those. The ends of the radials of my large vertical are only 20-30cm away from the power lines:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/m2HPt.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/m2HPt.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have found two things:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Noise is lower (1-2 S-units) with the smaller vertical&lt;/li&gt;&#xA;&lt;li&gt;The internet doesn't drop when I transmit 100W into the smaller vertical&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;Could both observations be attributed to just lower performance from the small vertical? The radiator is only 1.5M long, a coil, and some more whip. The larger vertical is 6M, coil, 1.2M.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I might consider moving my larger vertical and put it on top of my yagi, if this helps me reduce noise and avoid interference to CATV. &#xA;But I'm not sure how a &quot;yagi as a groundplane&quot; would affect performance vs &quot;16 5m long radials&quot; as I have now. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another question is: will the mast act as a radiator or counterpoise too? Is it beneficial for my application, or do I now have a off-center fed vertical dipole?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I had to choose between the ability of transmitting 50W in a vertical with plenty of radials, and 100W in a vertical with few short radials (a yagi), what would be the best choice?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally, a photo of the small vertical clamped to the yagi:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AQWrV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AQWrV.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-05-21T22:35:24.147" Title="Vertical antenna near power and cable lines" Tags="&lt;vertical-antenna&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16720" PostTypeId="1" CreationDate="2020-05-21T23:24:12.203" Score="0" ViewCount="215" Body="&lt;p&gt;I've read the manual twice, and watched programming guide videos on youtube, but while I can program hotkey 1-6 just fine, I can't find how to actually trigger them.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found how to trigger the &quot;Fun key+N&quot; keys, also mentioned in the manual. The green key appears to have the name &quot;Func&quot;, even though I can't find that actually in any manual. You long press the green key, and then can trigger 0-9, and * and #.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what about the &quot;Hotkeys&quot;? How do I trigger them?&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="76" LastEditDate="2020-05-22T00:32:38.393" LastActivityDate="2021-05-16T00:04:10.173" Title="How do I trigger hotkeys on AnyTone 878UV?" Tags="&lt;ht&gt;&lt;equipment-operation&gt;&lt;radio-programming&gt;&lt;anytone&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16721" PostTypeId="2" ParentId="16715" CreationDate="2020-05-22T01:01:37.027" Score="1" Body="&lt;p&gt;If you want or need to use mobile antenna's on a tower, you should use two of them, arranged opposing base to base, and wired to make them a vertical dipole.  That, plus the height above ground, makes up for the lack of a vehicle ground plane.  This solution may also be cheaper than the expensive discone you reference.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-05-22T11:44:22.550" LastActivityDate="2020-05-22T11:44:22.550" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16722" PostTypeId="2" ParentId="16715" CreationDate="2020-05-22T01:48:30.400" Score="1" Body="&lt;p&gt;A discone would appear to be an excellent choice for this application, provided it can be mounted away from conductive structures that would distort the radiation pattern. NEC-2 modeling confirms that the discone should deliver gain comparable to a dipole, but omnidirectional in the azimuth like a vertical, giving it superior performance to the unity-gain vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TELEWAVE ANT280S datasheet specifies the vertical beamwidth as 110&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt;. With vertical and horizontal beamwidths &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\beta$&lt;/span&gt; specified in degrees and gain in dBi, &lt;a href=&quot;http://teletopix.org/4g-lte/beamwidth-and-relation-between-beamwidth-and-gain/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Teletopix&lt;/a&gt; shows how to calculate beamwidth as a function of gain:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$G \approx 10 log \frac{32400}{\theta \beta}$$&lt;/span&gt;&#xA;Since an omnidirectional antenna has an azimuthal beamwidth of 360&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt;, the TELEWAVE ANT280S' 2.1-dBi gain translates to a vertical beamwidth of about 55&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt;, half the quoted value. It would be interesting to know why the manufacturer specifies the beamwidth as they do.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-05-22T09:27:49.317" LastActivityDate="2020-05-22T09:27:49.317" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16724" PostTypeId="1" CreationDate="2020-05-23T02:38:09.323" Score="1" ViewCount="59" Body="&lt;p&gt;I want to solve the equations for wire antennas where the wires are not all parallel. The classic method for parallel wires is to compute the magnetic potential at points on one wire due to current segments of the other wires (and its own)  and solve a matrix equation. Been there done that successfully for parallel wires.&#xA;The magnetic vector potential has the same direction as the current segment that gave rise to it. That math says that two wires or segments  at right angles don't couple as the magnetic vector potential  due to one wire is at right angles to the other wire.&#xA;OK. Now consider two short dipoles a few wavelengths apart,  one transmitting,the other receiving. Now rotate the transmitting one 45 degrees. That puts the other about 3dB down on its polar pattern. Now rotate the receiving dipole 45 degrees the other way.Another 3dB loss. But now they are  wires at right angles to eachother (but not to the line drawn between them,  the direction of propagation)  So why is the received signal only 6dB down and not zero?  There is something missing in the math. Wires at right angles DO couple,  as two +/_ 45 deg skewed dipoles demonstrate. The angle of the wire to the line drawn between them has to have something to do with it.&#xA;Cannot find any formula in any book that elucidates this. Help?&lt;/p&gt;&#xA;" OwnerUserId="15172" LastActivityDate="2020-05-23T18:58:06.333" Title="What is the formula for coupling between non-parallel wires?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16725" PostTypeId="2" ParentId="16724" CreationDate="2020-05-23T09:44:07.177" Score="1" Body="&lt;p&gt;RE this clip from the OP: &lt;em&gt;Now consider two short dipoles a few wavelengths apart, one transmitting, the other receiving. Now rotate the transmitting one 45 degrees. That puts the other about 3dB down on its polar pattern. Now rotate the receiving dipole 45 degrees the other way. Another 3dB loss.&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below is an analysis of that final configuration using Numerical Electromagnetics Code (NEC4.2).  The graphic shows that the radiation pattern of the transmit dipole is unaffected by the presence of the other dipole two wavelengths away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Xj5Qc.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Xj5Qc.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-05-23T09:44:07.177" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16727" PostTypeId="2" ParentId="16724" CreationDate="2020-05-23T18:58:06.333" Score="1" Body="&lt;p&gt;If each short (~0.1&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;) dipole is rotated by 45&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt; about &lt;em&gt;its own center&lt;/em&gt;, then neither dipole lies in the null of the other. The current excited in the &quot;receiving&quot; dipole is &lt;span class=&quot;math-container&quot;&gt;$(cos(45^o))^2$&lt;/span&gt;, or 1/2 of the current observed when the two dipoles are broadside to each other. This is confirmed by NEC-2 modeling.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-23T18:58:06.333" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16729" PostTypeId="1" CreationDate="2020-05-24T02:55:25.623" Score="0" ViewCount="199" Body="&lt;p&gt;I have been trying for ages to find a way to mount a 10 m vertical Yagi properly, so that the mounting pole doesn't stuff up the impedance and radiation pattern, and have had no luck so far. Apart from using a non-metallic pole or using 2 phased vertical Yagis on a cross boom just so that they can be mounted so the mounting pole is not in line with the elements, there doesn't seem to be a practical method. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If I mount two Yagis on the same boom each with a polarization of 45 degrees or half way between vertical and horizontal and each antenna rotated around the boom 90 degrees from the other so that the antenna looks like a set of X's or a quad with no wires around the outside, then if I phase the driven elements of the two antennas together using coaxial matching stubs or similar, then can I adjust the feed point phase so that I can get either horizontal (or more importantly vertical) polarization and therefore minimize the effect of a metal mounting pole because it's not in the same plane as the antenna elements ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2020-05-25T01:45:01.767" LastActivityDate="2020-05-26T17:17:38.450" Title="Variable polarization Yagi using two antennas on the same boom, joined together with variable feedpoint phase?" Tags="&lt;antenna-theory&gt;&lt;yagi&gt;&lt;phased-array&gt;&lt;polarization&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16730" PostTypeId="2" ParentId="16729" CreationDate="2020-05-24T09:01:07.397" Score="0" Body="&lt;p&gt;Treated as an issue for a &lt;em&gt;practical&lt;/em&gt; solution, probably a v-pol yagi with a good F/B ratio in free space could be mounted so that it is sufficiently decoupled from a conducting/re-radiating, vertical support mast adjacent to it so as not to seriously affect the far-field radiation pattern of that yagi+mounting environment.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-05-24T09:35:12.083" LastActivityDate="2020-05-24T09:35:12.083" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16733" PostTypeId="1" CreationDate="2020-05-24T09:39:15.863" Score="4" ViewCount="955" Body="&lt;p&gt;This morning I tuned in to a repeater about 12km from me (in the UK). I could hear activity, but from only one station. I could tell that there were other stations using that repeater from the comments of the station that I could hear. Why couldn't I hear the other stations? Doesn't the repeater re-transmit the other stations with the same signal strength as the station that I could hear? &lt;/p&gt;&#xA;" OwnerUserId="17121" LastEditorUserId="8717" LastEditDate="2020-05-24T18:52:58.387" LastActivityDate="2020-05-25T12:13:50.783" Title="Beginner listening to a repeater - only hearing one station" Tags="&lt;baofeng&gt;&lt;repeater&gt;&lt;united-kingdom&gt;&lt;repeater-coverage&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16734" PostTypeId="2" ParentId="16733" CreationDate="2020-05-24T12:46:51.223" Score="8" Body="&lt;p&gt;It is presumed that you were receiving on the 2m band.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It appears that you were listening in, using 'repeater reverse' mode. In other words, you were listening in on the repeater's input frequency rather than on it's output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On 'reverse', you would hear all the stations within range. In this case only one station would have been within range. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Had you tuned in 600kHz above or below, you would have heard all the stations accessing the repeater, either above or below, depending on whether the repeater input frequency was 600kHz above or below its output frequency.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-05-25T12:13:50.783" LastActivityDate="2020-05-25T12:13:50.783" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16735" PostTypeId="2" ParentId="16733" CreationDate="2020-05-24T17:07:45.467" Score="3" Body="&lt;p&gt;The concept is called &quot;offset&quot;. The repeater is listening on one frequency, and is repeating it verbatim in real time on another frequency, but typically at a higher power so more people can hear it further away.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most repeaters (numbers specific for the US anyway, but the concept applies internationally) have a plus or minus 600 khz offset. This is not a legislated requirement, it just a convention people came to over the years. What this means is that a repeater that transmits at 146.000 MHz with a -6khz offset will be listening at 145.400 MHz.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In practice, what this means is that you were listening on your radio to one of those two frequencies, and thus only hearing half the conversation. If it was the repeater's input frequency (145.400 in my example), then you are listening to whoever was nearby talking directly from their radio to the repeater (and also your radio). However, whoever was talking to him was too far away for your radio to hear directly. If you tried talking back, no one would hear you because they are all listening on 146.000, and they won't even know you're there!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you were on 146.000 though, you would hear everyone talking on the repeater, but the only people that would hear you are the ones close enough for their radios to pick you up directly. Because you were only hearing half the conversation, I suspect you were monitoring the repeater's input frequency, not the output.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Try using a resource like &lt;a href=&quot;https://www.repeaterbook.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.repeaterbook.com/&lt;/a&gt; to find the repeater and look up what their offset is. Your radio instruction book should show you how to program it. Best of luck!&lt;/p&gt;&#xA;" OwnerUserId="9450" LastActivityDate="2020-05-24T17:07:45.467" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16737" PostTypeId="2" ParentId="16729" CreationDate="2020-05-24T22:56:27.750" Score="3" Body="&lt;p&gt;Yes, it is possible given two antennas at orthogonal angles to adjust the relative amplitude and phase between them and create vertical, horizontal, or anything between polarization. You can even create circular polarization of either chirality, or elliptical polarization.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, this does not solve the problem of the antenna interacting with the mast. The coupling between the mast and the antenna is proportional to the cosine of the angle between them. When the mast and antenna are aligned, coupling is at a maximum. When the mast and antenna are at right angles, the coupling is theoretically zero.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your described arrangement places the mast at 45 degrees relative to each antenna, meaning there will be less than maximal, but still significant coupling with the mast. Unless of course the antennas are phased to provide horizontal polarization when the mast is vertical, but this is no different than could be achieved with a single antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="9621" LastEditDate="2020-05-24T23:12:51.257" LastActivityDate="2020-05-24T23:12:51.257" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16738" PostTypeId="2" ParentId="16729" CreationDate="2020-05-25T19:12:38.273" Score="1" Body="&lt;p&gt;You should be able to use a traditional offset mount:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7M4U6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7M4U6.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The counterweight balances the weight and the wind-generated torque of the yagi. If you want to use a different offset for either side, use simple proportions to create the same gravity- and wind-driven torques. Given the relatively small offset required, this doesn't seem too onerous. &lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-25T19:12:38.273" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16739" PostTypeId="2" ParentId="14505" CreationDate="2020-05-26T02:49:19.527" Score="0" Body="&lt;p&gt;Inductively tuned transmitting antennas were used in the military on HF man-pack radios. In the USA the Stoner company made a man-pack whip antenna in the 1970's for the US military that tuned 2 - 15 Mhz, if you search ebay and/or the net you might still be able to find examples described or offered for sale, but they weren't cheap. An Australian man-pack military transceiver 2 - 10 MHz from the 1950's also use an inductively tuned matching unit for its whip antenna. Both these designs used an aluminum sleeve to shield an iron core ferrite rod around which the coil was wound on a former which had enough clearance between the former and the rod to allow the sleeve to pass. The tuning was achieved by moving the sleeve back and forth shielding more or less of the ferrite rod as required. Both these tuning units were designed for low power radios, I believe the Stoner unit was quoted to handle about 25 watts of RF while the Australian design was used on a man-pack that produced about 2 -3 watts of RF. I have used the Australian unit and found it very effective in tuning the 8ft whip antenna at low HF frequencies around 3 MHz.&lt;/p&gt;&#xA;" OwnerUserId="17132" LastActivityDate="2020-05-26T02:49:19.527" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16740" PostTypeId="1" CreationDate="2020-05-26T09:18:31.197" Score="2" ViewCount="121" Body="&lt;p&gt;I have a 5 ele YAGI which, once we can go multi-op portable again in the UK, I shall be taking to the hills with me.&#xA;The idea being to make it quick and simple to get the dimensions and element positions right when erecting in the half light without looking for pencil or indelible pen marks that tend to rub out/scrape off.&#xA;I have not painted the whole thing! - just a small area of the thinner diameter reflector plus the directors, where they slide in/out to adjust the length of the element, the paint stops at exactly the right place for the correct dimension. I have used a different colour for each element with a match on the boom&#xA;I have not done this to the driven element.&#xA;Now I have done it I find myself thinking: Could this small area of spray paint in any way have affected the antenna? Somehow I think not but...&lt;/p&gt;&#xA;" OwnerUserId="9323" LastEditorUserId="9621" LastEditDate="2020-05-26T12:25:41.030" LastActivityDate="2020-05-27T18:55:29.350" Title="Should I not have &quot;painted&quot; my YAGI?" Tags="&lt;yagi&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16741" PostTypeId="2" ParentId="16729" CreationDate="2020-05-26T17:17:38.450" Score="0" Body="&lt;p&gt;I think you are giving too much credence to the vertical support interfering. I have been designing and installing similar antennas since the 1960's. I have installed hundreds of vertical beams with an omni directional on top I have done this from 20 meters up through 450MHz including lots on 6 10 and 2 meters oh yeah and untold amounts of CB antennas. Yes the vertical tube makes a little difference but it is so infinitesimal it is not worth worrying about. Remember antennas in the real world are all about compromise. If it works use it! There are hundreds of things that affect antenna functionality some in good ways some in bad. Theory is great but it is just that THEORY! Theory is our way of explaining why and how things work, BUT in the real world grounds are not consistent neither are other obstructions, so build it the best you can then using the instrumentation at your disposal tweak it to the best you can, then quit worrying about it and enjoy using it. Conditions are going to be in flux so deal with it! We do not live in a perfect world enjoy the ride quit worrying about the color of the fenders it doesn't change the trip or the destination! Laurin WB4IVG&lt;/p&gt;&#xA;" OwnerUserId="17136" LastActivityDate="2020-05-26T17:17:38.450" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16742" PostTypeId="2" ParentId="12919" CreationDate="2020-05-26T17:25:09.433" Score="0" Body="&lt;p&gt;Mount the antenna at a non resonate point so it has the least amount of play in the scheme of things. It is simple look at your YAGI design just put the pole (mast) in between two of the elements that way it is in a null as far as the antenna is concerned. Laurin WB4IVG&lt;/p&gt;&#xA;" OwnerUserId="17136" LastActivityDate="2020-05-26T17:25:09.433" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16743" PostTypeId="2" ParentId="16740" CreationDate="2020-05-27T17:59:19.057" Score="3" Body="&lt;p&gt;Generally speaking paint will not affect the performance of the antenna. If the paint contained metal then in theory it might, but even then I doubt a small amount of metal would have an affect. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would be concerned if the paint covered mating surfaces, like where two sections screwed together. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastEditorUserId="9621" LastEditDate="2020-05-27T18:55:29.350" LastActivityDate="2020-05-27T18:55:29.350" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16744" PostTypeId="2" ParentId="7169" CreationDate="2020-05-27T19:18:02.317" Score="1" Body="&lt;p&gt;One way of minimizing RF in the shack is to make a short, practical, twin-coax feedline from the tuner to the ladder line. Each coax center conductor connects to one end of the ladder line. The braids are grounded at the station ground. I've used such an antenna during a Field Day and I was rewarded with a QSO with Hawaii from Montreal, SSB with 100 W of power. Not bad, and it's fun to hear 'Aloha' on the air! Try it!  &lt;/p&gt;&#xA;" OwnerUserId="17140" LastActivityDate="2020-05-27T19:18:02.317" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16745" PostTypeId="2" ParentId="7169" CreationDate="2020-05-27T22:00:09.657" Score="3" Body="&lt;p&gt;You might find some advantage to using a Slightly Off-Center Fed Dipole, as described in &lt;em&gt;QST&lt;/em&gt; for September 2019. Feeding a single wire through a 4:1 step-down balun 45% from one end produces a usable match to 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; coax on eight HF ham bands:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Be003.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Be003.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With low-loss coax like your LMR-400, the additional mismatch loss is quite low, allowing you to match the coax to the rig in the shack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The antenna is simple to build:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lYK1y.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lYK1y.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You may find that a slightly longer wire will give lower SWR if the antenna is mounted more than 30-feet above ground. Planning to run no more than 150-watts, I used speaker wire to wind a 4:1 Guanella balun:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RIlL3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RIlL3.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Making a compact and lightweight feedpoint insulator assembly:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EtUwl.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EtUwl.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the dimensions shown and the antenna mounted 30-feet above ground, I obtained this plot of the SWR &lt;em&gt;at the junction of the coax and the balun:&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OdjYz.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OdjYz.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I've received notes from dozens of satisfied builders of this antenna. I've used it for portable DXpedition and FD operations with good success.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-05-28T18:41:03.670" LastActivityDate="2020-05-28T18:41:03.670" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16746" PostTypeId="1" CreationDate="2020-05-28T08:37:58.850" Score="1" ViewCount="175" Body="&lt;p&gt;I have searched image banks and Googled period radios, but I can not identify these old units. I picked them up overseas in SE Asia and I got them as projects to teach myself enough to challenge the Advanced Amatuer Operators certification exam. I find hands on better than books all the time so these got my interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some model numbers like the American set, but it is a control set...without frequency tuner? There are some sort of numbers on one of the Asian character sets, but I can not translate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;They are without battery packs or antenna so I need to replace/bodge alternates. I am not licensed to transmit in my current country but would like to revive these units, I am no expert and will learn by doing.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The hand sets are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Telephone Set TA-1/PT...Jeep handset?&lt;/li&gt;&#xA;&lt;li&gt;NHA MAY THONG TIN M3 DT-97 (No: 01-03-03-010)...Vietnamese telephone?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aazDV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aazDV.jpg&quot; alt=&quot;2x chinese and 1x american military radios&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/R7rwM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/R7rwM.jpg&quot; alt=&quot;Control, Radio SETC-2329A/GRA-39&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZxyQy.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZxyQy.jpg&quot; alt=&quot;Id plate for above set&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JSoUW.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JSoUW.jpg&quot; alt=&quot;No ID plate Korean/Chinese/Vietnamese radio?&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9b0OE.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9b0OE.jpg&quot; alt=&quot;Seems to be a ??:72-05031 ?-251A radio&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17143" LastEditorUserId="8717" LastEditDate="2020-05-29T16:47:18.890" LastActivityDate="2020-06-03T09:49:47.600" Title="Can't identify old Chinese(?) and American radio/telephone" Tags="&lt;electronics&gt;&lt;transceiver&gt;&lt;military-surplus&gt;" AnswerCount="4" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16747" PostTypeId="1" CreationDate="2020-05-28T09:42:00.107" Score="-1" ViewCount="45" Body="&lt;p&gt;how to set up remote push to talk&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I work in an extremely really noisy area&lt;/p&gt;&#xA;&#xA;&lt;p&gt;headset connected to some radio&lt;/p&gt;&#xA;&#xA;&lt;p&gt;but others can do remote push to talk and hear me answer&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I need my hand for working what I'm doing&lt;/p&gt;&#xA;&#xA;&lt;p&gt;or&lt;/p&gt;&#xA;&#xA;&lt;p&gt;is it better to go down&#xA;have a mic that picks up the background sound and then sound process that noise out&lt;/p&gt;&#xA;" OwnerUserId="16356" LastEditorUserId="16356" LastEditDate="2020-05-28T22:29:13.817" LastActivityDate="2020-05-28T22:29:13.817" Title="remote push to talk or process background sound out" Tags="&lt;microphone&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16748" PostTypeId="2" ParentId="16747" CreationDate="2020-05-28T15:41:11.663" Score="1" Body="&lt;p&gt;I'm not sure exactly what you mean by &quot;remote push to talk&quot;, but one possibility is that you want a switch that is more convenient, such as a foot switch.  In that case you would want to get such a switch, and make sure that it's wired to be normally open, rather than normally closed.  (Foot switches often have a micro switch inside with three contacts.  Depending on where the wires are soldered, such a micro switch can function either normally-open or normally-closed.  So if such a switch is wired normally-closed, moving a wire can change it to be normally-open.)  Rigging your radio to use a different switch is a matter of rewiring your microphone plug to use the external switch, or better yet, making an adapter between the microphone and the radio to ignore the microphone's PTT switch and use the external switch instead.  Using an external adapter means that the microphone doesn't need to be modified.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another possibility is that you want the radio to automatically start transmitting when you talk into the microphone.  This is a feature called &quot;VOX&quot;, which is built into many radios.  If your radio has VOX, then all you need to do is to turn it on.  If your radio doesn't include VOX then it would be &lt;a href=&quot;https://ham.stackexchange.com/questions/12746/vox-mic-that-emulates-ptt&quot;&gt;possible&lt;/a&gt;, but not necessarily practical, to add it by buying a microphone that includes VOX, or by building a circuit to implement it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you do use VOX, you might consider using a noise-cancelling microphone, so that external noise doesn't trigger the VOX as much.  Noise-cancelling microphones work by actually having more than one microphone; circuitry compares the signal from the microphones, and removes the part of the signal that is common to all the microphones.  What signal is left must be from a sound that was emitted close to one of the microphones, which was hopefully your voice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you're talking about a true remote PTT, where someone else pushes a button that turns transmit on for your radio over a wireless connection, then that is technically possible but would be difficult to implement.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-05-28T15:41:11.663" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16749" PostTypeId="2" ParentId="830" CreationDate="2020-05-28T21:00:05.120" Score="1" Body="&lt;p&gt;As has been pointed out, one factor of the folded dipole that explains greater bandwidth is that it is effectively thicker. The main reason however is that it's impedance is effectively the parallel combination of a half wsve dipole and a 1/4 wave stub shorted at the far end. The reactance/susceptance of this stub varies in the opposite direction to that of the dipole,  thus compensating it.&#xA;The best way to think of it is in terms of even and odd modes.&#xA; If you split the folfed dipole into two U:s,  you can feed both legs of the U in parallel in phase as a non'folded dipole where the current in each leg of the U is in the same direction. This is the even mode and the impedance will be that of a fat dipole. 75 ohms say,  or 150 for each of the two U legs in parallel. Now feed the two legs of the U in antiphase,  with current in opposite directions. This is the odd mode and it doesn't radiate and has the impedance of a short circuited stub. Now feed both modes at once. You will have even+odd=2  on one U leg and even-odd=0 on the other. The 0 volt leg can be shorted across to the 0 volt leg of the other U  completing the folded dipole. You  now have a 300 ohm nominal feedpoint but the current is the sum of the even and odd mode currents,  the odd mode current being that of the stub,  the impedance of which is therefore in parallel with the dipole.&#xA;You can get a similat effect by connecting a 1/4  S.C. stub across a non-folded dipole,  except the impedance will not be multiplied by 4&lt;/p&gt;&#xA;" OwnerUserId="15172" LastEditorUserId="15172" LastEditDate="2020-05-28T21:08:03.133" LastActivityDate="2020-05-28T21:08:03.133" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16751" PostTypeId="1" AcceptedAnswerId="16778" CreationDate="2020-05-29T02:58:26.027" Score="4" ViewCount="113" Body="&lt;p&gt;I am creating an Echolink simplex link using a Raspberry Pi 3 B+, a Pluggable USB sound adapter, and an &lt;a href=&quot;https://www.ebay.com/itm/Easy-Digi-Radio-Interface-to-computer-APRS-Packet-larger-mounting-holes/232792067058&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;Easy Digi&quot;&lt;/a&gt; sound card interface which has 2 - 600ohm isolation transformers for audio in/out as well as an opto isolated interface for the PTT into my Yaesu FT-1900R.  The basic hookup is essentially like this:&lt;a href=&quot;https://i.stack.imgur.com/hDvop.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hDvop.png&quot; alt=&quot;Hookup Diagram&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even with the isolation transformer, I am getting a terrible hum when receiving transmissions.  I finally got it to stop by connecting the ground from the output of the USB sound card to the PTT ground connected to the radio.  This is negates the ground isolation and I can't figure out why this fixes it.  Any ideas?&lt;/p&gt;&#xA;" OwnerUserId="17150" LastActivityDate="2020-06-02T23:56:06.710" Title="Easy Digi hum with isolated ground" Tags="&lt;grounding&gt;&lt;noise&gt;&lt;audio-interface&gt;&lt;echolink&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16755" PostTypeId="1" AcceptedAnswerId="16756" CreationDate="2020-05-29T21:36:38.440" Score="0" ViewCount="116" Body="&lt;p&gt;I have two antennas in my station: a 10-15-20M yagi, and a loaded 40M vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With the ATU built into my Kenwood TS-450S I can operate 80, 60 a and 30M with the 40M vertical too. Though, in 80M I have had very little luck being heard except for local stations.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Would it make a significant difference if I used an ATU at the base of my vertical, instead of tuning it with the built-in tuner?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm aware of the feedline losses due to mismatching, but I'm not sure how this translates to real world ability to transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm an electronics hobbyist and I've been thinking of building a remote ATU: switchable inductors of 8-4-2-1-0.5uH (which should be able to make any combination of 0 to 15.5uH in 0.5uH steps), and a similar arrangement for capacitance, to build a L-network that should be able to tune the monopole to basically any frequency in the 80, 60, 40 and 30M bands. But I'm wondering if going through all this hassle would give me any significant advantage over just using my built-in ATU.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-05-30T10:04:20.620" Title="Built-in ATU vs Remote?" Tags="&lt;antenna-tuner&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16756" PostTypeId="2" ParentId="16755" CreationDate="2020-05-29T23:09:59.540" Score="2" Body="&lt;p&gt;Even if the mismatch losses are relatively low, since your loaded 40-m vertical is electrically short on &lt;em&gt;that&lt;/em&gt; band, it's &lt;em&gt;really&lt;/em&gt; short on 80-m and your expectations need to scale down in a similar ratio.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The amount of mismatch loss you experience depends on the degree of mismatch between the load and the feedline, as well as the feedline's matched loss. You can calculate the loss using AC6LA's free &lt;em&gt;&lt;a href=&quot;https://ac6la.com/tldetails1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;TLDetails&lt;/a&gt;&lt;/em&gt; calculator:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bCR24.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bCR24.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To get accurate results, it's important to know the impedance on 80m looking into either the feedline or the feedpoint of your 40m vertical.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you decide the loss is excessive and you are running 100-W or less, you might want to construct a kit based on the &lt;a href=&quot;https://github.com/Dfinitski/N7DDC-ATU-100-mini-and-extended-boards/blob/master/ATU_100_EXT_board/ATU-100_Extended_Board_User_Manual_eng.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;ATU-100 developed by N7DDC&lt;/a&gt;. As of this writing, full kits are available on eBay for about US$35.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-29T23:09:59.540" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16757" PostTypeId="2" ParentId="16755" CreationDate="2020-05-30T10:04:20.620" Score="1" Body="&lt;p&gt;In a comment, the OP asks an interesting and important question: &quot;...where does the 'mismatched power' go when using a match at the feedpoint? Is it dissipated by the matching network?&quot; AE6TY's &lt;em&gt;&lt;a href=&quot;http://www.ae6ty.com/Smith_Charts.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;SimSmith&lt;/a&gt;&lt;/em&gt;, another excellent and free tool, lets us get the answer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For demonstration purposes, I assumed your feedline is 50-ft of RG58-A/U and that inductors of &lt;em&gt;Q&lt;/em&gt;=200 could be used. &lt;em&gt;(Note: from experience, I know that this is easily achieved, even using powdered-iron toroid cores.)&lt;/em&gt; Working from the 8-j245 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; at 3.5-MHz provided in the OP's comment, &lt;em&gt;SimSmith&lt;/em&gt; shows that a simple L-network of inductors will match the antenna to 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; cable:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W1qIr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W1qIr.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of the 1.0-W applied to the transmission line, 908-mW makes it to L2 and 788-mW makes it to the load. Those ratios represent about 1-dB of total loss in the L-network and TL, of which 0.4-dB are lost in the TL.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For comparison purposes, let's examine what would happen if the match was effected at the rig end of the TL:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UqHjF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UqHjF.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Only 95-mW of the 1-W applied to the matching network makes it to the load, a loss of 10-dB, nearly all of which is dissipated in the TL! &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the answer is that using quality components in a properly designed matching network placed at the load, the power delivered to the antenna for radiation can be increased by about 9-dB rather than being dissipated in the transmission line.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-30T10:04:20.620" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16758" PostTypeId="2" ParentId="16720" CreationDate="2020-05-30T11:11:04.357" Score="0" Body="&lt;p&gt;From what I remember, after you program the Hot Keys, you then need to apply them to an actual key (PF1, PF2, PF3, P1, P2) to access them. Basically they are like functions that you can define (things that are not otherwise available for key assignment). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you look at the options that are available for, let's say the PF2 key, Hot Keys 1-6 should be available as options to select. So Program Hot Key 1 to access the SMS menu, then apply that to PF2 and now PF2 will open the SMS menu for you.&lt;/p&gt;&#xA;" OwnerUserId="17157" LastActivityDate="2020-05-30T11:11:04.357" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16759" PostTypeId="1" AcceptedAnswerId="16760" CreationDate="2020-05-30T15:05:55.037" Score="3" ViewCount="151" Body="&lt;p&gt;I'm having difficulties to understand how does &lt;a href=&quot;https://dh1tw.de/3db-splitter/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this circuit&lt;/a&gt; work:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qEJXJ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qEJXJ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Apparently T1 is a regular 50 Ohm to 22.2 Ohm autotransformer. Turns ratio 2:3 gives a 0.66**2 impedance converation. Since the load is two 50 Ohm ports in parallel, the total load impedance will be 25 Ohm. In other words T1 is just for impedance matching.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From what I know T2 and R are needed for isolation of port 2 and port 3. This is the part I don't quite understand. What happens when the circuit is used as a splitter? And what happens when it's used as a combiner? What prevent the current just to flow from port 3 to port 2 through R?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Could you please explain it?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="4076" LastEditDate="2020-05-30T15:28:41.607" LastActivityDate="2020-05-30T20:17:26.117" Title="How does this 3 dB splitter/combiner work?" Tags="&lt;ferrite&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16760" PostTypeId="2" ParentId="16759" CreationDate="2020-05-30T15:59:05.887" Score="4" Body="&lt;p&gt;SPICE modeling shows that replacing T2 and R with a 22.2-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; resistor, the impedance looking into T1 is indeed 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, as expected:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xEq9m.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xEq9m.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, replacing the 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; generator and T1 with a 25-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; generator shows that the impedance looking into T2 is 25-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TS29A.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TS29A.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a result of the electrical symmetry about a &quot;virtual ground&quot; established by the junction of the two windings of T2 and the &quot;midpoint&quot; of the 100-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; resistor. Thus, each side of T2 is terminated by two paralleled 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; resistances, or 25-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, matching the generator.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note, though, that the composite circuit presents a slight mismatch of 56-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; to the generator:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/McjUB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/McjUB.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is a result of the difference between the 22.2-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; transformation of T1 and the 25-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; input to T2. That is, 50*(25/22.2)=56-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The isolation between the two output ports can be measured by driving one of the output ports, terminating the &quot;input&quot; port in its characteristic impedance and measuring the response at the other output port:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ndGny.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ndGny.png&quot; alt=&quot;![enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As shown the isolation between the two output ports is better than 30-dB as long as all ports are terminated in 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;. The strong coupling between the windings of T2 means that equal but opposite currents flow with respect to their connections to R1. Whereas the driving current I(V1) is split between L4 and R1, the current in L5 cancels the current flowing into node &lt;strong&gt;&lt;em&gt;out2&lt;/em&gt;&lt;/strong&gt; from R1, effectively isolating it from node &lt;strong&gt;&lt;em&gt;out1&lt;/em&gt;&lt;/strong&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[Note: in LTSpice convention, I(V1), I(R1) and I(L4) are all &lt;em&gt;leaving&lt;/em&gt; node &lt;strong&gt;&lt;em&gt;out1&lt;/em&gt;&lt;/strong&gt;, while I(L5), I(R1) and I(RL2) are all &lt;em&gt;entering&lt;/em&gt; node &lt;strong&gt;&lt;em&gt;out2&lt;/em&gt;&lt;/strong&gt;.]&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-05-30T20:17:26.117" LastActivityDate="2020-05-30T20:17:26.117" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16761" PostTypeId="1" AcceptedAnswerId="16763" CreationDate="2020-05-30T16:28:50.510" Score="2" ViewCount="425" Body="&lt;p&gt;In the 1970s I made a CW “filter” based on a phase locked loop that detected a specific audio frequency, and this drove an NE555 oscillator: the result seemed at first like a “zero bandwidth” CW filter because as you tuned across the band, you only heard CW with one pitch.  This was no doubt also invented by others, so not claiming anything here! But it always struck me that there was no ringing like we always got when using narrow CW filters of the type available back then. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Some people said that ringing was some kind of result from information theory, but I didn’t understand the argument. Maybe they were referring to what you get if you put pure noise through an infinitely steep bandpass filter...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;What is the state of the art in narrow CW filters nowadays, and do they always ring?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Someone suggested the best might be found in the SDR field, but my knowledge of SDR is very basic. I can’t understand the technical SDR posts... yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One idea I had way back was having a very slight time delay so the filter could “look into the future” slightly, thereby increasing information content.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also I wonder if a neural network could be trained on noisy CW so as to outperform humans on weak signal work? That sounds like a second question, but I am imagining AI-enhanced SDR, or maybe an AI-enhanced DSP (so same question actually).&lt;/p&gt;&#xA;" OwnerUserId="17088" LastActivityDate="2020-06-10T15:08:00.363" Title="What is the current state of the art in CW filters?" Tags="&lt;software-defined-radio&gt;&lt;cw&gt;&lt;filter&gt;&lt;dsp&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16762" PostTypeId="2" ParentId="16761" CreationDate="2020-05-30T17:19:47.780" Score="4" Body="&lt;p&gt;Ringing in narrow filters may already have an answer here: &lt;a href=&quot;https://dsp.stackexchange.com/questions/2170/why-do-i-see-ringing-in-the-output-of-a-digital-filter-with-a-narrow-transition&quot;&gt;https://dsp.stackexchange.com/questions/2170/why-do-i-see-ringing-in-the-output-of-a-digital-filter-with-a-narrow-transition&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;looking into the future&quot;, or more realistically, a filter delay, seems to be a requirement to reliably estimate the shape and time location of the falling (and rising) edges of a CW envelope, if one is doing envelope (dot or dash duration and shape) detection, say by using some matched filters.  You can get rid of ringing by using leading and trailing edge detection to gate a resynthesis audio oscillator on and off (or use your preferred audio tone envelope).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;AG1LE has blogged about training a LSTM neural net to decode whole Morse Code characters (rather than just dots and dashes) from an FFT/STFT waterfall.  See:&#xA;&lt;a href=&quot;http://ag1le.blogspot.com/2017/11/tensorflow-revisited-new-lstm-dynamic.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://ag1le.blogspot.com/2017/11/tensorflow-revisited-new-lstm-dynamic.html&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;My experiments tend to confirm that data augmentation by adding various noise sources commonly found in RF to Morse Code training data improves ML/DNN inference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;After decoding, one could feed the ML inference output to a tone resynthesizer. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;IIRC, CW Skimmer reportedly uses statistical signal detection methods, e.g. updating the Bayesian probability that a tone pulse of a particular length has occurred based on previous and subsequent tone pulse and common Morse character sequence likelihoods.  I suppose you could resynthesize things that have a 99% chance of being a dot or dash, and squelch (or reduce volume on) the rest.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-06-10T15:08:00.363" LastActivityDate="2020-06-10T15:08:00.363" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16763" PostTypeId="2" ParentId="16761" CreationDate="2020-05-30T18:03:40.537" Score="5" Body="&lt;p&gt;I like your PLL approach, because it doesn't try to &quot;recover the original signal from noise&quot;, but actually goes ahead and detects what you're actually interested in, the presence of a specific frequency, and uses that to generate a &quot;perfect&quot; tone. Much cleverer than spending hundreds on the best thinkable crystal filter on the market! (I'm always baffled when I go to ham trade shows and people boast how much they spent on the filters for their analog receivers. Congratulations, these people have found an expensive way to do something that is not what they want.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When we say &quot;filter&quot;, we usually mean the linear time-invariant system that convolves the filter impulse response with the signal (either in analog or digital). And for these, the math is non-negotiable: A narrow bandwidth (for a low-pass filter) literally means &quot;nothing can change fast&quot;. A &quot;end of CW pulse&quot; is a fast change, end hence gets dragged into length. (We can do the same math for a band-pass filter, it doesn't change). That's the Fourier transform for you: can't be sharply defined in both domains, time and frequency (just as you can't know the position in impulse space and location exactly; Heisenberg says hello and wants his math back).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If &lt;em&gt;convolution&lt;/em&gt; is a new term for you, look it up, there's a lot of nice animations out there; it's very intuitive. You're a theoretical physicist, so I assume you'll understand when I say that convolution is just the inner product of an &lt;span class=&quot;math-container&quot;&gt;$\mathcal L^2$&lt;/span&gt; space of functions. For linear, time-invariant systems like classical filters, you get a very nice set of eigenfunctions: &lt;span class=&quot;math-container&quot;&gt;$\left\{e^{i\omega t}\right\},\,\omega\in\mathbb R$&lt;/span&gt;, and that tells you how it is that we can select frequencies with a filter: for any given LTI system, the response of the system to a given &lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt; is just the eigenvalue.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, with linear filters, ringing and narrow bandwidth are one and the same phenomenon.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, nothing says that a filter that we optimize for a narrow bandwidth is the best solution here - on the contrary: although it's called &quot;CW&quot;, it's not a continuous wave at all (such a bad usage of words!): it's a sequence of modulated pulses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you know the length of the potential pulses, you could build a filter that is &lt;em&gt;matched&lt;/em&gt; to the transmitted pulse shape. Again, pulling the theoretical physicist card on you: that's the filter that maximizes the convolution; i.e. the one that maxes the inner product. And if Cauchy-Schwarz inequality has told us anything, than that for complex-valued functions, that means that your receive filter needs to have an impulse response that is the conjugate time-inverse of the transmit signal's pulse shape.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That would essentially mean that the filter impulse response that the receiver convolves the received signal with a mirror of the expected transmit signal for a &quot;dit&quot; (or a &quot;dah&quot;, when you think of that as a different pulse shape).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That's rather trivial to do if your signal is already digital – i.e. instead of continuous complex functions over &lt;span class=&quot;math-container&quot;&gt;$\mathbb R$&lt;/span&gt;, you only consider a sequence of complex values in a computer. Then, the convolution integral collapses to a sum, and with the length of these pulses, it's even a finite sum.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Implementing it like that means that you get a system where you get a clear peak at the output when there's a &quot;dit&quot; on the air. It's not as long as a &quot;dit&quot; anymore, mind you, just a high value when there's a &quot;dit&quot;. Well, seeing that high value, you could of course then synthesize a &quot;dit&quot;. Same for &quot;dah&quot;. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, small problem here: there's humans shaping the pulse, and that's a terrible idea (for many reasons, but let's stay focused on this one): that makes the shape of the &quot;dit&quot; and the &quot;dah&quot; not exactly known.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You could solve that by giving your &quot;dit&quot; (and &quot;dah&quot;) detectors more &quot;leeway&quot; to signal detection of a pulse even when the peak isn't that clear, or you could have a full bank of filters for different pulse shapes, and see which ones trigger. All these things are done in practice.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not quite sure, though, how to answer the question of&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What's state of the art in CW filters&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;because state of the art would &lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;not do CW, that wastes the precious bandwidth-power product that makes your signal differ from measurement noise, and&lt;/li&gt;&#xA;&lt;li&gt;when trying to detect CW, one wouldn't do a pure filtering – but, really, use a PLL like you did, to first recover the frequency, and then use something that tries to make sense of the different pulses visible there.&lt;br&gt;&#xA;There's a lot of approaches there – from &quot;modern style&quot; machine learning with neural networks to empirical models.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-05-30T18:19:08.087" LastActivityDate="2020-05-30T18:19:08.087" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16764" PostTypeId="1" AcceptedAnswerId="16766" CreationDate="2020-05-30T21:55:17.403" Score="3" ViewCount="82" Body="&lt;p&gt;Question from new ham here, regarding ways of matching impedances between a feedline and an antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is it possible to fashion a broadband HF impedance matcher from a length of windowed twinlead, in which the size of the cutout windows along the length of the matching section is smoothly varied from one end to the other?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternatively, is this possible by using a length of twinlead in which the distance between the conductors is smoothly varied from one end of the line to the other?&lt;/p&gt;&#xA;" OwnerUserId="10598" LastEditorUserId="4076" LastEditDate="2020-05-31T16:12:35.170" LastActivityDate="2020-05-31T16:12:35.170" Title="impedance matching with window twinlead" Tags="&lt;antenna&gt;&lt;antenna-system&gt;&lt;impedance-matching&gt;&lt;feed-line&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16765" PostTypeId="2" ParentId="16746" CreationDate="2020-05-31T08:16:53.787" Score="2" Body="&lt;p&gt;Here's some information on GRA-39 Radio Set Control, TA-1 Telephone Set and Chinese 251A Radio Set.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.prc68.com/I/GRA39.shtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.prc68.com/I/GRA39.shtml&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.prc68.com/I/TA1.shtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.prc68.com/I/TA1.shtml&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://chinesemilitaryradio.blogspot.com/2008/10/silicon-two-watt-short-wave-transceiver.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://chinesemilitaryradio.blogspot.com/2008/10/silicon-two-watt-short-wave-transceiver.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-06-02T15:37:09.003" LastActivityDate="2020-06-02T15:37:09.003" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16766" PostTypeId="2" ParentId="16764" CreationDate="2020-05-31T13:36:15.383" Score="3" Body="&lt;p&gt;According to Vincent D. Matarrese's Master's thesis, &quot;&lt;a href=&quot;https://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=5339&amp;amp;context=open_access_etds&quot; rel=&quot;nofollow noreferrer&quot;&gt;Tapered radio frequency transmission lines&lt;/a&gt;&quot; (Portland State University, 1992), there is a long history of using tapered-impedance transmission lines in matching systems. It's much too big a topic to review in an SE post, but the thesis is loaded with references for exploration. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://www.qsl.net/va3iul/Antenna/Wire%20Antennas%20for%20Ham%20Radio/17-Delta-Fed%20Dipole%20Antenna.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;Delta match&lt;/a&gt; is an example of the application of this technique:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0UGON.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0UGON.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It has been described in the ARRL &lt;em&gt;Antenna Book&lt;/em&gt; for decades. &lt;a href=&quot;https://www.qsl.net/pa3hbb/DeltaM1.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;PA3HBB&lt;/a&gt; gives equations that can be used to construct a delta match for a given matching situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;We can begin to consider the prospects for your proposal by evaluating the impedance of bare-wire twinlead and fully-immersed twinlead. The impedance of a two-parallel-wire transmission line is:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$Z_0=\frac{276\Omega}{\sqrt{\epsilon_r}}log_{10} \frac{D}{d}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;valid for &lt;span class=&quot;math-container&quot;&gt;$(\frac{D}{d}&amp;gt;10)$&lt;/span&gt;, where &lt;span class=&quot;math-container&quot;&gt;$\epsilon_r$&lt;/span&gt; is the relative permittivity of the dielectric material between the wires, &lt;span class=&quot;math-container&quot;&gt;$d$&lt;/span&gt; is the wire diameter and &lt;span class=&quot;math-container&quot;&gt;$D$&lt;/span&gt; is the spacing between them. For window line, the wires are not completely immersed in the dielectric material, so the lowering of the line's impedance is considerably reduced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Using &lt;a href=&quot;https://en.wikipedia.org/wiki/Relative_permittivity&quot; rel=&quot;nofollow noreferrer&quot;&gt;Polyethylene's &lt;span class=&quot;math-container&quot;&gt;$\epsilon_r$&lt;/span&gt; of 2.5&lt;/a&gt; as an example, the impedance of 18-ga conductors (&lt;a href=&quot;https://en.wikipedia.org/wiki/American_wire_gauge&quot; rel=&quot;nofollow noreferrer&quot;&gt;d=0.0403-in&lt;/a&gt;) spaced 1-in apart would vary between &lt;span class=&quot;math-container&quot;&gt;$385\Omega$&lt;/span&gt; for bare wires and &lt;span class=&quot;math-container&quot;&gt;$243\Omega$&lt;/span&gt; if the wires were fully immersed in the dielectric. Even without &quot;windows&quot; in the dielectric, its effect is probably ameliorated by at least a factor of two, reducing the impedance variation to about &lt;span class=&quot;math-container&quot;&gt;$344\Omega$&lt;/span&gt;, which wouldn't provide very much impedance transforming capability.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As theorized by the OP, both the spacing and the quantity of dielectric material between  the wires could be varied to increase the impedance range. Materials with higher &lt;span class=&quot;math-container&quot;&gt;$\epsilon_r$&lt;/span&gt; would increase the impedance variation, but their cost-effective application to this problem seems challenging.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-05-31T13:36:15.383" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16767" PostTypeId="2" ParentId="15151" CreationDate="2020-05-31T21:24:57.607" Score="1" Body="&lt;p&gt;The code is too complex for the time that I have available. Since nobody reacts: probably this can help you to understand what I think is realised in the code.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Your assumption that the phase of the recovered carrier must be unique and related to the phase of the pilot tone is correct. A zero crossing of the 19 kHz pilot tone must correspond to a zero crossing of the 38 kHz (the reverse is not, because there are more zero crossings in 38 kHz recovered carrier). Observed as time division multiplex signal: after a zero crossing of the 19 kHz first there is the left channel audio signal and then, 90 degrees later in the 19 kHz signal, there is the right hand channel audio signal; up to 180 degrees phase of the 19 kHz pilot. And so on, that alternating left/right.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To come back to your question: it is not necessary to make that analog PLL for subcarrier 38 kHz synchronous detection in the digital domain. With a complex multiplier or a CORDIC it is possible to multiply a DSP-clock frequency of about 19 kHz, not exactly but close, multiply estimated (generated) 19 kHz with the pilot tone, and filter the output low-pass (this error signal is the offset frequency between the two systems) and construct the wanted 38 kHz with correct frequency and phase. This is a feed-forward system without locking. The figure attached is easier to understand than my words. PA0FSB Copyright for the document: I am the source.&lt;a href=&quot;https://i.stack.imgur.com/Wc0py.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Wc0py.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2020-06-03T20:27:48.647" LastActivityDate="2020-06-03T20:27:48.647" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16768" PostTypeId="1" AcceptedAnswerId="16769" CreationDate="2020-06-01T15:23:01.823" Score="4" ViewCount="327" Body="&lt;p&gt;I'm about to permanently move to another US state, which is in another callsign zone.  Will I be forced to get a new callsign in the new zone?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, when I started, when one was traveling in another zone, one was required to identify that fact, e.g. &quot;W6HAM/7&quot; in CW, or &quot;W6HAM mobile 7&quot; on voice.  I have vague memories of that requirement being lifted, maybe in the late 70's or early 80's...  But just to check, that's not required, right?  Do people still sometimes give their callsign that way anyway, or has the numeric zone largely lost its social significance, the way area codes mostly have in the cellphone era?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I haven't really been active for several decades :-)&lt;/p&gt;&#xA;" OwnerUserId="17166" LastEditorUserId="10859" LastEditDate="2020-06-01T21:15:12.607" LastActivityDate="2020-06-01T21:15:12.607" Title="Change of Address and Callsign Zone" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16769" PostTypeId="2" ParentId="16768" CreationDate="2020-06-01T17:30:25.393" Score="8" Body="&lt;p&gt;No — as of 2020 you're not obligated to change your callsign if you move within the US. Even if you have an Alaska/Hawaii/Guam &quot;restricted&quot; callsign, you can keep it if you leave. All you need to do is notify the FCC of your new mailing address via ULS.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, if you &lt;em&gt;want&lt;/em&gt; to change your callsign when you move, you can. You can request the next available systematic callsign (it will be assigned based on your registered address at the time you make the request) or using the vanity system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also no requirement to sign portable if you're outside of your &quot;home&quot; call district. You &lt;em&gt;can&lt;/em&gt;, if you want to highlight the fact, but it's not common.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's still true that the majority of hams live and operate in the region indicated by their callsign, and you can still talk about working 6-land from 2-land, but exceptions aren't that much of a rarity, and there's no procedural stuff to deal with anymore.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-06-01T19:07:07.453" LastActivityDate="2020-06-01T19:07:07.453" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16770" PostTypeId="2" ParentId="16746" CreationDate="2020-06-02T08:04:55.133" Score="0" Body="&lt;p&gt;It's Chinese on last two photos. The tag information on the last photo is: Transistor 2W HF Radio Mode 2. Serial No: 72-05031, Comm 251A. It's a very widely used HF radio in CPLA in 70s. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here're some specs I found online. &#xA;Frequency: Band 1: 1.7 - 3.2 MHz &#xA;           Band 2: 3.2 - 6.0 MHz&#xA;RF output Power: AM phone &gt;= 1W &#xA;                 CW       &gt;= 2W&#xA;Power consumption: RX 24V/40-45mA&#xA;                   TX 24V/550mA&#xA;Sensitivity: AM &amp;lt;10uV&#xA;             CW &amp;lt;5uV&#xA;Range:   1.5m antenna:  10km(day)/5km(night)&#xA;         15m  antenna:  20km(day)&#xA;         44m dipole antenna 90km(day)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nRbu8.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nRbu8.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17169" LastEditorUserId="17169" LastEditDate="2020-06-02T08:19:32.120" LastActivityDate="2020-06-02T08:19:32.120" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16771" PostTypeId="1" AcceptedAnswerId="16773" CreationDate="2020-06-02T14:50:46.677" Score="9" ViewCount="733" Body="&lt;p&gt;The question is quite simple: When making a coax choke balun, does the size of the ferrite matter, and if so, why?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have seen design notes that say to use a single FT240-43 toroid for powers up to 400W, and then to use two stacked FT240-43 toroids for powers up to 1 or 2 kW. I am specifically talking about choke baluns here, I understand that other designs operate differently. In a choke balun, the ferrite is only stopping current from travelling along the outside braid of the coax - it does not see the main transmitter power (as this is contained inside the coax).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Example:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/61wdL.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/61wdL.png&quot; alt=&quot;Single and double toroid choke baluns&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;[&lt;em&gt;Image used with permission - source &lt;a href=&quot;http://m0taz.co.uk/2018/04/how-good-is-that-choke/&quot; rel=&quot;noreferrer&quot;&gt;M0TAZ Blog&lt;/a&gt;&lt;/em&gt;]&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My understanding of the theory is that these ferrites are only (ideally) effective on currents along the outside of the coax - the currents that are to be choked - and the internal currents are not affected.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since the purpose of this is to reduce the current flowing along the coax screen outer to nothing, why does the ferrite need to be so large? A typical configuration would see a choking impedance of above 3kΩ even at the LF bands, so I am at a loss as to why such huge large masses of ferrite are needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I assume the basis for such &quot;rules&quot; is that the ferrite will saturate if there is not enough of it. But will it?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I am ignoring things like AL value, etc., since this can be achieved over a range of ferrite sizes/turns. &lt;/p&gt;&#xA;" OwnerUserId="8520" LastActivityDate="2020-06-05T15:02:12.157" Title="Importance of Ferrite Size in Coax Choke Balun" Tags="&lt;rf-power&gt;&lt;balun&gt;&lt;transmission-line&gt;&lt;ferrite&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16772" PostTypeId="1" AcceptedAnswerId="16782" CreationDate="2020-06-02T16:01:02.007" Score="0" ViewCount="214" Body="&lt;p&gt;I remember long range radio stations which still worked 30yrs ago. I could listen to the whole Europe. I also think I saw movies where radio enthusiasts could talk all over the world..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I never looked up how it works. But I had impression that it's quite simple to send a radio signal around the globe (you just need very tall antenna). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However I now am trying to figure out how to do it exactly and there is nothing much..&lt;/p&gt;&#xA;&#xA;&lt;p&gt;My questions are to envisage a technical solution for 5,000 km range with short on-off signal:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;what kind of wavelength can travel that far&lt;/li&gt;&#xA;&lt;li&gt;what kind of transmitter power is required&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Another question:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I understand that such long propagation range is only possible by reflection from ionised atmosphere layers - how do you estimate actual path length then ? &lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="17172" LastEditorUserId="17172" LastEditDate="2020-06-04T12:14:16.680" LastActivityDate="2020-06-05T04:51:56.493" Title="Send on-off radio signal 5,000km" Tags="&lt;propagation&gt;" AnswerCount="4" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16773" PostTypeId="2" ParentId="16771" CreationDate="2020-06-02T16:10:11.023" Score="5" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;When making a coax choke balun, does the size of the ferrite matter, and if so, why?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Simplest answer:  If the choke impedance is low enough to allow some common mode power through, then there is a possibility of overheating.  The bigger cores either dissipate heat better or provide higher impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another way to say the same thing:  As long as the choke impedance is high enough, ferrite size does not matter.  &quot;High enough&quot; depends on a lot of factors, but &quot;5,000 Ohm&quot; seems to be the target.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Jim Brown, K9YC, has a publication (&quot;A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing&quot; &lt;a href=&quot;http://k9yc.com/RFI-Ham.pdf&quot; rel=&quot;noreferrer&quot;&gt;http://k9yc.com/RFI-Ham.pdf&lt;/a&gt; ) which goes into this in great detail.  A small excerpt from Revision 7, 2019 (page 30) states 1 of 4 criteria for using common mode chokes as baluns:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Dissipation  The choking impedance must be high enough to reduce&#xA;  common mode current to the level such that the choke cannot overheat&#xA;  and damage the core or the coax&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Jim Brown advocates choke impedance to be around 5,000 Ohm.  Some older references considered 1,000 Ohm to be sufficient.  But it depends on how much power you are running and how imbalanced your antenna is.&lt;/p&gt;&#xA;" OwnerUserId="11434" LastActivityDate="2020-06-02T16:10:11.023" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16774" PostTypeId="2" ParentId="16772" CreationDate="2020-06-02T16:45:52.220" Score="5" Body="&lt;p&gt;Kind of in a hurry, so only a quick answer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That was &lt;a href=&quot;https://en.wikipedia.org/wiki/Longwave&quot; rel=&quot;noreferrer&quot;&gt;longwave&lt;/a&gt; (LW) radio (150 kHz to ca 380 kHz), or medium wave (MW) (530 kHz to 1600 kHz). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Wavelength &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is related to frequency as &lt;span class=&quot;math-container&quot;&gt;$\lambda = \frac{c_0}{f}$&lt;/span&gt;, with &lt;span class=&quot;math-container&quot;&gt;$c_0=3\cdot10^8\,\frac{\text m}{\text s}$&lt;/span&gt; the speed of light, and &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; the frequency.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;LW still exists, not very popular for broadcast these days since higher frequency installations are practically full-coverage, unless you're at sea. In most of central Europe, MW has been shut off, because there was no sweet spot between LW and the VHF bands (30 to 300 MHz, which includes the &quot;usual&quot; 88 to 108 MHz FM broadcasting band with music and news stations).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Newer longwave installations don't use the (noise-sensitive) AM (amplitude modulation) use DRM (Digital Radio Mondiale).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Existing longwave transmitters use lots of power. Typical MW AM stations have 50 kW to 2 MW (!) in power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;India has relatively recently build a transmission system for DRM, to cover most of the subcontinent, and it uses about 1 MW – much less than a AM system achieving the same would have to use.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;you just need very tall antenna&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The antenna needs to be typically a quarter wavelength in size (roughly), so often complex arrays of tall antennas are necessary to achieve that. They extend, usually, down to the ground, so they are not &quot;Mounted at height&quot;, they are simply &quot;high&quot;. &lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;what kind of wavelength can travel that far&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Generally, in free space, all wavelengths travel infinitely far, but you're right, only certain ones fall in a region where you can exploit the bending properties of the ionosphere, for example.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the power density per area (i.e. how much RF power hits 1 m²) goes down with the square of the distance and with the square of the wavelength. (however, that is at least partially compensated by the fact that an antenna of a given size can be made to have a higher effective area for a higher frequency. The increase in &quot;picking up power&quot; area is also square with the inverse of wavelength). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the fact that LW reached and reaches so far is:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;atmospheric and ground-conducted wave phenomena, as you've mentioned&lt;/li&gt;&#xA;&lt;li&gt;the relative ease at which a highest-power amplifier for these frequencies can be built (1940's engineers simply &lt;em&gt;couldn't&lt;/em&gt; build a 100 MHz amplifier that does 500 kW of output power; the technology didn't exist.)&lt;/li&gt;&#xA;&lt;li&gt;The low expectations for transmission quality on the existing bands.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So, it's a mixture of physical, technical and historical reasons.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;how do you estimate actual path length then ? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Using a propagation model. There's quite a few of these, some are very complex and include sun activity, weather and angles of antennas, others are more rules of thumbs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, notice that there's not necessarily a &lt;em&gt;single&lt;/em&gt; path. In fact, that's usually not the case, or only the case if you restrict yourself to a very narrow bandwidth. As an example: &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The aforementioned DRM system (deployed with the intent of reaching &gt; 1 billion people!) is designed with a mode that can tolerate 7.5 ms of delay spread, i.e. a signal travelling the longest path reaches the receiver 7.5 ms after it already reached it via the shortest path. The tolerable path length &lt;em&gt;difference&lt;/em&gt;, thus, has to be up to &lt;span class=&quot;math-container&quot;&gt;$7.5 \cdot10^{-3}\,\text{s}\,\cdot\,c_0 =2.25\cdot10^6\text{m}=2250\,\text{km}$&lt;/span&gt;. So, it's really impossible to talk about &quot;path length&quot;, you need to account for the multiple different paths. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The DRM receiver actually calculates the way the multipath environment looks like – and compensates the effect of that; &lt;br&gt;&#xA;which is the main reason why DRM works better at the same power:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Imagine you listen to someone talking. However, that's overlaid with an echo coming in 7.5 ms later; that simply means that when his voice hits 266.67 Hz – that's a middle C in musical notation – the echo happens to be the same tone, but half a tone period later, so that it cancels out!&lt;br&gt;&#xA;We call that &lt;em&gt;frequency-selectivity&lt;/em&gt; of the &lt;em&gt;multipath&lt;/em&gt; channel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, DRM has built-in RF &quot;echo cancellation&quot;, and hence works better, and you thus can get better audio (remember Longwave broadcast, that was always very narrowband, and sounded muffled, and there was no chance to get music). Or, you can use the same advantage to get the same audio quality, but with less power; or with the same power, but further away.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;I saw movies where radio enthusiasts could talk all over the world.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Right place to mention this – radio amateurs tend to do such things (and others). &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Now, when you want to do this, you don't need a 1 MW amateur band AM transmitter. You can actually &quot;work the world&quot; with far less power, assuming you don't try to get something as &quot;bandwidth-hungry&quot; as music across. In fact, with maybe 0.1 W, you can get very far on a continent, if you use a very robust transmission scheme, a &quot;mode&quot;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just as AM and DRM are two methods of transporting broadcast &lt;em&gt;audio&lt;/em&gt;, there's methods for just transporting textual methods that need far less power at the receiver, and hence far less power at the transmitter. &quot;WSPR&quot; and &quot;FT-8&quot; are such modes.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For example, to transmit WSPR, you technically need nothing but something that can switch a voltage on and off at the desired rate; and people &lt;a href=&quot;http://pa0rob.vandenhoff.info/article/wspr-tx-raspberry-pi&quot; rel=&quot;noreferrer&quot;&gt;built such things&lt;/a&gt; and &lt;a href=&quot;https://ftp.fau.de/fosdem/2015/devroom-software_defined_radio/rpisdr.mp4&quot; rel=&quot;noreferrer&quot;&gt;made talks about such things&lt;/a&gt;, using nothing but a raspberry Pi (a 35€ computer).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-02T16:45:52.220" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16775" PostTypeId="2" ParentId="16746" CreationDate="2020-06-02T17:00:43.607" Score="0" Body="&lt;p&gt;@Brian K1LI. It's from Chinese BBS. Here's one with manual. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.360doc.com/content/13/0304/21/8482771_269312580.shtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.360doc.com/content/13/0304/21/8482771_269312580.shtml&lt;/a&gt; &lt;/p&gt;&#xA;" OwnerUserId="17173" LastActivityDate="2020-06-02T17:00:43.607" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16776" PostTypeId="2" ParentId="16772" CreationDate="2020-06-02T19:46:08.920" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;...solution for 5,000 km range with unmodulated signal:&lt;/p&gt;&#xA;  &#xA;  &lt;ul&gt;&#xA;  &lt;li&gt;&lt;p&gt;what kind of wavelength can travel that far&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;what kind of transmitter power is required&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;li&gt;&lt;p&gt;ionized atmosphere layers how do you estimate actual path length&lt;/p&gt;&lt;/li&gt;&#xA;  &lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;It is possible to communicate 5000-km over a wide range of frequencies. The effective radiated power required (transmitter power x antenna gain) depends on propagation of a given wavelength over a given path at a given moment. To first order, propagation depends on:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Wavelength: frequencies that are not absorbed or passed through the&#xA;ionosphere&lt;/li&gt;&#xA;&lt;li&gt;Path: over land or sea, conductive or lossy terrain, smooth (reflective) or&#xA;mountainous (dispersive), etc.&lt;/li&gt;&#xA;&lt;li&gt;Time of day: the sun ionizes the atmospheric layers that reflect or&#xA;absorb radio waves&lt;/li&gt;&#xA;&lt;li&gt;Time of year: day length and degree of ionization vary&lt;/li&gt;&#xA;&lt;li&gt;Status of the ~11-year long sunspot cycle&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;Free tools are available to estimate the probability of being able to communicate over a given path. My personal preference is the PropView component of the &lt;a href=&quot;https://www.dxlabsuite.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Lab Suite&lt;/a&gt;, but there are others, and web sites like &lt;a href=&quot;https://www.voacap.com/hf/&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP Online&lt;/a&gt; allow you to identify &quot;best&quot; frequency between geographical coordinates.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-06-02T19:46:08.920" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16777" PostTypeId="2" ParentId="16772" CreationDate="2020-06-02T23:17:32.637" Score="1" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;5,000 km range with unmodulated signal&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Either anything can do that, or nothing, depending on your perspective.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, slower modulations can propagate a farther distance and still be successfully demodulated. This is because transmitting a particular symbol for a longer time accumulates more energy in the symbol, and thus it is easier to detect.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An unmodulated signal is just one symbol for an infinite time. So the energy in it is infinite, and so it will always be detectable, provided one is willing to wait long enough. Of course some propagation modes will work better than others, and so the unmodulated signal will be detected sooner rather than later. But even propagation modes that are very poor will still work, eventually.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;On the other hand, an unmodulated signal contains no information, so what does it even mean to receive it? Also, for the signal to be unmodulated it must have no start and no end, so how is that even possible to transmit?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-02T23:17:32.637" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16778" PostTypeId="2" ParentId="16751" CreationDate="2020-06-02T23:56:06.710" Score="3" Body="&lt;p&gt;TLDR: 60 volts AC divided by the transformer CMRR is much greater than 1 mA times the resistance of the wire installed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;--&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the first case - the raspberry Pi was floating at 60 V AC above ground, being powered by a two-pin USB adapter. The radio was earthed by its power supply, coax, etc. So the transformers have 60 volts across them, and even the smallest asymmetry of capacitance will generate a large differential-mode signal.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In the second case, there's a maximum of (say) 1 mA flowing on the ground wire (there's a legal limit for leakage, something like that). A small voltage develops across this resistance, which is added to the audio signal.  The transformers are probably still helping.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;--&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Transformer isolation is much more important in cases like this:&lt;br&gt;&#xA;Imagine you have a &lt;em&gt;grounded&lt;/em&gt; computer plugged in on one end of the room, and a &lt;em&gt;grounded&lt;/em&gt; rig plugged in on the other. Your air conditioner is causing a 1 volt drop in the ground/neutral potential between the two sockets, but this 1 volt is at &lt;em&gt;a very low impedance&lt;/em&gt;. The simple sound-card earth wire is completely overwhelmed by this, and simply drops the 1 volt too, resulting in a 1 volt differential AC signal added to the audio at the rig/PC. In this case, the transformers provide a vital function, breaking the so-called ground loop.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your first case, you have a high voltage, high impedance voltage difference between the two halves, so the right solution is a heavy ground wire. Then you use the transformer in the USB power supply for ground isolation.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-06-02T23:56:06.710" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16779" PostTypeId="2" ParentId="16746" CreationDate="2020-06-03T09:49:47.600" Score="0" Body="&lt;p&gt;GRA-39 Radio Set Control, &#xA;TA-1 Telephone Set, &#xA;Silicon 2W Short Wave Transceiver, &#xA;884 VHF FM Backpack (also known as a Comm 251A),&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I think 'NHA MAY THONG TIN M3' refers to an Information Tech manufacturer named 'M3' and DT-97 is a model number, but I haven't found documentation on it yet.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Joe&#xA;73 V01WJG&lt;/p&gt;&#xA;" OwnerUserId="17143" LastActivityDate="2020-06-03T09:49:47.600" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16780" PostTypeId="1" CreationDate="2020-06-03T11:30:43.870" Score="3" ViewCount="42" Body="&lt;p&gt;I have a Hytera PD785G. Typically, I charge it overnight, then take it out and use it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Since this is currently my only radio station, I'd like to misuse it as a stationary device. Most of the time, I'm just listening and waiting for calls. For making a call, I'd then take it out of the charger.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have looked up the User Guide, which says (emphasis mine)&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Charging the Battery&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Caution:&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;● &lt;strong&gt;Make sure the radio is powered off before charging.&lt;/strong&gt; Read the Safety Information Booklet in advance to get necessary safety information.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;● To achieve optimal battery performance, please charge the battery for at least 5 hours before initial use.&lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;Please use the charger specified by the Company to charge the battery. Charging Diagram is listed below.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This lets me assume, I cannot simply put it into the charger. Is there some acessoire that would let me use it in a more stationary way?&lt;/p&gt;&#xA;" OwnerUserId="890" LastEditorUserId="5222" LastEditDate="2020-06-05T20:08:35.087" LastActivityDate="2020-06-05T20:08:35.087" Title="Can I have the Hytera PD785G turned on in the charger?" Tags="&lt;safety&gt;&lt;battery-charging&gt;&lt;hytera&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16781" PostTypeId="2" ParentId="16780" CreationDate="2020-06-03T11:55:55.793" Score="5" Body="&lt;p&gt;Never owned a similar device, but judging from the product pictures:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Indeed, the charging logic for the battery is not inside the handset, but the charging cradle, and hence, that would quite likely be confused should you transmit while charging, as that looks like a sudden drop in battery voltage.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, the other option is what Hytera sells as &lt;a href=&quot;https://www.hytera-mobilfunk.com/en/product/details/sab04-battery-eliminator/&quot; rel=&quot;noreferrer&quot;&gt;&quot;Battery Eliminator&quot;&lt;/a&gt;, which has the shape and handset contacts that &lt;a href=&quot;https://www.hytera-mobilfunk.com/en/product/details/bl2510-lithium-ion-battery-2500-mah/&quot; rel=&quot;noreferrer&quot;&gt;a battery&lt;/a&gt; has, but is actually nothing but a step-down voltage converter giving you something in the range of 7.4 V, plus probably just a resistor to emulate the temperature sensor of the battery pack.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's that easy, you can either buy the Hytera battery eliminator, and attach the cigarrette lighter plug to a 12V supply, or you can zurechtbastel something that just happens to have contacts in the right places:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Check the number of contacts on the device side of the battery.&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;2 only: simplest case, you just need to connect a 7.4 V power supply to these (watch polarity)&lt;/li&gt;&#xA;&lt;li&gt;3 or 4: there's a sensor to measure the battery temperature built in to the battery pack, and your handheld &lt;em&gt;might&lt;/em&gt; check that to make sure the battery isn't overheating.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;In that case: you need to emulate that sensor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Verify which pins are the positive and negative contact with a multimeter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Measure whether there's a voltage between the other two (4 contacts), or between the third and the negative contact. If that's the case, it's a thermocouple. If no reasonable voltage is found:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;put the battery in the fridge, measure the resistance between the two contacts that aren't + and -. Let it warm up (sun, heating, body warmth!), and compare. If it drastically changes, yep, there's a thermistor attached here, and you might need to emulate that so that the handset doesn't think the battery is overheating.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-03T11:55:55.793" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16782" PostTypeId="2" ParentId="16772" CreationDate="2020-06-03T17:44:22.223" Score="1" Body="&lt;p&gt;This question is clearly asking about commercial shortwave broadcast radio, but since this is the amateur radio forums, here's an answer with an amateur radio slant instead of shortwave broadcast.  But this still applies to shortwave broadcast.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Generally, anything below 30MHz (wavelength roughly longer than 10m) will bounce (or more accurately, refract) off the ionosphere.  However, the location and nature of the ionosphere changes periodically and randomly based on time of day and solar activity, which shifts exactly what frequencies bounce best.  Generally, 14MHz works best during day, and 4MHz works best in deep night, but this may vary based on actual conditions.   30MHz works best during high solar activity, which occurs roughly 5 years out of every 11.  These are broad generalizations, and more detailed accurate answers can be found in extensive literature on propagation and on live propagation measurement websites.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Presuming amateur radio use, the antenna doesn't actually have to be that large or high.  It does help to be close to 1/4 wavelength, and larger antennas tend to work better, but there are many shortened antennas that still work acceptably well.  Radiation angle is actually much more important (for transmission) than height -- you want to aim at the horizon to get maximum distance, but not so low that it's absorbed by trees and buildings first.  It turns out that low antennas typically have a lower radiation angle, which is also why broadcast shortwave antennas start at ground level.  (Radiation angle matters for reception too, but it's not as critical.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Amateur radio can use power as low as 5w, but 100w is more typical for long range communications.  Slower and narrow bandwidth modulations can use lower power, so, for instance, CW, PSK31, and FT8 typically use 30w, but can go much lower and still propagate to the other side of the world.   Again, this is very sensitive to &quot;band conditions&quot;, so if the ionosphere is not right for the frequency, even very high power will not propagate well, and if it is right, 5w might do as well as 100w.  Or, if there's a lightning storm, the noise from the lightning might drown out your transmissions.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Contrast amateur radio power (1w - 1500w in the US) with commercial broadcast station power (up to 2Mw) -- amateur radio receivers are typically more sensitive (and expensive) than commercial shortwave broadcast receivers, and amateur radio operators typically use much larger antennas.  Inexpensive commercial shortwave receivers frequently use a very small internal loopstick antenna (about the size of your hand), and if a larger external antenna is used, can pick up much weaker signals.  These two differences necessitate the higher power for broadcast stations. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are multiple bands appropriate for shortwave broadcast, between 2MHz and 26MHz.  Each of these bands has different propagation characteristics that make them usable at different ranges and times of day, same as for amateur radio.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-06-05T04:51:56.493" LastActivityDate="2020-06-05T04:51:56.493" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16784" PostTypeId="1" AcceptedAnswerId="16785" CreationDate="2020-06-03T23:42:24.267" Score="3" ViewCount="164" Body="&lt;p&gt;Based on another question here, I think it is legal, but I would like it directly from the people who know. Thank you for your time.&lt;/p&gt;&#xA;" OwnerUserId="16868" LastActivityDate="2020-06-07T12:54:50.530" Title="Is it legal for an unlicensed person to transmit as long as they are under the direct supervision of a licensed amateur?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16785" PostTypeId="2" ParentId="16784" CreationDate="2020-06-04T02:14:22.307" Score="5" Body="&lt;p&gt;Yep, according to FCC part 97.115...as long as the licenced control operator is present and supervising. There is at least one exception though - the third-party operator cannot have previously had a license revoked.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Here is section 115:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;§ 97.115 Third party communications. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(a) An amateur station may transmit  messages for a third party to: &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(1) Any station within the jurisdiction of the United States. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(2) Any station within the jurisdiction of any foreign government when&#xA;  transmitting emergency or disaster relief communications and any&#xA;  station within the jurisdiction of any foreign government whose&#xA;  administration has made arrangements with the United States to allow&#xA;  amateur stations to be used for transmitting international&#xA;  communications on behalf of third parties. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;No station shall transmit messages for a third party to any station&#xA;  within the jurisdiction of any foreign government whose administration&#xA;  has not made such an arrangement. This prohibition does not apply to a&#xA;  message for any third party who is eligible to be a control operator&#xA;  of the station. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(b) The third party may participate in stating the message where: &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(1) The control operator is present at the control point and is&#xA;  continuously  monitoring and supervising the third party’s&#xA;  participation; and &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(2) The third party is not a prior amateur service licensee whose&#xA;  license  was revoked or not renewed after hearing and re-licensing has&#xA;  not taken  place; suspended for less than the balance of the license&#xA;  term and the suspension is still in effect; suspended for the balance&#xA;  of the license term and re-licensing has not taken place; or&#xA;  surrendered for cancellation following notice of revocation,&#xA;  suspension or monetary forfeiture proceedings. The third  party may&#xA;  not be the subject of a cease and desist order which relates to&#xA;  amateur service operation and which is still in effect. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(c) No station may transmit third party communications while being&#xA;  automatically controlled except a station transmitting a RTTY or data&#xA;  emission. &lt;/p&gt;&#xA;  &#xA;  &lt;p&gt;(d) At the end of an exchange of international third party&#xA;  communications, the station must also transmit in the station&#xA;  identification procedure the call sign of the station with which a&#xA;  third party message was exchanged.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerDisplayName="user14945" LastEditorUserId="218" LastEditDate="2020-06-07T12:54:50.530" LastActivityDate="2020-06-07T12:54:50.530" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16786" PostTypeId="2" ParentId="14409" CreationDate="2020-06-04T05:49:17.060" Score="1" Body="&lt;p&gt;There is a trick to balance the notch tuning johannsen cap adjustment with the coupling ring loops to meet the required rejection per side with minimum insertion loss. I believe I tuned mine to reject 40-45dB rejection per cavity at max. First, I would get the pass rod approximately at the pass frequency, then tune notch under cap. If too deep or shallow a notch, less than -40 or more than -50dBm, rotate coupling loop slightly and retune pass and adjust notch cap until you find notch maximized at about 45dB on rejection frequency. Just make sure you aren't fully open or tightened on the notch cap or else you cannot fine tune the notch later. Once you get one cavity right you can approx the others by copying position, but they will still need to be adjusted finely with service monitor the same way because cans are not exact. Then do same for cans on other side. After done connect harness and fine tune pass rods. Then adjust notch caps. You should see around &amp;lt;= -1.5dB Insertion loss with over 100dB rejection... You must balance the rejection with rotating the coupling loops which is what most people don't expect they need to do. &lt;/p&gt;&#xA;" OwnerUserId="17178" LastActivityDate="2020-06-04T05:49:17.060" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16787" PostTypeId="2" ParentId="16771" CreationDate="2020-06-04T12:48:45.803" Score="2" Body="&lt;p&gt;I believe the choice of the core size is twofold.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As from K8NVH good answer a minimum impedance is needed for the balun to do its job.&#xA;A common mode impedance much higher than differtial ones involved makes sure the balanced to/from unbalanced convertion takes place.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This somehow drives the size of the core for its mechanical dimensions shall allow the cable winding.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A second point is avoiding core saturation which would turn into heat, reduced impedance and balun effect and possibly intermodulation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is obviously power dependant, one simple way to reckon core size is ferrite maximum induction and its cross section found on relevant datasheets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;From the electrical point of view one can just consider the balun as an ideal transformer&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/oUray.png&quot; alt=&quot;schematic&quot;&gt;&lt;/p&gt;&#xA;&#xA;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2foUray.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;converting, say Vp=100V@50ohm (200W) single ended into +Vp/2=50V/0V/-50V=-Vp/2 balanced.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is done by 1:1  transformer built on the core by the two windings made of the inner and braid of the coaxial cable.&#xA;Each of these windings developes the same voltage (1:1 turn ratio) &quot;shifting&quot; the output voltages as required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Just the same as any transformer it ideally let the power go through without &quot;eating&quot; any significative part of it. Then of course losses come into play. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;And now, back to K8NVH point form a differnt point of view, the balun impedance is now clearly what is also called magnetizing inductance of a transformer.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Again, just any other transformer, core induction is ruled by frequency, voltage across and number of turns.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Back from basics Faraday-Neumann-Lenz law states that&#xA;&lt;span class=&quot;math-container&quot;&gt;$$ v=\frac{\mathrm{d} \Phi_\mathrm{B}}{ \mathrm{dt}} $$&lt;/span&gt; for each turn and given a supposed uniform field inside the core we have total voltage given by &lt;span class=&quot;math-container&quot;&gt;$$ v=N\, A \frac{\mathrm{d} B}{ \mathrm{dt}} $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;where  N is the number of turns and A the toroid cross section.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If we finally take the hypothesis of sinusoidal voltage and induction we boil down to&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_\mathrm{P}\sin \omega t = N\,A\,\omega B_\mathrm{max} \sin \omega t $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;which after removing time dependance gives the relation between the peak voltage and the maximun induction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$V_\mathrm{P}= N\,A\,\omega B_\mathrm{max}$$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This at the lowest working frequency could be used to reckon peak voltage the windings on the  core can bear at the core manufacturer maximum specified induction.&lt;/p&gt;&#xA;" OwnerUserId="15476" LastEditorUserId="15476" LastEditDate="2020-06-05T15:02:12.157" LastActivityDate="2020-06-05T15:02:12.157" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16790" PostTypeId="1" CreationDate="2020-06-07T10:43:11.440" Score="2" ViewCount="91" Body="&lt;p&gt;What kind of interference or other receiver issues can cause a constant buzzing noise (picket fence lines in the audio spectrum) in the demodulated audio of a received NFM VHF signal?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;With AM, it could be additive RF noise; but shouldn't a fully captured FM demodulation ignore that?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This particular noise is not due to a transmitter issue or PL tone or weak FM capture, as the buzzing appears and disappears depending on the location of the receiving station, not the particular transmitting station or receiver equipment (2M HT or SDR) used.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="8717" LastEditDate="2020-06-07T21:08:07.090" LastActivityDate="2021-03-08T16:57:23.630" Title="Buzzing FM interference" Tags="&lt;receiver&gt;&lt;rfi&gt;&lt;fm&gt;&lt;noise&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16791" PostTypeId="1" AcceptedAnswerId="16792" CreationDate="2020-06-07T15:19:32.983" Score="5" ViewCount="684" Body="&lt;p&gt;I only studied monopole in sending mode or receiving mode alone but never in both modes together, I have this question which says:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Two vertical λ/4 monopoles are parallel to each other with 20 meters&#xA;  separation between them at 5 GHz. The first monopole is used as a&#xA;  transmitting antenna, while the second one is used as a receiving&#xA;  antenna to receive power from the first one. The transmitting monopole&#xA;  is connected to a 50 ohms lossless transmissions line. The input power&#xA;  to the transmission line of the transmitting monopole is 200 watts.&#xA;  What is the power received by the receiving monopole?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I tried to solve it as follows:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;I know that quarter-wavelength monopole has impedance = 36.5 ohms&#xA;so I calculated the reflection efficiency to be = 0.975&lt;/li&gt;&#xA;&lt;li&gt;since no polarization efficiency is given and the line is lossless I assumed the total efficiency = 0.975&lt;/li&gt;&#xA;&lt;li&gt;So the total power transmitted = &lt;span class=&quot;math-container&quot;&gt;$0.975\cdot  200 = 195 \,\text{watt}$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;I found a law on the web called Friis transmission equation&#xA;&lt;span class=&quot;math-container&quot;&gt;$$P_r = P_t\cdot G_1\cdot G_2 \cdot\left(\frac{\lambda}{(4\pi R)}\right)^2$$&lt;/span&gt;&#xA;and I already know that Directivity = 3.2&#xA;so &#xA;&lt;span class=&quot;math-container&quot;&gt;$$ Pr = 195\cdot 3.2\cdot 3.2\cdot 0.975\cdot (0.06/(4\pi 20))^2 = 1\cdot 10^{-4} $$&lt;/span&gt;&#xA;which I think is too low power.&#xA;What did I do wrong or how to use this law?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="17194" LastEditorUserId="76" LastEditDate="2020-06-07T16:14:57.127" LastActivityDate="2020-06-07T22:58:02.067" Title="How to calculate power transmitted by monopoles?" Tags="&lt;receiver&gt;&lt;dipole&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16792" PostTypeId="2" ParentId="16791" CreationDate="2020-06-07T16:50:22.170" Score="9" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;10⁻⁴&lt;br&gt;&#xA;  which I think is too low power.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Why? Gut feeling says that is actually pretty good a transmission for such a distance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Notice how your free space path loss is &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\left(\frac{\lambda}{R}\right)^2\cdot\frac1{16\pi^2}\approx \left(\frac{\lambda}{R}\right)^2 \cdot \frac1{160}$$&lt;/span&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;and &lt;span class=&quot;math-container&quot;&gt;$\frac\lambda R=3\cdot10^{-3}, \left(\frac\lambda R\right)^2=9\cdot10^{-6}$&lt;/span&gt;, so it sounds pretty OK that only a tiny fraction of power reaches the receiver. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;10⁻⁴ W is still -10 dBm. That's &quot;screaming loud&quot; in terms of received radio power. GSM phones work at -110 dBm. That's ten billion times less power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To compare this to a different system running at around 5 GHz: IEEE802.11ac (modern Wifi), using a 80 MHz channel, can run at full 433 Mb/s (without even using MIMO) when received signal power is -50 dBm.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, the order of magnitude of the free space path loss coefficient highlights a different aspect: It really doesn't matter whether your antenna is perfectly matched. A couple centimeters in distance make up for your 97% efficiency. (also, strictly speaking, the quarter-wavelenght monopole doesn't have a 36Ω impedance, it has (36+j21)Ω or so impedance. Again, this doesn't matter in reality as much as people tend to think.)&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-07T16:50:22.170" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16793" PostTypeId="2" ParentId="16791" CreationDate="2020-06-07T22:58:02.067" Score="3" Body="&lt;p&gt;Your calculation looks all correct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A quick conceptual way to check it is this:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;picture a 200 watt light bulb&lt;/li&gt;&#xA;&lt;li&gt;20 metres away, work out how much light falls on an area of about &lt;span class=&quot;math-container&quot;&gt;${\lambda\over{2}}$&lt;/span&gt; by &lt;span class=&quot;math-container&quot;&gt;$ {\lambda\over{2}} $&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;This is the power received by the second antenna. The area of a 20 metre sphere is 5000 &lt;span class=&quot;math-container&quot;&gt;$m^2$&lt;/span&gt; and the capture area is &lt;span class=&quot;math-container&quot;&gt;${1\over1600} m^2$&lt;/span&gt; so you can see the large ratio right there.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There is no polarisation loss, as you say, but I would call it mismatch loss, not efficiency. Although the net effect is the same, efficiency implies a loss of power in the antenna, while mismatch between 37 and 50 Ohms results in some power being reflected back to the source instead of being radiated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The question doesn't say what the receiver impedance is, it's reasonable to assume 50 Ohms. Then you can calculate the mismatch loss on receive, which is the same as on transmit.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One last interesting point - the gain of the monopole is only 3, or 5 dBi, &lt;em&gt;when you are above the same infinite conducting ground.&lt;/em&gt; So for this example to work, there would have to be a continuous sheet of metal, not just 20 metres long, but perhaps 40 x 40 metres, with the monopoles mounted in it. No problem for an example, but unlikely in practice. Perhaps this could happen on the top of an aircraft or a ship.&lt;br&gt;&#xA;The antenna described as &quot;monopole_with_limited_ground&quot; like you might make with a piece of wire and a tin can has a gain of more like 1.0 or 0 dBi, on the horizon, when considered as a whole, so the figures would be a bit different.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-06-07T22:58:02.067" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16794" PostTypeId="1" AcceptedAnswerId="16797" CreationDate="2020-06-08T07:51:26.193" Score="1" ViewCount="90" Body="&lt;p&gt;Im new on RF circuit designing. Im designing an circuit with GSM and GPS capabilities. I know when using high frequency signals the RF traces must be impedance matched. Now what I understand is, I can make it by impedance mathing circuits like pi-network but this will require antenna tuning and I dont have the tools for that, or I can use impedance controlled traces(microstrip line) on my PCB. What I don't understand is: which one is better or must I use impedance controlled lines and impedance matching circuit?&lt;/p&gt;&#xA;" OwnerUserId="17197" LastActivityDate="2020-06-27T20:19:55.757" Title="RF PCB Design Difference Between Controlled Impedance Track and Impedance Matching Circuit" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;impedance-matching&gt;&lt;equipment-design&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16795" PostTypeId="1" CreationDate="2020-06-08T10:31:13.863" Score="0" ViewCount="59" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SbGDf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SbGDf.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;I planning to use RF module for communication of high precision GNSS module. So I am doing detail study on RF module. In one of the datasheets of RF module (part no: &lt;a href=&quot;http://store.rfdesign.com.au/rfd-868ux/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RFD868ux&lt;/a&gt;) mentioned that 'Duty cycle is percentage of time to allow transmit'.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I don't understand how the duty cycle of RF module effects transmission. Can someone please let me know how the transmission rate in the RF depends on the duty cycle?&lt;/p&gt;&#xA;" OwnerUserId="17199" LastEditorUserId="17199" LastEditDate="2020-06-09T04:18:49.530" LastActivityDate="2020-06-09T12:46:22.913" Title="How Duty cycle affects transmission rate in RF module?" Tags="&lt;uhf&gt;&lt;rfi&gt;&lt;transceiver&gt;&lt;transmission&gt;&lt;gnss&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16796" PostTypeId="2" ParentId="16795" CreationDate="2020-06-08T12:55:39.280" Score="0" Body="&lt;p&gt;Duty cycle of a radio is the percentage of time it is putting out full power.  You can calculate this by averaging off time with the duty cycle of the signal you are transmitting, weighted by the amount of time for each.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The duty cycle of the signal you are transmitting depends on the modulation method, and sometimes the information being modulated.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's FSK or PSK, it may be 100% duty cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If it's on off keying, the duty cycle will possibly vary, and you'd have to do some statistics on the source data to figure out the duty cycle.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Similarly, if it's amplitude modulation of phone, the duty cycle will vary, but there's rules of thumb for, say, talking vs. music.  Obiously, a slow speaker that leaves lots of gaps will have a lower duty cycle that someone who doesn't. :)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;AM modulation of other media (i.e., video) is also possible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;FM modulation is probably constant duty cycle.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-06-09T12:46:22.913" LastActivityDate="2020-06-09T12:46:22.913" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16797" PostTypeId="2" ParentId="16794" CreationDate="2020-06-08T13:06:40.817" Score="4" Body="&lt;p&gt;It is not an either/or situation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance controlled traces make feedlines of a known &lt;a href=&quot;https://en.wikipedia.org/wiki/Characteristic_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;characteristic impedance&lt;/a&gt;, just like most coax is 50 or 75 ohms, and ladder-line is often 300 or 450 ohms. As a rule of thumb, any trace or wire longer than 1/10th the wavelength has to be considered a transmission line, in which case you must know the characteristic impedance. Trying to use a transmission line in your circuit without knowing the characteristic impedance is like trying to use a resistor without knowing the resistance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Impedance matching circuits are circuits which transform one impedance to another. Designers usually try to keep them to a minimum since they cost something both in money and signal power. The matching circuit might consist of short (usually 1/4 wavelength or less) sections of transmission lines, but also inductors, capacitors, transformers, and (less commonly) resistors.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-08T13:06:40.817" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16798" PostTypeId="1" AcceptedAnswerId="16799" CreationDate="2020-06-08T15:17:27.750" Score="5" ViewCount="1282" Body="&lt;p&gt;Why are chokes usually placed at the feedpoint, can't common-mode currents occur below the choke as well?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I understand it's placed at the feedpoint to keep everything balanced by eliminating common-mode currents on the outside of the shield, but i thought they can occur below the choke too (unless i've misunderstood?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;For the purposes of this discussion let's assume the antenna is a dipole and is fed by coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks :)&lt;/p&gt;&#xA;" OwnerUserId="17200" LastActivityDate="2020-12-31T09:40:38.560" Title="Common-mode current and choke placement" Tags="&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16799" PostTypeId="2" ParentId="16798" CreationDate="2020-06-08T19:08:44.013" Score="3" Body="&lt;p&gt;Common mode current occurs due to coupling between the antenna and the coax shield, so if you place the choke at the feedpoint, you break the circuit and most of the common mode current will be blocked.  (The circuit is from the antenna, though the coax, and back to the antenna via RF.)  You shouldn't get any significant amount of common mode current further down the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, nothing is perfect, and some common mode current may leak past the choke, especially if it is at a nodal point.   If this is the case, placement of a second choke somewhat further down the line (say, 1/8 wavelength velocity factor corrected) may hit a maximum and block more current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Alternately, if you don't place a balun at the feedpoint, then the coax between the balun and the antenna can become part of the antenna and will radiate.  If that length of coax is resonant (say, 1/4 wavelength), then this will have minimal impact on SWR shouldn't cause more common mode current past the balun.  It will, however, change your radiation pattern, which could increase or decrease your gain, depending on the direction of interest.   This is one way to soften the directionality of a beam where you want to get some omnidirectional radiation, or even add a band to an antenna.   (For example, the carolina windom uses a 1/4 wavelength of coax with a choke for 10m.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Placement of a choke at the transmitter might also help, but it only helps common mode from getting into the transmitter -- it may still be on the coax.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are two primary reasons why we care about common mode current at all.  First, common mode current on the coax in the shack is dangerous -- it means you are radiating in the shack, but also you could get RF burns from touching surfaces carrying that common mode current.   Secondly, common mode current sourced from the feedpoint is power that is not going into the antenna, and may be radiating in directions we don't want and causing high swr.   Other sources of common mode current should be negligible and inconsequential.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-06-09T13:09:43.083" LastActivityDate="2020-06-09T13:09:43.083" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16800" PostTypeId="2" ParentId="16795" CreationDate="2020-06-09T00:46:46.033" Score="1" Body="&lt;p&gt;Under the heading of &quot;Software features include,&quot; the landing page for the &lt;a href=&quot;http://store.rfdesign.com.au/rfd-868ux/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RFD868ux&lt;/a&gt; says, &quot;Automatic duty cycle throttling based on radio temperature to avoid overheating&quot;. This means that transmit will not be allowed if the temperature of the radio is too high. In this case, the &quot;duty cycle&quot; is the average fraction of time that the radio may transmit, given the temperature limitation.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-06-09T00:46:46.033" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16801" PostTypeId="2" ParentId="16798" CreationDate="2020-06-09T01:52:02.410" Score="5" Body="&lt;p&gt;You are right that common-mode currents can occur elsewhere. A common-mode choke with an ideal infinite impedance essentially &quot;disconnects&quot; the common-mode of the feedline, but common-mode currents can still find their way onto the feedline through mutual coupling through the electromagnetic field.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Fortunately, in most antenna and feedline arrangements this coupling isn't very strong. For example, a dipole is usually symmetrical around the feedline's axis. In this arrangement, there is no electric field along the axis of the feedline, and so there is no coupling. For a monopole, the feedline exits below the ground plane and is thus &quot;hidden&quot; from the antenna fields.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Of course real-world installations are always a little bit away from these ideals, and thus there might be a little coupling between the antenna fields and the feedline common-mode. But in most cases this coupling is negligible.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In cases where it's not negligible, it's certainly possible to install additional chokes on the feedline to break it into segments that won't couple as effectively. This just isn't common practice since it's not a common problem.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-09T01:52:02.410" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16802" PostTypeId="2" ParentId="16798" CreationDate="2020-06-09T14:00:16.700" Score="2" Body="&lt;p&gt;Dr Chuck Counselman, W1HIS, stresses the advantages to lowering your station's receiving noise floor in his paper on &lt;a href=&quot;http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Common Mode Chokes&lt;/a&gt;. It's important to note that two high-impedance points created by chokes on a coax shield create a conductor that will be resonant at &lt;em&gt;some&lt;/em&gt; frequency. Significant currents can be induced on that conductor by wideband EMI sources like noisy consumer electronics, power lines, solar-panel inverters and industrial machinery as well as by narrowband sources like industrial RF generators, commercial broadcast and ham radio stations. Those currents will (re)radiate and be picked up by your station antenna and receiver, eroding all the time and treasure you invested in building up your station's capabilities.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-06-09T14:00:16.700" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16803" PostTypeId="1" CreationDate="2020-06-09T23:04:30.070" Score="1" ViewCount="57" Body="&lt;p&gt;The &lt;a href=&quot;http://www.ui-view.net/files/APRS101.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;APRS specification document&lt;/a&gt; says the following:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Although there is no restriction on the nature of user-defined data, it&#xA;  is highly recommended that it is represented in printable 7-bit ASCII&#xA;  character form.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;What is the reason for this suggestion? Is it a matter of hardware/software compatibility and if so how relevant is this today?&lt;/p&gt;&#xA;" OwnerUserId="17117" LastActivityDate="2020-06-10T00:11:37.773" Title="Why does the APRS specification suggest to use 7-bit ASCII for user-defined data formats?" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16804" PostTypeId="2" ParentId="16803" CreationDate="2020-06-10T00:11:37.773" Score="3" Body="&lt;p&gt;So far as I know, nobody here is on the APRS Working Group, so it's difficult to say exactly what their motivations were, but I'll make a few guesses.  First, Unicode was still fairly young in 2000, and personally I still have a horror of Windows code pages and other ugly mechanisms used to represent other character sets in hardware and software before Unicode came along.  In those pre-Unicode days the printable ASCII characters, the ones represented by decimal numbers 32 through 126, were a sort of &quot;lingua franca&quot; understood by most hardware devices and operating systems, at least in the US.  Many OSes and hardware devices couldn't tolerate character encodings that used more than one byte per character.  Many OSes and devices used codes outside of the ASCII 32-126 range as control codes, so for instance if a file containing such codes was attempted to be printed, then one such code that happened to occupy a byte of the file might signal the printer to eject the page being printed and start a new page.  Another such code might tell the printer to switch to its largest font.  Such behaviors were device-, OS-, or software-specific, because for a long time there was no universal way to handle codes outside of the ASCII 32-126 range.  Unicode existed in the year 2000, but its use was far from universal, and many OSes, devices, and software packages were completely ignorant of it.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I feel fairly certain that the motivation of the group was to minimize the confusion and incompatibility issues that were still common in the year 2000 with characters outside the ASCII 32-126 range.  Also, all the members of the APRS Working Group had US call signs, and it's possible that some group members were somewhat ignorant of the need for other character sets by different languages and cultures.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding how relevant the recommendation to use the ancient ASCII subset is today, I would say that how software and hardware should handle the user-defined data section is undefined.  Many software packages still act strangely when asked to edit files with data of an unknown format in them, or print such files.  So my advice would be to feel free to experiment, but be very careful to test as much hardware and software as you can before commonly sending packets with other character encodings in the user-defined data field out &quot;into the wild&quot;.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-06-10T00:11:37.773" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16805" PostTypeId="2" ParentId="10283" CreationDate="2020-06-10T05:49:39.937" Score="0" Body="&lt;p&gt;I have had good results with a 160 dipole at 35ft and fed with a 9-1 balun that is reversed feeding 50ohm to 5.5ohm. Match is 2-1 across a 40kc spread. &lt;/p&gt;&#xA;" OwnerUserId="17209" LastActivityDate="2020-06-10T05:49:39.937" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16806" PostTypeId="1" CreationDate="2020-06-10T06:41:32.490" Score="0" ViewCount="80" Body="&lt;p&gt;I started working with HF frequency. Right now, I am working with 7 MHz frequency. I have been provided a range of 7-7.5 MHz. I have to divide that range into 132 distinct frequencies to assign each frequency to a different node. Please let me know what is the minimum frequency resolution for 2 frequencies which do not interfere with each other.&#xA;For example, 7.001 and 7.002 MHz freq will interfere with each other or not??&lt;/p&gt;&#xA;" OwnerUserId="16061" LastActivityDate="2020-06-18T01:32:55.890" Title="What is minimum resolution for 2 frequencies to interfere each other" Tags="&lt;antenna&gt;&lt;hf&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16808" PostTypeId="1" AcceptedAnswerId="17676" CreationDate="2020-06-10T09:07:31.840" Score="-2" ViewCount="479" Body="&lt;p&gt;According to a few descriptions of antenna fundamentals i've read recently including that in Wikipedia and the ARRL handbook, when a half wave dipole is resonant, the inductive and capacitive reactances cancel out, and that's why there is no reactance in the impedance.&lt;/p&gt;&#xA;&lt;p&gt;My understanding is that the amount of reactance seen at the feed point of a center fed half wave dipole is determined by the phase relationship in time between the applied AC electric potential at the feed point and the resultant AC current which arrives at the feed point after being reflected back from the ends of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;So keeping in mind that a half wave dipole appears to be a series RLC circuit, what are the values of reactance that cancel out at resonance ?&lt;/p&gt;&#xA;&lt;p&gt;And why is an antenna resonant, because the voltage and current are in phase or because the reactances cancel out, or both ?&lt;/p&gt;&#xA;&lt;p&gt;See this question &lt;a href=&quot;https://ham.stackexchange.com/questions/17641/exactly-what-is-the-cause-for-the-zero-reactance-seen-in-the-impedance-at-the-ce&quot;&gt;Exactly what is the cause for the zero reactance seen in the impedance at the center feed point of a resonant half wave dipole?&lt;/a&gt; which i have also posted which asks about the same subject.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-11-28T01:44:36.260" LastActivityDate="2020-12-04T13:38:03.690" Title="For a half wave dipole antenna, what's the value of the reactances that cancel out when the antenna is resonant?" Tags="&lt;antenna-theory&gt;&lt;dipole&gt;" AnswerCount="5" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16809" PostTypeId="2" ParentId="16808" CreationDate="2020-06-10T11:04:48.980" Score="4" Body="&lt;p&gt;An antenna is not a series RLC circuit, but it can be modeled with lumped circuit elements over a certain frequency range. See, for example, Tang et al, &lt;a href=&quot;http://fides.fe.uni-lj.si/~arpadb/rnv/antenna-model.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;&quot;Equivalent Circuit of a Dipole Antenna Using Frequency-Independent Lumped Elements.&quot;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A thought experiment shows why: we observe that the feedpoint impedance of a half-wave dipole exhibits periodic behavior at harmonics of its design frequency, but a simple lumped circuit does not. For example, using the formulas of &lt;em&gt;Tang et al,&lt;/em&gt; we can model the &quot;input impedance&quot; of the equivalent circuit of a 20-m half-wave dipole:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oyurD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oyurD.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It &quot;resonates&quot; at about 14.3-MHz. The same antenna modeled by NEC-2 shows the very different behavior to which we are accustomed:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OyOgm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OyOgm.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The input impedance behavior of the half-wave dipole is more reminiscent of a transmission line, which can also be modeled with lumped elements. But, since the object of the lumped-element model is computational simplicity, the number of elements required to produce an accurate transmission line model would probably defeat the purpose.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-06-10T11:04:48.980" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16810" PostTypeId="1" AcceptedAnswerId="16818" CreationDate="2020-06-10T11:43:27.217" Score="1" ViewCount="347" Body="&lt;p&gt;When it's not possible to be at the same location as a TX/RX appliance, some form of remote control is needed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's basically two ways to TX/RX:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;classical radio appliance, with or without digital functions&lt;/li&gt;&#xA;&lt;li&gt;SDR appliance solely manipulated in a digital fashion&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;The advantage of option #1 is that there's usually an amplifier built-in which provides a decent amount of power output. Most #2 solutions would require an additional device to achieve a similar state.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another key difference is flexibility. Indeed, a digital system with a single SDR at its core could hop between multiple bands (and so antennas) with the help of a switching mechanism, whereas a &quot;normal radio&quot; can only TX/RX over bands it's been made and has antennas for.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I might skip on some pros and cons, but being a starter in the field of amateur radio (though with a strong IT background) I'm wondering which of the two options is best for remote operation.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is there any definite answer to this, taking into account the latest capabilities given to us by new IT &amp;amp; RF hardware, or is it more of a personal thing ?&lt;/p&gt;&#xA;" OwnerUserId="17196" LastActivityDate="2020-06-13T15:18:47.250" Title="Practicality of SDR-based TX/RX" Tags="&lt;software-defined-radio&gt;&lt;remote-control&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16812" PostTypeId="1" AcceptedAnswerId="16820" CreationDate="2020-06-10T12:28:23.707" Score="2" ViewCount="424" Body="&lt;p&gt;Some books on antenna fundamentals i've read recently say that, for a half wave resonant dipole when transmitting for example, the traveling wave of movement of charges reflected back from the ends of the antenna constructively adds to the incident waveform emanating from the feed point, resulting in the standing wave of current having the maximum amplitude for a given input. And since the electric field intensity (according to the ARRL handbook) is proportional to antenna current, this means at resonance the antenna produces the most output for a given input. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The books also say that at resonance for transmit ignoring resistive losses an antenna converts all of the applied energy to electromagnetic radiation, and conversely that when there is reactance present some of the applied energy is wasted in 'circulating' (for want of a better word) currents due to the reactance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In addition to this, a resonant antenna apparently has the desirable effect of reducing the ratio of out of band interference to wanted signals that are within the frequency band of interest.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is resonance for an antenna something that should be aimed for in the interests of improved antenna performance ? or doesn't it make much difference ...&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-06-11T00:18:37.313" LastActivityDate="2020-06-15T16:03:57.087" Title="Does a resonant antenna work better than a non-resonant antenna?" Tags="&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16813" PostTypeId="2" ParentId="16812" CreationDate="2020-06-10T13:01:57.390" Score="2" Body="&lt;p&gt;From a system point of view, an antenna's feedpoint impedance is important only inasmuch as it can be efficiently matched to the feedline, maximizing the transfer of power from the generator. While the feedpoint of &lt;em&gt;some&lt;/em&gt; antennas reflects other aspects of its behavior, this is not &lt;em&gt;generally&lt;/em&gt; true. For example, a center-fed length of wire - e.g., a &quot;20-meter half-wave dipole&quot; that resonates at a particular frequency exhibits less than 1-dB variation in field strength over an octave of frequency:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AGldV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AGldV.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This results from the fact that the current distribution over the antenna's length is substantially the same:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wyfXs.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wyfXs.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Considerable gain results at approximately twice the frequency of the antenna's half-wave resonance:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dSAdu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dSAdu.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;where the antenna comprises two half-waves in phase. But, the feedpoint impedance is 3958-j1531 ohms, a very difficult match to any conventional feedline.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-06-10T13:01:57.390" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16815" PostTypeId="2" ParentId="16806" CreationDate="2020-06-10T14:04:14.850" Score="1" Body="&lt;p&gt;That would depend on the bandwidth of the transmission.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hMHac.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hMHac.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RSGB 'Amateur Radio Band Plans' is a very good reference.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.hflink.com/bandplans/UK_bandplan.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hflink.com/bandplans/UK_bandplan.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-06-11T02:45:29.980" LastActivityDate="2020-06-11T02:45:29.980" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16817" PostTypeId="2" ParentId="16810" CreationDate="2020-06-10T15:18:56.437" Score="2" Body="&lt;p&gt;I think you're over-estimating the flexibility of SDR for transmitting on ham bands.  SDR may simplify modulation from a hardware point of view, but transmitters for most bands and modes require amplification of the signal, and filtering to suppress harmonics, phase noise, etc.  Filtering circuits are definitely band-specific.  Also, hams are limited to transmitting on designated bands.  What I'm trying to say is that I've never heard of a legal SDR-based multi-band ham transmitter that is just &lt;code&gt;SDR&lt;/code&gt; &gt; &lt;code&gt;amplifier&lt;/code&gt; &gt; &lt;code&gt;universal antenna&lt;/code&gt;.  The ones I know of are more like &lt;code&gt;SDR&lt;/code&gt; &gt; &lt;code&gt;amplifier&lt;/code&gt; &gt; &lt;code&gt;band-specific filter&lt;/code&gt; &gt; &lt;code&gt;band-specific impedance matching circuit (as required)&lt;/code&gt; &gt; &lt;code&gt;band-specific antenna&lt;/code&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To sum up so far, it is possible to have an SDR-based multi-band receiver and antenna that  is inexpensive and has simple hardware.  A multi-band ham transmitter and antenna(s) that puts out a useful level of power, SDR-based or not, are more complicated and expensive.  In fact commercially-made ham SDR-based multi-band multi-mode transceivers are comparable in price to the more traditional kind.  (I doubt there are many new designs that don't use SDR for modulation.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Regarding remote control of a ham station, for commercially-made equipment it makes little difference whether the &quot;appliance&quot; is SDR-based or not; most premium multi-band HF radios have been remotely-controllable for 10 or 20 years now.  Some of the SDR-based radios make getting remote audio in and out a bit easier, but that's just one of the challenges of setting up a remote station.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-06-10T15:18:56.437" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16818" PostTypeId="2" ParentId="16810" CreationDate="2020-06-10T19:40:19.683" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;The advantage of option #1 is that there's usually an amplifier built-in which provides a decent amount of power output. Most #2 solutions would require an additional device to achieve a similar state.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'll challenge that.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As a counterexample, the &lt;a href=&quot;https://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&amp;amp;ProdCatID=102&amp;amp;encProdID=959169DE998192AB87295E90077D740D&amp;amp;DivisionID=65&amp;amp;isArchived=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;FTDX101D&lt;/a&gt; is an SDR that provides 200W of output power without an external amplifier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;https://qrpver.com/transceivers/qrpver_1_v_3.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRPver-1 v.3&lt;/a&gt; is a superheterodyne transceiver with only 3 W of output power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whether a transmitter modulates a signal in software or with analog electronics, the problem of subsequently amplifying that signal to 100 W or more is the same problem. Consequently, being an SDR or not has no fundamental bearing on the attainable output power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The bigger determinant in output power is cost. RF power transistors aren't cheap, so you won't find more than a few watts coming from a $30 radio.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Another key difference is flexibility. Indeed, a digital system with a single SDR at its core could hop between multiple bands (and so antennas) with the help of a switching mechanism, whereas a &quot;normal radio&quot; can only TX/RX over bands it's been made and has antennas for.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;I'll challenge this too.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.wb5rvz.org/softrock_lite_ii/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Softrock Lite II&lt;/a&gt; is an SDR and can not change bands -- in fact it can't tune at all. This is because it utilizes a simple crystal oscillator, and has only a single filter.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Meanwhile, the &lt;a href=&quot;https://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&amp;amp;ProdCatID=102&amp;amp;encProdID=0372FA803B7BBADBF3076C94ACA7A8C5&amp;amp;DivisionID&quot; rel=&quot;nofollow noreferrer&quot;&gt;FT-897D&lt;/a&gt; is not an SDR, yet covers all HF bands plus 6m, 2m, and 70cm bands. It can do this because it has a variable local oscillator, and it has a bank of filters. You can hear the relays switching when changing bands.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;An SDR would need precisely the same hardware to achieve similar coverage. And in either case, a multi-band antenna, or a way to switch between antennas is still required.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It seems like the attributes you ascribe to SDRs are not really a property of SDRs generally, but perhaps just the SDRs you have seen. What distinguishes an SDR is the use of software and digital processing to perform modulation and demodulation. But these other attributes, like transmit power and band coverage, are not part of the (de)modulator. They are part of the other bits of the radio, which will be the same whether that radio is an SDR or not.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;To answer your question, an SDR transceiver is entirely practical. In fact if you were to go out today and buy a &quot;nice&quot; commercial radio, there's a pretty good chance it's an SDR. It comes down to economics: the price of digital electronics has decreased so much that an SDR architecture usually yields better performance per dollar.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-10T19:40:19.683" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16819" PostTypeId="2" ParentId="16806" CreationDate="2020-06-10T21:52:36.370" Score="5" Body="&lt;p&gt;Very basic wave propagation theory says:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;No two different frequencies ever interfere in a linear system. So, any separation, no matter how small, of the occupied bands is enough in a perfect world!&lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, we don't live in a perfect world. So you need to model your system more detailledly, think about bandwidths, filters, frequency uncertainty of oscillators.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'll be a bit blunt, in hopes it helps you find a better question, sorry: you graduated in EE with specializations in RF design. I'd have expected you to ask a more detailed question here with way more background on your overall system! I think you can do better – interference happens only under circumstances where energy of one thing ends up in the other, so maybe you'd want to analyze your proposed system more for the places where that might happen!&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-10T21:52:36.370" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16820" PostTypeId="2" ParentId="16812" CreationDate="2020-06-11T03:18:31.763" Score="4" Body="&lt;p&gt;You are probably familiar with impedance. It is a complex number, made of the sum of a real and imaginary number. The real part is called resistance, and the imaginary part reactance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You've probably seen some equation like this to describe the power dissipated by a current through a resistor:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ P = I^2 R $$&lt;/span&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But what happens when the load can have reactance? Without going into the math, it should be obvious that if the load can be a complex number, than power can also be a complex number.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;When power is represented as a complex number, it's called (uncreatively) &lt;em&gt;complex power&lt;/em&gt;. It is the sum of &lt;em&gt;active power&lt;/em&gt;, which is the real part, and &lt;em&gt;reactive power&lt;/em&gt; which is the imaginary part.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Plotting complex power on the complex plane is called the &lt;em&gt;power triangle&lt;/em&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Oeez6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Oeez6.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Cmplxpower.svg&quot; rel=&quot;nofollow noreferrer&quot; title=&quot;via Wikimedia Commons&quot;&gt;Eli Osherovich&lt;/a&gt; / &lt;a href=&quot;https://creativecommons.org/licenses/by-sa/3.0&quot; rel=&quot;nofollow noreferrer&quot;&gt;CC BY-SA&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$S$&lt;/span&gt; is complex power, &lt;span class=&quot;math-container&quot;&gt;$P$&lt;/span&gt; active power, and &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; reactive power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As with impedance, thinking of this complex number in polar form yields some intuition. The angle to the real axis, &lt;span class=&quot;math-container&quot;&gt;$\varphi$&lt;/span&gt;, is the phase difference between current and voltage, just like impedance. And the magnitude &lt;span class=&quot;math-container&quot;&gt;$|S|$&lt;/span&gt; is called &lt;em&gt;apparent power&lt;/em&gt;: it's RMS voltage multiplied by RMS current.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This is all relevant because only the active power does work. One way to demonstrate this: build a circuit of any impedance with resistors, inductors, and capacitors, and apply an AC power source to it. The resistors get hot, whereas the capacitors and inductors do not (except to the extent they have non-ideal resistance).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The reactive power does no work. Consider a tank circuit of an ideal inductor and capacitor. The energy in the inductor and capacitor oscillate, but the total energy remains the same. No work is performed.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That works for ideal components, but real inductor and a real capacitor would have to be connected by a real wire. A real wire has resistance, and the wire will do work by converting electrical energy to heat according to &lt;span class=&quot;math-container&quot;&gt;$P = I^2 R$&lt;/span&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Antennas are no exception. A lot of antennas have feedlines. Feedlines have resistance. Refer to the power triangle above, and note that &lt;span class=&quot;math-container&quot;&gt;$|S|$&lt;/span&gt; is a little bit longer than &lt;span class=&quot;math-container&quot;&gt;$P$&lt;/span&gt;. The former is proportional to the current in the feedline, whereas the latter is proportional to the work done by the antenna (radiating, if it's an efficient antenna). More reactance means higher apparent power, and thus higher current, and thus higher feedline losses for a given active power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;You asked:&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Is resonance for an antenna something that should be aimed for in the interests of improved antenna performance ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;The answer, as with most engineering, is &quot;it depends&quot;. Some people will get pedantic and argue that even if the antenna is highly reactive, it radiates just as effectively. That may be true, but a device must be usable to be performant. If the antenna is too reactive, there's simply no way to efficiently couple active power into it: all the available energy will go into overcoming losses due to the reactive power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;That said, if you look at the power triangle again, you'll notice that as long as the reactive power is small compared to the active power, &lt;span class=&quot;math-container&quot;&gt;$|S|$&lt;/span&gt; isn't that much greater than &lt;span class=&quot;math-container&quot;&gt;$P$&lt;/span&gt;. Meaning, RMS current, and thus resistive losses, won't be substantially increased. It's certainly possible to imagine antenna designs where accepting a reasonable reactance enables an improvement in some other respect which works out to a net improvement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's also relevant to consider that resonance implies zero reactive power, but not necessarily a good match to the feedline. Resonance is in some cases close to the points of minimum VSWR, but that is not generally true for all possible antennas and feedlines. A VSWR above 1:1 is also associated with voltage and current in excess of the useful work performed. While any zero-reactance impedance could theoretically be matched by some feedline, such a feedline may not be practical or available. As such, it's important to not only consider reactive power, but also feedline match and the capabilities of the receiver and/or transmitter in optimizing a radio system.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Furthermore, feedline losses can largely be mitigated with the addition of a matching network at the feedpoint. The reactive power doesn't go away, but the associated increased voltage and current is then restricted to just the matching network rather than the entire feedline. If the losses in the matching network are less than they would have been in the feedline, losses can be reduced.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In addition to this, a resonant antenna apparently has the desirable effect of reducing the ratio of out of band interference to wanted signals that are within the frequency band of interest.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Yeah, somewhat. To some out of band signals, the antenna will appear reactive and thus they will experience higher loss.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But also consider many antennas that are resonant on frequency &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; are also resonant on all odd harmonics: &lt;span class=&quot;math-container&quot;&gt;$3f$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$5f$&lt;/span&gt;, etc. At the same time, these odd harmonics are very much the ones you might want to attenuate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-06-13T19:45:57.833" LastActivityDate="2020-06-13T19:45:57.833" CommentCount="14" ContentLicense="CC BY-SA 4.0" />
  <row Id="16822" PostTypeId="2" ParentId="16812" CreationDate="2020-06-11T21:18:10.867" Score="0" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;resulting in the standing wave of current having the maximum amplitude for a given input. And since the electric field intensity (according to the ARRL handbook) is proportional to antenna current, this means at resonance the antenna produces the most output for a given input.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Only if the impedance feeding the antenna is purely real! In general, you get maximum power transfer when the load impedance is the complex conjugate of the source impedance, which includes the case of a reactive (non-resonant) antenna and a reactive source (e.g. a matching network).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;The books also say that at resonance for transmit ignoring resistive losses an antenna converts all of the applied energy to electromagnetic radiation, and conversely that when there is reactance present some of the applied energy is wasted in 'circulating' (for want of a better word) currents due to the reactance.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This is somewhat true, but in many cases the losses are acceptably small, or a valid trade for some other aspect of the design (like size, or frequency agility). Especially on lower bands, the loss due to standing-wave currents is relatively insignificant.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;In addition to this, a resonant antenna apparently has the desirable effect of reducing the ratio of out of band interference to wanted signals that are within the frequency band of interest.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;This isn't a function of the resonant frequency of the antenna, it's a function of the resonant frequency of the antenna &lt;em&gt;system&lt;/em&gt; including any matching. See the first point about maximum power transfer. &lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-06-11T21:18:10.867" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16825" PostTypeId="1" AcceptedAnswerId="16842" CreationDate="2020-06-13T12:26:44.643" Score="1" ViewCount="97" Body="&lt;p&gt;Have a K4KIO Hexbeam up at around 20-feet on the corner of a flat metal roof pointing at 290-degrees bearing (Europe, from Sydney Australia). Currently the Hexbeam is fixed to that direction as i don't yet have a rotator, and it's fed with ~25M of RG8.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There's also clamp-on ferrites at the feedpoint (supplied by K4KIO) and at the radio end.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Being pointed to Europe it works as i'd expect, but i also notice it receives USA as well which is off to the side of the antenna by a fair amount, when the band is open (on 40M &amp;amp; 20M mainly).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Even compensating for a very wide beam-width, the fact the Hexbeam is a 2-element beam, and not very high, it's interesting (to me anyway) it receives USA quite well when not pointed in that direction.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I work FT8 alot and can see via the pskreporter website this is the case. This happens regularly.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Was just wondering if this is a propagation phenomenon, a factor of it's current height, or something deeper i need to address?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastEditorUserId="17200" LastEditDate="2020-06-13T13:41:20.007" LastActivityDate="2020-06-15T22:38:14.700" Title="Hexbeam receiving in other directions" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16826" PostTypeId="2" ParentId="16810" CreationDate="2020-06-13T15:12:50.517" Score="0" Body="&lt;p&gt;There are at least a couple differences that aren't just based on the specs (wattage, etc.) of current commercial offerings known to the OP.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One advantage of SDRs is that some SDR setups (Hermes Lite 2, et.al.) allow not only monitoring the final RF output, but also allow the use of computer/DSP pre-distortion to help clean up the signal all the way from or through any added linear/final amplifier(s).  This would be much harder to do using a legacy analog transceiver with just a remote front panel.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Another advantage of many SDR setups is that they can stream a remotely observable panadapter or waterfall display to see if the band is active enough to bother, or where the activity is located within the band.  An legacy analog setup would require extra equipment (boxes, cables) to do this.  Some SDRs even allow (locally or remotely) monitoring multiple HF bands simultaneously (4 or more band &quot;slices&quot; in the case of some OpenHPSDR systems), if you have a receive antenna system that allows this.  &lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-06-13T15:18:47.250" LastActivityDate="2020-06-13T15:18:47.250" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16827" PostTypeId="1" AcceptedAnswerId="16844" CreationDate="2020-06-13T17:01:04.343" Score="3" ViewCount="146" Body="&lt;p&gt;Given a dipole approximately 0.48 wavelengths long, such that when fed in the center the feedpoint impedance has zero reactance, how does the complex impedance change as the feedpoint is moved away from the center?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-16T01:07:46.590" Title="What is the impedance of an off-center fed resonant dipole?" Tags="&lt;dipole&gt;&lt;impedance&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16828" PostTypeId="1" CreationDate="2020-06-13T17:40:07.597" Score="0" ViewCount="113" Body="&lt;p&gt;So given a choice between a non-resonant length of wire antenna center fed by 50 Ohm coax, or a resonant length of wire fed highly off-center by 50 Ohm coax, or a resonant length of wire fed by high impedance open twin lead, and with no matching networks of any kind either way, what would be the difference in advantages or disadvantages, if any?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-06-15T14:52:28.433" Title="Relative disadvantages of impedance mismatch vs. non-resonant length wire antenna" Tags="&lt;wire-antenna&gt;&lt;antenna-system&gt;&lt;feed-line&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16829" PostTypeId="1" CreationDate="2020-06-13T20:50:06.117" Score="0" ViewCount="149" Body="&lt;p&gt;See the unconventional antenna shown below, The whole antenna is made of two mirror-imaged Alum metal stampings on either side of a 2-cm hollow 31-cm long rectangular plastic boom. The antenna top and bottom Alum stampings make up one active element. With it I am barely able to receive some TV channels that are about 25-40 km away(depending on weather). It is just shy of what I need to receive several channels up to 40Km away. regardless of weather. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;I want to completely strip the useless much larger yagi-hybrid antenna&lt;/strong&gt; (shown below the LDPA) to salvage only the dipole and the main boom. Then &lt;strong&gt;I want to improve/kinda clone the smaller antenna on the big boom to get better performance than I have now only limiting bandwidth to 500-670 mHz of the Dig T2 spectrum.&lt;/strong&gt; &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I see a possible big problem in making the new antenna in that he smaller lPDA design antenna has a plastic boom and the big antenna boom is made of hollow rect. alum. &#xA;&lt;strong&gt;How can I improve/clone the unconventional antenna to get it to work even better?&lt;/strong&gt;&lt;br&gt;&#xA;**&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The FDLA antenna is an unusually fabricated antenna designed for the Terrestial Digital TV band.  Its two-piece construction design does not fit any conventional antenna geometry. &lt;strong&gt;It was initially made for indoor use&lt;/strong&gt; but I have mounted it outside and 75-ohm coax from the antenna's front position of elements is feeding a 18 dB wideband VHF/UHF preamp through a 4:1 balun with no  LTE filter, with the preamp output then feeding 75-ohm coax down to the a TV though a power power supply feed point box. &#xA;&lt;a href=&quot;https://i.stack.imgur.com/Y4nLf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y4nLf.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;&lt;strong&gt;This antenna is so much smaller, works so much better (was able to receive stations &gt;25 Km versus 5 km) than the commercially made antenna shown below it:&lt;/strong&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Below: **poor performing yagi.&#xA;This yagi-hybrid antenna was on fire sale to get rid of remaining stock and priced at 1/10th the usual retail price, likely because it was so often sold and returned because it didn't work well.*&#xA;** &lt;/p&gt;&#xA;&#xA;&lt;p&gt;5-Ft boom, kinda 3-stacked angle Yagi antenna with 2-Ft reflectors and angled booms of 8 directors each with each boom end nearest the dipole expanding up/level to boom/down to stack together to at a 25-degree to the center main boom. Each of the 8 evenly-spaced  (len=13cm) director elements has a half-wave wavelength &gt;1000Mhz. The dipole active element is two separate closed loops on either side of the boom, the resulting modified 1/2-wave dipole(approx ~400mHz half-wave) make up the single dipole that is the only active element. &#xA;See Image:&lt;a href=&quot;https://i.stack.imgur.com/RlsVU.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RlsVU.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;The split dipole is two closed loops with the bottom of the loop split to opposite sides of the main boom and feed the LTE filter (A PCB 2-cm sq. which has two holes for screws connecting the two split dipoles, these connections are approx 2-cm spread apart) and long threaded screws connect each of the dipole halves to the LTE filter PCB mounted inside a plastic box that itself is clamped to the 5-ft boom.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The dipole is positioned about 1/4 wavelength(@500mHz) from the reflectors and 4.5 cm behind the triple array of 8 identical directors on three booms, folded together and placed about 4.5cm forward from the dipole active element.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;This large antenna works very poorly(with/without) the same preamp, barely better than a single folded-loop dipole(550mHz 1/2 wave)soldered directly to the ends of a 75-ohm coax cable going to the same preamp to the TV receiver.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Questions:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;This antenna is made of two stamped aluminum sheets with top and bottom mirror imaged. What type of antenna is this and why does it outperform a large 3-boom kinda Yagi so well?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="17230" LastEditorUserId="8717" LastEditDate="2020-06-17T22:25:21.877" LastActivityDate="2020-11-15T00:06:10.637" Title="Outdoor Terrestial Digital TV Receiver Antenna: 500-700 MHz Band, Can I Make It Work Better?" Tags="&lt;antenna-theory&gt;&lt;uhf&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16830" PostTypeId="1" CreationDate="2020-06-14T02:41:40.590" Score="0" ViewCount="505" Body="&lt;p&gt;I have been trying to create a low cost communication setup for when I go hunting.  Using this setup the hope is to be able to talk to one another while separated without having the audio up too loud.  Here is what I have:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Baofeng UV-5R radio&lt;/li&gt;&#xA;&lt;li&gt;Howard Leight Impact Sport Ear Protection Muffs&lt;/li&gt;&#xA;&lt;li&gt;3.5mm Right Angle Male to Male Auxiliary Jack Cable&lt;/li&gt;&#xA;&lt;li&gt;Baofeng BF-S112 Two Way Radio Speaker&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;So, I plug the mic into the radio, one end of the auxiliary jack cable into the mic, and then the other end of the auxiliary jack cable into the ear muffs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The idea is to be able to ear my radio through the earmuffs and use the mic to transmit.  But, I am having several problems.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;First, the baofeng mic is crap.  I can't really tell if it works at all even though it is brand new.  when everything is set up and I click the mic, sometimes it keys the radio and I see the screen color change, and sometimes I don't.  Even when it does change the color of the radio display indicating it is transmitting, I can't hear anything in the earmuffs.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Second, the auxiliary cable.  I put the radio of FM just to see if I can hear anything and I was only getting audio out of one side of the muffs.  That is sometimes.  Sometimes I could not hear anything at all.  &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Any thoughts are welcome and better low-cost solutions are especially welcome. &lt;/p&gt;&#xA;" OwnerUserId="17233" LastEditorUserId="76" LastEditDate="2020-07-17T19:06:03.307" LastActivityDate="2021-04-13T20:59:11.310" Title="Creating a low cost ear protection/ PTT setup for hunting" Tags="&lt;baofeng&gt;&lt;audio-interface&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16831" PostTypeId="2" ParentId="16812" CreationDate="2020-06-14T07:20:55.593" Score="2" Body="&lt;p&gt;A short answer, in two parts:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Irrespective of their natural &quot;resonance,&quot; &lt;strong&gt;ALL&lt;/strong&gt; non-zero electrical lengths of the conductors of a &quot;standing wave&quot; antenna  radiate virtually ALL of the r-f energy that flows along them, as electromagnetic waves into space.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Other things equal, the natural resonance of such radiating conductors enables more efficient transfer of the r-f energy from the transmitter to flow along the antenna conductors, increasing its useful radiation of e-m waves.&lt;/p&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-06-15T16:03:57.087" LastActivityDate="2020-06-15T16:03:57.087" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16832" PostTypeId="2" ParentId="16827" CreationDate="2020-06-14T08:08:48.740" Score="5" Body="&lt;p&gt;Both the real and the imaginary terms of the complex impedance across the feedpoint terminals will change as the feedpoint moves away from the electrical center of the antenna.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an example, a NEC4.2 calculation for a nominally 1/2 wavelength radiator in free space when the feedpoint is located 0.05 wavelengths from one end is about 1340 -j1100 Ω.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A center-fed, nominally 1/2-wavelength dipole at first self-resonance in free space has a feedpoint impedance of about 65 ±j0 Ω.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-06-14T08:08:48.740" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16833" PostTypeId="2" ParentId="16829" CreationDate="2020-06-14T08:41:42.373" Score="1" Body="&lt;hr&gt;&#xA;&#xA;&lt;p&gt;I'm not giving consumer device advice here; that wouldn't fit the blue areas of things on-topic here:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/help/on-topic&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UrhX9.png&quot; alt=&quot;help: on topic&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, instead I'll concentrate on the general radio and antenna engineering aspects of this.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;This antenna is made of two stamped aluminum sheets with top and bottom mirror imaged. What type of antenna is this&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Wow, that looks like a logarithmic-periodic antenna, which is an antenna design meant for high bandwidths, meaning that the difference between the lowest frequency it works OK and the highest frequency is relatively large compared to the center frequencies. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;However, the logpers I know are typically made of much thinner elements. This is a pretty interesting design that looks like it takes into account other design aspects like H-plane beam width...&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In general, &quot;what type of antenna is this?&quot; questions are often not uniquely answerable in the world of commercial antennas: Every antenna is the result of an optimization for way more things than the &quot;classical antenna types&quot; things account for. In this very case, I'd like to point out how much this antenna design might also be the result of optimization for mechanical stability and erosion resistance. A lot of antennas for the end-consumer market are also highly optimized for looks, since it doesn't matter how great your antenna is if nobody buys it.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;and why does it outperform a large 3-boom kinda Yagi so well?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Probably because your Yagi is very good! When you, for example, optimize an antenna for high directionality, i.e. it can pick up a signal coming from a specific direction very well, that means it picks up from other directions worse – there's no free lunch.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, when you now &quot;roughly&quot; point both antennas at the transmitter, but are off by a couple degrees in horizontal and/or vertical direction, then the &quot;worse&quot; antenna in terms of antenna gain suddenly picks up more signal, exactly because the &quot;better&quot; antenna was &lt;em&gt;designed&lt;/em&gt; to pick up little power from any direction but the main beam.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What impedance is the split dipole on the crappy antenna? &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Probably something in the 75Ω region. But really, receiver antenna matching is far less important than people think. Before worrying about that, make a worst-case mismatch estimate, then calculate the mismatch loss you're getting, and ask yourself whether these usually-less-than-6 dB actually make the amount of quality of service difference (and what distance variation in free space path loss would be equivalent to the same amount of lost signal).&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Why are all the directors of the crap big antenna cut the same and spaced the same and all with a 1/2 wavelength of approx. 1000 MHz &lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Can we stop calling that antenna &quot;crap&quot;? This looks like a very sophisticated design, and multiple engineers worked hard to design that antenna. Chances are the antenna, cabling, active components or anything else are broken, it's meant for a different band than you're using, you're using it in the wrong polarization (in Germany, for example, digital TV has orthogonal polarization to analog TV) or you're just not pointing it exactly enough, as this definitely looks like a high-gain design, considering the size.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The directors on the main boom might be mounted in the same distance, but they don't exist in isolation – the reflector is angled relative to them, so that the phase centers of passive dipole + reflector are most definitely not uniformly spaced; and the upper and lower boom is there to give rise to phase shifts, too, and you will only make sense of this antenna if you look at all these in combination; so, this is a pretty complex antenna and it's certainly not easy to design. A lot of simulations, prototype testing, optimization for reliable manufacturability.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-14T08:41:42.373" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16834" PostTypeId="1" AcceptedAnswerId="16837" CreationDate="2020-06-14T23:56:17.597" Score="1" ViewCount="1133" Body="&lt;p&gt;An Ebay search for &quot;fm demodulator&quot; results in a whole slew of ICs, but even after reading their datasheets, I have no idea what I should connect where and what input signals the chips will work with. Take an &lt;a href=&quot;http://www.nce.ru/pdf/08762.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;AN7411&lt;/a&gt; for instance. Page 3 of the linked datasheet (see image) includes an application circuit that &lt;em&gt;might&lt;/em&gt; work, but, as with every single one of these ICs, I don't know what I am supposed to connect to the input. Will the chip demodulate a signal with a 100 MHz carrier, or is it limited by the 19 kHz clock signal? (Why would an FM demodulator IC have a maximum frequency of 19 kHz?)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iz7q7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iz7q7.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The same questions arise with the &lt;a href=&quot;http://pdf.datasheetcatalog.com/datasheet/stmicroelectronics/1444.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;TDA1220&lt;/a&gt; (datasheet mentions up to 30 MHz), &lt;a href=&quot;http://pdf.datasheetcatalog.com/datasheet/nationalsemiconductor/DS007888.PDF&quot; rel=&quot;nofollow noreferrer&quot;&gt;LM1800&lt;/a&gt;, and many others. Am I expected to frequency shift the signal from the radio station down to whatever the chip may support, or what are these inputs supposed to be?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are some schematics available for the &lt;a href=&quot;http://electronics-diy.com/fm-radio-with-tda7000.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;TDA7000&lt;/a&gt; (its datasheet specifies an RF input frequency range up to 110 MHz, unlike all the others!), but the chip is old and hard to source. Am I missing something? Am I looking at the wrong chips or misreading the datasheets?&lt;/p&gt;&#xA;" OwnerUserId="17237" LastActivityDate="2020-06-16T09:43:47.500" Title="FM radio demodulator IC usage" Tags="&lt;fm&gt;" AnswerCount="3" CommentCount="3" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16835" PostTypeId="2" ParentId="16834" CreationDate="2020-06-15T08:25:03.640" Score="6" Body="&lt;p&gt;So, coming at this from an engineer's perspective:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If a device has a datasheet that doesn't tell you how to use it, it's not the device you need – end of story.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, by the way, ebay searches aren't a clever way to design electronics! There's several large, reliable component distributors that have searches, too. Try &lt;a href=&quot;https://digikey.com&quot; rel=&quot;noreferrer&quot;&gt;https://digikey.com&lt;/a&gt;.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sure, there might be outdated components that you can't get on digikey and mouser and farnell and so on, but that is actually because the manufacturers of these chips said that they don't produce them anymore - simply because nobody would sensibly still use them in a modern device.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;And that's actually not a bad reason to not use them, either. So, ditch ebay as electronics source. (it's often/usually not even cheaper!)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Modern receiver ICs are simply better: they typically come with all the frequency correction you need, adjustable audio enhancement, audio de-emphasis and whatnot. They also tend to have useful data sheets.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So, what I did: went to digikey, clicked through to the &quot;RF receivers&quot; category, and selected everything that said &quot;FM&quot; in the &quot;modulations and protocols&quot; list, then selected to only get ICs that are currently stocked, entered a quantity of 5 let it give me a list, then sorted that by price. &lt;a href=&quot;https://www.digikey.com/products/en/rf-if-and-rfid/rf-receivers/870?FV=205%7C313196%2C205%7C313200%2C205%7C313201%2C205%7C313203%2C205%7C313204%2C205%7C313208%2C205%7C348572%2C205%7C348583%2C205%7C348585%2C-8%7C870&amp;amp;quantity=5&amp;amp;ColumnSort=1000011&amp;amp;page=1&amp;amp;nstock=1&amp;amp;pageSize=25&amp;amp;pkeyword=fm+receiver&quot; rel=&quot;noreferrer&quot;&gt;Here's the list&lt;/a&gt; I got. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The cheapest is the SI4708. You can read more about it on the SiLabs &lt;a href=&quot;https://www.silabs.com/audio-and-radio/fm-radios/si4708-09-radio-receivers/device.si4708&quot; rel=&quot;noreferrer&quot;&gt;product page&lt;/a&gt;. The &lt;a href=&quot;https://www.silabs.com/documents/public/data-sheets/si4708-09-C.pdf&quot; rel=&quot;noreferrer&quot;&gt;datasheet&lt;/a&gt;, on its first page, shows schematically what to connect where (doesn't fully explain how, however):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VyYCS.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VyYCS.png&quot; alt=&quot;Block diagram&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and the &lt;a href=&quot;https://www.silabs.com/documents/public/application-notes/AN350.pdf&quot; rel=&quot;noreferrer&quot;&gt;App Note 350&lt;/a&gt; comes with a schematic that actually shows how to connect everything.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/U4GML.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/U4GML.png&quot; alt=&quot;schematic&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.silabs.com/documents/public/application-notes/AN383.pdf&quot; rel=&quot;noreferrer&quot;&gt;AN383&lt;/a&gt; explains how to connect different antenna types (including &quot;headphone cable antennas&quot; and such trickery).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The nice thing about this device is that all you need to do is&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Connect power&lt;/li&gt;&#xA;&lt;li&gt;Connect an antenna&lt;/li&gt;&#xA;&lt;li&gt;Connect a 32.768 kHz clock&lt;/li&gt;&#xA;&lt;li&gt;Connect your audio amplifier&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;to get a working and finely tuned FM receiver – no need to hand-adjust anything until it works &quot;just right&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tuning hence isn't done via an adjustable capacitor, but by adjusting the frequency synthesized internally in the chip. So, you just tell the chip that you want to tune to this and that channel, and be done with it. Of course, this needs you to have a way of telling the IC you want that – via a digital bus. So, you'll need some kind of microcontroller, or Raspberry Pi or similar attached to the IC's digital control interface. (sounds harder than it is, really.)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If that's not what you want, there's also modern mechanically tuned FM receivers, like the &lt;a href=&quot;https://www.silabs.com/audio-and-radio/multiband-radios/si4825-31-35-36-radio-receivers/device.si4825-a20-cs&quot; rel=&quot;noreferrer&quot;&gt;SI4825&lt;/a&gt;. Internally, it's kind of similar to the digitally controlled one, but it allows you to adjust the channel via a potentiometer, which feeds an analog-to-digital-converter internally and that is then used to control the digital part of the chip.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Note how both solutions are essentially digital receivers? That's because it's easier to build exact digital logic than to make analog circuitry work well, and also, much more power-efficient. Since the receive signal amplitude doesn't matter at all in FM, for example, you can apply very nonlinear techniques (like just clipping the signal, and counting zero crossings; looking at the datasheet, these are smarter, though) to demodulate it. &lt;br&gt;&#xA;Doing things in digital makes a lot of sense, quality-wise, too: You need good filters; the imperfection of how your filter lets through signal you don't want, and distorts the signal you do want is limiting to your quality of reception. Steep band edge, flat passband analog filters are hard to impossible. They're very possible to implement in digital, though, especially considering how small the necessary digital signal sample rates are. So, going digitally simply gives you an advantage that you'd have to pay &lt;em&gt;a lot&lt;/em&gt; of money on to get even close to with an analog superhet receiver.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-15T08:25:03.640" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16837" PostTypeId="2" ParentId="16834" CreationDate="2020-06-15T09:47:23.863" Score="6" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;...I don't know what I am supposed to connect to the input... Am I&#xA;  expected to frequency shift the signal from the radio station down to&#xA;  whatever the chip may support...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Several of the demodulator chips you linked would occupy the dashed box in the architecture of a &lt;em&gt;superheterodyne&lt;/em&gt; FM stereo receiver:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oTbq9.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oTbq9.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;(diagram courtesy ARRL &lt;em&gt;&lt;a href=&quot;http://www.arrl.org/shop/ARRL-Handbook-2020-Softcover/&quot; rel=&quot;noreferrer&quot;&gt;Handbook for Radio Communications&lt;/a&gt;&lt;/em&gt;)&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The RF filter &quot;protects&quot; the succeeding stages from overload by strong, unwanted signals. In a consumer FM radio, the LO and mixer produced an &lt;em&gt;intermediate frequency&lt;/em&gt; (IF) signal at 10.7-MHz; standardizing on this frequency made radios cheaper by increasing the numerical volume of similar IF filters. The &lt;em&gt;detector&lt;/em&gt; - in your case the &lt;em&gt;demodulator&lt;/em&gt; - recovered the audio source material (AF) from the IF, for subsequent amplification to a speaker or headphones.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As you observed by the increasing input frequencies from the AN7411 to the TDA7000, the advent of high-speed, low-cost integrated analog and digital circuitry has made parts like these almost completely obsolete.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-06-15T09:47:23.863" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16838" PostTypeId="2" ParentId="16828" CreationDate="2020-06-15T13:27:30.803" Score="0" Body="&lt;p&gt;Non resonate antennas used with out match networks, usually an antenna tuner, will result in high VSWR and low efficiency. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;For receivers you can use them without many problems. They will not be able to receive very weak signals, but other than that they will work.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The issues become much greater when you transmit. The high VSWR causes voltage feedback into your transmitter which can damage the final amplifier. There will almost always be some mismatch between the antenna, feed-line, and transmitter, but you want to minimize it. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The mismatch also results in less of the transmitter's power actually being converted into RF signals. &lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-06-15T13:27:30.803" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16839" PostTypeId="2" ParentId="16834" CreationDate="2020-06-15T14:42:13.593" Score="6" Body="&lt;p&gt;That AN7411 is not an FM demodulator. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;It's a stereo demodulator, taking audio (0 to 57 kHz) from an FM demodulator, recovering the stereo multiplex signal (DSBSC at 38 kHz carrier), adding that (L - R) to the baseband mono (L+R) signal to give L and R outputs. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;The 19kHz &quot;clock&quot; is a pilot tone, frequency doubled to generate the 38 kHz carrier.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The LM1800 is another of the same.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The TDA7000 was a low power implementation of a complete FM (mono) receiver. It's relatively recent, so its transistors stand a fighting chance of being able to amplify at 100 MHz, which is why it stands out from the others like the TDA1220. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;TDA1220 was a complete solution for AM ( up to 30 MHz allowing it to cover the shortwave bands), but on FM it could only handle the IF (10.7 MHz) and later stages, requiring a discrete component front end to amplify and mix at 100 MHz.&lt;/p&gt;&#xA;" OwnerUserId="17240" LastEditorUserId="17240" LastEditDate="2020-06-16T09:43:47.500" LastActivityDate="2020-06-16T09:43:47.500" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16840" PostTypeId="2" ParentId="16828" CreationDate="2020-06-15T14:52:28.433" Score="1" Body="&lt;p&gt;All these options are bad. It's a bit like asking if it's better to drive a nail with a floppy shoe or a glass jar.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;If you really had to make a decision between these contrived options, you'd have to flesh out the details to make a decision. There are a few things to consider.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Firstly, a half-wave dipole may have a substantially different radiation pattern from some other length of dipole. Or they may be substantially similar. One may be better or worse for your application.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Secondly, any mismatch is going to cause &lt;a href=&quot;https://ham.stackexchange.com/q/7333/218&quot;&gt;additional loss in the feedline&lt;/a&gt;. How much loss will depend significantly on the details, like the reflection coefficient, the length of the line, and so on.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But I suspect what you're really asking about is &lt;a href=&quot;https://ham.stackexchange.com/a/16820/218&quot;&gt;my answer&lt;/a&gt; to &lt;a href=&quot;https://ham.stackexchange.com/questions/16812/does-a-resonant-antenna-work-better-than-a-non-resonant-antenna&quot;&gt;Does a resonant antenna work better than a non-resonant antenna?&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The situation of a non-resonant antenna is similar in many ways to a resonant antenna with a mismatched feedline. In either case, the feedline will operate at an elevated VSWR and this will increase losses.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But there are differences as well. A resonant antenna will have a purely resistive impedance, by definition. This means there is theoretically &lt;em&gt;some&lt;/em&gt; feedline that will match it, even if that feedline isn't available or practical to construct.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;But a non-resonant antenna will have non-zero reactance. While the characteristic impedance of a feedline can also include a reactive component, and so maybe there's theoretically still some feedline that could achieve a conjugate match, &lt;a href=&quot;https://electronics.stackexchange.com/q/332906/17608&quot;&gt;that means the feedline is lossy&lt;/a&gt;. Making a feedline deliberately lossy to achieve a better match to reduce losses doesn't make any sense.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Finally there are also losses in the antenna to consider. For example, a very short dipole becomes more like a capacitor than an antenna. Significant current will go towards charging and discharging that capacitor while relatively little goes towards radiation. Of course this will mean additional losses in the feedline as previously mentioned. But it will additionally mean higher losses in the antenna itself.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-15T14:52:28.433" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16841" PostTypeId="2" ParentId="16830" CreationDate="2020-06-15T19:08:08.030" Score="0" Body="&lt;p&gt;I always wondered what the extra jack on my Baofeng microphone was for.  I was able to find &lt;a href=&quot;https://qsl.net/nf4rc/2019/BaofengHeadphone.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;another reference on the web (PDF)&lt;/a&gt; that described plugging headphones into the microphone.  That reference implies that the jack is a two-conductor mono jack, or possibly a three-conductor jack with one conductor not wired.  You didn't mention whether your 3.5 mm male-to-male cable is mono (2-conductor) or stereo (3-conductor), but these days most such cables are sold as audio patch cables and have three conductors, with TRS plugs on both ends.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;In your shoes, I think first I'd do a little troubleshooting: see if the radio works with nothing plugged into it.  Then try the radio with just the speaker-microphone plugged into it.  If that works, then you know the trouble is in the microphone's accessory jack, your cable, or the earmuffs (headset).  In that case I'd try getting a 3.5 mm mono-to-stereo adapter.  Plug that into the microphone, and then plug the earmuffs into the adapter.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-06-15T19:08:08.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16842" PostTypeId="2" ParentId="16825" CreationDate="2020-06-15T20:12:58.493" Score="3" Body="&lt;p&gt;Looking at an azimuthal map centered on Sydney, Europe looks to be at about 300° and the USA looks to be at about 60°.  So if the antenna is pointed at Europe, then the USA is about 120° off to the side.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Looking at an antenna gain plot of the K4KIO hex beam from K4KIO's web site, it looks as though the gain in the direction of 120° off to the side is about 11 dB lower than straight ahead.  The plot doesn't specify which band it's being used for, or how high the antenna is, but since it's for marketing purposes, we can assume that the plot attempts to put the antenna in the best possible light, which probably means 20m with the antenna up high.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;So the best-case rejection of the USA compared to Europe for your antenna is 11 dB, which is about two S-units.  Since your antenna isn't up as high, and is used for 40m some of the time, you probably have less rejection, especially on 40m.  This sounds like fairly normal behavior for your antenna.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-06-15T20:12:58.493" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16843" PostTypeId="2" ParentId="16825" CreationDate="2020-06-15T22:38:14.700" Score="3" Body="&lt;p&gt;I used a Traffie Hexbeam antenna for about 12 years.  Even though I had a rotator for the antenna there were many times that I did not move the antenna in the direction of a given signal because I could work them just fine.  Sure, if I rotated it, I might get another S-unit on receive or even 2 S-units but I was lazy.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I found that working off the side was not a big problem, the directivity of a hex beam, especially at the 35 foot elevation I had was not that great.  I think front to back was about 15 dB or so.  Rotating front to back though was about 15 seconds so if I could work a station, I never bothered to rotate.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I gave the hex beam to a local ham radio club so that they could use it as a portable antenna for Field Day and other activities.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2020-06-15T22:38:14.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16844" PostTypeId="2" ParentId="16827" CreationDate="2020-06-15T22:55:41.170" Score="4" Body="&lt;p&gt;Using a NEC-2 model, here's how R and X of a free-space 20-meter dipole made from #14 copper wire vary with feedpoint position (50 = center fed; 0 = end fed):&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AJDLZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AJDLZ.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-06-16T01:07:46.590" LastActivityDate="2020-06-16T01:07:46.590" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16845" PostTypeId="2" ParentId="16041" CreationDate="2020-06-15T22:56:37.957" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://www.alibaba.com/countrysearch/CN/ferrite-coil.html?spm=a2700.7724857.22.2.39a54807W9PFes&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.alibaba.com/countrysearch/CN/ferrite-coil.html?spm=a2700.7724857.22.2.39a54807W9PFes&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Many Chinese suppliers offer these on Alibaba&lt;/p&gt;&#xA;" OwnerUserId="17230" LastActivityDate="2020-06-15T22:56:37.957" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16847" PostTypeId="1" CreationDate="2020-06-16T09:25:09.910" Score="1" ViewCount="38" Body="&lt;p&gt;I'm building RHCP crossed dipole for 137 MHz satellites reception (I'm using 137.5 as a central frequency). My calcs are:&lt;/p&gt;&#xA;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;frequency is 137.5 MHz&lt;/li&gt;&#xA;&lt;li&gt;λ is 2.18 m&lt;/li&gt;&#xA;&lt;li&gt;one dipole leg length equals to the λ/4 so 54.5 cm&lt;/li&gt;&#xA;&lt;li&gt;phasing RG58 50 Ohm cable is of 36.0 cm&lt;/li&gt;&#xA;&lt;li&gt;28 to 50 Ohm transformer made of 2 parallel RG6 75 Ohm cables; each cable is of 36.0 cm&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;I've decided to solder second dipole to the one side of RG58 coax and join first dipole together with other end of RG58 coax and with RG6 feeder transformer by choc block (to ease possible future change of RHCP -&gt; LHCP). I haven't faced phasing and transformer units earlier so I wonder how to perform right cut.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Right now I've cut RG58 and RG6 coaxes exactly at 36.0 cm. However for soldering and joining purposes I have stripped a part of external and internal insulation on all coaxes so actual length of untouched coax become smaller - about 30-32 centimeters. Also because of lack of space and to save coax length I've connected stripped parts of RG6 transformer to the choc block with small pieces of copper wire.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm not sure if I've done it in a right way. Should I cut coaxes a bit longer (let's say 42 cm) and strip insulation in a way that final untouched coax pieces would be 36.0 cm? What kind of side-effects this could render? Also I want to know if it is ok to use choc blocks and copper wires to interconnect all necessary parts because they increases effective length of dipole legs and/or signal path.&lt;/p&gt;&#xA;" OwnerUserId="14179" LastActivityDate="2020-06-16T09:25:09.910" Title="How to cut phasing/transformer coax in a right way?" Tags="&lt;antenna&gt;&lt;transformer&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16848" PostTypeId="2" ParentId="16808" CreationDate="2020-06-16T12:38:28.970" Score="0" Body="&lt;p&gt;The value of reactance varies both in magnitude and sign as functions of the operating frequency, the radiating length of the antenna, and the physical location of the feedpoint terminals along that length. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;At resonance, jX = 0.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-06-16T12:44:21.453" LastActivityDate="2020-06-16T12:44:21.453" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16849" PostTypeId="1" CreationDate="2020-06-16T13:40:30.963" Score="1" ViewCount="77" Body="&lt;p&gt;I was reading up on the different amplified loop antennas, like the W6LVP or the MLA-30. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;Most reviews say &quot;great reception&quot;, or show a SDR waterfall with a lot of stations, or show a random station coming in really strong. They also talk about how good they are for &quot;serious SWL&quot;.  But in most cases they don't show a 2-way QSO with a DX station. And SWL isn't really that relevant since the remote commercial station may be pushing 250KW anyways.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Are those antennas any good for &lt;strong&gt;amateur radio DX&lt;/strong&gt; operation? &lt;/p&gt;&#xA;&#xA;&lt;p&gt;I'm in South America. So basically all I do is DX: 8000km is usually the minimum kind of distances I operate to (there are few stations in SA except for Brazil, who are at least 1500km from me anyways).&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-06-17T22:27:45.020" Title="Amplified RX-only loop antennas for DX operation?" Tags="&lt;loop-antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16850" PostTypeId="1" CreationDate="2020-06-16T14:33:37.520" Score="1" ViewCount="143" Body="&lt;p&gt;I'm building a &lt;strong&gt;Double Cross Dipole antenna&lt;/strong&gt; for 437 MHz to be used with a SDR receiver for CW cubesat.&#xA;The idea is to follow &lt;a href=&quot;https://drive.google.com/file/d/0B1q-psxlp3IwamN0VFZORmw3UjQ/view?usp=sharing&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; &quot;classic&quot; paper from &lt;strong&gt;&lt;em&gt;Gerald Martes, KD6JDJ&lt;/em&gt;&lt;/strong&gt;.&#xA;I tuned every single dipole (8 mm aluminium bar + ferrite + coax cable) using a &lt;em&gt;nanoVNA&lt;/em&gt; with - i think - good result(eg. here the return loss of first dipole) &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XeSJ8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XeSJ8.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I use a coax cable to measure the SWR like this&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5nf0M.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5nf0M.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;and the coax length is taken from end of the shield (as in this images :))&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/i6711.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/i6711.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&#xA;but when I connect all the 4 dipole ... &lt;strong&gt;craziest thing happened&lt;/strong&gt; ...and it seems to me that every dipole change the proper resonant frequency to a different one. &lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/b8mVl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/b8mVl.png&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Is &lt;strong&gt;the problem&lt;/strong&gt; in the cabling between all the dipole ? Or (as I suppose) &lt;strong&gt;I followed a wrong apporoach tuning separately every dipole&lt;/strong&gt; and the proper way is to tune &lt;strong&gt;all the arms&lt;/strong&gt; after connect them together?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Can someone give me some hints on how to proceed?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Tks a lot&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Carlo, IU2KQB&lt;/p&gt;&#xA;" OwnerUserId="17217" LastEditorUserId="8717" LastEditDate="2020-06-17T01:06:15.307" LastActivityDate="2020-08-03T23:34:01.523" Title="Double Cross Dipole antenna for 437 MHz don't tune" Tags="&lt;antenna&gt;&lt;uhf&gt;&lt;dipole&gt;&lt;satellites&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="16852" PostTypeId="2" ParentId="16849" CreationDate="2020-06-16T16:38:31.763" Score="1" Body="&lt;p&gt;What's the background RF noise level at your antenna's locations for your bands of interest?  In environments with high levels of broadband background RF noise (neighborhood or computer EMI, etc.), a receive-only loop can help reduce the RF noise pickup, especially if the noise is directional and/or polarized the same as your non-loop antenna(s), and thus improve the S/N of weak DX signals.  But in quiet RF environments, the advantage is far less.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-06-17T22:27:45.020" LastActivityDate="2020-06-17T22:27:45.020" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16853" PostTypeId="1" CreationDate="2020-06-16T17:00:38.567" Score="-2" ViewCount="107" Body="&lt;p&gt;I am trying to understand if it's feasible to transmit -1,0,+1 data using FM on 20-30m wavelength to be received 10,000km away. From Europe to US.&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;Ultimately I would like to create a solution which is sensitive to wave slope. I know it is possible as I read GPS time signal works this way. Hence I can transmit trinary signal not binary&lt;/em&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What SNR should I expect?&lt;/li&gt;&#xA;&lt;li&gt;What kind of power on TX side?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&amp;quot;Desired performance&amp;quot; here is (if the trinary data achievable as above):&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;latency is 4ms&lt;/li&gt;&#xA;&lt;li&gt;data rate 2 tribit per second&lt;/li&gt;&#xA;&lt;li&gt;as its not commercial i'd rather calibrate optimal missing reception etc per session (dependent on weather etc), so 20-80%..&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Also note: I looked into known ham radio digital modes and signal processing algorithms - they seems to be too slow as they are designed to use minimal power for reasonable detection rates with pretty much infinite latency. My task is the other way around - to use maximal reasonable power to achieve low latency.&lt;/p&gt;&#xA;" OwnerUserId="17172" LastEditorUserId="4076" LastEditDate="2020-06-25T18:54:09.893" LastActivityDate="2020-06-25T18:54:09.893" Title="Can I transmit bit data over FM signal on 30m wave 10,000km away?" Tags="&lt;hf&gt;&lt;digital-modes&gt;" AnswerCount="2" CommentCount="9" ClosedDate="2020-06-17T00:07:33.417" ContentLicense="CC BY-SA 4.0" />
  <row Id="16854" PostTypeId="2" ParentId="16853" CreationDate="2020-06-16T17:17:59.240" Score="1" Body="&lt;p&gt;If you have a Ham license, and your application is for ham use, not encrypted, non commercial, and follows proper amateur radio etiquette, bandwidth, and power limits, you can. You will be also required to sit at the radio (no automatic operation for this band in the US IIRC).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As for transmitting FM, I'm not sure what you mean. There are plenty of digital modes you can base your application on. FT8 is the hottest right now. PSK31 may be worth investigating into.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Whatever you do, you're in for a LOT of error correction, like Reed-Solomon coding or other FEC algorithms.&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-06-16T17:17:59.240" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16855" PostTypeId="2" ParentId="16853" CreationDate="2020-06-16T21:00:25.313" Score="2" Body="&lt;blockquote&gt;&#xA;  &lt;p&gt;What SNR should I expect?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Wrong question! You need to ask yourself: What's the SNR I &lt;strong&gt;need&lt;/strong&gt; to still achieve my desired performance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&quot;Desired performance&quot; here is&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;How much data do I need to transmit in a definite time (data rate)&lt;/li&gt;&#xA;&lt;li&gt;How long can I wait for the transmission to complete (latency)&lt;/li&gt;&#xA;&lt;li&gt;Which probability of missing the reception can I accept?&lt;/li&gt;&#xA;&lt;li&gt;Which probability of detecting a reception where there is none can I accept?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;You need to answer all these four questions. Then, a theoretical lower bound for the necessary SNR can be given.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Also, it will then be possible to actually give practical &quot;how to&quot; advice.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;What kind of power on TX side?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That depends on how much the channel attenuates your signal (we can find that out), times how much power needs to reach RX - which is defined by the necessary SNR above.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Can it be done on amateur licence?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;That depends mainly on the TX power you'll need, which depends on the SNR you need.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Can I use polarization to transmit two sets -1,0 and +1,0?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Probably not on 30m, not realistically. You can use MIMO techniques if you have multiple far-distributed transmitters, though. Maybe, that is. If the channels are different enough. I'd call this &quot;very advanced design topics, however&quot;.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;Would it improve SNR?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;If you &lt;em&gt;could&lt;/em&gt; use independent polarizations, yes, you'd have one more degree of independent transmissions which you could use for diversity combining schemes. However, over that distance, I'd be very surprised if two orthogonal polarizations would see1 wildly different channels. So, no.&lt;/p&gt;&#xA;&#xA;&lt;blockquote&gt;&#xA;  &lt;p&gt;How difficult is to build it?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&#xA;&lt;p&gt;Depends on the techniques and power you use, which both depend on the SNR you need.&lt;/p&gt;&#xA;&#xA;&lt;hr&gt;&#xA;&#xA;&lt;p&gt;Start with asking a question where you describe your use case and answer the four performance requirements above.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-16T21:00:25.313" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16856" PostTypeId="1" AcceptedAnswerId="16869" CreationDate="2020-06-17T13:42:17.597" Score="1" ViewCount="252" Body="&lt;p&gt;Is it possible to polarize HF signal (20-30m) at long range (thousands of km)?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;em&gt;It was commented in my over questions that polarization is not feasible at long range. However in this article is specifically mentioned long range HF polarization: &lt;a href=&quot;https://www.electronics-notes.com/articles/antennas-propagation/antenna-theory/polarisation-polarization.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.electronics-notes.com/articles/antennas-propagation/antenna-theory/polarisation-polarization.php&lt;/a&gt;&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="17172" LastActivityDate="2021-04-10T14:05:18.003" Title="Long range HF polarization" Tags="&lt;hf&gt;&lt;propagation&gt;&lt;polarization&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16857" PostTypeId="1" CreationDate="2020-06-15T07:04:14.120" Score="5" ViewCount="144" Body="&lt;p&gt;Is there a simple (by simple, I mean a hobby friendly method that trades some accuracy for expense) method of measuring the &quot;actual&quot; output impedance of an active or &quot;hot&quot; RF (HF to VHF) circuit?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;As an amateur radio enthusiast, I often find myself in a situation where I'd like to measure the actual output impedance of some amplifier or oscillator (type of amplifier).  Right now, I have an oscillator operating in the low VHF region and I'd like to match its output to a mixer that has a well defined input impedance.  But that's just one example, I've had plenty others in the past.  I can calculate the output impedance theoretically, but it would be nice to confirm the theory with a practical measurement.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I have some hobby or entry grade tools to hand, including an oscilloscope and a NanoVNA.  Is there a reasonably accurate measurement method using these tools?  One that doesn't damage the measurement device (especially the VNA).&lt;/p&gt;&#xA;&#xA;&lt;p&gt;One I read somewhere that made some kind of sense was to match the output with a (passive) device that varied the resistance, inductance and capacitance (a type of complex load). You could use a power meter to find the match point.  Then measure the input impedance of the device/load with a VNA and use the conjugate as the output impedance.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Sounds simple enough, but I'm guessing the devil is in the construction of the complex load.  What other methods are there?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;strong&gt;UPDATE:&lt;/strong&gt; Since asking this on EE SE, I've solved my immediate problem by using the two measurement technique (wonderfully explained in this video by &lt;a href=&quot;https://www.youtube.com/watch?v=ieAhBejHe2M&quot; rel=&quot;noreferrer&quot;&gt;W2AEW&lt;/a&gt;).  However, I believe this approach becomes less accurate at RF frequencies and I have a continuing interest in discovering a practical, simple and inexpensive solution - if it exists!?&lt;/p&gt;&#xA;" OwnerUserId="11875" OwnerDisplayName="Buck8pe" LastEditorUserId="11875" LastEditDate="2020-06-17T14:46:22.207" LastActivityDate="2020-06-19T17:57:16.650" Title="Measuring Output Impedance of an RF (HF/VHF) Active Circuit with Hobby-level Tools" Tags="&lt;impedance&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16858" PostTypeId="2" ParentId="16856" CreationDate="2020-06-17T14:37:29.860" Score="4" Body="&lt;p&gt;From the &lt;a href=&quot;https://en.wikipedia.org/wiki/High_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia article on HF&lt;/a&gt;: &quot;Long-distance (skywave) receiving antennas can generally be oriented either vertically or horizontally since refraction through the ionosphere usually scrambles signal polarization, and signals are received directly from the sky to the antenna.&quot;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;Every RF signal radiated by an antenna is polarized.  I believe you meant to ask if an antenna receiving a long-range HF signal can take advantage of the polarization of the incoming signal.  If that's what you meant to ask, then the answer is generally no, because typically long-range HF signals arrive randomly polarized, because they are &quot;sky wave&quot; signals that have been bounced off of the ionosphere, or to be more correct, refracted through the ionosphere.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;There are a few exceptions.  If the receiving antenna is more-or-less within line of sight of the transmitting antenna, then the signal will be received in the same polarization as it was sent.  &lt;a href=&quot;https://en.wikipedia.org/wiki/Ground_wave_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ground wave propagation&lt;/a&gt; is another exception; that requires vertical polarization, and generally requires lower frequencies (that are strongly attenuated in the daytime) and has shorter range than sky wave propagation.  Ground wave propagation is typically how AM broadcast stations can be received beyond line-of-sight range during the daytime.  Unfortunately, both of the mentioned exceptions have shorter range.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-06-17T14:37:29.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16859" PostTypeId="1" AcceptedAnswerId="16862" CreationDate="2020-06-17T15:09:59.917" Score="4" ViewCount="191" Body="&lt;p&gt;It's a well-known fact among hams who use HF frequencies that horizontally-polarized RF waves reflect better off of ground than vertically-polarized waves.  This explains why ground conductivity is so important to the performance of a vertical monopole antenna, and not as important for a horizontally-polarized antenna.  Can someone explain, hopefully in layman's terms, why this is so?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;I would also like to know why vertically-polarized waves propagate much better via ground-wave propagation than horizontally-polarized waves.  My intuition tells me that this question is the other side of the same coin as the first question.  (But my intuition is often wrong.)  If the same explanation can easily answer both questions, great; if not, then I'll ask my second question separately.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="8717" LastEditDate="2020-06-17T17:31:39.233" LastActivityDate="2020-06-24T01:16:36.773" Title="Why do horizontally-polarized RF waves reflect better off ground than vertically-polarized waves?" Tags="&lt;antenna-theory&gt;&lt;hf&gt;&lt;polarization&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16860" PostTypeId="2" ParentId="16849" CreationDate="2020-06-17T15:50:00.397" Score="2" Body="&lt;p&gt;In short, yes. Receive antennas can do lots of good things for hams. They're most popular on the &quot;low bands&quot; (80 meters and longer), but can be built and used for any band. They're not magical, but they do offer chances to null out local noise sources if carefully placed and adjusted. Some hams go to the length of installing 4 or more receive antennas with phasing combiners so that they can electronically &quot;steer&quot; their pattern to maximize SNR for the station they want to hear. This can be expensive, but it's cheaper than doing the same thing for transmit because the power levels involved are much lower.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;A single active loop won't let you do that, but:&lt;/p&gt;&#xA;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;It's a decent receive antenna with a stable pattern for several bands.&lt;/li&gt;&#xA;&lt;li&gt;Since it's physically small, and pre-amplified, you can place it on whatever part of your lot has the least near-field RFI (useful if interference is coming from your own house/shack, or one noisy neighbor).&lt;/li&gt;&#xA;&lt;li&gt;It has two nulls that you can point towards offending noise sources.&lt;/li&gt;&#xA;&lt;li&gt;It has a good (almost hemispherical) elevation pattern, with very little sensitivity to height above ground, so it's as good for DX as NVIS.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&#xA;&lt;p&gt;One caution with any kind of pre-amplified antenna; if you live within a few km of a strong (10kW or more) broadcast station, you may have a &lt;em&gt;very&lt;/em&gt; hard time preventing overload of the preamp. I know from experience — I have three different 50kW stations &quot;in my back yard&quot;.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-06-17T15:50:00.397" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16861" PostTypeId="2" ParentId="16859" CreationDate="2020-06-17T19:03:09.213" Score="4" Body="&lt;p&gt;RE:  &lt;em&gt;&quot;I would also like to know why vertically-polarized waves propagate much better via ground-wave propagation than horizontally-polarized waves.&quot;&lt;/em&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;This subject is treated in various textbooks relating to antennas and propagation.  An example clip from one of them is shown below.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;The last sentence in the column on the far right-hand side of the clip is especially relevant, here.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/yompJ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yompJ.jpg&quot; alt=&quot;enter image description here&quot;&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-06-17T19:03:09.213" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16862" PostTypeId="2" ParentId="16859" CreationDate="2020-06-18T00:39:14.033" Score="5" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;It's a well-known fact among hams who use HF frequencies that horizontally-polarized RF waves reflect better off of ground than vertically-polarized waves. This explains why ground conductivity is so important to the performance of a vertical monopole antenna, and not as important for a horizontally-polarized antenna.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I don't think this is true. Actually, vertical and horizontal waves reflect from the ground about equally. The difference is that when a vertically-polarized wave reflects off of the ground, the reflected wave is &lt;em&gt;in phase&lt;/em&gt; with the incident wave, but when a horizontally polarized-wave reflects off of the ground, the reflected wave is &lt;em&gt;180° out of phase&lt;/em&gt; with the incident wave at that point. (This is the opposite of what my intuition tells me, but it's true.)&lt;/p&gt;&#xA;&lt;p&gt;For a vertical monopole, the in-phase reflection is a good thing; it means that the reflected image of the antenna forms the &amp;quot;missing half&amp;quot; of a vertical dipole. If the ground was lossless, the signal reflecting off the ground at a given point would be exactly the same as if the ground didn't exist and the antenna continued below ground level. Since a vertical dipole has peak gain towards the horizon, this phenomenon makes DXers happy. Making the ground lossy is like putting a big resistor between the halves of this imaginary dipole (this is a cheap explanation but close enough for the moment) — it doesn't take very many ohms for the ground loss to start competing with the radiation resistance and eating most of your power. We use radials to artificially enhance the ground conductivity and decrease this loss.&lt;/p&gt;&#xA;&lt;p&gt;For a horizontal antenna, the out-of-phase reflection from the ground is a mixed bag. In the case of a low dipole, once you get far away, the reflection and the original signal are basically &amp;quot;coming from the same place&amp;quot;, so the in-phase original and the out-of-phase reflection add up and cancel out. A low dipole has maximum gain straight up, because that's the direction that maximizes the path length difference between the original and the reflected signal, so the phase difference at the receiver will be less than 180° and the cancellation will be less complete.&lt;/p&gt;&#xA;&lt;p&gt;Once you raise the horizontally polarized antenna more than a quarter-wavelength above the ground, though, you make it so that there is some angle where the length of the reflected path to a distant point will be a &lt;em&gt;half wavelength longer&lt;/em&gt; than the direct path to the same point. The 180° shift from the path length difference adds to the 180° shift from the reflection to give 360° (or 0°), which means the signal is reinforced instead of canceled. By placing an antenna at just the right height, you can make the ground contribute to DX performance instead of detracting from it.&lt;/p&gt;&#xA;&lt;p&gt;So it's not that horizontal signals reflect better, it's that reflection is &lt;em&gt;less important&lt;/em&gt; to the whole antenna system. A vertical antenna with no reflections is a dummy load. A horizontal antenna with no reflections is... just fine (the best the reflection could ever do is give you +3dB, and other times it's actively harmful). Horizontally polarized antennas still have to deal with induced ground losses if they're low, but that's not a question about &lt;em&gt;reflections&lt;/em&gt;, and I've already said enough :)&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I would also like to know why vertically-polarized waves propagate much better via ground-wave propagation than horizontally-polarized waves.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Ground waves propagate &amp;quot;half in and half out&amp;quot; of the ground. The portion of the wave that's underground travels slower than the portion that's above ground (dirt and rock and stuff has a higher dielectric constant than air), so the wave &amp;quot;bends down&amp;quot; and follows the curvature of the earth, allowing it go go beyond line of sight. But the ground loss is attenuating the signal as it goes, and at higher frequencies, the groundwave is completely dissipated before it goes any useful distance. Horizontally polarized signals don't propagate at all through groundwave because they can't be &amp;quot;half in and half out&amp;quot; in the same sense... any measured groundwave propagation of a horizontal signal is either direct-path (not groundwave), or groundwave propagation of a scattered vertically-polarized component (the signal bounced off of something that converted it to partially vertically polarized) or a residual vertically-polarized component (the antenna wasn't &lt;em&gt;perfectly&lt;/em&gt; level to begin with, so a small fraction of its output is vert pol).&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-06-24T01:16:36.773" LastActivityDate="2020-06-24T01:16:36.773" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16863" PostTypeId="2" ParentId="16806" CreationDate="2020-06-18T01:26:21.017" Score="0" Body="&lt;p&gt;If you want 2 unmodulated finite length sinusoids to be mathematically orthogonal, then the frequency separation is 1/T, where T is the length in time of a DFT used to detect them, and the period of the carriers are an integer submultiple of T. If you want a 3 dB gap between signals or the carriers are not integer periodic in T, then double that separation or a little more. If you use a non-rectangular window, then the separation roughly doubles again.  If the channel has an impulse response, then you may need to add a cyclic prefix to cover the multi-path skew, which typically increases T by 25% for a given carrier frequency separation to be orthogonal.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-06-18T01:32:55.890" LastActivityDate="2020-06-18T01:32:55.890" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16864" PostTypeId="1" AcceptedAnswerId="16866" CreationDate="2020-06-18T12:00:57.620" Score="-1" ViewCount="193" Body="&lt;p&gt;I would like to transmit trinary data (-1,0,+1) on 20-30m wave to be received 10,000km away. From Europe to US.&lt;/p&gt;&#xA;&lt;p&gt;My first thought was this: &lt;a href=&quot;https://www.researchgate.net/figure/Burst-modulation-mode-f-BM-280-Hz-duty-cycle-50-as-an-example_fig2_231130256&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.researchgate.net/figure/Burst-modulation-mode-f-BM-280-Hz-duty-cycle-50-as-an-example_fig2_231130256&lt;/a&gt; I am open to different suggestions&lt;/p&gt;&#xA;&lt;p&gt;Desired performance here is:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;max latency of signal processing (to increase SNR) is 4ms&lt;/li&gt;&#xA;&lt;li&gt;data rate 2 tribit per second&lt;/li&gt;&#xA;&lt;li&gt;as its not commercial i'd rather calibrate optimal missing reception etc per session (dependent on weather etc), so 20-80%..&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;What kind of power would I need on TX side for the above SNR?&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;Also note: I looked into known ham radio digital modes and signal processing algorithms - they seems to be too slow as they are designed to use minimal power for reasonable detection rates with pretty much infinite latency. My task is the other way around - to use maximal reasonable power to achieve low latency.&lt;/em&gt;&lt;/p&gt;&#xA;" OwnerUserId="17172" LastEditorUserId="17172" LastEditDate="2020-06-19T12:40:35.153" LastActivityDate="2020-06-24T21:52:26.147" Title="Transmit data over HF signal 10,000km away" Tags="&lt;hf&gt;&lt;digital-modes&gt;&lt;propagation&gt;" AnswerCount="1" CommentCount="13" ClosedDate="2020-06-25T19:30:50.143" ContentLicense="CC BY-SA 4.0" />
  <row Id="16865" PostTypeId="1" CreationDate="2020-06-18T14:21:07.127" Score="1" ViewCount="484" Body="&lt;p&gt;I was looking for a secondary radio for RX only and I thought a SDR may be a better option. I read about upconverters but then I saw Airspy has a SDR with the upconverter onboard, and claims to have &amp;quot;&lt;strong&gt;low-loss preselection filter, high linearity LNA, high linearity tunable RF filter, a polyphase harmonic rejection (HR) mixer that rejects up to the 21st harmonic and multi-stage analog and digital IF filtering&lt;/strong&gt;&amp;quot;, which got me curious, since most &amp;quot;cheap&amp;quot; SDRs don't have preselection filters and are easily overloaded (this is also true for cheap HTs like the BAOFENG which, in my experience, are significantly improved by an external filter).&lt;/p&gt;&#xA;&lt;p&gt;The specs on this radio are (I have highlighted specs which I discusse further down):&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;HF coverage between 0.5 kHz .. 31 MHz&lt;/li&gt;&#xA;&lt;li&gt;VHF coverage between 60 .. 260 MHz&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Sensitivity: -140.0 dBm (0.02 µV / 50 ohms at 15MHz) MDS Typ. at 500Hz bandwidth in HF&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Sensitivity: -141.5 dBm MDS Typ. at 500 Hz bandwidth in FM Broadcast Band (64 – 118 MHz)&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Sensitivity: -141.0 dBm MDS Typ. at 500 Hz bandwidth in VHF Aviation Band (118 – 260 MHz)&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;Linearity: +15 dBm IIP3 on HF at maximum gain&lt;/li&gt;&#xA;&lt;li&gt;Linearity: +13 dBm IIP3 on VHF at maximum gain&lt;/li&gt;&#xA;&lt;li&gt;Dynamic Range: 110 dB blocking dynamic range (BDR) in HF&lt;/li&gt;&#xA;&lt;li&gt;Dynamic Range: 95 dB blocking dynamic range (BDR) in VHF&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Selectivity: 150+ dB combined selectivity (hardware + software)&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;Image Rejection: 120 dB (software)&lt;/li&gt;&#xA;&lt;li&gt;Filtering: Polyphase Tracking filters for close range interference suppression&lt;/li&gt;&#xA;&lt;li&gt;Filtering: New High Performance Pre-selector for HF with 4 filter banks (corners at ~DC, 5, 10, 17 and 31 MHz)&lt;/li&gt;&#xA;&lt;li&gt;Filtering: New High Performance Pre-selector for VHF (Air, HAM, Commercial and Military VHF)&lt;/li&gt;&#xA;&lt;li&gt;Filtering: New High Performance Pre-selector for the FM band (Japan, US, EU, OIRT)&lt;/li&gt;&#xA;&lt;li&gt;Up to 660 kHz alias and image free output for 768 ksps IQ&lt;/li&gt;&#xA;&lt;li&gt;18 bit Embedded Digital Down Converter (DDC)&lt;/li&gt;&#xA;&lt;li&gt;22 bit Resolution at 3 kHz channel using State of the Art DDC (SDR# and SDR-Console)&lt;/li&gt;&#xA;&lt;li&gt;+10 dBm Maximum RF input&lt;/li&gt;&#xA;&lt;li&gt;0.5 ppm high precision, low phase noise clock&lt;/li&gt;&#xA;&lt;li&gt;1 PPB frequency adjustment capability&lt;/li&gt;&#xA;&lt;li&gt;Very low phase noise PLL (-110 dBc/Hz @ 1kHz separation @ 100 MHz)&lt;/li&gt;&#xA;&lt;li&gt;Best Noise reduction of the market using state of the art algorithms&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I tried to compare it to my TS-450S which, in page 6 of the manual states a sensitivity of 2uV for SSB, but it doesn't specify the bandwidth. The claims in the Airspy product specify 0.02uV a 500Hz bandwidth. That's a whopping FORTY dB improvement. Which to me sounds &amp;quot;too good to be true&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;My kenwood also states a selectivity of &amp;quot;-6dB: More than 2.2khz, -60dB: Less than 4.4khz&amp;quot;. The Airspy HF claims &amp;quot;150dB+&amp;quot;, which I don't know how to compare.&lt;/p&gt;&#xA;&lt;p&gt;In all, would this be a good addition to my shack? I believe even if the analog specs are similar to my almost-30-year-old-radio, it has the advantage of IF DSP, which is something that didn't exist back then, and something I can't afford afford at the moment.&lt;/p&gt;&#xA;&lt;p&gt;Will it be an improvement over what I have now?&lt;/p&gt;&#xA;" OwnerUserId="14642" LastActivityDate="2020-06-18T23:08:13.650" Title="How does an Airspy HF+ Discovery compare to a &quot;real&quot; radio?" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16866" PostTypeId="2" ParentId="16864" CreationDate="2020-06-18T17:57:54.623" Score="6" Body="&lt;p&gt;What you're asking for is a &lt;a href=&quot;https://ham.stackexchange.com/q/352/218&quot;&gt;link budget&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;For HF, you can use software like &lt;a href=&quot;https://www.voacap.com/hf/&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt; to estimate path loss. There are several ways you might use the software, but to start I'd suggest:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Click the antennas button, and enter the kinds of antennas you have available for each band.&lt;/li&gt;&#xA;&lt;li&gt;Drag the location markers to the relevant places. Not all 10,000 km paths are the same. Things like water vs land make a difference, as well as alignment with the &lt;a href=&quot;https://www.electronics-notes.com/articles/antennas-propagation/ionospheric/greyline-propagation.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;greyline&lt;/a&gt;, among other factors.&lt;/li&gt;&#xA;&lt;li&gt;Change the date in the lower-left to at least the month of interest. The sun influences HF propagation significantly, so the season is important. Over longer timescales, the &lt;a href=&quot;https://scied.ucar.edu/sunspot-cycle&quot; rel=&quot;nofollow noreferrer&quot;&gt;sunspot cycle&lt;/a&gt; is also relevant.&lt;/li&gt;&#xA;&lt;li&gt;After editing these and other relevant parameters, click the &amp;quot;Prop Charts&amp;quot; button, and select the &amp;quot;SDBW Short-Path&amp;quot; chart. This shows the received power in &lt;a href=&quot;https://en.wikipedia.org/wiki/Decibel_watt&quot; rel=&quot;nofollow noreferrer&quot;&gt;dBW&lt;/a&gt; for each band and each hour of the day.&lt;/li&gt;&#xA;&lt;li&gt;Note the transmit power selected in the upper-right. It's in watts, but if you convert it to dBW then the difference between that and the &amp;quot;SDBW&amp;quot; chart is the path loss. It includes propagation loss and antenna gain.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Of note, HF propagation is highly variable. The number VOACAP gives for SDBW is a median value. Half the days will be better, half will be worse. Add or subtract some margin depending on how many days out of the month you are OK with communication not working. VOACAP can also generate 10th and 90th percentile values for this metric, but as far as I've found not in the online version.&lt;/p&gt;&#xA;&lt;p&gt;Great, now you know how much power from the transmitter arrives at the receiver. Now how much power must arrive at the receiver to achieve your communication objectives?&lt;/p&gt;&#xA;&lt;p&gt;The first part of this question is determining the noise at the receiver site. Perhaps you can measure it directly. If not, &lt;a href=&quot;https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.372-13-201609-I!!PDF-E.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU-R P.372-13&lt;/a&gt; is a good source of data on what noise can be expected generally.&lt;/p&gt;&#xA;&lt;p&gt;Now you need to set a &lt;a href=&quot;https://en.wikipedia.org/wiki/Signal-to-noise_ratio&quot; rel=&quot;nofollow noreferrer&quot;&gt;signal to noise ratio&lt;/a&gt; (SNR) objective. You could do this a couple ways:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Use the &lt;a href=&quot;https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;Shannon-Haltley theorem&lt;/a&gt; to put a best-case lower-bound on the required SNR, or&lt;/li&gt;&#xA;&lt;li&gt;Find the &lt;a href=&quot;https://en.wikipedia.org/wiki/Bit_error_rate&quot; rel=&quot;nofollow noreferrer&quot;&gt;bit error rate curve&lt;/a&gt; for a specific modulation you are considering. I have no idea what the thing you linked in the question is. BPSK might be a good starting point.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;If this sounds complicated, it's because it is. There are a lot of variables required besides &amp;quot;how much power&amp;quot;. But hopefully this gives you enough of an outline of the procedure that you can &lt;a href=&quot;https://ham.stackexchange.com/questions/ask&quot;&gt;ask follow-up questions&lt;/a&gt; for additional detail as you need it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-06-18T22:27:22.977" LastActivityDate="2020-06-18T22:27:22.977" CommentCount="16" ContentLicense="CC BY-SA 4.0" />
  <row Id="16867" PostTypeId="2" ParentId="16865" CreationDate="2020-06-18T22:20:19.600" Score="3" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;I tried to compare it to my TS-450S which, in page 6 of the manual states a sensitivity of 2uV for SSB, but it doesn't specify the bandwidth.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes, because you can't adjust the filtering bandwidth, so there's only one sensitivity here.&lt;/p&gt;&#xA;&lt;p&gt;Of course, the smaller you make your bandwidth, the lower the amount of noise is you receive, and the less signal power you need for detection.&lt;/p&gt;&#xA;&lt;p&gt;If you can only design a radio once, you need to pick a middle ground between low noise bandwidth (little noise power, but also cuts off parts of the audio) and high audio bandwidth (which makes for better audio at good SNRs, but for worse sensitivity).&lt;/p&gt;&#xA;&lt;p&gt;An SDR has its filtering in software or programmable logic – so it's flexible, and you can basically program &lt;em&gt;any&lt;/em&gt; bandwidth you like. It hence makes sense for the SDR system (SDR hardware + receiver software) to specify the bandwidth used for a sensitivity measurement.&lt;/p&gt;&#xA;&lt;p&gt;Generally: SDRs themselves don't have &amp;quot;sensitivity&amp;quot;, because they don't detect anything by themselves. Only the software part (hence the S) makes the detection, and that's usually only limited by mathematical bounds. These bounds are actually typically of an information-theoretical nature: you might be familiar with Shannon Capacity, for example, which says that given an SNR, it's impossible to get more than a specific data rate across, &lt;em&gt;no matter what you do&lt;/em&gt;. Similar things exist for all kinds of estimators – and remember, no matter which receiver you look at, whether it's analog or digital, whether it's a TV receiver or a radio-controlled clock, they're all nothing but estimators of the signal that was transmitted.&lt;/p&gt;&#xA;&lt;p&gt;I have replied to very many customers (I work tech support, but for a competitor of the Airspy, in a very broad sense) that the SDR they bought doesn't have a sensitivity. If they can put a number on the SNR their detector mathematically needs to work, and a bandwidth it operates on, giving them the Noise figure is totally sufficient for them to calculate the sensitivity of the system they're building from an SDR device and their own software.&lt;/p&gt;&#xA;&lt;p&gt;In the Airspy sense, a bit of software seems to come with the hardware (otherwise, the software-based claims make no sense).&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The claims in the Airspy product specify 0.02uV a 500Hz bandwidth.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yeah, that's good,&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;That's a whopping FORTY dB improvement. Which to me sounds &amp;quot;too good to be true&amp;quot;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;but not &amp;quot;incredibly good&amp;quot;: It's solid engineering, but look at it this way.&lt;/p&gt;&#xA;&lt;p&gt;Receiver noise is mostly Johnson-Nyquist thermal noise, which is, at room temperature, -174 dBm/Hz. At 500 Hz (that's 27 dBHz), that's -147 dBm.&lt;/p&gt;&#xA;&lt;p&gt;So, that's a required SNR of 7 dB, roughly. You'd typically need some 3 to 5 dB of SNR for SSB detection, so that leaves us with a noise figure of 2 to 4 dB – that sounds pretty realistic for good equipment.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;My kenwood also states a selectivity of &amp;quot;-6dB: More than 2.2khz, -60dB: Less than 4.4khz&amp;quot;. The Airspy HF claims &amp;quot;150dB+&amp;quot;, which I don't know how to compare.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Me neither.&lt;/p&gt;&#xA;&lt;p&gt;The Airspy specs are probably for signals that are aliased into the digitized bandwidth, but not into the channel to be received. But that's speculation, and I must say this spec isn't overly helpful.&lt;/p&gt;&#xA;&lt;p&gt;The Kenwood spec needs to be read like this:&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;For adjacent channels, we can guarantee a suppression of at least 6 dB for anything more than 2.2 kHz from the channel of interest, which increases to -60 dB before you even move 4.4 kHz away from the channel center&amp;quot;, I think. The spec doesn't seem to be overly well-written either.&lt;/p&gt;&#xA;&lt;p&gt;In radio measurement equipment, you'd usually just get a measurement graph, where the x-axis is frequency distance from your channel center, and y is the suppression. Would make more sense, if you asked me, and be easy to measure for the manufacturer.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;In all, would this be a good addition to my shack? I believe even if the analog specs are similar to my almost-30-year-old-radio,&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It's thoroughly possible that your 30-year-old radio has better amplifiers, and better analog filters - but the analog filters don't matter, when you intend to do the filtering in software, where you can build arbitrarily good filters.&lt;/p&gt;&#xA;&lt;p&gt;Whether or not it's a good addition to your shack is hard to know – but I honestly think you could do worse :) It's a very flexible thing. You can just use it with a lot of different software, i.e. you can use it to receive SSB just as much as satellite data just as much as digital radio mondiale, just as much as airplane transponders, or…&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;it has the advantage of IF DSP, which is something that didn't exist back then, and something I can't afford afford at the moment.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Well, didn't exist in consumer radios, yes. Military radio surveillance pretty certainly did it back then; I happen to know a device that was produced in the last years of the former GDR which architecturally looks &lt;em&gt;a lot&lt;/em&gt; like a superhet SDR. It's orange, very robust, was probably pretty expensive, and weighs about 20 kg.&lt;/p&gt;&#xA;&lt;p&gt;But really, basically all low-cost low-bandwidth receivers you can buy these days are based on IF sampling and DSP. The &amp;lt;1€ fully integrated AM/FM broadcast receiver IC in your phone (if you have one where you can use the headphone cable as antenna) is one. Your Zigbee receiver very likely is one. If you still have an old GSM phone lying around: chances are not that bad it has an IF and samples that. It's a pretty common technique, exactly &lt;em&gt;because&lt;/em&gt; it makes high low-noise receivers well implementable with the modern technology mix of cheap CMOS ADCs, and logic that doesn't even break a sweat processing a couple hundred kilosamples a second.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-06-18T23:08:13.650" LastActivityDate="2020-06-18T23:08:13.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16869" PostTypeId="2" ParentId="16856" CreationDate="2020-06-19T10:58:09.927" Score="3" Body="&lt;p&gt;It is useful to use polarization of HF signals, but not for the same reasons you'd do that with a VHF signal, and the effects are radically different for groundwave vs. skywave propagation.&lt;/p&gt;&#xA;&lt;p&gt;Groundwave propagation is generally considered the same as line of sight, but this isn't strictly true, as line of sight is free space propagation, where groundwave propagation is ... near the ground.  As such, conductivity of the ground affects it and some refraction occurs towards the ground, extending the range of propagation on a curved surface.  Horizontally polarized signals are refracted differently than vertically polarized signals, allowing vertically polarized signals to travel slightly further.  (Also, the amount of refraction is larger for longer wavelengths, and different polarizations have to deal with different types of noise.)&lt;/p&gt;&#xA;&lt;p&gt;Skywave propagation occurs when a signal bounces (really, refracts) from the ionosphere.  Part of the refraction process can cause the linear polarized signal (both H and V) to be split into two circular polarized signals, clockwise and counterclockwise (faraday rotation).  These signals may have variations in their propagation such that when received, they may be somewhat out of phase with each other.  A linear polarized receive antenna will mix the two signals.  Under certain conditions, after mixing, constructive and destructive interference effects will cause the mixed signal to fade and become stronger in a periodic fashion (selective fading).  A circular polarized antenna can be used to try to receive only one of the two signals and reduce selective fading.&lt;/p&gt;&#xA;&lt;p&gt;So, for a groundwave signal (hundreds of miles), picking your (linear) polarization may help.&lt;/p&gt;&#xA;&lt;p&gt;For skywave propagation (more than 400 miles), the transmitted polarization will be randomized (as the path length changes), but a circular polarized receive antenna may help.  In this case, transmitted polarization can't be controlled, but received (circular) polarization can be taken advantage of.&lt;/p&gt;&#xA;&lt;p&gt;The understanding of polarization effects on groundwave propagation has been well understood for a long time, but complete understanding of the causes and effects of polarization on skywave propagation by the amateur radio community is relatively recent, and a lot of literature predates this and just says you can't polarize skywave, which while mostly true, is not the whole story.  (Constructing an HF circular polarized antenna is left as an exercise for the reader.)&lt;/p&gt;&#xA;&lt;p&gt;Edit: Here is a 1967 paper that goes into detail on this topic.&#xA;&lt;a href=&quot;https://apps.dtic.mil/dtic/tr/fulltext/u2/663707.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://apps.dtic.mil/dtic/tr/fulltext/u2/663707.pdf&lt;/a&gt;&#xA;Polarization of Ionospherically Propagated Waves, M. R. Epstein.  October 1967.  Technical Report No. 143, Office of Naval Research Contract Nonr-225(64)&lt;/p&gt;&#xA;&lt;p&gt;Page 6-7 describes how the signal is split into LCP and RCP signals.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-04-10T14:05:18.003" LastActivityDate="2021-04-10T14:05:18.003" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16872" PostTypeId="2" ParentId="16857" CreationDate="2020-06-19T17:57:16.650" Score="2" Body="&lt;p&gt;According to &lt;em&gt;&lt;a href=&quot;https://www.microwaves101.com/encyclopedias/load-pull-for-power-devices&quot; rel=&quot;nofollow noreferrer&quot;&gt;Microwaves101&lt;/a&gt;&lt;/em&gt;, the &amp;quot;load pull&amp;quot; technique may fulfill your need:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Load pull involves varying the load impedance presented to a device&#xA;under test and monitoring a single or set of performance parameters.&#xA;When used in conjunction with a signal source and signal analyzer&#xA;(spectrum analyzer, power meter, vector receiver…), load pull can be&#xA;used to measure parameters such as output power, gain, and efficiency&#xA;as a function of load impedance presented to the DUT.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Relying on the &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_matching&quot; rel=&quot;nofollow noreferrer&quot;&gt;maximum power theorem&lt;/a&gt;, the load will see maximum power when it represents a &amp;quot;conjugate match&amp;quot; to the source. Matching the output of your circuit to a known load value using an SWR meter would allow you to &amp;quot;back out&amp;quot; the impedance of the generator. At UHF and above, the lumped matching network you would use at HF and, probably, VHF is replaced by a transmission-line based &amp;quot;&lt;a href=&quot;https://www.microwaves101.com/encyclopedias/microwave-impedance-tuners&quot; rel=&quot;nofollow noreferrer&quot;&gt;microwave impedance tuner&lt;/a&gt;.&amp;quot;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-06-19T17:57:16.650" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16874" PostTypeId="1" CreationDate="2020-06-20T00:55:19.457" Score="0" ViewCount="98" Body="&lt;p&gt;For a center fed half wave dipole operated at resonance, the voltage and current at the feed point are in phase in time and there is zero reactance present in the impedance seen at the feed point.&lt;/p&gt;&#xA;&lt;p&gt;For the points in between the center feed point and the ends of the antenna, are the voltage and current also in phase in time ? which would mean that everywhere on the antenna at resonance V and I are in phase and there is no reactance present anywhere ?&lt;/p&gt;&#xA;&lt;p&gt;This is a different question to :&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/16827/what-is-the-impedance-of-an-off-center-fed-resonant-dipole&quot;&gt;What is the impedance of an off-center fed resonant dipole?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Which asks how the feed point impedance changes as the feed point is moved away from the center.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-06-20T01:52:32.423" LastActivityDate="2020-06-24T00:47:54.890" Title="For a center fed half wave dipole operated at resonance, are the voltage and current in phase only at the feed point?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16875" PostTypeId="2" ParentId="9962" CreationDate="2020-06-20T04:12:06.457" Score="0" Body="&lt;p&gt;To answer my own question:&lt;/p&gt;&#xA;&lt;p&gt;An article titled &amp;quot;The FT4 and FT8 Communications Protocols&amp;quot;, by S. Franke K9AN, B. Sommerville G4WJS, and J. Taylor K1JT, in &lt;a href=&quot;http://www.arrl.org/files/file/QEX_Next_Issue/July-August2020/TOFC.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;the July/August 2020 edition of QEX magazine&lt;/a&gt;, published by the ARRL, appears to be a (nearly?) complete (textual, not code!) specification of the FT8 protocol, including data formatting, forward error correction, framing, and waveform modulation descriptions.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2020-07-10T03:11:22.930" LastActivityDate="2020-07-10T03:11:22.930" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16876" PostTypeId="1" CreationDate="2020-06-20T08:51:30.313" Score="2" ViewCount="289" Body="&lt;p&gt;&lt;strong&gt;Important note:&lt;/strong&gt; After consulting another source, I learned that the article calls for the first pair of opposing dipoles to be fed &lt;em&gt;in phase&lt;/em&gt;, with the second pair fed &lt;em&gt;in quadrature&lt;/em&gt; to the first pair (but in phase with each other). Sadly, the results are the same, so I still don't know what's wrong with the model.&lt;/p&gt;&#xA;&lt;p&gt;An &lt;a href=&quot;https://ham.stackexchange.com/questions/16850/double-cross-dipole-antenna-for-437-mhz-dont-tune&quot;&gt;earlier question&lt;/a&gt; asked about the tuning of the four dipoles that comprise the &lt;a href=&quot;https://drive.google.com/file/d/0B1q-psxlp3IwamN0VFZORmw3UjQ/view?usp=sharing&quot; rel=&quot;nofollow noreferrer&quot;&gt;&amp;quot;Double Cross&amp;quot;&lt;/a&gt; antenna, intended for hemispherical reception of satellite signals:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7KEBK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7KEBK.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;While attempting to respond to the question, I found that I was unable to reproduce the free-space radiation pattern claimed in the article:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8525g.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8525g.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Using the dimensions specified in the article for 435-MHz:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3Q8dA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3Q8dA.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I constructed a free-space NEC-2 model with increases in source phase of &lt;span class=&quot;math-container&quot;&gt;$90^o$&lt;/span&gt; proceeding around the circle of elements. I obtained these results with the elements tilted &lt;span class=&quot;math-container&quot;&gt;$45^o$&lt;/span&gt; from the vertical:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0PYma.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0PYma.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;lightbulb&amp;quot; shaped pattern is clearly not what the author intended, although the impedance at the feedpoint of each dipole seems to approach the author's goal, re:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The input impedance of each of the λ/2 dipoles when configured as&#xA;shown will be very close to 50 Ω. Each pair is wired in series to have&#xA;an impedance of 100 Ω. After connecting the two pairs in parallel, as&#xA;shown in the harness diagram of Figure 9, we end up with the desired&#xA;50 Ω for the run to the radio.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Tilting the elements more toward the vertical reduces the &amp;quot;lightbulb&amp;quot; shape of the pattern, but approximately halves each dipole's feedpoint impedance:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UFoAO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UFoAO.png&quot; alt=&quot;![enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Can anyone clue me in to what I have done wrong in the model?&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-06-22T11:31:32.653" LastActivityDate="2020-06-22T13:47:31.683" Title="Double Cross antenna: what's wrong with my model?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16877" PostTypeId="2" ParentId="14629" CreationDate="2020-06-20T21:48:29.020" Score="2" Body="&lt;p&gt;If the diameter of the glass base (just above the metal mounting bracket) is approx 5 &amp;quot;, its a type 5948 or 5948A, If the diameter o the glass base( just above the metal mounting ring) is apprx 7&amp;quot;, its a type 1247. Both tubes are pulse modulators for radar with built in hydrogen replenishment.So they are nothing more than a high power switch. The 5948 will switch 12 Mw and the 1247 will switch 30Mw. Certainly the latter will generate x-rays with 30KV on the plate. They are of no use in amateur service. The filament of the 1247 takes 5V @40amps.pretty costly transformer for playing. I can tell you the filament is highly shielded and you can't see it when the filamen is lit.&#xA;Technical specs for the 1247 are contained in the February 1953 edition of &amp;quot;Electronics&amp;quot;magazine.&lt;/p&gt;&#xA;" OwnerUserId="17276" LastActivityDate="2020-06-20T21:48:29.020" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16880" PostTypeId="2" ParentId="16876" CreationDate="2020-06-21T20:02:29.830" Score="1" Body="&lt;p&gt;This is as close to an answer as I'll be able to give:&lt;/p&gt;&#xA;&lt;p&gt;I simulated the &lt;a href=&quot;https://www.qsl.net/5/5b4az//pkg/nec2/examples/2m_Lindenblad.nec&quot; rel=&quot;nofollow noreferrer&quot;&gt;Lindenblad 2m&lt;/a&gt; antenna (which should scale, &lt;em&gt;right&lt;/em&gt;?) that came with the xnec2c examples.&lt;/p&gt;&#xA;&lt;p&gt;view from side&#xA;&lt;a href=&quot;https://i.stack.imgur.com/kne9Z.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kne9Z.png&quot; alt=&quot;radiation pattern side view lindenblad 2m antenna&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;view from top&#xA;&lt;a href=&quot;https://i.stack.imgur.com/jAAQR.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jAAQR.png&quot; alt=&quot;radiation pattern top view Lindenblad 2m antenna&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;In conclusion: yeah, in my simulation, things are symmetrical, as promised for the 30° slant.&lt;/p&gt;&#xA;&lt;p&gt;So, Martes' design seems to stand out pretty singularly, and simulation can't seem to reproduce it: Hm. Maybe it's plain wrong, maybe the description doesn't really match what he did, maybe we're too stupid to do it right. Hm.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Double Cross antenna: what's wrong with my model?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;nothing, maybe.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-21T20:02:29.830" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16881" PostTypeId="2" ParentId="16876" CreationDate="2020-06-22T07:59:03.267" Score="2" Body="&lt;p&gt;From the Answer of Marcus Müller: &lt;em&gt;I simulated the Lindenblad 2m antenna (which should scale, right?) that came with the xnec2c examples. ...&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;The &lt;strong&gt;unedited&lt;/strong&gt; *.nec file included in Marcus' answer was downloaded into 4nec2 and analyzed using the NEC4.2 Engine — which produced the graphic shown below.  Two items of interest appeared...&lt;/p&gt;&#xA;&lt;p&gt;(1) The az/el radiation patterns are ~perfectly circular, but h-pol gain in the horizontal plane is about 5 dB less than v-pol gain.  This means that the axial ratio of its net radiation pattern is not unity.&lt;/p&gt;&#xA;&lt;p&gt;(2)  The calculated feedpoint terminal impedance (outlined in red) does not provide a good match to a 50 Ω source connected to it.&lt;/p&gt;&#xA;&lt;p&gt;Some refinement of the geometry of this design might be worth pursuing before such a wire model is actually constructed.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/l06zF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/l06zF.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-06-22T13:47:31.683" LastActivityDate="2020-06-22T13:47:31.683" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16883" PostTypeId="2" ParentId="16856" CreationDate="2020-06-22T15:17:17.530" Score="5" Body="&lt;p&gt;All radio signals are polarized. You can't &lt;em&gt;not&lt;/em&gt; polarize an HF signal.&lt;/p&gt;&#xA;&lt;p&gt;The problem with HF is often we're considering &lt;a href=&quot;https://en.wikipedia.org/wiki/Skywave&quot; rel=&quot;noreferrer&quot;&gt;skywave propagation&lt;/a&gt;, which involves reflections off the ionosphere and ground. Every reflection has the potential to alter the polarization. Furthermore, there are usually many &lt;a href=&quot;https://en.wikipedia.org/wiki/Multipath_propagation&quot; rel=&quot;noreferrer&quot;&gt;possible paths from transmitter to receiver&lt;/a&gt;, involving reflections at different angles and different atmospheric heights. All theses paths happen simultaneously, and they may interfere with each other constructively or destructively.&lt;/p&gt;&#xA;&lt;p&gt;As such, it's not feasible to predict what the polarization will be at the receiver. And worse yet, the ionosphere consists of gasses moving all the time, so the conditions are changing every second. So at any given time, there is an optimal polarization for the receiving antenna, but:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;it's not feasible to predict what it will be, and&lt;/li&gt;&#xA;&lt;li&gt;every few seconds the polarization may change.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Consequently, if you can pick only one polarization, it doesn't really matter what you pick. Sometimes it will be the right one, and sometimes it will be the wrong one, and one must simply deal with the consequent variable fading of the signal.&lt;/p&gt;&#xA;&lt;p&gt;Alternatively, it's possible to set up two antennas with orthogonal polarization, and then dynamically pick the best one in the moment. This is called &lt;a href=&quot;https://en.wikipedia.org/wiki/Diversity_scheme&quot; rel=&quot;noreferrer&quot;&gt;polarization diversity&lt;/a&gt;. While this is common practice in all kinds of modern communication (cell phones, WiFi, military communications) it's not so common for amateurs. &lt;a href=&quot;http://www.lz1aq.signacor.com/docs/antenna-performance/switching-technique-compare-receiving-antenna-performance.htm&quot; rel=&quot;noreferrer&quot;&gt;LZ1AQ has some nice demonstrations&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-22T15:17:17.530" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16887" PostTypeId="2" ParentId="16874" CreationDate="2020-06-23T23:17:43.993" Score="2" Body="&lt;p&gt;The short answer is yes, a theoretical, ideal, resonant dipole has no reactance.  This statement break down at the ends of the dipole because there cannot be any current at and beyond the wire end.&lt;/p&gt;&#xA;&lt;p&gt;In practice, a dipole has distributed resistance, capacitance and inductance due to material properties, physical dimensions and the environment (e.g. height above ground).&lt;/p&gt;&#xA;&lt;p&gt;The link you provided actually does have the answer to your question if you study the graph carefully.  I.e. reactance is close to zero up to approx 1/8 of a WL from the center.  This can be used to T-match a dipole to a 300Ω or 450Ω balanced feed line.&lt;/p&gt;&#xA;&lt;p&gt;Note that if you asymmetrically feed a 0.5 WL antenna (i.e. not in the center) then you no longer have a resonant dipole and on the longer section a phase reversal will occur.&lt;/p&gt;&#xA;&lt;p&gt;More information: &lt;a href=&quot;https://www.electronics-notes.com/articles/antennas-propagation/dipole-antenna/dipole-feed-matching.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;dipole feed matching&lt;/a&gt; and with a bit more theory: &lt;a href=&quot;https://www.ece.mcmaster.ca/faculty/nikolova/antenna_dload/current_lectures/L11_Match.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Practical Dipole/Monopole Geometries. Matching Techniques for Dipole/Monopole Feeds&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17284" LastEditorUserId="13450" LastEditDate="2020-06-24T00:47:54.890" LastActivityDate="2020-06-24T00:47:54.890" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16888" PostTypeId="1" CreationDate="2020-06-24T17:21:17.873" Score="1" ViewCount="116" Body="&lt;p&gt;I read this antenna theory statement &lt;a href=&quot;https://ham.stackexchange.com/a/16689/1362&quot;&gt;somewhere&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;And, for next-step or future thoughts: &lt;strong&gt;a receiving antenna can be as small as you can imagine, without loss of signal to noise.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Is this BS or not?&lt;/p&gt;&#xA;" OwnerUserId="17230" LastEditorUserId="1362" LastEditDate="2020-06-25T17:32:59.033" LastActivityDate="2020-06-25T17:32:59.033" Title="Can a receiving antenna really be &quot;as small as you can imagine&quot;?" Tags="&lt;antenna&gt;&lt;theory&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16889" PostTypeId="2" ParentId="16888" CreationDate="2020-06-24T18:00:21.190" Score="0" Body="&lt;p&gt;Yes (No BS).&lt;/p&gt;&#xA;&lt;p&gt;Transmitter antenna without loss, think of a black box that has coax input and in the box is a loss-free antenna. There is no dissipation; all the power is converted into EM-field that is radiated. A directivity pattern can be measured.&lt;/p&gt;&#xA;&lt;p&gt;---&amp;gt; From reciprocity, or passive two-port theory: that same antenna used as reception antenna converts the received EM-field into available power, in your feedline to the receiver. Same assumption: loss-free matching!&lt;/p&gt;&#xA;&lt;p&gt;Of course there is a practical limitation. A small antenna can't be matched without losses. As soon as the size is below 10 % of the wavelength, the losses explode almost. Also the bandwidth of the matching network is narrow-band for smaller antennas.&lt;/p&gt;&#xA;&lt;p&gt;Mentioned is a receiver antenna:&#xA;Power loss is very important for transmission. For reception however some loss is acceptable since received noise can (LF, SW) be stronger than the thermal noise from the losses. Radiation resistance apparent temperature is thousands or even million degrees Kelvin. Losses in a matching unit are at room temperature.&lt;/p&gt;&#xA;&lt;p&gt;Brightnoise, PA0FSB&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2020-06-24T21:40:30.097" LastActivityDate="2020-06-24T21:40:30.097" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16891" PostTypeId="1" CreationDate="2020-06-24T18:59:00.560" Score="2" ViewCount="80" Body="&lt;p&gt;My license is set to expire in a couple of days. I know there is a grace period but I'd like to know if I were to take an exam &lt;em&gt;after&lt;/em&gt; the grace period I would be reassigned the same callsign or a new one?&lt;/p&gt;&#xA;" OwnerUserId="16578" LastEditorUserId="4076" LastEditDate="2020-06-25T18:47:30.863" LastActivityDate="2020-06-25T18:47:30.863" Title="Would the same callsign be issued after a license has fully lasped?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16892" PostTypeId="2" ParentId="16888" CreationDate="2020-06-24T19:15:50.513" Score="3" Body="&lt;p&gt;Mostly true, with a number of significant practical caveats.&lt;/p&gt;&#xA;&lt;p&gt;The problem with making an antenna small is that it becomes inefficient. But for receiving this may not be a problem, as antenna inefficiency attenuates signal as well as noise. It is the ratio of signal to noise, not simply signal power, that determines if reception is successful or not.&lt;/p&gt;&#xA;&lt;p&gt;However, as the antenna becomes less efficient it adds thermal noise. Consider the limiting case of inefficient antennas: the dummy load. A 50 ohm dummy load produces thermal noise equivalent to a 50 ohm resistor, because it &lt;em&gt;is&lt;/em&gt; a 50 ohm resistor. An ideal, 100% efficient antenna produces no thermal noise at all. An inefficient antenna is somewhere between.&lt;/p&gt;&#xA;&lt;p&gt;This may not matter. On HF, the ambient thermal noise is very high, and the worst-case thermal noise of a dummy load is utterly irrelevant when compared to the ambient RF noise the antenna will pick up regardless.&lt;/p&gt;&#xA;&lt;p&gt;At the other extreme, for a deep-space antenna this would be terrible. The antenna is pointed into space where the ambient noise is orders of magnitude lower, and these antennas tend to utilize cryogenically cooled LNAs. Adding thermal noise would significantly raise the noise floor of the antenna system.&lt;/p&gt;&#xA;&lt;p&gt;For further reading, see &lt;a href=&quot;https://ham.stackexchange.com/q/9832/218&quot;&gt;How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Additionally, in practice any very small antenna is going to require matching components and/or active circuitry to extract any useful signal from it. This additional circuitry will add noise and nonlinear distortion. It's possible to make receiving antennas pretty small and still get good performance. But there is a point where the antenna becomes so small that the engineering challenges become impractical.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-24T19:15:50.513" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16895" PostTypeId="2" ParentId="16888" CreationDate="2020-06-25T01:05:22.783" Score="0" Body="&lt;p&gt;True only if you do not want to detect or receive the signal.&lt;/p&gt;&#xA;&lt;p&gt;Any physically realizable (e.g. made out of atoms) feedline, passive network, or receiver input connected to the antenna will add thermal and quantum noise, which can overwhelm a small enough signal from even a perfect noiseless source (theoretic infinitesimal antenna).&lt;/p&gt;&#xA;&lt;p&gt;At that point there will exist quantum uncertainty about whether an RF photon even existed in the vicinity of the antenna within the reception timeframe.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-06-25T01:12:03.487" LastActivityDate="2020-06-25T01:12:03.487" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16896" PostTypeId="2" ParentId="16891" CreationDate="2020-06-25T03:10:19.603" Score="8" Body="&lt;p&gt;The grace period is two years.&lt;/p&gt;&#xA;&lt;p&gt;You can renew your license within the grace period, but after that, the call sign will be available for reassignment.&lt;/p&gt;&#xA;&lt;p&gt;If you were to take and pass an exam after the grace period, you would be assigned a new call sign. However, if at that time, your old call sign is still available, you would be able to apply for it as a vanity call.&lt;/p&gt;&#xA;&lt;p&gt;There are certainly no guarantees, but if your old call sign was an automatically-assigned one, and not, say, a desirable 1x2 or 2x1, it will likely still be available for quite some time.&lt;/p&gt;&#xA;&lt;p&gt;Just as an example, my father-in-law passed away in 1990 and no-one notified the FCC, so the license expired &amp;quot;naturally&amp;quot; in 1998. About a year ago (2019) when I got my General license, his old call sign was still available, approx. 21 years after it expired, so I applied for his call sign, and got it.&lt;/p&gt;&#xA;" OwnerUserId="14463" LastActivityDate="2020-06-25T03:10:19.603" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16897" PostTypeId="2" ParentId="9777" CreationDate="2020-06-25T13:36:38.477" Score="0" Body="&lt;p&gt;A 283Ft circumference horizontal wire loop, fed with 60Ft of 300 ohm ladder line straight into a balanced atu probably would. Such an antenna would work on several bands and present low receive noise. Limits of real estate could make this impractical for domestic use, but field days would be a brilliant test scenario. Aim for a height above ground of 20Ft or more. The upper HF bands will have progressively lower and lower angles of radiation. Notably, 10 metres would produce a daisy petal radiation pattern of almost horizon kissing low angle, ideal for Dx. 80metres (fundamental design freq) 500 miles with ease at night with a balloon shaped pattern overhead. Forty metre radiation would produce a two balloons shape (held together at their necks) rather more like a dipole would. Keep the wire loop as open a shape as possible, ideally a square, although a triangle would still work. Just avoid the letter box slot shape. I can assure readers that this will work brilliantly in the category of &amp;quot;100 watts and a wire.&amp;quot; It is easy to make and doesn't break the bank !  For the mathematicians out there, the single band formula for a full wave loop (copper wire) is 1005/f MHz, where 'f' is the frequency in Megahertz and the answer is in Feet. This holds good up to uhf! Have fun, Mike, G4HOL / EA7JVZ&lt;/p&gt;&#xA;" OwnerUserId="17292" LastActivityDate="2020-06-25T13:36:38.477" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16898" PostTypeId="1" AcceptedAnswerId="16901" CreationDate="2020-06-25T23:21:59.590" Score="3" ViewCount="666" Body="&lt;p&gt;I read &lt;a href=&quot;https://ham.stackexchange.com/questions/16856/long-range-hf-polarization/16883?noredirect=1#comment27630_16883&quot;&gt;in a comment&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;it doesn't matter which circular polarization you choose, because they are both present, and the whole point here is to select one of them instead of receiving both and getting mixing.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The premise of the point being made seems to be that an HF signal received after making a pass or passes through the ionosphere will be &lt;em&gt;both&lt;/em&gt; left-hand and right-hand circularly polarized, and so a receiving antenna of either chirality will not be subject to fading as a linearly polarized antenna would be.&lt;/p&gt;&#xA;&lt;p&gt;Is this possible, for a signal to be &lt;em&gt;both&lt;/em&gt; left- and right-hand polarized?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-26T22:29:12.993" Title="Can left-hand and right-hand circular polarizations exist at the same time?" Tags="&lt;circular-polarization&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16899" PostTypeId="2" ParentId="16898" CreationDate="2020-06-25T23:21:59.590" Score="4" Body="&lt;p&gt;No, it's not possible. The electric field vector can only point in one direction at a time, so there's no way it could simultaneously rotate in two directions.&lt;/p&gt;&#xA;&lt;p&gt;However it is possible to consider any possible polarization as a &lt;a href=&quot;https://en.wikipedia.org/wiki/Superposition_principle&quot; rel=&quot;nofollow noreferrer&quot;&gt;superposition&lt;/a&gt; of left- and right-handed circular polarization.&lt;/p&gt;&#xA;&lt;p&gt;When there are multiple radiation sources, either because there are multiple transmitters or because the same signal is being received through multiple paths, then the result at the receiver is the addition of each source. Adding two circular polarizations of opposite chirality together produces a linear polarization.&lt;/p&gt;&#xA;&lt;p&gt;This can be shown graphically as a 3D parametric plot:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/c9EK0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/c9EK0.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;br&gt;&#xA;(&lt;a href=&quot;https://christopherchudzicki.github.io/MathBox-Demos/parametric_curves_3D.html?settings=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&quot; rel=&quot;nofollow noreferrer&quot;&gt;editable source&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;On the left in yellow, we have:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;\left\{&#xA;\begin{aligned} &#xA;x(t) &amp;amp;= \cos(t) \\ &#xA;y(t) &amp;amp;= \sin(t)&#xA;\end{aligned} &#xA;\right. &#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;On the right in blue we have:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;\left\{&#xA;\begin{aligned} &#xA;x(t) &amp;amp;= -\cos(t) \\ &#xA;y(t) &amp;amp;= \sin(t)&#xA;\end{aligned} &#xA;\right. &#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;And the middle in green is the addition of these two:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;\left\{&#xA;\begin{aligned} &#xA;x(t) &amp;amp;= \cos(t) - \cos(t) \\ &#xA;y(t) &amp;amp;= \sin(t) + \sin(t)&#xA;\end{aligned} &#xA;\right. &#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;It's pretty plain to see this simplifies to &lt;span class=&quot;math-container&quot;&gt;$x(t) = 0$&lt;/span&gt; as the opposite electric fields along the x axis cancel each other.&lt;/p&gt;&#xA;&lt;p&gt;As the two sources change in relative phase, the plane of the resulting linear polarization rotates:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DANQy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DANQy.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;br&gt;&#xA;(&lt;a href=&quot;https://christopherchudzicki.github.io/MathBox-Demos/parametric_curves_3D.html?settings=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&quot; rel=&quot;nofollow noreferrer&quot;&gt;editable source&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;Here, green is showing&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;\left\{&#xA;\begin{aligned} &#xA;x(t) &amp;amp;= \cos(t+2) - \cos(t) \\ &#xA;y(t) &amp;amp;= \sin(t+2) + \sin(t)&#xA;\end{aligned} &#xA;\right. &#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;While it's not so immediately obvious to see the cancellation, it remains true that opposite helices like this will cancel each other in &lt;em&gt;some&lt;/em&gt; plane, as long as they are equal in amplitude.&lt;/p&gt;&#xA;&lt;p&gt;If the two sources are not equal in amplitude, then the result is elliptical polarization:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cb96w.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cb96w.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;br&gt;&#xA;(&lt;a href=&quot;https://christopherchudzicki.github.io/MathBox-Demos/parametric_curves_3D.html?settings=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&quot; rel=&quot;nofollow noreferrer&quot;&gt;editable source&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;It is true that the ionosphere is time-variant, and so at one time the signal as received may be left-handed, and some time later right-handed. But is impossible for it to be &lt;em&gt;both at the same time&lt;/em&gt;, although one could consider a linear polarization to be the superposition of both circular polarizations in equal amplitude.&lt;/p&gt;&#xA;&lt;p&gt;The problem is an ionospheric channel does not guarantee equal amplitude. Thus, a circularly polarized receive antenna will still be subject to fading as the signal randomly wanders between left- and right-handed chirality, as well as linear and all the points between (elliptical polarizations).&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-06-26T15:35:49.637" LastActivityDate="2020-06-26T15:35:49.637" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="16901" PostTypeId="2" ParentId="16898" CreationDate="2020-06-26T12:14:05.817" Score="3" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Is this possible, for a signal to be both left- and right-hand polarized?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes, it's very much possible:&lt;/p&gt;&#xA;&lt;p&gt;While the superposition of two orthogonal circular polarizations might¹ indeed look linear (just as the superposition of a horizontal and a vertical polarized wave at appropriate phasing is a circularly polarized wave), of course that means that a linearly polarized wave is at the same time circularly polarized in both directions.&lt;/p&gt;&#xA;&lt;p&gt;Technically, this is widely exploited: Satellite receivers use polarization multiplex. That is awesome, because you get two totally independently useful &amp;quot;subchannels&amp;quot;, as long all media the wave travels through is a largely a linear medium and isotropic. (And the microwave frequencies geostationary satellite downlink channel fulfills that pretty well.)&lt;/p&gt;&#xA;&lt;p&gt;Even if that's not the case, you still get &lt;em&gt;some&lt;/em&gt; isolation between RHCP and LHCP, and can use that for MIMO techniques to increase your data rate or robustness beyond what you can do on a single polarization.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;¹ might because that's not necessarily the case. Remember the Poincaré sphere: &#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Poincaresp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/thumb/a/a7/Poincaresp.png/512px-Poincaresp.png&quot; alt=&quot;2128506 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;When you add waves of different polarizations, you wander on the surface of that sphere; only when you add RHCP and LHCP with the same magnitude, you end up with a linear polarization. The angle of that is then defined by the phase between the two constituent waves; every other combination, every attenuation that affects one rotational sense more than the other, will produce an elliptic polarization.&lt;/p&gt;&#xA;&lt;p&gt;Let me rephrase your question:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Is this possible, for a &lt;em&gt;wave&lt;/em&gt; to be both left- and right-hand polarized at the same time?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;No, that's not possible, because any wave can only occupy &lt;strong&gt;one&lt;/strong&gt; point in polarization space.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-06-26T22:29:12.993" LastActivityDate="2020-06-26T22:29:12.993" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16903" PostTypeId="1" CreationDate="2020-06-26T16:13:43.187" Score="3" ViewCount="200" Body="&lt;p&gt;Consider the common scenario of two amateur radio operators communicating through an ionospheric channel. Typically, each station will have a linearly polarized antenna, like a dipole or a vertical. I understand that the ionosphere will randomize the wave's polarization over time, and so there will be some time-variant fading as the polarization changes.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.lz1aq.signacor.com/docs/antenna-performance/switching-technique-compare-receiving-antenna-performance.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;LZ1AQ has some nice demonstrations of this&lt;/a&gt;, where the receiver is switched between horizontally and vertically polarized antennas. The difference between the two polarizations is sometimes as great as 20 dB, and the best choice of polarization varies over time. It would then follow that in the typical situation where the receiver has only one antenna to choose from, fades as deep as 20 dB would be experienced.&lt;/p&gt;&#xA;&lt;p&gt;Now say the receiving antenna is circularly polarized while the transmitting antenna remains unchanged. Does this eliminate fading due to polarization mismatch?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-27T18:42:56.940" Title="Are circular polarized antennas on HF subject to polarization fading?" Tags="&lt;hf&gt;&lt;polarization&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16904" PostTypeId="2" ParentId="16903" CreationDate="2020-06-26T21:19:15.570" Score="3" Body="&lt;p&gt;This question is &lt;em&gt;on point&lt;/em&gt;. Let me make a quick excursion on how we physically model the rotating effect that the ionosphere has on linear polarizations.&lt;/p&gt;&#xA;&lt;p&gt;You have &lt;a href=&quot;https://ham.stackexchange.com/a/16899/4076&quot;&gt;elegantly shown&lt;/a&gt; in a previous answer that you can decompose any linearly polarized wave into two orthogonal circularly polarized ones of equal magnitude.&lt;/p&gt;&#xA;&lt;p&gt;And that's exactly how we describe the &lt;em&gt;Faraday effect&lt;/em&gt; in the ionosphere.&lt;/p&gt;&#xA;&lt;p&gt;A ionosphere is a plasma, i.e. there's a lot of unboond charged particles floating around relatively freely, swinging around some drifting places, doing nothing inherently very specific. A charged particle moving about is essentially an electric current – and that causes a magnetic field. But, when these movements are random, all these magnetic fields just cancel and there's no net magnetic field.&lt;br&gt;&#xA;Now, the earth's ionosphere is a bit special, because there's the earth magnetic field applied to it. That forces ions to move in circles, in a plane perpendicular to the magnetic field lines. Imagine a copper ring in which a current flows around – it will align exactly that the induced electromagnet's north pole points in the south pole &amp;quot;direction&amp;quot; of the field lines.&lt;/p&gt;&#xA;&lt;p&gt;Back to our circularly polarized &amp;quot;composite&amp;quot; wave: When that wave travels in parallel to the field lines, the direction of the E-field of the circularly wave rotates at the wave's frequency. That in turn exerts a force on charged particles.&lt;/p&gt;&#xA;&lt;p&gt;Now comes the interesting part: There's rotational sense that goes well with the circling of the charged particles due to the earth magnetic field, and one that has to work against that. The LHCP wave component of the linear polarization &amp;quot;sees&amp;quot; a different medium than the RHCP one¹! There's one circular polarization which experiences a higher refractive index than the other, so they don't travel at the same speed.&lt;/p&gt;&#xA;&lt;p&gt;Thus, the phase between RHCP and LHCP changes over distance; since the phase defines the angle of the linearly polarized sum wave, that wave experiences &lt;em&gt;Faraday Rotation&lt;/em&gt;².&lt;/p&gt;&#xA;&lt;p&gt;That would mean that the magnitude of what a circularly polarized receive antenna could pick up wouldn't ever change.&lt;/p&gt;&#xA;&lt;p&gt;However, on HF, we don't see pure linear polarizations, but more elliptic ones, too. I must admit I'm not 100% sure how that physically happens - it has got to have something to do with a different attenuation for the two circular polarizations, because an elliptic polarization can be modeled as the sum of RHCP and LHCP with &lt;em&gt;different&lt;/em&gt; magnitudes (and the angle of the main axis still defined as the phase between these two).&lt;/p&gt;&#xA;&lt;p&gt;No matter &lt;em&gt;where&lt;/em&gt; that comes from, it means that one circular polarization doesn't come through as well as the other. The more the ellipse looks like a circle, the less the opposing rotational sense circular polarization is present. So, concluding:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Are circular polarized antennas on HF subject to polarization fading?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes, but only as far as one can observe elliptic polarizations.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Now say the receiving antenna is circularly polarized while the transmitting antenna remains unchanged. Does this eliminate fading due to polarization mismatch?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Not completely, because of the above reason.&lt;/p&gt;&#xA;&lt;p&gt;I don't know anything from experience to recommend, but consider this: If you build two compact linearly polarized receive antennas, and mount them perpendicularly, then you can combine them with a phase shifter and variable attenuators to find the optimum polarization.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;¹ Please don't ask me which is which,  I'll have to throw strange gang signs with my hands and put my head at unhealthy angles, cry a bit and then start over to remember my microwave engineering classes in such detail.&#xA;&lt;p&gt;² By the way, we do the same in small scale using magnetic materials in waveguides to change polarizations. And because feeds can be made polarization-selective, and because we can switch magnetic fields on and off, that's a way to build a high-power microwave switch without moving parts.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-26T21:19:15.570" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16905" PostTypeId="1" AcceptedAnswerId="16908" CreationDate="2020-06-26T22:24:45.787" Score="10" ViewCount="1852" Body="&lt;p&gt;There are various techniques for locating a radio emitter. But what are some methods to make this really difficult? There is usually a patch to every vulnerability, at least from the world where I come from.&lt;/p&gt;&#xA;" OwnerUserId="17297" LastEditorUserId="17297" LastEditDate="2020-06-27T11:45:36.233" LastActivityDate="2020-06-29T14:50:08.233" Title="Non-traceable radio emitters" Tags="&lt;propagation&gt;&lt;fox-hunt&gt;&lt;location&gt;" AnswerCount="5" CommentCount="12" FavoriteCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16906" PostTypeId="2" ParentId="16905" CreationDate="2020-06-26T23:58:16.553" Score="4" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;at least in the world where I come from&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Assuming this is the world of arrogant computer security experts (sorry I'm a bit allergic to this):&lt;/p&gt;&#xA;&lt;p&gt;Well, unlike computers, physics wasn't designed by humans.&lt;/p&gt;&#xA;&lt;p&gt;So, any signal that contains significant information needs to contain significant power (that's a direct result of Shannon capacity), and if it has significant power, it's also localizable.&lt;/p&gt;&#xA;&lt;p&gt;Of course, localization resolution is proportional to wavelength. But, so are antennas. So, while you can not be very sure from where an extremely low frequency (ELF, typically used for communication to submerged submarines) transmission came from, but once you look at an aerial picture, you will notice the 500 km long antenna in the Russian forest...&lt;/p&gt;&#xA;&lt;p&gt;Rodrigo recommended &amp;quot;Burst transmission&amp;quot;, but that's really no solution. If I can detect it as anything but noise with a high probability with multiple receivers, then I can also localize it. This is done, and has been done, since the 1970s for bursty military transmissions in HF bands (because they reach very far on earth). For higher frequency signals, you really don't need state actor equipment: a two- or better four-channel MIMO receiver allows you to put an unambiguous direction on where a signal came from. Use two of these, and you know where a transmission came from. In fact, a transmission being a very short burst implies a high bandwidth, and that is &lt;em&gt;good&lt;/em&gt; for location accuracy. (You need good SNR for low estimator variance, on the other hand, so there &lt;em&gt;are&lt;/em&gt; limits. It's just not as easy as &amp;quot;use a bursty transmission scheme&amp;quot;.)&lt;/p&gt;&#xA;&lt;p&gt;So, your only choice is to make a signal that someone can't detect as being anything but noise, not even if he correlates multiple observations. Sadly, such signals have practically no information content.&lt;/p&gt;&#xA;&lt;p&gt;The only thing you can do is hope that you find a part of the spectrum where the propagation properties are so random, and so different in different directions, that the probability of simultaneous detection at multiple points approaches zero. Good luck with that; in essence, that channel would have what is called a &amp;quot;secrecy rate&amp;quot; in physical layer security research (i.e. an observation of one channel doesn't give you all the bits of information in the entropy of a different channel), and we're talking about secrecy rates of &amp;lt; 100 bits per minute for indoor channels. That is an upper bound for how much information you could send there, without giving away information about the channel, and thus your location.&lt;/p&gt;&#xA;&lt;p&gt;TL;DR: Nope.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-06-27T00:20:59.277" LastActivityDate="2020-06-27T00:20:59.277" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16907" PostTypeId="2" ParentId="16903" CreationDate="2020-06-27T00:50:11.067" Score="1" Body="&lt;p&gt;It's true that a circularly polarize antenna can mitigate &lt;a href=&quot;https://ham.stackexchange.com/q/768/218&quot;&gt;spin fading&lt;/a&gt; in satellite communications. This works because a linear wave is always received by a circular antenna at a uniform 3 dB loss. They are a couple equivalent ways to explain it:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;A linearly polarized wave is a &lt;a href=&quot;https://ham.stackexchange.com/q/16898/218&quot;&gt;superposition of left- and right-hand circularly polarized waves&lt;/a&gt;, in equal amplitude. Thus, any circularly polarized antenna will receive half the signal power, regardless of the polarization angle. Half power is a 3 dB loss.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A circularly polarized antenna consists of a horizontal component and a vertical component. Say the incoming wave is vertically polarized: it will be received by the vertical component of the receiving antenna but not the horizontal component (which will receive only noise), thus a 3 dB loss. Likewise if the incoming wave is horizontally polarized. And it can be shown with a bit of trigonometry that for polarization angles between horizontal and vertical, the coupling is still -3 dB.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Underpinning each of these explanations is the fact that any possible polarization of a wave propagating in a particular direction can be expressed as the superposition of two orthogonal polarizations of specified amplitude and phase. Horizontal/vertical is one possible orthogonal pair, though any two angles separated by 90 degrees will do. Left- and right-hand circular polarizations will also do. There are also orthogonal pairs of elliptical polarizations. In general, any two points on opposite sides of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Polarization_(waves)#Poincar%C3%A9_sphere&quot; rel=&quot;nofollow noreferrer&quot;&gt;Poincaré sphere&lt;/a&gt; will do.&lt;/p&gt;&#xA;&lt;p&gt;Any possible receive antenna will have some polarization that can be represented by some point on the Poincaré sphere. As such, any incoming wave can be considered the superposition of two components:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the polarization that matches the antenna, and&lt;/li&gt;&#xA;&lt;li&gt;the orthogonal point opposite the antenna's polarization.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;At any given time, some percentage of the available signal power will fall into the first component, with the remainder in the second component. Polarization fading occurs when a large proportion falls into the second component rather than the first.&lt;/p&gt;&#xA;&lt;p&gt;For example, if the receiving antenna is a horizontal dipole, then the orthogonal polarization is vertical. When the incoming wave is vertically polarized, all of the signal power falls into the orthogonal polarization which is not received by the antenna, and the received signal power is zero.&lt;/p&gt;&#xA;&lt;p&gt;Likewise, if the receiving antenna is right-hand circularly polarized, then polarization fading will occur when the incoming wave is close to left-hand circular polarization.&lt;/p&gt;&#xA;&lt;p&gt;Since any possible antenna will have an orthogonal polarization for which the antenna will receive no energy, the question becomes: is there something about circular polarizations which makes their orthogonal polarization less likely to be observed when receiving a transmission through an ionospheric channel?&lt;/p&gt;&#xA;&lt;p&gt;In general: no. Circular polarization works to mitigate spin fading because the line-of-sight channel over which satellite communications happen preserves polarization. If the satellite transmits a vertical polarization, it will still be a vertical polarization when the wave arrives at the receiver. If the satellite transmits right-hand circular polarization, it will still be right-hand circular polarization at the receiver.&lt;/p&gt;&#xA;&lt;p&gt;This is not generally true in an ionospheric channel. A single path through the ionosphere can display &lt;a href=&quot;https://en.wikipedia.org/wiki/Faraday_effect&quot; rel=&quot;nofollow noreferrer&quot;&gt;Faraday rotation&lt;/a&gt;, which rotates the polarization. But ionospheric paths often exhibit strong &lt;a href=&quot;https://en.wikipedia.org/wiki/Multipath_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;multipath propagation&lt;/a&gt; as the transmitted wave reflects off multiple layers of the ionosphere at different heights. Each possible path can exhibit a different phase delay and rotation.&lt;/p&gt;&#xA;&lt;p&gt;This means an ionospheric channel, unlike a line-of-site channel, can take any polarization from the transmitter, and transform it to any other possible polarization by the time the wave reaches the receiver. For example, an ionospheric channel can transform a vertically polarized wave into a circularly polarized one by having two paths which differ in length by 90 degrees, with one having a 90 degree greater rotation than the other.&lt;/p&gt;&#xA;&lt;p&gt;Not all paths are as bad as others: NVIS paths are relatively mild, and may preserve linear polarization well enough that circularly polarized antennas are still of some use to mitigate fading. Multipath interference becomes more severe as the path becomes more oblique, and as more skips are added.&lt;/p&gt;&#xA;&lt;p&gt;The ionosphere is in motion, so the polarization of the wave when it arrives at the receiver changes over time. In general, the polarization of the received wave will be a random point on the Poincaré sphere: it could be vertical, horizontal, right-hand circular, left-hand circular, or any of the many possible elliptical polarizations that lie between these points on the Poincaré sphere.&lt;/p&gt;&#xA;&lt;p&gt;Because the polarization of the received wave is random and time-variant, there is no possible single antenna which will mitigate polarization fading on ionospheric paths that exhibit significant multipath propagation.&lt;/p&gt;&#xA;&lt;p&gt;There is however a solution: if the receiver is allowed two antennas of orthogonal polarization, there always exists some combination of these antennas that precisely matches the incoming wave. A simple approach is to switch between the antennas and select the one with the better signal-to-noise ratio: this limits polarization fading to no more than -3dB. Slightly better but more complex to implement is to combine the two antennas by dynamically determined complex coefficients which can effectively move the antenna to any point on the Poincaré sphere to match the polarization of the incoming wave: this eliminates polarization fading entirely (or at least to the extent the algorithm is accurate)&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;As has been &lt;a href=&quot;https://ham.stackexchange.com/questions/16898/can-left-hand-and-right-hand-circular-polarizations-exist-at-the-same-time/16900?noredirect=1#comment27702_16900&quot;&gt;rightly pointed out&lt;/a&gt;, this theoretical explanation doesn't matter if experimental evidence doesn't agree.&lt;/p&gt;&#xA;&lt;p&gt;The most pro-circular evidence I could find is &lt;a href=&quot;https://k9la.us/Dec15_Circular_Polarization_-_Is_It_Worth_the_Effort.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;a paper by Drew Schoen O'Shaughnessy of the Worcester Polytechnic Institute&lt;/a&gt;. This paper states:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;From  the  data,  it  is  clear  that  in  many  of  the  test  transmissions  circular  polarization yielded  a  maximum  SNR  improvment  of  approximately  3  dB  over  the  strongest  channel using linear polarization.  A 3 dB improvement is a non-negligible increase in signal strength,which roughly translates to a doubling of the effective range of the HF link.  Although the SNR degradation due to polarization fading could not be measured directly, the tests show that the SNR performance of this link did improve when circular polarization was in use. It  is  unlikely  that  the  differences  in  SNR  between  linear  and  circular  polarization  can  be attributed to something other than polarization fading, given that the only change between them was the polarization of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;Although right hand circular polarization was dominant in these tests, the usage of left hand circular polarization should also be considered.  Given simple phasing methods, it is not  difficult  to  construct  a  ground  based  antenna  system  that  would  allow  for  switching between RHCP and LHCP. If the radios in a hypothetical HF link are operated manually,the operators could choose a polarization based on a test transmission scheme similar to the one used in this experiment.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I'm a little skeptical of the recommendation. The data consist of a limited number of observations over a limited number of paths, and the researcher found &amp;quot;There were several tests where linear polarization was actually stronger than either circular polarization. Circular polarization is not a universal solution for improving signal to noise ratio.&amp;quot; The paper does not appear to be peer reviewed, and there's no analysis of the statistical significance of the results.&lt;/p&gt;&#xA;&lt;p&gt;I also found &lt;a href=&quot;https://k9la.us/Dec15_Circular_Polarization_-_Is_It_Worth_the_Effort.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Circular Polarization – Is It Worth the Effort? by Carl Luetzelschwab K9LA&lt;/a&gt;, which mostly includes anecdotal evidence such as:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I also talked to Woody WW1WW. He has a 6-element crossed-Yagi array at 50 feet on 10-Meters. He brings equal length coaxes from each Yagi into the shack, and can lead or lag either one by 90oto achieve left-hand or right-hand circular polarization. When I talked to him in early 2013,this antenna had been up for only a year and 10-Meter propagation was not great. Thus his observations were somewhat limited. He said he had observed up to 30 dB difference between left-handand right-handpolarization under fading conditions, and it does not seem predictable. He did not offer any comments on the duration of openings or on fading.&lt;/p&gt;&#xA;&lt;p&gt;As for ‘cons’ with circular polarization, the last paragraph highlights the fact that you need to be able to select either left-hand or right-hand circular polarization (which means only one of the characteristic waves may be propagating at any given time)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I suspect switching between vertical and horizontal polarization works just as well as LHCP/RHCP, but given the antenna in either case is the same there's little practical reason to do one or the other. The author of this paper at least seems to have reached the same conclusion as I have: the ability to &lt;em&gt;switch&lt;/em&gt; polarization is necessary, since circularly polarized antennas are still subject to fading.&lt;/p&gt;&#xA;&lt;p&gt;I am finding indirect evidence that some ionospheric paths, especially NVIS paths maintain polarization well enough that circularly polarized antennas may be applicable to reducing fading. Mostly this comes from research on HF MIMO techniques, such as &lt;a href=&quot;http://www.kumasignals.com/wp-content/uploads/2013/08/daniels_peters_heath_milcom2013.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; and &lt;a href=&quot;https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2010RS004416&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;, which find an NVIS path maintains orthogonality well enough to support some MIMO capacity gains. This implies that the polarization is not entirely random.&lt;/p&gt;&#xA;&lt;p&gt;But as the path becomes more oblique things get worse, especially when the path involves multiple hops. For example &lt;a href=&quot;http://www.jpier.org/PIERC/pierc94/09.19042702.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;HF Skywave Polarized MIMO Channels with Oblique One-Hop Paths by Umaisaroh Umaisaroh, Gamantyo Hendrantoro, *, and Varuliantor Dear&lt;/a&gt;, states:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;If an implementation over a local area of up to a 200 km radius is desired, NVIS propagation with almost 90◦ elevation angles can be exploited [12].  However, for wider coverage area, the path of the radio waves should take a slanted elevation angle. In a single-hop radio wave transmission through the ionosphere, the elevation angle varies with the ground range between the transmitter and receiver. As the paths become oblique, the orthogonally polarized horizontal antennas do not appear as orthogonal as in NVIS case for the departing and arriving waves, which cause differences in MIMO capacity. This paper shows that oblique paths reduce the capacity  gain relative to the SISO capacity  due to the decreasing orthogonality between the cross-dipoles.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I can find very little research on MIMO over single-hop paths, and none on multi-hop paths. I suspect it's because the polarization is so well randomized that no useful orthogonality is preserved.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-06-27T18:42:56.940" LastActivityDate="2020-06-27T18:42:56.940" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16908" PostTypeId="2" ParentId="16905" CreationDate="2020-06-27T04:15:17.577" Score="13" Body="&lt;p&gt;IMO, your question is too general to give a good, specific answer.  Also, it would help if you elucidated the motivation for the question.&lt;/p&gt;&#xA;&lt;p&gt;I am a semi-retired electrical engineer, not a security or RF expert but I'll give it a go anyway.&lt;/p&gt;&#xA;&lt;p&gt;The first assumption is that the transmitting equipment is hidden from plain sight and other non radio-related detection.&lt;/p&gt;&#xA;&lt;p&gt;To locate a hidden radio station your adversary must be able to receive the emissions.  It follows that you could use a highly directional (beam) antenna which only illuminates the intended receiver.  There would be no countermeasure.&lt;/p&gt;&#xA;&lt;p&gt;The next possibility is that the signal can be received by your adversary but they do not have direction finding equipment within the footprint of your beam.  This is potentially the case with (older) satellite transponders which simply re-transmit everything they receive in the transponder's pass band.  So, you could beam a signal to such a satellite and as long as the intended receiver is somewhere in the satellite's footprint you can effectively hijack the satellite service (has happened).&lt;/p&gt;&#xA;&lt;p&gt;Now to the cases where your signal can be directly received by your adversary.  AFAIK, there are two basic methods for locating the source of radio signal.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Two or more receivers with steerable, directional antennas (including&#xA;beam-forming phased arrays).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Three or more time synchronized receivers (spectrum analyzers) which&#xA;compare the arrival time of a specific signal at their accurately&#xA;known locations.  At one nano-second time resolution, such a system&#xA;can potentially pinpoint an emission with an accuracy of better&#xA;than 1 meter, even if the signal is only a very short burst.  I know&#xA;that such systems exist and are deployed around sensitive&#xA;infrastructure such as airports.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;To locate an emission your adversary must know what to look for.  That opens up additional possibilities but does not directly relate to your question.&#xA;Anyway, here are two that I can think of:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;A radio could potentially masquerade as valid by adopting the&#xA;frequencies and low-level transmission protocols of a legitimate service.&lt;/li&gt;&#xA;&lt;li&gt;Direct sequence spread spectrum can spread a signal over a bandwidth&#xA;of many MHz and make it appear as undetectable, random noise to a&#xA;narrow band receiver.  Such a signal may go unnoticed for a long&#xA;time.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="17284" LastActivityDate="2020-06-27T04:15:17.577" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16910" PostTypeId="2" ParentId="126" CreationDate="2020-06-27T13:17:33.150" Score="1" Body="&lt;p&gt;Verticals work very well near the sea or salt water lake, your ground radials can be minimal and there is a good 6-10dB uplift in your sent and received signal. This is mainly due to much better ground conductivity and lack of obstructions. The much improved ground conductivity lowers the angle of radiation even more and lowers ground losses considerably.&lt;/p&gt;&#xA;&lt;p&gt;This is backed up by practice and documented in plenty of articles, books and journals. (Look up Naval shore electronics criteria, it's been digitised by Googl)&lt;/p&gt;&#xA;&lt;p&gt;To get close to this on dry land, you'll need plenty of ground radials. Rudy Severns, N6LF has done some very good empirical research on this. He suggests using around 32 radials and they don't have to be 1/4 wavelength.&#xA;Source : &lt;a href=&quot;https://www.antennasbyn6lf.com/design_of_radial_ground_systems/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.antennasbyn6lf.com/design_of_radial_ground_systems/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17300" LastActivityDate="2020-06-27T13:17:33.150" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16913" PostTypeId="2" ParentId="16905" CreationDate="2020-06-27T19:37:15.117" Score="11" Body="&lt;p&gt;Another possibility to look into is meteor burst communication. This is a well-established technology. You beam a VHF signal up into the sky, it bounces off a meteor trail, and your recipient picks up the reflected signal. Since transmission is  upwards, picking up the transmitter's location would require being above the transmitter at the time (making certain assumptions about directionality).&lt;/p&gt;&#xA;&lt;p&gt;There is a short article in &lt;a href=&quot;https://www.nsa.gov/Portals/70/documents/news-features/declassified-documents/cryptologic-quarterly/meteo_burst.pdf&quot; rel=&quot;noreferrer&quot;&gt;NSA Cryptologic Quarterly&lt;/a&gt; and a &lt;a href=&quot;https://apps.dtic.mil/dtic/tr/fulltext/u2/a207831.pdf&quot; rel=&quot;noreferrer&quot;&gt;Navy Postgraduate School thesis&lt;/a&gt; from 1989. An article I have been unable to locate online is: Elliott, Ronald D. &amp;quot;Meteor Burst Communications in Tactical Intelligence Support,&amp;quot; SIGNAL, November 1986, pp. 80-88.&lt;/p&gt;&#xA;&lt;p&gt;Amateurs, it seems, tend to experiment with lower frequencies, which may have implications for directionality: see, for example, &lt;a href=&quot;https://www.electronics-notes.com/articles/ham_radio/amateur-propagation/meteor-scatter-burst-communications.php&quot; rel=&quot;noreferrer&quot;&gt;this page&lt;/a&gt;. The RSGB &lt;a href=&quot;https://rsgb.org/main/technical/propagation/meteor-scatter/&quot; rel=&quot;noreferrer&quot;&gt;also has a page&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;It would be interesting to know if anyone on this forum has had any experience with this. It may be well known.&lt;/p&gt;&#xA;" OwnerUserId="17305" LastActivityDate="2020-06-27T19:37:15.117" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16914" PostTypeId="2" ParentId="16794" CreationDate="2020-06-27T20:19:55.757" Score="1" Body="&lt;p&gt;To add to Phil's answer: if your antenna, source and transmission line (the impedance controlled traces) are all of the same impedance, you don't need an impedance matching circuit. Most common impedance for RF applications is 50 ohms.&lt;/p&gt;&#xA;&lt;p&gt;The impedance matching circuits are only there to connect two systems with a different impedance to each other.&lt;/p&gt;&#xA;&lt;p&gt;Creating impedance matched traces is not necessarily hard to do. Take a look at a page like &lt;a href=&quot;https://www.eeweb.com/tools/symmetric-stripline-impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.eeweb.com/tools/symmetric-stripline-impedance&lt;/a&gt; to calculate which dimensions to use. However, the frequencies you are talking about are rather high so things get harder to do &amp;quot;right&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Then again, you might not require the &amp;quot;perfect&amp;quot; board to get your &amp;quot;product&amp;quot; to work, it depends on the application... So try it out and see where you end up.&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2020-06-27T20:19:55.757" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16915" PostTypeId="1" CreationDate="2020-06-27T23:39:49.460" Score="3" ViewCount="332" Body="&lt;p&gt;The animation below from Wikipedia shows the standing waves of voltage and current on an ideal center fed resonant half wave dipole in free space.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8niio.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8niio.gif&quot; alt=&quot;Dipole standing waves animation&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The red and blue curves show the change in amplitude of the actual voltage and current which exists on the antenna at each point during one cycle of the applied RF energy. The arrows are the AC current which flows through the antenna and the source. The voltage depicted is the amplitude of the electric potential at each point, and the current is the amplitude of the AC current which flows along the antenna elements at each point. The amplitude of both voltage and current changes in sinusoidal fashion at the same frequency as that of the applied RF energy, and as can be seen the voltage and current are 90 deg out of phase in time and space, in fact the voltage lags the current by 90 deg (you can't see this in the animation) which makes sense because the dipole is a big capacitor in which the voltage also lags the current by 90 deg.&lt;/p&gt;&#xA;&lt;p&gt;But everyone knows that the voltage and current are in phase at the feed point of a resonant half wave dipole and the animation shows that the voltage and current are clearly not in phase, so it all seems very self contradictory and incestuously mutually exclusive. The phase difference between the standing waves cannot be the condition which determines the reactance present on the antenna, even though the amplitudes of the standing waves at the feed point determine the real part of the impedance of the dipole at the feed point ie: Z = E / I.&lt;/p&gt;&#xA;&lt;p&gt;The amplitudes of the standing waves of voltage and current vary in sympathy with the sinusoidal change in amplitude of the applied RF energy at the feed point. The positions of the peaks and troughs of the standing wave remain stationary and fixed in space along the length of the antenna. The standing waves result from the vectorial addition of the amplitudes of voltage and current of the traveling wave emanating from the feed point towards the ends of the dipole, and that of the reflected wave, and are the actual conditions present on the antenna which can be measured. The original incident and reflected traveling waves cannot exist independently of each other and cannot be measured as their existence is obscured by the vectorial addition of each to the other.&lt;/p&gt;&#xA;&lt;p&gt;Even though the voltage and current of the incident and reflected traveling waves can't be seen because they have been added together and so result in the standing waves present, they must exist otherwise there would be no standing waves.&lt;/p&gt;&#xA;&lt;p&gt;Is it the difference in phase of the voltage and current which results from addition of the incident and reflected traveling waves at any point along the lengths of the dipole elements which determines the amount of reactance present at each point ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-06-29T00:10:26.250" LastActivityDate="2020-07-03T10:27:59.213" Title="Confusion about dipole standing waves and feed point impedance" Tags="&lt;antenna-theory&gt;&lt;transmission-line&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16916" PostTypeId="1" AcceptedAnswerId="16932" CreationDate="2020-06-28T00:04:25.823" Score="0" ViewCount="149" Body="&lt;p&gt;Is the following explanation correct ?&lt;/p&gt;&#xA;&lt;p&gt;RF energy with a wavelength equal to twice the electrical length of the dipole is applied to the feed point at the center of the half wave dipole.&lt;/p&gt;&#xA;&lt;p&gt;To understand the following, it's necessary to visualize in your head a number of different things which happen during the time it takes for one cycle of the applied RF  energy to occur.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The amplitude of the voltage of the RF energy applied at the center feed point which is varying in sinusoidal fashion at it's frequency of oscillation.&lt;/li&gt;&#xA;&lt;li&gt;The waves of RF energy which emanate away from the feed point on each half of the dipole towards the ends of the antenna and which are then reflected and arrive baat the feed point.&lt;/li&gt;&#xA;&lt;li&gt;The change in phase of the waves as they move from center to ends and back again.&lt;/li&gt;&#xA;&lt;li&gt;The effect that the reflection has at the ends of the dipole on the phase of the voltage and current of the waves.&lt;/li&gt;&#xA;&lt;li&gt;The difference in phase between voltage and current of the RF energy applied at the feed point compared to the phase of the voltage and current of the reflected wave which arrive back at the feed point.&lt;/li&gt;&#xA;&lt;li&gt;The standing waves of voltage and current which exist along the length of the antenna.&lt;/li&gt;&#xA;&lt;li&gt;The value of reactance that the difference in phase of the voltage and current of the incident and reflected waves produces at each point on the antenna elements.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;A positive half cycle of applied RF energy at the feed point emanates away from the feed point towards one end of the antenna, and a negative half cycle of RF energy at the feed point emanates away from the feed point towards the other end of the antenna. The waves are reflected from the ends of the antenna, arriving back at the feed point in the time it takes for one half of the cycle of the applied AC to occur because the element lengths are exactly 1/4 of the wave length of the applied AC.&lt;/p&gt;&#xA;&lt;p&gt;At the same time as the positive wave on one side and the negative wave on the other caused by the applied RF energy are traveling from the feed point to the ends and back again, the amplitude of voltage of the applied AC is changing in a sinusoidal fashion, from zero to maximum positive amplitude one side and zero to maximum negative amplitude on the other side, and back again, and so progresses through half of one AC cycle or undergoes a total change in phase of 180 deg.&lt;/p&gt;&#xA;&lt;p&gt;Between the feed point and the end of each element, the traveling wave changes phase 90 deg in time and space in 1/4 of the time it takes for one cycle of the applied AC to occur. The same phase change occurs in the same amount of time from each end back to the feed point. Excluding what happens at the reflection, this means that both the voltage and the current of the wave changes in phase by 180 deg just because of the fact that the wave has traveled a distance of 1/4 wave length twice.&lt;/p&gt;&#xA;&lt;p&gt;The reflection occurs at an open circuit, and so the phase of the voltage of the reflected wave does not change, and the phase of the current of the wave is reversed.&lt;/p&gt;&#xA;&lt;p&gt;The amplitudes spoken about as follows are the independent instantaneous amplitudes of the voltage and current of the incident and reflected waves which change in sinusoidal fashion over the period of 1/2 a cycle of the applied AC.&lt;/p&gt;&#xA;&lt;p&gt;At the reflection, the amplitude of the positive voltage of the incident wave adds to the amplitude of the positive voltage of the reflected wave to produce double the amplitude of each, and the positive amplitude of the current of the incident wave adds to the negative amplitude of the reversed in phase current of the reflected wave to produce zero current amplitude.&lt;/p&gt;&#xA;&lt;p&gt;So at the ends of the antenna there is an AC voltage maximum and a current minimum, and an impedance maximum.&lt;/p&gt;&#xA;&lt;p&gt;When the reflected wave arrives back at the feed point, its voltage is 180 deg out of phase in time with the voltage of the next cycle of the applied ac waveform, and it's current is 360 deg out of phase in time, or in phase, with the current of the next cycle of the applied AC.&lt;/p&gt;&#xA;&lt;p&gt;The entire process repeats for the negative cycle of the applied RF energy, with everywhere a reversal of polarity of amplitudes.&lt;/p&gt;&#xA;&lt;p&gt;So at the feed point, the sinusoidal variation of the amplitude of the voltage of the reflected wave is exactly out of phase in time with that of the next cycle of the applied AC, and so they cancel each other out. The sinusoidal variation of the amplitude of the current of the reflected wave is exactly in phase in time with that of the next cycle of the applied AC,  and so they add together. The phase of the current of the reflected wave is the same as the phase of the voltage of the next cycle of the applied AC, the voltage and current at the feed point are in phase, there is no reactance present, and the antenna is resonant.&lt;/p&gt;&#xA;&lt;p&gt;At the inner feed point ends of the antenna elements, there is an AC voltage minimum and an AC current maximum, and an impedance minimum.&lt;/p&gt;&#xA;&lt;p&gt;At the same time as all that is going on, the incident and reflected waves traveling in opposite directions on the antenna are combining to produce standing waves of voltage  and current on the antenna.&lt;/p&gt;&#xA;&lt;p&gt;The amplitude of the voltage and current of the incident and reflected waves add as they pass each other on the dipole elements to produce a standing wave of voltage and current. The maximum amplitude of the standing wave is the addition of the maximum amplitudes of the incident and reflected waves and this changes at each point along the antenna. At the ends the amplitude of the voltage peak is at a maximum, and the maximum diminishes in sinusoidal fashion as the point along the antenna approaches the center, to arrive at a minimum peak value at the feed point end of each dipole element. At the ends, the amplitude of the current peak is at a minimum, and the maximum increases in a sinusoidal fashion as the point along the antenna approaches the center, to arrive at a maximum peak value at the feed point.&lt;/p&gt;&#xA;&lt;p&gt;The amplitudes of the standing waves of voltage and current vary in sympathy with the sinusoidal change in amplitude of the applied RF energy at the feed point. The positions of the peaks  and troughs of the standing wave remain stationary and fixed in space along the length of the antenna. The standing waves result from the vectorial addition of the amplitudes of voltage and  current of the incident and reflected waves and are the actual conditions present on the antenna which can be measured. The original incident and reflected traveling waves cannot exist independently  of each other and cannot be measured as their existence is obscured by the vectorial addition of each to the other.&lt;/p&gt;&#xA;&lt;p&gt;Despite this, the difference in phase of the voltage and current which results from addition of the incident and reflected traveling waves at any point along the lengths of the dipole elements determines the amount of reactance present at each point.&lt;/p&gt;&#xA;&lt;p&gt;?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-06-28T01:52:52.737" LastActivityDate="2020-07-03T05:16:14.753" Title="Why is a half wave dipole resonant?" Tags="&lt;antenna-theory&gt;&lt;transmission-line&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16917" PostTypeId="2" ParentId="15775" CreationDate="2020-06-28T02:33:17.700" Score="-3" Body="&lt;p&gt;A half wave dipole which is physically half a wave length long is not resonant.&lt;/p&gt;&#xA;&lt;p&gt;This is confusing because the term &amp;quot;half wave dipole&amp;quot; seems to inherently describe an antenna with a length which is the same as one half the wavelength of the applied RF energy, and so technically should always be exactly resonant because the two dipole element lengths are each exactly 1/4 of the wavelength of the applied RF.&lt;/p&gt;&#xA;&lt;p&gt;The confusion arises because the actual length of a half wave length can be unclear.&lt;/p&gt;&#xA;&lt;p&gt;For an EMF wave, the wavelength has one value when the wave travels in free space, and another lesser value (usually about 5 % less) when the wave travels along a piece of metal. This is because EMF energy travels slower in a medium which is more dense than air.&lt;/p&gt;&#xA;&lt;p&gt;So often a half wave dipole is described with a length that is the value of the half wave length in free space. If the dipole was made of air then doing this would be correct. But a half wave dipole made of metal with a length of the half a wave length of the EMF in free space is not the length that makes the dipole resonant.&lt;/p&gt;&#xA;&lt;p&gt;And so the impedance for this lie is about 73 + j73 ohms, and this antenna which is technically not a half wave dipole is not exactly resonant.&lt;/p&gt;&#xA;&lt;p&gt;So there is the term &amp;quot;electrical half wave length&amp;quot; which is the actual length of the half wave length of the EMF wave when it travels inside the material that the antenna is made from, noting that the length / diameter ratio of the elements and the immediate surrounding also have an effect on this length.&lt;/p&gt;&#xA;&lt;p&gt;The length of a half wave dipole which by definition is resonant is the electrical half wave length of the EMF wave in the actual antenna elements, and then the impedance has no reactance.&lt;/p&gt;&#xA;&lt;p&gt;Also, adding reactance to a non-resonant antenna to cancel out antenna reactance of the opposite sign doesn't make the antenna resonant. It just cancels out the reactance, resulting in a non-resonant antenna with added reactance to give a combined system which makes the antenna appear resonant.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-07-09T22:41:32.910" LastActivityDate="2020-07-09T22:41:32.910" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16918" PostTypeId="2" ParentId="7687" CreationDate="2020-06-28T04:14:53.993" Score="5" Body="&lt;p&gt;from ARRL:&#xA;Q. What equipment at our Field Day site must be operated off of the emergency power in order to claim the 100-point per transmitter bonus?&#xA;A. You must operate all transmitting and receiving equipment from emergency power. If you use a computer for digital modes, and/or to control or operate the radio, it also must use emergency power. &lt;strong&gt;If the computer is used only for logging and is not keying&#xA;the transmitter, it does not need to be emergency powered.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Field-Day/2019/1_62-2019%20FD%20FAQ.pdf&quot; rel=&quot;noreferrer&quot;&gt;http://www.arrl.org/files/file/Field-Day/2019/1_62-2019%20FD%20FAQ.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17308" LastActivityDate="2020-06-28T04:14:53.993" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16919" PostTypeId="2" ParentId="16915" CreationDate="2020-06-28T04:20:31.923" Score="3" Body="&lt;p&gt;You're reading too much into the Wikipedia picture! I think it's been asked before. It's also wrong about the zero voltage at the middle.&lt;/p&gt;&#xA;&lt;p&gt;Voltage and current can never be exactly 90 degrees apart because this would imply pure capacitive or inductive reactance, and antennas have some radiation resistance too.&lt;/p&gt;&#xA;&lt;p&gt;The angle changes fairly quickly near resonance though, if the dipole is too long or too short, it will be about 45 degrees leading or lagging.&lt;/p&gt;&#xA;&lt;p&gt;Here's a graph (&lt;a href=&quot;https://www.oreilly.com/library/view/rf-and-microwave/9781118349571/c07_level1_4.xhtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;source&lt;/a&gt;):&lt;br /&gt;&#xA;&lt;img src=&quot;https://www.oreilly.com/library/view/rf-and-microwave/9781118349571/images/c07f009.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;On the right hand figure, the angle between voltage and current is the angle of the point from the origin - the argument of the complex impedance. So if you consider the mismatched scales, you can see the full range of angles is about +-45 degrees.&lt;/p&gt;&#xA;&lt;p&gt;The Wikipedia animation could be correct if the antenna is just a little longer than a half wave. More likely it was made by someone who thought they should be 90 degrees apart, like a TEM wave.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-06-28T15:02:15.560" LastActivityDate="2020-06-28T15:02:15.560" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16921" PostTypeId="2" ParentId="16915" CreationDate="2020-06-28T10:52:46.127" Score="1" Body="&lt;p&gt;Consider an RLC resonant circuit. The current through the resistor is in phase with the voltage across it, while those through the inductor and the capacitor lag and lead their corresponding voltages by 90°. The inductive and capacitive currents cancel out leaving the overall resistive current, flowing into the RLC circuit terminals, in phase with the applied voltage.&lt;/p&gt;&#xA;&lt;p&gt;A resonant antenna is equivalent to an RLC resonant circuit. Even though the voltage and current distribution across the antenna is 90° out of phase, the current fed into the antenna is in phase with the applied voltage and together they constitute the power that is radiated, ignoring any losses.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-06-28T10:57:59.063" LastActivityDate="2020-06-28T10:57:59.063" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16922" PostTypeId="2" ParentId="16916" CreationDate="2020-06-28T17:33:18.520" Score="1" Body="&lt;p&gt;Here's another slant on the standing waves of voltage and current in a resonant dipole antenna, cut to a half-wavelength considering the velocity factor.&lt;/p&gt;&#xA;&lt;p&gt;When such an antenna has been energized at its resonant frequency, the current reaches the end of the antenna at the end of a half-cycle, with the voltage at a maximum and the current at zero.&lt;/p&gt;&#xA;&lt;p&gt;The current now reverses direction for the next half-cycle. The voltage and current follow a sinusoidal waveform, the current touching maximum and the voltage zero midway through, till the end of the half-cycle at the other end of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;The process repeats with the antenna current doing a to and fro traverse every cycle.&lt;/p&gt;&#xA;&lt;p&gt;The fixed voltage and current values along the antenna are represented by the standing waves which reverse polarity every half cycle.&lt;/p&gt;&#xA;&lt;p&gt;Electromagnetic radiation/reception from the antenna is a result of these standing waves.&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2020-06-29T09:35:54.947" LastActivityDate="2020-06-29T09:35:54.947" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16923" PostTypeId="2" ParentId="16916" CreationDate="2020-06-28T18:21:18.760" Score="1" Body="&lt;p&gt;You don't need standing waves or a sinusoidal input to find the resonant frequency of a dipole.&lt;/p&gt;&#xA;&lt;p&gt;Zap the feed point of a conductive dipole with a very short (much much less than one period) voltage impulse.  That voltage pulse will travel to one end (due to limiting speed of light in some dielectric) in finite time, then bounce to the other end at that same speed, then travel back to the feed point (its second pass).  How long does that full round trip of the dipole take?  Call that one period of the resonant frequency.&lt;/p&gt;&#xA;&lt;p&gt;All you need is a fast storage oscilloscope and a fast single shot pulse generator.&lt;/p&gt;&#xA;&lt;p&gt;If off-center fed, you will see two mid-period negative voltage passes, but the same positive impulse for one full period.&lt;/p&gt;&#xA;&lt;p&gt;If the total antenna resistance is low enough, that round trip will repeat until it decays away (partially radiated as EM if the radiation resistance is high enough, the rest as heat).&lt;/p&gt;&#xA;&lt;p&gt;Linear superposition says your transmit waveform is just the arithmetic sum of a bunch of these impulses tracing out the same shape.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-06-30T16:50:12.660" LastActivityDate="2020-06-30T16:50:12.660" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16924" PostTypeId="2" ParentId="16915" CreationDate="2020-06-28T22:10:44.780" Score="4" Body="&lt;p&gt;So yeah, this image is confusing. There's actually a &lt;a href=&quot;https://en.wikipedia.org/wiki/Talk:Dipole_antenna#Animated_graphic_incorrect&quot; rel=&quot;nofollow noreferrer&quot;&gt;section on the talk page questioning its correctness&lt;/a&gt;. I've considered a few times just deleting it, because it's so damn confusing.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The arrows are the AC current which flows through the antenna and the source.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I'm not sure we can say that. Notice the arrows are at any instant of equal magnitude at all points on the antenna, from the tips to the center. If we make the assumption (a reasonable one, I think) that the length of the arrow corresponds to the instantaneous current at that point, this suggests the instantaneous current at the end of the antenna at any point is equal to the same at the feedpoint. Which is impossible, since the current at the end of the antenna has no further length of wire in which to flow, and it's this abrupt end of the wire that's responsible for making the dipole resonant.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The voltage depicted is the amplitude of the electric potential at each point, and the current is the amplitude of the AC current which flows along the antenna elements at each point.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Here I guess you're talking about the area under the solid curves.&lt;/p&gt;&#xA;&lt;p&gt;The current curve has the problem of being in direct contradiction with the arrows. Ostensibly both represent current somehow, but the arrows don't taper towards the ends while the curve does.&lt;/p&gt;&#xA;&lt;p&gt;The voltage curve has the problem of being rather vague. It can't be voltage at some point on the wire, because if we consider this dipole to be made of an ideal conductor then the electric potential at every point on the wire is equal, because that's the definition of an ideal wire. And sure a real dipole is made of a wire with resistance where this isn't true, but a theoretical dipole made with an ideal conductor still works (again, theoretically) so this can't be important to the fundamental operation of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;So then we can say the curve represents electric potential or field intensity or something, but at what point? 1 cm from the wire? 1 mm? And the electric field is pointing in what direction? Does the area under the curve represent only that part of the electric field vector that's parallel to the antenna, or is it simply the field vector's magnitude? If it's just the magnitude then what's it mean when the curve reverses polarity? Why the electric field would be represented by this filled curve is beyond me, since we already have &lt;a href=&quot;https://en.wikipedia.org/wiki/Field_line&quot; rel=&quot;nofollow noreferrer&quot;&gt;a way to represent electric fields&lt;/a&gt; in a drawing which is widely understood and unambiguous.&lt;/p&gt;&#xA;&lt;p&gt;There is perhaps &lt;em&gt;one thing&lt;/em&gt; about this image that's insightful, and it comes from the Wikipedia talk page:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The graphic is correct. The misunderstanding arises from the misapplication of the statement &amp;quot; Voltage and current are of course always in phase in a resonant antenna (a purely resistive load)&amp;quot;. The load seen at the feed point will be resistive in a resonant antenna (at the exact resonant frequency), and any energy being fed into the dipole will be composed of in phase current and voltage. However, the energy STORED in the antenna (and any resonant circuit) is stored in electric and magnetic fields which are continuously &amp;quot;sloshing&amp;quot; back and forth. In a high Q circuit the stored energy will dwarf the energy being added and lost. It is this stored energy that produces the current and voltage that is shown in the graphic. Energy is conserved. If the energy being added fro the source and that being radiated away equal each other, and if these are small compared to the stored energy, then we know that the energy stored in the electric field will be proportional to the square of the voltage on the ends of the dipole. The energy stored in the magnetic field will be proportional to the square of the current in the center of the dipole. For the total energy to be constant, the current and voltage MUST BE OUT OF PHASE. At one moment all the energy is in the magnetic field, 90 degrees later it is all in the elecric field. At any other moment it is shared but the total is not changed. This applies to all resonant circuits, not just a dipole. I hope this helps.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Besides being one giant paragraph with a lot of ALL CAPS, there's a kernel of insight in there. Paraphrasing:&lt;/p&gt;&#xA;&lt;p&gt;A dipole, like any resonant system, involves the storage of energy alternating between two forms. In mechanical oscillators (bells, springs, pendulums, ...) the forms are gravitational potential and kinetic energy. In a dipole, the energy oscillates between the electric and magnetic fields.&lt;/p&gt;&#xA;&lt;p&gt;In many such resonant systems, to the extent that it has no losses, when one form is at a maximum the other will be at zero. The two, plotted over time, will be in quadrature. &lt;a href=&quot;https://youtu.be/p_di4Zn4wz4?t=661&quot; rel=&quot;nofollow noreferrer&quot;&gt;3Blue1Brown has a nice visualization of this for a pendulum&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fuH34.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fuH34.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Here the horizontal axis (labeled &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt;) is the pendulum's angle from vertical, and the vertical axis (&lt;span class=&quot;math-container&quot;&gt;$\dot\theta$&lt;/span&gt;) is the angular velocity. Notice: the state of the pendulum traces circular shapes. Additionally this particular illustration includes a small loss due to air friction, but regardless you can see the two variables are mostly in quadrature and mostly trace a circle because the loss is small compared to the energy stored: it has a high Q-factor.&lt;/p&gt;&#xA;&lt;p&gt;Antennas are no different: they tend to be resonant systems with a high Q-factor. And likewise, if you were to plot the potential energy of the electric field and the magnetic field around the antenna over time, you would find these to be sinusoidal functions approximately in quadrature. The higher the Q factor, the more true this is.&lt;/p&gt;&#xA;&lt;p&gt;I believe this is what the image is trying to convey, it just does a terrible job due to the numerous ambiguities as mentioned.&lt;/p&gt;&#xA;&lt;p&gt;It may help to further consider that the voltage at the feedpoint terminals need not necessarily relate to the red &amp;quot;voltage&amp;quot; curve. Part of what makes the image confusing is it just says &amp;quot;voltage&amp;quot;. But this isn't rigorous language: it could mean &amp;quot;electric potential difference&amp;quot; (the thing an ordinary voltmeter with two leads measures) but it could also mean electric potential, not easily measured with common equipment. According to my best guess at what the image is trying to convey, what's intended is the latter, while what nearly everyone will think &amp;quot;voltage&amp;quot; means is the former.&lt;/p&gt;&#xA;&lt;p&gt;Put another way: there's no reason peak electric potential difference between the feedpoint's terminals must coincide with peak energy stored in the electric field.&lt;/p&gt;&#xA;&lt;p&gt;Further consider: if we assume maximum voltage (ahem...electric potential difference) is applied at the feedpoint at the same time feedpoint current is at a maximum, we would expect (due to the length of the dipole arm) to see maximum voltage at the end of the antenna a quarter-cycle later. And in fact, this is precisely what's shown in the image.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;I think this is a much better image to communicate the point:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lCiXw.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lCiXw.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is actually a cheap crop of &lt;a href=&quot;https://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer#/media/File:Transmission_line_animation_open_short2.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;an animation of a transmission line&lt;/a&gt;. It is open on the right side, and imagine the left side as the feedpoint. It is a quarter-wavelength long.&lt;/p&gt;&#xA;&lt;p&gt;You can see that the arrows, representing the electric field between the two conductors of the transmission line, are strongest when current is zero. Meanwhile the current is strongest when the arrows are zero. Thus these two quantities are in quadrature, as in the dipole image in the question.&lt;/p&gt;&#xA;&lt;p&gt;A dipole is simply a quarter-wave section of transmission line like this which has been cut down the middle and pulled apart.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-06-29T03:39:32.370" LastActivityDate="2020-06-29T03:39:32.370" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16925" PostTypeId="1" AcceptedAnswerId="16926" CreationDate="2020-06-28T22:59:32.987" Score="2" ViewCount="200" Body="&lt;p&gt;In a paper cited in comments to &lt;a href=&quot;https://astronomy.stackexchange.com/a/36708/7982&quot;&gt;this answer&lt;/a&gt; to &lt;em&gt;In the 1950's how were radio-astrometric positions with portable dishes so precise they could be assigned to their dim optical counterparts (Quasars)?&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;The 1963 paper is &lt;a href=&quot;https://ui.adsabs.harvard.edu/abs/1963ApJ...138....1R/abstract&quot; rel=&quot;nofollow noreferrer&quot;&gt;Accurate Measurement of the Declinations of Radio Sources&lt;/a&gt; (click the little PDF icon) and the two excerpts containing the phrase &amp;quot;crystal mixer&amp;quot; are quoted below along with the block diagram.&lt;/p&gt;&#xA;&lt;p&gt;When I hear &amp;quot;crystal&amp;quot; I think of either quartz crystals for oscillators, or metal crystals (e.g. galena) with oxide surfaces used to make diodes using &lt;a href=&quot;https://en.wikipedia.org/wiki/Crystal_detector&quot; rel=&quot;nofollow noreferrer&quot;&gt;cat's whisker contacts&lt;/a&gt;, but for diode detection in the mixer certainly both vacuum tube and solid state semiconductor diodes existed in the 1960's, though I don't know about the performance at 960 MHz.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question:&lt;/strong&gt; What would a &amp;quot;crystal mixer&amp;quot; have been in an 1960's radio telescope at 960 MHz?&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Block diagram of an astronomical interferometer made from two radio telescopes separated by 200, 400 or 1600 feet and operated at 960 MHz. The mixers in question are shown just below each dish:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sMNNr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sMNNr.png&quot; alt=&quot;Fig. 1.—Block diagram of the receiver (Owens Valley radio telescope interferometer circa 1960's&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;Crystal mixer&amp;quot; appears twice in the paper; on page 2:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The arrangement of the components of the receiving equipment is shown by the block diagram of Figure 1. The receivers were of the superheterodyne type, and the crystal mixers were connected by short lengths of cable to the antenna feeds without any pre- amplification at the signal frequency. The local oscillator frequency was 960 Mc/s, and the center frequency of the IF amplifiers was 10 Mc/s, with a band width of about 4 Mc/s. No attempt was made to reject the image response of the superheterodyne. Note that the IF amplifiers were split into two sections. The IF preamplifier was located at the prime focus of the paraboloid along with the mixer and amplified the signal sufficiently to allow it to be fed through a long connecting cable to the remainder of the receiver, which was located in the laboratory building.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;and again on page 3:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The local oscillator power for each half of the receiver was supplied by a separate klystron oscillator, which was phase-locked by a closed-loop servo system to reference signals of a common, central origin. The high-frequency refer- ence signal power required by the system for a satisfactory lock was about six orders of magnitude weaker than the available local oscillator power required by the crystal mixers of the superheterodyne receivers. The problem of getting phased local oscillator power to the two antennas when they were being used at large separations was thus greatly simplified.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8643" LastActivityDate="2020-06-29T01:03:25.997" Title="What would a &quot;crystal mixer&quot; have been in an 1960's radio telescope at 960 MHz?" Tags="&lt;history&gt;&lt;mixer&gt;" AnswerCount="1" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16926" PostTypeId="2" ParentId="16925" CreationDate="2020-06-29T01:03:25.997" Score="3" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;No attempt was made to reject the image response of the&#xA;superheterodyne.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This suggests that the designers wanted &lt;em&gt;nothing to phase-shift&lt;/em&gt; RF signals...important in an interferometer - everything between antenna feed and the 10 MHz I.F. amplifier would be quite broad-band. And gain (actually loss) of diode mixers is fairly well-controlled.&lt;br&gt; Keeping those two RF paths identical was likely an important design goal. Perhaps their signal source was a strong one so that receiver sensitivity was not a limiting factor.&lt;/p&gt;&#xA;&lt;p&gt;Have a 1960-era VHF mobile phone that used a single point-contact germanium diode mixer very much like this, very first stage of the receiver. However, tuned circuits were placed between antenna and mixer to reject the image response. Many TV tuners of that era used a similar approach.&lt;br&gt;&#xA;Diode mixers work nicely at very high frequency - generating the local oscillator power to drive them is the bigger problem.&lt;/p&gt;&#xA;" OwnerUserId="11132" LastActivityDate="2020-06-29T01:03:25.997" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16927" PostTypeId="1" CreationDate="2020-06-29T10:37:25.040" Score="2" ViewCount="197" Body="&lt;p&gt;The NEC4.2 comparison in the answer below shows one example, for a practical set of installation conditions.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-07-29T19:02:10.407" Title="How Does the Performance of an Inverted V Dipole Compare to a Linear Dipole?" Tags="&lt;dipole&gt;&lt;radiation-pattern&gt;&lt;dx&gt;&lt;inverted-vee&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16928" PostTypeId="2" ParentId="16927" CreationDate="2020-06-29T10:41:04.367" Score="2" Body="&lt;p&gt;NEC4.2 comparison of an inverted V, center-fed dipole with a linear center-fed dipole:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tQffK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tQffK.png&quot; alt=&quot;&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;AUTHOR EDITS:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The apex angle in my plots here is mislabeled.  The correct value is 120°.&lt;/li&gt;&#xA;&lt;li&gt;The graphic below compares the elevation pattern gains at 90° azimuth intervals for these two configurations; posted in response to the comment of rclocher3.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ChLZm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ChLZm.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-06-29T18:20:25.817" LastActivityDate="2020-06-29T18:20:25.817" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16929" PostTypeId="1" CreationDate="2020-06-29T12:34:20.510" Score="2" ViewCount="179" Body="&lt;p&gt;This question has been suggested in the comments to a &lt;a href=&quot;https://ham.stackexchange.com/q/16885&quot;&gt;closed question&lt;/a&gt; a couple of days ago. I have nothing to do with the original question, but this aspect of the problem made me quite curious, so it would be great if someone could make an attempt at answering it. The context of the question is long-distance transmission over HF.&lt;/p&gt;&#xA;&lt;p&gt;No particular constraints on locations, equipment or power other than those following from amateur radio regulations (HF: mostly 400W maximum power), but more efficient (low-cost or low-power) and more reliable solutions are preferred. The time between start of transmission and finished decoding shall not exceed 4 ms.&lt;/p&gt;&#xA;&lt;p&gt;Assume that no communication channel has yet been established, and no additional infrastructure is to be used besides a transmitter and a receiver.&lt;/p&gt;&#xA;&lt;p&gt;Assume there's no need to decode the callsign&lt;/p&gt;&#xA;" OwnerUserId="17321" LastEditorUserId="4076" LastEditDate="2020-06-29T17:01:27.030" LastActivityDate="2020-06-29T19:35:24.630" Title="What would be a good modulation scheme for communicating a single bit of information with no more than 4ms of latency?" Tags="&lt;hf&gt;&lt;modes&gt;" AnswerCount="1" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="16930" PostTypeId="2" ParentId="16905" CreationDate="2020-06-29T13:55:04.450" Score="1" Body="&lt;p&gt;There are several techniques.&lt;/p&gt;&#xA;&lt;p&gt;first physically hide the transmitter and antenna. While this is hard for large antennas, it becomes more feasible at higher frequencies. I read a story about a HAM radio fox hunt where the fox (transmitter / antenna) was hidden in a coed's swim suit as she was sunbathing in a park. The hunters knew the transmitter was in the park, but no one dared to ask the young lady if they could inspect her suit.&lt;/p&gt;&#xA;&lt;p&gt;Use low power. Low power signals are hard to detect. This does limit how far the signal can reach and to an extend how much information it can carry.&lt;/p&gt;&#xA;&lt;p&gt;Spread spectrum / frequency hopping. To partially overcome the information issue, broadcast using several frequencies at the same time. You can lower the signal strength down to the noise level or even a bit below. This works best with digital data and error correction.&lt;/p&gt;&#xA;&lt;p&gt;Directional antennas. By putting the majority of the RF in a narrow lobe, you will make it harder for others who are not in lobe to detect the signal.&lt;/p&gt;&#xA;&lt;p&gt;Scattering, sometimes you can effectively &amp;quot;bounce&amp;quot; a signal of off another object like a bridge or building. doing this does require higher power as the reflected signal loses much of its energy.&lt;/p&gt;&#xA;&lt;p&gt;Final hijacking. This would be illegal, but inject your signal into another broadcast system so it is coming from their equipment. it is easier to hide your tap on their hardware than it is to hide your broadcast.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-06-29T13:55:04.450" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16931" PostTypeId="2" ParentId="16905" CreationDate="2020-06-29T14:50:08.233" Score="1" Body="&lt;p&gt;I remember an episode of the live action TMNT series in which Mike had a pirate radio station. To make detection harder, the transmitter was in his truck.&lt;/p&gt;&#xA;&lt;p&gt;I believe everyone here has been thinking about stationary radio sources so far. By keeping your transmitter moving, and going dark as needed, you may avoid detection for a while longer. They will only be able to track you while you are transmitting, and by the time they arrive where they thought you were, you may be long gone.&lt;/p&gt;&#xA;" OwnerUserId="17323" LastActivityDate="2020-06-29T14:50:08.233" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16932" PostTypeId="2" ParentId="16916" CreationDate="2020-06-29T16:40:24.210" Score="1" Body="&lt;p&gt;I can't follow your explanation to the end, so I can't say if it's correct or not. Please enjoy a simpler explanation:&lt;/p&gt;&#xA;&lt;p&gt;Consider not a dipole, but a quarter-wave section of balanced transmission line. One end is an open circuit, and the other end is the &amp;quot;feedpoint&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Now say you apply a 1 volt step to that feedpoint. &lt;a href=&quot;https://electronics.stackexchange.com/q/19759/17608&quot;&gt;It's not yet &amp;quot;known&amp;quot; the end is open&lt;/a&gt;, so a wave travels down the transmission line, with voltage and current in proportion with the transmission line's characteristic impedance. Let's say it's a 300 ohm line, so 1/300 = 3.3 mA is the current your voltage source will have to supply.&lt;/p&gt;&#xA;&lt;p&gt;Some time later, the wavefront corresponding to the start of the voltage step reaches the end of the line. But wait, the circuit is open! The open at the end of the line needs to &amp;quot;tell&amp;quot; the voltage source that it has sent too much current. The voltage source initially thought 3.3 mA was required to make 1 V, but actually only 0 mA is required because the impedance of an open circuit is infinite.&lt;/p&gt;&#xA;&lt;p&gt;It does this by initiating a 2nd wavefront, superimposed on the first one. This 2nd wavefront is 3.3 mA in the &lt;em&gt;opposite&lt;/em&gt; direction. The superposition of these two waves is 0 mA, the &amp;quot;right&amp;quot; amount of current.&lt;/p&gt;&#xA;&lt;p&gt;This 2nd wavefront arrives at the voltage source some time later, and this is the first time the voltage source has learned anything about what's at the end of the transmission line. The -3.3 mA opposite wave will also be accompanied by 1 V, again due to the characteristic impedance of the line. When this reaches the voltage source it will reduce the current its producing to hold its output voltage to 1 V rather than allowing voltage to rise to 2 V. This sets off another superimposed wave (but smaller this time) that goes through the same process, and this process repeats until the current through the voltage source approaches 0 mA.&lt;/p&gt;&#xA;&lt;p&gt;Impedance describes the relationship between current and voltage. One way to measure it is to attach a voltage source (fixed, known voltage) and then measure the current. The real part of impedance (resistance) tells us &lt;em&gt;how much&lt;/em&gt; current to expect. The complex part of impedance (reactance) tells us &lt;em&gt;when&lt;/em&gt; to expect the current. If peak current coincides with peak voltage, reactance is zero and the dipole is resonant.&lt;/p&gt;&#xA;&lt;p&gt;Now consider the current that was observed in response to the voltage step in the example above. Ignore the 3.3 mA that initially flows when the step occurs, because with AC analysis we are concerned with the equilibrium condition at a single frequency, not the transient analysis.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;It takes 90 degrees for the wavefront to reach the end of the transmission line, because it's a 1/4 wave long.&lt;/li&gt;&#xA;&lt;li&gt;The current of the reflected wave is inverted, so that's another 180 degrees.&lt;/li&gt;&#xA;&lt;li&gt;It takes another 90 degrees for the reflected wave to reach the feedpoint.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;90 + 180 + 90 = 360 degrees, and since in AC analysis we assume sinusoidal inputs with no start or end, 360 is equivalent to 0 degrees. In other words, voltage and current are in phase, and reactance is zero.&lt;/p&gt;&#xA;&lt;p&gt;From here it's just a small step to a resonant dipole. Cut the transmission line down the middle and pull the conductors apart (and possibly make some minor adjustment to the length to account for the altered velocity factor) and you've got yourself a dipole.&lt;/p&gt;&#xA;&lt;p&gt;The only difference is that in the case of an ideal 1/4 wave open, transmission line, 100% of the energy sent into the line ends up reflected back at the voltage source with current in phase, meaning with each reflection the voltage source must produce &lt;em&gt;more&lt;/em&gt; current to maintain its output voltage. Thus the current approaches infinity: the voltage source sees a short circuit.&lt;/p&gt;&#xA;&lt;p&gt;But in a dipole some of the energy is lost to radiation, and so the voltage source sees a low but non-zero impedance in the neighborhood of 75 ohms, depending on wire diameter, interaction with the ground, resistive losses, etc.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-06-29T16:40:24.210" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16933" PostTypeId="2" ParentId="16929" CreationDate="2020-06-29T19:35:24.630" Score="4" Body="&lt;p&gt;So, I'll go ahead and &lt;em&gt;include&lt;/em&gt; the callsign, if we're sticking to regulation, in what needs to be decodable (though not necessary within the 4 ms). I'll also assume 4ms is from the point in time the signal starts reaching the receiver until it knows what was sent. Makes no sense to include the propagation delay: 4 ms is only 1200 km of distance at speed of light, and the original question was about 10000 km (and HF travels slower than vacuum speed of light).&lt;/p&gt;&#xA;&lt;p&gt;WSPR reserves 28 bits for a callsign, and that seems about right, so I'll go with that.&lt;/p&gt;&#xA;&lt;p&gt;Together with a 1 bit payload, that makes 29 bit.&lt;/p&gt;&#xA;&lt;p&gt;We have 400 W in 4 ms, so we can send 4·10² W · 4·10⁻³ s = 1.6 Ws = 1.6 J. Not bad at all!&lt;/p&gt;&#xA;&lt;p&gt;What matters at the receiver is that we make the right decision about having detected a 0 or a 1. That's an &lt;em&gt;data estimation from a noisy observation&lt;/em&gt;, and that's pretty simple to model: We receive something, quantify it as a number, and mark somewhere that &amp;quot;left of this mark, it's a 0, right of this mark, it's a 1&amp;quot;. All we have to find is a sensible method of mapping our received signal to a number, then find the optimal place to set that decision boundary.&lt;/p&gt;&#xA;&lt;p&gt;Now, we have to deal with &lt;em&gt;noisy&lt;/em&gt; reception. That means that the receiver can never be actually sure what was sent, because the received signal is added to noise.&lt;/p&gt;&#xA;&lt;p&gt;We can put a number on how likely it is that it was wrong, a &lt;em&gt;bit error probability&lt;/em&gt;, however, on a system, as soon as we understand how the noise amplitudes compare to the signal amplitudes.&lt;/p&gt;&#xA;&lt;p&gt;Typically, this looks like this:&lt;/p&gt;&#xA;&lt;p&gt;Say, this is your noise probability density function (PDF). Noise is a bit unnerving, because it's not a deterministic thing: Noise is by definition random. We can't know what its value is, and we thus can't simply subtract it from what we've observed. But we can describe that &lt;em&gt;random variable&lt;/em&gt; by its pdf:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://commons.wikimedia.org/wiki/File:Fig3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/c/cd/Fig3.png&quot; alt=&quot;Normal distribution PDF&quot; /&gt;&lt;/a&gt;&lt;sub&gt;&lt;br&gt;Normal PDF, Tmennink / CC BY-SA&lt;/sub&gt;&lt;/p&gt;&#xA;&lt;p&gt;You need to read it as such: &amp;quot;The probability that the noise amplitude is between 1 and 2 is the area below the curve, below the points (on the horizontal axis) 1 and 2&amp;quot;, or &amp;quot;The probability that the noise takes a value lower than -2 is the area under the curve (that's an integral, by the way) from -infinity to -2&amp;quot;, or &amp;quot;The probability that an absolute amplitude no higher than 1 ocurred is the area between -1 and +1&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Let's do an example; imagine this: you know that your transmitter sends a positive +1 to signal a &amp;quot;0&amp;quot; bit, and a negative -1 to signal a &amp;quot;1&amp;quot; bit.&lt;/p&gt;&#xA;&lt;p&gt;However, you don't know how much your channel attenuated your signal. So, your +1/-1 might have been shrunk to +0.1/-0.1 or to +0.00000000000001/-0.00000000000001(= +10⁻¹⁴/-10⁻¹⁴) (more realistic for a long range channel...).&lt;/p&gt;&#xA;&lt;p&gt;You observe a negative value -0.45. What was sent?&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Either, a negative &lt;em&gt;-amplitude&lt;/em&gt; was received, and the noise didn't add enough to make it positive, so that you're still seeing the negative value, or&lt;/li&gt;&#xA;&lt;li&gt;a positive &lt;em&gt;+amplitude&lt;/em&gt; was received, but the noise added enough negative amplitude, so that the noise converted your positive value to the negative -0.45.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Both happens in reality. So, we can't be &lt;em&gt;sure&lt;/em&gt;. What that looks like in the terms of the above plot is that if we know that a &lt;em&gt;+amplitude&lt;/em&gt; reached us, we know that the value of signal + noise amplitude has the same pdf as noise, but with the horizontal 0 point shifted right to &lt;em&gt;+amplitude&lt;/em&gt;, so that the &amp;quot;bell&amp;quot; now is centered around the actual received signal. &lt;br&gt;&#xA;The same happens when &lt;em&gt;-amplitude&lt;/em&gt; reaches us, but in that case, the noise pdf bell curve is shifted to the left:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EGB1b.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EGB1b.png&quot; alt=&quot;Conditional PDFs&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;We never &lt;em&gt;see&lt;/em&gt; that bell, it's just a hidden property of the random variable &amp;quot;receiver output&amp;quot;, but that allows us to reason about things:&lt;/p&gt;&#xA;&lt;p&gt;Of course, we want to make a decision that makes most sense. In our example, that means we'll assume that +amplitude was sent when we observe an &lt;span class=&quot;math-container&quot;&gt;$r$&lt;/span&gt; right of the vertical axis, and -amplitude when we observe an &lt;span class=&quot;math-container&quot;&gt;$r$&lt;/span&gt; left of the vertical axis. But note that this is only true if we assume both to be equally likely, and if our PDF is symmetrical! (this is the &lt;em&gt;Maximum-Likelihood estimator&lt;/em&gt;, by the way.)&lt;/p&gt;&#xA;&lt;p&gt;This lets us reason what influences the probability that we make an error. It's two things:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the width of these bell curves. If they get wider, more of the area &amp;quot;laps&amp;quot; over the vertical axis, and that's our error probability! In terms of probability theory, the width of the curve is proportional to the square root of the &lt;em&gt;variance&lt;/em&gt; of the noise, which is the same as noise power.&lt;/li&gt;&#xA;&lt;li&gt;the distance between &lt;em&gt;+amplitude&lt;/em&gt; and &lt;em&gt;-amplitude&lt;/em&gt;. The wider we put them apart, the less of the bells lap over to the other side, and the lower our error probability gets. Since we can't modify the channel, the attenuation is given, and the only way to influence the received amplitude is to increase the transmitted amplitude proportionally.  Sadly, amplitude is the square root of signal power, so this find legal and technical bounds quickly.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;What this shows us is that to design a system for a given error probability (99%, in your case), we need to think about the ratio of power in the received signal, and power of the received noise.&lt;/p&gt;&#xA;&lt;p&gt;Now, if we really encode the one payload bit separately from the 28 callsign bits,  that's a &lt;em&gt;bit energy&lt;/em&gt; &lt;span class=&quot;math-container&quot;&gt;$E_b = 1.6\,\text{J}$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Let's say we have an attenuation &lt;span class=&quot;math-container&quot;&gt;$a$&lt;/span&gt; over the channel (in fact, &lt;span class=&quot;math-container&quot;&gt;$a$&lt;/span&gt; will very much depend on the time of day, sun activity, weather, mood of your cat, …, so we'll have a probability distribution for a random variable &lt;span class=&quot;math-container&quot;&gt;$a$&lt;/span&gt;, and we need to pick &lt;span class=&quot;math-container&quot;&gt;$a$&lt;/span&gt; such that it's at least as good as that 99% of times).&lt;/p&gt;&#xA;&lt;p&gt;That means of the 1.6 J, a·1.6 J reach the receiver.&lt;/p&gt;&#xA;&lt;p&gt;The receiver has a noise floor density &lt;span class=&quot;math-container&quot;&gt;$N_0$&lt;/span&gt;, a &lt;em&gt;noise power per bandwidth&lt;/em&gt;. Now, bandwidth is an inverse of time, so that the physical entity &lt;span class=&quot;math-container&quot;&gt;$N_0$&lt;/span&gt; is indeed &lt;em&gt;power times duration&lt;/em&gt;, i.e. has the same physical meaning as the bit energy.&lt;/p&gt;&#xA;&lt;p&gt;Hence, &lt;span class=&quot;math-container&quot;&gt;$E_b/N_0$&lt;/span&gt;, &lt;em&gt;energy per bit to noise power spectral density ratio&lt;/em&gt;, is dimensionless. Makes sense: if we send more bits per second, we get proportionally more bit energies per unit of time, but we need proportionally more bandwidth, and with noise being white, we get proportionally more noise power.&lt;/p&gt;&#xA;&lt;p&gt;So, doesn't really matter how much bits per second we send; the &lt;span class=&quot;math-container&quot;&gt;$E_b/N_0$&lt;/span&gt; value is defined by the transmit power and the unit-bandwidth noise variance.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;I'll now tell you something that you might have guessed all along: Physics doesn't&#xA;exacly &lt;em&gt;like&lt;/em&gt; us. Physics has it that every device at room temperature sees a noise power density of -174 dBm/Hz = -204 dBW/Hz (that's &lt;span class=&quot;math-container&quot;&gt;$10^{-17.4}\,\text{mW/Hz}=10^{-20.4}\,\text{W/Hz}$&lt;/span&gt;).&lt;/p&gt;&#xA;&lt;p&gt;Also, receivers aren't perfect. So, we can add 2 to 4 dB of noise figure to that, which is roughly a factor of 2.&lt;/p&gt;&#xA;&lt;p&gt;So, sadly, it's not for us to choose 1., the noise variance, in what determines the probability of error.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;That leaves us with choosing 2, the power of the received value.&lt;/p&gt;&#xA;&lt;p&gt;Armed with a table for the integrals of the bell curve we've shown above, we can look up the &lt;span class=&quot;math-container&quot;&gt;$E_b/N_0$&lt;/span&gt; value that we need for a given maximum error probability.&lt;/p&gt;&#xA;&lt;p&gt;This table can be put into a plot: The BER curve. If we receive +1/-1, we call that BPSK, and the BER curve looks like this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.dsplog.com/2007/08/05/bit-error-probability-for-bpsk-modulation/&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rH2so.jpg&quot; alt=&quot;BER curve BPSK&quot; /&gt;&lt;/a&gt;&lt;br&gt; &lt;sub&gt;from DSPLog&lt;/sub&gt;&lt;/p&gt;&#xA;&lt;p&gt;We can see that for your acceptable BER of 1/1000 = 10⁻³, we need an &lt;span class=&quot;math-container&quot;&gt;$E_b/N_0$&lt;/span&gt; of about 7 dB.&lt;/p&gt;&#xA;&lt;p&gt;That means that, since our &lt;span class=&quot;math-container&quot;&gt;$N_0=-204\,\text{dBJ}$&lt;/span&gt;, our &lt;span class=&quot;math-container&quot;&gt;$E_b$&lt;/span&gt; needs to be at least &lt;span class=&quot;math-container&quot;&gt;$-197\,\text{dBJ} = 10^{-19.7}\,\text{J}$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;We can transmit 1.6 J of energy legally for that single bit. As long as far-range transmission doesn't impose more than about 196 dB of attenuation, we're fine.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;I don't know current channel conditions on say the 40 m band. I really don't. If someone has a current table that says &quot;with a probability of x, we see such and such an attenuation&quot;, I could tell you what is OK to assume in your 99% of cases. (By the way, that would again take the form of a PDF, not of noise as random variable, but as the channel attenuation as random variable.)&#xA;&lt;p&gt;What I do know is that we don't know the channel beforehand. That means we don't know the phase that the channel imposes on us (which simply depends on the exact length, and medium effects, reflections and so on).  Since that includes 180° phase shifts, we &lt;em&gt;can't&lt;/em&gt; just transmit a single +1 or -1 with a high power, because the receiver simply couldn't tell the sign.&lt;/p&gt;&#xA;&lt;p&gt;Also, we're far from the only people to use that band. So, just sending a tone will not work out – other do the same, and suddenly our noise isn't only the receiver noise, but also the interference from others.&lt;/p&gt;&#xA;&lt;p&gt;So, what we need to do is to give our signal&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;as long-as possible shape to maximize power&lt;/li&gt;&#xA;&lt;li&gt;a as-unique-as-possible shape to maximize &amp;quot;identifiability&amp;quot; among interfering signals.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;em&gt;The&lt;/em&gt; standard way of doing that is &lt;em&gt;spreading&lt;/em&gt; the signal. So, you use a spreading sequence. Say, &lt;span class=&quot;math-container&quot;&gt;$+1, -1, +1, -1$&lt;/span&gt;. You multiply what you want to send, let's say the &lt;span class=&quot;math-container&quot;&gt;$+1$&lt;/span&gt;, with each element of that sequence. You then send the result, but with only 1/(length of sequence) of time per resulting number, so that you still send the same amount of &amp;quot;payload&amp;quot; bits per time.&lt;/p&gt;&#xA;&lt;p&gt;At the receiver, you take the same spreading sequence, and multiply every value you receive with it, and sum up. You &lt;em&gt;correlate&lt;/em&gt;. For example, you receive &lt;span class=&quot;math-container&quot;&gt;$0.2, 0.1, 0.1, -0.5$&lt;/span&gt;, and you know the spreading sequence as specified above. Then you calculate the sum: &lt;span class=&quot;math-container&quot;&gt;$0.2·(+1)+0.1·(-1)+0.1·(+1)+(-0.5)·(-1)=0.2-0.1+0.1+0.5=0.7$&lt;/span&gt;&#xA;&lt;br&gt;&#xA;Notice how 0.7 is larger than any of the noisy values you received, individually? That makes sense: the &lt;span class=&quot;math-container&quot;&gt;$+1,-1,+1,-1$&lt;/span&gt; &amp;quot;content&amp;quot; was multiplied with itself (&lt;span class=&quot;math-container&quot;&gt;$(+1)·(+1)+(-1)·(-1)+(+1)·(+1)+(-1)·(-1)=1+1+1+1$&lt;/span&gt;, which gives you 4, i.e. the length of the sequence.&lt;/p&gt;&#xA;&lt;p&gt;Sadly, you mustn't forget that in order to convert that single bit into four bits and transmit them, you had to use only one quarter of the original energy for each transmitted bit. But, since you added up signal, which was always the same, your signal gain is quadratic, whereas your noise gain only linear to sequence length. You generally gain SNR as a function of the length of the sequence.&lt;/p&gt;&#xA;&lt;p&gt;That's exactly how cheap-as-hell GPS receivers can fish GPS signals from far, far below the noise floor.&lt;/p&gt;&#xA;&lt;p&gt;A big bonus of using a sequence is also that you can use a &lt;em&gt;unique&lt;/em&gt; one. Which means that if you correlate with some signal that wasn't shaped with the same or a similar sequence, it, just like noise, doesn't add up constructively. So, you can &amp;quot;isolate&amp;quot; your receiver from interferers. Neat!&lt;/p&gt;&#xA;&lt;p&gt;Now, it seems intuitive that you'd want to spread as much as possible. Make your sequence a million elements long. Be totally unimpressed by any interferer.&lt;/p&gt;&#xA;&lt;p&gt;Sadly, you need to send more symbols the longer your sequence get. Where we had 1 bit that took 4 ms to begin with, equivalent to 250 bits per second, we'd need to transmit 250 million bits per second. Since we can't transmit more than 1 symbol/s/Hz, that would require us to use a bandwidth of at least 250 MHz (assuming binary symbols). You can't get that bandwidth around 7 MHz...&lt;/p&gt;&#xA;&lt;p&gt;Another problem with bandwidth: you'd also need to make sure that if your signal finds more than one path to your receiver, the &amp;quot;later&amp;quot; copy of the symbol doesn't disturb the next symbol. (We call that inter-symbol-interference, ISI.)&lt;/p&gt;&#xA;&lt;p&gt;There's three ways of managing that:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Simply don't. Your symbol rate needs to be low enough that all copies land in the same symbol, because the symbol is just so looooong. But that means no or little spreading.&lt;/li&gt;&#xA;&lt;li&gt;Take your wide channel and say: &amp;quot;hey, if I act as if this wide thing, in which symbols are so short that the echos overlap into the next one, is actually &lt;em&gt;many&lt;/em&gt; narrow channels next to each other, and I divide my input data into these channels evenly&amp;quot;, you've solved the hard ISI-problem by reducing it to many, &amp;quot;how do I deal with these many different easier channels&amp;quot;-problem. That's what &lt;em&gt;OFDM&lt;/em&gt; does. And that's what Wifi, LTE, DVB-T, DAB+, but also HF modes like DRM+ and FreeDV do.&lt;/li&gt;&#xA;&lt;li&gt;Use an Equalizer. That's an algorithm that needs to estimate when later copies come in, and then adds them to the first copy and subtracts them from the symbol that they leaked into.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;The first option is not an option. This system won't work without identifiability.&lt;/p&gt;&#xA;&lt;p&gt;The second option requires a separate decision of what was sent on &lt;em&gt;many&lt;/em&gt; channels, and requires that you really send enough data to even fill all the subchannels. Also, we can't really do many subchannels: our frequency resolution is 1/duration, duration is limited to 4 ms, so our channel spacing is 250 Hz, at least. We have at most 2700 Hz of overall bandwidth in the 40 m band, so that's at most 10 channels (there's some non-negligible overhead for such methods). 10 is not &amp;quot;many&amp;quot; subchannels. (Really useful would be 128 to 4096 or something like that).&lt;/p&gt;&#xA;&lt;p&gt;The third option sounds best, but it requires that you &lt;em&gt;estimate the channel impulse response&lt;/em&gt;, so that it can be reverted by the equalizer.&#xA;&lt;br&gt;&#xA;Now comes why it's bad to not consider the callsign alongside with the 1 bit of info:&lt;/p&gt;&#xA;&lt;p&gt;If we need to send 29 bits in total, sending 1 bit of known preamble to allow the receiving end to identify the properties of the channel doesn't hurt much – it's less than 4% of the energy we would have invested to send the over the whole shabang. If we only send 1 bit, then that 1 bit of preamble means 50% of energy lost to channel estimation. Ouch.&lt;/p&gt;&#xA;&lt;p&gt;Also, remember the BER above? Yeah, that's not optimal. If your &lt;span class=&quot;math-container&quot;&gt;$E_b/N_0$&lt;/span&gt; isn't outright terrible (which we can avoid, with but &lt;em&gt;a bit&lt;/em&gt; of spreading), and you transmit &lt;em&gt;enough&lt;/em&gt; bits (1 doesn't allow for much) we can apply &lt;em&gt;channel coding&lt;/em&gt; with an &lt;em&gt;forward error-correcting code&lt;/em&gt; (FEC) to make that line better, i.e. needing less bit energy for the same amount of data. That &amp;quot;blows up&amp;quot; the amount of data you need to transmit by a factor of &lt;span class=&quot;math-container&quot;&gt;$1/R&amp;gt;1$&lt;/span&gt;. The good thing about error-correcting codes is that they are even more efficient than spreading at converting more bandwidth into better &lt;span class=&quot;math-container&quot;&gt;$E_b/N_0$&lt;/span&gt;, but they can't help you much with telling your signal from noise or other people's signals.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;So, all in all, your transmitter would &lt;em&gt;likely&lt;/em&gt; look like this:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Add robust error correction coding to all your 29 bits that you needed to send (that's a rate of (1/R)·original rate)&lt;/li&gt;&#xA;&lt;li&gt;Use a relatively benign spreading code (maybe, length 32) to reduce the likelihood of misidentifying your signal (rate 32·(1/R)·original rate)&lt;/li&gt;&#xA;&lt;li&gt;Use a modulation that doesn't require you to intensely estimate the channel beforehand. For HF, FSK modes have proven to work well (won't go into the math why, but there's plenty of math to show that's the case). Using FT-8 as a guideline, say, 4-FSK, ie. every symbol you transmit carries 2 bits (&lt;span class=&quot;math-container&quot;&gt;$=\log_2(4)$&lt;/span&gt;). (symbol rate = 1/2·32·(1/R)·original rate)&lt;/li&gt;&#xA;&lt;li&gt;Since we're very time-constrained, we decide to use the full 2700 Hz channel, and divide it into as many parallel channels as possible to achieve the complete transmission in 4 ms = 1/250 s. That means, we need the number of channels to be 16/R. R would realistically be something like 1/2, so 32 subchannels (each of which does a 4-FSK) doesn't sound so bad. 2700 Hz / 32 = 84 Hz per subchannel bandwidth.&lt;/li&gt;&#xA;&lt;li&gt;add a bit of overhead everywhere: you're now collecting &lt;em&gt;all&lt;/em&gt; energy of the full band in your receiver. It's not even question anymore &lt;em&gt;whether&lt;/em&gt; you will have an interferer that has far more power than your transmitter in there, but only &lt;em&gt;how many&lt;/em&gt;.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Notize how the FT-8 bandwidth is 50 Hz, and thus pretty close to that 84 Hz?  Makes a lot of sense, FT-8 is meant to be &lt;em&gt;nice&lt;/em&gt; for many people playing together at the same time, and doesn't have a (hard to ridiculous) 4 ms constraint.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-06-29T19:35:24.630" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="16934" PostTypeId="2" ParentId="15853" CreationDate="2020-06-29T22:35:09.893" Score="0" Body="&lt;p&gt;Add a delay capacitor to the base of the switching transistor.....&lt;/p&gt;&#xA;" OwnerUserId="17327" LastActivityDate="2020-06-29T22:35:09.893" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16935" PostTypeId="1" CreationDate="2020-06-29T23:15:27.487" Score="2" ViewCount="285" Body="&lt;p&gt;I have two trees about 135 feet apart and about 55 to 65 feet tall.  I have been trying to determine which kind of wire antenna to put up there.&lt;/p&gt;&#xA;&lt;p&gt;Initially I was considering either a fan dipole or ZS6BKW.  But then a few hams suggested a doublet fed with ladder line.  And mentioned the site trueladderline.com where you can buy wire antennas with homebrew 600ohm feedline.&lt;/p&gt;&#xA;&lt;p&gt;I don't think I can get the open wire feedline through my window since the frames have metal in them.  I'm currently using a Comet CTC-50M, which is a flat 50 ohm coax jumper, to feed coax through my window.&lt;/p&gt;&#xA;&lt;p&gt;It seems I can either feed the open wire directly into a remote antenna tuner that accepts balanced feedline, or terminate the open wire into a balun then run coax to a tuner indoors. It seems the coax losses would be terrible if I went with the latter.&lt;/p&gt;&#xA;&lt;p&gt;&lt;s&gt;Are there any remote automatic tuners that can be fed directly with open wire?  So far the only ones I found are indoor tuners.&lt;/s&gt;&lt;/p&gt;&#xA;&lt;p&gt;UPDATE: turns out my windows are vinyl.  and i can fit open wire through them.  can i just feed it straight to a balanced tuner (like an MFJ-993B) and be good to go?&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="12939" LastEditDate="2020-06-30T20:24:02.130" LastActivityDate="2020-07-01T00:27:58.733" Title="Should I bother with a doublet if I can't go straight to the tuner with open wire?" Tags="&lt;wire-antenna&gt;&lt;antenna-system&gt;&lt;feed-line&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16936" PostTypeId="1" AcceptedAnswerId="16940" CreationDate="2020-06-30T05:27:59.097" Score="1" ViewCount="274" Body="&lt;p&gt;I'm a beginner trying to use one of my two CB radios as a &amp;quot;base station.&amp;quot; The problem is that the power cable is just two wires (no connectors/12v car plug) and a 2A fuse along one. Is it possible/safe to splice these to one of my million extra AC converters (pic below) and plug it into the wall? I know that the CB runs off of 12v, not sure about current. The adapter has a DC output of 12v 0.3a. This stuff is probably really obvious but I just want to be extra careful not to fry things. Thanks!&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/J3MGY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/J3MGY.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/d0aoj.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/d0aoj.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17328" LastActivityDate="2021-01-04T12:08:38.623" Title="Wiring Cobra 29LTD CB for home use?" Tags="&lt;power-supply&gt;&lt;dc-power&gt;&lt;citizens-band&gt;&lt;wiring&gt;" AnswerCount="3" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16937" PostTypeId="1" AcceptedAnswerId="17007" CreationDate="2020-06-30T05:51:52.440" Score="3" ViewCount="181" Body="&lt;p&gt;I've build a trap dipole for 20/40m bands. Traps are made of a coil wound on an insulator of RG213 coax and 3 kV NP0 capacitors. The impedance measured with EU1KY antenna analyzer is following:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AeqN7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AeqN7.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is a single trap, before and after putting a heatshrink. The final version of this one is for 14.080 MHz. The second one turned out a bit different, the resonant frequency is 14.150 MHz.&lt;/p&gt;&#xA;&lt;p&gt;Here is an SWR plot of a final antenna:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3xR4n.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3xR4n.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The mast is non-conductive, 10 meter high. The balun is 7 turns of RG58 on FT140-43 core. The active impedance is &amp;gt; 1000 Ohm from 80 to 15 meters. The antenna is used in &lt;strong&gt;inverted-V&lt;/strong&gt; configuration.&lt;/p&gt;&#xA;&lt;p&gt;The antenna was tested using 100W CW. It works OK. However I was surprised to get such a narrow band and SWR &amp;gt;= 1.5 on 20 meters. What brings a question - is it an expected result for trap dipoles? I always thought that it supposed to be more narrowband on lowest band, because traps work as loading coils there. Can it indicate that something is wrong with the antenna?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-07-02T12:21:52.493" LastActivityDate="2020-07-15T06:42:35.937" Title="What is an expected SWR plot for a trap dipole?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;inverted-vee&gt;&lt;trap&gt;" AnswerCount="3" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="16939" PostTypeId="2" ParentId="16935" CreationDate="2020-06-30T16:10:29.137" Score="1" Body="&lt;p&gt;Any of these antennas would work. My advice: do what's easy or whatever leverages what you already own.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Are there any remote automatic tuners that can be fed directly with open wire? So far the only ones I found are indoor tuners.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It may exist somewhere, but it's probably not very common, because:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;coax feedlines are popular for their ease of routing, and all-weather performance, and&lt;/li&gt;&#xA;&lt;li&gt;a balanced tuner requires twice as many components.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;You could however use a balun between the balanced transmission line and the unbalanced tuner.&lt;/p&gt;&#xA;&lt;p&gt;But, why would you want to do this?&lt;/p&gt;&#xA;&lt;p&gt;There's nothing &amp;quot;magic&amp;quot; about ladder line, except that it's much cheaper than coax of similar loss, and it's easy to make at home with a spool of wire and some suitable material for insulators. The idea is that the low loss will offset the high loss due to SWR and the end result will be acceptable loss.&lt;/p&gt;&#xA;&lt;p&gt;But if you have a remote tuner you can just put the tuner right at the feedpoint. Now there isn't any section of feedline with high SWR, so there's substantially less benefit to go replacing your feedline with a lower loss feedline.&lt;/p&gt;&#xA;&lt;p&gt;If you don't already have a remote tuner, but you do already have a coax feedline to a dipole, I'd say you're much better off with a fan dipole.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="9621" LastEditDate="2020-07-01T00:27:58.733" LastActivityDate="2020-07-01T00:27:58.733" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16940" PostTypeId="2" ParentId="16936" CreationDate="2020-06-30T16:36:10.343" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/citizens-band-radio-service-cbrs&quot; rel=&quot;nofollow noreferrer&quot;&gt;CB radio service&lt;/a&gt; transmitters are limited to 4 watts output power. Figure that that output circuit is only 50% efficient &lt;em&gt;at most&lt;/em&gt;, and in round numbers you'll need probably at least a 10W input if not more.&lt;/p&gt;&#xA;&lt;p&gt;For DC circuits the power (watts) is equal to the voltage times the current (amps). Your 12V, 0.3A adapter is therefore rated to supply 3.6 watts which is not nearly enough. When you try to transmit, the voltage into the radio will likely drop and cause the radio to &amp;quot;brown out&amp;quot;. (This probably won't permanently damage anything except maybe the power supply, but the radio won't &amp;quot;work&amp;quot; while it's happening either and might need a power cycle to clear any lingering control circuit glitches…)&lt;/p&gt;&#xA;&lt;p&gt;The 2A fuse on your radio is a clue that you'll probably want at least a 1A power supply for it. Is there a sticker somewhere on the radio that gives a specific current expectation?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-06-30T16:36:10.343" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16941" PostTypeId="1" AcceptedAnswerId="16942" CreationDate="2020-07-01T02:36:06.837" Score="8" ViewCount="3957" Body="&lt;p&gt;In a world where common mode current is the enemy, and we're constantly doing what we can to avoid RF in the shack, why would we ever choose a voltage type balun over a current balun?&lt;/p&gt;&#xA;&lt;p&gt;I understand that, in general, one uses a voltage balun to keep the voltages equal and opposite.  But what would be an example of a real world application of that in ham radio?&lt;/p&gt;&#xA;&lt;p&gt;Even the DX Engineering site says that a current balun is almost always the better choice.  So then why are they even selling voltage baluns?  What's this rare condition where a voltage balun is the better choice?&lt;/p&gt;&#xA;" OwnerUserId="12939" LastActivityDate="2020-07-01T16:46:22.573" Title="When would we ever want to use a voltage balun in ham radio?" Tags="&lt;balun&gt;&lt;choke-balun&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16942" PostTypeId="2" ParentId="16941" CreationDate="2020-07-01T04:34:23.090" Score="11" Body="&lt;p&gt;You'll find voltage baluns in plenty of circuits. For example,&lt;/p&gt;&#xA;&lt;p&gt;the &lt;a href=&quot;https://www.qrp-labs.com/receiver.html&quot; rel=&quot;noreferrer&quot;&gt;QRP Labs receiver module&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YMUQq.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YMUQq.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://github.com/TAPR/OpenHPSDR-SVN/blob/master/PennyWhistle/Documentation/PennyWhistle%20Manual%20V1.2.pdf&quot; rel=&quot;noreferrer&quot;&gt;HPSDR Pennywhistle&lt;/a&gt; (twice, T1 and T3):&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/9MZcr.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9MZcr.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The &lt;a href=&quot;https://ftp.elecraft.com/KX3/Manuals%20Downloads/KX3SchematicDiagramDec2012.pdf&quot; rel=&quot;noreferrer&quot;&gt;Elecraft KX3&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Aafaa.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Aafaa.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;A voltage balun can do some things a current balun can not.&lt;/p&gt;&#xA;&lt;p&gt;Firstly, the turns ratio can be varied to provide impedance transformation. Some of these circuits use something other than a 1:1 turns ratio to optimally load the transistors.&lt;/p&gt;&#xA;&lt;p&gt;Also, a voltage balun provides galvanic isolation. This can be useful for example to avoid ground loops which might be problematic with audio interfaces. It also allows a DC bias to be added: all three of these designs make use of that feature.&lt;/p&gt;&#xA;&lt;p&gt;One advantage of a common-mode choke as a balun is the core needs to be sized only to handle the common-mode current, not the full current of the signal. This is a significant advantage when designing a balun for a 1 kW antenna, but in a receiver or at the output of a 20 W amplifier, this particular advantage isn't of much value.&lt;/p&gt;&#xA;&lt;p&gt;Furthermore, in these applications the load is a circuit with equal impedances, and not an antenna which could be mounted asymmetrically or even deliberately unbalanced such as an off-center fed dipole. Thus another advantage of current baluns is again not especially needed in this application.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;As for why companies continue to sell voltage baluns &lt;em&gt;for antennas&lt;/em&gt;, I suspect they do so because people continue to buy them. A solution does not need to be technically the best to be economically viable.&lt;/p&gt;&#xA;&lt;p&gt;I haven't done a rigorous cost analysis, but I'd suspect 4:1 voltage baluns may be cheaper to manufacture:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;they require only 1 core where a 4:1 current balun requires 2&lt;/li&gt;&#xA;&lt;li&gt;for powers of 100W or less, the necessary core may be smaller than what's required to get a useful choking impedance from a common-mode choke&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;A voltage balun works fine when the load really is balanced. This isn't always the case so a voltage balun may not be a robust solution, but there will always be buyers that value low cost over robustness, or may not even be aware of the issues. So I'm not surprised manufacturers continue to make voltage baluns.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-07-01T16:46:22.573" LastActivityDate="2020-07-01T16:46:22.573" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="16943" PostTypeId="2" ParentId="16941" CreationDate="2020-07-01T04:52:24.327" Score="2" Body="&lt;p&gt;I attended a seminar on baluns --as applied to antennas-- at a local hamfest, given by no less a guru than &lt;a href=&quot;https://ham.stackexchange.com/users/9493/glenn-w9iq?tab=profile&quot;&gt;Glenn Shultz, W9IQ&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;He nicely explained that &lt;em&gt;the only place we need to use a voltage balun in an antenna system is &lt;strong&gt;for end-fed antennas&lt;/strong&gt;&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Every place else, use a current balun. And the simpler, the better.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-07-01T04:52:24.327" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16945" PostTypeId="2" ParentId="16937" CreationDate="2020-07-02T05:51:47.340" Score="1" Body="&lt;p&gt;My quick opinion is that this looks reasonable. A trapped dipole will likely have a smaller bandwidth than a regular dipole. A short simulation is what is required to be sure.&lt;/p&gt;&#xA;&lt;p&gt;You're getting 5% bandwidth at 40 m (the traps don't load it very much at 40 m) which is normal. And to be generous 1% at 20 m. The traps are working on the high impedance tips of the dipole, the frequency range where they're high enough impedance is quite small.&lt;/p&gt;&#xA;&lt;p&gt;Do check that the traps are tuned to the same frequency, it won't help if they aren't.&lt;/p&gt;&#xA;&lt;p&gt;The impedance never goes through 50 Ohms, so there's a further reduction in usable bandwidth there. With a VNA, calibrated to the end of the cable, you could try to figure out whether it's high or low, and put in the appropriate parallel cap or series inductor (and re-trim the antenna).&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-07-02T05:51:47.340" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16947" PostTypeId="2" ParentId="16937" CreationDate="2020-07-02T21:09:11.593" Score="3" Body="&lt;p&gt;I don't know how much of an impact it might make, but you might try moving the trap resonance to be outside the 20m band.&lt;/p&gt;&#xA;&lt;p&gt;Trap losses are highest at the trap's resonant frequency because at this frequency the current circulating between the inductance and capacitance is at a maximum. Thus, ohmic losses within the trap are maximized.&lt;/p&gt;&#xA;&lt;p&gt;At resonance is also where the rate of change of impedance with respect to frequency is highest. Designing the trap to be resonant within the 20m band means the trap impedance will vary rapidly over the band, which could explain the narrow SWR bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;To work as a trap you don't need the impedance to be infinite: only high enough to sufficiently isolate the following length of the antenna. Moving the resonant frequency of the trap may lower its impedance, but you can compensate for that by adjusting the length of the antenna. On the up side, losses may be lower and SWR bandwidth may be improved.&lt;/p&gt;&#xA;&lt;p&gt;Further reading:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.falstad.com/circuit/e-res-par.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.falstad.com/circuit/e-res-par.html&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.w8ji.com/traps.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.w8ji.com/traps.htm&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-02T21:09:11.593" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16948" PostTypeId="1" AcceptedAnswerId="16949" CreationDate="2020-07-03T02:21:15.393" Score="3" ViewCount="197" Body="&lt;p&gt;I have an AA-230 Pro Antenna Analyzer.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y3R9p.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y3R9p.jpg&quot; alt=&quot;AA-230 Pro Antenna Analyzer&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Its similar about 5-10 years old with a failing battery. The battery will only hold a charge for a day or so, and only for minutes while in use.&lt;/p&gt;&#xA;&lt;p&gt;I tried:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;looking for a manufacturer's replacement, but it's a &lt;a href=&quot;https://rigexpert.com/discontinued-products/&quot; rel=&quot;nofollow noreferrer&quot;&gt;discontinued product&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;looking for a way to open the plastic battery case, but its sealed pretty tight.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;How can I replace the battery?&lt;/p&gt;&#xA;" OwnerUserId="70" LastActivityDate="2020-07-03T02:35:47.177" Title="How can I replace the NiMH battery in an old RigExpert AA230 Antenna Analyzer?" Tags="&lt;repair&gt;&lt;battery&gt;&lt;antenna-analyzer&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16949" PostTypeId="2" ParentId="16948" CreationDate="2020-07-03T02:21:15.393" Score="4" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;With the battery case detached from the device, look at the side with the copper terminals.  You should see several seams that can be exploited with a sufficiently thin shim. I carefully used a box cutter on the right hand inner seam of the battery case and separated the battery case into two pieces without actually cutting or breaking any of the small plastic tabs that allow reassembly.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Inside the battery case you will find a standard 4xAA NiMH pack wired to the copper terminals, with soldered connections.  Cut the wires as close to the battery end as possible and strip a small amount for re-use or connection to a new pack or connector.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7cwlQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7cwlQ.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Here an Eneloop NiMH AA is shown for comparison.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6X4id.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6X4id.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;ol start=&quot;3&quot;&gt;&#xA;&lt;li&gt;You can find 4 AA NiMH packs pre-made on eBay and Amazon for under $20.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;4 eneloops will also fit in the compartment. I made a pack by taping and soldering 4 of them together in series.&lt;/p&gt;&#xA;&lt;p&gt;But I think it would be better to buy a pre-made NiMH pack because (i) &lt;a href=&quot;https://electronics.stackexchange.com/questions/75057/is-soldering-wires-directly-on-a-nimh-battery-safe&quot;&gt;consumer NiMH batteries are not really made for direct soldering and could fail early or create a hazard&lt;/a&gt;, and (ii) if you try it anyway, you'll fight with some issues with melting plastic and clamping/geometry to get good connections.&lt;/p&gt;&#xA;&lt;ol start=&quot;4&quot;&gt;&#xA;&lt;li&gt;Reassembly is simply snapping the two pieces of the battery case back together.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="70" LastEditorUserId="70" LastEditDate="2020-07-03T02:35:47.177" LastActivityDate="2020-07-03T02:35:47.177" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16950" PostTypeId="2" ParentId="16916" CreationDate="2020-07-03T04:12:13.993" Score="0" Body="&lt;p&gt;Here is another very simple answer.&lt;/p&gt;&#xA;&lt;p&gt;There is only one condition which determines when a half wave dipole can be resonant, and that's when the electrical lengths of the dipole elements are each precisely 1/4 the wavelength of the applied RF energy.&lt;/p&gt;&#xA;&lt;p&gt;A half wave dipole is not resonant because the capacitive and inductive reactances cancel out, because at resonance there is no reactance of any kind present because the AC voltage and current at the feed point are in phase.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-07-03T05:16:14.753" LastActivityDate="2020-07-03T05:16:14.753" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16952" PostTypeId="2" ParentId="16936" CreationDate="2020-07-03T06:17:53.077" Score="1" Body="&lt;p&gt;Galaxy, there are a number of things to watch out for when connecting power to your Cobra 29LTD AM only CB radio.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The power supply must be a regulated DC power supply, which outputs between 12 and 14 V DC. An adapter which outputs AC is no good. Note that many adapters like the one in your picture are not regulated, and when nothing is connected to them they can output a few volts higher than what they have printed on them. Any DC output voltage in excess of 15 V will damage the radio.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The power supply must be at least 2.5 A. That radio draws about 0.5 A on receive and about 2.5 A when transmitting. If you power it with say a 500 mA plug pack, it will receive ok, but when you try to transmit the lights on the radio will all go dim and TX won't work.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Do not connect the plus and minus power wires around the wrong way. If you do the fuse will blow, or if the fuse is the wrong one and rated too high, there is a reverse polarity protection diode inside the radio that will go short circuit and it will need to be replaced.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;CB radios need a special matched CB antenna. If you transmit while using the wrong antenna or one that is not tuned properly the radio will get hot and you risk damaging the main RF output transistor in the radio. Any antenna can be used if you are only receiving without any risk to the radio.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Hope that helps.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2020-07-03T06:17:53.077" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16954" PostTypeId="2" ParentId="16808" CreationDate="2020-07-03T18:19:55.413" Score="1" Body="&lt;p&gt;In my mind the difference is that:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;An RLC circuit &amp;quot;resonates&amp;quot; by bouncing energy back and forth within itself. And at a particular frequency this stored energy is retained for a particularly long time. (The &lt;a href=&quot;https://en.wikipedia.org/wiki/Q_factor&quot; rel=&quot;nofollow noreferrer&quot;&gt;Q&lt;/a&gt; of such a circuit represents the tradeoff between ringing for an extra long time at only one particular frequency, versus the energy bouncing around with still somewhat acceptable efficiency across a wider range of frequencies.)&lt;/li&gt;&#xA;&lt;li&gt;The &amp;quot;resonance&amp;quot; of an antenna usually has more to do with its &lt;a href=&quot;https://en.wikipedia.org/wiki/Radiation_resistance&quot; rel=&quot;nofollow noreferrer&quot;&gt;radiation resistance&lt;/a&gt; at a particular frequency. Here's where I don't want to steer you wrong since maybe this &lt;strong&gt;is&lt;/strong&gt; more conceptually related than I imagine, but the resistive energy loss in an RLC circuit is something of an inevitable &amp;quot;defect&amp;quot; whereas it's the entire point in a good antenna. You just want the energy to be lost as EMF radiation rather than thermally.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;That said, a &lt;a href=&quot;http://www.aa5tb.com/loop.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;small loop antenna&lt;/a&gt; is decidedly &lt;strong&gt;both&lt;/strong&gt;: it's an RLC circuit designed so that ideally all the &lt;code&gt;R&lt;/code&gt; would be due to radiation rather than loss. This is again related to Q — and with resonance being at an exact &amp;quot;point&amp;quot; frequency means that any modulation sidebands need to be taken up by a lossy resistance &lt;em&gt;somewhere&lt;/em&gt; but in practice with most antennas, and even many small loop antennas, the Q curve tends to be on the scale of e.g. the entire 80m &amp;quot;band&amp;quot; rather than anywhere near a concern for the bandwidth of a single CW/SSB transmission.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-07-03T18:19:55.413" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16955" PostTypeId="1" CreationDate="2020-07-06T15:33:26.850" Score="3" ViewCount="237" Body="&lt;p&gt;I designed an analog FM transmitter with GNU Radio Companion in order to understand the tool better. The hardware I use is an USRP B200. The carrier was built with a Signal Source block and the baseband was obtained from a .wav file. The last block of the diagram is a UHD: USRP Sink block with Center Freq set to 98.4 MHz (&lt;em&gt;this does not matter much, could be any frequency between 88 MHz and 108 MHz&lt;/em&gt;).&lt;/p&gt;&#xA;&lt;p&gt;The thing is that in order for the design to work I have to set the Frequency parameter of the Signal Source block to 0 and the Center Freq parameter in USRP Sink in the one I am interested in (&lt;em&gt;in this case 98.4 MHz&lt;/em&gt;). With this setup the transmitter works perfectly.&lt;/p&gt;&#xA;&lt;p&gt;On the other hand, if I set up the Frequency parameter of the Signal Source block to 98.4 MHz (&lt;em&gt;which i think is the right thing to do&lt;/em&gt;) the trasmitter does not work, it transmits the original audiofile with a lot of background noise, like if the signal source is messing with the baseband signal. Can someone please explain the reason of this behaviour? I don't understand how it can work if the output of the Signal Source is a signal of frequency 0 and constant amplitude.&lt;/p&gt;&#xA;&lt;p&gt;This is my flow graph in GNU Radio:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/njECD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/njECD.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17338" LastActivityDate="2020-07-06T15:58:40.420" Title="GNU Radio - Frequency parameter of Signal Source Block" Tags="&lt;gnuradio&gt;&lt;fm&gt;&lt;usrp&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16956" PostTypeId="2" ParentId="16955" CreationDate="2020-07-06T15:58:40.420" Score="4" Body="&lt;p&gt;For a complex-valued sampled stream, the sample rate must be &lt;a href=&quot;https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;greater than twice the signal represented&lt;/a&gt;. The sample rate in your graph is set to 384k, so it's not possible to represent a 98400 kHz signal.&lt;/p&gt;&#xA;&lt;p&gt;GNU Radio won't stop you, though. Mathematically, when you try to generate a sampled signal that's too high, you get &lt;a href=&quot;https://en.wikipedia.org/wiki/Aliasing#Sample_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;aliasing&lt;/a&gt;. As an experiment, try creating a graph with a signal source going into a frequency sink, and observe what happens when you try generating a signal at or above the sample rate.&lt;/p&gt;&#xA;&lt;p&gt;While you could theoretically increase the sample rate, this would be computationally inefficient. If you sampled at (for example) 200 MHz, you could represent signals anywhere between but not including -100 MHz and 100 MHz. The bandwidth of your signal is probably much less than 200 MHz, and all the bandwidth that isn't occupied by your signal contains no information. Thus you use a lot of compute resources calculating nothing.&lt;/p&gt;&#xA;&lt;p&gt;So most radios, with the exception of those that work at frequencies low enough where the computational overhead isn't too high, include a &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_mixer&quot; rel=&quot;nofollow noreferrer&quot;&gt;frequency mixer&lt;/a&gt; to convert a &amp;quot;baseband&amp;quot; input (often at 0 Hz, or sometimes a little higher to avoid negative frequencies) up to RF, in your case 98.4 MHz. A mixer can also perform the opposite operation on receive so a signal at some high radio frequency can be mixed down to a lower baseband frequency for more efficient processing.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-06T15:58:40.420" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16957" PostTypeId="1" CreationDate="2020-07-06T17:29:18.547" Score="1" ViewCount="32" Body="&lt;p&gt;I have one of those wireless weather sensor things that stopped transmitting.  Inside is one of those ubiquitous R433A SAW resonators that transmit on 433.92MHz.  I've verified that the board it's on is getting V+ and Data, so clearly problem is on the transmitter board itself.  So the question is, are those R433As known to go bad often?  (Often when something goes bad, someone will say, &amp;quot;Oh, trying replacing that first, it's usually the problem.&amp;quot;)&lt;/p&gt;&#xA;" OwnerUserId="9974" LastEditorUserId="8713" LastEditDate="2021-02-08T00:26:52.040" LastActivityDate="2021-02-08T00:26:52.040" Title="R433A SAW Resonator" Tags="&lt;transmission&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16958" PostTypeId="1" AcceptedAnswerId="16962" CreationDate="2020-07-06T19:54:31.220" Score="5" ViewCount="146" Body="&lt;p&gt;Just made my first 2m/70cm diplexer. Important: I aim to be able to use this up to 50 Watts.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/m3qUZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/m3qUZ.jpg&quot; alt=&quot;layout with broken 0603 caps&quot; /&gt;&lt;/a&gt;&#xA;S21 from the LP section:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Trjwv.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Trjwv.jpg&quot; alt=&quot;S21 LP section&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Having access to regular distributors such as Farnell/Element14, Mouser, Digikey,... I searched for RF capacitors with a voltage rating of over 200Volts, and only found SMD parts. Most of them 0603.&#xA;In theory not an issue, in practice they don't handle the stress of the inductors very well. Some of them cracked quite quickly and it's clear this is not permanent option.&lt;/p&gt;&#xA;&lt;p&gt;Searching around it seems that C0G or SL dielectric caps could be used for RF capacitors, but I can't seem to find out what kind of specifications I would be checking.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;What kind of caps are readily available, and how to choose them (for frequencies up to 450MHz)?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I have a bunch of these variable capacitors (gift from a -now SK- elmer), but no specifications. They do trim to all the values I'd need, but since there is just a tiny bit of space between the plates, I suppose these won't be useable (or at least not for long) for my application?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0NZAp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0NZAp.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Close-up of the plates (there's a thin layer of plastic in between):&#xA;&lt;a href=&quot;https://i.stack.imgur.com/CN5o5.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CN5o5.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qsfSz.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qsfSz.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;[EDIT]&#xA;I think the issue is with my construction technique.&lt;/p&gt;&#xA;&lt;p&gt;I've tried to keep lengths as short as possible, maybe too short. In the lowpass leg for example, I soldered the capacitors tombstone (standing up) to the grounplane and soldered the inductors directly to the capacitors. So one side of the cap is literally the connection point for two inductors.&lt;/p&gt;&#xA;&lt;p&gt;The start of the high-pass leg is a capacitor soldered to the center pin of the n connector, with an inductor soldered to the other side. That mechanical force of that inductor has torn the capacitor in two (possible to see that in the last picture below, bottom left).&lt;/p&gt;&#xA;&lt;p&gt;I guess I should better cut out &amp;quot;pads&amp;quot; in the ground plane to serve as connection points instead of using the capacitors as direct connections?&#xA;Feels a bit stupid now...&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Q3Bia.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Q3Bia.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8263" LastEditorUserId="8263" LastEditDate="2020-07-13T13:51:36.990" LastActivityDate="2020-07-13T13:51:36.990" Title="How to prevent cracking the capacitors in my diplexer?" Tags="&lt;diplexer&gt;&lt;components&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="16959" PostTypeId="2" ParentId="12999" CreationDate="2020-07-06T20:47:44.320" Score="3" Body="&lt;p&gt;I received such notification while listening on 2182 kHz and phoned the Coast Guard with the broadcast-in-blind details I copied.&lt;/p&gt;&#xA;&lt;p&gt;Their Coast station told the ship in distress to call the commercial station that was copying them! I called the Coast Guard back to notify them that I couldn't respond and was not a maritime station.&lt;/p&gt;&#xA;&lt;p&gt;Happy ending, ship met by coast guard, dewatering pumps delivered and ship pumped out in time to avert sinking, ship towed to nearest port.&lt;/p&gt;&#xA;" OwnerUserId="17360" LastActivityDate="2020-07-06T20:47:44.320" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16960" PostTypeId="1" AcceptedAnswerId="17003" CreationDate="2020-07-07T01:20:53.143" Score="3" ViewCount="282" Body="&lt;p&gt;I want to measure quartz crystal motional parameters with a VNA, unfortunately all Google searches I've done have lead me to nothing in concrete. I know how to get an impedance curve and measure the parallel and series resonant frequencies but I dont know how to extract the motional parameters from it. Im looking for a relatively easy way to do it, rather than a lot of tweaking in computer software.&#xA;I found this YouTube video &lt;a href=&quot;https://www.youtube.com/watch?v=LyAQqqIsBOM&quot; rel=&quot;nofollow noreferrer&quot;&gt;Crystal Filters &amp;amp; Crystals, Part 1 (Adv. 13)&lt;/a&gt; which finds the motional parameters but it is an overly complicated process and you need extra software.&lt;/p&gt;&#xA;&lt;p&gt;I am using a miniVna Pro. Is there a way to do this?&lt;/p&gt;&#xA;" OwnerUserId="4491" LastActivityDate="2020-07-17T00:37:52.997" Title="How to measure quartz crystal motional parameters using a VNA?" Tags="&lt;filter&gt;&lt;crystal-radio&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16961" PostTypeId="2" ParentId="12928" CreationDate="2020-07-07T15:33:35.773" Score="0" Body="&lt;p&gt;You can get foam to cover the drivers from AKG parts supplier eg for AKG K240, at cost of a few backs. Also polyester fabric can be used.&#xA;&lt;a href=&quot;https://www.fullcompass.com/brand/akg-akg/accessories/parts-replacement-service/?page=2&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fullcompass.com/brand/akg-akg/accessories/parts-replacement-service/?page=2&lt;/a&gt;&#xA;Also this one from Beyerdynamics might fit your needs&#xA;&lt;a href=&quot;https://www.fullcompass.com/prod/130753-beyerdynamic-908669-earpad-foam-insert-for-dt100-and-dt480&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.fullcompass.com/prod/130753-beyerdynamic-908669-earpad-foam-insert-for-dt100-and-dt480&lt;/a&gt;&#xA;Normally the foam and fabric are used to control frequency response above 1kHz and depending on foam and fabric sound characteristics the company tunes their headphones. In DIY, for less highs or opposite people will play with the thickness or kind of material to tune headphones to their liking.&#xA;DIY Audio Heaven site has some interesting reading on headphone and mods.&lt;/p&gt;&#xA;" OwnerUserId="17363" LastEditorUserId="17363" LastEditDate="2020-07-07T15:43:07.987" LastActivityDate="2020-07-07T15:43:07.987" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16962" PostTypeId="2" ParentId="16958" CreationDate="2020-07-07T17:03:28.410" Score="4" Body="&lt;p&gt;I bet you can make this work reliably with an SMT MLCC. You just need something bigger than an 0603. If you switch to leaded capacitors you're going to have a much harder time finding high frequency data since the lead inductance starts to become significant at hundreds of MHz.&lt;/p&gt;&#xA;&lt;p&gt;I'd suggest searching with manufacturer tools rather than distributor tools. You'll find the manufacturers have better tools that will provide more data so you can make the right part selection.&lt;/p&gt;&#xA;&lt;p&gt;For example, muRata has &lt;a href=&quot;https://www.murata.com/en-us/tool&quot; rel=&quot;nofollow noreferrer&quot;&gt;SimSurfing&lt;/a&gt;. If you look at the &lt;a href=&quot;https://ds.murata.co.jp/simsurfing/mlcc.html?lcid=en-us#&quot; rel=&quot;nofollow noreferrer&quot;&gt;MLCC tool&lt;/a&gt;, select a part (or a few parts) and then go to &amp;quot;Characteristic Graph&amp;quot; -&amp;gt; &amp;quot;Individual Characteristic Data&amp;quot; -&amp;gt; &amp;quot;Temp rise&amp;quot;, and you can get a little graph like this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eVqND.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eVqND.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;You can also get plots of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Dissipation_factor&quot; rel=&quot;nofollow noreferrer&quot;&gt;dissipation factor&lt;/a&gt; (DF), complex impedance, and all kinds of other stuff that will help you not only ensure the capacitor won't overheat and crack, but also select a capacitor with low losses so that your diplexer will have sufficient performance.&lt;/p&gt;&#xA;&lt;p&gt;Be sure to do a little analysis or simulation of your circuit to find the RMS current and peak voltage, which could be a lot more than what you'd expect from just 50 watts into 50 ohms. And be sure to build in a healthy safety margin. Remember larger packages can dissipate more heat, so you may need to look for devices with a higher voltage rating just for the larger package, even if you don't need to handle that much voltage.&lt;/p&gt;&#xA;&lt;p&gt;I just picked muRata as an example, but every major manufacturer has something like this. Usually a search for &amp;quot;[manufacturer] mlcc selection tool&amp;quot; will find it.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;While I suspect you do need bigger capacitors to make this work, and you can get better performance with a larger capacitor as well, additionally I'll suggest an alternative construction technique. MLCCs are very fragile (they are a bunch of thin, brittle ceramic layers, after all) so you definitely don't want any mechanical strain on them.&lt;/p&gt;&#xA;&lt;p&gt;One solution is to etch out little pads on the main board for the caps.&lt;/p&gt;&#xA;&lt;p&gt;If you don't want to do that, you could cut little pieces of board with the copper cut away in the middle, solder the caps to that, and then solder the inductors to the board. This way the PCB takes all the strain. Also keep in mind the PCB acts as a heat sink, so you might want to deliberately keep these mini-boards wider than necessary.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-07-12T19:09:46.293" LastActivityDate="2020-07-12T19:09:46.293" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="16963" PostTypeId="1" CreationDate="2020-07-07T21:00:10.150" Score="2" ViewCount="179" Body="&lt;p&gt;Beverage antenna consist of pair of transmission lines - one being the &amp;quot;antenna proper&amp;quot;, the other ground.&#xA;The antenna is being fed via open feed line ( approximately 450 Ohms ) - one side of line being &amp;quot;hot&amp;quot; and the other grounded.&#xA;To achieve directivity , the antenna is also grounded , via 600 Ohm resistor at the far end.&lt;/p&gt;&#xA;&lt;p&gt;The antenna is designed to be used on 14MHZ band and is little over  2 wavelength long.&lt;/p&gt;&#xA;&lt;p&gt;The antenna works adequately as a receiving antenna.&#xA;I can adjust my antenna coupler for maximum signal strength.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;How do I adjust&lt;/strong&gt; this , non - resonant antenna ,  to have MAXIMUM transfer of RF when used as transmitting antenna with 50Ohms &amp;quot;source&amp;quot; ?&lt;/p&gt;&#xA;" OwnerUserId="17365" LastEditorUserId="8717" LastEditDate="2020-08-06T14:40:10.577" LastActivityDate="2020-08-06T15:36:56.457" Title="How to match transmitter to Beverage antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="2" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16964" PostTypeId="2" ParentId="16963" CreationDate="2020-07-07T21:33:37.027" Score="2" Body="&lt;p&gt;Beverage antennas are extremely inefficient. For receive applications this is not much of a problem, but for transmitting it's a big problem.&lt;/p&gt;&#xA;&lt;p&gt;As such, trying to match a transmitter to such an antenna is a futile exercise. At best, what you would achieve would not be much better than a dummy load. Most of your transmitter power will just make warm soil. You would get much better results from nearly any other antenna, even if it is just a mobile whip with a terrible ground plane.&lt;/p&gt;&#xA;&lt;p&gt;That said, matching a transmitter to a Beverage antenna is no different than matching a transmitter to any other antenna. You could use an antenna tuner or make a fixed matching network from capacitors, inductors, transformers, and/or transmission lines.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-07T21:33:37.027" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16966" PostTypeId="1" AcceptedAnswerId="16969" CreationDate="2020-07-08T15:00:18.113" Score="2" ViewCount="62" Body="&lt;p&gt;I bought a Baofeng UV-5RE of Alibaba for a little over $30. It seems to work as expected, all the menu items are consistent with the YouTube videos I watched but... the little power icon at the top of the display is reversed.&lt;/p&gt;&#xA;&lt;p&gt;When I change the TXP setting to LOW a little &lt;code&gt;H&lt;/code&gt; appears at the top of the display. When I change the TXP setting the HIGH the &lt;code&gt;H&lt;/code&gt; icon disappears again. I would expect the &lt;code&gt;H&lt;/code&gt; to be visible when the transmission power is set to HIGH, not the other way round.&lt;/p&gt;&#xA;&lt;p&gt;The WN setting makes more sense. A little &lt;code&gt;N&lt;/code&gt; is shown when I set it to narrow band and disappears when it's set to wide band.&lt;/p&gt;&#xA;&lt;p&gt;Anyone knows if this a simple bug or did I buy a fake radio?&lt;/p&gt;&#xA;" OwnerUserId="17370" LastEditorUserId="17370" LastEditDate="2020-07-08T18:38:53.437" LastActivityDate="2020-07-08T18:38:53.437" Title="Baofeng UV-5RE shows wrong TXP icon" Tags="&lt;baofeng&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16967" PostTypeId="1" AcceptedAnswerId="16970" CreationDate="2020-07-08T16:34:22.517" Score="1" ViewCount="72" Body="&lt;p&gt;I've seen &lt;a href=&quot;https://ventenna.com/Ham-Description.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;ham radio antennas that slide over a vent stack&lt;/a&gt;. The usually way to connect them to the transceiver is to lay the feedline across the roof. However, the manufacturer provides instructions for &lt;a href=&quot;https://ventenna.com/files/Inside-Coax.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;hiding the feedline inside the vent&lt;/a&gt;. They suggest poking a hole in the existing vent and sealing it around the feedline.&lt;/p&gt;&#xA;&lt;p&gt;I'd like to do something similar, except in my case I'd like to replace an abandoned weatherhead  (which used to run to the load center) with a PVC pipe which looks like just another vent pipe. I'd check to make sure the weatherhead really is disconnected from the house wiring first. Then I'd put an antenna inside this PVC pipe. There are a few advantages to this:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;I can get rid of part of the ugly weatherhead.&lt;/li&gt;&#xA;&lt;li&gt;I don't have to re-do the flashing around the vent.&lt;/li&gt;&#xA;&lt;li&gt;I'll gain a 2m / 70cm antenna on the roof.&lt;/li&gt;&#xA;&lt;li&gt;Since the PVC pipe isn't really a vent at all, I'm free to run the feedline through it instead of across the top of the roof.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;However, I'm concerned about proper lightning protection. I don't live in an area with much lightning, but what's preventing lightning from striking my PVC pipe antenna and traveling down the shield of my feedline inside the attic down to my transceiver? The Ventenna article I reference makes no mention of lightning protection. Is there something intrinsic about a PVC vent stack antenna that obviates the need for lightning protection on the feedline when the feedline goes inside the vent itself?&lt;/p&gt;&#xA;&lt;p&gt;If I did want to provide some lightning protection on my feedline, how should I do that? I don't want sparks inside the attic. I might just end up with a &lt;a href=&quot;https://www.firefighternation.com/2011/11/28/fire-cellulose-insulation/#gref&quot; rel=&quot;nofollow noreferrer&quot;&gt;smoldering fire in the 50-year old cellulose insulation&lt;/a&gt; that burns down the structure at a later date.&lt;/p&gt;&#xA;" OwnerUserId="5820" LastActivityDate="2020-07-08T20:48:32.563" Title="Lightning protection for a vent stack antenna" Tags="&lt;antenna-construction&gt;&lt;lightning&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16968" PostTypeId="1" CreationDate="2020-07-08T17:22:28.680" Score="2" ViewCount="154" Body="&lt;p&gt;I'm trying to make learning of the NATO alphabet interesting for kids. I invite them to spell car plate numbers during vacation with their parents. So both, the kids and the parents will learn the alphabet.&lt;/p&gt;&#xA;&lt;p&gt;Personally, I think knowing the NATO alphabet is something you learn for your whole life, not just because it's required for the amateur radio license. It's also simple enough. Both my 10 and 7 year old children know it already.&lt;/p&gt;&#xA;&lt;p&gt;I'm trying to find more examples where the NATO alphabet is used. So far I have:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;radio amateurs, of course&lt;/li&gt;&#xA;&lt;li&gt;pilots&lt;/li&gt;&#xA;&lt;li&gt;military&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I'm not sure about&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;international aid agencies&lt;/li&gt;&#xA;&lt;li&gt;fire fighters in countries which have English as the primary language&lt;/li&gt;&#xA;&lt;li&gt;police -&amp;quot;-&lt;/li&gt;&#xA;&lt;li&gt;ISS, the space station&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I'd like my list of uncertain uses be confirmed or falsified and what other uses of the NATO alphabet could I list to emphasize the importance of the NATO alphabet?&lt;/p&gt;&#xA;" OwnerUserId="890" LastEditorUserId="873" LastEditDate="2021-02-10T12:57:09.757" LastActivityDate="2021-02-11T14:54:05.580" Title="Convincing kids to learn NATO alphabet" Tags="&lt;phonetic-alphabet&gt;&lt;children&gt;" AnswerCount="3" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16969" PostTypeId="2" ParentId="16966" CreationDate="2020-07-08T18:24:19.517" Score="0" Body="&lt;p&gt;Seems like a bug to me, or at least a mismatch between the firmware/board and the display used. On both my [somewhat] newer BTech UV-5X3 and older Baofeng BF-F8+ radios the displays show nothing with TXP set to HIGH and show an &lt;code&gt;L&lt;/code&gt; with TXP set to LOW. On my son's Baofeng BF-F9V2+ it has three settings corresponding to three separate &lt;code&gt;L&lt;/code&gt;/&lt;code&gt;M&lt;/code&gt;/&lt;code&gt;H&lt;/code&gt; cells on its LCD activating as one would expect.&lt;/p&gt;&#xA;&lt;p&gt;What this means as to whether you got a &amp;quot;fake&amp;quot; I have no idea. There can be lots of confusion, miscommunication, and simple prejudices against even genuine Baofeng radios, and many resellers add to this with their own marketing claims as well. It does seem there are many enclosure variations, model numberings, firmware builds, and probably circuitry that get combined in mysterious ways.&lt;/p&gt;&#xA;&lt;p&gt;If you have access to RF test equipment or even just a basic RTL-SDR [and attenuator for close-up testing!] you might check its transmissions in case the mismatch extends beyond the display and to the radio circuitry — does it transmit the correct frequency and modulation index? Does it seem to be filtering as well as to be expected? &amp;quot;The proof of the pudding is in the eating&amp;quot; and whether the display glitch itself is worth a dispute is between you and the seller and the marketplace I suppose!&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-07-08T18:24:19.517" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16970" PostTypeId="2" ParentId="16967" CreationDate="2020-07-08T20:48:32.563" Score="3" Body="&lt;p&gt;Protecting equipment and property with an antenna such as this is no different than with any other antenna. See &lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-08T20:48:32.563" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16971" PostTypeId="1" AcceptedAnswerId="16973" CreationDate="2020-07-09T04:27:52.720" Score="1" ViewCount="111" Body="&lt;p&gt;I live in an apartment. I don't have control over all of the appliances but perhaps I can mitigate if I know where the noise is coming from and under what circumstances.&lt;/p&gt;&#xA;&lt;p&gt;If I'm shopping for such a detection device, what are the keywords I should be using? What is the name of the device I am looking for? Could I make my own? How tough would that be?&lt;/p&gt;&#xA;&lt;p&gt;Edit: It's occurred to me that the RFI at this location could be coming from more than just Common Mode. The massive radio tower near the National Voice of American Museum is nearly within sight from here and I can see a cell tower also. Not so much for power transmition cables. They all seem to be underground in the immediate area of this complex. Maybe I'm just too close to these?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://mediad.publicbroadcasting.net/p/wvxu/files/styles/x_large/public/201702/voa_may_2015_w_sign.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;National Voice Of America Museum&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://worldradiomap.com/us-oh/cincinnati_img/wlw_09.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;Nearby Radio Towers&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15859" LastEditorUserId="15859" LastEditDate="2020-07-09T19:30:11.303" LastActivityDate="2020-07-10T23:07:26.057" Title="What is the name of a device used to detect noisy appliances?" Tags="&lt;rfi&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16972" PostTypeId="2" ParentId="16971" CreationDate="2020-07-09T07:54:32.713" Score="0" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;If I'm shopping for such a detection device, what are the keywords I should be using? What is the name of the device I am looking for?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Now, I'm interepreting this as&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;em&gt;I'm looking for sources of radio-frequency noise, and I need to find them, for reasons that are professional and not limited to a specific interference ocurrence.&lt;/em&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The device that you want to use for that purpose is a &lt;em&gt;Spectrum Analyzer&lt;/em&gt;. It is a measurement device that shows at which frequencies there is power &amp;quot;in the air&amp;quot;. It typically works over a large range of frequencies, e.g. from 800 kHz up to 8 GHz.&lt;/p&gt;&#xA;&lt;p&gt;You'll also want a set of  antennas that work on a very wide band, so you don't have to switch antennas for every single band you test.&lt;/p&gt;&#xA;&lt;p&gt;Just like the me measurement device, if you want these power readings to be physically meaningful, your antennas need to be calibrated, if you want the output to actually represent the power that is in the air. This is kind of important, considering &amp;quot;off by a factor of 100&amp;quot; not unusual for antenna properties for the same antenna at different frequencies.&lt;/p&gt;&#xA;&lt;p&gt;Such (entry-level) devices look like &lt;a href=&quot;https://de.farnell.com/rohde-schwarz/r-s-fph-p6/spektrumanalysator-hh-5khz-bis/dp/2924689&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WNAOM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WNAOM.jpg&quot; alt=&quot;Rohde und Schwarz handheld spectrum analyzer&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;or &lt;a href=&quot;https://de.farnell.com/keysight-technologies/n9322c/spektrumanalysator-tisch-9khz/dp/3262660?st=spektrumanalysator&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/teY3I.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/teY3I.jpg&quot; alt=&quot;Keysight Desktop spectrum analyzer&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;You'll pretty quickly notice the price of these things is in the region of &amp;quot;car&amp;quot; if you have modest requirements. (There's literally no limit upwards – at some point you get into the range where Keysight will offer you a custom solution, but then you're in the ballpark of megaeuros.) The price very much scales with the range of frequencies that can be observed, so in the interest of your savings account, you will need to first understand what you're trying to measure (&amp;quot;noise&amp;quot; isn't really telling us anything), and then define requirements for your device from that.&lt;/p&gt;&#xA;&lt;p&gt;There are things on amazon that are scams, but try to take money from people worried about &amp;quot;noise&amp;quot; with no understanding of what that is. Don't buy them, they are a scam. &lt;a href=&quot;https://electronics.stackexchange.com/questions/264011/how-to-improve-rf-meter/264016#264016&quot;&gt;I've covered that before&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Could I make my own?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Technically: yes. A spectrum analyzer is a technical device, and given theoretically unlimited resources, anything in existence is possible to engineer.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;How tough would that be?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Since you had to ask what kind of device you needed, and it's (and that's OK) not clear you fully understand what you're measuring there: In all honesty, very tough.&lt;/p&gt;&#xA;&lt;p&gt;An electrical engineering degree with a focus on RF electronics, plus signal processing and estimation knowledge would be a plus.&lt;/p&gt;&#xA;&lt;p&gt;It takes decades of experience and large engineering teams to produce sensible spectrum analyzers.&lt;/p&gt;&#xA;&lt;p&gt;You could try to implement one based on an SDR, but the problem will be making it reliable enough so that a calibration would still mean something the next time you turn it on. Also, there's analog reasons that SDRs are available cheaper than spectrum analyzers, and it's that the filters and dynamic ranges necessary for a measurement device are simply way more expensive to buy or build than what SDRs come with.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-07-10T08:57:29.363" LastActivityDate="2020-07-10T08:57:29.363" CommentCount="18" ContentLicense="CC BY-SA 4.0" />
  <row Id="16973" PostTypeId="2" ParentId="16971" CreationDate="2020-07-09T12:55:23.537" Score="3" Body="&lt;p&gt;How do you know the appliances are noisy? Are you hearing noise in your radio? If so, you already have the necessary detection equipment.&lt;/p&gt;&#xA;&lt;p&gt;You can do OK simply unplugging things or flipping circuit breakers to see what makes a difference, and locating the noise source by process of elimination. It can help to have a battery to power your radio: then you can turn off your main breaker and know if the noise sources are even in your apartment.&lt;/p&gt;&#xA;&lt;p&gt;A battery also means you can move around with the radio, and you can find the noise source like playing a game of hot and cold.&lt;/p&gt;&#xA;&lt;p&gt;A portable radio and/or directional antenna can also be useful. There is an activity called &lt;a href=&quot;https://en.wikipedia.org/wiki/Transmitter_hunting&quot; rel=&quot;nofollow noreferrer&quot;&gt;fox hunting&lt;/a&gt; where the participants try to locate a hidden radio beacon. This is essentially the same problem as finding a noise source, and the same equipment is applicable.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-09T12:55:23.537" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="16974" PostTypeId="1" CreationDate="2020-07-09T15:22:47.850" Score="3" ViewCount="185" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hF3hp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hF3hp.jpg&quot; alt=&quot;frame from waterfall display video&quot; /&gt;&lt;/a&gt;I'm getting a lot of noise now that I have a dipole higher up. The pattern on the waterfall makes it seem man made.&lt;/p&gt;&#xA;&lt;p&gt;Could it be power line? Or is it some kind of motor?&lt;/p&gt;&#xA;&lt;p&gt;Here's a short video of the display and waterfall: &lt;a href=&quot;https://streamable.com/podpf3&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://streamable.com/podpf3&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;EDIT: as requested here is the same frequency in AM mode&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://streamable.com/sjfydc&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://streamable.com/sjfydc&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Also here are some other higher frequencies&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://streamable.com/5il04h&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://streamable.com/5il04h&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="12939" LastEditorUserId="12939" LastEditDate="2020-07-09T18:23:51.367" LastActivityDate="2020-07-10T20:04:46.097" Title="What kind of RFI is this?" Tags="&lt;rfi&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16975" PostTypeId="2" ParentId="16974" CreationDate="2020-07-09T15:31:50.063" Score="1" Body="&lt;p&gt;That sounds like an arc in an insulator, lightning arrestor, or loose hardware on a 7 kV power line.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;The repeating patterns might indicate otherwise, but I have seen those on the wideband SDR that the power company's chief engineer brought over a couple of years ago. They were the results of certain lengths of the 7850v line resonating with an odd harmonic of the 60 Hz power line frequency.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;Seeing that that noise is present on another band &lt;strong&gt;without&lt;/strong&gt; those repeating vertical bars on your 7300's FFT display, it is very likely power line noise.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-07-10T20:04:46.097" LastActivityDate="2020-07-10T20:04:46.097" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16976" PostTypeId="2" ParentId="16971" CreationDate="2020-07-09T17:56:53.393" Score="3" Body="&lt;p&gt;For first-pass broadband EMI fox-hunting, I use an old pocket-sized transistor AM radio with a ferrite loopstick antenna.  You can get them as electronic kits, which makes for a nice educational construction project for the kids.  When constructing such a kit, I left the loopstick antenna exposed as an LF/MF EM sniffer probe.&lt;/p&gt;&#xA;&lt;p&gt;I tune between stations, so that I only hear hiss when away from anything powered.  The old AM radio will start buzzing loudly when I get roughly on the order of a meter or so from the offending (LED lamp, USB wall wart, appliance, etc.) EMI emitter.&lt;/p&gt;&#xA;&lt;p&gt;This is several orders of magnitude cheaper than a spectrum analyzer, and vastly more portable as well, for finding what to try unplugging.  Then recheck with your HF/VHF radio to see if the noise floor looks better.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-07-10T23:07:26.057" LastActivityDate="2020-07-10T23:07:26.057" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16977" PostTypeId="2" ParentId="16974" CreationDate="2020-07-09T18:42:37.493" Score="1" Body="&lt;p&gt;It's possible that someone on this site may be able to definitively identify your RFI by watching the short video of your waterfall display, but I doubt it.  Perhaps the best way to identify the type of RFI that you're dealing with is to discover where the RFI is coming from.&lt;/p&gt;&#xA;&lt;p&gt;A simple test could be to switch circuit breakers in your house or apartment off.  If the noise goes away when a breaker is off, then you know the noise generator is powered by that circuit.  It's possible the noise could have something to do with your radio because intermodular distortion, a bad component, etc.  In that case, if you can get your hands on another receiver with a waterfall display, then you might learn something by temporarily using the other radio in place of yours.&lt;/p&gt;&#xA;&lt;p&gt;If you are reasonably certain that the problem isn't in your radio, your house or your apartment, then there's a good chance that the noise is coming from your neighborhood.  An easy thing to do is ask another nearby ham if he or she can hear the noise.  A portable receiver and antenna can be a big help here.  Maybe someone in your club has an HF rig installed in his or her car, and wouldn't mind driving around with you to see where the noise is stronger and weaker.  If the noise is clearly coming from a neighbor's house, maybe the neighbor wouldn't mind flipping circuit breakers to help you find the source of the RFI.&lt;/p&gt;&#xA;&lt;p&gt;The ARRL has a very helpful web page about RFI &lt;a href=&quot;http://www.arrl.org/radio-frequency-interference-rfi&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; containing lots of links to other articles.  Also the ARRL has written a book about the subject, the ARRL RFI Book, which is surely packed with excellent advice.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-07-09T18:42:37.493" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16978" PostTypeId="1" CreationDate="2020-07-10T07:50:53.037" Score="1" ViewCount="35" Body="&lt;p&gt;I'm working on a &lt;a href=&quot;https://www.st.com/resource/en/datasheet/s2-lp.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;S2LP from ST&lt;/a&gt; and I am configuring the RX digital filter.&#xA;I need to calculate the bandwidth of the signal which has 2GFSK modulation.&lt;/p&gt;&#xA;&lt;p&gt;Do you think the code below is correct for estimating the signal bandwidth for a given XO and a given datarate ?&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;    uint8_t xo_ppm = 10;&#xA;    xRadioInit.lFrequencyBase = 869400000;&#xA;    xRadioInit.lDatarate = 80000;&#xA;    xRadioInit.lFreqDev = xRadioInit.lDatarate / 2;&#xA;&#xA;    double drift = (xo_ppm / 1e6) * xRadioInit.lFrequencyBase;&#xA;    xRadioInit.lBandwidth = xRadioInit.lDatarate + 2 * xRadioInit.lFreqDev + 2 * uint32_t(drift);&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TKwCz.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TKwCz.jpg&quot; alt=&quot;Screenshot of PDF&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17377" LastEditorUserId="8717" LastEditDate="2020-07-10T20:14:10.467" LastActivityDate="2020-07-10T20:14:10.467" Title="2GFSK digital filter bandwidth calculation" Tags="&lt;software-defined-radio&gt;&lt;modes&gt;&lt;software-development&gt;&lt;components&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16979" PostTypeId="2" ParentId="15626" CreationDate="2020-07-10T11:15:26.830" Score="1" Body="&lt;p&gt;What is interesting is I have the exact schematic from Beric Dunn's analyzer using the Si5351a chip.&lt;/p&gt;&#xA;&lt;p&gt;When I use a the germanium diodes,  I get a flat 1.0 reading across the bands with a 50 Ohm resistor load as expected.&lt;/p&gt;&#xA;&lt;p&gt;When I try just replacing the germanium with Schottky (1N5711) I get an SWR of around 3 that slowly creeps up to 4.&lt;/p&gt;&#xA;&lt;p&gt;I would really like to use SMD parts and try the design you came up with Peter.  Any chance you can share the final schematic?&lt;/p&gt;&#xA;&lt;p&gt;73 Jeff I&lt;/p&gt;&#xA;" OwnerUserId="17222" LastActivityDate="2020-07-10T11:15:26.830" CommentCount="16" ContentLicense="CC BY-SA 4.0" />
  <row Id="16980" PostTypeId="1" CreationDate="2020-07-10T13:48:49.143" Score="5" ViewCount="83" Body="&lt;p&gt;Looking at the diplexer schematic from &lt;a href=&quot;https://ham.stackexchange.com/questions/16958/where-to-get-leaded-rf-capacitors&quot;&gt;this&lt;/a&gt; nice question,&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uz8Wg.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uz8Wg.png&quot; alt=&quot;Diplexer schematic&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I realized this can completely be done in PCB-formed elements (minus the connectors). (As a kind of counter-action to the original question's intent to get leaded capacitors, I'm not only trying to eliminate the leads, but also the discrete components.)&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the 50Ω aren't actually resistors, they are the wave impedance of the cable / device you attach there&lt;/li&gt;&#xA;&lt;li&gt;a 20mm × 20mm rectangular plate capacitor formed by patches on the top and bottom layer of a 0.8mm thick piece of FR-4 (&lt;span class=&quot;math-container&quot;&gt;$\varepsilon=4.7\varepsilon_0$&lt;/span&gt;) is about 20 pF&lt;/li&gt;&#xA;&lt;li&gt;There's PCB coil designs that provice up to µH in inductance.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Now, assuming I don't plan to work with as high power as the original question, but still substantial power (5W) in a relevant range of 20 MHz – 500 MHz:&lt;/p&gt;&#xA;&lt;p&gt;Would&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;a planar coil antenna &lt;br&gt;&#xA;&lt;a href=&quot;https://www.pcbway.com/project/shareproject/30_turn__6_5_Ohm__1__PCB_coil__stackable_.html&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VO9An.png&quot; alt=&quot;planar coil, field normal to substrate&quot; /&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;a coil formed through alternating between layers (so that the main magnetic flux is inside the substrate)&#xA;&lt;a href=&quot;https://i.stack.imgur.com/j15yn.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/j15yn.png&quot; alt=&quot;PCB in substrate coil&quot; /&gt;&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;be most effective?&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I'm &lt;em&gt;told&lt;/em&gt; (but I don't have access to the software to simulate that) that planars have low Q. I have no such information on the other choice.&lt;/li&gt;&#xA;&lt;li&gt;Which design has lower self-capacitance?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-07-10T13:48:49.143" Title="Choice of PCB coil design for filter inductor at ca 20 to 400 MHz, 5 W" Tags="&lt;filter&gt;&lt;inductor&gt;" AnswerCount="0" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16981" PostTypeId="1" CreationDate="2020-07-10T17:15:15.537" Score="5" ViewCount="342" Body="&lt;p&gt;I was searching for 1:1 balun designs that would be efficient at VHF yet could easily be made from commonly available materials when I came across these two:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SmYif.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SmYif.png&quot; alt=&quot;two coax baluns&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;While the design on the right seems pretty straightforward, the workings of the left one are a bit of a mystery to me. A quarter-wave shorted stub will, as far as I understand, look like an open circuit at the resonant frequency, so it seems like it shouldn't have any effect, at least if treated as a perfect transmission line...&lt;/p&gt;&#xA;&lt;p&gt;So how (if at all) does it function as a balun, and what are the necessary conditions?&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it important for the coax from which the stub is made to have the same impedance as the antenna (75 ohms)?&lt;/li&gt;&#xA;&lt;li&gt;Is the crossover (i.e. connecting the shield of the stub to the feedline's center conductor and vice versa) important, or will the balun also work without it?&lt;/li&gt;&#xA;&lt;li&gt;Does the stub have to be oriented in a particular manner relative to the main feedline in order for it to work?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13775" LastEditorUserId="13775" LastEditDate="2020-07-10T23:52:29.750" LastActivityDate="2020-07-17T22:45:55.007" Title="How does this quarter-wave stub balun work?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="16982" PostTypeId="2" ParentId="16981" CreationDate="2020-07-11T04:31:41.160" Score="2" Body="&lt;p&gt;I've never seen a balun design like this and and I'm not entirely certain it works. But if it does, here's how I think it could work:&lt;/p&gt;&#xA;&lt;p&gt;As you say, a shorted quarter-wave stub appears like an open circuit. So the stub is a parallel open circuit to the differential mode: it has no effect.&lt;/p&gt;&#xA;&lt;p&gt;To the common-mode, the stub and the parallel section of feedline make a quarter-wave transmission line.&lt;/p&gt;&#xA;&lt;p&gt;Hm, a quarter-wave transmission line at the feedpoint sounds like a &lt;a href=&quot;http://www.antenna-theory.com/definitions/bazooka.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;sleeve or bazooka balun&lt;/a&gt;. These baluns are made from coaxial, not balanced feedlines. And they can be open or short on the feedline end: if they are open, the sleeve radiates. If they are closed, the sleeve does not radiate.&lt;/p&gt;&#xA;&lt;p&gt;I suspect (though I'm not entirely certain) this is the same idea. If you try to make a sleeve balun that's short on the feedline end and thus does not radiate but with balanced rather than coaxial transmission line, you get a &lt;a href=&quot;https://ham.stackexchange.com/q/3591/218&quot;&gt;folded balun&lt;/a&gt;. If you make it open on the feedline end, you get this design.&lt;/p&gt;&#xA;&lt;p&gt;It works because the common-mode sees, from the perspective of the feedpoint, a short (because the transmission line is open 1/4 wavelength away). This ensures the voltage at each leg of the dipole is symmetrical, which is good. But what's making them symmetrical is common-mode current on that 1/4 wave section of balanced transmission line, which is probably not the best since that means the final 1/4 wavelength of the feedline is radiating and that's probably not what you want. There won't be any common-mode currents on the rest of the feedline, at least.&lt;/p&gt;&#xA;&lt;p&gt;Again, not entirely certain this is correct. But maybe someone can show that I'm right or wrong in the comments.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-11T04:31:41.160" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16984" PostTypeId="1" AcceptedAnswerId="16988" CreationDate="2020-07-11T23:33:41.020" Score="3" ViewCount="109" Body="&lt;p&gt;I searched and couldn't find a direct answer so thought I'd ask.&lt;/p&gt;&#xA;&lt;p&gt;We all know the mantra &amp;quot;traps aren't good as they have losses&amp;quot;, but how much loss are we talking about, really?&lt;/p&gt;&#xA;&lt;p&gt;Am I correct in understanding it is mainly (only?) resistive losses by having more metal to travel through?&lt;/p&gt;&#xA;&lt;p&gt;I'm guessing there's more to it.&lt;/p&gt;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastActivityDate="2020-07-13T17:07:13.273" Title="How much loss is there in traps, really?" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16986" PostTypeId="2" ParentId="16984" CreationDate="2020-07-12T14:55:02.283" Score="2" Body="&lt;p&gt;A trap is usually a notch filter, designed to stop frequencies within a certain band from passing. The theory is that if you have a wire dipole that is electrically tuned for 20m, and then you put a pair of traps in there to ‘cut the antenna short’ when a signal at 21MHz is presented, you can effectively have an antenna that is resonant on 20m and 15m.&lt;/p&gt;&#xA;&lt;p&gt;This cutting short is achieved by having a small LC circuit (inductance and capacitance) that acts as a notch at 15m.&lt;/p&gt;&#xA;&lt;p&gt;But in order for this to work, the trap needs to have zero impedance at 20m, and infinite impedance at 15m. Of course this is not the case, and so adding the trap affects the overall properties of the dipole. Usually, this means that when the traps are added, the wire dipole needs to be shortened to make it resonant on 20m again. A multi band antenna with traps for 10m, 12m, 15m, 20m and 30m will still work on 40m, it will just not be as effective as a 40m dipole.&lt;/p&gt;&#xA;&lt;p&gt;This is all to say that there can be losses of a few dB in an antenna with multiple traps when it is used on its lowest bands.&lt;/p&gt;&#xA;&lt;p&gt;A trap antenna is (as usual with all multi band antennas!) basically a compromise. In an ideal world we would all have the means to put up a resonant antenna for every band we would like to work, but this is not an ideal world.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-07-12T14:55:02.283" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16987" PostTypeId="1" AcceptedAnswerId="17076" CreationDate="2020-07-12T18:49:34.043" Score="3" ViewCount="85" Body="&lt;p&gt;I want to crimp a connector onto some RG58 A/U cable. The cable has a foil shield under the braided shield. What's the recommended way to deal with the foil?&lt;/p&gt;&#xA;&lt;p&gt;Should I treat it just like the braided shield, peeling it back from the dialectic and then putting it between the connector and the ferrule?  Or, should I tear the exposed foil off and discard it?&lt;/p&gt;&#xA;" OwnerUserId="6080" LastActivityDate="2020-07-29T05:02:21.590" Title="How to deal with foil shield when adding a connector?" Tags="&lt;coaxial-cable&gt;&lt;connectors&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16988" PostTypeId="2" ParentId="16984" CreationDate="2020-07-12T18:52:21.800" Score="7" Body="&lt;p&gt;&lt;a href=&quot;https://www.w8ji.com/traps.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;W8JI has some measurements&lt;/a&gt;, and the worst case loss he found for two traps in a dipole was 1.6 dB. These were coaxial traps, operated at their resonant frequency, which is both the worst way to tune a trap, and the worst kind of trap.&lt;/p&gt;&#xA;&lt;p&gt;The losses are indeed mostly resistive losses, but not just because there is more metal. Losses are highest at resonance because this is where current in the trap is at a maximum. The current circulating in the trap at resonance is much higher than it would be if there were no trap. Since resistive losses are proportional to the square of current, this makes a big difference.&lt;/p&gt;&#xA;&lt;p&gt;As such, it's a good idea to move the resonant frequency a little out of the band. This will reduce current and consequently loss in the trap significantly while still providing sufficient impedance for the trap to be effective.&lt;/p&gt;&#xA;&lt;p&gt;Far away from resonance, the trap is effectively a loading coil. Current isn't very high and so losses in the trap itself are negligible, however the shortening of the antenna reduces radiation resistance and thus makes all the other losses in the antenna system more significant. More traps for more bands means more shortening and less efficiency.&lt;/p&gt;&#xA;&lt;p&gt;It's hard to say generally just how much loss this ends up being: I'd bet in most situations ground losses are the most significant source of loss, and that can vary quite a bit between local ground conductivity, antenna height (for dipoles), and radials installation (for monopoles).&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-07-13T17:07:13.273" LastActivityDate="2020-07-13T17:07:13.273" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16989" PostTypeId="1" CreationDate="2020-07-13T00:08:17.890" Score="0" ViewCount="298" Body="&lt;p&gt;This is my first ever experience with GNU Radio. I am trying to implement a simple FM receiver shown below with its C++ API.&lt;/p&gt;&#xA;&lt;p&gt;I seem to have pedantically deconstructed this receiver into its smallest components and implemented them with GNU Radio's C++ API but does not work.&lt;/p&gt;&#xA;&lt;p&gt;It runs but I hear no sound which makes me suspect I have misconfigured some component, missed to set some sort of gain, etc.&lt;/p&gt;&#xA;&lt;p&gt;Any feedback is appreciated. Thank you.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y5rkz.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y5rkz.png&quot; alt=&quot;FM Receiver in GNU Radio&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;#include &amp;lt;gnuradio/analog/quadrature_demod_cf.h&amp;gt;&#xA;#include &amp;lt;gnuradio/audio/sink.h&amp;gt;&#xA;#include &amp;lt;gnuradio/blocks/null_sink.h&amp;gt;&#xA;#include &amp;lt;gnuradio/filter/fir_filter_blk.h&amp;gt;&#xA;#include &amp;lt;gnuradio/filter/firdes.h&amp;gt;&#xA;#include &amp;lt;gnuradio/filter/freq_xlating_fir_filter.h&amp;gt;&#xA;#include &amp;lt;gnuradio/filter/iir_filter_ffd.h&amp;gt;&#xA;#include &amp;lt;gnuradio/filter/pfb_arb_resampler_ccf.h&amp;gt;&#xA;#include &amp;lt;gnuradio/top_block.h&amp;gt;&#xA;#include &amp;lt;osmosdr/source.h&amp;gt;&#xA;#include &amp;lt;gnuradio/analog/simple_squelch_cc.h&amp;gt;&#xA;&#xA;void calculate_iir_taps(double tau, float d_quad_rate);&#xA;&#xA;std::vector&amp;lt;double&amp;gt; d_fftaps;  /*! Feed forward taps. */&#xA;std::vector&amp;lt;double&amp;gt; d_fbtaps;  /*! Feed back taps. */&#xA;&#xA;using namespace gr;&#xA;&#xA;int main(int argc, char** argv)&#xA;{&#xA;    int sample_rate = 2.88e6; // audio card sample rate&#xA;    int audio_decimation = 5;&#xA;&#xA;    // Build a top block that ill contain flowgraph blocks&#xA;    top_block_sptr top_block = make_top_block(&amp;quot;fm_radio&amp;quot;);&#xA;&#xA;    osmosdr::source::sptr osmocom = osmosdr::source::make(&amp;quot;rtl=0,repeat=true,throttle=true&amp;quot;);&#xA;    osmocom-&amp;gt;set_center_freq(96.3e6);&#xA;    osmocom-&amp;gt;set_sample_rate(sample_rate);&#xA;    osmocom-&amp;gt;set_gain(20, 0);&#xA;    osmocom-&amp;gt;set_if_gain(20, 0);&#xA;    osmocom-&amp;gt;set_bb_gain(20, 0);&#xA;&#xA;    // Low pass filter&#xA;    unsigned int flt_size = 1024;&#xA;    std::vector&amp;lt;float&amp;gt; low_pass_filter = filter::firdes::low_pass(1, sample_rate, 100e3, 10e3);&#xA;    filter::pfb_arb_resampler_ccf::sptr d_filter = filter::pfb_arb_resampler_ccf::make(288, low_pass_filter, flt_size);&#xA;&#xA;    // WBFM Receive&#xA;    int max_dev = 75e3;&#xA;    int quad_rate = 288e3;&#xA;    float fm_demod_gain = quad_rate / (2 * M_PI * max_dev);&#xA;    analog::quadrature_demod_cf::sptr d_quad = analog::quadrature_demod_cf::make(fm_demod_gain);&#xA;&#xA;    d_fftaps.resize(2);&#xA;    d_fbtaps.resize(2);&#xA;&#xA;    calculate_iir_taps(50.0e-6, quad_rate);&#xA;&#xA;    filter::iir_filter_ffd::sptr d_deemph = \&#xA;        filter::iir_filter_ffd::make(d_fftaps, d_fbtaps, false);&#xA;&#xA;    int audio_rate = quad_rate / audio_decimation;&#xA;    int width_of_transition_band = audio_rate / 32;&#xA;    std::vector&amp;lt;float&amp;gt; d_pll_taps = \&#xA;        filter::firdes::low_pass(1, quad_rate, audio_rate / 2 - width_of_transition_band, width_of_transition_band);&#xA;    filter::fir_filter_fff::sptr low_pass_filter2 = \&#xA;        filter::fir_filter_fff::make(1, d_pll_taps);&#xA;&#xA;    // Rational Resamplifier - might not be needed hence not used atm&#xA;    filter::freq_xlating_fir_filter_ccf::sptr filt = \&#xA;    gr::filter::freq_xlating_fir_filter_ccf::make(288, {1}, 0.0, sample_rate);&#xA;&#xA;    audio::sink::sptr sink = audio::sink::make(48000);&#xA;&#xA;    top_block-&amp;gt;connect(osmocom, 0, d_filter, 0);&#xA;    top_block-&amp;gt;connect(d_filter, 0, d_quad, 0);&#xA;    top_block-&amp;gt;connect(d_quad, 0, d_deemph, 0);&#xA;    top_block-&amp;gt;connect(d_deemph, 0, low_pass_filter2, 0);&#xA;    top_block-&amp;gt;connect(low_pass_filter2, 0, sink, 0);&#xA;&#xA;    top_block-&amp;gt;run();&#xA;&#xA;    return 0;&#xA;}&#xA;&#xA;void calculate_iir_taps(double tau, float d_quad_rate)&#xA;{&#xA;    if (tau &amp;gt; 1.0e-9)&#xA;    {&#xA;        // copied from fm_emph.py in gr-analog&#xA;        double  w_c;    // Digital corner frequency&#xA;        double  w_ca;   // Prewarped analog corner frequency&#xA;        double  k, z1, p1, b0;&#xA;        double  fs = d_quad_rate;&#xA;&#xA;        w_c = 1.0 / tau;&#xA;        w_ca = 2.0 * fs * tan(w_c / (2.0 * fs));&#xA;&#xA;        // Resulting digital pole, zero, and gain term from the bilinear&#xA;        // transformation of H(s) = w_ca / (s + w_ca) to&#xA;        // H(z) = b0 (1 - z1 z^-1)/(1 - p1 z^-1)&#xA;        k = -w_ca / (2.0 * fs);&#xA;        z1 = -1.0;&#xA;        p1 = (1.0 + k) / (1.0 - k);&#xA;        b0 = -k / (1.0 - k);&#xA;&#xA;        d_fftaps[0] = b0;&#xA;        d_fftaps[1] = -z1 * b0;&#xA;        d_fbtaps[0] = 1.0;&#xA;        d_fbtaps[1] = -p1;&#xA;    }&#xA;    else&#xA;    {&#xA;        d_fftaps[0] = 1.0;&#xA;        d_fftaps[1] = 0.0;&#xA;        d_fbtaps[0] = 0.0;&#xA;        d_fbtaps[1] = 0.0;&#xA;    }&#xA;}&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;&lt;code&gt;CMakeLists.txt&lt;/code&gt; for those wanting to try it out:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;cmake_minimum_required(VERSION 3.8)&#xA;&#xA;include_directories(&#xA;    &lt;span class=&quot;math-container&quot;&gt;${GNURADIO_ALL_INCLUDE_DIRS}&#xA;    $&lt;/span&gt;{Boost_INCLUDE_DIRS}&#xA;    $ENV{HOME}/.grc_gnuradio&#xA;)&#xA;&#xA;set(GR_LIBRARIES&#xA;    boost_system&#xA;    gnuradio-blocks&#xA;    gnuradio-filter&#xA;    gnuradio-analog&#xA;    gnuradio-audio&#xA;    gnuradio-runtime&#xA;    gnuradio-pmt&#xA;    gnuradio-osmosdr&#xA;    log4cpp&#xA;)&#xA;&#xA;add_executable(fm_radio fm_radio.cpp)&#xA;target_link_libraries(fm_radio ${GR_LIBRARIES})&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="16422" LastEditorUserId="16422" LastEditDate="2020-07-13T01:50:40.817" LastActivityDate="2020-07-13T01:50:40.817" Title="Implementing FM receiver using GNU Radio C++ API" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16990" PostTypeId="2" ParentId="16989" CreationDate="2020-07-13T00:49:40.837" Score="2" Body="&lt;p&gt;There is at least one error in your code that would result in silence:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;std::vector&amp;lt;double&amp;gt; d_fftaps;  /*! Feed forward taps. */&#xA;std::vector&amp;lt;double&amp;gt; d_fbtaps;  /*! Feed back taps. */&#xA;d_fftaps.resize(2);&#xA;d_fbtaps.resize(2);&#xA;&#xA;filter::iir_filter_ffd::sptr d_deemph = \&#xA;    filter::iir_filter_ffd::make(d_fftaps, d_fbtaps, false);&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;The taps of this IIR filter are all zero (because you &lt;code&gt;resize&lt;/code&gt;d the vectors but did not write any values into them), so the output signal will be always zero.&lt;/p&gt;&#xA;&lt;p&gt;As a quick test to see if this is the sole problem, you can remove the deemphasis filter block entirely; the audio frequency response will be wrong but you'll still be able to tell the difference.&lt;/p&gt;&#xA;&lt;p&gt;You could also remove the squelch block temporarily, as one fewer thing to go wrong. The absolute minimum you need for a receiver that will pass some coherent signal is a decimating low-pass filter to select the desired signal and adapt the sample rate, and the quadrature demodulator; everything else is refinement.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-07-13T00:49:40.837" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16991" PostTypeId="1" CreationDate="2020-07-13T07:45:12.993" Score="1" ViewCount="395" Body="&lt;p&gt;Surprisingly, I am unable to find much info comparing these two antennas. Essentially, they are the same except the one is shorter and top loaded with one wire. Does anyone have any performance data available? The basics I know is that the 1/4 wave vertical will have a lower angle of radiation, but is there any difference in efficiency? Will the 1/4 wave actually have worse local performance than the L?&lt;/p&gt;&#xA;&lt;p&gt;It would be a major expense and work to install, so I want to know the worth. Maybe even just personal anecdotal evidence.&lt;/p&gt;&#xA;&lt;p&gt;In addition, I notice an interesting phenomenon. I currently have a 70ft inverted L. I compared to similar low power MW stations because they are 100% duty cycle, so I can see the effects more clearly. What is interesting is that my signal under good conditions, seems to reach a higher S level (listening through MW SDRs), but under bad conditions, it is worse than the MW station. So it has higher highs, but lower lows. I wonder what causes that? But either way, it leads me to believe that I won't have much better performance, just higher reliability. This is just one comparison however, so it could be in the noise :)&lt;/p&gt;&#xA;" OwnerUserId="1817" LastEditorUserId="1817" LastEditDate="2020-07-13T07:52:52.570" LastActivityDate="2020-07-13T14:04:55.650" Title="Is a 1/4 wave vertical actually better than inverted L on 160m?" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;&lt;tower&gt;&lt;160m-band&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="16992" PostTypeId="1" CreationDate="2020-07-13T09:45:27.867" Score="1" ViewCount="48" Body="&lt;p&gt;A NEC4.2 analysis of the performance of a buried ground rod at the A-C mains entrance of a building shows it be ineffective in removing the common-mode r-f current that can flow along the OD of the shield of a coaxial cable between the transmitter and the input terminals of a dipole antenna.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-07-13T09:45:27.867" Title="Is a Buried Ground Rod for the A-C Mains Service Entrance to a Building Also Useful as an R-F Ground?" Tags="&lt;grounding&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16993" PostTypeId="2" ParentId="16992" CreationDate="2020-07-13T09:45:27.867" Score="1" Body="&lt;p&gt;A rather common expectation is that bonding the outer surface of the shield of a coaxial cable to a buried ground rod effectively &amp;quot;grounds&amp;quot; that conducting surface at radio frequencies.  If that was true, then it would be a good means of removing common-mode currents that can be present in some typical antenna/transmit systems.&lt;/p&gt;&#xA;&lt;p&gt;The study below is an examination of this, leading to the OBSERVATION it includes for the conditions shown there.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tri47.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tri47.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-07-13T09:45:27.867" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16994" PostTypeId="2" ParentId="16991" CreationDate="2020-07-13T11:13:44.180" Score="2" Body="&lt;p&gt;Below is the result of a NEC4.2 comparison of the radiation patterns &amp;amp; gains of the two configurations of radiators, with other things the same.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pdmyA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pdmyA.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-07-13T11:13:44.180" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="16995" PostTypeId="2" ParentId="16991" CreationDate="2020-07-13T13:52:51.227" Score="1" Body="&lt;p&gt;There should be &lt;em&gt;some&lt;/em&gt; difference in efficiency, on the basis that the vertical portion of an inverted-L is &amp;quot;pure radiator&amp;quot;, whereas the horizontal portion functions partially as a capacity hat (but not entirely — it also radiates). You can see this in the fact that an inverted-L has a lower feedpoint impedance than a quarter-wave built for the same band. However, the difference might not be &lt;em&gt;much&lt;/em&gt; in your case.&lt;/p&gt;&#xA;&lt;p&gt;The closest thing I can find to a direct treatment of your question is in W4RNL's &lt;a href=&quot;http://on5au.be/Cebik-2/StraighteningOutTheInverted-l.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Straightening out the inverted-L&lt;/a&gt;. On pages 15-18 of the PDF he considers an inverted-L for 80 meters of 69' total wire length (approximately a half-size version of your antenna) over modest radials and average ground. He doesn't discuss the quarter-wave vertical, but what he does do is look at three variants of the inverted-L: one with the vertical and horizontal segments both 34.5' (&amp;quot;balanced&amp;quot;), one with 23' vertical and 46' horizontal (&amp;quot;short&amp;quot;), and one with 46' vertical and 23' horizontal (&amp;quot;tall&amp;quot;). As expected there are differences in pattern, especially when the antenna is used on higher bands, but focusing just on the design band, he comes up with these numbers:&lt;/p&gt;&#xA;&lt;p&gt;Short: -2.1dBi peak gain at 33° elevation, 31+j7 ohms Z&lt;br /&gt;&#xA;Balanced: -1.5dBi peak gain at 29° elevation, 40+j7 ohms Z&lt;br /&gt;&#xA;Tall: -1.4dBi peak gain at 26° elevation, 49+j10 ohms Z&lt;/p&gt;&#xA;&lt;p&gt;Which suggests that the efficiency effect is definitely there, but that the &amp;quot;balanced&amp;quot; configuration has already reached a point of diminishing returns. If two-thirds vertical is only 0.1dB better than one-half vertical, then all-vertical is probably only 0.1dB better than two-thirds vertical. The radials in Cebik's model are pretty marginal, so maybe an antenna over a better radial field would benefit more from the additional height — but if you don't already &lt;em&gt;have&lt;/em&gt; great radials, then you might find more payoff there.&lt;/p&gt;&#xA;&lt;p&gt;All that said, if you &lt;em&gt;want&lt;/em&gt; to lower your pattern, then additional height will do that for you.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-07-13T14:04:55.650" LastActivityDate="2020-07-13T14:04:55.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16996" PostTypeId="1" AcceptedAnswerId="17327" CreationDate="2020-07-13T15:10:30.140" Score="3" ViewCount="549" Body="&lt;p&gt;I'm just trying to make sure I understand the theory correctly.&lt;/p&gt;&#xA;&lt;p&gt;I have some triband VHF/UHF/800MHz antennas, I need to mount on a tower so I plan on using a &amp;quot;mobile to base&amp;quot; conversion kit.  The kits i'm mostly looking at are specified for VHF/UHF, which in my mind should be sufficient for 800MHz.&lt;/p&gt;&#xA;&lt;p&gt;The way I understand it is that the radials should be &lt;strong&gt;at least&lt;/strong&gt; 1/4 of the wavelength of the antenna, so if the antenna is operating in the 800MHz range the radials that are much longer than 1/4 wave of the 800MHz frequency will not be detrimental in any way at that frequency.&lt;/p&gt;&#xA;&lt;p&gt;Does anyone see any problem with my reasoning?&lt;/p&gt;&#xA;&lt;p&gt;[Update]  ---&lt;/p&gt;&#xA;&lt;p&gt;I just edited my post to provide an example photo/diagram.  I'm looking at a system like this, but the anennas I'm using are multiband VHF/UHF/700/800.  So my resoning is that the ground plane radials should be sized for the VHF band, and that the extra length for the higher frequencies will not negatively affect the antenna.  My understanding is that the radials provide a reflective plane which just must be at least a quarter wave length.  I hope this provides some clearification.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7F718.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7F718.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17109" LastEditorUserId="17109" LastEditDate="2020-07-20T18:06:57.310" LastActivityDate="2020-09-21T15:56:38.780" Title="Ground-Plane radial sizing, is there such thing as too long?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;radial&gt;" AnswerCount="3" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="16997" PostTypeId="1" AcceptedAnswerId="17000" CreationDate="2020-07-13T19:12:13.050" Score="3" ViewCount="822" Body="&lt;p&gt;It seems common knowledge that a choke at the antenna feedpoint stops the outside of the coax shield from radiating when transmitting into the antenna.  But what about stopping the outside of the coax shield from picking up noise and sending it to the receiver?  Will that feedpoint choke do anything in that case?  Or does one need another choke at the receiver end as well?&lt;/p&gt;&#xA;" OwnerUserId="12939" LastActivityDate="2020-07-17T23:13:16.897" Title="Do chokes at the antenna feedpoint stop the coax from receiving signals as well, or just transmitting?" Tags="&lt;rfi&gt;&lt;choke-balun&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="16998" PostTypeId="2" ParentId="7847" CreationDate="2020-07-13T19:24:01.487" Score="0" Body="&lt;p&gt;How about a J pole with decoupling below the feed point.&lt;/p&gt;&#xA;" OwnerUserId="17395" LastActivityDate="2020-07-13T19:24:01.487" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="16999" PostTypeId="2" ParentId="16997" CreationDate="2020-07-13T21:56:28.010" Score="0" Body="&lt;p&gt;An RF choke works exactly the same for transmit as it does for receive and will also block any noise or received signals induced in the outer of the coax from reaching the receiver.&lt;/p&gt;&#xA;&lt;p&gt;Adding an RF choke at the receiver won't help with blocking any common mode current which exists on the outside of the coax as this current flows into the coax at the antenna end and adds to the current traveling towards the receiver on the inside of the shield of the coax.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-07-13T23:28:17.463" LastActivityDate="2020-07-13T23:28:17.463" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17000" PostTypeId="2" ParentId="16997" CreationDate="2020-07-13T22:02:34.193" Score="6" Body="&lt;p&gt;By the principle of &lt;a href=&quot;https://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)&quot; rel=&quot;noreferrer&quot;&gt;reciprocity&lt;/a&gt;, if it works for transmit, it works for receive also.&lt;/p&gt;&#xA;&lt;p&gt;Possibly if your receiver and transmitter are separate devices you may end up with a situation where no common-mode current was detectable on transmit, and yet common-mode signals did appear in the receiver. However with modern equipment having both receiver and transmitter in the same shielded enclosure, I don't expect this is likely to occur.&lt;/p&gt;&#xA;&lt;p&gt;If you have any doubt, it should not be difficult to test. &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;How to detect common-mode currents or “RF in the shack”?&lt;/a&gt; describes a way to make a common-mode current detector with a clamp-on ferrite bead. Replacing the diode detector with an oscillator turns it into a common-mode current injector. You could then clamp this injector somewhere on the feedline and measure the received power, then repeat with it clamped around something on the other side of the choke.&lt;/p&gt;&#xA;&lt;p&gt;The difference of these measurements will give you a rough estimate of the common-mode isolation. While none of this is calibrated and the measurement setup is also subject to all kinds of leakage paths which will skew the results, you then at least have some number which can demonstrate some improvement if the tests are repeated again after adding an additional choke, running the feedline underground, or undertaking any other measures to suppress or isolate common mode currents.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-13T22:02:34.193" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17001" PostTypeId="1" AcceptedAnswerId="17002" CreationDate="2020-07-14T07:42:49.147" Score="0" ViewCount="77" Body="&lt;p&gt;For a &lt;span class=&quot;math-container&quot;&gt;$N$&lt;/span&gt;-element planar phased array, all the elements are same isotropic antennas. Then, what is the effective area of this array? Is it&#xA;&lt;span class=&quot;math-container&quot;&gt;$$A_e=\frac{\lambda^2}{4\pi}GN$$&lt;/span&gt;&#xA;where &lt;span class=&quot;math-container&quot;&gt;$G$&lt;/span&gt; is the directivity of a fixed angle &lt;span class=&quot;math-container&quot;&gt;$(\theta,\phi)$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&#xA;Meanwhile, as the antennas are isotropic, is the beamforming cause the &lt;span class=&quot;math-container&quot;&gt;$G$&lt;/span&gt; times change in effective area?&lt;/p&gt;&#xA;" OwnerUserId="17397" LastActivityDate="2020-07-14T12:23:39.240" Title="Effective area of a phased array" Tags="&lt;antenna&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17002" PostTypeId="2" ParentId="17001" CreationDate="2020-07-14T12:23:39.240" Score="0" Body="&lt;p&gt;Yes, that's correct.&lt;/p&gt;&#xA;&lt;p&gt;If the elements are isotropic then as you've written it, &lt;span class=&quot;math-container&quot;&gt;$G=1$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;And the effective aperture increases by &lt;span class=&quot;math-container&quot;&gt;$N$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Of course this new aperture is only effective in the direction of the peak(s) of the response, elsewhere it will be less. And this assumes that the elements are far enough apart that there's no coupling between them.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-07-14T12:23:39.240" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17003" PostTypeId="2" ParentId="16960" CreationDate="2020-07-14T15:27:17.117" Score="6" Body="&lt;p&gt;I don't know if this counts as &amp;quot;easy&amp;quot;, but:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Find the series resonant frequency. Multiply this frequency by &lt;span class=&quot;math-container&quot;&gt;$2\pi$&lt;/span&gt; to convert it to an angular frequency, and call that &lt;span class=&quot;math-container&quot;&gt;$\omega_s$&lt;/span&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Note the resistance at this frequency. That's &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Find the parallel resonant frequency, multiply by &lt;span class=&quot;math-container&quot;&gt;$2\pi$&lt;/span&gt;, and call it &lt;span class=&quot;math-container&quot;&gt;$\omega_p$&lt;/span&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Halfway between these resonant frequencies is &lt;span class=&quot;math-container&quot;&gt;$\omega_t$&lt;/span&gt;. Measure the impedance there and call it &lt;span class=&quot;math-container&quot;&gt;$Z_t$&lt;/span&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Calculate the remaining values:&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_p = \mathrm{Re} \left(&#xA;i (\omega_s^2 - \omega_t^2)&#xA;\over&#xA;\omega_t Z_t (\omega_t^2 - \omega_p^2)&#xA;\right) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_s = {C_p (\omega_p^2 -\omega_s^2) \over \omega_s^2} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L = {1 \over C_s \omega_s^2} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;These are derived below as equations 13, 7, and 2.&lt;/p&gt;&#xA;&lt;p&gt;If you can &lt;a href=&quot;https://ham.stackexchange.com/questions/17019/can-the-parallel-capacitance-of-a-quartz-crystal-be-directly-measured&quot;&gt;measure &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; some other way&lt;/a&gt;, then you can skip the measurement at &lt;span class=&quot;math-container&quot;&gt;$\omega_t$&lt;/span&gt; and just use the latter 2 of these equations and the resonant frequencies.&lt;/p&gt;&#xA;&lt;p&gt;Another method is to &lt;a href=&quot;https://www.giangrandi.org/electronics/crystalfilters/xtaltest.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;measure the series resonant frequency with some variable capacitance in series&lt;/a&gt;. This might result in some simpler math, and it doesn't require a VNA: only a sweep generator and a power detector.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Explanation:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/C2VUm.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fC2VUm.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;The impedance of this circuit is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z(\omega) = \left({1 \over -i/(C_s\omega) + i L \omega + R} + i C_p \omega \right)^{-1} \tag 0 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;When &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$C_s$&lt;/span&gt; have reactance equal in magnitude but opposite in sign, we are very close to series resonance. I say close because &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; has some effect, but it's small because the impedance of the lower components is very much lower. The error is about 0.25 Hz for the 14 MHz crystal in the video. If we neglect that error, the math is simpler.&lt;/p&gt;&#xA;&lt;p&gt;Let's define &lt;span class=&quot;math-container&quot;&gt;$\omega_s$&lt;/span&gt; as the series resonant angular frequency. We can then solve this equation for &lt;span class=&quot;math-container&quot;&gt;$C_s$&lt;/span&gt; or &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i \omega_s L = -{1 \over i \omega_s C_s} \tag 1 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L = {1 \over C_s \omega_s^2} \tag 2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_s = {1 \over L \omega_s^2} \tag 3 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The series resonance can be found by the VNA by looking for a frequency where reactance is zero and resistance is on the order of 10 ohms. At this frequency, &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; is the only significant impedance, so:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z(\omega_s) = R \tag 4 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Parallel resonance occurs when the &lt;a href=&quot;https://en.wikipedia.org/wiki/Admittance&quot; rel=&quot;nofollow noreferrer&quot;&gt;admittance&lt;/a&gt; of the two parallel branches of the circuit are equal. Again we're going to accept a little bit of error to simplify the math by neglecting the influence of &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt;. Let's call the parallel resonance angular frequency &lt;span class=&quot;math-container&quot;&gt;$\omega_p$&lt;/span&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = - \left(&#xA;i\omega_p L&#xA;+ {1 \over i\omega_p C_s}&#xA;\right)^{-1} \tag 5 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Substitute equation 2 for &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; and simplify:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = - \left(&#xA;  {i\omega_p \over C_s \omega_s^2}&#xA;+ {1 \over i\omega_p C_s}&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = - \left(&#xA;  {i^2 \omega_p^2  \over i\omega_p C_s \omega_s^2}&#xA;+ {\omega_s^2      \over i\omega_p C_s \omega_s^2}&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = - \left(&#xA;  {i^2 \omega_p^2 + \omega_s^2 \over i\omega_p C_s \omega_s^2}&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = - \left(&#xA;  {i\omega_p C_s \omega_s^2 \over \omega_s^2 - \omega_p^2 }&#xA;\right) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = &#xA;  {i\omega_p C_s \omega_s^2 \over \omega_p^2 - \omega_s^2 }&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_p = {C_s \omega_s^2 \over \omega_p^2 -\omega_s^2 } \tag 6 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_s = {C_p (\omega_p^2 -\omega_s^2) \over \omega_s^2} \tag 7 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Just one more degree of freedom to solve for. Pick some angular frequency that isn't resonant, call it &lt;span class=&quot;math-container&quot;&gt;$\omega_t$&lt;/span&gt;. The impedance measured at this frequency is &lt;span class=&quot;math-container&quot;&gt;$Z_t$&lt;/span&gt;. From equation 0, we can write:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_t = \left({1 \over -i/(C_s\omega_t) + i L \omega_t + R} + i C_p \omega_t \right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Substitute equations 2 and 6 for &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_t = \left(&#xA; {1 \over -i/(C_s\omega_t) + i {1 \over C_s \omega_s^2} \omega_t + R}&#xA; + i {C_s \omega_s^2 \over \omega_p^2 -\omega_s^2 } \omega_t&#xA;\right)^{-1} \tag 8 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now there is only one variable that can't be measured directly by the VNA: &lt;span class=&quot;math-container&quot;&gt;$C_s$&lt;/span&gt;. If we can solve for &lt;span class=&quot;math-container&quot;&gt;$C_s$&lt;/span&gt; we're golden.&lt;/p&gt;&#xA;&lt;p&gt;Unfortunately the solution is &lt;a href=&quot;https://www.wolframalpha.com/input/?i=solve%20z%3D%28%28-i%2F%28C*t%29%20%2B%20i%2F%28C*s%5E2%29*t%2BR%29%5E-1%20%2B%20i%20*%20%28C*s%5E2%29%2F%28p%5E2-s%5E2%29*t%29%5E-1%20for%20C&quot; rel=&quot;nofollow noreferrer&quot;&gt;very hairy&lt;/a&gt;. But it gets &lt;a href=&quot;https://www.wolframalpha.com/input/?i=solve%20z%3D%28%28-i%2F%28C*t%29%20%2B%20i%2F%28C*s%5E2%29*t%29%5E-1%20%2B%20i%20*%20%28C*s%5E2%29%2F%28p%5E2-s%5E2%29*t%29%5E-1%20for%20C&quot; rel=&quot;nofollow noreferrer&quot;&gt;substantially simpler&lt;/a&gt; if we ignore &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_s = {&#xA;i(\omega_p^2 - \omega_s^2)(\omega_s^2 - \omega_t^2)&#xA;\over&#xA;\omega_s^2 \omega_t Z_t (\omega_t^2-\omega_p^2)&#xA;} \tag 9 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Of course, this is going to give you a complex number, and you can't really have a complex-valued capacitor. But we can gloss over that! Just ignore the complex part. As long as we pick a frequency where &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; isn't too significant, the error will be small.&lt;/p&gt;&#xA;&lt;p&gt;Halfway between the series and parallel resonant frequencies seems to work pretty well.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Addendum: it's also possible to start with equation 5 and substitute equation 3 for &lt;span class=&quot;math-container&quot;&gt;$C_s$&lt;/span&gt; instead. I wonder if that leads to a simpler solution:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = - \left(&#xA;i\omega_p L&#xA;+ {1 \over i\omega_p {1 \over L \omega_s^2}}&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = - \left(&#xA;i\omega_p L&#xA;+ {L \omega_s^2 \over i\omega_p}&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = - \left(&#xA;{i^2\omega_p^2 L + L \omega_s^2 \over i\omega_p}&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = -&#xA;{i\omega_p \over i^2\omega_p^2 L + L \omega_s^2}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ i\omega_p C_p = -&#xA;{i\omega_p \over L (\omega_s^2 - \omega_p^2)}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_p =&#xA;{1 \over L (\omega_p^2 - \omega_s^2)}&#xA;\tag{10}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L =&#xA;{1 \over C_p (\omega_p^2 - \omega_s^2)}&#xA;\tag{11}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now we can express the impedance in terms of &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; with substitutions from equations 10 and 3:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_t = \left(&#xA;  {1 \over -i L \omega_s^2 / \omega_t + i L \omega_t + R}&#xA;  + {i \omega_t \over L (\omega_p^2 - \omega_s^2)}&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Which is &lt;a href=&quot;https://www.wolframalpha.com/input/?i=solve%20Z%20%3D%20%281%2F%28-i*L*s%5E2%2Ft%20%2B%20i*L*t%20%2B%20R%29%20%2B%20%28i*t%29%20%2F%20%28L*%28p%5E2-s%5E2%29%29%29%5E-1%20for%20L&quot; rel=&quot;nofollow noreferrer&quot;&gt;still pretty bad&lt;/a&gt; unless &lt;a href=&quot;https://www.wolframalpha.com/input/?i=solve%20Z%20%3D%20%281%2F%28-i*L*s%5E2%2Ft%20%2B%20i*L*t%20%29%20%2B%20%28i*t%29%20%2F%20%28L*%28p%5E2-s%5E2%29%29%29%5E-1%20for%20L&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; is dropped&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ L = {&#xA;i \omega_t Z_t (\omega_p^2 - \omega_t^2)&#xA;\over&#xA;(\omega_p^2 - \omega_s^2)(\omega_s^2 - \omega_t^2)&#xA;} \tag{12} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Or, we can do the same thing for &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; with equations 11 and 7:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_t = \left(&#xA;  {&#xA;1&#xA;\over&#xA;-i/\left({C_p (\omega_p^2 -\omega_s^2) \over \omega_s^2}\omega_t\right)&#xA;+ {i \omega_t \over C_p (\omega_p^2 - \omega_s^2)} + R&#xA;  }&#xA;  + i C_p \omega_t&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_t = \left(&#xA;  {&#xA;1&#xA;\over&#xA;{-i \omega_s^2 \over \omega_t C_p (\omega_p^2 -\omega_s^2)}&#xA;+ {i \omega_t \over C_p (\omega_p^2 - \omega_s^2)} + R&#xA;  }&#xA;  + i C_p \omega_t&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_t = \left(&#xA;  {&#xA;1&#xA;\over&#xA;{-i \omega_s^2 + i \omega_t^2 \over \omega_t C_p (\omega_p^2 - \omega_s^2)}&#xA;+ R&#xA;  }&#xA;  + i C_p \omega_t&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_t = \left(&#xA;  {&#xA;1&#xA;\over&#xA;{i (\omega_t^2-\omega_s^2) \over \omega_t C_p (\omega_p^2 - \omega_s^2)}&#xA;+ R&#xA;  }&#xA;  + i C_p \omega_t&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.wolframalpha.com/input/?i=solve%20Z%20%3D%20%281%2F%28%28i*%28t%5E2-s%5E2%29%29%2F%28t*C*%28p**2-s**2%29%29%2BR%29%2Bi*C*t%29%5E-1%20for%20C&quot; rel=&quot;nofollow noreferrer&quot;&gt;Still hairy&lt;/a&gt;, unless again &lt;a href=&quot;https://www.wolframalpha.com/input/?i=solve%20Z%20%3D%20%281%2F%28%28i*%28t%5E2-s%5E2%29%29%2F%28t*C*%28p**2-s**2%29%29%29%2Bi*C*t%29%5E-1%20for%20C&quot; rel=&quot;nofollow noreferrer&quot;&gt;removing &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt;&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_t = \left(&#xA;{\omega_t C_p (\omega_p^2 - \omega_s^2) \over i (\omega_t^2-\omega_s^2)}&#xA;  + i C_p \omega_t&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_p Z_t = \left(&#xA;{\omega_t (\omega_p^2 - \omega_s^2)&#xA; \over i (\omega_t^2-\omega_s^2)}&#xA;  + i \omega_t&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_p Z_t = \left(&#xA;{\omega_t (\omega_p^2 - \omega_s^2) + i^2 \omega_t (\omega_t^2-\omega_s^2)&#xA; \over i (\omega_t^2-\omega_s^2)}&#xA;\right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_p Z_t = {&#xA;  i (\omega_t^2-\omega_s^2)&#xA;  \over&#xA;  \omega_t (\omega_p^2 - \omega_s^2) - \omega_t (\omega_t^2-\omega_s^2)&#xA;} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_p Z_t = {&#xA;  i (\omega_t^2-\omega_s^2)&#xA;  \over&#xA;  \omega_t (\omega_p^2 - \omega_s^2 - (\omega_t^2-\omega_s^2)) &#xA;} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ C_p = {&#xA;i (\omega_s^2 - \omega_t^2)&#xA;\over&#xA;\omega_t Z_t (\omega_t^2 - \omega_p^2)}&#xA;\tag {13} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is a little better!&lt;/p&gt;&#xA;&lt;p&gt;I threw together an &lt;a href=&quot;https://gist.github.com/bitglue/62526fb031dd0f75e423dacc344de5c9&quot; rel=&quot;nofollow noreferrer&quot;&gt;ugly script&lt;/a&gt; to check the math, using the values from W0QE's video, and the numbers seem to add up.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-07-17T00:37:52.997" LastActivityDate="2020-07-17T00:37:52.997" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="17005" PostTypeId="2" ParentId="16997" CreationDate="2020-07-14T23:45:33.553" Score="0" Body="&lt;p&gt;A common mode choke at the antenna feedpoint will have little to no affect on whether received RF induces signals on the outside shield of a long (relative to the wavelength) coax.&lt;/p&gt;&#xA;&lt;p&gt;If you disconnect and completely take down the antenna, but leave the coax up; then connect the coax shield to a receiver, it will still receive HF signals, likely less than a dozen dB down from when connected to the antenna.  It’s wire in the air.  Perpendicular far field RF will induce currents in it, even if exactly balanced near field EM doesn’t. Think long wire antenna.&lt;/p&gt;&#xA;&lt;p&gt;A choke at the radio would be a better attenuator for this (blocking coax RFI/EMI pickup).&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-07-14T23:45:33.553" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17006" PostTypeId="2" ParentId="16850" CreationDate="2020-07-15T06:05:17.427" Score="1" Body="&lt;p&gt;I am sure the phasing and proper connection of the coax to the individual dipoles will get you a pretty good hemispherical CP pattern.  It is easy to get confused when connecting the coax to the dipole.&lt;/p&gt;&#xA;" OwnerUserId="17404" LastEditorUserId="8717" LastEditDate="2020-08-03T23:34:01.523" LastActivityDate="2020-08-03T23:34:01.523" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17007" PostTypeId="2" ParentId="16937" CreationDate="2020-07-15T06:42:35.937" Score="0" Body="&lt;p&gt;OK, I've checked 5 or 6 types of traps made of different materials, tuned to the same or slightly different frequencies, tuned right on the band, below the band and above the band. Most of them were not better than the first pair. Tuning above the band doesn't work. Traps made of RG58 coax work best. You get SWR 1:1 on both bands, 320 kHz bandwidth on 20m and 225 kHz bandwidth on 40m with SWR &amp;lt;= 2. According to WSPR report the antenna is no less effective than my previous fan dipole was. The article &lt;a href=&quot;https://eax.me/diy-trap-dipole/&quot; rel=&quot;nofollow noreferrer&quot;&gt;An Attic Coaxial-Cable Trap Dipole for 10, 15, 20, 30, 40, and 80 Meters&lt;/a&gt; by John DeGood, NU3E  explains how to make such traps in great detail. Turned out these traps are tuned to the slightly different frequencies below the band.&lt;/p&gt;&#xA;&lt;p&gt;Answering my own question: &lt;strong&gt;NO&lt;/strong&gt;, this is not an expected result. Although such antenna kind of works, you can make a much better one.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-07-15T06:42:35.937" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17008" PostTypeId="1" CreationDate="2020-07-15T06:53:17.587" Score="1" ViewCount="79" Body="&lt;p&gt;I am beginner in designing GNSS receiver design and facing concern while testing the high precision GNSS survey.I am using GNSS survey grade antenna for my GNSS receiver application testing, the antenna cable obtained from the antenna is very short(2meter) when compared with test set up location and antenna.&#xA;So my concern is if i increase my antenna cable will there be any signal loss? What is the maximum antenna cable length allowed for GNSS signal?&lt;/p&gt;&#xA;&lt;p&gt;Regards&#xA;Balkis&lt;/p&gt;&#xA;" OwnerUserId="17199" LastActivityDate="2020-07-15T13:48:40.310" Title="What is the maximum antenna cable length allowed in GNSS application?" Tags="&lt;antenna-construction&gt;&lt;rfi&gt;&lt;rf-power&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17009" PostTypeId="1" CreationDate="2020-07-15T11:44:31.623" Score="2" ViewCount="88" Body="&lt;p&gt;43' vertical monopoles sometimes are used with an auto-tuner at their input as radiators in the ham bands from 40m through 10m, but are any performance compromises required to do that?&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-07-15T11:51:51.913" LastActivityDate="2020-07-15T11:51:51.913" Title="What Are the Properties of 43' Vertical Monopoles Used as Multiband Radiators?" Tags="&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17010" PostTypeId="2" ParentId="17009" CreationDate="2020-07-15T11:50:39.127" Score="3" Body="&lt;p&gt;While using a 43' vertical monopole as a Z-matched radiator on the upper ham bands through 10 meters can make the transmitter happy, it has considerably less gain/usefulness on 10 meters than a typical Ground Plane antenna installation does for the greatest range, single-hop DX contacts from the important elevation sector below about 25 degrees (see following graphic):&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0I0e5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0I0e5.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-07-15T11:50:39.127" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17011" PostTypeId="2" ParentId="17008" CreationDate="2020-07-15T13:48:40.310" Score="2" Body="&lt;p&gt;Although this has nothing to do with &lt;em&gt;amateur radio&lt;/em&gt;, this can be broken down to a general radio technology question.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;So my concern is if i increase my antenna cable will there be any signal loss?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Of course! Nothing (aside from superconductors) is lossless.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I am using GNSS survey grade antenna for my GNSS receiver application testing,&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I don't know what antenna that specifically is.&lt;/p&gt;&#xA;&lt;p&gt;GNSS antennas tend to be active, i.e. actually an antenna plus an amplifier.&lt;/p&gt;&#xA;&lt;p&gt;This tends to make reception pretty robust against cable losses – the signal is already amplified once it enters the cable.&lt;/p&gt;&#xA;&lt;p&gt;No general statement on cable loss can be made: That's a key parameter of the coax you want to use, and differences over several orders of magnitude in loss for a cable of the same length but different specifications are not unusual.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;What is the maximum antenna cable length allowed for GNSS signal?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;No such thing can be stated. It depends on the acceptable loss – and that's a property of your antenna, its amplifier, and your receiver, and most importantly, how much SNR loss you're willing to accept.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-07-15T13:48:40.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17012" PostTypeId="2" ParentId="16997" CreationDate="2020-07-15T16:42:26.663" Score="0" Body="&lt;p&gt;Other answers address well how to measure it and how it affects transmit, but there is little discussion of receive.&lt;/p&gt;&#xA;&lt;p&gt;For transmit, the choke's purpose is to reduce external coupling between the antenna and the coax when the antenna needs to be balanced and the coax geometry might disturb this.  The ideal location for the choke in this situation is at the antenna feedpoint where it is suppose to be balanced.&lt;/p&gt;&#xA;&lt;p&gt;For receive, I assume you are asking if you can reduce received noise received by common mode -- presumably noise that the antenna itself wouldn't also receive.  This would assume that some part of the coax shield is itself acting as an antenna.  In this case, any part of the coax could do this.  A choke at the receiver should reduce such noise, assuming the antenna isn't also getting that noise.&lt;/p&gt;&#xA;&lt;p&gt;But note another answer in another question brought up the point that multiple chokes on the coax could accidentally create a resonant section which could amplify the noise instead. For example, the Carolina Windom adds 10m to the system by intentionally setting up a vertical 10m resonant section of coax between two chokes.  As with many things in amateur radio, the best way to get a practical answer is to try it and maybe move it around a bit until you get best results.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-07-15T16:42:26.663" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17013" PostTypeId="1" AcceptedAnswerId="17037" CreationDate="2020-07-15T23:59:41.327" Score="0" ViewCount="194" Body="&lt;p&gt;&lt;a href=&quot;http://www.hamqsl.com/solar.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.hamqsl.com/solar.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Why is 40m shown as &amp;quot;fair&amp;quot; while 20m is &amp;quot;poor&amp;quot; during the day. Shouldn't 7 MHz be getting absorbed by the D-layer more than 14 MHz?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MVRtx.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MVRtx.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="997" LastEditorUserId="997" LastEditDate="2020-07-20T18:08:30.320" LastActivityDate="2020-07-23T09:54:59.980" Title="Why does the HamQSL website say the 40m band is fair and the 20m band is poor during the day?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17014" PostTypeId="1" AcceptedAnswerId="17017" CreationDate="2020-07-16T02:07:12.960" Score="1" ViewCount="293" Body="&lt;p&gt;friends!&lt;/p&gt;&#xA;&lt;p&gt;Finally found my next antenna project..a collinear dipole array for the 70cm US ham band.&lt;/p&gt;&#xA;&lt;p&gt;The general idea:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/s1Mq8.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/s1Mq8.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;(image courtesy &lt;a href=&quot;https://link.springer.com/referenceworkentry/10.1007%2F978-981-4560-75-7_52-1&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://link.springer.com/referenceworkentry/10.1007%2F978-981-4560-75-7_52-1&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;I don't have enough RG58 or LMR240 on hand to use for this, but I have a ton of RG8...would that be suitable?&lt;/p&gt;&#xA;" OwnerDisplayName="user14945" LastEditorUserId="8717" LastEditDate="2020-07-16T05:00:32.943" LastActivityDate="2020-07-16T13:36:33.177" Title="440MHz collinear dipole array - suitable coax?" Tags="&lt;antenna-construction&gt;&lt;uhf&gt;&lt;coaxial-cable&gt;&lt;dipole&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17015" PostTypeId="1" AcceptedAnswerId="17016" CreationDate="2020-07-16T07:14:00.963" Score="1" ViewCount="440" Body="&lt;p&gt;I don't &amp;quot;get&amp;quot; CW.&lt;/p&gt;&#xA;&lt;p&gt;I can't understand the chatter on an FM radio broadcast when my radio is set to AM. This makes sense, the signal is modulated using frequency modulation and I am trying to decode it with amplitude modulation so the result is scrambled nonsense.&lt;/p&gt;&#xA;&lt;p&gt;Now, I often hear Morse code on the same channels and I can perfectly hear the dots and dashes when listening in FM mode. I guess the simple explanation is that the Morse code was FM modulated at the source, so there is no CW involved here, correct? Did I simply never listen to a CW modulated Morse broadcast?&lt;/p&gt;&#xA;&lt;p&gt;The reason to use CW is the reduced bandwidth. Does this simply mean it's frequency modulated with a &amp;quot;smaller filter&amp;quot; or is CW really a different modulation type?&lt;/p&gt;&#xA;&lt;p&gt;You can use AM or FM for voice, depending on the use case. Is this the same for Morse? You can use AM, FM or whatever mode to send Morse but CW is preferred since it's the most efficient mode? If so why do people use CW and Morse interchangeably? Are there any other reasons why you would use CW?&lt;/p&gt;&#xA;" OwnerUserId="17370" LastEditorUserId="8717" LastEditDate="2020-09-21T21:02:09.910" LastActivityDate="2020-09-21T21:02:09.910" Title="Why can I hear Morse when not in CW mode?" Tags="&lt;cw&gt;&lt;baofeng&gt;&lt;modes&gt;&lt;reception&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17016" PostTypeId="2" ParentId="17015" CreationDate="2020-07-16T09:31:05.467" Score="6" Body="&lt;p&gt;You don't say where you are hearing the Morse code. You say &amp;quot;on the same channels&amp;quot;, but don't specify where you are listening.&lt;/p&gt;&#xA;&lt;p&gt;If you send Morse code using a buzzer, then that generates an audio tone. As with any audio, that can be sent over AM, FM, SSB or any other mode that can send audio.&lt;/p&gt;&#xA;&lt;p&gt;It is quite common for Morse code to be sent as an audio tone on FM channels usually on the 2m band, to assist people in learning Morse code. This might be becoming less common nowadays, since Morse code is not a licensing requirement in many countries.&lt;/p&gt;&#xA;&lt;p&gt;However, if you are listening at the bottom of the HF bands, those are CW portion of the bands. There you will come across Morse code being sent using CW, and you will need a BFO to hear it properly. By which I mean you will need to select SSB or CW on your radio to demodulate it.&lt;/p&gt;&#xA;&lt;p&gt;EDIT: Why would anyone use CW in preference to generating an audio tone and modulating that? Basically because the signal is much simpler - it's a single frequency being switched on and off, and so all the energy in the signal is in that one frequency; there are no sidebands and no signal bandwidth to worry about.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-07-16T09:31:05.467" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17017" PostTypeId="2" ParentId="17014" CreationDate="2020-07-16T13:36:33.177" Score="2" Body="&lt;p&gt;Good RG8 such as Belden 9913 has less loss than RG58 or LMR240, so as long as the thicker diameter doesn't cause you trouble, then it should work fine for your project.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-07-16T13:36:33.177" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17018" PostTypeId="2" ParentId="17015" CreationDate="2020-07-16T18:21:28.157" Score="2" Body="&lt;p&gt;Morse Code is a timed on-off signaling method that is not restricted to CW radio, as it was invented decades before Maxwell hypothesized the existence of radio waves. Morse Code can be used for communicating with clicking relays, buzzers, flashlights, mirrors, eye blinks, printed text, flag waving, Zoom, one or more sound channels of a highly encoded ATSC television signal, etc., as well as RF CW.&lt;/p&gt;&#xA;&lt;p&gt;CW or continuous wave is when an almost unmodulated (except for rise-fall transitions) single “continuous” radio frequency wave is used to carry an on-off code, sometime not using just standard ISO Morse Code sequences in some regions, where they need a different character set.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-07-21T20:31:26.220" LastActivityDate="2020-07-21T20:31:26.220" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17019" PostTypeId="1" CreationDate="2020-07-16T18:42:25.940" Score="5" ViewCount="150" Body="&lt;p&gt;A quartz crystal is often represented by this equivalent schematic:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/PpuXN.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fPpuXN.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/q/16960/218&quot;&gt;How to measure quartz crystal motional parameters using a VNA?&lt;/a&gt; discusses measuring these parameters with a VNA, and there the most mathematically complex step is determining &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt;. Is it feasible to measure &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; directly with an LCR meter?&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8713" LastEditDate="2021-02-08T00:26:40.350" LastActivityDate="2021-02-08T00:26:40.350" Title="Can the parallel capacitance of a quartz crystal be directly measured?" Tags="&lt;measurement&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17020" PostTypeId="2" ParentId="17019" CreationDate="2020-07-16T18:42:25.940" Score="4" Body="&lt;p&gt;The impedance of &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; is&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_p(\omega) = {1 \over i \omega C_p } $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;and the impedance of the other branch is&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_s(\omega) = R + i \omega L + {1 \over i \omega C_s} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;and the impedance of the entire crystal is the parallel combination of these:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_x(\omega) = \left( {1\over Z_p(\omega)} + {1\over Z_s(\omega)} \right)^{-1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Typical values for an approximately 14 MHz crystal are:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\begin{align}&#xA;R &amp;amp;= 7.37 \:\Omega\\&#xA;C_s &amp;amp;= 18.8\:\mathrm{fF}\\&#xA;C_p &amp;amp;= 4.15\:\mathrm{pF}\\&#xA;L &amp;amp;= 6.57\:\mathrm{mH}&#xA;\end{align}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;At 1.4 MHz:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{align}&#xA;Z_p(2\pi 1400000) &amp;amp;= 0-27393i\\&#xA;Z_s(2\pi 1400000) &amp;amp;= 7.37 - 5989128i\\&#xA;Z_x(2\pi 1400000) &amp;amp;= 0.000152779-27269i&#xA;\end{align}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;An LCR meter is probably just measuring the magnitude of the voltage when applying a known AC current, so it will be off by a factor of:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {|Z_x(2\pi 1400000)| \over |Z_p(2\pi 1400000)|} = 0.995447 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;So for this particular crystal, measuring the impedance with an LCR meter (assuming no other inaccuracy in the device) at approximately 1/10th the serial resonance frequency of the crystal yields an error of less than 1%.&lt;/p&gt;&#xA;&lt;p&gt;So, given an LCR meter that can be accurate with a reactance on the order of 30kΩ, this is not a bad way to go.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-16T18:42:25.940" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17022" PostTypeId="1" CreationDate="2020-07-17T09:02:43.553" Score="1" ViewCount="103" Body="&lt;p&gt;A rather popular belief on this topic is that h-pol is superior to v-pol.  Probably that is traceable to published &amp;quot;far-field&amp;quot; patterns over a lossy ground plane generated by Method of Moments software such as NEC (Numerical Electromagnetics Code).  This post is a deeper dive into the topic.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2021-04-14T12:57:16.420" Title="How Does the Propagation of H-pol E-M Fields Compare to That of V-pol E-M Fields (other things equal)?" Tags="&lt;propagation&gt;&lt;dipole&gt;&lt;vertical-antenna&gt;&lt;polarization&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17023" PostTypeId="2" ParentId="17022" CreationDate="2020-07-17T09:02:43.553" Score="1" Body="&lt;p&gt;As clearly shown in the graphic clip first below, h-pol e-m waves radiated at low elevation angles tend to be canceled by their reflections from the Earth near the antenna site. Note the last sentence in the text column at the right side of that graphic. (This clip is taken from a textbook printed in the 1940s, but Physics hasn't changed in the interim.)&lt;/p&gt;&#xA;&lt;p&gt;The graphic second below shows a NEC4.2 comparison of the E-fields existing over a zero to 45° elevation sector, 0.1 km downrange from an h-pol and v-pol radiator both radiating 100 watts.  (Note that an h-distance of 0.1 km from these radiators lies well within their far field.)&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;The reduced fields from the h-pol radiator are clearly evident.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VGr31.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VGr31.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bFenM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bFenM.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-07-18T09:32:26.657" LastActivityDate="2020-07-18T09:32:26.657" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17024" PostTypeId="1" AcceptedAnswerId="17028" CreationDate="2020-07-17T11:46:12.143" Score="2" ViewCount="95" Body="&lt;p&gt;Follow-up on this question: &lt;a href=&quot;https://ham.stackexchange.com/questions/16958/how-to-prevent-cracking-the-capacitors-in-my-diplexer&quot;&gt;How to prevent cracking the capacitors in my diplexer?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Short story: 2m/70cm diplexer, to be used up to 50W.&lt;/p&gt;&#xA;&lt;p&gt;Schematic from Elsie:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/vREWt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vREWt.png&quot; alt=&quot;Schematic&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;S21/S11:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/0lNJ8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0lNJ8.png&quot; alt=&quot;S21/11&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I don't know exactly what to look for when choosing capacitors. Phils answer helps somewhat but I'd need some additional help.&#xA;For example the 15pF capacitor. While looking through one distributor I found the folowing two candidates:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.farnell.com/datasheets/2237903.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;AVX    SQCB7M150FATME\500&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;ESR @ 145/445MHz: 0.03/0.09&lt;/p&gt;&#xA;&lt;p&gt;Q @ 145MHz/445MHz: ?&lt;/p&gt;&#xA;&lt;p&gt;SRF: +/-5GHz&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.farnell.com/datasheets/2049205.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Vishay VJ1111D150GXRAJ&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;ESR @ 145/445MHz:0.09/0.09&lt;/p&gt;&#xA;&lt;p&gt;Q @ 145/445MHz:200/40&lt;/p&gt;&#xA;&lt;p&gt;SRF:750MHz&lt;/p&gt;&#xA;&lt;p&gt;Which one would be a good candidate (if any), and why exactly? How do I choose in practice? I realize these might not be good options, but if I better know what to look for I can continue my search.&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2020-07-18T15:46:23.087" Title="How to select capacitor for diplexer use" Tags="&lt;filter&gt;&lt;components&gt;&lt;diplexer&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17025" PostTypeId="2" ParentId="17019" CreationDate="2020-07-17T12:47:55.783" Score="2" Body="&lt;p&gt;Short answer: measure &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; at a frequency far from any one of the crystal's resonant frequencies.&lt;br&gt; Be aware that not only is a crystal resonant on harmonics of its primary (printed) frequency, but spurious resonances also appear.&lt;br&gt;&lt;/p&gt;&#xA;&lt;p&gt;It is probably safest to measure the parallel-plate capacitance below resonant frequency. So yes, LCR bridges often use a signal source at low frequency. Since &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; may be in the single-digit picofarad range, care should be taken to reduce stray capacitance of the measurement fixture.&lt;br&gt;&#xA;You might measure &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; with the crystal mounted in the LCR meter, then carefully remove the crystal without disturbing the environment, and measure stray capacitance. The true(er) &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; is the difference between the two measurements.&lt;br&gt;&lt;/p&gt;&#xA;&lt;p&gt;For quartz AT-cut crystals, &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; is very roughly 250 times larger than &lt;span class=&quot;math-container&quot;&gt;$C_s$&lt;/span&gt;.&lt;br&gt;&#xA;You're unlikely to measure &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; so accurately in a LCR meter or bridge that this factor need be considered.&lt;br&gt;&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Ceramic resonators are not as piezo-active as quartz, so the disturbing effect of &lt;span class=&quot;math-container&quot;&gt;$C_s$&lt;/span&gt; requires factoring-in its effect on a &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; measurement.&lt;br&gt;&#xA;For example, an ultrasonic transducer was measured where &lt;span class=&quot;math-container&quot;&gt;$C_p$&lt;/span&gt; was only 7.5 times larger than &lt;span class=&quot;math-container&quot;&gt;$C_s$&lt;/span&gt;.&lt;br&gt;&#xA;Quartz has amazing qualities: very piezo-active, temperature-stable. Most other materials that are piezo-active pale in comparison.&lt;/p&gt;&#xA;" OwnerUserId="11132" LastActivityDate="2020-07-17T12:47:55.783" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17026" PostTypeId="2" ParentId="16981" CreationDate="2020-07-17T22:45:55.007" Score="1" Body="&lt;p&gt;I think it does not work. In the first place, the shorted quarter wave will present a very high impedance between screen and center conductor so there will be almost no current in the center conductor. Just removing the center conductor and in effect place a metal rod or metal tube with the same outer diameter would give exactly the same function.&#xA;What you then have is two quarter wave radiators connected to the center conductor with a single radiator as a counterweight. You would get a tilted polarization plane and a significant current on the feedline towards the radio.&lt;/p&gt;&#xA;&lt;p&gt;The proper way is to place a tube alongside the feeder and connect it to the screen of the feeder at a distance of a quarter wave. Look here: https://diydrones.com/profiles/blogs/some-more-antennae-and-when-is-a-balun-not-a-balun&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2020-07-17T22:45:55.007" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17027" PostTypeId="2" ParentId="16997" CreationDate="2020-07-17T23:13:16.897" Score="0" Body="&lt;p&gt;Yes - and No !! The use of ferrite chokes for receive is far more critical than for transmit. Typically you have electric and magnetic fields in your schack originating in switch power supplies. Computers, lamps, almost anything these days.. The fields will induce currents on the outside of your coax and they will travel up to the feedpoint and enter your center conductor and then get into your RX. A feedpoint choke would present a series resistance and in that way reduce the interference to some extent - just like it attenuates the transmit current. On the TX side 10 dB of attenuation is plenty, but on the RX side you might want 30 dB or more. The trick is to place a second choke 0.25 wavelengths from the feedpoint along the feedline. For the current on the outside of the coax this is a high impedance point (because of the choke at the feedpoint) so this second choke has a multiplicative effect. Note that a choke half a wavelength from the feedpoint does not help much because it would sit on a high impedance point for currents along the feeder.&#xA;I have uploaded 4 videos about related problems. Search the Internet for &amp;quot;Sensors sm5bsz&amp;quot; These videos might convey some useful ideas on how to manage currents on the coax screen for the receive side.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2020-07-17T23:13:16.897" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17028" PostTypeId="2" ParentId="17024" CreationDate="2020-07-18T04:59:12.687" Score="5" Body="&lt;p&gt;Many of these specs are different ways of expressing the same thing.&lt;/p&gt;&#xA;&lt;p&gt;Q and ESR (equivalent series resistance) both express the loss in the capacitor.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Q = {\left| 1 / (2 \pi f C)\right| \over \text{ESR}}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Strictly speaking ESR can change with frequency due to things like skin effect, but this equation can get you close enough to make a comparison as long as you aren't taking specifications for 60 Hz and trying to apply them to 1 GHz.&lt;/p&gt;&#xA;&lt;p&gt;Self-resonant frequency (SRF) is another way to specify the equivalent series inductance (ESL):&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{SRF} = {1 \over 2 \pi \sqrt{LC} } $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Lower ESR (higher Q) is better. Higher ESR means more loss in the capacitor, which will increase insertion loss, decrease stopband attenuation, and contribute to potential overheating.&lt;/p&gt;&#xA;&lt;p&gt;Lower ESL (higher SRF) is better. Above the SRF, the capacitor isn't a capacitor anymore: it's an inductor. At the SRF, it's just a resistor (the ESR). So for the capacitor to work as intended in the filter, the frequency must be significantly below the SRF, where the ESL is negligible.&lt;/p&gt;&#xA;&lt;p&gt;So based on that, the AVX product has superior specifications.&lt;/p&gt;&#xA;&lt;p&gt;But an engineer's objective isn't to buy the best thing possible, but rather to buy the best acceptable thing. The question isn't which is better, but which is good enough.&lt;/p&gt;&#xA;&lt;p&gt;To answer that question, simulation is probably the easiest solution. I'm not very familiar with Elsie, but I bet it has some way to enter at least the Q or ESR and plot the resulting frequency response. You can also use some flavor of SPICE.&lt;/p&gt;&#xA;&lt;p&gt;CircuitLab built into this site should also work:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/XrhEB.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fXrhEB.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;Click &amp;quot;Simulate&amp;quot;, then &amp;quot;AC analysis&amp;quot;, and you can generate this plot:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2B46U.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2B46U.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This compares two implementations of the top half of your diplexer. The blue line shows the circuit build with caps with a 0.03 ohm ESR, and the orange line is 3 ohms ESR.&lt;/p&gt;&#xA;&lt;p&gt;The result of 3 ohms ESR is about 0.5 dB of insertion loss. If you plot at higher frequencies you can also see the stopband attenuation is worse (though at high enough frequencies, ESL also becomes significant, and that's not modeled here).&lt;/p&gt;&#xA;&lt;p&gt;Of course the ESR and parasitic capacitance of the inductors matters too. Since you're using air-core inductors there won't be any core loss, so ESR is just the resistance of the wire with adjustments for proximity and skin effect.&lt;/p&gt;&#xA;&lt;p&gt;Simulation will also help you find the current and voltage each component is subject to, which will help with the other selection criteria in the other question.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-07-18T15:46:23.087" LastActivityDate="2020-07-18T15:46:23.087" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17029" PostTypeId="1" AcceptedAnswerId="17030" CreationDate="2020-07-18T09:30:53.627" Score="2" ViewCount="262" Body="&lt;p&gt;Recently, I read something about &lt;strong&gt;EIS (effective isotropic sensitivity)&lt;/strong&gt; and &lt;strong&gt;TIS (total isotropic sensitivity).&lt;/strong&gt; I'm trying to understand the concept, but I find it's quite hard for me.&lt;/p&gt;&#xA;&lt;p&gt;In the book &lt;em&gt;&lt;strong&gt;Antenna Design for Mobile Devices&lt;/strong&gt;&lt;/em&gt;, there is a vague definition, which is&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;EIS&lt;/strong&gt; and &lt;strong&gt;TIS&lt;/strong&gt; are analogous to &lt;strong&gt;EIRP&lt;/strong&gt; and &lt;strong&gt;TRP&lt;/strong&gt;. The &lt;strong&gt;EIS&lt;/strong&gt;  test method is similar to the &lt;strong&gt;EIRP&lt;/strong&gt; method; in that, the range reference measurement is used to correct the unknown performance of a device back to values relative to that of a theoretical isotropic receiver.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;For &lt;strong&gt;EIRP&lt;/strong&gt;, I can understand it can also be thought of as the amount of power a perfectly isotropic antenna would need to radiate to achieve the measured value.&lt;/p&gt;&#xA;&lt;p&gt;However, for &lt;strong&gt;EIS&lt;/strong&gt;, I don't know how to connect it with the performance of an isotropic receive antenna. And what does this term actually define? Does it define the minimum input power of the antenna?&lt;/p&gt;&#xA;" OwnerUserId="17397" LastEditorUserId="5222" LastEditDate="2020-07-29T15:41:03.360" LastActivityDate="2020-07-29T15:41:03.360" Title="Questions about effective isotropic sensitivity(EIS)" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;measurement&gt;&lt;jargon&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17030" PostTypeId="2" ParentId="17029" CreationDate="2020-07-18T16:53:27.197" Score="2" Body="&lt;p&gt;If you were designing a link budget, EIS is the minimum power required at the receiver, assuming the receiver is an ideal isotropic receiver. The EIS encapsulates the effects of both the receiver's sensitivity and antenna system.&lt;/p&gt;&#xA;&lt;p&gt;A link budget might look like this:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;transmitter power&lt;/li&gt;&#xA;&lt;li&gt;+/- adjustment due to antenna mismatch&lt;/li&gt;&#xA;&lt;li&gt;- transmitter feedline loss&lt;/li&gt;&#xA;&lt;li&gt;+ transmitter antenna gain&lt;/li&gt;&#xA;&lt;li&gt;- path loss&lt;/li&gt;&#xA;&lt;li&gt;+ margin for interference, fading&lt;/li&gt;&#xA;&lt;li&gt;+ receiver antenna gain&lt;/li&gt;&#xA;&lt;li&gt;- receiver feedline loss&lt;/li&gt;&#xA;&lt;li&gt;+ margin for self-interference, antenna efficiency, and other practical details&lt;/li&gt;&#xA;&lt;li&gt;&amp;gt;= receiver sensitivity&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;The objective is to ensure the final sum (item 10) is at least the receiver's sensitivity, otherwise the BER will be too high and communication unreliable.&lt;/p&gt;&#xA;&lt;p&gt;But all this detail in the link budget can be complicated, so EIRP and EIS exist to simplify the parts specific to the radios and the antennas.&lt;/p&gt;&#xA;&lt;p&gt;EIRP encapsulates items 1 through 4. Essentially, EIRP tells you how much power is actually radiated from the transmitter, including all the details of the antenna and how that antenna interacts with the transmitter.&lt;/p&gt;&#xA;&lt;p&gt;Similarly, EIS encapsulates items 7 through 10, including everything about the receiver's antenna, the receiver's sensitivity, and all the details about how that antenna actually interfaces with that receiver.&lt;/p&gt;&#xA;&lt;p&gt;So if you know EIRP and EIS, the link budget calculation simplifies to:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;EIRP&lt;/li&gt;&#xA;&lt;li&gt;- path loss&lt;/li&gt;&#xA;&lt;li&gt;+ margin for interference, fading&lt;/li&gt;&#xA;&lt;li&gt;&amp;gt;= EIS&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;EIS (like EIRP) applies to only a single direction and polarization. If that's not specified, then it's the &amp;quot;best&amp;quot; direction possible. That is, the minimum EIS over all possible directions and polarizations. Which is probably (but not necessarily) the direction of maximum antenna gain.&lt;/p&gt;&#xA;&lt;p&gt;EIS might seem a little silly, if it's just sensitivity + antenna gain - feedline loss. But it also incorporates subtle details that might otherwise escape attention.&lt;/p&gt;&#xA;&lt;p&gt;For example, the receiver generates some amount of noise which will be picked up by its own antenna, raising the noise floor and degrading sensitivity. A simple measurement of receiver sensitivity, which involves applying a test signal directly to the receiver module's terminals, would not account for this effect because there is no antenna to receive noise from the receiver (and whatever device it may be a part of).&lt;/p&gt;&#xA;&lt;p&gt;Or, the presence of the receiver module or the feed arrangement may unintentionally alter the antenna's radiation pattern.&lt;/p&gt;&#xA;&lt;p&gt;In other words, receiver sensitivity and antenna gain are idealized numbers, whereas EIS represents the actual performance of the combination which may be less.&lt;/p&gt;&#xA;&lt;p&gt;To measure EIS, a test signal source is set up to produce a known signal. The field intensity is measured at the position where the device under test (DUT, which will be a receiver and its antenna) will be located. From this field intensity, the power that would be received by an ideal isotropic receiver is calculated.&lt;/p&gt;&#xA;&lt;p&gt;Let's say that's calculated to be -60dBm. The DUT is put in position, the test signal transmitted, and the bit error rate (BER) calculated. If the BER is above the specified threshold, the power is reduced in increments, -61 dBm, -62 dBm, etc. until the BER falls below the threshold.&lt;/p&gt;&#xA;&lt;p&gt;The EIS is the minimum such power where the BER is still above the threshold.&lt;/p&gt;&#xA;&lt;p&gt;Because the EIS is measured with an actual receiver and antenna combination in an anechoic chamber, it will represent the full and actual performance of that particular combination of devices.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-07-19T19:30:16.407" LastActivityDate="2020-07-19T19:30:16.407" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17031" PostTypeId="1" CreationDate="2020-07-19T09:16:50.790" Score="4" ViewCount="182" Body="&lt;p&gt;Teaching myself 4NEC2 and have most of it under control, which is good.&lt;/p&gt;&#xA;&lt;p&gt;Regarding radials &amp;amp; grounds, i've been learning the &amp;quot;rules&amp;quot; NEC(2) has, summarised below.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;4.1. Free space.&lt;/p&gt;&#xA;&lt;p&gt;In the simulations in free space, logically there is no ground.&#xA;Normally, the results will be similar to those one may find in the&#xA;textbooks.&lt;/p&gt;&#xA;&lt;p&gt;4.2. Perfect ground.&lt;/p&gt;&#xA;&lt;p&gt;The perfect ground consists of a perfect electrical conductor ground&#xA;plane, without losses. It is a good option to make simulations&#xA;omitting the losses of the ground, a task which may allow to evaluate&#xA;those losses comparing the results with further simulations using more&#xA;realistic ground types.&lt;/p&gt;&#xA;&lt;p&gt;The wires of a model can touch the perfect ground.&lt;/p&gt;&#xA;&lt;p&gt;4.3. Fast ground.&lt;/p&gt;&#xA;&lt;p&gt;With the fast ground type, NEC-2 uses a method based on complex&#xA;reflection coefficients.&lt;/p&gt;&#xA;&lt;p&gt;The wires of the model cannot touch the fast ground.&lt;/p&gt;&#xA;&lt;p&gt;In the case of the horizontal wires, it is necessary to observe a&#xA;height over the ground of at least one tenth of the working wavelength&lt;/p&gt;&#xA;&lt;p&gt;[Ref.4,8]: Zs &amp;gt; (lambda / 10) for horizontal wires.&lt;/p&gt;&#xA;&lt;p&gt;4.4. MININEC ground.&lt;/p&gt;&#xA;&lt;p&gt;The MININEC ground model assumes a perfect ground for the computation&#xA;of the currents and changes to a dielectric ground for the computation&#xA;of the far field patterns (ground without losses). With the MININEC&#xA;ground, hybrid calculations designed for the first generation of less&#xA;powerful computers are used.&lt;/p&gt;&#xA;&lt;p&gt;The vertical wires can touch the MININEC ground.&lt;/p&gt;&#xA;&lt;p&gt;The horizontal wires cannot touch the ground. They must be placed at a&#xA;height over the ground of at least one fifth of the working&#xA;wavelength:&lt;/p&gt;&#xA;&lt;p&gt;[Ref.4,8]: Zs &amp;gt; (lambda / 5) for horizontal wires over MININEC ground.&lt;/p&gt;&#xA;&lt;p&gt;If this rule is not observed, the simulations with NEC-2 will provide&#xA;as a result erroneous impedances and anomalous high gains, especially&#xA;for horizontal polarisation.&lt;/p&gt;&#xA;&lt;p&gt;4.5. Sommerfeld-Norton (S-N) ground.&lt;/p&gt;&#xA;&lt;p&gt;The Sommerfeld-Norton (S-N) is the most precise ground model, with the&#xA;highest computational cost and is the best method to simulate&#xA;horizontal wires very close to the ground.&lt;/p&gt;&#xA;&lt;p&gt;Using the S-N ground it is important to take into account that both&#xA;the vertical and the horizontal wires cannot touch ground.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It's nice to use &amp;quot;fast ground&amp;quot; and define radials in 4NEC2's ground-tab, but it wont be accurate having the vertical wire touch the ground in the model per NEC2's rules, i could use Sommerfield-Norton ground, which is more accurate, but i'd have to elevate the radials (ground plane), which doesn't match reality (this is for a 1/4wl ground-mounted monopole).&lt;/p&gt;&#xA;&lt;p&gt;I could draw/define them in the geometry tab i guess, but it would be handy to use fast-ground if i could get reasonable accuracy, to leverage it drawing many radials in, with equal spacing (just a pain to do it manually, especially for large numbers of radials).&lt;/p&gt;&#xA;&lt;p&gt;To achieve reasonable accuracy, is there any middle-ground (pun unintentional lol), or is it basically one or the other?&lt;/p&gt;&#xA;" OwnerUserId="17200" LastEditorUserId="76" LastEditDate="2020-07-22T23:23:27.170" LastActivityDate="2020-07-22T23:23:27.170" Title="4NEC2 radials &amp; grounds" Tags="&lt;grounding&gt;&lt;antenna-modeling&gt;&lt;counterpoise&gt;" AnswerCount="0" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17032" PostTypeId="1" AcceptedAnswerId="17034" CreationDate="2020-07-19T11:10:45.183" Score="0" ViewCount="53" Body="&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/w/index.php?title=PSK31&amp;amp;oldid=959962411#BPSK31_and_QPSK31_variants&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia says&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Colloquial usage of the term 'PSK31' in amateur radio usually implies&#xA;the use of the most commonly used variant of PSK31: binary phase shift&#xA;keying (BPSK). &lt;strong&gt;BPSK uses no error control, but an &lt;em&gt;allied mode&lt;/em&gt;&lt;/strong&gt;, QPSK31&#xA;quadrature phase shift keying, uses four phases instead of two, to&#xA;provide a degree of forward error correction. It is simple to switch&#xA;from BPSK to QPSK if difficulties arise during a contact.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;What is an &amp;quot;allied mode&amp;quot;? What are they talking about?&lt;/p&gt;&#xA;" OwnerUserId="8553" LastEditorUserId="4076" LastEditDate="2020-07-19T11:47:07.643" LastActivityDate="2020-07-19T11:48:33.240" Title="What is &quot;allied mode&quot; with regards to PSK31?" Tags="&lt;digital-modes&gt;&lt;jargon&gt;&lt;psk31&gt;&lt;modem&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17033" PostTypeId="2" ParentId="17032" CreationDate="2020-07-19T11:26:14.673" Score="2" Body="&lt;p&gt;In this case, &amp;quot;allied mode&amp;quot; can be replace with &amp;quot;associated mode&amp;quot; or &amp;quot;kindred mode.&amp;quot; The phrase indicates that there is a relationship between the two modes, BPSK and QPSK, without specifying the particulars of the relationship. &amp;quot;Allied mode&amp;quot; is not meant to convey or identify any specific technical content.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-07-19T11:26:14.673" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17034" PostTypeId="2" ParentId="17032" CreationDate="2020-07-19T11:28:01.253" Score="4" Body="&lt;p&gt;That was just added by someone who's primary language probably isn't English. What they meant to say is &amp;quot;QPSK31, a mode that is &lt;strong&gt;related&lt;/strong&gt; to PSK31, uses...&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;Other than that, the claim &amp;quot;it uses more constellation points, that's a means error-correction coding&amp;quot;, is plain wrong.&lt;/p&gt;&#xA;&lt;p&gt;The error coding used is this, just one sentence later:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;A sliding window of five bits is used to select one of the four possible phase shifts, providing a means of error correction by spreading each bit of data across adjacent bits.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I'd word this completely differently. Maybe like this.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Error correction is used: a rate-1/2 channel code is implemented with a constraint length of 5 bits (i.e. the past 5 input bits are used to determine the next output two bits). Two bits of the resulting bitstream are then grouped into one QPSK symbol. Using QPSK instead of BPSK allows the doubled data rate to be sent through exactly the same bandwidth without reducing robustness.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The whole paragraph is confusingly worded, to put it mildly. I've reworded it to be clearer (and not make incorrect claims, like that you need 20 2-bit symbols to decode a constraint length 5 convolutional code – that's plain wrong).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-07-19T11:48:33.240" LastActivityDate="2020-07-19T11:48:33.240" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17037" PostTypeId="2" ParentId="17013" CreationDate="2020-07-20T01:43:02.023" Score="-1" Body="&lt;p&gt;The reason is because of SFI (solar flux index). Solar flux (10.7 cm) indicates the level of ionization, which affects HF propagation &lt;strong&gt;above 10 MHz&lt;/strong&gt;. The solar flux does not affect 40m and below, since the MUF rarely drops below 10 MHz. This is why the lower bands are &lt;em&gt;always open&lt;/em&gt;.&lt;/p&gt;&#xA;" OwnerUserId="997" LastActivityDate="2020-07-20T01:43:02.023" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17038" PostTypeId="1" CreationDate="2020-07-20T05:04:22.800" Score="1" ViewCount="116" Body="&lt;p&gt;I am transmitting a 16khz data signal using OFDM 16-QAM x 6 carriers and the library &lt;a href=&quot;https://github.com/romanz/amodem&quot; rel=&quot;nofollow noreferrer&quot;&gt;amodem&lt;/a&gt; using a HackRF. However, I am having issues receiving this signal as the frequency the HackRF  transmits on does not match the actual frequency, and the offset is not static.&lt;/p&gt;&#xA;&lt;p&gt;I want to find the peak of this transmitted data signal through a given start and end frequency range and decode it. I think the best approach to do this would to be to &amp;quot;center&amp;quot; the HackRF on the peak of the signal through a given start and end frequency range. For example, if I was transmitting the data on 451 mhz, and my frequency range was 450mhz and 452mhz, I want GNU radio to automatically set the HackRF's frequency to 451mhz and &amp;quot;lock on&amp;quot; to the data signal.&lt;/p&gt;&#xA;" OwnerUserId="17428" LastEditorUserId="218" LastEditDate="2020-07-21T13:34:24.983" LastActivityDate="2020-07-21T13:34:24.983" Title="Frequency synchronization in GNU Radio for OFDM 16-QAM x 6" Tags="&lt;gnuradio&gt;&lt;software&gt;" AnswerCount="0" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17039" PostTypeId="1" AcceptedAnswerId="17047" CreationDate="2020-07-21T18:36:06.230" Score="5" ViewCount="226" Body="&lt;p&gt;Either there's a simple answer that I'm not finding in a spec sheet somewhere, or, I'm asking the wrong question!&lt;/p&gt;&#xA;" OwnerUserId="17130" LastActivityDate="2020-07-22T14:10:56.807" Title="50Ohm Coax presents 50 Ohms of impedance on which frequency?" Tags="&lt;coaxial-cable&gt;&lt;impedance&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17040" PostTypeId="2" ParentId="17039" CreationDate="2020-07-21T19:05:40.053" Score="1" Body="&lt;p&gt;Ideally, the impedance is not dependent on frequency. Practical limitations should be stated in the specs.&lt;/p&gt;&#xA;&lt;p&gt;Also note, that the effective impedance seen at the end of the coax is affected by power travelling &amp;quot;upstream&amp;quot;, for example reflected/standing waves. These have to be taken into consideration when there is an impedance mismatch down the transfer line causing part of the power to be reflected back.&lt;/p&gt;&#xA;" OwnerUserId="16245" LastActivityDate="2020-07-21T19:05:40.053" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17041" PostTypeId="1" AcceptedAnswerId="17048" CreationDate="2020-07-21T20:48:23.870" Score="1" ViewCount="214" Body="&lt;p&gt;Surely a 1m copper stake provides better ground connectivity for a vertical dipole?&lt;/p&gt;&#xA;" OwnerUserId="17130" LastEditorUserId="8717" LastEditDate="2020-07-21T22:29:28.180" LastActivityDate="2021-03-18T22:48:32.050" Title="Why are many ground radials preferable to a single ground stake buried 1m deep?" Tags="&lt;vertical-antenna&gt;&lt;grounding&gt;&lt;counterpoise&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17042" PostTypeId="2" ParentId="17041" CreationDate="2020-07-21T21:00:52.440" Score="2" Body="&lt;p&gt;Because the radials act as ground, and they're better at it than actual ground.&lt;/p&gt;&#xA;&lt;p&gt;Ground (as in: dirt) isn't a great conductor. A couple laid out good conductors hence work much better as ground plane than well-connected earth.&lt;/p&gt;&#xA;&lt;p&gt;For RF, a good connection to ground potential isn't necessary – what's necessary is that there's a large plane that conducts.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-07-21T21:00:52.440" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17043" PostTypeId="2" ParentId="16996" CreationDate="2020-07-21T21:04:31.320" Score="0" Body="&lt;p&gt;According to this guidance from &lt;a href=&quot;https://www.pulseelectronics.com/docs/library/Amateur%20Short%20Form%20Catalog%20Volume%202.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Pulse Electronics&lt;/a&gt;, makers of Larsen amateur antennas, the only limitation on the &amp;quot;ground plane&amp;quot; is that it exceed a minimum size:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Ground plane availability is [a] critical factor in mobile antenna&#xA;performance ...  Ground plane requirements vary given the type of&#xA;mobile antenna and the frequency of operation.  A typical 5/8 wave&#xA;antenna at 150 MHz requires a ground plane at least 42” in diameter.&#xA;At 450 MHz a 15” diameter ground plane is required,  At 800 MHz a&#xA;minimum of 8” is considered sufficient.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Note that 42&amp;quot; is a bit more than a half-wavelength at 150-MHz, so the radius is about a quarter-wavelength, as one would expect for a ground plane antenna using a traditional monopole radiator.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-07-21T21:04:31.320" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17044" PostTypeId="2" ParentId="17041" CreationDate="2020-07-21T22:25:18.017" Score="6" Body="&lt;p&gt;The purpose of the ground radials isn’t to ground the counterpoise.&lt;/p&gt;&#xA;&lt;p&gt;The purpose of a dense field of radials is to emulate as much as possible a perfect mirror surface, so that, to the far field, the vertical monopole seems to have a mirror image half that makes the monopole seem more like a full size vertical dipole, with a pattern maxima orthogonal to the monopole (zero “takeoff” angle).&lt;/p&gt;&#xA;&lt;p&gt;Whereas a buried rod doesn’t look at all like half a dipole to the far field.  More like an extremely resistive, lossy, and too short counterpose, causing a much higher “takeoff” angle main lobe.&lt;/p&gt;&#xA;&lt;p&gt;Similar to a dense field of radials, a large solid metal roof on top of a car makes a good &amp;quot;ground&amp;quot; plane for a UHF vertical antenna, even though the car is on rubber tires insulating the vehicle from the actual earth ground potential.&lt;/p&gt;&#xA;&lt;p&gt;On the other hand, dirt is a terrible mirror surface, both for light and for HF EM.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-18T22:48:32.050" LastActivityDate="2021-03-18T22:48:32.050" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17045" PostTypeId="2" ParentId="17039" CreationDate="2020-07-22T00:29:03.127" Score="1" Body="&lt;p&gt;The impedance given in a coaxial cable data sheet is its &amp;quot;characteristic&amp;quot; impedance, not its actual impedance.  What that means is that &amp;quot;50 Ω&amp;quot; coax will have the least loss when the output impedance of the transmitter is 50 Ω with no reactance, and the impedance of the load (the antenna) is also 50 Ω with no reactance, irregardless of frequency.  In the real world the characteristic impedance does vary a little when the frequency changes, but those slight changes result in losses that are too small for hams to worry about.&lt;/p&gt;&#xA;&lt;p&gt;For people who aren't electrical engineers, the behavior of transmission lines can be quite confusing at first.  RF circuits just behave very differently from DC circuits.  For instance, if you were to short the far end of a transmission line that is electrically a quarter-wavelength long and then measure its impedance at the near end, you would find a very high impedance, essentially an open circuit.  The ARRL Antenna Book does a good job of explaining the subject.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-07-22T00:29:03.127" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17046" PostTypeId="2" ParentId="17041" CreationDate="2020-07-22T02:11:26.227" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Surely a 1m copper stake provides better ground connectivity for a vertical dipole?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;What really matters is &lt;em&gt;conductivity&lt;/em&gt;. Current doesn't just go in the ground rod and then it's done. It has to flow through the surrounding soil.&lt;/p&gt;&#xA;&lt;p&gt;Soil isn't a very good conductor:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XMAxX.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XMAxX.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;(68.2 kΩ, says the display)&lt;/p&gt;&#xA;&lt;p&gt;Now imagine how much lower this resistance would be with a copper wire between the meter probes.&lt;/p&gt;&#xA;&lt;p&gt;Of course a ground rod has more contact area than my meter probes, and also what's relevant is not the DC resistance, but the resistance at RF. The multimeter probes stuck in the soil make an easy if not accurate demonstration, but just take my word for it: soil isn't nearly as good a conductor as copper.&lt;/p&gt;&#xA;&lt;p&gt;In fact, soil is such a poor conductor that lightning would rather &lt;a href=&quot;https://www.w8ji.com/lightning_strikes.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;arc through 6 feet of air to get to a Beverage antenna&lt;/a&gt; than flow through the soil.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-07-22T20:54:12.023" LastActivityDate="2020-07-22T20:54:12.023" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17047" PostTypeId="2" ParentId="17039" CreationDate="2020-07-22T02:38:38.413" Score="8" Body="&lt;p&gt;For practical purposes, all frequencies.&lt;/p&gt;&#xA;&lt;p&gt;If you cut a transmission line into infinitesimal segments, each segment can be modeled as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/ph3ei.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fph3ei.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;noreferrer&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;(&lt;span class=&quot;math-container&quot;&gt;$G$&lt;/span&gt; is conductance, the inverse of resistance)&lt;/p&gt;&#xA;&lt;p&gt;The characteristic impedance is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ Z_0 = \sqrt{ R + j\omega L \over G+j\omega C } $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;(&lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt; is the angular frequency, two pi times the ordinary frequency in hertz)&lt;/p&gt;&#xA;&lt;p&gt;Wikipedia has the full &lt;a href=&quot;https://en.wikipedia.org/wiki/Characteristic_impedance#Derivation&quot; rel=&quot;noreferrer&quot;&gt;derivation&lt;/a&gt;, if you're interested.&lt;/p&gt;&#xA;&lt;p&gt;For a lossless transmission line, the resistance and conductance are zero. So the equation simplifies:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \require{cancel} \begin{align}&#xA;Z_0 &amp;amp;= \sqrt{ 0+j\omega L \over 0+j\omega C } \\&#xA;&amp;amp;= \sqrt{ \cancel{j\omega} L \over \cancel{j\omega} C } \\&#xA;&amp;amp;= \sqrt{ L \over C }&#xA;\end{align} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;and there is no longer any frequency term.&lt;/p&gt;&#xA;&lt;p&gt;Real transmission lines of course have some loss, but if the transmission line is any good the loss will be low, and have negligible effect on the characteristic impedance.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-22T02:38:38.413" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17048" PostTypeId="2" ParentId="17041" CreationDate="2020-07-22T10:12:44.863" Score="5" Body="&lt;p&gt;A dipole antenna does not require a connection to an &amp;quot;r-f ground&amp;quot; reference, either in the form of a ground rod or a set of buried radials.  Its radiation efficiency typically is ~95% or more without it.&lt;/p&gt;&#xA;&lt;p&gt;OTOH, a vertical monopole &lt;strong&gt;does&lt;/strong&gt; require a path to an r-f ground reference, because that path provides the 2nd terminal of the antenna &lt;em&gt;system&lt;/em&gt;, which is required to provide a complete circuit for r-f current to flow into and out of the source (the transmitter).  Without that path, a monopole essentially has zero radiation of e-m waves into space.&lt;/p&gt;&#xA;&lt;p&gt;R-F currents flow on, and just below the surface of the Earth out to a radius of 1/2 wavelength from the base of a monopole, as a result its radiation.  The sum of those currents equals the current that flows along the monopole itself.  Therefore it is important to minimize the I²R losses in that path in the area of Earth around the monopole.&lt;/p&gt;&#xA;&lt;p&gt;The function of a buried ground rod or a set of buried radials used with a monopole is to collect the r-f currents in that area of Earth, and deliver them back to the antenna/transmit system.&lt;/p&gt;&#xA;&lt;p&gt;The equivalent series resistance (ESR) at the operating frequency for a buried ground rod can be upwards of 50 Ω.  But a set of many radial wires buried symmetrically around the base of the monopole can have an ESR of 1 Ω or less — which is the reason why buried radials are preferred for this application.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-07-22T10:12:44.863" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17049" PostTypeId="2" ParentId="16968" CreationDate="2020-07-22T10:17:59.137" Score="1" Body="&lt;p&gt;As someone that had to take and make a number of customer support phone calls the NATO phonetic alphabet comes in handy.  This avoids having to try to come up with something on the spot that would not confuse the person on the other end even more.  Call centers for customer support will likely be trained to use the NATO phonetics as its unlikely to confuse or lead to someone being insulted over a poor choice of words.  911 dispatch centers would likely be trained on it as well.&lt;/p&gt;&#xA;&lt;p&gt;The NATO phonetics are used for merchant marine communications, this is some kind of international standard or agreement.  Railroads likely use it too.  People that use CB, GMRS, or business band radios on trucks, busses, and such might not use this alphabet regularly but they'd know what it means if used with them.&lt;/p&gt;&#xA;&lt;p&gt;This might come in handy for use over a PA.  So, lots of places where the NATO phonetics would be useful.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2020-07-22T10:17:59.137" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17050" PostTypeId="2" ParentId="16968" CreationDate="2020-07-22T11:01:33.697" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;I'm trying to make learning of the NATO alphabet interesting for kids.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I am a superfan of activity-based education. To help a Caribbean island nation prepare for its upcoming hurricane season, we staged &lt;a href=&quot;https://dominicanewsonline.com/news/homepage/news/general/ntrc-presents-ham-software-to-schools/&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Haminica 2016&lt;/em&gt;&lt;/a&gt; in Roseau, Dominica for over 50 secondary school and university students, their teachers and security staff. We created formal emergency messages for two-student teams to pass to each other using &lt;a href=&quot;https://hamsphere.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;HamSphere&lt;/em&gt;&lt;/a&gt;, the internet simulation of ham radio.&lt;/p&gt;&#xA;&lt;p&gt;It was an eye-opening experience for all. Numerous issues, with clear analogs to &amp;quot;real world&amp;quot; emergency challenges, had to be solved on-the-fly to keep the event going. Plus, not only does &lt;em&gt;HamSphere&lt;/em&gt; include simulated static (QRN) and signal fading (QSB), but stations from all over the world were constantly interrupting our stations to make contacts for award points. The interference (QRM) felt all too real!&lt;/p&gt;&#xA;&lt;p&gt;The students found it extremely difficult to accurately pass the messages, but &lt;strong&gt;their efforts were saved by use of the NATO phonetic alphabet.&lt;/strong&gt; With patience and determination, they gradually achieved their goals and the smiles of satisfaction proved glowing testimony to the sense of accomplishment they felt.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LjRYf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LjRYf.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;(NTRC's George James and two Dominica students at &lt;em&gt;Haminica 2016&lt;/em&gt;)&lt;/p&gt;&#xA;&lt;p&gt;The students' struggles stood in stark contrast to the abilities of seasoned operators to pass similar messages much more quickly. As a result of this training exercise, more than a dozen participants obtained their amateur licenses and made tangible contributions to Dominica's stabilization and recovery from &lt;a href=&quot;https://www.facebook.com/HurricaneMariaDARCI/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hurricane Maria&lt;/a&gt; in 2017.&lt;/p&gt;&#xA;&lt;p&gt;Without provoking anxiety or alarm, it's important for the kids to understand that we are all just one severe weather event or internet attack away from a communications emergency. Knowing how to use the NATO phonetic alphabet can make a life-or-death difference when it really counts.&lt;/p&gt;&#xA;&lt;p&gt;Special thanks to &lt;a href=&quot;http://www.qrz.com/db/oh2bh&quot; rel=&quot;nofollow noreferrer&quot;&gt;OH2BH&lt;/a&gt;, &lt;a href=&quot;http://www.ntrcdom.org/index.php/en/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dominica's NTRC&lt;/a&gt; and the country's ham operators for making &lt;em&gt;Haminica&lt;/em&gt; such a rousing success that Dominica plans annual repetitions.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-07-22T14:27:45.797" LastActivityDate="2020-07-22T14:27:45.797" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17051" PostTypeId="2" ParentId="17039" CreationDate="2020-07-22T13:49:14.173" Score="4" Body="&lt;p&gt;The characteristic impedance of a line does change with frequency.&lt;/p&gt;&#xA;&lt;p&gt;At high frequencies the loss components are effectively zero and &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; depends only on &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$C$&lt;/span&gt; (per unit length).&lt;/p&gt;&#xA;&lt;p&gt;But at low frequencies, &lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt; (and &lt;span class=&quot;math-container&quot;&gt;$G$&lt;/span&gt;) cannot be ignored and contribute significantly to the line impedance. There is a &amp;quot;corner frequency&amp;quot; where one regime takes over from the other.&lt;/p&gt;&#xA;&lt;p&gt;Belden publishes a graph on &lt;a href=&quot;https://www.belden.com/blog/broadcast/understanding-skin-effect-and-frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;their blog&lt;/a&gt; which I reproduce here:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/NjRbg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NjRbg.png&quot; alt=&quot;Belden 75 impedance at low freq&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The site &lt;a href=&quot;http://www.prc68.com/I/Zo.shtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;PRC68&lt;/a&gt; (&lt;a href=&quot;https://web.archive.org/web/20200417171027/http://www.prc68.com/I/Zo.shtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;Archived&lt;/a&gt;) has a detailed derivation of the equations, which I won't transcribe here, but the summary of the examples includes these surprising figures:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;strong&gt;&lt;span class=&quot;math-container&quot;&gt;$600\Omega$&lt;/span&gt; Open Wire Lines&lt;/strong&gt; as seen on telephone poles, the corner frequency is 194 Hz.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;CAT5 cable&lt;/strong&gt;, with two AWG24 wires twisted together, has a nominal impedance at high frequencies of about &lt;span class=&quot;math-container&quot;&gt;$110\Omega$&lt;/span&gt;. Below 100 kHz though, its impedance rises to &lt;span class=&quot;math-container&quot;&gt;$750\angle{-46}^\circ \Omega$&lt;/span&gt; (yes, a complex &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt;)&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;RG-58&lt;/strong&gt; has a corner frequency of 36 kHz, below this its impedance rises.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;See also this &lt;a href=&quot;http://audiosystemsgroup.com/TransLines-LowFreq.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;excellent PDF&lt;/a&gt; by Audio Systems Group, which shows the impedance of a &lt;span class=&quot;math-container&quot;&gt;$75\Omega$&lt;/span&gt; coaxial cable rising to &lt;span class=&quot;math-container&quot;&gt;$1000\Omega$&lt;/span&gt; at 1 kHz, and almost &lt;span class=&quot;math-container&quot;&gt;$10k\Omega$&lt;/span&gt; at 1 Hz.&lt;/p&gt;&#xA;&lt;p&gt;None of this really matters for hams! You can see the impedance of the coaxial cable is stable down to 100 kHz. It matters (used to matter) to telephone companies, running many kilometres of cable, and carrying frequencies down to 300 Hz.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Upper frequency limit&lt;/strong&gt;: At even higher frequencies, the coaxial cable starts to support higher order waveguide modes, when its impedance (and loss) changes dramatically. This occurs when the cable diameter is more than &lt;span class=&quot;math-container&quot;&gt;$\lambda/2$&lt;/span&gt;, approximately.&lt;br /&gt;&#xA;This effect could possibly be a problem for hams.&lt;br /&gt;&#xA;On cellular phone towers, before the radios were moved to the mast top, the long run of coax introduced a significant loss. Large diameter cables are used to keep this loss as small as possible, but the cable can't go bigger than about 2 1/4&amp;quot; because the cut-off frequency then gets below 2 GHz, where the cable is used.  High power VHF transmitters for example use much larger cable.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-07-22T14:10:56.807" LastActivityDate="2020-07-22T14:10:56.807" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17052" PostTypeId="1" CreationDate="2020-07-22T16:25:57.843" Score="0" ViewCount="139" Body="&lt;p&gt;I've seen these antennas built out of coax that are called a bazooka vertical.  It's a kind of 1/4 wave vertical, or perhaps a 1/2 wave dipole.  Constructing such an antenna is to roll back the outer braid of coax to expose 1/4 wavelength of the center conductor, the braid being folded back over the braid towards the radio to make the other 1/4 wave of this dipole.  The interaction between the two layers of the braid makes a kind of balun to keep common mode RF from feeding back into the radio, or picking up noise.&lt;/p&gt;&#xA;&lt;p&gt;This sounds like a simple variation of a balun made of a few loops of coax at the center of a dipole.  I keep seeing claims that a properly constructed dipole will be close enough to 50 ohms that a balun is not needed.  But then I see real world demonstrations on how a lack of a balun is bad because a balun is not just an impedance match transformer, it's matching a balanced dipole to an unbalance coax.&lt;/p&gt;&#xA;&lt;p&gt;The reason I ponder this is because I'll see tape measure Yagi antennas with no balun as being quite routine.  Would not this bazooka vertical balun effect happen if only the coax was run on top of the element fed by the coax shield?  Does it take more than being close, does it have to surround the coax?&lt;/p&gt;&#xA;&lt;p&gt;If it must surround the coax to get the balun effect then what of a Yagi were the driven elements were made of small copper pipe, just big enough to easily slip some coax inside?  Then the element with the coax inside would be soldered to the shield of the coax at the center, and the other element soldered to the center conductor.&lt;/p&gt;&#xA;&lt;p&gt;Then ponder a dipole made similarly for 10 meters, 12 meters, or perhaps 15 meters.  A common 10 foot length of copper pipe could be cut to be 1/4 wavelength (adjusted for velocity factor), feed the coax through the pipe and solder the shield to the pipe, then solder on a 1/4 wavelength wire to the center to complete the 1/2 wave dipole.  This would become a kind of end fed half wave dipole.&lt;/p&gt;&#xA;&lt;p&gt;I left out a lot of finer details, as I'm sure there is much left for interpretation on how to hang this, weather proof it, and so forth.&lt;/p&gt;&#xA;&lt;p&gt;The questions I have are... Has this been done?  I'm sure it has somewhere so perhaps, how practical is this?  How well would this work?  The bazooka vertical seems to be all over.  I'm not seeing bazooka dipoles for HF, or as part of a tape measure UHF/VHF Yagi.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2020-07-22T18:28:50.077" Title="Pondering variations on the vertical bazooka antenna" Tags="&lt;antenna-construction&gt;&lt;dipole&gt;&lt;balun&gt;&lt;yagi&gt;&lt;end-fed-antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17053" PostTypeId="2" ParentId="17052" CreationDate="2020-07-22T18:28:50.077" Score="1" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;I keep seeing claims that a properly constructed dipole will be close enough to 50 ohms that a balun is not needed.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The necessity for a balun has nothing to do with how close the feedpoint impedance is to 50 ohms. Rather, a balun is required because a dipole does not have equal impedance from each half to the coax shield. Consequently, the current will not split equally among the two dipole halves, with the remainder being made up by common-mode current on the shield. See &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;Using a balun with a resonant dipole&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Does it take more than being close, does it have to surround the coax?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It has to make a transmission line, somehow. In the typical construction where the shield is folded back over the coax, what you're doing is making another piece of coax over the coax: the coax shield that you didn't strip is the center conductor, and the shield that was folded back is the shield. See more at &lt;a href=&quot;http://www.antenna-theory.com/definitions/bazooka.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;antenna-theory.com - Bazooka Baluns&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;The transmission line doesn't need to be coaxial, it could be a balanced transmission line too. In that case you could have to conductive things nearby and parallel, instead of concentric.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;what of a Yagi were the driven elements were made of small copper pipe, just big enough to easily slip some coax inside?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I guess you could do this, but then you'd have the coax exiting off the side of the Yagi, which isn't especially convenient. How will you get the coax back to the tower so it can run down to the ground and back to the radio? What advantage is there of having the coax stick out the side of the Yagi?&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Then ponder a dipole made similarly for 10 meters, 12 meters, or perhaps 15 meters. A common 10 foot length of copper pipe could be cut to be 1/4 wavelength (adjusted for velocity factor), feed the coax through the pipe and solder the shield to the pipe, then solder on a 1/4 wavelength wire to the center to complete the 1/2 wave dipole.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I don't see any reason that wouldn't work, though it does sound a little heavy and challenging to make mechanically robust. If I wanted a rigid dipole, it's mechanically easier to support it in the middle since that means a significantly reduced bending moment. A wire strung between two trees works pretty well too: I'm not sure what advantage there would be to the bazooka construction.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-22T18:28:50.077" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17054" PostTypeId="2" ParentId="17013" CreationDate="2020-07-23T09:54:59.980" Score="0" Body="&lt;p&gt;The &amp;quot;HF Conditions&amp;quot; indicate the general, worldwide, &lt;em&gt;relative&lt;/em&gt; propagation to be expected from the bands during your station's local day or night. I wrote to Paul, N0NBH, for his response to your question, which he agreed could be posted here:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Thanks for the email and question.   I’ll do my best to answer it, but&#xA;have to remind all using these that its not an exact science.  It’s a&#xA;prediction based on available data and a most likely scenario.&lt;/p&gt;&#xA;&lt;p&gt;For HF predictions I use what’s available to predict the band&#xA;conditions, given the obvious night vs day differences (given SFI does&#xA;not differentiate, its 3 measurements in Canada).  Also note I&#xA;combined 80-40, 30-20, 17-15 and 12-10 to simplify, but that adds a&#xA;level of error in the calculations.  And of course the dayline, short&#xA;and long hops, etc all are impacted but not in the predictions.&lt;/p&gt;&#xA;&lt;p&gt;For HF predictions I use K-Index, Solar Wind, X-Ray, and Solar Flux&#xA;reading for the predictions.  In your example of 20 and 40, you are&#xA;right the D-Layer impacts 80-40 meters the most, but the primary&#xA;factor for D-Layer Ionization is X-Ray (Hard).  And lately its been&#xA;&amp;lt;A1.0 or non existent.  And at Night the D-Layer goes away, hence the&#xA;difference between day and night.  That leaves only the F Layer at&#xA;Night to impact 20m, but during the day both E and F2 impact that&#xA;band.  That’s where the SFI reading most impacts the band.  I created&#xA;the following slide to try and put all together.  Hope it helps.&lt;/p&gt;&#xA;&lt;p&gt;Again, I am open and honest about the predictions that are based on&#xA;available data and a likely scenario BASED ON DATA ALONE, but I always&#xA;recommend the only way to know for sure is to turn on the rig and call&#xA;CQ!&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/q2N6Y.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/q2N6Y.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-07-23T09:54:59.980" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17055" PostTypeId="2" ParentId="15502" CreationDate="2020-07-23T18:08:32.800" Score="1" Body="&lt;p&gt;I have not found any of the Alinco models in CHIRP to work with the DR-635T.  In an effort to add it none of the methods used by the other models returned any useful data.  I tried contacting Alinco for information but was ignored.&lt;/p&gt;&#xA;" OwnerUserId="14055" LastActivityDate="2020-07-23T18:08:32.800" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17056" PostTypeId="2" ParentId="12752" CreationDate="2020-07-24T01:05:19.003" Score="0" Body="&lt;p&gt;Try putting power to high. I think low is not supported.&lt;/p&gt;&#xA;" OwnerUserId="17458" LastActivityDate="2020-07-24T01:05:19.003" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17057" PostTypeId="1" CreationDate="2020-07-24T17:20:44.170" Score="4" ViewCount="380" Body="&lt;p&gt;Going a bit further I'll ask, for which licenses (all or just for licenses for HF operation) and at what speed (5 WPM, 10 WPM, none specified)?&lt;/p&gt;&#xA;&lt;p&gt;The reason I ask is because every so often I'll see people from the USA wanting to visit another nation and operate their ham radio there.&lt;/p&gt;&#xA;&lt;p&gt;The problem then comes in how to show Morse code proficiency when there's no Morse code requirement, or a kind of &amp;quot;endorsement&amp;quot; available to people licensed by the FCC. People that have had their license for the last 20 years can often show they meet the Morse code proficiency requirement for reciprocal licensing. This is difficult or impossible if the person upgraded their license since then or has not been licensed before the Morse code testing went away.&lt;/p&gt;&#xA;&lt;p&gt;I've seen exceptions but the general rule is that to get full privileges (or perhaps any at all) under a reciprocity agreement means being able to show having an Amateur Extra issued before the year 2000, or perhaps an Advanced (which by definition would have been issued before the 13 WPM Morse testing went away).  Doing some searching on the web I can see some nations accepting General as sufficient for full privileges if there's evidence of being issued before 2000 (13 WPM) or 2007 (5 WPM), but generally this may be no better than Technician.&lt;/p&gt;&#xA;&lt;p&gt;The exceptions to the rule can be nations that accept a temporary International Amateur Radio Permit issued by the ARRL, which appears to be largely limited to those on the American continents.  The ARRL will issue an IARP that notes Morse code proficiency based on any FCC licenses or Morse code testing that the ARRL would administer themselves.  Another wide reaching international agreement in ham radio licensing is the CEPT permit.  Apparently the CEPT permit does not require Morse code proficiency but for those that demonstrated it to the issuing authority will have Morse code proficiency noted for those nations that do require it.&lt;/p&gt;&#xA;&lt;p&gt;Another exception was a story from a couple of licensed hams that traveled to a small Pacific island on short notice and was able to get their license issued personally by their equivalent of the FCC director on the spot (I did say SMALL island nation) by showing their FCC issued ham and commercial licenses.  This is an exceedingly exceptional means to obtain a license in a foreign nation by an FCC licensed ham operator.&lt;/p&gt;&#xA;&lt;p&gt;The reason I'd like to collect this information is to determine how often this could come up of not having Morse code proficiency noted on one's FCC issued ham license and therefore prevent operating a ham radio overseas.  I can imagine this does not come up often but if there is sufficient demand then perhaps a group of people could get together to petition the FCC to allow for a Morse code proficiency endorsement on ham radio licenses to facilitate US hams operating overseas.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastEditorUserId="8717" LastEditDate="2020-07-24T20:41:50.247" LastActivityDate="2021-01-10T22:04:44.203" Title="What nations still require Morse code testing for Amateur radio license?" Tags="&lt;legal&gt;&lt;license&gt;&lt;cw&gt;&lt;fcc&gt;&lt;international-operating&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17059" PostTypeId="1" AcceptedAnswerId="17064" CreationDate="2020-07-25T14:59:23.117" Score="3" ViewCount="233" Body="&lt;p&gt;I was wondering how the Radio interfaced with a TNC. I thought the computer sent digital data (in a serial format) to the data port on the radio, but from what I read online, it is &lt;strong&gt;not&lt;/strong&gt; a data port.&lt;br /&gt;&#xA;From &lt;a href=&quot;http://www.wa8lmf.net/6-Pin-MiniDin-Data-Connector/index.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.wa8lmf.net/6-Pin-MiniDin-Data-Connector/index.htm&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;This jack is variously called &amp;quot;data&amp;quot;, &amp;quot;packet&amp;quot;, &amp;quot;auxiliary&amp;quot;, etc, but actually there are no data connections on this connector. This IS NOT a serial data or RTTY direct FSK port. Only various forms of receive and transmit audio are present. The connector provides receive audio output at a fixed level of about 100-300mV, transmit audio input at about the same level, transmit PTT keying, receiver squelch status (COR), and ground/common.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;But on the yaesu's manual, it mentions about packet data rates. So if the signal received by the radio over the data port is good ol' FM, how can it have a bit rate?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/crgku.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/crgku.png&quot; alt=&quot;Yaesu manual&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15878" LastActivityDate="2020-07-25T20:18:03.430" Title="If the data port on a Yaesu FT-7800R only communicates FM signals, why does the manual mention the port having a bit rate?" Tags="&lt;bandwidth&gt;&lt;packet&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17060" PostTypeId="2" ParentId="17057" CreationDate="2020-07-25T15:37:35.143" Score="4" Body="&lt;h1&gt;India&lt;/h1&gt;&#xA;&lt;p&gt;India has two classes of licenses - general and restricted.&#xA;Getting the general license requires sending and receiving morse at 8 wpm. [Source][1]&lt;/p&gt;&#xA;&lt;p&gt;[1]: https://arsi.info/wpc-rules/#post-5:~:text=PART%20II%20%E2%80%93%20Morse%20(Only%20for,Morse%20reception%20and%20sending%20(8%20wpm)&lt;/p&gt;&#xA;" OwnerUserId="15878" LastActivityDate="2020-07-25T15:37:35.143" CommentCount="2" CommunityOwnedDate="2020-07-25T15:37:35.143" ContentLicense="CC BY-SA 4.0" />
  <row Id="17061" PostTypeId="1" CreationDate="2020-07-25T16:35:44.103" Score="1" ViewCount="133" Body="&lt;p&gt;I am transmitting OFDM 16-QAM x 6 carriers packets using the python library &lt;a href=&quot;https://github.com/romanz/amodem&quot; rel=&quot;nofollow noreferrer&quot;&gt;amodem&lt;/a&gt; and a HackRF. My setup is very simple for the transmission side, it takes the .wav generated by amodem from data and transmits on 470.00mhz (for testing purposes)&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2cJKO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2cJKO.png&quot; alt=&quot;Transmit Setup&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;However, when I transmit using the HackRF there is a offset between the actual frequency vs the frequency the HackRF is transmitting the signal on. Usually by 20 - 30 khz.&lt;/p&gt;&#xA;&lt;p&gt;I can decode this signal manually by tuning to the frequency using a SDR program like gqrx, but I want to automate this process in GNU Radio and automatically determine the offset and &amp;quot;center&amp;quot; to where the data signal is coming from.&lt;/p&gt;&#xA;&lt;p&gt;According to the GNU Radio wiki, there is a block that can do this called the &lt;a href=&quot;https://wiki.gnuradio.org/index.php/Schmidl_%26_Cox_OFDM_synch.&quot; rel=&quot;nofollow noreferrer&quot;&gt;Schmidl &amp;amp; Cox OFDM synch.&lt;/a&gt; which outputs &amp;quot;Fine frequency offset, scaled by the OFDM symbol duration&amp;quot;. When I connect this block to an RTL-SDR source and connect the first output to a QT GUI Number Sink, the number for &lt;code&gt;freq_offset&lt;/code&gt; seems to be random ranging from -0.95 to 3 and has no consistent pattern. How do I use this number in calculating the frequency offset in Hertz? Is this the right block for doing an OFDM sync?&#xA;&lt;a href=&quot;https://i.stack.imgur.com/p9w6W.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/p9w6W.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17428" LastActivityDate="2020-07-25T16:35:44.103" Title="How to use OFDM Synch in GNU Radio?" Tags="&lt;gnuradio&gt;&lt;software-development&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17062" PostTypeId="2" ParentId="17059" CreationDate="2020-07-25T19:09:47.537" Score="0" Body="&lt;p&gt;The 9600 baud rate was popular on packet radio in the past but nowhere near as popular as 1200 baud, the 9600 speed bypasses the audio shaping.&lt;/p&gt;&#xA;" OwnerUserId="16744" LastActivityDate="2020-07-25T19:09:47.537" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17063" PostTypeId="1" CreationDate="2020-07-25T19:54:47.707" Score="3" ViewCount="221" Body="&lt;p&gt;I'm looking at picking up the TYT TH-9800, which is a Quad-Band FM radio on 10m/6m/2m and 440 (I'm lucky enough to have some 6m and 10m repeaters in the area). I know there exists quad band antennas for this radio, however not only are they a bit of a compromise on all bands, but they all use UHF connectors for the mount connection - which I am very against. So I began my search for a triplexer so I could use 3 separate antennas, this should be more efficient than the one quad band, allow me to swap out the HF antennas as needed, have a much larger selection of antennas, and allow me to switch the HF side (via antenna switch) to another radio while also not sacrificing 6m/2m/440.&lt;/p&gt;&#xA;&lt;p&gt;I started searching online, however no one that I've found makes such a triplexer - the best off the shelf solution I can do is 2 diplexers; one VHF/UHF and 6m/HF diplexer with a second 6m and HF diplexer. I'm not the biggest fan of that solution. So I started looking into the DIY/Homebrew approach, which also was unfruitful. I found plenty of resources for making diplexers, but very little for triplexers.&lt;/p&gt;&#xA;&lt;p&gt;So here's the TL;DR: does anyone know the proper formulas to make triplexers and/or know of any good resources for building?&lt;/p&gt;&#xA;&lt;p&gt;Below is what the end state would look like, also with an AnyTone 6666 for 10m AM/SSB/CW. I should also note this will be a mobile solution, thus only focusing on 10m for now.&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;                    TYT 9800                 AT6666&#xA;                    --------                 ------&#xA;                        |                      |&#xA;                        |                      |&#xA;                   -----------                 |&#xA;           ___     |triplexer|                 |&#xA;    2m/440 \|/     -----------                 |&#xA;            |       |   |   |                  |&#xA;            |-------|   |   |    ----------    |&#xA;     ___                |   |----| sw box |----|      ___&#xA;     \|/ 6m             |        ----------           \|/ HF/10m&#xA;      |                 |            |                 |&#xA;      |-----------------|            |-----------------|&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="17471" LastEditorUserId="76" LastEditDate="2020-07-25T22:07:37.673" LastActivityDate="2020-07-25T22:07:37.673" Title="DIY Triplexer for HF (low), 6m (med), and 2m/440 (high)" Tags="&lt;diy&gt;&lt;antenna-system&gt;&lt;mobile&gt;&lt;filter&gt;&lt;diplexer&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17064" PostTypeId="2" ParentId="17059" CreationDate="2020-07-25T20:18:03.430" Score="5" Body="&lt;p&gt;The data port does not carry FM signals: it carries demodulated audio. The radio performs FM demodulation and &lt;a href=&quot;https://en.wikipedia.org/wiki/FM_broadcasting#Pre-emphasis_and_de-emphasis&quot; rel=&quot;noreferrer&quot;&gt;de-emphasis&lt;/a&gt;, and the output is heard on the speaker and is also present on the 1200 baud data output. On most multi-mode radios this port caries the demodulated audio for other mode selections as well.&lt;/p&gt;&#xA;&lt;p&gt;The data input is similar, but in reverse. The only difference from the microphone input is the level.&lt;/p&gt;&#xA;&lt;p&gt;The 9600 baud data output is similar, but bypasses the de-emphasis.&lt;/p&gt;&#xA;&lt;p&gt;These connections are named &amp;quot;1200 baud&amp;quot; or &amp;quot;9600 baud&amp;quot; because they were first developed to interface to a 1200 or 9600 baud TNC. The convention has stuck, even after other uses for these ports have been developed.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-25T20:18:03.430" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17065" PostTypeId="2" ParentId="17057" CreationDate="2020-07-26T08:50:27.593" Score="3" Body="&lt;p&gt;&lt;strong&gt;Thailand&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;For its own amateur radio licences, Thailand has three grades - Basic, Intermediate and Advanced. Basic allows access to the 2m VHF band only, and the higher two grades allow access to HF as well.&lt;/p&gt;&#xA;&lt;p&gt;The Intermediate and Advanced licences require a basic Morse code test, although it looks like it's very simple.&lt;/p&gt;&#xA;&lt;p&gt;However, Thai amateur radio licences are only available to Thai citizens.&lt;/p&gt;&#xA;&lt;p&gt;For a reciprocal licence, you need a full amateur radio licence from one of a handful of countries. For US licences, I believe that you need a General licence or higher. I do know that for a UK licence you need a full licence (not a novice or intermediate licence).&lt;/p&gt;&#xA;&lt;p&gt;Source: &lt;a href=&quot;https://www.qsl.net/rast/text/licensing2014.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.qsl.net/rast/text/licensing2014.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Thai licensees get callsigns beginning with HS or E2 (but not beginning with HS0Z). Reciprocal licences begin with HS0Z followed by two more letters.&lt;/p&gt;&#xA;&lt;p&gt;Sidenote: I have heard it said that some Thai citizens who are able to speak enough English have gone the route of getting a US licence and using that to get a reciprocal licence, since the US General test is much easier than the Thai Intermediate written test.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-07-26T08:50:27.593" CommentCount="3" CommunityOwnedDate="2020-07-26T08:51:45.857" ContentLicense="CC BY-SA 4.0" />
  <row Id="17067" PostTypeId="1" AcceptedAnswerId="17069" CreationDate="2020-07-27T15:56:46.727" Score="3" ViewCount="131" Body="&lt;p&gt;Here are two messages I received:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;10:50:53R W2MEB-9&amp;gt;SX2X9U,W0BJ-1*,K0ATT-10*,WIDE2* &amp;lt;UI R Len=34&amp;gt;:`vNN&amp;quot; dk/]&amp;quot;64}Monitoring 144.905=&#xA;10:50:58R WB9QPM-4&amp;gt;APBPQ1,AD9OV-8*,WIDE2* &amp;lt;UI Len=47&amp;gt;:!3924.30N/08848.72WI Shelbyville Igate EM59oj  &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;What I'm asking about are the 6 characters after the &amp;gt; (the beacon &amp;quot;To&amp;quot; field).  I've found that values starting with &amp;quot;A&amp;quot; indicate software version (in this example, APBPQ1 maps to &amp;quot;John G8BPQ Digipeater/IGate&amp;quot; from &lt;a href=&quot;http://aprs.org/aprs11/tocalls.txt&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://aprs.org/aprs11/tocalls.txt&lt;/a&gt;) by I can't find any resource that defines values starting with &amp;quot;S&amp;quot;.  Is there one somewhere?  What does it mean?&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2020-07-28T01:48:36.857" Title="String in APRS report" Tags="&lt;aprs&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17069" PostTypeId="2" ParentId="17067" CreationDate="2020-07-28T01:48:36.857" Score="3" Body="&lt;p&gt;You're looking at a Mic-E packet. The Mic-E format uses the TOCALL to encode part of the position data (the entire latitude and two bits of the longitude) and a three-bit &amp;quot;message ID&amp;quot;. This allows for very small packets. See Chapter 10, &amp;quot;Mic-E Data Format&amp;quot;, of the &lt;a href=&quot;http://aprs.org/doc/APRS101.PDF&quot; rel=&quot;nofollow noreferrer&quot;&gt;APRS spec&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-07-28T01:48:36.857" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17070" PostTypeId="1" CreationDate="2020-07-28T04:45:05.610" Score="0" ViewCount="100" Body="&lt;p&gt;Straight dipoles. I can't get the Yagi to tune.  I have tried the 4:1 Balun method with coax but not able to tune.  With the straight unbalanced input to the dipole I get a 1:1 swr on about 129 MHz Suggestions? Shall I shorten the dipole?&lt;/p&gt;&#xA;" OwnerUserId="17480" LastActivityDate="2020-07-28T04:45:05.610" Title="Built a 2 meter 5 element Yagi" Tags="&lt;antenna-construction&gt;&lt;dipole&gt;&lt;yagi&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17071" PostTypeId="1" CreationDate="2020-07-28T08:48:17.010" Score="1" ViewCount="130" Body="&lt;p&gt;The suggestion has been made on various ham-related websites that improving the conductivity of the Earth around a ground rod produces a worthwhile improvement in the e-m radiation from a vertical monopole using that ground rod. How effective &lt;strong&gt;is&lt;/strong&gt; that?&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-10-07T07:42:25.853" Title="Does Improving Earth Conductivity Near a Buried Ground Rod Improve Antenna System Performance?" Tags="&lt;vertical-antenna&gt;&lt;grounding&gt;&lt;efficiency&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17072" PostTypeId="2" ParentId="17071" CreationDate="2020-07-28T08:48:17.010" Score="3" Body="&lt;p&gt;Below for some perspective on this topic is a NEC4.2 analysis showing the difference in performance of a 40m, 1/4-wavelength, unloaded, base-fed vertical monopole antenna system when driven against either a 5/8&amp;quot; OD or a 12&amp;quot; OD, copper-clad, 8-ft long ground rod buried in poor Earth (1 mS/m, d.c. 5).&lt;/p&gt;&#xA;&lt;p&gt;Increasing the ground rod OD up to 12&amp;quot; is the equivalent of modifying the Earth in that radius area around a 5/8&amp;quot; OD ground rod to be nearly a perfect conductor of the radial r-f currents in the Earth around the monopole, that flow toward the ground rod.&lt;/p&gt;&#xA;&lt;p&gt;An improvement in system performance results, but not a very &lt;strong&gt;&lt;em&gt;significant&lt;/em&gt;&lt;/strong&gt; improvement.&lt;/p&gt;&#xA;&lt;p&gt;[&lt;em&gt;Added October 7, 2020&lt;/em&gt;]:&#xA;Improving the conductivity of Earth for several meters around ground rods buried at the base of a vertical monopole (or anywhere else) does almost nothing toward improving the conductivity of the ground plane out to a 1/2WL radius of the base of a vertical monopole.&lt;/p&gt;&#xA;&lt;p&gt;Regardless of the height of that monopole in physical, free-space wavelengths, minimizing the ESR of the entire ground plane within 1/2WL radius around its base is critical to the radiation efficiency of that antenna system. That ESR is a series circuital element with a large affect on the relative amount of r-f current from the source (transmitter) that will flow along the monopole itself.&lt;/p&gt;&#xA;&lt;p&gt;RF energy dissipated in the ESR of a set of radials buried in soil is converted to heat, rather than to useful e-m energy radiated into space.&lt;/p&gt;&#xA;&lt;p&gt;Reference: &lt;strong&gt;Ground Systems as a Factor in Antenna Efficiency&lt;/strong&gt;, Brown, Lewis &amp;amp; Epstein (RCA Labs); Proceedings of the I.R.E., 1937.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gYrvQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gYrvQ.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-10-07T07:42:25.853" LastActivityDate="2020-10-07T07:42:25.853" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17073" PostTypeId="2" ParentId="17071" CreationDate="2020-07-29T00:34:26.643" Score="1" Body="&lt;p&gt;If by improving conductivity, you mean flooding several acres or square miles with ocean (or saltier) sea water (or via natural intrusion near a low lying shoreline or wetlands), or installing a solid copper floor several square wavelengths in size in the parking lot, yes.&lt;/p&gt;&#xA;&lt;p&gt;But some people have reported improved antenna performance by putting a metal mesh of gopher wire (not too deep) under their lawn, with the vertical antenna grounded in the middle.  Probably soldering or crimping adjacent mesh sheets is desirable.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-07-29T00:34:26.643" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17074" PostTypeId="1" CreationDate="2020-07-29T01:22:48.830" Score="3" ViewCount="654" Body="&lt;p&gt;What is the value of more than one VFO in an HF transceiver?&lt;/p&gt;&#xA;&lt;p&gt;Many novice rigs only have a single crystal oscillator, and a vast number of famous classic transceivers, HF kits, and QRP rigs only have a single VFO.  So more than one VFO is obviously not a requirement for successfully operating in the HF bands&lt;/p&gt;&#xA;&lt;p&gt;So what's the typical use case and advantage of having more than one VFO?  For what situations is another VFO needed, and when can one do without?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-07-29T04:25:48.013" LastActivityDate="2020-07-29T16:54:13.147" Title="What is the use of dual VFOs?" Tags="&lt;hf&gt;&lt;transceiver&gt;&lt;vfo&gt;" AnswerCount="4" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17075" PostTypeId="1" CreationDate="2020-07-29T03:59:58.397" Score="0" ViewCount="58" Body="&lt;p&gt;I plan to build omni antenna. My goal all about better gain versus a 1/4 wave antenna.&lt;/p&gt;&#xA;&lt;p&gt;I am curious about radial position of the legendary ARX2B Ringo Ranger.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Why is the position in below feed point?&lt;/li&gt;&#xA;&lt;li&gt;What does the cable do?&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it some kind balun?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;Will this add extra db to the gain ?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Maybe i will build a Hustler &amp;quot;G7 like&amp;quot;  with lower ground plane.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Will this odd ground plane position give better gain?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Preferred design was 2 or 3 times of 5/8 wave length.&lt;/p&gt;&#xA;" OwnerUserId="1196" LastEditorUserId="4076" LastEditDate="2020-07-29T06:42:01.060" LastActivityDate="2020-07-29T06:42:01.060" Title="Omni 144 MHz antenna" Tags="&lt;antenna-construction&gt;&lt;144mhz&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17076" PostTypeId="2" ParentId="16987" CreationDate="2020-07-29T04:21:13.010" Score="1" Body="&lt;p&gt;I tried it both ways using the same 20 foot piece of cable and measured the power loss. Cutting off the exposed foil is the best way to do it. That reduced the power loss by 0.25 dB at 146 MHz compared to leaving the foil with the braid.&lt;/p&gt;&#xA;&lt;p&gt;I wonder if it has something to do with the blue coating on the inside of the foil, which might have some resistance.  I didn't measure the DC resistance, but I verified DC continuity in both tests.&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2020-07-29T05:02:21.590" LastActivityDate="2020-07-29T05:02:21.590" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17077" PostTypeId="2" ParentId="17074" CreationDate="2020-07-29T04:56:44.217" Score="4" Body="&lt;p&gt;Dual VFOs are needed for transmitting on one frequency but listening on another. The reason why this is done is nicely explained &lt;a href=&quot;https://ham.stackexchange.com/questions/1104/why-do-some-dx-listen-on-a-different-frequency-than-they-transmit-on&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;This is called operating &amp;quot;split&amp;quot; and it takes a certain amount of skill to work a DX operator working split and even more to operate split.&lt;/p&gt;&#xA;&lt;p&gt;The reason this is done is to help manage the pileup. If too many stations are calling and the pileup becomes unmanageable it takes longer and longer to complete an exchange. This is less fun for everyone.&lt;/p&gt;&#xA;&lt;p&gt;By working split, the DX operator keeps his transmit frequency clear so that the callers will hear him well making the exchange go more smoothly. He also has the opportunity to spread out the calling stations on several frequencies near his transmit frequency.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-07-29T04:56:44.217" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17078" PostTypeId="2" ParentId="17074" CreationDate="2020-07-29T12:33:52.903" Score="2" Body="&lt;p&gt;Many radios will have buttons labeled &amp;quot;VFO1&amp;quot; and &amp;quot;VFO2&amp;quot;, suggesting there are two oscillators when actually there is only 1. The buttons simply store a frequency in memory which is restored at the appropriate time, not unlike the &amp;quot;recall&amp;quot; button on a TV remote. In the past, this would have actually required two oscillators since they were not digitally controlled and also not so stable.&lt;/p&gt;&#xA;&lt;p&gt;Largely, it's a convenience. For example, you may be having a QSO when someone else starts using your frequency. By switching to the other VFO you can tune around to find a free frequency, then switch back to propose the new frequency.&lt;/p&gt;&#xA;&lt;p&gt;Or you may use it as sort of a &amp;quot;memory&amp;quot;. Perhaps you often operate FT8 and CW: one VFO can be left on the FT8 frequency, and the other in the CW portion of the band, and the buttons provide a quick means of switching between the two.&lt;/p&gt;&#xA;&lt;p&gt;Radios that actually have two VFOs are capable of operating on two frequencies simultaneously.&lt;/p&gt;&#xA;&lt;p&gt;Some can operate as a cross-band repeater. This may allow the operator to have a mobile station on a higher frequency which can remotely access the greater HF capabilities of the base station.&lt;/p&gt;&#xA;&lt;p&gt;Two VFOs also allows the simultaneous monitoring of two frequencies without scanning between them. While this isn't such a common use case as it is on VHF/UHF, it does exist: there are repeaters on 10 meters in some places, and 6 meters although not technically HF is part of many HF radios, and there can be repeaters there, too.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-07-29T12:33:52.903" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17079" PostTypeId="2" ParentId="17074" CreationDate="2020-07-29T14:59:46.550" Score="0" Body="&lt;p&gt;And extending the concept to SDRs, some can have up to 8 VFOs (slices).&lt;/p&gt;&#xA;&lt;p&gt;You could (as one example), run multiple copies of WSJT monitoring 80M, 40M, 20M, 15M, 10M FT8, and monitor a few phone frequencies/bands all simultaneously. Having a waterfall to view, makes easy work of finding stations to tune across the VFOs (slices).&lt;/p&gt;&#xA;&lt;p&gt;SDRs are usually better integrated to PC(s) and more flexible than what an appliance style radio can do with VFOs.&lt;/p&gt;&#xA;&lt;p&gt;That being said, same as a traditional radio, SDRs usually have a single transmitter only.&lt;/p&gt;&#xA;&lt;p&gt;Just wanted to mention SDRs for completeness.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastActivityDate="2020-07-29T14:59:46.550" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17080" PostTypeId="2" ParentId="17074" CreationDate="2020-07-29T16:54:13.147" Score="2" Body="&lt;p&gt;For anyone new to ham radio: in the analog era, in order to listen on one frequency and transmit on another with a single HF receiver or transceiver, by flipping a switch rather than turning a knob I mean, two VFOs were needed.  That generally meant two oscillators and two tuning knobs.  Now that oscillators are digitally-controlled frequency synthesizers, the frequency can be easily and accurately changed in a fraction of a second.  These days a &amp;quot;VFO&amp;quot; is just a few bytes of memory holding the frequency in a computer.  Modern HF radios typically offer two &amp;quot;VFOs&amp;quot;.  They could easily offer many more; the only reason they don't is that more buttons on a front panel that is already crammed with buttons would be required.  (This is true whether there is a physical front panel on the radio, or a virtual front panel created in software.)&lt;/p&gt;&#xA;&lt;p&gt;As @MikeWaters said, the main reason for the dual VFO function is to enable operating &amp;quot;split&amp;quot;, that is listening and transmitting on different frequencies.  This is sometimes used because the stations in a QSO can't legally transmit on the same frequency as the DX station, but it's more commonly used in DX pileups.  In a pileup, there are so many stations all trying to call a single rare DX station that the DX station can't pick individual call signs out of the howling noise of many stations all transmitting on the same frequency.  So the DX station announces that they are operating split, and the calling stations spread themselves over several kilohertz, typically higher than the DX's frequency.  The DX station's frequency is supposed to be left to the DX station alone.&lt;/p&gt;&#xA;&lt;p&gt;The OP asked why transceivers have a split mode at all, rather than just using RIT or XIT.  The reason is that the RIT and XIT functions are intended to solve different problems, and using them to operate split in a DX pileup would be more complicated than using the transceiver's split mode.  Operating split in a pileup takes skill, timing, and fast button-pushing, and anything that makes that easier is welcome.  Also, RIT and XIT are usually limited to a range of a few kilohertz in the same band, and sometimes that range isn't wide enough.  Sometimes people have a cross-band QSO in which one station transmits on one band and the other station transmits on a different band; in that case, the RIT and XIT ranges &lt;em&gt;definitely&lt;/em&gt; aren't enough, and split mode is the only practical way to make it work.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-07-29T16:54:13.147" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17081" PostTypeId="1" CreationDate="2020-07-30T00:34:27.697" Score="4" ViewCount="676" Body="&lt;p&gt;What is the difference between RIT and XIT?  When would one use one and not the other for split (or other) HF operation?  When would one need both?  Which one is more useful for a transceiver to have if it only had one?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2020-07-30T01:37:12.010" LastActivityDate="2020-08-04T12:41:44.910" Title="What is the difference between RIT and XIT?" Tags="&lt;transceiver&gt;&lt;jargon&gt;&lt;vfo&gt;&lt;split-frequency&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17082" PostTypeId="2" ParentId="1271" CreationDate="2020-07-30T02:20:36.743" Score="5" Body="&lt;p&gt;Another way to detect current on the outside of coax is to run your hand up and down the coax wile an analyzer is connected , if you see a fluctuation on the meter then current is following on the outside. On vhf I built sleeve chokes to remove it with great results.&#xA;KC5ULU&lt;/p&gt;&#xA;" OwnerUserId="17490" LastActivityDate="2020-07-30T02:20:36.743" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17083" PostTypeId="2" ParentId="17081" CreationDate="2020-07-30T03:25:09.607" Score="2" Body="&lt;p&gt;RIT means that your VFO frequency will be offset from your dial frequency (usually by a relatively small amount) while you are receiving. XIT means that your VFO frequency will be offset from your dial frequency while you are transmitting.&lt;/p&gt;&#xA;&lt;p&gt;So a dial frequency of 7125 kHz and a RIT of +1000Hz will accomplish exactly the same thing as a dial frequency of 7126 kHz and an XIT of -1000Hz (that is, receive on 7126 and transmit on 7125), but the controls you use to get there are different.&lt;/p&gt;&#xA;&lt;p&gt;As &lt;a href=&quot;https://ham.stackexchange.com/a/14403/8717&quot;&gt;this linked answer&lt;/a&gt; mentions, RIT can be used to clear up an SSB QSO partner's offset during the QSO without inducing them to &amp;quot;chase you up the band&amp;quot;. It's also useful for &amp;quot;listening up&amp;quot; when operating split CW — you leave your dial at your transmit frequency, and spin the RIT up a kHz or two to listen for responses. I don't know of any good use of XIT, and I have never used it myself. It seems less convenient in every way, to me.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-07-30T03:30:53.967" LastActivityDate="2020-07-30T03:30:53.967" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17084" PostTypeId="1" CreationDate="2020-07-30T12:57:23.633" Score="5" ViewCount="201" Body="&lt;p&gt;On a recent trip to China I photographed a number of &amp;quot;antennas&amp;quot; that I do not recognize. Are they even antennas?&#xA;&lt;a href=&quot;https://i.stack.imgur.com/RhGES.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RhGES.jpg&quot; alt=&quot;1st antenna&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uwhzx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uwhzx.jpg&quot; alt=&quot;2nd antenna&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15289" LastEditorUserId="8717" LastEditDate="2020-07-31T02:01:05.880" LastActivityDate="2020-07-31T18:30:48.450" Title="What are these antennas?" Tags="&lt;antenna&gt;&lt;lightning&gt;&lt;safety&gt;&lt;equipment-protection&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17085" PostTypeId="2" ParentId="17084" CreationDate="2020-07-31T01:55:18.387" Score="1" Body="&lt;p&gt;Those are not antennas, but intended to be &lt;em&gt;lightning dissipators&lt;/em&gt;. Basically, they are a type of &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Lightning_rod&quot; rel=&quot;nofollow noreferrer&quot;&gt;lightning rod&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;A lightning rod or lightning conductor (UK) is a metal rod mounted on a structure and intended to protect the structure from a lightning strike. If lightning hits the structure, it will preferentially strike the rod and be conducted to ground through a wire, instead of passing through the structure, where it could start a fire or cause electrocution.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The following related questions and answers go into more detail:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/5115/lightning-dissipators&quot;&gt;Lightning Dissipators&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The lightning dissipator consists of many small spikes and prevents a strike by slowly discharging through each little spike.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/15226/do-lightning-rods-attract-or-do-they-help-prevent-lightning&quot;&gt;Do lightning rods attract or do they help prevent lightning?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://physics.stackexchange.com/questions/65825/does-a-lightning-rod-prevent-lightning-strikes&quot;&gt;https://physics.stackexchange.com/questions/65825/does-a-lightning-rod-prevent-lightning-strikes&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/15129/how-does-a-higher-antenna-reduce-rain-static-on-a-lower-antenna/15144#15144&quot;&gt;How does a higher antenna reduce rain static on a lower antenna?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;In summary, several answers support that they can prevent a lightning strike &lt;em&gt;under some circumstances&lt;/em&gt;. Others disagree and vehemently declare that they are of no value whatsoever. I strongly believe that the truth lies somewhere in the middle.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;On top of this corona-discharge &lt;a href=&quot;https://web.archive.org/web/20190113132858/http://www.negativeiongenerators.com/roomionizers.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;negative ion generator&lt;/a&gt; is an effective (if fragile) ion emitter, which appearance and function is very similar to those photos in the question. There were actually eight of those .005&amp;quot; diameter stainless steel wires.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/up9Xd.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/up9Xd.jpg&quot; alt=&quot;Tabletop negative ion generator with plug-in ion emitter&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;(No longer manufactured)&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-07-31T18:30:48.450" LastActivityDate="2020-07-31T18:30:48.450" CommentCount="15" ContentLicense="CC BY-SA 4.0" />
  <row Id="17086" PostTypeId="2" ParentId="17081" CreationDate="2020-07-31T02:11:58.957" Score="3" Body="&lt;p&gt;Modern radios that have RIT and XIT typically also have a button that you can use to listen on your transmit frequency. This means that if you use XIT or RIT, then you can listen on your transmit frequency (rather than on your receive frequency) to check conditions on there.&lt;/p&gt;&#xA;&lt;p&gt;The typical use case for RIT is if you are calling CQ and you start to get a pileup, so you shift to listening “up” or “down”. If you say “UP 5” then you would shift the RIT up 5kHz and listen to people calling there. You would occasionally listen on your transmit frequency to make sure conditions there are still OK and you don’t have too many people ignoring the UP instructions (if you do, you can send “UP” several times in the hope that they get the hint).&lt;/p&gt;&#xA;&lt;p&gt;For most of us though, we are on the opposite side of this pileup. And this is where XIT is useful: We set our VFO to the DX’s transmit frequency, and tune XIT up 5kHz. Then while the DX station is running through a bunch of people calling we use the “listen on my transmit frequency” button to determine exactly where the station currently being worked is. Then we listen to the DX and as soon as the current contact is completed we know where the last contact was transmitting, and we can call right away on exactly the same frequency. This can greatly improve our chances of being heard by the DX. Or we can listen to several contacts in succession, and find a pattern in where the DX is listening - for example, slowly working stations on higher and higher offsets, then returning to UP 5, and repeating. Working out patterns in a pileup can almost guarantee that even with a smaller station, we can break through the pileup.&lt;/p&gt;&#xA;&lt;p&gt;The final part of the question asks which is more useful if you could have only XIT or RIT. I say that depends on which side of the pileup you usually sit. If you’re the DX listening up, you want RIT. If you spend a lot of time trying to break pileups, you want XIT and a “listen on my transmit” button.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-07-31T02:11:58.957" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17087" PostTypeId="2" ParentId="17084" CreationDate="2020-07-31T07:26:56.433" Score="2" Body="&lt;p&gt;A possibility for their use is suggested by the small &amp;quot;globes&amp;quot; at the free ends of the conductors in the 2nd photo.  If this array of conductors was intended for lightning protection, they better would have very sharp tips in order to reduce the flashover voltage appearing at the ends of the conductors.  Also, ~vertical conductors would be better for lightning protection, as they would better protect the structure to which they are attached.&lt;/p&gt;&#xA;&lt;p&gt;Instead those conductors might be co-driven radiators of a semi-wideband, ~directional antenna system.&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-07-31T14:28:26.980" LastActivityDate="2020-07-31T14:28:26.980" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17088" PostTypeId="1" CreationDate="2020-07-31T21:31:19.467" Score="5" ViewCount="116" Body="&lt;p&gt;I'm trying to figure out how to design power amplifiers which input and output are properly matched to 50 Ohm. My thinking was that the most bullet proofed approach would be to model an amplifier in LTspice and estimate R as U/I on both input and output. After all usually LTspice models are more or less accurate and impedance is nothing more than U/I ratio (assuming U and I are in phase, of course).&lt;/p&gt;&#xA;&lt;p&gt;I took &amp;quot;Hand-on Radio Experiments&amp;quot; book by Ward Silver, N0AX and modeled a few amplifiers described in this book (Experiment #45 on page 93 and Experiment #46 on page 95). Since both schematic were published in QST and then in the book, they went through review by the editors and readers many times, and supposably are well designed.&lt;/p&gt;&#xA;&lt;p&gt;Here is the first one:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/rGPqz.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/rGPqz.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Not surprisingly the output is 50 Ohms:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/kRRAE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kRRAE.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;However it seems that the input is reactive:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qz3nV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qz3nV.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;OK, maybe the input impedance is not that important in this case, since the amplifier was described as a buffer for an oscillator.&lt;/p&gt;&#xA;&lt;p&gt;Let's check the second schematic:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/chrVc.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/chrVc.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This one supposed to amplify the output of the first circuit. The output impedance is OK:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/p3gfj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/p3gfj.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The input current and voltage are almost in phase, but U/I is far from 50 Ohms:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/V37pF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/V37pF.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Regardless of what model tells I've built the first circuit with minor changes and in practice it works OK, giving about 10 dB amplification on HF.&lt;/p&gt;&#xA;&lt;p&gt;The above models can be downloaded &lt;a href=&quot;https://afiskon.ru/public/ltspice/amplifiers-by-ward-silver.tgz&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Here is what I'm trying to understand. Is the described method suitable to determine input and output impedance of the amplifiers or maybe I should use some other method? Should I bother if the input impedance of the amplifier is mismatched? Or maybe it's fine? If not, how large SWR can I afford? Since hFE of a transistor can vary from 30 to 300 for 2N2222 and 2N3904, and μ of Amidon ferrite cores (if used) can vary ±20% maybe LTspice is not much help anyway?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-08-04T11:46:50.607" LastActivityDate="2020-08-04T11:46:50.607" Title="How to estimate input and output impedance of an amplifier?" Tags="&lt;diy&gt;&lt;electronics&gt;&lt;impedance-matching&gt;" AnswerCount="0" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="17089" PostTypeId="1" AcceptedAnswerId="17090" CreationDate="2020-08-02T06:39:36.843" Score="0" ViewCount="1563" Body="&lt;p&gt;Which cable is better for ham radio antenna? RG 58, RG 59, or RG 6?&lt;/p&gt;&#xA;&lt;p&gt;Based on [1], RG6 has lower signal loss. So, is RG 6 a better cable? Or there are no differences?&lt;/p&gt;&#xA;&lt;p&gt;[1] &lt;a href=&quot;https://sewelldirect.com/blogs/learning-center/what-is-the-difference-between-rg59-and-rg6&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://sewelldirect.com/blogs/learning-center/what-is-the-difference-between-rg59-and-rg6&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17492" LastActivityDate="2020-08-04T12:18:26.157" Title="Which cable is better for ham radio antenna? RG58, RG59, or RG6?" Tags="&lt;coaxial-cable&gt;" AnswerCount="2" CommentCount="4" ClosedDate="2020-08-04T14:32:16.607" ContentLicense="CC BY-SA 4.0" />
  <row Id="17090" PostTypeId="2" ParentId="17089" CreationDate="2020-08-02T14:35:25.357" Score="2" Body="&lt;p&gt;Loss is pretty important, but it's not the only thing to consider.&lt;/p&gt;&#xA;&lt;p&gt;Firstly keep in mind while all RG-6 (or any other RG-*) is of similar physical dimensions and should be compatible with the same connectors, the quality of a particular cable can vary a lot. The loss you'll see quoted in tables typically assume a high-quality cable from a major manufacturer like Times Microwave, Belden, or CommScope. There are however a great many no-name manufacturers making much lower quality cable that will have much higher loss.&lt;/p&gt;&#xA;&lt;p&gt;So to get an accurate number on loss, you want to find the manufacturer's datasheet. If you find some cheap cable on Ebay or Amazon and there's no datasheet, the cable will probably have higher loss, as its cheaply made. This is especially true for RG-59 and RG-6, which are aimed at nontechnical consumers wanting to put CATV cabling in their home.&lt;/p&gt;&#xA;&lt;p&gt;Besides loss, coax has a characteristic impedance. Most coax is either 50 ohms or 75 ohms. RG-58 is 50 ohms, RG-59 and RG-6 are 75 ohms.&lt;/p&gt;&#xA;&lt;p&gt;CATV and video applications conventionally use 75 ohm. Ham and other radio applications usually use 50 ohms.&lt;/p&gt;&#xA;&lt;p&gt;You can use 75 ohm cable with radio equipment. In fact it can be quite a good match for a dipole, which has a feedpoint impedance around 75 ohms. Ideally you want to match the feedline to the antenna's feedpoint impedance, thus &lt;a href=&quot;https://ham.stackexchange.com/questions/7333/what-is-the-actual-loss-in-a-feed-line-with-high-swr&quot;&gt;minimizing SWR loss&lt;/a&gt;. But you must also ensure the impedance seen by your radio, which is a function of the antenna impedance, feedline characteristic impedance, and feedline length, is within your radio's specification, or use a tuner or matching network.&lt;/p&gt;&#xA;&lt;p&gt;On the other hand, 50 ohm coax, with a 50 ohm antenna, will work without a tuner with any modern radio.&lt;/p&gt;&#xA;&lt;p&gt;You might also want to consider connector availability. Because RG-59 and RG-6 are used predominately for CATV, you will probably have a very hard time finding anything but an F connector for them. This means you will also need adapters to make any use of the cable.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-08-03T02:48:42.387" LastActivityDate="2020-08-03T02:48:42.387" CommentCount="13" ContentLicense="CC BY-SA 4.0" />
  <row Id="17091" PostTypeId="1" CreationDate="2020-08-02T15:53:00.563" Score="2" ViewCount="153" Body="&lt;p&gt;What is an Audio Peaking Filter?  And how might that be different from an ordinary (narrow) CW bandpass filter, or from tunable audio filters (with fully configurable upper and lower cutoffs)?&lt;/p&gt;&#xA;&lt;p&gt;Does a peaking filter have anything in common with an audio notch filter?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-08-02T19:39:05.670" LastActivityDate="2020-08-03T02:38:06.343" Title="What is an Audio Peaking Filter?" Tags="&lt;cw&gt;&lt;filter&gt;&lt;audio&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17092" PostTypeId="2" ParentId="17091" CreationDate="2020-08-03T02:38:06.343" Score="1" Body="&lt;p&gt;A standard CW filter operates on the IF (RF after at least one stage of downmixing, but before demodulation). Elecraft's APF operates on the demodulated audio.&lt;/p&gt;&#xA;&lt;p&gt;The reason most filtering is done at IF is because making a nice sharp filter becomes easier the higher the filter's center frequency (within reason). &lt;a href=&quot;https://ftp.elecraft.com/KX3/Mod%20Notes%20Alerts/Using%20APF%20for%20weak%20signal%20CW%20work%20the%20K3%20and%20KX3.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;In Elecraft's opinion&lt;/a&gt;, a filter with the more gradual roll-off implied by a center frequency of only ~1kHz is beneficial to CW copying, when used &lt;em&gt;in addition&lt;/em&gt; to the ordinary IF filter.&lt;/p&gt;&#xA;&lt;p&gt;Since this is a bandpass filter, it's the exact opposite of a notch filter, but other than that, it's the same :)&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-08-03T02:38:06.343" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17093" PostTypeId="1" CreationDate="2020-08-04T09:06:34.963" Score="1" ViewCount="27" Body="&lt;p&gt;I need some help with a simple thing. I am trying to simulate carrier frequency offset model for Bluetooth Low Energy standard in GNURadio (I am bit new to this). For this purpose, there is a CFO model already available in it details of which are available here &lt;a href=&quot;https://wiki.gnuradio.org/index.php/CFO_Model&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wiki.gnuradio.org/index.php/CFO_Model&lt;/a&gt; . I need to correctly parameterize the model with some values according to some of the knowns about the standard&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Channel Bandwidth  2MHz&lt;/li&gt;&#xA;&lt;li&gt;Frequency (f)      2.4GHz&lt;/li&gt;&#xA;&lt;li&gt;Maximum crystal Oscilator inaccuracy  (ppm)   20.8ppm   dictated by standard&lt;/li&gt;&#xA;&lt;li&gt;Maximum CFO bound (f*ppm/10^6)        49920Hz&lt;/li&gt;&#xA;&lt;li&gt;Sample rate ( R )                     4MHz&lt;/li&gt;&#xA;&lt;li&gt;Sample duration (1/R)                 0.00000025s&lt;/li&gt;&#xA;&lt;li&gt;CFO standard deviation (Hz per sample)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Can you please check if parameter values are correct. How can I determine the CFO standard deviation (Hz per sample) as described in the above link in this case?&lt;/p&gt;&#xA;" OwnerUserId="17515" LastEditorUserId="218" LastEditDate="2020-08-04T13:27:11.767" LastActivityDate="2020-08-04T13:27:11.767" Title="how to set the CFO standard deviation in CFO models" Tags="&lt;gnuradio&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17094" PostTypeId="2" ParentId="17089" CreationDate="2020-08-04T12:18:26.157" Score="1" Body="&lt;p&gt;Phil is correct the major issue is the impedance needs to match to prevent SWR losses. Normally the impedance of our radios output is 50 ohms. Using a 50 ohm cable connecting it to a 50 ohm input on our antenna gives us the lowest SWR.&lt;/p&gt;&#xA;&lt;p&gt;Signal loss is also important and it varies with the length of the cable and with the frequency. At the 3- 30 MHz HF frequencies the signal loss for most coax is minimal. The loss increases when you get to UHF and VHF. A 50 ft length of RG 58 at HF is acceptable for most people, but the loss is higher at UHF frequencies. You either want a shorter length or go to a cable like LMR 400 which does not have as much loss.&lt;/p&gt;&#xA;&lt;p&gt;While it costs a little more, I buy LMR 400 for all of my coax cables. I can use it with HF, VHF, and UHF with fairly good results.&lt;/p&gt;&#xA;&lt;p&gt;Spending a little more for coax and putting some effort in to improving antennas gives a good return on my investment.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-08-04T12:18:26.157" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17095" PostTypeId="2" ParentId="17081" CreationDate="2020-08-04T12:41:44.910" Score="1" Body="&lt;p&gt;While most modern radios are vary accurate in regards to frequency, not all radios are. Our signals get garbled with the transmitting frequency of one radio is not the same as the receiving frequency of the other.&lt;/p&gt;&#xA;&lt;p&gt;By slightly adjusting the receiver frequency with RIT, you can sometimes get better reception of a station that is transmitting slightly off frequency. Your transmitting frequency for not change when adjusting RIT.&lt;/p&gt;&#xA;&lt;p&gt;While less common you can also slightly adjust your transmit frequency with XIT so the receiving station can hear you better. Adjusting XIT does not change your receiving frequency.&lt;/p&gt;&#xA;" OwnerUserId="9425" LastActivityDate="2020-08-04T12:41:44.910" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17096" PostTypeId="1" CreationDate="2020-08-04T19:51:43.420" Score="4" ViewCount="270" Body="&lt;p&gt;In installed a couple of compression style PL-259 connectors to the ends of RG8/U FOAM coax.  It's about 16 feet in length.  Here is an example of one of the connectors:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JM4Qe.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JM4Qe.jpg&quot; alt=&quot;PL-259&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;How do I know if the coax is &amp;quot;good&amp;quot;?  The multi-meter test for shorts doesn't seem like it's a complete test.  It lets you know for sure if there's a problem when there's a short.  But it doesn't necessarily tell you everything is good when there's an open.&lt;/p&gt;&#xA;&lt;p&gt;I used my NanoVNA to perform a sweep on the cable with the 50 ohm load at the end.  The VSWR and RL tends to go up and down from 1MHz to 500MHz.  Is this normal?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/5CMF7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5CMF7.png&quot; alt=&quot;VSWR&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/V4k0b.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/V4k0b.png&quot; alt=&quot;RL&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Other than those sweeps, is there any kind of &amp;quot;red light; green light&amp;quot; test to make sure a piece of coax and the connectors are good?&lt;/p&gt;&#xA;" OwnerUserId="12939" LastActivityDate="2020-08-06T14:25:09.137" Title="How do I know if my coax connectors are good?" Tags="&lt;coaxial-cable&gt;&lt;connectors&gt;&lt;pl259-so239-connector&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17097" PostTypeId="2" ParentId="17096" CreationDate="2020-08-04T21:12:10.430" Score="1" Body="&lt;p&gt;Per &lt;a href=&quot;https://ham.stackexchange.com/questions/17096/how-do-i-know-if-my-coax-connectors-are-good#comment28238_17096&quot;&gt;Hobbs-KC2G's comment&lt;/a&gt;, you should now try and vary your load resistance, &lt;em&gt;as your load might not equal the impedance of your coax&lt;/em&gt;. The procedure below will tell you if that is the case or not.&lt;/p&gt;&#xA;&lt;p&gt;One way of doing this to to solder a small non-inductive 50 ohm resistor directly to the far end of the coax. Cut the leads just short enough to solder them to the shield and center conductor, or their inductance will affect the reading at higher frequencies. If you have any on hand, I would use some older 1/4 or 1/2 watt resistors with a solid cylinder of carbon inside. Measure them. If necessary, parallel another resistor with it to get exactly 50 ohms.&lt;/p&gt;&#xA;&lt;p&gt;If you still get these results, then change the resistance value using this same method until the VSWR is nearly flat.&lt;/p&gt;&#xA;&lt;p&gt;If all you have on hand are smaller resistors that have an internal, spiral cut carbon layer, try (for example) paralleling four 200 ohm resistors using this same method. Start at 1 MHz and go up. You should see a nearly flat VSWR that gradually rises with frequency, due to the resistor's inductance, even with a PL-259 connector at the VNA.&lt;/p&gt;&#xA;&lt;p&gt;This is assuming that the coax is exactly 50 ohms! &lt;em&gt;It might not be&lt;/em&gt;. The goal here is to adjust these resistors so it matches the impedance of the coax. (Hopefully, your VNA is close to that. ;-)&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;Per the OP's &lt;a href=&quot;https://ham.stackexchange.com/questions/17096/how-do-i-know-if-my-coax-connectors-are-good/17097#comment28254_17097&quot;&gt;comment&lt;/a&gt;, another way is to open the far end of the coax:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I did a Lambda/8 test with the coax. It’s about quarter wave long at 12MHz and appears as a short on the Smith chart when the other end is open. Sliding down to 6MHz and the reactance is around -61j ohms. On good coax the same test shows -50j.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-08-06T14:25:09.137" LastActivityDate="2020-08-06T14:25:09.137" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17098" PostTypeId="2" ParentId="17096" CreationDate="2020-08-04T21:12:35.297" Score="4" Body="&lt;p&gt;So, what your measurement indicates is two things:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;yep, the thing is somehow connected. The deep dips in the return loss are points when the characteristic impedance of the connector+cable+connector+termination look like the source impedance of the VNA&lt;/li&gt;&#xA;&lt;li&gt;yep, it's a terrible non-constant complex impedance seen from the perspective of the VNA that's everything but 50 Ω. A &amp;quot;good&amp;quot; cable starts at a return loss of -20 dB, but typically, general-purpose pre-configured coax cabling has more like -30 dB to -50 dB of loss. Your connector reflects power, and pretty strongly so! That's no surprise: In the 1930s, it was designed as a &lt;em&gt;cheap&lt;/em&gt; connector for frequencies below 100 MHz, mostly for low power systems. It doesn't have a constant (or even defined) impedance and thus no general guarantees about its performance &lt;a href=&quot;https://ham.stackexchange.com/questions/13061/pl-259-so-239-vs-n-type-vs-bnc-which-is-best-connector-to-use-when/13062#13062&quot;&gt;can be made&lt;/a&gt;. The tolerances of the connectors, and the lack of mechanical design specification, in fact &lt;em&gt;force&lt;/em&gt; the connector to be bad: there's no way to produce a connector that has constant characteristic impedance over a significant range of frequencies with arbitrary counterparts.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;So, sorry, I can't tell you based on these measurement if that cable is &amp;quot;as good as it can be&amp;quot;. I can tell you, however, that you really can't &lt;em&gt;rely&lt;/em&gt; on PL-259 for UHF (even if it's called &amp;quot;UHF connector&amp;quot;; UHF meant &amp;gt; 30 MHz back when it was invented). You might find one PL-259 jack that works beautifully up to 400 MHz with a given PL-259 connector, and another one that looks like your measurements or even worse.&lt;/p&gt;&#xA;&lt;p&gt;Really, if you can: replace PL-259 with BNC or Type-N or SMA.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-08-04T21:12:35.297" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17099" PostTypeId="1" AcceptedAnswerId="17102" CreationDate="2020-08-05T03:12:42.190" Score="2" ViewCount="60" Body="&lt;p&gt;I know getting my Technician License is the place to start, however, I have in my head a clear path that I want to achieve and am looking for guidance for the most efficient way to achieve that goal.&lt;/p&gt;&#xA;&lt;p&gt;The goal is to set-up my family and I with APRS so in the event of a disaster as apart of my PACE plan we can set up a laptop (heard this is possible with a radio like the Kenwood D74) and be able to share coordinates and even send text communications to each other.&lt;/p&gt;&#xA;&lt;p&gt;I am using Online resources now to study and get my Technician.&#xA;I am not specifically looking for a dissertation in the practice of using APRS just good resources, pitfalls things to look out for as well as a lapse in my reasoning or things I am not understanding with my current thinking.&lt;/p&gt;&#xA;&lt;p&gt;I appreciate any and all help and in advance, Thank you for sharing your expertise.&lt;/p&gt;&#xA;" OwnerUserId="17521" LastEditorUserId="4665" LastEditDate="2020-08-05T21:55:49.887" LastActivityDate="2020-08-05T21:55:49.887" Title="Resources and guidance regarding APRS" Tags="&lt;aprs&gt;&lt;emergency&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17100" PostTypeId="1" AcceptedAnswerId="17103" CreationDate="2020-08-05T10:27:12.413" Score="4" ViewCount="287" Body="&lt;p&gt;I want to build an external beat frequency oscillator (BFO) for an old valve Eddystone receiver I have.&lt;/p&gt;&#xA;&lt;p&gt;There are many circuits for BFOs on the internet, they are mostly similar, the idea seems simple enough, the two most important criteria it seems being frequency stability and output level.&lt;/p&gt;&#xA;&lt;p&gt;I found a couple of circuits designed by W1FB DeMaw and built these, the first one didn't work at all and the second one has an output that looks nothing like a sine wave.&lt;/p&gt;&#xA;&lt;p&gt;Is it important for a BFO to have a pure sine wave output if you want to  use it to resolve SSB signals giving decent audio quality? What happens to SSB demodulation if the BFO output is a triangle or square wave, for instance?&lt;/p&gt;&#xA;&lt;p&gt;For the moment there is a HP signal generator connected to the radio and that works very well.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="8717" LastEditDate="2020-08-06T02:46:28.763" LastActivityDate="2020-08-06T02:46:28.763" Title="Does the output of a BFO for a short wave receiver have to be exactly a sine wave?" Tags="&lt;receiver&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17101" PostTypeId="2" ParentId="17100" CreationDate="2020-08-05T13:38:43.380" Score="6" Body="&lt;p&gt;So, the job of a BFO is essentially &amp;quot;faking&amp;quot; the carrier oscillation of the AM transmission that was suppressed, together with the other sideband, so that the rest of the receiver can demodulate the SSB signal.&lt;/p&gt;&#xA;&lt;p&gt;As such, it's the input to a specific nonlinear device: the mixer (sometimes combined with a power detector, then called &amp;quot;product detector&amp;quot;, as far as I know).&lt;/p&gt;&#xA;&lt;p&gt;Now, an ideal mixer does a very simple thing: It multiplies two signals. That's all.&lt;/p&gt;&#xA;&lt;p&gt;The trick why multiplication is frequency mixing is pretty intuitive:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Trigonometric identities say that&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\cos(x)\cdot\cos(y)=\frac12 (\cos(x+y)+\cos(x-y))\text;\tag1\label{trig}$$&lt;/span&gt; similar things for &lt;span class=&quot;math-container&quot;&gt;$\sin\cdot\sin$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\cos\cdot\sin$&lt;/span&gt;.&lt;/li&gt;&#xA;&lt;li&gt;Every signal can be decomposed into a sum of cosines and sines.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;h1&gt;Mixing = Multiplication + Filtering&lt;/h1&gt;&#xA;&lt;p&gt;When you look at &lt;span class=&quot;math-container&quot;&gt;$\eqref{trig}$&lt;/span&gt;, you can imagine what happens when you multiply say, a cosine of 1.2 MHz with one of 1 MHz frequency:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;\begin{align}&#xA;x &amp;amp;= 2\pi\;1\,200\,000\;t &amp;amp;= 2\pi f_1t\\&#xA;y &amp;amp;= 2\pi\;1\,000\,000\;t&amp;amp;=2\pi f_2t\\&#xA;&amp;amp;\text{insert into \eqref{trig}:}\\&#xA;\cos(x)\cos(y) &amp;amp;= \cos(2\pi f_1t)\cos(2\pi f_2t)\\&#xA;&amp;amp;=\frac12\left[\cos(2\pi f_1t + 2\pi f_2t)+\cos(2\pi f_1 t -2\pi f_2 t)\right]\\&#xA;&amp;amp;=\frac12\left[\cos(2\pi (f_1+f_2)t)+\cos(2\pi(f_1-f_2) t)\right]\label{prods}\tag2&#xA;\end{align}&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;So, multiplying two cosines gives you two new cosines, one at a frequency that is at the sum of the two input frequencies, the other at the difference.&lt;/p&gt;&#xA;&lt;p&gt;Usually, you only want either, not both new tones. We're trying to get an RF signal down to audio frequency, so we care about difference. We simply use a low-pass filter to filter out the sum frequency component.&lt;/p&gt;&#xA;&lt;p&gt;Where do we let that low-pass filter cut off? Well, essentially, anywhere above the audible frequency range works. If &lt;span class=&quot;math-container&quot;&gt;$f_1$&lt;/span&gt; was the frequency of the RF (or IF, depending on your receiver's architecture) signal, our job in tuning to a transmission is nothing but adjusting &lt;span class=&quot;math-container&quot;&gt;$f_2$&lt;/span&gt; (which is our BFO frequency!) so that the difference &lt;span class=&quot;math-container&quot;&gt;$f_1-f_2$&lt;/span&gt; is such that the resulting frequencies are exactly the audible frequencies used to excite the transmitter!&lt;/p&gt;&#xA;&lt;h1&gt;Everything is a sum of cosines and sines&lt;/h1&gt;&#xA;&lt;p&gt;In general, what Fourier derived is that every periodic signal can be written as a discrete sum of cosines and sines. Say, we have a signal (for example, a square wave or a triangle or a chirp sequence) &lt;span class=&quot;math-container&quot;&gt;$s(t)$&lt;/span&gt;, which repeats every for every difference in &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt; of &lt;span class=&quot;math-container&quot;&gt;$1$&lt;/span&gt;, then  we can write that as&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$s(t) = \sum_{n=0}^{\infty} a_n\cdot \cos (2\pi n t) + b_n\cdot\cos(2\pi n t)\text.\tag3\label{fseries}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Repeat that mentally: What &lt;span class=&quot;math-container&quot;&gt;$\eqref{fseries}$&lt;/span&gt; means is that hey, if something is periodic, it can be understood as sum of cosines and sines, and the &amp;quot;weights&amp;quot; of these are in the different &lt;span class=&quot;math-container&quot;&gt;$a_1, a_2, \ldots$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$b_1, b_2,\ldots$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;If it's actually a sine or cosine, then this is pretty simple. For a cosine wave, all but one &lt;span class=&quot;math-container&quot;&gt;$a_n$&lt;/span&gt; are zero, and all &lt;span class=&quot;math-container&quot;&gt;$b_n$&lt;/span&gt; are zero. For a sine wave, all &lt;span class=&quot;math-container&quot;&gt;$a_n$&lt;/span&gt; are zero and only a single &lt;span class=&quot;math-container&quot;&gt;$b_n$&lt;/span&gt; is not.&lt;/p&gt;&#xA;&lt;p&gt;For everything that is not a pure sine or cosine, there will be more than one &lt;span class=&quot;math-container&quot;&gt;$a_n$&lt;/span&gt; and/or &lt;span class=&quot;math-container&quot;&gt;$b_n$&lt;/span&gt; that is not 0.&lt;/p&gt;&#xA;&lt;p&gt;For example, the square wave with fundamental frequency &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; has the formula&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$s_{\text{sq. wave}}(t) = \frac 4\pi\left(\frac 11 \sin(1\cdot2\pi f t)+\frac 13 \sin(3\cdot2\pi f t)+\frac15 \sin(5\cdot2\pi f t)+\frac 17 \sin(7\cdot2\pi f t)+\cdots \right)$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;h1&gt;Mixing with things that aren't pure sines&lt;/h1&gt;&#xA;&lt;p&gt;When you look at that, it'll become apparent that if you mix with anything but a clean sine, or cosine, you end up with more products.&lt;/p&gt;&#xA;&lt;p&gt;For example, multiplying with a square wave BFO with fundamental frequency &lt;span class=&quot;math-container&quot;&gt;$f_2$&lt;/span&gt; will not only mix what is at &lt;span class=&quot;math-container&quot;&gt;$f_1$&lt;/span&gt; down to &lt;span class=&quot;math-container&quot;&gt;$f_1-f_2$&lt;/span&gt;, because there's not only a sine with a single frequency in there, but also harmonics. So, you get what you want, but also things that are at every odd multiple of &lt;span class=&quot;math-container&quot;&gt;$f_2$&lt;/span&gt; apart to your &amp;quot;target frequency&amp;quot;. Uff! Not good. You wanted to mix what is at 100.001 MHz to 1 kHz, so you used a 100 MHz square wave, so you actually did get what was at 100.001 MHz at 1 kHz, but also what was at 300.001 MHz, and at 500.001 MHz, and so on, mixed to 1 kHz.&lt;/p&gt;&#xA;&lt;h1&gt;Effects of that on receivers&lt;/h1&gt;&#xA;&lt;p&gt;Often, that's undesirable. (because you don't care what is at 300.001 MHz, it only interferes with your 100 MHz signal of interest.) Sometimes, it doesn't matter, because the signal mixture you put into your mixer is already filtered sufficiently, so that there's nothing at 300.001, 500.001, … MHz to begin with. (that is typically the case for a well-filtered IF.)&lt;/p&gt;&#xA;&lt;p&gt;So, it depends on your receiver architecture whether the BFO not being a single tone is critical or not. In general, it's advisable that it is!&lt;/p&gt;&#xA;&lt;p&gt;#Generating a pure-sine BFO from a square wave&lt;/p&gt;&#xA;&lt;p&gt;that's easily done:&lt;br&gt;&#xA;Say, you want to use a microcontroller to generate a square wave BFO between 10 Hz and 20 Hz (just an example). If you look at the formula of the square wave, you'll notice that the first harmonic is at three times the fundamental frequency – a low pass filter at 29 Hz converts any square wave between 10 Hz and 29 Hz to a pure sine wave, because none of the harmonics make it through.&lt;/p&gt;&#xA;&lt;h1&gt;Other aspects of BFOs that affect your quality&lt;/h1&gt;&#xA;&lt;p&gt;If your BFO has so-called phase noise (i.e. it might be a single sine, but that sine isn't really clean and shifts a bit in frequency, i.e. is a bit faster or slower than it should be at times), then that's a problem, and this noise ends up being very detrimental to your audio quality. In general, because as shown above, filtering out harmonics is easy, but getting rid of phase noise is not, it's more important that your oscillator is very stable than that it's a perfect sine wave.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-08-05T13:38:43.380" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17102" PostTypeId="2" ParentId="17099" CreationDate="2020-08-05T15:05:25.123" Score="2" Body="&lt;p&gt;As you already know, amateur radio is an excellent resource for emergency communications, and APRS is a fine tool for it.  However, APRS is not the only tool, and I would caution you to not obsess over this one tool.  For instance, I'd advise you to make sure that you and your family also know how to communicate using the simplest technology available, which is generally VHF/UHF FM for local communications, or HF SSB for longer distances.  For FM you should know what your active local repeaters are and have practice using them, and also know how to use simplex when the repeaters are down.  Having a plan for emergency power would also be a good thing.&lt;/p&gt;&#xA;&lt;p&gt;Regarding APRS, I don't know of any books that comprehensively describe it, but such a book may be out there.  However, the official APRS web site &lt;a href=&quot;http://www.aprs.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;aprs.org&lt;/a&gt; does a pretty good job of covering the subject, even if it does ramble a bit.  Most APRS packets are received by gateway stations, which copy the packets&#xA;to an internet network of servers called APRS-IS.  The web site &lt;a href=&quot;https://aprs.fi/&quot; rel=&quot;nofollow noreferrer&quot;&gt;aprs.fi&lt;/a&gt; receives APRS packets from APRS-IS, filters the packets for a local area, and displays the information on a map.  You can use aprs.fi to see APRS activity in your local area, even without a license.&lt;/p&gt;&#xA;&lt;p&gt;APRS is intended to be a tactical information system that can be used to broadcast all sorts of interesting information.  Unfortunately it hardly ever gets used as such, and instead is mostly used by weather stations and people broadcasting the location of their cars.  However it is still tremendously useful for some things.  In many places the network of APRS digipeaters has better coverage than the mobile phone network, and as you noted, APRS can be used to deliver short text messages.  The International Space Station has a digipeater, and it could possibly be used as a last-ditch emergency way to get a message out of a wilderness area, although these days there are &lt;a href=&quot;https://ham.stackexchange.com/questions/6645/how-to-do-aprs-in-real-wilderness/6647&quot;&gt;better tools for that job&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Unfortunately I haven't done a review of available APRS software in several years, but if you want to send text messages via APRS then you'll probably want to use software to do it.  I've heard that there is interesting APRS software for Android and iOS.&lt;/p&gt;&#xA;&lt;p&gt;Let me point out some related ham technologies/tools that you might find interesting.  First, &lt;a href=&quot;https://winlink.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Winlink&lt;/a&gt; allows a station to send text-based messages over HF, VHF or UHF.  These messages are in the format of emails, and the Winlink network interoperates with the internet, so emails can be sent by radio and then go through a gateway station to the recipient over the internet, and vice-versa.  Second, &lt;a href=&quot;https://en.wikipedia.org/wiki/D-STAR&quot; rel=&quot;nofollow noreferrer&quot;&gt;D-STAR&lt;/a&gt; is a digital mode for VHF and UHF that can carry voice and data simultaneously.  D-STAR can also be used for location data and text messaging using a tool called &lt;a href=&quot;http://www.d-rats.com/download/doc/contrib/D-RATS_operating_guide_0.3.3.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;D-RATS&lt;/a&gt;, and I believe the location data is shared with APRS-IS (I'm not positive about that).  The downside of D-STAR for such purposes is that the radios and repeaters tend to be expensive, and there are not nearly as many D-STAR repeaters as APRS digipeaters.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-08-05T15:05:25.123" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17103" PostTypeId="2" ParentId="17100" CreationDate="2020-08-05T17:45:22.483" Score="4" Body="&lt;p&gt;The BFO is one input to the mixer, the other being the RF signal you're wanting to receive. An ideal mixer simply multiplies its inputs: if at one instant one input is 2V, and the other input is 3V, the output will be 6V.&lt;/p&gt;&#xA;&lt;p&gt;This is useful because multiplication like this can accomplish a frequency shift. The objective in receiving USB is simply to take all the frequencies at RF, say 10,000,000 Hz to 10,004,000 Hz for example, and shift them down to something you can hear like 0 to 4000 Hz. LSB is similar except &lt;a href=&quot;https://ham.stackexchange.com/a/16481/218&quot;&gt;you're aiming for 0 to -4000 Hz&lt;/a&gt;, which has the effect of &amp;quot;flipping&amp;quot; the spectrum.&lt;/p&gt;&#xA;&lt;p&gt;The ideal mixer products output frequency components that are the sum and difference of its inputs. So if one input to the mixer is a sinusoid at 10 MHz, and the other is a sinusoid at 9 MHz, then the output will be sinusoids at 1 MHz and 19 MHz.&lt;/p&gt;&#xA;&lt;p&gt;What if one or both of the inputs is not a simple sinusoid? By &lt;a href=&quot;https://en.wikipedia.org/wiki/Superposition_principle&quot; rel=&quot;nofollow noreferrer&quot;&gt;superposition&lt;/a&gt; the input(s) can be &lt;a href=&quot;https://en.wikipedia.org/wiki/Fourier_series&quot; rel=&quot;nofollow noreferrer&quot;&gt;decomposed into sinusoids&lt;/a&gt;, so the above still holds.&lt;/p&gt;&#xA;&lt;p&gt;For example, a square wave consists of a sinusoid at the fundamental frequency, and then every odd multiple thereof. So if the BFO is a square wave at 10 MHz, this is equivalent to having a series of separate mixers, one with a sine wave BFO at 10 MHz, another at 30 MHz, another at 50 MHz, and so on, and then summing all the outputs of these mixers together.&lt;/p&gt;&#xA;&lt;p&gt;What this means is if the BFO is a square wave, additional frequencies in the RF input can also be mixed to baseband where they will add and interfere with your desired signal. For example if the desired USB signal is at 10 MHz the BFO will be set to 10 MHz to mix that signal down to baseband. But if there's also a signal (or any noise) at 30 MHz you'll hear that too, added to the desired signal.&lt;/p&gt;&#xA;&lt;p&gt;There's a simple solution: filter the RF input to the mixer such that there is nothing at 30, 50, 70, ... MHz. A lot of times, such a filter is already present in the receiver anyway, since it's generally desirable to minimize the power at all points in the circuit since this minimizes nonlinear distortion.&lt;/p&gt;&#xA;&lt;p&gt;In fact, many receiver architectures use a mixer that is deliberately far from ideal. For example, the Elecraft receivers use an &lt;a href=&quot;https://www.onsemi.com/products/interfaces/analog-switches/fst3253&quot; rel=&quot;nofollow noreferrer&quot;&gt;FST3253&lt;/a&gt; as the mixer. This is an analog multiplexer IC which is functionally similar to a switch, with the position of the switch controlled by a digital input. The BFO provides this digital input, and the analog inputs and outputs are arranged so when the &amp;quot;switch&amp;quot; is flipped, the polarity of the analog signal is inverted.&lt;/p&gt;&#xA;&lt;p&gt;As such, this is far from an ideal mixer. Effectively, it can only multiply by 1 or -1, so even if the BFO was a sine wave, it would become a square wave by nature of the digital input.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-08-05T17:45:22.483" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17104" PostTypeId="1" CreationDate="2020-08-05T21:38:31.370" Score="0" ViewCount="105" Body="&lt;p&gt;I'm building myself an Excel Cheat Sheet.&lt;/p&gt;&#xA;" OwnerUserId="15859" LastEditorUserId="4665" LastEditDate="2020-08-05T22:45:05.393" LastActivityDate="2020-08-07T10:12:56.957" Title="Where can I find a table listing the maximum PEP per band?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;rf-power&gt;&lt;ssb&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17105" PostTypeId="2" ParentId="17104" CreationDate="2020-08-05T22:41:40.330" Score="4" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/o6swv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/o6swv.png&quot; alt=&quot;The ARRL's band chart, color version&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The ARRL's &lt;a href=&quot;http://www.arrl.org/files/file/Regulatory/Band%20Chart/Band%20Chart%20-%2011X17%20Color.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;band chart (PDF)&lt;/a&gt; includes the maximum allowed power for stations in the United States and its territories.  Sometimes the power limit depends on the license class of the operator and/or the band; in that case, the power limit is adjacent to the graphic for that license class and/or band.  If no power limit is listed there, then the power limit is 1.5 kW, unless other restrictions apply.  All power limits are measured as &lt;a href=&quot;https://en.wikipedia.org/wiki/Peak_envelope_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;Peak Envelope Power (PEP)&lt;/a&gt; unless noted; the exceptions are the 2,200m and 630m bands, which specify &lt;a href=&quot;https://en.wikipedia.org/wiki/Effective_radiated_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;Equivalent Isotropic Radiated Power (EIRP)&lt;/a&gt;, and the 60m band, which specifies &lt;a href=&quot;https://en.wikipedia.org/wiki/Effective_radiated_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;Effective Radiated Power (ERP)&lt;/a&gt;.  According to the chart, &amp;quot;Geographical and power restrictions may apply to all bands above 420 MHz.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;According to Wikipedia, &amp;quot;PEP is normally considered the occasional or continuously repeating crest of the modulation envelope under normal operating conditions.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;Wikipedia's definition of EIRP is, &amp;quot;the hypothetical power that would have to be radiated by an isotropic antenna to give the same ('equivalent') signal strength as the actual source antenna in the direction of the antenna's strongest beam.&amp;quot;  In other words, the EIRP is the PEP multiplied by the maximum gain of the antenna, where the gain is measured compared to an ideal isotropic antenna.&lt;/p&gt;&#xA;&lt;p&gt;Wikipedia's definition of ERP is, &amp;quot;the total power in watts that would have to be radiated by a half-wave dipole antenna to give the same radiation intensity (signal strength or power flux density in watts per square meter) as the actual source antenna at a distant receiver located in the direction of the antenna's strongest beam (main lobe).&amp;quot;  In other words, the ERP is the PEP multiplied by the maximum gain of the antenna, where the gain is measured relative to the maximum gain of a half-wave dipole, presumably in free space.  I seem to recall that the maximum gain of a dipole in free space compared to an ideal isotropic antenna is +2.15 dB.&lt;/p&gt;&#xA;&lt;p&gt;It should be mentioned that &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.313&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR § 97.313&lt;/a&gt; (a) says, &amp;quot;An amateur station must use the minimum transmitter power necessary to carry out the desired communications.&amp;quot;&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-08-05T22:41:40.330" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17106" PostTypeId="1" AcceptedAnswerId="17107" CreationDate="2020-08-05T23:47:12.513" Score="0" ViewCount="99" Body="&lt;p&gt;I'm very much a beginner with radio. I have a simple set of Baofeng BF-888S radios, and in my basic use with those, I got very curious about something: when you push the PTT button on one radio to speak, what is happening in the other radios on the same frequency that lights their LEDs green and they are seemingly unable to transmit until the one radio stops transmitting?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://baofengtech.com/usermanual/BF888s_Manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;PDF manual&lt;/a&gt;, 7 pages&lt;/p&gt;&#xA;&lt;p&gt;I'm imagining that the single radio starts transmitting at a certain threshold, even before the user starts speaking, and the other radios are configured to go into this receive/prevent-transmit mode when they pick up signals beyond a threshold? But I have no idea, and whatever keywords I'm using to search aren't revealing the answer.&lt;/p&gt;&#xA;" OwnerUserId="17455" LastEditorUserId="8717" LastEditDate="2020-08-06T13:45:47.133" LastActivityDate="2020-08-06T13:45:47.133" Title="How does PTT from one two-way radio prevent input on another?" Tags="&lt;transceiver&gt;&lt;baofeng&gt;&lt;ht&gt;&lt;transmission&gt;&lt;reception&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17107" PostTypeId="2" ParentId="17106" CreationDate="2020-08-06T07:26:38.550" Score="2" Body="&lt;p&gt;Well, it's a combination of two features: The squelch setting, and the busy channel lockout setting.&lt;/p&gt;&#xA;&lt;p&gt;Namely, when a sufficiently strong signal has been received, the squelch system will activate the audio part of the receiver, and allow you to hear transmission.&lt;/p&gt;&#xA;&lt;p&gt;Many radios also have more or less complicated busy channel lockout feature, which prevents the radio from transmitting. If the squelch is open, and the BCL is active, then the radio won't transmit. The general idea is, since you can't interrupt the person transmitting, you should get notified and prevented from transmitting yourself. This way, you can't &amp;quot;step&amp;quot; onto other users using the channel.&lt;/p&gt;&#xA;&lt;p&gt;On the BF-888, you should be able to disable this feature with programming software.&lt;/p&gt;&#xA;" OwnerUserId="77" LastActivityDate="2020-08-06T07:26:38.550" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17108" PostTypeId="2" ParentId="16963" CreationDate="2020-08-06T15:19:40.063" Score="2" Body="&lt;p&gt;A non-resonant Beverage antenna shouldn't need a tunable matching network for either transmitting or receiving (but as Phil nicely stated, you certainly can use one). All you really need is a &lt;a href=&quot;https://web.archive.org/web/20181115070846/http://www.w0btu.com/Beverage_antennas.html#Beverage_Antenna_Transformers&quot; rel=&quot;nofollow noreferrer&quot;&gt;proper broadband matching transformer&lt;/a&gt;, 9:1 for a 50 ohm feedline and 6.25:1 for 75 ohm. It is better to connect the Beverage directly to it and then run coax between it and your station.&lt;/p&gt;&#xA;&lt;p&gt;Phil is correct about the losses (&lt;a href=&quot;https://web.archive.org/web/20181115070846/http://www.w0btu.com/Beverage_antennas.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;my Beverages&lt;/a&gt; have about 10 dB of loss) and that it mostly futile to transmit on them. However, myself and other happy Beverage antenna users have &lt;a href=&quot;https://web.archive.org/web/20181115070846/http://www.w0btu.com/Beverage_antennas.html#transmitting_on_a_Beverage&quot; rel=&quot;nofollow noreferrer&quot;&gt;successfully transmitted on them&lt;/a&gt;. Among other things, it's a matter of how the gain and takeoff angle of a Beverage compares with another antenna over a given DX path and band conditions.&lt;/p&gt;&#xA;&lt;p&gt;For example, one afternoon last year I compared my low N-S 75m dipole with my 580' NE Beverage. I was in QSO with a couple of hams in New York State from my QTH in SW Missouri. I had to transmit on my Beverage because they could barely hear me on my dipole. On another occasion, I had a significant signal into Europe transmitting on this same Beverage compared to another antenna.&lt;/p&gt;&#xA;&lt;p&gt;Usually, 40 or 30 meters is about the highest band that they are useful on, but there have been exceptions. W8JI told me that on occasion, his 580' Beverages heard a 20m DX signal that his high Yagi could not.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-08-06T15:36:56.457" LastActivityDate="2020-08-06T15:36:56.457" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17110" PostTypeId="2" ParentId="17104" CreationDate="2020-08-07T10:12:56.957" Score="3" Body="&lt;p&gt;In &lt;a href=&quot;http://www.arrl.org/part-97-text&quot; rel=&quot;nofollow noreferrer&quot;&gt;Part 97&lt;/a&gt;, of course. Specifically, section 97.313, &amp;quot;Transmitter Power Standards&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;But of course it's not just per band... there are several limits that only apply to Novice license holders (none of those have been issued since 2000, but existing holders can still have them), one limit only applies to US territories outside of IARU Region 2 (i.e. places like Hawaii and Guam), a few apply within proximity to certain military bases, and one applies to... Arizona, New Mexico, Florida, half of California, the bottom piece of Nevada, and the western bit of Texas. Really.&lt;/p&gt;&#xA;&lt;p&gt;So a universal table doesn't really work, but if you read through the actual requirements and pick out the ones that apply to you at your home QTH, &lt;em&gt;then&lt;/em&gt; you'll end up with something nice and simple with a number per band.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-08-07T10:12:56.957" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17111" PostTypeId="2" ParentId="13074" CreationDate="2020-08-07T11:03:56.800" Score="1" Body="&lt;p&gt;My understanding of how RF gain works (or does in my own SDR design) is that RF/IF gain alters the gain BEFORE the AGC mechanism and the AF gain alters the gain AFTER the AGC. For a signal that is strong enough to activate the AGC, the AF gain sets the volume of the audio.&lt;/p&gt;&#xA;&lt;p&gt;With the AF gain set at a suitable level, lowering the RF/IF gain should reduce the background noise by stopping the AGC from lifting the noise up to the full level. Sure, lowering the RF/IF gain will NOT improve the SNR of any received signal but it can allow the operator to choose the worst case SNR that is coming out of the loudspeaker.&lt;/p&gt;&#xA;&lt;p&gt;I set my SDR Rx so that the band noise is about 10dB lower than a strong signal - this lowers listening fatigue. If a weak signal is then received (not strong enough to activate my AGC) then it just sounds quiet - just what I want as it still reduces listening fatigue.&lt;/p&gt;&#xA;&lt;p&gt;Tim G0ETP&lt;/p&gt;&#xA;" OwnerUserId="17534" LastActivityDate="2020-08-07T11:03:56.800" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17112" PostTypeId="2" ParentId="16554" CreationDate="2020-08-07T21:18:11.790" Score="1" Body="&lt;p&gt;Part of what makes a repeater valuable is it filters out &amp;quot;invalid&amp;quot; or weak signals.  This makes them efficient in power use as it's not transmitting all the time.  This makes them valuable to the users as they aren't hearing noise all the time through their radios.&lt;/p&gt;&#xA;&lt;p&gt;What makes the signal &amp;quot;valid&amp;quot; is having sufficient power, at the correct kind of modulation, and often with other factors like a PL tone.  Once it is considered &amp;quot;valid&amp;quot; then it repeats the incoming signal on its outbound channel.&lt;/p&gt;&#xA;&lt;p&gt;There are repeaters made to repeat digital and analog signals, they are still transmitting a phone mode but with the &amp;quot;valid&amp;quot; signal being FM or a specific digital phone mode.  Depending on how the repeater is configured it can then transmit the same signal it receives or convert the audio to FM for backward compatibility with those that have not yet upgraded to digital radios.&lt;/p&gt;&#xA;&lt;p&gt;A digital signal can be sent through an analog repeater but it must be done in a way that is compatible with the analog systems it uses.  A series of DTMF tones is a simple example of digital information sent by an analog repeater.&lt;/p&gt;&#xA;&lt;p&gt;A linear translator can retransmit an analog or digital signal, as pointed out by W8II in another answer, but this comes with costs.  A linear translator will retransmit the noise with the signal.  An analog repeater will do this as well to some extent but the noise is not retransmitted constantly and the inherent filtering of demodulating and remodulating filters some noise.  A digital repeater will cut out more of the noise because of this same demodulation and remodulation.  Without that filtering the increased range benefits of a repeater will be diminished.&lt;/p&gt;&#xA;&lt;p&gt;Linear translators are still used and considered superior in many applications from a repeater precisely because it doesn't try to demodulate.  This means it will work with any kind of modulation so long as it fits within the frequency, power, and other limits of the translator.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2020-08-07T21:18:11.790" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17113" PostTypeId="1" CreationDate="2020-08-08T05:27:24.577" Score="0" ViewCount="92" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AxmrT.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AxmrT.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;I just bought a magnet-mount whip antenna at a garage sale. It has no brand markings anywhere on it. it is 32&amp;quot; long overall but is broken up into three segments by what appear to be two small potted loading coils. The shortest segment is at the bottom and measures 4 1/2&amp;quot; from the top of the base to the center of the first coil. the next segment measures 9 1/2&amp;quot; between the centers of the coils and the topmost segment measures 18&amp;quot; from the center of the second coil to the tip of the whip. the coils are equipped with setscrews for clamping onto the whip segments and the coax connector looks like a BNC.&lt;/p&gt;&#xA;&lt;p&gt;Can anyone tell me what frequencies this antenna was intended for?&lt;/p&gt;&#xA;" OwnerUserId="10598" LastEditorUserId="10598" LastEditDate="2020-08-09T06:09:32.057" LastActivityDate="2020-08-09T06:09:32.057" Title="what frequencies is this antenna cut for?" Tags="&lt;antenna-construction&gt;&lt;vertical-antenna&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17115" PostTypeId="1" AcceptedAnswerId="17119" CreationDate="2020-08-08T19:07:36.697" Score="4" ViewCount="83" Body="&lt;p&gt;When I transmit, it there seems to be something mixing and reflecting my signal.&#xA;For example, when I transmit on 14.300 MHz, I see signals above my transmitted signal at at 14.500, 14.700, 14.900, etc. and below my signal at 14.100, 13.900, 13.700, and so on. I tested on another frequency in twenty meters and saw the same pattern, with both tests radiating signals with frequencies &amp;quot;reflected&amp;quot; around 14.400 MHz.&lt;/p&gt;&#xA;&lt;p&gt;This sounds like some issue with my signal getting unintentionally mixed with some other signal. The weirdest thing is that I still see at least the primary reflection---e.g. the 14.500 MHz signal when I transmit on 14.300 MHz---when I'm using a dummy load.&lt;/p&gt;&#xA;&lt;p&gt;I even see noise signals being reflected around this 14.400 MHz point. What could possibly be doing this, and how can I track it down?&lt;/p&gt;&#xA;&lt;p&gt;Some information about my system:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I am watching the spectrum using an RTL-SDR, with SDR# software&lt;/li&gt;&#xA;&lt;li&gt;Rig is an Icom IC-718&lt;/li&gt;&#xA;&lt;li&gt;Antenna is a dipole cut for 20 meters, run around the interior perimeter of my shack&lt;/li&gt;&#xA;&lt;li&gt;Antenna is connected to the radio with 12ft of DXE400MAX coax&lt;/li&gt;&#xA;&lt;li&gt;Transmission line has a common-mode choke wound into the receiver end of the coax&lt;/li&gt;&#xA;&lt;li&gt;There is a 1:1 current balun is at the antenna side&lt;/li&gt;&#xA;&lt;li&gt;The following points are all bonded together, however they are only bonded to the AC ground since I am in a third-floor apartment:&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The transmission line shield at the antenna end&lt;/li&gt;&#xA;&lt;li&gt;The transceiver (ICOM IC-728)&lt;/li&gt;&#xA;&lt;li&gt;The power distribution bar (MFJ-1129)&lt;/li&gt;&#xA;&lt;li&gt;The power strip this is all powered by (an MFJ-4230MV)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="17421" LastEditorUserId="17421" LastEditDate="2020-08-09T20:55:20.140" LastActivityDate="2020-08-09T20:55:20.140" Title="How to track down and neutralize this apparent mixer creating noisy emissions around my signal?" Tags="&lt;rtl-sdr&gt;&lt;noise&gt;&lt;mixer&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="17117" PostTypeId="2" ParentId="6340" CreationDate="2020-08-09T10:34:03.120" Score="3" Body="&lt;p&gt;&lt;a href=&quot;https://www.gpscentral.ca/manuals/Icom_IC-R8600_ENG_Manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.gpscentral.ca/manuals/Icom_IC-R8600_ENG_Manual.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Page 21 explains the difference between regular squelch and s-meter squelch on any Icom radio.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;h3&gt;Noise squelch&lt;/h3&gt;&#xA;&lt;p&gt;The Noise Squelch allows the audio to be heard only while receiving a&#xA;signal that includes less noise than a set level.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Activates when the squelch level is set to between 30% and 50% in&#xA;the FM, AM, S-AM or DIGITAL mode.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A higher level blocks weak signals. A lower level allows you to hear&#xA;weak signals including noise.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;...&lt;/p&gt;&#xA;&lt;h3&gt;S-meter squelch&lt;/h3&gt;&#xA;&lt;p&gt;The S-meter Squelch mutes the speaker sounds when the signal strength&#xA;is less than the set value.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Activates when the squelch level is set to between 50% and 100% in any mode.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="17546" LastEditorUserId="76" LastEditDate="2020-08-09T18:14:22.750" LastActivityDate="2020-08-09T18:14:22.750" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17118" PostTypeId="1" CreationDate="2020-08-09T15:16:36.547" Score="1" ViewCount="115" Body="&lt;p&gt;A few months ago, I built a 6 element yagi: 3 driven elements, and 3 reflectors. For 10-15-20m. I was able to tune it to SWR 1:1 for the FT8 frequencies in each band. &lt;strong&gt;This antenna is only 6m above ground&lt;/strong&gt;, since that's what I can manage without guy wires (and the fact that steel tube is sold in 6m lengths too).&lt;/p&gt;&#xA;&lt;p&gt;The 20 and 15m elements are coil loaded, as I didn't want the antenna to exceed my property limits, and I wanted to use whole aluminium tubes (which are sold in 6 meter lengths). I think this is the main issue here.&lt;/p&gt;&#xA;&lt;p&gt;I've been happy with this setup for a few months, as I thought it was working properly.&lt;/p&gt;&#xA;&lt;p&gt;Since my mom is also a ham, my dad installed a trapped 20-40m dipole. &lt;strong&gt;It's about 9m off the ground&lt;/strong&gt;. It's only a couple of meters away from my yagi. I noticed her radio was getting FAR more FT8 decodes per cycle: while my computer only showed 3 or 4, hers would show 12 to 15.&lt;/p&gt;&#xA;&lt;p&gt;So I've been trying to figure out what the problem with my yagi was. Here's what I tried:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Cut the 20m element in half and feed it like a dipole&lt;/li&gt;&#xA;&lt;li&gt;Remove the rest of the driven elements and leave only the 20m one&lt;/li&gt;&#xA;&lt;li&gt;Remove all the reflectors, turning the yagi into just a rigid dipole&lt;/li&gt;&#xA;&lt;li&gt;Changed the coax to the antenna to RG-213&lt;/li&gt;&#xA;&lt;li&gt;Removed the coax switch, connecting the antenna directly to the radio&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I even tried taking the dipole down to rule out interactions between the two antennas, and lack of height in my yagi. And even laying on the roof, lower than the yagi, it works better in RX than my yagi, so I think it's neither height, nor interaction between the two.&lt;/p&gt;&#xA;&lt;p&gt;I designed this yagi based on other designs online, and simulated it with 4NEC2. I built it down to the millimeter and it was very easy to tune: I didn't have to trim any tubes once I put it together, it just resonated at the calculated frequencies. The simulations did show lobes to the front (which I measured with a function generator and an antenna 1km away. Only a few milliwatts CW, while i rotated the antenna, and indeed, pointing the antenna towards the source gave me a higher reading, by 2 points in the s-meter: S9 vs S7), so the directionality was also spot on.&lt;/p&gt;&#xA;&lt;p&gt;What's the problem here? Could it be that being coil loaded makes it perform significantly worse? It's only 7 meters long instead of the 10m required for a true half-wave dipole.&#xA;Or is this a height problem and I should take it much higher than it is now? Lifting it is not an easy task. It would be expensive, too, so I would prefer to avoid it if possible at all.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6JXxx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6JXxx.jpg&quot; alt=&quot;Photo&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14642" LastEditorUserId="76" LastEditDate="2020-08-09T18:18:18.337" LastActivityDate="2020-08-10T00:32:35.623" Title="Yagi performing far worse than a dipole" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;yagi&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17119" PostTypeId="2" ParentId="17115" CreationDate="2020-08-09T20:51:29.433" Score="5" Body="&lt;p&gt;This is caused by the RTL-SDR I was using to view my signal.&#xA;Here's a quote from the guide at &lt;a href=&quot;https://www.rtl-sdr.com/rtl-sdr-blog-v-3-dongles-user-guide/&quot; rel=&quot;noreferrer&quot;&gt;https://www.rtl-sdr.com/rtl-sdr-blog-v-3-dongles-user-guide/&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Note that this feature makes use of direct sampling and so aliasing will occur. The RTL-SDR samples at 28.8 MHz, thus you may see mirrors of strong signals from 0 - 14.4 MHz while tuning to 14.4 - 28.8 MHz and the other way around as well. To remove these images you need to use a low pass filter for 0 - 14.4 MHz, and a high pass filter for 14.4 - 28.8 MHz, or simply filter your band of interest.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="17421" LastActivityDate="2020-08-09T20:51:29.433" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17120" PostTypeId="2" ParentId="17118" CreationDate="2020-08-10T00:32:35.623" Score="1" Body="&lt;p&gt;It doesn't makes sense that a 6 element yagi doesn't work a good as a half wave dipole. Even a 6 element yagi with the worst design should still work better than a half wave dipole.&lt;/p&gt;&#xA;&lt;p&gt;I don't think the antenna is the problem.&lt;/p&gt;&#xA;&lt;p&gt;It sounds to me like one side of the feed line is open circuit at the antenna, if you are using coax the shield might not be connected.&lt;/p&gt;&#xA;&lt;p&gt;This would mean you are effectively running a long wire antenna with a lump of 6 element yagi connected at the end.&lt;/p&gt;&#xA;&lt;p&gt;The low SWR could just be a coincidence.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2020-08-10T00:32:35.623" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17121" PostTypeId="1" AcceptedAnswerId="17160" CreationDate="2020-08-10T08:23:19.417" Score="1" ViewCount="321" Body="&lt;p&gt;I realise there have been many great posts on hunting RFI, i've got pretty close to tracking mine down, but would appreciate some insights from the ham.se experts :)&lt;/p&gt;&#xA;&lt;p&gt;I've done quite a lot of work to hunt this down. The background - using a FlexRadio 6000 series inside a computer rack, radio is grounded to the rack via a short ground wire #6 awg (~40cm), rack is grounded currently to AC ground (work to be done in this area..)&lt;/p&gt;&#xA;&lt;p&gt;Antenna is a K4KIO Hexbeam relatively low, around 20-feet above a flat metal roof on an insulated tripod, fed with RG8 around 25M, with the supplied Fairrite clamps on the RG8 at the antenna feedpoint. Ferrites (clamps) are on all cables, with the dc power-cable wrapped around a ferrite-ring around 4 or 5 turns at the radio end. An ethernet-switch (Ubiquiti) is outside the rack, and connected via a CAT8 cable (0.5M) to the FlexRadio via a narrow opening in the rack.&lt;/p&gt;&#xA;&lt;p&gt;Using a switch-mode 40A psu (Manson) that has pretty good filtering within, and disconnecting the antenna, the RFI completely disappears, so i'm fairly sure everything around the radio itself is RF quiet.&lt;/p&gt;&#xA;&lt;p&gt;Every 61khz precisely i have solid bars on 20M and 15M (40M is clear), that look like this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cuWxu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cuWxu.png&quot; alt=&quot;15M screenshot&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I've used a vertical in the past and the bars were less obvious, so i'd assume this RFI is horizontally polarised. There is an Ethernet cable running under the antenna with PoE (indoors), but i've disconnected the cable and the bars are still there. There are ferrite clamps on each endpoint of that particular cable.&lt;/p&gt;&#xA;&lt;p&gt;I've gone RFI hunting with a laptop and SDRPlay RSP1 and a random 800mhz yagi (i happened to have) and tried both orientations horizontal/vertical but the SDRPlay waterfall was fairly clear.&lt;/p&gt;&#xA;&lt;p&gt;My belief is Ethernet interference, not from my equipment, but a neighbour. Wether it's home-internet, or perhaps a solar-inverter's IP interface, but that's just a guess.&lt;/p&gt;&#xA;&lt;p&gt;Having 61khz bars around 14-21mhz is the signature of this particular RFI.&lt;/p&gt;&#xA;&lt;p&gt;Apart from this issue, it's pretty RFI clean. Was wondering if anyone has any advice given the findings to date?&lt;/p&gt;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastEditorUserId="17200" LastEditDate="2020-08-10T08:48:27.953" LastActivityDate="2020-08-17T14:45:02.617" Title="Hunting RFI with bars every 61 khz" Tags="&lt;rfi&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17123" PostTypeId="1" AcceptedAnswerId="17127" CreationDate="2020-08-10T14:24:02.813" Score="3" ViewCount="269" Body="&lt;p&gt;I thought that &amp;quot;Talk Around&amp;quot; and &amp;quot;Reverse&amp;quot; were two ways of referring to the same thing: swapping a channel's transmit and receive frequencies so that one could e.g. listen for other stations trying to reach a downed repeater. However, my Anytone radios expose both &amp;quot;Talk Around&amp;quot; and &amp;quot;Reverse&amp;quot; as options. What makes them different?&lt;/p&gt;&#xA;&lt;p&gt;Edit: Adding image from manual &amp;quot;describing&amp;quot; them:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/F6gV6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/F6gV6.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14609" LastEditorUserId="8717" LastEditDate="2020-08-11T00:23:15.407" LastActivityDate="2020-08-11T23:06:35.500" Title="Talk Around vs Reverse" Tags="&lt;repeater&gt;&lt;anytone&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17124" PostTypeId="1" AcceptedAnswerId="17128" CreationDate="2020-08-10T18:28:15.550" Score="3" ViewCount="228" Body="&lt;p&gt;I bought a Yaesu FT-60R years ago. Instead of coming with a charging cradle, it came only with the NC-88B power supply. The NC-88B power supply isn't very intelligent--I don't believe it stops charging the radio on its own--the radio gets hot if I leave it plugged in too long.&lt;/p&gt;&#xA;&lt;p&gt;So I'm thinking of purchasing an &lt;a href=&quot;https://www.hamradio.com/detail.cfm?pid=H0-012794&quot; rel=&quot;nofollow noreferrer&quot;&gt;SBH-13 charging cradle&lt;/a&gt;. However, that cradle says it's compatible with the PA-48B power supply, not the NC-88B. The PA-48B is the replacement for the NC-88B. Do I need to purchase a PA-48B power supply for use with the charging cradle or will my old NC-88B work fine?&lt;/p&gt;&#xA;" OwnerUserId="5820" LastActivityDate="2020-12-26T01:18:13.293" Title="For the FT-60R, does the NC-88B power supply work with the YAESU SBH-13 charging cradle?" Tags="&lt;yaesu&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17125" PostTypeId="1" AcceptedAnswerId="17126" CreationDate="2020-08-11T04:49:50.140" Score="1" ViewCount="73" Body="&lt;p&gt;I'm trying to follow this &lt;a href=&quot;https://www.youtube.com/watch?v=o8OBF47UkeI&amp;t=11s&quot; rel=&quot;nofollow noreferrer&quot;&gt;tutorial&lt;/a&gt; I almost got to the end, about 9:15 was where I got stuck. Right about there, the speaker is about to wrap up- but I get a couple error messages.&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;2020/8/10 22:22:33 HTTP service (0.0.0.0:5000) 2020/08/10 22/22/33 Listen tcp 0.0.0.0:5000 bind address already in use. &#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;FYI, I am using a different commputer from the pi, so I will not be able to send over images. Basically though, What I am trying to do is connect the ax.25 so that I can set up Winlink on two meters. There's on option to connect, and then you click on AX.25, followed by my call sign. That's where I get my second error message.&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;connection refused&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;Can anyone shed some light on this? By the way, originally the message was somewhat different. I don't remember the exact details, but I remember the words &amp;quot;data port&amp;quot;. Thank you so much, if there's anything I can do to help you solve this mystery, please let me know.&lt;/p&gt;&#xA;" OwnerUserId="1861" LastEditorUserId="76" LastEditDate="2020-08-11T10:04:16.047" LastActivityDate="2020-08-11T17:26:51.793" Title="How do you open ax.25 ports?" Tags="&lt;digital-modes&gt;&lt;software&gt;&lt;packet&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17126" PostTypeId="2" ParentId="17125" CreationDate="2020-08-11T17:26:51.793" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Listen tcp 0.0.0.0:5000 bind address already in use.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This sounds like a somewhat generic error, not necessarily related to your AX.25 software itself but certainly a bummer to encounter it while setting up!&lt;/p&gt;&#xA;&lt;p&gt;What this means is the software you're trying to run wants to listen on port 5000, on all network interfaces (the &lt;code&gt;0.0.0.0&lt;/code&gt; part). But something is already listening on that port. Are you already running the same program in a different window?&lt;/p&gt;&#xA;&lt;p&gt;Depending on your operating system, you may find the following Q&amp;amp;A's helpful:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Windows: &lt;a href=&quot;https://stackoverflow.com/questions/48198/how-can-you-find-out-which-process-is-listening-on-a-port-on-windows&quot;&gt;https://stackoverflow.com/questions/48198/how-can-you-find-out-which-process-is-listening-on-a-port-on-windows&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;macOS: &lt;a href=&quot;https://stackoverflow.com/questions/4421633/who-is-listening-on-a-given-tcp-port-on-mac-os-x&quot;&gt;https://stackoverflow.com/questions/4421633/who-is-listening-on-a-given-tcp-port-on-mac-os-x&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Linux: &lt;a href=&quot;https://unix.stackexchange.com/questions/9252/determining-what-process-is-bound-to-a-port&quot;&gt;https://unix.stackexchange.com/questions/9252/determining-what-process-is-bound-to-a-port&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;connection refused&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Without watching the video, this one's a little harder to guess at because you don't say what you were trying to do/run when you got this message. If you're curious in general, you might find the answers at &lt;a href=&quot;https://serverfault.com/questions/725262/what-causes-the-connection-refused-message&quot;&gt;https://serverfault.com/questions/725262/what-causes-the-connection-refused-message&lt;/a&gt; interesting but it's possible that once you fix the first error, then this one might go away on its own.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-08-11T17:26:51.793" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17127" PostTypeId="2" ParentId="17123" CreationDate="2020-08-11T23:06:35.500" Score="6" Body="&lt;p&gt;Talkaround: Transmitting and receiving on the repeater output frequency.  Thus, you &amp;quot;talk around&amp;quot; the repeater directly with the other station. (Same as simplex).  Both stations in a conversation can do this.&lt;/p&gt;&#xA;&lt;p&gt;Reverse: Switching transmit and receive frequencies.  Thus, you can talk directly to another station that is still on the repeater's frequency.  But if both stations reverse, then they can not hear each other.&lt;/p&gt;&#xA;" OwnerUserId="17422" LastActivityDate="2020-08-11T23:06:35.500" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17128" PostTypeId="2" ParentId="17124" CreationDate="2020-08-12T04:31:54.037" Score="1" Body="&lt;p&gt;The shortest possible answer...the SBH-13 will function on any supply that can provide 12V DC and is rated at 500mA of output current. The NC-88B is a no go.&lt;/p&gt;&#xA;&lt;p&gt;Longer answer...I've used three different 12V supplies on my SBH-13, each one has worked with no issues. The SBH-13 just wants 12V DC, at some current obviously not exceeding 500mA. The circuitry in the charging cradle does the rest.&lt;/p&gt;&#xA;&lt;p&gt;I dug into the Yaesu AC adapter situation a bit and it looks to me like the PA-48B is discontinued, and the current equivalent is the SAD-25B - according the Yaesu website this is the AC adpater that is specified for use with the SBH-13. The FT-60R I purchased a year ago (Summer 2019) came with the SBH-13 cradle and an AC adapter that says &amp;quot;SAD-25&amp;quot;  on it. I don't know why my adapter doesn't have the &amp;quot;B&amp;quot;, it may just be part of Yaesu's part numbering..in any case, the specification is still 12V DC at 500mA.&lt;/p&gt;&#xA;&lt;p&gt;Also...all of the above applies to the US version, which will not allow battery charging via the DC power jack on the radio. Since you mention in your question charging via the power jack, either you have a non-US version, or this was previously a feature on the US version FT-60.&lt;/p&gt;&#xA;" OwnerDisplayName="user14945" LastEditorDisplayName="user14945" LastEditDate="2020-08-12T06:21:06.740" LastActivityDate="2020-08-12T06:21:06.740" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17129" PostTypeId="1" AcceptedAnswerId="17132" CreationDate="2020-08-12T20:17:04.257" Score="2" ViewCount="146" Body="&lt;p&gt;I've bought the QCX+ 40 m band radio. I will be powering this off a 12 V battery. I read on the manual the RF power at 12 V is just 3 W whereas on 15 V it is 5 W. Should I buy a boost converter for the battery to up the voltage to 15 V?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WJoKN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WJoKN.png&quot; alt=&quot;RF power output on 40 m&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15878" LastActivityDate="2020-08-14T11:02:47.363" Title="Does 3 W vs 5 W TX power make a huge difference in QRP CW operation?" Tags="&lt;rf-power&gt;&lt;power-supply&gt;&lt;dc-power&gt;&lt;qrp&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17130" PostTypeId="2" ParentId="17129" CreationDate="2020-08-12T22:17:10.023" Score="0" Body="&lt;p&gt;For any transmitter, if you double the power, this might seem a lot, but at the other end at a receiver the signal  will increase by only 3 dB which is half an S point.&lt;/p&gt;&#xA;&lt;p&gt;So an increase of 3W to 5W is 2.2 dB which is a bit less than half an S point.&lt;/p&gt;&#xA;&lt;p&gt;This change is negligible and you won't notice much difference.&lt;/p&gt;&#xA;&lt;p&gt;However if the level of your transmitted signal is down in the noise at a receiver, it could make the difference between being able to hear it or not.&lt;/p&gt;&#xA;&lt;p&gt;To answer your question, it is probably not worth the effort to try and increase the supply because no one will notice. Having said that every bit counts and increasing the supply will help a little bit.&lt;/p&gt;&#xA;&lt;p&gt;Personally i would only make the supply 15 V if it was easy to do.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-08-12T22:23:31.553" LastActivityDate="2020-08-12T22:23:31.553" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17131" PostTypeId="2" ParentId="17129" CreationDate="2020-08-12T22:28:55.240" Score="4" Body="&lt;p&gt;It makes a difference of:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 10 \times \log_{10}\left(3 \over 5\right) = 2.2 \:\mathrm{dB} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;How big is 2.2 dB? See &lt;a href=&quot;https://ham.stackexchange.com/questions/6676/how-big-is-a-decibel&quot;&gt;How big is a decibel?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It's also relevant to note: if the 12V battery is lead acid, the charged voltage can be as high as 13.7.&lt;/p&gt;&#xA;&lt;p&gt;Furthermore, while a boost converter might further increase your transmit power, it's likely to make noise which will degrade your receive performance.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-08-12T22:52:12.463" LastActivityDate="2020-08-12T22:52:12.463" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17132" PostTypeId="2" ParentId="17129" CreationDate="2020-08-12T22:51:35.087" Score="3" Body="&lt;p&gt;If you haven't done much QRP operating, QRP is a funny thing.  Sometimes propagation is great, and you wonder why anyone would bother with 100 W or more.  I'll never forget my first DX QSO, from Oregon to Estonia, running 11 W to a vertical, by gray-line propagation at the bottom of the sunspot cycle in 2006.  Other times it seems like a complete waste of time, calling station after station that boom into your headphones but can't hear you at all.&lt;/p&gt;&#xA;&lt;p&gt;The difference between 3 W and 5 W is 2.2 dB, which is about a third of an S-unit.  (An S-unit is 6 dB.)  The question is, how much does that mean to you?  That depends on what kind of operating you do, or want to do, with your QRP rig.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If you're a QRP contester, then 2 dB can make quite a difference, because every decibel matters to contesters.  Contesters generally have very good ears, and serious ones are willing to work hard to decode signals just above the noise floor to get the contact.  Losing 2 dB means potentially losing a few contacts in your next major contest.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you're a casual QRPer who makes contacts on the QRP calling frequency, then you'll potentially lose a fraction of potential contacts.  QRPers are also generally willing to work at pulling in your weak signal, so every decibel helps.  You can always spot yourself on &lt;a href=&quot;http://qrpspots.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;qrpspots.com&lt;/a&gt;, which encourages other operators to listen for you.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you're a Morse ragchewer, then lots of hams either won't be able to hear you at all, or won't tune slowly enough to hear your CQ, or won't be willing to work at pulling in a very weak signal on a noisy band, so you're generally limited to stations that are exactly one skip away.  To those stations you might be S-5 on their meters.  For those stations, there usually isn't much difference between S-5 and S-4.6.  I'd think you wouldn't notice much difference between 3 W and 5 W when ragchewing with random hams.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;My advice would be to try the radio at 3 W, and see how you like QRP.  If you like it enough, it might be worth buying that battery booster.  The battery booster will drain your battery faster though, because the radio would consume more power and the booster itself consumes power, since it's not 100% efficient.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-08-12T22:51:35.087" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17133" PostTypeId="1" CreationDate="2020-08-13T07:07:43.220" Score="1" ViewCount="1151" Body="&lt;p&gt;I have designed a half-wave dipole antenna for frequency range of 150 to 200 MHz. Due to resonant frequency of 175 MHz, Its dimensions are:&#xA;L=817.44 mm, R=1.71 mm. Impedance is also equal to 73 ohms.&#xA;After simulating in CST MWS, the bandwidth was about 18.64 MHz. How I can increase the bandwidth? I want to use this antenna for frequencies of 150 to 200 MHz. What's the method?&lt;/p&gt;&#xA;" OwnerUserId="17568" LastActivityDate="2020-08-19T21:01:27.170" Title="How to increase the bandwidth of half-wave dipole antenna?" Tags="&lt;dipole&gt;&lt;bandwidth&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17134" PostTypeId="2" ParentId="17133" CreationDate="2020-08-13T07:42:36.983" Score="4" Body="&lt;p&gt;You might experiment with increasing the diameter of the conductors of the dipole to improve its SWR bandwidth, along with optimizing the physical lengths of those conductors (equally) to center the low-SWR bandwidth of the dipole in your r-f spectrum of interest.&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;Author edit of 14 Aug 2020:&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;Below for &amp;quot;calibration&amp;quot; is a comparison of a case where the radius of the conductors stated in the OP was increased by a factor of 5:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uQdN1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uQdN1.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-08-14T10:39:38.563" LastActivityDate="2020-08-14T10:39:38.563" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17135" PostTypeId="1" CreationDate="2020-08-13T08:55:02.303" Score="1" ViewCount="218" Body="&lt;p&gt;I have scoured the internet for info on this radio. Specs, programming, manuals, to be exact, yet I can find NOTHING other than sellers of the radio. Anyone have any links they'd be able to share!  I appreciate the help&lt;/p&gt;&#xA;" OwnerUserId="5726" LastActivityDate="2020-09-14T00:06:30.707" Title="Baofeng UV-9 Info and Help Please!" Tags="&lt;baofeng&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17136" PostTypeId="2" ParentId="17133" CreationDate="2020-08-13T10:43:18.567" Score="3" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;After simulating in CST MWS, the bandwidth was about 18.64 MHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;According to which definition of bandwidth?&lt;/p&gt;&#xA;&lt;p&gt;I'm asking this because every antenna is a tradeoff. The easiest way, probably, to deal with this is to simply reduce your requirements for what &amp;quot;bandwidth&amp;quot; is.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;How I can increase the bandwidth?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;You're using a dipole, but you want a bandwidth of more than a fourth of the center frequency.&lt;/p&gt;&#xA;&lt;p&gt;That's usually not going to work; you need a different design if you need to use a bandwidth that large relative to your center frequency, or relax your definition of &amp;quot;bandwidth&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;You can of course help the situation by doing as Richard recommends: a larger-diameter conductor usually helps a bit with bandwidth, but I don't think you'll increase your bandwidth by a factor of 3 that way.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-08-13T10:43:18.567" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17137" PostTypeId="2" ParentId="17133" CreationDate="2020-08-13T14:03:23.073" Score="5" Body="&lt;p&gt;Marcus and Richard have answered the question that you asked, how to triple the bandwidth of a dipole, with the correct answer that it can't be done.  I suggest that you edit your question to give us more information about the problem that you're trying to solve and its constraints, and then we can offer more targeted suggestions.  In the meantime, here are some generic suggestions of ways to increase bandwidth of an antenna system:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Use a &lt;a href=&quot;https://en.wikipedia.org/wiki/Log-periodic_antenna&quot; rel=&quot;noreferrer&quot;&gt;log-periodic&lt;/a&gt; antenna.  There are many existing commercial antenna models that use a log-periodic for the 174–216 MHz VHF television band.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Use a &lt;a href=&quot;https://en.wikipedia.org/wiki/Discone_antenna&quot; rel=&quot;noreferrer&quot;&gt;discone&lt;/a&gt; antenna.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Redesign the radio to tolerate a larger impedance mismatch.  This would not be easy for a high-powered transmitter.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Use an automatic &lt;a href=&quot;https://en.wikipedia.org/wiki/Antenna_tuner&quot; rel=&quot;noreferrer&quot;&gt;antenna tuner&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-08-13T14:03:23.073" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17138" PostTypeId="2" ParentId="17121" CreationDate="2020-08-13T14:49:52.977" Score="0" Body="&lt;p&gt;finding rfi source: you must use a battery operated radio, sw &amp;amp; bcast bands. usually switching supplies are at fault. cheaply made, no filtering, made in china. plug in types, led shoplights, inverter controlled motors on treadmills, battery chargers for cordless saws, drills, are very bad.they can be heard sometimes up to a km away.don't forget modems, 2.5 ghz units produce carriers in lower vhf and down to lower hf as well. I use a zenith radio that has rdf that was used for direction finding.&lt;/p&gt;&#xA;" OwnerUserId="17576" LastActivityDate="2020-08-13T14:49:52.977" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17139" PostTypeId="2" ParentId="9882" CreationDate="2020-08-13T15:57:02.867" Score="1" Body="&lt;p&gt;On a vehicle with a steel body and roof, the most feasible 2 meter slot antenna design is a pair of square flat plates with spacers to maintain the space between them. The slot ends up being the horizontal space between the plates. The top plate is connected to the center of the coax feed line, and the ground is the bottom plate to which is joined the braided conductor of the feed line. This can be magnet mounted to the roof by placing the magnets on the underside of the bottom plate, and then placing that side down on the roof.&lt;/p&gt;&#xA;&lt;p&gt;Also it is important to insulate the top from the bottom plates in the corners where they are spaced apart. One method is to use a tubular plastic spacer of the proper length, and using short self tapping screws that only go into the plastic - do not use full length bolts, washers and nuts as they will provide an electrical connection between the plates that will short the antenna.&lt;/p&gt;&#xA;&lt;p&gt;This particular design was explained in QST - you will have to search for 2 meter slot mobile antenna as I do not have the exact volume information.&lt;/p&gt;&#xA;" OwnerUserId="17577" LastActivityDate="2020-08-13T15:57:02.867" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17140" PostTypeId="2" ParentId="17129" CreationDate="2020-08-13T16:24:33.257" Score="1" Body="&lt;p&gt;Generally QRP is considered to be 10 watts or less. A small RF amp could get your 3 watts up to 9 which would be a more powerful signal but this is something you would have to homebrew. You can get the power needed to drive this transceiver and amp by wiring the batteries to increase the voltage to the level required, (series vs. parallel wiring).&lt;/p&gt;&#xA;&lt;p&gt;This all depends on how hardy the radio circuitry is. If it can take the power - no problems - if it can't, then you have a short duration heating unit.&lt;/p&gt;&#xA;&lt;p&gt;I understand the thinking of less is more when it comes to using CW and QRP, and a different radio would be an expense you may not want to go for, but all of this depends on how you intend to approach the hobby.&lt;/p&gt;&#xA;&lt;p&gt;I am not into QRP as a discipline of the practice of amateur radio operations, however I can understand the appeal. If it were me, on the other hand, I would get a 10 watt radio that I could adjust the output power level on for times when I wanted to transmit at a reduced power level.&lt;/p&gt;&#xA;&lt;p&gt;Of course, that might mean more of an investment in equipment which may or may not be what you are after in the amateur radio hobby.&lt;/p&gt;&#xA;&lt;p&gt;73!&lt;/p&gt;&#xA;" OwnerUserId="17577" LastActivityDate="2020-08-13T16:24:33.257" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17141" PostTypeId="1" CreationDate="2020-08-13T19:37:14.080" Score="5" ViewCount="272" Body="&lt;p&gt;Via the &lt;a href=&quot;https://ham.stackexchange.com/a/9883/1362&quot;&gt;https://ham.stackexchange.com/a/9883/1362&lt;/a&gt; answer regarding a slot antenna for a 2m mobile application, I was introduced to &lt;a href=&quot;http://www.w6nbc.com/articles/2018-03QSTdesigncompetition.pdf&quot; rel=&quot;noreferrer&quot;&gt;this (pdf)&lt;/a&gt; interesting antenna design:&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/3tqTf.png&quot; alt=&quot;A durable, low profile [vertically polarized] 2-Meter Mobile Antenna article headline, with photograph&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;The designer John Portune (W6NBC) introduces it as &amp;quot;a derivative of the&#xA;classical slot antenna&amp;quot; but then notes:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;In contrast to a conventional slot antenna, the slot and antenna surfaces are not in the same plane. The slot, formed by the aluminum shorting bars connecting the two antenna surfaces, is orthogonal to the two planes.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Should the explanations on &lt;a href=&quot;https://ham.stackexchange.com/questions/3531/how-does-a-slot-antenna-work&quot;&gt;How does a slot antenna work?&lt;/a&gt; still apply to this slot antenna &amp;quot;derivative&amp;quot;, or are the variations significant enough to warrant a different analysis?&lt;/p&gt;&#xA;&lt;p&gt;In particular, a commenter on this site expressed skepticism regarding the efficiency of this design (&amp;quot;an extremely short vertical radiator with a large capacitor&amp;quot;) which to me sounds like the design could be functioning more as a &amp;quot;dual&amp;quot; of a &lt;em&gt;loading coil&lt;/em&gt;, rather than as the dual of a dipole like a true slot antenna?&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-08-14T05:44:11.430" Title="How does this W6NBC &quot;derivative of the classical slot antenna&quot; work?" Tags="&lt;antenna-theory&gt;&lt;mobile&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17142" PostTypeId="2" ParentId="17141" CreationDate="2020-08-14T04:17:42.627" Score="4" Body="&lt;p&gt;The antenna is most like a Planar Inverted F Antenna, or PIFA. Wikipedia has a &lt;a href=&quot;https://en.wikipedia.org/wiki/Inverted-F_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;brief introduction&lt;/a&gt; to them. Here is my sketch of a classic example:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/hLoLO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hLoLO.png&quot; alt=&quot;PIFA sketch&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The PIFA is a wider bandwidth version of the IFA, distinguished by a radiator parallel to the ground (the upright of the F), a shorting bar at one corner or edge (the top of the F) and the feed a short distance away from it (the middle of the F).&lt;/p&gt;&#xA;&lt;p&gt;The inductance of the short circuit compensates for the capacitance of the shortened antenna. The radiation resistance of a short or low antenna is usually quite small, but the parallel inductance raises it to 50 Ohms when properly designed.&lt;/p&gt;&#xA;&lt;p&gt;The IFA or PIFA is unbalanced and easy to feed with coax from below the groundplane.&lt;br /&gt;&#xA;It's a good antenna for a mobile phone, it can be made a lot smaller than a quarter wave in any dimension, as long as the groundplane is a reasonable size. It is quite efficient unless made extremely small or with lossy material (PCB...) but tends to radiate in all directions, not just around the car like a monopole. They can be made dual- or tri-band by cutting various slots into the top of the F, though the radiation patterns of those modes are even more strange.&lt;/p&gt;&#xA;&lt;p&gt;Here are a few photos of IFAs and PIFAs as used on mobile phones, (scraped from patent documents so in the public domain)&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/nasWe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nasWe.png&quot; alt=&quot;IFA&quot; /&gt;&lt;/a&gt;  &lt;a href=&quot;https://i.stack.imgur.com/pzNhU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pzNhU.png&quot; alt=&quot;PIFA&quot; /&gt;&lt;/a&gt; &lt;a href=&quot;https://i.stack.imgur.com/3icQ9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3icQ9.png&quot; alt=&quot;PIFA&quot; /&gt;&lt;/a&gt;&lt;br /&gt;&#xA;A &lt;a href=&quot;https://www.google.com/search?tbm=isch&amp;amp;q=planar%20inverted%20F%20antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;google image search&lt;/a&gt; turns up lots of good examples too.&lt;/p&gt;&#xA;&lt;p&gt;The QST antenna has two shorting pins at opposite corners; this could still be considered to be two slots, with one of them fed directly and the other coupled somehow.&lt;/p&gt;&#xA;&lt;p&gt;This all said, there are many antenna geometries which defy simple explanation, but still work well. Any unconnected metal part, or gap in a metal part, can be fed in a way that will radiate, and if the structure is reasonably large it will make a fine antenna. Antennas that have become popular are usually valued as much for their mechanical simplicity and reliability as their electrical performance.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-08-14T05:44:11.430" LastActivityDate="2020-08-14T05:44:11.430" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17143" PostTypeId="2" ParentId="17133" CreationDate="2020-08-14T10:47:15.587" Score="4" Body="&lt;p&gt;You can increase the bandwidth of a dipole by adding capacitive hats (you may have to shorten the dipole to maintain a given resonant frequency).  Conical hats, hemispherical hats, or hats with a circular rim will work better than short 90 degree radial spikes at the ends, or an H shaped dipole.&lt;/p&gt;&#xA;&lt;p&gt;Small capacitive hats might even raise the radiation resistance, as well as broadening the dipole's bandwidth. Maybe 10% or less in size compared to the long dimension of the dipole (which, again, will have to be resized to re-center the resonance frequency to the desired value.)&lt;/p&gt;&#xA;&lt;p&gt;You also can increase the bandwidth by adding wires spread apart a little, and turning your dipole into either a cage dipole or a fan dipole.  A fan dipole with each fan element a slightly different length will also broaden the bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;At the limit you can turn these (fan or cage) wires into conical sheets centered at the feed, and end up with a discone or biconical dipole, which have much wider bandwidths than a wire dipole (but are still 2-element dipoles of a sort).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-08-19T21:01:27.170" LastActivityDate="2020-08-19T21:01:27.170" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17144" PostTypeId="2" ParentId="17129" CreationDate="2020-08-14T11:02:47.363" Score="0" Body="&lt;p&gt;You can test the value of this difference.  Emit a WSPR beacon, vary every other one in transmit power by 2.2 dB, and gather statistics over multiple cycles of the number of spots at each power level.  Then turn down the WSPR power util you get about the same number or distance of WSPR spots as contacts you expect to make in you desired mode, and rerun the A/B trial to see how much difference 2.2 dB makes in actual contact potential from your location and antenna.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-08-14T11:02:47.363" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17146" PostTypeId="1" AcceptedAnswerId="17147" CreationDate="2020-08-14T15:59:29.173" Score="2" ViewCount="128" Body="&lt;p&gt;I was looking for a 40 m antenna for QRP CW operation at 3 W. I looked at the Wolf river coil which is a nice portable antenna. From speaking with other hams they mentioned loaded coils are poor for QRP operations and told me to DIY a quarter wave antenna&#xA;I've already spent like \$140 on the parts for my DIY antenna including a $100 telescopic pole and I am considering if I should just return all these and get a prebuilt loaded coil antenna instead.&lt;/p&gt;&#xA;&lt;p&gt;Am I making the right choice opting for a DIY antenna over a prebuilt loaded coil?&lt;/p&gt;&#xA;" OwnerUserId="15878" LastActivityDate="2020-08-14T17:56:43.257" Title="Will using a loaded coil antennas have detrimental effects on QRP operations?" Tags="&lt;antenna&gt;&lt;qrp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17147" PostTypeId="2" ParentId="17146" CreationDate="2020-08-14T17:56:43.257" Score="5" Body="&lt;p&gt;Generally, making an antenna shorter makes it less efficient. This means some fraction of your transmitter's power is used to make the antenna and/or surrounding soil warmer instead of radiating where someone might receive it.&lt;/p&gt;&#xA;&lt;p&gt;The fraction of power lost is the same whether the transmit power is 3W or 300W. So the detrimental effects of a loading coil are not specific to QRP operations.&lt;/p&gt;&#xA;&lt;p&gt;But perhaps you are interested in QRP because you enjoy the challenge of making the very best use of the limited transmit power. In this case, you'll want to do everything you can to increase &lt;a href=&quot;https://en.wikipedia.org/wiki/Effective_radiated_power&quot; rel=&quot;noreferrer&quot;&gt;EIRP&lt;/a&gt; except increase transmit power, which means having the very best antenna system possible. In this case you would not want a loading coil.&lt;/p&gt;&#xA;&lt;p&gt;Alternately, you may be interested in QRP operation because you enjoy operating a small, portable, or inexpensive station. In such a case a loading coil may be a good way to make the antenna smaller and more portable.&lt;/p&gt;&#xA;&lt;p&gt;So should you return what you've bought and buy a loading coil instead? It depends on your objectives. A loading coil will be smaller. A quarter-wave antenna will be more efficient. We're probably talking about a difference somewhere between 0.5 dB and 5 dB. It's hard to put a precise number on it because there are loading coils that shorten the antenna just a little and thus introduce only a little inefficiency, and there are loading coils that shorten the antenna a lot, and introduce a lot of inefficiency. The efficiency is also impacted on where on the antenna it's placed, ground losses, and other factors.&lt;/p&gt;&#xA;&lt;p&gt;My general advice: if this is your first antenna, don't overthink it. Get something up and on the air, then experiment. Just about any antenna will work, and it doesn't need to be expensive to work well. &lt;a href=&quot;https://physics.princeton.edu/pulsar/K1JT/wspr.html&quot; rel=&quot;noreferrer&quot;&gt;WSPR&lt;/a&gt; is a good way to see how well your signal is getting out, and thus how effective your antenna system is, especially if you can do A/B testing with two antennas. If you have the time and the space, you can do quite a lot of experimentation with a spool of wire and some cheap items from a hardware store.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-08-14T17:56:43.257" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17148" PostTypeId="2" ParentId="17135" CreationDate="2020-08-14T23:12:41.460" Score="2" Body="&lt;p&gt;I found a &lt;a href=&quot;https://www.genkin.name/2017/11/baofeng-uv-9r-users-manual/&quot; rel=&quot;nofollow noreferrer&quot;&gt;user manual&lt;/a&gt; online for the &amp;quot;Baofeng UV-9R&amp;quot;. (backup on &lt;a href=&quot;https://web.archive.org/web/20200814231842/https://www.genkin.name/2017/11/baofeng-uv-9r-users-manual/&quot; rel=&quot;nofollow noreferrer&quot;&gt;archive.org&lt;/a&gt;).&lt;/p&gt;&#xA;&lt;p&gt;Transmit is 5 W/1 W and the range for VHF is 136-174 MHz, UHF is 400-520 MHz. It also receives broadcast FM from 65-108 MHz.&lt;/p&gt;&#xA;&lt;p&gt;It looks as if this is a standard Baofeng - meaning the instructions for the UV-5R or UV-82 will probably work as well.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2020-08-14T23:24:05.823" LastActivityDate="2020-08-14T23:24:05.823" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17149" PostTypeId="1" AcceptedAnswerId="17173" CreationDate="2020-08-15T03:39:10.660" Score="1" ViewCount="118" Body="&lt;p&gt;The &lt;a href=&quot;https://lab599.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Lab599 Discovery TX-500&lt;/a&gt; is coming out soon. A lot has been said about that radio's use of weather-resistant proprietary connectors, but what are the actual connector types?&lt;/p&gt;&#xA;&lt;p&gt;The antenna is female BNC, but the power, speaker mic and other connectors are all circular connectors with keyways and threaded retaining rings.&lt;/p&gt;&#xA;&lt;p&gt;Searching around, I found similar-looking connectors under Amphenol 97 Series, SAE AS50151 and MIL-DTL-5015, but I can't find anything definitive about what Lab599 is using.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3tbDP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3tbDP.png&quot; alt=&quot;TX-500 connectors pinout diagram&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14609" LastEditorUserId="8717" LastEditDate="2020-08-15T13:43:18.387" LastActivityDate="2020-08-20T19:34:05.153" Title="Lab599 Discovery TX-500 connectors?" Tags="&lt;software-defined-radio&gt;&lt;transceiver&gt;&lt;connectors&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17150" PostTypeId="2" ParentId="17149" CreationDate="2020-08-15T14:01:13.610" Score="2" Body="&lt;p&gt;They appear to be &lt;a href=&quot;https://en.m.wikipedia.org/wiki/DIN_connector&quot; rel=&quot;nofollow noreferrer&quot;&gt;DIN connectors&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;But &lt;em&gt;proprietary&lt;/em&gt; implies that they are custom connectors only available from the manufacturer of this radio. They are weatherproof, and that feature may be what is proprietary.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://lab599.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;At the bottom of the webpage&lt;/a&gt; under &amp;quot;Package Includes&amp;quot;, it looks like the connectors are included.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;The connectors below are not waterproof.&lt;/p&gt;&#xA;&lt;p&gt;&lt;sup&gt;Photo from &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B07QKWKMWF&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amazon.com&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IyjZE.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IyjZE.jpg&quot; alt=&quot;DIN microphone connectors&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-08-15T14:32:19.107" LastActivityDate="2020-08-15T14:32:19.107" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17151" PostTypeId="2" ParentId="17149" CreationDate="2020-08-15T16:03:07.847" Score="1" Body="&lt;p&gt;These indeed look a lot like DIN connectors, but if they're waterproof, they are some vendor-specific extension to that standard. Best guess is to ask the manufacturer, because telling people who want to work with their device can only increase their sales.&lt;/p&gt;&#xA;&lt;p&gt;Alternatively wait until you hold the device in your hands, and then do something like going through a &lt;a href=&quot;https://www.newark.com/w/c/connectors/circular-connectors-components/circular-industrial-connectors/prl/results?no-of-contacts=7contacts&amp;amp;sort=P_PRICE&quot; rel=&quot;nofollow noreferrer&quot;&gt;reputable distributor's list of circular connectors&lt;/a&gt; (I picked out things that have 7 contacts in that link), and look for a match.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-08-15T16:03:07.847" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17152" PostTypeId="1" CreationDate="2020-08-15T19:58:09.587" Score="4" ViewCount="147" Body="&lt;p&gt;Well, the title says it all: I want to start making EME contacts with the lowest possible budget, and I doubt between 2m, 70cm and 23cm. Since I cannot afford those expensive power amplifiers for these frequencies, I decided to go for a big yagi array instead (increase the gain of the antenna in order to get an equivalent EIRP compared to the PA). I have a lot of experience in antennae design and simulation software, so this won't be an issue.&lt;/p&gt;&#xA;&lt;p&gt;These are the options I have:&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;2m:&lt;/strong&gt; I have a 50W TX, and could afford a cheap 100W VHF amplifier &lt;a href=&quot;https://a.aliexpress.com/_B1MtEc&quot; rel=&quot;nofollow noreferrer&quot;&gt;such as this one&lt;/a&gt;. For the antennae, I would build an array of four 6-element yagis. Each yagi should have a gain of around 9,7dBi, so the whole array should provide around 15,5dBi.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;70cm:&lt;/strong&gt; My rig is able to provide 35W at this frequency. However, I did not find any affordable amplifier for this frequency. For the antenna, I could use some four yagi array, that would provide an overall gain of around 16dBi.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;23cm:&lt;/strong&gt; Due to the smaller wavelength, I could try some 6 or even 9 yagi array. They would be around 12 element arrays and provide a global gain of 18,5dBi. Nevertheless, my rig (ICOM IC-7100) does not work at this frequency, so I would need some kind of upconverter. I did not find any cheap solution that works at the desired power outputs (around 50/100W).&lt;/p&gt;&#xA;&lt;p&gt;This analysis suggests me that I should go for the 2m option. Moreover, path loss is smaller at 2m than at 70cm or 23cm. However, all of the beginner/small EME station work on either 70cm or 23cm. Moreover, I fear choosing a frequency that is not being used too much, and making few contacts because of this.&lt;/p&gt;&#xA;&lt;p&gt;Any advice or recommendation will be appreciated.&lt;/p&gt;&#xA;&lt;p&gt;BTW: for working EME, is there any noticeable difference between building an array of 2x2 or of 4x1 yagi antennae?&lt;/p&gt;&#xA;&lt;p&gt;73 de EA4HFV!&lt;/p&gt;&#xA;" OwnerUserId="14937" LastEditorUserId="9621" LastEditDate="2020-08-18T19:39:49.490" LastActivityDate="2020-08-18T19:39:49.490" Title="What is the best frequency to start working EME on a budget?" Tags="&lt;antenna&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17153" PostTypeId="1" AcceptedAnswerId="17157" CreationDate="2020-08-16T03:05:25.920" Score="4" ViewCount="109" Body="&lt;p&gt;Would love some advice from you seasoned vets.&#xA;I have an FT857D in my car which I tend to only use (and really want to use) when I'm stopped and setup camping. I bought a portable Windom antenna which I've been mounting horizontally (about 65cm/2ft from the ground) and i have a 15M/45ft lead line which connects staight to the radio.&lt;/p&gt;&#xA;&lt;p&gt;I'm just not getting out and I don't know why. My radio is putting out power, low SWR on the antenna and eveything seems ok. Yesterday I ran a sanity test where I continuously broadcasted a recording on FM at 100W on 40M, 20M and 10M and listened to a number of KiwiSDRs near me. Nothing - not a peep. I tried different distances, different states - not a peep. Where's all this energy going?!&lt;/p&gt;&#xA;&lt;p&gt;The only thing I can think of is that I've a grounding issue - but with the Windom or similar is it reliant on a ground given it's not balanced? Do I need an earth stake connected to my vehicle ground? Perhaps the radio isn't well enough grounded to the chassis - It's only attached to the battery earth at the moment.&lt;/p&gt;&#xA;&lt;p&gt;I'd love some advice and help here as I'm incredibly keen to start playing with some digital modes like PSK and Winlink but don't seem to be able to get out.&lt;/p&gt;&#xA;" OwnerUserId="17588" LastActivityDate="2020-08-17T17:46:12.317" Title="I just can't get out on my car mounted HF" Tags="&lt;antenna&gt;&lt;hf&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17154" PostTypeId="2" ParentId="17152" CreationDate="2020-08-16T11:08:09.540" Score="5" Body="&lt;p&gt;You're generally right, the free space path loss formula incorporates wavelength quadratically, so it would seem wise use the lowest available frequency.&lt;/p&gt;&#xA;&lt;p&gt;Since you're bouncing off an object, you get a loss that is quadratically proportional to both frequency, and distance, on each direction, where the reflected power can only be as much as reached the object, so overall, you get a fourth power (&lt;a href=&quot;https://www.radartutorial.eu/01.basics/The%20Radar%20Range%20Equation.en.html&quot; rel=&quot;noreferrer&quot;&gt;radar equation&lt;/a&gt;).&lt;/p&gt;&#xA;&lt;p&gt;However, what it does forgo to account for is the fact that if you keep the dimensions of your antenna fixed, the gain of said antenna grows quadratically.&lt;/p&gt;&#xA;&lt;p&gt;So, overall, the loss on your earth-moon-earth path, including your antenna, is proportional to the fourth power of distance, and quadratic to the frequency, if you say &amp;quot;the best antenna I can have on any frequency can never be larger than this and that&amp;quot;, and that is pretty realistic.&lt;/p&gt;&#xA;&lt;p&gt;That is, given you can still build a high-gain antenna under these constraints. This becomes impossible as soon as antenna dimensions become significantly smaller than wavelength.&lt;/p&gt;&#xA;&lt;p&gt;Sooooo: you can guy a used / thrown out 1 m satellite dish, and work 0.7 m on it, giving you some hm, say, 10 to 12 dB of gain. Can't do that with 2m, dish is simply too small, can't really make much use of it, because you can't even realistically build a feed.&lt;/p&gt;&#xA;&lt;p&gt;The very nice thing about dishes is that they usually don't exhibit much of a gain in directions you don't want, which is nearly more important than having gain in the direction you're interested in, since you'd be working in bands where other people have fun, too. What counts at the receiver is not signal power, but signal power in relation to noise plus interference power.&lt;/p&gt;&#xA;&lt;p&gt;Then, go for a low-rate digital mode. FT8, JT65B.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-08-16T11:08:09.540" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17155" PostTypeId="1" AcceptedAnswerId="17233" CreationDate="2020-08-16T12:40:52.297" Score="2" ViewCount="71" Body="&lt;p&gt;I've heard that there are countries where you start as SWL and have to collect some number of QSL cards to get a license. Or maybe there are places where QSLs are required to upgrade a license and get an access to more bands and/or more power.&lt;/p&gt;&#xA;&lt;p&gt;Is anyone aware of such countries, or maybe it's just a rumor?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-08-31T20:39:52.357" Title="Are there countries where QSLs are required to get or upgrade a license?" Tags="&lt;qsl-card&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17156" PostTypeId="1" CreationDate="2020-08-16T17:49:47.013" Score="0" ViewCount="168" Body="&lt;p&gt;When I was visiting the ARRL/become a VE site on my iPhone and I try to download the PDF for the application form, it redirects me to a malware site. I have confirmed this with other ham friends and we are sure our phones don't have any locally installed malware. Some times it won't redirect you, but if you keep trying to click on the pdf link, it will redirect.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/become-an-arrl-ve&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/become-an-arrl-ve&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The link is  ARRL VE pdf application at the bottom of the page.  ONLY CLICK ON THE PDF LINK IF YOU KNOW WHAT YOU'RE DOING&lt;/p&gt;&#xA;&lt;p&gt;Who do I contact in ARRL regarding this issue?&lt;/p&gt;&#xA;&lt;p&gt;EDIT: this can be reproduced by visting the link on an iPhone&lt;/p&gt;&#xA;&lt;p&gt;EDIT 2: I have sent an email to ARRL. I will post an answer with their response&lt;/p&gt;&#xA;" OwnerUserId="15878" LastEditorUserId="15878" LastEditDate="2020-08-17T15:32:25.943" LastActivityDate="2020-08-26T12:33:41.697" Title="Is the ARRL website distributing malware? I'm not sure who to contact" Tags="&lt;arrl&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17157" PostTypeId="2" ParentId="17153" CreationDate="2020-08-17T04:35:06.087" Score="4" Body="&lt;p&gt;Advice on antennas for portable operation.  First suggestion: get rid of the windom.   Instead, consider end-fed antenna with a counterpoise wire that is laying on the ground.  The end-fed antenna can be different lengths but I have been successful with 40 to about 60 feet depending on the band I am operating.&lt;/p&gt;&#xA;&lt;p&gt;My procedure is to use a nearby tree -- hopefully there is a nearby tree, if not there are some other solutions.  Get yourself a sling-shot and some fishing line and a fishing lead weight (not too heavy).  Run out about 50 to 75 feet of fishing line, laying on the ground in a way that it will not get tangled when you launch one end of the line up into a tree or over a tree using the sling shot and lead weight.  Practice doing this at home -- I am pretty good, normally takes one shot, rarely more than two.&lt;/p&gt;&#xA;&lt;p&gt;Using the fishing line, now attached at one end to your antenna wire, haul up the antenna wire to a good height.  Branches are usually not a problem with most trees as the wire just sits on top of them.  Attach the antenna wire at your transceiver to the adapter using  a convenient method.  I modified a PL-259 to connect the antenna wire to the center pin and a ground counterpoise wire to the ground side of the PL-259.  The counterpoise merely lays on the ground stretched out in a direction that works best for the direction you want.  Experiment.  I use a length of counterpoise wire of about 28 to 30 feet and sometimes more.  I have lots of little homemade spools of counterpoise wire of varying lengths.&lt;/p&gt;&#xA;&lt;p&gt;If you have no trees available, you can do something I did a few times although it costs a little.  A telescoping fiberglass pole.  I usually had my pickup truck with me and I could put the bottom of the telescoping pole in the stake hole in the back.  I have used such a pole for center fed 20-meter V-dipole and for end-Fed antennas.  Unfortunately, I broke the fiberglass pole and never replaced it.&lt;/p&gt;&#xA;&lt;p&gt;I bought a Buddipole Delux antenna with an additional 18 foot telescoping pole that I use most of the time now.  I use Dacron lines to guy the extended 18 foot pole though most of the time I do not go all the way to 18 feet, usually about 15 feet but it is sitting in a tripod which lifts it off the ground about 2 feet.  The Buddipole works great and I have the most contacts on that antenna -- usually near the ocean on the Oregon coast or Washington coast.&lt;/p&gt;&#xA;&lt;p&gt;All my QSOs are CW QRP with a variety of transceivers (Norcal 40A on 40-meters, Elecraft KX1, Elecraft KX3 and KX2 on 40/20/17/15.  I always use an antenna tuner but with the Buddipole I can usually get a good match at under 2:1 SWR, in fact on 20 usually 1.5:1.  I just recently sold the KX2 so my next portable ops will be with the KX3.&lt;/p&gt;&#xA;&lt;p&gt;I typically use antennas that are easy and fast to setup and take down.  After arriving at a site, I am usually operating with the Buddipole in 30 minutes or less.&lt;/p&gt;&#xA;" OwnerUserId="1563" LastActivityDate="2020-08-17T04:35:06.087" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17158" PostTypeId="2" ParentId="17156" CreationDate="2020-08-17T05:06:24.047" Score="1" Body="&lt;p&gt;I visited the page and clicked on all application links and had no issue getting to the PDF page as one might expect. For reference, I am running Firefox v79 on a Windows 10 PC. I am not sure where the problem is stemming from, but if you haven't already I would see if you or any of your ham friends could reproduce on a PC. If the problem is still present, I would suggest using the contact info on the page (vec@arrl.org) as they would either be able to check the page or would be in close contact with someone who can.&lt;/p&gt;&#xA;" OwnerUserId="17597" LastActivityDate="2020-08-17T05:06:24.047" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17159" PostTypeId="2" ParentId="17156" CreationDate="2020-08-17T07:52:09.030" Score="1" Body="&lt;p&gt;It sounds like you have maybe got some antivirus software installed on your computer that is being overly sensitive with links to PDF files served from HTTP sites (rather than HTTPS).&lt;/p&gt;&#xA;&lt;p&gt;My Mac opened the PDF just fine without complaints.&lt;/p&gt;&#xA;&lt;p&gt;I don't think there is any actual malware on there, but it might be tripping your antivirus or malware-detection software as a false positive.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-08-17T07:52:09.030" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17160" PostTypeId="2" ParentId="17121" CreationDate="2020-08-17T12:16:20.930" Score="3" Body="&lt;p&gt;Further research has revealed the origin of the 61 kHz spacing between the RFI carriers.&lt;/p&gt;&#xA;&lt;p&gt;100BASE-TX uses a 125 MHz clock, which is divided by 2047 in a scrambling circuit.&lt;/p&gt;&#xA;&lt;p&gt;This is intended, ironically enough, to reduce EMI by spreading the signal across a wide portion of the spectrum, rather than generating very strong peaks at frequencies such as 31.25 MHz (125 MHz / 4) which would otherwise be generated by the MLT-3 coding scheme used. 125 MHz / 2047 = ~61.064973 kHz, explains the spacing of the offending signals.&lt;/p&gt;&#xA;&lt;p&gt;Additionally, I have found similar carriers offset by 1/2 of the expected 61.06 kHz spacing in certain portions of the spectrum. This appears to be particularly pronounced in the upper HF and VHF region.&lt;/p&gt;&#xA;&lt;p&gt;UTP Cat 5 or Cat 5e should absolutely never be used for anything higher than 10 Mbps Ethernet, especially in an environment where any type of HF or VHF receiver will be used.&lt;/p&gt;&#xA;&lt;p&gt;Note that gigabit Ethernet generates a similar overall spectral profile, though with different modulation characteristics; it appears to generate more of a broadband hash than discrete carriers, but still causes interference.&lt;/p&gt;&#xA;&lt;p&gt;Take a handheld radio with HF receive coverage and a VHF/UHF rubber duck antenna, and tune it to 14.275 MHz AM. It may be necessary to open the squelch on the radio. Hold the antenna next to an Ethernet cable with an active 100 Mbps connection on it, and there is virtually guaranteed to be a strong signal present.&lt;/p&gt;&#xA;&lt;p&gt;Move the antenna along (and perpendicular to) the cable slowly, and the signal will increase and decrease in strength several times per inch of cable. This is literally a result of each individual twist in the twisted pair converting some of the differential signal into common mode radiation. The worst offenders can be heard for some distance away from the cable, even with such an intentionally insensitive receive setup.&lt;/p&gt;&#xA;&lt;p&gt;Note that shielded Cat 5 or 5e (if properly terminated), as well as quality unshielded Cat 6, do not generate nearly as much interference.&lt;/p&gt;&#xA;&lt;p&gt;I recently discovered that even some unshielded Cat 6 cable is capable of radiating considerable RFI. As already dictated by common sense anyway, shielded cable is simply the only way to go to assure a clean installation.&lt;/p&gt;&#xA;&lt;p&gt;Credit to KA3RCS's work.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastEditorUserId="17200" LastEditDate="2020-08-17T14:45:02.617" LastActivityDate="2020-08-17T14:45:02.617" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17161" PostTypeId="2" ParentId="17156" CreationDate="2020-08-17T15:09:31.387" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://sitecheck.sucuri.net/results/Arrl.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://sitecheck.sucuri.net/results/Arrl.org&lt;/a&gt; didn't find any malware.&lt;/p&gt;&#xA;&lt;p&gt;However, one of the things it reports is:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Our automated scan detects outdated software on your site. Missing security updates can leave your site vulnerable.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;However, their outdated Apache webserver is considered low risk.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;Clicking on &lt;a href=&quot;https://www.arrl.org/news/search/Tag.name:digital%20mode&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.arrl.org/news/search/Tag.name:digital%20mode&lt;/a&gt; just now redirected me to a gambling website. Seems they DO have some issues!&lt;/p&gt;&#xA;&lt;p&gt;This was on an Android tablet in Chrome. It even circumvented the 'no malware' &lt;a href=&quot;https://blog.cloudflare.com/introducing-1-1-1-1-for-families/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Cloudflare DNS IPs&lt;/a&gt; and &lt;a href=&quot;https://protectli.com/kb/how-to-setup-pfblockerng/&quot; rel=&quot;nofollow noreferrer&quot;&gt;PfblockerNG&lt;/a&gt; in my &lt;a href=&quot;https://www.pfsense.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;pfSense&lt;/a&gt; router.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-08-26T12:33:41.697" LastActivityDate="2020-08-26T12:33:41.697" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17162" PostTypeId="2" ParentId="17153" CreationDate="2020-08-17T17:46:12.317" Score="6" Body="&lt;p&gt;An HF antenna only 2 feet from the ground is mostly a device for making warm soil. With such close proximity to the ground, the RF current in the soil will be very high, and ground losses will be very significant.&lt;/p&gt;&#xA;&lt;p&gt;A low SWR is not indicative of an effective antenna. Consider a dummy load: great SWR, abysmal radiation. In fact, a way to make an antenna with good SWR over a largee bandwidth is to make the antenna lossy. I suspect you will find the SWR bandwidth of your antenna is very good: that implies it's very lossy.&lt;/p&gt;&#xA;&lt;p&gt;If you want to stick with a wire antenna, try getting it higher, as high as possible. You'll need a portable mast or a big tree on at least one end, ideally both.&lt;/p&gt;&#xA;&lt;p&gt;If you can't get the antenna higher, try some kind of shortened vertical mounted on a metal vehicle. The &lt;a href=&quot;https://mfjenterprises.com/products/mfj-2675t&quot; rel=&quot;noreferrer&quot;&gt;MFJ Ham Stick&lt;/a&gt; is an inexpensive example.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-08-17T17:46:12.317" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17164" PostTypeId="1" AcceptedAnswerId="17169" CreationDate="2020-08-18T15:00:46.393" Score="2" ViewCount="72" Body="&lt;p&gt;Helping a friend with his RFI problem.&lt;/p&gt;&#xA;&lt;p&gt;He has a SDR HF radio and Hustler BTV antenna with a toroid choke and about 32-radials. He has vertical bars on his panadaptor around 20 khz apart, mainly on 40M.&lt;/p&gt;&#xA;&lt;p&gt;Disconnecting the antenna at the radio-end the bars go away, unscrewing the PL-259 so only the centre-pin is connected the RFI is mostly gone, fully connecting the PL-259 the bars are there.&lt;/p&gt;&#xA;&lt;p&gt;Disconnected the coax at the antenna end, bars are also gone (thus i don't think this is common-mode RFI on the coax).&lt;/p&gt;&#xA;&lt;p&gt;We've deduced his RFI is getting into his system from a radial wire ran under the BTV with RFI coming from a neighbours device (he's going to disconnect bunches of radials to triangulate which neighbour is the source of the RFI).&lt;/p&gt;&#xA;&lt;p&gt;As this RFI is entering the system from a wire (radial(s)) and transported inside the coax, rather than the outer-shield, is there anything he can do on his equipment to remove this RFI?&lt;/p&gt;&#xA;&lt;p&gt;As far as i know, the only solution would be for him to track the noisy device and put some ferrites on them, assuming a compliant neighbour. Did i miss anything?&lt;/p&gt;&#xA;&lt;p&gt;Thanks :)&lt;/p&gt;&#xA;" OwnerUserId="17200" LastEditorUserId="17200" LastEditDate="2020-08-19T10:14:00.907" LastActivityDate="2020-08-20T15:08:27.410" Title="RFI from radials" Tags="&lt;rfi&gt;&lt;radial&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17166" PostTypeId="1" AcceptedAnswerId="17447" CreationDate="2020-08-19T18:09:44.453" Score="4" ViewCount="202" Body="&lt;p&gt;I'm intending to make a sleeve balun (aka bazooka) for 2m, but rather than keep the lossy coax jacket as a dielectric (I have some RG58), was considering to remove it and replace it with heat shrink tubing.&lt;/p&gt;&#xA;&lt;p&gt;I haven't been able to find anything here or via google, and am hopeful that some folks here might have some experience, insight, or resource pointers.&lt;/p&gt;&#xA;&lt;p&gt;Otherwise I'm just going to try it both ways and measure.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="8717" LastEditDate="2020-08-19T19:57:30.693" LastActivityDate="2020-10-18T13:05:35.630" Title="Heat-shrink as dielectric for bazooka balun?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;vhf&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17168" PostTypeId="2" ParentId="17166" CreationDate="2020-08-20T01:55:15.210" Score="-1" Body="&lt;p&gt;For a bazooka balun, you want the &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; of the transmission line to be as high as possible. A thin layer of heat shrink is not ideal.&lt;/p&gt;&#xA;&lt;p&gt;If you must use a sleeve balun for mechanical reasons, rather use a 30 mm diameter pipe with the coax inside it.&lt;/p&gt;&#xA;&lt;p&gt;The impedance of a short circuited transmission line is&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$Z_{SC} =jZ_0\tan(\beta x)$&lt;/span&gt; where &lt;span class=&quot;math-container&quot;&gt;$\beta=2\pi/\lambda$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;At a quarter wave this is an open circuit,  but at any frequency away from a quarter wave, the impedance drops quickly and the line &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; matters a lot.&lt;/p&gt;&#xA;&lt;p&gt;If the frequency changes by 10%, (or you get the velocity factor of the line wrong by 10%, very likely if you don't know the dielectric well, or measure it), then the impedance is &lt;span class=&quot;math-container&quot;&gt;$j6Z_0$&lt;/span&gt;. If your line &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; is &lt;span class=&quot;math-container&quot;&gt;$25\space\Omega$&lt;/span&gt;, that's only &lt;span class=&quot;math-container&quot;&gt;$150\space\Omega$&lt;/span&gt;, not a very good choking impedance. If you make a &lt;span class=&quot;math-container&quot;&gt;$120\space\Omega$&lt;/span&gt; two wire line with a second piece of coax taped against the feed, it could be almost &lt;span class=&quot;math-container&quot;&gt;$1000\space\Omega$&lt;/span&gt; at the same frequency offset.&lt;/p&gt;&#xA;&lt;p&gt;So I suggest a kind of pitch fork of two parallel wires, a quarter wave long, one each side for symmetry, spaced about one coax diameter apart. Braids soldered together at the short circuit side, don't worry about the inners. No need to remove the jackets.&lt;/p&gt;&#xA;&lt;p&gt;Like this, if you're using the outside of the bazooka as a dipole element (diameters and widths exaggerated a lot):&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/nvx9f.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nvx9f.png&quot; alt=&quot;sleeve dipole 1&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Or like this if you need a balun for a balanced antenna like a dipole:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Dw7Lp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Dw7Lp.png&quot; alt=&quot;sleeve balun&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Finally, you don't know the RF properties of the plastic and glue in the heat shrink. You can compare it to the coax jacket by putting a piece of both in a microwave oven, with a small glass of water on the far side. Cook them for a bit and see which plastic gets hot first. A good dielectric like PTFE or PE won't get hot at all.&lt;/p&gt;&#xA;&lt;p&gt;It's a great idea to build and measure these things. The way to test for unbalanced currents is to mount the antenna say 2 or 3 metres high on a wooden pole, and watch the VSWR display while you run your hand down coax. If the graph jumps around then there are currents on the coax. Be sure to evaluate the whole frequency range you're interested in. At slightly higher frequencies, I remember seeing the trace dancing around in most of the graph, and being stable in the middle where the balun was working.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-08-20T02:23:41.253" LastActivityDate="2020-08-20T02:23:41.253" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17169" PostTypeId="2" ParentId="17164" CreationDate="2020-08-20T12:37:11.713" Score="2" Body="&lt;p&gt;You might look into a &lt;a href=&quot;https://mfjenterprises.com/products/mfj-1026#description&quot; rel=&quot;nofollow noreferrer&quot;&gt;noise cancelling device&lt;/a&gt;. The principle of operation on this is to use a second antenna to 1) capture the same noise but phase shifted 180º and 2) mix/add to the primary antenna's signal to leave just the desired signal.&lt;/p&gt;&#xA;&lt;p&gt;The second antenna doesn't need to be huge or effective... in fact, if it's &lt;strong&gt;not&lt;/strong&gt; very sensitive and the only thing it picks up is the RFI, that will be perfect for your application. And as Mike points out in the comments below, placed and oriented to pick up the RFI as strongly as possible.&lt;/p&gt;&#xA;&lt;p&gt;The product link I shared is to an MFJ product I've never used, but there are other manufacturers or you can home-brew your own.&lt;/p&gt;&#xA;&lt;p&gt;I know this doesn't &lt;em&gt;directly&lt;/em&gt; answer how to find the RFI source, but hopefully this will help you in getting to what you really want anyway: RFI out of your receiver!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2020-08-20T15:08:27.410" LastActivityDate="2020-08-20T15:08:27.410" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17170" PostTypeId="2" ParentId="16135" CreationDate="2020-08-20T15:35:10.013" Score="5" Body="&lt;p&gt;Some googling for &amp;quot;ionosonde operation&amp;quot; reveals some applications (&lt;a href=&quot;https://apps.fcc.gov/els/GetAtt.html?id=208039&amp;amp;x=&quot; rel=&quot;noreferrer&quot;&gt;for example&lt;/a&gt;) to the FCC to operate under &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/5.3&quot; rel=&quot;noreferrer&quot;&gt;47 C.F.R. §§ 5.3&lt;/a&gt;(c) and (e) which details that &amp;quot;Stations operating in the Experimental Radio Service will be permitted to conduct the following type of operations&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;So it seems that ionosondes in the US are governed by the FCC rules of the Experimental Radio Service. There may be other services that also govern long term use such as &lt;a href=&quot;https://www.ngdc.noaa.gov/stp/IONO/Dynasonde/whatis.htm&quot; rel=&quot;noreferrer&quot;&gt;those operated by NOAA/NCEI&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;These licensures by the FCC seem to satisfy the ITU requirements.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2020-08-20T15:35:10.013" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17171" PostTypeId="2" ParentId="9882" CreationDate="2020-08-20T16:37:28.040" Score="1" Body="&lt;p&gt;Check out &lt;a href=&quot;https://www.youtube.com/watch?v=I144kzJxzDA&quot; rel=&quot;nofollow noreferrer&quot;&gt;this video from AG6IF&lt;/a&gt; who built a 2m slot antenna out of an old parabolic dish. His application was for home mounting a stealthy antenna, but the interesting notion there is that the slot is curved. His video shows a chart from an analyzer as well.&lt;/p&gt;&#xA;&lt;p&gt;This indicates to me that it's worth trying your idea too.&lt;/p&gt;&#xA;&lt;p&gt;Hope this is helpful!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2020-08-20T16:37:28.040" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17172" PostTypeId="1" CreationDate="2020-08-20T18:53:29.617" Score="1" ViewCount="141" Body="&lt;p&gt;I don't see any mention about the dummy loads rating. Since I'm operating at &lt;span class=&quot;math-container&quot;&gt;$13.8~V$&lt;/span&gt; the power output is about &lt;span class=&quot;math-container&quot;&gt;$4~W$&lt;/span&gt;. I'm looking to use what I have on hand as I have a field day approaching soon and if I order a dummy load online it won't get here by the time the event begins&lt;/p&gt;&#xA;" OwnerUserId="15878" LastActivityDate="2020-08-20T19:57:32.280" Title="Can I use the dummy load provided with the nanoVNA for adjusting my QCX+" Tags="&lt;dummy-load&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17173" PostTypeId="2" ParentId="17149" CreationDate="2020-08-20T19:34:05.153" Score="1" Body="&lt;p&gt;Based on Marcus Müller's advice, I contacted Lab599 and got a definitive answer:&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;The TX-500 uses GX12 connectors.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Thanks all! 73&lt;/p&gt;&#xA;" OwnerUserId="14609" LastActivityDate="2020-08-20T19:34:05.153" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17174" PostTypeId="2" ParentId="17172" CreationDate="2020-08-20T19:48:53.573" Score="3" Body="&lt;p&gt;I'm assuming your nanoVNA came with just a small SMA &amp;quot;terminator&amp;quot; load. I'm seeing various specs in various listings for various similar parts, but most of them are in the 0.5 to 4W range. This partly depends on the duty cycle/duration: one I found is rated for 2W &amp;quot;average&amp;quot; power at 125ºC [presumably continuous usage] but also claims a &amp;quot;peak&amp;quot; power handling of 1kW … for 50µs!&lt;/p&gt;&#xA;&lt;p&gt;If you look at the type of loads rated for 10W continuous power you will see they are quite a bit heftier than these little 50Ω terminators! So I certainly wouldn't do extended (continuous unmodulated carrier) tests at 4W with your load.&lt;/p&gt;&#xA;&lt;p&gt;But if it's all you have, you could probably get away with some short tests giving it time to cool in between — but be particularly careful because &lt;strong&gt;it may become hot&lt;/strong&gt; enough to burn &lt;strong&gt;you&lt;/strong&gt; long before it's hot enough to damage the resistor itself. [Come to think of it this may the &lt;em&gt;main&lt;/em&gt; reason why the higher-power dummy loads have such large heatsinks!?]&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2020-08-20T19:48:53.573" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17175" PostTypeId="2" ParentId="17172" CreationDate="2020-08-20T19:57:32.280" Score="3" Body="&lt;p&gt;I wouldn't recommend it.&lt;/p&gt;&#xA;&lt;p&gt;The NanoVNA SMA calibration kits for sale online are quite small. They don't seem to have specifications for power, but &lt;a href=&quot;https://www.minicircuits.com/pdfs/ANNE-50+.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;similar dummy loads do&lt;/a&gt;, and they're rated for 1 W or less. You may get away with 2 W for short times, like a series of Morse dots, but not key down for long enough to adjust anything.&lt;/p&gt;&#xA;&lt;p&gt;At HF you can easily make a dummy load - and especially if you have a NanoVNA. Size and shape aren't critical - 10 or 20 small quarter-watt resistors in series and parallel will easily take 5 watts.&lt;br /&gt;&#xA;20 x 1k, arranged in a radial pattern, would work well up to VHF at least. If you have more 10 or 100 ohm resistors, then you'll need series and parallel arrangements. Check the load with the VNA, to be sure the resistors aren't too inductive.&lt;/p&gt;&#xA;&lt;p&gt;Here is one from VK2HHS, you could do it with just an offcut of coax, no PCBs:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/BeVrv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BeVrv.png&quot; alt=&quot;dummy&quot; /&gt;&lt;/a&gt;&lt;br /&gt;&#xA;&lt;a href=&quot;https://duckduckgo.com/?q=home%20made%20dummy%20load&amp;amp;atb=v179-1&amp;amp;iax=images&amp;amp;ia=images&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here are some more photos&lt;/a&gt; of various construction methods.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-08-20T19:57:32.280" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17177" PostTypeId="2" ParentId="16996" CreationDate="2020-08-21T13:45:48.107" Score="1" Body="&lt;p&gt;I think Kevin's link in the comments to &amp;quot;&lt;a href=&quot;https://ham.stackexchange.com/a/7645/1550&quot;&gt;when and why does the size of a ground plane matter&lt;/a&gt;&amp;quot; is spot on for this question. You should definitely hit the link for a high quality and well explained answer, but the tl;dr of it is:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Perhaps consider that the objective of the ground plane is to present a low impedance. At the feedpoint, the hope is to have all the current go into the antenna, and none of it on the coax common-mode. The lower the impedance of the ground plane, the less current will be on the coax common-mode due to its relatively high impedance.&lt;/p&gt;&#xA;&lt;p&gt;...&lt;/p&gt;&#xA;&lt;p&gt;If the idea is to make the ground plane as small as possible, an electrical quarter wavelength radius is a good length.&lt;/p&gt;&#xA;&lt;p&gt;...&lt;/p&gt;&#xA;&lt;p&gt;This quarter-wavelength size is especially critical in elevated monopoles, that is those without radials buried in soil.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2020-08-21T13:45:48.107" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17178" PostTypeId="1" CreationDate="2020-08-21T14:16:58.137" Score="4" ViewCount="307" Body="&lt;p&gt;I'm planning to build a vertical dipole for 4m and a club member pointed out that my design needs to allow for a boom that should be at least a 1/4 wave long.  Why does a vertical dipole need a boom that offsets the radiating elements from the mount?  I'm guessing it has something to do with the interaction between the feed (coax) and the elements? Can the boom length be shortened by using a balun (choke)?&lt;/p&gt;&#xA;&lt;p&gt;Thanks in advance for your advice!&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hC1QS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hC1QS.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Image taken from &lt;a href=&quot;https://palembangbadboys.blogspot.com/2013/02/w7lpn-2m440-vertical-dipole.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="1550" LastEditDate="2020-08-21T19:15:17.440" LastActivityDate="2021-03-18T23:11:04.727" Title="Is the Boom Strictly Necessary in a Vertical Dipole?" Tags="&lt;antenna-construction&gt;&lt;diy&gt;&lt;vhf&gt;&lt;vertical-antenna&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17179" PostTypeId="2" ParentId="17178" CreationDate="2020-08-21T17:09:36.967" Score="1" Body="&lt;p&gt;You're right, the concern is coupling the feedline with the element.&lt;/p&gt;&#xA;&lt;p&gt;But there's a neat trick: if your bottom element is a tube of large enough diameter to accommodate your coax, you can run the coax &lt;em&gt;thru&lt;/em&gt; the bottom element... and now you don't need a boom.&lt;/p&gt;&#xA;&lt;p&gt;Additionally, the bottom element will then act as a sleeve/bazooka balun.&lt;/p&gt;&#xA;&lt;p&gt;You'll still need to insulate the antenna from the mast of course, but that can be accomplished with an appropriate PVC coupler.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2020-08-21T17:09:36.967" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17180" PostTypeId="2" ParentId="17178" CreationDate="2020-08-21T18:58:42.693" Score="5" Body="&lt;p&gt;If you don't route the feed line away from a center-fed dipole antenna at 90 degrees, it will be in an unbalanced RF field, and thus will couple to the unbalanced RF field, to some degree, even with a perfect (infinite impedance) balun.&lt;/p&gt;&#xA;&lt;p&gt;Depending on the distance and angle of feed, an RF coupled feed line can act like an angled antenna director or reflector element and distort the antenna pattern, perhaps sending it off at some undesired angle. (or perhaps, if you are really lucky, or design for this pattern, adds gain to your desired direction).&lt;/p&gt;&#xA;&lt;p&gt;A bazooka balun will reduce direct electrical coupling, but the high voltage RF field near the dipole tip will still couple to the feedline shield at some distance away from the balun.  You can simulate this by putting an unconnected wire next the nearby feed line, using something like the NEC antenna modeling software.  Or hold an RF meter up against this unconnected wire.  At certain distances and lengths, a completely disconnected coax shield will pick up plenty of RF voltage if not closer to 90 degrees from dipole center.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-18T22:47:06.353" LastActivityDate="2021-03-18T22:47:06.353" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17181" PostTypeId="1" AcceptedAnswerId="17189" CreationDate="2020-08-21T20:02:23.390" Score="3" ViewCount="64" Body="&lt;p&gt;I want to send some QSL cards for contacts I've made while portable/horseback mobile and thus could not have written the details down immediately. I remember the callsigns and reports, and everything was on 2m FM, so I've got most of the data, but one bit I don't have is the exact time. I could probably narrow it down to the hour, but not further. &lt;strong&gt;Is such a precision acceptable? Generally, how accurate should the time be on a card?&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;And while we're at it, if a QSO is prolonged (e.g. a ragchew), which moment should I log as the time of the QSO? Beginning, end, or otherwise?&lt;/p&gt;&#xA;" OwnerUserId="13775" LastActivityDate="2020-08-24T14:05:45.837" Title="How precise should the time be on a QSL card?" Tags="&lt;logging&gt;&lt;qsl-card&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17182" PostTypeId="1" AcceptedAnswerId="17183" CreationDate="2020-08-21T22:31:47.033" Score="1" ViewCount="86" Body="&lt;p&gt;I am thinking about getting my technician license. Recently, I saw a video from ARRL which said &amp;quot;Ham's also provide communication for events.&amp;quot; with a picture of a marathon. My question is what the definition of that is. Does it mean that as a HAM, I can program radios to stay within legal limits and then give them to event staff for the day? Or does it mean that HAM's communicate with each other on behalf of other people? I can't seem to find the answer elsewhere. Thanks!&lt;/p&gt;&#xA;" OwnerUserId="17625" LastEditorUserId="8717" LastEditDate="2020-08-22T15:55:18.133" LastActivityDate="2020-08-22T15:55:18.133" Title="Sharing radios with other people" Tags="&lt;legal&gt;&lt;ht&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17183" PostTypeId="2" ParentId="17182" CreationDate="2020-08-22T02:07:06.657" Score="4" Body="&lt;p&gt;Hams communicate with each other on behalf of other people.&lt;/p&gt;&#xA;&lt;p&gt;An amateur radio operator license is required for someone to act as control operator for an amateur radio station.  A non-licensed person can act communicate over your radio, but a licensed person must be the control operator.  So you can not just give your radio to event staff for the day.&lt;/p&gt;&#xA;&lt;p&gt;Amateur radio is different from various other services such as FRS, GMRS, land mobile,... which do not require an operator license to use.&lt;/p&gt;&#xA;" OwnerUserId="17422" LastEditorUserId="17422" LastEditDate="2020-08-22T15:45:32.267" LastActivityDate="2020-08-22T15:45:32.267" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17184" PostTypeId="2" ParentId="13086" CreationDate="2020-08-22T03:07:07.417" Score="0" Body="&lt;p&gt;Personally, I don't hear the repeater &amp;quot;tones&amp;quot; or &amp;quot;static&amp;quot; in a consistent of enough way to use them to quality test my transmission to repeater. Maybe my ears aren't refined enough or that's just not indicative of the repeaters I'm using.&lt;/p&gt;&#xA;&lt;p&gt;Getting a signal check from listeners is great when it's a one-and-done situation. But it's not so great if you need to experiment. Who wants to wait while you adjust your antenna or walk up the street &amp;quot;Can you hear me now?&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;One solution if you have two radios or can borrow someone's (lots of us have a spare HT laying around) is to leave your smart phone recording your spare that's listening while you wander around and test as long as you want (if no one else is using the repeater that is.) Just remember to use a reference like &amp;quot;Standing on the roof of my car.&amp;quot; And make sure your &amp;quot;listening&amp;quot; radio is far enough away that you don't interfere with it - easy enough since you can test it to make sure.&lt;/p&gt;&#xA;&lt;p&gt;Brian&#xA;KN6KJO&lt;/p&gt;&#xA;" OwnerUserId="17626" LastEditorUserId="17626" LastEditDate="2020-08-22T03:14:16.223" LastActivityDate="2020-08-22T03:14:16.223" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17185" PostTypeId="2" ParentId="13086" CreationDate="2020-08-22T04:44:16.673" Score="0" Body="&lt;p&gt;Ideally a typical repeater when you stop transmitting will have a short delay, the courtesy tone (it's courtesy to wait for that tone so that other people can get a chance to break in), and then another delay, and then they drop carrier.  In an ideal situation, you should be able to hear that tone, and rely on weak reciprocity -- if you can hear the tone clearly, there's a good chance you got into the repeater clearly.&lt;/p&gt;&#xA;&lt;p&gt;However, lots of things can go wrong with that.  Some repeaters leave out some or all of those delays, and then you have to get lucky that your radio's transmit to receive transition is fast enough to catch some part of the tail of the repeater's transmission.  Some of them leave out the courtesy tone too, and then it's guesswork if you got in at all.&lt;/p&gt;&#xA;&lt;p&gt;Also, some repeaters are not well balanced on receive sensitivity vs. transmit power, so the reciprocity might not be there, as maybe the repeater doesn't hear was well as it speaks (or vice versa).  You might be strong enough to key the repeater but not enough to get a clear transmission into it.&lt;/p&gt;&#xA;&lt;p&gt;A few repeaters have a repeat delay, so that if you speak and then unkey quickly, you might catch the tail of the delayed repeat of your transmission.  (This might be half a syllable or so.)&lt;/p&gt;&#xA;&lt;p&gt;A very few rare repeaters have instrumentation in them that can actually measure your signal strength and report it back to you.  This is obviously more reliable (and really cool).  Typically this is triggered by some touchtone sequence that might be published.&lt;/p&gt;&#xA;&lt;p&gt;A few more repeaters are able to actually record what they hear and when you unkey, repeat it back to you.  Any repeater with echolink or IRLP capability can do this.  Usually repeaters like this have their touch tone sequence to active echolink or irlp published, and the internet test reflectors are published in their respective documentation online.&lt;/p&gt;&#xA;&lt;p&gt;And, all of that failing, your best bet is to call out for a signal report and see if someone will respond and let you know what they hear!  Many repeaters have members who can give you a technical description of your signal quality that might be very helpful.  You might even want to try this as a first approach, and introduce yourself while you are at it.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-08-22T04:44:16.673" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17186" PostTypeId="2" ParentId="15018" CreationDate="2020-08-22T06:51:31.597" Score="0" Body="&lt;p&gt;See this YouTube video titled:&#xA;&amp;quot;The 49:1 Half-Wave End-Fed Antenna Transformer, Part 1.&amp;quot;&#xA;&lt;a href=&quot;https://www.youtube.com/watch?v=MgZap6xWZLs&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=MgZap6xWZLs&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It says:&lt;/p&gt;&#xA;&lt;p&gt;49:1 with 3 to 21 windings on the transformer is good for 40m &amp;amp; 80m bands&lt;/p&gt;&#xA;&lt;p&gt;and&lt;/p&gt;&#xA;&lt;p&gt;49:1 with 2 to 14 windings on the transformer is good for 40m, 20m &amp;amp; 15m bands.&lt;/p&gt;&#xA;&lt;p&gt;I made the 2 to 14 with an FT240-43 toroid and 100 pF capacitor.&#xA;I connected a 66ft vertical wire up a tree with 15 meters of coax and SWR is less than 1.3 on 40m, 20m &amp;amp; 15m bands.&lt;/p&gt;&#xA;" OwnerUserId="17627" LastEditorUserId="17627" LastEditDate="2020-08-22T13:14:23.233" LastActivityDate="2020-08-22T13:14:23.233" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17187" PostTypeId="1" CreationDate="2020-08-22T11:47:54.143" Score="1" ViewCount="55" Body="&lt;p&gt;When working through a cross band repeater, either the two sides are using different bands or both sides are using two bands at once. At the same time, most if not all logging software (as well as most QSL card layouts) seem to assume that only one band is in use for any given QSO. Despite this, such QSOs must be logged (and QSL cards sent) all the time by satellite enthusiasts and users of terrestrial cross band repeaters.&lt;/p&gt;&#xA;&lt;p&gt;So, &lt;strong&gt;what is the &amp;quot;right&amp;quot; or customary way to log a crossband contact?&lt;/strong&gt; What does one write in the band field? Does anything need to be written in other fields? Should &amp;quot;cis&amp;quot; contacts (where both parties transmit on, say, VHF and listen on UHF) be logged differently from &amp;quot;trans&amp;quot; contacts (where one party uses only VHF and the other only UHF)?&lt;/p&gt;&#xA;" OwnerUserId="13775" LastActivityDate="2020-08-24T16:58:59.400" Title="How does one log a QSO via a cross-band repeater?" Tags="&lt;satellites&gt;&lt;logging&gt;&lt;qsl-card&gt;&lt;crossband-repeat&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17188" PostTypeId="1" AcceptedAnswerId="17190" CreationDate="2020-08-22T18:46:27.427" Score="1" ViewCount="116" Body="&lt;p&gt;I would like to have a convenient tool to measure filters and amplifiers in 20 Hz - 20 kHz frequency range. Currently I'm doing this with a signal generator, an oscilloscope and LibreOffice. It's not the fastest and not the most convenient method, but it gives a nice looking result:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8Bhu2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8Bhu2.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I've tried several software solutions for my primary OS, which is MacOS. The closest things I could find were iSpectrum and Friture, but they don't do exactly what I wanted to. I couldn't find a way to determine a 0 dB reference. I also tried to run several Windows tools using CrossOver - some of them didn't work, some were no better than Friture.&lt;/p&gt;&#xA;&lt;p&gt;I very much like my Rigol DSA815-TG. But the problem is that it doesn't work well below 9 kHz and is completely deaf below 1 kHz. I tried to use a diode ring mixer to upconvert the frequencies of interest above, say, 10 Mhz. It works, but this mapping turns out to be non-linear. I.e. 1 dB change in DUT frequency response doesn't cause 1 dB change on upconverted frequencies. This is actually to be expected, since audio devices are usually not matched to 50 Ohm. It means that I have to design some sort of compensation network to make this work. This starts to sound complicated.&lt;/p&gt;&#xA;&lt;p&gt;In theory I could also write a little piece of software for STM32 microcontroller to automate the task.&lt;/p&gt;&#xA;&lt;p&gt;Basically what I'm looking for is a frequency analyzer, but for low frequencies. Or like HP 35660A dynamic signal analyzer, but for a resonable price.&lt;/p&gt;&#xA;&lt;p&gt;I find it hard to belive that I'm the first one who encountered this issue. Is there really no software, no open source MCU based project and no upconverter that already make plots like the one shown above?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-08-23T07:31:54.570" LastActivityDate="2020-08-24T09:25:32.027" Title="Looking for a convenient audio frequency spectrum analyzer" Tags="&lt;filter&gt;&lt;spectrum-analyzer&gt;&lt;audio&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17189" PostTypeId="2" ParentId="17181" CreationDate="2020-08-23T04:03:23.980" Score="2" Body="&lt;p&gt;&amp;quot;As accurate as feasible&amp;quot;, I'd say. There are no hard and fast rules.&lt;/p&gt;&#xA;&lt;p&gt;The nice thing about a paper QSL card is you can write anything you want in the box. Can't remember the time? Write &amp;quot;about 19:00&amp;quot;. QSO went on for a while? How about &amp;quot;03:15 to 04:09&amp;quot;?&lt;/p&gt;&#xA;&lt;p&gt;If you're recording contacts for a contest or award, the rules may have more stringent requirements. Otherwise, you're just sending a postcard to another ham for fun, and there's no need to be precise on the details.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-08-23T04:03:23.980" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17190" PostTypeId="2" ParentId="17188" CreationDate="2020-08-23T10:59:58.783" Score="7" Body="&lt;p&gt;So, &lt;strong&gt;requirements&lt;/strong&gt;:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;runs on OS X and windows&lt;/li&gt;&#xA;&lt;li&gt;easy to work with&lt;/li&gt;&#xA;&lt;li&gt;quicker than &amp;quot;tone and excel&amp;quot; method&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;If you don't like writing software yourself, this should still be pretty doable with just your soundcard and a quick signal flow graph design (in GNU Radio Companion) of your own.&lt;/p&gt;&#xA;&lt;p&gt;So, first off: Exciting with a single tone and stepping through all frequencies is fine. But a lot of work.&lt;/p&gt;&#xA;&lt;p&gt;The linearity of the Fourier transform says that&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;if you feed a single tone into a system that is linear (e.g. a filter), you will only get that tone out&lt;/li&gt;&#xA;&lt;li&gt;you can either&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;take one tone, observe how it gets attenuated (and phase shifted) by your linear system, then move up to the next tone, and so on, and then add everything up, OR,&lt;/li&gt;&#xA;&lt;li&gt;take all the tones at once, and observe which frequency gets attenuated how.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;The second part tends to be quicker :)&lt;/p&gt;&#xA;&lt;p&gt;So, without much ado: here's what &lt;a href=&quot;https://gist.github.com/marcusmueller/ce1f1c638e271e0f4b32a076fbdaa69f&quot; rel=&quot;nofollow noreferrer&quot;&gt;it&lt;/a&gt;'d look like to me:&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://raw.githubusercontent.com/gist/marcusmueller/ce1f1c638e271e0f4b32a076fbdaa69f/raw/069b1852d5c80d45e8f374ac1a43c4fa52a3f142/audio_sounder.svg&quot; alt=&quot;flow graph&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;The low-pass filter is optional and just there because my experience tells me you want one sooner or later.&lt;/p&gt;&#xA;&lt;p&gt;When run (purely with my laptop speakers and microphone, outdoors, lots of noise around me) that's what it looks like:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/HdSJV.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HdSJV.gif&quot; alt=&quot;Running program&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The soundcard plays the blue line, to the best of its abilities. It digitizes the microphone audio, which yields the green line.&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;To the best of its abilities&amp;quot; is of course an important thing here: This needs calibration. Sound cards aren't flat in frequency, because a) that's expensive to build and b) that doesn't help human hearing find things pleasurable.&lt;/p&gt;&#xA;&lt;p&gt;So, you'd&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;run with a simple cable loopback, so that you get the frequency response of your sound card. (Save the image for later: click with your middle mouse button on the graph, &amp;quot;save image&amp;quot;)&lt;/li&gt;&#xA;&lt;li&gt;run with your filter-under-test between soundcard input and output. Subtract the dB values from previous cable calibration from each point.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;That gives you a nice, normalized frequency response: if your filter is the perfect lossless all-pass (just like your cable), then you'd be getting 0 dB at all frequencies. The frequencies where it attenuates, you get exactly the attenuation, where it resonates, you'll see the gain.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Indeed, the manual calibration (i.e. point-wise subtraction) step is ... annoying. If your soundcard has two input channels, which are well-isolated from each other (my laptop doesn't), then you could also connect your sound card output to loopback cable and device under test in parallel, and each to their own sound card inputs. Then, you could modify the above to calculate the logarithmic power from each channel, and subtract the calibration channel data from the measurement channel and get the calibrated result right away.&lt;/p&gt;&#xA;&lt;p&gt;I couldn't test this with my laptop, so I didn't test it for you, but it'd be relatively simple and look like &lt;a href=&quot;https://gist.github.com/marcusmueller/fcf8431d776b778e1d822b4dec18847c&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://raw.githubusercontent.com/gist/marcusmueller/fcf8431d776b778e1d822b4dec18847c/raw/ba181c02d01f1c6c7467b3c5a5eb23b8f996f15e/diff_audio_sounder.svg&quot; alt=&quot;normalized/calibrating soundcard sounder&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;and the output would look like (I tried to highlight in green the area you need to look at; the rest is just noise, because we're suppressing the output signal with the low-pass filter everywhere else). Again, this isn't what a filter response would look like if you measured it with the method (sound card output-&amp;gt; Device under test -&amp;gt; left sound card input; sound card output -&amp;gt; cable -&amp;gt; right sound card input), because this is just &amp;quot;sound over the air with birds&amp;quot;, but I think a picture still helps understand what's happening here:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bIeTe.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bIeTe.png&quot; alt=&quot;Differential Channel Sounder Display&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-08-24T09:25:32.027" LastActivityDate="2020-08-24T09:25:32.027" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17191" PostTypeId="2" ParentId="17181" CreationDate="2020-08-23T14:17:00.703" Score="1" Body="&lt;p&gt;As long as you receive the confirming card, you have what you need as a souvenir or to submit for an award. In my experience, online records need to agree withing 15 minutes to qualify for confirmation, but nothing stops you from correcting an existing record or submitting an additional record once you learn the time logged by the other station. I would also guess that many stations don't log the times of their 2m FM QSOs, so they are likely to respond to your card with the same logged time.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-08-23T14:17:00.703" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17192" PostTypeId="2" ParentId="17181" CreationDate="2020-08-24T14:05:45.837" Score="1" Body="&lt;p&gt;On HF, or for contest QSOs, most hams keep exact logs with times accurate to the minute, so if you were sending QSL cards for HF or contest contacts, then the polite thing to do would be to be accurate to the minute.  Using one's memory for such a log doesn't usually suffice.  Where immediate paper or electronic logging can't be used many hams use an audio recorder to keep a log, which is then later transcribed into a paper or electronic log.&lt;/p&gt;&#xA;&lt;p&gt;For 2m FM contacts that were just for fun and won't be used for a contest, then as Phil says there is no need for precision in the QSL.&lt;/p&gt;&#xA;&lt;p&gt;The time logged on a QSL is the time that the contact began.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-08-24T14:05:45.837" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17193" PostTypeId="2" ParentId="17187" CreationDate="2020-08-24T15:19:56.703" Score="1" Body="&lt;p&gt;For cross-band satellite contacts, the uplink and downlink frequencies, or at least the nominal frequencies of the bands used, should be logged.  Typically the frequencies are both stuffed into a &amp;quot;MHz&amp;quot; field, with an up arrow symbol next to the uplink frequency and a down arrow symbol next to the downlink frequency.  The name of the satellite should go on the QSL card somewhere, either in its own field or stuffed in the &amp;quot;Mode&amp;quot; field if a generic QSL card is being used.  (The &amp;quot;Mode&amp;quot; field should also show the mode, of course.)  A web search for &amp;quot;satellite QSL card&amp;quot; will show many examples.&lt;/p&gt;&#xA;&lt;p&gt;A QSL card for a terrestrial cross-band contact should list the transmit and receive frequencies separately, showing which was which.&lt;/p&gt;&#xA;&lt;p&gt;Most terrestrial repeaters don't operate cross-band, and the vast majority of repeater contacts aren't followed up by a QSL card.  Any QSL card for a repeater contact should explicitly make it clear that the QSO was over a repeater, since repeater contacts are not allowed in many contests.  I'd suggest stuffing &amp;quot;FM repeater K1ABC&amp;quot; into the &amp;quot;Mode&amp;quot; field, where &amp;quot;K1ABC&amp;quot; should be replaced by the call sign of the repeater used.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-08-24T16:58:59.400" LastActivityDate="2020-08-24T16:58:59.400" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17194" PostTypeId="2" ParentId="9074" CreationDate="2020-08-24T17:04:00.657" Score="1" Body="&lt;p&gt;This handy item at least makes the disconection easier: &lt;a href=&quot;https://wr9r.com/product/antenna-disconnect/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wr9r.com/product/antenna-disconnect/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17637" LastActivityDate="2020-08-24T17:04:00.657" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17195" PostTypeId="2" ParentId="7300" CreationDate="2020-08-24T18:41:40.633" Score="1" Body="&lt;p&gt;I know this post is over 3 years old but I felt I must do a post that includes what I have found to be one of the best balun building YouTube videos I have ever seen.  See the &amp;quot;TRXBENCH&amp;quot; balun videos.  I believe there are 4 total.  Peter explains what makes a good balun, why the balun works as it does, and what materials to use.  He also shows how to build a 1:1, 4:1, and a 9:1 balun.  He has a German accent and mis-pronounces in English the word &amp;quot;balun&amp;quot; (he says BALLOON) and the word &amp;quot;series&amp;quot; (he says SERIOUS). Get past that and listen to him explain everything and you can learn alot!  He is a great HAM and I commend him for taking the time to post so many videos on antennas, radio repairs, baluns, etc. I also appreciate his learning the English language so that we can learn so much from him.  By-the-way, he uses FT240-43 mix cores and 18 AWG PTFE - silver plated, stranded wire on his 1:1 and 4:1 baluns.  I have made several of these and have them on all my wire antennas.  I have a few local friends that are trying them out and so far they like them.  With a MFJ-269 AND my VNA these baluns show a pretty flat SWR from 1.8 through 30 mhz and under 1.6:1 up to 54 mhz.  So, watch Peters videos and have fun building some great working baluns!  73 de Jim&lt;/p&gt;&#xA;" OwnerUserId="17638" LastActivityDate="2020-08-24T18:41:40.633" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17196" PostTypeId="2" ParentId="2285" CreationDate="2020-08-25T02:34:56.860" Score="0" Body="&lt;p&gt;Visit my web page and click on the National Packet Directory. It will help you with determining what is in your area.&#xA;&lt;a href=&quot;http://www.ww2bsa.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ww2bsa.org&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17640" LastEditorUserId="8717" LastEditDate="2020-08-25T17:25:16.667" LastActivityDate="2020-08-25T17:25:16.667" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17197" PostTypeId="1" AcceptedAnswerId="17204" CreationDate="2020-08-25T12:43:25.763" Score="1" ViewCount="108" Body="&lt;p&gt;I've begun setting up a ham station at a rural home with a 3 acre deeply wooded rectangular lot, and a width of at least 100'. Picture shows the house portion of the lot.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MstvE.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MstvE.jpg&quot; alt=&quot;QTH&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Currently my primary send and receive antenna is a &lt;a href=&quot;https://www.amateurradiosupplies.com/product-p/10099.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;full-size G5RV&lt;/a&gt; (102' dipole, 31' ladder line, 1:1 balun/choke) strung about 45' between 2 trees in the small cleared back yard. I have a remote antenna switcher and a diversity-capable receiver, so am looking to add a few more antennas to optimize working 40 and 20. I've been reading a lot about the receive benefits of horizontal loop antenna (see designs &lt;a href=&quot;http://www.k5rcd.org/hor%20loop%20instruct.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt; and &lt;a href=&quot;https://wireless-girl.com/Projects/Horizontal-Loop/&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;, for example.) Would it be feasible to run a very long wire loop strung 15' in the air into the wooded area and expect to get better receive performance than the G5RV? Most internet resources appear to treat horizontal loops as NVIS antennas (presumably better to transmit shorter distances), but does that mean they will not also pick up DX as receive antennas?&lt;/p&gt;&#xA;&lt;p&gt;Its also very unclear the implications of running antennas in such a densely wooded area. Most of what I read on the net suggests that this doesn't matter that much.&lt;/p&gt;&#xA;&lt;p&gt;I'm also curious if such a setup could be made to be a transmit antenna as well. Different resources on the web claim the DX performance is somehow better than NVIS depending on the frequency. Is that true?&lt;/p&gt;&#xA;&lt;p&gt;If a horizontal loop is not a great next antenna to build (lets assume towers/beams are out of the question for the moment) what would hams here recommend?&lt;/p&gt;&#xA;" OwnerUserId="11878" LastActivityDate="2020-09-26T01:01:31.860" Title="Receive antenna design for large wooded lot" Tags="&lt;antenna&gt;&lt;reception&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17199" PostTypeId="1" CreationDate="2020-08-25T14:45:21.487" Score="1" ViewCount="210" Body="&lt;p&gt;I want to get a Garmin Astro 320 (or 430) which transmits GPS coordinates to a Garmin handheld unit on frequency 151.820-ish and 154.600-ish.  But I would like to have the Garmin Astro GPS collar on my dog and receive the coordinates on a handheld APRS ham radio (thinking of getting the Kenwood D74A).  Is this possible?&lt;/p&gt;&#xA;" OwnerUserId="17642" LastEditorUserId="8573" LastEditDate="2020-09-15T13:20:38.993" LastActivityDate="2020-09-15T13:20:38.993" Title="Can you receive GPS coordinates from a Garmin Astro dog collar on a handheld ham radio that has APRS?" Tags="&lt;united-states&gt;&lt;aprs&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17200" PostTypeId="2" ParentId="17199" CreationDate="2020-08-25T14:59:48.287" Score="4" Body="&lt;p&gt;I don't know what protocol the Garmin 320 and 430 dog tracking collars use, but it is highly unlikely that they use AX.25 packet as their protocol, because that protocol is old and slow, and therefore harder on batteries.  If they don't use AX.25-based APRS packets, then you wouldn't be able to receive the packets on a Kenwood TH-D74A.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-08-25T14:59:48.287" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17201" PostTypeId="1" CreationDate="2020-08-25T16:55:14.177" Score="2" ViewCount="85" Body="&lt;p&gt;I'm trying to analyse a signal from a HVAC remote control (864 MHz) with my HackRF, but I'm facing an interrogation about the used modulation:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Is it &lt;strong&gt;BFSK&lt;/strong&gt; (frequency modulation) or &lt;strong&gt;BPSK&lt;/strong&gt; (phase modulation) ?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Here's what the signal looks like, once visualised from the HackRF raw data:&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;(with both &lt;em&gt;I&lt;/em&gt; and &lt;em&gt;Q&lt;/em&gt; waveforms, each one shifted from 90°)&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/leGlQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/leGlQ.png&quot; alt=&quot;BFSK-OR-BPSK&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;NB:&lt;/strong&gt; I can notice two different frequencies but sometimes it looks like both are shifted apart from 90° between transitions. Or maybe the ratio &lt;em&gt;(bit width / modulation period)&lt;/em&gt; is really low in this example?&lt;/p&gt;&#xA;&lt;p&gt;Here is a zoom on a part of the sample that gave me headaches:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/82aVW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/82aVW.png&quot; alt=&quot;BFSK-OR-BPSK-ZOOM&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;EDIT: Like pointed out in the comments, the question was missing a lot of information and visualisation about the signal. Thanks for helping me guys... here is more:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;Spectogram along time:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GDg9m.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GDg9m.jpg&quot; alt=&quot;FFT-visualisation&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Zoom-in part of the first &amp;quot;symbols&amp;quot; with FFT, Amplitude, Phase and Frequency&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mUL2g.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mUL2g.jpg&quot; alt=&quot;FFT-details&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;FFT visualisation with max detection enabled (under GNU radio companion, with a DC blocker):&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I've recorded the samples close to the signal frequency, I realised I might have done something wrong...&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UF2CH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UF2CH.png&quot; alt=&quot;FFT-peak-hold&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Constellation plot (under GNU radio companion, with a DC blocker):&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DM1jO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DM1jO.png&quot; alt=&quot;constellation&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17644" LastEditorUserId="17644" LastEditDate="2020-08-26T15:33:13.940" LastActivityDate="2020-08-26T15:33:13.940" Title="Is this signal BFSK or BPSK?" Tags="&lt;digital-modes&gt;&lt;modes&gt;&lt;hackrf&gt;&lt;spectrum-analyzer&gt;" AnswerCount="0" CommentCount="9" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17202" PostTypeId="1" CreationDate="2020-08-25T21:41:01.413" Score="2" ViewCount="47" Body="&lt;p&gt;The FT8/FT4 communication protocols use an 83x91 generator matrix for the low-density parity check code. I am interested in MATLAB recasting of portions of these protocols. Can anyone explain to me where the numbers in the generator matrix come from?&lt;/p&gt;&#xA;" OwnerUserId="17603" LastActivityDate="2020-08-25T21:41:01.413" Title="FT8 low-density parity check code" Tags="&lt;ft8&gt;&lt;encoding&gt;" AnswerCount="0" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17203" PostTypeId="2" ParentId="17199" CreationDate="2020-08-26T04:17:32.187" Score="4" Body="&lt;p&gt;No. These collars do not transmit in the ham bands nor do they use APRS.&lt;/p&gt;&#xA;&lt;p&gt;While many ham receivers can receive outside the ham bands, the protocol used by the Astro is proprietary, best I can tell. So to demodulate and decode it with anything except Garmin equipment will require some reverse engineering.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-08-26T04:17:32.187" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17204" PostTypeId="2" ParentId="17197" CreationDate="2020-08-26T04:24:59.900" Score="3" Body="&lt;p&gt;Put a dipole in the highest trees you can manage. The higher you get it, the better the performance will be. For good DX performance it should be at least 1/4 wavelength high.&lt;/p&gt;&#xA;&lt;p&gt;The trees will not significantly affect the performance.&lt;/p&gt;&#xA;&lt;p&gt;It is hard to beat a dipole on price, performance, or simplicity, especially when you already have these wonderful trees to support it. A beam can perform better, but without a tower and a significant budget it's out of the question.&lt;/p&gt;&#xA;&lt;p&gt;On 40 meters, you might have luck with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Beverage_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Beverage antenna&lt;/a&gt;. They are quite inefficient and so not of much use for transmitting, but they are simple to construct and have great directivity, so are great for receiving, provided they point in the right direction. But you certainly have the space, so there's no reason you couldn't build several and switch between them.&lt;/p&gt;&#xA;&lt;p&gt;Personally I would not bother with the horizontal loop. An antenna that's good for NVIS is necessarily worse for DX because the two have contradictory objectives. For NVIS, you want most of your radiation in an upward direction so it's reflected back down to provide coverage for local contacts, but for DX you want your radiation aimed at the horizon to maximize your skip distance. Besides, the horizontal loop requires twice the wire and twice the supports of a dipole.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-08-26T14:54:08.113" LastActivityDate="2020-08-26T14:54:08.113" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17205" PostTypeId="1" AcceptedAnswerId="17206" CreationDate="2020-08-26T16:09:39.187" Score="13" ViewCount="2603" Body="&lt;p&gt;Specifically, my Icom ID-4100a.&lt;/p&gt;&#xA;&lt;p&gt;What's interesting, is that this happens in MR and VFO modes... but NOT when using the built-in WX stations. For example listening to WX-01 (162.550 MHz), no problem. Listening to 162.550 via VFO and I get the problem.&lt;/p&gt;&#xA;&lt;p&gt;I first noticed it during a local repeater QSO and thought it was the other station experiencing an intermittent fault... and then noticed it with another station later that day, so it had to be me. Opening up the squelch let me catch it in the act, and it seemed so regular that I thought to time it: every 5.5 seconds on the nose.&lt;/p&gt;&#xA;&lt;p&gt;If you have any thoughts or suggestions for further diagnosis and remediation, I'd love to hear it! My instinct is to first try a Partial Reset followed by an All Reset before cracking open the case on the workbench.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="76" LastEditDate="2020-08-26T16:25:27.113" LastActivityDate="2020-08-26T16:25:27.113" Title="Why does the audio on my FM transceiver cut out every 5.5 seconds?" Tags="&lt;receiver&gt;&lt;fm&gt;&lt;equipment-operation&gt;&lt;icom&gt;&lt;weather&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17206" PostTypeId="2" ParentId="17205" CreationDate="2020-08-26T16:09:39.187" Score="27" Body="&lt;p&gt;It's a feature not a bug.&lt;/p&gt;&#xA;&lt;p&gt;When turned on, the &lt;strong&gt;weather alert&lt;/strong&gt; function checks the local NOAA station for its alert tone every 5 seconds for half a second... doing so takes over the receiver.&lt;/p&gt;&#xA;&lt;p&gt;I'd turned it on, and forgotten I'd done so; and how that feature is implemented never registered in my mind. Turning it off solves my &amp;quot;problem.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;Thanks to reddit user /u/hobbified for the answer!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2020-08-26T16:09:39.187" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17207" PostTypeId="1" CreationDate="2020-08-26T22:00:54.270" Score="4" ViewCount="148" Body="&lt;p&gt;My understanding is a J pole is a &lt;span class=&quot;math-container&quot;&gt;$\frac{1}{2} \lambda$&lt;/span&gt; dipole attached to a &lt;span class=&quot;math-container&quot;&gt;$\frac{1}{4} \lambda$&lt;/span&gt; impedance matching element.&lt;/p&gt;&#xA;&lt;p&gt;How does this dual band work? What acts as the impedance matching element and what is the radiating element?&#xA;Does the smaller rod act as the impedance match for 2 m and the larger one for 440 MHz with the longest rod acting as the radiating element?&lt;/p&gt;&#xA;&lt;p&gt;How is a feedline connected to this?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UTkk2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UTkk2.png&quot; alt=&quot;http://ve3elb.ham-radio.ch/2m70cm/ajpole.gif&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;From &lt;a href=&quot;http://ve3elb.ham-radio.ch/2m-70cm%20antennas.html#:%7E:text=ARROW%20ANTENNAS%20DUAL%20BAND%20J%2DPOLE&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://ve3elb.ham-radio.ch/2m-70cm%20antennas.html#:~:text=ARROW%20ANTENNAS%20DUAL%20BAND%20J%2DPOLE&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15878" LastActivityDate="2020-08-27T02:57:44.630" Title="How do dual band J poles work?" Tags="&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="12" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17208" PostTypeId="1" AcceptedAnswerId="17209" CreationDate="2020-08-26T22:32:33.030" Score="5" ViewCount="85" Body="&lt;p&gt;I have recently started getting into wireless digital communications and I read about QAM modulation.&lt;/p&gt;&#xA;&lt;p&gt;But I am a little confused as to how the receiving demodulator would know which symbol it is reading.&lt;/p&gt;&#xA;&lt;p&gt;For example with 64-QAM there would be 8 amplitude levels transmitted over the air. I understand these levels are modulated as voltage in the baseband quadrature modulator. But when the receiver receives the signal and demodulates, the voltage has been significantly attenuated.&lt;/p&gt;&#xA;&lt;p&gt;So how does the reciver know if it is receiving &amp;quot;level 4&amp;quot; or &amp;quot;level 7&amp;quot; in the amplitude carrier if the voltage has attenuated?&lt;/p&gt;&#xA;&lt;p&gt;Eg. The transmitter sends voltages between 2-10 volts (1 volt difference per level for 64 QAM). But the receiver can read any voltage depending on its distance from the transmitter e.g 0.1-0.5 V or even 0.002-0.01V. How would the receiver know which symbol it is reading?&lt;/p&gt;&#xA;" OwnerUserId="17654" LastActivityDate="2020-08-27T08:08:47.970" Title="How does a digital demodulator know which level it is reading?" Tags="&lt;digital-modes&gt;&lt;rfi&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17209" PostTypeId="2" ParentId="17208" CreationDate="2020-08-27T00:55:10.413" Score="4" Body="&lt;p&gt;This same problem of discriminating symbols can appear in as simple a system as transmitting an &amp;quot;unmodulated&amp;quot; binary code (2 symbols) over an AC-coupled cable (such as is used in Ethernet). If your message has a long string of 1s or 0s, how does the receiver tell them apart?&lt;/p&gt;&#xA;&lt;p&gt;The solution in either case is to use a coding which ensures that &lt;strong&gt;all symbols occur in the message&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;p&gt;In the binary case, this is known as &lt;a href=&quot;https://en.wikipedia.org/wiki/Bit_stuffing&quot; rel=&quot;nofollow noreferrer&quot;&gt;bit stuffing&lt;/a&gt;; and it can be done by a rule as simple as, for example, &amp;quot;if you would transmit 000000, transmit 0000001 instead; if you would transmit 111111, transmit 1111110&amp;quot;. The receiver knows the rule in use and can therefore remove the extra symbols, and the rule ensures that every message longer than six bits contains a transition.&lt;/p&gt;&#xA;&lt;p&gt;And every message will be at least that long, because (especially in QAM) you also want to use a &lt;a href=&quot;https://en.wikipedia.org/wiki/Syncword&quot; rel=&quot;nofollow noreferrer&quot;&gt;preamble&lt;/a&gt; to ensure that every message is not just long enough to have a symbol transition, but long enough for the receiver's synchronization to lock onto the timing, amplitude, and phase of the signal — it should contain &lt;em&gt;many&lt;/em&gt; symbol transitions.&lt;/p&gt;&#xA;&lt;p&gt;I don't know what methods are used in practice for QAM.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-08-27T00:55:10.413" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17210" PostTypeId="2" ParentId="17207" CreationDate="2020-08-27T02:57:44.630" Score="2" Body="&lt;p&gt;In the J146/440 antenna, on the right:&lt;/p&gt;&#xA;&lt;p&gt;For 2m, the leftmost and rightmost element form the J-pole, and the center element is too short to matter very much. (It probably adds some inductance, which could explain why the left element seems a little shorter than it should be for 2m).&lt;/p&gt;&#xA;&lt;p&gt;For 70cm, the center and leftmost element form the J-pole, and the rightmost element, being a little over 2WL long, isn't resonant and doesn't have much of an effect.&lt;/p&gt;&#xA;&lt;p&gt;It's not super important whether a J-pole is fed at the &amp;quot;long&amp;quot; or the &amp;quot;short&amp;quot; element; since the leftmost (medium length) one is the one that both bands have in common, that's the one that gets fed. The coax center goes to the left rod (which is insulated from the aluminum angle). The coax shield goes to the aluminum angle itself, which the center and right rods are in electrical contact with.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-08-27T02:57:44.630" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17211" PostTypeId="1" CreationDate="2020-08-27T03:00:02.650" Score="0" ViewCount="1044" Body="&lt;p&gt;I have a Baofeng UV-5R and I have been using it as a police/EMS scanner. I have used it before and it has worked perfectly. I just recently moved to a new area and yet when I went to listen into the frequency I found I got intermittent static. Not just the little blips that come often with a Baofeng, its actual transmissions of the expected length of radio communications but all that comes through is static. I know I'm close enough; I am watching ambulances running code go by. I tried programming them into my channel memory and that made no difference. I tried holding down the MONI button but there was just the expected static. I have changed the squelch several times from all the way to from one to nine. At squelch zero, there isn't all static like I would expect, it made no difference to what I heard on that frequency. Is it possible my antenna was damaged unintentionally during travel? I don't see any damage and I have checked it several times. Thank you so much for any help!&lt;/p&gt;&#xA;" OwnerUserId="17656" LastActivityDate="2020-08-27T16:43:05.340" Title="Baofeng UV-5R Receiving Intermittent Static? Please help!" Tags="&lt;baofeng&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17214" PostTypeId="2" ParentId="17208" CreationDate="2020-08-27T08:08:47.970" Score="5" Body="&lt;p&gt;You're asking exactly the right question – &lt;em&gt;my receiver can't know this property of the transmission, how do I figure it out reliably&lt;/em&gt; – and that way of thinking makes for good receiver designs :)&lt;/p&gt;&#xA;&lt;p&gt;There's two classes of methods to solve this:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;statistics-based methods&lt;/li&gt;&#xA;&lt;li&gt;transmitter data assisted methods&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;What is very common in receiver design is that you have an automatic gain control (AGC) that amplifies your receive signal to a fixed &lt;em&gt;average&lt;/em&gt; power. That makes a lot of sense from the analog hardware point of view, because no amplifier is &lt;em&gt;really&lt;/em&gt; linear over its full range, and thus, if possible, you'd always want to work your amplifiers in roughly the same power region.&lt;/p&gt;&#xA;&lt;p&gt;Finding the average power and scaling so that the result is always the same power works, because you can be pretty sure that all symbols in your transmission are equally likely; if that's not the case, you could have compressed your source data (using source coding, i.e. lossless entropy coding) better. Furthermore, as Kevin illustrated for binary wired systems, you employ techniques to avoid the signal having a distinct pattern (e.g. constant, or only alternating between the corner points of a QAM, or..:).&lt;/p&gt;&#xA;&lt;p&gt;In wireless systems, bit stuffing isn't common, because the problem that solves (&amp;quot;consecutive runs of the same symbol&amp;quot;) is just a subclass of the problem that you need to solve in wireless comms, namely that you need your data symbols to look uncorrelated, so that their spectrum is white. That is important so you can make the most use of the bandwidth you're given¹ but also because of statistical methods in the receiver².&lt;/p&gt;&#xA;&lt;p&gt;Instead, &lt;em&gt;scramblers&lt;/em&gt; are used. Often, that's nothing but a simple pseudo-random bit generator that is XORed both on the transmitter side and the receiver side bits after channel coding or before channel decoding, respectively.&lt;/p&gt;&#xA;&lt;p&gt;Armed with that, it's very unlikely that the average power of your signal (say, averaged over a hundred symbols) varies a lot. Thus, you can scale your signal's amplitude with the inverse of the square root of the received power.&lt;/p&gt;&#xA;&lt;p&gt;This is often not sufficient for QAM, since small fluctuations are very likely, and because QAM is indeed pretty sensitive to amplitude variations.&lt;/p&gt;&#xA;&lt;p&gt;So, alternatively, but more often, in combination with that, the transmitter is designed to include pilot symbols or sequences, which can be easily detected: either on frame start something like a fixed preamble that can be found using correlation, or simply at known positions in the frame.&lt;/p&gt;&#xA;&lt;p&gt;These aren't data, but fixed values that some standard defines. The receiver observes them, says, &amp;quot;ah, they should be this, but they are that, so we need to scale accordingly&amp;quot;. &lt;em&gt;Data-aided recovery&lt;/em&gt; of amplitdue would be how this is called.&lt;/p&gt;&#xA;&lt;p&gt;Some channels can be assumed to stay constant for the duration of one frame³. Then, a single pilot sequence or symbol might suffice. If the channel changes, you'll need a new pilot occassionally, to keep track of things. Of course, if you have a sufficiently fine resolving receiver, and enough error correction, you could also keep track of how the amplitudes change in your symbols by reconstructing what you should have received under your current channel state information, and continuously compare that to what you've actually receive and notice a drift early on. Then you're even &lt;em&gt;decision-feedback recovering&lt;/em&gt; amplitude of your signal.&lt;/p&gt;&#xA;&lt;p&gt;In practice, you use QAM when you need a high data rate, which most often⁴ means it uses a large bandwidth, and the channel is hence a  wideband channel and needs an equalizer to look flat. In this common case, the data-aided or decision-feedback amplitude recovery doesn't happen as its own step, but as part of the equalizer.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;¹ if you have 20 MHz of bandwidth and a peak power over any 1 kHz swath in that that you can legally use, you'll make damn sure your data spectrum is flat and doesn't have spikes at any frequency, because that would mean you need to reduce your transmit power overall.&lt;/p&gt;&#xA;&lt;p&gt;² not only for amplitude recovery, but also for phase and frequency recovery. The same problem you noticed about levels also applies to rotations!&lt;/p&gt;&#xA;&lt;p&gt;³ that's actually an inversion of reality: I should have said &amp;quot;some systems were designed so that frames are short enough, so that the ever-changing channel can be considered to not change within the duration of a frame. But putting it like that gives you all the headaches of the designer of the whole system when you should just be developing a receiver.&lt;/p&gt;&#xA;&lt;p&gt;⁴ not always; some channels, for example satellite communications, typically form an exception to that. For the satcom channel, you often prefer to use high-number-of-points PSK over QAM, because you have good phase recovery, but don't need an equalizer to combat multipath, and thus, you want to avoid going through the extra effort of having amplitude recovery, especially because neither atmosphere nor the very high-gain LNAs will make that any easier for you.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-08-27T08:08:47.970" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="17215" PostTypeId="2" ParentId="17211" CreationDate="2020-08-27T14:43:43.613" Score="0" Body="&lt;p&gt;It's hard to say what went wrong from here, but handheld transceiver antennas fail often, usually because the radio is dropped.  I suggest trying some systematic troubleshooting.  If you can borrow another Baofeng that is known to work, try swapping antennas.  You surely reprogrammed the radio when you moved, so the programming is suspect; try reprogramming the radio.  You are using software to program the radio, I presume.  If you have trouble with the programming, your local ham radio club surely has plenty of people who could help.&lt;/p&gt;&#xA;&lt;p&gt;I hadn't thought about the possibility @hobbs-KC2G mentioned, that the new ambulance service could be using a digital mode, which could sound like static.  One way to test that theory would be to tune in a known FM signal, like a local &lt;a href=&quot;https://www.weather.gov/nwr/&quot; rel=&quot;nofollow noreferrer&quot;&gt;NOAA Weather Radio&lt;/a&gt; station.  If that comes in loud and clear, then the radio probably works fine.&lt;/p&gt;&#xA;&lt;p&gt;Unfortunately the squelch function isn't very adjustable on the UV-5R.  The setting that I put in doesn't seem to make any difference on mine.&lt;/p&gt;&#xA;&lt;p&gt;If all else fails, another Baofeng isn't very expensive...&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-08-27T16:43:05.340" LastActivityDate="2020-08-27T16:43:05.340" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17216" PostTypeId="2" ParentId="17211" CreationDate="2020-08-27T15:48:42.537" Score="3" Body="&lt;p&gt;This isn't a broken antenna, or you wouldn't be able to tell the difference between transmission and no transmission. Most likely the department in your new location is using digital radios which can't be received by your UV5R. What sounds like static to you is actually the digital signal.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-08-27T15:48:42.537" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17217" PostTypeId="2" ParentId="17211" CreationDate="2020-08-27T15:55:34.980" Score="0" Body="&lt;p&gt;This sounds like your receiver is being overloaded by a very strong signal, too strong for your Baofeng to handle. They are noted for this.&lt;/p&gt;&#xA;&lt;p&gt;Try removing the antenna. If the signal is not strong enough to hear like that, then plug the antenna back in and try wrapping aluminum foil around part of it, with the foil touching the metal antenna connector. It may reduce the incoming interfering signal enough for you to listen to what you want to. &lt;em&gt;Do not transmit like this&lt;/em&gt;; it can damage the radio.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;It could also be &lt;a href=&quot;https://ham.stackexchange.com/a/17216/8717&quot;&gt;this&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-08-27T15:55:34.980" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17218" PostTypeId="2" ParentId="2477" CreationDate="2020-08-27T18:20:08.330" Score="0" Body="&lt;p&gt;After looking at several wire antennas decided to build my own and save money plus having the satisfaction of knowing I built a successful antenna. Wire, insulators, solder and rope plus sling shot to elevate antenna at a reasonable height. Had plenty of room for dipoles or loops.&#xA;468 divided by frequency will give you a usable wire antenna. Different gauges of wire will give different results. For those with limited space coils will shrink physical size to fit your space with some trade-off. Rotatable dipoles for 10, 20 meters are easy to build with nesting aluminum tubing. Antenna analyzers help for those who want a more accurate deigns but not necessary. My 560 foot loop for 160 out performed beams and at time 100 watts was enough to beat amps.&lt;/p&gt;&#xA;" OwnerUserId="13592" LastActivityDate="2020-08-27T18:20:08.330" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17219" PostTypeId="1" AcceptedAnswerId="17220" CreationDate="2020-08-28T06:09:01.437" Score="2" ViewCount="130" Body="&lt;p&gt;I am a newbie trying to detect NOAA 15, 18, and 19 satellites, which have downlink frequencies between 137 MHz and 138 MHz. I am using an SDR dongle and attached a photo of it to this post.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/TleeM.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TleeM.jpg&quot; alt=&quot;&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Of course, I will be constructing an antenna specified for the 137 MHz later. However, I wanted to see if I could observe anything with this configuration. Observing the 137-138 MHz band, I observed an interesting pattern, which seems like a sinc function as if some square signal is multiplied with a sinusoidal signal. Here is a photo of my observation below.&lt;a href=&quot;https://i.stack.imgur.com/p9Rai.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/p9Rai.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now here are my questions about these:&lt;/p&gt;&#xA;&lt;p&gt;-&amp;gt; What this frequency might be about? I can detect it inside my house and outside as well. I looked it up and could not find a corresponding signal. Is this something caused by my setup? How can I observe NOAA satellites with similar frequencies?&lt;/p&gt;&#xA;&lt;p&gt;-&amp;gt; There is also a peak that I could not decode at 137.5 MHz. Seemed like an FM signal to me but not sure. Do you have any idea on that as well?&lt;/p&gt;&#xA;&lt;p&gt;Any idea would help if you have an opinion on what these signals might be about. Take care in the quarantine times.&lt;/p&gt;&#xA;" OwnerUserId="17674" LastEditorUserId="8717" LastEditDate="2020-08-29T20:42:19.167" LastActivityDate="2020-08-29T20:42:19.167" Title="Receiving an Coded Odd Signal at 137.25MHz but don't know what it might be. It can affect my detection on NOAA 19. Need help" Tags="&lt;software-defined-radio&gt;&lt;receiver&gt;&lt;rfi&gt;&lt;fm&gt;&lt;reception&gt;" AnswerCount="1" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17220" PostTypeId="2" ParentId="17219" CreationDate="2020-08-28T14:53:23.383" Score="5" Body="&lt;p&gt;That looks like you're strongly overdriving your receiver. Drastically reduce gain. This signal might not come from 137.5 MHz at all but be mixed there by the nonlinear effect of overdriving your amplifiers.&lt;/p&gt;&#xA;&lt;p&gt;The fact you can receive FM (a different signal at a different frequency) doesn't mean the gain is appropriate for this signal. Also, FM, being FM, is relatively robust against nonlinearity (i.e. distortion by too much gain bringing your receiver to the edges of its value range).&lt;/p&gt;&#xA;&lt;p&gt;Less gain doesn't mean less reception — imagine this: you use a hearing aid. Somebody screams into your ear. Is it wise to have your hearing aid's gain at a high level?&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-08-28T14:53:23.383" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17221" PostTypeId="1" CreationDate="2020-08-28T18:52:10.757" Score="2" ViewCount="125" Body="&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Orbital_angular_momentum_multiplexing&quot; rel=&quot;nofollow noreferrer&quot;&gt;OAM (Orbital Angular Momentum) Multiplexing&lt;/a&gt; is a form of multiplexing capable of high data speeds on limited bandwidth using the physical properties of EM waves.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://iopscience.iop.org/article/10.1088/1367-2630/14/3/033001&quot; rel=&quot;nofollow noreferrer&quot;&gt;An experiment in 2012&lt;/a&gt; transmitted two data signals simultaneously on the same frequency over a distance of 442 meters on the 5ghz band.&lt;/p&gt;&#xA;&lt;p&gt;Would the properties of OAM multiplexing work on the same level if done on the HF band (say for example 20 meters) with ionospheric propagation? If this was possible, could the signal coherently be transmitted and received?&lt;/p&gt;&#xA;" OwnerUserId="17681" LastEditorUserId="17681" LastEditDate="2020-08-28T18:57:35.247" LastActivityDate="2020-09-02T14:22:25.017" Title="Would Orbital Angular Momentum (OAM) multiplexing work over HF bands?" Tags="&lt;hf&gt;&lt;modes&gt;" AnswerCount="2" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17222" PostTypeId="2" ParentId="17221" CreationDate="2020-08-28T19:29:47.903" Score="4" Body="&lt;p&gt;This is a physicist level experiment, and its benefit over established methods disputed, and even Wikipedia says that it's performance benefit over MIMO are nonexistent to negligible.&lt;/p&gt;&#xA;&lt;p&gt;So, no. Not in any realistic way.&lt;/p&gt;&#xA;&lt;p&gt;Also, orbital angular momentum is a result of the &lt;em&gt;mode&lt;/em&gt; of the electromagnetic wave and its propagation. Hence, if you want to use it, you'd need precise control of the mode.&lt;/p&gt;&#xA;&lt;p&gt;You can (maybe) do that (at high effort) for light (which is also an electromagnetic wave) in a glass fibre (which is a waveguide). Cross-mode talk is a thing in the finely controlled environment of a fiber, still.&lt;/p&gt;&#xA;&lt;p&gt;You can certainly not do that reliably for HF in propagation over a medium as inconsistent as the air, with boundaries varying in material and shape as the earth and ionosphere.&lt;/p&gt;&#xA;&lt;p&gt;So, no. Totally different realm in which this highly immature thing is happening.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;I find it kind of entertaining that someone would mention this moonshot technology in the context of HF communications in amateur radio applications.&lt;/p&gt;&#xA;&lt;p&gt;I find it hard to find any area of hobbyist technology usage where the difference between the actual state of the art and the way the technology is used is as large as in HF communications done by amateur radio enthusiasts. Seriously, there's 60 to 90 years between what science and commercial technology can do, and what the average ham operator on HF does. Maybe we should catch up these decades, before you start following methods that try to improve upon what can be done so far.&lt;/p&gt;&#xA;&lt;p&gt;That starts with retiring all analog modes, and all transceivers that are basically AM or SSB devices in favor of proper devices that can deal with both sides of a spectrum. Then, application of modern modulation, channel sensing and synchronization methods. Going for modern channel codes. Classical MIMO. Proper network and routing protocol design. Lobbying against counter-productive rate-limiting and legacy-mode-preserving regulation. Requiring a minimum effective spectral efficiency, &lt;em&gt;especially&lt;/em&gt; for higher-powered transmitters.&lt;/p&gt;&#xA;&lt;p&gt;Things like FT8 are a &lt;em&gt;start&lt;/em&gt;. They tackle maybe half of these points.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-08-28T19:38:59.443" LastActivityDate="2020-08-28T19:38:59.443" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17224" PostTypeId="1" CreationDate="2020-08-29T21:29:02.840" Score="0" ViewCount="93" Body="&lt;p&gt;I have an antenna on a building. It is made of steel and is about 10ft long. It wobbles a bit in high winds.&lt;/p&gt;&#xA;&lt;p&gt;It is not going to do a Tacoma Narrows but it is a bit annoying.  Can I tie stainless steel marine wire to the top of the mast then weld a couple of steel tubes (2 feet) at the 5ft mark to hold the wire out 2ft (&lt;em&gt;this is all the space I have above the roof and then tie these below the antenna support&lt;/em&gt;)&lt;/p&gt;&#xA;&lt;p&gt;The antenna is supported on the wall in two places with a 2ft section of the same pipe.&lt;/p&gt;&#xA;" OwnerDisplayName="Trevor McGregor" LastEditorUserId="4665" LastEditDate="2020-08-31T15:33:04.840" LastActivityDate="2020-08-31T15:36:20.233" Title="How to stabilize an antenna" Tags="&lt;antenna-construction&gt;&lt;vertical-antenna&gt;" AnswerCount="0" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17225" PostTypeId="1" CreationDate="2020-08-30T12:40:35.053" Score="1" ViewCount="202" Body="&lt;p&gt;Every so often while shortwave listening I’ll come across a frequency where tons of hams are talking all over each other giving a call sign and a six digit number only (not a QSO). I imagine these numbers may be club membership numbers but I can’t figure out the purpose. Is this some way to build up a large number of QSOs? Doesn’t seem like the requirements of a QSO are met by just getting a call sign and number. And how on earth does anyone copy all of these contacts given that everyone is pretty much talking over themselves, voices overlapping, with no moderator or any attempt to direct traffic?&lt;/p&gt;&#xA;&lt;p&gt;What makes this even weirder is that I’ll sometimes hear other hams on the band who mention this but don’t know what it’s for either.&lt;/p&gt;&#xA;" OwnerUserId="11878" LastActivityDate="2020-09-28T23:09:29.173" Title="What are these serial number pileups on 20m and 40m?" Tags="&lt;license&gt;&lt;swl&gt;" AnswerCount="4" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17226" PostTypeId="2" ParentId="17225" CreationDate="2020-08-30T13:34:11.610" Score="2" Body="&lt;p&gt;Guessing it was a contest, and the numbers were the exchanges, per the contest rules.&lt;/p&gt;&#xA;&lt;p&gt;The exchanges vary by contest, so it depends on which contest you heard.&lt;/p&gt;&#xA;&lt;p&gt;Try searching the contest-calendar, here:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.contestcalendar.com/weeklycont.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.contestcalendar.com/weeklycont.php&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Perhaps with some more information we can narrow it down.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastActivityDate="2020-08-30T13:34:11.610" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17228" PostTypeId="2" ParentId="16534" CreationDate="2020-08-30T23:04:18.460" Score="2" Body="&lt;pre&gt;&lt;code&gt;$ od -txC QSOPCTDIR.dat &#xA;0000000    60  00  00  08  20  20  20  20  20  41  4c  4c  20  20  20  20&#xA;0000020    20  20  20  20  20  20  20  20  20  45  41  47  4a  44  52  32&#xA;0000040    41  55  49  20  20  20  20  20  20  20  20  20  20  20  20  08&#xA;0000060    30  20  30  00  20  08  30  20  30  00  20  08  30  19  43  00&#xA;0000100    32  30  32  30  2f  30  38  2f  33  30  20  31  39  3a  34  33&#xA;0000120    00  00  2f  35  48  45  41  36  34  63  30  30  30  30  30  31&#xA;0000140    2e  6a  70  67  ff  ff  ff  ff  ff  ff  ff  ff  ff  ff  ff  ff&#xA;0000160    ff  ff  ff  ff  ff  ff  ff  ff  00  00  00  00  00  00  00  00&#xA;0000200&#xA;&#xA;$ od -txC QSOPCTFAT.dat &#xA;0000000    40  00  00  00                                                &#xA;0000004&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;I've also found this &lt;a href=&quot;https://docs.google.com/spreadsheets/d/1PwzVF22pcLmB04uWrRkx8IWbQs3NnVsqAb-y3qHnhVk/edit#gid=1180833404&quot; rel=&quot;nofollow noreferrer&quot;&gt;spreadsheet&lt;/a&gt; that might help&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/X76ag.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/X76ag.png&quot; alt=&quot;yaesu file structure&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17697" LastEditorUserId="17697" LastEditDate="2020-09-05T10:47:19.173" LastActivityDate="2020-09-05T10:47:19.173" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17230" PostTypeId="2" ParentId="17225" CreationDate="2020-08-31T15:20:15.183" Score="3" Body="&lt;p&gt;What you're talking about sounds like activity that is common for a contest or a QSO party.  If you're not familiar with QSO parties they are organized like contests, but the organizers try to emphasize everyone having fun, and don't focus quite as much on scores.  There is a saying though, that if something smells, looks, and feels like an elephant then it's probably an elephant; in other words, QSO parties are generally regarded as contests, and are included in contest calendars.&lt;/p&gt;&#xA;&lt;p&gt;Contests and QSO parties almost always include a signal report, which makes them bona-fide contacts in the eyes of most hams.  However these days the signal report is almost always &amp;quot;59&amp;quot; for phone or &amp;quot;599&amp;quot; for Morse.  Were the first two digits of the six-digit number &amp;quot;59&amp;quot;?  Contesters like to leave a little pause between the signal report and the &amp;quot;exchange&amp;quot;, but to outsiders, &amp;quot;five nine, one three seven six&amp;quot; might sound like a six-digit number.  What's an exchange, you ask?  It's a piece of data that the contest rules require to be exchanged.  It might be the location of the station encoded in a numeric format, or a sequential serial number, or the year the operator was first licensed, or the name of the state or province the station is in, or just about anything else the contest organizers can dream up.  For some contests the exchange changes every contact, but for others it's always the same for a particular station.&lt;/p&gt;&#xA;&lt;p&gt;As for all talking at once, contests are competitive and operators will talk over each other in an attempt to get a contact with a rare multiplier.  What's a multiplier?  As an example, rules for a state's QSO party might define a contester's score as the number of contacts times the number of counties contacted (usually on a per-band basis).  Typically there are rare multipliers, like a sparsely-populated county in the state's QSO party, that everyone is trying to contact.  It's not uncommon for several stations to try to work the same station, usually a rare multiplier, at the same time, a situation known as a pileup.  A skilled operator can pick individual call signs out of the cacophony and keep calling operators happy.&lt;/p&gt;&#xA;&lt;p&gt;Here's a typical contest exchange (&amp;quot;W1ABC&amp;quot; and &amp;quot;VA3XYZ&amp;quot; were made up for this example, but may well exist as real call signs):&lt;/p&gt;&#xA;&lt;p&gt;VA3XYZ: victor alpha three x-ray yankee zulu QRZ&lt;br /&gt;&#xA;W1ABC: whiskey one alpha bravo charlie&lt;br /&gt;&#xA;VA3XYZ: W1ABC, five-nine, one three seven six&lt;br /&gt;&#xA;W1ABC: thanks, five nine, four eight seven&lt;br /&gt;&#xA;VA3XYZ: seventy-three QRZ&lt;/p&gt;&#xA;&lt;p&gt;So that was a valid QSO because signal reports were exchanged, although the reports were the standard 59s, and acknowledged with &amp;quot;thanks&amp;quot; and &amp;quot;seventy-three&amp;quot;.  VA3XYZ repeated the calling station's call sign; the calling station W1ABC didn't repeat VA3XYZ's, but &lt;em&gt;implied&lt;/em&gt; that he or she did, because if he or she didn't copy the call sign then he or she would have requested a repeat (a &amp;quot;fill&amp;quot; in contest jargon).  They were valid QSOs for this particular imaginary contest because the exchange included serial numbers, &amp;quot;1376&amp;quot; and &amp;quot;487&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Does that describe what you heard?  If not, the next time you hear such activity, please make a note of details such as date, time, frequency, and transcriptions of a few QSOs, and we can probably help you out.  Or write down a few call signs and email the operators to ask, and then come back here and answer your own question.  (Many operators list their email addresses in qrz.com.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-08-31T15:20:15.183" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17231" PostTypeId="1" AcceptedAnswerId="17238" CreationDate="2020-08-31T16:36:04.320" Score="5" ViewCount="365" Body="&lt;p&gt;I've heard lots of contest exchanges, and the signal report almost always seems to be 59 for phone or 599 for Morse, even when the operator giving the report has to request information to be repeated several times.  Why is the signal report almost always 59 or 599?  If the report never changes, why do contest rules still require signal reports, when cutting out phony reports would speed things up?&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-08-31T22:21:11.737" LastActivityDate="2021-04-26T08:45:30.840" Title="Why are contest signal reports always &quot;59&quot; or &quot;599&quot;?" Tags="&lt;cw&gt;&lt;contest&gt;&lt;phone&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17232" PostTypeId="2" ParentId="17231" CreationDate="2020-08-31T17:01:04.427" Score="6" Body="&lt;p&gt;Signal reports are sent because the contest may require them. Every contest I can think of requires some exchange of information, and a signal report may or may not be among the required information. For example, the &lt;a href=&quot;http://www.arrl.org/10-meter&quot; rel=&quot;noreferrer&quot;&gt;ARRL 10 meter contest&lt;/a&gt; specifies signal reports must be exchanged:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;4. Contest Exchange:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;4.1. W/VE stations (including Hawaii and Alaska) send RS(T) and state or province (District of Columbia stations send signal report and DC).&lt;/p&gt;&#xA;&lt;p&gt;4.2. DX stations (including KH2, KP4, etc) send RS(T) &amp;amp; sequential serial number starting with 001.&lt;/p&gt;&#xA;&lt;p&gt;4.3. Mexican stations transmit RS(T) and their state.&lt;/p&gt;&#xA;&lt;p&gt;4.4. Maritime mobile stations send RS(T) and ITU Region (R1, R2 or R3).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;However, the &lt;a href=&quot;http://www.arrl.org/september-vhf&quot; rel=&quot;noreferrer&quot;&gt;ARRL September VHF contest&lt;/a&gt; has optional signal reports:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;ol start=&quot;4&quot;&gt;&#xA;&lt;li&gt;&lt;strong&gt;Exchange:&lt;/strong&gt; Maidenhead grid-square locator (see &lt;a href=&quot;http://www.arrl.org/grid-squares&quot; rel=&quot;noreferrer&quot;&gt;www.arrl.org/grid-squares&lt;/a&gt;)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;4.1. Exchange of grid square is required. Exchange of signal report is optional.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Though optional, operators may exchange signal reports anyway out of habit.&lt;/p&gt;&#xA;&lt;p&gt;Why always 59 or 599? Well, it's easier. Contest operators may use a keyer, and reprogramming the keyer for each contact wouldn't be feasible. It's also one less thing to think about. Furthermore, if everyone understands the signal report is always 59(9), that's one less detail that must be carefully confirmed between parties. Many contests include penalties, or at least the contact may not count, if both stations don't submit the same information.&lt;/p&gt;&#xA;&lt;p&gt;If you hear stations repeating the signal report, I'd guess it's simply inexperienced operators that haven't caught on to the &amp;quot;always 59(9)&amp;quot; convention yet.&lt;/p&gt;&#xA;&lt;p&gt;Of course if the signal report is always 59(9), there's no &lt;em&gt;real&lt;/em&gt; information being exchanged. Consequently some contests require an exchange of grid squares, serial numbers, or other information which varies between contacts to make things a little more challenging.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-08-31T17:01:04.427" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17233" PostTypeId="2" ParentId="17155" CreationDate="2020-08-31T20:39:52.357" Score="2" Body="&lt;p&gt;I believe the rationale is not a &amp;quot;measurement&amp;quot; of popularity but 1) an assessment of activity, i.e. it will take a certain amount of dedication and time to log stations as a listener, combined with 2) an assessment of the listener's abilities when, for example, the requirement is to log and confirm a certain number of DXCC countries or similar achievements. An implicit assumption is probably that the SWL will progress along a learning curve (about equipment, propagation, operating procedures etc).&lt;/p&gt;&#xA;&lt;p&gt;I am not aware of any country employing such a requirement at present. However, pre-1990, amateur radio beginners in the German Democratic Republic typically started out as listeners. One condition for advancing towards a transmitting license was to log and confirm a number of different countries, participate in SWL contests, or meet the requirements for certain SWL awards. Similar rules may well have been in place in other Eastern European countries at that time.&lt;/p&gt;&#xA;" OwnerUserId="17676" LastActivityDate="2020-08-31T20:39:52.357" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17234" PostTypeId="2" ParentId="17231" CreationDate="2020-09-01T08:00:00.797" Score="6" Body="&lt;p&gt;&amp;quot;If the report never changes, why do contest rules still require signal reports, when cutting out phony reports would speed things up?&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;This question comes up frequently, among contesters (e.g. on &lt;a href=&quot;http://lists.contesting.com/mailman/listinfo/cq-contest&quot; rel=&quot;nofollow noreferrer&quot;&gt;CQ-Contest&lt;/a&gt;, an email reflector for contesters) as well as among those who criticise contests. Reasons for the signal report often include (in no particular order):&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;meeting the somewhat arbitrary definition of what constitutes a &amp;quot;complete&amp;quot; QSO&lt;/li&gt;&#xA;&lt;li&gt;the signal report acts as a signalling, attention-grabbing phrase for the important part of the exchange that follows (e.g. a serial number, location designator etc)&lt;/li&gt;&#xA;&lt;li&gt;it's in the rules :-)&lt;/li&gt;&#xA;&lt;li&gt;without some agreement on receiver settings (rx bandwidth, rf-gain, attenuator, S-meter accuracy...) a signal report is pretty meaningless anyway&lt;/li&gt;&#xA;&lt;li&gt;no contest rules demand an unchanging 59 or 599 signal report, feel free to send a signal report you consider accurate&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Finally, some contest rules do not prescribe a signal report, for example the ARRL Sweepstakes, the Stew Perry Topband Distance Challenge, North American QSO Parties, North American Sprints.&lt;/p&gt;&#xA;" OwnerUserId="17676" LastEditorUserId="17676" LastEditDate="2021-04-26T08:45:30.840" LastActivityDate="2021-04-26T08:45:30.840" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17235" PostTypeId="1" AcceptedAnswerId="17264" CreationDate="2020-09-01T10:00:51.147" Score="8" ViewCount="132" Body="&lt;p&gt;I have a couple of Ferrite beads that are advertised as effective for suppressing conductive noise around 150kHz which I'm trying to monitor their actual performance with noise filtering.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LbHU4.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LbHU4.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;In my set up I have a ferrite core where I  made a number of turns on. I connected the signal from my signal generator and one channel of the oscilloscope to one end of the wire to monitor the input.&lt;/p&gt;&#xA;&lt;p&gt;On the other end of the winding another channel of the oscilloscope is connected to monitor the output.&lt;/p&gt;&#xA;&lt;p&gt;I then conducted a signal sweep from 1kHz to 1MHz and monitored the input and output as shown, input is red, output is blue.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DUkwJ.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DUkwJ.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It is noticeable that there is a signal increase at approximately 40kHz before peak at 105Khz and a decrease.&lt;/p&gt;&#xA;&lt;p&gt;How can I interpret this result (making sense of it with regards to it's actual performance with regards to suppressing noise  at 150kHz?&lt;/p&gt;&#xA;&lt;p&gt;Is it possible for me to make even more turns to &amp;quot;shift&amp;quot; the graph to the left so that a lower output can happen at even lower frequencies? Is there any impact in the performance if too many turns are used?&lt;/p&gt;&#xA;" OwnerUserId="17699" LastEditorUserId="4665" LastEditDate="2020-11-04T16:16:49.360" LastActivityDate="2020-11-04T16:16:49.360" Title="How to effectively test and interpret the &quot;working range&quot; of a ferrite core with a signal analyzer?" Tags="&lt;filter&gt;&lt;ferrite&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17237" PostTypeId="2" ParentId="17221" CreationDate="2020-09-02T14:22:25.017" Score="2" Body="&lt;p&gt;Orbital angular momentum is a near-field property of the electromagnetic field. To detect the orbital angular momentum one has to use a receive antenna that is big enough to detect the different phase and/or amplitude at different points in space. This can be used in optical communication where a light beam can use different OAM modes to transmit multiple messages on the same frequency between two antennas at the same time. It is a special case of MIMO. &lt;br&gt; &lt;br&gt;&#xA;To illustrate: Think of two large antenna arrays pointing towards each other at a modest distance. One antenna can then form a lobe that is small enough to illuminate only the upper left corner of the receiving antenna. It is then possible to simultaneously form three more lobes that illuminate the other three quadrants at the same time on the same frequency and thus transmit four channels on the same frequency. Instead one could combine those four channels to form a field with orbital angular momentum at the receive side. Imagine four feed-points each one exciting the entire tx array to point to one of the four quadrants. Feed them all with the same power but with different phases.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The same phase in all four quadrants.&lt;/li&gt;&#xA;&lt;li&gt;0 degrees in the upper two and 180 degrees in the lower two&lt;/li&gt;&#xA;&lt;li&gt;0 degrees in the left side pair and 180 degrees in the right side pair.&lt;/li&gt;&#xA;&lt;li&gt;0 degrees in the upper left and the lower right, 180 degrees in the other two.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Arrange the rx array as four independent antennas. Each one would have a twice as wide lobe and thus see the entire tx antenna. Combine the four rx antenna cables according to the above pattern to get four independent channels on the same frequency. As I see it, using OAM would be nearly equivalent to MIMO in which case one would have four independent channels by using the four channels of the tx side independently to point to the four parts of the rx antenna. Possibly the combination to make OAM waves would make the system more robust to variations in the transmission path, in particular if the near field is extended by being confined in an optical fibre. &lt;br&gt;&lt;br&gt;&#xA;The near field can be very far from the transmit location. Here is an example &amp;quot;Measurement of the spin of the M87 black hole from its observed twisted light&amp;quot;:&#xA;&lt;a href=&quot;https://arxiv.org/pdf/1904.07923.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://arxiv.org/pdf/1904.07923.pdf&lt;/a&gt;&#xA;They write &amp;quot;because the radio source has been spatially resolved at 1.3 mm wavelength by the ∼10000km EHT radio-interferometric baseline.&amp;quot; &lt;br&gt;&lt;br&gt;&#xA;It seems to me OAM might become useful at very high frequencies for short range communication to 5G base stations where extremely high data rates are needed and optical fibres might be unpractical:&#xA;&lt;a href=&quot;https://www.nec.com/en/press/201812/global_20181219_02.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.nec.com/en/press/201812/global_20181219_02.html&lt;/a&gt;&#xA;I do not think OAM would be useful on HF with ionospheric propagation. The antennas would have to be big enough to form lobes that are narrower than the size of the antenna on the other side.&lt;br&gt;&lt;br&gt;&#xA;Certainly an antenna system like this one will easily detect OAM on HF:&#xA;&lt;a href=&quot;http://www.lofar.org/about-lofar/general-information/introduction.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.lofar.org/about-lofar/general-information/introduction.html&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2020-09-02T14:22:25.017" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17238" PostTypeId="2" ParentId="17231" CreationDate="2020-09-02T15:58:40.440" Score="3" Body="&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/R-S-T_system&quot; rel=&quot;nofollow noreferrer&quot;&gt;RS(T)&lt;/a&gt; reporting system has always been arbitrary.  The original intent was for the receiving operator to estimate readability, signal strength, and tone by ear; there never have been universally-recognized standards regarding what should be R5 or S9.  Manufacturers muddied the waters somewhat by putting &lt;a href=&quot;https://en.wikipedia.org/wiki/S_meter&quot; rel=&quot;nofollow noreferrer&quot;&gt;S-meters&lt;/a&gt; in receivers, with S9 set as -73 dBm, which was reinforced by an &lt;a href=&quot;https://en.wikipedia.org/wiki/International_Amateur_Radio_Union#IARU_Region_1&quot; rel=&quot;nofollow noreferrer&quot;&gt;IARU Region 1&lt;/a&gt; technical recommendation.&lt;/p&gt;&#xA;&lt;p&gt;Because contests are competitions, parts of the QSO not necessary for efficient communication resulting in points are streamlined as much as possible.  Estimating a more realistic signal report, and more importantly copying varying signal reports, would require mental effort that would not result in more points, so it's not surprising that the contesting community has largely eliminated meaningful signal reports.  The fact that the RS(T) system is subjective and arbitrary provides sufficient cover for arguments about ethics, in the eyes of most contesters, and anyone who disagrees is free to transmit realistic signal reports.  All major contests that require signal reports compare transmitted and received signal reports like the rest of the exchange during the scoring process, and penalize contestants for incorrect copy.&lt;/p&gt;&#xA;&lt;p&gt;If most contesters clearly think meaningful signal reports serve no purpose in contests, why are signal reports still required in most contests?  I can think of several reasons:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Not every contest participant believes signal reports are useless.&lt;/li&gt;&#xA;&lt;li&gt;The vast majority of contest participants are casual, participating just to hand out a few contacts or to get a few more DX entities, states, provinces, grid squares, etc. in the log.  Casual contest participants expect contacts to include an exchange of signal reports, and many would be confused if the signal report were completely eliminated.  Confusion greatly slows the QSO rate, and is therefore avoided.&lt;/li&gt;&#xA;&lt;li&gt;When copying a contest QSO, especially a high-speed Morse QSO, the dummy 59 or 599 serves as a valuable delimiter: it alerts the receiving operator that the exchange, which must be quickly and accurately copied, comes next.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-09-02T15:58:40.440" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17240" PostTypeId="1" AcceptedAnswerId="17242" CreationDate="2020-09-03T09:14:06.633" Score="4" ViewCount="547" Body="&lt;p&gt;Per the subject, what is the capacitors purpose on a balun?&lt;/p&gt;&#xA;&lt;p&gt;Used a lot on wire wound ferrite toroidal baluns.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xfLXg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xfLXg.png&quot; alt=&quot;Balun&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17200" LastEditorUserId="17200" LastEditDate="2020-09-03T13:21:28.087" LastActivityDate="2020-11-02T20:57:47.877" Title="What is the capacitors purpose on a balun?" Tags="&lt;balun&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17241" PostTypeId="2" ParentId="17240" CreationDate="2020-09-03T13:28:07.113" Score="10" Body="&lt;p&gt;Without having the ability to measure this particular one, I expect that it's to counteract the inductive reactance introduced as a side-effect of the balun design/implementation.&lt;/p&gt;&#xA;&lt;p&gt;Edited to add: check out &lt;a href=&quot;https://ham.stackexchange.com/a/15412/1550&quot;&gt;this semi-related answer&lt;/a&gt;. In constructing his balun, he used a prototype with a variable capacitor to find the value with lowest SWR for his application, which implies a matching function.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2020-09-03T13:36:04.057" LastActivityDate="2020-09-03T13:36:04.057" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17242" PostTypeId="2" ParentId="17240" CreationDate="2020-09-03T22:42:04.797" Score="3" Body="&lt;p&gt;Adding a capacitor to a balun like that is not standard practice and is probably a bad idea.&lt;/p&gt;&#xA;&lt;p&gt;A bulun is supposed to be a somewhat frequency independent device which cancels out common mode current and a soon as that capacitor is added the unit becomes a tuned circuit with a limited bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;My guess is that someone added the capacitor to adjust the SWR, which might fix a matching problem but will also limit the bandwidth of whatever antenna system this is used with.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2020-09-03T22:42:04.797" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17243" PostTypeId="5" CreationDate="2020-09-04T03:17:12.443" Score="0" Body="" OwnerUserId="-1" LastEditorUserId="-1" LastEditDate="2020-09-04T03:17:12.443" LastActivityDate="2020-09-04T03:17:12.443" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17244" PostTypeId="4" CreationDate="2020-09-04T03:17:12.443" Score="0" Body="UV-5R is a series of handheld transceivers manufactured by Baofeng." OwnerUserId="17616" LastEditorUserId="17616" LastEditDate="2020-09-05T17:05:21.903" LastActivityDate="2020-09-05T17:05:21.903" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17245" PostTypeId="1" CreationDate="2020-09-04T09:04:14.683" Score="4" ViewCount="97" Body="&lt;p&gt;I have Echolink 2.0.908 installed in the default folder C:\Program Files (x86)\K1RFD\EchoLink&#xA;Every time I click on the shortcut to launch it, a copy of echolink.exe is created in the root of my G:drive.&lt;/p&gt;&#xA;&lt;p&gt;Every time I delete it from my G:\ drive and relaunch it creates another copy. If a copy already exists then it does not attempt to create another one. There is some dialoque when it does this but it goes away too fast for me to catch it.&lt;/p&gt;&#xA;&lt;p&gt;Why does it do that?&lt;/p&gt;&#xA;" OwnerUserId="17711" LastEditorUserId="8717" LastEditDate="2020-09-05T17:18:13.560" LastActivityDate="2021-02-03T02:03:45.603" Title="Why is Echolink copying the exe file to another drive letter everytime I launch it?" Tags="&lt;software&gt;&lt;echolink&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17246" PostTypeId="1" AcceptedAnswerId="17251" CreationDate="2020-09-04T15:50:50.187" Score="1" ViewCount="100" Body="&lt;p&gt;I have few similar questions regarding Radio waves communication particularly FM and AM type of Radio wave communication. Please bear with the naivety of the questions.&lt;/p&gt;&#xA;&lt;p&gt;Questions:&lt;/p&gt;&#xA;&lt;p&gt;Radio waves in FM and AM communications are transmitted through Air and we pick those signals with the help of our receivers.&lt;/p&gt;&#xA;&lt;p&gt;Assume few FM Radio stations such as 91.1MHz, 93.5MHz and 94.3MHz. (Area size radius - 10-15km)&lt;/p&gt;&#xA;&lt;p&gt;All these stations are operating simultaneously and depending on what frequency I tune receiver, that radio station is played. But the idea is that all the above 3 radio stations are working and operating simultaneously.&lt;/p&gt;&#xA;&lt;p&gt;Since the radio waves are EM waves, they propagate in air in the form of waves. So, technically, do these EM Waves propagate through the atmosphere by disturbing the air particles, I mean like, compression and rarefaction? I just want to understand how does these waves move from the transmitter to the receiver.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question 1 :&lt;/strong&gt; Do the EM waves travel by creating disturbances in the air particles such as compression and rarefaction?&lt;/p&gt;&#xA;&lt;p&gt;If they travel like that, won't the compression and rarefaction pattern of the 91.1MHz radio station affect the compression and rarefaction pattern of the 93.5MHz radio station and cause any disturbance/interference/cross-talk between each other before they even reach my receiver? How won't those 2 radio stations interfere between each other ?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question 2 :&lt;/strong&gt; What would be typical distance range in terms of radius (in km) of an FM/AM radio station? I tried to find. But unable to find it. Somewhere, I have read that the distance coverage is dependent upon the power of the FM Radio Transmitter? Could someone please throw some more information like a certain table which would provided the distance covered and the radius of coverage of the FM Radio?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question 3 :&lt;/strong&gt; If the FM Radio communication are a type of line of sight communication, how am I able to receive the FM Signal even if my receiver is not in direct line of sight of the FM Transmitter?&lt;/p&gt;&#xA;&lt;p&gt;P.S. The reason why I didn't make it as 3 separate questions because all these questions are very closely related so that I didn't want to burden the answer-er to the question or a similar fellow person who is having the same queries to find the answer under a single question itself.&lt;/p&gt;&#xA;" OwnerUserId="17049" LastActivityDate="2020-09-05T17:36:32.327" Title="Radio Waves propagation (Intuitive Understanding of Wave propagation)" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;propagation&gt;&lt;fm&gt;&lt;am&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17247" PostTypeId="1" CreationDate="2020-09-04T17:32:45.040" Score="2" ViewCount="84" Body="&lt;p&gt;I am currently trying to observe and obtain data from the meteorological satellites. I have constructed a V-dipole specifically for the 137 MHz and was able to observe the NOAA 15, NOAA 18, and NOAA 19. I was even able to decode some part of it to obtain images.&lt;/p&gt;&#xA;&lt;p&gt;Recently I found out that Meteor M2 satellite is going to be in my sight today and went out to record the baseband to observe it for later. However, even though I was directing towards the azimuth angles that the satellite needs to be with their elevation angles included, I could not receive anything that might resemble the existence of the satellite. I checked whether I can listen to FM radios as well right before trying to observe the satellite. This seems to point out that it is not about the setup. Also checked that the satellite I was observing is the alive one, not the one that crashed some time ago and there are images in the internet from that satellite approximately one week ago.&lt;/p&gt;&#xA;&lt;p&gt;Now, I am really curious on why I could not receive even a single part of the signal. Is there anyone with an idea on the topic?&lt;/p&gt;&#xA;" OwnerUserId="17674" LastActivityDate="2020-09-05T18:21:39.693" Title="Could not observe the Meteor M2 even though I scanned the sky at the time it passes with a high elevation degree (77). What might have happened?" Tags="&lt;software-defined-radio&gt;&lt;satellites&gt;&lt;sdrsharp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17248" PostTypeId="2" ParentId="17246" CreationDate="2020-09-04T19:44:19.963" Score="4" Body="&lt;p&gt;Radio waves (such as broadcast AM and FM) can travel through a vacuum (thus do not require air).  They are electro-magnetic (or EM) waves, the same as light waves (from the sun and stars, etc.), that can travel through space, but at a vastly lower frequency.&lt;/p&gt;&#xA;&lt;p&gt;The radius these EM waves can travel (unless blocked or absorbed) is the radius of the universe; but they fade with distance at r^3, so at some distance become smaller than background or thermal or quantum noise, and thus become undetectable.  Plus you would need to wait a long time for a signal if you are a light-year or so away from the source.&lt;/p&gt;&#xA;&lt;p&gt;EM Photons of different frequencies (or colors) do not interact or mix in free space, however a strong signal could jam your receiver from hearing a weaker signal that is nearby in frequency (because transistors and circuits, etc. turn out to be non-linear mixers.)&lt;/p&gt;&#xA;&lt;p&gt;EM waves travel not just line-of-sight, but also refract and reflect off of various media, including buildings and atmospheric layers, and thus depending on the environment, can be received &amp;quot;around corners&amp;quot;.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-09-05T17:36:32.327" LastActivityDate="2020-09-05T17:36:32.327" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17249" PostTypeId="2" ParentId="5397" CreationDate="2020-09-04T23:12:04.457" Score="1" Body="&lt;p&gt;This problem is very easy to model with any MOM tool, like EZNEC. E and H fields can be calculated using Near Field grid. Even better, exact power transfer from Tx to Rx antenna can be modeled. Modeling should include both Tx and Rx antenna, including Rx antenna termination resistance. Ratio of transmitted power and dissipation on Rx termination resistor becomes your coupling.&lt;/p&gt;&#xA;" OwnerUserId="17714" LastActivityDate="2020-09-04T23:12:04.457" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17250" PostTypeId="2" ParentId="17246" CreationDate="2020-09-05T00:31:25.957" Score="3" Body="&lt;p&gt;Question 2 &amp;amp; 3 not fully answered...&lt;/p&gt;&#xA;&lt;p&gt;You probably actually are within line of sight of the FM transmitter.  Broadcast transmitter antennas are typically placed on high towers specifically so that more people will be within line of sight of the tower.  Of course, you may not actually be able to &amp;quot;see&amp;quot; the tower because of atmospheric attenuation of visible light, trees and buildings in the way, etc.  Radio waves can easily pass through trees (with only some attenuation) and through or around buildings.  The power of the transmitter helps with weak receivers and penetrating thick buildings, but doesn't really help with propagation distance much.  The groundwave propagation distance is almost entirely reliant on the height of the antenna on the tower.&lt;/p&gt;&#xA;&lt;p&gt;However, there are multiple ways for the radio waves to get to you:&lt;/p&gt;&#xA;&lt;p&gt;Ground wave propagation is more or less line of sight, but also includes a slight refraction of the wave against the ground, which may extend propagation further depending on the wavelength.  Longer wavelengths refract more; FM broadcast is roughly 3m wavelength, and the refraction distance is roughly 3-7 miles beyond the 50-200 miles you'd already get from the height of the tower.  AM might get 100 miles groundwave propagation due to refraction.&lt;/p&gt;&#xA;&lt;p&gt;When you are just slightly beyond the range of line of sight propagation, you can get edge propagation, where radio waves refract around the edges of obstructions (like tall buildings or mountains) and create fresnel zones, alternating bands of good and bad reception, caused by constructive and destructive interference of multipath propagation.&lt;/p&gt;&#xA;&lt;p&gt;Finally, there's all kinds of strange propagation modes that are unreliable and a bit random.  For instance, ducting, where weather events can cause sharp changes in air layers that radio waves can reflect off of -- this can allow a weak signals to propagate hundreds of miles, but this occurs maybe only a few weeks of the year.  Meteor propagation, where the waves reflect off of the ionization trail from meteors (this might only last 10-30 seconds).  Or reflecting off of airplanes even.&lt;/p&gt;&#xA;&lt;p&gt;Radio waves can also reflect off of the ionosphere and travel 400 miles or more.  Typically this can't happen with 3m, unless conditions are just right, like with a strong solar flare.  However, this can easily happen under normal conditions with broadcast AM, which has a wavelength 150m - 500m, especially at night.  Generally, wavelengths longer than 10m start reflecting off of the ionosphere, but the effects of this are variable depending on the time of day and the time within the sun's 11 year sunspot cycle (in other words, space weather).&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-09-05T00:45:01.767" LastActivityDate="2020-09-05T00:45:01.767" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17251" PostTypeId="2" ParentId="17246" CreationDate="2020-09-05T05:47:43.873" Score="1" Body="&lt;p&gt;Question 1 : Do the EM waves travel by creating disturbances in the air particles such as compression and rarefaction?&lt;/p&gt;&#xA;&lt;p&gt;The answer is no. Electromagnetic propagation is not dependent on air, unlike sound waves. It can travel in free space. That being said, electrically or magnetically charged air particles, and Earth's magnetosphere can alter the trajectory (and phase) of the EM wave depending on frequency (as will gravity). This frequency dependence in the atmosphere is the reason lower(HF and below) frequencies bounce back to Earth and higher frequencies pass through to space. I would be remiss not to mention the Earth magneto-sphere's influence on bounced polarization for HF frequencies, they tend to become elliptical upon bouncing depending on the incidence angle to the magnetosphere.&lt;/p&gt;&#xA;&lt;p&gt;Question 2 : What would be typical distance range in terms of radius (in km) of an FM/AM radio station? I tried to find. But unable to find it. Somewhere, I have read that the distance coverage is dependent upon the power of the FM Radio Transmitter? Could someone please throw some more information like a certain table which would provided the distance covered and the radius of coverage of the FM Radio?&lt;/p&gt;&#xA;&lt;p&gt;This is a matter of height of the transmitting antenna, the power of the transmitting station and the frequency used.&lt;/p&gt;&#xA;&lt;p&gt;In the US, AM stations are in the range of 550 to 1720 KHz. At these frequencies, the signal may bounce several times in the atmosphere, with power dissipating with each bounce. It is not uncommon for a 50 KW transmitter to be heard 1,200 to 1,700 KM away. More distance is possible, depending on solar activity.&lt;/p&gt;&#xA;&lt;p&gt;The FM part of the question is answered in the response to the next question(3).&lt;/p&gt;&#xA;&lt;p&gt;Question 3 : If the FM Radio communication are a type of line of sight communication, how am I able to receive the FM Signal even if my receiver is not in direct line of sight of the FM Transmitter?&lt;/p&gt;&#xA;&lt;p&gt;This question is a matter of directed power versus atmospheric reflection. The FM acceptable bands, 29-~109MHz through the highest frequency current TV band, less than 700MHz in the US, are all reflected by the atmosphere (The higher the frequency the less atmospheric reflection occurs.)&lt;/p&gt;&#xA;&lt;p&gt;The answer to wasting power by shooting signals into space, is to design the antennas to maximally radiate at the lowest take-off angles. This technique maximizes the reflection to receiving stations well beyond the radio horizon even at higher frequencies.&lt;/p&gt;&#xA;&lt;p&gt;At US FM frequencies and maximum power levels(100 KW), the power on the third or fourth bounce is enough to receive a signal well beyond the radio horizon.&lt;/p&gt;&#xA;" OwnerUserId="16873" LastActivityDate="2020-09-05T05:47:43.873" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17252" PostTypeId="2" ParentId="17245" CreationDate="2020-09-05T06:14:59.173" Score="1" Body="&lt;p&gt;Remove all copies of your Echolink program and install it from a reputable source. This sounds like a virus or worm.&lt;/p&gt;&#xA;&lt;p&gt;From my experience, Echolink runs fine and the only files created are in the %temp% folder.&lt;/p&gt;&#xA;" OwnerUserId="16873" LastActivityDate="2020-09-05T06:14:59.173" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17253" PostTypeId="1" CreationDate="2020-09-05T08:20:35.953" Score="4" ViewCount="170" Body="&lt;p&gt;I'm looking for a good tutorial about oscillator design (electronically) for transmitter. The problems with current tutorials are almost all provide only schematics, some explain how it works. But noone show how we determine the transistor (select beta, or frequency range), determine resistor values (bias voltage and output modulation voltage), or capacitor values, etc. It is so hard to experiment and learn by myself about transmitter.&lt;/p&gt;&#xA;&lt;p&gt;Not to mention about next stage amplifier, how sound added to the signal, and how filter works (I heard for x'tall filter, we should select x'talls with the closest frequency as possible. But why, I don't know. No need to answer this.). Basically, not practical thus cannot learn in depth.&lt;/p&gt;&#xA;" OwnerUserId="17716" LastActivityDate="2020-09-13T17:12:31.467" Title="Design of oscillator" Tags="&lt;electronics&gt;&lt;oscillator&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17255" PostTypeId="2" ParentId="17253" CreationDate="2020-09-05T16:00:04.920" Score="6" Body="&lt;p&gt;I would like to applaud your interest not only for homemade transmitters but also a theory! I started to build my own receivers and transmitters not a long time ago and completely understand how frustrating it can be at the beginning.&lt;/p&gt;&#xA;&lt;p&gt;However this is a broad and complicated topic. If we consider only oscillators for transmitters, there are LC oscillators - Clapp, Colpits, Hartley, and several other, crystal oscillators, various types of VFOs, also PLLs, DDSs, you name it. People write not a single tutorial but &lt;strong&gt;books&lt;/strong&gt; on this subject.&lt;/p&gt;&#xA;&lt;p&gt;OK I can give you a simple VXO schematic that I used in a CW transmitter not a long time ago:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/45cyh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/45cyh.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is a so-called Super VXO. Q2 is a buffer, Q1 and all the left part is an oscillator. How does it work? OK basically it's a Clapp crystal oscillator, but a crystal is de-Q'ed with a second crystal and also L1 and VC1. What brings a question like &amp;quot;what is Q&amp;quot;, &amp;quot;what I need a buffer for&amp;quot;, &amp;quot;what are R5 and C3 for&amp;quot;, also about oscillator stability, amplification (it's output is only 4 dBm, now what is dBm and how much of it do I need...), filtering, keying, and &lt;a href=&quot;https://en.wikipedia.org/wiki/Barkhausen_stability_criterion&quot; rel=&quot;nofollow noreferrer&quot;&gt;Barkhausen criterion&lt;/a&gt;. If you are interested in this particular schematic here is a &lt;a href=&quot;https://eax.me/supervxo/&quot; rel=&quot;nofollow noreferrer&quot;&gt;tutorial&lt;/a&gt;. It's in Russian, but Google Translate should help.&lt;/p&gt;&#xA;&lt;p&gt;However the goal was to show how a simple schematic creates more and more questions, which create even more questions, and this is why it's impossible just to write a simple tutorial on oscillators.&lt;/p&gt;&#xA;&lt;p&gt;Here are several books that helped me a lot:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;strong&gt;ARRL Handbook&lt;/strong&gt;. Consider it a starting point with a list of your future projects and references to further reading.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Hands-On Radio Experiments&lt;/strong&gt;, vol 1, 2 and 3. Ditto. Vol 1 is especially worth reading.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Practical Electronics for Inventors, 4th Edition&lt;/strong&gt;. Good source of information on various topics, not excluding oscillators and filters. Especially filters.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Amateur Radio Transceiver Performance Testing&lt;/strong&gt;. This one explains in great detail what are IMD, MDS, etc and how to measure them. You will need this.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Solid State Design for the Radio Amateur&lt;/strong&gt;. It's not new, circa 1977. But it explains many things well, mixers especially. The good thing about SSD is that it's &lt;a href=&quot;https://archive.org/details/SolidStateDesignForTheRadioAmateur1986/mode/2up&quot; rel=&quot;nofollow noreferrer&quot;&gt;available for free&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Experimental Methods in RF Design&lt;/strong&gt;. The newer book by the authors of SSD. It's great but I wouldn't recommend to start from it. Some context is required for better understanding.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;My advice would be to read at least (1), (5) and (6), but better - all of them. Start with simple projects. Build an attenuator or a 50 Ohm dummy load. Measure them. You will need both to test your transmitter. Then build a simple LC oscillator. Measure it. Is it stable? Why not? Build a crystal oscillator. Is it better? Is it possible to make the frequency adjustable? How clean is an output signal? Is it possible to clean it up? Build a filter. Is it any good? Did it help?&lt;/p&gt;&#xA;&lt;p&gt;In other words proceed one little step after another. And soon you will be on the air with your first QRP rig. 73s de R2AUK&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-09-06T21:13:13.363" LastActivityDate="2020-09-06T21:13:13.363" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17256" PostTypeId="1" CreationDate="2020-09-05T16:27:29.623" Score="3" ViewCount="173" Body="&lt;p&gt;I tried to use SA612 as a frequency mixer. Since it's a Gilbert cell, it has a high input impedance. Thus I added a pair of transformers as &amp;quot;Experimental Methods in RF Design&amp;quot; book suggests:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/N1gKo.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/N1gKo.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The mixer seems to work:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aBKqy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aBKqy.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Here I'm using 15 Mhz 12 dBm LO signal, RF is -16 dBm and I change it in 1-3 Mhz range to make sure that the mixer works as it supposed to. Two smaller signals on the left and on the right are IF, e.g. mixing products. 15 Mhz signal in the middle is a LO leakage. It's something you would expect to see in a mixer. LO can be lowered to 8 dBm, which causes 3 dB loss in mixing products.&lt;/p&gt;&#xA;&lt;p&gt;(For the record, I also tried to use a simpler circuit without transformers. It kind of worked but the level of mixing products where MUCH lower.)&lt;/p&gt;&#xA;&lt;p&gt;The result surprised me. I've been using diode ring mixers before and observed a much higher level of IF. For instance here I'm using a balanced diode ring mixer made of two FT50-43 ferrite cores and four 1N5818 Schottky diodes:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cMj89.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cMj89.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;RF is the same -16 dBm, but LO is only -18 dBm. This mixer can be safely driven with 10-13 dBm which gives a much higher IF level.&lt;/p&gt;&#xA;&lt;p&gt;This brings me to the question. Is an IF level which I got with SA612 an expected result or maybe I'm doing something wrong? Maybe you could suggest another test circuit?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-09-06T09:43:44.380" LastActivityDate="2020-09-06T09:43:44.380" Title="What is an expected IF level of SA612?" Tags="&lt;diy&gt;&lt;electronics&gt;" AnswerCount="0" CommentCount="13" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17257" PostTypeId="2" ParentId="17247" CreationDate="2020-09-05T18:21:39.693" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;I checked whether I can listen to FM radios as well right before trying to observe the satellite. This seems to point out that it is not about the setup.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;That's not true. Your ability to receive something else is &lt;strong&gt;still&lt;/strong&gt; (like in your last question) not an indication of you being able to receive this.&lt;/p&gt;&#xA;&lt;p&gt;On the contrary. If the settings, especially the antenna, is right for a local FM station, chances are they are suboptimal for receiving a QPSK satellite downlink. You might actually be blocked by these things you were able to receive properly!&lt;/p&gt;&#xA;&lt;p&gt;All in all, nobody can tell you why you couldn't hear the satellite. Maybe the space weather was suboptimal, maybe some nearby transmitter saturated your receiver, maybe your gain was too high, or too low, maybe you would have needed an LNA and a proper bandpass filter, maybe you have a faulty antenna connector...&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-09-05T18:21:39.693" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17260" PostTypeId="1" AcceptedAnswerId="17262" CreationDate="2020-09-05T23:06:58.853" Score="1" ViewCount="191" Body="&lt;p&gt;I’m in Sacramento and have an EFHW antenna about 30’ up. I expected to be able to hear the W6WX 14.100 beacon without issue but I cannot. The distance is about 140 miles and the beacon transmits its call at 100w.&lt;/p&gt;&#xA;&lt;p&gt;I’m trying to determine if I have an antenna issue (I &lt;strong&gt;can&lt;/strong&gt; hear some 20m CW signals) or if my expectations are just wrong.&lt;/p&gt;&#xA;" OwnerUserId="17712" LastActivityDate="2020-09-07T20:14:51.097" Title="Sanity check: Should I be able to hear this 20m beacon?" Tags="&lt;antenna&gt;&lt;propagation&gt;&lt;beacon&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17261" PostTypeId="2" ParentId="5397" CreationDate="2020-09-06T07:25:36.260" Score="1" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;In my situation, do I have to use the second formula to find near-field reactive region boundary?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The choice between the two equations you provide is determined by if the antenna is &amp;quot;electromagnetically short&amp;quot;, so it isn't about if it is &amp;quot;very short&amp;quot; from a human's perspective of short, but rather how its length compares to the wavelength it emits. More specifically the equation &lt;span class=&quot;math-container&quot;&gt;$n_n = \lambda$&lt;/span&gt;, where &lt;span class=&quot;math-container&quot;&gt;$n_n$&lt;/span&gt; is the radius of the near field, is used anytime the length of the antenna is less than half of the wavelength of the frequency it is transmitting. Note that the far-field is considered to be &lt;span class=&quot;math-container&quot;&gt;$n_f = 2\lambda$&lt;/span&gt; where &lt;span class=&quot;math-container&quot;&gt;$n_f$&lt;/span&gt; is the distance from the antenna where the far-field beings, so there is some area between these two where you are neither in the near-field or the far-field and instead expiernce effects of both.&lt;/p&gt;&#xA;&lt;p&gt;2.45 GHz has a wavelength of 12cm. Since your antenna is 14 cm in length it is not &amp;quot;electromagnetically short&amp;quot; and as such would not use the above equation and instead would use what is called the Fraunhofer Distance which is governed by the following equation &lt;span class=&quot;math-container&quot;&gt;$n_n = \frac{2D^2}{\lambda}$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;If I have to harvest within the reactive field of the transmitting antenna, can I use a dipole antenna or do I have to use a coil?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Coils are basically space-efficient for interacting with the near-field, specifically the magnetic field. They wont be very good at transmitting or receiving far-field, but they will be optimal at interacting with near-field. A capacitor design would be similarly true for the electric field component of the near-field. So a dipole would be less efficient for the space it took up for either meanwhile a inductor or capacitor configuration or a combination of the two would be your best bet if your only interest is harvesting in the near-field. the more the better. You can actually think of a faraday cage as the capacitor version of this if it were to encase the antenna completely. then the usual grounding cable you would attach to it would instead be your power line where you siphon off the power. Since it would completely envelop the antenna it would be pretty effective too. But a series of coils would also be effective.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;If I can use a dipole antenna within the reactive region for harvesting, how would I find its impedance?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;You can use it, and it will harvest energy, but you'll just waste a lot of space and it wont be nearly as efficient. You wont even be able to harvest all the flux that passes through it as it will re-radiate any energy it harvests to a certain extent. So a dipole really isnt your best way to harvest at all. But if you do use it just make sure its an antenna tuned to the frequency of the transmission for best results. The exact impedance isnt really the important part in the dipole case. The impedance will matter, however, if your using a coil. In that case just calculate the cut off frequency of the coil and make sure your coil is ideally about 10x bigger than that. If you want to harvest even more energy use additional coils rather than a single bigger coil.&lt;/p&gt;&#xA;&lt;p&gt;All the above equations and a bit of detail and references on them can be found on wikipedia here: &lt;a href=&quot;https://en.wikipedia.org/wiki/Near_and_far_field#Regions_according_to_electromagnetic_length&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Near_and_far_field#Regions_according_to_electromagnetic_length&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17721" LastActivityDate="2020-09-06T07:25:36.260" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17262" PostTypeId="2" ParentId="17260" CreationDate="2020-09-06T08:02:08.417" Score="6" Body="&lt;p&gt;140 miles is too far away on 20m for groundwave propagation and the &amp;quot;skip&amp;quot; zone or first hop distance, given 20m's general DX capabilities, is much longer than 140 miles. So, I wouldn't expect to hear it &amp;quot;without issue&amp;quot;. However, when you're tuned to 14.100, you should be able to copy other beacons in the rotation, if your antenna works.&lt;/p&gt;&#xA;" OwnerUserId="17676" LastActivityDate="2020-09-06T08:02:08.417" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17263" PostTypeId="2" ParentId="17235" CreationDate="2020-09-06T09:03:11.380" Score="3" Body="&lt;p&gt;So the problem here is that your setup is not sufficient to tell you what you want to know about the ferrite core.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;In my set up I have a ferrite core where I made a number of turns on. I connected the signal from my signal generator and one channel of the oscilloscope to one end of the wire to monitor the input.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;So in this setup your first probe is basically just sampling the input signal, and your second probe is wired to ground. If this were an ideal circuit where the wires connected to the inductor had no parasitics (namely inductance or capacitance) then all you would see would be two flat graphs with no variation at all.&lt;/p&gt;&#xA;&lt;p&gt;The reason your seeing variation in the graph is because there is a length of wire between the output of your inductor of some length before connecting to your ground. As such this length of wire has some small amount of parasitics but is also being inductively coupled with your inductor and thus is inducing some voltage swing as seen in the graph. Effectively the red wire your output probe is connected to is creating a transformer with the coil you are testing. This is why you notice a larger impact on the blue line than the red, because the red wire is very short and connected very close to the signal source.&lt;/p&gt;&#xA;&lt;p&gt;The peak your seeing in the blue line around 0.1MHz also has little to do with the ferrite core's maximum frequency. It is most likely the coils self resonance. You have to understand a coil has parasitic capacitance sitting between each loop of the coil. This essentially causes it to have a relatively large inductance but also a smaller parasitic capacitance. This will cause any coil to self-resonate at a given frequency as you see here. Even if you had an air-core with no upper frequency limit you'd see a similar self-resonance (though at a different frequency). You could test this theory by spreading your coil out. Take the coil you wound there and keep the same number of windings but instead of having it all bunched up to one side of the core try to evenly space it across the core. This will significantly lower the parasitic capacitance and the peak you see should be much less noticable if not go away completely.&lt;/p&gt;&#xA;&lt;p&gt;So long story short, I'm sorry to say, none of what you have here is really going to help you.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;How can I interpret this result (making sense of it with regards to it's actual performance with regards to suppressing noise at 150kHz?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Well you cant, the results are bogus. but lets try to address how you can determine if its good at suppressing noise at 150kHz.. but the answer is, it depends. As a general rule if you start pushing a core past its frequency limit they become lossy. That is your inductor's impedance will shift to have a &lt;strong&gt;real&lt;/strong&gt; resistance and the reactance may also be affected. this may or may not be a problem depending on the details.&lt;/p&gt;&#xA;&lt;p&gt;If all you want to do is reject any signals below 150kHz or any signals above 150kHz and let the others pass, then I would not use an inductor at all. for that you can use a single capacitor in a low-pass or high-pass configuration, capacitors can be a bit less problematic than inductors so its usually what I'd recommend.&lt;/p&gt;&#xA;&lt;p&gt;For a high-pass filter that only rejects signals below 150kHz then put a 10nF capacitor in series with the signal and a 100 ohm resistor after the capacitor attached to ground. For a low-pass filter that only rejects signals above 150kHz use the same components but swap the resistor and the capacitors position.&lt;/p&gt;&#xA;&lt;p&gt;The only way you'd have to use a inductor here is if you want a band-pass filter. that means if you want to reject frequencies above &lt;strong&gt;and&lt;/strong&gt; below 150kHz and only let frequencies at or near 150kHz pass. For that you would put a 10nF capacitor in series with the signal, and then a 112uH inductor in series with that.&lt;/p&gt;&#xA;&lt;p&gt;The nice thing is that the inductor's value is low enough that you have no need to use a ferrite core at all, which is really only needed when you need a large value inductor. For a 112uH inductor you can wind an air-core inductor which has effectively no frequency limitations and is much easier to work with than one with a core. for that take some really thin wire and rap it around a 0.5&amp;quot; diameter tube with 200 turns, and make sure the overall length is evenly spaced about 2 inches. Or you can use this &lt;a href=&quot;https://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml&quot; rel=&quot;nofollow noreferrer&quot;&gt;online calculator&lt;/a&gt; to try to get dimensions that suit you. You can use some clue to ensure the inductor keeps its shape.&lt;/p&gt;&#xA;&lt;p&gt;If you really do want to try to calculate the upper frequency limit on a ferrite core inductor, though, you'd have to measure the voltage across it and the current through it. You could then look at the phase difference between this two values as well as the amplitude and use that to calculate the complex impedance at a given frequency. Ideally it should have very low real component and most of its impedance would be the imaginary component. This would show as a 90 degree, or very close to 90 degree phase shift between the two graphs when it is operating at an optimal frequency and the phase shift would decrease as the inductor is pushed passed its maximum frequency.&lt;/p&gt;&#xA;" OwnerUserId="17721" LastActivityDate="2020-09-06T09:03:11.380" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17264" PostTypeId="2" ParentId="17235" CreationDate="2020-09-06T16:29:39.833" Score="6" Body="&lt;p&gt;It appears that all three 'scope probes are set to their &amp;quot;X1&amp;quot; position.&lt;br&gt;&#xA;As such, each probe includes the oscilloscope's internal 1M input resistance in parallel with about 20pF input capacitance. But more importantly, the capacitance of the probe's cable is in parallel too. The total 'scope parallel capacitance is roughly 100pf.&lt;br&gt;&lt;/p&gt;&#xA;&lt;p&gt;Since there are &lt;em&gt;two&lt;/em&gt; probes on the function generator's output, the generator is loaded with about 200pf in parallel with 1M resistance. Both are mostly insignificant compared with a function generator's 50 ohm output resistance, especially below 1MHz.&lt;br&gt;&lt;/p&gt;&#xA;&lt;p&gt;The 100pf capacitance from the probe at test-inductor output &lt;strong&gt;is significant&lt;/strong&gt;. It resonates with inductance - frequency gives a rough clue of the test-inductor inductance. Since resonance is at roughly 100kHz, inductance would be near 25mH.&lt;br&gt; The Q of the resonant peak also gives a clue of resonant losses in the inductor at 100 kHz., shown as R5 (45k) in the circuit below:&lt;br&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/qK49O.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qK49O.png&quot; alt=&quot;inductor test fixture schematic&quot; /&gt;&lt;/a&gt;&lt;br&gt; The plot below shows V(n001) at the &amp;quot;'scope input&amp;quot;. Function generator output resistance is guessed at R3=50 ohms:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Fpwy7.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Fpwy7.png&quot; alt=&quot;frequency plot&quot; /&gt;&lt;/a&gt;&#xA;&lt;br&gt; Some function generators have output resistance of 600 ohms. This resistance actually gives a better match to OP's graph:&lt;a href=&quot;https://i.stack.imgur.com/LJP3d.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LJP3d.png&quot; alt=&quot;Function generator output resistance = 600 ohms&quot; /&gt;&lt;/a&gt;&#xA;&lt;br&gt; Be aware that setting probe to &lt;strong&gt;X10&lt;/strong&gt; attenuator setting will dramatically reduce probe input capacitance from about 100pf down to about 11pf. And input resistance changes to 10MEGohm from 1MEGohm.&lt;br&gt;&#xA;A scan to higher frequency might reveal the inductor's &lt;strong&gt;self-resonant-frequency&lt;/strong&gt;, which could be used to estimate the value of a capacitor in parallel with R5. It would cause an anti-resonant dip in the plot. This frequency might allow you to estimate the upper limit of the inductor's usefulness as a choke.&lt;br&gt;&#xA;In the OP plot that omits frequency above 1MHz., the self-resonant frequency would either be greater than 1MHz., or else the inductor is so lossy, that it is not visible.&lt;/p&gt;&#xA;" OwnerUserId="11132" LastEditorUserId="11132" LastEditDate="2020-09-06T19:13:44.653" LastActivityDate="2020-09-06T19:13:44.653" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17265" PostTypeId="1" CreationDate="2020-09-07T03:37:46.560" Score="2" ViewCount="104" Body="&lt;p&gt;I am currently modeling a yagi antenna using Matlab and after I optimized the antenna, it gave me a director length shorter than the exciter itself (even if the optimization gave me a good gain).&lt;/p&gt;&#xA;&lt;p&gt;From what I have read and learned from textbooks, the directors of a yagi Antenna should always be shorter than the dipole in order to help direct the EM waves forward in a specific direction, and hence, increase the directivity.&lt;/p&gt;&#xA;&lt;p&gt;In fact, when I even tried to reduce the length of the director to a dimension shorter than the dipole, it gave me a lower dBi (9.17dBi instead of 13dBi).&lt;/p&gt;&#xA;&lt;p&gt;Why does &lt;strong&gt;DirectorLength &amp;gt; DipoleLength&lt;/strong&gt; gives better gain (dBi)? Shouldn't it be the opposite instead?&lt;/p&gt;&#xA;&lt;p&gt;Properties of the antenna simulated with Matlab:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8uG6m.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8uG6m.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17725" LastEditorUserId="76" LastEditDate="2020-09-07T14:03:50.360" LastActivityDate="2020-09-07T20:31:04.033" Title="Yagi Antenna - Elements Length" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;yagi&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17266" PostTypeId="2" ParentId="17265" CreationDate="2020-09-07T11:24:46.187" Score="5" Body="&lt;p&gt;I suspect your results are an artifact of your optimization methodology.&lt;/p&gt;&#xA;&lt;p&gt;I simulated the design described in the link with NEC2 using the &lt;em&gt;EZNEC&lt;/em&gt; front-end. For reference, &lt;em&gt;EZNEC&lt;/em&gt; calculates the gain as 13.03-dBi in free space with 2-mm diameter elements (the link doesn't specify element diameter). I believe this is close enough to your model's gain of 13.6-dBi for the purpose of answering your question.&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;EZNEC&lt;/em&gt; calculates the driving-point impedance of your model's driven element as 40-j99 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, which is not a good match to the 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; transmission lines in common use. Increasing the length of the driven element by about 14% - thus, making it &lt;em&gt;longer&lt;/em&gt; than the directors - improves the match by changing the input impedance to 59+j6 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; while maintaining the 13.03-dBi forward gain.&lt;/p&gt;&#xA;&lt;p&gt;Interestingly, the driven element is now longer than the &lt;em&gt;reflector&lt;/em&gt;, which is also not usual. The radiation pattern of your design show many side-lobes:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zLH43.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zLH43.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I suspect that &amp;quot;cleaning up&amp;quot; the pattern will result in a design with elements whose lengths obey the customary relationships seen in the hundreds of antennas described in the literature.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-09-07T11:24:46.187" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17267" PostTypeId="2" ParentId="17253" CreationDate="2020-09-07T13:54:09.053" Score="1" Body="&lt;p&gt;I find these &lt;em&gt;&lt;a href=&quot;https://www.electronics-tutorials.ws/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Electronics Tutorials&lt;/a&gt;&lt;/em&gt; on &lt;a href=&quot;https://www.electronics-tutorials.ws/oscillator/oscillators.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Oscillators&lt;/a&gt; to be very instructive. &lt;em&gt;&lt;a href=&quot;https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;LTSpice&lt;/a&gt;&lt;/em&gt;, the free electronic simulator from Analog Devices, includes example circuits for Clapp, Colpitts and Hartley oscillators. Perturbing the values of the example circuits' elements can help you develop a fuller understanding of how each affects the oscillators' performance parameters.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-09-07T13:54:09.053" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17268" PostTypeId="2" ParentId="17265" CreationDate="2020-09-07T17:07:39.690" Score="1" Body="&lt;p&gt;The driven element length is chosen to give the right impedance for your matching network. There's no rule about it being longer or shorter than anything.&lt;/p&gt;&#xA;&lt;p&gt;The directors(s) are always shorter than the reflector(s) because their &lt;em&gt;self&lt;/em&gt; impedance, combined with their spacing, is important in establishing the correct currents on each element.&lt;br /&gt;&#xA;(of course I mean simple thin free dipoles, if they're loaded or bent etc then their physical length doesn't reflect their electrical length any more)&lt;/p&gt;&#xA;&lt;p&gt;The impedance of a resonant driven element is usually lower than 50 Ohms, so there are various tricks to match it. One of them would be a parallel capacitor, for that you would need to lengthen the driven element to make it inductive. Another would be a parallel inductor, though I've never seen this in practice, that would require a shorter driven element. But it is entirely your choice, depending on what impedance you want to see. Any length within reason is going to be ok.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-09-07T17:07:39.690" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17269" PostTypeId="2" ParentId="17260" CreationDate="2020-09-07T20:14:51.097" Score="5" Body="&lt;p&gt;Rather than just answer your question, I'll show you how to answer it yourself.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.voacap.com/&quot; rel=&quot;noreferrer&quot;&gt;VOACAP&lt;/a&gt; is a good tool for all kinds of HF propagation questions. Entering your location and the location of the beacon into the point-to-point predictions tool, with parameters set to CW, 100 W, dipoles at 33 feet, and &amp;quot;Residential&amp;quot; noise, clicking on &amp;quot;Prop Charts&amp;quot; and then selecting only the 20 meter trace yields this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/sRKdY.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/sRKdY.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;With these parameters, this shows that at best you'll be able to hear the beacon 5% of the time, and only between 05:00 and 15:00 UTC, optimally around 11:00 UTC. So it is not unusual that you are unable to hear the beacon.&lt;/p&gt;&#xA;&lt;p&gt;Clicking &amp;quot;REL map&amp;quot; (REL means reliability) at the bottom generates this insightful image:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/pCBxG.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/pCBxG.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is only valid for one time of day and year, and one band, which you can see in the text at the top. At this particular time (September, 19:00 UTC, 20 meters) you have good coverage of the Midwestern United States, Mexico, Central America, Central and Western Canada, and a lot of the Atlantic Ocean, with fair coverage of Northern Africa, Europe, and some of the Middle East. I'd wager you can find beacons in those regions that you can hear.&lt;/p&gt;&#xA;&lt;p&gt;That big blue area (indicating unreliable communication) around your station at Sacramento is called the &amp;quot;skip zone&amp;quot;. 20 meters doesn't travel too far by ground wave, so to communicate with a nearby station you'd have to reflect the signal off the ionosphere almost directly overhead. But at this time of day, at these frequencies, the ionosphere isn't reflective at those angles: all the radiation at near vertical angles simply escapes to space.&lt;/p&gt;&#xA;&lt;p&gt;You can also see a 2nd skip zone (passing through Ohio and Kentucky) where 1 skip is too short but 2 skips is too far, and 3rd skip zone through the middle of the Atlantic Ocean.&lt;/p&gt;&#xA;&lt;p&gt;Decreasing the frequency shrinks the skip zone as the ionosphere becomes more reflective at nearly vertical angles. This is the same map, only for 30 meters:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fXvaj.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fXvaj.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Notice how the the ring around your station is smaller. Your maximum distance is less, but the skip zone is smaller. This is because during the day, absorption of lower frequencies is higher (limiting the maximum range) but reflection at high angles is better (shrinking the skip zone).&lt;/p&gt;&#xA;&lt;p&gt;At 40 meters, the skip zone is pretty much gone, but it's also quite useless for long-distance communication:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vKFwk.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vKFwk.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;But if you did want to communicate over long distances on 40 meters, you only need to wait for night. This is 40 meters 12 hours later, at 07:00 UTC:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tJZxj.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tJZxj.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-07T20:14:51.097" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17270" PostTypeId="2" ParentId="17265" CreationDate="2020-09-07T20:31:04.033" Score="3" Body="&lt;p&gt;There are many properties of an antenna that could be optimized:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Maximum gain&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.tutorialspoint.com/antenna_theory/antenna_theory_beam_width.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Beam width&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Front-to-back ratio&lt;/li&gt;&#xA;&lt;li&gt;Feedpoint impedance&lt;/li&gt;&#xA;&lt;li&gt;SWR bandwidth&lt;/li&gt;&#xA;&lt;li&gt;Robustness to manufacturing variation&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Typical designs aim for &amp;quot;pretty good&amp;quot; in all of these parameters. Optimizing for one parameter exclusively will typically come at the detriment of others, and result in unusual designs.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-07T20:31:04.033" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17271" PostTypeId="1" AcceptedAnswerId="17499" CreationDate="2020-09-08T13:09:14.943" Score="2" ViewCount="79" Body="&lt;p&gt;I am in the process of building a SWR meter with VNA-like features. I'd be really interested to hear from fellow hams any input, suggestions, or tips they have regarding this before I go get it mass produces. I'll share the schematic and technical details but I am also looking for feedback just in terms of usability or features or any criticism really&lt;/p&gt;&#xA;&lt;p&gt;So basically I'm building an Arduino shield where the primary use case is to be a SWR meter with an LCD display (not depicted here as that is a seperate shield). But it provides all the functions of a Vector Network Analyzer (VNA) and as such goes well beyond your typical SWR meter.&lt;/p&gt;&#xA;&lt;p&gt;Because the primary use case here is to act as an inline meter on a transmission line with an existing transmitter its not designed as a typical VNA would be using mixers. The only thing it doesn't have that a VNA would have is a function generator, as it relies on the transmitter to do that, and the directional coupler would be external. However I have designed it in a modular way so not only can the directional coupler be swapped out for one the user prefers or more suited for their setup, but it can also be configured to work more like a traditional VNA as well. With the additional of an additional shield with an in-built low power directional coupler and a sine wave generator it would be possible to also pop on this other shield and effectively have a handheld VNA instead. Being modular there are also several other possibilities for how this device can be configured including as a remote SWR meter so you can have a meter at both the transmitter and the antenna to properly calculate feedline loss, or to understand how the complex impedance of your antenna changes with frequency.&lt;/p&gt;&#xA;&lt;p&gt;Because of its role as an in-line meter in an existing antenna system it also provides functions a traditional VNA would not, specifically the ability to analyze properties of the transmitter such as accurately determining the true RMS under modulation or precisely determining the frequency the transmitter is transmitting on. Perhaps in the future I may add other features as well either in software of hardware.&lt;/p&gt;&#xA;&lt;p&gt;Some specifications:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Operates 1 MHz to 500 MHz&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Can measure input signals from -52dBm to 0dBm (adjust external directional coupler and attenuator to handle any power transmitter).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Inputs are 50 ohm matched but if building yourself you can switch out different resistors to match different impedances&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Note: This is an open-source project and free for anyone else to replicate my work. At some point I may sell kits and/or the printed PCB to people to make it cheaper than needing to pay to get your own PCB printed. So I'd like to make sure if I provide PCBs they have been scrutinized and tested first.&lt;/p&gt;&#xA;&lt;p&gt;The link to the projects source can be found here for anyone who wants to access the actual files.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://git.qoto.org/roes/roes-hardware/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://git.qoto.org/roes/roes-hardware/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Here is a picture of the schematic:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GznW4.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GznW4.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Here is an older picture of the UI in demo mode. The data on the screen is intentionally bogus, and the glitches in the rendering have since been fixed.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WeLib.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WeLib.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is a four layer board so youll have to see the GIT repo if you want to pick apart my layout in detail. But for now I will share the front side and back side so you can at least get a sense of my placement of the chips and my use of shielding.&lt;/p&gt;&#xA;&lt;p&gt;Front:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dzv7l.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dzv7l.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Back:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vL7QG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vL7QG.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17721" LastEditorUserId="17721" LastEditDate="2020-09-08T15:16:33.360" LastActivityDate="2020-10-22T10:31:39.910" Title="Looking for criticisms on my VNA-like SWR meter I am designing" Tags="&lt;diy&gt;&lt;antenna-system&gt;&lt;impedance&gt;&lt;impedance-matching&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17272" PostTypeId="2" ParentId="16318" CreationDate="2020-09-08T13:31:01.383" Score="1" Body="&lt;p&gt;Well this is rather simple and in reality you dont need to ensure the far end is open, you can leave your antenna attached and it will still work just fine if all you are trying to do is determine the length of your feedline.&lt;/p&gt;&#xA;&lt;p&gt;Before I get into the explanation let me share a video I did years ago demonstrating the exact setup you are trying to do using a function generator and oscilloscope to determine the length of a feedline. You can see that &lt;a href=&quot;https://youtu.be/BzseBv0hhWA&quot; rel=&quot;nofollow noreferrer&quot;&gt;video here&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;So its actually really simple, you hook a line from the output of your function generator into a Tee connector which connects to the port of your oscilloscope and the other port into the end of your feedline that is in your shack. Next you setup your function generator to produce a pulse output, that is a the a short pulse repeatedly over and over, make sure the pulse is significantly shorter in time than the space between pulses. While not strictly needed you will get the best results if yoru function generators output impedance is set to match the feedline (usually 50 ohms) and if your oscilloscope is set to high impedance mode (the default and sometimes only mode for some lower end o-scopes).&lt;/p&gt;&#xA;&lt;p&gt;Next you set the trigger on your oscope until its able to detect the pulse. At this point what youll notice is the initial pulse on your oscope created from the outgoing pulse, but then shortly after that shifted a bit to the right you will se a second pulse. The second pulse may be of a slightly different shape or may even be completely inverted depending on the characteristics of your antenna. Now since you only care about the length of your feedline the actual shape of the return pulse really doesnt matter. What you want to do is compare the time difference between the very start of the rise on the first pulse with that of the rise (or if inverted fall) of the second pulse. Not that time difference and we will call that Δt.&lt;/p&gt;&#xA;&lt;p&gt;So Δt is basically the time it took for the pulse to go from the feed point on your feedline where the o-scope is connected to your antenna and back again. Therefore since we only care about the length of the antenna we really only care about half that value, which will tell you the time it took for the pulse to go from your oscope to the antenna.&lt;/p&gt;&#xA;&lt;p&gt;Now electrical waves through a feedline move fairly close to the speed of light but still not quite. Look up the model of feedline you have and in the datasheet a value is always reported called the Velocity Factor, this represents the percentage of the speed of light a wave will move through your feedline so basically c = C*vf, where c is the speed of an electrical wave in your feedline, C is the speed of light in a vacuum, and vf is the velocity factor of your feedline.&lt;/p&gt;&#xA;&lt;p&gt;So now we know the speed the wave moves, and the time it takes to traverse the feedline, so it is a simple matter to actually calculate the distance, that would just be c*Δt/2, and now you have your feedline length.&lt;/p&gt;&#xA;" OwnerUserId="17721" LastActivityDate="2020-09-08T13:31:01.383" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17274" PostTypeId="2" ParentId="5228" CreationDate="2020-09-08T17:09:22.183" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://www.amsat.org/status/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amsat.org/status/&lt;/a&gt; will show you a list of birds and if there has been any activity reported during the last week.  Reports are crowd-sourced, the page allows you to drill down into each report and see who reported and when.  Even reports of &amp;quot;not heard&amp;quot; are shown.&lt;/p&gt;&#xA;" OwnerUserId="17733" LastActivityDate="2020-09-08T17:09:22.183" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17275" PostTypeId="1" CreationDate="2020-09-08T17:37:31.233" Score="4" ViewCount="77" Body="&lt;p&gt;In a few weeks I'm hoping to set up a solid state linear amplifier at a remote shack that I've set up at the house of a friend who lives in a rural area. I've been connecting to this shack remotely using the SmartLink protocol offered by FlexRadio, and made about a hundred QSOs with this setup. Because I won't be physically there during operating at power most of the time, I want to be very certain everything is set up properly, I've debugged any RF-in-shack issues, and generally made sure I'm not going to cause any problems for my friend. I've been heavily using the radio right now at 100W with no issues reported for at least several weeks. I plan to run SSB primarily at 600W.&lt;/p&gt;&#xA;&lt;p&gt;I've already performed an RF evaluation per &lt;a href=&quot;http://www.arrl.org/fcc-rf-exposure-regulations-the-station-evaluation&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL guidance&lt;/a&gt;, and because the TX antenna is a 50' high dipole quite far away from the dwelling, I'm not concerned about RF exposure either controlled or uncontrolled, even if I were to run at full power assuming I keep to the 80,40, and 10 meter bands.&lt;/p&gt;&#xA;&lt;p&gt;With RF exposure evaluated and not a primary worry, my main concern is causing unwanted interference or electrical problems at higher power.&lt;/p&gt;&#xA;&lt;p&gt;Currently my plan:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Perform and document RF exposure station evaluation (already done)&lt;/li&gt;&#xA;&lt;li&gt;Use only TX antennas rated for QRO (already done)&lt;/li&gt;&#xA;&lt;li&gt;Only run a maximum of 600 watts&lt;/li&gt;&#xA;&lt;li&gt;Verify all SWRs are less than 2:1 untuned&lt;/li&gt;&#xA;&lt;li&gt;Perform 600 watt tune ups and operate on the air for an hour at 600W on a few different bands to make sure the home network, cable tv, etc are all working properly and nothing is burning&lt;/li&gt;&#xA;&lt;li&gt;Place a 1500 watt rated common mode choke on my transmit antenna (or verify that the transmit antenna already has one, which I think it does)&lt;/li&gt;&#xA;&lt;li&gt;Disable TX on any antennas with wiring near the ground (currently just a vertical), as well as any antennas, or baluns, not rated for 1500 watts&lt;/li&gt;&#xA;&lt;li&gt;Triple check all TX antennas have insulators and are securely roped to their anchor points&lt;/li&gt;&#xA;&lt;li&gt;Verify my ground system with a voltmeter&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Can anyone opine what other things tend to go wrong with QRO setups or things I should check for?&lt;/p&gt;&#xA;" OwnerUserId="11878" LastEditorUserId="8717" LastEditDate="2021-04-07T21:57:38.120" LastActivityDate="2021-04-07T21:57:38.120" Title="Checklist for QRO remote setup" Tags="&lt;rfi&gt;&lt;amplifier&gt;&lt;safety&gt;&lt;remote-control&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17276" PostTypeId="2" ParentId="12557" CreationDate="2020-09-09T01:20:08.077" Score="2" Body="&lt;p&gt;Magnetic loops do not need a choke more than other kinds of antennas but I recommend you have one anyway especially if you will have coax running through your house. The reason to have a choke with a magloop is to reduce rf receive noise which can be picked up by the coax from local rf noise sources in your house. This is also valid for other types of antennas.&lt;/p&gt;&#xA;" OwnerUserId="14671" LastActivityDate="2020-09-09T01:20:08.077" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17277" PostTypeId="2" ParentId="9132" CreationDate="2020-09-09T01:56:24.267" Score="1" Body="&lt;p&gt;I understand people like to use coax for antenna experiments but in this case I don't think its a good choice.&lt;/p&gt;&#xA;&lt;p&gt;That outer loop diameter is too small for 40 meters and it is a wire when it really needs to be a tube.&lt;/p&gt;&#xA;&lt;p&gt;What I would suggest is making this thing again but using copper tubing for the outer loop and simple insulated wire for the inner loop(inner loop thickness does not matter).  Use it for transmitting on 20 meters and up. If you have a big enough capacitor you can TUNE 40 meters but as you have discovered it will not transmit very well.&lt;/p&gt;&#xA;&lt;p&gt;For a quick experiment all you need is wire and something to hold the wire in roughly a square or circular shape for receiving purposes. You can make these multi-turn and receive all the way down to broadcast AM band.&lt;/p&gt;&#xA;" OwnerUserId="14671" LastActivityDate="2020-09-09T01:56:24.267" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17278" PostTypeId="2" ParentId="16375" CreationDate="2020-09-09T02:30:06.090" Score="0" Body="&lt;p&gt;The performance difference between horizontal and vertical is about the radiation pattern and what objects are near the antenna.&lt;/p&gt;&#xA;&lt;p&gt;A horizontal loop really cannot be placed above metal surfaces because this will screw up the radiation pattern. Also the higher it is above ground the better.&lt;/p&gt;&#xA;&lt;p&gt;A vertical loop can be above any surface no problem and it does not need to be high off the ground.&lt;/p&gt;&#xA;&lt;p&gt;If there is no metal in your attic  , attic insulation foil , or your roof , then you can mount your loop horizontally in the attic but it would be better if you could put it on the roof outside and get it up maybe 10 feet above the roof.&lt;/p&gt;&#xA;&lt;p&gt;If it was me I would put a vertical loop 10 feet off the ground and at least 10 feet away from anything in the backyard , patio , whatever. If you aren't receiving anything you can go out in the yard and twist the pole and make it point a different direction.&lt;/p&gt;&#xA;" OwnerUserId="14671" LastActivityDate="2020-09-09T02:30:06.090" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17279" PostTypeId="1" CreationDate="2020-09-10T02:49:11.023" Score="2" ViewCount="187" Body="&lt;p&gt;Is there a way I can connect a 2&amp;quot;x.025&amp;quot; copper strap to a 5/8&amp;quot; grounding rod that can be buried?&lt;/p&gt;&#xA;&lt;p&gt;I've seen the bolt-on strap clamps, but those need to be inspected periodically. I've also been looking at cadweld one shots, but haven't found any that appear to work with thin strap. Are there any options I'm missing?&lt;/p&gt;&#xA;" OwnerUserId="11639" LastActivityDate="2020-09-18T01:20:00.727" Title="Connecting copper strap to grounding rod" Tags="&lt;grounding&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17280" PostTypeId="2" ParentId="17279" CreationDate="2020-09-10T12:53:39.267" Score="5" Body="&lt;p&gt;There are some suitable connections in the &lt;a href=&quot;https://www.erico.com/catalog/literature/E524C-ASEN.pdf&quot; rel=&quot;noreferrer&quot;&gt;reusable Cadweld product line&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SbDBA.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SbDBA.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;But you're right, there don't appear to be any similar connections in the One Shot line.&lt;/p&gt;&#xA;&lt;p&gt;An alternative is brazing. An alloy like &lt;a href=&quot;https://www.harrisproductsgroup.com/en/Products/Alloys/Brazing/Phos-Copper/Stay-Silv-15.aspx&quot; rel=&quot;noreferrer&quot;&gt;Harris Stay-Silv 15&lt;/a&gt; works well. I've managed to make acceptable connections (barely) with a good MAP plumbing torch to ground rods that are not buried yet and 6 AWG wire, but with wider copper strap and/or ground rods that are already buried, you'll need a larger oxyacetylene torch to get the components hot enough.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-10T12:53:39.267" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17281" PostTypeId="1" AcceptedAnswerId="17282" CreationDate="2020-09-10T15:01:06.967" Score="2" ViewCount="96" Body="&lt;p&gt;Good Morning all,&lt;/p&gt;&#xA;&lt;p&gt;I want to calculate the mutual impedance of two parallel dipole.&lt;/p&gt;&#xA;&lt;p&gt;The first hypothesis is to assume that the dipole 2 is in open circuit, nothing difficult here I knew how to do it&#xA;&lt;a href=&quot;https://i.stack.imgur.com/TfMPE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TfMPE.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Hypothesis 2 is to assume that dipole 2 is short circuited or loaded with some impedance&lt;/p&gt;&#xA;&lt;p&gt;Are there equations for hypothesis 2, or is there a parameter to add or modify on Baker's equations?&lt;/p&gt;&#xA;&lt;p&gt;thank you&lt;/p&gt;&#xA;" OwnerUserId="17741" LastEditorUserId="9621" LastEditDate="2020-09-10T23:07:24.653" LastActivityDate="2020-09-10T23:07:24.653" Title="Mutual impedance of two parallel dipole" Tags="&lt;impedance&gt;&lt;antenna-modeling&gt;&lt;parallel-dipole&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17282" PostTypeId="2" ParentId="17281" CreationDate="2020-09-10T17:46:36.423" Score="3" Body="&lt;p&gt;I think if you're worried about the &lt;em&gt;load&lt;/em&gt; on the other dipole, you need to go back and look at how &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_parameters&quot; rel=&quot;nofollow noreferrer&quot;&gt;Z parameters&lt;/a&gt; work.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_{21}$&lt;/span&gt; doesn't assume anything about the impedance on the two dipoles. It's just one of the impedance parameter term - &lt;span class=&quot;math-container&quot;&gt;$Z_{21}$&lt;/span&gt; is the voltage developed on dipole 2 &lt;em&gt;due to&lt;/em&gt; a current in dipole 1. It's not the final voltage or current present on dipole 2, for that you need to know other things.&lt;br /&gt;&#xA;I can't find the equations online, they're in any good electromagnetics book, I can't find mine either.&lt;/p&gt;&#xA;&lt;p&gt;To calculate the &lt;em&gt;input impedance&lt;/em&gt; on port 1, you need to consider the impedance on port 2, whether that's a short or an open.&lt;/p&gt;&#xA;&lt;p&gt;So if you know &lt;span class=&quot;math-container&quot;&gt;$Z_{11}$&lt;/span&gt; (self-impedance of the dipole alone), &lt;span class=&quot;math-container&quot;&gt;$Z_{21}$&lt;/span&gt; (mutual impedance from the equation, same as &lt;span class=&quot;math-container&quot;&gt;$Z_{12}$&lt;/span&gt; in a passive system), and &lt;span class=&quot;math-container&quot;&gt;$Z_{22}$&lt;/span&gt; (self-impedance of dipole 2) and choose &lt;span class=&quot;math-container&quot;&gt;$Z_L$&lt;/span&gt;, then&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/O6zHm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O6zHm.png&quot; alt=&quot;Zin equation from wikipedia&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is how you can calculate the currents on a yagi antenna, for example, without resorting to numerical methods. &lt;a href=&quot;https://en.wikipedia.org/wiki/Yagi%E2%80%93Uda_antenna#Analysis&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia Yagi Antenna&lt;/a&gt; actually has a nice section about this, now that I scratch a bit.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-09-10T17:46:36.423" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17283" PostTypeId="1" AcceptedAnswerId="17284" CreationDate="2020-09-10T18:03:29.057" Score="4" ViewCount="773" Body="&lt;p&gt;In a communication Satellite system, there are losses that occur when the signal is received at the antenna and then passed through a communication link to the output stage which could be the receiver. Among these losses free space seems to be the highest loss that can happen why ?&lt;/p&gt;&#xA;" OwnerUserId="17743" LastActivityDate="2020-09-13T22:55:01.150" Title="Why does Free space have the highest loss compared to other losses like atmospheric loss, feeder loss etc?" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17284" PostTypeId="2" ParentId="17283" CreationDate="2020-09-10T18:26:38.007" Score="11" Body="&lt;p&gt;Free space loss is the power lost because it &lt;em&gt;doesn't reach the receiving antenna&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;An example using an analogy is your eye, looking at the light from a light bulb.&lt;/p&gt;&#xA;&lt;p&gt;If you stand 10 metres away from a light bulb, and your pupil has a diameter of 2 mm, then you can see that only a tiny fraction of the power radiated from the light bulb actually enters your eye. The rest of the power is lost.&lt;/p&gt;&#xA;&lt;p&gt;The formula is simply the ratio of the areas:&#xA;&lt;span class=&quot;math-container&quot;&gt;$${Pout\over{Pin}} = {\pi0.001^2\over{4\pi10^2}} = 2.5\times10^{-9} = -86\text{ dB}$$&lt;/span&gt;&#xA;Where the numerator is the area of your pupil, and the denominator is the area of a 10 m sphere.&lt;/p&gt;&#xA;&lt;p&gt;Antennas have a capture area too, based on their gain and the wavelength, or for dish antennas, it's usually easier to consider the whole aperture of the antenna, and then some efficiency factor.&lt;/p&gt;&#xA;&lt;p&gt;The transmit antenna also has gain - this can be compared to focussing of the light. You know that a distant light bulb looks much brighter if it has a reflector - compare how much brighter a car headlight looks (55 watts, focussed forwards) to a naked porch light.&lt;/p&gt;&#xA;&lt;p&gt;For satellite communications, picture the transmitter high up there looking at nearly half of the earth. Even if its transmitter power is concentrated just on earth, not wasting any power to space, only a very small fraction of the transmitted power will be intercepted by your little dish antenna!&lt;/p&gt;&#xA;&lt;p&gt;Other losses, as you say, are quite small - just a dB here and there for cable and things.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-09-11T05:01:33.700" LastActivityDate="2020-09-11T05:01:33.700" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17285" PostTypeId="1" CreationDate="2020-09-13T02:28:51.093" Score="0" ViewCount="45" Body="&lt;p&gt;Once you program a memory name on this radio, it displays the name only. Is there any way to quickly confirm the actual frequency of a named memory?&lt;/p&gt;&#xA;" OwnerUserId="11639" LastActivityDate="2020-09-30T18:36:01.030" Title="Viewing current frequency on Kenwood TM-281" Tags="&lt;kenwood&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17286" PostTypeId="2" ParentId="17253" CreationDate="2020-09-13T02:47:48.143" Score="0" Body="&lt;p&gt;The good news is you must know that engineers must learn to read and write specifications before they can learn how to design.&#xA;So don't even try.  You must start with good specs !!! (lots of measurable values)&lt;/p&gt;&#xA;&lt;p&gt;What does it do? [ppm, ppm/'C, Rs, parallel, series or harmonic (overtone) etc ? tolerance?/stability?/aging? sine or square out?&lt;/p&gt;&#xA;&lt;p&gt;Once you know what is required, your options are &lt;strong&gt;&amp;quot;make or buy&amp;quot;&lt;/strong&gt; on every little circuit.    Discrete, IC, module or the final product?  What makes radios bad or better?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Fortunately, XO's are cheap now&lt;/strong&gt; so you don't have to learn a book's worth of info.  Just buy a ready-made Crystal Oscillator for not much more than the crystal.  But what specs?&lt;/p&gt;&#xA;&lt;p&gt;X = Crystal or Xtal  (x looks like a criss-cross)&lt;br /&gt;&#xA;XO = Crystal Oscillator&lt;br /&gt;&#xA;VCXO = Voltage Controlled XO&lt;br /&gt;&#xA;TCXO = Temp. Compensated XO ( often -40 ~ +70'C or 0 to 70'C)  graded by tolerance in ppm, parts per million (error) at room, 25'C and stability = over Vcc &amp;amp; temp. range.&lt;br /&gt;&#xA;VCTCXO Volt. controlled TCXO (THese can be nulled)&lt;br /&gt;&#xA;OCXO ( Ovenized SC cut crystal ~1000x more stable and 200x more expensive for 1e-11 type accuracy.  The others above are all AT cut X's.   Of course, DIY AT-cut OCXO's are cheap if you know-how but that takes a 2 stage thermal design and a 2 stage heater at the 3rd order minimum.&lt;br /&gt;&#xA;DTXO  Digitally tuned XO with PLL and you serially program the string into its non-volatile memory, so one xtal can do many frequencies.&lt;/p&gt;&#xA;&lt;p&gt;I've probably left some acronyms out, but you'll figure it out.&lt;/p&gt;&#xA;&lt;p&gt;Digikey has all of these.&lt;/p&gt;&#xA;&lt;h2&gt;What is a crystal&lt;/h2&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JweYt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JweYt.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&#xA;What are the common attributes must be understood?&lt;br /&gt;&#xA;&lt;a href=&quot;https://www.changpuak.ch/electronics/Quartz_Crystal_Filter_Designer_1.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.changpuak.ch/electronics/Quartz_Crystal_Filter_Designer_1.php&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Q for an X is ~&amp;gt;10k whereas,&lt;br /&gt;&#xA;Q for an LC resonator based on impedance ratio with R might be 100 to be reasonably stable.&lt;/p&gt;&#xA;&lt;p&gt;I can remember being an undergrad and reading the ARRL Handbook with &lt;em&gt;glazed eyes&lt;/em&gt; as if, I was reading a book on &lt;em&gt;vector economics&lt;/em&gt; and then 30 years later asking a grad student from Philly when I was in San Diego, &amp;quot;what is a crystal ?&amp;quot; and he admitted no idea.  Yet upon graduation in EE, I had the necessary theory and self-taught skills to understand how to read datasheets and schematics and designed several 2 stage Xtal VLF filters for a Doppler Rx easily in my 1st job.&lt;/p&gt;&#xA;&lt;h2&gt;What are the Filter Specs?&lt;/h2&gt;&#xA;&lt;p&gt;Again same thing , don't think about design until you find your specs.&lt;/p&gt;&#xA;&lt;p&gt;What is the best filter spec and is it possible to learn how in a short time?  For each stage, RF, IF , Antenna, PS, how many stages, what group delay, BW, Q stop band?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.google.com/search?client=firefox-b-d&amp;amp;q=crystal+filter+design+calculator&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.google.com/search?client=firefox-b-d&amp;amp;q=crystal+filter+design+calculator&lt;/a&gt;&lt;/p&gt;&#xA;&lt;h2&gt;Must read&lt;/h2&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Crystal_oscillator&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Crystal_oscillator&lt;/a&gt;&lt;/p&gt;&#xA;&lt;h2&gt;Addendum&lt;/h2&gt;&#xA;&lt;p&gt;How to understand Filters the easy way.&#xA;Instant design with all the variables on sliders. Choose circuits&amp;gt; larger passive filters &amp;gt; choose order 7th &amp;gt; increase spectrum , &amp;gt; choose centre frequency, BW Chebychev, Ripple dB, add phase response, Pole Zero plots and change to any spec, eg. 2.4GHz BW 30MHz 5th order or 12 th order .. (random)&lt;/p&gt;&#xA;" OwnerUserId="11155" LastEditorUserId="11155" LastEditDate="2020-09-13T17:12:31.467" LastActivityDate="2020-09-13T17:12:31.467" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17287" PostTypeId="2" ParentId="17285" CreationDate="2020-09-13T02:51:16.387" Score="0" Body="&lt;p&gt;I guess &lt;kbd&gt;F&lt;/kbd&gt;, &lt;kbd&gt;VFO&lt;/kbd&gt; would do it since that copies the memory to the VFO, and the name doesn't appear in VFO mode. Given the small number of buttons on this radio, there's probably not a better way to do it.&lt;/p&gt;&#xA;" OwnerUserId="11639" LastActivityDate="2020-09-13T02:51:16.387" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17289" PostTypeId="1" CreationDate="2020-09-14T02:20:45.510" Score="2" ViewCount="177" Body="&lt;p&gt;I'm installing a transceiver in an office on the ground floor of a warehouse. The antenna will be 45 feet above the office on the roof of the warehouse.  The ceiling of the office is a drop ceiling, and above that is empty space until the roof of the warehouse.&lt;/p&gt;&#xA;&lt;p&gt;My questions is about placement of the polyphasor lighting suppressor.&lt;/p&gt;&#xA;&lt;p&gt;I know that usually it is desirable to put the lightning suppression as close to the antenna cable entry point as possible, and then to ground it, but I was wondering if it would be acceptable to install the lightning suppressor about 25 feet from the entry point into the building, right before it enters the office building where the radio is, and then ground it with grounding cable clamped to a grounded pipe.&lt;/p&gt;&#xA;&lt;p&gt;My rationale is that it will be physically difficult to install it right on the inside under where the coaxial cable penetrated the roof, because it will be difficult to access.  If it does take a lighting strike, and needs replacement, it will be very difficult to access if its near the topmost roof.&lt;/p&gt;&#xA;&lt;p&gt;On the other hand, if it's right above the office, and it needs servicing, it's just a matter of using a standard ladder, and popping a ceiling tile.  Keep in mind there are no offices above the first floor, only open space above the drop ceiling.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zbU5A.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zbU5A.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17109" LastEditorUserId="17109" LastEditDate="2020-09-16T18:23:30.667" LastActivityDate="2020-09-16T18:23:30.667" Title="How far from a cable entry point can the lighting suppressor be installed" Tags="&lt;grounding&gt;&lt;safety&gt;&lt;lightning&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17291" PostTypeId="2" ParentId="17289" CreationDate="2020-09-14T05:52:52.390" Score="6" Body="&lt;p&gt;The picture you have drawn suggests a lightning suppressor installed in this way will do little to nothing to protect your station.&lt;/p&gt;&#xA;&lt;p&gt;The suppressor does only one thing: it limits the maximum voltage between the center conductor and the shield. It doesn't do anything to limit strike current on the shield, which is where most of the energy is anyhow.&lt;/p&gt;&#xA;&lt;p&gt;The protected equipment inside the office is almost certainly grounded either directly or indirectly through AC mains, Ethernet cables, etc. Remember that at the voltages lightning can generate, anything anywhere near something even a little bit conductive (like wood) is potentially a path to ground.&lt;/p&gt;&#xA;&lt;p&gt;As such, a more complete picture of your proposal is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/NtPJg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/NtPJg.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Note that you have multiple ground paths, and the one you've added in green has a high impedance because it is so long. As such, most of the strike current will go through your equipment.&lt;/p&gt;&#xA;&lt;p&gt;As such, most of lightning protection is not about the suppressor at all, but rather:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;ensuring strike current has no path to ground that goes &lt;em&gt;through&lt;/em&gt; protected equipment, and&lt;/li&gt;&#xA;&lt;li&gt;establishing a single-point ground so all protected equipment floats at the same voltage.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;To be effective, the connection labeled &amp;quot;to grounding&amp;quot; you've drawn:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;must be a short, direct path to ground. Not a meandering, horizontal connection as you've drawn&lt;/li&gt;&#xA;&lt;li&gt;must be the &lt;em&gt;only&lt;/em&gt; path to ground. If any of your equipment is mains powered, it's likely that connection provides an additional path to ground, and thus much of the strike current will flow through your equipment to get to the mains ground.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Something like this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FjxIv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FjxIv.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Importantly, &lt;em&gt;all&lt;/em&gt; wires must go to a single point ground. At this ground point, everything is bolted to a conductive panel so they remain at the same voltage. Anything that can't be directly grounded (like the coax center conductor, and the non-ground conductors of the mains wiring) go through some protective device like a gas discharge tube or an MOV. And that grounding panel is near the ground, and grounded with a short, low impedance connection.&lt;/p&gt;&#xA;&lt;p&gt;Ideally, the antenna feedline doesn't run through the plenum, since there's likely all kinds of conductive stuff in there (other wiring, HVAC ducting, ceiling support structure...) which would also provide a nice path the strike current will use, potentially breaking electronics and starting fires as it does so.&lt;/p&gt;&#xA;&lt;p&gt;For additional detail, see &lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-09-14T16:45:34.667" LastActivityDate="2020-09-14T16:45:34.667" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17292" PostTypeId="2" ParentId="15226" CreationDate="2020-09-14T06:24:08.650" Score="4" Body="&lt;p&gt;These ideas have been around for centuries as &lt;em&gt;lightning dissipation theory&lt;/em&gt; and &lt;em&gt;lightning diversion theory&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Notably, Benjamin Franklin was an early proponent of lightning dissipation theory. He noticed on a small scale that a static charge could be dissipated without a spark by bringing a grounded needle near a charged object. He correctly reasoned lightning was static electricity on a larger scale. He then hypothesized it could be discharged in the same way by putting pointy, grounded lightning rods at the tops of buildings.&lt;/p&gt;&#xA;&lt;p&gt;This experiment works in the lab because the sharp point of the needle creates a high local potential gradient that facilitates corona discharge. And it was empirically shown that structure fires were reduced when Franklin's lightning rods were installed. So does that mean lightning dissipation theory is correct?&lt;/p&gt;&#xA;&lt;p&gt;No. Structures with pointed rods are still frequently struck by lightning, but they don't burn down. While Franklin's idea works well at small scales, the difference with lightning is the static charge is &lt;em&gt;many&lt;/em&gt; orders of magnitude greater. Trying to discharge a thundercloud with a lightning rod, or even hundreds of them, is like trying to put out a forest fire with a garden hose.&lt;/p&gt;&#xA;&lt;p&gt;Fortunately, a lightning rod intended to dissipate lightning also works well to divert it. As the rod is solidly grounded, the strike current prefers to follow the grounding conductors and as such does not create arcing within the structure. It's the high temperature of the arc that starts fires. No arc, no fire.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-14T06:24:08.650" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17293" PostTypeId="2" ParentId="17289" CreationDate="2020-09-14T13:16:30.843" Score="1" Body="&lt;p&gt;Ground wire is very inductive and thus high impedance to sub-nanosecond arc rise time when the leader path finally conducts.&lt;/p&gt;&#xA;&lt;p&gt;Therefore you want the shortest path to the air gap arc suppressor which is sub-picofarad higher impedance then the current will have a greater chance of following the ground wire.&lt;/p&gt;&#xA;&lt;p&gt;The voltage induced may still be high but hopefully suppressed by a 2nd stage &amp;lt;~1kV suppressed with lower current in its path in the unit. This depends on coax cable quality, skin effects and mutual induction from the ground current 3kA to 75kA worst case for 1us. (&amp;lt;~1MHz mostly)&lt;/p&gt;&#xA;&lt;p&gt;• The lower the coax is grounded to the tower, the less shield current there will be on coax line.&lt;br /&gt;&#xA;• The lower the inductance path to ground from the MGB or bulkhead, the less shield current will enter the building.&lt;/p&gt;&#xA;&lt;p&gt;The best lightning protector blocks DC to 1MHz which is the bulk of the RF energy , so the equivalent circuit has 0.1 dB insertion loss in the RF band selected and shunts the antenna with an LCL or Pi filter for high pass or low block . An air gap or properly designed rugged proper gas tube is in parallel with the incoming  shunt L then HPF with series C and output shunt L.&lt;/p&gt;&#xA;&lt;h2&gt;Caveat&lt;/h2&gt;&#xA;&lt;p&gt;If there is nothing in the roof and below to divert the coax current and rising voltage to another electrical path with flammable materials or other electrical equipment, you may consider your original plan.&lt;/p&gt;&#xA;&lt;p&gt;But if inside, there will be ground shift pulse with ringing, which now can radiate the diverted lightning energy.&lt;/p&gt;&#xA;&lt;p&gt;Consult with supplier and show wire type and lengths of all from antenna to Unit and earth gnd.&lt;/p&gt;&#xA;&lt;p&gt;Gold centre pin contacts are recommended.&lt;/p&gt;&#xA;" OwnerUserId="11155" LastEditorUserId="11155" LastEditDate="2020-09-14T14:04:44.023" LastActivityDate="2020-09-14T14:04:44.023" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17296" PostTypeId="1" AcceptedAnswerId="17297" CreationDate="2020-09-14T19:05:12.183" Score="1" ViewCount="29" Body="&lt;p&gt;I am looking for the original papers describing both MSK144 and JT4 protocols. I can easily find the corresponding papers for some other digital modes such as JT65 or FT8 (mainly at the Princeton Physics website), but no information about these protocols.&lt;/p&gt;&#xA;&lt;p&gt;It would be great if anyone could provide me any link or reference to the original publications.&lt;/p&gt;&#xA;&lt;p&gt;Thank you in advance.&#xA;73.&lt;/p&gt;&#xA;" OwnerUserId="14937" LastActivityDate="2020-09-14T20:08:32.367" Title="Does anyone have any link to the original papers describing MSK144 and JT4?" Tags="&lt;digital-modes&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17297" PostTypeId="2" ParentId="17296" CreationDate="2020-09-14T20:08:32.367" Score="2" Body="&lt;p&gt;The &lt;a href=&quot;http://physics.princeton.edu/pulsar/k1jt/wsjtx-doc/wsjtx-main-2.0.0.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;WSJT User Guide version 2.0.0&lt;/a&gt;, which is hosted at the Princeton Physics website, was written by Joe Taylor W1JT himself, who wrote much of the WSJT code.  In the Protocol Specifications chapter there are links to QEX articles and other references, including one about the JT65 protocol.&lt;/p&gt;&#xA;&lt;p&gt;Given Professor Taylor's academic background, to me it seems safe to say that if there is no reference or link to an article or paper in the User Guide for a particular protocol, then no more authoritative article or paper exists.  In that case, the User Guide, other cited references, and the &lt;a href=&quot;https://sourceforge.net/projects/wsjt/&quot; rel=&quot;nofollow noreferrer&quot;&gt;published source code for WSJT&lt;/a&gt; probably are the most definitive references.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-09-14T20:08:32.367" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17298" PostTypeId="2" ParentId="11588" CreationDate="2020-09-15T09:38:43.820" Score="1" Body="&lt;p&gt;This might be the same problem as described by LA1K in &lt;a href=&quot;https://www.la1k.no/2018/05/02/how-to-fix-ic-9100-usb-hub-problem/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this blog post&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;The integrated USB hub is apparently powered by the USB port, not the radio's power supply. A powered USB hub is the solution if you don't have a USB port supplying enough current.&lt;/p&gt;&#xA;" OwnerUserId="17759" LastActivityDate="2020-09-15T09:38:43.820" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17299" PostTypeId="1" CreationDate="2020-09-15T13:58:11.240" Score="1" ViewCount="53" Body="&lt;p&gt;I own a &lt;a href=&quot;https://www.google.com/search?q=Kenwood+TM-D710E&quot; rel=&quot;nofollow noreferrer&quot;&gt;Kenwood TM-D710E&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;I connected it via the COM-connector on the panel to a Raspberry pi.&#xA;On the panel I selected &amp;quot;packet12&amp;quot; (with the TNC button). After&#xA;that, I can send TNC commands to the device using minicom.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Next step: I enter &amp;quot;KISS ON&amp;quot; and &amp;quot;RESTART&amp;quot; in minicom to activate&#xA;KISS mode on the Kenwood.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;After that I run &lt;strong&gt;/usr/sbin/kissattach -l /dev/ttyUSB1 ax0&lt;/strong&gt; on the&#xA;Raspberry.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If I now enter &lt;strong&gt;axlisten -t -a&lt;/strong&gt; and send packets using an other&#xA;system (baofeng + tnc-pi), I can indeed see those packets via the&#xA;Kenwood!&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;strong&gt;The problem now is sending.&lt;/strong&gt; If I do:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;beacon -s ax0 'this is a test - PD9FVH'&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;then the panel shows for a fraction of a second 'STA' but the Kenwood does not transmit anything - I verified this by listening on that frequency using the Baofeng.&lt;/p&gt;&#xA;&lt;p&gt;Note that in &amp;quot;audio mode&amp;quot; everything works both ways. I can hear myself via the Baofeng and via the Kenwood.&lt;/p&gt;&#xA;&lt;p&gt;The power supply can deliver 25A.&lt;/p&gt;&#xA;&lt;p&gt;My question now is: Does anyone know why the Kenwood won't send?&lt;/p&gt;&#xA;" OwnerUserId="15420" LastEditorUserId="8717" LastEditDate="2020-09-15T19:30:58.737" LastActivityDate="2020-09-16T11:17:43.120" Title="Kenwood TM-D710E in packet mode: does not transmit" Tags="&lt;kenwood&gt;&lt;packet&gt;&lt;equipment-troubleshooting&gt;&lt;computer-control&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17300" PostTypeId="2" ParentId="17299" CreationDate="2020-09-15T19:41:01.097" Score="0" Body="&lt;p&gt;This &lt;em&gt;might&lt;/em&gt; be caused by RFI.&lt;/p&gt;&#xA;&lt;p&gt;Perhaps RF might be getting into the other equipment —especially the Raspberry Pi— and causing this problem.&lt;/p&gt;&#xA;&lt;p&gt;Does it help if you turn the Kenwood's power down to 5 watts, or better yet replacing the antenna with a dummy load?&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-09-15T19:41:01.097" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17301" PostTypeId="1" AcceptedAnswerId="17307" CreationDate="2020-09-16T10:53:15.840" Score="1" ViewCount="111" Body="&lt;p&gt;I'm trying to wrap my head around software defined radios and antennas and noticed that lots of antennas are described in terms of a frequency range. For example, &lt;a href=&quot;https://www.passion-radio.com/sdr-antennas/antenne-ant700-408.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt; is described as operating from 300 to 1100 MHz. What confuses me is where these numbers come from / what about the antenna design (size? filters?) gives rise to these values.&lt;/p&gt;&#xA;&lt;p&gt;If I were to hook such an antenna up to an SDR and attempt to transmit slightly outside of that range (e.g. 1200 MHz), what should I expect to happen? What about if I attempted to transmit massively outside of that range (e.g. 2 GHz)? Are there general principles for modeling these dynamics?&lt;/p&gt;&#xA;" OwnerUserId="17767" LastEditorUserId="8717" LastEditDate="2020-09-16T13:32:57.627" LastActivityDate="2020-09-17T12:16:24.890" Title="What does antenna frequency range mean in practice?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;software-defined-radio&gt;&lt;theory&gt;&lt;bandwidth&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17302" PostTypeId="2" ParentId="17299" CreationDate="2020-09-16T11:17:43.120" Score="1" Body="&lt;p&gt;Found out what it is. Something really stupid.&lt;/p&gt;&#xA;&lt;p&gt;Before I had a TNC-PI. That TNC-PI modem just starts sending as sook as it gets data. The Kenwood on the other hand checks for a signal on the waves. If any; no packet transmission. And apparently this controlled by the squelch. I had the squelch set to &amp;quot;always listen&amp;quot; but then the radio things there's a transmission...&lt;/p&gt;&#xA;&lt;p&gt;@mike waters: I also had problems with RF in equipment, but that was not related to this problem. Replacing the powersupply of the RPI by something more sane and moving it away from the radio (it was lying on top of it) helped (the problem showed up by the serial-to-usb converter &amp;quot;falling from the USB bus&amp;quot;).&lt;/p&gt;&#xA;" OwnerUserId="15420" LastActivityDate="2020-09-16T11:17:43.120" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17304" PostTypeId="1" CreationDate="2020-09-16T13:02:17.097" Score="1" ViewCount="194" Body="&lt;p&gt;How can I check if my CB radio is AM or AM/SSB? I know that it is a CB UHF radio but there is no information of whether it is AM or AM/SSB.&lt;/p&gt;&#xA;" OwnerUserId="17769" LastEditorUserId="8717" LastEditDate="2020-09-16T20:09:00.550" LastActivityDate="2020-09-20T07:19:40.087" Title="How can I check if my CB radio is AM or AM/SSB?" Tags="&lt;ssb&gt;&lt;citizens-band&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17306" PostTypeId="2" ParentId="17304" CreationDate="2020-09-16T14:28:37.427" Score="6" Body="&lt;p&gt;As mentioned in another answer, it sounds like it’s not SSB. The next question is whether it’s AM or FM.&lt;/p&gt;&#xA;&lt;p&gt;“CB” can mean different things in different countries, and you don’t say which country you are in. But you say that it’s UHF - and FM is a much more common mode to use at UHF frequencies (and even at VHF) than AM.&lt;/p&gt;&#xA;&lt;p&gt;If it were SSB, it would usually have a switch to select USB or LSB, and it would need a clarifier, or a full VFO.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-09-16T14:28:37.427" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17307" PostTypeId="2" ParentId="17301" CreationDate="2020-09-16T16:01:15.623" Score="6" Body="&lt;p&gt;It means the range of frequencies in which the antenna is designed to operate. Operated outside that range, the antenna may not meet its specifications.&lt;/p&gt;&#xA;&lt;p&gt;This particular antenna is a telescopic whip, a kind of &lt;a href=&quot;http://www.antenna-theory.com/antennas/monopole.php&quot; rel=&quot;noreferrer&quot;&gt;monopole antenna&lt;/a&gt;. Such antennas are typically 1/4 wavelength long. It is advertised for 300 to 1100 MHz, and it's length can be adjusted from 24.5 cm to 9.5 cm. Not surprisingly, the bounds of these lengths correspond approximately to 1/4th the wavelength of the frequency bounds.&lt;/p&gt;&#xA;&lt;p&gt;Ostensibly, the notion is that the length can be adjusted to be appropriate for the desired frequency. Adjusting the length changes the resonance of the antenna, and thus its feedpoint impedance. Your transmitter has a specification for the range of feedpoint impedance it wants to see: transmitting outside this range can mean reduced performance or sometimes even damage.&lt;/p&gt;&#xA;&lt;p&gt;Receive applications are more forgiving: a mismatched antenna means at worst reduced performance. Some receivers degrade rapidly when the antenna is not matched, others are quite tolerant of a much wider range of antenna impedances. It depends on the design of the particular receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-16T16:01:15.623" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17309" PostTypeId="1" CreationDate="2020-09-17T08:14:38.507" Score="1" ViewCount="161" Body="&lt;p&gt;I have an EARCHI EFHW (40:1 unun)antenna that I used quite successfully until it fell from a tree.  I wasn't able to get it back up, so ran it along my wooden fence temporarily.  Unfortunately, the wire was shorter than the original (~60 ft), and I had trouble getting it to match with a less than 3:1 SWR on several bands.&lt;/p&gt;&#xA;&lt;p&gt;Somehow, I ended up adding a couple of shorter (about 10ft) lengths of wire to the antenna terminal of the match box.  NOW the thing matches on 80-6 meters, with SWR of less than 3:1!  And with a decent signal (I get out to South America for example). Note these are not like radials for a vertical which are connected to ground, these are connected to the center or positive terminal of the coax. Is this a sort of off center fed fan dipole? Whatever it is it works surprisingly well...especially on 80m!&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/MEuHe.png&quot; alt=&quot;Diagram1&quot; /&gt;&lt;/p&gt;&#xA;&lt;p&gt;I have added the NanoVNA charts.  Today I also raised the lower end of the antenna up to about 7 feet above ground.  Note, these are WITH the wires.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Uuwu9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Uuwu9.png&quot; alt=&quot;3.5MHz to 29Mhz&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/aJz2W.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aJz2W.png&quot; alt=&quot;1.8 to 10Mhz&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;And these are without the wires:&#xA;3.9 to 29MHZ WITHOUT wires&#xA;&lt;a href=&quot;https://i.stack.imgur.com/ZUYOD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZUYOD.png&quot; alt=&quot;3.5 to 29Mhz WITHOUT wires&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;1.8 to 10.5MHz WITHOUT wires&#xA;&lt;a href=&quot;https://i.stack.imgur.com/QbYzy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QbYzy.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17775" LastEditorUserId="17775" LastEditDate="2020-09-19T01:55:02.500" LastActivityDate="2020-09-19T11:26:28.830" Title="Multi-wire EFHW?" Tags="&lt;antenna&gt;&lt;efhw&gt;" AnswerCount="2" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="17310" PostTypeId="5" CreationDate="2020-09-17T08:47:57.770" Score="0" Body="" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-09-17T08:47:57.770" LastActivityDate="2020-09-17T08:47:57.770" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17311" PostTypeId="4" CreationDate="2020-09-17T08:47:57.770" Score="0" Body="End-Fed Half Wave is a type of antenna." OwnerUserId="4076" LastEditorUserId="8717" LastEditDate="2020-09-19T00:37:27.657" LastActivityDate="2020-09-19T00:37:27.657" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17312" PostTypeId="2" ParentId="17301" CreationDate="2020-09-17T12:16:24.890" Score="1" Body="&lt;p&gt;A more general answer...&lt;/p&gt;&#xA;&lt;p&gt;Antennas have a number of characteristics critical to their performance, including but not limited to gain, radiation pattern, impedance, and sometimes efficiency and polarization.  These performance characteristics are all tied to frequency.  When designing an antenna, these characteristics can be graphed vs. frequency and there will be peaks where each characteristic is optimal and areas where they are not.&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;frequency range&amp;quot; of the antenna is where all of the desired characteristics are within an acceptable range.  The difference between the lowest and highest acceptable frequency is called &amp;quot;bandwidth&amp;quot;.  When describing an antenna's range, sometimes only one of these parameters is focused on, and which one depends on the intent of use for the antenna, but ideally multiple parameters are considered.&lt;/p&gt;&#xA;&lt;p&gt;These graphs are not necessarily simple, and there may be multiple peaks where an antenna works, and this can be designed for to get a &amp;quot;multi band&amp;quot; antenna (for instance, one that works on both 2m and 70cm), although antennas typically work at harmonic frequencies anyway.&lt;/p&gt;&#xA;&lt;p&gt;As an example, if an antenna is designed for the amateur radio 2m band, then it would be expected that it's impedance is close to 50 ohms from 144MHz to 148Mhz so that SWR will be below (hopefully) 1.5 for the entire range. Outside of the range, the SWR may climb rapidly and become unsuitable for transmission.  Reception will be attenuated as well.  Also, the antenna's gain and radiation pattern will be close to what it is advertised.  If this is a directional antenna, this means that it remains directional within the range; outside of the range, it may become less directional or directional in unexpected directions.  For an &amp;quot;omnidirectional&amp;quot; antenna, this usually means that its angle of elevation stays low enough for good gain.  Outside of the range, the elevation angle typically rises until so much energy is going up that the gain in lower angles is very low.  (Gain and directionality are tied together for antennas.)&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-09-17T12:16:24.890" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17313" PostTypeId="2" ParentId="17309" CreationDate="2020-09-17T15:31:47.080" Score="1" Body="&lt;p&gt;It looks to me like the additional short wires are acting like some kind of a capacitive load (which will be especially helpful on longer λs like 80m) AND a contributor to radiation (though certainly with an unusual pattern).&lt;/p&gt;&#xA;&lt;p&gt;If you have a nanovna or similar, I'd love to see some plots with &amp;amp; without the shorter wires connected!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2020-09-17T15:31:47.080" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17314" PostTypeId="2" ParentId="17279" CreationDate="2020-09-17T21:39:33.687" Score="1" Body="&lt;p&gt;As Phil Frost mentioned, you can try the MAPP gas and silver brazing rods.  There is a good article which has some suggestions on doing all this, including how to get the materials on a budget (scrap copper roof flashing, for example, instead of expensive strapping). Lowes has a MAPP gas cylinder and torch for about $55.&lt;/p&gt;&#xA;&lt;p&gt;See &lt;a href=&quot;https://topbandhams.com/Tech/Lightning%20Protection-Taming%20Thors%20Thunder-On%20A%20Budget.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this article&lt;/a&gt; for details.  It describes how ham radio operators can use inexpensive materials to create a lightning protection system for their stations that is similar to what a commercial transmtter site would use: how to place ground rods and copper strapping, a description of the (very expensive) Cadweld process and the MAPP gas and silver brazing rod alternative, and building a single point ground along with antenna discharge units, etc. so as to have a station that will survive a lightning hit (something many Amateurs think is impossible but that commercial operators have happen all the time).  If you read it, along with Mike Holt's &lt;a href=&quot;http://file:///C:/Users/Administrator/Downloads/Radio_and_Television_2014NEC.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Illustrated Guide to the NEC for Radio and TV Equipment&lt;/a&gt;, it gives an excellent description of how to do what you're trying to do.&lt;/p&gt;&#xA;" OwnerUserId="17775" LastEditorUserId="17775" LastEditDate="2020-09-18T01:20:00.727" LastActivityDate="2020-09-18T01:20:00.727" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17315" PostTypeId="2" ParentId="14425" CreationDate="2020-09-18T11:22:05.187" Score="-1" Body="&lt;p&gt;One of the FT891 manuals says that by grounding the ACC jack the rig will transmit a carrier for tuning. Ungrounding automatically returns the rig to whatever mode it had been on. There is no mention that power is reduced so I assume the power is whatever was set for CW.&lt;/p&gt;&#xA;&lt;p&gt;I don't know how the automatic tuners for the 891 achieve reduced power for tuning.&lt;/p&gt;&#xA;" OwnerUserId="17783" LastActivityDate="2020-09-18T11:22:05.187" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17316" PostTypeId="1" CreationDate="2020-09-18T17:03:36.880" Score="3" ViewCount="143" Body="&lt;p&gt;How much do transceivers drop their output power, when the SWR is high?&lt;/p&gt;&#xA;&lt;p&gt;Most amateur solid state amplifiers or transceivers are (fully?) protected against high SWR, by a circuit which reduces the power and protects the final transistors.&lt;/p&gt;&#xA;&lt;p&gt;In a &lt;span class=&quot;math-container&quot;&gt;$50\Omega$&lt;/span&gt; system an infinite SWR implies a voltage of about double the Voltage (at 1:1 SWR), or a current of about double, depending on the phase. An SWR of 1.5:1 is only 1.2 x peak voltage or current. As you don't know the phase of the load, or how far it is down the line, the amplifier could see any of these numbers, with the extremes being more likely.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EGCqV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EGCqV.png&quot; alt=&quot;line voltage&quot; /&gt;&lt;/a&gt;&lt;br /&gt;&#xA;So to prevent the final transistors seeing an unreasonable voltage or current from an open or short circuit, the power needs to be reduced only to half. This graph shows the voltage ratio and the &amp;quot;safe power&amp;quot; assuming there is no other safety margin in the transistors:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Nz6kB.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Nz6kB.png&quot; alt=&quot;safe power&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Laboratory amplifiers produce full power into any load, but these are about 100 x more expensive than amateur amplifiers.&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/b7l99.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/b7l99.png&quot; alt=&quot;AR amplifier&quot; /&gt;&lt;/a&gt;&lt;br /&gt;&#xA;It's obviously desirable to have as much power as possible, even when operating into a mismatched load, to keep the system as flexible as possible.&lt;/p&gt;&#xA;&lt;p&gt;Has anyone measured how much the power drops on a transceiver with higher SWR? Ideally for different phases of high SWR, not just one.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-09-19T20:28:21.137" LastActivityDate="2020-09-30T00:26:56.893" Title="Reduction in transceiver power output into high SWR" Tags="&lt;transmitter&gt;&lt;impedance-matching&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17317" PostTypeId="1" CreationDate="2020-09-18T17:21:16.467" Score="1" ViewCount="81" Body="&lt;p&gt;can someone tell me what are the formulas of HPBW for a helical antenna?&lt;/p&gt;&#xA;&lt;p&gt;I've searched a lot and I saw that there are two different formulas of HPBW for the helical antenna,&lt;/p&gt;&#xA;&lt;p&gt;this one,&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \mathbf{(HPBW)} = [\frac{52}{C} \sqrt{\frac{\lambda^2}{NS}}] $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;and this one,&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \mathrm{HPBW} \simeq \frac{52}{\frac C\lambda \sqrt\frac{NS}{\lambda}} \mathrm{degrees} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;so what is the difference between both ?&lt;/p&gt;&#xA;" OwnerUserId="17785" LastEditorUserId="8717" LastEditDate="2020-11-29T02:03:21.647" LastActivityDate="2020-11-29T02:03:21.647" Title="The HPBW of a helical antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;math&gt;&lt;circular-polarization&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17318" PostTypeId="2" ParentId="17317" CreationDate="2020-09-18T17:45:40.760" Score="2" Body="&lt;p&gt;Kraus says&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$${52}\over{{C\over\lambda} \sqrt{n{S\over\lambda}}} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Which is your second equation.&lt;/p&gt;&#xA;&lt;p&gt;Be aware that this only holds for a narrow range of diameters and spacings: &lt;span class=&quot;math-container&quot;&gt;$0.8&amp;lt;{C\over{\lambda}} &amp;lt;1.8$&lt;/span&gt; ; &lt;span class=&quot;math-container&quot;&gt;$12&amp;lt;\alpha&amp;lt;14$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$n\ge4$&lt;/span&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-10-29T23:06:45.050" LastActivityDate="2020-10-29T23:06:45.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17319" PostTypeId="2" ParentId="17225" CreationDate="2020-09-19T05:43:14.397" Score="-1" Body="&lt;p&gt;If it was on the 10m band then it could have been the 10-10 club net.https://www.ten-ten.org/&lt;/p&gt;&#xA;" OwnerUserId="17786" LastActivityDate="2020-09-19T05:43:14.397" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17320" PostTypeId="2" ParentId="17309" CreationDate="2020-09-19T11:26:28.830" Score="2" Body="&lt;p&gt;Some antenna designs use multiple parallel elements like this. For example, fan dipoles. Or, as you can see the &lt;a href=&quot;https://www.dxengineering.com/parts/but-hf9v&quot; rel=&quot;nofollow noreferrer&quot;&gt;Butternet HF9V&lt;/a&gt; has a couple parallel wires hanging off it in the upper half:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/C8dJL.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/C8dJL.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;These extra elements add additional resonant modes to the antenna, which is what makes these antennas multi-band. In a fan dipole, if the elements are kept some distance apart they don't interact much and so for many fan dipoles it's effectively several dipoles in parallel. As you may know from parallel resistors, the resistance of the parallel combination is dominated by the lowest impedance in the group. This works if the impedance in question is the feedpoint of an antenna, too. When the elements get closer they also start to function like transmission line stubs which contribute to the antenna impedance.&lt;/p&gt;&#xA;&lt;p&gt;In engineered antennas the length of these elements are selected deliberately to introduce a good match with good radiation on the design bands, but if you're starting with any wire of arbitrary length and add more wires of arbitrary length, you're effectively &amp;quot;rolling the dice&amp;quot;. Since a &amp;quot;good match&amp;quot; is usually at the minimum of likely feedpoint impedances (excluding electrically small antennas) then adding more wires usually only makes things better.&lt;/p&gt;&#xA;&lt;p&gt;Taking this idea of adding more wires to the extreme you get antenna designs like the fractal antenna which can be very broadband.&lt;/p&gt;&#xA;&lt;p&gt;Note however that a good match and a good antenna are not always the same thing. A good antenna must additionally radiate energy (not just make the antenna or soil warm) and radiate that energy in a useful direction.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-19T11:26:28.830" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17321" PostTypeId="1" AcceptedAnswerId="17329" CreationDate="2020-09-19T15:59:08.113" Score="2" ViewCount="388" Body="&lt;p&gt;There seem to be lots of descriptions and/or articles on using multiple turns of conducting element in small magnetic loop antennas (STLs).  But I haven't found any information on full size full wave loops with more than one turn.&lt;/p&gt;&#xA;&lt;p&gt;What happens if one uses multiple turns in a larger full wave in circumference loop antenna?  (e.g. using integer multiples of one wavelength of wire around a loop support system or lot only big enough for one wavelength in circumference)?&lt;/p&gt;&#xA;&lt;p&gt;Are there no descriptions of large multi-turn loops because they don't match or radiate?  Or because it's just a waste of wire?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-09-19T18:54:18.470" LastActivityDate="2020-09-21T16:50:15.370" Title="Multi-turn large/full-wave loop antennas?" Tags="&lt;wire-antenna&gt;&lt;loop-antenna&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17322" PostTypeId="2" ParentId="17304" CreationDate="2020-09-20T07:19:40.087" Score="4" Body="&lt;p&gt;Australia has two CB bands, the old 27MHz band, where radios were either AM or SSB, &amp;amp; the UHF one, which uses FM.(which is apparently, the one you have.)&lt;/p&gt;&#xA;&lt;p&gt;Other countries have variations in either the band or mode of their 27MHz CB operations (27MHz FM is common in Europe), but although many have &amp;quot;CB like&amp;quot; frequency allocations at UHF, Australia &amp;amp; NZ seem to be the only ones where there is a band officially designated &amp;quot;CB&amp;quot; in the UHF region.&lt;/p&gt;&#xA;&lt;p&gt;If you should come across some 27 MHz CB radios, you can tell if they are &amp;quot;SSB/AM&amp;quot;, or &amp;quot;AM only&amp;quot;,by looking ar the front panel controls.&#xA;An SSB radio will have a switch with positions marked &amp;quot;USB&amp;quot;, &amp;quot;LSB &amp;quot; &amp;amp; &amp;quot;AM&amp;quot;, &amp;amp;&#xA;a variable control marked &amp;quot;clarifier&amp;quot;.&#xA;An &amp;quot;AM only&amp;quot; radio will not have these controls.&lt;/p&gt;&#xA;" OwnerUserId="17792" LastActivityDate="2020-09-20T07:19:40.087" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17323" PostTypeId="1" AcceptedAnswerId="17325" CreationDate="2020-09-20T07:47:35.003" Score="0" ViewCount="68" Body="&lt;p&gt;&lt;strong&gt;Situation:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I have an old 144MHz rig from the 2000's, an IC-271. I am trying to get it up and running.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Summary of the problem:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I can receive fine on the rig, except for from my HT.&lt;/p&gt;&#xA;&lt;p&gt;I can transmit a strong signal from the rig, but not my voice.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Are there any simple operator error explanations for this behavior?&lt;/p&gt;&#xA;&lt;p&gt;Or does it seem like an electronics problem inside the rig?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;All troubleshooting attempts:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I have an appropriate power supply (DM-320MV), a brand new microphone, and an antenna. (two, actually, one homebrew, one a 50 ohm impedance retractable Diamond RH775, which is for an HT, but I can use it with the rig with a connector, at the rig's low power setting).&lt;/p&gt;&#xA;&lt;p&gt;Scanning the air, I pick up conversations loud and clear.&lt;/p&gt;&#xA;&lt;p&gt;However, strangely, the rig cannot receive from my own HT (have used the HT for contacts, so I assume it is in working order). When I transmit from my HT to the rig in the same  room, the signal meter on the rig goes up to 60+ dB (off the chart), but I don't hear my voice. I am testing with the squelch open, and the static noise becomes silent during my HT transmit.&lt;/p&gt;&#xA;&lt;p&gt;In reverse, I tried transmitting from my rig to my HT. The rig's meter shows RF out, and my HT picks up the signal, but again I do not hear my own voice.&lt;/p&gt;&#xA;&lt;p&gt;Finally, one more test: I tried to contact a friend (several kilometers away) with the rig. I could hear his voice clearly, but he could not hear my voice, only silence during my transmissions.&lt;/p&gt;&#xA;&lt;p&gt;I read the manual for the rig and checked how each setting should be. On the rig, I have all tones/special processing circuits, automatic gain control, etc turned off. RF GAIN is set low. The rig is in FM mode, as is the HT.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;My level&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Basic electronics knowledge, have read the manuals of the radios, have done some ham radio activities years ago under supervision from pros. Otherwise a newbie.&lt;/p&gt;&#xA;" OwnerUserId="17050" LastActivityDate="2020-09-20T10:28:40.187" Title="Old 144MHz rig can transmit/receive signal but not voice" Tags="&lt;transceiver&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17324" PostTypeId="2" ParentId="15921" CreationDate="2020-09-20T07:56:48.413" Score="1" Body="&lt;p&gt;Commercially, the distribution of the two modes is pretty much as you say,but in Amateur Radio, SSB is used in all bands.&lt;/p&gt;&#xA;&lt;p&gt;Generally, FM is also usable in all bands, but usually, only very small frequency&#xA;deviations are allowable below the Ham &amp;quot;10 metre band&amp;quot;.(about 28 MHz to 29.9MHz)&lt;/p&gt;&#xA;&lt;p&gt;In Commercial &amp;quot;two way radio&amp;quot;, FM is preferred over SSB, because, in use, the probable necessity of adjusting a &amp;quot;clarifier&amp;quot; control wastes time.&lt;/p&gt;&#xA;&lt;p&gt;To hams, neither careful tuning nor using the clarifier to resolve an SSB signal are particularly onerous tasks, so commercially produced Amateur Radio transceivers for VHF/UHF can be either &amp;quot;FM only&amp;quot; for the least expensive, or &amp;quot;multimode&amp;quot; for the more costly ones.&lt;/p&gt;&#xA;&lt;p&gt;Older VHF or UHF SSB radios are often used with &amp;quot;transverters&amp;quot; to produce output in that mode on microwave frequencies.&lt;/p&gt;&#xA;&lt;p&gt;There have been handheld SSB radios, but they were mainly on the 10m band.&lt;/p&gt;&#xA;&lt;p&gt;Not quite &amp;quot;HTs&amp;quot;, were the single mode Icom IC 202 &amp;amp; IC502 &amp;quot;handbag&amp;quot; sized SSB/CW radios on 2m &amp;amp; 6m back in the 1970s.&lt;/p&gt;&#xA;&lt;p&gt;The Yaesu FT290/490/690 of the 1980s/90s were nearly small enough to be handheld, &amp;amp; were multimode radios on 2m, 6m, &amp;amp; 70cm, respectively.&lt;/p&gt;&#xA;" OwnerUserId="17792" LastActivityDate="2020-09-20T07:56:48.413" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17325" PostTypeId="2" ParentId="17323" CreationDate="2020-09-20T10:28:40.187" Score="0" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;When I transmit from my HT to the rig in the same room, the signal meter on the rig goes up to 60+ dB (off the chart), but I don't hear my voice&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This doesn't surprise – you're overdriving your receiver. That's why there's an upper end to the &amp;quot;chart&amp;quot;; there's regions of power that simply can't be dealt with.&lt;/p&gt;&#xA;&lt;p&gt;Non-radio Analogy: Your head got unfortunately stuck in a police announcement car's main megaphone horn due to a freak human catapult accident. Are you able to clearly understand what the police is shouting at a demonstration 200 m away?&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;In reverse, I tried transmitting from my rig to my HT. The rig's meter shows RF out, and my HT picks up the signal, but again I do not hear my own voice.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;might be the same in reverse&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Finally, one more test: I tried to contact a friend (several kilometers away) with the rig. I could hear his voice clearly, but he could not hear my voice, only silence during my transmissions.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Which mode was that?&lt;/p&gt;&#xA;&lt;p&gt;Because if FM, and if your friend disabled their squelch: Um, you sent a carrier but did not modulate it (otherwise the unsquelched reception would be noise, not silence). The most likely reason would be a misconfiguration of the audio input, but it might also be a broken audio modulator.&lt;/p&gt;&#xA;&lt;p&gt;I'm an SDR guy. I'd get out my USD7 (bought them in bulk in China...) rtl2832u dongle (you might really be better off buying one of the nicely engineered ones of the rtl-sdr.com or noeelec brand directly), a hefty attenuator¹ and connect my SDR directly to my transmitter, and observe whether the spectrum looks right (e.g. with gqrx), and whether I can make out features like squelch tones when I enable them, see AM when I put the device in AM mode and so on. Narrow it down!&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;¹  your rig has 25 W = 14 dBW = 44 dBm max output power, we don't want to damage our receivers, so let's say -20 dBm is a good target, so ca (44-(-20)) dB ~= 60 dB of attenuation&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-09-20T10:28:40.187" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17326" PostTypeId="2" ParentId="17015" CreationDate="2020-09-20T13:38:27.150" Score="2" Body="&lt;p&gt;Although what you heard was keyed audio transmitted by FM, you can often hear Morse sent by keying a carrier (OK, Hams call it &amp;quot;CW&amp;quot;), with an FM receiver.&#xA;It usually requires a relatively strong signal, however.&lt;/p&gt;&#xA;&lt;p&gt;The receiver goes into &amp;quot;full quieting&amp;quot; during the carrier &amp;quot;on&amp;quot; time, &amp;amp; returns to&#xA;background &amp;quot;hiss&amp;quot;during the &amp;quot;off&amp;quot; time.&lt;/p&gt;&#xA;&lt;p&gt;Although this sounds backwards, you hear the &amp;quot;dits &amp;amp; dahs&amp;quot; as distinct sounds, rather than periods of silence, something like &amp;quot;crunch, crunch, crunchity crunch&amp;quot;, &amp;amp; can read the Morse from that.&lt;/p&gt;&#xA;&lt;p&gt;You can also hear the change in background noise for a strong CW signal with your receiver in AM mode.&lt;/p&gt;&#xA;&lt;p&gt;You mentioned not being able to resolve an FM signal when your Rx is set to AM.&#xA;This is probably because your Baofeng's frequency intervals are too wide to use&#xA;&amp;quot;slope tuning&amp;quot;.&#xA;With a continuously tunable AM, or even SSB receiver, slope tuning will allow you to resolve FM quite well, although the quality on wider deviation signals may not be the best.&lt;/p&gt;&#xA;" OwnerUserId="17792" LastActivityDate="2020-09-20T13:38:27.150" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17327" PostTypeId="2" ParentId="16996" CreationDate="2020-09-20T17:20:09.800" Score="2" Body="&lt;p&gt;Infinitely long radials are ideal. So to directly answer your question: no, there is no such thing as &amp;quot;too long&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;However, infinitely long radials work because the current in the radials approaches zero as distance from the base approaches infinity. At some point the current is negligible, so truncating the radial at any point makes no significant different. As a rule of thumb, 1.5 wavelengths is long enough to be considered infinitely long.&lt;/p&gt;&#xA;&lt;p&gt;More problematic are radials which are not very much larger than a 1/4 wavelength, but are also not resonant. Because the end of the radial is close enough to be significant, the impedance of the radials matters. And because they aren't resonant, they will introduce a reactive component into the impedance. Compensating for that reactance may require modifying the length of the vertical element or introducing a matching network to compensate. This may or may not be a significant problem. Modelling or empirical measurement is the way to figure it out, since it depends on the specific lengths involved.&lt;/p&gt;&#xA;&lt;p&gt;But I understand your underlying problem is getting the antenna to work on 3 bands. If the bands are related in frequency by an odd multiple (for example, 70 cm is 3 times the frequency of 2 meters) then just make the radials a 1/4 wavelength on the lower band and they will also be resonant (or close enough, no need to be exact) on the higher band.&lt;/p&gt;&#xA;&lt;p&gt;For bands that are not harmonically related, another solution is to have a pair of radials that's resonant for each band. Each pair of radials is effectively in parallel: the one that's resonant will have a minimum impedance and thus will take most of the current. The other radials will not be very significant because their relatively high impedance means they have low current. A &lt;em&gt;fan dipole&lt;/em&gt; works on this principle.&lt;/p&gt;&#xA;&lt;p&gt;Or if a lower band already requires radials that are at least 1.5 wavelengths for some higher band, you can probably not worry about dedicated radials for this higher band since the radials are long enough to be considered infinitely long.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="6080" LastEditDate="2020-09-21T15:56:38.780" LastActivityDate="2020-09-21T15:56:38.780" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17328" PostTypeId="2" ParentId="17321" CreationDate="2020-09-20T17:40:22.407" Score="4" Body="&lt;p&gt;Small loops and full-wave loops are very different antennas.&lt;/p&gt;&#xA;&lt;p&gt;There isn't a well-defined distinction between &amp;quot;small loops&amp;quot; and &amp;quot;large loops&amp;quot;, but a typical rule of thumb is a loop is &amp;quot;small&amp;quot; when its diameter is less than 1/10th of a wavelength. At such a size, the phase delay around the loop is negligible and thus the current can be considered equal at any instant for the entire loop. This significantly simplifies the analysis of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;A full-wave loop is electrically not at all like a small loop. Rather, it is similar to a folded dipole. RMS current will be at a maximum at the feedpoint and directly opposite it, and at 90 degrees to those points RMS current will be at a minimum, and voltage at a maximum. Just as in a dipole.&lt;/p&gt;&#xA;&lt;p&gt;In a small loop with multiple turns, the turns are tightly coupled through their shared magnetic field. The tight coupling follows from the small (compared to wavelength) size of the antenna. Putting more turns on a small loop is like putting more turns on a transformer. (Though it's usually better to increase the diameter if possible, if the objective is to encircle the maximum magnetic flux with the least amount of material and lowest resistive loss.)&lt;/p&gt;&#xA;&lt;p&gt;An antenna which was one wavelength is diameter with more than 2 turns would be a very odd antenna indeed. I'm going to guess it's a waste of wire, by this reasoning:&lt;/p&gt;&#xA;&lt;p&gt;The two turns form a balanced transmission line. If you cut this transmission line and unroll it, you get:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/F9aSw.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fF9aSw.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;The feedpoint is N1 and N4: these would be on the same side of the antenna had we not &amp;quot;unrolled&amp;quot; it.&lt;/p&gt;&#xA;&lt;p&gt;What then is going on at N3 and N2? Well, the entire transmission line is 1 wavelength long, so the differential voltage at N1 and N2 must equal the same at N3 and N4.&lt;/p&gt;&#xA;&lt;p&gt;Furthermore, N3 and N2 are actually the same node, because when the loop is put back together this is where the two turns connect.&lt;/p&gt;&#xA;&lt;p&gt;Thus, N1 = N2, and the voltage source is effectively driving both sides of the transmission line in parallel. But the current is split across the two turns, so the feedpoint impedance is quadrupled. (Thanks to Brian K1LI for pointing this out.) While this might be useful in some circumstances, a 4:1 balun might be an easier way to achieve the same effect.&lt;/p&gt;&#xA;&lt;p&gt;If the electrical length of the transmission line isn't exactly 1 wavelength, then there will be some reactive power circulating in this transmission line. Maybe someone will do some NEC modelling to know for sure, but my intuition says this doesn't do anything especially useful.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-09-21T16:50:15.370" LastActivityDate="2020-09-21T16:50:15.370" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17329" PostTypeId="2" ParentId="17321" CreationDate="2020-09-20T18:22:37.887" Score="2" Body="&lt;p&gt;Well put, Phil. According to a simulation comparing a 1-turn full-wave loop to 2-turns of the same loop, the radiation pattern is the same while the feedpoint impedance increases by a factor of four:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ePUhu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ePUhu.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;These values are for an antenna less than a half-wave above the ground. Raising it to a half-wave above ground does move the maximum radiation to lower angles, but the impedance increases by the same ratio.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-09-20T18:22:37.887" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17330" PostTypeId="1" AcceptedAnswerId="17334" CreationDate="2020-09-22T04:53:42.043" Score="0" ViewCount="169" Body="&lt;p&gt;For a typical EFHW antenna, let's say we are in a very space-restricted environment, says a hotel room.&#xA;I am thinking of the idea loop around the wire around the room, maybe even many loops.&lt;/p&gt;&#xA;&lt;p&gt;This is just an &amp;quot;get on the air somehow&amp;quot; antenna, and I know it would be very compromised.&lt;/p&gt;&#xA;&lt;p&gt;What I am curious is how this will likely change SWR curve and pattern? Would the turns add the inductance?&lt;/p&gt;&#xA;&lt;p&gt;Sorry if I make it confusing EFHW and Long Wire, I don't really understand the detailed difference.&lt;/p&gt;&#xA;" OwnerUserId="13362" LastEditorUserId="8717" LastEditDate="2020-09-23T18:30:14.670" LastActivityDate="2020-09-26T17:28:34.597" Title="Loop a long wire antenna or EFHW" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wire-antenna&gt;&lt;efhw&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17331" PostTypeId="2" ParentId="9098" CreationDate="2020-09-22T12:14:06.393" Score="2" Body="&lt;p&gt;The sidebands generated by frequency modulation are not as simple as those with AM, as their distribution is affected by both the amplitude &amp;amp; frequency of the modulating signal.&#xA;A normal VHF station with a &amp;quot;max deviation&amp;quot; of 50 kHz will actually deviate 50kHz above &amp;amp; above the unmodulated carrier frequency, for a total bandwidth of 100kHz.&#xA;In practice, a stereo FM station will have sideband components occupying out to near 200kHz in total.&lt;/p&gt;&#xA;&lt;p&gt;In contrast, an AM Tx with a similar audio bandwidth will occupy a tad over 30kHz RF bandwidth.&#xA;In Australia, MF AM stations normally transmit an audio bandwidth of 9kHz, amounting to an occupied RF bandwidth of 18kHz-----other countries use much more constrained bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;OK, why not reduce deviation so an FM signal fits into the same bandwidth as an AM station?&lt;/p&gt;&#xA;&lt;p&gt;As you reduce the deviation of FM, two limiting factors start to occur.&#xA;Narrow band FM cannot reproduce the same bandwidth audio as AM or VHF WBFM.&#xA;Unfortunately, there is also a &amp;quot;double whammy&amp;quot;, in that its noise rejection deteriorates.&lt;/p&gt;&#xA;&lt;p&gt;If you increase the deviation to avoid these problems,you are back to &amp;quot;square one&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;NBFM &lt;strong&gt;is&lt;/strong&gt; used for communications work, where 'speech quality&amp;quot;audio is satisfactory.&lt;/p&gt;&#xA;&lt;p&gt;Unintended long distance propagation of WBFM VHF broadcasts, or even analog VSB TV with its accompanying FM sound signal is not uncommon during Tropospheric ducting conditions.&#xA;This can be 100s to 1000s of km.&lt;/p&gt;&#xA;&lt;p&gt;Amateur Radio operators( &amp;quot;hams&amp;quot;) using VHF &amp;amp; UHF NBFM radios more consistently make use of this phenomenon, usually during summer.&lt;/p&gt;&#xA;&lt;p&gt;Hams do use FM below VHF, as does the old EU 27 MHz CB band.&#xA;Long distance reception of both full sideband AM &amp;amp; NBFM via ionospheric propagation can suffer from &amp;quot;selective fading&amp;quot;.&#xA;This is because the various sidebands are refracted slightly differently by the ionosphere, so they are shifted in phase, &amp;amp; begin to cancel.&lt;/p&gt;&#xA;&lt;p&gt;That said, under good ionospheric propagation conditions, a distant 29MHz NBFM signal sounds very much like a distant 146MHz NBFM signal received under good Tropospheric propagation conditions.&lt;/p&gt;&#xA;&lt;p&gt;It is almost impossible to answer this question in a few paragraphs, as it is difficult to avoid introducing terms which require study in their own right.&lt;/p&gt;&#xA;" OwnerUserId="17792" LastActivityDate="2020-09-22T12:14:06.393" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17332" PostTypeId="2" ParentId="17330" CreationDate="2020-09-22T14:30:46.747" Score="1" Body="&lt;p&gt;&amp;quot;EFHW&amp;quot; means end-fed half-wave. It is by definition a half-wavelength long, so it is not short. And it's fed at the end, so it can't be a loop, which has no ends. I wouldn't say it's a very good choice for a space-limited application.&lt;/p&gt;&#xA;&lt;p&gt;There are loop antennas too, and any wire antenna can be bent or curved, though that may make it a very different antenna. Any wire will radiate, but the radiation pattern and feedpoint impedance may be substantially altered. That doesn't mean it won't work, it just means someone would need to build the antenna and measure it to find out, or enter the precise geometry into a modeling program.&lt;/p&gt;&#xA;&lt;p&gt;However, in your situation, I would recommend looking at antennas designed for mobile use, rather than trying to cram a large antenna in a small space. Going this way I think you'll get more consistent performance.&lt;/p&gt;&#xA;&lt;p&gt;For example, see the MFJ Ham Stick. Ideally you can mount it on a balcony railing similar, but if such a thing isn't available you can lay out some radials made of ordinary copper wire. There are also brackets that mount two of these antennas base-to-base, making a short dipole which requires no radials.&lt;/p&gt;&#xA;&lt;p&gt;Of course there are many such antennas, and some are tunable, can operate on multiple bands, and so on. The Ham Stick isn't anything magic, it's a &lt;a href=&quot;http://www.antenna-theory.com/antennas/monopole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;monopole antenna&lt;/a&gt; with some inductive loading. You can make your own such antenna by winding a coil and sticking it in the middle of a stiff wire. And if you enjoy antenna experimentation I absolutely encourage you to try it, but if you just want to get on the air you can find mobile antennas that are really cheap and don't need anything but minor tuning adjustments to get on the air.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-22T14:30:46.747" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17333" PostTypeId="1" AcceptedAnswerId="17336" CreationDate="2020-09-23T04:10:50.110" Score="2" ViewCount="962" Body="&lt;p&gt;Are there any antenna that have disk like lobes :&#xA;&lt;a href=&quot;https://i.stack.imgur.com/FK6Df.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FK6Df.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Or are there any antenna that have very thin directivity, say lobes be no more wide than few mm.&lt;/p&gt;&#xA;" OwnerUserId="17805" LastActivityDate="2020-09-25T08:05:41.090" Title="Are there any antenna that can create disk like lobes?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;radio-programming&gt;" AnswerCount="4" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17334" PostTypeId="2" ParentId="17330" CreationDate="2020-09-23T10:42:48.630" Score="0" Body="&lt;p&gt;I had an antenna like this in an apartment many years ago. I was able to get out somewhat. Most likely the higher up you are in your complex, the better. But it took a kW amp and a matchbox to generally let my signal be heard. It was a fun project and did keep me on the air. Not well but on the air none the less. If I were to do it again I think I would try for a drop down wire out the window, retrievable after the session was over with and probably best at night time under the cover of darkness.&lt;/p&gt;&#xA;&lt;p&gt;As an aside I had a couple of visitors who also resided in the complex over and their eyes caught the wire strung all around at the ceiling level and they had questions. I explained that it was for my stereo (never mind that there was no connection of the wire to the stereo. And that it allowed me to receive a desired distant station that I could not hear without it). They accepted the answer as very reasonable and forgot about it.&lt;/p&gt;&#xA;&lt;p&gt;A plus for the setup was that one of my neighbors liked to leave the bars at closing time and bring the party back to his unit accompanied by full on volume of music rattling the walls. Not wanting any involvement by the super for obvious reasons of my own stealth operations I proceeded to crank up the kW on 10 meters and sure enough his stereo was a fine one for picking up the stray RF,  the buzz's and whistles that out of tune and near proximity from a tx can produce. It was even more hilarious when I took to the morse code key allowing many thumps to be added to the music beat. The stereo would be shut off and re fired up over and over a few times to 'fix' it and failing that all of a sudden car doors could be heard opening and slamming shut, signaling that the party was moving to a more hospitable location and one with a 'working' stereo.  True Story both.&lt;/p&gt;&#xA;" OwnerUserId="17808" LastEditorUserId="76" LastEditDate="2020-09-24T15:15:32.823" LastActivityDate="2020-09-24T15:15:32.823" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17335" PostTypeId="2" ParentId="17333" CreationDate="2020-09-23T12:17:49.470" Score="4" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;antenna that have disk like lobes&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The pattern of an antenna is &lt;em&gt;never&lt;/em&gt; going to be disk-shaped (because the directivity is angle-dependent, not limited to a volume).&lt;/p&gt;&#xA;&lt;p&gt;But:  an omnidirectional antenna (in azimuth) with a very high directive gain in elevation  approximates what you want.&lt;/p&gt;&#xA;&lt;p&gt;A simple vertical stack of vertical half-wavelength dipoles, driven in phase, gets that directivity. See: &amp;quot;array gain&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Notice that&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the more gain an antenna has in one direction (here: vertical), the longer it has to be in that direction.&lt;/li&gt;&#xA;&lt;li&gt;Building antennas with high gain that also have the same pattern for a large range of frequencies is very hard to physically impossible&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-09-23T12:17:49.470" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17336" PostTypeId="2" ParentId="17333" CreationDate="2020-09-23T12:42:06.897" Score="12" Body="&lt;p&gt;The answer from a theoretical purist is probably, &amp;quot;No,&amp;quot; because your diagram specifies zero radiation outside of the disk. Practically speaking, there will always be some radiation above and below the disk and the shape of the disk will not be as perfect as you describe.&lt;/p&gt;&#xA;&lt;p&gt;A well known solution that approaches your requirements comprises multiple collinear elements with carefully-chosen current amplitudes and phases. Here are plots from a NEC-2 simulation of a simple example with three elements:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/clymn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/clymn.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Each element is 0.615&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; long, the vertical spacing between the element feedpoints is 0.6275&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; and the center element is driven with twice the current amplitude of the outer elements. Notice the not-perfectly-disk-shaped pattern and the deeply-attenuated side-lobes.&lt;/p&gt;&#xA;&lt;p&gt;Varying any of these parameters will affect the results, as well as the driving-point impedance of each element, to a greater or lesser degree according to your needs.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-09-24T16:08:40.830" LastActivityDate="2020-09-24T16:08:40.830" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17337" PostTypeId="1" CreationDate="2020-09-23T14:14:25.057" Score="2" ViewCount="90" Body="&lt;p&gt;I am looking for a simple schematic for building an effective RF detector which can trigger a GPIO. The goal is to (passively?) detect a 10 mW RF signal (10% duty cycle) and have that raise voltage on a pin to somewhere north of 0.5V within 2 seconds of the signal going live.&lt;/p&gt;&#xA;&lt;p&gt;I have some Avago/Broadband/Agilent/HP HSMS-2855 chips coming my way, which I understand are wonderfully good zero-bias RF detectors. However, it's not clear to me whether I can slap a random antenna on and go have some fun, or if I still need to pay careful attention to impedance matching, filtering, etc...&lt;/p&gt;&#xA;&lt;p&gt;I have read &lt;a href=&quot;https://www.semanticscholar.org/paper/An-Ultra-Low-Power-Wake-Up-Receiver-for-Real-time-Bdiri-Derbel/c24c7e48095a204ca69534cf4bd1ef5c3ed52152?p2df&quot; rel=&quot;nofollow noreferrer&quot;&gt;An Ultra-Low Power Wake-Up Receiver for Real-time constrained Wireless Sensor Networks&lt;/a&gt;, but the pictured board shows a complex PCB with a high part count and large footprint.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.cs.virginia.edu/%7Estankovic/psfiles/RadioTrigger.JRTS.10.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio-Triggered Wake-Up for Wireless Sensor Networks&lt;/a&gt; is wonderfully well written and gives great hand-holding in case the designer wants to add range. However, Figure 3, where it gives a simple RF detector schematic, is confusing to the layman because there's no ground drawn to the antenna [Update: see comment section below].  Here's Figure 3 from that paper:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DnPXp.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DnPXp.png&quot; alt=&quot;Figure 3 from the second reference, showing a very simple radio detector schematic&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://repository.library.northeastern.edu/files/neu:1340/fulltext.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Design Optimization and Implementation for&#xA;RF Energy Harvesting Circuits&lt;/a&gt; (related spinoff papers &lt;a href=&quot;http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=81F2DDBF5A8DAB65D8DBBC232448F572?doi=10.1.1.232.9878&amp;amp;rep=rep1&amp;amp;type=pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;1&lt;/a&gt; and &lt;a href=&quot;http://raiith.iith.ac.in/1851/1/KaushikMDSJCBH15.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;2&lt;/a&gt;) is another very well written resource, diving into fascinating detail on practical optimality choices, but it does not present the final tested schematic.&lt;/p&gt;&#xA;&lt;p&gt;I'm hoping this is the RF detector equivalent of a paperweight, that is to say there's no need for refinement, it doesn't matter if it's ugly, and there's almost no way to do it wrong.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;h2&gt;Appendix&lt;/h2&gt;&#xA;&lt;p&gt;Typically, one would want an OOK stage in order to disambiguate between other signals which might trigger a false positive, but because in my application the nearest possible source of EM radiation is hundreds of meters away, and because the consequences of a false positive-- even if it's tens of times a day-- are negligible there's much less need for complexity. KISS, price, and compactness are higher priorities.&lt;/p&gt;&#xA;" OwnerUserId="17809" LastEditorUserId="76" LastEditDate="2020-09-24T15:19:11.850" LastActivityDate="2020-09-24T15:19:11.850" Title="Building a low-power simple RF frequency (433MHz or 900MHz (but not both)) detector effective at 5m with a 10mW signal" Tags="&lt;antenna&gt;&lt;rfi&gt;&lt;equipment-design&gt;&lt;testing&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17338" PostTypeId="2" ParentId="17333" CreationDate="2020-09-23T15:35:42.130" Score="7" Body="&lt;p&gt;Achieving such a sharp radiation pattern is difficult. There are many effects that can can cause the radiation pattern of an antenna to be less &amp;quot;sharp&amp;quot;. Some of them can be fixed through engineering, such as by manufacturing components to tighter tolerances. Others are unavoidable physical limits. In the best case, &lt;a href=&quot;https://en.wikipedia.org/wiki/Diffraction-limited_system&quot; rel=&quot;noreferrer&quot;&gt;diffraction will limit the maximum sharpness&lt;/a&gt; of the disk. The very sharpest sources of electromagnetic radiation are lasers, which achieve a &lt;a href=&quot;https://en.wikipedia.org/wiki/Beam_divergence&quot; rel=&quot;noreferrer&quot;&gt;beam divergence&lt;/a&gt; approaching:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \theta = {\lambda \over \pi w} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt; is the angle between the edges of the beam, &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; is the wavelength, and &lt;span class=&quot;math-container&quot;&gt;$w$&lt;/span&gt; is the diameter of the &amp;quot;waist&amp;quot; of the beam, that is the beam's diameter at its narrowest point. Often, this is the aperture of the laser cavity.&lt;/p&gt;&#xA;&lt;p&gt;It follows then if you want a laser with very low beam divergence, and thus, a very &amp;quot;sharp&amp;quot; radiation pattern, you require a very large aperture.&lt;/p&gt;&#xA;&lt;p&gt;Radio antennas aren't lasers, but like lasers they are emitters of coherent electromagnetic radiation. But very significantly, the wavelength (&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;) of radio waves is much greater than in a laser. Thus, achieving a smaller beam divergence requires a much larger aperture.&lt;/p&gt;&#xA;&lt;p&gt;Not all antennas have an obvious physical aperture, but some do, such as dish antennas. An antenna with a larger dish will have a sharper radiation pattern than a smaller dish. Likewise, the same dish size at a higher frequency will be sharper than a lower frequency.&lt;/p&gt;&#xA;&lt;p&gt;If you want a disk and not a beam, you're looking for a low beam divergence in just one dimension. You could achieve that with a custom reflector, and the bigger you can make the reflector the sharper the disk will be. Alternately, you can use a co-linear array like &lt;a href=&quot;https://ham.stackexchange.com/a/17336/218&quot;&gt;Brian K1LI suggests&lt;/a&gt;. The more elements in the array, the sharper the radiation pattern becomes.&lt;/p&gt;&#xA;&lt;p&gt;But if your objective is to detect the position of a falling object (with some kind of radio transmitter on it, I presume), you can do even better by using an array of antennas as an &lt;a href=&quot;https://en.wikipedia.org/wiki/Interferometry&quot; rel=&quot;noreferrer&quot;&gt;interferometer&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1xs6f.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1xs6f.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://xkcd.com/1922/&quot; rel=&quot;noreferrer&quot;&gt;XKCD: Interferometry&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The idea is to compare the &lt;em&gt;phase&lt;/em&gt; of the received signal at two or more antennas. The difference in phase corresponds to the difference in path length between them, and from that you can triangulate the position of the object.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-23T15:35:42.130" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17339" PostTypeId="1" AcceptedAnswerId="17342" CreationDate="2020-09-23T16:35:28.433" Score="1" ViewCount="77" Body="&lt;p&gt;Trying to grasp antenna phase, reading through ham.se and youtube but haven't come across a clear (enough) explanation.&lt;/p&gt;&#xA;&lt;p&gt;I understand the basics of antenna phase (i think), where E leads I that's inductive-reactance, where E lags I that's capacitive-reactance, and where E=I that's resonance.&lt;/p&gt;&#xA;&lt;p&gt;Easy enough, but then in phased-arrays (say verticals), how does phase relate to beam-formation?&lt;/p&gt;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="17200" LastActivityDate="2020-09-25T11:06:15.560" Title="Antenna phase explanation" Tags="&lt;antenna&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17340" PostTypeId="2" ParentId="17337" CreationDate="2020-09-23T16:49:23.090" Score="2" Body="&lt;p&gt;Well, your GPIO will need a defined voltage level and a couple of µA of drive strength, so completely &amp;quot;passive&amp;quot; is probably not really possible.&lt;/p&gt;&#xA;&lt;p&gt;Now, you'll need  the following:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Antenna&#xA;&lt;ol&gt;&#xA;&lt;li&gt;potentially, amplification here&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;Filtering&#xA;&lt;ol&gt;&#xA;&lt;li&gt;potentially, amplification here&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;Rectification&lt;/li&gt;&#xA;&lt;li&gt;Thresholding&lt;/li&gt;&#xA;&lt;li&gt;GPIO activation&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;For antenna choices, see &lt;a href=&quot;https://e2echina.ti.com/cfs-file/__key/telligent-evolution-components-attachments/13-110-00-00-00-00-89-27/AN058-_2D002D00_-Antenna-Selection-Guide.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Texas Instrument's antenna selection guide&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Will probably simply be a stumpy coil antenna for 433 MHz, and might be PCB antenna or even a chip antenna for 900 MHz.&lt;/li&gt;&#xA;&lt;li&gt;Antenna  -&amp;gt; capacitor -&amp;gt; LNA (&lt;a href=&quot;https://de.farnell.com/nxp/bga2800-115/rf-amplifier-2-2ghz-tssop-6/dp/2890366&quot; rel=&quot;nofollow noreferrer&quot;&gt;example&lt;/a&gt;, ca 10 ct) -&amp;gt; Filter (&lt;a href=&quot;https://de.farnell.com/stmicroelectronics/balf-spi2-02d3/hf-filter-balun-433mhz-flip-chip/dp/2980867&quot; rel=&quot;nofollow noreferrer&quot;&gt;example&lt;/a&gt;, ca 40ct)&lt;/li&gt;&#xA;&lt;li&gt;RF Schottky Diode (&lt;a href=&quot;https://de.farnell.com/infineon/bat1707e6327htsa1/schottky-diode-0-13a-sot-143/dp/3155004RL&quot; rel=&quot;nofollow noreferrer&quot;&gt;example&lt;/a&gt;) -&amp;gt; RC low-pass filter with cutoff above 1/(minimum pulse length)&lt;/li&gt;&#xA;&lt;li&gt;opamp in comparator configuration (DON'T use any opamp before 1984): connecting the non-inverting input to a virtual ground defined by a trimmer between VCC and ground&lt;/li&gt;&#xA;&lt;li&gt;(optional) buffering of opamp output with MOSFET or BJT&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Important: learn to use SPICE so that you can simulate the elements of your detector. It's time well-invested, as &amp;quot;KISS&amp;quot; means &amp;quot;don't try to measure something for hours that simply doesn't work, which you could have seen in simulation&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Your RF detectors can take jobs 3 to 5, but you'll still have to make the things frequency selective, so there's little way around 2.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-09-23T16:49:23.090" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17341" PostTypeId="2" ParentId="17339" CreationDate="2020-09-23T17:02:04.130" Score="2" Body="&lt;p&gt;Well, what you describe is the phase of a complex current. That's not inherently the same thing as the phase of an electromagnetic wave! But it's the basics of all electrical theory, so it's necessary you understand it, so you've got a good basic education there.&lt;/p&gt;&#xA;&lt;p&gt;So, sorry to drop more theory on you:&lt;/p&gt;&#xA;&lt;p&gt;In free space propagation, there's no current, and no voltage. There's an instantaneous magnetic field &lt;span class=&quot;math-container&quot;&gt;$H(t)$&lt;/span&gt;, and an instantaneous electrical field &lt;span class=&quot;math-container&quot;&gt;$E(t)$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;In vacuum or air, these two are always in phase; that's a result of Maxwell's formulas, which explain how a changing electrical field can lead to an electromagnetic wave that propagates.&lt;/p&gt;&#xA;&lt;p&gt;So, it doesn't really matter whether you look at the E-field or the H-field of an electromagnetic wave – the other is in phase.&lt;/p&gt;&#xA;&lt;p&gt;Thus, we simply give the whole wave a property &amp;quot;phase&amp;quot;, and that's a relative quality: Two RF things have a phase &lt;span class=&quot;math-container&quot;&gt;$\alpha$&lt;/span&gt; if one thing is, at the same instant,  &lt;span class=&quot;math-container&quot;&gt;$\alpha$&lt;/span&gt; degrees behind the other.&lt;/p&gt;&#xA;&lt;p&gt;For example, two dipole antennas that get excited by exactly the same current have 0° phase. If instead the current feeding the antenna has to travel half a wavelength more to the antenna than to the other, that antenna has a phase of 180° (relative to the other – there's not really an &amp;quot;absolute phase&amp;quot;).&lt;/p&gt;&#xA;&lt;p&gt;Now, what does that have to do with beam forming?&lt;/p&gt;&#xA;&lt;p&gt;Because that is a complex topic, I'll remind you of the &lt;a href=&quot;https://en.wikipedia.org/wiki/Double-slit_experiment#Classical_wave-optics_formulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;double-slit experiment&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;img src=&quot;https://upload.wikimedia.org/wikipedia/commons/4/4c/Ebohr1.svg&quot; &gt;&#xA;&lt;p&gt;If you have two slits on a line, in a defined distance, from which both concentrical waves emit, then there will be points on the plane where the waves interfere. The phase of the waves, and the distance from a point to the slits, defines whether that interference is constructive or destructive.&lt;/p&gt;&#xA;&lt;p&gt;That works with water waves in a harbour, as it does with electromagnetic waves such as laser light or radio waves.&lt;/p&gt;&#xA;&lt;p&gt;You can influence where the constructive interference happens by&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;varying the distance between the emitters (your antennas!) or by&lt;/li&gt;&#xA;&lt;li&gt;giving one a phase relative to the other.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-09-25T11:06:15.560" LastActivityDate="2020-09-25T11:06:15.560" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17342" PostTypeId="2" ParentId="17339" CreationDate="2020-09-23T18:08:53.947" Score="4" Body="&lt;p&gt;What you are describing is not &amp;quot;antenna phase&amp;quot; but &lt;a href=&quot;https://en.wikipedia.org/wiki/Electrical_impedance&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance&lt;/a&gt;. An antenna, like many two-terminal devices, is a load that can be described by an impedance. It can be purely resistive (like a resistor), meaning current and voltage are in phase. Or it can be reactive (like a capacitor or inductor) with current and voltage being 90 degrees out of phase. Or it can be some combination of both.&lt;/p&gt;&#xA;&lt;p&gt;The feedpoint impedance does not influence the radiation pattern of the antenna per se. However, the &lt;a href=&quot;https://en.wikipedia.org/wiki/AC_power#Active,_reactive,_and_apparent_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;reactive power&lt;/a&gt; doesn't contribute to radiation, so efficient antennas will often have a mostly resistive feedpoint impedance.&lt;/p&gt;&#xA;&lt;p&gt;There is a notion of &amp;quot;antenna phase&amp;quot; that is different from what you describe but relevant in phased arrays. In this sense, &amp;quot;phase&amp;quot; doesn't refer to the phase relationship between current and voltage, but rather the phase relationship between different elements in the array. Assume (because it's a common case) that all the antennas have a purely resistive, 50 ohm impedance. So current and voltage and any feedpoint will have the same phase. &lt;em&gt;Antenna phase is not about that&lt;/em&gt;. Rather, compare the phase of the signal fed to each antenna: are they all reaching peak at the same time? Or is one lagging behind the other?&lt;/p&gt;&#xA;&lt;p&gt;Manipulating the phase of the antennas in this way influences the direction in which the array achieves maximum gain. Maximum gain is realized where the wavefronts from each antenna in the array arrive in the same phase, and thus add constructively. That phase is influenced by the distance the wave had to travel &lt;em&gt;and&lt;/em&gt; the phase of the wave at the radiating antenna.&lt;/p&gt;&#xA;&lt;p&gt;If you had for example 2 verticals spaced 1/4 wavelength apart, then feeding them with the same phase will create maximum gain broadside to the array. But if the signal to one of these verticals is delayed by 90 degrees, for example by adding a quarter wavelength of feedline to it, you will have created an endfire array with a cardioid pattern.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-23T18:08:53.947" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17343" PostTypeId="1" CreationDate="2020-09-23T23:11:54.037" Score="0" ViewCount="90" Body="&lt;p&gt;How should a coax-to-housing connection like this be weatherproofed? It doesn't seem like taping is going to do much good here&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/h6IDC.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/h6IDC.jpg&quot; alt=&quot;balun housing with SO-239&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="11639" LastActivityDate="2020-09-26T17:15:08.283" Title="Weatherproofing coax connection to balun" Tags="&lt;coaxial-cable&gt;&lt;balun&gt;&lt;weather&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17344" PostTypeId="2" ParentId="17337" CreationDate="2020-09-24T03:40:09.317" Score="2" Body="&lt;p&gt;I'm going to disagree with Marcus and say that you can probably get this to work, for some relaxed definition of &amp;quot;work&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;The detector you've drawn has poor &lt;em&gt;selectivity&lt;/em&gt;, meaning it will detect quite a lot of stuff besides the intended signal. The inductor and capacitor provide some amount of filtering, but not nearly as good as you'd get in any basic receiver.&lt;/p&gt;&#xA;&lt;p&gt;Aside: the better that filter is, the more sensitive to temperature variation it will be. Also, at 900 MHz you'll have to give some thought to the circuit layout, since at this frequency parasitics can be pretty significant.&lt;/p&gt;&#xA;&lt;p&gt;On the other hand, path loss at 900 MHz and 5 meters is only 45.5 dB. Assuming 0 dBi of gain on both antennas that means you're looking at a received power around -36 dBm. That's pretty strong, even feasibly the strongest thing around if there are no other electronics nearby. This is good news because it means poor selectivity of the detector is not much of a problem. If you're near any WiFi radios, cell towers, broadcast stations, or even very near any digital electronics, you'll probably have trouble.&lt;/p&gt;&#xA;&lt;p&gt;The one area you'll probably need to improve is amplification of Vout. Although -35.5 dBm is fairly strong for a received RF signal, it's probably not going to be enough to reach the GPIO's threshold. Addressing that is a simple matter of adding a comparator, op-amp, or even a simple transistor.&lt;/p&gt;&#xA;&lt;p&gt;If you want a step up in sophistication, there are integrated RF transmitters and receivers that are &lt;em&gt;really&lt;/em&gt; cheap. Besides helping with a lot or all of the amplification and filtering, they also provide digital modulation and demodulation.&lt;/p&gt;&#xA;&lt;p&gt;Or if you want the satisfaction of building something yourself, it wouldn't be too complex to make a mixer, which would convert the 433 or 900 MHz down to a frequency low enough that it could be sampled by the ADC on a microcontroller. Then you can do some very simple demodulation to confirm the signal is from your device and not noise. A good receiver will include some filtering to reject image frequencies and maximize dynamic range, etc., but if your performance requirements are low then you can skip all that stuff and simplify the circuit substantially.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-24T03:40:09.317" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17345" PostTypeId="1" CreationDate="2020-09-24T08:22:40.130" Score="0" ViewCount="174" Body="&lt;p&gt;I am new at gnuradio companion and USRP and I am a little bit confused with UHD:USRP Sink block. I am trying to build an FMCW radar in USRP N210 with CBX40 daughterboard. I want to generate a sweep from 2GHz to 3GHz. First, I’ve generated the sweep in baseband which I want to upconvert to my desired frequency range. My grc diagram is the following:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/n75eq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/n75eq.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;At the output of the Hilbert block I can see the baseband frequency sweep. However, I connect my USRP to an Spectrum Analyzer and I only see a tone at 2.2GHz (the Center Frequency I set in the UHD:USRP Sink block).&lt;/p&gt;&#xA;&lt;p&gt;I expected the frequency at the output of my usrp to be the sum of the baseband frequency and the center frequency.&lt;/p&gt;&#xA;&lt;p&gt;Is there anything I am misunderstanding? Should I modify any of the settings?&lt;/p&gt;&#xA;&lt;p&gt;Thank you in advance,&lt;/p&gt;&#xA;" OwnerUserId="17812" LastEditorUserId="17812" LastEditDate="2020-09-24T15:14:37.180" LastActivityDate="2020-09-24T15:14:37.180" Title="FMCW radar with USRP and GNU Radio Companion" Tags="&lt;gnuradio&gt;&lt;frequency&gt;&lt;usrp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17346" PostTypeId="2" ParentId="17343" CreationDate="2020-09-24T11:41:39.193" Score="4" Body="&lt;p&gt;In my experience, the small amount of exposed thread on the SO-239 after inserting the PL-259 is the primary challenge in weatherproofing this connection. The first line of defense is to orient the housing with the connector pointing toward the ground to prevent water from pooling around the joint, particularly in the presence of ice and snow.&lt;/p&gt;&#xA;&lt;p&gt;I break the challenge down into two parts:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;preventing water from getting to the joint&lt;/li&gt;&#xA;&lt;li&gt;since you may not be able to &lt;em&gt;completely&lt;/em&gt; and &lt;em&gt;forever&lt;/em&gt; prevent water from getting to the joint, preventing water from progressing along the threads of the joint once it has gained access&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;In order of application, my solution to (2) comes first: apply a &lt;em&gt;very thin&lt;/em&gt; film of NoAlOx or similar loaded grease to the threads of the SO-239 on the housing. By &lt;em&gt;very thin,&lt;/em&gt; I mean the threads should have a uniformly black appearance from the grease compared to their metallic appearance without the grease, and a PL-259 should screw on more smoothly. Excess grease may impair RF contact between the PL (plug) and the SO (socket). I have found it sufficient to wipe the threads with fingers or a soft cloth. This thin layer of loaded grease also prevents the PL from seizing on the SO, which can be very annoying or even make it impossible to remove the PL from the SO without damage.&lt;/p&gt;&#xA;&lt;p&gt;My preferred solution to (1) comes in the form of rubber splicing tape. Even in my rural QTH, this product is available at the local hardware store. &lt;a href=&quot;https://static.dxengineering.com/pdf/WeatherProofingCoax-TechTip.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Engineering&lt;/a&gt; posted some helpful guidance on the use of this tape, but the essence is to remove the backing from a length of tape and stretch the tape as you wind it over to the joint, overlapping succeeding layers by about 50% on the preceding layers. A primary benefit of rubber splicing tape over adhesive products like &lt;a href=&quot;http://coaxseal.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Coax-Seal&lt;/a&gt; is the ease of removal: no need for exhaustive mechanical or solvent cleanup.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-09-24T12:34:39.753" LastActivityDate="2020-09-24T12:34:39.753" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17347" PostTypeId="2" ParentId="17345" CreationDate="2020-09-24T12:45:19.033" Score="2" Body="&lt;p&gt;You've got a few very concerning conceptual and technical problems there, many of which will be adressed by the console output, which you should probably read!&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You can only sweep within your nyquist bandwidth. That is at most 25 MS/s (at 16 bit sample depth) or 50 MS/s (at 8 bit sample depth) for the N210&lt;/li&gt;&#xA;&lt;li&gt;You want a single-tone sweep from negative baseband to positive baseband frequencies. So, generate a complex oscillation from the start; don't use a real-valued oscillator and a Hilbert transformer.&lt;/li&gt;&#xA;&lt;li&gt;200 kHz is far too low a sampling rate. Try 2 or 20 MS/s. Again, this defines the bandwidth you can sweep in. (read the console)&lt;/li&gt;&#xA;&lt;li&gt;The 30.72 MHz master clock rate is impossible for an N210 – leave that field blank, you'll get 100 MHz (the only possible rate). (read the console)&lt;/li&gt;&#xA;&lt;li&gt;0 gain: Practically zero output&lt;/li&gt;&#xA;&lt;li&gt;The bandwidth of the CBX is fixed at 40 MHz, your bandwidth setting will be ignored(read the console)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I'll allow myself the assessment that you're not really aware of what &lt;em&gt;complex baseband&lt;/em&gt; is, and haven't really realized how bandwidth of a system relates to sample rate. I'm afraid that's something you should really read up on if you're doing SDR.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-09-24T12:45:19.033" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17348" PostTypeId="2" ParentId="17343" CreationDate="2020-09-24T17:50:50.493" Score="2" Body="&lt;p&gt;Properly applied tape is the appropriate solution: &lt;a href=&quot;https://ham.stackexchange.com/a/12564/218&quot;&gt;https://ham.stackexchange.com/a/12564/218&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The box, and the connection between the connector and the box should already be waterproofed if the balun is made well. If not, you could always disassemble and put it back together with some silicone sealant, and add a weep hole somewhere for residual moisture to get out.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-24T17:50:50.493" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17349" PostTypeId="2" ParentId="17333" CreationDate="2020-09-25T08:00:14.757" Score="0" Body="&lt;p&gt;&amp;quot;Square corners&amp;quot; cannot be generated on the radiation patterns of antennas.&lt;/p&gt;&#xA;&lt;p&gt;The graphic below shows an example of the relative field* gain vs. elevation angle of a commercially-made antenna used for UHF television broadcast stations, and shows the envelope of a practical, high-gain antenna with 0.5° beam tilt and a radiation pattern that is omnidirectional in the horizontal plane.&lt;/p&gt;&#xA;&lt;p&gt;.      *E/Emax&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/2dIcF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/2dIcF.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastEditorUserId="10565" LastEditDate="2020-09-25T08:05:41.090" LastActivityDate="2020-09-25T08:05:41.090" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17350" PostTypeId="1" CreationDate="2020-09-25T14:58:56.060" Score="0" ViewCount="72" Body="&lt;p&gt;I'm using a USRP N210 with this GRC diagram where I'm trying to upconvert a 1kHz sinewave.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ugKLE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ugKLE.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I tried just upconverting the signal from the signal source to 2.5GHz. However, I keep getting the output signal at the frequency of the UHD:USRP Sink Block; this is, I'm not getting the sum of the baseband signal and the USRP signal as expected. What could be the reason?&lt;/p&gt;&#xA;" OwnerUserId="17812" LastEditorUserId="76" LastEditDate="2020-09-25T16:29:35.243" LastActivityDate="2020-09-25T16:29:35.243" Title="Upconvert Signal with USRP N210 in GNU Radio Companion" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;frequency&gt;&lt;usrp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17351" PostTypeId="1" AcceptedAnswerId="17353" CreationDate="2020-09-25T16:01:23.713" Score="2" ViewCount="865" Body="&lt;p&gt;It's understood that ground rods should be spaced by a distance equal to twice their length.  I read one &lt;a href=&quot;https://topbandhams.com/Tech/Lightning%20Protection-Taming%20Thors%20Thunder-On%20A%20Budget.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;source&lt;/a&gt; that claimed reduced effectiveness if the rods are closer than that.  Is that correct?  Or would putting them close together simply be a waste of materials because it would require more rods?&lt;/p&gt;&#xA;" OwnerUserId="6080" LastEditorUserId="6080" LastEditDate="2020-09-25T17:40:02.683" LastActivityDate="2020-09-27T01:39:19.403" Title="Why is it bad to put ground rods too close together?" Tags="&lt;grounding&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17352" PostTypeId="2" ParentId="17350" CreationDate="2020-09-25T16:29:08.727" Score="1" Body="&lt;p&gt;500 kHz = 0.5 MHz = 0.0005 GHz.&lt;/p&gt;&#xA;&lt;p&gt;You're providing a signal at +500 kHz, and then upconverting it to produce a signal at 2.5005 GHz. Are you sure that your measurement of the output frequency (and the USRP's oscillator) is precise enough to distinguish between 2.5000 GHz and 2.5005 GHz, absolute?&lt;/p&gt;&#xA;&lt;p&gt;A way to tell if your signal generation is having any effect is to add modulation. This can be as simple as adding a GUI slider to control the frequency setting of the signal source, and moving it while you watch your spectrum analyzer. It's a lot easier to measure relative values than absolute ones.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-09-25T16:29:08.727" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17353" PostTypeId="2" ParentId="17351" CreationDate="2020-09-25T16:39:34.920" Score="7" Body="&lt;p&gt;Depends on how you want to look at it. Two ground rods spaced close together will be less effective than two rods with sufficient spacing, but still at least as effective as just one rod. So it's not like adding the additional rod will make things &lt;em&gt;worse&lt;/em&gt;, but it won't add as much as it could have.&lt;/p&gt;&#xA;&lt;p&gt;The reason for this: the real earth isn't a perfect conductor (in fact, pretty far from it). You can think of it as something like an infinite grid of low-value resistors, with &amp;quot;true ground&amp;quot; out at infinity. If you raise the voltage at one point (by feeding a current into your ground rod), each resistor will drop a little bit of voltage, and the potential at any node in the grid will be a decreasing function of the distance between that point and the voltage source.&lt;/p&gt;&#xA;&lt;p&gt;Now consider adding a second ground rod — the further it is from the first one, the lower the potential at the point where it ties in, and the more current it will be able to accept, and vice-versa.&lt;/p&gt;&#xA;&lt;p&gt;Caveats of this simple explanation: of course, it should be a 3D mesh, and not a 2D grid — this affects &lt;em&gt;how quickly&lt;/em&gt; the potential drops off, and also explains why the length of the ground rod matters. And this explanation is done at DC — for RF (or lightning, which has a very fast rise time), you would rightfully want to consider capacitive and inductive contributions as well. But hopefully it gives you a rough intuition of why you need to space ground rods apart to get a benefit from having more than one.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-09-25T16:39:34.920" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17354" PostTypeId="2" ParentId="17351" CreationDate="2020-09-25T17:23:10.740" Score="7" Body="&lt;p&gt;One of my favorite lightning anecdotes is &lt;a href=&quot;https://www.w8ji.com/lightning_strikes.htm&quot; rel=&quot;noreferrer&quot;&gt;this story by W8JI&lt;/a&gt;. He had lightning strike a tree, blowing the bark off down the trunk, and making a huge hole in the ground. And then &lt;em&gt;some 20 feet away&lt;/em&gt;, the current arced to a Beverage antenna and traveled the length of the antenna to get to the ground on the other side of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DLBpM.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DLBpM.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The reason for this is soil is a pretty poor conductor. The strike isn't done as soon as it hits soil. Lightning is transferring a huge quantity of electric charge into the soil, and all that charge now wants to spread out over the entire Earth. This means high current in the soil, and since the soil has resistance, by Ohm's law this also means high electric potential.&lt;/p&gt;&#xA;&lt;p&gt;The potential was high enough to create an electrical arc several feet long so the strike current could get to the antenna wire, which presented a much lower impedance path to the distant ground.&lt;/p&gt;&#xA;&lt;p&gt;So because the soil has resistance, and the strike current is very high, the electric potential near where the current is entering the ground is very high, and decreasing with distance:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EnkwN.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EnkwN.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;If one ground rod is placed near another, the current from one ground rod will increase the electric potential of the other, thus making it a less effective sink for current. Two ground rods near each other is never worse than just one ground rod, but increasing the spacing of the ground rods reduces their interaction and makes an overall lower impedance path to ground.&lt;/p&gt;&#xA;&lt;p&gt;Putting ground rods too far apart is also not ideal, because at some length the inductance of the conductor between them becomes detrimental. The optimal spacing depends on soil conductivity and what's connecting them, but a simple rule of thumb is the distance between ground rods should be equal to the length of the rods.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="8717" LastEditDate="2020-09-25T20:41:21.447" LastActivityDate="2020-09-25T20:41:21.447" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17355" PostTypeId="2" ParentId="17197" CreationDate="2020-09-25T22:03:10.710" Score="0" Body="&lt;p&gt;I used a large (roughly 100 foot on leg triangle) for quite a while.  I fed it with parallel feed line and tuned it in the shack.  On higher bands it seemed to have a very low angle of radiation.  On receive all loops I have used delta, quad, folded dipole have so much lower noise that it seems like you are getting gain.  Don't have room for something like that or I'd do it again.  But a couple of 100' trees gets a guy thinking...&lt;/p&gt;&#xA;&lt;p&gt;The loop was in a heavily wooded area about 30 feet off the ground.  Got DXCC off it.&lt;/p&gt;&#xA;" OwnerUserId="17823" LastActivityDate="2020-09-25T22:03:10.710" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17356" PostTypeId="2" ParentId="17197" CreationDate="2020-09-26T01:01:31.860" Score="1" Body="&lt;p&gt;I have been astonished by the receive-only performance of the &lt;a href=&quot;https://www.kkn.net/dayton2014/AntennaForum_SharedApexLoop_KB7GF.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Shared-Apex Loop Array&lt;/a&gt; (SALA) that I have used at a friend's contest station:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gCRfV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gCRfV.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Unlike a beverage, which I believe will run out of gas at 20 meters, the SALA works well from 160 through 20. The SALA also takes up a lot less room than a beverage and erecting an orthogonal pair allows the receive direction can be conveniently switched. Commercial units, offered to cover particular frequency ranges, are available to shorten your time-to-enjoyment.&lt;/p&gt;&#xA;&lt;p&gt;Ideally, I believe you would like to have antennas with horizontal and vertical polarization to realize the benefits of diversity reception. I can't find any documentation of the polarization of the SALA, but it looks like it should be vertical, which could complement your G5RV.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-09-26T01:01:31.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17357" PostTypeId="1" CreationDate="2020-09-26T09:33:48.550" Score="0" ViewCount="27" Body="&lt;p&gt;I'm pretty sure this will be fine but thought I'd ask.&lt;/p&gt;&#xA;&lt;p&gt;A Hustler 5btv antenna, the coax from the feedpoint (ground mounted) runs for 3 or 4 meters along with the radials, and am thinking of going up in the air 4 or 5M to a building into the shack. An overhead run.&lt;/p&gt;&#xA;&lt;p&gt;Ground is concrete so can't dig it in.&lt;/p&gt;&#xA;&lt;p&gt;I can do a ground mount but foot traffic might squash the coax, so overhead would be ideal.&lt;/p&gt;&#xA;&lt;p&gt;There's an RF choke at the feedpoint (2 x FT240-31s wound with 11 turns of rg400) which im thinking should stop the coax from coupling with the RF (my main concern).&lt;/p&gt;&#xA;&lt;p&gt;Thoughts?&lt;/p&gt;&#xA;&lt;p&gt;Thanks.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastEditorUserId="17200" LastEditDate="2020-09-26T09:48:30.133" LastActivityDate="2020-09-26T12:35:46.503" Title="Hustler BTV coax overhead run" Tags="&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17358" PostTypeId="2" ParentId="17357" CreationDate="2020-09-26T12:35:46.503" Score="2" Body="&lt;p&gt;The feedpoint choke will help keep unbalance currents from flowing on the outside of the coax, which is helpful. Being a conductor in the presence of an electromagnetic field, currents may be induced on the coax by radiation from the antenna. This effect will be more pronounced if the coax runs close to the antenna, if it runs parallel to the polarization of the radiation or if the length the coax resonates at the operating frequency. Since currents flow on the radials, they are part of the radiating system and can induce currents on the feedline, so the same effects apply.&lt;/p&gt;&#xA;&lt;p&gt;You can minimize the induced currents on the outside of the coax shield by winding turns of the coax through ferrite toroids - 31 material should be a good choice - at &lt;strong&gt;spacings&lt;/strong&gt; that &lt;strong&gt;avoid&lt;/strong&gt; half wavelengths on the bands you operate. This has two benefits: 1) it prevents the outside of the coax shield from behaving like a half-wave dipole, which would experience maximum induced current; 2) it puts the high choking reactances at lower-impedance points on the shield, where it can be proportionally more effective.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://audiosystemsgroup.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Brown, K9YC&lt;/a&gt;, has published a lot of useful information on techniques, materials and turns required.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-09-26T12:35:46.503" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17360" PostTypeId="2" ParentId="17343" CreationDate="2020-09-26T17:15:08.283" Score="0" Body="&lt;p&gt;Here is one of recommended methods:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/42CmS.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/42CmS.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It's from The ARRL Handbook if I'm not mistaken. Personally I use two layers of electrical tape covered with two layers of varnish.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-09-26T17:15:08.283" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17361" PostTypeId="2" ParentId="17330" CreationDate="2020-09-26T17:28:34.597" Score="0" Body="&lt;p&gt;I've beed working in &amp;quot;very space-restricted environment&amp;quot;. From what I know there are two options:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Shortened vertical, like OPEK HVT-400B and similar. Can be home made as well. Such vertical will work OK on 10m-40m from a balcony, assuming there is space for 5m+ radials.&lt;/li&gt;&#xA;&lt;li&gt;Magnetic loop antenna. Doesn't require radials but it's very narrowband and typically can accept only 10-40W unless a vacuum capacitor is used. Still it works quite well for CW and FT8.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;If you have a window and a tree nearby I highly recommend long wire antenna. A peace of 23m wire + 7m counterpoise + antenna tuner will bring you on all HF bands with good performance. Another option is &lt;a href=&quot;https://m0ukd.com/homebrew/baluns-and-ununs/end-fed-half-wave-antenna-tuned-coupler-efhw/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Fuchs antenna&lt;/a&gt;. It doesn't require a long counterpoise, but will bring you to 40-10 meters with the same matching unit.&lt;/p&gt;&#xA;&lt;p&gt;From my experience the main challenge of working in such environments is not antenna performance, but the noise from switching power supplies though.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2020-09-26T17:28:34.597" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17362" PostTypeId="1" CreationDate="2020-09-26T21:11:55.377" Score="0" ViewCount="33" Body="&lt;p&gt;I'd like to collaborate (e.g. play together) with other musicians in my local area and/or beyond.&lt;/p&gt;&#xA;&lt;p&gt;Coronavirus has made in-person collaboration difficult.  Latency makes internet-based collaboration difficult.&lt;/p&gt;&#xA;&lt;p&gt;Is there a legal way for a group of musicians to play together using radio in the united states?&lt;/p&gt;&#xA;" OwnerUserId="17828" LastEditorUserId="8717" LastEditDate="2020-09-26T22:25:27.103" LastActivityDate="2020-09-26T22:25:27.103" Title="Using radio for musical collaboration" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;transceiver&gt;&lt;transmission&gt;&lt;music&gt;" AnswerCount="0" CommentCount="2" ClosedDate="2020-09-26T22:17:03.420" ContentLicense="CC BY-SA 4.0" />
  <row Id="17363" PostTypeId="2" ParentId="17351" CreationDate="2020-09-27T01:39:19.403" Score="0" Body="&lt;p&gt;Less effective.&lt;/p&gt;&#xA;&lt;p&gt;Too close and not much better than just one of the rods hence making the second one a waste of time money effort to put in.&lt;/p&gt;&#xA;" OwnerUserId="17830" LastActivityDate="2020-09-27T01:39:19.403" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17364" PostTypeId="1" CreationDate="2020-09-27T02:58:54.623" Score="6" ViewCount="252" Body="&lt;p&gt;I'd like to collaborate (e.g. play together) with other musicians in my local area and/or beyond.&lt;/p&gt;&#xA;&lt;p&gt;Coronavirus has made in-person collaboration difficult. Latency makes internet-based collaboration difficult.&lt;/p&gt;&#xA;&lt;p&gt;Is there a legal way for a group of musicians to play together using amateur radio in the United States?&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&lt;strong&gt;Here's what I've found so far:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;The Electronic Code of Federal Regulations (e-CFR), under &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=d4b3c60d2d60000a147f885bdee88264&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5#se47.5.97_1113&quot; rel=&quot;nofollow noreferrer&quot;&gt;Part 97.113&lt;/a&gt; (Amateur Radio Service - Prohibited transmissions), lists&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(4) &lt;strong&gt;Music using a phone emission&lt;/strong&gt; except as specifically provided&#xA;elsewhere in this section; ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;Two notes about the above excerpt:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The &lt;a href=&quot;http://www.arrl.org/ham-radio-glossary&quot; rel=&quot;nofollow noreferrer&quot;&gt;ARRL glossary&lt;/a&gt; defines &amp;quot;phone emission&amp;quot; as &amp;quot;The FCC name for voice or other sound transmissions.&amp;quot;&lt;/li&gt;&#xA;&lt;li&gt;Regarding the &amp;quot;... except ...&amp;quot;, I can only find one other use of the word &amp;quot;music&amp;quot; in Part 97:&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(c) No station shall retransmit programs or signals emanating from any&#xA;type of radio station other than an amateur station, except&#xA;propagation and weather forecast information intended for use by the&#xA;general public and originated from United States Government stations,&#xA;and communications, including incidental music, originating on United&#xA;States Government frequencies between a manned spacecraft and its&#xA;associated Earth stations. ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I think this is saying it's ok for amateurs to retransmit a signal which includes incidental music if that signal originates from the listed government/spacecraft-related sources.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Here are questions I believe are unanswered by Part 97:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Does &amp;quot;phone emissions&amp;quot; include digitally encoded audio emissions?  This would imply it is illegal for a ham radio network to provide access to a musical mp3 file on the internet or any video that contains even incidental music.  Both &lt;a href=&quot;http://www.broadband-hamnet.org/documentation/70-how-to-use-the-web-interface.html#setup&quot; rel=&quot;nofollow noreferrer&quot;&gt;Broadband-Hamnet&lt;/a&gt; and &lt;a href=&quot;https://hamwan.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;HamWAN&lt;/a&gt; include a statement to the effect of &amp;quot;... be sure that any internet traffic that will be sent over radio will comply with Part 97 rules.&amp;quot; If it were clear that accessing any file on the internet incidentally containing music is not Part 97 compliant, they would probably provide that information.  That would mean it's illegal even to transfer (almost) any video game or other software that includes musical sounds using a ham radio network.  It would be nearly impossible in some cases for a ham to know they are even doing something illegal.  It may be that the mention of music in these regulations was not meant to cover these situations, but instead to allow for so-called &amp;quot;&lt;a href=&quot;https://en.wikipedia.org/wiki/Pirate_radio&quot; rel=&quot;nofollow noreferrer&quot;&gt;pirate radio&lt;/a&gt;&amp;quot; broadcasts to be shut down.&lt;/li&gt;&#xA;&lt;li&gt;Imagine there are two individuals having a conversation over ham radio in a perfectly legal fashion.  If they begin singing to each other instead of talking, their conversation then becomes illegal?  Even if suggested by the language in Part 97, this may not be true in any legally defensible way unless there is some legal precedent that would help draw a line between speech and music (e.g. something relating to the intent of the transmission).  A similar discussion is given in a related question &lt;a href=&quot;https://ham.stackexchange.com/questions/356/what-defines-music-per-amateur-radio-regulations&quot;&gt;here&lt;/a&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&lt;strong&gt;A note on why this question is distinct from &lt;a href=&quot;https://ham.stackexchange.com/questions/356/what-defines-music-per-amateur-radio-regulations&quot;&gt;what-defines-music-per-amateur-radio-regulations&lt;/a&gt;:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;The question &lt;a href=&quot;https://ham.stackexchange.com/questions/356/what-defines-music-per-amateur-radio-regulations&quot;&gt;what-defines-music-per-amateur-radio-regulations&lt;/a&gt; focuses on short musical sounds for another listener to receive and what defines &amp;quot;music&amp;quot;.  The accepted answer states &amp;quot;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;... Bottom line, if something that is purely incidental to the&#xA;conversation, or if you are transmitting it digitally, you can&#xA;actually have a bit of music and not get your hand slapped by the FCC.&#xA;Thus, the doorbell seems fine, and most likely the types of &amp;quot;Windows&#xA;Sounds&amp;quot; that sometimes come up, but personally, I wouldn't risk it. If&#xA;you are trying to broadcast then you are almost certainly in violation&#xA;of the law.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The answer, just like the question, focuses on the applications of DJing music and sending bell sounds, presumably as indicators to aid in communications.  Admittedly, the question does center around the lack of clarity related to the term &amp;quot;music&amp;quot;.  However the accepted answer does not provide a clear answer to whether musical collaboration in all forms is disallowed on radio, digital or analog.  It even could reasonably be interpreted as suggesting (e.g. &amp;quot;... or if you are transmitting it digitally ...&amp;quot;) that musical digital audio streams are allowed.&#xA;Also, in contrast to the applications in the &lt;a href=&quot;https://ham.stackexchange.com/questions/356/what-defines-music-per-amateur-radio-regulations&quot;&gt;what-defines-music-per-amateur-radio-regulations&lt;/a&gt;, the application of musical collaboration between two (or more) individuals does not involve an audience. Musical collaboration is more in-line with a conversation than a musical broadcast.  This changes the intention of the transmission away from amateur DJing (or so called &amp;quot;&lt;a href=&quot;https://en.wikipedia.org/wiki/Pirate_radio&quot; rel=&quot;nofollow noreferrer&quot;&gt;pirate radio&lt;/a&gt;&amp;quot;), an application that these laws were possibly designed to prevent.  Many musicians and music teachers are, due to covid-19, currently struggling with figuring out how to collaborate and teach music remotely.  Radio may be the only practical widely available solution for this application.  Assuming the intent of the law or the radio operator are legally important, I believe this post asks a distinct question from that of &lt;a href=&quot;https://ham.stackexchange.com/questions/356/what-defines-music-per-amateur-radio-regulations&quot;&gt;what-defines-music-per-amateur-radio-regulations&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&lt;strong&gt;Update -- Part 97 does give a definition of &amp;quot;phone&amp;quot; in section &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?rgn=div5;node=47%3A5.0.1.1.6;cc=ecfr#se47.5.97_13&quot; rel=&quot;nofollow noreferrer&quot;&gt;97.3.c.5&lt;/a&gt;:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(c) The following terms are used in this part to indicate emission types. Refer to &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=b09965dbe3271d2c4b38a0caa0b7b319&amp;amp;mc=true&amp;amp;node=se47.1.2_1201&amp;amp;rgn=div8&quot; rel=&quot;nofollow noreferrer&quot;&gt;§2.201&lt;/a&gt; of the FCC Rules, Emission, modulation and transmission characteristics, for information on emission type designators.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(5) &lt;em&gt;Phone.&lt;/em&gt; Speech and other sound emissions having designators with A,&#xA;C, D, F, G, H, J or R as the first symbol; 1, 2, 3 or X as the second&#xA;symbol; E as the third symbol. Also speech emissions having B or F as&#xA;the first symbol; 7, 8 or 9 as the second symbol; E as the third&#xA;symbol. MCW for the purpose of performing the station identification&#xA;procedure, or for providing telegraphy practice interspersed with&#xA;speech. Incidental tones for the purpose of selective calling or&#xA;alerting or to control the level of a demodulated signal may also be&#xA;considered phone.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;A couple notes:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Only &amp;quot;speech emissions&amp;quot; (and not &amp;quot;other sound emissions&amp;quot;) are stated to be considered as phone emissions for emissions having B or F as the first symbol.&lt;/li&gt;&#xA;&lt;li&gt;From &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=b09965dbe3271d2c4b38a0caa0b7b319&amp;amp;mc=true&amp;amp;node=se47.1.2_1201&amp;amp;rgn=div8&quot; rel=&quot;nofollow noreferrer&quot;&gt;§2.201&lt;/a&gt;, the definition of type E information is &amp;quot;Telephony (including sound broadcasting)&amp;quot;.&lt;/li&gt;&#xA;&lt;li&gt;As far as I can tell, even if speech and telephony both &lt;em&gt;do&lt;/em&gt; include music, &amp;quot;phone&amp;quot; doesn't include all telephony (i.e. xxExx) emission types.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="17828" LastEditorUserId="17828" LastEditDate="2020-10-04T00:13:34.190" LastActivityDate="2020-10-08T06:14:33.473" Title="Using radio for musical collaboration -- the line between conversation and broadcasting" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;music&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17365" PostTypeId="2" ParentId="17364" CreationDate="2020-09-28T03:00:39.817" Score="3" Body="&lt;p&gt;I think that the FCC does not want to allow people to send music over the airwaves, due to the (extremely complicated, arcane, and heavily-legislated) issues around the right to perform music in a non-private setting.&lt;/p&gt;&#xA;&lt;p&gt;For example, if you were to sing a song written by The Beatles, do you have the right to perform that where anyone else is listening? (Unless you licensed it, the answer is &amp;quot;no&amp;quot;.) Do you have the right to sing your own compositions in the same place? Probably yes, as long as you hold the rights to those compositions.&lt;/p&gt;&#xA;&lt;p&gt;If you are just with a group of friends in your own living room or garage, there is no problem as those sounds don't travel very far. If you are transmitting them over the radio, then the FCC gets involved, because the sounds can be listened to by anyone with the right equipment, within a certain range.&lt;/p&gt;&#xA;&lt;p&gt;If you really really want to do socially-distanced jam sessions, I would suggest using a private communications medium such as over the phone (landline or mobile phone), or maybe something like FRS would be suitable? I don't know what the regulations are about allowed content over FRS or similar services, but they will be a lot more lenient than the regulations over amateur radio.&lt;/p&gt;&#xA;&lt;p&gt;The point of amateur radio is more to do with the means of communication (e.g. self-training on the technology of radio) than it is to do with the actual content of transmissions, and as such I think amateur radio is a bad fit for what you are proposing.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-09-28T03:00:39.817" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17368" PostTypeId="1" CreationDate="2020-09-28T20:38:03.930" Score="3" ViewCount="71" Body="&lt;p&gt;What might be the tradeoffs between choosing varicap diodes versus air variable capacitors in the design and construction of tunable bandpass filters for HF receivers?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-09-29T16:07:13.600" Title="Tradeoffs: varicap vs. air variable capacitor for Rx bandpass?" Tags="&lt;receiver&gt;&lt;filter&gt;&lt;components&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17370" PostTypeId="2" ParentId="17225" CreationDate="2020-09-28T23:09:29.173" Score="1" Body="&lt;p&gt;You may have stumbled onto a net that is specifically designed to allow amateurs to work on getting awards quickly by contacting others via net, such as the ARRL Worked All States (WAS) award.  There's several nets that do this but perhaps the largest one is the OMISS (Old Man International Sideband Society) net.  They hold several nets on several bands daily.  OMISS has their own awards system also.  More info at omiss.net.&lt;/p&gt;&#xA;&lt;p&gt;Hope this helps.&lt;/p&gt;&#xA;&lt;p&gt;73,&#xA;Sean KS4TD&lt;/p&gt;&#xA;" OwnerUserId="5631" LastActivityDate="2020-09-28T23:09:29.173" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17371" PostTypeId="2" ParentId="1646" CreationDate="2020-09-29T11:37:32.963" Score="1" Body="&lt;p&gt;As a repeater owner, people who connect and say nothing are beyond irritating.&lt;/p&gt;&#xA;&lt;p&gt;When you connect, you are announced.   Now you won't talk to us?  Why did you bother connecting.  And now you're going to drop the connection without saying anything?  That also is announced.  So all these &amp;quot;listen only&amp;quot; users are constantly connecting and disconnecting, getting announced each time, and not saying a word.&lt;/p&gt;&#xA;&lt;p&gt;Additionally, many repeaters have a limited number (sometimes only one) of available connection slots.  So you are going to now sit there and just listen, taking up a slot that a real live person could have used.   And I can't call out while you are connected either, even if there are multiple slots.&lt;/p&gt;&#xA;&lt;p&gt;Yes, connecting without saying anything is rude.  If you are not going to talk on this two way medium, why are you bothering to participate at all?  To say the least, if I see you connecting to my repeater and disconnecting and not saying anything when directly spoken to, you're going to end up on my blacklist and not allowed to connect at all.  You wouldn't walk into a restaurant, stand in the middle of the dining room, and stare at people, and then refuse to sit at a table.  You shouldn't expect to connect to a repeater via echolink and refuse to talk either.&lt;/p&gt;&#xA;&lt;p&gt;Similarly, why would you connect and then immediately disconnect?  If you're having technical difficulties with your audio, use the echolink test server until you have it fixed.  If you're disconnecting because you connected and didn't immediately hear any activity, you're doing it wrong.  If you want activity, put out a call.  Maybe conversation just paused when your connection was announced.  If you immediately disconnect without talking first, you'll never know if people were talking before you connected or if people are there but listening.&lt;/p&gt;&#xA;&lt;p&gt;As an alternative to connecting to repeaters and listening, find a conference server instead. Conference servers have a very high number of slots, and I think they don't announce when you connect and disconnect, and won't prevent anyone from dialing out. Also, if you want to exercise your language, I can understand not wanting to initiate a conversation, but at least try to respond if someone talks to you. Amateur radio is all about communication, and I'm sure if you try you can find someone who is willing to help you stumble through and improve. Mentoring is a big part of amateur radio, but if you refuse to talk, we can't mentor you.&lt;/p&gt;&#xA;&lt;p&gt;It is good amateur radio practice to listen before speaking.  So if you connect, wait a minute or so, and &lt;em&gt;then&lt;/em&gt; say something, that's perfect.  Just don't sit there for hours, or connect and then disconnect right away, especially if someone tries to talk to you.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-03-16T11:53:14.407" LastActivityDate="2021-03-16T11:53:14.407" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17372" PostTypeId="2" ParentId="17368" CreationDate="2020-09-29T14:58:24.750" Score="4" Body="&lt;p&gt;First and foremost, varicaps aren't mechanical. If you want a rapidly tunable thing, that's a necessity; even if you just want something tunable by electronics, it's very desirable (otherwise you'll need to motorize your air gap cap...).&lt;/p&gt;&#xA;&lt;p&gt;Air gap capacitors can be made to withstand very high voltages, which makes them desirable for anything that has to handle power – like transmit filters to suppress harmonics. On the other hand, you often don't need high flexibility in that, as you'd rarely use the same antenna for an octave or more of spectrum, so that a simple fixed filter (and a low pass at that!) would suffice.&lt;/p&gt;&#xA;&lt;p&gt;Varicaps, especially together with digitally controlled voltages (DACs!) are a cheaper way of getting reproducible values, which seems very desirable: when you tune your receiver, you want the RX bandpass to (roughly) follow, right?&lt;/p&gt;&#xA;&lt;p&gt;However, being semiconductor devices, varicaps are in fact temperature-dependent. In higher-end devices, this gets compensated, usually per measuring temperature and having a table for temperature adjustments, or via holding components at a constant temperature.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YYnIM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YYnIM.png&quot; alt=&quot;SMV130-040LF Varicap temperature dependency&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Note how the temperature dependency of &lt;a href=&quot;https://www.digikey.com/product-detail/en/skyworks-solutions-inc/SMV1430-040LF/863-1733-1-ND/5396047&quot; rel=&quot;nofollow noreferrer&quot;&gt;that varicap&lt;/a&gt; is in the low single-digit percentage region; I'm told there's high-quality large variable air gap capacitors that can be tuned reproducibly to the same capacity with a comparable accuracy, but keep in mind this is a 0.65€/piece varicap – again, with a temperature compensation loop, you could get these tolerances much lower, for a fraction of the price of something mechanical and good.&lt;/p&gt;&#xA;&lt;p&gt;Also note that unless you somehow mechanically link your air gap capacitor, multiple variable stages of a higher-order filter will be kind of hard to get right. With a varicap, you could just implement both capacitors in a multiple-feedback active low-noise bandpass:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OGCWw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OGCWw.png&quot; alt=&quot;Multiple-feedback active BPF&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The image is from my &lt;a href=&quot;http://sim.okawa-denshi.jp/en/OPttool.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;favourite filter toolbox&lt;/a&gt;; try R1=470 kΩ, R2=100 kΩ, R3=5.1 kΩ; C1=5 pF, C2=5 pF to get a feeling for this topology; then, read &lt;a href=&quot;https://www.analog.com/media/en/training-seminars/tutorials/MT-220.pdf?doc=MT-220.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Analog Device's MT-220 note on design of MFBBPFs&lt;/a&gt;:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/DuYvI.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fDuYvI.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;it comes with design instructions. Use a low-noise opamp such as LT6233; you'll have to build the circuit in SPICE and vary C3=C4 to form a look up table for frequency to desired reverse voltage).&lt;/p&gt;&#xA;&lt;p&gt;You'd want your DAC-generated voltage source V_DAC (you could also generate that with a potentiometer!) to have a high impedance (relative to R1, and to C3=C4 at HF) so that you don't cancel your signal with it.&lt;/p&gt;&#xA;&lt;p&gt;As you can see, for variable receiver bandpasses, varicaps and modern Opamp offer an elegant implementation methodology that makes building multiple stage filters easier – the output here is buffered, and hence, it's easy to concatenate multiple of these stages for higher selectivity (can't do that as easily with passive RLCs - the second stage loads the first).&lt;/p&gt;&#xA;&lt;p&gt;In a real-world flexible HF receiver: I'd probably go for a simple selection between fixed bandpasses for say half a band each, and then throw a relatively high-dynamic range ADC at the problem to directly sample and thereby oversample the bandwidth. The amounts of problems that in-band blockers pose for ADCs are usually overestimated in this hobby; &lt;a href=&quot;https://www.digikey.com/product-detail/en/maxim-integrated/MAX1421ECM-D/MAX1421ECM-D-ND/1475085&quot; rel=&quot;nofollow noreferrer&quot;&gt;10€ ADCs&lt;/a&gt; do &amp;gt; 70 dB of spurious-free dynamic range at 40 MHz bandwidth; and for a 0.5 MHz wide band, that is an oversampling factor of 80, which will put your (noise-dithered) sensitivity into thermal noise regions of CW channels, even if there's a +10 dBm interferer in the same band!&lt;/p&gt;&#xA;&lt;p&gt;If that's not enough, you'll have to go with frontend band passes, followed by one or multiple stages of superheterodyne mixing/filtering.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-09-29T16:07:13.600" LastActivityDate="2020-09-29T16:07:13.600" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17373" PostTypeId="2" ParentId="17364" CreationDate="2020-09-29T16:27:42.940" Score="6" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Does &amp;quot;phone emissions&amp;quot; include digitally encoded audio emissions?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes. For example, &lt;a href=&quot;https://freedv.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV&lt;/a&gt; is a phone emission. &lt;a href=&quot;https://freedv.org/freedv-specification/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV consists of multiple PSK carriers&lt;/a&gt;: first symbol G. These carriers transmit a stream of bits: second symbol 1. And it is designed to take a sound at one station and reproduce it at the other station. That is telephony: third symbol E. Emission G1E fits the definition of &amp;quot;phone&amp;quot; in part 97. This is why the canonical &lt;a href=&quot;http://wiki.oz9aec.net/index.php/Freedv_frequencies&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV frequencies&lt;/a&gt; are in the phone section of the bands, and not the data sections.&lt;/p&gt;&#xA;&lt;p&gt;At least, that's my interpretation. &lt;a href=&quot;https://groups.google.com/g/digitalvoice/c/7_gQLNGB3lk/m/u1lXIm8wRJQJ&quot; rel=&quot;nofollow noreferrer&quot;&gt;There doesn't seem to be great agreement&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;The important part of the &amp;quot;phone&amp;quot; definition is &amp;quot;E as the third symbol&amp;quot;. This means &amp;quot;telephony&amp;quot;. I don't see how any emission designed to take music at the transmitting station and reproduce it as the receiving station could have any other symbol in the third place.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;As far as I can tell, even if speech and telephony both do include music, &amp;quot;phone&amp;quot; doesn't include all telephony (i.e. xxExx) emission types.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;True, however, it does include all &lt;em&gt;authorized&lt;/em&gt; emission types with the third symbol &amp;quot;E&amp;quot;. The other emissions that are allowed (somewhere) in the amateur service are CW, data, image, MCW, pulse, RTTY, SS (spread spectrum), and &amp;quot;test&amp;quot;. They are all defined in the same area as you found the phone definition. None allow &amp;quot;E&amp;quot; as the third symbol.&lt;/p&gt;&#xA;&lt;p&gt;So avoiding the definition of &amp;quot;phone&amp;quot; doesn't mean your musical transmission is authorized. If you accept that reproducing music over distance is &amp;quot;telephony&amp;quot;, the third symbol must be &amp;quot;E&amp;quot;, which can't be CW, data, image, MCW, pulse, RTTY, or SS. So you must either meet the definition of &amp;quot;phone&amp;quot; (in which case you aren't allowed to transmit music) or not (in which case you aren't allowed to transmit anything at all).&lt;/p&gt;&#xA;&lt;p&gt;You could claim you are transmitting &amp;quot;data&amp;quot; which &lt;em&gt;happens to be&lt;/em&gt; music, however I'm fairly certain you will lose this case and you'll need the resources to fight it. Furthermore, there are significant restrictions on what data can be which will be a serious technical challenge, not least among them an upper limit of 300 baud.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Imagine there are two individuals having a conversation over ham radio in a perfectly legal fashion. If they begin singing to each other instead of talking, their conversation then becomes illegal?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Technically yes, though I doubt the FCC would care enough to act unless it was a regular thing.&lt;/p&gt;&#xA;&lt;p&gt;While we can quibble about whether an 8-note chime is &amp;quot;music&amp;quot; and we can make jokes about hams not being able to sing &amp;quot;music&amp;quot;, your use case is very clearly music:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I'd like to collaborate (e.g. play together) with other musicians&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I'm afraid part 97 is quite clear: no music. I don't see any wiggle room to argue collaborating with musicians isn't music.&lt;/p&gt;&#xA;&lt;p&gt;Besides the issues of legality, I think you'll find the idea is difficult to implement technically as well. The best-case speed-of-light delay from San Francisco to New York is 14 ms. Real-time collaboration &lt;a href=&quot;https://www.highfidelity.com/blog/how-much-latency-can-live-musicians-tolerate-da8e2ebe587a&quot; rel=&quot;nofollow noreferrer&quot;&gt;requires less than 20 ms&lt;/a&gt;, so most of your latency budget is blown just in propagation delay. If you digitally encode the signal (which would be required if you want music-quality audio) you'll have even more latency from the codec. You'll also require quite a lot of transmitter power and/or antenna gain to get sufficient fidelity and reliability.&lt;/p&gt;&#xA;&lt;p&gt;Your best bet is to delay the streams to something musically tolerable, like some integer number of beats or measures. For example, &lt;a href=&quot;https://www.cockos.com/ninjam/&quot; rel=&quot;nofollow noreferrer&quot;&gt;NINJAM&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Alternatively, use a radio service which does not have a restriction on music. Amateur radio is unique in having large allocations in HF which can be used for worldwide communication, but if only shorter distances are necessary you could do fine with a pair of WiFi APs and a point-to-point link which come with no encumbrances on the kinds of things you can transmit. WiFi is by no means optimal for latency, but the equipment is cheap and easy to integrate.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-10-05T15:36:19.730" LastActivityDate="2020-10-05T15:36:19.730" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17375" PostTypeId="2" ParentId="17316" CreationDate="2020-09-30T00:26:56.893" Score="3" Body="&lt;p&gt;Radio amateur transceivers differ a lot, their finals differ a lot, too. But their SWR protection mostly start somewhere between 2:1 and 3:1, some of them are even more touchy, and they mostly have quiet steep foldback characteristics - for a reason described later. Also, there can be differencies when the internal tuner, if exists, is turned on or off.&lt;/p&gt;&#xA;&lt;p&gt;Some of them measure only the reflected energy, not the ratio, some of them have only a comparator and shuts down the P.A. entirely for a while or until a reset button is pressed - homebrew units tend to use these latter solutions.&lt;/p&gt;&#xA;&lt;p&gt;So, why limiting the current the final stage may draw is not enough? Because this statement is not true:&#xA;&amp;quot;So to prevent the final transistors seeing an unreasonable voltage or current from an open or short circuit, the power needs to be reduced only to half.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;Analyzing the whole situation would take a lot of times and you can find great descriptions on the web, also, I'm not the best person for it, but usually there is not only one reflection in a real system, nor only resistive load(s) are there, which is an even worse phenomenon than the first one.&lt;/p&gt;&#xA;&lt;p&gt;When a radio wave reflected by the antenna is travelling back on the transmission line, it will probably be reflected again when it reaches the power amplifier (unless they match prefectly) and starts going toward the antenna again through the transmission line, and despite of its reduced energy caused by this subsequent reflection, it also has voltage maximums and minimums, and so on.&lt;/p&gt;&#xA;&lt;p&gt;Also, if a load is reactive, there will be capacitive and inductive maximums as well along the feedline, and it de-tunes the generator. A peak current at it can be handled fairly easy, but this is not true for the superimposed voltage peaks, which for example try to drive more current if a final stage transistor is open at that moment, and so. We are not speaking of just 20-30 percent overvoltages, things may go out of control easy, otherwise I haven't had to see a couple of arching capacitors and RF connectors in my life. :-)&lt;/p&gt;&#xA;" OwnerDisplayName="user17494" LastActivityDate="2020-09-30T00:26:56.893" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17376" PostTypeId="1" AcceptedAnswerId="17380" CreationDate="2020-09-30T17:22:37.663" Score="1" ViewCount="303" Body="&lt;p&gt;I have been watching and reading about the time when receiver/transmitter were separated and T/R switches were used. Current transceivers are still sharing a single antenna to transmit and receive. What component/circuitry replaced the T/R switches?&lt;/p&gt;&#xA;" OwnerUserId="1816" LastEditorUserId="1816" LastEditDate="2020-10-01T18:34:34.163" LastActivityDate="2020-10-01T18:34:34.163" Title="What replaces the T/R switch in modern transceiver" Tags="&lt;transceiver&gt;&lt;transmitter&gt;&lt;equipment-design&gt;&lt;history&gt;&lt;panadapter-and-waterfall&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17377" PostTypeId="2" ParentId="17376" CreationDate="2020-09-30T17:47:14.953" Score="2" Body="&lt;p&gt;As far as your question regards components: T/R switching is usually done with either relays, reed relays (often faster than other types of relays; also more quiet), or PIN diodes (even more quiet and faster). Where high voltages and/or currents are present (and fast switching is needed) vacuum relays are also used. Circuitry may involve circuits that ensure a fast and also safe changeover (e.g. by sequencing which parts of the transmit and receive blocks should become active or inactive in a particular order).&lt;/p&gt;&#xA;" OwnerUserId="17676" LastEditorUserId="17676" LastEditDate="2020-10-01T07:08:07.937" LastActivityDate="2020-10-01T07:08:07.937" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17378" PostTypeId="2" ParentId="17285" CreationDate="2020-09-30T18:36:01.030" Score="1" Body="&lt;p&gt;It doesn't look like it can be done quickly, but you can change the settings to display the freq instead of the memory name. From page 32 of the &lt;a href=&quot;http://manual.kenwood.com/files/4ee059ba1d903.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;manual&lt;/a&gt; (&lt;a href=&quot;http://manual.kenwood.com/en_contents/search&quot; rel=&quot;nofollow noreferrer&quot;&gt;available from the Kenwood website&lt;/a&gt;):&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;To display the frequency rather than Memory Name, access Menu No. 17 (MDF) and select “FRQ”.  This menu toggles the display mode between the Memory Name (“MN”) and frequency display (“FRQ”).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="236" LastActivityDate="2020-09-30T18:36:01.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17379" PostTypeId="2" ParentId="7199" CreationDate="2020-09-30T18:45:21.387" Score="1" Body="&lt;p&gt;The Kantronics KAM XL uses the HBAUD command to set the baud rate for the radio ports. HBAUD 1200/1200 will set the baud rate to 1200 on both ports.&lt;/p&gt;&#xA;&lt;p&gt;Also, I don't see what you've set your UNPROTO destination to be. For the ISS digipeater, your messages need to be sent via ARISS to trigger the digipeater. For keyboard contacts, you would set UNPROTO CQ VIA ARISS&lt;/p&gt;&#xA;&lt;p&gt;KAM manual: &lt;a href=&quot;https://kantronics.com/wp-content/uploads/2018/10/KAM-XL-Manual-RevE.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://kantronics.com/wp-content/uploads/2018/10/KAM-XL-Manual-RevE.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Info on ARISS packet usage: &lt;a href=&quot;https://www.ariss.org/uploads/1/9/6/8/19681527/k9jkm_2012_symposium_ver2.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ariss.org/uploads/1/9/6/8/19681527/k9jkm_2012_symposium_ver2.pdf&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="236" LastActivityDate="2020-09-30T18:45:21.387" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17380" PostTypeId="2" ParentId="17376" CreationDate="2020-09-30T23:24:00.303" Score="8" Body="&lt;p&gt;Receivers and transmitters are still separated today, they are just in the same box. There is still a T/R switch too, integrated in the box.&lt;/p&gt;&#xA;&lt;p&gt;In many radios, it's a relay, same as they have been for decades. Relays are hard to beat for isolation and maximum power ratings. Their downside is relatively slow speed, which prevents really good QSK operation. They are also kinda noisy.&lt;/p&gt;&#xA;&lt;p&gt;A few radios, especially those that operate at lower powers, have replaced the relay with solid-state electronics. This can be a diode or FET. This is more popular in lower power radios because these solid-state electronics, at prices similar to relays, can't handle as much power. Of course there are solid-state electronics that can handle more power, but they're more expensive than a relay.&lt;/p&gt;&#xA;&lt;h1&gt;Examples&lt;/h1&gt;&#xA;&lt;p&gt;The &lt;a href=&quot;https://ftp.elecraft.com/KX3/Manuals%20Downloads/KX3SchematicDiagramDec2012.pdf&quot; rel=&quot;noreferrer&quot;&gt;KX3 uses an integrated PIN diode switch&lt;/a&gt;, &lt;a href=&quot;https://www.psemi.com/pdf/datasheets/pe4283ds.pdf&quot; rel=&quot;noreferrer&quot;&gt;PE4283&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0jGmR.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0jGmR.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The PE4283 has an absolute maximum power input of 34 dBm, which is only 2.5 watts. This part is advertised as a &amp;quot;high power&amp;quot; RF switch, which gives you some idea of the expectations people have for solid-state RF switching.&lt;/p&gt;&#xA;&lt;p&gt;The &lt;a href=&quot;http://www.wb5rvz.org/ensemble_rxtx/&quot; rel=&quot;noreferrer&quot;&gt;Softrock RXTX&lt;/a&gt; uses a BS170 MOSFET (Q10, bottom-right):&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EFqKf.png&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EFqKf.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-09-30T23:24:00.303" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17381" PostTypeId="1" AcceptedAnswerId="17383" CreationDate="2020-10-01T09:06:30.600" Score="0" ViewCount="73" Body="&lt;p&gt;I know how shielded loop antenna work as a receiver antenna. (How behave electric and magnetic field).&lt;/p&gt;&#xA;&lt;p&gt;But I can not understand how shielded loop antenna works as a transmitter.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Will it produce only magnetic waves?&lt;/li&gt;&#xA;&lt;li&gt;Or will it produce magnetic and electric waves?&lt;/li&gt;&#xA;&lt;li&gt;And it will produce the signal from the air gap?&lt;/li&gt;&#xA;&lt;li&gt;Or It will behave like a usual antenna without shielding?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="17864" LastEditorUserId="4076" LastEditDate="2020-10-01T12:06:10.397" LastActivityDate="2020-10-01T12:12:47.330" Title="60cm 9 kHz 30 MHz Shielded loop antenna behavior as a transmitting antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17382" PostTypeId="2" ParentId="17376" CreationDate="2020-10-01T12:01:57.523" Score="2" Body="&lt;p&gt;As both previous answers mention, the T/R switch functionality is just something that moved into existing boxes, not something that disappeared.&lt;/p&gt;&#xA;&lt;p&gt;The only ways to make that functionalies disappear would be&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;making the receive end tolerant of the transmit power and still a sensitive receiver (practically impossible at any significant power – the difference between receive and transmit powers is typically beyond 80 dB)&lt;/li&gt;&#xA;&lt;li&gt;circulators/isolators (which is a funky kind of 3-port device that allows power to flow from port 1 to 2, 2 to 3 and 3 to 1, but not in the other way), which rarely achieve more than 20 dB of isolation and become very expensive very quickly if you need more (which is why you'll mostly find these in long-range radar applications)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Whether a relay is the &amp;quot;best&amp;quot; switch really depends on your requirements: at microwave frequencies, your HF relay really is about as transparent in every direction... But:&lt;/p&gt;&#xA;&lt;p&gt;In addition to what &lt;a href=&quot;https://ham.stackexchange.com/a/17380/4076&quot;&gt;Phil mentioned&lt;/a&gt; (PIN diodes and MOSFETs), there is a third increasingly important type of RF switch IC: MEMS (microelectromechanical system) switches, which kind of are quite a bit like relays (as in they're mechanically making contacts) and kind of like MOSFETs (as in that they use an electrical field to effect the switching).&lt;/p&gt;&#xA;&lt;p&gt;They achieve relatively high powers (+36 dBm) and good isolation (40 dB), even at very high frequencies. So, that's another class of devices to look at.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Generally, all the RF switch ICs have gotten better. For &lt;a href=&quot;https://eu.mouser.com/datasheet/2/412/RFSW6024_Data_Sheet-1500569.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;example&lt;/a&gt;, Qorvo has switches with input IP3 of 35 dBW (!), but since such devices dissipate, you &lt;em&gt;really&lt;/em&gt; want to not transmit power while the switch is RX position.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-10-01T12:01:57.523" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17383" PostTypeId="2" ParentId="17381" CreationDate="2020-10-01T12:12:47.330" Score="1" Body="&lt;p&gt;There's no such thing as a &amp;quot;magnetic&amp;quot; and an &amp;quot;electric&amp;quot; wave. Only &lt;em&gt;electromagnetic waves&lt;/em&gt; propagate – that's at the very basis of wave theory, so 1. is definitely wrong, and 2. would need rephrased to &amp;quot;will it produce an electromagnetic wave&amp;quot;, and the answer to that is &amp;quot;yes!&amp;quot;, otherwise it would not be an antenna.&lt;br&gt;&#xA;So, you really might want to revisit your antenna theory when you say you know how your antenna works as a receiver.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;ol start=&quot;3&quot;&gt;&#xA;&lt;li&gt;And it will produce the signal from the air gap?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Not quite sure which air gap you mean?&lt;/p&gt;&#xA;&lt;p&gt;Generally, any antenna is always the same in receive as in transmit direction, when it comes on how it allows energy to flow between the free-space electromagnetic waves in free-space wave impedance and the conducted wave in a feed cable, waveguide, ladder line... with their respective impedance.&lt;/p&gt;&#xA;&lt;p&gt;The only difference is when you look at how you deal with impedance mismatches that are inherent to the working principles of the antenna. But that's not about whether the antenna is magnetic or electric (or a mixture), but about whether it actually has transmission line and free space impedance, or just an approximation to these.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-10-01T12:12:47.330" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17384" PostTypeId="1" AcceptedAnswerId="17386" CreationDate="2020-10-01T15:15:33.670" Score="2" ViewCount="187" Body="&lt;p&gt;I followed an article &lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/9106023.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna Here is a Dipole [PDF]&lt;/a&gt; by James Hearly, NJ2L to build a dual band 40/15m dipole:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W5t41.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W5t41.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The antenna works more or less as expected. My 40m dipole was resonant at 7.030 MHz and 21.600 MHz. Adding capacitance hats according to the scheme almost doesn't affect 40m and shifts the second resonance to 21.300 MHz.&lt;/p&gt;&#xA;&lt;p&gt;Although I don't understand how it works. Why capacitance hats make the dipole electically longer on 15m, but don't affect 40m? Also why the third harmonic resonance turns out to be ~2.5% higher than 7.030 x 3?&lt;/p&gt;&#xA;&lt;p&gt;I realize this might be a complicated question. In this case maybe there is a book on this subject you could recommend? &amp;quot;The ARRL Antenna Book&amp;quot; doesn't give such details. Should I try &amp;quot;Antenna Physics: An Introduction&amp;quot; also by ARRL?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2020-10-01T15:42:10.920" LastActivityDate="2020-10-02T12:25:28.153" Title="How does a 40/15m dipole with capacitance hats work?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;dipole&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17385" PostTypeId="2" ParentId="17384" CreationDate="2020-10-01T23:40:40.397" Score="4" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Also why the third harmonic resonance turns out to be ~2.5% higher than 7.030 x 3?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This is because of &amp;quot;end effect&amp;quot;, caused by the discontinuity where the wire stops at the end of the dipole. I'm fuzzy on the theory, but the ends act like capacitors, which adds a little bit of loading, and makes the wire's electrical length about 0.02 WL longer than it would be otherwise.&lt;/p&gt;&#xA;&lt;p&gt;Assuming 1.0 velocity factor (to avoid distraction), that means that if we want a dipole to resonate, instead of cutting it to be 0.5 WL long, we cut it to be 0.48 WL physically so it acts like 0.5 WL electrically.&lt;/p&gt;&#xA;&lt;p&gt;But if we operate this 0.48 WL dipole on the third third harmonic, it will be 0.48*3 = 1.44 WL long physically, and &lt;em&gt;end effect still adds 0.02 WL at the new frequency, not 0.06&lt;/em&gt;, so the antenna will be 1.46 WL long electrically — about about 2.5% short of resonant.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-10-01T23:40:40.397" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17386" PostTypeId="2" ParentId="17384" CreationDate="2020-10-02T12:25:28.153" Score="3" Body="&lt;p&gt;As you know, the 40m half-wave is three half-waves on 15m. The two end half-wave sections are 180&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt; out of phase with the center section:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Kl90T.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Kl90T.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Overlaying the current distribution after adding &amp;quot;capacitive hats&amp;quot; spaced &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;/2 on 15m:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ibyy7.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ibyy7.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The size and position of the &amp;quot;hats&amp;quot; establishes the resonance point of the center half-wave section on 15m. If one extrapolated to zero the current distributions at the ends of the center half-wave section, the result would be consistent with a physically longer element.&lt;/p&gt;&#xA;&lt;p&gt;As noted by others, the resonant feedpoint impedance of this antenna tends toward 100-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; on 15m:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/JrBrm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JrBrm.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;An electrical &lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt;/4 section of 75-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; coax is often used to match a 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; feedline.&lt;/p&gt;&#xA;&lt;p&gt;Increasing the size of the &amp;quot;hats&amp;quot; tends to raise the resistive part of the feedpoint impedance; moving the &amp;quot;hats&amp;quot; toward the feedpoint lowers it. Judicious position and sizing of the &amp;quot;hats&amp;quot; delivers a better match to 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; without the need for a transformer:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lP50a.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lP50a.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cy6Un.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cy6Un.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;hats&amp;quot; have little to no effect on 40m because their small capacitance is a large reactance that adds little coupling between the small potential differences on either side of each &amp;quot;hat.&amp;quot;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-10-02T12:25:28.153" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17387" PostTypeId="1" CreationDate="2020-10-03T16:48:32.460" Score="0" ViewCount="40" Body="&lt;p&gt;Looking for advice/assistance in Retrofitting sans Cabinet Antique 2 and 3 Dialer 1920's TRF tube radios to operate with low safe Plate voltages.Both Hollow State and Solid State. The plan is to remove all antique high voltage tubes.&#xA;We need a low-cost minimal component Small Signal RF amplifier Design.&lt;/p&gt;&#xA;" OwnerUserId="17263" LastEditorUserId="8717" LastEditDate="2020-10-03T18:19:03.170" LastActivityDate="2020-10-03T18:19:03.170" Title="Simple minimum component RF Amplifier Design" Tags="&lt;equipment-design&gt;&lt;amplifier&gt;&lt;vacuum-tubes&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17388" PostTypeId="1" CreationDate="2020-10-04T01:46:37.933" Score="0" ViewCount="44" Body="&lt;p&gt;I am trying to work a 700mhz LTE signal with a DB2 uhf bowtie television antenna. I find the cellular signal to be horizontally polarized. Can the bowties simply be twisted 45 degrees in both directions to obtain the correct polarity, or will the difference in element spacing defeat the attempt?&lt;/p&gt;&#xA;" OwnerUserId="17875" LastEditorUserId="8717" LastEditDate="2020-10-04T02:07:25.210" LastActivityDate="2020-10-04T11:01:20.043" Title="Can I slant-polarize a bay antenna?" Tags="&lt;antenna-theory&gt;&lt;uhf&gt;&lt;polarization&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17389" PostTypeId="2" ParentId="12976" CreationDate="2020-10-04T08:50:42.973" Score="0" Body="&lt;p&gt;It's possible they're aircraft backscatter (ft8 signals bouncing from planes in the sky), or anything largely metallic really.&lt;/p&gt;&#xA;&lt;p&gt;They look something like this.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8FQBl.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8FQBl.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17200" LastActivityDate="2020-10-04T08:50:42.973" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17390" PostTypeId="2" ParentId="17388" CreationDate="2020-10-04T09:27:09.113" Score="4" Body="&lt;p&gt;Welcome to HamSE, Gary, and thanks for an interesting question.&lt;/p&gt;&#xA;&lt;p&gt;We should be grateful to Russel Renaud, VA3RR, for posting his NEC2 simulation model of the &lt;a href=&quot;https://www.qsl.net/va3rr/hdtv/hoverman.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;DB2 antenna&lt;/a&gt;. Importing the model to the &lt;a href=&quot;https://www.qsl.net/4nec2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;4NEC2 simulator&lt;/a&gt;, we find that the antenna pattern is primarily horizontally polarized:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3qxsl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3qxsl.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Assuming the antenna is &amp;quot;in the clear&amp;quot; - that is, no other conductive structures are present to affect the situation - simply rotate &lt;em&gt;the entire antenna&lt;/em&gt; to achieve a different angle of polarization.&lt;/p&gt;&#xA;&lt;p&gt;As you surmise, twisting &lt;em&gt;only the elements&lt;/em&gt; will very probably disturb the overall pattern and the impedance of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-10-04T09:27:09.113" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17392" PostTypeId="2" ParentId="12065" CreationDate="2020-10-04T16:49:06.140" Score="0" Body="&lt;p&gt;@MarcusMüller&lt;/p&gt;&#xA;&lt;p&gt;PARIS may have a typical length in Morse code for words in English, but that wouldn't hold in other languages, you're right about that. I assume someone took some text samples of English (perhaps even samples of typical plaintext messages sent by Morse code) and calculated the average length of the words in Morse, and then found the word PARIS to be very close to this length.&lt;/p&gt;&#xA;&lt;p&gt;But CODEX is language-agnostic, assuming we're still talking about the basic 26-character version of the Latin alphabet + the 10 numbers. This is because that one was mentioned to be the standard for groups of 5 &lt;strong&gt;random&lt;/strong&gt; characters (either 26 from the alphabet or 36 alphanumeric ones). If you're transmitting code groups like that, it's likely a plaintext message that has been encrypted into 5-character groups, those are transmitted, then decrypted again by the receiver of the message (you'll have agreed beforehand what the encryption keys are, and the encryption algorithm). It doesn't matter what the language of the plaintext is, that just necessitates making new algorithms that convert the text to those same 36 characters (a-z and 0-9).&lt;/p&gt;&#xA;&lt;p&gt;For CODEX, I assume someone calculated the average character length for those 36 characters, then found a 5-letter word where the average character length was about the same as that for the whole character set. As for &amp;quot;why a 5-character word&amp;quot;, I assume that one is to match the 5-character word of PARIS, and/or to match the random 5-character groups used when sending encoded messages.&lt;/p&gt;&#xA;" OwnerUserId="17880" LastActivityDate="2020-10-04T16:49:06.140" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17393" PostTypeId="2" ParentId="15452" CreationDate="2020-10-05T03:21:43.567" Score="3" Body="&lt;p&gt;Take three 1/4 wave sections of 75 ohm coaxial cable (let's say RG11) and solder together. You now have a 1/4 wave section of 25 ohm. Doing the math (25 * 25) / 12.5 = 50 ohm. Now use any 50 ohm coxial cable length to the radio. Ps: don't forget to take into account the 75 ohm cable speed factor to calculate the 1/4 wave section. Good luck. Luiz PY4ACP&lt;/p&gt;&#xA;" OwnerUserId="17882" LastActivityDate="2020-10-05T03:21:43.567" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17394" PostTypeId="1" AcceptedAnswerId="17395" CreationDate="2020-10-05T08:53:29.463" Score="0" ViewCount="67" Body="&lt;p&gt;I noticed that on some higher-end transceivers, the panadapter/waterwall is still being displayed during transmission. How is this possible? If the panadapter is part of the receiver, it should be disconnected from the antenna during transmission and if it was using some sort of directional coupler or tap it would lose way to much signal to be of any use.&lt;/p&gt;&#xA;&lt;p&gt;Is there some special circuitry at play here or is it only a display trick?&lt;/p&gt;&#xA;" OwnerUserId="1816" LastActivityDate="2020-10-06T00:28:29.430" Title="How can the waterfall still be displayed during transmission" Tags="&lt;transceiver&gt;&lt;equipment-design&gt;&lt;panadapter-and-waterfall&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17395" PostTypeId="2" ParentId="17394" CreationDate="2020-10-05T13:13:50.163" Score="4" Body="&lt;p&gt;I don't know what the specific devices you're referring to do, but a couple of things are all technically possible without great effort:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the ADC that is used to calculate the waterfall in receive-only mode is still connected to the antenna, maybe with additional physical attenuation (which you could trivially reverse in digital domain by multiplication with a constant, the only thing you trade is sensitivity)&lt;/li&gt;&#xA;&lt;li&gt;it displays the transmit spectrum, which is inherently known to the digital logic, anyways, since it defines the transmit signal&lt;/li&gt;&#xA;&lt;li&gt;A combination of the above&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-10-05T13:13:50.163" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17396" PostTypeId="2" ParentId="17394" CreationDate="2020-10-05T13:37:05.017" Score="3" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The radio has multiple antenna ports and full-duplex capability, and the operator has selected different antennas for transmit and receive. Or,&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The radio just displays the transmit spectrum on the waterfall, and it isn't coming from the antenna at all.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I've used radios with both of those options, so they're both definite possibilities.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-10-05T13:37:05.017" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17397" PostTypeId="1" CreationDate="2020-10-05T16:21:57.150" Score="0" ViewCount="45" Body="&lt;p&gt;On some (most?) receivers, if the RF gain is turned up too high, intermodulation distortion increases due to increasing non-linearities (maybe even clipping, etc.)&lt;/p&gt;&#xA;&lt;p&gt;Is it possible, just by examining typical received over-the-air RF signals during normal operating (e.g. no testing via artificially injected 2-tone signals), to detect the amount of IM distortion in order to determine whether the front-end RF gain should be reduced (or attenuation should be added) to lessen the distortion?   Either by listening to the demodulated audio or by examining the FFT spectrum?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-10-06T19:50:19.523" Title="Detecting receiver intermodulation distortion?" Tags="&lt;receiver&gt;&lt;dsp&gt;&lt;agc&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17398" PostTypeId="2" ParentId="17397" CreationDate="2020-10-05T18:07:55.483" Score="1" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;On some (most?) receivers, if the RF gain is turned up too high, intermodulation distortion increases due to increasing non-linearities (maybe even clipping, etc.)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I'd argue that's &lt;em&gt;all&lt;/em&gt; receivers, even, since that's exactly what &amp;quot;turned up too high&amp;quot; would imply. You get a non-linear effect, and that always leads to intermodulation. If that doesn't happen (significantly), you can increase gain ;)&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Is it possible, just by examining typical received over-the-air RF signals during normal operating (e.g. no testing via artificially injected 2-tone signals), to detect the amount of IM distortion in order to determine whether the front-end RF gain should be reduced (or attenuation should be added) to lessen the distortion?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Ah, that requires a bit of knowledge on the side of your signal. If you don't know anything about your signal, it's hard to tell whether it's distorted.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Either by listening to the demodulated audio or by examining the FFT spectrum?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Haha! &lt;em&gt;Demodulated Audio&lt;/em&gt; means you know quite a lot about the signal, right?&lt;/p&gt;&#xA;&lt;p&gt;So, the first place to look is simply at a time-domain amplitude statistic: if the amount of amplitudes that are really high is unusual for your type of signal. The classical stochastic property that reflects how much the signal amplitude distribution is &lt;em&gt;not&lt;/em&gt; at its center of weight is &lt;em&gt;kurtosis&lt;/em&gt;, i.e. the fourth central moment.&lt;/p&gt;&#xA;&lt;p&gt;Sadly, that's not something you &amp;quot;see&amp;quot; in the spectrum. What you &lt;em&gt;do&lt;/em&gt; see is the spectral widening of the channel.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://mobile.twitter.com/dEnergy_dTime/status/844126825383153664&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nt9Cj.jpg&quot; alt=&quot;Strongly overdriven waterfall&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Note how instead of the single central channel, the whole spectrum is filled with intermodulation products. This might be an extreme example, but it illustrates the issue well.&lt;/p&gt;&#xA;&lt;p&gt;When dealing with modes with (unsuppressed) carrier, a typical sign of things that look a bit or ever more like a square wave and not like a perfect sine due to overdriving are &lt;em&gt;lines in the spectrum at equal distances&lt;/em&gt;. Whenever I see a nice comb on a spectrum display, I'm pretty sure I see the leakage of a digital clock, or an overdriven sine wave.&lt;/p&gt;&#xA;&lt;p&gt;There's other indications. If your noise floor pulses: it's kind of unlikely that natural noise sources do that, and unlikely that a lot of interferers decide to synchronously go up and down in power. More likely is that a strong  signal in a strong moment leads to more intermodulation, and a weaker strong signal to less intermodulation.&lt;/p&gt;&#xA;&lt;p&gt;If you know you're dealing with OFDM (e.g. in the FreeDV voice mode), then that's a spectrum with steep edges, and small sidelobes to either side. If your channel was flat, it'd be flat-top (but for a few sinc-induced ripples), but you're using OFDM because your channel isn't flat, so you'll have something that has a few trenches/hills, but still has a steep transition at the edges. If the spectrum starts looking symmetrically round, then the best explanation is usually nonlinearity.&lt;/p&gt;&#xA;&lt;p&gt;If you have a digital system with constellation points of different power: If the outer points seem to suffer a larger amount of noise variance, that's nonlinearity that's worse for large amplitudes.&lt;/p&gt;&#xA;&lt;p&gt;It's hard to pinpoint a &amp;quot;audio&amp;quot; effect for too high gain, because all modes are affected in different ways: FM is relatively robust (there's but one tone in your channel at any time, so not really much to intermodulate with, so your receiver's PLL will track that tone usually quite reliably), whereas AM will suffer intermodulation (which would probably sound like a really weak amplifier trying to drive a large speaker, or a small speaker being beaten to death by a monster amplifier).&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-10-05T18:07:55.483" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17399" PostTypeId="1" AcceptedAnswerId="17400" CreationDate="2020-10-05T21:07:22.503" Score="0" ViewCount="225" Body="&lt;p&gt;I have a full SSTV transmission pre-recorded. Is there any way that I could take the audio file and decode it?&lt;/p&gt;&#xA;&lt;p&gt;Alternatively, is there a way to select the audio device (for example, to read an audio file), to allow the file to be played into any existing decoder?&lt;/p&gt;&#xA;" OwnerUserId="17328" LastEditorUserId="873" LastEditDate="2020-10-29T13:51:37.120" LastActivityDate="2020-10-29T13:51:37.120" Title="SSTV decoder for already-recorded files?" Tags="&lt;audio-interface&gt;&lt;sstv&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17400" PostTypeId="2" ParentId="17399" CreationDate="2020-10-05T22:56:52.520" Score="2" Body="&lt;p&gt;I don't know of digital-mode software that has the capability to open a file, but that doesn't mean that it doesn't exist.  However, there is a handy work-around to your problem: a virtual audio cable.&lt;/p&gt;&#xA;&lt;p&gt;A &amp;quot;virtual audio cable&amp;quot; is a piece of software that registers itself with the operating system as being both an audio input device and an audio output device.  Of course the audio input and output devices are connected together in software, which is why it's called a virtual cable.&lt;/p&gt;&#xA;&lt;p&gt;So you install virtual audio cable software, and then you connect it to both your software that plays back the recording and your digital-mode software, which interprets the audio as SSTV.  Then you press &amp;quot;play&amp;quot; in your audio playback software, and your digital-mode software should be able to decode the SSTV for you.&lt;/p&gt;&#xA;&lt;p&gt;There is Windows software called Virtual Audio Cable, which is not free to use, but there are other software packages that can be found with a web search that do the same thing, and many of those are free.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-10-05T22:56:52.520" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17401" PostTypeId="2" ParentId="17394" CreationDate="2020-10-06T00:28:29.430" Score="1" Body="&lt;p&gt;I havent looked into the mechanics too deep, but FlexRadio has a full-duplex feature for those models with 2 SCUs (spectral capture units) in the radio.&lt;/p&gt;&#xA;&lt;p&gt;Each SCU goes off to a different antenna, and as long as antenna separation and monitoring (or precalculating) dbm levels happens, it works well.&lt;/p&gt;&#xA;&lt;p&gt;I dont believe however you can do full duplex on the same band for obvious reasons.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastActivityDate="2020-10-06T00:28:29.430" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17402" PostTypeId="1" AcceptedAnswerId="17404" CreationDate="2020-10-06T09:31:26.717" Score="0" ViewCount="56" Body="&lt;p&gt;I had a quick look at a practice exam for the license in my country and had a question on stacked Yagi antenna. I have been looking around but the only thing I can find is the mention of an additional 3db gain, increased sidelobes and reduced take-off angle. But nothing authoritative on this.&lt;/p&gt;&#xA;&lt;p&gt;So here is my question:&lt;/p&gt;&#xA;&lt;p&gt;For horizontally polarized Yagi antennas stacked vertically, how to calculate the gain provided by each additional antenna in the stack?&lt;/p&gt;&#xA;" OwnerUserId="1816" LastActivityDate="2020-10-06T11:02:08.637" Title="Stacked Yagi Gain calculation" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17403" PostTypeId="1" AcceptedAnswerId="17423" CreationDate="2020-10-06T10:43:09.263" Score="1" ViewCount="136" Body="&lt;p&gt;I have a Hustler 5BTV antenna i resurrected after a previous monopole succumbed to birds.&lt;/p&gt;&#xA;&lt;p&gt;It is giving me a world of trouble trying to get it tuned for resonance.&lt;/p&gt;&#xA;&lt;p&gt;For those not familiar with the antenna its a 5-band trapped vertical.&lt;/p&gt;&#xA;&lt;p&gt;It is ground-mounted (about 1 foot off the ground on a 1.5ft metal pole) with 8 radials below it (insulated electrical wire) running flat on the ground in each direction. 270-degrees is concrete underneath, and 90-degrees is dirt (garden bed).&lt;/p&gt;&#xA;&lt;p&gt;Directly below the antenna on the pole is a home-made 1:1 choke (2 x FairRite FT240-31's w/11 turns of RG-400 around both toroids). An SO-239 on one side, and 2 bolts, one to centre element of the 5BTV via a 2&amp;quot; wire pigtail, and 1/2 foot wire pigtail to connect to radials below.&lt;/p&gt;&#xA;&lt;p&gt;Transmission line is 32M of RG-213.&lt;/p&gt;&#xA;&lt;p&gt;Below are the results from a NanoVNA (from nanovna-saver)&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;NanoVNA calibrated at load/feedpoint overlaid over NanoVNA calibrated at source/generator end (in blue) with 1:1 choke &amp;amp; 5BTV, RG-213:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BapJD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BapJD.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;And the same chart for the 1:1 choke with 2x100ohm wire-wound resistors in parallel replacing the antenna, VNA calibrated for load-end:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/liTna.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/liTna.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;(grey bars are the ham bands from 160M-10M)&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;I can get an acceptable tune on 80M (narrow-band as it's a coil), and 40M is ok on the low-side, but most other bands aren't usable (too high an SWR, mostly over 4:1 up to &amp;gt; 10:1).&lt;/p&gt;&#xA;&lt;p&gt;I'm wondering if the SWR curve in the bottom-most image (choke) is what should be expected for 2xFT240-31's? Because the SWR of the choke rises on higher bands, i'm wondering if that's why i'm having trouble getting a tune on the higher bands?&lt;/p&gt;&#xA;&lt;p&gt;Would appreciate any thoughts/insights..&lt;/p&gt;&#xA;" OwnerUserId="17200" LastEditorUserId="17200" LastEditDate="2020-10-06T11:22:39.097" LastActivityDate="2020-10-10T03:44:27.863" Title="Troubleshooting 5BTV antenna" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17404" PostTypeId="2" ParentId="17402" CreationDate="2020-10-06T11:02:08.637" Score="4" Body="&lt;p&gt;I don't know your country's questionaire, but:&lt;/p&gt;&#xA;&lt;p&gt;This is just asking for &lt;a href=&quot;https://en.wikipedia.org/wiki/Array_factor&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;Array Factor&lt;/em&gt;&lt;/a&gt; for a specific array. There's nothing specific about Yagi, or any other antenna.&lt;/p&gt;&#xA;&lt;p&gt;When arranging identical antennas in an array, and specifying with which phase they are fed, we can calculate the antenna array's pattern from the individual antennas' patterns, their position and phase.&lt;/p&gt;&#xA;&lt;p&gt;Basically, what happens is that you calculate a pattern, the array factor, that says how much gain and phase you have in every direction &lt;span class=&quot;math-container&quot;&gt;$\vec r$&lt;/span&gt;,&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$AF(\vec{r}) = \sum_{n=1}^N a_n e^{jk\vec{r}\cdot\vec{p}_n}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;where&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\vec r$&lt;/span&gt; is the direction that you're looking at (in 3D radians)&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$N$&lt;/span&gt; is the number of antennas,&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$a_n=e^{j2\pi\varphi_n}$&lt;/span&gt; is the phase vector of the &lt;span class=&quot;math-container&quot;&gt;$n$&lt;/span&gt;th antenna (can also scale this if you don't feed the same power into every antenna),&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$p_n$&lt;/span&gt; is the position of the &lt;span class=&quot;math-container&quot;&gt;$n$&lt;/span&gt;th antenna in 3D space&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$k=\frac{2\pi}\lambda$&lt;/span&gt; the wave number of the free-space wave of the frequency you're interested in&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;(loosely based on Balanis' &amp;quot;Antenna Theory&amp;quot; 2nd ed; that's pretty much &lt;em&gt;the&lt;/em&gt; standard book for antenna studies.)&lt;/p&gt;&#xA;&lt;p&gt;Long story short: if you squint, and imagine that &lt;span class=&quot;math-container&quot;&gt;$\vec p_n$&lt;/span&gt; are just equidistant points on a straight line, this looks like a DFT; i.e. if you have a linear array and do a DFT on the phase vectors of that, you get (due to annoyingly necessary coordinate transforms) a pattern in &lt;span class=&quot;math-container&quot;&gt;$\sin \theta$&lt;/span&gt; space. That's a radiation pattern &amp;quot;just like an antenna has one&amp;quot;, and we call it array factor, because we multiply it with the &lt;em&gt;antenna factor&lt;/em&gt;, which is the actual individual antenna's pattern.&lt;/p&gt;&#xA;&lt;p&gt;Rough calculation for this case: assume your yagis are both looking in the same direction, and are mounted half a wavelength apart right next to each other, the first at &lt;span class=&quot;math-container&quot;&gt;$(0,0,0)$&lt;/span&gt;, the second at &lt;span class=&quot;math-container&quot;&gt;$(\pi/2,0,0)$&lt;/span&gt;. Then, &lt;span class=&quot;math-container&quot;&gt;$k\cdot\vec p_n$&lt;/span&gt; reduces to to &lt;span class=&quot;math-container&quot;&gt;$k\vec p_0=(0,0,0), k\vec p_1=(\pi,0,0)$&lt;/span&gt;. If you feed them in-phase, then &lt;span class=&quot;math-container&quot;&gt;$a_0=a_1=1$&lt;/span&gt; w.l.o.g., and we get a result that says &amp;quot;twice the amplitude at &lt;span class=&quot;math-container&quot;&gt;$\sin\theta=0\implies \theta \in\{0,\pi\}$&lt;/span&gt; and no amplitude orthogonal to that&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Now, you multiply the &amp;quot;twice to the front, 0 to the side&amp;quot; thing with your yagi gain pattern and see that you actually had an array gain of 3 dB to the front, which was your Yagi's main lobe to begin with!&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;reduced take-off angle&amp;quot; belongs in the category of Dreckeffekte (German: dirt(y) effects) and doesn't spring from the analytic consideration with perfect antennas mounted on an infinitely high mast, but are more from the &amp;quot;either you know by experience, or you've run a larger simulation&amp;quot; category.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-10-06T11:02:08.637" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17405" PostTypeId="2" ParentId="17397" CreationDate="2020-10-06T14:31:37.440" Score="1" Body="&lt;p&gt;IMD will respond more to attenuation as the receiver will be operating in a more linear region. This is your best bet for detecting IMD: If you add 3 dB of attenuation (or reduce gain by 3 dB) and you see some signals or the noise floor go down by more than 3 dB, you've significantly reduced IMD.&lt;/p&gt;&#xA;&lt;p&gt;There is another way to determine if attenuation should be added: add too much, then remove a little. Ideally you want enough power to put the RF noise floor maybe 10 dB above the receiver's noise floor: at this point the receiver's noise doesn't contribute significantly, and more power is just increasing distortion.&lt;/p&gt;&#xA;&lt;p&gt;You can find this point by adding attenuation until the noise floor drops by less than the added attenuation. Then remove some attenuation.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-10-06T19:50:19.523" LastActivityDate="2020-10-06T19:50:19.523" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17406" PostTypeId="2" ParentId="17403" CreationDate="2020-10-06T15:01:07.460" Score="4" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Directly below the antenna on the pole is a home-made 1:1 choke (2 x FairRite FT240-31's w/11 turns of RG-400 around both toroids). An SO-239 on one side, and 2 bolts, one to centre element of the 5BTV via a 2&amp;quot; wire pigtail, and 1/2 foot wire pigtail to connect to radials below.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I would guess the pigtails and balun are large enough to be significant, and the source of your problem. You can see from your second VNA screenshot that the balun is introducing some significant impedance. If it weren't, the Smith chart should just be a dot in the center, as if you put a 50 ohm load right on the VNA.&lt;/p&gt;&#xA;&lt;p&gt;I've had a 4BTV, and initially tried installing it in a similar manner with a similar balun I used to use for a dipole, and I had a hard time getting it to tune even though I had no issues with the antenna in a previous installation.&lt;/p&gt;&#xA;&lt;p&gt;Ultimately, I ditched the balun and made a bracket to mount an N connector right on the base. &lt;a href=&quot;https://www.dxengineering.com/parts/dxe-aok-dcf&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Engineering sells a similar, fancier bracket&lt;/a&gt;, but I just made my own from a bit of the copper strap I had for grounding, bending it into a box and brazing the corners. The objective is to get the connector very close to the bolt which connects to the vertical element. Then the radials attach directly to the antenna base, to which the coax connector is also bolted.&lt;/p&gt;&#xA;&lt;p&gt;The coax ran from the antenna connector into a weatherhead on some conduit, which went about 80 feet buried just a few inches underground to the shack. The balun proved unnecessary. The coax looks just like one more radial, so the more radials you have the less common current will be on the coax. And since it's buried, and long, I figured there wouldn't be any significant common mode current at the shack end, which I &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;confirmed with measurement&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;If your situation is different (especially if you can't bury the coax and it's not very long) and you do need a balun (we better call it a common-mode choke, because there's no &amp;quot;balanced&amp;quot; in this system) then I'd suggest making a choke with coax connectors on both ends, and adding it in the middle of your feedline at some point at least 1/4 wave away from the antenna. Trying to choke the common mode current at the feedpoint can be futile because the coax wants to be a radial. Move the choke away from the feedpoint and you just let part of the coax be a radial (free efficiency gain!) and you avoid any possibility of affecting the tuning.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-06T15:01:07.460" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17408" PostTypeId="1" AcceptedAnswerId="17414" CreationDate="2020-10-07T13:49:41.567" Score="2" ViewCount="98" Body="&lt;p&gt;good morning all,&lt;/p&gt;&#xA;&lt;p&gt;I have difficulties to find the correct formula that allows me to calculate the gain of half wave dipole in parallel with another parasitic half wave dipole.&lt;/p&gt;&#xA;&lt;p&gt;I'm trying to calculate the gain(theta,phi) of this array for different distances bentween the two dipoles.&lt;/p&gt;&#xA;&lt;p&gt;I found the equation &lt;span class=&quot;math-container&quot;&gt;$|E_T|$&lt;/span&gt; down below and i want to know how can i calculat the gain frome this equation ?&lt;/p&gt;&#xA;&lt;p&gt;I'm admitting the reciprocity of the antennas so:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_{21}=Z_{12}$&lt;/span&gt; and  &lt;span class=&quot;math-container&quot;&gt;$Z_{11}=Z_{22}$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\gamma_{12}=\frac{Z_{22}-Z_{0}}{Z_{22}+Z_{0}}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\gamma_{12}=\frac{Z_{12}-Z_{0}}{Z_{12}+Z_{0}}$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_{11}=73.12 +42.54i$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\beta=\frac{2\pi}{\lambda}$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$E_{T}=\frac{KI_{1}}{r} \sqrt{1+\frac{|Z_{12}|^2}{|Z_{22}|}-2\frac{|Z_{12}|}{|Z_{22}|}\cos(\gamma_{12}-\gamma_{22}-\beta d \cos{\phi\sin{\theta})}}$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;I plotted the value of &lt;span class=&quot;math-container&quot;&gt;$Z_{21}$&lt;/span&gt;  with respect of d (separation distance between the dipoles&lt;/p&gt;&#xA;&lt;p&gt;Best regards&#xA;&lt;a href=&quot;https://i.stack.imgur.com/bfjWD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bfjWD.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/g2M0p.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/g2M0p.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/lIJUS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lIJUS.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17741" LastEditorUserId="17741" LastEditDate="2020-10-22T08:07:51.857" LastActivityDate="2020-10-22T08:07:51.857" Title="Half wave dipole with parasitic element, (Gain calculation)" Tags="&lt;dipole&gt;&lt;yagi&gt;&lt;radiation-pattern&gt;&lt;parallel-dipole&gt;" AnswerCount="1" CommentCount="4" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17409" PostTypeId="1" AcceptedAnswerId="17418" CreationDate="2020-10-07T19:48:19.840" Score="1" ViewCount="472" Body="&lt;p&gt;It is commonly known that electromagnetic radiation from an antenna is polarized; the electric field is parallel to the rod and the magnetic component is perpendicular to it.&lt;/p&gt;&#xA;&lt;p&gt;What does the radiation of a magnetron look like? Is this radiation polarized, is it continuously or periodically declining and increasing? Is it nearly monochromatic or does it consist of many frequencies?&lt;/p&gt;&#xA;" OwnerUserId="13834" LastEditorUserId="8717" LastEditDate="2020-10-08T03:44:42.373" LastActivityDate="2020-10-08T20:35:13.093" Title="What are the properties of the radiation of a magnetron?" Tags="&lt;microwave&gt;&lt;polarization&gt;&lt;vacuum-tubes&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17410" PostTypeId="2" ParentId="17409" CreationDate="2020-10-07T20:52:42.320" Score="7" Body="&lt;p&gt;I'm sorry if this answer doesn't answer your literal questions – it's just that these questions aren't strictly answerable.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;it is commonly known that electromagnetic radiation from an antenna is polarized; the electric field is parallel to the rod and the magnetic component is perpendicular to it.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It is commonly known that antennas come in more shapes than rods, and can have all kinds of polarizations, linear or circular or anything in between.&lt;/p&gt;&#xA;&lt;p&gt;The magnetron is a microwave resonator that feeds into a waveguide. That waveguide's geometry then defines the modes that propagate in the waveguide. (Modes are a bit more complicated than just &amp;quot;this is a linear polarization&amp;quot;)&lt;/p&gt;&#xA;&lt;p&gt;If you want the energy from that waveguide to be radiated, you need to convert the waveguide into an antenna – for example, attach a specifically shaped horn, or helical cavity, or … That feed will then define the polarization of the free-space wave.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;What does the radiation of a magnetron look like?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;warm!&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Is this radiation polarized,&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Depends on the waveguide, but for guided waves, as said before, they have a &lt;em&gt;mode&lt;/em&gt;, not just a polarization.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;is it continuously or periodically declining and increasing?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Don't know what that means, but every wave's field amplitudes are periodically decreasing/increasing, that's what makes it a wave.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Is it nearly monochromatic or does it consist of many frequencies?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;A magnetoron is a resonator, and thus produces mainly one tone.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-10-07T20:52:42.320" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17411" PostTypeId="1" CreationDate="2020-10-07T22:02:22.017" Score="1" ViewCount="143" Body="&lt;p&gt;I have some Retevis MURS two-way radios model number RT27V. In the programing software there is an option for DCS encrypt.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YEcCP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YEcCP.png&quot; alt=&quot;MURS programming software, showing DCS encrypt option&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now I turned on and off the DCS encrypt option and using my NooElec SDR with SDR# I can see the DCS tone with DCS encryption OFF. With DCS encryption ON I don't see the DCS tone in SDR# which makes sense since the DCS tone was encrypted.&lt;/p&gt;&#xA;&lt;p&gt;So my questions are:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;What kind of encryption would be used to encrypt the DCS tone?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;And how can I see and analyze the coded squelch in SDR# or some other equivalent software for an SDR?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I'm thinking the encryption used is plain old XOR. I know a good majority of wireless computer keyboards use XOR for encryption, so I'm thinking in the realm of keeping it simple for electronics, this too may be XOR. In order to confirm this I'd have to see the carrier squelch  somehow in SDR# or some other program. There is a web-like program at Github called Cyber Chef that I may be able to use with this to decode the digital string.&lt;/p&gt;&#xA;&lt;p&gt;Thanks in advance.&lt;/p&gt;&#xA;&lt;p&gt;PS: Keep in mind this DCS encrypt option in the software is NOT turning on and off DCS. That option is the QT/DQT option you see in the software pictured in the link above. This DCS encrypt option literally encrypts the DCS tone. I never new about this technology myself until I bought this radio.&lt;/p&gt;&#xA;" OwnerUserId="17898" LastEditorUserId="4665" LastEditDate="2020-10-07T23:07:23.160" LastActivityDate="2020-10-07T23:07:23.160" Title="Retevis MURS radio and encrypted sub codes" Tags="&lt;tone-squelch&gt;&lt;encryption&gt;&lt;murs&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17413" PostTypeId="2" ParentId="17409" CreationDate="2020-10-08T04:47:21.843" Score="2" Body="&lt;p&gt;I once wondered if a microwave oven magnetron might make a good transmitter, for CW for EME.&lt;/p&gt;&#xA;&lt;p&gt;I took a spectrum analyser and antenna to the kitchen and microwaved a glass of water, and I saw...&lt;/p&gt;&#xA;&lt;p&gt;The most awful collection of strong tones, covering a large part of 2.4 to 2.5 GHz, all of them shifting up and down in frequency, rising and falling, as the water rotated.&lt;/p&gt;&#xA;&lt;p&gt;I think the magnetron was strongly influenced by the food cavity, and the very many fast-changing modes supported there, depending on the position of the absorber. (imagine measuring the return loss of a microwave oven cavity, what a mess it would be. Remember a glass of water in a microwave oven is hardly a 1:1 SWR - it's still a terrible match and there are enormous standing waves). I've no idea what the spectrum would look like into a perfect load.&lt;/p&gt;&#xA;&lt;p&gt;I didn't get a picture, this was before phone cameras, but I found a video that looks similar, &lt;a href=&quot;https://youtu.be/kCoucYFKTFY?t=35&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Magnetron for radio transmission, as opposed to heating, might be different. At least, with the right external cavity, they can probably be cleaned up a lot compared to the one I saw. The magnetron alone is not particularly high Q, a microwave oven one is probably happy to &amp;quot;whistle&amp;quot; at any frequency between 2.4 and 2.5 GHz, depending on the external circuit.&lt;/p&gt;&#xA;&lt;p&gt;As for polarisation - remember the power from a magnetron is coupled out by a small slot or loop, into the waveguide. So there is no &amp;quot;magnetron polarisation&amp;quot;, any more than there is &amp;quot;transistor polarisation&amp;quot; - its entirely due to the following components. If it goes into a simple rectangular waveguide and then a pyramidal horn, it will be perfectly linear, but that's just one choice.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-10-08T18:40:54.060" LastActivityDate="2020-10-08T18:40:54.060" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17414" PostTypeId="2" ParentId="17408" CreationDate="2020-10-08T06:14:17.417" Score="1" Body="&lt;p&gt;The demo version of EZNEC software (free) would be able to do that, with a fairly short learning curve:  &lt;a href=&quot;https://www.eznec.com/demoinfo.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.eznec.com/demoinfo.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-10-08T06:14:17.417" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17416" PostTypeId="1" AcceptedAnswerId="17417" CreationDate="2020-10-08T14:26:44.740" Score="2" ViewCount="354" Body="&lt;p&gt;I've been just scanning through the HF band at night seeing what all I can pick up, and I'm trying to figure out a particular signal. I'm using a VHF discone, which isn't ideal, but it works well enough for simple reception with an RTL-SDR.&lt;/p&gt;&#xA;&lt;p&gt;22.695mhz. When I tune in the evening (roughly midnight UTC) here in Baltimore, MD I receive an AM broadcast in Japanese that a friend tells me is NHK World Radio. The station goes off the air after a bit, but then came back a few hours later the other night broadcasting several hours of pro-Cuba and pro-North Korea propaganda in English.&lt;/p&gt;&#xA;&lt;p&gt;What is also strange is that the specific frequency seems to deviate by a couple kHz over time.&lt;/p&gt;&#xA;&lt;p&gt;The contents of the broadcast, the unusual frequency I'm receiving it on, and the slow shifting of the frequency has me very curious where this is coming from and why I'm receiving the signal where it is.&lt;/p&gt;&#xA;" OwnerUserId="17901" LastEditorUserId="5776" LastEditDate="2020-10-09T12:21:14.620" LastActivityDate="2020-10-09T12:21:14.620" Title="Broadcast signal deviating with time" Tags="&lt;hf&gt;&lt;rtl-sdr&gt;&lt;am&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17417" PostTypeId="2" ParentId="17416" CreationDate="2020-10-08T16:36:44.260" Score="7" Body="&lt;p&gt;Since you said you're using an RTLSDR, it's very likely that you aren't receiving a station on 22,695 kHz, but rather one on 6,105 kHz. NHK World Radio does broadcast on that frequency (according to the schedule I'm looking at, they broadcast between 0200 and 0400 UTC from a transmitter in France). The RTLSDR &amp;quot;direct sampling&amp;quot; mode is a hack, and it can't distinguish between a signal at a frequency &lt;em&gt;f&lt;/em&gt; and one at 28,800 kHz - &lt;em&gt;f&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;As for changes in content and variation in frequency... well, you're hearing different stations. It's common for there to be many unaffiliated stations around the world sharing a single frequency, and with shortwave's global propagation, it's possible for you to hear different ones at different times (or even at the same time). Long reach also makes shortwave a good medium for distributing propaganda, and some countries even run high-powered transmitters for the specific purpose of drowning out other stations that they don't want their citizens to be able to hear.&lt;/p&gt;&#xA;&lt;p&gt;It also wouldn't be surprising for one of the transmitters to be a kHz or two off-frequency.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-10-08T16:36:44.260" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17418" PostTypeId="2" ParentId="17409" CreationDate="2020-10-08T20:35:13.093" Score="2" Body="&lt;p&gt;Paraphrasing the &lt;a href=&quot;https://en.wikipedia.org/wiki/Cavity_magnetron&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia entry for the magnetron&lt;/a&gt;, we learn that,&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;... a stream of electrons passes by the openings to metal cavity resonators and causes microwaves to oscillate within, similar to the way a whistle produces a tone when excited by an air stream blown past its opening. The resonant frequency is determined by the cavities' physical dimensions.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;A magnetron produces microwave energy, but it is not meant to radiate that energy. The microwaves which oscillate within the cavity resonators are not polarized in the sense that an antenna can be horizontally, vertically, circularly, co-polarized or cross-polarized. Rather, they correspond to particular field &lt;em&gt;modes&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;This page on &lt;a href=&quot;https://www.tpub.com/neets/book11/45i.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;magnetron coupling methods&lt;/a&gt; informs us that the energy is coupled from the magnetron to the load - which could be an antenna - via an E-field loop (A), an H-field loop (C), or an aperture (E), as shown below:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fEjUt.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fEjUt.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-10-08T20:35:13.093" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17419" PostTypeId="2" ParentId="17416" CreationDate="2020-10-08T22:01:40.297" Score="3" Body="&lt;p&gt;As hobbs - KC2G says, there could easily be multiple stations transmitting.&lt;/p&gt;&#xA;&lt;p&gt;Also, the frequency stability of the RTLSDR is quite poor. If you are seeing the frequency drift slowly over time (and not jump discretely) it's likely what you're observing is a side effect of the oscillator in the RTLSDR slowly changing as a function of temperature and other environmental variables.&lt;/p&gt;&#xA;&lt;p&gt;Fun test: try deliberately changing the temperature of your RTLSDR and see what happens. A duster can held upside down to spray liquid can get it cold real fast. You could also pop it in the freezer for a minute, then turn it on and warm it with your hand or a blow dryer.&lt;/p&gt;&#xA;&lt;p&gt;It's also technically possible a similar thing is happening at the transmitter site, though it's much less likely since transmitters are usually engineered to a higher standard.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-08T22:01:40.297" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17420" PostTypeId="1" CreationDate="2020-10-09T14:53:55.117" Score="0" ViewCount="83" Body="&lt;p&gt;Will the &lt;a href=&quot;https://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&amp;amp;ProdCatID=102&amp;amp;encProdID=870B3CA7CFCB61E6A599B0EFEA2217E4&amp;amp;DivisionID=65&amp;amp;isArchived=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;450D&lt;/a&gt; computer control program interface with &lt;a href=&quot;https://www.winlink.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;Winlink&lt;/a&gt; and allow Winlink to change radio frequencies/bands?&lt;/p&gt;&#xA;" OwnerUserId="17909" LastEditorUserId="8717" LastEditDate="2020-10-12T17:36:54.490" LastActivityDate="2020-11-12T19:03:05.333" Title="Does the 450D work with Winlink and allow Winlink to control changing frequencies and bands?" Tags="&lt;software&gt;&lt;computer-control&gt;&lt;ft-450d&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17421" PostTypeId="1" CreationDate="2020-10-09T18:58:49.847" Score="1" ViewCount="79" Body="&lt;p&gt;Recently licensed technician here, and going straight into my general class, I'm keeping an eye on cheap (sub-$400) HF radios. I keep reading articles that suggest used radios that normally sell for under 350, but I can only find them on Ebay for over 400 right now, and rising, it seems. Is this a seasonal thing, or is this relatively abnormal, like the recent rise in price of firearms and ammo?&lt;/p&gt;&#xA;" OwnerUserId="17328" LastActivityDate="2020-10-09T18:58:49.847" Title="Does the price of ham equipment normally rise during winter?" Tags="&lt;hf&gt;&lt;equipment&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17422" PostTypeId="1" AcceptedAnswerId="17426" CreationDate="2020-10-09T20:48:04.053" Score="0" ViewCount="175" Body="&lt;p&gt;I know that there have  been many similar threads on this, but I still need clarification. At the moment, the only thing I have is a 500' roll of RG-6 and a (very) tight budget, and I should be getting &lt;a href=&quot;https://www.ebay.com/p/22023582788?iid=153552704218&amp;amp;chn=ps&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; cheap VHF/UHF 25W mobile soon (mostly going to use it as a base though).&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question:&lt;/strong&gt;&#xA;Could I safely use this coax and radio safely? Would I have to do anything &amp;quot;special&amp;quot;? Would this vary with the type of antenna that I use?&lt;/p&gt;&#xA;" OwnerUserId="17328" LastActivityDate="2020-10-12T15:18:22.383" Title="How to use 75ohm (RG6) coax?" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;&lt;impedance&gt;&lt;impedance-matching&gt;&lt;feed-line&gt;" AnswerCount="2" CommentCount="7" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17423" PostTypeId="2" ParentId="17403" CreationDate="2020-10-10T03:06:55.410" Score="0" Body="&lt;p&gt;Ran a little experiment to try what Phil mentioned, i raised the radial ring from ground-level to just below the balun, and used a shorter (3&amp;quot; or so) pigtail to connect to the radials as a test.&lt;/p&gt;&#xA;&lt;p&gt;Pigtail between the choke centre-pin and and centre screw on the 5btv is exactly the same pigtail as before (around 3&amp;quot; as well..)&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;NanoVNA calibrated at load/feedpoint overlaid over NanoVNA calibrated at source/generator end (in blue) with 1:1 choke &amp;amp; 5BTV, RG-213:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MN15m.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MN15m.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;So, the moral of the story is to keep the centre and braid connections short by either using a so-239 and a coax pigtail, or if using wires, keep them as short as possible.&lt;/p&gt;&#xA;&lt;p&gt;Studying DX Engineerings PDF on the BTV this isn't mentioned explicitly, but one can notice all the intra choke/radial-plate connections are short, wether it's a direct so-239 to the btv itself, a bulkhead so239 on the radial-plate with coax pigtail, or a short tinned copper-braid from DX Engineerings own choke.&lt;/p&gt;&#xA;&lt;p&gt;The proof is in the pudding :) Thanks to all who provided advice, this is a test setup, now i'll have re-design the pigtails more permanently, soon.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastEditorUserId="17200" LastEditDate="2020-10-10T03:44:27.863" LastActivityDate="2020-10-10T03:44:27.863" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17424" PostTypeId="1" CreationDate="2020-10-10T08:02:29.253" Score="2" ViewCount="82" Body="&lt;p&gt;I have a remote wireless water tank level sensor.&#xA;It transmits at 439 MHz with an apparent max range of 100 metres.&#xA;Unfortunately I need about 200 metres.&lt;/p&gt;&#xA;&lt;p&gt;How can I extend that range?&lt;/p&gt;&#xA;" OwnerUserId="17916" LastEditorUserId="2988" LastEditDate="2020-10-10T20:28:31.773" LastActivityDate="2020-10-10T22:54:45.310" Title="Help with Repeating 439 MHz signal" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17425" PostTypeId="2" ParentId="17424" CreationDate="2020-10-10T15:07:56.467" Score="4" Body="&lt;p&gt;A repeater would be complicated, you'd need to get into the details of how the signal works.&lt;/p&gt;&#xA;&lt;p&gt;Fortunately 439 MHz is in or near the amateur band, so external antennas are available. I suggest you modify the receiving end of the system to include an external antenna.&lt;/p&gt;&#xA;&lt;p&gt;To double the range of a radio link, all things equal, you need an additional 6 dB of gain. At 439 MHz you'll easily buy plenty of gain with a yagi antenna. There are many for sale, if you search for &amp;quot;70 cm yagi antenna&amp;quot;, here's one from &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B083GG3ZQ6&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amazon&lt;/a&gt;:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/Nbtp6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Nbtp6.png&quot; alt=&quot;yagi&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I suggest opening up the display unit instead of the transmitter, as increasing the transmitter effective radiated power with an external antenna will make the unit violate its type approval. Also the transmitter will be outdoors, need to be waterproof etc.&lt;/p&gt;&#xA;&lt;p&gt;Find the antenna on the PCB, and a nearby ground point. Disconnect the antenna and solder on a coaxial cable. Ideally it would look like this photo &lt;a href=&quot;https://electronics.stackexchange.com/questions/360202/soldering-rg-405-coaxial-cable-directly-to-pcb-pads-meant-for-u-fl-connector&quot;&gt;from SE&lt;/a&gt;:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/EaxsK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EaxsK.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;br /&gt;&#xA;But more likely it'll end up looking like this (photo from &lt;a href=&quot;https://ac0c.com/main/page_ft2k_ns_filter_installation.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;AC0C&lt;/a&gt;):&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/nRFc2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nRFc2.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;It's important that the ground be close to the antenna connection, no more than 10 mm away, not on the other side of the board.&lt;/p&gt;&#xA;&lt;p&gt;Mount the yagi antenna outside, aimed at the transmitter, and rotate it to find the polarisation that works best for you.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-10-10T22:54:45.310" LastActivityDate="2020-10-10T22:54:45.310" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17426" PostTypeId="2" ParentId="17422" CreationDate="2020-10-11T10:43:54.613" Score="3" Body="&lt;p&gt;Well, according to the spec tables in the &lt;a href=&quot;https://www.passion-radio.com/index.php?controller=attachment&amp;amp;id_attachment=419&quot; rel=&quot;nofollow noreferrer&quot;&gt;manual&lt;/a&gt; the thing expects a 50 Ω antenna impedance.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.maximintegrated.com/en/design/technical-documents/tutorials/7/742.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Mismatch means a loss of signal energy&lt;/a&gt;. How much exactly &lt;a href=&quot;https://en.wikipedia.org/wiki/Smith_chart#The_variation_of_complex_reflection_coefficient_with_position_along_the_line&quot; rel=&quot;nofollow noreferrer&quot;&gt;depends on the length of the 75 Ω transmission line&lt;/a&gt; – this makes a system much harder to design predictably.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&lt;strong&gt;I wrote all the following (up to the next horizontal line), then stopped to wonder &amp;quot;&lt;em&gt;what might be the antenna connector on this thing?&lt;/em&gt;&amp;quot;, and then saw what it was. All I wrote doesn't matter to your problem, more in the general case (future readers), jump ahead to the next horizontal line&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Three options here:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Matching circuitry to match your 50 Ω transceiver to 75 Ω&lt;/li&gt;&#xA;&lt;li&gt;Buying 50 Ω cable&lt;/li&gt;&#xA;&lt;li&gt;Ignore the problem and hope that worst case, the transmitter would withstand its whole output power being reflected back at him if you happen to experience a full reflection due to the length of the cable.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Between 1. and 2., I'd go with:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;If distance is short, buy cheap 50 Ω cable&lt;/li&gt;&#xA;&lt;li&gt;If distance is long, add matching circuitry&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;em&gt;in general&lt;/em&gt;, 75 Ω line can be made lower-loss at the same cost. If you know your spool of 75 Ω is &amp;quot;fresh&amp;quot; as in &amp;quot;no water has seeped in from the ends&amp;quot;, it's probably wisest to simply match. The matching circuit for a single band (especially if it's as low in frequency as VHF) is easy (you'll find plenty of examples on the web), a series inductor and a shunt capacitor, and cheap.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&lt;strong&gt;here is where you'd jump if you just want to read the answer to your specific case&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;So, you'd technically need to match your transmission line to your radio's impedance, and/or vice versa.&lt;/p&gt;&#xA;&lt;p&gt;But, looking at the antenna connector on your device:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BkElR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BkElR.jpg&quot; alt=&quot;SO-239 female&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;h1&gt;&lt;/h1&gt;&#xA;&lt;p&gt;That's SO-239, for a PL-259 connector! No way that's matched to any particular impedance. These connectors should have been dead since ca 1948, &lt;a href=&quot;https://ham.stackexchange.com/questions/13061/pl-259-so-239-vs-n-type-vs-bnc-which-is-best-connector-to-use-when/13062#13062&quot;&gt;and really are sub-par&lt;/a&gt;. That means that no matter what the impedance of the electronics inside are, the connector ruins them. It's also definitely not designed to go as high as 480 MHz like your radio. By far not.&lt;/p&gt;&#xA;&lt;p&gt;So, in other words, since these radios don't come with a datasheet that contains any performance / impedance curves to begin with, and just claim 50 Ω, but have a connector that doesn't even allow for that impedance, and in fact doesn't even allow for low-leakage operation at the higher frequencies your radio works at, at all, I wouldn't worry.&lt;/p&gt;&#xA;&lt;p&gt;You might be losing a bit of power with your 75 Ω line, because the device might actually be maybe 60 Ω (I &lt;em&gt;really&lt;/em&gt; doubt you can make this connector be as low as 50 Ω at 500 MHz, it's just too friggin large), but you might also be in luck and your device is closer to 75 Ω than the manual claims.&lt;/p&gt;&#xA;&lt;p&gt;So, heck, just connect your 75 Ω line to this. It shouldn't work great if the datasheet was right, but should still work with a high probability, but the manual very likely isn't right, so here's to &amp;quot;best effort&amp;quot;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Would this vary with the type of antenna that I use?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes. Just as your transceiver, the antenna needs to be matched to your transmission line impedance.&lt;/p&gt;&#xA;&lt;p&gt;In your case, you need to match your antenna to the 75Ω line, but that's often as easy as soldering in a capacitor and inductor and that's it. And again, you can probably just ignore all this, because we know so little about the radio that all things that we optimize might simply be going in the wrong direction.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-10-11T10:53:31.593" LastActivityDate="2020-10-11T10:53:31.593" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17427" PostTypeId="1" CreationDate="2020-10-11T18:57:08.017" Score="1" ViewCount="115" Body="&lt;p&gt;I've been using FT8 on my Yaesu FT-450D for quite some time. I decided to try to talk on phone frequencies and discovered neither one of my mics will transmit. My mics are the original hand mic and a Heil headset. I've tried all bands and cannot transmit on any of them. I had successfully talked on the radio but not now. The only change I have made was to change from a switching power supply to a linear power supply. The radio will not transmit on either supply. It only transmits in digital modes. Does anyone have any ideas?&lt;/p&gt;&#xA;" OwnerUserId="17924" LastEditorUserId="8717" LastEditDate="2020-10-13T21:21:34.143" LastActivityDate="2021-03-16T22:04:05.480" Title="FT-450D not transmitting with microphone" Tags="&lt;digital-modes&gt;&lt;transmitter&gt;&lt;equipment-troubleshooting&gt;&lt;microphone&gt;&lt;ft-450d&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17428" PostTypeId="1" CreationDate="2020-10-12T01:21:49.563" Score="1" ViewCount="44" Body="&lt;p&gt;I have the RCS-4 with two MFJ-4116.&lt;/p&gt;&#xA;&lt;p&gt;Prior to installing my motorized HF antenna system topside, I bench-tested the core of the assembly in my shack.&lt;/p&gt;&#xA;&lt;p&gt;The MFJ-4116 near my transceiver was injected with reversible 12vDC which was successfully decoupled at the MFJ-4116 near the motor.&lt;/p&gt;&#xA;&lt;p&gt;So I installed the antenna-side of the assembly topside, then came into the shack to apply a reversible dc.&lt;/p&gt;&#xA;&lt;p&gt;I expected to have bidirectional control of the motor to resonate the antenna.&#xA;As I've done on the bench, by toggling reversible DC as I transmitted and watching for any SWR change.&lt;/p&gt;&#xA;&lt;p&gt;It didn't work - Apparently the RCS-4 is somehow impeding the process.&lt;/p&gt;&#xA;&lt;p&gt;Any thoughts, anyone?&lt;/p&gt;&#xA;" OwnerUserId="17927" LastEditorUserId="8717" LastEditDate="2020-12-13T19:25:50.357" LastActivityDate="2020-12-13T19:25:50.357" Title="Bidirectional motor control using MFJ-4116 with RCS-4" Tags="&lt;antenna&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17429" PostTypeId="2" ParentId="17422" CreationDate="2020-10-12T15:18:22.383" Score="2" Body="&lt;p&gt;Smith chart shows that 50 Ohm antenna (assumed perfect 50 Ohm real!) connected to 75 Ohm coax cable can result in impedances between 50 and 112.5 Ohm. SWR 1: 1.5. So this so far not mentioned possible solution in this thread may be usefull for your problem: for a single frequency, or for a small frequency band, the use of cable with a multiple of half wavelengths (electrical wavelength! I.E. calculate the physical length from the shortening factor of the cable!) can give or maintain impedance matching. Recommended is measurement with a NanoVNA to assure the impedance at the antenna connector before powering up the transmitter. PA0FSB&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-10-12T15:18:22.383" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17430" PostTypeId="1" AcceptedAnswerId="17443" CreationDate="2020-10-12T16:28:10.877" Score="1" ViewCount="106" Body="&lt;p&gt;Lots of information about shielded loop antennas is available on the internet. However, antenna manufacturers do not indicate the number of turns. How can I find the number of turns of a manufactured 60 cm shielded loop antenna rated for 9 kHz – 30 MHz without destroying the antenna?&lt;/p&gt;&#xA;" OwnerUserId="17864" LastEditorUserId="8717" LastEditDate="2020-10-12T17:20:27.170" LastActivityDate="2020-10-26T09:59:08.827" Title="How many turns of wire inside 60 cm shielded loop antenna (9kHz - 30 MHz). How can I find this number without destroying the antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;antenna-system&gt;&lt;magnetic-loop&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17431" PostTypeId="1" AcceptedAnswerId="17433" CreationDate="2020-10-12T17:15:31.420" Score="0" ViewCount="64" Body="&lt;p&gt;(I'm asking this in the context of a Cobra 29LTD CB, but I think that it also applies to amateur radio in general.)&lt;/p&gt;&#xA;&lt;p&gt;In SWR mode, the needle swings all the way to the right, hitting the limit. The (mag mount 35&amp;quot; K30) antenna is indoors, grounded to a filing cabinet. I believe it has not been tuned. I have continuity from the center coax to the antenna whip. I don't have continuity between the center and ground from one end, but I can't test the continuity of the entire length of ground because the cable goes straight into the base of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;It does transmit to an HT that can receive 10 meters, as well as to some cheap speakers across the room. :D&lt;/p&gt;&#xA;&lt;p&gt;SWR should never be this high, even under bad conditions, right?&lt;/p&gt;&#xA;" OwnerUserId="17328" LastEditorUserId="17328" LastEditDate="2020-10-12T21:11:29.003" LastActivityDate="2020-10-12T23:30:42.877" Title="SWR jumps to maximum of gauge" Tags="&lt;impedance-matching&gt;&lt;swr-meter&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17432" PostTypeId="2" ParentId="17430" CreationDate="2020-10-12T20:01:35.773" Score="0" Body="&lt;p&gt;If you can find out the diameter or AWG of the wire used, then you can find a resistance-per-foot (cm) chart in a Google search&lt;/p&gt;&#xA;&lt;p&gt;If the wire is connected directly to a connector or terminals, then measure the total resistance of the coil of wire, assuming that 60 cm is the distance measured from center-to-center rather than the OD or ID.&lt;/p&gt;&#xA;&lt;p&gt;With some simple math, you have your answer. 60 cm average diameter * 3.1416 = 188.5 cm/turn or 6.21 feet of wire per turn.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-10-12T20:01:35.773" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17433" PostTypeId="2" ParentId="17431" CreationDate="2020-10-12T23:30:42.877" Score="3" Body="&lt;p&gt;An antenna that's&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Pretty short (0.08 wavelength),&lt;/li&gt;&#xA;&lt;li&gt;Not tuned,&lt;/li&gt;&#xA;&lt;li&gt;Mag-mounted to an inadequate counterpoise,&lt;/li&gt;&#xA;&lt;li&gt;Indoors with who-knows-how-much metal in its near field,&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;could certainly have a 5:1 or worse SWR, which is enough to &amp;quot;peg the needle&amp;quot; on most meters I've seen.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-10-12T23:30:42.877" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17435" PostTypeId="2" ParentId="17427" CreationDate="2020-10-13T10:33:22.867" Score="0" Body="&lt;p&gt;Try changing mode from DATA-USB to USB/LSB.&lt;/p&gt;&#xA;" OwnerUserId="17936" LastActivityDate="2020-10-13T10:33:22.867" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17437" PostTypeId="2" ParentId="17420" CreationDate="2020-10-13T18:37:51.817" Score="1" Body="&lt;p&gt;With correct settings for the transceiver's CAT interface in the Winlink software, Winlink should be able to control the transceiver. There should be no need for another &amp;quot;computer control program&amp;quot; interfacing with Winlink.&lt;/p&gt;&#xA;" OwnerUserId="17676" LastActivityDate="2020-10-13T18:37:51.817" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17438" PostTypeId="1" CreationDate="2020-10-14T00:42:27.040" Score="1" ViewCount="94" Body="&lt;p&gt;I'm looking for some QRN/M audio files to &amp;quot;show&amp;quot; someone what said noise can sound like, particularly interested in static crashes or lightening bursts.  Have Googled same with no joy other than definitions and what the Q signals mean.  Anyone?&#xA;73,&#xA;NX7D&lt;/p&gt;&#xA;" OwnerUserId="17938" LastEditorUserId="4665" LastEditDate="2021-03-17T16:23:02.170" LastActivityDate="2021-03-17T16:23:02.170" Title="Where to find QRM and/or QRN audio files?" Tags="&lt;noise&gt;&lt;qrn&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17439" PostTypeId="2" ParentId="17438" CreationDate="2020-10-14T02:33:35.250" Score="2" Body="&lt;p&gt;I don't know about recordings, but &lt;a href=&quot;http://websdr.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://websdr.org/&lt;/a&gt; has a directory of radios you can access through the internet and listen to real live noise.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-14T02:33:35.250" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17440" PostTypeId="2" ParentId="17438" CreationDate="2020-10-14T14:04:38.937" Score="1" Body="&lt;p&gt;I did a web search myself without much luck.  It's a bit surprising to me, in this era of all information migrating its way online.  Maybe someone would be kind enough to make a recording from the 40m or 80m bands at night.&lt;/p&gt;&#xA;&lt;p&gt;The American Radio Relay League, the national organization for amateur radio in the US, has shared a &lt;a href=&quot;http://www.arrl.org/sounds-of-rfi&quot; rel=&quot;nofollow noreferrer&quot;&gt;collection of recordings of RFI&lt;/a&gt;.  They call these noises QRN, probably because many sound a lot like static, but I'd call them QRM, because their origin is man-made.  Old-fashioned QRN from lightning doesn't seem to be present in their recordings.&lt;/p&gt;&#xA;&lt;p&gt;Randy K5ZD has shared &lt;a href=&quot;https://k5zd.com/audio-archive/&quot; rel=&quot;nofollow noreferrer&quot;&gt;audio recordings he made of several of his HF contest efforts&lt;/a&gt;.  If you listen long enough you'll probably hear QRN when he operates on the low bands.  Unfortunately you might have to listen a while before you hear some, because the big HF contests are generally held in the northern hemisphere's winter, when there is less QRN.&lt;/p&gt;&#xA;&lt;p&gt;I discovered some &lt;a href=&quot;http://www.astrosurf.com/luxorion/qsl-audiofiles.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;recordings of HF QSOs&lt;/a&gt;, some of which are listed as having QRN.  I listened to a few, but all I heard was static rather than lightning crashes.&lt;/p&gt;&#xA;&lt;p&gt;Finally I was able to find some &lt;a href=&quot;https://www.sigidwiki.com/wiki/Lightning_Sferics&quot; rel=&quot;nofollow noreferrer&quot;&gt;recordings of lightning crashes&lt;/a&gt; at &lt;a href=&quot;https://www.sigidwiki.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;sigidwiki.com&lt;/a&gt;, a website dedicated to sharing recordings and waterfall images of strange noises for identification purposes.  The lightning crash recordings aren't recordings of ham QSOs, but they do get the idea across.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-10-14T14:20:30.553" LastActivityDate="2020-10-14T14:20:30.553" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17442" PostTypeId="1" AcceptedAnswerId="17444" CreationDate="2020-10-14T18:34:26.797" Score="2" ViewCount="99" Body="&lt;p&gt;I have a K40 Plus CB antenna, which is supposed to be attached to a car roof for the ground plane. However, I would like to set this up as a base antenna. Could I instead attach the ground to separate radials? If so, what would be the requirements of the radials (number of radials, diameter, length, material, etc)? How would I angle them? How would this affect tuning/SWR? How would it affect performance in general?&lt;/p&gt;&#xA;&lt;p&gt;Just to make this relevant to ham, how does this apply to the other bands and their antennas?&lt;/p&gt;&#xA;" OwnerUserId="17328" LastActivityDate="2020-10-14T20:20:28.810" Title="Substitute a car roof with radials?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17443" PostTypeId="2" ParentId="17430" CreationDate="2020-10-14T18:54:31.297" Score="2" Body="&lt;p&gt;Measure the inductance of the loop (without anything else connected). One winding: 2.5 uH, two windings: 10 uH (quadratic relation).&lt;/p&gt;&#xA;&lt;p&gt;Most shortwave wideband (non-tuned) loop antennas are just a single turn. Inductance will be around 2 to 3 uH. To have constant conversion from field strength to unloaded output voltage, the short-circuited output current of the loop must be converted into an output voltage. The active part of the antenna is a transimpedance with input impedance of 100 milli Ohm and noise matching to the source impedance/inductance.&lt;/p&gt;&#xA;&lt;p&gt;The low load impedance is seldom realised: the input impedance of the transimpedance amplifier (for example a transistor or FET circuit in common base /common gate) with or without an input transformer is in the order of one to ten Ohm. Result: frequency response for lower frequencies is reduced. Example: Wellbrook ALA 1530 conversion (Vout/Field strength) is reduced below 1 MHz. That is not a problem for the reception sensitivity of weaker signals, since the external noise is higher for lower frequencies.&lt;/p&gt;&#xA;&lt;p&gt;For measurement purposes only, the &amp;quot;load impedance of the loop&amp;quot; must be low.&lt;/p&gt;&#xA;&lt;p&gt;There are some examples of mult-turn wideband loop antennas with a shield: these antennas mostly have resonances in their frequency response. I have never seen a good multi-turn shielded active loop antenna without resonances in the 15 to 30 MHz region.&lt;/p&gt;&#xA;&lt;p&gt;PA0FSB&#xA;Brightnoise&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2020-10-26T09:59:08.827" LastActivityDate="2020-10-26T09:59:08.827" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17444" PostTypeId="2" ParentId="17442" CreationDate="2020-10-14T20:20:28.810" Score="6" Body="&lt;p&gt;Don't worry, your question is fine, because what works for a CB antenna works just as well for a 10m antenna.&lt;/p&gt;&#xA;&lt;p&gt;Yes, you could certainly substitute radials for the car roof.  The general rule for radials laid along the ground is that they should be at least 1/4λ long.  That's 1/4λ electrically; RF current flows more slowly through a radial than through vacuum or air, so the wires don't need to be as long.  If the radials are laid along the ground, having the radials be a little longer than 1/4λ is no big deal.  Material?  Copper or aluminum is best electrically; most people use copper wire.  Stranded or solid?  There isn't much difference.  Wire diameter?  Thicker is better; 14 AWG would be deluxe, a bit thinner is probably OK.  Insulated or not?  Doesn't make much of a difference.  How many radials?  More is better; I'd say use at least four.&lt;/p&gt;&#xA;&lt;p&gt;If you plan to elevate the radials, then things change.  Then it becomes more important that the radials be as close as possible to 1/4λ long, because the radials aren't just returning current absorbed by the ground any more (that's an oversimplification BTW, but somewhat useful conceptually); elevated radials radiate RF because they are part of the antenna.  Do make sure that elevated radials are where people and animals can't touch them.&lt;/p&gt;&#xA;&lt;p&gt;As I mentioned, elevated radials are ideally 1/4λ long, which works out to be about 2.62 m long for US channel 19 and a 95% velocity factor.  That's 8' 7&amp;quot; in imperial units.  When a CB antenna is mounted on the roof of a car, very few cars have round roofs that are 5.24 m (17' 2&amp;quot;) in diameter.  So a mobile antenna already has some tuning circuit designed to compensate for a ground plane less than 1/2λ in diameter.  So how long should your radials actually be?  That's hard to say without knowing a lot more about the construction of your antenna and exactly how you want to use it.&lt;/p&gt;&#xA;&lt;p&gt;I'd recommend experimentation.  Start with long radials, and then trim them for the best SWR.  When I say &amp;quot;trim&amp;quot;, you don't actually have to cut the radials; if you fold the wire so the short end lays next to the long end, then electrically the short piece of wire will be part of the long piece of wire, as if you had cut the wire where you folded it.  That way if you want to try a different length, you can just unfold the wire and fold it somewhere else.  You can experiment with the length, and if the radials are elevated then you can experiment with their angle also.&lt;/p&gt;&#xA;&lt;p&gt;If you're going to all the trouble of creating a radial system, if I were you I'd just cut one more 1/4λ radial and put it inside a piece of PVC pipe pointing up in the middle of the radials in place of the mobile antenna.  (You'd have to experiment a bit with its length also.)  Connect the vertical wire to the center of the coax rather than the shield.  Then you would have homebrewed the entire antenna for not very much money, and you could save the mobile antenna for a vehicle.&lt;/p&gt;&#xA;&lt;p&gt;If you do homebrew a radial system or an entire antenna, please come back here and answer your own question with the details of what you did, to help others.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-10-14T20:20:28.810" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17445" PostTypeId="1" CreationDate="2020-10-14T23:05:08.147" Score="0" ViewCount="135" Body="&lt;p&gt;I am just getting into ham radio, and I find it very interesting, but to make phone calls, you have to be on a 10 meter band. Does anyone know how to infer the band you're on is 10 meter? Thank you very much.&lt;/p&gt;&#xA;" OwnerUserId="17947" LastEditorUserId="8717" LastEditDate="2020-10-19T19:46:27.720" LastActivityDate="2020-10-19T19:46:27.720" Title="How do you know if you're on a 10 meter band?" Tags="&lt;hf&gt;&lt;jargon&gt;&lt;phone&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17446" PostTypeId="2" ParentId="17445" CreationDate="2020-10-14T23:20:00.103" Score="4" Body="&lt;p&gt;Frequency and wavelength of a wave are related: the frequency times the wavelength equals the speed of the wave, in this case the speed of light.  For HF, the frequency in megahertz times the wavelength in meters equals 300.  Modern radios display the frequency.  Bands are referred to by their approximate wavelength for historical reasons.&lt;/p&gt;&#xA;&lt;p&gt;If the frequency displayed on your radio is between 28 MHz and 29.7 MHz, then you're on the 10m band.&lt;/p&gt;&#xA;&lt;p&gt;For hams in the US, the ARRL's &lt;a href=&quot;http://www.arrl.org/graphical-frequency-allocations&quot; rel=&quot;nofollow noreferrer&quot;&gt;band charts&lt;/a&gt; come in handy for remembering what band is where.&lt;/p&gt;&#xA;&lt;p&gt;By the way Jon, I think ham radio jargon may have gotten in the way.  In the US, Technician-class licensees have &amp;quot;phone&amp;quot; privileges between 28.3 MHz and 28.5 MHz only.  But &amp;quot;phone&amp;quot; here means radiotelephone, which means any analog mode used to carry voice sounds, such as AM, FM, or SSB.  So ham radio &amp;quot;phone&amp;quot; isn't the same as telephone.  In other words, one can't ordinarily use a ham radio to place a telephone call.  There is such a thing as an autopatch, which is a device to connect a radio to a landline telephone.  So if you're talking on the radio to someone with an autopatch, the other operator could make a telephone call for you and connect the radio to the call.  But autopatches are rare these days.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-10-15T15:21:11.137" LastActivityDate="2020-10-15T15:21:11.137" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17447" PostTypeId="2" ParentId="17166" CreationDate="2020-10-15T18:53:39.913" Score="3" Body="&lt;p&gt;The spies from CIA had this problem solved long ago.&#xA;See &lt;a href=&quot;https://www.cryptomuseum.com/covert/bugs/ec/sleevex/index.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.cryptomuseum.com/covert/bugs/ec/sleevex/index.htm&lt;/a&gt;&#xA;You need to have the relative dielectric constant between the coax shield and the sleeve equal to the dielectric of the cable. By this you maintain same velocity. Also you want to keep the impedance same, which requires quite a thick layer of polyethylene tube in place of the PVC on the outside of the shield. There is a fine calculator at &lt;a href=&quot;https://www.pasternack.com/t-calculator-coax-cutoff.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.pasternack.com/t-calculator-coax-cutoff.aspx&lt;/a&gt;&#xA;Take 2.3 as relative dielectric constant of PE.&lt;/p&gt;&#xA;&lt;p&gt;There is an article covering every aspect of sleeve baluns at &lt;a href=&quot;http://www.w8ji.com/sleeve_baluns.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w8ji.com/sleeve_baluns.htm&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;If you do not need flexibility, try this &lt;a href=&quot;http://www.w6nbc.com/articles/2009-07QSTcoaxialdipole.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w6nbc.com/articles/2009-07QSTcoaxialdipole.pdf&lt;/a&gt;&#xA;which uses air as dielectric.&lt;/p&gt;&#xA;" OwnerUserId="17953" LastEditorUserId="17953" LastEditDate="2020-10-18T13:05:35.630" LastActivityDate="2020-10-18T13:05:35.630" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17448" PostTypeId="1" CreationDate="2020-10-15T22:37:50.693" Score="0" ViewCount="21" Body="&lt;p&gt;In the contexte of my reaserch about antenna conceptions,&#xA;I'm trying to simulate using CST Microwave a cavity antenna based on metamaterial structure and a slot antenna as a GND,However I got as a results:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Total efficiency near to 130%.&lt;/li&gt;&#xA;&lt;li&gt;The impedance decreased from 50 ohm to 28 ohm.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Are those results correct [note that I used a cavity] ? or not?&lt;/p&gt;&#xA;" OwnerUserId="17955" LastActivityDate="2020-10-15T23:17:10.443" Title="Is this result correct ? [ impedance cavity based on emtamaterials using CST Microwave]" Tags="&lt;antenna&gt;&lt;impedance&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17449" PostTypeId="2" ParentId="17448" CreationDate="2020-10-15T23:17:10.443" Score="5" Body="&lt;p&gt;Antenna efficiency over 130% would mean a perpetual motion machine, so probably not.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-15T23:17:10.443" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17450" PostTypeId="2" ParentId="356" CreationDate="2020-10-15T23:19:43.390" Score="2" Body="&lt;p&gt;The &amp;quot;plain meaning rule&amp;quot; applies. If the law doesn't define a word, the word has its everyday meaning. If an ordinary person would say that what you transmitted is music, then a judge would normally be required to agree. If you want to test the limits and argue before a judge that something isn't music, or that a particular interpretation would be &amp;quot;cruel or absurd&amp;quot; then you can, but generally speaking I wouldn't recommend it.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-10-15T23:19:43.390" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17451" PostTypeId="2" ParentId="356" CreationDate="2020-10-16T12:00:51.317" Score="2" Body="&lt;p&gt;With a few exceptions, broadcasting in amateur frequencies is separately illegal.  Transmissions should generally be intended to get a responding transmission, but it's probably a good benchmark that it's music if you play a tune with no expectation to get a response.&lt;/p&gt;&#xA;&lt;p&gt;Amateur radio is for communication.  If it's a series of tones intended to communicate a meaning, in other words, data modulation, a courtesy tone from a repeater, doorbell, etc., it's not music.  But if your &amp;quot;doorbell&amp;quot; is 2 minutes long, there's something wrong.&lt;/p&gt;&#xA;&lt;p&gt;If you are speaking while transmitting and there happens to be music playing faintly in the background, as long as that music is not your primary intended transmission, you are probably OK.  However, loud music in the background makes your speech unintelligible, it's poor practice anyway, and you should fix that if possible.   For instance, let's say I'm doing an ARES event at a parade, and I'm trying to relay a message, and a marching band goes by...  it's gonna be difficult, but it's not illegal, as long as the intent is the speech, not the band.&lt;/p&gt;&#xA;&lt;p&gt;The reasoning behind this rule is that the amateur radio bandwidth is a scarce resource, and individuals trying to communicate can't compete with commercial broadcasters transmitting music.  So commercial, broadcast, and music are all illegal in amateur radio, to preserve the spectrum for our use.&lt;/p&gt;&#xA;&lt;p&gt;A lot of the law here is about intent.  If the intent is to communicate, it probably isn't music.  If the intent is to entertain, it probably is music.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-10-16T12:00:51.317" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17453" PostTypeId="2" ParentId="15123" CreationDate="2020-10-16T17:31:01.937" Score="2" Body="&lt;p&gt;It is more than 15 years ago, that I've done it.&#xA;But if I remember correctly, the 3D screenshot you're showing is quite misleading. The pattern is drawn around the 1st antenna / center of coordinate system.&#xA;Delete the 2nd antenna and compare the gains to make sure nothing changes at all.&lt;/p&gt;&#xA;" OwnerUserId="17958" LastActivityDate="2020-10-16T17:31:01.937" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17454" PostTypeId="2" ParentId="16335" CreationDate="2020-10-16T17:40:58.240" Score="2" Body="&lt;p&gt;To the best of my knowledge, both of your features are not implemented.&lt;/p&gt;&#xA;&lt;p&gt;You can choose either name or frequency in &amp;quot;channel mode&amp;quot; and assign a key to switch between channel and VFO mode.&lt;/p&gt;&#xA;" OwnerUserId="17958" LastActivityDate="2020-10-16T17:40:58.240" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17455" PostTypeId="1" AcceptedAnswerId="17470" CreationDate="2020-10-16T18:48:54.750" Score="3" ViewCount="128" Body="&lt;p&gt;I've been scanning through the bands using WSJT-X to pick up FT8 and WSPR. Using a VHF discone, I decode messages from nearly 10,000 km away, consistently, when listening for FT8. But when switching to WSPR I'm lucky to get anything even 1/10 that distance. This is using the exact same setup, and I've tried a variety of HF bands. Why is that? My understanding of WSPR was that it should be legible at far greater distances than FT8.&lt;/p&gt;&#xA;" OwnerUserId="17901" LastActivityDate="2020-10-19T15:17:13.277" Title="If WSPR can go further than FT8, why do I only see local WSPR signals?" Tags="&lt;ft8&gt;&lt;wsjt-x&gt;&lt;wspr&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17456" PostTypeId="1" CreationDate="2020-10-16T19:02:33.347" Score="1" ViewCount="109" Body="&lt;p&gt;Is there a way to determine whether a station or operator still sends physical QSL cards, rather than only uploading some data online? (or doing nothing at all.)&lt;/p&gt;&#xA;&lt;p&gt;If so, what is the current procedure for successfully requesting a QSL card?  Do I mail something?  A QSL card of my own, a polite letter, or something else?  An envelope?  How does one discover the proper mailing address for the contact station?&lt;/p&gt;&#xA;&lt;p&gt;For International contacts, do I need to include cash for return postage; and if so, how do I reduce the chances it will be stolen en-route?  How about PayPal or bitcoin (et.al.)?  Do operators ever use DHL or other commercial/non-postal carriers to send or obtain physical QSL cards?&lt;/p&gt;&#xA;&lt;p&gt;And lastly, under what circumstances should I mail my own QSL card?  Only in response to a request?  Or otherwise?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-10-16T21:58:00.427" Title="Physical QSL card request procedures?" Tags="&lt;qsl-card&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17457" PostTypeId="1" CreationDate="2020-10-16T19:26:18.627" Score="1" ViewCount="200" Body="&lt;p&gt;I note that many popular kit and QRP radios do not include any AGC capability.  Thus it must be possible to operate successfully without AGC.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Are there difficulties involved in manual gain control?  And if so, what are they?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What are the primary benefits of AGC?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is AGC most beneficial if implemented in the RF stage (LNA?), IF stage (if any), or audio output stage, or for multiple blocks/stages?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If AGC is implemented across multiple receiver blocks (say both RF and audio), how is loop stability accomplished?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="556" LastEditorUserId="8717" LastEditDate="2020-10-16T19:27:42.570" LastActivityDate="2020-10-19T00:57:27.657" Title="Benefits of AGC?" Tags="&lt;receiver&gt;&lt;equipment-design&gt;&lt;agc&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17458" PostTypeId="2" ParentId="17457" CreationDate="2020-10-16T20:08:04.717" Score="3" Body="&lt;p&gt;The dynamic range of (shortwave) received signal strength varies from noise equivalent field strength (in the order of 250 nV/m in 3 kHz SSB bandwidth) to 1 mV/m (for radio ham transmissions via the ionosphere). Local signal can go over 1 mV/m. In short: dynamic range is in the order of 72 dB. AGC doesn't have to cover that range, but 50 dB is &amp;quot;nice to have&amp;quot;. The slope of the AGC has an effect on how the difference between weaker and stronger signals are perceived. With rigid AGC, zero dB output variation for 50 dB input variation,  you loose the &amp;quot;band feeling&amp;quot;. Good choice is 10 dB per 50 dB.&lt;/p&gt;&#xA;&lt;p&gt;Your questions:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Manual control requires continuous action for this control.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Benefit of AGC is an automatic gain control; that is in the name.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;AGC at the antenna looks like a good solution to prevent audio level variations, but results in a very limited maximum signal to noise ratio. Beginning at the start of the AGC, the S/N will not grow further. On the other extreme: AGC after the receiver demodulator leads to excessive requirements for large signal handling up to the demodulator. Gain variation for AGC must start at the last IF stage, just to prevent overload, and then anywere in front of this, in the mixer section, and then, for the strongest signals, in the front end LNA, or even at the input of the LNA: the antenna input.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Stability of such a multi-AGC loop is best obtained when the gain variation is a FACTOR per volt AGC control voltage, I.E. a constant decibel per volt gain control. Only then the AGC feedback loop is constant, with a fixed time constant. Any other attempt results in instability or variation of the time constant (and thus the frequency response: a disaster for AM envelope distortion!). Best AGC is a single time constant or a PID controller.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Experience obtained in 40 years radio development at Philips/Magnavox and Catena (NXP).&#xA;Brightnoise, PA0FSB&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-10-16T20:08:04.717" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17459" PostTypeId="2" ParentId="17456" CreationDate="2020-10-16T21:58:00.427" Score="3" Body="&lt;p&gt;There are several ways to find out whether a station/operator sends QSL cards:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;ask during your QSO&lt;/li&gt;&#xA;&lt;li&gt;check the callsign profile on &lt;a href=&quot;https://qrz.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;qrz.com&lt;/a&gt; for the station's preferred way of exchanging QSO confirmation&lt;/li&gt;&#xA;&lt;li&gt;in case it is a station in a &amp;quot;rare&amp;quot; country, check a QSL manager database, such as the &lt;a href=&quot;https://www.ik3qar.it/manager/&quot; rel=&quot;nofollow noreferrer&quot;&gt;IK3QAR QSL manager database&lt;/a&gt; (that is just an example, there are more), to find out if someone else manages the exchange of QSL cards for this station.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Likewise, procedures for requesting a card can vary.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;In some cases it may be sufficient to send a card through your IARU member society's QSL bureau and hope for a card in return.&lt;/li&gt;&#xA;&lt;li&gt;In case a station manages QSL traffic through a QSL manager, you'd send a card to the manager, either via the bureau or &amp;quot;direct&amp;quot;, i.e. snail mail. In that case, it is usually expected to include an envelope addressed to yourself and some funds to cover the return postage, either in the form of stamps that are valid in the QSL manager's country, some money, or with an IRC - International Reply Coupon, although these seem to have gone out of fashion pretty fast during the last few years.&lt;/li&gt;&#xA;&lt;li&gt;Finally, many QSL managers and &amp;quot;rare&amp;quot; stations nowadays put their log online at e.g. &lt;a href=&quot;https://clublog.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;Club Log&lt;/a&gt;, which includes an Online QSL Request Service, where a request for a card sent to you via the QSL bureau or via mail can be placed. In the latter case, payment for the postage is handled through paypal.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;As I wrote above, if you decide to mail your card to confirm an international contact, some form of covering the return postage is usually expected. Reduce the chances of theft by making your envelope as inconspicuous as possible, don't put fancy stamps on it, don't write callsigns on it. Non-postal services are fine in theory, but remember that not all countries are serviced as perfectly as the first world. Operators or managers in remote places may well get annoyed having to travel, be present in person, or otherwise make sure to receive a delivery by a non-postal carrier.&lt;/p&gt;&#xA;&lt;p&gt;Depending on how &amp;quot;rare&amp;quot; or desirable a confirmation of a contact with you may appear to your QSO partner, waiting for requests can become a very boring waiting game. If you are interested in exchanging QSL cards don't expect your QSO partner to make the first step.&lt;/p&gt;&#xA;" OwnerUserId="17676" LastActivityDate="2020-10-16T21:58:00.427" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17460" PostTypeId="2" ParentId="17438" CreationDate="2020-10-16T21:59:39.240" Score="0" Body="&lt;p&gt;A websdr provides more opportunity for catching lightning QRN. Go to the lightning rather than waiting for it to come to you, and as Phil mentioned its (near) live.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://lightningmaps.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://lightningmaps.org&lt;/a&gt; to find it, &lt;a href=&quot;http://websdr.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://websdr.org&lt;/a&gt; to find and hear it.&lt;/p&gt;&#xA;" OwnerUserId="17200" LastActivityDate="2020-10-16T21:59:39.240" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17461" PostTypeId="2" ParentId="17427" CreationDate="2020-10-17T20:40:39.890" Score="0" Body="&lt;p&gt;My Xiegu G90 radio has to have the output from the 8-pin connector in the back set to line instead of mic for it to transmit a digital signal into my SignalLink sound card. Could it be that the FT-450D has the same type of settings. which may need to be changed back again from line to mic to send SSB or voice.&lt;/p&gt;&#xA;" OwnerUserId="17962" LastActivityDate="2020-10-17T20:40:39.890" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17462" PostTypeId="2" ParentId="17445" CreationDate="2020-10-17T21:08:59.580" Score="3" Body="&lt;p&gt;If you are a new ham, you need to go to the &lt;a href=&quot;https://arrl.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://arrl.org&lt;/a&gt; web site and get a listing of the ham bands that they publish. You can find them on their site by searching for &lt;em&gt;ham bands&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Print out one of the listings; the 8.5 by 11 inch chart is in color. They also have some that are able to be printed in black and white. On those charts, it lists that you with a Technician class license can transmit Phone from 28.30 to 28.50 MHz in the ten meter band.&lt;/p&gt;&#xA;&lt;p&gt;I would also recommend you search for local clubs nearby you and see if they have a web site and try to join. Local hams usually enjoy helping new hams get started in this hobby.&lt;/p&gt;&#xA;" OwnerUserId="17962" LastEditorUserId="8717" LastEditDate="2020-10-19T17:43:57.997" LastActivityDate="2020-10-19T17:43:57.997" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17463" PostTypeId="1" AcceptedAnswerId="17479" CreationDate="2020-10-18T12:59:00.457" Score="0" ViewCount="48" Body="&lt;p&gt;What’s the best way to connect a station (desk) ground bus to an outside ground rod?&lt;/p&gt;&#xA;&lt;h2&gt;Is it viable to double-sleeve a copper tube through existing PVC pipe?&lt;/h2&gt;&#xA;&lt;p&gt;For coax pass thru, I have a 1.5” PVC pipe through a cinder-block wall that connects to an outside junction box (entrance box) with steel plate.&lt;/p&gt;&#xA;&lt;p&gt;I’d like to also connect a ground bus bar on the desk to a grounding-rod in the ground outside.&#xA;Why not use a copper pipe sleeved through the PVC, and cut a couple of tabs in it?  This would gain surface area and minimize the intrusion in the pipe to insert future coax lines.&lt;/p&gt;&#xA;&lt;p&gt;Or do I need to use:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Braided copper to the steel plate (3/4” or 1”)&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Stranded copper to the steel plate (minimum gauge?)&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/UnNUX.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/UnNUX.jpg&quot; alt=&quot;inner photo&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/CFdey.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CFdey.jpg&quot; alt=&quot;outer photo&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="5025" LastEditorUserId="5025" LastEditDate="2020-10-18T16:05:13.913" LastActivityDate="2020-10-20T14:00:37.357" Title="Ground pass through cinder block — copper pipe, braid, stranded?" Tags="&lt;grounding&gt;" AnswerCount="1" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17464" PostTypeId="1" CreationDate="2020-10-18T16:08:40.793" Score="1" ViewCount="98" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qDap2.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qDap2.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Hello, what kind of antenna is this? I’ve been trying to figure it out for 14 years. None of my neighbors know. Whomever installed it either moved or passed away.&lt;/p&gt;&#xA;" OwnerUserId="17972" LastEditorUserId="76" LastEditDate="2020-10-18T16:57:06.117" LastActivityDate="2020-10-18T16:57:06.117" Title="Anyone know what this antenna is?" Tags="&lt;antenna&gt;" AnswerCount="1" CommentCount="13" ContentLicense="CC BY-SA 4.0" />
  <row Id="17465" PostTypeId="2" ParentId="17464" CreationDate="2020-10-18T16:56:28.517" Score="2" Body="&lt;p&gt;The antenna is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Yagi%E2%80%93Uda_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yagi-Uda, or Yagi, antenna&lt;/a&gt;. It is a highly directional type of antenna (and this one has 4 director elements, making it particularly so). Yagi antennas are recognizable by the structure of having a series of parallel elements (rods) of slightly varying length, with the feed line (wiring) running to the element adjacent to the rear &amp;quot;reflector&amp;quot; element (the longest element).&lt;/p&gt;&#xA;&lt;p&gt;A directional antenna with a fixed (not rotatable) mount is only useful for point-to-point communications; in other words, it's pointing at a specific other station with its own antenna (which may or may not be directional). Possible uses for this include:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Point-to-point wireless networking (either to provide Internet access, or as a dedicated link between two buildings). However, this antenna looks a little lower in frequency range than I'd expect for that application.&lt;/li&gt;&#xA;&lt;li&gt;Voice communication (which could be amateur, public service, or commercial); talking to a repeater that is also used by handheld/mobile radios. The directional antenna and fixed radio installation is used to cover a longer distance, or be more reliable, than otherwise.&lt;/li&gt;&#xA;&lt;li&gt;Telemetry from remote stations (unlikely in an urban area).&lt;/li&gt;&#xA;&lt;li&gt;…and probably other uses I'm not familiar with.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Another common use of directional antennas mounted on poles is for television reception, but television antennas are generally horizontally polarized (the rods would be horizontal rather than vertical) and closer to the &lt;a href=&quot;https://en.wikipedia.org/wiki/Log-periodic_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;log-periodic&lt;/a&gt; design than Yagi-Uda (because they need to be able to receive many different stations and thus need a wider frequency range).&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-10-18T16:56:28.517" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17466" PostTypeId="1" CreationDate="2020-10-18T21:16:24.713" Score="1" ViewCount="59" Body="&lt;p&gt;I'm just getting into ham radio. I'm trying to connect to a repeater here in Ireland:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Channel: RU260(RB10)&lt;/li&gt;&#xA;&lt;li&gt;Output: 433.250&lt;/li&gt;&#xA;&lt;li&gt;Input:   434.850&lt;/li&gt;&#xA;&lt;li&gt;Call sign:EI7SHR&lt;/li&gt;&#xA;&lt;li&gt;Access: Carrier&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;What does the &amp;quot;Carrier&amp;quot; mean here?&lt;/p&gt;&#xA;&lt;p&gt;I was expecting a PL/CTCSS frequency.&lt;/p&gt;&#xA;" OwnerUserId="17973" LastEditorUserId="218" LastEditDate="2020-10-20T13:32:38.650" LastActivityDate="2020-10-20T13:32:38.650" Title="Repeater carrier as access" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17467" PostTypeId="2" ParentId="17466" CreationDate="2020-10-18T21:38:30.900" Score="4" Body="&lt;p&gt;&amp;quot;Carrier access&amp;quot; just means that you do not need a CTCSS tone to access the repeater.  Your carrier brings up the repeater.&lt;/p&gt;&#xA;&lt;p&gt;CTCSS access may reduce co-channel interference between repeaters if their coverage area overlaps, but it is not technically necessary for access.&lt;/p&gt;&#xA;" OwnerUserId="17422" LastActivityDate="2020-10-18T21:38:30.900" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17468" PostTypeId="2" ParentId="17457" CreationDate="2020-10-18T22:24:19.383" Score="1" Body="&lt;p&gt;There's a huge variance in signal levels — the lowest signal that's readable above the noise floor and the strongest signal that won't overload the receiver are probably at least 60dB apart. To get that into a comfortable listening range without AGC, the operator has to adjust the receive level. Maybe that doesn't sound like a big deal (can't you just set it for your QSO partner and leave it?) but:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;If you're scanning the band, there will be lots of different signals, and you would like to be able to hear the quieter ones without blowing your ears away when you tune to one that's 30 or 40 dB higher.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Maybe you're listening to a net, and different participants have vastly different signal strengths. Do you want to have to spin the volume knob every time someone new starts talking (and do it quickly, to avoid missing the beginning of a sentence, or getting ringing ears)?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Even in a single QSO, signal levels can change rapidly due to fading.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;While AGC isn't perfect, it greatly reduces all of these effects, making life much more comfortable for the operator. That could be accomplished by AGC near the end of the chain (AF or last IF), but doing it earlier in the chain might be necessary to keep later stages in their best (most linear regions) and reduce overall distortion and noise.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-10-19T00:57:27.657" LastActivityDate="2020-10-19T00:57:27.657" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17469" PostTypeId="2" ParentId="7420" CreationDate="2020-10-18T22:28:20.167" Score="1" Body="&lt;p&gt;Lightning takes the path of least resistance I believe. If you have a larger conductor just above the highest point of your antenna going to ground that is a better conductor than your antenna I would think that would cover you.&lt;/p&gt;&#xA;" OwnerUserId="17974" LastActivityDate="2020-10-18T22:28:20.167" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17470" PostTypeId="2" ParentId="17455" CreationDate="2020-10-19T05:36:01.207" Score="4" Body="&lt;p&gt;My guess, looking at WSPR reports, is that, on average (median), WSPR beacons are transmitted at power levels maybe in the range of 10 to 30 dB lower than the median of FT8 transmissions.  e.g. 20 dBm Raspberry Pi hat vs. 37 dBm QRP SDR, or 30 dBm WSPR appliance vs 50+ dBm desktop transceiver and/or QRO amp, as bracketing examples.&lt;/p&gt;&#xA;&lt;p&gt;So the reported 10 dBm advantage of a WSPR beacon (usually just left running on auto-pilot) is swamped by a typical range of 10 to 30 dBm higher power used by people actively trying to add FT8 contacts (and DX contacts) to their logbooks.  Maybe even rotating their antennas in your direction for even higher radiated gains.&lt;/p&gt;&#xA;&lt;p&gt;And given a constant receiver noise floor and constant propagation attenuation per unit distance (neither of which are actually constants), 20 dB of increased power corresponds to 10X greater communication range (for similar coding).  So if you are seeing a 10X range difference, that corresponds finding the Tx power on the FT8 signals you receive to be 30 dB greater that the WSPR signals you receive.&lt;/p&gt;&#xA;&lt;p&gt;Another possibility is that your RF noise floor is high, as some people get reports for their milliWatt WSPR beacons from 1/4 of the way around the planet, or farther.  So, due to your noise floor, you can only hear high powered stations, and not any milliWatt beacons.  So your statistical sample set has an artificially truncated bottom end.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-10-19T15:17:13.277" LastActivityDate="2020-10-19T15:17:13.277" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17471" PostTypeId="5" CreationDate="2020-10-19T18:15:43.520" Score="0" Body="&lt;p&gt;For basic, mostly non-technical questions&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-10-19T18:15:43.520" LastActivityDate="2020-10-19T18:15:43.520" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17472" PostTypeId="4" CreationDate="2020-10-19T18:15:43.520" Score="0" Body="Questions about getting started in amateur radio etc." OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-10-19T18:15:43.520" LastActivityDate="2020-10-19T18:15:43.520" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17474" PostTypeId="1" CreationDate="2020-10-20T08:28:04.180" Score="3" ViewCount="75" Body="&lt;p&gt;I'm a CS college student working on the flight computer of my Rocketry Club's rocket. My flight computer has a 915MHz radio transceiver, and it needs to transmit data to my computer with another radio receiver on the ground. The rocket at the maximum height will be at least 10,000 feet (3048 meters) away from the ground radio, and probably no more than +2,000 feet of that.&#xA;(Specifically, I'm using an Arduino paired with an &lt;a href=&quot;https://www.adafruit.com/product/3070&quot; rel=&quot;nofollow noreferrer&quot;&gt;Adafruit RFM69HCW&lt;/a&gt; @915MHz radio breakout board for both the flight and ground computers)&lt;/p&gt;&#xA;&lt;p&gt;Both the ground and rocket radios have SMA connectors. I have not yet figured out how to deal with the antenna situation.&lt;/p&gt;&#xA;&lt;p&gt;I don't know too much about amateur radios and whatnot, so I was wondering if anyone had a suggestion for an antenna that could handle the needed range, and if not, suggestions on what/how to build an antenna for the radios to handle my required range.&lt;/p&gt;&#xA;&lt;p&gt;Thanks so much in advance!&lt;/p&gt;&#xA;" OwnerUserId="17980" LastEditorUserId="17980" LastEditDate="2020-10-20T17:23:09.360" LastActivityDate="2020-10-29T13:47:29.533" Title="Recommendation for hobbyist flight computer radio antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17475" PostTypeId="1" AcceptedAnswerId="17482" CreationDate="2020-10-20T11:40:28.757" Score="1" ViewCount="85" Body="&lt;p&gt;&lt;em&gt;The Situation:&lt;/em&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Very new Ham&lt;/li&gt;&#xA;&lt;li&gt;I have a 2m/70cm 48&amp;quot; Abree whip antenna, originally designed to be connected directly to an HT&lt;/li&gt;&#xA;&lt;li&gt;I would like to mount this antenna to the side of my hiking backpack, likely using the built in MOLLE system.&lt;/li&gt;&#xA;&lt;li&gt;It is my &lt;em&gt;understanding&lt;/em&gt; that adding radials to act as a counterpoise would improve the performance because in normally HT use the user acts as the counterpoise.&lt;/li&gt;&#xA;&lt;li&gt;My Instinct is to do a single 1/4 wave for each of the bands I want to use, running the shorter length along the waist strap, and the longer around the backpack and onto the waist strap as needed.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;em&gt;The Question:&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;How many radials would I need to happily balance this antenna for 2m/70cm, and how would you recommend hiding/weaving them into a backpack?&lt;/p&gt;&#xA;" OwnerUserId="13219" LastEditorUserId="13219" LastEditDate="2020-10-20T11:46:47.370" LastActivityDate="2020-11-19T16:00:35.183" Title="What length and number of radials should be used for a dual band vertical whip backpack antenna?" Tags="&lt;antenna-theory&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;portable&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17476" PostTypeId="2" ParentId="17474" CreationDate="2020-10-20T13:14:14.100" Score="1" Body="&lt;p&gt;The rocket will have significant physical and aerodynamic constraints, so the best you can hope there is a whip.  I'd design the rocket's antenna so that the rocket flies right and worry less about the RF.  3000m isn't all that far for light-of-sight radio, except that you're using low power, and moving really fast.  That implies a receiving antenna with some gain (a Yagi, a quad or stacked Yagis or quads) that you can point toward where the rocket will be.  It doesn't have to be fancy, just something you can move with your hands may work ok.  Try it out on the ground first of course.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2020-10-20T13:14:14.100" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17477" PostTypeId="1" CreationDate="2020-10-20T13:32:01.540" Score="1" ViewCount="45" Body="&lt;p&gt;A lot of article about 60 cm shielded loop antennas and how to measure antenna factor using antennas with already known antenna factor.&lt;/p&gt;&#xA;&lt;p&gt;But for example if I have one shielded loop antenna (construction &lt;a href=&quot;http://www.rfmw.cmi.cz/documents/deliverables/Traceable_loop_antenna_calibration_VNA.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.rfmw.cmi.cz/documents/deliverables/Traceable_loop_antenna_calibration_VNA.pdf&lt;/a&gt; ) with unknown antenna factor. Is it possible theoretically find Antenna factor if I know the current ant voltage throw antenna, radius and antenna inner conductor length.&lt;/p&gt;&#xA;&lt;p&gt;Kind regards&#xA;Francisco&lt;/p&gt;&#xA;" OwnerUserId="17864" LastActivityDate="2020-11-19T19:01:00.200" Title="How to calculate of shielded loop antenna correction factor without extra antenna measurements" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;antenna-system&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17478" PostTypeId="1" CreationDate="2020-10-20T13:53:08.757" Score="1" ViewCount="99" Body="&lt;p&gt;I am curious whether the Anytone AT-D878UV (which is a DMR radio) can be programmed to receive dPMR channels.&lt;/p&gt;&#xA;&lt;p&gt;I understand that the big difference between DMR and dPMR is the technique used to divide the  12.5kHz channels into 2 6.25kHz sub-channels: DMR uses TDMA (time division) while dPMR uses FDMA (frequency division).&lt;/p&gt;&#xA;&lt;p&gt;Is there a way to switch the radio to FDMA? Would it be enough to support dPMR channels?&lt;/p&gt;&#xA;" OwnerUserId="17695" LastEditorUserId="17695" LastEditDate="2020-10-20T20:26:02.290" LastActivityDate="2021-02-05T07:04:50.560" Title="Can the AT-D878UV be programmed for dPMR channels?" Tags="&lt;dmr&gt;&lt;anytone&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17479" PostTypeId="2" ParentId="17463" CreationDate="2020-10-20T14:00:37.357" Score="1" Body="&lt;p&gt;Just about anything should do. The ground connection between the entrance panel and the desk shouldn't carry any current if everything else is properly installed. I'd probably use some tinned copper braid because I already have some and it would be easy to install.&lt;/p&gt;&#xA;&lt;p&gt;It's not too important what's connecting the desk and that exterior panel because:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;it shouldn't carry any current under normal circumstances, and&lt;/li&gt;&#xA;&lt;li&gt;there should already be many connections between the two, made by the coax and mains grounds of all the equipment&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Connecting a desk ground bus and the exterior panel is just to maintain a connection if somehow you manage to disconnect all the other grounds, which is especially difficult if you're using modern AC outlets with a ground connection.&lt;/p&gt;&#xA;&lt;p&gt;For further reading I suggest &lt;a href=&quot;https://ham.stackexchange.com/questions/51/how-can-i-protect-equipment-against-a-lightning-strike&quot;&gt;How can I protect equipment against a lightning strike?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-20T14:00:37.357" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17481" PostTypeId="1" CreationDate="2020-10-20T15:05:13.850" Score="1" ViewCount="75" Body="&lt;p&gt;I have a general license but I do not know when it expires, please help.&lt;/p&gt;&#xA;" OwnerUserId="17986" LastActivityDate="2020-10-21T13:22:28.013" Title="How do I find when my license expires?" Tags="&lt;license&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17482" PostTypeId="2" ParentId="17475" CreationDate="2020-10-20T15:16:04.563" Score="1" Body="&lt;p&gt;Ideally you would want four or more radials for each band extending out horizontally.  Any antenna intended to be mounted on an HT has performance that is greatly compromised in favor of convenience.  It's hard to say what method would work best to improve such an antenna.  My advice would be to experiment.  Your idea sounds like a reasonable thing to try; just keep in mind that the elevated (i.e. not ground-mounted) radials will be part of the antenna and will radiate, so use insulated wire and tape over the ends so they are insulated too.  I'd suggest over-the-air testing of antenna &amp;quot;A&amp;quot; versus antennas &amp;quot;B&amp;quot; and &amp;quot;C&amp;quot; to see whether your idea works better than the same antenna directly attached to the HT, and better than a shorter, more convenient antenna.&lt;/p&gt;&#xA;&lt;p&gt;Whether or not going to all this trouble is worthwhile depends on your intended scenario.  If your plan is to hike around a valley dominated by a massive mountain with a repeater on top, then it's probably not worth the trouble, because any old antenna would work fine.  In my rural area, hiking with an HT is a very good idea, because one can contact a repeater many kilometers outside of cell phone coverage.  In one &lt;a href=&quot;https://en.wikipedia.org/wiki/James_Kim&quot; rel=&quot;nofollow noreferrer&quot;&gt;famous case&lt;/a&gt;, a family was lost and stranded in their station wagon for over a week, and the husband and father died of hypothermia after he left on foot to find help; if they had had an HT, they could have easily contacted civilization.&lt;/p&gt;&#xA;&lt;p&gt;For emergencies I carry a dual-band J-pole antenna along with my HT when I'm hiking.  A dual-band J-pole is the gold standard for HT antennas.  Its downside is that one can't walk around with the antenna connected to the HT, because the antenna is long and floppy; one throws a cord over a branch of a tree, ties it to the antenna, and pulls the antenna up.  The antenna was designed by Ed Fong WB6IQN, who published an article about the antenna in QST magazine.  Ed also sells the antennas very reasonably on a popular auction site.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-10-20T15:16:04.563" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17483" PostTypeId="2" ParentId="17474" CreationDate="2020-10-20T15:59:54.700" Score="2" Body="&lt;p&gt;Your project may demand some engineering, I'm afraid.  I see that Adafruit quote a range of 500 m with simple wire antennas for those modules, and that range is probably with optimal orientation of the antennas; in other words, the antennas oriented vertically with the antennas separated horizontally.  You probably wouldn't be able to put a gain antenna on the rocket, and your antenna orientation may not be so favorable, so you may not even get 500 m.&lt;/p&gt;&#xA;&lt;p&gt;You might try buying a couple modules, attaching simple wire antennas like in the picture on the Adafruit site, putting a module and antenna in a rocket body, and seeing what kind of range you actually get.  Try all sorts of antenna orientations that you might encounter in a real flight.  (Hint: you might be better off with the ground antenna a ways away from the launch pad, so you can trade range for a more favorable antenna orientation.)  Maybe Adafruit are being very conservative.&lt;/p&gt;&#xA;&lt;p&gt;If you don't have enough range, then you need to start thinking about your &lt;a href=&quot;https://ham.stackexchange.com/questions/352/what-is-a-link-budget-and-how-do-i-make-one&quot;&gt;link budget&lt;/a&gt;.  In other words, how do you get enough signal strength for a reliable connection.  The answer might be more transmitter power, or a directional antenna on the ground.  Maybe it would be easier to just store the data, and then process it after you recover the rocket.&lt;/p&gt;&#xA;&lt;p&gt;If the answer is a better receiving antenna, one could be built very cheaply with solid copper wire on a handheld wooden boom aimed at the rocket.  What isn't so cheap is the expertise and test equipment you would need to design and test such an antenna.  Perhaps you could join forces with an amateur radio club.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-10-20T15:59:54.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17484" PostTypeId="2" ParentId="17481" CreationDate="2020-10-20T16:28:00.037" Score="0" Body="&lt;p&gt;The expiration date may be on the paper copy of your license.&lt;/p&gt;&#xA;&lt;p&gt;If you lost your paper copy, you simply can do a Google search (or other search engine search) for your callsign + &amp;quot;FCC&amp;quot;.  For a U.S. license, that will usually find the wireless2.FCC.gov web site with information on when the license with that callsign was issued plus its expiration date (assuming its still valid).&lt;/p&gt;&#xA;&lt;p&gt;If you are not licensed in the U.S., replace &amp;quot;FCC&amp;quot; with the governmental licensing entity (or an appropriate abbreviation) in your jurisdiction, which will work if its records are public.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-10-21T13:22:28.013" LastActivityDate="2020-10-21T13:22:28.013" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17485" PostTypeId="1" CreationDate="2020-10-20T16:53:13.363" Score="1" ViewCount="82" Body="&lt;p&gt;I am trying to build an FMCW radar using a USRP N210 with a CBX40 daughterboard. I generate a sweep from 1.5GHz to 5GHz. According to their respective datasheets, the daughterboard and the USRP should work fine up to 6GHz. However, as the frequency increases, the output power from the TX/RX port decreases significantly, even though the transmitted power and gain are constant in GNURadio.&lt;/p&gt;&#xA;&lt;p&gt;I attach a frequency domain graph of the received signal's power when connecting a wire between them. The wire could introduce some losses, but still the power decrease with frequency is very evident.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/JGDED.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/JGDED.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I would appreciate if you could tell me the reason why this is happening, and if you know the way to solve it.&lt;/p&gt;&#xA;&lt;p&gt;Thanks in advance,&lt;/p&gt;&#xA;" OwnerUserId="17812" LastActivityDate="2020-10-20T18:09:44.753" Title="Output power from the TX/RX port of the USRP N210 decreases as the frequency increases" Tags="&lt;antenna&gt;&lt;rf-power&gt;&lt;gnuradio&gt;&lt;frequency&gt;&lt;usrp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17486" PostTypeId="2" ParentId="17477" CreationDate="2020-10-20T17:29:30.913" Score="1" Body="&lt;p&gt;Assumed the frequency range of interest is up to and including shortwave then the description below is the approach. A loop antenne can be used as passive antenna with or without tuning, or as active antenna with an amplifier. Most probably your question relates to passive wideband reception antennas. Then you can read further. Active antenna can be deduced from the info.&lt;/p&gt;&#xA;&lt;p&gt;Conversion from H-field A/m (magnetic component) into induced voltage. Common radio use is expression of field strength in the E-field component V/m. Relation: E/H equals 376.73... Ohm. Depending on the environment (in-house or otherwise shielded, or in a wood) this relation deviates: in many practical cases the E-field is more attenuated than the H-field.&lt;/p&gt;&#xA;&lt;p&gt;The induced voltage from a EM-field is now, metric non-US values:&lt;/p&gt;&#xA;&lt;p&gt;EMF = 2 * PI * A * N / Lambda for 1 V/m  where A is the area of the loop in square meters, N the number of turns and Lambda the wavelength in meters.&lt;/p&gt;&#xA;&lt;p&gt;The source impedance can be measured and will be in the order of circumference (meters!) multiplied with 1 microHenry (per meter) and multiplied with N^2 in case of more than one winding. Do not forget the load impedance. A circuit simulator can help you to do the math.&lt;/p&gt;&#xA;&lt;p&gt;Important to know: the short-circuit current of such a loop is a frequency-independent measure of the field strength.&lt;/p&gt;&#xA;&lt;p&gt;Practical use:&#xA;Wideband active loop antenna for use with receivers needs conversion factor (effective height since dimension follows from &amp;quot;volts per volt per meter&amp;quot;) of factor 0.4 in load when receiver noise figure is 10 dB, to be sure that:&lt;/p&gt;&#xA;&lt;p&gt;---&amp;gt;  received noise floor on a quiet location converted in an output voltage for the antenna that corresponds to the input noise of the receiver.&lt;/p&gt;&#xA;&lt;p&gt;Depending on the environmental noise and on the need for better large signal behavior the conversion factor can be (must be) adjusted for local situation.&lt;/p&gt;&#xA;&lt;p&gt;Brightnoise&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2020-10-20T18:47:26.520" LastActivityDate="2020-10-20T18:47:26.520" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17487" PostTypeId="2" ParentId="17481" CreationDate="2020-10-20T17:35:10.743" Score="2" Body="&lt;p&gt;For the United States, the FCC has an online license search function, currently at: &lt;a href=&quot;https://wireless2.fcc.gov/UlsApp/UlsSearch/searchLicense.jsp&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://wireless2.fcc.gov/UlsApp/UlsSearch/searchLicense.jsp&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;You can choose to type in your call sign to look it up, or if you don't know your call sign, you can look up by name.&lt;/p&gt;&#xA;" OwnerUserId="1183" LastActivityDate="2020-10-20T17:35:10.743" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17488" PostTypeId="2" ParentId="17485" CreationDate="2020-10-20T18:09:44.753" Score="6" Body="&lt;p&gt;That's an expected phenomenon: Real-world physical systems tend to be frequency-selective (i.e. not constant over frequency), and &amp;quot;at large scale&amp;quot; low-pass systems.&lt;/p&gt;&#xA;&lt;p&gt;This applies to amplifiers, mixers, oscillators, and even transmission lines and connectors.&lt;/p&gt;&#xA;&lt;p&gt;So that's normal.&lt;/p&gt;&#xA;&lt;p&gt;Ettus even publishes exactly such measurements at &lt;a href=&quot;https://files.ettus.com/performance_data/cbx/&quot; rel=&quot;noreferrer&quot;&gt;https://files.ettus.com/performance_data/cbx/&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;When you see a device that doesn't have such behaviour, there's either something very expensive going on – that's why high-end spectrum analyzers are way more expensive than USRPs – or someone measured this and then applied correction for that. Usually, it's a mix of both.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2020-10-20T18:09:44.753" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17489" PostTypeId="1" AcceptedAnswerId="17491" CreationDate="2020-10-20T19:48:58.430" Score="2" ViewCount="111" Body="&lt;p&gt;I'm building a simple ground plane antenna for VHF, and I'm doing some research on grounding in case I want to permanently install it. I keep hearing that the ground rod is connected to the &lt;em&gt;outer&lt;/em&gt; coax conductor, but wouldn't it make sense for the highest (thus most likely to get struck?) part of the antenna to be grounded?&lt;/p&gt;&#xA;" OwnerUserId="17328" LastActivityDate="2020-10-21T18:19:03.610" Title="Why is outer coax usually grounded?" Tags="&lt;antenna-system&gt;&lt;grounding&gt;&lt;lightning&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17490" PostTypeId="1" CreationDate="2020-10-20T20:47:29.987" Score="2" ViewCount="164" Body="&lt;p&gt;I have studied for and am ready to take my amateur radio license test but there are currently no licensed instructors available in my region to administer the test. Can I start acquiring ham radio equipment without being licensed?&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;radio apparatus&lt;/strong&gt; means a device or combination of devices intended for, or capable of being used for, radiocommunication;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;4(1)(b) of the &lt;a href=&quot;https://laws-lois.justice.gc.ca/eng/regulations/sor-96-484/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radiocomunication Act&lt;/a&gt; essentially says that possession of radio apparatus is prohibited unless allowed by the act or a regulation&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Prohibitions&lt;/p&gt;&#xA;&lt;p&gt;4 (1) No person shall, except under and in accordance with a radio authorization, install, operate or possess radio apparatus, other than&lt;/p&gt;&#xA;&lt;p&gt;(a) radio apparatus exempted by or under regulations made under paragraph 6(1)(m); or&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;3(a)(ii) of the &lt;a href=&quot;https://laws-lois.justice.gc.ca/eng/acts/R-2/FullText.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radiocommunication Regulations&lt;/a&gt; essentially says a licensed amateur is authorized to possess amateur radio equipment&lt;/p&gt;&#xA;" OwnerUserId="17988" LastEditorUserId="17988" LastEditDate="2020-10-22T22:43:36.207" LastActivityDate="2020-12-29T03:10:14.207" Title="In Canada, does a person need to be licensed to buy amateur radio equipment?" Tags="&lt;legal&gt;&lt;license&gt;&lt;canada&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17491" PostTypeId="2" ParentId="17489" CreationDate="2020-10-20T20:48:50.660" Score="2" Body="&lt;p&gt;The coax shield must be at ground potential if you want the coax to function as a non-radiating transmission line. If the shield isn't at ground potential, then there will be a non-zero electromagnetic field between the coax and its surroundings. Meaning, it will radiate.&lt;/p&gt;&#xA;&lt;p&gt;The shield could be left floating, but the shield can be grounded without changing the operation of the circuit since no current will flow in this ground connection since both the shield and the ground are at the same potential. The same is not true of the center conductor.&lt;/p&gt;&#xA;&lt;p&gt;Furthermore, some antenna types don't give you much choice about which part to ground. For example, a vertical has radials buried (or very near to it) in soil: they are grounded. If you ground the vertical part also, effectively the transmitter is trying to drive a short. That won't radiate very well.&lt;/p&gt;&#xA;&lt;p&gt;In any case, the current from a strike on the center conductor (or part of the antenna attached to it) is largely the same as a strike on the shield. A good part of the strike's energy is at high frequencies, and thus the current will migrate to the shield due to skin effect, and probably also arcing, either intentional or not. The shield will (hopefully) be effectively grounded, so a good portion of the strike current goes directly to ground. What residual current remains on the center conductor is shunted to the shield by a gas discharge tube or other surge protection device.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-10-21T18:19:03.610" LastActivityDate="2020-10-21T18:19:03.610" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17492" PostTypeId="2" ParentId="17489" CreationDate="2020-10-21T13:14:32.467" Score="2" Body="&lt;p&gt;One important reason is safety. One wants the exposed metal part of the coax connector to be at the same potential as the Transmitter case at one end, and any grounded equipment at the other end.  Not at a high (RF or A/C) voltage.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-10-21T13:14:32.467" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17493" PostTypeId="1" CreationDate="2020-10-21T13:36:04.693" Score="4" ViewCount="75" Body="&lt;p&gt;Are there any requirements to post, carry, or have available an official paper copy of one's radio license in order to operate in the U.S.?  Do any states require physical possession of a printed paper license for mobile operation?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="873" LastEditDate="2020-10-22T05:02:23.633" LastActivityDate="2020-10-26T19:16:56.690" Title="License document requirements" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;license&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17494" PostTypeId="2" ParentId="2268" CreationDate="2020-10-21T16:38:21.707" Score="2" Body="&lt;p&gt;Welcome to ham radio!&lt;/p&gt;&#xA;&lt;p&gt;Discussion of some of the simplest and most common forms of ham radio antennas (aerials) begins on page 72 of the &lt;a href=&quot;http://www.niar.org/downloads/Study-Manual-Restricted-Grade.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Study Manual for the Restricted Grade&lt;/a&gt; Indian amateur radio licence. The half-wave dipole may be the single most common amateur antenna at HF because it is simple and inexpensive to build, easy to erect and almost 100% assured of working the first time if the wire is cut to the correct length.&lt;/p&gt;&#xA;&lt;p&gt;Sadly, the Study Manual doesn't give the formula for the length of the half-wave dipole antenna, which is:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$l=\frac{0.95*c}{2f}$$&lt;/span&gt;&#xA;where is is the speed of light (3x10&lt;span class=&quot;math-container&quot;&gt;$^8$&lt;/span&gt;-m/sec) and &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is the operating frequency in Hz. The factor of 0.95 in the numerator is the &lt;em&gt;velocity factor&lt;/em&gt;; it reflects the fact that the wave propagating along the antenna wire is slightly slower than the speed of light. The factor of 2 in the denominator reflects the fact that the antenna is a half-wavelength.&lt;/p&gt;&#xA;&lt;p&gt;Using the 20-meter ham band as an example:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$l=\frac{0.95 * 3x10^8-m/sec}{2 * 14.1x10^6-Hz}=10.1-m$$&lt;/span&gt;&#xA;This makes sense, since this value is about 1/2 of the wavelength in the &amp;quot;20-meter&amp;quot; ham band.&lt;/p&gt;&#xA;&lt;p&gt;I'm sure your university library will contain numerous books on antenna theory and design. Hopefully their collection will include some publications from ARRL, RSGB or other noteworthy sources, or you may be able to borrow a book from a local ham or club.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-11-17T11:56:16.367" LastActivityDate="2020-11-17T11:56:16.367" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17495" PostTypeId="2" ParentId="17489" CreationDate="2020-10-21T17:35:19.463" Score="1" Body="&lt;p&gt;A part of the antenna system (system = antenna + transmission line) that is truly grounded can't radiate.  Most antenna systems are more efficient when the antenna, the part that is designed to radiate, is up high.  So the antenna is deliberately ungrounded.  Antennas are usually designed with the assumption that the transmission line doesn't radiate much; if the transmission line isn't supposed to radiate and it does, then that will affect the antenna's radiation pattern, usually not in a good way.  The coax is grounded in part to discourage it from radiating.  (One other thing is usually necessary to keep the coax from radiating, and that is something to discourage RF from flowing through the shield of the coax.  The most practical way to do that is usually to use a balun that presents a resistance to common-mode currents, which flow through the shield.)&lt;/p&gt;&#xA;&lt;p&gt;Please keep in mind that grounding at RF frequencies is very different from grounding at DC, or at AC frequencies (50 or 60 Hz).  At RF frequencies, a connection to ground is only a ground if the connection is short, a small fraction of a wavelength long.  If the connection is longer, then it becomes a transmission line that radiates and transforms impedances.  A would-be ground connection to the highest part of a transmission line is likely to be longer than a small fraction of a wavelength, so the would-be ground connection will just be another wire that is part of the antenna and radiates.&lt;/p&gt;&#xA;&lt;p&gt;While I'm on the subject I'd like to mention lightning, even though it's not directly relevant to your question.  Grounding against lightning is different from any other kind of grounding, because lightning has plenty of power to arc through air and burn holes through insulators.  The idea there is to dissipate the power of the bolt into the earth as quickly and efficiently as possible, to reduce the damage radius.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-10-21T17:35:19.463" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17496" PostTypeId="2" ParentId="17490" CreationDate="2020-10-21T19:07:13.430" Score="1" Body="&lt;p&gt;It was the case, once, that countries of the British Commonwealth required a license for private ownership of a radio or television &lt;em&gt;receiver&lt;/em&gt;, not just equipment for transmitting. As radio broadcasting developed during war times in Europe, I believe this was meant to register potential points of espionage and as a source of funding for the BBC and the administrative organs of state. This is no longer the case, though it is still a widely held belief and misunderstood &amp;quot;tradition.&amp;quot; I was confronted with this challenge and threatened with dire consequences when delivering ham radio equipment to a hurricane-ravaged Commonwealth country just three years ago. It made particularly little sense since unlicensed persons were authorized to possess and operate ham equipment in the ham bands in the case of dire emergencies such as they were then experiencing.&lt;/p&gt;&#xA;&lt;p&gt;In response, I lodged a return challenge: is a ham who allows one's license to expire breaking the law by continuing to own the equipment he or she lawfully purchased for private use? The local authorities conceded it was no longer the law, though still held as a tradition, in part to deprive smugglers of a useful communication medium.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-10-21T19:07:13.430" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17497" PostTypeId="1" AcceptedAnswerId="17506" CreationDate="2020-10-22T02:01:02.347" Score="0" ViewCount="43" Body="&lt;p&gt;I just bought a &lt;em&gt;Diamond CP-5NMO&lt;/em&gt; hatch/lip mount and intend to put it on the hatchback lip of our 2018 Subaru Forester and, if it will fit, another one on our 2019 Kia Niro EV. I understand that hatch mounts typically present terrible ground planes - which makes sense - but that some types of antennas are more or less sensitive to this.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question&lt;/strong&gt;: What (amateur dual-band) antennas are a better or worse fit for this kind of installation?&lt;/p&gt;&#xA;&lt;p&gt;My point of comparison is a dual-band 5/8 wave (Comet SBB-5) that I previously had roof mounted on my truck before an unfortunate incident involving a tree branch. I've installed this and, for what it's worth, it gets an SWR of ~1.3 on 146MHz.&lt;/p&gt;&#xA;" OwnerUserId="6295" LastEditorUserId="6295" LastEditDate="2020-10-22T22:36:06.197" LastActivityDate="2020-10-23T05:35:26.290" Title="Hatch Mount Antenna Selection - Dual Band 2m/70cm" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;mobile&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17498" PostTypeId="2" ParentId="17493" CreationDate="2020-10-22T04:17:27.700" Score="2" Body="&lt;p&gt;No. The &lt;a href=&quot;https://www.fcc.gov/wireless/systems-utilities/universal-licensing-system&quot; rel=&quot;nofollow noreferrer&quot;&gt;ULS&lt;/a&gt; is the official document.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/news/fcc-paperless-amateur-radio-license-policy-goes-into-effect-on-february-17&quot; rel=&quot;nofollow noreferrer&quot;&gt;Since February 2015 the FCC no longer routinely issues paper licenses&lt;/a&gt;, although a paper copy can be &lt;a href=&quot;http://www.arrl.org/obtain-license-copy&quot; rel=&quot;nofollow noreferrer&quot;&gt;obtained by request&lt;/a&gt;. The &lt;a href=&quot;https://www.fcc.gov/document/wtb-announces-access-electronic-authorizations-seeks-comment&quot; rel=&quot;nofollow noreferrer&quot;&gt;paperless policy was published October 2014&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;We deem the electronic version of an authorization stored in ULS or the ASR System as the official Commission document.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Furthermore, &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=d4b3c60d2d60000a147f885bdee88264&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5#se47.5.97_15&quot; rel=&quot;nofollow noreferrer&quot;&gt;§97.5 describes the station license requirements&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(a) The station apparatus must be under the physical control of a person named in an amateur station license grant on the ULS consolidated license database or a person authorized for alien reciprocal operation by §97.107 of this part, before the station may transmit on any amateur service frequency [...]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-22T04:17:27.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17499" PostTypeId="2" ParentId="17271" CreationDate="2020-10-22T10:31:39.910" Score="3" Body="&lt;p&gt;I think the problem you will run into is that people will want this to be plug and play. They may not have a directional coupler, or know or feel like to calibrate it and all that other stuff. Even if they do it, they may wonder if they did it right and if the reading will be accurate or not. I think you will need to handle this part in your design and support much greater power handling. Make it a pass-through, one connector on each side and that's it.&lt;/p&gt;&#xA;" OwnerUserId="17896" LastActivityDate="2020-10-22T10:31:39.910" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17500" PostTypeId="2" ParentId="17428" CreationDate="2020-10-22T14:22:11.227" Score="1" Body="&lt;p&gt;I'm not clear on your setup, but I'm guessing that you bench tested the setup without the RCS4 and it worked.  You then put the RCS4 in line, and it no longer did?  If the far side MFJ device is between the RCS4 and the antenna, a look at the schematic (&lt;a href=&quot;https://www.gpscentral.ca/manuals/Ameritron_RCS-4_Manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.gpscentral.ca/manuals/Ameritron_RCS-4_Manual.pdf&lt;/a&gt; page 4) makes it obvious why, there are capacitors in series with the center conductor, so the DC can't get to the MFJ.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2020-10-22T14:22:11.227" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17501" PostTypeId="1" AcceptedAnswerId="17502" CreationDate="2020-10-22T16:16:41.947" Score="3" ViewCount="86" Body="&lt;p&gt;I'm looking at a simple FM transmitter output (see picture). It is from the collector of a transistor and it goes through a DC blocking capacitor before the antenna would be connected. The entire circuit is floating from true ground. I'm thinking of making the antenna a dipole and suddenly I'm stumbled whether to make the other leg the circuit GND or positive rail. The supply voltage is 3VDC and the RF signal is about 1.8Vpp 100MHz. Part of me thinks that the main antenna port will be floating somewhere between GND and VCC. The other part of me thinks that the DC blocking capacitor will be a low impedance at RF so that the RF is actually &amp;quot;pushing against&amp;quot; GND or VCC but I don't know which one. I also know that if I didn't make it a dipole, the one antenna lead would form a capacitor back to the circuit to complete the circuit, again I don't know if it's to GND or VCC, for some reason I just can't wrap my head around this. I thought maybe I measure it with an oscilloscope, I even tried to clip the ground leads from the scope to VCC or GND trying to figure this out but I think the 1M-Ohm probes just pull the RF to one or the other.&#xA;I hope someone can help me understand this and I would really appreciate any help.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iWTbD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iWTbD.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Note: Decoupling capacitors are not shown but they are between GND and VCC. You can see them here:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/wUySv.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wUySv.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17896" LastEditorUserId="8717" LastEditDate="2020-10-23T22:11:29.253" LastActivityDate="2020-10-23T22:11:29.253" Title="Is this &quot;floating&quot; output single-ended or differential and against GND or VCC?" Tags="&lt;antenna&gt;&lt;electronics&gt;&lt;balun&gt;&lt;transmitter&gt;&lt;testing&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17502" PostTypeId="2" ParentId="17501" CreationDate="2020-10-22T17:37:48.193" Score="6" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;The other part of me thinks that the DC blocking capacitor will be a low impedance at RF so that the RF is actually &amp;quot;pushing against&amp;quot; GND or VCC but I don't know which one.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This appears to be a kink in your understanding. RF doesn't &amp;quot;push against&amp;quot; one or the other.&lt;/p&gt;&#xA;&lt;p&gt;Let's be more specific about what we mean by &amp;quot;pushing against&amp;quot;: let's talk about the flow of electrical charge: &amp;quot;current&amp;quot;. The charges move because they are moving through an electric potential gradient: &amp;quot;voltage&amp;quot;. Charge wants to follow the voltage gradient just like mass wants to follow the gravity gradient.&lt;/p&gt;&#xA;&lt;p&gt;Like mass, charge is conserved. It is neither created nor destroyed. So if some charge comes out of one node of the circuit, an equal amount must go into another node. So the power supply doesn't produce charge nor consume it: it's a &amp;quot;pump&amp;quot; for charge that sucks charge in one side and pumps an equal amount out the other side. It's not &amp;quot;one or the other&amp;quot;: it's both.&lt;/p&gt;&#xA;&lt;p&gt;If a rock is dropped from an airplane, is it falling from the sky or plummeting towards the ground? It's not one or the other: it's both.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I'm thinking of making the antenna a dipole and suddenly I'm stumbled whether to make the other leg the circuit GND or positive rail.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Why does it matter?&lt;/p&gt;&#xA;&lt;p&gt;Firstly, remember that there's nothing special about ground except that it's 0V by definition. We could easily call the node labeled &amp;quot;+3VDC&amp;quot; ground instead, and then label what's currently &amp;quot;GND&amp;quot; as &amp;quot;-3VDC&amp;quot; instead, and the circuit would be precisely the same.&lt;/p&gt;&#xA;&lt;p&gt;And because the output capacitor is effectively an open at DC, the amplifier doesn't really care if at DC there's a 0V difference between the dipole legs or a 1000V difference. Whatever the difference happens to be, the amplifier will superimpose the RF input on top of that. And since only RF radiates, and this being an antenna that's probably all we care about, does it matter if the other leg of the dipole is connected to 3VDC or GND?&lt;/p&gt;&#xA;&lt;p&gt;In fact, for the purposes of AC analysis any node which is a constant voltage is &amp;quot;ground&amp;quot;. If that isn't intuitively obvious, ruminate on how the circuit might &amp;quot;know&amp;quot; the difference between 3VDC and GND.&lt;/p&gt;&#xA;&lt;p&gt;In practice, there might be some factors not captured in your schematic that favor doing it one way or another. For example, you might anticipate people could touch the antenna, completing a circuit between ground and the antenna. In that case it would be much better if the antenna was at ground, since no current would flow. With this circuit's 3VDC supply there's no real hazard either way, but imagine if Vcc was 1000V instead.&lt;/p&gt;&#xA;&lt;p&gt;Or you might prefer that the antenna is (&lt;a href=&quot;https://ham.stackexchange.com/questions/17489/why-is-outer-coax-usually-grounded&quot;&gt;as much as possible&lt;/a&gt;) grounded for lightning protection. If the antenna should be struck, it would be nice if you could shunt a lot of that current directly to a ground rod, rather than going through your power supply then to ground.&lt;/p&gt;&#xA;&lt;p&gt;But if all you care about is making the antenna radiate, then it doesn't really matter if you consider the output to be the difference between ANT and GND, or ANT and +3VDC.&lt;/p&gt;&#xA;&lt;p&gt;What does matter though, if your antenna is a dipole, is that the current to each dipole leg is equal and opposite. Consider the impedance between each dipole leg and the parts of the circuit driving it, including capacitive coupling. If this device is powered by a battery and the entire thing is floating, and it's physically small, then there's really no significant difference between ANT, GND, and +3VDC, and you can just hook up the dipole either way and there's no problem. But if GND is connected to Earth, maybe through the power supply, a USB cable, or some coax imput, now the impedance to that node is very different from the others because it's attached to a giant ball of iron. In this case you will want to &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;consider a balun&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-22T17:37:48.193" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17503" PostTypeId="1" CreationDate="2020-10-22T18:04:41.210" Score="1" ViewCount="102" Body="&lt;p&gt;&lt;em&gt;&lt;strong&gt;ORIGINAL QUESTION&lt;/strong&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;I am trying to increase the range of communication between two SDRs to simulate near space communication. The output power of TX is 10dBm but I would need 37dBm for near space communication. That would mean that a power amplifier would be required at the transmitter side. I am wondering if it is possible to do without the power amplifier at TX and instead increase the RX's power to receive a stronger signal by using a high gain antenna for RX? Would it be possible to amplify the signal at RX with an amplifier?&lt;/p&gt;&#xA;&lt;p&gt;Communication is not a field that I am familiar with. Would greatly appreciate any advice given!&lt;/p&gt;&#xA;&lt;p&gt;&lt;em&gt;&lt;strong&gt;--EDITED WITH ADDITIONAL INFORMATION BELOW--&lt;/strong&gt;&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;Thank you for the answers given by everyone, I really appreciate them!&lt;/p&gt;&#xA;&lt;p&gt;I am planning to conduct transmission and receiving of txt file using SDRs. I have decided to utilise a ground station in my university to receive the signal from the transmitting SDR, which is controlled by Rpi. I will be using attenuation at ground station to simulate the environment of near space transmission of 30km. The actual physical distance is across a building&lt;/p&gt;&#xA;&lt;p&gt;My transmitting set up will be Raspberry Pi 3B+, LimeSDR, LimeSDR antenna, ANT500 Telescopic antenna. I am planning to transmit at 433MHz and 2.4GHz at the same time. I will be using BPSK modulation.&lt;/p&gt;&#xA;&lt;p&gt;My receiving set up will be a ground station, which I assume that I could adjust the gain of the antenna.&lt;/p&gt;&#xA;" OwnerUserId="16692" LastEditorUserId="4665" LastEditDate="2020-12-17T23:29:57.243" LastActivityDate="2020-12-17T23:29:57.243" Title="Increasing communication range by boosting output and input power" Tags="&lt;software-defined-radio&gt;&lt;rf-power&gt;&lt;amplifier&gt;&lt;range&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17504" PostTypeId="2" ParentId="17503" CreationDate="2020-10-22T22:38:00.333" Score="6" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Is it possible to do without the power amplifier at TX ... by using a&#xA;high gain antenna for RX?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It is. You need another 27 dB (37-10) of antenna gain in addition to whatever you included in your existing link budget. You can split that gain between the RX and TX antennas to avoid needing a very high gain antenna at one end. High gain antennas are also highly directional. If the two ends of the link are moving with respect to each other, your real, rather than simulated, system would need to make provision for tracking the antennas. (I see you have an earlier question on high altitude balloons. Does this question also relate to them? What frequency range are you considering?)&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Would it be possible to amplify the signal at RX with an amplifier?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;That's trickier as receive performance is affected by background noise in addition to amplifier gain. You would benefit from reading up on receiver noise figure calculations (e.g. see W8II's answer &lt;a href=&quot;https://ham.stackexchange.com/a/9833/15924&quot;&gt;here&lt;/a&gt;). A receiver pre-amp would need to have a much better noise figure than the SDR receiver if it is to benefit the overall performance. It also reduces the receiver's strong signal handling (by its gain) should that be significant. It's generally better to use higher gain antennas than a pre-amp (unless the tracking is a problem).&#xA;A specific answer requires calculations but as a rough guide you'd only get another 27 dB system performance from a receiver pre-amp if the SDR receiver had a truly terrible performance.&lt;/p&gt;&#xA;&lt;p&gt;As with most engineering design communications systems are subject to trade-offs between conflicting objectives. As you mention you are not familiar with this area if you can tell us more about the system you are trying to simulate we can provide better suggestions.&lt;/p&gt;&#xA;" OwnerUserId="15924" LastEditorUserId="15924" LastEditDate="2020-10-25T16:17:05.223" LastActivityDate="2020-10-25T16:17:05.223" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17505" PostTypeId="2" ParentId="16639" CreationDate="2020-10-22T22:56:23.983" Score="0" Body="&lt;p&gt;The answer to your second question is no, you will not receive the gains equal to, or even close to half of a Yagi-Uda or HB9CV, either of these designs requires proper phasing of  of the signal which is not present on the other(virtual) half of the monopole.&lt;/p&gt;&#xA;&lt;p&gt;Half of the signal is in the ground plane (which is phase variant with moisture and material).&lt;/p&gt;&#xA;&lt;p&gt;The same is true with artificial grounds such as a radial system. Even with a radial ground system, the ground conductivity still causes some impedance, although greatly reduced, to signal flow. Thus reducing the velocity of the wave in a non-predicable way.&lt;/p&gt;&#xA;&lt;p&gt;If you are asking if such a design can produce gain the answer is maybe sometimes; this depends on the phase of ground conductivity.&lt;/p&gt;&#xA;&lt;p&gt;The length of the above-ground parasitic element is not properly represented in the ground reflection, due to the differing wave velocities between the two mediums. This phase difference mostly invalidates the advantages of element distance(phase)/length dependent designs.&lt;/p&gt;&#xA;&lt;p&gt;Given a common ground(radials) and proper spacing/phasing between driven elements of the same size, gain can be achieved through phasing of the elements since their local ground plane reflections are close equivalent.&lt;/p&gt;&#xA;&lt;p&gt;Adding a 90 degree corner reflector to a monopole antenna will still increase directivity and gain since phase is corrected and reflected by the reflector(including most of the image giving a ~2.7 db gain).&lt;/p&gt;&#xA;&lt;p&gt;Since you did not specify a target frequency or ground plain height in your question, for a monopole antenna mounted at least 1/2 wavelength above the ground with the boom connected to a radial, a Yagi-Uda design antenna will improve directional gain by a small amount, but the gain will be restricted by the ground plane reflections(really poor f/b ratio).&lt;/p&gt;&#xA;&lt;p&gt;As indicated by the the previous answer, driven elements of the same size over an artificial ground radial plane will give an improved dx pattern/gain.&lt;/p&gt;&#xA;&lt;p&gt;As to the comment of the ground plane attached, most mag mount antennas rely on coupling to ground as opposed to a direct electrical connection.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;While I have attempted to generalize this answer, the values given are only theoretical approximations based on empirical results in certain environments. The expansion of claims to any real world applications may result in different values.&lt;/p&gt;&#xA;&lt;p&gt;I welcome any corrections or clarifications on any points presented.&lt;/p&gt;&#xA;" OwnerUserId="16873" LastActivityDate="2020-10-22T22:56:23.983" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17506" PostTypeId="2" ParentId="17497" CreationDate="2020-10-23T05:35:26.290" Score="1" Body="&lt;p&gt;Some (in fact quite a few) mobile antennas are effectively an &amp;quot;end-fed&amp;quot; design rather than a &amp;quot;ground-plane&amp;quot; design. One way to identify them is that they will generally have a noticeable transformer coil at the bottom (usually enclosed) to transform the impedance. If an antenna's description includes the words &amp;quot;ground-independent&amp;quot; or &amp;quot;radialless&amp;quot;, or specifically mentions being suitable for pipe mount or luggage-rack mount, then there's a good chance it's this type. If the literature says it's a half-wave for 2m, then there's a good chance it's this type. If it has an element sticking straight out of the top of an NMO connector with no room for a coil, it's not that type.&lt;/p&gt;&#xA;&lt;p&gt;There's a lot of misleading and confusing information out there when it comes to mobile antennas, both from manufacturers and from hams, so unfortunately the best solution is just to try it out, but at least hopefully you can find some likely suspects.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-10-23T05:35:26.290" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17507" PostTypeId="1" CreationDate="2020-10-24T00:59:18.187" Score="2" ViewCount="92" Body="&lt;p&gt;What are currently the (5 or 10) biggest amateur radio contests in terms of Worldwide participation (total number of stations or operators on the air during the contest)?&lt;/p&gt;&#xA;&lt;p&gt;Are they the ones with &amp;quot;ARRL&amp;quot; or &amp;quot;CQ magazine&amp;quot; in the name or sponsorship?  Or are there other organization generating contests with even greater participation?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-12-29T16:32:17.793" Title="What are the biggest amateur radio contests (&quot;radiosport&quot;)?" Tags="&lt;contest&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17508" PostTypeId="2" ParentId="17507" CreationDate="2020-10-24T07:21:56.407" Score="2" Body="&lt;p&gt;Yes, ARRL and CQ sponsored contests on HF are certainly among the &amp;quot;biggest&amp;quot; (I don't think any other contests draw larger participation than the CQ Worldwide DX and the CQ WPX contests). Other very popular worldwide ones include the Russian DX Contest, the Worked All Europe, the IARU HF Championship, or the All Asia contests.&lt;/p&gt;&#xA;" OwnerUserId="17676" LastActivityDate="2020-10-24T07:21:56.407" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17509" PostTypeId="2" ParentId="17503" CreationDate="2020-10-25T15:37:39.173" Score="3" Body="&lt;p&gt;Amplification at the receiver is not equivalent to amplifying at the transmitter. This is because at the receiver, the signal is mixed with signal &lt;em&gt;and noise&lt;/em&gt;. An amplifier can not distinguish between the two, and so an amplifier at the receiver does not improve the signal-to-noise ratio.&lt;/p&gt;&#xA;&lt;p&gt;The only time additional amplification at the receiver improves performance is when a low noise amplifier (meaning, one that adds little internally-generated noise) is added where there was not one previously. For space communications there can be significant gains to be realized here since the RF noise background in space is extremely low, however this requires an expensive cryogenic LNA. You can read more about this at &lt;a href=&quot;https://ham.stackexchange.com/questions/9832/how-can-i-calculate-the-effects-of-an-lna-antenna-gain-etc-on-noise-performan/9833&quot;&gt;How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;What you can do is add antenna gain at either end, or transmit with more power. For that, see &lt;a href=&quot;https://ham.stackexchange.com/questions/352/what-is-a-link-budget-and-how-do-i-make-one&quot;&gt;What is a link budget, and how do I make one?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-25T15:37:39.173" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17510" PostTypeId="1" AcceptedAnswerId="17511" CreationDate="2020-10-26T14:47:41.027" Score="2" ViewCount="48" Body="&lt;p&gt;This is my first time ever asking a question on stack exchange or any stack site, so please be gentle if I missed something here.&lt;/p&gt;&#xA;&lt;p&gt;I am currently working on building a UHF (GMRS) repeater, and while picking equipment and such, I got to thinking about whether a power amplifier is something that can be used with a repeater. I don't intend to run an amplifier, but was wondering if it is theoretically possible. I have done some web searching and haven't had a whole lot of luck finding the answer I am looking for. I was wondering if someone could confirm whether my theory is correct..&lt;/p&gt;&#xA;&lt;p&gt;Consider the following, fairly basic, setup: Dual commercial radios connected to a properly tuned UHF cavity duplexer sharing a single antenna for both RX and TX. If I were to put an amplifier on this rig, I would need to place it on the transmit radio side of the duplexer, NOT on the antenna side, correct? I assume that, if placed on the antenna side, the moment the transmit radio keyed up, it would shut off any signals coming in to the receive radio effectively disabling the system to be used as a repeater at all.&lt;/p&gt;&#xA;&lt;p&gt;In short, if you want to run a power amplifier with a repeater, you would potentially need two devices.. a pre-amp for the receive, and a power amp for the transmit, connected as follows:&lt;/p&gt;&#xA;&lt;pre&gt;&#xA;RX &amp;lt;== Pre-Amp &amp;lt;===== |----------|&#xA;                      | Duplexer | &amp;lt;===&amp;gt; Antenna&#xA;TX ==&amp;gt; Power Amp ===&amp;gt; |----------|&#xA;&lt;/pre&gt;&#xA;&lt;p&gt;(I hope the diagram makes sense lol)&lt;/p&gt;&#xA;&lt;p&gt;Is my thinking on this correct?&lt;/p&gt;&#xA;&lt;p&gt;73s,&#xA;Steve&lt;/p&gt;&#xA;" OwnerUserId="17995" LastActivityDate="2020-10-26T15:14:31.710" Title="Hypothetical question: Repeater with power amplifier" Tags="&lt;repeater&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17511" PostTypeId="2" ParentId="17510" CreationDate="2020-10-26T15:14:31.710" Score="3" Body="&lt;p&gt;Yes, your diagram makes sense.&lt;/p&gt;&#xA;&lt;p&gt;And yes, it's doable, given that your amp operates within the power limits of the duplexer and the antenna, and the duplexer isolates the receiver from enough of the amplifier's output.&lt;/p&gt;&#xA;&lt;p&gt;Every solid-state rig that outputs more than a watt has a power amp inside of it already, so it's not a question of &amp;quot;can it be done&amp;quot; but one of &amp;quot;how much?&amp;quot;.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-10-26T15:14:31.710" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17512" PostTypeId="1" AcceptedAnswerId="17514" CreationDate="2020-10-26T16:45:13.427" Score="5" ViewCount="176" Body="&lt;p&gt;The point I'm confused about is the antenna. Depending on the environment, there are tons of different frequencies passing through you (FM, AM, 4G, SAT, etc). The electrons in the wire will move as the radio frequencies pass by. One wave will move the electrons at a certain rate. Another wave will move the same electrons at a different rate. All these waves will interfere with each other. You get some weird movement or none at all on the wire depending on the different frequencies hitting the antenna.&lt;/p&gt;&#xA;&lt;p&gt;I kind of understand a tuning circuit (LC). How is the tuner picking up anything when the antenna is giving the LC circuit a complex wave? It's like you mixed up paint and the LC tuner somehow unmixes it. For some reason, it's not clicking for me. So what if it resonates at a certain frequency. The wave it's feeding is complete gibberish. Two different frequencies hitting the antenna could cancel out each other so electrons don't move.&lt;/p&gt;&#xA;&lt;p&gt;I do not understand how a tuner (LC) can pick up a certain frequency.&lt;/p&gt;&#xA;&lt;p&gt;Once I understand that this only makes sense for a specific frequency.  FM radio works on a range of frequencies. How does a tuner &amp;quot;catch&amp;quot; a range of them?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://physics.stackexchange.com/questions/326727/how-can-an-antenna-pick-up-thousands-of-frequencies-at-the-same-time&quot;&gt;https://physics.stackexchange.com/questions/326727/how-can-an-antenna-pick-up-thousands-of-frequencies-at-the-same-time&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://physics.stackexchange.com/questions/223469/how-does-the-tuner-really-work-in-a-crystal-set&quot;&gt;https://physics.stackexchange.com/questions/223469/how-does-the-tuner-really-work-in-a-crystal-set&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://physics.stackexchange.com/questions/8310/how-does-a-digital-radio-tuner-work&quot;&gt;https://physics.stackexchange.com/questions/8310/how-does-a-digital-radio-tuner-work&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Edit: I'd like to give everybody a green checkmark. :) I still have a long way to go to be satisfied with my understanding but this is a great start. I've always been interested in radios. I'm going to start by creating my own AM then FM radio. I just needed the theory because anybody can put a kit together. I want to know the WHY in detail. I have so many more questions but I think this is enough to satisfy this post. You guys are the best!&lt;/p&gt;&#xA;" OwnerUserId="18005" LastEditorUserId="18005" LastEditDate="2020-10-28T01:05:33.710" LastActivityDate="2020-10-28T01:05:33.710" Title="How can a tuner pick up a specific frequency?" Tags="&lt;antenna&gt;&lt;frequency&gt;&lt;antenna-tuner&gt;" AnswerCount="5" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17513" PostTypeId="2" ParentId="17507" CreationDate="2020-10-26T17:56:31.867" Score="4" Body="&lt;p&gt;All major contests report detailed statistics for the benefit of contest participants, who want to know how they did in the contest.  I compiled reported totals of logs submitted for several major contests.  These numbers are not entirely consistent, because some contests include check logs and disqualified entries in the results, and some don't.  The most recent numbers that I could find are reported, but these are not all in the same calendar year.  I didn't report all contests, and it's quite possible that I missed contests that deserve to be on this list.  (If so, let me know and I'll edit them in.)  In some cases I had to add numbers to arrive at a total; I trust my addition, but I could have missed numbers that should have been included in the total.  (Thanks to &lt;a href=&quot;https://www.electronics-notes.com/articles/ham_radio/amateur-contests/contesting-overview-calendar.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;electronics-notes.com&lt;/a&gt; for giving me a list to start with.)&lt;/p&gt;&#xA;&lt;p&gt;The list is sorted by logs submitted.  I would think that the order of contests in the list would fluctuate quite a bit when comparing different years.&lt;/p&gt;&#xA;&lt;p&gt;(In the table, &amp;quot;W/E&amp;quot; means &amp;quot;weekend&amp;quot;.)&lt;/p&gt;&#xA;&lt;div class=&quot;s-table-container&quot;&gt;&#xA;&lt;table class=&quot;s-table&quot;&gt;&#xA;&lt;thead&gt;&#xA;&lt;tr&gt;&#xA;&lt;th&gt;Rank&lt;/th&gt;&#xA;&lt;th&gt;Contest&lt;/th&gt;&#xA;&lt;th&gt;Dates&lt;/th&gt;&#xA;&lt;th&gt;Results Year&lt;/th&gt;&#xA;&lt;th&gt;Logs Submitted&lt;/th&gt;&#xA;&lt;/tr&gt;&#xA;&lt;/thead&gt;&#xA;&lt;tbody&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;1&lt;/td&gt;&#xA;&lt;td&gt;CQ-WorldWide (CW)&lt;/td&gt;&#xA;&lt;td&gt;Last full W/E November&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;7,821&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;2&lt;/td&gt;&#xA;&lt;td&gt;CQ-WorldWide (SSB)&lt;/td&gt;&#xA;&lt;td&gt;Last full W/E October&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;7,741&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;3&lt;/td&gt;&#xA;&lt;td&gt;CQ-Worked PrefiXes (WPX)(SSB)&lt;/td&gt;&#xA;&lt;td&gt;Last full W/E March&lt;/td&gt;&#xA;&lt;td&gt;2020&lt;/td&gt;&#xA;&lt;td&gt;7,604&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;4&lt;/td&gt;&#xA;&lt;td&gt;CQ-Worked PrefiXes (WPX) (CW)&lt;/td&gt;&#xA;&lt;td&gt;Last full W/E May&lt;/td&gt;&#xA;&lt;td&gt;2020&lt;/td&gt;&#xA;&lt;td&gt;5,912&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;5&lt;/td&gt;&#xA;&lt;td&gt;Russian DX Contest (SSB/CW)&lt;/td&gt;&#xA;&lt;td&gt;Third full W/E March&lt;/td&gt;&#xA;&lt;td&gt;2020&lt;/td&gt;&#xA;&lt;td&gt;5,212&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;6&lt;/td&gt;&#xA;&lt;td&gt;IARU-HF Championship (SSB/CW)&lt;/td&gt;&#xA;&lt;td&gt;Second full W/E July&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;4,354&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;7&lt;/td&gt;&#xA;&lt;td&gt;ARRL DX Contest (CW)&lt;/td&gt;&#xA;&lt;td&gt;Third full W/E February&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;4,136&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;8&lt;/td&gt;&#xA;&lt;td&gt;CQ-WorldWide (RTTY)&lt;/td&gt;&#xA;&lt;td&gt;Fourth full W/E September&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;3,103&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;9&lt;/td&gt;&#xA;&lt;td&gt;CQ-Worked PrefiXes (WPX)(RTTY)&lt;/td&gt;&#xA;&lt;td&gt;Second full W/E February&lt;/td&gt;&#xA;&lt;td&gt;2020&lt;/td&gt;&#xA;&lt;td&gt;3,088&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;10&lt;/td&gt;&#xA;&lt;td&gt;ARRL DX Contest (SSB)&lt;/td&gt;&#xA;&lt;td&gt;First full W/E March&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;3,062&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;11&lt;/td&gt;&#xA;&lt;td&gt;Island On The Air (SSB/CW)&lt;/td&gt;&#xA;&lt;td&gt;Last full W/E July&lt;/td&gt;&#xA;&lt;td&gt;2020&lt;/td&gt;&#xA;&lt;td&gt;2,237&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;12&lt;/td&gt;&#xA;&lt;td&gt;All Asia DX (CW)&lt;/td&gt;&#xA;&lt;td&gt;Third full W/E June&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;1,543&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;13&lt;/td&gt;&#xA;&lt;td&gt;Worked All Europe-DX (CW)&lt;/td&gt;&#xA;&lt;td&gt;Second full W/E August&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;1,187&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;14&lt;/td&gt;&#xA;&lt;td&gt;Worked All Europe-DX (RTTY)&lt;/td&gt;&#xA;&lt;td&gt;Second full W/E November&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;1,131&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;15&lt;/td&gt;&#xA;&lt;td&gt;Worked All Europe-DX (SSB)&lt;/td&gt;&#xA;&lt;td&gt;Second full W/E September&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;953&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;16&lt;/td&gt;&#xA;&lt;td&gt;All Asia (SSB)&lt;/td&gt;&#xA;&lt;td&gt;First full W/E September&lt;/td&gt;&#xA;&lt;td&gt;2019&lt;/td&gt;&#xA;&lt;td&gt;870&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;/tbody&gt;&#xA;&lt;/table&gt;&#xA;&lt;/div&gt;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-12-29T16:32:17.793" LastActivityDate="2020-12-29T16:32:17.793" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17514" PostTypeId="2" ParentId="17512" CreationDate="2020-10-26T18:39:31.003" Score="2" Body="&lt;p&gt;There's something called the &amp;quot;principle of superposition&amp;quot; — in a linear system (which we can consider an antenna and the &amp;quot;front end&amp;quot; of a receiver to be), if the current resulting from signal A is &lt;span class=&quot;math-container&quot;&gt;$C_A$&lt;/span&gt;, and the current resulting from signal B is &lt;span class=&quot;math-container&quot;&gt;$C_B$&lt;/span&gt;, then the current resulting from both signals at once is simply &lt;span class=&quot;math-container&quot;&gt;$C_{A}+C_{B}$&lt;/span&gt;. Even if you have a million signals, they all just add to one another linearly, without being &amp;quot;modified&amp;quot;. And as long as each one has its own frequency, we can use things like LC filters to pick out the one we want. In a time-domain graph it might look like &amp;quot;complete gibberish&amp;quot;, but all of the original structure is still there (and much more easily seen in a frequency-domain plot).&lt;/p&gt;&#xA;&lt;p&gt;It &lt;em&gt;is&lt;/em&gt; a little bit like mixing paint and separating it out again, but imagine that every different color of paint was made of different-sized particles. When you mix the paints together, it looks like a muddy mess, but all the individual particles are still in there. If you had some very good, very fine mesh filters that could filter particles precisely by their size, you &lt;em&gt;could&lt;/em&gt; separate one color back out of the mix! With real paints, that's not practical, but with real radio waves, it is.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-10-26T18:39:31.003" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="17515" PostTypeId="1" CreationDate="2020-10-26T19:09:07.163" Score="2" ViewCount="95" Body="&lt;p&gt;Why are notch filters used on the transmit side of a repeater duplexer?&lt;/p&gt;&#xA;&lt;p&gt;The primary purpose of a duplexer is to keep the transmitter output out of the receiver input, since they both operate at the same time from a common antenna on frequencies which are closely spaced.  Secondarily, (say, at a hilltop radio site where a bunch of transmitters are clustered) it keeps strong signals from neighboring transmitters out of both the receiver and transmitter, so the receiver doesn't desense and the transmitter doesn't suffer/produce IMD.&lt;/p&gt;&#xA;&lt;p&gt;The secondary purpose is obviously accomplished with bandpass cavities in line with both the transmitter and the receiver, and the primary purpose is accomplished by also adding notch filter cavities.  My question is:  Why are there always notch filters (on the receiver frequency) shown in line with the transmitter output?&lt;/p&gt;&#xA;&lt;p&gt;Obviously, you want notch filters (on the transmitter frequency) in line with the receiver to keep the transmitter output out of the receiver input. But you don't want notches (on the transmit frequency!) in line with the transmitter output, because that would block the transmitter from the antenna. And if they're tuned to the receiver frequency, what exactly are they accomplishing in the transmit circuit? The transmitter doesn't need protection from the receiver, because the receiver doesn't transmit any signal.&lt;/p&gt;&#xA;&lt;p&gt;It seems like it would be better served by placing those notch filters on the receive side to further attenuate the transmit energy, or else spend the money on bandpass cavities instead of notch cavities to better isolate the repeater from everyone else on the hilltop.&lt;/p&gt;&#xA;&lt;p&gt;And yet, every duplexer diagram or setup I've seen seems to have notches between the transmitter and the antenna (usually the same number as on the receive side). Am I missing something here?&lt;/p&gt;&#xA;" OwnerUserId="18006" LastActivityDate="2020-10-28T22:27:26.587" Title="Why do repeater duplexers have notch cavities between transmitter and antenna?" Tags="&lt;repeater&gt;&lt;transmitter&gt;&lt;duplexer&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17516" PostTypeId="2" ParentId="17493" CreationDate="2020-10-26T19:16:56.690" Score="2" Body="&lt;p&gt;It looks like the only requirement for license information in physical form are 97.213(d) for telecommand of an amateur station (license and label with contact information posted at the station location); and 97.215(b) for telecommand of model craft (label with contact information on the station transmitter).&lt;/p&gt;&#xA;&lt;p&gt;Being able to show your license while out and about &amp;quot;doing radio&amp;quot; is probably a good idea in this day and age, though.&lt;/p&gt;&#xA;&lt;p&gt;HTH de AC0CW&lt;/p&gt;&#xA;" OwnerUserId="18006" LastActivityDate="2020-10-26T19:16:56.690" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17517" PostTypeId="2" ParentId="17512" CreationDate="2020-10-26T19:30:29.727" Score="2" Body="&lt;p&gt;It's not like mixing paint.  That's because it's a just a simple sum or linear mix, rather than a chaotic or non-linear mix with intermodulation products.&lt;/p&gt;&#xA;&lt;p&gt;It's like a duet with a soprano and a bass singer.  You can easily transcribe the low frequency bass voice and semi-ignore the soprano, or vice versa, because the frequency ranges are so different, and your ear's cochlea has a filter mechanism that is a mechanical analog to electronic LC filters.&lt;/p&gt;&#xA;&lt;p&gt;And tuners have a bandwidth. A filter can be either narrow or wide, depending on the design spec.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-10-26T19:30:29.727" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17518" PostTypeId="2" ParentId="17512" CreationDate="2020-10-26T23:42:33.137" Score="1" Body="&lt;p&gt;Propagation of waves in free space is both electronic and magnetic in nature. Both field components combine to induce the movement of electrons in an antenna.&lt;/p&gt;&#xA;&lt;p&gt;All frequencies are added together to make up the radio spectrum (a single entity per polarization, Horizontal and Vertical). The entire thing is combined into a grand complex wave.&lt;/p&gt;&#xA;&lt;p&gt;For completeness, circular and elliptical waves shift the polarization between horizontal and vertical at a constant rate. This adds a time(phase) factor to the H,V transition.&lt;/p&gt;&#xA;&lt;p&gt;The wave speed is completely frequency independent and mostly constant and is close to the speed of light. This speed is irrelevant of frequency, only medium. Although it does change between different mediums air/wire/vacuum... and with movement velocity(Doppler effect, only noticeable from spacecraft at RF frequencies).&lt;/p&gt;&#xA;&lt;p&gt;All frequencies are combined at the transmitting antenna with the the existing wave, either constructively or destructively to a form single complex wave.&lt;/p&gt;&#xA;&lt;p&gt;So to answer your question, the tuner is a (LC)filter network that produces a low impedance to the desired signal frequency range and a high impedance to all other frequencies causing a reflection to be either re-radiated or consumed as heat, through recirculation between the inductor and capacitor.&lt;/p&gt;&#xA;&lt;p&gt;The bandwidth allowed is determined by the Q factor of the inductor and capacitor chosen and the driven frequency.The Q factor is the ratio of bandwidth to center frequency.  A higher Q indicates a narrower filter and less insertion loss. The Q is determined by the losses and efficiency of the materials used to construct the inductors and capacitors and interconnection between them.&lt;/p&gt;&#xA;&lt;p&gt;The selection of values for the inductance and capacitance form an oscillator with a resonant frequency. The signals close to the resonant frequency pass through with little loss as a purely resistive impedance with no reactance, while frequencies further away are attenuated by the lack of balance between the inductor and capacitor; thereby increasing the impedance to signals outside of the pass-band by increasing the reactance component.&lt;/p&gt;&#xA;&lt;p&gt;This question forms the basis of  software defined radios: The sample rate defines the maximum bandwidth, in the case of direct-sampled radios the maximum  frequency detectable, but with decimation lower frequencies can be ascertained.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;&amp;quot;The antenna at the end is coiled up and feeds the inductor which is part of the LC circuit. It looks like a transformer to me.&amp;quot; Antennas that are electrically short present a capacitive reactance that is canceled out by the inductor; the capacitor cancels out the overshoot due to winding limitations of the inductor.  In this form, this is a matching transformer and not a filter per se (although some filtering will occur). Its purpose is to transform the reactive component to -j0 (zero reactance) to ensure maximum power transfer.&lt;/p&gt;&#xA;&lt;p&gt;I have left many things out to simplify this answer. I would be glad to elaborate.&lt;/p&gt;&#xA;" OwnerUserId="16873" LastEditorUserId="16873" LastEditDate="2020-10-27T23:03:25.683" LastActivityDate="2020-10-27T23:03:25.683" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17521" PostTypeId="2" ParentId="17512" CreationDate="2020-10-27T15:30:36.550" Score="2" Body="&lt;p&gt;Consider a swing, like the kind found at a playground. If you sit on it and shift your weight forward and backward at just the right rhythm, you can get the swing to go very high.&lt;/p&gt;&#xA;&lt;p&gt;It goes high because the combination of the swing and the mass of your body is &lt;em&gt;resonant&lt;/em&gt; at a particular frequency. When you shift your weight to &amp;quot;pump&amp;quot; the swing, you add just a little more energy to the swing. And when you pump at the right time, this extra energy is added to the stored energy from all the previous pumps, so with each swing you go a little higher than the last one. But this only works if you pump at the &lt;em&gt;resonant frequency&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;If you pump at some other frequency, you just jiggle around a little bit. You don't go higher and higher, because the actions of each pump don't reinforce each other.&lt;/p&gt;&#xA;&lt;p&gt;Imagine you are swinging along happily, and simultaneously you receive a phone call, and your phone in your pocket is on vibrate. The vibration from your phone is also a shifting of weight, just as you are doing to pump the swing. But it is at a much higher frequency. Does it alter your motion on the swing? Technically yes, but the effect is very small because the vibration is not at the swing's resonant frequency. Imagine any perturbation you like: perhaps another person on the swing with you, but pumping at some other frequency. These actions might alter the swinging motion a &lt;em&gt;little bit&lt;/em&gt;, but the swing responds most significantly to its resonant frequency, even if there are other oscillations going on at the same time.&lt;/p&gt;&#xA;&lt;p&gt;An LC filter is a resonant system, like a swing. The difference is a swing involves an oscillation between gravitational potential energy (at the top of the swing) and kinetic energy (at the bottom of the swing), whereas an LC filter oscillates between energy stored in the electric and magnetic field of the capacitor and inductor respectively. The LC filter will respond strongly to oscillations at its resonant frequency, while other oscillations at other frequencies have only a negligible effect.&lt;/p&gt;&#xA;&lt;p&gt;All modulations, not just FM, can be considered a &amp;quot;range&amp;quot; of frequencies. The only signal which is &lt;em&gt;exactly&lt;/em&gt; just one frequency is an unmodulated carrier, which contains no information and so isn't used for communication. Some modulations use a wider range of frequencies than others, but no practical modulation uses a range of zero width.&lt;/p&gt;&#xA;&lt;p&gt;That said, how can a filter work when the signal consists of a range of frequencies?&lt;/p&gt;&#xA;&lt;p&gt;Real filters, even swings, have a resonant frequency where they are most sensitive. As the frequency deviates above or below that resonant frequency, the filter response diminishes, but it does not immediately drop to zero. The objective in designing a filter for a radio is to design a filter which passes the range of frequencies allocated to the signal, but no more. A very simple filter, like one made of a single inductor and capacitor, is &amp;quot;good enough&amp;quot; for some applications. But a radio designed for performance rather than simplicity will have more complicated filters, with more than one inductor and capacitor, to make the filter perform better. There are often multiple stages of filtering. Filtering, whether analog or digital, is a significant part of designing a radio, and a complex topic in itself.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-27T15:30:36.550" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17522" PostTypeId="2" ParentId="17512" CreationDate="2020-10-27T16:55:06.770" Score="2" Body="&lt;p&gt;Radio waves are waves, which have many similarities to other waves, which allows us to consider analogies.  Here's one: if you put your ear firmly to the end of a long tube, the sound will be different than if you weren't listening through the tube.  Instead of hearing the usual mix of high-pitched sounds, low-pitched sounds, and mid-range-pitch sounds, you will hear mostly sounds near the resonant frequency of the tube (and harmonics).  What's happening is that sounds of all frequencies are entering the other end of the tube, but sounds of frequencies near the resonant frequency of the tube (and harmonics) propagate through the tube better, because the sound waves reflecting off the far end of the tube (your ear) reinforce the sound waves coming in at that narrow range of frequencies.  At other frequencies, the sound waves coming in partially cancel themselves out with reflections of the sound waves.  This happens because a tube is a resonator.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Analogue_filter&quot; rel=&quot;nofollow noreferrer&quot;&gt;Filtering in analog RF circuits&lt;/a&gt; is somewhat like that.  Analog filters use &lt;a href=&quot;https://en.wikipedia.org/wiki/Resonance&quot; rel=&quot;nofollow noreferrer&quot;&gt;resonance&lt;/a&gt; to reinforce desired frequencies, and cancel (attenuate) undesired ones.&lt;/p&gt;&#xA;&lt;p&gt;You mention radio waves interfering with each other.  &amp;quot;Interfere&amp;quot; might not be the best word for someone learning about the phenomenon, because two people interfering in a narrow hallway can't get by each other, but two waves interfering pass right through each other.  They might cancel each other at one point for an instant, but the waves continue on.&lt;/p&gt;&#xA;&lt;p&gt;You might be confused, because in one paragraph I talk about waves canceling through resonance, and in another I say that waves pass right through each other.  It's true that two waves pass through each other without being annihilated.  So how can waves cancel?  They cancel at a point where the two waves meet with opposite amplitudes.  If the two waves have the same frequency and amplitude and meet at a point where they are 180° out of phase, then they will consistently sum to zero &lt;em&gt;at that point&lt;/em&gt;, even though the waves themselves continue on.&lt;/p&gt;&#xA;&lt;p&gt;One situation in which two waves meet with the same frequency is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Standing_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;standing wave&lt;/a&gt;, in which a wave meets its reflection.  If the reflection is perfect, meaning that it has the same amplitude as the original wave, then the waves will consistently cancel each other at certain points and sum to zero.  The points where the sum of wave and its reflection are minimized, ideally to zero, are called nodes.  But at other points the waves do not always sum to zero.  The animation below, borrowed from the Wikipedia page, illustrates a standing wave well: the blue and green waves are the original wave and its reflection, and the red wave is the sum of the blue and green waves.  See how the amplitude of the red wave is always zero at the nodes, which are spaced a half-wavelength apart?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uLs2g.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uLs2g.gif&quot; alt=&quot;animation of a standing wave&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;So to sum up, an analog filter circuit selects a narrow range of frequencies because the filter components cleverly use resonance to preferentially transmit those frequencies, similar to the way that a long tube capped on one end preferentially transmits sound waves of a narrow range of frequencies.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-10-27T16:55:06.770" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17523" PostTypeId="1" AcceptedAnswerId="17528" CreationDate="2020-10-27T23:01:57.100" Score="2" ViewCount="153" Body="&lt;p&gt;I have an EFHW 40-10 in inverted L configuration on a fiberglass mast.  I'd like to put an aluminum push-up mast nearby for a 6 meter antenna.&lt;/p&gt;&#xA;&lt;p&gt;How close can I get to the EFHW with the push-up mast?&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;The ~67 ft. EFHW extends from 3 feet up to 46 feet on the fiberglass mast, and then over to another mast for the horizontal section. The most convenient location for the aluminum mast is 6 feet away from the fiberglass mast, on a right angle to the horizontal portion of the EFHW (think &amp;quot;L&amp;quot;, where the horizontal portion of the EFHW extends due north). The aluminum mast extends fully to between 20 and 25 feet.&lt;/p&gt;&#xA;&lt;p&gt;Update:  Took SWR readings after work.  Green is without the mast, orange with the mast.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6MrFT.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6MrFT.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Another update:  Moved the mast 12 feet away, this time due south instead of east.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/S0PMa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/S0PMa.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9772" LastEditorUserId="9772" LastEditDate="2020-10-30T17:11:44.537" LastActivityDate="2020-10-30T17:11:44.537" Title="Antenna Mast near EFHW Inverted L" Tags="&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17524" PostTypeId="1" AcceptedAnswerId="17527" CreationDate="2020-10-28T01:24:26.713" Score="0" ViewCount="89" Body="&lt;p&gt;My understanding is the earbuds that connect to the aux port act as the antenna. It's a long wire. The problem is that the same wire is being used to power your earbuds so you can hear the radio station. This is common on iPods, Zunes, and Smartphones. How can it be an antenna and push audio at the same time?&lt;/p&gt;&#xA;" OwnerUserId="18005" LastActivityDate="2020-10-29T02:07:08.370" Title="How does a smartphone FM antenna work?" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17525" PostTypeId="2" ParentId="17524" CreationDate="2020-10-28T01:58:06.777" Score="1" Body="&lt;p&gt;FM broadcast RF frequencies(88-107 MHz) are independent of lower frequencies in the the audio domain even of they share the same wire.&lt;/p&gt;&#xA;&lt;p&gt;The earbuds only respond to ~30 to ~3000 KHz thus, ignoring(filtering) the RF on the same wire.&lt;/p&gt;&#xA;&lt;p&gt;Along the same idea, the radio receiver is tuned to 88 - 107 MHz ignoring(filtering) the audio frequencies. The tuner circuit will exclude all of the lower frequencies by design.&lt;/p&gt;&#xA;&lt;p&gt;On the earbud side, RF frequencies cannot be produced by the the earbuds, they appear as a short circuit to the earbuds and skip quite happily over them, and are then passed on to the tuner.&lt;/p&gt;&#xA;&lt;p&gt;Remember that waves continue on no matter the frequency (unless identical frequencies that add together depending on phase either constructively, adding to the power output or destructively reducing the power output through increased standing waves.)&lt;/p&gt;&#xA;&lt;p&gt;The incidental overlap of destructive possible interference of AF to RF is an instant point in time(every few time-spans) for waves moving close to the speed of light. The interference is so minute it is not detectable using electronic means.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Bottom Line,&lt;/p&gt;&#xA;&lt;p&gt;For all practical purposes the frequencies on a line are independent of each other.&lt;/p&gt;&#xA;" OwnerUserId="16873" LastEditorUserId="16873" LastEditDate="2020-10-28T02:36:54.047" LastActivityDate="2020-10-28T02:36:54.047" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17527" PostTypeId="2" ParentId="17524" CreationDate="2020-10-28T13:35:04.040" Score="2" Body="&lt;p&gt;Audio frequencies are from about 20 to 20,000 Hz. FM broadcast is from 88,000,000 to 108,000,000 Hz.&lt;/p&gt;&#xA;&lt;p&gt;The current on the wire (let's assume there's just one, to simplify) is just a sum of both the AF and RF signals. Imagine a greatly simplified situation where there is an unmodulated RF transmission at 103 MHz, and an audio tone at 440 Hz. The voltage on the wire is something like:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ V(t) = \cos(440 \cdot 2 \pi t) + \cos(103000000 \cdot 2 \pi t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Of course in practice, the FM station isn't broadcasting just an unmodulated carrier, but a more complex waveform. And there aren't just 2 terms in this equation, but thousands: the sum of all the radio transmitters around. And also there's a noise term. But the basic principle stands: the voltage on the wire is a sum of all the things interacting with it through the electromagnetic field.&lt;/p&gt;&#xA;&lt;p&gt;The FM receiver has a filter, not just to isolate the RF from the AF, but also to select the particular station you want to receive. So it's going to ignore all frequencies except for a 200,000 Hz wide slice somewhere in the FM band, so it sees only the &lt;span class=&quot;math-container&quot;&gt;$\cos(103000000 \cdot 2 \pi t)$&lt;/span&gt; term.&lt;/p&gt;&#xA;&lt;p&gt;Likewise there's a low-pass filter between the audio driver and the wire, isolating the audio circuit from all RF.&lt;/p&gt;&#xA;&lt;p&gt;It's not magic, really. Filters are everywhere in everyday life. Your eyes, for example, have 3 kinds of cone cells each sensitive to a different range of frequencies. These cells are sensitive to a specific range of frequencies because they filter out all other frequencies. And visual light is just a small slice of the electromagnetic spectrum, but your eyes filter out most of it. It's for this reason you can't see infrared, x-rays, or indeed even the FM radio station you are listening to on the radio, which is electromagnetic radiation exactly like your eyes detect, just at a different frequency.&lt;/p&gt;&#xA;&lt;p&gt;There are other engineering applications of this principle too. For example, power-line ethernet superimposes a high-frequency data stream on top of the 60 or 50 Hz power that's in your home's mains wiring. Many antennas that require power are powered through their feedline with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Bias_tee&quot; rel=&quot;nofollow noreferrer&quot;&gt;bias tee&lt;/a&gt;, which allows a DC power feed (0 Hz) and the RF signal to coexist on the same feedline. &lt;a href=&quot;https://en.wikipedia.org/wiki/Phantom_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;Phantom power for microphones&lt;/a&gt; is the same idea applied to audio frequencies.&lt;/p&gt;&#xA;&lt;p&gt;For a visual example, look at a &lt;a href=&quot;https://www.wolframalpha.com/input/?i=sin%28x%29%20%2B%20sin%286x%29&quot; rel=&quot;nofollow noreferrer&quot;&gt;graph of &lt;span class=&quot;math-container&quot;&gt;$\sin(x) + \sin(6x)$&lt;/span&gt;&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OU5IS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OU5IS.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Just by looking at it, you can see there are two sine waves here, a low-frequency one and a high-frequency one. They can both exist within the same function without any loss of information. And with a filter, they can be separated.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-10-28T16:57:28.467" LastActivityDate="2020-10-28T16:57:28.467" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17528" PostTypeId="2" ParentId="17523" CreationDate="2020-10-28T15:25:32.053" Score="1" Body="&lt;p&gt;Sounds like a small-lot problem.  Nobody with personal experience with a 40m - 10m end-fed half-wave antenna has responded, so I'll chime in.  I don't like unanswered questions ;)&lt;/p&gt;&#xA;&lt;p&gt;If you bring a metal mast &amp;quot;near&amp;quot; your EFHW, the two antennas will interact.  (Some would say that they won't be two antennas, they will be a single antenna with two ports.)  I can think of two effects that you might notice: impedance changes and antenna radiation patterns.  The impedance changes can change the SWR of one or both antennas.&lt;/p&gt;&#xA;&lt;p&gt;So how close is too close?  That's difficult for me to say without very specific details of your setup.  It would be possible, but difficult, to model the antennas using antenna modeling software such as 4NEC2 or EZNEC.  First we'd want to start with a 3D model of both antennas, their coax, and other nearby conductors.  That would give us a good idea of the radiation pattern and impedance changes.  Then if we knew details about your antenna tuner and your radio, we could estimate if the SWR would change enough to prevent a usable match or not.&lt;/p&gt;&#xA;&lt;p&gt;Sorry, I'm not trying to be a smart aleck, it's just that I have more experience with modeling antennas than using EFHW antennas.  Personally if I were in your shoes I would just try it, and make careful impedance measurements on both antennas with a good antenna analyzer before and after.  If the impedance of either antenna system at the radio end of the coax changes enough to make a significant change in the SWR of either antenna, then I'd say that the aluminum mast is too close.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-10-28T15:25:32.053" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17529" PostTypeId="2" ParentId="17515" CreationDate="2020-10-28T21:31:36.537" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;The transmitter doesn't need protection from the receiver, because the receiver doesn't transmit any signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Indeed. The notch filter in the transmit side is instead to protect the receiver from the transmitter.&lt;/p&gt;&#xA;&lt;p&gt;As well as the familiar harmonics and spur signals generated on specific frequencies by the transmitter it also produces broadband noise centred on the transmit frequency and extending out far enough to cover the receive frequency.&lt;/p&gt;&#xA;&lt;p&gt;If the broadband noise on the receive frequency was allowed to enter the receiver it would desense (i.e. desensitise) it; incoming receive signals would need to be strong enough to exceed the transmitter broadband noise level.&lt;/p&gt;&#xA;&lt;p&gt;We get rid of this noise (or at least reduce it below the receiver's own noise floor) by putting a notch filter tuned to the receive frequency in the transmit path. Note we can't put this filter in the receive path as it would filter out the desired incoming receive signals.&lt;/p&gt;&#xA;&lt;p&gt;Some more reading:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://urgentcomm.com/2000/09/01/transmitter-noise-receiver-desense-primer/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Transmitter noise/receiver desense primer&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.sciencedirect.com/topics/engineering/broadband-noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;Transmitter Broadband Noise&lt;/a&gt; (shows calculations)&lt;/p&gt;&#xA;&lt;p&gt;Or try your preferred search engine.&lt;/p&gt;&#xA;" OwnerUserId="15924" LastActivityDate="2020-10-28T21:31:36.537" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17530" PostTypeId="2" ParentId="17515" CreationDate="2020-10-28T22:27:26.587" Score="1" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;The transmitter doesn't need protection from the receiver, because the receiver doesn't transmit any signal.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Perhaps not, but consider:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The transmitter makes broadband noise and intermodulation products that may fall on the receive frequency. More isolation is better. And,&lt;/li&gt;&#xA;&lt;li&gt;The transmitter should ideally also not load the antenna at the receive frequency. If you imagined the transmitter as an ideal voltage source, this would reduce the available signal at the receiver to zero, were it not for the notch filters!&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-10-28T22:27:26.587" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17531" PostTypeId="2" ParentId="17524" CreationDate="2020-10-29T02:07:08.370" Score="1" Body="&lt;p&gt;Quite apart from the huge difference in frequency, another point is that, for the earbuds, the two conductors of the cord carry a &lt;em&gt;&lt;strong&gt;&amp;quot;differential&amp;quot;&lt;/strong&gt;&lt;/em&gt; signal.&#xA;In other word, they, with the earbuds, constitute a complete circuit, break one conductor, &amp;amp; your earbud won't work.&#xA;As an FM antenna, however, the RF pickuo is &lt;em&gt;&lt;strong&gt;&amp;quot;common mode&amp;quot;&lt;/strong&gt;&lt;/em&gt;-----to the RF signal, both conductors appear to be part of the same conductor.&#xA;The phone's FM radio input circuits have inherent rejection of the differential component.&lt;/p&gt;&#xA;" OwnerUserId="17792" LastActivityDate="2020-10-29T02:07:08.370" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17533" PostTypeId="2" ParentId="17474" CreationDate="2020-10-29T13:47:29.533" Score="1" Body="&lt;p&gt;While someone flagged this question as off-topic for this site, I think as a “technology of radio” question, it still stands. And I would say that it should be amateur radio-related, as I would recommend using ham bands for this application. Simply because a licensed amateur can use more power than is possible on an unlicensed band. With a good &lt;a href=&quot;https://en.wikipedia.org/wiki/Yagi%E2%80%93Uda_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;yagi-uda antenna&lt;/a&gt; on the ground pointed at the rocket, the rocket itself would not need much of an antenna at all (or much power), in order to be received from the ground. And if the ground station wanted to send signals to the rocket, a few watts of power into a yagi-uda antenna would be plenty.&lt;/p&gt;&#xA;&lt;p&gt;Anyone wanting to use radio applications in a hobby environment should at least consider getting even the most basic amateur radio licence, just for the avenues it opens up for future experimentation. For UHF, you could use the 430MHz or 1296MHz bands, and have some very good antennas in a very small space.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-10-29T13:47:29.533" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17534" PostTypeId="1" CreationDate="2020-10-29T20:47:50.197" Score="0" ViewCount="38" Body="&lt;p&gt;Is it possible to obtain the S-parameters of a circuit with only S11 measurements (S11 measurement with a VNA)?&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;My gut tells me that it should be possible by connecting open, short and characteristic impedance to the system but for my life I cannot figure how.&lt;/li&gt;&#xA;&lt;li&gt;What is the DUT has unknown characteristic impedance (or is a complex circuit of lumped elements)? Then I cannot terminate with Z0 exactly. Can I just use a known reference resistor?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Background: I have a PCB with a single SMA as input; the first part is a delay line, then a matching network and then VNA input. I want to design the L-match on the PCB properly.&lt;/p&gt;&#xA;&lt;p&gt;PS: frequency is 900 MHz (UHF). I can desolder/resolder components on the PCB which are 0402 (for example, I can remove the L-match)&lt;/p&gt;&#xA;" OwnerUserId="15972" LastActivityDate="2020-10-30T03:33:14.337" Title="Obtaining S parameters using S11 measurements?" Tags="&lt;uhf&gt;&lt;impedance&gt;&lt;impedance-matching&gt;&lt;measurement&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17535" PostTypeId="1" CreationDate="2020-10-29T21:10:32.640" Score="0" ViewCount="49" Body="&lt;p&gt;What are the real losses associated with a typical gamma match at a set frequency? Furthermore, are there good designs or dimensions to minimise these losses?&lt;/p&gt;&#xA;" OwnerUserId="18008" LastEditorUserId="-1" LastEditDate="2020-11-01T15:44:01.457" LastActivityDate="2020-11-01T15:53:30.740" Title="How lossy are gamma matches?" Tags="&lt;antenna-system&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17536" PostTypeId="1" CreationDate="2020-10-29T23:10:32.087" Score="3" ViewCount="45" Body="&lt;p&gt;I have installed a grounding system just outside my radio shack and was careful to avoid a quarter wavelength or multiples thereof (for single band use), or anything in total length that is close to this. However, I then thought to myself, what if I have created a quarter wavelength by not including the six foot copper earth rod? What are people's thoughts on this please?&lt;/p&gt;&#xA;" OwnerUserId="18008" LastEditorUserId="-1" LastEditDate="2020-11-03T02:02:25.667" LastActivityDate="2020-11-03T02:02:25.667" Title="Should the earth rod be incorporated in the total length of an RF grounding system?" Tags="&lt;grounding&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17537" PostTypeId="2" ParentId="256" CreationDate="2020-10-29T23:54:32.267" Score="2" Body="&lt;p&gt;The Christman feed system using 84 and 71 degree lines is an example in ON4UN's Low Band DXing book where 1/4 wave ground mounted verticals are used. The line lengths are calculated from feed line impedance and driving impedance of each antenna in the array.&lt;/p&gt;&#xA;&lt;p&gt;If the antenna configuration is changed so does the driving impedance, and the phase shift will no longer be 90 degrees. As a result the pattern degrades with a loss of front to back ratio and reduced forward gain. I explored this recently with EZNEC models in &lt;a href=&quot;https://lonneys-notebook.blogspot.com/2020/10/phased-arrays-christman-feed-system.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Phased Arrays - Christman Feed System&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;I'm not aware of a convenient calculator for the Christman feed system. However Roy Lewallen W7EL has a similar feed system called current forcing and wrote an application called &lt;a href=&quot;https://eznec.com/misc/Arrayfeed/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Arrayfeed1&lt;/a&gt; that will calculate the line lengths if you know the driving impedances. This you can find by modeling the antenna system EZNEC with two sources then look at the Source Data for the values to plug into Arrayfeed1. You can then use the transmission lines function with the calculated line lengths in EZNEC to see that it works. I worked through an exercise in doing this here &lt;a href=&quot;https://lonneys-notebook.blogspot.com/2020/10/phased-arrays-lewallens-simple-feed.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Phased Arrays - Lewallen's Simple Feed&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Lastly when building you need to use an antenna analyzer to measure the VF of the coax you have and use that figure in the calculations, the VF can vary between manufactures and manufacturing runs compared to the published VF.&lt;/p&gt;&#xA;" OwnerUserId="18022" LastEditorUserId="18022" LastEditDate="2020-10-31T03:39:34.953" LastActivityDate="2020-10-31T03:39:34.953" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17538" PostTypeId="2" ParentId="256" CreationDate="2020-10-30T01:07:26.913" Score="1" Body="&lt;p&gt;From memory, that looks the same as an end fire arrangement for a pair of verticals, uni-directional that is.&#xA;As suggested by other members, you need to take into account for the velocity factor for each type of coaxial. And you only get one chance once you've cut it. So I would strongly advise to use MIL- Spec cables as you can rely on the data sheet more so, that it is correct. Some of these cables like RG8X and RG6 will have a variation in velocity factor from manufacturer to manufacturer, batch to batch... from my experiences.&lt;/p&gt;&#xA;" OwnerUserId="18008" LastActivityDate="2020-10-30T01:07:26.913" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17539" PostTypeId="2" ParentId="17536" CreationDate="2020-10-30T01:39:24.130" Score="1" Body="&lt;p&gt;Assuming that the copper earth/ground rod is buried in earth, it is tightly coupled to the earth.  Because of the tight coupling to a lossy material, there will be no resonance effects at the end.  In other words, the length of the earth/ground rod doesn't matter for resonance purposes, as long as it's buried.&lt;/p&gt;&#xA;&lt;p&gt;Your connection to earth must be short, a small fraction of a wavelength, to be a true RF ground.  If it's any longer then it will behave as a transmission line and radiate and transform impedances.  If it's longer than a small fraction of a wavelength it's not the end of the world; many radio stations have antennas on top of tall buildings where such an RF ground is unavailable.  If it's longer than a small fraction of a wavelength it may still be useful as an electrical safety ground or for lightning damage reduction, if you have done your homework and built it with those goals in mind and according to code.  Your station grounding system must be bonded to the ground rod at the service entrance.  In the US, I seem to remember that code requires a bonding cable of 4 AWG or larger, but I'm not positive about that.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-10-30T01:39:24.130" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17540" PostTypeId="1" CreationDate="2020-10-30T02:38:38.480" Score="3" ViewCount="148" Body="&lt;p&gt;I have all the space in the world and wish to errect a single random longwire &lt;strong&gt;to use on the 10 meter band only&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;p&gt;I understand that once such a wire is very long, losses associated with the wire itself (a wire of suitable gauge) mean that after a certain length, there is little more to gain.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;So at what point would it become impractical based on performance?&lt;/li&gt;&#xA;&lt;li&gt;Also, is there some way of calculating the optimum length where space is not a real limitation?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I used the term 'random longwire' because a longwire is defined as a length of wire at least two or more multiples of a wavelength (and I made it clear that it is for single band use), and random is in reference to the fact that it doesn't have a relationship to the wavelength within.&lt;/p&gt;&#xA;&lt;p&gt;The height is rather varied, as it will be strung over a deep gorge. Minimum height will start at a quarter wavelength, then travel for some length averaging three quarters of a wavelength. The maximum height above ground will be between 100 and 200 metres depending on droop.&lt;/p&gt;&#xA;" OwnerUserId="18008" LastEditorUserId="8717" LastEditDate="2020-12-18T00:42:22.203" LastActivityDate="2020-12-18T00:42:22.203" Title="What is the optimum length for a random longwire on 10m?" Tags="&lt;antenna&gt;&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17541" PostTypeId="2" ParentId="17534" CreationDate="2020-10-30T03:33:14.337" Score="1" Body="&lt;p&gt;S11 is one of the S-parameters. It uses 1 port on the VNA to look into something and look at the reflection coming back to determine reflection coefficient / VSWR. If the device was calibrated properly then it can also tell you the complex impedance of what it is &amp;quot;seeing&amp;quot;. To calibrate you have to use open, short, and load (99% this is 50 ohm), but these have to take the place of the DUT. Then after you calibrate each, the DUT takes their place. The closer you can get it the more accurate. You can use a resistor on your PCB or right before it enters, use 2x 100 ohm resistors to reduce inductance and get ones that are accurate too. of course the circuit (DUT) has to be disconnected for calibration. lot's of info online go check it out. If you want S21 parameter you need 2 ports, one is tx the other one is rx, it will tell you how much power gets through vs frequency. It will take a 4th calibration step which is a 'through' if you want to go that route.&lt;/p&gt;&#xA;" OwnerUserId="17896" LastActivityDate="2020-10-30T03:33:14.337" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17542" PostTypeId="1" CreationDate="2020-10-30T07:22:52.077" Score="1" ViewCount="63" Body="&lt;p&gt;Are there lengths of feed line to avoid or ones that may cause problems with an antenna system? For single band use.&#xA;Appendix: The run of coaxial will be for the 10 metre band. I would imagine this has no or little relevance as lengths can be expressed in a manner for any desired frequency.&lt;/p&gt;&#xA;" OwnerUserId="18008" LastEditorUserId="18008" LastEditDate="2020-11-01T09:25:24.947" LastActivityDate="2020-11-01T14:33:45.903" Title="What lengths of coaxial feed lines should you avoid?" Tags="&lt;antenna-system&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17543" PostTypeId="1" CreationDate="2020-10-30T08:35:46.760" Score="1" ViewCount="30" Body="&lt;p&gt;I am planning on utilising a ferrite choke on a J Pole antenna for CMC. Placement directly on the feedpoint poses possible mechanical restraints. Is it okay to place it a quarter wave down the coaxial feed line in free space from the feed point. Is this the maximum point of resistance to the flow of CMC? Or is this a bad idea due to resonant coupling?&#xA;Addition:&#xA;From reading one of the suggested articles it mentioned measuring from the ends of the antenna and to place a choke at odd multiples of a quarter wavelength... where convenient. So I assume that with a J Pole, this would be measured from the top of this antenna. Have I interpreted this correctly? Anyone, anyone? The article was a little vague and skimmed over a few things. A mere squire like myself struggles to join the dots or 'missing links' if you will.&lt;/p&gt;&#xA;" OwnerUserId="18008" LastEditorUserId="18008" LastEditDate="2020-11-01T07:12:26.443" LastActivityDate="2020-11-01T07:12:26.443" Title="J Pole, what is the best way to deal with Common Mode Current?" Tags="&lt;coaxial-cable&gt;&lt;antenna-system&gt;&lt;feed-line&gt;&lt;choke-balun&gt;" AnswerCount="0" CommentCount="3" ClosedDate="2020-11-03T02:09:24.983" ContentLicense="CC BY-SA 4.0" />
  <row Id="17544" PostTypeId="1" CreationDate="2020-10-30T12:14:01.570" Score="1" ViewCount="34" Body="&lt;p&gt;I connected USRP (together with antenna) to my computer to receive some signals. For this purpose, I used the built-in module &amp;quot;Spectral Monitoring (Interactive)&amp;quot;. Unfortunately I noticed that I'm not receiving almost anything. I wanted to change the frequency and expand the band, but I don't know exactly where to do it. Do I have to change the &amp;quot;Carrier Frequency [Hz]&amp;quot; from 915MHz to 2.45GHz for example, and do I have to change the IQ Sampling Rate (i don't know this term, I'm only used to Sampling Rate, not IQ Sampling Rate, is this the same?) from 200k to some other value to expand the band?&lt;/p&gt;&#xA;&lt;p&gt;An overview picture from the GUI of the Spectral Monitoring (Interactive) module.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Gdkvw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Gdkvw.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18026" LastActivityDate="2020-10-30T12:14:01.570" Title="Labview Spectral Monitoring (USRP) - Bandwidth expansion and frequency change" Tags="&lt;frequency&gt;&lt;bandwidth&gt;&lt;usrp&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17545" PostTypeId="1" AcceptedAnswerId="17547" CreationDate="2020-10-30T21:17:24.010" Score="1" ViewCount="73" Body="&lt;p&gt;When a cellphone is near an electronic device with speakers and someone's calling, we may hear a sound like this due to interference: &lt;a href=&quot;https://youtu.be/uPYyrS7fc7g?t=15&quot; rel=&quot;nofollow noreferrer&quot;&gt;Cell Phone Interference Sound&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Can we obtain any useful information from this sound such as phone number?&lt;/p&gt;&#xA;" OwnerUserId="18029" LastActivityDate="2020-10-31T11:00:31.403" Title="Can sound generated by interference of cell phone signals contain any useful data?" Tags="&lt;rfi&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17546" PostTypeId="2" ParentId="6545" CreationDate="2020-10-31T04:10:02.810" Score="-6" Body="&lt;p&gt;cheap baofengs work great and many of the cheap china radios work great on packet radio is a radio if it tx/rx and links up to your tnc and pc your going to make it happen never issues.......been in packet going back to 1982 in canada and later liveing in Utah  now the east coast RF Engineer for over 50 years...all the cheap radios works great and great for any type of experimenting...dont beleive the naaayyyers  have fun being a HAM is what realy are hobby is about.&lt;/p&gt;&#xA;" OwnerUserId="18030" LastActivityDate="2020-10-31T04:10:02.810" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17547" PostTypeId="2" ParentId="17545" CreationDate="2020-10-31T10:36:44.347" Score="3" Body="&lt;p&gt;Short answer: No.&lt;/p&gt;&#xA;&lt;p&gt;Long answer: Your accidental receiver can't see the data that's being received. Also, you're listening to an effect of the uplink, not the downlink. Also, cryptography.&lt;/p&gt;&#xA;&lt;p&gt;Longer answer:&lt;/p&gt;&#xA;&lt;p&gt;What you're referring to is interference where you can hear the power modulation by data bursts emitted by your phone.&lt;/p&gt;&#xA;&lt;p&gt;Why your phone and not the mast? Your phone is way, way closer to you, and power density drops with the inverse of the surface of a sphere with the distance as radius. And that's quadratic.&lt;/p&gt;&#xA;&lt;p&gt;The base station your phone communicates with will tell the phone pretty early on how to regulate its power so that the signal is strong enough, but not too strong, when it reaches the mast. The other way around, it does the same: a GSM tower will not send vast amounts of RF power for your phone; it will send at most as much as necessary to your phone that at the point that it is, it has good reception.&lt;/p&gt;&#xA;&lt;p&gt;The powers for &amp;quot;good reception&amp;quot; are due to the &amp;quot;power goes down with the square of distance&amp;quot; argument above very much lower than what the other side has to emit. Therefore, your radio receiver doesn't even remotely notice the far-away transmitter. It only &amp;quot;sees&amp;quot; the phone right next to it. And it really needs that close-by transmitter to be strong (see next paragraph).&lt;/p&gt;&#xA;&lt;p&gt;Why power modulation? Because you're not actually using a receiver for GSM or even GSM frequencies, your radio receiver is just not sufficiently protected against interference from other frequencies¹. You don't have a demodulator for the data, it's just the nonlinearities in some component that mix down the signal to baseband.&lt;/p&gt;&#xA;&lt;p&gt;Thus, what you hear is the rapid succession of &amp;quot;data burst&amp;quot; – &amp;quot;silence&amp;quot; – &amp;quot;data burst&amp;quot;... ; the symbols in the data burst itself are too short to be audible². So, the fact that you hear something is not the actual data in GSM, it's that a burst is 577 µs long (and consist of 156 symbols or so), and followed by silence. That's what makes the sound while you're having a call!&lt;/p&gt;&#xA;&lt;p&gt;Now, the data modulation itself for GSM is GFSK³, which is essentially a constant envelope modulation, which means that after (inadvertent) mixing to baseband, even if you had a 280 kHz observation bandwidth, all the data would have been mathematically erased – there's no mutual information between the data in the symbols and the baseband result.&lt;/p&gt;&#xA;&lt;p&gt;You can build a proper RF receiver for GSM for 10 to 30€⁴. Then, your computer would get a mixed-down version of the signal that retains the phase information, and thus, can actually be used to recover the bits that were sent. There's software for that!&lt;/p&gt;&#xA;&lt;p&gt;The number of the caller belongs to the things that aren't necessary to communicate at any point to establish the connection, so they're not sent at all: A phone number is not really a concept to a GSM network - it doesn't care about phone numbers, really, until they are necessary to know where to send call data, and that's very far away from the RF interface.&lt;br&gt; As a subscriber, you're identified by other means. So, your phone doesn't send its phone number at any point, far as I know. There's no reason it should.&lt;/p&gt;&#xA;&lt;p&gt;The phone number of the caller is optional, and only &lt;em&gt;received&lt;/em&gt; by your phone; but you don't hear what is received, for power reasons as explained above, you only hear when something has been transmitted by your phone!&lt;/p&gt;&#xA;&lt;p&gt;However, as said above, GSM networks are encrypted. Even if you have a proper receiver for GSM frequencies, properly lock on to the network, properly demodulate GSM messages: you still have to break the encryption on these. That's not impossible for a couple of the older encryptions that exist in the GSM standards, but it's still significant effort that requires a bit more understanding.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;¹ as it should be – modern high-fi stereos with high audio gain probably are well-designed to keep typical domestic sources of RF power out of their signal path, say phones, wifi, bluetooth, 700 / 900 MHz ISM band automation...&lt;/p&gt;&#xA;&lt;p&gt;² that would require audio to go up to above 280.333 kHz, the GSM symbol rate.&lt;/p&gt;&#xA;&lt;p&gt;³ I think 8PSK might also be standardized, but that would be another constant-envelope modulation&lt;/p&gt;&#xA;&lt;p&gt;⁴ 6€ if you directly order an RTL-SDR dongle from China.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastEditorUserId="4076" LastEditDate="2020-10-31T11:00:31.403" LastActivityDate="2020-10-31T11:00:31.403" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17549" PostTypeId="1" CreationDate="2020-10-31T21:49:17.220" Score="2" ViewCount="144" Body="&lt;p&gt;I am wondering if using a VHF/UHF ham radio for emergency (I get injured, become ill, run out of water/food, etc.) communication while hiking &lt;a href=&quot;https://continentaldividetrail.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;the Continental Divide Trail&lt;/a&gt; would be possible.&lt;/p&gt;&#xA;&lt;p&gt;I see that the area I am looking to go has repeaters along the route so my theoretical range would be extended.  I see there is some sparse contact information, other than that, I have no guarantee that it exists beforehand short of verifying those few contacts.  Then, I must be tuned to that frequency to have my transmissions repeated at a greater power.  Additionally, if I were in an emergency, it would boil down to whether or not someone is actually listening to those frequencies.&lt;/p&gt;&#xA;" OwnerUserId="18034" LastEditorUserId="18034" LastEditDate="2020-11-03T18:17:57.850" LastActivityDate="2020-11-22T23:19:53.477" Title="Ham radio repeater" Tags="&lt;repeater&gt;&lt;emergency&gt;" AnswerCount="4" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17550" PostTypeId="1" AcceptedAnswerId="17551" CreationDate="2020-10-31T23:47:33.037" Score="3" ViewCount="466" Body="&lt;p&gt;How does a ham Internet gateway work?&lt;/p&gt;&#xA;&lt;p&gt;Is it possible for someone to use that to listen for my transmissions (over the Internet without needing a ham radio)?&lt;/p&gt;&#xA;&lt;p&gt;Wouldn't the Internet gateway need to be setup for the same frequency I'm transmitting on and in the same area, again, no guarantee and highly unlikely?&lt;/p&gt;&#xA;&lt;p&gt;Ie, if I'm going to be broadcasting in California and I would like someone in New York, Peru, Greenland, etc., is it possible for them to listen?  Would it also be available in real-time or close to real-time or would there be a substantial delay.&lt;/p&gt;&#xA;" OwnerUserId="18034" LastEditorUserId="8717" LastEditDate="2020-11-02T03:50:04.563" LastActivityDate="2020-11-02T05:36:30.267" Title="Ham radio Internet gateway" Tags="&lt;internet&gt;" AnswerCount="2" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17551" PostTypeId="2" ParentId="17550" CreationDate="2020-11-01T03:41:56.253" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;How does a ham Internet gateway work?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;Check out http://websdr.org.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;All over the world, many amateur radio stations have connected software-defined-receivers (WebSDRs) to their computers, using software specifically designed for the purpose.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Is it possible for someone to use that to listen for my transmissions (over the Internet without needing a ham radio)?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It certainly is! Go have a listen &lt;a href=&quot;http://websdr.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;there&lt;/a&gt; yourself. And it's free.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Wouldn't the Internet gateway need to be setup for the same frequency I'm transmitting on and in the same area ...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Basically. However, they receive a wide band of frequencies. If someone wanted to listen to you, they would have to tune their Web SDR of choice to your frequency. This quote from &lt;a href=&quot;http://websdr.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://websdr.org&lt;/a&gt; explains:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&amp;quot;A WebSDR is a Software-Defined Radio receiver connected to the internet, allowing many listeners to listen and tune it simultaneously. SDR technology makes it possible that all listeners tune independently, and thus listen to different signals; this is in contrast to the many classical receivers that are already available via the internet.&amp;quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;... no guarantee and highly unlikely?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;No guarantee, but I wouldn't say that it's highly unlikely.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;If I'm going to be transmitting in California and I would like someone in New York, Peru, Greenland, etc., is it possible for them to listen?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It's possible. But whether they can hear you depends on many factors, which I won't go into because there is another question (somewhere) that answers that here.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Would it also be available in real-time or close to real-time, or would there be a substantial delay.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I've been in conversation with other hams over the radio. When I used a WebSDR to listen to them as well, I have never heard a delay of more than a second compared to the sound coming out of the radio's speaker. Usually, it's significantly less than a second.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;&lt;strong&gt;There is also &lt;a href=&quot;http://www.echolink.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;Echolink&lt;/a&gt;.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;EchoLink® software allows licensed Amateur Radio stations to communicate with one another over the Internet, using streaming-audio technology.  The program allows worldwide connections to be made between stations, or from computer to station, greatly enhancing Amateur Radio's communications capabilities.  There are more than 200,000 validated users worldwide — in 151 of the world's 193 nations — with about 6,000 online at any given time.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-11-02T01:19:48.000" LastActivityDate="2020-11-02T01:19:48.000" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17552" PostTypeId="1" CreationDate="2020-11-01T09:44:15.537" Score="2" ViewCount="143" Body="&lt;p&gt;For Yagi antennas where the driven element is electrically connected to the boom like the parasitic elements, how can this function without diminished performance outside of the design frequency? In other words, how can it achieve any kind of bandwidth? Frequency is the centre of the 10 metre band. Antenna feed is via the usual gamma match.&lt;/p&gt;&#xA;" OwnerUserId="18008" LastEditorUserId="8717" LastEditDate="2020-11-05T21:34:23.247" LastActivityDate="2020-11-05T21:34:23.247" Title="How do 'plumber's delight' type Yagi antennas have a bandwidth?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;yagi&gt;&lt;bandwidth&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17553" PostTypeId="2" ParentId="17552" CreationDate="2020-11-01T14:26:08.720" Score="6" Body="&lt;p&gt;The elements of a Yagi are dipoles. If you look at a dipole at any instant, the voltage at one tip will be some value, and the voltage at the other tip has the same magnitude, but opposite polarity.&lt;/p&gt;&#xA;&lt;p&gt;So let's say at some instant, the left side is at +50V and the right side is at -50V. Consider these relative to the soil at the base of the mast, if you like. What about other points on the dipole? The voltage distribution is sinusoidal, so it must be 0V in the middle.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vFEJH.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vFEJH.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The boom and mast must also be at 0V (ie, the same voltage as the ground rod at the base) if we intend for these things to not radiate. So, the voltage at the ends of the antenna can oscillate symmetrically but the center remains always at 0V, not unlike a &lt;a href=&quot;https://en.wikipedia.org/wiki/Seesaw&quot; rel=&quot;nofollow noreferrer&quot;&gt;seesaw&lt;/a&gt; (except the function is sinusoidal, not linear). Since there is no difference in electric potential between the center of the elements and the boom, no current flows in this connection, so it doesn't matter if the impedance is zero (connected) or infinite (insulated).&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-11-01T19:33:40.503" LastActivityDate="2020-11-01T19:33:40.503" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17554" PostTypeId="2" ParentId="17542" CreationDate="2020-11-01T14:33:45.903" Score="1" Body="&lt;p&gt;Unless your antenna system relies on common-mode radiation of the feedline (most do not &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;when properly installed&lt;/a&gt;), feedline length is irrelevant to the operation of the antenna. So, the usual approach is to make the feedline as short as possible (possibly with a short loop somewhere, for future maintenance) since a shorter length minimizes losses and cost.&lt;/p&gt;&#xA;&lt;p&gt;See also &lt;a href=&quot;https://ham.stackexchange.com/questions/1628/is-there-an-optimum-antenna-feedline-length-for-mobile-installations&quot;&gt;Is there an optimum Antenna Feedline Length for mobile installations?&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-01T14:33:45.903" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17555" PostTypeId="2" ParentId="17540" CreationDate="2020-11-01T14:50:02.300" Score="7" Body="&lt;p&gt;A &lt;em&gt;random&lt;/em&gt; longwire is just that, a random length. There is no optimum length, by definition. Usually people use random longwires for multi-band operation. Since the design frequency is &amp;quot;a lot of them&amp;quot;, the strategy of a random longwire is more or less to give up on making the wire suit any particular frequency, and just deal with the mismatch with a tuner.&lt;/p&gt;&#xA;&lt;p&gt;If you are wondering what the optimal length is for &amp;quot;some single-wire antenna for use on one band&amp;quot;, the answer is probably &amp;quot;about 0.47 wavelengths&amp;quot;. Without defining &amp;quot;optimal&amp;quot; I'm making some assumptions, but I would very much recommend you install a half-wave dipole because:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;No tuner is required, minimizing losses&lt;/li&gt;&#xA;&lt;li&gt;Making the wire longer does not improve performance&lt;/li&gt;&#xA;&lt;li&gt;Unlike and end-fed antenna, it is quite easy to  &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;address feedline common-mode current with a balun&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;For height, &amp;quot;as high as possible&amp;quot; is generally a good answer, since this minimizes ground losses. But if you have the time and space, you can squeeze out a few more decibels by being more precise. &lt;a href=&quot;https://www.voacap.com/antennas/squeezing-decibels-out-of-dipole/&quot; rel=&quot;noreferrer&quot;&gt;This analysis by by Jari Perkiömäki OH6BG/OG6G&lt;/a&gt; suggests a multiple of 0.5 wavelengths, plus 0.1 wavelengths (0.6, 1.1, 1.6, 2.1, ...)&lt;/p&gt;&#xA;&lt;p&gt;If you wish to further improve your antenna performance, you'll want to consider antennas which can improve your gain and/or directivity. Some of the more popular choices on HF being Yagi, 4-square, and Beverage antennas.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-01T14:50:02.300" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17556" PostTypeId="2" ParentId="17536" CreationDate="2020-11-01T15:14:53.913" Score="4" Body="&lt;p&gt;The reason to avoid multiple of a quarter-wavelength is that &lt;a href=&quot;https://en.wikipedia.org/wiki/Quarter-wave_impedance_transformer&quot; rel=&quot;nofollow noreferrer&quot;&gt;by virtue of the length&lt;/a&gt; this will transform the low impedance at the ground rod into a high impedance. This implies you are expecting this ground connection to carry significant RF current when you transmit.&lt;/p&gt;&#xA;&lt;p&gt;Such antenna system designs are not usually good ones, for a couple reasons.&lt;/p&gt;&#xA;&lt;p&gt;Firstly, soil is not a great conductor. Any antenna system with significant current in the soil will experience significant resistive loss. Antenna efficiency will suffer.&lt;/p&gt;&#xA;&lt;p&gt;Secondly, if your desk must be grounded that implies high RF current at the desk. That presents a higher risk of RF burns if you're operating at higher power. It also means your desk and everything around it is part of the &lt;em&gt;receiving&lt;/em&gt; antenna, which will be profoundly horrible for performance since nearly every modern desk is surrounded by digital noise sources.&lt;/p&gt;&#xA;&lt;p&gt;In the early days of radio it was common practice to ground the transmitter, and for the antenna to be just a wire coming out of the transmitter. This is effectively what we could call a &amp;quot;vertical&amp;quot; or a &lt;a href=&quot;http://www.antenna-theory.com/antennas/monopole.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;monopole&lt;/a&gt; today, but with the transmitter right at the feedpoint, and no radials.&lt;/p&gt;&#xA;&lt;p&gt;But in the decades since, we've developed convenient and inexpensive coax feedlines, and RF engineering is much better understood. Station designs that require a low-impedance ground as part of the deliberate RF path might still have a valid application in temporary, low-power stations where the ease of setup is more important than efficiency and the risk of RF burns is non-existent. But for any semi-permanent station, it's time this design is relegated to history books.&lt;/p&gt;&#xA;&lt;p&gt;Instead of trying to make your ground system a particular length so it can have a low impedance for common-mode current, strive to eliminate the common-mode current at the source. This means &lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;if you are using a dipole with a coax feed, use a balun&lt;/a&gt;. If you are using a vertical, install radials. If you are using some other kind of antenna which has just one terminal at the feedpoint, don't use that kind of antenna.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/1271/how-to-detect-common-mode-currents-or-rf-in-the-shack&quot;&gt;Measure the common-mode current&lt;/a&gt; on the feedline and/or your ground connection to guide your efforts.&lt;/p&gt;&#xA;&lt;p&gt;There are still reasons to ground your equipment, such as to avoid electrocution if a live mains wire comes in contact with a chassis through some fault, or for &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;lightning protection&lt;/a&gt;. But these applications don't require a low-impedance ground at your specific transmitting frequency, so there are no particular lengths to avoid.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-01T15:14:53.913" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17557" PostTypeId="2" ParentId="17535" CreationDate="2020-11-01T15:53:30.740" Score="1" Body="&lt;p&gt;There are no resistive components in a gamma match, so with idealized components the loss is theoretically zero.&lt;/p&gt;&#xA;&lt;p&gt;In practice, I'd expect if we could somehow measure the heat coming off the match we'd find it's less than 1 dB.&lt;/p&gt;&#xA;&lt;p&gt;The sources of loss will include resistive losses in the conductor, and dielectric losses in the coaxial capacitor. To minimize these, you'll want to use highly conductive metals, of the biggest practical size, and a low-loss dielectric.&lt;/p&gt;&#xA;&lt;p&gt;Practically speaking, the gamma match is there because it's solving a problem: the antenna (often, a Yagi) is mismatched. The problems associated with driving such a mismatched load are more significant than the small loss introduced by the match. So comparing a gamma match with a realistic alternative, the losses are &lt;em&gt;negative&lt;/em&gt;: it's a gain.&lt;/p&gt;&#xA;&lt;p&gt;A gamma match also steps up common-mode impedance of the feedline. While this doesn't affect efficiency, it is important to preserving the directivity of the antenna. It still doesn't hurt to have a choke, but the effects are cumulative: if the gamma match has a 4x step-up then it makes the choke 4x more effective.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-01T15:53:30.740" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17558" PostTypeId="1" CreationDate="2020-11-01T17:09:50.923" Score="0" ViewCount="50" Body="&lt;p&gt;Do FT8 operators typically respond to very late replies for an entire QSO?  (for instance, transmitting in the 3rd slot or 5th slot after a CQ, to maintain even/odd alternation, instead of the time slot immediately after the corresponding FT8 reception)&lt;/p&gt;&#xA;&lt;p&gt;The reason I'm asking is for minimum carry weight POTA/SOTA type ops, I'm thinking of trying a very lightweight computer (Raspberry Pi Zero W, et.al.) to run the FT8 decode/encode stack; and the processors in those tiny computers can't demodulate, decode and encode an FT8 signal in circa 1 to 2 seconds.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-11-01T19:28:04.093" Title="FT8 in slow motion?" Tags="&lt;ft8&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17559" PostTypeId="2" ParentId="17558" CreationDate="2020-11-01T19:28:04.093" Score="1" Body="&lt;p&gt;Having nothing but my own personal experience as data, I would say, no this is not common. Sometimes people can't click fast enough to respond to a CQ and so their response comes on the &amp;quot;2nd time around&amp;quot;, but after that all the responses are usually immediate.&lt;/p&gt;&#xA;&lt;p&gt;Though I wouldn't say that means your idea wouldn't work. QSOs that are right on the edge of the minimum SNR sometimes take a few retries to work, and the WSJT-X software just keeps re-transmitting the same step in the exchange until a response is received.&lt;/p&gt;&#xA;&lt;p&gt;As such, you'll probably eliminate contacts with especially impatient operators, but I'd bet most operators will wait for at least 1 retransmission before giving up, and you'll still have plenty of successful QSOs.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-01T19:28:04.093" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17560" PostTypeId="2" ParentId="12203" CreationDate="2020-11-01T20:15:08.860" Score="1" Body="&lt;p&gt;&lt;a href=&quot;http://ngspice.sourceforge.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;ngspice&lt;/a&gt; is free and can read and write S2P models.&lt;/p&gt;&#xA;&lt;p&gt;You can also just open the file with a text editor and &lt;a href=&quot;https://electronics.stackexchange.com/questions/128503/reading-s2p-files-what-does-each-column-represent&quot;&gt;read the S-parameters manually&lt;/a&gt;. With the appropriate skill and care, you can then manually calculate the desired matching with no electronics software at all.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-01T20:15:08.860" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17561" PostTypeId="2" ParentId="15970" CreationDate="2020-11-01T20:35:18.940" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://www.itu.int/rec/R-REC-F.1487-0-200005-I/en&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU-R F.1487-0&lt;/a&gt; (&lt;em&gt;Testing of HF modems with bandwidths of up to about 12 kHz using ionospheric channel simulators&lt;/em&gt;) seems like what you're looking for. It discusses briefly how an HF channel can be modeled, and provides 9 sets of parameters, every combination of (low, mid, high) latitudes and (quiet, moderate, disturbed) conditions, as well as statistics on how frequently those conditions can be expected.&lt;/p&gt;&#xA;&lt;p&gt;For completeness, other resources which are useful for a complete model:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.voacap.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt;, for path loss and channel reliability estimation&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.itu.int/rec/R-REC-P.372-14-201908-I/en&quot; rel=&quot;nofollow noreferrer&quot;&gt;ITU-R P.372-14&lt;/a&gt; for data on ambient radio noise&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-01T20:35:18.940" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17562" PostTypeId="2" ParentId="17552" CreationDate="2020-11-02T02:27:56.100" Score="-3" Body="&lt;p&gt;The boom is like two end-fed right-angle fan-dipole elements for some completely different frequency added to the driven element.  Elements of a fan dipole for a very off frequency typically do not take much of the Rf current away from the on-frequency resonant element of a fan-dipole.&lt;/p&gt;&#xA;&lt;p&gt;My guess is that some RF current will travel down the boom (and back), but in opposite directions from the feed point at the same time. Thus the EM field generated by the front and back of the boom will cancel out, as well as being orthogonal to the beam direction, and thus have little to no effect on the pattern or bandwidth of the Yagi elements.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-11-02T02:27:56.100" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17563" PostTypeId="2" ParentId="17550" CreationDate="2020-11-02T05:36:30.267" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;How does a ham Internet gateway work?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Someone, or often an amateur radio club, installs a radio at a site with internet access. From there, they upload the received signals to a network of servers on the internet, or host the server themselves.&lt;/p&gt;&#xA;&lt;p&gt;There are many such services. Here are a few, and by no means exhaustive:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.websdr.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;WebSDR&lt;/a&gt; (predominantly independent HF receivers)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://brandmeister.network/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Brandmeister&lt;/a&gt; (mostly linked DMR repeaters, anyone can listen via internet)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.dmr-marc.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DMR-MARC&lt;/a&gt; (also DMR repeaters, but this one less open than Brandmeister. No internet listening capability, but no license is required to &lt;em&gt;listen&lt;/em&gt; on a DMR radio in the US)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.echolink.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EchoLink&lt;/a&gt; (Used to link FM repeaters, also runs as Windows software)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.p25nx.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;P25NX&lt;/a&gt; (a similar thing to Brandmeister and DMR-MARC, but for P25)&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.dstarinfo.com/reflectors.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;D-STAR reflectors&lt;/a&gt; (similar to DMR except much less mature. You can probably find a place to listen online that isn't broken if you try hard)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Wouldn't the Internet gateway need to be setup for the same frequency I'm transmitting on&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;and in the same area,&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Well, the receiver has to be in range at least. The effective range of your transmission will depend on the frequency, power, antenna, terrain, and other factors; and could be anywhere from global to less than a mile.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;again, no guarantee and highly unlikely?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I wouldn't say it's highly unlikely. Nearly all digital repeaters, and most analog FM repeaters, are on some kind of linking system. And HF has such a long range, it's quite likely there's a receiver in range somewhere.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Ie, if I'm going to be broadcasting in California and I would like someone in New York, Peru, Greenland, etc., is it possible for them to listen?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Assuming they have internet access, and aren't in some jurisdiction that heavily censors the internet, then yes.&lt;/p&gt;&#xA;&lt;p&gt;More problematic though is &lt;a href=&quot;https://www.ecfr.gov/cgi-bin/text-idx?SID=d4b3c60d2d60000a147f885bdee88264&amp;amp;mc=true&amp;amp;node=pt47.5.97&amp;amp;rgn=div5#se47.5.97_1113&quot; rel=&quot;nofollow noreferrer&quot;&gt;you can't legally &lt;em&gt;broadcast&lt;/em&gt; in California, or any other part of the US&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§97.113   Prohibited transmissions.&lt;/p&gt;&#xA;&lt;p&gt;(b) An amateur station shall not engage in any form of broadcasting, nor may an amateur station transmit one-way communications except as specifically provided in these rules; nor shall an amateur station engage in any activity related to program production or news gathering for broadcasting purposes, except that communications directly related to the immediate safety of human life or the protection of property may be provided by amateur stations to broadcasters for dissemination to the public where no other means of communication is reasonably available before or at the time of the event.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Would it also be available in real-time or close to real-time or would there be a substantial delay.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Delay won't be more than a couple seconds, probably less.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-02T05:36:30.267" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17564" PostTypeId="1" CreationDate="2020-11-02T08:27:48.620" Score="0" ViewCount="81" Body="&lt;p&gt;Like the question says, can you feed a dipole with coax with no ill effects? Nothing else in the system, just the antenna and the cable.&lt;/p&gt;&#xA;" OwnerUserId="18008" LastActivityDate="2021-04-17T10:00:35.210" Title="Is there an instance where you can directly feed a half wave dipole with coaxial cable without having to worry about balanced to unbalance?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;feed-line&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17565" PostTypeId="1" CreationDate="2020-11-02T10:03:52.703" Score="1" ViewCount="59" Body="&lt;p&gt;Can I use 2 identical rubber ducky antennas with a splitter on my CB HT radio to improve range?&lt;/p&gt;&#xA;" OwnerUserId="18041" LastEditorUserId="8717" LastEditDate="2020-11-03T23:53:47.910" LastActivityDate="2020-11-03T23:53:47.910" Title="Dual Rubber Ducky antennas" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;ht&gt;&lt;phased-array&gt;&lt;citizens-band&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17567" PostTypeId="2" ParentId="17565" CreationDate="2020-11-02T15:12:30.813" Score="4" Body="&lt;p&gt;Theoretically yes, if you carefully control the lengths of the cables and the placement of the antennas. This is called a &lt;a href=&quot;https://en.wikipedia.org/wiki/Phased_array&quot; rel=&quot;nofollow noreferrer&quot;&gt;phased array&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;However, you would get a far better improvement in range by using an antenna which is not a rubber ducky, like a 1/4 wave whip or a dipole. Rubber ducky antennas are electrically shortened, making them smaller. The price of that reduction in size is reduced efficiency.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-02T15:12:30.813" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17568" PostTypeId="2" ParentId="17564" CreationDate="2020-11-02T15:14:08.440" Score="2" Body="&lt;p&gt;If &amp;quot;ill effects&amp;quot; include &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;common-mode current on the feedline&lt;/a&gt;, no.&lt;/p&gt;&#xA;&lt;p&gt;You can of course just tolerate the common-mode feedline current. In some situations it may not matter.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-11-02T18:45:41.263" LastActivityDate="2020-11-02T18:45:41.263" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17569" PostTypeId="2" ParentId="17549" CreationDate="2020-11-02T15:17:19.393" Score="-1" Body="&lt;p&gt;The short answer is &amp;quot;yes&amp;quot; you can use Ham Radio as backup communications for anything legal in ham radio.  (You can't use it as a fireman or police officer for example.)  Back before cell phones were ubiquitous, it was reassuring to have a radio in the car &amp;quot;just in case.&amp;quot;  Of course, as you stated, it's most useful when someone else is listening.  There may be repeaters with &amp;quot;autopatch&amp;quot;, meaning you can make a telephone call over the radio.  But even those are becoming obsolete.&lt;/p&gt;&#xA;&lt;p&gt;All that said though, these days you're better off counting on your cellphone.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastEditorUserId="9974" LastEditDate="2020-11-02T16:06:13.710" LastActivityDate="2020-11-02T16:06:13.710" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17570" PostTypeId="2" ParentId="17549" CreationDate="2020-11-02T19:56:40.243" Score="1" Body="&lt;p&gt;In an area with good cellular (mobile) phone service, then a cell phone is hands-down the best option for everyday emergency communications.&lt;/p&gt;&#xA;&lt;p&gt;However, many parts of the world, particularly rural and mountainous areas, have better coverage through ham radio repeaters than the mobile (cell) phone network.  There are several reasons for this:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;A cell phone tower must have coverage that is limited to a reasonable number of subscribers, or the service will be poor.  The trend for cellular phone companies is to build more towers with smaller coverage areas.  Newer technologies such as 5G are accelerating this trend.  Ham repeaters on the other hand are placed as high as possible, on high mountains and tall broadcast antenna towers, to have as much coverage as possible.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Cell phone towers are enormously expensive.  Ham radio repeaters are relatively cheap.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Ham repeaters can be powered by solar panels and wind turbines, allowing them to go places where the electrical grid doesn't reach.  Mobile phone towers require a lot of power, and are almost always connected to the electrical grid.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;In extended emergencies such as long-term electrical grid failures, mobile phone towers tend to go down.  Mobile phone towers often have emergency generators, but typically only a few days' fuel.  If the grid is down for more than a few days, there will be no mobile phone network.  Some ham repeaters are solar-powered and can continue to work for months or years without power from the grid.&lt;/p&gt;&#xA;&lt;p&gt;Here in the US, there are many repeaters, but often not many people are listening.  I have a few tips:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Some repeaters are linked to networks of other repeaters, temporarily through technologies such as IRLP or Echolink, or permanently.  A distress call to such a repeater could be heard by many more hams, increasing the odds of a timely response.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Some areas are served by many repeaters.  Some are more popular than others.  It helps to find out in advance which ones are popular.  The ham club closest to the area should know which repeaters are the most popular.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If a mayday call is not answered at first, don't give up!  Keep trying!  If limited battery life is an issue and there are no answers, turn off the radio and wait a while if that is possible, and then call again.  You should get a response eventually.  Prime time on repeaters is usually the hours when people commute to and from work, and in the early evening when nets are typically scheduled.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-11-02T19:56:40.243" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17571" PostTypeId="2" ParentId="17564" CreationDate="2020-11-02T20:35:38.027" Score="1" Body="&lt;p&gt;You certainly can feed the dipole with coax without a balun at the feedpoint, you will be able to work stations that would not be good on the dipole alone.   The downside is that the noise level of the whole system dipole + coax will be higher.   As the coax will radiate and also receive signals you will have a very different &amp;quot;radiation pattern&amp;quot; than with a balun at the feedpoint.&lt;/p&gt;&#xA;&lt;p&gt;I suspect many of us &amp;quot;old hands&amp;quot; used to just attach 50 Ohm coax to a dipole before we learned better.    You can use a 1:1 balun or &amp;quot;line isolator&amp;quot; close to your rig to reduce the amount of noise pickup etc but this will not be as effective as a 1:1 balun at the dipole's feedpoint.&lt;/p&gt;&#xA;&lt;p&gt;So, it's try and see, if you like the sort-of dipole then OK, if not use the balun at the feedpoint and turn the aerial into a real dipole    Vy 73  Tony G3ZRJ&lt;/p&gt;&#xA;" OwnerUserId="18047" LastActivityDate="2020-11-02T20:35:38.027" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17572" PostTypeId="2" ParentId="17240" CreationDate="2020-11-02T20:57:47.877" Score="0" Body="&lt;p&gt;The capacitor in the photo is to help the unit work better on the higher HF bands, can we leave it there as things will get rather technical.&lt;/p&gt;&#xA;&lt;p&gt;The example in the photo is really not a Balun, I don't want to get into deep waters, but it is a simple transformer wound onto a suitable toroid material good at HF frequencies.&#xA;This type of transformer is often used in End Fed Half Wave  (EFHW) antenna matching units and are usually 49:1 ratio.&lt;/p&gt;&#xA;&lt;p&gt;As you probably know the ends of a half wave antenna are at a high voltage and virtually no current, whereas at the centre of the half wave antenna you have the reverse situation high current and low voltage.&lt;/p&gt;&#xA;&lt;p&gt;If you try and feed a half wave antenna at the end you will have an impedance in the order of several thousand Ohms.   The SWR if you just fed this with coax would be enormous and your rig would certainly not be happy, even if you used the internal ATU.&lt;/p&gt;&#xA;&lt;p&gt;EFHW matching units permit a match from say, 2500 Ohms to the 50 Ohms that you need to match the coax and of course the input impedance of virtually every modern HF transceiver.&lt;/p&gt;&#xA;" OwnerUserId="18047" LastActivityDate="2020-11-02T20:57:47.877" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17573" PostTypeId="1" CreationDate="2020-11-03T00:54:28.790" Score="1" ViewCount="199" Body="&lt;p&gt;Baofeng radio's have two menu options for squelch tail elimination (STE). Item 35 is for general simplex STE, and item 36 is for repeater STE.&lt;/p&gt;&#xA;&lt;p&gt;My question is how would the radio know if a transmission is coming from a repeater in order to apply the setting from #36 instead of the setting for #35?&lt;/p&gt;&#xA;&lt;p&gt;Also menu 36 (RP-STE) has ten settings 1-10, is there an intuitive way to think about what this sensitivity means? At least whether value 1 or value 10 is the most aggressive squelch setting.&lt;/p&gt;&#xA;&lt;p&gt;The simplex version (item 35, &amp;quot;STE&amp;quot;) is just off or on, so I'm not sure how that maps to the 1-10 settings in the repeater version.&lt;/p&gt;&#xA;" OwnerUserId="18049" LastActivityDate="2020-11-06T07:52:50.710" Title="How does a Baofeng radio know an incoming transmission is from a repeater?" Tags="&lt;baofeng&gt;&lt;repeater&gt;&lt;squelch&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17574" PostTypeId="1" AcceptedAnswerId="17576" CreationDate="2020-11-03T06:08:52.440" Score="1" ViewCount="72" Body="&lt;p&gt;I have vague memories from the early 1990:s of some sort of service that broadcast &lt;em&gt;something&lt;/em&gt; related to sunspot numbers, in CW, probably shortwave. I think the world &amp;quot;BOULDER&amp;quot; was in there somewhere. Whatever it was, I could hear it in southern Sweden. What was it? Is is still there? On what frequency?&lt;/p&gt;&#xA;" OwnerUserId="17214" LastActivityDate="2020-11-03T17:58:01.077" Title="Sunspot numbers? forecast? broadcast on CW/HF" Tags="&lt;hf&gt;&lt;cw&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17575" PostTypeId="2" ParentId="17549" CreationDate="2020-11-03T17:07:16.420" Score="6" Body="&lt;p&gt;Possible, yes. A good idea as your plan for emergency communication while hiking on a remote and hazardous trail? I wouldn't count on it.&lt;/p&gt;&#xA;&lt;p&gt;As you've already observed, although there are repeaters along the way, you have to know what they are, you have to be in range of them, and someone has to be listening.&lt;/p&gt;&#xA;&lt;p&gt;Consider the things that could go wrong:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;You discover the repeater that you thought would cover this area of the trail is no longer operational.&lt;/li&gt;&#xA;&lt;li&gt;You are in a canyon with no repeater coverage.&lt;/li&gt;&#xA;&lt;li&gt;You have incorrect CTCSS or other access information which means you can't access the repeater, even if you can hear it and it's operational.&lt;/li&gt;&#xA;&lt;li&gt;You are lost, and not be able to figure out what repeater to use, even with a prepared list.&lt;/li&gt;&#xA;&lt;li&gt;You are lost, and can access a repeater, but you're unable to describe your position in sufficient detail for rescue crews to find you in time.&lt;/li&gt;&#xA;&lt;li&gt;You lack the presence of mind to find your location, consult your repeater list, program the radio, access the repeater, and articulate your situation.&lt;/li&gt;&#xA;&lt;li&gt;You can access a repeater, but either no one is listening at the time, or anyone listening is unable to effectively relay your message to someone that can help you.&lt;/li&gt;&#xA;&lt;li&gt;You are off your planned course, either because you are lost or were forced to detour, and you don't have access to a list of repeaters in the area.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;A much better solution for this use case is a satellite tracker, for example &lt;a href=&quot;https://www.findmespot.com/en-us/products-services/service-plans&quot; rel=&quot;nofollow noreferrer&quot;&gt;SPOT&lt;/a&gt; or an &lt;a href=&quot;https://en.wikipedia.org/wiki/Emergency_position-indicating_radiobeacon_station&quot; rel=&quot;nofollow noreferrer&quot;&gt;EPIRB&lt;/a&gt;. It works pretty much anywhere with a view of the sky, it notifies search and rescue at the press of a button, and it &lt;em&gt;tells them where you are&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Seriously, don't underestimate the probability that you will be lost. It's called &amp;quot;&lt;em&gt;search&lt;/em&gt; and rescue&amp;quot; and not just &amp;quot;rescue&amp;quot; because people get lost, a lot. Sometimes they just lose the trail. Sometimes they fall, and they survive but can't get back to their route so they detour, and &lt;em&gt;then&lt;/em&gt; they get lost. Sometimes, due to hypothermia/dehydration/hypoxia/hypoglycemia/drug use/etc they manage to get lost when it seems like no reasonable person could. It's not uncommon to find people dead one mile from a trail or road that would have led them to help.&lt;/p&gt;&#xA;&lt;p&gt;By all means, bring a radio and plan to use it: it will be a useful means of non-emergency communication or a backup in case the satellite tracker is damaged or lost. Bring a cell phone too: you can send a text from a lot of mountain peaks. But I wouldn't count on it as your &lt;em&gt;only&lt;/em&gt; means of communication.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-11-03T20:59:23.443" LastActivityDate="2020-11-03T20:59:23.443" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17576" PostTypeId="2" ParentId="17574" CreationDate="2020-11-03T17:58:01.077" Score="1" Body="&lt;p&gt;The beacon &lt;a href=&quot;http://www.dk0wcy.de/schedule_en.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;DK0WCY&lt;/a&gt; transmits such information on 80 and 30m.&lt;/p&gt;&#xA;" OwnerUserId="17676" LastActivityDate="2020-11-03T17:58:01.077" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17577" PostTypeId="1" CreationDate="2020-11-03T19:01:56.777" Score="2" ViewCount="144" Body="&lt;p&gt;I am attempting to hunt down many sources of RFI in and near the UHF amateur bands at my home, but I stumbled across a very specific one that I have definitely never heard before. This one sounds less like interference and more like an intentional signal of some kind. I have listened to every type of UHF signal on the &lt;a href=&quot;http://www.sigidwiki.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sigidwiki.com&lt;/a&gt; and none of them line up with what I am hearing here. I set my SDR mode to LSB so that the audio would be easily discernible.&lt;/p&gt;&#xA;&lt;p&gt;I first discovered this with my Yaesu FT-60R in AM mode on 446MHz out in the yard ~100ft from my house. I pulled it up on the SDR to easily record the signal for posting here.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Itcuq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Itcuq.png&quot; alt=&quot;Signal &quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I have also recorded audio of the signal in hopes it will help someone to help me ID this signal.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://cozy.foxhollow.cc/rfi/03-Nov-2020%2018h46m01sZ,%20446%20MHz,%20LSB.mp3&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://cozy.foxhollow.cc/rfi/03-Nov-2020%2018h46m01sZ,%20446%20MHz,%20LSB.mp3&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;If audio recordings are not allowed on this site, please forgive me. I am very new to this!&lt;/p&gt;&#xA;&lt;p&gt;So I guess my real question is.. is this RFI, or is this an intentional signal? If intentional, I'm curious what it is. If RFI, then I need to go digging through my house trying to find the source.&lt;/p&gt;&#xA;&lt;p&gt;73s&#xA;Steve&lt;/p&gt;&#xA;&lt;p&gt;EDIT: Apologies, I forgot to mention. I am located in the US (NE Florida) and 446MHz is allocated as the national 70cm calling frequency.&lt;/p&gt;&#xA;&lt;p&gt;EDIT2: Here is a wider view of the spectrum around 446MHz. It appears that there is a constant spike around 445.993MHz, and then on each side there are numerous &amp;quot;copies&amp;quot; of the signal dancing back and forth that you can see in the waterfall. It seems that certain ones are dancing &amp;quot;backwards&amp;quot; from the others, as if the signal in certain spots is inverted. I officially have no idea.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4wdPM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4wdPM.png&quot; alt=&quot;Wider spectrum view&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17995" LastEditorUserId="17995" LastEditDate="2020-11-03T20:14:24.587" LastActivityDate="2020-11-20T23:12:56.210" Title="Unknown signal on 446MHz LSB (possible RFI?)" Tags="&lt;rfi&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="17578" PostTypeId="2" ParentId="15018" CreationDate="2020-11-03T22:23:10.050" Score="0" Body="&lt;p&gt;Please excuse me for perhaps stating the obvious, but you need to cut the antenna wire for a half wave on 40M approx 66 feet, it will work ok on 20 and 10 Metres where there are multiple half waves on a 66 foot wire.&lt;/p&gt;&#xA;&lt;p&gt;My homebrew EFHW 49:1 matching unit is attached to 132 feet of wire and works very nicely on the normal harmonically related bands 3.5 - 28 MHz and not too badly on the WARC 10.1, 18 and 24 MHz bands.    Photo before I added the capacitor.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/blk9V.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/blk9V.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I used dual FT240-43 cores and 1.6mm enamelled copper wire  14 AWG.&lt;/p&gt;&#xA;&lt;p&gt;Having been a seagoing radio officer, I learned to over engineer things a bit HI&lt;/p&gt;&#xA;&lt;p&gt;73 and good luck    Tony G3ZRJ&lt;/p&gt;&#xA;" OwnerUserId="18047" LastActivityDate="2020-11-03T22:23:10.050" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17581" PostTypeId="2" ParentId="17552" CreationDate="2020-11-04T12:31:07.567" Score="1" Body="&lt;p&gt;Bandwidth of a yagi is largely controlled by the diameter of the elements.  Generally, the larger the diameter, the larger the bandwidth.   However, the yagi is also helped by very slightly tapered elements.&lt;/p&gt;&#xA;&lt;p&gt;The impedance matching network may also affect the SWR bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;The boom conductivity does not affect bandwidth, as well explained by Phil.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-11-04T12:31:07.567" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17583" PostTypeId="5" CreationDate="2020-11-04T16:28:55.470" Score="0" Body="&lt;p&gt;If your question asks about a recording of an unknown signal, or a snapshot of a waterfall display, then this tag fits.  This tag also covers topics like &lt;a href=&quot;https://en.wikipedia.org/wiki/Numbers_station&quot; rel=&quot;nofollow noreferrer&quot;&gt;numbers stations&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-11-04T16:28:55.470" LastActivityDate="2020-11-04T16:28:55.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17584" PostTypeId="4" CreationDate="2020-11-04T16:28:55.470" Score="0" Body="Questions about identifying signals of unknown mode or origin." OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-11-04T16:28:55.470" LastActivityDate="2020-11-04T16:28:55.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17585" PostTypeId="1" CreationDate="2020-11-04T17:53:36.910" Score="0" ViewCount="119" Body="&lt;p&gt;This site gets many questions about people trying to track down RFI, or interesting signals picked up on radios.  Often the exact location of the transmitter or the antenna would be a valuable clue to how to solve the RFI, or how to characterize the mysterious signal.  How should someone go about finding the transmitter or antenna of a radio signal, whether the signal is RFI or not?  Let's assume that the signal could be generated locally or far away.&lt;/p&gt;&#xA;&lt;p&gt;There are many questions on this site asking about specific RFI problems or specific interesting signals.  I'm asking the question generally, to be useful as a resource for people searching the web, or for people asking questions here in the future.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-11-06T00:10:05.933" LastActivityDate="2020-11-09T16:27:21.810" Title="How should I go about finding the transmitter or antenna of a radio signal?" Tags="&lt;antenna&gt;&lt;rfi&gt;&lt;transmitter&gt;&lt;direction-finding&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17586" PostTypeId="5" CreationDate="2020-11-04T18:02:59.737" Score="0" Body="&lt;p&gt;This tag covers questions about radio direction finding (RDF), which is finding the location of the transmitter or antenna sending a radio signal.  This is different from fox hunting (see the &amp;quot;fox-hunt&amp;quot; tag), which is a radio sport (or radiosport, if you prefer) in which people participate in organized events to find carefully-hidden transmitters according to specific rules.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-11-04T18:02:59.737" LastActivityDate="2020-11-04T18:02:59.737" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17587" PostTypeId="4" CreationDate="2020-11-04T18:02:59.737" Score="0" Body="Questions about radio direction finding (RDF), which is finding the location of the transmitter or antenna sending a radio signal." OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-11-04T18:02:59.737" LastActivityDate="2020-11-04T18:02:59.737" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17588" PostTypeId="1" CreationDate="2020-11-05T11:47:29.890" Score="0" ViewCount="39" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;We are currently deciding between a dipole and a monopole for uplink (435MHz) , while the monopole is easier to feed, we are unsure of how effectively we'll be able to implement the ground plane, while the ground plane won't be needed for dipole antenna, we are unsure on how to feed them.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;In many of dipoles in cubesats we have seen so far the elements of the dipoles are placed on opposite ends of the cubesat, this means that feeding points of both elements of the dipole is separated by about 10cm. In this situation, how exactly do we feed the dipole, since using a coax, and then using connecting wires, wouldn't the wires themselves contribute to the length of the antenna?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Also, what other parameters should we consider while deciding which antenna to use?&lt;/p&gt;&#xA;" OwnerUserId="18061" LastEditorUserId="1550" LastEditDate="2020-11-05T17:33:48.047" LastActivityDate="2020-11-05T17:33:48.047" Title="How to decide between Dipole and Monopole antenna for Cubesat Uplink (433 MHz)?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;satellites&gt;&lt;feed-line&gt;" AnswerCount="0" CommentCount="6" ClosedDate="2020-11-19T12:45:10.257" ContentLicense="CC BY-SA 4.0" />
  <row Id="17589" PostTypeId="2" ParentId="17577" CreationDate="2020-11-05T15:55:36.867" Score="3" Body="&lt;p&gt;From the wide spectrum screenshot it's evident your receiver is seriously overloaded. Note:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the signal around 445.982 which appears to be identical other than being &amp;quot;flipped&amp;quot;, and a little stronger. This comes from IQ imbalance in the receiver.&lt;/li&gt;&#xA;&lt;li&gt;additional copies of the signal all over the place. These are caused by intermodulation and harmonic distortion.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;This means the signal probably isn't at 446 MHz. It might not be at any of the frequencies you see on the spectrum at all: they could all be distortion products.&lt;/p&gt;&#xA;&lt;p&gt;One thing you can do to show it's not a real signal, but a distortion product: tune the receiver (change the center frequency of the receiver itself, not just move the cursor in your SDR software) by some amount, say 20 kHz. If the suspected signal moves by something other than 20 kHz, or it moves in the wrong direction, it's a distortion product.&lt;/p&gt;&#xA;&lt;p&gt;Hard to say what it is. If it's overloading your receiver it's probably close. Find it by walking in whatever direction makes it stronger.&lt;/p&gt;&#xA;&lt;p&gt;It's also possible this isn't a real signal at all, but instead an artifact of a broken or low-quality receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-11-19T22:50:14.910" LastActivityDate="2020-11-19T22:50:14.910" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17590" PostTypeId="2" ParentId="17573" CreationDate="2020-11-06T07:52:50.710" Score="3" Body="&lt;p&gt;It doesn't know anything.&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;STE&amp;quot; is the easier one to explain. It controls transmit, not receive. When STE is enabled, when you let go of the PTT button, the radio will send a 55Hz tone for a moment. Other Baofeng radios mute the receive when they hear a 55Hz tone... whether or not the STE option is enabled, whether or not you want it. It has no (useful) effect when the receiver is another type of radio, and if you use it with a repeater, the repeater won't recognize it, and the 55Hz tone won't get through the repeater's high-pass, so it does nothing at all. There's really no use turning this one on in a ham environment.&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;RP-STE&amp;quot; is more mysterious, but what I'm gleaning from several sources including &lt;a href=&quot;https://www.midlandeurope.com/pub/media/Lyb/Assets/ManualiProdotti/AMATORIALI/CT690//Manual_CT690_UK.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;this poorly translated Midland manual&lt;/a&gt; and the &lt;a href=&quot;https://wiki.radioreference.com/index.php/Baofeng_UV-5R&quot; rel=&quot;nofollow noreferrer&quot;&gt;RadioReference wiki&lt;/a&gt; is that it only stops you from hearing your &lt;em&gt;own&lt;/em&gt; tails by muting the receive for a moment after you let go of PTT, and you adjust the timing to match how long the repeater holds the channel after it stops hearing input. This is a lousy idea (among other things it makes it harder to tell if you doubled with someone, and might cut off the beginning of a reply to something you said), so everyone recommends that this option is set to OFF as well.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-11-06T07:52:50.710" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17591" PostTypeId="1" AcceptedAnswerId="17592" CreationDate="2020-11-06T22:56:39.677" Score="1" ViewCount="1147" Body="&lt;p&gt;I've got a question and any clarification on that would be greatly appreciated.&#xA;For calculating the pathloss in wireless communication we usually use the following formula:&#xA;PL = pathloss (in dB) + shadow fading (in dB) + antenna gain (in dBi) + noise floor (in dBm) + penetration loss(in dB)&lt;/p&gt;&#xA;&lt;p&gt;My question is: do I need to convert dBm to dB and then add all of these value together to calculate PL. Would be the PL in dB?&lt;/p&gt;&#xA;&lt;p&gt;For example if I have a scenario in which path loss modeled as&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{Pathloss(dB)}=148.1+37.6\ \log_{10}(d) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;shadowing  is equal to 8dB, antenna gain is 10dBi, penetration loss is 5 dB and noise floor is 54 dBm, what would be the PL and what is its unit?&lt;/p&gt;&#xA;" OwnerUserId="18071" LastEditorUserId="218" LastEditDate="2020-11-07T01:21:39.943" LastActivityDate="2020-11-25T22:35:44.380" Title="Adding and subtracting dB/dBm/dBi values" Tags="&lt;antenna&gt;&lt;math&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17592" PostTypeId="2" ParentId="17591" CreationDate="2020-11-07T01:23:44.753" Score="5" Body="&lt;p&gt;A value given in &amp;quot;dB&amp;quot; is a dimensionless ratio. 10dB is a ratio of 10:1, -10dB is a ratio of 1:10, 3dB is a ratio of approximately 2:1, etc.&lt;/p&gt;&#xA;&lt;p&gt;dBi is dimensionless; it represents decibels relative to an isotropic radiator.&lt;/p&gt;&#xA;&lt;p&gt;Values given in &amp;quot;dBm&amp;quot;, &amp;quot;dBW&amp;quot;, &amp;quot;dBV&amp;quot;, etc. are dimensioned values, given as decibels &lt;em&gt;relative to some specific unit&lt;/em&gt;. 0 dBm = 1 milliwatt, 0 dBW = 1 watt, 0 dBV = 1 volt, etc.; and e.g. 20dBm = 100 mW.&lt;/p&gt;&#xA;&lt;p&gt;Keeping this in mind, it should be clear how you can and can't mix these units. If you add dB and dB, the result is dB. If you add dB and a dimensioned value, the result has the same unit. If you subtract two dB values with the same unit, the result is plain dB.&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;13dBm + 3dB = 16dBm&amp;quot; is okay; this is the same statement as &amp;quot;20mW * 2 = 40mW&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;16dBm - 10dBm = 6dB&amp;quot; is okay; this is the same statement as &amp;quot;40mW / 10mW = 4&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;10dBm + 3dBm = ???&amp;quot; isn't okay; this is equivalent to &amp;quot;10mW * 2mW = ???&amp;quot; (okay, it's 20 mW^2, but what's the physical significance of a square milliwatt?)&lt;/p&gt;&#xA;&lt;p&gt;And since &amp;quot;dBi&amp;quot; is dimensionless, you can use it the same as you would &amp;quot;dB&amp;quot;, but remember that adding a dBi figure is &amp;quot;taking into account antenna gain&amp;quot; (e.g. 50dBm input power + 15dBi gain = 65dBm EIRP) and subtracting a dBi figure is the inverse operation.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-11-25T22:35:44.380" LastActivityDate="2020-11-25T22:35:44.380" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17593" PostTypeId="2" ParentId="17591" CreationDate="2020-11-07T01:28:30.867" Score="2" Body="&lt;p&gt;A decibel (dB) expresses a ratio. So:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ -35\:\mathrm{dB} = 10^{-35/10} = 0.0003162 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is a dimensionless number. Maybe it's the ratio of input power to output power, or something like that.&lt;/p&gt;&#xA;&lt;p&gt;A dBm expresses a ratio relative to 1 milliwat. So:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 20\:\mathrm{dBm} = 10^{20/10} \times 1\:\mathrm{mW} = 100\:\mathrm{mW} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;When you do:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 20\:\mathrm{dBm} - 35\:\mathrm{dB} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;this is equivalent to:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 10^{20/10} \times 1\:\mathrm{mW} \times 10^{-35/10} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Which is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ 100\:\mathrm{mW} \times 0.0003162 = 0.03162\:\mathrm{mW} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;dBm can't be converted to dB any more than 100 mW can be converted to 100 (no unit); doing so would be &lt;a href=&quot;https://en.wikipedia.org/wiki/Dimensional_analysis&quot; rel=&quot;nofollow noreferrer&quot;&gt;dimensionally  inconsistent&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Adding (or subtracting) decibels is equivalent to multiplying (or dividing) ratios because:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ b^c \times b^d = b^{c+d} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;and,&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \log(xy) = \log(x) + \log(y) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Multiplying a number in watts by a dimensionless number yields a number in watts. Likewise, adding or subtracting dB to dBm yields a number in dBm.&lt;/p&gt;&#xA;&lt;p&gt;dBi is a bit unusual because you might think the &amp;quot;i&amp;quot; at the end implies some dimension, but dBi expresses a ratio of antenna gain relative to an isotropic radiator. And the gain of an isotropic radiator is just 1 (dimensionless) by definition, so dBi are also dimensionless.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-07T01:28:30.867" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17594" PostTypeId="1" AcceptedAnswerId="17602" CreationDate="2020-11-07T03:03:56.647" Score="2" ViewCount="157" Body="&lt;p&gt;I just got all the parts to make a simple AM transmitter from &lt;a href=&quot;https://scitoys.com/scitoys/scitoys/radio/am_transmitter.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Scitoys&lt;/a&gt;. I followed the instructions from different websites and they still don't work. I don't know why it's not working. On my breadboard, the power rail is working. I used a multimeter to test various parts of the circuit. The transformer seems to work. There is some resistance with ohms. I don't hear anything on my AM receiver. Where do I even begin?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/G7hqA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/G7hqA.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/uQSVp.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/uQSVp.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18005" LastEditorUserId="8717" LastEditDate="2020-11-09T21:29:41.907" LastActivityDate="2020-11-10T02:42:45.030" Title="Simple AM Radio Troubleshooting" Tags="&lt;diy&gt;&lt;transmitter&gt;&lt;am&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17595" PostTypeId="2" ParentId="17585" CreationDate="2020-11-08T03:45:51.890" Score="0" Body="&lt;p&gt;One thing most certain is that you need a directional antenna (most popular is Yagi). They are pretty easy and cheap to build and will help tremendously because you can triangulate the signal.&lt;/p&gt;&#xA;&lt;p&gt;The remaining answer depends how much money you want to spend. The cheapest would probably be a $20 RTL SDR dongle (if you have a laptop). Many people use an actual radio transceiver and look at the signal level, but those can be expensive. There are other solutions too but they will take more time and experience to implement, so I'm giving you the simple and most straight-forward methods.&lt;/p&gt;&#xA;&lt;p&gt;Once you get close to the signal your signal strength meter may start to max out so for this reason you may need to attenuate the input, which you can also build yourself with resistors.&lt;/p&gt;&#xA;" OwnerUserId="17896" LastActivityDate="2020-11-08T03:45:51.890" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17596" PostTypeId="1" CreationDate="2020-11-08T14:18:54.600" Score="0" ViewCount="192" Body="&lt;p&gt;I have 2 Baofeng bt-888 radios coming out of the box. The problem is that the radios still growl on all channels and the light stays green. Le Griche stops when we send a communication or when we receive one. I have already tried to clone the radios with another one that I have that works fine without success.&lt;/p&gt;&#xA;&lt;p&gt;Original French:&lt;/p&gt;&#xA;&lt;p&gt;Bonjour j'ai 2 radios Baofeng bt-888 qui sorte de la boite. Le problème est que les radios griche toujours sur tout les canaux et la lumière reste verte. Le Griche arrête lorsque nous envoyons un communication ou lorsque nous en recevons une. J'ai déjà essayer de cloné les radios avec un autre que j'ai qui fonctionne très bien sans succès.&lt;/p&gt;&#xA;" OwnerUserId="18073" LastEditorUserId="8717" LastEditDate="2020-11-09T00:04:11.617" LastActivityDate="2020-12-15T07:07:55.940" Title="Problem with Baofeng BF-888 radios" Tags="&lt;baofeng&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17597" PostTypeId="1" CreationDate="2020-11-08T23:41:47.733" Score="2" ViewCount="116" Body="&lt;p&gt;Contemplating a big &lt;strong&gt;magnetic loop&lt;/strong&gt; antenna.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Would a wide copper &lt;strong&gt;strip&lt;/strong&gt; be better than a &lt;strong&gt;tube&lt;/strong&gt; with the same conducting surface?&lt;/li&gt;&#xA;&lt;li&gt;&lt;strong&gt;Where&lt;/strong&gt; will all the current be due to the skin effect?&lt;/li&gt;&#xA;&lt;li&gt;Would a &lt;strong&gt;flat&lt;/strong&gt; ring be better or a &lt;strong&gt;wide&lt;/strong&gt; ring, when looking at the broad side of antenna?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Ohmic loss is very important for this type of antenna.&#xA;(Interested, because new design from DL5MCC &lt;a href=&quot;http://www.dl5mcc.de/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.dl5mcc.de/&lt;/a&gt; does not need high voltage variable capacitor.)&lt;/p&gt;&#xA;&lt;p&gt;By &amp;quot;big&amp;quot; i meant at least 2 meter diameter.&lt;/p&gt;&#xA;" OwnerUserId="17953" LastEditorUserId="17953" LastEditDate="2020-11-09T12:01:20.320" LastActivityDate="2020-11-11T16:35:56.097" Title="Magnetic loop antenna: Which side of conductor is the current due to skin effect?" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;magnetic-loop&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17599" PostTypeId="2" ParentId="17597" CreationDate="2020-11-09T01:30:37.360" Score="1" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;On a &lt;em&gt;closed&lt;/em&gt; tube, the current only flows on the &lt;em&gt;outside&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;On a strip, the current flows on &lt;em&gt;both sides&lt;/em&gt;. It might not be equally distributed, but I don't believe that there is enough difference between the current density between the center and the edges to matter.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2020-11-09T01:30:37.360" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17600" PostTypeId="2" ParentId="17597" CreationDate="2020-11-09T12:51:56.707" Score="0" Body="&lt;p&gt;For a theoretical answer to the first two questions, the skin effect is caused by magnetic fields generated by the currents repelling each other, so the current flows as far away from current of the same direction as it can get.  The overall result spreads the current out over the entire outer surface, with an exponential weakening of the current as you go deeper in, which is described as skin depth or penetration depth.  All of this is frequency dependant and there is corresponding math to describe it.  (Conductivity and magnitivity of the alloy also affect this.)&lt;/p&gt;&#xA;&lt;p&gt;For the third answer, articles I've read from Cebik lead me to believe it generally doesn't matter what orientation flat strips are in as long as it isn't folded or layered or something like that.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-11-11T16:35:56.097" LastActivityDate="2020-11-11T16:35:56.097" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17601" PostTypeId="2" ParentId="17585" CreationDate="2020-11-09T16:27:21.810" Score="1" Body="&lt;p&gt;For the purpose of this answer, I'll lump interesting unknown signals and RFI together and call them &amp;quot;mysterious signals&amp;quot;, since the techniques for finding where they come from are often the same.  Some of the techniques listed below may not work for all bands and power levels.&lt;/p&gt;&#xA;&lt;p&gt;Often it would help to know how local the mysterious signal is.  If you can ask another operator (or an automated receiver connected to the internet) to listen to the signal, then that might help; if the signal can be heard some distance away, then its origin may not be local.  Of course line-of-sight and other range issues make this technique more practical at some bands and power levels than others.&lt;/p&gt;&#xA;&lt;p&gt;Some mysterious signals could be spurious, generated by your own station, or even inside your receiver.  Receivers, computers, switching power supplies, and other station equipment are full of oscillators, and sometimes these oscillators are heard in a receiver, in which case they are called &amp;quot;birdies&amp;quot; or &amp;quot;spurs&amp;quot;.  &lt;a href=&quot;https://ham.stackexchange.com/search?q=birdies&quot;&gt;Birdies&lt;/a&gt; are often unmodulated sine waves, but if the source of the birdie is a digital signal, then it may not be just a pure sine wave.  If the receiver is self-contained (not connected to a computer), is being powered by a battery, and is connected to a dummy load, then the signal you're hearing is probably a birdie.  (A receiver connected to a dummy load can sometimes pick up strong external signals, because coaxial cable shielding isn't perfect.)&lt;/p&gt;&#xA;&lt;p&gt;Another source of spurious signals is &lt;a href=&quot;https://en.wikipedia.org/wiki/Intermodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;intermodulation&lt;/a&gt;, often called &amp;quot;intermod&amp;quot; or intermodulation distortion (IMD), which is caused by the unintentional mixing of two or more signals and/or their harmonics.  Intermod is sometimes generated inside a receiver, for instance when a strong signal inside the receiver's passpand gets sent to a mixer in a superheterodyne receiver.  Any nonlinear device can act as a mixer, whether it's in a radio or not, and sometimes the nonlinear device is two different metals touching that are exposed to RF, such as an aluminum gutter touching a steel pipe.  The RF signals generally must be strong to generate noticeable intermod from just two pieces of metal touching.  If you suspect intermod from inside your receiver, check to see if there are very strong signals inside the passband, and then see if the mysterious signal is still there when the strong signals go away.&lt;/p&gt;&#xA;&lt;p&gt;Then of course there is plain old distortion, caused by too much gain in an amplifier stage of the receiver.  Distortion is at least easy to troubleshoot: if reducing the gain or adding attenuation makes the mysterious signal go away, then it's probably distortion.&lt;/p&gt;&#xA;&lt;p&gt;A good way to check if a mysterious signal is spurious and generated inside the receiver is to try a different receiver, preferably of a different type.&lt;/p&gt;&#xA;&lt;p&gt;In the modern era when we are surrounded by more and more electronic equipment, often mysterious signals are generated from other equipment in the same house or building.  Troubleshooting these can be simple: switch off circuit breakers, or unplug equipment from mains power, and if the mysterious signal suddenly disappears, then it probably was generated by a piece of equipment that had its power interrupted.&lt;/p&gt;&#xA;&lt;p&gt;If you suspect that the mysterious signal comes from a neighboring property, and if you are on very good terms with your neighbor, perhaps he or she will let you switch things off to see if the mysterious signal stops.&lt;/p&gt;&#xA;&lt;p&gt;If you believe that the mysterious signal is real, and not coming from equipment you can disconnect from power, then it's time for other troubleshooting techniques.&lt;/p&gt;&#xA;&lt;p&gt;If you have a portable receiver with a signal strength indicator (sometimes just &amp;quot;full of static&amp;quot; vs &amp;quot;clear&amp;quot; is good enough) and a portable antenna, which doesn't necessarily need to be directional, then you can go looking for nearby sources of a mysterious signal.  In the simplest case, if the signal strength goes up when you are moving around, then you are getting closer to the transmitter or antenna.  But be aware that radio signals can reflect off objects (mountains, hills, buildings, vehicles, trees, etc.) or refract around them.  It's common for a radio signal to not be coming from the direction of the transmitter or antenna.  But if you can rove around the entire area where the mysterious radio signal might be coming from, then the signal is probably strongest near the transmitter or antenna.&lt;/p&gt;&#xA;&lt;p&gt;You might experience the problem that near the transmitter the receiver's signal strength indicator reads maximum whichever way you go, which prevents you from finding the exact location of the transmitter.  In that case the solution is an attenuator.  Sometimes traditional attenuators don't have enough attenuation, because leakage around the attenuator is still strong enough to cause a maximum signal strength reading in the receiver.  In that case an offset attenuator can sometimes help.  An offset attenuator is a simple circuit, often home-brewed, that mixes the signal with a local oscillator to produce a mixed signal near the original signal, but not so close as to be in the receiver's passband with the original signal.  The receiver is then tuned to the mixed signal rather than the original signal.  The strength of the mixed signal can be easily reduced by reducing the strength of the local oscillator.  In that way an offset attenuator can inexpensively permit more attenuation than a traditional attenuator.&lt;/p&gt;&#xA;&lt;p&gt;If the portable station has a directional antenna, then that often allows a portable station to find the transmitter or antenna more quickly.  Often an antenna doesn't need to be very directional to be helpful.  Sometimes just using one's own body as an attenuator between the transmitter and the receiving antenna can give some idea which way the transmitter is.&lt;/p&gt;&#xA;&lt;p&gt;If the mysterious signal's transmitter is too far away to rove around, or if the receiver or its antenna isn't portable, then all may not be lost.  Directional antennas can give an idea of the direction of the transmitter.  Ideally, several stations working together can triangulate the approximate location of the transmitter.  Unfortunately this technique often doesn't work as well as it does in movies, because many directional antennas have very broad lobes, and because the radio signal may have been reflected or refracted.  Or the signal may be arriving from several directions simultaneously, which are also interfering constructively or destructively, a situation known as &lt;a href=&quot;https://en.wikipedia.org/wiki/Multipath_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;multipath interference&lt;/a&gt;, which can make determining the direction of the transmitter difficult.  So sometimes triangulation doesn't work very well.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-11-09T16:27:21.810" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17602" PostTypeId="2" ParentId="17594" CreationDate="2020-11-10T02:42:45.030" Score="1" Body="&lt;p&gt;I'm not sure how to give proper credit but I figured it out with your help. I'd like to thank all of you for helping me. It really means a lot even though it was a bit rough. Don't push away newcomers. But anyways you've all been a great help! Each one of you gets two brownies.&lt;/p&gt;&#xA;&lt;p&gt;The issue was the oscillator. Either it was dead on arrival or scitoys misspoke on the proper voltage. The new one megahertz crystal full can oscillator I got off of Amazon requires 5 volts. I put three AA batteries together and my AM receiver went instantly quiet. I knew it was transmitting something and I was so excited. I hooked up my phone to play some music and I was blown away at the quality. It sounded way better than I expected. I'm actually kind of shocked at how good it is.&lt;/p&gt;&#xA;&lt;p&gt;This is my first step in making a super awesome AM radio. The next steps for me are creating different modules to create the best signal possible for output. The modulator, amplifier, and antenna design.&lt;/p&gt;&#xA;" OwnerUserId="18005" LastActivityDate="2020-11-10T02:42:45.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17604" PostTypeId="2" ParentId="13085" CreationDate="2020-11-14T21:08:28.553" Score="0" Body="&lt;p&gt;I was able to use Baofeng's VIP software to program independent RX and TX frequencies so you don't have to do it manually for every single one. (I have a BF-F8HP).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://baofengtech.com/download&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://baofengtech.com/download&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;(Windows only)&lt;/p&gt;&#xA;&lt;p&gt;I have Windows 7 (it's an old laptop) so I had to download some drivers for my FTDI USB cable: &lt;a href=&quot;https://www.ftdichip.com/Drivers/VCP.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ftdichip.com/Drivers/VCP.htm&lt;/a&gt; (I used the Windows* one that was listed first)&lt;/p&gt;&#xA;&lt;p&gt;Curiously, when I downloaded to the laptop the current radio state on VIP my previously programmed in repeater channels using CHIRP uploaded with correct RX and TX offsets, even though they weren't showing up on the radio before when I switched between normal and reverse mode via the */SCAN key.&lt;/p&gt;&#xA;&lt;p&gt;I then reuploaded the same settings to the radio and now when I switch between normal and reverse mode (RX freq is shown in normal mode in channel mode, TX freq is shown in reverse mode in channel mode) I see the correct frequency offsets!&lt;/p&gt;&#xA;&lt;p&gt;The Baofeng VIP software isn't that easy to use and is not translated well, but you can figure it out if you experiment.&lt;/p&gt;&#xA;" OwnerUserId="18102" LastActivityDate="2020-11-14T21:08:28.553" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17605" PostTypeId="1" CreationDate="2020-11-14T23:08:10.343" Score="0" ViewCount="92" Body="&lt;p&gt;I have a Kenwood TH-F7E handheld transceiver, bought second-hand a bit less than a year ago. Until about 3 weeks ago, it worked perfectly, then I put it in a drawer and didn't touch it until yesterday, when I noticed that it didn't switch on on battery power, and the charge light didn't come on when plugged in. Here's what I've found out so far:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;I measured the voltage between the battery terminals as 0 volts, so my first thought was the battery had simply gone bad. The battery is a PB-42L Li-Ion pack.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;However, there are also some signs of a problem with the transceiver. When the mains adapter is plugged in, the receiver seems to work normally, but the device heats up a lot after a couple of minutes. This happens even if I remove the battery pack.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;With the mains adapter plugged it, I can transmit with extra-low (0.5 W) or low (2 W) power. In the high-power setting (5 W), the transceiver restarts as soon as I hit PTT.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I tried connecting a 7 V power supply directly to the battery terminals of the transceiver and noticed that it draws 900 mA &lt;em&gt;even while turned off&lt;/em&gt;. I immediately disconnected the power again, without any testing, when I noticed that.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I've found the &lt;a href=&quot;http://www.fracassi.net/iw2ntf/manuali/kenwood_th-f6_th-f7_serv.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;service manual&lt;/a&gt; and was planning to open it up to figure out what exactly is producing the excess heat and make some measurements, but I was hoping to get some advice on how to troubleshoot this before I start digging around in the transceiver.&lt;/p&gt;&#xA;" OwnerUserId="17321" LastActivityDate="2020-11-15T11:40:54.530" Title="Kenwood TH-F7E power supply troubleshooting" Tags="&lt;kenwood&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17607" PostTypeId="2" ParentId="17596" CreationDate="2020-11-15T06:15:40.687" Score="1" Body="&lt;p&gt;It looks like the problem is that the squelch is &amp;quot;open,&amp;quot; so that any weak signal is let in and heard. The squelch needs to be increased, using software, so that you can only hear signals that are strong enough.&lt;/p&gt;&#xA;&lt;p&gt;I don't have this radio, so my answer might not be completely correct.&lt;/p&gt;&#xA;&lt;p&gt;In &lt;a href=&quot;https://www.youtube.com/watch?v=S1yiaNhU38g&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; video (I know that it's English, but hopefully it has useful information), at around 1 minute and 55 seconds, the software used to program the radio is shown. What you're looking for is &amp;quot;Squelch Level&amp;quot; (see original English) near the top and center of the program window. I don't know exactly what to set this to, but you should try to set it low enough that you hear strong signals but not constant noise.&lt;/p&gt;&#xA;&lt;p&gt;I hope this helps. I've tried to use words that the translator program will translate correctly.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Bonjour,&lt;/p&gt;&#xA;&lt;p&gt;Il semble que le problème soit que le silencieux est «ouvert», de sorte que tout signal faible est laissé entrer et entendu. Le silencieux doit être augmenté, à l'aide d'un logiciel, de sorte que vous ne puissiez entendre que des signaux suffisamment puissants.&lt;/p&gt;&#xA;&lt;p&gt;Je n'ai pas cette radio, donc ma réponse n'est peut-être pas tout à fait correcte.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=S1yiaNhU38g&quot; rel=&quot;nofollow noreferrer&quot;&gt;Dans cette vidéo&lt;/a&gt; (je sais que c'est en anglais, mais j'espère qu'elle contient des informations utiles), à environ 1 minute et 55 secondes, le logiciel utilisé pour programmer la radio est montré. Ce que vous recherchez est &amp;quot;Squelch Level&amp;quot; (en anglais) près du haut et au centre de la fenêtre du programme. Je ne sais pas exactement sur quoi régler cela, mais vous devriez essayer de le régler suffisamment bas pour entendre des signaux forts mais pas un bruit constant.&lt;/p&gt;&#xA;&lt;p&gt;J'espère que ça aide. J'ai essayé d'utiliser des mots que le programme de traduction traduira correctement.&lt;/p&gt;&#xA;" OwnerUserId="17328" LastActivityDate="2020-11-15T06:15:40.687" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17608" PostTypeId="2" ParentId="17605" CreationDate="2020-11-15T11:40:54.530" Score="1" Body="&lt;p&gt;I suspect you have a plastic brick.  Unless you have the skills at working on surface mount pcb, like a steady hand and good magnification lens  or video microscope, needle probes (easy to make)  and suitable soldering equipment repair of these tiny radios is quite difficult but not impossible.&lt;/p&gt;&#xA;&lt;p&gt;I prefer an old fashioned VOM like a Simpson 260 when troubleshooting for shorts and opens as there is no lag in a digital display count updating.  The meter needle instantly moves or it doesnt.  Also you are not looking for precise measurements at this point of troubleshooting.     So follow the schematic and probe accordingly following the circuit path from the external  charger and battery inputs, of course with all power off.  You dont want to fry your meter.    Since the radio draws high current with it turned off it should simplify locationing the short.  It has to be before the power switch.  Which means the charging circuit / jack/ battery  circuit paths.&#xA;And always double check the the setup you used to determine your initial findings of current draw under the various input and battery connection scenarios. In other words, start over.   And document each step as you go.    It often helps to develop a fault tree when before troubleshooting complex problems.  It will keep you on track in a orderly and sequential manner of troubleshooting, so that your not guessing and randomly probing around, although many problems have been solved by random probing.&lt;/p&gt;&#xA;" OwnerUserId="18104" LastActivityDate="2020-11-15T11:40:54.530" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17609" PostTypeId="1" CreationDate="2020-11-16T22:36:47.583" Score="1" ViewCount="50" Body="&lt;p&gt;I'm in the process of planning a UHF CB radio repeater. And I've heard there are ones around that  transmit a voice message/warning on their input frequency (as well as standard output channel ident) to warn/nag people against using the input in simplex mode without knowing/caring.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;How would this be done, and how would your diplexer/cavity setup affect this?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I'm guessing it would mean you are blocking your repeater input while this happens?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Does this feature exist in commercial off the shelf products?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="17758" LastEditorUserId="4076" LastEditDate="2020-11-17T13:25:18.150" LastActivityDate="2020-11-17T13:25:18.150" Title="Repeater transmit voice message/warning on input frequency?" Tags="&lt;repeater&gt;&lt;citizens-band&gt;&lt;duplexer&gt;&lt;australia&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17610" PostTypeId="1" AcceptedAnswerId="17611" CreationDate="2020-11-17T13:04:45.320" Score="0" ViewCount="81" Body="&lt;p&gt;Just moved from SoCal and there were sites out there for exchanging code plugs for the Anytone 878uv.  I was wondering if there are similar sites for the northeast of the US.  I would love to get a basic set to start the process.&lt;/p&gt;&#xA;" OwnerUserId="18112" LastEditorUserId="8717" LastEditDate="2020-11-18T01:46:10.833" LastActivityDate="2020-11-18T01:46:10.833" Title="DMR code plug for Anytone d878uv" Tags="&lt;united-states&gt;&lt;dmr&gt;&lt;anytone&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17611" PostTypeId="2" ParentId="17610" CreationDate="2020-11-17T18:27:29.310" Score="1" Body="&lt;p&gt;I did a web search for &amp;quot;new york code plugs&amp;quot; and found a bunch from various sites:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.cidcomm.com/codeplugs/&quot; rel=&quot;nofollow noreferrer&quot;&gt;N2CID Digital Repeater Network&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://hvdn.org/%2B-dmr-code-plugs&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hudson Valley Digital Network&lt;/a&gt; no Anytone plugs yet&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.bridgecomsystems.com/pages/new-york&quot; rel=&quot;nofollow noreferrer&quot;&gt;BridgeCom Systems&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I also found some for surrounding areas:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://nedecn.org/downloads/codeplugs/&quot; rel=&quot;nofollow noreferrer&quot;&gt;New England Digital Emergency Communications Network&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://frederickarc.org/codeplugs/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Frederick Amateur Radio Club&lt;/a&gt; in Frederick, Maryland&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Your local ham club can probably hook you up with some.  Make your own and share!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-11-17T18:27:29.310" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17612" PostTypeId="1" CreationDate="2020-11-17T18:38:36.473" Score="1" ViewCount="104" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hPklQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hPklQ.png&quot; alt=&quot;40 MHz crystal Oscillator for VHF Fm transmitter&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I am working on a project designing a 40 MHz radio transmitter, but I need some clarifications. I need to know how to calculate its output impedance.&lt;/p&gt;&#xA;&lt;p&gt;I know how to calculate common collector's output impedance, but this circuit has 2 capacitors (C2,C3=100pF) in series which are connected to the emitter.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;What will be the &lt;strong&gt;output impedance&lt;/strong&gt;, and how will I &lt;strong&gt;calculate&lt;/strong&gt; it? I need the specific formula for it if I change those capacitors somehow.&lt;/li&gt;&#xA;&lt;li&gt;I also want to know how to calculate its output voltage, because I will connect this circuit with a &lt;strong&gt;buffer&lt;/strong&gt; to amplify its power.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16001" LastEditorUserId="8717" LastEditDate="2020-11-18T01:38:18.677" LastActivityDate="2020-11-18T10:20:26.220" Title="Crystal Oscillator Output Impedance and Output Voltage" Tags="&lt;impedance&gt;&lt;equipment-design&gt;&lt;voltage&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17615" PostTypeId="2" ParentId="17612" CreationDate="2020-11-17T23:02:05.403" Score="2" Body="&lt;p&gt;The output impedance is not that important: the (lowest) allowed load impedance is important. And the assumption is right: from the output impedance it is possible to calculate the effect of load on the output voltage. But be aware of frequency deviation as a function of load variation, and also eventual stop of oscillation with serious load.&lt;/p&gt;&#xA;&lt;p&gt;This is not a linear circuit that can be described only with its output impedance. Insert an impedance buffer when using the signal. And indeed: the effect of the buffer rises the same question, but at a different level.&lt;/p&gt;&#xA;&lt;p&gt;Your question is the output impedance. It is an emitter follower with a resonant circuit. Put it in a simulator. I guess it will be a few hundred Ohm's or lower.&#xA;PA0FSB&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2020-11-18T10:20:26.220" LastActivityDate="2020-11-18T10:20:26.220" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17616" PostTypeId="1" AcceptedAnswerId="17627" CreationDate="2020-11-19T02:04:07.613" Score="3" ViewCount="177" Body="&lt;p&gt;I'm brainstorming methods of mounting an EFHW. Unfortunately, I have no trees, so I'm considering a horizontal gutter mount which would afford me about 70 feet. Is this workable or should I consider a telescopic mast like a spiderbeam instead?&lt;/p&gt;&#xA;" OwnerUserId="16274" LastEditorUserId="8717" LastEditDate="2020-11-21T03:30:17.323" LastActivityDate="2020-11-23T17:16:19.993" Title="horizontal EFHW antenna attached to gutter" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;antenna-system&gt;&lt;efhw&gt;" AnswerCount="2" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="17617" PostTypeId="1" CreationDate="2020-11-19T12:14:38.840" Score="1" ViewCount="82" Body="&lt;p&gt;I want to adapt the DVB-T AverMedia TV Pilot&amp;quot; tuner as a software defined radio, but it is not built on a RTL chip, so the question arises, is there some kind of driver to use my tuner as a radio?&lt;a href=&quot;https://i.stack.imgur.com/yqMkk.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yqMkk.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18124" LastEditorUserId="18124" LastEditDate="2020-11-19T12:22:04.860" LastActivityDate="2020-11-28T08:18:46.200" Title="Adapt old AvermediaTV DVB-T tuner as SDR" Tags="&lt;rtl-sdr&gt;&lt;sdrsharp&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17618" PostTypeId="1" AcceptedAnswerId="17619" CreationDate="2020-11-20T07:36:04.877" Score="0" ViewCount="365" Body="&lt;p&gt;I have a Baofeng UV-5R with stock and a Nagoya 701 (maybe fake?) antennas and wonder how I can receive voice from ISS astronauts? Do they have a schedule for going on air?&lt;/p&gt;&#xA;&lt;p&gt;I live in Romania so probably I have more chance receiving signals for Russian headquarters.&lt;/p&gt;&#xA;" OwnerUserId="18125" LastEditorUserId="17676" LastEditDate="2020-11-21T01:10:58.633" LastActivityDate="2020-12-16T22:24:43.157" Title="How can you receive ISS broadcast using a Baofeng?" Tags="&lt;baofeng&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17619" PostTypeId="2" ParentId="17618" CreationDate="2020-11-20T11:45:33.890" Score="2" Body="&lt;p&gt;Frequency 145825 kHz FM when ISS is within 800 km from your geographical position. That corresponds with visual line between ISS and your location.&lt;/p&gt;&#xA;&lt;p&gt;Normal transmission is digital (FSK) and very sporadic you can hear voice. Doppler effect on frequency requires tuning of plus and minus 3.5 kHz (2.5 or 5 kHz) higher and/or lower frequency.&lt;/p&gt;&#xA;&lt;p&gt;Position of the ISS can be found here: &lt;a href=&quot;https://www.astroviewer.net/iss/en/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.astroviewer.net/iss/en/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Forecast for ISS pass-over for your location can be found on &lt;a href=&quot;http://www.heavens-above.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;www.heavens-above.com&lt;/a&gt; (do not forget to set your location!).&lt;/p&gt;&#xA;&lt;p&gt;Communication with ISS requires minus 600 kHz TX offset: TX on 145.225 Mhz.&lt;/p&gt;&#xA;&lt;p&gt;Fake antenna Nagoya 701 analysis: &lt;a href=&quot;https://www.youtube.com/watch?v=lrcY7adFBbw&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=lrcY7adFBbw&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Succes,&lt;/p&gt;&#xA;&lt;p&gt;PA0FSB&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2020-11-20T12:20:21.217" LastActivityDate="2020-11-20T12:20:21.217" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17621" PostTypeId="1" AcceptedAnswerId="17626" CreationDate="2020-11-21T01:06:40.260" Score="3" ViewCount="261" Body="&lt;p&gt;I found this old log periodic antenna that I assume was from a TV. Could I, or how would I, use this on the amateur radio bands? My main focus would be VHF, with UHF being secondary and HF would also be nice. I'd like to keep it as cheap as possible.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zaIEl.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zaIEl.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Largest: 4' 5&amp;quot; (134.62 cm) - seems to be electrically connected to form a 8' 10&amp;quot; element?&lt;/p&gt;&#xA;&lt;p&gt;smallest: 5&amp;quot; (12.7 cm) (unfolds to be parallel with another 5&amp;quot; element)&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;Other&amp;quot; smallest: 6&amp;quot; (15.24 cm) (by itself)&lt;/p&gt;&#xA;" OwnerUserId="17328" LastEditorUserId="17328" LastEditDate="2020-11-21T04:42:05.680" LastActivityDate="2020-11-22T01:57:19.810" Title="Use (TV?) Log-Periodic antenna for VHF" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;vhf&gt;" AnswerCount="3" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17622" PostTypeId="2" ParentId="17618" CreationDate="2020-11-21T01:09:47.767" Score="1" Body="&lt;p&gt;I have a UV-5R with the stock antenna. I've been able to successfully listen to astronaut contacts with schools on 144.825 MHz and to the new cross-band voice repeater downlink on 437.800 MHz. You need to find out when the various modes are active. (The voice repeater worked for a couple of weeks then went off-air.)&lt;/p&gt;&#xA;&lt;p&gt;I use the Android app version of the &lt;a href=&quot;https://www.heavens-above.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;heavens-above&lt;/a&gt; website to tell me when the ISS is within range and the ISS Now app by VKL Apps for an easier display of where the ISS is when out of range as well as various space and launch videos. (Other apps exist but I haven't tried them.)&lt;/p&gt;&#xA;" OwnerUserId="15924" LastActivityDate="2020-11-21T01:09:47.767" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17623" PostTypeId="1" AcceptedAnswerId="17640" CreationDate="2020-11-21T01:30:50.200" Score="2" ViewCount="169" Body="&lt;p&gt;My brother and I are considering designing and building a remotely controlled submarine. As far as experience, I have some knowledge on RC systems, and I am almost done with my General license. My brother hasn't completed his license yet, but shares much of my experience.&lt;/p&gt;&#xA;&lt;p&gt;The problem we're facing is getting a live video feed/FPV from the craft while under fresh water. We don't need great range, just enough to get down 10-15 feet vertically, maybe (though more would be much better, of course). Our &lt;em&gt;goal&lt;/em&gt; is for it to be completely wireless, avoiding having some type of umbilical cord.&lt;/p&gt;&#xA;&lt;p&gt;The question is, &lt;strong&gt;how low frequency can you go so that it is not absorbed, but intelligible enough to maintain (visual) control the craft at as low as around, say, one frame per second?&lt;/strong&gt; I don't need amazing reaction speed like you'd need with a quadcopter.&lt;/p&gt;&#xA;&lt;p&gt;Next would be finding what frequencies you can legally transmit this on (I think this would be classified as &amp;quot;remote vehicle control&amp;quot;?), and where to get equipment for it. (We haven't even gotten here yet, but when we do, I'd like it to stay under $500.)&lt;/p&gt;&#xA;&lt;p&gt;Edit - so far, there are a few options I'm keeping in mind, along with others' advice (I'll accept the answer that I think most resembles the original idea):&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Physical cable&lt;/li&gt;&#xA;&lt;li&gt;Surface floating &amp;quot;buoy&amp;quot; antenna&lt;/li&gt;&#xA;&lt;li&gt;long antenna to surface (similar to last option)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="17328" LastEditorUserId="17328" LastEditDate="2020-11-22T22:37:50.657" LastActivityDate="2020-11-23T21:40:49.520" Title="Transmitting Video Underwater" Tags="&lt;theory&gt;&lt;remote-control&gt;&lt;sstv&gt;&lt;automation&gt;&lt;atv&gt;" AnswerCount="3" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17624" PostTypeId="2" ParentId="17621" CreationDate="2020-11-21T02:40:48.903" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://en.m.wikipedia.org/wiki/Log-periodic_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;Log-periodic antennas&lt;/a&gt; have a very wide bandwidth. One designed for TV would not work at HF, but it may very well work on 2 meters, 6 meters, and some UHF amateur bands.&lt;/p&gt;&#xA;&lt;p&gt;I suggest that you measure the SWR and see. However, unless its impedance is 50 to 75 ohms, you will need a suitable matching device.&lt;/p&gt;&#xA;&lt;p&gt;Can you post photos of it? While you're at it, include the minimum and maximum lengths of the elements.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;Countless hams have used TV log-periodic antennas on the ham bands, and with little or no modifications.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-11-21T04:14:15.567" LastActivityDate="2020-11-21T04:14:15.567" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17625" PostTypeId="2" ParentId="16335" CreationDate="2020-11-21T03:47:46.920" Score="1" Body="&lt;p&gt;I'm posting this answer —by someone else— below. I'm &lt;em&gt;assuming&lt;/em&gt; that it's a good one.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;You CAN assign a button to switch between Name and Frequency.&lt;/p&gt;&#xA;&lt;p&gt;Menu/Settings/Radio Set/(choose key like PF3 Long Press)/Ch.Name — When pressed, it will alternate between Frequency and Name on the display.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;Per Thomas's comment, this required a firmware update to v. 1.21 to work.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-11-22T22:32:31.090" LastActivityDate="2020-11-22T22:32:31.090" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17626" PostTypeId="2" ParentId="17621" CreationDate="2020-11-21T05:38:55.570" Score="6" Body="&lt;p&gt;I'm sorry to say that's not a simple log-periodic antenna, it's a hybrid monstrosity to meet some particular need.&lt;/p&gt;&#xA;&lt;p&gt;Guessing from the element lengths:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;136 cm each side would work at about 50 MHz, so &lt;strong&gt;low-band TV&lt;/strong&gt;. Two-element log-P with a reflector. OK.&lt;/li&gt;&#xA;&lt;li&gt;12 cm each side would work at about 550 MHz, so &lt;strong&gt;mid UHF TV&lt;/strong&gt;. Some sort of Yagi&lt;/li&gt;&#xA;&lt;li&gt;15 cm total would be a director for about 900 MHz, so the &lt;strong&gt;top end of UHF TV&lt;/strong&gt;.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;It doesn't seem to cover the VHF ham band, and it probably only starts working above the 440 MHz ham band.&lt;/p&gt;&#xA;&lt;p&gt;You could probably re-use the mounting and feed hardware, cut the feed down to work at 145 MHz, and then install new directors to give it some gain. But you are basically building a new yagi, and with very non-ideal director spacing.&lt;/p&gt;&#xA;&lt;p&gt;If you need a directional antenna (for satellites?) rather build a new yagi from scratch. You can make a nice one in a few hours with some bits of brazing rod and a broomstick.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-11-21T05:38:55.570" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17627" PostTypeId="2" ParentId="17616" CreationDate="2020-11-21T15:13:25.173" Score="2" Body="&lt;p&gt;My gutter antenna experiments revealed that the gutter (metal of course!) itself can be used as end-fed half-wave antenna on the self resonance frequency. The efficiency is poor: the losses to conducting environment are very high, even with dry weather.&lt;/p&gt;&#xA;&lt;p&gt;For reception such antenna can be used, but all the interference generated in the house is coupled to the antenna: the counterpoise is electrically polluted and this interference is in series with the received signal. When used as TX antenna the losses are high and the impedance must be matched to off-resonance frequencies.&lt;/p&gt;&#xA;&lt;p&gt;Even with a poor antenna it is possible to make radio contacts. When possible: use a separate wire with a resonating length and then the end of the antenna must be spaced from the gutter: the antenna wire coupling to the gutter must be as low as possible.&lt;/p&gt;&#xA;&lt;p&gt;One of my experiments was a sloped half wave, starting anywhere in the middle of the gutter, and the gutter metal used as ground/counterpoise. The other end of the half wave (also a quarter wave works fine) free hanging to its end, only two meters high. With 10 meters wire and 10 watt power I had SSB QSO's with Canada an USA on 14 MHz.&lt;/p&gt;&#xA;&lt;p&gt;For RX: the induced noise from all electric interference generated in my home is present in the counterpoise (ground if you want to call it). In the same dimensions it must be possible to make a dipole with lower losses and lower interference when receiving. That is preferred.&#xA;PA0FSB&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-11-21T15:13:25.173" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17628" PostTypeId="2" ParentId="17623" CreationDate="2020-11-21T20:54:24.893" Score="2" Body="&lt;p&gt;Any antenna under water is creates a far more difficult problem than that of the main focus of the school project.&lt;/p&gt;&#xA;&lt;p&gt;I would put a WiFi transmitter (ESP32, et.al., inexpensive loss if drowned) on a float above the submersible, and run a fiber optic cable to transfer image files from the FPV camera (connected to say an inexpensive Raspberry Pi Zero that won't be a major financial loss if drowned) up to the floater.   That way the antenna can be up out of the water.  And most of the software needed to generate and transfer image files over WiFi is already available.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-11-21T20:54:24.893" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17629" PostTypeId="2" ParentId="17621" CreationDate="2020-11-22T01:57:19.810" Score="5" Body="&lt;p&gt;Those antennas are held together with aluminum pop rivets which are easily drilled out. In less than an hour you can completely disassemble a TV antenna like that and salvage the main mast, all the dipole elements, and the plastic element mounts- and use these and some fresh pop rivets and an electric drill to build yourself a two meter yagi beam with excellent performance, for which there are numerous plans available on the web.&lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2020-11-22T01:57:19.810" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17630" PostTypeId="1" AcceptedAnswerId="17638" CreationDate="2020-11-22T16:36:54.820" Score="1" ViewCount="92" Body="&lt;p&gt;I'm working on a project in microfluidics and it has become apparent that a significant challenge to overcome is a lack of consensus in connector design.&lt;/p&gt;&#xA;&lt;p&gt;I have been thinking about my time working with microwave filters and the fact that the vast majority of devices were connected to the VNA with SMA connectors.&lt;/p&gt;&#xA;&lt;p&gt;My question is, what was the driving force behind that design becoming the standard?&lt;/p&gt;&#xA;&lt;p&gt;Any insight or history would be appreciated.&lt;/p&gt;&#xA;" OwnerUserId="18133" LastActivityDate="2020-11-23T18:11:14.397" Title="How did SMA connector size become standard?" Tags="&lt;antenna-system&gt;&lt;connectors&gt;&lt;history&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17632" PostTypeId="2" ParentId="17549" CreationDate="2020-11-22T23:19:53.477" Score="1" Body="&lt;p&gt;Just adding to the previous answers. Many people, mostly preppers, throw a cheap Baofeng into their emergency kit or whatnot. Here's the problem with that: so many people have no idea how to use it. I'm almost done with my general license and I still have to use the internet o figure out how my new radios work. Not a bragging/insulting point, but rather showing the importance of knowing how your specific radio, and radios in general, work.&lt;/p&gt;&#xA;" OwnerUserId="17328" LastActivityDate="2020-11-22T23:19:53.477" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17633" PostTypeId="1" AcceptedAnswerId="17634" CreationDate="2020-11-22T23:50:12.970" Score="5" ViewCount="129" Body="&lt;p&gt;&lt;strong&gt;Situation:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;You  want to know when a satellite will pass in order to receive an image transmission or to work an amateur satellite. However, you cannot access internet for whatever reason, and therefore can't simply look up a pass prediction chart or live tracker.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Can you/how would you calculate approximately where a satellite would be at any given time, or calculate when the next pass would be? Do satellites always follow a scheduled path to repeat and cycle through? What basic orbit information should I collect about each satellite I need beforehand?&lt;/p&gt;&#xA;&lt;p&gt;Is the satellite always &lt;em&gt;actively&lt;/em&gt; kept in this exact timing, or does it slowly &amp;quot;drift&amp;quot; from its scheduled path? I ask this because if it does drift, this would eventually make any planning useless without direct connection to the satellite, if that makes any sense.&lt;/p&gt;&#xA;&lt;p&gt;A simple path/time map (like below) would be best, but (offline) software also works.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/T18kq.png3&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/T18kq.png3&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Edit - Do the satellites transmit data about their position that I would be able to receive and decode?&lt;/p&gt;&#xA;" OwnerUserId="17328" LastActivityDate="2020-12-02T13:21:20.277" Title="Calculating satellite passes without an internet tracker?" Tags="&lt;satellites&gt;&lt;software&gt;&lt;software-development&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17634" PostTypeId="2" ParentId="17633" CreationDate="2020-11-23T00:54:19.013" Score="8" Body="&lt;p&gt;The simplest might be to use an app.&lt;/p&gt;&#xA;&lt;p&gt;On Android, &lt;a href=&quot;https://play.google.com/store/apps/details?id=com.heavens_above.viewer&quot; rel=&quot;nofollow noreferrer&quot;&gt;Heavens Above&lt;/a&gt;, a product of the 25-year-old website of the same name, stores the orbital elements of the satellites of interest, and does the pass calculations on your phone.&lt;/p&gt;&#xA;&lt;p&gt;The app uses the GPS to find your location. It likes to get fresh elements from the Internet on startup, but it caches them, so as long as you download them before you leave, for radio amateur purposes they will be fine for a week or more.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://play.google.com/store/apps/details?id=com.coolprimes.sattrack&quot; rel=&quot;nofollow noreferrer&quot;&gt;W1ANT satellite tracker&lt;/a&gt; is designed specifically for amateur satellite operation.&lt;/p&gt;&#xA;&lt;p&gt;See &lt;a href=&quot;https://en.wikipedia.org/wiki/List_of_satellite_pass_predictors&quot; rel=&quot;nofollow noreferrer&quot;&gt;this Wikipedia entry&lt;/a&gt; for a solid summary of desktop and web software available.&lt;/p&gt;&#xA;&lt;p&gt;Satellites do drift away from simple orbits, and almost none of them maintain them deliberately (Starlink does, with ion thrusters). Perturbations from the changing solar wind, atmosphere, the moon's gravity, and non-ideal shape of the earth result in the keplerian elements getting stale. It depends on how accurately you need the position - for a visual pass, 100 km accuracy is probably good enough. For pointing a small dish, 10 km. For GNSS you need to know their position to better than about 50 m for them to be useful, the operator updates the almanac of orbital elements every few hours.&lt;/p&gt;&#xA;&lt;p&gt;Most satellites don't transmit their position, you need an external database. They are tracked daily by the US military and others, by a combination of radar and optical systems, and the updated elements are published on &lt;a href=&quot;https://celestrak.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Celestrak&lt;/a&gt; and elsewhere. GNSS satellites are different, because position is at the heart of what they do, and you need to be able to use them without another data connection, they do broadcast their position all the time.&lt;/p&gt;&#xA;&lt;p&gt;There are many hobbyists that track down satellites and determine their orbits, even unpublished military satellites.&lt;/p&gt;&#xA;&lt;p&gt;Finally - &lt;a href=&quot;https://fas.org/spp/military/program/track/predict.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;here is a method from 1958&lt;/a&gt; do allow computing of a pass just with pencil, paper and a slide rule. (remember, we've been in orbit longer than we've had integrated circuits).&lt;br /&gt;&#xA;Some beautiful diagrams from the paper:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/RVT14.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RVT14.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/xTuu8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xTuu8.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-11-29T14:36:30.510" LastActivityDate="2020-11-29T14:36:30.510" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17635" PostTypeId="1" CreationDate="2020-11-23T11:26:52.003" Score="0" ViewCount="99" Body="&lt;p&gt;Trying to lengthen my 10mtr. end fed to 39 metres in length. To do this I need the first leg (10mtr.) to run at a lower height approx (5mtr)turning back on a dog leg, and the final 29 meters then gaining height to approx. 9 metres high to of Gable end of house.&#xA;Observing the correct Unun and correct installation which I have already with the 10 meter wire.&#xA;My question is would the fold back, although climbing in height interfere with radiating correctly.&lt;/p&gt;&#xA;&lt;p&gt;I can not find anything which suggests its unwise.&lt;/p&gt;&#xA;&lt;p&gt;Thanks  for any input.&#xA;CHRIS.&lt;/p&gt;&#xA;" OwnerUserId="18137" LastEditorUserId="8717" LastEditDate="2020-11-25T14:52:53.680" LastActivityDate="2020-11-25T14:52:53.680" Title="Long wire antenna end fed random length folded back on incline" Tags="&lt;antenna-theory&gt;&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17636" PostTypeId="1" CreationDate="2020-11-23T14:55:44.900" Score="1" ViewCount="84" Body="&lt;p&gt;I am an extreme beginner with SDR. I am trying to use the &lt;a href=&quot;https://www.petervis.com/Digital%20Terrestrial%20Receivers/dvb-t+fm+dab-820t2-and-sdr/dvb-t+fm+dab-820t2-and-sdr.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;820T2 &amp;amp; SDR&lt;/a&gt; device to capture uplink gsm packets sent by my phone to the nearest Base Station. I have an Rx Monitor App installed on my phone to see my Uplink and Downlink channel frequency (904MHz and 949MHz respectively). I am using &lt;a href=&quot;https://manpages.debian.org/testing/gr-gsm/grgsm_livemon.1.en.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;grgsm_livemon&lt;/a&gt; on a Ubuntu VM installed on VMWare to scan for packets.&#xA;I am able to capture downlink data easily via gr_gsm. However, I see no signals on the frequency monitor of gr_gsm in the uplink frequency. I tried to move a few steps within the band to find any peaks, but unfortunately no result.&lt;/p&gt;&#xA;&lt;p&gt;I also tried getting a call on my phone and then I see some instantaneous peaks throughout the whole Uplink spectrum for unknown reasons. (This is totally opposite of what I thought, I believed a GSM uses TDM and FDM for multiplexing multiple users. And a particular user would be assigned a static frequency and one or multiple time-slots for communication, and hence I should see instantaneous peaks at my uplink frequency only). Also, I am unable to capture any packets from these instantaneous peaks.&lt;/p&gt;&#xA;&lt;p&gt;I would appreciate it if I get to know what am I missing to capture the uplink data or any tweaks to do it. In case you need any more information, Let me know. Thanks in advance!&lt;/p&gt;&#xA;&lt;p&gt;EDIT:&#xA;So I am sharing a couple of screenshots to have a better understanding of the problem.&#xA;a) Network Details normal. Here the Frequency hopping is off which is not seen in SS.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/oclzLm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oclzLm.jpg&quot; alt=&quot;UE Network Details normal&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;b) grgsm output during Call. The peak is prominent but I couldn't take an SS as it's too fast.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/OBk1B.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OBk1B.png&quot; alt=&quot;Frequency spectrtum during call&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;c) Network details when I picked up the call&#xA;&lt;a href=&quot;https://i.stack.imgur.com/fmusYm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fmusYm.jpg&quot; alt=&quot;UE during call&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;d) grgsm DOWNLINK output&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y4thK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y4thK.png&quot; alt=&quot;downlink without call&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18138" LastEditorUserId="18138" LastEditDate="2020-11-24T09:22:01.817" LastActivityDate="2020-11-24T09:22:01.817" Title="Capture Uplink GSM packets using 820T2 and SDR" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;rtl-sdr&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17637" PostTypeId="2" ParentId="17616" CreationDate="2020-11-23T17:16:19.993" Score="0" Body="&lt;p&gt;As you are talking about the guttering I can imagine you may well then have access to a loft area. If so, Consider an end fed wire installed as high as possible, in this space, then zig zag to get a little extra length, run it into a SG239 smart tuner and feed the coaxial down to your transceiver. Hey ho! it works! Problem is an SG239 is expensive to purchase new, but I managed to find a secondhand one!&lt;/p&gt;&#xA;" OwnerUserId="18137" LastActivityDate="2020-11-23T17:16:19.993" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17638" PostTypeId="2" ParentId="17630" CreationDate="2020-11-23T18:11:14.397" Score="1" Body="&lt;p&gt;I wouldn't say that SMA is &amp;quot;the&amp;quot; standard RF coaxial connector, I would say that it is one standard among many.  No connector has emerged as the best for all uses, which is why there are many standards.  Other connectors such as the &amp;quot;&lt;a href=&quot;https://en.wikipedia.org/wiki/UHF_connector&quot; rel=&quot;nofollow noreferrer&quot;&gt;UHF&lt;/a&gt;&amp;quot; (badly-named because its performance is terrible at UHF), &lt;a href=&quot;https://en.wikipedia.org/wiki/BNC_connector&quot; rel=&quot;nofollow noreferrer&quot;&gt;BNC&lt;/a&gt;, &lt;a href=&quot;https://en.wikipedia.org/wiki/F_connector&quot; rel=&quot;nofollow noreferrer&quot;&gt;F&lt;/a&gt;, and &lt;a href=&quot;https://en.wikipedia.org/wiki/N_connector&quot; rel=&quot;nofollow noreferrer&quot;&gt;N&lt;/a&gt; connectors were invented earlier, and these that I mentioned are still in wide use.&lt;/p&gt;&#xA;&lt;p&gt;I wasn't there when the SMA connector was invented, but I'll guess that the designers had in mind a small and inexpensive connector with a low insertion loss up to frequencies of a few gigahertz.  The SMA has shortcomings for sure, such as not being able to handle lots of power, but the designers surely assumed that users needing better power handling, for instance, would just use a different connector.  People have voted with their money and made the SMA connector a resounding success, just as other connectors have been successful for other niches.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-11-23T18:11:14.397" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17639" PostTypeId="2" ParentId="17623" CreationDate="2020-11-23T18:57:22.690" Score="3" Body="&lt;p&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/99753.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;SSTV could be an interesting answer here&lt;/a&gt;. Bandwidth requirement is about 30 KHz to reach your goal of 1 frame per second AND it's proven tech on HF bands... though you'll need to multiplex the video feed yourself (or another strategy) to use 30 KHz instead of the typical 3 KHz.&lt;/p&gt;&#xA;&lt;p&gt;This may be a great opportunity to use a loopstick antenna. Yes for transmitting.&lt;/p&gt;&#xA;&lt;p&gt;Typically operating temperature becomes an issue as resistive losses in the ferrite bar heat it up. Using whatever body of water you're in as a heatsink should get you several watts on 40m or even longer wavelengths, which should be enough to get through the 10-15 feet of water you're looking at.&lt;/p&gt;&#xA;&lt;p&gt;Check out &lt;a href=&quot;https://sites.google.com/site/g3xbmqrp3/antennas/ferrite_tx&quot; rel=&quot;nofollow noreferrer&quot;&gt;this fellow's experiments&lt;/a&gt; for starters.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2020-11-23T20:20:52.947" LastActivityDate="2020-11-23T20:20:52.947" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17640" PostTypeId="2" ParentId="17623" CreationDate="2020-11-23T21:22:08.890" Score="4" Body="&lt;p&gt;Here is some useful scholarly information about the signal attenuation (in dB) of EM waves through freshwater &lt;em&gt;at various frequencies and depths&lt;/em&gt;. You will find a formula that you can use.&lt;/p&gt;&#xA;&lt;p&gt;You will also need to know the antenna gains, transmitter power levels, and the receiver sensitivity at the bandwidth.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;RF Path and Absorption Loss Estimation for Underwater Wireless Sensor Networks in Different Water Environments:&#xA;&lt;a href=&quot;https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4934316&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4934316&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Using RF Technology to Form a Wireless Network Under Water:&#xA;&lt;a href=&quot;https://www.aerodefensetech.com/component/content/article/adt/supplements/rfm/features/articles/17526&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.aerodefensetech.com/component/content/article/adt/supplements/rfm/features/articles/17526&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Below is just one page from &lt;a href=&quot;https://www.scirp.org/pdf/jemaa20110700001_18390291.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.scirp.org/pdf/jemaa20110700001_18390291.pdf&lt;/a&gt;. You will find more useful information on other pages.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://www.google.com/search?newwindow=1&amp;amp;sxsrf=ALeKk01isxsuVJRFd5Kq6zOcyu3yHXeqVQ:1606158971910&amp;amp;source=univ&amp;amp;tbm=isch&amp;amp;q=RF+attenuation+in+freshwater&amp;amp;safe=active&amp;amp;client=tablet-android-samsung&amp;amp;fir=0NkwQ0OgV171ZM%252Cd0mswROR4VIoSM%252C_%253BXbU13MFHxb9tkM%252Cd0mswROR4VIoSM%252C_%253BVAWEZgugfmGkoM%252CHvhpANY37ctNBM%252C_%253BwyUgQHrjF-KPZM%252CHvhpANY37ctNBM%252C_%253BNHxeNBC2A4d4eM%252Cd0mswROR4VIoSM%252C_%253BXZ42Y9R6X6vhLM%252CAq1j7evDu7QwNM%252C_%253BMJglXwy61R7NYM%252CVIzl1tSu_1aboM%252C_%253BR1DNt4HkBNcO1M%252CuwsPMXaJR9OEYM%252C_%253BIVzQsoLdzZy_rM%252CR61QLeX4G0ToPM%252C_%253BhshREXCAgo0k1M%252CuwsPMXaJR9OEYM%252C_%257Cattenuation%2520coefficient%253Babsorption%2520spectrum%253Bpath%2520loss%253Bwater%2520absorption%253Batmospheric%2520absorption%253Batmospheric%2520attenuation%253Batmospheric%2520gases%253Bsea%2520water%253Babsorption%2520coefficient%253Babsorption%2520bands&amp;amp;usg=AI4_-kQ9E_Mru-is-7gGNSwI1l4gybY7PA&amp;amp;sa=X&amp;amp;ved=2ahUKEwifpuS3sJntAhVF7qwKHaSXCNcQ7Al6BAgREFg&amp;amp;biw=768&amp;amp;bih=1024&quot; rel=&quot;nofollow noreferrer&quot;&gt;More information&lt;/a&gt; in this Google search.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vdocj.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vdocj.jpg&quot; alt=&quot;Electromagnetic wave propagation into fresh water&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-11-23T21:40:49.520" LastActivityDate="2020-11-23T21:40:49.520" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17641" PostTypeId="1" CreationDate="2020-11-24T02:00:19.233" Score="-5" ViewCount="198" Body="&lt;p&gt;Lots of explanations i've read on the internet written by ham radio operators and in some text books state that a half wave dipole is resonant when the inductive and capacitive reactances cancel out.&lt;/p&gt;&#xA;&lt;p&gt;Exactly what is the cause for the zero reactance seen in the impedance at the center feed point of a resonant half wave dipole?&lt;/p&gt;&#xA;&lt;p&gt;The image below is from Wikipedia and shows the voltage and current distribution for the standing wave which exists on a half wave dipole at resonance.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WZg96.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WZg96.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Resonance is determined by the fact that the length of each antenna element is exactly 1/4 of the wavelength of the applied signal, and so the wave reflected from the ends is exactly 360º behind in phase which is the same thing as being in phase with the applied signal and the two add together to produce a resultant waveform with larger amplitude.&lt;/p&gt;&#xA;&lt;p&gt;Wikipedia describes this as &amp;quot;When an oscillating force is applied at a resonant frequency of a dynamical system, the system will oscillate at a higher amplitude than when the same force is applied at other, non-resonant frequencies.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Resonance&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Resonance&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;My understanding is that at resonance the voltage of the standing wave which is 90 deg out of phase with the applied current is always zero at the feed point at resonance. For an antenna which is longer or shorter the zero crossing point no longer occurs at the feed point and then the feed point has a non-zero voltage which is out of phase with the feed point current.&lt;/p&gt;&#xA;&lt;p&gt;So at resonance the voltage of the standing wave which is 90 deg out of phase with the current at the feed point is zero and it doesn't contribute any reactance to the feed point impedance.&lt;/p&gt;&#xA;&lt;p&gt;Is this correct ?&lt;/p&gt;&#xA;&lt;p&gt;See following some of the resources i used to try and find an answer to this question.&lt;/p&gt;&#xA;&lt;p&gt;Chapter 5 of Practical Antenna Handbook by Joseph J. Carr Fourth Edition.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Dipole_antenna#Half-wave_dipole&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Dipole_antenna#Half-wave_dipole&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Talk:Dipole_antenna#Animated_graphic_incorrect&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Talk:Dipole_antenna#Animated_graphic_incorrect&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://nvhrbiblio.nl/biblio/boek/R-F%20Transmission%20Lines%20-%20Alexander%20Schure.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://nvhrbiblio.nl/biblio/boek/R-F%20Transmission%20Lines%20-%20Alexander%20Schure.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://nvhrbiblio.nl/biblio/boek/Resonant%20Circuits%20-%20Alexander%20Schure.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://nvhrbiblio.nl/biblio/boek/Resonant%20Circuits%20-%20Alexander%20Schure.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://nvhrbiblio.nl/biblio/boek/Antennas%20-%20Alexander%20Schure.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://nvhrbiblio.nl/biblio/boek/Antennas%20-%20Alexander%20Schure.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=DovunOxlY1k&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=DovunOxlY1k&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2020-12-04T23:05:30.343" LastActivityDate="2020-12-04T23:05:30.343" Title="Exactly what is the cause for the zero reactance seen in the impedance at the center feed point of a resonant half wave dipole?" Tags="&lt;antenna-theory&gt;&lt;dipole&gt;&lt;transmission-line&gt;" AnswerCount="4" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="17642" PostTypeId="2" ParentId="17641" CreationDate="2020-11-24T03:31:14.253" Score="4" Body="&lt;p&gt;What you miss is that a resonant dipole doesn't need to be a half wave length long.  You can add series inductors near the center or part way out from the middle, and/or capacitors (hats) near the tip ends, with L's and C's varying in value from small to large, to vary the dipole length from a just tiny bit shorter to significantly smaller (e.g. HT rubber duckies or 80M hamstick dipoles).  And still be resonant at exactly the same frequency.  (alas, with worse radiation efficiency and a narrower SWR bandwidth.)&lt;/p&gt;&#xA;&lt;p&gt;Note that if you do the above mods, but keep the identical resonant frequency, the length can change drastically, but the LC ratio stays the same.  So LC product is the constant for resonance, not the physical length.&lt;/p&gt;&#xA;&lt;p&gt;Added: In fact, if you gradually change the L and C loading values as you shrink the dimensions of a dipole antenna from half wavelength down to the size of a few small lumped components, the resonant antenna will gradually become a non(or barely)-radiating lumped resonant LC circuit (with a center-tapped/split inductor at the feedpoint).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-11-28T07:05:15.990" LastActivityDate="2020-11-28T07:05:15.990" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17643" PostTypeId="2" ParentId="17641" CreationDate="2020-11-24T03:59:31.657" Score="0" Body="&lt;p&gt;To add to &lt;a href=&quot;https://ham.stackexchange.com/a/17642/8717&quot;&gt;what Hotpaw stated&lt;/a&gt; ...&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;There's the &lt;em&gt;theoretical&lt;/em&gt; half-wave dipole, which is &lt;strong&gt;492/f&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;However, &lt;em&gt;a practical resonant dipole&lt;/em&gt; is shorter. When making one, we must account for the &lt;em&gt;end effect&lt;/em&gt;, by cutting its length to &lt;strong&gt;468/f&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The end effect results from the fact that the antenna is normally operating surrounded by air, and the signal is travelling in a conductor which is of finite length. More specifically, the antenna end effect results from a decrease in inductance and an increase in capacitance towards the end of the antenna conductor.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Quote from &lt;a href=&quot;https://www.electronics-notes.com/articles/antennas-propagation/dipole-antenna/length-calculations-equation-formula.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.electronics-notes.com/articles/antennas-propagation/dipole-antenna/length-calculations-equation-formula.php&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-11-24T04:04:42.987" LastActivityDate="2020-11-24T04:04:42.987" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="17645" PostTypeId="2" ParentId="17641" CreationDate="2020-11-24T21:35:11.120" Score="3" Body="&lt;p&gt;The original question was, &amp;quot;Why do ham radio operators insist that a half wave dipole is resonant when the inductive and capacitive reactances cancel out?&amp;quot; That question seems to be about psychology, and I will answer accordingly.  I don't know that my answer will be very useful to others, but I'll proceed anyway.&lt;/p&gt;&#xA;&lt;p&gt;People who are hams come from all walks of life, and their understanding of the technology of radio is imperfect, as it is for everyone.  Many hams know a bit about antennas and a bit about RLC circuits.  They observe that the impedance of a dipole that is shorter than resonant is capacitive, and the impedance of a dipole longer than resonant is inductive.&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;Aha&amp;quot;, someone must have said to himself, &amp;quot;a dipole must be like a series RLC circuit, and the capacitive reactance must go up and the inductive reactance must go down when the antenna gets shorter, and vice-versa.&amp;quot;  It's a gross oversimplification, as demonstrated by your observation that the dipole is also resonant for odd harmonics, but it worked for him at the time.  The model was shared, and it made sense to other people, who passed it on and perpetuated it.&lt;/p&gt;&#xA;&lt;p&gt;Fragile and incomplete mental models are how we humans make sense of the world; we need some sort of mental model to begin to understand just about anything, and we do the best we can with what we have available.  In this case a better understanding is possible for some with a bit of work.  At least the misunderstanding is understandable.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-11-25T16:04:03.607" LastActivityDate="2020-11-25T16:04:03.607" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="17650" PostTypeId="1" CreationDate="2020-11-26T19:55:54.010" Score="2" ViewCount="193" Body="&lt;p&gt;There is an FM station in my city which transmits at 105 MHz.&lt;/p&gt;&#xA;&lt;p&gt;Today I discovered that I can also hear it quite well if I set the LO to 32.6 MHz and then shift the signal a bit.  I'm using an rtlsdr with RT820T2 and &lt;a href=&quot;https://gqrx.dk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;gqrx&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Some of the combinations that work are:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;LO: 32.6 MHz Broadcast: 32.4 MHz&#xA;LO: 32.7 MHz Broadcast: 32.8 MHz&#xA;LO: 32.8 MHz Broadcast: 33.2 MHz&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;So, an LO increase by 100kHz shifts the signal by 400kHz.  How is this effect called and what is the formula to compute the frequencies?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Edit 28.12.2020&lt;/strong&gt;&lt;br /&gt;&#xA;I was able to research this a bit more today.&lt;/p&gt;&#xA;&lt;p&gt;First, I found a lot of other posts describing the same effect, for example:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.rtl-sdr.com/forum/viewtopic.php?t=4229&quot; rel=&quot;nofollow noreferrer&quot;&gt;FM broadcast mirrored to different bands - fault?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.reddit.com/r/RTLSDR/comments/1t11an/picking_up_fm_radio_in_the_2030mhz_range/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Picking up FM Radio in the 20-30MHz range&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.reddit.com/r/RTLSDR/comments/5csmu4/hearing_fm_broadcast_radio_at_around_30mhz/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hearing FM Broadcast radio at around 30mhz&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.reddit.com/r/RTLSDR/comments/6qgqh2/why_do_i_see_commercial_fm_in_the_20_mhz_range/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Why do I see commercial FM in the ~20 MHz range?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.reddit.com/r/RTLSDR/comments/kl5l8f/radio_stations_at_2430_mhz_band_in_montreal_qc/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Radio stations at 24-30 MHz band in Montreal, QC, Canada&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;The problem is that none of the answers in those threads satisfies me. They usually throw around terms like &amp;quot;overloading&amp;quot; and &amp;quot;intermodulation&amp;quot; without further explanation.  I want to know exactly why, for example, 103.0MHz mirrors at 32.0MHz, and 106.0MHz mirrors at 33.0MHz - these are nice, exact integers, so I suppose that some rather simple formula which explains them should exist.&lt;/p&gt;&#xA;&lt;p&gt;Second, I created a more detailed table of some of those frequencies in the range 32.0MHz - 33.0MHz (The range where this happens is much larger however, for me it's 26.6MHz - 33.7MHz):&lt;/p&gt;&#xA;&lt;div class=&quot;s-table-container&quot;&gt;&#xA;&lt;table class=&quot;s-table&quot;&gt;&#xA;&lt;thead&gt;&#xA;&lt;tr&gt;&#xA;&lt;th&gt;LO&lt;/th&gt;&#xA;&lt;th&gt;Freq&lt;/th&gt;&#xA;&lt;th&gt;Shift&lt;/th&gt;&#xA;&lt;th&gt;Real Freq&lt;/th&gt;&#xA;&lt;/tr&gt;&#xA;&lt;/thead&gt;&#xA;&lt;tbody&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.0&lt;/td&gt;&#xA;&lt;td&gt;31.4&lt;/td&gt;&#xA;&lt;td&gt;-0.6&lt;/td&gt;&#xA;&lt;td&gt;103.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.0&lt;/td&gt;&#xA;&lt;td&gt;32.0&lt;/td&gt;&#xA;&lt;td&gt;+0.0&lt;/td&gt;&#xA;&lt;td&gt;103.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.0&lt;/td&gt;&#xA;&lt;td&gt;32.8&lt;/td&gt;&#xA;&lt;td&gt;+0.8&lt;/td&gt;&#xA;&lt;td&gt;104.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.1&lt;/td&gt;&#xA;&lt;td&gt;31.4&lt;/td&gt;&#xA;&lt;td&gt;-0.7&lt;/td&gt;&#xA;&lt;td&gt;104.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.1&lt;/td&gt;&#xA;&lt;td&gt;31.8&lt;/td&gt;&#xA;&lt;td&gt;-0.3&lt;/td&gt;&#xA;&lt;td&gt;103.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.1&lt;/td&gt;&#xA;&lt;td&gt;32.4&lt;/td&gt;&#xA;&lt;td&gt;+0.3&lt;/td&gt;&#xA;&lt;td&gt;103.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.2&lt;/td&gt;&#xA;&lt;td&gt;31.8&lt;/td&gt;&#xA;&lt;td&gt;-0.4&lt;/td&gt;&#xA;&lt;td&gt;104.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.2&lt;/td&gt;&#xA;&lt;td&gt;32.2&lt;/td&gt;&#xA;&lt;td&gt;+0.0&lt;/td&gt;&#xA;&lt;td&gt;103.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.2&lt;/td&gt;&#xA;&lt;td&gt;32.8&lt;/td&gt;&#xA;&lt;td&gt;+0.6&lt;/td&gt;&#xA;&lt;td&gt;103.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.3&lt;/td&gt;&#xA;&lt;td&gt;31.4&lt;/td&gt;&#xA;&lt;td&gt;-0.9&lt;/td&gt;&#xA;&lt;td&gt;103.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.3&lt;/td&gt;&#xA;&lt;td&gt;32.2&lt;/td&gt;&#xA;&lt;td&gt;-0.1&lt;/td&gt;&#xA;&lt;td&gt;104.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.3&lt;/td&gt;&#xA;&lt;td&gt;32.6&lt;/td&gt;&#xA;&lt;td&gt;+0.3&lt;/td&gt;&#xA;&lt;td&gt;103.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.3&lt;/td&gt;&#xA;&lt;td&gt;33.2&lt;/td&gt;&#xA;&lt;td&gt;+0.9&lt;/td&gt;&#xA;&lt;td&gt;103.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.4&lt;/td&gt;&#xA;&lt;td&gt;31.6&lt;/td&gt;&#xA;&lt;td&gt;-0.8&lt;/td&gt;&#xA;&lt;td&gt;105.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.4&lt;/td&gt;&#xA;&lt;td&gt;32.6&lt;/td&gt;&#xA;&lt;td&gt;+0.2&lt;/td&gt;&#xA;&lt;td&gt;104.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.4&lt;/td&gt;&#xA;&lt;td&gt;33.0&lt;/td&gt;&#xA;&lt;td&gt;+0.6&lt;/td&gt;&#xA;&lt;td&gt;103.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.5&lt;/td&gt;&#xA;&lt;td&gt;31.6&lt;/td&gt;&#xA;&lt;td&gt;-0.9&lt;/td&gt;&#xA;&lt;td&gt;103.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.5&lt;/td&gt;&#xA;&lt;td&gt;32.0&lt;/td&gt;&#xA;&lt;td&gt;-0.5&lt;/td&gt;&#xA;&lt;td&gt;105.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.5&lt;/td&gt;&#xA;&lt;td&gt;33.0&lt;/td&gt;&#xA;&lt;td&gt;+0.5&lt;/td&gt;&#xA;&lt;td&gt;104.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.5&lt;/td&gt;&#xA;&lt;td&gt;33.4&lt;/td&gt;&#xA;&lt;td&gt;+0.9&lt;/td&gt;&#xA;&lt;td&gt;103.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.6&lt;/td&gt;&#xA;&lt;td&gt;31.8&lt;/td&gt;&#xA;&lt;td&gt;-0.8&lt;/td&gt;&#xA;&lt;td&gt;105.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.6&lt;/td&gt;&#xA;&lt;td&gt;32.4&lt;/td&gt;&#xA;&lt;td&gt;-0.2&lt;/td&gt;&#xA;&lt;td&gt;105.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.6&lt;/td&gt;&#xA;&lt;td&gt;33.4&lt;/td&gt;&#xA;&lt;td&gt;+0.8&lt;/td&gt;&#xA;&lt;td&gt;104.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.7&lt;/td&gt;&#xA;&lt;td&gt;31.8&lt;/td&gt;&#xA;&lt;td&gt;-0.9&lt;/td&gt;&#xA;&lt;td&gt;106.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.7&lt;/td&gt;&#xA;&lt;td&gt;32.2&lt;/td&gt;&#xA;&lt;td&gt;-0.5&lt;/td&gt;&#xA;&lt;td&gt;105.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.7&lt;/td&gt;&#xA;&lt;td&gt;32.8&lt;/td&gt;&#xA;&lt;td&gt;+0.1&lt;/td&gt;&#xA;&lt;td&gt;105.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.7&lt;/td&gt;&#xA;&lt;td&gt;33.6&lt;/td&gt;&#xA;&lt;td&gt;+0.9&lt;/td&gt;&#xA;&lt;td&gt;106.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.8&lt;/td&gt;&#xA;&lt;td&gt;32.2&lt;/td&gt;&#xA;&lt;td&gt;-0.6&lt;/td&gt;&#xA;&lt;td&gt;106.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.8&lt;/td&gt;&#xA;&lt;td&gt;32.6&lt;/td&gt;&#xA;&lt;td&gt;-0.2&lt;/td&gt;&#xA;&lt;td&gt;105.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.8&lt;/td&gt;&#xA;&lt;td&gt;33.2&lt;/td&gt;&#xA;&lt;td&gt;+0.4&lt;/td&gt;&#xA;&lt;td&gt;105.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.9&lt;/td&gt;&#xA;&lt;td&gt;32.6&lt;/td&gt;&#xA;&lt;td&gt;-0.3&lt;/td&gt;&#xA;&lt;td&gt;106.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.9&lt;/td&gt;&#xA;&lt;td&gt;33.0&lt;/td&gt;&#xA;&lt;td&gt;+0.1&lt;/td&gt;&#xA;&lt;td&gt;105.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;32.9&lt;/td&gt;&#xA;&lt;td&gt;33.6&lt;/td&gt;&#xA;&lt;td&gt;+0.7&lt;/td&gt;&#xA;&lt;td&gt;105.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;td&gt;&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;33.0&lt;/td&gt;&#xA;&lt;td&gt;33.0&lt;/td&gt;&#xA;&lt;td&gt;+0.0&lt;/td&gt;&#xA;&lt;td&gt;106.0&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;tr&gt;&#xA;&lt;td&gt;33.0&lt;/td&gt;&#xA;&lt;td&gt;33.4&lt;/td&gt;&#xA;&lt;td&gt;+0.4&lt;/td&gt;&#xA;&lt;td&gt;105.6&lt;/td&gt;&#xA;&lt;/tr&gt;&#xA;&lt;/tbody&gt;&#xA;&lt;/table&gt;&#xA;&lt;/div&gt;&#xA;&lt;p&gt;Third, this is a screenshot as I move from 32.5 to 32.6MHz.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/jTAaX.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/jTAaX.jpg&quot; alt=&quot;32.5MHz-32.6MHz waterfall&quot; /&gt;&lt;/a&gt;&#xA;Things that I want to note:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The strange way the frequencies move - they move up in frequency as the LO moves up - which is the opposite of what usually happens.  You can see other weaker signals moving the usual way to the left.&lt;/li&gt;&#xA;&lt;li&gt;These signals are really strong - the audio quality is actually great.&lt;/li&gt;&#xA;&lt;li&gt;The amplifier gain is set to auto here, but I can hear audio if I set it as low as 20dB, and on some frequencies I can go down to 2.8dB and still hear the station.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="10631" LastEditorUserId="10631" LastEditDate="2020-12-28T13:53:29.510" LastActivityDate="2021-03-28T20:11:24.903" Title="rtlsdr - hearing an FM broadcast on different frequencies" Tags="&lt;rtl-sdr&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17651" PostTypeId="2" ParentId="7642" CreationDate="2020-11-26T20:07:52.907" Score="0" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;This is commonly described as the ground plane acting as a reflector, so that there is effectively a second quarter-wave element “below the ground plane”.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It IS commonly described that way, but it is wrong.&lt;/p&gt;&#xA;&lt;p&gt;Tom Rauch, W8JI —in a 2010 post on qrz.com— correctly stated:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The &amp;quot;image&amp;quot; is not formed by the radials any significant amount, and it is a theoretical tool that is used to calculate patterns, not something that actually exists. We used the image to calculate elevation patterns before modeling programs...now there is no need to even think about that concept unless you are doing pattern calculations without a computer.&lt;/p&gt;&#xA;&lt;p&gt;By the way, the radials BELOW the antenna do not make an &amp;quot;image plane&amp;quot;. The &amp;quot;image plane&amp;quot; is the accumulation of re-radiation from everything out to several wavelengths, primarily the earth.&lt;/p&gt;&#xA;&lt;p&gt;All the radial system does below the antenna is provide something for the feed system to push against, and it also radiates to some extent like an antenna.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Another person stated:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The mirror image is a ficticious tool created to explain patterns. Using it as a literal example creates mental image problems.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I agree.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-11-26T20:13:13.943" LastActivityDate="2020-11-26T20:13:13.943" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17652" PostTypeId="1" AcceptedAnswerId="17653" CreationDate="2020-11-27T03:04:44.727" Score="1" ViewCount="45" Body="&lt;p&gt;I made an 2m / 70cm tape measure antenna using RG-8 coax. That part was quite a bit of fun and went fine. But when I tried to connect the coax to my Yaesu FT-70DR, the copper core of the RG-8 was too thick to fit into the SMA adapter. How do I connect my antenna to my HT? Thanks in advance!&lt;/p&gt;&#xA;" OwnerUserId="18111" LastEditorUserId="8717" LastEditDate="2020-11-27T19:57:12.877" LastActivityDate="2020-11-27T19:57:12.877" Title="How do I connect a homebrew antenna using RX-8 to a Yaesu FT-70DR (SMA)?" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;coaxial-cable&gt;&lt;yaesu&gt;&lt;connectors&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17653" PostTypeId="2" ParentId="17652" CreationDate="2020-11-27T11:19:36.517" Score="2" Body="&lt;p&gt;Either find an adapter that will work or cut the end off the RG-8 and solder on the proper connector.&lt;/p&gt;&#xA;&lt;p&gt;You could also find an SMA cable and replace the RG-8 entirely.&lt;/p&gt;&#xA;" OwnerUserId="18154" LastActivityDate="2020-11-27T11:19:36.517" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17654" PostTypeId="2" ParentId="17650" CreationDate="2020-11-27T14:21:44.427" Score="1" Body="&lt;p&gt;Likely 5th order IMD (inter-modulation distortion), caused by a strong signal mixing with the 4th harmonic of another frequency (internal digitally synthesized signal or oscillator) related to the “LO” setting.&lt;/p&gt;&#xA;&lt;p&gt;RTL2832 USB SDRs use an offset LO in the R820T mixer to produce an IF signal.  A superhet, of sorts, followed by an IQ sampler at the IF.&lt;/p&gt;&#xA;&lt;p&gt;Try an FM band blocking filter to reduce the level of the strong FM signal, and thus reduce non-linear mixing (clipping or overload) byproducts.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-11-27T14:45:49.050" LastActivityDate="2020-11-27T14:45:49.050" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17656" PostTypeId="2" ParentId="16808" CreationDate="2020-11-27T17:35:34.590" Score="4" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;And why is an antenna resonant, because the voltage and current are in phase or because the reactances cancel out, or both ?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Reactance (&lt;span class=&quot;math-container&quot;&gt;$X$&lt;/span&gt;), resistance (&lt;span class=&quot;math-container&quot;&gt;$R$&lt;/span&gt;), and the phase difference between voltage and current (&lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt;) are related by:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \tan \theta = { X \over R } $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;So if reactance is zero then &lt;span class=&quot;math-container&quot;&gt;$X/R$&lt;/span&gt; is zero, so &lt;span class=&quot;math-container&quot;&gt;$\theta$&lt;/span&gt; must be zero, meaning voltage and current are in phase.&lt;/p&gt;&#xA;&lt;p&gt;In other words, &amp;quot;zero reactance&amp;quot; means &amp;quot;voltage and current are in phase&amp;quot;. One does not cause the other: they are two ways of saying the same thing.&lt;/p&gt;&#xA;&lt;p&gt;Likewise, resonance is defined as zero reactance. It's not &amp;quot;caused&amp;quot; by zero reactance or voltage and current being in phase: it simply &lt;em&gt;is&lt;/em&gt;, by definition.&lt;/p&gt;&#xA;&lt;p&gt;In other words, if you design an antenna with any one of these three objectives:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;current and voltage are in phase at the feedpoint,&lt;/li&gt;&#xA;&lt;li&gt;feedpoint reactance is zero, or&lt;/li&gt;&#xA;&lt;li&gt;antenna is resonant&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;you will find the other two are satisfied. There is no ordering or causality between any of them: they are each mathematically equivalent.&lt;/p&gt;&#xA;&lt;p&gt;If you are concerned only about the feedpoint, asking what the inductive and capacitive reactances are which sum to zero reactance is like solving &lt;span class=&quot;math-container&quot;&gt;$x-x=0$&lt;/span&gt; for &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;. It's not possible, and also it doesn't matter.&lt;/p&gt;&#xA;&lt;p&gt;Besides, a dipole isn't an RLC circuit, so there is no inductance in henrys or capacitance in farads that can be found, although as Brian K1LI explains it is possible to approximate a dipole as an RLC circuit over a limited frequency range.&lt;/p&gt;&#xA;&lt;p&gt;There is perhaps a slightly different question you could ask which does have an answer. A dipole, like any resonant system, has a &lt;a href=&quot;https://en.wikipedia.org/wiki/Q_factor&quot; rel=&quot;nofollow noreferrer&quot;&gt;Q factor&lt;/a&gt;. We know that a dipole must store some energy in its electromagnetic field, and some of this energy is lost to radiation and possibly other losses, like resistive losses in the conductor and ground. The Q factor relates to the ratio of these quantities.&lt;/p&gt;&#xA;&lt;p&gt;One way to think of Q is as the ratio of &lt;a href=&quot;https://en.wikipedia.org/wiki/AC_power#Active,_reactive,_and_apparent_power&quot; rel=&quot;nofollow noreferrer&quot;&gt;reactive power&lt;/a&gt; to real power. The reactive power has current and voltage 90 degrees out of phase. The energy associated with this power doesn't go anywhere and doesn't do any real work: it just oscillates between the electric and magnetic fields, forever. The real power has voltage and current in phase, and does real work: mostly (ideally, entirely) radiation.&lt;/p&gt;&#xA;&lt;p&gt;A good half-wave dipole will &lt;a href=&quot;https://owenduffy.net/blog/?p=7480&quot; rel=&quot;nofollow noreferrer&quot;&gt;have a Q of about 10&lt;/a&gt;. Which means if the antenna is radiating 100 watts, there is about 1000 watts of reactive power. You could measure this with electric and magnetic field probes in the near field of the antenna. With the electromagnetic fields known you can calculate the &lt;a href=&quot;https://en.wikipedia.org/wiki/Poynting_vector&quot; rel=&quot;nofollow noreferrer&quot;&gt;Poynting vector&lt;/a&gt;. In the near field of the antenna you should expect to find the imaginary part of the Poynting vector is about 10 times that of the real part, meaning the electric and magnetic fields are almost but not quite 90 degrees out of phase. Of course the precise values will depend on just where you place the probes, and the construction and environment of the particular antenna.&lt;/p&gt;&#xA;&lt;p&gt;While this is not exactly what you asked, it does seem closer to the understanding you're seeking. Unfortunately it does require thinking beyond just what's happening at the feedpoint, and instead considering what's happening in the electromagnetic fields in space around the antenna, and this requires some more complicated mathematics.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-11-27T17:35:34.590" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17657" PostTypeId="2" ParentId="17617" CreationDate="2020-11-28T08:18:46.200" Score="3" Body="&lt;p&gt;Probably not. Looking at the chips:&lt;/p&gt;&#xA;&lt;p&gt;NXP TDA18271HDC2 is the RF frontend / &amp;quot;tuner&amp;quot; chip.&lt;/p&gt;&#xA;&lt;p&gt;Afatech AF9033B is the DVB-T demodulator.&lt;/p&gt;&#xA;&lt;p&gt;Conexant CX23102 is the analog TV demodulator.&lt;/p&gt;&#xA;&lt;p&gt;NEC (now Renesas) uPD720114 is a USB hub, which shares the USB port between the AF9033B and the CX23102.&lt;/p&gt;&#xA;&lt;p&gt;Neither the AF9033B nor the CX23102 seems to have a feature to directly sample the IF signal reaching it, the way the RTL2832 does, so there's no SDR potential here. It's a perfectly good TV receiver, but an entirely &amp;quot;fixed-function&amp;quot; one.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-11-28T08:18:46.200" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17658" PostTypeId="2" ParentId="17641" CreationDate="2020-11-28T17:35:50.290" Score="3" Body="&lt;p&gt;Zero reactance means voltage and current are in phase.&lt;/p&gt;&#xA;&lt;p&gt;For example, consider a voltage source connected to a nonreactive load. This means the peaks of the applied voltage should coincide with the peaks of the resulting current.&lt;/p&gt;&#xA;&lt;p&gt;It's equally valid to consider a current source connected to a nonreactive load. In this case the peaks of the applied current should coincide with the peaks of the resulting voltage.&lt;/p&gt;&#xA;&lt;p&gt;Either way, reactance is part of impedance, and impedance is the relationship between voltage and current.&lt;/p&gt;&#xA;&lt;p&gt;A dipole is just a bit of balanced transmission line that's been pulled apart. What happens when a DC voltage step is applied to the end of a section of transmission line that's open on the end opposite the voltage source?&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/jxU6h.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fjxU6h.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;If we want to know the impedance of this &amp;quot;load&amp;quot; (the transmission line) we need to know how much current flows. We know that eventually the current must be zero, because the circuit is open at the end. But &lt;a href=&quot;https://electronics.stackexchange.com/q/19759/17608&quot;&gt;how can the voltage step know that, not yet having seen the open end?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;So what happens is initially some current flows, in an amount defined by the surge impedance (also known as characteristic impedance) of the transmission line. But the current is constrained to zero at the open end, so a reflected wave is superimposed on the initial wave, propagating from the open end and back to the voltage source. It may help to play with &lt;a href=&quot;http://helloworld922.blogspot.com/2013/04/online-transmission-line-simulation.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;a time domain transmission line simulator&lt;/a&gt; to get an intuition for this process.&lt;/p&gt;&#xA;&lt;p&gt;What happens when the reflected wave gets back to the source is key. In the case of a DC step, the source will see too much voltage, and so it will reduce current. And this sets off another round of wave propagation, with each iteration getting closer to what we know the DC solution must be: zero current, that is infinite impedance.&lt;/p&gt;&#xA;&lt;p&gt;But in the case of AC, the voltage source is not a step but rather a sinusoid. We must consider both the phase of the reflected wave, and the additional phase delay introduced by the propagation of the forward wave and then the reflected wave.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Exactly what is the cause for the zero reactance seen in the impedance at the center feed point of a resonant half wave dipole?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;When the transmission line is open, the current of the reflected wave will always be equal but opposite the forward wave, because the open end always wants to cancel the current to make it zero. In other words, the reflection adds 180 degrees of phase delay.&lt;/p&gt;&#xA;&lt;p&gt;When the length of the transmission line is 90 degrees, it is resonant. This is due to the 90 degrees of delay for the forward wave, plus 90 degrees for the reflected wave, plus 180 degrees for the phase of the reflection equals 360 or 0 degrees. Current is in phase with voltage, which means zero reactance, which means resonance.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I don't understand yet how the radiation resistance fits into all of this.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;In the case of an ideal 1/4 wave transmission line, the impedance seen by the voltage source is exactly 0+0j ohms. This is because the current from each reflected wave reinforces each forward wave, and there's no loss in the system, so the current builds to infinity. But in an ideal resonant dipole some energy is lost to radiation (represented by a resistance), and so the current builds to a high but finite quantity, resulting in the low but non-zero impedance of about 70+0j ohms.&lt;/p&gt;&#xA;&lt;p&gt;Now, what about this graphic:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/WZg96.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/WZg96.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;At a glance, it looks like the red and blue curves, labeled &amp;quot;voltage&amp;quot; and &amp;quot;current&amp;quot; respectively, are not in phase, but quadrature. How is this reconciled with the above explanation, where voltage and current are in phase?&lt;/p&gt;&#xA;&lt;p&gt;More confusing, but perhaps more helpful is the old version of the image which shows only the standing wave, but does not include the influence of the voltage source (perhaps it would be better if the illustration did not include a voltage source, since its effects are not illustrated):&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1LZSD.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1LZSD.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Here, the red and blue curves are exactly in quadrature. And this is no mistake, since the standing wave is purely reactive.&lt;/p&gt;&#xA;&lt;p&gt;I think the confusing thing about this image is it just says &amp;quot;V&amp;quot; (for voltage) without really explaining what that means. Anything measured in volts could be called voltage. That's not very specific or helpful.&lt;/p&gt;&#xA;&lt;p&gt;If we are concerned about the feedpoint impedance, the voltage we are concerned about is more specifically the electric potential difference between the two feedpoint terminals.&lt;/p&gt;&#xA;&lt;p&gt;If we are concerned about the electromagnetic fields around the dipole, we are probably more concerned about the electric field intensity, which is a vector quantity for some point in space around the antenna, measured in volts per meter.&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;voltage&amp;quot; in the graphic shows the electric potential for each point along the length of the antenna. &lt;em&gt;Electric potential&lt;/em&gt; is the &lt;em&gt;electric potential difference&lt;/em&gt; between the measured point, and a theoretical point infinitely far away, which is 0 volts by definition. In the case of a dipole, the electric potential right at the center is also 0 volts.&lt;/p&gt;&#xA;&lt;p&gt;Now the question is: how can the electric potential difference between the feedpoint terminals be in phase with current when on the graphic the blue curve is clearly not in phase with the red curve?&lt;/p&gt;&#xA;&lt;p&gt;The answer is quite simple: theoretically the feedpoint terminals are separated by only an infinitesimal distance. It doesn't actually matter what the blue curve is doing, because the electric potential &lt;em&gt;difference&lt;/em&gt; between two points approaches zero as the two points approach zero separation.&lt;/p&gt;&#xA;&lt;p&gt;Put another way, electric potential difference between two points in a uniform electric field is the electric field intensity (volts/meter) multiplied by the distance between the points (meter). If the distance is small, the electric potential difference can be neglected.&lt;/p&gt;&#xA;&lt;p&gt;The full picture of what happens on the dipole is the superposition of:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the standing waves, shown in the image above, where the electric and magnetic fields are in quadrature, and&lt;/li&gt;&#xA;&lt;li&gt;the influence of the voltage (or current) source driving the antenna, where voltage and current are in phase.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;My understanding which is becoming more and more confused as time goes on is that at resonance the voltage of the standing wave which is 90 deg out of phase with the applied current is always zero at the feed point at resonance.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Although it is true the standing waves are associated with a high electric field intensity around the feedpoint terminals, as long as the terminals are not far apart this has negligible significance to the electric potential difference between the terminals.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-11-28T17:54:36.370" LastActivityDate="2020-11-28T17:54:36.370" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17660" PostTypeId="2" ParentId="17633" CreationDate="2020-11-29T22:14:00.403" Score="3" Body="&lt;p&gt;To track the satellites, you need the Keplerian TLE orbital coefficients.  Once you have those, you can track the sats without internet access.  The TLE's are accurate enough for about a week.  The TLE file format is standardized and works with nearly all the tracking software, and most software either downloads them on command or can import from a file.&lt;/p&gt;&#xA;&lt;p&gt;As already mentioned, sats like GPS and GNSS continuously broadcast their orbital parameters.  I believe GPS updates them every 6 hours or something, based on ground station data uploaded to the GPS network.  (In other words, the data is not exactly live, it doesn't change that fast.)&lt;/p&gt;&#xA;&lt;p&gt;However, other sats don't broadcast their positions.&lt;/p&gt;&#xA;&lt;p&gt;So there are three ways you could do this:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;(easiest) Download the TLE's for the sats you want to track ahead of time when you do have internet.  Hopefully you'll be able to update them a week or two later.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;(the hard way) Use the stale TLE to guess where the sat is and use visual or radio methods to track it and measure the drift.  This might have to be done daily or the drift will be great enough to make it hard to find.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;There is an amateur radio digital HF net that broadcasts a number of static files, including the current TLE's for popular satellites.  I believe the net is daily (or weekly) and runs for a few hours.  Software like fldigi along with one of its accessory programs can listen to the broadcast and save the files.  There may be other radio sources (including a satellite network) for this information as well.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Some resources are:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.amsat.org/keplerian-elements-resources/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amsat.org/keplerian-elements-resources/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.kc4mcq.us/?page_id=24816&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.kc4mcq.us/?page_id=24816&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/digital-transmissions&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/digital-transmissions&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-12-02T13:21:20.277" LastActivityDate="2020-12-02T13:21:20.277" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17661" PostTypeId="1" AcceptedAnswerId="18326" CreationDate="2020-11-30T19:24:17.140" Score="9" ViewCount="183" Body="&lt;p&gt;The following are fairly common knowledge:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Transmitting at full power with too much of an impedance mismatch can damage your finals.&lt;/li&gt;&#xA;&lt;li&gt;If we do so inadvertently, modern radios drop the power significantly for self-protection.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Yet, it's still very common to hear people suggesting that high SWR risks damaging your transmitter. How much of an issue is this with modern radios? Do we really still need to be concerned about damaging our finals, or is it outdated advice that refuses to die?&lt;/p&gt;&#xA;&lt;p&gt;In the extreme case, can we freely transmit at (attempted) full-power into an empty jack without shortening the lifetime of the finals?&lt;/p&gt;&#xA;" OwnerUserId="8940" LastEditorUserId="8717" LastEditDate="2020-12-01T16:04:45.520" LastActivityDate="2021-04-15T16:33:46.783" Title="How effectively do modern transmitters protect against high SWR?" Tags="&lt;impedance-matching&gt;&lt;amplifier&gt;&lt;equipment-protection&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="17662" PostTypeId="1" CreationDate="2020-12-01T01:30:36.287" Score="0" ViewCount="21" Body="&lt;p&gt;I am struggling with the problem of measuring the Packet Error Rate (PER) in my receiver. I have implemented BER in the receiver system, but I don't know how to add a function that will also test PER (I haven't seen any PER block anywhere, even in the Labview Modulation kit). In the attachment, I'm adding a QAM modulator and demodulator (transmitter and receiver). The problem is that I don't have a CRC calculator anywhere in my code and I think I will need it.&lt;/p&gt;&#xA;&lt;p&gt;From what I've learned, the easiest way to do it is to number the frames and check if they come properly. If the CRC is correct then we intercept the frame. All this is done on the basis of a clock or timer (I don't know how to do it exactly). Unfortunately from what I saw after the transmitter, the only things I send are bits, not frames, so I don't know how to do it (or how to change it).&lt;/p&gt;&#xA;&lt;p&gt;Does anyone have any ideas how to solve these problems?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MyT19.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MyT19.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7tLJP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7tLJP.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wOLm6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wOLm6.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="13706" LastActivityDate="2020-12-01T01:30:36.287" Title="Packet Error Rate measurement" Tags="&lt;packet&gt;&lt;usrp&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17663" PostTypeId="1" AcceptedAnswerId="17664" CreationDate="2020-12-01T13:43:28.200" Score="2" ViewCount="211" Body="&lt;p&gt;I have been working at educating myself on how SDR and GNU Radio works.&lt;/p&gt;&#xA;&lt;p&gt;In order to demonstrate heterodyning, I set up a flow-graph consisting of 2 signal generators, a Multiply block, and QT GUI Frequency Sink. The generators are connected to the Multiply block inputs, and the Multiply block output is connect to the Freq Sink, in order to heterodyne the two generator signals.&lt;/p&gt;&#xA;&lt;p&gt;The frequency of the generators are linked to a slider. One generator is slider_value, the other is slider_value + 2000. The generators are both outputting a cosine waveform.&lt;/p&gt;&#xA;&lt;p&gt;When setting all the inputs to float, as I move the slider I get the results I would expect:&lt;/p&gt;&#xA;&lt;p&gt;I see one peak always at 2000 Hz: slider_value - slider_value + 2000 = 2000. Ie, the difference signal.&lt;/p&gt;&#xA;&lt;p&gt;I see another peak at the sum of the generator outputs: slider_value + slider_value + 2000 = (2 * slider_value) + 2000.&lt;/p&gt;&#xA;&lt;p&gt;However, if I switch all the inputs and outputs to complex, I only see one peak which is at the sum of the values. I do not see a peak at the difference, ie, nothing at 2000 (except when slider_value = 0).&lt;/p&gt;&#xA;&lt;p&gt;Can someone explain to me why I don't see the difference signal when multiplying complex signals?&lt;/p&gt;&#xA;" OwnerUserId="18177" LastEditorUserId="4665" LastEditDate="2020-12-01T16:47:54.083" LastActivityDate="2020-12-01T16:47:54.083" Title="Heterodyning complex values in gnuradio" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;rtl-sdr&gt;" AnswerCount="1" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17664" PostTypeId="2" ParentId="17663" CreationDate="2020-12-01T14:47:40.553" Score="6" Body="&lt;p&gt;This is how the mathematics of complex signals work.&lt;/p&gt;&#xA;&lt;p&gt;The proof begins with &lt;a href=&quot;https://en.wikipedia.org/wiki/Euler%27s_formula&quot; rel=&quot;noreferrer&quot;&gt;Euler's formula&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{i\varphi} = \cos \varphi + i \sin \varphi \tag 1 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;For signal processing, instead of &lt;span class=&quot;math-container&quot;&gt;$\varphi$&lt;/span&gt;, we are usually thinking about some sinusoidal oscillation at angular frequency &lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt; that varies with time &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt;, which we can write as:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{i\omega t} \tag 2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is what the signal generator block outputs, when in sine mode and with a complex output. By (1) above you can see both the real and imaginary parts are sinusoids at angular frequency &lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt;, just offset 90 degrees in phase.&lt;/p&gt;&#xA;&lt;p&gt;When you multiply two of these complex sinusoids together, at frequencies &lt;span class=&quot;math-container&quot;&gt;$\omega_1$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\omega_2$&lt;/span&gt;, you get:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{i\omega_1 t} e^{i\omega_2 t} \tag 3 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;which simplifies to&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{i (\omega_1 + \omega_2) t} \tag 4 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;which, again by (1), is a single complex sinusoid at frequency &lt;span class=&quot;math-container&quot;&gt;$\omega_1 + \omega_2$&lt;/span&gt;. There is no difference term.&lt;/p&gt;&#xA;&lt;p&gt;A consequence of this math is that &lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt; can be negative. Which is why in GNU Radio if you have a complex stream at a sample rate of say 48 kHz, that can represent 96 kHz of bandwidth: from -48 kHz to 48 kHz.&lt;/p&gt;&#xA;&lt;p&gt;The sum &lt;em&gt;and difference&lt;/em&gt; terms when heterodyning real-valued functions comes about because a real function can not unambiguously represent positive and negative frequencies, but mathematically, they are still there.&lt;/p&gt;&#xA;&lt;p&gt;How? Consider &lt;em&gt;two&lt;/em&gt; complex sinusoids, at frequencies &lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$-\omega$&lt;/span&gt;, summed together:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{i\omega t} + e^{-i\omega t}&#xA;= \cos \omega t + i \sin \omega t&#xA;+ \cos -\omega t + i \sin -\omega t&#xA;\tag 5 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Considering the trigonometric identities:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos x  = \cos −x \\&#xA;   \sin x + \sin -x = 0 \tag 6&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now (5) simplifies to:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{i\omega t} + e^{-i\omega t} = 2\cos(\omega t) \tag 7 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Which means when you multiply two real sinusoids to heterodyne a signal:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos \omega_1 t \times \cos \omega_2 t \tag 8 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Then by (7) and neglecting the factor of 2 (since it only changes the amplitude of the result, and that's not important), equivalently you're doing:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ (e^{i\omega_1 t} + e^{-i\omega_1 t})&#xA;   (e^{i\omega_2 t} + e^{-i\omega_2 t}) \\&#xA;= (e^{-i(\omega_1-\omega_2)} +&#xA;  e^{i(\omega_1-\omega_2)}) +&#xA;  (e^{-i(\omega_1+\omega_2)} +&#xA;  e^{i(\omega_1+\omega_2)}) \tag 9 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Notice the difference of the frequencies on the left, and the sum on the right. Each group is comprised of positive and negative variations of the same frequency, which by (7) we know simplifies to just a real-valued sinusoid. So (9) further simplifies (again neglecting that factor of 2) to:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos((\omega_1-\omega_2) t) + \cos((\omega_1+\omega_2) t) \tag {10} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;And there you have your common real-valued function heterodyning equation.&lt;/p&gt;&#xA;&lt;p&gt;Thus, any real-valued function has both positive and negative frequencies in it, but the negative frequencies are just a &amp;quot;mirror&amp;quot; of the positive ones. It's because of those negative frequencies that &lt;a href=&quot;https://ham.stackexchange.com/a/16481/218&quot;&gt;LSB demodulation can &amp;quot;flip&amp;quot; the spectrum&lt;/a&gt;, and it's the negative frequencies that cause the difference term when heterodyning real-valued functions.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-12-01T15:18:40.003" LastActivityDate="2020-12-01T15:18:40.003" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="17665" PostTypeId="1" AcceptedAnswerId="17668" CreationDate="2020-12-01T15:22:09.050" Score="3" ViewCount="473" Body="&lt;p&gt;Are magnetic loops a good choice for those living in apartments or condos where a permanent installation is often not an option and the operator still wants access to the HF bands? Why or Why not?&lt;/p&gt;&#xA;&lt;p&gt;Edit: Building is from the 1800's, the roof of this building is sheets of steel and the walls are just brick, I am just under the roof, walls are brick, I am on the 4th (top) floor.&lt;/p&gt;&#xA;&lt;p&gt;Edit2: I have enough options for portable stations i am only looking for an apartment solution at this time.&lt;/p&gt;&#xA;" OwnerUserId="13219" LastEditorUserId="13219" LastEditDate="2020-12-03T13:39:39.023" LastActivityDate="2020-12-03T13:39:39.023" Title="Is a magnetic loop antenna a good option for those in an apartment?" Tags="&lt;antenna&gt;&lt;magnetic-loop&gt;" AnswerCount="5" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17666" PostTypeId="2" ParentId="17665" CreationDate="2020-12-01T23:32:33.787" Score="1" Body="&lt;p&gt;For wavelengths larger than the dimension of your window (assumed indoor use): small and not 100 % efficient but the best choice. Less RX-interference from local sources. You did not mention RX or TX, but that makes in fact no difference. RX wideband without tuning is also good option. For transmit tuning is required.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-12-01T23:32:33.787" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17667" PostTypeId="2" ParentId="17665" CreationDate="2020-12-01T23:59:13.480" Score="5" Body="&lt;p&gt;In, meaning Inside an apartment, a magnetic loop may not be a good idea for transmit, as the RF magnetic field can couple very strongly to any household wiring or appliances inside, window frames, etc., possibly causing hazards as well as severe pattern distortions and losses.  For receive it might be Ok if the walls (stucco wire, metal siding, etc.) do not approximate a Faraday cage.&lt;/p&gt;&#xA;&lt;p&gt;Outside on an apartment balcony or small yard, a magnetic loop is likely fairly efficient compared to anything else of similar height and spherical volume, and there are reports of this working for both Rx and Tx.  A mag loop on an extended horizontal flagpole off a balcony railing might be a workable placement, if safe.  But as with any antenna placement, YMMV... by a lot.&lt;/p&gt;&#xA;&lt;p&gt;If you can get roof or attic access over your apartment, you may have more options.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-12-02T00:12:16.243" LastActivityDate="2020-12-02T00:12:16.243" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17668" PostTypeId="2" ParentId="17665" CreationDate="2020-12-02T05:55:37.763" Score="9" Body="&lt;p&gt;If you're talking about placing the antenna indoors, there are no &lt;em&gt;good&lt;/em&gt; options. A magloop might be your &lt;em&gt;best&lt;/em&gt; option, but:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;It's still going to receive plenty of noise (stuff you may have heard about them being insensitive to E-field noise is overblown; it's only true for a specific range of distances, and in any case isn't enough of an effect to override the fact that a noise source ten feet away is orders of magnitude louder than the signal you're trying to receive).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Modern construction apartment buildings often make good approximations of Faraday cages at HF frequencies. Practically no signal makes it in or out. I once played around with operating from a waterfront penthouse (19th floor) apartment on the east coast of the US (sounds like pretty good conditions!), with 100W into a coil-loaded dipole. The result: I could hear very little, and I couldn't even get a single spot on FT8. I could have gotten more signal out operating with 1W from the roof than I did with 100W indoors.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Unless you're willing to go very expensive, loops tend to be limited in power to significantly less than 100W, and they also tend to be pretty inefficient. Probably you're looking at a radiated power equivalent to what you would get from putting 10W or less into a full-size dipole. This isn't impossible, but it does compound with issue #2.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If you &lt;em&gt;do&lt;/em&gt; go all-out on a large, heavy loop with a high-voltage vacuum capacitor so that you can get more power output, your new problem is that the high voltages and high field strengths near the antenna make it unsafe to get within a few feet of it. Not very easy to reconcile with apartment life.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Again, my opinion is that an indoor apartment antenna for HF is a lose-lose proposition. If you have some kind of outdoor space (like a balcony) then you might be able to put a magloop there without too much trouble, and it might work to some extent (#1 becomes less of an issue if you move it away from the noise and on the other side of a wall, #2 becomes less of an issue for at least one direction, #4 becomes less of an issue, #3 doesn't really change). However if I was stuck in that situation I would probably look for alternatives like a loaded vertical (with a downspout or fire escape as counterpoise), a loaded dipole, or a &amp;quot;throw it out the window&amp;quot; end-fed, all of which might be more tractable than a magloop.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-12-02T05:55:37.763" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17669" PostTypeId="2" ParentId="17665" CreationDate="2020-12-02T16:32:22.567" Score="2" Body="&lt;p&gt;Mag Loops are very expensive ( I have one The MFJ 1888X) and therefore if you are considering a piece of equipment  of that calibre also consider hanging a simple wire (end fed)  a length as long as possible (but not touching earth) out of the window and then attaching it to a SG239 Smart Tuner which can be just inside the window. Feeding your coax cable to your transmitter. 95% of RF will be outside and you will be somewhat surprise what the tuner can do. Yes also an expensive piece of equipment is the SG239 but a great alternative.&lt;/p&gt;&#xA;" OwnerUserId="18137" LastActivityDate="2020-12-02T16:32:22.567" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17670" PostTypeId="2" ParentId="17665" CreationDate="2020-12-02T18:27:43.897" Score="3" Body="&lt;p&gt;Definitely &lt;a href=&quot;https://ham.stackexchange.com/a/17668/1550&quot;&gt;read Hobbs's answer&lt;/a&gt; re ins-and-outs of mag loops, spot on... I don't have anything to add on that part.&lt;/p&gt;&#xA;&lt;p&gt;Another option is to make friends with the building super. Depending on his/her disposition, you may be able to get permission to drop a line from the roof to your window. I had GREAT luck with this in one of the buildings I lived in (Washington DC) and also struck out in another building... it just depends.&lt;/p&gt;&#xA;&lt;p&gt;Finally, if your window opens and you're on a high enough floor, you may have great success with a dangling EFHW or OCFD (whip up, long wire down) or other similar options.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2020-12-02T18:27:43.897" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17671" PostTypeId="1" AcceptedAnswerId="17672" CreationDate="2020-12-03T16:52:23.137" Score="0" ViewCount="94" Body="&lt;p&gt;Could you kindly explain me or advise following please...&lt;/p&gt;&#xA;&lt;p&gt;I have a TP-link wifi router .... when i measure signal strength just in the vicinity of the router- literally i touch my smartphone (with wifi signal strength measurement application) to a wifi router antena - i get signal strength -15dbm.&#xA;The manufacturer datasheet says -  &amp;quot;wifi transmission power &amp;lt;30dbm&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;So why do i have -15dbm then just at immediate vicinity of the router ?&#xA;Where does 45 dbm go? (from 30 dbm down to -15)&lt;/p&gt;&#xA;&lt;p&gt;Thank you so much.&lt;/p&gt;&#xA;" OwnerUserId="18186" LastActivityDate="2020-12-07T15:04:52.540" Title="Wireless signal strength explanation needed" Tags="&lt;wifi&gt;&lt;signal-identification&gt;&lt;rssi&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17672" PostTypeId="2" ParentId="17671" CreationDate="2020-12-03T18:21:47.020" Score="-1" Body="&lt;p&gt;I can think of a few reasons why your WiFi signal strength is 45 dB down from what your router's documentation suggests.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Your phone and antenna aren't calibrated.  Your app makes signal strength estimates using a guess about what kind of phone and antenna you're using, but that's just a guess: mobile phone handsets' WiFi antennas vary widely, and the orientation of the phone, how you're holding it, and where it is relative to other conductive objects can make a difference of many decibels.  The signal levels given by your app are surely meant to be relative, so you can compare reception at one location to reception at another location, rather than absolute.  An accurate absolute measurement of signal strength requires expensive calibrated test equipment with exact placement and orientation in a calibrated test range.  Typically the test range includes a Faraday-cage enclosure that seals other signals out.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Your router may not be set for maximum power.  Maximum power is completely unnecessary for most people, and more power contributes to interference in the common situation where there are many routers with overlapping WiFi coverage, so manufacturers often set the default power level to medium, rather than high.  If you log into your router's command interface you can adjust the band, channel, and power level settings.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Then of course there is the free-space path loss; your phone isn't directly connected by cable to the router, so a lot of the power transmitted by the router is broadcast into space and bypasses your phone's antenna.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-12-07T15:04:52.540" LastActivityDate="2020-12-07T15:04:52.540" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17673" PostTypeId="2" ParentId="17671" CreationDate="2020-12-03T19:02:33.167" Score="2" Body="&lt;p&gt;A Wi-Fi transmitter, like a lightbulb, throws out photons in a lot of directions. Only some of them will be captured by the receiver. Most will go elsewhere, eventually being absorbed by walls, atmospheric water vapor, and so on to be converted to heat.&lt;/p&gt;&#xA;&lt;p&gt;The &lt;a href=&quot;https://ham.stackexchange.com/q/1539/218&quot;&gt;Friis transmission equation&lt;/a&gt; explains this in more rigorous terms.&lt;/p&gt;&#xA;&lt;p&gt;Even if the two antennas are touching, it's unlikely 100% of the transmitted signal will go into the receiver. This is easy to verify if you have a third device, like a laptop. When you touch your phone to the access point, does your laptop entirely lose the WiFi signal? If all the power was going to the phone there would be none left to reach the laptop.&lt;/p&gt;&#xA;&lt;p&gt;Perhaps if you connected the transmitter and receiver directly with a transmission line, you would receive nearly the full power. However this would almost certainly not work, since the receiver is not designed to handle that much power. The receiver may even be damaged. -15 dBm is an extremely good WiFi signal.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-12-03T19:02:33.167" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17674" PostTypeId="2" ParentId="17671" CreationDate="2020-12-03T23:51:21.140" Score="1" Body="&lt;p&gt;First, the router power will be +20 or +22 dBm. Subtract a few dB on the way to the antenna, more if it's an internal antenna.&lt;/p&gt;&#xA;&lt;p&gt;Second, the free space path loss will be at least 20 dB, from phone to router, a few cm apart. This means that even held close by, the phone antenna only captures 1% of the transmitted signal. This will be made worse by the polarisation not being well matched, you might need to rotate the phone to get maximum coupling.&lt;/p&gt;&#xA;&lt;p&gt;Also, the phone antenna probably has a gain of -2 dBi, being so compact and squeezed in to the phone with several other antennas.&lt;/p&gt;&#xA;&lt;p&gt;But most importantly, your phone probably can't measure powers above -15 dBm anyway. That's off the scale for a wifi chip, which usually operates between -30 and -90 dBm.&lt;/p&gt;&#xA;&lt;p&gt;Try about 1 m away, rotating the phone to find the maximum, then you might get more realistic numbers. I get about -25 dBm which is as expected.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2020-12-04T00:13:56.913" LastActivityDate="2020-12-04T00:13:56.913" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17675" PostTypeId="2" ParentId="12203" CreationDate="2020-12-04T13:35:36.977" Score="0" Body="&lt;p&gt;If you have a calculator that can do matrix math with the S-parameters, you can manually compute the required matching components for a given frequency. S-parameters are given over a wide frequency range for the part so the data can look intimidating, but really the worst thing you'll have to do is interpolate between two given frequency points to arrive at the S-parameters for your given frequency (which will be just one 2x2 matrix). Then you can easily use those to figure out how to match your system for best performance.&lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2020-12-04T13:35:36.977" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17676" PostTypeId="2" ParentId="16808" CreationDate="2020-12-04T13:38:03.690" Score="1" Body="&lt;p&gt;If a half wave dipole is resonant, there is no reactance to cancel out. The definition of resonance is when there is no reactance, because there is no phase between voltage and current.&lt;/p&gt;&#xA;" OwnerUserId="8837" LastActivityDate="2020-12-04T13:38:03.690" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17678" PostTypeId="1" CreationDate="2020-12-05T03:25:15.453" Score="1" ViewCount="69" Body="&lt;p&gt;i am considering a &amp;quot;no tune&amp;quot; efhw antenna: &lt;a href=&quot;https://qrpguys.com/qrpguys-end-fed-wire-antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://qrpguys.com/qrpguys-end-fed-wire-antenna&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;i also saw one with a tuner: &lt;a href=&quot;https://qrpguys.com/end-fed-half-wave-sota-antenna-tuner&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://qrpguys.com/end-fed-half-wave-sota-antenna-tuner&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;do resonant antennas need to be tuned when moved or over time? if not, why would someone choose the tuner one? random length antennas?&lt;/p&gt;&#xA;&lt;p&gt;(i will probably use 30m 40m or 80m with my qrp mountain topper.)&lt;/p&gt;&#xA;" OwnerUserId="18192" LastActivityDate="2020-12-06T16:50:14.543" Title="do resonant antennas need to be re-tuned in the field?" Tags="&lt;antenna&gt;&lt;qrp&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17679" PostTypeId="1" AcceptedAnswerId="17681" CreationDate="2020-12-05T04:05:27.100" Score="2" ViewCount="190" Body="&lt;p&gt;morse code signals are only carrier waves, right? so a transceiver transmits a 14 MHz wave, unmodulated, or nothing at all. but i can't hear 14 mhz.&lt;/p&gt;&#xA;&lt;p&gt;i know my radio plays a 700 Hz &amp;quot;side tone&amp;quot; when i transmit (i think) but when i listen to others, the tone can change, so i don't think the tone is being generated locally.&lt;/p&gt;&#xA;&lt;p&gt;so what am i hearing when i am listening to morse code?&lt;/p&gt;&#xA;" OwnerUserId="18192" LastEditorUserId="17305" LastEditDate="2020-12-13T02:43:06.130" LastActivityDate="2020-12-13T02:43:06.130" Title="what am i listening to when i listen to morse code?" Tags="&lt;cw&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17680" PostTypeId="1" CreationDate="2020-12-05T04:06:18.153" Score="0" ViewCount="323" Body="&lt;p&gt;I have a Baofeng and all the people that I have asked said that I can use 144mhz and below without a license but what I see on the internet is that I can’t use the Baofeng without a license at all can I?&lt;/p&gt;&#xA;" OwnerUserId="18195" LastEditorUserId="4665" LastEditDate="2020-12-07T15:42:11.250" LastActivityDate="2020-12-07T19:06:40.310" Title="Can you use 144mhz and below without a license with a Baofeng" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;baofeng&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17681" PostTypeId="2" ParentId="17679" CreationDate="2020-12-05T12:54:55.957" Score="3" Body="&lt;p&gt;A CW receiver works by first tuning an oscillator to the dial frequency, minus the difference frequency. This is called the local oscillator or &amp;quot;LO&amp;quot;. The LO is then &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_mixer&quot; rel=&quot;nofollow noreferrer&quot;&gt;mixed&lt;/a&gt; with the LO. The difference frequency is usually the same as the sidetone frequency, so the sidetone you hear when transmitting is at the same pitch as a properly tuned signal being received. It's typically between 400 and 700 Hz, and in most modern radios is configurable.&lt;/p&gt;&#xA;&lt;p&gt;This mixing, with the appropriate filtering, has the effect of &amp;quot;shifting down&amp;quot; the RF in frequency, so for example a carrier at 14,000,000 Hz makes a tone at 700 Hz, and a carrier at 14,000,100 Hz makes a tone at 800 Hz.&lt;/p&gt;&#xA;&lt;p&gt;This is identical in operation to USB, the only difference being CW mode usually has a narrower filter, and applies a fixed offset (in this example, 700 Hz) to the&#xA;LO. This is why you can also hear CW transmissions in Morse code in USB mode, if you tune 700 Hz below them.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-12-06T04:07:44.107" LastActivityDate="2020-12-06T04:07:44.107" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17683" PostTypeId="2" ParentId="7225" CreationDate="2020-12-06T00:50:54.783" Score="0" Body="&lt;p&gt;If you're looking to minimize common mode current with a choke balun (like that returning from a balanced dipole down an unbalanced coax line), then you could slip a ferrite sleeve around the wire before crimping and heat-shrink it in place.  These can be found at Mouser, Digikey, etc.  Sleeves are much cheaper than clamp-ons.&lt;/p&gt;&#xA;&lt;p&gt;Filter by your cable size (sleeve inside diameter), check the spec sheet to make sure it meets your MHz range and impedance requirements, and slip a few of these on your cable before crimping:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.mouser.com/Passive-Components/EMI-Filters-EMI-Suppression/Ferrites/Ferrite-Cable-Cores/_/N-bw7t5&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ferrite Cable / Ferrite Bead Cores&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16278" LastActivityDate="2020-12-06T00:50:54.783" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17684" PostTypeId="2" ParentId="17678" CreationDate="2020-12-06T14:44:58.780" Score="1" Body="&lt;p&gt;The choice between the &amp;quot;no tune&amp;quot; antenna and the use of a &amp;quot;mini tuner&amp;quot; probably concerns the amount of flexibility that any given installation may require to provide an adequate match to a 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; transmitter. I have not used this antenna, but the &lt;a href=&quot;https://qrpguys.com/qrpguys-end-fed-wire-antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;description&lt;/a&gt; and &lt;a href=&quot;https://qrpguys.com/wp-content/uploads/2019/05/hwwa_assy_052919.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;assembly manual&lt;/a&gt; of the &amp;quot;no tune&amp;quot; antenna give us some valuable clues:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Your feed line is essentially the counterpoise, so a separate one is&#xA;not needed.&lt;/p&gt;&#xA;&lt;p&gt;There can be some significant changes in (radiator) length  due  to  your&#xA;environment.  Your  results  can  vary  depending  on  local&#xA;conditions  and  wire deployment.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The first clue tells us that the feedline - actually, the outside of the coax shield - is part of the antenna system. Since the coax shield is (presumably) connected to the transmitter case and the case may be touched by a person (a big bag of electrolytes!) and/or connected to an electrical ground system, the antenna's &amp;quot;environment&amp;quot; may be quite complex, indeed. The impedance looking into the feedline will, therefore, depend on the lengths and configurations of all directly-connected and nearby conductors that comprise the antenna system and its environment.&lt;/p&gt;&#xA;&lt;p&gt;What is &lt;em&gt;not&lt;/em&gt; stated in the manual may be as important as what &lt;em&gt;is&lt;/em&gt; stated:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;There is no mention of feedline: the feedline is always very short in the drawings and there is no mention of SWR vs. feedline length, so it may be assumed that the stated results correspond to a very short feedline between the transmitter and the matching unit.&lt;/li&gt;&#xA;&lt;li&gt;There is no mention of a grounding system for the transmitter case: in light of the foregoing discussion, it may be surmised that the case is not to be grounded.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;A simple model of an EFHW shows that the impedance varies quite rapidly with frequency. If you wanted to use the antenna across a large part of a band, or on multiple bands, an adjustable matching unit will almost certainly be needed.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2020-12-06T16:50:14.543" LastActivityDate="2020-12-06T16:50:14.543" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17685" PostTypeId="2" ParentId="17680" CreationDate="2020-12-06T15:16:22.160" Score="5" Body="&lt;p&gt;In general, in the USA, transmitting without a license is only permissible under Part 15.  Generally, this imposes limitations in the form of either radiated power restrictions (for instance, building an experimental transmitter to operate in the AM broadcast band, so you can use a common consumer radio to check operation) or in the type/model of device used.&lt;/p&gt;&#xA;&lt;p&gt;Since a Bao-Feng hand held transceiver can't be dialed down to Part 15 power levels, in order to transmit with one without a license requirement, the device would have to be &amp;quot;licensed by type.&amp;quot;  CB radios are one common &amp;quot;license by type&amp;quot; device, along with Family Band (FMRS) transceivers (which have largely replaced CB frequency toy walkie-talkies), FM microphones for PA use, wireless networking devices, etc.&lt;/p&gt;&#xA;&lt;p&gt;Bao-Feng transceivers as currently sold are disabled from transmitting outside the Amateur bands -- for instance, my BF-F8HP has the weather bands and emergency bands, well within the frequency range of the device, and open to receive, locked out from transmission (though older ones reportedly could illegally transmit on those frequencies).  There are no license-by-type provision in the Amateur bands in the United States, so any transmission on those bands requires an Amateur license (with the exception of transmissions of such low power as not to cause interference -- typically this would be power measured in milliwatts, and would be a homebrew transmitter, since no such unit is sold).&lt;/p&gt;&#xA;&lt;p&gt;So, TL;DR: No, you cannot legally transmit with your Bao-Feng transceiver on any frequency it is capable of emitting, without an Amateur radio license, Technician or better (no lower privilege license is still issued).&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2020-12-06T15:16:22.160" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17686" PostTypeId="2" ParentId="17679" CreationDate="2020-12-06T17:17:53.330" Score="0" Body="&lt;p&gt;There are several methods to allow hearing CW as a audible sidetone on receive.  Regenerative and direct conversion receivers often use the same method as they use for LSB/SSB receive and tune above the actual CW spectrum.  Some superhets and SDR radios actually zero beat the CW signal with the main VFO, and then inject a separate BFO oscillator into a separate audio modulator.  This allows using a low-pass CW filter at one of the IF stages instead of an offset bandpass filter.&lt;/p&gt;&#xA;&lt;p&gt;CW-R uses the USB/SSB receive path instead of LSB.  Weird, because when you tune upwards in frequency with the VFO, the CW audio sidetone goes lower in frequency.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-12-06T17:17:53.330" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17687" PostTypeId="1" CreationDate="2020-12-07T04:58:35.367" Score="0" ViewCount="62" Body="&lt;p&gt;I would like to build an FM repeater using a short stack of Kenwood TK-890H rigs adjusted to 70cm USA amateur band, but the model has a 100W rating with a duty cycle of only 20%.  20% isn't nearly enough to keep up with modest repeater usage, even if I reduce the transmit power for longevity.  Is there any open solution that would let me gang them together in a sort of &amp;quot;transmitter voting system&amp;quot;, and have the software take turns using them (using a relay switch to swap one in as needed)?  In this way the work could be divided up by round robin, or by thermistor voting, or whatever.  (I realize a dedicated amp for TX is probably the most correct solution, but I already have these rigs and want to put them to use).&lt;/p&gt;&#xA;" OwnerUserId="17736" LastActivityDate="2020-12-07T20:08:32.823" Title="Repeater design using round robin transmitters to increase duty cycle?" Tags="&lt;rf-power&gt;&lt;repeater&gt;&lt;transmitter&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17688" PostTypeId="1" CreationDate="2020-12-07T10:29:39.220" Score="0" ViewCount="35" Body="&lt;p&gt;I have some very basic question of the ofdm carrier allocation in gnu radio that am not understanding.please help me to understand. I want to pass a LTE  based ofdm modulated signal simply like the attached picture. In that case the fft length is 128 and cyclic prefix is 32. The total number of used carried is 90 and pilot carrier is 10. How can I interpret this things in the ofdm carrier allocator blocks, I have gone through the gnu-radio references yet am not clear on this. Please help me to learn this,I appreciate your help.&#xA;Regards.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/28K80.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/28K80.png&quot; alt=&quot;OFDM transmitter&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18210" LastActivityDate="2020-12-07T10:29:39.220" Title="Ofdm carrier allocator block in gnu radio" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17689" PostTypeId="2" ParentId="17687" CreationDate="2020-12-07T18:44:03.663" Score="1" Body="&lt;p&gt;Sure, I suppose it's possible. Any sort of &amp;quot;voting&amp;quot; seems overcomplicated to me. Simply have a timer that switches to the next radio every 30 seconds or so. If you have five of these radios and switch between them periodically, no one will have a duty cycle above 20%. If you have less than 5 radios then reduce power.&lt;/p&gt;&#xA;&lt;p&gt;The complicated part I suppose is sequencing the switching. You need to:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Stop transmitting on radio A&lt;/li&gt;&#xA;&lt;li&gt;Disconnect radio A&lt;/li&gt;&#xA;&lt;li&gt;Connect radio B&lt;/li&gt;&#xA;&lt;li&gt;Start transmitting on radio B&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;You need a little delay between each of these steps to wait for relays to react, etc. If you connect radio B while radio A is still transmitting, radio B's receiver will probably be blown out. If you transmit on radio B while radio A is transmitting, similarly bad things are likely to happen.&lt;/p&gt;&#xA;&lt;p&gt;Of course there will be a glitch in the transmission every time a switch happens, but probably you can make it fast enough that it's not a serious problem. And I doubt you'll find any off the shelf thing to do this, so you'll have to build it yourself. The sequencing could be done by a simple microcontroller.&lt;/p&gt;&#xA;&lt;p&gt;Alternatively, you could open the radios and extract their power amplifiers, operate each at a reduced power that could be sustained at 100% duty cycle, then combine their output power.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-12-07T18:44:03.663" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17690" PostTypeId="2" ParentId="17680" CreationDate="2020-12-07T18:55:16.217" Score="1" Body="&lt;p&gt;144-148MHz: No, that's a ham radio licensed band.&lt;/p&gt;&#xA;&lt;p&gt;Below 144MHz: That's A LOT of spectrum. A LOT. Some is ham, some is Airplanes (airband), some is commercial FM, some is military. &lt;strong&gt;But in short: No, in no way is this legal to transmit on without a license, and people have been given tens of thousand dollar fines for transmitting where they are not allowed to.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I only add this answer to point out that your question is asking about a huge chunk of spectrum, and it belongs to many different owners.&lt;/p&gt;&#xA;&lt;p&gt;There are &lt;a href=&quot;https://en.wikipedia.org/wiki/ISM_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;a couple of ISM bands that are license free below 144MHz&lt;/a&gt;, but your baofeng is not able to transmit on them, nor is it probably capable of lowering power sufficiently to be ISM-compatible.&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="9636" LastEditDate="2020-12-07T19:06:40.310" LastActivityDate="2020-12-07T19:06:40.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17691" PostTypeId="2" ParentId="17687" CreationDate="2020-12-07T20:08:32.823" Score="2" Body="&lt;p&gt;It is likely that you can operate the TK-890H at 100% duty with better cooling. This would be a lot less work than the scheme you propose.&lt;/p&gt;&#xA;&lt;p&gt;The Kenwood TK-890H has no fan - a good thing for mobile use, it's quiet and it will stay clean and last longer. But to keep it compact, the heatsink is much too small for continuous transmission.&lt;/p&gt;&#xA;&lt;p&gt;My reasoning: The radio must however be able to tolerate a single long &lt;em&gt;over&lt;/em&gt; without burning out or reducing power - at least 20 seconds of continuous talking. There is nothing in the electronics that can have such a long thermal time constant - the components on the PCB will heat up to full temperature in a few seconds, and the power transistors will be fully warmed up and dissipating into the heatsink. The only thing that is &amp;quot;slow&amp;quot; enough to be OK at 20 seconds, but not OK at 60 seconds, is the big heatsink itself. With a small heatsink, they're relying on the aluminium to sink all the energy from the transmission period, and dissipate it over a longer period. You can see that in the design too - it's heavy on metal, light on fins, so it can store more heat.&lt;/p&gt;&#xA;&lt;p&gt;By adding a fan, you can dramatically improve the cooling effectiveness of a heatsink. Scratching on Digikey you'll find examples of heatsink thermal performance changing from 0.6 deg/watt (100 watts = 60 degrees rise, too hot) to 0.15 deg C/watt (100 watts = 15 degrees rise, OK) with forced air.&lt;/p&gt;&#xA;&lt;p&gt;So I would say first test one radio with some fans blowing on it, through the heatsink in the best way you can think of. An array of fans would be better for tolerance of failure. I recommend small 10000+ RPM fans typically used in 1U servers as these move a large volume of air.  They could be thermostatically controlled, or just use a timer, for the time it's transmitting plus 10 minutes.&#xA;It might help to remove the case of the radio and have some air blowing over the PCB.&lt;/p&gt;&#xA;&lt;p&gt;Finally, of course, the fans don't help if the air stays in a sealed box - they just make it worse by increasing the thermal load in the box. You'll need to have some sort of vent to the outside, with a filter to keep things clean inside.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2020-12-07T20:08:32.823" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17692" PostTypeId="1" AcceptedAnswerId="17699" CreationDate="2020-12-07T21:01:17.633" Score="4" ViewCount="224" Body="&lt;p&gt;I am a power electrical engineer college student, and I have a project to make an antenna for magnetic direction finding.&lt;/p&gt;&#xA;&lt;p&gt;My main topic is to detect lightning strikes, but its to hard due to randomness of the lightning occurence. So my lecturer suggest me to model the lightning strike into a spark gap from impulse voltage generator. I learned that lightning spark radiates electromagnetic waves on radio frequency&lt;/p&gt;&#xA;&lt;p&gt;My question:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;How can I know on which frequency I need to make my receiver antenna resonate?&lt;/li&gt;&#xA;&lt;li&gt;Is it true that I can model lightning strike into spark gap from impulse voltage generator? (I can't just write on my paper that my lecturer told me to.)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="18214" LastEditorUserId="8717" LastEditDate="2020-12-13T22:59:36.253" LastActivityDate="2020-12-17T21:56:24.960" Title="Electromagnetic signal from spark gap" Tags="&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;&lt;frequency&gt;&lt;lightning&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17693" PostTypeId="1" CreationDate="2020-12-07T21:08:36.613" Score="1" ViewCount="26" Body="&lt;p&gt;has anyone DIY datamodes cable for HobbyPCB IQ32 SDR ?&lt;/p&gt;&#xA;&lt;p&gt;Im thinking of using SPKR/MIC/PTT port and expose it either towards external USB soundcard (or USB soundcard stick), or directly to laptop USB.&lt;/p&gt;&#xA;&lt;p&gt;Port is Baofeng UV-R3 TRRS wired (Sleeve-GND, 2nd ring - PTT, 1st ring - MIC, Tip - SPKR).&lt;/p&gt;&#xA;&lt;p&gt;Thanks, 73 Vlado 9A5MPV&lt;/p&gt;&#xA;" OwnerUserId="18215" LastActivityDate="2020-12-07T21:08:36.613" Title="HobbyPCB IQ32 SDR Data modes cable?" Tags="&lt;hf&gt;&lt;digital-modes&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17695" PostTypeId="1" CreationDate="2020-12-08T04:38:47.560" Score="0" ViewCount="55" Body="&lt;p&gt;i have been told time of day matters for hf propagation. for example, 80m works best at night. but if i qso with someone on the other side of the world, it's daytime. do they just need more power? can i expect to tx better at night and rx better during daytime (or vice versa)?&lt;/p&gt;&#xA;" OwnerUserId="18192" LastActivityDate="2020-12-08T05:45:08.517" Title="why does time of day affect propagation when talking to the other side of the earth?" Tags="&lt;hf&gt;&lt;propagation&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17696" PostTypeId="2" ParentId="17695" CreationDate="2020-12-08T05:45:08.517" Score="1" Body="&lt;p&gt;Feel free to read up on the following articles:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/Radio_propagation&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Radio_propagation&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://en.wikipedia.org/wiki/High_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/High_frequency&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;With HF ( High Frequency ) the signals are refracted by the &amp;quot;Ionospheric modes (skywave)&amp;quot; back to earth and reflected by the earth itself.&lt;/p&gt;&#xA;&lt;p&gt;The ionosphere is impacted by the sun spots from the sun.&lt;/p&gt;&#xA;&lt;p&gt;I've checked this forum and these articles may interest you:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/17574/sunspot-numbers-forecast-broadcast-on-cw-hf&quot;&gt;Sunspot numbers? forecast? broadcast on CW/HF&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/16859/why-do-horizontally-polarized-rf-waves-reflect-better-off-ground-than-vertically&quot;&gt;Why do horizontally-polarized RF waves reflect better off ground than vertically-polarized waves?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13099" LastActivityDate="2020-12-08T05:45:08.517" CommentCount="1" CommunityOwnedDate="2020-12-08T05:45:08.517" ContentLicense="CC BY-SA 4.0" />
  <row Id="17697" PostTypeId="1" CreationDate="2020-12-08T05:59:46.073" Score="1" ViewCount="118" Body="&lt;p&gt;I know that there is another thread that asks a similar question however the questioner there had DSL internet, so I think my question is sufficiently different to warrant a new thread.&lt;/p&gt;&#xA;&lt;p&gt;(&lt;a href=&quot;https://ham.stackexchange.com/questions/6887/can-my-neighbors-ham-radio-antenna-be-interfering-with-my-internet-signal-or-is?newreg=9c23be1508dd472baafcb2b3424231ca&quot;&gt;Can my neighbor&amp;#39;s ham radio antenna be interfering with my internet signal or is my internet provider just throwing blame elsewhere?&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;I have wireless internet service using LTE signal.  I have had constant problems for several years. The tech from the ISP was here AGAIN last week and is throwing up his hands not knowing what to do.  His report to his boss is that ‘the signal sucks and there’s nothing he can do about it’. He says that other customers several miles away have ‘great signal’ and that our stretch of road and the adjoining road was a ‘black hole’.&lt;/p&gt;&#xA;&lt;p&gt;I am not a techie…just trying to figure out this mess so my kids can do their online school!&lt;/p&gt;&#xA;&lt;p&gt;A neighbour who lives about 500m away at the corner of the adjoining road is a ham radio operator.  He has been there for years. It just dawned on me tonight that maybe his equipment was causing interference with my LTE signal. So searched and came across this site.  Nice to meet you all :)&lt;/p&gt;&#xA;&lt;p&gt;I believe that this is the info on my LTE system.&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;Frequency 3615.0 MHz&#xA;&#xA;Bandwidth 20 MHz&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;The SINR number for my signal is inexplicably VERY low (0-2 and even sometimes -1) indicating high level of signal interference. I'm led to understand that this should be up higher than 12 or 13, preferably 20.&lt;/p&gt;&#xA;&lt;p&gt;QUESTIONS&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;So is it possible that interference from the ham radio is the source?&lt;/li&gt;&#xA;&lt;li&gt;Is it possible that the signal from the ham radio is aimed in a certain 'direction', or is it 360deg?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I understand from the discussion on 6887 that it's not the ham radio operator’s ’fault’ and that the wireless internet equipment should filter interference out, and it may not be doing what it is supposed to be doing.&lt;/p&gt;&#xA;&lt;p&gt;If you need more info to help answer, please let me know and I will edit the question to make it more complete.&lt;/p&gt;&#xA;&lt;p&gt;Any assistance is appreciated!&lt;/p&gt;&#xA;&lt;p&gt;Phil&lt;/p&gt;&#xA;" OwnerUserId="18219" LastEditorUserId="18219" LastEditDate="2020-12-08T06:29:29.943" LastActivityDate="2020-12-10T13:19:38.020" Title="Can ham radio interfere with LTE wireless internet signal?" Tags="&lt;rfi&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17698" PostTypeId="2" ParentId="17697" CreationDate="2020-12-08T14:11:28.457" Score="5" Body="&lt;p&gt;the short answer to #1 is that it is &lt;em&gt;possible&lt;/em&gt; but not at all &lt;em&gt;likely&lt;/em&gt; for the same reasons &lt;a href=&quot;https://ham.stackexchange.com/a/6888/1550&quot;&gt;Kevin outlines in his answer&lt;/a&gt; to the question you linked to, especially the fact that almost no ham radio operators transmit continuously... only when actually having a conversation, and only when it's our turn to speak in the conversation.&lt;/p&gt;&#xA;&lt;p&gt;Answering #2, the directivity of the ham's signal: it depends on the antenna. If the antenna he has is just a wire or pole sticking straight up in the air, it's pretty close to 360° even. If it's any other configuration, it's stronger in some directions and weaker in others.&lt;/p&gt;&#xA;&lt;p&gt;A note regarding interpreting your measured signal to noise ratio (SINR), it may indicate a higher noise floor where you are OR a lower signal from your carrier. Without measuring the noise floor and signal strength separately at a location that &amp;quot;works,&amp;quot; it's difficult to understand what's &amp;quot;really&amp;quot; happening.&lt;/p&gt;&#xA;&lt;p&gt;It may be (likely is) that the antenna configuration &amp;amp; power from your service provider in your direction is just not strong enough for the service level expected. Or perhaps your antenna is either misconfigured or not the most appropriate for service operation... this seems especially likely given your comment below re immediate neighbors' service level seems good with their antennas.&lt;/p&gt;&#xA;&lt;p&gt;Finally: go introduce yourself to the ham! Many of us LOVE figuring out stuff like this. It may be that he even has the equipment to measure your signal issues and help diagnose and get to a solution.&lt;/p&gt;&#xA;&lt;p&gt;BEWARE: you may become interested enough to get a license and pick up a fascinating new hobby... if that happens, we'll be here to welcome you in :-)&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2020-12-10T13:19:38.020" LastActivityDate="2020-12-10T13:19:38.020" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17699" PostTypeId="2" ParentId="17692" CreationDate="2020-12-08T16:41:00.080" Score="6" Body="&lt;p&gt;Don't worry, there have been many researchers before you, and you can borrow some of their work.  Your English is fine.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;If you do a web search for &amp;quot;lightning spectrum&amp;quot;, you will find a graph showing lightning intensity vs. frequency.  The range of frequencies emitted by lightning discharges is very broad.  From amateur radio experience I can tell you that in the US, the 160m, 80m, 60m, and 40m bands (wavelengths) are difficult to use in summer because of noise from lightning.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Try it and see!  Build a high-voltage source, discharge it through a spark gap, and listen with a radio, such as an AM radio or shortwave radio receiver.  I think that you will hear a noise.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-12-08T16:41:00.080" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17700" PostTypeId="1" AcceptedAnswerId="17703" CreationDate="2020-12-08T21:09:37.550" Score="2" ViewCount="65" Body="&lt;p&gt;Hello I am a beginner on radio and also In speaking english. I hope you will understand what I say.&lt;/p&gt;&#xA;&lt;p&gt;Let's say I have an impulse generator and the air gap breakdown. I am already able to see the impulse breakdown wave in my oscilloscope and it's has about 1.2 ns rise time.&lt;/p&gt;&#xA;&lt;p&gt;I know that spark gap will radiated electromagnetic wave on a wideband of frequency.&lt;/p&gt;&#xA;&lt;p&gt;1.Can I count or measure the wave on frequency domain? If I can, what is the tool that I need? Is it spectrum analyzer? Or oscilloscope can do that?&lt;/p&gt;&#xA;&lt;p&gt;2.continue from Question 1, does the impulse breakdown wave that I see on my oscilloscope have a relation with the electromagnetic wave radiated from the spark gap? I see some equation that related to the rise time to measure a bandwidth, but Im do not sure what it is.&lt;/p&gt;&#xA;&lt;p&gt;My goal is to design an antenna to detect the electromagnetic radiated by spark gap.&lt;/p&gt;&#xA;&lt;p&gt;Once again, I hope you understand what I mean. And I am sorry if its a silly question since I really am a beginner and if you have a suggestion topic for me to learn the detail for your answer, I will really thankful! Hope you all have a great life!&lt;/p&gt;&#xA;" OwnerUserId="18214" LastEditorUserId="4665" LastEditDate="2020-12-09T22:10:55.233" LastActivityDate="2020-12-09T22:10:55.233" Title="Signal frequency domain" Tags="&lt;antenna&gt;&lt;frequency&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17701" PostTypeId="1" AcceptedAnswerId="17702" CreationDate="2020-12-08T21:56:21.843" Score="4" ViewCount="238" Body="&lt;p&gt;My son &lt;a href=&quot;https://www.qrz.com/db/KJ7NLL&quot; rel=&quot;nofollow noreferrer&quot;&gt;KJ7NLL&lt;/a&gt; just got his general, and while we don't (yet?) have plans to transmit at 1.5kW, he asks if the 1.5kW limit is per-antenna?&lt;/p&gt;&#xA;&lt;p&gt;If it is per-antenna, and you use an antenna array of 8 antennas (phased array, multi-antenna stack of Yagis, etc), then you could get 8x 1.5kW for things like EME.&lt;/p&gt;&#xA;&lt;p&gt;This seems like an edge case, not sure if the rules cover it or not but would like to know to at least satisfy curiosity, perhaps even for future EME.&lt;/p&gt;&#xA;" OwnerUserId="16278" LastEditorUserId="218" LastEditDate="2020-12-09T14:14:42.987" LastActivityDate="2021-05-14T22:39:27.990" Title="Is the 1.5kW power limit per antenna? What about antenna arrays?" Tags="&lt;antenna&gt;&lt;united-states&gt;&lt;legal&gt;&lt;rf-power&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17702" PostTypeId="2" ParentId="17701" CreationDate="2020-12-08T22:37:31.353" Score="10" Body="&lt;p&gt;Here's &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.313&quot; rel=&quot;noreferrer&quot;&gt;47 CFR § 97.313&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§ 97.313 Transmitter power standards.&lt;/p&gt;&#xA;&lt;p&gt;(a) An amateur station must&#xA;use the minimum transmitter power necessary to carry out the desired&#xA;communications.&lt;/p&gt;&#xA;&lt;p&gt;(b) No station may transmit with a transmitter power exceeding 1.5 kW&#xA;PEP.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;So sorry, you're only allowed a maximum of 1.5 kW per station, not per antenna.&lt;/p&gt;&#xA;&lt;p&gt;I can anticipate a further question, &amp;quot;what about multiple transmitters, with one antenna per transmitter?&amp;quot;  I'm no lawyer, but I'd think that the FCC would consider multiple synchronized transmitters transmitting the same thing on the same frequency with a phased antenna array to be a single station under the law.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-12-08T22:37:31.353" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17703" PostTypeId="2" ParentId="17700" CreationDate="2020-12-09T03:23:10.200" Score="1" Body="&lt;p&gt;You could do it with a spectrum analyzer, but there's not a lot of point to it. If you know the rise time of a current impulse, then a quick estimate is that it carries significant energy at every frequency between 0 and the inverse of the rise time, e.g. 833 MHz for 1.2 ns.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-12-09T03:23:10.200" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17704" PostTypeId="1" CreationDate="2020-12-09T03:56:57.943" Score="1" ViewCount="52" Body="&lt;p&gt;I am going through a bit of a headache trying to find this information. I have a lot of people interested in a private simplex node/repeater network using Asterisk/app_rpt, the same software AllStarLink uses. Instead of using dynamic DNS or OpenVPN, I would like to use their technique on node lookup, that is, DNS. They state in their wiki that they utilize a PowerDNS server with MySQL. How would I go about doing this? I hope I am asking in the right place. I know how it works, I just don't know how to implement it on my system. I would preferably want to know how HamVoIP does it as well. The way I am doing it now is everybody hears everybody by everyone connecting to a central hub. I don't want that type of system. Thanks!&lt;/p&gt;&#xA;" OwnerUserId="18225" LastEditorUserId="4665" LastEditDate="2020-12-09T16:48:40.477" LastActivityDate="2020-12-09T16:48:40.477" Title="Is it possible to setup a private network with DNS lookup using app_rpt?" Tags="&lt;repeater&gt;&lt;linux&gt;&lt;internet&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17705" PostTypeId="1" CreationDate="2020-12-09T21:45:19.197" Score="4" ViewCount="116" Body="&lt;p&gt;The way I understand how SDR works, there is a receiver input, generally connected to an antenna pulling in signals from the ether.  That input is connected to two mixers (linear multipliers), being mixed with the same LO frequency in both mixers, however, the two LO signals are 90º out of phase.  This results in two output signals, commonly referred to as I and Q, I for the &amp;quot;in phase&amp;quot; signal, and Q for the &amp;quot;quadrature&amp;quot;, or 90º out of phase signal.&lt;/p&gt;&#xA;&lt;p&gt;Then, if there is a modulated (say AM modulated with voice) frequency of interest, we can tune the LO to the carrier frequency, and because of heterodyning principles we are now only having to deal with the baseband frequencies, which is much easier/cheaper to digitize.&lt;/p&gt;&#xA;&lt;p&gt;Now if we would have only heterodyned with a single mixer, we would get the difference between the carrier frequency and the baseband frequencies, thus the upper sideband would now appear as frequencies from zero to the upper limit of the baseband frequencies, and the lower sideband would appear as a mirror image to that, thus, would be negative frequencies.&lt;/p&gt;&#xA;&lt;p&gt;How do we deal with negative frequencies?  FWIU, this is where the quadrature (Q) heterodyning comes in.  Somehow by shifting the LO frequency 90º, the output from the Q mixer contains the information which was present in the lower sideband.&lt;/p&gt;&#xA;&lt;p&gt;This is what I am having difficulty understanding/visualizing.  I am sure Euler's formula comes into this, and could probably follow the math if presented to me (and by all means don't get me wrong, I am interested in seeing the math as well,) but I am having difficulty &lt;em&gt;visualizing&lt;/em&gt; how this can be so.&lt;/p&gt;&#xA;&lt;p&gt;For one thing, we talk about 2 LO signals 90º apart.  But what determines which one is which?  Ie, if I were to mix the incoming signal with only one LO output or the other, the incoming signal would not know the difference and in either case would give me difference frequency between the carrier and the baseband.  It would look the same whether I heterodyned it with a sine wave of a cosine wave, because who knows what phase angle either of those waveforms would be to the carrier?  It could be anything.  At least in traditional superhet radios, it didn't matter.&lt;/p&gt;&#xA;&lt;p&gt;So then why is I the &amp;quot;in phase&amp;quot; signal?  In phase to what?  The carrier?  But then, following the reasoning of the previous paragraph, why would this matter?&lt;/p&gt;&#xA;" OwnerUserId="18177" LastActivityDate="2020-12-16T17:41:32.613" Title="Understanding how quadrature heterodyning captures information from negative frequencies" Tags="&lt;software-defined-radio&gt;&lt;dsp&gt;" AnswerCount="4" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17706" PostTypeId="1" CreationDate="2020-12-09T21:55:31.317" Score="3" ViewCount="186" Body="&lt;p&gt;I'm planning to build a 20m SSB transceiver and I want to get the overall architecture straight in my head first.  Here's what I'm thinking so far, a single conversion superhet design with a 9MHz IF and a homemade crystal filter.  The problem I'm struggling with is in relation to mixers and inversion.&lt;/p&gt;&#xA;&lt;p&gt;Because it's 20m and conventionally broadcasts are USB, lets say we're tuned to 14.1MHz and there is a USB signal from 14.1 to 14.103 MHz. 14.1 equates to 0Hz audio and 14.103 is the highest audio frequency.  My filter has a BW of 3KHz and a centre frequency of 9 MHz.  If I tune my VFO to 23.1015 MHz then I end up with an inverted USB signal through my filter.  Do I have that correct?&lt;/p&gt;&#xA;&lt;p&gt;So, 23.1015 - 14.1 = 9.0015 (i.e., the lowest audio frequency in my signal ends up at the highest frequency through my filter)&#xA;Likewise, 23.1015 - 14.103 = 8.9985 (highest audio is lowest through filter)&#xA;But, it's often said that a crystal filter favours LSB, is this setup going to cause any issues?&lt;/p&gt;&#xA;&lt;p&gt;So, if I set my BFO to 9.0015 MHz, I get: 9.0015 - 9.0015 = 0 Hz and 9.0015 - 8.9985 = 3 KHz.  So, the highest filtered signal becomes the lowest audio signal and vice-versa..  Do I have that right?&lt;/p&gt;&#xA;&lt;p&gt;I'm not sure if this is the standard way to build a simple SSB transceiver, are there any pitfalls in this approach?&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="8717" LastEditDate="2020-12-13T03:12:39.570" LastActivityDate="2020-12-13T03:12:39.570" Title="SSB Transceiver Architecture - USB with Crystal Filter" Tags="&lt;transceiver&gt;&lt;equipment-design&gt;&lt;filter&gt;&lt;ssb&gt;&lt;mixer&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17707" PostTypeId="2" ParentId="17705" CreationDate="2020-12-09T22:47:09.467" Score="4" Body="&lt;p&gt;A negative frequency is just a positive frequency &amp;quot;in the opposite direction&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Imagine I have a transparent wheel, which has a black disc inside of it at one point near the edge. Now imagine I shine a light through the wheel's diameter from the side, so that the shadow of the disc appears on the wall. If I spin the wheel, you can watch the shadow going up and down on the wall in a sinusoidal pattern. If you graphed the height of the shadow on the wall vs. time, you could tell the frequency of the sine wave, and therefore the frequency of the wheel's rotation. But nothing you recorded from that shadow could tell you whether the wheel was spinning clockwise or counterclockwise!&lt;/p&gt;&#xA;&lt;p&gt;Now imagine I added a second light, above the wheel (at a 90° angle from the first in the plane of the wheel), casting a shadow on the table below. This shadow will also move in a sinusoidal pattern, at the same rate as the other one, but with a 90° phase shift, and you could recover exactly the same frequency information by watching this shadow alone.&lt;/p&gt;&#xA;&lt;p&gt;But if you recorded &lt;em&gt;both&lt;/em&gt; shadows at the same time, you might notice that in some cases the &amp;quot;positive peak&amp;quot; of one shadow is 90° &lt;em&gt;ahead&lt;/em&gt; of the other, and sometimes it's 90° &lt;em&gt;behind&lt;/em&gt; instead. And in fact, the one case is when the wheel is turning clockwise, and the other is when the wheel is turning counterclockwise. (It doesn't matter which axis you define as the &amp;quot;first&amp;quot; axis, which direction you define as positive, or which direction you define as clockwise... as long as you make a choice and stick to it. Any change to one of them will swap the sign of your result).&lt;/p&gt;&#xA;&lt;p&gt;So, sine and cosine are both 1-D projections of something happening in 2-D. With only one of them, we can't distinguish a &amp;quot;positive&amp;quot; frequency from a negative one, but with both of them, positive and negative frequencies behave differently, and we can use this property to recover information from frequencies that were downmixed &amp;quot;below zero&amp;quot; without running into the aliasing problems that we would have if we only used one.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2020-12-10T04:56:15.187" LastActivityDate="2020-12-10T04:56:15.187" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17708" PostTypeId="2" ParentId="17705" CreationDate="2020-12-10T04:34:20.107" Score="4" Body="&lt;p&gt;Some quick definitions: a sinusoid with angular frequency &lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt; and phase &lt;span class=&quot;math-container&quot;&gt;$\varphi$&lt;/span&gt; at time &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt; is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(\omega t + \varphi ) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now let's consider a scenario: we have an ideal mixer with an LO with &lt;span class=&quot;math-container&quot;&gt;$\omega = 1$&lt;/span&gt; and variable phase, and we want to produce an output at &lt;span class=&quot;math-container&quot;&gt;$\omega = 0.3$&lt;/span&gt;. We know we can do that with an input to the mixer with either:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\omega = 0.7$&lt;/span&gt; (because &lt;span class=&quot;math-container&quot;&gt;$1 - 0.7 = 0.3$&lt;/span&gt;), or&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\omega = 1.3$&lt;/span&gt; (because &lt;span class=&quot;math-container&quot;&gt;$1.3 - 1 = 0.3$&lt;/span&gt;).&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Now if I might reframe your question a bit, you've been told in the first case, somehow we get a negative frequency, because the input is below the LO; and in the second case we get a positive frequency because the input is above the LO. The question is, how can the mixer &amp;quot;know&amp;quot; if a frequency is positive or negative?&lt;/p&gt;&#xA;&lt;p&gt;We are going to consider four ways we might mix:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Input below the LO, LO phase = 0&lt;/li&gt;&#xA;&lt;li&gt;Input above the LO, LO phase = 0&lt;/li&gt;&#xA;&lt;li&gt;Input below the LO, LO phase = &lt;span class=&quot;math-container&quot;&gt;$-\pi/2$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;Input above the LO, LO phase = &lt;span class=&quot;math-container&quot;&gt;$-\pi/2$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;h2&gt;First case: Input below the LO, LO phase = 0&lt;/h2&gt;&#xA;&lt;p&gt;Mathematically, this is&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(t) \times \cos(0.7 t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Plot it:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ChJmh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ChJmh.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It's plain enough to see this does indeed produce an output that's a low frequency sinusoid superimposed on a higher frequency one. Now, we are really only interested in the lower frequency term (1 - 0.7). We know that lower frequency term has &lt;span class=&quot;math-container&quot;&gt;$\omega = 0.3$&lt;/span&gt;, what's it's phase? Just eyeballing it, it looks like 0. So let's plot that again, with the low frequency term &lt;span class=&quot;math-container&quot;&gt;$\cos(0.3 t + 0)$&lt;/span&gt; included:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MTaUK.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MTaUK.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;So we can say:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(t) \times \cos(0.7 t) = {\cos(0.3t + 0) \over 2} + \dots $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Here, &lt;span class=&quot;math-container&quot;&gt;$\dots$&lt;/span&gt; denotes the higher frequency term that we don't really care about for this example.&lt;/p&gt;&#xA;&lt;h2&gt;Second case: Input above the LO, LO phase = 0&lt;/h2&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(t) \times \cos(1.3 t) = {\cos(0.3t + 0) \over 2} + \dots $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QL6ey.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QL6ey.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;OK, the higher frequency term has changed of course, but the &lt;span class=&quot;math-container&quot;&gt;$\omega=0.3$&lt;/span&gt; term we are interested in is exactly the same. It doesn't seem like there's any way to differentiate negative from positive frequencies from this.&lt;/p&gt;&#xA;&lt;h2&gt;Third case: Input below the LO, LO phase = &lt;span class=&quot;math-container&quot;&gt;$-\pi/2$&lt;/span&gt;&lt;/h2&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(t-\pi/2) \times \cos(0.7 t) = { \cos(0.3t - \pi/2) \over 2 } + \dots $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Dfv8U.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Dfv8U.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;OK, there's still an &lt;span class=&quot;math-container&quot;&gt;$\omega = 0.3$&lt;/span&gt; output, but the phase has changed. That would make sense, because the phase of the LO also changed. Moving on...&lt;/p&gt;&#xA;&lt;h2&gt;Fourth case: Input above the LO, LO phase = &lt;span class=&quot;math-container&quot;&gt;$-\pi/2$&lt;/span&gt;&lt;/h2&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(t-\pi/2) \times \cos(1.3 t) = { \cos(0.3t + \pi/2) \over 2 } + \dots $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/TqQhE.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/TqQhE.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Similar to the last case, but the phase has flipped by 180 degrees. It seems the phase of the mixer's output &lt;em&gt;changes&lt;/em&gt; depending on whether the input was above or below the LO!&lt;/p&gt;&#xA;&lt;h2&gt;Conclusion&lt;/h2&gt;&#xA;&lt;p&gt;When multiplying two sinusoids of the same phase, the output does not depend on whether the input to the mixer is above or below the LO.&lt;/p&gt;&#xA;&lt;p&gt;But when the LO and the mixer input are 90 degrees out of phase, the output will be &lt;em&gt;inverted&lt;/em&gt;, or not, depending on whether the input was above or below the LO.&lt;/p&gt;&#xA;&lt;p&gt;It's this difference that allows an IQ mixer to &amp;quot;know&amp;quot; if a frequency is positive or negative. And it's also this difference that explains why &lt;a href=&quot;https://ham.stackexchange.com/questions/17663/heterodyning-complex-values-in-gnuradio&quot;&gt;complex multiplication can shift frequencies without dealing with image frequencies&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;When an IQ mixer multiplies the same signal by two LOs each 90 degrees out of phase, it is effectively converting the input signal (which is a real function) into a complex function. Multiplying by &lt;span class=&quot;math-container&quot;&gt;$\cos(\omega_\text{LO}t)$&lt;/span&gt; produces the real part, and multiplying by &lt;span class=&quot;math-container&quot;&gt;$\sin(\omega_\text{LO}t)$&lt;/span&gt; produces the imaginary part.&lt;/p&gt;&#xA;&lt;p&gt;If you think about this as plotted on the &lt;a href=&quot;https://en.wikipedia.org/wiki/Complex_plane&quot; rel=&quot;nofollow noreferrer&quot;&gt;complex plane&lt;/a&gt;, two sinusoids 90 degrees apart will will trace a circle:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/IR9nE.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/IR9nE.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;br&gt;&#xA;&lt;em&gt;&lt;a href=&quot;http://www.math.tamu.edu/%7Ealarios/courses/TAMU/2013_fall_M151/mathgifs.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;image source&lt;/a&gt;, which is unfortunately no longer online&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;If you invert one of those functions but not the other by moving the signal to the other side of the LO, the result is tracing the same circle but spinning in the other direction.&lt;/p&gt;&#xA;&lt;p&gt;If you want a purely real function, then what you need are two circles spinning in opposite directions. Added together, and in the right phase, their imaginary parts will cancel and you're left with only the real part.&lt;/p&gt;&#xA;&lt;p&gt;And the same logic in the other direction, if you start with a purely real function, &amp;quot;under the hood&amp;quot; that's two circles spinning in opposite directions, a positive and negative frequency counterpart.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-12-10T14:27:41.610" LastActivityDate="2020-12-10T14:27:41.610" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="17709" PostTypeId="2" ParentId="17706" CreationDate="2020-12-10T11:12:43.360" Score="4" Body="&lt;p&gt;All OK. Pitfall for 14 MHz RX and 9 MHz crystal filter is choice of oscillator frequency. 5 MHz is possible but a bad choice, because the harmonics of the oscillator give unwanted spurious reception.&lt;/p&gt;&#xA;&lt;p&gt;By the way: I did identical things. See pictures. In my opinion there is no preference for LSB or USB based on such passband characteristics.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/dB5q6.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dB5q6.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-12-10T11:12:43.360" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17710" PostTypeId="2" ParentId="17706" CreationDate="2020-12-10T14:13:05.980" Score="3" Body="&lt;p&gt;Using an example from &lt;a href=&quot;https://www.arrl.org/files/file/QEX_Next_Issue/Nov-Dec_2009/QEX_Nov-Dec_09_Feature.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Crystal Ladder Filters for All&lt;/a&gt;, a crystal filter response might look like this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zze0O.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zze0O.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Indeed, this filter might &amp;quot;prefer&amp;quot; LSB, because that would place the carrier near the right side of the passband which has a steeper attenuation. That would mean you'd design your IF like this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/E4BrZ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/E4BrZ.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;When the IF is subsequently heterodyned down to baseband, there are two bands that will be audible: the desired signal in green, and the image frequencies in red. Designing the IF in this way is good because it maximizes attenuation of the image frequencies.&lt;/p&gt;&#xA;&lt;p&gt;Insufficient attenuation to the left of the green area maps to audible frequencies above 3400 Hz. The filter between your ears is very good at removing this interference because its frequency does not overlap with the signal.&lt;/p&gt;&#xA;&lt;p&gt;But insufficient attenuation to the right maps to audible frequencies that overlap with the signal. Your brain can not filter out this interference.&lt;/p&gt;&#xA;&lt;p&gt;If the IF were designed the other way, then attenuation of the image frequencies (in red) would not be as good:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Lao8o.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Lao8o.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Of course, whether this particular issue is more relevant than other concerns, and if your particular filter response is like this example is a different matter. If you look at F. Sessink's image for example, it looks like the filter response is essentially symmetrical. And even in the example here with the carrier to the left of the passband, the attenuation of the image frequencies is still at worst 50 dB, which isn't terrible. As F. Sessink notes in the comments and other answer, other concerns such as phase noise and other spurious reception may likely be more significant.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-12-10T22:28:11.807" LastActivityDate="2020-12-10T22:28:11.807" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17711" PostTypeId="2" ParentId="17701" CreationDate="2020-12-10T14:50:54.097" Score="5" Body="&lt;p&gt;The 1.5kW limit is really per transmission.  But there are other limits as well that may be reached first.  Some bands have a much lower power limit.&lt;/p&gt;&#xA;&lt;p&gt;Also, high on that list is safety, and this isn't just a good idea, it's legally required in the amateur radio regulations.  Above 50w and certainly above 100w you should be doing an environmental study to make sure that people in the environment of your antenna are not absorbing radiation above safe levels.  In a multi-antenna or multi-transmitter situation, the radiation from each adds up to a total that may not be safe.  (Note: the FCC recently dropped the amateur radio exemption for low power stations.  Now all stations are suppose to do an environmental study.)&lt;/p&gt;&#xA;&lt;p&gt;Also, high gain antennas can focus power to unsafe levels even when transmitter power is low, and it is important to make sure people can't walk through the beam of such an antenna.&lt;/p&gt;&#xA;&lt;p&gt;Physics may also limit your power.  As your power level increases, SWR and loss in your antenna system become more and more critical.  At high power levels, loss translates to heat, and enough heat can burn through components, and SWR becomes a multiplier for these problems.  While low power stations try to minimize loss and swr for efficiency reasons (to make best use of power available), high power stations must fix these issues to operate at all.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-05-14T22:39:27.990" LastActivityDate="2021-05-14T22:39:27.990" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17712" PostTypeId="2" ParentId="17705" CreationDate="2020-12-10T17:21:06.180" Score="2" Body="&lt;p&gt;Negative frequencies in the real (single DOF measurement) world are just what we call positive frequencies that happen to below some other frequency.&lt;/p&gt;&#xA;&lt;p&gt;Above baseband, that LSB signal isn't really negative, just lower than some reference frequency (the carrier).&lt;/p&gt;&#xA;&lt;p&gt;The in phase signal alone isn't in phase to anything.  It just has a related phase to a second (quadrature) signal.  If the other signal (2) matches 90 degrees later (e.g. is less than half a period delayed), then the earlier signal (1) is the in phase signal.  If the other signal (2) is delayed by more than half a period, that the same as that other signal (2) being earlier by less than half a period, making that other signal (2) the in phase signal.&lt;/p&gt;&#xA;&lt;p&gt;When an RF signal is singly modulated down to baseband, its LSB will alias with its USB and thus both sidebands will get mixed together into a single signal.  And if you FFT any strictly real signal (non-DC), you will see a complex conjugate mirror image.  And can't tell original (before mixing) USB from LSB data.&lt;/p&gt;&#xA;&lt;p&gt;When quadrature modulated down to baseband, you get two resulting signals.&lt;/p&gt;&#xA;&lt;p&gt;When mixing (by multiplication) two sinusoids different in frequency, a beat note at the difference between the two input frequencies will appear.  The zero crossings of the beat note will appear when the 2 sinusoids are temporarily 90 degrees apart, e.g a peak of one sinusoid near the same time as a zero crossing of the other.  The peaks of the beat note will occur when the peaks of the two sinusoids either align or go in opposite directions.  Which (same or opposite peak alignment) happens next will depend on whether the difference between in frequency between in input signal and the modulating signal is positive (higher) or negative (lower).&lt;/p&gt;&#xA;&lt;p&gt;When quadrature modulated down to baseband, you get two &amp;quot;beat note&amp;quot; results; one for I, and one for Q.  The phase difference of the two &amp;quot;beat note&amp;quot; results from an LSB signal will be opposite to that of phase difference between the two &amp;quot;beat note&amp;quot; results from an USB signal (of the same offset).&lt;/p&gt;&#xA;&lt;p&gt;Thus a complex FFT of the IQ baseband signal can differentiate between the two different sidebands, as they won't be strict conjugate mirror images, due to this phase difference in the two different &amp;quot;beat notes&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;And you can thus &amp;quot;get&amp;quot; one or the other sideband by looking at the FFT result, or any similar process.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-12-11T00:00:19.067" LastActivityDate="2020-12-11T00:00:19.067" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17713" PostTypeId="1" CreationDate="2020-12-11T15:46:05.930" Score="1" ViewCount="32" Body="&lt;p&gt;&lt;strong&gt;Disclaimer&lt;/strong&gt;: I'm aware of legal issues regarding EWS! Rest assured that there is no need for concern as this is a small-scale, proof of concept done in a controlled enviroment!&lt;/p&gt;&#xA;&lt;p&gt;Greetings!&lt;/p&gt;&#xA;&lt;p&gt;I'm trying to send EWS signals over DAB+ with my HackRF One, but I haven't really been able to figure it out yet. Is there someone who has attempted the same and had success?&lt;/p&gt;&#xA;&lt;p&gt;I have been reading ETSI's &lt;a href=&quot;https://www.etsi.org/deliver/etsi_en/300400_300499/300401/02.01.01_60/en_300401v020101p.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;European Standard&lt;/a&gt; and their &lt;a href=&quot;https://www.etsi.org/deliver/etsi_ts/101700_101799/101756/02.02.01_60/ts_101756v020201p.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Technical Specification&lt;/a&gt;. But that doesn't really give examples for implementation. I do however have some vague gist as to how the protocol works after reading those but that's about it.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://github.com/Opendigitalradio/data-over-dab-example&quot; rel=&quot;nofollow noreferrer&quot;&gt;There is an existing, open-source project available on Github for sending custom data over DAB+&lt;/a&gt; but that has only gotten me so far. I did however manage to send custom, non-EWS signals over DAB+ but I digress.&lt;/p&gt;&#xA;&lt;p&gt;After some closer inspection of their project, I did see some recurring things come by such as &lt;a href=&quot;https://github.com/Opendigitalradio/ODR-DabMux/tree/master/src/fig&quot; rel=&quot;nofollow noreferrer&quot;&gt;FIG&lt;/a&gt; and FIG0. Having read the ETSI documents, EWS could be enabled if some bit field (&lt;a href=&quot;https://www.etsi.org/deliver/etsi_ts/101700_101799/101756/02.02.01_60/ts_101756v020201p.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;bit field 0 according to ETSI TS 101 700&lt;/a&gt;) is turned on by a simple 1 (?). This is as far as my knowledge regarding EWS and DAB+ goes. I was hoping that some other knowledgeable individual has had succes in doing this.&lt;/p&gt;&#xA;&lt;p&gt;Any kind of input regarding how, whether it's possible with that open-source project, or anything else is greatly appreciated! Thank you for your time!&lt;/p&gt;&#xA;" OwnerUserId="18240" LastEditorUserId="18240" LastEditDate="2020-12-11T20:41:51.647" LastActivityDate="2020-12-11T20:41:51.647" Title="Sending custom EWS over DAB+ with a HackRF One" Tags="&lt;software-defined-radio&gt;&lt;software-development&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17714" PostTypeId="1" AcceptedAnswerId="17715" CreationDate="2020-12-11T22:49:39.280" Score="2" ViewCount="113" Body="&lt;p&gt;Maybe this is a really silly question even from me, a completely amateur...&lt;/p&gt;&#xA;&lt;p&gt;But I like to know about how's the antenna output when its receive multiple signal&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Is it possible  different signals on same frequency exist? And can they resonate to antenna at the same time?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If it's possible how's the antenna response? Is it will sum up or superposition all the signals?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I am confuse with a wideband signal or wideband antenna fundamental. I learned about FM and AM modulation and these question appears.&lt;/p&gt;&#xA;&lt;p&gt;Thanks!! Sry bad english&lt;/p&gt;&#xA;" OwnerUserId="18214" LastEditorUserId="8717" LastEditDate="2020-12-18T21:58:09.933" LastActivityDate="2020-12-18T21:58:09.933" Title="Receiving multiple signal" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;receiver&gt;&lt;frequency&gt;&lt;signal-identification&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17715" PostTypeId="2" ParentId="17714" CreationDate="2020-12-11T23:26:33.190" Score="3" Body="&lt;p&gt;Transmission between antennas is &amp;quot;two port in to two port out&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;But: in between there is a transmission path with reflections. Some frequencies are attenuated and some other frequencies are even stronger than average. That is called Rayleigh path (sorry, not complete for the moment). The transfer is frequency-dependent AND antenna position dependent.&lt;/p&gt;&#xA;&lt;p&gt;A different receiving antenna position has different effect from that &amp;quot;selective fading&amp;quot;. The frequency transfer between transmitter antenna and receiver antenna can be completely different. That is why MIMO works.&lt;/p&gt;&#xA;&lt;p&gt;Back to your questions: different signal on same frequency can. From different TX-positions. Same TX position can also but same frequency and same position makes separation impossible (....other options...).&lt;/p&gt;&#xA;&lt;p&gt;Question 2 can't be answered: the propagation path between TX and RX is a not-used variable in your imagination. Position of (TX and) RX antenna in a Rayleigh path, and also frequency offset give new opportunities.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2020-12-11T23:26:33.190" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17716" PostTypeId="2" ParentId="17714" CreationDate="2020-12-12T06:53:06.100" Score="1" Body="&lt;p&gt;Yes, multiple signals can exist on the same frequency at once.  In a net, this could happen if two people tried to talk at the same time.  This is called a &amp;quot;double&amp;quot;.  When this happens, the signals mix, or add together.&lt;/p&gt;&#xA;&lt;p&gt;If the two signals are AM, the amplitudes of the radio waves add, which corresponds to the amplitudes of the audio, so you get pretty much the same effect if two people were talking at once -- you hear them both.&lt;/p&gt;&#xA;&lt;p&gt;For FM, when the radio amplitudes add, it doesn't help the audio at all.  Instead, the FM receiver will try to lock on to one signal (&amp;quot;the capture effect&amp;quot;) and if one signal is stronger than the other, it will lock on.  You'll still hear buzzing interference from the other signal.  If the two signals are close in power, the receiver will alternately lock on to one and then the other, possibly getting nothing intelligible from either, or maybe getting short pieces of each alternately.&lt;/p&gt;&#xA;&lt;p&gt;With FM, it is possible to capture both signals using software defined radio, and then subtract the stronger signal and recover some of the weaker signal, but this is more theoretical and not commonly done.&lt;/p&gt;&#xA;&lt;p&gt;To the antenna, when it gets the energy from both signals; it doesn't see them as separate signals.  It also gets the energy from all the other frequencies around it, some of which it absorbs and these all mix and appear as voltages and currents on the antenna feed line.  This signal is then fed into your radio, which has to amplify and discriminate the desired frequencies from, and then demodulate those into the information -- possibly audio -- that you want.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2020-12-12T06:53:06.100" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17717" PostTypeId="1" AcceptedAnswerId="17730" CreationDate="2020-12-12T15:18:11.670" Score="3" ViewCount="31" Body="&lt;p&gt;I want to send some test data via a reflector, to be picked up by my OpenSpot hotspot linked to that data reflector. My local repeater is pretty much always linked to another reflector.&lt;/p&gt;&#xA;&lt;p&gt;There's not much activity though (especially locally, though technically I don't know if there's someone listening to the reflector), so I wouldn't feel bad tying up the RX on the repeater for a few seconds during quiet times. It's more disruptive to re-link.&lt;/p&gt;&#xA;&lt;p&gt;Can I, and if so how?&lt;/p&gt;&#xA;&lt;p&gt;That is, can I set &lt;code&gt;UR&lt;/code&gt; and &lt;code&gt;RPT&lt;/code&gt; and stuff to have just this burst go to a particular reflector?&lt;/p&gt;&#xA;&lt;p&gt;It doesn't seem to be an option on &lt;a href=&quot;http://www.dstarinfo.com/dstar-web-calculator.aspx&quot; rel=&quot;nofollow noreferrer&quot;&gt;the calculator&lt;/a&gt;. That only says how to &amp;quot;source route&amp;quot; to a repeater, or how to TX to &lt;em&gt;a callsign&lt;/em&gt;, not to a given reflector.&lt;/p&gt;&#xA;&lt;p&gt;Maybe I can TX to a call sign (my entry level call sign is still valid)? Will that work with an OpenSpot, or does it have to be a real repeater for that to work?&lt;/p&gt;&#xA;" OwnerUserId="9636" LastActivityDate="2020-12-15T20:20:11.557" Title="Can I send to a D-Star reflector other than the one a repeater is linked to?" Tags="&lt;d-star&gt;&lt;reflector&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17718" PostTypeId="2" ParentId="17714" CreationDate="2020-12-12T16:08:52.277" Score="3" Body="&lt;p&gt;There's multiple way that multiple signals can be sent at the same time on the same frequency.&lt;/p&gt;&#xA;&lt;p&gt;One is to have multiple antennas, where even though the antennas themselves can be omnidirectional, they can be used to &amp;quot;beam form&amp;quot; by carefully offsetting the signal. And likewise the receiver can do this trick. Also see this article on &lt;a href=&quot;https://en.wikipedia.org/wiki/MIMO&quot; rel=&quot;nofollow noreferrer&quot;&gt;MIMO&lt;/a&gt;. Wifi can get faster using these spacial streams, using the same amount of spectrum. See &lt;a href=&quot;https://en.wikipedia.org/wiki/IEEE_802.11ac-2013#Data_rates_and_speed&quot; rel=&quot;nofollow noreferrer&quot;&gt;this table on 802.11ac&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Then there's &lt;a href=&quot;https://en.wikipedia.org/wiki/Code-division_multiple_access&quot; rel=&quot;nofollow noreferrer&quot;&gt;CDMA&lt;/a&gt;, where multiple transmitters are sending different signals on the same frequency. The individual transmissions can be differentiated because they all have different &amp;quot;codes&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;CDMA can be more efficient than separating by frequency or in time, since separation by frequency requires a quiet border between channels, and in time (TDMA) requires a guard interval, and transmitters that are well synchronized and able to turn on and off very quickly. In this way CDMA is more efficient, since the transmitter just blasts a continuous spread signal, and the receiver has to extract the desired signal by processing.&lt;/p&gt;&#xA;&lt;p&gt;A single transmitter could transmit two different CDMA channels &amp;quot;on top of&amp;quot; each other. There's nothing particularly strange about it. From the antenna (and before that, the Digital-To-Analog converter) perspective two signals is just an oscillating electric signal, just like one signal is.&lt;/p&gt;&#xA;&lt;p&gt;For FM the other comment about &amp;quot;capture effect&amp;quot; is what practically happens. But FM is just one mode. E.g. in AM if two transmit on the same frequency at the same time receivers will hear both, as if it were two people in a room talking at the same time. AM doesn't have capture effect. Nor, of course, does LSB or USB, so same there.&lt;/p&gt;&#xA;" OwnerUserId="9636" LastActivityDate="2020-12-12T16:08:52.277" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17720" PostTypeId="1" CreationDate="2020-12-10T12:03:48.857" Score="3" ViewCount="92" Body="&lt;p&gt;I powered up my Kenwood TS 520 without connecting the antenna and after 1 hour realized it was not connected, after connecting the antenna I noticed the S-meter was not giving me a reading and I have no idea why&lt;/p&gt;&#xA;" OwnerDisplayName="Ian Brown" LastEditorUserId="4665" LastEditDate="2020-12-17T23:27:45.927" LastActivityDate="2020-12-17T23:27:45.927" Title="Kenwood TS 520 S Meter accidentally run without an antenna connected" Tags="&lt;transceiver&gt;&lt;kenwood&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17721" PostTypeId="2" ParentId="17720" CreationDate="2020-12-13T00:36:23.237" Score="2" Body="&lt;p&gt;Unless you tried to transmit without an antenna, it should be fine.&lt;/p&gt;&#xA;&lt;p&gt;If the radio is in receive mode without an antenna, it won't hurt it.  But if you transmit without an antenna, especially at high power, the high SWR could damage the final amplifier in the radio.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2020-12-13T01:38:50.130" LastActivityDate="2020-12-13T01:38:50.130" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17722" PostTypeId="2" ParentId="9132" CreationDate="2020-12-13T02:06:04.147" Score="1" Body="&lt;p&gt;I suggest you disconnect the loop from the central part of the variable cap . Instead connect to the other section...you then have a more efficient cap without the losses of the mechanical contact. By using both sides or both sections you convert the cap into a poor man's butterfly cap&lt;/p&gt;&#xA;" OwnerUserId="18244" LastActivityDate="2020-12-13T02:06:04.147" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17723" PostTypeId="1" CreationDate="2020-12-13T03:16:01.400" Score="1" ViewCount="80" Body="&lt;p&gt;I have a homebrew motorized hf tuner which is controlled by coupling dc from the shack through two BiasTs - one topside, the other in the shack.&lt;/p&gt;&#xA;&lt;p&gt;As I reverse polarity to adjust tuner, will two LEDs, one LED reversed from the other, connected in parallel to the DC line at the shack end, work well to indicate when rotary inductor reaches its limit switches, so I may then know to reverse polarity to adjust the tuner toward resonance?&lt;/p&gt;&#xA;&lt;p&gt;thanks in advance&lt;/p&gt;&#xA;" OwnerUserId="17927" LastEditorUserId="8717" LastEditDate="2020-12-13T23:27:30.067" LastActivityDate="2021-01-07T18:25:55.413" Title="Need way to indicate when rotary inductor reached its limit switches on a remote homebrew motorized hf tuner" Tags="&lt;hf&gt;&lt;equipment-design&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17725" PostTypeId="2" ParentId="14425" CreationDate="2020-12-13T05:03:55.120" Score="1" Body="&lt;p&gt;I use my FT-891 with an MFJ 939Y auto tuner. When selecting TNR from the menus (I mapped the TNR function to one of the front panel A/B/C keys) holding TNR for over a second does drop the power to 5 watts carrier and the ATU does its thing.  After the &amp;quot;ok&amp;quot; beep and green light on the tuner is on, the rig goes back to whatever mode and power setting it was configured for.&lt;/p&gt;&#xA;" OwnerUserId="18247" LastActivityDate="2020-12-13T05:03:55.120" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17726" PostTypeId="2" ParentId="17692" CreationDate="2020-12-13T21:30:54.477" Score="4" Body="&lt;p&gt;&lt;strong&gt;A bolt of lightning has an average center frequency of about 16 kHz&lt;/strong&gt;, which varies with the height of the bolt.&lt;/p&gt;&#xA;&lt;p&gt;This is a distant stroke that I captured on one of my SDR lightning receivers, using three 4-turn 1-meter dia. vertical loop antennas, spaced 120° apart:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0EsDq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0EsDq.jpg&quot; alt=&quot;Blitzortung lightning waveform and FFT spectrum&quot; /&gt;&lt;/a&gt;&#xA;&lt;sub&gt;(Ignore the apparent 50 mV offset)&lt;/sub&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Note how the energy on this particular stroke is concentrated below&#xA;20 kHz, in the LF region (very typical). The two higher frequency, broad areas&#xA;are almost certainly due to ionospheric Doppler shifting.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The harmonics extend up into to the VHF region. However, since this&#xA;FFT spectrogram's vertical axis is based on power —and the filters&#xA;roll off the unneeded higher frequencies— the much weaker harmonics&#xA;do not display.&lt;/p&gt;&#xA;&lt;p&gt;Having said that, occasionally I see many significant&#xA;ionospherically-Doppler-shifted &amp;quot;bounces&amp;quot; up to 80 or 90 kHz. They&#xA;appear as equally-spaced bell curves that decrease in height with&#xA;each higher frequency-shifted bounce.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;The 16 kHz figure is based on many observations of mine over a long period of time.&lt;/p&gt;&#xA;&lt;p&gt;This signal was sent to the blitzortung.org and lightningmaps.org servers in Europe, and was displayed on the map at &lt;a href=&quot;https://lightningmaps.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://lightningmaps.org&lt;/a&gt; as a line from my rural location in SW Missouri to the distant (&amp;gt;1300 km) stroke.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;A short spark gap on a laboratory tabletop&lt;/strong&gt; will tend to produce much higher frequencies, unless you incorporate a suitable tuned circuit in your design. (Googling &lt;em&gt;spark transmitter&lt;/em&gt; will return many designs and information from the late 18th and 19th century up to 1927.) Heinrich Hertz' first spark experiment was centered somewhere in the VHF region, IIRC.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;&lt;strong&gt;The antenna does not necessarily have to be resonant.&lt;/strong&gt; No one on the Blitzortung network uses resonant antennas. You might get more ideas if you also ask this on &lt;a href=&quot;https://forum.blitzortung.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://forum.blitzortung.org&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Some radio amateurs that operate on 137 kHz and 630 kHz use loop antennas with many turns of wire for receiving.&lt;/p&gt;&#xA;&lt;p&gt;Others report success with short, high vertical antennas with a high-gain, high-impedance preamp &lt;a href=&quot;http://njdtechnologies.net/the-e-probe-a-compact-yet-very-powerful-receive-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;like this one from PA0RDT&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2020-12-14T03:14:55.247" LastActivityDate="2020-12-14T03:14:55.247" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17727" PostTypeId="2" ParentId="6317" CreationDate="2020-12-14T04:02:08.420" Score="2" Body="&lt;p&gt;The distance of a point in the constellation diagram from the origin gives the amplitude while the angle each point makes with the horizontal axis gives the phase. PSK can't be the right option here because the amplitudes are different and we have the same phases with respect to the horizontal axis. However, in the case of PSK, we have the same amplitude and different phases(this depends on the order of modulation). For 8-PSK, we have a single amplitude and eight different phases. This means that the constellation points lie on a circle. This also eliminates option c.) This also eliminates QAM because QAM has multiple amplitudes as well as phases which is not the case here. &lt;a href=&quot;https://i.stack.imgur.com/SGt7P.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SGt7P.png&quot; alt=&quot;Amplitude only variation&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18254" LastActivityDate="2020-12-14T04:02:08.420" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17729" PostTypeId="1" AcceptedAnswerId="17740" CreationDate="2020-12-14T17:37:50.880" Score="3" ViewCount="123" Body="&lt;p&gt;I would like to decode the signal from a RS41 radiosonde (from a weather balloon), which are suggested open-source software to do that?&lt;/p&gt;&#xA;&lt;p&gt;I tried &lt;a href=&quot;https://github.com/rs1729/RS&quot; rel=&quot;nofollow noreferrer&quot;&gt;RS&lt;/a&gt; but after compiling the code and executing &lt;code&gt;sox wav/20140717_402MHz.wav -t wav - lowpass 2800 2&amp;gt;/dev/null | ./rs41 --crc -vx&lt;/code&gt; it only returns&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;sample_rate: 48000&#xA;bits       : 8&#xA;channels   : 1&#xA;samples/bit: 10.00&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;without any actual decoding of the wav recording.&lt;/p&gt;&#xA;&lt;p&gt;Sorry if this is a stupid question, but I'm new in the &amp;quot;radio-world&amp;quot; and the documentation I found online was quite limited or outdated, thanks.&lt;/p&gt;&#xA;" OwnerUserId="18258" LastEditorUserId="8717" LastEditDate="2020-12-14T21:56:33.310" LastActivityDate="2020-12-17T11:36:20.380" Title="Open source RS41 decoder" Tags="&lt;digital-modes&gt;&lt;software&gt;&lt;signal-identification&gt;&lt;weather&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17730" PostTypeId="2" ParentId="17717" CreationDate="2020-12-15T18:24:22.753" Score="3" Body="&lt;p&gt;No, you can't transmit to a different reflector than the one your repeater is currently linked to.  When the JARL designed the linking parts of D-STAR, they had in mind flexible user-driven routing to a repeater, or to the repeater that an operator most recently used.  The reflector linking business is a very clever hack that works when the repeater operator loads software called DPlus on the gateway computer.  DPlus is popular in most of the world, but from what I've heard, most repeater operators in Japan don't use it, probably because DPlus reflectors go against the linking philosophy that the JARL originally had in mind.&lt;/p&gt;&#xA;&lt;p&gt;Anyway, because reflectors are a hack not envisioned by the inventors of D-STAR, you can't do fancy things like using &lt;code&gt;URCALL&lt;/code&gt;, &lt;code&gt;RPT1&lt;/code&gt;, and &lt;code&gt;RPT2&lt;/code&gt; to route your transmission to a designated reflector.  To answer your last question, if you route to a call sign, you're not really routing to that call sign; you're routing to the repeater that that D-STAR-registered call sign was last seen on.&lt;/p&gt;&#xA;&lt;p&gt;If you want to send data to be picked up by your OpenSpot, then the thing to do would be unlink the repeater, link the repeater to the reflector your OpenSpot is monitoring, and then unlink and switch the repeater back when you're done.  That might be a little bit annoying to anyone monitoring the repeater, but personally I'm glad to hear someone using our local repeater for anything.  In your shoes, I'd consider making a short announcement on the repeater (locally, not on a reflector) to tell people what you're doing.  Someone listening might be very interested in such things!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-12-15T20:20:11.557" LastActivityDate="2020-12-15T20:20:11.557" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17731" PostTypeId="1" CreationDate="2020-12-16T02:39:30.277" Score="3" ViewCount="41" Body="&lt;p&gt;i am a beginner on signal processing.&lt;/p&gt;&#xA;&lt;p&gt;I learned from some papers, site online, including this forum that lightning discharge or any electrical arc emits wideband radio frequency. because the odd integer harmonic of a square wave. and electrical arc is similar to a square wave (Correct me if i am wrong, please)&lt;/p&gt;&#xA;&lt;p&gt;So today i try to generate impulse voltage with multistage impulse generator, and here is the picture  of the waveform from the oscilloscope&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/PEkil.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/PEkil.jpg&quot; alt=&quot;Test&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;White : impulse voltage without air breakdown.&lt;/p&gt;&#xA;&lt;p&gt;yellow: impulse voltage with air breakdown (electrical arc occurred on the sphere gap)&lt;/p&gt;&#xA;&lt;p&gt;So when i generate the impulse voltage with air breakdown, its create an arc on the sphere gap. my question is can i get the frequency domain from this yellow wave with fourier transform? i am not really understand it yet, but since this is a non-periodic wave, can i get the frequency spectrum?&lt;/p&gt;&#xA;&lt;p&gt;i want to know what exactly the &lt;strong&gt;electrical arc create electromagnetic wave on a very wide frequency&lt;/strong&gt; really mean, and how.&lt;/p&gt;&#xA;&lt;p&gt;Thankyou!&lt;/p&gt;&#xA;" OwnerUserId="18214" LastActivityDate="2020-12-16T03:00:45.933" Title="Fourier transform of air breakdown impulse waveform" Tags="&lt;antenna-theory&gt;&lt;frequency&gt;&lt;signal-identification&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17732" PostTypeId="2" ParentId="17731" CreationDate="2020-12-16T03:00:45.933" Score="3" Body="&lt;p&gt;If you approximate the yellow trace as a rectangular function:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \text{rect}(ax) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;then the Fourier transform of this is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ {1 \over |a|} \cdot \text{sinc}\left(\xi \over a\right )$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Of course, a lightning impulse isn't exactly a rectangular pulse, but I suspect that does not substantially change the character of the frequency response: infinite, with periodic peaks that decay with increasing frequency.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-12-16T03:00:45.933" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17733" PostTypeId="2" ParentId="17692" CreationDate="2020-12-16T09:33:18.840" Score="0" Body="&lt;ol&gt;&#xA;&lt;li&gt;The spark gap spectrum is highly determined by the frequency transfer of the (to the spark-gap source) connected antenna.&lt;/li&gt;&#xA;&lt;li&gt;Near EM-field from a spark gap radio spectrum generator differs essentially from a remote lightning discharge.&lt;/li&gt;&#xA;&lt;li&gt;Both E and H field sense antennas can be used for lightning detection. A combination is very powerfull (direction finding).&lt;/li&gt;&#xA;&lt;li&gt;Approach to find the location of a spark gap (radio) source in the near field (within half a mile of that spark gap!) is diffuse: the magnetic field is the result from the connected wires of the spark gap circuit. The spark gap is a kind of switch in this circuit. The magnetic field is rather homogeneous, NOT stronger near the gap. The E-field is transmitted by the connected wires: the wires function as antenna and mainly the spectral content varies when coming closer to the gap.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Conclusion: the spark gap generator is diffusing the location of the spark and is less usable for the development or investigation of lightning detection equipment.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2020-12-17T21:56:24.960" LastActivityDate="2020-12-17T21:56:24.960" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17734" PostTypeId="2" ParentId="17705" CreationDate="2020-12-16T17:41:32.613" Score="1" Body="&lt;p&gt;A less mathematical answer, this sentence: &amp;quot;Then, if there is a modulated (say AM modulated with voice) frequency of interest, we can tune the LO to the carrier frequency, and because of heterodyning principles we are now only having to deal with the baseband frequencies, which is much easier/cheaper to digitize.&amp;quot;&#xA;When the LO is tuned to &amp;quot;the same frequency&amp;quot; the LO phase matters. If you arrange the LO phase to be 0 degrees with respect to the carrier phase you have a synchronous AM detector. The output would be the amplitude of the carrier - i.e. a DC voltage with the AM modulation on it. In case the phase would be 90 degrees, the (average) DC output would be zero and independent on any AM modulation. In case there is any phase/frequency modulation the output would be proportional to the phase offset times the carrier amplitude.(One can use that to phase lock the LO.)&#xA;In the SDR world the LO might be close to the carrier so the phase would rotate slowly. That means that the AM component and the FM component would rotate between I and Q. To detect AM one would compute the square root of I squared + Q squared (after having filtered I and Q to remove unwanted frequencies) while the phase would be atan(Q,I). The frequency is the change of phase with time. That gives an FM detector. This works also if the LO is far from the carrier frequency of the desired modulated signal.&lt;/p&gt;&#xA;&lt;p&gt;In fact the pair of I and Q at sample rate F can be transformed to a single stream of samples at twice the sampling rate 2*F without any loss of information or S/N ratio. This can be done in the analog world as well as in the digital.&lt;/p&gt;&#xA;&lt;p&gt;In an SDR we have usually one A/D converter that gives amplitude vs time. It could be a data stream at 80 megasamples per second. We could apply a digital bandpass filter at 7 MHz with a bandwidth of 1 MHz and then reduce the sampling rate to 2 MHz. As an alternative we could apply two mixers in quadrature to get two signals, I and Q at 80 MHz sampling rate, then apply two low pass filters DC to 1 MHz after which we could downsample to I and Q at 1 MHz. The second strategy turns out to be far more favourable in terms of cpu (fpga) load so that is what we use, but both processes are equivalent.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2020-12-16T17:41:32.613" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17735" PostTypeId="1" AcceptedAnswerId="17739" CreationDate="2020-12-16T18:55:25.357" Score="4" ViewCount="338" Body="&lt;p&gt;I'm new to digital radios and signal processing, so I apologize if this question is trivial but I haven't been able to find an answer here or by googling. Also, some terminology might be off, please feel free to refer me to correct sources or to correct my basic understanding.&lt;/p&gt;&#xA;&lt;p&gt;Reading various sources (e.g. &lt;a href=&quot;https://pysdr.org/content/sampling.html#&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;), it seems to me that the I and Q components of a sample correspond to the complex representation of a portion of a sine wave described by &lt;span class=&quot;math-container&quot;&gt;$I \cdot  \cos(2 \pi f t) + Q \cdot \sin(2 \pi f t)$&lt;/span&gt; w.r.t. &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt;, where &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; denotes the frequency of interest.&#xA;My question is, how does the receiver actually compute &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; when a sample is needed?&lt;/p&gt;&#xA;&lt;p&gt;Suppose that a sample is taken at a time &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt;, I don't think that the receiver could just multiply the &lt;em&gt;instantaneous&lt;/em&gt; strength &lt;span class=&quot;math-container&quot;&gt;$V$&lt;/span&gt; (voltage?) of the incoming signal by &lt;span class=&quot;math-container&quot;&gt;$\cos(2\pi ft)$&lt;/span&gt; and by &lt;span class=&quot;math-container&quot;&gt;$\sin(2 \pi f t)$&lt;/span&gt; to recover &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; (as the diagram in section &amp;quot;Receiver Side&amp;quot; of the linked article appears to suggests) since this would carry no more information than reporting &lt;span class=&quot;math-container&quot;&gt;$V$&lt;/span&gt; itself.&lt;/p&gt;&#xA;&lt;p&gt;Moreover, in principle, the incoming voltage from the antenna on the receiver side could be any continuous (and differentiable?) function &lt;span class=&quot;math-container&quot;&gt;$V(t)$&lt;/span&gt;... so how are &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; recovered? Are they actually the values that minimize some error function between the incoming voltage and the function described by &lt;span class=&quot;math-container&quot;&gt;$I \cdot \sin(f) + Q \cdot  \cos(f)$&lt;/span&gt; over a length of time corresponding to some sampling interval &lt;span class=&quot;math-container&quot;&gt;$[t, t']$&lt;/span&gt;? E.g. something along the lines of:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;I,Q = \arg\min_{I,Q \in \mathbb{R}}\int_{\tau=t}^{t'} \big(  I \cdot \cos(2 \pi f \tau) + Q \cdot \sin(2 \pi f \tau) - V(\tau) \big)^2 \;\mbox{d}\tau \;\mbox{ ?}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Thank you!&lt;/p&gt;&#xA;" OwnerUserId="18277" LastEditorUserId="18277" LastEditDate="2020-12-16T19:29:29.530" LastActivityDate="2020-12-16T22:57:26.717" Title="SDR: How are I and Q determined from the incoming signal in quadrature sampling on the receiver side?" Tags="&lt;software-defined-radio&gt;&lt;receiver&gt;&lt;theory&gt;" AnswerCount="3" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17736" PostTypeId="2" ParentId="17735" CreationDate="2020-12-16T19:44:22.557" Score="1" Body="&lt;p&gt;In most typical SDR receivers, I and Q are not determined from the instantaneous RF voltage input, but from a reduced bandwidth slice of the RF spectrum.  The slice is taken by quadrature heterodyning/mixing (with a quadrature local oscillator (LO) near the frequency slice of interest), thus producing two signals.  This pair of mixer results is typically low pass filtered, then sampled by 2 ADCs, usually at a much lower rate than the LO frequency, to produce sampled IQ data suitable for software processing.  The low pass filtering plus sampling thus sort-of averages the RF within a certain band or slice, but with two different or offset time comb windows (the 2 quadrature mixer LO inputs), thus producing I and Q magnitude and phase information about all the various signals within the band-limited spectrum slice.&lt;/p&gt;&#xA;&lt;p&gt;A direct sampling SDR receiver also does the above, but inverts the order of the mixing and the ADC sampling to sample first then quadrature mix (then filter and decimate digitally, perhaps in an FPGA). The mixing and filtering can also be done in multiple stages, some in hardware/gateware, some in software, using multiple quadrature LOs, multiple filter stages, and digital complex multiplication.&lt;/p&gt;&#xA;&lt;p&gt;If you want to use that integral, it needs to integrate over a window function that is a composite of the impulse response of the low pass filter(s) and the capture window(s) of the ADC(s). For each sample. For each of I and Q.&lt;/p&gt;&#xA;&lt;p&gt;No instantaneous voltages are measured (because capacitance in the real world requires finite time to charge up or down to any measurable level).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-12-16T20:07:36.923" LastActivityDate="2020-12-16T20:07:36.923" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17737" PostTypeId="2" ParentId="17735" CreationDate="2020-12-16T19:53:59.450" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;the I and Q components of a sample correspond to the complex representation of a portion of a sine wave described by &lt;span class=&quot;math-container&quot;&gt;$I \cdot  \cos(2 \pi f t) + Q \cdot \sin(2 \pi f t)$&lt;/span&gt; w.r.t. &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt;, where &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; denotes the frequency of interest&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This is correct (if we suppose the incoming signal is a sine wave, i.e. an unmodulated carrier).&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I don't think that the receiver could just multiply the &lt;em&gt;instantaneous&lt;/em&gt; strength &lt;span class=&quot;math-container&quot;&gt;$V$&lt;/span&gt; (voltage?) of the incoming signal by &lt;span class=&quot;math-container&quot;&gt;$\cos(2\pi ft)$&lt;/span&gt; and by &lt;span class=&quot;math-container&quot;&gt;$\sin(2 \pi f t)$&lt;/span&gt; to recover &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; … since this would carry no more information than reporting &lt;span class=&quot;math-container&quot;&gt;$V$&lt;/span&gt; itself.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Actually, this is useful. The key facts are:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;This multiplication can done in the analog domain, using a &lt;em&gt;quadrature mixer,&lt;/em&gt; to produce a new pair of “downconverted” signals &lt;em&gt;without sampling them yet.&lt;/em&gt; This is how SDRs avoid needing gigahertz-rate analog-to-digital conversion.&lt;/li&gt;&#xA;&lt;li&gt;A signal of actually interesting content (modulation) is not just a pure sine wave, but has other frequency components.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;These I and Q signals have had all their frequency components shifted down in frequency by &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; — this is known as “baseband”. The signals are then low-pass filtered (which removes all frequencies outside of the range &lt;span class=&quot;math-container&quot;&gt;$f ± \text{filter frequency}$&lt;/span&gt; in the original signal) and sampled by an ADC to produce the digital baseband signal.&lt;/p&gt;&#xA;&lt;p&gt;Note that this means that an incoming signal at frequency &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; has frequency &lt;em&gt;zero&lt;/em&gt; in the baseband representation. If the signal is a sine wave with a small difference from &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; (e.g. perhaps it is frequency-modulated around &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt;) then the baseband form has a small difference from zero. If it has more frequency components, all of those are still present in the baseband signal, just translated.&lt;/p&gt;&#xA;&lt;p&gt;You're correct to think that an IQ form of the original RF signal contains no more information than the original instantaneous voltage. The point of IQ is to allow us to throw out something we don't need — the extremely high carrier frequency &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; — without discarding the &lt;em&gt;information we care about&lt;/em&gt; in the signal (provided it is limited to a small band around &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt;), so as to be able to receive, digitize, and demodulate it with simple general-purpose hardware.&lt;/p&gt;&#xA;" OwnerUserId="76" LastActivityDate="2020-12-16T19:53:59.450" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17739" PostTypeId="2" ParentId="17735" CreationDate="2020-12-16T22:38:08.370" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Suppose that a sample is taken at a time &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt;, I don't think that the receiver could just multiply the &lt;em&gt;instantaneous&lt;/em&gt; strength &lt;span class=&quot;math-container&quot;&gt;$V$&lt;/span&gt; (voltage?) of the incoming signal by &lt;span class=&quot;math-container&quot;&gt;$\cos(2\pi ft)$&lt;/span&gt; and by &lt;span class=&quot;math-container&quot;&gt;$\sin(2 \pi f t)$&lt;/span&gt; to recover &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; (as the diagram in section &amp;quot;Receiver Side&amp;quot; of the linked article appears to suggests) since this would carry no more information than reporting &lt;span class=&quot;math-container&quot;&gt;$V$&lt;/span&gt; itself.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It can, and it does precisely this. But you are right that it carries no more information.&lt;/p&gt;&#xA;&lt;p&gt;In practice it carries less, and that's the point. Say we want to make a WiFi radio operating in the 5 GHz band. This would require a sample rate of at least 10 GHz. That would be an expensive ADC, as would the computing power to process such a high sample rate.&lt;/p&gt;&#xA;&lt;p&gt;But the bandwidth of a WiFi signal is only some 10s of MHz. The point of the mixer is to convert the signal at high frequency (somewhere in the 5 GHz band) down to a lower frequency which can be represented at a lower sample rate and thus more easily digitized and processed.&lt;/p&gt;&#xA;&lt;p&gt;So, the output of the mixer is low-pass filtered before being digitized by the ADC.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Moreover, in principle, the incoming voltage from the antenna on the receiver side could be any continuous (and differentiable?) function &lt;span class=&quot;math-container&quot;&gt;$V(t)$&lt;/span&gt;... so how are &lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$Q$&lt;/span&gt; recovered? Are they actually the values that minimize some error function [...]&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;No, it's nothing so complex. Remember the mixer is an analog component, so there's no need for any &amp;quot;sampling interval&amp;quot;, and an arbitrary continuous function is no problem. The ideal mixer performs simply:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ I = V(t) \cdot \cos(2\pi f) \\&#xA;Q = V(t) \cdot \sin(2\pi f) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;If I and Q are interpreted as the real and imaginary parts of a complex number respectively, it is simpler (by &lt;a href=&quot;https://en.wikipedia.org/wiki/Euler%27s_formula&quot; rel=&quot;nofollow noreferrer&quot;&gt;Euler's formula&lt;/a&gt;) to think of the mixer as performing:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ V(t) \cdot e^{i 2 \pi f} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is useful because multiplying by &lt;span class=&quot;math-container&quot;&gt;$e^{i 2 \pi f}$&lt;/span&gt; shifts all frequencies by &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt;, which you can see for example in rule 103 of &lt;a href=&quot;https://en.wikipedia.org/wiki/Fourier_transform#Tables_of_important_Fourier_transforms&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia's list of Fourier transforms&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;These &lt;em&gt;analog&lt;/em&gt; signals are then low-pass filtered and digitized by the ADC.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-12-16T22:57:26.717" LastActivityDate="2020-12-16T22:57:26.717" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17740" PostTypeId="2" ParentId="17729" CreationDate="2020-12-17T11:36:20.380" Score="3" Body="&lt;p&gt;You have to provide the &lt;code&gt;-i&lt;/code&gt; option to invert the signal in order to decode it properly. The lowpass filter is not really required as this is a quite strong signal (but does not harm either).&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;$ ./rs41ptu -i --crc -vx wav/20140717_402MHz.wav&#xA;sample_rate: 48000&#xA;bits       : 8&#xA;channels   : 1&#xA;samples/bit: 10.00&#xA;[ 5047] (K1930308) Do 2014-07-17 12:32:13.999  lat: 45.66939  lon: 15.87963  alt: 28527.17   vH:  9.8  D: 251.8  vV: 6.1  # [00000]&#xA;[ 5048] (K1930308) Do 2014-07-17 12:32:14.999  lat: 45.66937  lon: 15.87951  alt: 28533.45   vH:  8.4  D: 259.7  vV: 6.3  # [00000]&#xA;[ 5049] (K1930308) Do 2014-07-17 12:32:15.999  lat: 45.66936  lon: 15.87939  alt: 28541.13   vH: 10.6  D: 270.8  vV: 8.7  # [00000]&#xA;[ 5050] (K1930308) Do 2014-07-17 12:32:16.999  lat: 45.66936  lon: 15.87924  alt: 28549.00   vH: 13.8  D: 273.0  vV: 6.5  # [00000]: fq 402000 &#xA;[ 5051] (K1930308) Do 2014-07-17 12:32:17.999  lat: 45.66937  lon: 15.87905  alt: 28554.51   vH: 16.3  D: 270.9  vV: 4.6  # [00000]: fw 0x4e25 &#xA;[ 5052] (K1930308) Do 2014-07-17 12:32:18.999  lat: 45.66937  lon: 15.87883  alt: 28560.22   vH: 17.6  D: 267.7  vV: 6.8  # [00000]: BK 01 &#xA;[ 5053] (K1930308) Do 2014-07-17 12:32:19.999  lat: 45.66935  lon: 15.87862  alt: 28567.80   vH: 15.7  D: 262.6  vV: 8.7  # [00000]&#xA;[ 5054] (K1930308) Do 2014-07-17 12:32:20.999  lat: 45.66933  lon: 15.87843  alt: 28574.92   vH: 14.1  D: 258.0  vV: 5.4  # [00000]&#xA;&amp;lt;SNIP, output abbreviated&amp;gt;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;pre&gt;&lt;code&gt;$ sox wav/20140717_402MHz.wav -t wav - lowpass 2800 2&amp;gt;/dev/null | ./rs41ptu -i --crc -vx&#xA;sample_rate: 48000&#xA;bits       : 8&#xA;channels   : 1&#xA;samples/bit: 10.00&#xA;[ 5047] (K1930308) Do 2014-07-17 12:32:13.999  lat: 45.66939  lon: 15.87963  alt: 28527.17   vH:  9.8  D: 251.8  vV: 6.1  # [00000]&#xA;[ 5048] (K1930308) Do 2014-07-17 12:32:14.999  lat: 45.66937  lon: 15.87951  alt: 28533.45   vH:  8.4  D: 259.7  vV: 6.3  # [00000]&#xA;[ 5049] (K1930308) Do 2014-07-17 12:32:15.999  lat: 45.66936  lon: 15.87939  alt: 28541.13   vH: 10.6  D: 270.8  vV: 8.7  # [00000]&#xA;[ 5050] (K1930308) Do 2014-07-17 12:32:16.999  lat: 45.66936  lon: 15.87924  alt: 28549.00   vH: 13.8  D: 273.0  vV: 6.5  # [00000]: fq 402000 &#xA;[ 5051] (K1930308) Do 2014-07-17 12:32:17.999  lat: 45.66937  lon: 15.87905  alt: 28554.51   vH: 16.3  D: 270.9  vV: 4.6  # [00000]: fw 0x4e25 &#xA;[ 5052] (K1930308) Do 2014-07-17 12:32:18.999  lat: 45.66937  lon: 15.87883  alt: 28560.22   vH: 17.6  D: 267.7  vV: 6.8  # [00000]: BK 01 &#xA;[ 5053] (K1930308) Do 2014-07-17 12:32:19.999  lat: 45.66935  lon: 15.87862  alt: 28567.80   vH: 15.7  D: 262.6  vV: 8.7  # [00000]&#xA;[ 5054] (K1930308) Do 2014-07-17 12:32:20.999  lat: 45.66933  lon: 15.87843  alt: 28574.92   vH: 14.1  D: 258.0  vV: 5.4  # [00000]&#xA;&amp;lt;SNIP, output abbreviated&amp;gt;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;Note: I assume your &lt;code&gt;rs41&lt;/code&gt; executable is compiled from &lt;code&gt;rs41.c&lt;/code&gt; The &lt;a href=&quot;https://github.com/rs1729/RS/tree/master/rs41&quot; rel=&quot;nofollow noreferrer&quot;&gt;documentation&lt;/a&gt; lists &lt;code&gt;rs41.c&lt;/code&gt; as an old version (source code was last updated 4 years ago). The latest implementation is in &lt;code&gt;rs41ptu.c&lt;/code&gt;&#xA;I did not do a detailed analysis of the source code, but based on this output from this one sample there do seem to be some (small) differences in the decoded values:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;$ ./rs41 -i --crc -vx wav/20140717_402MHz.wav&#xA;sample_rate: 48000&#xA;bits       : 8&#xA;channels   : 1&#xA;samples/bit: 10.00&#xA;[ 5047] (K1930308) Do 2014-07-17 12:32:13.999  lat: 45.66939  lon: 15.87963  alt: 28527.17   vH:  9.8  D: 251.8°  vV: 6.1 &#xA;[ 5048] (K1930308) Do 2014-07-17 12:32:14.999  lat: 45.66937  lon: 15.87951  alt: 28533.45   vH:  8.4  D: 259.7°  vV: 6.3 &#xA;[ 5049] (K1930308) Do 2014-07-17 12:32:15.999  lat: 45.66936  lon: 15.87939  alt: 28541.13   vH: 10.6  D: 270.8°  vV: 8.7 &#xA;[ 5050] (K1930308) Do 2014-07-17 12:32:16.999  lat: 45.66936  lon: 15.87924  alt: 28549.00   vH: 13.8  D: 273.0°  vV: 6.5 : fq 402000 &#xA;[ 5051] (K1930308) Do 2014-07-17 12:32:17.999  lat: 45.66937  lon: 15.87905  alt: 28554.51   vH: 16.3  D: 270.9°  vV: 4.6 &#xA;[ 5052] (K1930308) Do 2014-07-17 12:32:18.999  lat: 45.66937  lon: 15.87883  alt: 28560.22   vH: 17.6  D: 267.7°  vV: 6.8 : BK 01 &#xA;[ 5053] (K1930308) Do 2014-07-17 12:32:19.999  lat: 45.66935  lon: 15.87862  alt: 28567.80   vH: 15.7  D: 262.6°  vV: 8.7 &#xA;[ 5054] (K1930308) Do 2014-07-17 12:32:20.999  lat: 45.66933  lon: 15.87843  alt: 28574.92   vH: 14.1  D: 258.0°  vV: 5.4 &#xA;&amp;lt;SNIP, output abbreviated&amp;gt;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;" OwnerUserId="18293" LastActivityDate="2020-12-17T11:36:20.380" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17741" PostTypeId="5" CreationDate="2020-12-17T17:06:07.457" Score="0" Body="&lt;p&gt;In a radio transmitter, a sine wave at a particular frequency, the carrier signal, is modified by incorporating a second signal, the modulating signal, that contains information to be transmitted.  This process is known as modulation.  In the radio receiver, the process is reversed to recover the modulating signal; this process is called demodulation.&lt;/p&gt;&#xA;&lt;p&gt;For analog signals such as voice, frequency modulation (FM) is a modulation method in which the frequency of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal.  FM was invented by Edwin H. Armstrong in 1935, and has been popular in amateur use on the VHF and UHF bands since the 1950s.&lt;/p&gt;&#xA;&lt;p&gt;More information about FM is available on &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_modulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikipedia&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-12-17T17:06:07.457" LastActivityDate="2020-12-17T17:06:07.457" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17742" PostTypeId="4" CreationDate="2020-12-17T17:06:07.457" Score="0" Body="Questions about Frequency Modulation, the analog modulation scheme commonly used for voice on VHF and UHF frequencies." OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2020-12-17T17:06:07.457" LastActivityDate="2020-12-17T17:06:07.457" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17744" PostTypeId="1" AcceptedAnswerId="17745" CreationDate="2020-12-19T18:00:56.410" Score="1" ViewCount="50" Body="&lt;p&gt;I know that a Full license is recognised in the US, but is the same true for a Foundation or Intermediate license? On the surface they look equivalent to the US Technician and General licenses, so are they treated as such?&lt;/p&gt;&#xA;&lt;p&gt;For context, we are a UK team entering a rocketry competition in the US that has a telemetry requirement, for which we need a Technician or higher radio license, but none of us currently have a license. The time frame makes it impractical to go for a Full license, so we're hoping that getting a Foundation license here will be good enough.&lt;/p&gt;&#xA;" OwnerUserId="18320" LastActivityDate="2020-12-19T19:43:46.140" Title="Is a Foundation or Intermediate license from the UK recognised in the US?" Tags="&lt;united-states&gt;&lt;license&gt;&lt;united-kingdom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17745" PostTypeId="2" ParentId="17744" CreationDate="2020-12-19T19:43:46.140" Score="3" Body="&lt;p&gt;The US has no specific reciprocity agreement with the UK, but both countries have adopted &lt;a href=&quot;https://docdb.cept.org/document/925&quot; rel=&quot;nofollow noreferrer&quot;&gt;CEPT T/R 61-01&lt;/a&gt;, which is what allows reciprocal operation between them. Only the UK full license is regarded as equivalent to a CEPT license; Foundation and Intermediate don't count for anything.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-12-19T19:43:46.140" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17746" PostTypeId="1" AcceptedAnswerId="17747" CreationDate="2020-12-19T23:27:00.620" Score="1" ViewCount="244" Body="&lt;p&gt;I'm pretty new to SDR, but I understand a little bit about RF.&lt;/p&gt;&#xA;&lt;p&gt;On all 3 of my SDR device (two RTL one HackRF) The center frequency is always full of interference from something unknown.....it doesn't appear to be static, because if I use a chirpchat demodulator, it's picking up data (even if the protocols wrong, I'm assuming there is still some sort of bit information)&lt;/p&gt;&#xA;&lt;p&gt;Any idea what this interference is? How do I fix it? Thank you!&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Np7zs.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Np7zs.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18322" LastActivityDate="2020-12-30T15:08:43.923" Title="Signal in the center frequency of my SDR spectrum always" Tags="&lt;software-defined-radio&gt;&lt;audio-interface&gt;&lt;hackrf&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17747" PostTypeId="2" ParentId="17746" CreationDate="2020-12-19T23:42:12.853" Score="4" Body="&lt;p&gt;That is DC offset, either in the analog to digital converters, or their driving circuitry.&lt;/p&gt;&#xA;&lt;p&gt;The average voltage at the ADC's input is ideally exactly in the middle of the ADC's range, since this maximizes the maximum voltage swing up or down before clipping. The DC offset is the difference between the ADC's &amp;quot;middle&amp;quot; voltage and the average voltage present at the ADC's input. The analog circuitry in the SDR will contain &lt;a href=&quot;https://en.wikipedia.org/wiki/Biasing&quot; rel=&quot;nofollow noreferrer&quot;&gt;biasing&lt;/a&gt; circuitry designed to minimize the DC offset.&lt;/p&gt;&#xA;&lt;p&gt;But, the biasing circuitry and the ADC are subject to manufacturing and temperature variation among other things. It's theoretically possible to reduce the DC offset to an insignificant amount, but in practice this would require such precision that the expense would be unacceptable.&lt;/p&gt;&#xA;&lt;p&gt;So, nearly every practical SDR with a quadrature mixer has this issue, and engineers work around it in other ways. Many modern modulations designed to be received by SDRs are designed to have no significant signal in the middle of their spectrum for this reason. For signals that don't require the total bandwidth of your device you can tune above or below the signal frequency so it doesn't overlap with the DC offset.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-12-20T15:20:52.327" LastActivityDate="2020-12-20T15:20:52.327" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17748" PostTypeId="1" AcceptedAnswerId="17751" CreationDate="2020-12-20T08:26:30.390" Score="1" ViewCount="165" Body="&lt;p&gt;I have a loop antenna.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/A3o4G.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/A3o4G.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;When I connect the probe from my oscilloscope, does the probe also act as an antenna? If so, how should I fix that? I read about feeding technique, but I still do not understand it clearly.&lt;/p&gt;&#xA;&lt;p&gt;Is it okay that I cover my antenna with scotch tape? Is this a correct way of &amp;quot;shielding antenna&amp;quot;?&lt;/p&gt;&#xA;&lt;p&gt;I want to test the magnetic direction finding method and the source of the signal is an electric spark. I read that loop antenna is suitable for this. I find a loop antenna in my lab and this is the specification I figured&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Turn              : 10 turns&lt;/li&gt;&#xA;&lt;li&gt;Loop diameter     : 11.6 cm&lt;/li&gt;&#xA;&lt;li&gt;wire diameter     : around 0.08 mm&lt;/li&gt;&#xA;&lt;li&gt;length of winding : 0.9 cm&lt;/li&gt;&#xA;&lt;li&gt;frequency         : ?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I dont know how to calculate the inductance and capacitance for this circular loop antenna, ir how to measure it with tools in my lab, so I don't know its resonance frequency yet.&#xA;But, I already test it with dc spark generator (pictured) and yes it detects something when the spark occurred. But, I am not sure about the frequency shown on the oscilloscope (around 130 kHz), and also about my question above.&lt;/p&gt;&#xA;&lt;p&gt;So moving from this, I decided that I want to make my own square loop antenna, mainly because I already found the legit equation/formula on the book and internet for the inductance and capacitance, so I can calculate the resonance frequency.&lt;/p&gt;&#xA;&lt;p&gt;About feeding the antenna: is it critical for any regular loop? Or at least in my case? I read that feeding antenna technique is connecting and transforming the radio signal into electrical signal (or vice versa); since I use an oscilloscope, is it balanced already? I only made the end of the loop on the bottom, so I suppose it is symmetric. and I cover all of the surface with scotch tape on top of it.&lt;/p&gt;&#xA;&lt;p&gt;Note: Even if this experiment fails, I still need something to write about in the project report.&lt;/p&gt;&#xA;" OwnerUserId="18214" LastEditorUserId="76" LastEditDate="2020-12-20T18:55:58.873" LastActivityDate="2020-12-21T13:48:53.670" Title="Loop Antenna Construction" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;loop-antenna&gt;&lt;magnetic-loop&gt;" AnswerCount="2" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="17749" PostTypeId="2" ParentId="17748" CreationDate="2020-12-20T19:27:09.900" Score="2" Body="&lt;p&gt;Partial answer to part 1 of your question.  Yes, the loop created by the open space between the ground lead of your scope probe and the probe tip acts as a small (parasitic) loop antenna.  But mostly for wavelengths much shorter than 1/10th the diameter of the loop (potentially caused by the rising and falling edges of a spark).  If you are just testing directionality, you might orient any parasitic loops to be in the same plane as that of the loop antenna under test.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-12-20T19:27:09.900" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17751" PostTypeId="2" ParentId="17748" CreationDate="2020-12-21T13:48:53.670" Score="3" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;When I connect the probe from my oscilloscope, does the probe also act as an antenna?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;As it appears in your photo, yes. In some applications this may not matter, but in your case it sounds like your experiment relies on the loop having a predictable pattern for direction finding. In this case, having the probe (and also the scope chassis, and its power cord) as part of the antenna is going to significantly alter the directionality of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;Do address this, &lt;a href=&quot;https://ham.stackexchange.com/q/538/218&quot;&gt;you require some kind of balun&lt;/a&gt;. One way to do this is to obtain a &lt;a href=&quot;http://www.compliance-club.com/archive/old_archive/030718.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;magnetic field probe&lt;/a&gt; for your scope and place it inside and coplanar with the antenna. The leads of the main loop where you have the scope probe now are then either shorted together or perhaps connected to a capacitor to make the loop resonant on the desired frequency. The antenna and the magnetic field probe are then coupled through their shared magnetic flux as a transformer.&lt;/p&gt;&#xA;&lt;p&gt;There are other ways to do it of course, but it's a big enough topic for a question of its own.&lt;/p&gt;&#xA;&lt;p&gt;You might try &lt;a href=&quot;https://ham.stackexchange.com/q/1271/218&quot;&gt;measuring the common-mode current&lt;/a&gt; to determine if your balun is effective. If handling or moving the scope probe changes your measurement, that's a sure indication that your feed method is ineffective, and what you are seeing on the scope isn't coming just from the loop.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Is it okay that I cover my antenna with scotch tape? Is this a correct way of &amp;quot;shielding antenna&amp;quot;?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Covering the antenna with tape is fine, but it's not any kind of &amp;quot;shielding&amp;quot;. Perhaps you are referring to a &lt;a href=&quot;https://ham.stackexchange.com/q/899/218&quot;&gt;shielded loop&lt;/a&gt;, which when properly designed is similar to a magnetic field probe. A shielded loop may be nice for your application as it contains a balun, but I'm not sure how one could be made with multiple turns. I don't know if that's problematic or not for your application.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-12-21T13:48:53.670" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17752" PostTypeId="1" CreationDate="2020-12-21T18:08:12.537" Score="4" ViewCount="262" Body="&lt;p&gt;I have a V5000 antenna and I’m tuning it but can’t get the Reactance (X) on my MFJ 259B down. Resistance is at 50 ohms, SWR reading 1.2 to 1.3 (I don’t give that much credence) but the Reactance (X) is around 15. Any ideas how to get that down? LMR 400 coax if it matters.&lt;/p&gt;&#xA;&lt;p&gt;That's what I'm still trying to get a grip on! From what I've been told it has to do with the capacitance of the antenna which is affected by the proximity of the driven element to ground plane radials or whatever your ground plane is. I'm still figuring that one out!&lt;/p&gt;&#xA;" OwnerUserId="18333" LastEditorUserId="218" LastEditDate="2020-12-21T19:06:55.330" LastActivityDate="2020-12-27T16:58:45.717" Title="What is antenna reactance?" Tags="&lt;impedance-matching&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17753" PostTypeId="2" ParentId="17752" CreationDate="2020-12-21T19:02:58.123" Score="6" Body="&lt;p&gt;Reactance is the imaginary part of impedance. Together with the real part, resistance, impedance describes how a given load will respond to an AC voltage or current source. While for DC analysis resistance alone is sufficient for this purpose, for AC analysis we need to know not only the magnitude of the voltage or current, but the phase angle between them, which is given by:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \theta = \tan^{-1}\left( X \over R \right) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Inductors and capacitors are examples of discrete components that have reactance but no resistance. In an antenna, the reactance comes from the timing of the wave reflected from the ends of the antenna. At some length, the reflections align such that voltage and current are in phase at the feedpoint terminals, which means reactance is zero, and the antenna is said to be resonant.&lt;/p&gt;&#xA;&lt;p&gt;I should note there's no particular reason reactance needs to be zero. An SWR of 1.3 is perfectly acceptable, and there's likely no practical performance gain to be realized by reducing it further. Furthermore, reactance will be zero only at one particular frequency (and likely harmonics thereof) but it is impossible for the SWR to be 1:1 or for the reactance to be zero across the entire band.&lt;/p&gt;&#xA;&lt;p&gt;However if you want to get reactance to zero you can do that by adjusting the length of the antenna or whatever other mechanisms your antenna has for tuning it. If you have an antenna analyzer then measure the reactance over a range of frequencies:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A little below the resonant frequency, the antenna is &amp;quot;too short&amp;quot; and reactance will be negative.&lt;/li&gt;&#xA;&lt;li&gt;A little above the resonant frequency, the antenna is &amp;quot;too long&amp;quot; and reactance will be positive.&lt;/li&gt;&#xA;&lt;li&gt;Precisely at the resonant frequency, reactance will be zero.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;If you get very far away from the resonant frequency these rules will not hold, but you would not ordinarily operate an antenna this far away from resonance.&lt;/p&gt;&#xA;&lt;p&gt;Make the necessary adjustments to your antenna and repeat your measurements until you have the resonant frequency where you want it.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2020-12-21T23:43:59.440" LastActivityDate="2020-12-21T23:43:59.440" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17755" PostTypeId="1" CreationDate="2020-12-22T15:05:45.767" Score="-2" ViewCount="85" Body="&lt;p&gt;With my headphones put on I thought what if is possible to generate some induction to my brain with the headphones speakers? some RF right into my mind.&lt;/p&gt;&#xA;" OwnerUserId="18339" LastActivityDate="2020-12-22T18:44:32.867" Title="Is it possible to generate RF with a speaker?" Tags="&lt;speaker&gt;" AnswerCount="2" CommentCount="0" ClosedDate="2020-12-28T02:41:40.753" ContentLicense="CC BY-SA 4.0" />
  <row Id="17756" PostTypeId="2" ParentId="17755" CreationDate="2020-12-22T15:33:05.040" Score="0" Body="&lt;p&gt;Speakers work by varying the pressure of the air to generate sound waves (they travel at the speed of sound, and require a medium to travel through). Radio waves are electromagnetic waves (travel at the speed of light, and do not need a transmission medium). Totally different things.&lt;/p&gt;&#xA;&lt;p&gt;However, it depends what you mean by RF. “Radio frequency” is just electromagnetic waves at any frequency, so it is possible to generate radio waves at 3kHz. Sound waves at this frequency would be audible, but radio waves would not.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-12-22T15:33:05.040" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17757" PostTypeId="2" ParentId="16311" CreationDate="2020-12-22T17:22:52.723" Score="3" Body="&lt;p&gt;First off, a 1 Watt transmitter puts 7.07 volts RMS across a 50 ohm load, or 10 volts peak.  So most any diode detector circuit using a silicon signal diode (perhaps a 1n4148) would be plenty accurate for ham uses.  For a 0.1 Watt QRP transmitter (3.16 volts peak), a schottky 1n5711 diode would still keep it accurate within 10%.  If the voltmeter has a 10meg impedance (to keep diode currents low), you could accurately measure down to 0.01 Watts using that 1n5711 and a calibration chart.  Note that the voltage drop across a diode is a logarithmic function of the current, that drop can be astonishingly low when currents are under a microamp.  Germanium diodes can have lower voltage drops than schottky diodes, though are hard to obtain and are more sensitive to temperature.  Many shops selling cheap 1n34a's these days actually ship a schottky instead.&lt;/p&gt;&#xA;&lt;p&gt;Phil's diode probe looks good, though the meter sees peak, not peak-to-peak, so should divide by sqrt(2) to obtain the RMS voltage, not 2*sqrt(2).  I would do away with R1, relying instead on the meters input resistance to perform that function, keeping diode currents to a minimum.  The bias source may not be as useful as you might think, since larger signals will create larger diode currents and thus larger diode drops.&lt;/p&gt;&#xA;&lt;p&gt;Jim's classic 1n34a probe is similar to Phil's, but a bit harder to understand.  Not obvious to me why either topology is inherently better.  Jim does show the cap and diode in their correct positions.  The cap does double duty, both DC blocking of the incoming RF, and it gets charged up whenever the diode's anode is above ground.  The result is that the diode's anode has an RF signal equal to that being measured, but with a DC shift such that the bottom tip of that RF signal is at ground.  The voltmeter (he shows a scope) is assumed to have sufficient input capacitance to create a low pass filter with the 4.7meg resistor.  The 4.7meg resistor in series with the assumed 11meg internal resistance of the voltmeter (typical of many DVM's, and VTVM's too if you remember what those were) scales the voltage reading down to give volts RMS.&lt;/p&gt;&#xA;&lt;p&gt;The AD8307 is easy to work with, can be bought on ebay for well under a dollar, good to 500mhz (which is plenty for most of us), has a 90dB dynamic range, and is easier to dead bug than an ADL5904.  That would be my second choice if the classic 1n34a/1n5711 diode probe was not sensitive enough.  You can buy a complete AD8307 RF probe on ebay for $10.&lt;/p&gt;&#xA;&lt;p&gt;Getting back to basics, I have measured power output from transmitters by putting a finger on the 50 ohm load to see how hot it is getting as suggested by Marcus.  Compare the rate of temperature rise to a similar load driven from an adjustable DC power supply, adjust the DC voltage until the temperature rise is identical.&lt;/p&gt;&#xA;" OwnerUserId="18342" LastEditorUserId="18342" LastEditDate="2020-12-22T17:44:02.540" LastActivityDate="2020-12-22T17:44:02.540" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17758" PostTypeId="2" ParentId="17755" CreationDate="2020-12-22T18:44:32.867" Score="1" Body="&lt;p&gt;Just about anything will radiate to some extent if you feed it with RF. It's actually more difficult &lt;a href=&quot;https://en.wikipedia.org/wiki/Electromagnetic_compatibility&quot; rel=&quot;nofollow noreferrer&quot;&gt;to make devices not radiate&lt;/a&gt;. An antenna is just more efficient. So sure, you can get your headphones to radiate RF simply by connecting them to an RF amplifier.&lt;/p&gt;&#xA;&lt;p&gt;Unfortunately, this doesn't do anything useful. Put your head between two cell phones, WiFi radios, or Bluetooth headsets. Does anything interesting happen?&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-12-22T18:44:32.867" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17759" PostTypeId="1" CreationDate="2020-12-23T00:40:06.613" Score="1" ViewCount="67" Body="&lt;p&gt;I’d like to add an aftermarket antenna to my cobra HH50wxst to boost my range. My only concern is if I got a longer antenna, could it possibly throw off the SWR and damage the radio? I am totally new to this hobby and am afraid to break things. Any advice on this matter would be greatly appreciated.&lt;/p&gt;&#xA;" OwnerUserId="18332" LastEditorUserId="8717" LastEditDate="2020-12-24T04:50:16.490" LastActivityDate="2020-12-24T04:50:16.490" Title="Cobra hand held 50wxst aftermarket antenna" Tags="&lt;antenna&gt;&lt;ht&gt;&lt;range&gt;&lt;citizens-band&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17760" PostTypeId="2" ParentId="17759" CreationDate="2020-12-23T14:31:46.537" Score="2" Body="&lt;p&gt;If you are going to buy an antenna designed for use with that handheld, then it should work fine. Otherwise, you need to make sure that you get an antenna designed for the frequencies used by the radio (in this case around 27MHz, or 11-metre band), that has an impedance of 50 ohms, and has a BNC plug on it.&lt;/p&gt;&#xA;&lt;p&gt;As long as the antenna meets those criteria, it should perform at least as well as the included antenna. For best results, an externally-mounted antenna is recommended if you will be operating from home or from within a vehicle. This is because signals will be attenuated by the walls or your house, or by the body of a car or truck.&lt;/p&gt;&#xA;&lt;p&gt;This is the case for all radios, including but not limited to: CB, amateur, commercial, government, or emergency services.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-12-23T14:31:46.537" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17763" PostTypeId="1" AcceptedAnswerId="17777" CreationDate="2020-12-25T11:14:11.833" Score="4" ViewCount="63" Body="&lt;p&gt;A little background. My uncle devoted part of his late life to ham radio, he had his callsign and would go install/fix radio systems all the time,travel across the country and would teach newcomers and lived the ham radio way and I'm thinking of following in the tradition he started.&lt;br /&gt;&#xA;Full disclosure: I know nothing at all about any of it and I'm for now researching to then decide the path to take.&lt;/p&gt;&#xA;&lt;p&gt;Here is the question: How do I get a permit/license and get my own callsign to operate in Canada?&lt;/p&gt;&#xA;" OwnerUserId="18362" LastActivityDate="2020-12-28T16:26:44.140" Title="What are the steps to become an amateur operator in Canada?" Tags="&lt;license&gt;&lt;canada&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17764" PostTypeId="2" ParentId="17124" CreationDate="2020-12-26T00:19:56.797" Score="1" Body="&lt;p&gt;The Yaesu FT-60R Ni-Mh FNB-83 battery can most certainly be charged via the FT-60R DC Power Jack while the battery is attached to the FT-60R, by using the Yaesu NC-88b wall-wart which came supplied with the earlier units for just this purpose. I know, because i own two of the earlier FT-60R's and have charged them for over 8 years in this manner!&lt;/p&gt;&#xA;&lt;p&gt;I am not certain if it is accurate, but I've read that when Yaesu started supplying the PA-48B and the SBH-13 with the FT-60R (versus the NC-88b walwart) that it removed the internal charging circuitry from the FT-60R, requiring the SBH-13 cradle/PA-48B combo to be used as the means of charging the battery (and then the SAD-25, I guess).  But again, I am not certain if this information is accurate.&lt;/p&gt;&#xA;&lt;p&gt;My manual says &amp;quot;Copyright 2011&amp;quot; on the back cover, so I guess that I'm going to have to take a look at the newer manual, assuming one exists, to see what it says about charging.&lt;/p&gt;&#xA;&lt;p&gt;It just seems odd to me that the newer models can't still use the NC-88B for charging via the DC power port... But then again, I need to carefully watch my earlier model FT-60R while it is charging via the NC-88B into the DC Power input jack to prevent it from over charging the FNB-83 Ni-Mh (10 hours max per the manual), because it will continue charging the battery just as long as the NC-88B is attached to it, and Ni-Mh type batteries can be ruined by long term overcharging.  Don't ask me how I know...&lt;/p&gt;&#xA;&lt;p&gt;Which is why Yaesu most likely changed its design in the first place, I'm guessing?&#xA;bob -- k4sss&lt;/p&gt;&#xA;" OwnerUserId="18364" LastEditorUserId="8717" LastEditDate="2020-12-26T01:18:13.293" LastActivityDate="2020-12-26T01:18:13.293" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17767" PostTypeId="1" CreationDate="2020-12-26T12:06:00.643" Score="1" ViewCount="142" Body="&lt;h3&gt;GNU Radio v3.8 with Qt-GUI on Ubuntu 20.04&lt;/h3&gt;&#xA;&lt;p&gt;Before starting on something new I always test my setup with this &lt;a href=&quot;https://ham.stackexchange.com/q/12833/13000&quot;&gt;GNURadio hello world&lt;/a&gt; flow graph which I know for sure, that it used to work.&lt;/p&gt;&#xA;&lt;p&gt;The other day, on Ubuntu when I fired up the above flow graph with GNU Radio, there were missing blocks everywhere. Apparently the GNU Radio version that comes with &lt;code&gt;Ubuntu 20.04&lt;/code&gt; is &lt;code&gt;version 3.8&lt;/code&gt;, where the &lt;code&gt;WX GUI&lt;/code&gt; has been deprecated.&lt;/p&gt;&#xA;&lt;p&gt;I replaced the &lt;code&gt;WX GUI Slider&lt;/code&gt;with &lt;code&gt;Qt GUI Range&lt;/code&gt; and the &lt;code&gt;WX GUI Sinks&lt;/code&gt; with the &lt;code&gt;Qt GUI sinks&lt;/code&gt; and so on. The important blocks such as &lt;code&gt;WBFM Receive&lt;/code&gt;, &lt;code&gt;Audio Sink&lt;/code&gt;, &lt;code&gt;Rational Resampler&lt;/code&gt;, &lt;code&gt;RTL-SDR Source&lt;/code&gt; are still the same and remain untouched. All their sample-rates, etc are as before.&lt;/p&gt;&#xA;&lt;h3&gt;Overflows or underruns&lt;/h3&gt;&#xA;&lt;p&gt;The flow graph runs, except it kept giving me &lt;code&gt;aU&lt;/code&gt; (or &lt;code&gt;O&lt;/code&gt;) symbols in the console with very funny audio.&lt;/p&gt;&#xA;&lt;p&gt;I duckduckgo-ed and found out that the problem could be with the sample rate that I am feeding to the audio sink. Strange, as I have not touched that and it used to work fine.&lt;/p&gt;&#xA;&lt;p&gt;Anyways, for fun's sake, I checked all the audio sample rates for the audio sink from 16kHz to 48kHz one after the other but nothing helped. For the lower rates I kept getting overruns and for the higher rates, I kept getting underflows.&lt;/p&gt;&#xA;&lt;h3&gt;The Numbers&lt;/h3&gt;&#xA;&lt;p&gt;I then rechecked the numbers, and the &lt;code&gt;WBFM Receive&lt;/code&gt; block outputs a &lt;code&gt;quadrature rate&lt;/code&gt; of &lt;code&gt;250k&lt;/code&gt;. The &lt;code&gt;Rational Resampler&lt;/code&gt; decmiates by 250 and interpolates by 24. So 24kHz does seem to be the right sample rate for the audio sink. So the numbers add up. Don't know where's the problem.&lt;/p&gt;&#xA;&lt;p&gt;Just for fun I changed the &lt;code&gt;interpolation rate&lt;/code&gt; to be above the &lt;code&gt;Sample Rate&lt;/code&gt; of the &lt;code&gt;Audio Sink&lt;/code&gt;. For the &lt;code&gt;24kHz&lt;/code&gt; sample rate on the &lt;code&gt;Audio Sink&lt;/code&gt;an &lt;code&gt;interpolation rate&lt;/code&gt; of &lt;code&gt;40&lt;/code&gt; would, e.g. give at the beginning underflow errors but then after a few seconds it would start giving overruns. The lower I brought the interpolation rate, the quicker the flowgraph went from underflows to overruns. BUT there was no interpolation rate for which I could get a stable error free output.&lt;/p&gt;&#xA;&lt;h3&gt;Can my hardware handle it? YES!&lt;/h3&gt;&#xA;&lt;p&gt;From one of the &lt;a href=&quot;https://www.ruby-forum.com/t/first-time-user-fm-radio-tutorial-has-choppy-audio/233815/7&quot; rel=&quot;nofollow noreferrer&quot;&gt;other forums&lt;/a&gt;, I saw that someone mentioned that maybe the hardware just cannot handle that (or any of the given) sample rate(s).&lt;/p&gt;&#xA;&lt;p&gt;I tested with &lt;code&gt;dial_tone.py&lt;/code&gt; on my PC and got no errors. All worked fine, just like it had with GNU Radio v3.7.&lt;/p&gt;&#xA;&lt;h3&gt;Compare with GNU Radio on Windows 10&lt;/h3&gt;&#xA;&lt;p&gt;So as a quick test, I rebooted the PC and fired up Windows 10 where I had GNU Radio v3.7.13.5 installed. Unforunately, I had forgotten about &lt;a href=&quot;https://ham.stackexchange.com/q/15102/13000&quot;&gt;this problem&lt;/a&gt; with GNU Radio v3.7.13.5.&lt;/p&gt;&#xA;&lt;p&gt;So I downgraded to an &lt;a href=&quot;http://www.gcndevelopment.com/gnuradio/downloads/installers/v1.3.0/gnuradio_3.7.11_win64.msi&quot; rel=&quot;nofollow noreferrer&quot;&gt;older version&lt;/a&gt; from &lt;a href=&quot;http://www.gcndevelopment.com/gnuradio/downloads.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;, where I remember the original FM flow graph worked long time ago.&lt;/p&gt;&#xA;&lt;p&gt;Unfortunately, that version of GNU Radio v3.7.11 on Windows does NOT open the Qt flow graph for FM Receiver but IF I run the WX GUI based FM Receiver it worked fine. (a bug in v3.7.11?)&lt;/p&gt;&#xA;&lt;h3&gt;Conclusion&lt;/h3&gt;&#xA;&lt;p&gt;So apparently GNU Radio v3.8 on Ubuntu has a bug with the audio sink sample rate?&lt;/p&gt;&#xA;" OwnerUserId="13000" LastEditorUserId="8717" LastEditDate="2020-12-27T20:30:53.127" LastActivityDate="2020-12-27T20:30:53.127" Title="GNU Radio FM Receiver does not work on Ubuntu 20.04 nor on Windows 10" Tags="&lt;gnuradio&gt;&lt;rtl-sdr&gt;&lt;linux&gt;&lt;windows&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17768" PostTypeId="1" AcceptedAnswerId="17770" CreationDate="2020-12-27T06:21:02.707" Score="2" ViewCount="60" Body="&lt;p&gt;I can explain almost every part of the Kenwood TM-D710(G) display &lt;em&gt;except&lt;/em&gt; the letter &amp;quot;D&amp;quot; that appears on the second line of the B band next to the power level. I've poured over the manual and can't find any reference to what that indicates. I've only seen it on the B band, and I haven't seen any setting that turns it off.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CKmfA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CKmfA.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="14609" LastActivityDate="2020-12-27T14:03:21.737" Title="On the Kenwood TM-D710, what is the &quot;D&quot; on the B band?" Tags="&lt;kenwood&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17769" PostTypeId="1" CreationDate="2020-12-27T07:08:01.533" Score="3" ViewCount="53" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xD1MX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xD1MX.png&quot; alt=&quot;RF Amplifier Schematic&#xA;&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I chose the resistor values in the following schematic to set the DC bias point of VCE=6V and IC=5mA because the transistor data sheet gave the S-parameters at 162MHz for these values. I learned how to do this by studying the book &amp;quot;Rf Circuit Design&amp;quot; by Chris Bowick. Early on in the book he mentions that stray capacitance inherent in the DC bias network resistors can effect the &amp;quot;RF operating point&amp;quot;. I know what the DC operating point is ,obviously, but what is the RF operating point and how is it effected by the stray parallel capacitance of the bias network resistors? In this case I'm referring to the stray capacitance of the 3.240K Ohm resistor only because the other three resistors are RF bypassed by the .1 micro Farad capacitors. Bowick does explain how the impedance of a resistor can lessen with an increase in frequency but I just don't know what the RF operating point of the bias network is much less how the reduced impedance of the resistor effects it.&lt;/p&gt;&#xA;" OwnerUserId="11230" LastActivityDate="2020-12-28T11:18:52.343" Title="What is the difference between an RF amplifier's DC or quiescent operating point and the RF operating point?" Tags="&lt;amplifier&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17770" PostTypeId="2" ParentId="17768" CreationDate="2020-12-27T14:03:21.737" Score="2" Body="&lt;p&gt;According to the manual, it says &amp;quot;Appears while using the External data band&amp;quot;, and all of the images of the display in the manual show it only appearing on the B band.&lt;/p&gt;&#xA;&lt;p&gt;However, menu setting (according to the manual, again) 517 allows you to set how the external TNC data band setup is defined (A band, B band, Tx on A and Rx on B, or Tx on B, Rx on A).&lt;/p&gt;&#xA;&lt;p&gt;I suggest you give the whole manual a thorough read-through - many radios that have APRS and built-in TNCs have many many settings that can be overwhelming. I have a Yaesu FT-2DR that I have to check the manual for regularly just because I forget which settings are kept where ...&lt;/p&gt;&#xA;&lt;p&gt;I hope this is useful - I am not really sure that it is, as I am not familiar with that specific radio, and only downloaded the manual to see what it said in there.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2020-12-27T14:03:21.737" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17771" PostTypeId="2" ParentId="17752" CreationDate="2020-12-27T16:58:45.717" Score="0" Body="&lt;p&gt;Any physical object where there are potential voltage or current reflections off of impedance mismatches or open circuits (such as the ends of a wire antenna) can change the AC waveform of the current to be different from that of the voltage at the feedpoint.  And wherever the current doesn't exactly follow the voltage (or vice versa), that is defined in linear electrical systems as a non-zero reactance.&lt;/p&gt;&#xA;&lt;p&gt;Nothing has to be imaginary about either the current or the voltage.  Just certain mathematical forms of the description of such, often to save chalk on the chalkboard.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2020-12-27T16:58:45.717" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17772" PostTypeId="1" AcceptedAnswerId="17773" CreationDate="2020-12-27T17:41:48.790" Score="2" ViewCount="54" Body="&lt;p&gt;Let's consider a simple antenna array. For instance, this three-elements equispaced dipole array:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/QVcm0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QVcm0.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Each dipole is connected to a signal voltage source. It's well known that it's possible to choose the phase delay between the input voltage sources of the elements in order to decide the direction of the maximum radiated power (beam scanning for phased arrays). It's known also that, if all the elements have the same voltage signal, without phase delays between them, the peak direction is orthogonal to the array axis.&lt;/p&gt;&#xA;&lt;p&gt;I understand this in theory. But in practice, let's consider the previous picture, in which all voltage sources are supposed to be identical (let's call their signal &lt;span class=&quot;math-container&quot;&gt;$V_i$&lt;/span&gt; like in the picture), without phase delays. Each dipole has two arms, which I have indicated with A and B.&lt;/p&gt;&#xA;&lt;p&gt;Which is the connection (between &lt;span class=&quot;math-container&quot;&gt;$V_i$&lt;/span&gt; and the dipole arms A and B), with respect to which we say there are phase delays or not?&lt;/p&gt;&#xA;&lt;p&gt;Does 0 phase delay means all + terminals of all sources connected to A arms (so, not adjacent arms of adjacent dipoles)? Or does it means + terminals connected to A for an element and to B for the adjacent element?&lt;/p&gt;&#xA;&lt;p&gt;The voltage source is alsways &lt;span class=&quot;math-container&quot;&gt;$V_i$&lt;/span&gt;, but according to how we connect its poles, we may introduce a 180° phase shift, and so a 0.5T delay (with T period of the input signal).&lt;/p&gt;&#xA;" OwnerUserId="16739" LastActivityDate="2020-12-28T14:29:57.433" Title="Phase shifts in antenna arrays" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;dipole&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17773" PostTypeId="2" ParentId="17772" CreationDate="2020-12-27T18:36:25.827" Score="1" Body="&lt;p&gt;In your diagram, the + terminals would all be connected to the A arms.&#xA;Assuming a half wave spacing of the dipole feedpoints, the EM fields can cancel parallel to the antenna elements, then add up to a stronger waveform propagating in the perpendicular direction.&lt;/p&gt;&#xA;&lt;p&gt;Assuming all the voltage sources are isolated, the EM field will simply keep &amp;quot;adding up&amp;quot; right to left; and the EM coupling between dipoles might generate a much higher voltage differential across the entire array than within any individual dipole.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-12-28T14:29:57.433" LastActivityDate="2020-12-28T14:29:57.433" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17774" PostTypeId="1" CreationDate="2020-12-27T20:35:52.740" Score="2" ViewCount="41" Body="&lt;p&gt;let's consider a printed dipole on a substrate with a GND plane:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Dk6U9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Dk6U9.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I've seen many times an equivalent model which uses transmission lines like this (&lt;a href=&quot;https://www.researchgate.net/publication/224076753_Frequency_Selective_Surfaces_for_Extended_Bandwidth_Backing_Reflector_Functions&quot; rel=&quot;nofollow noreferrer&quot;&gt;reference&lt;/a&gt;):&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qFbuJ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qFbuJ.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This model is useful to understand the effect of the presence of the GND plane (or other objects) on the antenna input impedance. In this model there are:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;A Short circuit which represents the GND plane&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A transmission line which represents the EM wave propagation inside the substrate&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A transmission line which represents the EM wave propagation above the substrate (in vacuum)&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;A current source which represents the printed dipole&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I have two question:&lt;/p&gt;&#xA;&lt;p&gt;I) Is the line in vacuum left open, or is it unterminated (that means matched impedance?)&lt;/p&gt;&#xA;&lt;p&gt;II) If someone asked me to evaluate the dipole input impedance in this situation, I'd evaluate the impedance seen by the current source &lt;span class=&quot;math-container&quot;&gt;$I_g$&lt;/span&gt; in the model, which is the parallel between the input impedance of transmission line closed on short circuit and of the input impedance of the transmission line in vacuum.&lt;/p&gt;&#xA;&lt;p&gt;But, I cannot see the dipole impedance in this model. It's known that a dipole may show an inductive or capacitive impedance according to the ratio between its length and the wavelength. In this case it seems totally ignored. How should we take it into account? With a parallel impedance to the current source?&lt;/p&gt;&#xA;" OwnerUserId="16739" LastActivityDate="2020-12-27T20:35:52.740" Title="Printed Dipole Transmission Line Equivalent Model" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;dipole&gt;&lt;transmission-line&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17775" PostTypeId="1" CreationDate="2020-12-28T02:08:19.327" Score="3" ViewCount="147" Body="&lt;p&gt;I have a mid-era Hammarlund HQ-129-x.  It sounds great if I don't count the motorboating.  But the problem is in the middle bands.  I got the radio way out of alignment, and managed (I think) to get the IF working.&lt;/p&gt;&#xA;&lt;p&gt;I receive strong stations (folded, loaded, irregular-dipole) okay, no images.  Even the blasting AM station on 1450 sounds great, so long as I throttle way back on the sensitivity control.  I only hear it on 1450, so the selectivity is good.  No images!&lt;/p&gt;&#xA;&lt;p&gt;But the weirdest part is: I get WWV interference across the bands, all six, but it's the middle four that gets it the most.  I can pick up the WWV signal when it's clear, and it interferes with itself.  I could understand if 1450 were the noisy cricket, but... WWV?&lt;/p&gt;&#xA;&lt;p&gt;How can I snuff out WWV from wherever it's not supposed to be?&lt;/p&gt;&#xA;&lt;p&gt;Caoimhin&lt;/p&gt;&#xA;" OwnerUserId="18383" LastActivityDate="2020-12-28T02:08:19.327" Title="WWV interference all over the band!" Tags="&lt;receiver&gt;" AnswerCount="0" CommentCount="18" ContentLicense="CC BY-SA 4.0" />
  <row Id="17776" PostTypeId="2" ParentId="17769" CreationDate="2020-12-28T11:18:52.343" Score="3" Body="&lt;p&gt;In typical circuit analysis, it's customary to consider the DC model (short all inductors, open all caps, resistors all ideal) and AC model separately. The AC model is simplified by assuming that resistors are ideal and that the AC component simply &amp;quot;rides along&amp;quot; on the DC op point.&lt;/p&gt;&#xA;&lt;p&gt;However, at RF frequencies, the inherent parasitic capacitance and inductance of resistors changes the operating point (imagine a capacitor in parallel and inductor in series with the 3.24k base biasing resistor). I think this is what he means by RF operating point.&lt;/p&gt;&#xA;&lt;p&gt;Most of the familiar equations for amplifier circuits assume ideal components (i.e., a resistor is a resistor and a capacitor is a capacitor, etc).  This keeps the analysis (relatively) simple.  However, as Bowick points out, if you're operating at frequencies where the fact that a resistor is really an RLC circuit matters, then the analysis gets much more complicated.  The transistor at very high frequencies is pretty formidable, with internal capacitance between its leads (the one between collector and base is well-known, but there are others) and inductances in the bonding wires, etc.&lt;/p&gt;&#xA;&lt;p&gt;If I were you, I'd simulate the model. Maybe insert some ballpark parasitic values alongside the components to see what effect they have.  If you're planning to build, try to use SMD parts to reduce parasitic effects.&lt;/p&gt;&#xA;" OwnerUserId="11875" LastActivityDate="2020-12-28T11:18:52.343" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17777" PostTypeId="2" ParentId="17763" CreationDate="2020-12-28T13:22:59.253" Score="2" Body="&lt;p&gt;The &amp;quot;Radio Amateurs of Canada&amp;quot; national club seems to offer a number of resources and pointers on &amp;quot;How to Start&amp;quot; at &lt;a href=&quot;https://www.rac.ca/&quot; rel=&quot;nofollow noreferrer&quot;&gt;RAC&lt;/a&gt; and how to self-study. They also provide a list of local clubs; getting into contact with a club close to you may be a good alternative to starting and studying completely on your own.&lt;/p&gt;&#xA;" OwnerUserId="17676" LastActivityDate="2020-12-28T13:22:59.253" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17778" PostTypeId="1" CreationDate="2020-12-28T14:08:02.270" Score="1" ViewCount="84" Body="&lt;p&gt;When I transmit the there is a delay in the receiving. When I let off of the mic it still transmits for a few milli-seconds. The transfer to receive is not instantaneous.&lt;/p&gt;&#xA;&lt;p&gt;Which setting controls this ?&lt;/p&gt;&#xA;&lt;p&gt;de  W3ASW&lt;/p&gt;&#xA;" OwnerUserId="18387" LastActivityDate="2020-12-28T23:20:33.827" Title="UV9RTP Slow transmit to receive" Tags="&lt;baofeng&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17779" PostTypeId="2" ParentId="17763" CreationDate="2020-12-28T16:26:44.140" Score="1" Body="&lt;p&gt;The following Government of Canada links may be of interest:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/h_sf01709.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/h_sf01709.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/h_sf06073.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/h_sf06073.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Good luck.&lt;/p&gt;&#xA;" OwnerUserId="15289" LastActivityDate="2020-12-28T16:26:44.140" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17780" PostTypeId="2" ParentId="6847" CreationDate="2020-12-28T17:54:45.263" Score="-2" Body="&lt;p&gt;I'm amazed at how many people can't ever answer this question. If you keep these things in mind you should be able to understand the difference between AM, SSB &amp;amp; FM&#xA;Remember that humans need two components to make sound, intelligible: frequency,and volume. A &amp;quot;narrower channel&amp;quot; does not correlate to the efficiency that people ascribe to SSB. SSB is more &amp;quot;efficient&amp;quot; because of the peak envelope power can be over 30db in range, while in AM you're luck to get 9db. And as far as your amplifier transistors are concerned, with SSB you are not using them unless you are transmitting sound, unlike AM where you are always transmitting at least a carrier.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;In AM radio, the demodulation of an AM carrier, into its original audio signal, is not dependent on side-bands.&lt;/li&gt;&#xA;&lt;li&gt;Side bands are a natural result of the mixing of two or more electro-magnetic wave-forms, and and SSB is the use of one of those wave-forms to transmit information.&lt;/li&gt;&#xA;&lt;li&gt;In demodulating SSB, unlike AM, the audio heard after demodulation, is actually the resultant frequency difference between the carrier or &amp;quot;center frequency&amp;quot; and the imposed audio. In upper side-band, it is the &amp;quot;center frequency&amp;quot; + the audio frequency,and in lower side-band it is the &amp;quot;center frequency&amp;quot; - the audio frequency.&lt;/li&gt;&#xA;&lt;li&gt;Like AM, the amplitude of the SSB wave, determines the demodulated &amp;quot;volume&amp;quot;.&lt;/li&gt;&#xA;&lt;li&gt;With FM, the frequency change or deviation, above and below the &amp;quot;center&amp;quot; frequency, determines the &amp;quot;volume&amp;quot;/output level of a decoded signal, while the frequency of that output is determined by the rate of change of the frequency deviation.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="18388" LastActivityDate="2020-12-28T17:54:45.263" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17781" PostTypeId="2" ParentId="17778" CreationDate="2020-12-28T23:20:33.827" Score="2" Body="&lt;p&gt;If the UV-9RTP is like the UV-5R, then that sounds like either the squelch tail elimination (STE) feature, which is menu item 35 in a UV-5R, or the repeater squelch tail elimination (RP-STE), which is menu item 36.&lt;/p&gt;&#xA;&lt;p&gt;When STE is enabled, then the radio transmits a 55 Hz tone (FM modulated as usual) for a moment after the PTT button is let go.  Other Baofeng radios will mute the receiver when they hear the 55 Hz tone in the received audio.  (This only works in a simplex communication with another Baofeng.  Radio models by other manufacturers don't mute the receiver for a 55 Hz tone, and a repeater will ignore the tone and filter it out of the audio before repeating it.)&lt;/p&gt;&#xA;&lt;p&gt;For a radio with RP-STE enabled, it mutes its own receiver for a moment after PTT is let go, so that the radio won't pick up the repeater's squelch tail.  The radio doesn't actually transmit after PTT is let go, but you might think that it's still transmitting, because the receiver doesn't operate for a moment.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2020-12-28T23:20:33.827" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17782" PostTypeId="1" CreationDate="2020-12-29T00:36:29.110" Score="3" ViewCount="100" Body="&lt;p&gt;I think I'm having a hard time understanding HF antennas because they go against everything I've been taught about analyzing circuits.&lt;/p&gt;&#xA;&lt;p&gt;If we look at a dipole antenna, there is the highest current in the middle and zero current at the ends. So if we consider any point along the dipole to be a Kirchhoff's current law (KCL) node, then there is less current going out of the node than flowing in. Does KCL not work with RF circuits?&lt;/p&gt;&#xA;" OwnerUserId="18394" LastEditorUserId="4665" LastEditDate="2020-12-29T01:32:01.683" LastActivityDate="2020-12-31T14:53:30.283" Title="Does Kirchhoff's current law (KCL) apply to antennas?" Tags="&lt;antenna&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17783" PostTypeId="2" ParentId="17782" CreationDate="2020-12-29T01:19:44.353" Score="2" Body="&lt;p&gt;You are not considering distance, time, frequency, and the speed of light (or EM propagation) being finite.&lt;/p&gt;&#xA;&lt;p&gt;If the current flowing into on end (point A) of a segment of wire changes, that change won't occur at the other end of the wire segment (point B) until later in time, due to the finite speed of light between the two points.  If it's AC current, then the current will change again at point A before the first change in current reaches point B.  So the current flowing in and out of end of each inch/foot/meter of wire in an antenna can be almost always non-equal for any non-zero frequency signal.&lt;/p&gt;&#xA;&lt;p&gt;Thus KCL won't apply unless the antenna is infinitely small (or close enough given your calculation error bounds), or the frequency is zero (or low enough given your error bounds or measurement resolution, etc.).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2020-12-30T02:23:32.967" LastActivityDate="2020-12-30T02:23:32.967" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17784" PostTypeId="2" ParentId="17490" CreationDate="2020-12-29T03:10:14.207" Score="3" Body="&lt;p&gt;In short, by the letter of the law you cannot posess a transmitter in Canada without a license. In practice, no one gets worked up about it, and people often buy gear before getting their license.&lt;/p&gt;&#xA;" OwnerUserId="8160" LastActivityDate="2020-12-29T03:10:14.207" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17785" PostTypeId="1" AcceptedAnswerId="17788" CreationDate="2020-12-30T10:34:36.997" Score="3" ViewCount="235" Body="&lt;h2&gt;In short&lt;/h2&gt;&#xA;&lt;p&gt;I am trying to receive &lt;a href=&quot;https://ariss-sstv.blogspot.com/2020/12/ariss-20-years-of-operations-on-iss.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;SSTV Images from the ISS&lt;/a&gt; (145.8Mhz) and I all have is a simple &amp;quot;bunny ears&amp;quot; dipole antenna.&#xA;In what configuration (straight, vee shaped, upside down vee, ...) and orientation should I place the antenna to optimize signal reception?&#xA;Could you please explain why and/or link to some sources where I can learn how to find the proper orientation myself?&lt;/p&gt;&#xA;&lt;h2&gt;More details&lt;/h2&gt;&#xA;&lt;p&gt;I've tried answering this question myself but I all found was tutorials that either didn't specify the antenna configuration/orientation or even contradict each other.&lt;/p&gt;&#xA;&lt;p&gt;While vertically dipoles are widely discussed, there are not many sources (that I could find) that discuss other dipole configurations.&#xA;Since the radiation pattern of a vertical dipole is shaped like a doughnut (where the dipole is passing through the doughnut hole), I was expecting that rotating the dipole by 90 degrees (so that it lies in the horizontal plane) would also rotate the radiation pattern accordingly.&#xA;Apparently &lt;a href=&quot;https://www.qsl.net/kk4obi/Standard%20dipole.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;I was wrong&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Assuming that the information on that website is correct, I can't really find an orientation for good reception of a signal coming almost-vertically from the sky.&lt;/p&gt;&#xA;&lt;p&gt;Also, I wasn't able to figure out what polarization is being used by the ISS SSTV transmission.&#xA;&lt;a href=&quot;http://www.amsat.it/arissfreq.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;This website&lt;/a&gt; reports it as &amp;quot;U: linear, V: linear&amp;quot;, but there is no explanation of what U and V mean in this context (I assume it's a standard notion but I haven't been able to find an explanation either).&lt;/p&gt;&#xA;&lt;p&gt;What does this polarization refer to anyway? Since the ISS rotates I assume the polarization will also shift by 90 degrees (twice) from the perspective of the receiver. At what point in the orbit does the apparent polarization match the nominal one?&lt;/p&gt;&#xA;&lt;p&gt;Finally, to optimize reception I assume I'd need to rotate the antenna  along with the ISS pass (to properly direct the radiation pattern and match polarization). What's the correct orientation at any given point in the orbit?&lt;/p&gt;&#xA;&lt;p&gt;If reorienting the antenna is not possible, are there any tips for choosing a fixed antenna position? Is it better to optimize for reception when the station is directly overhead, for when it's rising/setting, somewhere in-between, ...?&lt;/p&gt;&#xA;&lt;p&gt;As you can see I'm a little confused, and I would be grateful for any guidance from anyone more expert than me.&lt;/p&gt;&#xA;" OwnerUserId="18277" LastEditorUserId="18277" LastEditDate="2020-12-30T15:23:59.347" LastActivityDate="2021-02-16T00:26:37.737" Title="Receiving the ISS SSTV: dipole antenna configuration and orientation" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;satellites&gt;&lt;polarization&gt;&lt;sstv&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17786" PostTypeId="1" AcceptedAnswerId="17792" CreationDate="2020-12-30T12:17:03.053" Score="2" ViewCount="63" Body="&lt;p&gt;I want to transmit an ASK signal with GNU Radio and HackRF, the parameters are:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Frequency: 27.12 MHz (ISM)&lt;/li&gt;&#xA;&lt;li&gt;Sample rate: 2MSPS&lt;/li&gt;&#xA;&lt;li&gt;Symbol rate: 2000 bps&lt;/li&gt;&#xA;&lt;li&gt;Samples per symbol: 1000&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;The flowgraph currently looks like this (SDR sink is not included here):&#xA;&lt;a href=&quot;https://i.stack.imgur.com/7Tydh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7Tydh.png&quot; alt=&quot;ask_flowgraph&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;What bothers me, is the following: in the baseband I have a square wave. Square waves have infinite bandwidth. After amplitude modulation with the carrier, this means that in the passband, the signal will also take infinite bandwidth? This somehow doesn't feel right. So I think that I need to lowpass filter it first, but I don't know how to compute the lowpass filter parameters (cutoff frequency, etc)?&lt;/p&gt;&#xA;" OwnerUserId="10631" LastActivityDate="2020-12-31T15:22:13.310" Title="Transmit filter for Amplitude-shift keying" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17787" PostTypeId="2" ParentId="17746" CreationDate="2020-12-30T15:08:43.923" Score="0" Body="&lt;p&gt;I want to mention that the technique described at the end of the accepted answer can be seen very clearly in the LuaRadio documentation: &lt;a href=&quot;https://luaradio.io/examples/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://luaradio.io/examples/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Each of the examples defines a variable &lt;code&gt;tune_offset&lt;/code&gt;, whose value is slightly larger than the bandwidth of the desired signal.  In the first example, which is an FM receiver, the bandwidth of interest is 200kHz, and tune_offset is -250kHz. Say that we want to receive a signal at 101.00MHz:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The source block will tune the SDR to 101.00MHz - 250kHz = 100.75MHz. Now in the baseband the signal that we care about will be centered at 250kHz (from 150kHz to 350kHz) - far away from the DC spike at 0Hz.&lt;/li&gt;&#xA;&lt;li&gt;After that, the tuner block will shift all frequencies down by the same (250kHz) amount - now our signal will move where we want it to be - centered around 0Hz, and the DC offset will appear at -250kHz. Next, the tuner block will also filter everything above 200kHz, so the DC offset won't interfere with the subsequent processing.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="10631" LastActivityDate="2020-12-30T15:08:43.923" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17788" PostTypeId="2" ParentId="17785" CreationDate="2020-12-30T15:35:30.237" Score="3" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;reports it as &amp;quot;U: linear, V: linear&amp;quot;&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Satellites which transmit and receive at the same time frequently do one on VHF (2m) and the other on UHF (70cm), and they frequently have separate antennas for each (rather than a dual-band antenna). This notation is saying that the ISS's UHF and VHF antennas are both linearly polarized.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;What does this polarization refer to anyway? Since the ISS rotates I assume the polarization will also shift by 90 degrees (twice) from the perspective of the receiver. At what point in the orbit does the apparent polarization match the nominal one?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;There is no nominal one. It's just linear &lt;em&gt;something&lt;/em&gt;, as opposed to circular. With satellites you don't really know which way they're pointing. That's the advantage of circular polarization — you don't have to know, you just have to get the correct handedness.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Finally, to optimize reception I assume I'd need to rotate the antenna along with the ISS pass (to properly direct the radiation pattern and match polarization). What's the correct orientation at any given point in the orbit?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;With regard to polarization, again, you don't really know. With regard to pattern... whichever way gives you gain in the direction of the ISS :)&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;If reorienting the antenna is not possible, are there any tips for choosing a fixed antenna position? Is it better to optimize for reception when the station is directly overhead, for when it's rising/setting, somewhere in-between, ...?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;A good trick in this case is to orient the dipole horizontally, and perpendicular to the track of the satellite's pass. i.e. if the ISS is going to be coming over from the northwest to the southeast, point the ends of the antenna to the northeast and southwest. This places your nulls roughly on the northeast and southwest horizon, which are the points furthest from where the satellite will be at any point in the pass, so you should enjoy decent reception throughout.&lt;/p&gt;&#xA;&lt;p&gt;Finally, as Duston mentions in a comment, the ISS is pretty darn loud compared to most amateur satellites... in most cases you can do everything wrong and still hear it fine, so don't worry too hard.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2020-12-30T15:35:30.237" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17789" PostTypeId="2" ParentId="16798" CreationDate="2020-12-31T09:40:38.560" Score="0" Body="&lt;p&gt;The NEC4.2 analysis below shows the performance of a CM choke at the feedpoint of an elevated, center-fed, h-pol dipole at 10m AGL, and the radiation pattern of that antenna system.&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;observations&amp;quot; in the graphic may be surprising, especially when considering the presence of CM current along the entire length of the coaxial line of that system — even though the OD of its shield is connected to a buried ground rod.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/66ztV.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/66ztV.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2020-12-31T09:40:38.560" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17790" PostTypeId="2" ParentId="17782" CreationDate="2020-12-31T10:35:28.023" Score="1" Body="&lt;p&gt;The current described in classic dipole antenna depictions is, already, the &lt;em&gt;net&lt;/em&gt; current at each point along the radiator. Thus, KCL is satisfied by the superposition of two current waves: one traveling from the generator and incident upon the open end, the other reflected from the open end back toward the generator.&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;transmission line analog&amp;quot; to the dipole antenna is instructive: imagine a transmission line comprising two parallel wires which are opened up to form the dipole antenna. Like the dipole, there is no &lt;em&gt;net&lt;/em&gt; current at the open-circuit end of the transmission line, but the incident current wave is perfectly reflected to result in net zero current at the open end.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2020-12-31T10:35:28.023" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17791" PostTypeId="2" ParentId="17782" CreationDate="2020-12-31T14:53:30.283" Score="4" Body="&lt;p&gt;Wikipedia states the KCL as:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The algebraic sum of currents in a network of conductors meeting at a point is zero.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The key word here is &lt;em&gt;point&lt;/em&gt;. If you pick a single geometric point on the antenna, then yes, this law holds. It's fairly easy to see why intuitively from the law of &lt;a href=&quot;https://en.wikipedia.org/wiki/Charge_conservation&quot; rel=&quot;nofollow noreferrer&quot;&gt;charge conservation&lt;/a&gt;: since charge can't be created or destroyed, if an electron enters the point it will create a net negative charge at that point, which is associated with an electromotive force that will push some other electron out.&lt;/p&gt;&#xA;&lt;p&gt;But KCL is often applied to nodal analysis problems. For example consider these two equivalent circuits:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/kGm88.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fkGm88.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;In this schematic it doesn't really matter if we pick node A or B, because the circuit can be redrawn as show to have all three current sources and the LED meet at one point. We can do this because a line in a schematic isn't a real conductor, but rather an idealized connection. Everything connected by a line in the schematic has the same electric potential, and any changes propagate instantly throughout the entire net.&lt;/p&gt;&#xA;&lt;p&gt;This is such a useful and ubiquitous simplification we tend to apply it without even thinking. Here's the trap: an antenna, although it may be just a conductor, is not a line on a schematic.&lt;/p&gt;&#xA;&lt;p&gt;Neither are the wires in the circuit above, for that matter. Even just a wire is an inductor, albeit a small one. And two wires separated by a dielectric (like air, silicone, PTFE, or PVC) are a capacitor. So if we really wanted to draw an LED driven by three current sources, it might look more like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/f5yJC.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2ff5yJC.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;Of course we haven't put any discrete inductors or capacitors in the circuit: we are simply including in the schematic (some of the) non-ideal behavior of actual wires. Normally we omit them because the capacitance and inductance is too small to be relevant to the operation of the circuit. For example if we just want to blink an LED at 1 Hz, all this parasitic capacitance and inductance doesn't matter at all.&lt;/p&gt;&#xA;&lt;p&gt;But in antennas it absolutely does matter. Imagine a dipole as a bunch of short sections of wire, each having a little inductance, and some capacitance to ground, at least. You might draw that as:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/EVnZe.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fEVnZe.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;If you continue dividing the antenna into smaller and smaller segments forever, until each segment is infinitesimal and you have infinitely many of these inductors and capacitors, you're getting close to the theoretical model of a transmission line. You just need to add some resistance to account for energy lost to radiation, finite conductivity of the metal making the antenna, and dielectric losses.&lt;/p&gt;&#xA;&lt;p&gt;While in the LED circuit this level of detail wasn't necessary because it was insignificant, in an antenna it is not so. Remember above when we assumed changes in electric potential propagate instantly across schematic lines? An antenna is explicitly designed for this to be untrue. Real changes only propagate at the speed of light, and antennas are big enough and the frequency high enough that this propagation delay is significant. Consider a half-wave dipole: being a half-wavelength long means any change at one end of the antenna takes a full half cycle before its propagated to the other end. So, the conductors in an antenna are very much not simply lines on a schematic.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-12-31T14:53:30.283" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17792" PostTypeId="2" ParentId="17786" CreationDate="2020-12-31T15:22:13.310" Score="2" Body="&lt;p&gt;A low-pass filter is one way to do it. Due to the interpolation done in the repeat block, you are representing a symbol with 1000 samples, and your sample rate is 2 million samples per second (the &lt;code&gt;samp_rate&lt;/code&gt; variable). So your square wave has a frequency of:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \require{cancel}&#xA;{2000000\ \cancel{\text{samples}} \over \text{second}}&#xA;{1\ \text{symbol} \over 1000\ \cancel{\text{samples}}}&#xA;= {2000\ \text{symbols} \over \text{second}} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Or more simply, 2 kHz. Square waves have odd harmonics, so the first harmonic you need to worry about is &lt;span class=&quot;math-container&quot;&gt;$2\:\mathrm{kHz} \times 3 = 6\:\mathrm{kHz}$&lt;/span&gt;. So you want a filter with a cutoff a little above 2 kHz with a transition width of a little less than 4 kHz, so he harmonic at 6 kHz gets attenuated.&lt;/p&gt;&#xA;&lt;p&gt;But this isn't a great way to do it. Consider transmitting a single '1' symbol, surrounded by infinite '0' symbols. Assuming 1 is represented by &amp;quot;full amplitude&amp;quot;, and 0 by &amp;quot;zero amplitude&amp;quot;, then the result is some kind of pulse. Due to the filtering, this pulse will happen gradually, with the transmitter amplitude rising gradually to a maximum, then gradually going back to zero, maybe with some ringing, and maybe with some time held at maximum.&lt;/p&gt;&#xA;&lt;p&gt;But what exactly is this pulse shape? If we want to build the best receiver, we need to know. Also, will the pulse for one symbol interfere with the pulses for adjacent symbols? Hopefully not, if we want the best performance. The low-pass filter approach isn't especially amenable to addressing these concerns.&lt;/p&gt;&#xA;&lt;p&gt;So, the canonical solution to this problem is a &lt;a href=&quot;https://en.wikipedia.org/wiki/Pulse_shaping#Pulse_shaping_filters&quot; rel=&quot;nofollow noreferrer&quot;&gt;pulse shaping filter&lt;/a&gt;. In GNU Radio you'll probably implement this with the &lt;a href=&quot;https://wiki.gnuradio.org/index.php/Interpolating_FIR_Filter&quot; rel=&quot;nofollow noreferrer&quot;&gt;Interpolating FIR Filter&lt;/a&gt; block, and calculating the taps for that block with &lt;a href=&quot;https://wiki.gnuradio.org/index.php/RRC_Filter_Taps&quot; rel=&quot;nofollow noreferrer&quot;&gt;RRC Filter Taps&lt;/a&gt;. The &lt;a href=&quot;https://wiki.gnuradio.org/index.php/Guided_Tutorial_PSK_Demodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;PSK tutorial&lt;/a&gt; or the &lt;a href=&quot;https://wiki.gnuradio.org/index.php/Simulation_example:_BPSK_Demodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;BPSK&lt;/a&gt; tutorials give some examples in context. Unfortunately there isn't and ASK tutorial, but consider that BPSK and ASK are nearly the same thing: in ASK the amplitude is either 0 or 1, whereas in BPSK the amplitude is -1 or 1. Otherwise they are essentially the same thing.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2020-12-31T15:22:13.310" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17793" PostTypeId="1" CreationDate="2020-12-31T19:59:54.883" Score="0" ViewCount="67" Body="&lt;p&gt;I am getting no NOAA weather broadcasts, after loading all NOAA weather channels into memory or entering the frequencies manually on a new Baofeng UV-5R?? Why? Do I need to do something else?&lt;/p&gt;&#xA;" OwnerUserId="18414" LastActivityDate="2020-12-31T21:29:09.940" Title="NOAA weather broadcasts" Tags="&lt;reception&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17794" PostTypeId="2" ParentId="17793" CreationDate="2020-12-31T21:29:09.940" Score="2" Body="&lt;p&gt;If you are checking the correct frequencies (162.400 MHz, 162.425 MHz, 162.450 MHz, 162.475 MHz, 162.500 MHz, 162.525 MHz, 162.550 MHz), have all settings properly set (ex. volume control), and have a decent antenna installed and can't hear anything, then the NOAA signal entering your radio is simply too weak.&#xA;Try holding the MONI button for each frequency to bypass the squelch to see if you can make out any faint reception. Use a good grip on the radio while holding it upright (antenna pointing up) or try a few different orientations. Try it outside and try it in different locations. Compare it with another weather radio to find out if there is really no signal or perhaps something wrong with the Baofeng radio. Also look at the NOAA transmitter and coverage map to see which direction the closest transmitter is from and if something might be blocking the path such as a hill.&#xA;&lt;a href=&quot;https://www.weather.gov/nwr/Maps&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.weather.gov/nwr/Maps&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17896" LastActivityDate="2020-12-31T21:29:09.940" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17796" PostTypeId="1" CreationDate="2021-01-01T03:45:42.457" Score="-1" ViewCount="63" Body="&lt;p&gt;Imagine a group of eight or more vertical masts. On each mast is a Yagi antenna pointed upward toward the sky. The elements are inverted with the idea being that the incoherent RF coming down is given constructive interference to become useable coherent current.  How to successfully connect multiple feeds together to support this desired outcome?&lt;/p&gt;&#xA;" OwnerUserId="18423" LastActivityDate="2021-01-08T16:49:09.083" Title="Using inverted Yagi antennas to gather and cohere RF from the sky" Tags="&lt;antenna-theory&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17797" PostTypeId="2" ParentId="17796" CreationDate="2021-01-01T08:15:36.693" Score="4" Body="&lt;p&gt;Using several antennas to improve HF reception is an old and very effective idea. The trick is combining them correctly. Simply connecting them to a splitter will generate fixed-position lobes of high gain in the sky, and regions of lower gain. For amateurs who are looking for contacts in a wide area, not a single place, this is quite advantageous already.&lt;/p&gt;&#xA;&lt;p&gt;The udeal is to have the feeds connected to separate receivers, and then to a computer that combines them in the appropriate phase for best SNR.&lt;/p&gt;&#xA;&lt;p&gt;The computer would first do some direction-finding to find the angle of arrival of the signal, then synthesize a beam in that direction.&lt;/p&gt;&#xA;&lt;p&gt;The RF from the sky is not incoherent - it is very much coherent and to your &amp;quot;radio eyes&amp;quot; would appear to be coming from a fairly small spot in the sky. This is the basis of Single Site Location, where a single DF system can find the position of a transmitter, using only the angles of arrival and a model of the ionosphere.&lt;/p&gt;&#xA;&lt;p&gt;Once you have several elements, the advantage (in receiving) of using yagis is reduced. The synthesised beam is fairly small anyway. Commercially available HF DF arrays use a pattern of crossed loops and dipoles laid out on the ground.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-01-08T16:49:09.083" LastActivityDate="2021-01-08T16:49:09.083" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17799" PostTypeId="2" ParentId="9108" CreationDate="2021-01-01T16:23:29.330" Score="3" Body="&lt;p&gt;If you purchase a radome antenna, like a Comet gp6, they are painted and can be painted again for color change ..using non conductive paint&#xA;They are made of fiberglass which is not uv tolerant and will deteriorate if left unpainted.&#xA;Pvc pipe is not uv resistant and should be painted.  I've done this before and found a Rustoleum product spray on paint with primer labelled 2x. In a flat color called &amp;quot;Perfect Grey&amp;quot;.&#xA;Did a before and after and resonance did not change, and Q.bandwidth seemed the same altho not precisely measured.&lt;/p&gt;&#xA;" OwnerUserId="18429" LastActivityDate="2021-01-01T16:23:29.330" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17800" PostTypeId="1" AcceptedAnswerId="17801" CreationDate="2021-01-02T01:32:33.420" Score="0" ViewCount="102" Body="&lt;p&gt;I'm trying to identify the type of RFI I'm seeing on the waterfall in the picture below.  It occurs mainly at night, every night, starting at about 6:30 p.m. and ending in the morning, and I have yet to identify the source.  It occurs within the same frequency range (around 6300 kHz to about 7200 kHz) every night.  It happens regardless whether I'm using a mag loop antenna, my 150' sky loop antenna, or my vertical.  Any help is greatly appreciated.  I've been working on this for the last two months and am stumped.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8XIOi.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8XIOi.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9772" LastActivityDate="2021-01-14T00:52:35.820" Title="Identifying type of RFI by waterfall" Tags="&lt;rfi&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17801" PostTypeId="2" ParentId="17800" CreationDate="2021-01-02T13:49:21.773" Score="2" Body="&lt;p&gt;Identifying RFI just by the waterfall is not usually possible.&lt;/p&gt;&#xA;&lt;p&gt;A more productive approach is to find the source physically, then the source will be obvious. If it's in your house, you can narrow down the source by turning off breakers and unplugging individual devices until the culprit is identified. If turning off your main breaker doesn't eliminate the noise then the source is somewhere else and can be found with a directional and portable antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-01-02T13:49:21.773" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17802" PostTypeId="1" AcceptedAnswerId="17805" CreationDate="2021-01-03T03:24:49.467" Score="3" ViewCount="95" Body="&lt;p&gt;I want to build a common mode choke for my end-fed wire antenna, using turns of coax through an FT140 or FT240 ferrite.  I can find various finished products for sale, but I want to make my own.  I found plenty of YouTube videos telling me how they built theirs, but I cannot seem to figure out how they knew what to build.  How do I determine, given a target band or set of bands, the appropriate ferrite size, ferrite mix, and coax turn count?&lt;/p&gt;&#xA;" OwnerUserId="18437" LastActivityDate="2021-01-03T19:01:18.053" Title="How do you calculate the number of turns for a common mode choke?" Tags="&lt;diy&gt;&lt;ferrite&gt;&lt;choke-balun&gt;&lt;efhw&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17803" PostTypeId="2" ParentId="17802" CreationDate="2021-01-03T14:57:58.547" Score="1" Body="&lt;p&gt;You build a few and measure them with a vector impedance meter.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-01-03T14:57:58.547" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17804" PostTypeId="1" CreationDate="2021-01-03T16:12:59.303" Score="1" ViewCount="74" Body="&lt;p&gt;Please forgive me, my native language is not English.&lt;/p&gt;&#xA;&lt;p&gt;I'm new to radio, but I have several years of programming experience.&lt;/p&gt;&#xA;&lt;p&gt;I have a &lt;code&gt;raspberry pi 4 model B&lt;/code&gt; (hereinafter referred to as &lt;code&gt;pi&lt;/code&gt;), &lt;code&gt;433Mhz RF Wireless Receiver &amp;amp; Transmitter pair&lt;/code&gt; (about the &lt;a href=&quot;https://www.geekbuying.com/item/MX-05V-433MHZ-RF-Wireless-Receiver-Module-MX-FS-03V-Transmitter-Module-Kit-For-Arduino-Raspberry-Pi-AVR-ARM-344591.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;receiver and transmitter details&lt;/a&gt;, &lt;a href=&quot;https://gemischtwaren-haendler.de/shopdateien/5299_1.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;manual&lt;/a&gt;).&lt;/p&gt;&#xA;&lt;p&gt;I want use the &lt;code&gt;pi&lt;/code&gt; and &lt;code&gt;receiver&lt;/code&gt; to learn control code (or signals?) of my home remote control switch, then use the &lt;code&gt;pi&lt;/code&gt; to control the &lt;code&gt;transmitter&lt;/code&gt; to send the learned code (or signals?) to control my switch.&lt;/p&gt;&#xA;&lt;p&gt;But I learned that wireless modulation has FSK, OOK, ASK, PSK and so on. And I found that the operation mode of &lt;code&gt;receiver &amp;amp; transmitter pair&lt;/code&gt; is &lt;code&gt;AM&lt;/code&gt; (is it equals to ASK?).&lt;/p&gt;&#xA;&lt;p&gt;So how can I know (check or detect or analyze) which modulation using of my remote control switch?&lt;/p&gt;&#xA;&lt;p&gt;Does they all need to match same modulation for communicating?&lt;/p&gt;&#xA;&lt;p&gt;Forgive me for being a newbie at radio, anything that you think is very basic could be very helpful to me.&lt;/p&gt;&#xA;" OwnerUserId="18439" LastEditorUserId="18439" LastEditDate="2021-02-05T17:36:54.710" LastActivityDate="2021-03-07T18:03:30.347" Title="How can I know (check or detect or analyze) which modulation using of my remote control switch?" Tags="&lt;software-defined-radio&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17805" PostTypeId="2" ParentId="17802" CreationDate="2021-01-03T19:01:18.053" Score="1" Body="&lt;p&gt;The very best source of information that you'll find about making common-mode chokes is available at Jim Brown, K9YC's site &lt;a href=&quot;http://k9yc.com/publish.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://k9yc.com/publish.htm&lt;/a&gt;. Download his PDF &lt;a href=&quot;http://k9yc.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://k9yc.com/RFI-Ham.pdf&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://k9yc.com/RFI-Ham.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;RFI, Ferrites, and Common Mode Chokes For Hams&lt;/strong&gt;&lt;/a&gt;&#xA;Most recent update April 2019. This tutorial is directed specifically to RFI in ham radio applications. It includes an extended discussion of the use of common mode chokes in antenna systems and for suppression of RFI.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;No matter what band or application, you'll find it all there.&lt;/p&gt;&#xA;&lt;p&gt;Note, however, that the impedance of an end-fed antenna will change drastically on different bands.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2021-01-03T19:01:18.053" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17806" PostTypeId="2" ParentId="16936" CreationDate="2021-01-04T12:08:38.623" Score="3" Body="&lt;p&gt;Those &amp;quot;wall wart&amp;quot; style power supplies are likely to lack the power needed here.  As others point out here the radio will likely somewhere between 1.5 to 2 amps to operate as intended.  I don't recall seeing a 12 volt wall wart that can provide more than 1 amp.  Do you have a &amp;quot;soap on a rope&amp;quot; kind of power supply in your parts bins?  That would be the kind where the power supply is a brick with a 120 VAC cord to the wall outlet and another for the low voltage DC.  It doesn't have to be 12 volts either, that's just the nominal voltage of a typical car battery.  The actual voltage will vary from about 11 volts when the car is off and close to 14 volts when running.  Double check the specs on the radio to make sure but it's likely built to handle 15 or 16 volts.  This can widen your options if you can't find a 12 VDC supply rated for sufficient current.&lt;/p&gt;&#xA;&lt;p&gt;As an example I have an old 15 VDC power supply from a long gone laptop just waiting to be put to use.  I already put a 12 VDC @ 4 amp laptop supply into service for running and testing automotive electronics at home.  5 VDC supplies will be far too low of voltage.  9 VDC supplies are common and might light up the radio but I wouldn't even try.  Laptop supplies in the 12 VDC to 15 VDC range should be easy to find, and provide enough voltage and current for your CB radio.  There's lots of laptop power supplies, especially as laptops are getting more powerful and more people are switching to USB-C, in the 16 VDC to 20 VDC range.  16 VDC is likely too much, and anything over that is asking for something to start smoking.&lt;/p&gt;&#xA;&lt;p&gt;Any wall wart supply is not likely to work for you.  That doesn't mean give up on them, it means think bigger.  It doesn't have to be exactly 12 volts, but not too high or too low.  Check the manual or manufacturer website, it should give a safe range of voltages for you.  If at all in doubt then keep it below 13.8 volts, that's the regulated voltage of a standard car alternator, and above 11 volts.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2021-01-04T12:08:38.623" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17807" PostTypeId="2" ParentId="4996" CreationDate="2021-01-04T17:46:36.240" Score="0" Body="&lt;p&gt;Use the normal PTT and audio connections. Similar to what you would use with a digital connection.&lt;/p&gt;&#xA;" OwnerUserId="18451" LastActivityDate="2021-01-04T17:46:36.240" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17808" PostTypeId="1" CreationDate="2021-01-04T22:24:33.437" Score="1" ViewCount="64" Body="&lt;p&gt;I'm trying to build a UHF repeater using two Motorola radios.  I have a cable connecting the two radios that was built for doing such a project.  The radios have been programmed for the appropriate inputs/outputs for connection in the repeater mode. The homemade repeater operates flawlessly at my home feeding into a dummy load.  However, when I take the radios to the site where my antenna is, the repeater seems to break into some type of oscillation (when accessed).  The receiver will receive a transmission from a good four miles away via a handie-talkie....but whenever it starts receiving the signal from the handie-talkie, the repeater will go into transmit for about a half-second, then receive, transmit, then receive, over and over again.  I have run tests to see if the receiver is getting a good signal from the handie-talkie and it has crystal clear audio from the repeater receiver (when the repeater transmitter is off).  I have checked the reflected power from the antenna.....very low.  I have checked the duplexer to see if it is working properly......seems to be working properly.  I am running the repeater using CTCSS tones in/out.  The repeater also works great (with no issue) if I am at the antenna site using a handie-talkie.  I can't understand why (if I'm getting clear audio from 4 miles away) the repeater breaks into this sort of oscillation when trying to access it from 4 miles away, but works perfectly if I transmit on handie-talkie at the repeater site. Any suggestions would be sincerely appreciated.  I've worked on this (what I thought would be a simple project) until I'm blue in the face.  Thanks, Rusty&lt;/p&gt;&#xA;" OwnerUserId="18454" LastEditorUserId="4665" LastEditDate="2021-01-04T22:40:11.927" LastActivityDate="2021-01-15T02:13:28.520" Title="Repeater build problems" Tags="&lt;repeater&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17809" PostTypeId="2" ParentId="17808" CreationDate="2021-01-05T00:05:05.173" Score="4" Body="&lt;p&gt;This sounds like desense cycling:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Repeater receiver detects signal.&lt;/li&gt;&#xA;&lt;li&gt;Controller keys transmitter.&lt;/li&gt;&#xA;&lt;li&gt;Signal from transmitter gets into receiver and blocks incoming signal.&lt;/li&gt;&#xA;&lt;li&gt;Controller decides input signal gone, unkeys transmitter.&lt;/li&gt;&#xA;&lt;li&gt;Transmitter off, receiver detects signal.&lt;/li&gt;&#xA;&lt;li&gt;Cycle repeats.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Your duplexer might not be working as well as it should.&#xA;Or possibly, you don't have enough isolation between your receiver and transmitter radios.  You aren't using RG-58 are you?&lt;/p&gt;&#xA;&lt;p&gt;It is difficult to completely eliminate desense.  But you should be able to get it down to a negligible level.&lt;/p&gt;&#xA;&lt;p&gt;[Edit to add:] Here is a way to get an estimate of desense.  Requires a signal source with adjustable output level (e.g. signal generator).&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Have repeater set up normally with its antenna.&lt;/li&gt;&#xA;&lt;li&gt;Have signal source connected to another antenna setup some distance from repeater (not too close or too far.  Need to be picked up by antenna, but be able to put in strong enough signal).&lt;/li&gt;&#xA;&lt;li&gt;Adjust signal level up and down to get an idea of what it takes to bring up repeater.&lt;/li&gt;&#xA;&lt;li&gt;Set signal level somewhat below minimum to bring up the repeater.&lt;/li&gt;&#xA;&lt;li&gt;Increase level in small (1 dB) steps until repeater just barely comes up.  At this point the desense cycling will start.&lt;/li&gt;&#xA;&lt;li&gt;Keep increasing level until cycling stops and repeater stays up.&lt;/li&gt;&#xA;&lt;li&gt;Difference between these levels is a measure of desense.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Ideally, you'll get it down to zero.  You can probably live with up to about 3 dB desense.  If it is much more, you have a problem to work on.&lt;/p&gt;&#xA;" OwnerUserId="17422" LastEditorUserId="17422" LastEditDate="2021-01-05T02:05:16.080" LastActivityDate="2021-01-05T02:05:16.080" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17810" PostTypeId="1" AcceptedAnswerId="17827" CreationDate="2021-01-05T08:52:04.947" Score="2" ViewCount="72" Body="&lt;p&gt;let's consider this two planar biconical dipoles of total length and width each one 10mm, at a distance D = 25.6mm.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/wGBAO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/wGBAO.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;They are excited with the discrete ports in the picture, which corresponds in this case to a voltage source with 150&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; of source impedance. The two voltage sources, as indicated by the ports arrows in figure, are with opposite polarities. In other words, there is a 180° phase shift.&lt;/p&gt;&#xA;&lt;p&gt;In this condition, I'm expecting that the radiation pattern of this system (for instance in terms of directivity) falls at the wavelength equal to R = 25.6mm (11.72GHz), because there will be destructive interference between the waves emitted by each antenna. And, in fact, that's what I've got by a simulation in CST MWS:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/j4jZk.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/j4jZk.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This graph represents the Directivity on Theta = 90° plane (XY plane) averaged with respect to Phi. &lt;strong&gt;There is a directivity drop at 12GHz because of destructive interference&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Nice, it's well predictable.&lt;/p&gt;&#xA;&lt;p&gt;Why have I thought it's a destructive interference? Because the single elements patterns are, at 12GHz, on XY plane (&lt;span class=&quot;math-container&quot;&gt;$\theta = 90°$&lt;/span&gt;):&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OwmKN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OwmKN.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;So, each element irradiates with peaks of 1.99dBi along y-axis. But, if we look at the radiation pattern of the total system, we have an hole along y-axis.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nzYEN.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nzYEN.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Since this happens at the frequency whose wavelength is equal to the y-axis distance between the two elements, I'd say it's caused by a field cancellation.&lt;/p&gt;&#xA;&lt;p&gt;Now let's consider a more complex case with more elements in a circular array:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/e7iu1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/e7iu1.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;In this case, the simulation has shown me that the &lt;strong&gt;destructive interference frequency is shifted from about 12GHz to 14GHz&lt;/strong&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vYSjI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vYSjI.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question:&lt;/strong&gt; Can you help me on understanding (also qualitatively) how can the presence of other elements shift this frequency (and why it has been increased)?&lt;/p&gt;&#xA;" OwnerUserId="16739" LastEditorUserId="2988" LastEditDate="2021-01-06T17:27:58.570" LastActivityDate="2021-01-06T17:36:01.343" Title="Destructive interference between two close antennas" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;phased-array&gt;" AnswerCount="2" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17811" PostTypeId="1" CreationDate="2021-01-05T14:05:55.433" Score="1" ViewCount="58" Body="&lt;p&gt;I'm very new to this radio stuff and I've come across a problem.&lt;/p&gt;&#xA;&lt;p&gt;I have two BF-888S', along with two other radios. (Binatone Terrain 750)&#xA;All of which are on the same frequency and have the same settings. The problem is that whenever I transmit with of the Baofengs, the other doesn't receive it - but the other two radios do.&#xA;If I transmit on the Binatones, the other three radios receive the signal. If I transmit on one of the Baofengs, the Binatones receive it but not the other Baofeng.&lt;/p&gt;&#xA;&lt;p&gt;Like I said, all are on the same frequency. I'm using PMR446 range, if that's relevant.&lt;/p&gt;&#xA;&lt;p&gt;Thanks in advance!&#xA;&lt;a href=&quot;https://i.stack.imgur.com/F40SU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/F40SU.png&quot; alt=&quot;Frequencies&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/maTPC.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/maTPC.png&quot; alt=&quot;Settings&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18462" LastEditorUserId="18462" LastEditDate="2021-01-05T19:28:30.300" LastActivityDate="2021-01-05T19:28:30.300" Title="Baofeng's won't talk to each other - but other radios receive the signal" Tags="&lt;baofeng&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17812" PostTypeId="2" ParentId="16116" CreationDate="2021-01-05T16:34:39.503" Score="1" Body="&lt;p&gt;FYI C4FM is not allowed below 29 Mhz. This is because it is a wide band modulation and uses more than the allowable bandwidth for HF band transmission. Straight FM is not allowed below 29 Mhz for the same reason.&lt;/p&gt;&#xA;" OwnerUserId="18465" LastActivityDate="2021-01-05T16:34:39.503" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17813" PostTypeId="2" ParentId="17811" CreationDate="2021-01-05T16:47:05.370" Score="1" Body="&lt;p&gt;Most likely you have the CTCSS or DCS settings wrong on the Baofengs.  Assuming you're trying to talk simplex and not through a repeater, turn all those settings off, and all three radios should be able to talk to each other.&lt;/p&gt;&#xA;&lt;p&gt;I suspect the real problem is unfamiliarity with the software.  I get tripped up using manufacturers' programming software.  If you're using the Baofeng software, try using &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP&lt;/a&gt; instead; it's better-written, better-documented, and easier to use.&lt;/p&gt;&#xA;&lt;p&gt;You might consider editing your question to include a screenshot of the software if you're still stuck.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-01-05T16:47:05.370" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="17814" PostTypeId="1" CreationDate="2021-01-05T18:02:20.547" Score="2" ViewCount="225" Body="&lt;p&gt;I've put up a &amp;quot;random&amp;quot; length long wire antenna for HF in my yard at about 124ish feet about 15' off the ground. I got this length from an online resource.  Here's my questions:&lt;/p&gt;&#xA;&lt;p&gt;How does the anchor loop on each of the wire affect the length?  Do I need to account for/add 6&amp;quot;ish of extra line to the measurement for each loop?&lt;/p&gt;&#xA;&lt;p&gt;Because of the size of my property, power lines and tree I chose to run the wire from one end, bend at a 90 and end at the far corner.  Basically this looks like an L or 1/2 of a square from above.  Does the bend in the line negatively affect or negate the radiation of the signal?  Would it be better to run a shorter line diagonal from point A -&amp;gt; C skipping the corner at point B?&lt;/p&gt;&#xA;" OwnerUserId="18468" LastActivityDate="2021-01-05T19:52:29.923" Title="How does end loops on a long wire antenna affect antenna length" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17815" PostTypeId="2" ParentId="17814" CreationDate="2021-01-05T19:43:51.950" Score="1" Body="&lt;p&gt;It's not clear to me from your question, so I'll mention here that best practice is to end your antenna with an insulator and attach the insulator via rope or whatever to your tree or building. And yes, the length of the antenna includes that loop of wire around the insulator.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/lNiVI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/lNiVI.png&quot; alt=&quot;antenna-insulator-rope&quot; /&gt;&lt;/a&gt;&#xA;[image credit: DX Engineering]&lt;/p&gt;&#xA;&lt;p&gt;HOWEVER, it's not unusual for a testing setup (or perhaps a lazy setup) to simply loop the antenna wire around a tree or whatever, and you should include that extra length in your calculations as well... it's part of the antenna and will develop RF current and voltages (which is why you should &lt;strong&gt;really&lt;/strong&gt; be using an insulator).&lt;/p&gt;&#xA;&lt;p&gt;If needed, you can minimize the effective added length by attaching the tip of the wire back to the body of the wire where the loop is formed.&lt;/p&gt;&#xA;&lt;p&gt;Happy building!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2021-01-05T19:43:51.950" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17816" PostTypeId="2" ParentId="17814" CreationDate="2021-01-05T19:52:29.923" Score="3" Body="&lt;p&gt;A random long wire is just that, random. While large loops at the end or bending the wire might change the resonant frequency, a random wire isn't (unless by chance) resonant anyway. So loops and bends just make a different random wire antenna which is neither better nor worse.&lt;/p&gt;&#xA;&lt;p&gt;The shape of the antenna isn't going to affect efficiency directly. Think about conservation of energy: all your transmitter's generated power is either radiated or converted to heat in some form of loss. What kinds of loss are there?&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Losses in the resistance of the soil and other things near the antenna&lt;/li&gt;&#xA;&lt;li&gt;Losses in the tuner and the feedline&lt;/li&gt;&#xA;&lt;li&gt;Losses in the antenna wire's resistance&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Of these three, the first two are by far the most significant. So worry about those things, if you're going to worry about efficiency.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-01-05T19:52:29.923" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17817" PostTypeId="2" ParentId="17810" CreationDate="2021-01-05T21:18:35.367" Score="3" Body="&lt;p&gt;There is no single &amp;quot;destructive interference frequency&amp;quot;. There is maybe a frequency where destructive interference occurs in a useful direction. &lt;a href=&quot;https://en.wikipedia.org/wiki/Hairy_ball_theorem&quot; rel=&quot;nofollow noreferrer&quot;&gt;It can be shown&lt;/a&gt; that for any array, at any frequency, for any given polarization, there exists at least one (and often more) nulls in the radiation pattern, which must occur due to destructive interference between the elements.&lt;/p&gt;&#xA;&lt;p&gt;Furthermore, directivity alone is not necessarily a figure of merit. Remember that the radiation pattern is a 3-dimensional function, and directivity is a measure of just &lt;em&gt;one point&lt;/em&gt; on that function. Some array may have at some frequency a high directivity, but the radiation pattern may look like a sea urchin. This wouldn't be of much practical use: usually we want one lobe, not 50. So if you want to understand your arrays, look at the whole pattern, not just directivity.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-01-05T21:18:35.367" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17818" PostTypeId="2" ParentId="15018" CreationDate="2021-01-06T01:21:59.943" Score="0" Body="&lt;p&gt;This is NOT 64:1 more like 144:1 and  core is wrong must be 240-43 go back to the PA3HHO, PD7MMA,  webb and read again the short an t with out smal coil wil be 10-20m only fit small coil it will be 19/20/and 40m&#xA;Pieter&lt;/p&gt;&#xA;" OwnerUserId="18471" LastActivityDate="2021-01-06T01:21:59.943" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17819" PostTypeId="2" ParentId="17804" CreationDate="2021-01-06T05:02:01.163" Score="0" Body="&lt;p&gt;After reading this question a few times, I think I have a good idea what you are asking.&lt;/p&gt;&#xA;&lt;p&gt;I am not familiar with the transmitter or receiver you mention, but you say they use AM.&lt;/p&gt;&#xA;&lt;p&gt;Using an AM transmitter, you can not easily (I mean, I guess it might be technically possible if you can vary the frequency of the carrier accurately, extremely quickly) generate FSK, and if you could switch the transmitter on and off quickly, you could generate OOK. I think PSK would not be possible, because you probably have no control of the phase of the carrier. So ... I think the transmitter would not generate the modes you are talking about. As for receiving, I think you can’t receive any of those modes (except perhaps OOK) with an AM receiver.&lt;/p&gt;&#xA;&lt;p&gt;It looks like you probably need a proper SDR, that can generate all these modes, and others. It will cost more than a simple AM transmitter/receiver, though.&lt;/p&gt;&#xA;" OwnerUserId="873" LastActivityDate="2021-01-06T05:02:01.163" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17820" PostTypeId="2" ParentId="4996" CreationDate="2021-01-06T06:16:18.327" Score="1" Body="&lt;p&gt;You will need a VOX circuit, and optionally, a VOX program. As long as the radio you are connected to is type certified, it is perfectly legal to connect it to a PC for the purposes of transmitting voice.&lt;/p&gt;&#xA;&lt;p&gt;First off, you need some aux cables, and if you PC has a combined speaker and mic jack, you need a TRRS splitter. You also may need a 3.5 mm to 2.5 mm adapter since most HTs use Kenwood-style connectors.&lt;/p&gt;&#xA;&lt;p&gt;For the VOX circuit, either get a soldering iron or a breadboard, and &lt;a href=&quot;http://www.rason.org/Projects/basicvox/basicvox.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;construct one of these&lt;/a&gt;. Your power supply needs to match the specifications (+9 to +14 VDC), and you can use a 9V battery if you don't have a power supply. You can connect your computer to the &amp;quot;MIKE INPUT&amp;quot;, and put another jack in parallel with the vox circuit to connect to your radio.&lt;/p&gt;&#xA;&lt;p&gt;In Kenwood-style connectors (which, from my research, your radio has), the radio is told to transmit when the two &amp;quot;ring&amp;quot; conductors are shorted together. This can be done through the final transistor on the right.&lt;/p&gt;&#xA;&lt;p&gt;If you have no idea how to breadboard, you can shell out and buy a &lt;a href=&quot;https://www.tigertronics.com/slusbmain.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;SignaLink&lt;/a&gt;. You plug your PC into the SignaLink via USB, and plug the radio into the audio jacks. Once you configure the SignaLink, you need to configure your PC to send your microphone audio to an output device (in this case, the SignaLink).&lt;/p&gt;&#xA;" OwnerUserId="16689" LastEditorUserId="16689" LastEditDate="2021-01-06T07:26:13.347" LastActivityDate="2021-01-06T07:26:13.347" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17821" PostTypeId="1" AcceptedAnswerId="17829" CreationDate="2021-01-06T06:40:07.007" Score="1" ViewCount="120" Body="&lt;p&gt;My understanding of a naive PSK scheme is that you have some frequency(s), f(n), at baseband, and you modulate information by shifting the phase (what &amp;quot;point in time&amp;quot;) the signal is at. Isn't the phase shift instantaneous? In this case, isn't the frequency constant? Why do PSK modes look vaguely like MFSK in a waterfall?&lt;/p&gt;&#xA;" OwnerUserId="16689" LastEditorUserId="4665" LastEditDate="2021-01-06T16:56:51.033" LastActivityDate="2021-01-07T03:12:09.973" Title="Why do PSK modes have &quot;bandwidth&quot;?" Tags="&lt;modes&gt;&lt;bandwidth&gt;&lt;theory&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17822" PostTypeId="2" ParentId="17478" CreationDate="2021-01-06T06:52:19.083" Score="1" Body="&lt;p&gt;I'm tempted to believe that using dual time slots (DCDM) mode might work with dPMR, since you are no longer bothering with TDMA. However, I couldn't find anything in my research. Try switching the AT-D878UV to use both time slots at the same time and test it with a dPMR radio on simplex. While it probably won't work, it's your best bet since DCDM does not rely on time synchronization, so it may just be a rebranded dPMR mode for simplex.&lt;/p&gt;&#xA;" OwnerUserId="16689" LastActivityDate="2021-01-06T06:52:19.083" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17824" PostTypeId="2" ParentId="16662" CreationDate="2021-01-06T10:37:14.457" Score="2" Body="&lt;p&gt;Menu option for ssb filter (38?) should be &amp;quot;off&amp;quot;, if no filter.&lt;/p&gt;&#xA;" OwnerUserId="16088" LastActivityDate="2021-01-06T10:37:14.457" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17825" PostTypeId="5" CreationDate="2021-01-06T17:30:59.093" Score="0" Body="" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-01-06T17:30:59.093" LastActivityDate="2021-01-06T17:30:59.093" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17826" PostTypeId="4" CreationDate="2021-01-06T17:30:59.093" Score="0" Body="Questions about bandwidth used by various modes, theoretical questions about bandwidth, and questions about other amateur radio aspects of bandwidth." OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-01-06T17:30:59.093" LastActivityDate="2021-01-06T17:30:59.093" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17827" PostTypeId="2" ParentId="17810" CreationDate="2021-01-06T17:36:01.343" Score="3" Body="&lt;p&gt;Look at the radiation patterns in all cases, and do that before you start plotting over frequency. What looks like &amp;quot;destructive interference&amp;quot; only happens in a certain direction, where the spacing and phasing of the elements result in a smaller far field strength. This is just a hole in the radiation pattern - the power is going somewhere else. As the frequency changes, the blob that is your radiation pattern will change shape.&lt;/p&gt;&#xA;&lt;p&gt;The graphs of Directivity @ Theta-90 (phi=?) are a very narrow view of the antenna's behaviour and hard to interpret alone.&lt;/p&gt;&#xA;&lt;p&gt;Since you're plotting directivity, the power &lt;em&gt;must&lt;/em&gt; have gone &lt;em&gt;somewhere&lt;/em&gt; on the sphere (losses and mismatch are ignored). The average directivity of an antenna is always 1.0, the antenna will be doing something to concentrate it in certain directions and not others.&lt;/p&gt;&#xA;&lt;p&gt;Here are a few 3D pattern animations I found on the web:  from OpenEMS:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/oHepf.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oHepf.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;br /&gt;&#xA;and from &lt;a href=&quot;https://www.jemengineering.com/antenna-testing-services/&quot; rel=&quot;nofollow noreferrer&quot;&gt;JEM engineering&lt;/a&gt; (just rotating, not changing frequency):&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/LhQKa.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LhQKa.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;So I'd suggest starting with some 3D patterns, see if they make any sense at all, and if they almost do what you want, then only start making cuts through the pattern, and/or plotting the gain at some point over frequency.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2021-01-06T17:36:01.343" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17828" PostTypeId="2" ParentId="17821" CreationDate="2021-01-06T18:21:48.857" Score="1" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Isn't the phase shift instantaneous?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Ideally yes, in practice it is not.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;In this case, isn't the frequency constant?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;No, phase and frequency are related.  A shift in phase is equivalent to a shift in frequency.  People found that looking for a phase shift instead of a frequency shift can take less RF bandwidth for the same data throughput.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Why do PSK modes look vaguely like MFSK in a waterfall?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Because, in a manner of speaking, PSK is a lot like MFSK.  Nyquist-Shannon says that data transmission takes bandwidth.  There is a minimum bandwidth required for any data to move at a given rate.  The more noise on the data path the greater the bandwidth is needed to overcome this.  Because noise is, roughly speaking, correlated to the bandwidth of the channel it helps to minimize the bandwidth to minimize noise.&lt;/p&gt;&#xA;&lt;p&gt;With a noiseless wire that has no resistance or capacitance the bandwidth needed for infinite data throughput is zero.  Since we don't live in an ideal world data takes bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;I don't know if I'm helping here since my vocabulary may have some nuanced differences to yours.  Looking up the theory on Shannon and Nyquist bandwidth will help.  As will the relationships between phase, frequency, and amplitude.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2021-01-06T18:21:48.857" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="17829" PostTypeId="2" ParentId="17821" CreationDate="2021-01-06T19:05:48.333" Score="6" Body="&lt;p&gt;Binary PSK with instantaneous phase shifts would be equivalent to multiplying a sine wave (the carrier) with a square wave with values at 1 or -1.&lt;/p&gt;&#xA;&lt;p&gt;When two signals are multiplied, this forms a &lt;a href=&quot;https://en.wikipedia.org/wiki/Frequency_mixer&quot; rel=&quot;noreferrer&quot;&gt;frequency mixer&lt;/a&gt;. A mixer with inputs at frequencies &lt;span class=&quot;math-container&quot;&gt;$f_1$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$f_2$&lt;/span&gt; creates outputs at &lt;span class=&quot;math-container&quot;&gt;$f_1 + f_2$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$|f_1 - f_2|$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;A sine wave is just one frequency, let's call that &lt;span class=&quot;math-container&quot;&gt;$f_c$&lt;/span&gt; for the carrier frequency. And the square wave will be at the symbol rate, which for PSK31 is 31.25 symbols per second. &lt;a href=&quot;https://en.wikipedia.org/wiki/Square_wave#Fourier_analysis&quot; rel=&quot;noreferrer&quot;&gt;A square wave is a series of odd harmonics&lt;/a&gt;. More specifically, a square wave at frequency &lt;span class=&quot;math-container&quot;&gt;$f$&lt;/span&gt; is equivalent to the infinite sum:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \sin(2\pi f) + {1\over 3} \sin(3\pi f) +{1 \over 5} \sin(5\pi f) + \dots$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This means a square wave at 31.25 Hz has frequency components at:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;31.25 Hz&lt;/li&gt;&#xA;&lt;li&gt;93.75 Hz (31.25 * 3)&lt;/li&gt;&#xA;&lt;li&gt;156.25 Hz (31.25 * 5)&lt;/li&gt;&#xA;&lt;li&gt;187.5 Hz (31.25 * 7)&lt;/li&gt;&#xA;&lt;li&gt;...&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;So say you're transmitting PSK at 14.075 MHz at a symbol rate of 31.25 per second. This means you'll be emitting power on frequencies:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$14.075\:\mathrm{MHz} \pm 31.25\:\mathrm{Hz} $&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$14.075\:\mathrm{MHz} \pm 93.75\:\mathrm{Hz} $&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$14.075\:\mathrm{MHz} \pm 156.25\:\mathrm{Hz} $&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$14.075\:\mathrm{MHz} \pm 187.5\:\mathrm{Hz} $&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$\dots$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;As you can see, the bandwidth extends out to infinity. The power diminishes as you get away from the carrier frequency, but not very rapidly, and it never reaches zero. If you're transmitting with 1 kW then you'll be spewing significant harmonics over the entire band, and even outside it.&lt;/p&gt;&#xA;&lt;p&gt;Consequently, except for very low power, cheap radios you might find in part 15 devices, the phase shifts are not instantaneous but gradual. For example PSK31 uses a cosine envelope, meaning in the case of alternating between phases it multiplies the carrier not by a square wave, but rather by a cosine. Since a cosine consists of just one frequency component, this generates not an infinite series of frequency components in the output of the mixer, but just two: the carrier frequency, plus and minus 31.25 Hz.&lt;/p&gt;&#xA;&lt;p&gt;Things get a little worse when the phase isn't strictly alternating between states, because the first derivative of phase is discontinuous. This does generate an infinite series of harmonics (I have a graph in &lt;a href=&quot;https://ham.stackexchange.com/a/7744/218&quot;&gt;another answer&lt;/a&gt;) but one which decreases much more rapidly than the square wave case before. It should be noted the technical design of PSK31 isn't especially good, and professionally design PSK implementations often use a &lt;a href=&quot;https://en.wikipedia.org/wiki/Root-raised-cosine_filter&quot; rel=&quot;noreferrer&quot;&gt;root-raised cosine pulse shaping filter&lt;/a&gt; which is better in this regard.&lt;/p&gt;&#xA;&lt;p&gt;In general, the only thing which occupies just one frequency is a sinusoid with no start and no end which isn't modulated at all. Changing the amplitude or phase &lt;em&gt;in any way&lt;/em&gt; will cause the signal to occupy more bandwidth. It's rather easy to demonstrate why this must be true intuitively: were it possible to transmit information with just one frequency, signals could be crammed infinitely close together, so an infinite number of users could be crammed in a finite amount of bandwidth. There'd be no need to license or sell spectrum because there'd always be room to add more users. Also, we could fit infinite information bandwidth in any slice of spectrum, so we wouldn't need more bandwidth signals for higher data rates.&lt;/p&gt;&#xA;&lt;p&gt;The more gradually amplitude or phase change, the less bandwidth will be occupied. Ideally the derivative of amplitude and phase are continuous functions, as well as the second, third, and so on derivatives. A &lt;a href=&quot;https://en.wikipedia.org/wiki/Gaussian_function&quot; rel=&quot;noreferrer&quot;&gt;gaussian function&lt;/a&gt; higher-order derivatives are all continuous, which is why you see gaussian functions come up in modulations like &lt;a href=&quot;https://en.wikipedia.org/wiki/Minimum-shift_keying#Gaussian_minimum-shift_keying&quot; rel=&quot;noreferrer&quot;&gt;GMSK&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-01-06T19:05:48.333" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17830" PostTypeId="2" ParentId="10129" CreationDate="2021-01-06T20:57:45.343" Score="2" Body="&lt;p&gt;For me I didn't have my radio cable fully pushed into my radio. It took some extra pressure and then it snapped in place.&lt;/p&gt;&#xA;" OwnerUserId="18481" LastEditorUserId="18481" LastEditDate="2021-01-06T23:40:32.017" LastActivityDate="2021-01-06T23:40:32.017" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17831" PostTypeId="2" ParentId="17821" CreationDate="2021-01-07T02:59:59.117" Score="1" Body="&lt;p&gt;For a mathematical sinusoid, instantaneous frequency is the first derivative of the phase of that sinusoid with respect to time.  So if the phase isn't changing at a constant rate with respect to time, the first derivative will change, and thus so will the instantaneous frequency.&lt;/p&gt;&#xA;&lt;p&gt;Also, in the real world, there can be no instantaneous discontinuous phase changes, as all capacitors (including all the parasitic ones and in the wires) require finite time to charge up or down in order to change signal levels.  Any band-limiting filters reduce the rate of change even further.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-01-07T03:12:09.973" LastActivityDate="2021-01-07T03:12:09.973" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17832" PostTypeId="1" CreationDate="2021-01-07T05:52:01.957" Score="2" ViewCount="142" Body="&lt;p&gt;I know that 144-148 and 156-157 mhz ranges are in use, and various fire/ems/police, but outside of that, I see a lot of earth-to-space, weather stuff and space research allotments (talking about Canada here).  Outside of using a scanner, is there any way to know if the metrology / space / satellite allotments are in actual use in a particular area?&lt;/p&gt;&#xA;" OwnerUserId="18486" LastEditorUserId="8717" LastEditDate="2021-01-08T03:35:40.523" LastActivityDate="2021-01-08T03:35:40.523" Title="How much of the 136 - 174 mhz spectrum is actually in use?" Tags="&lt;satellites&gt;&lt;2m-band&gt;&lt;canada&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17833" PostTypeId="2" ParentId="17057" CreationDate="2021-01-07T06:55:42.260" Score="1" Body="&lt;p&gt;In South Korea, CW must take the CW test in order to qualify for a possible grade (the practice has been abolished and only the written test is required).&lt;/p&gt;&#xA;" OwnerUserId="18487" LastActivityDate="2021-01-07T06:55:42.260" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17834" PostTypeId="2" ParentId="17723" CreationDate="2021-01-07T11:03:41.273" Score="2" Body="&lt;p&gt;Parallel LEDs across the power source will only indicate the presence of voltage and its polarity.&lt;/p&gt;&#xA;&lt;p&gt;Parallel LEDs in the line can indicate current flow and its direction. However, the LEDs cannot carry the motor current.&lt;/p&gt;&#xA;&lt;p&gt;The LED in the following circuit will be lit as long as the motor is running in either direction.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/19AlH.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/19AlH.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="1569" LastEditorUserId="1569" LastEditDate="2021-01-07T18:25:55.413" LastActivityDate="2021-01-07T18:25:55.413" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17835" PostTypeId="2" ParentId="17832" CreationDate="2021-01-07T16:39:58.363" Score="2" Body="&lt;p&gt;In my experience the parts allocated to PMR are extremely busy, it's the most popular band for walkie talkies and car radios, best compromise between antenna length (60 MHz is quite bulky) and path loss + diffraction (450 MHz is not as nice).&lt;/p&gt;&#xA;&lt;p&gt;But busy doesn't mean 0.5 &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Erlang_(unit)&quot; rel=&quot;nofollow noreferrer&quot;&gt;Erlang&lt;/a&gt;, because analog FM and Push To Talk are so inefficient.&lt;/p&gt;&#xA;&lt;p&gt;Without actually analysing the traffic yourself, you could:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;look for research papers that do just that, in a similar city&lt;/li&gt;&#xA;&lt;li&gt;try to find the allocations from the spectrum management authority. If they're not already public information, It's possible you could retrieve the entire list of allocations, perhaps anonymised, with an FOIA request or similar.&#xA;Bear in mind that allocated will just mean someone is paying for their spectrum license, not necessarily using it.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2021-01-07T16:39:58.363" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17836" PostTypeId="1" AcceptedAnswerId="17837" CreationDate="2021-01-07T17:12:36.013" Score="1" ViewCount="154" Body="&lt;p&gt;The Kenwood TS-570S comes with a warning against using the internal antenna tuner for antennas with SWR &amp;gt; 3, even though it may tune (e.g. at SWR 3.5 or 4).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/YIxhw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YIxhw.png&quot; alt=&quot;warning&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It says the transceiver or antenna may be damaged. What specific damage might occur, and under what circumstances?&lt;/p&gt;&#xA;&lt;p&gt;Second, if the radio can handle an SWR of up to 3 without a tuner (what I've heard), what's the point of having an internal tuner if it shouldn't be used with SWR &amp;gt; 3?&lt;/p&gt;&#xA;&lt;p&gt;I am using 50 ft of RG-8X coax to feed an &lt;a href=&quot;https://myantennas.com/wp/product/efhw-8010-2k/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EFHW-1080-2k antenna&lt;/a&gt;. This antenna typically doesn't require a tuner, but the higher SWR is due to a horizontally bent configuration conforming to the limits of my outdoor space.&lt;/p&gt;&#xA;" OwnerUserId="17488" LastActivityDate="2021-01-07T17:43:37.910" Title="What may be damaged when using an internal antenna tuner on SWR above 3?" Tags="&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17837" PostTypeId="2" ParentId="17836" CreationDate="2021-01-07T17:29:51.507" Score="3" Body="&lt;p&gt;First, even if the radio won't be damaged by 3:1 SWR, it will certainly have to cut back the output power, perhaps to 1/10 of full power. So the tuner will be what allows it to function correctly even with a modest SWR antenna.&lt;/p&gt;&#xA;&lt;p&gt;The problem with operating a tuner with high SWR is that for some antenna impedances, typically the Low R High C of a short whip, it will generate very high Q solutions that result in very high circulating currents. These can overheat the inductors. Even if the tuner is not intended to tune a short whip, and won't have enough series inductance to do it at low frequencies like 3.5 MHz, at a higher frequency like 14 MHz there might be accidental tuning solutions that do seem to work and provide a good match.&lt;/p&gt;&#xA;&lt;p&gt;For example (without pulling out my calculator) - if the antenna is 3:1, being about 20-j100 Ohms,  this can be tuned to resonance by an inductor of about 1+j100 Ohms, and the inductor loss will be a small fraction of the total power.&lt;/p&gt;&#xA;&lt;p&gt;But if the antenna is 1-j200 Ohms, the tuner might manage to match this using all its inductors, say 3+j300 Ohms, and then some parallel capacitance to bring it back near to 50 Ohms. In this case you can see the tuner will absorb 75% of the transmitter power, which is not ok.&lt;/p&gt;&#xA;&lt;p&gt;And the examples above could happen to the same tuner, at different frequencies, depending on the antenna. The tuner doesn't measure the antenna impedance, it just searches for low SWR.&lt;/p&gt;&#xA;&lt;p&gt;A clue that the tuner is overloaded is that the SWR will climb up while you are transmitting, as the inductor heats up and changes shape.&lt;/p&gt;&#xA;&lt;p&gt;Finally - the antenna you link to (seems too good to be true, for a simple wire antenna) says it shouldn't require a tuner, but the SWR might go up to 2:1 in places. This are exactly what the rig's built-in tuner is designed for.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-01-07T17:43:37.910" LastActivityDate="2021-01-07T17:43:37.910" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17838" PostTypeId="1" CreationDate="2021-01-07T23:05:59.253" Score="1" ViewCount="93" Body="&lt;p&gt;I have an old &amp;quot;Walkera-RC 2.4ghz Radio Transmitter WK-2401&amp;quot; radio transmitter from an RC Helicopter. I want to use this transmitter with a receiver in order to transmit some sort of data about throttle position to an Arduino.&lt;/p&gt;&#xA;&lt;p&gt;Can this be done? I have no idea how to figure out what protocol the transmitter uses and how to bind it to a new receiver. Any help would be appreciated!&lt;/p&gt;&#xA;" OwnerUserId="18496" LastEditorUserId="8717" LastEditDate="2021-01-08T22:07:50.537" LastActivityDate="2021-01-10T05:24:33.037" Title="Help getting use out of an old RC radio transmitter" Tags="&lt;transmitter&gt;&lt;remote-control&gt;&lt;radio-control&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17839" PostTypeId="1" CreationDate="2021-01-08T01:42:35.580" Score="4" ViewCount="83" Body="&lt;p&gt;Not necessarily an amateur radio question (but perhaps a licensed amateur should know the answer?) - I note that the specifications for marine VHF radio operating in the 156-157 mhz band call for both (or allow both - or either?) frequency-modulation and phase modulation.  So my question is - can typical civilian equipment (ie scanners, ham radio tranceivers, etc) discriminate or decode phase-modulated signals from marine VHF radios?  Or are those transmissions only receivable by other marine radios?&lt;/p&gt;&#xA;&lt;p&gt;(I note that &amp;quot;modulation&amp;quot; does not appear to be a valid or available tag, which is surprising given the forum)&lt;/p&gt;&#xA;" OwnerUserId="18486" LastEditorUserId="4665" LastEditDate="2021-01-08T02:20:46.780" LastActivityDate="2021-01-08T18:42:58.953" Title="Can a phase-modulated voice radio transmission be received and heard properly by an &quot;FM&quot; radio?" Tags="&lt;modes&gt;&lt;fm&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17840" PostTypeId="2" ParentId="17832" CreationDate="2021-01-08T02:51:12.847" Score="1" Body="&lt;p&gt;Canadian frequency spectrum allocations can be found here: &lt;a href=&quot;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf10759.html#t2&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf10759.html#t2&lt;/a&gt;&#xA;Hope this helps.&lt;/p&gt;&#xA;" OwnerUserId="15289" LastActivityDate="2021-01-08T02:51:12.847" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17841" PostTypeId="1" AcceptedAnswerId="17843" CreationDate="2021-01-08T06:58:30.983" Score="2" ViewCount="56" Body="&lt;p&gt;let's consider a simple linear uniform spaced array:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/YyjLM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YyjLM.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;We know that, from elementary array theory, the total pattern (for instance in terms of E-field) may be evaluated, in case no phase shift is applied to the excitations, as:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{total} = \vec{E}_{single\,element} \cdot \sum_{n=1}^{M} e^{j\cdot (n-1)\cdot k \cdot d \cdot (\theta)}$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;where the last term is the array factor. &lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{single\,element}$&lt;/span&gt; is the single element pattern when it's isolated in free space.&lt;/p&gt;&#xA;&lt;p&gt;Obviously it is an approximation, since in real life all the array elements won't have the same radiation pattern, because of their different position inside the array and mutual coupling effects. For instance, an element which is at the edge of the array will have around himm less elements than one at the centre, and so will interact with less elements. To take into accounts this effects, I'll call single elements pattern not simply as a unique quantity &lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{single\,element}$&lt;/span&gt;, but as:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{n}$&lt;/span&gt;, with n = 1,2,3,...,M&lt;/p&gt;&#xA;&lt;p&gt;If I simulate an antenna array with a simulator, I've the possibility to see both the total pattern &lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{total}$&lt;/span&gt; and all the single elements patterns &lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{n}$&lt;/span&gt; &lt;strong&gt;evaluated inside the array&lt;/strong&gt;. Now, if I want to check my simulation of the overall array from single patterns &lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{n}$&lt;/span&gt;, should I use:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;This:&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{total} = \sum_{n=1}^{M}\vec{E}_{n}\cdot e^{j\cdot (n-1)\cdot k \cdot d \cdot (\theta)}$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;OR&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;This:&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{total} = \sum_{n=1}^{M}\vec{E}_{n}$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;My attempts&lt;/strong&gt;: in my attemps, it seems that &lt;strong&gt;2)&lt;/strong&gt; is true. But I'm asking this question because I'm not sure of I from a theory point of view, and because if it's wrong, I have probably done a mistake in my code for evaluating the total field.&lt;/p&gt;&#xA;" OwnerUserId="16739" LastEditorUserId="16739" LastEditDate="2021-01-08T07:12:40.460" LastActivityDate="2021-01-08T14:15:20.473" Title="Total radiation pattern in antenna arrays" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;radiation-pattern&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17842" PostTypeId="2" ParentId="135" CreationDate="2021-01-08T07:00:40.870" Score="1" Body="&lt;p&gt;I'd like to add two more reasons people still use Morse code that haven't been mentioned much: DXing and contesting on HF.&lt;/p&gt;&#xA;&lt;p&gt;When people earn their licenses and HF privileges, the next challenge, besides learning about antennas and how to operate the radio and such, is figuring out what to &lt;em&gt;do&lt;/em&gt; on the air.  Ragchewing is a natural way to start of course, but soon many people start keeping track of states, provinces, and entities (countries) in the log, and then find themselves actively seeking new ones.  In short, they start DXing.&lt;/p&gt;&#xA;&lt;p&gt;Many of the same people who enjoy DXing find themselves operating in contests to get some easy new states, provinces, and entities in the log, and soon find themselves enjoying contesting also.  Contesting and DXing are similar and complimentary.&lt;/p&gt;&#xA;&lt;p&gt;I doubt that many people learn Morse code just for contesting and DXing, but those who do learn the code and try using it for HF DXing and contesting quickly discover that the narrow bandwidth of the mode yields a better signal-to-noise ratio and therefore better power efficiency, i.e. more miles or kilometers per watt, than wide-band modes like SSB.  In short, Morse code is well-suited for DXing and contesting, and enhances those activities.  Many people who try Morse code contesting also discover &lt;em&gt;how much fun it can be&lt;/em&gt;.  Many contesters apparently agree with me, as shown by the fact that &lt;a href=&quot;https://ham.stackexchange.com/questions/17507/what-are-the-biggest-amateur-radio-contests-radiosport/17513#17513&quot;&gt;many of the most popular contests exclusively or partially use Morse code&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Operating efficiently in a Morse code contest is a unique cerebral challenge to copy fast code well, get the information into the computer, and quickly make an efficient reply.  It can be intimidating at first, but for those who enjoy such things, each fast and efficient contact is rewarded by a feeling of pleasure, a &amp;quot;dopamine hit&amp;quot;, that encourages the operator to keep at it.  Personally I enjoy contesting, and I can tell you that efficiently &amp;quot;running&amp;quot; a constant stream of callers answering my CQs at 25 or 30 WPM offers a thrill that I haven't experienced any other way.  It demands 100% of one's attention, the time flies by, and it can be tremendous fun!  (I like SSB contesting also, but because it's usually less of a challenge it doesn't seem as much fun to me.)&lt;/p&gt;&#xA;&lt;p&gt;Morse code is good for DXing and contesting, and in return DXing and contesting support Morse code and help keep it alive.  In my opinion, if Morse code were only used for ragchewing like (amateur) AM, then Morse code would be nearly dead like AM.  (To be fair, there are also other reasons why amateur AM usage has declined.)&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-01-08T07:00:40.870" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17843" PostTypeId="2" ParentId="17841" CreationDate="2021-01-08T14:15:20.473" Score="2" Body="&lt;p&gt;The first is still correct, and can be evaluated at any position.&lt;/p&gt;&#xA;&lt;p&gt;The second is true only at broadside, when &lt;span class=&quot;math-container&quot;&gt;$\theta=0$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;In your attempts, do you find that &lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{total}$&lt;/span&gt; is the same in all directions? Then you are doing something else wrong, or &lt;span class=&quot;math-container&quot;&gt;$d \ll {2\pi\over{\lambda}}$&lt;/span&gt;&lt;br /&gt;&#xA;Or are you accidentally including the &lt;span class=&quot;math-container&quot;&gt;$e^{-j{Phase}}$&lt;/span&gt; in the individual element pattern? If you are simulating the elements one by one, with the others' excitation at &lt;span class=&quot;math-container&quot;&gt;$0 V$&lt;/span&gt; then of course they already include the whole array term. Perhaps start by considering &lt;span class=&quot;math-container&quot;&gt;$\vec{E}_{n} = 1$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;As a hint for getting clean array patterns without mutual coupling: use very short dipoles as elements, instead of resonant dipoles. The radiated power scales down but you can just normalise this, but they don't interact with each other very much.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2021-01-08T14:15:20.473" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17844" PostTypeId="2" ParentId="17839" CreationDate="2021-01-08T14:30:53.760" Score="2" Body="&lt;p&gt;FM and PM are almost identical; the answer is yes.&lt;/p&gt;&#xA;&lt;p&gt;PM is limited in phase deviation, FM is not. The audio frequency response is different: PM received on a(n) FM receiver lacks lower audio frequencies due to the (apparent) differentiation of the frequency modulation.&lt;/p&gt;&#xA;&lt;p&gt;In a formula: FM audio equals the actual deviation of the frequency; PM audio equals the actual deviation of the phase. Relation: Phase(PM) = d/dt{Phase(FM)}.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-01-08T14:30:53.760" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17845" PostTypeId="2" ParentId="17839" CreationDate="2021-01-08T16:25:23.650" Score="4" Body="&lt;p&gt;Consider an unmodulated carrier. It has a phase that increases with time at some constant rate. The rate that phase increases is what we call the frequency.&lt;/p&gt;&#xA;&lt;p&gt;What if the frequency isn't constant, but a function of time &lt;span class=&quot;math-container&quot;&gt;$\omega(t)$&lt;/span&gt;? If the frequency goes higher, phase increases faster. A lower frequency is a slower frequency increase. The phase at any given time is the accumulated phase change since the beginning of of time. In other words, phase is the integral of the instantaneous frequency:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ y(t) = \cos\left(\int_0^t \omega(\tau) d \tau \right) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;We can extend this a bit to also allow a phase offset to be added at any time:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ y(t) = \cos\left(\theta(t) + \int_0^t \omega(\tau) d \tau \right) \tag 1 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is a general expression we can use to represent any phase or frequency modulated signal with the functions &lt;span class=&quot;math-container&quot;&gt;$\theta(t)$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\omega(t)$&lt;/span&gt; representing the phase and the angular frequency at any given time.&lt;/p&gt;&#xA;&lt;p&gt;For frequency modulation, we don't add any phase offset, but the baseband signal &lt;span class=&quot;math-container&quot;&gt;$x(t)$&lt;/span&gt; is added to the carrier frequency &lt;span class=&quot;math-container&quot;&gt;$\omega_c$&lt;/span&gt;. So:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \theta(t) = 0 \\&#xA;\omega(t) = \omega_c + x(t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Substituting these into equation 1, we get frequency modulation as:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{align}&#xA;y(t) &amp;amp;= \cos\left(0 + \int_0^t \omega_c + x(\tau) d \tau \right) \\&#xA;&amp;amp;= \cos\left(\omega_c t + \int_0^t x(\tau) d \tau \right)&#xA;\tag 2&#xA;\end{align}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;For phase modulation, the phase offset is the baseband signal, and the frequency is just the carrier frequency. So:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \theta(t) = x(t) \\&#xA;\omega(t) = \omega_c $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;So phase modulation is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{align}&#xA;y(t) &amp;amp;= \cos\left(x(t) + \int_0^t \omega_c d \tau \right) \\&#xA;&amp;amp;= \cos\left(\omega_c t + x(t) \right)&#xA;\tag 3&#xA;\end{align} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The only difference then between frequency modulation (equation 2) and phase modulation (equation 3) is that the baseband signal &lt;span class=&quot;math-container&quot;&gt;$x(t)$&lt;/span&gt; has been integrated in frequency modulation. Therefore:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;phase modulation is equivalent to frequency modulation with the baseband signal differentiated, and&lt;/li&gt;&#xA;&lt;li&gt;frequency modulation is equivalent to phase modulation with the baseband signal integrated.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Differentiation is a high-pass filter, and integration is a low-pass filter, so the two are really the same thing except for the frequency response. Especially considering radio standards already specify some kind of modification to the frequency response called &lt;a href=&quot;https://en.wikipedia.org/wiki/FM_broadcasting#Pre-emphasis_and_de-emphasis&quot; rel=&quot;nofollow noreferrer&quot;&gt;pre-emphasis&lt;/a&gt;, one can convert a phase modulation radio into frequency modulation or vice-versa just by the modification of one term in the pre-emphasis function. As such, the difference between phase and frequency modulation is just in how we model the function of the device mathematically, while the two functionally are essentially the same.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-01-08T18:42:58.953" LastActivityDate="2021-01-08T18:42:58.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17846" PostTypeId="1" CreationDate="2021-01-08T19:26:48.497" Score="1" ViewCount="92" Body="&lt;p&gt;This L network intend to transform Z1 to 50ohms. The design was made using a smith chart:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aTovn.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aTovn.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eAdje.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eAdje.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The s-parameters plotted (S11 red - S22 green) in the smith chart is done sweeping the frequency from 200MHz to 5GHz for this L network. If the reflection parameters represents the input/output impedance of the network, looking to the markers we have:&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;m1: f=900MHz, Z1=29+j22.5&lt;/strong&gt; (~ as expected)&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;m2: f=900MHz, Z2=66-j43,5&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Considering ideal components in simulation, why the marker 2 (m2) is not in 50ohms?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zWtsl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zWtsl.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="18509" LastEditorUserId="18509" LastEditDate="2021-01-14T15:59:47.270" LastActivityDate="2021-02-13T16:05:40.517" Title="Obtaining input/out impedance from S-parameters for a L network" Tags="&lt;uhf&gt;&lt;impedance&gt;&lt;impedance-matching&gt;&lt;smith-chart&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17847" PostTypeId="2" ParentId="17838" CreationDate="2021-01-08T20:25:32.543" Score="2" Body="&lt;p&gt;If you have the receiver that goes with it, perhaps you can reuse it.&lt;/p&gt;&#xA;&lt;p&gt;I am not very familiar with RC transmitters, but on a cursory search it appears 2.4 GHz transmitters don't use any standard protocol, nor could I find any datasheet for this particular unit. As such, if you don't have the receiver, you'll have to reverse-engineer the protocol.&lt;/p&gt;&#xA;&lt;p&gt;While this is technically possible, it's not easy. You'll need significant expertise in radio engineering and a lot of time. It's not something that could be covered within the scope of a single Stack Exchange answer. If you wanted to go down this route for educational or entertainment purposes, I'd suggest gaining some familiarity implementing receivers for protocols that don't require reverse engineering first. With the ubiquity of wireless electronics you probably already have at your disposal many devices that transmit some standardized, documented wireless protocol.&lt;/p&gt;&#xA;&lt;p&gt;Furthermore it's not really worth the effort. For just a few dollars you can &lt;a href=&quot;https://www.digikey.com/en/products/filter/rf-transceiver-modules-and-modems/872?s=N4IgjCBcoLQExVAYygFwE4FcCmAaEA9lANogCsIAuvgA6pQggC%2BT%2BAbIiAJYAmDMYAAwRa9SI3yoAnjWwMAhgGcULIA&quot; rel=&quot;nofollow noreferrer&quot;&gt;buy all kinds of transceivers&lt;/a&gt; which would be easy to interface with a microcontroller and which come with a datasheet so you don't need to reverse-engineer how they work. You would certainly spend more than the cost of a pair of such devices just on the equipment you'd need to reverse engineer your RC transmitter.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-01-08T20:25:32.543" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17851" PostTypeId="1" AcceptedAnswerId="17853" CreationDate="2021-01-10T20:36:27.263" Score="3" ViewCount="139" Body="&lt;p&gt;Here is a crystal filter used in uBITX transceiver:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7eiOF.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7eiOF.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I've never seen such a topology in any other transceiver and decided to invest some time in exploring it. Turned out it's quite interesting. Eight crystals for any frequency from 11 to 12 Mhz and C217-C221 = 82 pF will give you a decent SSB filter with ~200 Ohm impedance and 2000-2300 Hz bandwidth depending on crystals. You can play with given crystals and capacitance value in LTspice to make the bandwidth more or less narrow. It also works with 9 MHz crystals if you change C217-C221 to 120 pF. The impedance in this case is still ~200 Ohm, the frequency response is fine.&lt;/p&gt;&#xA;&lt;p&gt;I'm curious who invented this topology and/or in which publication it was first described and/or what software calculates filters like this one?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;UPD:&lt;/strong&gt; The documentation for uBITX &lt;a href=&quot;https://www.hfsignals.com/index.php/ubitx-v4-archived/&quot; rel=&quot;nofollow noreferrer&quot;&gt;states&lt;/a&gt;: &amp;quot;The ladder topology is now enhanced with the improvisation suggested by G3UUR. Paralleling up crystals at two ends of the regular ladder filter of Cohn topology really flattens out the response and even improves the losses.&amp;quot; However from this text it's not quite clear if Dr. Dave Gordon-Smith, G3UUR invented this particular topology or maybe he suggested some other improvements in the schematic.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2021-01-11T09:18:11.160" LastActivityDate="2021-01-11T10:19:50.827" Title="Looking for origins of a crystal filter schematic used in uBITX" Tags="&lt;diy&gt;&lt;transceiver&gt;&lt;electronics&gt;&lt;filter&gt;&lt;ubitx&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17852" PostTypeId="2" ParentId="17057" CreationDate="2021-01-10T20:44:04.743" Score="1" Body="&lt;p&gt;&lt;strong&gt;Russia&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;There are four categories of amateur radio license in Russia. The first category gives you most privileges, including the possibility to use short callsing like R1AB. The exam for this category is most difficult and includes the test on receiving CW at ~12 WPM with Russian letters (that's a few additional symbols e.g. Ш is ----). Other categories don't require the knowledge of morse code.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2021-01-10T22:04:44.203" LastActivityDate="2021-01-10T22:04:44.203" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17853" PostTypeId="2" ParentId="17851" CreationDate="2021-01-11T09:44:28.197" Score="3" Body="&lt;p&gt;After a little bit of searching I discovered that this topology is called &lt;strong&gt;QER filter&lt;/strong&gt;, where QER stands for Quasi-EquiRipple. This topology is attributed to Dr. Dave Gordon-Smith, G3UUR, who is also well-known for inventing a popular method (the G3UUR method) of measuring crystals. Apparently it was first described in The QRP Quarterly, Spring 2010 under the title &amp;quot;Further Thoughts on Crystal Ladder Filter Design&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;As a side note, it's most unfortunate that old issues of The QRP Quarterly don't seem to be available anywhere. I was hoping to read this article.&lt;/p&gt;&#xA;&lt;p&gt;Links:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://ka7exm.net/emrfd/Messages/thread_10742.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://ka7exm.net/emrfd/Messages/thread_10742.htm&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.vk2sja.org/piffle/?p=254&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.vk2sja.org/piffle/?p=254&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://www.qrpforum.de/forum/index.php?thread/10139-literatur-zu-g3uurs-qer-quarzfilter-qrp-quarterly-u-arrl-handbook/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.qrpforum.de/forum/index.php?thread/10139-literatur-zu-g3uurs-qer-quarzfilter-qrp-quarterly-u-arrl-handbook/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;The ARRL Handbook 2011, sections &amp;quot;11.6.2 Crystal Filter Design&amp;quot; and &amp;quot;11.11 Filter Projects&amp;quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2021-01-11T10:19:50.827" LastActivityDate="2021-01-11T10:19:50.827" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17854" PostTypeId="2" ParentId="17846" CreationDate="2021-01-11T13:03:01.893" Score="0" Body="&lt;p&gt;.... The frequency is 900MHz, Z1=29-j23 and the network is a series L (8.4nH) and a parellel C (3pF).....&lt;/p&gt;&#xA;&lt;p&gt;That is correct; transformation is OK. The impedance is 50 Ohm real at 900 Mhz.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dzrys.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dzrys.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Picture belonging to comment. Comment doesn't allow pictures.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2021-01-11T15:58:06.603" LastActivityDate="2021-01-11T15:58:06.603" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17856" PostTypeId="1" CreationDate="2021-01-11T19:51:02.543" Score="2" ViewCount="120" Body="&lt;p&gt;Would it be possible to make an alert radio... for shortwave? Out of something like Arduino, or RPi. Sort of like the NOAA Weather Radios. I got to thinking one day. Say you wanted to send a message to a far away friend, but you don't know if he's home or not. Well, what if you could fix that, with a radio that alerts you of the incoming message, and records it as well? I don't think it's impossible, but I've already looked for help, and I've gotten nowhere, so I figured I'd come here. Thanks!&lt;/p&gt;&#xA;" OwnerUserId="18541" LastActivityDate="2021-01-13T21:06:26.077" Title="Is it at all possible to make a ham alert radio?" Tags="&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17857" PostTypeId="2" ParentId="17856" CreationDate="2021-01-11T22:16:34.520" Score="1" Body="&lt;p&gt;You might consider looking at packet radio. It allows for this kind of message passing to reach recipients similar to BBS-style messages or email. Similarly &lt;a href=&quot;https://www.winlink.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;winlink&lt;/a&gt; is worth checking out.&lt;/p&gt;&#xA;&lt;p&gt;Neither of these are exactly the point-to-point alert-style you mention above, but both are implementable on a RPi which can be scripted to have a klaxon or spinny light activate when a message comes in.&lt;/p&gt;&#xA;&lt;p&gt;Hope this is helpful!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2021-01-11T22:16:34.520" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17860" PostTypeId="2" ParentId="17856" CreationDate="2021-01-12T00:19:29.813" Score="3" Body="&lt;p&gt;I get the impression that this answer is too long for many people, so here's the abstract: I presume your goal is to make a system that will automatically record a message when someone calls a particular operator on HF SSB and the operator doesn't respond, like an answering machine.  Also the system will alert the operator to an incoming call for him or her.  Assuming you are talking about SSB, then you'd need some sort of digital message, a selective calling signal containing the call signs of the two stations, that is quickly sent before the SSB call on the same channel.  Well there is an existing protocol called Automatic Link Establishment (ALE) that was created for the US military back in the late 70s and early 80s, which is now being used in ham radio, that is used to automatically find the best band and clearest frequency for an SSB QSO.  That protocol uses a simple digital mode sent in a short burst before an SSB QSO on the same channel.  You could study how ALE works, and possibly find an open-source ALE program and use its code as a starting point, and do some reverse engineering, to create a digital mode and the software to do what you want.&lt;/p&gt;&#xA;&lt;p&gt;You didn't think this would be easy, did you?&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;You didn't say what mode you had in mind, but I'll presume that you meant SSB.  If you're content with a text-based message, then there is a digital message mode already in widespread use with servers to store and forward messages: &lt;a href=&quot;https://www.winlink.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Winlink&lt;/a&gt;.  You did mention short wave, which I'll interpret as 160m – 10m.  By the way, I do have an HT that does have a feature that lights an LED when someone calls using a particular CTCSS tone or CDCSS (Continuous Digital-Coded Squelch System) code, IIRC.  I think the intent was to let you know someone had called on the calling frequency if you had walked away from the radio temporarily.  But that feature works using FM, which allows the subtones in the audio that CTCSS and CDCSS require.  SSB doesn't allow such subtones.&lt;/p&gt;&#xA;&lt;p&gt;To let a radio know that a call is coming for a particular operator, I would think that some sort of digital transmission containing the &amp;quot;to&amp;quot; and &amp;quot;from&amp;quot; call signs would be required.  For SSB, I would think that this would take the form of a digital burst before the traditional analog hail.  In order to stop the recording, presumably some sort of digital notification of the end of the transmission would also be required.&lt;/p&gt;&#xA;&lt;p&gt;There is a similar protocol already in use: &lt;a href=&quot;https://en.wikipedia.org/wiki/Automatic_link_establishment&quot; rel=&quot;nofollow noreferrer&quot;&gt;Automatic Link Establishment (ALE)&lt;/a&gt;.  ALE was created for the US military to allow operators who are unfamiliar with the vagaries of the ionosphere to make SSB contact over HF.  The initiating operator gives the ALE controller (a computer, possibly built into the radio) the ALE address of the station to be called.  The controller sends a short digital message, a selective calling signal, over many channels on many bands, using a digital 8ary Frequency Shift Keying or 8FSK modulation that uses eight orthogonal tones between 750 and 2500 Hz.  The receiving operator's ALE controller listens for calls on the same channels.  When the receiving controller picks up a call for it, it sends a message back to the originating station and together the two controllers select the clearest channel on the best band, and then the operators are alerted to make the SSB contact.  When the contact is over, one station sends a disconnect signal, and both controllers return to scanning for incoming calls.&lt;/p&gt;&#xA;&lt;p&gt;By the way, ALE is used in ham radio, but there are disadvantages.  As I understand (and I haven't used ALE), in the US, because signals to establish an ALE contact are sent on many channels without direct guidance from an operator, the full ALE protocol suite is only allowed in the narrow sub-bands for automatically controlled data stations.  (&lt;a href=&quot;http://hflink.com/alehamradiousa/&quot; rel=&quot;nofollow noreferrer&quot;&gt;This page&lt;/a&gt; seems to disagree; it says the selective calling features can be used on any SSB frequency.  I'm not so sure that allowing a computer to send a digital transmission on any channel that seems to be idle for a few milliseconds is a good idea.)  The radio must be able to automatically change frequency and band quickly, so the antennas must have low SWR on all the frequencies used for ALE, or the radio must have a fast automatic antenna tuner.&lt;/p&gt;&#xA;&lt;p&gt;Anyway, the ALE 8FSK digital mode is intended to encode the call sign of the sending and receiving stations and be transmitted quickly immediately before and after an SSB contact.  This sounds very much like what you're asking for, so perhaps you could have a look at ALE  and develop a new similar protocol that does what you want.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-01-13T21:06:26.077" LastActivityDate="2021-01-13T21:06:26.077" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17861" PostTypeId="1" CreationDate="2021-01-12T01:16:06.680" Score="0" ViewCount="66" Body="&lt;p&gt;I am a beginner with not much experience in HF. My shack consists of a Xiegu G90 connected with 20ft of RG-8x to an MFJ 1982 end fed half wave antenna. There is a small coil of coax next to the matching transformer box. The radiating element is suspended in an inverted V configuration with the midpoint around 30ft above the ground. The unun is connected to the eave of my house around 9 feet in the air. There is also a 10ft counterpoise connected to the matching unit. My problem is that I am only hearing the very strongest signals on some HF bands, On the other bands, I am hearing nothing at all! I know that the manual says to leave the matching unit near the ground, but performance is maybe even worse when I do that. The SWR on all the bands it covers is very good, never exceeding 2:1. I was wondering if someone could possibly shed some light on my predicament. Thank you all in advance,&#xA;Levi, WH6GBR&lt;/p&gt;&#xA;" OwnerUserId="18547" LastActivityDate="2021-01-12T02:15:12.380" Title="Troubleshooting the MFJ 1982 EFHW" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;wire-antenna&gt;&lt;end-fed-antenna&gt;&lt;efhw&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17862" PostTypeId="2" ParentId="17861" CreationDate="2021-01-12T02:08:10.160" Score="1" Body="&lt;p&gt;First, what bands are you listening to?  You should hear activity on roughly 20m – 40m during the day (and 15m sometimes), and 40m – 160m at night.  This is close to the bottom of the sunspot cycle, so signals are often fairly weak, but there should be a few loud stations on 20m and 40m.&lt;/p&gt;&#xA;&lt;p&gt;Your antenna would do better to be higher, but it's high enough for starters.&lt;/p&gt;&#xA;&lt;p&gt;Your biggest problem is most likely that it's end-fed, and that it has such a tiny counterpoise.  Marketing claims aside, end-fed antennas are finicky and difficult to feed efficiently.  Also a transmitter trying to transmit into a high-impedance load needs an efficient RF ground to &amp;quot;push against&amp;quot;, and your counterpoise, a single wire a fraction of a wavelength long, doesn't offer much of an RF ground.  Your coax to the feedline would radiate if you transmitted, and you would probably have RF in the shack, which causes all sorts of weird problems with other electronics nearby.  Poor transmit antennas almost always make poor receive antennas (there are exceptions), because if power doesn't get out efficiently then it doesn't get in efficiently either.&lt;/p&gt;&#xA;&lt;p&gt;If you can, try putting up a dipole antenna, or a variation of a dipole antenna that's fed in or near the middle, with a good balun.  Raising the coax to the center of the antenna might be tricky, and you might need an antenna tuner to get a good SWR, and you might not have very many bands; but you'll be amazed how much better it works than your EFHW, and you won't need a counterpoise for it.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-01-12T02:15:12.380" LastActivityDate="2021-01-12T02:15:12.380" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17863" PostTypeId="1" CreationDate="2021-01-12T07:13:39.133" Score="1" ViewCount="38" Body="&lt;p&gt;CQ CQ CQ de BH4FHO.&lt;/p&gt;&#xA;&lt;p&gt;I have been fixing some radios recently - buying used radios for cheap, fix them up and modify them to transmit in ham bands. When testing them out, I am using my Baofeng DM-1801 HT (with OpenGD77 firmware) as a test target - tune the Baofeng to the same test channel as the DUT radio, and try to call each other.&lt;/p&gt;&#xA;&lt;p&gt;However, whenever I press the PTT button on either radio, there is is a chance for some very loud acoustic feedback hitting my head with a screech. How to avoid that?&lt;/p&gt;&#xA;" OwnerUserId="18548" LastActivityDate="2021-01-12T15:15:57.827" Title="How to avoid acoustic feedback while fixing radios?" Tags="&lt;repair&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17864" PostTypeId="2" ParentId="17863" CreationDate="2021-01-12T15:15:57.827" Score="5" Body="&lt;p&gt;You could use a headset or earphones with the receiving radio, so the received audio goes straight into your ears instead of to the microphone of the transmitting radio.  Or you could use an assistant to take one radio to another room for your communications tests.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-01-12T15:15:57.827" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17865" PostTypeId="2" ParentId="7847" CreationDate="2021-01-12T16:16:31.787" Score="-4" Body="&lt;p&gt;It's a Bodge job.&#xA;People are always seeking to improve on 'standard' designs but in reality, virtually all the possible workable designs already exist.  I see absolutely no merit to this 'design'.&lt;/p&gt;&#xA;" OwnerUserId="18552" LastActivityDate="2021-01-12T16:16:31.787" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17867" PostTypeId="1" AcceptedAnswerId="17868" CreationDate="2021-01-12T18:42:59.513" Score="0" ViewCount="76" Body="&lt;p&gt;I have a basic question about sweep times and number of points.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;My frequency span of interest is: &lt;span class=&quot;math-container&quot;&gt;$f_{span} = 30\ \rm MHz$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;My resolution bandwidth is: &lt;span class=&quot;math-container&quot;&gt;$RBW = 10\ \rm kHz$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;The minimum number of points is: &lt;span class=&quot;math-container&quot;&gt;$n = 2\frac{f_{span}}{RBW} =  6000\ \rm points$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;My minimum dwell time per point is: &lt;span class=&quot;math-container&quot;&gt;$T_s = 15\ \rm msec$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;My scan time for this measurement would be:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$t_1 = n T_s = 6000 \cdot 15\ \rm msec = 90\ \rm sec$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;If I exceed the number of points in the required span by 2, can I decrease my required dwell time by 2?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$t_2 = 90\ \rm sec = 12,000 \cdot 7.5\ \rm msec$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;&lt;p&gt;Can these 2 measurements on a Spectrum Analyzer be considered &amp;quot;equivalent&amp;quot;?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;What are the trade offs?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;To give some background, I am using a software tool that fixes the number of points in a span to default value.&lt;/p&gt;&#xA;&lt;p&gt;Since I cannot set number of points to exactly what is required, I would like to set the sweep times to the smallest allowed time. Is my reasoning correct?&lt;/p&gt;&#xA;" OwnerUserId="18554" LastActivityDate="2021-01-12T22:41:51.023" Title="Sweep times for Spectrum Analyzer" Tags="&lt;measurement&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17868" PostTypeId="2" ParentId="17867" CreationDate="2021-01-12T22:41:51.023" Score="1" Body="&lt;p&gt;Old skool basics:&lt;/p&gt;&#xA;&lt;p&gt;RBW sets detector time: 3 periods; there is a relation with the accuracy (exponential settling). RBW of 10 kHz requires about 300 uS for measurement time of level.&lt;/p&gt;&#xA;&lt;p&gt;RBW sets als maximum frequency step size: half the RBW, otherwise you miss power in-between points. For 10 kHz RBW the maximum step is 5 kHz.&lt;/p&gt;&#xA;&lt;p&gt;Number of steps for 30 MHz span is consequently N = 2 * span / RBW = 6000 points.&lt;/p&gt;&#xA;&lt;p&gt;Settling of PLL is in a good design, and depending on the required frequency accuracy 30 to 40 periods of the reference frequency. For step of 5 kHz the reference frequency must be (still old skool!) maximum 5 kHz and frequency settling requires at least 30 periods or 6 mS.&lt;/p&gt;&#xA;&lt;p&gt;Summed-up: 6000 points * (6 mS +0.3 mS) = 37.8 seconds&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;SDR type receivers with a microcomputer (sufficient calculation power) and FFT analysis can do this in a fraction of this time. Don't waste time with oldskool stuff.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-01-12T22:41:51.023" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17869" PostTypeId="2" ParentId="17800" CreationDate="2021-01-14T00:52:35.820" Score="1" Body="&lt;p&gt;Check this video of one hams quest to stop some RFI&#xA;&lt;a href=&quot;https://youtu.be/Pwbk8yP6SIk&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://youtu.be/Pwbk8yP6SIk&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18567" LastActivityDate="2021-01-14T00:52:35.820" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17870" PostTypeId="1" AcceptedAnswerId="17871" CreationDate="2021-01-14T03:51:55.680" Score="4" ViewCount="219" Body="&lt;p&gt;Newbe here,&lt;/p&gt;&#xA;&lt;p&gt;I was looking through repeaters in my area and I noticed that there were a few repeaters that shared the same call sign(even though they run on different frequencies).  Does this mean that the repeaters are connected and transmitting on one will transmit on all?&lt;/p&gt;&#xA;&lt;p&gt;For example:  &lt;a href=&quot;https://i.stack.imgur.com/Ebj2k.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Ebj2k.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Thanks&lt;/p&gt;&#xA;" OwnerUserId="18481" LastActivityDate="2021-01-15T00:24:24.430" Title="If repeaters share the same call sign are they &quot;Connected&quot;" Tags="&lt;repeater&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17871" PostTypeId="2" ParentId="17870" CreationDate="2021-01-14T13:17:36.857" Score="8" Body="&lt;p&gt;I wouldn't assume that repeaters with the same call are connected.  What the call sign denotes is that they're owned and operated by the same operator or club -- for instance, in my area, there are multiple repeaters on W4NC (Forsyth Amateur Radio Club), but calling through the one on Sauratown Mountain doesn't let you talk to someone tuned to the one on Wake Forest Baptist Hospital.  Same repeater call sign (on different frequencies; there are locations where you can reach and hear both), but not connected in any way.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastActivityDate="2021-01-14T13:17:36.857" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17872" PostTypeId="1" CreationDate="2021-01-14T16:01:38.140" Score="3" ViewCount="212" Body="&lt;p&gt;In &lt;a href=&quot;https://prism.ucalgary.ca/handle/1880/106467&quot; rel=&quot;nofollow noreferrer&quot;&gt;this thesis&lt;/a&gt; the following model for an antenna is proposed:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/646mD.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/646mD.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It is seen as a 2 port network, in which only port 1 is accessible (port 2 is an imaginary connection between the antenna and the free space). Precisely:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; is the feed line impedance.&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$jX_a$&lt;/span&gt; is the antenna reactance.&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$R_l$&lt;/span&gt; is the antenna parasitic resistance (which accounts for losses).&lt;/li&gt;&#xA;&lt;li&gt;&lt;span class=&quot;math-container&quot;&gt;$Z_{fs}$&lt;/span&gt; is the free space impedance (377 Ohm)&lt;/li&gt;&#xA;&lt;li&gt;The transformer represents what an antenna really does: it transforms the free space impedance &lt;span class=&quot;math-container&quot;&gt;$Z_{fs}$&lt;/span&gt; to a radiation resistance (which is the impedance seen at the primary of the transformer.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;This description is quite clear. But then, the author says:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Since free space represents a matched termination, there would not be any reflection occurring (&lt;span class=&quot;math-container&quot;&gt;$\Gamma_L = 0$&lt;/span&gt;).&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It does not seem too obvious for me.&lt;/p&gt;&#xA;&lt;p&gt;As seen above, an antenna may be seen as a two - port network in which port 2 is closed on 377 Ohm. I'd say that usually there exists a mismatch on port 2, and so there is reflection at port 2. This doesn't mean there will be reflection at port 1 too, it depends if the antenna is able to match those 377 Ohm to the feed line impedance.&lt;/p&gt;&#xA;&lt;p&gt;But I don't understand why there shouldn't be reflection at port 2. Maybe the author is considering a specific assumption he hasn't written, even because I've read somewhere that reflection along (not at the feeding port) some antennas exists and is a problem.&lt;/p&gt;&#xA;&lt;p&gt;For instance, an infinite biconical antenna is perfectly matched to free space because it's like an infinite transmission line&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/J1aom.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/J1aom.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;A real biconical antenna is not matched to free space because it's truncated.&lt;/p&gt;&#xA;" OwnerUserId="16739" LastActivityDate="2021-01-15T18:49:39.097" Title="Is an antenna always matched to free space impedance?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;impedance&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17873" PostTypeId="2" ParentId="17872" CreationDate="2021-01-14T17:40:07.323" Score="3" Body="&lt;p&gt;I don't think the &amp;quot;matching to free space&amp;quot; should be taken so literally. I've never seen an actual equivalent circuit in a textbook or used it to derive any property of an antenna.&lt;/p&gt;&#xA;&lt;p&gt;Sure an antenna is the &lt;em&gt;interface&lt;/em&gt; between the transmission line (which has an impedance) and free space (which also has an impedance, same units but different in nature).&lt;/p&gt;&#xA;&lt;p&gt;But the behaviour of an antenna is well described by solving the field equations near the antenna. Some antennas can be solved or approximated analytically, and then the solutions contain the permittivity and permeability of free space and the speed of light.&lt;/p&gt;&#xA;&lt;p&gt;As for solving transmission line equations - you generally work from right to left, transforming the impedance, until the input impedance is found. So in this model you'd take 377 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, then apply some transformer and some RLC network, and that would yield the input impedance of the antenna. There's no transmission line, so no need to talk about reflections, it's just impedances being transformed by circuit elements. (until you connect it to a piece of 50 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; coax, then you can calculate the reflected power etc. if that's what you need).&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-01-15T18:49:39.097" LastActivityDate="2021-01-15T18:49:39.097" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17874" PostTypeId="2" ParentId="14981" CreationDate="2021-01-14T23:29:12.780" Score="0" Body="&lt;p&gt;There is an electrical discontinuity at the center point of the dipole; where the dipole is &amp;quot;balanced&amp;quot;, and the feed coax is &amp;quot;unbalanced&amp;quot;. This discontinuity causes some disruption in the flow of energy, a reflection of some amount of it.&lt;/p&gt;&#xA;&lt;p&gt;Specifically in the center-fed resonant dipole, this engineer recommends a 1:1 voltage balun (aka transformer). It will overcome the discontinuity while also greatly reducing any &amp;quot;feedback&amp;quot; RF energy from traveling back down the coax.&lt;/p&gt;&#xA;&lt;p&gt;KK4IB&lt;/p&gt;&#xA;" OwnerUserId="18577" LastActivityDate="2021-01-14T23:29:12.780" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17875" PostTypeId="2" ParentId="17872" CreationDate="2021-01-15T00:15:22.820" Score="1" Body="&lt;p&gt;Let's assume the answer to your question is yes: an antenna can be mismatched to free space. What would that look like?&lt;/p&gt;&#xA;&lt;p&gt;Well, the feedline, let's say it's 50 ohms, is matched to the antenna's feedline port, so no reflection there. But at the mismatch to free space there'd be a mismatch, generating some reflection.&lt;/p&gt;&#xA;&lt;p&gt;Is this any different than the antenna being mismatched to the feedline? I think it's not.&lt;/p&gt;&#xA;&lt;p&gt;Consider the same thing in reverse: say you begin with an antenna that provides a good 50 ohm match to the feedline. Let's assume this antenna is matched to free space.&lt;/p&gt;&#xA;&lt;p&gt;Now, say we fill the area around the antenna in PTFE foam or some other material with a dielectric constant significantly different from air out to several wavelengths away. Do you think this antenna will still present a good 50 ohm match to the feedline?&lt;/p&gt;&#xA;&lt;p&gt;Probably not. So if one port is mismatched, then the antenna transforms that to a mismatch as seen from the other port. The mismatch isn't a property of one port or another, but rather is an error in the transformation function inside the antenna, which works in either direction.&lt;/p&gt;&#xA;&lt;p&gt;I think what the author meant to convey is you might as well just &lt;em&gt;assume&lt;/em&gt; the antenna is matched to free space, then calculate what the feedpoint impedance is. And of course that can be mismatched.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-01-15T00:23:57.717" LastActivityDate="2021-01-15T00:23:57.717" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17876" PostTypeId="2" ParentId="17872" CreationDate="2021-01-15T00:21:51.927" Score="0" Body="&lt;p&gt;Matching an antenna to free space can be read as &amp;quot;radiation efficiency&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Dipoles occur in nature; so a dipole becomes the most common element of most antennae, for that reason. A resonant dipole ... even better.&lt;/p&gt;&#xA;&lt;p&gt;And half wavelength dipoles still better, because electrically they are well behaved, ... meaning their radiation efficiency is about as good as you can get. A dose of physics [that part about a current in a wire produces a magnetic field around that wire, applies.]&lt;/p&gt;&#xA;" OwnerUserId="18578" LastActivityDate="2021-01-15T00:21:51.927" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17877" PostTypeId="2" ParentId="17870" CreationDate="2021-01-15T00:24:24.430" Score="3" Body="&lt;p&gt;Different frequencies and different locations ... many clubs operate multiple repeaters to give their members access in extended areas. They are NOT necessarily connected.&lt;/p&gt;&#xA;&lt;p&gt;MGRA (Middle GA) has several, two of them CAN be linked via EchoLink; but normally are not. The have the same club call sign.&lt;/p&gt;&#xA;" OwnerUserId="18578" LastActivityDate="2021-01-15T00:24:24.430" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17878" PostTypeId="2" ParentId="7847" CreationDate="2021-01-15T00:27:38.207" Score="0" Body="&lt;p&gt;It appears to mimic the most common configuration use today in dual-band U/V verticals. Good home brew project.&lt;/p&gt;&#xA;" OwnerUserId="18578" LastActivityDate="2021-01-15T00:27:38.207" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17879" PostTypeId="2" ParentId="13379" CreationDate="2021-01-15T00:30:58.427" Score="1" Body="&lt;p&gt;QRP simply refers to low output power. What modulation you use is up to you. Voice, CW, digital mode like JS8Call .... Using 5 Watts to contact a DX station in SSB is quite a thrill.&lt;/p&gt;&#xA;" OwnerUserId="18578" LastActivityDate="2021-01-15T00:30:58.427" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17880" PostTypeId="2" ParentId="135" CreationDate="2021-01-15T02:07:00.140" Score="0" Body="&lt;p&gt;Why use &lt;a href=&quot;https://en.wikipedia.org/wiki/Continuous_wave&quot; rel=&quot;nofollow noreferrer&quot;&gt;CW&lt;/a&gt;? Because it's fun!!! It is a secret language of sorts.&lt;/p&gt;&#xA;" OwnerUserId="18578" LastEditorUserId="366" LastEditDate="2021-01-19T18:01:39.907" LastActivityDate="2021-01-19T18:01:39.907" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17881" PostTypeId="2" ParentId="10129" CreationDate="2021-01-15T02:09:22.287" Score="0" Body="&lt;p&gt;the most common problem I have encountered with folks I've helped ... the connector is not all the way seated in the radio.&lt;/p&gt;&#xA;" OwnerUserId="18578" LastActivityDate="2021-01-15T02:09:22.287" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17883" PostTypeId="2" ParentId="16093" CreationDate="2021-01-15T04:45:42.790" Score="-1" Body="&lt;p&gt;Here is the adapter you will need:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B01FVAW57Y&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.amazon.com/Movo-TCB1-Microphone-Smartphone-Headphone/dp/B01FVAW57Y&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18580" LastActivityDate="2021-01-15T04:45:42.790" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17884" PostTypeId="1" CreationDate="2021-01-17T15:37:17.053" Score="1" ViewCount="44" Body="&lt;p&gt;it's well known that in a linear and equispaced antenna array, the array factor is equal to:&lt;a href=&quot;https://i.stack.imgur.com/4os9T.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4os9T.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cJVfr.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cJVfr.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The array is then called uniform if &lt;span class=&quot;math-container&quot;&gt;$|I_n| = I$&lt;/span&gt; is the same for all elements. The phase terms &lt;span class=&quot;math-container&quot;&gt;$\angle I_n$&lt;/span&gt; is chosen to decide the peak direction of the beam.&lt;/p&gt;&#xA;&lt;p&gt;My question is: which current is &lt;span class=&quot;math-container&quot;&gt;$I_n$&lt;/span&gt;? I'm supposing that each cell is connected to a (physical or equivalent) current source. So, is &lt;span class=&quot;math-container&quot;&gt;$I_n$&lt;/span&gt; the incident current  (let's call it &lt;span class=&quot;math-container&quot;&gt;$a$&lt;/span&gt;) on the elements ports or the sum of incident and reflected current (&lt;span class=&quot;math-container&quot;&gt;$a-b$&lt;/span&gt;, where &lt;span class=&quot;math-container&quot;&gt;$b$&lt;/span&gt; is the reflected current)?&lt;/p&gt;&#xA;" OwnerUserId="16739" LastActivityDate="2021-01-20T01:27:25.270" Title="Excitation coefficient of a linear phased array" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;feed-line&gt;&lt;phased-array&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17885" PostTypeId="1" CreationDate="2021-01-17T18:01:18.790" Score="3" ViewCount="75" Body="&lt;p&gt;What is the signal processing model of a simple regenerative or super-regenerative receiver?&lt;/p&gt;&#xA;&lt;p&gt;Is it just a linear 2-pole IIR filter with gain?  How does a single regen control knob control both selectivity and gain?  What causes the super-regenerative effect (a sub-harmonic oscillation?) to occur?&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-01-21T11:05:27.693" Title="Modeling a regenerative receiver" Tags="&lt;receiver&gt;&lt;theory&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17886" PostTypeId="1" AcceptedAnswerId="17887" CreationDate="2021-01-17T18:26:35.013" Score="2" ViewCount="57" Body="&lt;p&gt;I'm planning to use a multiwave horizontal dipole oriented to work comms toward Alaska from Colorado.  That ends up being awkwardly oriented to work east coast and Europe.  If I placed a second identical dipole oriented more or less 90 degrees from the first one, how far apart would the antennas have to be to avoid perturbing radiation patterns between them?  Obviously, only one would be in use at a time.  I'm looking at an off center fed 7 band 135 ft dipole for this project if that makes a difference.  The initial look at my property to mount them ends up creating a giant L with the ends being about 50 feet apart.  I know if they are mounted more or less parallel to one another it will get interesting but I haven't seen anything about a perpendicular association.  In a perfect world I would just put up a yagi or so but I don't have the ability to get that up and running.&lt;/p&gt;&#xA;" OwnerUserId="18546" LastActivityDate="2021-01-17T20:38:26.907" Title="Identical HF Horizonal Dipoles Operating in Close Proximity" Tags="&lt;antenna&gt;&lt;dipole&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17887" PostTypeId="2" ParentId="17886" CreationDate="2021-01-17T20:38:26.907" Score="3" Body="&lt;p&gt;Perpendicular dipoles don't interact at all, theoretically.&lt;/p&gt;&#xA;&lt;p&gt;Of course in practice you won't be able to get them perfectly perpendicular, nor can you completely isolate common mode current on the feedline, but still the interaction is small enough to be negligible, especially considering a dipole isn't very directional to begin with.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-01-17T20:38:26.907" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17888" PostTypeId="1" CreationDate="2021-01-18T01:25:35.833" Score="5" ViewCount="97" Body="&lt;p&gt;In in Russia I saw a phone cable called &amp;quot;field cable&amp;quot; (провод полевой П-274-М). It is a loosely twisted pair with some iron strains added alongside with copper ones.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fzObL.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fzObL.jpg&quot; alt=&quot;Field cable&quot; /&gt;&lt;/a&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/QPjBx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QPjBx.jpg&quot; alt=&quot;Another field cable&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I tried to lookup something similar but I failed to find it.&#xA;I used phrases like &amp;quot;field cable&amp;quot; and &amp;quot;military cable&amp;quot; but got nothing like that.&lt;/p&gt;&#xA;&lt;p&gt;Such cable is really good to make a wire antennas on trees because it has teflon-like surface and tolerant against harsh environment.&lt;/p&gt;&#xA;" OwnerUserId="11243" LastEditorUserId="8717" LastEditDate="2021-01-18T18:48:54.940" LastActivityDate="2021-01-19T17:59:54.117" Title="How is phone cable with iron called?" Tags="&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17889" PostTypeId="1" CreationDate="2021-01-18T01:27:41.570" Score="5" ViewCount="569" Body="&lt;p&gt;What is ALC on an HF transceiver?&lt;br /&gt;&#xA;What are the disadvantages (if any) of operating using a rig without ALC?&#xA;What might be the difference between a good and bad implementation of ALC?&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-01-22T16:49:49.927" LastActivityDate="2021-01-25T20:10:09.683" Title="What does ALC do on a transceiver?" Tags="&lt;transceiver&gt;&lt;ssb&gt;&lt;agc&gt;&lt;alc&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17890" PostTypeId="2" ParentId="15102" CreationDate="2021-01-18T08:15:35.123" Score="1" Body="&lt;p&gt;In 3.7.13.5, thanks to Duck Dodgers (I think) who mentioned block paths coming up twice, such as:&lt;/p&gt;&#xA;&lt;p&gt;Block paths:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks&#xA;&#xA;C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;I too (after fresh install of 3.7.13.5) got the very long and slow-building text list of 'already exist' warnings, before finally starting up the GNU radio companion window.&lt;/p&gt;&#xA;&lt;p&gt;So I went into the directory C:\Program Files\GNURadio-3.7\bin to edit the &amp;quot;run_gr.bat&amp;quot; file. I simply commented out the line that has 'set' in it (eg. see below where I added a rem to comment out the 'set' line).&lt;/p&gt;&#xA;&lt;p&gt;REM --- Set GRC environment ---&lt;/p&gt;&#xA;&lt;p&gt;rem set GRC_BLOCKS_PATH=%~dp0..\share\gnuradio\grc\blocks&lt;/p&gt;&#xA;&lt;p&gt;That then allowed the gnu radio companion of 3.7.13.5 to start up without a hiccup at all. Getting no more of those 'already exist' warnings upon startup. All good now. I'm running Windows 8.1 64-bit.&lt;/p&gt;&#xA;&lt;p&gt;Earlier today, I installed (GR 3.8.1.0 py2.7), which was a total fail. The radio companion window was able to start. But the DOS window indicated some components couldn't be found - and also python 2.7 crash message came up after hitting the 'play' (simulate) button.&lt;/p&gt;&#xA;" OwnerUserId="18593" LastEditorUserId="18593" LastEditDate="2021-01-18T08:21:00.330" LastActivityDate="2021-01-18T08:21:00.330" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17891" PostTypeId="1" AcceptedAnswerId="17892" CreationDate="2021-01-18T12:54:59.147" Score="9" ViewCount="2543" Body="&lt;p&gt;I have been using an Ettus B200 SDR to receive &lt;a href=&quot;https://en.wikipedia.org/wiki/WSJT_(amateur_radio_software)#FT8&quot; rel=&quot;nofollow noreferrer&quot;&gt;FT8&lt;/a&gt; transmissions in the &lt;a href=&quot;https://en.wikipedia.org/wiki/2-meter_band&quot; rel=&quot;nofollow noreferrer&quot;&gt;2-meter band&lt;/a&gt; (144.174 MHz) using the WSJT-X software. Signals are received using a telescopic antenna inside on a window ledge with approximately 1 m of cable. I have made no effort to ensure the antenna is tuned, e.g., by adjusting the length.&lt;/p&gt;&#xA;&lt;p&gt;I am located in the UK in grid square IO91. As expected, I mostly receive signals from the same grid square, and occasionally the grid squares adjacent. I see replies to messages which originated further away (based on the call sign).&lt;/p&gt;&#xA;&lt;p&gt;Some received messages are obviously &amp;quot;incorrect&amp;quot;, for example:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;210113_084530   144.174 Rx FT8    -18  1.0 1545 Z50H+TSKY-JHO&#xA;210115_114630   144.174 Rx FT8    -17 -1.6  685 SIDE LOBE&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;Others seem like they might be real, but they are located in grid squares more than 10,000 km away.&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;210111_195445   144.174 Rx FT8    -16  0.3 1728 VI7JOW/P TO7JRB R BO96&#xA;210113_163545   144.174 Rx FT8    -17  1.3 1247 J06NQY A68ITS/R R QM30&#xA;210114_100830   144.174 Rx FT8    -18  1.0 2653 YI7ORO VD7XLO R CK63&#xA;210115_051015   144.174 Rx FT8    -23  1.8 2388 8L9VCM 3K9WKZ/P MF32&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;The call signs don't appear to be real. Is it safe to assume the message is corrupt? Or is there another explanation?&lt;/p&gt;&#xA;" OwnerUserId="1727" LastEditorUserId="366" LastEditDate="2021-01-19T18:03:17.893" LastActivityDate="2021-01-19T18:03:17.893" Title="Am I really receiving FT8 signals from 12,000 km away on 144 MHz?" Tags="&lt;digital-modes&gt;&lt;united-kingdom&gt;&lt;ft8&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17892" PostTypeId="2" ParentId="17891" CreationDate="2021-01-18T15:18:43.500" Score="9" Body="&lt;p&gt;I'd say these are simply corrupt. Take for example:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;210113_163545   144.174 Rx FT8    -17  1.3 1247 J06NQY A68ITS/R R QM30&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;A68ITS doesn't seem to be a real call, but if it was, it would be a UAE call. The grid QM30 is in the Pacific ocean, about 800 km off the coast of Japan. This is a pretty unlikely combination.&lt;/p&gt;&#xA;&lt;p&gt;The FT8 protocol includes error correction which reduces, but does not eliminate the possibility of false decodes. The nature of the coding also means when there are errors it doesn't change a character or two, but scrambles the entire message. The compression used by the WSJT protocols, which is optimized for the canonical WSJT QSO format, also means random garbage is biased towards producing something that looks like a QSO.&lt;/p&gt;&#xA;&lt;p&gt;So while you shouldn't see this sort of thing day-to-day, if you search your logs for outliers you'll certainly find some.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-01-18T15:18:43.500" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17893" PostTypeId="2" ParentId="17891" CreationDate="2021-01-18T17:47:52.080" Score="9" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;210115_114630   144.174 Rx FT8    -17 -1.6  685 SIDE LOBE&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This is probably the one real one of the bunch, actually! The odds of random noise decoding as a freetext message with sensible English in it are vanishingly small. This was probably from someone who worked someone on 2m FT8, and then after exchanging their grid squares, sent a followup message to say &amp;quot;that wasn't even off the front of the beam!&amp;quot; But since freetext messages don't carry a callsign or a grid square, you don't really know where it came from, unless you observed other messages on the same frequency nearby in time.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2021-01-18T17:54:56.260" LastActivityDate="2021-01-18T17:54:56.260" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17894" PostTypeId="2" ParentId="17884" CreationDate="2021-01-18T18:13:16.723" Score="1" Body="&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$I_n$&lt;/span&gt; is the current on the element, the current which gives rise the to the fields. It has a magnitude and phase. From that you can derive the array patterns.&lt;/p&gt;&#xA;&lt;p&gt;This is a big simplification from a real-world array, but is useful to allow you to derive some array details in a clean environment. For example:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;it's a two dimensional design&lt;/li&gt;&#xA;&lt;li&gt;it doesn't consider the element patterns (they produce the same fields in all directions)&lt;/li&gt;&#xA;&lt;li&gt;element length is 1 (they're just unit length elements of current out of the page)&lt;/li&gt;&#xA;&lt;li&gt;there must be some feed that produces the current, but that's not what's being investigated&lt;/li&gt;&#xA;&lt;li&gt;if all &lt;span class=&quot;math-container&quot;&gt;$I_n$&lt;/span&gt; are the same, then there's no coupling (or it's taken care of by the feed somehow)&lt;/li&gt;&#xA;&lt;li&gt;The elements are short enough that they can be approximated by a simple short element of current. No current distribution or self-impedance etc.&lt;/li&gt;&#xA;&lt;li&gt;The only things you need to know to describe an element and calculate its contribution are:&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Current magnitude, &lt;span class=&quot;math-container&quot;&gt;$|I_n|$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;Current phase, &lt;span class=&quot;math-container&quot;&gt;$\angle I_n$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;li&gt;X-position in terms of wavelength, &lt;span class=&quot;math-container&quot;&gt;$knd$&lt;/span&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-01-20T01:27:25.270" LastActivityDate="2021-01-20T01:27:25.270" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17895" PostTypeId="2" ParentId="17888" CreationDate="2021-01-18T18:46:42.267" Score="2" Body="&lt;p&gt;That is WD-1 or WD-1A military telephone line.&lt;/p&gt;&#xA;&lt;p&gt;Lots of hams use it for &lt;a href=&quot;https://web.archive.org/web/20181115070846/http://www.w0btu.com/Beverage_antennas.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;switchable-direction Beverage receiving antennas&lt;/a&gt;, and with good results.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;p&gt;The steel strands provide extra tensile strength.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2021-01-19T17:59:54.117" LastActivityDate="2021-01-19T17:59:54.117" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17896" PostTypeId="2" ParentId="17888" CreationDate="2021-01-18T19:09:18.570" Score="0" Body="&lt;p&gt;I am basing this mostly off of web searches rather than industry experience but it looks like there's two potential terms for a related cable. At least related as to the general purpose — reinforcing conductive wires to better hold their own weight — if not exact construction/materials:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Aerial Service Wire — i.e. wire used the delivery of a utility service is done via above-ground poles with the wires in the air. This term might be a bit more used in high-current AC power delivery, but I do also see it in relation to telephone/cables as well. E.g. &lt;a href=&quot;http://www.newtechindustries.com/aerial-service-wire-asw-6-pair-22-awg-400-coil-adp-nms/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.newtechindustries.com/aerial-service-wire-asw-6-pair-22-awg-400-coil-adp-nms/&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;Drop Cable — i.e. a conductor assembly used for the final &amp;quot;drop&amp;quot; (e.g. from a telephone pole down to a house) and seems to be a little more common for the communication industry rather than power companies. E.g. &lt;a href=&quot;https://www.nordencommunication.com/en-in/product/telephone-drop-cable-no-1-2-6-and-8&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.nordencommunication.com/en-in/product/telephone-drop-cable-no-1-2-6-and-8&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Again, neither of my example links show the exact kind of wire you show but I think you were primarily wanting some ideas for what this sort of reinforced-for-hanging is called in general and I hope this helps!&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2021-01-18T19:09:18.570" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17897" PostTypeId="1" AcceptedAnswerId="17906" CreationDate="2021-01-18T21:45:15.263" Score="3" ViewCount="101" Body="&lt;p&gt;Recently I've made a simple single IF superheterodyne SSB receiver for 40 meter band. The schematic is &lt;a href=&quot;https://eax.me/files/2021/01/40m-superhet-receiver.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;available here [PDF]&lt;/a&gt;. VFO and BFO are based on Si5351, the AF amplifier is LM386. It works OK but there is one annoying issue I couldn't solve so far. When I change the frequency I can hear a popping sound in the headphones.&lt;/p&gt;&#xA;&lt;p&gt;I thought this could be an RFI from an 1602 LCD and/or the I2C bus. However this theory was not confirmed. When the text is updated on the LCD without changing the frequency there is no popping sound. I also tried to add a simple RC high-pass filter to the AF amplifier. According to the datasheet, LM386 has input impedance ~50 kOhm. Thus with 10 nF capacitor on the input it will form an high-pass filter with cutoff frequency ~300 Hz. This didn't help either.&lt;/p&gt;&#xA;&lt;p&gt;Then I thought maybe the problem will go away when I place the receiver in a proper aluminum enclosure with good ground plane and move AF amplifier away from the VFO. Sadly this made no difference.&lt;/p&gt;&#xA;&lt;p&gt;The problem is that I have little understanding of what exactly causes this popping sound and how to diagnose such problems. Hopefully someone who also encountered such an issue could explain how to deal with it? I tried to Google the problem. It seems to be quite common, but I didn't manage to find a solution or an explanation of the effect.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastActivityDate="2021-01-21T08:46:16.217" Title="What causes an AF amplifier to make popping sounds in a superheterodyne receiver?" Tags="&lt;receiver&gt;&lt;diy&gt;&lt;electronics&gt;&lt;superheterodyne&gt;&lt;si5351&gt;" AnswerCount="3" CommentCount="2" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17898" PostTypeId="2" ParentId="17897" CreationDate="2021-01-19T05:12:42.523" Score="3" Body="&lt;p&gt;Try powering the LM386 temporarily off a battery. if the popping stops, then the cause is a surge being conducted into the 386 from the supply that feeds the rest of your circuit.&lt;/p&gt;&#xA;&lt;p&gt;Normally, you would bypass the power input of the 386 to ground with a hefty electrolytic capacitor (50 to 100mfd) and then shunt that with a fast-acting cap (0.01 to 0.1uF) to prevent surges from upsetting the 386. If your circuit doesn't have these bypass caps, try adding them.&lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2021-01-19T05:12:42.523" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17900" PostTypeId="2" ParentId="17889" CreationDate="2021-01-19T09:53:14.290" Score="4" Body="&lt;p&gt;ALC, in general, stands as an abbreviation for Automatic Level Control, which is a class of circuits designed to back-feed information about the output signal to an amplifier. The goal is to change the parameters of the amplifier so that a clean output that remains within certain parameters is attained.&lt;/p&gt;&#xA;&lt;p&gt;In normal HF transceivers, such a circuit will most likely be used to control the final amplifier's output. The goal here is to enable use of the final amplifier to precisely it's specified capabilities, but not beyond. This is important since otherwise, simply feeding a signal with too high power into the transceiver (by speaking too loudly into the microphone or connecting a digital modem with too high an output voltage) would overdrive the amplifier stages, adding distortion to the output signal.&lt;/p&gt;&#xA;&lt;p&gt;Similarly, most transceivers offer an ALC OUT connector that allows an analogous control loop for external, higher power amplifiers.&lt;/p&gt;&#xA;&lt;p&gt;In both cases, the ALC circuit creates a negative DC voltage that is proportional to the output level and is used to change the gain of the preamplifier stage in the transceiver (which, in turn, will result in more or less input to the final amplifier stage and perhaps the external high power amplifier).&lt;/p&gt;&#xA;&lt;p&gt;When you are operating a transceiver without ALC, you lose the feedback described above, which will result in (possibly severe) distortion of your output signal if you overdrive the amplifiers with a too loud signal.&lt;/p&gt;&#xA;&lt;p&gt;With regard to the implementation, ALC circuits, like all control loops, have an &amp;quot;attack&amp;quot; and &amp;quot;decay&amp;quot; time constant which need to be tweaked for the use case (most likely voice transmission, in this case). They need to &amp;quot;attack&amp;quot; quickly, i.e. dampen the total amplification quickly in case a sudden loud noise comes in, and then &amp;quot;decay&amp;quot; a bit slower, allowing again more amplification. If this is not tuned well, voice will sound strange due to the alternating amplification factors over time.&lt;/p&gt;&#xA;&lt;p&gt;And finally, there is an enlightening rant at &lt;a href=&quot;http://www.sm5bsz.com/dynrange/alc.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.sm5bsz.com/dynrange/alc.htm&lt;/a&gt; in which the author describes the potential of ALC circuits creating splatter-type interference if they are, as is done often in practice, (mis-)used as a cheap voice limiter.&lt;/p&gt;&#xA;" OwnerUserId="15707" LastEditorUserId="15707" LastEditDate="2021-01-19T21:49:00.027" LastActivityDate="2021-01-19T21:49:00.027" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17901" PostTypeId="1" AcceptedAnswerId="17902" CreationDate="2021-01-19T18:12:34.753" Score="3" ViewCount="157" Body="&lt;p&gt;I saw a &lt;a href=&quot;https://ham.stackexchange.com/questions/17897/what-causes-an-af-amplifier-to-make-popping-sounds-in-a-superheterodyne-receiver/17898#17898&quot;&gt;recent answer&lt;/a&gt; that mentioned &amp;quot;mfd&amp;quot; as a unit of capacitance, and I can recall having seen that term in old schematics and ham radio articles.  I've also seen other non-&lt;a href=&quot;https://en.wikipedia.org/wiki/International_System_of_Units&quot; rel=&quot;nofollow noreferrer&quot;&gt;SI&lt;/a&gt; unit abbreviations, such as &amp;quot;kc&amp;quot; on old equipment and in old articles.  The non-SI units don't stop there of course; I've seen &amp;quot;mcg&amp;quot; in medical contexts, and I've seen &amp;quot;kgf&amp;quot; used as a unit of force, and I'm sure there are many more, but please let's mostly confine the discussion to units used in amateur radio.&lt;/p&gt;&#xA;&lt;p&gt;Would someone please explain older units and their abbreviations used in amateur radio such as &amp;quot;mfd&amp;quot; and &amp;quot;kc&amp;quot;?  I would also welcome any relevant history that helps illuminate the topic.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-01-21T02:37:06.423" LastActivityDate="2021-01-21T02:37:06.423" Title="What do old unit abbreviations like &quot;mfd&quot; and &quot;kc&quot; mean, and where did they come from?" Tags="&lt;frequency&gt;&lt;history&gt;&lt;capacitance&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17902" PostTypeId="2" ParentId="17901" CreationDate="2021-01-19T18:23:40.130" Score="8" Body="&lt;p&gt;These were common abbreviations in use for Components, Radio equipment, and Printed publications in the 19th and most of the 20th century.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Mfd = &lt;em&gt;microfarad&lt;/em&gt; or &lt;strong&gt;μF&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;kc = &lt;em&gt;kilocycles&lt;/em&gt; or &lt;strong&gt;kHz&lt;/strong&gt;. 1,000 cycles per second.&lt;/li&gt;&#xA;&lt;li&gt;μμf or mmf = pF (picofarad)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;hr&gt;&#xA;&lt;h3&gt;Frequency&lt;/h3&gt;&#xA;&lt;p&gt;The change from &lt;em&gt;kc&lt;/em&gt; to &lt;em&gt;kHz&lt;/em&gt; and &lt;em&gt;mc&lt;/em&gt; to &lt;em&gt;MHz&lt;/em&gt; were done because someone though that &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Heinrich_Hertz&quot; rel=&quot;noreferrer&quot;&gt;Heinrich Hertz&lt;/a&gt; ought to be given credit for his work.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Heinrich Rudolf Hertz was a German physicist who first conclusively proved the existence of the electromagnetic waves predicted by James Clerk Maxwell's equations of electromagnetism. The unit of frequency, cycle per second, was named the &amp;quot;hertz&amp;quot; in his honor. ... The SI unit hertz (Hz) was established in his honor by the International Electrotechnical Commission in 1930 for frequency, ... It was adopted by the CGPM (Conférence générale des poids et mesures) &lt;strong&gt;in 1960, officially replacing the previous name, &amp;quot;cycles per second&amp;quot; (cps)&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Many commercial and amateur radios were labeled &lt;strong&gt;kc&lt;/strong&gt; or &lt;strong&gt;mc&lt;/strong&gt;. My 1960s Collins S-Line manuals didn't use kHz or MHz.&lt;/p&gt;&#xA;&lt;hr&gt;&#xA;&lt;h3&gt;Capacitance&lt;/h3&gt;&#xA;&lt;p&gt;Informal and &lt;strong&gt;deprecated terminology&lt;/strong&gt;, from &lt;a href=&quot;https://ham.stackexchange.com/questions/17901/old-units-and-abbreviations&quot;&gt;Wikipedia&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The picofarad (pF) is sometimes colloquially pronounced as &amp;quot;puff&amp;quot; or &amp;quot;pic&amp;quot;, as in &amp;quot;a ten-puff capacitor&amp;quot;. Similarly, &amp;quot;mic&amp;quot; (pronounced &amp;quot;mike&amp;quot;) is sometimes used informally to signify microfarads.&lt;/p&gt;&#xA;&lt;p&gt;Nonstandard abbreviations were and are often used. Farad has been abbreviated &amp;quot;f&amp;quot;, &amp;quot;fd&amp;quot;, and &amp;quot;Fd&amp;quot;. ... μ &amp;quot;micro&amp;quot; ... was also substituted with the similar-sounding &amp;quot;M&amp;quot; or &amp;quot;m&amp;quot;, which can be confusing because M officially stands for 1,000,000 (or 1,000), and m preferably stands for 1/1000.&lt;/p&gt;&#xA;&lt;p&gt;In texts prior to 1960, and on capacitor packages until more recently, &amp;quot;microfarad(s)&amp;quot; was abbreviated &amp;quot;mf&amp;quot; or &amp;quot;MFD&amp;quot; rather than the modern &amp;quot;µF&amp;quot;. A 1940 Radio Shack catalog listed every capacitor's rating in &amp;quot;Mfd.&amp;quot;, from 0.000005 Mfd. (5 pF) to 50 Mfd. (50 µF).&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;Micromicrofarad&amp;quot; or &amp;quot;micro-microfarad&amp;quot; is an obsolete unit found in some older texts and labels, contains a nonstandard metric double prefix. It is exactly equivalent to a picofarad (pF). It is abbreviated μμF, uuF, or (confusingly) &amp;quot;mmf&amp;quot;, &amp;quot;MMF&amp;quot;, or &amp;quot;MMFD&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Summary of obsolete capacitance units: (upper/lower case variations aren't shown)&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;µF (microfarad) = mf, mfd&lt;/li&gt;&#xA;&lt;li&gt;pF (picofarad) = mmf, mmfd, pfd, µµF&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2021-01-19T19:52:28.410" LastActivityDate="2021-01-19T19:52:28.410" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="17903" PostTypeId="1" CreationDate="2021-01-19T23:52:31.177" Score="1" ViewCount="77" Body="&lt;p&gt;This radio has a commercial mode but no where that I can find does it describe which commercial license. Looking at the tag under the battery...&lt;/p&gt;&#xA;&lt;p&gt;FCC ID T4KD887UV&#xA;&lt;a href=&quot;https://fccid.io/T4KD878UV&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://fccid.io/T4KD878UV&lt;/a&gt;&#xA;...so part 22 and part 90?&lt;/p&gt;&#xA;&lt;p&gt;Part 90 is &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/private-land-mobile-radio-services&quot; rel=&quot;nofollow noreferrer&quot;&gt;Commercial, public safety and Government&lt;/a&gt;, but what is Part 22 exactly? Trying to figure this out is like looking for a sentence in War and Peace.&lt;/p&gt;&#xA;" OwnerUserId="15859" LastEditorUserId="15859" LastEditDate="2021-01-24T03:09:49.037" LastActivityDate="2021-01-24T03:09:49.037" Title="Anytone 878 UV Commercial license?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;anytone&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17904" PostTypeId="2" ParentId="17903" CreationDate="2021-01-20T00:20:30.373" Score="1" Body="&lt;p&gt;If you click on &amp;quot;22&amp;quot; in the web page you linked to, you're taken to &lt;a href=&quot;https://ecfr.io/Title-47/pt47.2.22&quot; rel=&quot;nofollow noreferrer&quot;&gt;this page&lt;/a&gt;, which reveals that Part 22 is CFR ›  Title 47 ›  Volume 2 ›  Chapter I ›  Subchapter B ›  &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/part-22&quot; rel=&quot;nofollow noreferrer&quot;&gt;Part 22 - Public Mobile Services&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;So I think the answer that you were looking for is that Part 22 is Public Mobile Services.  I was surprised to see that Wikipedia doesn't have an article about Public Mobile Services.  &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/22.99&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR § 22.99&lt;/a&gt; defines Public Mobile Services as, &amp;quot;Radio services in which licensees are authorized to offer and provide mobile and related fixed radio telecommunication services for hire to the public.&amp;quot;&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-01-20T00:20:30.373" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17905" PostTypeId="2" ParentId="17897" CreationDate="2021-01-20T14:02:57.247" Score="1" Body="&lt;p&gt;Since it happens when switching frequencies, I suspect glitches of some form in the local or beat frequency oscillators' output.&lt;/p&gt;&#xA;&lt;p&gt;The mixers simply multiply the &amp;quot;signal&amp;quot; by the oscillator.  Any noise or glitch in the oscillator outputs will be reflected in the mixed outputs.&lt;/p&gt;&#xA;&lt;p&gt;You may be more sensitive to BFO glitches, since the output is at DC, not a higher intermediate frequency.&lt;/p&gt;&#xA;&lt;p&gt;The glitch could be as simple as a phase change in the oscillator or a missed cycle.  That will add a DC component to the signal, which will turn into a DC shift in the mixer output.&lt;/p&gt;&#xA;&lt;p&gt;Since the passband of the mixer and audio amplifier probably does not go to zero Hz, it will sound like a click.&lt;/p&gt;&#xA;&lt;p&gt;Are you actually changing the BFO frequency?  In most multi-conversion receivers it is only the first local oscillator whose frequency changes by tuning.  Other oscillators may change frequency for other purposes, such as switching between USB and LSB, but for tuning up and down the band they are typically constant frequency.&lt;/p&gt;&#xA;" OwnerUserId="9109" LastActivityDate="2021-01-20T14:02:57.247" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17906" PostTypeId="2" ParentId="17897" CreationDate="2021-01-20T15:40:18.297" Score="4" Body="&lt;p&gt;I think I figured this out. By looking at VFO with an oscilloscope I could catch a brief glitch (~1.5ms) in the signal when the frequency is changed:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OzQ8i.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OzQ8i.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It was hard to notice because you can't easily trigger on this. I had to manually trigger single captures while tuning for some time to see this.&lt;/p&gt;&#xA;&lt;p&gt;Then by googling &amp;quot;si5351 output glitches&amp;quot; I've found &lt;a href=&quot;https://www.qrp-labs.com/images/synth/demo2/si5351a.c&quot; rel=&quot;nofollow noreferrer&quot;&gt;this piece of code&lt;/a&gt; on the &lt;a href=&quot;https://www.qrp-labs.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRP Labs&lt;/a&gt; website. The comment states:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;Reset the PLL. This causes a glitch in the output. For small changes to&#xA;the parameters, you don't need to reset the PLL, and there is no glitch.&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;Then I realized the source of the problem and how to fix it. Here is the original version of my code:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;void changeFrequency(int32_t delta) {&#xA;    targetFrequency += frequencyStep*delta;&#xA;    if(targetFrequency &amp;lt; 7000000) {&#xA;        targetFrequency = 7000000;&#xA;    } else if(targetFrequency &amp;gt; 7200000) {&#xA;        targetFrequency = 7200000;&#xA;    }&#xA;&#xA;    if(targetFrequency &amp;lt; 10000000) {&#xA;        Fvfo  = Fbfo-targetFrequency; // LSB&#xA;    } else {&#xA;        Fvfo = Fbfo+targetFrequency; // USB&#xA;    }&#xA;    si5351_EnableOutputs((1&amp;lt;&amp;lt;2));&#xA;    si5351_SetupCLK0(Fvfo, SI5351_DRIVE_STRENGTH_4MA);&#xA;    si5351_EnableOutputs((1 &amp;lt;&amp;lt; 2)|(1&amp;lt;&amp;lt;0));&#xA;}&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;Here &lt;code&gt;si5351_SetupCLK0&lt;/code&gt; is called every time the frequency is changed. The &lt;a href=&quot;https://github.com/afiskon/stm32-si5351/blob/main/si5351/si5351.c#L291&quot; rel=&quot;nofollow noreferrer&quot;&gt;procedure&lt;/a&gt; changes the PLL, MS and Rdiv settings for the channel. As an author of this Si5351 driver I'm well aware that PLL settings are always the same for frequencies below 81 MHz (also this is a &lt;a href=&quot;https://github.com/afiskon/stm32-si5351/blob/main/si5351/si5351.h#L52&quot; rel=&quot;nofollow noreferrer&quot;&gt;documented behavior&lt;/a&gt; which can be relied on in the future versions).&lt;/p&gt;&#xA;&lt;p&gt;Thus the code was changed as following:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;void changeFrequency(int32_t delta) {&#xA;    static bool pllSetupDone = false;&#xA;    si5351PLLConfig_t pll_conf;&#xA;    si5351OutputConfig_t out_conf;&#xA;&#xA;    targetFrequency += frequencyStep*delta;&#xA;    if(targetFrequency &amp;lt; 7000000) {&#xA;        targetFrequency = 7000000;&#xA;    } else if(targetFrequency &amp;gt; 7200000) {&#xA;        targetFrequency = 7200000;&#xA;    }&#xA;&#xA;    if(targetFrequency &amp;lt; 10000000) {&#xA;        Fvfo  = Fbfo-targetFrequency; // LSB&#xA;    } else {&#xA;        Fvfo = Fbfo+targetFrequency; // USB&#xA;    }&#xA;    si5351_EnableOutputs((1&amp;lt;&amp;lt;2));&#xA;&#xA;    si5351_Calc(Fvfo, &amp;amp;pll_conf, &amp;amp;out_conf);&#xA;    if(!pllSetupDone) {&#xA;        // Setting up the PLL causes a brief (~1.5ms) glitch in the VFO output&#xA;        // which sounds like a loud popping sound the the speaker.&#xA;        // By setting up the PLL only once we get rid of this popping sound.&#xA;        si5351_SetupPLL(SI5351_PLL_A, &amp;amp;pll_conf);&#xA;        pllSetupDone = true;&#xA;    }&#xA;    si5351_SetupOutput(0, SI5351_PLL_A, SI5351_DRIVE_STRENGTH_4MA, &amp;amp;out_conf);&#xA;&#xA;    si5351_EnableOutputs((1 &amp;lt;&amp;lt; 2)|(1&amp;lt;&amp;lt;0));&#xA;}&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;Now the expansive call &lt;code&gt;si5351_SetupPLL&lt;/code&gt; is made only once, the glitch is gone and the popping sound is eliminated. Well, almost. You can still hear a very quiet popping when the antenna is disconnected. But there is no popping when the antenna is connected. Interestingly you can observe the exactly same behavior in QCX transceiver made by guess which company.&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2021-01-21T08:46:16.217" LastActivityDate="2021-01-21T08:46:16.217" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17907" PostTypeId="1" AcceptedAnswerId="17908" CreationDate="2021-01-21T00:58:07.990" Score="1" ViewCount="63" Body="&lt;p&gt;As a US license holder (and duel citizen of the US and UK) I know that I can operate in the UK for a couple of months using the M/W2*** prefix, while holding Amateur Extra, but I cannot apply for a UK license using my US license, like Japan for example which has exchanges.&lt;/p&gt;&#xA;&lt;p&gt;So I have three questions for the minds out there in Stack Exchange,&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Will Brexit affect this situation.&lt;/li&gt;&#xA;&lt;li&gt;Can I still operate over there when travel resumes?&lt;/li&gt;&#xA;&lt;li&gt;Will there be movement so that there is cross recognition of more foreign license holders?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="18112" LastEditorUserId="18112" LastEditDate="2021-01-21T04:33:15.240" LastActivityDate="2021-01-21T06:40:13.683" Title="Will Brexit have any impact on UK recognition of foreign licenses" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;united-kingdom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17908" PostTypeId="2" ParentId="17907" CreationDate="2021-01-21T06:40:13.683" Score="4" Body="&lt;ol&gt;&#xA;&lt;li&gt;No.&lt;/li&gt;&#xA;&lt;li&gt;Yes.&lt;/li&gt;&#xA;&lt;li&gt;There's no particular reason to think so.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;The UK and the US have both adopted CEPT T/R 61-01 regarding reciprocal amateur operation. Despite the fact that CEPT is the &amp;quot;European Conference of Postal and Telecommunications Administrations&amp;quot;, it's independent of the EU (it long predates the EU), and parties to T/R 61-01 don't have to be members of the EU or members of CEPT (the US, Canada, Australia, New Zealand, Peru, and South Africa are non-CEPT members).&lt;/p&gt;&#xA;&lt;p&gt;So Brexit has no &amp;quot;automatic&amp;quot; impact, and I don't see any reason why the UK would go out of their way to terminate the existing arrangement. In any case, they're probably far too busy to give it any thought ;)&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-01-21T06:40:13.683" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17909" PostTypeId="2" ParentId="17885" CreationDate="2021-01-21T10:58:22.863" Score="2" Body="&lt;p&gt;This is a basic question and needs an answer.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Regenerative receiver or audion. Single LC-filter with undamping: Q-multiplier. The frequency transfer of such a filter can be obtained from a simulation. See figure. As you can see: the AM demodulated audio response is affected when selectivity is too high. The example shows 1 MHz mediumwave. Audio bandwidth of 3 kHz requires sideband transfer of plus and minus 3 kHz. That is 6 kHz top bandwidth or a maximum Q-factor of 1000 kHz / 6 kHz = 167. Higher selectivity at the cost of audio bandwidth.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;For shortwave the effective Q-factor can be much higher: 6 Mhz and 6 kHz BW allows Q_eff = 1000.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hktV9.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hktV9.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The single control knob adjusts the Q multiplication. In the simulation this is the negative resistance. In practice obtained from vacuum tube, bipolar transistor or field effect transistor.&lt;/p&gt;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;Super-regenerative reception is an effect that the undamping is too strong and leads to oscillation AND that the DC operating point is affected in such a way that the oscillation stops. The oscillator starts again and the process is repeated. The sequence of start-stop is in the order of 20 to 50 kHz for most superregenerative receivers. The high sensitivity follows from the initial phase of the radiofrequency signal during startup of the oscillation: in phase with the oscillator  &amp;quot;eigenfrequency&amp;quot; helps and out of phase is opposite.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Not in your question is a third option: synchrodyne reception. The oscillator is synchronised to the received carrier, simply by pushing. The audio response is now mainly the result of the post-detection audio bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;Have fun with these simple experiments!&#xA;They lead to insight that is important for education.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2021-01-21T11:05:27.693" LastActivityDate="2021-01-21T11:05:27.693" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17910" PostTypeId="1" AcceptedAnswerId="17922" CreationDate="2021-01-21T18:39:09.073" Score="6" ViewCount="224" Body="&lt;p&gt;The popular question  &amp;quot;&lt;a href=&quot;https://ham.stackexchange.com/questions/382/what-is-the-relationship-between-swr-and-receive-performance&quot;&gt;What is the relationship between SWR and receive performance?&lt;/a&gt;&amp;quot; asks if a receiver with a well-matched antenna (low SWR) beats a receiver with a poorly-matched antenna, with everything else being equal.  The consensus opinion of the answers, weighted according to the votes on the answers, is no; the two receivers should receive about the same.&lt;/p&gt;&#xA;&lt;p&gt;The idea is that an impedance mismatch leads to power loss, and a weaker signal at the receiver.  But losses shouldn't affect receiver performance as long as the signal-to-noise ratio (SNR) is the same, because the receiver's automatic gain control (AGC) feedback circuit can easily add a few more decibels of gain to compensate for any such losses.  There is an important caveat to this rule that the received RF noise floor must be above the receiver's noise floor, because otherwise the signal-to-noise ratio will be affected.&lt;/p&gt;&#xA;&lt;p&gt;This logic makes sense to me, and I can find no flaws in it.  But if that is so, then why is it that when I use my manual T-network transmatch (antenna tuner) to tune my ZS6BKW antenna on various HF bands such as 40m and 20m, I can get a fairly good match without transmitting by turning the knobs to maximize the band noise in my headphones?  (I say &amp;quot;band noise&amp;quot; because I tune the radio to an unused frequency and then adjust the transmatch for maximum static, but if there were a signal on the frequency then I would adjust the transmatch to make the signal the loudest.)  If the consensus answers to the other question are correct, then I would think that turning the knobs would make no difference at all to the volume of sound in the headphones.&lt;/p&gt;&#xA;&lt;p&gt;My HF rig is an Elecraft K2, which has an excellent receiver.  The caveat to the rule shouldn't apply, because the RF noise floor should be well above the receiver's noise floor on 40m and 20m.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-01-22T00:12:34.837" LastActivityDate="2021-01-24T01:29:40.433" Title="If receive performance doesn't depend on SWR, then how can I tune my manual HF antenna tuner by band noise?" Tags="&lt;hf&gt;&lt;antenna-system&gt;&lt;impedance-matching&gt;&lt;noise&gt;" AnswerCount="6" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17911" PostTypeId="2" ParentId="17910" CreationDate="2021-01-21T19:15:26.290" Score="3" Body="&lt;p&gt;The noise you hear in your headphones is coming from the antenna. When you tune the antenna and minimize the SWR, the losses between the antenna and the receiver are minimized, thus more of the noise received by the antenna makes it to the receiver, and you hear more noise in your headphones.&lt;/p&gt;&#xA;&lt;p&gt;(Assuming of course the receiver is set to a mode where power is proportional to noise, as in AM, SSB, or CW.)&lt;/p&gt;&#xA;&lt;p&gt;It's also possible that the noise you hear in the headphones comes from thermal sources in the feedline or the receiver, or something other than the electromagnetic field around the antenna. In this case tuning the antenna would &lt;em&gt;not&lt;/em&gt; significantly increase the noise volume in the headphones, and improving SWR would indeed increase receive performance. This is however very unlikely on HF, since the electromagnetic noise floor is so high compared to the internal noise of even a very inexpensive receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-01-22T15:44:40.823" LastActivityDate="2021-01-22T15:44:40.823" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17912" PostTypeId="2" ParentId="17910" CreationDate="2021-01-21T22:52:37.033" Score="2" Body="&lt;p&gt;You can get a good match by maximizing received noise, because that is the point where more RF noise might be transferred from the antenna to your receiver, and thus indicate where the SWR is lower (e.g. less noise is reflected back to the antenna at the frequency of interest).&lt;/p&gt;&#xA;&lt;p&gt;Tuning to minimize SWR might improve receiver performance by changing the efficiency of RF transfer near the frequency of interest compared with that of other frequency ranges where the SWR is higher.  (e.g. some antenna tuner circuit configurations act as bandpass filters).  But it can also reduce receiver performance by reducing total usable dynamic range (e.g. if your receiver's front end needs some attenuation of the RF input, rather than gain, to possibly reduce IMD).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-01-24T01:29:40.433" LastActivityDate="2021-01-24T01:29:40.433" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17913" PostTypeId="2" ParentId="17910" CreationDate="2021-01-22T00:08:16.990" Score="1" Body="&lt;p&gt;As per Phil's answer, the idea that a matched system is most efficient from a system level perspective is undeniable.&lt;/p&gt;&#xA;&lt;p&gt;However, at VHF and UHF the receiver noise is well above the noise received by the antenna, so then without doubt less mismatch means better system signal to noise ratio.&lt;/p&gt;&#xA;&lt;p&gt;Also, i imagine that the signal to noise ratio probably changes for active electronic circuits depending on where on their operational characteristic curves the signal levels are sitting, so maybe signal to noise ratio is better at higher gain for a device which doesn't have AGC applied for example. In that case less mismatch could mean better signal to noise ratio.&lt;/p&gt;&#xA;&lt;p&gt;Apart from all that, it always seems to me that a matched system appears to be more 'sensitive' or responsive regardless of what the overall S/N ratio is, even if it is only because the noise received by the antenna is also amplified along with the desired signals, so from a psychological perspective it makes you more confident that you have a system that's working well.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2021-01-22T00:08:16.990" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17914" PostTypeId="2" ParentId="17910" CreationDate="2021-01-22T01:10:38.773" Score="1" Body="&lt;p&gt;A possible answer came to me in a flash of insight.  It occurred to me that the AGC in my Elecraft K2 does not try to make the volume in the headphones constant wherever I tune the receiver; if the AGC worked that way then the static of an unused frequency would be exactly as loud in the headphones as a contest station transmitting 1,500 W from 10 km away.  I'll call that &amp;quot;naïve AGC&amp;quot;.  Hearing loud static on every unused frequency would be very annoying, so receiver manufacturers don't design their AGCs to work that way.  If the AGC did work that way, then I do think I wouldn't notice any volume difference in the headphones when I adjust the knobs of my transmatch.&lt;/p&gt;&#xA;&lt;p&gt;Instead, my Elecraft K2 is designed so that the AGC only &lt;em&gt;partially&lt;/em&gt; boosts the gain for weak signals.  Because the AGC action is not as aggressive as &amp;quot;naïve AGC&amp;quot; by design, strong signals are louder in the headphones than weak signals.  (That's one of the features that I like about my K2 compared to Yaesu/Icom/Kenwood HF rigs, in which the audio volume of a weak station seems almost as loud as the volume of a strong station.)&lt;/p&gt;&#xA;&lt;p&gt;Because stronger RF signals are actually louder in my headphones than weaker signals thanks to the partial action of the AGC, adjusting the transmatch for a stronger received signal will result in more audio volume in my headphones.  A better impedance match will result in less mismatch loss and therefore a stronger signal.  So that's how I can adjust my transmatch fairly well by adjusting the controls so the static of an unused HF frequency is loudest in my headphones.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-01-22T01:10:38.773" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17915" PostTypeId="1" CreationDate="2021-01-22T05:51:26.083" Score="0" ViewCount="68" Body="&lt;p&gt;I have searched, installed, and tried every package there is to get AIS processing using the gnu-radio companion to no avail.&lt;/p&gt;&#xA;&lt;p&gt;I tried installing gnu-radio both with conda and apt on Ubuntu 20.04. The conda way raises issues when I try to install gr-ais; doing it the &amp;quot;apt install&amp;quot; the modules do not show up on gnuradio-companion. I tried finding the GNUradio Bootable Live CD online, could not find it. I tried several other AIS related repos claiming to work with gnuradio, to no avail once again.&lt;/p&gt;&#xA;&lt;p&gt;I have an STL-SDR dongle. At least I got that to work.&lt;/p&gt;&#xA;&lt;p&gt;So, the question is: if I want to process AIS using GNUradio 3.8(latest) on ubuntu 20.04, how can I do that? What packages/modules/environment are the appropriate ones to use?&lt;/p&gt;&#xA;&lt;p&gt;Thank you.&lt;/p&gt;&#xA;" OwnerUserId="18615" LastActivityDate="2021-01-22T05:51:26.083" Title="gnu-radio on Ubuntu 20.04 and AIS processing seems impossible" Tags="&lt;gnuradio&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17916" PostTypeId="2" ParentId="17910" CreationDate="2021-01-22T11:23:25.120" Score="2" Body="&lt;p&gt;Missing in this discussion is the fact that optimum power matching does not necessarily correspond with optimum noise matching.&lt;/p&gt;&#xA;&lt;p&gt;Antenna tuner alignment on band noise is possible when the input impedance of the receiver is 50 Ohms real. Then maximum received noise corresponds to correct antenna tuner alignment.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-01-22T11:23:25.120" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="17917" PostTypeId="2" ParentId="17889" CreationDate="2021-01-22T17:40:50.317" Score="2" Body="&lt;p&gt;ALC limits the the input power to the power amplifier (PA). Overdriving the PA would be bad: it might overheat, or exceed the voltage or current ratings of the components, eventually, or sometimes immediately, damaging the PA. Or it might just cause a lot of distortion and spurious emissions.&lt;/p&gt;&#xA;&lt;p&gt;If the radio has adjustable output power, often this controls the point at which ALC will begin to reduce the PA drive.&lt;/p&gt;&#xA;&lt;p&gt;Operating without ALC simply means controlling the PA drive by some other means, manually. With this comes the risk of inadvertently overdriving the PA, leading to damage or spurious emissions.&lt;/p&gt;&#xA;&lt;p&gt;There seems to be folklore around that claims &amp;quot;bad ALC&amp;quot; is responsible for &amp;quot;splatter&amp;quot; or transmitter power outside the intended channel. For example, &lt;a href=&quot;http://www.sherweng.com/ctu2012/NC0B-CU-2012-6a.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Transceiver Performance&#xA;10 Years of Change&lt;/a&gt; gives this example on page 27:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/bhd3J.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/bhd3J.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The claim seems to be that as the ALC responds to peaks and dips in the input power, it modulates the output power, effectively becoming an amplitude modulator. This modulation broadens the spectrum and is responsible for the out-of-band emissions.&lt;/p&gt;&#xA;&lt;p&gt;However, the data here do not prove that point. Notice the &amp;quot;ALC Half Scale&amp;quot; has about 7 dB more power in the intended channel. For every 1 dB increase in output power, &lt;a href=&quot;https://en.wikipedia.org/wiki/Intermodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;third order intermodulation products&lt;/a&gt; will increase by 3 dB. Now observe the spectral power at the point labeled &amp;quot;1.8 kHz away&amp;quot;: if these skirts are caused by intermodulation we'd expect a 21 dB difference (because that's 3 * 7 dB), and indeed that looks about right.&lt;/p&gt;&#xA;&lt;p&gt;All real amplifiers have some amount of intermodulation distortion, so this behavior is exactly what we'd expect of any real amplifier which is asked to produce 7 dB more output power. ALC has nothing to do with it: more output power means more distortion for any real amplifier.&lt;/p&gt;&#xA;&lt;p&gt;Here's an experiment to try: instead of increasing ALC by increasing the input power until the ALC meter reads half scale, &lt;em&gt;decrease&lt;/em&gt; the output power setting on the radio. This will cause ALC to reduce the PA drive, so there will be less output power, and thus less IMD. I think you'll see that when the test is performed this way, more ALC leads to less distortion, so it can't be true that ALC is causing the distortion.&lt;/p&gt;&#xA;&lt;p&gt;It's technically true that ALC could broaden the spectrum though amplitude modulation, it can't be broadened more than the bandwidth of the ALC control signal, which is typically quite low. Making it very high would distort the signal, not just broadening the spectrum but also rendering it unintelligible. While I'm sure somewhere, someone has managed to implement a really bad ALC which causes significant distortion, and it's also true splatter can be an observed problem with some stations, I haven't seen any evidence that it's specifically ALC causing splatter in practice.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-01-25T20:10:09.683" LastActivityDate="2021-01-25T20:10:09.683" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17918" PostTypeId="1" CreationDate="2021-01-22T20:43:46.587" Score="0" ViewCount="62" Body="&lt;p&gt;The idea was to send GPS data from the rocket to the ground station at 433 MHz using a Lo Ra transmitter - mainly to help locate it once it lands and also to provide in-flight telemetry.&lt;/p&gt;&#xA;&lt;p&gt;I have a similar transceiver on the ground - but lack an appropriate antenna design.&#xA;I have had it suggested that a Circular Polarised Antenna for the mobile ground station would beneficial, but I have no idea of what form this would take - either to buy or construct one from scratch.&lt;/p&gt;&#xA;" OwnerUserId="18619" LastActivityDate="2021-01-22T21:11:48.040" Title="I have a 433MHz LoRa Dipole antenna mounted on a rocket. I am looking for a suitable Antenna to receive data from this. Any Suggestions?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;circular-polarization&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17919" PostTypeId="2" ParentId="17918" CreationDate="2021-01-22T21:11:48.040" Score="3" Body="&lt;p&gt;You could, very quickly and cheaply, experiment with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Turnstile_antenna#Axial_mode&quot; rel=&quot;nofollow noreferrer&quot;&gt;turnstile antenna&lt;/a&gt;. Alternatively, checkout a &lt;a href=&quot;https://www.google.com/search?q=qfh%20antenna%2070cm&quot; rel=&quot;nofollow noreferrer&quot;&gt;QFH antenna&lt;/a&gt; which are also inexpensive to make, but require a little more skill.&lt;/p&gt;&#xA;&lt;p&gt;And there are plenty of other designs as well that you'll find with very little googling!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2021-01-22T21:11:48.040" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17920" PostTypeId="1" CreationDate="2021-01-22T21:44:11.203" Score="0" ViewCount="49" Body="&lt;p&gt;Some times ago I tried to decode the signal from a weather radiosonde (RS41) passing in my area using a cheap RTL SDR (using both standard antenna and a home-made one, with similar result).&lt;/p&gt;&#xA;&lt;p&gt;The recorded audio file is &lt;a href=&quot;https://www.wikiupload.com/28YY68SMX3AJ73S/&quot; rel=&quot;nofollow noreferrer&quot;&gt;this one&lt;/a&gt;, it's a bit noisy, but the transmission is clearly audible.&#xA;Using the &lt;a href=&quot;https://github.com/rs1729/RS&quot; rel=&quot;nofollow noreferrer&quot;&gt;RS&lt;/a&gt; software I wasn't able to decode any data, whereas it works perfectly with the example wav file that is in the same repository (after suggestions from &lt;a href=&quot;https://ham.stackexchange.com/questions/17729/open-source-rs41-decoder&quot;&gt;here&lt;/a&gt;).&lt;/p&gt;&#xA;&lt;p&gt;The command I used was like &lt;code&gt;sox wav/20140717_402MHz.wav -t wav - lowpass 2800 2&amp;gt;/dev/null | ./rs41ptu -i --crc -vx&lt;/code&gt;.&lt;/p&gt;&#xA;&lt;p&gt;I also tried reducing the noise using Audacity, but without any success.&lt;/p&gt;&#xA;&lt;p&gt;Is it a software or hardware/noise problem?&lt;/p&gt;&#xA;&lt;p&gt;Thanks and sorry if it is a trivial problem, but I'm a beginner and I wasn't able to solve that in any way.&lt;/p&gt;&#xA;" OwnerUserId="18258" LastActivityDate="2021-01-22T21:44:11.203" Title="RS41 weather balloon unable to decode data" Tags="&lt;software-defined-radio&gt;&lt;digital-modes&gt;&lt;software&gt;&lt;signal-identification&gt;&lt;weather&gt;" AnswerCount="0" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17922" PostTypeId="2" ParentId="17910" CreationDate="2021-01-23T19:00:41.387" Score="4" Body="&lt;p&gt;Receive power &lt;em&gt;does&lt;/em&gt; vary with SWR; but for reception quality we're interested in signal-to-noise ratio. As long as you're getting enough receive power that the noise received from the antenna is greater than the receiver's own noise floor, getting more power from the antenna won't result in any noticeable improvement to your ability to copy. That's why we say things like &amp;quot;gain doesn't matter for receive antennas&amp;quot; or &amp;quot;SWR doesn't matter for receive&amp;quot;. It's not an absolute truth, but it's a good starting point. For a typical HF noise floor, you need a lot of negative gain or a lot of mismatch loss before you'll notice any difference.&lt;/p&gt;&#xA;&lt;p&gt;So why can you tune an antenna by peaking the noise? Because, again, receive power &lt;em&gt;does&lt;/em&gt; vary, and because receiver AGC is (deliberately) imperfect, especially at low levels. So when you're just listening to noise, and turning the knobs on the tuner, the audio level &lt;em&gt;will&lt;/em&gt; go up and down — not by as many dB as the RF level goes up and down, but by enough to notice. If you do the same thing while tuned to a good signal, you might or might not notice the effect, but in any case after making any necessary volume adjustments to equalize the signal level, the noise level should end up the same as it was before.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-01-23T19:00:41.387" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17923" PostTypeId="1" CreationDate="2021-01-24T00:00:36.617" Score="3" ViewCount="119" Body="&lt;p&gt;I am using a simple Baofeng H6 dual band radio and I programmed weather channels.&#xA;Well, on frequency 161.77500 I am actually picking up WGN, a local tv network.&#xA;This frequency should be reserved to transmitting weather, no?&#xA;Why can I be picking a TV signal in this frequency?&lt;/p&gt;&#xA;" OwnerUserId="18626" LastEditorUserId="8717" LastEditDate="2021-01-25T22:17:27.770" LastActivityDate="2021-01-26T14:04:28.663" Title="Why am I receiving a local tv channel on a CMB frequency" Tags="&lt;receiver&gt;&lt;propagation&gt;&lt;vhf&gt;&lt;rfi&gt;&lt;baofeng&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17924" PostTypeId="2" ParentId="17923" CreationDate="2021-01-24T11:49:43.747" Score="0" Body="&lt;p&gt;Probably, not sure, WGN is very strong at your location. Tuned to 161.775 the oscillator of the Baofeng is 172.475 MHz. The third harmonic of the oscillator is 517.425. That results in a low sensitivity for unwanted signal at 506.725 (WGN frequency I assume) and 528.125, not of interest for now.&lt;/p&gt;&#xA;&lt;p&gt;I do not know that type radio, Baofeng H6, and single conversion with IF of 10.7 MHz is an assumption for lower-cost equipment.&lt;/p&gt;&#xA;&lt;p&gt;Added-  Jan 26  - My explanation is probably not correct. Baofeng makes use of a different frequency conversion system: one-step conversion to a low IF frequency, almost baseband. Measuring the spurious signal reception of Baofeng UV3R and UV5R I found many spots that can't be simply explained without taking into account RF distortion. In older documents this effect is also known as repeat-spots. I give up. I think the explanation here below makes more sens.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2021-01-26T14:04:28.663" LastActivityDate="2021-01-26T14:04:28.663" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17926" PostTypeId="1" AcceptedAnswerId="17927" CreationDate="2021-01-25T00:17:34.957" Score="1" ViewCount="81" Body="&lt;p&gt;I see that RT-Systems sells programming software and a cable so you can program the Alinco DR-635's internal memory via your laptop instead of through the Alinco's cryptic and hostile user interface. Has anybody tried this product? Is its user interface any better than that of the Alinco itself? I'd hate to pay $50 for this and find it just as buggy and poorly-documented as the Alinco.&lt;/p&gt;&#xA;&lt;p&gt;If I decide to give up on the Alinco and switch to a Yaesu 2-meter rig, which Yaesu's are CHIRP-programmable?&lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2021-01-27T16:31:07.917" Title="Alinco DR-635 programming software" Tags="&lt;yaesu&gt;&lt;alinco&gt;&lt;chirp&gt;&lt;144mhz&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17927" PostTypeId="2" ParentId="17926" CreationDate="2021-01-25T03:18:44.740" Score="2" Body="&lt;p&gt;I can't speak to how it compares to the Alinco software, but I've used the RT software for a few different radios and it's straightforward, if pricey.&lt;/p&gt;&#xA;&lt;p&gt;But $50 for the RT solution is probably cheaper than a new mobile/base rig, and if I were in your shoes it's the route I'd take.&lt;/p&gt;&#xA;&lt;p&gt;As for CHIRP compatibility for Yaesu radios, &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Supported_Radios&quot; rel=&quot;nofollow noreferrer&quot;&gt;check out the project's compatibility page&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Best of luck to you!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2021-01-27T16:31:07.917" LastActivityDate="2021-01-27T16:31:07.917" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17929" PostTypeId="2" ParentId="17926" CreationDate="2021-01-25T17:01:23.977" Score="1" Body="&lt;p&gt;I have a different model Alinco radio.  I presume that the &amp;quot;cryptic and hostile user interface&amp;quot; you speak of is not the front panel of the radio, but rather part of Alinco's programming software.&lt;/p&gt;&#xA;&lt;p&gt;I didn't want to pay for RT-Systems' expensive software and cable, so I persevered and figured out Alinco's software.  What helped a lot was programming a memory through the front panel of the radio, and then seeing how the software saw that memory slot.&lt;/p&gt;&#xA;&lt;p&gt;The list of radio models supported by CHIRP is right on their &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;home page&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-01-25T17:01:23.977" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17930" PostTypeId="2" ParentId="300" CreationDate="2021-01-25T22:20:00.333" Score="0" Body="&lt;p&gt;My new 50Watt transceiver requires a 12V 15A power source.  I've connected it to a bench power supply delivering 10A and that was not enough.  That said, connecting the transceiver to a cigarette plug is not suggested, as it is fused at 10A.&lt;/p&gt;&#xA;" OwnerUserId="18639" LastEditorUserId="1550" LastEditDate="2021-01-26T02:11:41.917" LastActivityDate="2021-01-26T02:11:41.917" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17931" PostTypeId="2" ParentId="17923" CreationDate="2021-01-26T02:28:58.477" Score="4" Body="&lt;p&gt;161.775 isn't a frequency reserved for weather broadcasts in the US, no. CMB is a Canadian service; the same allocation doesn't exist in the US. NOAA All Hazards Weather Radio stations are on channels from 162.400 to 162.550 MHz.&lt;/p&gt;&#xA;&lt;p&gt;According to &lt;a href=&quot;https://www.radioreference.com/apps/db/?aid=2820&quot; rel=&quot;nofollow noreferrer&quot;&gt;RadioReference&lt;/a&gt;, WGN-TV has an IFB channel at 161.74875 and a remote audio channel at 161.77250. These are channels that broadcasters use &amp;quot;in the back-end&amp;quot; for studio monitoring and for transmitting audio over short distances; they aren't part of the actual broadcast product, but anyone with a narrowband FM receiver capable of tuning those frequencies can listen in. You're probably hearing the latter one — a small tuning error doesn't affect an FM signal very much.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2021-01-26T05:24:28.397" LastActivityDate="2021-01-26T05:24:28.397" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17932" PostTypeId="1" AcceptedAnswerId="17937" CreationDate="2021-01-26T12:28:56.080" Score="2" ViewCount="85" Body="&lt;p&gt;I was reading on &lt;a href=&quot;https://en.wikipedia.org/wiki/Cable_television&quot; rel=&quot;nofollow noreferrer&quot;&gt;wikipedia&lt;/a&gt; this:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;the subscriber's television or a set-top box provided by the cable company translates the desired channel back to its original frequency (baseband)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;But when I checked the block diagram of the receiver it doesn't&#xA;talk about a baseband but (IF)&#xA;&lt;a href=&quot;http://www.brainkart.com/article/Monochrome-TV-receiver_3017/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.brainkart.com/article/Monochrome-TV-receiver_3017/&lt;/a&gt;&#xA;so what could the baseband here or what is the baseband of video streaming?&lt;/p&gt;&#xA;" OwnerUserId="18527" LastEditorUserId="5222" LastEditDate="2021-01-29T18:52:39.667" LastActivityDate="2021-01-29T21:47:08.423" Title="what is the baseband for CATV?" Tags="&lt;receiver&gt;&lt;satellites&gt;&lt;frequency&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17933" PostTypeId="1" CreationDate="2021-01-26T17:30:42.827" Score="4" ViewCount="290" Body="&lt;p&gt;Is spacing of parallel dipoles necessary.  Could they be banded together and then trimmed or is there some consideration, other than tuning, requiring separation.&lt;/p&gt;&#xA;&lt;p&gt;I was considering a fan dipole. I have seen one where 300 ohm twin lead was used for two dipoles and I believe a 2nd piece for another 2 dipoles, all fed from a single line. I haven't seen one of those in use but assuming it worked (it's in the antenna bk) the spacing is about 1/2&amp;quot;.&lt;/p&gt;&#xA;" OwnerUserId="18647" LastEditorUserId="4665" LastEditDate="2021-01-27T20:12:35.697" LastActivityDate="2021-04-17T10:10:26.740" Title="Is spacing of fan dipoles necessary?" Tags="&lt;antenna-construction&gt;&lt;parallel-dipole&gt;" AnswerCount="5" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="17934" PostTypeId="2" ParentId="17933" CreationDate="2021-01-26T19:05:27.677" Score="3" Body="&lt;p&gt;&lt;strong&gt;Spacing is &lt;em&gt;absolutely&lt;/em&gt; required between the antennas.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;You cannot bundle all the wires together. They must be spaced apart, or the interaction between them will be too great. You'll have a mostly useless &amp;quot;multiband&amp;quot; antenna.&lt;/p&gt;&#xA;&lt;p&gt;Some of these &lt;a href=&quot;https://ham.stackexchange.com/search?q=Fan+dipole+spac*+-loading+-noise&quot;&gt;search results&lt;/a&gt; indicate the need for spacing, as does &lt;a href=&quot;https://ham.stackexchange.com/questions/14415/3-band-80-40-20-meter-fan-dipole-tuning-question&quot;&gt;this question&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2021-01-26T19:18:08.760" LastActivityDate="2021-01-26T19:18:08.760" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17935" PostTypeId="2" ParentId="17933" CreationDate="2021-01-26T19:21:01.047" Score="2" Body="&lt;p&gt;You don't say if you're talking about several dipoles connected together into a single antenna, which is an arrangement usually called a &lt;a href=&quot;https://ham.stackexchange.com/questions/14415/3-band-80-40-20-meter-fan-dipole-tuning-question&quot;&gt;fan dipole&lt;/a&gt;, or several nearby dipole antennas that each have separate feed lines.&lt;/p&gt;&#xA;&lt;p&gt;If you consider a piece of metal up in the air near a transmitting antenna, it is not difficult to imagine that the metal absorbs some of the RF from the antenna, which induces currents in the metal, which cause the piece of metal to re-radiate RF at the same frequency.  The radiation pattern from the piece of metal interferes with the radiation pattern from the antenna, constructively in some directions (more gain) and destructively in others (less gain).  So if the piece of metal is close enough to the antenna to absorb a meaningful amount of energy from the antenna, then one can see that the radiation pattern and impedance of the antenna are affected.  That's how a &lt;a href=&quot;https://en.wikipedia.org/wiki/Yagi%E2%80%93Uda_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;yagi antenna&lt;/a&gt; works; a yagi is just a dipole (the &amp;quot;driven element&amp;quot;) with a few metal rods (&amp;quot;passive elements&amp;quot;) cleverly placed near it in a way that enhances gain in one direction.  The same principles work in reverse for receiving, so if an antenna has more gain when transmitting in a certain direction, then it typically will have more gain receiving from that direction also.  (There are exceptions.)&lt;/p&gt;&#xA;&lt;p&gt;So a fan dipole is a bunch of dipoles cut for different frequencies that are strung near each other, and connected at the middle.  (If you were to tightly band the dipoles together they would mostly act like a single dipole made with the longest wire, and not like a multi-band antenna.  The wires in a fan dipole are typically held some distance apart by spacers.)  Fan dipoles work, but if you were to build one by making several individual dipoles and then connecting them together, then you would find that the impedance and radiation pattern at one of the old resonant frequencies has changed quite a bit.  They typically need careful adjustment of the lengths of all the wires, and the spacing between the wires, to have low SWR at the right frequencies.  That's one of the main drawbacks of fan dipoles, that they need lots of careful tweaking to work well.&lt;/p&gt;&#xA;&lt;p&gt;If you were talking about several dipoles with individual feed lines near each other, then similar considerations apply.  The closer the antennas are together, the more they will interact with each other.  (I've heard several closely-spaced antennas described as &amp;quot;a single antenna with multiple feed ports&amp;quot;.)  The more they interact, the more the radiation patterns and impedances will change, and the more they will need to be tweaked to work well together.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-01-26T19:21:01.047" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17936" PostTypeId="2" ParentId="17932" CreationDate="2021-01-26T21:17:02.110" Score="0" Body="&lt;p&gt;I think that Wikipedia article fragment that you quoted is misleading or incorrect, but I'm not an electrical engineer and I've never designed a cable TV box.  The article implies that the cable TV box plugged into the customer's television translates the frequency back to the original frequency that was used before the signal for that channel was multiplexed with the signals for the many other channels.&lt;/p&gt;&#xA;&lt;p&gt;I think that your intuition is correct.  I don't see any reason that the customer's cable TV box should translate the signal back to whatever frequency was used as an intermediate frequency in the transmitting equipment.  It's far more likely that the customer's cable TV box translates the frequency of the signal to an intermediate frequency that is convenient for the downstream electronic components that further process the signal and send it to the customer's television.&lt;/p&gt;&#xA;&lt;p&gt;Of course it is possible that the IF used in the receiver is the same frequency in the IF used in the transmitting equipment, either because of coincidence or because that frequency is commonly used as an IF by the television industry.  But the IF of the receiver was surely chosen by the engineers who designed the receiver, and not by the engineers who designed the transmitting equipment.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-01-26T21:17:02.110" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17937" PostTypeId="2" ParentId="17932" CreationDate="2021-01-26T22:06:53.333" Score="5" Body="&lt;p&gt;Baseband video is the DC to about 6 MHz signal that encodes the brightness channel, and sync. If it includes colour too then it's called &lt;a href=&quot;https://en.m.wikipedia.org/wiki/Composite_video&quot; rel=&quot;nofollow noreferrer&quot;&gt;Composite video&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Brightness and sync are truly baseband, a specific voltage range represents the black to white brightness over time as the beam scans the display, with sync represented by pulses to a different voltage. Colour is actually modulated onto a carrier, even at 'baseband'.&lt;/p&gt;&#xA;&lt;p&gt;In the diagram you quote, the baseband is effectively the signal just after the detector block. In a receiver+display there's no need to generate a standards-compliant video signal.&lt;/p&gt;&#xA;&lt;p&gt;IF, as you correctly surmise, contains the baseband video but modulated to some intermediate, frequency, perhaps about 50 MHz, suitable for further filtering and amplification before detection. It is solely a choice of the receiver designer, and is invisible from the outside. The receiver you're thinking of, takes in RF and produces baseband video.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-01-26T23:38:21.130" LastActivityDate="2021-01-26T23:38:21.130" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17938" PostTypeId="1" CreationDate="2021-01-27T11:23:46.503" Score="0" ViewCount="30" Body="&lt;p&gt;I'm looking for help with one exercise. Firstly I was supposed to download modulated signal. (It's Olivia 16-FSK)&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;[y,fs] = audioread('Olivia16-500.wav');&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;And then I have to recover bits that&#xA;are coded by different frequency values. How can I do that?&lt;/p&gt;&#xA;&lt;p&gt;I used FSKDemodulator to display bits but I'm not sure if the output is correct&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;fc=6; %default&#xA;M=16;&#xA;fskdemod=comm.FSKDemodulator(M, fc, 'SamplesPerSymbol', 4, 'BitOutput', true); &#xA;x=fskdemod(y);&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VMdeL.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VMdeL.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;And there is fragment&#xA;&lt;a href=&quot;https://i.stack.imgur.com/6H2F1.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6H2F1.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18655" LastActivityDate="2021-01-27T11:23:46.503" Title="16-FSK recovering bits" Tags="&lt;modes&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17940" PostTypeId="1" CreationDate="2021-01-27T23:15:00.807" Score="0" ViewCount="82" Body="&lt;p&gt;I have a bftech bf-f8rt and they dont show that radio on chirp will they update chirp for that radio? Is there another place like chirp to program it or do i have to do it manual&lt;/p&gt;&#xA;" OwnerUserId="18663" LastActivityDate="2021-01-28T18:30:21.350" Title="cant get my bftech radio to program with chirp software" Tags="&lt;radio-programming&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17941" PostTypeId="1" AcceptedAnswerId="17948" CreationDate="2021-01-28T15:56:54.233" Score="1" ViewCount="259" Body="&lt;p&gt;Ok so I am in the USA, and I have just bought a BFTECH BF-F5XP. I have a couple of questions. First of all, could I make my own Privacy code (Interference prevention code), and channels? What I am basically asking, is can I alter my radio, into a talkie and communicate with another BFTECH radio without getting in trouble with the feds? I bought a 35 dollar radio and dont really feel like buying a 70 dollar license so im trying to make the best of it. I do not intend to go on a public channel and chat with random people, but I have seen how Public Saftey have created channels where one or more people can go on and communiate, and I kind of want to just do that, So can I alter/use my BFTECH as a communications radio?&lt;/p&gt;&#xA;" OwnerDisplayName="user18671" LastEditorUserId="4665" LastEditDate="2021-01-28T20:02:32.747" LastActivityDate="2021-01-31T17:03:41.423" Title="Will the feds show up to my door? Is there a way to not get in trouble?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="4" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17942" PostTypeId="2" ParentId="17940" CreationDate="2021-01-28T16:02:08.637" Score="0" Body="&lt;p&gt;Ok so yes I have seen this problem alot, Its a very complicated process, but it can be done. Just about any Baofeng radio can be programmed with chirp software, but its just a matter of figuring it out. When a friend had previously encountered this problem, I showed him this website down below, and it helped him out.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://chirp.danplanet.com/projects/chirp/wiki/Home&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Hope this eased some stress.&lt;/p&gt;&#xA;" OwnerDisplayName="user18671" LastActivityDate="2021-01-28T16:02:08.637" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17944" PostTypeId="2" ParentId="17941" CreationDate="2021-01-28T17:02:14.790" Score="8" Body="&lt;p&gt;The good news is that the license you'll need for that particular radio is an amateur radio license which is only a $35 application fee. You will need to pass an exam before you can apply.&lt;/p&gt;&#xA;&lt;p&gt;As far as I'm aware, to operate that radio without violating FCC regs, you will have to have a license. Also, as Zeiss notes in the comment below, there's no practical way to alter this radio to encrypt communications, though using a PL tone is probably what you mean.&lt;/p&gt;&#xA;&lt;p&gt;If you'd like a no-license option, I'd suggest returning this one and finding a cheap FRS walkie talkie to do the same thing on appropriate frequencies.&lt;/p&gt;&#xA;&lt;p&gt;Following up on &amp;quot;private code/private channels&amp;quot; they don't exist. The tones and codes are implemented to prevent you from hearing others who don't transmit the tone/code... they cannot prevent others from hearing you.&lt;/p&gt;&#xA;&lt;p&gt;If the FCC takes an interest in your unlicensed activity with this radio, yes they could issue a warning, a fine, and/or confiscate your equipment. I won't speculate on the likelyhood of this, rather I'd suggest you shouldn't.&lt;/p&gt;&#xA;&lt;p&gt;Best of luck to you!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2021-01-28T20:59:16.840" LastActivityDate="2021-01-28T20:59:16.840" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="17945" PostTypeId="2" ParentId="17940" CreationDate="2021-01-28T18:30:21.350" Score="1" Body="&lt;p&gt;Baofeng's &lt;a href=&quot;https://baofengtech.us/index.php/product/bf-f8rt-2-pcs/&quot; rel=&quot;nofollow noreferrer&quot;&gt;web page for the BFTECH BF-F8RT&lt;/a&gt; says &amp;quot;You can use Chirp to program the BF-F8RT radio. Please select the Baofeng UV-5X model and program it.&amp;quot;  So I'd think that CHIRP is the way to go.&lt;/p&gt;&#xA;&lt;p&gt;However, &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Home&quot; rel=&quot;nofollow noreferrer&quot;&gt;CHIRP's home page&lt;/a&gt; says nothing about the BF-F8RT.  Usually the volunteers who update the CHIRP software and its web page are good about listing every model that has been successfully tested with CHIRP, even if the solution is just to use the setting for a different radio model, as often happens.  Also there is no such thing as a Baofeng &amp;quot;UV-5X&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Aha, there is a link next to the listing for the Baofeng UV-5R on the CHIRP home page, for a page specifically about &lt;a href=&quot;https://chirp.danplanet.com/projects/chirp/wiki/Baofeng_UV5R_Variants&quot; rel=&quot;nofollow noreferrer&quot;&gt;UV-5R variants&lt;/a&gt;.  The UV-5R and its many variants are probably the HT model in most common use worldwide.  That page says,&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The Baofeng UV-5R is the basis for many other models. Any vendor that&#xA;purchases a large quantity of radios can have a private label (and in&#xA;some cases, firmware version) applied to the radio. There is, in most&#xA;cases, almost no actual difference between the variants, which is very&#xA;confusing for customers.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The page goes on to list &amp;quot;BF-F8/BF-F8+&amp;quot; as a known UV-5R variant.&lt;/p&gt;&#xA;&lt;p&gt;So the information is incomplete and confusing.  You could always ask the question on the CHIRP mailing list, which is followed by many people who are better-informed such things than I am.&lt;/p&gt;&#xA;&lt;p&gt;If someone gave me a BF-F8RT, I would try using CHIRP with the UV-5R setting.  If you try it there's a small chance that you'll &amp;quot;brick&amp;quot; the radio (i.e. break the radio permanently and make it only useful as a paper weight or door stop, like a brick), but if the software really doesn't support your radio then most likely you would just get an error message.&lt;/p&gt;&#xA;&lt;p&gt;If you do try it, please come back here and let us know what your results were.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-01-28T18:30:21.350" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17947" PostTypeId="1" AcceptedAnswerId="17950" CreationDate="2021-01-29T06:13:56.873" Score="4" ViewCount="96" Body="&lt;p&gt;Newbie here, with a 2 meter mobile rig and a magnet-mount antenna. I am currently routing the coax out an almost-closed window and am tired of having rain water enter the car through it. Is there such a thing as a commercially available feed-thru kit that can be attached to the roof of my vehicle, through which I can route my coax? Ideally I would want to send both my 2M and 10M coax through the roof to separate antennas.&lt;/p&gt;&#xA;" OwnerUserId="10598" LastEditorUserId="8717" LastEditDate="2021-01-29T13:51:32.110" LastActivityDate="2021-02-02T15:11:06.677" Title="antenna coax feed-thru for a car roof" Tags="&lt;antenna&gt;&lt;mobile&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17948" PostTypeId="2" ParentId="17941" CreationDate="2021-01-29T09:20:56.013" Score="3" Body="&lt;p&gt;If you're looking for a secure but legal communications channel where you can do whatever you want but don't feel like spending more than 35 dollars, I'm afraid you will have a hard time finding a good solution.&lt;/p&gt;&#xA;&lt;p&gt;Modifying the radio will render it incompatible with the regulations that it needs to conform to, so don't attempt doing that if you want to remain within the law.&lt;/p&gt;&#xA;&lt;p&gt;If,however, you're interested in learning more about these &amp;quot;codes&amp;quot; and how the radio works, welcome to amateur radio ;).&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2021-01-29T09:20:56.013" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17949" PostTypeId="2" ParentId="11750" CreationDate="2021-01-29T09:47:50.037" Score="1" Body="&lt;p&gt;I have an Icom IC-T81A that will transmit and receive on 6 meters.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.universal-radio.com/catalog/ht/3795.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.universal-radio.com/catalog/ht/3795.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Or at least it did at one time.  I haven't used that feature in a long time and my IC-T81A has seen better days.  I haven't even powered it up in quite some time.&lt;/p&gt;&#xA;" OwnerUserId="16392" LastActivityDate="2021-01-29T09:47:50.037" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17950" PostTypeId="2" ParentId="17947" CreationDate="2021-01-29T12:37:47.103" Score="3" Body="&lt;p&gt;The &lt;em&gt;Hints and Hacks&lt;/em&gt; column on page 30 of the July 2020 edition of ARRL's &lt;em&gt;On the Air&lt;/em&gt; magazine carries an item titled, &amp;quot;Mounting an Antenna to the Body of Your Car.&amp;quot; The author explains the process:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Use a &lt;a href=&quot;https://www.lairdconnect.com/rf-antennas/antenna-accessories/holesaw-lmr-accessories&quot; rel=&quot;nofollow noreferrer&quot;&gt;specialized hole saw&lt;/a&gt; to make the opening in your car's body - carefully avoiding critical physical, electrical and hydraulic obstacles&lt;/li&gt;&#xA;&lt;li&gt;Rust-proof the edges of the opening with an appropriate paint - ask your local dealer, garage, auto parts store or body shop for recommendations&lt;/li&gt;&#xA;&lt;li&gt;Place the &lt;a href=&quot;https://www.lairdconnect.com/documentation/ant-ds-mounts-0420&quot; rel=&quot;nofollow noreferrer&quot;&gt;mount of your choice&lt;/a&gt;, per the manufacturer's instructions, tightening against the supplied O-ring to seal the opening without distorting the opening or the mount&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;(I have no affiliation with Laird Connectivity. Pointing to the resources on their web site was the easiest way to provide the basic information needed to answer the question.)&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-01-31T07:35:51.877" LastActivityDate="2021-01-31T07:35:51.877" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17952" PostTypeId="2" ParentId="17932" CreationDate="2021-01-29T21:47:08.423" Score="0" Body="&lt;p&gt;The TV receiver reference you cite is for an (ancient) analog television. Since the migration from the analog &lt;a href=&quot;https://en.wikipedia.org/wiki/NTSC&quot; rel=&quot;nofollow noreferrer&quot;&gt;NTSC&lt;/a&gt; to the digital &lt;a href=&quot;https://en.wikipedia.org/wiki/ATSC_standards&quot; rel=&quot;nofollow noreferrer&quot;&gt;ATSC&lt;/a&gt; standard for high-definition content, much has changed.&lt;/p&gt;&#xA;&lt;p&gt;As you see in this diagram showing the connections to a modern cable TV set-top box, the RF signal coming from the service provider is converted into a wide range of signals to support connection to not only an HDTV monitor but also to A/V receivers, digital video recorders, etc.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/HvDFY.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HvDFY.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;baseband&amp;quot; signal to which your ancient reference points is the &amp;quot;composite video&amp;quot; signal number 8 above. But, since the &amp;quot;Cable In&amp;quot; signal from the service provider is digital, the composite video signal must be separately produced from the digital information, not simply translated in frequency from the input. Note that this baseband signal is modulated onto Ch 3/4 to produce the &amp;quot;RF Out&amp;quot; signal 2 in the diagram.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-01-29T21:47:08.423" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17953" PostTypeId="1" AcceptedAnswerId="17955" CreationDate="2021-01-29T22:08:51.173" Score="5" ViewCount="641" Body="&lt;p&gt;It's my understanding that active superhet receivers can be detected by looking for the emissions from the local oscillator, particularly because the LO's frequency is usually set at some fixed offset from the carrier.&lt;/p&gt;&#xA;&lt;p&gt;Is a similar technique applicable to software-defined radios, especially if the LO is set exactly at the carrier frequency? Are there SDRs that don't have an RF LO at all to be detected?&lt;/p&gt;&#xA;" OwnerUserId="17659" LastActivityDate="2021-02-04T19:41:05.467" Title="Can SDR receivers be detected remotely?" Tags="&lt;software-defined-radio&gt;&lt;oscillator&gt;&lt;superheterodyne&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17955" PostTypeId="2" ParentId="17953" CreationDate="2021-01-30T03:28:55.337" Score="12" Body="&lt;p&gt;You might be able to detect a &lt;em&gt;regenerative&lt;/em&gt; receiver. This is because this receiver topology uses positive feedback to increase the Q of the tuned circuit. If the feedback is too much it becomes an oscillator which transmits quite conspicuously.&lt;/p&gt;&#xA;&lt;p&gt;Detecting just any huperhet receiver is a different matter. The coupling between the LO and the antenna is not deliberate as it is in a regenerative receiver.&lt;/p&gt;&#xA;&lt;p&gt;That's not to say there aren't detectable emissions. &lt;em&gt;Anything&lt;/em&gt; with an oscillator could be detected. That includes all digital electronics, and every switch mode power supply. In fact looking around me now the only electronic device I see which does not have an oscillator in it is a fish tank heater.&lt;/p&gt;&#xA;&lt;p&gt;All these oscillators are detectable, if you know well enough what you're looking for and have enough resources. But detecting the emissions from a superhet receiver among all the noise of everything else with an oscillator in it is a challenge, to say the least.&lt;/p&gt;&#xA;&lt;p&gt;If anything, SDRs are easier to detect. Some SDRs have at least one mixer which would have an LO. Some are direct sampling, meaning they ADC runs at such a high rate it doesn't need to down-convert the signal before sampling it. But all SDRs have an ADC, and an ADC requires a clock, which is another oscillator. Whatever is processing the digital data will undoubtedly have another clock and a plethora of other noisemakers.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-01-30T03:28:55.337" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17959" PostTypeId="2" ParentId="17941" CreationDate="2021-01-30T20:32:35.613" Score="4" Body="&lt;p&gt;I'll post this as a separate answer since it isn't meant as a thorough technical answer. I haven't thoroughly researched everything below and I figure one of the mods might decide to remove it. However... It seems to me that you don't have a clear understanding of the different radio &amp;quot;systems&amp;quot; (for lack of a better word that comes to mind now), so some of the above comments might be rather confusing. Hope this does help a bit in demystifying...&lt;/p&gt;&#xA;&lt;p&gt;To be clear, I don't know the exact details of your radio, neither do I know the exact ins and outs of the American regulations. However, the general principles are mostly similar everywhere.&lt;/p&gt;&#xA;&lt;p&gt;There is only a limited amount of spectrum (a range of frequencies) that can be used for practical radio communications. There are international agreements on which frequencies (or rather, ranges of frequencies) can be used for which applications, with what kind of equipment, what power, which modes (voice, data, ...) and so on. Local authorities might follow the general agreements or have their own version of it. In any case, there are rules for who can use which frequencies to do what with what kind of gear and with what kind of power (and plenty of other rules). Local bodies govern those rules. I believe the FCC is in charge of that in the US. They are also the people that should make sure no one broadcasts where (spectrum-wise) he shouldn't. This also includes broadcasting noise by using equipment that isn't properly shielded/manufactured/filtered or just broken.&lt;/p&gt;&#xA;&lt;p&gt;As an example, if you're still using analog television (or radio) over the air, imagine your tv signal dropping out from time to time because someone in the neighourhood has equipment that doesn't function properly or isn't even allowed (but &amp;quot;it was cheap and who is going to find me, so I'll do whatever...&amp;quot;), that is what we're trying to prevent.&lt;/p&gt;&#xA;&lt;p&gt;As with most limited things, prices go up. Frequency spectrum is no different. Mobile (cellular) carriers pay incredible amounts of money to license certain frequencies in certain areas. Still, there are some frequency ranges that are free to use, within strict constraints. One example is PMR (which we use in Europe). That is a range that &amp;quot;everyone&amp;quot; is free to use, if the equipment has the appropriate limitations (500mW power, fixed antenna, ...) and type approvals (!). These PMR radios are the kind of two-way radio's that are cheap to get and work for a few kilometers (in open terrain) without requiring a license. However, these same radio's can't be used in the US, since the frequencies used for PMR are in use for other purposes in the States. You have FRS radios which I believe are largely similar but work on other frequencies.&lt;/p&gt;&#xA;&lt;p&gt;These types of radios (which I think is what you're after) only work on a couple of channels (frequencies) and if there are other people in your area using these radios as well, you might find them using the same channel as you're on. Your radio would let you hear their communications because your receiver just looks at what level and modulation of signal gets received on the frequency you're listening to. This is where the codes you talk about come in. Manufacturers have devised a system where you can select a certain tone that you can't hear but gets sent with every broadcast you make. If someone else programs their radio on the same frequency as yours and selects the tone you agreed on, their radio will only make sound if it &amp;quot;hears&amp;quot; a broadcast accompanied with the same tone. This way, you have somewhat less reception of other peoples communication and possibly a -false- sense of security. It might seem like your signal is encoded or somehow &amp;quot;protected&amp;quot; but it really isn't. Disable the tone selection on your receiving radio (which is most often the default setting) so that it receives all communication on that channel, and you hear all communication again. There's no encryption, only a basic sense of identification. There might be (or have been) some scrambling options that allow you to scramble your audio, but as far as I know this isn't allowed on these frequencies. I hope that demistifies the &amp;quot;codes&amp;quot; a bit.&lt;/p&gt;&#xA;&lt;p&gt;Then there's the type of radio. As mentioned above, certain frequencies require certain types of approvals on the transmitters that are used. To use a device for these FRS/PMR frequencies, it needs to perform within certain specifications and needs to be tested and approved against them. I have an amateur radio license and a portable radio that I can program to use the PMR frequencies and use less than 500mW. Still, the radio isn't type approved for use as a PMR radio, so I can't (legally) use it as such. Your radio can likely be used for a lot of different types of communication, but that doesn't mean that you can legally do so. I think a lot of the initial succes of the Baofeng kind of radios is that they were dirt cheap and could be used for lots of different applications. People seemed to think that since this radio was sold and could do thing X, it must be legal to do thing X with it. Except for amateur radio and (most) receiving applications, that isn't the case.&lt;/p&gt;&#xA;&lt;p&gt;So...&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;If you're looking for a reasonably cheap way of doing short distance communication without getting a license or be bothered with learning about radio, I'd get one of these (approved) FRS radios.&lt;/li&gt;&#xA;&lt;li&gt;If you have a technical interest in radio and wish to know more, either contact a local radio club, the ARRL, find some in your area or just study up for one of the exams. It's really not that difficult or pricey to get started if you look around. There are plenty of bargains if you look around and are willing to settle on a slightly older model of handheld. You'll (likely) spent more than what you paid on your radio but you'll have much more you can do with it. I've given radio's that I repaired or simply had no use for to new radio amateurs, you might even find a radio for free.&lt;/li&gt;&#xA;&lt;li&gt;If you're not sure where you want to go, stay around here and ask questions. There are plenty of people on here that are more than willing to help. There are a lot of great/cool things you can do with amateur radio. I really like the theory and the idea that I can use an old handheld and existing satellites to communicate (for free, except for my yearly license fee) with other hams. That's just one example of what people do...&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2021-01-30T20:32:35.613" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17963" PostTypeId="1" AcceptedAnswerId="17964" CreationDate="2021-01-31T00:41:59.737" Score="-4" ViewCount="107" Body="&lt;p&gt;Ok so lets say we have communications tower number 1 and comms tower number 2, if one were to get wiped out by a power surge, could the other sustain connection to the area?&lt;/p&gt;&#xA;" OwnerUserId="18685" LastActivityDate="2021-01-31T01:38:45.757" Title="Power, Tower, and connection" Tags="&lt;tower&gt;&lt;radio-control&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2021-01-31T15:02:52.557" ContentLicense="CC BY-SA 4.0" />
  <row Id="17964" PostTypeId="2" ParentId="17963" CreationDate="2021-01-31T00:55:04.803" Score="-2" Body="&lt;p&gt;It depends, If both towers are in the same place or the one tower that doesnt get cut out can reach past the other ones bounties, then yes it is possible. That is a very good question by the way.&lt;/p&gt;&#xA;" OwnerDisplayName="user18671" LastActivityDate="2021-01-31T00:55:04.803" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17972" PostTypeId="2" ParentId="17947" CreationDate="2021-01-31T02:05:48.313" Score="0" Body="&lt;p&gt;Now you could buy a kit, or you could buy a water shield (Window roof) to put over your windows so rainwater wouldnt go in the car. This is just a suggestion. Do as YOU please.&lt;/p&gt;&#xA;" OwnerUserId="18685" LastActivityDate="2021-01-31T02:05:48.313" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17973" PostTypeId="2" ParentId="17941" CreationDate="2021-01-31T02:14:39.247" Score="-1" Body="&lt;p&gt;Ok so my idea, Just dont transmit... if you think its illegal, then dont do it. You can ask us, we will be glad to answer your questions, but just enough about it.&lt;/p&gt;&#xA;" OwnerUserId="18685" LastActivityDate="2021-01-31T02:14:39.247" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17986" PostTypeId="1" CreationDate="2021-01-31T18:10:37.620" Score="4" ViewCount="95" Body="&lt;p&gt;I've noticed that increasing load on magloop reduces it's Q-factor, it becomes less selective.&#xA;Traditional way to approach this is reducing size of pickup loop, or alternatively, using transformer.&lt;/p&gt;&#xA;&lt;p&gt;But is it possible/known approach to build FET high-Z preamp, which is connected to pickup loop?&#xA;Being high-Z it should allow to reach maximum possible selectivity for magloop, as only minimal current will flow due to capacitance of the gate. One might even make it resonant.&lt;/p&gt;&#xA;&lt;p&gt;I understand that high-Z would not be impedance-matched to 50-Ohm, but in this case it's not the goal. Goal is to let main loop oscillate with high-Q. This will increase field strength, and might allow good reception even with mismatched pickup loop.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Magloop example:&lt;/strong&gt; This one is from KR1ST, but mine is similar. Depending on size of the small, low-Z coupling loop - looses in main loop increase and it becomes less selective.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/VP3zI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VP3zI.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="546" LastEditorUserId="546" LastEditDate="2021-02-02T14:52:53.003" LastActivityDate="2021-02-02T16:10:06.320" Title="High-Z RF amplifier for magloop RX vs Q-factor" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;amplifier&gt;&lt;magnetic-loop&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="17987" PostTypeId="1" CreationDate="2021-01-31T18:27:54.163" Score="5" ViewCount="162" Body="&lt;p&gt;I just recently acquired a slightly functional Icom IC-735 HF radio, and am trying to resurrect it.&lt;/p&gt;&#xA;&lt;p&gt;The service manual outlines procedures that specify the use of an RF Voltmeter, which I do not own. I do have a Tektronix 2236 dual channel 100MHz analog scope. Is there any reason I cannot use the scope to obtain the Voltage measurements (at least, the ones that don't approach the BW limit of the scope)?&lt;/p&gt;&#xA;" OwnerDisplayName="user14945" LastEditorUserId="76" LastEditDate="2021-01-31T18:43:39.343" LastActivityDate="2021-02-01T22:21:57.733" Title="Can an oscilloscope be used as an RF voltmeter?" Tags="&lt;measurement&gt;&lt;testing&gt;&lt;repair&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17988" PostTypeId="2" ParentId="17987" CreationDate="2021-01-31T21:56:08.300" Score="4" Body="&lt;p&gt;One of the functions of an oscilloscope is actually to measure RF volts, just make sure to use the x 10 function to minimize loading on the circuit you are measuring, and keep in mind that some high impedance circuits will still be affected even if you use the x 10 function.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2021-01-31T21:56:08.300" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17989" PostTypeId="2" ParentId="17986" CreationDate="2021-01-31T23:57:39.287" Score="4" Body="&lt;p&gt;Certainly it is possible to build a high-impedance amplifier. If you resonate the loop with a parallel capacitor (which perhaps includes the input capacitance of the amplifier), you've made a &lt;a href=&quot;https://en.wikipedia.org/wiki/LC_circuit#Parallel_circuit&quot; rel=&quot;nofollow noreferrer&quot;&gt;parallel LC circuit&lt;/a&gt; which at resonance has minimum current and maximum voltage. A high-impedance amplifier is what you'd want to best extract that signal.&lt;/p&gt;&#xA;&lt;p&gt;But if your objective is to use the loop on a wide frequency range without retuning, this is the opposite of what you want. Instead, you want a low-impedance amplifier, the lower the better. You can think of the loop as a current source by Faraday's law of induction. The lower the input impedance of the amplifier, less impedance to this current. &lt;a href=&quot;https://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;LZ1AQ has an example of such an amplifier&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xhCvd.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xhCvd.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;In this design there is a passive filter at the input to attenuate the AM broadcast band and avoid overloading the amplifier. The low input impedance is achieved through the &lt;a href=&quot;https://en.wikipedia.org/wiki/Common_base&quot; rel=&quot;nofollow noreferrer&quot;&gt;common-base&lt;/a&gt; Q3 and Q4, then Q1 and Q2 further buffer the signal and are designed to drive a twisted pair.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-01-31T23:57:39.287" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="17990" PostTypeId="1" AcceptedAnswerId="17993" CreationDate="2021-02-01T00:24:03.750" Score="3" ViewCount="26" Body="&lt;p&gt;Newbie here with a question:&lt;/p&gt;&#xA;&lt;p&gt;I have programmed my Alinco DR-635T for use with a variety of local repeaters. Half of these are opened with CTCSS codes and the rest with DCS codes. When monitoring any of the CTCSS repeater frequencies, the Tx/Rx diode lights up and shows Rx and I can hear static, repeater traffic and repeater ID transmissions. When I key my transmitter, the diode lights up for Tx and I can hit the repeaters and hear the repeater squelch closure after I stop transmitting, so all is OK with talking to the CTCSS repeaters and hearing their responses.&lt;/p&gt;&#xA;&lt;p&gt;But when I am tuned to any of the DCS repeater frequencies (all in the same Peak Radio Service Oregon network, all using the same DCS code 023, which is set on my 635) the following things happen:&lt;/p&gt;&#xA;&lt;p&gt;The Tx/Rx indicator diode goes OUT and the audio is silenced (no static with the squelch setting wide open). The S-meter jumps around and pops up to +9 when someone else opens the repeater but at no time does the squelch on my radio open, nor does the Rx diode light up.&lt;/p&gt;&#xA;&lt;p&gt;When I key transmit, the Tx diode lights up and when I watch the S-meter, I can see it hold at +9 for one second after I switch to Rx, indicating that I did hit the repeater and it then gave me the normal squelch closure tail, but then there is no audio and the Rx light never comes on. Then I watch the S-meter jump up to +9, indicating that someone out there heard my transmission through the repeater and is trying to answer, but the Rx diode stays dark and there is no audio- while the S-meter is at +9. Then they sign off, the S-meter drops down- and the Rx diode stays out and the audio stays off.&lt;/p&gt;&#xA;&lt;p&gt;It is as if the 635's squelch is always closed when I am in DCS mode, and here is the puzzle: I successfully programmed the radio over a year ago and it worked properly on both CTCSS and DCS repeaters, but I did not use it again until just now. Did the radio's memory fail while it sat idle? If so, how could it remember everything else except opening the Rx squelch while monitoring a DCS repeater frequency? Please help! I am new to this business and do not know what to do.&lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2021-02-01T05:27:44.993" Title="alinco dr-635T receive squelch will not open in DCS mode" Tags="&lt;tone-squelch&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17991" PostTypeId="2" ParentId="17987" CreationDate="2021-02-01T01:51:52.153" Score="3" Body="&lt;p&gt;Maybe.&lt;/p&gt;&#xA;&lt;p&gt;If measuring a circuit output that expects a load impedance, such as a 50 Ohm coax or antenna, then to measure the RF voltage at that point with an oscilloscope, you should terminate that circuit output with the expected impedance (a dummy load), and measure the voltage waveform across that impedance load with a much higher impedance probe (x10 or x100 or resistor divider).&lt;/p&gt;&#xA;&lt;p&gt;Also make sure the peak voltages and currents are well within the specified limits for your scope input.  If you exceed the power input limits, then you may end up with smoke instead of a RF voltage measurement.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-02-01T22:21:57.733" LastActivityDate="2021-02-01T22:21:57.733" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="17992" PostTypeId="2" ParentId="16068" CreationDate="2021-02-01T04:45:55.910" Score="3" Body="&lt;p&gt;My personal experience: Baofeng UV-5R, works fine with stock rubber ducky antenna. Made a simple quarter-wave dipole antenna, connected to my radio with about 10 feet of cable. It transmitted much better than stock antenna. However, there was a problem with reception. The radio would receive the first transmission, and but would not re-open the squelch until I pressed the [EXIT] key. If I didn't press the [EXIT] key the radio remained silent, no matter the squelch setting, whether 0 through 9. When I pressed the [EXIT] key I immediately began receiving the contact's transmission.&lt;/p&gt;&#xA;&lt;p&gt;I concluded that the radio was too near the antenna. I connected a 25-foot cable between the radio and the quarter-wave dipole antenna, and transmission and reception worked normally.&lt;/p&gt;&#xA;" OwnerUserId="17616" LastActivityDate="2021-02-01T04:45:55.910" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17993" PostTypeId="2" ParentId="17990" CreationDate="2021-02-01T05:27:44.993" Score="1" Body="&lt;p&gt;I too have an Alinco radio with a channel set for a Peak Radio Association repeater, which uses the same CDCSS (DCS) code.  I just tried, and I was able to key up my local PRA repeater and hear its call sign back.&lt;/p&gt;&#xA;&lt;p&gt;My radio is not yet supported by CHIRP, so I had to use the Alinco software to program the radio.  For that channel I have encode set to &lt;code&gt;D023N&lt;/code&gt; (that's how the software shows it), which I interpret to mean &amp;quot;digital code 023 normal&amp;quot;, as opposed to &lt;code&gt;D023I&lt;/code&gt;, which would be &amp;quot;digital code 023 inverse&amp;quot;.  Decode is set to &lt;code&gt;None&lt;/code&gt; for that channel.&lt;/p&gt;&#xA;&lt;p&gt;Perhaps you have decode set to something other than &lt;code&gt;None&lt;/code&gt; for that channel in your radio, which I'd think would be incorrect.  As I understand, most repeaters don't encode their output, so if you were to have decode set to something other than &lt;code&gt;None&lt;/code&gt; for a repeater, then you wouldn't hear any of the repeater's output.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-02-01T05:27:44.993" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17994" PostTypeId="2" ParentId="17986" CreationDate="2021-02-01T09:21:19.607" Score="2" Body="&lt;p&gt;If you prefer to purchase rather than build your own, high-input impedance preamps from &lt;a href=&quot;https://www.hizantennas.com/high_impedance_amps.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hi-Z Antennas&lt;/a&gt; sold by &lt;a href=&quot;https://www.dxengineering.com/search?keyword=hi-z&amp;amp;SortBy=BestKeywordMatch&amp;amp;SortOrder=Ascending&quot; rel=&quot;nofollow noreferrer&quot;&gt;DX Engineering&lt;/a&gt; may work for you. Because they are often used to drive multi-element phased array systems at long wavelengths, they are designed to work with inexpensive 75-ohm coax, but should work fine with 50-ohm cable in your application.&lt;/p&gt;&#xA;&lt;p&gt;Two bullet points from the manual may be important considerations for use with a small receiving loop:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The amplifier input Resistance is approximately 54KOhms in parallel with 12 Picofarads&lt;/li&gt;&#xA;&lt;li&gt;The Antenna Ground input terminal is AC coupled to eliminate any ground related DC current&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Many other features that you might value. I have no affiliation with Hi-Z Antennas or with DX Engineering.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-01T09:21:19.607" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17995" PostTypeId="2" ParentId="17986" CreationDate="2021-02-01T12:48:58.067" Score="2" Body="&lt;p&gt;John Kaufmann, W1FV, published a two-part article in the &lt;a href=&quot;https://www.pi4cc.nl/tech-info/rx-array/images/NJC-1&quot; rel=&quot;nofollow noreferrer&quot;&gt;September/October&lt;/a&gt; and &lt;a href=&quot;https://www.pi4cc.nl/tech-info/rx-array/images/NJC-2&quot; rel=&quot;nofollow noreferrer&quot;&gt;November/December 2011&lt;/a&gt; issues of the ARRL's &lt;em&gt;National Contest Journal&lt;/em&gt; titled, &amp;quot;A Compact Dual-Band, 9 Circle Receiving Array.&amp;quot; The phased-array system uses a simple amplifier with high input impedance:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/n5zb7.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/n5zb7.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The AD8055 op amp has a gain-bandwidth product of 300-MHz, so there's only about 10-dB of gain on the 10-meter band. Note that this &amp;quot;amplifier&amp;quot; is meant primarily to provide a wideband match between an electrically short antenna and a feedline. Its overall gain, as evidenced by the two 470-ohm resistors on the op amp inputs, is close to 0-dB.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-02-02T16:10:06.320" LastActivityDate="2021-02-02T16:10:06.320" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17996" PostTypeId="2" ParentId="12827" CreationDate="2021-02-01T20:10:22.353" Score="2" Body="&lt;p&gt;C (E)  =  I (t)&lt;/p&gt;&#xA;&lt;p&gt;E= I (t) / C&lt;/p&gt;&#xA;&lt;p&gt;C = Capacitance in uF&#xA;E = Ripple Voltage, p-p&#xA;I = Max Load in mA&#xA;t = &amp;quot;7.5mSec&amp;quot; for 60Hz line&lt;/p&gt;&#xA;&lt;p&gt;Vpeak (.707) = Vrms&#xA;Vp-p = Vrms (1.414)&lt;/p&gt;&#xA;&lt;p&gt;THEN,   E = I (t) / C   (in Vp-p)&#xA;Then, Vrms  =  Vp-p / 1.414  (Ripple Voltage p-p)&lt;/p&gt;&#xA;&lt;p&gt;SO, if C (E) = I (t)&#xA;Then E = I (t) /C&lt;/p&gt;&#xA;&lt;p&gt;Trans Vrms *  1.414  * 0.9 = No Load D.C.&lt;/p&gt;&#xA;&lt;p&gt;Ripple Voltage Vrms / No Load D.C. = Ripple Voltage Percent&lt;/p&gt;&#xA;" OwnerUserId="18703" LastActivityDate="2021-02-01T20:10:22.353" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="17997" PostTypeId="2" ParentId="17953" CreationDate="2021-02-02T03:18:01.567" Score="2" Body="&lt;p&gt;A direct sampling SDR does not need a LO anywhere within the frequency range or tracking the signal of interest.&lt;/p&gt;&#xA;&lt;p&gt;A processor running off of a fixed clock frequency well above twice the RF signal frequency of interest could use that clock to run an ADC and directly sample the RF signals, producing no other RF noise other than the EMI from the processor and its assorted power, IO, and memory subsystems.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-02-02T03:18:01.567" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17998" PostTypeId="1" CreationDate="2021-02-02T09:08:16.597" Score="3" ViewCount="275" Body="&lt;p&gt;Intuition might lead one to believe that the antenna configuration with the lowest SWR(50) across its input terminals would provide the best radiation efficiency for the antenna &lt;em&gt;&lt;strong&gt;system&lt;/strong&gt;&lt;/em&gt;.  But is that always a correct assumption?&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2021-02-15T11:35:56.273" Title="Is The Lowest Antenna Terminal Feedpoint SWR Always Optimal?" Tags="&lt;vertical-antenna&gt;&lt;radial&gt;&lt;efficiency&gt;&lt;radiation&gt;&lt;monopole&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="17999" PostTypeId="2" ParentId="17998" CreationDate="2021-02-02T09:44:31.437" Score="2" Body="&lt;p&gt;Below is a table showing that this is not always the result, for every antenna configuration.  In this case, the configuration with the lowest system SWR(50) also has the lowest system radiation efficiency.&lt;/p&gt;&#xA;&lt;p&gt;The system in this analysis using 0.5λ buried radials has higher SWR(50), with higher system gain and higher radiation efficiency than the system using 0.1λ radials.  But even though that SWR(50) is higher, a well-designed matching network could be added to its feedpoint terminals to produce nearly a perfect match to a 50 j0 Ω transmission line connected there, with a matching loss that would reduce system gain and radiation efficiency by only several tenths of a decibel.&lt;/p&gt;&#xA;&lt;p&gt;The gain and system radiation efficiency of that Z-matched system using 0.5λ buried radials (and other rows of that table) could be greater than from the system using 0.1λ radials — even though the 0.1λ system has lower SWR(50) before any matching networks are added.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nzIAl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nzIAl.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10565" LastActivityDate="2021-02-02T09:44:31.437" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18000" PostTypeId="2" ParentId="17998" CreationDate="2021-02-02T14:47:27.237" Score="1" Body="&lt;p&gt;Radiation efficiency and radiated power from a system (transmitter, feedline and antenna) are different things. Lowest SWR minimizes losses in the transmission line.&lt;/p&gt;&#xA;&lt;p&gt;Example for more power at mismatch: assume a TX with a low-impedance output, designed for termination with 50 Ohm but allowing some mismatch. With 40 Ohm load the SWR is 1.25 and the output power is higher.&lt;/p&gt;&#xA;&lt;p&gt;Another important thing is the mis-use of tables with transmission line losses resulting from mismatch. These tables are only valid for systems with 50 Ohm source and 50 Ohm, or deviating from that 50 Ohm, load impedance. Common TX output is a voltage or a current source or something in-between. Most probably NOT 50 Ohm.&lt;/p&gt;&#xA;&lt;p&gt;The correct system is a TX with transmission line (50 Ohm is common) and antenna matching unit or tuner directly connected to the antenna feedpoint. Common systems have the tuner in the shack. Works OK when the antenna is not that far deviating from 50 Ohm.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-02-02T14:47:27.237" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18001" PostTypeId="2" ParentId="17947" CreationDate="2021-02-02T15:11:06.677" Score="1" Body="&lt;p&gt;For two meters there is an option to have a capacitor on glass as feed-through. Just stick it on both sides of a non-metallized window screen and use a quarter lambda vertical with a small inductor to compensate the feed-through series capacitance. Coax screen must be connected to the car body with a short connection. No hole in your car, no rain water inside.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-02-02T15:11:06.677" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18002" PostTypeId="1" AcceptedAnswerId="18003" CreationDate="2021-02-02T16:17:59.630" Score="2" ViewCount="102" Body="&lt;p&gt;New to this community and also a newish Ham. Hello everyone.&lt;/p&gt;&#xA;&lt;p&gt;This question could easily have been posted under 'Astronomy', but I thought I would start here since Hams tend to be quite knowledgeable about many things that have to do with radio.&lt;/p&gt;&#xA;&lt;p&gt;I am interested in building a backyard radio telescope. The radio window that allows in radio frequencies through the Earth's atmosphere have wavelengths between about 0.5 cm to about 30 m. If I got this right, a quarter wavelength receiver would need to be about 7.5 m in length.&lt;/p&gt;&#xA;&lt;p&gt;I have seen the &lt;em&gt;radio dishes&lt;/em&gt; that SETI uses and I can tell you right now that my HOA will not allow any sort of radio dish in the backyard, especially one that is 7.5 m in diameter. As part of my amateur license, I learned about radio antennas for transmitting and receiving.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question 1&lt;/strong&gt;: Is it possible to use a radio antenna like a Yagi to pick up interstellar emissions between 0.5 cm and 30 m with any kind of sensitivity?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question 2&lt;/strong&gt;: What about using an antenna like the one in the image? Would this enhance sensitivity? Would this antenna still function if it was laid flat on a field?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qVpJz.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qVpJz.jpg&quot; alt=&quot;Radar Antenna&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I can't suspend any antennas in the back yard, and I can't place any radio dishes. However, I can place quite a large antenna installation as long as it is at ground level and not readily visible from the road. This fixed installation would receive signals as the Earth rotated. I imagine that with the relatively clear view we have from the backyard, the right antenna installation could pick up emissions from a large part of the sky at the same time. I would be sacrificing the ability to pinpoint &lt;em&gt;where&lt;/em&gt; the emission was coming from, but gaining the ability to monitor a large part of the sky for a relatively long period of time. Am I right with this train of thought?&lt;/p&gt;&#xA;&lt;p&gt;My plan is to connect (several?) SDRs to the antenna and monitor frequencies between 10 MHz and 100 GHz. I would also have a dedicated SDR that would automatically tune to any areas that have a high power signal. So one group of SDRs would focus on monitoring the entire frequency range, while one SDR would serve as the fine tuned receiver.&lt;/p&gt;&#xA;&lt;p&gt;More details to come (with probably a million questions). Thanks for reading this long post.&lt;/p&gt;&#xA;&lt;p&gt;-- Edited on Feb 3 --&lt;/p&gt;&#xA;&lt;p&gt;Thanks to some of the answers and comments below, I was inspired to look in a different direction. Ideally, I am looking for an antenna that offers a broad bandwidth so that I can pick up on as much of the cosmos as possible. In my reading, I came across &lt;strong&gt;biconical antennas&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ahsystems.com/articles/antenna-selection.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;strong&gt;Biconical antennas&lt;/strong&gt;&lt;/a&gt;&#xA;Biconical antennas are a modified type of dipole where the two&#xA;elements form a roughly conical shape. This change allows them to have&#xA;a wider bandwidth versus a regular dipole. The cones used on these are&#xA;rarely solid and are often made of multiple elements, making them&#xA;easier to fold or transport. Their broadband nature allows quick&#xA;testing without having to adjust or change the antenna. They are&#xA;linearly polarized and typically work in frequency from 20 MHz to 300&#xA;MHz, but when designed for it, they can work as high as 18 GHz.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The frequency response for biconical antennas is pretty close to the radio window (which is about 10 MHz to 60 GHz, but more practically 10 MHz to 6 GHz).&lt;/p&gt;&#xA;&lt;p&gt;So the answer to question 1 is &lt;em&gt;possibly yes&lt;/em&gt; using a biconical antenna. Am I understanding this correctly before I go too far down this rabbit hole?&lt;/p&gt;&#xA;&lt;p&gt;-- Edit #2 on Feb 3 --&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/18009/biconical-antennas-bandwidth-and-installation&quot;&gt;In a different thread&lt;/a&gt; I asked a question related to the feasibility of building a biconical antenna and putting it in my attic. Based off feedback from @Phil Frost - W8II, it looks like that won't work due to the amount of background noise it would pick up - especially from terrestrial sources.&lt;/p&gt;&#xA;&lt;p&gt;I'm back to looking at directional antennas again. Ultimately, I'm looking for what is beginning to sound like a pipe dream - a wide bandwidth antenna that will pick up stellar emissions but filter out terrestrial noise.&lt;/p&gt;&#xA;" OwnerUserId="18715" LastEditorUserId="18715" LastEditDate="2021-02-03T18:33:57.123" LastActivityDate="2021-02-03T18:33:57.123" Title="Constructing a ground level antenna array to monitor radio frequencies using SDR" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;&lt;antenna-construction&gt;" AnswerCount="3" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18003" PostTypeId="2" ParentId="18002" CreationDate="2021-02-02T17:17:39.097" Score="3" Body="&lt;p&gt;Ground-mounted horn antennas seem a popular choice for amateur radio astronomy.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/CVTIf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/CVTIf.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;&lt;a href=&quot;https://spectrum.ieee.org/geek-life/hands-on/track-the-movement-of-the-milky-way-with-this-diy-radio-telescope&quot; rel=&quot;nofollow noreferrer&quot;&gt;Track the Movement of the Milky Way With This DIY Radio Telescope&lt;/a&gt;&amp;quot; on the &lt;em&gt;IEEE Spectrum&lt;/em&gt; website and the &lt;a href=&quot;https://wvurail.org/dspira-lessons/tour/&quot; rel=&quot;nofollow noreferrer&quot;&gt;DSPIRA Guided Tour&lt;/a&gt; on the Digital Signal Processing in Radio Astronomy (DSPIRA) portal describe &lt;a href=&quot;https://drive.google.com/file/d/1qdc5lhKErFyIsc8b52ZIkCPJLi-XykSb/view&quot; rel=&quot;nofollow noreferrer&quot;&gt;how to build&lt;/a&gt; and &lt;a href=&quot;https://wvurail.org/dspira-lessons/categories/horn-operation/&quot; rel=&quot;nofollow noreferrer&quot;&gt;use&lt;/a&gt; ground-mounted horn antennae for frequencies around 1420-MHz.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Uc2Ym.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Uc2Ym.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-02T17:17:39.097" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18004" PostTypeId="2" ParentId="18002" CreationDate="2021-02-02T19:20:17.350" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;I imagine that with the relatively clear view we have from the backyard, the right antenna installation could pick up emissions from a large part of the sky at the same time. I would be sacrificing the ability to pinpoint where the emission was coming from, but gaining the ability to monitor a large part of the sky for a relatively long period of time. Am I right with this train of thought?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Not really. The sky is full of noise sources, and the Earth is full of even more. The point of a directional antenna isn't just knowing where a signal is coming from, it's &lt;em&gt;excluding everything else&lt;/em&gt;, to lower the noise level to the point where you can actually make out a particular signal. Otherwise, it's a lot like standing down the hall from a crowded party — there are lots of voices, but you can't understand any of them, you just hear a roar.&lt;/p&gt;&#xA;&lt;p&gt;You can get some directionality even with antennas that are relatively small (and in any case probably most of what you're interested in will be wavelengths of 2 meters or less, which makes the problem much easier). I'll let other answers deal with that.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-02-02T19:20:17.350" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18005" PostTypeId="2" ParentId="17933" CreationDate="2021-02-02T19:24:06.320" Score="3" Body="&lt;p&gt;In my experience no need for any spacing at all. I've made 80-10m fan dipoles with ribbon cable. Yes, the wires interact but after tuning I got nice clean resonances on all bands. Start with the shortest wavelength first and work down.&lt;/p&gt;&#xA;&lt;p&gt;Just my $0.02.&lt;/p&gt;&#xA;" OwnerUserId="1098" LastActivityDate="2021-02-02T19:24:06.320" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18006" PostTypeId="2" ParentId="18002" CreationDate="2021-02-02T19:36:33.043" Score="1" Body="&lt;p&gt;Crossed-dipole style antennas, sometimes used by hams for satellite reception, might fit your requirements. Their low directivity obviates the need for azimuth and/or elevation rotators to keep them pointed at their targets.&lt;/p&gt;&#xA;&lt;p&gt;Examples are described in, &lt;a href=&quot;https://drive.google.com/file/d/0B1q-psxlp3IwamN0VFZORmw3UjQ/view&quot; rel=&quot;nofollow noreferrer&quot;&gt;&amp;quot;Double Cross — A NOAA Satellite Downlink Antenna&amp;quot;&lt;/a&gt; by Gerald Martes, KD6JDJ,&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/FspPj.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/FspPj.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;and &lt;a href=&quot;https://www.amsat.org/amsat/articles/w6shp/lindy.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;&amp;quot;The Lindenblad: The Ultimate Satellite Omni Antenna,&amp;quot;&lt;/a&gt; by Howard Sodja, W6SHP.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gjYhm.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gjYhm.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;While the published articles on the Lindenblad antenna orient the folded-dipole elements 30-degrees from the horizon, I found through NEC-2 modeling that increasing the angle to 70-degrees dramatically reduced the overhead null, which might make the antenna more useful in your application.&lt;/p&gt;&#xA;&lt;p&gt;Analysis with NEC-2 modeling software indicates that either antenna could be useable over at least a 2:1 range of frequencies. These antennas are not trivial for a beginner to construct, but you might garner assistance from members of your local ham radio club, which might also be fertile ground for recruiting budding radio astronomers!&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-02-02T19:41:44.203" LastActivityDate="2021-02-02T19:41:44.203" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18007" PostTypeId="1" AcceptedAnswerId="18008" CreationDate="2021-02-03T06:44:54.813" Score="1" ViewCount="154" Body="&lt;p&gt;This is the insides of a common dual band antenna 2m/70cm, made by diamond or nagoya.&#xA;its generally labelled as: 1/2 wave radialless (144MHz), 2 x 5/8 wave radialless (430MHz)&#xA;Its meant to be ground independant.&lt;/p&gt;&#xA;&lt;p&gt;Im trying to find the design name for the tuning/matching circuit at the bottom and how it works.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;For example what stops the signal going down to ground at L1 rater than going up the elements ?&lt;/li&gt;&#xA;&lt;li&gt;Does the coil below the C1 tap point provide the counterpoise/ground for the antenna, and the part of coil above act as matching/loading coil for lower element ?&lt;/li&gt;&#xA;&lt;li&gt;calculators/plans around for this type or antenna ?&lt;/li&gt;&#xA;&lt;li&gt;generally how does it work, im also trying to model it such as in 4nec2&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/YEwX6.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fYEwX6.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="17758" LastEditorUserId="9621" LastEditDate="2021-02-03T08:37:41.103" LastActivityDate="2021-02-05T01:52:30.500" Title="Trying to identify and understand this antenna design - ground independent dual band vertical" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;vhf&gt;&lt;uhf&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18008" PostTypeId="2" ParentId="18007" CreationDate="2021-02-03T15:32:56.940" Score="3" Body="&lt;p&gt;This arrangement:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/p1uOz.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fp1uOz.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;is called an L-match.&lt;/p&gt;&#xA;&lt;p&gt;Adding a tap to the inductor creates an autotransformer which allows an additional degree of freedom in the tuning network. It's useful here because the impedance of the half-wave element is much too high; the autotransformer steps it down to something closer to 50 ohms, reducing the mismatch that must be corrected by the L-match.&lt;/p&gt;&#xA;&lt;p&gt;This is very similar to &lt;a href=&quot;https://ham.stackexchange.com/a/1899/218&quot;&gt;an equivalent circuit for a gamma match&lt;/a&gt;, the only difference being the autotransformer is flipped around.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-02-03T15:32:56.940" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18009" PostTypeId="1" CreationDate="2021-02-03T16:12:18.083" Score="2" ViewCount="55" Body="&lt;p&gt;I am posting this question (&lt;a href=&quot;https://ham.stackexchange.com/questions/18002/constructing-a-ground-level-antenna-array-to-monitor-radio-frequencies-using-sdr&quot;&gt;and its related question&lt;/a&gt;) here because of the unique expertise that Ham Radio Operators have as it relates to antennas. I'm a newish Ham and really appreciate your help with this challenge.&lt;/p&gt;&#xA;&lt;p&gt;As discussed in the related question, I am interested in building an antenna array that picks up on stellar emissions. I am trading localizability (i.e. the ability to pinpoint the source) for recording as much of the sky in as broad a bandwidth as possible. Practically speaking, that means recording EM emissions within the &amp;quot;Radio Window&amp;quot;, which is about 0.5 cm to about 30 m.&lt;/p&gt;&#xA;&lt;p&gt;The answers in the other question were extremely helpful, and in doing further research, I stumbled upon &lt;strong&gt;biconical antennas&lt;/strong&gt;. A search on this forum only yields a handful of questions that touch on this antenna type in passing. It appears that biconical antennas have a broad bandwidth with considerable overlap to the radio window - 20 MHz to as high as 300 MHz (I need 10 MHz to 60 GHz). Theoretically, a second antenna (log periodic?? loop??) to pickup on the 10 MHz to 20 MHz spectrum.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Y0kJV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Y0kJV.jpg&quot; alt=&quot;Biconical Antenna&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Here's the question: my HOA prohibits mounting anything that looks like an antenna on the property. I can place an antenna flat on the ground, but that's not going to work with a biconical antenna as far as I can tell. I read in &lt;a href=&quot;https://www.amsat.org/amsat/articles/w6shp/lindy.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this article&lt;/a&gt; that someone mounted a Double Cross antenna in their attic and received decent signals. My house has concrete shingle tile. If I built a biconical antenna and mounted in my attic, would I still receive transmissions in the frequency range I am looking for?&lt;/p&gt;&#xA;&lt;p&gt;Thanks for all your advice!&lt;/p&gt;&#xA;" OwnerUserId="18715" LastActivityDate="2021-02-03T16:12:18.083" Title="Biconical antennas - bandwidth and installation" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;installation&gt;" AnswerCount="0" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="18010" PostTypeId="1" CreationDate="2021-02-03T16:12:51.520" Score="4" ViewCount="151" Body="&lt;p&gt;I had &lt;a href=&quot;https://swling.com/blog/2018/05/how-to-build-sm0vpos-20-meter-magnetic-loop-antenna/&quot; rel=&quot;nofollow noreferrer&quot;&gt;built SM0VPO's spiral loop antenna&lt;/a&gt;. And here it is.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GJROK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GJROK.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Recently I got myself a NanoVNA to see how finnicky it is to be tuned with that poor man's tuning cap. I brought it from 12 MHz into the 14 MHz 20 m band range by cutting off the extra wire to reduce the capacitance at the end.&lt;/p&gt;&#xA;&lt;p&gt;But it is still not ideal. Here is the NanoVNA measurements:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/THeBc.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/THeBc.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I can't get the SWR under the 1.67:1 and essentially the impedance is 80Ω instead of 50Ω.&lt;/p&gt;&#xA;&lt;p&gt;I also note that this antenna is pretty bad at receiving. I have no comparison to anything better at this point as it's really constraining inside an apartment where I'm still stuck, but I don't trust this baby.&lt;/p&gt;&#xA;&lt;p&gt;I know that a spiral loop may not be the ideal antenna, but this has got a bit of fame because it is such an easy thing to build from scratch, so I wanted to give it the best chance.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Questions:&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;How can I improve the matching to get 50Ω impedance / 1.0:1 SWR?&lt;/p&gt;&#xA;&lt;p&gt;From the Extra exam I just took, I remember you could put a length of 75Ω coax in series on the feed point to adapt 50Ω to 100Ω.&lt;/p&gt;&#xA;&lt;p&gt;I also remember the stub match. Especially the very simple technique to just run a parallel open piece of coax from the feed point. But I guess that can only work at precisely one frequency and cannot be tuned, even a little bit. Given that mag-loops in general are such low bandwidth antennas, tuning ability is essential.&lt;/p&gt;&#xA;&lt;p&gt;There seems to be excess capacitive reactance, what can I do to counteract it and not just reduce the (already bad?) efficiency of the antenna even more? I mean, I could perhaps insert a coil at the feed point, but I was hoping perhaps I could tweak something else?&lt;/p&gt;&#xA;&lt;p&gt;I twisted and pushed and shoved the wire around to see if I can make an impact, and also moved to different locations, away from that lamp thing, away from the wall, etc. to no decisive avail.&lt;/p&gt;&#xA;&lt;p&gt;Could I tweak this &lt;a href=&quot;https://vk6ysf.com/balun_1-1.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;1:1 Ruthroff balun, as there is apparently tweak-ability&lt;/a&gt;? Mine is according to the instructions done with 7 turns.&lt;/p&gt;&#xA;" OwnerUserId="16238" LastActivityDate="2021-02-03T17:16:54.883" Title="Debugging SM0VPO's spiral loop antenna build" Tags="&lt;balun&gt;&lt;impedance-matching&gt;&lt;loop-antenna&gt;&lt;magnetic-loop&gt;" AnswerCount="1" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18011" PostTypeId="2" ParentId="18010" CreationDate="2021-02-03T17:10:31.933" Score="3" Body="&lt;p&gt;When tuning can be achieved then the only variables you have to optimize is the coupling and the compensation of the feed loop inductance (because k &amp;lt; 1). Just modify the area of the feed loop by bending the wires to a smaller or a larger area. You will end-up close to 50 Ohm. But resonance of the loop does not exactly correspond with lowest impedance. See below.&lt;/p&gt;&#xA;&lt;p&gt;Second, not very critical and not essential, but just a recommendation: the tuning of the uncoupled part of the feed loop inductance. That can be done with series capacitance between the inner coax and the connection with the feed loop. Value probably 500 pF film or low-loss RF capacitor (estimation, based on experience with this type of loops).&lt;/p&gt;&#xA;&lt;p&gt;Finally: the feed loop is already floating. The transformers adds only to the losses. There is no need to insert that transformer.&lt;/p&gt;&#xA;&lt;p&gt;For reception the loop is OK and not that critical w.r.t. losses. For transmitter use I schould go for lower loss copper or alumin material and a variable capacitor made from copper PCB-material and teflon or nylon dielectricum (cutting board, more than 2 mm thickness, white material without color pigment).&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2021-02-03T17:16:54.883" LastActivityDate="2021-02-03T17:16:54.883" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18012" PostTypeId="2" ParentId="18007" CreationDate="2021-02-03T23:22:40.303" Score="1" Body="&lt;p&gt;The matching circuit looks similar to the type of N:1 balun/unun used to feed an end-fed half-wave without too great an impedance mismatch. Except in this case L3 shortens the dipole at its center, and the portion below half of L3 is the counter-pose to the quarter wave section above half of L3.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-02-05T01:52:30.500" LastActivityDate="2021-02-05T01:52:30.500" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18013" PostTypeId="2" ParentId="17933" CreationDate="2021-02-04T01:10:17.717" Score="1" Body="&lt;p&gt;Consider this &amp;quot;mind experiment&amp;quot; for a limiting factor&#xA;in the separation required for &amp;quot;Fan Dipole Radiators&amp;quot;.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Given a Fan-Dipole for 28MHz and 4MHz.&lt;/li&gt;&#xA;&lt;li&gt;Given a Effective Power Out of 1KW,&#xA;from a tube amp of 1000 V Plate Voltage.&lt;/li&gt;&#xA;&lt;li&gt;Given a distance between radiators of 0.5 inch.&lt;/li&gt;&#xA;&lt;li&gt;Given that the peak voltage (RF) may reach 3KV.&lt;/li&gt;&#xA;&lt;li&gt;Given that the 28MHz Voltage Lobe is&#xA;located 0.5 inch away from the 4MHz Current Lobe .&lt;/li&gt;&#xA;&lt;li&gt;Question: Will the 28MHz Voltage Lobe arc from one bare wire to another, through air , to the 4MHz Current Lobe ?&lt;/li&gt;&#xA;&lt;li&gt;Question: Will there be &amp;quot;de-Tuning&amp;quot; in this extreme example ?&lt;/li&gt;&#xA;&lt;li&gt;The previously supplied &amp;quot;answers&amp;quot; and &amp;quot;cautionary methods&amp;quot;&#xA;are a good faith effort in managing any &amp;quot;De-Tuning&amp;quot; that may arise.&lt;/li&gt;&#xA;&lt;li&gt;My method has been to use 5 inch spacers,&#xA;and 'stack&amp;quot; the dipoles progressively ( 80,40,20,15,10M , side by side.)&#xA;such that Voltage Lobes are as separated as much as they can be.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="8402" LastActivityDate="2021-02-04T01:10:17.717" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18016" PostTypeId="2" ParentId="17953" CreationDate="2021-02-04T19:41:05.467" Score="0" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;It's my understanding that active superhet receivers can be detected by looking for the emissions from the local oscillator.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I have it on good authority that that information originated with the German radio government authorities years ago. They tax every home radio receiver, and that helped bring more tax money into their coffers. :-) They allegedly drove detection vehicles up and down every street to see who didn't report their radios, and then sent letters out demanding that they register theirs.&lt;/p&gt;&#xA;&lt;p&gt;Having said that, I once raised the question whether German broadcast receivers were modified to radiate a signal. But since only one or two Germans answered, I am not going to say whether that's true. ;-)&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2021-02-04T19:41:05.467" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18017" PostTypeId="1" CreationDate="2021-02-04T20:12:34.220" Score="0" ViewCount="28" Body="&lt;p&gt;I am looking for advice on new to HAM studies.&#xA;I have a pair of FRS Motorola T800 walkie talkies and an old pair of REalistic TRC-215 6 channel, 5W, CB handhelds.&lt;/p&gt;&#xA;&lt;p&gt;As I read, and ask questions, a friend suggested Baufeng units. They are made in China and seem less than quality?&lt;/p&gt;&#xA;&lt;p&gt;Thanks,&lt;/p&gt;&#xA;&lt;p&gt;Gerry&lt;/p&gt;&#xA;" OwnerUserId="18729" LastActivityDate="2021-02-04T20:12:34.220" Title="USA made handheld" Tags="&lt;ht&gt;" AnswerCount="0" CommentCount="3" ClosedDate="2021-02-05T17:01:18.727" ContentLicense="CC BY-SA 4.0" />
  <row Id="18018" PostTypeId="1" CreationDate="2021-02-04T21:44:43.357" Score="3" ViewCount="61" Body="&lt;p&gt;gpredict is nice. Well, it's OK, to find the next passes for a set of satellites with sufficient elevation for one location.&lt;/p&gt;&#xA;&lt;p&gt;What I want is something where I can put in two coordinates, and get out the next of a &lt;em&gt;set&lt;/em&gt; of satellites that will have a simultaneous pass for two locations, so that I can try to make a specific contact, or a specific square contact.&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="8717" LastEditDate="2021-02-04T21:48:55.993" LastActivityDate="2021-02-04T21:48:55.993" Title="Any tool for finding satellite passes that overlap *two* given locations?" Tags="&lt;satellites&gt;&lt;software&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18019" PostTypeId="1" AcceptedAnswerId="18020" CreationDate="2021-02-05T02:08:07.547" Score="9" ViewCount="678" Body="&lt;p&gt;I want to upgrade the stock antenna on my Baofeng uv-5r for which I mostly use the 2 meter band.  The quarter wavelength for this band is about 19.2 inches, but when I look for antennas, they are typically 15.6 or 7.5, or some other seemingly random number of inches.  Not to mention for 70cm, which they advertise they work for, the length is way off.  Would these non-19.2 inch antennas work correctly since they are not a resonant length?  Could they cause damage when transmitting?&lt;/p&gt;&#xA;" OwnerUserId="18733" LastActivityDate="2021-02-05T13:18:32.897" Title="What is the appropriate length of an antenna for a handheld on 2 meters?" Tags="&lt;antenna&gt;&lt;baofeng&gt;&lt;ht&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18020" PostTypeId="2" ParentId="18019" CreationDate="2021-02-05T03:57:52.353" Score="12" Body="&lt;p&gt;These antennas don't always contain a simple straight length of conductor, but rather usually have coils of wire inside, so the actual physical length doesn't mean that much. They are designed so that the antenna is wound into a coil normally to make the antenna shorter which is more practical for a hand held radio.&lt;/p&gt;&#xA;&lt;p&gt;That's why  you don't see a whip that is exactly the 1/4 wave in length you expect.&lt;/p&gt;&#xA;&lt;p&gt;There are many different types of whip antennas and they all probably look similar on the outside but are very different inside.&lt;/p&gt;&#xA;&lt;p&gt;For example some are designed for a single band made from one long helically wound coil, while others might be multi band with a few coils in series or even multiple separate antennas all contained within the one whip.&lt;/p&gt;&#xA;&lt;p&gt;Also keep in mind that some handheld antennas may be specific to the model radio they were designed to work with, and might use a custom matching network that won't work on other radios.&lt;/p&gt;&#xA;&lt;p&gt;So to answer your questions, most antennas will work for receive to some extent on just about any band, but for optimum performance you need to choose the correct antenna for the bands you are using, and you must use the correct antenna for transmitting otherwise you risk damaging the radio if the antenna is not resonant on the bands you are transmitting on.&lt;/p&gt;&#xA;&lt;p&gt;Hope that helps !&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2021-02-05T04:03:28.017" LastActivityDate="2021-02-05T04:03:28.017" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18021" PostTypeId="2" ParentId="18019" CreationDate="2021-02-05T13:18:32.897" Score="3" Body="&lt;p&gt;70cm is not quite but almost a third harmonic of 2m.   What this means is that a 2m antenna that has sufficient bandwidth will also be a good match for 70cm.   Sometimes the radiation pattern is not good, but it will still radiate with a good SWR.&lt;/p&gt;&#xA;&lt;p&gt;Also, it is possible to add inline loading coils to antennas to make them work on multiple bands without being harmonically related.&lt;/p&gt;&#xA;&lt;p&gt;And a good antenna is not necessarily an actual physical 1/4 wavelength due to stray inductance and capacitance of surrounding parts.  For example, adding dielectric insulation can have a very small effect that would change the ideal length a bit.  Adding a knob on the tip (so it is less sharp and also to prevent arcing) acts as a capacitive hat.&lt;/p&gt;&#xA;&lt;p&gt;And 1/4 wavelength isn't the only &amp;quot;ideal&amp;quot; length.  Antennas that are 3/8, 5/8, and even 1/2 wavelength can be found.   (A 1/2 wavelength antenna usually has a huge loading coil on the bottom.)&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2021-02-05T13:18:32.897" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18023" PostTypeId="1" AcceptedAnswerId="18032" CreationDate="2021-02-06T17:29:04.970" Score="1" ViewCount="206" Body="&lt;p&gt;I recently purchased a Yaesu FT-70DR and would like to use an earphone of some sort just to listen. On &lt;a href=&quot;https://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&amp;amp;ProdCatID=249&amp;amp;encProdID=7CDB93B02164B1FB036530FBD7D37F1A&amp;amp;DivisionID=65&amp;amp;isArchived=0&quot; rel=&quot;nofollow noreferrer&quot;&gt;Yaesu's site&lt;/a&gt;, there seem to be only 2 official options:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;SSM-57A Earbud speaker mic with PTT (doesn't have very good reviews)&lt;/li&gt;&#xA;&lt;li&gt;CT-44 Microphone Adapter (2 conductor female mic to single jack)&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I'm interested in option 2, but I have no idea what can actually be plugged into it, and I can't seem to find anything helpful online. I'm hoping there is some standard type of earphone that can be used with the CT-44. Any help / description of alternatives would be greatly appreciated.&lt;/p&gt;&#xA;" OwnerUserId="18746" LastEditorUserId="8717" LastEditDate="2021-02-06T18:10:00.930" LastActivityDate="2021-02-08T19:16:36.920" Title="Yaesu FT-70DR Earpiece" Tags="&lt;yaesu&gt;&lt;microphone&gt;&lt;speaker&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18025" PostTypeId="2" ParentId="18023" CreationDate="2021-02-07T06:39:55.073" Score="1" Body="&lt;p&gt;Going by the pictures (not much other information to go by), it seems the breakout cable has a standard headphone Jack and a smaller plug for the microphone. That seems a standard configuration. I would give your local (or less local) ham shop a call and just ask them.&lt;/p&gt;&#xA;&lt;p&gt;Or,honestly,i'd prefer to buy the two connectors and solder it myself. If you have no experience soldering it might be a good little project to get started with, or you might be able to ask a fellow ham to do it for you. That way,you know what quality you have and can fix it if it would get damaged/cut/.. . It also allows you to use a longer piece of cable if that would help...&#xA;Good luck!&lt;/p&gt;&#xA;" OwnerUserId="8263" LastActivityDate="2021-02-07T06:39:55.073" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18026" PostTypeId="2" ParentId="12065" CreationDate="2021-02-08T09:39:27.450" Score="1" Body="&lt;p&gt;Language as such has nothing to do with the CW speed measurement STANDARDs. In amateur radio we are oblicated to use plain text (encryption is not allowed), so the standard word PARIS is used to check CW speed and CODEX word does not apply. OK, the PARIS word may (or may not) have been originally based on English language, but you do not need to concern yourself about that. If you have a WPM count, multiply it with 5 to get CPM and if you have CPM count, divide it with 5 to get WPM.&lt;/p&gt;&#xA;&lt;p&gt;In real life many (if not most) plain text langugaes do not produce the correct CW speed, if calculated (or measured) from a length of text. That doesn't have any significance, however. The PARIS (and CODEX) words are the STANDARD, to which all CW speed measurement is based, so do not try to use anything else for CW speed testing, or you will get wrong results.&lt;/p&gt;&#xA;&lt;p&gt;By the way, what we now call (International) Morse code, was NOT created by Samuel Morse. His wire telegraph code had significant differences to the CW code we use today. The international telegraph code, to which our over-the-air CW is based today, was agreed upon at a conference in Berlin in 1851.&lt;/p&gt;&#xA;" OwnerUserId="18761" LastActivityDate="2021-02-08T09:39:27.450" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18027" PostTypeId="2" ParentId="16059" CreationDate="2021-02-08T11:00:38.877" Score="3" Body="&lt;p&gt;My experienses on 2 meters when I was living in southern Finland (near Helsinki). My Finnisf call sign was (and still is) OH2AXE. I did not have 70 cm equipment.&lt;/p&gt;&#xA;&lt;p&gt;Antenna: 2 x 2 stack of double hybrid quads, gain about +12 dBd, about 10 m above ground. 50 W homemade linear amplifier.&lt;/p&gt;&#xA;&lt;p&gt;Most of the time the TX power is not so critical, even 5 or 10 W is enough to work DX. The  limiting factor is your ability to hear the DX stations and for that a higher gain antenna helps a lot. I seems to me that +10 dBd (over dipole) is the minimum for DX. At the same time it increases your ERP (Effective Radiated Power) for TX by the gain (in dB) given for the antenna.&lt;/p&gt;&#xA;&lt;p&gt;FM contacts up to about 250 km away were always possible in more or less any direction.&lt;/p&gt;&#xA;&lt;p&gt;SSB contacts via sporadic E to Yugoslavia (as it was then), England, Poland, Germany, Italy and other parts of Central Europe. To my experience sporadic E is specifically a summer phenomenon, between abou April and September. I have never experienced it during winter. It is somewhat rare on 2 meters, though. But if you start hearing strange stations from your FM (89 - 108 MHz) radio, check the 2 meter situation immediately, the sporadic E may reach even up to 145 MHz.&lt;/p&gt;&#xA;&lt;p&gt;CW contacts via aurora to Russia (longest to Archangel, Moscow and the Ural mountains), the Baltic states, Sweden, Norway, Denmark, Poland, North Germany. Via aurora only CW is intelligible and it sounds like hiss-hiss-hisssss-hiss ---. There is no tone and the report is given for instance as 59A (A for aurora tone). To my experience radio aurora is mostly a winter phenomenon and in Southern Finland the antenna had to be pointed more or less to North (say from NW to NE) for contacts. Note that most of the time there is no visible aurora, but the radio aurora may still be quite strong.&lt;/p&gt;&#xA;" OwnerUserId="18761" LastActivityDate="2021-02-08T11:00:38.877" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18028" PostTypeId="1" CreationDate="2021-02-08T12:04:14.557" Score="3" ViewCount="169" Body="&lt;p&gt;Imagine that someone has built a 4 element horizontal yagi antenna for 28 MHz with elements insulated from the boom, and with the driven element not split in the middle and using a gamma match to set the feed point impedance to 50 ohms.&lt;/p&gt;&#xA;&lt;p&gt;Then, assuming a non-metallic mounting pole, if vertical elements were added which are identical in length and spacing and then joined exactly in the middle to the middles of the horizontal elements so the result is an antenna that looks like 4 plus s (+s) in a row, and keeping just the one gamma match on the horizontal driven element, is the following true ?&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The feed point impedance of the antenna will now be about 25 ohms.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The same gamma match can be used to adjust the impedance back up to 50 ohms.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The antenna will now be both horizontally and vertically polarized.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;For transmit, half the applied power will be radiated by each of the two driven elements.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The radiation pattern will be the same in the plane of each set of elements.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Will this antenna give any advantages over a standard yagi with one set of elements ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2021-02-08T12:47:14.007" LastActivityDate="2021-02-08T20:51:57.027" Title="Dual Polarization Yagi Antenna for 10 m" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;polarization&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18030" PostTypeId="2" ParentId="18028" CreationDate="2021-02-08T13:32:42.563" Score="4" Body="&lt;p&gt;From your description:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the vertical polarized antenna has no feed point. Since the antennas are orthogonal and on-axis there is almost no mutual effect, no coupling: the feed impedance of the horizontal antenna does not change. (2) No need for re-adjustment of the gamma match. (3) Not any effect from the vertical antenna parts. (4) No coupling, no power from that vertical part. (5) no change in polarization or radiation pattern.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;When both antenna's are connected to the feeder line (and indeed: two gamma matches that need realignment) and there is no phase difference you end up with a 45 degrees polarization; in-between H and V.&lt;/p&gt;&#xA;&lt;p&gt;When there is 90 degrees (or -90 degrees) phase difference between the H and V antenna then you have a circular polarization antenna. Effective in reduction of fading in skywave transmissions (DX).&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-02-08T13:32:42.563" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18032" PostTypeId="2" ParentId="18023" CreationDate="2021-02-08T19:16:36.920" Score="1" Body="&lt;p&gt;The FT-70DR uses the same microphones as the FT-60, including the SSM-17A that you seem to have missed.  The plug looks to be a 3.5 mm &lt;a href=&quot;https://en.wikipedia.org/wiki/Phone_connector_(audio)&quot; rel=&quot;nofollow noreferrer&quot;&gt;TRRS&lt;/a&gt;.  The FT-60 is a common HT that has been produced for years, and there should be lots of accessories for it.  It's not clear if the FT-60 and FT-70DR use dynamic or electret (condenser) microphones, but most radios these days tend to use electret microphones because they're cheaper and work just as well for HTs.&lt;/p&gt;&#xA;&lt;p&gt;You should be able to find nearly any type of headset or hand microphone you like that is compatible with the FT-60 and FT-70DR on the accessory market.  But if you don't like the available accessories then it shouldn't be too difficult to wire up an adapter cable or adapter box to use a headset or microphone with a different plug; such an adapter may need to supply amplification or attenuation, and bias voltage for an electret microphone.&lt;/p&gt;&#xA;&lt;p&gt;You could also find a microphone or headset that uses the older two-plug standard used by that CT-44 adapter, with one plug 3.5 mm and the other 2.5 mm.  I tried to quickly find a diagram for the wiring for that standard for Yaesu radios, but couldn't.  I know that other manufacturers (Baofeng comes to mind) use a similar double-plug standard, but there is no agreement between manufacturers for microphone standards, so beware: a microphone that works with a different manufacturer's radio and physically plugs into the CT-44 adapter may not work, and might damage the microphone and/or the radio.  Personally I wouldn't bother with that annoying adapter; I'd just find a microphone or headset with a TRRS plug that is made to work with the FT-60 and FT-70DR.&lt;/p&gt;&#xA;&lt;p&gt;When looking for accessory microphones or headsets, your best bet IMO is to contact a well-known amateur radio equipment retailer.  They are likely to sell you something of reasonable quality that will work with your radio.  The manufacturer &lt;a href=&quot;https://mfjenterprises.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;MFJ Enterprises&lt;/a&gt; makes a variety of accessories, but they have a reputation for erratic quality.  (I have an MFJ speaker/mic that works fine.  I have no association with MFJ, except as a customer.)  Then there is the army of sellers on eBay, Amazon, Alibaba, etc., which sell at low prices, but buyer beware: there is a lot of out-and-out junk out there on the market, and lots of products that are advertised as being compatible turn out not to be.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-02-08T19:16:36.920" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18033" PostTypeId="2" ParentId="18028" CreationDate="2021-02-08T20:51:57.027" Score="3" Body="&lt;p&gt;From what you describe, it doesn't seem the vertical elements would be fed at all. Since they pass directly through the plane of symmetry of the horizontal elements they experience no electric field along the vertical axis, and so, aren't driven at all. It's as if they aren't there.&lt;/p&gt;&#xA;&lt;p&gt;Furthermore, there's a simpler way for the antenna to be &amp;quot;both horizontally and vertically polarized&amp;quot;: mount it such that the elements are at a 45 degree angle relative to the horizon.&lt;/p&gt;&#xA;&lt;p&gt;Alternatively, you could build elements like you describe, and feed them both with a 90 degree phase offset to obtain circular polarization.&lt;/p&gt;&#xA;&lt;p&gt;In either case, if the receiving antenna is either horizontally or vertically polarized, it will incur an additional 3 dB loss since half the power is in whichever polarization the receiving antenna isn't.&lt;/p&gt;&#xA;&lt;p&gt;More generally, any possible polarization can be visualized on the &lt;a href=&quot;https://en.wikipedia.org/wiki/Polarization_(waves)#Poincar%C3%A9_sphere&quot; rel=&quot;nofollow noreferrer&quot;&gt;Poincaré_sphere&lt;/a&gt;. Your radiation in any one direction can occupy only one point on this sphere at a time. If the receiving antenna's polarization is the opposite point on that sphere, polarization loss is infinite. If the polarization of receiving and transmitting antennas are 90 degrees apart, the loss is 3 dB. If they're the same, 0 dB.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-02-08T20:51:57.027" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18035" PostTypeId="2" ParentId="17998" CreationDate="2021-02-09T17:27:15.727" Score="2" Body="&lt;p&gt;No, minimizing the SWR at load (antenna) interface is not sufficient for the minimization of the end-to-end loss at system level (Transducer Loss).&lt;/p&gt;&#xA;&lt;p&gt;A Figure (screenshot) might be helpful for illustration. The case is for SWR=2.06 at load, implying a SWR=1.88 at the input of an example lossy transmission line (50Ω). The purple curve is the total system loss as function of normalized cable length, and with the thick black dot representing the nominal cable length of here 100 feet. If we increase the cable length to 135 feet, the SWR at load remains constant but the total system loss decreases from 1.39dB to about 1dB. If we shorten the cable from 100 to 90 feet, the total loss will increase to almost 1.5dB. This might appear very strange at first reading. However, as we change the cable length, we also change the input impedance of the transmission line at its interface with the source – and therefore the extent of match, or mismatch, w.r.t. the output impedance of the source at its operating point.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dmEfl.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dmEfl.jpg&quot; alt=&quot;Figure 1&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now, if we deploy an impedance matching (next Figure) at load to enable SWR=1, then the input impedance of the line at the interface with the source equals the characteristic impedance of the line (50Ω). This impedance might still be mismatched with the given output impedance of the source (like in the considered example). Therefore, SWR=1 at load is not sufficient to reduce the total system loss of now 0.62dB further down to the matched line loss (0.54dB) as would be implied by solely the transmission line.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EIcKq.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EIcKq.jpg&quot; alt=&quot;Figure 2&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It makes a difference, if the impedance matching at the load aims at SWR=1, or at a complex conjugate matching which is considered in the third Figure. The total system loss is now further reduced to 0.56dB, but the SWR at load is SWR=1.28. So, we accept this SWR and tolerate reflections on the line for the benefit of increased delivered power. (This seems like the point S. Sessink makes in his posting.)&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/fGzLu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/fGzLu.jpg&quot; alt=&quot;Figure 3&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;If we would deploy two matchings (assumed lossless in this discussion about principles) for both, SWR=1 at load and complex conjugate matching at source, the total system loss would eventually equal the matched line loss (0.54dB).&lt;/p&gt;&#xA;&lt;p&gt;The applied tool allows to compare the case of no-matching with eight different matching approaches and the implied losses at system level. Such assessment does matter when answering how much of the maximum available power from a given source can be delivered to the load, commonly referred to as the system Transducer Loss. (Although not essential for the above discussion, the characteristic impedance becomes complex at relatively low RF frequencies and could be considered as such but would not compromise the above remarks.)&lt;/p&gt;&#xA;&lt;p&gt;@ Phil:&lt;/p&gt;&#xA;&lt;p&gt;I took your example and added a corresponding figure. – Indeed, when looking into the line, the source will see a transmission line input impedance that moves on a perfect circle as we change the cable length – on a perfect circle because the line is assumed now lossless. The power mismatch between source and line, or loss, is determined by the &lt;strong&gt;radius&lt;/strong&gt; (ρ=|Γ|) of that circle (in a Smith-Chart). As the changing impedance stays on that circle, the source will always deliver the same power into the line, and eventually to the load at the other end, because the line is assumed lossless. Therefore, the system loss vs. cable length is in this case constant and a straight horizontal line (see figure).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eKQ06.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eKQ06.jpg&quot; alt=&quot;Figure 4&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;@ Phil:&lt;/p&gt;&#xA;&lt;p&gt;From your previous question with “the load impedance around a constant SWR circle (neglecting losses)” I thought a lossless line should be considered for the answer.&lt;/p&gt;&#xA;&lt;p&gt;I go back to a lossy line, and the source has exactly 50 Ohm output impedance. To see waviness, we consider a line which is lossy and with characteristic impedance that is complex. The next figure shows the resulting waviness.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vGYM9.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vGYM9.jpg&quot; alt=&quot;Figure 5&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The waviness becomes more pronounced if additionally, complex conjugate matching is applied at the input of the line (see next Figure, because the significant reflection at the source enhances the waviness). For short cable lengths, the overall system loss of now (P2/Pmax)=(P2/P1) is lower than the matched line loss, which is a known phenomenon attributed to the nodes affected by the phase-shift between voltage and current waves due to the now complex line impedance.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vwtj4.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vwtj4.jpg&quot; alt=&quot;Figure 6&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The waviness becomes practically ignorable at higher RF frequencies. It disappears whenever the line characteristic impedance is, or is assumed to be, a real value.&lt;/p&gt;&#xA;&lt;p&gt;As the big advantage, the used tool allows to incorporate the complex characteristic impedance of real-world transmission lines. This is very much in contrast to the popular ARRL equation that is included in the plots for comparison. Furthermore, the ARRL equation (like TLW) calculates only (P1/P2), and the ARRL equation allows this only for real-valued characteristic impedances;  matching at the source side cannot be addressed; therefore, the approach is not a transducer loss assessment at system level.&#xA;Good luck to those who wish to explore the waviness with the existing ARRL tool (or TLW).&lt;/p&gt;&#xA;&lt;p&gt;For interesting comparison and perspective, the following diagram is published by the ARRL frequently and again in the QST Magazine, March 2021, p. 53. The Figure shows the “Additional Loss in dB Caused By Standing Waves” as function of “Line Loss in dB When Matched,” with SWR at Load as parameter.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/3HdQA.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/3HdQA.jpg&quot; alt=&quot;Figure 7: QST Magazine, March 2021, p. 53&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;For example, a source with 50 Ohms output impedance is considered. The source is connected to a 50 Ohms line that is terminated by 200 Ohms; this implies SWR=4 at load. Further, we consider a Matched Line Loss of 1 dB, which together with the Additional Loss Caused by SWR (0.8dB from the diagram) implies 1dB + 0.8dB = 1.8dB. From the Figure, readers are inclined to conclude this 1.8dB would be the total system loss. However, SWR not only affects the line-related loss but also the mismatch between source and the connected transmission line. (See screenshot below.) This impedance mismatch loss on its own is 1.1dB for the considered example and indeed exceeds the “Additional Loss in dB Caused by Standing Waves” (of 0.8dB).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/a5oC5.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/a5oC5.jpg&quot; alt=&quot;Figure 8&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The true system loss of 2.9dB (49% power loss) significantly exceeds a total of 1.8dB (34% power loss) which one might erroneously conclude from the diagram in QST.&#xA;The QST diagram can represent a total system loss on the specific assumption of a lossless complex conjugate matching at the input of the transmission line and if the line has a real-valued characteristic impedance (which is not the case at lower RF frequencies). Regrettably, QST articles regularly fail to highlight these crucial conditions. So, the plot in QST can very much misinform because it is incomplete to assess the total end-to-end system loss (Transducer Loss) of a real-world transmatch.&lt;/p&gt;&#xA;&lt;p&gt;Besides considering typical real-world transmatches, the applied tool considers the impact of mismatches on system loss, as well as the impact of intended impedance matching for zero-reflection or, alternatively, the impact of complex conjugate matching, or combinations thereof. Therefore, the tool allows to assess the merit of matching, or if the deployment of lossy match circuit/s might not be worth the effort or be even counterproductive in terms of overall system loss.&lt;/p&gt;&#xA;" OwnerUserId="18763" LastEditorUserId="18763" LastEditDate="2021-02-15T11:35:56.273" LastActivityDate="2021-02-15T11:35:56.273" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18037" PostTypeId="1" CreationDate="2021-02-10T05:38:48.257" Score="5" ViewCount="69" Body="&lt;p&gt;I recently bought a pair of self-adhesive thru-glass antenna couplers for my mobile radios and erred in mounting both of them, which required me to peel them off the side window glass in my minivan. The doublestick tape compound used on them exhibited such terrific adhesion that it was ruined in the removal process. Is there any way that I can possibly re-use these antenna mounts?&lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2021-02-10T05:38:48.257" Title="can the adhesive used in thru-glass antenna couplers be replaced?" Tags="&lt;antenna&gt;&lt;windows&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18038" PostTypeId="2" ParentId="18037" CreationDate="2021-02-10T05:38:48.257" Score="4" Body="&lt;p&gt;Yes, there is. The protective tape that you peel off the mount before pressing it onto the window glass bears the emblem &amp;quot;3M&amp;quot;, identifying it as a product of the 3M adhesives group. A web search then reveals that fresh 3M industrial strength indoor/outdoor doublestick tape can be bought in rolls and precut squares at hardware stores as &amp;quot;Scotchmount Extreme&amp;quot; double-sided mounting tape. This product is almost identical to the original material, and I used it to re-attach both antenna mounts in their correct positions on my van.&lt;/p&gt;&#xA;&lt;p&gt;It is stout and weather-resistant enough that it can be used to attach license plates to car bumpers, and to attach chrome trim strips to automotive bodywork.&lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2021-02-10T05:38:48.257" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18039" PostTypeId="5" CreationDate="2021-02-10T12:59:29.167" Score="0" Body="" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2021-02-10T12:59:29.167" LastActivityDate="2021-02-10T12:59:29.167" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18040" PostTypeId="4" CreationDate="2021-02-10T12:59:29.167" Score="0" Body="For questions involving children, or young people. Either children in the hobby, or for teachers or elmers of children in the hobby" OwnerUserId="873" LastEditorUserId="873" LastEditDate="2021-02-10T12:59:29.167" LastActivityDate="2021-02-10T12:59:29.167" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18041" PostTypeId="2" ParentId="1985" CreationDate="2021-02-10T19:57:13.453" Score="1" Body="&lt;p&gt;The analogy between a guitar string and an antenna can be extended.&lt;/p&gt;&#xA;&lt;p&gt;A &lt;em&gt;disturbance&lt;/em&gt; traveling along the guitar string is reflected from the fixed ends, producing a standing wave on the string, while the individual molecules of the string are displaced relatively little. Similarly, a &lt;em&gt;disturbance&lt;/em&gt; travels at nearly light speed along the antenna conductor, while the antenna's individual electrons travel a relatively small distance in the duration of one cycle of excitation. Note that &lt;em&gt;harmonics&lt;/em&gt; can appear on the guitar string just as a linear conductor can be excited at multiples of its fundamental half-wave resonant frequency.&lt;/p&gt;&#xA;&lt;p&gt;Further, the &amp;quot;emitted&amp;quot; wave - whether sound or radio - travels in a direction perpendicular to the medium being excited. In a sound wave, it is the &lt;em&gt;disturbance&lt;/em&gt; (i.e., oscillating pressure) of air molecules that travels, not the air molecules themselves. For radio, the wave travels in a direction perpendicular to the varying electric and magnetic fields comprising the &lt;em&gt;transverse electromagnetic&lt;/em&gt; (TEM) wave.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-02-11T14:43:28.290" LastActivityDate="2021-02-11T14:43:28.290" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18042" PostTypeId="1" CreationDate="2021-02-10T20:22:49.307" Score="2" ViewCount="106" Body="&lt;p&gt;Imagine two dipole (or Yagi) antennas as might be used to create a circularly polarized combination antenna. The two are physically oriented (rotated) by 90 deg, and if in the same receiving plane, one signals is also delayed by 90 deg. The two signals can be combined with a duplexer and match to a common line (e.g. this: &lt;a href=&quot;https://www.qsl.net/sv1bsx/antenna-pol/polarization.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.qsl.net/sv1bsx/antenna-pol/polarization.html&lt;/a&gt; ). My interest is in 2m (~ 144 MHz).&lt;/p&gt;&#xA;&lt;p&gt;Now -- if used as a transmitter, it is easy to see how a circularly polarized signals is generated -- both antennas receive equal power with the correct phasing relationship. However as a receiver, if a linearly polarized signal is received, it may be picked up by only one of the two antennas, and the matching network will deliver some power to the feed line (as desired), but also some to the second (90 deg) antenna, which will re-radiate it thus degrading the overall antenna gain.&lt;/p&gt;&#xA;&lt;p&gt;Can this be mitigated ? Is it possible to build a practical (at 144 MHz) coupler-type circuit that eliminates cross-transfer between the two antennas ?&lt;/p&gt;&#xA;" OwnerUserId="18785" LastActivityDate="2021-02-12T21:03:14.100" Title="Coupling 2 Antennas to one line?" Tags="&lt;antenna&gt;&lt;polarization&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18043" PostTypeId="2" ParentId="18042" CreationDate="2021-02-10T21:03:27.610" Score="1" Body="&lt;p&gt;There is no passive solution which can magically choose the matching polarisation solution for the combiner.&lt;/p&gt;&#xA;&lt;p&gt;There are two types of splitters - a simple impedance match (say transforming 50 to 25 Ohms, with the two output cables in parallel), or a &lt;a href=&quot;https://en.wikipedia.org/wiki/Wilkinson_power_divider&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wilkinson-type splitter&lt;/a&gt; that does this but includes a resistor. The resistor provides isolation between the ports - so if a signal arrives at port 2, half of it leaves from port 1, and half is absorbed, none leaves from port 3.&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;splitter&amp;quot; used in the transmit case, splits the signal in half without loss, feeding both antennas equally. This works as you expect.&lt;/p&gt;&#xA;&lt;p&gt;In the receive case the two types of splitter end up giving the same result:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The simple impedance matching splitter will reflect some power and radiate some of the power out of the other polarisation antenna.&lt;/li&gt;&#xA;&lt;li&gt;The Wilkinson splitter will absorb half of the power from the receiving antenna, and not re-radiate it on the other polarisation. Half the power leaves at the common port.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;strong&gt;More general rambling&lt;/strong&gt;&lt;br /&gt;&#xA;I like to look it like this: whatever is going on inside the antenna, in the end it is a 1 port device with some radiation pattern and polarisation. If its a circularly polarised antenna, then it will behave like one, whatever is going on inside.&lt;/p&gt;&#xA;&lt;p&gt;Remember even when matched, all antennas scatter a fair fraction of the received power, they're not blackbodies that capture all the incident energy. Of course the two types will differ. But the scattering of incident fields is not (directly) part of how we measure an antenna.&lt;/p&gt;&#xA;&lt;p&gt;The QSL site mentions using a splitter for &lt;em&gt;stacking&lt;/em&gt; yagis for higher gain. This shows the fallacy even more clearly - it's like asking the array, on receive, to have the same high gain as the peak of the stacked array, but &lt;em&gt;everywhere&lt;/em&gt;, which is also not possible from a passive antenna.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-02-10T21:42:42.883" LastActivityDate="2021-02-10T21:42:42.883" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18044" PostTypeId="2" ParentId="16968" CreationDate="2021-02-11T14:54:05.580" Score="0" Body="&lt;p&gt;I've used the NATO phonetic alphabet to do business by teleconference with six continents. All but one of the letters works well: I have problems with &amp;quot;Lima&amp;quot; whether I'm on the air, speaking to a foreign call center or doing business.&lt;/p&gt;&#xA;&lt;p&gt;Suspecting that the &amp;quot;DX&amp;quot; were trained in &amp;quot;the Queen's English&amp;quot; rather than &amp;quot;American English,&amp;quot; I began replacing my American pronunciation - &amp;quot;Leema&amp;quot; - with what I hoped was a more &amp;quot;English&amp;quot; pronunciation - &amp;quot;Loima&amp;quot;. Sure enough, the error rate dropped precipitously.&lt;/p&gt;&#xA;&lt;p&gt;This demonstrates a practical use for the NATO alphabet in cross-cultural education.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-11T14:54:05.580" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18045" PostTypeId="2" ParentId="18042" CreationDate="2021-02-11T16:37:25.660" Score="4" Body="&lt;p&gt;It may help to be familiar with the concept of &lt;a href=&quot;https://en.wikipedia.org/wiki/Scattering_parameters&quot; rel=&quot;nofollow noreferrer&quot;&gt;scattering parameters&lt;/a&gt; or S-parameters. The S-parameters are the elements of a matrix which tell you the amplitude and phase coming out of every port, for the signal going into any other port. It assumes all the ports are terminated in matched loads, and it's usually valid for only one frequency.&lt;/p&gt;&#xA;&lt;p&gt;For a 3-port device, there are 9 S-parameters. They are written in a matrix like this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;[S] =&#xA;\begin{bmatrix}&#xA;S_{11} &amp;amp; S_{12} &amp;amp; S_{13} \\&#xA;S_{21} &amp;amp; S_{22} &amp;amp; S_{23} \\&#xA;S_{31} &amp;amp; S_{32} &amp;amp; S_{33}&#xA;\end{bmatrix}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The subscripts are ordered output, then input. So, &lt;span class=&quot;math-container&quot;&gt;$S_{21}$&lt;/span&gt; is related to how the input at port 1 contributes to what's observed at port 2.&lt;/p&gt;&#xA;&lt;p&gt;In the case of feeding an array of two antennas, you'll probably use a &lt;a href=&quot;https://en.wikipedia.org/wiki/Wilkinson_power_divider&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wilkinson power divider&lt;/a&gt;. Such a power divider with a 50/50 power split, where port 1 is the transceiver and ports 2 and 3 are the antennas, has a scattering matrix of:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;[S] =&#xA;\begin{bmatrix}&#xA;0 &amp;amp; {-j \over \sqrt 2} &amp;amp; {-j \over \sqrt 2} \\&#xA;{-j \over \sqrt 2} &amp;amp; 0 &amp;amp; 0 \\&#xA;{-j \over \sqrt 2} &amp;amp; 0 &amp;amp; 0&#xA;\end{bmatrix}&#xA;$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Consider transmitting: we're really only concerned with the power in to port 1, so we only need to look at the first column of the matrix. &lt;span class=&quot;math-container&quot;&gt;$S_{11}$&lt;/span&gt; is 0, meaning none of the power into port 1 is reflected back out port 1, meaning the SWR is 1:1.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$S_{21}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$S_{31}$&lt;/span&gt; are each &lt;span class=&quot;math-container&quot;&gt;${-j \over \sqrt 2}$&lt;/span&gt;. The &lt;span class=&quot;math-container&quot;&gt;$-j$&lt;/span&gt; term just means the phase of the output is rotated 90 degrees from the input, which would make sense because the power divider is constructed from 1/4-wave transmission lines. The need for the &lt;span class=&quot;math-container&quot;&gt;$\sqrt{2}$&lt;/span&gt; term should be obvious considering this is a passive network, and here we're also assuming ideal, lossless components. Thus, power out can't be more than power in. The S-parameters relate to amplitude and phase, so we must square them to get power. &lt;span class=&quot;math-container&quot;&gt;$ \left(1/\sqrt 2\right)^2 = {1 / 2} $&lt;/span&gt;, so half the power coming in port 1 goes out port 2, the other half goes out port 3.&lt;/p&gt;&#xA;&lt;p&gt;Now what if a signal is applied to port 2? &lt;span class=&quot;math-container&quot;&gt;$S_{12} = {-j \over \sqrt 2}$&lt;/span&gt;, so half the power goes back to the transceiver. &lt;span class=&quot;math-container&quot;&gt;$S_{22} = S_{32} = 0$&lt;/span&gt;, meaning none of the power goes to the other ports. The remaining half of the power is lost in the resistor.&lt;/p&gt;&#xA;&lt;p&gt;Port 3 is identical to port 2.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;However as a receiver, if a linearly polarized signal is received, it may be picked up by only one of the two antennas, and the matching network will deliver some power to the feed line (as desired), but also some to the second (90 deg) antenna, which will re-radiate it thus degrading the overall antenna gain.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Not quite! Because &lt;span class=&quot;math-container&quot;&gt;$S_{23} = S_{32} = 0$&lt;/span&gt;, none of the power received at one antenna port makes it to the other antenna port. There is no re-radiation. But because &lt;span class=&quot;math-container&quot;&gt;$S_{12} = S_{13} = {-j \over \sqrt 2}$&lt;/span&gt;, only half the power received at one of the antennas (assuming for now that only one antenna is receiving a signal) makes it to the receiver, which does indeed reduce antenna gain by 3 dB.&lt;/p&gt;&#xA;&lt;p&gt;Now what if &lt;em&gt;both&lt;/em&gt; antennas are receiving a signal simultaneously? Let's say the signal at each antenna port is &lt;span class=&quot;math-container&quot;&gt;$1 / \sqrt 2$&lt;/span&gt;, so that combined they have power 1. In order to determine what appears at the receiver, we must calculate:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{align}&#xA;&amp;amp;S_{12} {1 \over \sqrt 2} + S_{13} {1 \over \sqrt 2} \\&#xA;= &amp;amp;{-j \over \sqrt 2} {1 \over \sqrt 2} + {-j \over \sqrt 2} {1 \over \sqrt 2} \\&#xA;= &amp;amp;{-j \over 2} + {-j \over 2}\\&#xA;= &amp;amp;-j&#xA;\end{align}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$-j$&lt;/span&gt; is just 1 with a 90 degree phase shift, so all the power received by the antennas makes it to the receiver, just shifted in phase.&lt;/p&gt;&#xA;&lt;p&gt;But this only works when the signals are in phase. What if port 2 is receiving &lt;span class=&quot;math-container&quot;&gt;$1 / \sqrt 2$&lt;/span&gt; but port 3 is receiving the same thing, but 90 degrees shifted: &lt;span class=&quot;math-container&quot;&gt;$-j / \sqrt 2 $&lt;/span&gt;?&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{align}&#xA;&amp;amp;S_{12} {1 \over \sqrt 2} + S_{13} {-j \over \sqrt 2} \\&#xA;= &amp;amp;{-j \over \sqrt 2} {1 \over \sqrt 2} + {-j \over \sqrt 2} {-j \over \sqrt 2} \\&#xA;= &amp;amp;{-j \over 2} + {1 \over 2}&#xA;\end{align}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Converting this to &lt;a href=&quot;https://en.wikipedia.org/wiki/Complex_number#Polar_complex_plane&quot; rel=&quot;nofollow noreferrer&quot;&gt;polar form&lt;/a&gt; we find the magnitude is &lt;span class=&quot;math-container&quot;&gt;$1/\sqrt 2$&lt;/span&gt;, so we lost half the power. So in the case of receiving, the Wilkinson power divider (or I guess combiner, in this direction) is lossless only when ports 2 and 3 are in phase.&lt;/p&gt;&#xA;&lt;p&gt;Unsurprisingly, repeating the same thing with the antennas 180 degrees out of phase results in all the power lost.&lt;/p&gt;&#xA;&lt;p&gt;When you want to generate circular polarization, the transmitter will feed the power divider, then one of the power divider's outputs will have an additional 90 degree delay in it. On receive, this delay has the effect of combining received signals of the same circular polarization to be in-phase at the power divider's (or now, combiner) antenna ports to be in-phase, and they will make it to the receiver without loss.&lt;/p&gt;&#xA;&lt;p&gt;If the received signal is circularly polarized with opposite chirality, the signals are opposite phase at the power combiner, and the loss is theoretically infinite.&lt;/p&gt;&#xA;&lt;p&gt;If the received signal is linearly polarized (at any angle, horizontal, vertical, or otherwise) then the phase shift is 90 degrees and half the power is lost.&lt;/p&gt;&#xA;&lt;p&gt;There is no way around this with just receiver and one antenna. More generally, any antenna or antenna array you build must pick one point on the &lt;a href=&quot;https://en.wikipedia.org/wiki/Polarization_(waves)#Poincar%C3%A9_sphere&quot; rel=&quot;nofollow noreferrer&quot;&gt;Poincaré sphere&lt;/a&gt;, and there will always be an opposite point on that sphere that's orthogonal to your antenna which you can't receive, with all other possible polarizations on the sphere having some loss between zero and infinity.&lt;/p&gt;&#xA;&lt;p&gt;If you want to receive any polarization without loss, then you must build two antennas and two receivers, each occupying opposite points on the Poincaré sphere. There is then some combination of amplitude and phase coefficients with which those signals can be combined to receive an incoming signal at any polarization with zero loss.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-02-12T21:03:14.100" LastActivityDate="2021-02-12T21:03:14.100" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18046" PostTypeId="1" AcceptedAnswerId="18047" CreationDate="2021-02-11T20:44:24.527" Score="3" ViewCount="65" Body="&lt;p&gt;I was looking at the selection of modem bauds for DireWolf and it seems the highest baud modem is 9600 baud, and I am using a sound card that can reach 48 khz. Is there any way that I can write a modem for DireWolf to utilize the 48 khz capabilities of the sound card?&lt;/p&gt;&#xA;" OwnerUserId="10855" LastEditorUserId="1550" LastEditDate="2021-02-11T20:48:44.417" LastActivityDate="2021-02-12T00:16:37.480" Title="How do I write a modem for DireWolf?" Tags="&lt;packet&gt;&lt;software-development&gt;&lt;modem&gt;&lt;direwolf&gt;&lt;tnc&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18047" PostTypeId="2" ParentId="18046" CreationDate="2021-02-12T00:16:37.480" Score="4" Body="&lt;p&gt;Actually, direwolf already supports higher data rates since 2017; it will use the G3RUH modem for a speed of 9600 &lt;em&gt;or higher&lt;/em&gt;. As shipped it can be configured up to 40000 bps.&lt;/p&gt;&#xA;&lt;p&gt;But it's a mistake to think that 9600bps isn't making use of a 48kHz sample rate. The author has &lt;a href=&quot;https://github.com/wb2osz/direwolf/blob/master/doc/Going-beyond-9600-baud.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;done some testing&lt;/a&gt; which shows that 9600bps is about the highest rate that works reliably with 48KHz (and in fact it benefits slightly from 96kHz); 14.4kbps and 19.2kbps require 96kHz sampling to work respectably, and higher rates require 192kHz.&lt;/p&gt;&#xA;&lt;p&gt;You can, of course, attempt to write your own modem that performs better; I can't provide much advice on how to do it, except... do it. Look at &lt;code&gt;demod_afsk.c&lt;/code&gt; (300 and 1200), &lt;code&gt;demod_psk.c&lt;/code&gt; (2400 and 4800), and &lt;code&gt;demod_9600.c&lt;/code&gt; (9600+), make your own with a corresponding set of public functions, wire it into &lt;code&gt;demod.c&lt;/code&gt; and &lt;code&gt;config.c&lt;/code&gt;, and give it a try. The included &lt;code&gt;gen_packets&lt;/code&gt; and &lt;code&gt;atest&lt;/code&gt; utilities will be helpful for testing.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-02-12T00:16:37.480" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18048" PostTypeId="1" AcceptedAnswerId="18049" CreationDate="2021-02-13T02:45:53.637" Score="2" ViewCount="67" Body="&lt;p&gt;I have a noise problem on 40, 20, and 15 meters originating from the plasma TV I own. Turning on the TV raises the noise level by 2–4 S units, depending on the frequency. The TV is located below the antenna in the attic. The RFI also affects my outdoor antenna, to a lesser extent. My troubleshooting so far:&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Things that don’t help&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Plug either the TV or the transceiver into a battery power station, while the other is on grid power.&lt;/li&gt;&#xA;&lt;li&gt;Wrap the TV’s power cable through a toroid core close to the TV (3–4 turns through an FT240-43).&lt;/li&gt;&#xA;&lt;li&gt;Same type toroid core at antenna feed point, 8 turns.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;Things that eliminate the noise&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Power off the TV.&lt;/li&gt;&#xA;&lt;li&gt;Unplug the coax feed line from the transceiver.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;Things that reduce the noise strength&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Unplug the antenna from the coax feed line. Noise is still present but quieter. Touching the center prong of the PL-259 coax feeds noise into it, as if I'm also an antenna.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;My conclusion is that the TV is radiating RFI, without even the cables acting as antenna wires. Perhaps the metal mounting frame is acting as an antenna?&lt;/p&gt;&#xA;&lt;p&gt;What might I do to eliminate the noise? Do I have options for this indoor attic antenna other than an expensive noise cancellation device?&lt;/p&gt;&#xA;&lt;p&gt;FYI, the TV is an &lt;a href=&quot;https://ham.stackexchange.com/questions/18048/reducing-cross-band-noise-from-plasma-tv?noredirect=1#comment31291_18048&quot;&gt;LG 60PB5600&#xA;60” Class Full HD 1080p Plasma TV&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17488" LastEditorUserId="17488" LastEditDate="2021-02-15T19:32:47.890" LastActivityDate="2021-02-15T19:32:47.890" Title="Reducing cross-band noise from plasma TV" Tags="&lt;rfi&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18049" PostTypeId="2" ParentId="18048" CreationDate="2021-02-13T19:17:18.147" Score="4" Body="&lt;p&gt;The RFI is generated by —and is radiated from— the screen itself.&lt;/p&gt;&#xA;&lt;p&gt;You would have to put the plasma TV inside a Faraday cage to eliminate your RFI. This is why plasma TVs are no longer being made. (Having said that, there was at least one brand of plasma TV (Panasonic?) that was not a prolific RFI generator.)&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;A plasma set, unlike a LCD, requires relatively high voltage to turn the pixels on and off (rather like a neon bulb) and this is occurring at the refresh rate of the TV. This generates significant wideband interference due to the harmonics from this high voltage switching.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.electro-tech-online.com/threads/plasma-tv-radiation.133048/&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;sup&gt;Reference&lt;/sup&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://youtu.be/_5VsDxIglCE&quot; rel=&quot;nofollow noreferrer&quot;&gt;YouTube: the sound of the RFI from a Samsung P2 plasma TV&lt;/a&gt;. Note the text below it, where Samsung exchanged it for a P3.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://www.dxengineering.com/techarticles/lightningandrfiinfo/plasma-tv-mother-of-all-rfi-producers&quot; rel=&quot;nofollow noreferrer&quot;&gt;Plasma TV --- Mother Of All RFI Producers&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://www.google.com/search?&amp;amp;q=%2Bplasma+tv+rfi+interference&quot; rel=&quot;nofollow noreferrer&quot;&gt;More information: Google search&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/search?q=%22Plasma+tv%22&quot;&gt;Previous Q&amp;amp;As here about them&lt;/a&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Sorry to be the bringer of bad news here, but about the only solution is to sell the plasma TV and buy a newer type that doesn't spew RFI.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2021-02-14T18:36:23.497" LastActivityDate="2021-02-14T18:36:23.497" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18050" PostTypeId="1" AcceptedAnswerId="18076" CreationDate="2021-02-13T23:29:01.733" Score="0" ViewCount="22" Body="&lt;p&gt;I am not sure what to put in the TNC Port window on Xastir if I'm using a Mobilinkd TNC2.  Xastir has directions for just this however, it is for Ubuntu Linux. &lt;a href=&quot;https://xastir.org/index.php/HowTo:BluetoothTNC&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://xastir.org/index.php/HowTo:BluetoothTNC&lt;/a&gt;  I'm on Mac OSX 10.15.5 and rfcomm doesn't exist.&lt;/p&gt;&#xA;&lt;p&gt;I think I need to bind the bluetooth device/port to another port to keep it open.  I may be making stuff up though.&lt;/p&gt;&#xA;&lt;p&gt;I have tried entering the ports from /dev/* that are related to the device (ie. tty.MobilinkdTNC2-DevB) but it still fails.&lt;/p&gt;&#xA;" OwnerUserId="18818" LastActivityDate="2021-02-20T19:19:07.370" Title="Connecting Mobilinkd TNC2 to Mac for Xastir" Tags="&lt;aprs&gt;&lt;tnc&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18051" PostTypeId="1" AcceptedAnswerId="18053" CreationDate="2021-02-14T12:26:51.083" Score="2" ViewCount="100" Body="&lt;p&gt;I'm currently in a rocket team and we are building a rocket that can reach 3000m (10.000 feet). I am responsible to find an antenna for the telemetry system. I was searching on the net to find the best antenna but I didn't understand most of the technical terms. Can someone answer these questions? Thanks :)&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;We are using a 433 MHz RF module. Is the antenna should be 433&#xA;MHz or can it be more? Can I use 868 MHz antenna?&lt;/li&gt;&#xA;&lt;li&gt;Is 433 MHz RF Module enough for the 10.000 feet? (The distance could be more than 10K feet.)&lt;/li&gt;&#xA;&lt;li&gt;There are some details of our RF Module. I found this antenna but I'm not sure that it can work at 10.000 feet (The total distance could be more than 10K feet. We are assuming that distance is 20K feet). Can someone say to me his/her thoughts?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;strong&gt;RF MODULE DETAILS&lt;/strong&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/puems.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/puems.jpg&quot; alt=&quot;RF MODULE DETAILS&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.m2mmarket.com.tr/e32-ttl-1w-302&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.m2mmarket.com.tr/e32-ttl-1w-302&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;ANTENNA DETAILS&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SdqXv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SdqXv.png&quot; alt=&quot;https://www.m2mmarket.com.tr/U151,36,2j010-868-mhz-rf-anten-2j.htm&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.m2mmarket.com.tr/U151,36,2j010-868-mhz-rf-anten-2j.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.m2mmarket.com.tr/U151,36,2j010-868-mhz-rf-anten-2j.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18820" LastEditorUserId="9621" LastEditDate="2021-02-15T12:48:12.493" LastActivityDate="2021-02-19T14:11:27.567" Title="Selecting antenna for rocket telemetry system" Tags="&lt;antenna&gt;&lt;antenna-system&gt;&lt;telemetry&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18052" PostTypeId="1" CreationDate="2021-02-14T18:46:04.987" Score="0" ViewCount="49" Body="&lt;p&gt;I've recently become interested in ham radio, particularly AX.25/FX.25 packet radio. I ordered the basic setup (RPI, DireWolf, BaoFeng, a sound card, and some cables) and I was wondering with this setup if I could work the ISS digipeater. If this is not possible an explaination about how would be nice, or even a point in the right direction would be welcome. I'm here to learn, so any guidance would be a blessing!&lt;/p&gt;&#xA;" OwnerUserId="10855" LastEditorUserId="8717" LastEditDate="2021-02-15T20:00:00.667" LastActivityDate="2021-02-15T20:00:00.667" Title="Can I use a DireWolf based digipeater to work the ISS digipeater?" Tags="&lt;satellites&gt;&lt;packet&gt;&lt;direwolf&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18053" PostTypeId="2" ParentId="18051" CreationDate="2021-02-15T13:27:47.603" Score="3" Body="&lt;p&gt;You should use an antenna that is designed for the frequency of your RF module unless you have a compelling reason to choose a different antenna. A properly designed antenna will make the best use of the RF module's output power and avoid damage to the RF module.&lt;/p&gt;&#xA;&lt;p&gt;If you decide to use an antenna designed for a different frequency range from the RF module, you should probably design and insert an impedance-matching network between the RF module and the antenna to protect the RF module from power reflected by the mismatched antenna. Here's an example from the datasheet for a PCB-mounted chip antenna:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/cVKYh.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/cVKYh.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The chip antenna is the 4.5-mm x 13-mm rectangle on the right-hand side of the diagram. The black rectangles in the &amp;quot;Matching Circuit&amp;quot; are surface-mount (SMT) inductors and/or capacitors in a &lt;span class=&quot;math-container&quot;&gt;$\pi$&lt;/span&gt;-network configuration. The rectangle at the bottom of the &amp;quot;Matching Circuit&amp;quot; is a ground pad with vias that pass through the PCB to make a low-impedance connection to the copper plane on the back side.&lt;/p&gt;&#xA;&lt;p&gt;Well-known electronic parts distributors sell a variety of &lt;a href=&quot;https://www.mouser.com/datasheet/2/238/ant-410-cw-qw-ds-1841219.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;monopole&lt;/a&gt;, &lt;a href=&quot;https://www.mouser.com/datasheet/2/238/ant-433-cw-rah-1506928.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;helical monopole&lt;/a&gt;, &lt;a href=&quot;https://www.mouser.com/datasheet/2/398/PC240.09.0300K-1220729.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;dipole&lt;/a&gt;, &lt;a href=&quot;https://www.mouser.com/datasheet/2/238/ant_433_fpc_ufl_100_ds-1928404.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;patch&lt;/a&gt; and &lt;a href=&quot;https://www.yageo.com/upload/media/product/productsearch/datasheet/wireless/An_SMD_UHF_433_1204_0.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;chip&lt;/a&gt; antennas that might work in your application. Your antenna of choice must survive high acceleration in atmosphere and add as little drag as possible to the rocket assembly. The size, shape and mounting arrangement will all be important. An antenna with very low gain (large negative dB value) and/or low efficiency will not radiate the signal from the RF module as well as an antenna with more gain and higher efficiency.&lt;/p&gt;&#xA;&lt;p&gt;The &lt;a href=&quot;https://linxtechnologies.com/wp/support/application-notes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;application notes&lt;/a&gt; section of the &lt;a href=&quot;https://linxtechnologies.com/wp/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Linx Technologies&lt;/a&gt; web page contains numerous useful documents with which you could educate yourself. I refer you, in particular to &lt;a href=&quot;https://linxtechnologies.com/wp/wp-content/uploads/an-00501.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;AN-00501: Understanding Antenna Specifications and Operation&lt;/a&gt;, which discusses all of the important factors you need to consider when choosing your antenna.&lt;/p&gt;&#xA;&lt;p&gt;I provide the links only as examples of your antenna options. I am not affiliated with any distributor or manufacturer.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-02-16T10:27:35.387" LastActivityDate="2021-02-16T10:27:35.387" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18054" PostTypeId="2" ParentId="17785" CreationDate="2021-02-16T00:15:01.707" Score="2" Body="&lt;p&gt;The ionosphere conversion to circular is not particularly good - e.g. see &lt;a href=&quot;https://web.archive.org/web/20200624114945/cv.nrao.edu/%7Edemerson/ionosphere/ionopol.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;cv.nrao.edu/~demerson/ionosphere/ionopol.html&lt;/a&gt;. This means that the circular polarization is very variable (ratio of major:minor axis signal strengths). Conversely the (linear) polarization alignment of most satellite signals is unpredictable from the receiver's point of view - maybe the satellite is tumbling. Because of that, a circularly polarized receiving antenna will work 'least bad' -- it's sensitivity is independent of the actual alignment of the linear polarization, although it is about 3 dB worse than a correctly aligned linear antenna would be (but you'd have to continually rotate it to align with the transmitter).&lt;/p&gt;&#xA;&lt;p&gt;So a circularly polarized receiving antenna won't have any nulls when receiving a linearly polarize signal (at any angle), while a linearly polarized (e.g. a standard) antenna could have nulls if misaligned by 90°, and will be worse than the circular one for misalignments of between -45° and +45°. Thus, unless you can control or adjust a linearly polarized antenna, on average, 50% of the time, the circular one will be better (all other things being equal), and the circular will never have a null where it receives nothing.&lt;/p&gt;&#xA;" OwnerUserId="18785" LastEditorUserId="4665" LastEditDate="2021-02-16T00:26:37.737" LastActivityDate="2021-02-16T00:26:37.737" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18055" PostTypeId="1" AcceptedAnswerId="18057" CreationDate="2021-02-16T01:28:56.963" Score="2" ViewCount="111" Body="&lt;p&gt;If one tunes an HF/MF radio at night, the lower the frequency (or the longer the wavelength) of the band, the more QRN (static and atmospheric noise) there is.  80m is noisier than 40m, and 160m is noisier than 80m.  (I haven't operated on the exotic new 630m or 2200m bands yet, but I wouldn't be surprised to hear that they are even worse.)&lt;/p&gt;&#xA;&lt;p&gt;Why is the QRN worse the lower one tunes in frequency on the HF and MF bands?&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-03-17T16:23:26.010" LastActivityDate="2021-03-17T16:23:26.010" Title="Why is QRN so bad on the low HF and MF bands?" Tags="&lt;hf&gt;&lt;noise&gt;&lt;mf&gt;&lt;160m-band&gt;&lt;qrn&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18056" PostTypeId="1" AcceptedAnswerId="18059" CreationDate="2021-02-16T09:24:52.737" Score="1" ViewCount="147" Body="&lt;p&gt;I currently own a 7 Watt Frequency Modulation (FM) transmitter that I purchased from &lt;a href=&quot;https://www.ebay.com/itm/CZE-7C-7W-Stereo-PLL-FM-Transmitter-Broadcast-Radio-Station-Kit-Original/224263129602?hash=item34371fca02:g:XRoAAOSwrEJfyTQn&quot; rel=&quot;nofollow noreferrer&quot;&gt;eBay&lt;/a&gt; some years ago.&lt;/p&gt;&#xA;&lt;p&gt;We are planning a drive-in cinema setup where the transmitter will be placed 5 meters above ground at &lt;a href=&quot;https://goo.gl/maps/tPffnyfQ8r8WKLE57&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt; location.&lt;/p&gt;&#xA;&lt;p&gt;A technician I interacted with informs me that considering the number of cars that might show up, about 300, the transmitter signal will severaly degrade as the cars will pretty much cause interference and signal power will have to be boosted.&lt;/p&gt;&#xA;&lt;p&gt;Is there a formula / mathematical calculation that can help me determine how many cars can tune into the assigned frequency without experiencing a drop in audio quality?? Or a formula to help determine how much transmission power is needed?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/X1PrG.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/X1PrG.jpg&quot; alt=&quot;picture from online auction of a monopole whip antenna&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18832" LastEditorUserId="4665" LastEditDate="2021-02-16T14:43:10.293" LastActivityDate="2021-02-17T15:29:49.700" Title="How many cars/devices can connect to a transmission from a 7 Watt FM transmitter" Tags="&lt;frequency&gt;&lt;transmitter&gt;&lt;fm&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18057" PostTypeId="2" ParentId="18055" CreationDate="2021-02-16T11:24:57.123" Score="4" Body="&lt;p&gt;The primary source of atmospheric radio noise is the &lt;a href=&quot;https://web.archive.org/web/20140324022356/http://www.sos.noaa.gov/Datasets/dataset.php?id=6#&quot; rel=&quot;nofollow noreferrer&quot;&gt;estimated 40&lt;/a&gt; lightning strikes that occur each second around the world. NASA's &lt;a href=&quot;https://ntrs.nasa.gov/api/citations/19870001225/downloads/19870001225.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Review of Measurements of the RF Spectrum of Radiation from Lightning&lt;/a&gt; (1986) shows a 1/f decline in electromagnetic field strength vs. frequency from lightning discharge:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mwFfu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mwFfu.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Electromagnetic energy radiated from these strikes at the varying frequencies propagates to different distances via the usual means of reflection and refraction from the earth and the ionosphere.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-16T11:24:57.123" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18058" PostTypeId="2" ParentId="18056" CreationDate="2021-02-16T15:24:33.193" Score="1" Body="&lt;p&gt;In my experience, RF noise from vehicles comes from engine ignition systems (distributors, ignition coils, spark plugs, and spark plug cables) of gasoline-fueled vehicles, but ignition systems in cars made over the last 30 years or so are much better shielded than older cars' ignition systems.  Diesel-fueled vehicles don't have ignition systems at all.  The customers of your drive-in cinema will hopefully stop their engines to watch the films, anyway.&lt;/p&gt;&#xA;&lt;p&gt;I doubt that you will have a problem.  Good luck, and please come back and tell us how things went.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-02-16T15:24:33.193" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18059" PostTypeId="2" ParentId="18056" CreationDate="2021-02-16T20:59:11.180" Score="5" Body="&lt;p&gt;The number of cars is not an issue. Driving in a city with thousands of cars in your vicinity still allows FM reception. Engines are running, which is probably not the case when watching a film in a drive-in cinema.&lt;/p&gt;&#xA;&lt;p&gt;For good stereo reception (26 dB audio signal to noise) you need a field strength of 100 µV/m or more. In a Rayleigh path with reflections you need about 26 dB reserve to guarantee that 100 µV/m is reached at 97 % of the positions. In case of no reception the car must be moved a few centimeters. The statistics are from experience; not from mathematics. This is valid for a receiver with a single antenna. Antenna diversity in the receiver is another situation; much better reception.&lt;/p&gt;&#xA;&lt;p&gt;So design your system for 2 mV/m for the largest distance on the parking of that cinema. I assume the screen size does not allow more than 200 meters distance.&lt;/p&gt;&#xA;&lt;p&gt;See: &lt;a href=&quot;https://electronics.stackexchange.com/questions/284699/formula-for-field-strength&quot;&gt;https://electronics.stackexchange.com/questions/284699/formula-for-field-strength&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;and then you see that 5 mW TX-power can give that reception.&#xA;The mentioned 7 watts gives acceptable reception in 6 to 7 km.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="18450" LastEditDate="2021-02-17T15:29:49.700" LastActivityDate="2021-02-17T15:29:49.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18060" PostTypeId="2" ParentId="356" CreationDate="2021-02-17T00:45:47.533" Score="0" Body="&lt;p&gt;ACMA (Australia) allows 30 seconds of non-copyrighted music. If you listen to the WIA news broadcast you will see examples of that. ACMA also has no issues with with background music if you are in a noisy location and need to transmit.&lt;/p&gt;&#xA;" OwnerUserId="18839" LastActivityDate="2021-02-17T00:45:47.533" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18061" PostTypeId="2" ParentId="356" CreationDate="2021-02-17T01:55:08.943" Score="1" Body="&lt;p&gt;This is strictly my opinion, and I'm not a lawyer, but I did once read &lt;a href=&quot;http://www.arrl.org/shop/200-Meters-and-Down/&quot; rel=&quot;nofollow noreferrer&quot;&gt;200 Meters and Down&lt;/a&gt; by Clinton B. DeSoto.  I don't have sources.&lt;/p&gt;&#xA;&lt;p&gt;In the early days of radio in the US there were few rules, and hams and broadcasters used the same frequencies and interfered with each other.  When rules were created separate roles for broadcasters and hams were defined and codified into law.  Hams were given their own bands.  However early receivers could easily pick up ham bands as well as broadcast bands, so the broadcasters asked for, and received, a law that hams would not be allowed to transmit anything that could be construed as entertainment, especially not music, so that broadcasters would have the exclusive right to broadcast entertainment.&lt;/p&gt;&#xA;&lt;p&gt;This law, &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.113&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR § 97.113(a)(4)&lt;/a&gt;, was essentially written before World War II, when the only form of broadcasting in widespread use was AM.  This law is still with us.  However, the original motivation for the law prohibiting music evaporated decades ago; there is essentially no way for a ham who wanted to broadcast entertainment on the ham bands to reach a significant audience.  Hams aren't allowed to transmit wideband FM or digital television.  Hams are allowed to transmit AM, but only at low power levels that would be difficult to pick up well with a typical AM broadcast receiver, but broadcast receivers no longer cover the ham bands.  Ham radio could conceivably be broadcast by a special interest group to allow them to get their message out, but really a low-powered broadcast TV or radio station or the internet would suit that purpose far better.&lt;/p&gt;&#xA;&lt;p&gt;Because the original motivation for the law has completely evaporated and someone broadcasting music on the ham bands would only reach other hams, the FCC is unlikely to care much if some misguided individual were to try.  Sure, the broadcasting ham would be reported, and the FCC might even bring enforcement action for the sake of form, but any such action would likely be very slow.&lt;/p&gt;&#xA;&lt;p&gt;So the answer to the original poster's questions about whether specific things would be allowed or not is that it doesn't really matter, because nobody really cares but us hams.  Let's use common sense as our guide when deciding what is allowed under the law.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-02-17T02:00:47.193" LastActivityDate="2021-02-17T02:00:47.193" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18063" PostTypeId="2" ParentId="6438" CreationDate="2021-02-17T04:55:06.363" Score="-2" Body="&lt;p&gt;Scramble the characters 5 in a group. Start listening at 6 wpm. Repeat daily for 45 minutes per session. It'll take approximately 3 months where a student will be able to read at 12 wpm.&lt;/p&gt;&#xA;" OwnerUserId="18842" LastActivityDate="2021-02-17T04:55:06.363" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18064" PostTypeId="1" CreationDate="2021-02-17T21:40:46.493" Score="0" ViewCount="34" Body="&lt;p&gt;I have an IQ file and have the following information:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;7.171Mhz / 2.5 megasamples per second&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;My question is with this information, can I view view from the IQ file with the above settings? Is it possible with QSSTV or GQRX?&lt;/p&gt;&#xA;&lt;p&gt;Would I need to convert it to a WAV file first?&lt;/p&gt;&#xA;&lt;p&gt;Thanks&lt;/p&gt;&#xA;" OwnerUserId="18847" LastActivityDate="2021-02-17T21:40:46.493" Title="Viewing SSTV with QSSTV/GQRX" Tags="&lt;sstv&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18065" PostTypeId="2" ParentId="16443" CreationDate="2021-02-18T07:29:45.390" Score="1" Body="&lt;p&gt;I had the same problem, and found that the noise was due to electric meter telemetry.  Our neighborhood is awash in this.  It is regular, and it disappears on its own in about the same time to give the power button a meaningless quick push!  Rather than push the power button for momentary relief, I 'found' that switching the channel and returning it 'did the trick'!  But, alas, I think it was my imagination and not flipping the channel selector back and forth that was eliminating the static.  A better radio with front end bandpass filter won't suffer this issue.  The QYT lets anything in.  I can transmit much farther than I can receive, and the noise floor rises considerably coming up to Interstate speed.  With the squelch off, this is very noticeable.&lt;/p&gt;&#xA;" OwnerUserId="18849" LastActivityDate="2021-02-18T07:29:45.390" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18066" PostTypeId="1" AcceptedAnswerId="18067" CreationDate="2021-02-19T00:49:10.360" Score="4" ViewCount="227" Body="&lt;p&gt;I know that a Hustler MO-3 54&amp;quot; mast with something like a RM-20S resonator on top is officially an example of a center-loaded quarter-wave vertical...&lt;/p&gt;&#xA;&lt;p&gt;... but Hustler also allows you to mount &lt;em&gt;multiple&lt;/em&gt; resonators (say, a RM20 or RM20S + RM30 + RM40 or RM40S) by using their VP-1 bracket, which basically looks like a metal triangle whose ends are bent at an angle &amp;amp; have a hole centered within the bent ends for mounting up to 3 such resonators, and a hole in the middle to mount the whole assembly to the top of a mast (like the MO-3).&lt;/p&gt;&#xA;&lt;p&gt;I'm scratching my head trying to figure out what you'd actually &lt;em&gt;call&lt;/em&gt; that type of antenna, though.&lt;/p&gt;&#xA;&lt;p&gt;On one hand, the coils might act kind of like traps... but &lt;em&gt;then&lt;/em&gt;, that logically implies that it only acts like a single-band antenna for frequencies at or above the frequency of the highest band's resonator mounted to it. In other words, if you had resonators for 20m, 30m, and 40m mounted, 28MHz would see it as a single center-loaded quarter-wave vertical (because it would be blocked by the 30m and 40m resonators' coils), but wtf happens when you're transmitting on 7-10MHz?It seems like at 7mhz, you'd have RF dividing itself up among &lt;em&gt;all three&lt;/em&gt; of the resonators (and their whips at the top) &amp;amp; end up with an antenna type that probably has a different name than merely &amp;quot;center-loaded quarter-wave vertical&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;If it's not obvious, I'm seriously intrigued by the idea of combining multiple Hustler resonators on a mast via something like their VP-1 bracket. Given that these products have been around since before most of us were even born, &lt;em&gt;someone&lt;/em&gt; has to have written about them, their design, and their theory of operation by now. If not a dissertation, maybe an article in QST or 73 magazine sometime in the 1970s or 1980s. But without knowing the proper name for an antenna that results from mounting two or more resonators above a shared mast, I'm searching for a needle in a haystack.&lt;/p&gt;&#xA;&lt;p&gt;Some photos  &amp;amp; a description of an antenna like this are at &lt;a href=&quot;https://ab4bj.com/wordpress/2017/01/ab4bj-portable-antenna-system/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ab4bj.com/wordpress/2017/01/ab4bj-portable-antenna-system/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;img src=&quot;https://i1.wp.com/ab4bj.com/wordpress/wp-content/uploads/kennesaw2-600x800-e1483401648452.jpg?ssl=1&quot; alt=&quot;One photo from the above-linked site&quot; /&gt;&lt;/p&gt;&#xA;" OwnerUserId="9101" LastEditorUserId="9101" LastEditDate="2021-02-20T04:56:49.650" LastActivityDate="2021-02-20T04:56:49.650" Title="What do you call antenna that combines multiple Hustler resonators (using a VP-1) above a shared mast?" Tags="&lt;antenna-theory&gt;&lt;vertical-antenna&gt;&lt;theory&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18067" PostTypeId="2" ParentId="18066" CreationDate="2021-02-19T01:17:46.937" Score="3" Body="&lt;p&gt;It appears that Hustler simply calls it a multiband vertical. I would call it a &amp;quot;center loaded fan vertical.&amp;quot; It's definitely a vertical, being operated against some conductor that represents &amp;quot;ground&amp;quot; (e.g., auto body). And, the coil-loaded elements fan out in an arrangement similar to a fan dipole. Searching the internet turns up a coining of the term &amp;quot;fan dipole&amp;quot; by &lt;a href=&quot;https://www.qrz.com/db/vk6flab&quot; rel=&quot;nofollow noreferrer&quot;&gt;VK6FLAB&lt;/a&gt; in a &lt;a href=&quot;https://forums.qrz.com/index.php?threads/fan-vertical-antenna.641971/&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRZ forum&lt;/a&gt; post from 2019, but he appears to be referring to a monopole adaptation of the fan dipole.&lt;/p&gt;&#xA;&lt;p&gt;Each &amp;quot;resonator&amp;quot; - a loading coil plus whip - allows current to pass only on its design band of operation, but not on other bands. On bands &lt;em&gt;below&lt;/em&gt; the resonator's design frequency, the resonator presents a large &lt;em&gt;capacitive&lt;/em&gt; reactance, while on bands &lt;em&gt;above&lt;/em&gt; the resonator's design frequency, the resonator presents a large &lt;em&gt;inductive&lt;/em&gt; reactance, both of which impede the flow of RF current to render that resonator electrically open.&lt;/p&gt;&#xA;&lt;p&gt;As you point out, this product has been around since long before the allocation of the WARC bands to amateur operation. Individual resonators are available for bands from 80m through 10m, so it may be necessary to evaluate possible interactions between resonators on closely-spaced bands, e.g., 20-17-15 as a trio. I can't find any documentation on the response of combined resonators.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-02-19T12:19:10.373" LastActivityDate="2021-02-19T12:19:10.373" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18068" PostTypeId="2" ParentId="18066" CreationDate="2021-02-19T01:19:14.037" Score="3" Body="&lt;p&gt;It's analogous to a fan dipole, where you feed multiple dipoles, with different resonant frequencies, in parallel, under the assumption that if one of them corresponds to the band you're transmitting on, then it will have the lowest |Z| and therefore take most of the current, while the other elements remain more-or-less inactive. Except that:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;It's not a dipole, it's a monopole.&lt;/li&gt;&#xA;&lt;li&gt;The elements are coil-loaded rather than depending on their length for resonance.&lt;/li&gt;&#xA;&lt;li&gt;There's a shared segment (the mast) before the different elements split off, so it's not quite a proper &amp;quot;fan&amp;quot;.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I would just call it a multiband loaded vertical and call it a day. The theory behind it is going to be that of a loaded short vertical, combined with that of a fan dipole (for how the bands interact).&lt;/p&gt;&#xA;&lt;p&gt;The coils don't act as traps; instead, the wrong-band coil+whip combinations have (presumably) a large reactance, therefore a large overall impedance, which limits the share of current it will take compared to the right-band coil+whip combination. And when you add one small impedance in parallel with two much larger ones, the result will be pretty close to the small one, so the overall contraption is still a decent SWR match to your transmitter, provided that one of the elements alone would have been.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2021-02-19T01:30:31.883" LastActivityDate="2021-02-19T01:30:31.883" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18070" PostTypeId="1" AcceptedAnswerId="18078" CreationDate="2021-02-19T08:19:39.133" Score="4" ViewCount="100" Body="&lt;p&gt;I've seen that sometimes frequency selective surfaces are used to load a certain impedance to a certain antenna (for instance for input matching purposes).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tUs18.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tUs18.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;These surfaces act like a filter on the equivalent transmission line that describes the radiated wave propagation in the space surrounding the antenna.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.scielo.br/scielo.php?script=sci_arttext&amp;amp;pid=S2179-10742015000200217&quot; rel=&quot;nofollow noreferrer&quot;&gt;In this article&lt;/a&gt; an incident electromagnetic plane wave on a frequency selective surface made of a periodic sequence of square metal rings is considered.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6k8Qv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6k8Qv.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The authors say:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;When the transverse magnetic field faces the vertical strips, it induces current in the loop.&#xA;This current leads to a secondary magnetic field around the strips, within which magnetic energy is&#xA;stored. Thus, the vertical strips have an inductive effect.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Well, there are some things I don't understand:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;How can a time - varying magnetic field induce current in vertical strips and so in the loops? I have always been using the Faraday law in this way: time - varying magnetic flux across a surface =&amp;gt; Induced current along the loop that defines that surface.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;In this case, the magnetic field does not enter the surfaces of the loops.&lt;/p&gt;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;&lt;p&gt;Can we say that it's the Electric field of the wave that moves electrons in the vertical strips and causes current to flow?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Next, the article says that the magnetic field surrounds two adjacent vertical strips, like in the following picture:&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xA4j9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xA4j9.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Is it the magnetic field created by induced currents in the loops?&lt;/p&gt;&#xA;" OwnerUserId="16739" LastActivityDate="2021-02-21T23:58:33.627" Title="Frequency selective surfaces working principle" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;frequency&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18071" PostTypeId="1" CreationDate="2021-02-19T14:07:39.487" Score="0" ViewCount="25" Body="&lt;p&gt;In order to simulate the measurements on the computer (in the WinProp environment) I have to set the maximum Tx power:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7yff6.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7yff6.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;To find out what the transmitter signal power is, I checked it on the spectrum analyzer on the receiver. The receiver path gain was set to 6dB [Rx Gain] (USRP devices are uncalibrated, this 6dB setting in the receiver is a 'calibration' - Comparison with a calibrated device shows that then the results are correct. This is how my advisor told me to measure it). The results from the spectrum analyzer are shown in the figure below:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/x64rP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/x64rP.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I read from the analyzer that the power value is equal to -55 dBm. However, I measured for a receiver gain of 6dB. In fact, in the measurements I am operating at a receiver gain of 20 dB [Rx gain]. In this case, should I add 14 dB to the -55 dBm power value? Will this be my Tx power that I can enter in WinProp?&lt;/p&gt;&#xA;&lt;p&gt;The transmitter path gain was set to 10 dB [Tx gain]. The receiver gain was set to 20 dB [Rx gain]. How to calculate max Tx Power from this, taking into account my calculations above (for 6dB receiver gain)?&lt;/p&gt;&#xA;" OwnerUserId="18026" LastActivityDate="2021-02-19T14:07:39.487" Title="Setting the maximum Tx Power value for the USRP transmitter" Tags="&lt;receiver&gt;&lt;rf-power&gt;&lt;transceiver&gt;&lt;transmitter&gt;&lt;usrp&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18072" PostTypeId="2" ParentId="18051" CreationDate="2021-02-19T14:11:27.567" Score="1" Body="&lt;p&gt;It may be possible to use a conductive surface mounted on the outside of the rocket body as an antenna. Not knowing the dimensions of your rocket and without the benefit of any design equations, I used &lt;em&gt;EZNEC+&lt;/em&gt; to create a crude model of a &lt;em&gt;cavity-backed cylindrical slot&lt;/em&gt; antenna:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/LJFfP.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/LJFfP.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;cylinder&amp;quot; is about 6.5-m tall and 920-mm in &amp;quot;diameter,&amp;quot; the &amp;quot;slot&amp;quot; is about 4.2-m tall and 381-mm wide, producing this SWR curve with a 200-ohm reference impedance:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GrSZb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GrSZb.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot;Shortening&amp;quot; the slot while maintaining its &amp;quot;width&amp;quot; raises the resonant frequency and the feedpoint impedance. A &amp;quot;shorter&amp;quot; and &amp;quot;narrower&amp;quot; slot will produce a match at the desired frequency.&lt;/p&gt;&#xA;&lt;p&gt;The radiation is strongest and fairly omnidirectional off the ends of the cylinder:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/hefjU.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/hefjU.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-19T14:11:27.567" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18073" PostTypeId="2" ParentId="606" CreationDate="2021-02-20T03:30:53.253" Score="0" Body="&lt;p&gt;I have seen articles on antennas that use resistors have a lower noise floor . The Tilted Terminated Folded Dipole is one such antenna. This antenna was long used by the military and government entities.&lt;/p&gt;&#xA;" OwnerUserId="18864" LastActivityDate="2021-02-20T03:30:53.253" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18074" PostTypeId="1" CreationDate="2021-02-20T08:18:16.947" Score="0" ViewCount="32" Body="&lt;p&gt;I have several ground independent dual band antenna of different makes, but they all have the same type of matching circuit to make them ground independent / radial-less and match say 5/8 elements, something like pictured below. Ive been trying to model this in 4nec2 to get a similar result to what my nano vna shows, but not able to get there. Not sure this is the right software or approach to use. If its possible id like some tips, or advice on more suitable software.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xoap2.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xoap2.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17758" LastActivityDate="2021-02-20T12:14:08.613" Title="Software to model autotransformer matched end fed dual band, 4nec2?" Tags="&lt;impedance-matching&gt;&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18075" PostTypeId="2" ParentId="18074" CreationDate="2021-02-20T12:14:08.613" Score="1" Body="&lt;p&gt;Here's an example of what you could do with &lt;a href=&quot;https://eznec.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC+&lt;/a&gt;, a graphical user interface to the NEC2 computing engine. Note that the values below are not meant to represent a working design, they only serve to illustrate one use of the program. It may be possible to accomplish the same results with other (and free) software.&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;Wires&amp;quot; pane shows that the radiator is about 1/3-&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; long on 14.2-MHz. The square markers on the radiator are &amp;quot;loads,&amp;quot; while the circle on the radiator is the &amp;quot;source.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;The &amp;quot;Loads&amp;quot; pane shows:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The tapped coil is split into 1-&lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;H and 2-&lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;H sections placed towards the bottom of the radiator&lt;/li&gt;&#xA;&lt;li&gt;A 5-&lt;span class=&quot;math-container&quot;&gt;$\mu$&lt;/span&gt;H loading coil is placed near the middle of the upper section.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;The &amp;quot;Sources&amp;quot; pane shows that a current source is placed between the two sides of the tapped feedpoint coil.&lt;/p&gt;&#xA;&lt;p&gt;The SWR plot bottoms out at 13.85-MHz with an impedance of 42.5+j1.7&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, but we want to operate the antenna on the 20m band. The impedance is 49.8+j79&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; at 14.2-MHz; the 79&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; of inductive reactance could be canceled with a series-connected 142-pF capacitor, as shown in the OP's drawing, to deliver a near-perfect match.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EU5cq.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EU5cq.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-20T12:14:08.613" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18076" PostTypeId="2" ParentId="18050" CreationDate="2021-02-20T19:19:07.370" Score="2" Body="&lt;p&gt;After pairing to the TNC, use the &amp;quot;cu.***&amp;quot; port as the address in Xastir.&lt;/p&gt;&#xA;&lt;p&gt;For me it was: &amp;quot;/dev/cu.MobilinkdTNC2-DevB&amp;quot;. Set the baud to 9600 and click done.&lt;/p&gt;&#xA;&lt;p&gt;My connection failed after about 15 minutes.  I unpaired, repaired, and then the connection stayed up.&lt;/p&gt;&#xA;" OwnerUserId="18818" LastActivityDate="2021-02-20T19:19:07.370" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18077" PostTypeId="1" AcceptedAnswerId="18083" CreationDate="2021-02-21T05:52:50.730" Score="2" ViewCount="115" Body="&lt;p&gt;The way I understand it, is that to avoid aliasing on an ADC, you have to be in the first Nyquist zone (so half the sampling speed). What doesn't make sense to me is how the Hackrf is able to bypass this, and achieve 20MHz of bandwidth, even though the 1st Nyquist zone would be only 11MHz.&lt;/p&gt;&#xA;&lt;p&gt;I notice from the schematics that the MAX5864 ADC is two channels, with the baseband I signal going into one channel, and the baseband Q signal going into another. Do the two channels get added together, to form an overall bandwidth of 20MHz?&lt;/p&gt;&#xA;&lt;p&gt;Also, while I'm at it, what exactly is the purpose of using in an sdr? Is it to make modulation/demodulation easier?&lt;/p&gt;&#xA;" OwnerUserId="18868" LastActivityDate="2021-02-22T12:46:46.917" Title="How is the Hackrf able to achieve 20MHz of bandwidth with an ADC that only allows 22Msps?" Tags="&lt;software-defined-radio&gt;&lt;hackrf&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18078" PostTypeId="2" ParentId="18070" CreationDate="2021-02-21T09:36:26.497" Score="1" Body="&lt;p&gt;You had three separate questions there, I'll try to clarify some concepts:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;How can a time - varying magnetic field induce current in vertical&#xA;strips&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Faraday's law of induction tells us how much there is electromotive force (a kind of sum of voltages that must be dissipated in the loop) along a conductive loop when a magnetic field passing through that loop changes. However, a varying magnetic field can drive a charged particle in a single wire that is orthogonal to the direction of the magnetic field. In this case, there are moving electrons that act as current. For more explanation, see:&lt;br /&gt;&#xA;&lt;a href=&quot;https://physics.stackexchange.com/questions/211293/does-a-changing-magnetic-field-impart-a-force-on-a-stationary-charged-particle&quot;&gt;https://physics.stackexchange.com/questions/211293/does-a-changing-magnetic-field-impart-a-force-on-a-stationary-charged-particle&lt;/a&gt;&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Can we say that it's the Electric field of the wave that moves&#xA;electrons in the vertical strips and causes current to flow?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes, but that is not the whole story and is not enough to fully explain how the FSS works.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Next, the article says that the magnetic field surrounds two adjacent&#xA;vertical strips, like in the following picture: -- Is it the magnetic&#xA;field created by induced currents in the loops?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This graph seems to be a simplified representation of two parallel wires that carry current in the same direction (either directly in or out of your monitor). A single current-carrying wire has a magnetic field that loops around the wire. If you place two wires next to each other, then exactly between these two wires one wire creates a magnetic field pointing up and the other pointing down, causing them to cancel each other out. The authors of the paper use this to illustrate how they calculate the combined inductance of the two parallel wires from adjacent unit cells.&lt;/p&gt;&#xA;" OwnerUserId="194" LastEditorUserId="194" LastEditDate="2021-02-21T15:01:44.570" LastActivityDate="2021-02-21T15:01:44.570" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18079" PostTypeId="2" ParentId="18077" CreationDate="2021-02-21T16:26:24.153" Score="2" Body="&lt;p&gt;Are the two channels added together?  Yes and no.&lt;/p&gt;&#xA;&lt;p&gt;The whole point of collecting I and Q is so they can be treated as real and imaginary parts of a single complex sample.&lt;/p&gt;&#xA;&lt;p&gt;This is one of the key methods of SDR.&lt;/p&gt;&#xA;&lt;p&gt;This answer explains it well: &lt;a href=&quot;https://electronics.stackexchange.com/questions/39796/can-somebody-explain-what-iq-quadrature-means-in-terms-of-sdr&quot;&gt;https://electronics.stackexchange.com/questions/39796/can-somebody-explain-what-iq-quadrature-means-in-terms-of-sdr&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-02-21T18:18:43.060" LastActivityDate="2021-02-21T18:18:43.060" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18080" PostTypeId="2" ParentId="18077" CreationDate="2021-02-21T18:22:32.330" Score="4" Body="&lt;p&gt;The Nyquist limit is half the sampling rate because otherwise you can't distinguish a signal at a frequency &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt; from a signal at &lt;span class=&quot;math-container&quot;&gt;$f_s - x$&lt;/span&gt; which starts 180° out of phase from the first one — they give exactly the same sequence of real samples. But &lt;a href=&quot;https://ham.stackexchange.com/questions/17705/understanding-how-quadrature-heterodyning-captures-information-from-negative-fre&quot;&gt;quadrature sampling gives &lt;em&gt;exactly&lt;/em&gt; the phase information needed to resolve this ambiguity&lt;/a&gt;. Knowing &lt;span class=&quot;math-container&quot;&gt;$\sin \omega t$&lt;/span&gt; limits us to two of four quadrants, but knowing &lt;span class=&quot;math-container&quot;&gt;$\sin \omega t$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\cos \omega t$&lt;/span&gt; at the same time limits us to one quadrant. With this distinction provided, it's possible to distinguish frequencies up to &lt;span class=&quot;math-container&quot;&gt;$f_s$&lt;/span&gt; — or a little less, given that we still need to filter out frequencies above the sample rate, and filters have skirts.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-02-21T18:22:32.330" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18082" PostTypeId="1" AcceptedAnswerId="18086" CreationDate="2021-02-22T02:04:05.257" Score="1" ViewCount="72" Body="&lt;p&gt;I recently learned that these fancy modern ultra-low noise MMIC, while having &amp;lt;1dB noise figure around 1Ghz could be quite bad at low frequencies due to 1/f noise.&lt;/p&gt;&#xA;&lt;p&gt;What is lowest noise MMIC then for 160-20M bands?&#xA;I am only aware of MAR-6 and INA-02184/INA-02186 having noise figure of ~2-3dB.&lt;/p&gt;&#xA;&lt;p&gt;Does it even make sense to try to reduce noise figure of preamp below 3dB in these bands or environment noise is stronger anyway?&lt;/p&gt;&#xA;" OwnerUserId="546" LastActivityDate="2021-02-23T17:46:55.690" Title="Lowest noise MMIC for HF? (160-20M)" Tags="&lt;hf&gt;&lt;lna&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18083" PostTypeId="2" ParentId="18077" CreationDate="2021-02-22T12:46:46.917" Score="3" Body="&lt;p&gt;Another way to look at it is that an IQ ADC is really taking 2 independent (not added together) samples per IQ sample.  Thus the rate of information gathered is double from a just scalar sampling at 22 MHz.  The 90 degree offset between the 2 IQ sample components allows capturing phase information that can help a complex FFT (et.al.) differentiate between what would have been aliasing between spectrum above and below the heterodyning LO frequency.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-02-22T12:46:46.917" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18085" PostTypeId="1" AcceptedAnswerId="18099" CreationDate="2021-02-22T17:49:38.660" Score="4" ViewCount="91" Body="&lt;p&gt;I submitted an application for a vanity call sign &lt;a href=&quot;https://ham.stackexchange.com/q/16426/17659&quot;&gt;a little over 18 days ago&lt;/a&gt;, and it's marked &amp;quot;pending&amp;quot;. I presume that it will be processed soon, but the FCC's ULS search page is being slow and glitchy. Will the FCC e-mail me when the application is approved or rejected?&lt;/p&gt;&#xA;" OwnerUserId="17659" LastActivityDate="2021-02-23T23:25:39.427" Title="Does the FCC e-mail when a vanity call sign is approved?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;callsign&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18086" PostTypeId="2" ParentId="18082" CreationDate="2021-02-22T18:52:33.630" Score="4" Body="&lt;p&gt;The ambient noise on HF is so high that such a low noise figure will not appreciably improve performance. On 20 meters, the minimum ambient noise temperature you will encounter is about &lt;span class=&quot;math-container&quot;&gt;$3 \times 10^6 \:\mathrm K$&lt;/span&gt;, which corresponds to a noise figure of about 40 dB. Noise goes up with wavelength, reaching &lt;span class=&quot;math-container&quot;&gt;$3 \times 10^{10} \:\mathrm K$&lt;/span&gt; or 80 dB around 1 MHz.&lt;/p&gt;&#xA;&lt;p&gt;As a rule of thumb, if the noise figure of your receiver is 10 dB below the ambient noise, it adds no significant noise. So for HF, a receiver with a noise figure below 30 dB is already as good as it gets. See &lt;a href=&quot;https://ham.stackexchange.com/q/9832/218&quot;&gt;How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?&lt;/a&gt; for some additional detail.&lt;/p&gt;&#xA;&lt;p&gt;Also a point of fact: the second &amp;quot;M&amp;quot; in &amp;quot;MMIC&amp;quot; is for &amp;quot;microwave&amp;quot;. As such, there are no MMICs for HF. At HF, wavelengths are so long that there's no need to shrink things to MMIC sizes. By modern standards HF hardly even qualifies as RF, and excellent performance can be achieved with discrete components or ICs not even marketed for RF.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-02-23T17:46:55.690" LastActivityDate="2021-02-23T17:46:55.690" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18087" PostTypeId="1" CreationDate="2021-02-22T19:08:54.010" Score="1" ViewCount="22" Body="&lt;p&gt;I'm playing with Nodered that I'm trying to use to place an aprs object: it works but it does not suit me!&lt;/p&gt;&#xA;&lt;p&gt;No error on findu.com, correct display of frames on aprs.fi or on aprsdirect.com ... but on the other hand aprsr-is server is reporting a problem to me.&#xA;(call f5rvx-10 here : &lt;a href=&quot;http://france.aprs2.net:14501/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://france.aprs2.net:14501/&lt;/a&gt; )&lt;/p&gt;&#xA;&lt;p&gt;I've searched for a long time, tried different frames  but I can't find what's wrong : I only managed to get ... more errors ;)&lt;/p&gt;&#xA;&lt;p&gt;So, what means this remark ?&#xA;&lt;a href=&quot;https://i.stack.imgur.com/SzE9N.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SzE9N.png&quot; alt=&quot;error on aprsc status page&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;No column : in packet ... but where in it ?&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;F5RVX-10&amp;gt;APN100,TCPIP*,qAC,T2FRANCE:;TTN KONK *111111z4753.81N/00354.48Wrhttps://www.thethingsnetwork.org/community/concarneau/&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;(&lt;a href=&quot;https://aprs.fi/?c=raw&amp;amp;call=F5RVX-10&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://aprs.fi/?c=raw&amp;amp;call=F5RVX-10&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;thanks for your help and best 73,&#xA;Philippe, f5rvx&lt;/p&gt;&#xA;" OwnerUserId="18882" LastActivityDate="2021-02-22T19:08:54.010" Title="#APRS error ? (only visible on aprsc status)" Tags="&lt;aprs&gt;" AnswerCount="0" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18088" PostTypeId="1" AcceptedAnswerId="18103" CreationDate="2021-02-23T01:21:02.130" Score="3" ViewCount="99" Body="&lt;p&gt;I'm building a vertical antenna. The lowest portion of its element consists of 3/4&amp;quot; type M copper pipe, with end caps that will be soldered on and 3/8-24 screws poking through at both ends (so the bottom can screw into a 3/8-24 mobile mount, and the top can attach to Hustler mobile resonators like the RM-30 and RM-40).&lt;/p&gt;&#xA;&lt;p&gt;So far, so good... mechanically and electrically, it's decent (I wouldn't want to depend upon a single 3/8-24 screw to secure the entire lever force of an 8-10 foot antenna, but I'll have a second strap a few inches higher to secure it against swaying and lever force, so the lower screw's main purpose is to provide electrical contact with the RF signal, support its vertical weight, and keep it from drifting horizontally). However...&lt;/p&gt;&#xA;&lt;p&gt;I'm a Floridian, and I know from years of hard firsthand experience that any outdoor cavity that isn't airtight &lt;em&gt;inevitably&lt;/em&gt; ends up with water trapped inside. Why? Humid air gets inside, condenses when it eventually gets &amp;quot;cold&amp;quot;(-ish), and the same seal that keeps rainwater out eventually drowns the very circuit it's naively meant to protect.&lt;/p&gt;&#xA;&lt;p&gt;Is this an actual problem with antenna elements that have non-airtight cavities inside? Or is trapped water inside a hollow antenna element not actually a problem (because RF runs along the surface, or condensate is deionized &amp;amp; basically an insulator, etc)?&lt;/p&gt;&#xA;&lt;p&gt;If it IS a problem, how big of a hole do I need to put at the bottom for water to drain out, keeping in mind that the copper end caps aren't very thick to begin with, and any hole I drill is going to have a negative impact on what little structural strength it &lt;em&gt;has&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Putting the various dimensions into perspective, 3/4&amp;quot; type M copper pipe has an inside dimension of .8125&amp;quot;. A 3/8&amp;quot; screw is 0.375&amp;quot;. That means a perfectly-centered screw hole has at most .21875&amp;quot; of copper between the center hole and inside surface of the pipe.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;A 2mm hole is approximately .08&amp;quot; wide (2mm x 1 inch/25.4mm), or approximately 1/3 of the area. Probably ok, though, if it's drilled near the edge of the area.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;At 0.25&amp;quot;, 1/4&amp;quot; hole would literally be wider than the distance between the 3/8&amp;quot; screw and pipe wall. A 1/4&amp;quot; hole would HAVE to be drilled through the side, instead (i.e., perpendicular to the 3/8-24 screw... through the 3/4&amp;quot; pipe itself and side of the end cap).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="9101" LastEditorUserId="9101" LastEditDate="2021-02-23T18:32:46.940" LastActivityDate="2021-02-24T15:37:58.207" Title="If a sealed, non-airtight pipe is used as antenna element, how big of a problem is condensate trapped inside?" Tags="&lt;antenna-construction&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18089" PostTypeId="1" CreationDate="2021-02-23T05:45:18.890" Score="2" ViewCount="79" Body="&lt;p&gt;I want to install this miracle program on my smartphone in order to get more mobility.&lt;/p&gt;&#xA;&lt;p&gt;I found such a solution exists:&#xA;&lt;a href=&quot;https://github.com/bastibl/gnuradio-android&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/bastibl/gnuradio-android&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;However, I could not do everything as indicated in that article.&#xA;As I understand it, you need to create an installation file yourself, which can only then be installed as an application. But isn't there still a ready-made installation file?&#xA;I am not good at programming, so nothing works. I understand that maybe I wrote in the wrong area, but suddenly one of you wondered this question and found an easier installation solution. I will be glad to any answer, thanks!&lt;/p&gt;&#xA;&lt;p&gt;I also saw a video where the GNU radio companion is also opened^&#xA;&lt;a href=&quot;https://www.youtube.com/watch?v=DfCjLYp-apY&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=DfCjLYp-apY&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18124" LastEditorUserId="5222" LastEditDate="2021-02-28T10:15:54.427" LastActivityDate="2021-02-28T10:15:54.427" Title="Installing GNU radio on android" Tags="&lt;gnuradio&gt;&lt;mobile&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18090" PostTypeId="2" ParentId="18088" CreationDate="2021-02-23T09:31:32.703" Score="2" Body="&lt;p&gt;Despite the intuitive feeling that water somehow might make a metal tube more conductive or something, for an antenna made from hollow mostly sealed tubular metal, regardless of which metal the tube is made from, water inside the tube will in fact make zero difference to the way the antenna performs in an RF sense electrically for receive or transmit.&lt;/p&gt;&#xA;&lt;p&gt;This is  due to a phenomenon call Skin Effect, where RF current mostly always only travels on the outer surface of a conductor. For example when used for transmitting, RF applied at the base of your vertical antenna will only flow on the outside of the tube. Signals received from the atmosphere also will only flow on the outside of the tube.&lt;/p&gt;&#xA;&lt;p&gt;In both case there will be extremely little or no RF current flowing inside the tube, and so the water doesn't do anything,&lt;/p&gt;&#xA;&lt;p&gt;Of course there are mechanical considerations. Water adds weight at the rate of 1 kg per litre ! Added weight might result in bent or broken elements. Also, water inside a tube might cause corrosion or rust depending on the metal used.&lt;/p&gt;&#xA;&lt;p&gt;And of course if you live in a cold area, frozen water which expands might cause a sealed tube to distort or burst, or the ends you soldered on might pop off.&lt;/p&gt;&#xA;&lt;p&gt;In contrast, an additional consideration is that a tube filled with water might make less noise in the wind, but generally it's probably a bad idea for water to be present inside the elements of an antenna.&lt;/p&gt;&#xA;&lt;p&gt;My suggestion is to use metal that doesn't rust much ie copper or aluminium and try and leave the ends open and not make the antenna elements sealed, or in your case at least leave the bottom end open, then water can't fill it up. If you do this, RF current still mostly flows on the outside of the tube.&lt;/p&gt;&#xA;&lt;p&gt;If you must have ends on your elements, for mounting reasons or if it just makes you feel better, to drain any water which accumulates, you could drill a small hole about 2 mm in diameter right at the bottom of the element if it's vertically positioned. If the hole is at one of the ends, then it won't make much difference to the strength of the element.  The hole will make zero difference to how antenna works electrically, but if the hole freezes over then you no longer have a hole and the antenna element will be sealed again.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2021-02-23T10:26:46.993" LastActivityDate="2021-02-23T10:26:46.993" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18091" PostTypeId="2" ParentId="18088" CreationDate="2021-02-23T14:10:16.853" Score="3" Body="&lt;p&gt;Welcome to ham SE. I recommend that you add a weep hole to the bottom of your trap. If structurally possible, a second weep hole might allow at least a small amount of air circulation in the cavity. Just as important is to periodically inspect the weep hole to be sure it's open. If you make a second weep hole, periodically blowing pressurized air into one weep hole will help to drive water vapor out the other weep hole.&lt;/p&gt;&#xA;&lt;p&gt;I have rebuilt numerous units of a particular aluminum multiband trapped yagi antenna that begs the question you asked. My local environment experiences extremes of weather from +35&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt;C to -40&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt;C, heavy rain/snow/ice, high humidity and sometimes drought conditions.&lt;/p&gt;&#xA;&lt;p&gt;I have always left open the small weep hole that the manufacturer drilled into the trap body and ensured the hole faced the ground when the antenna was mounted. I have never had a problem with this approach; I removed, inspected and sold one of the antennas after 9 years. Some users of this antenna have complained that insects enter the trap through the weep hole and either wreak havoc or plug the weep hole. Installing find-mesh screen kept out the bugs but the small mesh retained moisture, defeating the purpose of the weep hole.&lt;/p&gt;&#xA;&lt;p&gt;A nearby friend, who shares a penchant for the same antenna, decided to seal the traps with layers of conformable rubber tape and adhesive &amp;quot;goop.&amp;quot; He experienced trap failures within two years owing to moisture that bypassed his sealing regimen and created a layer of corrosion that was sufficiently conductive to arc over.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-23T14:10:16.853" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18092" PostTypeId="1" CreationDate="2021-02-23T15:27:04.970" Score="1" ViewCount="28" Body="&lt;p&gt;I am in kindergarten with 4NEC2 and trying to model a Gray-Hoverman TV antenna. I have someone else's model and understand most of the file parameters. I have added VHF elements that have S curves at each end but I can't find any info as to how to model the curves.&#xA;I also want to model a folded dipole. Is there any hope for me?&#xA;Thanks&lt;/p&gt;&#xA;" OwnerUserId="18895" LastActivityDate="2021-02-23T18:24:36.017" Title="How to model a curved element in 4NEC2" Tags="&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18093" PostTypeId="1" CreationDate="2021-02-23T15:48:43.107" Score="6" ViewCount="384" Body="&lt;p&gt;I'm trying to get my head around IQ modulation. What I understand so far is that each of the I and Q branches of the mixer produce two sidebands with the same frequency components, but in the Q branch, these sidebands have opposite phase to each other. So when we add the I and Q components together, we get an upper sideband consisting of I+Q and a lower sideband consisting of I-Q.&lt;/p&gt;&#xA;&lt;p&gt;Then, on the receiver side, the I mixer causes the two sidebands to be imaged onto each other (giving I + Q + I - Q), while the Q mixer does the same thing, but shifts the phase of the lower sideband again, giving I + Q. And the point of all this is that we don't waste any bandwidth with redundant sidebands.&lt;/p&gt;&#xA;&lt;p&gt;Assuming that this &amp;quot;signal cancellation&amp;quot; view is correct, is there an intuitive way to understand why the lower sideband of the Q output gets phase shifted relative to the upper sideband? &lt;a href=&quot;https://www.markimicrowave.com/blog/how-to-think-about-iq-mixers/&quot; rel=&quot;nofollow noreferrer&quot;&gt;This article&lt;/a&gt; seems to say that it can be understood simply in terms of the basic trigonometric identities&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\cos A \cos B = {\cos(A+B) + \cos(A-B) \over 2}\\&#xA;\cos A \sin B = {\sin(A+B) - \sin(A+B) \over 2}$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;It's easy to see why this has the desired effect when both baseband signals are represented simply as &lt;span class=&quot;math-container&quot;&gt;$\cos A$&lt;/span&gt;: the second term in the second identity is negative. But does that explain it completely? Other sources suggest (eg. &lt;a href=&quot;https://www.microwavejournal.com/ext/resources/pdf-downloads/IQTheory-of-Operation.pdf?1336590796&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;) that this phenomenon involves the Hilbert Transform (which I don't really understand). Although, strangely, they're only saying that Hilbert is needed to understand the demodulation side, whereas with my view of things I was expecting the process to work the same way for both modulation an demodulation.&lt;/p&gt;&#xA;&lt;p&gt;So does the trigonometry above explain it, or is that just a special case when both I and Q are cosines? Or am I on the wrong track completely?&lt;/p&gt;&#xA;" OwnerUserId="18855" LastEditorUserId="8717" LastEditDate="2021-02-25T18:26:03.430" LastActivityDate="2021-03-18T17:55:58.920" Title="How does IQ modulation work (intuitively)?" Tags="&lt;software-defined-radio&gt;&lt;theory&gt;&lt;math&gt;&lt;mixer&gt;&lt;modem&gt;" AnswerCount="7" CommentCount="2" FavoriteCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18094" PostTypeId="1" CreationDate="2021-02-23T18:08:39.333" Score="0" ViewCount="24" Body="&lt;p&gt;I read on pg5 of Antenna Simulation with 4NEC2 about &lt;strong&gt;shortening factor &amp;quot;x&amp;quot;&lt;/strong&gt;.&#xA;It is very specific and I can't figure out how to use it in a general nec file.&#xA;It sounds like SY x=0.907 in the nec file will shorten all the Y parameters, but that doesn't make sense to this newbee.&#xA;I would think it would reduce the larger dimension (end) to yield the 0.907 reduction. Maybe it does. I tried it on my file with no apparent result. IE, the plots did not change to reflect a different resonant frequency.&#xA;Anyplace I can find a better explanation of this feature?&#xA;thanks&lt;/p&gt;&#xA;" OwnerUserId="18895" LastActivityDate="2021-02-23T18:39:49.110" Title="4NEC2 shortening factor &quot;x&quot;" Tags="&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18096" PostTypeId="2" ParentId="18092" CreationDate="2021-02-23T18:24:36.017" Score="1" Body="&lt;p&gt;Curves must be broken into a series of straight segments. The accuracy of your results will depend on the size of the segments relative to the wavelength of operation.&lt;/p&gt;&#xA;&lt;p&gt;For the example below, I used the Create &amp;gt; Loop feature of &lt;a href=&quot;https://eznec.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;EZNEC&lt;/a&gt; to produce numbered segments, each of which is further broken down (see the green dots), then reconfigured into an &amp;quot;S&amp;quot; shape:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/L09Z8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/L09Z8.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;There are many other means and tools for doing this. I have used spreadsheets to generate segment endpoints, a feature which is now powerfully amplified in &lt;a href=&quot;https://ac6la.com/autoez.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;AutoEZ&lt;/a&gt; by &lt;a href=&quot;https://ac6la.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;AC6LA&lt;/a&gt; (I take no credit for this, I just appreciate and routinely use the tool's many powerful features). The spreadsheet-like formula features of &lt;a href=&quot;https://www.qsl.net/4nec2/&quot; rel=&quot;nofollow noreferrer&quot;&gt;4NEC2&lt;/a&gt; could also be used in this application.&lt;/p&gt;&#xA;&lt;p&gt;I have no affiliation with any of the products mentioned in this post.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-23T18:24:36.017" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18097" PostTypeId="2" ParentId="18094" CreationDate="2021-02-23T18:39:49.110" Score="2" Body="&lt;p&gt;The answer to your question is on page 6 of &lt;a href=&quot;http://www.vhfcomm.co.uk4nec2%20antenna%20simulation%20english.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna simulations with 4NEC2 including an application example for 2300MHz&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/EEnpo.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/EEnpo.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;A symbol (SY), x, is defined as having the value 0.907. This value is used in the calculations for the lengths of the dipole arms in the following GW statement.&lt;/p&gt;&#xA;&lt;p&gt;I prefer doing this with the Symbols tab in 4NEC2's &amp;quot;NEC Editor (new)&amp;quot; (see Settings). The defined symbols are used in entries on the Geometry tab to define wire endpoints and other values.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-23T18:39:49.110" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18098" PostTypeId="2" ParentId="18093" CreationDate="2021-02-23T21:13:12.163" Score="10" Body="&lt;p&gt;I think it's more intuitive if you unlearn some things first.&lt;/p&gt;&#xA;&lt;p&gt;Oscillation is &lt;em&gt;not&lt;/em&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(\omega t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;where &lt;span class=&quot;math-container&quot;&gt;$\omega$&lt;/span&gt; is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Angular_frequency&quot; rel=&quot;noreferrer&quot;&gt;angular frequency&lt;/a&gt; in radians per second, and &lt;span class=&quot;math-container&quot;&gt;$t$&lt;/span&gt; is time.&lt;/p&gt;&#xA;&lt;p&gt;Rather, oscillation is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{i \omega t} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;By &lt;a href=&quot;https://en.wikipedia.org/wiki/Euler%27s_formula&quot; rel=&quot;noreferrer&quot;&gt;Euler's formula&lt;/a&gt; this can be expanded to:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(\omega t) + i \sin(\omega t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;If you plot this function on the &lt;a href=&quot;https://en.wikipedia.org/wiki/Complex_plane&quot; rel=&quot;noreferrer&quot;&gt;complex plane&lt;/a&gt;, you get a circle:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/SEFKf.gif&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SEFKf.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Why bother with this circle thing? Well, the circle can spin counterclockwise with a positive frequency as shown in the animation. Or it can spin clockwise, and that's a negative frequency. You can't unambiguously represent negative frequencies with just a line wave because &lt;span class=&quot;math-container&quot;&gt;$\cos -x = \cos x$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\sin -x = -\sin x$&lt;/span&gt;. Thus you can't tell with just a sine wave if a frequency is positive or negative, but you can tell with a circle by which way its spinning.&lt;/p&gt;&#xA;&lt;p&gt;This is useful because it's simple. Frequency mixers multiply things; what happens when you multiply two of these circle-oscillations together?&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{i\omega_1 t} \times e^{i\omega_2 t} = e^{i(\omega_1 + \omega_2)t} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;So, this circle-mixer doesn't make sum and difference terms at its output: there's just a sum term. There are not two sidebands: there's just one. There is no image frequency. And since frequency can be negative, this circle-mixer can convert frequencies up or down. Much simpler than the old kind of mixer.&lt;/p&gt;&#xA;&lt;p&gt;The only trouble is this: to implement this in analog electronics, where the signal is represented as a voltage, and where voltage can have only real values, how to we represent the complex numbers in this math?&lt;/p&gt;&#xA;&lt;p&gt;You'll have to build two analog circuits, where the voltage of one represents the real part, the other the imaginary part. You are trying to understand an IQ demodulator as two mixers. But you've got it backwards: an IQ demodulator is just one mixer. And what you previously thought of as a mixer is actually two mixers.&lt;/p&gt;&#xA;&lt;p&gt;Why? Well, consider what happens if you add two circle-oscillations together, one with the negative frequency of the other:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{i\omega t} + e^{i (-\omega) t} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Expand with Euler's formula:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(\omega t) + i \sin(\omega t) + \cos(-\omega t) + i \sin(-\omega t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Using the identities &lt;span class=&quot;math-container&quot;&gt;$\cos -x = \cos x$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\sin -x = -\sin x$&lt;/span&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(\omega t) + i \sin(\omega t) + \cos(\omega t) - i \sin(\omega t) \\&#xA;= 2 \cos(\omega t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;So when you have a sinusoidal function which is purely real, &lt;em&gt;you can think of that as the superposition of a positive and negative frequency&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;So you might have thought mixers multiply some input &lt;span class=&quot;math-container&quot;&gt;$x(t)$&lt;/span&gt; by a sinusoid to compute their output, like this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ x(t) \times \cos(\omega t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;But really that one physical device is simultaneously computing &lt;em&gt;two&lt;/em&gt; multiplications, because &lt;span class=&quot;math-container&quot;&gt;$\cos(\omega t)$&lt;/span&gt; is a superposition of positive and negative circle-oscillations:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ x(t) \times e^{i \omega t} + x(t) \times e^{i (-\omega) t} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now you see where the sum and difference frequencies come from.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-02-23T21:13:12.163" CommentCount="16" ContentLicense="CC BY-SA 4.0" />
  <row Id="18099" PostTypeId="2" ParentId="18085" CreationDate="2021-02-23T23:25:39.427" Score="4" Body="&lt;p&gt;As of 2021, the FCC &lt;strong&gt;will&lt;/strong&gt; send an e-mail to your address on file when your application is approved with a link to your updated license PDF (but no details in the e-mail body itself). It will be sent later on the day your batch is processed; mine was sent at 17:55 ET.&lt;/p&gt;&#xA;" OwnerUserId="17659" LastActivityDate="2021-02-23T23:25:39.427" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18100" PostTypeId="2" ParentId="9351" CreationDate="2021-02-24T00:36:06.867" Score="1" Body="&lt;p&gt;Talk to the Ham Op next door. We are more than happy to help cure a problem, and&#xA;as a Ham myself, I have these Filters all over the place,&amp;quot;Hams have RFI also&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;73 de kg0tr&lt;/p&gt;&#xA;" OwnerUserId="18898" LastActivityDate="2021-02-24T00:36:06.867" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18101" PostTypeId="2" ParentId="18093" CreationDate="2021-02-24T06:20:21.923" Score="-1" Body="&lt;p&gt;Forget sinewaves and complex exponentials.  Many, perhaps most QRP SDR IQ modulators actually use square wave modulators (they are implemented as Tayloe quadrature switching mixers).  And imaginary components are usually not included in the BOM or on the PCB.&lt;/p&gt;&#xA;&lt;p&gt;So you have a square wave switch turning on at a certain frequency.  Call its phase zero.  Turn on a 2nd square wave switch a quarter cycle later and add the outputs of the two switches.  Adding a cosine at phase zero and a cosine at phase 90 gives you an output at phase 45.  Now turn off the 1st switch, you end up with an output at phase 90.  Now turn on the 1st switch but invert it's output. The sum is now at phase 135. Now turn off the 2nd switch. The output is now at phase 180.  Now turn on the 2nd switch but invert its output,  The sum is now at phase 225.  Etc.&lt;/p&gt;&#xA;&lt;p&gt;So notice you can rotate the phase of the output at some rate by modulating the two switches (call them I and Q) at some rate.  If you rotate the phase forward in time you end up with an upper sideband.  If you rotate the phase backwards (by inverting the output of the second switch, etc.) you end up with a lower sideband.  Because frequency is defined as the 1st derivative of phase.&lt;/p&gt;&#xA;&lt;p&gt;You can rotate the phase faster or slower, which will increase if decrease the side and excursion (either upper upward or lower downward), etc.&lt;/p&gt;&#xA;&lt;p&gt;Now to create a legal SSB signal you probably need to send these two modulated and summed quadrature square wave thru a bandpass filter to clean them up (remove spurious harmonics, etc.)&lt;/p&gt;&#xA;&lt;p&gt;If you create a hypothetical model using sinewaves or complex exponentials, it might produce the same result.  But that's not what's really going on.  A scope probe placed anywhere will only measure scalar voltages.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-02-25T03:24:04.567" LastActivityDate="2021-02-25T03:24:04.567" CommentCount="9" ContentLicense="CC BY-SA 4.0" />
  <row Id="18102" PostTypeId="1" CreationDate="2021-02-24T14:42:52.300" Score="0" ViewCount="67" Body="&lt;p&gt;Does anyone know of any resources which describe how to design a circuit with one RF input and multiple (at least 6) RF outputs, whereby the signal strength of each output matches (does not exceed and is not less than) the input signal strength? I'm thinking this would be some kind of self limiting amplifier, but not sure the best way to think about this. For non-RF there would be some classic OmpAmp circuits which may work. But I'm talking UHF and above here.&lt;/p&gt;&#xA;&lt;p&gt;NB: Must be 50ohm input and output.&lt;/p&gt;&#xA;&lt;p&gt;Many thanks!&lt;/p&gt;&#xA;" OwnerUserId="18904" LastEditorUserId="4665" LastEditDate="2021-02-24T16:15:10.187" LastActivityDate="2021-02-24T19:13:28.560" Title="Circuit for RF Splitter" Tags="&lt;equipment-design&gt;&lt;amplifier&gt;" AnswerCount="1" CommentCount="3" ClosedDate="2021-02-24T22:19:25.890" ContentLicense="CC BY-SA 4.0" />
  <row Id="18103" PostTypeId="2" ParentId="18088" CreationDate="2021-02-24T15:37:58.207" Score="2" Body="&lt;p&gt;Trapped vapor inside the element isn't a problem.&lt;/p&gt;&#xA;&lt;p&gt;The problem is that with repeated heating and cooling cycles, a sealed cavity will develop pinhole leaks.  If you don't make your own hole, it will form somewhere random.  If it is on a top surface, then when the cavity heats, air escapes, and when it cools, it will suck in vapor, which will then condense and drop to the bottom, and this repeats until the cavity is mostly water.&lt;/p&gt;&#xA;&lt;p&gt;If instead you make the hole on the bottom, then when the cavity heats, it will push out any condensed liquid, so hopefully it doesn't get a chance to accumulate.&lt;/p&gt;&#xA;&lt;p&gt;If this was coax rather than an antenna element, ideally, the unsealed end would be in an air conditioned (humidity depleted) environment so that when it cooled, it would suck in drier air.&lt;/p&gt;&#xA;&lt;p&gt;The hole doesn't have to be very large.  Just large enough that if it clogs, it will still be weaker than any other pinhole and liquid can still be pushed out of it during the heating cycle.  Clearing it periodically could help.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2021-02-24T15:37:58.207" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18104" PostTypeId="2" ParentId="18102" CreationDate="2021-02-24T19:13:28.560" Score="1" Body="&lt;p&gt;Given your requirement to operate down to 1-MHz, it seems likely you will have to use a lumped-element design. &lt;a href=&quot;https://www.mwrf.com/technologies/passive-components/article/21845377/trm-microwave-ferrite-transformers-fuel-broadband-power-dividers&quot; rel=&quot;nofollow noreferrer&quot;&gt;Ferrite Transformers Fuel Broadband Power Dividers&lt;/a&gt;, by Dr. Karen Kocharyan, gives useful information on lumped-element divider design.&lt;/p&gt;&#xA;&lt;p&gt;Commercially available units, like the MiniCircuits &lt;a href=&quot;https://www.minicircuits.com/WebStore/dashboard.html?model=ZFSC-6-110&quot; rel=&quot;nofollow noreferrer&quot;&gt;ZFSC-6-110&lt;/a&gt;, suggest that a design approaching your requirements may be achievable. Judging from the specifications of this product, it seems likely that it comprises multiple instantiations of the company's wideband &amp;quot;core and wire&amp;quot; transformer products, for which the company provides S-parameters. The company also provides a wide range of MMIC amplifiers which could make up the &amp;quot;loss&amp;quot; encountered at each output port as a result of the division of input power.&lt;/p&gt;&#xA;&lt;p&gt;Resistive power splitters, described at &lt;a href=&quot;https://www.microwaves101.com/encyclopedias/resistive-power-splitters&quot; rel=&quot;nofollow noreferrer&quot;&gt;Microwaves101&lt;/a&gt;, are a lossier solution but may fit your needs since you already plan to recover the &amp;quot;lost&amp;quot; power through amplification.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-02-24T19:13:28.560" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18105" PostTypeId="1" AcceptedAnswerId="18109" CreationDate="2021-02-24T19:53:24.647" Score="0" ViewCount="51" Body="&lt;p&gt;I am planning to buy a Xiegu G90. It has an internal tuner that can tune up to SWR 5:1. Does anyone know if I have a resonant antenna on 40m, what I will have for a SWR on 80m?&lt;/p&gt;&#xA;" OwnerUserId="11842" LastEditorUserId="4665" LastEditDate="2021-02-25T01:21:44.873" LastActivityDate="2021-02-25T02:42:53.460" Title="Estimating SWR based on multiples of resonant length" Tags="&lt;impedance-matching&gt;&lt;antenna-tuner&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18106" PostTypeId="2" ParentId="9351" CreationDate="2021-02-24T20:15:45.340" Score="1" Body="&lt;p&gt;Ferrites can certainly be effective in blocking RF. But so can capacitors which short RF energy to ground. Place them on incoming lines and anywhere rectification of the RF signal could be occurring. Both methods can be used in stubborn cases.&lt;/p&gt;&#xA;" OwnerUserId="14159" LastActivityDate="2021-02-24T20:15:45.340" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18107" PostTypeId="2" ParentId="18093" CreationDate="2021-02-24T20:44:35.993" Score="2" Body="&lt;p&gt;First let's look at what happens in the case of a single mixer:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/U5CXG.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fU5CXG.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;We know that mixers produce sum and difference frequencies. That is to say, the Fourier transform will contain impulses at &lt;span class=&quot;math-container&quot;&gt;$f_1 + f_2$&lt;/span&gt; and also &lt;span class=&quot;math-container&quot;&gt;$f_2 - f_1$&lt;/span&gt;. Or is it &lt;span class=&quot;math-container&quot;&gt;$f_1 - f_2$&lt;/span&gt;?&lt;/p&gt;&#xA;&lt;p&gt;It doesn't actually matter, and it's important to understand why. The Fourier transform is defined in terms of complex exponentials:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \hat f(\xi) = \int_{-\infty}^\infty f(x)e^{-2 \pi i x \xi} dx \tag 1 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;By &lt;a href=&quot;https://en.wikipedia.org/wiki/Euler%27s_formula&quot; rel=&quot;nofollow noreferrer&quot;&gt;Euler's formula&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{ix} = \cos x + i \sin x \tag 2 $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;To by taking the Fourier transform we are &lt;a href=&quot;https://en.wikipedia.org/wiki/Convolution&quot; rel=&quot;nofollow noreferrer&quot;&gt;convolving&lt;/a&gt; &lt;span class=&quot;math-container&quot;&gt;$f(x)$&lt;/span&gt; with a complex exponential at every possible frequency to answer the question &amp;quot;how much does this function look like this frequency?&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;But the inputs and outputs to this mixer are single voltages and thus must be real functions, so how can real functions look like complex exponentials which have a non-zero imaginary part?&lt;/p&gt;&#xA;&lt;p&gt;To resolve this, it's important to understand that a real function can be represented by adding together complex exponentials of positive and negative frequencies. Brian K1LI has provided a nice graphical animation of this. You can also convince yourself that &lt;span class=&quot;math-container&quot;&gt;$e^{-ix} + e^{ix} = 2 \cos x$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;With that in mind, what's the mixer above do? Multiplication of two functions is equivalent to convolving their Fourier transforms. So considering that real functions have Fourier transforms which are symmetrical about frequency 0, what the mixer above calculates is:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/t9sjg.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/t9sjg.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Notice that the assumption is made that &lt;span class=&quot;math-container&quot;&gt;$f_2&amp;lt;f_1$&lt;/span&gt;, which makes &lt;span class=&quot;math-container&quot;&gt;$f_2-f_1$&lt;/span&gt; positive. But if it was the other way around it wouldn't matter, since a negative answer is &lt;em&gt;also&lt;/em&gt; correct. Because the output of this mixer is a real voltage, the Fourier transform of the output must contain both positive and negative frequencies.&lt;/p&gt;&#xA;&lt;p&gt;Because real functions have Fourier transforms that are symmetrical about zero, talking about their negative frequencies doesn't add any insight. But it is critical to grasp that they are there anyway, because that leads to a much simpler mathematical explanation, and thus better intuition about how things like mixers work.&lt;/p&gt;&#xA;&lt;p&gt;Now what about an IQ mixer, like this:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/EWwNM.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fEWwNM.png&quot;&gt;simulate this circuit&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;While your first instinct may be to think of this as two mixers, I find it more insightful to view it as a single mixer which can operate on complex numbers by representing the real part as one voltage, and the imaginary part as another voltage. Viewed this way, this mixer is simply multiplying by a complex exponential:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{align}&#xA;y(t) &amp;amp;= \cos(2\pi f_1 t) \cdot e^{2\pi f_2 t} \\&#xA;&amp;amp;= \cos(2\pi f_1 t) \cdot \cos(2\pi f_2 t)&#xA; + \cos(2\pi f_1 t) \cdot i \sin(2\pi f_2 t)&#xA;\end{align} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Recall from equation 2 that the &lt;span class=&quot;math-container&quot;&gt;$e^{2\pi f_2 t}$&lt;/span&gt; is comprised of real cosine and imaginary sine terms, which are the inputs to each branch of the mixer.&lt;/p&gt;&#xA;&lt;p&gt;Now the complex exponential, unlike a sinusoid, has a Fourier transform which doesn't need to be symmetrical about zero. So in the frequency domain, this mixer calculates:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1Adiu.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1Adiu.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Now the output isn't symmetrical about zero in the frequency domain, and so negative frequencies have some utility.&lt;/p&gt;&#xA;&lt;p&gt;Notice that there are now half as many impulses in the Fourier transform. The mixer no longer calculates sum and difference frequencies, but just sum frequencies. Pretty handy, if we can figure out a to separate negative and positive frequencies! But...&lt;/p&gt;&#xA;&lt;h1&gt;What's a negative frequency?&lt;/h1&gt;&#xA;&lt;h2&gt;Explanation 1: spinning backwards&lt;/h2&gt;&#xA;&lt;p&gt;A sinusoid is a real function. It can move only in one dimension: the real number line. Sinusoids oscillate only &amp;quot;left to right&amp;quot;. So only positive frequencies make sense.&lt;/p&gt;&#xA;&lt;p&gt;But a complex exponential is a complex function. It can move in two dimensions, the imaginary and real axes on the complex plane. Complex exponentials oscillate in circles, like a spinning top or wheel. Things can spin in two directions. Frequency is how fast phase changes over time, and phase can increase (move counter-clockwise around the circle) or decrease (clockwise).&lt;/p&gt;&#xA;&lt;p&gt;So think of frequency as a one-dimensional vector with both a magnitude (how many times per second it spins) and direction (counter-clockwise or clockwise). Just as a negative current doesn't mean less than zero charge is moving, but rather just means charge is moving is the opposite the conventionally positive direction, a negative frequency doesn't mean the top is spinning less than zero times per second, it just means it's spinning the other way.&lt;/p&gt;&#xA;&lt;h2&gt;Explanation 2: math&lt;/h2&gt;&#xA;&lt;p&gt;This is a positive frequency:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ e^{ix} = \cos x + i \sin x $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/ZoExa.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/ZoExa.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This the negative of that frequency is just the negation of &lt;span class=&quot;math-container&quot;&gt;$x$&lt;/span&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{align}&#xA;e^{-ix} &amp;amp;= \cos -x + i \sin -x \\&#xA;&amp;amp;= \cos x - i \sin x&#xA;\end{align} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/iXICl.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iXICl.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Notice that positive and negative frequencies are identical in the real part (blue), but have opposite phase in the imaginary part (red). For a positive frequency, the imaginary part leads by 90 degrees. For a negative frequency, the imaginary part lags 90 degrees.&lt;/p&gt;&#xA;&lt;h2&gt;Explanation 3: mixers&lt;/h2&gt;&#xA;&lt;p&gt;This is not a complete explanation, but maybe insightful regardless. Consider the multiplication of a sine and a cosine, of different frequencies. In one case the sine is 1.6 the frequency of the cosine, and in the other case the cosine is 1.6 times the frequency of the sine:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/1WHMQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/1WHMQ.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;You can see in either both the upper and lower sideband. But notice that the phase of the upper sideband is equal in either case, while for the lower sideband the phase is opposite in each case.&lt;/p&gt;&#xA;&lt;p&gt;Notice also this doesn't work when both functions are &lt;span class=&quot;math-container&quot;&gt;$\cos$&lt;/span&gt;, because obviously&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \cos(x) \cos(1.6x) = \cos(1.6x) \cos(x) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;So clearly there is some way to distinguish between signals that are above the LO versus those that are below, but it only works when the inputs are in quadrature, which is why if you don't know the phase of the signal you're looking for, you need two mixers to do this trick.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;Now back to our problem. We're looking at the output of the IQ mixer, which has a Fourier transform like:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/nDh91.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/nDh91.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;If you were to casually look at either the real or imaginary parts of this mixer output, you might not notice that it's different than the single mixer case. Given the above explanations about negative frequency, you can tell from this Fourier transform that the impulse at &lt;span class=&quot;math-container&quot;&gt;$-f_1+f_2$&lt;/span&gt; still means something is happening &lt;span class=&quot;math-container&quot;&gt;$|-f_1+f_2| = f_1-f_2$&lt;/span&gt; times per second, just as before. You can't tell that it's a negative frequency because what makes it negative or positive is not how many times per second it happens, but rather the relative phase of when it happens between the imaginary and real parts. You can't tell that by looking at just the real or just the imaginary.&lt;/p&gt;&#xA;&lt;p&gt;But if you were to look closely at the thing happening &lt;span class=&quot;math-container&quot;&gt;$f_1-f_2$&lt;/span&gt; times per second, you'd notice that it happens first on the real part, with the imaginary part lagging behind 90 degrees. That is what makes it a negative frequency.&lt;/p&gt;&#xA;&lt;p&gt;You would also notice something happening &lt;span class=&quot;math-container&quot;&gt;$f_1+f_2$&lt;/span&gt; times per second. But there you would notice that it is the imaginary part leading with the real part lagging. That is what makes it a positive frequency.&lt;/p&gt;&#xA;&lt;h1&gt;Converting back to a real function&lt;/h1&gt;&#xA;&lt;p&gt;You could digitize the I and Q parts in an ADC, then process them digitally as complex numbers. But regardless, if this is something like an SSB signal, at some point you'll want to convert it to a real function because obviously complex numbers aren't compatible with headphones and microphones.&lt;/p&gt;&#xA;&lt;p&gt;To do that, you require something that can introduce a phase shift of 90 degrees for all frequencies. Mathematically, that is the &lt;a href=&quot;https://en.wikipedia.org/wiki/Hilbert_transform&quot; rel=&quot;nofollow noreferrer&quot;&gt;Hilbert Transform&lt;/a&gt;. The Hilbert transform can be approximated with discrete components, such as in the &lt;a href=&quot;https://www.qrp-labs.com/polyphase.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;QRP Labs polyphase network&lt;/a&gt;. One of the articles you linked calls it a &amp;quot;90 degree hybrid&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Given such a device, separating positive and negative frequencies is possible. If you shift the imaginary part forward 90 degrees, then for positive signals the imaginary and real parts have equal phase and reinforce, but negative frequencies have real and imaginary parts in opposite phase and cancel. If you swap the phase shift or do it to the real part instead of the imaginary, you can just as easily keep the negative frequencies and discard the positive ones, which is what you might want to do for LSB demodulation.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-02-26T19:15:53.443" LastActivityDate="2021-02-26T19:15:53.443" CommentCount="13" ContentLicense="CC BY-SA 4.0" />
  <row Id="18108" PostTypeId="2" ParentId="18093" CreationDate="2021-02-24T22:18:51.967" Score="4" Body="&lt;p&gt;I believe a good point of view is the concept of orthogonality.&lt;/p&gt;&#xA;&lt;p&gt;This is clear under everybody's eyes when seen in physical space, take for instance a 2-dimension space, a plane.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qJUvv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qJUvv.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;In the example above any point on the plane can bear two &lt;em&gt;indipendent&lt;/em&gt; informations, its x and y.&#xA;The keyword here is indipendent, I can freely change one, let's say go from x1 to x2 while leaving the other unchanged.&lt;/p&gt;&#xA;&lt;p&gt;This indipendence is given by the orthogonality of the two axes choosen, in the plane depicted we may say that &lt;span class=&quot;math-container&quot;&gt;$\alpha=90^\circ$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;In more general way we might say that orthogonality/indipendance is given by the dot-product of any vector laying on the two axis being zero, for instance&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\bar x_1 \cdot \bar y_1=|x_1|\,|y_1| \cos \alpha=0$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This same concept of orthogonality can be extended to any space where such a dot-product can be defined.&lt;/p&gt;&#xA;&lt;p&gt;Electrical signals are (surprisingly) such a space, and a good dot-product suitable for periodic signals is the average over one period of their product.&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\bar{ x(t)} \cdot \bar{y(t)}=\frac{1}{T}\int_T x(t)y(t)\mathrm{d}t$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;It can be easily proved that any &lt;span class=&quot;math-container&quot;&gt;$\cos(\omega t)$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$\sin(\omega t)$&lt;/span&gt; are orthogonal&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$\frac{1}{T}\int_T \sin\left(\frac{2\pi}{T}t\right)\cos\left(\frac{2\pi}{T}t\right)\mathrm{d}t=0$$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;and can hence be used as carriers to bear two indipendent information, namely I and Q channels.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eXugf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eXugf.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;A lot of details has been left over but I believe that's the core.&lt;/p&gt;&#xA;" OwnerUserId="15476" LastActivityDate="2021-02-24T22:18:51.967" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18109" PostTypeId="2" ParentId="18105" CreationDate="2021-02-25T02:42:53.460" Score="5" Body="&lt;p&gt;Very high. Harmonics work the other way around — antennas can be useful on &lt;em&gt;higher&lt;/em&gt; bands than the design band, but almost never &lt;em&gt;lower&lt;/em&gt; bands. A dipole cut for 40m might be good on 15m. An end-fed or a loop for 40m might be good on 20m and 10m. But pretty much any design of 40m antenna is going to be a &lt;em&gt;half-size antenna&lt;/em&gt; on 80m, and very unlikely to be tunable with any builtin ATU.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-02-25T02:42:53.460" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18110" PostTypeId="2" ParentId="18093" CreationDate="2021-02-25T14:18:46.753" Score="1" Body="&lt;p&gt;The concept of &amp;quot;negative frequency&amp;quot; deserves more attention. Real-world signals can be described in a number of ways to submit them to mathematical manipulation.&lt;/p&gt;&#xA;&lt;p&gt;This video shows two phasors rotating at the same rate &lt;em&gt;but in opposite directions&lt;/em&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AehG7.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AehG7.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;(&lt;a href=&quot;http://dspfirst.gatech.edu/chapters/03spect/demos/phasors/graphics/phasorsn.mp4&quot; rel=&quot;nofollow noreferrer&quot;&gt;original source&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;Each phasor represents a signal. Each signal comprises a &amp;quot;real&amp;quot; part mapped along the horizontal axis and an &amp;quot;imaginary&amp;quot; part mapped along the vertical axis. (We call the sum of the &amp;quot;real&amp;quot; and &amp;quot;imaginary&amp;quot; parts a &amp;quot;complex&amp;quot; number; there's really nothing complex about it, this is just a mathematical notation that keeps track of two related things in one &amp;quot;number.&amp;quot;) The phasor rotating counter-clockwise expresses a positive frequency while the phasor rotating clockwise expresses a negative frequency.&lt;/p&gt;&#xA;&lt;p&gt;The important feature of the video is that the &lt;em&gt;imaginary&lt;/em&gt; parts of the two phasors always have opposite signs, while the &lt;em&gt;real&lt;/em&gt; parts of the two phasors always have the same sign. When we sum the two real values and separately sum the two imaginary values, the real parts reinforce, while the imaginary parts cancel, always resulting in a real-valued signal - the kind we experience in the &amp;quot;real&amp;quot; world.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="218" LastEditDate="2021-02-25T22:47:02.943" LastActivityDate="2021-02-25T22:47:02.943" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18112" PostTypeId="2" ParentId="18093" CreationDate="2021-02-26T02:08:21.270" Score="0" Body="&lt;p&gt;As to the Hilbert transform for Rx or Tx?&lt;/p&gt;&#xA;&lt;p&gt;If you have a strictly real signal X (you calling CQ into a mic, etc.), it has conjugate symmetric sidebands, which is necessary for all the imaginary stuff to cancel out, which is required if your signal is actually strictly real.  If you want to transmit an SSB signal Y from this strictly real input X, you will need to kill off one of the sidebands.  You could take the FT, zero half, double the other half, and the take the IFT, and you end up with a complex result. but that is exactly what a Hilbert transform does, generate (or approximate) the imaginary component half of the desired complex result Y, from strictly real X.  Now you’re good to try using that for SSB.&lt;/p&gt;&#xA;&lt;p&gt;On the receive end, if you IQ downconvert, you already get a complex signal (or a really close approximation), so you don’t need a Hilbert hack to make one up.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-02-26T02:08:21.270" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="18113" PostTypeId="2" ParentId="18093" CreationDate="2021-02-26T02:41:12.640" Score="-1" Body="&lt;p&gt;How can adding a modulated I and Q result in an SSB signal?&lt;/p&gt;&#xA;&lt;p&gt;Let’s start with an LO at f0.&lt;/p&gt;&#xA;&lt;p&gt;The complex FFT of a cosine has a real spike at f0.&lt;/p&gt;&#xA;&lt;p&gt;The complex FFT of a sine has an imaginary spike at f0.&lt;/p&gt;&#xA;&lt;p&gt;Let’s 100% amplitude modulate (DSB) both at by a sinusoid of frequency f2, where f2 &amp;lt;&amp;lt; f0&lt;/p&gt;&#xA;&lt;p&gt;And look at the FFTs of both, one at a time.&lt;/p&gt;&#xA;&lt;p&gt;The FFT of the modulated cosine ends up with positive real spikes at&#xA;f0+f2 and f0-f2&#xA;and a positive imaginary spike at&#xA;f0+f2&#xA;and a negative imaginary spike at&#xA;f0-f2&lt;/p&gt;&#xA;&lt;p&gt;All the above spikes are half size due to conservation of energy.&lt;/p&gt;&#xA;&lt;p&gt;The FFT of the modulated sine ends up with&#xA;a positive imaginary spike at&#xA;f0+f2 and f0-f2&#xA;and a positive real spike at&#xA;f0+f2&#xA;and a negative real spike at&#xA;f0-f2&lt;/p&gt;&#xA;&lt;p&gt;Why?&#xA;Because the FFT of a sine is strictly imaginary, the real parts have to cancel out, or else the result won’t be strictly imaginary.&lt;/p&gt;&#xA;&lt;p&gt;Now look what happens when you add the FFT of the modulated cosine to the FFT of the modulated sine.&lt;/p&gt;&#xA;&lt;p&gt;Hey all the spikes at f0-f2 (a positive frequency by the way) cancel out.&lt;/p&gt;&#xA;&lt;p&gt;If you infer a bunch of spikes near -f0 in the FFTs, due to using a strictly real LO, this conjugate mirror image cancels out in a mirror symmetric way as well.&lt;/p&gt;&#xA;&lt;p&gt;(a tilted 3D graph of this might be nice)&lt;/p&gt;&#xA;&lt;p&gt;And the spikes at f0+f2 double (back to full size).&lt;/p&gt;&#xA;&lt;p&gt;Since adding FFTs is the same of FFTing an addition (due to them both being linear operations), by adding those two modulated 90 degree offset sinusoids you end up with an SSB signal.&#xA;Non-zero.  No spectrum below f0.  Thus must be USB.&lt;/p&gt;&#xA;&lt;p&gt;QED&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-18T17:55:58.920" LastActivityDate="2021-03-18T17:55:58.920" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18115" PostTypeId="1" AcceptedAnswerId="18120" CreationDate="2021-02-28T10:57:17.243" Score="1" ViewCount="76" Body="&lt;p&gt;I have a Kenwood TS-480S and a Kenwood TS-870S both with built in antenna tuners. On the TS-870S I have a ZS6BKW multiband antenna and on the TS-480S I have a vertical whip with two counterpoise lines which gives me an SWR of around 1.4 ON 40m. It works but is noisy.&lt;/p&gt;&#xA;&lt;p&gt;On the TS-870S the only band I get a good SWR is on 40m of 1.6. On the other bands the SWR is as high as 3.0 and 80m is 4.1. Now my question is this: How high can the SWR be before the antenna tuners will no longer tune?&lt;/p&gt;&#xA;" OwnerUserId="5784" LastEditorUserId="8717" LastEditDate="2021-03-01T22:57:08.893" LastActivityDate="2021-03-01T22:57:08.893" Title="Antenna Tuner Range" Tags="&lt;antenna&gt;&lt;impedance-matching&gt;&lt;antenna-tuner&gt;&lt;kenwood&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18116" PostTypeId="1" CreationDate="2021-02-28T15:37:38.013" Score="5" ViewCount="244" Body="&lt;p&gt;While programming my Icom radio it has MR (memory)channels, VFO (Variable Freq) channels and Call Channels. What are call channels as comparred to memory or vfo channels? What is their use?&lt;/p&gt;&#xA;" OwnerUserId="18935" LastActivityDate="2021-03-19T13:49:59.220" Title="What is a 'Call' Channel?" Tags="&lt;icom&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18117" PostTypeId="2" ParentId="18116" CreationDate="2021-02-28T17:30:14.533" Score="6" Body="&lt;p&gt;From the radio device perspective, a call channel is not that different from a regular memory channel, except it doesn't have a number, there's usually one per band, and typically you can get to it quickly with a single button press.  It may be preprogrammed with the conventional per band calling frequencies, but typically it's just a regular memory so you can change it.&lt;/p&gt;&#xA;&lt;p&gt;From the use perspective, most bands have a calling frequency as part of the band plan.  By convention you would call on that frequency to initiate a contact and then move off to another frequency to rag chew so you don't clog it up.  More typically, on a band that isn't very busy, the activity is so low it wouldn't matter if you moved off or not.&lt;/p&gt;&#xA;&lt;p&gt;Near highways, sometimes the calling frequency is used for unplanned local vehicle to vehicle contacts in a small area.   For this use, a continuing conversation on the calling freqency is ok, but you should be sure to leave large gaps between every transmission so that others can join in or use the frequency for calling others.&lt;/p&gt;&#xA;&lt;p&gt;The calling frequency is also part of the wilderness protocol, which can be used for emergency call outs.  So if you are using the calling frequency, by this protocol you are suppose to listen for the first 5 minutes of each hour in case someone is calling for help and not resume normal use sooner than 4 minutes after the hour.&lt;/p&gt;&#xA;&lt;p&gt;In the US, the FM calling frequency for 2m is 146.520&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-03-02T12:19:40.047" LastActivityDate="2021-03-02T12:19:40.047" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18119" PostTypeId="1" CreationDate="2021-03-01T16:13:42.780" Score="1" ViewCount="132" Body="&lt;p&gt;I have read a lot of times in this forum that C-Band TV dishes are not suitable for operating 70cm. However:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Suppose that we have a 2,4m dish. By assuming a global efficiency of a 60%, our total gain would be around &lt;em&gt;18,5dBi&lt;/em&gt;&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;On the other hand, suppose that we want to achieve such gain with a common yagi antenna. Taking &lt;a href=&quot;https://www.changpuak.ch/electronics/yagi_uda_antenna_DL6WU.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;this calculator&lt;/a&gt; as an approximate reference, we would need a Yagi with more than 22 elements - which would be approximately 5 m long&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;In this case, I find worth going for a parabolic dish, since it can be shared between different bands (with different feeders) and is more mechanically consistent than a 5m long boom. Am I missing something? Why is then everyone so against dishes for UHF operation?&lt;/p&gt;&#xA;&lt;p&gt;I know that the &amp;quot;optimal&amp;quot; way to obtain high gains at these frequencies would be using an antenna array. Nevertheless, a dish offers the possibility of working more than a single frequency band and takes up less space than a full 2x2 array.&lt;/p&gt;&#xA;" OwnerUserId="14937" LastActivityDate="2021-03-22T22:06:33.783" Title="Using a parabolic dish for working the 70cm band - Am I missing something?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-system&gt;&lt;antenna-reflector&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18120" PostTypeId="2" ParentId="18115" CreationDate="2021-03-01T18:29:02.670" Score="3" Body="&lt;p&gt;I found a &lt;a href=&quot;https://www.kenwood.com/i/products/info/amateur/ts_480/&quot; rel=&quot;nofollow noreferrer&quot;&gt;list of specifications for the TS-480SAT&lt;/a&gt; giving the matching range as 16.7 Ω – 150 Ω.  Another &lt;a href=&quot;https://www.universal-radio.com/catalog/hamhf/0870spec.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;list of specifications for the TS-870SAT&lt;/a&gt; says that model's matching range is 20 Ω – 150 Ω.  Both ranges roughly correspond to a 3:1 SWR, which is typical for antenna tuners built into transceivers.  External antenna tuners generally offer more tuning range than built-in tuners, so you might consider adding an external antenna tuner.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-03-01T18:29:02.670" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18121" PostTypeId="2" ParentId="18119" CreationDate="2021-03-01T19:37:20.457" Score="1" Body="&lt;p&gt;How will you feed this dish? The feed antenna that comes on these antennas is not suitable for 70cm. The ideal feed antenna illuminates the dish and nothing else. To achieve such an illumination you'd want something like a Yagi or a horn antenna.&lt;/p&gt;&#xA;&lt;p&gt;After building such an antenna for 70cm and attempting to mount it on the dish, I think you'll quickly realize the dish appears ridiculously small in comparison. The reason you don't see tiny dishes on large feed antennas is they are very inefficient. Diffraction around the edges of the dish, which is not very large compared to wavelength, will degrade efficiency. Furthermore, the dish is most effective when the feed antenna is a single point at the focal point: when the feed antenna is relatively large this is less true, leading to degraded focus and efficiency.&lt;/p&gt;&#xA;&lt;p&gt;In the end, you'll find adding more elements to a Yagi is more effective than adding a dish, unless you plan to add a much larger dish. For these reasons, parabolic reflectors usually only make sense when they are large compared to wavelength, which a typical rooftop dish is not on 70 cm.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-03-01T19:37:20.457" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18122" PostTypeId="2" ParentId="18119" CreationDate="2021-03-02T00:18:06.573" Score="4" Body="&lt;p&gt;First, the gain or efficiency of the dish will be lower than you estimate.&lt;/p&gt;&#xA;&lt;p&gt;The outer quarter wave of the dish is substantially lost to diffraction. This is a 26% loss of area.&lt;/p&gt;&#xA;&lt;p&gt;If it's centre fed, feed blockage will cost about 0.3 m² or another 10%, in practice double this because this is the best illuminated part of the dish.&lt;/p&gt;&#xA;&lt;p&gt;Then uneven illumination and spillover will further reduce the efficiency by the usual 30-40%. For example, a yagi as a feed doesn't have symmetrical E and H plane patterns, so one will under-illuminate, the other will spill over.&lt;/p&gt;&#xA;&lt;p&gt;So on a small dish, only 3.5 wavelengths across, I think efficiency will be well under 50%.&lt;/p&gt;&#xA;&lt;p&gt;Finally the VSWR will be quite poor, with a yagi pointing almost straight at a reflector only 1 m away. This is where some of the feed blockage power goes.&lt;/p&gt;&#xA;&lt;p&gt;The next step would be to simulate the whole dish and feed, try to optimise it and see what gain you can achieve.&lt;/p&gt;&#xA;&lt;p&gt;By comparison, a yagi is quite a lightweight, low wind area construction. A 5 m long 70 cm yagi can be held in one hand, and it's balanced in the middle against gravity and wind. A 2.4 m dish, even if it's made of wires 5 cm apart, will be heavier and unbalanced and have a lot more wind resistance.&lt;/p&gt;&#xA;&lt;p&gt;In the right regime dishes have a lot of advantages - you can use the same reflector at many frequencies, gain keeps rising with increased frequency, it's easy to make it circular or dual-polarised, wide-band feeds of 2:1 or more are possible. But the example you chose is on the wrong side of the line. For gains under 18 dBi, and narrow amateur bands, I think the yagi will be a simpler, lighter antenna.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2021-03-02T00:18:06.573" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18124" PostTypeId="2" ParentId="7081" CreationDate="2021-03-02T14:47:46.317" Score="1" Body="&lt;p&gt;There are EFHW antenna designs that have a so called short section 'Counter Poise' (CP) used as the return (or second) connection for the feed line to the antenna.&lt;/p&gt;&#xA;&lt;p&gt;The CP is however the second element of the EFHW with its total length being the sum of both element lengths. The EFHW&#xA;can therefore logicaly be viewed as an Off Center Fed Half Wave (OCFD) antenna).&lt;/p&gt;&#xA;&lt;p&gt;As expected, initial attemtps of modeling an EFHW (without a CP) with EZNEC produced feed point impedances tending to infinity.&lt;/p&gt;&#xA;&lt;p&gt;BUT when treating the antenna as an OCFD and varying the feed point, meaningful results become possible and a feed point ~13 % from the end of the antenna was found to provide a near perfect match to a 9:1 (50 to 450 Ohm) balun as shown below for a 40 m antenna.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GmZjA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GmZjA.png&quot; alt=&quot;Resultant matching&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Further work shall be done to see how the antenna interacts with support poles.&lt;/p&gt;&#xA;" OwnerUserId="18950" LastActivityDate="2021-03-02T14:47:46.317" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18125" PostTypeId="1" AcceptedAnswerId="18129" CreationDate="2021-03-02T19:24:10.710" Score="3" ViewCount="75" Body="&lt;p&gt;I installed &lt;code&gt;tqsl&lt;/code&gt; to get started with LotW, but the first screen requires me to enter &amp;quot;Date of the first QSO you made or will make using this callsign&amp;quot;. I haven't made any yet, and I don't know the future, so what do I put in this field? Is it simply used as the certificate start-of-validity date, so I enter today's date?&lt;/p&gt;&#xA;" OwnerUserId="17659" LastActivityDate="2021-03-03T04:53:26.637" Title="How do I sign up for LotW as a new ham?" Tags="&lt;lotw&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18126" PostTypeId="1" CreationDate="2021-03-02T21:24:48.627" Score="0" ViewCount="81" Body="&lt;p&gt;My question relates to the specific programming of an R820T/ R820T2 based SDR for a specific frequency.&lt;/p&gt;&#xA;&lt;p&gt;I'm trying to build a self contained and auto initializing Raspberry Pi 4-based (ignore that detail, not central to the question) Automated Dependant Surveillance Broadcast (ADS-B) data signal receiver/ decoder because I'm an airplane nerd.&lt;/p&gt;&#xA;&lt;p&gt;I'm only interested in the 1090MHz band of ADS-B (There is a US-only secondary system for General Aviation aircraft called UAT which operates on 978MHz which I don't need), and if anyone can tell me where the specific 1090MHz frequency is configured.&lt;/p&gt;&#xA;&lt;p&gt;SDR manufacturers offer pre-programmed SDR units which arrive apparently set to 1090MHz already. I'm trying to figure out how one goes about setting this frequency, or any frequency the SDR is capable of, but can't find a simple answer.&lt;/p&gt;&#xA;&lt;p&gt;I am actually starting to wonder if the factory pre-programming is actually not a thing and they just tell them ignorant like me to keep me depending on them. This would indicate that the decoder software (Dump1090) is responsible for setting the SDR to the appropriate frequency every time the power initiation script on the Raspberry Pi runs.&lt;/p&gt;&#xA;&lt;p&gt;How do I set the RX frequency on a R820T/ R820T2 based Software Defined Radio, that maybe I'm trying to do some Amateur Radio shenanigans with?&lt;/p&gt;&#xA;" OwnerUserId="18955" LastEditorUserId="218" LastEditDate="2021-03-03T15:02:14.827" LastActivityDate="2021-03-04T19:42:47.060" Title="How do I set the RX frequency on a R820T/ R820T2 based SDR" Tags="&lt;rtl-sdr&gt;&lt;frequency&gt;&lt;sdrsharp&gt;" AnswerCount="2" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18128" PostTypeId="2" ParentId="18126" CreationDate="2021-03-03T02:51:26.800" Score="3" Body="&lt;p&gt;A lot of the RTL-SDR code is &lt;a href=&quot;https://github.com/osmocom/rtl-sdr&quot; rel=&quot;nofollow noreferrer&quot;&gt;open source on GitHub&lt;/a&gt;.  This code runs just fine on a Raspberry Pi 3B or 4.&lt;/p&gt;&#xA;&lt;p&gt;The C code inside rtl_tcp to set the frequency is only a few lines long.  From a remote system, after starting the TCP connection, send 5 bytes, 1st command byte 0x01, then 4 bytes containing the desired frequency in little-endian 32-bit integer format.  One also usually needs to set the sample rate,  which uses a first command byte of 0x02.  (I use a network connection to set the SDR frequency and sample rate from my iPhone.)&lt;/p&gt;&#xA;&lt;p&gt;If you want to use RTL2832 USB dongles for the amateur radio HF bands, note that frequencies below 30 MHz or so require using an HF Direct Sampling mode that completely bypasses the R820T2 tuner chip.  Some models of USB dongle require circuit board modifications to do this.  Others vendors have the Direct Sampling feature built-in to their RTL-SDRs.&lt;/p&gt;&#xA;&lt;p&gt;R820T/RTL-SDR dongles are easily overloaded from nearby strong broadcast transmissions.  The USB dongles sold for ADS-B often have RF band-pass filtering to block out interference from other frequency bands, possibly as part of an added LNA RF front-end.  Those models may or may not be suitable for use on amateur bands (without circuit modification).&lt;/p&gt;&#xA;&lt;p&gt;A forum with a lot of SDR Q&amp;amp;A activity related to RTL-SDRs is &lt;a href=&quot;https://www.rtl-sdr.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.rtl-sdr.com&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-03T05:22:42.473" LastActivityDate="2021-03-03T05:22:42.473" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18129" PostTypeId="2" ParentId="18125" CreationDate="2021-03-03T04:53:26.637" Score="3" Body="&lt;p&gt;Any day after the day your license was issued will work fine. What it's really trying to tell you is that your certificate can't be used to sign any QSO made &lt;em&gt;before&lt;/em&gt; its start date.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-03-03T04:53:26.637" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18130" PostTypeId="1" CreationDate="2021-03-03T12:32:23.767" Score="3" ViewCount="101" Body="&lt;p&gt;I have a 190 foot tall am/fm radio tower I need to take down.  Taking it down with big enough crane and manlifts and a torque crew will be quite expensive.  It is a guyed lattice tower that if necessary I will let fall over by disconnecting one of the guys.  Then of course the tower will be scrap.  Any other ideas?&lt;/p&gt;&#xA;" OwnerUserId="18954" LastActivityDate="2021-03-03T12:32:23.767" Title="have an unwanted radio tower" Tags="&lt;antenna-construction&gt;" AnswerCount="0" CommentCount="16" ClosedDate="2021-03-18T02:23:07.497" ContentLicense="CC BY-SA 4.0" />
  <row Id="18131" PostTypeId="1" CreationDate="2021-03-03T16:21:31.367" Score="1" ViewCount="151" Body="&lt;p&gt;Currently trying to transmit a BPSK and a 4-FSK(MFSK) signal via GRC using USRP, I have two attempts at it but don't seem to be going anywhere. Still fairly new to GRC. For the BPSK, how will this signal appear on the spectrum analyzer? I have seen general images of the signal shape online but pretty sure what I see is not it. Will I be able to hear the BPSK signal, if so what will it sound like?&lt;a href=&quot;https://i.stack.imgur.com/3I7fw.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;BPSK Flowgraph&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;As for the 4-FSK, I seem to have something but the spikes I generate are at different amplitudes in comparison with a FSK signal I had generated a while ago that had the spikes at the same/similar amplitudes.&lt;a href=&quot;https://i.stack.imgur.com/9dK3p.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/9dK3p.png&quot; alt=&quot;4FSK Flowgraph&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I can share my flowgraphs if it helps. Also it would be great if anyone had known working flowgraphs for these concepts to share for comparison or even be able to edit some features of mine. As for the details I care about, I really need to be able to specify the excursion/deviation between the spikes.&lt;/p&gt;&#xA;" OwnerUserId="18957" LastEditorUserId="18957" LastEditDate="2021-03-04T14:15:33.537" LastActivityDate="2021-04-03T15:02:45.253" Title="Implementing a BPSK and 4-FSK transmitters in GnuRadio (GRC) with USRP?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;transmitter&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18132" PostTypeId="1" AcceptedAnswerId="18139" CreationDate="2021-03-04T12:57:55.143" Score="6" ViewCount="151" Body="&lt;p&gt;I am considering a new ham station in a relatively urban environment on the South coast of England, and would like like some ideas / feedback on antenna options.&lt;/p&gt;&#xA;&lt;p&gt;Aim is to get reasonable performance for 40/20/15/10m bands with 100W TX power from an ICOM 7300 using the internal tuner (ie SWR &amp;lt;= 3). Aim is to get contact around Europe (note compass orientation of SatImage below).&lt;/p&gt;&#xA;&lt;p&gt;Trying to avoid putting up large structures on roof, and utilise nearby Chestnut tree on edge of property. My current simplest idea is a fan dipole, with some concerns/buts (see below)... Some sketches:&lt;/p&gt;&#xA;&lt;p&gt;Side view looking towards ENE:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/YWmHY.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/YWmHY.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Top View:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/620Zu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/620Zu.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;SatView to give impression of urban environment. Note that north is up on this image. Note the large &amp;quot;block&amp;quot; of flats about 20m to the ENE. This block is uphill from house and their top floor is about 5m(?) above where the diploe would be (ie 15m off &amp;quot;my ground&amp;quot;)&#xA;&lt;a href=&quot;https://i.stack.imgur.com/VAsny.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VAsny.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I have only shown some end-insulators on a single dipole with coax centre feed into a 1:1 balun. Basic plan is currently for a fan dipole to get reasonable resonance in each of the bands.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Unless I butt right up to the tree and the roof, I probably won't have room for a 40m band half-wavelength dipole. The length from end of roof ridge to fork in tree is just over 20m. There might a possibility of attaching to the other top ridge running ENE (ref sat image), which would give me the extra length but put a significant part of the antenna length over the roof.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The neighbours.... The top floors is 20m away horizontally and 5m above vertically. Broadside to the dipole. Bad idea?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&amp;quot;False ground&amp;quot; where the dipole overhangs the roof. And plenty of &amp;quot;foliage&amp;quot; above the dipole in chestnut tree (total height 20m+ above ground). Also the metal roofed garage to the right of dipole in SatImage, it's only 2.5m high, so probably 7-8m from dipole. How serious are these effects likely to be? Suck it and see?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Other Antenna types other than fan dipole which include 40m band? Perhaps something like this: &lt;a href=&quot;http://www.m0pzt.com/fan-dipole/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.m0pzt.com/fan-dipole/&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If above can't work, is there anything that could? Happy to go for external tuner or external amp for matching and more power up to UK legal limit of 400W. Central tower to &amp;quot;drape&amp;quot; inverted V dipole over the house? Or throw money and install a tower with a Yagi Beam. Or give up on 40m and stick to &amp;lt;=30m?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Many thanks&lt;/p&gt;&#xA;" OwnerUserId="18951" LastEditorUserId="18951" LastEditDate="2021-03-05T18:19:45.443" LastActivityDate="2021-03-07T19:02:40.630" Title="Antenna options" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;wire-antenna&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18133" PostTypeId="2" ParentId="18131" CreationDate="2021-03-04T14:30:08.650" Score="0" Body="&lt;p&gt;There are a lot of ways to make those transmitters, but I think for a beginner the simplest options are:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;for BPSK you can just use the constellation modulator block.  It is written in python so you can easily see how it is constructed from other blocks: &lt;a href=&quot;https://github.com/gnuradio/gnuradio/blob/master/gr-digital/python/digital/generic_mod_demod.py&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/gnuradio/gnuradio/blob/master/gr-digital/python/digital/generic_mod_demod.py&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;for FSK you can use the VCO block.  Here is an example from the GNU Radio wiki, it's not 4FSK, but it can get you started: &lt;a href=&quot;https://wiki.gnuradio.org/index.php/Simulation_example:_FSK&quot; rel=&quot;nofollow noreferrer&quot;&gt;Simulation example: FSK - GNU Radio&lt;/a&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;You can also check the examples here: &lt;a href=&quot;http://aaronscher.com/GNU_Radio_Companion_Collection/GNU_Radio_Companion.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Collection of GNU Radio Companion Flow Graphs&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10631" LastActivityDate="2021-03-04T14:30:08.650" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18134" PostTypeId="2" ParentId="18126" CreationDate="2021-03-04T19:36:39.360" Score="1" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;This would indicate that the decoder software (Dump1090) is responsible for setting the SDR to the appropriate frequency&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Yes, this is exactly what happens.  You can see the relevant code here:&#xA;&lt;a href=&quot;https://github.com/antirez/dump1090/blob/master/dump1090.c#L381&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/antirez/dump1090/blob/master/dump1090.c#L381&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The function that dump1090 calls, rtlsdr_set_center_freq() and all other functions that start with rtlsdr_ are from the rtl-sdr library, some of them are documented in the main header file: &lt;a href=&quot;https://github.com/osmocom/rtl-sdr/blob/master/include/rtl-sdr.h&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://github.com/osmocom/rtl-sdr/blob/master/include/rtl-sdr.h&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="10631" LastActivityDate="2021-03-04T19:36:39.360" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18136" PostTypeId="1" CreationDate="2021-03-04T23:00:34.767" Score="0" ViewCount="113" Body="&lt;p&gt;Here's what I am working on, and someone please tell me if I'm doing this right or wrong, but be kind and gentle.&lt;/p&gt;&#xA;&lt;p&gt;Center frequency 146.520MHz&lt;/p&gt;&#xA;&lt;p&gt;Driven element is 1/8 wave 10.25&amp;quot; long set at 6.125&amp;quot; from the front.&#xA;Reflector element is 5/8 wave at 15.3&amp;quot; and 15.3&amp;quot; from driven element to the back.&#xA;Director element is 1/2 wave at 12.25&amp;quot; and set at the front.&lt;/p&gt;&#xA;&lt;p&gt;Also, trying to figure out how to connect my SO239.&lt;/p&gt;&#xA;&lt;p&gt;Trying to make it as small as possible for easy bugout if it comes to it, but also out of strong and durable materials.&lt;/p&gt;&#xA;&lt;p&gt;Am I doing this all wrong?&lt;/p&gt;&#xA;&lt;p&gt;Still trying to figure this out...&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;:&lt;/p&gt;&#xA;&lt;p&gt;After finding more information, I have found new knowledge...&lt;/p&gt;&#xA;&lt;p&gt;This project ends up being in a Quad beam format with a reflector, driven and director in a 1/8WL configuration.&lt;/p&gt;&#xA;&lt;p&gt;Here's the info:&lt;/p&gt;&#xA;&lt;p&gt;Element Lengths:&#xA;Driven = 10-1/16”&#xA;Reflector = 10-9/16” (5% larger)&#xA;Director = 9-9/16” (5% smaller)&lt;/p&gt;&#xA;&lt;p&gt;Element separation:&#xA;Reflector to Driven = 2.5”&#xA;Driven to Director = 1.5”&lt;/p&gt;&#xA;&lt;p&gt;It's a 5&amp;quot; design.&lt;/p&gt;&#xA;&lt;p&gt;I also realize that tuning this will not be easy.&lt;/p&gt;&#xA;&lt;p&gt;Hopefully, this helps?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;: Typo correction SO239.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;EDIT&lt;/strong&gt;:  I have added a photo of the 3 elements - Like I said, it is very small.&lt;/p&gt;&#xA;&lt;p&gt;IF it works, then it does... If not, then I have gained a good amount of knowledge from the experiment.  Isn't that what HAM is all about?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eAfDR.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eAfDR.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerDisplayName="user18968" LastEditorDisplayName="user18968" LastEditDate="2021-03-06T23:29:23.887" LastActivityDate="2021-03-07T12:33:21.513" Title="1/8 wave 3-element 2m beam antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;antenna-construction&gt;&lt;antenna-system&gt;&lt;2m-band&gt;" AnswerCount="2" CommentCount="5" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18137" PostTypeId="2" ParentId="18136" CreationDate="2021-03-04T23:45:24.533" Score="3" Body="&lt;p&gt;Yagi antennas require an exact set of lengths and spacings to work properly.&lt;/p&gt;&#xA;&lt;p&gt;The lengths are all near a half wave but there is some subtle tuning to get the currents to the appropriate phase.&lt;/p&gt;&#xA;&lt;p&gt;Spacing can be between a quarter and a half wave but different spacings affect the optimum lengths.&lt;/p&gt;&#xA;&lt;p&gt;So your example of a 5/8 wave reflector won't work as a reflector, and 12 inch spacings sound a bit too small. The driven element needs to be about 1/2 wave long as well, slightly shorter if it's a folded dipole.&lt;/p&gt;&#xA;&lt;p&gt;I recommend looking at some standard yagi designs from page 67 onwards in &lt;a href=&quot;https://www.slideshare.net/mobile/AndreFourie4/antennas-in-practice-em-fundamentals-and-antenna-selection&quot; rel=&quot;nofollow noreferrer&quot;&gt;this book - Antennas in practice&lt;/a&gt; for some ideas. I've built a few of these and they've worked well.&lt;/p&gt;&#xA;&lt;p&gt;For example: The smallest one has these parameters:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Reflector of 0.482 wavelengths (39.25&amp;quot;), 0.2 wavelength spacing (16.55&amp;quot;)&lt;/li&gt;&#xA;&lt;li&gt;Driven element is a folded dipole 0.389 wavelengths long, about 34 Ohms&lt;/li&gt;&#xA;&lt;li&gt;One director, 0.442 wavelengths (36.58&amp;quot;), 0.2 wavelength spacing&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;This has a gain of 9.1 dBi.  You can see the subtle change in length between reflector and director. At this frequency these probably need to be correct to about 1/4&amp;quot; at the most.  The document has more detail about correcting for different element diameters and if they're connected to a metallic boom.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-03-05T14:28:57.207" LastActivityDate="2021-03-05T14:28:57.207" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="18138" PostTypeId="1" AcceptedAnswerId="18142" CreationDate="2021-03-05T06:37:39.593" Score="1" ViewCount="71" Body="&lt;p&gt;Some dedicated hams have spent a lot of effort gathering empirical data on various constructions for common-mode chokes. For example, &lt;a href=&quot;http://www.karinya.net/g3txq/chokes/&quot; rel=&quot;nofollow noreferrer&quot;&gt;G3TXQ's work&lt;/a&gt; is commonly referenced, and &lt;a href=&quot;http://k9yc.com/2018Cookbook.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;K9YC's&lt;/a&gt; is pretty well-known as well.&lt;/p&gt;&#xA;&lt;p&gt;However, I'd like to build a 4:1 current balun. Several sources (&lt;a href=&quot;http://www.w8ji.com/balun_single_core_41_analysis.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;like this one&lt;/a&gt;) describe why two cores are necessary. They are wired in parallel on the 50Ω (transceiver) side and in series on the 200Ω (antenna) side.&lt;/p&gt;&#xA;&lt;p&gt;The question is, what ferrites and windings should I use in this case? Is it sufficient to construct two 1:1 common mode chokes according to G3TXQ's or K9YC's instructions for the bands of interest, then wire them together as described in the previous paragraph? Or is it not that simple?&lt;/p&gt;&#xA;" OwnerUserId="8940" LastEditorUserId="8940" LastEditDate="2021-03-06T16:35:00.750" LastActivityDate="2021-03-06T16:35:00.750" Title="There are good guides for building 1:1 current baluns. What about 4:1?" Tags="&lt;balun&gt;&lt;choke-balun&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18139" PostTypeId="2" ParentId="18132" CreationDate="2021-03-05T18:42:29.317" Score="4" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Unless I butt right up to the tree and the roof, I probably won't have room for a 40m band half-wavelength dipole.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Then butt up to the tree and the roof. Of course it would be better if you had an enormous pair of towers in the middle of nowhere. It will still work.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The neighbours.... The top floors is 20m away horizontally and 5m above vertically. Broadside to the dipole. Bad idea?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It will be fine. And there's nothing you can do about it anyway, besides move to a location where you have more land.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&amp;quot;False ground&amp;quot; where the dipole overhangs the roof. And plenty of &amp;quot;foliage&amp;quot; above the dipole in chestnut tree&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I wouldn't worry about it. Perhaps if you had a metal roof it would be somewhat significant, but it's just one of many things you can compensate for when tuning the antenna. If you wanted to run much higher power you might start to worry about arcing off the ends of the antenna, but at 100W that won't happen.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Other Antenna types other than fan dipole which include 40m band?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;A trap vertical is another option to get multiple bands in one antenna with a small footprint. You could possibly mount it in the middle of your roof, with radials extending to the edges of the house. But the fan dipole probably works better and is cheaper to build.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;If above can't work, is there anything that could? Happy to go for external tuner or external amp for matching and more power up to UK legal limit of 400W. Central tower to &amp;quot;drape&amp;quot; inverted V dipole over the house? Or throw money and install a tower with a Yagi Beam. Or give up on 40m and stick to &amp;lt;=30m?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;More power will make it easier for other people to hear you, but it won't make it any easier for you to hear other people over the noise, which is going to be significant due to all the houses nearby.&lt;/p&gt;&#xA;&lt;p&gt;Getting the antenna higher with a tower could be an improvement, but definitely not necessary. The improvement would probably be most significant on 40 meters, since 10 meters is only a 1/4 wavelength high there.&lt;/p&gt;&#xA;&lt;p&gt;A directional antenna is likely the biggest improvement you could make, especially if you can also put it up higher. This is because the antenna directivity will also eliminate the noise you receive. But again, by no means necessary.&lt;/p&gt;&#xA;&lt;p&gt;Overall, your plan sounds fine. My advice would be to get an antenna in the air and see how it works.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-03-05T18:42:29.317" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18140" PostTypeId="2" ParentId="12260" CreationDate="2021-03-06T10:18:08.007" Score="0" Body="&lt;p&gt;I'm getting the same noise levels in the Philippines as the gray line passes over and it advances one minute per day. Noise level jumps S20 here and the net that I listen to goes away. Both 40 and 80 meters are effected. This has been going on for about a week and a half that I'm aware of.&lt;/p&gt;&#xA;&lt;p&gt;73 Dennis&#xA;DU3/KB7DV&lt;/p&gt;&#xA;" OwnerUserId="18979" LastActivityDate="2021-03-06T10:18:08.007" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18141" PostTypeId="2" ParentId="18132" CreationDate="2021-03-06T14:49:20.067" Score="3" Body="&lt;p&gt;Here's the SWR curve for a half-sized &amp;quot;Slightly Off-Center Fed Dipole&amp;quot; described in the September 2019 issue of &lt;em&gt;QST&lt;/em&gt; magazine:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RdkRv.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RdkRv.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The antenna provides an SWR on your bands of interest that any rig's built-in matching network should handle with ease and mismatch losses in a modest run of coax should be minimal.&lt;/p&gt;&#xA;&lt;p&gt;Notice that the SWR is calculated for 200-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; characteristic impedance. The wire is 20.9-m long and is fed 40% from one end through a 200-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;:50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; balun for convenient coax feed. (Note: not a typo, this feedpoint is slightly different from the article.) As the author of the original article I received dozens of letters, some of which claimed success with a variety of balun designs, but I recommend a two-core Guanella type &amp;quot;current balun&amp;quot;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GgPCO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GgPCO.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;with a choke of coax turns on a ferrite ring below but near the balun to prevent common-mode current on the outside of the coax shield.&lt;/p&gt;&#xA;&lt;p&gt;Because the feedpoint is not far off center, it's possible this balun is somewhat over-designed, but the parts are relatively inexpensive and readily available. I wound the balun for the article with two-conductor speaker wire to illustrate the utility of low-cost, everyday items one might find lying around the house:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DQoTK.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DQoTK.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It's abundantly possible that, with sag, the entire wire will just fit in the 20-m space between your house and tree. But, if it doesn't, &amp;quot;drooping&amp;quot; the far end of the wire will have very little effect on the antenna's behavior.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-03-06T14:49:20.067" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18142" PostTypeId="2" ParentId="18138" CreationDate="2021-03-06T15:03:27.340" Score="2" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Is it sufficient to construct two 1:1 common mode chokes ... then wire them together as described in the previous paragraph?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It is nearly as simple as that. Here's a wiring diagram:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/AxwG8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/AxwG8.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;In a perfect world, the transmission line wound around each core would have a characteristic impedance of &lt;span class=&quot;math-container&quot;&gt;$\sqrt{200*50}$&lt;/span&gt;=100-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;. Books on this subject by &lt;a href=&quot;https://store.cq-amateur-radio.com/shop/understanding-building-using-baluns-ununs/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Sevick&lt;/a&gt; and the ARRL &lt;a href=&quot;http://www.arrl.org/shop/ARRL-Antenna-Book-Softcover/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Antenna Book&lt;/a&gt; describe means for achieving the required impedance using insulated copper wire and teflon tubing. In his &lt;a href=&quot;http://www.kn5l.net/swbalun&quot; rel=&quot;nofollow noreferrer&quot;&gt;Speaker Wire Balun Test&lt;/a&gt;, KN5L demonstrates the efficacy of a readily-available household item in this application.&lt;/p&gt;&#xA;&lt;p&gt;For use at the 100-W power level, I constructed a balun of this type with 18-ga speaker wire wound on FT140-43 ferrite toroid cores:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qgzOM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qgzOM.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I did not perform any loss measurements on this balun. It's possible -61 material would deliver lower loss, as long as the wound turns deliver sufficient choking reactance for your application.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-03-06T15:31:21.933" LastActivityDate="2021-03-06T15:31:21.933" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18144" PostTypeId="2" ParentId="18136" CreationDate="2021-03-07T01:37:34.250" Score="1" Body="&lt;p&gt;I applaud your attempt to satisfy a need. Unfortunately, your design will not achieve your goals.&lt;/p&gt;&#xA;&lt;p&gt;Here is a model of your design:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/I00dQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/I00dQ.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The pattern shows none of the front-to-back directivity you want from a &amp;quot;beam&amp;quot; antenna. In fact, the pattern is not affected at all by the addition of the &amp;quot;reflector&amp;quot; or the &amp;quot;director&amp;quot;. The pattern has about 1.4-dB gain over an &amp;quot;isotropic&amp;quot; or point-source radiator and the feedpoint resistance is &lt;em&gt;very&lt;/em&gt; low, about 0.2-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;, with a lot of capacitance reactance, as one would expect from an electrically-short, bent, &amp;quot;doublet&amp;quot; radiator. It would be &lt;em&gt;very&lt;/em&gt; difficult to match this impedance to a coax feedline.&lt;/p&gt;&#xA;&lt;p&gt;The parasitic elements don't influence the radiation pattern because no current flows in them. No current flows because, like the driven element, they also possess very high reactance, which impedes the flow of RF current.&lt;/p&gt;&#xA;&lt;p&gt;If one closes the driven element to form a loop, its pattern changes:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/npt8o.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/npt8o.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The maximum gain of this antenna is about -2.5-dB; that is, only about half the incident power is radiated in the preferred direction, which is perpendicular to the axis of the &amp;quot;beam&amp;quot; ... and even less in other directions. This is the same pattern as the driven element only because, again, no current flows in the &amp;quot;reflector&amp;quot; or &amp;quot;director.&amp;quot; This is the pattern you would expect from a single loop (the driven element) that is, electrically, very small. This fact is reinforced by the very low feedpoint resistance of less than 0.1-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; with a very large series reactance.&lt;/p&gt;&#xA;&lt;p&gt;Closing the &amp;quot;reflector&amp;quot; and &amp;quot;director&amp;quot; loops has very little affect on the current that flows in the elements; it merely changes the sign of the very high series equivalent reactance. The closed loop elements of a quad must have a circumference &lt;em&gt;on the order&lt;/em&gt; of a wavelength at the operating frequency to perform the way you intend. Non-closed elements, like those of a Yagi-Uda type array, must have lengths &lt;em&gt;on the order&lt;/em&gt; of a half-wavelength. Reducing the size of a quad loop element by a factor of 8 defeats the element behavior on which the array depends, regardless of whether the elements are parasitic or individually driven.&lt;/p&gt;&#xA;&lt;p&gt;You could rotate the elements and feed them with currents that would produce a directional pattern:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/DwKCt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/DwKCt.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;But the maximum gain in the favored direction is still negative and the feedpoint impedance is still very low, making it very difficult to match to a coax feedline. This arrangement is similar to the arrays of small loops used for &lt;a href=&quot;https://www.contestuniversity.com/wp-content/uploads/2018/10/Easy-to-Build-Low-Band-Receiving-Antennas-for-small-and-large-lots-Sept-2018.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;directional &lt;em&gt;receiving&lt;/em&gt; antennas&lt;/a&gt; on the lower frequency bands where wavelengths are much longer. Low band receiving antennas profit from their ability to reject noise from non-favored directions, improving the signal-to-noise ratio of the signals from the desired direction. Negative gain in a receiving antenna can be compensated by the addition of preamplifiers of sufficiently low noise figure.&lt;/p&gt;&#xA;&lt;p&gt;Like many budding hams, I traveled the same intellectual road. Finally, I was forced to realize that you (or, at least, most of us) can't break the laws of physics. The only way I have seen to accomplish your goal is to use an array of &lt;a href=&quot;https://en.wikipedia.org/wiki/Fractal_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;fractal antenna&lt;/a&gt; elements which, essentially, fold a wavelength of wire into a much smaller area than the classic quad-type loop occupies.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/m9QM3.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/m9QM3.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-03-07T12:33:21.513" LastActivityDate="2021-03-07T12:33:21.513" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18145" PostTypeId="2" ParentId="18132" CreationDate="2021-03-07T19:02:40.630" Score="0" Body="&lt;p&gt;With 20 meters form house to tree you cloud also use an end fed half-wave antenna on 40 meters which is also resonant on 20, 15 and 10m. You can build it yourself searching for 64:1 unun and adding the length of wire needed.&lt;/p&gt;&#xA;&lt;p&gt;Maybe it is a good idea to use a pulley for your wire as the tree might shake in the wind (and the house not :-). I assume you will need a tuner to get a really good swr.&lt;/p&gt;&#xA;" OwnerUserId="18986" LastActivityDate="2021-03-07T19:02:40.630" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18146" PostTypeId="1" AcceptedAnswerId="18148" CreationDate="2021-03-08T01:32:55.213" Score="4" ViewCount="302" Body="&lt;p&gt;Totally new amateur operator and I've noticed that a lot of material e.g. Your Tube videos, blogs, forums when discussing metering VSWR mainkly seem to be talking about HF bands. I also see fewer VSWR meters that cover the VHF/UHF bands in stores.&lt;/p&gt;&#xA;&lt;p&gt;In PRACTICE is metering and adjustimg VSWR less of an issue for the higher frequencies?&lt;/p&gt;&#xA;&lt;p&gt;I understand that for optimal performance you're going to want to meter and tune your antennae for each frequency, but it appears to this obsever that measuring VSWR and  tuning antennas or matching impedance is less common on the VHF/UHF bands and from this I infer that VHF/UHF bands may be less sensitive to VSWR issues  or perhaps there are fewer VSWR issues in those bands?&lt;/p&gt;&#xA;" OwnerUserId="18970" LastActivityDate="2021-03-08T12:50:25.990" Title="Is testing SWR *practically* less important for 2m/70cm than HF bands?" Tags="&lt;hf&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;impedance-matching&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18147" PostTypeId="2" ParentId="18146" CreationDate="2021-03-08T03:05:23.147" Score="0" Body="&lt;p&gt;Beginner here too, maybe because HF more commonly transmits at much higher power with much more expensive equipment, over much longer distances that makes it more relevant, but id see swr important to any band, and i just picked up a meter that does 2-500mhz&lt;/p&gt;&#xA;" OwnerUserId="17758" LastActivityDate="2021-03-08T03:05:23.147" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18148" PostTypeId="2" ParentId="18146" CreationDate="2021-03-08T04:30:28.897" Score="6" Body="&lt;p&gt;I would say in practice it is less important because hams use different types of antennas for HF and for VUHF.&lt;/p&gt;&#xA;&lt;p&gt;At HF, the same antenna is often used for many bands. The bands have large fractional bandwidth. Antennas are often simple wire, very thin compared to wavelength. And finally, because the wavelength is quite long, they are often too short for the band of interest, and very close to the ground.&#xA;All of these factors mean we can't buy an antenna that simply works, or tune it once. We often have to use an antenna tuner to adjust the antenna impedance at a particular operating frequency, and we need an SWR meter to see how we're doing.&lt;/p&gt;&#xA;&lt;p&gt;At VUHF, the antennas are more often full size, single band, tuned once, parhaps at the factory (base collinears or yagis) or during installation (whips on cars), and then working well after that. If they do need tuning, it's done occasionally by adjusting the antenna dimensions, not with a tuner. This means we don't need to regularly measure the SWR of VUHF antennas. It is useful to check it though, as high SWR might indicate a problem with the antenna or feed.&lt;/p&gt;&#xA;&lt;p&gt;One counter-example would be an HF single or multi-band beam, designed and tuned for a few specific frequencies. These will have consistent, low SWR at these frequencies, no need for a tuner or to check SWR regularly.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-03-08T04:45:54.767" LastActivityDate="2021-03-08T04:45:54.767" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18149" PostTypeId="1" CreationDate="2021-03-08T09:33:08.783" Score="0" ViewCount="65" Body="&lt;p&gt;I need to burn an audio file received from a computer sound card. But in the new version of the gnu radio, I found that the &amp;quot;Wav File Sink&amp;quot; and &amp;quot;Wav File Source&amp;quot; blocks were gone. Tell me, how can I write to the WAV file now?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/aW0r8.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aW0r8.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I am using the graph as in the picture, but the recorded file cannot be opened by the audio player: I get the error &amp;quot;The file cannot be played. The file format may not be supported, the file extension is incorrect, or the file is damaged&amp;quot;. In this case, in the &amp;quot;file sink&amp;quot; block, I manually wrote the file extension &amp;quot;.wav&amp;quot;&lt;/p&gt;&#xA;" OwnerUserId="18124" LastEditorUserId="218" LastEditDate="2021-03-09T13:40:54.657" LastActivityDate="2021-03-09T13:40:54.657" Title="Writing &quot;Wav&quot; file in GNU Radio 3.9.0" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;audio&gt;" AnswerCount="0" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18150" PostTypeId="2" ParentId="18146" CreationDate="2021-03-08T12:50:25.990" Score="2" Body="&lt;p&gt;Welcome to hamSE, Jason.&lt;/p&gt;&#xA;&lt;p&gt;Assuming you can match your rig to the load at the shack end of the transmission line, the importance of SWR depends primarily on how much transmission line loss affects your operations and how much money you're willing to spend on transmit power amplifiers, receive preamplifiers and lower-loss transmission lines to compensate for it.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ac6la.com/swrloss.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;AC6LA&lt;/a&gt; describes the calculation of transmission line losses, including a thorough analysis of why the assumptions built into some of the available tools may produce inaccurate results. His program &lt;a href=&quot;https://ac6la.com/tldetails1.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Transmission Line Details&lt;/a&gt; breaks losses down into contributions from conductor, dielectric and reflection. This detailed picture tells you exactly how important SWR will be to your operation.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-03-08T12:50:25.990" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18151" PostTypeId="2" ParentId="16790" CreationDate="2021-03-08T16:57:23.630" Score="2" Body="&lt;p&gt;The answer...  Various sources can cause this.  One common source of interference are battery chargers; either at your house or a neighbor's.&lt;/p&gt;&#xA;" OwnerUserId="18992" LastActivityDate="2021-03-08T16:57:23.630" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18152" PostTypeId="1" CreationDate="2021-03-09T00:49:02.427" Score="1" ViewCount="96" Body="&lt;p&gt;A SWR meter will vary in swr with coax length if unbalanced as your coax length is around 1/2 wave length multiple.&lt;/p&gt;&#xA;&lt;p&gt;Does a VNA ( nanoVna ) in this case experience the same effect, (obviously assuming calibration is done for varying lengths) will a certain length coax lead to a incorrectly low swr ??&lt;/p&gt;&#xA;" OwnerUserId="17758" LastActivityDate="2021-03-09T22:58:27.687" Title="Do VNA (nano) suffer the same effect of coax length to swr, as swr meters do?" Tags="&lt;impedance-matching&gt;&lt;swr-meter&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18153" PostTypeId="2" ParentId="18152" CreationDate="2021-03-09T03:28:47.990" Score="2" Body="&lt;p&gt;The NanoVNA, and any VNA, when calibrated with open, short and load standards, can correctly measure through an arbitrary two port network, like a lossy, imperfect cable.&lt;/p&gt;&#xA;&lt;p&gt;Any combination of reflections and losses, like a series of cables, adapters, etc, can be reduced to a single reflection and transmission device, and fully calibrated. Calibration is done at each frequency independently, and the exact length of the cable doesn't matter.&lt;/p&gt;&#xA;&lt;p&gt;Here is a &lt;a href=&quot;http://www.hpmemoryproject.org/an/pdf/an_1287-3.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;classic application note from Hewlett Packard about network analyser calibration&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;But your statement about a regular SWR meter isn't correct. A working SWR meter should read the same for modest changes in cable length, because the standing wave ratio or the magnitude of the reflection coefficient does not change with cable length, only the phase does. The forward and reflected power are the same at any position in the cable.&#xA;One caveat - if the cable is long enough that the loss starts to become significant, then the SWR will appear lower than it is at the antenna.&lt;/p&gt;&#xA;&lt;p&gt;A few ways you might see the SWR change with cable length, apart from a defective SWR meter:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If there's a secondary reflection, perhaps from a bad adapter in the middle of the cable, then there will be continuous changes to the SWR over frequency, but these are real from the point of view of the SWR meter, so correctly measured.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If the antenna is using the coax as part of the antenna, like an &amp;quot;end fed&amp;quot; or dipole without a balun, then changing the cable length will affect the actual antenna behavior, which will change the SWR. This will affect a VNA measurement too. In fact, one way of judging the amount of current on the cable, is to run your hand down the cable and watch the SWR on the VNA.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Very long cables can be a problem for a VNA as the source and hence receiver has changed by the time the reflection arrives, this can sometimes be managed by selecting a slower sweep or increasing the dwell time per point. This usually only happens over 30 metres, or more.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Long lossy cables also reduce the dynamic range of the calibrated instrument, making the measurements more noisy. This also makea it much more sensitive to imperfect, time-varying RF connectors at the instrument end of the cable.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-03-09T20:35:22.637" LastActivityDate="2021-03-09T20:35:22.637" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18154" PostTypeId="2" ParentId="5563" CreationDate="2021-03-09T17:18:02.753" Score="-1" Body="&lt;p&gt;A 1:1 balun is a transformer, which also blocks cmc (common mode current).&lt;br /&gt;&#xA;A balun choke is not a transformer, it passes current without magnetic intermediate. It only chokes (blocks) cmc.&lt;/p&gt;&#xA;" OwnerUserId="16088" LastActivityDate="2021-03-09T17:18:02.753" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18155" PostTypeId="2" ParentId="5563" CreationDate="2021-03-09T20:50:38.997" Score="4" Body="&lt;p&gt;A &lt;a href=&quot;https://en.wikipedia.org/wiki/Choke_(electronics)&quot; rel=&quot;nofollow noreferrer&quot;&gt;choke&lt;/a&gt; is an inductor which is used to block high frequencies while allowing DC to pass. All chokes are inductors (though sometimes more than one inductor), but not all inductors are chokes: to be called a choke the application must be to block high frequencies. Counterexample: an inductor in a matching network is not a choke, but the same inductor, used to filter RF from a DC power supply, could be called a choke.&lt;/p&gt;&#xA;&lt;p&gt;A balun is any device designed to connect a balanced source to an unbalanced load or vice-versa. Since most baluns are passive devices they are also reciprocal, meaning they work equally well in either direction. There are many ways to build a balun. Many HF balun designs use a choke, but &lt;a href=&quot;https://ham.stackexchange.com/questions/7225/where-are-the-baluns-for-vhf-and-higher-how-can-one-be-made&quot;&gt;chokes are less commonly used in baluns at higher frequencies&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;This is a common-mode choke:&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/4f5Ew.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f4f5Ew.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;Common-mode current sees a high impedance, and is thus &amp;quot;choked&amp;quot;. (Of course there's nothing drawn in this schematic which would introduce such a current, but the real world is not so simple.)&lt;/p&gt;&#xA;&lt;p&gt;If you put a common-mode choke in a box with a coax connector at one end and screw terminals or some other balanced connector at the other end, you've made one kind of balun. It's 1:1 (because it performs no impedance transformation) and a current balun (because with high choking impedance, common-mode current approaches zero). And while theoretically there may be other possible designs for a 1:1 current balun, in practice &amp;quot;1:1 current balun&amp;quot; means &amp;quot;a common-mode choke with balanced and unbalanced connectors on it&amp;quot;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-03-09T20:50:38.997" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18156" PostTypeId="2" ParentId="18152" CreationDate="2021-03-09T22:58:27.687" Score="1" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;A SWR meter will vary in swr with coax length if unbalanced as your coax length is around 1/2 wave length multiple.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I have never seen an SWR measuring device that was designed to be used with a balanced load. This could certainly be done, but such devices are usually intended to measure SWR on a coaxial, i.e., unbalanced, line.&lt;/p&gt;&#xA;&lt;p&gt;For the purposes of SWR measurement, the feedline is part of the &amp;quot;load.&amp;quot; The load attached to the SWR meter includes the feedline and everything attached to it; e.g., antennas, splitters, stubs, etc. A properly designed and operated SWR meter will correctly measure SWR regardless of the load.&lt;/p&gt;&#xA;&lt;p&gt;In general, the SWR at the shack end of the feedline will not be the same as the SWR at the antenna. Feedline loss attenuates the driving signal as it travels forward along the line, so the signal available to be reflected at any point is reduced. Similarly, feedline loss attenuates the reflected signal as it travels back along the line, reducing the signal available to be detected by the SWR meter. In general, feedline loss reduces the SWR observed at the shack end of the feedline.&lt;/p&gt;&#xA;&lt;p&gt;In addition to loss, the transmission line changes the phase of the incident signal traveling forward along the line and the phase of the reflected signal as it travels back. The incident and reflected signals are superimposed on (i.e., add to) each other at every point along the line. At some points, the incident and reflected signals will tend to reinforce each other, while at others they will tend to cancel each other. These reinforcing and canceling effects produce the standing waves we measure.&lt;/p&gt;&#xA;&lt;p&gt;The effects of loss and phase can be seen by plotting the impedance along a transmission line on a &lt;a href=&quot;http://www.ae6ty.com/Smith_Charts.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Smith chart&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OhIxO.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OhIxO.png&quot; alt=&quot;![enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The SWR at the 1K&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; resistor is 20. Traveling 60&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt; toward the generator on RG58/U coax, the impedance changes dramatically to 5.9-j31 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; and the SWR is about 11.7; 45&lt;span class=&quot;math-container&quot;&gt;$^o$&lt;/span&gt; further toward the generator, the impedance changes to 9.4+j13 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; and the SWR is about 6.2; completing the half-wavelength journey toward the generator, the impedance changes to 257-j0.6 &lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; and the SWR is about 5.1. (Note: the small differences in distances along the transmission lines are a consequence of the parametrized model used.)&lt;/p&gt;&#xA;&lt;p&gt;This tool also shows that, of the 1.00-W incident on T3, only 0.247-W arrives at the 1k&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt; resistor, representing about 6.1-dB of loss. By comparing this loss to what would be lost on a matched line (resistor = 50-&lt;span class=&quot;math-container&quot;&gt;$\Omega$&lt;/span&gt;), we see that more that more than 77% of the loss is a result of the large mismatch.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-03-09T22:58:27.687" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18158" PostTypeId="2" ParentId="1646" CreationDate="2021-03-10T15:27:18.767" Score="3" Body="&lt;p&gt;Wow, in response to the comment above, when has listening ever been considered rude? Most consider it a critical skill to use in ham radio. With so many repeater groups jumping down people's throat for transmitting on their repeaters, is it no wonder that many choose to listen for extended times before jumping in to initiate a contact on their own? So many grumpy people so fast to say what's rude. I thought ham radio was about learning. One of the ways people learn in this hobby is by listening. Why in the world would that ever be considered rude? Each repeater and group can have its own culture, so to speak. That can take more than 'a minute or two' to get a sense of. Here's a case of one person trying to be polite and another getting all judgy with the response. Blacklisting? For someone LISTENING? Wow. Ooohh, feel the power. No wonder people are hesitatant to broadcast; sadly, we see similar responses on the air all the time. Less judgment, more patience and mentoring please.&lt;/p&gt;&#xA;" OwnerUserId="19014" LastActivityDate="2021-03-10T15:27:18.767" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18159" PostTypeId="1" AcceptedAnswerId="18160" CreationDate="2021-03-10T17:30:02.493" Score="2" ViewCount="64" Body="&lt;p&gt;I am transmitting a QPSK signal via GRC and when I look at it on the spectrum analyzer, the signal is shifted away from my center frequency. This shift increases the higher the center frequency (i.e. 1 MHz = almost no shift, 10 MHz = 1kHz shift, 50 kHz = 2.3kHz shift, 900 MHz = 43.5 kHz shift). Why does this shift occur? I have attached my flowgraph screenshot below. &lt;a href=&quot;https://i.stack.imgur.com/SR2mz.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/SR2mz.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18957" LastActivityDate="2021-03-10T17:47:52.213" Title="Why does QPSK signal in GNU Radio shift away from my center frequency at higher frequencies?" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18160" PostTypeId="2" ParentId="18159" CreationDate="2021-03-10T17:47:52.213" Score="3" Body="&lt;p&gt;Sounds like your SDR transmitter has a frequency error of 40-50 ppm (or, less likely, your transmitter is fine but your spectrum analyzer has the error). Try transmitting pure carrier, without modulation, and see if you get the same amount of offset. If so, you might be able to adjust some calibration in hardware or firmware to fix it, or connect an external frequency reference to your SDR to improve its accuracy. If you can't do any of those, you can fit a curve to the error and correct the center frequency in software so that the transmitted signal shows up where you want.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-03-10T17:47:52.213" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18161" PostTypeId="1" AcceptedAnswerId="18162" CreationDate="2021-03-10T22:33:10.243" Score="3" ViewCount="93" Body="&lt;p&gt;I'm trying to get into backpacking QRP, which has lead me to read up on various ways to construct very portable wire antennas. I would ideally like to have a single antenna for the CW parts of the 40, 30 and 20 m bands, while avoiding having to bring a general purpose tuner.&lt;/p&gt;&#xA;&lt;p&gt;There are various options, but one that caught my eye and which I want this question to be about is the use of &lt;strong&gt;crocodile clips&lt;/strong&gt; to simply disconnect parts of the wire. Using my current needs as an example, an end fed wire around 20 meter long could thus work as half wave on 40 m and as a full wave on 20 m, and if I want to work 30 m I just disconnect 5 meter at the end to get a half wave once again. Perhaps I could even put a pair of clips in the middle as well if I want a half wave antenna for 10 m as well(?) I don't want to get the question too stuck on this precise design though, but keep the focus on the technique itself.&lt;/p&gt;&#xA;&lt;p&gt;My main question is: Are there any downsides to using crocodile clips to change the length of the antenna? (or even to change its topology?) Is there anything special I need to keep in mind if I go with this approach?&lt;/p&gt;&#xA;&lt;p&gt;I could see how this could be less appropriate if you plan to transmit several hundred Watts, but I'm thinking QRP.&lt;/p&gt;&#xA;&lt;p&gt;I imagine it might be hard to get the connection good enough in terms of resistance. Also, the resistance of the clips themselves, being different from the wire, might be a problem. I've tried using a search engine, but it's hard to separate pages where crocodile clips are discussed from those where they are simply used in experiments.&lt;/p&gt;&#xA;" OwnerUserId="18450" LastActivityDate="2021-03-11T02:42:49.140" Title="Using crocodile clips to make modular QRP antennas? Are there downsides?" Tags="&lt;wire-antenna&gt;&lt;qrp&gt;&lt;portable&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18162" PostTypeId="2" ParentId="18161" CreationDate="2021-03-11T02:42:49.140" Score="7" Body="&lt;p&gt;If you look up &amp;quot;link dipole&amp;quot; or &amp;quot;linked dipole&amp;quot; you will find several designs that do just that. It works well for QRP or even for 100W. The ones I've seen have used several different connectors: alligator clips, quick disconnect spade terminals, Anderson PowerPoles, and banana plugs, to name a few. Of those, alligator clips are probably my &lt;em&gt;least&lt;/em&gt; favorite in terms of reliability, and banana plugs or PowerPoles my favorite, providing an easy and low-resistance connection. But pick anything you have on hand and it will probably work alright. Just make sure to provide some strain relief so that any tension in the wire isn't carried by the connectors.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-03-11T02:42:49.140" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18165" PostTypeId="1" CreationDate="2021-03-14T17:45:52.620" Score="3" ViewCount="105" Body="&lt;p&gt;I have an old IC-745 I bought used last year. Recently it seems to be malfunctioning intermittently. It is receiving well on all bands as far as I can tell. Sometimes when transmitting, there is no RF power shown on the meter. I've tried the built in SWR meter when this happens, and there is no movement of the needle when I adjust the RF power with the meter in SET mode. My NanoVNA shows an SWR of &amp;lt; 1.1 on the frequencies I'm using (40m, 20m), so there doesn't seem to be any problem with the antenna.&lt;/p&gt;&#xA;&lt;p&gt;The transceiver has seemed to work well (aside from being noisy, which is probably due to living in a city). I've received good signal reports since this began, but have only tried when the meter is working and showing a low SWR.&lt;/p&gt;&#xA;&lt;p&gt;What's the best way to troubleshoot? I'm guessing the first step is to figure out whether the problem is actually low power or just a bad meter? I don't have an HF wattmeter, but have ordered one. I do have an oscilloscope and NanoVNA. Any suggestions on what this could be and how to troubleshoot?&lt;/p&gt;&#xA;" OwnerUserId="19077" LastActivityDate="2021-03-14T18:05:40.667" Title="Troubleshoot ICOM IC-745 intermittently shows no power on transmit" Tags="&lt;hf&gt;&lt;rf-power&gt;&lt;icom&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18166" PostTypeId="2" ParentId="18165" CreationDate="2021-03-14T18:05:40.667" Score="6" Body="&lt;p&gt;Without any radio shack tools? Connect a bulb to the antenna output to indicate RF. Two times 12 volt 5 Watt in series (rear light of car bulb) can indicate RF. Reduce RF power before hitting the TX-button.&lt;/p&gt;&#xA;&lt;p&gt;Problem is similar (looking) to the problem with an IC-720 that I owned. Reason was the rotary switch used for the band pass switching. Poor contacts. The built-in program, in the IC-720, was a cleaning sequence. Rather annoying rattling sound. That should stop after 30 seconds maximum.&lt;/p&gt;&#xA;&lt;p&gt;In my 720 there was no RF in some cases, just as your description. Most of the time it was possible to recover from that by manually selecting another band: the rotary switch was forced to move and did work at the second or third attempt.&lt;/p&gt;&#xA;&lt;p&gt;When the 745 has a similar switch than it must be cleaned. But the Icom is a service-unfriendly construction...&#xA;Succes.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-03-14T18:05:40.667" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18167" PostTypeId="1" AcceptedAnswerId="18168" CreationDate="2021-03-16T15:59:17.620" Score="0" ViewCount="36" Body="&lt;p&gt;I am trying to transmit a signal in gnu radio and after a set amount of time have the transmission cut off. For simple example, I have a sine wave that I want to transmit for 30 seconds then after that I want the transmission to cut off. Is there a block that can do that or a combination of blocks I can trick into doing that or anyone with a custom block?&lt;/p&gt;&#xA;" OwnerUserId="18957" LastActivityDate="2021-03-16T18:24:52.313" Title="GNU Radio transmission for a set amount of time" Tags="&lt;gnuradio&gt;&lt;dsp&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18168" PostTypeId="2" ParentId="18167" CreationDate="2021-03-16T18:24:52.313" Score="2" Body="&lt;p&gt;The Head block does that: End the operation of the flow graph after an amount of samples have passed. Since your sample rate is fixed, that's the way you want to go.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2021-03-16T18:24:52.313" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18169" PostTypeId="1" CreationDate="2021-03-16T19:00:07.070" Score="4" ViewCount="288" Body="&lt;p&gt;So I am working on a project that involves me to check real time difference between samples.I am fairly new to this so after a bit of researching  I wrote a simple python script for it, here is the script. Here is the script:&#xA;import time&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;from rtlsdr import RtlSdr&#xA;sdr = RtlSdr()&#xA;sdr.sample_rate = 2e6    # sampling rate&#xA;sdr.center_freq = 413e6   &#xA;sdr.gain = 36&#xA;sdr.freq_correction = 60 &#xA;while(1):&#xA;    &#xA;    s = time.perf_counter() &#xA;    y = sdr.read_samples(512)&#xA;    print('seconds elapsed:',time.perf_counter() - s)&#xA;    time.sleep(0.5)&#xA;sdr.close()&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;Now this is the output I get:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;seconds elapsed: 0.00020965299336239696&#xA;seconds elapsed: 0.00024505300098098814&#xA;seconds elapsed: 0.00026376899768365547&#xA;seconds elapsed: 0.000233347003813833&#xA;seconds elapsed: 0.00021806899894727394&#xA;seconds elapsed: 0.00022980299399932846&#xA;seconds elapsed: 0.0002400680023129098&#xA;seconds elapsed: 0.0002324250017409213&#xA;seconds elapsed: 0.00022879400057718158&#xA;seconds elapsed: 0.00018380500114290044&#xA;seconds elapsed: 0.00022288499894784763&#xA;seconds elapsed: 0.000273057994490955&#xA;seconds elapsed: 0.00028443100018193945&#xA;seconds elapsed: 0.00027377300284570083&#xA;seconds elapsed: 0.00026877300115302205&#xA;seconds elapsed: 0.00023158000112744048&#xA;seconds elapsed: 0.00024587199732195586&#xA;seconds elapsed: 0.00022548100241692737&#xA;seconds elapsed: 0.0002632289979374036&#xA;seconds elapsed: 0.0002523060029488988&#xA;seconds elapsed: 0.00026537499797996134&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;As can be seen it is a fairly random output, ideally the time difference should be constant I suppose, what exactly am I doing wrong?&#xA;I am using a rtlsdr blog v3&lt;/p&gt;&#xA;" OwnerUserId="19099" LastEditorUserId="4665" LastEditDate="2021-03-18T17:24:54.723" LastActivityDate="2021-03-18T17:24:54.723" Title="Problem with sample rate" Tags="&lt;rtl-sdr&gt;&lt;software&gt;&lt;dsp&gt;&lt;software-development&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18170" PostTypeId="2" ParentId="18169" CreationDate="2021-03-16T19:32:16.317" Score="4" Body="&lt;p&gt;512 samples should take 256 microseconds, so your times look about right.&lt;/p&gt;&#xA;&lt;p&gt;The exact time it takes to execute those lines of code will depend on the rest of what your computer is busy with. And it's unlikely that the elapsed time counter will be accurate to better than 10 us anyway (but I may be wrong, try it yourself by timing a delay loop).&lt;/p&gt;&#xA;&lt;p&gt;Whats slightly concerning is that the average seems to be less than 256 us. Perhaps it's reading off a buffer, perhaps it will average up a bit later on.&lt;/p&gt;&#xA;&lt;p&gt;To get the accuate (relative) time of a particular sample, take the sample number and divide by the sampling rate :)&#xA;Absolute time is more complicated, because of all of the buffers and devices between the ADC and your python code, USB for example will delay the samples by hundreds of microseconds. If you want to know the absolute time of a sample, you need to inject a time marker signal into the front of the receiver, and find its position in the samples later.&lt;/p&gt;&#xA;&lt;p&gt;What else are you expecting?&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2021-03-16T19:32:16.317" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18171" PostTypeId="2" ParentId="18169" CreationDate="2021-03-16T23:24:57.563" Score="4" Body="&lt;p&gt;The RTL-SDR interfaces to your computer via USB.  The USB interface and driver will buffer the data and send it to your software at the requested sample rate on average (baring underflow due to software glitches), but with varying timing due to interface jitter.  The RTL2832U USB is likely sending larger chunks of data over USB in blocks of far more than 512 samples at a time, and the driver is chopping up these large chunks at slightly random times.  So the per 512 sample time stamps are irrelevant except to indicate if you are losing data long term.   Use the sample count divided by the sample rate instead.&lt;/p&gt;&#xA;&lt;p&gt;Even the time stamps will have OS latency jitter.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-17T16:30:04.533" LastActivityDate="2021-03-17T16:30:04.533" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18172" PostTypeId="1" AcceptedAnswerId="18175" CreationDate="2021-03-17T01:12:12.520" Score="4" ViewCount="599" Body="&lt;p&gt;I'm a US extra class, but a little late to the party, so to get a short 1x2 I have to fight it out at the vanity call sign fair. I thought I understood the rules, but apparently I don't.&lt;/p&gt;&#xA;&lt;p&gt;The only chance we have to get a concise 1x2 call sign (or by all means 2x1) is to get one that has been cancelled or expired and not renewed. In my research I found that the case of cancelled is most likely. The web sites are misleading as they show the original expiration date next to the cancelled status. But since I am fluent in data, I downloaded the full data dump and went hunting and found some candidates. I thought a callsign becomes available if not claimed otherwise after 2 years of the cancellation date.&lt;/p&gt;&#xA;&lt;p&gt;But apparently I am wrong. I had an application dismissed. But the call sign I was eying for is still not otherwise assigned and it was cancelled more than 2 years ago as of the date on my application. Why was my application dismissed then (after waiting 18 + then some days for the automated decision)? Where do we find the exact rules (and how they are actually implemented)? I don't suppose there is any official I can ask with some kind of dispute over their decision, or is there a way to argue a decision?&lt;/p&gt;&#xA;" OwnerUserId="16238" LastActivityDate="2021-03-17T17:08:08.083" Title="What are the EXACT rules about FCC vanity call sign assignments?" Tags="&lt;fcc&gt;&lt;callsign&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18173" PostTypeId="1" CreationDate="2021-03-17T02:38:38.487" Score="3" ViewCount="86" Body="&lt;p&gt;I want to create a battery backup for my radios. Initially I'm thinking of using an Epic PWRgate and a LiFePo4 battery, so the battery is charged by the same power supply that's running the radios. The LiFePo4 batteries require a charge voltage of 14.4v. Radio gear all appears to require 13.8v±15% (11.7-15.8v), so no problem with raising the voltage there. My current power supply isn't adjustable though, and the few I've found that are have a big knob on the front which seems too easy to bump and end up damaging something.&lt;/p&gt;&#xA;&lt;p&gt;Is there a better way to go about this? Or another precaution I can take to prevent an incorrect voltage from starting a fire?&lt;/p&gt;&#xA;" OwnerUserId="11639" LastActivityDate="2021-04-30T02:15:21.687" Title="power supply / LiFePo4 battery backup compatibility" Tags="&lt;power-supply&gt;&lt;battery-charging&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18175" PostTypeId="2" ParentId="18172" CreationDate="2021-03-17T06:20:12.797" Score="7" Body="&lt;p&gt;Your application submitted on February 18th requested two callsigns.&lt;/p&gt;&#xA;&lt;p&gt;One of them was granted to another application submitted on the 16th, and so was unavailable when yours was processed, even though it hadn't yet been assigned when you made your application. If you submitted on the 16th or 17th you would have had a chance to get that one (along with 12 other people who submitted), but the 18th was too late.&lt;/p&gt;&#xA;&lt;p&gt;The other callsign you requested was canceled in June of 2019, and therefore isn't available for assignment until &lt;em&gt;June&lt;/em&gt; of 2021. You can still try for it then.&lt;/p&gt;&#xA;&lt;p&gt;The exact rules are in Part 97, and you can find some useful explanatory text on &lt;a href=&quot;http://ae7q.com/query/&quot; rel=&quot;nofollow noreferrer&quot;&gt;AE7Q&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;There is an appeals process, but it won't do you any good in this case.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2021-03-17T17:08:08.083" LastActivityDate="2021-03-17T17:08:08.083" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18176" PostTypeId="1" CreationDate="2021-03-17T09:39:18.677" Score="3" ViewCount="55" Body="&lt;p&gt;Where does the noise I can hear on my 28 MHz receiver come from? I'm not talking about the inherent noise produced by the internal circuitry of the radio, I mean the noise received by the antenna. It's always there, no matter where I am, even if I am in the middle of nowhere and there are no nearby noise sources. If it were noise from outer space, then it would be blocked by the ionosphere when there are skip conditions, but when there is skip the noise is still there. Is it dead people?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="4665" LastEditDate="2021-03-17T16:09:24.053" LastActivityDate="2021-03-17T16:09:24.053" Title="Where exactly does atmospheric noise (QRN) come from?" Tags="&lt;reception&gt;&lt;qrn&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18177" PostTypeId="2" ParentId="18176" CreationDate="2021-03-17T13:53:53.153" Score="2" Body="&lt;p&gt;Atmospheric noise does not go as high as 28MHz, it becomes less dominant above 10MHz, see figure: &lt;a href=&quot;https://en.wikipedia.org/wiki/Atmospheric_noise&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Atmospheric_noise&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;At 28MHz it is the thermal noise of the earth, either directly picked by the antenna or coming from further and reflected.&#xA;Thermal noise formula: &lt;a href=&quot;https://en.wikipedia.org/wiki/Noise_temperature&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://en.wikipedia.org/wiki/Noise_temperature&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8579" LastActivityDate="2021-03-17T13:53:53.153" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18178" PostTypeId="5" CreationDate="2021-03-17T16:19:02.933" Score="0" Body="" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-03-17T16:19:02.933" LastActivityDate="2021-03-17T16:19:02.933" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18179" PostTypeId="4" CreationDate="2021-03-17T16:19:02.933" Score="0" Body="QRN is the amateur radio term for &quot;atmospheric&quot; noise originating neither from the transmitting station nor the receiving station that is of natural origin, especially on the HF and MF bands.  For discussions about noise as an inevitable component of a real signal, see [noise].  For questions about unintentional manmade signal interference, see [rfi]." OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-03-17T16:19:02.933" LastActivityDate="2021-03-17T16:19:02.933" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18180" PostTypeId="2" ParentId="18172" CreationDate="2021-03-17T16:58:55.113" Score="3" Body="&lt;p&gt;Here is the most relevant section of &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.19&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;§ 97.19 Application for a vanity call sign.&lt;/p&gt;&#xA;&lt;p&gt;(a) The person named in an&#xA;operator/primary station license grant or in a club station license&#xA;grant is eligible to make application for modification of the license&#xA;grant, or the renewal thereof, to show a call sign selected by the&#xA;vanity call sign system. Effective February 14, 2011, the person named&#xA;in a club station license grant that shows on the license a call sign&#xA;that was selected by a trustee is not eligible for an additional&#xA;vanity call sign. (The person named in a club station license grant&#xA;that shows on the license a call sign that was selected by a trustee&#xA;is eligible for a vanity call sign for his or her operator/primary&#xA;station license grant on the same basis as any other person who holds&#xA;an operator/primary station license grant.) Military recreation&#xA;stations are not eligible for a vanity call sign.&lt;/p&gt;&#xA;&lt;p&gt;(b) Each application for a modification of an operator/primary or club&#xA;station license grant, or the renewal thereof, to show a call sign&#xA;selected by the vanity call sign system must be filed in accordance&#xA;with § 1.913 of this chapter.&lt;/p&gt;&#xA;&lt;p&gt;(c) Unassigned call signs are available to the vanity call sign system&#xA;with the following exceptions:&lt;/p&gt;&#xA;&lt;p&gt;(1) A call sign shown on an expired license grant is not available to&#xA;the vanity call sign system for 2 years following the expiration of&#xA;the license.&lt;/p&gt;&#xA;&lt;p&gt;(2) A call sign shown on a surrendered or canceled license grant&#xA;(except for a license grant that is canceled pursuant to § 97.31) is&#xA;not available to the vanity call sign system for 2 years following the&#xA;date such action is taken. (The availability of a call sign shown on a&#xA;license canceled pursuant to § 97.31 is governed by paragraph (c)(3)&#xA;of this section.)&lt;/p&gt;&#xA;&lt;p&gt;(i) This 2-year period does not apply to any license grant pursuant to&#xA;paragraph (c)(3)(i), (ii), or (iii) of this section that is&#xA;surrendered, canceled, revoked, voided, or set aside because the&#xA;grantee acknowledged or the Commission determined that the grantee was&#xA;not eligible for the exception. In such a case, the call sign is not&#xA;available to the vanity call sign system for 30 days following the&#xA;date such action is taken, or for the period for which the call sign&#xA;would not have been available to the vanity call sign system pursuant&#xA;to paragraphs (c)(2) or (3) of this section but for the intervening&#xA;grant to the ineligible applicant, whichever is later.&lt;/p&gt;&#xA;&lt;p&gt;(ii) An applicant to whose operator/primary station license grant, or&#xA;club station license grant for which the applicant is the trustee, the&#xA;call sign was previously assigned is exempt from the 2-year period set&#xA;forth in paragraph (c)(2) of this section.&lt;/p&gt;&#xA;&lt;p&gt;(3) A call sign shown on a license canceled pursuant to § 97.31 of&#xA;this part is not available to the vanity call sign system for 2 years&#xA;following the person's death, or for 2 years following the expiration&#xA;of the license grant, whichever is sooner. If, however, a license is&#xA;canceled more than 2 years after the licensee's death (or within 30&#xA;days before the second anniversary of the licensee's death), the call&#xA;sign is not available to the vanity call sign system for 30 days&#xA;following the date such action is taken. The following applicants are&#xA;exempt from this 2-year period:&lt;/p&gt;&#xA;&lt;p&gt;(i) An applicant to whose operator/primary station license grant, or&#xA;club station license grant for which the applicant is the trustee, the&#xA;call sign was previously assigned; or&lt;/p&gt;&#xA;&lt;p&gt;(ii) An applicant who is the spouse, child, grandchild, stepchild,&#xA;parent, grandparent, stepparent, brother, sister, stepbrother,&#xA;stepsister, aunt, uncle, niece, nephew, or in-law of the person now&#xA;deceased or of any other deceased former holder of the call sign,&#xA;provided that the vanity call sign requested by the applicant is from&#xA;the group of call signs corresponding to the same or lower class of&#xA;operator license held by the applicant as designated in the sequential&#xA;call sign system; or&lt;/p&gt;&#xA;&lt;p&gt;(iii) An applicant who is a club station license trustee acting with a&#xA;written statement of consent signed by either the licensee ante mortem&#xA;but who is now deceased, or by at least one relative as listed in&#xA;paragraph (c)(3)(ii) of this section, of the person now deceased or of&#xA;any other deceased former holder of the call sign, provided that the&#xA;deceased former holder was a member of the club during his or her&#xA;life.&lt;/p&gt;&#xA;&lt;p&gt;(d) The vanity call sign requested by an applicant must be selected&#xA;from the group of call signs corresponding to the same or lower class&#xA;of operator license held by the applicant as designated in the&#xA;sequential call sign system.&lt;/p&gt;&#xA;&lt;p&gt;(1) The applicant must request that the call sign shown on the license&#xA;grant be vacated and provide a list of up to 25 call signs in order of&#xA;preference. In the event that the Commission receives more than one&#xA;application requesting a vanity call sign from an applicant on the&#xA;same receipt day, the Commission will process only the first such&#xA;application entered into the Universal Licensing System. Subsequent&#xA;vanity call sign applications from that applicant with the same&#xA;receipt date will not be accepted.&lt;/p&gt;&#xA;&lt;p&gt;(2) The first assignable call sign from the applicant's list will be&#xA;shown on the license grant. When none of those call signs are&#xA;assignable, the call sign vacated by the applicant will be shown on&#xA;the license grant.&lt;/p&gt;&#xA;&lt;p&gt;(3) Vanity call signs will be selected from those call signs&#xA;assignable at the time the application is processed by the FCC.&lt;/p&gt;&#xA;&lt;p&gt;(4) A call sign designated under the sequential call sign system for&#xA;Alaska, Hawaii, Caribbean Insular Areas, and Pacific Insular areas&#xA;will be assigned only to a primary or club station whose licensee's&#xA;mailing address is in the corresponding state, commonwealth, or&#xA;island. This limitation does not apply to an applicant for the call&#xA;sign as the spouse, child, grandchild, stepchild, parent, grandparent,&#xA;stepparent, brother, sister, stepbrother, stepsister, aunt, uncle,&#xA;niece, nephew, or in-law, of the former holder now deceased.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;So those are the core of the vanity call sign regulations, verbatim. I haven't read them; the FCC may have left themselves some room in there for flexible policies as far as they are implemented.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastActivityDate="2021-03-17T16:58:55.113" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18181" PostTypeId="1" AcceptedAnswerId="18183" CreationDate="2021-03-17T21:41:22.550" Score="0" ViewCount="47" Body="&lt;p&gt;Here is the part of the program I am having problems with:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt; samples = sdr.read_samples(16*1024)&#xA;    power, _ = mlab.psd(samples, NFFT=1024, Fs=sdr.sample_rate /1e6)&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;NFFT is the data points iin each block of FFT and Fs is the sampling frequency. Now, here are my questions:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;What does 12*1024 signify&lt;/li&gt;&#xA;&lt;li&gt;why do we do sdr.sample_rate /1e6&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="19099" LastActivityDate="2021-03-18T02:51:58.977" Title="Not able to understand some operations in rtlsdr library in python" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;frequency&gt;&lt;software&gt;&lt;software-development&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18182" PostTypeId="2" ParentId="18181" CreationDate="2021-03-18T02:46:14.770" Score="1" Body="&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;The number of samples to read.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Probably because whoever wrote it wants the graph to read in MHz rather than Hz.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-03-18T02:46:14.770" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18183" PostTypeId="2" ParentId="18181" CreationDate="2021-03-18T02:51:58.977" Score="2" Body="&lt;p&gt;More than one block can be read into the psd if you want a result that is averaged (thus usually smoother) over several blocks.&lt;/p&gt;&#xA;&lt;p&gt;A sample rate in Hz can be divided by 1e6 if you want a spectral plot labeled in MHz, instead Hz.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-03-18T02:51:58.977" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18185" PostTypeId="2" ParentId="17178" CreationDate="2021-03-18T23:05:51.727" Score="0" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Why does a vertical dipole need a boom that offsets the radiating elements from the mount? I'm guessing it has something to do with the interaction between the feed (coax) and the elements?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;If the mounting post is conductive, it may interact with both the antenna elements and with any currents flowing on the outside of the coax shield. I believe this is the primary motivation for separating the antenna from the post. Using the configuration shown in the OP and neglecting currents on the shield, NEC simulation shows significant pattern distortion even with quarter-wavelength separation.&lt;/p&gt;&#xA;&lt;p&gt;Either the separation should be increased, or the mount should be made of a nonconductive material, or the length of the post should be adjusted for anti-resonance. For example, the same NEC simulation shows that a 0.8-&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; &lt;em&gt;conductive&lt;/em&gt; support distorts the azimuth pattern less than 2-dB, while a 1-&lt;span class=&quot;math-container&quot;&gt;$\lambda$&lt;/span&gt; conductive support introduces about 6-dB of pattern distortion.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-03-18T23:11:04.727" LastActivityDate="2021-03-18T23:11:04.727" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18186" PostTypeId="1" CreationDate="2021-03-19T08:35:14.237" Score="2" ViewCount="55" Body="&lt;p&gt;I have recently bought second hand MFJ-939Y for FT-450/950. I have Yaesu FT-450 (plain, without D or AT). Since the tuner did not come with a cable, I have built my own. (I am 33yo IT engineer with experience in building custom electronics, so no problem in quality here.)&lt;/p&gt;&#xA;&lt;p&gt;The tuner was reset to factory defaults.&lt;/p&gt;&#xA;&lt;p&gt;Jumpers were configured for: Yaesu, pull up resistor, external power.&lt;/p&gt;&#xA;&lt;p&gt;Now I am facing strange issue:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;If the antenna is NOT YET tuned and I press the TUNE button on the&#xA;FT-450, the tuning sequence starts and finishes sucesfully.&lt;/li&gt;&#xA;&lt;li&gt;If the antenna is ALREADY tuned and I press the TUNE button on the FT-450,&#xA;the tuner correctly does not do anything. However on the FT-450 the&#xA;TUNE symbol keeps blinking and eventually disappears. After that, the&#xA;tuner cannot be enabled on the FT-450 by the TUNE button until I&#xA;powercycle the tuner.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;My assumption is that when the tuning sequence in the tuner is running, the tuner communicates back to the radio over the serial line. When there is nothing to be tuned, the tuner remains silent on the serial line. That makes the radio think the tuner communication was lost and disables the tuner as faulty.&lt;/p&gt;&#xA;&lt;p&gt;Thank you for any suggestions how to overcome this issue.&lt;/p&gt;&#xA;&lt;p&gt;EDIT: Just noticed that when I turn the tuner off and press the TUNE button on the radio in order to disable the function, the TUNE will start blinking exactly the same way. If anytime during the blinking I power the tuner back on again, the TUNE will disappear right away. So simply put the TUNE blinking means the serial communication is lost.&lt;/p&gt;&#xA;" OwnerUserId="19039" LastEditorUserId="19039" LastEditDate="2021-03-19T08:46:18.900" LastActivityDate="2021-03-19T08:46:18.900" Title="MFJ-939 not working with FT-450 - TUNE blinking" Tags="&lt;antenna-tuner&gt;" AnswerCount="0" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18188" PostTypeId="2" ParentId="9451" CreationDate="2021-03-20T03:12:36.257" Score="0" Body="&lt;p&gt;Both anecdotal experience and lore support the proposition that there is a substantial difference in the diameter required for an equal length, or length required for an equal diameter, of aluminum tubing vs. copper tubing in order for the aluminum and copper conductors to produce the same resonances and feedpoint impedances in identical antennas constructed of those respective materials.&lt;/p&gt;&#xA;&lt;p&gt;For example, if one constructs two j-pole type vertical antennas at the same 144 MHz or 440 MHz band frequencies, one constructed of 1/2&amp;quot; copper tubing and the other of 1/2&amp;quot; aluminum tubing, using the formulae for the typical copper tubing specimen for both antennas, one will find that the copper antenna is brought to resonance and ~50Ω feedpoint impedance as per the design prediction, whereas this cannot be done with the aluminum example.&lt;/p&gt;&#xA;&lt;p&gt;The difference is indeed explained by various authorities in terms of velocity factor differences between the two materials.&lt;/p&gt;&#xA;&lt;p&gt;Regardless of the explanation, this phenomenon is simply empirical fact. Hence, the categorical claim that there is no significant difference between the two metals at VHF and UHF, is false.&lt;/p&gt;&#xA;" OwnerUserId="19129" LastActivityDate="2021-03-20T03:12:36.257" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18189" PostTypeId="1" AcceptedAnswerId="18191" CreationDate="2021-03-20T07:25:36.380" Score="0" ViewCount="74" Body="&lt;p&gt;&lt;strong&gt;LC&lt;/strong&gt; circuit is the main element of every frequency generator, I intend to make an &lt;strong&gt;FM&lt;/strong&gt; transmitter, but many opensource circuit use analog variable &lt;strong&gt;L&lt;/strong&gt; or &lt;strong&gt;C&lt;/strong&gt; part to set and adjust the target frequency&#xA;My question is :&#xA;is there any IC or digital circuit to set the &lt;strong&gt;LC&lt;/strong&gt; parameter digitally&lt;/p&gt;&#xA;" OwnerUserId="19130" LastActivityDate="2021-03-20T18:10:35.753" Title="change LC parameter digitally" Tags="&lt;frequency&gt;&lt;fm&gt;&lt;inductor&gt;&lt;capacitance&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18190" PostTypeId="2" ParentId="18189" CreationDate="2021-03-20T09:21:07.050" Score="1" Body="&lt;p&gt;Frequency setting and control can be achieved with a phase locked loop (PLL). The frequency of the oscillator is compared to a known and stable reference frequency. Look for further explanation with search terms: radio PLL, RF synthesizer and frequency stabilisation.&lt;/p&gt;&#xA;&lt;p&gt;Digital control of frequency: fractional PLL and All Digital PLL.&#xA;See picture. Copyright? I am the source.&lt;a href=&quot;https://i.stack.imgur.com/58WsZ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/58WsZ.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;For your application: &lt;a href=&quot;https://nl.aliexpress.com/item/33007293736.html?spm=a2g0o.search0302.0.0.39fc252dsBbdPJ&amp;amp;algo_pvid=null&amp;amp;algo_expid=null&amp;amp;btsid=0b0a0ac216162316241256289e28f3&amp;amp;ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://nl.aliexpress.com/item/33007293736.html?spm=a2g0o.search0302.0.0.39fc252dsBbdPJ&amp;amp;algo_pvid=null&amp;amp;algo_expid=null&amp;amp;btsid=0b0a0ac216162316241256289e28f3&amp;amp;ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603&lt;/a&gt;_&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2021-03-20T10:59:45.267" LastActivityDate="2021-03-20T10:59:45.267" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18191" PostTypeId="2" ParentId="18189" CreationDate="2021-03-20T09:35:42.487" Score="2" Body="&lt;p&gt;Perhaps you are thinking of a switched capacitor filter?  Unfortunately, most switched capacitor IC components are (were) designed for audio frequencies, not VHF.&lt;/p&gt;&#xA;&lt;p&gt;Another possibility is to use an LC  tuned circuit containing a voltage controlled varicap diode capacitor, controlled by a (digital input) DAC.  As per the earlier answer, you can use a use a programmable divider (or two) to compare and help lock a varicap LC oscillator frequency to a more stable fixed frequency reference.&lt;/p&gt;&#xA;&lt;p&gt;If you want to select a frequency purely digitally, you can use a (expensive?) high-speed ADC to sample the RF (direct sampling of RF) and then hetrodyne, filter, and/or demodulate the desired frequencies using DSP hardware (FPGA) or DSP software. For a transmitter you can use a DAC to synthesize RF from samples generated digitally (hardware or software).&#xA;Or you can use a digital frequency synthesizer IC (Si5351A et.al.) to mix your desired FM/VHF frequency up from baseband using a Tayloe mixer.&#xA;Both of the above usually still require some sort of fixed frequency reference (TCXO, etc.). Open source SDR transceiver projects based on both of these methods exist.&lt;/p&gt;&#xA;&lt;p&gt;Yet another option is to use a high speed digital timer, but vary the timer period at a very high rate for modulation.  The PiFM project (available on GitHub) does this to produce broadcast FM frequency signals directly from a Raspberry Pi GPIO pin.  All these digital RF outputs still need to be passively filtered to remove spurious out-of-band harmonics.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-20T10:14:30.997" LastActivityDate="2021-03-20T10:14:30.997" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18192" PostTypeId="1" CreationDate="2021-03-20T12:01:17.273" Score="3" ViewCount="717" Body="&lt;p&gt;I've been learning to decode cw for a while now, mainly by using the &lt;em&gt;Word training&lt;/em&gt; feature of &lt;a href=&quot;https://lcwo.net&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://lcwo.net&lt;/a&gt; . I use this rather than the exercises with random characters, both because it's more fun to hear words and because a hand injury makes it hard to type fast enough.&lt;/p&gt;&#xA;&lt;p&gt;I've heard that it's good to learn at a &amp;quot;high&amp;quot; speed, like 20 wpm to get the feel for how each symbol sounds rather than counting dits and dah's. Now here's the thing: I find the easiest speed to hear is somewhere at 30+ wpm, while the 20 wpm words are harder by comparison! At 20 wpm, I hear dits and dah's, and I just can't &amp;quot;hear&amp;quot; the separate units as easily.&lt;/p&gt;&#xA;&lt;p&gt;My question is: Should I try to practice more at the slower 20 wpm, or can i just go on practicing at becoming more confident at 30+ wpm, and hope the slower speed will come naturally later?&lt;/p&gt;&#xA;&lt;p&gt;I can't decode longer texts at 30 wpm without longer spaces between the words, but I know it's common to learn with letters at high speed with gaps between them, and maybe this could be effective by a similar logic... ?&lt;/p&gt;&#xA;&lt;p&gt;Many guides give warnings like &amp;quot;5 wpm and 20 wpm are different skills, so learn the right one&amp;quot;. I find nothing on my problem, but I worry slightly I might be doing work I'll have to redo later.&lt;/p&gt;&#xA;" OwnerUserId="18450" LastActivityDate="2021-04-01T20:50:10.673" Title="Can I learn cw at too high wpm? Should I slow it down?" Tags="&lt;cw&gt;" AnswerCount="5" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18193" PostTypeId="2" ParentId="18192" CreationDate="2021-03-20T15:17:06.700" Score="5" Body="&lt;p&gt;It is one thing to know the English word &amp;quot;car&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;It is another thing to be able to understand this word in all the ways it may be spoken. American English will end it with a rhotic &amp;quot;r&amp;quot; (/kɑɹ/), while a &lt;a href=&quot;https://www.bl.uk/british-accents-and-dialects/articles/received-pronunciation&quot; rel=&quot;noreferrer&quot;&gt;RP accent&lt;/a&gt; will omit the &amp;quot;r&amp;quot; entirely and just say /kɑː/. Some people speak fast, some people slowly. Sometimes you will have to understand the word in a noisy room.&lt;/p&gt;&#xA;&lt;p&gt;In other words, vocabulary and proficiency are different skills.&lt;/p&gt;&#xA;&lt;p&gt;Currently you are focused on learning vocabulary. You will gain proficiency later. I would not worry too much about the settings you are using at this stage in your learning. Proficiency comes from practice, not the settings you are using in your training program now.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-03-20T15:17:06.700" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18194" PostTypeId="2" ParentId="18192" CreationDate="2021-03-20T16:23:33.380" Score="3" Body="&lt;p&gt;CW is an interesting discipline. There are two distinct elements, encoding and decoding. You reference decoding yet refer to encoding guidelines.&lt;/p&gt;&#xA;&lt;p&gt;Learning CW, I was taught to associate the DIT, DAH and REST as music, both in tempo and beat. The principle being to process a combination of sounds reflexively not analytically, as you stated in your initial post. It is more efficient to recognize how each symbol “sounds” rather than counting dits and dah’s. Progressing in that thought, it is more efficient to recognize how common or repetitive words sound i.e., rhythmically. This applies specifically to the “Q” code shorthand such as QRV; QRZ; QRM; QRA and so on. One can see how the ability to decode CW will quickly outpace the ability to encode CW.&lt;/p&gt;&#xA;&lt;p&gt;Encoding CW by nature of mechanical transfer is much slower when doing it by hand. CW is all about timing, the accuracy in timing should take precedence over speed. You are probably aware there are a couple different methods, Koch; Farnsworth; Paris and others. Everything about CW is proper timing/spacing.&lt;/p&gt;&#xA;&lt;p&gt;The goal then, learning to encode CW with metronomic precision. Anyone listening will enjoy exchanging information with you. Sloppy timing increases both errors in decoding and frustration for the decoder. The most important thing to remember in the discipline of CW, its always about the ability of the decoder. Listening to clearly articulated 5wpm may be frustrating because you can decode much faster. Yet you can only transmit as fast as the receiver can decode. While you maybe competent to transmit at 20wpm if the receiver can only decode 5wpm that is all you can send. The continually QRS will slow efficient communication just as quickly if not more so then the poor discipling of timing/spacing.&lt;/p&gt;&#xA;" OwnerUserId="19133" LastActivityDate="2021-03-20T16:23:33.380" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18195" PostTypeId="2" ParentId="18192" CreationDate="2021-03-20T16:41:03.540" Score="4" Body="&lt;p&gt;If you want to actually successfully operate, then you should (eventually) practice copying Morse Code at the full range of WPM speeds you expect to hear over the air.  Most Morse Code practice software allows you to change the WPM, try from maybe 12-20 WPM for SKN (straight key nights) up to 24-40 WPM for CW contesting.  If one practices on only slow characters, it will be hard (if not impossible) to copy at higher WPM speeds.  This is likely at least partially true for the inverse as well.  If you vary your practice WPM rate, you will likely be more successful once you get on the air.&lt;/p&gt;&#xA;&lt;p&gt;For QSOs (especially for DX), don't forget to learn to reliably copy random callsigns, not just common words and abbreviations.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-21T05:07:24.933" LastActivityDate="2021-03-21T05:07:24.933" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18196" PostTypeId="2" ParentId="18189" CreationDate="2021-03-20T18:10:35.753" Score="1" Body="&lt;p&gt;A &lt;a href=&quot;https://wiki.analog.com/university/courses/electronics/text/chapter-4#simulated_inductor&quot; rel=&quot;nofollow noreferrer&quot;&gt;&amp;quot;simulated inductor&amp;quot;&lt;/a&gt; might work in your application:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/55TyQ.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/55TyQ.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;You could adjust the simulated inductance by using an analog multiplexer IC and resistive ladder array IC to change the values of RL and R1.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-03-20T18:10:35.753" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18197" PostTypeId="1" CreationDate="2021-03-21T14:30:02.380" Score="2" ViewCount="72" Body="&lt;p&gt;A number of years ago I was very much into Ham Radio in Canada.&lt;/p&gt;&#xA;&lt;p&gt;I have now moved to Sweden and am thinking about getting back into it again.&lt;/p&gt;&#xA;&lt;p&gt;I can not find any clear set of rules as to how Sweden handles Ham Radio. Any help would be much appreciated.&lt;/p&gt;&#xA;&lt;p&gt;I have been told anything from there are no rules this I do not believe to No you can not do that here.&lt;/p&gt;&#xA;&lt;p&gt;One guy told me oh just walk into the store and buy what you want.&lt;/p&gt;&#xA;&lt;p&gt;BTW I am as the bird flies about 10 km from the local airport&lt;/p&gt;&#xA;" OwnerUserId="19132" LastEditorUserId="19132" LastEditDate="2021-03-22T09:31:30.643" LastActivityDate="2021-03-22T16:17:10.507" Title="Where can I find the official rules for Amateur Radio usage in Sweden" Tags="&lt;legal&gt;&lt;sweden&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18198" PostTypeId="1" CreationDate="2021-03-21T16:07:57.240" Score="5" ViewCount="222" Body="&lt;p&gt;I've seen many &lt;a href=&quot;https://www.rtl-sdr.com/cheap-and-easy-hydrogen-line-radio-astronomy-with-a-rtl-sdr-wifi-parabolic-grid-dish-lna-and-sdrsharp/&quot; rel=&quot;nofollow noreferrer&quot;&gt;examples&lt;/a&gt; of roughly 1 metre sized dishes being used w H+ sawbird and an SDR to detect and analyze Hydrogen line signal, and have been trying myself but can't seem to get anything beyond maybe a small whiff. I'm using a 105cm satellite tv dish with a paint can roughly 13 cm in diameter as my feed, going into the H+ sawbird and then into my laptop, but not getting any signal when pointed in the Cygnus region (although pointing an offset dish isn't particularly nice either, maybe I'm screwing that up). If anyone can think of something I might be missing, that'd be great. Maybe my paint can is too garbage a feed - what are the best designs for this purpose?&lt;/p&gt;&#xA;&lt;p&gt;Photo of dish and feed:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/7RcNx.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7RcNx.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19137" LastEditorUserId="2988" LastEditDate="2021-03-23T05:16:22.243" LastActivityDate="2021-03-23T05:26:04.727" Title="Failing to detect Hydrogen line with 105cm dish" Tags="&lt;antenna-theory&gt;&lt;software-defined-radio&gt;&lt;uhf&gt;&lt;rtl-sdr&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18200" PostTypeId="2" ParentId="18198" CreationDate="2021-03-21T16:45:31.913" Score="5" Body="&lt;p&gt;The sawbird H+ looks like a nice LNA, do you have the H+ H1 version?&lt;/p&gt;&#xA;&lt;p&gt;The plan version seems to be for 1542 MHz, &amp;quot;center frequency of the module is 1.542GHz with approximately 80MHz of bandwidth (-6dB rolloff). As such, it should be used for reception of frequencies between 1.50GHz-1.58GHz&amp;quot;  but the H+ H1 has &amp;quot;65MHz bandpass region, centered near 1.42GHz&amp;quot; which is perfect.&lt;/p&gt;&#xA;&lt;p&gt;Try measuring the Sun Noise of your dish at 1420 MHz - how many dB does the noise floor rise when pointed at the sun, compared to pointing 45 degrees away from the sun but still high in the sky? Make sure all AGC is off. This is the first test of the sensitivity of your system.  You can also try cold sky vs warm ground.&lt;/p&gt;&#xA;&lt;p&gt;Try also the feed alone - straight up (Tsky = a few K) vs straight down (300 K) vs on dish. Try to estimate the system temperature from this.&lt;/p&gt;&#xA;&lt;p&gt;Feeding an offset dish generally requires a much smaller feed angle - higher gain - than a centre-fed dish. It's possible your can feed is much too broad, resulting in a lot of ground noise pick-up. Your can does look too close to the dish, but you can determine that by experiment.&lt;/p&gt;&#xA;&lt;p&gt;Aiming is usually along the arm that holds the feed, or sight along (bottom-of-dish) to (top of where the Ku-band feed would have been) as that's how the offset is designed.&lt;/p&gt;&#xA;&lt;p&gt;Take a look at the &lt;a href=&quot;http://w1ghz.org/antbook/contents.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;classic microwave book by W1GHz&lt;/a&gt; Chapter 6 is all about dish feeding, including detailed notes about &amp;quot;coffee can feeds&amp;quot;.&lt;br /&gt;&#xA;Figure 6.3-2 (from 1988) is for a &lt;span class=&quot;math-container&quot;&gt;$0.6\lambda$&lt;/span&gt; coffee can and includes a graph of dish efficiency considering spillover. Your dish F/D will be about 0.65, so the illumination efficiency might be below 30%, and with 70% spillover the antenna temperature will be very high.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-03-23T05:26:04.727" LastActivityDate="2021-03-23T05:26:04.727" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18201" PostTypeId="1" CreationDate="2021-03-21T19:36:19.370" Score="2" ViewCount="68" Body="&lt;p&gt;I'm building a full-size quarter-wave 20m vertical antenna (approx. 18 feet long, plus a trio of Hustler mobile resonators at the top to add 30, 40, and 80 meters). To make the top 12-14 feet stiff enough to survive random 40-50mph (non-sustained) wind gusts from daily summer South Florida thunderstorms, I'm planning to &amp;quot;double up&amp;quot; the aluminum tubing for the portion for the top 12 feet (basically, making the element from three 6-foot 3/4&amp;quot; diameter tubes, joined together and strengthened on the inside with snugly-nested 5/8&amp;quot; tubes offset by 50% from the outer tubes).&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Should the &amp;quot;inside&amp;quot; tubes firmly butt up against each other, or should I try to separate them slightly to ensure that the gap between the inside tubes is always at least as great as any gap between the inside and outside tube?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is it OK to drill a hole through (and perpendicular to the direction of) both tubes &amp;amp; secure them with a stainless steel nut and bolt that passes through both sides of both tubes perpendicular to their orieintation? Or would it be better to use a pair of shorter screws that are just long enough to penetrate the outer tube and dig into the inner one, without actually bridging all the way across?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I know that with DC, providing multiple parallel paths for current to flow is generally a &lt;em&gt;good&lt;/em&gt; thing... but from what I've read, RF is &amp;quot;weird&amp;quot;, and providing multiple parallel paths for RF to flow along the same antenna isn't necessarily desirable. But, I've also gotten the impression that with HF, there are literally &lt;em&gt;so many&lt;/em&gt; things that can unpredictably go wrong to screw things up, it's almost futile to even &lt;em&gt;bother&lt;/em&gt; worrying about the effect of things like one long perpendicular bolt penetrating from end to end vs two.&lt;/p&gt;&#xA;" OwnerUserId="9101" LastEditorUserId="218" LastEditDate="2021-03-22T03:21:00.517" LastActivityDate="2021-03-22T19:32:53.573" Title="antenna element with &quot;doubled up&quot; nested aluminum rods for added stiffness" Tags="&lt;antenna-construction&gt;&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18202" PostTypeId="2" ParentId="18201" CreationDate="2021-03-22T00:46:06.520" Score="4" Body="&lt;p&gt;As you are discovering, antennas are primarily mechanical beasts.&lt;/p&gt;&#xA;&lt;p&gt;I recommend the book &amp;quot;&lt;strong&gt;Physical Design of Yagi Antennas&lt;/strong&gt;&amp;quot; by David B Leeson - it has lots of relevant detail about element strength, tapering, connection, mounting.&lt;/p&gt;&#xA;&lt;p&gt;A few thoughts that might help with your design:&lt;/p&gt;&#xA;&lt;p&gt;Adding metal to make a pole stiffer and more resistant to wind, is much better added as extra diameter, than extra wall thickness. And a thicker wall is much better than a second tube free sliding inside.&lt;/p&gt;&#xA;&lt;p&gt;Finally, the part you need to strengthen most is the bottom, which has to withstand a larger total wind force, and a longer lever arm. Thinner at the top is also good to reduce the wind load there, but the hustler resonators provide a minimum wind load so very thin won't help.&lt;/p&gt;&#xA;&lt;p&gt;So in order of preference in my opinion:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;5/8&amp;quot; is quite thin for a self-supporting 18' aluminium mast. Perhaps in steel... Go at least 1.5&amp;quot;, 2&amp;quot; is better if you don't have other constraints like visual appearance. Wall thickness for 2&amp;quot; need only be 1/16&amp;quot;, if you strengthen it carefully at the bottom, 1/8 is better...&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Use a larger diameter tube rather than a thicker wall tube, especially for the lower half of the vertical where the stress is greater.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Use a thicker wall tube, rather than two tubes that fit into each other. The inner tube adds very little strength.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Make joints overlap by about 3 or 4 diameters, if they fit snugly, more is not much better.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Bolt holes through the tube make it weaker, and drilling through all four walls in the same place is the worst thing. If the tubes fit tightly, one bolt in the centre of the overlap portion is probably fine. Bolts through clearance holes in both tubes do not stop the concentric tubes sliding against each other by the tiny amount they move when bending.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;At HF don't worry too much about RF effects. Make sure there is some tight metal-to-metal contact at the point where the outside diameter changes, a bolt or a hose clamp and some slots cut in the outer. Tubes inside are invisible to the RF so don't make any difference. The only thing which will make a small difference is if you form a deep coaxial well where the inner is well separated from the outer for some distance, then connected.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-03-22T19:32:53.573" LastActivityDate="2021-03-22T19:32:53.573" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18203" PostTypeId="2" ParentId="18201" CreationDate="2021-03-22T01:33:09.220" Score="1" Body="&lt;p&gt;You may find it very difficult to &amp;quot;telescope&amp;quot; aluminum tubing for more than a few feet. In my experience, it's critical to lubricate the interface between the inner and outer tubing with a loaded grease commonly known as NoAlOx, as in &amp;quot;No Aluminum Oxidation.&amp;quot; Not only will it ease the initial telescoping, but it will prevent seizing over time and allow you to pull the assembly apart in the future.&lt;/p&gt;&#xA;&lt;p&gt;It seems probable that you will build an 18-ft radiator from 6-ft lengths of tubing. A key to strength is to be sure that the joints of the inner and outer sections are offset. This may be most easily done by positioning 3-ft lengths at the top and bottom of the inner section, with 6-ft lengths between. Making the outer section from 6-ft lengths ensures that the outer section joints are bridged by continuous inner sections.&lt;/p&gt;&#xA;&lt;p&gt;Long overlaps create ample opportunity for low-stress connections. Without specialized equipment and/or ability, it could be challenging to through-drill inner and outer sections of tubing with sufficient accuracy to make parts interchangeable; i.e., the antenna could only go together one way. Drilling and screwing can &lt;em&gt;create&lt;/em&gt; stresses, especially in the windy conditions you anticipate, that could fracture the tubing over time. Sawing slots into the ends of outer tubing sections and compressing the slotted sections over the inner sections with hose clamps is a long-lasting way to create strong, reliable joints that can assembled with great flexibility.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-03-22T01:33:09.220" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18204" PostTypeId="2" ParentId="18197" CreationDate="2021-03-22T09:49:59.133" Score="5" Body="&lt;p&gt;The authoritative source for Swedish ham radio regulations is the Post and Telecom Authority (PTS): &lt;a href=&quot;https://hamradio.pts.se/&quot; rel=&quot;noreferrer&quot;&gt;https://hamradio.pts.se/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;There's useful information on the website of the Swedish amateur radio society, Föreningen Svenska Sändaramatörer (SSA, &lt;a href=&quot;https://www.ssa.se/&quot; rel=&quot;noreferrer&quot;&gt;https://www.ssa.se/&lt;/a&gt;), as well.&lt;/p&gt;&#xA;&lt;p&gt;Unfortunately, most of the resources are in Swedish.&lt;/p&gt;&#xA;&lt;p&gt;In Sweden, as in most other countries, the amateur radio service is regulated. In order to transmit, you need an amateur radio certificate and you have to adhere to the band plans, power limits, etc.  In my experience, PTS is a bit more hands off than the regulators in some other countries, but there are clearly defined rules and you can't just do whatever you want.&lt;/p&gt;&#xA;" OwnerUserId="17321" LastActivityDate="2021-03-22T09:49:59.133" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18205" PostTypeId="2" ParentId="18197" CreationDate="2021-03-22T09:59:53.393" Score="2" Body="&lt;p&gt;The following link at the national ham radio association (SSA) should be of interest:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.ssa.se/international/amateur-radio-visitors-to-sweden/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ssa.se/international/amateur-radio-visitors-to-sweden/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It reads:&#xA;&amp;quot;Foreign radio amateurs with a CEPT HAREC (acc. T/R 61-01) license  staying for a longer time [than three months] and having an address in Sweden can apply for a permanent Swedish call sign. Apply to SSA, e-mail address signal@ssa.se.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;The link also contains further links to Swedish bandplans for HF and VHF. They are written in Swedish, but should be decipherable with a dictionary if you don't read the language.&lt;/p&gt;&#xA;&lt;p&gt;There's only one license level in Sweden, and it doesn't require cw.&lt;/p&gt;&#xA;" OwnerUserId="18450" LastEditorUserId="18450" LastEditDate="2021-03-22T16:17:10.507" LastActivityDate="2021-03-22T16:17:10.507" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18206" PostTypeId="2" ParentId="18197" CreationDate="2021-03-22T15:51:15.480" Score="1" Body="&lt;p&gt;I hope this will be useful to you.&#xA;&lt;a href=&quot;https://www.ssa.se/international/amateur-radio-visitors-to-sweden/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ssa.se/international/amateur-radio-visitors-to-sweden/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18042" LastEditorUserId="4665" LastEditDate="2021-03-22T16:13:39.657" LastActivityDate="2021-03-22T16:13:39.657" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18207" PostTypeId="2" ParentId="18192" CreationDate="2021-03-22T17:06:42.770" Score="1" Body="&lt;p&gt;If you listen on the air, you'll hear Morse QSOs at a wide range of speeds.  These days probably most code is formed by keyers, which form individual characters perfectly, but you'll also hear people sending code with straight keys and bugs, which can have very different timing.  In particular, many operators who use bugs send code with fast closely-spaced dits and relatively-long dahs.  In addition to wide variety in speed and timing, real QSOs on HF bands often feature noise, sending mistakes, interference, fading, weak signals, and so on.  All this makes copying real QSOs often much more difficult than copying practice recordings.&lt;/p&gt;&#xA;&lt;p&gt;If your goal is to learn Morse code so you can make Morse QSOs, then my advice would be to abandon practice copying 30+ WPM code for now.  You'll need to learn to walk before you can run, even if &amp;quot;running&amp;quot; is easier with practice recordings.  I'd recommend practicing copying 15 WPM code.  Most QSOs at speeds slower than that is sent using the Farnsworth method, with the characters sent at 15 WPM or so with longer spacing between the characters and words, so there's not much need to copy characters slower than that.  If you can copy 30+ WPM code already then you may be a natural, so your speed may quickly increase once you start making real QSOs.&lt;/p&gt;&#xA;&lt;p&gt;By the way, for me one of the key skills for making faster Morse QSOs was learning to &amp;quot;throw away the pencil&amp;quot; and copy what the other operator was sending in my head, rather than writing or typing each character as it's copied.  But that's a skill for later; before trying to learn that I'd recommend just making a bunch of QSOs at moderate speeds.  In other words, make sure you've mastered the basic skills first.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-03-22T17:06:42.770" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18208" PostTypeId="1" AcceptedAnswerId="18213" CreationDate="2021-03-22T18:09:32.993" Score="3" ViewCount="65" Body="&lt;p&gt;I have a NanoVNA (v2), and I'm using it with vna-qt. I want to capture the raw data from a sweep for posterity, so that I can someday compare different antenna variants for things like SWR, resonance, etc. I'm pretty sure vna-qt itself can't load captured data and display it, but if I at least HAVE a copy of the raw sweep data saved somewhere, I can cross THAT particular bridge later &amp;amp; either find some other program that can, or maybe write my own program to do it.&lt;/p&gt;&#xA;&lt;p&gt;But first... I need to figure out how to capture an save a sweep's raw data to a file. How can I do this? I've tried the various capture &amp;amp; export options under the &amp;quot;S Parameters&amp;quot; menu, but they all seem to either work only once, or hang the app completely when I try using them, and as far as I can tell, the app's official documentation says &lt;em&gt;nothing whatsoever&lt;/em&gt; about &lt;em&gt;anything&lt;/em&gt; under the &amp;quot;S Parameters&amp;quot; menu.&lt;/p&gt;&#xA;" OwnerUserId="9101" LastActivityDate="2021-03-25T17:17:15.107" Title="Saving snapshot of NanoVNA (v2) data for later review, analysis, comparison, etc" Tags="&lt;nanovna&gt;" AnswerCount="2" CommentCount="0" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18209" PostTypeId="1" CreationDate="2021-03-22T19:21:03.643" Score="0" ViewCount="44" Body="&lt;p&gt;so I am fairly new to this SDR and dsp thing, I am working on a project that calculates the ppm and adjusts the offset, now I kinda got the idea of how to calculate the ppm after going through the rtl_test source code, but for that, I need the number of samples in a time frame( as in frequency offset, the sample rate changes a tad bit). Now I am not sure how to approach that, can someone guide me on that? I see there is some rtl_read_async function in c that probably has a parameter that is passed by reference and returns the number of samples received, but I am not sure how to use it as I can't seem to find any documentation.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;" OwnerUserId="19099" LastEditorUserId="19099" LastEditDate="2021-03-22T19:35:34.053" LastActivityDate="2021-03-23T15:08:16.717" Title="How to get the &quot;real&quot; number of samples coming in an sdr" Tags="&lt;software-defined-radio&gt;&lt;rtl-sdr&gt;&lt;frequency&gt;&lt;software&gt;&lt;software-development&gt;" AnswerCount="1" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18210" PostTypeId="2" ParentId="18208" CreationDate="2021-03-22T19:42:54.210" Score="5" Body="&lt;p&gt;Looks like you have to use &lt;a href=&quot;https://nanovna.com/?page_id=90&quot; rel=&quot;noreferrer&quot;&gt;NanoVNASaver&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;This software connects to a NanoVNA and extracts the data for display on a computer, and for saving to Touchstone files.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Download it from &lt;a href=&quot;https://github.com/mihtjel/nanovna-saver/releases&quot; rel=&quot;noreferrer&quot;&gt;github&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-03-22T19:42:54.210" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18212" PostTypeId="2" ParentId="18209" CreationDate="2021-03-23T03:40:20.247" Score="2" Body="&lt;p&gt;The real number of samples from an RTL-SDR is not available via the USB interface.  The RTL2832U chip samples at 28.8 Msps, but then mixes and downsamples the internal samples to lower rate IQ samples at from 240k to about 3 Msps, to allow transport over its slower USB 2.0 bus.  The front-end R820T tuner can first downconvert VHF and UHF signal to a low HF IF frequency for sampling.  Or HF under 14.4 MHz can be directly sampled by the RTL chip on some models of the device (V3, and clones). Undersampling is possible for higher HF.&lt;/p&gt;&#xA;&lt;p&gt;Normally the PPM (parts per million frequency calibration offset) is determined by tuning the SDR to a commercial or standards transmitter at a known frequency (WWV, et.al.), or a GPS disciplined oscillator, and zero beating to measure any indicated offset from the known carrier frequency.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-23T15:08:16.717" LastActivityDate="2021-03-23T15:08:16.717" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18213" PostTypeId="2" ParentId="18208" CreationDate="2021-03-23T17:31:41.007" Score="3" Body="&lt;p&gt;When I want to look at the raw data, I simply use a serial terminal application to connect to my nanoVNA at 9600 baud.  Then type &amp;quot;frequencies&amp;quot; to get the current list of sweep frequencies.  Then type &amp;quot;data&amp;quot; to get the current list of IQ parameters from the last sweep.  Then cut-and-paste the terminal's text output into a spreadsheet, where I can graph/analyze/compare/export/etc. the data any way I want.&lt;/p&gt;&#xA;&lt;p&gt;You can type &amp;quot;help&amp;quot; into the nanoVNA's console for a longer list of interesting commands.&lt;/p&gt;&#xA;&lt;p&gt;If you connect to a nanoVNA's serial console via python or Basic (et.al.) you can also script a sequence of sweep commands and data downloads.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-25T17:17:15.107" LastActivityDate="2021-03-25T17:17:15.107" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18214" PostTypeId="1" AcceptedAnswerId="18215" CreationDate="2021-03-24T14:18:53.963" Score="5" ViewCount="122" Body="&lt;p&gt;I'm experimenting with RF reception in the 433MHz band and have made the most simple &amp;quot;whip&amp;quot; monopole antenna with 17.6 centimeters of wire.&lt;/p&gt;&#xA;&lt;p&gt;Out of curiosity, I tried various designs for the antenna among which the one described in the step by step instructions created by Ben Schueler in 2013 and republished a large number of times since then, such as &lt;a href=&quot;https://arduinodiy.wordpress.com/2015/07/25/coil-loaded-433-mhz-antenna/&quot; rel=&quot;noreferrer&quot;&gt;here&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This design also works quite well for my application and using online calculators such as this &lt;a href=&quot;https://coil32.net/online-calculators/one-layer-coil-calculator.html&quot; rel=&quot;noreferrer&quot;&gt;one&lt;/a&gt; and this &lt;a href=&quot;https://www.qsl.net/in3otd/indcalc.html&quot; rel=&quot;noreferrer&quot;&gt;one&lt;/a&gt;, I can compute the inductor value.&lt;br/&gt;&#xA;But why is 0.220µH right?&lt;br/&gt;&#xA;And what about the size of the two straight parts? They are given as 17 and 53 millimeters but how does one gets these values?&lt;/p&gt;&#xA;&lt;p&gt;I'm asking because I would like to replicate this design, but tuned for 868MHz reception.&lt;/p&gt;&#xA;&lt;p&gt;Would you have the link to a reference document so that I can compute the values for 868MHz myself? Or should I just go ahead and divide every value by two as 868 is roughly 433 multiplied by two?&lt;/p&gt;&#xA;&lt;p&gt;Thanks for any pointers.&lt;/p&gt;&#xA;" OwnerUserId="19163" LastEditorUserId="8573" LastEditDate="2021-03-26T08:25:05.297" LastActivityDate="2021-03-26T08:25:05.297" Title="How to compute the required length and turns for an air-cored antenna" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18215" PostTypeId="2" ParentId="18214" CreationDate="2021-03-24T16:42:24.397" Score="4" Body="&lt;p&gt;A quick simulation with NEC2 indicates that scaling the wire lengths and the inductance by a factor of 0.5 will give the results you seek.&lt;/p&gt;&#xA;&lt;p&gt;As for why a smaller, loaded monopole gives better results than a full-sized monopole, that is a mystery.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-03-24T16:42:24.397" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18216" PostTypeId="2" ParentId="9299" CreationDate="2021-03-25T11:11:55.663" Score="1" Body="&lt;p&gt;I know this is old, but my friends recommend Troy Radio.  They are an authorized FlexRadio shop and specialize in the 5000.  You can reach them at:&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Link:&lt;/strong&gt;  &lt;a href=&quot;http://troyradio.net/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Troy Radio&lt;/a&gt;&#xA;&lt;strong&gt;Phone:&lt;/strong&gt; 254-239-3893&#xA;&lt;strong&gt;Email:&lt;/strong&gt; toby@troyradio.net&lt;/p&gt;&#xA;&lt;p&gt;I am not associated with Troy Radio nor ever used their service, but have heard they are good.&lt;/p&gt;&#xA;" OwnerUserId="19177" LastActivityDate="2021-03-25T11:11:55.663" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18217" PostTypeId="2" ParentId="16222" CreationDate="2021-03-25T11:22:17.160" Score="0" Body="&lt;p&gt;i just found this..........shall test today.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://f6dqm.free.fr/soft/simplex/en/simplex.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://f6dqm.free.fr/soft/simplex/en/simplex.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19178" LastEditorUserId="19178" LastEditDate="2021-03-25T11:57:04.583" LastActivityDate="2021-03-25T11:57:04.583" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18218" PostTypeId="1" CreationDate="2021-03-25T17:14:07.483" Score="5" ViewCount="99" Body="&lt;p&gt;What is a band stacking register and/or band stacking buttons on a transceiver?  And why would this be useful to an amateur radio operator?&lt;/p&gt;&#xA;&lt;p&gt;Is using &amp;quot;band stacking&amp;quot; a current operating technique, or are there more modern operating methods? (such as wide panadapters with spotting network annotations, etc.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="76" LastEditDate="2021-03-28T21:19:37.437" LastActivityDate="2021-03-31T13:22:57.917" Title="What is band stacking?" Tags="&lt;transceiver&gt;&lt;jargon&gt;&lt;equipment-operation&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18219" PostTypeId="1" CreationDate="2021-03-25T17:53:16.400" Score="1" ViewCount="48" Body="&lt;p&gt;I just built a homebrew antenna that consists of a full-length quarter-wave vertical sized for 20m, with a &amp;quot;top hat&amp;quot; consisting of a Hustler VP-1 and trio of Hustler mobile resonators (RM-80S, RM-40, and a RM-20 with extra-long whip repurposed to do 30m instead).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/gswnm.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/gswnm.jpg&quot; alt=&quot;View of the antenna itself&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The antenna works extremely well on 30 and 40 meters. It works as well as can be reasonably expected (for a ~22 foot tall antenna) on 80m. It works surprisingly well on 15m. &lt;strong&gt;It's absolutely &lt;em&gt;dysfunctional&lt;/em&gt; on 20m.&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;More specifically, according to NanoVNA &lt;strong&gt;it's completely dysfunctional between approximately 14.04MHz and 14.16Mhz&lt;/strong&gt; (the precise chunk of 20m I actually &lt;em&gt;care&lt;/em&gt; about). It's like there's a bubble around that range of frequencies that adjusting the lower portion of the antenna simply can't fix.&lt;/p&gt;&#xA;&lt;p&gt;Here's an example sweep from NanoVNA (ignore markers 0 and 1):&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/oMHIy.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oMHIy.png&quot; alt=&quot;80 to 15 meter sweep&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;If I lengthen or shorten the lower element by up to a foot either way from ~17' (from ~18 feet to 16 feet), the pair of SWR valleys above and below 14.10Mhz shift left/right and slowly move towards each other... but right around 14.05 and 14.15Mhz, the minimum SWR value shoots up towards infinity as the two merge together somewhere far above the graphed range, leapfrog over the 100KHz chunk I care about, then come down and form a new pair of SWR curves flanking 14.10MHz. Eventually, if I keep lengthening or shortening the element, one of them has its SWR start to rise until it merges into the larger inter-band curve, and the other flattens out at a low SWR somewhere around 12 or 18Mhz.&lt;/p&gt;&#xA;&lt;p&gt;Spoiler alert: the reason why I was using the RM-20 with a longer whip for 30m is because an earlier iteration of the antenna (built with a 5' lower shared mast) that tried using the RM-20 &lt;em&gt;for&lt;/em&gt; 20 meters had the exact same problem... a SWR bubble centered around 14.10Mhz. What I failed to realize at the time was that even though I re-tuned it for 10.13Mhz by lengthening the whip, the same coil problem that screwed up its ability to work for 14.07Mhz was going to &lt;em&gt;keep&lt;/em&gt; screwing up the ability of the antenna to work near that frequency.&lt;/p&gt;&#xA;" OwnerUserId="9101" LastEditorUserId="9101" LastEditDate="2021-03-26T18:02:16.690" LastActivityDate="2021-03-26T18:02:16.690" Title="Unable to tune 20m vertical with trio of Hustler resonators on top" Tags="&lt;antenna-construction&gt;&lt;vertical-antenna&gt;" AnswerCount="1" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="18221" PostTypeId="1" AcceptedAnswerId="18224" CreationDate="2021-03-26T04:30:44.173" Score="5" ViewCount="56" Body="&lt;p&gt;I'm wondering if there are any general guidelines or rules of thumb about the exposure of electronic equipment to RF transmissions, 150 MHz - 900 MHz.&lt;/p&gt;&#xA;&lt;p&gt;The background is that we are looking to install an LMR antenna for a 35 to 50 Watt radio above an office, inside of the drop ceiling. Using the FCC guidelines we would be well below the limit for human exposure. On the other hand, the office will operate as an LE dispatch center and have a lot of PC based, and other electronic equipment. Inside the drop ceiling there's quite a few network cables and others that are unidentified. I've also run into dispatchers with pacemakers, and don't see that covered in the FCC human exposure guidelines.&lt;/p&gt;&#xA;&lt;p&gt;I know that the FCC part 15 limits the permissible amount of radiation from an electronic device, but is there a general rule about what the acceptable power density is around any class of equipment?&lt;/p&gt;&#xA;" OwnerUserId="17109" LastActivityDate="2021-03-26T21:29:48.760" Title="Acceptable RF radiation exposure to electronic equipment" Tags="&lt;antenna-system&gt;&lt;rf-power&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18222" PostTypeId="2" ParentId="18219" CreationDate="2021-03-26T18:01:00.020" Score="2" Body="&lt;p&gt;OK, it turns out, the Hustler RM-20 resonator was the culprit, after all. I removed it from the VP-1 mount (leaving only the RM-80S and RM-40), and the problem completely went away.&lt;/p&gt;&#xA;&lt;p&gt;NanoVNA sweep with RM-20 removed:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/XQyVM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XQyVM.png&quot; alt=&quot;NanoVNA sweep with RM-20 resonator removed&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I did more research this morning, and learned that apparently, the RM-20's inability to work on the lower 20 meter band (where digimodes like FT8 live) is well known. Apparently, its designer pulled some optimization tricks that make it work better than expected (wider bandwidth, flatter and lower SWR curve) on the &lt;em&gt;upper&lt;/em&gt; (SSB phone) portion of the 20m band, at the cost of rendering it completely unfit for use within a small chunk of the lower 20m band (which, unfortunately, is almost precisely centered on the chunk of frequencies used for 20m FT8).&lt;/p&gt;&#xA;&lt;p&gt;The work-around is to buy a Hustler RM-17 instead, and pair it with a longer 3/32&amp;quot; diameter whip.&lt;/p&gt;&#xA;" OwnerUserId="9101" LastActivityDate="2021-03-26T18:01:00.020" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18223" PostTypeId="1" AcceptedAnswerId="18238" CreationDate="2021-03-26T20:12:08.080" Score="0" ViewCount="117" Body="&lt;p&gt;Is it possible to modify a CB radio to connect to a wireless network, and potentially send any data sent from the radio as a buffer to an outside source like an API? If so, what would be the best way to go about architecting something like this? I essentially just need a way to pull the audio buffer that is created when someone speaks into the mic, and forward that to an API.&lt;/p&gt;&#xA;&lt;p&gt;I want to connect a microcontroller with WiFi/Sim internet connectivity to the CB and:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Send the audio buffer from the transmitter to the microcontroller&lt;/li&gt;&#xA;&lt;li&gt;Forward the audio buffer data from the microcontroller to the API&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="19185" LastEditorUserId="19185" LastEditDate="2021-03-26T20:54:54.990" LastActivityDate="2021-03-29T19:28:44.263" Title="Modify a CB radio to connect to a wireless network?" Tags="&lt;software-defined-radio&gt;&lt;citizens-band&gt;" AnswerCount="1" CommentCount="9" ClosedDate="2021-03-30T04:23:03.550" ContentLicense="CC BY-SA 4.0" />
  <row Id="18224" PostTypeId="2" ParentId="18221" CreationDate="2021-03-26T21:23:30.670" Score="4" Body="&lt;p&gt;The FCC does not regulate what is called Radiated Susceptibility for consumer electronics, the sensitivity of an electronic device to external RF but many manufacturers will test their equipment.&lt;/p&gt;&#xA;&lt;p&gt;For example a cellphone generates up to 30 V/m near the phone, and is pulsed on and off a few hundred times per second. When cellphones first appeared, they would announce themselves by interfering with any nearby audio device. These days phone audio breakthrough is not very common and you expect car radios and computers to work normally even with a phone lying on top of them.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;&lt;a href=&quot;http://everyspec.com/MIL-STD/MIL-STD-0300-0499/MIL-STD-461G_53571/&quot; rel=&quot;nofollow noreferrer&quot;&gt;MIL-STD-461G&lt;/a&gt; test RS103&lt;/strong&gt; describes the tests in detail. The device under test must operate normally when exposed to 10, 50 or even 200 V/m, depending on the intended mounting position of the device. The test uses 100% AM at 1 kHz, which is the most disruptive radio interference. The frequency is swept slowly over the chosen range, 30 MHz - 3 GHz or wider.&lt;/p&gt;&#xA;&lt;p&gt;At your frequency, for vehicle electronics in Navy and Air Force, the test limit is 10 V/m, so this seems like a reasonable limit to start with. This would cover handheld radios in a vehicle. 10 V/m is present about 5 m from a dipole transmitting 50 W, call it 10 m to be safe considering reflections and guiding from metal in the building.&lt;/p&gt;&#xA;&lt;p&gt;It does seem like a bad idea to put 50 Watt transmitting antenna in the room space. It won't harm the people but&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;the transmit performance of the radio will be degraded by 10 or 100 x compared to being outdoors, due to the metalwork of a false ceiling, and concrete and reinforcing above, and the long path to get out of the building, through a window eventually.&lt;/li&gt;&#xA;&lt;li&gt;the receive performance will be further degraded by noise from all the consumer electronics in the room, including nearby network cables.&lt;/li&gt;&#xA;&lt;li&gt;there is some potential for disruption of electronics in the room, especially if it is near to network, phone or power cables. Network cables, analog monitors using VGA cables and amplified speakers will be the first to be affected.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;If at all possible the antenna should be routed outside. If not, consider reducing the transmitter power to 5 Watts and placing the antenna against a window - the performance outdoors will be the same but the interference potential will be much reduced.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-03-26T21:29:48.760" LastActivityDate="2021-03-26T21:29:48.760" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18226" PostTypeId="1" CreationDate="2021-03-27T11:04:44.927" Score="4" ViewCount="43" Body="&lt;p&gt;I'm new to HFSS Software and I'm trying to plot Scattering parameters for a dielectric resonator excited by a probe (shown in image). I know that the top cylinder has a higher dielectric than the bottom cylinder. I also know that the cavity is a metal. The structure is from chapter 11 of &amp;quot;Microwave Filters for Communication Systems: Fundamentals, Design, and Applications&amp;quot; book (&lt;a href=&quot;https://ieeexplore.ieee.org/book/8341843&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ieeexplore.ieee.org/book/8341843&lt;/a&gt;). Now my questions are:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Do I provide waveport excitation to outer part of the probe?&lt;/li&gt;&#xA;&lt;li&gt;Since the cavity is a metal is that my ground or do I need to have a ground beneath the substrate?&lt;/li&gt;&#xA;&lt;li&gt;I know that inside the cavity should be air. How do I make that happen in HFSS?&lt;/li&gt;&#xA;&lt;li&gt;I need to basically cut a hole in the cavity structure to place the probe in right?&lt;/li&gt;&#xA;&lt;li&gt;What is the difference between waveport and lumped port excitation?&lt;/li&gt;&#xA;&lt;li&gt;What is the difference between modal and terminal solution types?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;Help in any of the questions will be greatly appreciated.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/K95Dz.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/K95Dz.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19189" LastEditorUserId="76" LastEditDate="2021-04-19T16:39:05.087" LastActivityDate="2021-04-19T16:39:05.087" Title="S Parameters in HFSS" Tags="&lt;antenna-theory&gt;&lt;rfi&gt;&lt;antenna-system&gt;&lt;microwave&gt;&lt;hfss&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18228" PostTypeId="1" AcceptedAnswerId="18229" CreationDate="2021-03-28T11:20:12.230" Score="1" ViewCount="54" Body="&lt;p&gt;I have a 2.4 GHz transceiver that outputs 4.5 DBm. I wish to amplify the signal using a 15.5 DBi antenna so that the signal reaches 20 DB, the maximum legal limit. Preferably, the antenna would be of a type that I can make myself. Any suggestions on what type and design of antenna that fits my needs?&lt;/p&gt;&#xA;" OwnerUserId="8594" LastEditorUserId="8717" LastEditDate="2021-03-28T16:18:42.513" LastActivityDate="2021-03-28T16:18:42.513" Title="What type of omnidirectional antenna gives the most gain for a frequency of 2.4 GHz?" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;microwave&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18229" PostTypeId="2" ParentId="18228" CreationDate="2021-03-28T13:57:45.863" Score="7" Body="&lt;p&gt;An antenna can't &amp;quot;amplify&amp;quot; a signal, it can only concentrate it in certain directions. If you want a peak gain of 15 dB (about 30x the power density of an isotropic radiator), you can only get it over a very small portion of the sphere (about 3% or less).&lt;/p&gt;&#xA;&lt;p&gt;When we talk about &amp;quot;omnidirectional&amp;quot; antennas, usually we mean that the antenna element is vertical, and the antenna radiates equally in all directions in the horizontal plane. But the gain has to come from somewhere, and in this case it comes from compressing the pattern &lt;em&gt;vertically&lt;/em&gt;, so that the signal strength  decreases if you go above or below the plane of the antenna. At 15dB, the pattern is very squished, and the vertical beamwidth is quite small (around 6°).&lt;/p&gt;&#xA;&lt;p&gt;That said, if you want one, there is a &amp;quot;simple&amp;quot; design that will at least come close: it's a collinear array of around 25 elements (roughly 1.5 meters tall, for 2.4 GHz).&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2021-03-28T15:17:44.533" LastActivityDate="2021-03-28T15:17:44.533" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18230" PostTypeId="1" CreationDate="2021-03-28T19:29:52.977" Score="1" ViewCount="77" Body="&lt;p&gt;I'm restricted to putting antennas in my attic which is 50 feet long and peaks at about 8 feet. I'm currently using the Nelson UJM-150-50 end-fed dipole 80-10 meter antenna. The attic is about 25 feet above the ground. Would the MFJ (or other) magnetic loop antenna be better? Is there a better option?&lt;/p&gt;&#xA;" OwnerUserId="19204" LastActivityDate="2021-03-29T06:23:43.593" Title="Is a MagLoop antenna better than my 50ft end fed di-pole for 20-80 meters?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;magnetic-loop&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18232" PostTypeId="2" ParentId="17650" CreationDate="2021-03-28T20:11:24.903" Score="1" Body="&lt;p&gt;I repeat my comment now as answer. With a small addition.&lt;/p&gt;&#xA;&lt;p&gt;Depending on the settings in the RTL control program there is a first conversion to zero-IF or near-zero, or low IF, offset from zero. The front-end mixer for the range 24 MHz and higher is a mixer with a variable LO that converts the FM broadcast frequency to that lower IF frequency. The LO contains harmonics and at one third of the LO frequency there is a spurious reception.&lt;/p&gt;&#xA;&lt;p&gt;Addition: the I-Q properties of a third harmonic are swapped, i.e. positive or negative frequencies swap.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-03-28T20:11:24.903" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18235" PostTypeId="2" ParentId="18230" CreationDate="2021-03-29T00:54:21.037" Score="2" Body="&lt;p&gt;Both an end-fed and a small loop antenna might couple into the house wiring on transmit.  You might be able to orient a mag loop to minimize RF noise pickup from the house environment on receive.&lt;/p&gt;&#xA;&lt;p&gt;As an alternative, I might consider testing a balanced fan dipole for Tx.  For a receive antenna, another possibility might be a large loop around the entire attic, if the EMI/RFI pickup isn’t too bad.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-03-29T06:23:43.593" LastActivityDate="2021-03-29T06:23:43.593" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18236" PostTypeId="1" CreationDate="2021-03-29T03:04:52.383" Score="3" ViewCount="49" Body="&lt;p&gt;I bought a euro Yaesu 991a . The vhf/uhf band plan is severely limited for use in the US . I have tried the button presses as shown for the earlier 991 and the service mode works to open the frequency for transmission but setting offsets etc are not possible . There must be a permanent fix because service mode shows than the unit can actually&#xA;transmit on the US band plan. Any help would be appreciated&lt;/p&gt;&#xA;" OwnerUserId="19209" LastEditorUserId="8717" LastEditDate="2021-04-01T16:05:42.090" LastActivityDate="2021-04-01T16:33:37.950" Title="Is it possible to convert a euro Yaesu 991a to US band plan?" Tags="&lt;vhf&gt;&lt;uhf&gt;&lt;yaesu&gt;&lt;europe&gt;&lt;modification&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18237" PostTypeId="2" ParentId="16298" CreationDate="2021-03-29T14:57:44.097" Score="0" Body="&lt;p&gt;You still need to tune them to frequency just like any other antenna. I tuned my 18 inch to gmrs recently. And I got much better results. So my recommendation would be to get close to the wavelength you need with room to trim down the tape measure on the inside of the antenna. I think it's funny that its actual tape measure inside with numbers and all.&lt;/p&gt;&#xA;" OwnerUserId="19215" LastActivityDate="2021-03-29T14:57:44.097" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18238" PostTypeId="2" ParentId="18223" CreationDate="2021-03-29T19:20:54.470" Score="3" Body="&lt;p&gt;There's a lot of pieces to this question and it sounds like you've already split some of them off to other sites which is good. It's still a little unclear what you're trying to do with the radio itself:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Send the audio buffer from the transmitter to the microcontroller&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;In the United States, the &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/citizens-band-radio-service-cbrs&quot; rel=&quot;nofollow noreferrer&quot;&gt;Citizens Band Radio Service&lt;/a&gt; refers to just one specific set of channels and those are only allowed to be used for &lt;strong&gt;voice&lt;/strong&gt; transmissions (among other restrictions). There are similar restrictions on the &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/family-radio-service-frs&quot; rel=&quot;nofollow noreferrer&quot;&gt;Family Radio Service&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;That is, neither CB (&amp;quot;trucker&amp;quot; radios) nor FRS (&amp;quot;hiking&amp;quot; walkie-talkies) are allowed for much beyond people talking live with nearby people, and only using unmodified store-bought equipment.&lt;/p&gt;&#xA;&lt;p&gt;There are only a few casual options where data transmission is allowed:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;other more specialized Part 95 devices like &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/radio-control-radio-service-rcrs&quot; rel=&quot;nofollow noreferrer&quot;&gt;remote controllers&lt;/a&gt; or &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/multi-use-radio-service-murs&quot; rel=&quot;nofollow noreferrer&quot;&gt;Multi-Use Radio Service&lt;/a&gt; equipment may transmit data but end-users might not be allowed to modify it much&lt;/li&gt;&#xA;&lt;li&gt;the &lt;a href=&quot;https://www.fcc.gov/wireless/bureau-divisions/mobility-division/amateur-radio-service&quot; rel=&quot;nofollow noreferrer&quot;&gt;Amateur Radio Service&lt;/a&gt; has relatively few &lt;em&gt;technical&lt;/em&gt; restrictions, but may only be used for certain &lt;em&gt;purposes&lt;/em&gt; — and requires a &amp;quot;ham&amp;quot; license&lt;/li&gt;&#xA;&lt;li&gt;Low power &lt;a href=&quot;https://en.wikipedia.org/wiki/Title_47_CFR_Part_15&quot; rel=&quot;nofollow noreferrer&quot;&gt;Part 15&lt;/a&gt; stuff (e.g. WiFi, Bluetooth, tiny FM transmitters for your car)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;But from some of your other comments, it sounds like you might only be interested in gathering &lt;em&gt;received&lt;/em&gt; audio rather than transmitting it yourself? (In radio terms we distinguish a &amp;quot;transmitter&amp;quot; sending signals from a &amp;quot;receiver&amp;quot; listening for them. A &amp;quot;transceiver&amp;quot; can do both, though not necessarily at the same time.)&lt;/p&gt;&#xA;&lt;p&gt;If you are trying to do something like &amp;quot;scanner monitoring&amp;quot; that's a bit different situation. There may already be lots of options available for that, if you gather the right pieces:&lt;/p&gt;&#xA;&lt;p&gt;For example the &lt;a href=&quot;https://uniden.com/products/bcd536hp-homepatrol-series-scanner-with-wi-fi&quot; rel=&quot;nofollow noreferrer&quot;&gt;Uniden BCD536HP&lt;/a&gt; scanner is a receiver only but can be configured to listen to the CB (and many many other) bands and has Wi-Fi feature already.&lt;/p&gt;&#xA;&lt;p&gt;Or with the right adapters to reduce the speaker output level of the CB receiver safely as a mic input to an old smartphone, there is likely software available to &amp;quot;stream&amp;quot; that audio to an Internet protocol server.&lt;/p&gt;&#xA;&lt;p&gt;Similar if you need to use a microcontroller instead: if you already have a solution for the &amp;quot;capturing and/or generating audio&amp;quot; piece and the &amp;quot;connecting to WiFi&amp;quot; piece and the &amp;quot;transmitting audio data to a server&amp;quot; piece, then perhaps you might open a new question about any remaining radio-specific pieces (e.g. dealing with the audio input/output of a transceiver) here on this StackExchange site.&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="1362" LastEditDate="2021-03-29T19:28:44.263" LastActivityDate="2021-03-29T19:28:44.263" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18240" PostTypeId="2" ParentId="9459" CreationDate="2021-03-30T08:43:29.330" Score="6" Body="&lt;p&gt;I signed up here just to reply to this great (the only one I could find on the internet) question/experience that helped me with an identical problem. I was so close to giving up when I read this thread and went to examine the component that looks like a coin battery (as the original poster described)&#xA;&lt;a href=&quot;https://i.stack.imgur.com/QlWMY.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QlWMY.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt; &lt;a href=&quot;https://i.stack.imgur.com/xT4Kg.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xT4Kg.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;and having owned a sucking hakko soldering gun&lt;a href=&quot;https://i.stack.imgur.com/8JOr1.jpg&quot; rel=&quot;noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8JOr1.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;, i managed to remove it from the board (you'll have to remove the metal shield under the board first, which makes it even harder, but a piece of cake for an expert like me). I then soldered two tiny wires to it's pins and connected to a power supply that I started at 1.0v and incremented 0.1v at a time. The radio's dead screen came to life at 2v and everything was normal. The screen was on even with no AA batteries, but the &amp;quot;low battery&amp;quot; symbol was blinking and the radio won't turn on until the AA's were installed.&#xA;This component looks like two small coin batteries stacked over one another. Upon further investigation, I discovered that it is actually a very small super capacitor of .22F and 5.5v that is relatively expensive (around $10 a pop). I put a 2200uf that i had and the screen came on for only a second. I'm not sure if supercaps (very high capacitance electrolytics) can be tested just like a regular cap and if they have a short life time but i'm still researching and would love to hear from others (especially the original poster from 4 years ago!).&#xA;It could be that tecsun put very bad quality component there purposely to sell more radios!!! that's for them to answer.&lt;/p&gt;&#xA;" OwnerUserId="19228" LastEditorUserId="19228" LastEditDate="2021-03-30T08:53:16.057" LastActivityDate="2021-03-30T08:53:16.057" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18242" PostTypeId="2" ParentId="18173" CreationDate="2021-03-31T01:20:43.750" Score="0" Body="&lt;p&gt;One option appears to be using a DC to DC converter designed for charging house batteries in RVs, which will automatically correct the incoming 13.8v to whatever the battery requires. There are some 20A models that are cheaper than a PWRgate.&lt;/p&gt;&#xA;&lt;p&gt;120v AC -&amp;gt; Power supply -&amp;gt; 13.8v DC -&amp;gt; DC-to-DC converter -&amp;gt; LiFePo4 battery -&amp;gt; rigrunner -&amp;gt; radios&lt;/p&gt;&#xA;&lt;p&gt;It's possible I'm still making this more complicated than necessary though.&lt;/p&gt;&#xA;" OwnerUserId="11639" LastActivityDate="2021-03-31T01:20:43.750" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18243" PostTypeId="2" ParentId="18218" CreationDate="2021-03-31T13:22:57.917" Score="2" Body="&lt;p&gt;Looks like it's just a fancy memory feature to let you quickly switch to a preset frequency and operating mode. &lt;a href=&quot;https://www.k0pir.us/icom-band-stacking-register-and-memo-pad/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.k0pir.us/icom-band-stacking-register-and-memo-pad/&lt;/a&gt; and &lt;a href=&quot;https://www.manualslib.com/manual/965457/Icom-Ic-7600.html?page=38&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.manualslib.com/manual/965457/Icom-Ic-7600.html?page=38&lt;/a&gt; .  As the second URL mentions, it would be useful if you operate multiple modes in one band, so you can quickly switch from (for example) 40m RTTY to 40m CW to 40m SSB by just pushing one button.&lt;/p&gt;&#xA;" OwnerUserId="9974" LastActivityDate="2021-03-31T13:22:57.917" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18244" PostTypeId="1" AcceptedAnswerId="18248" CreationDate="2021-03-31T18:45:45.327" Score="4" ViewCount="102" Body="&lt;p&gt;In the ARRL Ham Radio License Manual (4th Edition) an Amateur Allocation chart labels VLF with &amp;quot;Audible Range&amp;quot;:&lt;/p&gt;&#xA;&lt;pre&gt;&lt;code&gt;                    Very Low Frequency (VLF)&#xA;              0Hz             10Hz                  10kHz          100kHz&#xA; Activities                      [   Audible Range   ]&#xA;              &amp;lt;- Infra-sonics -&amp;gt; &amp;lt;-     Sonics      -&amp;gt; &amp;lt;- Ultra-sonics -&amp;gt;&#xA;&lt;/code&gt;&lt;/pre&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/HYYQd.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HYYQd.jpg&quot; alt=&quot;ARRL Figure 7.3 Amateur Allocations&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Is there a reason this is included? The other activities listed are referencing EM waves: Microwaves (in the photo), Infrared, and X-rays. I agree that if this were an acoustic wave these frequencies would be in the audible spectrum.&lt;/p&gt;&#xA;&lt;p&gt;The &lt;a href=&quot;https://en.wikipedia.org/wiki/Very_low_frequency#Amateur_use&quot; rel=&quot;nofollow noreferrer&quot;&gt;wikipedia page for VLF amateur use&lt;/a&gt; mentions QRSS, MFSK, and coherent BPSK as the modes used. I was at first thinking the carrier wave with no modulation could be associated with sound somehow. Maybe submarines (not amateur!) interpret the carrier wave as a continuous tone as it relates to some existing system. Maybe it means the mathematics of digital audio can be applied here, so traditional sound cards can be used as receivers.&lt;/p&gt;&#xA;&lt;p&gt;Or maybe it is just a reference to something more familiar, like comparing a wavelength to the size of the Eiffel Tower, and I'm reading into it too much. Are there some audio applications with VLF?&lt;/p&gt;&#xA;" OwnerUserId="19128" LastActivityDate="2021-04-07T21:53:21.840" Title="Why are VLF EM waves labeled as &quot;sonic&quot; in ARRL charts?" Tags="&lt;vlf&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18245" PostTypeId="2" ParentId="1646" CreationDate="2021-03-31T22:10:29.760" Score="0" Body="&lt;p&gt;I do not consider it rude if I listen to see if anyone is online.  I do the same with my 2 meter.  It is called &amp;quot;common courtesy&amp;quot;.  If there is someone online, and talking about something that is of interest, I will join in if possible...otherwise I will listen to see if I have anything to add to the conversation.  Again...&amp;quot;common courtesy&amp;quot;.  In fact, there was a &amp;quot;node&amp;quot; in Alaska that said LISTEN before first transmission to make sure the frequency is clear.&lt;/p&gt;&#xA;" OwnerUserId="19248" LastEditorUserId="19248" LastEditDate="2021-03-31T22:48:52.517" LastActivityDate="2021-03-31T22:48:52.517" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18246" PostTypeId="1" AcceptedAnswerId="18247" CreationDate="2021-04-01T11:38:34.973" Score="0" ViewCount="51" Body="&lt;p&gt;Looking at solar systems Hams mention that solar often brings RFI into the system, what part of the system in most likely to introduce RFI detectable on the ham bands?&lt;/p&gt;&#xA;" OwnerUserId="13219" LastActivityDate="2021-04-02T04:46:06.577" Title="In most Solar Systems what causes more QRM on HF ham bands, the panels, the charge controller, or the distribution system?" Tags="&lt;rfi&gt;&lt;solar&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18247" PostTypeId="2" ParentId="18246" CreationDate="2021-04-01T12:50:50.787" Score="4" Body="&lt;p&gt;In the April 2016 issue of the ARRL's &lt;em&gt;QST&lt;/em&gt; magazine article, &amp;quot;Can Home Solar Power and Ham Radio Coexist?,&amp;quot; K1KP tracks down and attenuates RFI generated by his multi-kW rooftop solar installation. Using sensing loops and antennas connected to an all-band HF transceiver, Tony detected RFI from every part of the installation, though radiation from some of the sources dropped rapidly with distance.&lt;/p&gt;&#xA;&lt;p&gt;The net of his analysis: RFI depends on the design and manufacture of the active system components (inverters, &amp;quot;optimizers&amp;quot;) as well as the lengths and shielding of the passive components (wires). K1KP concluded that you may have to spend as much as 10% of the system cost and a considerable amount of time to identify and mitigate RFI using ferrite chokes.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-04-01T12:50:50.787" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18248" PostTypeId="2" ParentId="18244" CreationDate="2021-04-01T14:06:16.263" Score="7" Body="&lt;p&gt;You're reading into it too much. It just means signals that, if you were to receive them directly, with no demodulation or frequency mixing, they would fall into (or near) the audible frequency range. And indeed, some people do receive these kinds of signals using a loop antenna connected directly to a PC sound card's line-in.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-04-01T14:06:16.263" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18249" PostTypeId="2" ParentId="18244" CreationDate="2021-04-01T16:01:15.867" Score="-1" Body="&lt;p&gt;When VLF EM waves interact with the material world, they can not only induce voltages and currents, but mechanical displacements or pressure waves than are in the range of human hearing.&lt;/p&gt;&#xA;&lt;p&gt;Lots of people used to be annoyed by CRT monitor/TV flyback hum, and horizontal scan rate is VLF.  And Van Eck remote mirroring (spying) shows that these CRT signals are indeed RF EM.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-07T21:53:21.840" LastActivityDate="2021-04-07T21:53:21.840" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18250" PostTypeId="1" CreationDate="2021-04-01T16:21:37.687" Score="3" ViewCount="70" Body="&lt;p&gt;Need help in setting up the Kenwood TH-D72A for ECHOLINK. Cannot find if I need to connect to computer or some node through a local repeater.&lt;/p&gt;&#xA;" OwnerUserId="18689" LastEditorUserId="8717" LastEditDate="2021-04-01T21:53:38.190" LastActivityDate="2021-04-01T21:53:38.190" Title="How do I set up my radio for Echolink?" Tags="&lt;ht&gt;&lt;kenwood&gt;&lt;echolink&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18251" PostTypeId="2" ParentId="18236" CreationDate="2021-04-01T16:24:07.713" Score="1" Body="&lt;p&gt;This &lt;a href=&quot;https://www.youtube.com/watch?v=xNUnyZxu918&quot; rel=&quot;nofollow noreferrer&quot;&gt;YouTube video&lt;/a&gt; says that pressing FAST + A/B + A+B during power-on puts the radio into Service Mode, allowing you to extend the transmit frequency range. You must follow the steps indicated in the video precisely; in particular, you must set the radio's transmit frequency to the range on which you want to transmit before putting the radio in Service Mode.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="9621" LastEditDate="2021-04-01T16:33:37.950" LastActivityDate="2021-04-01T16:33:37.950" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18252" PostTypeId="2" ParentId="18250" CreationDate="2021-04-01T17:00:31.143" Score="2" Body="&lt;p&gt;&lt;a href=&quot;https://secure.echolink.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Echolink&lt;/a&gt; allows repeaters to be connected over the internet, and also allows licensed hams with computers to connect to the system directly without using a radio.  So there are two ways to participate:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Find a local repeater that is connected to the Echolink system, and access that repeater with your radio.&lt;/li&gt;&#xA;&lt;li&gt;Download, install, and run the Echolink software on your computer.  You'll need a microphone or a headset with a microphone.  You'll need to validate your callsign with the administrators, which I seem to remember means sending a scanned copy of your license.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;If you have a local repeater connected to the Echolink system, then configuring your radio is simple.  Just set it up to talk to the repeater in the same way you configure your radio to talk to any other FM repeater: frequency, offset, CTCSS tone or CDCSS code, etc.&lt;/p&gt;&#xA;&lt;p&gt;Generally the administrators of a repeater decide if the repeater should be connected to Echolink and when, and what other repeaters or conferences the repeater should be linked to when it is connected.  If you run the software, then you can decide to which repeater or conference to connect, so the software is more flexible.&lt;/p&gt;&#xA;&lt;p&gt;If you do run the software and connect to a repeater, know that you are announced when you connect and that you are taking up a connection slot, so please only connect if you plan to actively participate.  To connect and just listen, especially when someone hails you directly, is &lt;a href=&quot;https://ham.stackexchange.com/questions/1646/is-just-listening-on-echolink-considered-bad-etiquette&quot;&gt;generally considered to be rude&lt;/a&gt;.  If your goal is to just listen, connect to a conference server instead; conference servers have many more connection slots, and your arrival isn't announced, so it's not considered rude.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-04-01T17:07:33.040" LastActivityDate="2021-04-01T17:07:33.040" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18253" PostTypeId="2" ParentId="18192" CreationDate="2021-04-01T20:50:10.673" Score="3" Body="&lt;p&gt;I learned it years ago by listening to the dits and Dahas spacing with the spacing much slower.  I would recommend  go as fast as where you can make out the different dits and dahas.  Then as your Think about it&amp;quot; time gets shorter, decrease the spacing pad.  For example, the individual letters at 10 or 15 wpm but the spacing is 5 wpm.  I also hit a plateau every now and then.  I put it down for a week or two and go back to it.  Good luck and don't get discouraged.  It helps to find a ham learning CW also.  I once called up another ham on the phone so we could interact.&lt;/p&gt;&#xA;" OwnerUserId="19253" LastActivityDate="2021-04-01T20:50:10.673" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18254" PostTypeId="1" CreationDate="2021-04-01T21:10:00.620" Score="1" ViewCount="57" Body="&lt;p&gt;I installed a Yaesu System 600with a MFJ Versatuner 2 on my 31ft sailboat and Idont know what type of cable should I use between the MFJ and the long wire antenna I have on my back Stay.&#xA;Any suggestions?&lt;/p&gt;&#xA;&lt;p&gt;Fernando from Buenos Aires, Argentina.&lt;/p&gt;&#xA;" OwnerUserId="19255" LastEditorUserId="8717" LastEditDate="2021-04-01T21:47:02.587" LastActivityDate="2021-05-02T20:01:00.123" Title="What type of Cable Should I use between a Long Wire antenna and a Transmatch?" Tags="&lt;wire-antenna&gt;&lt;mobile&gt;&lt;impedance-matching&gt;&lt;feed-line&gt;&lt;end-fed-antenna&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18255" PostTypeId="1" AcceptedAnswerId="18260" CreationDate="2021-04-01T22:10:52.373" Score="9" ViewCount="770" Body="&lt;p&gt;A &lt;a href=&quot;https://en.wikipedia.org/wiki/PIN_diode&quot; rel=&quot;noreferrer&quot;&gt;PIN diode&lt;/a&gt; varies its capacitance based on a DC bias, and a &lt;a href=&quot;https://en.wikipedia.org/wiki/Varicap&quot; rel=&quot;noreferrer&quot;&gt;Varicap&lt;/a&gt; exhibits this effect even more clearly. What limits the use of &amp;quot;solid state variable capacitors&amp;quot; like these for dynamically filtering (low power/received) RF signals?&lt;/p&gt;&#xA;&lt;p&gt;The question at &lt;a href=&quot;https://ham.stackexchange.com/questions/18189/change-lc-parameter-digitally&quot;&gt;change LC parameter digitally&lt;/a&gt;&#xA;is related, but was asked in the context of a tunable &lt;strong&gt;oscillator&lt;/strong&gt;. That is already a ± &amp;quot;solved problem&amp;quot; in the SDR world. What would be useful in conjunction with a DCO that can operate in a 24–1766 MHz range would be a correspondingly flexible bandpass filter to limit receiver overload/aliasing!&lt;/p&gt;&#xA;" OwnerUserId="1362" LastEditorUserId="8717" LastEditDate="2021-04-01T22:27:27.927" LastActivityDate="2021-04-02T19:27:30.903" Title="What limits a PIN diode or varicap from being used in a &quot;Software Defined [Radio] Filter&quot;?" Tags="&lt;software-defined-radio&gt;&lt;equipment-design&gt;&lt;filter&gt;&lt;capacitance&gt;" AnswerCount="5" CommentCount="1" FavoriteCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18256" PostTypeId="2" ParentId="18255" CreationDate="2021-04-02T00:22:49.857" Score="5" Body="&lt;p&gt;Technically, the utility of a variable capacitor in a receive filter depends on the amount of available capacitance variation and its &lt;em&gt;Q&lt;/em&gt; - the quality factor, which is the ratio of the capacitor's reactance at the operating frequency to the series parasitic resistance. (In some applications, parasitic series inductance may also be a factor.) Commercially, price is a primary concern.&lt;/p&gt;&#xA;&lt;p&gt;Fixed-value ceramic chip capacitors commonly have a &lt;em&gt;Q&lt;/em&gt; value of 2000 or more and, obviously, no variability - at a &lt;em&gt;very&lt;/em&gt; low unit price. Perusing an online distributor's catalog, I see varactor diodes with capacitance ratios of around 10:1 down to around 4:1, some with &lt;em&gt;Q&lt;/em&gt; factors over 1000 but most with &lt;em&gt;Q&lt;/em&gt; factors in the hundreds or less - and with prices of 15X to 150X that of a fixed cap.&lt;/p&gt;&#xA;&lt;p&gt;When taken together, fixed-value capacitors deliver the needed cost-performance balance for all but a small fraction of all such applications.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-04-02T00:22:49.857" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18257" PostTypeId="2" ParentId="18255" CreationDate="2021-04-02T04:16:33.003" Score="1" Body="&lt;p&gt;Consider increasing the dynamic range of the ADC to obtain many of the same performance benefits. This can be done by either upgrading the ADC, or low-pass filtering the ADC input below the Nyquist frequency and &lt;a href=&quot;https://www.analog.com/en/technical-articles/increase-dynamic-range-of-sar-adcs-using-oversampling.html#&quot; rel=&quot;nofollow noreferrer&quot;&gt;oversampling&lt;/a&gt;. Often this is the cheaper and more flexible approach, especially given the limitations of the varicap's Q-factor and capacitance range, and explained by Brian K1LI.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-02T04:16:33.003" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18258" PostTypeId="2" ParentId="18255" CreationDate="2021-04-02T04:39:47.773" Score="4" Body="&lt;p&gt;Another difference between using a varicap for oscillators versus for input filters is feedback.  You can feed the output of a variable oscillator into a phase comparator or frequency counter to determine if the component values are correct, and run a feedback loop correction algorithm or circuit to maintain lock.  This can be done while the oscillator is performing in-circuit Rx or Tx. It's a little harder to determine if an RF input filter is set correctly during actual Rx.&lt;/p&gt;&#xA;&lt;p&gt;Because varicaps can have (large?) temperature coefficients, they present a greater problem making sure the filter passband stays at the desired frequency than with oscillator circuits that can use feedback.  You might have to take the radio off-line to sweep the filter and recalibrate whenever the temperature changes.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-04-02T04:39:47.773" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18259" PostTypeId="2" ParentId="18246" CreationDate="2021-04-02T04:46:06.577" Score="3" Body="&lt;p&gt;The panels themselves are essentially photodiodes, producing DC when exposed to light, and so generating no RFI. A very simple system consisting just of panels and a battery could generate no RFI at all.&lt;/p&gt;&#xA;&lt;p&gt;However such a system system is not very efficient. There is an optimal impedance which the panels should see which optimizes the product of voltage and current and thus power they produce, but this varies depending on the light hitting the panels and temperature. Charge controller are thus essentially switch-mode power supplies (SMPS) which transform the load to this &lt;a href=&quot;https://en.wikipedia.org/wiki/Maximum_power_point_tracking&quot; rel=&quot;nofollow noreferrer&quot;&gt;optimal impedance&lt;/a&gt;. Like the SMPS in LED drivers and cell phone chargers the controller will spew RFI from the high frequency square-wave switching, but as the power handled by a charge controller can be much greater, so too can be the RFI.&lt;/p&gt;&#xA;&lt;p&gt;A quiet solar system thus depends on good PCB layout to minimize radiation, sufficient shielding around the controller to block radiation, and finally sufficient filtering to isolate the switching transients from being conducted on the input or output wiring.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-02T04:46:06.577" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18260" PostTypeId="2" ParentId="18255" CreationDate="2021-04-02T10:08:34.633" Score="13" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;What limits the use of &amp;quot;solid state variable capacitors&amp;quot; like these for dynamically filtering (low power/received) RF signals?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The main issue is bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;Although there are some varicaps that claim a 10:1 variation (or more) in capacitance, not all of this is useable. One end of the range may be low Q, or have a very steep curve. Once you have a varicap on a board, with pads and bias connections, you'll often find that the useable capacitance swing at the tuned circuit is no more than 4:1, giving you only 2:1 swing in centre frequency.&lt;/p&gt;&#xA;&lt;p&gt;Even if you did have a varactor that gave you more swing, or a construction technique that reduced the effect of strays, changing the LC ratio alters the impedance of the filter. There's only so much change you can make to the impedance of the resonators before a good filter becomes a bad filter.&lt;/p&gt;&#xA;&lt;p&gt;You may only want to operate in an octave. However you've asked specifically about SDRs, and the main benefit of those is a very wide frequency range.&lt;/p&gt;&#xA;&lt;p&gt;You could switch inductors into the filter, with the switching strays further reducing the capacitance swing available. Or you could build multiple filters and switch between them. Both of these add to the complexity. Once you have accepted the complexity of further switching, it often makes more sense to build a few, good, fixed frequency filters with stable components and switch between them.&lt;/p&gt;&#xA;" OwnerUserId="19257" LastActivityDate="2021-04-02T10:08:34.633" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18261" PostTypeId="2" ParentId="18254" CreationDate="2021-04-02T19:16:51.163" Score="0" Body="&lt;p&gt;The cable between antenna and tuner is part of your antenna. Use oxygen-free copper wire (its a boat on salt water...). In case of a long wire connection between the feed point of your antenna and the tuner consider to place the tuner at the feed point of your antenna and use a coax cable between RX/TX and tuner.&lt;/p&gt;&#xA;&lt;p&gt;When you use only RX than forget every recommendation and just use any wire.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-04-02T19:16:51.163" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18262" PostTypeId="2" ParentId="18255" CreationDate="2021-04-02T19:27:30.903" Score="5" Body="&lt;p&gt;Nobody mentions distortion (IM2 and IM3) of PIN diodes and varicap diodes. Tuning (center frequency) limitation range, required band switching and further requirements. Best solution is to start with a good system that can handle the dynamics without filtering. As W8II Phil Frost proposes.&lt;/p&gt;&#xA;&lt;p&gt;** Mentioned Q-factors (Brian K1LI) of 1000 are not feasible in a normal receiver and not necessary. Filter Q_loaded of 100 is practical; then unloaded Q is not necessary to be higher than 250. **&lt;/p&gt;&#xA;" OwnerUserId="16925" LastActivityDate="2021-04-02T19:27:30.903" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18263" PostTypeId="1" CreationDate="2021-04-03T00:33:54.537" Score="1" ViewCount="56" Body="&lt;p&gt;I've mostly been using a discone in the attic so far, but now I want to get proper antennas up for 2m/70cm and gmrs. I'll probably get common commercial vertical antennas. I'm not sure how much I really need to be worrying about them interacting, and since changing placement changes what sort of support system I need, which could change which antenna sizes I can use, I'm unsure about where to start.&lt;/p&gt;&#xA;&lt;p&gt;So far I've been looking at:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;GMRS (50W) looks like most antennas are about 5dbi&lt;/li&gt;&#xA;&lt;li&gt;2m/70cm (100W) - maybe comet gp-6 ? 6.5dbi on 2m, 9dbi on 70cm&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;How should I arrange these to avoid damaging one radio when transmitting in another?&lt;/p&gt;&#xA;" OwnerUserId="11639" LastEditorUserId="11639" LastEditDate="2021-04-04T14:50:28.150" LastActivityDate="2021-04-04T14:50:28.150" Title="Avoiding radio damage with closely spaced VHF/UHF antennas" Tags="&lt;antenna-theory&gt;&lt;vertical-antenna&gt;" AnswerCount="0" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18264" PostTypeId="2" ParentId="9459" CreationDate="2021-04-03T16:15:45.370" Score="1" Body="&lt;p&gt;my Tecsun PL-660 hadn’t been used for a while. It didn’t charge the batteries either. I put the batteries in a separate charger and brought them up to full charge. Still no joy with them in the radio. Occasionally the display came on but not clearly and with various segments missing. Over the course of a few weeks and after a little research I removed the .22F super capacitor and tested it. It seemed ok. After putting it back I managed to get the radio to function for a few minutes then it failed again leaving the backlight on and no functionality. Long story short.......get a very powerful magnifying glass and check for resin corrosion around the microprocessor. Clean with flux remover and then check again. Use a craft knife to clean between pins. Result!&lt;/p&gt;&#xA;" OwnerUserId="19267" LastActivityDate="2021-04-03T16:15:45.370" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18265" PostTypeId="1" AcceptedAnswerId="18269" CreationDate="2021-04-03T18:32:16.457" Score="0" ViewCount="94" Body="&lt;p&gt;Ferrite cores ain't cheap when you start talking about the 3 inch ID ones. I can see em for like 40 and 50 bucks....&lt;/p&gt;&#xA;&lt;p&gt;I don't see why I can't just ground a slinky or something.&lt;/p&gt;&#xA;" OwnerUserId="15859" LastEditorUserId="8717" LastEditDate="2021-04-07T22:31:01.673" LastActivityDate="2021-04-08T12:01:08.937" Title="Can a slinky serve as a ferrite core and if so, is there a prefered configuration?" Tags="&lt;rfi&gt;&lt;ferrite&gt;" AnswerCount="2" CommentCount="2" ClosedDate="2021-04-07T22:27:41.507" ContentLicense="CC BY-SA 4.0" />
  <row Id="18267" PostTypeId="2" ParentId="18265" CreationDate="2021-04-04T01:42:35.913" Score="1" Body="&lt;p&gt;A slinky as in the one you watch go down the stairs? I'd assume not. Any winding on a slinky would probably act as inductor/transformer with an air-core. Ferrites have special magnetic properties. There is a reason they are expensive.&lt;/p&gt;&#xA;" OwnerUserId="19273" LastActivityDate="2021-04-04T01:42:35.913" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18268" PostTypeId="1" CreationDate="2021-04-04T01:58:07.693" Score="4" ViewCount="85" Body="&lt;p&gt;Aloha!&lt;/p&gt;&#xA;&lt;p&gt;I have two HYS TC-YG05 Yagi antennas that were gifted to me and I would like to stack them side by side ( Collinear), in the vertical orientation for some local weather balloon telemetry data gathering.&lt;/p&gt;&#xA;&lt;p&gt;I have attempted to use my Google-Fu as the best that I can in the attempt to search in understanding the stacking of yagi antennas; it seems the boom spacing is not very critical so to speak when not utilizing long yagi antennas. I believe I can get away with the spacing @ 432mhz using .6λ @3dB which equates to a spacing of ~1.4 feet&lt;/p&gt;&#xA;&lt;p&gt;So after researching a bit more, appears there is a formula that can be used if you know the E/H Beamwidth information of the antenna;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://atlcllc.com/simple-formula-for-the-stacking-of-yagi-antennas/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://atlcllc.com/simple-formula-for-the-stacking-of-yagi-antennas/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;So stacking on the Stacking distance E plane in inches, looks like my distance between the Yagi antennas would be roughly 3 feet, center to center. Using the DL6WU calculator, it came out to be be 3.3 feet; however, from my understanding, the DL6WU calculator should be used for long yagi antennas.&lt;/p&gt;&#xA;&lt;p&gt;Any thoughts if I am correct in my research?&lt;/p&gt;&#xA;&lt;p&gt;Thanks!&lt;/p&gt;&#xA;" OwnerUserId="19272" LastEditorUserId="19272" LastEditDate="2021-04-04T04:23:22.877" LastActivityDate="2021-04-06T11:13:29.793" Title="Stacking Two UHF Yagi Antennas" Tags="&lt;antenna-theory&gt;&lt;uhf&gt;&lt;yagi&gt;" AnswerCount="2" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18269" PostTypeId="2" ParentId="18265" CreationDate="2021-04-04T06:05:30.550" Score="4" Body="&lt;p&gt;A ferrite core used for radio is specially constructed to conduct magnetic fields while not conducting electrical current, especially eddy currents.&lt;/p&gt;&#xA;&lt;p&gt;A slinky is (typically) an uninsulated conductive coil of variable spacing, and thus variable inductance.  It is nothing like a ferrite core. Typically they are made of steel which his high resistance (for metal), although I have seen copper &amp;quot;slinkies&amp;quot; made specifically for radio use.&lt;/p&gt;&#xA;&lt;p&gt;Ferrite cores are usually priced by size, which is proportional to the power they can handle.  A torioidal ferrite with a 3 inch inner diameter is quite large and likely would be heavy and be able to handle a quite large amount of power.  Perhaps you can make use of a much smaller one instead?  If you need that size for the power, you should be worried about safety, not cost.&lt;/p&gt;&#xA;&lt;p&gt;Some people have used slinkies as antennas.  In this use, they can act like a broadside helical antenna that you can tune by adjusting the spread of the coil.  However, as it is not very stable, the tuning will change randomly as it moves around, so this could be a bit of a problem.  Also, steel is generally a poor choice for antenna material due to its magnitivity and resistance (although it will work but with lots of resistive loss).&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-04-08T12:01:08.937" LastActivityDate="2021-04-08T12:01:08.937" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18270" PostTypeId="2" ParentId="18268" CreationDate="2021-04-04T12:11:38.383" Score="-1" Body="&lt;p&gt;&lt;a href=&quot;http://dg7ybn.de/Stacking/6WU_online_calc.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://dg7ybn.de/Stacking/6WU_online_calc.htm&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Probably a decent place to start.&lt;/p&gt;&#xA;" OwnerUserId="9550" LastActivityDate="2021-04-04T12:11:38.383" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18271" PostTypeId="1" AcceptedAnswerId="18272" CreationDate="2021-04-04T14:52:03.417" Score="5" ViewCount="82" Body="&lt;p&gt;I would like to know why are side lobes formed along with main beam in an antenna.&lt;/p&gt;&#xA;&lt;p&gt;I asked one of my colleague and he explained me that its due to radiation of frequencies near to the required center frequency. I'm not sure about this explanation and would like to about this in detail.&lt;/p&gt;&#xA;" OwnerUserId="7827" LastActivityDate="2021-04-06T03:14:31.127" Title="what is main reason for formation of side lobes in directional antennas?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;&lt;radiation-pattern&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18272" PostTypeId="2" ParentId="18271" CreationDate="2021-04-05T01:07:19.753" Score="4" Body="&lt;p&gt;Similar to optics or a water tank, waves passing through a finite aperture will produce a diffraction pattern.&lt;/p&gt;&#xA;&lt;p&gt;To over-simplify:  In the far field, the difference between the distance to the left and right side of a dipole's aperture will depend on the angle from the main beam.  That difference can produce a constructive or a destructive interference, again depending on the angle.  The sum of this interference pattern we call side lobes.&lt;/p&gt;&#xA;&lt;p&gt;For the size of an antenna's aperture, see this question: &lt;a href=&quot;https://ham.stackexchange.com/questions/11895/effective-area-of-a-dipole&quot;&gt;Effective area of a dipole&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;To get rid of these side lobes, you would need something like an infinitely small radiator with no gain (which seems to have a name).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-05T01:14:08.530" LastActivityDate="2021-04-05T01:14:08.530" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="18273" PostTypeId="2" ParentId="18268" CreationDate="2021-04-05T12:23:49.170" Score="2" Body="&lt;p&gt;The ARRL Antenna book has an article on stacked yagis that covers this.&lt;/p&gt;&#xA;&lt;p&gt;It states that colinear yagis have the &lt;em&gt;elements&lt;/em&gt; end to end, not the booms.  This could be horizontally polarized antennas horizontally stacked or vertically polarized antennas vertically stacked.  Alternately, they can be stacked side by side, with horizontally polarized yagis being vertically stacked or vertically polarized antennas horontally stacked, with the elements in parallel.  Which arrangement you use depends on the easiest way to mount them. For EME yagi arrays, a grid of antennas may be used, stacking them both horizontally and vertically.&lt;/p&gt;&#xA;&lt;p&gt;The antenna book article also states there are several reasons to do this, increased gain being only one of them.  Other reasons include broadening the radiation pattern, reducing noise, and reducing fading.  I have also seen applications where a variable phasing harness was used to do beam steering, to adjust the elevation angle of the primary lobe.&lt;/p&gt;&#xA;&lt;p&gt;The stacking distance depends greatly on which of these effects is your goal.  Spacing between 0.5 and 1.0 wavelengths are commonly used.   The antenna book article discusses not merely maximizing gain, but actually shaping multiple lobes of the radiation pattern for specific varieties of uses.  Also, different yagis with different numbers of elements and boom lengths have different ideal stacking distances.&lt;/p&gt;&#xA;&lt;p&gt;It is clear from reading this article that there is no simple formula for stacking distance.  To determine ideal stacking distance, you need to consider what goal you have for stacking them and the exact type of yagi you are using, and then model the system, optimizing the shape of the various lobes resulting in stacking them.  Basically, at best, there would be a different formula for each antenna model and usage goal.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-04-06T11:13:29.793" LastActivityDate="2021-04-06T11:13:29.793" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18275" PostTypeId="1" AcceptedAnswerId="18278" CreationDate="2021-04-05T16:15:48.613" Score="2" ViewCount="522" Body="&lt;p&gt;My Kenwood TH-D74 and ICom 7300 both have the ability to output IF instead AF.&#xA;Is this IQ signal at 12ksps, meaning 12kHz of bandwidth, or something else?&lt;/p&gt;&#xA;&lt;p&gt;What are some projects that can be done with these? Seems most digital modes work just fine with normal audio. Or is this for if I want to RX/TX digital modes up to 12kHz?&lt;/p&gt;&#xA;&lt;p&gt;Or only good for an extra wide waterfall?&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="9636" LastEditDate="2021-04-05T18:48:42.393" LastActivityDate="2021-04-08T15:22:57.320" Title="What exactly is the IF output on radios?" Tags="&lt;dsp&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18276" PostTypeId="2" ParentId="18275" CreationDate="2021-04-05T16:57:40.647" Score="1" Body="&lt;p&gt;Page 18-2 of the &lt;a href=&quot;https://www.icomjapan.com/support/manual/2272/&quot; rel=&quot;nofollow noreferrer&quot;&gt;IC-7300 full manual&lt;/a&gt; and page 12-2 of the &lt;a href=&quot;https://manual.kenwood.com/en_contents/attachDownload/98116&quot; rel=&quot;nofollow noreferrer&quot;&gt;TH-D74 User Manual&lt;/a&gt; describe a 12-KHz IF output signal. The IC-7300 manual suggests demodulating a DRM signal using software installed on a PC, but you could demodulate any signal present on the IF output, not just DRM.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastEditorUserId="1362" LastEditDate="2021-04-05T17:32:40.240" LastActivityDate="2021-04-05T17:32:40.240" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18277" PostTypeId="2" ParentId="18275" CreationDate="2021-04-05T19:23:46.967" Score="-1" Body="&lt;p&gt;The 7300 is a direct sampling SDR.  Thus, the 7300's &amp;quot;IF&amp;quot; output is really some sort of a splitter off of its RF input.  So this &amp;quot;IF&amp;quot; output can be used for connecting a second full HF receiver, SDR or otherwise, or custom panadapter, or even a spectrum analyzer covering the entire HF band.&lt;/p&gt;&#xA;&lt;p&gt;The TH-74D &amp;quot;IF&amp;quot; output appears to be wider in bandwidth than when used for demodulated audio, useful for capturing (skimming) multiple digital signals, often with FTx (et.al.) found both inside and outside (above and below) the usual SSB bandwidths at the same time.  Perhaps the same for CW skimming (simultaneous multiple frequency Morse Code decoding) more of entire CW sub-bands as well.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-05T19:29:21.057" LastActivityDate="2021-04-05T19:29:21.057" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18278" PostTypeId="2" ParentId="18275" CreationDate="2021-04-05T20:18:53.230" Score="5" Body="&lt;p&gt;The 7300's &amp;quot;IF output&amp;quot; is a USB digital signal at 48kSPS, the same as the USB AF output (and you can only have one or the other at a given time). It places the dial frequency at an IF frequency of 12kHz, and you can get a maximum bandwidth of around 16kHz (+/- 8kHz from the dial frequency) which is &lt;em&gt;dependent on the selected mode and filter settings&lt;/em&gt;, so you need to have the AM or FM mode selected on the 7300 to get more than a few kHz of bandwidth (yes, this is strange).&lt;/p&gt;&#xA;&lt;p&gt;Mostly it's useful for one thing, which is listening to DRM (&lt;a href=&quot;https://en.wikipedia.org/wiki/Digital_Radio_Mondiale&quot; rel=&quot;nofollow noreferrer&quot;&gt;Digital Radio Mondiale&lt;/a&gt;) HF signals using an IC-7300 and a PC; the IF mode is the only way to get the 10kHz-wide digital signal to the software, since the filter can only open up to 3.6kHz wide in USB-D mode.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2021-04-08T15:22:57.320" LastActivityDate="2021-04-08T15:22:57.320" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18279" PostTypeId="2" ParentId="18271" CreationDate="2021-04-06T03:14:31.127" Score="1" Body="&lt;p&gt;Here is an easy way to visualize what's going on with those pesky side lobes.&lt;/p&gt;&#xA;&lt;p&gt;We take the case of a centerfed resonant dipole with a wire a little longer than the dipole mounted behind it by some fraction of a wavelength. That wire is intended to reflect the output of the dipole in the &amp;quot;back&amp;quot; direction (by absorbing and immediately re-radiating it) so it adds to the output in the &amp;quot;forward&amp;quot; direction.&lt;/p&gt;&#xA;&lt;p&gt;We find that by playing with the offset distance, we can make the reflected wave be in phase with the wave train being radiated by the dipole, and get perhaps +3dB of gain in the forward direction, on-axis.&lt;/p&gt;&#xA;&lt;p&gt;But things are different as we move off-axis. If we model each element as a point source and sweep a receiving antenna through 180 degrees in front of the element pair, there will be certain angles in that sweep where the direct and reflected waves are 180 degrees out-of-phase, and cancel out. What remains is the on-axis &amp;quot;main lobe&amp;quot; and two off-axis &amp;quot;minor lobes&amp;quot;, separated from the main lobe by those &amp;quot;nulls&amp;quot; where the cancellation happens.&lt;/p&gt;&#xA;&lt;p&gt;By adding director elements in front of the active dipole, we can further concentrate the output of the antenna in the desired direction by squeezing the side lobes inwards, further strengthening the main lobe- but at the expense of adding even more &amp;quot;nulls&amp;quot; to the radiation pattern where the phases of the waves in the beam interfere and cancel each other out. So instead of two side lobes, now we have three or four flanking the main beam.&lt;/p&gt;&#xA;&lt;p&gt;So we see that by trying to further and further &amp;quot;confine&amp;quot; the radiation from the dipole into a collimated beam that gets stronger and stronger, we obtain more and more side lobes squeezed together around the main lobe.&lt;/p&gt;&#xA;" OwnerUserId="10598" LastActivityDate="2021-04-06T03:14:31.127" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18280" PostTypeId="1" AcceptedAnswerId="18283" CreationDate="2021-04-06T11:21:14.587" Score="17" ViewCount="2303" Body="&lt;p&gt;This may be slightly off topic (maybe there's a Legal Stack Exchange :-D), but how is it that codecs like Yaesu's C4FM are allowed to be proprietary while still being used on Amateur bands? At the very least, this does not seem to be in keeping with the nature of Amateur Radio.&lt;/p&gt;&#xA;" OwnerUserId="18693" LastEditorUserId="18693" LastEditDate="2021-04-06T19:07:51.893" LastActivityDate="2021-04-07T18:41:05.767" Title="Why are proprietary codecs used in amateur radio?" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;encoding&gt;" AnswerCount="3" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="18281" PostTypeId="2" ParentId="13074" CreationDate="2021-04-06T12:35:58.437" Score="1" Body="&lt;p&gt;All answers above somewhat miss the point of the original question. Lowering the RF Gain does not magically improve the SNR of all signals, but it surely does for the medium and strong ones on SSB. Since a voice in SSB varies its instantaneous power a lot during transmission, if you set you RFG to max and put your AGC to fast, you'll notice strong noise in between words as the AGC is always trying to follow the voice peaks. This is the worst you can do in most situations.&#xA;To improve this, if you lower the RFG to raise the S-meter exactly as the signal you're receiving, your receiver gain will be almost constant (as it should be) and the background noise will be greatly reduced.&#xA;Of course you won't obtain such a great effect if your signal is of the same magnitude as the noise: lowering the RFG will just lower your global audio volume since the AGC is already working at nearly constant gain.&lt;/p&gt;&#xA;&lt;p&gt;So, basically, the answer is this: lowering the RF Gain improves the resulting SNR since the noise between words doesn't get amplified as much as the useful signal during the peaks.&#xA;The answer citing non linearities within the RX are totally missing the point, but they're correct in saying that the lower the RFG, the lower the distortions, but then it's a matter of finding a compromise between sensitivity and distortion... and this could be summed up into: the lower the band, the lower your RFG should be set. Finally, your preamp should be used just above 21MHz.&lt;/p&gt;&#xA;&lt;p&gt;73&lt;/p&gt;&#xA;" OwnerUserId="19290" LastEditorUserId="19290" LastEditDate="2021-04-06T12:41:30.520" LastActivityDate="2021-04-06T12:41:30.520" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18282" PostTypeId="2" ParentId="18280" CreationDate="2021-04-06T15:52:00.430" Score="2" Body="&lt;p&gt;There is a legal corner of StackExchange, but the basic answer you seek is not very complicated. I am not a lawyer, but I am the inventor of a number of patented ideas, so I have experience in this area.&lt;/p&gt;&#xA;&lt;p&gt;DMR is another proprietary CODEC used by hams, so C4FM is not unique. &amp;quot;Proprietary&amp;quot; in this context simply means that it embodies intellectual property (IP) whose ownership has been claimed by an inventor and granted by a governing authority. In general, you must obtain the IP owner's permission to use it. The owner may allow you to use the IP for free, or may require that you pay, or may set other conditions to use it. The fact that you are using &amp;quot;owned&amp;quot; IP in an activity that must be conducted &amp;quot;without pecuniary interest&amp;quot; does not pertain; the development, manufacturing and distribution of the technologies that enable the activity are not covered by this limitation.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-04-06T15:52:00.430" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18283" PostTypeId="2" ParentId="18280" CreationDate="2021-04-06T16:06:22.377" Score="9" Body="&lt;p&gt;The requirement on the FCC side of this is that transmissions may not be encrypted in order to hide their content.  In the case of C4FM (or the other protocol mentioned in another answer, DMR, or as well in JT8/JT4) anyone can either obtain software or buy a device that supports these protocols and listen to the transmission.  There would only be a violation of the FCC regulation against encryption of amateur transmissions if (one of) these protocols used a key or other means to prevent unintended recipients from decoding the transmission -- and that is apparently not the case, at least with DMR, JT8, or C4FM.&lt;/p&gt;&#xA;&lt;p&gt;Even Morse code could be seen as a &amp;quot;transmission protocol&amp;quot; -- and one that &amp;quot;hides the content&amp;quot; from those who can't copy code.  However, the code is public, and (in theory) anyone can learn to read and send Morse.  Even if JT8/JT4 or C4FM aren't &amp;quot;public&amp;quot; in the meaning that anyone can write computer code to read the content of a JT8 or C4FM transmission, they are &amp;quot;public&amp;quot; in that anyone with an amateur radio license (of high enough grade) and money can buy the equipment or software that does this.&lt;/p&gt;&#xA;" OwnerUserId="13947" LastEditorUserId="13947" LastEditDate="2021-04-07T18:41:05.767" LastActivityDate="2021-04-07T18:41:05.767" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18284" PostTypeId="2" ParentId="18280" CreationDate="2021-04-06T18:39:13.597" Score="4" Body="&lt;p&gt;There are lots of proprietary codecs used in amateur radio.  They are allowed in most countries for amateur use simply because they have not been made illegal.  But I don't think that's what you're asking.&lt;/p&gt;&#xA;&lt;p&gt;I think most of us would agree that proprietary codecs are generally against the spirit of amateur radio; we prefer open protocols that anyone can use, adapt, and improve.  So why does amateur radio not shun such proprietary codecs?&lt;/p&gt;&#xA;&lt;p&gt;Every digital phone (voice) protocol in broad amateur or commercial use that I can think of, such as P25, DMR, and &lt;a href=&quot;https://en.wikipedia.org/wiki/D-STAR&quot; rel=&quot;nofollow noreferrer&quot;&gt;D-STAR&lt;/a&gt;, uses a proprietary codec, for the simple reason that at the time each protocol was developed, there was no alternative codec with the necessary performance.  D-STAR was designed by the Japan Amateur Radio League (JARL), the Japanese national amateur radio association, in partnership with Icom.&lt;/p&gt;&#xA;&lt;p&gt;Remember that one of the founding principles of amateur radio is &amp;quot;to contribute to the advancement of the radio art&amp;quot;, to quote US government law &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.1&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR § 97.1&lt;/a&gt;.  The designers of D-STAR had to choose between advancing the radio art and the principle that amateur radio protocols should be open and free.  The designers must have found the choice difficult: everything about D-STAR is open except the codec.&lt;/p&gt;&#xA;&lt;p&gt;It should be mentioned that there are now free and open codecs, which didn't exist when D-STAR was created, that aim to compete with the proprietary codecs.  &lt;a href=&quot;https://freedv.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;FreeDV&lt;/a&gt;, a digital phone protocol for HF, uses the free and open codec &lt;a href=&quot;https://en.wikipedia.org/wiki/Codec_2&quot; rel=&quot;nofollow noreferrer&quot;&gt;Codec 2&lt;/a&gt;.  &lt;a href=&quot;https://en.wikipedia.org/wiki/Winmor&quot; rel=&quot;nofollow noreferrer&quot;&gt;WINMOR&lt;/a&gt; competes with PACTOR for sending digital messages over HF in the Winlink system.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-04-06T18:39:13.597" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18285" PostTypeId="1" CreationDate="2021-04-06T19:01:14.787" Score="4" ViewCount="191" Body="&lt;p&gt;I am new to this, having just set up my station. I have &amp;quot;very bad&amp;quot; QRN on 40m: S9. Here is the setup:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;High density suburb with flats and houses&lt;/li&gt;&#xA;&lt;li&gt;Yaesu FT450D with fan dipole at 6m-9m above ground (sloping), this is lower than a building with flats to the North East. Wires for 40/20/10m, nicely resonant, checked with NanoVNA.&lt;/li&gt;&#xA;&lt;li&gt;1:1 Balun (ie choke) at feedpoint. 15 turns on FT240-52. No evidence of RF in shack.&lt;/li&gt;&#xA;&lt;li&gt;22m RG58 run back to station which is on first floor&lt;/li&gt;&#xA;&lt;li&gt;Station earth dropping about 3m from 1st floor to 1m driven ground stake (I realise this may not be effective, as run is too long)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;These are the things I have tried:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;40m QRN is consistently &amp;gt; S8 mostly S9 during the day. Grainy white noise.&lt;/li&gt;&#xA;&lt;li&gt;20m and 80m are only S3.&lt;/li&gt;&#xA;&lt;li&gt;Noise drops slightly at night but only 1S unit.&lt;/li&gt;&#xA;&lt;li&gt;Turning off all power in house with radio on battery reduces it to ~S7.5 so about 1 S-unit. Still a long way from level on 20m and 80m.&lt;/li&gt;&#xA;&lt;li&gt;I have tested calibration of S-meter on all bands with signal a generator and a 40db Attenuator. It's within spec acc to the service manual.&lt;/li&gt;&#xA;&lt;li&gt;There are some &amp;quot;VDSL&amp;quot; (UK broadband) training tones giving me a &amp;quot;birdie&amp;quot; every 4kHz. But this is only on some days and appears not related to the background S9 &amp;quot;grainy white noise floor&amp;quot;.&lt;/li&gt;&#xA;&lt;li&gt;Our own broadband line runs almost parallel to the dipole (I have put as much angle as I can but it's &amp;lt; 20 degrees). But turning our router off (as above) doesn't remove the &amp;quot;main&amp;quot; source.&lt;/li&gt;&#xA;&lt;li&gt;I cannot detect the &amp;quot;VDSL guard bands&amp;quot; at 5.2, 8.5, 12Mhz&lt;/li&gt;&#xA;&lt;li&gt;Noise appears solid across all of 40m, ~6Mhz to about 8Mhz&lt;/li&gt;&#xA;&lt;li&gt;I can make contacts on 40m but only with &amp;quot;booming&amp;quot; stations.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;Edit: additional info from discussion in comments below&lt;/strong&gt;&#xA;To test for radiated vs conducted noise I also performed these tests:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I have a second FT240-52 toroid with 10 turns of RG58 at the radio end about 10 inches before the PL259. It was spare so I thought I would add it. Made no difference.&lt;/li&gt;&#xA;&lt;li&gt;The radio running on battery without antenna is totally quiet on all bands.&lt;/li&gt;&#xA;&lt;li&gt;With linear 12V power supply it is also totally fine without antenna.&lt;/li&gt;&#xA;&lt;li&gt;As soon as I plug in the antenna I get S9 noise on 40m.&lt;/li&gt;&#xA;&lt;li&gt;The same even with a &amp;quot;random 5m wire thrown out the window and shoved into the centre of antenna connector on the back of the radio.&amp;quot;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;Also&lt;/strong&gt;: I was taking HTs for a walk with my son today, and we walked past one of those green (UK colours) Telecom boxes about 100m (?) from my dipole. The interference coming off that thing was enough to break through the squelch of our Baofeng HTs tuned to 2m. On FM! Similar cabinets around the neighbourhood showed no sign of interfering with the radios, even with the squelch fully off. Could be a lead?&lt;/p&gt;&#xA;&lt;p&gt;What is my logical next step?&lt;/p&gt;&#xA;&lt;p&gt;Run around the neighbourhood with a portable HF radio and a directional loop antenna? Requires some investment? How about a NanoSA, which might be a useful tool anyway?&lt;/p&gt;&#xA;&lt;p&gt;If I find source, what are options: 1. work with neighbours 2. use a phasing noise canceller?&lt;/p&gt;&#xA;&lt;p&gt;Any tips much appreciated&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Update:&lt;/strong&gt; I am in the process of building this loop: &lt;a href=&quot;https://ka7oei.blogspot.com/2021/02/rfi-radio-frequency-interference.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ka7oei.blogspot.com/2021/02/rfi-radio-frequency-interference.html&lt;/a&gt; The pre-amp is built and tested. Have made a wooden frame for the loop. Just needs putting together. I am hoping it will help me understand if I have one or many (major) noise sources. There is an 11kV distribution transformer about 40m from dipole, which would be a great candidate!&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Update#2&lt;/strong&gt;: Loop is built and seems to be working. I can receive distinct signals on the tinySA (see above link) and the loop is definitely very directional - able to completely null strong signals. What does it mean? I don't know yet. There is a contest on, so 40m band is drenched in &amp;quot;wanted&amp;quot; signals. :-) -- I may need another amplifier stage to look at the &amp;quot;noise&amp;quot; in more detail, but I suspected that, and left room for it on the circuit board. TBC... If anyone has experience in using such a loop with spectrum analyser please comment or add answer. I have a feeling operating the loop in a structured way to get meaningful results is going to be key.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Update#3&lt;/strong&gt;: First test results with loop - hard to interpret:&#xA;This is the Loop:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/C3ukT.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/C3ukT.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;And the preamp:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/yOE0Y.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/yOE0Y.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;And the tinySA fed from my dipole from 3-12Mhz, clearly showing the raised floor that I am also seeing on the S-meter.&#xA;&lt;a href=&quot;https://i.stack.imgur.com/oxIvc.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/oxIvc.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;And the tinySA showing the signal from the amplified loop &lt;strong&gt;standing under&lt;/strong&gt; the dipole.&lt;/p&gt;&#xA;&lt;p&gt;The loop is clearly working and showing signals. And these can be nulled by rotating, but it does not show the &amp;quot;raised floor&amp;quot;. Why? I am not sure how to interpret this.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/BIZCQ.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/BIZCQ.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;M7BTU&lt;/p&gt;&#xA;" OwnerUserId="18951" LastEditorUserId="18951" LastEditDate="2021-04-25T18:07:12.237" LastActivityDate="2021-04-25T18:07:12.237" Title="QRN: How to chase down a solid S9 noise floor on 40m only" Tags="&lt;hf&gt;&lt;rfi&gt;&lt;noise&gt;&lt;direction-finding&gt;&lt;reception&gt;" AnswerCount="5" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18286" PostTypeId="1" CreationDate="2021-04-06T19:47:43.233" Score="4" ViewCount="129" Body="&lt;p&gt;I know Morse code is sometimes used by &lt;a href=&quot;https://www.neilsquire.ca/about/history/&quot; rel=&quot;nofollow noreferrer&quot;&gt;people&lt;/a&gt; with limited use of their hands to &lt;a href=&quot;https://www.makoa.org/jlubin/morsecode.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;interact with their computer&lt;/a&gt;. One way is by using a straw connected to a pressure sensor, a so-called &lt;a href=&quot;https://en.wikipedia.org/wiki/Sip-and-puff&quot; rel=&quot;nofollow noreferrer&quot;&gt;sip-n-puff&lt;/a&gt; or SNP. I've also read mentions of people with handicaps &lt;a href=&quot;https://forums.qrz.com/index.php?threads/serious-question-about-deaf-hams-prior-to-droping-morse-code.483478/#post-3527035&quot; rel=&quot;nofollow noreferrer&quot;&gt;using it for ham radio purposes&lt;/a&gt;. Positive and negative pressure corresponds to dits or dahs, or maybe the other way around. There are several &lt;a href=&quot;http://www.tandemmaster.org/morse_code.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;commercial devices&lt;/a&gt;, and even &lt;a href=&quot;https://inclusivetechnologies.org/products/sip-n-puff-headset&quot; rel=&quot;nofollow noreferrer&quot;&gt;headsets&lt;/a&gt; that look quite handy, no pun intended.&lt;/p&gt;&#xA;&lt;p&gt;Reading about this has got me thinking: &lt;strong&gt;Is using your hand necessarily superior to using your mouth? Why not hook an SNP up to your keyer instead of a bug? Could you use even use it for QRQ? Are there examples of people doing this successfully on the air?&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Our mouths are very agile, and with some practice one can handle very quick and precisely timed breath changes. (In this I speak from my own experience playing fast paced Irish music music on the harmonica.)&lt;/p&gt;&#xA;&lt;p&gt;One big reason for looking at this in the first place is that I've been troubled by recurring hand pain. Being in possession of a perfectly healthy mouth, I can't help but think &amp;quot;why not use that instead of my hands?&amp;quot; Am I missing some reason not to do it this way? I wouldn't be able to talk while sending, but I would have both hands free.&lt;/p&gt;&#xA;&lt;p&gt;(If this works well, it might even be an option to practice my QRQ and use this with my computer to replace the keyboard eventually, if my hands keep messing with me.)&lt;/p&gt;&#xA;&lt;p&gt;EDIT: I got asked how fast I play in the comments. Just walking up and down the scale 500 breath changes per minute is not too hard to sustain. At 600 I keep missing holes and mess up the timing. 400 is easy. It doesn't translate perfectly to Morse characters, but with a keyer 200 cpm = 40 wpm doesn't sound unattainable. 30 wpm even more so. I'm just guessing though! It depends on the hardware and on exactly how reasonable the comparison is.&lt;/p&gt;&#xA;&lt;p&gt;EDIT2: I've gotten some suggestions for various computer interfaces. Using a computer, and even more units might be possible, but,  ideally, I would just have a small two-way switch that I can connect to a keyer or the keyer jack on my portable QRP station.&lt;/p&gt;&#xA;" OwnerUserId="18450" LastEditorUserId="18450" LastEditDate="2021-04-07T21:05:56.417" LastActivityDate="2021-04-10T16:47:36.223" Title="Could keying cw with your mouth using a sip-n-puff be as efficient as doing it by hand?" Tags="&lt;cw&gt;&lt;disability&gt;" AnswerCount="4" CommentCount="12" ContentLicense="CC BY-SA 4.0" />
  <row Id="18287" PostTypeId="2" ParentId="18285" CreationDate="2021-04-06T20:01:58.900" Score="2" Body="&lt;p&gt;I'd suggest trying a different time of day, a different radio, a different antenna, and a different location; not necessarily all at the same time though.  There's probably nothing wrong with your antenna, but you might get different results at different heights, or if you raise the height of the ends to the same height as the middle.&lt;/p&gt;&#xA;&lt;p&gt;Have you tested the noise level at different times of the day?  Maybe there is a lot less noise at 4 AM.  That would be a clue.&lt;/p&gt;&#xA;&lt;p&gt;You could ask other local hams who are on 40m.  What are their noise levels?  Are they using vertically-polarized or horizontally-polarized antennas?  Your high noise level might be particular to your neighborhood, and asking several different hams might help answer that question.  If a local ham reports that his or her noise level is lower, you might ask if you could test your radio in his or her shack.  The problem isn't likely to be the radio, but it's possible, and testing your radio against another radio with the same antenna could help determine whether the radio is the problem or not.&lt;/p&gt;&#xA;&lt;p&gt;You could try a portable HF radio and a loop antenna, but those can be expensive; you could also try your existing radio powered by a battery connected to a 40m dipole flung up into the trees in a nearby park or wilderness area, if you have such places in your area that allow such things.  If your problem is local noise, which it likely is, then your radio and a dipole in a rural or wilderness area would likely be quite an improvement (assuming that you live in an urban area).&lt;/p&gt;&#xA;&lt;p&gt;Once you have a better idea of the source of the problem, then you can think about potential ways to narrow the problem down further, or ameliorate or solve the it.  If your problem is local noise, then there are lots of questions and answers on this site about tracking down and dealing with local RFI.  Feel free to ask a new question once you know more.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-04-06T20:01:58.900" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18288" PostTypeId="2" ParentId="18285" CreationDate="2021-04-06T20:26:27.497" Score="2" Body="&lt;p&gt;Start by trying to determine if the noise is &amp;quot;conducted&amp;quot; or &amp;quot;radiated&amp;quot; into your receiver. Basically, &amp;quot;conducted&amp;quot; noise gets into your receiver from the power supply or a ground wire or some other cable. &amp;quot;Radiated&amp;quot; noise gets in via the antenna.&lt;/p&gt;&#xA;&lt;p&gt;Start by powering your radio with a battery instead of the mains-powered supply. Or borrow a battery-powered shortwave radio, preferably one that accepts an external antenna. (If the alternate radio is quiet, you've just learned something very useful!)&lt;/p&gt;&#xA;&lt;p&gt;Remove the antenna cable and &lt;strong&gt;all&lt;/strong&gt; other connections to the radio. All bands should be very quiet. (If they aren't, you have a more serious problem than I would know how to deal with!) Begin adding cables to the radio, starting with the mains-powered supply and ending with a short length of coax that is open at the far end. Finally, connect the coax that goes to the antenna.&lt;/p&gt;&#xA;&lt;p&gt;You may learn from this process that you have one or more major and/or minor culprits. What you learn will help determine the remedial steps to take. Please amend your question, or start a new question, when you have gone through this procedure.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-04-06T20:26:27.497" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18289" PostTypeId="1" AcceptedAnswerId="18290" CreationDate="2021-04-06T22:04:38.190" Score="1" ViewCount="49" Body="&lt;p&gt;I am trying to download my Baofeng UV-5R into CHIRP for the first time and it is asking what port to pull information from. How can I find what to input here since it isn't automatically updating/ what do I need to fix to get it to automatically input?&lt;a href=&quot;https://i.stack.imgur.com/5mfXS.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/5mfXS.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19296" LastActivityDate="2021-04-13T01:47:26.760" Title="How can I find the input port for downloading my radio information?" Tags="&lt;radio-programming&gt;&lt;uv-5r&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18290" PostTypeId="2" ParentId="18289" CreationDate="2021-04-07T00:32:44.980" Score="3" Body="&lt;p&gt;The program is asking you which serial port you're using to connect to the radio.  If CHIRP's list is empty, then you probably have no serial ports because the drivers for the virtual serial port chip in your cable aren't installed, or your cable or virtual serial port chip just isn't working.&lt;/p&gt;&#xA;&lt;p&gt;If CHIRP isn't picking a serial port for you automatically, but there are some in the list, then you may have more than one serial port or &amp;quot;virtual&amp;quot; serial port in your computer, and your problem is to figure out which one belongs to your cable.&lt;/p&gt;&#xA;&lt;p&gt;If you have more than one serial port in the list and you're using a USB-to-serial adapter cable, which most people use, then there are ways to find the identifier of the virtual serial port associated with your cable.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;In Windows, pull up the Device Manager and plug and unplug the cable a few times.  The serial port associated with your cable will appear and disappear in the Device Manager as you plug and unplug the cable.&lt;/li&gt;&#xA;&lt;li&gt;In macOS, open Terminal and enter the command &lt;code&gt;ls /dev/cu.*&lt;/code&gt; to list all serial devices, then unplug or plug in the cable, run the command again, and see what appeared or disappeared.&lt;/li&gt;&#xA;&lt;li&gt;In Linux, unplug and plug in the cable (once), and run &lt;code&gt;sudo dmesg | less&lt;/code&gt;; the output should give you a few clues.  If you only have one virtual serial port then the one you're looking for is probably /dev/ttyUSB0 in Linux.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="76" LastEditDate="2021-04-13T01:47:26.760" LastActivityDate="2021-04-13T01:47:26.760" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18291" PostTypeId="2" ParentId="18286" CreationDate="2021-04-07T00:55:52.173" Score="1" Body="&lt;p&gt;An SNP isn’t very fast at all*. If you’re okay with your mouth being “in use” perhaps a bite-actuated switch in place of (and configured the same as) a straight key would be better. You could “key” much faster that way, I’d bet.&lt;/p&gt;&#xA;&lt;p&gt;Just make absolutely sure to avoid RF burns in the mouth. :-)&lt;/p&gt;&#xA;&lt;p&gt;Prototype could be as simple as some contacts and wires on the “open” end of a spring-loaded clothespin with some kind of durable vinyl sleeve over it. Bite the clothespin “open” to close the contacts, release to let the clothespin close (opening the contacts). This way it would behave as a “normally-open” switch.&lt;/p&gt;&#xA;&lt;p&gt;*See comments. My info about SNP detection speed may be outdated.&lt;/p&gt;&#xA;" OwnerUserId="18693" LastEditorUserId="18693" LastEditDate="2021-04-07T11:28:52.590" LastActivityDate="2021-04-07T11:28:52.590" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18292" PostTypeId="2" ParentId="1646" CreationDate="2021-04-07T10:21:13.140" Score="0" Body="&lt;p&gt;We all listen to our radio parked on a certain frequency, that may happen to be a repeater output, we may or may not jump in, all the time.&lt;/p&gt;&#xA;&lt;p&gt;Echolink is just a different implementation of the same thing (IP instead of RF).&lt;/p&gt;&#xA;&lt;p&gt;Echolink may announce the connecting party, which i guess where the question of etiquette comes from.&lt;/p&gt;&#xA;&lt;p&gt;There's nothing official, but i don't think it's rude, others may disagree (which is fine).&lt;/p&gt;&#xA;" OwnerUserId="17200" LastActivityDate="2021-04-07T10:21:13.140" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18293" PostTypeId="2" ParentId="18285" CreationDate="2021-04-07T13:47:51.563" Score="2" Body="&lt;p&gt;If the RF noise is that strong, then you should be able to pick it up with a much smaller movable antenna.  Even scrap wire or conductive tape on a large cardboard box.  That may allow you to build small directional antennas (tiny loop and stub dipole) to determine if the noise is stronger from some specific directions, or a polarized antenna to determine the noise polarization, if any.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-04-07T13:47:51.563" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18294" PostTypeId="2" ParentId="18286" CreationDate="2021-04-07T14:13:59.677" Score="2" Body="&lt;p&gt;The SNP specs that I can find online say they can differentiate puffs shorter than 0.25 seconds, which should be good for use as a straight key at at least 5 wpm (maybe 3 to 5X slower than skilled hand keying).&lt;/p&gt;&#xA;&lt;p&gt;You’ll have to try one out to see if a trained wind instrument musician could operate one faster than these published numbers.  Or if a sideswiper, cootie, or bug mode could be used, with both sips and puffs.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-07T16:30:35.797" LastActivityDate="2021-04-07T16:30:35.797" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18295" PostTypeId="2" ParentId="18285" CreationDate="2021-04-07T16:58:19.720" Score="2" Body="&lt;p&gt;You might consider an RF choke at the interface between your radio and feed line.&lt;/p&gt;&#xA;&lt;p&gt;The choke at the feed point will help prevent common mode current reflecting from the antenna... but the outside of the shield can still be a source of noise on receive if it's not also choked at the receiver.&lt;/p&gt;&#xA;&lt;p&gt;In fact, you might test what happens when you put a dummy load at the feed point, and then with/without a choke at the transceiver/feedline.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Edited to add&lt;/strong&gt;: I think the next thing I'd suggest is to see if a local ham has something similar to the MFJ-1026 noise canceler (using a second antenna, mix the noise back into the line, phase-shifted 180° to blank it out). (am not affiliated w MFJ, and there are probably less expensive products out there).&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2021-04-21T16:11:45.887" LastActivityDate="2021-04-21T16:11:45.887" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18296" PostTypeId="2" ParentId="18285" CreationDate="2021-04-07T20:21:27.813" Score="1" Body="&lt;p&gt;You've received several good answers here. To Brian's &lt;a href=&quot;https://ham.stackexchange.com/a/18288/8717&quot;&gt;answer&lt;/a&gt; suggesting that you should try powering it from a battery, I would add start with your own house before running around the neighborhood with a radio by &lt;strong&gt;turning off your main circuit breaker&lt;/strong&gt;.  This will determine whether or not the RFI is coming from something in your house, which is quite likely.&lt;/p&gt;&#xA;&lt;p&gt;If your noise significantly decreases, then turn on one branch circuit at a time until it appears again. You may have more than one RFI source, so turn on just one breaker at a time.&lt;/p&gt;&#xA;&lt;p&gt;A nearby amateur mostly solved his noise by unplugging a laptop charger. Any unfiltered switching power supply will do this, even if the device is plugged in and not turned on.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2021-04-07T20:26:41.963" LastActivityDate="2021-04-07T20:26:41.963" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18297" PostTypeId="2" ParentId="18286" CreationDate="2021-04-07T20:43:40.503" Score="1" Body="&lt;p&gt;There appear to be MIDI harmonica controller products, as well as keyer software that takes MIDI input.  Probably designed from the start to be highly responsive to fast musical rhythms from air pressure change input.  And with keyer software support already adapted.&lt;/p&gt;&#xA;&lt;p&gt;See: &lt;a href=&quot;https://www.lekholminstruments.com&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.lekholminstruments.com&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-04-07T20:43:40.503" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18298" PostTypeId="1" CreationDate="2021-04-08T00:10:25.867" Score="4" ViewCount="121" Body="&lt;p&gt;I've seen a reference to the callsign A7RW. I can't find it in the FCC database or by searching the ARRL. Is it a legitimate US callsign?&lt;/p&gt;&#xA;" OwnerUserId="19309" LastEditorUserId="966" LastEditDate="2021-04-08T06:38:13.057" LastActivityDate="2021-04-08T06:38:13.057" Title="Is A7RW a legal call sign?" Tags="&lt;united-states&gt;&lt;legal&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18300" PostTypeId="2" ParentId="18298" CreationDate="2021-04-08T01:50:17.633" Score="6" Body="&lt;p&gt;A7RW would be the call sign of a ham in Qatar, rather than the United States.  The prefixes AA – AL are allocated to the United States.  So AA7RW, AB7RW, AC7RW, etc. up to AL7RW would be valid US call signs.&lt;/p&gt;&#xA;&lt;p&gt;The FCC have certain call signs that they won't issue, like a call sign with a three-letter suffix starting with X (so I heard, can't find a source), such as AA7XWW.  I don't know that such a call sign could be called &amp;quot;illegal&amp;quot; though, because the rule might not be codified into law.  The FCC issues all call signs, so they could simply refuse a request for such a vanity call sign according to an internal rule that hasn't been publicized or made law.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-04-08T01:50:17.633" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18301" PostTypeId="1" AcceptedAnswerId="18302" CreationDate="2021-04-08T17:55:31.310" Score="3" ViewCount="293" Body="&lt;p&gt;I recently moved to another house.  My setup's current coax is 50ft/RG8x/PL259 (bought in 2018), but it is not enough for connecting my antenna to where I want to place the radio.  I believe that 50ft more will be enough.&#xA;Should I:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Buy an additional 50ft rg8x coax?&lt;/li&gt;&#xA;&lt;li&gt;Buy an 100ft RG8x coax?&lt;/li&gt;&#xA;&lt;li&gt;Buy an 100ft coax of &amp;quot;better&amp;quot; quality (RG8, LMR-240, etc.)?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;My current home setup:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;TYT MD-9600 Dual Band DMR Digital Mobile Radio (UHF/VHF)&lt;/li&gt;&#xA;&lt;li&gt;Tram 1481 Amateur Dual Band Base Antenna&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="11385" LastActivityDate="2021-04-08T18:46:25.783" Title="Recomended coax for 100ft (2m/70cm)" Tags="&lt;coaxial-cable&gt;&lt;2m-band&gt;&lt;70cm-band&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18302" PostTypeId="2" ParentId="18301" CreationDate="2021-04-08T18:46:25.783" Score="6" Body="&lt;p&gt;According to &lt;a href=&quot;https://kv5r.com/ham-radio/coax-loss-calculator/&quot; rel=&quot;noreferrer&quot;&gt;this online coax loss calculator&lt;/a&gt;, the loss of 50 feet of new Belden 9258 RG-8X with an antenna with an SWR of 1.5 is 4.29 dB at 450 MHz (UHF), so the loss for 100 feet of the same coax would be 8.6 dB.  If you switched to fancier coax such as LMR-400, the loss for 100 feet of coax would be 2.8 dB.&lt;/p&gt;&#xA;&lt;p&gt;So if you bought another 50' of RG-8X your coax loss would be 4.3 dB worse than it was before (plus a little more for the connector between the two 50' pieces).  If you discarded the RG-8X and installed 100' of LMR-400, then your coax loss would be about 1.5 dB better than it was before.&lt;/p&gt;&#xA;&lt;p&gt;How much difference would another 4 dB of loss make?  (If you're unfamiliar with decibels, see &lt;a href=&quot;https://ham.stackexchange.com/questions/6676/how-big-is-a-decibel&quot;&gt;How big is a decibel?&lt;/a&gt;.)  4 dB is less than an S-unit (6 dB), if you're familiar with operating on HF.  If you were mainly connecting to repeaters and had good strong signals from those repeaters before, then you probably wouldn't notice another 4 dB of loss when connecting to those repeaters.  If you talked to simplex stations with weak scratchy FM audio that you could barely copy before, or digital stations that were right on the edge of the &amp;quot;digital cliff&amp;quot;, then you might not be able to copy similar stations if your coax had another 4 dB of loss.&lt;/p&gt;&#xA;&lt;p&gt;Mind you, these calculations are for the 70cm band.  You'll have a lot less loss at 2m.&lt;/p&gt;&#xA;&lt;p&gt;Another factor to take into consideration is that the rule-of-thumb I was taught is to replace coaxial cable roughly every ten years.  Your existing cable already has three years or so in it.&lt;/p&gt;&#xA;&lt;p&gt;TL;DR if you talk mainly to repeaters, another 50' of RG-8X would probably be fine.  If you like to work weak stations on UHF, consider upgrading your coax.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-04-08T18:46:25.783" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18303" PostTypeId="2" ParentId="18286" CreationDate="2021-04-09T21:07:37.203" Score="1" Body="&lt;p&gt;SNP keys have been built, and were apparently described  in Mars 2004 QST. As I'm not a member of ARRL I can't access it, but the first page of the article can bee seen in the following video:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://www.youtube.com/watch?v=wsE-S2eXhK0&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.youtube.com/watch?v=wsE-S2eXhK0&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;It says that &amp;quot;experienced users routinely reach 25 wpm or more&amp;quot;, which could be interpreted as being comparable with a paddle key. They do continue with saying that &amp;quot;for most of us the puff-and-sip key will never quite match the speed and convenience of paddles&amp;quot;, but this could mean various things. If the comparison concerns an operator with long experience with paddles and none with SNP, it doesn't necessarily reflect negatively on the latter.&lt;/p&gt;&#xA;&lt;p&gt;In the video, the author demonstrates a straight key version, with only one switch. He then notes that he can send faster than with a normal straight key! He only uses blowing to actuate the key, but his contraption seems to use Bernoulli's principle (?) and should work for inhaling as well. If that's correct, and if the switch is fast enough, it should be possible to operate it like a SNP cootie key!&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;All in all, it seems like SNP systems can be (at least) good enough to make full speed QSO's.&lt;/strong&gt;&lt;/p&gt;&#xA;" OwnerUserId="18450" LastEditorUserId="18450" LastEditDate="2021-04-10T16:47:36.223" LastActivityDate="2021-04-10T16:47:36.223" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18304" PostTypeId="1" AcceptedAnswerId="18321" CreationDate="2021-04-11T10:26:40.590" Score="1" ViewCount="67" Body="&lt;p&gt;&lt;a href=&quot;https://www.qsl.net/kd2bd/splat.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;Splat&lt;/a&gt; seems like it's a great tool for modelling what RF coverage I should have. It can create a nice circle around me, after I download topology data from USGS, namely SRTM-1.&lt;/p&gt;&#xA;&lt;p&gt;But when the coverage map (created using &lt;code&gt;-L 17&lt;/code&gt;) gets created it looks kind of like the logo on the Splat home page, which means I can't tell what's where on the map anymore.&lt;/p&gt;&#xA;&lt;p&gt;Is there data for London (UK) I can overlay to make it clearer? I think I'm looking for cartographic boundary data. So it's &lt;a href=&quot;https://data.london.gov.uk/dataset/statistical-gis-boundary-files-london&quot; rel=&quot;nofollow noreferrer&quot;&gt;this&lt;/a&gt;? But how do I convert it to the format that Splat wants?&lt;/p&gt;&#xA;" OwnerUserId="9636" LastEditorUserId="9636" LastEditDate="2021-04-11T10:38:49.617" LastActivityDate="2021-04-14T16:39:04.797" Title="Where can I find London borough outlines for SPLAT!" Tags="&lt;antenna-modeling&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18305" PostTypeId="1" CreationDate="2021-04-12T09:09:12.373" Score="2" ViewCount="64" Body="&lt;p&gt;&lt;strong&gt;KK4UOT&lt;/strong&gt;...   I'm moving from Nashville, to Barcelona area Spain.&#xA;My current license is for a technician, which I know is not enough to obtain an EU transmit operators, but I am curious, if I upgrade my license in the USA before completing my move, can it transfer? I am fully ready to take and almost surely pass the General license, but I would need to get it together/study for the Extra license.&lt;/p&gt;&#xA;&lt;p&gt;Or, perhaps it is simpler to start over in Europe? If I need to start all over in Europe, is the process ONLY 1 level of certification? (Specifically Spain) I am not sure of the local community as my HF radio is in the states, I can only see handheld/repeater/dmr traffic. As of now, I remain silent in Europe.&lt;/p&gt;&#xA;&lt;p&gt;Any advice from anyone who has been through this would be most welcome! Thanks!&lt;/p&gt;&#xA;" OwnerUserId="19358" LastEditorUserId="218" LastEditDate="2021-04-12T13:41:35.717" LastActivityDate="2021-04-15T03:59:42.440" Title="If I upgrade my USA license before moving to Spain, will it transfer?" Tags="&lt;legal&gt;&lt;license&gt;&lt;europe&gt;&lt;spain&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18306" PostTypeId="1" CreationDate="2021-04-12T09:38:54.290" Score="0" ViewCount="68" Body="&lt;p&gt;I was wondering whether quick testing of various commercial ISM band transmitters for operation can be accomplished with some sort of off the shelf universal receiver which only turns on a led upon getting anything in the ISM band. Think key fobs, wireless plugs and thermometers, etc. as transmitters.&lt;/p&gt;&#xA;&lt;p&gt;Maybe something like this thinggie - &lt;a href=&quot;https://www.ebay.com/itm/DC-12V-1-CH-433MHz-Relay-Switch-Receiver-Module-for-Garage-Door-LED-Light/274727253469?hash=item3ff70535dd:g:G8gAAOSwkp9gVcOq&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.ebay.com/itm/DC-12V-1-CH-433MHz-Relay-Switch-Receiver-Module-for-Garage-Door-LED-Light/274727253469?hash=item3ff70535dd:g:G8gAAOSwkp9gVcOq&lt;/a&gt; ?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;edit&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Does the key fob emit a spread spectrum signal ? Oh, I had no idea. Ok, let's stick to OOK, FSK at most. @Brian K1LI's solution is actually viable. IT was about 5 years ago when I took one such receiver, plugged it in to my PC's sound board through a 100nF cap and surely enough, Audacity showed up my signal: &lt;a href=&quot;https://ham.stackexchange.com/q/6916/8811&quot;&gt;different digital modulations interference. Does it happen?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I think that with a bigger cap / with this cap and a tiny led, what I am after can be done. But... I want it already built. User should have to only power on the device, maybe adjust a variable cap and watch the led.&lt;/p&gt;&#xA;" OwnerUserId="8811" LastEditorUserId="8811" LastEditDate="2021-04-12T16:09:02.180" LastActivityDate="2021-04-12T16:09:02.180" Title="universal 433 MHz test lamp (receiver)" Tags="&lt;receiver&gt;&lt;testing&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18307" PostTypeId="2" ParentId="18306" CreationDate="2021-04-12T11:53:27.483" Score="0" Body="&lt;p&gt;Here's an example of an inexpensive &lt;a href=&quot;https://rads.stackoverflow.com/amzn/click/com/B016V18KZ8&quot; rel=&quot;nofollow noreferrer&quot; rel=&quot;nofollow noreferrer&quot;&gt;unit&lt;/a&gt; that might meet your requirements:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/MXtbX.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/MXtbX.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The receiver module, on the right, has part number &lt;a href=&quot;https://acoptex.com/project/183/basics-project-037a-rf-315330433-mhz-xd-fst-xd-rf-5v-transmitterreceiver-at-acoptexcom/&quot; rel=&quot;nofollow noreferrer&quot;&gt;XD-RF-5V&lt;/a&gt;. According to several internet searches for &amp;quot;XD-RF-5V datasheet,&amp;quot; the system uses Amplitude Shift Keying - ASK. Inasmuch as the modules are intended for connection to an Arduino or other digital means for decoding, this implies that on/off from the transmitter produces on/off at the receiver's DATA pins. A &lt;a href=&quot;https://www.youtube.com/watch?v=RHJVyMYJ1XQ&quot; rel=&quot;nofollow noreferrer&quot;&gt;YouTube video&lt;/a&gt; demonstrates this simple mode of operation using a breadboard.&lt;/p&gt;&#xA;&lt;p&gt;Whether you can visually detect the presence of a particular input signal at the receiver by observing an LED may depend on the rate, duration and occurrence frequency of the transmitted signal. But, it would be a simple matter to connect the receiver to an Arduino and write a simple sketch to latch an LED &amp;quot;on&amp;quot; when a DATA pin goes high, or latch it with a simple IC.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-04-12T11:53:27.483" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="18308" PostTypeId="2" ParentId="18306" CreationDate="2021-04-12T13:39:16.157" Score="3" Body="&lt;p&gt;It is not generally feasible to detect &amp;quot;anything&amp;quot;. The problem is there's always &lt;em&gt;something&lt;/em&gt;, even if it is just noise. To know if something is signal or just noise you need to know something about the signal, but when you want to detect &amp;quot;anything&amp;quot; this means you must enumerate every kind of signal that could exist, which is of course not feasible.&lt;/p&gt;&#xA;&lt;p&gt;Your best bet is likely a cheap SDR, like many of those based on the RTL2832U. With such a device you can at least receive whatever signal and/or noise may exist in the ISM band and display it on a waterfall, and from there make some guesses about the presence or absence of a signal.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-12T13:39:16.157" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18309" PostTypeId="2" ParentId="9574" CreationDate="2021-04-12T20:54:01.750" Score="0" Body="&lt;p&gt;B210 over USB with stock UHD image can't act like that. Port A is for standard use which is controlled over USB, port B could be used with written custom program inside FPGA. BTW search some info about FULL DUPLEX mode in Open BTS project as for example.&lt;/p&gt;&#xA;" OwnerUserId="19377" LastEditorUserId="8573" LastEditDate="2021-04-17T08:44:13.680" LastActivityDate="2021-04-17T08:44:13.680" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18310" PostTypeId="1" AcceptedAnswerId="18315" CreationDate="2021-04-13T09:14:59.133" Score="0" ViewCount="92" Body="&lt;p&gt;I'm currently reading &amp;quot;Reflections: Transmission Lines and Antennas&amp;quot; by M. Walter Maxwell, W2DU. This book explains well why the energy is not lost because of high SWR during transmitting, assuming the feedline and ATU are lossless. It also provides plots that allow determining the actual loss when the feedline has losses.&lt;/p&gt;&#xA;&lt;p&gt;Related links:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/2297/what-happens-in-a-low-loss-feed-line-with-a-high-swr&quot;&gt;What happens in a low loss feed-line with a high SWR&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/7333/what-is-the-actual-loss-in-a-feed-line-with-high-swr&quot;&gt;What is the actual loss in a feed line with high SWR?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/18318/when-does-a-transceiver-re-reflect-100-of-reflected-power&quot;&gt;(When) does a transceiver re-reflect 100% of reflected power?&lt;/a&gt;&lt;/li&gt;&#xA;&lt;li&gt;&lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf&lt;/a&gt; (see Fig 1)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;What I don't quite understand though is what happens to the &lt;strong&gt;received&lt;/strong&gt; signal level in the high SWR case.&lt;/p&gt;&#xA;&lt;p&gt;Let's say the antenna impedance on a given frequency is 100 Ohm, the feedline is lossless 50 Ohm, the transceiver input impedance is 50 Ohm. Between the antenna feed point and the feedline SWR = 2, 11% reflected power. Case a) there is no ATU. Case b) there is a lossless LC-match between the transceiver and the feedline that matches seen impedance to 50 Ohm. How much of the received power will be delivered to the transciever in cases a) and b)?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2021-04-14T07:34:18.257" LastActivityDate="2021-04-14T07:34:18.257" Title="What happens to the signal level if the antenna has high SWR?" Tags="&lt;antenna-theory&gt;&lt;impedance-matching&gt;&lt;feed-line&gt;&lt;antenna-tuner&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18313" PostTypeId="2" ParentId="18310" CreationDate="2021-04-13T15:46:10.623" Score="1" Body="&lt;p&gt;If the antenna isn't lossless (e.g. not superconducting), then some of the received RF energy reflected back into the antenna due a feedpoint mismatch will eventually be dissipated as heat in the antenna, or re-radiated as RF.  But for received signals this is possibly only a loss of nanoWatts or picoWatts.&lt;/p&gt;&#xA;&lt;p&gt;However, not only is reflected signal energy dissipated or lost, but so is reflected noise (within the bandwidth of interest).  Thus, the signal-to-noise ratio at the receiver will stay roughly the same.  As long as they are above the receiver's input noise floor, the receiver AGC or RF gain can compensate for this slight signal level difference, and the lost energy due to the mismatch won't be noticed.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-13T15:58:59.297" LastActivityDate="2021-04-13T15:58:59.297" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18314" PostTypeId="2" ParentId="18310" CreationDate="2021-04-13T15:58:01.557" Score="2" Body="&lt;p&gt;I think you've answered your own question.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;In case a&lt;/strong&gt;, with an antenna with 2:1 SWR and an otherwise lossless system, 11% of the power will be reflected and re-radiated by the antenna, so 89% makes it to the receiver.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;In case b&lt;/strong&gt;, all of the power will be delivered to the receiver.&lt;/p&gt;&#xA;&lt;p&gt;Antennas are reciprocal, so all losses in transmit are the same as losses in receive. We usually calculate for the transmit case, the sequence of mismatches and losses is different in the receive case but the answer will be the same.&lt;br /&gt;&#xA;The matching circuit that makes the 100 ohm antenna look like 50 ohms, will also make the 50 ohm coax look like 100 ohms, for the antenna.&lt;/p&gt;&#xA;&lt;p&gt;Some interesting caveats:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The receiver input impedance may not be 50 ohms. Professional equipment is usually well matched so that its behaviour is predictable, but amateur transceivers might not be, and at least at HF, there is no strong reason to be at 50 ohms on receive.&lt;/li&gt;&#xA;&lt;li&gt;antennas, even a dipole well matched to the transmission line, still scatter a lot of the power. They have a significant radar cross section; the currents generated by the incident field will radiate as well as feeding the coax.&lt;/li&gt;&#xA;&lt;li&gt;so, saying &amp;quot;All the power&amp;quot; isn't all that clear; all of what power? It's really just the best case against which other scenarios can be measured.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-04-13T19:10:57.023" LastActivityDate="2021-04-13T19:10:57.023" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18315" PostTypeId="2" ParentId="18310" CreationDate="2021-04-13T16:46:01.533" Score="4" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;Let's say the antenna impedance on a given frequency is 100 Ohm, the feedline is lossless 50 Ohm, the transceiver input impedance is 50 Ohm. Between the antenna feed point and the feedline SWR = 2, 11% reflected power.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;This is a bit of dangerous thinking, because the distance between the antenna feedpoint and the feedline is zero. As such there can be no standing waves, and no ratio between the maximum and minimum RMS voltage.&lt;/p&gt;&#xA;&lt;p&gt;A 50 ohm feedline terminated in a 50 ohm load (the receiver) is indistinguishable from a 50 ohm load without a feedline. So really, what you are asking is what happens when a 100 ohm source is connected to a 50 ohm load. The feedline is irrelevant.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/596Uj.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2f596Uj.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;Is this necessarily bad? True, if you can't change R1, then R2 should also be 100 ohms if you want to maximize the power in R2. But if R2 is zero ohms, current is maximized. And if R2 is open, voltage is maximized. What do you want to maximize, power, current, or voltage?&lt;/p&gt;&#xA;&lt;p&gt;For a receiver, the answer is probably none of these. Instead, you want to maximize the signal to noise ratio. Extracting the maximum power from the antenna &lt;em&gt;might&lt;/em&gt; be important, especially as noise power from sources internal to the receiver, such as thermal noise, become significant relative to what's available from the feedpoint. But this is only one of many considerations. For example, the receiver likely has some passive filter which was designed with a particular source impedance assumed. When the source impedance deviates from the design value, the filter performance may degrade.&lt;/p&gt;&#xA;&lt;p&gt;So, your question is actually quite difficult to answer. Receivers aren't simply resistive loads: they also have filters and active, nonlinear electronics, and the power extracted from the antenna is only indirectly relevant to receiver performance. Ultimately the answer depends on the receiver details.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-13T16:46:01.533" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18316" PostTypeId="1" AcceptedAnswerId="18317" CreationDate="2021-04-14T05:16:58.717" Score="7" ViewCount="473" Body="&lt;p&gt;I am newly licensed (Technician) and bought a UV-5RA as a cheap way to check out what's going on in my area and see if I'm finding it interesting enough to get a better UHF/VHF HT.&lt;/p&gt;&#xA;&lt;p&gt;The other day I was listening to a conversation happening on a local repeater and when one of the guys gave their call I looked it up for the heck of it and it turned out he was near me.  That made me curious to see if I could receive him directly, so I switched the radio from &amp;quot;channel&amp;quot; mode to &amp;quot;free-tune&amp;quot; mode and tuned to the repeater's receive frequency.&lt;/p&gt;&#xA;&lt;p&gt;Turned out I could hear him.  However, I could not hear a CTCSS tone on his transmission.  The repeater in question uses one (I checked in the local listings and on RepeaterBook) so the person talking through the repeater had to be transmitting one.  And according to various references, the tones run (approximately) from 67Hz to 250Hz.&lt;/p&gt;&#xA;&lt;p&gt;Those frequencies are well within the human range of hearing (for example, the fundamental frequency for adult male speech is generally in the 85-180Hz range), so why didn't I hear them when listening to the repeater receiver frequency?&lt;/p&gt;&#xA;&lt;p&gt;Similarly, when doing some UV-5R receive testing by transmitting to it from an old Motorola GMRS Talkabout (I know not to transmit back to it) I did not hear any tones, even though the Talkabout has PL turned on.&lt;/p&gt;&#xA;&lt;p&gt;Is it as simple as the CTCSS tone is simply transmitted at a such low intensity level that it is hard to hear?  Or is something else going on?&lt;/p&gt;&#xA;" OwnerUserId="19193" LastEditorUserId="19193" LastEditDate="2021-04-14T14:06:44.000" LastActivityDate="2021-04-15T01:14:06.127" Title="Why don't I hear the CTCSS tones when listening on the repeater input frequency?" Tags="&lt;repeater&gt;&lt;uv-5r&gt;&lt;tone-squelch&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18317" PostTypeId="2" ParentId="18316" CreationDate="2021-04-14T05:38:08.423" Score="9" Body="&lt;p&gt;Many radio manufacturers are aware that people don't want to hear CTCSS tones - so they put high-pass filters on both the output (speaker) and input (microphone).&lt;/p&gt;&#xA;&lt;p&gt;That eliminates the tone before it gets to your ears, and will also prevent an errant tone near the microphone from triggering a repeater somewhere.&lt;/p&gt;&#xA;&lt;p&gt;Some of us might not agree that the tones are within human hearing range - at least, not all of them for all of us!&lt;/p&gt;&#xA;" OwnerUserId="966" LastActivityDate="2021-04-14T05:38:08.423" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18318" PostTypeId="1" CreationDate="2021-04-14T07:33:28.617" Score="4" ViewCount="269" Body="&lt;p&gt;There has been a long discussion of one question &lt;a href=&quot;https://ham.stackexchange.com/a/7348/13598&quot;&gt;here&lt;/a&gt;. Phil, W8II and I agreed that it's better to post a separate question.&lt;/p&gt;&#xA;&lt;p&gt;There are several sources (some editions of &amp;quot;The ARRL Handbook&amp;quot;, &amp;quot;Reflections: Transmission Lines and Antennas&amp;quot;, &lt;a href=&quot;http://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;Understanding SWR by Example&lt;/a&gt;) where you can find plots like this one:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/eRcag.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/eRcag.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Let's say the antenna impedance on a given frequency is 250 Ohm, the feedline is 50 Ohm. Between the antenna feed point and the feedline SWR = 5, ~44% reflected power. The model says that 44% of the transmitted power will be reflected from the antenna to the feedline, re-reflected by the transceiver, and go back to the antenna. If the feedline is lossless, eventually 100% of power will be radiated, regardless of SWR. If the feedline has losses, there will be additional losses as the plot shows.&lt;/p&gt;&#xA;&lt;p&gt;The problem is that none of the sources explains well &lt;strong&gt;why the transceiver suppose to re-reflect all the power&lt;/strong&gt;. Actually, in &amp;quot;Reflections&amp;quot; on p13-5 it's said that the model is not valid for modern solid-state PA. This is what the long discussion was about.&lt;/p&gt;&#xA;&lt;p&gt;Phil suggested that what actually was meant is that &lt;em&gt;a tuner&lt;/em&gt; between the transceiver and the feedline re-reflects the power (a tuner is lossless for this model), not the transceiver per se. If this is true, I don't quite understand the situation either. On one hand, it is stated that since the PA sees 1:1 SWR there is no reflected power going through the tuner. This makes sense. But for &lt;strong&gt;received&lt;/strong&gt; signals, we say that the same tuner matches whatever impedance it sees to 50 Ohm and passes all the signals through to the transceiver. I don't see how it's possible for the same device to pass signals in one case and reflect in another when signals go in the same direction, to the transceiver.&lt;/p&gt;&#xA;&lt;p&gt;So actually I have several questions: 1) is the described model accurate for modern transceivers? 2) if yes, is a tuner required? if no, why? 3) does the tuner actually passes the received signals and reflects the transmitted signals?&lt;/p&gt;&#xA;" OwnerUserId="13598" LastEditorUserId="13598" LastEditDate="2021-04-14T20:55:36.027" LastActivityDate="2021-05-30T00:59:30.303" Title="(When) does a transceiver re-reflect 100% of reflected power?" Tags="&lt;antenna-theory&gt;&lt;impedance-matching&gt;&lt;feed-line&gt;&lt;transmission-line&gt;" AnswerCount="5" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18320" PostTypeId="2" ParentId="18316" CreationDate="2021-04-14T12:15:06.430" Score="3" Body="&lt;p&gt;The volume of the tones is typically low enough with respect to the voice signal that you can't hear it.  Occasionally the tone generator in a radio will be poorly calibrated, and you do hear it.&lt;/p&gt;&#xA;&lt;p&gt;Usually the radio has a tone scan function, and you can use that to find out what tone is being used.  You can also turn on tone squelch if you have the tone set correctly, and if it is there, the radio will not block the signal.&lt;/p&gt;&#xA;&lt;p&gt;Repeaters frequently filter out tones on the incoming signal and then add it back in on transmit.  This allows using a different tone on input and output, although this is rare.  Many repeaters and nearly all regular radios just pass the tone through without attempting to filter it.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2021-04-14T12:15:06.430" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18321" PostTypeId="2" ParentId="18304" CreationDate="2021-04-14T16:39:04.797" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://gadm.org/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;GADM&lt;/a&gt; is an online project aspiring to provide maps and spatial data for all countries of the world and their administrative subdivisions at all levels. It also contains outlines of London boroughs. According to the asker, the KMZ file provided by GADM is easily convertible to the format required by Splat.&lt;/p&gt;&#xA;" OwnerUserId="17321" LastActivityDate="2021-04-14T16:39:04.797" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18322" PostTypeId="2" ParentId="18318" CreationDate="2021-04-15T01:01:53.777" Score="-5" Body="&lt;p&gt;The difference is that a (perfect) transmitter is trying to drive some (oscillating) current into or out of the feedline.  Any reflected voltage coming back will bounce off a source trying to drive that junction to a different voltage, if it's out of phase.  Or be amplified if it meets an in phase source.&lt;/p&gt;&#xA;&lt;p&gt;A receiver's passive impedance just eats the incoming energy (if matched to the line).&lt;/p&gt;&#xA;&lt;p&gt;A real transmitter has losses that eats a lot of its own power, as well as some of the reflected stuff sent into it from the feedline (or any other wire connections).  Eventually turning it into heat.&lt;/p&gt;&#xA;&lt;p&gt;If the system (transmitter, feedline, antenna) is really lossless, with perfect reflections, then energy fed into the system from the transmitter will build up, until the system melts, vaporizes, explodes, or turns into a black hole (due to E=MC2).&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-15T01:08:00.753" LastActivityDate="2021-04-15T01:08:00.753" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="18323" PostTypeId="2" ParentId="18316" CreationDate="2021-04-15T01:14:06.127" Score="3" Body="&lt;p&gt;Same with SDR software.  My SDR code runs on a iPhone that's connected to &amp;quot;HiFi&amp;quot; audio transducers.  So I had to add a 270 Hz high-pass biquad IIR audio filtering subroutine to get rid of annoying hum when listening to NFM from local 2M repeaters.  (I obviously switch that subroutine out when listening to broadcast wideband FM music.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-04-15T01:14:06.127" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18324" PostTypeId="2" ParentId="18305" CreationDate="2021-04-15T03:59:42.440" Score="2" Body="&lt;p&gt;An operator who holds an Amateur Extra license from the US is allowed to operate from Spain &lt;em&gt;as a visitor&lt;/em&gt; via CEPT reciprocity, but CEPT T/R 61-01 and the Spanish regulation both make it clear that you lose that right once you become a resident of Spain, and you will need a Spanish license.&lt;/p&gt;&#xA;&lt;p&gt;You might be able to petition SETSI for a temporary license valid for up to 90 days if you had your Extra (Article 15; it says it's for visiting foreigners from non-CEPT countries, but the way I'm reading things, it seems like they have some discretion, which is why I'm saying you &lt;em&gt;might&lt;/em&gt; get lucky), but in any case you would have to pass the Spanish test to be able to continue operating. Your US license doesn't provide any advantage or shortcut.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-04-15T03:59:42.440" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18325" PostTypeId="2" ParentId="18318" CreationDate="2021-04-15T15:56:15.287" Score="2" Body="&lt;p&gt;This model makes two simplifying assumptions:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;losses are uniform throughout the transmission line, and&lt;/li&gt;&#xA;&lt;li&gt;there is a lossless tuner between the transmitter and the feedline adjusted such that the transmitter sees a matched load&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;The first assumption isn't directly relevant to your question and is discussed in more details in &lt;a href=&quot;https://ham.stackexchange.com/a/7348/218&quot;&gt;the answer you linked&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Now about the second assumption, realize &amp;quot;the transmitter sees a matched load&amp;quot; implies &amp;quot;the transmitter sees no reflected power&amp;quot;. This is because any apparent deviation from the characteristic impedance of the feedline must be the result of reflected power. If the transmitter sees no reflected power and yet the antenna is known to be mismatched and thus did reflect some power, if the transmitter didn't see that reflection it must be because the tuner re-reflected the power back at the antenna.&lt;/p&gt;&#xA;&lt;p&gt;More rigorously, the tuner is a 2-port network which when properly adjusted presents a reflection coefficient which cancels any reflected power.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/C39ay.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fC39ay.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;Let's say looking at the antenna through the feedline, a &lt;a href=&quot;https://en.wikipedia.org/wiki/Reflection_coefficient&quot; rel=&quot;nofollow noreferrer&quot;&gt;reflection coefficient&lt;/a&gt; of &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt; is observed. We then want a tuner with a &lt;a href=&quot;https://en.wikipedia.org/wiki/Scattering_parameters&quot; rel=&quot;nofollow noreferrer&quot;&gt;scattering matrix&lt;/a&gt; of:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{bmatrix}&#xA;-\Gamma &amp;amp; ?\\&#xA;? &amp;amp; ?&#xA;\end{bmatrix} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;This means for a wave going into port 1 of the tuner (from the transmitter) of amplitude 1, a reflected wave back out port 1 of amplitude &lt;span class=&quot;math-container&quot;&gt;$-\Gamma$&lt;/span&gt; will be observed.&lt;/p&gt;&#xA;&lt;p&gt;With such a scattering matrix, the transmitter will see a reflection coefficient of &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt; from the antenna, and &lt;span class=&quot;math-container&quot;&gt;$-\Gamma$&lt;/span&gt; from the tuner, for a sum reflection coefficient of zero, meaning the transmitter sees no reflected power and a matched load.&lt;/p&gt;&#xA;&lt;p&gt;We assume the tuner is lossless and passive, which means the sum of squares of the values in any column of the matrix must be 1. Squares, because power is proportional to the square of amplitude. And a sum of 1, because no energy is lost or added. So:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ S_{11}^2 + S_{21}^2 = 1 \\&#xA;-\Gamma^2 + S_{21}^2 = 1 \\&#xA;S_{21}^2 = \Gamma^2 + 1 \\&#xA;S_{21} = \pm\sqrt{\Gamma^2 + 1} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The math is telling us we could make a tuner which inverts &lt;span class=&quot;math-container&quot;&gt;$S_{21}$&lt;/span&gt; or not; in practice we will have to pick one or the other when we build the tuner, so I'm just going to arbitrarily pick &lt;span class=&quot;math-container&quot;&gt;$S_{21} = \sqrt{\Gamma^2 + 1}$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Therefore, we can fill it a bit more of the matrix:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{bmatrix}&#xA;-\Gamma &amp;amp; ?\\&#xA;\sqrt{\Gamma^2 + 1} &amp;amp; ?&#xA;\end{bmatrix} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;The tuner is also passive and made of isotropic materials, and therefore is a reciprocal network. This means &lt;span class=&quot;math-container&quot;&gt;$S_{mn} = S_{nm} $&lt;/span&gt;, in other words, the matrix is symmetrical across the diagonal. So we can fill in more of the matrix:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{bmatrix}&#xA;-\Gamma &amp;amp; \sqrt{\Gamma^2 + 1}\\&#xA;\sqrt{\Gamma^2 + 1} &amp;amp; ?&#xA;\end{bmatrix} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;Again because the tuner is assumed lossless we can infer &lt;span class=&quot;math-container&quot;&gt;$S_{22}$&lt;/span&gt; from &lt;span class=&quot;math-container&quot;&gt;$S_{21}$&lt;/span&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{bmatrix}&#xA;-\Gamma &amp;amp; \sqrt{\Gamma^2 + 1}\\&#xA;\sqrt{\Gamma^2 + 1} &amp;amp; -\Gamma&#xA;\end{bmatrix} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;With the tuner's scattering matrix calculated we can answer all kinds of questions about how waves will reflect or pass through the tuner.&lt;/p&gt;&#xA;&lt;p&gt;We've already discussed how power into port 1 (from the transmitter) is partially reflected (&lt;span class=&quot;math-container&quot;&gt;$S_{11} = -\Gamma$&lt;/span&gt;), and this cancels the reflection that is seen from the mismatched antenna. But what about receive?&lt;/p&gt;&#xA;&lt;p&gt;Because a tuner is reciprocal, the same thing happens on receive: some of the power from the antenna is reflected back at the antenna. Is that a problem?&lt;/p&gt;&#xA;&lt;p&gt;Not really. An antenna is also a 2-port device: one port being the feedpoint, and the other &amp;quot;port&amp;quot; being free space. The antenna is also reciprocal and nearly lossless, so its scattering matrix is nearly the same as the tuner, just with the sign flipped. This means power into the free space port (the signal we wish to receive) will see some non-zero reflection coefficient (a mismatch), but it will also see the opposite reflection coefficient from port 2 of the tuner, the two summing to zero.&lt;/p&gt;&#xA;&lt;p&gt;What about this business of solid-state versus tube PAs?&lt;/p&gt;&#xA;&lt;p&gt;The distinction really has nothing to do with tubes vs. transistors, but rather the typical design around them. Nearly all tube amplifiers include a tuner: they must because the output impedance of a tube is very high, and thus a poor match for coax. Moreover, the output impedance varies with frequency and temperature, so the matching network must be variable. More moreover, in the days before transistors a coax feed wasn't as common as it is today. The feedline might be twin-lead with an impedance anywhere between 200 and 900 ohms, or even a random wire with who knows what impedance. A transmitter would be expected to drive all of these loads.&lt;/p&gt;&#xA;&lt;p&gt;For example:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/7d2pG.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/7d2pG.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is from &lt;a href=&quot;https://www.frostburg.edu/personal/latta/ee/6146amp/schematic/6146schematic.html#input&quot; rel=&quot;nofollow noreferrer&quot;&gt;a page by Greg Latta&lt;/a&gt;. Note the variable capacitor and switchable taps on the inductor: this is an &lt;a href=&quot;https://w5dxs.tripod.com/l-network.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;L-network&lt;/a&gt; and could be used as an antenna tuner on its own. &lt;a href=&quot;https://www.w8ji.com/loading_amplifier.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;Tuning this network&lt;/a&gt; is part of the standard operating procedure for a tube PA, so in practice a tube PA always has an &amp;quot;antenna tuner&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Solid-state transmitters on the other hand don't necessarily have this feature. The output impedance of a transistor is lower and more stable, and thus it's feasible to design the circuit to drive a 50 ohm load without variable components.&lt;/p&gt;&#xA;&lt;p&gt;For example here's the &lt;a href=&quot;http://www.wb5rvz.org/ensemble_rxtx/10_pa&quot; rel=&quot;nofollow noreferrer&quot;&gt;PA for the Softrock RXTX&lt;/a&gt;:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/KxtTA.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/KxtTA.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Q7 and Q8 are the PA finals: notice there's nothing matching them to the load except a fixed transformer, T4. (There is a filter that follows this, though at a glance it appears to have a 50 ohm input and output and thus serves no purpose in matching.)&lt;/p&gt;&#xA;&lt;p&gt;Of course many solid-state radios (especially modern ones at higher price points) include an automatic tuner for convenience, making them similar to tube PAs.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-15T15:56:15.287" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18326" PostTypeId="2" ParentId="17661" CreationDate="2021-04-15T16:33:46.783" Score="2" Body="&lt;p&gt;I believe the answer currently is: yes it matters less, but it still matters.&lt;/p&gt;&#xA;&lt;p&gt;Variables include 1) the mode of operation and 2) the speed of the foldback circuit in the radio that provides the trigger for power reduction on a bad match.&lt;/p&gt;&#xA;&lt;p&gt;While modern transceivers all seem to have a foldback circuit to limit potential damage (for ex, see ic7300 operator manual page 13-4, &amp;quot;The transceiver has a 2 step protection function to protect the final power amplifiers in case the antenna SWR becomes high.&amp;quot;), they depend on measuring the reflected power which means it's already inside the radio by the time the circuit can respond.&lt;/p&gt;&#xA;&lt;p&gt;If operating SSB, that may not be much of a problem since the modulated signal is likely not at full power (probably MUCH less) and doesn't give much opportunity to build-up heat before the foldback kicks in.&lt;/p&gt;&#xA;&lt;p&gt;If operating CW/digital/any instantaneously full-duty cycle mode, then there is more opportunity for maximized power reflection back into the PA before foldback kicks in... depending on component tolerances, radios from the same manufacturer may even have different foldback activation speed. At least SOME power will make it back to the PA, which are running at full power already... this is not ideal.&lt;/p&gt;&#xA;&lt;p&gt;So a scenario that I could envision is running a digital mode at high power on a band that the PAs are matched to, heating them up already, then moving to another band with high SWR. Now I've got pre-heated PAs, running at full duty, plus need to dissipate whatever large reflected power is... could be a life-shortener if not a blowout event.&lt;/p&gt;&#xA;&lt;p&gt;So in short, while not NEARLY as critical as back in the day, it's still important.&lt;/p&gt;&#xA;&lt;p&gt;I also recognize that this answer is VERY light on referenced material, and ENCOURAGE others to augment this answer (or provide a more robust additional) as they see fit.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2021-04-15T16:33:46.783" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18327" PostTypeId="2" ParentId="12619" CreationDate="2021-04-15T20:32:40.983" Score="3" Body="&lt;p&gt;Though this may seem somewhat counter-intuitive at first, I think it is also worth pointing out that certain call signs are better understood when the letters are pronounced together instead of the drawn out phonetic pronunciation of those letters. Of course this may depend highly upon the noise inherent in the band conditions. But I often find that many DX operators waste more time in repeating English phonetic voice sign transmissions when a quick burst of the letter pronunciation would be the most effective in a specific case.  For example, NK2I versus November Kilo Two India. It's 4 syllables of good formant transitions versus 9 syllables of less than perfect cadence transitions between word segments. So phonetics are not necessarily the best choice to increase the clarity of detection.&lt;/p&gt;&#xA;" OwnerUserId="19402" LastActivityDate="2021-04-15T20:32:40.983" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18328" PostTypeId="2" ParentId="12619" CreationDate="2021-04-15T21:53:22.820" Score="0" Body="&lt;p&gt;The answers so far seem to be mostly thinking about HF phone, where phonetic alphabets are customary.  But in my area, practices are very different on VHF/UHF FM.  Personally I find it quite annoying that someone identifies as &amp;quot;kay cee three zee bee gee&amp;quot; every twenty minutes on a distant repeater with scratchy copy that is even more difficult to hear over the wind noise in my convertible rolling down the highway.  (That's with the top up; with the top down there's no point in trying to listen to a radio while driving on the highway.)  I'd much prefer &amp;quot;kilo charlie tree zulu bravo golf&amp;quot;.  Personally I always use the ITU phonetic alphabet, even on D-STAR where it doesn't matter because the call sign is transmitted digitally simultaneously with the audio.&lt;/p&gt;&#xA;&lt;p&gt;So to answer the question, around here it's customary to &lt;em&gt;not&lt;/em&gt; use a phonetic alphabet on VHF/UHF FM, but I wish that it were.  In my opinion, not using a phonetic alphabet is, well, amateurish.  If nothing else, hams should be very familiar with a standard phonetic alphabet in case they need to pass information accurately in a stressful emergency situation.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-04-15T22:02:19.863" LastActivityDate="2021-04-15T22:02:19.863" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18329" PostTypeId="1" CreationDate="2021-04-16T06:30:32.653" Score="3" ViewCount="279" Body="&lt;p&gt;Yes, I know, this could very well be a controversial topic, so feel free to close this off if you feel it's not a good fit for this site.  That said, I'm posting it here because hams (and as a licensed ham, I count myself in that group) know a great deal about radio reception, and in the end, that's the issue.&lt;/p&gt;&#xA;&lt;p&gt;Since the start of the pandemic, I find myself working in the ham shack (like so many others!).  The problem is, the cabin is insulated with foil backed hard foam insulation, which I've noticed reduces radio reception by quite a bit.  For HF and VHF signals I have an antenna outside the shack, so that's not a problem.  However, I have real issues with mobile phone signals and since the reception is mediocre at best, the insulation just makes matters worse.&lt;/p&gt;&#xA;&lt;p&gt;So, the question is this: is there a legal and simple way to improve mobile phone reception within the shack that borrows from techniques commonly understood by amateur radio operators?  I've been careful about how I worded that question, since what I really need is a solution I can build myself! 73s&lt;/p&gt;&#xA;" OwnerUserId="11875" LastActivityDate="2021-04-16T21:32:24.487" Title="Boosting Mobile Phone Reception" Tags="&lt;antenna&gt;&lt;mobile&gt;&lt;phone&gt;&lt;reception&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18331" PostTypeId="1" AcceptedAnswerId="18341" CreationDate="2021-04-16T14:46:49.203" Score="1" ViewCount="61" Body="&lt;p&gt;I purchased a cell phone booster for the cottage that came with an external yagi. Since its important to get the antenna as far away as possible from the indoor omni, the yagi has about 25 meters of relatively thin coax, smaller than RJ59, permanently connected on the antenna side and with an N-connector on the other. This solution never worked very well, in spite of any geometry I tried I always ended up with feedback on LTE. So I got a ZTE288 wifi router which has external SMAs and plugged it into the same antenna with an N-&amp;gt;SMA adaptor. Presto, wifi calling, solid signal.&lt;/p&gt;&#xA;&lt;p&gt;Now the question(s): The antenna is less than 5 meters from the router, so I assume I could get even better signal if I were to cut the cable down. But I know that getting a good connection on the cable is not trivial.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;should I even bother, or is the line loss not worth worrying about?&lt;/li&gt;&#xA;&lt;li&gt;is putting an SMA on as easy as, say, an F-connector on RG6?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="6173" LastEditorUserId="8717" LastEditDate="2021-04-16T15:26:01.473" LastActivityDate="2021-04-19T00:10:06.780" Title="Replacing a N-connector with SMA, easy?" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18332" PostTypeId="2" ParentId="18329" CreationDate="2021-04-16T14:58:55.743" Score="4" Body="&lt;p&gt;There are a couple of options.&lt;/p&gt;&#xA;&lt;p&gt;If your phone supports WiFi calling and your provider allows it, I strongly recommend getting WiFi in the shack if you don’t have it already. If you don’t have it, and that’s because you’re remote, get a LTE&amp;lt;-&amp;gt;WiFi router with SMA connectors and an appropriate antenna.&lt;/p&gt;&#xA;&lt;p&gt;If you can’t use this solution you can buy cell phone boosters on amazon. Get one that has multi band support, the one I have is five band and that works. Get the model that comes with an appropriate antenna, if you’re anywhere near a tower an Omni will work fine.&lt;/p&gt;&#xA;&lt;p&gt;The downside to the booster is that you can get feedback between the interior and exterior antenna, which in my case rendered it useless- the cell tower was so far that any level of boost led to the local signal being strong enough to cause feedback. If you have a strong signal, combined with your foil shielding, I suspect it will work perfectly.&lt;/p&gt;&#xA;" OwnerUserId="6173" LastEditorUserId="6173" LastEditDate="2021-04-16T21:32:24.487" LastActivityDate="2021-04-16T21:32:24.487" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18333" PostTypeId="2" ParentId="17933" CreationDate="2021-04-16T19:52:36.637" Score="1" Body="&lt;p&gt;Spacing of parallel dipoles influences the bandwidth you can achieve on every particular band. The smaller the spacing, the more narrowband antenna becomes.&#xA;However, there is a trick you can use to achieve a little larger bandwidth while not spacing the dipoles too much. See my website &lt;a href=&quot;https://sites.google.com/view/sp3l-hf-antennas/home-page/multi-band-hf-antennas/sfp-mutli-dipole&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/akU0V.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/akU0V.png&quot; alt=&quot;The trick is to use a configuration I call a split feed point. &quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19409" LastEditorUserId="19409" LastEditDate="2021-04-17T10:10:26.740" LastActivityDate="2021-04-17T10:10:26.740" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="18335" PostTypeId="2" ParentId="1891" CreationDate="2021-04-16T21:56:50.373" Score="2" Body="&lt;p&gt;FWIW:  The Baofeng UV-5R HT supplies 3.3V through 100(*) ohms on the tip of the 3.5mm connector, not 5V as documented above.  Also, the PTT is pulled up thru 10K to 3.3V, and the MIC+ connection line also has a more complex (constant current source?) pullup to 3.3V.  [This is nice, as the PTT line can directly connect to a Raspberry Pi GPIO pin!]&lt;/p&gt;&#xA;&lt;p&gt;There's a (wrong in several places, but you can get the idea of the general functions) schematic at &lt;a href=&quot;http://static2.rigreference.com/manuals/baofeng/baofeng-uv5r-circuit-diagram.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://static2.rigreference.com/manuals/baofeng/baofeng-uv5r-circuit-diagram.pdf&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;(*) Correction!  The schematic says it's a 100 ohm pullup, one radio measured 10K and the other measured 100K, so it's anyone's guess what a particular radio might have installed.  I'm going to mark this pin as &amp;quot;Not Useful&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Further study shows a DC bias of about half the battery voltage across the speaker due to the external speaker being connected to only half of the bridged output amplifier, so you might want to use a DC blocking capacitor.&lt;/p&gt;&#xA;" OwnerUserId="19412" LastEditorUserId="19412" LastEditDate="2021-04-26T19:36:54.000" LastActivityDate="2021-04-26T19:36:54.000" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18337" PostTypeId="2" ParentId="12619" CreationDate="2021-04-17T08:08:27.150" Score="0" Body="&lt;p&gt;In the US:&lt;/p&gt;&#xA;&lt;p&gt;T1A03&lt;/p&gt;&#xA;&lt;p&gt;What are the FCC rules regarding the use of a phonetic alphabet for station identification in the Amateur Radio Service?&lt;/p&gt;&#xA;&lt;p&gt;&lt;s&gt;A. It is required when transmitting emergency messages&lt;/s&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;s&gt;B. It is prohibited&lt;/s&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;s&gt;C. It is required when in contact with foreign stations&lt;/s&gt;&lt;/p&gt;&#xA;&lt;p&gt;Correct Answer D. It is encouraged&lt;/p&gt;&#xA;&lt;p&gt;Note that the FCC does not say &lt;em&gt;which&lt;/em&gt; phonetic alphabet to use.- but the ITU / NATO alphabet is probably the most common.&lt;/p&gt;&#xA;" OwnerUserId="966" LastEditorUserId="966" LastEditDate="2021-04-17T08:25:03.960" LastActivityDate="2021-04-17T08:25:03.960" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18338" PostTypeId="2" ParentId="17564" CreationDate="2021-04-17T10:00:35.210" Score="0" Body="&lt;p&gt;Yes, you can if the feeder length is right.&#xA;It should be around 1/4 of the operating wavelength or any odd multitudes of 1/4 (i.e. 3/4, 5/4, and so on). For example, if the feeder length (measured from the feed point to the point where it touches the ground for the first time) is in the range of 0.2 - 0.3 wavelength, you can do quite OK without a current balun (a.k.a. RF choke). Common-mode current will be low and you will not experience any negative effect due to lack of the choke.&#xA;Examples:&#xA;80 m band dipole hanging about 20 m above ground level&#xA;40 m band dipole hanging about 10 m above ground level&lt;/p&gt;&#xA;&lt;p&gt;However, if the coaxial feeder length is closer to even multitudes of 1/4 WL (that is 2/4, 4/4, 6/4, and so on), large common-mode current will be excited in the feeder.&lt;/p&gt;&#xA;&lt;p&gt;In case of multiband antennas, achieving the &amp;quot;right&amp;quot; feeder length is often impossible.&lt;/p&gt;&#xA;&lt;p&gt;If you have access to the ARRL QEX magazine and want to learn a little more, you may want to read my article &amp;quot;Designing antenna systems for low common-mode current in coaxial feed lines&amp;quot; that is supposed to be published in the July/August issue of the QEX.&#xA;73&#xA;SP3L&lt;/p&gt;&#xA;" OwnerUserId="19409" LastActivityDate="2021-04-17T10:00:35.210" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18339" PostTypeId="2" ParentId="756" CreationDate="2021-04-17T13:13:03.283" Score="1" Body="&lt;p&gt;I found a very easy modification to this to make it an FM transmitter. Just connect your audio jack left or right (or both) via a 10K resistor to the base, and audio ground to ground. That's it. :)&lt;/p&gt;&#xA;" OwnerUserId="19416" LastActivityDate="2021-04-17T13:13:03.283" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18340" PostTypeId="2" ParentId="18318" CreationDate="2021-04-17T20:04:35.213" Score="2" Body="&lt;p&gt;The Question addresses a persistent confusion which is widespread especially in the ham radio community and can be tracked down to some published material (here no names!) and has survived since many years.&lt;/p&gt;&#xA;&lt;p&gt;However, a clarification can be straightforward and does not require complicated math. This answer starts from the “Total Feedline Loss” equation that had been derived in a previous thread and often appears in ham radio publications:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/vmSJV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/vmSJV.jpg&quot; alt=&quot;Equation&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Behind this correct loss equation there are crucial assumptions for its validity, including (1) The characteristic impedance of the feedline (e.g., coax) must be a real (not complex) value, which is reasonably satisfied at higher RF frequencies (but probably not for 40m, 80m, 160m bands for which additionally the physical line-length may become much shorter than the electrical wavelength on the line). – The second (2) assumption is much more relevant in the context of this thread: A (lossless) tuner is assumed at the input of the feedline. This tuner performs complex conjugate impedance matching such that the transceiver can feed its maximum available power into the feedline.&lt;/p&gt;&#xA;&lt;p&gt;Because of reflections at the far-end, e.g., at the feed-point of an antenna, a fraction of the transmit power (in terms of voltage/current waves) returns to the input of the feedline. There, the returning waves feel the output impedance of the matching network (tuner). This impedance is the complex conjugate of the feedline input impedance; it determines, together with the feedline characteristic impedance (e.g., 50Ω coax), the extent of reflection expressed by the (complex) reflection coefficient. Note, there is no total re-reflection. Such total re-reflection would require an infinite, or a zero, or a pure reactance impedance; all these cases do not apply here, regardless of the tuner being a lossless LC network which transforms the output impedance of the transceiver (e.g., 50Ω).&lt;/p&gt;&#xA;&lt;p&gt;However, the above “Total Feedline Loss” equation is frequently derived based upon a perception of total re-reflection and results from an infinite geometric series. And, indeed, the equation is correct! So, what is going on? Well, applying the idea of total re-reflection is a somewhat dirty way to arrive at a correct equation. The end-result for the total loss is the same, regardless of either applying the fake of total re-reflection, or the true physics of the actual phase-accurate superposition of partially reflected voltage/current signal components and applying the true reflection coefficient. Although the end-result is the same, the bouncing-steps during the transient period are quite different. The above “Total Feedline Loss” equation is valid, although its derivation is very often flawed, which leads to confusion, paradoxes and such concerns like expressed in the Question.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/qsEQP.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/qsEQP.jpg&quot; alt=&quot;Cartoon&quot; /&gt;&lt;/a&gt;&#xA;(Credit: Cartoon by Tayfun Agül)&lt;/p&gt;&#xA;&lt;p&gt;Under the condition of complex conjugate matching, the “Total Feedline Loss” formula does not show explicitly the reflection coefficient that is relevant for the re-reflection of voltage/current signal components that return to the feedline input.&lt;/p&gt;&#xA;&lt;p&gt;Of course, when arriving at the feedline input, the same partial re-reflection applies not only to a returning fraction of the transmit signal, but equally also to any receive signal; there is no difference, assuming the Tx and Rx signals are similar in frequency, implying similar reflection coefficients.&lt;/p&gt;&#xA;&lt;p&gt;The following experiment illustrates the difference in bouncing-steps. We assume a system that is easy to calculate (and easy to measure!). A lossy 50Ω coax is terminated into an ohmic resistor of 290Ω. This load resistor implies that half of the forward power is reflected at the load,&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|Γ|^2=|(290-50)/(290+50)|^{2}=0.5$$&lt;/span&gt;&#xA;The coax line attenuation is 3dB (i.e., L=0.5). The coax length is a multiple of (λ/2); such length-choice avoids here the hassle of complex values and implies that the feedline input impedance is also ohmic; it is 104.9Ω (obtained by calculation, or Smith Chart etc.). We assume a (lossless) LC tuner that matches the feedline input impedance of 104.9Ω to the transceiver output impedance (say, 50Ω). Thus, the tuner output impedance (seen when looking from the feedline into the tuner) is adjusted to be also 104.9Ω. The signal components that return to the feedline input, experience reflection with a coefficient &lt;span class=&quot;math-container&quot;&gt;$$Γ_s=(104.9–50)/(104.9+50)=0.35$$&lt;/span&gt; or &lt;span class=&quot;math-container&quot;&gt;$$|Γ_s|^2=0.13$$&lt;/span&gt; (instead of any faked &lt;span class=&quot;math-container&quot;&gt;$|Γ_s|^2=1$&lt;/span&gt;).&lt;/p&gt;&#xA;&lt;p&gt;Inserting the values into the “Total Feedline Loss” equation gives a system loss of 5.44dB (or linear 0.2857). If the maximum available power from the transceiver is 100W then – after the bouncing has finished – a steady power of 28.57W is delivered to the load resistor.&lt;/p&gt;&#xA;&lt;p&gt;Connecting to the diagram in the Question, our system loss of 5.44dB includes the 3dB “Line Loss in dB When Matched” plus 2.44dB “Additional Loss in dB Caused by Standing Waves”; note our SWR is here (290/50) =5.8. The transceiver pumps 100W into the feedline. Part of this power (28.57W) is dissipated in the load at the end of the feedline; the remaining part (71.43W) is dissipated in the feedline which is quite lossy (here 3dB, means 50W matched line loss plus 21.43W additional loss due to SWR). There is no power going back into the transceiver because it is (via a (lossless) tuner) impedance-matched to the input impedance of the feedline. All power of 100W remains, and is dissipated, inside the system of feedline plus connected load. This applies regardless of the actual reflection coefficient (here &lt;span class=&quot;math-container&quot;&gt;$Γ_s=0.35$&lt;/span&gt;) being different from 1.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;@sm5bsz (comment on separate Answer): “… &lt;em&gt;regarding the diagram … It shows the fraction of the power sent into the cable that is converted&#xA;to heat. (The rest is delivered to the antenna.)&lt;/em&gt;” (quote)  That is a&#xA;misleading statement. The curves in the diagram show only the&#xA;loss due to SWR. The total loss (and thus the total power converted to&#xA;heat) is higher by the added Matched Line Loss of the cable on its&#xA;own.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;For comparison, we also consider the case of a lossless line (L=1). The “Total Feedline Loss” becomes 0dB, regardless of mismatch at the load side. The input impedance of the feedline is now identical to the load resistor (remember the line being a (λ/2)-line), and the tuner is adjusted for an output impedance of also 290Ω. The reflection coefficient at TL input becomes &lt;span class=&quot;math-container&quot;&gt;$Γ_{in}=Γ=0.71$&lt;/span&gt;. The power delivered to the load resistor – after the bouncing has finished – equals now the maximum available power of 100W from the transceiver.&lt;/p&gt;&#xA;&lt;p&gt;The following table shows the bouncing for the two cases of line attenuations and for the “Reality” of true &lt;strong&gt;partial&lt;/strong&gt; re-reflection, and for the “Misconception” of &lt;strong&gt;total&lt;/strong&gt; re-reflection. &lt;span class=&quot;math-container&quot;&gt;$T_L$&lt;/span&gt; is the one-way delay time of the coax. The lower the line loss (in dB), the more evident become the transient discrepancies, and the bouncing will take longer until the steady state is reached.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/dUmqf.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/dUmqf.jpg&quot; alt=&quot;Table&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The “Reality” cases can be verified by measurements and by simple simulations; here is a simulation schematic (LTspice) for the discussed second case of 0dB feedline loss. The voltage &lt;span class=&quot;math-container&quot;&gt;$Us$&lt;/span&gt; is scaled accordingly for a maximum source power of 100W.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W3z9O.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W3z9O.jpg&quot; alt=&quot;LTspice Model&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;More general:&lt;/strong&gt; If the condition of complex conjugate impedance matching (e.g., by a tuner) is satisfied at the input of the transmission line, also the reflection coefficients &lt;span class=&quot;math-container&quot;&gt;$\Gamma_{in}$&lt;/span&gt; at TL input and &lt;span class=&quot;math-container&quot;&gt;$\Gamma_{s}$&lt;/span&gt; of the source (or tuner output) are complex conjugate to each other,&#xA;&lt;span class=&quot;math-container&quot;&gt;$$\Gamma_{s} = \Gamma_{in}^{\ ^{*}}$$&lt;/span&gt;&#xA;This implies&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|\Gamma_{s}| = |\Gamma_{in}| = L\cdot |\Gamma |$$&lt;/span&gt;&#xA;where &lt;span class=&quot;math-container&quot;&gt;$\Gamma$&lt;/span&gt; is the reflection coefficient at the load, and &lt;span class=&quot;math-container&quot;&gt;$L$&lt;/span&gt; (linear) is the Matched Line Loss. Therefore, we can rewrite the formula for the “Total Feedline Loss” as function of &lt;span class=&quot;math-container&quot;&gt;$|\Gamma_{s}|$&lt;/span&gt; explicitly:&#xA;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;-10\log \left( L\frac{1-|\Gamma |^{2}}{1-L^{2}|\Gamma |^{2}}\right) =&#xA;-10\log \left( L\frac{1-(|\Gamma_{s}|/L)^{2}}{1-|\Gamma_{s}|^{2}}\right)&#xA;$$&lt;/span&gt;&#xA;Obviously, the complex conjugate matching at the TL input (e.g., by a tuner) does &lt;strong&gt;not&lt;/strong&gt; imply &lt;span class=&quot;math-container&quot;&gt;$|\Gamma_{s}|=1$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;If no complex conjugate matching applies at the transmission line input, the “Total Feedline Loss” formula (in dB) becomes&#xA;&lt;span class=&quot;math-container&quot;&gt;$$&#xA;-10\log\left( L\cdot\frac{1-|\Gamma |^{2}}{1-L^{2}|\Gamma |^{2}} \cdot &#xA;                       \frac{4R_{s}R_{in}}{|Z_{s}+Z_{in}|^{2}}&#xA;             \right)&#xA;$$&lt;/span&gt;&#xA;where the (complex) &lt;span class=&quot;math-container&quot;&gt;$Z_{s}=R_{s}+jX_{s}$&lt;/span&gt; is the (Thévenin equivalent) source output impedance at the given operating point; and the (complex) &lt;span class=&quot;math-container&quot;&gt;$Z_{in}=R_{in}+jX_{in}$&lt;/span&gt; is the input impedance of the transmission line. – If the two impedances are complex conjugate to each other (tuner case), &lt;span class=&quot;math-container&quot;&gt;$Z_{s}=Z_{in}^{\ ^{*}}$&lt;/span&gt;, the corresponding last quotient in the above total loss formula becomes 1. Note the characteristic impedance, &lt;span class=&quot;math-container&quot;&gt;$Z_o$&lt;/span&gt;, of the transmission line is still assumed to be a real value. (Obtaining/measuring the two impedances &lt;span class=&quot;math-container&quot;&gt;$Z_{s}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$Z_{in}$&lt;/span&gt; is perhaps beyond the scope of this Question.)&lt;/p&gt;&#xA;&lt;p&gt;An Excel tool downloadable at &lt;a href=&quot;https://www.rfclb.space/#TLine&quot; rel=&quot;nofollow noreferrer&quot;&gt;www.rfclb.space/#TLine&lt;/a&gt; does all calculation and allows for “Total Feedline Loss” trade-offs considering different approaches of impedance matching by a tuner (far-end; near-end; complex conjugate matching; zero-reflection), or tuning by simple feedline extension; the tool covers also the case of complex characteristic impedance of the transmission line.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/zBtgJ.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zBtgJ.gif&quot; alt=&quot;Transmission Line Power Calculator&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Conclusion&lt;/strong&gt; answering to the 3-fold Question:&lt;/p&gt;&#xA;&lt;p&gt;(1) The diagram in the Question and the “Total Feedline Loss” formula are correct; both are based upon the condition of complex conjugate matching (CCM) at the feedline input, achievable for instance by a lossless tuner. This principle applies regardless of (modern or heritage) technology used in the transceiver. – (2) Whether a tuner is required depends on the situation and the question to what extend the CCM condition can be, or is already, achieved by the feedline system, including the transceiver, i.e., w/o insertion of a tuner. – (3) No, the tuner cannot distinguish between (a) transmit signal components that, due to reflection, might return to the feedline input; and (b) any receive signal. Partial re-reflection applies for both signal components, regardless of being Tx or Rx related. The CCM condition does &lt;strong&gt;NOT&lt;/strong&gt; imply any necessity of “total re-reflection” with &lt;span class=&quot;math-container&quot;&gt;$|Γ_s|=1$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ $$&lt;/span&gt;&#xA;&lt;strong&gt;PS:&lt;/strong&gt;&#xA;For those who wish to further dive into the nitty-gritty-down-in-the-weeds technical details, here is a diagram for a re-reflection assessment at the feedline input.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/VEiyG.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/VEiyG.jpg&quot; alt=&quot;Detailed Assessment&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18763" LastEditorUserId="18763" LastEditDate="2021-05-15T17:02:27.813" LastActivityDate="2021-05-15T17:02:27.813" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18341" PostTypeId="2" ParentId="18331" CreationDate="2021-04-18T15:41:50.943" Score="1" Body="&lt;p&gt;F connectors are stupid simple to install, the ones I've seen are screw on and you're done.  SMA is not going to be that easy.&lt;/p&gt;&#xA;&lt;p&gt;I've seen solder on SMA, and crimp on SMA might exist, but both require some skill and tools.  I've seen screw on BNC, but they require specific cable with a solid center conductor. Very likely your existing coax has a multi-strand center conductor and won't work with any screw on connector, even if an SMA one existed.&lt;/p&gt;&#xA;&lt;p&gt;It's hard to say without knowing exactly what coax is involved how much loss you are getting from the extra length.  There are some good low loss GHz rated skinny coax types.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-04-19T00:10:06.780" LastActivityDate="2021-04-19T00:10:06.780" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18343" PostTypeId="1" CreationDate="2021-04-18T17:04:04.797" Score="1" ViewCount="60" Body="&lt;p&gt;I'm building a kit for the LNR precision mountaintopper 3 band qrp radio.  I'm having problems wiring a panel mounted volume knob and speaker to hear the cw output. I'm new to home brew electronics and wanted some advice. My questions are as follows:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;When testing my speaker and volume knob(with music from my computer via audio cable), I the volume is too quiet. The potentiometer seems to only give me audio at the far end of its range, and still it's very quiet. What could be causing this? Wrong pot? Wrong speaker? How do I match a speaker and pot so they work well together and give good volume control?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The radio has a spec that says &amp;quot;headphone output  16ohm min&amp;quot;.  How do I know what speaker and pot combination would get the best result with this specification for good volume control?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;I've got 3 ring audio cable that I'm wiring to my small speaker. Do the left and right rings of the cable get wired to the 2 prongs on the speaker?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Please excuse my ignorance, I'm just trying to figure things out. Thanks for any help you can provide!&lt;/p&gt;&#xA;" OwnerUserId="19424" LastEditorUserId="8717" LastEditDate="2021-04-18T17:51:54.987" LastActivityDate="2021-04-20T23:08:00.540" Title="CW speaker and volume control" Tags="&lt;cw&gt;&lt;equipment-design&gt;&lt;qrp&gt;&lt;speaker&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18344" PostTypeId="1" CreationDate="2021-04-19T12:39:36.797" Score="0" ViewCount="22" Body="&lt;p&gt;I'm new to RF engineering and I want to ask how to draw magnetic and electric wall in HFSS software? I know magnetic Wall means open circuit in circuit model and electric wall means short circuit, but how do I plot make this on HFSS when I'm making the antenna as a physical system instead of circuit.&lt;/p&gt;&#xA;" OwnerUserId="19189" LastEditorUserId="76" LastEditDate="2021-04-19T16:38:32.217" LastActivityDate="2021-04-19T16:38:32.217" Title="Magnetic and Electric Wall in HFSS" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;antenna-modeling&gt;&lt;hfss&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18345" PostTypeId="2" ParentId="5905" CreationDate="2021-04-19T21:00:55.537" Score="0" Body="&lt;p&gt;In point of fact, I took two elements in one sitting in the fall of 2020, and I got my General ticket.  I was too exhausted to try the extra test but I could have.&lt;/p&gt;&#xA;" OwnerUserId="1426" LastActivityDate="2021-04-19T21:00:55.537" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18346" PostTypeId="2" ParentId="18343" CreationDate="2021-04-20T03:13:17.767" Score="1" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;When testing my speaker and volume knob(with music from my computer via audio cable), I the volume is too quiet.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;The line out on your computer is designed to drive the line in on some other equipment, not a speaker. The input impedance on a line input is typically around 10k ohms, and at maximum volume the voltage is around -10 dBV or 316 mV.&lt;/p&gt;&#xA;&lt;p&gt;This is simply not enough power to be very audible. Furthermore a speaker's impedance is much less than 10k ohms, so you're operating the equipment far out of spec. Fortunately most audio outputs are designed to at least not be damaged even if you connect them to a short.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The radio has a spec that says &amp;quot;headphone output 16ohm min&amp;quot;. How do I know what speaker and pot combination would get the best result with this specification for good volume control?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Well, if it says &lt;em&gt;headphone&lt;/em&gt; output then you probably won't get very good results with a &lt;em&gt;speaker&lt;/em&gt;. Headphones:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;do not require nearly as much power, since they are right on your ears, and&lt;/li&gt;&#xA;&lt;li&gt;they typically have a higher impedance, some hundreds of ohms, in contrast to speakers which are often less than 10.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;I've got 3 ring audio cable that I'm wiring to my small speaker. Do the left and right rings of the cable get wired to the 2 prongs on the speaker?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;No. A line output is not designed to be connected to a speaker at all. Instead it should be connected to an amplifier with a high input impedance. The amplifier in turn drives the speakers.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-04-20T23:08:00.540" LastActivityDate="2021-04-20T23:08:00.540" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18347" PostTypeId="1" CreationDate="2021-04-20T05:44:05.213" Score="3" ViewCount="67" Body="&lt;p&gt;I am having trouble understanding the 1:4 Guanella current balun here.  So at DC, or low frequencies, I think the current path would be a short to ground.  At higher frequencies, I am getting confused on how the current path through the lower coax's inner conductor, whose return path is along the shield of the outer conductor, behaves.  I get the concept that power is conserved, so if the voltage doubles, the resistance must quadruple (P=V^2/R).  But, why does the voltage double?  Does the extra current returning on the shield of the upper coax lower the ground potential?  Or does it double the returning current on the shield while the inner conductors current is left unchanged?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/RWua5.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/RWua5.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19435" LastEditorUserId="218" LastEditDate="2021-04-20T13:14:19.320" LastActivityDate="2021-04-21T23:30:50.007" Title="1:4 Guanella unun current balun" Tags="&lt;balun&gt;&lt;transformer&gt;" AnswerCount="2" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18348" PostTypeId="2" ParentId="18347" CreationDate="2021-04-20T14:15:18.220" Score="2" Body="&lt;p&gt;The voltage doubles because the two coaxial cables are connected in &lt;em&gt;parallel&lt;/em&gt; on the input side, but in &lt;em&gt;series&lt;/em&gt; on the right hand side.&lt;/p&gt;&#xA;&lt;p&gt;In the diagram, there shouldn't be a little i in the middle of the upper coax, no common-mode current can flow there.&lt;/p&gt;&#xA;&lt;p&gt;This trick doesn't work with batteries at DC, it just shorts out the supply, but at RF the choke, shown as the dotted lines on the upper coax, effectively disconnects it from the rest of the circuit. The coax through that choke, or wound around that core, is like a magic non-connected tunnel between left and right.&lt;/p&gt;&#xA;&lt;p&gt;The twin-coax unun has very good high frequency performance because the two coax lines mean that the added voltages on the output &lt;em&gt;are always in phase&lt;/em&gt;. The low frequency limit is where the choke no longer provides an impedance that is several times the output impedance, which depends on the ferrite, but within reason &lt;em&gt;there is no impact on the high frequency performance by using a larger core and/or more turns&lt;/em&gt;. If the high frequency performance isn't important, say you only need 1.8 to 14 MHz, then the lower coax can be omitted entirely. This is also what you get from a 1:4 bifilar-wound unun on a single core.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-04-21T23:30:50.007" LastActivityDate="2021-04-21T23:30:50.007" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18349" PostTypeId="1" AcceptedAnswerId="18397" CreationDate="2021-04-20T14:23:02.890" Score="2" ViewCount="96" Body="&lt;p&gt;I want to be able to get in touch with hams in my area when we are not both on air at the same time, but are close enough to each other for VHF communication. I want to be able to use my radio to call in a message for them to retrieve at a later time, like calling in for voicemail?&lt;/p&gt;&#xA;&lt;p&gt;What sort of existing solutions are there for setting up a base station that will record messages and then on command re-transmit them? It must work on FM, not a digital mode, and of course be legal in the US. I am a General class licensee.&lt;/p&gt;&#xA;&lt;p&gt;This repeater control software seems to have the functions I want, and a lot more: &lt;a href=&quot;http://www.arandis.se/rlm/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.arandis.se/rlm/index.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;But I wanted to have some more options to pick from, and really only need the voicemail type functionality.&lt;/p&gt;&#xA;" OwnerUserId="8066" LastEditorUserId="4665" LastEditDate="2021-04-21T18:49:42.193" LastActivityDate="2021-04-28T20:51:42.030" Title="Store and forward system like voicemail for hams" Tags="&lt;united-states&gt;&lt;legal&gt;&lt;repeater&gt;&lt;fm&gt;&lt;software&gt;" AnswerCount="3" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18350" PostTypeId="2" ParentId="18347" CreationDate="2021-04-20T16:08:46.530" Score="3" Body="&lt;p&gt;It may help to consider that this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/Tg41m.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/Tg41m.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;is equivalent to this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/mdI7j.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/mdI7j.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The lines above the transmission line indicate it is wound on a ferrite. Because only the common mode affects the electromagnetic fields outside the coax, the ferrite increases the common mode impedance but does not affect the differential mode. To simplify analysis we can assume the common-mode impedance is infinite, and so the common-mode current must be zero.&lt;/p&gt;&#xA;&lt;p&gt;The second diagram indicates two separate windings instead of coax. Because a differential current in the windings creates opposite magnetic fields that cancel, differential current doesn't &amp;quot;see&amp;quot; the core, and differential mode impedance is unchanged, whereas common mode current &amp;quot;sees&amp;quot; the core and a higher (assumed infinite) impedance. The mechanism is slightly different but the effect is the same.&lt;/p&gt;&#xA;&lt;p&gt;Having accepted the equivalence of these two constructions, you should be able to follow &lt;a href=&quot;https://ham.stackexchange.com/a/15119/218&quot;&gt;other explanations of a Guanella balun&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-20T16:08:46.530" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18352" PostTypeId="2" ParentId="18349" CreationDate="2021-04-21T00:17:56.903" Score="1" Body="&lt;p&gt;I can imagine a device that listens on a ham frequency to record voice messages and decode commands, and then retransmits recorded voice messages on the same frequency on command.  Such a device would be relatively easy to design and build.  But there are legal issues, at least in the US.&lt;/p&gt;&#xA;&lt;p&gt;Legally speaking, I presume that you're talking about an automated system that can transmit without being constantly monitored by a control operator.  I can think of three types of stations in which an automated system can transmit legally on the ham bands under US law (not including earth stations, space stations, and telecommand stations, which have to do with stations in orbit): propagation beacons, automatically-controlled digital stations, and &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.205&quot; rel=&quot;nofollow noreferrer&quot;&gt;repeaters&lt;/a&gt; under automatic control.  You ruled out digital modes, and propagation beacons aren't allowed to transmit voice messages, so as I see it, the only legal way to operate such a device in the US would be as a repeater under automatic control.  (Please know that I'm not a lawyer.)&lt;/p&gt;&#xA;&lt;p&gt;Unfortunately, your device has now gotten quite a bit more complicated: in addition to listening for messages and commands, and retransmitting stored messages and acknowledgements, now your device has to also retransmit everything it hears on another frequency, and also comply with other legal requirements for automatic control such as transmitting its call sign periodically, timing out after someone transmits through the repeater for more than a few minutes, and monitoring a separate control channel (another frequency, or a telephone line, or an internet connection) for commands.&lt;/p&gt;&#xA;&lt;p&gt;Repeaters are quite expensive, if your goal is simply to store and forward messages.  But if you have a repeater already, and the repeater controller is a computer, then installing some software that works with your repeater hardware sounds like a reasonable way to accomplish what you're asking for.&lt;/p&gt;&#xA;&lt;p&gt;The poster of the question has pointed out that there is a &lt;a href=&quot;https://www.argentdata.com/catalog/product_info.php?products_id=98&quot; rel=&quot;nofollow noreferrer&quot;&gt;device marketed as a &amp;quot;simplex repeater&amp;quot;&lt;/a&gt; that connects to a radio and does what the poster of the question is asking for: it records messages and retransmits them later upon command on the same frequency.  Unfortunately that device doesn't comply with the definition of a repeater in &lt;a href=&quot;https://www.law.cornell.edu/cfr/text/47/97.3&quot; rel=&quot;nofollow noreferrer&quot;&gt;47 CFR § 97.3&lt;/a&gt; (I added the bold face):&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;(40) Repeater. An amateur station that &lt;strong&gt;simultaneously&lt;/strong&gt; retransmits the transmission of another amateur station &lt;strong&gt;on a different channel&lt;/strong&gt; or channels.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Because that device marketed as a simplex repeater doesn't simultaneously retransmit on a different channel, legally it's not a repeater, and therefore such a device can't legally transmit under automatic control.  But the FCC has changed quite a bit from the old days, and their attention is on spectrum auctions, mobile phones, and broadband internet far more than on the amateur service, so unless they get quite a few complaints, in my opinion they are unlikely to act to prevent &amp;quot;simplex repeaters&amp;quot; from being sold.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-04-28T01:53:31.880" LastActivityDate="2021-04-28T01:53:31.880" CommentCount="7" ContentLicense="CC BY-SA 4.0" />
  <row Id="18353" PostTypeId="2" ParentId="18318" CreationDate="2021-04-21T00:27:21.117" Score="1" Body="&lt;p&gt;There is a very simple answer regarding the diagram &amp;quot;Additional loss in dB caused by standing waves.&amp;quot; It shows the fraction of the power sent into the cable that is converted to heat. (The rest is delivered to the antenna.) We could measure voltage, current and phase to compute power at both ends.&lt;/p&gt;&#xA;&lt;p&gt;There would be an additional loss if the transmitter can not deliver full power into the impedance the cable presents to it - but that is not a loss due to the cable, it is a loss due to an unsuitable transmitter having an inadequate impedance tuning range. (It could be converted to an adequate transmitter by adding a tuner to it.)&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2021-04-21T00:27:21.117" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18354" PostTypeId="1" CreationDate="2021-04-21T01:07:48.393" Score="0" ViewCount="72" Body="&lt;p&gt;This question is about digital voice modes that are used with AM / SSB / FM radios.  Dstar , FreeDV , etc.&lt;/p&gt;&#xA;&lt;p&gt;assumptions:&#xA;pulse width modulation amplifiers can take a digital signal as input.&lt;/p&gt;&#xA;&lt;p&gt;a software defined radio(SDR) is a sensor that can recive any kind of signal within a certain frequency range.&lt;/p&gt;&#xA;&lt;p&gt;SDR demodulation is just software and can theoretically process any signal.&lt;/p&gt;&#xA;&lt;p&gt;My question is , could traditional rf modulation techniques be removed entirely ?&lt;/p&gt;&#xA;&lt;p&gt;Scenario:&#xA;microphone in to computer such as microcontroller /  raspberry pi&#xA;I2C digital connection direct to PWM amplifier&#xA;PWM amplifier transmits raw signal at RF frequencies in exact frequency range&#xA;SDR set to receive any signal in exact known frequency range&#xA;PC software detects PWM signal in frequency range and converts to digital audio signal&#xA;PC outputs audio&lt;/p&gt;&#xA;&lt;p&gt;There is no audio conversion except what is normally done by a PC when you use a microphone&#xA;or speakers&#xA;.There is no separate RF modulation like FM / SSB.  The &amp;quot;modulation&amp;quot; is whatever the pulse width modulation of the amplifier is.&lt;/p&gt;&#xA;&lt;p&gt;This would be like a class D audio amp with digital input from a pc except that the amplifier is connected to an antenna instead of a speaker.&lt;/p&gt;&#xA;" OwnerUserId="14671" LastActivityDate="2021-04-23T01:43:27.373" Title="human voice / music radio signal without RF moduation" Tags="&lt;software-defined-radio&gt;&lt;gnuradio&gt;&lt;modes&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18355" PostTypeId="2" ParentId="18354" CreationDate="2021-04-21T03:09:02.230" Score="1" Body="&lt;p&gt;Yes.  In fact lots of digital signals already work this way.  That's what creates broadband RFI.&lt;/p&gt;&#xA;&lt;p&gt;Hold a cheap AM radio (ferrite antenna) fairly close to a running USB connection, ethernet connection, modulated switching power supply, or most any other fast digital signal wiring, etc., and you will hear the buzz sent by radio waves directly created by the digital drivers for those signals, no FM or SSB modulator required.&lt;/p&gt;&#xA;&lt;p&gt;However, it's really inefficient.  Note that you have to hold that AM radio fairly close to pick up the digital buzz.  (Maybe, with low background noise, a good receiver and antenna can pick it up that RFI a few hundred meters away?)  Whereas that same cheap AM radio can tune to properly modulated AM stations 100's to 1000's of miles away, due to the AM modulations more efficient use of bandwidth.&lt;/p&gt;&#xA;&lt;p&gt;If you amplify a digital RFI signal to get more range, you will likely violate many radio laws or regulations (FCC part 15 in the U.S.?) in your particular legal jurisdiction.&lt;/p&gt;&#xA;&lt;p&gt;Added:  Yet another way to think about it is that unmodulated digital signal are very broadband, and there are likely tons of digital signals in your building.  Modulation allows one to efficiently squeeze the information into a relatively tiny slice of spectrum where all those other digital signals in your environment are less likely to interfere and drown out your intended transmission.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-23T01:43:27.373" LastActivityDate="2021-04-23T01:43:27.373" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18356" PostTypeId="2" ParentId="18354" CreationDate="2021-04-21T14:03:59.517" Score="2" Body="&lt;p&gt;A radio without any modulation would simply take the input signal, amplify it, and feed it directly into an antenna. In other words, if &lt;span class=&quot;math-container&quot;&gt;$x(t)$&lt;/span&gt; is the signal to be transmitted, and &lt;span class=&quot;math-container&quot;&gt;$y(t)$&lt;/span&gt; is the transmitted signal, then we're looking for:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ y(t) = x(t) $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;There are some radios that could work somewhat like this. For example, the part of the radio spectrum from 0.3 to 3 kHz, which overlaps with the frequency range of human speech, is called &lt;a href=&quot;https://en.wikipedia.org/wiki/Ultra_low_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;ultra low frequency&lt;/a&gt;. But there are extreme practical challenges with transmitting a signal at such low frequencies: the antenna much be extremely large, and also the &lt;a href=&quot;https://www.antenna-theory.com/definitions/fractionalBW.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;fractional bandwidth&lt;/a&gt; would have to be extremely large.&lt;/p&gt;&#xA;&lt;p&gt;Now, if you wanted to &amp;quot;just&amp;quot; shift the baseband signal (say, an audio signal of your voice) up to RF and transmit that, that is possible: it's called &lt;a href=&quot;https://en.wikipedia.org/wiki/Single-sideband_modulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;upper-sideband modulation&lt;/a&gt;. Not only is it possible but it's very common. However, just shifting the frequency up or down still counts as modulation.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-21T14:03:59.517" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18357" PostTypeId="1" AcceptedAnswerId="18359" CreationDate="2021-04-21T17:12:02.907" Score="2" ViewCount="95" Body="&lt;p&gt;This question may be a little strange, but how can I receive radio waves from a country like North Korea (when I live in Poland)? I am interested in this topic, but I don't have that much knowledge. Can I use any radio working on UHF/VHF or do I need some other equipment using a different range? I will be grateful for any answer!&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/keoyw.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/keoyw.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18026" LastEditorUserId="8717" LastEditDate="2021-04-22T18:29:32.303" LastActivityDate="2021-04-22T18:29:32.303" Title="Receiving shortwave frequencies from different countries (e.g. North Korea)" Tags="&lt;hf&gt;&lt;receiver&gt;&lt;frequency&gt;&lt;swl&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18358" PostTypeId="1" AcceptedAnswerId="18360" CreationDate="2021-04-21T18:45:09.280" Score="0" ViewCount="63" Body="&lt;p&gt;I'm learning about shortwave listening. I want to listen to amateur/ham radio on a portable radio (eg a XHDATA d-808) with ssb, I hear ssb is the main place hams would be on. I know it's hard to give an exact figure on range as conditions vary. But how far in Kilometers am I likely to hear hams from with my portable radio? I live in Southern England, in the UK, in an urban area. Thanks&lt;/p&gt;&#xA;" OwnerUserId="19454" LastEditorUserId="19454" LastEditDate="2021-04-21T19:20:14.740" LastActivityDate="2021-04-21T21:29:36.780" Title="Receiving range of ham radio on SSB with a portable radio reciever" Tags="&lt;receiver&gt;&lt;ssb&gt;&lt;portable&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18359" PostTypeId="2" ParentId="18357" CreationDate="2021-04-21T19:14:03.160" Score="3" Body="&lt;p&gt;The frequencies in your pasted image of a table are in kilohertz (kHz).  These days frequencies are more often expressed in megahertz or gigahertz (MHz or GHz).  Anyway, frequencies ranging from 3560 kHz, also known as 3.56 MHz, to 15.245 MHz are in the high-frequency (HF) band, also commonly called &amp;quot;shortwave&amp;quot;, rather than the very-high-frequency (VHF) or ultra-high-frequency (UHF) bands, which generally range from 30 MHz to 3 GHz (also known as 3000 MHz).&lt;/p&gt;&#xA;&lt;p&gt;So if you have a radio that receives on the VHF and UHF bands, then you won't be able to receive the Voice of Korea from Poland.  A shortwave radio would work better, but you might have trouble receiving the signal in urban areas because the RF noise from modern electronics has gotten so bad.  These days, many shortwave broadcasters also make their broadcasts available via internet.  (I didn't see any way to stream the broadcast over the internet with a quick scan of the Voice of Korea's web site.)&lt;/p&gt;&#xA;&lt;p&gt;A local amateur radio club could be an excellent resource for setting up a shortwave receiver; they could give you valuable advice on the best time of day and band to listen, and help you with antennas.  An external wire antenna would probably work much better than the built-in whip antennas that many shortwave receivers have.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-04-21T19:14:03.160" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18360" PostTypeId="2" ParentId="18358" CreationDate="2021-04-21T19:24:21.877" Score="0" Body="&lt;p&gt;The range of amateur radio SSB over HF &amp;quot;shortwave&amp;quot; can be between a few meters to over 20000 kilometers, depending on frequency band, transmit power, antenna type/height/polarization/aim, solar weather (including sunspot cycle, solar flares, etc.), other ionospheric conditions, time of day, local RF noise floor (including your household electronics), and etc.&lt;/p&gt;&#xA;&lt;p&gt;Some major sources of likely distance limitations for urban area shortwave listening are, first, not being able to put up a large enough high enough antenna with respect to the wavelength of interest, and second, local RF noise from poorly shielded or malfunctioning electronics (power transformers, USB chargers, LED lights, solar panels, etc.) within your neighborhood or building.  This RF noise can drown out distant signals of interest.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-21T19:39:00.793" LastActivityDate="2021-04-21T19:39:00.793" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18361" PostTypeId="1" AcceptedAnswerId="18363" CreationDate="2021-04-21T21:22:29.170" Score="5" ViewCount="111" Body="&lt;p&gt;As a bit of curiosity, I was wondering what the longest path ever used by amateur radio operators has been.&lt;/p&gt;&#xA;&lt;p&gt;Of course the opposite side of the Earth is no problem with a good HF station. And you can work long-path, so that's at least the circumference of the Earth.&lt;/p&gt;&#xA;&lt;p&gt;EME contacts are an even longer path, even if the stations aren't as far apart.&lt;/p&gt;&#xA;&lt;p&gt;A longer path would seem to require reflection off a natural satellite (doesn't seem feasible) or via an artificial satellite with amateur radio equipment. Have any of the few artificial satellites to have left Earth orbit had any amateur radio equipment? Or is there some other mechanism I'm not considering?&lt;/p&gt;&#xA;&lt;p&gt;To be clear, receiving telemetry from any artificial satellite with amateur radio equipment does not count. I'm talking only about communications in the ham bands, intended to be used by the amateur radio service.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-22T05:23:26.923" Title="Has an amateur radio communication ever taken a path outside the Earth-Moon system?" Tags="&lt;satellites&gt;" AnswerCount="1" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18362" PostTypeId="2" ParentId="18358" CreationDate="2021-04-21T21:29:36.780" Score="3" Body="&lt;p&gt;The range of ham radio communications ranges from zero to unlimited. At the longer range of the scale, some hams direct there signal at the moon, where it's reflected back and received back on Earth. That's a round-trip distance of about 477,000 miles or 768,000 km. Communication over longer distances would be possible, but as far as I know &lt;a href=&quot;https://ham.stackexchange.com/q/18361/218&quot;&gt;there's nothing far enough away&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Unless you are using some very old, or very terrible equipment, range is limited not by your radio but by your antenna and the noise in your area, as well as the frequency and time you are listening on which will affect how well or not the signal can propagate over long distances.&lt;/p&gt;&#xA;&lt;p&gt;It's likely if you are interested in hams far away, perhaps as far as the opposite side of the planet, you will be most interested in the frequencies that fall in the &lt;a href=&quot;https://en.wikipedia.org/wiki/High_frequency&quot; rel=&quot;nofollow noreferrer&quot;&gt;HF band&lt;/a&gt;. Even within that band, the effective range varies by time of day, time of year, and the particular frequency. The best way to discover which frequencies work over what areas at what times is to use a prediction tool like &lt;a href=&quot;https://www.voacap.com/&quot; rel=&quot;nofollow noreferrer&quot;&gt;VOACAP&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Being in an urban environment, noise will probably be your biggest challenge. The best thing you could do would be to move (at least temporarily) to a very rural area. But if you can't do that, focus your efforts on getting an antenna outside and high up, and as far away from buildings and power lines as you can. If you have room for a directional antenna that will help a lot.&lt;/p&gt;&#xA;&lt;p&gt;Knowing the best frequencies and times to listen, and with some attempt to get a good antenna up, you should be able to occasionally hear stations on the opposite side of the planet. There are periodic contests where hams try to get the most points for making the most contacts with the most stations that are the most far away, during one of these would be a good time to listen as many more hams with powerful stations will be transmitting.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-21T21:29:36.780" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18363" PostTypeId="2" ParentId="18361" CreationDate="2021-04-22T05:23:26.923" Score="5" Body="&lt;p&gt;AMSAT-DL has &lt;a href=&quot;https://makezine.com/2009/03/29/amateur-eve-radio-bounce/&quot; rel=&quot;noreferrer&quot;&gt;heard their own echoes on an Earth-Venus-Earth path&lt;/a&gt;, on the 13cm band, with the help of the 20-meter dish at Bochum Observatory. It falls a little short of &amp;quot;communication&amp;quot;, but it seems that, given two stations with 20m dishes, a Venus-bounce QSO using QRSS, or perhaps one of the slow FSK modes (FST4?) would be achievable.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-04-22T05:23:26.923" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18365" PostTypeId="2" ParentId="4951" CreationDate="2021-04-22T20:33:43.423" Score="1" Body="&lt;p&gt;With respect to the fuse in the negative questions is straightforward. &lt;strong&gt;It protects nothing.&lt;/strong&gt; Remove the fuse, and the radio still operates because it is using the coax shield for DC power. The fuse that protects both positive and negative wires is the &lt;em&gt;&lt;strong&gt;positive fuse&lt;/strong&gt;&lt;/em&gt;. It is a &lt;strong&gt;Grounded system&lt;/strong&gt; where one circuit conductor is bonded to Ground like a frame of a vehicle. In an AC system, the grounded circuit conductor is Neutral.&lt;/p&gt;&#xA;&lt;p&gt;The whole point of a &lt;em&gt;&lt;strong&gt;Grounded System&lt;/strong&gt;&lt;/em&gt; is to facilitate simple, cost-efficient,  and effective over-current protection of the circuit conductors. Only requires the ungrounded circuit conductors to have a breaker or fuse located at the feed point.&lt;/p&gt;&#xA;&lt;p&gt;A Floating System like batteries or an AC Delta circuit where no circuit conductors are bonded to ground requires a fuse or breaker on &lt;strong&gt;all ungrounded circuit conductors&lt;/strong&gt;, plus ground fault detection in the event one of the circuit conductors is grounded. If you &lt;strong&gt;FLOAT&lt;/strong&gt; a battery system would require both positive and negative conductors to have an over-current protection device installed.&lt;/p&gt;&#xA;&lt;p&gt;Over Current Protection Devices (OCPD's) are not used to protect the load utilization equipment like your radios. Fuses and breakers are there to protect the wire connected to the load side terminal of the OCPD. Nothing else. Anything beyond that is collateral. All electrical codes have minimum size wire requirements based on the breaker Ampere rating. For example, a 20-amp OCPD requires a minimum of 12 AWG or larger wire. The insulation on a 12 AWG wire fed with a 20-amp breaker will never experience thermal damage to the wire's insulation preventing an electrical short or fire as a result. Electrical codes protect the power wiring only. What you plug in is an Equipment Code issue equipment manufacturers deal with.&lt;/p&gt;&#xA;&lt;p&gt;Electrical codes do not permit grounded circuit conductors to be switched, or have fuses and switches inserted. They must be solidly bonded and never interrupted. The reason is very simple. For sake of argument imagine this. Disconnect the radio coax from your radio, and assume your installation did not use any chassis-to-chassis bonding and is electrically isolated and floating. You slid the radio under the seat with carpet and rubber backing. Now pull the negative fuse while leaving the positive connected normally. Take a DMM and you will read 12 volts on the radio chassis and negative wire where you pulled the fuse. It is looking for a return path to the battery. The radio chassis is HOT.&lt;/p&gt;&#xA;&lt;p&gt;Granted 12-volts is not a shocking experience. Now repeat the experiment with a higher voltage, say 120 volts. Real simple to do using an old fashion incandescent hand test lamp like you would hang under the hood of a car while working; a test plug for an AC wall socket; and one test jumper with alligator clips. Use the test plug and jumper to connect Line to the lamp power plug line stab. Leave Neutral circuit open(DC negative equivalent). Turn the lamp switch on. The light will not come on because Neutral is open. Now wet both index fingers on each hand. Take one wet finger and place it on  ground, and the other to the lamp power plug neutral stab and watch the light come on and lights you up.&lt;/p&gt;&#xA;&lt;p&gt;Now imagine Mr Sparky, your friendly Electrician working in Sammy Hammy's house with a low voltage problem in the shack. Mr Sparky checks your AC power at the wall receptacle. Like all Mr. Sparky's know, Neutral is grounded and safe to touch. While checking your AC wall circuit,  he jumps and cusses because he got bit with 120-VAC touching the Neutral terminal. Checks the wiring and finds Sammy did some wiring work and put the AC wall receptacle on a wall switch switching the Neutral rather than Line. Mr. Sparky finds two problems. Undersized wire causing the voltage sag problem and improperly wired wall switch. He knows why electrical codes do not allow the grounded circuit conductor to be interrupted and must be solidly bonded.&lt;/p&gt;&#xA;&lt;p&gt;Connect your radio's negative power wire to the vehicle chassis as close to the radio as possible using a hard point like a seat bolt or ground terminals provided by the auto manufacture. They are under seats for things like Inverters, high power audio amps, heated/power seats, and accessories. Do not roll up the slack on positive, negative, and coax. Keep them as short as possible. Otherwise adds voltage loss and noise. Throw the second fuse in the parts bin.&lt;/p&gt;&#xA;&lt;p&gt;Manufactures provide the second fuse in the event sammy hammy installs the radio with negative power wire terminated directly the battery term post. It protects sammy hammy from himself in the event sammy hammy worked on the car and forgot to reconnect the vehicles factory bonding jumper back up. Pros call them dummy fuses or spare parts.&lt;/p&gt;&#xA;" OwnerUserId="19467" LastActivityDate="2021-04-22T20:33:43.423" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18366" PostTypeId="1" AcceptedAnswerId="18367" CreationDate="2021-04-23T11:50:38.227" Score="1" ViewCount="105" Body="&lt;p&gt;In many youtube videos about building low power radio transmeters , I have seen a piece of regular wire or extension cord used as a antenna. But , it seems like telecommunication antennas have specific geometry (like dipole antenna , dish antenna etc).But why do we have to follow specific geometry for designing antenna?&lt;/p&gt;&#xA;&lt;p&gt;Is it because using an extension cord as a antenna have much more power losses? If it does have , how do we calculate it?&lt;/p&gt;&#xA;" OwnerUserId="19472" LastActivityDate="2021-04-27T23:22:18.307" Title="Why do we need special geometry for telecommunication antennas?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="3" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18367" PostTypeId="2" ParentId="18366" CreationDate="2021-04-23T12:48:06.760" Score="3" Body="&lt;p&gt;A wire antenna that doesn't have a specific geometry may be called a random wire antenna.  Such an antenna will correspondingly have a random performance with a random radiation pattern.   In these cases, typically we care more about getting any signal out at all, rather than doing it efficiently or in a specific direction.  A random wire antenna might be cut to length for a specific frequency, or it may be a more or less random length with an antenna tuner between it and the radio to match the impedance.  (Even a random length wire may need to be cut within a range of lengths for some tuners to be able to tune it.)&lt;/p&gt;&#xA;&lt;p&gt;A dipole's most important characteristic is that it is close to a half wave long.  It's geometry isn't critical beyond that, but variations in geometry will change characteristic impedance and radiation pattern (and possibly polarization) at least.   Typically a dipole is depicted as two quarter wave segments that are colinear.  Practically, we may want to actually have them in an inverted V pattern for best impedance, but other patterns work as well, and may or may not affect radiation pattern significantly.  A dipole has some directionality, but typically the concern with a dipole is polarization (for vhf) and elevation angle of the radiation pattern (for vhf and hf).  For HF dipoles, height above ground may affect elevation angle of the radiation pattern more than the antenna's internal geometry.&lt;/p&gt;&#xA;&lt;p&gt;A dish is not an antenna, but may be part of an antenna system.  A dish is a reflector, and typically has an antenna near the focus of the dish with a radiation pattern that covers the dish; the dish shape is critical to focusing RF energy on the antenna, and the antenna's shape is important for optimizing the aiming of the energy at the dish.  The dish is typically parabolic but may be spherical or hyperbolic, and the curve may be in 2 or 3 dimensions.  The ideal antenna for the dish can be any number of models with a hemispherical or one sided conical radiation pattern.  (Although, a 2d parabolic dish could use a dipole exactly at the focus, parallel to the axis of curvature.)&lt;/p&gt;&#xA;&lt;p&gt;Other antennas, for example, yagi, moxon, patch, etc., are directional antennas, and their geometry is critical to forming their directionality.  The directionality also is coupled with making the antenna high gain.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-04-24T13:18:46.787" LastActivityDate="2021-04-24T13:18:46.787" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18368" PostTypeId="2" ParentId="18366" CreationDate="2021-04-23T17:46:03.560" Score="-2" Body="&lt;p&gt;There are at least 3 reasons for using &amp;quot;special geometries&amp;quot; for RF antennas: resonant frequency, impedance match, and pattern.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If the antenna is of a length and geometry that is resonant at the frequency of interest, then the antenna will be more efficient capturing energy from the airwaves at the frequency of interest.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If the antenna geometry has a matched feedpoint impedance at the frequency of interest, then it can pass power to the feedline or feedpoint with a lower likelihood of resistive losses (depending on the feed line or wire type).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;If the antenna geometry at the frequency of interest is sized, shaped, and angled to better capture signals in the polarization and direction of interest, and potentially less well positioned and angled to capture RF noise, then the signal transferred to the receiver will have a better S/N ratio (less noise that could completely cover up the signal(s) of interest).  Very short wires (relative to wavelengths) might capture more household RF noise than any interesting HF radio signals.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-23T17:51:25.990" LastActivityDate="2021-04-23T17:51:25.990" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18369" PostTypeId="1" CreationDate="2021-04-23T17:55:14.653" Score="4" ViewCount="129" Body="&lt;p&gt;I've been trying to understand how dipole antennas work, and I believe I understand the basics when they're fed via a balanced feed line. In fact, every dipole physics YouTube video and web page I can find explains how they work with a balanced feed line as the example.&lt;/p&gt;&#xA;&lt;p&gt;But how do they work with an unbalanced feed line, such as coax? In that case, the shield of the coax is connected to one half of the dipole. What's driving that half of the dipole?&lt;/p&gt;&#xA;&lt;p&gt;This is a closely related question:&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/16120/coax-fed-dipole-shield-goes-to-one-side-yet-is-grounded-via-chassis-line-to-ea&quot;&gt;Coax fed dipole: shield goes to one side, yet is grounded via chassis line to Earth&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;However, it never fully explains what's driving that grounded half of the dipole.&lt;/p&gt;&#xA;&lt;p&gt;The best I've managed to surmise, is that perhaps the center conductor of the coax somehow affects the inner diameter of the shield of the coax in an equal and opposite manner, and THAT force is what drives the 2nd half of the dipole. But I'm not sure, and no one seems to discuss this directly in any resource I can find.&lt;/p&gt;&#xA;&lt;p&gt;The other option I've considered is that perhaps the driven half of the dipole is influencing the non-driven half, due to its proximity to the EM field. In that case, the coax wouldn't really play a role other than giving the current somewhere to flow when that half of the antenna is influenced (but that seems wrong since that half should radiate that energy...).&lt;/p&gt;&#xA;&lt;p&gt;So put simply: in a dipole antenna driven by coax feedline, what's powering the half of the dipole that's connected to ground? Where does that current come from?&lt;/p&gt;&#xA;&lt;p&gt;Thank you!&lt;/p&gt;&#xA;" OwnerUserId="19474" LastActivityDate="2021-04-26T14:59:37.553" Title="When a dipole antenna is fed via coax, what powers the ground-side of the dipole?" Tags="&lt;antenna&gt;&lt;dipole&gt;&lt;coaxial-cable&gt;&lt;feed-line&gt;&lt;physics&gt;" AnswerCount="3" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18370" PostTypeId="2" ParentId="18369" CreationDate="2021-04-24T00:09:28.803" Score="3" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;But how do they work with an unbalanced feed line, such as coax? In that case, the shield of the coax is connected to one half of the dipole. What's driving that half of the dipole?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;The current in the shield is.&lt;/strong&gt; In the center conductor, current flows one direction, and in the shield, equal and opposite current flows. &lt;em&gt;This part&lt;/em&gt; of the situation is exactly the same as if there was a balanced feed line.&lt;/p&gt;&#xA;&lt;p&gt;Remember basic electric circuit principles: &lt;strong&gt;current flows in loops.&lt;/strong&gt; This is still true in RF, except that sometimes the loops extend out into air (by radiation). Your feed line is a two-wire circuit, and so the current through the coax in one direction must equal the current through the coax in the other direction — &lt;em&gt;unless&lt;/em&gt; there is “common-mode current”, in which case the feed line radiates and a portion of the return current loop is through other conductors connected by some path to the transmitter's ground. (But that situation can be analyzed as a &lt;a href=&quot;https://en.wikipedia.org/wiki/Superposition_principle&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;em&gt;superposition&lt;/em&gt;&lt;/a&gt; of the 'regular' current and the common-mode current.)&lt;/p&gt;&#xA;&lt;p&gt;You may be thinking: &amp;quot;But the shield is grounded!&amp;quot; That doesn't stop current from flowing in it; it only affects the &lt;em&gt;voltage&lt;/em&gt; of (the grounded point(s) on) the shield. Just like our ordinary circuit grounds, that we say are more-or-less &amp;quot;0 volts&amp;quot;: there are return currents flowing in the &amp;quot;ground&amp;quot; conductor. Suppose my &amp;quot;transmitter&amp;quot; is a battery instead: I can attach the negative terminal to the coax shield (and optionally to the earth), and the positive terminal to the center conductor, and put some DC load in place of the antenna, and I'm transferring power through the cable. &lt;strong&gt;This works the same whether you're looking at DC or RF;&lt;/strong&gt; the only thing RF adds is the complication of ensuring that the RF won't radiate away except for where we want it to (the antenna).&lt;/p&gt;&#xA;" OwnerUserId="76" LastEditorUserId="76" LastEditDate="2021-04-26T14:59:37.553" LastActivityDate="2021-04-26T14:59:37.553" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18371" PostTypeId="2" ParentId="2080" CreationDate="2021-04-24T14:31:01.147" Score="0" Body="&lt;p&gt;For those wanting to take the Canadian test, yes taking a course helps a lot if you have no electronics background. But what really helped was taking the practice test from ISED Canada online about 20 times until I regularly scored above 90%. Then I took the test and managed 99%. It is a 100 question test.&lt;/p&gt;&#xA;" OwnerUserId="19480" LastActivityDate="2021-04-24T14:31:01.147" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18372" PostTypeId="2" ParentId="18369" CreationDate="2021-04-24T16:26:27.593" Score="2" Body="&lt;p&gt;There is no &amp;quot;ground side&amp;quot; of an antenna or feed line at radio frequencies.&lt;/p&gt;&#xA;&lt;p&gt;A wire of any dimension longer than a fraction of a wavelength in an RF field can have very different voltages at one end than at the other end (or somewhere in the middle).  Thus, it's nearly impossible to absolutely &amp;quot;ground&amp;quot; the entire length of any wire or feed line of finite dimension, if any RF signal or RF field is present.  And if there’s a voltage differential and the impedance is finite, then current will flow along that path.&lt;/p&gt;&#xA;&lt;p&gt;Furthermore, an antenna in free space only cares about the voltage potential difference between the 2 sides of a feed point.  Both can be positive, both can be negative, one or the other can be grounded (with respect to Earth).  But as long as there is a changing potential difference between the two, charge can flow, and accelerating charges can radiate RF waves.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-24T22:57:06.180" LastActivityDate="2021-04-24T22:57:06.180" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18373" PostTypeId="1" CreationDate="2021-04-25T16:19:16.163" Score="0" ViewCount="10" Body="&lt;p&gt;I am seeking the parameter used with the LTEXT buffer parsed from GPSTEXT $GPGGA.  I have poured over a myriad of information without success.  The LTEXT must take an argument, otherwise LOC E will not execute.&lt;/p&gt;&#xA;" OwnerUserId="19487" LastActivityDate="2021-04-25T16:19:16.163" Title="Alinco GPSTEXT/LTEXT" Tags="&lt;alinco&gt;&lt;tnc&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18375" PostTypeId="1" CreationDate="2021-04-26T09:01:15.640" Score="2" ViewCount="40" Body="&lt;p&gt;It seems that a lot of cheap ASK transmitters (for remote controls, etc.) use a similar line encoding, an example can be seen here: &lt;a href=&quot;https://www.devmire.com/2019/06/14/reverse-engineering-a-wireless-doorbell-and-performing-a-replay-attack-part1/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Reverse Engineering a wireless doorbell and performing a replay attack – Part1&lt;/a&gt;. The one in this article can be described like that:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;0 is sent as: high - low - low&lt;/li&gt;&#xA;&lt;li&gt;1 is sent as: high - high - low&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I'm currently trying to replay a wireless doorbell (different from the one described in the article) and it seems similar but not exactly the same:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/g99bf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/g99bf.png&quot; alt=&quot;ASK signal&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I think that here:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;0 is sent as: low - high - low&lt;/li&gt;&#xA;&lt;li&gt;1 is sent as: high - high - low&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;So the signal in the screenshot can be interpreted as:&#xA;&lt;code&gt;001101010110011111&lt;/code&gt;&lt;/p&gt;&#xA;&lt;p&gt;I tried to look at some line encoding articles in wikipedia (Manchester code, NRZI, etc.) but I can't find an exact match.  How is this scheme called?&lt;/p&gt;&#xA;" OwnerUserId="10631" LastActivityDate="2021-04-26T09:01:15.640" Title="How is this line modulation scheme called" Tags="&lt;encoding&gt;" AnswerCount="0" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18376" PostTypeId="2" ParentId="18349" CreationDate="2021-04-26T11:59:25.113" Score="-2" Body="&lt;p&gt;&lt;a href=&quot;http://winlink.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;Winlink Global Radio Email&lt;/a&gt; &amp;quot;&lt;a href=&quot;https://en.wikipedia.org/wiki/Winlink#Technical_protocols&quot; rel=&quot;nofollow noreferrer&quot;&gt;is a worldwide radio messaging system&lt;/a&gt; that uses amateur-band radio frequencies and government frequencies to provide radio interconnection services that include email with attachments, position reporting, weather bulletins, emergency and relief communications, and message relay. The system is built and administered by volunteers and is financially supported by the Amateur Radio Safety Foundation.&amp;quot; Despite an apparent focus on a worldwide HF-based system, it can operate on any frequency with the right equipment (radio, TNC, etc.) and software.&lt;/p&gt;&#xA;" OwnerUserId="9621" LastActivityDate="2021-04-26T11:59:25.113" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18377" PostTypeId="2" ParentId="18369" CreationDate="2021-04-26T13:02:11.853" Score="2" Body="&lt;p&gt;Good question! Properly operating, the coax shield is at ground potential. But a dipole needs both sides driven, ideally with voltages symmetrical around ground potential. So how can this work?&lt;/p&gt;&#xA;&lt;p&gt;The first thing to realize is while the coax shield is at ground potential, it does not have zero current. Rather, the shield is at ground potential because it has equal in magnitude but opposite in direction currents to the center conductor. These opposite currents are associated with electromagnetic fields which cancel, resulting in no electromagnetic fields outside the shield. In other words, the shield is at ground potential if and only if there is zero common-mode current in the coax.&lt;/p&gt;&#xA;&lt;p&gt;So what's required is something that will allow this shield current to pass through to the dipole, while allowing the potential at the shield and at the shield-fed side of the dipole to be different. So there must be something in the circuit across which this voltage can appear.&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;img src=&quot;https://i.stack.imgur.com/aPzP1.png&quot; alt=&quot;schematic&quot; /&gt;&lt;/p&gt;&#xA;&#xA;&lt;p&gt;&lt;sup&gt;&lt;a href=&quot;/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2faPzP1.png&quot;&gt;simulate this circuit&lt;/a&gt; &amp;ndash; Schematic created using &lt;a href=&quot;https://www.circuitlab.com/&quot; rel=&quot;nofollow&quot;&gt;CircuitLab&lt;/a&gt;&lt;/sup&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/538/using-a-balun-with-a-resonant-dipole&quot;&gt;That's the balun's job&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-26T13:02:11.853" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18378" PostTypeId="1" CreationDate="2021-04-26T17:55:05.890" Score="2" ViewCount="63" Body="&lt;p&gt;I have a TV antenna on the top of my house that I don't use. It is the highest point around so I would like to hang a wire antenna (for HF) on it. Is an inactive antenna going to cause any interference? I found &lt;a href=&quot;https://ham.stackexchange.com/questions/9839/how-to-determine-the-minimum-distance-between-ham-and-tv-antennas&quot;&gt;this&lt;/a&gt;, but I think it is different because I don't care about affecting TV reception.&lt;/p&gt;&#xA;&lt;p&gt;As for antenna configuration, I will probably first try an end fed half wave with the wire going over the TV antenna about 75% of the way from the feed point. I could also attach it at the far end of the wire. If it helps I am hoping to use 20m 40m or 80m.&lt;/p&gt;&#xA;" OwnerUserId="19502" LastEditorUserId="8717" LastEditDate="2021-04-27T21:52:58.700" LastActivityDate="2021-04-27T21:52:58.700" Title="Hang wire antenna on TV antenna?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;&lt;hf&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18379" PostTypeId="1" CreationDate="2021-04-26T18:36:58.897" Score="1" ViewCount="75" Body="&lt;p&gt;I have a QRP rig (Mountain Topper) and a variable capacitor QRP end fed half wave antenna with an SWR LED indicator. The LED doesn't go fully out in all configurations but there is always a local minimum on the knob.&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Can this problem be fixed by changing the wire length? I would think so if the LED was most dim on one extreme of the knob, but since it is in the middle, I am doubtful the length can make it any better—only positioning. I am not sure though.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Can I tune an antenna wire length with this LED alone? How?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I have an antenna analyzer but it is broken right now so I am trying to do without. 73 73 73&lt;/p&gt;&#xA;" OwnerUserId="19502" LastActivityDate="2021-04-27T16:36:12.643" Title="Tuning wire with SWR LED" Tags="&lt;antenna&gt;&lt;hf&gt;&lt;qrp&gt;" AnswerCount="2" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18380" PostTypeId="2" ParentId="18379" CreationDate="2021-04-27T09:19:43.363" Score="2" Body="&lt;p&gt;A tuned antenna should result in a real load impedance for your transceiver. This impedance can deviate from 50 Ohm, resulting in an SWR deviating from 1:1.&lt;/p&gt;&#xA;&lt;p&gt;The EFHW antenna impedance can be as high as 1500 Ohm and can only be connected to the TX when there is a transformer at the feedpoint of the antenna; the base I assume. Without a transformer (common 1:5 winding ratio should do) the matching can't be obtained.&lt;/p&gt;&#xA;&lt;p&gt;First check the SWR indicator LED with a dummy load: does the LED dim completely? If not then the SWR indicator fails. Don't worry: a poor indication is better tha no indication.&lt;/p&gt;&#xA;&lt;p&gt;For QRP equipment: my experience is that a tool with a second LED, connected to an RF detector (telescope antenna) that indicates the local E-field is good addition for tuning the antenna to maximum voltage and maximum radiation. Together with the SWR indication this should give an idea of what happens when tuning the antenna.&#xA;(For a loop antenna this is not the best tuning indicator.)&lt;/p&gt;&#xA;&lt;p&gt;Or, best solution, use an impedance matching unit: antenna tuner, with SWR indication.&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2021-04-27T14:52:16.860" LastActivityDate="2021-04-27T14:52:16.860" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18381" PostTypeId="2" ParentId="18378" CreationDate="2021-04-27T12:13:49.133" Score="1" Body="&lt;p&gt;Just using it as a support will definitely have some kind of interaction with your antenna, unpredictable but empirically measurable.&lt;/p&gt;&#xA;&lt;p&gt;BTW, my first thought is that you can try to take advantage of that TV antenna as a capacitive load at the end of your EFHW (make sure to disconnect the TV antenna from any feed line of its own though).&lt;/p&gt;&#xA;&lt;p&gt;Using it like this will shorten the wire you need for the EFHW, and you'll need to use an analyzer to be able to sanely tune for the bands you want.&lt;/p&gt;&#xA;&lt;p&gt;Regardless, definitely worth putting it up and giving it a shot!&lt;/p&gt;&#xA;" OwnerUserId="1550" LastActivityDate="2021-04-27T12:13:49.133" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18382" PostTypeId="2" ParentId="18378" CreationDate="2021-04-27T15:22:20.243" Score="3" Body="&lt;p&gt;Of course, the answer to this question is certainly &amp;quot;it depends.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;Yes, different antenna elements in close proximity can interact and cause interference problems. The most notable issue would be a degradation of both antennas. You don't want that.&lt;/p&gt;&#xA;&lt;p&gt;But you might not have a problem - again depending on what sort of antenna you wanted to put up, and what sort of orientation the respective antenna elements would have with one another.&lt;/p&gt;&#xA;&lt;p&gt;Now, I'm going to assume that you are not using the TV antenna at all, so let's not worry about any deleterious affects there. The primary question would be, would the TV antenna affect an antenna hung from the same support.&lt;/p&gt;&#xA;&lt;p&gt;For example, if you used the TV mast to anchor one end of a 40m dipole, I doubt you would have any problems, particularly if the dipole element tips were 5-10 feet away from the TV antenna.&lt;/p&gt;&#xA;&lt;p&gt;If you used the TV mast to anchor the center of a 40m Inverted-V, you might have a little bit of interaction with the TV antenna -- moreso than you would have with the ends of the 40m dipole.&lt;/p&gt;&#xA;&lt;p&gt;That said, we Amateurs typically mount several antennas on a support, generally with some vertical separation. At my station in Gwinnett county, I have a 15m (50 foot) tower with a Cushcraft A3S / A743, an 80/40/20m trap dipole with one end anchored at the 12m (40 foot) level of the tower, and a 30/17/12m inverted V, whose apex is at 13m (43 foot) level of the tower. All of these antennas are in close proximity, but are mostly for different bands (the dipole and Cushcraft have 40 and 20m in common). From my testing, I don't see any interaction between them.&lt;/p&gt;&#xA;&lt;p&gt;If you aren't using the TV antenna, I would suggest you take it down and use the mast as a support for whatever antenna you like.&lt;/p&gt;&#xA;&lt;p&gt;Enjoy.&lt;/p&gt;&#xA;" OwnerUserId="19506" LastActivityDate="2021-04-27T15:22:20.243" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18383" PostTypeId="1" CreationDate="2021-04-27T15:48:53.133" Score="3" ViewCount="182" Body="&lt;p&gt;I saw an interesting assertion recently, that resonant antennas are more efficient because they provide a better impedance match to free space at the resonant frequency.  I &lt;em&gt;believe&lt;/em&gt; that to be untrue, and that resonant antennas are just easier to match to the output impedance of a transmitter, which is almost always non-reactive.  The consensus opinion of this group, as expressed by the votes on answers to two &lt;a href=&quot;https://ham.stackexchange.com/questions/12508/what-is-the-advantage-of-making-an-antenna-resonant&quot;&gt;related&lt;/a&gt; &lt;a href=&quot;https://ham.stackexchange.com/questions/16812/does-a-resonant-antenna-work-better-than-a-non-resonant-antenna&quot;&gt;questions&lt;/a&gt;, is clearly that generally resonant antennas are not more efficient.&lt;/p&gt;&#xA;&lt;p&gt;What do I mean by &amp;quot;efficient&amp;quot;, you ask?  I suppose I mean efficient in terms of receiving or transmitting power.  I'm talking about just the antenna, and not about any matching network or feed line that might be required to connect a real antenna to a radio.&lt;/p&gt;&#xA;&lt;p&gt;But maybe I'm wrong, or maybe I'm oversimplifying.  (There is a lot more that I don't know than I do know, and oversimplifying is how we humans make sense of the universe.)  I investigated the &lt;a href=&quot;https://www.antenna-theory.com/basics/friis.php&quot; rel=&quot;nofollow noreferrer&quot;&gt;Friis Transmission Formula&lt;/a&gt;, which I learned about thanks to this site, but it's no help.  It introduces the idea that an antenna has an &amp;quot;effective aperture&amp;quot;, which is unrelated to its physical size, but the effective aperture is a theoretical construct that is just a stand-in for the gain of the antenna.  The formula isn't helpful here because the equation says nothing about gain, which is what this question is about.&lt;/p&gt;&#xA;&lt;p&gt;So what about the assertion that the &lt;a href=&quot;https://en.wikipedia.org/wiki/Impedance_of_free_space&quot; rel=&quot;nofollow noreferrer&quot;&gt;impedance of free space&lt;/a&gt; has something to do with the gain of an antenna?  &amp;quot;Free space&amp;quot;, i.e. vacuum, has an impedance, about 377 Ω, that relates the strength of the electric-field component to the strength of the magnetic-field component of an electromagnetic wave passing through the vacuum.  When the electromagnetic wave encounters a conductive object then voltages and currents are induced in the object, which is how radio waves are received.  I doubt that how close the impedance of the object is to (377 + 0j) Ω has anything to do with the efficiency of the reception, but I don't have enough Calculus or Physics to pick apart and understand everything about &lt;a href=&quot;https://en.wikipedia.org/wiki/Maxwell%27s_equations&quot; rel=&quot;nofollow noreferrer&quot;&gt;Maxwell's equations&lt;/a&gt;, so again I could be wrong.&lt;/p&gt;&#xA;&lt;p&gt;So, is a resonant antenna inherently more efficient because it couples to free space more efficiently?&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-04-27T16:47:19.897" LastActivityDate="2021-04-28T17:41:04.063" Title="Is a resonant antenna inherently more efficient because it couples to free space more efficiently?" Tags="&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="10" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18384" PostTypeId="2" ParentId="18379" CreationDate="2021-04-27T16:36:12.643" Score="0" Body="&lt;p&gt;The instructions for your antenna kit say to start with a recommended length of wire for the antenna and a different recommended length for the counterpoise, and then decrease the length of the antenna wire by two to three inches (5 to 7.5 cm) until you have the best match, i.e. the LED is the dimmest at the minimum.  What the instructions don't say is that you don't need to cut the wire; you can tightly fold the wire back on itself instead.  (I'd recommend something non-conductive, like zip-ties or tape, to keep the wire folded.)&#xA;Electrically, the folded-back part of the wire will be ignored.  Folding back the wire is a good idea because the antenna wire length that works best in one location might not be the same length that works best in another location, so you might want to use the folded-back part of the wire again later.&lt;/p&gt;&#xA;&lt;p&gt;I'd recommend following the instructions in the kit.  You might get slightly more accurate results by using an accurate SWR meter or an antenna analyzer to do the tuning and testing (especially if it's bright outside and difficult to see how dim the LED gets).  But you're using an inefficient antenna tuner for the convenience of the end-fed antenna, not to mention a low-powered transmitter; so your practical results, meaning the number of stations you can work, will probably be about the same either way.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-04-27T16:36:12.643" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18385" PostTypeId="2" ParentId="18383" CreationDate="2021-04-27T20:28:31.030" Score="0" Body="&lt;p&gt;Effective coupling can result in either higher gain (into some feed point impedance) or to higher heating losses (due to the antenna's elements own real impedance == resistance).  Either way, energy is being removed from the RF field (to maintain conservation of energy).&lt;/p&gt;&#xA;&lt;p&gt;I hypothesize (needs an NEC model to confirm the current maxima?) that a resistor of some very low value in the middle of a tuned Yagi reflector or director element (close to the same length as the driven element) will get warmer than one in the middle of an antenna element much farther (especially much shorter) from any near resonant lengths.  Thus that element must be more efficiently coupled to the RF field to extract that energy, and turn it into heating.&lt;/p&gt;&#xA;&lt;p&gt;Whether any energy extracted from the RF field can be fed somewhere else is a separate issue.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-27T20:35:00.377" LastActivityDate="2021-04-27T20:35:00.377" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18386" PostTypeId="2" ParentId="18383" CreationDate="2021-04-27T20:40:19.830" Score="2" Body="&lt;p&gt;Not really answering the question but requesting more clarity in terms.&lt;/p&gt;&#xA;&lt;p&gt;From the &lt;a href=&quot;https://ieeexplore.ieee.org/document/6758443&quot; rel=&quot;nofollow noreferrer&quot;&gt;IEEE definition of standard terms for antennas&lt;/a&gt;: I redraw the diagram of power flow in an antenna, (ignoring the polarisation mismatch branch)&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/M5v4V.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/M5v4V.png&quot; alt=&quot;Antenna gain&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Where:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$P_A$&lt;/span&gt; = power available from the generator&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$P_M$&lt;/span&gt; = power to matched transmission line&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$P_O$&lt;/span&gt; = power accepted by antenna&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$P_R$&lt;/span&gt; = power radiated by antenna&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$I$&lt;/span&gt; = radiation intensity&lt;/p&gt;&#xA;&lt;p&gt;and&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$M_1$&lt;/span&gt; = mismatch between generator and line&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$M_2$&lt;/span&gt; = mismatch between line and antenna&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$G_R$&lt;/span&gt; = realised gain&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$G$&lt;/span&gt; = gain&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$D$&lt;/span&gt; = directivity&lt;br /&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$\eta$&lt;/span&gt; = radiation efficiency&lt;/p&gt;&#xA;&lt;p&gt;The above &amp;quot;loss&amp;quot; terms on the straight line each have a physical explanation:&lt;br /&gt;&#xA;Directivity is only affected by the geometry of the antenna; how it concentrates power.&lt;br /&gt;&#xA;Radiation efficiency is only affected by losses in the metal and the dielectric.&lt;/p&gt;&#xA;&lt;p&gt;The first part of the question is really about what type of antenna has the highest &lt;span class=&quot;math-container&quot;&gt;$\eta$&lt;/span&gt; given real-world materials. I can think of a few but would have to simulate to be sure. A dipole is a good start. A travelling wave antenna like an (unterminated) rhombic or very long dipole might be better, they have smaller standing waves.&lt;/p&gt;&#xA;&lt;p&gt;The second part of the question, &amp;quot;why&amp;quot;, is harder to answer, because it might not be possible to reduce the physics of the antenna to a simple explanation. It will certainly involve &lt;span class=&quot;math-container&quot;&gt;$Z_0$&lt;/span&gt; of free space but I don't think there will be a direct relationship between that and antenna impedance.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2021-04-27T20:40:19.830" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18387" PostTypeId="2" ParentId="18383" CreationDate="2021-04-27T22:03:15.710" Score="5" Body="&lt;p&gt;You could view an antenna as a two-port device. One port is the feedpoint, and the other port is &amp;quot;free space&amp;quot;. The antenna's job is to transform the free space impedance of 377 ohms to the specified feedpoint impedance such as 50 ohms.&lt;/p&gt;&#xA;&lt;p&gt;Ideally we want an antenna with scattering parameters like so:&lt;/p&gt;&#xA;&lt;p&gt;&lt;span class=&quot;math-container&quot;&gt;$$ \begin{bmatrix}&#xA;0 &amp;amp; 1 \\&#xA;1 &amp;amp; 0&#xA;\end{bmatrix} $$&lt;/span&gt;&lt;/p&gt;&#xA;&lt;p&gt;In other words, all the power coming in from free space makes it to the feedpoint, and all the power coming from the feedpoint radiates to free space.&lt;/p&gt;&#xA;&lt;p&gt;If port 1 is the feedpoint and port 2 is free space, then we would say the antenna is a &amp;quot;good match&amp;quot; when &lt;span class=&quot;math-container&quot;&gt;$S_{11} = 0$&lt;/span&gt;, meaning, no reflected power.&lt;/p&gt;&#xA;&lt;p&gt;Likewise, we could say the antenna is a &amp;quot;good match to free space&amp;quot; when &lt;span class=&quot;math-container&quot;&gt;$S_{22} = 0$&lt;/span&gt;, since port 2 is free space.&lt;/p&gt;&#xA;&lt;p&gt;So the question then becomes: does the antenna being non-resonant prevent &lt;span class=&quot;math-container&quot;&gt;$S_{22}$&lt;/span&gt; from being zero?&lt;/p&gt;&#xA;&lt;p&gt;And the answer is: no. If you can provide a matched termination at the feedpoint then the free space port will also be matched.&lt;/p&gt;&#xA;&lt;p&gt;How do we determine if an antenna is resonant? We connect port 2 to free space (no choice), and then we measure the impedance looking into port 1. If that impedance has zero reactance, it's resonant. Effectively we are discovering the impedance-transforming properties of the antenna by connecting one port to a matched and known load (free space) and seeing what impedance appears at the other port (the feedpoint).&lt;/p&gt;&#xA;&lt;p&gt;Assume for now we find that feedpoint impedance to be (50+0j) ohms. We know that if we want to capture the maximum power from free space we should put a 50 ohm resistor across the feedpoint. The antenna, being an impedance transforming network, makes this 50 ohm resistor look like 377 ohms from free space (looking in port 2).&lt;/p&gt;&#xA;&lt;p&gt;If we instead put a 25 ohm resistor there, looking in port 2 we won't see 377 ohms. Since this doesn't match the impedance of free space it means the antenna will scatter some power rather than absorbing it.&lt;/p&gt;&#xA;&lt;p&gt;If the antenna isn't resonant, this just means we need some reactive component at the feedpoint in addition to a resistor to achieve a complex conjugate match. So if we measure the feedpoint impedance to be (30+15j) ohms, this means simply we need to place a (30-15j) ohm impedance on the feedpoint if we want the other port to look like 377 ohms.&lt;/p&gt;&#xA;&lt;p&gt;The problem in practice is real capacitors and inductors which we would use to come up with that reactance at the feedpoint have loss. That means some of the power will be lost in those components before it can make it to the receiver, reducing overall efficiency. Or we can choose to omit the reactive components, in which case some of the power from free space will be scattered by the antenna rather than transferred to the feedpoint.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-27T22:03:15.710" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="18388" PostTypeId="1" AcceptedAnswerId="18407" CreationDate="2021-04-27T22:22:07.667" Score="2" ViewCount="40" Body="&lt;p&gt;I picked up a used Katsumi Elekey EK-150 (&lt;a href=&quot;https://www.dl0bn.de/dc7xj/Anleitungen/Katsumi%20EK-150%20Manual.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;manual&lt;/a&gt;) electronic keyer.&lt;/p&gt;&#xA;&lt;p&gt;I'm trying to get it working with my Kenwood TS-570S (&lt;a href=&quot;https://www.hamradio.co.uk/userfiles/file/Kenwood%20Manuals/TS-570-English.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;manual&lt;/a&gt;), which has a 3.5mm Key jack. With a male-male audio cable connected to the Key jack, if I short the positive and negative leads together, the transceiver transmits CW, as expected. The paddles on the keyer also produce tones through they keyer's own monitor speaker, as expected.&lt;/p&gt;&#xA;&lt;p&gt;However, I can't figure out how to get this keyer to interface with the radio properly. Regardless of the keyer mode (Relay / Tr. Switch) When I connect the keyer's Keyed Line output to the transceiver's Key jack, positive to positive (tip), negative to negative (sleeve), operating the paddle does not cause the transceiver to transmit. If I reverse the polarity, positive to sleeve, negative to top, the transceiver &lt;em&gt;constantly&lt;/em&gt; transmits, regardless of paddle operation.&lt;/p&gt;&#xA;&lt;p&gt;What would you expect a multimeter to be able to detect on the keyer's Keyed Line output? I detect a voltage of a fraction of a volt between the positive and negative leads, but neither the voltage, resistance, current, nor continuity between those leads changes when I'm keying vs when I'm not. I don't know exactly what is expected, but that seems strange to me. Is this thing broken?&lt;/p&gt;&#xA;" OwnerUserId="17488" LastEditorUserId="8717" LastEditDate="2021-04-27T22:36:40.780" LastActivityDate="2021-04-30T14:31:12.983" Title="Connecting a Katsumi Elekey EK-150 to my transceiver" Tags="&lt;cw&gt;&lt;kenwood&gt;&lt;equipment-troubleshooting&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18389" PostTypeId="2" ParentId="18366" CreationDate="2021-04-27T23:22:18.307" Score="-1" Body="&lt;p&gt;An antenna that is small in relation to the wavelength always has a dipole radiation pattern. Electric dipole or magnetic dipole or a combination of both. For transmit small antennas have a narrow bandwidth because they have to be power matched to the transmitter. Currents become very large in transmit so efficiency suffers. Small antennas may have a wide bandwidth for receive by use of special low noise amplifiers. As size grows antennas may get all sorts of interesting properties. Directivity (yagis) wide bandwidth (logperiodic) or both (parabolas) There are also interesting antennas with very long wires. There is no need to make an antenna &amp;quot;resonant&amp;quot; other than that the matching network needed to match it to a 50 ohm transmitter may become simpler or even superfluous.&lt;/p&gt;&#xA;&lt;p&gt;A non resonant extension cord as a antenna will need an antenna tuner for transmit because the impedance will be far from 50 ohms. In case the wire is thin there will be ohmic losses and if the wire is covered with thick PVC there will be dielectric losses. On receive losses do usually not matter at all since external noise is attenuated by losses to the same extent as the desired signals. External noise is typically much weaker than the receiver noise below 30 MHz. With high losses in the upper HF range one might need an antenna tuner also on receive.&lt;/p&gt;&#xA;" OwnerUserId="9758" LastActivityDate="2021-04-27T23:22:18.307" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18390" PostTypeId="1" CreationDate="2021-04-28T09:02:27.647" Score="3" ViewCount="93" Body="&lt;p&gt;This a follow up from this question:&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/18285/qrn-how-to-chase-down-a-solid-s9-noise-floor-on-40m-only&quot;&gt;QRN: How to chase down a solid S9 noise floor on 40m only&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Focusing on how to interpret the signals received with an electrically small, untuned &amp;quot;shielded loop&amp;quot;. The following background articles/questions on this type of antenna explain how it works, how &lt;strong&gt;not&lt;/strong&gt; to construct it (eg ARRL 1998), and what it can and cannot do:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;http://www.w8ji.com/magnetic_receiving_loops.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.w8ji.com/magnetic_receiving_loops.htm&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/899/what-does-the-addition-of-a-shield-to-a-small-loop-accomplish&quot;&gt;What does the addition of a shield to a small loop accomplish?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/questions/2455/is-it-possible-to-make-a-shield-that-blocks-time-varying-electric-fields-but-no&quot;&gt;Is it possible to make a shield that blocks time-varying electric fields, but not time-varying magnetic fields?&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I followed the construction advice in &lt;a href=&quot;https://ka7oei.blogspot.com/2021/02/rfi-radio-frequency-interference.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;this blog article&lt;/a&gt; quite closely, including the use of a pre-amp and a &lt;a href=&quot;https://www.tinysa.org/wiki/&quot; rel=&quot;nofollow noreferrer&quot;&gt;tinySA&lt;/a&gt; to amplify and analyse the signal (photos of my implementation in &lt;a href=&quot;https://ham.stackexchange.com/questions/2455/is-it-possible-to-make-a-shield-that-blocks-time-varying-electric-fields-but-no&quot;&gt;original question&lt;/a&gt;)&lt;/p&gt;&#xA;&lt;p&gt;The core of main challenge, which to find the source of my S8-S9 white noise floor, amounts to these tinySA screenshots.&lt;/p&gt;&#xA;&lt;p&gt;Elevated noise floor when tinySA connected to my fan dipole:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/0cQeV.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0cQeV.jpg&quot; alt=&quot;Noise floor when tinySA connected to my fan dipole&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Signal from the loop when standing under that dipole:&#xA;&lt;a href=&quot;https://i.stack.imgur.com/XB9zl.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/XB9zl.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The elevated noise floor is not present. (Note that that I have (hopefully) eliminated conducted noise and feed line shield noise in &lt;a href=&quot;https://ham.stackexchange.com/questions/18285/qrn-how-to-chase-down-a-solid-s9-noise-floor-on-40m-only&quot;&gt;original question&lt;/a&gt;).&lt;/p&gt;&#xA;&lt;p&gt;So the questions are:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;How to interpret the loop signal relative to the dipole?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Why is there no elevated noise floor on the loop?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Is it a matter of sensitivity / level of amplification? The comparative levels of identifiable signals (best reliable example is 7.074MHz FT8) seem to vary with FFT bin width on tinySA. If I scan 7Mhz to 7.2Mhz (as opposed to the wideband 3-12Mhz shown in pics above) which gives me a 3kHz bin width (very similar to LSB bandwidth used for S-level indication of about 2.7kHz) then FT8 is show on tinySA at about -90dBm on the loop after pre-amp (vs S9+20dB on the FT450D meter). The noise floor being about S8 on the radio at that time, would be 26dB down from that and would put it below the noise floor of the tinySA. Yet other information suggests that the loop with a 20dB pre-amp should show similar signal levels to the dipole?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Or are the dipole and the loop just detecting different signals? ie the loop is not seeing the noise floor? Lower height above ground? Near field vs far field debate.. etc.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;How can I further narrow this down? ie if I can't see the noise floor with the loop, I can't locate its source and can't hope to eliminate it.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;Update 28/4/2021&lt;/strong&gt;&#xA;Further to some very good suggestions from Phil Frost I have carried out some of the tests he suggested. Results below.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Baseline for today&lt;/strong&gt; (somewhat lower noise yeah! lowest I have ever seen during daytime - slight drizzle outside...)&#xA;Normal Antenna setup at radio:&lt;/p&gt;&#xA;&lt;p&gt;FT450D: 7.074Mhz FT8 S9+10 to S9+30 and baseline noise in 40m Band is 6.5S-units&lt;/p&gt;&#xA;&lt;p&gt;tinySA: on dipole via 22m feedline =&amp;gt; 3-12Mhz span base -80dB peaks -50dB&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Loop standing under dipole&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;Direct to tinySA via 10cm feedline =&amp;gt; -95dB with peaks to -70dB  &lt;strong&gt;no raised floor&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;FT450D via 22m feedline =&amp;gt; ft8 S4.5 on radio. Noise floor in Band &lt;strong&gt;S0&lt;/strong&gt;.&lt;/p&gt;&#xA;&lt;p&gt;TinySA via 22m feedline =&amp;gt; -95dB baseline with peaks to -70dB&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Dipole fed with short, vertical 5m RG58 feedline into tinySA&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;tinySA standing under Dipole fed by 5m coax =&amp;gt; Very similar to via the 22m feedline -80dB base with peaks to -50dB. Maybe slightly higher (less attenuation?)&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Conclusions from these measurements&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;The raised noise floor is not coming from the feedline. Both the&#xA;above tests, and earlier tests terminating the feedline at feedpoint&#xA;(under original question) agree on this.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The raised noise floor is not coming from my rig (FT450D) or anything connected to it, like power supply or ground, because the tinySA fed via 5m short coax standing under dipole produce same results as in shack and as the radio. The is also corroborated by earlier tests in original question, where I ran radio on battery with whole house turned off.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The loop receives far field signals (eg 40m FT8) much more weakly than the dipole. Compare S9+20dB to S4.5 on FT450D via the same 22m feedline. That's a  difference of 40dB+. The tinySA shows less of a difference but still 20-30dB. This is true when measured by 10cm coax feedline or via 22m feedline back in shack. The raised noise floor is not visible via the loop, could be because both wanted and unwanted signals are much smaller. Smaller signals could be because:&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the loop is lower to the ground / obscured by nearby buildings&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;the loop has much lower sensitity for which the 20dB preamp cannot compensate&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&#xA;&lt;ol start=&quot;3&quot;&gt;&#xA;&lt;li&gt;anything else?&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;It's hard to ascertain where the raised floor is coming from because our loop seems not sensitive enough. Or we need to get it experimentally closer to source of noise by trial and error. (eg area around tips of dipole).&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;The author of blog article I followed (KA7OEI) for loop construction seems to suggest that from his experience, such a loop with such a pre-amp should give signal strengths roughly comparable to a full size antenna. I tested the pre-amp with AWG and Oscilloscope, so I am pretty confident about that. So either my construction of the loop or some other factor is making my loop much less (20-40dB!) less sensitive than it should be??&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;-- end of update&lt;/p&gt;&#xA;&lt;p&gt;Many thanks&lt;/p&gt;&#xA;" OwnerUserId="18951" LastEditorUserId="18951" LastEditDate="2021-04-28T17:43:31.550" LastActivityDate="2021-04-28T22:46:42.403" Title="Interpreting (noise) signals from a small untuned shielded loop" Tags="&lt;antenna&gt;&lt;loop&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18391" PostTypeId="2" ParentId="1440" CreationDate="2021-04-28T11:38:44.067" Score="3" Body="&lt;p&gt;Power dB = 10 log10 (ratio)&lt;/p&gt;&#xA;&lt;p&gt;Power in dBm helps in quickly calculating the power at Rx end. Say a launch power of +13 dBm (=10^(1.3) mW = 20 mW) - with link loss of 6 dB - would give 13-6 = 7 dBm at the Rx end. We can verify.&lt;/p&gt;&#xA;&lt;p&gt;6dB = 10^(.6) = 4.&lt;/p&gt;&#xA;&lt;p&gt;-6dB = 1/4.&lt;/p&gt;&#xA;&lt;p&gt;So output power = 20 mW * 1/4 = 5 mW.&lt;/p&gt;&#xA;&lt;p&gt;10*log10 (5) = 7 dBm.&lt;/p&gt;&#xA;&lt;p&gt;So, it checks out.&lt;/p&gt;&#xA;&lt;p&gt;As suggested when launch power is in dBm - one can just subtract the losses in dB to get the dBm power received at the Rx end.&lt;/p&gt;&#xA;" OwnerUserId="19510" LastActivityDate="2021-04-28T11:38:44.067" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18392" PostTypeId="2" ParentId="18390" CreationDate="2021-04-28T13:02:00.993" Score="4" Body="&lt;p&gt;You've stated in your other question that you've tested the loop and you are able to receive signals, so it works to some extent. So a few possibilities remain.&lt;/p&gt;&#xA;&lt;p&gt;Firstly, the presence of signals does not necessarily mean the loop is working well. It could be that the noise you are trying to find with the loop is below the receiver's noise floor. Hard to test this for sure without an anechoic chamber, but you can get a pretty good idea just by comparing the number of signals you can hear (especially the weak ones) with your other radio. If the loop can hear many more stations, it's working. If it can't, it's likely the loop's noise floor is masking them.&lt;/p&gt;&#xA;&lt;p&gt;Another possibility is the noise isn't being received by the antenna, but something else in your station. That could be the feedline, the receiver, or any of the other wires connected to the receiver, including the power cord, all the electrical wiring in your home, any cables you may have to interface your radio with your computer, anything attached to your computer, or any ground connections or even the ground itself. Or anything connected to those things, such as the power lines, your neighbors, or communications cables running around the neighborhood. It could even be a noise source simply in the same room as the receiver: the receiver's shielding isn't perfect.&lt;/p&gt;&#xA;&lt;p&gt;To check this, I'd run a short feedline from the dipole to where you were standing when you made the measurement with the loop that showed no noise. Then listen to the dipole with the same receiver you used with the loop, while standing in the same spot.&lt;/p&gt;&#xA;&lt;p&gt;If the noise goes away, you know the antenna isn't the problem. Start walking around the house and disconnecting things and turning off things until you've narrowed down the source. Powering your radio from a battery and turning off your home's main circuit breaker, then turning circuits back on one at a time can be informative. It could be you need a better balun on the antenna: you can &lt;a href=&quot;https://ham.stackexchange.com/questions/1271/how-to-detect-common-mode-currents-or-rf-in-the-shack&quot;&gt;test your current balun for effectiveness&lt;/a&gt;. Or you may discover some noise sources in your house that can be controlled with ferrite beads or simply need to be removed.&lt;/p&gt;&#xA;&lt;p&gt;If you still get the noise even with the short feedline and the portable receiver, then you may just have to look around more. Of note, the near field of the loop and the dipole are substantially different, which means if the noise source is in the near field of the antennas then one may be very sensitive to it while the other is not. It could be you just need to explore the area immediately around the antenna a little more with your portable receiver.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-04-28T13:02:00.993" CommentCount="18" ContentLicense="CC BY-SA 4.0" />
  <row Id="18393" PostTypeId="2" ParentId="18383" CreationDate="2021-04-28T13:42:22.160" Score="1" Body="&lt;p&gt;Another example of an antenna without a connected feed point is a broadcast AM radio enhancer (MF band).  A multi-turn loop of wire with a capacitor to tune it can be placed around or near, but electrically disconnected from a small AM pocket radio.  The received signal will become stronger when the disconnected loop antenna circuit is tuned to (or very near) the receiver frequency.&lt;/p&gt;&#xA;&lt;p&gt;Here's an example of one, the Eton AN-200 Tunable Passive AM Radio Antenna Loop: &lt;a href=&quot;https://www.hamradio.com/detail.cfm?pid=H0-015461&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.hamradio.com/detail.cfm?pid=H0-015461&lt;/a&gt; , but there are construction articles on how to build one DIY with just wire and a variable capacitor, similar to making a DIY crystal radio.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-28T17:41:04.063" LastActivityDate="2021-04-28T17:41:04.063" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18394" PostTypeId="2" ParentId="18390" CreationDate="2021-04-28T17:16:40.790" Score="2" Body="&lt;p&gt;Did you try the loop sideways? (flat in a vertical plane both N/S and E/W, but with the feed out the side, not the bottom). Did you try the loop higher up, closer to the height of the dipole?  Did you try the loop near the tips of your fan dipole? Are the broadband lines in the near field of your fan dipole? (much less than a full wavelength away?)  If so, did you try the loop (in all 6 orientations) near the broadband lines.&lt;/p&gt;&#xA;&lt;p&gt;Added: How does the hump in your fan dipole's RF noise correspond with the SWR and impedance curves as measured by your nanoVNA?  Your RF noise floor may actually be closer to flat (no hump), as measured by your small loop antenna and tinySA.  No hump.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-04-28T22:46:42.403" LastActivityDate="2021-04-28T22:46:42.403" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18395" PostTypeId="2" ParentId="18388" CreationDate="2021-04-28T19:20:58.087" Score="2" Body="&lt;p&gt;In the keyer, PNP transistor Q4 should be on when the keyer is supposed to be keyed.  I assume that the transceiver's key jack goes to a CMOS high-impedance input and has a pull-up resistor, and that the key jack's sleeve terminal is tied to ground.  If all that is correct, and if the keyer is working correctly, then the positive output of the terminal should show logic high voltage (let's say &amp;gt; 3 VDC) when the keyer's output is not supposed to be keyed, and should show logic low voltage (say &amp;lt; 1 VDC) when the keyer's output should be keyed.  The voltage should change very quickly when the keyer's output turns on or turns off.&lt;/p&gt;&#xA;&lt;p&gt;I'd say that your keyer is broken.  That keyer is designed to key tube rigs.  If someone hooked it up incorrectly, like using the direct output when they should have used the relay output, then the keyer's transistor Q4 could have been exposed to many hundreds of volts, or it could have been asked to switch more current than it was designed for.  My guess is that Q4 is dead.&lt;/p&gt;&#xA;&lt;p&gt;If I were you, I'd try plugging my paddles directly into the radio's paddle jack, or try a different keyer.  The radio's built-in keyer should work just as well as your EK-150, and be better integrated with the radio of course.  Your EK-150 is fairly antiquated, so unless you have a specific reason to use an EK-150, you'll probably be quite satisfied with your Kenwood's built-in keyer, or any other modern keyer.  (Lots of people prefer the timing of a particular keyer brand, including me, so if you just prefer the timing of the EK-150, then there's nothing wrong with that.)&lt;/p&gt;&#xA;&lt;p&gt;Don't just throw out the EK-150 if you don't want it any more; see if anyone at your local ham club wants it, or take it to a hamfest and put a &amp;quot;free&amp;quot; sign on it first.  Some people really like old ham gear, and don't mind fixing things.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-04-28T19:20:58.087" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18396" PostTypeId="2" ParentId="14960" CreationDate="2021-04-28T19:57:24.470" Score="2" Body="&lt;p&gt;Practically speaking, the size and winding direction of the loading coil doesn't really matter.&lt;/p&gt;&#xA;&lt;p&gt;Unless the coils are monstrously huge compared to the wavelength involved, there will be a negligible effect on radiation.&lt;/p&gt;&#xA;&lt;p&gt;As for winding direction, if the coils are near the feed point of the dipole, you might see a difference if they are close enough to interact with each other's magnetic fields (essentially becoming a loosely-coupled transformer).&lt;/p&gt;&#xA;&lt;p&gt;But, since it is more efficient to place loading coils in the middle or ends of the element, that's not typically the case.&lt;/p&gt;&#xA;" OwnerUserId="19506" LastActivityDate="2021-04-28T19:57:24.470" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18397" PostTypeId="2" ParentId="18349" CreationDate="2021-04-28T20:46:30.827" Score="2" Body="&lt;p&gt;You may like checking out &lt;a href=&quot;http://www.svxlink.org&quot; rel=&quot;nofollow noreferrer&quot;&gt;svxlink&lt;/a&gt;. I've had success setting it up on a Raspberry Pi, interfaced with a baofeng (pls don't judge) to accomplish VM (as well as successfully interfacing with EchoLink) in a simplex configuration, but only as a prototype... I haven't experience running it for an extended period.&lt;/p&gt;&#xA;&lt;p&gt;Obviously, you can interface the RPi with the radio(s) of your choice for additional power or duplex configuration etc.&lt;/p&gt;&#xA;&lt;p&gt;From their site, a list of modules and their functions, including the VM you may enjoy experimenting with.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The SvxLink Server is a general purpose voice services system, which when connected to a transceiver, can act as both an advanced repeater system and can also operate on a simplex channel. One could call it a radio operating system since it sits between the hardware (transceiver) and the applications (modules) and handle basic system services as well as input and output.&lt;/p&gt;&#xA;&lt;p&gt;SvxLink is very extensible and modular. Voice services are implemented as modules which are isolated from each other. Modules can be implemented in either C++ or TCL. Examples of modules are:&lt;/p&gt;&#xA;&lt;p&gt;Help – A help system&lt;/p&gt;&#xA;&lt;p&gt;Parrot – Play back everything that is received&lt;/p&gt;&#xA;&lt;p&gt;EchoLink – Connect to other EchoLink stations&lt;/p&gt;&#xA;&lt;p&gt;DtmfRepeater – Repeater received DTMF digits&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;TclVoiceMail – Send voice mail to other local users&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;PropagationMonitor – Announce propagation warnings from dxmaps.com&lt;/p&gt;&#xA;&lt;p&gt;SelCall – Send selective calling sequences by entering DTMF codes&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2021-04-28T20:51:42.030" LastActivityDate="2021-04-28T20:51:42.030" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18398" PostTypeId="1" CreationDate="2021-04-28T23:25:12.230" Score="3" ViewCount="50" Body="&lt;p&gt;I'm trying to experimentally investigate the radiation resistance of a v-shaped antenna. When it's fully unfolded and the reactance is at resonance, the resistance is about 73Ω. When it's folded, it acts similar to an open coaxial cable.&lt;/p&gt;&#xA;&lt;p&gt;I'm wondering if there's a more general description of impedance for the v-shaped antenna as a function of the angle between the wires. I've tried looking through Antenna Theory: Analysis and Design by Balanis, but I couldn't find something. Are there any papers or textbooks out there that have the answer?&lt;/p&gt;&#xA;" OwnerUserId="19512" LastActivityDate="2021-04-29T15:09:28.200" Title="Impedance of V Antenna as Function of Angle" Tags="&lt;antenna-theory&gt;&lt;impedance&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18399" PostTypeId="1" AcceptedAnswerId="18400" CreationDate="2021-04-29T06:08:49.703" Score="0" ViewCount="72" Body="&lt;p&gt;I've heard that in the early spark-gap wireless telegraphy era people would use kites with a wire acting as antennas and if the receiving side had a wire length that was an even division or multiple of the wire length on the transmitting side, the two antennas would be tuned to each other - if transmitter sparked, the receiver would also produce sparks.&#xA;I suppose this was similar to how Lecher line works, where it is possible to obtain a standing wave with multiple peaks and nodes (higher order harmonics) when the wire length is a multiple of the wavelength of the RF signal propagating in the wire.&#xA;I haven't found any information on this subject and I'm wondering if anyone ever tried anything similar to this in the receiving antennas. Thanks&lt;/p&gt;&#xA;" OwnerUserId="19518" LastEditorUserId="8717" LastEditDate="2021-04-29T19:54:48.897" LastActivityDate="2021-05-03T13:26:49.890" Title="Tuning two antennas using wire length" Tags="&lt;antenna&gt;&lt;history&gt;&lt;reception&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18400" PostTypeId="2" ParentId="18399" CreationDate="2021-04-29T12:27:10.720" Score="1" Body="&lt;p&gt;A dipole is resonant on every frequency where it is an odd multiple of (slightly less than) &lt;span class=&quot;math-container&quot;&gt;$\lambda/2$&lt;/span&gt;. So normally we talk of half-wave dipoles, but 1.5-wave, 2.5 wave, and 3.5-wave dipoles are similarly resonant. They all have a feedpoint impedance of about (72+0j) ohms in free space.&lt;/p&gt;&#xA;&lt;p&gt;For monopoles, being half a dipole, the resonances occur at (slightly less than) odd multiples of &lt;span class=&quot;math-container&quot;&gt;$\lambda/4$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;Their radiation pattern is not identical, however. Whereas a half-wave dipole has two broad lobes, as the dipole gets longer it acquires more, narrower lobes.&lt;/p&gt;&#xA;&lt;p&gt;This effect of multiple resonances is sometimes used to an advantage in constructing multi-band antennas. For example, a dipole that is resonant on 40 meters (about 7 MHz) also works on 15 meters (about 21 MHz).&lt;/p&gt;&#xA;&lt;p&gt;But when operation in only one band is required, it's not common to use more than the first resonance. There's no particular advantage to making the antenna longer, and it's cheaper and mechanically easier to construct a smaller antenna.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="1550" LastEditDate="2021-05-03T13:26:49.890" LastActivityDate="2021-05-03T13:26:49.890" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18401" PostTypeId="2" ParentId="18399" CreationDate="2021-04-29T15:04:03.753" Score="3" Body="&lt;p&gt;Yes, in the early spark days, the fundamental frequency of the transmitter was largely determined by the self-resonance of the antenna system. Any sort of spark generator naturally generates RF energy at many frequencies, but those close the self-resonance of the antenna would be more likely to be effectively radiated.&lt;/p&gt;&#xA;&lt;p&gt;Receiving antenna self-resonance isn't as important.&lt;/p&gt;&#xA;" OwnerUserId="19506" LastActivityDate="2021-04-29T15:04:03.753" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18402" PostTypeId="2" ParentId="18398" CreationDate="2021-04-29T15:09:28.200" Score="1" Body="&lt;p&gt;This sort of questions is probably best answered by modeling an antenna using either a NEC2 or NEC4 model. There are a variety of such packages available for this for DOS, Windows and Mac.&lt;/p&gt;&#xA;&lt;p&gt;That makes for much easier experimentation rather than having to cut and raise a lot of wire!&lt;/p&gt;&#xA;" OwnerUserId="19506" LastActivityDate="2021-04-29T15:09:28.200" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18403" PostTypeId="2" ParentId="3834" CreationDate="2021-04-29T22:18:00.460" Score="0" Body="&lt;p&gt;They make 'electrical downtilt' omni antennas that focus a signal into a downward projecting cone, which is what you need here.&lt;/p&gt;&#xA;&lt;p&gt;However, did you test the ability to change the SSID?  Clients want to cache them and may not update the name displayed. It's worth checking.&lt;/p&gt;&#xA;" OwnerUserId="19522" LastEditorUserId="966" LastEditDate="2021-05-02T08:30:35.940" LastActivityDate="2021-05-02T08:30:35.940" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18404" PostTypeId="1" CreationDate="2021-04-30T01:04:34.987" Score="2" ViewCount="35" Body="&lt;p&gt;Assuming a rhombic antenna is:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;terminated for directionality&lt;/li&gt;&#xA;&lt;li&gt;electrically isolated at its mount point&lt;/li&gt;&#xA;&lt;li&gt;mounted to a metal mast partway up vs top of mast&lt;/li&gt;&#xA;&lt;li&gt;horizontally oriented (elements parallel to ground)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;… how might the mast affect its radiation pattern?&lt;/p&gt;&#xA;&lt;p&gt;Is it better to mount with the mast through the rhombus or at its feed end?&lt;/p&gt;&#xA;&lt;p&gt;Since the mast is outside the plane of polarization, I’d imagine it behaves the same as a horizontal Yagi if end-mounted (let’s ignore structural support for now).&lt;/p&gt;&#xA;&lt;p&gt;Also, while I’m aware you can electrically steer elevation (so articles say), what if for simplicity I did this simply by physically orienting the antenna to the desired elevation? Would I run into trouble as the elevation increased (ie, closer to parallel with the mast), assuming the mast extends far enough “up” the antenna to be a nearby, in-plane conductor?&lt;/p&gt;&#xA;&lt;p&gt;I realize this could all be modeled but I have zero experience with modeling tools and hoped some of this was known and at least some could be reasoned about.&lt;/p&gt;&#xA;" OwnerUserId="18693" LastActivityDate="2021-04-30T01:04:34.987" Title="How might various conductive mast mounting configurations affect an electrically isolated rhombic antenna?" Tags="&lt;antenna&gt;&lt;antenna-theory&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18405" PostTypeId="1" CreationDate="2021-04-30T01:05:40.640" Score="0" ViewCount="67" Body="&lt;p&gt;Looking for suggestions for a portable antenna for use with a SDRPlay RSP1A. I notice that most other SDRs come with a few antennas, but not the RSP1A. I have a 2m/70cm HT, so I own a Nagoya NA-771R whip and a mobile-mount 2m antenna. I also have a J-pole, but that’s not traveling with me. So, I’m looking for a portable antenna that I can take to the cabin this summer.&lt;/p&gt;&#xA;&lt;p&gt;I’m interested in the lower frequencies, so I was thinking about a loop, dipole, or long wire. I’ll have no mast, but lots of nearby trees. Does anyone make a dipole that can be hoisted over a branch — but collapsible for travel?&lt;/p&gt;&#xA;&lt;p&gt;What are others using with their SDRPlay?&lt;/p&gt;&#xA;" OwnerUserId="19524" LastActivityDate="2021-04-30T16:05:46.237" Title="Antenna suggestions for SDRPlay RSP1A" Tags="&lt;antenna&gt;&lt;software-defined-radio&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18406" PostTypeId="2" ParentId="18405" CreationDate="2021-04-30T09:11:53.187" Score="1" Body="&lt;p&gt;Most users of SDR receivers use active antenna for the frequency range up to 50 MHz.&lt;/p&gt;&#xA;&lt;p&gt;The choice for a loop antenna (magnetic field sensor) or a small telescope antenna (E-field sensor) depends mainly on the environment. Since you have plenty of room both options are good choice.&lt;/p&gt;&#xA;&lt;p&gt;When the tree density is high may be the loop is a better choice. When there is interference generated by local electronics, also the loop is a better choice. The disadvantage of the loop is the directivity, specially for ground wave signals: there is a null in the directional sensitivity. This can also be an advantage.&lt;/p&gt;&#xA;&lt;p&gt;Loop antennas for reception: tuned loop with high sensitivity can be small, circumference 1 meter is sufficient. Amplification is not necessary. Wideband loop needs no tuning but for good sensitivity the circumference must be 2 or 3 meters and a special amplifier is a must.&lt;/p&gt;&#xA;&lt;p&gt;Do not forget that the coaxial cable between the antenna and the SDR is a conductor that brings, via the screen, interference from computer and power supply to the base of the antenna and that interference will influence the lowest level signals: the noise floor. Use common-mode means in the coax and ground the coax were it is connected to the antenna. Also a loop antenna will benefit from this interference-to-grond path (poor description, yes).&lt;/p&gt;&#xA;&lt;p&gt;See also:&#xA;&lt;a href=&quot;https://ham.stackexchange.com/questions/16407/using-an-sdr-on-a-laptop-with-noisy-power-supply/16552#16552&quot;&gt;Using an SDR on a Laptop with Noisy Power Supply&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="16925" LastEditorUserId="16925" LastEditDate="2021-04-30T13:29:51.330" LastActivityDate="2021-04-30T13:29:51.330" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18407" PostTypeId="2" ParentId="18388" CreationDate="2021-04-30T14:31:12.983" Score="3" Body="&lt;p&gt;I took it apart and found a transistor that had been blown apart, pictured below (the black one with its metal innards showing), likely from a scenario described by @rclocher3. This is the NPN transistor that supplies voltage to the blue PNP transistor and should be switching based on its base input but instead is supplying a constant 5V. No surprise there, looking at it. If nothing else is wrong, this should be easy enough to repair!&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/GFyX0.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/GFyX0.png&quot; alt=&quot;Black transistor with its head blown off&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17488" LastActivityDate="2021-04-30T14:31:12.983" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18408" PostTypeId="2" ParentId="18405" CreationDate="2021-04-30T16:05:46.237" Score="1" Body="&lt;p&gt;I have an RSP1a and an RSP2.  For HF, I've used them with a long wire in a tree, and an isolated LOG (loop on ground).&lt;/p&gt;&#xA;&lt;p&gt;The LOG works better for me, because for some reason it picks up less RF noise from the local environment and thus provides me with a slightly better S/N signal.  The LOG is made from 40M of random scrap wire and a small ferrite toroid transformer.&lt;/p&gt;&#xA;&lt;p&gt;The long wire in a tree works for VHF receive as well.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-04-30T16:05:46.237" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18409" PostTypeId="1" CreationDate="2021-04-30T19:42:56.543" Score="3" ViewCount="66" Body="&lt;p&gt;&lt;strong&gt;What happens when a groundplane antenna's vertical element, bottom feedpoint, and/or bottom loading coil move down and encroach into the area &lt;em&gt;below&lt;/em&gt; the plane formed by its own perpendicular elevated radials?&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;p&gt;I have &lt;strong&gt;never&lt;/strong&gt; seen a book or article about ground plane antennas directly address this question.&lt;/p&gt;&#xA;&lt;p&gt;I've read that the feedpoint impedance is theoretically 35 ohms when the elevated radials are perpendicular to the vertical element, and that tilting their outer ends downward causes the impedance to increase until it reaches 50 ohms. What happens if you &lt;em&gt;continue&lt;/em&gt; tilting them never gets discussed. My hunch is that as the radials become increasingly vertical and merge into the bottom half of a vertical half-wave dipole, its impedance approaches that &lt;em&gt;of&lt;/em&gt; a dipole.&lt;/p&gt;&#xA;&lt;p&gt;Based upon that, I'd expect that if you tilted the radials &lt;em&gt;upwards&lt;/em&gt;, the feedpoint impedance would get smaller and smaller and approach zero as the radials effectively merged into the vertical element itself. Taking a wild guess... the (imaginary) &lt;em&gt;j&lt;/em&gt; component approaches infinity?&lt;/p&gt;&#xA;&lt;p&gt;I've read that with vertical antennas at ground level, a &amp;quot;virtual&amp;quot; bottom half of the dipole mirrors it below ground level. Assuming the same thing happens with the ground plane formed by elevated radials, it seems logical that pushing part of the vertical element below that plane would cause the &lt;em&gt;real&lt;/em&gt; vertical element's lower portion, and the upper portion of its imaginary mirror, to encroach into each other's space and virtually overlap. Once again, &lt;em&gt;j&lt;/em&gt;-&amp;gt;infinity, and Bad Things Happen?&lt;/p&gt;&#xA;&lt;h1&gt;Background&lt;/h1&gt;&#xA;&lt;p&gt;I live in a townhouse, and my back yard is surrounded by 6 foot tall concrete walls with an aluminum-framed screen enclosure (basically, like a typical Florida pool cage) on top (10 feet from ground to top, 2 feet from wall-top to enclosure-top).&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/6JTFu.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/6JTFu.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I'm presently re-screening it (for reasons that are obvious from the photo), and decided that I might as well take advantage of the opportunity to replace the dented downspout and improve it a bit in case I ever want/need to use it as a vertical antenna element in the future.&lt;/p&gt;&#xA;&lt;p&gt;The screen enclosure frame will serve as the ground plane. My neighbor graciously allowed me to connect their enclosure frame to mine near the proposed feedpoint and run a discreet AWG22 radial wire up along the edge of the sloping roof you see in the background, so the radial field ought to be &amp;quot;decent&amp;quot;, if not literally &amp;quot;good&amp;quot; (at least, towards the north, east, and south).&lt;/p&gt;&#xA;&lt;p&gt;I ran some preliminary tests using my NanoVNAv2, and was pleasantly surprised to see almost-perfect SWR on 20m (1.04:1 to 1.20:1), and SWR below 2.5:1 for both 15m and 17m.&lt;/p&gt;&#xA;&lt;p&gt;I also have a W3FF loading coil (formerly used with a Buddipole) available that I plan to use at the bottom as well, though I didn't test with it.&lt;/p&gt;&#xA;&lt;p&gt;I'm mentioning all of this to make it clear that I'm not just naively attaching wires to an as-is downspout in the hope it might randomly work. It's more like I'm deliberately building a coil-shortened quarter-wave groundplane vertical whose large-diameter rectangular radiating element hides in plain sight from the HOA as the upper portion of a downspout. ;-)&lt;/p&gt;&#xA;&lt;p&gt;Anyway, here's my quandary: the new downspout is 10 feet long. There are at least two ways I can use it:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;&lt;p&gt;Cut it down to 93&amp;quot; (like my experiments with the old one), so the insulator lies above the ground plane formed by the screen enclosure.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Leave it 120&amp;quot;, or cut it to some shorter length that's still long enough to put its lowermost portion below the ground plane.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Option 2 potentially offers a few advantages:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;If I use the full 120&amp;quot; length, and mount the coil slightly below it, I'll be able to reach up and change bands without needing a stepladder.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;When dealing with a coil-shortened quarter-wave vertical groundplane antenna, longer is (almost) always better. In this case, up to 120&amp;quot; vs 93&amp;quot;.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;However... I'm still trying to understand the &lt;em&gt;consequences&lt;/em&gt; of having a foot or two of the antenna's vertical element (and the loading coil) lying &lt;em&gt;below&lt;/em&gt; the antenna's ground plane.&lt;/p&gt;&#xA;&lt;p&gt;If it's genuinely no big deal, being able to change bands and get at the bottom from below the screen would certainly be convenient... but I don't want to do a lot of work and have it all be for nought because the portion below the ground plane ends up destroying the antenna's effectiveness.&lt;/p&gt;&#xA;" OwnerUserId="9101" LastEditorUserId="9101" LastEditDate="2021-05-03T22:05:25.920" LastActivityDate="2021-05-05T23:50:15.647" Title="Vertical antenna with feedpoint below ground plane?" Tags="&lt;vertical-antenna&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18410" PostTypeId="2" ParentId="7771" CreationDate="2021-04-30T20:53:26.897" Score="0" Body="&lt;p&gt;Thanks to the pandemic :( there is now much more of an ability to take tests online.  I know that the MIT Radio Society is doing on-line exams and are allowing people from outside the US to take it, for example.  Here's their page about their online exams: &lt;a href=&quot;http://w1mx.mit.edu/ham-exams/&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://w1mx.mit.edu/ham-exams/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19193" LastActivityDate="2021-04-30T20:53:26.897" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18411" PostTypeId="2" ParentId="18409" CreationDate="2021-04-30T22:46:21.930" Score="1" Body="&lt;p&gt;Mobile antennas permanently mounted on the roof of vehicles almost always have a feed line below the “ground” plane.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-04-30T22:46:21.930" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18412" PostTypeId="1" AcceptedAnswerId="18413" CreationDate="2021-05-01T23:42:34.447" Score="0" ViewCount="23" Body="&lt;p&gt;I've programmed both my UV-5RA and FT-4XR via CHIRP and it has generally worked fine.  However, one thing I'm not understanding is why it is refusing to program some stations from RepeaterBook input where plain, old FM appears to be listed as one of the supported modes.&lt;/p&gt;&#xA;&lt;p&gt;For example, this one: &lt;a href=&quot;https://www.repeaterbook.com/repeaters/details.php?state_id=25&amp;amp;ID=3277&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.repeaterbook.com/repeaters/details.php?state_id=25&amp;amp;ID=3277&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;That does say it is P25-enabled but it also says it is FM analog-capable.  And on the proximity search page it says &amp;quot;FM EchoLink P-25&amp;quot; for this station.  But CHIRP refuses to import it into the radio images.  How can I fix this?&lt;/p&gt;&#xA;" OwnerUserId="19193" LastActivityDate="2021-05-01T23:42:34.447" Title="How can I import stations listed by RepeaterBook as FM and other things into my HTs with CHIRP?" Tags="&lt;uv-5r&gt;&lt;ft-4x&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18413" PostTypeId="2" ParentId="18412" CreationDate="2021-05-01T23:42:34.447" Score="0" Body="&lt;p&gt;I'm pretty sure the problem is that RepeaterBook apparently is reporting &lt;code&gt;P25&lt;/code&gt; as the only supported mode when running (and importing) the RB proximity query from inside of CHIRP.&lt;/p&gt;&#xA;&lt;p&gt;The reason I believe this is that when I export the RepeaterBook search to a CHIRP-compatible CSV the value of the mode column for that station is &lt;code&gt;P25&lt;/code&gt;.&lt;/p&gt;&#xA;&lt;p&gt;If I then edit the CSV and change &lt;code&gt;P25&lt;/code&gt; to &lt;code&gt;FM&lt;/code&gt; and then do Import CSV instead of Import RB Proximity Query I get can that repeater uploaded into my radios.&lt;/p&gt;&#xA;" OwnerUserId="19193" LastActivityDate="2021-05-01T23:42:34.447" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18414" PostTypeId="1" CreationDate="2021-05-02T01:47:56.557" Score="0" ViewCount="45" Body="&lt;p&gt;I'm trying to build a transponder ramp test for mode c and s of aircrafts for my degree.&lt;/p&gt;&#xA;&lt;p&gt;I have a problem, I didn't understand reply system of transponde, how can I doba reply of a signal to test one?&lt;/p&gt;&#xA;" OwnerUserId="19534" LastActivityDate="2021-05-03T20:02:02.160" Title="How a reply system works on a aircraft transponder?" Tags="&lt;software-defined-radio&gt;&lt;transceiver&gt;" AnswerCount="1" CommentCount="1" ClosedDate="2021-05-03T22:13:49.570" ContentLicense="CC BY-SA 4.0" />
  <row Id="18415" PostTypeId="2" ParentId="9855" CreationDate="2021-05-02T04:04:01.640" Score="0" Body="&lt;p&gt;I had my General License in Haiti as HH2AR in 1959. During hurricane Flora in November 1963, as a teenager using my dad's radio (HH2GR) i provided the only communication link between the Capital Port-au-Prince and the North West City Port de Paix with a missionary radio situated there. We used the 40 meter band to relay critical casualty information and urgently needed rescue efforts. The US Navy then took over the rescue efforts. My AM transmissions relayed Red Cross and Haitian Military messages. At one point, I relayed a message from the infamous Papa Doc to his officials in Port de Paix. It was a sensitive position to be in since the regime's atrocities were well known. My amateur activities continued until the government suspended all Ham licenses and seized our radios: A Baker and Williamson 5100 running 100 watts push-pull with 2 5146 tubes. Our receiver was a Hallicrafter SX 100. After my family migrated to the US in 1964, I studied Electrical Engineering and passed my FCC General with required morse code speed. My QRA assigned is still WB2LIL. I am lately active as /DV7.&#xA;I would like to find some of my QSO contacts made during those days. QST magazine did mention my dx activities. Since that period, the Radio Club d'Haiti - a private entity that was run by our friend Louis Decatrel HH2LD who also migrated to the US, changed hands and its management and regulations may have been significantly modified. I understand that my call sign was assigned HH2AR to another ham.&#xA;I may be contacted via QRZ. 73's.&lt;/p&gt;&#xA;" OwnerUserId="19536" LastActivityDate="2021-05-02T04:04:01.640" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18416" PostTypeId="2" ParentId="12503" CreationDate="2021-05-03T18:16:08.890" Score="2" Body="&lt;p&gt;I have version 2.1.0.  Under File-&amp;gt;Settings, select the General tab. There is a box marked &amp;quot;Show DXCC, grid, and worked before status&amp;quot; that can be check marked.  I use that to identify stations I have worked before.&lt;/p&gt;&#xA;" OwnerUserId="19552" LastEditorUserId="966" LastEditDate="2021-05-04T02:10:02.313" LastActivityDate="2021-05-04T02:10:02.313" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18417" PostTypeId="2" ParentId="18414" CreationDate="2021-05-03T20:02:02.160" Score="1" Body="&lt;p&gt;I recommend you go to the Eurocontrol website.&#xA;Have a look for Asterix category 048. This is the definition for the Mode A Octal code for aircraft transponder, Mode C altitude, Mode S more data including callsign ICAO 24 bit identify code and lots more. There will lots of information about the radar calling and aircraft response exchanges as well.&#xA;Former air traffic controller, currently testing air traffic controller systems.&lt;/p&gt;&#xA;" OwnerUserId="19553" LastActivityDate="2021-05-03T20:02:02.160" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18418" PostTypeId="1" CreationDate="2021-05-03T21:39:12.940" Score="2" ViewCount="78" Body="&lt;p&gt;I've had my general class license for 20 years.  I never progressed farther.  This was back when you had to learn morse code at 13 WPM for General.&lt;/p&gt;&#xA;&lt;p&gt;I'm just curious what the procedures are to upgrade to extra now.  I think advanced is gone, right?&lt;/p&gt;&#xA;&lt;p&gt;And what are the best study guides and tools these days?&lt;/p&gt;&#xA;&lt;p&gt;Thank you&#xA;Monroe Mann N1JZS&lt;/p&gt;&#xA;" OwnerUserId="19554" LastEditorUserId="8717" LastEditDate="2021-05-05T14:56:27.810" LastActivityDate="2021-05-11T19:09:52.223" Title="Extra Class Requirements and Study Guides for a General Class operator" Tags="&lt;united-states&gt;&lt;license&gt;" AnswerCount="6" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18419" PostTypeId="2" ParentId="18418" CreationDate="2021-05-03T23:01:04.783" Score="1" Body="&lt;p&gt;I’m taking my Extra test this weekend. I’ve been using the spiral-bound ARRL study guide and HamStudy.org (mostly their app). The latter is good for drill-style study mode, which focuses on your weak areas as you study. It has explainers for each question too.&lt;/p&gt;&#xA;&lt;p&gt;I have no affiliation with either (except being an ARRL member), but I’m consistently testing in the 90% range on practice tests (which HamStudy tracks and plots), so I’m confident I won’t drive an hour only to fail.&lt;/p&gt;&#xA;&lt;p&gt;All that to say there are lots of great (and often free) study tools out there, but I'd definitely start with one of the study guides (ARRL isn't the only good set) and use a website or app (the latter is often cheap but not free) to study and take practice tests and you'll be fine.&lt;/p&gt;&#xA;" OwnerUserId="18693" LastEditorUserId="18693" LastEditDate="2021-05-04T13:06:58.647" LastActivityDate="2021-05-04T13:06:58.647" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18420" PostTypeId="2" ParentId="18418" CreationDate="2021-05-04T18:18:52.810" Score="1" Body="&lt;p&gt;The procedure is: find a testing session and take the test (have your FRN handy, and tell them that you're going for your Extra). When you pass the test, you should immediately get a Certificate of Successful Completion of Examination. That entitles you to operate using Extra privileges with a &amp;quot;/AE&amp;quot; callsign suffix right away. Once the examiner submits the test results to the FCC and the FCC processes it (usually within a few days), they'll issue your new license, and you can drop the /AE suffix. As you said, there's no practical test anymore, just the written, so that's all there is to it.&lt;/p&gt;&#xA;&lt;p&gt;As for study materials, I can also recommend HamStudy. It's a good and principled resource, and their practice tests are really a good way to gauge how ready you are, and which areas you need to study more.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-05-04T18:18:52.810" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18421" PostTypeId="1" CreationDate="2021-05-05T09:50:32.670" Score="5" ViewCount="1138" Body="&lt;p&gt;I'm building a low-power shack to operate on non-licensed bands (UHF PMR 0.5W + HF CB 4W). I don't have any &amp;quot;RF-grade&amp;quot; sources of 12(-ish) volts and don't want to buy a specialised power unit.&lt;/p&gt;&#xA;&lt;p&gt;I'm thinking of running the whole setup from a 12V battery (VRLA / NiCd / LiPoFe4).&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Here're my thoughts; am I missing something?&lt;/strong&gt;&lt;/p&gt;&#xA;&lt;h2&gt;Pros&lt;/h2&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Cheaper than a dedicated RF-grade power supply (USD30 for 40 Ah car battery)&lt;/li&gt;&#xA;&lt;li&gt;No interference from AC mains and/or cheap power supply&lt;/li&gt;&#xA;&lt;li&gt;Safer: no risks of electric shock (no AC mains on my table)&lt;/li&gt;&#xA;&lt;li&gt;Lightning safety: the equipment is not connected to the house AC, so potential bolt would only damage the radios&lt;/li&gt;&#xA;&lt;li&gt;No need to re-wire mains / use lengthening cable if I decide to move table&lt;/li&gt;&#xA;&lt;li&gt;Blackout proof :)&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;h2&gt;Cons (with my refutal ;)&lt;/h2&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;Runtime &lt;em&gt;[not a problem, I do not expect avg drain to be much more than 1A, so even a small car battery would give me over 20 hours, more than enough]&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;Need to charge &lt;em&gt;[I'm not operating the rig 24/7 so not an issue]&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;Voltage drop when battery is not fully charged &lt;em&gt;[might be small, depending on chemistry... and actually, cheap power supply that I'm using now drops from 12V when idle to 10V when Tx'ing, and the radio is still working]&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;Safety issues with large batteries sitting alone and unsupervised &lt;em&gt;[I will disconnect it every time and can stove it in shed when I'm away]&lt;/em&gt;&lt;/li&gt;&#xA;&lt;li&gt;Limited lifespan of batteries &lt;em&gt;[before the battery would die of old age/overuse, I'd either lose interest or decide to build something bigger anyway :)]&lt;/em&gt;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="15165" LastActivityDate="2021-05-05T21:01:20.327" Title="Are there any cons of running shack on battery?" Tags="&lt;power-supply&gt;&lt;dc-power&gt;&lt;battery&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18422" PostTypeId="2" ParentId="18421" CreationDate="2021-05-05T12:58:52.653" Score="2" Body="&lt;p&gt;Add portable.  You aren't stuck operating where there's an AC outlet.  That's why most POTA and SOTA operators run off batteries, even when carrying solar panels or in an RV.&lt;/p&gt;&#xA;&lt;p&gt;Also possible ground isolation, so your ground wire can't become yet another part of your antenna if the antenna is unbalanced.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-05-05T12:58:52.653" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18423" PostTypeId="2" ParentId="18421" CreationDate="2021-05-05T13:22:03.250" Score="4" Body="&lt;p&gt;Possibly an issue with your HF CB rig is that the output power will be lower at 12.1 than at 13.8 or 14.0 volts.&lt;/p&gt;&#xA;&lt;p&gt;I've seen on 100 watt ham rigs that the final amplifier runs directly from the DC supply, so the output power is quite sensitive to the supply voltage. So you might lose out on a few watts running from battery.&lt;/p&gt;&#xA;&lt;p&gt;This probably won't apply to the UHF CB.&lt;/p&gt;&#xA;&lt;p&gt;Make sure you have the correct fuses everywhere. Lead acid batteries can generate hundreds of amps. The fuse is there to protect the cable, not the radio, so you need a fuse at the battery itself, and then if that fuse is too large, another smaller fuse each time the cable gets thinner. The test is that at all points in the circuit, a short circuit should blow the fuse and not melt the cable.  This is how it's done in your car:&lt;br /&gt;&#xA;Large battery (500 Amps) --&amp;gt; 100 A fuse --&amp;gt; 100 A cable --&amp;gt; Fuse box&lt;br /&gt;&#xA;Fuse box --&amp;gt; 15 A fuse --&amp;gt; 15 A cable --&amp;gt; headlight.&lt;br /&gt;&#xA;You could also just have several 5 A fuses right at the battery and run the thin cables to the rigs from there.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2021-05-05T13:22:03.250" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18424" PostTypeId="2" ParentId="18421" CreationDate="2021-05-05T13:25:10.843" Score="7" Body="&lt;p&gt;I don't mean to talk you out of the idea, but I suspect the advantages are not nearly so great as you imagine.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Cheaper than a dedicated RF-grade power supply (USD30 for 40 Ah car battery)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;I don't know about that. While there are certainly people selling &amp;quot;RF-grade&amp;quot; supplies at high prices because there are people that will pay, we're not talking about a power supply for the first manned interplanetary mission here. Power supply requirements for RF are not especially stringent and any generic supply will do. The only requirement is it isn't terribly noisy.&lt;/p&gt;&#xA;&lt;p&gt;Any linear supply will have nearly no noise. A quick search for &amp;quot;12V linear supply&amp;quot; turns up plenty of candidates for about $30 USD.&lt;/p&gt;&#xA;&lt;p&gt;Most switching supplies are also fine. The very cheapest kind may not have sufficient filtering. Otherwise, the noise remaining after the built-in filtering in the supply and your radio is unlikely to be noticeable among the thousands of other switching supplies in a typical environment, and it's cheap to add a little more filtering, if required.&lt;/p&gt;&#xA;&lt;p&gt;Also keep in mind also car batteries are designed for short, high-current loads to start the car. They will not last long if they are repeatedly discharged. You will want a &amp;quot;deep cycle&amp;quot; battery or some other chemistry which is designed to be charged and discharged.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Safer: no risks of electric shock (no AC mains on my table)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Dubious. You probably use AC appliances all day (including to type this question) and don't give it a thought. Between device testing, electric codes, and inspections, AC is pretty safe.&lt;/p&gt;&#xA;&lt;p&gt;A 12V battery might not pose much of an electrocution hazard, but it can start fires if shorted, rupture and spew corrosive chemicals, or emit hydrogen gas which can accumulate in a building and explode. Will you have your installation inspected? Will you submit your designs to a testing facility?&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Lightning safety: the equipment is not connected to the house AC, so potential bolt would only damage the radios&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;A battery-powered shack certainly avoids some of the more &lt;a href=&quot;https://ham.stackexchange.com/q/51/218&quot;&gt;blatant problems&lt;/a&gt;, but don't assume because your house isn't connected it's now immune. It's still connected, through the soil.&lt;/p&gt;&#xA;&lt;p&gt;And besides, now you have the additional hazard of a battery fire if you forget to disconnect the battery.&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;No need to re-wire mains / use lengthening cable if I decide to move table&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Indeed, or even if you decide to put the entire station in the car.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Blackout proof :)&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Absolutely. Furthermore, you'll be surprised how much lower the noise floor is when all your neighborhood's RFI sources are switched off. A blackout can be a great time to get on the radio.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-05-05T13:25:10.843" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18425" PostTypeId="2" ParentId="18418" CreationDate="2021-05-05T15:06:25.193" Score="1" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;I think advanced is gone, right?&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Right. Although some of us older hams still hold Advanced class licenses (and can renew them), it is no longer possible to obtain a new one. You'll have to take the Extra exam to upgrade.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://ham.stackexchange.com/search?q=Advanced+%5Blicense%5D+&quot;&gt;Some previous questions and answers about Advanced licenses&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2021-05-05T15:06:25.193" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18426" PostTypeId="2" ParentId="18418" CreationDate="2021-05-05T18:12:51.603" Score="1" Body="&lt;p&gt;&lt;a href=&quot;https://www.kb6nu.com/study-guides/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.kb6nu.com/study-guides/&lt;/a&gt;&#xA;&lt;a href=&quot;https://hamstudy.org/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hamstudy.org/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;I used these while studying for my extra exam, highly recommended.&lt;/p&gt;&#xA;" OwnerUserId="9550" LastActivityDate="2021-05-05T18:12:51.603" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18427" PostTypeId="2" ParentId="18421" CreationDate="2021-05-05T21:01:20.327" Score="3" Body="&lt;p&gt;In addition to the points raised in the other fine answers, I'd like to add a few:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;A good three-stage battery charger for lead-acid batteries may cost more than a power supply.&lt;/li&gt;&#xA;&lt;li&gt;Many chargers make horrific RF noise, so you may not want to operate while the batteries are charging, or you may want to pay more for an RF-quiet charger.&lt;/li&gt;&#xA;&lt;li&gt;The actual capacity, as measured in amp-hours or watt-hours, of a lead-acid battery is about half the advertised capacity, assuming that you don't want to damage the battery by draining it down too far.&lt;/li&gt;&#xA;&lt;li&gt;The Lithium-chemistry batteries that I've seen specifications for can be fully discharged without damage.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;I'm not trying to talk you out of powering your station by battery; I'm thinking of investing in a solar and battery backup power system myself.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-05-05T21:01:20.327" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18428" PostTypeId="1" CreationDate="2021-05-05T22:31:36.597" Score="2" ViewCount="63" Body="&lt;p&gt;&lt;a href=&quot;https://space.stackexchange.com/a/49262/12102&quot;&gt;This excellent answer&lt;/a&gt; to &lt;em&gt;First Ham Radio contact from space; what frequency, what kind of antenna, and how did they route the coax out the window?&lt;/em&gt; in Space Exploration SE contains the block-quoted material below.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Question:&lt;/strong&gt; What might a &amp;quot;split-ring on a printed-circuit board&amp;quot; antenna for 144 MHz transmitting through a downward-looking Space Shuttle window look like? How big would it be?&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;This happened on the first Spacelab flight, &lt;a href=&quot;https://en.wikipedia.org/wiki/STS-9&quot; rel=&quot;nofollow noreferrer&quot;&gt;STS-9&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The antenna (&lt;strong&gt;split-ring on a printed-circuit board&lt;/strong&gt;)&#xA;will be placed in the upper crew compartment window on the aft flight deck.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Source, &lt;a href=&quot;https://files.eric.ed.gov/fulltext/ED239843.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;NASA Educational Brief for the Classroom, STS-9 and Amateur Radio&lt;/a&gt;_ This document gives a detailed writeup on the operations.&lt;/p&gt;&#xA;&lt;p&gt;(Owen) Garriott is pictured in JSC's Building 9 One-G Trainer with the handheld unit. The edge of the Orbiter starboard overhead window is visible behind him.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/W59YI.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/W59YI.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Source, NASA Photo&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;" OwnerUserId="8643" LastActivityDate="2021-05-06T02:39:50.743" Title="What might a &quot;split-ring on a printed-circuit board&quot; antenna for 144 MHz on a downward-looking Space Shuttle window look like? How big would it be?" Tags="&lt;antenna&gt;&lt;antenna-construction&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18429" PostTypeId="2" ParentId="18409" CreationDate="2021-05-05T23:50:15.647" Score="1" Body="&lt;p&gt;I mean no offense, but I think you're not using the term &amp;quot;ground plane&amp;quot; correctly.  A real ground plane extends quite a long ways horizontally away from the antenna.  How far is that?  Into the &amp;quot;far field&amp;quot;, which is at least several wavelengths away.&lt;/p&gt;&#xA;&lt;p&gt;What you would have is a system of elevated horizontal antenna elements that are not directly coupled to earth, and because they are not tightly coupled to earth, the real ground plane that does extend a long ways horizontally, they would radiate like the other antenna elements.  If your elevated horizontal antenna elements were to approximate a disc with radius a quarter-wavelength long electrically, then they can could behave a lot like a ground plane at that frequency.  (Such a disc is sometimes called a &amp;quot;counterpoise&amp;quot;, but that term gets abused so much that many experts don't use it any more.  I'm not an expert but I'll follow their lead.)&lt;/p&gt;&#xA;&lt;p&gt;I think the best way to get an idea of how such an antenna system might behave would be to model it in 4nec2 or EZ-NEC, which both use the same calculation engine.  Maybe your elevated horizontal elements would behave similar to a ground plane.  If you sketch a three-dimensional blueprint of your intended setup and edit your question to include the blueprint, then some kind person with more free time than me might help you model it.  Once you have a model, then the kind of &amp;quot;what-if&amp;quot; questions you are entertaining, such as what happens to the feed point impedance when certain antenna elements are tilted, become quite simple to explore.&lt;/p&gt;&#xA;&lt;p&gt;If you do sketch a blueprint, you probably should include the rough locations of large nearby passive conductors, such as the wiring in your wall, because they would affect the antenna also, and so they should probably be part of the model.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-05-05T23:50:15.647" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18430" PostTypeId="2" ParentId="18428" CreationDate="2021-05-06T02:11:44.603" Score="1" Body="&lt;p&gt;I went looking for photos of W5LFL operating in orbit that included a view of the antenna in the window, but I couldn't find any. I did find NASA Photo S83-36894: &lt;a href=&quot;https://i.stack.imgur.com/zQzvO.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/zQzvO.jpg&quot; alt=&quot;Astronaut Owen Garriott trains for a space shuttle mission using ham radio&quot; /&gt;&lt;/a&gt; which is described as &amp;quot;Astronaut Owen Garriott in Ham Radio simulation in One-G trainer in bldg 9A&amp;quot; and I think there's a &lt;em&gt;pretty good&lt;/em&gt; chance that the white thing in the lower-right corner of the window is the antenna.&lt;/p&gt;&#xA;&lt;p&gt;No construction details are visible, but we can at least get an idea about the size: the aft viewing windows, according to &lt;a href=&quot;https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts_coord.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;NASA materials&lt;/a&gt;, were 14.5&amp;quot; x 11&amp;quot; (368 x 279 mm). Assuming the thing we see in the photo I found, it seems to be about half the size in each dimension (~ 180 x 150 mm). Even if that's not it, it probably wasn't &lt;em&gt;bigger&lt;/em&gt; than the window.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastEditorUserId="8016" LastEditDate="2021-05-06T02:39:50.743" LastActivityDate="2021-05-06T02:39:50.743" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18431" PostTypeId="1" AcceptedAnswerId="18432" CreationDate="2021-05-06T16:14:45.790" Score="20" ViewCount="4076" Body="&lt;p&gt;Sometimes, I'll hear someone say &amp;quot;wait a moment, I'm getting a nickel,&amp;quot; and then drop the carrier only to resume talking. Why?&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="8717" LastEditDate="2021-05-10T20:00:49.737" LastActivityDate="2021-05-10T20:00:49.737" Title="Why do people say, &quot;get a nickel,&quot; on repeaters?" Tags="&lt;vhf&gt;&lt;repeater&gt;&lt;jargon&gt;&lt;etiquette&gt;" AnswerCount="1" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18432" PostTypeId="2" ParentId="18431" CreationDate="2021-05-06T16:14:45.790" Score="31" Body="&lt;p&gt;&amp;quot;Getting a nickel&amp;quot; is a reference to how metered pay phones work (worked?). You'd put in some coins, make your call, and when the time you'd payed for expired, the phone operator would demand another nickel to buy more time and keep the call going.&lt;/p&gt;&#xA;&lt;p&gt;Repeaters on automatic control typically have a &amp;quot;time-out&amp;quot; function that acts as a protection mechanism from someone or something triggering prolonged transmission, like sitting on the microphone. The repeater time-out function will then trigger and turn off transmissions for a short time before resuming normal functions.&lt;/p&gt;&#xA;&lt;p&gt;When an amateur radio operator &amp;quot;grabs a nickel,&amp;quot; they're typically letting go of the microphone long enough for the repeater to reset its timer, and then picking back up to finish their transmission.&lt;/p&gt;&#xA;&lt;p&gt;This self-interruption keeps the repeater from turning off, and lets other parties participating on the repeater know that Chatty Cathy isn't quite yet done.&lt;/p&gt;&#xA;&lt;p&gt;Many radios have their OWN time out timer as well, and this same mechanism may be used to reset an individual operator's radio timer as well.&lt;/p&gt;&#xA;" OwnerUserId="1550" LastEditorUserId="1550" LastEditDate="2021-05-07T19:06:30.037" LastActivityDate="2021-05-07T19:06:30.037" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18433" PostTypeId="2" ParentId="18418" CreationDate="2021-05-07T00:11:18.377" Score="0" Body="&lt;p&gt;I did well using HamStudy.org practice tests and an Anki flash card deck (religiously doing my daily reviews). The Anki desktop app is free (have to pay for the mobile one so I stuck with desktop): &lt;a href=&quot;https://ankiweb.net/shared/info/1701037970&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://ankiweb.net/shared/info/1701037970&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19193" LastActivityDate="2021-05-07T00:11:18.377" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18435" PostTypeId="1" AcceptedAnswerId="18436" CreationDate="2021-05-07T03:48:36.110" Score="4" ViewCount="178" Body="&lt;p&gt;As a new ham, just for fun, I'm planning to hike up to the local high point (which while not high in an absolute sense does have a commanding view of the surroundings) with my 5 watt FT-4XR and a slim jim antenna for 2m and see what kind of distance I can get by calling for contacts on 146.52 on analog FM voice.&lt;/p&gt;&#xA;&lt;p&gt;So I was wondering what the calling procedure is to ask for &amp;quot;distant&amp;quot; contacts. (I put distant in scare quotes because this would be just plain old LOS transmission, nothing fancy, so while I hope there'd be some decent reach I wouldn't be expecting &lt;em&gt;real&lt;/em&gt; distance.)  What's the proper way of indicating I'm not looking for &amp;quot;town next door&amp;quot; kind of contacts?&lt;/p&gt;&#xA;" OwnerUserId="19193" LastEditorUserId="8717" LastEditDate="2021-05-10T19:57:18.590" LastActivityDate="2021-05-10T19:57:18.590" Title="What is proper procedure for asking for &quot;distant&quot; contacts on 2m FM on simplex?" Tags="&lt;vhf&gt;&lt;procedure&gt;&lt;dx&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18436" PostTypeId="2" ParentId="18435" CreationDate="2021-05-07T05:44:13.077" Score="10" Body="&lt;p&gt;One would usually call CQ DX, but on 2 m FM that would sound a bit odd. Also FM will be heard by many people close by, who will find CQ DX quite funny. You could simply call and explain what you're trying to achieve, some hams would find that interesting and reply.&lt;/p&gt;&#xA;&lt;p&gt;If you find &lt;em&gt;anyone&lt;/em&gt; on a calling channel, you could talk about the weather for a bit and then say that you are trying to see how far you can reach. This might attract a more distant contact.&lt;/p&gt;&#xA;&lt;p&gt;2m FM simplex in my experience is rarely used for speculative contacts of any sort, let alone some sort of DX. Longer distance contacts and records are usually by arranged contact, and usually on horizontally polarised SSB.&lt;/p&gt;&#xA;&lt;p&gt;Something else you could try is to print out a list of fairly far away repeaters all around the hill in question, and see if you can hit them from there. Lots of people monitor on the repeaters, and they generally know their coverage area. They might jump in to say they're surprised to hear from you so far away.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2021-05-07T05:44:13.077" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18437" PostTypeId="1" AcceptedAnswerId="18457" CreationDate="2021-05-07T12:00:23.070" Score="3" ViewCount="172" Body="&lt;p&gt;I am restoring a Hallicrafters S-120 receiver and when trying to unsolder the wires, from the electrolytic capacitor, I noticed that one of the terminals of the Globar resistor (880-100 Ohm / 023-00327) was loose. Common soldering practices to resolder the lead were unsuccessful.&#xA;Question: is there a way to fix the Globar resistor? Any ideas (including alternatives) will be greatly appreciated. Thank you.&lt;/p&gt;&#xA;&lt;p&gt;May, 09 added picture (click image to expand)&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/X4e6K.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/X4e6K.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;@W5VO  As explained before, I opted for the &amp;quot;2 resistors + switch&amp;quot; but instead of a switch, I will be using a simple circuit to circumvent the flaw mentioned in the last paragraph of your proposed solution.  The 12VDC will be derived, from a point after the power-on switch, by means of a rectifier, resistor, and electrolytic capacitor, Thanks for your support.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/4ogG8.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/4ogG8.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Acknowledgment: &lt;a href=&quot;http://www.bowdenshobbycircuits.info/page2.htm#delay.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;http://www.bowdenshobbycircuits.info/page2.htm#delay.gif&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19589" LastEditorUserId="19589" LastEditDate="2021-05-18T13:05:21.117" LastActivityDate="2021-05-18T13:05:21.117" Title="Globar resistor repair or alternative(s)?" Tags="&lt;receiver&gt;&lt;repair&gt;&lt;components&gt;" AnswerCount="1" CommentCount="10" ContentLicense="CC BY-SA 4.0" />
  <row Id="18439" PostTypeId="1" CreationDate="2021-05-07T17:22:25.543" Score="3" ViewCount="66" Body="&lt;p&gt;I've been trying to devise an experiment to produce a third order harmonic in radio receiver that's been saturated, but I'm not seeing the expected results.&lt;/p&gt;&#xA;&lt;p&gt;My understanding of the theory is that when you drive an amplifier &lt;em&gt;&lt;strong&gt;( refer to the diagram below )&lt;/strong&gt;&lt;/em&gt;, past the point of linear operation whether by an on or off frequency signal, it will produce harmonics of and primary frequencies input into it.  (  See diagram below )  I thought I could observe this effect with a handheld two-way radio and 2 signal generators I have on hand.&lt;/p&gt;&#xA;&lt;p&gt;My experiment set up is thus:  A multiple band, 2-way FM transceiver, programmed to to receive on 471MHZ and two signal generators. One signal generator generates an FM 157MHZ signal, modulated with a 1kHz tone, the other signal generator is used to produce an unmodulated CW carrier.  Note that 157MHZ x 3 = 471MHZ. I expected that I could use the CW signal to force the receiver into non-linear operation causing the amplifier to produce 3rd order harmonics of the 157MHZ FM signal injected below saturation.&lt;/p&gt;&#xA;&lt;p&gt;First I inject the 157MHZ signal into the 471MHZ radio.  At about -60 dBm the receiver of the radio would open and produce a fairly clean 1k tone: this to me indicates that the FM signal forced the receiver into non-linear operation, causing the 3rd order harmonic, 471MHZ to be demodulated on the radio. This I expected. Next, I used a combiner to inject the 157MHZ FM signal and the CW signal into the receiver.  I injected the FM signal first to find the spot where the receive became non-linear and demodulating the 1k tone.  I decreased the FM signals power just below the threshold.  Then I turned on the CW generator and increased the power slowly. I assumed that the CW signal would drive the receiver into non-linearity causing the receiver to produce the 3rd order harmonic of the FM signal, and thus the receiver would open up with the primary FM signal injected at a lower power than by itself.&lt;/p&gt;&#xA;&lt;p&gt;The results were not what I expected.  No matter what frequency or power level the CW was set to, it didn't seem to affect when the receiver opened up.  If the FM signal was set so that it's 3rd order harmonic was being received, I could overload the receiver by cranking up the CW wave though, so I know it was getting into the receiver.  I was expecting that the CW signal would force the receiver into non-linear operation, and that I would be able to receive the 3rd order harmonic of the FM signal at a lower threathold than by itself.  Anyone have an idea why I didn't see what I expected?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/tYPCt.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/tYPCt.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="17109" LastActivityDate="2021-05-10T14:07:58.413" Title="Why is my experiment to produce 3rd order harmonics by saturating a receiver not working" Tags="&lt;receiver&gt;&lt;amplifier&gt;&lt;testing&gt;&lt;education&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18440" PostTypeId="2" ParentId="18439" CreationDate="2021-05-07T19:02:03.867" Score="4" Body="&lt;p&gt;Receivers have passive band-pass filters at their input. Except possibly ferrite cores (which are unlikely to be used for a filter above HF), the components used to construct these filters are very linear. For a receiver tuned to 471MHz, the output of your signal generators at 157MHz is surely well within the filter stop-band.&lt;/p&gt;&#xA;&lt;p&gt;Although the filter's stop-band attenuation isn't infinite, and this means at some power you could still saturate the receiver, it's going to require a very high power for the fundamental, after being attenuated, to have enough power to cause significant nonlinear behavior in the active components behind the filter.&lt;/p&gt;&#xA;&lt;p&gt;Further consider, the signal generators produce harmonics as well. The receiver's filter attenuates the fundamental from the signal generators, but not the harmonics.&lt;/p&gt;&#xA;&lt;p&gt;So, it's likely you're just hearing the harmonics of your signal source, and not overloading the receiver.&lt;/p&gt;&#xA;&lt;p&gt;If you want to observe non-linear behavior in your receiver, you need to generate two or more &lt;em&gt;in band&lt;/em&gt; signals. The &lt;a href=&quot;https://en.wikipedia.org/wiki/Two-tone_testing&quot; rel=&quot;nofollow noreferrer&quot;&gt;two tone test&lt;/a&gt; is a common way to do this.&lt;/p&gt;&#xA;&lt;p&gt;The image you included that mentions &amp;quot;IM products&amp;quot; hints at this. It sounds like with your setup you're trying to measure harmonic distortion, but &amp;quot;IM products&amp;quot; refers to &lt;a href=&quot;https://en.wikipedia.org/wiki/Intermodulation&quot; rel=&quot;nofollow noreferrer&quot;&gt;intermodulation products&lt;/a&gt;. Unlike harmonic distortion which produces spurious signals at multiples of the fundamental, IM distortion produces spurious signals related to the difference between two signals and multiples of that difference. Since the distortion products lie much closer to the signal or signals of interest, this makes them much more difficult to remove with a passive filter, and thus much more problematic in practice.&lt;/p&gt;&#xA;" OwnerUserId="218" LastEditorUserId="218" LastEditDate="2021-05-10T14:07:58.413" LastActivityDate="2021-05-10T14:07:58.413" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18442" PostTypeId="1" AcceptedAnswerId="18468" CreationDate="2021-05-08T14:54:51.110" Score="3" ViewCount="119" Body="&lt;p&gt;I built a two-band antenna (20 and 40m) with traps.&#xA;I made the traps as a parallel LC circuit on the AL7 toroidal core (3 MHz - 40 MHz), I also used a 1KV ceramic capacitor. I've tuned everything up and it works very well.&lt;/p&gt;&#xA;&lt;p&gt;The problem appears when I increase the power above 50W. The antenna resonance shifts to the right by approx &lt;strong&gt;200kHz&lt;/strong&gt;. When I shift the transmit frequency towards the antenna resonance, it shifts again by &lt;strong&gt;200kHz&lt;/strong&gt;. When I finish the transmission, the antenna's resonance slowly returns to its place.&lt;/p&gt;&#xA;&lt;p&gt;I am looking for an answer to what could be causing this.&lt;/p&gt;&#xA;&lt;p&gt;I checked that nothing heats up during this power.&#xA;I am concerned that I used the wrong type of capacitor - ceramic, which is not very stable?&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;Edit:&lt;/strong&gt;&#xA;I tried with a T94-6 double core and a thicker winding wire. Nothing has changed&lt;/p&gt;&#xA;" OwnerUserId="19590" LastEditorUserId="19590" LastEditDate="2021-05-11T05:53:31.697" LastActivityDate="2021-05-14T20:02:50.590" Title="Antenna traps - problem with frequency change" Tags="&lt;antenna-construction&gt;&lt;trap&gt;" AnswerCount="2" CommentCount="13" ContentLicense="CC BY-SA 4.0" />
  <row Id="18445" PostTypeId="2" ParentId="18435" CreationDate="2021-05-10T16:00:53.327" Score="2" Body="&lt;p&gt;I live in a mountainous area, and when my VHF/UHF FM radio is on, I have it on scan, with the calling frequency in the scan bank of course.  Every once in a while I'll hear someone on a mountain peak calling on the 2m calling frequency asking for SOTA (&lt;a href=&quot;https://www.sota.org.uk/&quot; rel=&quot;nofollow noreferrer&quot;&gt;Summits on the Air&lt;/a&gt;) contacts, which I'm happy to hand out.  So it does happen.  If you're on the mountain peak, just explain what you're trying to do, and if anyone is listening then they will probably be glad to accommodate you.&lt;/p&gt;&#xA;&lt;p&gt;And if you want to make a habit of making contacts from high places, consider joining SOTA, it's lots of fun!&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-05-10T16:00:53.327" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18447" PostTypeId="1" CreationDate="2021-05-10T20:05:50.120" Score="3" ViewCount="198" Body="&lt;p&gt;I'm designing a HF antenna that uses a portion of a downspout (electrically isolated from the gutters above and lower portion) as a bottom-loaded shortened quarter-wave vertical.&lt;/p&gt;&#xA;&lt;p&gt;I'm about to trim the downspout down to what I'm planning to use as its final length, but want to cut off 2-3 inches at a time &amp;amp; capture a sweep at each length for posterity, just so I can document any &amp;quot;golden&amp;quot; length I encounter along the way &amp;amp; find it again in the future if I end up being dissatisfied with a shorter length. I'm also planning to document the performance of a vertical wire of comparable length hanging in the same location, to see whether I'd be better off replacing the 8-9 foot aluminum segment between the insulators with vinyl and hiding an antenna wire inside (or adhering 1&amp;quot; copper foil tape to the front &amp;amp; painting over it).&lt;/p&gt;&#xA;&lt;p&gt;To that end... what 4 &amp;quot;format&amp;quot; values should I be capturing at my 4 marker-position frequencies of interest (10.08, 14.07, 18.13, and 21.07MHz)?&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;SWR&lt;/strong&gt; is probably an obvious one&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;&lt;strong&gt;SMITH&lt;/strong&gt; is probably another&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;... but that leaves two more available. Are there two other format values that, if captured, will ensure that I have all the information I'll need to derive any other values?&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;&lt;p&gt;Real and Imaginary?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Resistance and Reactance?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Logmag, Phase, Delay, and/or Polar?&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;One obvious thing I think I want to have available is &lt;strong&gt;Feedpoint Impedance&lt;/strong&gt; (ie, Z = r + jx), because (I &lt;em&gt;think&lt;/em&gt;) that will allow me to design a coil+capacitor matching network to bring that particular length to 50 ohm feedpoint impedance for the frequency in question, and/or give insight into whether an unun would at least improve matters when used in conjunction with the radio's built-in antenna tuner (and if so, what ratio it ought to have).&lt;/p&gt;&#xA;&lt;p&gt;I &lt;em&gt;thought&lt;/em&gt; that was supposed to be what &amp;quot;Smith&amp;quot; conveys... but on MY NanoVNA (v2_2), at least, &amp;quot;Smith&amp;quot; shows the value as {resistance}ohms + {capacitance}(nano|micro)Farads.&lt;/p&gt;&#xA;&lt;p&gt;So... if the values I really will need in the future are r + jx, can they be derived directly from the Smith value pair, or will I need to capture one or two other values (real, imaginary, resistance, reactance, or ???) to have the information I'll need to do it?&lt;/p&gt;&#xA;" OwnerUserId="9101" LastActivityDate="2021-05-11T15:45:00.597" Title="NanoVNA(v2)... what to capture for future reference when comparing past antennas?" Tags="&lt;nanovna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18448" PostTypeId="2" ParentId="18447" CreationDate="2021-05-10T20:18:36.853" Score="6" Body="&lt;p&gt;The real+imaginary S11 and the frequency, &lt;em&gt;or&lt;/em&gt; the resistance and reactance (R+jX) and the frequency, along with a known Z0 (which I think is always going to be 50 ohm for a NanoVNA), are enough to re-derive every other variable of interest for a single-port measurement, whether that's return loss, SWR, phase angle, or equivalent capacitance or inductance. So given those three things, you can get anywhere; anything else you capture (like SWR) is just for your convenience.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-05-10T20:18:36.853" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18449" PostTypeId="2" ParentId="8984" CreationDate="2021-05-10T21:49:19.717" Score="2" Body="&lt;p&gt;Because ferrites aren’t marked, it is difficult to know what frequencies they work on. However, now we can use the popular NanoVNA along with free software (and Excel) to graph the unknown ferrite’s impedance over frequency.&lt;/p&gt;&#xA;&lt;p&gt;&lt;strong&gt;YouTube video by Fair-Rite Corporation&lt;/strong&gt;, using a Nano VNA and software:&#xA;&lt;a href=&quot;https://youtu.be/KmKQibSDzqM&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://youtu.be/KmKQibSDzqM&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;sup&gt;(Sorry that more info from this can't be easily copied here.)&lt;/sup&gt;&lt;/p&gt;&#xA;" OwnerUserId="8717" LastActivityDate="2021-05-10T21:49:19.717" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18450" PostTypeId="5" CreationDate="2021-05-10T21:59:12.887" Score="0" Body="&lt;p&gt;What is DX on the various amateur radio bands? Since propagation varies with the frequency, DX distance on VHF and above is generally much shorter than DX on MF or HF.&lt;/p&gt;&#xA;" OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2021-05-10T21:59:12.887" LastActivityDate="2021-05-10T21:59:12.887" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18451" PostTypeId="4" CreationDate="2021-05-10T21:59:12.887" Score="0" Body="Long distance radio communications, propagated through the ionosphere or troposphere " OwnerUserId="8717" LastEditorUserId="8717" LastEditDate="2021-05-10T21:59:12.887" LastActivityDate="2021-05-10T21:59:12.887" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18452" PostTypeId="2" ParentId="18447" CreationDate="2021-05-11T02:06:09.517" Score="2" Body="&lt;p&gt;A nanoVNA will sweep 101 frequency points.  So I would sweep a frequency range that includes the entire band, for each of your radio bands of interest.&lt;/p&gt;&#xA;&lt;p&gt;You can connect to the nanoVNA via its USB serial port, and send it commands.  The “frequencies” command will print out a list of frequencies swept.  The “data” command will print out a list of IQ values for the entire swept frequency range.  Save these to a file.  You can convert your frequency and IQ tables into an either a Smith chart or an SWR plot, using a spreadsheet or etc.&lt;/p&gt;&#xA;&lt;p&gt;There may be software utilities that automate this, but I’ve downloaded the data manually, and used a Basic program or Python notebook to do the plotting.&lt;/p&gt;&#xA;&lt;p&gt;Then I compare plots of my antenna changes to see whether I made things better or worse, and where across the entire band.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-05-11T15:45:00.597" LastActivityDate="2021-05-11T15:45:00.597" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18453" PostTypeId="1" CreationDate="2021-05-11T03:37:20.123" Score="18" ViewCount="7994" Body="&lt;p&gt;I had applied for a vanity callsign which wasn't available. That was in March. The FCC license system shows my old callsign is still in effect.&lt;/p&gt;&#xA;&lt;p&gt;Today, after a longer absence from my mail, I open a &amp;quot;Notice of Dismissal&amp;quot; which says in a wordy way lots of scary stuff:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Your application is in a dismissal status effective 03/09/2021 without prejudice in accordance with Section 1.934 of the Commission's Rules for the reason(s) indicated below. If you still wish to be licensed, you must file a new application, ... If you currently hold a valid license, you may continue to operate under the parameters of that authorization.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;If you are currently operating under authority provided by the Commission's Rules based on your submission of the above references application, you must immediately cease operation until such time as you come into compliance with the Rules.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The call sign(s) you requested is/are not available. To pursue another call sign, submit a new vanity request.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;I currently hold a valid license, and therefore I may continue to operate under the parameters of that authorization.&lt;/li&gt;&#xA;&lt;li&gt;I do not need to &lt;em&gt;immediately cease operation until such time as&lt;/em&gt; I &lt;em&gt;come into compliance with the Rules&lt;/em&gt;, because I &lt;strong&gt;am&lt;/strong&gt; in compliance to begin with, especially because I am &lt;strong&gt;not&lt;/strong&gt; &lt;em&gt;currently operating under authority provided by the Commission's Rules &lt;strong&gt;based on my submission of the above referenced application&lt;/strong&gt;&lt;/em&gt;, but instead, I am operating based on my existing license and the existing unchanged call sign.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;The FCC makes it sound as if I'm in trouble. Based on my thoughts above, I believe I can safely ignore the &amp;quot;Notice of Dismissal.&amp;quot; Am I correct?&lt;/p&gt;&#xA;" OwnerUserId="16238" LastEditorUserId="966" LastEditDate="2021-05-14T06:31:15.053" LastActivityDate="2021-05-14T06:31:15.053" Title="FCC sends &quot;Notice of Dismissal&quot; with quite threatening language just for denial of a vanity callsign?" Tags="&lt;fcc&gt;&lt;authorization&gt;" AnswerCount="5" CommentCount="6" FavoriteCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18454" PostTypeId="2" ParentId="18442" CreationDate="2021-05-11T13:12:58.137" Score="3" Body="&lt;p&gt;What you describe does indeed sound like a thermal issue. If you have some unstable components, even a small change in temperature which is difficult to detect can be sufficient to cause the issues you describe.&lt;/p&gt;&#xA;&lt;p&gt;Are you tuning the trap such that its resonance is in the 20 meter band? This would mean when you transmit on 20 meters, &lt;a href=&quot;https://www.w8ji.com/traps.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;current circulating in the trap is at a maximum, and so are losses&lt;/a&gt;. If any of your components are not so thermally stable, this could be enough to shift the resonance frequency.&lt;/p&gt;&#xA;&lt;p&gt;This would also explain why the resonance drifts away, and when you &amp;quot;chase&amp;quot; it, it drifts away more. It's drifting away until the losses are low enough that it reaches thermal equilibrium, but when you subsequently increase the transmitter frequency the losses go up again, further heating the components, causing the resonance to shift yet more. I'd suspect if you keep repeating this, eventually you'll notice something getting warm, and then quite hot. Of course you probably don't want to be transmitting outside the ham band at 50 watts.&lt;/p&gt;&#xA;&lt;p&gt;Here's a way to test this hypothesis: get a &amp;quot;compressed air&amp;quot; (they don't actually contain air) duster, like this:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/O0zB9.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/O0zB9.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Fire up the transmitter, and get the resonance frequency to drift up.&lt;/p&gt;&#xA;&lt;p&gt;Now turn the can upside down, and spray it on your trap for a fraction of a second. The can contains a rapidly evaporating liquid: normally the &amp;quot;air&amp;quot; these spray is the vapors from this liquid. When upside down, the liquid will evaporate on your trap, cooling it. Take care to avoid spraying your skin unless you enjoy a little frostbite. Safety glasses also not a bad idea.&lt;/p&gt;&#xA;&lt;p&gt;Does the resonance come back down after you do this? If so, thermal instability is the issue.&lt;/p&gt;&#xA;&lt;p&gt;What can you do to fix this? A simple solution may be to tune the trap so its resonance is outside the 20 meter band. The idea is to find a place where the impedance is high enough to mostly isolate the upper section of the antenna, but with enough distance between transmit and resonance frequencies that losses are lower. Besides avoiding the thermal stability issue this will also increase your antenna efficiency.&lt;/p&gt;&#xA;&lt;p&gt;Of course, if you identify which components are causing the problem you could pursue alternatives with a lower temperature coefficient. Ceramic capacitors come in varieties with different dielectrics, and some are very stable and some are very much not.&lt;/p&gt;&#xA;&lt;p&gt;You can also consider alternative construction methods. A common technique is to use some length of coax instead of discrete capacitors. Searching for &amp;quot;coaxial trap&amp;quot; should turn up some resources.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-05-11T13:12:58.137" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18455" PostTypeId="2" ParentId="18453" CreationDate="2021-05-11T13:49:51.823" Score="37" Body="&lt;p&gt;Isn't bureaucracy wonderful? Perhaps I can translate into plain English:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Your application is in a dismissal status effective 03/09/2021 without prejudice in accordance with Section 1.934 of the Commission's Rules for the reason(s) indicated below. If you still wish to be licensed, you must file a new application, ... If you currently hold a valid license, you may continue to operate under the parameters of that authorization.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;We looked at your application on 3/9/2021, but unfortunately we had several applications for this call. According to our published procedures for fairly resolving this conflict we randomly selected someone to receive the call from all the applications on this day, and unfortunately it wasn't you. &lt;/p&gt;&#xA;&lt;p&gt;But don't worry: you can still use your existing license, and apply for another vanity call.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;If you are currently operating under authority provided by the Commission's Rules based on your submission of the above references application, you must immediately cease operation until such time as you come into compliance with the Rules.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;We really appreciate that you follow the Rules.&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The call sign(s) you requested is/are not available. To pursue another call sign, submit a new vanity request.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Please try again, and better luck next time!&lt;/p&gt;&#xA;&lt;p&gt;Your friend,&lt;br&gt;&#xA;The Federal Communications Commission&lt;/p&gt;&#xA;&lt;hr /&gt;&#xA;&lt;p&gt;The only parts of the letter which are really specific to you are:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;The date in the first paragraph&lt;/li&gt;&#xA;&lt;li&gt;The last paragraph.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Everything else is boilerplate legal diarrhea which is included with every application they might dismiss, not just for vanity call signs, and not just for the amateur radio service. The objective is to minimize their responsibility, and maximize yours.&lt;/p&gt;&#xA;&lt;p&gt;It makes a little more sense considering the party on the receiving side of this letter is often not a ham, but a huge commercial interest like Verizon, Comcast, or AT&amp;amp;T. Imagine Verizon asks, &amp;quot;can we commandeer this spectrum?&amp;quot; or &amp;quot;Can we have a special regulatory exemption which would be hugely beneficial to us at the expense of our competitors and/or allow us to exploit the public for profit?&amp;quot; The FCC must send a very carefully worded &amp;quot;nope&amp;quot; to avoid a costly legal challenge.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-05-11T13:49:51.823" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18457" PostTypeId="2" ParentId="18437" CreationDate="2021-05-11T16:10:12.330" Score="4" Body="&lt;p&gt;This is an Inrush Current Limiter (ICL). You can still get them today, but they look quite a bit different. See Digikey for a wide range of parts. Typically, these are used for reducing the inrush current of main power supply capacitors instead of filament protection, so they're optimized a bit differently.&#xA;&lt;a href=&quot;https://www.digikey.com/en/products/filter/inrush-current-limiters-icl/151&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.digikey.com/en/products/filter/inrush-current-limiters-icl/151&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;What you would need to know to design this circuit is how much current it normally draws, the starting resistance, and the ending resistance. There's a bit of experimentation I think you would want to do in order to make sure the circuit is working right.&lt;/p&gt;&#xA;&lt;p&gt;Taking a look at an example &lt;a href=&quot;https://www.digikey.com/en/products/detail/ametherm/SL15-22101/2614363&quot; rel=&quot;nofollow noreferrer&quot;&gt;higher starting resistance ICL part here&lt;/a&gt;, you could put 3-4x 220Ω ICL parts in series to get your starting resistance. When they get up to temperature, their resistance drops to 2-5Ω, which is much lower than your ending resistance of 100Ω. To compensate, plan on putting a large power resistor in the 80-100Ω range in series with this mess.&lt;/p&gt;&#xA;&lt;p&gt;They come in different current ratings and sizes, so I'd say get a few options to play around with. Neither the starting resistance or the final resistance are going to be &lt;em&gt;that&lt;/em&gt; critical.&lt;/p&gt;&#xA;&lt;p&gt;I would hate to have a manual inrush switch - I know I would forget to switch it from &amp;quot;Run&amp;quot; to &amp;quot;Start&amp;quot; at the end.&lt;/p&gt;&#xA;" OwnerUserId="18" LastActivityDate="2021-05-11T16:10:12.330" CommentCount="11" ContentLicense="CC BY-SA 4.0" />
  <row Id="18460" PostTypeId="1" CreationDate="2021-05-11T16:36:09.257" Score="1" ViewCount="30" Body="&lt;p&gt;I want to imitate this cable, but I don't know-how. Yaesu FT-65 TNC cable. Is it need to series a resistor inside of those?&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/0M0sb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/0M0sb.png&quot; alt=&quot;Yaesu FT-65 TNC cable&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19653" LastActivityDate="2021-05-11T16:36:09.257" Title="Audio Interface wiring diagram of Yaesu FT-65 TNC cable" Tags="&lt;yaesu&gt;&lt;audio&gt;&lt;tnc&gt;&lt;wiring&gt;" AnswerCount="0" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18461" PostTypeId="2" ParentId="18418" CreationDate="2021-05-11T19:09:52.223" Score="0" Body="&lt;p&gt;I used HamTestOnline to upgrade from Advanced to Extra. There is about a $35 charge for six months of access to the computer training.  The thing that I liked most about it was that the program keeps working on new questions from the FCC question bank while continually going back to the questions you have missed.  Very good supporting documentation for each question.&lt;/p&gt;&#xA;" OwnerUserId="19655" LastActivityDate="2021-05-11T19:09:52.223" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18462" PostTypeId="2" ParentId="18453" CreationDate="2021-05-11T19:21:04.623" Score="18" Body="&lt;p&gt;I am not a lawyer, so I cannot provide actual legal advice.&#xA;However, I have dealt with a lot of governmental legalese in the past, so I am perhaps partially qualified to parse the legalese you've posted.&lt;/p&gt;&#xA;&lt;p&gt;As the O.P. aptly pointed out, probably the most important &amp;quot;operant&amp;quot; part of the verbiage posted reads:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;&lt;strong&gt;If&lt;/strong&gt; you are currently operating under authority provided by the Commission's Rules &lt;strong&gt;based on your submission of the above references application&lt;/strong&gt;, you must immediately cease operation...&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;[Emphasis mine.]&lt;/p&gt;&#xA;&lt;p&gt;The key words are &amp;quot;IF  ... you are operating&amp;quot; and &amp;quot;based on your submission ... above.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;In other words, this statement most likely means &amp;quot;if you have been operating your station under any interim rules &lt;em&gt;using this callsign&lt;/em&gt;, you must cease doing so.&amp;quot;   By extension, it would also mean &amp;quot;if you have no other call sign, you must cease operating &lt;em&gt;entirely&lt;/em&gt; until you've asked for a different callsign.&amp;quot;   It would also (by omission) mean &amp;quot;none of these warnings apply to operations permitted by &lt;em&gt;other&lt;/em&gt; rules or permits that are associated with other callsigns.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;To be safe, you should consult a lawyer well-versed in this kind of law to be sure, or... directly seek clarification from the FCC.&lt;/p&gt;&#xA;&lt;p&gt;Hope this helps!&lt;/p&gt;&#xA;" OwnerUserId="19658" LastActivityDate="2021-05-11T19:21:04.623" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18463" PostTypeId="2" ParentId="707" CreationDate="2021-05-11T23:10:19.700" Score="0" Body="&lt;p&gt;The closest to store and forward used right now which is easily doable is JS8CALL on, believe it or not, HF. A station can put a message on a ground station , say a California station, could put one on a south African station in a mailbox on that station. A station which sends out a beacon, say in Europe, is notified that a message is waiting for it from the California station , with a small added notification IN a response the the European beacon with a message number, which hopefully is seen by the European station.&#xA;The reason store and forward is so helpful from the world perspective is that the South African station may not be awake, nor the European station , when the California Station initially stores its message on the South African stations mailbox. Also, these stations are using simple low powered (30w) transmitters on 40m . Nothing exotic and costly.&#xA;There is also a direct relay set up available, the California station could relay THROUGH the South African station to the European station or perhaps to a station in Antarctica at the base? Also, the message length shouldn't be too long but could be long enough to give weather warnings or health and welfare messages and do incorporate the CRC verification system.&lt;/p&gt;&#xA;" OwnerUserId="19660" LastActivityDate="2021-05-11T23:10:19.700" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18464" PostTypeId="2" ParentId="18453" CreationDate="2021-05-11T23:35:00.763" Score="15" Body="&lt;blockquote&gt;&#xA;&lt;p&gt;If you are currently operating under authority provided by the Commission's Rules based on your submission of the above referenced application, you must immediately cease operation until such time as you come into compliance with the Rules.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;It's not uncommon for an application to a government agency (especially for an application to renew an existing permit or license) to allow the applicant to proceed as though the application was granted until/unless the application is denied.  I don't know of any specific examples with the FCC, but a common example that I see day-to-day is elevator permits in California, for which &lt;a href=&quot;https://law.justia.com/codes/california/2011/lab/division-5/7300-7324.2/7302/&quot; rel=&quot;noreferrer&quot;&gt;CA Labor Code § 7302&lt;/a&gt; states that:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Any person who has requested the issuance or renewal of a permit if the request has not been acted upon by the division may not be prosecuted for a violation of this section [requiring a permit to operate certain conveyances such as elevators].&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Basically, you're allowed to operate the elevator as long as you've applied for the permit.  This allows for day-to-day operations to continue even if the agency is behind on processing the permit applications (or the processing is otherwise time-consuming).  I imagine there are similar rules for at least some applications to the FCC.&lt;/p&gt;&#xA;&lt;p&gt;This generic language is telling you that if there &lt;em&gt;was&lt;/em&gt; anything you were allowed to do &lt;em&gt;solely&lt;/em&gt; by having submitted the application to the FCC, you're no longer allowed to do that.  Since I don't believe a pending application for a vanity call sign grants you any such rights, this doesn't actually forbid you from doing anything that you could do before receiving this notice.&lt;/p&gt;&#xA;" OwnerUserId="19661" LastEditorUserId="19661" LastEditDate="2021-05-11T23:45:59.077" LastActivityDate="2021-05-11T23:45:59.077" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18465" PostTypeId="2" ParentId="18453" CreationDate="2021-05-12T11:54:17.917" Score="9" Body="&lt;p&gt;This isn't overly harsh, it's overly formal.   I get that from the first sentence.&lt;/p&gt;&#xA;&lt;p&gt;My translation:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;Your application is in a dismissal status&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;We aren't going to give you what you asked for&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;[...] without prejudice&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;but we won't hold it against you and you can ask again.&lt;/p&gt;&#xA;&lt;p&gt;This is what makes it &amp;quot;not harsh&amp;quot;.  If it said &amp;quot;with prejudice&amp;quot; that would translate to &amp;quot;...and you'll never get it, and don't ask again or we'll get annoyed with you, possibly with penalties.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;And just in case you missed that, they repeat it at the end with more specificity:&lt;/p&gt;&#xA;&lt;blockquote&gt;&#xA;&lt;p&gt;The call sign(s) you requested is/are not available. To pursue another call sign, submit a new vanity request.&lt;/p&gt;&#xA;&lt;/blockquote&gt;&#xA;&lt;p&gt;Everything else in between (which all starts with &amp;quot;If&amp;quot;) either doesn't apply to you, or basically says you can continue with your existing license.  (Assuming you weren't trying to renew it.)&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2021-05-12T11:54:17.917" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18467" PostTypeId="2" ParentId="18453" CreationDate="2021-05-13T14:57:31.183" Score="4" Body="&lt;p&gt;IANAL, but I spent a fair amount of my career writing and negotiating contracts. Others have addressed the meaning(s) of the language in the notice, I wanted to address more of the &amp;quot;&lt;em&gt;why is it written this way?&lt;/em&gt;&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;First, my reading of the &amp;quot;scary&amp;quot; language is that all it is saying is that:&lt;/p&gt;&#xA;&lt;p&gt;&amp;quot; &lt;em&gt;If you are/were already using the requested callsign, then you must stop using it right now.&lt;/em&gt; &amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;That's all, nothing more.  You weren't using the requested callsign, so that part doesn't apply to you.&lt;/p&gt;&#xA;&lt;p&gt;The reason it's written that way is that&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;It's technically a legal notice so it has to be written in &amp;quot;legalese&amp;quot; (formal legal English), and&lt;/li&gt;&#xA;&lt;li&gt;It's an authoritative notice from the government, so it has to be clear, directive and leave no wiggle room.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;For instance, if it more politely said &amp;quot;&lt;em&gt;should&lt;/em&gt;&amp;quot; instead of &amp;quot;&lt;em&gt;must&lt;/em&gt;&amp;quot; you'd end up with a court case where defense attorney's would argue (sometimes successfully) that the notice didn't make it clear that their client had no choice in the matter.  Likewise, if it didn't say &amp;quot;&lt;em&gt;immediately&lt;/em&gt;&amp;quot;  someone would argue that they waited a &amp;quot;reasonable period of time&amp;quot; before they stopped using the wrong callsign, which they interpreted as 6 months.  And so on.  They have to be clear, strict and absolute in their wording or someone &lt;em&gt;will&lt;/em&gt; try to squirm around it.&lt;/p&gt;&#xA;&lt;p&gt;There's nothing personal here, it's just a formal government legal notice explaining what your current situation is in no uncertain terms.&lt;/p&gt;&#xA;" OwnerUserId="19687" LastEditorUserId="19687" LastEditDate="2021-05-13T15:04:22.290" LastActivityDate="2021-05-13T15:04:22.290" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18468" PostTypeId="2" ParentId="18442" CreationDate="2021-05-14T06:51:35.297" Score="3" Body="&lt;p&gt;I am very pleased that my traps have started working properly! The problem was solved by mica capacitors. It turned out that the ceramic capacitors I used had poor temperature and capacity parameters. Mica capacitors have proven themselves perfectly and the frequency does not shift any more. I made the antenna for the bands that I like best 20/40/80/17 / 30m. Everything works very well! Here's my trap in action:&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://photos.app.goo.gl/x3KnzwkGkJfjQo7d9&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/kZACm.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Thanks to everyone for your help.&lt;/p&gt;&#xA;" OwnerUserId="19590" LastEditorUserId="218" LastEditDate="2021-05-14T20:02:50.590" LastActivityDate="2021-05-14T20:02:50.590" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18469" PostTypeId="2" ParentId="1405" CreationDate="2021-05-14T21:50:59.643" Score="1" Body="&lt;p&gt;One important aspect of antennas in close proximity of trees or even touching branches is problem with correct and persistent tuning of such antennas. Needles to say totally unknown characteristic of radiation. Correctly calculated and tuned length of wires are often no longer correct in trees. SWR is something magically changing or flat across whole band without abilities to lower it down in any frequency etc. Generally speaking antennas going between trees and branches it is bad idea and may bring a lot of frustration during setting up an antenna. Trees as support isolated from antenna yes that works quite well.&lt;/p&gt;&#xA;" OwnerUserId="19701" LastActivityDate="2021-05-14T21:50:59.643" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18470" PostTypeId="2" ParentId="1405" CreationDate="2021-05-14T22:36:43.577" Score="1" Body="&lt;p&gt;If you do put your antennas in or between trees, make sure no uninsulated part of the antenna touches the tree, especially when wet.  Because if it does, the tree becomes part of the antenna and will detune it.   (Catching on fire or worrying your tree might get radiation burns is a separate issue.)&lt;/p&gt;&#xA;&lt;p&gt;But even if the tree doesn't detune it, it may absorb some of the energy and attenuate it, especially if the antenna is parallel to parts of the tree, or you are doing vhf or uhf where the leaves absorb even more.&lt;/p&gt;&#xA;&lt;p&gt;I also have my HF antenna hanging from a tree.  But I also use an antenna tuner with a wide band antenna, and the antenna is pretty far out from the trunk.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-05-15T05:27:22.187" LastActivityDate="2021-05-15T05:27:22.187" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18471" PostTypeId="2" ParentId="5498" CreationDate="2021-05-15T02:29:29.603" Score="1" Body="&lt;p&gt;Like others have suggested, radios in the frequency bands stated are not for leisure use. If you're looking for a radio for casual leisure use, you'd want to consider either:&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;The low-power (0.1W) Tokutei Shoudenryoku Musen (Specified Low Powered Radio) (特定小電力無線局) radios, which are ready to use out of the box with no registration, license, or yearly spectrum use fees. These have a range of about 0.3km to 1km).   &lt;strong&gt;OR&lt;/strong&gt;&lt;/li&gt;&#xA;&lt;li&gt;The high-power (~5W, range of about 1km to 5km, and somewhat expensive) digital kan-i registration radios デジタル簡易無線, which are super powerful and don't need a license, &lt;strong&gt;but must be registered in Japan&lt;/strong&gt;. These operate on UHF 351Mhz. Costs about 2,400yen to register one handset for 5 years, plus 450yen per year in spectrum use fees.&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;&lt;p&gt;&lt;strong&gt;There's a super deep-dive here:&lt;/strong&gt; &lt;a href=&quot;https://hokkaidowilds.org/two-way-radios-in-the-hokkaido-backcountry&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hokkaidowilds.org/two-way-radios-in-the-hokkaido-backcountry&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Apologies for the self-promotion, but I've also made a free English-language tool to generate printable Japanese registration docs here: &lt;a href=&quot;https://hokkaidowilds.org/how-to-register-two-way-digital-kan-i-radios-in-japan-in-english&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://hokkaidowilds.org/how-to-register-two-way-digital-kan-i-radios-in-japan-in-english&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;You can also register devices just by filling in the Japanese forms and sending them away. You can get the Japanese forms from each telecommunications bureau jurisdiction's website. E.g., Hokkaido - &lt;a href=&quot;https://www.soumu.go.jp/soutsu/hokkaido/E/cr/dwn10.htm&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.soumu.go.jp/soutsu/hokkaido/E/cr/dwn10.htm&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19704" LastActivityDate="2021-05-15T02:29:29.603" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18472" PostTypeId="1" CreationDate="2021-05-15T03:38:07.197" Score="0" ViewCount="49" Body="&lt;p&gt;Diagnosed three nonfunctional TECSUN PL-660 radios (one from eBay Anon-CO, and two from Amazon) where can I find a service manual to replace the failed circuit board flex cable board assembly part?&#xA;Demonstration video of failed circuit board flex cable board assembly part = youtu.be/4XbAnSX2FHk&lt;/p&gt;&#xA;" OwnerUserId="13597" LastEditorUserId="8717" LastEditDate="2021-05-18T18:08:41.460" LastActivityDate="2021-05-20T11:44:25.993" Title="Where can I find a service manual for the TECSUN PL-660 to replace the failed circuit board flex cable myself?" Tags="&lt;receiver&gt;&lt;equipment-troubleshooting&gt;&lt;repair&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18473" PostTypeId="2" ParentId="16720" CreationDate="2021-05-16T00:04:10.173" Score="2" Body="&lt;p&gt;&lt;em&gt;The green key appears to have the name &amp;quot;Func&amp;quot;, even though I can't find that actually in any manual. You long press the green key, and then can trigger 0-9, and * and #.&lt;/em&gt;&lt;/p&gt;&#xA;&lt;p&gt;On my brand new 878, a long-press of the &lt;strong&gt;Menu&lt;/strong&gt; key acts as the 'Function' button (not sure that's in the manual anywhere, either). The Green key (PF3) is assignable as all the other keys are, but it's not the 'Function' key in my radio.&lt;/p&gt;&#xA;" OwnerUserId="19710" LastActivityDate="2021-05-16T00:04:10.173" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18474" PostTypeId="1" AcceptedAnswerId="18475" CreationDate="2021-05-17T22:33:48.570" Score="4" ViewCount="71" Body="&lt;p&gt;I'm trying to produce a Yagi antenna for the 2.45 GHz band using a 3D dual extruder printer. The idea is to print the antenna elements using a metal filament and encasing it all in plastic.&lt;/p&gt;&#xA;&lt;p&gt;The antenna needs to be highly directional, with 8 elements or more. Will it work?&lt;/p&gt;&#xA;&lt;p&gt;Another option is to print the antenna plastic casing and then insert the metal rods through openings created during the printing process.&lt;/p&gt;&#xA;&lt;p&gt;Any thoughts? Thanks&lt;/p&gt;&#xA;" OwnerUserId="19729" LastEditorUserId="8717" LastEditDate="2021-05-18T18:02:07.607" LastActivityDate="2021-05-19T13:34:04.037" Title="3D Printed yagi antenna" Tags="&lt;antenna&gt;&lt;diy&gt;&lt;yagi&gt;&lt;microwave&gt;" AnswerCount="3" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18475" PostTypeId="2" ParentId="18474" CreationDate="2021-05-18T04:00:50.130" Score="2" Body="&lt;p&gt;Not likely. To the best of my knowledge, any &amp;quot;metal filament&amp;quot; that's printable with a home 3D printer is PLA with 10%-50% of metal powder. This is good enough to make prints that look and feel metallic, but it's &lt;em&gt;not&lt;/em&gt; enough for good electrical conductivity. Most likely it won't work as an antenna at all; definitely it won't have positive gain in any direction.&lt;/p&gt;&#xA;&lt;p&gt;The idea with putting rods into a 3D-printed form is more hopeful. The low-dielectric-loss plastics you would &lt;em&gt;really&lt;/em&gt; want to use for antennas (PTFE or polystyrene) aren't very practical to print with; PLA and ABS are very printable, but electrically they're much worse. But you might be able to get away with it if you take care to decrease the plastic coverage as much as possible.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-05-18T04:00:50.130" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18476" PostTypeId="2" ParentId="18474" CreationDate="2021-05-18T13:23:50.893" Score="1" Body="&lt;p&gt;It's is my understanding, from my days taking the advanced radio license, is that as RF travels along the surface of the driven elements, and that the reflectors and directors should be the same diameter as the driven elements, coupled with the fact, again to my understanding, that the greater the diameter of the elements increases the bandwidth of the antenna from the cut frequency (length) of the driven element.&lt;/p&gt;&#xA;&lt;p&gt;Even if one could print, (practically), a good quality (electrically, see previous answer) it would seem impractical. What I would suggest, and would be very useful is the 3D print a good quality sturdy boom, and element supports, (which I have always found the difficult part in antenna builds). The support structure needs to be very sturdy, UV resistant, and provide for easy attachment of the metal elements, (I have always been a fan of aluminum tubing), you could also print thin element covers with covered ends to keep the bugs out.&lt;/p&gt;&#xA;" OwnerUserId="19535" LastEditorUserId="8717" LastEditDate="2021-05-18T18:34:25.397" LastActivityDate="2021-05-18T18:34:25.397" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18477" PostTypeId="1" CreationDate="2021-05-18T20:24:05.920" Score="0" ViewCount="48" Body="&lt;p&gt;I’m trying to locate the source of some interference on the FM band — it’s audible as 3 quick staccato bursts of brownish noise approximately every 3.5 seconds. It’s more pronounced at the low end of the commercial FM radio band.&lt;/p&gt;&#xA;" OwnerUserId="19741" LastActivityDate="2021-05-18T22:38:36.427" Title="What would cause 3 bursts of FM radio interference every ~3.5 seconds" Tags="&lt;rfi&gt;&lt;fm&gt;" AnswerCount="1" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18478" PostTypeId="2" ParentId="18477" CreationDate="2021-05-18T22:38:36.427" Score="3" Body="&lt;p&gt;Solved! It was the wireless charging pad integrated into the top surface of the device, which thankfully they provided a means to disable.&lt;/p&gt;&#xA;" OwnerUserId="19741" LastActivityDate="2021-05-18T22:38:36.427" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18479" PostTypeId="1" AcceptedAnswerId="18481" CreationDate="2021-05-19T00:47:40.283" Score="2" ViewCount="81" Body="&lt;p&gt;We are building a multi-stage LNA for a TR module we are building in the 144MHz and 440MHz range. This LNA we are considering (&lt;a href=&quot;https://www.qorvo.com/products/d/da007268&quot; rel=&quot;nofollow noreferrer&quot;&gt;Qorvo QPL9547&lt;/a&gt;) provides about 22dB gain in the 2m and about 27dB in the 440MHz according to the Gain vs Frequency graph.&lt;/p&gt;&#xA;&lt;ul&gt;&#xA;&lt;li&gt;How much dB gain do you need to get from an LNA for good low-signal reception for satellite communications in the 2m and 70cm bands?&lt;/li&gt;&#xA;&lt;li&gt;What about for EME?&lt;/li&gt;&#xA;&lt;li&gt;How many LNA stages should I plan for?&lt;/li&gt;&#xA;&lt;/ul&gt;&#xA;" OwnerUserId="16278" LastEditorUserId="8717" LastEditDate="2021-05-20T21:25:37.900" LastActivityDate="2021-05-28T13:28:45.000" Title="How much dB gain do you need from an LNA in front of an antenna for great low-signal reception from satellites in the 2m and 70cm bands?" Tags="&lt;antenna&gt;&lt;vhf&gt;&lt;uhf&gt;&lt;satellites&gt;&lt;lna&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18481" PostTypeId="2" ParentId="18479" CreationDate="2021-05-19T03:22:58.230" Score="4" Body="&lt;p&gt;A LNA amplifies signal and noise. It is of some use only if:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;the noise power from the antenna is higher than the noise floor of your receiver, and&lt;/li&gt;&#xA;&lt;li&gt;the LNA has a lower noise floor.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;Many VHF/UHF receivers already have sufficiently good noise performance that one or both of these things is not true, and so adding an LNA will not improve performance. Typically, an LNA improves performance only after the antenna is very directional, and in a quiet environment. A not-so-directional antenna, or one in any urban or semi-urban environment, will be subject to high RF noise, rendering the first point untrue and thus an LNA of no benefit.&lt;/p&gt;&#xA;&lt;p&gt;Moreover, if an LNA is potentially of some benefit, it's not just because it has high gain, but because it has low noise. The &amp;quot;LN&amp;quot; in &amp;quot;LNA&amp;quot; is for &amp;quot;low noise&amp;quot;, after all. If it was just a question of gain maybe it would be a &amp;quot;HGA&amp;quot;, or &amp;quot;high gain amplifier&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;How much gain is useful, and how low the noise must be depends on several variables. See &lt;a href=&quot;https://ham.stackexchange.com/q/9832/218&quot;&gt;How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?&lt;/a&gt; for details.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-05-19T03:22:58.230" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18482" PostTypeId="2" ParentId="18474" CreationDate="2021-05-19T13:34:04.037" Score="2" Body="&lt;p&gt;Some general hints from my experience:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Use wires not printed metal. You could stop the print for a while to drop in the wires, then finish it, or push them in later. For sanity's sake, design your yagi to use identical directors, and make or buy a wire cutting machine to produce lots of wires of the same length.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;ol start=&quot;2&quot;&gt;&#xA;&lt;li&gt;&lt;p&gt;Plastic will have an effect on tuning - the wires will need to be 10% to 20% shorter than the simulation design, and you will have to experiment to find out how much. Element spacing is not affected much, and what effect there is will be taken up by the length trimming that you do.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Because you need to trim and measure many many times, you will need to print a &amp;quot;tuning model&amp;quot; antenna that can be opened and shut easily. It's nearly impossible to tune an antenna when the parts you need to adjust are sealed inside. Make sure the tuning model is representative of the plastic density of the final model.&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Water is a problem on tuned antennas like yagis, droplets on the elements will detune them. But if you have the elements embedded in slightly porous 3D-printed plastic, then the antenna will be completely useless if it gets wet. Printing a thin boom and letting the elements stick out will reduce the effect, but test it if it matters to you!&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;li&gt;&lt;p&gt;Feed design - for 2.4 GHz, this would usually a small PCB connected to the coax, possibly with the reflector built in.  See &lt;a href=&quot;https://ham.stackexchange.com/a/3594/2988&quot;&gt;this answer&lt;/a&gt; for some PCB design ideas for the feed:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/HdDsb.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/HdDsb.png&quot; alt=&quot;PCB feed&quot; /&gt;&lt;/a&gt;&lt;br /&gt;&#xA;( the elements are a bit truncated )&lt;/p&gt;&#xA;&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;This is an ABS plastic yagi we used to make. Elements were 1.2 mm tinned steel wire. It could be tuned over 1.4 to 2.6 GHz by adjusting the length of the directors. The feed and director were on a credit-card sized PCB at the back. Two identical housing halves were glued together.&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/iFb5I.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/iFb5I.jpg&quot; alt=&quot;YAGI-A0005&quot; /&gt;&lt;/a&gt;&lt;br /&gt;&#xA;Gain was about 12 dBi, I think the plastic cost us 2 or 3 dB in losses, it was quite thick around the elements.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastActivityDate="2021-05-19T13:34:04.037" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18483" PostTypeId="1" CreationDate="2021-05-19T18:59:24.317" Score="3" ViewCount="61" Body="&lt;p&gt;I'm still confused with the purpose of a ground plane purpose in an antenna.&lt;/p&gt;&#xA;&lt;p&gt;My understanding is this. If an antenna is perfectly balanced, there will be no common-mode currents going to ground. If an antenna is unbalanced in any way, there will be common mode currents returning back towards the radio.&lt;/p&gt;&#xA;&lt;p&gt;If the feeder is coaxial cable, does the outer shield carry this return current?&lt;/p&gt;&#xA;&lt;p&gt;If so , we must try and get this return current into the ground and away from us and the equipment?&lt;/p&gt;&#xA;&lt;p&gt;Why do I then read that ground planes or radials are used to reflect this RF away from the ground and not carry it to the ground?&lt;/p&gt;&#xA;&lt;p&gt;Feel free to correct me, and / or criticize any statement I made:) I'm still learning here.&lt;/p&gt;&#xA;" OwnerUserId="19751" LastEditorUserId="4665" LastEditDate="2021-05-19T23:47:12.140" LastActivityDate="2021-05-20T16:56:09.283" Title="Ground plane reflects RF or brings it to ground" Tags="&lt;antenna&gt;&lt;coaxial-cable&gt;&lt;radial&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18484" PostTypeId="1" CreationDate="2021-05-19T19:22:39.643" Score="-3" ViewCount="75" Body="&lt;p&gt;I need to make this project, plase help me with some ideas&lt;/p&gt;&#xA;" OwnerUserId="19752" LastEditorUserId="218" LastEditDate="2021-05-20T20:08:39.467" LastActivityDate="2021-05-20T20:08:39.467" Title="How can I jam cell phone communications with gnu radio and hackrf?" Tags="&lt;gnuradio&gt;&lt;hackrf&gt;" AnswerCount="1" CommentCount="5" ClosedDate="2021-05-20T20:42:39.010" ContentLicense="CC BY-SA 4.0" />
  <row Id="18485" PostTypeId="2" ParentId="18483" CreationDate="2021-05-19T19:54:19.350" Score="0" Body="&lt;p&gt;The actual antenna is always balanced (as there are no magnetic monopoles in nature at any frequency, including RF).  However, the actual antenna may include stuff that most people do not normally include in what they call &amp;quot;the antenna&amp;quot;.  And the balance may or may not have geometric symmetry.&lt;/p&gt;&#xA;&lt;p&gt;This stuff is many, such as, with a handheld HT, ones hand, arm, and body.  Or in a typical HF setup, the feedline, mast, guy wires, radio case, transmitter power feed, ground lines, computer network cables, household wiring, gutters, metal fences, trees, salt water/moisture, and etc.  All of which can end up with accelerated current flow from the transmitted RF field or feed, and thus affect the RF radiation pattern, &lt;strong&gt;even if&lt;/strong&gt; completely disconnected, but still reasonably close to the RF near-field (such as with electrically isolated Yagi-Uda director and reflector elements).&lt;/p&gt;&#xA;&lt;p&gt;In the case of a VHF HT, the operator's body being part of the antenna system may actually be an advantage.  Same with the feedline when operating an end-fed antenna SOTA QRP.  But in the case of HF at higher power levels, touching the case of a transmitter (etc.) connected to an unbalanced feedline located at an SWR peak may cause unpleasant surprises.&lt;/p&gt;&#xA;&lt;p&gt;For safety, an operator might want to minimize these unpleasant surprises in those parts of the antenna that are not called &amp;quot;the antenna&amp;quot;.   For communication efficiency, one might not want those parts of the antenna other than what one calls the antenna to distort the expected radiation pattern and aim it in useless directions, such as directly into the dirt, or sideways from the desired target.&lt;/p&gt;&#xA;&lt;p&gt;Radials, or a solid ground plane, are one mechanism to aid in reflecting the antenna's RF pattern back up out of the dirt, and more into more useful directions.  But even directly into the dirt might be more pleasant (and safe!) than though your body into the dirt.  Thus safety grounds.&lt;/p&gt;&#xA;&lt;p&gt;But sometimes, grounding a portion of the (named) antenna just makes the antenna modeling (completely correct math with mostly bogus assumptions) easier.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-05-20T04:18:42.083" LastActivityDate="2021-05-20T04:18:42.083" CommentCount="8" ContentLicense="CC BY-SA 4.0" />
  <row Id="18486" PostTypeId="2" ParentId="18484" CreationDate="2021-05-19T22:47:57.117" Score="2" Body="&lt;p&gt;Do you mean you want to put your phone and a small SDR in a faraday cage together such that the SDR only receives the phone’s emissions? If so, a metal lunch box should work for everything except the power and data cables. Heavy RF choking of the cables just outside the box entry would take care of common mode current but you may face other RFI issues from the computer-to-SDR connection you’d have to solve. I hope this helps.&lt;/p&gt;&#xA;&lt;p&gt;(Hopefully I won’t get downvotes for a best-guess answer to the question as currently stated.)&lt;/p&gt;&#xA;" OwnerUserId="18693" LastActivityDate="2021-05-19T22:47:57.117" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18489" PostTypeId="2" ParentId="18472" CreationDate="2021-05-20T11:44:25.993" Score="0" Body="&lt;p&gt;Try this link and check if it is what you are searching for:&lt;br /&gt;&#xA;&lt;a href=&quot;https://elektrotanya.com/tecsum_pl-660_schematic.pdf/download.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://elektrotanya.com/tecsum_pl-660_schematic.pdf/download.html&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;Note: Google Safe Browsing deems this site as 'No unsafe content found'.&#xA;&lt;a href=&quot;https://transparencyreport.google.com/safe-browsing/search&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://transparencyreport.google.com/safe-browsing/search&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;More information on repairs:&#xA;TECSUN PL-600 – Electrostatic Discharge Repair&lt;br /&gt;&#xA;&lt;a href=&quot;https://swling.com/blog/tag/tecsun-pl-600-repair/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://swling.com/blog/tag/tecsun-pl-600-repair/&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19589" LastActivityDate="2021-05-20T11:44:25.993" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18490" PostTypeId="2" ParentId="18483" CreationDate="2021-05-20T16:56:09.283" Score="1" Body="&lt;p&gt;I think you're right that common-mode currents will flow if the antenna system isn't balanced.  It's my understanding that common-mode currents will flow on the outside of the shield of coaxial cable.  There are some excellent explanations in answers to the question &amp;quot;&lt;a href=&quot;https://ham.stackexchange.com/questions/9543/can-a-common-mode-current-exist-on-the-inside-of-a-coax-shield&quot;&gt;Can a common-mode current exist on the inside of a coax shield?&lt;/a&gt;&amp;quot;.  We often try to reduce common-mode currents because they make the coax radiate, since the RF caused by the common-mode current isn't opposed by equal-and-opposite RF from an equal-and-opposite current.  Radiating coax often causes problems because it skews the antenna pattern and often leads to RF-in-the-shack problems.  Also, if the feed line is radiating then it is also receiving, so the feed line will pick up more undesirable noise from the other electronics in the house.&lt;/p&gt;&#xA;&lt;p&gt;Your term &amp;quot;return current&amp;quot; seems misleading and unhelpful to me.  Power is delivered to the antenna, which requires current to flow in the feed line to deliver the power.  The transmitter, feed line, and ground connections form a circuit in which all current that flows &amp;quot;from&amp;quot; the transmitter returns &amp;quot;to&amp;quot; the transmitter.  I put quotes around &amp;quot;from&amp;quot; and &amp;quot;to&amp;quot; because the current is alternating, so it would be just as accurate to say that current flows from the antenna to the transmitter.  In this case I think it's better to think in terms of common-mode currents and differential-mode currents.  If you're wondering what those are, Jeff K6JCA wrote up a &lt;a href=&quot;https://k6jca.blogspot.com/2018/07/thoughts-and-notes-common-mode-current.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;nice explanation&lt;/a&gt;.  Both current modes describe currents flowing between the transmitter and the antenna via various paths, but differential-mode currents are equal and opposite through parallel conductors and therefore the emitted radio waves tend to cancel each other out, but common-mode currents aren't equal and opposite and therefore their emitted radio waves don't cancel.&lt;/p&gt;&#xA;&lt;p&gt;You can try to ameliorate RF-in-the-shack problems by connecting the coax shield to a good RF ground so that some of the common-mode current flows to ground.  That was a popular approach to the problem for hams in earlier years.  But that really only works if the RF ground is quite good, such as a field of buried radials (the ground rod at the electrical service entrance is typically a poor RF ground), and the ground connection is a small fraction of a wavelength long.  But connecting the coax shield to a good RF ground still doesn't solve the problem of the radiating feed line.  In practice keeping the antenna system balanced, with the help of a balun as necessary, usually yields better results for the effort.&lt;/p&gt;&#xA;&lt;p&gt;Vertically-polarized radio waves (from vertically-polarized antennas, naturally) interact differently from the ground plane than horizontally-polarized waves.  Vertically-polarized waves are said to reflect off the ground, but horizontally-polarized waves are said not to.  It turns out that this is a simplification; see the question &amp;quot;&lt;a href=&quot;https://ham.stackexchange.com/questions/16859/why-do-horizontally-polarized-rf-waves-reflect-better-off-ground-than-vertically/&quot;&gt;Why do horizontally-polarized RF waves reflect better off ground than vertically-polarized waves?&lt;/a&gt;&amp;quot;.  I think talk about RF current being absorbed by radials on the ground and returned to the antenna is also a simplification.  These simplifications can be helpful, until two different simplifications seem to conflict, which causes confusion.  Your question could be rephrased, &amp;quot;Does the RF from a vertical reflect off the ground plane, or does it induce currents in the ground that are returned to the antenna via the radials?&amp;quot;  I'd say the answer is yes; they are both simplifications that help to describe what happens.&lt;/p&gt;&#xA;&lt;p&gt;The questions you ask are about complicated topics.  It took me years to better my understanding of them, since I learned as a ham in my spare time rather than as an Electrical Engineering student.  Don't be surprised if it takes a while for you to get your head around these ideas also.  This is a good place to learn.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-05-20T16:56:09.283" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18492" PostTypeId="1" CreationDate="2021-05-20T22:45:01.703" Score="1" ViewCount="54" Body="&lt;p&gt;I have multiple Yagi antennas horizontally polarized. They are all placed in closed proximity at the same height horizontally and operating in a similar frequency.&lt;/p&gt;&#xA;&lt;p&gt;The yagis are 2.45GHz, bluetooth band, so they are quite small in size. There is an array of them (PCB antennas) mounted in a radial array of 180. The back of the antennas are very close together, like an 1&amp;quot; apart. The purpose of this design is to be able to gather where a signal is coming from. Is there a way to make them so directional or introducing an element, such as a metal panel that would prevent them from overlapping?&lt;/p&gt;&#xA;&lt;p&gt;The back lobe from the antenna's is overlapping with the from lobe with other antennas. I'm wishing to be able to prevent that.&lt;/p&gt;&#xA;&lt;p&gt;The only idea that does to mind but I don't know if it would work is to place a solid piece of metal, grounded, in between the antennas.&lt;/p&gt;&#xA;&lt;p&gt;Will this work? Are there better ways of creating this antenna to antenna isolation?&lt;/p&gt;&#xA;" OwnerUserId="19729" LastEditorUserId="2988" LastEditDate="2021-05-21T03:02:41.727" LastActivityDate="2021-05-21T03:02:41.727" Title="Yagi antenna isolation from other Yagi antennas" Tags="&lt;antenna&gt;&lt;yagi&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18495" PostTypeId="1" AcceptedAnswerId="18496" CreationDate="2021-05-21T20:10:08.847" Score="2" ViewCount="51" Body="&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/8lOAl.jpg&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/8lOAl.jpg&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;The transmission line is without loss of length λ / 4, the load &lt;span class=&quot;math-container&quot;&gt;$Z_L$&lt;/span&gt; is a short circuit and &lt;span class=&quot;math-container&quot;&gt;$Z_G = Z_0$&lt;/span&gt;.&lt;/p&gt;&#xA;&lt;p&gt;At &lt;span class=&quot;math-container&quot;&gt;$t = 0$&lt;/span&gt;, an incident wave of voltage &lt;span class=&quot;math-container&quot;&gt;$V_1$&lt;/span&gt; and current &lt;span class=&quot;math-container&quot;&gt;$I_1$&lt;/span&gt; such that &lt;span class=&quot;math-container&quot;&gt;$V_1 = Z_0 * I_1$&lt;/span&gt; travel to the load, before &lt;span class=&quot;math-container&quot;&gt;$V_1$&lt;/span&gt; reaches plane B the source &lt;span class=&quot;math-container&quot;&gt;$V_G$&lt;/span&gt; delivers a power &lt;span class=&quot;math-container&quot;&gt;$P_G = V_G^2 / (Z_G + Z_0)$&lt;/span&gt;, then the waves &lt;span class=&quot;math-container&quot;&gt;$V_1$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$I_1$&lt;/span&gt; reach the plane B and are fully reflected, generating reflected waves &lt;span class=&quot;math-container&quot;&gt;$V_2$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$I_2$&lt;/span&gt; such that &lt;span class=&quot;math-container&quot;&gt;$V_2 = Z_0 * I_2$&lt;/span&gt; that travel towards the source &lt;span class=&quot;math-container&quot;&gt;$V_G$&lt;/span&gt;, both form standing waves of total voltage &lt;span class=&quot;math-container&quot;&gt;$V = V_1 + V_2$&lt;/span&gt; and total current &lt;span class=&quot;math-container&quot;&gt;$I = I_1 + I_2$&lt;/span&gt; such that in plane A, &lt;span class=&quot;math-container&quot;&gt;$V / I = Z_{in} = ∞$&lt;/span&gt; then the source sees an open circuit at A and cannot deliver any more energy.&lt;/p&gt;&#xA;&lt;p&gt;If the above is correct, my questions are:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;once the &lt;span class=&quot;math-container&quot;&gt;$V_2$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$I_2$&lt;/span&gt; waves reached the source, what happens to them?&lt;/li&gt;&#xA;&lt;li&gt;If the answer is that they dissipate in &lt;span class=&quot;math-container&quot;&gt;$Z_G$&lt;/span&gt;, where does that energy come from? since the source sees an open circuit (&lt;span class=&quot;math-container&quot;&gt;$Z_{in} = ∞$&lt;/span&gt;) and for this to happen I need &lt;span class=&quot;math-container&quot;&gt;$V_1$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$I_1$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$V_2$&lt;/span&gt;, &lt;span class=&quot;math-container&quot;&gt;$I_2$&lt;/span&gt; at all times.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;" OwnerUserId="19690" LastActivityDate="2021-05-22T01:11:31.333" Title="Apparent Paradox about wave reflection in a transmission line?" Tags="&lt;transmission-line&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18496" PostTypeId="2" ParentId="18495" CreationDate="2021-05-22T00:59:59.500" Score="2" Body="&lt;p&gt;The source resistor will dissipate the vector sum of what can be modeled as the forward and reverse currents.  Thus, for a pure sinusoid in steady state, if the forward and reverse currents are equal in magnitude but 180 degrees out of phase, they will vector sum to zero, which leads to the resistor dissipating zero power.&lt;/p&gt;&#xA;&lt;p&gt;Linear time invariant systems are nice because you can sum things (or even make up non-zero things that sum to zero.)&lt;/p&gt;&#xA;&lt;p&gt;Yet another way to look at it is that, in steady state, the instantaneous generated voltage on the left side of the resistor will equal the instantaneous reflected voltage on the right side, at all times.  Thus with no voltage difference across the resistor, there will be no current through the resistor, thus no power dissipation. (assuming ideal lumped component models, and etc.)&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-05-22T01:11:31.333" LastActivityDate="2021-05-22T01:11:31.333" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18498" PostTypeId="1" CreationDate="2021-05-23T00:57:32.420" Score="0" ViewCount="24" Body="&lt;p&gt;Got the firmware updated.&lt;/p&gt;&#xA;&lt;p&gt;Got the Driver updated.&lt;/p&gt;&#xA;&lt;p&gt;Got the software updated.&lt;/p&gt;&#xA;&lt;p&gt;Went through instructions several times.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/N1uLW.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/N1uLW.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="15859" LastEditorUserId="4665" LastEditDate="2021-05-24T19:31:48.433" LastActivityDate="2021-05-24T19:31:48.433" Title="I'm trying to configure HRD for IC7300 but cannot connect / detect frequency" Tags="&lt;software&gt;&lt;icom&gt;&lt;computer-control&gt;" AnswerCount="0" CommentCount="4" ContentLicense="CC BY-SA 4.0" />
  <row Id="18500" PostTypeId="2" ParentId="12925" CreationDate="2021-05-23T18:41:50.353" Score="1" Body="&lt;p&gt;Receivers for listening to Jupiter signals must have the AGC control turned to OFF. Also, the optimal frequency for reception should be in the vicinity of 20.1 Mhz.&lt;/p&gt;&#xA;&lt;p&gt;The antenna should be a dipole, built to a wavelength of approx. 15 meters, oriented East-West (Northern Hemisphere).&lt;/p&gt;&#xA;&lt;p&gt;Also, please take into account the following:&#xA;&amp;quot;When the sun is active, as it is near solar maximum, the earth’s ionosphere is heavily ionized during daylight hours (due to solar UV and X-ray emissions). The ionosphere is then opaque to Jovian signals from shortly after sunrise to a few hours after sunset.&amp;quot;&lt;/p&gt;&#xA;&lt;p&gt;Bibliography:&#xA;&lt;a href=&quot;https://radiojove.gsfc.nasa.gov/&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://radiojove.gsfc.nasa.gov/&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://radiojove.gsfc.nasa.gov/telescope/Single_Dipole_suppl_man_rev_1-1.doc&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://radiojove.gsfc.nasa.gov/telescope/Single_Dipole_suppl_man_rev_1-1.doc&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19589" LastEditorUserId="19589" LastEditDate="2021-05-23T19:33:29.713" LastActivityDate="2021-05-23T19:33:29.713" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18502" PostTypeId="1" CreationDate="2021-05-24T20:04:41.777" Score="1" ViewCount="22" Body="&lt;p&gt;The emission of EM radiation is based on an induction process in which a periodic electrical voltage creates a magnetic field that is offset by 90° in time and space, also known as the starting near field of the radiation.&lt;/p&gt;&#xA;&lt;p&gt;If the receiving antenna rod is aligned in the same way as the transmitting antenna, the incoming EM radiation again becomes an oscillating voltage. What is the temporal phase of the magnetic field in relation to the electric field? Of course, the question could also have been asked for a magnetic antenna, where the incoming magnetic field component of the radiation triggers the induction process in the receiving antenna.&lt;/p&gt;&#xA;" OwnerUserId="13834" LastActivityDate="2021-05-24T20:04:41.777" Title="How does the inductive reversal process of the emission of EM radiation at the receiving antenna work?" Tags="&lt;radiation&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18503" PostTypeId="1" CreationDate="2021-05-25T02:15:36.977" Score="0" ViewCount="41" Body="&lt;p&gt;To my comprehension a BALUN/UNUN is an RF Transformer. If this is correct and since a BALUN/UNUN is part of the antenna system ... how much power does one expect to lose there?&lt;/p&gt;&#xA;&lt;p&gt;Specifically, how much sense does it make to compromise ERP in lieu of band choice when a rig is capable of perhaps 15W at best?&lt;/p&gt;&#xA;" OwnerUserId="5" LastActivityDate="2021-05-25T17:45:04.490" Title="At near-QRP levels should I include a balun/unun in the antenna system?" Tags="&lt;antenna&gt;&lt;balun&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18504" PostTypeId="2" ParentId="18503" CreationDate="2021-05-25T13:23:22.550" Score="2" Body="&lt;p&gt;A balun is any device for converting between balanced and unbalanced systems. Not all of them are transformers.&lt;/p&gt;&#xA;&lt;p&gt;Losses depend on the kind of balun. On HF, it's common to use a common-mode choke as a balun. Losses on this type of balun are quite low: just the additional loss of the transmission line wound around the ferrite. It will depend on your transmission line and frequency, but this is likely less than 0.1 dB. If you want a more specific number, the spec sheet for your feedline will have a loss specification.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-05-25T13:23:22.550" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18505" PostTypeId="2" ParentId="18503" CreationDate="2021-05-25T14:08:32.663" Score="0" Body="&lt;p&gt;It depends.  A choke and/or transformer between the feedline and the antenna changes the ratio of currents flowing on each, and thus where the EM radiation and thermal losses occurs.  In some situations (SOTA QRP with a poor ground, short low antenna, low shock hazzards), additional EM radiation caused by unbalanced currents over a longer feedline might add up to send a better signal towards some destination. But with a better antenna (in terms of radiation resistance and directional gain) or a more lossy feedline, less likely so.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-05-25T17:45:04.490" LastActivityDate="2021-05-25T17:45:04.490" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18506" PostTypeId="1" CreationDate="2021-05-25T17:44:24.020" Score="3" ViewCount="99" Body="&lt;p&gt;Since all antennas require a ground, reference or otherwise, there are two poles for their operation. For a mag mount, the car body is the reference ground.  A vertical cannot operate without a ground or reference ground.  In reality, a vertical &amp;quot;monopole&amp;quot; uses capacitive coupling when it is mounted on an insulator.  Monopoles use the &amp;quot;mirror image&amp;quot; provided by the ground to operate.  As a clarification, imagine a satellite's antenna.  The case, or housing becomes the ground, again a &amp;quot;reference&amp;quot; ground.  In cases where the case is not used, the RF-negative portion of a circuit board becomes the reference.  Since two things are necessary to radiate a signal, doesn't that make a dipole?&lt;/p&gt;&#xA;" OwnerUserId="8496" LastEditorUserId="4665" LastEditDate="2021-05-25T18:07:32.800" LastActivityDate="2021-05-30T01:29:35.503" Title="Aren't all antennas technically dipoles?" Tags="&lt;antenna-theory&gt;" AnswerCount="4" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18507" PostTypeId="2" ParentId="18506" CreationDate="2021-05-25T19:46:40.327" Score="-2" Body="&lt;p&gt;This depends on your definition of &amp;quot;dipole&amp;quot;, as in actual use (which may or may not conform to anyone's particular dictionary of terms) the meaning of the term is varied.&lt;/p&gt;&#xA;&lt;p&gt;The EM field generated by an antenna depends on accelerating charge.  And conservation of charge always requires that for charge to accelerate to some physical part of the antenna, it has to come from some other part, and vice versa.  You can call those two parts the two poles of a dipole.  Or maybe you don't like calling it a dipole if the feed point isn't anywhere near the center, or if the majority of the charge doesn't travel in anything like a straight line to a single point.  In some cases, one &amp;quot;pole&amp;quot; might be too defuse to recognize as a pole (for instance, an entire planet, as in Earth ground, or other vast astronomic object, such as solar plasma toroidal currents which may or may not have any poles, and may or may not radiate any EM, as in solar storms, etc.)&lt;/p&gt;&#xA;&lt;p&gt;A magnetic loop antenna, magnetically fed (no electrical feedpoint or blocking series capacitor) might not be a dipole.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-05-25T20:05:33.220" LastActivityDate="2021-05-25T20:05:33.220" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18508" PostTypeId="2" ParentId="18506" CreationDate="2021-05-25T20:57:05.047" Score="3" Body="&lt;p&gt;No.&lt;/p&gt;&#xA;&lt;p&gt;A dipole antenna is so named because the electric field around it is an &lt;a href=&quot;https://en.wikipedia.org/wiki/Electric_dipole_moment&quot; rel=&quot;nofollow noreferrer&quot;&gt;electric dipole&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/D6ncI.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/D6ncI.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;&lt;p&gt;&lt;i&gt;Derived from work by Geek3, &lt;a href=&quot;https://creativecommons.org/licenses/by-sa/4.0&quot; rel=&quot;nofollow noreferrer&quot;&gt;CC BY-SA 4.0&lt;/a&gt;, via &lt;a href=&quot;https://commons.wikimedia.org/wiki/File:VFPt_dipoles_electric.svg&quot; rel=&quot;nofollow noreferrer&quot;&gt;Wikimedia Commons&lt;/a&gt;&lt;/i&gt;&lt;/p&gt;&#xA;&lt;p&gt;This is intuitively obvious: a dipole consists of two wires. At any instant, one has a positive potential and the other has a negative potential, except for the instant where the polarity flips and the potential is zero everywhere.&lt;/p&gt;&#xA;&lt;p&gt;You will notice that at all points equidistant from the two poles form a plane. The potential at this plane is zero. This is true because these points are balanced between the positive and negative potentials of each pole of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;A monopole antenna has just one wire, and a ground plane. The ground plane is both physically a conductive plane (or something made to approximate it, like radials), and the imaginary plane just described which is all the points that would be equidistant between the two poles a monopole would have if you considered it to have a &lt;a href=&quot;https://en.wikipedia.org/wiki/Image_antenna&quot; rel=&quot;nofollow noreferrer&quot;&gt;imaged second pole&lt;/a&gt;.&lt;/p&gt;&#xA;&lt;p&gt;So while a monopole does have two parts, one of them is not a pole. It's ground: not because it's in the dirt, and not because it's connected to the coax shield (although either of these things may be true), but because &lt;a href=&quot;https://electronics.stackexchange.com/a/73386/17608&quot;&gt;its potential is zero&lt;/a&gt;.&lt;/p&gt;&#xA;" OwnerUserId="218" LastActivityDate="2021-05-25T20:57:05.047" CommentCount="5" ContentLicense="CC BY-SA 4.0" />
  <row Id="18509" PostTypeId="2" ParentId="15035" CreationDate="2021-05-25T22:10:15.190" Score="0" Body="&lt;p&gt;I've been able to make mentioned SSTV decoder work on my older iMac with High Sierra (together with RTL-SDR USB dongle, FM decoded using CubicSDR and audio routed using Audio Hijack).&lt;/p&gt;&#xA;&lt;p&gt;MultiScan 3B unfortunately fails to aquire any Audio Inputs/Outputs on my Big Sur box (showing only Item 1, Item 2, Item 3 which seems like Interface Builder placeholders that were by developer expected to be refreshed before user clicks those, but nothing happens on Big Sur). Code is unfortunately not open-sourced so only author can help.&lt;/p&gt;&#xA;" OwnerUserId="19802" LastActivityDate="2021-05-25T22:10:15.190" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18510" PostTypeId="2" ParentId="18506" CreationDate="2021-05-26T21:22:41.553" Score="3" Body="&lt;p&gt;No.&lt;/p&gt;&#xA;&lt;p&gt;Aside from magnetic loop antennas, which are kind of the dual to dipoles (remember how a current in a conductor like a dipole causes a magnetic field? It makes no difference whether you hang a dipole into the electric field of an EM wave, or a coil into the magnetic field of the same EM wave.), there's many other types of antennas:&lt;/p&gt;&#xA;&lt;p&gt;Horn antennas, bowtie antennas, slot antennas, E-field lenses at the end of waveguides, …&lt;/p&gt;&#xA;&lt;p&gt;Your assumption that you always need to have a second electric branch simply doesn't hold.&lt;/p&gt;&#xA;" OwnerUserId="4076" LastActivityDate="2021-05-26T21:22:41.553" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18512" PostTypeId="1" CreationDate="2021-05-27T09:37:25.117" Score="4" ViewCount="82" Body="&lt;p&gt;As part of my 20m transceiver build I'm looking for a relay to by-pass an RF amplifier in the front-end board.  So, to be clear, that's after the 20m broad bandpass filter and before the RF mixer (it's a single-conversion superhet design).&lt;/p&gt;&#xA;&lt;p&gt;Being the enterprising individual I am, I would normally scavenge for relays from old scraped radio gear.  But, on this occasion I feel the need to invest in a few newly purchased relays to have on-hand.  Specialized RF relays can be quite expensive, so I'm wondering if there are specifications to watch out for to help choose a relay from the general herd.&lt;/p&gt;&#xA;&lt;p&gt;In my case, the coil voltage and contact voltage will be low, say 5 or 6 volts for the coil and a tiny voltage on the contacts.  The required current handling capability will also be low.  So, these parameters are a given.&lt;/p&gt;&#xA;&lt;p&gt;However, beyond that I'm wondering what I should be watching out for? For example, my local parts supplier has a class of relays called &amp;quot;Signal Relays&amp;quot;, which I assume are aimed primarily at the telco market.  Here's one I pulled at random (sort of): &lt;a href=&quot;https://www.farnell.com/datasheets/1683386.pdf&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.farnell.com/datasheets/1683386.pdf&lt;/a&gt;.  Are there any aspects or specifications of this particular relay that would make it a bad candidate for HF RF applications?  Regards!&lt;/p&gt;&#xA;" OwnerUserId="11875" LastEditorUserId="76" LastEditDate="2021-05-27T14:33:44.847" LastActivityDate="2021-05-27T18:25:00.517" Title="Choosing a Relay for HF Applications" Tags="&lt;hf&gt;&lt;electronics&gt;&lt;equipment-design&gt;&lt;relay&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18513" PostTypeId="1" AcceptedAnswerId="18518" CreationDate="2021-05-27T14:49:31.440" Score="1" ViewCount="78" Body="&lt;p&gt;I am working on a system whereby a smartphone may receive signals simultaneously from different sources.&#xA;As we know, the fading and pathloss will make the transmitters send their traffic with different modulation schemes. I have also done some research on the transmission and reception for a smartphone and understand that a smartphone with single antenna can transmit and receive at the same time.&lt;/p&gt;&#xA;&lt;p&gt;However, there is few materials mentions that if a smartphone can demodulate two signals modulated with different MCS simultaneously. The only paper I found(&lt;a href=&quot;https://www.researchgate.net/publication/322615927_Reconfigurable_Modulation_Scheme_for_Communication_System&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://www.researchgate.net/publication/322615927_Reconfigurable_Modulation_Scheme_for_Communication_System&lt;/a&gt;) was published in 2018. It states that they are proposing a communication system that can use different modulation/demodulation schemes at a given point of time, but it also mentions that the &amp;quot;current system&amp;quot; can only use one scheme at a time.&lt;/p&gt;&#xA;&lt;p&gt;My questions:&#xA;Can a smartphone support different modulation/demodulation schemes with single receiver antenna at a time now? Or if multiple antennas are required to achieve this?&lt;/p&gt;&#xA;&lt;p&gt;Thank you.&lt;/p&gt;&#xA;" OwnerUserId="19825" LastActivityDate="2021-05-29T18:56:32.500" Title="Can a smartphone with single antenna receive signals modulated by different schemes" Tags="&lt;antenna&gt;&lt;receiver&gt;&lt;mobile&gt;" AnswerCount="2" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18514" PostTypeId="2" ParentId="18512" CreationDate="2021-05-27T15:47:12.440" Score="3" Body="&lt;p&gt;Antenna tuners use fairly standard 250 V relays, so this would be a good place to start.&lt;/p&gt;&#xA;&lt;p&gt;The SGC-230 is an example I know. &lt;a href=&quot;https://oddballhfssbradio.groups.io/g/AntennaTuners/topic/sgc_sg_230_fixed_one_issue/77273709?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,77273709&quot; rel=&quot;nofollow noreferrer&quot;&gt;This post&lt;/a&gt; has some nice photos of its relays. Smaller tuners use little black relays, if you scratch around for photos you might be able to read the specifications printed on the relays.&lt;/p&gt;&#xA;&lt;p&gt;The SGC-235 is a claimed 400 watt tuner. If I recall correctly, in its output section, they used four relays in series for each switching element, to increase the breakdown voltage.&lt;/p&gt;&#xA;&lt;p&gt;In a transceiver you have the advantage that the line is mostly well matched so the voltages are much lower than in a tuner. 20 watts in 50 ohms at 2:1 SWR is a peak voltage of about 60 V, or an RMS current of 0.9 A, so any mains rated relay should be able to handle that, and possibly small automotive relays too. You could always experiment to confirm that the breakdown voltage is high enough.&lt;/p&gt;&#xA;&lt;p&gt;You may find a small reed relay that meets your needs. &lt;a href=&quot;https://www.digikey.ca/en/products/detail/standex-meder-electronics/DIP05-1A72-11L/2171028&quot; rel=&quot;nofollow noreferrer&quot;&gt;Here's an example&lt;/a&gt; at Digikey:&lt;br /&gt;&#xA;&lt;a href=&quot;https://i.stack.imgur.com/aWljM.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/aWljM.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;br /&gt;&#xA;It has 1 Amp contacts, 200 volts, and the coil takes 10 mA at 5 V! I see they recommend 10 watts total power, so you might need a larger one.&#xA;If it matters to you, a reed relay should have less capacitance to ground, and definitely less series inductance than a regular relay, because of its geometry. It is SPST so you need two of them to switch T/R etc.&lt;/p&gt;&#xA;&lt;p&gt;It will always be important not to switch the relay while the high power RF is turned on, but you can take care of that in software.&lt;/p&gt;&#xA;" OwnerUserId="2988" LastEditorUserId="2988" LastEditDate="2021-05-27T18:25:00.517" LastActivityDate="2021-05-27T18:25:00.517" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18515" PostTypeId="2" ParentId="18513" CreationDate="2021-05-27T19:04:05.920" Score="0" Body="&lt;p&gt;Modern mobile phones already receive many signals simultaneously: phone calls and notifications from the mobile phone towers (several bands), Wi-Fi (several bands), GPS, NFC, Qi, etc.  Typically each use will use a different modulation scheme, and each will use its own band or bands.  Phones typically have several different antennas to work on different frequency bands.&lt;/p&gt;&#xA;&lt;p&gt;If you are asking if a phone can demodulate multiple signals with different modulation schemes on the same frequency or channel, then I would say yes, such a thing can be done theoretically.  In practice, multiple signals using different modulation schemes are not used on the same channel for commercial purposes because it's inefficient; to one modulation scheme the other schemes are noise, which limit the distance the signals travel and reduce the bandwidth.  (CDMA allows many phone signals to share the same channel simultaneously, but the signals all use the same modulation scheme and the power of each signal must be rapidly and continuously controlled by the mobile tower.)  In practice it is more efficient to put each modulation scheme on its own band or bands.  Each mobile phone company has the exclusive license to the channels it uses for phone calls in a particular location, in order to reduce inefficient competition to use the same channel.&lt;/p&gt;&#xA;&lt;p&gt;It would be theoretically possible to design two or more modulation schemes that could coexist on the same channel, but it would require a great deal of work for very little benefit, so in practice this is seldom done for commercial purposes.  (The military regularly uses modulation schemes that are designed to work when competing signals are on the same frequency.)&lt;/p&gt;&#xA;&lt;p&gt;Two narrow-banded modulation schemes could be used on different channels on the same band.  That has been done since vacuum tubes (valves) were created in the early days of radio.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastActivityDate="2021-05-27T19:04:05.920" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18516" PostTypeId="1" CreationDate="2021-05-28T01:33:45.230" Score="1" ViewCount="53" Body="&lt;p&gt;I have read everything I can find about monopole (vertical antenna) radials, and also watched many YouTube videos that touch on the topic. I see conflicting information about what they do, where a particular article or video tends to fall into one of two camps:&lt;/p&gt;&#xA;&lt;ol&gt;&#xA;&lt;li&gt;Radials are used to increase the conductivity of the ground surrounding a vertical antenna, to aid in returning current efficiently to the transmitter.&lt;/li&gt;&#xA;&lt;li&gt;Radials create a mirror-like reflection around the vertical antenna, which reflects radio waves that hit the ground off at an angle that simulates an &amp;quot;image antenna&amp;quot; beneath the surface, as though it were a vertical dipole instead of a monopole.&lt;/li&gt;&#xA;&lt;/ol&gt;&#xA;&lt;p&gt;I can't find any resources that brings these 2 things together, so I'm left confused about how radials work from a physics standpoint.&lt;/p&gt;&#xA;&lt;p&gt;How do radials work?&lt;/p&gt;&#xA;&lt;p&gt;P.S. explanation #1 further confuses me because I'd expect that we don't want to &amp;quot;capture&amp;quot; the energy from the radiated signal and return it to the transmitter, since we want it to radiate! So if #1 turns out to be the true purpose of radials, I'd love to have that clarified as well.&lt;/p&gt;&#xA;&lt;p&gt;Thank you!&lt;/p&gt;&#xA;&lt;p&gt;EDIT: Anyone else who has this question, here's the best video I found that really gave me an &amp;quot;a hah&amp;quot; moment as to what's happening with the ground around a vertical antenna and why radials help (I recommend entire video, but I started it at the most relevant part):&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://youtu.be/XMxaYj7Xs5k?t=1169&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://youtu.be/XMxaYj7Xs5k?t=1169&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="19476" LastEditorUserId="19476" LastEditDate="2021-05-29T00:26:16.297" LastActivityDate="2021-05-29T00:26:16.297" Title="What do radials really do for a vertical antenna?" Tags="&lt;antenna&gt;&lt;vertical-antenna&gt;&lt;radial&gt;&lt;physics&gt;" AnswerCount="2" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18517" PostTypeId="1" CreationDate="2021-05-28T01:57:50.563" Score="0" ViewCount="27" Body="&lt;p&gt;A Ham buddy of mine and I were trying to setup a UHF repeater in our area due to a lack of them. We had two Motorola CDMs, one a 1250 and one a 1550, and we purchased a $200 or so &lt;strong&gt;reject only&lt;/strong&gt; duplexer to use from a seller on eBay. When we received the duplexer, we hooked it up and the TX radio severely overpowered the RX and therefore the repeater was useless. We reached out to a local radio shop who found out the duplexer tuning was off due to vibration of shipping and he retuned it for us. The issue was still there and wasn't resolved. RX was perfectly fine until the TX radio keyed up and the repeater went dead on the receiving end out in the coverage area. The TX CDM was transmitting between 30-50 watts. If we were to reduce the output power to say 10-15, would it improve anything? Even then, is the output power even the issue? I know many repeaters in my area that are 45-50 watts that are similar setups that have no issue yet ours gives us problems. Did we just flat out purchase the wrong duplexer (as ours is reject only) and we should explore other options?&lt;/p&gt;&#xA;" OwnerUserId="19831" LastActivityDate="2021-05-28T23:37:17.677" Title="Is power output or something else to blame for my duplexer failing?" Tags="&lt;diy&gt;&lt;uhf&gt;&lt;rf-power&gt;&lt;repeater&gt;&lt;duplexer&gt;" AnswerCount="1" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18518" PostTypeId="2" ParentId="18513" CreationDate="2021-05-28T11:39:40.513" Score="1" Body="&lt;p&gt;The antenna has nothing to do with the modulation scheme.&lt;/p&gt;&#xA;&lt;p&gt;The selection of antenna affects frequency and polarization.  It may be tricky or very difficult to receive and transmit on the same antenna at the same time.  Even with two antennas that are adjacent, this may be an issue, although careful placement, orthogonal polarizations, and good filter circuits would help.&lt;/p&gt;&#xA;&lt;p&gt;Having said that, it is possible to have a wide band antenna that gets a wide range of frequencies, and antennas typically work at third harmonics of their base frequency, so it is trivial to work in multiple harmonic bands.  Both of these involve compromises in directivity and sensitivity, but that may not be a big obstacle.&lt;/p&gt;&#xA;&lt;p&gt;So other than that, I see no problem with dealing with multiple modulations on the same antenna.  This is an issue for the demodulation portion of the phone, not the antenna.  And most phones these days use SDR internally, so this becomes a software problem.&lt;/p&gt;&#xA;&lt;p&gt;You aren't going to find many mentions of multiple modulations on the same antenna in technical literature, because it's not special.  Where you will find mentions of this is in the data sheets for amateur radios, where supporting multiple modulations is common and ubiquitous, even before SDR made it trivial.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastEditorUserId="10489" LastEditDate="2021-05-29T18:56:32.500" LastActivityDate="2021-05-29T18:56:32.500" CommentCount="6" ContentLicense="CC BY-SA 4.0" />
  <row Id="18519" PostTypeId="2" ParentId="18479" CreationDate="2021-05-28T13:28:45.000" Score="1" Body="&lt;p&gt;An earlier Answer mentioned LNAs would be “of some use only if ... the noise power from the antenna is higher than the noise floor of your receiver” (quote). That statement appears in need of some clarification. If the receiver, on its own, has a high noise figure, or is preceded by a (long) lossy feedline (which contributes/adds to the system noise figure) then it is useful to place an LNA close to the antenna feed point, to reduce the receive-chain’s (own) system noise figure. (This is common practice in satellite comms/broadcasting with LNA (and converter) inside the feed of TV parabolic dish antennas at home.) About high noise power intercepted by the antenna, an LNA cannot do anything, except amplifying this noise in the same way as it amplifies the intended signal intercepted by the antenna.&lt;/p&gt;&#xA;&lt;p&gt;A second LNA behind the first LNA does usually not significantly improve the system noise figure and consequently also not the (S/N) ratio. However, additional amplification might still be essential in low-signal environment to realize the system gain necessary to reach the absolute signal level (power in dBm, or rms voltage in μV) which satisfies the absolute input signal level required by the (given) receiver. For such second amplifier its own noise figure is usually not critical for the system noise figure.&lt;/p&gt;&#xA;&lt;p&gt;Other parameters like signal bandwidth; power level of the signal from the antenna; relative receiver sensitivity (S/N); etc., are important parameters in a typical RF receiver cascade system trade-off, which is a perfect application for spreadsheet tools of which numerous are freely available.&lt;/p&gt;&#xA;&lt;p&gt;The MS Excel macro-enabled tool “Cascade” shown below, can be downloaded &lt;a href=&quot;https://www.rfclb.space/downloads/Cascade_R2_1.xlsm&quot; rel=&quot;nofollow noreferrer&quot;&gt;here&lt;/a&gt;. It includes comments to make the tool easy-to-use and self-explanatory; it is useful especially also for ham radio applications. The tool has been validated and is maintained regularly. User feedback and comments are welcome to further develop the tool.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/xIQyy.gif&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/xIQyy.gif&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18763" LastActivityDate="2021-05-28T13:28:45.000" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18520" PostTypeId="2" ParentId="18517" CreationDate="2021-05-28T23:06:17.293" Score="1" Body="&lt;p&gt;In the absence of test equipment there is no way to know for certain what went wrong, or what to do about it.  The duplexer sounds like the most likely culprit, but the problem could be something else, like inadequate shielding in the receiver.&lt;/p&gt;&#xA;&lt;p&gt;If you ask around, maybe someone in your area has the necessary test equipment and wouldn't mind helping.&lt;/p&gt;&#xA;" OwnerUserId="4665" LastEditorUserId="4665" LastEditDate="2021-05-28T23:37:17.677" LastActivityDate="2021-05-28T23:37:17.677" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18521" PostTypeId="2" ParentId="18516" CreationDate="2021-05-28T23:12:59.163" Score="1" Body="&lt;p&gt;Radials do both, but reflect is the wrong word and the reasoning behind increasing conductivity misses the point.&lt;/p&gt;&#xA;&lt;p&gt;A monopole vertical antenna is really still a dipole, except that the vertical portion of the antenna is only half of the dipole.  The other half of the dipole must exist for the antenna to work correctly, but it can take many forms.&lt;/p&gt;&#xA;&lt;p&gt;If the ground has a high conductivity, then the ground (as in dirt under the antenna) itself can act as the other half.  (Water, especially salt water, would work better than dirt.)  But even if the ground is high conductivity, it likely is not as high as metal wires, so placing ground radials around the base of the antenna will be more efficient, as there will be less loss resistance.  Some efficiency is also lost if those radials are buried, but this may be small enough to not care.  Also, the ground radials do not have to be horizontal -- in fact, they work better if they are at an angle below the vertical element.  (This gives the antenna a more ideal radiation pattern.)&lt;/p&gt;&#xA;&lt;p&gt;Typically, ground radials are attached to and part of the antenna.  Antennas are typically fed with two wires (either parallel as in ladder line, or concentric, as in coax).  One wire goes to the antenna vertical element, the other wire goes to the ground radials.&lt;/p&gt;&#xA;&lt;p&gt;However, it is also possible to capacitively couple the ground to the antenna -- and this is how mag mount monopoles work, with the car body (or other large metal surface under the antenna) acting as part of the antenna.&lt;/p&gt;&#xA;&lt;p&gt;Don't think of it as the antenna reflecting off the ground -- this is wrong.   The ground is actually &lt;em&gt;part&lt;/em&gt; of the antenna, and it radiates with the other half of the antenna.   The shape of the ground also affects the shape of the radiation moving away from the antenna.  So if your ground radials are not symmetrical, or the magmount antenna is not in the center of the car roof, it will skew the radiation pattern towards the directions where there is more metal.&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2021-05-28T23:12:59.163" CommentCount="3" ContentLicense="CC BY-SA 4.0" />
  <row Id="18522" PostTypeId="2" ParentId="18516" CreationDate="2021-05-28T23:47:33.307" Score="0" Body="&lt;p&gt;Both #1 and #2 are the same.&lt;/p&gt;&#xA;&lt;p&gt;Accelerating currents are what sum up to create an EM field.  And the law of conservation of charge requires that the currents be balanced.  If you have a quarter wave vertical over a vast and solid highly conductive ground plane, then whatever current you accelerate up the vertical from the feed point will be balanced by an equal amount of current on the ground plane accelerating towards the feed point from all directions (360 degrees, due to symmetry).&lt;/p&gt;&#xA;&lt;p&gt;In the far field, the EM field generated from all those ground plane currents coming from all directions towards the feedpoint will just happen to sum up (integrate in calculus) to create exactly the same EM field as if there were a mirror image of the vertical below the ground plane, creating a virtual dipole.  However, this mirror is an “as if”, the real currents will be on the ground plane, not some imaginary reflection that would (if it existed) just happen to produce the same EM result in the far field.&lt;/p&gt;&#xA;&lt;p&gt;If you don’t use a vast number of radials over dirt, then the return currents end up coming to the feed point from, not on a conductive plane, but a through a vast resistive blob of dirt (the other half of the dipole fading out gradually to being some fraction of the entire planet) near to the antenna ground and/or transmitter ground.  Resistive blobs convert some of the energy from any return currents into heat (warming up the planet by a near infinitesimal amount), thus leaving less energy to radiate as the EM field.  Or if you are (un)lucky, some fraction of return current EM will radiate from the feedline.  Thus radials (or a solid metal ground under a mobile roof mount vertical, etc.) are desirable if you want to maximize efficiency of radiating an RF field.&lt;/p&gt;&#xA;" OwnerUserId="556" LastEditorUserId="556" LastEditDate="2021-05-29T00:10:56.277" LastActivityDate="2021-05-29T00:10:56.277" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18523" PostTypeId="1" AcceptedAnswerId="18524" CreationDate="2021-05-29T02:23:01.270" Score="0" ViewCount="17" Body="&lt;p&gt;Good day! I ask for help with repairing the hackrf one amplifier. Doesn't work at all. Accepts signals without amplifier, and LNA and VGA adjustment in SDR sharp works too!&#xA;But when I put a tick on &amp;quot;Amp&amp;quot;, then all signals disappear.&#xA;As I understand it, I punched through the static through the antenna input.&#xA;This is not a program error for sure, since I checked it both on the phone and using a portapack. Everywhere the result is the same - I turn on the amplifier - the signal disappears.&#xA;At the same time, I tried to transmit signals. Everything works for the transfer.&#xA;I ask for help in identifying the faulty part. I want to renovate.&#xA;After reading this article &lt;a href=&quot;https://pc7x.net/archive/mirrors/hackrf-repair/articles/repairing-the-hackrf/index.html&quot; rel=&quot;nofollow noreferrer&quot;&gt;https://pc7x.net/archive/mirrors/hackrf-repair/articles/repairing-the-hackrf/index.html&lt;/a&gt;, I realized that most likely my LNA chip (U25 in the diagram) burned out. But after all, the LNA gain control works for me. How so? This article also describes that switches U14 and U12 can be broken.&#xA;Tell me how to determine what is broken, please.&lt;a href=&quot;https://i.stack.imgur.com/QJj8R.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/QJj8R.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18124" LastActivityDate="2021-05-29T05:38:23.440" Title="The amplifier does not work for hack rf one" Tags="&lt;amplifier&gt;&lt;hackrf&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18524" PostTypeId="2" ParentId="18523" CreationDate="2021-05-29T05:38:23.440" Score="1" Body="&lt;p&gt;There are &lt;em&gt;three&lt;/em&gt; receive gain stages in the HackRF one. Two of them are on the MAX2837 chip (the ones controlled by &amp;quot;LNA gain&amp;quot; and &amp;quot;VGA gain&amp;quot;), and the third is the MGA81563 preamp, which is either on (+14dB) or off (+0dB), and controlled by the &amp;quot;amp&amp;quot; toggle. You have indeed blown the MGA81563. I did the same thing to one of mine several years back and it behaved exactly the way you described.&lt;/p&gt;&#xA;" OwnerUserId="8016" LastActivityDate="2021-05-29T05:38:23.440" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18525" PostTypeId="1" CreationDate="2021-05-29T13:11:21.117" Score="0" ViewCount="27" Body="&lt;p&gt;Wikipedia says &amp;quot;SWR is defined as the ratio of the partial standing wave's amplitude at an antinode (maximum) to the amplitude at a node (minimum) along the line&amp;quot;.&lt;/p&gt;&#xA;&lt;p&gt;Standing wave voltage nodes and anti-nodes appear at points which are odd and even multiples of 1/4 wave length back from the junction of a transmission line and an antenna if there is a mismatch, and everyone knows that when there are standing waves the impedance along a transmission line changes depending on the distance from the load.&lt;/p&gt;&#xA;&lt;p&gt;Knowing that SWR is totally dependent on the ratio of the impedance of the transmission line to load, does this mean an SWR meter must be placed at a voltage node or anti-node to get an accurate reading ? Or is the SWR constant everywhere along the transmission line ?&lt;/p&gt;&#xA;&lt;p&gt;When i move my SWR meter along a coaxial transmission line the reading changes depending on where along the line the SWR meter is, why is this ? I checked and there is no RF current flowing on the outside of the coax so that's not the reason.&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2021-05-29T13:25:24.947" LastActivityDate="2021-05-29T19:56:26.230" Title="Does SWR change along the length of a transmission line?" Tags="&lt;transmission-line&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18526" PostTypeId="1" CreationDate="2021-05-29T13:34:57.887" Score="0" ViewCount="8" Body="&lt;p&gt;For a resonant half wave dipole, the voltage and current of the standing waves on the antenna are 90 degrees out of phase with each other. At resonance, is the phase of the current reflected back from the ends of the antenna when it arrives back at the feed point the same as the phase of the voltage of the applied RF at the feed point ? And if so is this why there is no reactance seen in the impedance at the feed point at resonance ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastActivityDate="2021-05-29T13:34:57.887" Title="For a resonant half wave dipole, is the phase of the applied RF voltage at the feedpoint in phase with the current reflected from the ends?" Tags="&lt;antenna-theory&gt;&lt;dipole&gt;" AnswerCount="0" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18527" PostTypeId="1" CreationDate="2021-05-29T13:46:29.753" Score="0" ViewCount="16" Body="&lt;p&gt;Impedance can be defined as cause / effect or Z = E / I.&lt;/p&gt;&#xA;&lt;p&gt;This means that a difference in voltage potential causes a flow of current, the rate of current flow depending on the impedance.&lt;/p&gt;&#xA;&lt;p&gt;In a dipole antenna, does this mean the applied RF voltage at the feed point causes the flow of RF current in the antenna ?&lt;/p&gt;&#xA;" OwnerUserId="13450" LastEditorUserId="13450" LastEditDate="2021-05-30T02:50:32.607" LastActivityDate="2021-05-30T02:50:32.607" Title="What comes first, Voltage or Current?" Tags="&lt;antenna-theory&gt;" AnswerCount="2" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18528" PostTypeId="2" ParentId="18527" CreationDate="2021-05-29T16:51:07.733" Score="0" Body="&lt;p&gt;Voltage and current are coupled by resistance in a passive device.  V=IR.  However, in an AC circuit, R can be complex, which allows a phase difference between current and voltage.   Neglecting that, or looking at average over time, voltage and current are proportionally related, and you can't have one without the other if there is conduction and resistance.  Voltage over a resistance induces current.  Current over a resistance induces voltage.  The only way to have one without the other is to have infinite resistance (voltage without current) or zero resistance (current without voltage).&lt;/p&gt;&#xA;&lt;p&gt;An antenna has loss resistance and radiation resistance.  Current and voltage together over these resistances cause the antenna to radiate (and heat up).  (One hopes the loss resistance heating the antenna is much smaller than the radiation resistance causing it to radiate.)&lt;/p&gt;&#xA;" OwnerUserId="10489" LastActivityDate="2021-05-29T16:51:07.733" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
  <row Id="18529" PostTypeId="1" CreationDate="2021-05-29T17:33:22.383" Score="1" ViewCount="8" Body="&lt;p&gt;I was participating in an emergency radio training and I was asked how long I could operate.&lt;/p&gt;&#xA;&lt;p&gt;I'm using an old car battery, which was sometimes not capable of starting the car in winter, which is why I have it. It has a nominal capacity of 45Ah.&lt;/p&gt;&#xA;&lt;p&gt;Is there a good way to find out its real remaining capacity except draining it by a known current and measuring time?&lt;/p&gt;&#xA;" OwnerUserId="890" LastActivityDate="2021-05-29T17:50:08.953" Title="How to figure out my car battery's capacity?" Tags="&lt;battery&gt;&lt;capacitance&gt;" AnswerCount="1" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18530" PostTypeId="2" ParentId="18529" CreationDate="2021-05-29T17:50:08.953" Score="0" Body="&lt;p&gt;There are many ways to do this. My favorite and I would assume you have these items in your shack. Most inverters have an automatic low-voltage disconnect feature. It makes a beeping sound and stops putting out 110AC when the battery voltage drops below 11 volts or so. You have probably encountered this feature while using your inverter. You connect a load to the inverter (light bulbs work great) and an electric clock (I start at 12:00) to determine how long it runs. When the inverter quits the clock will tell you how long it ran. If you have a&#xA;24 hour electric clock it would would be perfect for this however a 12 hour will work just as good. A 60 watt light bulb makes my inverter draw about 5 amps from the battery. Using your favorite math formula from OHM: Watts = Volts * Amps.&#xA;60 watts = 12 volts * 5 Amps. 5 Amps = 60 Watts / 12 Volts to be sure, check the current and voltage with your meter(s).&lt;/p&gt;&#xA;" OwnerUserId="19837" LastActivityDate="2021-05-29T17:50:08.953" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18531" PostTypeId="2" ParentId="18525" CreationDate="2021-05-29T18:09:19.690" Score="0" Body="&lt;p&gt;The &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt; is, in principle, defined as a ratio of maximum and minimum voltages that exist at different locations of the transmission line. These two different voltages &lt;span class=&quot;math-container&quot;&gt;$U_{max}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$U_{min}$&lt;/span&gt; can be measured to determine &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt;. - However, &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt; can also be determined by the absolute value of the reflection coefficient, &lt;span class=&quot;math-container&quot;&gt;$|\Gamma |$&lt;/span&gt;, according to&#xA;&lt;span class=&quot;math-container&quot;&gt;$$SWR = \frac{1+|\Gamma |}{1 – |\Gamma |} = \frac{U_{max}}{U_{min}} =&#xA;        \frac{U_{forward}+U_{return}}{U_{forward}-U_{return}}$$&lt;/span&gt;&#xA;&lt;span class=&quot;math-container&quot;&gt;$$|\Gamma | = \sqrt{\frac{P_{return}}{P_{forward}}}=\frac{U_{return}}{U_{forward}}$$&lt;/span&gt;&#xA;The absolute value of the reflection coefficient, &lt;span class=&quot;math-container&quot;&gt;$|\Gamma |$&lt;/span&gt;, is the square-root of the ratio of return-power to forward-power, both now measured at one and the same location along the feedline (e.g., coax) to determine &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt;. Equally, one can measure the forward and return voltages at the same location, or their sum and their difference to determine &lt;span class=&quot;math-container&quot;&gt;$U_{max}$&lt;/span&gt; and &lt;span class=&quot;math-container&quot;&gt;$U_{min}$&lt;/span&gt;, respectively.&lt;/p&gt;&#xA;&lt;p&gt;Yes, the &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt; can change along the transmission line. This is the case if the line is lossy. The &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt; is constant along the transmission line if the line is, or may be considered, lossless.&lt;/p&gt;&#xA;&lt;p&gt;Assume we are at the end of the transmission line. The mismatch between load and characteristic impedance of the line determines the reflection coefficient and &lt;span class=&quot;math-container&quot;&gt;$|\Gamma |$&lt;/span&gt;, which is the square-root of the ratio of return-power to forward-power at the end of the feedline.&#xA;Now, we move away from the end of the line und closer to the feedline input; we consider a lossy line. At the new location, the forward-power is higher than the forward-power reaching the end of the line, due to the attenuation of the line. But the return-power at the new location is lower than measured at the end of the line because it has been attenuated along its path from the end of the line to the new location. Consequently, with lower return-power and higher forward-power, the ratio, &lt;span class=&quot;math-container&quot;&gt;$|\Gamma |$&lt;/span&gt;, i.e., the square-root of the ratio of return-power to forward-power at the new location is smaller than measured at end of the line. The smaller the &lt;span class=&quot;math-container&quot;&gt;$|\Gamma |$&lt;/span&gt;, the smaller and closer the &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt; gets to 1. (The same discussion can be presented in terms of forward and return voltages, of course.)&lt;/p&gt;&#xA;&lt;p&gt;Your observation of &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt; changing along a (lossy) line confirms that &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt; measurements are best performed at the load if one wishes to determine the actual load mismatch.&lt;/p&gt;&#xA;&lt;p&gt;For a lossy line, in a Smith-Chart the transformed load impedance moves along a spiral, which is the curve of the complex reflection coefficient, &lt;span class=&quot;math-container&quot;&gt;$\Gamma $&lt;/span&gt;. Asymptotically, the spiral merges into the center of the chart, as the distance to the load becomes longer and longer. At the center of the Smith-Chart, the transformed load impedance equals the characteristic impedance of the feedline; the reflection coefficient becomes zero, i.e., &lt;span class=&quot;math-container&quot;&gt;$\Gamma =0$&lt;/span&gt; and consequently &lt;span class=&quot;math-container&quot;&gt;$SWR=1$&lt;/span&gt;. If the lossy line gets very long, at the input we will no longer feel the actual mismatch that might exist at the far end of the line. Therefore, the &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt; measurement at the input of a long feedline can significantly underestimate the &lt;span class=&quot;math-container&quot;&gt;$SWR$&lt;/span&gt; given at the load side. Perhaps, in practice one might like to keep this in mind.&lt;/p&gt;&#xA;&lt;p&gt;The following Smith chart shows an example of a very lossy line to see the effect. Example: 50Ω lossy feedline terminated into 200Ω (DP 1), i.e., &lt;span class=&quot;math-container&quot;&gt;$(V)SWR=4$&lt;/span&gt; at load. Two circles of constant &lt;span class=&quot;math-container&quot;&gt;$(V)SWR$&lt;/span&gt; (4 and 2) are shown in green.&lt;/p&gt;&#xA;&lt;p&gt;&lt;a href=&quot;https://i.stack.imgur.com/OPSpf.png&quot; rel=&quot;nofollow noreferrer&quot;&gt;&lt;img src=&quot;https://i.stack.imgur.com/OPSpf.png&quot; alt=&quot;enter image description here&quot; /&gt;&lt;/a&gt;&lt;/p&gt;&#xA;" OwnerUserId="18763" LastEditorUserId="18763" LastEditDate="2021-05-29T19:56:26.230" LastActivityDate="2021-05-29T19:56:26.230" CommentCount="2" ContentLicense="CC BY-SA 4.0" />
  <row Id="18532" PostTypeId="2" ParentId="18318" CreationDate="2021-05-30T00:59:30.303" Score="0" Body="&lt;p&gt;TECHNICALLY NEVER WILL 100% OF YOUR POWER BE RADIATED, AND CONVERSELY WILL IT BE RE-REFLECTED BY / FROM ITS SOURCE.&#xA;IN EITHER SITUATION, YOU WOULD HAVE THE EQUIVALENT OF PERPETUAL MOTION OR 100% EFFICIENCY. BOTH OF THE LATTER DO NOT EXIST. THAT IS ONE ANSWER TO YOUR QUESTION.&lt;/p&gt;&#xA;&lt;p&gt;NEXT IS THE OFT UTTERED, FALSE IDEA THAT A HIGH SWR WILL REFLECT POWER BACK INTO YOUR TX. IF THERE IS 187 WATTS COMING OUT OF THE SO-239 ON YOUR RIG, DO YOU HAVE POWER LEFT TO GET BACK INTO THE TX? CAN YOU FORCE ONE WATT INTO AND THRU THAT SO-239 AGAINST THE 186 LEFT? NO. YOU CAN WARM UP COAX, BALUNS, MATCHBOXES, (NO SUCH THING AS AN ANTENNA &amp;quot;TUNER&amp;quot;), AND RADIATION RESISTANCE LOSS. - (MINIMAL). BUT YOU ARE NOT GOING TO PUT POWER IN. YOU MAY CAUSE YOUR TX TTO BURN UP BECAUSE ITS BEING LOADED DOWN TO THE POINT IT FAILS, BUT POWER DID NOT, DID NOT GO BACK IN. HENCE NO REFLECTION.&lt;/p&gt;&#xA;&lt;p&gt;A MIRROR REFLECTS YOUR IMAGE. THAT IMAGE IS PRODUCED BY LIGHT ENERGY - WHICH HAPPENS TO BE ELECTROMAGNETIC ENERGY.&#xA;BUT THERE IS ALWAYS ATTENUATION - EVERYWHERE IN THE ELECTROMAGNETIC SPECTRUM.&lt;/p&gt;&#xA;&lt;p&gt;THAT SAID WHEN REFLECTED ENERGY MEETS ITS ORIGINAL SOURCE - YOUR TX, IT CANNOT BE REFLECTED BY IT. ASSUMING FOR A MOMENT THE EXISTENCE OF 100% EFFICIENCY IN A CIRCUIT SO THAT THE 341.2 BTU OF HEAT YOUR 100 W. TX GAVE OUT IT WOULD BE CONSUMED IN THE LOAD.&lt;/p&gt;&#xA;&lt;p&gt;LOOK AT IT THIS WAY, YOU HAVE A GARDEN HOSE WITH 60 POUNDS OF WATER PRESSURE. FOLDING THE HOSE OVER, SHUTTING THE NOZZLE OFF, DOES NOT CAUSE WATER TO GO BACK THRU THE HOSE BIBB, AND INTO THE WATER SUPPLY. THE BATHTUB, SINK, AND LAVATORY WILL HAVE THE 60 POUNDS OF WATER TO SHAVE BY, WASH DISHES, AND SHOWER WITH. BUT, NO WATER PRESSURE FORCED WATER BACK INTO ITS SOURCE. IT JUST STOPPED IT. YOU ASK DOES ENERGY RE-REFLECT FROM THE TX. NO.&lt;/p&gt;&#xA;" OwnerUserId="8496" LastActivityDate="2021-05-30T00:59:30.303" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18533" PostTypeId="2" ParentId="18506" CreationDate="2021-05-30T01:29:35.503" Score="0" Body="&lt;p&gt;MY QUESTION TECHNICALLY REFERS TO THE NEED FOR A REAL, ACTUAL &amp;quot;IN CIRCUIT&amp;quot; GROUND OR A REFERENCE GROUND AS I MENTIONED ORIGINALLY. (BY THE WAY, SORRY FOR ALL UPPER CASE, BUT I WILL BE TOTALLY SIGHTLESS NEXT YEAR, SO THEY TELL ME. I MENTIONED THE NEED FOR A GROUND, BECAUSE WITHOUT ONE TO MAKE UP THE REFLECTED OR CAPACITIVELY COUPLED ENERGY TO THE EARTH, THERE WOULD BE NO ENERGY TO FORM YOUR SIGNAL.&#xA;MAGNETS ARE DIPOLES BECAUSE TWO OPPOSING FIELDS EXIST. ONE 180DEG. AGAINST THE OTHER (NEGLECTING HYSTERISIS, FLUX DIFFERENCES ETC) AS I SAID, EVEN ANTENNAS ON A SATELLITE HAVE TO HAVE A &amp;quot;MIRROR IMAGE&amp;quot; PRODUCED, CAUSED BY, REFLECTED FROM THE CASE, THE CIRCUIT BOARD &amp;quot;R.F.NEGATIVE&amp;quot;, USING THEM AS A REFERENCE GROUND TO RADIATE. NO GROUND, NO RADIATE WHY BECAUSE WITHOUT A GROUND, REFERENCE GROUND, YOU HAVE NO DIPOLE. NO MIRROR IMAGE, NO REFLECTION. LIGHT ENERGY REQUIRES A REFLECTION NO REFLECTION, NO SEE?? HA. BEEN HAM 60 YEARS, TAUGHT ELECTRONICS FOR A LIVING. YES A DIPOLE RADIATION PATTERN SHOWS, AND I AGREE WITH THAT, BUT NOTICE AT ANY GIVEN INSTANT THE ENERGY IS 180 OUT OF PHASE ONE POLE GENERATED EACH PHASE. AT 76, MAYBE I WILL STOP THEORIZING AND UPSETTING PEOPLE HA. '73 KF9F (HOPE I HAVE CLARIFIED??? THE CAPS ISSUE) RICH&lt;/p&gt;&#xA;" OwnerUserId="8496" LastActivityDate="2021-05-30T01:29:35.503" CommentCount="0" ContentLicense="CC BY-SA 4.0" />
  <row Id="18534" PostTypeId="2" ParentId="18527" CreationDate="2021-05-30T02:13:09.617" Score="0" Body="&lt;p&gt;In a transmitter with a capacitively coupled output, a change in instantaneous voltage created at the transmitter causes current to accelerate up the feedline (if the impedance is less than infinite). And down the return path(s) as well.  But according to Maxwell's equations, you also get changing magnetic and electric fields traveling along with the accelerating current up the feedline.  You can't get one without the other given the known laws of physics.  By the time the current waves reach the antenna feed point, the voltage there may or may not be different (magnitude and phase) from at the transmitter due to propagation speed, and impedance mismatches and reflections along the way.&lt;/p&gt;&#xA;" OwnerUserId="556" LastActivityDate="2021-05-30T02:13:09.617" CommentCount="1" ContentLicense="CC BY-SA 4.0" />
</posts>